JP4531574B2 - Method for producing polyvinyl alcohol film and method for producing polarizing film using the film - Google Patents

Description

  The present invention relates to a method for producing a polyvinyl alcohol film excellent in uniformity of film thickness and optical performance, and particularly, a raw material for obtaining a polarizing film excellent in optical appearance free from obstacles such as optical unevenness. The present invention relates to a method for producing a polyvinyl alcohol film useful as an anti-film.

Conventionally, a polyvinyl alcohol film is prepared by dissolving a polyvinyl alcohol resin in a solvent, defoaming to prepare a stock solution, and then forming the film by a solution casting method (casting method) using a metal heating roll or the like. And then dried.
The polyvinyl alcohol film thus obtained is used in many applications as a film having excellent shape stability, and one of its useful applications is an optical film, particularly 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, applications have been expanded to high-quality and high-reliability devices, especially large-screen liquid crystal displays, etc., and the required physical properties, such as increased size and in-plane uniformity, have been improved. Is strongly demanded.

Under such circumstances, when producing a polarizing film using a polyvinyl alcohol film as an original film, in order to have excellent optical properties, for example, the film thickness of the polyvinyl alcohol film is made uniform, that is, film thickness unevenness. It is necessary that there is no.
As a method for obtaining film thickness uniformity of a polyvinyl alcohol film, a method of casting a stock solution for film formation on a metal surface having a temperature unevenness of 2 ° C. or less has been proposed (for example, Patent Document 1). reference.).
JP 2001-315139 A

However, the technique disclosed in the publication is still not satisfactory, and in order to obtain higher quality and higher optical characteristics, further improvement in film thickness uniformity is required.
Therefore, in the present invention, under such a background, a method for producing a polyvinyl alcohol film excellent in uniformity in film thickness and uniformity in optical performance, in particular, production of a polyvinyl alcohol film useful as a raw film for a polarizing film. It is intended to provide a method.

  However, as a result of intensive studies by the inventor to solve the above-mentioned problems, the stock solution containing the polyvinyl alcohol-based resin is cast on a drum-type roll heated through a die, and the film is formed. Starting the casting after raising the surface temperature of the drum type roll to the range of 70 to 100 ° C. under the condition of 3 ° C./hr or less, more desirably, the surface temperature unevenness of the drum type roll after the temperature rise. It was found that forming a film with a (temperature difference) of 2 ° C. or less gives a polyvinyl alcohol film excellent in uniformity of film thickness and optical performance, thereby completing the present invention.

  In the present invention, when a stock solution containing a polyvinyl alcohol-based resin is cast on a drum-type roll heated through a die, the surface temperature of the drum-type roll is 3 ° C./hr or less. After raising the temperature to the range of 70 to 100 ° C., casting is started, and more desirably, after the temperature rise, the surface temperature unevenness of the drum-type roll is reduced to 2 ° C. or less to form a film thickness. In addition, it is possible to obtain a polyvinyl alcohol film useful as an original film of a polarizing film.

Hereinafter, the present invention will be specifically described.
First, the polyvinyl alcohol resin used in producing the polyvinyl alcohol film of the present invention is usually produced by saponifying polyvinyl acetate obtained by polymerizing vinyl acetate, but the present invention is not necessarily limited to this. Rather than a small amount of unsaturated carboxylic acid (including salts, esters, amides, nitriles, etc.), olefins having 2 to 30 carbon atoms (ethylene, propylene, n-butene, isobutene, etc.), vinyl ethers, unsaturated sulfonic acids A modified polyvinyl alcohol resin containing a component copolymerizable with vinyl acetate such as a salt may be used.

  In addition to this modification, a polyvinyl alcohol-based resin containing a silyl group may be used. Polyvinyl alcohol may be post-modified using a silylating agent, or a silyl group-containing olefinically unsaturated monomer and vinyl acetate may be used together. Examples thereof include a method of saponifying a copolymer obtained by polymerization. Examples of the silyl group-containing olefinically unsaturated monomer include vinyl silane and (meth) acrylamide-alkyl silane.

