JP2006305924A - Method of manufacturing polyvinylalcohol-based film and the polyvinylalcohol-based film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a polyvinylalcohol-based film having no optical irregularity and excellent in surface smoothness, and the polyvinylalcohol-based film obtained by the manufacturing method. <P>SOLUTION: The polyvinylalcohol-based film is manufactured by a process for forming the same by a casting method using a casting base material having a fluoroplastic resin film formed on its surface. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing a polyvinyl alcohol film useful as a raw film for a polarizing film used for polarized sunglasses, a liquid crystal display device, or the like, or as a packaging material used for packaging clothing or food. More specifically, the present invention relates to a method for producing a polyvinyl alcohol film having no optical unevenness and excellent surface smoothness, and a polyvinyl alcohol film obtained by the production method.

  Conventionally, a polyvinyl alcohol film is prepared by dissolving a polyvinyl alcohol resin in a solvent such as water to prepare a stock solution, and then forming a film by a solution casting method (cast method), using a metal heating roll or a hot air dryer. And then dried. The polyvinyl alcohol film thus obtained is used in many applications as a film excellent in transparency, and one of its useful applications is a polarizing film. Such a polarizing film is a film obtained by uniaxially stretching and dyeing the polyvinyl alcohol film, and is used as a basic component of a liquid crystal display.

  In recent years, with an increase in display area and resolution, a polarizing film having no optical unevenness and excellent surface smoothness, and a polyvinyl alcohol film serving as a raw material thereof have been demanded. As such countermeasures, many proposals have been made. For example, Patent Document 1 discloses a manufacturing method for improving the appearance of a film using a cast drum having a surface tension of 25 to 50 mN / m. A method of casting a stock solution for film formation on a metal surface having a surface roughness of 3S or less to form a polyvinyl alcohol film having excellent thickness uniformity is disclosed in Patent Document 3 as a surface active agent. A method of forming a polyvinyl alcohol film with reduced thickness unevenness by regulating the agent, the amount of volatile matter at the time of peeling, and the speed of the film forming drum is disclosed in Patent Document 4 as the moisture content of the film at the time of peeling. A polyvinyl alcohol film in which the birefringence unevenness is reduced by setting it to less than% by weight and a method for producing a polarizing film in which the transmittance unevenness and the dichroic ratio unevenness are reduced have been proposed.

  However, these disclosed techniques are not a drastic measure for eliminating the optical unevenness of the film. Examples of the optical unevenness of the polyvinyl alcohol film include unevenness of birefringence of the film, unevenness of light scattering accompanying the distribution of surface roughness, unevenness of transparency of the film, and unevenness of dyeing when used as a polarizing film. There are various forms of optical unevenness that can be visually confirmed, such as stripes and circles, and further improvements are desired in view of the recent increase in area and definition.

  It is also described in Patent Document 1 and Patent Document 4 that such optical unevenness occurs when the film is peeled from the cast base material. Therefore, if the film is peeled off smoothly from the substrate surface, the optical unevenness associated with the adhesion stress can be greatly reduced. As the technique, the technique as in the known literature is not sufficient, and the surfactant added to improve the peelability from the cast drum is originally to reduce the purity of the polyvinyl alcohol resin, This is a factor that reduces other physical properties such as light transmittance. That is, a method for changing the viewpoint and improving the surface of the cast base material is a drastic measure.

  As the surface treatment of the cast substrate, a wet coat using a polymer solution other than a fluorinated alkyl group-containing alkoxysilane or a dry coat such as vapor deposition using an inorganic compound is generally used. However, in a polymer film formed by wet coating, it is difficult to ensure adhesion with a metal substrate, and it is also difficult to control the coating thickness on the order of microns or less. In addition, although the dry coat can ensure adhesion and film thickness accuracy, it is disadvantageous in terms of cost considering that the length and width of the cast base material are several meters or more. In addition, as a surface treatment agent, a general silicon treatment agent together with a fluorine treatment agent can form a silicon film having a reduced surface tension and a water repellency effect. Although it was possible to form a monomolecular film on the material, it was difficult to ensure oil repellency, and it was difficult to prevent the adhesion of plasticizers and surfactants and various oil stains. . Therefore, the conventional method has been insufficient in improving the cast base material surface.

JP 2004-142228 A JP 2001-315138 A JP 2002-79531 A JP-A-6-138319

  The present invention provides a method for producing a polyvinyl alcohol-based film excellent in surface smoothness, free from optical unevenness, and a polyvinyl alcohol-based film obtained thereby, corresponding to an increase in area, brightness and definition. It is for the purpose.

