JP2002144403A - T-die for manufacturing vinyl alcohol polymer film and polarizing film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a T-die which stably produces a vinyl alcohol polymer film with a uniform thickness, best-suited for a polarizing film for a long time and also the polarizing film almost free from optical mottles, manufactured using the vinyl alcohol polymer film with the help of the T-die. SOLUTION: The T-die 1 for manufacturing the vinyl alcohol polymer film has a packing 8 which is arranged between a die body 1a and a side plate 9 and seals a raw material for manufacturing the film containing a vinyl alcohol polymer. The packing 8 is made of a plastic with the surface, of a part coming into contact with the liquid, which shows a melt point of 170 deg.C or higher and a critical surface tension of 30 μN/cm or less.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a T-die for producing a vinyl alcohol polymer film which is useful as a raw material for producing a polarizing film and has excellent thickness uniformity, and a vinyl alcohol polymer obtained thereby. The present invention relates to a polarizing film produced using a film.

[0002]

2. Description of the Related Art A polarizing plate having a function of transmitting and blocking light is a fundamental component of a liquid crystal display (LCD) together with a liquid crystal having a function of switching light. The field of application of this LCD is from small devices such as calculators and watches in the early stages of development to laptop computers,
There is a need for a polarizing plate that spreads over a wide range, such as a word processor, a liquid crystal color projector, an in-vehicle navigation system, and a liquid crystal television, and has less optical spots than before.

In general, a polarizing plate is a vinyl alcohol polymer film (hereinafter abbreviated as "PVA film", and a vinyl alcohol polymer as a raw material thereof may be abbreviated as "PVA"). Is uniaxially stretched and dyed, and a protective film such as a cellulose triacetate (TAC) film is bonded to both sides of a polarizing film produced by dyeing.

[0004]

In order to reduce optical spots on the polarizing plate, there are many points to be taken such as stretching the PVA film evenly and laminating it evenly, but the most important point is the polarization. The purpose is to make the thickness of the PVA film used as the material of the film uniform. When the thickness of the PVA film is not uniform, it is difficult to reduce optical spots on the obtained polarizing plate.

Accordingly, an object of the present invention is to provide a T-die capable of stably obtaining a PVA film having a uniform thickness particularly suitable for a polarizing film over a long period of time, and an optical spot produced by using the PVA film obtained thereby. It is in providing a small number of polarizing films.

[0006]

In order to achieve the above object, a T-die for producing a PVA film according to the present invention is disposed between a die body and a side plate to seal a PVA-containing film-forming material. As a packing, the surface of the liquid contact part has a melting point of 170 ° C or more and a critical surface tension of 30 μN.
/ Cm or less plastic is used.

By using the above-mentioned T-die, a PVA film having a uniform thickness can be stably obtained over a long period of time.

The packing is made of a fluororesin having a thickness of 0.5 mm to 5 mm, and the tip of the packing preferably protrudes from the tip of the lip by 0 μm to 500 μm. According to this, a PVA film having a more uniform thickness can be obtained.

The above-mentioned T-die is suitably used when producing a PVA film for a polarizing film. In addition, by using this PVA film, a good polarizing film with less optical spots can be obtained.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an example of an apparatus for producing a PVA film using a T-die for producing a PVA film according to the present invention, which is made by melt extrusion in which hydrated PVA (which may contain an organic solvent; the same applies hereinafter) is extruded. The main part of the film machine is shown. The T die 1 used in this film forming machine is
The die body 1a has a manifold (hollow portion) 2 for temporarily storing the injected molten PVA and a lip 3 having a narrow gap. Each part penetrates in the width direction W. Side plates 9 are attached to both sides of the die body 1a via packings 8, respectively, and the molten PVA is sealed at both sides of each part. The molten PVA is discharged from the die discharge section 5 at the tip of the lip 3. The liquid contact portions of the packing 8 refer to the manifold 2 where the packing 8 is in direct contact with the molten PVA, the lip surface 10 on the inner surface of the lip 3, and the respective portions of both ends of the die discharge portion 5.

