TWI790207B - Method for producing polarizing film - Google Patents

Abstract

A method for producing a stretched film, which is a method for producing a polarizing film in which at least a swelling step, a dyeing step, and a stretching step are applied to a polyvinyl alcohol film, wherein polyvinyl alcohol having a dry thickness B of 0.001 mm to 0.045 mm is used The film is used as a raw material. In at least one of the aforementioned steps, after immersing the polyvinyl alcohol film in water, taking it out from the water and removing the water adhering to both ends from both sides of the film, the film is kept away from the water until it is removed. The distance A between the water positions is 28mm or less. According to this production method, even when a thin PVA film is used, cracking of the film is less likely to occur during stretching or drying, and a polarizing film excellent in polarizing performance can be easily produced.

Description

Manufacturing method of polarizing film

The present invention relates to a manufacturing method of a polarizing film using a thin polyvinyl alcohol film as a raw material.

Polarizers with light transmission and shielding functions are the same basic components of liquid crystal displays (LCDs) as liquid crystals that change the polarization state of light. Polarizing plates often have a structure in which a protective film such as a triacetate cellulose (TAC) film is attached to the surface of a polarizing film. As a polarizing film constituting a polarizing plate, an iodine-based dye (I ₃ ^- or I ₅ ^-etc .) or dichroic dyes such as dichroic organic dyes are the mainstream. This kind of polarizing film is uniaxially stretched the PVA film containing the dichroic dye in advance, adsorbing the dichroic dye while uniaxially stretching the PVA film, or adsorbing the dichroic dye after uniaxially stretching the PVA film. Manufactured from pigments, etc.

LCDs are used in a wide range of applications such as small devices such as computers and watches, notebook computers, LCD monitors, LCD color projectors, LCD TVs, vehicle navigation systems, mobile phones, and measuring instruments used inside and outside the house. In recent years, the demand for LCDs for mobile applications such as small notebook computers and mobile phones has increased, and the thinning of polarizing plates has been strongly demanded.

Therefore, thinning of the polarizing film is required, and as one of the means, a method of using a thin PVA film as a raw material is mentioned. However, a thin PVA film tends to be cracked during stretching or drying, which tends to increase costs due to a reduction in the production speed of polarizing films and an increase in defective products. In particular, in the swelling step, dyeing step, etc., the PVA film will be crimped at the end of the film after being immersed in water, and this will cause a problem that the PVA film will be broken during stretching or drying.

As a method of producing a thin polarizing film, a method of stretching the obtained laminate after forming a thin PVA layer on a plastic film by a coating method has been proposed (for example, Patent Documents 1 and 2). However, in this method, the coating operation and the subsequent drying operation are complicated. In addition, heat treatment of the laminate is required to insolubilize the PVA layer. Therefore, it is necessary to use a plastic film that can also be stretched after heat treatment, and the cost is relatively high. Furthermore, due to the high bonding strength between the plastic film and the PVA layer, the proper neck-in of the PVA layer will be hindered during stretching, making it difficult to obtain a polarizing film with excellent polarizing properties.

In addition, there is a proposal to remove the liquid on one side of the PVA film taken out from each treatment tank, and then apply a process of expanding the width of the PVA film at both ends using an expander roll or the like (Patent Document 3) . However, even if the two ends of the PVA film are expanded by using expansion rolls, it is difficult to eliminate the thin folds of a few millimeters wide that occur after the thin PVA film is immersed in water. Cracking of the PVA film occurred. In addition, by applying the treatment of expanding the both ends of the PVA film, the PVA film tends to be wrinkled, and appearance abnormalities tend to occur.

[Prior Art Literature] [Patent Document]

[Patent Document 1] Japanese Patent Laid-Open No. 2012-133303

[Patent Document 2] Japanese Patent Laid-Open No. 2012-73570

[Patent Document 3] International Publication No. 2014/115897

The present invention was completed in order to solve the above-mentioned problems, and aims to provide a method for producing a polarizing film that is difficult to cause film cracking during stretching or drying even when a thin PVA film is used. cracks, and a film with excellent polarizing performance can be easily obtained.

As a result of repeated studies by the present inventors in order to achieve the above object, it was found that when a polarizing film is manufactured using a thin PVA film, after the PVA film is immersed in water, it is easy to produce wrinkles at the end immediately after taking it out. Because of this, stretch breakage becomes likely to occur in the subsequent stretching step, or breakage due to shrinkage of the film becomes likely to occur in the drying step. And find: after the PVA film is immersed in water, just after taking out, by removing the water attached to the PVA film from its both sides, the generation of the fold at the end of this PVA film can be suppressed, and the rupture of the film can be prevented ( tensile fracture, etc.). As a result of further repeated studies based on these findings, the present invention was finally completed.

That is, the present invention relates to: [1] A method for producing a stretched film, which is a method for producing a polarizing film in which at least a swelling step, a dyeing step, and a stretching step are applied to a polyvinyl alcohol film, wherein the dry thickness B A polyvinyl alcohol film with a thickness of 0.001 mm to 0.045 mm is used as a raw material. In at least one of the aforementioned steps, after immersing the polyvinyl alcohol film in water, it is taken out from the water and the water adhering to both ends of the film is removed from both sides of the film. , the distance A between the position where the aforementioned film is away from the water and the position where the water is removed is 28 mm or less; [2] The manufacturing method as in [1] above, wherein the width of both ends of the aforementioned film where the water is removed is 1 cm or more; [ 3] The production method according to the above [2], which is to remove the water from the entire surface of the film; [4] The production method according to any one of the above [1] to [3], wherein the polyvinyl alcohol film as the raw material is dried The thickness B (mm) and the aforementioned distance A (mm) satisfy the following formula (1): A≦B×1000 (1); [5] The manufacturing method according to any one of the above [1] to [4], It removes water adhering to both ends of the above-mentioned film by clamping the above-mentioned film with a pair of rollers; [6] the production method as in the above-mentioned [5], wherein the above-mentioned roller is a sponge roller; [7] as in the above-mentioned [ 6] The production method, wherein the water retention rate of the sponge roller is not less than 50% and not more than 95%; The distance a (cm) and the radius b1 (cm) and b2 (cm) of each roller satisfy the following formula (2): 0.1≦a/(b1+b2)≦0.97 (2); [9] as above [ 1] The production method of any one of [8], wherein water adhering to both ends of the aforementioned film is removed before the stretching step; [10] The method of any one of the above-mentioned [1] to [9] A manufacturing method wherein a crosslinking step or a fixation treatment step is further applied.

