JP2004020634A - Polyvinyl alcohol film for polarizing film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide 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: The polyvinyl alcohol film has ten or more of irregularities of 0.5 to 5μm difference to average thickness per 5mm of the film in a width direction. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a polyvinyl alcohol film for a polarizing film used as a component of a liquid crystal display device, a method for producing the same, and a polarizing plate and a liquid crystal display device manufactured using the polyvinyl alcohol film for a polarizing film.
[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. The application fields of this LCD include small devices such as calculators and wristwatches in the early stages of development, and in recent years, laptop computers, word processors, liquid crystal color projectors, in-vehicle navigation systems, liquid crystal televisions, personal phones, and indoor and outdoor measuring instruments. Thus, a polarizing plate having a large area with less color spots than conventional products has been required.
[0003]
Generally, a polarizing plate is dyed by uniaxially stretching a polyvinyl alcohol-based polymer film (hereinafter, a polyvinyl alcohol-based polymer film may be abbreviated as “PVA film” and a polyvinyl alcohol-based polymer film may be abbreviated as “PVA film”). Or, after dyeing and uniaxially stretching, by performing a fixing treatment with a boron compound (the dyeing and the fixing treatment may be simultaneous), a cellulose triacetate (TAC) film or cellulose acetate / butyrate is obtained. (CAB) A structure in which a protective film such as a film is bonded.
[0004]
[Problems to be solved by the invention]
Even if the PVA film looks uniform at first glance, the polarizing film obtained by uniaxially stretching the film sometimes contains color spots which are difficult to distinguish. This color spot is difficult to confirm 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 are rarely a problem.However, when the display area is large, the entire display area is uniform. For example, the problem of color unevenness has become apparent due to the demand for high performance and the increased use of the film in combination with other films 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. This is thought to be due to a thickness variation in the width direction of the film, which is emphasized because it is uniaxially stretched in the flow direction. Variations in the thickness of the polarizing film cause irregularities in transmittance and the like, and thus, when the polarizing film is incorporated in a liquid crystal display device or the like, there is a problem that the quality is reduced. In particular, as the display screen of the liquid crystal display device becomes larger, if there are continuous streaks in the flow direction, it becomes difficult to collect the product while avoiding such locations, which is a major industrial problem.
[0006]
Conventionally, it has been attempted to reduce the color unevenness of the polarizing film by improving the uniformity of the thickness and the like of the PVA film used as the material of the polarizing film. As we went up, it became difficult to meet that demand.
[0007]
Therefore, an object of the present invention is to provide a PVA film that is useful as a raw material for producing a polarizing film for a high-quality liquid crystal display with less color spots.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, the polyvinyl alcohol film for a polarizing film according to the present invention needs to have 10 or more irregularities having a difference of 0.5 to 5 μm with respect to the average thickness per 5 mm in the width direction of the film. It is.
The polyvinyl alcohol film for a polarizing film of the present invention is characterized by having minute irregularities on the film surface, so that even when a polarizing film is produced by uniaxially stretching the film, it is incorporated into an LCD. In this case, there is an effect that it is possible to prevent the occurrence of large color spots which may cause a problem in quality.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
In the PVA film for a polarizing film of the present invention, as shown in FIG. 1, the thickness in the width direction of the film fluctuates minutely, and the magnitude of the fluctuation is 0.5 to 5 μm with respect to the average thickness. It is formed as it is. In the PVA film for a polarizing film of the present invention, it is necessary that there are 10 or more irregularities in the range of 0.5 to 5 μm with respect to the average thickness per 5 mm in the width direction of the film, more preferably 15 or more, and 20 or more. More than one is particularly preferred. If the number is less than 10, color unevenness when a polarizing film is produced is large and unsuitable. Even if there is only one unevenness having a difference of 0.5 to 5 μm per 5 mm in the width direction defined in the present invention, since the thickness unevenness of the ordinary optical vinylon film is large, It is not suitable as a film. As shown in FIG. 1, the unevenness having a difference of 0.5 to 5 μm defined in the present invention has a maximum value and a minimum value of 0. The thickness is in the range of 5 to 5 μm, and is added to the number defined in the present invention when the thickness before and after the thickness exceeds the value of the average thickness.