[0011] The roll film forming machine uses a T-die 1 to melt PVA (film forming material) extruded from an extruder (not shown).
In order to distribute uniformly over the entire length of the inner lip 3, first, the manifold 2 is once filled and aligned, and a fixed amount of molten PVA (film forming material) is determined from the die discharge unit 5 through the lip surface 10 on the inner surface of the lip 3. The PVA film is extruded onto a metal roll 6 rotating at a high speed and passed through a part of the circumferential surface of the metal roll 6 to dry the PVA film. The lip 3 is, for example, a flexible lip, and fine adjustment of the lip opening is performed by a lip opening adjustment bolt 7. After this, this P
The VA film passes through a not-shown floating dryer, a metal roll for drying, an inspection machine, and the like, and is wound on a winder.

In this embodiment, a roll film forming machine is used for producing a PVA film, but a belt film forming machine may be used.

In the present invention, when a PVA film is manufactured using a roll film forming machine or a belt film forming machine, the PVA film is disposed between the die main body 1a and the side plate 9 and the PVA film is formed.
Is used as a packing 8 for sealing a film-forming material containing
At a temperature of at least 00 ° C, particularly preferably at least 230 ° C, the critical surface tension is at most 30 μN / cm, more preferably at least 25 μN / cm.
cm or less, particularly preferably 20 μN / cm or less.

When the melting point of the plastic on the surface of the liquid contact portion (hereinafter sometimes abbreviated as Tm) is lower than 170 ° C., the plastic softens during the film formation and does not serve as a packing, so that PVA does not function. Is leaked from the junction of the side plates of the T-die, making it impossible to form a stable film over a long period of time.
If the critical surface tension of the plastic on the surface of the liquid-contact part exceeds 30 μN / cm, the packing and PV
A familiarity with the film-forming raw material containing A as a component is improved,
Since the formation of both ends of the web discharged from the T-die is not stable, a PVA film having a uniform thickness near the ends of both ends cannot be obtained, and the width yield deteriorates. The melting point of the plastic was measured by a differential scanning calorimeter (DSC) (SSC / 52).
00H, manufactured by Seiko Denshi Kogyo Co., Ltd.) in a nitrogen stream at a rate of 10 ° C./min to 350 ° C.,
After rapidly cooling to room temperature, the temperature was increased again to 350 ° C. in a nitrogen stream at a rate of 10 ° C./min to obtain an endothermic peak top temperature measured. In addition, the critical surface tension of plastic (hereinafter,
γc) is described in W.W. A. Zisman
Was measured according to the method described above.

As the plastic having the above-mentioned properties, a tetrafluoroethylene-hexafluoropropylene copolymer (Tm = 270 ° C., γc = 18 μN / c)
m), polytetrafluoroethylene (Tm = 320 ° C., γ
c = 19 μN / cm), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (Tm = 310)
° C, γc = 19 µN / cm), polymethylpentene (T
m = 235 ° C., γc = 24 μN / cm), polyvinylidene fluoride (Tm = 170 ° C., γc = 25 μN / cm),
Ethylene-tetrafluoroethylene copolymer (Tm = 26
0 ° C., γc = 26 μN / cm), and polyvinylyl fluoride (Tm ≧ 300 ° C., γc = 28 μN / cm). Among them, a fluororesin, particularly a polytetrafluoroethylene and a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, is preferred.

In the present invention, it is important to use a T-die. For I-die and round die, PV with poor thickness uniformity
Only A film can be obtained. The T-die is preferably a coat hanger type rather than a straight type.

In the present invention, when assembling the T-die, the tip of the packing is set at 0 μm to 50 μm from the tip of the lip.
It is preferable to assemble with a protrusion of 0 μm, more preferably 0 μm to 300 μm. If the tip of the packing protrudes more than 500 μm from the tip of the lip, or if the tip of the lip projects more than the tip of the packing, the thickness of the web discharged from the die will be near the ends of both ends. A uniform PVA film cannot be obtained, and the width yield tends to deteriorate.

