JP3942923B2 - Polyvinyl alcohol film - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a polyvinyl alcohol film useful as a material for a polarizing plate used as a component of a liquid crystal display device, and a polarizing film and a polarizing plate comprising a uniaxially stretched polyvinyl alcohol film using the same.
[0002]
[Prior art]
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 having a light switching function. This LCD can be applied to small devices such as calculators and wristwatches in the early days 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 devices. There is a demand for a polarizing plate having a large area that spreads over a wide range and has less color spots than conventional products.
[0003]
The polarizing plate is generally dyed by uniaxially stretching a polyvinyl alcohol film (hereinafter, polyvinyl alcohol may be abbreviated as “PVA” and polyvinyl alcohol film may be abbreviated as “PVA film”), or dyed and uniaxially stretched. Then, a polarizing film obtained by fixing with a boron compound (the dyeing and fixing may be performed at the same time) can be used to protect cellulose triacetate (TAC) film, acetic acid / cellulose butyrate (CAB) film, etc. The film is bonded.
[0004]
[Problems to be solved by the invention]
By the way, even if it is a PVA film that looks uniform in appearance, the resulting polarizing film may have color spots that are difficult to distinguish from the outside. This color spot is difficult to confirm unless it is a final product (polarizing plate) in which a protective film or the like is laminated. When color spots appear in the final product, a secondary material such as a protective film, which is a good product, is discarded as a defective product, resulting in a large manufacturing loss. As a conventional method for reducing color spots, studies have been made from the viewpoint of reducing thickness spots and birefringence spots on a polyvinyl alcohol film, as described in JP-A-6-138319. By reducing the thickness spots and birefringence spots on the polyvinyl alcohol film, it was possible to reduce the color spots to some extent and satisfy the required level at the time, but the final product (polarizing plate and It has been found difficult to reduce the level of color spots that are problematic in liquid crystal display devices.
[0005]
In addition, a large-area polarizing film has been demanded with an increase in size of a liquid crystal display device. The conventional liquid crystal display device has a relatively small display area and is used alone with a polarizing plate, so color spots were not a problem, but when the display area is large, the entire display area must be uniform. The problem of color spots has become apparent for reasons such as being used in combination with other films such as viewing angle correction films. In particular, in the case of a polarizing plate produced by stretching a polyvinyl alcohol film uniaxially, a difference in optical properties between the central portion and the end portion of the film may be a problem. Therefore, when manufacturing a polarizing plate for a large-screen liquid crystal display, there is a problem that the color efficiency is relatively small, for example, since the product is collected only from the central portion, the production efficiency is lowered.
[0006]
Accordingly, an object of the present invention is to provide a polyvinyl alcohol film and a stretched polyvinyl alcohol film that are useful as a raw material for producing a polarizing film that has few color spots and can cope with an increase in the size of a liquid crystal display.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, the polyvinyl alcohol film according to the present invention has a thickness (A) at the center in the width direction of the film and a thickness (C) at a position 100 cm from the center in the width direction of 0.91. It is necessary to have a relationship of ≦ C / A ≦ 0.96. Moreover, as a polyvinyl alcohol film after uniaxial stretching, thickness (a) in the center part of the width direction of a film and thickness (b) in the position of 50 cm from the center part to the width direction are 0.92 <= b / a. It is necessary to have a relationship of ≦ 1.07. The conventional polyvinyl alcohol film used as the material of the polarizing film has been aimed at reducing color spots by improving the uniformity of the film before stretching, but in the present invention, the polyvinyl alcohol film after stretching is not before stretching. It is characterized by adjusting the thickness in the width direction of the film before stretching for the purpose of improving the uniformity.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
[0009]
As shown in FIG. 1, the polyvinyl alcohol film of the present invention is characterized in that the thickness in the width direction of the film gradually decreases toward the end. The thickness (A) at the center in the width direction of the polyvinyl alcohol film and the thickness (C) at a position 100 cm in the width direction from the center may have a relationship of 0.91 ≦ C / A ≦ 0.96. More preferably, the relationship is 0.92 ≦ C / A ≦ 0.95. Even when C / A is smaller than 0.91 or larger than 0.96, the change in the thickness of the polyvinyl alcohol film after uniaxial stretching is increased, and the color spots of the polarizing film are increased accordingly.
