JP2002060505A - Polyvinyl alcohol film, method for producing the same, and use of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyvinyl alcohol film for producing a polarizing film which has the excellent in-plane uniformity of the polarizing performance, and to provide a method for producing the same. SOLUTION: This polyvinyl alcohol film characterized by satisfying the following expression (1): 0.0003<=(nx+ny)/2-nz<=0.01...(1), wherein (nx) is the refractive index of the film in the longitudinal direction; (ny) is the refractive index of the film in the width direction; (nz) is the refractive index of the film in the thickness direction.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a polyvinyl alcohol-based film, and more particularly, to a polyvinyl alcohol-based film for producing a polarizing film having excellent in-plane uniformity of polarization performance (degree of polarization, single transmittance). And a method of manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, a polyvinyl alcohol-based film is prepared by dissolving a polyvinyl alcohol-based resin in a solvent, kneading and defoaming to prepare a stock solution, and then forming a film by a solution casting method (casting method). It is manufactured by drying using a heating roll or the like. The polyvinyl alcohol-based film thus obtained is used for many applications as a film having excellent shape stability, and one of its useful applications is a polarizing film. Such a polarizing film is used as a basic component of a liquid crystal display, and in recent years, its use has been expanded to devices requiring high quality and high reliability.

Under such circumstances, there has been a demand for a polarizing film having more excellent polarization characteristics, durability and in-plane uniformity of polarization performance than conventional products.
In 5857, JP-product of the hot water breaking temperature and weight swelling degree be used a polyvinyl alcohol film is 13000 or more, in Japanese Unexamined 6-138319, JP-average birefringence 1.0 × 10 ^- It has been proposed to use a polyvinyl alcohol-based film having a birefringence unevenness of not more than ³ and an unevenness of birefringence of not more than 0.13 × 10 ⁻³ .

[0004]

However, in the technique disclosed in JP-A-5-245857, when the obtained polyvinyl alcohol-based film is used as a polarizing film, the in-plane uniformity of the polarizing performance is insufficient. In addition, Japanese Unexamined Patent Publication
In the technique disclosed in Japanese Patent Publication No. 138319, although a polarizing film with less polarization performance unevenness can be obtained, it is still unsatisfactory in view of recent high quality and widening, and further improvement is desired.

Under such circumstances, the present invention provides a method for manufacturing a polarizing film having excellent in-plane uniformity of polarization performance (degree of polarization and single transmittance) corresponding to higher quality and wider width. An object of the present invention is to provide a polyvinyl alcohol-based film and a method for producing the same.

[0006]

The present inventors have conducted intensive studies to solve the above-mentioned problems. As a result, the refractive index in the longitudinal direction of the film (nx), the refractive index in the width direction of the film (ny), The present inventors have found that a polyvinyl alcohol-based film having a refractive index (nz) in the thickness direction that satisfies the following formula (1) meets the above object, and has completed the present invention. 0.0003 ≦ (nx + ny) /2−nz≦0.01 (1)

Further, in the present invention, a polyvinyl alcohol-based resin aqueous solution is cast on a drum-type roll to form a film, and the film is dried while alternately contacting the front and back surfaces of the film with a plurality of drying rolls. In producing the base film, the relationship between the diameter (R1) of the drum type roll and the diameter (R2) of the drying roll is adjusted under the condition satisfying the following formula (2) to produce the polyvinyl alcohol-based film. Is preferred in view of film transport and in-plane uniformity. 0.5 ≦ nxR2 / R1 ≦ 3.0 (2) (where n represents the number of drying rolls and is an integer of 2 to 30)

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described specifically. The polyvinyl alcohol-based film of the present invention,
It is obtained by forming a polyvinyl alcohol-based resin into a film, and as the polyvinyl alcohol-based resin, usually,
It is produced by saponifying polyvinyl acetate obtained by polymerizing vinyl acetate. However, the present invention is not limited to this, and a small amount of unsaturated carboxylic acid (including salt, ester, amide, nitrile, etc.), carbon It may contain components copolymerizable with vinyl acetate, such as olefins of 2 to 30 (ethylene, propylene, n-butene, isobutene, etc.), vinyl ethers, unsaturated sulfonates, and the like. or,
Polyvinyl alcohol resins containing silyl groups may be used, such as post-modification using a silylating agent, copolymerization with silyl group-containing olefinically unsaturated monomers and saponification, and the like. Can be Examples of the silyl group-containing olefinically unsaturated monomer include vinyl silane and (meth) acrylamide-alkyl silane.

