JP2022008895A - Method for manufacturing polarization film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a polarization film that can hardly be broken during drawing and drying even when a thin PVA film is used and is excellent in polarization performance.

SOLUTION: A method for manufacturing a polarization film executes at least a swelling process, a dyeing process, and a drawing process, and includes: using a polyvinyl alcohol film having a dry thickness B of 0.001 mm or more and 0.045 mm or less as a raw material; in at least one of the processes, impregnating the polyvinyl alcohol film in water, and subsequently taking out the film from the water and removing the water attached to both ends from both sides of the film, with a distance A from a position at which the film is taken out from the water to a position at which the water is removed being determined to be 28 mm or less; and nipping the film with a pair of rolls to remove the water attached to both ends of the film. The distance a (cm) between rotational shafts of the pair of rolls and the radii b1 (cm) and b2 (cm) of the rolls satisfy the following formula (2). 0.5≤a/(b1+b2)≤0.90 (2).

SELECTED DRAWING: Figure 1

COPYRIGHT: (C)2022,JPO&INPIT

Description

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

A polarizing plate having a function of transmitting and shielding light is a basic component of a liquid crystal display (LCD) together with a liquid crystal that changes the polarization state of light. Many polarizing plates have a structure in which a protective film such as a cellulose triacetate (TAC) film is bonded to the surface of a polarizing film. As the polarizing film constituting the polarizing plate, a polyvinyl alcohol film (hereinafter, “polyvinyl alcohol” may be abbreviated as “PVA”) is uniaxially stretched and oriented on a stretched film, and an iodine-based dye (I _3- ^or I) is used. ₅ ^- etc.) And dichroic organic dyes that have adsorbed dichroic dyes are the mainstream. In such a polarizing film, a PVA film containing a dichroic dye in advance is uniaxially stretched, a bicolor dye is adsorbed at the same time as the uniaxial stretching of the PVA film, or a dichroic after the PVA film is uniaxially stretched. Manufactured by adsorbing dyes.

LCDs are used in a wide range of applications such as small devices such as calculators and watches, notebook computers, liquid crystal monitors, liquid crystal color projectors, liquid crystal televisions, in-vehicle navigation systems, mobile phones, and measuring devices used indoors and outdoors. In recent years, there has been an increasing demand for LCDs for mobile applications such as small notebook computers and mobile phones, and there is a strong demand for thinner polarizing plates.

For these reasons, thinning of the polarizing film is required, and one of the means thereof includes a method of using a thin PVA film as a raw material. However, since the thin PVA film is liable to break during stretching or drying, the production speed of the polarizing film is likely to decrease and the cost is likely to increase due to an increase in defective products. In particular, in the swelling step, the dyeing step, and the like, after the PVA film is immersed in water, the end portion of the film is folded, which causes a problem that the PVA film is broken during stretching or drying.

As a method for producing a thin polarizing film, a method of forming a thin PVA layer on a plastic film by a coating method and then stretching the obtained laminate has been proposed (for example, Patent Documents 1 and 2). However, in such a method, the coating work and the subsequent drying work are complicated. In addition, it was necessary to heat-treat the laminated body in order to insolubilize the PVA layer. Therefore, it is necessary to use a plastic film that can be stretched even after the heat treatment, which is costly. Further, since the adhesive strength between the plastic film and the PVA layer is relatively high, an appropriate neck-in of the PVA layer is hindered during stretching, and it is difficult to obtain a polarizing film having excellent polarizing performance.

Further, there has been proposed a method of removing the liquid on one side of the PVA film taken out from each treatment tank and then widening both ends of the PVA film in the width direction using an expander roll or the like (Patent Document 3). .. However, even if both ends of the PVA film are widened using an expander roll or the like, it is difficult to eliminate the narrow folds having a width of several mm that occur after immersing the thin PVA film in water. Breakage of the PVA film occurred during drying. Further, by performing the treatment of widening both ends of the PVA film, wrinkles are likely to occur in the PVA film, and an abnormality in appearance is likely to occur.

Japanese Patent Application Laid-Open No. 2012-133303 JP 2012-73570 International Publication No. 2014/1158997

The present invention has been made to solve the above problems, and even when a thin PVA film is used, the film is less likely to break during stretching or drying, and a film having excellent polarization performance can be obtained. It is an object of the present invention to provide a method for producing a polarizing film which can be easily obtained.

As a result of diligent studies to achieve the above object, the present inventors, when producing a polarizing film using a thin PVA film, immerse the PVA film in water and immediately after taking it out, the end portion thereof. It was found that creases are likely to occur in the film, which causes stretch breakage in the subsequent stretching step and breakage due to shrinkage of the film in the drying step. Then, after the PVA film is immersed in water and immediately after being taken out, the water adhering to the PVA film is removed from both sides thereof, whereby the occurrence of folding at the end portion of the PVA film is suppressed, and the film It has been found that breakage (breaking of stretch, etc.) can be prevented. As a result of further studies based on these findings, the present invention was completed.

That is, the present invention
[1] A method for producing a polarizing film, wherein a polyvinyl alcohol film is subjected to at least a swelling step, a dyeing step, and a stretching step.
A polyvinyl alcohol film having a dry thickness B of 0.001 mm or more and 0.045 mm or less was used as a raw material.
In at least one of the above steps, when the polyvinyl alcohol film is immersed in water and then taken out from the water to remove the water adhering to both ends from both sides of the film, water is discharged from the position where the film comes out of the water. A method for producing a stretched film in which the distance A to the removed position is 28 mm or less;
[2] The production method of the above [1], wherein the width of both ends of the film for removing water is 1 cm or more.
[3] The production method of the above [2] for removing water on the entire surface of the film;
[4] The production method according to any one of the above [1] to [3], wherein the dry thickness B (mm) of the raw material polyvinyl alcohol film and the distance A (mm) satisfy the following formula (1);
A ≤ B x 1000 (1)
[5] The production method according to any one of the above [1] to [4], wherein the film is niped with a pair of rolls to remove water adhering to both ends of the film.
[6] The method for producing the above [5], wherein the roll is a sponge roll;
[7] The production method of the above [6], wherein the water retention rate of the sponge roll is 50% or more and 95% or less;
[8] Any of the above [5] to [7], wherein the distance a (cm) between the rotation axes of the pair of rolls and the radii b1 (cm) and b2 (cm) of each roll satisfy the following formula (2). Manufacturing method;
0.1 ≤ a / (b1 + b2) ≤ 0.97 (2)
[9] The production method according to any one of the above [1] to [8], which removes water adhering to both ends of the film before the stretching step;
[10] The production method according to any one of the above [1] to [9], which further performs a crosslinking step or a fixing treatment step;
Regarding.

