JP2001315144A - Method for manufacturing polyvinyl alcohol polymer film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a PVA film useful as a manufacturing raw material of a polarizing film and excellent in thickness uniformity. SOLUTION: When the PVA film 6 is manufactured from a film forming raw material containing PVA using a drum film forming machine, hot air of which the wind velocity in the widthwise direction of the film is 5 m/sec or less is blown against the PVC film 6 on the surface of a first drying drum 3 in a circumferential direction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a polyvinyl alcohol polymer film having excellent smoothness and useful as a raw material for producing a polarizing film.

[0002]

2. Description of the Related Art A polarizing plate having a function of transmitting and blocking light is a fundamental component of a liquid crystal display (LCD) together with a liquid crystal having a function of switching light. The application field of this LCD is wide ranging from small devices such as calculators and watches in the early days to laptop computers, word processors, liquid crystal color projectors, in-vehicle navigation systems, liquid crystal televisions, etc., and is expected to be used on large screens. Therefore, there is a demand for a polarizing plate which is more excellent in uniformity of optical characteristics on a large screen than a conventional product.

A polarizing plate is generally made of a polyvinyl alcohol film (hereinafter, a polyvinyl alcohol-based polymer is referred to as “P”).
VA ", and a polyvinyl alcohol (based polymer) film may be abbreviated as" PVA film "), and a polarizing film produced by uniaxially stretching and dyeing is supported on both sides of a cellulose triacetate (TAC) film or the like. It has a configuration in which boards are attached.

[0004]

By the way, there are many precautions such as uniform stretching of the PVA film and bonding without unevenness for the uniformity of the polarization performance, but the most important points are as follows. This is the uniformity of the thickness of the PVA film serving as the base of the polarizing plate. If the thickness of the PVA film is not uniform, uniform polarization performance cannot be obtained over a large area even when precision stretching is performed. Conventionally, in order to improve the uniformity of the thickness of the PVA film, casting is performed using a diluted solution of PVA, but the uniformity of the thickness is not sufficient.

Accordingly, an object of the present invention is to provide a method for producing a PVA film having excellent thickness uniformity, which is useful as a raw material for producing a polarizing film.

[0006]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, the film-forming raw material on the first drum has uneven wind speed in the width direction within a specific range. It has been found that spraying with air and drying is useful as a method for producing a PVA film having excellent thickness uniformity, and has completed the present invention.

That is, in the method for producing a PVA film according to the present invention, when a polyvinyl alcohol film is produced using a drum film forming machine, the wind speed unevenness in the width direction is 5 m.
/ Sec or less is blown to the first drying drum to dry the PVA film.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A film-forming machine used for drum-forming according to the present invention usually comprises one or more rotating metal drying drums, a drying device, a humidity control device and a winding device. In addition, a motor, a transmission, and the like are used to drive each device, and the speed is adjusted. Drying temperature is 50 ℃ ～ 1
50 ° C. is common. As a method for producing a PVA film, for example, a cast film forming method, an extrusion film forming method, and the like using a film forming raw material containing PVA are known.

FIG. 1 shows an example of a method for producing a PVA film of the present invention, in which a film forming raw material (which may contain an organic solvent or the like), which is a PVA solution or a melt, is uniformly discharged onto a heated drum. 1 shows a drum type film forming machine for forming a film. This film-forming machine is composed of a T-shaped slit die 1 and a film-forming material 2.
Is discharged onto the surface of the first drying drum 3, and further from one or a plurality of locations toward the film forming raw material 2 on the surface of the first drying drum 3, in the circumferential direction. Drying is performed by blowing hot air having a wind speed unevenness of 5 m / sec or less, and then drying is performed by a drying / humidifying device 4 having a plurality of drums.
The VA film is uniformly dried from both sides, and after adjusting the humidity, the VA film is taken up by a take-up device (not shown) via a peeling roller 5.

As the PVA constituting the PVA film, those obtained by saponifying a vinyl ester polymer obtained by polymerizing a vinyl ester monomer and using a vinyl ester unit as a vinyl alcohol unit can be used. As the vinyl ester monomer, for example,
Vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl laurate, vinyl stearate,
Examples thereof include vinyl benzoate, vinyl pivalate, and vinyl versatate. Of these, vinyl acetate is preferably used.