The degree of polymerization of the polyvinyl alcohol resin is not particularly limited, but is preferably 1,000 to 7000, particularly preferably 1200 to 6000, and more preferably 1400 to 5000. When the degree of polymerization is 10
If it is less than 00, sufficient optical performance cannot be obtained in the case of forming an optical film, and if it exceeds 7000, stretching in the case of forming a polarizing film becomes difficult, and industrial production becomes difficult, which is not preferable.

Further, the degree of saponification of the polyvinyl alcohol-based resin is preferably at least 80 mol%, particularly preferably 8 mol%.
It is preferably from 5 to 100 mol%, more preferably from 98 to 100 mol%. When the degree of saponification is less than 80 mol%, sufficient optical performance cannot be obtained in the case of forming an optical film, which is not preferable.

[0011] The polyvinyl alcohol-based resin may be used, if necessary, with a commonly used plasticizer such as glycerin, diglycerin, triglycerin, ethylene glycol, triethylene glycol, or polyethylene glycol. Less than 30% by weight,
The content is preferably 3 to 25% by weight, more preferably 5 to 20% by weight. If the amount of the plasticizer exceeds 30% by weight, the film strength is poor, which is not preferable.

More preferably, a nonionic, anionic or cationic surfactant, particularly preferably a release agent such as polyoxyethylene alkylamino ether, is used in an amount of 5% by weight or less based on the polyvinyl alcohol resin.
Preferably, it is 0.001 to 3% by weight, more preferably 0.1% by weight.
001 to 2% by weight. If the amount of the release agent exceeds 5% by weight, the film surface appearance becomes poor, which is not preferable.

Using the polyvinyl alcohol-based resin thus obtained, an aqueous solution of the polyvinyl alcohol-based resin is prepared, and the aqueous solution is cast on a drum-type roll, formed into a film, and dried to produce a polyvinyl alcohol-based film. However, in the present invention, in such a polyvinyl alcohol-based film, the refractive index (nx) in the film longitudinal direction, the refractive index (ny) in the film width direction, and the refractive index (nz) in the film thickness direction are as follows: The greatest feature is that the expression (1) is satisfied, and the effect of excellent in-plane uniformity of polarization performance is exhibited. 0.0003 ≦ (nx + ny) /2−nz≦0.01 (1)

If the relationship between the refractive index (nx) in the longitudinal direction of the film, the refractive index (ny) in the width direction of the film, and the refractive index (nz) in the thickness direction of the film is out of the range of the above-mentioned formula (1), the in-plane polarization performance is improved. The uniformity is insufficient and the effect of the present invention is not exhibited.

Hereinafter, a method for producing the polyvinyl alcohol-based film of the present invention will be described. First, the powder of the polyvinyl alcohol-based resin is washed to remove sodium acetate. Washing is performed with methanol or water, but a method of washing with methanol is more preferable because a method of washing with methanol requires solvent recovery and the like.

Next, the aqueous polyvinyl alcohol-based resin wet cake after washing is dissolved to prepare an aqueous solution of the polyvinyl alcohol-based resin. If the wet aqueous polyvinyl alcohol-based resin wet cake is directly dissolved in water, a desired high-concentration aqueous solution is obtained. , It is preferable to carry out dehydration once. The dehydration method is not particularly limited, but a method using centrifugal force is generally used.

By such washing and dehydration, it is preferable to obtain a wet polyvinyl alcohol resin wet cake having a water content of 50% by weight or less, preferably 30 to 45% by weight. When the water content exceeds 50% by weight, it is difficult to obtain a desired aqueous solution concentration, which is not preferable.

