JPH05301239A - Method and apparatus for producing polyvinyl alcohol polymer film - Google Patents

Abstract

PURPOSE:To enhance the quality of a film by a method wherein chips of a PVA polymer are heated while stirring within a hermetically closed first tank to be dissolved in a solvent and the obtained raw solution is stored in a second tank to be defoamed under stirring and the defoamed raw solution is sent out to a die by definite quantity to be cast on a running belt. CONSTITUTION:Chips of a PVA polymer are charged in a first tank 1 from the charging port 1a thereof and a solvent is charged in the tank 1 from the supply port 1b thereof to hermetically close the tank 1 and the chips are stirred by stirring blades 1e in such a state that the temp. in the tank 1 is held to 140 deg.C by a first heater 2 and easily dissolved in the solvent to prepare a raw solution L. The raw solution L is transferred to a second tank 5 and defoamed through a vent 5c while stirring to be sent in a definite quantity by a screw pump 5b. The raw solution L is uniformly cooled by a heat exchanger 30 and sent to a filter 8 under pressure by a gear pump 7 to remove dust and the temp. of the raw solution is uniformized by a static mixer 9. Then, the raw solution is allowed to flow out of the opening of a die 10 to be cast on a belt 13 and dried by hot air H.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for producing a polyvinyl alcohol-based polymer film suitable for, for example, a polarizing film and an optical component used as a retardation plate.

[0002]

2. Description of the Related Art Polyvinyl alcohol (hereinafter referred to as "PV
"A". ) Type polymer film is generally produced by a casting method (solution casting method) (for example,
(See Japanese Patent Publication No. 51-23981). In the conventional production method, a PVA polymer chip is dissolved in a solvent in a tank and kneaded to obtain a stock solution, and the stock solution is cast from a slit-shaped opening to the outer circumference of a rotating drum and cast. At the same time, it was dried to obtain a film.

[0003]

However, in the above-mentioned prior art, since the chips of the PVA polymer are dissolved in the solvent and kneaded in the tank, the kneading becomes insufficient or the bubbles in the stock solution are defoamed. It is difficult to obtain a homogeneous stock solution. Therefore, the quality of the film may deteriorate.

Further, in the above-mentioned prior art, the stock solution is dried on a rotating drum, but a large one having a diameter of about 4 m or more cannot be obtained from this drum due to restrictions in manufacturing and transportation, so that the drying time is sufficient. If set long, the peripheral speed of the drum becomes slow, and the production capacity of the line decreases.

On the other hand, if the film is peeled off from the drum before the film is sufficiently dried, the following problems occur. 1) Since a wide film cannot be uniformly peeled from the roll, unevenness in peeling causes uneven thickness (thickness unevenness). 2) When the drying is insufficient, it is necessary to increase the peeling tension as compared with the case where the drying is sufficient, and since the strength of the film is small, a large molecular orientation in the length direction of the film is generated. Occurs. This molecular orientation is large at both ends of the film due to neck-in and peeling unevenness at the time of peeling, and also at the central portion, large unevenness in molecular orientation occurs due to peeling unevenness. The degree of this molecular orientation is measured by the birefringence.

Due to these problems 1) and 2), the value of retardation (birefringence × film thickness) becomes high, and particularly, as shown by the broken line in FIG. As the value of retardation increases, the unevenness of retardation also increases. Further, due to the problem of 2) above, a large molecular orientation occurs in the length direction of the film, so that the stretchability of the dried film in the length direction is reduced.

The present invention has been made in view of the above conventional problems, and an object of the present invention is to provide a method and an apparatus for producing a PVA-based polymer film having excellent quality and productivity.

[0008]

In order to achieve the above object, the method of the present invention is as follows. First, the PVA polymer is dissolved in a solvent by stirring while heating the sealed first tank. Produce a stock solution. Next, this stock solution is supplied into the second tank, and the supplied stock solution is temporarily stored in the second tank and degassed while stirring. Then, the undiluted solution in the second tank is sent to the die by a fixed amount. An undiluted solution is cast from a die onto a belt that runs while being stretched between a pair of rollers. The cast stock solution is dried on the belt.