  The present invention relates to a method for producing a polyvinyl alcohol film including a step of forming a polyvinyl alcohol film by a casting method using a cast base material having a fluororesin film formed on the surface thereof.

  It is preferable that the fluorine resin film is formed of a fluorinated alkyl group-containing alkoxysilane.

  The fluorinated alkyl group is preferably a perfluoroalkyl group.

The fluorinated alkyl group-containing alkoxysilane is preferably represented by the following formula (1).
CF ₃ · (OCF ₂ ) _l · (OC ₂ F ₄ ) _m · (OC ₃ F ₆ ) _n · Si (OR ₃ ) _a R ' _3-a
(1)
(In Formula (1), l is 0-400, m is 1-400, n is 0-400, a is 1-3. R and R 'are C1-C6 hydrocarbon groups, They may be the same or different.)
The contact angle between the surface of the cast base material on which the fluororesin film is formed and water is preferably 100 ° or more.

  It is preferable that the surface of the cast base material before forming the fluororesin film contains chromium oxide.

  It is preferable that the surface of the cast substrate before the formation of the fluororesin film is polished with fine particles of chromium oxide or cerium oxide.

  Moreover, this invention relates to the polyvinyl alcohol-type film which is manufactured with the said manufacturing method and does not contain surfactant.

  The film preferably has a film surface roughness Ra of 100 nm or less.

  The present invention relates to a polyvinyl alcohol film used for obtaining a raw film of a polarizing film.

  The present invention also relates to a polarizing film comprising the polyvinyl alcohol film, and further to a polarizing plate.

  In the production method of the present invention, since a polyvinyl alcohol film is formed by a casting method using a cast base material having a fluororesin film formed on the surface, the film can be easily peeled off from the drum. It is also possible to prevent seizure of the surfactant or polyvinyl alcohol resin used in the film formation on the drum. Therefore, it is possible to produce a polyvinyl alcohol-based film having no surface unevenness and excellent surface smoothness.

  The present invention relates to a method for producing a polyvinyl alcohol film including a step of forming a polyvinyl alcohol film by a casting method using a cast base material having a fluororesin film formed on the surface thereof.

  The polyvinyl alcohol film produced by the production method of the present invention is obtained by forming a polyvinyl alcohol resin. As the polyvinyl alcohol-based resin, a resin obtained by saponifying polyvinyl acetate obtained by polymerizing vinyl acetate is usually used, but the production method of the present invention is not necessarily limited to this, and other than vinyl acetate. , Small amounts of unsaturated carboxylic acids (including salts, esters, amides, nitriles, etc.), olefins having 2 to 30 carbon atoms (ethylene, propylene, n-butene, isobutene, etc.), vinyl ethers, unsaturated sulfonates, etc. Further, it may contain a component copolymerizable with vinyl acetate.

  Further, as the polyvinyl alcohol resin, it is also preferable to use a polyvinyl alcohol resin having a 1,2-glycol bond in the side chain, and the polyvinyl alcohol resin having a 1,2-glycol bond in the side chain is, for example, ( A) a method of saponifying a copolymer of vinyl acetate and 3,4-diacetoxy-1-butene, (a) a method of saponifying and decarboxylating a copolymer of vinyl acetate and vinyl ethylene carbonate, A method of saponifying and deketalizing a copolymer of vinyl acetate and 2,2-dialkyl-4-vinyl-1,3-dioxolane, and (d) a copolymer of vinyl acetate and glycerol monoallyl ether. It is obtained by a saponification method or the like.

  Although the weight average molecular weight of polyvinyl alcohol-type resin is not specifically limited, 120,000-300000 are preferable, More preferably, it is 140000-200000, More preferably, it is 160000-200000. When the weight average molecular weight is less than 120,000, sufficient optical performance cannot be obtained when the polyvinyl alcohol film of the present invention is used as an optical film, and when it exceeds 300,000, stretching becomes difficult and industrial production becomes difficult, which is not preferable. In addition, the weight average molecular weight of the polyvinyl alcohol-type resin used for manufacture of the polyvinyl alcohol-type film of this invention is a weight average molecular weight measured by GPC-LALLS method.

  The saponification degree of the polyvinyl alcohol-based resin is preferably 97 mol% or more, more preferably 98 to 100 mol%, and particularly preferably 99 to 100 mol%. If the saponification degree is less than 97 mol%, sufficient optical performance cannot be obtained when a film obtained from a polyvinyl alcohol-based resin is used as an optical film, which is not preferable.