When copolymerizing a vinyl ester-based monomer, if necessary, a copolymerizable monomer may be used within a range not impairing the effects of the present invention (preferably 15 mol% or less, more preferably 5 mol% or less. ).

Examples of such a monomer copolymerizable with the vinyl ester monomer include olefins having 3 to 30 carbon atoms such as ethylene, propylene, 1-butene and isobutene; acrylic acid and its salts; methyl acrylate , Ethyl acrylate, n-propyl acrylate, i-propyl acrylate, n-butyl acrylate, i-butyl acrylate, t-butyl acrylate, acrylic acid 2
Acrylates such as ethylhexyl, dodecyl acrylate and octadecyl acrylate; methacrylic acid and salts thereof; methyl methacrylate, ethyl methacrylate;
Methacrylates such as n-propyl methacrylate, i-propyl methacrylate, n-butyl methacrylate, i-butyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate, octadecyl methacrylate And acrylamide,
Acrylamide derivatives such as N-methylacrylamide, N-ethylacrylamide, N, N-dimethylacrylamide, diacetoneacrylamide, acrylamidopropanesulfonic acid and salts thereof, acrylamidopropyldimethylamine and salts thereof, N-methylolacrylamide and derivatives thereof; methacryl Amide, N-
Methacrylamide derivatives such as methyl methacrylamide, N-ethyl methacrylamide, methacrylamidopropanesulfonic acid and salts thereof, methacrylamidopropyldimethylamine and salts thereof, N-methylol methacrylamide and derivatives thereof; methyl vinyl ether, ethyl vinyl ether, n- Vinyl ethers such as propyl vinyl ether, i-propyl vinyl ether, n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, dodecyl vinyl ether, and stearyl vinyl ether; nitriles such as acrylonitrile and methacrylonitrile; vinyl chloride, vinylidene chloride, and fluorine. Vinyl halides such as vinyl halide and vinylidene fluoride; allyl compounds such as allyl acetate and allyl chloride; Salts or esters thereof; itaconic acid and salts or esters thereof; vinylsilyl compounds such as vinyltrimethoxysilane; N-vinylamides such as isopropenyl acetate, N-vinylformamide, N-vinylacetamide and N-vinylpyrrolidone; Can be.

The average degree of polymerization of the PVA constituting the PVA film is preferably at least 500 from the viewpoint of film strength, more preferably at least 1,000 from the viewpoint of polarization performance,
It is more preferably at least 000, particularly preferably at least 3,500. On the other hand, the upper limit of the degree of polymerization of PVA is preferably 10,000 or less from the viewpoint of film forming properties. The degree of polymerization (P) of PVA is measured according to JIS K 6726. That is, after PVA is re-saponified and purified, 30 ° C.
Intrinsic viscosity [η] (unit: dL / g, L
Is obtained from the following formula from liter). P = ([η] × 10 ³ /8.29) ^{(1 / 0.62)}

The degree of saponification of the PVA constituting the PVA film is preferably 90 mol% or more, more preferably 95 mol% or more, and more preferably 98 mol%, from the viewpoint of the durability of the polarizing film.
The above is more preferred. On the other hand, from the viewpoint of the dyeability of the film, the content is preferably 99.99 mol% or less.

The degree of saponification indicates the ratio of units actually saponified to vinyl alcohol units among units that can be converted to vinyl alcohol units by saponification. In addition, the saponification degree of PVA was measured by the method described in JIS.

In producing the PVA film, it is preferable to add a polyhydric alcohol as a plasticizer. Examples of the polyhydric alcohol include ethylene glycol, glycerin, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, trimethylolpropane, and the like. One or more of these may be used. it can. Among these, ethylene glycol or glycerin is preferably used from the viewpoint of the effect of improving stretchability.

The amount of polyhydric alcohol to be added is PVA
1 to 30 parts by weight, preferably 3 to 30 parts by weight, per 100 parts by weight
It is more preferably 25 parts by weight, particularly preferably 5 to 20 parts by weight. If the amount is less than 1 part by weight, the dyeing properties and the stretchability may decrease. If the amount is more than 30 parts by weight, the film may be too flexible and the handleability may decrease.