According to the production method of the present invention, even when a thin PVA film is used, film cracking hardly occurs during stretching or drying, and a polarizing film excellent in polarizing performance can be easily produced.

1‧‧‧PVA film

2‧‧‧Roller

3‧‧‧guide roller

4‧‧‧Travel roller

5‧‧‧Swelling step

6‧‧‧water

7‧‧‧PVA film film roll

8‧‧‧Position to remove PVA film from water

9‧‧‧Position where water is removed by PVA film

10‧‧‧dyeing steps

11‧‧‧Crosslinking step

Fig. 1 is a schematic diagram showing an example of the swelling step.

Fig. 2 is a schematic diagram showing the distance A from the position where the PVA film leaves the water to the position where the water is removed.

FIG. 3 is a schematic view showing a swelling step, a dyeing step, and a crosslinking step by continuously unwinding a PVA film in Example 1. FIG.

[Mode of Implementing the Invention]

The manufacturing method of the polarizing film of the present invention is the manufacturing method of the polarizing film that at least applies swelling step, dyeing step and stretching step to the PVA film, wherein, use the PVA film that dry thickness B is 0.001mm to 0.045mm as raw material, in In at least one of the aforementioned steps, after immersing the PVA film in water, taking it out from the water and removing the water adhering to both ends from both sides of the aforementioned film, the distance A between the position where the aforementioned film leaves the water and the position where the water is removed is: Below 28mm.

In the present invention, the PVA used in the manufacture of PVA film can be prepared by polymerizing vinyl acetate, vinyl formate, vinyl propionate, vinyl butyrate, trimethyl vinyl acetate, vinyl neodecanoate (vinyl versatate), vinyl laurate, vinyl stearate, vinyl benzoate, isopropenyl acetate and other vinyl esters, such as saponification of polyvinyl esters, etc. Among the aforementioned vinyl esters, compounds having a vinyloxycarbonyl group (H ₂ C=CH-O-CO-) in the molecule are preferred in terms of ease of production of PVA, ease of acquisition, and cost reduction. More preferred is vinyl acetate.

The aforementioned polyvinyl ester is preferably obtained using only vinyl ester as a monomer. The vinyl ester used at this time may be 2 or more types, but 1 type is preferable. The above-mentioned polyvinyl ester may be a copolymer of one or more types of vinyl esters and other monomers copolymerizable therewith as long as the effects of the present invention are not impaired.

As other monomers that can be copolymerized with the aforementioned vinyl esters, for example, α-olefins with 2 to 30 carbon atoms such as ethylene, propylene, 1-butene, and isobutylene; (meth)acrylic acid or its salts; (meth)acrylic acid or its salts; ) methyl acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, isopropyl (meth) acrylate, n-butyl (meth) acrylate, isobutyl (meth) acrylate, ( (meth)acrylates of tertiary butyl methacrylate, 2-ethylhexyl (meth)acrylate, dodecyl (meth)acrylate, octadecyl (meth)acrylate, etc.; ( Meth)acrylamide; N-methyl(meth)acrylamide, N-ethyl(meth)acrylamide, N,N-dimethyl(meth)acrylamide, diacetone (meth)acrylamide base) acrylamide, (meth)acrylamidopropanesulfonic acid or its salts, (meth)acrylamidopropyldimethylamine or its salts, N-methylol (meth)acrylamide or its salts (Meth)acrylamide derivatives such as derivatives; N-vinylamides such as N-vinylformamide, N-vinylacetamide, N-vinylpyrrolidone, etc.; methyl vinyl ether , ethyl vinyl ether, n-propyl vinyl ether, isopropyl vinyl ether, n-butyl vinyl ether, isobutyl vinyl ether, tertiary butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether, etc. vinyl ethers; vinyl cyanides such as (meth)acrylonitrile; vinyl halides such as vinyl chloride, vinylidene chloride, vinyl fluoride, and vinylidene fluoride; allyl compounds such as allyl acetate and allyl chloride; Maleic acid or its salt, ester or anhydride; itaconic acid or its salt, ester or anhydride; vinyl silicon-based compounds such as vinyltrimethoxysilane; unsaturated sulfonic acid or its salt, etc. The said polyvinyl ester may have 1 type, or 2 or more types of structural units derived from the said other monomer.

Based on the molar number of the total structural units constituting the polyvinyl ester, the proportion of structural units derived from other monomers in the aforementioned polyvinyl ester is preferably 15 mol % or less, more preferably 10 mol % or less, More preferably, it is 5 mol% or less.

As long as the effect of the present invention is not impaired, PVA may be modified by one or two or more graft-copolymerizable monomers. At this time, polyvinyl ester or PVA can be graft-copolymerized. Examples of graft-copolymerizable monomers include unsaturated carboxylic acids or derivatives thereof; unsaturated sulfonic acids or derivatives thereof; α-olefins having 2 to 30 carbon atoms, and the like. Based on the molar number of the total structural units constituting polyvinyl ester or PVA, the proportion of structural units derived from graft-copolymerizable monomers in polyvinyl ester or PVA is preferably 5 mol% or less. The PVA used in the present invention is preferably non-graft copolymerized.

The aforementioned PVA may or may not be crosslinked with some of its hydroxyl groups. In addition, some hydroxyl groups of the above-mentioned PVA may react with an aldehyde compound such as acetaldehyde or butyraldehyde to form an acetal structure, or may not form an acetal structure.

The average degree of polymerization of the aforementioned PVA is not particularly limited, but is preferably 1,000 or more. Since the average degree of polymerization of PVA is more than 1,000, the polarizing performance of the obtained polarizing film can be further improved. When the average polymerization of PVA is too high, there is a possibility that the production cost of PVA will increase, or the step-passability at the time of film formation may be poor. Therefore, the average degree of polymerization of PVA is preferably 1,000-10,000, more preferably 1,500-8,000, most preferably 2,000-5,000. In this invention, the average polymerization degree of PVA means the average polymerization degree measured based on the description of JISK6726-1994.

The saponification degree of the PVA is preferably at least 99.0 mol %, more preferably at least 99.8 mol %, and still more preferably at least 99.9 mol %, from the viewpoint of improving the moisture and heat resistance of the obtained polarizing film. In the present invention, the degree of saponification of PVA refers to the total number of moles of structural units (typically vinyl ester units) and vinyl alcohol units that PVA has that can be converted into vinyl alcohol units by saponification. Proportion of moles of vinyl alcohol units (mole %). The degree of saponification can be measured in accordance with the description of JIS K6726-1994.