  In the method for producing a polyvinyl alcohol film of the present invention, a plasticizer generally used such as glycerin or a nonionic, anionic or cationic surfactant, if necessary, for the polyvinyl alcohol resin. And the like are added in an amount of 30% by weight or less, preferably 3 to 25% by weight, more preferably 5 to 20% by weight based on the polyvinyl alcohol resin. If the blending amount of these additives exceeds 30% by weight, the film strength is inferior, which is not preferable.

  When producing a polyvinyl alcohol film, first, an aqueous solution is prepared using the polyvinyl alcohol resin. It is practical that the resin concentration in the polyvinyl alcohol-based resin aqueous solution is 5 to 50% by weight. In preparing the polyvinyl alcohol resin aqueous solution, in addition to water, dimethyl sulfoxide (DMSO); N-methylpyrrolidone; ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, trimethylolpropane and the like A monohydric alcohol; amines such as ethylenediamine and diethylenetriamine, and mixtures thereof may be used. At this time, the use ratio of the solvent other than water is set to 50% by weight or less with respect to the whole solvent.

  In the production method of the present invention, the prepared polyvinyl alcohol-based resin aqueous solution is cast on a cast base material such as an endless belt or a drum-type roll (hereinafter referred to as a cast drum) to form a film, and then dried. A polyvinyl alcohol film is produced.

  Hereinafter, taking the case where a cast drum is used as a cast base material as an example, the production method of the present invention will be described.

  As the cast drum used as the cast base material, a drum having a smooth surface is used. As the material for the drum, stainless steel (SUS) mainly containing Fe is preferably used. The SUS surface is preferably metal-plated to prevent scratches. As the type of metal plating, for example, chromium plating, nickel plating, zinc plating and the like are suitable, and these platings can be used alone or in combination of two or more kinds of multilayers. In particular, the outermost surface is preferably chrome plating from the viewpoint of ease of smoothing the drum surface and its durability.

The metal surface of such a cast drum is more or less oxidized. In particular, when a small amount of moisture adheres to the surface or when moisture exists in the environment, the alkoxysilane compound is present when the alkoxysilane compound is present. The elimination reaction of alcohol from the catalyst is promoted, and the reaction occurs rapidly between the alkoxysilane compound and the metal surface of the cast drum. Therefore, it is preferable that chromium oxide derived from chromium plating is present particularly on the metal surface of the cast drum. The reaction between the alkoxysilane compound as described above and the metal surface of the cast drum is performed when the SUS or plating surface of the cast base material is further coated with an inorganic material such as SiO ₂ or TiO ₂ . But it progresses promptly.

  In the production method of the present invention, the surface of the cast drum before forming the fluororesin film is preferably polished. In particular, using a paste containing fine particles of chromium oxide or cerium oxide as an abrasive, the surface roughness of the base material is 100 nm or less, more preferably 50 nm or less, in terms of surface roughness (Ra) in JIS B 0601. Is preferably suppressed to 30 nm or less. Even after the formation of the fluororesin film, the surface roughness does not change, and a film having better smoothness and free from defects such as minute protrusions and depressions can be obtained.

In the production method of the present invention, the fluororesin film formed on the cast drum surface is formed of a fluorinated alkyl group-containing alkoxysilane. As such an alkoxysilane, the general formula (2):
Rf · Si (OR ₃ ) _a R ′ _3-a (2)
An alkoxysilane having a fluoroalkyl group represented by:
General formula (3):
Rf · PO (OH) ₂ (3)
A phosphonic acid having a fluoroalkyl group represented by the general formula (4):
Rf · P (OH) ₂ (4)
And phosphonous acid having a fluoroalkyl group represented by the formula:

  In the general formulas (2) to (4), Rf represents a fluoroalkyl group. Rf may or may not contain an ether bond. R and R ′ represent a hydrocarbon group having 1 to 6 carbon atoms and may be the same or different. Moreover, a represents 1-3.

  Specific examples of the alkoxysilane having a fluoroalkyl group represented by the general formula (2) in which Rf is a fluoroalkyl group not containing an ether bond include fluoromethyltrimethoxysilane, fluoromethyldimethoxymonomethylsilane, and fluoromethyl. Triethoxysilane, fluoromethyltripropoxysilane, fluoromethyltributoxysilane, difluoromethyltrimethoxysilane, trifluoromethyltrimethoxysilane, trifluoromethyltriethoxysilane, trifluoroethyltriepoxysilane, pentafluoroethyltrimethoxysilane, Heptafluoropropyltrimethoxysilane, nonafluorobutyltrimethoxysilane, pentadecafluoroheptyltrimethoxysilane, heptadecafluorooctane Le trimethoxysilane, nonadecafluorononyl trimethoxysilane, such as alkoxysilane having an nonadecafluorononyl dimethoxy monomethyl silane and having 10 or more fluorinated higher alkyl group having a carbon and the like. Among these, those having a perfluoroalkyl group such as nonadecafluorononyltrimethoxysilane are preferable from the viewpoint of water repellency.

