WO2018016542A1

WO2018016542A1 - Method for producing polarizing film

Info

Publication number: WO2018016542A1
Application number: PCT/JP2017/026159
Authority: WO
Inventors: 絵美川崎; 修風藤
Original assignee: 株式会社クラレ
Priority date: 2016-07-20
Filing date: 2017-07-19
Publication date: 2018-01-25
Also published as: JPWO2018016542A1; JP2022008895A; TW201819151A; TWI790207B

Abstract

Provided 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, wherein a stretched film is produced using, as a starting material, a polyvinyl alcohol film having a dry film thickness B between 0.001-0.045 mm inclusive, and in at least one of said steps, following immersion of the polyvinyl alcohol film in water, when the film is taken out of the water and water adhering to both ends of the film is removed from both surfaces thereof, a distance A from a position at which the film is taken out of the water to a position at which the water is removed is set to 28 mm or less. This production method enables easy production of a polarizing film having excellent polarization performance, and is less likely to cause damage to a film during stretching or drying even when a thin polyvinyl alcohol film is used.

Description

Manufacturing method of polarizing film

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 light transmission and shielding function is a basic component of a liquid crystal display (LCD) together with a liquid crystal that changes a 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 a polarizing film constituting the polarizing plate, a polyvinyl alcohol film (hereinafter, “polyvinyl alcohol” may be abbreviated as “PVA”) is uniaxially stretched and oriented with an iodine dye (I ₃ ^- or I ₅ ^- such dichroic dyes, etc.) or a dichroic organic dye has become mainstream those adsorbed. Such a polarizing film can be obtained by uniaxially stretching a PVA film preliminarily containing a dichroic dye, adsorbing a dichroic dye simultaneously with uniaxial stretching of the PVA film, or dichroic after uniaxially stretching the PVA film. 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, demand for LCDs for mobile applications such as small notebook computers and mobile phones has increased, and there is a strong demand for thinner polarizing plates.

For these reasons, it is required to make the polarizing film thin, and one of the means is a method using a thin PVA film as a raw material. However, since a thin PVA film is likely to break when stretched or dried, the production speed of the polarizing film is reduced and the cost is increased due to an increase in defective products. In particular, in the swelling process, the dyeing process, etc., the film ends are folded after the PVA film is immersed in water, and this causes a problem that the PVA film breaks during stretching or drying.

As a method for producing a thin polarizing film, there has been proposed a method in which a thin PVA layer is formed on a plastic film by a coating method and then the obtained laminate is stretched (for example, Patent Documents 1 and 2). However, such a method requires complicated coating work and subsequent drying work. Moreover, in order to insolubilize a PVA layer, it was necessary to heat-process a laminated body. For this reason, it is necessary to use a plastic film that can be stretched even after heat treatment, which is expensive. Furthermore, since the adhesive strength between the plastic film and the PVA layer is relatively high, an appropriate neck-in of the PVA layer is prevented at the time of stretching, and it is difficult to obtain a polarizing film having excellent polarization performance.

Moreover, after removing the liquid of the single side | surface of the PVA film taken out from each processing tank, the method of giving the process which expands the both ends of the width direction of a PVA film using an expander roll etc. is proposed (patent document 3). . However, it is difficult to eliminate the thin folds of several mm width that occur after the thin PVA film is immersed in water even if the both ends of the PVA film are widened using an expander roll or the like. The PVA film broke during drying. Moreover, by performing the process which expands the both ends of a PVA film, it became easy to wrinkle a PVA film and it was easy to generate | occur | produce abnormal appearance.

JP 2012-133303 A JP 2012-73570 A International Publication No. 2014/115897

The present invention has been made in order 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 is obtained. It aims at providing the manufacturing method of the polarizing film which can be obtained easily.