It is particularly preferred that the packing is a single layer of plastic, but powder coating is applied to a metal plate such as aluminum, copper or brass on all surfaces which come into contact with a film forming material containing PVA as a constituent. A laminate obtained by laminating the above plastic by a method such as baking, solution coating, extrusion lamination, lamination with a film adhesive, or the like can also be used. At this time, the thickness of the laminated plastic layer is 10 μm to 250 μm.
Is preferred.

Further, the thickness of the packing (the thickness of the entire packing when laminated) is preferably 0.5 mm to 5 mm, more preferably 0.8 mm to 3 mm. If the thickness of the packing is less than 0.5 mm or more than 5 mm, the film forming material containing PVA as a component leaks from the joint of the side plate of the T-die, and there is a tendency that stable film forming cannot be performed for a long time. .

The material of the liquid contacting part of the T-die used in the present invention is that a stainless steel is plated with chromium or the like, and the surface roughness of the plating surface is polished to 0.3 S or less. It is preferable because uniformity in thickness is easily obtained.

Here, the unit "S" of the surface roughness indicates the degree of unevenness of the surface, and the surface roughness is represented by the maximum height. The maximum height ( _Rmax ) is JIS
In accordance with B0601, the distance between two straight lines contacting the highest peak and the deepest valley parallel to the average line of a portion extracted by the reference length from the cross-sectional curve of the object is defined as a micrometer (μ).
m) It is expressed in units. The surface roughness of 0.3 S means that the maximum height is 0.3 μm.

It is preferable that the straightness of the plating surface of the lip be 50 μm or less in the entire width and be finished to an accuracy of 10 μm or less between two points 200 mm apart from each other because the uniformity of the thickness of the PVA film can be easily obtained. .

The PVA used in the present invention is produced by saponifying a polyvinyl ester obtained by polymerizing a vinyl ester monomer. For example, a modified PVA obtained by graft copolymerizing PVA with an unsaturated carboxylic acid or a derivative thereof, an unsaturated sulfonic acid or a derivative thereof, an α-olefin having 2 to 30 carbon atoms, a vinyl ester and an unsaturated carboxylic acid or a derivative thereof, A modified PVA produced by saponifying a modified polyvinyl ester obtained by copolymerizing an unsaturated sulfonic acid or a derivative thereof, an α-olefin having 2 to 30 carbon atoms, or unmodified or modified PVA is converted into formalin, butyraldehyde, and benzaldehyde. For example, a so-called polyvinyl acetal resin in which some of the hydroxyl groups are cross-linked with an aldehyde such as the above is used.

The vinyl ester monomers include:
Examples include vinyl acetate, vinyl formate, vinyl propionate, vinyl butyrate, vinyl pivalate, vinyl versatate, vinyl laurate, vinyl stearate, and vinyl benzoate, and use of one or more of these. Can be.

The comonomer used in the modified PVA is copolymerized mainly for the purpose of modification, and is used within a range not to impair the purpose of the present invention. Such comonomers include, for example, olefins, acrylic acid, salts thereof,
Its esters and its derivatives, methacrylic acid, its salts, its esters and its derivatives, maleic acid, its salts, its esters and its derivatives, itaconic acid,
Examples thereof include salts, esters and derivatives thereof, acrylamide derivatives, methacrylamide derivatives, N-vinylamides, vinyl ethers, nitriles, vinyl halides, allyl compounds, vinylsilyl compounds, and isopropenyl acetate. Species or two or more can be used.

When using modified PVA, the amount of modification is 15
Preferably it is at most 5 mol%, more preferably at most 5 mol%.
As the comonomer, α-olefin is preferable,
Particularly, ethylene is preferred.

The degree of saponification of PVA is preferably at least 95 mol%, more preferably at least 99.5 mol%, particularly preferably 99.9 mol%, in view of the polarizing performance and durability of the obtained polarizing film.
Most preferred is at least mol%.

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

The degree of polymerization of PVA is preferably 1000 or more from the viewpoint of the polarizing performance and durability of the obtained polarizing film.
2500 or more is more preferable, and 3500 or more is particularly preferable. The upper limit of the PVA polymerization degree is preferably 8000 or less, more preferably 6000 or less.