According to the production method of the present invention, even when a thin PVA film is used, the film is less likely to break during stretching or drying, and a polarizing film having excellent polarization performance can be easily produced. ..

It is a schematic diagram which shows an example of a swelling process. It is a schematic diagram which shows the distance A from the position where the PVA film comes out of water to the position where water is removed. FIG. 5 is a schematic diagram showing that in Example 1, a PVA film is continuously unwound and subjected to a swelling step, a dyeing step, and a crosslinking step.

The method for producing a polarizing film of the present invention 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 PVA film, and the dry thickness B as a raw material is 0.001 mm or more and 0.045 mm or less. In at least one of the above steps, the PVA film is immersed in water and then taken out of the water to remove water adhering to both ends of the film. The distance A from the position where water is removed from the position where water is removed is set to 28 mm or less.

In the present invention, the PVA used for producing the PVA film is vinyl acetate, vinyl formate, vinyl propionate, vinyl butyrate, vinyl pivalate, vinyl versatic acid, vinyl laurate, vinyl stearate, vinyl benzoate, isoacetate. It can be produced by a method of saponifying a polyvinyl ester obtained by polymerizing one or more vinyl esters such as propenyl. Among the vinyl esters, vinyl oxycarbonyl group (H ₂ C = CH-O-CO-) in the molecule is easy to produce, easily available, and low in cost. The compound having is preferable, and vinyl acetate is more preferable.

The polyvinyl ester is preferably obtained by using only vinyl ester as a monomer. The vinyl ester used at this time may be two or more kinds, but one kind is preferable. The polyvinyl ester may be a copolymer of one kind or two or more kinds of vinyl esters and another monomer copolymerizable therewith, as long as the effect of the present invention is not impaired. ..

Examples of other monomers copolymerizable with the vinyl ester include α-olefins having 2 to 30 carbon atoms such as ethylene, propylene, 1-butene and isobutene; (meth) acrylic acid or a salt thereof; (meth). ) Methyl acrylate, (meth) ethyl acrylate, (meth) n-propyl acrylate, (meth) i-propyl acrylate, (meth) n-butyl acrylate, (meth) i-butyl acrylate, (meth) (Meta) acrylates such as t-butyl acrylate, 2-ethylhexyl (meth) acrylate, dodecyl (meth) acrylate, octadecyl (meth) acrylate; (meth) acrylamide; N-methyl (meth) ) Acrylamide, N-ethyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide, diacetone (meth) acrylamide, (meth) acrylamide propanesulfonic acid or its salts, (meth) acrylamide propyldimethylamine or its salts, N -(Meta) acrylamide derivatives such as methylol (meth) acrylamide or derivatives thereof; N-vinylamides such as N-vinylformamide, N-vinylacetamide, N-vinylpyrrolidone; methylvinyl ether, ethylvinyl ether, n-propylvinyl ether, i- Vinyl ethers such as propyl vinyl ether, n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether; vinyl cyanide such as (meth) acrylonitrile; vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride Vinyl halides such as, allyl compounds such as allyl acetate and allyl chloride; maleic acid or salts thereof, esters or acid anhydrides; itaconic acid or salts thereof, esters or acid anhydrides; vinylsilyl compounds such as vinyltrimethoxysilane; Saturated sulfonic acid or a salt thereof and the like can be mentioned. The polyvinyl ester can have one or more structural units derived from the other monomer.

The ratio of structural units derived from other monomers to the polyvinyl ester is preferably 15 mol% or less, preferably 10 mol% or less, based on the number of moles of all structural units constituting the polyvinyl ester. More preferably, it is more preferably 5 mol% or less.

The PVA may be modified with one or more graft-copolymerizable monomers as long as the effects of the present invention are not impaired. At this time, graft copolymerization can be performed on polyvinyl ester or PVA. Examples of the graft copolymerizable monomer include unsaturated carboxylic acid or a derivative thereof; unsaturated sulfonic acid or a derivative thereof; and α-olefin having 2 to 30 carbon atoms. The proportion of structural units derived from the graft copolymerizable monomer in the polyvinyl ester or PVA is preferably 5 mol% or less based on the number of moles of all structural units constituting the polyvinyl ester or PVA. The PVA used in the present invention is preferably not graft-copolymerized.

The PVA may or may not be partially crosslinked. Further, the above PVA may or may not form an acetal structure by reacting a part of its hydroxyl group with an aldehyde compound such as acetaldehyde or butyraldehyde.

The average degree of polymerization of PVA is not particularly limited, but is preferably 1,000 or more. When the average degree of polymerization of PVA is 1,000 or more, the polarization performance of the obtained polarizing film can be further improved. If the average degree of polymerization of PVA is too high, the production cost of PVA may increase and the process passability during film formation may be poor. Therefore, the average degree of polymerization of PVA is more preferably 1,000 to 10,000, further preferably 1,500 to 8,000, and particularly preferably 2,000 to 5,000. In the present invention, the average degree of polymerization of PVA means the average degree of polymerization measured according to the description of JIS K6726-1994.

The saponification degree of the PVA is preferably 99.0 mol% or more, more preferably 99.8 mol% or more, and 99.9 mol%, from the viewpoint of improving the moisture and heat resistance of the obtained polarizing film. The above is more preferable. In the present invention, the degree of saponification of PVA is the structural unit (typically a vinyl ester unit) that can be converted into vinyl alcohol unit by saponification and the vinyl alcohol unit with respect to the total number of moles of the vinyl alcohol unit. The ratio of the number of moles (mol%). The degree of saponification can be measured according to the description of JIS K6726-1994.

