Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J5/00—Manufacture of articles or shaped materials containing macromolecular substances
  • C08J5/18—Manufacture of films or sheets
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K5/00—Use of organic ingredients
  • C08K5/04—Oxygen-containing compounds
  • C08K5/05—Alcohols; Metal alcoholates
  • C08K5/053—Polyhydroxylic alcohols
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08K—Use of inorganic or non-macromolecular organic substances as compounding ingredients
  • C08K5/00—Use of organic ingredients
  • C08K5/04—Oxygen-containing compounds
  • C08K5/09—Carboxylic acids; Metal salts thereof; Anhydrides thereof
  • C08K5/098—Metal salts of carboxylic acids
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B5/00—Optical elements other than lenses
  • G02B5/30—Polarising elements
  • G02B5/3025—Polarisers, i.e. arrangements capable of producing a definite output polarisation state from an unpolarised input state
  • G02B5/3033—Polarisers, i.e. arrangements capable of producing a definite output polarisation state from an unpolarised input state in the form of a thin sheet or foil, e.g. Polaroid
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J2329/00—Characterised by the use of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by an alcohol, ether, aldehydo, ketonic, acetal, or ketal radical; Hydrolysed polymers of esters of unsaturated alcohols with saturated carboxylic acids; Derivatives of such polymer
  • C08J2329/02—Homopolymers or copolymers of unsaturated alcohols
  • C08J2329/04—Polyvinyl alcohol; Partially hydrolysed homopolymers or copolymers of esters of unsaturated alcohols with saturated carboxylic acids
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
  • C08L29/00—Compositions of homopolymers or copolymers of compounds having one or more unsaturated aliphatic radicals, each having only one carbon-to-carbon double bond, and at least one being terminated by an alcohol, ether, aldehydo, ketonic, acetal or ketal radical; Compositions of hydrolysed polymers of esters of unsaturated alcohols with saturated carboxylic acids; Compositions of derivatives of such polymers
  • C08L29/02—Homopolymers or copolymers of unsaturated alcohols
  • C08L29/04—Polyvinyl alcohol; Partially hydrolysed homopolymers or copolymers of esters of unsaturated alcohols with saturated carboxylic acids
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S524/00—Synthetic resins or natural rubbers -- part of the class 520 series
  • Y10S524/903—Aerosol compositions

Definitions

• the present invention relates to a polyvinyl alcohol polymer film which has small number of defects and is useful as a production raw material of a polarization film, and to a polarization film produced using this.
• a polarizer having functions of transmission and shielding of light is a fundamental constituent element of a liquid crystal display (LCD), together with a liquid crystal having a function of switching light.
• LCD liquid crystal display
• This LCD is applied to portable apparatuses such as electronic calculators, wristwatches and the like in the initial period of development of LCD, and recently, to apparatuses in a wider range such as lap top personal computers, word processors, liquid crystal color projectors, navigation systems for automobiles, liquid crystal televisions, personal phones, indoor and outdoor measuring apparatuses and the like, and there is a need for polarizer having higher polarization characteristic and smaller defects than conventional products.
• a polyvinyl alcohol polymer film (hereinafter, polyvinyl alcohol polymer is abbreviated as “PVA”, and a polyvinyl alcohol film is abbreviated as “PVA film”, in some cases) is monoaxially stretched before dyeing, or dyed before monoaxial stretching, and subjected to fixing treatment with a boron compound (in some cases, dyeing and fixing treatment are conducted simultaneously, or monoaxial stretching and fixing treatment are conducted simultaneously), then, a protection film such as a triacetic cellulose (TAC) film, cellulose acetate butyrate (CAB) and the like is laminated on the polarization film.
• TAC triacetic cellulose
• CAB cellulose acetate butyrate
• dichroic display such as white and black display is enabled, and color display is realized by combination of a color filter.
• color filter For improving color reproducibility of a liquid crystal display, more white hue and more black hue are required without using color filter, and for this, smaller unnecessary coloration on a polarizer is necessary.