When producing a PVA film, it is preferable to add a surfactant. The type of the surfactant is not particularly limited, but an anionic or nonionic surfactant is preferable. As the anionic surfactant,
For example, a carboxylic acid type such as potassium laurate, a sulfate type such as octyl sulfate, and a sulfonic acid type anionic surfactant such as dodecylbenzenesulfonate are preferable. As the nonionic surfactant,
For example, alkyl ether type such as polyoxyethylene oleyl ether, alkyl phenyl ether type such as polyoxyethylene octyl phenyl ether, alkyl ester type such as polyoxyethylene laurate, alkyl amine type such as polyoxyethylene lauryl amino ether, poly Nonionics such as alkyl amides such as oxyethylene lauric amide, polypropylene glycol ethers such as polyoxyethylene polyoxypropylene ether, alkanolamides such as oleic acid diethanolamide, and allyl phenyl ethers such as polyoxyalkylene allyl phenyl ether Nonionic surfactants are preferred. One or a combination of two or more of these surfactants can be used.

The amount of the surfactant added is PVA 10
0.01 to 1 part by weight is preferable for 0 part by weight, and 0.1 to 1 part by weight is preferable.
02-0.5 part by weight is more preferable, and 0.05-0.5 part by weight.
3 parts by weight are particularly preferred. If the amount is less than 0.01 part by weight, the effect of improving the stretchability and the dyeing property is difficult to appear, and if it is more than 1 part by weight, it is eluted on the film surface to cause blocking, and the handleability may be reduced.

The volatile matter content of the PVA-containing film-forming raw material used for producing the PVA film is preferably from 50 to 90% by weight, more preferably from 55 to 80% by weight.
If the volatile content is less than 50% by weight, the viscosity may be high, so that film formation may be difficult. If the volatile content is greater than 90% by weight, the viscosity tends to be low, and the uniformity of the film thickness tends to be impaired.

On the PVA film on the first drying drum,
When drying by blowing the wind, the unevenness in the width direction of the blown wind is 5 m / sec or less, preferably 4 m / sec or less, and more preferably 3 m / sec or less. When the wind speed unevenness is larger than 5 m / sec, temperature unevenness occurs in the width direction and drying of the PVA film becomes uneven, and P
The thickness uniformity of the VA film may be impaired.

The wind speed of the blowing wind is 1 to 60 m /
sec is preferable, and 1 to 50 m / sec is more preferable. Further, it is preferable that the wind speed is 1 to 30 m / sec from the position where the film forming raw material containing PVA is discharged to about 1/4 rotation of the drum, that is, in the initial stage of drying. If the wind speed is lower than 1 m / sec, dew condensation such as water vapor may occur in the drying device, and the water droplets may drop and become a defect of the PVA film. The wind speed is 60m / s
If ec is exceeded, the PVA film on the first drying drum may be deformed, resulting in increased thickness unevenness. In particular, deformation tends to occur in the initial stage of drying. There is no particular limitation on the method of equalizing the wind speed in the width direction of the blowing wind,
A structure for reducing the unevenness of the blowing wind is preferable, and a nozzle system, a current plate system, or a combination thereof is generally used. Also not particularly limited opening area of the outlet of the air, but preferably the opening area per 1m wide of outlet is 20cm ² ~1000cm ^2.

Although there is no limitation on the number of the blowing locations, the number of the blowing locations is preferably two or more. Further, it is preferable to exhaust the volatile matter and the blown air from around the first drying drum. There is no particular limitation on the method of exhaustion, but it is preferable to prevent unevenness in the velocity of the blown wind and uneven temperature.

The temperature of the blown air is preferably 50 to 150 ° C, more preferably 60 to 120 ° C. Further, the temperature unevenness in the width direction of the blowing wind is preferably 10 ° C. or less,
5 ° C. or lower is more preferable.

The width of the blowing air is preferably the same as the width of the discharged PVA-containing film-forming raw material, more preferably wider than the width of the PVA-containing film-forming raw material, than the width of the first drying drum. It is even more preferable that the width is wide. The direction of the blowing air is preferably blown from the circumferential direction to the first drying drum, and more preferably from the circumferential direction to the film flow direction.

In the present invention, the width of the PVA film is not particularly limited, but a PVA film having excellent thickness uniformity can be obtained even when the width exceeds 2 m for a large LCD screen as well as a width of 2 m or less. Can be

The thickness of the PVA film is 20 to 1
50 μm is preferable, and 40 to 120 μm is more preferable.