Further, the device of the present invention includes the first tank and the second tank.
It is characterized in that a stock solution is produced by a tank and a screw pump, and a belt-type film-forming machine is used for film formation. That is, in the device of the present invention, first, a PVA-based polymer is dissolved in a solvent and stirred to produce a stock solution, and a sealed first tank, and the inside of the first tank is heated to increase the pressure in the first tank. A warming device for heating, a second tank for defoaming by venting while temporarily storing and stirring the stock solution supplied from the first tank, and a constant amount of the stock solution in the second tank is fed. It is equipped with a screw pump. Also, a heat exchanger that controls the temperature of the undiluted solution supplied from the screw pump,
It is equipped with a gear pump that pressurizes the stock solution, a die that uniformly flows the stock solution supplied from the gear pump in the width direction, and a belt-type film forming machine that casts the stock solution that has flowed from the die onto a belt and dries it. .. The belt runs while being stretched between a pair of rollers.

[0010]

According to the present invention, the PVA polymer chips are melted while heating in the closed first tank, so that the pressure in the first tank rises. Therefore, the boiling point of the solvent is increased, and the temperature of the solvent is increased, so that the chip is easily dissolved. Further, the dissolved stock solution is degassed by the vent while being temporarily stored and stirred in the second tank. In this way, since the dissolution, stirring, and defoaming are performed, it is possible to produce a homogeneous stock solution even if the stock solution has a relatively high concentration.

Further, since a belt type film forming machine is used to form a film, the stock solution can be sufficiently dried on a long belt by setting the length of the belt to be long. Therefore, the following advantages are obtained. 1) Thickness unevenness can be reduced. 2) It is possible to reduce the molecular orientation and uneven molecular orientation of the film. 3) Due to the effects of 1) and 2), the retardation value can be lowered and the unevenness of retardation can be reduced. 4) Stretchability of the film in the length direction is improved. A film having such performance cannot be obtained without any one of the first tank for dissolving the PVA polymer, the second tank for stirring and defoaming the stock solution, and the belt film forming machine. ..

As described above, according to the present invention, by combining the first tank for dissolving the PVA-based polymer, the second tank for stirring and defoaming the stock solution, and the belt film-forming machine, the above performance is obtained. It is possible to provide a PVA-based polymer film suitable for a polarizing film and a retardation film, in particular, by producing a film having

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. In FIG. 1 (a), a pair of first tanks 1 are provided, and a PVA-based polymer chip inlet 1 is provided on the upper portion.
a and a solvent (for example, water) supply port 1b, and a stock solution extraction pipe 1c at the bottom. The chip input port 1a is provided with an opening / closing lid 1d, and the solvent supply port 1b.
An on-off valve 1f is provided in the. A first heating device 2 that heats the inside of the first tank 1 with steam to maintain the temperature at about 140 ° C. is provided on the outer periphery of the first tank 1. The first tank 1 dissolves the introduced PVA-based polymer chips with a solvent and agitates the mixture thereof with a stirring blade 1e.
Stock solution L is produced by stirring at. At this time, the first
Since the opening / closing lid 1d of the tank 1 is closed to seal the first tank 1 and the first tank 1 is warmed by the first warming device 2, the first solvent is evaporated by the first solvent.
The pressure in the tank 1 rises.

Stock solution extraction pipes 1c of the two first tanks 1
Communicates with the nozzle 4 of the second tank 5 via the switching valve 3. The switching valve 3 sets either one or both of the two undiluted solution extraction pipes 1c to an open state or a closed state.

The second tank 5 includes a stirring blade 5a and a screw pump 5b provided coaxially with the stirring blade 5a.
Is equipped with. On the outer circumference of the second tank 5, there is provided a second heating device 6 that keeps the inside of the second tank 5 at a temperature slightly higher than 100 ° C. with warm water. This second tank 5
The stock solution L is stirred by the stirring blade 5a. Also, the second
A degassing vent 5c is provided on the top of the tank 5. The undiluted solution L is fed by a fixed amount by the screw pump 5b provided in the lower part of the second tank 5, and the liquid is fed as shown in FIG.
The stock solution L is supplied to the heat exchanger 30 of FIG.