• PVA in the PVA film may be partially dissolved in a dyeing process and a fixing treatment process with a boron compound in the case of dry stretching, and also in a swelling process before stretching and a stretching process in addition to the dyeing process and fixing treatment process in the case of wet stretching.
• the dissolved PVA is deposited in a vessel and adheres to a PVA film and polarization film, or deposited on a PVA film and polarization film, providing a defect, and consequently, decreases the yield of the polarization film.
• dissolved PVA which has not been deposited causes expensive waste water treatment, problematically.
• a conventional PVA film which is a raw material of a polarization film has a problem that unnecessary coloration tends to occur by conducting heat treatment in producing a polarization film. Particularly when a polarizer is made by a dry stretching method, unnecessary coloration such as yellowing and the like tends to occur. Therefore, a PVA film causing little unnecessary coloration even if heat treatment is effected in producing a polarization film has been desired to be realized.
• an object of the present invention is to provide a PVA film useful as a raw material for producing a polarization film having a small number of defects, and a polarization film made by using this PVA film.
• Another object of the present invention is to provide a PVA film which causes little unnecessary coloration and is useful as a raw material of a polarization film, and a polarization film made by using this PVA film.
• the amount of PVA eluted when a 10 cm square PVA film is left in 1 liter of water of 50° C. for 4 hours is from 1 to 100 ppm.
• the PVA film of the present invention gives lower amount of PVA eluted in each process (dyeing, fixing treatment, swelling, stretching or the like) in producing a polarization film, therefore, a polarization film having a smaller number of defects is obtained in high yield by using this PVA film. Also, waste water treatment becomes easy.
• unnecessary coloration can be decreased by controlling the content of an alkali metal compound to 0.5% by weight or less based on polyvinyl alcohol.
• the method of producing a PVA film of the present invention is characterized in that film formation is conducted using a PVA raw material having a content of an alkali metal compound of 0.5% by weight or less based on PVA, and further preferably, film formation is conducted using a film formation raw material prepared at temperatures of 150° C. or less.
• the intended PVA film for a polarization film can be obtained assuredly.
• PVA used in the present invention is produced, for example, by hydrolyzing a polyvinyl ester obtained by polymerizing a vinyl ester. Further, there are listed modified PVAs obtained by graft copolymerization of the above-mentioned PVA with unsaturated carboxylic acids or derivatives thereof, unsaturated sulfonic acids or derivatives thereof, ⁇ -olefins having 2 to 30 carbon atoms and the like in a proportion of less than 15 mol %, modified PVAs produced by hydrolyzing modified polyvinyl esters obtained by copolymerizing a vinyl ester with unsaturated carboxylic acids or derivatives thereof, unsaturated sulfonic acids or derivatives thereof, oc-olefins having 2 to 30 carbon atoms and the like in a proportion of less than 15 mol %, so-called polyvinyl acetal resins obtained by partially crosslinking hydroxyl groups of non-modified or modified PVA with aldehydes such as
• vinyl ester vinyl acetate, vinyl formate, vinyl propionate, vinyl butyrate, vinyl pivalate, vinyl versatate, vinyl laurate, vinyl stearate, vinyl benzoate and the like are listed, and mixtures of two or more of these compounds are also listed.
• the comonomer used in the modified PVA is copolymerized mainly for the purpose of modifying PVA, therefore, used in an amount which does not lose the purpose of the present invention providing it can be copolymerized with the above-mentioned vinyl ester.
• ⁇ -olefins such as ethylene, propylene, 1-butene, isobutene and the like; acrylic acid and salts thereof; acrylates such as methyl acrylate, ethyl acrylate, n-propyl acrylate, i-propyl acrylate, n-butyl acrylate, i-butyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, octadecyl acrylate and the like; methacrylic acid and salts thereof; methacrylates such as methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, i-propyl methacrylate, n-butyl methacrylate, i-butyl methacrylate, t-butyl methacrylate, 2-ethylhe
• the modification amount of modified PVA is preferably less than 15 mol %.