Among the alkoxysilanes having a fluoroalkyl group represented by the general formula (2), as specific examples of those in which Rf is a fluoroalkyl group containing an ether bond,
Methyloxydifluoromethyltrimethoxysilane, methyloxytetrafluoroethyltrimethoxysilane, methyloxyhexafluoropropyltrimethoxysilane, trifluoromethyloxymethyltrimethoxysilane, trifluoromethyloxydifluoromethyltrimethoxysilane, trifluoromethyloxyethyl Trimethoxysilane, trifluoromethyloxypropyltrimethoxysilane, trifluoromethyloxyhexafluoropropyltrimethoxysilane, ethyloxydifluoromethyltrimethoxysilane, ethyloxytetrafluoroethyltrimethoxysilane, ethyloxyhexafluoropropyltrimethoxysilane, Pentafluoroethyloxymethyltrimethoxysilane, pentafluoroethyloxydi Fluoromethyltrimethoxysilane, pentafluoroethyloxyethyltrimethoxysilane, pentafluoroethyloxytetrafluoroethyltrimethoxysilane, pentafluoroethyloxypropyltrimethoxysilane, pentafluoroethyloxyhexafluoropropyltrimethoxysilane, propyloxydifluoro Methyltrimethoxysilane, propyloxytetrafluoroethyltrimethoxysilane, propyloxyhexafluoropropyltrimethoxysilane, heptafluoropropyloxymethyltrimethoxysilane, heptafluoropropyloxydifluoromethyltrimethoxysilane, heptafluoropropyloxyethyltrimethoxysilane , Heptafluoropropyloxytetrafluoroethyltrimethoxy Run, heptafluoropropyloxypropyltrimethoxysilane, heptafluoropropyloxyhexafluoropropyltrimethoxysilane, trifluoromethyloxymethyloxyethyltrimethoxysilane, trifluoromethyloxymethyloxytetrafluoroethyltrimethoxysilane, trifluoromethyloxy Methyloxypropyltrimethoxysilane, trifluoromethyloxymethyloxyhexafluoropropyltrimethoxysilane, trifluoromethyloxydifluoromethyloxyethyltrimethoxysilane, trifluoromethyloxydifluoromethyloxypropyltrimethoxysilane, trifluoromethyloxydifluoromethyl Oxyhexafluoropropyltrimethoxysilane, trifluoromethylo Examples thereof include xyltetrafluoroethyloxypropyltrimethoxysilane and alkoxysilane having a high molecular weight type fluoroalkyl group containing an ether bond represented by the following formula (1).
CF ₃ · (OCF ₂ ) _l · (OC ₂ F ₄ ) _m · (OC ₃ F ₆ ) _n · Si (OR ₃ ) _a R ' _3-a
(1)
(In Formula (1), l is 0-400, m is 1-400, n is 0-400, a is 1-3. R and R 'are C1-C6 hydrocarbon groups, They may be the same or different.)

  Among these, alkoxysilanes containing a perfluoroalkyl group as a fluorinated alkyl group are preferable, and a high molecular weight type alkoxysilane represented by the formula (1) is more preferable.

  Moreover, in the alkoxysilane represented by Formula (1), the thing of molecular weight 200-10000 is preferable, the thing of molecular weight 1000-7000 is more preferable, and the thing of molecular weight 3000-5000 is further more preferable. By using an alkoxysilane compound having a long-chain fluoroalkyl group, fine defects on the cast drum surface can be filled. As a result, the surface roughness of the cast drum can be reduced, and a film with more excellent surface smoothness can be produced.

  Examples of the phosphonate represented by the general formula (3) include 2- (perfluorooctyl) ethylphosphonic acid, and examples of the phosphonate represented by the general formula (4) include 2- (perfluorooctyl). ) Ethylphosphonous acid and the like.

  These fluorinated alkyl group-containing alkoxysilanes may be used alone or in combination of two or more.

  As a method for forming a fluororesin film using the fluorinated alkyl group-containing alkoxysilane, a normal wet coating method can be used. For example, by dissolving or dispersing the fluorinated alkyl group-containing alkoxysilane in an organic solvent and applying it to the cast base material surface, the base material itself is heated or blown with hot air to remove the solvent, A fluorine resin film can be formed. Although it does not specifically limit as an organic solvent used at this time, A halogen-type solvent is preferable from a soluble viewpoint, More preferably, perfluorohexane, perfluoro-1, 3- dimethylcyclohexane, dichloropentafluoropropane (HCFC) -225) and alcohols such as ethanol.

