JP2002079531A - Method for producing polyvinyl alcohol film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a film which is excellent in thickness uniformity and smoothness even in a large area and especially to provide a method for producing a film which can be a polarizing film excellent in optical performance with optical spots reduced when it is used for producing a film for a polarizing film. SOLUTION: When a polyvinyl alcohol film (a product film) 9 is produced from a film-making raw material containing polyvinyl alcohol by using a drum film-making machine having at least two drums, when the content of the volatile component of a polyvinyl alcohol film (PVA film) 4 reaches 10-50 wt.%, the polyvinyl alcohol film is peeled off from the drum located on the most upstream side, and the speed ratio V2/V1 between the speed V1 of the drum located on the most upstream side and the speed V2 of the drum located in a process in which the content of the volatile component of the polyvinyl alcohol film is less than 10 wt.% for the first time is adjusted to be 1.0-1.3.

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 film which is useful as a material for producing a polarizing film and has a uniform thickness and excellent smoothness.

[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 is from small devices such as calculators and watches in the early stages of development to laptop computers,
Widely used in large screens such as word processors, liquid crystal color projectors, in-vehicle navigation systems, and liquid crystal televisions, and are now being used on large screens. Is required.

[0003] A usual polarizing plate is a polyvinyl alcohol film (hereinafter abbreviated as "PVA film", and polyvinyl alcohol as a raw material thereof is referred to as a polyvinyl alcohol-based polymer, which is abbreviated as "PVA". Is sometimes uniaxially stretched and dyed, and a protective film such as a cellulose triacetate (TAC) film is bonded to a polarizing film produced by 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 The purpose is to make the thickness of the PVA film used as the material of the polarizing plate 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.

An object of the present invention is to provide a method for producing a PVA film which is useful as a material for producing a film for a polarizing plate, has a uniform thickness even in a large area, and has excellent smoothness.

[0006]

In order to solve the above-mentioned problems, a method for producing a PVA film according to the present invention uses a drum film forming machine having two or more drums to convert a polyvinyl alcohol-containing film-forming material into a polyvinyl alcohol. When the alcohol film is manufactured, when the volatile content of the polyvinyl alcohol film reaches 10 to 50% by weight, the polyvinyl alcohol film is peeled off from the drum located on the most upstream side, and further, it is located on the most upstream side. The speed ratio V2 / V1 of the drum speed V1 and the speed V2 of the drum located at the step where the volatile content of the polyvinyl alcohol film became less than 10% by weight for the first time was 1.0 to 1.3.

According to the present invention, a PVA film having a uniform thickness and excellent smoothness even in a large area can be obtained.

Further, a PVA film for a polarizing film is manufactured by this manufacturing method.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. Figure 1 shows PVA for polarizing film
As an example of producing a film, a drum film forming machine that uniformly discharges a film forming raw material (which may contain an organic solvent or the like) composed of a PVA solution or a melt onto a heated drum to form a film is used. Is shown. This film forming machine uses T-die 1
A predetermined amount of the film forming raw material 2 is discharged onto the rotating first drum 3 located at the most upstream side and rotating, and is brought into contact with its circumferential surface to dry the PVA film 4 as an intermediate product.
Subsequently, the PVA film 4 is dried by passing over the circumferential surface of the second drum 5 and further dried by passing through a plurality of drums 6 on the downstream side.
Finally, the product film (PVA film) 9 is taken up by the take-up device 8. This drum coater has a volatile content of 1
After the amount becomes less than 0% by weight, a floating drier, a drier that passes through a roll in the drier, or a humidity controller may be additionally provided. Here, the floating dryer refers to a device that blows hot air from a lower portion, an upper portion, or both of the film instead of drying the film on a drum to dry the film in a floating state. The method of blowing hot air is not particularly limited, but it is preferable to blow hot air by providing a nozzle or a slit. The wind speed is preferably 5 to 80 m / min.
More preferably, it is 0 to 50 m / min. At this time,
The drying section can be separated into several sections.
The floating state includes a method of fixing both ends of the film, such as a clip tenter and a pin tenter, or a method of making the film free, but there is no particular limitation. In addition, a motor, a transmission, or the like is used for driving so that the speed during drying and humidity control can be adjusted. The drying temperature is generally from 50C to 160C.

