JP2004020635A - Manufacturing method of polyvinyl alcohol film for optical use - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a polyvinyl alcohol film which has little color shade and is useful as a raw material for production of a polarizing film for liquid crystal display of high quality. <P>SOLUTION: Water content of the polyvinyl alcohol film of ≥2m width is adjusted while giving the film tension of 10 to 50 N/m in a flow direction of the film and then the film is drawn. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for producing an optical polyvinyl alcohol film useful as a material for a polarizing plate used as a component of a liquid crystal display device.
[0002]
[Prior art]
A polarizing plate having a function of transmitting and blocking light is a fundamental component of a liquid crystal display device (LCD) together with a liquid crystal having a function of switching light. This LCD can be applied to small devices such as calculators and watches in the early stages of development, but recently to laptop computers, word processors, liquid crystal color projectors, in-vehicle navigation systems, liquid crystal televisions, personal phones, and indoor and outdoor measuring instruments. Therefore, a polarizing plate having a large area and a uniform optical performance over the entire area is required more than conventional products.
[0003]
A polarizing plate is generally used for uniaxially stretching and dyeing a polyvinyl alcohol film (hereinafter, polyvinyl alcohol film may be abbreviated as “PVA” and polyvinyl alcohol film may be abbreviated as “PVA film”), or after dyeing and uniaxially stretching. A protective film such as a cellulose triacetate (TAC) film or a cellulose acetate / butyrate (CAB) film is applied to a polarizing film obtained by performing a fixing treatment with a boron compound (the dyeing and the fixing treatment may be performed simultaneously). It is configured to be stuck.
[0004]
[Problems to be solved by the invention]
In some cases, a polarizing plate has color spots caused by variations in optical performance over the entire area. Since there are various causes for the occurrence of this color spot, it is difficult to confirm it unless it is a final product (polarizing plate) on which a protective film or the like is laminated. If color spots appear at the stage of the final product, secondary materials such as a protective film having no problem in quality are also discarded together with the polarizing plate as defective, resulting in a large loss. Conventionally, as a method for reducing color spots, studies have been made on reducing the thickness spots and birefringence spots of a PVA film as proposed in Japanese Patent Application Laid-Open No. 6-138319. By the method of reducing the thickness unevenness and birefringence unevenness of the PVA film, the color unevenness of the polarizing plate can be reduced to some extent, and it became possible to satisfy the required level at the time, but the performance in recent years has been improved. It has proven difficult to reduce the level of color spots that is problematic in end products (polarizers and liquid crystal display devices).
[0005]
Also, with the increase in the size of the liquid crystal display device, a polarizing film having a large area has been required. Conventional liquid crystal display devices have a relatively small display area and use a polarizing plate alone, so color spots rarely become a problem.However, when the display area is large, the uniformity of the entire display area is low. Is required, and the film is often used in combination with another film such as a film for correcting a viewing angle. In particular, in the case of a polarizing film produced by uniaxially stretching a PVA film in the film flow direction, streak-like color spots are likely to occur in the film flow direction. It is considered that this is because the film is not stretched uniformly in the width direction, and the stretching variation appears as optical color spots. In the case where a PVA film having a film width of less than 2 m was stretched as in the related art, it was relatively easy to uniformly stretch the film in the width direction. As it spreads, it has become difficult to stretch uniformly. In particular, when the PVA film is uniaxially stretched by the dry method, as compared to the case where the PVA film is uniaxially stretched by the wet method, streak-like color spots which are considered to be caused by stretch spots are more remarkable.
Since color spots cause phenomena such as brightness spots when incorporated in a liquid crystal display device or the like, there is a problem that causes quality deterioration. In particular, as the screen becomes larger, if a streak-like color spot exists in the flow direction, it becomes difficult to collect the product while avoiding the spot, which is a big industrial problem.
[0006]
Therefore, an object of the present invention is to provide a method for producing a polyvinyl alcohol film which is useful as a raw material for producing a polarizing film for a high quality liquid crystal display with less color spots.