Then, the dehydrated water-containing polyvinyl alcohol-based resin wet cake is dissolved in water to form an aqueous solution of the polyvinyl alcohol-based resin. Such a polyvinyl alcohol-based resin aqueous solution is prepared by adding a polyvinyl alcohol-based resin wet cake after dehydration using a dissolving vessel, water, a plasticizer, and additives as necessary, heating, stirring, and dissolving, or a multi-screw extruder. Prepare the dehydrated polyvinyl alcohol-based resin wet cake or dried polyvinyl alcohol-based resin using, and add water, plasticizer, and additives as needed, dissolve them while heating and shearing by side feeding. In the present invention, an aqueous solution obtained by blowing steam in a dissolving vessel equipped with a vertically circulating flow generating type stirring blade to dissolve the wet polyvinyl alcohol-based resin wet cake may be used. Is preferred.

In the present invention, a stirring blade having a large blade is preferred as a vertical circulation flow generating stirring blade. In particular, a Max Blend type blade manufactured by Sumitomo Heavy Industries, Ltd., manufactured by Shinko Pantech Co., Ltd. Is preferably used.
However, it is not limited to these. The shape of the stirring blade is not particularly limited, but it is preferable that the diameter (d) of the blade / the inner diameter (D) of the melting vessel is about 0.5 to 0.8. In addition, it is preferable that a plurality of baffle plates along the rotation axis direction are arranged at intervals on the side wall surface of the melting vessel as required.

In dissolving the wet polyvinyl alcohol-based resin wet cake in a dissolving vessel equipped with such a vertically circulating flow generating type stirring blade, steam is blown. When the steam is blown, a desired concentration is obtained. It is also preferable to add water. Moreover, you may add a plasticizer and an additive as needed.

The amount of the steam blown is preferably 0.5 to 5 times (in terms of weight) the amount of the polyvinyl alcohol resin to be dissolved, and the blowing time is preferably 0.5 to 3 hours. If the blowing amount is less than 0.5 times, the dissolution becomes insufficient, and if it exceeds 5 times, the amount of drain becomes too large, and the desired concentration cannot be obtained. Further, when blowing steam, it is preferable to blow from the bottom of the can, but it is not limited to this, and it may be blown from the side or the like.

In addition, steam is blown, and the resin temperature is 40 to
When the temperature reaches 80 ° C., preferably 45 to 70 ° C., it is preferable to start stirring, since uniform dissolution can be achieved. If the resin temperature is lower than 40 ° C., the load on the motor increases,
If the temperature exceeds 0 ° C., the polyvinyl alcohol-based resin is solidified and cannot be uniformly dissolved, which is not preferable.

Further, steam is blown, and the resin temperature is 90
When the temperature reaches about 100 ° C., preferably 95 ° C. to 100 ° C., it is also preferable to pressurize the inside of the can in that uniform dissolution can be achieved.

Then, when the resin temperature reaches 130 to 150 ° C., the blowing of steam is stopped, and
Stirring is continued for a time to effect dissolution. After dissolution, the concentration is adjusted to a desired concentration. In adjusting the concentration of the aqueous solution, a part of the liquid in the can is withdrawn and circulated, and the concentration is measured using a process refractometer (manufactured by K-PATENTS).

The concentration of the aqueous solution of the polyvinyl alcohol resin thus obtained is preferably 15 to 60% by weight, particularly preferably 17 to 55% by weight, and further preferably 20 to 50% by weight. When the concentration is less than 15% by weight, the drying load is increased and the production capacity is deteriorated. When the concentration is more than 60% by weight, the viscosity becomes too high to achieve uniform dissolution, which is not preferable.

Next, the obtained polyvinyl alcohol-based resin aqueous solution is subjected to a defoaming treatment. Examples of the defoaming method include static defoaming and defoaming with a multi-screw extruder. In the present invention, a method of defoaming using a multi-screw extruder (A) is preferable.
The multi-screw extruder (A) is not particularly limited as long as it is a multi-screw extruder having a vent.
A screw extruder is used.