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

The PVA film may contain a plasticizer. When the PVA film contains a plasticizer, handleability, stretchability and the like 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 can contain one or more of these plasticizers. Of these, glycerin is preferable from the viewpoint of further improving the stretchability of the PVA film.

The content of the plasticizer in the PVA film is preferably 3 to 20 parts by mass, more preferably 5 to 17 parts by mass, and further preferably 7 to 14 parts by mass with respect to 100 parts by mass of PVA. .. When the content of the plasticizer in the PVA film is 3 parts by mass or more with respect 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 prevent the plasticizer from bleeding out to the surface of the PVA film and deteriorating the handleability of the PVA film. be able to.

Further, when a PVA film is produced using a film-forming stock solution described later, the film-forming property is improved and the occurrence of thickness unevenness of the film is suppressed, and when a metal roll or a belt is used for film-forming, the film-forming property is suppressed. From the viewpoint that the PVA film can be easily peeled off from these, it is preferable to include a surfactant in the film-forming stock solution. When a PVA film is produced using a film-forming stock solution containing a surfactant, the obtained PVA film may contain the surfactant. The type of the surfactant is not particularly limited, but an anionic surfactant and a nonionic surfactant are preferable, and a nonionic surfactant is more preferable, from the viewpoint of easily peeling the PVA film from the metal roll or the belt. These surfactants can be used alone or in combination of two or more.

As the anionic surfactant, for example, a carboxylic acid type such as potassium laurate; a sulfate ester type such as octyl sulfate; and a sulfonic acid type such as dodecylbenzene sulfonate are suitable.

Examples of the nonionic surfactant include an alkyl ether type such as polyoxyethylene oleyl ether; an alkylphenyl ether type such as polyoxyethylene octylphenyl ether; an alkyl ester type such as polyoxyethylene laurate; and polyoxyethylene laurylamino. Alkylamine type such as ether; Alkylamide type such as polyoxyethylene lauric acid amide; Polypropylene glycol ether type such as polyoxyethylene polyoxypropylene ether; Alkanolamide type such as lauric acid diethanolamide and oleic acid diethanolamide; Polyoxy An allylphenyl ether type such as alkylene allylphenyl ether is suitable.

The content of the surfactant in the film-forming stock solution is preferably 0.01 to 0.5 parts by mass, more preferably 0.02 to 0.3 parts by mass with respect to 100 parts by mass of PVA. When the content of the surfactant is 0.01 parts by mass or more, the film-forming property and the peelability can be improved. On the other hand, when the content of the surfactant is 0.5 parts by mass or less, it is possible to prevent the surfactant from bleeding out on the surface of the PVA film, causing blocking and deteriorating the handleability. The content of the surfactant in the PVA film is preferably in the above-mentioned range as the content of the surfactant in the film-forming stock solution.

The PVA film may consist only of PVA, or may consist only of PVA and a plasticizer and / or a surfactant. Further, if necessary, it may contain components other than PVA, plasticizers and surfactants such as antioxidants, antifreeze agents, pH regulators, concealing agents, anticoloring agents and oils.

The method for producing a PVA film is not particularly limited, but a cast film forming method, an extrusion film forming method, a wet film forming method, a gel film forming method, or the like is preferable from the viewpoint that a film having a uniform thickness and width can be obtained. The method and the extrusion film forming method are more preferable. Among these film-forming methods, the extrusion film-forming method is particularly preferable because a PVA film having a uniform thickness and width and good physical characteristics can be obtained. As these film forming methods, only one kind may be adopted or two or more kinds may be adopted in combination.

As the film-forming stock solution used for producing PVA film, PVA, a plasticizer if necessary, a surfactant, a film-forming stock solution in which other components are dissolved in a liquid medium, PVA, a plasticizer if necessary, and a surfactant are used. It contains an agent, other components, and a liquid medium, and can be produced using a film-forming stock solution in which PVA is melted. It is preferable that each component in the film-forming stock solution is uniformly mixed.

Examples of the liquid medium used for the film-forming stock solution include water, dimethylsulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, glycerin, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, and trimethylol. Examples thereof include propane, ethylenediamine, and diethylenetriamine, and one or more of these can be used. Of these, water is preferable because it has a small impact on the environment and is recoverable.

The volatile fraction of the membrane-forming stock solution (the content ratio of volatile components such as liquid media removed by volatilization or evaporation during membrane-forming in the membrane-forming stock solution) varies depending on the membrane-forming method, membrane-forming conditions, etc., but is 50 to 95. The mass% is preferable, 55 to 90% by mass is more preferable, and 60 to 85% by mass is further preferable. When the volatile content of the film-forming stock solution is 50% by mass or more, the viscosity of the film-forming stock solution does not become too high, filtration and defoaming during preparation of the film-forming stock solution are smoothly performed, and PVA with few foreign substances and defects. The production of the film becomes easy. On the other hand, when the volatile fraction 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 the industrial PVA film can be easily produced. The PVA film obtained by forming a film can be dried or heat-treated as needed.

The shape of the PVA film is not particularly limited, but a long PVA film is preferable because the polarizing film can be continuously produced with good productivity. The length of the PVA film is not particularly limited and can be appropriately set according to the intended use of the polarizing film to be manufactured, for example, 5 to 20,000 m. The width of the PVA film is not particularly limited, but it is preferably 50 cm or more, more preferably 2 m or more, and further preferably 4 m or more because a wide polarizing film has been demanded in recent years. The upper limit of the width of the PVA film is not particularly limited, but if it is too wide, it tends to be difficult to uniformly stretch the polarizing film when the polarizing film is manufactured by a practical device. The width is preferably 7 m or less.

