JP3588308B2 - Method for producing polyvinyl alcohol film - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention provides a polyvinyl alcohol having a small number of disadvantages and useful as a raw material for producing a polarizing film. Film production method It is about.
[0002]
[Prior art]
A polarizing plate having a function of transmitting and blocking light is a fundamental component of a liquid crystal display (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. There is a demand for a polarizing plate which has a wide range of properties and has higher polarization performance and less defects than conventional products.
[0003]
Polarizers are generally Polyvinyl alcohol film (Less than, Polyvinyl alcohol For "PVA", Polyvinyl alcohol film Is sometimes abbreviated as "PVA film") and dyed by uniaxial stretching, or after dyeing, uniaxially stretched, and then fixed with a boron compound (dyeing and fixing, or uniaxially stretching and fixing). Are sometimes used simultaneously). A protective film such as a cellulose triacetate (TAC) film or a cellulose acetate / butyrate (CAB) film is bonded to a polarizing film.
[0004]
[Problems to be solved by the invention]
By the way, when a PVA film is stretched, a PVA film is stretched in a dyeing step or a fixing treatment step with a boron compound in the case of stretching by a dry method, and in a swelling step or a stretching step before stretching in the case of a wet method. PVA in the film may be partially dissolved. The dissolved PVA precipitates in the tank and adheres to the PVA film or the polarizing film, or precipitates on the PVA film or the polarizing film to become a defect, thereby lowering the yield of the polarizing film. Furthermore, PVA which remains dissolved without being precipitated is a problem because of the expense of wastewater treatment.
[0005]
Accordingly, an object of the present invention is to provide a PVA film useful as a raw material for producing a polarizing film having a small number of defects. Manufacturing method Is to provide.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, the method for producing a PVA film of the present invention is a method of producing a PVA film having a 1 cm to 100 ppm PVA elution amount when the 10 cm square PVA film is left in 1 liter of water at 50 ° C. for 4 hours. , 1 or more and less than 100 PVA in a chip state obtained by washing with water or warm water at a temperature of 10 ° C. or more and 90 ° C. or less of a weight bath ratio, and a film-forming material containing 1 to 30 parts by weight of a polyhydric alcohol with respect to 100 parts by weight of the PVA The film is formed using
[0007]
PVA film of the present invention Manufacturing method Is a small amount of PVA eluted in each step (a step of dyeing, fixing, swelling, stretching, etc.) when producing a polarizing film. Manufacturing method By using, a polarizing film having a small number of defects can be obtained in a high yield. Also, wastewater treatment is simplified.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail.
The PVA used in the present invention is produced, for example, by saponifying a polyvinyl ester obtained by polymerizing a vinyl ester. Modified PVA obtained by graft copolymerizing 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 at a ratio of less than 15 mol%, or a vinyl ester and a modified PVA. A modified PVA produced by saponifying a modified polyvinyl ester obtained by copolymerizing a saturated carboxylic acid or a derivative thereof, an unsaturated sulfonic acid or a derivative thereof, an α-olefin having 2 to 30 carbon atoms at a ratio 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.
[0009]
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. A mixture of two or more kinds can also be mentioned.
[0010]
On the other hand, the comonomer used for the modified PVA is mainly copolymerized for the purpose of modifying the PVA, and any copolymerizable with the above-mentioned vinyl ester is used within 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, acrylic Acrylates such as n-butyl acrylate, i-butyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, octadecyl acrylate; methacrylic acid and salts thereof; methyl methacrylate, methacrylic acid Ethyl acrylate, n-propyl methacrylate, i-propyl methacrylate, n-butyl methacrylate, i-butyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate, octadecyl methacrylate and the like Methacrylic acid S 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-vinylamides such as N-vinylformamide, N-vinylacetamide, N-vinylpyrrolidone; 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 chloride Vinyl halides such as 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 trimethoxysilane And vinylsilyl compounds such as isopropenyl acetate. Of these, α-olefins are preferred, and ethylene is particularly preferred.
[0011]
The amount of modification of the modified PVA is preferably less than 15 mol%.
[0012]
The saponification degree of PVA is preferably 97 mol% or more, more preferably 98 mol% or more, still more preferably 99 mol% or more, and most preferably 99.5 mol% or more, from the viewpoint of elution amount and durability.