Then, the aqueous solution of the polyvinyl alcohol resin having a concentration of 15 to 50% by weight is mixed with the multi-screw extruder (A).
And the extruder tip pressure is ² to 100 kg / cm ² , preferably 5 to 70 kg / c.
Degassing is performed under conditions in the range of m ² .

If the resin temperature at the vent section is lower than 105 ° C., defoaming becomes insufficient, and if the resin temperature exceeds 180 ° C., resin deterioration occurs. The extruder tip pressure is 2kg / c.
If it is less than m ² , defoaming will be insufficient, and if it exceeds 100 kg / cm ² , resin leakage will occur in the piping, and stable production will not be possible.

In the present invention, a gear pump (P1) and a gear pump (P2) are provided before and after the multi-screw extruder (A).
An aqueous polyvinyl alcohol-based resin solution is supplied to the multi-screw extruder (A) by the gear pump (P1), and the gear pump (P1) is used.
According to 2), the aqueous solution of the polyvinyl alcohol resin is discharged from the multi-screw extruder (A). The inlet pressure of the gear pump (P2) is in the range of ² to 70 kg / cm ² .
It is preferable to control the gear pump (P1) so as to exhibit a constant value in a range of preferably 5 to 70 kg / cm ^{2 from} the viewpoint of improving the accuracy of the film thickness. The inlet pressure is 2kg
/ Cm ² , the defoaming becomes insufficient, and 70 kg / cm ²
If the ratio exceeds the above range, the resin will come out from the vent portion, which is not preferable, and if the value is not a certain value even in the above range, the accuracy of the film thickness is insufficient, which is not preferable.
Note that the constant value here allows a range within ± 2%, preferably ± 1.5% from the specified value.

The defoaming treatment is performed by the multi-screw extruder (A), and the polyvinyl alcohol-based resin aqueous solution discharged from the multi-screw extruder (A) is introduced into a T-shaped slit die by a fixed amount, and is fed into a drum type. It is cast on a roll, formed into a film, and dried.

In such a T-shaped slit die, usually, a T-shaped slit die having an elongated rectangle is used.
It is also preferable to use a T-shaped slit die in which the slit interval is smaller than the central slit interval at any portion within 5%, and by using such a T-shaped slit die, The effect of excellent film peelability is exhibited without increasing the film thickness.

The T-shaped slit die is particularly preferably a T-shaped slit die in which the slit interval at any portion within 15% from both ends is 80% or less of the central interval. And more preferably a T-shaped slit die in which the slit interval gradually decreases from the portion within 15% of both ends toward the ends.

In casting a film with a drum type roll,
For example, the rotation speed of a drum type roll is 5 to 30 m / min.
And particularly preferably 6 to 20 m / m
in, and the surface temperature of the drum type roll is 70 to 99 ° C.
And more preferably 75 to 97 ° C. If the surface temperature of the drum type roll is less than 70 ° C., drying becomes poor, and if it exceeds 99 ° C., foaming is not preferred.

The resin temperature at the exit of the T-shaped slit die is 8
Preferably it is 0-100 degreeC, More preferably, it is 8
5-98 ° C. If the resin temperature at the exit of the T-shaped slit die is lower than 80 ° C., the flow becomes poor, and if it exceeds 100 ° C., foaming is not preferred.

Although the size of the drum type roll is not particularly limited, for example, the diameter of the roll is 2,000 to 400.
0 mm is preferable, and more preferably 2500-3800
mm.

A film is formed by casting from a drum type roll and dried to form a polyvinyl alcohol-based film. In the present invention, in particular, an aqueous polyvinyl alcohol-based resin solution is cast on a drum-type roll to form a film. In producing the polyvinyl alcohol-based film by drying the film while alternately contacting the front and back surfaces thereof with a plurality of drying rolls, the diameter of the drum type roll (R1) and the diameter of the drying roll (R2) are determined. It is preferable to adjust the relationship under the condition satisfying the following expression (2) from the viewpoint of in-plane uniformity of film transport and polarization performance. 0.5 ≦ nxR2 / R1 ≦ 3.0 (2) (where n represents the number of drying rolls and is an integer of 2 to 30)

Under the condition not satisfying the above expression (2), the in-plane uniformity is insufficient, and the film transport is also unstable, which is not preferable. The number (n) of the drying rolls is particularly 3 to 26.
Are preferred, more preferably 4 to 20. Further, the diameter (R1) of the drum type roll is 2000 to 5000 m.
m is preferable, and 2400-4500 m is more preferable.
m, particularly preferably 2800 to 4000 mm, and the diameter (R2) of the drying roll is preferably 100 to 1000, more preferably 150 to 900 mm, and particularly preferably 200 to 800 mm.