[0007]
[Means for Solving the Problems]
The present inventors have conducted intensive studies in order to solve the above-described problems, and as a result, applied a polyvinyl alcohol film having a width of 2 m or more to the polyvinyl alcohol film while applying a tension of 10 to 50 N / m in the flow direction of the film. It has been found that by adjusting the moisture content contained and then stretching, a polyvinyl alcohol film for optics in which the degree of color spots is significantly reduced can be produced, and the present invention has been completed.
According to the production method of the present invention, a polyvinyl alcohol film having a width of more than 2 m, which has been considered difficult in the prior art, can be easily stretched by a dry method. Color spots can be effectively reduced.
In the method for producing an optical polyvinyl alcohol film according to the method of the present invention, when adjusting the moisture content contained in the polyvinyl alcohol film, a driving roll having a surface roughness of 50 to 100 S is used, or an expander roll or a bend roll is used. By using, color spots can be more effectively reduced.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
In the present invention, the humidity of the PVA film is adjusted while applying a tension of 10 to 50 N / m in the flow direction of the film. When adjusting the humidity of the PVA film, if the tension of the film is less than 10 N / m, problems such as curling of the film, bending of the end portion, and winding around a roll are likely to occur. On the other hand, if the tension of the film exceeds 50 N / m, the film is partially stretched due to the tension, which tends to hinder uniform stretching in the width direction in the stretching step of the PVA film, which is not preferable.
The tension applied at the time of adjusting the humidity of the PVA film is preferably from 15 to 45 N / m, more preferably from 20 to 40 N / m.
[0009]
In the present invention, a preferable mode for adjusting the moisture content contained in the PVA film is to use a drive roll having a surface roughness of 50 to 100 S, or to use an expander roll or a bend roll.
In the aspect in which the drive roll having a surface roughness of 50 to 100 S is used, a more preferable range of the surface roughness of the drive roll is 60 to 90 S. When the surface roughness of the drive roll is smaller than 50S, the film easily adheres to the drive roll, and is partially stretched while being peeled off from the roll. Therefore, in the stretching step of the PVA film, uniform stretching in the width direction is performed. Is likely to be inhibited. When the surface roughness of the roll is larger than 100S, the adhesion between the film and the driving roll is too low, and the driving force of the roll tends to be hardly transmitted to the film.
[0010]
When the humidity control is performed while applying a low tension to the PVA film as employed in the production method of the present invention, the film may be bent, the ends may be bent, or the film may be wound around a roll. Although the problem is likely to occur, as described above, the use of an expander roll or a bend roll can prevent such a problem from occurring when adjusting the moisture content contained in the PVA film. The use of two or more expander rolls or bend rolls is more effective than the use of only one roll, and the expander rolls and bend rolls may be used in combination.
[0011]
The PVA used in the present invention is produced, for example, by saponifying a polyvinyl ester obtained by polymerizing a vinyl ester. Modified PVA in which unsaturated carboxylic acid or its derivative, unsaturated sulfonic acid or its derivative, α-olefin having 2 to 30 carbon atoms, or the like is graft-copolymerized in the main chain of PVA at a ratio of less than 5 mol%; Manufactured by saponifying a modified polyvinyl ester obtained by copolymerizing an ester with 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 in a proportion of less than 15 mol%. And so-called polyvinyl acetal resin obtained by cross-linking a part of hydroxyl groups of unmodified or modified PVA with aldehydes such as formalin, butyraldehyde and benzaldehyde.
[0012]
Examples of the vinyl ester include vinyl acetate, vinyl formate, vinyl propionate, vinyl butyrate, vinyl pivalate, vinyl versatate, vinyl laurate, vinyl stearate, and vinyl benzoate.