• the degree of hydrolysis of PVA is preferably at least 97 mol %, more preferably at least 98 mol %, further preferably at least 99 mol %, most preferably at least 99.5 mol %, from standpoints of elution amount and durcharacteristic.
• the above-mentioned degree of hydrolysis represents a ratio of units actually hydrolyzed into vinyl alcohol units in units which can be converted into vinyl alcohol units by hydrolysis.
• the degree of hydrolysis of PVA was measured by a method described in JIS.
• the degree of polymerization of PVA is preferably at least 1000 from the standpoints of reduction in the elution amount of PVA and the strength of a PVA film, and more preferably at least 1500, further preferably at least 2000, and particularly, most preferably at least 2500, from the standpoint of polarization characteristic.
• the upper limit of degree of polymerization of PVA is preferably at least 8000, and more preferably at least 6000.
• the above-mentioned degree of polymerization of PVA is measured according to JIS K 6726. Namely, PVA is re-hydrolyzed and purified, then, intrinsic viscosity is measured in water at 30° C. from which the degree of polymerization is calculated.
• the water or hot water used for washing may also contain an organic solvent, plasticizer and surfactant such as acetic acid, methanol, glycerin, and the like, in an amount which does not lose the object of the present invention.
• the temperature of the water or hot water used for washing is preferably from 10 to 90° C., more preferably from 20 to 80° C., further preferably from 25 to 70° C., and particularly, most preferably from 30 to 60° C.
• the temperature of water is lower than 10° C., washing of an eluted substance can not be conducted sufficiently, while, when the temperature of hot water is over 90° C., the elution amount of PVA in washing is large, increasing loss, and PVAs are stuck mutually, deteriorating workcharacteristic in the following solution process and the like, undesirably.
• the bath ratio by weight of water or hot water to PVA tips is preferably at least 1, more preferably at least 1.5, and particularly, most preferably at least 2.
• the upper limit of the bath ratio is 100 or less. Namely, even if the bath ratio is over 100, there is no corresponding large improvement in the washing effect, and water or hot water is futile, leading to diseconomy.
• the time of washing a PVA tip is preferably at least 30 seconds, more preferably at least 1 minute, further preferably at least 5 minutes, and particularly, most preferably at least 10 minutes.
• the method of washing a PVA tip is not particularly restricted, and there are listed a method in which water or hot water is showered on PVA tips on a net or belt, then, drained, a method in which water or hot water and PVA tips are placed batch-wise in a tower or vessel and allowed to stand still or stirred, then, drained, a method in which water or hot water and PVA tips are fed continuously in a tower or vessel, and washed in countercurrent flow or concurrent flow (may be accompanied by stirring), then, drained, and other methods.
• the draining method after washing is also not particularly restricted, and there are listed centrifugal separation, vacuum suction, filter press, compression using rolls and belts, separation by gravity using a porous plate such as a net, and cloth, non-woven cloth and the like, decantation, and the like.
• Washing water such as water adhered on surface, releasing water and the like may remain, in an amount which does not lose the object of the present invention, on PVA tips after drainage, however, it is preferable that water used in washing is separated and removed from PVA tips as completely as possible.
• a PVA solution prepared by dissolving PVA tips in a solvent is subjected to a casting film formation method, wet film formation method (discharging into a poor solvent), gel film formation method (a PVA aqueous solution is once cooled and gelled, then, water is removed by extraction to obtain a PVA film), and a combination method thereof, or a melt extrusion film formation method in which water-containing PVA prepared by allowing PVA tips to contain water (may also contain an organic solvent and the like) is melt-extruded, and other methods can be used.
• the casting film formation method and melt extrusion film formation method are preferable since an excellent polarization film is obtained.
• Examples of the solvent for dissolving PVA tips washed preliminaryly used in producing a PVA film include dimethylsulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrolidone, ethylene glycol, glycerin, diglycerin, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, trimethylolpropane, ethylenediamine, diethylenetriamine, water and the like, and one or more of them can be used.
• water, dimethylsulfoxide, or a mixed solvent of water and dimethylsulfoxide is suitably used.