In order to produce a polarizing film from the PVA film 6 obtained in the present invention, for example, the PVA film 6
May be dyed, uniaxially stretched, fixed, and dried, and if necessary, heat-treated. The order of each step is not particularly limited, and two steps such as dyeing and uniaxial stretching may be performed simultaneously, or each step may be repeated plural times.

The dyeing can be performed before, simultaneously with, or after the uniaxial stretching. However, since the degree of crystallinity of PVA is easily increased by the uniaxial stretching and the dyeing property may be reduced, the uniaxial stretching may be performed. Any process prior to stretching or
It is preferable to dye during the uniaxial stretching step. As a dye used for dyeing, iodine-potassium iodide or Di
rect black 17, 19, 154; Direct brown 44, 106,
195, 210, 223; Direct red 2, 23, 28, 31, 37, 3
9, 79, 81, 240, 242, 247; Direct blue 1, 15, 2
2, 78, 90, 98, 151, 168, 202, 236, 249, 270
Direct violet 9, 12, 51, 98; Direct green 1, 8
5; Direct yellow 8, 12, 44, 86, 87; Direct orange
Dichroic dyes such as 26, 39, 106 and 107 can be used. Dyeing can be usually performed by immersing the PVA film in a solution containing the dye,
The processing conditions and processing method are not particularly limited.

The uniaxial stretching can be performed by a wet stretching method or a dry heat stretching method, and is performed in warm water (which may be in a solution containing the dye or in a fixing treatment bath described later) or in air using a PVA film after water absorption. be able to. Stretching is preferably carried out as far as possible, up to slightly before the PVA film is cut, specifically, preferably at least 4 times, particularly preferably at least 5 times. When the stretching ratio is smaller than 4 times, it is difficult to obtain practically sufficient polarization performance and durability performance. The stretching temperature is not particularly limited, but is preferably 30 to 90 ° C. when the PVA film is stretched in warm water (wet stretching), and 50 to 180 ° C. when the dry stretching is performed by dry heat. P after stretching
The thickness of the VA film is preferably 3 to 75 μm,
-50 μm is more preferable.

For the purpose of strengthening the adsorption of the dye to the PVA film, a fixing treatment is performed. Usually, boric acid and / or a boron compound is added to the treatment bath used for the fixing treatment. Further, if necessary, an iodine compound may be added to the treatment bath.

The drying treatment (heat treatment) of the polarizing film produced through the above treatment steps is preferably carried out at 30 to 150 ° C., more preferably at 50 to 150 ° C.

As described above, the PVA film obtained by the production method of the present invention is usually used as a polarizing plate by laminating a protective film that is optically transparent and has mechanical strength on both sides or one side thereof. used. As the protective film, usually, a cellulose acetate film, an acrylic film, a polyester film, or the like is used.

[0034]

EXAMPLES The present invention will now be described specifically with reference to examples, but the present invention is not limited to these examples. In addition, the wind speed unevenness, the thickness unevenness of the PVA film, and the dichroic ratio described in Examples and Comparative Examples were evaluated by the following methods, respectively, and a polarizing film was produced by the following method.

Wind speed unevenness The wind speed unevenness was measured at 20 points in the width direction of the wind blown out to the first drum using an Anemomaster Model 6112 manufactured by Nippon Kanomax Co., Ltd., and the difference between the maximum value and the minimum value was calculated.

The thickness unevenness of the PVA film;
Anritsu Corporation Film Thickness Tester KG60
1A, 1.5 m in width direction of film, 2 in flow direction
Three points were measured at 5 cm intervals, and the difference between the maximum value and the minimum value was calculated.

Dichroic ratio: The dichroic ratio was used as an index for evaluating the polarizing performance of the obtained polarizing film. This dichroic ratio is based on the standards of the Electronic Machinery Manufacturers Association of Japan (EIAJ) LD-2.
The transmittance Ts obtained by measuring and calculating in a C light source and a 2 degree field of view using a spectrophotometer in accordance with 01-1983.
(%) And P (%) were obtained from the following equation. Dichroic ratio = log (TS / 100−TS / 100 × P /
100) / log (TS / 100 + TS / 100 × P /
100)