  The concentration of the fluorinated alkyl group-containing alkoxysilane dissolved or dispersed in an organic solvent is preferably 0.1 to 10% by weight. If it is less than 0.1% by weight, it is not an amount sufficient to form a fluororesin film on the entire cast substrate, and if it exceeds 10% by weight, the silane coupling agent is only consumed wastefully.

  Moreover, the application method to the cast base material surface of the solution or dispersion of a fluorinated alkyl group-containing alkoxysilane is not particularly limited as long as the solution or dispersion can be spread over the entire cast base material surface. For example, the solution or dispersion may be cast while rotating the cast drum, or may be applied to the entire substrate surface with a cloth soaked with the solution or dispersion.

  In the heat treatment performed after applying the solution or dispersion of the fluorinated alkyl group-containing alkoxysilane to the cast substrate, the heating temperature is preferably 50 to 200 ° C. More preferably, it is 80-120. The heating time is preferably 1 minute to 200 minutes. More preferably, it is 10 minutes to 100 minutes.

  The cast drum surface-treated as described above is washed with an organic solvent such as alcohol as necessary. As a cleaning method, an organic solvent may be cast while rotating the cast drum to remove excess alkoxysilane together with the organic solvent, or the substrate surface may be wiped with a cloth soaked with the organic solvent. Good.

  The reason why such a treatment method is simple is that the alkoxysilane easily reacts with the metal of the cast substrate by the heat treatment, and excess alkoxysilane after the formation of the fluororesin film can be easily removed with a solvent. Moreover, even if it does not wash | clean specially, if a film is formed even once with the cast base material in which the fluororesin film | membrane was formed, unnecessary alkoxysilane will be removed with a film and ensuring favorable peelability. Only the fluororesin film necessary for the film remains on the substrate.

  In the production method of the present invention, a strong chemical bond of M (metal) -O-Si is formed by the reaction between the metal on the surface of the cast substrate and the alkoxysilane site of the fluorinated alkyl group-containing alkoxysilane compound, A film is formed so that the fluorinated alkyl group site | part of covers the surface layer of a base material. Since the alkoxysilane portion cannot further react with the fluorinated alkyl layer formed on the cast substrate, a fluororesin film is formed on the substrate, making it water and oil repellent. Is expressed.

  Thus, the fluorinated alkyl layer formed on the surface of the cast substrate has both water repellency and oil repellency, and facilitates the peeling of the polyvinyl alcohol resin. At the same time, it prevents the adhesion of plasticizers and surfactants contained in the resin solution used for film formation, the adhesion of various oil stains, the adhesion of metal ions that cause water and water, and the adhesion of foreign substances. As a result, the cast substrate and the film surface to be formed are always kept clean and smooth.

  The thickness of the fluororesin film is preferably 0.1 μm or less, more preferably 0.01 μm or less. When the thickness is 0.1 μm or more, the resulting polyvinyl alcohol film tends to be inferior in surface smoothness.

  The contact angle between the cast base material having a fluororesin film formed on the surface and water is preferably 100 ° or more, more preferably 105 to 130 °, and particularly preferably 110 to 120 °. If the contact angle is less than 100 °, sufficient water repellency cannot be obtained.

  In the production method of the present invention, the above-mentioned polyvinyl alcohol-based resin aqueous solution is cast from a T-type slit die on a cast drum having a fluorine-based resin film formed on the surface in this manner, and dried to form a polyvinyl alcohol-based film. A film is manufactured.

  The temperature of the cast drum during film formation is practically 50 to 120 ° C. Subsequently, after drying using a single roll or a multi-stage roll, alternating drying of the front and back surfaces of the film is preferably continued using a multi-stage roll, and after drying, an unstretched polyvinyl alcohol film is formed. If necessary, after drying, heat treatment and humidity control are performed to obtain a polyvinyl alcohol film. The obtained polyvinyl alcohol film is wound around the core tube in a roll state.

  The width, length and thickness of the polyvinyl alcohol film produced by the production method of the present invention are arbitrary, but in view of the recent widening, the width is 2 m or more, preferably 2.5 m or more, particularly It is preferable that it is 3 m or more. The length is 1000 m or more, preferably 2000 m or more, particularly preferably 3000 m or more. The thickness is 10 to 200 μm, preferably 30 to 100 μm, and particularly preferably 50 to 80 μm.

  In the production method of the present invention, since the film can be easily peeled off from the cast substrate during film formation, a surfactant usually added to the resin solution used for film formation is unnecessary, or It can be greatly reduced. Therefore, according to the production method of the present invention, it is possible to produce a polyvinyl alcohol film which does not substantially contain a surfactant.