• the PVA concentration of a PVA solution or water-containing PVA used in producing a PVA film is preferably from 3 to 70% by weight, more preferably from 10 to 60% by weight, further preferably from 13 to 55% by weight, an particularly, most preferably from 15 to 50% by weight.
• This PVA solution or water-containing PVA may also contain a plasticizer, surfactant, dichroic dye and the like, if necessary.
• a polyhydric alcohol is preferably added as the plasticizer used in producing a PVA film.
• the polyhydric alcohol include ethylene glycol, glycerin, propylene glycol, diethylene glycol, diglycerin, triethylene glycol, tetraethylene glycol, trimethylolpropane and the like, and one or more of them can be used.
• diglycerin, ethylene glycol and glycerin are suitably used for improving stretching property.
• the amount of polyhydric alcohol used is preferably from 1 to 30 parts by weight, more preferably from 3 to 25 parts by weight, and particularly, most preferably from 5 to 20 parts by weight, based on 100 parts by weight of PVA.
• the use amount is less than 1 part by weight, dyeing property and stretching property may decrease, and when over 30 parts by weight, a PVA film may become too soft, leading to reduction in handling.
• a surfactant In producing a PVA film, it is preferable to add a surfactant.
• the kind of the surfactant is not particularly restricted, and anionic surfactants or nonionic surfactants are preferable.
• anionic surfactant for example, carboxylic acid-type anionic surfactants such as potassium laurate, sulfate-type anionic surfactants such as octyl sulfate and the like, and sulfonic acid-type anionic surfactants such as dodecylbenzenesulfonate and the like, are suitable.
• nonionic surfactant for example, alkyl ether-type nonionic surfactants such as polyoxyethylene oleyl ether and the like, alkylphenyl ether-type nonionic surfactants such as polyoxyethylene octylphenyl ether and the like, alkyl ester-type nonionic surfactants such as polyoxyethylene laurate and the like, alkylamine-type nonionic surfactants such as polyoxyethylene laurylamino ether and the like, alkylamide-type nonionic surfactants such as polyoxyethylene lauric amide and the like, polypropylene glycol ether-type nonionic surfactants such as polyoxyethylene polyoxypropylene ether and the like, alkanolamide-type nonionic surfactants such as oleic acid diethanol amide and the like, allylphenyl ether-type nonionic surfactants such as polyoxyalkylene allylphenyl ether and the like, are suitable.
• the amount of the surfactant added is preferably from 0.01 to 1 part by weight, more preferably from 0.02 to 0.5 parts by weight, and particularly, most preferably from 0.05 to 0.3 parts by weight, based on 100 parts by weight of PVA.
• the addition amount is less than 0.01 part by weight, effects of improving stretching property and improving dyeing property are not manifested easily, and when over 1 part by weight, the surfactant may be eluted on the surface of a PVA film and cause blocking, leading to reduction in handling.
• the amount of PVA eluted when a 10 cm square PVA film is left in 1 liter of water of 50° C. for 4 hours is from 1 to 100 ppm.
• this elution amount is from 5 to 80 ppm, and particularly, most preferably from 10 to 60 ppm.
• the elution amount of PVA is over 100 ppm, the elution amount of PVA into a vessel increases and the amount of PVA deposited on a PVA film and a polarization film increases, obtaining a polarization film having a smaller number of defects becomes difficult, and problems occur in waste water treatment.
• the method for measuring the elution amount of PVA is as follows. A 10 cm square PVA film is left in 1 liter of distilled water of 50° C. for 4 hours, and the eluted liquid thereof is colored with an iodine-potassium iodide solution, and within 10 minutes, the absorbancy of a peak showing the maximum absorption is measured by a spectrophotometer, UV1200 manufactured by Shimadzu Corp.
• raw PVA or PVA obtained by preliminaryly removing and purifying additives and the like from a PVA film is used to make a calibration curve, and the elution amount of PVA (PVA concentration in eluted liquid) is quantified from absorbancy obtained from a sample.