  Although the weight average molecular weight of a polyvinyl alcohol-type resin is not specifically limited, Preferably it is 60000-300000, More preferably, it is 120000-26000. If the weight average molecular weight is less than 60,000, sufficient optical performance cannot be obtained when a polyvinyl alcohol-based resin is used as an optical film, and if it exceeds 300,000, when the film is used as a polarizing film, stretching becomes difficult and industrial production is difficult. Is difficult and undesirable. In addition, the weight average molecular weight of polyvinyl alcohol-type resin is measured by GPC-LALLS method.

  Furthermore, the saponification degree of the polyvinyl alcohol-based resin is preferably 80 mol% or more, particularly 85 to 100 mol%, more preferably 98 to 100 mol%. When the saponification degree is less than 80 mol%, sufficient optical performance cannot be obtained when an optical film is used, which is not preferable.

  The polyvinyl alcohol resin may include one or more commonly used plasticizers such as glycerin, diglycerin, triglycerin, ethylene glycol, triethylene glycol, polyethylene glycol, etc. 30 wt% or less, preferably 3 to 25 wt%, more preferably 5 to 20 wt%. When the plasticizer exceeds 30% by weight, the film strength is inferior, which is not preferable.

More preferably, in order to improve the peelability of the film, one or more of the various release agents is 5% by weight or less, preferably 0.001 to 3% by weight, more preferably, based on the polyvinyl alcohol resin. It is also possible to contain 0.001 to 2% by weight. When the release agent exceeds 5% by weight, the appearance of the film surface is poor and the films are unfavorably blocked.
Furthermore, in order to prevent yellowing of the film, the addition of an antioxidant is also useful, and an arbitrary antioxidant such as a phenolic antioxidant is exemplified, and 2,6-di-t-butyl-p -Cresol, 2,2'-methylenebis (4-methyl-6-t-butylphenol), 4,4'-butylidenebis (3-methyl-6-t-butylphenol) and the like are useful. The antioxidant is used in the range of about 2 to 100 ppm with respect to the polyvinyl alcohol resin.

  Thus, in the present invention, a polyvinyl alcohol-based resin aqueous solution is prepared using the polyvinyl alcohol-based resin, and the aqueous solution is cast from a T-type slit die onto a drum-type roll to form a film, followed by drying. Manufactures film.

In preparing the polyvinyl alcohol resin aqueous solution, water, dimethyl sulfoxide (DMSO), N-methylpyrrolidone, glycerin, ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, trimethylolpropane and the like Use is made of amines such as alcohol, ethylenediamine, diethylenetriamine, and mixtures thereof.
The concentration of the polyvinyl alcohol resin in the aqueous polyvinyl alcohol resin solution is practically 5 to 50% by weight.

Next, the aqueous polyvinyl alcohol resin solution is cast from a T-type slit die onto a drum-type roll to form a film.
In the present invention, in performing the casting operation, first, the surface temperature of the drum-type roll used before casting is 3 ° C./hr or less, preferably 70 to 100 ° C., preferably 1 to 3 ° C./hr. It is necessary to raise the temperature to a range of 75 to 97 ° C. When the temperature exceeds 3 ° C./hr, cracks occur in the plated portion on the surface of the drum-type roll, or a reversal defect occurs in the film, and the film thickness uniformity is significantly impaired. Similarly, when the temperature of the drum-type roll is outside the range of 70 to 100 ° C., the uniformity of the film thickness is remarkably impaired and the purpose cannot be achieved.

  Casting is started after pre-operation of the drum-type roll. More desirably, the surface temperature unevenness (temperature difference) of the drum-type roll after the temperature rise is 2 ° C. or less, preferably 1 ° C. or less, particularly preferably. It is more effective to form the film at 0.8 ° C. or lower. Steam, a heating medium, hot water, an electric heater, or the like is employed as the drum-type roll heating means. Also, it is possible to install an auxiliary device for blowing warm air, cold air, or the like, or sucking air or steam around the device.