  In the production method of the present invention, since a film is formed using a cast base material having a small surface roughness, the surface roughness (Ra) in JIS B 0601 is preferably 100 nm or less, more preferably 70 nm or less. More preferably, a polyvinyl alcohol film of 50 nm or less can be produced.

  The polyvinyl alcohol film produced by the production method of the present invention has no optical unevenness and is useful as a raw film for optics, particularly for a polarizing film.

  Hereinafter, the manufacturing method of the polarizing film of this invention using the polyvinyl alcohol-type film of this invention is demonstrated.

  As a film thickness of the polyvinyl alcohol-type film used for the polarizing film of this invention, 30-100 micrometers is preferable, More preferably, it is 50-80 micrometers. If the film thickness is less than 30 μm, stretching is difficult, while if it exceeds 100 μm, the film thickness accuracy is lowered, which is not preferable.

  As a method for producing the polarizing film of the present invention, a polyvinyl alcohol film is stretched and dyed by dipping in a solution of iodine or a dichroic dye, and then treated with a boron compound. There are a method of compound treatment, a method of dyeing with iodine or a dichroic dye and stretching and then a method of treating with boron compound, a method of dyeing and then stretching in a solution of boron compound, etc., which can be appropriately selected and used. . As described above, in stretching, dyeing, and boron compound treatment of a polyvinyl alcohol film (unstretched film), stretching and dyeing and further boron compound treatment may be performed separately or simultaneously. It is desirable to carry out uniaxial stretching during at least one of the processing steps.

  The stretching is desirably performed in a uniaxial direction by 3 to 10 times, preferably 3.5 to 6 times. At this time, the film may be slightly stretched in the direction perpendicular to the stretching direction (stretching to prevent shrinkage in the width direction or more). The temperature condition during stretching is desirably selected from 40 to 170 ° C. Furthermore, the draw ratio may be finally set within the above range, and the drawing operation may be carried out not only in one stage but also in any stage of the production process.

  The film is dyed by bringing the film into contact with a liquid containing iodine or a dichroic dye. Usually, an aqueous solution of iodine-potassium iodide is used, the concentration of iodine is 0.1 to 20 g / l, the concentration of potassium iodide is 10 to 70 g / l, and the weight ratio of potassium iodide / iodine is 10 to 100. Is appropriate. The dyeing time is practically about 30 to 500 seconds. The temperature of the treatment bath is preferably 5 to 60 ° C. In addition to the water solvent, a small amount of an organic solvent compatible with water may be used. As the contact means, any means such as dipping, coating, spraying and the like can be applied.

  The dyed film is then treated with a boron compound. As the boron compound, boric acid or borax is practical. The boron compound is used in the form of an aqueous solution or a water-organic solvent mixture at a concentration of about 0.3 to 2 mol / l, and it is practically desirable that a small amount of potassium iodide coexists in the solution. The treatment method is preferably an immersion method, but, of course, a coating method and a spraying method can also be implemented. The temperature during the treatment is preferably about 40 to 70 ° C., and the treatment time is preferably about 2 to 20 minutes, and if necessary, the stretching operation may be performed during the treatment.

  The polarizing film of the present invention thus obtained can be used as a polarizing plate by laminating and bonding an optically isotropic polymer film or sheet as a protective film on one or both sides thereof. Examples of the protective film include films of cellulose triacetate, cellulose diacetate, polycarbonate, polymethyl methacrylate, polystyrene, polyethersulfone, polyarylene ester, poly-4-methylpentene, polyphenylene oxide, cyclo or norbornene polyolefin, and the like. Or a sheet | seat is mentioned.

  The polarizing film of the present invention may be laminated by applying a curable resin such as urethane resin, acrylic resin, urea resin or the like on one or both sides of the polarizing film for the purpose of thinning the film. it can.

  The polarizing film of the present invention (or at least one surface thereof laminated with a protective film or a curable resin) is a method in which a transparent pressure-sensitive adhesive layer is usually known on one surface as necessary. In some cases, it is formed and used as a polarizing plate. As the pressure-sensitive adhesive layer, acrylic acid esters such as butyl acrylate, ethyl acrylate, methyl acrylate, 2-ethylhexyl acrylate, and α- such as acrylic acid, maleic acid, itaconic acid, methacrylic acid, and crotonic acid are used. Copolymers with monoolefin carboxylic acids (including those added with vinyl monomers such as acrylonitrile, vinyl acetate, and styrene) do not interfere with the polarizing properties of the polarizing film. Therefore, it is particularly preferable. However, the present invention is not limited to these, and any pressure-sensitive adhesive having transparency can be used. For example, polyvinyl ether or rubber may be used.