[0010]
The PVA film for a polarizing film of the present invention can be manufactured by forming a film-forming raw material comprising a polyvinyl alcohol-based polymer solution on a metal roll having a surface roughness of 0.5 to 5S. The surface roughness of the metal roll is preferably 0.5 to 5S, more preferably 0.8 to 4S, and particularly preferably 1 to 3S. If the surface roughness of the metal roll is smaller than 0.5S, the size of the irregularities on the film surface becomes too small, and it becomes difficult to form the desired minute irregularities on the film surface. If the surface roughness of the metal roll is greater than 5S, the unevenness of the cast surface of the metal roll is reduced when the concentration of the PVA solution as the film forming stock solution is made similar to that of the PVA solution generally used for industrial production. Becomes too large, and it becomes difficult to smoothly cast the PVA solution along the irregular shape of the cast surface of the metal roll. In this case, the unevenness of the PVA film obtained after drying is insufficiently formed, or bubbles are formed in the film, which is likely to cause color unevenness when a polarizing film is produced.
[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 degree of polymerization of PVA 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 takes a lot of 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 properties 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 width of the PVA film for a polarizing film of the present invention is preferably 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.
[0026]
In order to produce a polarizing film from the PVA film for a polarizing film of the present invention, for example, a uniaxial stretching of a PVA film by a dry method, dyeing, if necessary, a second-stage uniaxial stretching 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 the wet method or the 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.
[0027]
The dyeing of the PVA film may be performed 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.
[0028]
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. The thickness of the stretched film is preferably from 3 to 45 μm, more preferably from 5 to 30 μm.
[0029]
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.
[0030]
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.
[0031]
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 obtained in this way, the thickness of the adhesive layer is preferably 0.5 to 10 μm, more preferably 0.8 to 8 μm, and particularly preferably 1 to 5 μm. It is preferable that the thickness of the adhesive layer is larger than the fine irregularities of the film so that the thickness of the polarizing plate after bonding is constant. When the thickness is smaller than 0.5 μm, in the present invention, since there are many fine irregularities on the film surface, uniform adhesion tends to be difficult, and bubbles are formed, and optical defects are easily formed, which is problematic. There are cases. When the thickness is larger than 10 μm, it takes a long time to dry, and if an inadvertent force is applied while drying is inadequate, it tends to cause an optical defect. In addition, there is a disadvantage that air bubbles easily enter.
[0032]
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.
[0033]
【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 average thickness of the PVA film, the size of the irregularities, the optical performance of the polarizing film, and the color unevenness of the polarizing plate were evaluated by the following methods.
[0034]
Average thickness of PVA film:
The thickness in the film width direction was continuously measured using a contact thickness gauge (K-402B, head size 5 mm, manufactured by Anritsu Corporation), and the average value was determined.
[0035]
Size of unevenness of PVA film:
The size of the unevenness in the film width direction was measured using a contact type surface roughness meter (SE-3C, measuring needle tip R1 μm, manufactured by Kosaka Laboratory Co., Ltd.).
[0036]
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 Japan Electronics Machinery Manufacturers Association (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.
[0037]
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 laminated in parallel, a degree of polarization of 99.99% or more), and the degree of color spot was determined by visual observation.
[0038]
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, and after defoaming, a metal roll having a surface roughness of 3S from a T die. And extruded into a film. Thereafter, the width of the PVA film obtained by drying and heat treatment was 3 m, and the average thickness was 50 μm. When the surface roughness was measured by sampling three arbitrary positions in the width direction of the PVA film, 30 irregularities having a difference of 0.5 to 5 μm with respect to the average thickness per 5 mm in the width direction of the film, 32 And 31 pieces.