[0010]
There are several methods for gradually decreasing the thickness in the width direction of the film as it goes to the end, but in order to reduce the occurrence of color spots, the thickness of the film needs to change gently. Examples of the method include a method of gradually changing the lip interval in the width direction, a method of gradually changing the temperature of the die lip portion in the width direction, and the lip interval is gradually changed because the thickness can be easily controlled. Particularly preferred is a method of making them. It is inappropriate to change the shape of the end of the lip largely because it causes color spots. For example, the lip of the die, which is usually parallel, can be used with a lip interval adjusting bolt to obtain the desired film. A method of gradually narrowing as the end of the lip is reached is adopted.
In the polyvinyl alcohol film of the present invention, the thickness (A) at the center in the width direction of the film and the thickness (B) at a position 50 cm from the center in the width direction are 0.96 ≦ B / A ≦ 1.0. More preferably, the relationship is 0.97 ≦ B / A ≦ 0.99. About the polarizing film obtained from the polyvinyl alcohol film in which B / A falls in the range described above, the effect of reducing color spots is increased.
[0011]
Furthermore, in the polyvinyl alcohol film of the present invention, the thickness (A) at the center in the width direction of the film and the thickness (D) at a position 150 cm from the center in the width direction are 0.84 ≦ D / A ≦ 0. .92 is more preferable, and a relationship of 0.86 ≦ D / A ≦ 0.90 is particularly preferable. About the polarizing film obtained from the polyvinyl alcohol film in which B / A falls in the range described above, the effect of reducing color spots is further increased.
[0012]
In the present invention, the uniaxially stretched polyvinyl alcohol film used for the production of the polarizing film is characterized in that the thickness in the width direction of the film is uniform as shown in FIG. In such a uniaxially stretched polyvinyl alcohol film, the thickness (a) at the center in the width direction of the film and the thickness (b) at a position 50 cm from the center in the width direction are 0.92 ≦ b / a ≦ 1. 0.07, and more preferably 0.96 ≦ b / a ≦ 1.04.
Such a uniaxially stretched polyvinyl alcohol film has a thickness (a) at the center in the width direction of the film and a thickness (c) at a position 100 cm from the center in the width direction of 0.92 ≦ c / a ≦ 1.07. More preferably, the relationship is 0.96 ≦ c / a ≦ 1.04.
[0013]
The PVA used in the present invention is produced, for example, by saponifying a polyvinyl ester obtained by polymerizing a vinyl ester. Further, the modified PVA obtained by graft copolymerization of the PVA 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 or the like at a ratio of less than 5 mol%, a vinyl ester, Modified PVA produced by saponifying a modified polyvinyl ester obtained by copolymerizing unsaturated carboxylic acid or derivative thereof, unsaturated sulfonic acid or derivative thereof, α-olefin having 2 to 30 carbon atoms or the like in a proportion of less than 15 mol% In addition, a so-called polyvinyl acetal resin obtained by crosslinking a part of the hydroxyl group of unmodified or modified PVA with aldehydes such as formalin, butyraldehyde, and benzaldehyde can be given.
[0014]
Examples of the vinyl ester include vinyl acetate, vinyl formate, vinyl propionate, vinyl butyrate, vinyl pivalate, vinyl versatate, vinyl laurate, vinyl stearate, vinyl benzoate and the like.
[0015]
On the other hand, the comonomer used in the modified PVA is copolymerized mainly for the purpose of modifying the PVA, and is used within a range not impairing the gist of the present invention. Examples of such comonomers include olefins such as ethylene, propylene, 1-butene, and isobutene; acrylic acid and salts thereof; methyl acrylate, ethyl acrylate, n-propyl acrylate, i-propyl acrylate, and n-acrylate. -Acrylic esters such as butyl, i-butyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, octadecyl acrylate; methacrylic acid and salts thereof; methyl methacrylate, ethyl methacrylate , Methacrylic acid such as n-propyl methacrylate, i-propyl methacrylate, n-butyl methacrylate, i-butyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate, octadecyl methacrylate ester Acrylamides such as acrylamide, N-methyl acrylamide, N-ethyl acrylamide, N, N-dimethyl acrylamide, diacetone acrylamide, acrylamide propane sulfonic acid and salts thereof, acrylamide propyl dimethylamine and salts thereof, N-methylol acrylamide and derivatives thereof; Derivatives; Methacrylamide derivatives such as methacrylamide, N-methyl methacrylamide, N-ethyl methacrylamide, methacrylamide propane sulfonic acid and salts thereof, methacrylamide propyl dimethylamine and salts thereof, N-methylol methacrylamide and derivatives thereof; N -N-vinylamides such as vinylformamide, N-vinylacetamide, N-vinylpyrrolidone; methyl vinyl ether, Vinyl ethers such as ruvinyl 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; nitriles such as acrylonitrile and methacrylonitrile; vinyl chloride , Vinyl halides such as vinylidene chloride, vinyl fluoride and vinylidene fluoride; allyl compounds such as allyl acetate and allyl chloride; maleic acid and salts thereof or esters thereof; itaconic acid and salts thereof or esters thereof; vinyltrimethoxysilane And vinyl silyl compounds such as isopropenyl acetate. Of these, α-olefins are preferable, and ethylene is particularly preferable. The modified amount of the modified PVA is preferably less than 15 mol%.