As a result of intensive studies to achieve the above object, the inventors of the present invention have produced a polarizing film using a thin PVA film. As a result, it has been found that it is easy to cause breakage in the subsequent stretching process, and breakage due to film shrinkage is likely to occur in the drying process. And after immersing a PVA film in water, immediately after taking out, by removing the water adhering to a PVA film from the both surfaces, generation | occurrence | production of the folding in the edge part of the said PVA film is suppressed, It has been found that breakage (breakage of stretching, 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 for subjecting a polyvinyl alcohol film to at least a swelling step, a dyeing step, and a stretching step,
Using a polyvinyl alcohol film having a dry thickness B of 0.001 mm to 0.045 mm as a raw material,
In at least one of the steps, after immersing the polyvinyl alcohol film in water, when removing the water adhering to both ends from both sides of the film, water is removed 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 from which water is removed is 1 cm or more;
[3] The production method of the above [2], wherein water on the entire surface of the film is removed;
[4] The production method of any one of [1] to [3], wherein the dry thickness B (mm) of the raw polyvinyl alcohol film and the distance A (mm) satisfy the following formula (1):
A ≦ B × 1000 (1)
[5] The method according to any one of [1] to [4] above, wherein water attached to both ends of the film is removed by nipping the film with a pair of rolls;
[6] The method according to [5], wherein the roll is a sponge roll;
[7] The production method of the above [6], wherein the water retention 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 method according to any one of [1] to [8], wherein water attached to both ends of the film is removed before the stretching step;
[10] The production method of any one of [1] to [9], wherein a crosslinking step or a fixing treatment step is further performed;
About.

According to the production method of the present invention, even when a thin PVA film is used, the film is not easily broken during stretching or drying, and a polarizing film having excellent polarization performance can be easily produced. .

It is the schematic which shows an example of a swelling process. It is the schematic which shows the distance A from the position where a PVA film comes out of water to the position where water is removed. In Example 1, it is the schematic which shows unwinding a PVA film continuously and performing a swelling process, a dyeing process, and a bridge | crosslinking process.

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 process, a dyeing process, and a stretching process are performed on a PVA film, and a 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 steps, the PVA film is immersed in water and then removed from the water, and when the water adhering to both ends of the film is removed, the film is water. The distance A from the position where the water exits to the position where the water is removed is 28 mm or less.

In the present invention, PVA used for the production of PVA film is vinyl acetate, vinyl formate, vinyl propionate, vinyl butyrate, vinyl pivalate, vinyl versatate, vinyl laurate, vinyl stearate, vinyl benzoate, 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, a vinyloxycarbonyl group (H ₂ C═CH—O—CO—) is included in the molecule from the viewpoints of easy production of PVA, easy availability, and cost reduction. Are preferred, and vinyl acetate is more preferred.

The polyvinyl ester is preferably obtained using only vinyl ester as a monomer. Two or more vinyl esters may be used at this time, but one is preferable. As long as the effects of the present invention are not impaired, the polyvinyl ester may be a copolymer of one or two or more vinyl esters and other monomers copolymerizable therewith. .

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 salts thereof; ) Methyl acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, i-propyl (meth) acrylate, n-butyl (meth) acrylate, i-butyl (meth) acrylate, (meth ) (Meth) acrylate esters 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) acrylic (Meth) acrylamide derivatives such as amide, (meth) acrylamide propanesulfonic acid or a salt thereof, (meth) acrylamide propyldimethylamine or a salt thereof, N-methylol (meth) acrylamide or a derivative thereof; N-vinylformamide, N-vinyl N-vinylamides such as acetamide and N-vinylpyrrolidone; methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, stearyl vinyl ether, etc. Vinyl ether; vinyl cyanide such as (meth) acrylonitrile; halogenated vinyl such as vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride; vinegar Allyl compounds such as allyl acid 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; unsaturated sulfonic acids or salts thereof And so on. The polyvinyl ester can have one or more structural units derived from the other monomers.

The proportion of structural units derived from other monomers in 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 preferred is 5 mol% or less.

As long as the effect of the present invention is not impaired, the PVA may be modified with one or two or more types of graft copolymerizable monomers. At this time, graft copolymerization can be performed on the polyvinyl ester or PVA. Examples of the graft copolymerizable monomer include an unsaturated carboxylic acid or a derivative thereof; an unsaturated sulfonic acid or a derivative thereof; an 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.

In the PVA, a part of the hydroxyl group may be cross-linked or may not be cross-linked. The PVA may have a hydroxyl group partially reacted 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 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 polarizing 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, still more 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 heat and heat resistance of the obtained polarizing film. It is still more preferable that it is above. In the present invention, the degree of saponification of PVA means that the PVA has a vinyl alcohol unit relative to the total number of moles of structural units (typically vinyl ester units) that can be converted to vinyl alcohol units by saponification and vinyl alcohol units. It refers to the mole ratio (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, and still more preferably 85 to 100% by mass.

The PVA film may contain a plasticizer. When the PVA film contains a plasticizer, the handleability and stretchability are improved. A polyhydric alcohol is preferably used as the plasticizer, and specific examples include ethylene glycol, glycerin, propylene glycol, diethylene glycol, diglycerin, triethylene glycol, tetraethylene glycol, trimethylolpropane, and the like. The PVA film can contain one or more of these plasticizers. Among 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 still more 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, the plasticizer bleeds out on the surface of the PVA film and the handling property of the PVA film is reduced. be able to.