[0013]
The comonomer used for the modified PVA is copolymerized mainly for the purpose of modifying the PVA, and is used in a range that does not impair the purpose of the present invention. Examples of such comonomers include α-olefins such as ethylene, propylene, 1-butene, and isobutene; acrylic acid and its salts; methyl acrylate, ethyl acrylate, n-propyl acrylate, i-propyl acrylate, Acrylates such as n-butyl acrylate, i-butyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, octadecyl acrylate; methacrylic acid and its salts; methyl methacrylate; Ethyl methacrylate, n-propyl methacrylate, i-propyl methacrylate, n-butyl methacrylate, i-butyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate, octadecyl methacrylate, etc. Methacrylic acid Ters; acrylamide, N-methylacrylamide, N-ethylacrylamide, N, N-dimethylacrylamide, diacetoneacrylamide, acrylamidepropanesulfonic acid and its salts, acrylamidopropyldimethylamine and its salts, N-methylolacrylamide and its derivatives, etc. Methacrylamide derivatives such as methacrylamide, N-methyl methacrylamide, N-ethyl methacrylamide, methacrylamide propanesulfonic acid and salts thereof, methacrylamidopropyl dimethylamine and salts thereof, N-methylol methacrylamide and derivatives thereof N-vinyl amides such as N-vinyl formamide, N-vinyl acetamide, N-vinyl pyrrolidone; methyl vinyl ether , Vinyl ethers such as 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 and stearyl vinyl ether; nitriles such as acrylonitrile and methacrylonitrile; Vinyl halides such as vinyl, vinylidene chloride, vinyl fluoride and vinylidene fluoride; allyl compounds such as allyl acetate and allyl chloride; maleic acid and its salts or esters; itaconic acid and its salts or esters; vinyl trimethoxy Vinylsilyl compounds such as silane; and isopropenyl acetate. Of these, α-olefins are preferred, and ethylene is particularly preferred. The amount of modification of the modified PVA is preferably less than 15 mol%.
[0014]
The degree of saponification of PVA is preferably at least 95 mol%, more preferably at least 98 mol%, further preferably at least 99 mol%, and most preferably at least 99.5 mol%, from the viewpoint of polarization performance and durability.
[0015]
The saponification degree of the PVA indicates the ratio of units actually saponified to vinyl alcohol units among units that can be converted to vinyl alcohol units when the polyvinyl ester is saponified. In addition, the saponification degree of PVA was measured by the method described in JIS.
[0016]
The polymerization degree of PVA is preferably 500 or more, more preferably 1000 or more, still more preferably 1500 or more, and most preferably 2500 or more, from the viewpoint of polarization performance and durability. The upper limit of the PVA polymerization degree is preferably 8000 or less, more preferably 6000 or less.
[0017]
The polymerization degree of the PVA is measured according to JIS K 6726. That is, it is determined from the intrinsic viscosity measured in water at 30 ° C. after the PVA is re-saponified and purified.
[0018]
As a method for producing a PVA film using the above PVA, for example, a PVA solution (a stock solution of a polyvinyl alcohol film) in which PVA is dissolved in a solvent is used in addition to a film forming method by a melt extrusion method using hydrated PVA. Casting method, wet film forming method (discharge into poor solvent), gel film forming method (after once cooling and gelling the PVA aqueous solution, the solvent is extracted and removed, and the PVA film is removed. And a method based on a combination thereof. Among these, the casting film forming method and the melt extrusion film forming method are preferable because a good polarizing film can be obtained.
[0019]
As a solvent for dissolving PVA used in producing a PVA film, for example, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, Examples thereof include trimethylolpropane, ethylenediamine, diethylenetriamine, glycerin, and water, and one or more of these can be used. Among them, dimethyl sulfoxide, water, or a mixed solvent of glycerin and water is preferably used.
[0020]
The proportion of PVA in the PVA solution or the hydrated PVA used when producing the PVA film varies depending on the degree of polymerization of PVA, but is preferably 20 to 70% by weight, more preferably 25 to 60% by weight. And more preferably from 30 to 55% by weight, and most preferably from 35 to 50% by weight. When the proportion of PVA is large, the viscosity becomes too high, so that filtration and defoaming become difficult, and it becomes difficult to obtain a film free of foreign matter and defects. If the proportion of PVA is small, drying requires much time and energy, which is not preferable from an industrial viewpoint. Further, the PVA solution or the water-containing PVA may contain a plasticizer, a surfactant, a dichroic dye, and the like, if necessary.