The content of the aforementioned PVA in the PVA film used as a raw material in the present invention is preferably from 50 to 100% by mass, more preferably from 80 to 100% by mass, and still more preferably from 85 to 100% by mass.

PVA films may also contain plasticizers. By containing plasticizer in the PVA film, the handleability, stretchability, etc. are improved. Polyhydric alcohol is preferably used as the plasticizer, and specific examples thereof include ethylene glycol, glycerin, propylene glycol, diethylene glycol, diglycerin, triethylene glycol, tetraethylene glycol, and trimethylolpropane. The PVA film may contain 1 type or 2 or more types of these plasticizers. Among them, glycerin is preferred from the viewpoint of further improving the stretchability of the PVA film.

With respect to 100 parts by mass of PVA, the content of the plasticizer in the PVA film is preferably 3-20 parts by mass, more preferably 5-17 parts by mass, and even more preferably 7-14 parts by mass. By making the content of the plasticizer in the PVA film 3 parts by mass or more relative to 100 parts by mass of PVA, the stretchability of the PVA film is further improved. On the other hand, when the content of the plasticizer in the PVA film is 20 parts by mass or less with respect to 100 parts by mass of PVA, it is possible to suppress the plasticizer from bleeding out on the surface of the PVA film to reduce the handleability of the PVA film.

In addition, when a PVA film is produced using the film-forming stock solution described later, the thickness unevenness of the film is suppressed by improving the film-forming property, and when a metal roll or belt is used for film production, it becomes easy to peel off the PVA film. In other words, it is preferable to make the film-forming stock solution contain a surfactant. When a PVA film is manufactured using a film-forming stock solution containing a surfactant, the obtained PVA film may contain a surfactant. The type of the aforementioned surfactant is not particularly limited, but from the standpoint of easy peeling of the PVA film from the metal roll or belt, anionic surfactants and nonionic surfactants are preferred, and nonionic surfactants are more preferred. These surfactants can be used alone or in combination of two or more.

Suitable anionic surfactants are, for example, carboxylic acid types such as potassium laurate; sulfate ester types such as octyl sulfate; and sulfonic acid types such as dodecyl benzenesulfonate.

As the nonionic surfactant, for example, alkyl ether type such as polyoxyethylene oleyl ether; alkyl phenyl ether type such as polyoxyethylene octylphenyl ether; alkyl group such as polyoxyethylene laurate, etc. are suitable. Ester type; Alkylamine type such as polyoxyethylene lauryl amino ether; Alkylamide type such as polyoxyethylene lauric acid amide; Polypropylene glycol ether type such as polyoxyethylene polyoxypropylene ether; Alkanolamide type such as ethanolamide and oleic acid diethanolamide; Allylphenyl ether type such as polyoxyalkylene allylphenyl ether, etc.

With respect to 100 parts by mass of PVA, the content of the surfactant in the film-forming stock solution is preferably 0.01-0.5 parts by mass, more preferably 0.02-0.3 parts by mass. When the content of the surfactant is 0.01 parts by mass or more, film forming properties and peeling properties can be improved. On the other hand, when the content of the surfactant is 0.5 parts by mass or less, it can be suppressed that the surfactant oozes out on the surface of the PVA film, causing blocking (blocking) and lowering the handleability. The content of the surfactant in the PVA film is preferably within the above-mentioned range in terms of the content of the surfactant in the film-forming stock solution.

The PVA film may contain only PVA, or may contain only PVA and a plasticizer and/or a surfactant. In addition, other components other than PVA, plasticizers, and surfactants such as antioxidants, antifreeze agents, pH adjusters, masking agents, anti-coloring agents, and oil agents may be included as needed.

The manufacturing method of the PVA film is not particularly limited. From the point of view of obtaining a film with uniform thickness and width, casting (cast) film-making method, extrusion film-making method, wet-type film-making method, and gel film-making method are preferred. Etc., more preferably cast film-making method, extrusion film-making method. Among these film-forming methods, the extrusion film-forming method is particularly preferable in that a PVA film having uniform thickness and width and good physical properties can be obtained. These film forming methods may be used alone or in combination of two or more.

As a film-making stock solution for the manufacture of PVA films, a film-making stock solution made by dissolving PVA, plasticizers, surfactants, and other components on demand in a liquid medium can be used; or a plasticizing stock solution containing PVA and on demand Agents, surfactants, other components, liquid media, and the film-making stock solution obtained by melting PVA. Preferably, the components in the film-forming stock solution are uniformly mixed.

Examples of the liquid medium used in the membrane-forming stock solution include water, dimethylsulfide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, glycerin, and propylene glycol. , diethylene glycol, triethylene glycol, tetraethylene glycol, trimethylolpropane, ethylenediamine, and diethylenetriamine, and one or more of these can be used. Among them, water is preferable in terms of less burden on the environment and recyclability.

The volatile content of the film-making stock solution (the proportion of volatile components in the film-making stock solution that are removed by volatilization or evaporation during film making) varies according to the film-making method, film-making conditions, etc., preferably 50-95% by mass, more preferably 55-90% by mass, even more preferably 60-85% by mass. Since the volatile content of the membrane-forming stock solution is more than 50% by mass, the viscosity of the film-forming stock solution does not become too high, and the filtration or defoaming during the preparation of the film-forming stock solution proceeds smoothly, making it easier to produce impurities or defects. Less PVA film. On the other hand, since the volatile content of the film-forming stock solution is 95% by mass or less, the concentration of the film-forming stock solution does not become too low, and it becomes easy to industrially manufacture a PVA film. The PVA film obtained from film making can be dried and heat-treated as required.

The shape of the PVA film is not particularly limited, but it is preferably a long PVA film in order to continuously produce a polarizing film with good productivity. The length of this PVA film is not specifically limited, It can set suitably according to the use etc. of the polarizing film to manufacture, For example, it can set it as 5-20,000m. The width of the PVA film is not particularly limited, but it is preferably at least 50 cm, more preferably at least 2 m, and still more preferably at least 4 m for polarizing films that require a wide width in recent years. The upper limit of the width of the PVA film is not particularly limited, but if it is too large, uniform stretching tends to become difficult when manufacturing a polarizing film with a practical device, so the width of the PVA film is preferably 7 m or less.