In addition, when producing a PVA film using a film-forming stock solution described later, the film-forming property is improved and the occurrence of uneven thickness of the film is suppressed, and when a metal roll or belt is used for film-forming, From the viewpoint that the PVA film can be easily peeled from these, it is preferable to contain a surfactant in the film-forming stock solution. When a PVA film is produced using a film-forming stock solution containing a surfactant, a surfactant may be contained in the obtained PVA film. The type of the surfactant is not particularly limited, but anionic surfactants and nonionic surfactants are preferable, and nonionic surfactants are more preferable from the viewpoint of easily peeling the PVA film from a metal roll or 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; a sulfonic acid type such as dodecylbenzene sulfonate is suitable.

Nonionic surfactants include, for example, alkyl ether types such as polyoxyethylene oleyl ether; alkylphenyl ether types such as polyoxyethylene octylphenyl ether; alkyl ester types such as polyoxyethylene laurate; 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 allyl phenyl ether type such as alkylene allyl phenyl ether is preferred.

The content of the surfactant in the membrane 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 suppress the surfactant from bleeding out on the surface of the PVA film, causing blocking, thereby reducing the handleability. The content of the surfactant in the PVA film is preferably in the range described above as the content of the surfactant in the film forming stock solution.

The PVA film may be composed only of PVA, or may be composed only of PVA and a plasticizer and / or a surfactant. Moreover, you may contain other components other than PVA, a plasticizer, and surfactant, such as antioxidant, an antifreezing agent, a pH adjuster, a masking agent, a coloring inhibitor, and an oil agent as needed.

The method for producing the 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, etc. are preferable from the viewpoint that a film having a uniform thickness and width is obtained. 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 properties can be obtained. These film forming methods may be used alone or in combination of two or more.

As a film-forming stock solution used for the production of PVA film, PVA, a film-forming stock solution in which a plasticizer, a surfactant and other components are dissolved in a liquid medium, or PVA, if necessary, a plasticizer, surface-active It can be produced using a film-forming stock solution containing an agent, other components, and a liquid medium and 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, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, glycerin, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, and trimethylol. Propane, ethylenediamine, and diethylenetriamine can be mentioned, and one or more of these can be used. Among these, water is preferable from the viewpoint of low environmental load and recoverability.

The volatile fraction of the film-forming stock solution (the content ratio of volatile components such as a liquid medium removed by volatilization or evaporation during film-forming in the film-forming stock solution) varies depending on the film-forming method, film-forming conditions, etc., but 50 to 95 % By mass is preferable, 55 to 90% by mass is more preferable, and 60 to 85% by mass is still more preferable. When the volatile fraction 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, and filtration and defoaming are smoothly performed during preparation of the film-forming stock solution, and there are few foreign matters and defects. Film production is facilitated. 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 production of an industrial PVA film becomes easy. The PVA film obtained by film formation can be dried or heat-treated as necessary.

The shape of the PVA film is not particularly limited, but is preferably a long PVA film because the polarizing film can be continuously produced with high productivity. The length of the PVA film is not particularly limited, and can be set as appropriate according to the application of the polarizing film to be produced. For example, the length can be 5 to 20,000 m. Although the width | variety of the said PVA film is not specifically limited, Since the wide polarizing film is calculated | required in recent years, it is preferable that it is 50 cm or more, It is more preferable that it is 2 m or more, It is further more preferable that it is 4 m or more. Although it is not particularly limited to the upper limit of the width of the PVA film, if it is too wide, it tends to be difficult to stretch uniformly when a polarizing film is produced with a practically used apparatus. 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. Thus, when the thing thinner than the PVA film conventionally used is used as a raw material of a polarizing film, it was easy to generate | occur | produce in the edge part of the width direction, and had become a problem. On the other hand, according to the production method of the present invention, even when a thin PVA film is used, the end portion is prevented from being folded, so that it is difficult to break during stretching or drying, and is high. Since the film can be stretched at a stretch ratio, a polarizing film having excellent polarization performance can be easily produced. The dry thickness B of the PVA film is preferably 0.035 mm or less. Although the minimum of the thickness of a PVA film is not specifically limited, Since a polarizing film can be manufactured still more easily, it is preferable that it is 0.003 mm or more. Further, the PVA film may be a single layer or a laminate in which a PVA layer and other layers are laminated, but it is a single layer because the effects of the present invention are more remarkably exhibited. It is preferable. In the case of a laminate, 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 process, a dyeing process, and a stretching process. At this time, it is preferable to perform a crosslinking process or a fixing process on the PVA film. Hereinafter, these steps will be specifically described.