[0021]
When producing a PVA film, it is preferable to add a polyhydric alcohol as a plasticizer. Examples of the polyhydric alcohol include ethylene glycol, glycerin, propylene glycol, diethylene glycol, diglycerin, triethylene glycol, tetraethylene glycol, trimethylolpropane, and the like. One or more of these may be used. can do. Among these, diglycerin, ethylene glycol and glycerin are preferably used because they have an excellent effect of improving stretchability.
[0022]
The amount of the plasticizer added is preferably 1 to 30 parts by weight, more preferably 3 to 25 parts by weight, and most preferably 5 to 20 parts by weight based on 100 parts by weight of PVA. If the amount is less than 1 part by weight, the dyeing property and the stretchability may be reduced. If the amount is more than 30 parts by weight, the PVA film may be too flexible and the handleability may be reduced.
[0023]
When producing a PVA film, it is preferable to add a surfactant. The type of the surfactant is not particularly limited, but an anionic or nonionic surfactant is preferable. Suitable examples of the anionic surfactant include a carboxylic acid type such as potassium laurate, a sulfate type such as octyl sulfate, and a sulfonic acid type such as dodecylbenzenesulfonate. Examples of the nonionic surfactant include an alkyl ether type such as polyoxyethylene oleyl ether, an alkyl phenyl ether type such as polyoxyethylene octyl phenyl ether, an alkyl ester type such as polyoxyethylene laurate, and polyoxyethylene lauryl amino. Alkylamine type such as ether, alkylamide type such as polyoxyethylene lauric amide, polypropylene glycol ether type such as polyoxyethylene polyoxypropylene ether, alkanolamide type such as diethanolamide oleate, polyoxyalkylene allyl phenyl ether Nonionic surfactants such as the allyl phenyl ether type are preferred. These surfactants can be used alone or in combination of two or more.
[0024]
The addition amount of the surfactant is preferably 0.01 to 1 part by weight, more preferably 0.02 to 0.5 part by weight, and most preferably 0.05 to 0.3 part by weight based on 100 parts by weight of PVA. When the amount is less than 0.01 part by weight, the effect of improving the film forming property and the releasability to be brought about by the addition of the surfactant is difficult to appear, and when the amount is more than 1 part by weight, the surfactant elutes on the surface of the PVA film. This may cause blocking and reduce the handleability.
[0025]
The PVA film used in the present invention preferably has a width of 2 m or more, more preferably 2.5 m or more, further preferably 2.8 m or more, and particularly preferably 3 m or more. The greater the width of the film, the more difficult it is to achieve uniform stretching, so that the effects of the present invention are more likely to appear. Originally, a PVA film having a width of less than 2 m is relatively easy to uniformly stretch in the width direction, so that color unevenness is hardly generated, and the effect of the present invention is hardly exhibited.
[0026]
In the present invention, there is no particular limitation on the method of adjusting the moisture content contained in the PVA film. For example, a moisture absorption zone in which the PVA film is brought into contact with fine water droplets generated from steam or the like, or a hot air flowing therethrough. By providing a wet zone or the like and passing the PVA film through these zones, the moisture content contained in the PVA film, particularly the moisture content in the width direction, can be controlled to be constant.
[0027]
The method of the present invention can be preferably applied to the production of a polarizing film. In this case, it is preferable to uniaxially stretch the PVA film after adjusting the moisture content by a dry method. As a specific method, for example, the PVA film of which the moisture content is adjusted according to the method of the present invention is uniaxially stretched by a dry method, dyed, and if necessary, the second-stage uniaxially stretched by a dry method or a wet method, fixing treatment, A drying treatment and, if necessary, a heat treatment may be performed, and there is no particular limitation on the order of the dyeing, the second-stage uniaxial stretching by the dry method or the wet method, and the fixing treatment. The second-stage uniaxial stretching by a dry method or a wet method may be performed twice or more times.
In the present invention, the stretching by the dry method refers to an operation of stretching the PVA film in the air, while the stretching by the wet method refers to stretching the PVA film in water or an aqueous solution such as an aqueous boric acid solution or a plasticizer. And the like, which is an operation for stretching in a solvent, and the two are distinguished.