  As a means for controlling temperature unevenness, for example, when using a liquid heat medium as a heat source, a method of providing a jacket having a parallel or spiral channel on the inner surface of a drum-type roll, or when using a gaseous heat medium as a heat source The method of installing a vacuum steam generator for forcibly removing the drain inside the drum type roll to improve humidity control accuracy, or when using a heater or induction heating coil as a heat source A method of narrowing the interval and a combination of these methods can be appropriately employed.

  The surface temperature unevenness of the drum roll is measured by setting the surface temperature of the roll to the target casting temperature, and then performing the idle operation without supplying the raw material for 2 hours at a peripheral speed of 5 m / min, and then stopping the operation. Immediately after that, using a digital surface thermometer manufactured by Anritsu Keiki Co., Ltd., the roll surface temperature was measured over the entire width at intervals of 5 cm in the width direction, and further measured over the entire width at intervals of 1 m in the flow direction. This is done by calculating the difference between the maximum and minimum values of the surface temperature.

The material of such a drum-type roll is not particularly limited, but usually stainless steel is preferably used, and the surface of the roll is preferably metal-plated to prevent damage. As the type of metal plating, for example, chrome plating, nickel plating, galvanization, etc. are preferably used, and they can be used alone or in combination of two or more kinds of multilayers. From the viewpoint of properties, it is preferable that the outermost surface is chrome plated and the surface roughness is 3S or less, particularly 0.5S or less. The diameter of the drum-type roll is preferably 1 m to 5 m and a width of 2 m to 5 m.
When the moisture content of the film reaches 5 to 30% by weight, the film is peeled off from the roll.

In the present invention, after the film obtained by casting as described above is peeled from the drum-type roll, the film is dried with a plurality of metal rolls, preferably a plurality of films so that the front and back surfaces of the film are alternately in contact with the roll. It passes between the metal rolls for drying and is dried.
In the present invention, it is advantageous to use a plurality of metal rolls for drying, preferably 3 to 30, particularly 3 to 26.

The material of the metal roll for drying is not particularly limited as in the case of the drum-type roll, but the outermost surface is chrome-plated from the viewpoint of ease of surface smoothing and durability, and the surface roughness is 3S or less, particularly 0.5S. The following is preferable. As for the diameter of a roll, 100 mm-1000 mm and width 2m-5m are suitable.
The temperature of the drying metal roll is practically 40 to 100 ° C., and a temperature gradient or a rotational speed difference may be appropriately provided between the rolls.

The heating means for the drying metal roll is the same as the drum-type roll, and steam, a heat medium, hot water, an electric heater or the like is employed. Also, it is possible to install an auxiliary device for blowing warm air, cold air, or the like, or sucking air or steam around the device.
When the moisture content of the film reaches about 3 to 15% by weight, the film is peeled off from the metal roll for drying.

In the present invention, the film can be produced with high productivity by adjusting the wetting tension of the drum-type roll and / or the metal roll for drying to 25 to 50 mN / m.
The wetting tension is measured according to JIS K 6768.
The means for adjusting the wet tension to the above range is not particularly limited. (A) A roll having a mirror-finished chromium surface is used, and the surface is treated with an acid aqueous solution having a pH of 1 to 3 (measured at 20 ° C., the same applies hereinafter). do it.
Examples of such an acid aqueous solution having a pH of 1 to 3 include aqueous solutions of acetic acid, sulfuric acid, hydrochloric acid, nitric acid, and the like, and aqueous solutions of acetic acid and nitric acid are particularly preferable. In an acid aqueous solution having a pH outside the above range, it is difficult to obtain a wetting tension in the above range.