[0016]
The saponification degree of PVA is preferably 95 mol% or more, more preferably 98 mol% or more, further preferably 99 mol% or more, and more preferably 99.5 mol% or more from the viewpoint of the polarizing performance and durability of the polarizing film and polarizing plate. Most preferred.
[0017]
The saponification degree indicates the proportion of units that are actually saponified to vinyl alcohol units among the units that can be converted to vinyl alcohol units by saponification. The saponification degree of PVA was measured by the method described in JIS.
[0018]
The polymerization degree of PVA is preferably 500 or more, more preferably 1000 or more, further preferably 1500 or more, and most preferably 2500 or more from the viewpoint of the polarization performance and durability of the polarizing film and polarizing plate. The upper limit of the degree of polymerization of PVA is preferably 8000 or less, and more preferably 6000 or less.
[0019]
The degree of polymerization of the PVA is measured according to JIS K 6726. That is, it is calculated | required from the intrinsic viscosity measured in 30 degreeC water after re-saponifying and refine | purifying PVA.
[0020]
As a method for producing a PVA film using the PVA described above, in addition to a film forming method by a melt extrusion method using water-containing PVA, for example, using a PVA solution in which PVA is dissolved in a solvent, A film method, a wet film formation method (discharge into a poor solvent), a gel film formation method (a method in which a PVA aqueous solution is once cooled and gelated, and then a solvent is extracted and removed to obtain a PVA film), and a combination thereof Etc. can be adopted. Among these, the casting film forming method and the melt extrusion film forming method are preferable from the viewpoint of obtaining a good polarizing film.
[0021]
Examples of the solvent for dissolving PVA used in producing the PVA film include dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, glycerin, propylene glycol, diethylene glycol, triethylene glycol, and tetraethylene. Glycol, trimethylolpropane, ethylenediamine, diethylenetriamine, glycerin, water and the like can be mentioned, and one or more of these can be used. Among these, dimethyl sulfoxide, water, or a mixed solvent of glycerin and water is preferably used.
[0022]
The proportion of PVA in the PVA solution or hydrous 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. 30 to 55% by weight is more preferred, and 35 to 50% by weight is most preferred. When the ratio of PVA is high, the viscosity of the PVA solution or hydrous PVA becomes too high, and it becomes difficult to filter and degas when preparing the stock solution of the film, and it is difficult to obtain a film free from foreign matters and defects. In addition, when the ratio of PVA is low, the viscosity of the PVA solution or water-containing PVA becomes low, so the PVA film becomes flat due to the leveling effect during film production, and the film has a specific thickness tendency that is characteristic of the PVA film of the present invention. It becomes difficult to manufacture. Further, the PVA solution or the hydrous PVA may contain a plasticizer, a surfactant, a dichroic dye or the like as necessary.
[0023]
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, etc., and one or more of these are used. can do. Among these, diglycerin, ethylene glycol, and glycerin are preferably used because of the effect of improving stretchability.
[0024]
The addition amount of the polyhydric alcohol 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 with respect to 100 parts by weight of PVA. If the amount is less than 1 part by weight, the dyeability and stretchability of the PVA film may be lowered. If the amount is more than 30 parts by weight, the PVA film may be too flexible and the handleability may be lowered.
[0025]
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. As the anionic surfactant, for example, a carboxylic acid type such as potassium laurate, a sulfate type such as octyl sulfate, and a sulfonic acid type anionic surfactant such as dodecylbenzenesulfonate are 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, and polyoxyethylene laurylamino. Alkylamine type such as ether, alkylamide type such as polyoxyethylene lauric acid amide, polypropylene glycol ether type such as polyoxyethylene polyoxypropylene ether, alkanolamide type such as oleic acid diethanolamide, polyoxyalkylene allyl phenyl ether, etc. Nonionic surfactants such as allyl phenyl ether type are preferred. These surfactants can be used alone or in combination of two or more.