• the coloration method with an iodine-potassium iodide solution is as follows. 450 ml of a boric acid aqueous solution prepared by dissolving 40 g of boric acid in 1000 ml of ion-exchange water, and 90 ml of an iodine-potassium iodide aqueous solution prepared by dissolving 12.7 g of potassium iodide and 25 g of iodine in 100 ml of ion exchange water are mixed, and to the resulted mixture is added 300 ml of ion exchange water for dilution, and the temperature of this mixture is controlled to 20° C. to give a coloration reagent.
• the extracted liquid cooled to 20° C. is added 10 ml of the coloration reagent to give a mixture which was left for 15 minutes at 20° C.
• the extracted liquid may be diluted with ion exchange water, if necessary.
• the content of an alkali metal compound in the PVA film of the present invention is preferably 0.5% by weight or less, more preferably 0.3% by weight or less, more further preferably 0.1% by weight or less, based on PVA.
• content of an alkali metal compound is over 0.5% by weight, coloration occurs on a polarization film, when heated in a process of dry heat stretching, and the like.
• concentration of an alkali metal compound in PVA is more preferable, and from the industrial standpoint, the lower limit is preferably 0.001% by weight.
• the alkali metal compound means a compound containing an alkali metal such as lithium, sodium, potassium and the like, and for example, lithium acetate, sodium acetate, potassium acetate, sodium hydroxide, potassium hydroxide, sodium tartarate, sodium lactate, sodium phosphate and the like are listed. Among them, it is preferable to control the content of sodium acetate since sodium acetate tends to exert an influence on coloration of a PVA film.
• an alkali metal compound in the PVA film of the present invention to 0.5% by weight or less, preferably 0.3% by weight or less, further preferably 0.1% by weight or less, it is necessary that the content of an alkali metal compound in a PVA raw material used as a film formation raw material is 0.5% by weight or less, preferably 0.3% by weight or less, further preferably 0.1% by weight or less.
• a PVA film using a film formation raw material containing PVA prepared at temperatures of 150° C. or less.
• treating temperature in preparing a film formation raw material temperature in dissolving a PVA raw material in solvent or in melting water-containing PVA
• the treating temperature in preparing a film formation raw material is preferably 150° C. or less, further preferably 140° C. or less.
• the drying temperature in a process of drying a PVA film is preferably 150° C. or less, further preferably 140° C. or less. When the drying temperature is over 150° C., the resultant PVA film may manifest yellowish color.
• the thickness of a PVA film is preferably from 5 to 150 ⁇ m, more preferably from 20 to 100 ⁇ m, further preferably from 30 to 90 ⁇ m, most preferably from 35 to 80 ⁇ m.
• the PVA film may advantageously be subjected to dyeing, monoaxial stretching, fixing treatment, drying treatment, further if necessary, heat treatment, and the operation order of dyeing, monoaxial stretching and fixing treatment is not particularly restricted. Further, monoaxial stretching may also be conducted twice or more times.
• the dyeing can be effected at any period before monoaxial stretching, in monoaxial stretching and after monoaxial stretching.
• dichroic dyes such as 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 Yellow 8, 12, 44, 86, 87; Direct Orange 26, 39, 106, 107, and the like can be used alone or in combination of two or more.
• dyeing is conducted, usually, by immersing a PVA film in a solution containing the above-mentioned dye, however, treatment conditions and treatment methods thereof such as mixing of a dye with a PVA film before film formation, and the like, are not particularly restricted.
• a wet stretching method or dry heat stretching method can be used, and it can be conducted in hot water (may also in a solution containing the above-mentioned dye or a fixing treatment bath described below) or in air using a PVA film after water absorption.
• the hot water used in the monoaxial stretching is preferably a boric acid aqueous solution.
• the stretching temperature is not particularly restricted, and when a PVA film is stretched in hot water (wet stretching), temperatures from 30 to 90° C. are suitable, and when dry heat stretching is conducted, temperatures from 50 to 180° C. are suitable.
• the stretching ratio in monoaxial stretching is preferably at least 4-fold, and particularly, most preferably at least 5-fold, from the standpoint of polarization characteristic.