[0013]
The degree of saponification indicates the ratio of units actually saponified to vinyl alcohol units among units that can be converted to vinyl alcohol units by saponification. In addition, the saponification degree of PVA was measured by the method described in JIS.
[0014]
The degree of polymerization of PVA is preferably at least 1,000 from the viewpoint of decreasing the amount of PVA eluted and the strength of the PVA film, more preferably at least 1500, still more preferably at least 2,000, particularly preferably at least 2,500 from the point of polarization performance. . The upper limit of the degree of polymerization of PVA is preferably 8000 or less, more preferably 6000 or less.
[0015]
The degree of polymerization 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.
[0016]
It is important that the PVA is washed with water or hot water in a chip state before the step of preparing a PVA solution for film formation or a step of preparing a water-containing PVA described below to remove PVA which is easily eluted in advance. The water or warm water to be washed may contain an organic solvent such as acetic acid, methanol, glycerin, a plasticizer, a surfactant, or the like as long as the object of the present invention is not impaired.
[0017]
The temperature of the water or hot water used for washing is preferably from 10 ° C to 90 ° C, more preferably from 20 ° C to 80 ° C, even more preferably from 25 ° C to 70 ° C, particularly from 30 ° C to 60 ° C. Is most preferred. If the temperature of the water is less than 10 ° C., the eluate cannot be sufficiently washed, while if the temperature of the hot water exceeds 90 ° C., the amount of the eluted PVA increases during the washing, and the loss increases. It is not preferable because the workability in the next dissolving step or the like is deteriorated due to sticking.
[0018]
The weight bath ratio of water or hot water to PVA chips is preferably 1 or more, more preferably 1.5 or more, and most preferably 2 or more. If the bath ratio is less than 1, the amount of water or hot water is small and washing cannot be performed sufficiently, and the effect of reducing the amount of PVA eluted is small. The upper limit of the bath ratio is less than 100. That is, even if the bath ratio is set to 100 or more, no significant improvement in the cleaning effect is seen, and water or hot water is wasted and uneconomical.
[0019]
The washing time of the PVA chip (the time from the contact of the PVA chip with water to the completion of drainage) is preferably 30 seconds or more, more preferably 1 minute or more, still more preferably 5 minutes or more, and particularly preferably 10 minutes or more. Is most preferred.
[0020]
There is no particular limitation on the method of cleaning the PVA chip, and a method of draining water after showering water or hot water on the PVA chip on a net or a belt, putting water or hot water and the PVA chip in a batch or tower and standing or stirring them in a tower or tank And a method in which water or hot water and PVA chips are continuously put into a tower or a tank, washed countercurrently or cocurrently (may be accompanied by stirring), and then drained.
[0021]
There is no particular limitation on the draining method after washing, and there is no particular limitation, such as a centrifuge, vacuum suction, a filter press, squeezing using rolls or belts, separation by gravity using a perforated plate such as a net or cloth or nonwoven fabric, decane And the like.
[0022]
As long as the purpose of the present invention is not impaired, washing water such as surface adhesion water or water separation may remain on the PVA chip after draining, but water used at the time of washing may be separated and removed from the PVA chip as much as possible. preferable.
[0023]
As a method of manufacturing a PVA film using a washed PVA chip, a casting film forming method and a wet film forming method (discharging into a poor solvent) using a PVA solution obtained by dissolving a PVA chip in a solvent. A gel film forming method (a method of once cooling and gelling a PVA aqueous solution and then extracting and removing water to obtain a PVA film), a method based on a combination of these methods, and a method of immersing PVA chips in water-containing PVA (including an organic solvent and the like). Can be produced by a melt-extrusion film-forming method in which melt extrusion is carried out. Among these, the casting film forming method and the melt extrusion film forming method are preferable because a good polarizing film can be obtained.
[0024]
As a solvent for dissolving the washed PVA chip used in producing the PVA film, for example, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, glycerin, diglycerin, propylene glycol, diethylene glycol, Examples thereof include triethylene glycol, tetraethylene glycol, trimethylolpropane, ethylenediamine, diethylenetriamine, and water, and one or more of these can be used. Among them, water, dimethyl sulfoxide, or a mixed solvent of water and dimethyl sulfoxide is preferably used.