[Swelling process]
The swelling process which performs the swelling process of a PVA film can be performed by immersing a PVA film in water. Usually, a swelling process is first given to the raw material PVA film. The temperature of water when swelling the PVA film is preferably 20 to 40 ° C., more preferably 22 to 38 ° C., and further preferably 25 to 35 ° C. The time for immersion in water is preferably 0.5 to 5 minutes, and more preferably 1 to 3 minutes. In addition, the water at the time of immersing in water is not limited to pure water, The aqueous solution in which various components melt | dissolved may be sufficient, and the mixture of water and a water-soluble organic solvent may be sufficient.

[Dyeing process]
The dyeing process for 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 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 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 to the PVA film. The time for immersing the PVA film in the aqueous solution is preferably 0.1 to 10 minutes, and more preferably 0.2 to 5 minutes.

Examples of the dichroic dye, iodine based dye (I ₃ ^- and I ₅ ^-, etc.), and the like dichroic organic dyes. The iodine dye can be obtained, for example, by bringing iodine (I ₂ ) into contact with potassium iodide. Examples of the dichroic organic dye 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. Incidentally, the dichroic dye may either be two or more kinds even in one, for example, I ₃ ^- may be a balanced mixture as ^- and I _5.

[Crosslinking process]
The crosslinking step for crosslinking the PVA film can be performed by immersing the PVA film in an aqueous solution containing a crosslinking agent. By introducing a crosslinked structure into the PVA film, it is possible to effectively prevent the PVA in the film from eluting into water even when wet stretching is performed at a relatively high temperature. From such a viewpoint, the crosslinking step is preferably performed after the dyeing step. As the cross-linking agent, one or more boron compounds such as boric acid such as boric acid and borax can be used. The concentration of the crosslinking agent in the aqueous solution is preferably 1 to 15% by mass, more preferably 2 to 7% by mass. The aqueous solution containing a crosslinking 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.

Separately from the stretching process described later, the PVA film may be stretched during or between the above-described processes. By performing such stretching (pre-stretching), wrinkles can be prevented from entering the PVA film. From the viewpoint of the polarizing performance of the obtained polarizing film, the total stretching ratio of the pre-stretching is 4 times or less based on the original length of the raw PVA film before stretching from the viewpoint of the polarizing performance of the obtained polarizing film. It is 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, and 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, and 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, and further 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 may be performed by either a wet stretching method or a dry stretching method. In the case of the wet stretching method, it can be carried out in an aqueous solution containing one or two or more of boron compounds such as boric acid such as boric acid and borax, or in an aqueous solution containing the dichroic dye described above. It can also be performed in an aqueous solution used in the fixing treatment described below. 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. Moreover, you may extend | stretch, after making a PVA film absorb water. 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 the 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 still more preferably 1.5 to 4.0% by mass. The aqueous solution containing the boron compound may contain potassium iodide, and its concentration 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, and still more preferably 50 to 70 ° C.

The stretching 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. More preferably it is. In addition, the total draw ratio including the above-described draw ratio of the pre-stretch (the ratio obtained by multiplying the stretch ratio in each step) is 5.5 times or more based on the original length of the raw PVA film before stretching. 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, the PVA film is preferably uniaxially stretched from the viewpoint of the performance of the obtained polarizing film. The direction of uniaxial stretching is not particularly limited, and uniaxial stretching or transverse uniaxial stretching in the length direction of a long PVA film can be employed. Especially, the uniaxial stretching to a length direction is preferable from the point from which the polarizing film which is excellent by polarizing performance is obtained. Uniaxial stretching in the length direction can be performed by changing the peripheral speed between the rolls using a stretching apparatus including a plurality of rolls parallel to each other. On the other hand, lateral 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 to the stretched PVA film. Fixing treatment can be performed by immersing the stretched PVA film in a fixing treatment solution. As the fixing treatment liquid, an aqueous solution containing one or more boron compounds such as boric acid 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 and more preferably 3 to 10% by mass. The temperature of the fixing treatment solution is preferably 15 to 60 ° C, more preferably 20 to 40 ° C. Moreover, you may add an iodine compound and a metal compound in a fixed process liquid as needed.