  In the present invention, as a method of adjusting the wetting tension other than treating the roll surface with an acid aqueous solution as in (A) above, (B) a surfactant is added in advance to the polyvinyl alcohol-based resin aqueous solution, Can be cast on a drum-type roll to form a film. In this case, in addition to the uniformity of the film thickness and the film appearance characteristics, it is useful in that the long-run film forming property is further improved.

  The amount of the surfactant added is not particularly limited, but is 0.001 to 5% by weight, particularly 0.01 to 2% by weight, more preferably 0.01 to 1% by weight, based on the polyvinyl alcohol resin. It is preferable. If the added amount is less than 0.001% by weight, it is difficult to adjust the wetting tension, and if it exceeds 5% by weight, a problem of blocking occurs in the film, which is not preferable.

  Surfactants include fatty acid soaps, N-acyl amino acids and salts thereof, polyoxyethylene alkyl ester carboxylates, carboxylate types such as acylated peptides, alkyl benzene sulfonates, alkyl naphthalene sulfonates, and naphthalene sulfonic acids. Salt formalin polycondensate, melamine sulfonic acid salt formalin condensate, dialkyl sulfosuccinic acid ester salt, sulfosuccinic acid alkyl disalt, polyoxyethylene alkyl sulfosuccinic acid disalt, alkyl sulfoacetate, α-olefin sulphonate, N -Sulfonate type such as acylmethyl taurate salt, dimethyl-5-sulfoisophthalate sodium salt, sulfated oil, higher alkyl sulfate ester salt, polyoxyethylene alkyl ether sulfate, higher alcohol ethoxy sulfate, poly Such as sulfate ester type salts such as xylethylene alkyl phenyl ether sulfate, monoglyculate, phosphate ester type such as polyoxyethylene alkyl ether phosphate, polyoxyethylene alkyl phenyl ether phosphate, alkyl phosphate, etc. Anionic surfactants may be mentioned.

Also, polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether, ethylene oxide derivative of alkylphenol formalin condensate, polyoxyethylene polyoxypropylene block polymer, polyoxyethylene glycerin fatty acid ester, polyoxyethylene castor oil and hydrogenated castor oil, Ether-type nonionic surfactants such as polyoxyethylene sorbitan fatty acid esters and polyoxyethylene sorbitol fatty acid esters, ester-type surfactants such as polyethylene glycol fatty acid esters, sorbitan fatty acid esters, fatty acid monoglycerides, propylene glycol fatty acid esters and sucrose fatty acid esters Agent, higher fatty acid alkanolamide, higher fatty acid amide, polyoxyethylene alkylamine, etc. Nitrogen-containing type nonionic surface active agents may be used, which may be used independently or in combination.
In carrying out the method of the present invention, it is of course possible to form a film by using both the methods (A) and (B) described above.

  And after drying, an unstretched polyvinyl alcohol film is formed. If necessary, after drying, heat treatment and humidity control are performed to obtain the polyvinyl alcohol film of the present invention. The width of the film is arbitrary, and is generally about 50 cm to 4 m. However, in the case of a wide film having a strong demand in the recent market, 2 m or more, preferably 2.5 m or more, particularly 3 m or more is useful. The length of the film is also arbitrary between about 1000 m and 15000 m.

The polyvinyl alcohol film thus obtained is useful as an original film for optical use, particularly for polarizing film.
Hereinafter, a method for producing a polarizing film will be described.

  As a method for producing a polarizing film, such a polyvinyl alcohol film is stretched and immersed in an iodine or dichroic dye solution for dyeing, or stretching and dyeing are performed simultaneously, or dyed with iodine or a dichroic dye. A method of treating with a boron compound after stretching may be mentioned. There is also a method of drawing in a solution of a boron compound after dyeing, etc., which can be appropriately selected and used.

  The film thickness of the polyvinyl alcohol film used for the polarizing film is preferably 30 to 100 μm, more preferably 40 to 90 μm, and particularly preferably 50 to 80 μm. When the film thickness is less than 30 μm, stretching is difficult, and when it exceeds 100 μm Thickness accuracy is lowered, which is not preferable.

