JP2002166437A - Method for producing polyvinyl alcohol film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently produce a polyvinyl alcohol film which is useful as a raw material for producing a film for a polarization plate and excellent in thickness uniformity. SOLUTION: The polyvinyl alcohol film 4 is produced by forming jacket structure in which a spiral channel 10 through which the heating medium M of a heat source is passed is formed in the peripheral part of a drying drum 3 (5 and 6) in the drum and using the metal drum in which the temperature spot in the direction to be a film width of a film-making raw material 2 discharged on the drum is 10 deg.C or below, and the difference between the average temperature in the direction to be the film width of the raw material 2 and the average temperature of the medium M is 10 deg.C or below.

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 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 Conventionally, there has been known a manufacturing method using a drum film forming machine for forming a film by discharging a film forming material onto a rotating drying drum and drying it. In this drum film forming machine, a polyvinyl alcohol film (hereinafter, referred to as polyvinyl alcohol) (hereinafter, referred to as polyvinyl alcohol-based polymer, which may be abbreviated as "PVA") is used. Is sometimes abbreviated as "PVA film") as a drying drum in the past, a type in which a heating medium is supplied as a heat source to a tank-type metal drum having a hollow inside without a special structure. Was used.

[0003]

However, in the conventional drying drum, in order to make the drum surface temperature uniform, the supply amount of the heat medium is increased, the heat medium is supplied from both sides of the drum, or the heat medium is supplied. The medium supply port was extended and supplied to the center of the drum.However, when the heat medium was not sufficiently filled in the drum, or when the latent heat of Due to the influence, the surface temperature of the film forming raw material was lowered, and temperature unevenness occurred in the direction of the film width of the film forming raw material and in the flow direction.

Accordingly, an object of the present invention is to solve the above problems and efficiently produce a PVA film having excellent thickness uniformity, which is useful as a material for producing a polarizing plate film.

[0005]

Means for Solving the Problems The inventors of the present invention have made intensive studies to solve the above-mentioned problems, and as a result, have found that a method for producing a PVA film by discharging a film-forming raw material onto a rotating drying drum and drying it is performed. The drying drum has a jacket (double) structure in which a spiral flow path for flowing a heat medium as a heat source is provided around the outer periphery of the drying drum. A metal drum having a temperature unevenness of 10 ° C. or less and a difference between the average temperature of the film forming material in the direction of the film width and the average temperature of the heating medium of 10 ° C. or less was used.

The spiral number of the metal drum is 5 to 30.
The angle of the acute angle between the axis of the metal drum and the spiral flow path is preferably 50 to 88 degrees, and the thickness of each partition wall of the spiral flow path is 3 to 88 degrees.
It is preferable that a flow path extending in the axial direction is provided in the main shaft portion of the metal drum, which is connected to a spiral flow path in the outer peripheral portion of the metal drum. In addition, in order to manufacture a PVA film for obtaining a large-area polarizing film for a large-screen liquid crystal display, the outer diameter of the metal drum is 2.0 to 4.0 m, and the width (length in the axial direction) is large. It is preferably from 2.0 to 4.5 m.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows that a film forming raw material (which may contain an organic solvent or the like), which is a PVA solution or a melt, used in the method of manufacturing a PVA film for a polarizing film according to the present invention is uniformly placed on a heated drum. FIG. 1 is a schematic front view showing an example of a drum film forming machine for discharging a film to form a film by drying. This film forming machine feeds a fixed amount of film forming raw material 2 from T-die 1,
The PVA film 4 is discharged onto the rotating first drum 3 located at the most upstream side and rotating, and is brought into contact with the circumferential surface thereof to dry the PVA film 4. Subsequently, the PVA film 4 is dried by passing over the circumferential surface of the second drying drum 5 and further dried by passing through the drying drum 6 on the downstream side.
Is wound on a winding device 8. The drum film forming machine may be provided with a floating drying device, a humidity control device and the like. The speed of each drive is adjusted using a motor, a transmission, or the like. Drying temperature is 50 ° C ~ 150
C is common.