[0026]
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 with respect to 100 parts by weight of PVA. . If the amount is less than 0.01 part by weight, the effect of improving the film forming property and the peelability is hardly exhibited, and if it is more than 1 part by weight, the surfactant is eluted on the surface of the PVA film, causing blocking, and handling properties are improved. May decrease.
[0027]
In order to produce a polarizing film from the PVA film of the present invention, for example, the PVA film may be dyed, uniaxially stretched, fixed and dried, and further subjected to heat treatment as necessary. Dyeing, uniaxially stretched and fixed There is no particular restriction on the order of processing operations. Moreover, you may perform uniaxial stretching twice or more.
[0028]
Dyeing can be performed before uniaxial stretching, during uniaxial stretching, or after uniaxial stretching. As dyes used for dyeing, 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 , 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 Dichroic dyes such as yellow 8, 12, 44, 86, 87; direct orange 26, 39, 106, 107 can be used in one kind or a mixture of two or more kinds. Ordinary dyeing is generally performed by immersing the PVA film in a solution containing the above-mentioned dye, but the processing conditions and processing method are particularly limited, such as mixing with the PVA film to form a film. is not.
[0029]
Uniaxial stretching can be performed by a wet stretching method or a dry heat stretching method, and a PVA film after absorbing water in warm water such as an aqueous boric acid solution (in a solution containing the dye or in a fixing treatment bath described later) or water absorption. Can be used in air. There is no limitation in particular about extending | stretching temperature, When extending | stretching a PVA film in warm water (wet extending | stretching), 30-90 degreeC is suitable, and 50-180 degreeC is suitable when dry-heat extending | stretching. Further, the stretching ratio of uniaxial stretching (total stretching ratio in the case of multi-stage uniaxial stretching) is preferably 4 times or more, and particularly preferably 5 times or more from the viewpoint of the polarizing performance of the polarizing film and the polarizing plate. Although there is no upper limit in the strict sense about the draw ratio, it is preferable that the draw ratio is 8 times or less because uniform stretching can be easily obtained. The thickness of the film after stretching is preferably from 3 to 75 μm, more preferably from 5 to 50 μm.
[0030]
Fixing treatment is often performed for the purpose of strengthening the adsorption of the dye to the PVA film. Usually, boric acid and / or boron compounds are added to the treatment bath used for the fixing treatment. Moreover, you may add an iodine compound in a processing bath as needed.
[0031]
It is preferable to perform the drying process of the obtained polarizing film at 30-150 degreeC, and it is more preferable to carry out at 50-150 degreeC.
[0032]
The polarizing film obtained as described above is usually used as a polarizing plate by attaching a protective film optically transparent and having mechanical strength on both sides or one side. 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 is used. In addition, examples of the adhesive for bonding include a PVA-based adhesive and a urethane-based adhesive, among which a PVA-based adhesive is preferable.
[0033]
The polarizing plate obtained as described above is coated as a pressure sensitive adhesive such as acrylic, and then bonded to a glass substrate and used as a component of a liquid crystal display device, or a retardation film, a viewing angle improving film, and a luminance improving It is used by being bonded to a film or the like.
[0034]
【Example】
Hereinafter, the present invention will be specifically described with reference to examples, but the present invention is not limited thereto. In addition, the thickness of the film in an Example was evaluated with the following method.
[0035]
Film thickness:
Using a contact-type thickness meter (K-402B, head size 5 mm, manufactured by Anritsu Co., Ltd.), the thickness was measured at five locations within a range of about 3 cm including the target measurement point, and the average value was obtained.
[0036]
Example 1
100 parts by weight of PVA having a saponification degree of 99.95 mol% and a polymerization degree of 2400 was melt-kneaded with 10 parts by weight of glycerin and 170 parts by weight of water, and after defoaming, melt extrusion from a T die to a metal roll was performed. Filmed. By adjusting the opening degree of the lip of the T die, a PVA film having a thick central portion and a thin end and a width of 3 m was obtained. The thickness of the film obtained after drying and heat treatment was 65 μm, 70 μm, 73 μm, 75 μm, 73 μm, 70 μm, and 65 μm every 50 cm from the end. The thickness (A) at the central portion in the width direction of the film was 75 μm, the thickness (C) at a position 100 cm from the central portion in the width direction was 70 μm, and C / A was 0.93.