In the present invention, the dry thickness B of the above-mentioned PVA film needs to be not less than 0.001 mm and not more than 0.045 mm. Thus, when using a polarizing film thinner than the PVA film conventionally used as a raw material, it becomes easy to generate|occur|produce a wrinkle at the edge part of the width direction, and it becomes a problem. On the other hand, according to the production method of the present invention, even if it is the case of using a thin PVA film, it still prevents the edge from being wrinkled, so it is difficult to break when stretching or drying, and can be stretched at a high stretching ratio. Since it is stretched, a polarizing film excellent in polarizing performance can be easily produced. The dry thickness B of the aforementioned PVA film is preferably 0.035 mm or less. Although the lower limit of the thickness of a PVA film is not specifically limited, Since a polarizing film can be manufactured more easily, it is preferable that it is 0.003 mm or more. Also, the PVA film may be a single layer or a laminate of a PVA layer and other laminated layers, and is preferably a single layer in order to exhibit the effect of the present invention more remarkably. In the case of a laminate, the thickness of the PVA layer is preferably within the above range.

A polarizing film is produced by applying at least a swelling step, a dyeing step, and a stretching step to the PVA film thus obtained as a raw material. At this time, it is preferable to further apply a crosslinking step or a fixing treatment step to the PVA film. Hereinafter, these steps will be specifically described.

[Swelling step]

The swelling step of the swelling treatment of the PVA film can be performed by immersing the PVA film in water. Usually, the swelling step is initially applied to the PVA film as the raw material. The temperature of the water for swelling the PVA film is preferably 20-40°C, more preferably 22-38°C, and even more preferably 25-35°C. Moreover, the time for immersing in water is preferably 0.5 to 5 minutes, more preferably 1 to 3 minutes. In addition, water at the time of immersion in water is not limited to pure water, and may be an aqueous solution in which various components are dissolved, or a mixture of water and a water-soluble organic solvent.

[Dyeing procedure]

The dyeing process of performing the dyeing process of a PVA film can be performed by immersing a PVA film in the aqueous solution containing a dichroic dye. The concentration of the dichroic dye in the aforementioned aqueous solution can be appropriately set depending on the type of dichroic dye, and can be set within a range of, for example, 0.001 to 1% by mass. When an iodine-potassium iodide aqueous solution [an aqueous solution containing iodine (I ₂ ) and potassium iodide (KI)] is used as the aqueous solution, the iodine-based dye can be efficiently adsorbed to the PVA film. The concentration of iodine (I ₂ ) in the aqueous solution is preferably 0.01-1.0% by mass, and the concentration of potassium iodide (KI) is preferably 0.01-10% by mass. The temperature of the aqueous solution containing the dichroic dye during the dyeing process is preferably 20 to 50°C, more preferably 25 to 40°C from the point of view that the dichroic dye can be efficiently adsorbed to the PVA film. The time for immersing the PVA film in the aqueous solution is preferably 0.1-10 minutes, more preferably 0.2-5 minutes.

Examples of the aforementioned dichroic dyes include iodine dyes (I ₃ ^- or I ₅ ^- , etc.), dichroic organic dyes, and the like. An iodine-based dye can be obtained, for example, by bringing iodine (I ₂ ) into contact with potassium iodide. Also, examples of dichroic organic dyes include Direct Black 17, 19, 154; Direct Brown 44, 106, 195, 210, 223; Direct Red 2, 23, 28, 31, 37, 39, 79, 81, 240, 242, 247; direct blue 1, 15, 22, 78, 90, 98, 151, 168, 202, 236, 249, 270; direct purple 9, 12, 51, 98; direct green 1, 85; Direct Yellow 8, 12, 44, 86, 87; Direct Orange 26, 39, 106, 107, etc. Among these dichroic dyes, iodine-based dyes are preferred from the viewpoints of handleability, availability, polarizing performance, and the like. In addition, the dichroic dye may be 1 type or any of ² or more types, For example, it may be the balanced mixture of _I3- ^and _I5- .

[Cross-linking step]

The cross-linking step of performing the cross-linking treatment of the PVA film can be performed by immersing the PVA film in an aqueous solution containing a cross-linking agent. By introducing a cross-linked structure to the PVA film, even when wet stretching is carried out at a relatively high temperature, the PVA in the film can still be effectively prevented from dissolving into water. From this point of view, the crosslinking step is preferably performed after the dyeing step. As the crosslinking agent, boron compounds such as boric acid or borates such as boric acid or borax may be used in one or more types. The concentration of the crosslinking agent in the aforementioned aqueous solution is preferably 1-15% by mass, more preferably 2-7% by mass. The aqueous solution containing a crosslinking agent may also contain auxiliary agents such as potassium iodide. The temperature of the aforementioned aqueous solution during the crosslinking treatment is preferably from 20 to 50°C, more preferably from 25 to 40°C.

Different from the stretching step described later, the PVA film can also be stretched in or between the above steps. By performing such stretching (pre-stretching), the PVA film can be prevented from being wrinkled. From the viewpoint of the polarizing performance of the obtained polarizing film, based on the original length of the raw material PVA film before stretching, the total stretching ratio of the pre-stretching (the ratio obtained by multiplying the stretching ratios in each step) is better. It is less than 4 times, more preferably 1.5 to 3.5 times. The stretch ratio in the swelling step is preferably 1.1 to 3 times, more preferably 1.2 to 2.5 times, and still more preferably 1.4 to 2.3 times. The draw ratio in the dyeing step is preferably at most 2 times, more preferably at most 1.8 times, and even more preferably at most 1.1 to 1.5 times. The draw ratio in the crosslinking step is preferably at most 2 times, more preferably at most 1.5 times, and even more preferably at most 1.05 to 1.3 times.

[stretch step]

In the stretching step of stretching the PVA film, the stretching method is not particularly limited, and either of a wet stretching method and a dry stretching method can be used. In the wet stretching method, it can be carried out in an aqueous solution containing one or more boron compounds such as borates such as boric acid and borax, or in the above-mentioned aqueous solution containing a dichroic dye or in the fixation treatment described later. in the aqueous solution used. In addition, in the dry stretching method, the PVA film may be stretched at room temperature, or the PVA film may be stretched while heating. Moreover, you may stretch after making a PVA film absorb water. Among these, the wet stretching method is preferable from the point of the uniformity of the thickness of the width direction of the polarizing film obtained. As the wet stretching method, a method of stretching in a boric acid aqueous solution is preferable. The concentration of boric acid in the aqueous solution is preferably 0.5-6.0% by mass, more preferably 1.0-5.0% by mass, even more preferably 1.5-4.0% by mass. The aqueous solution containing a boron compound may also contain potassium iodide, and its concentration is preferably within a range of 0.01 to 10% by mass.

