JP2001315145A - Method for manufacturing film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a polyvinyl alcohol film excellent in thickness uniformity and smoothness even in a large area and capable of becoming a polarizing film reduced in optical irregularity and excellent in optical capacity, in the case utilized as a method for manufacturing polyvinyl alcohol film for the polarizing film. SOLUTION: When the polyvinyl alcohol film 4 is manufactured using a drum film forming machine or a belt type film forming machine, the interval L between the discharge orifice 11 of a film forming raw material 2 containing polyvinyl alcohol and the drum 3 or belt is set to 10 mm or less.

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 film having a uniform thickness and excellent smoothness, which is useful as a 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 field of application of this LCD has expanded from small devices such as calculators and watches in the early days to recent years, such as laptop computers, word processors, liquid crystal color projectors, in-car navigation systems, and liquid crystal televisions. As a result, there has been a demand for a polarizing plate that is more excellent in uniformity of optical characteristics on a large screen than conventional products.

[0003] A polarizing plate is generally a polyvinyl alcohol film (hereinafter abbreviated as "PVA film", and polyvinyl alcohol as a raw material thereof is referred to as "PVA film").
A) (which may be abbreviated as A)), and a protective film such as a cellulose triacetate (TAC) film is bonded to both surfaces of a polarizing film produced by uniaxially stretching and dyeing.

[0004]

In order to make the polarization performance of the polarizing plate uniform, there are many precautions such as uniform stretching of the PVA film and bonding evenly, but the most important point is PVA used as a material for polarizing films
This is to make the thickness of the film uniform. 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. In order to make the thickness of the PVA film uniform, casting is performed with a dilute solution of PVA, but sufficient thickness uniformity has not been obtained.

Accordingly, an object of the present invention is to provide a PVA film having a uniform thickness and excellent smoothness even in a large area, and is particularly useful as a method for producing a PVA film for a polarizing film, and has less optical unevenness. An object of the present invention is to provide a method for producing a PVA film that can be a polarizing film having excellent optical performance.

[0006]

In order to achieve the above object, PVA is formed using a drum film forming machine or a belt type film forming machine.
When producing a film, the distance from the discharge port of the film forming raw material containing PVA to the drum or belt is 0.1 to 1
0 mm. At this time, the difference (W1−W2) between the film width (W1) at the discharge port of the film forming material and the film width (W2) when the film forming material is in contact with the drum or the belt is 0 to 1
The thickness is preferably 0 cm, and more preferably the thickness of the PVA film is 20 to 150 μm.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows an example of the production of a PVA film, in which a film-forming material (which may contain an organic solvent or the like) containing PVA in a solution or molten state is uniformly discharged onto a heated drum. 1 illustrates a drum film forming machine. This film forming machine converts a film forming raw material 2 from a T-die 1 into a first film forming film for a dry film forming which is positioned at the most upstream side and rotates.
The PVA film 4 is discharged onto the drum 3 and is brought into contact with the circumferential surface to dry one surface of the PVA film 4. Subsequently, the other surface of the PVA film 4 is dried by passing over the circumference of the second drum 5 and further dried by passing through a plurality of drums 6 on the downstream side. PVA
The film 4 is wound on a winding device 8. This drum film forming machine is provided with a drying device, a humidity control device, and the like. The speed of each drive is adjusted using a motor, a transmission, or the like. The drying temperature is generally from 50C to 150C.

When the PVA film 4 is manufactured by the above-mentioned drum film forming machine, the discharge port 11 of the die 1 and the film forming material 2
Is supplied, the distance L to the surface of the first drum 3 that comes into contact first must be 0.1 to 10 mm,
Preferably 0.1 to 8 mm, 0.1 to 5 mm
Is more preferable, and further preferably 0.1 to 3 mm. As the distance L is smaller, a PVA film 4 having a uniform thickness and excellent smoothness can be obtained. At this time, if the distance L is larger than 10 mm, the film forming raw material 2 does not contact the first drum 3 uniformly, so that the obtained PVA
The thickness uniformity of the film 4 is impaired. On the other hand, when the interval L is less than 0.1 mm, it is very difficult to form a film so that the discharge port 11 of the die 1 does not contact the surface of the first drum 3. It is important that the distance L is maintained uniformly in the width direction. further,
The difference (W1-W2) between the film width (W1) at the discharge port 11 of the die 1 and the film width (W2) when the film forming raw material comes into contact with the surface of the first drum 3 (hereinafter referred to as necking amount). Is sometimes 0 to 10 cm, more preferably 0 to 6 cm, and still more preferably 0 to 4 cm. As this value is closer to 0, a PVA film 4 having a uniform thickness and excellent smoothness is obtained.
When this value exceeds 10 cm, the film forming raw material 2
PVA film 4 obtained without uniform contact with drum 3
In some cases, the thickness uniformity may be impaired.