• the upper limit of the stretching is not particularly restricted, and ratios of 8-fold or less are preferable since then uniform stretching is obtained.
• the thickness of a film after stretching is preferably from 3 to 75 ⁇ m, more preferably from 5 to 50 ⁇ m.
• the fixing treatment is often conducted for the purpose of rendering adsorption of the above-mentioned dye onto a PVA film stronger.
• boric acid and/or boron compound is usually added into a treating bath used for the fixing treatment.
• an iodine compound may also be added into the treating bath.
• the drying treatment (heat treatment) of the above-mentioned PVA film is conducted at a temperature preferably from 30 to 150° C., more preferably from 50 to 150° C.
• a protective film having optically transparent and having mechanical strength is laminated on each surface or on one surface thereof to provide a polarizer to be used.
• a triacetic cellulose (TAC) film, cellulose acetate butyrate (CAB) film, acrylic film, polyester film and the like are used.
• TAC triacetic cellulose
• CAB cellulose acetate butyrate
• acrylic film acrylic film
• polyester film and the like are used.
• the adhesive for lamination PVA adhesives and urethane adhesives are listed, and of them, PVA adhesives are suitable.
• a* value is preferably from ⁇ 1.6 to +1.6, further preferably from ⁇ 1.5 to +1.5.
• b* value is preferably from ⁇ 3.0 to +3.0, further preferably from ⁇ 1.5 to +1.5.
• Dichroic ratio was used as an index for evaluating polarization characteristic of the resulted polarization film. This dichroic ratio was obtained from the following formula using transmittance Ts (%) and degree of polarization P (%) obtained by calculation and measurement at 2° field of view and C light souce using a spectrophotometer according to Standards of Electronic Industries Association of Japan (EIAJ) LD-20 1 -1983.
• Dichroic ratio log (Ts/100 ⁇ Ts/100 ⁇ P/100)/log(Ts/100+Ts/100 ⁇ P/100)
• Hue was measured according to JIS Z 8719 (light source: C, field of view: 2°).
• PVA tips were washed with hot water having a temperature of 40° C. for 15 minutes at a bath ratio by weight of 3.
• This PVA had a degree of hydrolysis of 99.9 mol % and a degree of polymerization of 1750.
• An aqueous solution was prepared having a PVA concentration of 15% by weight containing 100 parts by weight of this PVA and 10 parts by weight of glycerin. Then, this aqueous solution was cast on a metal roll of 90° C. to form a film which was dried, and the film was further dried on a metal roll of 100° C., to obtain a PVA film having a thickness of 75 ⁇ m.
• a 10 cm square PVA film cut out from this PVA film was left in 1 liter of water of 50° C. for 4 hours, and the amount of PVA eluted was 50 ppm at this point.
• the above-mentioned PVA film was subjected to preliminary swelling, dyeing, monoaxial stretching, fixing treatment, drying and heat treatment in this order, to produce a polarization film.
• this PVA film was immersed in water of 30° C. for 5 minutes to effect preliminary swelling, and immersed in an aqueous solution of 35° C. having an iodine concentration of 0.4 g/liter and a potassium iodide concentration of 40 g/liter for 3 minutes.
• monoaxial stretching was conducted at 5.3 times in an aqueous solution of 40° C. having a boric acid concentration of 4%, then the stretched film was immersed in an aqueous solution of 30° C.
• the PVA film was removed, and dried with hot air of 40° C. and further, heat-treated at 100° C. for 5 minutes, while maintaining the length constant.
• polarization film had a thickness of 22 ⁇ m, a transmittance of 43.3%, a degree of polarization of 98.5%, and a dichroic ratio of 33.3. Further, defects due to deposition of PVA was not found even when a polarization film was produced continuously using the above-mentioned PVA film.
• PVA tips were washed with hot water having a temperature of 35° C. for 2 hours at a bath ratio by weight of 4.
• This PVA had a degree of hydrolysis of 99.9 mol % and a degree of polymerization of 4000.