  Furthermore, it is also possible to provide various functional layers on one surface (the surface where the pressure-sensitive adhesive is not provided) of the polarizing plate (where the pressure-sensitive adhesive is provided). Examples of the functional layer include an antiglare layer, a hard coat layer, an antireflection layer, a half reflection layer, a reflection layer, a phosphorescent layer, a diffusion layer, an electroluminescence layer, a viewing angle expansion layer, and a brightness enhancement layer. Furthermore, it is also possible to provide a combination of two or more of these types, for example, an antiglare layer and an antireflection layer, a phosphorescent layer and a reflective layer, a phosphorescent layer and a half reflection layer, a phosphorescent layer and a light diffusion layer, a phosphorescent layer, A combination of an electroluminescence layer, a half reflection layer, an electroluminescence layer, and the like can be given. However, it is not limited to these.

  Hereinafter, the present invention will be specifically described with reference to examples. In the examples, “parts” and “%” are based on weight unless otherwise specified.

  In the examples, weight average molecular weight, contact angle, surface roughness, peelability, optical unevenness and color unevenness were evaluated as follows.

(1) Weight average molecular weight It measures on condition of the following by GPC-LALLS method.

1) GPC
Apparatus: Waters type 244 gel permeation chromatograph column: Tosoh Corporation TSK-gel-GMPW _XL (inner diameter 8 mm, length 30 cm, 2 pieces)
Solvent: 0.1 M Tris buffer (pH 7.9)
Flow rate: 0.5 ml / min Temperature: 23 ° C
Sample concentration: 0.040%
Filtration: 0.45 μm Mysori Disc W-25-5 manufactured by Tosoh Corporation
Injection volume: 0.2ml
Detection sensitivity (differential refractive index detector): 4 times

2) LALLS
Apparatus: Chromatrix KMX-6 type low angle laser light scattering photometer Temperature: 23 ° C
Wavelength: 633nm
Second virial coefficient × concentration: 0 mol / g
Refractive index density change (dn / dc): 0.159 ml / g
Filter: MILLIPORE 0.45 μm filter HAWP01300
Gain: 800mV

(2) Contact angle The contact angle between the water droplet and the cast drum is measured.

(3) Surface roughness Measured according to JIS B0601 using a laser focus microscope “VK-8500” manufactured by Keyence Corporation. The measurement conditions are as follows.
Measurement length: 0.3 mm, objective lens: 50 times, cutoff: 0.8 μm, smoothing: none

(4) Peelability When the film is peeled off from the cast drum, ○ indicates that the film does not adhere, Δ indicates that the product film of 4000 m is adhered, but the product film is obtained due to cracking or deflection caused by adhesion. What did not exist is set as x.

(5) Optical unevenness After sandwiching a polyvinyl alcohol film between two polarizing plates in a crossed Nicol state (single transmittance 43.5%, polarization degree 99.9%) at an angle of 45 °, the surface illuminance is Using a light box of 14000 lux, the optical unevenness is evaluated according to the following criteria in the transmission mode.
○: Nothing is visible and uniform.
X: Discontinuous shading and streaky shading can be confirmed.

(6) Color unevenness After sandwiching a polarizing film between two polarizing plates in a crossed Nicols state (single transmittance 43.5%, polarization degree 99.9%) at an angle of 45 °, surface illuminance of 14000 lux Using a light box, the optical color unevenness is observed in the transmission mode and evaluated according to the following criteria.
○: No color unevenness ×: Color unevenness

Example 1
A resin concentration of 30 using 100 parts of a polyvinyl alcohol resin having a weight average molecular weight of 142,000 and a saponification degree of 99.7 mol%, 12 parts of glycerin as a plasticizer, and 221 parts of a solvent mixture of 191 parts of water and 30 parts of dimethyl sulfoxide. % Aqueous polyvinyl alcohol resin solution was prepared.

  A cast drum made of SUS plated with chrome is polished with a paste containing cerium oxide (“WENOL” manufactured by HOHN AND HOHN GMBH), and “OPTOOL DSX” (produced by Daikin Industries, Ltd.) as a fluororesin film forming agent ( A 1% perfluorohexane solution of a fluorinated alkyl group-containing alkoxysilane containing an ether bond having a molecular weight of 4000 represented by the formula (1) was applied to the entire surface of the cast drum. The cast drum was heated at 100 ° C. for 1 hour to dry the solvent, and then the entire surface of the cast drum was wiped with a cloth impregnated with ethanol. The cast drum thus obtained had a surface roughness Ra of 30 nm and a contact angle with water of 112 °.