[0028]
The dyeing of the PVA film may be performed at any stage before, during or after the uniaxial stretching. Dyes used for dyeing include iodine-potassium iodide; direct black 17, 19, 154; direct brown 44, 106, 195, 210, 223; direct red 2, 23, 28, 31, 37, 39, 79, 81. Direct Blue 1, 15, 22, 78, 90, 98, 151, 168, 202, 236, 249, 270; Direct Violet 9, 12, 51, 98; Direct Green 1, 85; Dichroic dyes such as Yellow 8, 12, 44, 86, 87 and Direct Orange 26, 39, 106, 107 can be used alone or in a mixture of two or more. The dyeing of the PVA film is generally performed by immersing the PVA film in a solution containing the dye, but the processing method and processing conditions such as mixing the dye with the PVA film to form a film are as follows. There is no particular limitation.
[0029]
For the second-stage uniaxial stretching, the PVA film is stretched in a warm aqueous solution such as a boric acid aqueous solution (which may be in a solution containing the dye or in a fixing bath described below). A dry stretching method of stretching in air can be used. The stretching temperature is not particularly limited, but is preferably 30 to 90 ° C. when the PVA film is stretched in a warm aqueous solution or the like, and 50 to 180 ° C. when the PVA film is stretched in air.
Further, the stretching ratio of uniaxial stretching (in the case of performing uniaxial stretching in multiple stages, the total stretching ratio) is preferably at least 4 times, particularly preferably at least 5 times, from the viewpoint of polarization performance. The upper limit of the stretching ratio is not particularly limited, but is preferably 8 times or less since uniform stretching is easily obtained. In particular, in order to perform uniform stretching in the width direction, the first-stage stretching preferably exceeds 4 times, more preferably 4.2 times or more, and particularly preferably 4.5 times or more. The thickness of the stretched film is preferably from 3 to 45 μm, more preferably from 5 to 30 μm.
[0030]
In order to strengthen the adsorption of the dye to the PVA film, a fixing treatment is often performed. Usually, boric acid and / or a boron compound is added to the treatment bath used for the fixing treatment. Further, an iodine compound may be added to the treatment bath as needed.
[0031]
The drying treatment (heat treatment) of the obtained polarizing film is preferably performed at 30 to 150 ° C, more preferably at 50 to 150 ° C.
[0032]
The polarizing film obtained as described above is usually used as a polarizing plate by bonding an optically transparent protective film having mechanical strength to both surfaces or one surface thereof. As the protective film, a cellulose triacetate (TAC) film, a cellulose acetate / butyrate (CAB) film, an acrylic film, a polyester film, or the like is used. Examples of the adhesive used for bonding include a PVA-based adhesive and a urethane-based adhesive. Among them, a PVA-based adhesive is preferable. In the polarizing plate thus obtained, the thickness of the adhesive layer is preferably 0.5 to 10 μm.
[0033]
The polarizing plate obtained as described above is used as a component of a liquid crystal display device by being coated with a pressure-sensitive adhesive such as an acrylic resin and then bonded to a glass substrate. When bonding a polarizing plate to a glass substrate, a retardation film, a viewing angle improving film, a brightness improving film, and the like may be simultaneously bonded.
[0034]
【Example】
Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited thereto. In Examples and Comparative Examples, the optical performance of the polarizing film and the color unevenness of the polarizing song were evaluated by the following methods.
[0035]
Optical performance of polarizing film:
A sample of a polarizing film of about 4 cm × 4 cm was measured using a spectrophotometer UV-2200 (supplied with an integrating sphere) manufactured by Shimadzu Corporation in accordance with the standards of the Electronic Machinery Manufacturers Association of Japan (EIAJ) LD-201-1983, using a C light source. The Y value was corrected for the visibility in the visible light region of the 2 degree visual field, and the transmittance was determined from the average value in the 45 ° and −45 ° directions with respect to the stretching axis direction of the polarizing film. In the same manner as above, the Y values of the parallel Nicols and the cross Nicols were measured to determine the degree of polarization.
[0036]
Color spots on polarizing plate:
A polarizing plate having a full width was placed in a direction orthogonal to a polarizing plate for observation (two stacked in parallel, a degree of polarization of 99.99% or more), and the degree of color spot was determined by visual observation.