In the heat exchanger 30, the temperature of the stock solution L is uniformly lowered to about 100 ° C. with warm water, and fixed blades are provided inside. This is to prevent the strain. A gear pump 7, a filter 8 and a static mixer 9 are provided downstream of the heat exchanger 30. Filter 8
Is to remove dust in the stock solution, while the static mixer 9 is to supply the stock solution to the die 10 after the stock solution is agitated by a large number of fixed blades to make the temperature of the stock solution uniform. The gear pump 7, the filter 8 and the static mixer 9 may be provided if necessary, and are not necessarily provided.

The die 10 is, as shown in the front view of FIG.
It has a slit-shaped opening 10a that is long in the width direction D,
The stock solution is discharged from the opening 10a onto the belt 13 below with a uniform thickness in the width direction D.

The belt type film forming machine 11 shown in FIG. 1 (b) has the endless belt 13 which is laid between a pair of rollers 12 and 12 and runs, and the stock solution flowing out from the die 10 is belted. It is cast on 13 and dried. The belt 13 is made of stainless steel, for example, and the outer peripheral surface thereof is mirror-finished.
Partition walls 14 that partition the space in the traveling direction of the belt 13 are provided on the outer circumference and the inner circumference of the belt 13, respectively. A hot air blower (not shown) blows hot air H at 80 ° C. to 170 ° C. on the outer peripheral surface and the inner peripheral surface of the belt 13 to accelerate the drying of the stock solution. In the most downstream zone 14A, the film F may be cooled by the air C at room temperature.

A peeling roller 15 is provided near the roller 12 on the right side, and the film F dried to a predetermined density is peeled from the belt 13 by the peeling roller 15. The water content of the film F when peeled from the belt 13 is preferably 15% by weight or less, more preferably 2 to 10% by weight. The film F passes through the heat treatment machine 16, the humidity controller 17 and the inspection machine 18 shown in FIG. The heat treatment machine 16 blows hot air onto the film F to change the crystallinity of the film F and the like. The humidity controller 17 adjusts the humidity of the film F to about 5% on a wet basis, for example.
The inspection machine 18 inspects physical defects, thickness, moisture content, and the like with visible light, infrared light, and beta rays, respectively.

Next, a method for producing the PVA film will be described. First, the chips are loaded from the loading port 1a of the first tank 1 of FIG. 1 (a), and the solvent is fed from the feeding port 1b. Further, the plasticizer may be supplied from the supply port 1b. At this time, the concentration of the PVA-based polymer is 10 to 30% w
b [wt% in wet base: (PVA + additive) × 100 / (PVA + additive + solvent)] Then, the opening / closing lid 1d and the opening / closing valve 1f are closed.
After that, the inside of the first tank 1 is heated to 140 by the first heating device 2.
The stock solution L is obtained by stirring the mixture of the chip and the solvent with the stirring blade 1e while maintaining the temperature at about ℃. here,
Since the first tank 1 is sealed, the boiling point of the solvent rises as the pressure rises due to the evaporation of the solvent, and the temperature of the solvent rises sufficiently, so that the chips are easily dissolved.

The undiluted solution L in the first tank 1 is transferred from the nozzle 4 into the second tank 5. The stock solution L temporarily stored in the second tank 5 is stirred by the stirring blade 5a,
After degassing by the vent 5c, the screw pump 5b
The solution is delivered by a fixed amount. The stock solution L is 1 in the heat exchanger 30.
It is evenly cooled to 00 ° C. and sent to the gear pump 7.