• To 100 parts by weight of this PVA and 10 parts by weight of glycerin was added water so as to give a PVA concentration of 40% by weight and the mixture was melt-kneaded in an extruder, and melt-extruded through a dice onto a metal roll of 90° C. and dried thereon, to obtain a PVA film having a thickness of 75 ⁇ m.
• a 10 cm square PVA film cut out from this PVA film was left in 1 liter of water of 50° C. for 4 hours, and the amount of PVA eluted was 40 ppm at this point.
• the above-mentioned PVA film was subjected to preliminary swelling, dyeing, monoaxial stretching, fixing treatment, drying and heat treatment in this order, to produce a polarization film.
• this PVA film was immersed in water of 30° C. for 5 minutes to effect preliminary swelling, and immersed in an aqueous solution of 35° C. having an iodine concentration of 0.4 g/liter and a potassium iodide concentration of 40 g/liter for 3 minutes.
• monoaxial stretching was conducted at 5.5 times in an aqueous solution of 40° C. having a boric acid concentration of 4%, then the stretched film was immersed in an aqueous solution of 30° C.
• the PVA film was removed, and dried with hot air of 40° C. and further, heat-treated at 100° C. for 5 minutes, while maintaining the length constant.
• polarization film had a thickness of 22 ⁇ m, a transmittance of 43.0%, a degree of polarization of 99.6%, and a dichroic ratio of 41.7. Further, defects due to deposition of PVA was not found even when a polarization film was produced continuously using the above-mentioned PVA film.
• a PVA film was obtained in the same manner as in Example 1 except that PVA tips were not washed.
• a 10 cm square PVA film cut out from this PVA film was left in 1 liter of water of 50° C. for 4 hours, and the amount of PVA eluted was 200 ppm at this point.
• the above-mentioned PVA film was treated in the same manner as in Example 1.
• the obtained polarization film had a thickness of 23 ⁇ m. It had a transmittance of 43.2%, a degree of polarization of 98.5%, and a dichroic ratio of 32.8, showing no problem on abilities. Further, at the initial period of producing a polarization film, the film could be produced without problem, however, with progress of continuous production of a polarization film, defects due to deposition of PVA were found on scattered sites of the polarization film, and the yield of the polarization film decreased gradually.
• a PVA film was obtained in the same manner as in Example 1 except that glycerin was not added, and heat treatment at 190° C. was conducted instead of drying on a metal roll of 100° C.
• a 10 cm square PVA film cut out from this PVA film was left in 1 liter of water of 50° C. for 4 hours, and the amount of PVA eluted was 0.5 ppm at this point.
• PVA tips were washed with water having a temperature of 5° C. for 5 minutes at a bath ratio by weight of 0.8.
• This PVA had a degree of hydrolysis 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 to 100 parts by weight of this PVA and 10 parts by weight of glycerin was added water so as to give a PVA concentration of 50% by weight and the mixture was melt-kneaded in an extruder.
• a 10 cm square PVA film cut out from this PVA film was left in 1 liter of water of 50° C. for 4 hours, and the amount of PVA eluted was 150 ppm at this point.
• the above-mentioned PVA film was treated in the same manner as in Example 2.
• the obtained polarization film had a thickness of 22 ⁇ m. It had a transmittance of 42.5%, a degree of polarization degree of 99.7%, and a dichroic ratio of 40.6. Further, at the initial period of producing a polarization film, the film could be produced without problem, however, with progress of continuous production of a polarization film, defects due to deposition of PVA were found on scattered sites of the polarization film, and the yield of the polarization film decreased gradually.
• PVA film having a width of 1.2 m and an average thickness of 75 ⁇ m and a sodium acetate content of 0.1% by weight based on PVA.
• a 10 cm square PVA film cut out from this PVA film was left in 1 liter of water of 50° C. for 4 hours, and the amount of PVA eluted was 8 ppm at this point.
• This PVA film was subjected to monoaxial stretching, dyeing, fixing treatment, drying and heat treatment in this order, to produce a polarization film. Namely, this PVA film was monoaxially stretched at 4.5 times at 110° C.