[0010] When the product film 9 is manufactured by the above-mentioned drum film forming machine, the PVA film 4 is converted to a volatile matter of 10 to 10%.
When it reaches 50% by weight, preferably 15 to 40% by weight, it is peeled off from the first drum 3. If the volatile content is less than 10% by weight, the PVA film 4 may be whitened. On the other hand, if the volatile content is more than 50% by weight, wrinkles may occur on the PVA film, or PVA
The film may be wound and cut. If the product film 9 having whitening or wrinkles is processed into a polarizing film, it is not preferable because it may become stained spots or optical spots.

[0011] The PVA film 4 peeled off by the volatile matter
The speed ratio V2 / V1 of the speed V2 of the drum and the speed V1 of the first drum 3 in the process in which the first time is less than 10% by weight is 1.0 to 1.3, preferably 1.0 to 1.2;
More preferably, it is set to 1.0 to 1.1. This speed ratio is
The smaller one can increase the draw ratio when producing a polarizing film, but if it is smaller than 1.0, the thickness unevenness of the product film 9 becomes large and optical unevenness occurs when the polarizing film is formed. Also, the PVA film 4 may be wound around any one of the second drum 5 and the plurality of drums 6 in which the volatile content of the PVA film 4 does not reach less than 10% by weight and cut, thereby making production impossible. On the other hand, if the speed ratio is larger than 1.3, the desired draw ratio of 4 times or more may not be obtained when manufacturing a polarizing film.

In the present invention, the speed V2 of the drum located in the step where the volatile content of the PVA film is less than 10% by weight for the first time means that the PVA film peeled off from the first drum 3 Is gradually dried on the drum 6 of the second type, and the volatile content is less than 10% by weight for the first time.
This is the speed of one of the drums located in the process after the drum 5.

The speed of the first drum 3 and the speeds of the subsequent drums 5 and 6 are not particularly limited.
/ Min.

When the PVA film 4 is formed into a film, the surface temperature of the first drum 3 from which a predetermined amount of the film forming raw material 2 is discharged is preferably 50 to 110 ° C., and 60 to 10 ° C.
5 ° C is more preferred, and 70 to 100 ° C is even more preferred. If the temperature of the first drum 3 is lower than 50 ° C., air may enter between the discharged film forming material 2 and the first drum 3. If the temperature is higher than 110 ° C., the film forming material 2 foams,
It may be difficult to obtain a product film 9 having excellent thickness uniformity. Further, when the product film 9 having these disadvantages is processed into a polarizing film, the product film 9
May be cut in the middle of stretching or stain spots may occur, which may make it difficult to obtain a polarizing film having excellent uniformity.

The thickness of the product film 9 is 20 to 150.
μm is preferable, and 40 to 120 μm is more preferable. 2
If it is thinner than 0 μm, it may be cut when the product film 9 is uniaxially stretched when processed into a polarizing film,
On the other hand, if it is thicker than 150 μm, stretching spots may occur during uniaxial stretching, resulting in staining spots or optical spots. The width of the product film 9 is not particularly limited, but is preferably 2 m or more when used for a large LCD screen.

PVA constituting the PVA film of the present invention
For example, those obtained by saponifying a vinyl ester-based polymer obtained by polymerizing a vinyl ester-based monomer and using a vinyl ester unit as 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, vinyl pivalate, vinyl versatate, and the like. Of these, vinyl acetate is preferably used.

When copolymerizing a vinyl ester monomer, a copolymerizable monomer may be added, if necessary, within a range that does not impair the spirit of the 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, and octadecyl methacrylate And acrylamide,
Acrylamide derivatives such as N-methylacrylamide, N-ethylacrylamide, N, N-dimethylacrylamide, diacetone acrylamide, acrylamidopropanesulfonic acid and its salts, acrylamidopropyldimethylamine and its salts, N-methylolacrylamide and its derivatives; 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, 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.
It is more preferably at least 2,000, particularly preferably at least 3,500. Further, 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 (Po) of the PVA is determined according to JIS K
It is measured according to 6726. That is, after PVA is re-saponified and purified, it can be obtained from the intrinsic viscosity [η] (unit: deciliter / g) measured in water at 30 ° C. by the following formula. Po = ([η] × 10 ³ /8.29) ^{(1 / 0.62)}

The degree of saponification of the PVA constituting the PVA film is preferably at least 90 mol%, more preferably at least 95 mol%, even more preferably at least 98 mol% from the viewpoint of the durability of the polarizing film. Further, 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 into vinyl alcohol units by saponification. In addition, PV
The degree of saponification of A 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 the 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 be reduced. If the amount is more than 30 parts by weight, the film may be too flexible and the handleability may be reduced.