  In the stretching and dyeing of the polyvinyl alcohol film (unstretched film) and the boron compound treatment, the stretching and dyeing and the boron compound treatment may be performed separately or simultaneously. It is desirable to carry out uniaxial stretching during at least one of the 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 above (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 performed not only in one stage but also in any stage of the manufacturing 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 contained.
Any means such as dipping, coating, spraying, etc. can be applied as the contact means.

The dyed film is then treated with a boron compound. As the boron compound, boric acid and borax are 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 for a small amount of potassium iodide to coexist 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. If necessary, the stretching operation may be performed during the treatment.

The polarizing film thus obtained can also be used 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 or sheets of cellulose triacetate, cellulose diacetate, polycarbonate, polymethyl methacrylate, polystyrene, polyethersulfone, polyarylene ester, poly-4-methylpentene, polyphenylene oxide, and the like.

  In addition, instead of the protective film, such a polarizing film can be laminated by applying a curable resin such as a urethane resin, an acrylic resin, or a urea resin on one or both sides instead of the protective film.

  Such a polarizing film (or a laminate of a protective film or a curable resin on at least one surface thereof) has a transparent pressure-sensitive adhesive layer formed on a surface of the polarizing film as required by a generally known method. In some cases, it may be put to practical use. Examples of the pressure-sensitive adhesive layer include acrylic esters such as butyl acrylate, ethyl acrylate, methyl acrylate, 2-ethylhexyl acrylate, and α-monoolefin carboxylic acids such as acrylic acid, maleic acid, itaconic acid, methacrylic acid. Copolymers with acids, crotonic acid, etc. (including those added with vinyl monomers such as acrylonitrile, vinyl acetate and styrene) do not interfere with the polarization characteristics of the polarizing film. However, the present invention is not particularly limited to this, and any pressure-sensitive adhesive having transparency can be used. For example, polyvinyl ether or rubber may be used.

  Further, various functional layers can be provided on one side of the polarizing plate (the one provided with the pressure-sensitive adhesive) (the side where the pressure-sensitive adhesive is not provided). Antiglare layer, hard coat layer, antireflection layer, half reflection layer, reflection layer, phosphorescent layer, diffusion layer, electroluminescence layer, viewing angle expansion layer, brightness enhancement layer, etc. 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 and an electroluminescence layer, a half reflection layer and an electroluminescence layer, etc. Combinations are listed. However, it is not limited to these.

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

Weight average molecular weight:
The measurement was carried out under the following conditions by the GPC-LALLS method.

1) GPC
Apparatus: Waters type 244 gel permeation chromatograph column: Tosoh 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 disk W-25-5 made by Tosoh
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

Example 1
Using a polyvinyl alcohol resin having a weight average molecular weight of 80,000 and a saponification degree of 99.7 mol% determined by the GPC-LALLS method, a 40% concentration polyvinyl alcohol resin aqueous solution (10% glycerin relative to the polyvinyl alcohol resin) And 0.1% polyoxyethylene alkylamino ether.), The aqueous solution was cast from a T-type slit die with a drum-type roll as shown below, and the final content was obtained with a water content of 10%. The film was peeled off from the roll, further heat treated at 120 ° C. for 3 minutes, finally conditioned and wound on a core tube, whereby a polyvinyl alcohol film having a water content of 4% (width: 3.0 m, thickness) 75 μm, length 7000 m).

[Drum type roll]
A stainless steel base material with a diameter of 3.0m and a roll width of 4.0m, nickel-plated, chrome-plated, and mirror-finished drum-type roll with a surface roughness of 0.3S (with a spiral channel on the surface of the drum-type roll) The jacket structure) was heated at a rate of 2.5 ° C./hr for 26 hours, and the surface temperature of the roll was 90.0 ° C. In this case, the temperature unevenness at the ultimate temperature was 0.8 ° C.
[Metal roll for drying]
10 rolls with a surface roughness of 0.3S, nickel-plated on a stainless steel base with a diameter of 0.3m and a roll width of 4.0m, and then mirror-finished with chrome plating (no treatment with aqueous acid solution, wetting tension of 57mN / m ).