The stock solution L is pressure-fed from the gear pump 7 to the filter 8 to remove dust and the like, and after the temperature is further uniformized by the static mixer 9, the die 10 is used.
And is discharged onto the belt 13 through the slit-shaped opening 10a of the die 10 as shown in FIG. At this time, undiluted solution L
If the temperature is uneven in the width direction D of the belt 13, the outflow amount varies in the width direction D due to the difference in viscosity, so that the film thickness is not uniform. On the other hand, as described above, since the temperature is made uniform by the static mixer 9 shown in FIG. 1B, the film F having a uniform thickness can be obtained.

The stock solution flowing on the belt 13 is the belt 1.
3 is cast by traveling in the direction of arrow A, and drying is promoted on the belt 13 by the hot air H. Here, unlike the drum, the belt 13 can be made long, so that the film F can be sufficiently dried on the belt 13, so that the film F can be easily peeled off from the belt 13. Therefore, as shown by the solid line in FIG. 4, the retardation is uniform and low. Moreover,
Since the film F having a uniform retardation in the width direction and a low retardation can be obtained, the stretchability of the film is improved. Further, the belt-type film forming machine 11 is not particularly limited in lengthening the belt 13, so that the belt 13 can be lengthened to lengthen the drying time. Therefore, it is possible to increase the belt speed and increase the production capacity of the line while sufficiently drying the film F. The traveling speed of the belt 13 is appropriately selected within the range of about 5 to 50 m / min.
The residence time on the belt 13 is appropriately selected within the range of about 1 to 10 minutes.

When a plurality of partition walls 14 are provided in the running direction of the belt 13 and the hot air H is applied to the belt 13 as in this embodiment, the temperature of the hot air H is changed between the partition walls 14. be able to. Therefore, the optimum temperature can be selected according to the dry state (drying stage) of the film F.

In the present invention, water is preferably used as the solvent for the PVA polymer. However, when an explosion-proof type film forming apparatus is used, as a solvent, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, a diamine compound having 1 to 10 carbon atoms, a triamine compound having 1 to 10 carbon atoms, or the like can be used. An organic solvent may be used, and among these organic solvents, dimethyl sulfoxide is preferable. Also, a mixture of these solvents may be used.

Examples of the plasticizer for the PVA polymer include polyhydric alcohol plasticizers such as glycerin, diglycerin, triglycerin, ethylene glycol, triethylene glycol, polyethylene glycol and polypropylene glycol, and mixtures thereof. Among these polyhydric alcohol plasticizers, glycerin is preferable.

The degree of polymerization of the PVA polymer used in the present invention is not particularly limited, but is preferably 1,000 or more, more preferably 1,000 to 20,000, and more preferably 1,500 to 10,000.
Are even more preferred. The saponification degree of the PVA-based polymer is
Although not particularly limited, 80 mol% or more is preferable, 90 mol% or more is more preferable, and 95 mol% or more is still more preferable.

The PVA polymer of the present invention can be obtained by saponifying a polymer of vinyl ester monomer. Vinyl formate monomers include vinyl formate,
Vinyl acetate, vinyl propionate, vinyl valerate,
Examples include vinyl caprate, vinyl laurate, vinyl stearate, vinyl 2,2,4,4-tetramethylvalerate, vinyl benzoate, vinyl pivalate and vinyl versatate. Among these, vinyl acetate, vinyl propionate, vinyl pivalate, and vinyl versatate are preferably used alone or as a mixture.