In the stretching step, the temperature for stretching the PVA film is preferably 30-90°C, more preferably 40-80°C, and even more preferably 50-70°C.

The stretching ratio in the stretching step is preferably 1.2 times or more, more preferably 1.5 times or more, and still more preferably 2 times or more, in order to obtain a polarizing film having better polarizing performance. Also, based on the original length of the raw material PVA film before stretching, the total stretching ratio (multiplied by the stretching ratios in each step) including the above-mentioned stretching ratio before stretching is preferably 5.5 times or more , more preferably at least 5.7 times, even more preferably at least 5.8 times, particularly preferably at least 5.9 times. By making the total draw ratio into the said range, the polarizing film with more excellent polarizing performance can be obtained. The upper limit of the total draw ratio is not particularly limited, but is preferably 8 times or less.

In the stretching step of the present invention, it is preferable to uniaxially stretch the PVA film from the viewpoint of the performance of the obtained polarizing film. The direction of uniaxial stretching is not particularly limited, and uniaxial stretching in the longitudinal direction of a long PVA film or transverse uniaxial stretching can be used. Among them, uniaxial stretching in the longitudinal direction is preferable in terms of obtaining a polarizing film with better polarizing performance. The uniaxial stretching in the longitudinal direction can be performed by changing the peripheral speed between the respective rolls using a stretching device including a plurality of rolls parallel to each other. On the other hand, transverse uniaxial stretching can be performed using a tenter-type stretching machine.

[fixed processing steps]

The fixing treatment in the fixing treatment step is mainly performed to make the adsorption of the dichroic dye to the stretched PVA film stronger. Fixing treatment can be performed by immersing the stretched PVA film in a fixing treatment solution. As the immobilization treatment solution, an aqueous solution containing boron compounds such as boric acid or borates such as borax or the like may be used. Generally, the concentration of the boron compound in the aqueous solution is preferably from 2 to 15% by mass, more preferably from 3 to 10% by mass. The temperature of the fixing treatment liquid is preferably 15-60°C, more preferably 20-40°C. In addition, iodine compounds and metal compounds can also be added to the immobilization treatment solution as required.

In the production method of the present invention, at least one of the above-mentioned swelling step, dyeing step and stretching step is required. After the PVA film is immersed in water, it is taken out from the water and removed from both sides of the PVA film attached to both ends. of water. Furthermore, when taking the PVA film out of the water and removing the water adhering to the PVA film, the distance A between the position where the PVA film leaves the water and the position where the water is removed needs to be 28 mm or less.

The production method of the present invention in which the PVA film is soaked in water, taken out from the water, and the water adhering to the film is removed by a predetermined method will be described below using the swelling step as an example. FIG. 1 is a schematic diagram showing an example of the swelling step 5 . Fig. 2 is a schematic diagram showing the distance A from the position 8 where the PVA film 1 leaves the water 6 to the position 9 where the water is removed in the manufacturing method of the present invention. In the swelling step 5 , generally, the PVA film 1 is subjected to swelling treatment by immersing the PVA film 1 in water 6 . Then, the PVA film 1 was taken out from the water 6, and the water adhering to both ends in the width direction was removed from both surfaces of the PVA film 1 . By removing water from both surfaces of the PVA film 1 , generation of wrinkles at the ends of the PVA film 1 is suppressed.

As a method of removing water adhering to the PVA film 1 , a method of removing water adhering to both ends of the PVA film 1 by sandwiching the PVA film 1 with a pair of rollers 2 is preferable.

The outer diameter of the roller 2 used in the present invention (the maximum diameter when the diameter changes in the axial direction) is preferably 10 cm or less, more preferably 8 cm or less, and even more preferably from the point where the aforementioned distance A can be easily shortened. It is less than 6cm. The lower limit of the outer diameter of the roller 2 is not particularly limited, but is usually 1 cm or more. When the sponge roller 2 described later is used as the roller 2, if the outer diameter is less than 1 cm, the water absorption of the sponge roller 2 may become insufficient. Part or all of the roll 2 may be immersed in the water 6 . When the PVA film 1 is clamped by the rollers 2 , the water removed by the PVA film 1 and the water absorbed by the rollers 2 are twisted out on the opposite side of the machine direction of the PVA film 1 and discharged into the water 6 . Therefore, even if the roll 2 is immersed in the water 6, the water adhering to the PVA film 1 can be removed without any problem. From the viewpoint of further improving the removal efficiency of water, it is preferable that the roller 2 is not immersed in water.

The roller 2 may be either a non-rotating type or a rotating type, and the latter is preferable in that the friction between the PVA film 1 and the roller 2 is small and external disturbances such as scratches of the obtained polarizing film can be reduced.

The aforementioned roller 2 is preferably a sponge roller, a rubber roller, or the like, and among them, a sponge roller is more preferable. The sponge used as the outer layer of the sponge roller is not particularly limited, and examples thereof include polyurethane sponges, PVA sponges, and polyvinyl chloride-based sponges, among which polyurethane sponges are preferred.

The water retention rate of the aforementioned sponge roller 2 obtained by the following formula is not particularly limited, but it is preferably 50% or more, more preferably 67% or more, and more preferably 50% or more, and more preferably 67% or more, from the point of view that the time during which water can be continuously removed can be further extended. More preferably more than 75%. On the other hand, from the viewpoint that the water absorbed by the aforementioned sponge roll can be easily wrung out and the water adhering to the PVA film 1 can be removed more effectively, the water retention rate of the aforementioned sponge roll is preferably 95% or less, more preferably 92%. % or less, more preferably less than 90%. This water retention rate serves as an indicator of the water absorption performance of the sponge roller. The water retention rate can be obtained from the sponge mass a before water absorption and the sponge mass b after water absorption using a sponge sheet cut out from a part of the sponge part of the sponge roller 2 using the following formula. The mass b of the sponge after water absorption can be obtained by immersing the sponge piece before water absorption in water at 23°C for 24 hours, taking it out with tweezers, and measuring the mass of the sponge after dripping water for 1 minute.

Water retention rate (%)=100×(b-a)/b

In the formula, a represents the mass of the sponge before water absorption (g), and b represents the mass of the sponge after water absorption (g). In addition, a and b are the masses minus the mass of the mandrel part of the sponge roller.

In the present invention, the pressure at the time of clamping by the pair of rollers 2 is not particularly limited, but if the clamping pressure is too low, water adhering to the PVA film 1 may not be sufficiently removed. The clamping pressure is preferably at least 1 kgf/cm, more preferably at least 3 kgf/cm, and still more preferably at least 5 kgf/cm. The upper limit of the clamping pressure is not particularly limited, but the clamping pressure is preferably 15 kgf/cm or less from the viewpoint of reducing external disturbances such as scratches on the polarizing film.