When the PVA film 4 is manufactured, the surface temperature of the first drum 3 to which the film forming raw material 2 is supplied is 50
To 110 ° C, more preferably 60 to 105 ° C, even more preferably 70 to 100 ° C. If the temperature of the first drum 3 is lower than 50 ° C., air may enter between the film forming raw material 2 discharged from the discharge port 11 of the die 1 and the first drum 3, and if it is higher than 110 ° C. Since the film forming raw material 2 may foam, it becomes difficult to obtain the PVA film 4 having excellent thickness uniformity. Further, when the PVA film 4 having these disadvantages is processed into a polarizing film, the PVA film 4 may be cut off during stretching or may have stained spots, making it difficult to obtain a polarizing film having excellent uniformity. become.

The thickness of the PVA film 4 is 20 to 15
0 μm is preferable, and 40 to 120 μm is more preferable.
At this time, if the thickness is less than 20 μm, the PVA film 4 may be cut when uniaxially stretched when processed into a polarizing film. On the other hand, if the thickness is more than 150 μm, stretching unevenness occurs at the time of uniaxial stretching to cause staining unevenness or optical unevenness. May be. The width of the PVA film 4 is not particularly limited, but is preferably 2 m or more when used for a large LCD screen.

As the polyvinyl alcohol polymer (PVA) constituting the PVA film of the present invention, a vinyl ester polymer obtained by polymerizing a vinyl ester monomer is saponified, and the vinyl ester unit is replaced with a vinyl alcohol unit. Can be used. Examples of the vinyl ester monomer include vinyl formate, vinyl acetate, vinyl propionate, vinyl valerate, vinyl laurate, vinyl stearate, vinyl benzoate,
Examples thereof include vinyl pivalate and vinyl versatate, and among these, vinyl acetate is preferably used.

When copolymerizing a vinyl ester-based monomer, if necessary, a copolymerizable monomer may be used within a range that does not impair the purpose 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; N-vinylformamide, N-vinyl N-vinylamides such as acetamide and N-vinylpyrrolidone; methyl vinyl ether, ethyl vinyl ether, n-propyl vinyl ether, i-propyl vinyl ether, n-butyl vinyl ether, i
-Butyl vinyl ether, t-butyl vinyl ether,
Vinyl ethers such as dodecyl vinyl ether and stearyl vinyl ether; nitriles such as acrylonitrile and methacrylonitrile; vinyl chloride, vinylidene chloride;
Vinyl halides such as vinyl fluoride and vinylidene fluoride; allyl compounds such as allyl acetate and allyl chloride; maleic acid and its salts or esters; itaconic acid and its salts or esters; vinylsilyl compounds such as vinyltrimethoxysilane Isopropenyl acetate, N-
Examples include N-vinylamides such as vinylformamide, N-vinylacetamide, and N-vinylpyrrolidone.

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, further preferably at least 2,000, more preferably at least 3,500. preferable. 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 the PVA is JIS K
It is measured according to 6726. That is, after PVA is re-saponified and purified, the intrinsic viscosity [η] (unit: dL / g, L is liter) measured in water at 30 ° C. is determined by the following equation. P = ([η] × 10 ³ /8.29) ^{(1 / 0.62)}

The degree of saponification of the PVA constituting the PVA film is 90 mol% in view of the durability of the polarizing film.
Or more, more preferably 95 mol% or more, and 98% or more.
Mole% or more is more preferable. On the other hand, from the viewpoint of the dyeability of the PVA 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 into vinyl alcohol units by saponification. In addition, the saponification degree of PVA was measured by the method described in JIS.