[0025]
The PVA concentration of the PVA solution or the hydrated PVA used for producing the PVA film is preferably 3 to 70% by weight, more preferably 10 to 60% by weight, still more preferably 13 to 55% by weight, and particularly preferably 15 to 50% by weight. % By weight is most preferred. If necessary, the PVA solution or the water-containing PVA may contain a plasticizer, a surfactant, a dichroic dye, and the like.
[0026]
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 from the viewpoint of the effect of improving stretchability.
[0027]
The amount of the polyhydric alcohol to be 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.
[0028]
When manufacturing 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. One or a combination of two or more of these surfactants can be used.
[0029]
The amount of the surfactant to be added 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. preferable. When the amount is less than 0.01 part by weight, the effect of improving stretchability and dyeing property is difficult to appear, and when the amount is more than 1 part by weight, it is eluted on the surface of the PVA film, causing blocking, and the handleability may be reduced. is there.
[0030]
When manufacturing a PVA film, it is preferable to perform sufficient drying after film formation in order to reduce the amount of PVA eluted together with the above-mentioned washing.
[0031]
It is important that the PVA film of the present invention has an elution amount of 1 to 100 ppm when the 10 cm square PVA film is left in 1 liter of water at 50 ° C. for 4 hours. It is preferably from 5 to 80 ppm, particularly preferably from 10 to 60 ppm. If the amount of PVA eluted exceeds 100 ppm, the amount of PVA eluted into the tank or the amount of PVA deposited on the PVA film or polarizing film increases, making it difficult to obtain a polarizing film with a small number of defects, Problems arise when treating wastewater. In addition, in order to reduce the amount of PVA eluted to less than 1 ppm, a very large amount of pre-washing water is required, which is not only uneconomical, but also requires a high degree of heat treatment after film formation and drying, and the uniaxial stretching property is deteriorated. It is difficult to obtain a proper polarizing film.
[0032]
The measurement method of the amount of PVA elution is as follows. A 10 cm square PVA film was left in 1 liter of 50 ° C. distilled water for 4 hours, and the extract was colored with an iodine-potassium iodide solution. Within 10 minutes, a spectrophotometer manufactured by Shimadzu Corporation was used. The absorbance of the peak showing the maximum absorption at UV 1200 is measured. Since the wavelength showing the peak showing the maximum absorption differs depending on the degree of polymerization or the degree of saponification of PVA (generally, it exists around 650 to 700 nm), use PVA or raw material PVA in which additives and the like have been removed and purified from the PVA film in advance. A calibration curve is prepared in advance, and the amount of PVA eluted (the concentration of PVA in the extract) is quantified from the absorbance obtained from the sample.
[0033]
The coloration method using an iodine-potassium iodide solution is as follows. 450 ml of boric acid aqueous solution obtained by dissolving 40 g of boric acid in 100 ml of ion-exchanged water, 12.7 g of potassium iodide, and an aqueous solution of iodine-potassium iodide obtained by dissolving 25 g of iodine in 100 ml of ion-exchanged water 90 Milliliters were mixed, 300 ml of ion-exchanged water was added to dilute the mixture, and the mixture was heated to 20 ° C. to obtain a coloring reagent. In a Erlenmeyer flask with a stoppered stopper, 10 ml of a coloring reagent is added to 10 ml of the extract cooled to 20 ° C., mixed, and left at 20 ° C. for 15 minutes. When the PVA concentration in the extract is too high, the extract may be diluted with ion-exchanged water, if necessary.
[0034]
The thickness of the PVA film is preferably from 5 to 150 μm, more preferably from 20 to 100 μm, further preferably from 30 to 90 μm, and most preferably from 35 to 80 μm.
[0035]
In order to produce a polarizing film from the PVA film of the present invention, for example, the PVA film may be subjected to dyeing, uniaxial stretching, fixing treatment, drying treatment and, if necessary, heat treatment. There is no particular limitation in order. Further, the uniaxial stretching may be performed twice or more.