FIG. 2 is a side view showing an example of the metal drum of FIG. 1, and FIG. 3 is a longitudinal sectional view of FIG. As shown in FIGS. 2 and 3, the metal drum (the first drying drum 3, the second drying drum 5, and the drying drum 6) has a spiral flow path 10 concentric with the drum, in which the heat medium M flows through the outer periphery of the drum. Has a jacket (double) structure. The flow path 10 includes a drum outer peripheral wall 3a and a drum inner peripheral wall 3b forming a drum outer peripheral surface.
The inner wall 3b of the drum is supported by the drum main shaft 12 at the front and rear ends via end walls 3c and 3d. In FIG. 2, θ indicates the angle on the acute angle side between the drum axis O and the spiral flow path 10. In this example, the number of spiral strips is 8, and the flow path 10 has eight flow paths a to h. As shown in FIG. 3, for example, the drum main shaft portion 12 is a double tube,
In the outer cylinder and one end wall 3c, the heat medium M
A first flow path 13 for introducing the heat medium M from the flow path 10 in the inner cylinder and the other end wall 3d. It has become. The flow paths 13 and 14 and the spiral flow path 10 on the outer peripheral portion of the drum are connected at front and rear ends of the flow path 10, respectively, to form a series of paths for the heat medium M in the metal drum. A heat medium M whose temperature is controlled by a temperature control device (not shown) is supplied from a first flow path 13 in an outer cylinder at one end of the drum main shaft portion 12 to supply each spiral flow path 10.
After flowing through (a-h), the fluid flows into the second flow path 14 in the inner cylinder, and is returned from one end of the drum main shaft portion 12 to the temperature control device and circulated. A portion S surrounded by the drum inner peripheral wall 3b, the end walls 3c and 3d, and the drum main shaft portion 12 is hollow. In this example, all of the metal drums (the first drying drum 3, the second drying drum 5, and the drying drum 6) have the structure shown in FIGS. You may do it.

FIG. 4 is a longitudinal sectional view showing another example of the metal drum of FIG. In this example, the drum main shaft portion 12A is a double pipe having two cylinders provided at different positions in the axial direction, and one inside the inner cylinder and one inside the end wall 3c.
First flow path 14A for introducing heat medium M into flow path 10
Is formed in the outer cylinder and in the other end wall 3d, a second flow path 13A for drawing out the heat medium M from the flow path 10, and an opening 15 at one end in the second flow path 13A. It has a jacket structure in which a third flow path 14B in the other inner cylinder connected through the third flow path is formed. In this case, the heat medium M is supplied from the first flow path 14A in the inner cylinder at one end of the drum main shaft portion 12A and flows through each of the spiral flow paths 10 (a to h). It flows from the second flow path 13A to the third flow path 14B in the inner cylinder, and returns from the other end of the drum main shaft portion 12 to the temperature control device to circulate. Other configurations are the same as those in FIGS.

As shown in FIGS. 2 to 4, it is preferable to flow the heat medium also in the flow path of the drum main shaft portion. In some cases, the thermal expansion of the drum main shaft portion differs from that of the main drum portion, and distortion occurs on the drum surface and the inner surface, thereby deforming the metal drum. There is no particular limitation on the flow path, flow direction, and the like of the heat medium installed on the drum main shaft. In order to further reduce the temperature unevenness on the surface of the metal drum, a structure in which a heat medium is supplied from both side surfaces may be adopted.

Examples of the heat medium that can be used as a heat source for the metal drum shown in FIGS. 2 to 4 include heat medium oil, steam, water, glycerin, ethylene glycol, silicone oil, a mixture of water and glycerin, and water and ethylene glycol. And the like, and water (warm water) is particularly preferable.