Method for preparing a polarizing film; pre-swelling, dyeing, washing, uniaxial stretching, fixing, drying,
A polarizing film was prepared by treating in the order of heat treatment. That is, the PVA film was pre-swelled by immersing it in water at 30 ° C. for 1 minute, the weight ratio of iodine / potassium iodide was reduced to 1/10 in a 4% by weight aqueous solution of boric acid, and the iodine concentration was 50 g.
/ L in a 30 ° C. aqueous solution for 4 minutes, immersed in 30 ° C. water for 0.5 minute to wash, and uniaxially stretched in a 4% by weight boric acid aqueous solution at 50 ° C. to a stretch ratio of 5.0 times Was done. Subsequently, potassium iodide 40 g / L and boric acid 40 g / L 4
It was immersed in an aqueous solution at 0 ° C. for 5 minutes to perform a fixing treatment. Thereafter, the PVA film was taken out, dried with hot air at 40 ° C. under a constant length, and further heat-treated at 100 ° C. for 3 minutes.

Example 1 Using a drum type film forming machine constructed in the same manner as in FIG. 1, 100 parts by weight of PVA having a degree of saponification of 99.9 mol% and a degree of polymerization of 2400, 13 parts by weight of glycerin, and 0.1 parts of lauric acid diethanolamide were used. A film-forming material 2 consisting of parts by weight and water having a volatile content of 75% by weight is discharged onto the surface of the first drying drum 3 at a temperature of 90 ° C., and further formed on the surface of the first drying drum 3 The temperature is 90 ° C. and the average wind speed is 10 m / s from the circumferential direction toward the raw material 2 in the film flow direction.
ec, 10m / sec, 20m / sec, 30m / sec
c, 40 m / sec, and the hot air 91 to 95, each of which has a wind speed unevenness of 2.8 m / sec in the width direction, are blown from five places from the upstream side to the downstream side of the drum in the above order and dried. Average thickness 74.6 μm, thickness unevenness 1.9
A μm PVA film 6 was obtained.

When this PVA film 6 was processed into a polarizing film by the above-mentioned method for producing a polarizing film, the thickness of the center portion of the polarizing film was 26 μm, the transmittance was 43.8%, and the degree of polarization was 99.0. %, Dichroic ratio is 39.5
Met. When 1 m square of this polarizing film was placed at an angle of 45 ° between two polarizing plates in a crossed Nicols state, and transmitted light was visually observed, almost no optical unevenness was observed.

Example 2 Using a drum type film forming machine having the same structure as that shown in FIG. 1, 100 parts by weight of PVA having a degree of saponification of 99.9 mol% and a degree of polymerization of 4000, 12 parts by weight of glycerin and 0.1 part of lauric acid diethanolamide were used. A film-forming raw material 2 consisting of parts by weight and water having a volatile content of 80% by weight is discharged onto the surface of the first drying drum 3 at a temperature of 90 ° C., and further formed on the surface of the first drying drum 3 From the circumferential direction toward the raw material 2, the temperature and the average wind speed are 70 ° C. and 5 m / sec, respectively, from the circumferential direction to the film flowing direction.
c, 100 ° C, 10m / sec, 100 ° C, 20m / s
ec, 120 ° C, 20m / sec, 120 ° C, 20m /
sec, 100 ° C, 50m / sec, 100 ° C, 50m
/ Sec, 100 ° C, 50m / sec, 90 ° C, 20m
/ Sec, and the wind speed unevenness in the width direction is 3.
Hot air of 2 m / sec is blown from nine locations from the upstream side to the downstream side of the first drying drum 3 in the order described above and dried, and the average thickness is 75.2 μm and the thickness unevenness is 2.5 μm.
m of PVA film 6 was obtained.

When this PVA film 6 was processed into a polarizing film by the above-mentioned method for producing a polarizing film, the thickness of the center portion of the polarizing film was 26 μm, the transmittance was 43.2%, and the degree of polarization was 99.6. %, Dichroic ratio is 42.9
Met. When 1 m square of this polarizing film was placed at an angle of 45 ° between two polarizing plates in a crossed Nicols state, and transmitted light was visually observed, almost no optical unevenness was observed.