In the production method of the present invention, in at least one of the above-described swelling process, dyeing process and stretching process, the PVA film is immersed in water and then taken out from the water and adhered to both ends from both sides of the PVA film. Need to be removed. And when taking out the said PVA film from water and removing the water adhering to the said PVA film, it is necessary to make the distance A from the position where the said PVA film comes out of water to the position where water is removed be 28 mm or less. is there.

The manufacturing method of the present invention in which a PVA film is immersed in water and then taken out of the water and the water adhering to the film is removed by a predetermined method will be described below using a swelling process as an example. FIG. 1 is a schematic diagram illustrating 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 water is removed in the manufacturing method of the present invention. In the swelling process 5, the PVA film 1 is usually immersed in water 6 so that the swelling process is performed on the PVA film 1. And the said PVA film 1 is taken out from the water 6, and the water adhering to the width direction both ends is removed from both surfaces of the said PVA film 1. FIG. By removing water from both sides of the PVA film 1, the occurrence of folding at the end of the PVA film 1 is suppressed.

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

The outer diameter of the roll 2 used in the present invention (the maximum diameter when the diameter changes in the axial direction) is preferably 10 cm or less, and is preferably 8 cm or less from the viewpoint of easily reducing the distance A. Is more preferable, and it is still more preferable that it is 6 cm or less. The lower limit of the outer diameter of the roll 2 is not particularly limited, but is usually 1 cm or more. When the later-described sponge roll 2 is used as the roll 2, the water absorption amount of the sponge roll 2 may be insufficient if the outer diameter is less than 1 cm. A part or all of the roll 2 may be immersed in the water 6. When the roll 2 nips the PVA film 1, 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. The 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 reduces disturbance such as scratches in the polarizing film from which the friction between the PVA film 1 and the roll 2 is reduced. The latter is preferable because it can be produced.

The roll 2 is preferably a sponge roll, a rubber roll or the like, and more preferably a sponge roll. The sponge used as the outer layer of the sponge roll is not particularly limited, and examples thereof include polyurethane sponge, PVA sponge, polyvinyl chloride sponge, etc. Among them, polyurethane sponge is preferable.

The water retention rate obtained by the following formula of the sponge roll 2 is not particularly limited, but is preferably 50% or more, and preferably 67% or more from the point that the period during which continuous water removal can be performed is further extended. More preferably, it is more preferably 75% or more. On the other hand, from the viewpoint that water absorbed in the sponge roll can be easily squeezed out and water attached to the PVA film 1 can be more efficiently removed, the water retention rate of the sponge roll is 95% or less. Preferably, it is 92% or less, 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 by using the sponge piece obtained by cutting a part of the sponge portion of the sponge roll 2 using the following equation. 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 using tweezers, and measuring the sponge mass after water is dropped or dropped for 1 minute. It is done.
Water retention rate (%) = 100 × (ba) / b

In the formula, a represents the sponge mass (g) before water absorption, and b represents the sponge mass (g) after water absorption. Here, a and b are masses excluding the mass of the cored bar portion of the sponge roll.

In the present invention, the pressure when nipping with the pair of rolls 2 is not particularly limited. However, when the nip pressure is too low, water attached 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 further 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 disturbance such as scratches in 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 expressed by 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 attached 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 water removal efficiency 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 even more preferably 0.90 or less. On the other hand, from the viewpoint of further reducing disturbances such as scratches in the obtained polarizing film, the compression ratio [a / (b1 + b2)] is more preferably 0.3 or more, and further preferably 0.5 or more. The radii b1 and b2 of each roll are half of the roll outer diameter. The radii b1 and b2 when the roll 2 has a metal core are values including the metal core part.
0.1 ≦ a / (b1 + b2) ≦ 0.97 (2)

In the production method of the present invention, when water is removed 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 portion of the PVA film 1, the end portion is folded due to the surface tension of the water. Here, it is important to remove water from both sides of the end portion of the PVA film 1. Even when water adheres only to one surface of the end portion of the PVA film 1, folding occurs. From the viewpoint of suppressing the occurrence of folding more effectively, the width of each end of the PVA film 1 from which water is removed is preferably 1 cm or more from the end toward the center. More preferably, it is more preferably 5 cm or more. Moreover, it is preferable that the width | variety of each edge part of the said PVA film 1 which removes water is 1/100 or more with respect to the width | variety of the said PVA film 1, respectively, and it is more preferable that it is 1/20 or more, More preferably, it is 1/10 or more.