When producing a PVA film, the film-forming raw material 2 discharged onto the first drying drum 3 (metal drum)
Is 10 ° C. or less, preferably 8 ° C. or less, more preferably 6 ° C. or less, and more preferably 4 ° C. or less.
C. or lower is more preferable. When the temperature distribution exceeds 10 ° C., the discharged film-forming raw material 2 does not uniformly contact the dried first drum 3, so that it is difficult to obtain a PVA film having excellent thickness uniformity. Since the smaller the temperature unevenness is, the more uniform the PVA film obtained after drying is,
The smaller the temperature unevenness, the better.

The difference T2-T1 between the average temperature T1 in the direction of the film width of the film-forming raw material 2 discharged onto the first drying drum 3 and the average temperature T2 of the heat medium is 10 ° C. or less, and 8
C. or less, more preferably 6 C. or less. When the temperature difference T2−T1 exceeds 10 ° C., the drying efficiency of the film forming raw material 2 decreases, and the drying may not be sufficient and the thickness uniformity may be impaired. The smaller the temperature difference T2-T1, the more preferable.

In the present invention, in order to reduce temperature unevenness in the direction of the film width of the film forming raw material discharged onto the metal drum and to reduce the difference between the average temperature in this direction and the average temperature of the heat medium. , The metal drum, as described above,
In addition to having a jacket structure provided with a spiral flow path through which a heat medium as a heat source flows around the outer periphery of the drum, it has the following configuration mainly in the width direction (axial direction) of the metal drum.
The width of the metal drum corresponds to the width of the PVA film.

The number of spiral strips of the metal drum is 5 to 30.
And 7 to 25 are preferable, and 8 to 20 are more preferable. If the constant is smaller than 5, the number of drum rotations of the flow path may increase and the flow path may become longer, or the flow velocity of the heat medium may decrease, resulting in a large temperature unevenness in the width direction.
If it exceeds, the number of partition walls in the flow channel increases, so that temperature unevenness may occur.

The angle θ of the acute angle between the axis of the metal drum and the spiral flow path is 50 to 88 degrees,
86 degrees is preferable and 70 to 84 degrees is more preferable. If the angle is smaller than 50 degrees, the flow path becomes shorter and the temperature unevenness in the circumferential direction may become larger. If the angle exceeds 88 degrees, the flow path becomes longer and the temperature unevenness in the width direction becomes larger. May be.

The thickness of each partition in the spiral flow path of the metal drum is 3 to 20 mm, preferably 4 to 10 mm, more preferably 5 to 8 mm. The thickness is 3mm
If the thickness is smaller, the strength may be weakened and deformed at the time of processing. If the thickness exceeds 20 mm, heat conduction may be deteriorated and temperature unevenness may occur.

The outer diameter of the metal drum is 2.0 to 4.0 m.
And preferably 2.5 to 4.0 m, and 3.0 to 4.0 m.
m is more preferred. When the diameter is smaller than 2.0 m, PV
The A film may not be sufficiently dried, and the thickness uniformity may be impaired. PV obtained after drying as the outer diameter is larger
Since the uniformity of the A film is excellent, the larger one is preferable, but if it exceeds 4.0 m, there is a transportation problem.

The width (length in the axial direction) of the metal drum is 2.
0 to 4.5 m, preferably 3.0 to 4.5 m,
3.5 to 4.5 m is more preferable. The larger the width is, the wider the PVA film to be a large area polarizing film for a large-screen liquid crystal display. Further, since both ends of the drum are easily affected by the surrounding atmosphere, it is preferable that the width of the discharged film-forming material is larger than the width in the film width direction. The width is 4.5m
If it exceeds, it may be difficult to produce a PVA film having excellent thickness uniformity.

The flow rate of the heat medium flowing in the spiral flow path of the metal drum is not particularly limited, but is 1.0 to 3.0.
0 m / sec is preferred. If the flow velocity is less than 1.0 m / sec, temperature unevenness may occur in the width direction due to the latent heat of vaporization of the film forming raw material, and even if the flow velocity exceeds 3.0 m / sec, the uniformity of temperature changes. Only the pressure loss in the flow path increases without the need to improve the strength of the metal drum.
On the contrary, it leads to an increase in cost, which is uneconomical.