The degree of polymerization (Po) of the PVA is determined according to JIS.
It is measured according to K 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)}

As a method for producing a PVA film using the above-mentioned PVA, in addition to the above-mentioned melt-extrusion film forming method in which hydrated PVA is melt-kneaded by an extruder and extruded, for example,
A casting film forming method of casting using a PVA solution in which VA is dissolved in a solvent, a wet film forming method (discharging into a poor solvent), a gel film forming method (a method in which a PVA aqueous solution is once cooled and gelled, To obtain a PVA film) and a method based on a combination thereof.
Among these, the casting film forming method and the melt extrusion film forming method,
It is preferable because a good film having high transparency can be obtained.

As a solvent for dissolving PVA used in producing a PVA film, for example, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, N-methylpyrrolidone, ethylene glycol, glycerin, propylene glycol, diethylene glycol, triethylene glycol , Tetraethylene glycol, trimethylolpropane, ethylenediamine, diethylenetriamine, diglycerin, water and the like,
One or more of these can be used. Among them, dimethyl sulfoxide, water, or a mixed solvent of glycerin and water is preferably used.

The PVA solution or the water-containing PVA may contain a plasticizer, a surfactant, a dichroic dye, and the like, if necessary.

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

The amount of the polyhydric alcohol to be added is PVA
The amount is preferably 1 to 30 parts by weight, particularly preferably 5 to 20 parts by weight, per 100 parts by weight. If the amount is less than 1 part by weight, dyeability and stretchability may decrease,
On the other hand, if it exceeds 30 parts by weight, the PVA film becomes too flexible, and the handleability may decrease.

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, carboxylic acid type, sulfate type and sulfonic acid type are preferable. As the nonionic surfactant, alkyl ether type, alkyl ester type, alkyl amide type, polypropylene glycol ether type, alkanolamide type and allyl phenyl ether type are preferable.
One or a combination of two or more of these surfactants can be used.

The amount of the surfactant added is PVA 10
0.01 parts by weight to 1 part by weight, preferably 0.05 parts by weight to 0.3 parts by weight, based on 0 parts by weight.
If the amount is less than 0.01 part by weight, the effect of improving stretchability and dyeability is hardly exhibited, and if it exceeds 1 part by weight, it is eluted on the surface of the PVA film, causing blocking, and the handleability may be reduced. .

PVA solution or molten PVA (raw material for film formation)
The metal roll of the roll film forming machine for drying the paper and the belt of the belt film forming machine are heated by steam, a heating medium, hot water, an electric heater, or the like. In addition, warm air or cold air
Means such as spraying on the film or sucking air or vapor around the PVA film may be used.

The temperature of the metal roll or belt from which the film forming material is discharged is preferably 50 to 110 ° C., more preferably 60 to 105 ° C., and 70 to 100 ° C.
C is more preferred. If the temperature of the metal roll or the belt is lower than 50 ° C., drying of the discharged film forming material may be uneven, and if the temperature is higher than 110 ° C., the film forming material may foam, so that the thickness uniformity is reduced. It may be difficult to obtain an excellent PVA film.

The metal roll is preferably plated with nickel, chromium, chromium oxide, zinc, tin or the like. The surface roughness of the metal surface or the plating surface of the metal roll is preferably 3S or less, particularly preferably 0.5S or less. When the smoothness exceeds 3S, it may be difficult to obtain a PVA film having excellent thickness uniformity.

After the film-forming material is discharged onto a metal roll or belt, it is dried with a plurality of metal rolls, dried with a drying device such as a tenter type or free type floating dryer, or placed in a drying furnace. It may be made to pass through a plurality of rolls that have been dried. It is preferable that the rolls attached to these devices can be independently adjusted in speed by a speed reducer or inverter control. Further, in the process before winding the PVA film, a humidity controller, an inspection device, and the like may be installed.