In 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 such as dodecylbenzenesulfonate are preferable. 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 of these
Species or a combination of two or more can be used.

The amount of the surfactant added is PVA100
0.01 to 1 part by weight, preferably 0.0 to 1 part by weight,
2 to 0.5 part by weight is more preferable, and 0.05 to 0.3 part by weight.
Part by weight is particularly preferred. If less than 0.01 parts by weight,
The effect of improving the stretchability and the dyeability is difficult to appear, and if it is more than 1 part by weight, it is eluted on the film surface, causing blocking, and the handleability may be reduced.

The PVA-containing film-forming raw material used in producing the PVA film has a volatile matter concentration of 50 to 9%.
0% by weight is preferred, and 55-80% by weight is more preferred. If the volatile matter concentration is less than 50% by weight, the viscosity may be high, so that film formation may be difficult. Volatile concentration is 9
If it is more than 0% by weight, the viscosity becomes too low and the uniformity of the thickness of the PVA film tends to be impaired.

In producing the PVA film, besides the above-described T die, for example, a hopper plate, an I die,
Using a lip coater die or the like, the film forming raw material is supplied from these to the peripheral surface of the first drum located at the uppermost stream, and the volatile matter is reduced on this drum to form a film. It is also possible to adjust the humidity to a suitable product film by performing humidity control and wind the film on 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.

Dyeing can be carried out before, during or after uniaxial stretching. However, PVA tends to increase the crystallinity by uniaxial stretching and the dyeing property may be reduced. It is preferred to dye in any step or uniaxial stretching step.

The dyes used for dyeing include iodine-potassium iodide; direct black 17, 19, 154;
Direct Brown 44, 106, 195, 210,
223; Direct Red 2,23,28,31,3
7, 39, 79, 81, 240, 242, 247; Direct Blue 1, 15, 22, 78, 90, 98, 1
51, 168, 202, 236, 249, 270; Direct Violet 9, 12, 51, 98; Direct Green 1, 85; Direct Yellow 8, 12, 4
4, 86, 87; Direct Orange 26, 39, 1
Dichroic dyes such as 06 and 107 can be used alone or in a mixture of two or more. Dyeing is generally performed by immersing the PVA film in a solution containing the dye, but the processing conditions and processing method are not particularly limited, such as mixing with the PVA film to form a film. Absent.

For the uniaxial stretching performed in the length direction of the PVA film, a wet stretching method or a dry heat stretching method can be used. 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 performed as far as possible, just before the PVA film is cut, specifically, preferably 4 times or more, and 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 film after stretching is 3 to
75 μm is preferable, and 10 to 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 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 a protective film having optical transparency and mechanical strength on both surfaces or one surface thereof. As the protective film, usually, a cellulose acetate film, an acrylic film, a polyester film, or the like is used.

[0035]

EXAMPLES The present invention will now be described specifically with reference to examples, but the present invention is not limited to these examples. Processing of the polarizing film, measurement of volatile matter during the film forming process, evaluation of thickness unevenness, and calculation of dichroic ratio described in Examples and Comparative Examples were carried out by the following methods.

Processing Method of Polarizing Film A PVA film was preliminarily swollen, dyed, washed, uniaxially stretched, fixed, dried and heat-treated in the order given to form a polarizing film. That is, the PVA film was placed in water at 30 ° C. for 1 hour.
And pre-swelled by immersion for 30 minutes, fixing the weight ratio of iodine concentration / potassium iodide to 1/50, and adjusting the iodine concentration to 30 to 50 g / l so that the transmittance of the polarizing film becomes 43 to 44%.
4% by weight of boric acid at 30 ° C appropriately selected in liter range
The film was immersed in an aqueous solution for 4 minutes, immersed in water at 30 ° C. for 0.5 minute, and washed. The stretch ratio of the PVA film was as high as possible in an aqueous solution of 4% by weight of boric acid at 50 ° C. (PVA Uniaxial stretching was performed (until shortly before the film was cut). Subsequently, the substrate was immersed in an aqueous solution of 40 g / liter of potassium iodide and 40 g / liter of boric acid at 40 ° C. for 5 minutes to perform a fixing treatment. Thereafter, the PVA film was taken out and dried with hot air at 40 ° C. under a constant length.