[0037]
The 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. That is, the PVA film was immersed in 30 ° C. water for 30 seconds to be pre-swelled, and then immersed in an aqueous solution having an iodine concentration of 0.4 g / liter and a potassium iodide concentration of 40 g / liter for 3 minutes. Subsequently, uniaxial stretching was performed 5 times in a 50 ° C. aqueous solution with a boric acid concentration of 4%, in a 30 ° C. aqueous solution with a potassium iodide concentration of 40 g / liter, a boric acid concentration of 40 g / liter, and a zinc chloride concentration of 10 g / liter. For 5 minutes, and fixed. Thereafter, the PVA film was taken out, dried with hot air at 40 ° C. under a constant length, and further subjected to heat treatment at 100 ° C. for 5 minutes.
[0038]
The width | variety of the obtained polarizing film was 1.5 m, and the thickness from an edge part was 25 micrometers, 25 micrometers, and 25 micrometers every 50 cm on the basis of the center part. The thickness (a) at the center in the width direction of the film after uniaxial stretching was 25 μm, the thickness (b) at a position 50 cm from the center in the width direction was 25 μm, and b / a was 1.0. When the obtained polarizing film was placed at an angle of 10 degrees between two polarizing plates arranged in parallel to the stretching axis direction (0 degree), the central part and the end part of the polarizing film in the width direction. The difference in brightness was small and color spots were small and good.
[0039]
A polarizing plate was obtained by attaching a triacetate film to the obtained polarizing film using a 4% aqueous polyvinyl alcohol solution. The obtained polarizing plate was placed at an angle of 10 degrees between two polarizing plates arranged in parallel to the stretching axis direction (0 degree). The difference in luminance was small, and the color spots were small and good.
[0040]
Example 2
100 parts by weight of PVA having a saponification degree of 99.9 mol% and a polymerization degree of 4000 was melt-kneaded with 10 parts by weight of glycerin and 220 parts by weight of water. Filmed. By adjusting the lip opening of the T die, a PVA film having a thick central portion and a thin end and a width of 4 m was obtained. The thickness of the film obtained after drying and heat treatment was 61 μm, 66 μm, 70 μm, 73 μm, 75 μm, 73 μm, 71 μm, 67 μm, and 62 μm every 50 cm from the end. The thickness (A) at the center in the width direction of the film was 75 μm, the thickness (C) at a position 100 cm from the center in the width direction was 70 μm and 71 μm, and C / A was 0.93 and 0.95. .
[0041]
The 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. That is, the PVA film was preliminarily swollen in water at 30 ° C. for 0.5 minutes and immersed in an aqueous solution at 35 ° C. having an iodine concentration of 0.4 g / liter and a potassium iodide concentration of 40 g / liter for 3 minutes. Subsequently, uniaxial stretching was performed 5 times in a 50 ° C. aqueous solution with a boric acid concentration of 4%. For 5 minutes, and fixed. Thereafter, the PVA film was taken out, dried with hot air at 40 ° C. under a constant length, and further subjected to heat treatment at 100 ° C. for 5 minutes.
[0042]
The width | variety of the obtained polarizing film was 2 m, and the thickness from an edge part was 25 micrometers, 25 micrometers, 25 micrometers, 26 micrometers, and 26 micrometers every 50 cm. The thickness (a) at the center in the width direction of the film after uniaxial stretching is 25 μm, the thickness (b) at a position 50 cm from the center to the width is 25 μm and 26 μm, and b / a is 1.0 and 1. 04. When the obtained polarizing film was placed at an angle of 10 degrees between two polarizing plates arranged in parallel to the stretching axis direction (0 degree), the central part and the end part of the polarizing film in the width direction. The difference in luminance was small, and the color spots were small and good.
[0043]
A polarizing plate was obtained by attaching a triacetate film to the obtained polarizing film using a 4% aqueous polyvinyl alcohol solution. The obtained polarizing plate was placed at an angle of 10 degrees between two polarizing plates arranged in parallel to the stretching axis direction (0 degree). The difference in luminance was small, and the color spots were small and good.