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. Dyes used for dyeing include iodine-potassium iodide; direct black 1
7, 19, 154; Direct Brown 44, 10
6, 195, 210, 223; Direct Red 2,
23, 28, 31, 37, 39, 79, 81, 240,
242, 247; Direct Blue 1, 15, 22,
78, 90, 98, 151, 168, 202, 236,
249, 270; Direct Violet 9, 12,
Dichroic dyes such as 51, 98; direct green 1, 85; direct yellow 8, 12, 44, 86, 87; direct orange 26, 39, 106, 107 and the like are used in one kind or in a mixture of two or more kinds. it can.
Usually, the dyeing is generally carried out by immersing the PVA film in a solution containing the dye. However, the processing conditions such as coating on the PVA film or mixing with the PVA film to form a film are used. The processing method is not particularly limited.

For the uniaxial stretching, 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 in air using a PVA film after water absorption. It can be carried out. The stretching temperature is not particularly limited, but is preferably 30 ° C. to 90 ° C. when the PVA film is stretched in warm water (wet stretching), and 50 ° C. to 180 ° C. when the film is stretched by dry heat. The stretching ratio of uniaxial stretching (in the case of multi-stage uniaxial stretching, the total stretching ratio) is 4 from the viewpoint of the polarizing performance of the obtained polarizing film.
It is preferably at least 5 times, particularly preferably at least 5 times. The upper limit of the stretching ratio is not particularly limited, but is preferably 8 times or less since uniform stretching is easily obtained. The thickness of the stretched film is preferably 3 μm to 75 μm, more preferably 5 μm to 50 μm.

In order to strengthen the adsorption of the dye to the stretched film, a fixing treatment is often performed. Usually, boric acid and / or a boron compound is added to the treatment bath used for the fixing treatment. Further, an iodine compound may be added to the treatment bath as needed.

Drying (heat treatment) of the stretched film
Is preferably performed at 30 ° C. to 150 ° C., and more preferably at 50 ° C. to 150 ° C.

The polarizing film obtained as described above is usually used as a polarizing plate by bonding an optically transparent protective film having mechanical strength to both surfaces or one surface thereof. As the protective film, cellulose triacetate (T
AC) film, cellulose acetate / butyrate (CAB) film, acrylic film, polycarbonate film, polyolefin film, polyester film and the like are used. Examples of the adhesive for bonding include a PVA-based adhesive and a urethane-based adhesive, and a PVA-based adhesive is preferable.

[0048]

EXAMPLES The present invention will now be described specifically with reference to examples, but the present invention is not limited to these examples. Example 1 Tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer having a thickness of 1 mm (Tm = 310 ° C., γc =
19 μN / cm) was used as packing. Then, the packing was sandwiched between the main body of the T-die and the side plate such that the tip of the packing protruded from the tip of the lip by 100 μm to assemble the T-die, and assembled the roll film forming machine. At this time, a flexible lip die was used as the T die. The die lip has a surface roughness of 0.1S
Hard chrome plating is applied, and the straightness of the lip surface is 40 μm in full width and 8 between two points 200 mm apart.
μm. Further, as a roll of the film forming machine,
Using a metal roll having a surface roughness of 0.3S,
Heated.

Glycerin 10 was added to 100 parts by weight of PVA having a degree of saponification of 99.9 mol% and a degree of polymerization of 1750.
An aqueous solution containing 15 parts by weight of PVA containing 15 parts by weight of
The film is cast using the film forming machine, dried with hot air at 90 ° C., and then the front and back of the PVA film are alternately dried with 15 heated metal rolls to obtain a 75 μm thick polarizing film PVA film. Obtained. This PVA film had a smooth surface and no thickness unevenness even after 10 consecutive days of operation.