When the metal drum is used as a first drying drum to produce a PVA film from a film-forming material, the surface temperature of the drum is preferably 50 to 110 ° C.
0 to 105 ° C is more preferable, and 70 to 100 ° C is further preferable. If the temperature of the drum is lower than 50 ° C., air may bite between the discharged film forming material and the drum, and if the temperature is higher than 110 ° C., the film forming material may foam, so that the thickness uniformity may be increased. It is difficult to obtain an excellent PVA film. In addition, P which has these disadvantages
When processing the VA film into a polarizing film, the PVA film may be cut during stretching, or stained spots may occur,
It becomes difficult to obtain a polarizing film having excellent uniformity.

The peripheral speed of the first drying drum is not particularly limited, but is preferably adjusted in the range of 1 to 40 m / min.

As the vinyl alcohol polymer (PVA) constituting the PVA film according to the present invention, a vinyl ester polymer obtained by polymerization of 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 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, 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 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 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 (P) of the PVA is 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. P = ([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%, further preferably at least 98 mol%, from the viewpoint of the durability of the polarizing film. Further, the content is preferably 99.99 mol% or less from the viewpoint of dyeability of the film. 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, diglycerin, propylene glycol, diethylene glycol, triethylene glycol,
Examples thereof include tetraethylene glycol and trimethylolpropane, 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 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 diethanolamide oleate, polyoxyalkylene allyl phenyl ether Nonionic surfactants such as the 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 volatile matter concentration of the film forming raw material 2 is 5
It is preferably from 0 to 90% by weight, more preferably from 55 to 80% by weight. When the volatile matter concentration is less than 50% by weight, the viscosity becomes high, so that film formation becomes difficult. When the volatile matter concentration is more than 90% by weight, the viscosity becomes too low, and the uniformity of the thickness of the PVA film 4 is easily impaired. In addition, film forming raw material 2
Is preferably 50 ° C to 110 ° C.

The thickness of the PVA film 4 is 20 to 15
0 μm is preferable, and 40 to 120 μm is more preferable.
If the thickness is less than 20 μm, the PVA film 4 may be cut when uniaxially stretched when processed into a polarizing film. There are cases. 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.

[0035]

EXAMPLES The present invention will now be described specifically with reference to examples, but the present invention is not limited to these examples. (A) Dry first described in Examples and Comparative Examples
The following methods were used to evaluate the temperature unevenness of the film forming material on the drum, (b) the thickness unevenness of the PVA film, and (c) the volatile content of the film forming material.

(A) Temperature Variation of Film-Forming Raw Material on Drying First Drum The temperature distribution was measured using a digital radiation thermometer (IR-420, manufactured by Minolta Camera Co., Ltd.).
The 50cm downstream part discharged on the drum is 10c in the width direction.
The measurement was performed at m intervals, and the difference between the maximum value and the minimum value was calculated. (B) Thickness unevenness of PVA film Thickness unevenness is caused by a film thickness nest tester (KG601A,
Using an Anritsu Corporation), the total width of the PVA film was measured at five points at intervals of 25 cm in the flow direction, and the difference between the maximum value and the minimum value was calculated. (C) Volatile content of film forming raw materials As for the volatile content, about 10 g of a sample was measured using an automatic moisture meter (EB-340).
MOC, manufactured by Shimadzu Corporation).

Example 1 A metal drum structure similar to that shown in FIGS. 2 and 3 was used, the number of spirals was 12, the angle θ between the drum axis O and the spiral flow path 10 was 79 degrees, and the spiral flow path 10 was formed. Each partition 11
The metal drum having a thickness of 6 mm, an outer diameter of 3.2 m, a width of 4.2 m, and a flow rate of hot water used as the heat medium M of 1.8 m / sec and having a chrome-plated surface was used as the first drying drum 3. . Using a drum film forming machine configured in the same manner as in FIG. 1, volatilization consisting of 100 parts by weight of PVA having a saponification degree of 99.9 mol% and a polymerization degree of 2400, 15 parts by weight of glycerin, 0.1 part by weight of palmitic acid diethanolamide and water. Using a T die 1 having a width of 3.6 m at a temperature of 100 ° C., a fixed amount of 73% of the film forming raw material 2 was discharged onto the surface of the rotating first drying drum 3 in which the temperature of the heat medium M was 90 ° C. . At this time, the average temperature T1 of the discharged film forming raw material 2 was 86 ° C., and the temperature unevenness in the width direction was 6 ° C.
° C and a temperature difference T2-T from the average temperature T2 of the heat medium M.
1 was 4 ° C. Further, the film forming raw material 2 on the surface of the first drying drum 3 was dried with hot air at 100 ° C., and passed through a post-process to obtain a PVA film having a width of 2.5 m. The average thickness of this PVA film was 74.7 μm, and the thickness unevenness was 3.5 μm.