[0044]
Comparative Example 1
100 parts by weight of PVA having a saponification degree of 99.95 mol% and a polymerization degree of 2400 was melt-kneaded with 10 parts by weight of glycerin and 170 parts by weight of water, and after defoaming, melt extrusion from a T die to a metal roll was performed. Filmed. By adjusting the lip opening of the T die, a PVA film having a width of 3 m and a uniform thickness in the width direction was obtained. The thickness of the film obtained after drying and heat treatment was 75 μm, 74 μm, 75 μm, 75 μm, 75 μm, 76 μm, and 75 μm every 50 cm from the end. The thickness (A) at the central portion in the width direction of the film was 75 μm, the thickness (C) at a position 100 cm from the central portion in the width direction was 74 μm and 76 μm, and C / A was 0.99 and 1.01. .
[0045]
The 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. That is, the PVA film was immersed in 30 ° C. water for 30 seconds to be pre-swelled, and then immersed in an aqueous solution having an iodine concentration of 0.4 g / liter and a potassium iodide concentration of 40 g / liter for 3 minutes. Subsequently, uniaxial stretching was performed 5 times in a 50 ° C. aqueous solution with a boric acid concentration of 4%. For 5 minutes, and fixed. Thereafter, the PVA film was taken out, dried with hot air at 40 ° C. under a constant length, and further subjected to heat treatment at 100 ° C. for 5 minutes.
[0046]
The width of the obtained polarizing film was 1.5 m, and the thickness from the end portion was 27 μm, 25 μm, and 28 μm every 50 cm based on the center. The thickness (a) at the center in the width direction of the film after uniaxial stretching is 25 μm, the thickness (b) at a position 50 cm from the center to the width direction is 27 μm and 28 μm, and b / a is 1.08 and 1. It was 12. When the obtained polarizing film was placed at an angle of 10 degrees between two polarizing plates arranged in parallel to the stretching axis direction (0 degree), the central part and the end part of the polarizing film in the width direction. In addition to a large difference in brightness, color spots were also large, and it was predicted that the film was inappropriate as a polarizing film for large liquid crystal displays.
[0047]
A polarizing plate was obtained by attaching a triacetate film to the obtained polarizing film using a 4% aqueous polyvinyl alcohol solution. When the obtained polarizing plate is placed at an angle of 10 degrees between two polarizing plates arranged in parallel to the stretching axis direction (0 degree), the luminance at the center and the edge with respect to the width direction of the polarizing plate In addition, the color difference was large and the film was unsatisfactory as a polarizing film for a large liquid crystal display.
[0048]
【The invention's effect】
According to this invention, the PVA film which can reduce the color spot of a polarizing film is obtained. And using this PVA film, there can be obtained a polarizing film suitable for a large-sized liquid crystal display with few color spots.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing one embodiment of a polyvinyl alcohol film of the present invention.
FIG. 2 is a schematic configuration diagram showing an embodiment of a uniaxially stretched polyvinyl alcohol film used for producing a polarizing film in the present invention.
[Explanation of symbols]
A to D: thickness at each position in the width direction of the polyvinyl alcohol film, ac: thickness at each position in the width direction of the uniaxially stretched polyvinyl alcohol film.

Claims (5)

A polyvinyl alcohol film produced from a polyvinyl alcohol having an average degree of polymerization of 500 to 8000 and a saponification degree of 95 mol% or more, and a film forming raw material containing 1 to 30 parts by weight of a polyhydric alcohol with respect to 100 parts by weight of the polyvinyl alcohol. The thickness (A) at the center in the width direction of the film and the thickness (C) at a position 100 cm from the center in the width direction have a relationship of 0.91 ≦ C / A ≦ 0.96. A polyvinyl alcohol film characterized by that.   The thickness (A) at the central portion in the width direction of the film and the thickness (B) at a position 50 cm from the central portion in the width direction have a relationship of 0.96 ≦ B / A ≦ 1.0, The polyvinyl alcohol film according to claim 1.   The thickness (A) at the center in the width direction of the film and the thickness (D) at a position 150 cm from the center in the width direction are in a relationship of 0.84 ≦ D / A ≦ 0.92. The polyvinyl alcohol film according to claim 1 or 2. It is a polarizing film obtained by uniaxially stretching the polyvinyl alcohol film according to any one of claims 1 to 3, wherein the film has a thickness (a) at the center in the width direction of the film, and 50 cm in the width direction from the center. The polarizing film, wherein the thickness (b) at the position of is in a relationship of 0.92 ≦ b / a ≦ 1.07. A polarizing plate produced from the polarizing film according to claim 4 .

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