The compression ratio [a/(b1+b2)] of the roller 2 calculated from the distance a (cm) between the rotation axes of the aforementioned pair of rollers 2 and the radii b1 (cm) and b2 (cm) of each roller is better The following formula (2) is satisfied. At this time, the pair of rollers 2 contact each other and are compressed. By arranging the pair of rollers 2 so as to satisfy the following formula (2), the water adhering to the PVA film 1 becomes more easily absorbed by the rollers 2, and becomes easier to twist out and be absorbed by the aforementioned rollers 2. water, thus further improving the water removal efficiency. From the viewpoint of further improving the removal efficiency of water, the compression ratio [a/(b1+b2)] is more preferably 0.95 or less, and still more preferably 0.90 or less. On the other hand, the compression ratio [a/(b1+b2)] is more preferably 0.3 or more, still more preferably 0.5 or more, from the viewpoint of further reducing external disturbances such as scratches of the obtained polarizing film. In addition, the radii b1 and b2 of each roller are half of the outer diameter of the roller. When the roller 2 has a mandrel, the radii b1 and b2 are values including the mandrel part.

0.1≦a/(b1+b2)≦0.97 (2)

In the production method of the present invention, when removing water from the PVA film 1 , it is necessary to remove water adhering to both ends from both surfaces of the PVA film 1 . When water adheres to the end of the PVA film 1 , curling of the end will occur due to the surface tension of the water. Here, it is important to remove water from both surfaces of the ends of the PVA film 1 . Wrinkles also occur when water adheres to only one side of the end of the PVA film 1 . From the viewpoint of more effectively suppressing the generation of wrinkles, the width of each end of the PVA film 1 from which water is removed is preferably 1 cm or more, more preferably 3 cm or more, and even more preferably 5 cm from the end to the center. above. Also, the width of each end of the PVA film 1 from which water is removed is preferably 1/100 or more, more preferably 1/20 or more, and still more preferably 1/10 or more, relative to the width of the PVA film 1 . .

It is particularly preferable to remove water from the entire surface of the aforementioned PVA film 1 . Thereby, generation|occurrence|production of a wrinkle can be suppressed more effectively. Also, since water is prevented from adhering to the guide roller 3 or the drawing roller 4 disposed downstream, water does not drip from the guide roller 3 or the drawing roller 4, so water can be prevented from adhering to the PVA film 1 again. Furthermore, in the stretching step, since the occurrence of physical property unevenness such as swelling unevenness or stretchability unevenness in the width direction of the PVA film 1 can be reduced, stretching fracture or optical unevenness of the obtained polarizing film can be suppressed. generation etc.

In the present invention, when removing water adhering to the end of the PVA film 1, the distance A from the position 8 where the PVA film 1 is away from the water 6 to the position 9 where the water is removed from the PVA film 1 must be 28 mm or less. Between the position 8 where the water is removed and the position 9 where the water is removed, the PVA film 1 becomes the PVA film 1 that is independently transported with water attached to the end. The inventors of the present invention have found that if the PVA film 1 with water adhered to the end is transported alone, wrinkles will be generated in a short time. When the distance A exceeds 28 mm, the ends of the PVA film 1 are rapidly creased. As shown in Figures 2 and 3, when water is removed by clamping the PVA film 1 with rollers 2, the position where the PVA film 1 first contacts any one of the pair of rollers 2 is set to remove water from the PVA film 1. position 9.

The aforementioned distance A is preferably 25 mm or less, more preferably 20 mm or less, still more preferably 15 mm or less. This distance A may be 0 mm. For example, by disposing at least a part of the roller 2 in the water 6, directly clamping the PVA film 1 in the water 6 with the roller 2, and removing the water in advance, and then starting to transport the PVA film 1 taken out of the water, the distance A The system becomes 0mm. The amount of water attached to the surface of the PVA film becomes less as the distance A becomes longer. Therefore, by more effectively removing the water on the surface of the PVA film, the end of the width direction of the PVA film 1 can be more effectively suppressed. The distance A is preferably at least 1 mm, more preferably at least 3 mm, and still more preferably at least 5 mm in terms of the point at which the folds are generated.

The dry thickness B (mm) of the raw material PVA film 1 and the aforementioned distance A (mm) preferably satisfy the following formula (1). Thereby, even the extremely thin PVA film 1 can more effectively suppress the occurrence of wrinkles.

A≦B×1000 (1)

As mentioned above, the main feature of the present invention is that the PVA film 1 is taken out from the water 6 and the water attached to both ends is removed from both sides of the PVA film 1, and the PVA film 1 is separated from the position 6 to the position where the water is removed. The distance A is a predetermined range. The thicker PVA film used in the past does not have the problem of film rupture caused by the folds at the end. Therefore, in the manufacture of a polarizing film, although guide rolls or nip rolls are used for the purpose of conveying or holding the PVA film, they are not used to prevent curling at the ends, or are not arranged near the water surface of the treatment bath. . On the other hand, as a method for preventing the ends of thin PVA films from wrinkling, it is known to remove the liquid on one side of the PVA film and then apply a method of expanding the widthwise ends of the PVA film (Patent Document 3 ), but there is still the situation that the PVA film caused by the folds of the end is broken, and needs to be improved. In order to solve this problem, the inventors of the present invention have worked hard to study the results and found that: when the PVA film 1 is relatively thin, the folds at the ends will be produced immediately after the PVA film 1 is taken out from the water 6; When water is removed, curls at the end are generated by the surface tension of water remaining on the other side. And find: by removing water by both sides of PVA film 1, and make this PVA film 1 distance A from the position of water 6 to the position of removing water be a predetermined range, and suppress the generation of this kind of wrinkle, reduce when stretching or drying When the PVA film 1 rupture occurs.

In the production method of the present invention, a polarizing film is produced by at least applying the aforementioned swelling step, the aforementioned dyeing step, and the aforementioned stretching step to the PVA film as the raw material. At this time, it is preferable to further apply the aforementioned crosslinking step or the aforementioned fixation treatment step to the PVA film, more preferably to apply the aforementioned crosslinking step and the aforementioned fixation treatment step. In addition, in the production method of the present invention, a plurality of steps may be applied to the PVA film in one treatment bath. For example, the aforementioned crosslinking step, the aforementioned stretching step, and the like may be performed in one treatment bath.