The PVA film was pre-swelled, dyed, uniaxially stretched, fixed, dried, and heat-treated in this order to produce a polarizing film. That is, the PVA film is
It was immersed in water at 0 ° C. for 5 minutes for pre-swelling, and immersed in an aqueous solution of 35 ° C. having an iodine concentration of 0.4 g / l and a potassium iodide concentration of 40 g / l for 3 minutes. continue,
The film is uniaxially stretched 5.5 times in an aqueous solution of boric acid concentration of 4% at 40 ° C., and is dissolved in a 30 ° C. aqueous solution of potassium iodide concentration of 40 g / l, boric acid concentration of 40 g / l and zinc chloride concentration of 10 g / l. The fixing process was performed by immersion for 5 minutes. Thereafter, the stretched film is taken out, and at a constant length, at 40 ° C.
And then heat-treated at 100 ° C. for 5 minutes.

The thickness of the obtained polarizing film was 22 μm, and there was no color spot. Further, as a result of observing the transmitted light by sandwiching a 50 cm square of the obtained polarizing film at an angle of 45 ° between two polarizing plates in a crossed Nicols state, no abnormality was found.

Example 2 Polytetrafluoroethylene having a thickness of 2 mm (Tm = 32)
0 ° C., γc = 19 μN / cm) was used as the packing. Then, place this packing between the body of the T-die and the side plate so that the tip of the packing is 300
A T-die was assembled so as to protrude by μm, and assembled into a roll film forming machine. At this time, a flexible lip die was used as the T die. The lip of this die is hard chrome plated with a surface roughness of 0.1S,
The straightness of the lip surface is 40 μm in total width and 8 μm between two points 200 mm apart. Further, a metal roll having a surface roughness of 0.3 S was used as a roll of the film forming machine, and was heated to 90 ° C.

Then, 100 parts by weight of PVA having a degree of saponification of 99.9 mol% and a degree of polymerization of 4,000, 10 parts by weight of glycerin and 110 parts by weight of water are melt-kneaded by an extruder to form a melt-extruded film, and heated with 90 ° C. hot air. After drying, the front and back of the PVA film were alternately dried with 15 heated metal rolls to obtain a 75 μm thick PVA film for a polarizing film. The surface of this PVA film was smooth even after continuous operation for 10 days, and no uneven thickness was observed.

The PVA film was pre-swelled, dyed, uniaxially stretched, fixed, dried and heat-treated in this order to produce a polarizing film. That is, the PVA film is
It was immersed in water at 0 ° C. for 5 minutes for pre-swelling, and immersed in an aqueous solution of 35 ° C. having an iodine concentration of 0.4 g / l and a potassium iodide concentration of 40 g / l for 3 minutes. continue,
The film is uniaxially stretched 5.6 times in an aqueous solution of boric acid at a concentration of 4% at 40 ° C., and placed in a 30 ° C. aqueous solution of a potassium iodide concentration of 40 g / l, a boric acid concentration of 40 g / l, and a zinc chloride concentration of 10 g / l. The fixing process was performed by immersion for 5 minutes. Thereafter, the stretched film is taken out, and at a constant length, at 40 ° C.
And then heat-treated at 100 ° C. for 5 minutes.

The thickness of the obtained polarizing film was 22 μm, and there was no color spot. Further, as a result of observing the transmitted light by sandwiching a 50 cm square of the obtained polarizing film at an angle of 45 ° between two polarizing plates in a crossed Nicols state, no abnormality was found.

Example 3 A PVA film for a polarizing film was obtained in the same manner as in Example 2, except that the packing was changed to polymethylpentene (Tm = 235 ° C., γc = 24 μN / cm). . In this PVA film, slight thickness unevenness was observed near both ends in the film width direction after continuous 10 days of operation.

A polarizing film was produced in the same manner as in Example 2. When the transmitted light was observed by sandwiching a 50 cm square of this polarizing film at an angle of 45 ° between two polarizing plates in a crossed Nicols state, a slight irregular irregular spot was slightly observed, but it could be used for LCD applications. Level.

Example 4 In Example 2, the thickness of the packing was 0.05 mm.
A PVA film for a polarizing film was obtained in the same manner as in Example 2 except that the above was used. In this case, a small amount of resin leaked from the joints of the side plates with the operation, and slight unevenness of thickness was observed near both ends in the film width direction of the PVA film after continuous 10 days of operation.