Example 3 Using a drum type film forming machine having the same structure as that shown in FIG. 1, 100 parts by weight of PVA having a saponification degree of 99.9 mol% and a polymerization degree of 1700, 8 parts by weight of glycerin and 0.1 parts of lauric acid diethanolamide were used. A film forming raw material 2 consisting of parts by weight and water having a volatile content of 62% by weight is discharged onto the surface of the first drying drum 3 at a temperature of 90 ° C., and further formed on the surface of the first drying drum 3. The hot air having a temperature of 80 ° C., an average wind speed of 5 m / sec, and an uneven wind speed of 1.8 m / sec in the width direction is applied to the first drum 3 for drying in the circumferential direction from the circumferential direction toward the raw material 2. Sprayed from 7 places from upstream to downstream side and dried, average thickness 75.5μm, thickness unevenness 1.8μ
m of PVA film 6 was obtained.

When this PVA film 6 was processed into a polarizing film by the above-mentioned method for producing a polarizing film, the thickness of the center portion of the polarizing film was 27 μm, the transmittance was 43.0%, and the degree of polarization was 99.3. %, Dichroic ratio is 37.6
Met. When 1 m square of this polarizing film was placed at an angle of 45 ° between two polarizing plates in a crossed Nicols state, and transmitted light was visually observed, almost no optical unevenness was observed.

Example 4 Using a drum-type film-forming machine having the same structure as in FIG. 1, 100 parts by weight of PVA having a saponification degree of 99.9 mol% and a polymerization degree of 2400, 8 parts by weight of glycerin, and 0.1 parts of lauric acid diethanolamide were used. A film forming raw material 2 composed of parts by weight and water having a volatile content of 65% by weight is discharged onto the surface of the first drying drum 3 at a temperature of 90 ° C., and further formed on the surface of the first drying drum 3. The temperature is 80 ° C., the average wind speed is 40 m / sec, 50 m /
Drying is performed by blowing three types of hot air, each having a wind speed unevenness of 1.8 m / sec in the width direction at 65 m / sec and at a speed of 65 m / sec, from the upstream side to the downstream side of the first drying drum 3 in the order described above. Thus, a PVA film 6 having an average thickness of 74.9 μm and an uneven thickness of 3.4 μm was obtained.

When this PVA film 6 was processed into a polarizing film by the above-described method for producing a polarizing film, the thickness of the center portion of the polarizing film was 26 μm, the transmittance was 43.5%, and the degree of polarization was 99.3. %, Dichroic ratio is 40.6
Met. When 1 m square of this polarizing film is placed at an angle of 45 ° between two polarizing plates in a crossed Nicols state, and the transmitted light is visually observed, the width is 1 to 3 mm and the length is 10 to 30.
Two thin, thin, elliptical optical irregularities having a diameter of mm were observed.

Comparative Example 1 A drum type film forming machine constructed in the same manner as in FIG.
A film was formed in the same film-forming process as in Example 1 except that the wind speed unevenness in the width direction of the hot air was 5.4 m / sec, using the same film-forming raw material as in Example 1. Unevenness 5.5 μm of PVA film 6 was obtained.

When this PVA film 6 was processed into a polarizing film by the method for producing a polarizing film, the thickness of the center portion of the polarizing film was 27 μm, the transmittance was 43.5%, and the degree of polarization was 99.3. %, Dichroic ratio is 40.6
Met. A 1 m square of this polarizing film was placed at an angle of 45 ° between two polarizing plates in a crossed Nicols state, and when the transmitted light was visually observed, the width was 5 to 20 mm and the length was 50 to 1
50 mm stripes, ellipses, and irregular optical irregularities
Was confirmed.

Comparative Example 2 A drum type film forming machine constructed in the same manner as in FIG.
Using the same film-forming raw material as described above, a temperature of 100 ° C. and an average wind speed from the circumferential direction toward the film flow direction toward the film-forming raw material 2 on the surface of the first drying drum 3 at a temperature of 90 ° C. 5m / sec, 10m / sec, 20m / sec, 30
m / sec, 40m / sec, 40m / sec, 50m
/ Sec, the wind speed unevenness in the width direction is 6.2 m / s each
ec hot air is blown from seven locations from the upstream side to the downstream side of the first drying drum 3 in the order described above, and dried, and PV having an average thickness of 74.9 μm and an uneven thickness of 4.9 μm is dried.
A film 6 was obtained.