The above-mentioned PVA film was continuously processed in the order of preliminary swelling, dyeing, uniaxial stretching, fixing treatment, drying and heat treatment to prepare a polarizing film. The PVA film was pre-swelled by immersing it in water at 30 ° C. for 30 seconds, and immersed in an aqueous solution at 35 ° C. having an iodine concentration of 0.4 g / l and a potassium iodide concentration of 40 g / l for 3 minutes. Subsequently, the film is uniaxially stretched 5 times in an aqueous solution of boric acid at a concentration of 4% at 50 ° C. to obtain a solution of potassium iodide at a concentration of 40 g / l, boric acid at a concentration of 40 g / l, and zinc chloride at a concentration of 10 g / l at 30 ° C. 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 a transmittance of 44.60%, a degree of polarization of 99.05%, and a dichroic ratio of 45.86.
The obtained polarizing film was bonded to a triacetate film using a 10% PVA aqueous solution adhesive to obtain a polarizing plate. When the obtained polarizing plate was dried, the thickness of the adhesive layer was 3 μm. 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 2
100 parts by weight of PVA having a degree of saponification of 99.95 mol% and a degree of polymerization of 2400 are impregnated with 10 parts by weight of glycerin and 170 parts by weight of water, melt-kneaded, and after defoaming, a metal roll having a surface roughness of 2S from a T-die. And extruded into a film. Thereafter, the width of the PVA film obtained by drying and heat treatment was 3 m, and the average thickness was 50 μm. The surface roughness was measured by sampling three arbitrary positions in the width direction of the PVA film, and 25 irregularities having a difference of 0.5 to 5 μm with respect to the average thickness per 5 mm in the width direction of the film, 27 And 26.
A polarizing film was produced from the PVA film in the same manner as in Example 1. The polarizing performance of the obtained polarizing film was such that the transmittance was 44.72%, the degree of polarization was 98.90%, and the dichroic ratio was 45.38.
The obtained polarizing film was bonded to a triacetate film using a 10% PVA aqueous solution adhesive to obtain a polarizing plate. When the obtained polarizing plate was dried, the thickness of the adhesive layer was 2 μm. 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.
[0040]
Example 3
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, and after defoaming, have a surface roughness of 0.5 S from a T-die. It was melt extruded on a metal roll to form a film. Thereafter, the width of the film obtained by drying and heat treatment was 3 m, and the average thickness was 50 μm. When the surface roughness was measured by sampling three arbitrary positions in the width direction of the PVA film, 20 irregularities having a difference of 0.5 to 5 μm with respect to the average thickness per 5 mm in the width direction of the film, 22 Pieces and 21 pieces.
A polarizing film was produced from the PVA film in the same manner as in Example 1. The polarizing performance of the obtained polarizing film was such that the transmittance was 44.83%, the degree of polarization was 98.76%, and the dichroic ratio was 45.01.
The obtained polarizing film was bonded to a triacetate film using a 10% PVA aqueous solution adhesive to obtain a polarizing plate. When the obtained polarizing plate was dried, the thickness of the adhesive layer was 8 μm. When the color spots of the polarizing plate were observed, the color spots that could be managed by visual observation over the entire surface of the polarizing plate were small and favorable. When this polarizing plate was incorporated in a liquid crystal display device, the color spots were larger than in the case of visual observation, but were relatively small and good.
[0041]
Example 4
100 parts by weight of PVA having a saponification degree of 99.95 mol% and a polymerization degree of 2400 are impregnated with 10 parts by weight of glycerin and 170 parts by weight of water, melt-kneaded, and after defoaming, a metal roll having a surface roughness of 5S from a T-die. And extruded into a film. Thereafter, the width of the PVA film obtained by drying and heat treatment was 3 m, and the average thickness was 50 μm. When the surface roughness was measured by sampling three arbitrary positions in the width direction of the PVA film, 20 irregularities having a difference of 0.5 to 5 μm with respect to the average thickness per 5 mm in the width direction of the film, 22 Pieces and 21 pieces.
A polarizing film was produced from the film in the same manner as in Example 1. The polarizing performance of the obtained polarizing film was a transmittance of 44.45%, a degree of polarization of 99.02%, and a dichroic ratio of 44.35.