• This monoaxially stretched PVA film was immersed in an aqueous solution of 40° C. having an iodine concentration of 0.8 g/liter, a potassium iodide concentration of 50 g/liter and a boric acid concentration of 40 g/liter for 1 minute while maintaining this film under stressed condition. Subsequently, the film was immersed in an aqueous solution of 65° C.
• the obtained polarization film had a thickness of 35 ⁇ m at the central part along width direction, a transmittance of 44.0%, a degree of polarization of 99.2%, and a dichroic ratio of 42.8.
• the hue of a single body was measured according to JIS Z 8719 (light source: C, field of view: 2°), a* was ⁇ 1.2 and b* value was +0.8.
• a PVA film having a width of 1.2 m and an average thickness of 75 m and a sodium acetate content of 0.03% by weight based on PVA was obtained.
• a 10 cm square PVA film cut out from this PVA film was left in 1 liter of water of 50° C. for 4 hours, and the amount of PVA eluted was 2 ppm at this point.
• This PVA film was subjected to monoaxial stretching, dyeing, fixing treatment, drying and heat treatment in this order, to produce a polarization film. Namely, this PVA film was monoaxially stretched at 4.5 times at 100° C.
• This monoaxially stretched PVA film was immersed in an aqueous solution of 40° C. having an iodine concentration of 0.8 g/liter and a potassium iodide concentration of 50 g/liter for 1 minute while maintaining this film under stressed condition. Subsequently, the film was immersed in an aqueous solution of 65° C. having a potassium iodide concentration of 60 g/liter and a boric acid concentration of 70g/liter for 5 minutes to effect fixing treatment. Then, this was washed with distilled water of 20° C. for 10 seconds, then, dried with hot air of 40° C. and further, heat-treated at 100° C. for 5 minutes, while maintaining the length constant.
• the obtained polarization film had a thickness of 35 ⁇ m at the central part along width direction, a transmittance of 43.5%, a degree of polarization of 99.1%, and a dichroic ratio of 38.6.
• the hue of a single body was measured according to JIS Z 8719 (light source: C, field of view: 2°), a* was ⁇ 1.0 and b* value was +0.4.
• Water-containing PVA tips having a volatile content of 70% by weight composed of 100 parts by weight of PVA tips having a sodium acetate content of 1.9% by weight (degree of hydrolysis: 99.9 mol %, degree of polymerization: 2400), 15 parts by weight of glycerin and water was heat-melted in an extruder having a maximum temperature of 130° C. The melted substance was cooled to 100° C. by a heat exchanger, then, melt-extruded on a metal drum at 95° C. to form a film which was subsequently dried. A PVA film having a width of 1.2 m and an average thickness of 75 ⁇ m and a sodium acetate content of 1.9% by weight based on PVA was obtained. A 10 cm square PVA film cut out from this PVA film was left in 1 liter of water of 50° C. for 4 hours, and the amount of PVA eluted was 180 ppm at this point.
• This PVA film was subjected to monoaxial stretching, dyeing, fixing treatment, drying and heat treatment in this order, to produce a polarization film. Namely, this PVA film was monoaxially stretched at 4.5 times at 110° C. This monoaxially stretched PVA film was immersed in an aqueous solution of 40° C. having an iodine concentration of 0.8 g/liter and a potassium iodide concentration of 50 g/liter for 1 minute while maintaining this film under stressed condition. Subsequently, the film was immersed in an aqueous solution of 65° C. having a potassium iodide concentration of 60 g/liter and a boric acid concentration of 70 g/liter for 5 minutes to effect fixing treatment. Then, this was washed with distilled water of 20° C. for 10 seconds, then, dried with hot air of 40° C. and further, heat-treated at 100° C. for 5 minutes, while maintaining the length constant.
• the obtained polarization film had a thickness of 35 ⁇ m at the central part along width direction, a transmittance of 42.8%, a degree of polarization of 98.9%, and a dichroic ratio of 33.3.
• the hue of a single body was measured according to JIS Z 8719 (light source: C, field of view: 2°), a* was ⁇ 1.8 and b* value was +3.8.

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