When 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, and one or more of these can be used. Among them, ethylene glycol or glycerin is preferably used from the viewpoint of the effect of improving the stretchability.

The amount of the polyhydric alcohol 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 the 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, carboxylic acid type such as potassium laurate, sulfate type such as octyl sulfate,
Sulfonic acid type anionic surfactants such as dodecylbenzenesulfonate are preferred. Nonionic surfactants include, for example, alkyl ether types such as polyoxyethylene oleyl ether, alkyl phenyl ether types such as polyoxyethylene octyl phenyl ether, alkyl ester types such as polyoxyethylene laurate, and polyoxyethylene lauryl amino. Alkylamine type such as ether, alkylamide type such as polyoxyethylene lauric amide, polypropylene glycol ether type such as polyoxyethylene polyoxypropylene ether, alkanolamide type such as oleic acid diethanolamide, polyoxyalkylene allyl phenyl ether Nonionic surfactants such as allyl phenyl ether type 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 in producing the PVA film is 50 to 90.
% By weight, more preferably 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 more than 90% by weight, the viscosity becomes too low and the thickness uniformity of the PVA film may be impaired.

When manufacturing the PVA film,
In addition to the T die described above, for example, a hopper plate, an I-
Using a discharge device 1 such as a die or a lip coater die, the film forming raw material 2 is discharged from a discharge port 11 to a first drum 3 located on the most upstream side, and volatile components such as water content and organic solvent are discharged on the drum. May be evaporated to form a film, sent to a subsequent process, and further dried and conditioned to adjust to an appropriate PVA film 4 and wound around a winding device 8.

In the present invention, in addition to the extrusion film forming method described above, for example, a cast film forming method in which PVA is dissolved in a solvent and discharged in a solution state from a discharge port of a discharge device to a film forming machine can be used. . Further, as a film forming machine, in addition to the above-described drum film forming machine, a film forming material is supplied from an outlet of a discharging device onto an endless metal belt, and a PVA film formed by the belt is dried or adjusted. It is also possible to use a belt film forming machine which is adjusted by a wet device and wound up by a winding device.

In order to produce a polarizing film from the PVA film of the present invention, for example, the PVA film may be dyed, uniaxially stretched, fixed, 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. Further, each step may be repeated a plurality of times.

The dyeing is performed before the uniaxial stretching, simultaneously with the uniaxial stretching,
Although any method can be used after uniaxial stretching, PVA is preferably dyed in any step prior to uniaxial stretching or during the uniaxial stretching step because the degree of crystallinity tends to increase due to uniaxial stretching and the dyeability may decrease. .

The dye used for dyeing is iodine-potassium iodide or Direct black 17, 19, 154;
brown 44, 106, 195, 210, 223; Direct red 2, 2
3, 28, 31, 37, 39, 79, 81, 240, 242, 247; Direc
t blue 1, 15, 22, 78, 90, 98, 151, 168, 202, 2
36, 249, 270; Direct violet 9, 12, 51, 98; Dir
ect green 1, 85; Direct yellow 8, 12, 44, 86, 8
7; Dichroic dyes such as Direct orange 26, 39, 106 and 107 can be used. Dyeing can be usually performed by immersing the PVA film in a solution containing the dye, but the processing conditions and processing method are not particularly limited.

The uniaxial stretching performed in the length direction of the PVA film can be performed by a wet stretching method or a dry heat stretching method. The uniaxial stretching can be performed in hot water (which may be in a solution containing the dye or in a fixing bath described later) or after absorbing water. It may be performed in air using a PVA film. Stretching is preferably carried out as far as possible to a point shortly before the PVA film is cut, specifically, preferably 4 times or more, particularly preferably 5 times or more. 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 30 to 90 ° C. when the PVA film is stretched in warm water (wet stretching), and 50 to 1 ° C. when the dry heat stretching is performed.
80 ° C. is preferred. The thickness of the stretched PVA film is preferably from 3 to 75 μm, more preferably from 10 to 50 μm.