When this PVA film 6 was processed into a polarizing film by the above-mentioned method for producing a polarizing film, the thickness of the center portion of the polarizing film was 26 μm, the transmittance was 43.3%, and the degree of polarization was 99.5. %, Dichroic ratio is 41.9
Met. When 1 m square of this polarizing film is placed at an angle of 45 ° between two polarizing plates in a crossed Nicols state, and the transmitted light is visually observed, a width of 5 to 30 mm and a length of 50 to 2
5 mm of 00 mm stripes, ellipses, and irregular optical irregularities
Was confirmed.

Comparative Example 3 A drum type film forming machine constructed in the same manner as in FIG.
Using the same film forming raw material as described above, the temperature is 80 ° C. and the average wind speed is from the circumferential direction toward the film flowing direction toward the film forming raw material 2 on the surface of the first drying drum 3 at the temperature of 80 ° C. 6
Hot air with a wind speed unevenness of 6.8 m / sec at 5 m / sec is blown at one place and dried, and the average thickness is 75.2 μm.
m, a PVA film 6 having an uneven thickness of 10.9 μm was obtained.

When this PVA film 6 was processed into a polarizing film by the above-mentioned method for producing a polarizing film, the thickness of the center portion of the polarizing film was 27 μm, the transmittance was 43.2%, and the degree of polarization was 99.0. %, Dichroic ratio is 36.0
Met. When 1 m square of this polarizing film is placed at an angle of 45 ° between two polarizing plates in a crossed Nicols state and the transmitted light is visually observed, a width of 5 to 30 mm and a length of 100 to
Eleven 300 mm stripes, ellipses and irregular optical irregularities were confirmed.

Comparative Example 4 A drum type film forming machine constructed in the same manner as in FIG.
Using the same film forming raw material as described above, the temperature is 80 ° C. and the average wind speed is from the circumferential direction toward the film flow direction toward the film forming raw material 2 on the surface of the first drying drum 3 at a temperature of 90 ° C. 2
At 0 m / sec, 65 m / sec, and 70 m / sec, the hot air whose wind speed unevenness in the width direction is 5.5 m / sec is supplied from three places from the upstream side to the downstream side of the first drying drum 3 in the order described above. Spray and dry, average thickness 7
A PVA film 6 having a thickness of 5.0 μm and a thickness of 9.8 μm was obtained.

When this PVA film 6 was processed into a polarizing film by the above-described method for producing a polarizing film, the thickness of the center portion of the polarizing film was 27 μm, the transmittance was 43.6%, and the degree of polarization was 99.2. %, Dichroic ratio is 40.1
Met. When 1 m square of this polarizing film is placed at an angle of 45 ° between two polarizing plates in a crossed Nicols state and transmitted light is visually observed, a width of 10 to 30 mm and a length of 100
Eight striped, elliptical, and irregular optical irregularities of 〜250 mm were observed.

[0055]

As described above, according to the present invention, when producing a polyvinyl alcohol film using a drum film forming machine, the first drum for drying has a wind speed unevenness of 5 m / sec or less in the width direction. By spraying, a PVA film having excellent thickness uniformity can be obtained. And this PV
By using the A film, it is possible to obtain a polarizing film most suitable for a large liquid crystal display screen having a wide width and a small optical unevenness.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a drum type film forming machine used in the production method of the present invention.

[Explanation of symbols]

3 ... First drum for drying, 4 ... Drying / humidifying device, 6 ... PV
A film.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C08L 29:04 C08L 29:04 (72) Inventor Toru Shimito 892, Sakuhi-shi, Saijo-shi, Ehime Kuraray Co., Ltd. F term (reference) 2H049 BA02 BA27 BB43 BC03 BC09 4F071 AA29 AH12 BB02 BB06 BC01 4F205 AA19 AG01 AR08 GA07 GB02 GC02 GF24 GN21 GN24

Claims (3)

[Claims] When producing a polyvinyl alcohol film using a drum film forming machine, the wind speed unevenness in the width direction is 5%.
A method for producing a polyvinyl alcohol-based polymer film, characterized by blowing air having a flow rate of not more than m / sec to a first drying drum. 2. The method according to claim 1, wherein the wind speed is 1 to 60 m / m.
A method for producing a polyvinyl alcohol-based polymer film, characterized by blowing a second wind onto a first drying drum. 3. The method for producing a polyvinyl alcohol-based polymer film according to claim 1, wherein the film for a polarizing film is obtained.