It is particularly preferable to remove water from the entire surface of the PVA film 1. Thereby, generation | occurrence | production of a folding is suppressed more effectively. Moreover, since adhesion of water to the guide roll 3 and take-up roll 4 disposed downstream is prevented and water does not drip from the guide roll 3 or take-up roll 4, water adheres to the PVA film 1 again. Can be avoided. Furthermore, in the stretching step, occurrence of physical spots such as swellable 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 breaks and optical spots on the resulting polarizing film. .

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 comes out of the water 6 to the position 9 where water is removed from the PVA film 1 is 28 mm. It is necessary to do the following. Between the position 8 where the PVA film 1 comes out of the water and the position 9 where the water is removed, the PVA film 1 with water adhering to the end is conveyed alone. The present inventors have found that folding occurs in a short time when the PVA film 1 having water attached to the end is conveyed alone. When the distance A exceeds 28 mm, the occurrence of folding at the end of the PVA film 1 increases rapidly. As shown in FIGS. 2 and 3, when water is removed by niping the PVA film 1 with the roll 2, the position where the PVA film 1 first contacts one of the pair of rolls 2 is set to PVA. The position 9 is where water is removed from the film 1.

The distance A is preferably 25 mm or less, more preferably 20 mm or less, and further preferably 15 mm or less. The distance A may be 0 mm. For example, by disposing at least a part of the roll 2 in the water 6 and removing the water in advance by directly niping the PVA film 1 in the water 6 with the roll 2, When the conveyance is started, the distance A is 0 mm. Since the amount of water accompanying the surface of the PVA film decreases as the distance A becomes longer, the water on the surface of the PVA film 1 is more efficiently removed, and the occurrence of folding at the end in the width direction of the PVA film 1 is more effective. The distance A is preferably 1 mm or more, more preferably 3 mm or more, and still more preferably 5 mm or more from the viewpoint of being able to suppress it.

It is preferable that the dry thickness B (mm) of the raw PVA film 1 and the distance A (mm) satisfy the following formula (1). Thereby, even if it is the very thin PVA film 1, generation | occurrence | production of folding can be suppressed more effectively.
A ≦ B × 1000 (1)

As described above, the PVA film 1 is taken out from the water 6 to remove 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 great feature of the present invention that the distance A is within a predetermined range. In the comparatively thick PVA film conventionally used, there was no problem of film breakage due to folding at the end. Therefore, in the production of polarizing films, guide rolls and nip rolls have been used for the purpose of transporting and holding PVA films, but they can be used to prevent end folding, It was not placed near the water surface. On the other hand, as a method for preventing folding of the end portion of the thin PVA film, there is known a method (Patent Document 3) of performing a process of widening both end portions in the width direction of the PVA film after removing the liquid on one side of the PVA film. However, the breakage of the PVA film due to folding of the end portion may occur, and improvement is necessary. As a result of intensive studies by the present inventors to solve such a problem, when the PVA film 1 is thin, the end of the PVA film 1 is bent immediately after the PVA film 1 is taken out of the water 6, and the PVA film 1 When water was removed only from one side, it was found that the end portion was bent due to the surface tension of the water remaining on the other side. And while removing water from both surfaces of PVA film 1, the distance A from the position where the said PVA film 1 comes out of water 6 to the position where water is removed is made into a predetermined range, and generation | occurrence | production of such a fold. It was found that the occurrence of breakage of the PVA film 1 during stretching or drying is reduced.

In the production method of the present invention, a polarizing film is produced by subjecting at least the swelling step, the dyeing step and the stretching step to a raw material PVA film. At this time, it is preferable that the PVA film is further subjected to the crosslinking step or the fixing treatment step, and more preferably the crosslinking step and the fixing treatment step. Moreover, in the manufacturing method of this invention, you may give a several process with respect to a PVA film in one processing bath. For example, the crosslinking 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, the breakage of the PVA film is particularly likely to occur during stretching. Therefore, after the PVA film is immersed in water before the stretching process, the PVA film is taken out from the water and attached to both ends of the PVA film. By removing the water that has been removed using the method described above, 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. In at least one of these, it is preferable to remove water adhering to both ends of the PVA film. It is more preferable to remove water adhering to both ends of the film. When the production method of the present invention further includes the crosslinking step, examples of the step performed before the stretching step include the swelling step, the dyeing step, and the crosslinking step. In at least one of these, the PVA It is preferable to remove water attached to both ends of the film, and in the swelling step and the dyeing step, it is more preferable to remove water attached to both ends of the PVA film, and the swelling step, the dyeing step and the above In the crosslinking 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 attached to both ends of the PVA film is removed in the stretching step or a subsequent step (for example, the fixing treatment step). Is preferred.