Measurement of volatile matter during film formation process Fiber type infrared moisture meter (IM-3SCV MODEL)
-1900 (L), manufactured by Fuji Work Co., Ltd.), the volatile components (moisture) on the drum were measured.

Thickness unevenness of the PVA film Thickness unevenness was determined by using a film thick nest tester (KG601A,
Using Anritsu Corporation)
m, three points were measured at intervals of 25 cm in the flow 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 measured in a C light source and a 2 degree visual field using a spectrophotometer in accordance with the standard of the Electronic Machine Manufacturers Association of Japan (EIAJ) LD-201-1983.
The transmittance was calculated from the following equation using the calculated transmittances TS (%) and P (%). Dichroic ratio = log (TS / 100−TS / 100 × P /
100) / log (TS / 100 + TS / 100 × P /
100)

Example 1 Using a drum film forming machine 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 2400, and glycerin 12
Parts by weight of a film forming raw material 2 consisting of 0.1 part by weight of lauric acid diethanolamide and water and having a volatile content of 73% are discharged from the T-die 1 onto a first drum 3 having a surface temperature of 85 ° C. 3 was dried with hot air at 100 ° C. to obtain an average thickness of 74.8 μm and a thickness unevenness of 2.7.
A μm product film 9 was obtained. At this time, the first drum 3
The volatile content of the PVA film 4 when peeled off from the substrate was 17% by weight, and the speed V1 of the first drum 3 was 4.0 m / min.
The step in which the volatile content is less than 10% by weight is the third drum 6, counting from the first drum 3 on the most upstream side, at a speed V2 of 4.3 m / min and a speed ratio V2 / V1. Was 1.08.

When this product film was processed into a polarizing film, the stretching ratio of this polarizing film was 5.
The transmittance was 43.3%, the degree of polarization was 99.6%, and the dichroic ratio was 43.6. 50c of this polarizing film
45 m between two polarizing plates in a crossed Nicols state
When the transmitted light was visually observed at an angle of?, Almost no optical spot was observed, and the transmitted light was good.

Example 2 100 parts by weight of PVA having a degree of saponification of 99.9 mol% and a degree of polymerization of 4,000, and glycerin 18 were prepared using the drum film forming machine shown in FIG.
The film forming raw material 2 consisting of 0.1 parts by weight of polyoxyethylene lauryl ether and water and having a volatile content of 80% is quantitatively discharged from the T-die 1 onto the first drum 3 having a surface temperature of 90 ° C. The film forming raw material 2 discharged to the drum 3
The product film 9 was dried with hot air at 0 ° C. to have an average thickness of 75.9 μm and an uneven thickness of 2.2 μm. At this time, the first
The volatile content of the PVA film 4 when peeled from the drum 3 is 28% by weight, and the speed V1 of the first drum 3 is 3.0 m / min. In addition, the step in which the volatile content is less than 10% by weight includes
Seventh drum 6 counting from first drum 3 on the most upstream side
The speed V2 is 3.5 m / min and the speed ratio V2 /
V1 was 1.17.

When this product film was processed into a polarizing film, the stretching ratio of this polarizing film was 5.
At 6, the transmittance was 43.5%, the degree of polarization was 99.6%, and the dichroic ratio was 45.0. 50c of this polarizing film
45 m between two polarizing plates in a crossed Nicols state
When the transmitted light was visually observed at an angle of?, Almost no optical spot was observed, and the transmitted light was good.

Example 3 100 parts by weight of PVA having a saponification degree of 99.9 mol% and a polymerization degree of 1700, and glycerin 10 were prepared by using the drum film forming machine shown in FIG.
Parts by weight of a film-forming material 2 consisting of 0.1 parts by weight of lauric acid diethanolamide and water and having a volatile content of 70% are discharged from a T-die 1 onto a first drum 3 having a surface temperature of 85 ° C. 3 was dried with hot air at 85 ° C. to obtain an average thickness of 75.3 μm and a thickness unevenness of 2.0 μm.
m of product film 9 was obtained. At this time, the volatile content of the PVA film 4 when peeled from the first drum 3 is 30% by weight, and the speed V1 of the first drum 3 is 7.0 m / min. The step in which the volatile content is less than 10% by weight is the ninth drum 6, counting from the first drum 3 on the most upstream side, at a speed V2 of 8.7 m / min and a speed ratio V2 / V1. Is 1.
24.