The diameter (R1) of the drum type roll is 2000
If it is less than 5 mm, the drying length is insufficient and the speed does not come out.
When the diameter exceeds (R2) is less than 100 mm, an enormous number is required. When the diameter exceeds 1,000 mm, film transport becomes unstable, which is not preferable.

In the above drying, the surface temperature of the drying roll is not particularly limited, but is 60 to 100 ° C., more preferably 65 to 100 ° C.
Preferably it is 90 ° C. The surface temperature is 60 ° C
If it is less than 100 ° C., drying will be poor.

Further, in the present invention, heat treatment and humidity control are performed as necessary. Regarding the heat treatment, a method of passing a roll (1 to 30 rolls) having a surface of hard chromium plating or a mirror surface and having a diameter of 0.2 to 2 m adjusted to a temperature of 60 to 180 ° C., a floating dryer (length: (2 to 10 m, temperature: 80 to 180 ° C.).

For humidity control, a method of passing through a room conditioned at a temperature of 20 to 80 ° C. and a humidity of 65 to 95% RH, a method by a vapor condensation method using “Fludex” manufactured by Hirano Techseed Co., Ltd., etc. Is mentioned.

The thus obtained polyvinyl alcohol-based film is a polyvinyl alcohol-based film satisfying the above formula (1), and produces a polarizing film having excellent in-plane uniformity of polarization performance (degree of polarization, single transmittance). Alcohol film. Less than,
A method for producing a polarizing film using such a polyvinyl alcohol-based film will be described.

As a method for producing a polarizing film, such a polyvinyl alcohol-based film is stretched and dyed by dipping in a solution of iodine or a dichroic dye, stretching and dyeing are performed simultaneously, or iodine or a dichroic dye is used. After dyeing and stretching, there is a method of treating with a boron compound. In addition, there is a method of stretching in a solution of a boron compound after dyeing, and the like can be appropriately selected and used.

The thickness of the polyvinyl alcohol-based film used for the polarizing film is preferably from 30 to 100 μm, more preferably from 40 to 90 μm, and if it is less than 30 μm, stretching is difficult, and if it is more than 100 μm, the accuracy of the film thickness is undesirably reduced. .

The polyvinyl alcohol-based film (unstretched film) is then stretched, dyed, and treated with a boron compound. Stretching, dyeing, and boron compound treatment may be performed separately or simultaneously, but in the present invention, it is desirable to carry out uniaxial stretching during at least one of the dyeing step and the boron compound treatment step.

The stretching is preferably performed 3 to 10 times, preferably 3.5 to 6 times in the uniaxial direction. At this time, slight stretching (extending to the extent of preventing shrinkage in the width direction or more) may be performed in the direction perpendicular to the above. It is desirable to select the temperature condition during stretching from 40 to 170 ° C. Further, the stretching ratio may be finally set in the above range, and the stretching operation may be performed not only in one stage but also in any range of the manufacturing process.

The dyeing of the film is performed by contacting the film with a liquid containing iodine or a dichroic dye. Usually, an aqueous solution of iodine-potassium iodide is used, the concentration of iodine is 0.1 to 2 g / l, the concentration of potassium iodide is 10 to 50 g / l, and the weight ratio of iodine / potassium iodide is 20 to 100. Is appropriate. Staining time is 30-500
Seconds are practical. The temperature of the treatment bath is preferably 5 to 50C. A small amount of an organic solvent compatible with water other than the water solvent may be contained. Arbitrary means such as immersion, coating, spraying and the like can be applied as the contact means.