In the production method of the present invention, it is preferable to remove water attached to both ends of the PVA film before the aforementioned stretching step. In the manufacture of polarizing film, since the rupture of the PVA film is particularly easy to occur during stretching, the PVA film is soaked in water in the step before the aforementioned stretching step, then taken out from the water and used by the above method The water attached to both ends of the PVA film is removed, and the breakage of the PVA film is further suppressed. As the step carried out before the aforementioned stretching step, the aforementioned swelling step and the aforementioned dyeing step can be mentioned; preferably at least one of them removes the water attached to both ends of the PVA film, more preferably at least one of them. Both remove water attached to both ends of the PVA film. When the production method of the present invention further includes the aforementioned cross-linking step, the aforementioned swelling step, the aforementioned dyeing step, and the aforementioned cross-linking step are examples of the steps performed before the aforementioned stretching step; preferably at least one of these Or, remove the water attached to both ends of the PVA film, more preferably in the aforementioned swelling step and the aforementioned dyeing step, remove the water attached to the both ends of the PVA film, and more preferably in the aforementioned swelling step, the aforementioned dyeing step And the aforementioned cross-linking step, remove the water attached to both ends of the PVA film.

From the viewpoint of further reducing the occurrence of film cracks caused by shrinkage in the drying step described later, it is preferable to remove the PVA film attached to both ends of the PVA film in the aforementioned stretching step or a subsequent step (such as the aforementioned fixing treatment step). water.

As a suitable aspect of the production method of the present invention, the aforementioned swelling step, the aforementioned dyeing step, the aforementioned crosslinking step, and the aforementioned stretching step are sequentially applied to the PVA film, and the swelling step, the aforementioned dyeing step, and the aforementioned stretching step are sequentially applied. In at least one of the above-mentioned crosslinking steps, after immersing the PVA film in water, it is taken out from the water and the water adhering to both ends of the PVA film is removed using the above-mentioned method. At this time, it is preferable to remove the water attached to the PVA film in the aforementioned swelling step and the aforementioned dyeing step, more preferably to remove the water attached to the PVA film in the aforementioned swelling step, the aforementioned dyeing step and the aforementioned crosslinking step. Furthermore, it is also preferable to sequentially apply the aforementioned swelling step, the aforementioned dyeing step, the aforementioned crosslinking step, the aforementioned stretching step, and the aforementioned immobilization treatment step to the PVA film.

[Drying procedure]

A polarizing film can be manufactured by applying the above-mentioned stretching step to the PVA film, and further applying a fixing treatment step as required, and then usually drying the PVA film. The drying temperature is not particularly limited, but is preferably 30 to 150°C, more preferably 50 to 130°C. The dimensional stability of the polarizing film is improved by drying at such a temperature.

[polarizer]

An optically transparent protective film having mechanical strength is bonded to at least one side of the polarizing film obtained as described above, and used as a polarizing plate. As the protective film, a cellulose triacetate (TAC) film, a cellulose acetate-butyrate (CAB) film, an acrylic film, a polyester film, or the like can be used. In order to improve the adhesion of the adhesive to the polarizing film and protective film, surface treatments such as saponification treatment, corona treatment, plasma treatment, ultraviolet irradiation, and primer treatment can also be applied to the bonding surface of the polarizing film and protective film. As the adhesive for laminating the polarizing film and the protective film, a PVA-based adhesive, a urethane-based adhesive, an ultraviolet-curable adhesive, or the like can be used.

[Example]

Hereinafter, the present invention will be specifically described by means of examples, but the present invention is not limited by these examples. In addition, each measurement method and evaluation method used in the following Examples and Comparative Examples are shown below.

[Stretch ratio for continuous operation]

In the following examples, comparative examples, and reference examples, the total stretching ratio was increased stepwise by 0.1 times by adjusting the stretching ratio in the stretching step, and the total stretching ratio at the time of breaking of the film was lowered. A set total stretching ratio is used as the stretching ratio that can be operated continuously.

[Polarizing performance of polarizing film]

(a) Measurement of transmittance Ts

In the following examples, comparative examples, and reference examples, two rectangular samples of 3 cm in the longitudinal direction x 2 cm in the width direction of the polarizing film were taken from the central part of the obtained polarizing film in the width direction. Using a spectrophotometer with an integrating sphere (manufactured by JASCO Co., Ltd. "V7100"), according to JIS Z 8722: 2009 (measurement method of object color), the visibility correction of the C light source and the visible light region with a 2° field of view is performed. For one sample, measure the light transmittance when inclined at 45° and the light transmittance when inclined at -45° relative to the longitudinal direction, and obtain the average value Ts1 (%) of these. For the other sample, the light transmittance at 45° tilt and the light transmittance at -45° tilt were measured in the same manner, and their average value Ts2 (%) was obtained. Ts1 and Ts2 were averaged according to the following formula, and made into the transmittance Ts (%) of a polarizing film.

Ts=(Ts1+Ts2)/2

(b) Measurement of polarization degree V

The light transmittance T∥(%) when the two samples taken for the measurement of the above transmittance Ts are superimposed so that their longitudinal directions are parallel, and the light transmittance when they are superimposed so that the longitudinal directions are perpendicular The transmittance T⊥ (%) was measured in the same manner as in the aforementioned "(a) Measurement of transmittance Ts", and the degree of polarization V (%) was obtained from the following formula.

V={(T∥-T⊥)/(T∥+T⊥)} ^1/2 ×100

[the evaluation of the occurrence of the crease]

In the following examples, comparative examples, and reference examples, respectively, in the swelling step 5, the dyeing step 10, and the crosslinking step 11, the end of the PVA film immediately before contacting the guide roller 3 was visually observed to evaluate whether there were wrinkles. The following A and B were judged as pass, and C was judged as fail.

A: No creases were observed at the ends in the width direction of the PVA film after passing through any of the steps.

B: Only after passing through the crosslinking step 11, a slight wrinkle with a width of about 0.5 mm occurs at one end of the PVA film.

C: After passing through the cross-linking step 11 or after passing through other steps, a plurality of folds of about 0.5-3 mm are produced at both ends of the PVA film.

Example 1

A long-sized PVA film 1 having a thickness of 0.030 mm and a width of 65 cm when dried [containing 100 parts by mass of PVA (a saponified product of a homopolymer of vinyl acetate with a degree of polymerization of 2,400 and a degree of saponification of 99.9 mol%)), 12 parts by mass Parts of glycerin and 0.03 parts by mass of surfactant], continuously rolled out from its film roll 7, and supplied to swelling step 5, dyeing step 10 and crosslinking step 11 sequentially and continuously. FIG. 3 shows a schematic view showing that the PVA film 1 is continuously unwound from the film roll 7, and the swelling step 5, the dyeing step 10, and the crosslinking step 11 are applied.