A polarizing film was produced in the same manner as in Example 2. When the transmitted light was observed by sandwiching a 50 cm square of this polarizing film at an angle of 45 ° between two polarizing plates in a crossed Nicols state, a slight irregular irregular spot was slightly observed, but it could be used for LCD applications. Level.

Fifth Embodiment In the first embodiment, the tip of the lip is set at 2
A PVA film for a polarizing film was obtained in the same manner as in Example 1 except that the PVA film was protruded by 1 mm. In this PVA film, thickness unevenness was observed near both ends in the film width direction after continuous 10 days of operation, and as a result of removing the unevenness, the width yield was slightly deteriorated.

A polarizing film was produced in the same manner as in Example 1. When the transmitted light was observed by sandwiching a 50 cm square of this polarizing film at an angle of 45 ° between two polarizing plates in a crossed Nicols state, a slight irregular irregular spot was slightly observed, but it could be used for LCD applications. Level.

Comparative Example 1 The same procedure as in Example 1 was repeated except that the packing was changed to polyethylene terephthalate (Tm = 260 ° C., γc = 43 μN / cm).
A VA film was obtained. This PVA film has a continuous 1
After the operation for 0 days, large thickness unevenness was observed near both ends in the film width direction.

Then, a portion having a large thickness unevenness near both ends in the film width direction was removed, and a polarizing film was produced in the same manner as in Example 1. 5 of this polarizing film
0 cm square is placed between the two polarizing plates in the crossed Nicols state.
When the transmitted light was observed at an angle of 5 °, large irregular spots were observed and could not be used for LCD applications.

Comparative Example 2 In Example 2, the packing was replaced with polypropylene (T
m = 160 ° C., γc = 23 μN / cm)
In the same manner as in Example 2, a PVA film for a polarizing film was obtained. In this case, a good PVA film was obtained at the beginning of the operation, but the film-forming raw material immediately leaked from between the side plate and the operation had to be stopped.

Comparative Example 3 A PVA film for a polarizing film was obtained in the same manner as in Example 1, except that the packing was changed to an I die using an aluminum plate. In this PVA film, large thickness unevenness was observed near both ends in the film width direction after continuous 10 days of operation.

Then, portions having large thickness unevenness near both ends in the film width direction were removed, and a polarizing film was produced in the same manner as in Example 1. 5 of this polarizing film
0 cm square is placed between the two polarizing plates in the crossed Nicols state.
When the transmitted light was observed at an angle of 5 °, large irregular spots were observed and could not be used for LCD applications.

[0067]

As described above, according to the present invention, a PVA film having a uniform thickness suitable for a polarizing film can be stably obtained over a long period of time. Also, this PV
A polarizing film with less optical spots can be obtained by using the A film.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a main part of a roll film forming machine using a T-die for manufacturing a PVA film according to the present invention.

[Explanation of symbols]

1 ... T die, 1a ... Die body, 2 ... Manifold, 3 ...
Lip, 4 ... Molated PVA (film-forming raw material), 5 ... Die discharge part, 6 ... Metal roll, 7 ... Lip opening adjustment bolt, 8 ...
Packing, 9 ... side plate, 10 ... lip surface, W ...
Die width.

──────────────────────────────────────────────────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 Hideyuki Hata Saijo City, Ehime Prefecture 892 Sakuhiichi F-term in Kuraray Co., Ltd.

Claims (4)

[Claims] 1. A packing which is disposed between a die body and a side plate and seals a film forming material containing a vinyl alcohol-based polymer.
A T-die for producing a vinyl alcohol-based polymer film, wherein a plastic having a critical surface tension of 30 μN / cm or less at 0 ° C. or more is used. 2. The packing according to claim 1, wherein the packing is made of a fluororesin having a thickness of 0.5 mm to 5 mm, and the tip of the packing is 0 μm from the tip of the lip.
A T-die for producing a vinyl alcohol-based polymer film projecting from m to 500 μm. 3. The T-die according to claim 1, wherein the vinyl alcohol-based polymer film is for a polarizing film. 4. A polarizing film produced using the vinyl alcohol polymer film obtained by the T-die according to claim 3.