There is no problem in copolymerizing the above vinyl ester-based monomer with a copolymerizable monomer, and examples of the copolymerizable monomer include olefins 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-acrylic acid
-Acrylic acid esters such as butyl, t-butyl acrylate, 2-ethylhexyl acrylate, dodecyl acrylate, octadecyl acrylate; methacrylic acid and its salts, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, methacrylic acid I-propyl acid,
Methacrylic acid esters such as n-butyl methacrylate, i-butyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, dodecyl methacrylate, octadecyl methacrylate; acrylamide, N-
Methyl acrylamide, N-ethyl acrylamide,
Acrylamide derivatives such as N, N-dimethylacrylamide, diacetoneacrylamide, acrylamidopropanesulfonic acid and its salts, acrylamidopropyldimethylamine and its salts or quaternary salts thereof, N-methylolacrylamide and its derivatives; methacrylamide, N-methyl Methacrylamide, N-ethylmethacrylamide, methacrylamidopropanesulfonic acid and its salts, methacrylamidopropyldimethylamine and its salts or quaternary salts thereof, methacrylamido derivatives such as N-methylolmethacrylamido and its derivatives; methyl vinyl ether, n -Propyl vinyl ether, i-propyl vinyl ether, n-butyl vinyl ether, i-butyl vinyl ether, t-butyl vinyl ether, do Vinyl ethers such as silvinyl ether and stearyl vinyl ether; nitriles such as acrylonitrile and methacrylonitrile; vinyl halides such as vinyl chloride, vinylidene chloride, vinyl fluoride, vinylidene fluoride; allyl compounds such as allyl acetate and allyl chloride; Maleic acid and its salts or its esters; itaconic acid and its salts or its esters; vinylsilyl compounds such as vinyltrimethoxysilane; isopropenyl acetate. The content of these copolymerizable monomers is preferably 10 mol% or less, more preferably 5 mol% or less. The thickness of the PVA-based polymer film obtained by the present invention is preferably 20-100 μm.

Test Example 1 PVA100 was placed in the pressure-resistant dissolution tank (first tank) 1 in FIG.
12 parts by weight of glycerin were added, and the water content was 60.
Water corresponding to% wb was added, heated, stirred and dissolved to obtain a stock solution. Further, after stirring and defoaming in the second tank 5, the gear pump 7 quantitatively supplied to the die 10, and the belt type film forming machine 11 produced a PVA polymer film having a thickness of 75 μm and a width of 1.2 m. However, heat treatment was not performed. The main manufacturing conditions are shown below. Pressure-resistant dissolution tank: Temperature 140 ° C Die: T-type slit die Film forming machine: Stainless steel belt Material Austenite length 20m Belt speed 10m / min Drying condition Air temperature 120 ° C to 150 ° C Drying time 120sec Moisture at film peeling 8.5wt % As to the physical properties of the film F thus obtained, as shown in Table 1, uneven thickness, average retardation value, and uneven retardation were small. This is because the use of the belt-type film forming machine 11 allows a longer drying time and lowers the water content at the time of peeling the film.

Test Example 2 Using the same pressure-resistant dissolution tank 1, second tank 5 and belt-type film forming machine 11 as in Test Example 1, a film F was formed under the same conditions, and then a heat treatment was carried out by a heat treatment machine 16. A PVA film having a water resistance of 75 μm and a width of 1.2 m was produced. The main manufacturing conditions are shown below. Pressure-resistant dissolution tank: Same as in Test Example 1 Die: Same as in Test Example 1 Film forming machine: Same as in Test Example 1 Heat treatment machine: Hot air hot air temperature 160 ° C. Treatment time 15 seconds Film moisture at outlet 1.3 wt% Adjusted film Rolling water content 5.0 wt% Physical properties of the film thus obtained are shown in Table 1. Although this film was heat-treated, it had little unevenness in thickness, average retardation value and unevenness in retardation.

Comparative Example 1 A stock solution for dissolution was obtained under the same equipment and conditions as in Test Example 1. A constant amount was supplied to the die 10 by the gear pump 7, and a PVA film having a thickness of 75 μm and a width of 1.2 m was manufactured by a drum type film forming machine equipped with the casting roll 56 and the drying roll 57 shown in FIG. The main manufacturing conditions are shown below. Pressure-resistant dissolution tank: Same as in Test Example 1 Die: Same as in Test Example 1 Drum type film forming machine: Cast roll Diameter 2m Surface treatment Hard chrome plating Roll temperature 90 ° C Rotation speed 5m / min Drying time 62 seconds Film peeling moisture 24wt% Dry Roll Roll temperature 70 ° C. to 110 ° C. Drying time 100 seconds Film winding water content 5.0 wt% Physical properties of the film obtained by this method are shown in Table 1.
It can be seen that the film of Comparative Example 1 has larger thickness unevenness, absolute retardation value and uneven retardation as compared with Test Examples 1 and 2. When the rotation speed of the cast roll 56 was increased in order to increase the productivity, the water content of the film at the time of peeling was increased, and the uneven thickness, the average retardation value and the uneven retardation were further increased.