[0036]
Dyeing can be performed before, during, or after 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. Usually, the dyeing is generally performed by immersing the PVA film in a solution containing the dye, but the processing conditions and the processing method are particularly limited, such as mixing with the PVA film to form a film. is not.
[0037]
Uniaxial stretching can be performed by a wet stretching method or a dry heat stretching method, and can be performed in warm water (which may be in a solution containing the dye or in a fixing bath described later) or in air using a PVA film after water absorption. . The stretching temperature is not particularly limited, but is preferably 30 to 90 ° C. when the PVA film is stretched in warm water (wet stretching), and 50 to 180 ° C. when the dry stretching is performed. The stretching ratio of uniaxial stretching (in the case of multi-stage uniaxial stretching, 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 75 μm, more preferably from 5 to 50 μm.
[0038]
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.
[0039]
The drying treatment (heat treatment) of the PVA film is preferably performed at 30 to 150 ° C, more preferably at 50 to 150 ° C.
[0040]
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 for bonding include PVA-based adhesives and urethane-based adhesives. Among them, PVA-based adhesives are preferable.
[0041]
【Example】
Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited thereto. The dichroic ratio in the examples was evaluated by the following method.
[0042]
Dichroic ratio:
The dichroic ratio was used as an index for evaluating the polarizing performance of the obtained polarizing film. This dichroic ratio is based on the standard of the Electronic Machine Manufacturers Association of Japan (EIAJ) LD-201-1983, using a spectrophotometer, Twice Using the transmittance Ts (%) and the degree of polarization P (%) obtained by measurement and calculation in the visual field, the value was obtained from the following equation.
Dichroic ratio = log (Ts / 100−Ts / 100 × P / 100) / log (Ts / 100 + Ts / 100 × P / 100)
[0043]
Example 1
The PVA chip was washed with warm water at a temperature of 40 ° C. at a weight bath ratio of 3 for 15 minutes. This PVA has a degree of saponification of 99.9 mol% and a degree of polymerization of 1750. An aqueous solution containing 100 parts by weight of this PVA and 10 parts by weight of glycerin and having a PVA concentration of 15% by weight was prepared. Then, the aqueous solution was cast on a metal roll at 90 ° C., dried, and dried with a metal roll at 100 ° C. to obtain a PVA film having a thickness of 75 μm.
[0044]
When a 10 cm square PVA film cut out from this PVA film was left in 1 liter of water at 50 ° C. for 4 hours, the amount of PVA eluted was 50 ppm.
[0045]
The PVA film was preliminarily swelled, dyed, uniaxially stretched, fixed, dried, and heat treated in this order to produce a polarizing film. That is, the PVA film was immersed in water at 30 ° C. for 5 minutes to pre-swell, and immersed in an aqueous solution of 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 was uniaxially stretched 5.3 times in an aqueous solution of boric acid having a concentration of 4% at 40 ° C., and a potassium iodide concentration of 40 g / l, a boric acid concentration of 40 g / l, and a zinc chloride concentration of 10 g / l at 30 ° C. The fixation treatment was performed by immersing in an aqueous solution for 5 minutes. Thereafter, the PVA film was taken out, dried with hot air at 40 ° C. under a constant length, and further heat-treated at 100 ° C. for 5 minutes.
[0046]
The polarizing film thus obtained had a thickness of 22 μm, a transmittance of 43.3%, a degree of polarization of 98.5%, and a dichroic ratio of 33.3. Further, even when a polarizing film was continuously produced using the PVA film, no defect due to deposition of PVA was observed.
[0047]
Example 2
The PVA chip was washed with warm water at a temperature of 35 ° C. for 2 hours at a weight bath ratio of 4 and drained. This PVA has a degree of saponification of 99.9 mol% and a degree of polymerization of 4000. 100 parts by weight of this PVA and 10 parts by weight of glycerin are added with water in such an amount as to give a PVA concentration of 40% by weight, melt-kneaded in an extruder, melt-extruded on a metal roll at 90 ° C. from a die, dried and dried. A 75 μm PVA film was obtained.
[0048]
When a 10 cm square PVA film cut out from this PVA film was left in 1 liter of water at 50 ° C. for 4 hours, the amount of PVA eluted was 40 ppm.