  The polyvinyl alcohol-based resin aqueous solution was cast into a cast drum heated to 95 ° C. from a T-type slit die, and the obtained film was peeled off from the cast drum when the water content was 15%. Next, the film was dried using a drying roll at 50 ° C., followed by heat treatment at 120 ° C. for 3 minutes to obtain a polyvinyl alcohol film roll having an average thickness of 75 μm, a film width of 3 m, and a length of 4000 m.

  As shown in Table 1, there was no optical unevenness in the obtained polyvinyl alcohol film.

  Next, the polyvinyl alcohol film was unwound and swollen in a water washing tank (24 ° C.), then 1.3 times in a iodine tank (20 ° C., iodine concentration 0.05 g / l), a boric acid tank (50 ° C. In addition, the film was subjected to 1.7 times uniaxial stretching at an iodine concentration of 0.0012 g / l and boric acid concentration of 47 g / l). Further, the uniaxial stretching was continued for a total of 6 times to obtain a polarizing film.

  The obtained polarizing film did not have color unevenness as shown in Table 1.

Example 2
A polyvinyl alcohol film roll and a polarizing film were obtained in the same manner as in Example 1 except that “KBM-7803” (perfluoroalkyl group-containing alkoxysilane) manufactured by Shin-Etsu Chemical Co., Ltd. was used as the fluorine resin film forming agent. . As shown in Table 1, there was no optical unevenness in the obtained polyvinyl alcohol film, and there was no color unevenness in the obtained polarizing film.

Example 3
A polyvinyl alcohol film roll and a polarizing film were obtained in the same manner as in Example 1 except that polishing with cerium oxide was not performed. As shown in Table 1, there was no optical unevenness in the obtained polyvinyl alcohol film, and there was no color unevenness in the obtained polarizing film.

Comparative Example 1
A polyvinyl alcohol film was formed in the same manner as in Example 1 except that the fluororesin film was not formed, but the film adhered to the drum surface, and the intended polyvinyl alcohol film was not obtained.

Comparative Example 2
A polyvinyl alcohol film is formed in the same manner as in Example 1 except that a fluorine resin film is not formed and polished, and 0.001 part of polyoxyethylene laurylamine is added as a surfactant to the polyvinyl alcohol resin aqueous solution. Got a roll. As shown in Table 1, the obtained polyvinyl alcohol-based film had optical unevenness, and the polarizing film had color unevenness.

Claims (12)

A method for producing a polyvinyl alcohol film, comprising a step of forming a polyvinyl alcohol film by a casting method using a cast base material having a fluororesin film formed on a surface thereof. 2. The method for producing a polyvinyl alcohol film according to claim 1, wherein the fluorine resin film is formed of a fluorinated alkyl group-containing alkoxysilane. The method for producing a polyvinyl alcohol film according to claim 2, wherein the fluorinated alkyl group is a perfluoroalkyl group. The method for producing a polyvinyl alcohol film according to claim 2 or 3, wherein the alkoxysilane containing a fluorinated alkyl group is represented by the following formula (1).
CF ₃ · (OCF ₂ ) _l · (OC ₂ F ₄ ) _m · (OC ₃ F ₆ ) _n · Si (OR ₃ ) _a R ' _3-a
(1)
(In Formula (1), l is 0-400, m is 1-400, n is 0-400, a is 1-3. R and R 'are C1-C6 hydrocarbon groups, They may be the same or different.) 5. The method for producing a polyvinyl alcohol film according to claim 1, wherein a contact angle between the surface of the cast base material on which the fluororesin film is formed and water is 100 ° or more. The method for producing a polyvinyl alcohol film according to claim 1, 2, 3, 4, or 5, wherein the surface of the cast base material before forming the fluorine resin film contains chromium oxide. The polyvinyl alcohol according to claim 1, 2, 3, 4, 5 or 6, wherein the surface of the cast substrate before forming the fluororesin film is polished with fine particles of chromium oxide or cerium oxide. -Based film manufacturing method. A polyvinyl alcohol film produced by the production method according to claim 1, 2, 3, 4, 5, 6 or 7, and containing no surfactant. A polyvinyl alcohol film produced by the production method according to claim 1, wherein the film has a surface roughness Ra of 100 nm or less. The polyvinyl alcohol film according to claim 8 or 9, wherein the polyvinyl alcohol film is used as an original film of a polarizing film. A polarizing film comprising the polyvinyl alcohol film according to claim 8, 9 or 10. A polarizing plate comprising a protective film on at least one surface of the polarizing film according to claim 11.