In the present invention, the dry thickness B of the PVA film needs to be 0.001 mm or more and 0.045 mm or less. When a film thinner than the conventionally used PVA film is used as a raw material for the polarizing film, folds are likely to occur at the edges in the width direction, which is a problem. On the other hand, according to the production method of the present invention, even when a thin PVA film is used, the edges are prevented from being folded, so that the film is less likely to break during stretching or drying, and is expensive. Since it can be stretched at a stretch ratio, it is possible to easily manufacture a polarizing film having excellent polarizing performance. The dry thickness B of the PVA film is preferably 0.035 mm or less. The lower limit of the thickness of the PVA film is not particularly limited, but it is preferably 0.003 mm or more because the polarizing film can be produced more easily. Further, the PVA film may be a single layer or a laminated body in which a PVA layer and another layer are laminated, but the PVA film is a single layer because the effect of the present invention is more remarkable. Is preferable. In the case of a laminated body, the thickness of the PVA layer is preferably in the above range.

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

[Swelling process]
The swelling step of swelling the PVA film can be performed by immersing the PVA film in water. Usually, the raw material PVA film is first subjected to a swelling step. The temperature of water when the PVA film is swelled is preferably 20 to 40 ° C, more preferably 22 to 38 ° C, and even more preferably 25 to 35 ° C. The time for soaking in water is preferably 0.5 to 5 minutes, more preferably 1 to 3 minutes. The water when immersed in water is not limited to pure water, and may be an aqueous solution in which various components are dissolved, or may be a mixture of water and a water-soluble organic solvent.

[Dyeing process]
The dyeing step of dyeing the PVA film can be performed by immersing the PVA film in an aqueous solution containing a dichroic dye. The concentration of the dichroic dye in the aqueous solution can be appropriately set according to the type of the dichroic dye and the like, and can be, for example, in the range of 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 on the PVA film. The concentration of iodine (I ₂ ) in the aqueous solution is preferably 0.01 to 1.0% by mass, and the concentration of potassium iodide (KI) is preferably 0.01 to 10% by mass. The temperature of the aqueous solution containing the dichroic dye during the dyeing treatment is preferably 20 to 50 ° C, more preferably 25 to 40 ° C, from the viewpoint that the dichroic dye can be efficiently adsorbed on the PVA film. The time for immersing the PVA film in the aqueous solution is preferably 0.1 to 10 minutes, more preferably 0.2 to 5 minutes.

Examples of the above dichroic dye include iodine-based dyes (I _3- ^, I _5- ^, etc.), dichroic organic dyes, and the like. The iodine-based dye can be obtained, for example, by contacting iodine (I ₂ ) with potassium iodide. The 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 Violet 9, 12, 51, 98; Direct Green 1, 85; Direct Yellow 8, 12, 44, 86, 87; Direct Orange 26, 39, 106, 107 and the like. Among these dichroic dyes, iodine-based dyes are preferable from the viewpoints of handleability, availability, and polarization performance. The dichroic dye may be one kind or two or more kinds, ^and may be an equilibrium mixture such as I _3- ^and I _5- .

[Crosslinking process]
The cross-linking step of carrying out 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 the crosslinked structure into the PVA film, it is possible to effectively prevent the PVA in the film from elution into water even when wet stretching is performed at a relatively high temperature. From this point of view, it is preferable that the crosslinking step is performed after the dyeing step. As the cross-linking agent, one or more boron compounds such as borate such as boric acid and borax can be used. The concentration of the cross-linking agent in the aqueous solution is preferably 1 to 15% by mass, more preferably 2 to 7% by mass. The aqueous solution containing the cross-linking agent may contain an auxiliary agent such as potassium iodide. The temperature of the aqueous solution during the crosslinking treatment is preferably 20 to 50 ° C, more preferably 25 to 40 ° C.

Apart from the stretching step described later, the PVA film may be stretched during or between the above-mentioned steps. By performing such stretching (pre-stretching), it is possible to prevent the PVA film from wrinkling. The total stretching ratio of the pre-stretching (magnification obtained by multiplying the stretching ratio in each step) is 4 times or less based on the original length of the raw material PVA film before stretching from the viewpoint of the polarization performance of the obtained polarizing film. It is preferably present, and more preferably 1.5 to 3.5 times. The draw ratio in the swelling step is preferably 1.1 to 3 times, more preferably 1.2 to 2.5 times, still more preferably 1.4 to 2.3 times. The draw ratio in the dyeing step is preferably 2 times or less, more preferably 1.8 times or less, still more preferably 1.1 to 1.5 times. The draw ratio in the crosslinking step is preferably 2 times or less, more preferably 1.5 times or less, still more preferably 1.05 to 1.3 times.

[Stretching process]
In the stretching step of stretching the PVA film, the stretching method is not particularly limited, and either a wet stretching method or a dry stretching method may be used. In the case of the wet stretching method, it can be carried out in an aqueous solution containing one or more boron compounds such as borate such as boric acid and borax, or in an aqueous solution containing the above-mentioned bicolor dye. It can also be carried out in an aqueous solution used in the fixing treatment described later. In the case of the dry stretching method, the PVA film may be stretched at room temperature, or the PVA film may be stretched while applying heat. Further, the PVA film may be made to absorb water and then stretched. Among these, the wet stretching method is preferable from the viewpoint of the uniformity of the thickness in the width direction of the obtained polarizing film. As a wet stretching method, a method of stretching in an aqueous boric acid solution is preferable. The concentration of boric acid in the aqueous solution is preferably 0.5 to 6.0% by mass, more preferably 1.0 to 5.0% by mass, and even more preferably 1.5 to 4.0% by mass. The aqueous solution containing the above-mentioned boron compound may contain potassium iodide, and the concentration thereof is preferably in the range of 0.01 to 10% by mass.

The temperature at which the PVA film is stretched in the stretching step is preferably 30 to 90 ° C, more preferably 40 to 80 ° C, still more preferably 50 to 70 ° C.