As a preferred embodiment of the production method of the present invention, the swelling step, the dyeing step, the crosslinking step and the stretching step are performed in this order on the PVA film, and the swelling step, the dyeing step and the crosslinking step are performed. In at least one of them, after the PVA film is immersed in water, a method of taking out the water and removing the water adhering to both ends of the PVA film using the method described above can be mentioned. At this time, it is preferable to remove water attached to the PVA film in the swelling step and the dyeing step, and it is more preferable to remove water attached to the PVA film in the swelling step, the dyeing step, and the crosslinking step. preferable. Moreover, it is also preferable to perform the said swelling process, the said dyeing | staining process, the said bridge | crosslinking process, the said extending process, and the said fixing process process with respect to a PVA film in this order.

[Drying process]
A polarizing film can be usually produced by drying the PVA film after subjecting the PVA film to the stretching step and, if necessary, a fixing treatment step. The drying temperature is not particularly limited, but is preferably 30 to 150 ° C, more preferably 50 to 130 ° C. By performing drying at such a temperature, the dimensional stability of the polarizing film is improved.

[Polarizer]
The polarizing film obtained as described above is used as a polarizing plate by attaching an optically transparent protective film having mechanical strength to at least one surface of the polarizing film. As the protective film, a cellulose triacetate (TAC) film, an acetic acid / cellulose 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 and the protective film, the bonding surface of the polarizing film and the protective film may be subjected to surface treatment such as saponification treatment, corona treatment, plasma treatment, ultraviolet irradiation, primer treatment, etc. Good. As an adhesive for bonding the polarizing film and the protective film, a PVA adhesive, a urethane adhesive, an ultraviolet curable adhesive, or the like is used.

Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited to these examples. In addition, each measuring method and evaluation method which were employ | adopted in the following example and the comparative example are shown below.

[Stretch ratio for 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 drawing step, and the total draw ratio when the film breaks The total draw ratio set immediately before was set as a draw ratio at which continuous operation was possible.

[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 of the polarizing film and 2 cm in the width direction from the center in the width direction of the obtained polarizing film. Two were collected. Using a spectrophotometer with an integrating sphere ("V7100" manufactured by JASCO Corporation), in accordance with JIS Z8722: 2009 (measuring method of object color), correction of visibility in the visible light region of C light source and 2 ° field of view For each sample, the light transmittance when tilted by 45 ° with respect to the length direction and the light transmittance when tilted by −45 ° are measured, and the average value Ts1 (%) is obtained. Asked. Similarly, with respect to the other sample, the light transmittance when tilted by 45 ° and the light transmittance when tilted by −45 ° were measured, and an average value Ts2 (%) thereof was obtained. Ts1 and Ts2 were averaged by the following formula to obtain the transmittance Ts (%) of the polarizing film.
Ts = (Ts1 + Ts2) / 2

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

[Evaluation of occurrence of folding]
In the following examples, comparative examples and reference examples, in each of the swelling process 5, the dyeing process 10 and the crosslinking process 11, the end of the PVA film immediately before contacting the guide roll 3 is visually observed, and the occurrence of folding is observed. The presence or absence was evaluated. Next A and B were determined to be acceptable, and C was determined to be unacceptable.
A: Even after passing through any process, the generation | occurrence | production of the folding was not seen by the edge part of the width direction of a PVA film.
B: Only after passing through the cross-linking step 11, a slight fold of about 0.5 mm in width occurred at one end of the PVA film.
C: Many folds of about 0.5 to 3 mm occurred at both ends of the PVA film after passing through the crosslinking step 11 and other steps.

Example 1
100 parts by mass of a long PVA film 1 [PVA (saponification product of vinyl acetate homopolymer having a polymerization degree of 2,400, a saponification degree of 99.9 mol%) having a thickness of 0.030 mm when dried and a width of 65 cm , 12 parts by mass of glycerin and 0.03 parts by mass of surfactant] are continuously unwound from the film roll 7 and continuously provided in this order to the swelling process 5, the dyeing process 10 and the crosslinking process 11. did. FIG. 3 is a schematic view showing that the PVA film 1 is continuously unwound from the film roll 7 and subjected to the swelling process 5, the dyeing process 10 and the crosslinking process 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. Further, as the dyeing step 10, the PVA film 1 is immersed in an aqueous solution containing iodine pigment (iodine concentration: 0.05 mass%, potassium iodide concentration: 1.2 mass%, temperature: 30 ° C.) for 2 minutes. In the meantime, the film was uniaxially stretched in the length direction at a draw ratio of 1.2. Further, as the crosslinking 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, and uniaxial with a draw ratio of 1.1 times in the length direction. Stretched.