When this product film was processed into a polarizing film, the stretching ratio of this polarizing film was 5.
It was 4 times, the transmittance was 43.1%, the degree of polarization was 99.5%, and the dichroic ratio was 40.7. 50c of this polarizing film
45 m between two polarizing plates in a crossed Nicols state
When the transmitted light was visually observed at an angle of 1, one very thin streak-like optical spot was observed.

Comparative Example 1 A film-forming raw material 2 similar to that of Example 1 was placed on a T-die 1 to a surface temperature of 8
The product film having a mean thickness of 74.6 μm and a thickness unevenness of 3.5 μm is discharged by discharging a fixed amount onto the first drum 3 at 5 ° C., and further drying the film forming raw material 2 discharged onto the first drum 3 with hot air at 85 ° C. 9 was obtained. At this time, the volatile content of the PVA film 4 when peeled from the first drum 3 is 15% by weight, and the speed V1 of the first drum 3 is 4.0 m / min. The step in which the volatile content is less than 10% by weight is a third drum 6, counting from the first drum 3 on the most upstream side, at a speed V2 of 3.8 m / min and a speed ratio V2 / V1. Was 0.95.

When this product film was processed into a polarizing film, the stretching ratio of this polarizing film was 5.
Eight times, the transmittance was 43.4%, the degree of polarization was 99.6%, and the dichroic ratio was 44.3. 50c of this polarizing film
45 m between two polarizing plates in a crossed Nicols state
When the transmitted light is visually observed at an angle of
Two elliptical and irregular optical spots having a length of 5 cm to 7 cm and two band-shaped optical spots having a width of 0.5 to 1 cm were confirmed.

COMPARATIVE EXAMPLE 2 The same film forming raw material 2 as in Example 1 was applied from a T-die 1 to a surface temperature of 8
A fixed amount is discharged onto the first drum 3 at 5 ° C., and the film forming raw material 2 discharged onto the first drum 3 is dried with hot air at 100 ° C. to obtain a product film having an average thickness of 75.2 μm and a thickness unevenness of 1.9 μm. 9 was obtained. At this time, the volatile content of the PVA film 4 when peeled from the first drum 3 is 19% by weight, and the speed V1 of the first drum 3 is 4.0 m / min. The step in which the volatile content is less than 10% by weight is the fourth drum 6, counting from the first drum 3 on the most upstream side, at a speed V2 of 5.5 m / min and a speed ratio V2 / V1. Was 1.38.

When the product film was processed into a polarizing film, the stretching ratio of the polarizing film was 4.5.
The transmittance was 43.2%, the degree of polarization was 99.0%, and the dichroic ratio was 36.0. 50cm of this polarizing film
When the transmitted light is visually observed with the four sides placed at an angle of 45 ° between two polarizing plates in a crossed Nicols state, an extremely thin elliptical and irregular optical spot having a width of 1 to 3 cm and a length of 3 to 5 cm is obtained. Were confirmed.

Comparative Example 3 A film-forming raw material 2 similar to that in Example 2 was placed on a T-die 1 to a surface temperature of 9
A fixed amount is discharged onto the first drum 3 at 0 ° C., and the film forming raw material 2 discharged onto the first drum 3 is dried with hot air at 120 ° C. to obtain a product film having an average thickness of 74.2 μm and an uneven thickness of 4.1 μm. 9 was obtained. At this time, the volatile content of the PVA film 4 when peeled from the first drum 3 is 27% by weight, and the speed V1 of the first drum 3 is 3.0 m / min. The step in which the volatile content is less than 10% by weight is the seventh drum 6, counting from the first drum 3 on the most upstream side, at a speed V2 of 2.8 m / min and a speed ratio V2 / V1. Was 0.93.

When this product film was processed into a polarizing film, the stretching ratio of this polarizing film was 5.
The transmittance was 43.2%, the degree of polarization was 99.8%, and the dichroic ratio was 47.9. 50c of this polarizing film
45 m between two polarizing plates in a crossed Nicols state
When the transmitted light is visually observed at an angle of
Four elliptical and irregular optical spots of 5 cm to 15 cm in length were observed.

Comparative Example 4 A film-forming raw material 2 similar to that of Example 3 was placed on a T-die 1 to a surface temperature of 8
The product film having an average thickness of 75.5 μm and a thickness unevenness of 1.8 μm is discharged by discharging a fixed amount onto the first drum 3 at 5 ° C. and further drying the film forming raw material 2 discharged onto the first drum 3 with hot air at 85 ° C. 9 was obtained. At this time, the volatile content of the PVA film 4 when peeled from the first drum 3 is 33% by weight, and the speed V1 of the first drum 3 is 7.0 m / min. In the step in which the volatile content is less than 10% by weight, the speed V2 is 10.0 m / min and the speed ratio V2 / V1 is the tenth drum 6 counting from the first drum 3 on the most upstream side. Was 1.43.