Embodiment 2 The structure of the metal drum is the same as that shown in FIGS. 2 and 4, the number of spirals is 8, the angle θ between the drum axis O and the spiral flow path 10 is 82 degrees, and the spiral flow path 10 is formed. Drying a metal drum whose surface is chrome-plated with a thickness of 6 mm, an outer diameter of 2.5 m, a width of 3.1 m, and a flow rate of hot water used as a heat medium M of 1.6 m / sec. Drum 3 was used. Using a drum film forming machine configured in the same manner as in FIG. 1, volatilization comprising 100 parts by weight of PVA having a degree of saponification of 99.9 mol% and a degree of polymerization of 1700, 15 parts by weight of glycerin, 0.1 part by weight of lauric acid diethanolamide and water. Using a T-die 1 having a width of 3.0 m at a temperature of 100 ° C.
The fixed amount was discharged onto the surface of the rotating drying first drum 3 in which the temperature of the heat medium M was 85 ° C. At this time, the average temperature T1 of the discharged film forming raw material 2 was 80 ° C., the temperature variation in the width direction was 6 ° C., and the temperature difference T2−T1 from the average temperature T2 of the heat medium M was 5 ° C. Further, the film forming raw material 2 on the surface of the first drying drum 3 was dried with hot air at 100 ° C., and passed through a post-process to obtain a PVA film having a width of 2.0 m. The average thickness of this PVA film was 75.1 μm, and the thickness unevenness was 3.8 μm.

COMPARATIVE EXAMPLE 1 A conventional tank-type heating medium circulating drum having no special structure inside the drum and having an outer diameter of 2.5 m and a width of 3.1.
Dry metal drum with chrome-plated surface
I made a drum. Using a drum film forming machine configured in the same manner as in FIG. 1, PV having a saponification degree of 99.9 mol% and a polymerization degree of 2400 was used.
A 100 parts by weight, 15 parts by weight of glycerin, 0.1 part by weight of lauric acid diethanolamide, and a volatile matter 73 composed of water
% Of the raw material for film formation was discharged at 100 ° C. using a 3.0-m wide T-die onto the surface of a rotating and drying first drum having a temperature of a heating medium (hot water) of 90 ° C. At this time, the average temperature T1 of the discharged film forming raw material is 76 ° C., the temperature unevenness in the width direction is 17 ° C., and the temperature difference T2 from the average temperature T2 of the heat medium is obtained.
-T1 was 14 [deg.] C. Further, the film forming raw material on the surface of the first drying drum was dried with hot air at 100 ° C., and passed through a post-process to obtain a PVA film having a width of 2.0 m. This PVA
The average thickness of the film is 75.3μm, thickness unevenness is 10.8μ
m.