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

The drying treatment (heat treatment) of the PVA film is 3
It is preferably performed at 0 to 150 ° C, more preferably at 50 to 150 ° C.

The polarizing film obtained as described above is usually used as a polarizing plate by laminating an optically transparent protective film having mechanical strength on both surfaces or one surface thereof. As the protective film, a cellulose acetate film, an acrylic film, a polyester film or the like is usually used.

[0031]

EXAMPLES The present invention will now be described specifically with reference to examples, but the present invention is not limited to these examples. The production of the polarizing films described in Examples and Comparative Examples was performed by the following methods, and the thickness unevenness and dichroic ratio were measured by the following methods.

Preparation method of polarizing film: Preliminary swelling, dyeing, washing, uniaxial stretching, fixing, drying,
The films were processed in the order of heat treatment to produce a polarizing film. That is, the PVA film was immersed in water at 30 ° C. for 1 minute to pre-swell, and the weight ratio of iodine / potassium iodide was reduced to 1/10.
And immersed in a 4% by weight aqueous solution of boric acid at 30 ° C. for 4 minutes appropriately selected at an iodine concentration of 30 to 50 g / L so that the transmittance of the polarizing film is 43 to 44%,
It was immersed in water at 30 ° C. for 0.5 minutes for washing, and uniaxially stretched 5 times in a 50% aqueous solution of 4% by weight of boric acid. 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.

Thickness unevenness of PVA film: Thickness unevenness is caused by film thickness nest tester KG601A manufactured by Anritsu Corporation.
Was used to measure the thickness profile of the PVA film in the TD direction at three locations at 25 cm intervals in the MD direction, 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 the degree of polarization P (%) were determined from the following equation. Dichroic ratio = log (TS / 100−TS / 100 × P /
100) / log (TS / 100 + TS / 100 × P /
100)

Example 1 PVA 10 having a degree of saponification of 99.9 mol% and a degree of polymerization of 2400
0 parts by weight, 13 parts by weight of glycerin, 0.1 part by weight of lauric acid diethanolamide and a volatile matter content of 70
A film-forming material of weight% was formed on a drum film forming machine using a T-die. At this time, the distance L from the discharge port of the die to the first drum was 3 mm, and the necking amount (W1-W2) was 2 cm. Further, the surface temperature of the first drum is set to 90 ° C.
The raw material for film formation on the drum surface was dried with hot air at 90 ° C., and PVA having an average thickness of 75.3 μm and a thickness unevenness of 1.5 μm was obtained.
A film was obtained.

When this PVA film was processed into a polarizing film, the resulting polarizing film had a thickness of 28 μm at the center, a transmittance of 43.3%, and a degree of polarization of 9%.
The dichroic ratio was 9.5% and the dichroic ratio was 41.9. A 50 cm square of this polarizing film was placed at an angle of 45 ° between the two polarizing plates in a crossed Nicols state, and the transmitted light was visually observed.

Example 2 PVA10 having a degree of saponification of 99.9 mol% and a degree of polymerization of 4000
0 parts by weight, 15 parts by weight of glycerin, 0.1 part by weight of lauric acid diethanolamide and a volatile content of 85 consisting of water
The film forming raw material of weight% was formed by a belt film forming machine using a T die. At this time, the distance L from the discharge port of the die to the belt was 5 mm, and the necking amount was 4 cm. Further, the temperature of the belt was set to 90 ° C., and the film forming material on the belt surface was dried with hot air at 100 ° C. to obtain an average thickness of 74.9 μm.
m, a PVA film having a thickness unevenness of 2.5 μm was obtained.

When this PVA film was processed into a polarizing film, the obtained polarizing film had a thickness of 28 μm at the center, a transmittance of 43.5%, and a degree of polarization of 9
The dichroic ratio was 9.5% and the dichroic ratio was 43.5. A 50 cm square of this polarizing film was placed at an angle of 45 ° between the two polarizing plates in a crossed Nicols state, and the transmitted light was visually observed.