The following evaluation was performed about the obtained polyvinyl alcohol-type film.
(Thickness uniformity: thickness variation)
Based on JIS K 6900, the film thickness was measured over 1.5 m in the width direction of the film at three locations with a 25 cm interval in the flow direction using a film thickness tester (“K306C” manufactured by Anritsu Co., Ltd.). The difference (μm) in the minimum value was calculated.

(Optical color 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 14,000 lux in a dark room Using a light box, retardation uniformity was observed in a transmission mode, and optical color unevenness was evaluated according to the following criteria.
A: Nothing is visible and uniform B: Discontinuous shading can be confirmed C: Only streaky shading can be confirmed D: Streaky shading and discontinuous shading can be confirmed

  The obtained polyvinyl alcohol film was unwound at 1.25 m / min, swollen in a water washing tank (24 ° C.), and then 1.3 times in an iodine tank (20 ° C., iodine concentration 0.17 g / l). Uniaxially stretching 1.7 times in a boric acid bath (50 ° C., iodine concentration 0.0012 g / l, boric acid concentration 47 g / l), and further uniaxially 6 times in total at a winding speed of 7.5 m / min. Stretching was performed to obtain a polarizing film.

The obtained polarizing film was sandwiched between two polarizing plates in a crossed Nicols state (single transmittance 43.5%, polarization degree 99.9%) at an angle of 45 °, and then the surface illuminance of 14,000 lux was obtained in a dark room. Using a light box, optical color unevenness was observed in the transmission mode and evaluated according to the following criteria.
○ ・ ・ ・ No color unevenness × ・ ・ ・ Color unevenness

Example 2
Using a polyvinyl alcohol resin having a weight average molecular weight of 80,000 and a saponification degree of 99.7 mol% determined by the GPC-LALLS method, a 40% concentration polyvinyl alcohol resin aqueous solution (10% glycerin relative to the polyvinyl alcohol resin) And 0.1% polyoxyethylene alkylamino ether.), The aqueous solution was cast from a T-type slit die with a drum-type roll as shown below, and the final content was obtained with a water content of 10%. The film was peeled off from the roll, further heat treated at 120 ° C. for 3 minutes, finally conditioned and wound on a core tube, whereby a polyvinyl alcohol film having a water content of 4% (width: 3.0 m, thickness) 75 μm, length 7000 m).

[Drum type roll]
A drum-type roll with a surface roughness of 0.1S, which is nickel-plated on a stainless steel base material having a diameter of 3.0 m and a roll width of 4.0 m, and then chrome-plated to give a mirror finish (a spiral channel is formed on the surface of the drum-type roll). The jacket structure) was heated at a rate of 2.0 ° C./hr for 30 hours, and the surface temperature of the drum-type roll was 84.6 ° C. The temperature unevenness of the reached temperature at that time was 0.6 ° C.
At the start of operation, a pH 1 nitric acid aqueous solution (concentration 6%) was applied to the roll surface so that the total application amount was 460 g / m ^2, and the wetting tension of the roll surface was 32 mN / m.
[Metal roll for drying]
10 rolls with a surface roughness of 0.1S, nickel plated on a stainless steel base with a diameter of 0.3m and a roll width of 4.0m, and then mirror-finished with chrome plating. On the surface of the first roll, nitric acid with a pH of 1 An aqueous solution (concentration: 6%) was applied so that the total application amount was 460 g / m ^2, and the wetting tension on the roll surface was 32 mN / m.