The obtained polarizing film was bonded to a triacetate film using a 10% PVA aqueous solution adhesive to obtain a polarizing plate. When the obtained polarizing plate was dried, the thickness of the adhesive layer was 6 μm, and it was confirmed that bubbles were contained in a part between the polarizing film and the triacetate film. When the color spots of the polarizing plate were observed, color spots that could be discriminated by visual observation in the flow direction were present over the entire surface of the polarizing plate, but were within an acceptable range. In addition, because of the existence of unevenness presumably due to bubbles, the lower limit was acceptable depending on the application. When this polarizing plate was incorporated in a liquid crystal display device, the color spot became larger than that in the case of visual observation, which was an acceptable lower limit.
[0042]
Comparative Example 1
100 parts by weight of PVA having a degree of saponification of 99.95 mol% and a degree of polymerization of 2400 are impregnated with 10 parts by weight of glycerin and 120 parts by weight of water, melt kneaded, and after defoaming, a metal roll having a surface roughness of 6S from a T die. And extruded into a film. Thereafter, the width of the PVA film obtained by drying and heat treatment was 3 m, and the average thickness was 50 μm. When the surface roughness was measured by sampling three arbitrary positions in the width direction of the PVA film, five irregularities having a difference of 0.5 to 5 μm with respect to the average thickness per 5 mm in the width direction of the film, 8 And seven.
The above-mentioned PVA film was continuously treated in the order of preliminary swelling, dyeing, uniaxial stretching, fixing treatment, drying and heat treatment to prepare a polarizing film. The PVA film was pre-swelled by immersing it in water at 30 ° C. for 30 seconds, and immersed in an aqueous solution at 35 ° C. having an iodine concentration of 0.4 g / l and a potassium iodide concentration of 40 g / l for 3 minutes. Subsequently, the film is uniaxially stretched 5 times in an aqueous solution of boric acid at a concentration of 4% at 50 ° C. to obtain a solution of potassium iodide at a concentration of 40 g / l, boric acid at a concentration of 40 g / l, and zinc chloride at a concentration of 10 g / l at 30 ° C. 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 a transmittance of 44.94%, a degree of polarization of 98.55%, and a dichroic ratio of 44.16.
The obtained polarizing film was bonded to a triacetate film using a 10% PVA aqueous solution adhesive to obtain a polarizing plate. When the obtained polarizing plate was dried, the thickness of the adhesive layer was 3 μm. Observation of color spots on the polarizing plate revealed that three color spots were noticeable in the flow direction over the entire surface of the polarizing plate and were unsuitable as a commercial-grade polarizing plate. When this polarizing plate was assembled in a liquid crystal display device, color spots in the flow direction were visually recognizable, and were unsuitable as a liquid crystal display device.
[0043]
【The invention's effect】
The polyvinyl alcohol film for a polarizing film of the present invention has little color unevenness, and when the film is uniaxially stretched, it is possible to prevent the occurrence of large color unevenness which may cause a quality problem when incorporated into an LCD. A polarizing film suitable for display devices can be manufactured.
[Brief description of the drawings]
FIG. 1 is a schematic view showing one embodiment of a polyvinyl alcohol film for a polarizing film of the present invention.
[Explanation of symbols]
The thickness at each position in the width direction of the polyvinyl alcohol film for a polarizing film is shown.

Claims (5)

A polyvinyl alcohol film for a polarizing film, comprising 10 or more irregularities having a difference of 0.5 to 5 μm with respect to the average thickness per 5 mm in the width direction of the film. The method for producing a polyvinyl alcohol film for a polarizing film according to claim 1, wherein the film forming raw material comprising a polyvinyl alcohol-based polymer solution is formed on a metal roll having a surface roughness of 0.5 to 5S. A polarizing film obtained by uniaxially stretching the polyvinyl alcohol film for a polarizing film according to claim 1. A polarizing plate produced from the polarizing film according to claim 3. A liquid crystal display device manufactured from the polarizing plate according to claim 4.

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