[0049]
The PVA film was preliminarily swelled, dyed, uniaxially stretched, fixed, dried, and heat treated in this order to produce a polarizing film. That is, the PVA film was immersed in water at 30 ° C. for 5 minutes to pre-swell, and then immersed in an aqueous solution of 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 was uniaxially stretched 5.5 times in an aqueous solution of boric acid concentration of 4% at 40 ° C. to obtain a potassium iodide concentration of 40 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. under a constant length, and further heat-treated at 100 ° C. for 5 minutes.
[0050]
The polarizing film thus obtained had a thickness of 22 μm, a transmittance of 43.0%, a degree of polarization of 99.6%, and a dichroic ratio of 41.7. Further, even when a polarizing film was continuously produced using the PVA film, no defect due to deposition of PVA was observed.
[0051]
Comparative Example 1
A PVA film was obtained in the same manner as in Example 1, except that the PVA chip was not washed.
[0052]
When a 10 cm square PVA film cut from this PVA film was left in 1 liter of water at 50 ° C. for 4 hours, the amount of PVA eluted was 200 ppm.
[0053]
The PVA film was treated as in Example 1. The thickness of the obtained polarizing film was 23 μm. The transmittance was 43.2%, the degree of polarization was 98.5%, and the dichroic ratio was 32.8, and there was no problem in performance. In addition, although the polarizing film could be produced in the early stage of production without any problem, while continuously producing the polarizing film, defects due to the deposition of PVA were scattered on the polarizing film, and the yield of the polarizing film gradually decreased. .
[0054]
Comparative Example 2
A PVA film was obtained in the same manner as in Example 1 except that glycerin was not added and that heat treatment was performed at 190 ° C. instead of drying with a metal roll at 100 ° C.
[0055]
When a 10 cm square PVA film cut out from this PVA film was allowed to stand in 1 liter of water at 50 ° C. for 4 hours, the amount of eluted PVA was 0.5 ppm.
[0056]
An attempt was made to perform the same treatment as in Example 1 on the PVA film, but the cutting occurred frequently during stretching, and a polarizing film could not be obtained stably.
[0057]
Comparative Example 3
The PVA chip was washed with water at a temperature of 5 ° C. for 5 minutes at a weight bath ratio of 0.8. This PVA has a degree of saponification of 99.6 mol% and a degree of polymerization of 4000. A PVA film was obtained in the same manner as in Example 2 except that 100 parts by weight of this PVA and 10 parts by weight of glycerin were added with water in an amount such that the PVA concentration became 50% and melt-kneaded in an extruder. .
[0058]
When a 10 cm square PVA film cut out from this PVA film was allowed to stand in 1 liter of water at 50 ° C. for 4 hours, the PVA elution amount was 150 ppm.
[0059]
The PVA film was treated as in Example 2. The thickness of the obtained polarizing film was 22 μm. The transmittance was 42.5%, the degree of polarization was 99.7%, and the dichroic ratio was 40.6. In addition, although the polarizing film could be produced in the early stage of production without any problem, while continuously producing the polarizing film, defects due to the deposition of PVA were scattered on the polarizing film, and the yield of the polarizing film gradually decreased. .
[0060]
【The invention's effect】
As described above, according to the PVA film of the present invention, the amount of PVA eluted in each step of manufacturing a polarizing film is small, so that a polarizing film with a small number of defects can be obtained in high yield, and Wastewater treatment is also easy. Further, the polarizing film obtained from this PVA film exhibits excellent polarizing performance because of a small number of defects.

Claims (2)

The polyvinyl alcohol film dissolution of the polyvinyl alcohol is 100ppm 1 when allowed to stand for 4 hours polyvinyl alcohol film 10cm square in 1 liter of water of 50 ° C., 10 ° C. or more by weight bath ratio of less than 1 or more 100 90 Film forming using polyvinyl alcohol in a chip state obtained by washing with water or warm water at a temperature of not more than ℃ and a film forming raw material containing 1 to 30 parts by weight of polyhydric alcohol with respect to 100 parts by weight of the polyvinyl alcohol A method for producing a polyvinyl alcohol film. The method for producing a polyvinyl alcohol film according to claim 1, wherein a polyvinyl alcohol film for a polarizing film is produced .