Here, as the swelling step 5, the PVA film 1 was immersed in distilled water (temperature: 30° C.) for 1 minute, and uniaxially stretched at a stretch ratio of 2.0 times in the longitudinal direction during this time. Also, as the dyeing step 10, the PVA film 1 is immersed in an aqueous solution containing an iodine-based pigment (concentration of iodine: 0.05% by mass, concentration of potassium iodide: 1.2% by mass, temperature: 30° C.) for 2 minutes, and during this period Uniaxial stretching was performed at a stretch ratio of 1.2 times in the longitudinal direction. Furthermore, as the cross-linking step 11, the PVA film 1 is immersed in a boric acid aqueous solution (boric acid concentration: 2.6% by mass, temperature: 30° C.) for 2 minutes, and during this time, it is stretched 1.1 times in the longitudinal direction. Shaft stretched.

Also, as shown in FIG. 3, in the swelling step 5, the dyeing step 10, and the crosslinking step 11, a pair of sponge rollers 2 (AC sponge U manufactured by A.C.CHEMICAL Co., Ltd.; Ester sponge, water retention rate 78%, roller outer diameter 50mm, mandrel outer diameter 10mm, roller width 80cm, distance between rotating shafts 44mm, compression ratio 88%). At this time, the position of the sponge rollers 2 is adjusted so that the rotation axis of each sponge roller 2 is parallel to the width direction of the PVA film 1 and the plane including the rotation axis of each sponge roller 2 is perpendicular to the PVA film 1 . Then, the water-separated PVA film 1 is sandwiched across the entire area in the width direction, and the water adhering to the PVA film 1 is removed. Here, as shown in Figure 2, in the swelling step 5, the dyeing step 10 and the crosslinking step 11, the distance A between the position 8 where the PVA film 1 is separated from the water 6 and the position 9 where the water is removed from the PVA film 20mm. In addition, the position where the PVA film 1 first contacts any one of the two sponge rollers 2 is defined as a position 9 where water is removed from the PVA film. Also, in each step, as described above, after the PVA film 1 from which water has been removed contacts the guide roller 3 (a roller that is in contact across the entire width direction of the PVA film 1), it contacts a pair of pulling rollers 4 (horizontal). The guide roll 3 and the take-up roll 4 are provided downstream of the sponge roll 2 so as to be in contact across the entire width direction of the PVA film 1 .

Following the above-mentioned crosslinking step 11, the stretching step, the fixation step, and the drying step are sequentially and continuously performed to manufacture a polarizing film. The stretching step was carried out by uniaxially stretching the PVA film 1 in a boric acid aqueous solution (boric acid concentration: 2.8% by mass, potassium iodide concentration: 5% by mass, temperature: 57°C) in the longitudinal direction at a stretching ratio of 1.9 times (The total stretch ratio including the stretch ratio of the pre-stretch is 5.0 times). Also, the fixing treatment step was performed by immersing the stretched PVA film 1 in an aqueous boric acid solution (boric acid concentration: 2.6% by mass, potassium iodide concentration: 5% by mass, temperature: 22° C.) for 2 minutes. Furthermore, the drying step was performed by drying the stretched PVA film 1 at 60° C. for 1 minute to obtain a polarizing film.

Embodiment 2~5, comparative example 3

Except having changed the thickness of the PVA film 1 or the distance A as shown in Table 1, it carried out similarly to Example 1, and manufactured the polarizing film.

[Example 6]

A polarizing film was manufactured in the same manner as in Example 3, except that the pair of sponge rollers 2 was not installed in the crosslinking step 11 and the water adhering to the PVA film 1 was not removed.

[Comparative example 1]

Except that a pair of sponge rollers 2 are not installed in the swelling step 5, the dyeing step 10, and the crosslinking step 11, and the water adhering to the PVA film 1 is not removed, it is carried out in the same manner as in Example 2, and is continuously produced. Polarizing film.

[Comparative example 2]

Except in the swelling step 5, the dyeing step 10 and the crosslinking step 11, only the sponge roller 2 on the lower side of a pair of sponge rollers 2 is set, and the sponge roller 2 only contacts one side of the PVA film 1 to adhere to the PVA. A polarizing film was manufactured in the same manner as in Example 2 except for the removal of water from the thin film.

[Reference example 1]

Except that the thickness of the PVA film 1 is 0.060 mm, and a pair of sponge rollers 2 are not provided in the swelling step 5, the dyeing step 10 and the crosslinking step 11, and the removal of water attached to the PVA film 1 is not carried out, the system is as follows: It carried out similarly to Example 1, and produced the polarizing film.

Table 1 shows the production conditions and evaluation results of Examples 1-6, Comparative Examples 1-3, and Reference Examples above.

Claims (6)

A method for producing a polarizing film, which is a method for producing a polarizing film in which a polyvinyl alcohol film is subjected to at least a swelling step, a dyeing step, and a stretching step, characterized in that polyethylene having a dry thickness B of 0.001 mm to 0.045 mm is used Alcohol film is used as a raw material. In at least one of the steps, after immersing the polyvinyl alcohol film in water, taking it out from the water and removing the water attached to both ends from the two sides of the film, the film is separated from the water to The distance A of the water removal position is 28 mm or less, and the water attached to both ends of the film is removed by clamping the film with a pair of sponge rollers. The pair of rollers are rotary, and the pair of rollers The distance a (cm) between the rotating shafts and the radii b1 (cm) and b2 (cm) of each roller satisfy the following formula (2), and the water retention rate of the sponge roller is 50% to 95%; 0.5≦ a/(b1+b2)≦0.90 (2). The manufacturing method according to claim 1, wherein the width of both ends of the film from which water is removed is 1 cm or more. As the manufacturing method of claim 2, it is to remove the water on the entire surface of the film. The production method according to any one of claims 1 to 3, wherein the dry thickness B (mm) of the polyvinyl alcohol film and the distance A (mm) of the raw material satisfy the following formula (1): A≦B×1000 ( 1). The manufacturing method according to any one of claims 1 to 3, wherein water adhering to both ends of the film is removed before the stretching step. The manufacturing method according to any one of claims 1 to 3, wherein a cross-linking step or a fixing treatment step is further applied.

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