The draw ratio in the stretching step is preferably 1.2 times or more, more preferably 1.5 times or more, and more preferably 2 times or more, because a polarizing film having more excellent polarizing performance can be obtained. It is more preferable to have. Further, the total draw ratio (magnification multiplied by the draw ratio in each step) including the draw ratio of the above-mentioned pre-stretch is 5.5 times or more based on the original length of the raw material PVA film before stretch. It is preferably 5.7 times or more, more preferably 5.8 times or more, and particularly preferably 5.9 times or more. By setting the total draw ratio within the above range, a polarizing film having better 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 or lateral uniaxial stretching in the length direction in a long PVA film can be adopted. Among them, uniaxial stretching in the length direction is preferable from the viewpoint that a polarizing film having better polarizing performance can be obtained. Uniaxial stretching in the length direction can be performed by using a stretching device including a plurality of rolls parallel to each other and changing the peripheral speed between the rolls. On the other hand, the horizontal uniaxial stretching can be performed using a tenter type stretching machine.

[Fixing process]
The fixing treatment in the fixing treatment step is mainly performed to strengthen the adsorption of the dichroic dye on the stretched PVA film. The fixing treatment can be performed by immersing the stretched PVA film in the fixing treatment liquid. As the fixing treatment liquid, an aqueous solution containing one or more boron compounds such as borate such as boric acid and borax can be used. The concentration of the boron compound in the aqueous solution is generally preferably 2 to 15% by mass, more preferably 3 to 10% by mass. The temperature of the fixing treatment liquid is preferably 15 to 60 ° C, more preferably 20 to 40 ° C. Further, if necessary, an iodine compound or a metal compound may be added to the fixing treatment liquid.

In the production method of the present invention, in at least one of the above-mentioned swelling step, dyeing step and stretching step, the PVA film is immersed in water, then taken out from the water and adhered to both ends of the PVA film from both sides. Need to be removed. Then, when the PVA film is taken out from water and the water adhering to the PVA film is removed, the distance A from the position where the PVA film comes out of the water to the position where the water is removed needs to be 28 mm or less. be.

The production method of the present invention, in which the PVA film is immersed in water and then taken out from the water and the water adhering to the film is removed by a predetermined method, will be described below by using a swelling step as an example. FIG. 1 is a schematic view showing an example of the swelling step 5. FIG. 2 is a schematic view showing a distance A from a position 8 where the PVA film 1 comes out of the water 6 to a position 9 where the water is removed in the manufacturing method of the present invention. In the swelling step 5, the PVA film 1 is usually swelled by immersing the PVA film 1 in water 6. Then, the PVA film 1 is taken out from the water 6 and the water adhering to both ends in the width direction is removed from both sides of the PVA film 1. By removing water from both sides of the PVA film 1, the occurrence of folds at the edges of the PVA film 1 is suppressed.

As a method for removing the water adhering to the PVA film 1, a method of niping the PVA film 1 with a pair of rolls 2 to remove the water adhering to both ends of the PVA film 1 is preferable.

The outer diameter of the roll 2 used in the present invention (maximum diameter when the diameter changes in the axial direction) is preferably 10 cm or less, preferably 8 cm or less, from the viewpoint of easily shortening the distance A. Is more preferable, and 6 cm or less is further preferable. The lower limit of the outer diameter of the roll 2 is not particularly limited, but is usually 1 cm or more. When the sponge roll 2 described later is used as the roll 2, if the outer diameter is less than 1 cm, the water absorption amount of the sponge roll 2 may be insufficient. A part or all of the roll 2 may be immersed in water 6. When niping the PVA film 1 with the roll 2, the water removed from the PVA film 1 and the water absorbed by the roll 2 are squeezed out in the direction opposite to the flow direction of the PVA film 1 and discharged into the water 6. To. 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 water removal efficiency, it is preferable that the roll 2 is not immersed in water.

The roll 2 may be either a non-rotating type or a rotating type, but it is necessary to reduce disturbances such as scratches on the polarizing film obtained by reducing the friction between the PVA film 1 and the roll 2. The latter is preferable because it can be used.

As the roll 2, sponge rolls, rubber rolls and the like are preferable, and sponge rolls are more preferable. The sponge used as the outer layer of the sponge roll is not particularly limited, and examples thereof include polyurethane sponges, PVA sponges, and polyvinyl chloride sponges, and polyurethane sponges are preferable.

The water retention rate of the sponge roll 2 obtained by the following formula is not particularly limited, but is preferably 50% or more, preferably 67% or more, from the viewpoint of further extending the period during which continuous water can be removed. More preferably, it is more preferably 75% or more. On the other hand, the water retention rate of the sponge roll is 95% or less from the viewpoint that the water absorbed by the sponge roll can be easily squeezed out and the water adhering to the PVA film 1 can be removed more efficiently. It is preferably 92% or less, more preferably 90% or less, and even more preferably 90% or less. The water retention rate is an index of the water absorption performance of the sponge roll. 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 piece obtained by cutting off a part of the sponge portion of the sponge roll 2 by the following formula. The sponge mass b after water absorption is obtained by immersing the sponge piece before water absorption in water at 23 ° C. for 24 hours, taking it out with tweezers, and then measuring the sponge mass after watering or dropping for 1 minute. Be done.
Water retention rate (%) = 100 × (ba) / b

In the formula, a indicates the mass of the sponge before water absorption (g), and b indicates the mass of the sponge after water absorption (g). Note that a and b are masses excluding the mass of the core metal portion of the sponge roll.

In the present invention, the pressure when niping with the pair of rolls 2 is not particularly limited, but if the nip pressure is too low, the water adhering to the PVA film 1 may not be sufficiently removed. The nip pressure is preferably 1 kgf / cm or more, more preferably 3 kgf / cm or more, and even more preferably 5 kgf / cm or more. The upper limit of the nip pressure is not particularly limited, but the nip pressure is preferably 15 kgf / cm or less from the viewpoint of reducing disturbances such as scratches on the polarizing film.