The dyed film is then treated with a boron compound. Boric acid and borax are practical as boron compounds. The boron compound is used in the form of an aqueous solution or a mixed solution of water and an organic solvent at a concentration of about 0.5 to 2 mol / l, and it is practically desirable that a small amount of potassium iodide coexist in the liquid. The treatment method is preferably an immersion method, but of course, a coating method and a spraying method can also be performed. The temperature during processing is 50 ~
The temperature is preferably about 70 ° C., and the treatment time is preferably about 5 to 20 minutes. If necessary, a stretching operation may be performed during the treatment.

The polarizing film thus obtained can be used by laminating and adhering an optically isotropic polymer film or sheet on one or both sides thereof as a protective film. Examples of such a protective film include films or sheets of cellulose triacetate, cellulose diacetate, polycarbonate, polymethyl methacrylate, polystyrene, polyether sulfone, polyarylene esters, poly-4-methylpentene, polyphenylene oxide, and the like.

In order to reduce the thickness of the polarizing film, a curable resin such as a urethane resin, an acrylic resin, or a urea resin is applied on one or both sides of the protective film instead of the protective film and laminated. You can also.

Such a polarizing film (or a protective film or a curable resin laminated on at least one surface thereof) may be provided on one surface thereof with a transparent pressure-sensitive adhesive layer, if necessary, by a generally known method. It may be formed and put to practical use. Acrylic ester as the pressure-sensitive adhesive layer,
For example, a copolymer (acrylic) of butyl acrylate, ethyl acrylate, methyl acrylate, 2-ethylhexyl acrylate and the like with an α-monoolefin carboxylic acid such as acrylic acid, maleic acid, itaconic acid, methacrylic acid, crotonic acid, etc. Nitrile, vinyl acetate, and those containing a vinyl monomer such as styrene are also included.), But those which are particularly preferred because they do not inhibit the polarizing properties of the polarizing film, but are not limited thereto. Any pressure-sensitive adhesive having transparency can be used. For example, a polyvinyl ether-based or rubber-based adhesive may be used.

Such a polarizing film can be used as an electronic desk calculator, an electronic timepiece, a word processor, a personal computer, a portable information terminal, a liquid crystal display device such as an instrument of a car or a machine, a sunglass, an eye-glass, a three-dimensional glasses, a display element (CRT). , LCD etc.), medical devices, building materials, toys and the like.

[0053]

The present invention will be specifically described below with reference to examples. In the examples, “parts” and “%” are based on weight unless otherwise specified.

Example 1 200 kg of water at 18 ° C. was placed in a 500-liter tank, and while stirring, 40 kg of a polyvinyl alcohol resin having a polymerization degree of 1700 and a saponification degree of 99.7 mol% was added, and stirring was continued for 15 minutes. After draining water once more, water 200k further
g was added and stirred for 15 minutes. The obtained slurry was dehydrated with a super decanter (manufactured by Tomoe Industries), and the water content was 40%.
%, And a polyvinyl alcohol resin wet cake having a sodium content of 1500 ppm were obtained.

70 kg of the polyvinyl alcohol-based resin wet cake is placed in a dissolving can equipped with Max-blend type wings (manufactured by Sumitomo Heavy Industries, Ltd.), 4.2 kg of glycerin as a plasticizer, and 42 g of polyoxyethylene alkylamino ether as a release agent. , 10 kg of water, and steam was blown from the bottom of the can. When the internal resin temperature reached 50 ° C., stirring (rotation speed: 5 rpm) was performed, and the internal resin temperature was 1
When the temperature reached 00 ° C., the inside of the system was pressurized and heated up to 150 ° C., and then the blowing of steam was stopped (total of 75 kg of steam blowing), and the mixture was stirred for 30 minutes (rotation speed: 20 rpm).
After m) and uniform dissolution, a 45% aqueous polyvinyl alcohol-based resin aqueous solution (including a plasticizer and a release agent as solids) was obtained by adjusting the concentration.