About the obtained polyvinyl alcohol-type film, evaluation similar to Example 1 was performed.
The obtained polyvinyl alcohol film was unwound at 1.25 m / min, swollen in a water washing tank (24 ° C.), and then 1.3 times in an iodine tank (20 ° C., iodine concentration 0.17 g / l). Uniaxially stretching 1.7 times in a boric acid bath (50 ° C., iodine concentration 0.0012 g / l, boric acid concentration 47 g / l), and further uniaxially 6 times in total at a winding speed of 7.5 m / min. Stretching was performed to obtain a polarizing film.
The obtained polarizing film was evaluated in the same manner as in Example 1.

Example 3
The same experiment as in Example 2 was performed except that a polyvinyl alcohol-based resin having a weight average molecular weight of 130000 and a saponification degree of 99.7 mol% determined by the GPC-LALLS method was used. (Width 3.0 m, thickness 74 μm, length 7000 m) was obtained. However, the concentration of the polyvinyl alcohol resin aqueous solution was 33%.

About the obtained polyvinyl alcohol-type film, evaluation similar to Example 1 was performed. The obtained polyvinyl alcohol film was unwound at 1.25 m / min, swollen in a water washing tank (24 ° C.), and then 1.8 times in an iodine tank (20 ° C., iodine concentration 0.17 g / l). , 1.9 times uniaxial stretching in a boric acid bath (50 ° C., iodine concentration 0.0012 g / l, boric acid concentration 47 g / l), and a total of 4.5 times at a winding speed of 5.6 m / min. Uniaxial stretching was performed to obtain a polarizing film.
The obtained polarizing film was evaluated in the same manner as in Example 1.

Example 4
Using a polyvinyl alcohol resin having a weight average molecular weight of 24,000 and a saponification degree of 99.7 mol% determined by the GPC-LALLS method, a 25% concentration polyvinyl alcohol resin aqueous solution (10% glycerin relative to the polyvinyl alcohol resin) The same experiment as in Example 2 was carried out except that 0.1% polyoxyethylene alkylamino ether was used, and a polyvinyl alcohol film having a moisture content of 4% (width 3.0 m, thickness 75 μm, length 7000 m). )

About the obtained polyvinyl alcohol-type film, evaluation similar to Example 1 was performed.
The obtained polyvinyl alcohol film was unwound at 1.25 m / min, swollen in a water washing tank (24 ° C.), and then 1.7 times in an iodine tank (20 ° C., iodine concentration 0.17 g / l). Uniaxially stretching 1.8 times in a boric acid tank (50 ° C., iodine concentration 0.0012 g / l, boric acid concentration 47 g / l), and a total of 4.2 times at a winding speed of 5.3 m / min. Uniaxial stretching was performed to obtain a polarizing film.
The obtained polarizing film was evaluated in the same manner as in Example 1.

Example 5
In Example 3, the same experiment was performed except that the following drum-type rolls were used to obtain a polyvinyl alcohol film (width 3.0 m, thickness 50 μm, length 12000 m) having a moisture content of 3%.

[Drum type roll]
A drum-type roll with a surface roughness of 0.1S, which is nickel-plated on a stainless steel base material having a diameter of 3.0 m and a roll width of 4.0 m, and then chrome-plated to give a mirror finish (a spiral channel is formed on the surface of the drum-type roll). The jacket structure having a wetting tension of 57 mN / m) was heated at a rate of 3.0 ° C./hr for 20 hours, and the surface temperature of the roll was 85.2 ° C. At this time, the temperature unevenness of the reached temperature was 0.8 ° C.

About the obtained polyvinyl alcohol-type film, evaluation similar to Example 1 was performed.
The obtained polyvinyl alcohol film was unwound at 1.25 m / min, swollen in a water washing tank (24 ° C.), and then 1.7 times in an iodine tank (20 ° C., iodine concentration 0.17 g / l). , Uniaxial stretching of 2.0 times in a boric acid bath (50 ° C., iodine concentration of 0.0012 g / l, boric acid concentration of 47 g / l), and a total of 4.5 times at a winding speed of 5.6 m / min. Uniaxial stretching was performed to obtain a polarizing film.
The obtained polarizing film was evaluated in the same manner as in Example 1.