The compression ratio [a / (b1 + b2)] of the roll 2 calculated from the distance a (cm) between the rotation axes of the pair of rolls 2 and the radii b1 (cm) and b2 (cm) of each roll is the following formula ( It is preferable to satisfy 2). In this case, the pair of rolls 2 come into contact with each other and are compressed. By arranging the pair of rolls 2 so as to satisfy the following formula (2), the water adhering to the PVA film 1 is more easily absorbed by the rolls 2, and the water absorbed by the rolls 2 is more easily absorbed. Since it can be squeezed out, the efficiency of removing water is further improved. From the viewpoint of further improving the water removal efficiency, the compression ratio [a / (b1 + b2)] is more preferably 0.95 or less, and further preferably 0.90 or less. On the other hand, the compression ratio [a / (b1 + b2)] is more preferably 0.3 or more, and further preferably 0.5 or more, from the viewpoint of further reducing disturbances such as scratches on the obtained polarizing film. The radii b1 and b2 of each roll are half the outer diameter of the roll. The radii b1 and b2 when the roll 2 has a core metal are values including the core metal portion.
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 sides of the PVA film 1. When water adheres to the end of the PVA film 1, the surface tension of the water causes the end to fold. Here, it is important to remove water from both sides of one end of the PVA film. Even if water adheres to only one surface of one end of the PVA film, folding occurs. From the viewpoint of more effectively suppressing the occurrence of folds, the width of each end of the PVA film 1 from which water is removed is preferably 1 cm or more from the end to the center, and is preferably 3 cm. It is more preferably 5 cm or more, and further preferably 5 cm or more. Further, 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, with respect to the width of the PVA film 1, respectively. It is more preferably 1/10 or more.

It is particularly preferable to remove the water on the entire surface of the PVA film 1. As a result, the occurrence of folds is more effectively suppressed. Further, the adhesion of water to the guide roll 3 and the take-up roll 4 arranged downstream is prevented, and the water does not drip from the guide roll 3 and the take-up roll 4, so that the water adheres to the PVA film 1 again. Can be avoided. Further, in the stretching step, the occurrence of physical characteristics such as swelling spots and stretchable spots in the width direction of the PVA film 1 can be reduced, so that it is possible to suppress the occurrence of stretch breakage and optical spots of the obtained polarizing film. ..

In the present invention, when removing the water adhering to the end of the PVA film 1, the distance A from the position 8 where the PVA film 1 comes out of the water 6 to the position 9 where the water is removed from the PVA film 1 is 28 mm. It should be as follows. From the position 8 where the PVA film 1 comes out of the water to the position 9 where the water is removed, the PVA film 1 having water attached to the end portion is transported alone. The present inventors have found that when the PVA film 1 having water attached to the end portion is transported alone, folding occurs in a short time. When the distance A exceeds 28 mm, the occurrence of folding of one end of the PVA film increases sharply. As shown in FIGS. 2 and 3, when water is removed by niping the PVA film 1 with the roll 2, the PVA is where the PVA film 1 first contacts either of the pair of rolls 2. The position 9 where water is removed from the film 1 is set.

The distance A is preferably 25 mm or less, more preferably 20 mm or less, and even more preferably 15 mm or less. The distance A may be 0 mm. For example, the PVA film 1 taken out from the water after removing water in advance by arranging at least a part of the roll 2 in the water 6 and niping the PVA film 1 in the water 6 directly with the roll 2. When the transportation is started, the distance A becomes 0 mm. Since the amount of water accompanying the surface of the PVA film decreases as the distance A increases, the water on the surface of the PVA film can be removed more efficiently, and the occurrence of folds at the widthwise ends of the PVA film 1 is more effective. The distance A is preferably 1 mm or more, more preferably 3 mm or more, and further preferably 5 mm or more, from the viewpoint of being able to be effectively suppressed.

It is preferable that the dry thickness B (mm) of the raw material PVA film 1 and the distance A (mm) satisfy the following formula (1). This makes it possible to more effectively suppress the occurrence of folds even in the extremely thin PVA film 1.
A ≤ B x 1000 (1)

As described above, the PVA film 1 is taken out from the water 6 to remove the water adhering to both ends from both sides of the PVA film 1, and from the position where the PVA film 1 comes out of the water 6 to the position where the water is removed. It is a major feature of the present invention that the distance A of the above is within a predetermined range. In the relatively thick PVA film used conventionally, there was no problem of film breakage due to the folding of the end portion. Therefore, in the production of polarizing films, guide rolls and nip rolls were sometimes used for the purpose of transporting and holding PVA films, but they are also used to prevent folding of the edges, and these are used in the treatment bath. It was never placed near the surface of the water. On the other hand, as a method of preventing the end of the thin PVA film from folding, a method of removing the liquid on one side of the PVA film and then widening both ends of the PVA film in the width direction is known (Patent Document 3). However, the PVA film may still be broken due to the folding of the end portion, and improvement is required. As a result of diligent studies by the present inventors in order to solve such a problem, when the PVA film 1 is thin, the end portion is folded immediately after the PVA film 1 is taken out from the water 6, and the PVA film has a fold. It was found that when water was removed from only one side, the surface tension of the water remaining on the other side caused the edges to fold. Then, by removing water from both sides of the PVA film 1 and setting the distance A from the position where the PVA film 1 comes out of the water 6 to the position where the water is removed within a predetermined range, such folding occurs. It was found that the occurrence of breakage of the PVA film 1 during stretching and drying is reduced.

In the production method of the present invention, a polarizing film is produced by subjecting a raw material PVA film to at least the swelling step, the dyeing step, and the stretching step. At this time, it is preferable to further perform the cross-linking step or the fixing treatment step on the PVA film, and it is more preferable to carry out the cross-linking step and the fixing treatment step. Further, 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 cross-linking step and the stretching step can be performed in one treatment bath.