As shown in FIG. 3, in the swelling process 5, the dyeing process 10 and the crosslinking process 11, a pair of sponge rolls 2 (AC sponge U manufactured by AC Chemical Co., Ltd .; urethane sponge, 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 rotation axes 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. Adjusted. And the PVA film 1 which came out of water was nipped over the whole width direction, and the water adhering to the said PVA film 1 was removed. Here, as shown in FIG. 2, in the swelling process 5, the dyeing process 10 and the crosslinking process 11, the distance between the position 8 where the PVA film 1 comes out of the water 6 and the position 9 where water is removed from the PVA film. A was 20 mm. In addition, the position where the PVA film 1 first contacts one of the two sponge rolls 2 is a position 9 where water is removed from the PVA film. In each step, as described above, after the PVA film 1 from which water has been removed contacts 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 were installed downstream of the sponge roll 2 so as to come into contact with the roll 1 in the entire width direction of 1.

The polarizing film was manufactured by successively performing the stretching step, the fixing treatment step, and the drying step in this order following the crosslinking step 11 described above. In the stretching step, the PVA film 1 is uniaxially with a stretching ratio of 1.9 times in the length direction in a boric acid aqueous solution (boric acid concentration: 2.8 mass%, potassium iodide concentration: 5 mass%, temperature: 57 ° C.). This was carried out 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 a boric acid aqueous solution (boric acid concentration: 2.6 mass%, potassium iodide concentration: 5 mass%, temperature: 22 ° C.) for 2 minutes. It was. Furthermore, the drying process was performed by drying the stretched PVA film 1 at 60 ° C. for 1 minute to obtain a polarizing film.

Examples 2 to 5 and 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, in the crosslinking step 11, the pair of sponge rolls 2 was not installed and the water adhered to the PVA film 1 was not removed.

[Comparative Example 1]
In the swelling process 5, the dyeing process 10 and the cross-linking process 11, a pair of sponge rolls 2 were not installed and the water adhering to the PVA film 1 was not removed. A polarizing film was manufactured.

[Comparative Example 2]
In the swelling process 5, the dyeing process 10 and the crosslinking process 11, by installing only the lower sponge roll 2 of the pair of sponge rolls 2 and bringing the sponge roll 2 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]
Except that the thickness of the PVA film 1 is 0.060 mm, and the water attached to the PVA film 1 is not removed without installing the pair of sponge rolls 2 in the swelling process 5, the dyeing process 10 and the crosslinking process 11. Produced a polarizing film in the same manner as in Example 1.

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

DESCRIPTION OF SYMBOLS 1 PVA film 2 Roll 3 Guide roll 4 Take-off roll 5 Swelling process 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 process 11 Crosslinking process

Claims

A method for producing a polarizing film for subjecting at least a swelling process, a dyeing process and a stretching process to a polyvinyl alcohol film,
Using a polyvinyl alcohol film having a dry thickness B of 0.001 mm to 0.045 mm as a raw material,
In at least one of the steps, after immersing the polyvinyl alcohol film in water, when removing the water adhering to both ends from both sides of the film, water is removed from the position where the film comes out of the water. A method for producing a polarizing film, wherein the distance A to the removed position is 28 mm or less.
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.
The method according to claim 2, wherein water on the entire surface of the film is removed.
The production method according to any one of claims 1 to 3, wherein a dry thickness B (mm) of the raw material polyvinyl alcohol film and the distance A (mm) satisfy the following formula (1).
A ≦ B × 1000 (1)
5. The production method according to claim 1, wherein water adhering to both ends of the film is removed by nipping the film with a pair of rolls.
The manufacturing method according to claim 5, wherein the roll is a sponge roll.
The manufacturing method according to claim 6, wherein the water retention of the sponge roll is 50% or more and 95% or less.
The production method according to any one of claims 5 to 7, wherein a distance a (cm) between the rotation axes of the pair of rolls and radii b1 (cm) and b2 (cm) of each roll satisfy the following formula (2): .
0.1 ≦ a / (b1 + b2) ≦ 0.97 (2)
The production method according to any one of claims 1 to 8, wherein water adhering to both ends of the film is removed before the stretching step.
10. The production method according to claim 1, further comprising a crosslinking step or a fixing treatment step.