Comparative Example 1
In Example 1, the same experiment was performed except that the temperature rise rate of the drum type roll was 4.0 ° C./hr and the roll surface temperature was 90 ° C., and a polyvinyl alcohol film (width 3.0 m, thickness 75 μm) was obtained. Obtained.
About the obtained polyvinyl alcohol-type film, evaluation similar to Example 1 was performed.
Also, using the obtained polyvinyl alcohol film, a polarizing film was obtained in the same manner as in Example 1, and the same evaluation as in Example 1 was performed.

Comparative Example 2
In Example 1, the same experiment was performed except that the temperature rise rate of the drum type roll was 8.0 ° C./hr, the roll surface temperature was 90 ° C., and the temperature unevenness of the reached temperature was 4.0 ° C. A polyvinyl alcohol film (width 3.0 m, thickness 75 μm) was obtained.
About the obtained polyvinyl alcohol-type film, evaluation similar to Example 1 was performed.
Also, using the obtained polyvinyl alcohol film, a polarizing film was obtained in the same manner as in Example 1, and the same evaluation as in Example 1 was performed.

Comparative Example 3
In Example 1, the same experiment was performed except that the temperature rise rate of the drum-type roll was 2.5 ° C./hr and the roll surface temperature was 130 ° C., and a polyvinyl alcohol film (width 3.0 m, thickness 75 μm) was obtained. As a result, foaming occurred when the film-forming raw material was in contact with the drum-type roll, and a film containing a large amount of air bubbles resulting from the foaming was obtained.

Comparative Example 4
In Example 1, the same experiment was performed except that the temperature rise rate of the drum-type roll was 2.5 ° C./hr and the roll surface temperature was 65 ° C., and a polyvinyl alcohol film (width 3.0 m, thickness 75 μm) was obtained. Obtained.
About the obtained polyvinyl alcohol-type film, evaluation similar to Example 1 was performed.
Also, using the obtained polyvinyl alcohol film, a polarizing film was obtained in the same manner as in Example 1, and the same evaluation as in Example 1 was performed.
The results of Examples and Comparative Examples are shown in Table 1.

※）気泡を大量に含んだフイルムであったため、測定しなかった。

*) Measurement was not performed because the film contained a large amount of bubbles.

The polyvinyl alcohol film obtained by the production method of the present invention is excellent in film thickness uniformity and has excellent optical characteristics such as no optical color unevenness, and is an electronic desk calculator, electronic clock, word processor, personal computer. , Monitors, liquid crystal televisions, portable information terminals, liquid crystal display devices such as automobile and machinery instruments, sunglasses, anti-glare glasses, stereoscopic glasses, reflection reduction layers for display elements (CRT, LCD, etc.), medical equipment, architecture It is very useful as an original film of a polarizing film used for materials, toys and the like. Of course, it is also useful for applications such as packaging film, peelable film, agricultural film, and building material film.

Claims (4)

  In casting a stock solution containing a polyvinyl alcohol resin on a drum-type roll heated through a die, the surface temperature of the drum-type roll is 70 to 100 ° C. under a condition of 3 ° C./hr or less. A method for producing a polyvinyl alcohol film, characterized in that casting is started after the temperature is raised to the above range.   2. The method for producing a polyvinyl alcohol film according to claim 1, wherein after the temperature rise, the film is formed such that the temperature unevenness of the surface of the drum-type roll is 2 [deg.] C. or less.   3. The method for producing a polyvinyl alcohol film according to claim 1, wherein the polyvinyl alcohol film is used as a raw film for a polarizing film. A method for producing a polarizing film, comprising subjecting the polyvinyl alcohol film for polarizing film according to claim 3 to dyeing, uniaxial stretching, and treatment with a boron compound.