Example 3 PVA 10 having a saponification degree of 99.9 mol% and a polymerization degree of 1700
0 parts by weight, 10 parts by weight of glycerin, 0.1 part by weight of lauric acid diethanolamide, and a volatile content of 65 consisting of water.
A film-forming material of weight% was formed on a drum film forming machine using a T-die. At this time, the distance L from the discharge port of the die to the first drum was 5 mm, and the necking amount was 6 cm. Further, the surface temperature of the first drum was set to 80 ° C., and the film forming material on the drum surface was dried with hot air of 85 ° C. to obtain a PVA film having an average thickness of 75.6 μm and a thickness unevenness of 2.8 μm.

When this PVA film was processed into a polarizing film, the obtained polarizing film had a central part thickness of 27 μm, a transmittance of 43.1%, and a degree of polarization of 9%.
The dichroic ratio was 9.1% and the dichroic ratio was 36.3. A 50 cm square of this polarizing film is placed at an angle of 45 ° between two polarizing plates in a crossed Nicols state, and when the transmitted light is visually observed, an elongated ellipse having a width of 0.5 cm, a length of 3 cm, a width of 1 cm, and a length of 5 cm is obtained. Two very thin optical spots were observed.

Comparative Example 1 PVA10 having a degree of saponification of 99.9 mol% and a degree of polymerization of 2400
0 parts by weight, 13 parts by weight of glycerin, 0.1 part by weight of lauric acid diethanolamide, and a volatile content of 72 parts consisting of water
A film-forming material of weight% was formed on a drum film forming machine using a T-die. At this time, the distance L from the discharge port of the die to the first drum was 12 mm, and the necking amount was 8 cm. Further, the surface temperature of the first drum was set to 95 ° C., and the film forming raw material on the drum surface was dried with hot air at 95 ° C. to obtain a PVA film having an average thickness of 74.8 μm and an uneven thickness of 7.9 μm.

When this PVA film was processed into a polarizing film, the obtained polarizing film had a central part thickness of 27 μm, a transmittance of 43.2%, and a degree of polarization of 9%.
The dichroic ratio was 9.5% and the dichroic ratio was 41.3. A 50 cm square of this polarizing film is placed at an angle of 45 ° between two polarizing plates in a crossed Nicols state, and when the transmitted light is visually observed, an elliptical or irregular optical spot having a width of 1 to 5 cm and a length of 5 to 15 cm is obtained. Were confirmed.

Comparative Example 2 PVA10 having a degree of saponification of 99.9 mol% and a degree of polymerization of 4000
0 parts by weight, 20 parts by weight of glycerin, 0.1 part by weight of lauric acid diethanolamide and a volatile content of 82
The film forming raw material of weight% was formed by a belt film forming machine using a T die. At this time, the distance L from the discharge port of the die to the belt was 15 mm, and the necking amount was 10 cm. The temperature of the belt was set to 90 ° C., and the film forming material on the belt surface was dried with hot air at 100 ° C.
A PVA film having a thickness of 5.2 μm and a thickness unevenness of 10.1 μm was obtained.

When this PVA film was processed into a polarizing film, the resulting polarizing film had a thickness at the center of 28 μm, a transmittance of 43.1%, and a degree of polarization of 9%.
9.6%, dichroic ratio was 42.3. A 50 cm square of this polarizing film is placed at an angle of 45 ° between two polarizing plates in a crossed Nicols state, and when the transmitted light is visually observed, an elliptical or irregular optical spot having a width of 2 to 5 cm and a length of 5 to 20 mm is obtained. Were confirmed.

Comparative Example 3 PVA 10 having a saponification degree of 99.9 mol% and a polymerization degree of 1700
0 parts by weight, 10 parts by weight of glycerin, 0.1 part by weight of lauric acid diethanolamide, and a volatile content of 65 consisting of water.
A film-forming material of weight% was formed on a drum film forming machine using a T-die. At this time, the distance L from the discharge port of the die to the first drum was 15 mm, and the necking amount was 15 cm. The surface temperature of the first drum was set to 95 ° C., and the film forming material on the drum surface was dried with hot air at 95 ° C. to obtain a PVA film having an average thickness of 74.7 μm and an uneven thickness of 9.8 μm.