[0037]
Example 1
100 parts by weight of PVA having a degree of saponification of 99.95 mol% and a degree of polymerization of 2400, impregnated with 10 parts by weight of glycerin and 170 parts by weight of water are melt-kneaded. Filmed. Thereafter, by performing drying and heat treatment, a PVA film having a film width of 3 m and an average thickness of 50 μm was obtained.
The PVA film was passed through a humidity controller to adjust the moisture content of the film to 6% by weight. When the PVA film was conditioned, a tension of 20 N / m was applied to the film using a driving roll having a surface roughness of 80S. Then, among the free rolls incorporated in the humidity control apparatus, one near the middle of the humidity control apparatus was an expander roll, and one near the outlet of the humidity control apparatus was a bend roll. In the step of controlling the humidity of the PVA film, no bending of the film edge occurred, and no wrinkles were observed in the film.
The PVA film having the adjusted moisture content was continuously processed in the order of uniaxial stretching by a dry method, preliminary swelling, dyeing, uniaxial stretching by a wet method, fixing treatment, drying, and heat treatment to prepare a polarizing film. The PVA film is stretched by 4.1 times in the flow direction on a metal driving roll at 80 ° C. by a dry method, immersed in water at 30 ° C. for 30 seconds to be pre-swelled, and an iodine concentration of 0.6 g / liter, iodine It was immersed in a 35 ° C. aqueous solution having a potassium iodide concentration of 40 g / liter for 3 minutes. Subsequently, the film was uniaxially stretched 1.5 times in a 50% aqueous solution having a boric acid concentration of 4% to obtain a potassium iodide concentration of 60 g / l, a boric acid concentration of 40 g / l, and a zinc chloride concentration of 10 g / l at 30 ° C. It was immersed in an aqueous solution for 5 minutes to perform a fixing process. Thereafter, the PVA film was taken out, dried with hot air at 40 ° C., and heat-treated at 100 ° C. for 5 minutes. The polarizing performance of the obtained polarizing film was 44.00% in transmittance, 99.72% in degree of polarization and 51.84 in dichroic ratio.
The obtained polarizing film was bonded to a triacetate film using a 10% PVA aqueous solution adhesive to obtain a polarizing plate. Observation of the color spots on the polarizing plate revealed no color spots over the entire surface of the polarizing plate and was favorable. When this polarizing plate was incorporated in a liquid crystal display device, it was good without color spots.
[0038]
Example 2
The PVA film obtained in the same manner as in Example 1 was passed through a humidity controller to adjust the moisture content of the film to 8% by weight. When the PVA film was conditioned, a driving roll having a surface roughness of 70S was used to apply a tension of 30 N / m to the film. Further, among the free rolls incorporated in the humidity control device, one near the outlet of the humidity control device was used as a bend roll. In the step of controlling the humidity of the PVA film, no bending of the film edge occurred, and no wrinkles were observed in the film.
The PVA film having the adjusted moisture content was treated in the same manner as in Example 1 to produce a polarizing film. The obtained polarizing film was bonded to a triacetate film using a 10% PVA aqueous solution adhesive to obtain a polarizing plate. Observation of the color spots on the polarizing plate revealed no color spots over the entire surface of the polarizing plate and was favorable. When this polarizing plate was incorporated in a liquid crystal display device, it was good without color spots.
[0039]
Example 3
The PVA film obtained in the same manner as in Example 1 was passed through a humidity controller to adjust the moisture content of the film to 6%. When the humidity of the PVA film was adjusted, a tension of 40 N / m was applied to the film using a driving roll having a surface roughness of 50S. We did not incorporate expander rolls or bend rolls into the humidity controller. The tension applied to the film when the PVA film was conditioned was relatively high, and no bending of the edge of the film occurred, but several wrinkles were observed in the width direction of the film. The film was slightly stretched.
The PVA film having the adjusted moisture content was treated in the same manner as in Example 1 to produce a polarizing film. In producing a polarizing film, no abnormality was found in the film during uniaxial stretching by a dry method.