Table 1 Physical property measurement results Thickness unevenness Retardation unevenness R (μ) Average value (nm) R (nm) Test Example 1 1.6 14 6 Test Example 2 1.5 25 7 Comparative Example 1 5.5 52 35 Thickness unevenness was measured by continuously measuring the thickness in the vertical and horizontal directions, and indicated by the difference (R (μ)) between the maximum value and the minimum value. The retardation was measured at 20 points at a pitch of 5 cm in the width direction, and the average value (nm)
The retardation unevenness is indicated by the difference (R (nm)) between the maximum value and the minimum value.

[0034]

As described above, according to the present invention, the PVA-based polymer and the solvent are dissolved in the sealed first tank while heating and pressurizing, and the PVA polymer and the solvent are temporarily melted in the second tank. Since the liquid is stored and degassed while stirring, a homogeneous stock solution having a small amount of undissolved components and bubbles can be produced. Also,
Since the undiluted solution is supplied to the die by the screw pump, variations in the undiluted solution supply amount are unlikely to occur. In particular, since the film is formed using a belt type film forming machine, the stock solution can be sufficiently dried on a long belt. In this way, a uniform amount of the undiluted solution having a small amount of undissolved components and air bubbles can be supplied in a predetermined amount and sufficiently dried, so that the retardation of the film, that is, the quality is improved.

On the other hand, since the belt can be lengthened without much restrictions on manufacturing and transportation, the belt speed can be increased, and the productivity is also improved.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of a production apparatus from production of a stock solution to film formation according to the present invention.

FIG. 2 is a schematic configuration diagram showing an example of a heat treatment, humidity control, and winding device after film formation according to the present invention.

FIG. 3 is a front view of a die.

FIG. 4 is a characteristic diagram showing changes in retardation in the width direction of the film.

FIG. 5 is a schematic configuration diagram showing an example of a conventional drum type film forming machine.

[Explanation of symbols]

1 ... 1st tank, 2 ... (1st) heating device, 5 ... 2nd tank, 5b ... Screw pump, 5c ... Vent, 7 ... Gear pump, 10 ... Die, 11 ... Belt type film forming machine, 12 ... Roller , 13 ... Belt, 30 ... Heat exchanger, F ... Film,
L ... undiluted solution.

Claims (2)

[Claims] 1. A step of producing a stock solution by dissolving a polyvinyl alcohol polymer in a solvent by stirring while heating the closed first tank, and supplying the stock solution into the second tank, The step of temporarily storing the supplied undiluted solution in the second tank and defoaming it with stirring, the step of sending out the undiluted solution in the second tank to the die by a fixed amount, and bridging between the pair of rollers A method for producing a polyvinyl alcohol-based polymer film, comprising: a step of casting a stock solution from the die onto a running belt; and a drying step of drying the stock solution on the belt. 2. A closed type first method for producing a stock solution by dissolving a polyvinyl alcohol polymer in a solvent and stirring the solution.
A tank, a heating device for heating the inside of the first tank to raise the pressure in the first tank, and a stock solution supplied from the first tank is temporarily stored and stirred, and is defoamed by a vent. A second tank, a screw pump that feeds the undiluted solution in the second tank by a fixed amount, a heat exchanger that controls the temperature of the undiluted solution supplied from the screw pump, a gear pump that pressurizes the undiluted solution, and a gear pump It has a die that uniformly flows out the undiluted solution supplied from the width direction, and a belt that runs while running between a pair of rollers,
An apparatus for producing a polyvinyl alcohol-based polymer film, comprising: a belt-type film forming machine for casting the undiluted solution flowing out from the die onto the belt and drying the undiluted solution.