In the production method of the present invention, it is preferable to remove water adhering to both ends of the PVA film before the stretching step. In the production of the polarizing film, breakage of the PVA film is particularly likely to occur during stretching. Therefore, in the step prior to the stretching step, the PVA film is immersed in water and then taken out of the water and adhered to both ends of the PVA film. By removing the water obtained by using the method described above, the breakage of the PVA film is further suppressed. Examples of the step performed before the stretching step include the swelling step and the dyeing step, and it is preferable to remove water adhering to both ends of the PVA film in at least one of these steps, and PVA in both. It is more preferable to remove the water adhering to both ends of the film. When the production method of the present invention further includes the cross-linking step, the step performed before the stretching step includes the swelling step, the dyeing step and the cross-linking step, and in at least one of these, PVA It is preferable to remove the water adhering to both ends of the film, more preferably to remove the water adhering to both ends of the PVA film in the swelling step and the dyeing step, the swelling step, the dyeing step and the dyeing step. In the cross-linking step, it is more preferable to remove water adhering to both ends of the PVA film.

From the viewpoint of further reducing the occurrence of film breakage due to shrinkage in the drying step described later, water adhering to both ends of the PVA film is removed in the stretching step or a subsequent step (for example, the fixing treatment step). Is preferable.

As a preferred embodiment of the production method of the present invention, the PVA film is subjected to the swelling step, the dyeing step, the cross-linking step and the stretching step in this order, and the swelling step, the dyeing step and the cross-linking step are performed in this order. In at least one of them, there is a method of immersing the PVA film in water and then removing the water adhering to both ends of the PVA film by taking it out of the water by using the method described above. At this time, it is preferable to remove the water adhering to the PVA film in the swelling step and the dyeing step, and it is more preferable to remove the water adhering to the PVA film in the swelling step, the dyeing step and the cross-linking step. preferable. It is also preferable that the PVA film is subjected to the swelling step, the dyeing step, the cross-linking step, the stretching step and the immobilization treatment step in this order.

[Drying process]
A polarizing film can be produced by subjecting the PVA film to the stretching step and, if necessary, a fixing treatment step, 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. Drying at such a temperature improves the dimensional stability of the polarizing film.

[Polarizer]
A protective film that is optically transparent and has mechanical strength is bonded to at least one surface of the polarizing film obtained as described above to be 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 adhesiveness of the adhesive to the polarizing film or protective film, even if the bonded surface of the polarizing film or protective film is subjected to surface treatment such as saponification treatment, corona treatment, plasma treatment, ultraviolet irradiation, primer treatment, etc. good. As the adhesive for adhering the polarizing film and the protective film, a PVA-based adhesive, a urethane-based adhesive, an ultraviolet curable adhesive, or the like is used.

Hereinafter, the present invention will be specifically described with reference to Examples, but the present invention is not limited to these Examples. In addition, each measurement method and evaluation method adopted in the following Examples and Comparative Examples are shown below.

[Stretching ratio capable of continuous operation]
In the following Examples, Comparative Examples and Reference Examples, the total draw ratio is gradually increased by 0.1 times by adjusting the draw ratio in the stretching step, and the total draw ratio when the film breaks occurs. The total draw ratio set immediately before was set as the draw ratio capable of continuous operation.

[Polarization performance of polarizing film]
(A) Measurement of Transmittance Ts In the following Examples, Comparative Examples and Reference Examples, a rectangular sample of 3 cm in the length direction and 2 cm in the width direction of the obtained polarizing film from the central portion in the width direction. Two sheets were collected. Using a spectrophotometer with an integrating sphere (“V7100” manufactured by Nippon Kogaku Co., Ltd.), the visibility correction of the visible light region of the C light source and 2 ° field is performed in accordance with JIS Z8722: 2009 (measurement method of object color). Then, for one sample, the light transmittance when tilted 45 ° with respect to the length direction and the light transmittance when tilted −45 ° were measured, and their average value Ts1 (%) was calculated. I asked. Similarly for the other sample, the light transmittance when tilted by 45 ° and the light transmittance when tilted by −45 ° were measured, and their average value Ts2 (%) was obtained. Ts1 and Ts2 were averaged according to the following formula to obtain the transmittance Ts (%) of the polarizing film.
Ts = (Ts1 + Ts2) / 2

(B) Measurement of degree of polarization V Light transmittance T∥ (%) and length when two samples collected in the above-mentioned measurement of transmittance Ts are stacked so that their length directions are parallel to each other. The light transmittance T⊥ (%) when the light is overlapped so as to be orthogonal to each other is measured in the same manner as in the case of “(a) Measurement of transmittance Ts” above, and the degree of polarization V (%) is measured by the following formula. ) Was asked.
V = {(T∥-T⊥) / (T∥ + T⊥)} ^1/2 × 100

[Evaluation of the occurrence of folds]
In the following Examples, Comparative Examples, and Reference Examples, in each of the swelling step 5, the dyeing step 10, and the cross-linking step 11, the end portion of the PVA film immediately before contacting with the guide roll 3 was visually observed, and the occurrence of folds occurred. The presence or absence was evaluated. The following A and B were determined to be acceptable, and C was determined to be unacceptable.
A: No creases were observed at the widthwise edges of the PVA film after passing through any of the steps.
B: Only after passing through the cross-linking step 11, a slight crease having a width of about 0.5 mm occurred at one end of the PVA film.
C: After passing through the cross-linking step 11 and after passing through other steps, a large number of folds of about 0.5 to 3 mm occurred at both ends of the PVA film.

Example 1
100 parts by mass of long PVA film 1 [PVA (saponified product of vinyl acetate homopolymer having a degree of polymerization of 2,400 and a degree of saponification of 99.9 mol%) with a thickness of 0.030 mm and a width of 65 cm when dried) , 12 parts by mass of glycerin and 0.03 part by mass of surfactant] are continuously unwound from the film roll 7 and continuously subjected to the swelling step 5, the dyeing step 10 and the crosslinking step 11 in this order. did. FIG. 3 shows a schematic view showing that the PVA film 1 is continuously unwound from the film roll 7 and subjected to the swelling step 5, the dyeing step 10, and the crosslinking step 11.