The obtained polarizing film was bonded to a triacetate film using a 10% PVA aqueous solution adhesive to obtain a polarizing plate. When the color spots of the polarizing plate were observed, slight color spots were observed in the portions where wrinkles were observed during humidity control of the PVA film, but within the allowable range. When this polarizing plate was assembled into a liquid crystal display device and a portion where color spots were observed on the polarizing plate was observed, no color spots were found on the liquid crystal display device.
[0040]
Comparative Example 1
The PVA film obtained in the same manner as in Example 1 was passed through a humidity controller to adjust the moisture content of the film to 6% by weight. When the humidity of the PVA film was adjusted, a tension of 60 N / m was applied to the film using a driving roll having a surface roughness of 70S. We did not incorporate expander rolls or bend rolls into the humidity controller. Due to the high tension applied to the film when the PVA film was humidified, bending of the edge of the film did not occur, but several wrinkles were observed in the width direction of the film. Seemed to be growing a little.
A polarizing film was produced in the same manner as in Example 1 using the PVA film with the adjusted moisture content. In producing a polarizing film, no abnormality was found in the film during uniaxial stretching by a dry method.
The obtained polarizing film was bonded to a triacetate film using a 10% PVA aqueous solution adhesive to obtain a polarizing plate. Observation of the color spots on the polarizing plate revealed that color spots were observed in the portions of the PVA film where wrinkles were observed during humidity control. When this polarizing plate was assembled into a liquid crystal display device, and a portion where color spots were observed on the polarizing plate was observed, color spots were also observed on the liquid crystal display device, and it was determined that the liquid crystal display device was unsuitable.
[0041]
Comparative Example 2
The PVA film obtained in the same manner as in Example 1 was passed through a humidity controller to adjust the moisture content of the film to 6% by weight. When the PVA film was conditioned, a tension of 5 N / m was applied to the film using a drive roll having a surface roughness of 70S. We did not incorporate expander rolls or bend rolls into the humidity controller. Because the tension applied to the PVA film when the humidity was adjusted was low, bending of the edge of the film occurred, and several wrinkles were observed in the width direction of the film.
A polarizing film was produced in the same manner as in Example 1 using the PVA film with the adjusted moisture content. In producing a polarizing film, no abnormality was found in the film during uniaxial stretching by a dry method.
The obtained polarizing film was bonded to a triacetate film using a 10% PVA aqueous solution adhesive to obtain a polarizing plate. When the color spots of the polarizing plate were observed, color spots were observed toward the center in the width direction in the vicinity where the end of the PVA film was bent. In addition, color spots were also observed in portions where wrinkles were observed. Although the cause of the color spot is unknown, it is considered that some sort of color spot has occurred. When this polarizing plate was assembled into a liquid crystal display device, and a portion where color spots were observed on the polarizing plate was observed, color spots were also observed on the liquid crystal display device, and it was determined that the liquid crystal display device was unsuitable.
[0042]
【The invention's effect】
According to the present invention, it is possible to easily stretch a wide polyvinyl alcohol film having a width of more than 2 m, which has been considered difficult in the prior art, thereby effectively preventing color spots due to stretch spots in the width direction. It is possible to produce an optical polyvinyl alcohol film with less color spots by reducing the amount of color. The method of the present invention can be preferably applied particularly to the production of a polarizing film, and from this polarizing film, a polarizing plate capable of reducing color unevenness when incorporated in a liquid crystal display device can be produced. .

Claims (4)

A polyvinyl alcohol film having a width of 2 m or more is stretched while applying a tension of 10 to 50 N / m in a flow direction of the film while adjusting a moisture content contained in the polyvinyl alcohol film. Manufacturing method of alcohol film. The method for producing a polyvinyl alcohol film for optical use according to claim 1, wherein the drive roll used for adjusting the moisture content contained in the polyvinyl alcohol film is a roll having a surface roughness of 50 to 100S. The method for producing an optical polyvinyl alcohol film according to claim 2, wherein an expander roll is used when adjusting the moisture content contained in the polyvinyl alcohol film. The method for producing a polyvinyl alcohol film for optical use according to claim 2 or 3, wherein a bend roll is used when adjusting the moisture content contained in the polyvinyl alcohol film.