When this product film was processed into a polarizing film, the stretching ratio of this polarizing film was 3.
At 1, the transmittance was 43.0%, the degree of polarization was 98.2%, and the dichroic ratio was 30.8. 50c of this polarizing film
45 m between two polarizing plates in a crossed Nicols state
When the transmitted light is visually observed at two angles, two very thin elliptical and irregular optical spots with a width of 2 to 3 cm and a length of 3 to 10 cm, and two streaky optical spots are confirmed. Was done.

Comparative Example 5 In Example 1, when the film was formed at a speed of the first drum 3 of 15 m / min, the volatile content of the PVA film 4 when peeled from the first drum 3 was 54% by weight. , P
The VA film 4 was wound around the second drum 5 and cut, and the film could not be formed.

Comparative Example 6 A film-forming raw material 2 similar to that of Example 1 was placed on a T die 1 at a surface temperature of 9
A fixed amount of the film is discharged onto the first drum 3 at 0 ° C., and the film forming raw material 2 discharged onto the first drum 3 is dried with hot air at 120 ° C. to obtain a product film having an average thickness of 75.0 μm and a thickness irregularity of 3.0 μm. 9 was obtained, but the product film 9 was whitened. At this time, the PVA peeled off from the first drum 3
The volatile content of the film 4 is 9% by weight, and the speed V of the first drum 3 is
1 is 4.0 m / min. Further, the speed V2 of the second drum 5 having a volatile content of less than 10% by weight was 3.8 m / min, and the speed ratio V2 / V1 was 0.95.

When this product film was processed into a polarizing film, the stretching ratio of this polarizing film was 5.
The transmittance was 43.6%, the degree of polarization was 99.5%, and the dichroic ratio was 43.9. However, staining spots due to whitening of the PVA film were confirmed, and the use as a polarizing plate was inappropriate.

Table 1 shows the results of Examples 1 to 3 and Comparative Examples 1 to 6.

[0058]

[Table 1]

In Table 1, the speed ratio V2 / V1 is the first
The speed V1 of the drum 3 and the volatile content of the PVA film 4 are 10
It shows the speed ratio of the speed V2 of the drum located in the process after the second drum 5 which is less than the weight%. In each column of the above table, ◎ indicates the most excellent, 、 indicates a good one, Δ indicates an unfavorable one, and X indicates an unusable one.

As is clear from Table 1, when the speed ratio of the speed of the first drum 3 to the speed of the drum in the step in which the volatile content of the PVA film 4 is less than 10% by weight is smaller than 1.0, the PVA film becomes Thickness unevenness increases, and optical unevenness when a polarizing film is formed increases. In addition, the speed ratio is set to 1.3.
If it is larger, the stretching ratio of the polarizing film decreases,
The dichroic ratio decreases and the optical performance deteriorates. From this, it is understood that the speed ratio needs to be 1.0 to 1.3 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. it can.

[0061]

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 film forming machine used for a method of manufacturing a PVA film according to an embodiment of the present invention.

[Explanation of symbols]

2 ... film forming raw material, 3 ... drum (first drum), 4 ... polyvinyl alcohol film (PVA film), 9 ... polyvinyl alcohol film (product film).

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Toru Shimitsu 892 Sakuhi-shi, Saijo-shi, Ehime F-term in Kuraray Co., Ltd. GN21 GN29

Claims (2)

[Claims] When a polyvinyl alcohol film is produced from a film forming material containing polyvinyl alcohol using a drum film forming machine having two or more drums, the volatile content of the polyvinyl alcohol film is reduced to 10 to 50% by weight. At that point, the polyvinyl alcohol film is peeled off from the drum located on the most upstream side, and the speed V1 of the drum located on the most upstream side and the volatile content of the polyvinyl alcohol film are less than 10% by weight for the first time. Speed ratio V2 / V of the speed V2 of the drum located in the set process
1. The method for producing a polyvinyl alcohol film, wherein 1 is 1.0 to 1.3. 2. The method for producing a polyvinyl alcohol film according to claim 1, which is a method for producing a polyvinyl alcohol film for a polarizing film.