COMPARATIVE EXAMPLE 2 A conventional tank-type heating medium circulating drum having no special structure inside the drum and having an outer diameter of 2.0 m and a width of 2.5
Dry metal drum with chrome-plated surface
I made a drum. Using a drum film forming machine configured in the same manner as in FIG. 1, PV having a saponification degree of 99.9 mol% and a polymerization degree of 1700 was used.
A 100 parts by weight, 15 parts by weight of glycerin, 0.1 part by weight of lauric acid diethanolamide, and a volatile matter 70 composed of water
% Of the film forming raw material was discharged at 100 ° C. using a 2.3-m wide T-die onto the surface of the rotating first drying drum at which the temperature of the heating medium (hot water) was 85 ° C. At this time, the average temperature T1 of the discharged film forming raw material is 74 ° C., the temperature variation in the width direction is 12 ° C., and the temperature difference T2 from the average temperature T2 of the heat medium is obtained.
-T1 was 11 ° C. Further, the film forming raw material on the surface of the first drying drum was dried with hot air at 100 ° C., and passed through a post-process to obtain a PVA film having a width of 1.7 m. This PVA
The average thickness of the film is 74.9 μm, and the thickness unevenness is 8.1 μm.
Met.

As is clear from the results of Examples 1 and 2 and Comparative Examples 1 and 2, as a drying drum of a drum film forming machine, a spiral flow path through which a heat medium as a heat source flows is provided around the outer periphery of the drum. By using a metal drum with a jacket structure, the temperature unevenness in the direction of the film width of the film forming raw material discharged onto the drying drum is small, and the difference between the average temperature in this direction and the average temperature of the heating medium is small. PV with excellent thickness uniformity, useful as a material for manufacturing a polarizing plate film
A film can be manufactured efficiently.

[0042]

As described above, according to the present invention, a PVA film having improved drying efficiency, a uniform drum surface temperature, and excellent thickness uniformity useful as a material for producing a polarizing plate film can be efficiently produced. Obtainable.

[Brief description of the drawings]

FIG. 1 is a schematic front view showing an example of a drum film forming machine used in the present invention.

FIG. 2 is a side view showing an example of a metal drum.

FIG. 3 is a longitudinal sectional view of the metal drum of FIG. 2;

FIG. 4 is a longitudinal sectional view showing another example of the metal drum.

[Explanation of symbols]

2: film forming raw material, 3: metal drum (drying first drum), 4
... Polyvinyl alcohol film (PVA film),
10, 13, 14 ... flow path, M ... heat medium, O ... axis of metal drum.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B29L 11:00 B29L 11:00 C08L 29:04 C08L 29:04 (72) Inventor Yoichi Matsuoka Saijo, Ehime Prefecture 892 Sakuhi-shi, Kuraray Co., Ltd. (72) Inventor Hideyuki Hata 892, Sakuhi-shi, Saijo-shi, Ehime Prefecture Kuraray Co., Ltd.F-term (reference) AK01 AR06 GA07 GB02 GC02 GE01 GE06 GF23 GN13 GN21 GN24 GW06

Claims (7)

[Claims] 1. A method for producing a polyvinyl alcohol film by discharging a raw material for film formation onto a rotating drying drum and drying the film, wherein a spiral flow of a heat medium of a heat source is supplied to the outer peripheral portion of the drum. Having a jacket structure provided with a passage, the temperature unevenness in the direction of the film width of the film-forming material discharged onto the drum is 10 ° C. or less, and the average temperature in the direction of the film width of the film-forming material. A method for producing a polyvinyl alcohol film, comprising using a metal drum having a difference between the average temperature of the heat transfer medium and the average temperature of the heat medium. 2. The metal drum having a spiral number of 5 to 30.
The method for producing a polyvinyl alcohol film according to claim 1, wherein 3. The method for producing a polyvinyl alcohol film according to claim 1, wherein an acute angle between the axis of the metal drum and the spiral flow path is 50 to 88 degrees. 4. The method for producing a polyvinyl alcohol film according to claim 1, wherein the thickness of each partition in the spiral flow path of the metal drum is 3 to 20 mm. 5. A metal drum is provided with a flow path extending in an axial direction in a main shaft portion of the metal drum, the flow path being connected to a spiral flow path in a drum outer peripheral portion of the metal drum. A method for producing a polyvinyl alcohol film according to any one of the above. 6. The polyvinyl alcohol according to claim 1, wherein the metal drum has an outer diameter of 2.0 to 4.0 m and a width of 2.0 to 4.5 m. Film manufacturing method. 7. 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.