Here, as the swelling step 5, the PVA film 1 was immersed in distilled water (temperature: 30 ° C.) for 1 minute, and uniaxially stretched in the length direction at a stretching ratio of 2.0 times during that period. Further, as the dyeing step 10, the PVA film 1 is immersed in an aqueous solution containing an iodine-based dye (iodine concentration: 0.05% by mass, potassium iodide concentration: 1.2% by mass, temperature: 30 ° C.) for 2 minutes. In the meantime, uniaxial stretching was performed in the length direction at a stretching ratio of 1.2 times. Further, as the cross-linking step 11, the PVA film 1 is immersed in an aqueous boric acid solution (boric acid concentration: 2.6% by mass, temperature: 30 ° C.) for 2 minutes, during which the uniaxial film has a draw ratio of 1.1 times in the length direction. It was stretched.

Further, as shown in FIG. 3, in the swelling step 5, the dyeing step 10, and the cross-linking step 11, a pair of sponge rolls 2 (AC sponge U manufactured by AC Chemical Co., Ltd .; urethane sponge, arranged in parallel near the water surface). A water retention rate of 78%, a roll outer diameter of 50 mm, a core metal outer diameter of 10 mm, a roll width of 80 cm, a distance between rotating shafts of 44 mm, and a compression ratio of 88%) were installed. At this time, the position of the sponge roll 2 is such that the rotation axis of each sponge roll 2 is parallel to the width direction of the PVA film 1 and the plane including the rotation axis of each sponge roll 2 is perpendicular to the PVA film 1. Was adjusted. Then, the PVA film 1 discharged from the water was niped over the entire width direction to remove the water adhering to the PVA film 1. Here, as shown in FIG. 2, in the swelling step 5, the dyeing step 10, and the crosslinking step 11, the distance between the position 8 where the PVA film 1 comes out of the water 6 and the position 9 where the water is removed from the PVA film 9 A was set to 20 mm. The position where the PVA film 1 first contacts one of the two sponge rolls 2 is set to the position 9 where water is removed from the PVA film. Further, in each step, as described above, after the PVA film 1 from which water has been removed comes into contact with the guide roll 3 (the roll that contacts the entire width direction of the PVA film 1), the pair of take-up rolls 4 (the PVA film). The guide roll 3 and the take-up roll 4 are installed downstream of the sponge roll 2 so as to come into contact with the rolls that come into contact with each other over the entire width direction of 1.

Following the above-mentioned crosslinking step 11, a stretching step, a fixing treatment step, and a drying step were continuously performed in this order to produce a polarizing film. In the stretching step, the PVA film 1 is uniaxially arranged in a boric acid aqueous solution (boric acid concentration: 2.8% by mass, potassium iodide concentration: 5% by mass, temperature: 57 ° C.) at a stretching ratio of 1.9 times in the length direction. This was performed by stretching (the total stretching ratio including the stretching ratio of the previous stretching was 5.0 times). The fixing treatment step is 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. rice field. Further, the drying step was performed by drying the stretched PVA film 1 at 60 ° C. for 1 minute to obtain a polarizing film.

Examples 2-5, Comparative Example 3
A polarizing film was produced in the same manner as in Example 1 except that the thickness and distance A of the PVA film 1 were changed as shown in Table 1.

[Example 6]
A polarizing film was produced in the same manner as in Example 3 except that the water adhering to the PVA film 1 was not removed without installing the pair of sponge rolls 2 in the crosslinking step 11.

[Comparative Example 1]
Continuously in the same manner as in Example 2 except that the water adhering to the PVA film 1 was not removed in the swelling step 5, the dyeing step 10, and the crosslinking step 11 without installing the pair of sponge rolls 2. The polarizing film was manufactured.

[Comparative Example 2]
In the swelling step 5, the dyeing step 10, and the crosslinking step 11, only the lower sponge roll 2 is installed among the pair of sponge rolls 2, and the sponge roll 2 is brought into contact with only one surface of the PVA film 1. A polarizing film was produced in the same manner as in Example 2 except that the water adhering to the PVA film was removed.

[Reference Example 1]
The thickness of the PVA film 1 was set to 0.060 mm, and the water adhering to the PVA film 1 was not removed in the swelling step 5, the dyeing step 10, and the crosslinking step 11 without installing the pair of sponge rolls 2. Made a polarizing film in the same manner as in Example 1.

Table 1 summarizes the production conditions and evaluation results of Examples 1 to 6, Comparative Examples 1 to 3, and Reference Example.

1 PVA film 2 roll 3 guide roll 4 take-up roll 5 swelling step 6 water 7 film roll of PVA film 8 position where PVA film is taken out from water 9 position where water is removed from PVA film 10 dyeing step 11 cross-linking step

Claims (8)

A method for producing a polarizing film, which comprises performing at least a swelling step, a dyeing step, and a stretching step on a polyvinyl alcohol film.
A polyvinyl alcohol film having a dry thickness B of 0.001 mm or more and 0.045 mm or less was used as a raw material.
In at least one of the above steps, when the polyvinyl alcohol film is immersed in water and then taken out from the water to remove the water adhering to both ends from both sides of the film, water is discharged from the position where the film comes out of the water. The distance A to the removed position is set to 28 mm or less.
By niping the film with a pair of rolls, water adhering to both ends of the film is removed.
A method for producing a polarizing film, wherein the distance a (cm) between the rotation axes of the pair of rolls and the radii b1 (cm) and b2 (cm) of the rolls satisfy the following formula (2).
0.5 ≤ a / (b1 + b2) ≤ 0.90 (2) The manufacturing method according to claim 1, wherein the width of both ends of the film for removing water is 1 cm or more. The manufacturing method according to claim 2, wherein the water on the entire surface of the film is removed. The production method according to any one of claims 1 to 3, wherein the dry thickness B (mm) of the raw material polyvinyl alcohol film and the distance A (mm) satisfy the following formula (1).
A ≤ B x 1000 (1) The production method according to any one of claims 1 to 4, wherein the roll is a sponge roll. The production method according to claim 5, wherein the water retention rate of the sponge roll is 50% or more and 95% or less. The production method according to any one of claims 1 to 6, wherein water adhering to both ends of the film is removed before the stretching step. The production method according to any one of claims 1 to 7, further comprising a crosslinking step or a fixing treatment step.

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