When this PVA film was processed into a polarizing film, the resulting polarizing film had a thickness of 28 μm at the center, a transmittance of 43.5%, and a degree of polarization of 9
8.7%, dichroic ratio was 35.5. A 50 cm square of this polarizing film is placed at an angle of 45 ° between two polarizing plates in a crossed Nicols state, and when the transmitted light is visually observed, an elliptical or irregular optical spot having a width of 1 to 4 cm and a length of 3 to 20 cm is obtained. Were confirmed.

Comparative Example 4 PVA10 having a saponification degree of 99.9 mol% and a polymerization degree of 2400
A film forming raw material having a volatile content of 68% by weight, comprising 0 parts by weight, 5 parts by weight of glycerin, 0.1 part by weight of polyoxyethylene lauryl ether, and water, was formed by a drum film forming machine using a T-die. At this time, the interval L from the discharge port of the die to the first drum is 17 mm, and the necking amount is 16 cm.
Met. Further, the surface temperature of the first drum is set to 95 ° C.,
The film forming raw material on the drum surface was dried with hot air at 95 ° C. to obtain a PVA film having an average thickness of 169.7 μm and an uneven thickness of 12.3 μm.

When this PVA film was processed into a polarizing film, the obtained polarizing film had a thickness at the center of 49 μm, a transmittance of 43.5%, and a degree of polarization of 9%.
8.5%, dichroic ratio was 34.3. A 50 cm square of this polarizing film is placed at an angle of 45 ° between two polarizing plates in a crossed Nicols state, and when the transmitted light is visually observed, an elliptical or irregular optical spot having a width of 3 to 7 cm and a length of 5 to 25 mm is obtained. And 8 striped optical spots having a width of 7 cm were confirmed.

The results of Examples 1 to 3 and Comparative Examples 1 to 4 are shown in Table 1 below.

[0050]

[Table 1]

In Table 1 above, L indicates the distance from the discharge port of the die to the first drum or belt. Moreover, in the column of the optical spot of the polarizing film in Table 1 above,
Indicates the most excellent one, ○ indicates a good one, and X indicates an unusable one.

As is clear from the above table, the distance L from the discharge port of the die to the first drum or belt is 10 mm.
When it is larger, the thickness unevenness of the PVA film becomes large, and the optical unevenness when a polarizing film is formed increases. From this, it can be understood that the distance L needs to be 10 mm or less in order to reduce the thickness unevenness of the PVA film and to obtain a polarizing film having less optical unevenness and excellent optical performance.

Although the case of manufacturing a PVA film for a polarizing film has been described above, the film manufacturing method of the present invention can be applied to the manufacture of a PVA film other than a polarizing film.

[0054]

As described above, according to the production method of the present invention, a PV having a uniform thickness and excellent smoothness even in a large area.
A film can be obtained. In particular, when the present invention is used as a method for producing a PVA film for a polarizing film, a polarizing film having few optical spots and excellent optical performance can be obtained.

[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]

11: discharge section, 2: film forming material, 3: drum (first drum), 4: polyvinyl alcohol film (PVA film), L: interval.

Continuation of the front page (72) Inventor Toru Shito 892 Sakuhi-shi, Saijo-shi, Ehime F-term in Kuraray Co., Ltd. AG01 AP06 GA07 GB02 GC02 GC07 GF24 GN01 4F207 AA19 AG01 AP06 KA01 KK64 KK74 KK76 KM13

Claims (4)

[Claims] When producing a polyvinyl alcohol film using a drum film forming machine or a belt type film forming machine, the distance from a discharge port of a film forming raw material containing polyvinyl alcohol to a drum or a belt is 0.1 to 0.1. A method for producing a polyvinyl alcohol film, which has a thickness of 10 mm. 2. The difference (W1-W2) between the film width (W1) at the discharge port of the film forming material and the film width (W2) when the film forming material contacts the drum or the belt.
Is a method for producing a polyvinyl alcohol film having a thickness of 0 to 10 cm. 3. The method for producing a polyvinyl alcohol film according to claim 1, wherein the thickness of the polyvinyl alcohol film is 20 to 150 μm. 4. The method for producing a polyvinyl alcohol film according to claim 1, wherein the polyvinyl alcohol film for a polarizing film is obtained.