Next, the aqueous polyvinyl alcohol resin solution (liquid temperature: 147 ° C.) was supplied to a twin screw extruder (manufactured by Toshiba Machine Co., Ltd.) from a gear pump (P1), defoamed, and then discharged from a gear pump (P2). . The conditions of the gear pump (P1), the twin-screw extruder (A), and the gear pump (P2) are as follows.

Gear pump (P1) Number of gears: 2 gears Size: 50 cc / rev (discharge rate per rotation) Inlet pressure: 5 kg / cm ²

Twin screw extruder (A) Screw outer diameter: 35 mm Screw L / D: 40 (L: length, D: diameter) Extruder tip pressure: 50 kg / cm ² Revolution: 300 rpm C1 / C2 (vent) / C3 / C4 / C5 = 150/1
35/105/105/105

Gear pump (P2) Inlet pressure: 50 kg / cm ² Discharge amount: 41 kg / hr Number of gears: 2 gears Size: 50 cc / rev (discharge amount per rotation) Number of revolutions: 12.3 rpm Discharge from gear pump (P2) No bubbles or the like were observed in the obtained aqueous solution of the polyvinyl alcohol-based resin.

The aqueous solution of the polyvinyl alcohol resin discharged from the gear pump (P2) was cast on a drum type roll from a T-shaped slit die (a straight manifold die having a width of 450 mm) to form a film. The conditions for such casting film formation are as follows. Drum type roll Diameter (R1): 3200 mm, width:
1000mm Rotation speed: 8m / min Surface temperature: 90 ° C Resin temperature at T-type slit die outlet: 95 ° C

Then, drying was performed while alternately contacting the front and back surfaces of the obtained film with a drying roll under the following conditions. (It was a condition satisfying the expression (2).) Drying roll Diameter (R2): 320 mm, width: 1
000 mm Number (n): 10 Rotation speed: 8 m / min Surface temperature: 80 ° C.

Thereafter, further heat treatment (conditions: floating dryer (140 ° C., length 6 m)), humidity control (conditions:
Fludex) to obtain a polyvinyl alcohol-based film (F-1) (width 400 mm, thickness 75 μm). The obtained polyvinyl alcohol-based film (F-
1) has a refractive index (nx) of 1.52 in the longitudinal direction of the film.
83, the refractive index (ny) in the film width direction is 1.528
0, the refractive index (nz) in the film thickness direction is 1.5270
Was satisfied with the expression (1).

Next, the polyvinyl alcohol-based film (F-1) was treated with 0.2 g / l of iodine and potassium iodide 6
Immersed in an aqueous solution of 0 g / l at 30 ° C. for 240 seconds, then immersed in an aqueous solution (55 ° C.) having a composition of boric acid 60 g / l and potassium iodide 30 g / l, and simultaneously uniaxially stretched 4 times. After performing a boric acid treatment for 5 minutes while drying, the film was dried to obtain a polarizing film (H-1) (unit transmittance 41.0).
%, Degree of polarization of 99.9%). The obtained polarizing film was evaluated as follows.

(In-Plane Uniformity) A total of seven places, three each at a central part in the width direction of the obtained polarizing film and at intervals of 25 mm from the central part toward both ends, and seven parts in the flow direction. The single transmittance (5) was measured at a total of 35 locations at 5 locations at 1 m intervals from the locations, and evaluated as follows.・ ・ ・: Variation of single transmittance at 35 locations is within 1% ×: Variation of single transmittance at 35 locations exceeds 1% The single transmittance (%) is measured using a spectrophotometer. 40
The range of 0 to 700 nm was set at intervals of 10 nm, and the average of the value measured when the polarizing film was stretched up and down and the value measured when the polarizing film was measured left and right was taken as the average.

Example 2 180 kg of water at 18 ° C. was placed in a 500-liter tank, and while stirring, 36 kg of a polyvinyl alcohol resin having a polymerization degree of 2600 and a saponification degree of 99.7 mol% was added, and stirring was continued for 15 minutes. After once draining the water, and then water 180k
g was added and stirred for 15 minutes. The obtained slurry was dehydrated with a super decanter (manufactured by Tomoe Industries), and the water content was 40%.
%, A polyvinyl alcohol resin wet cake having a sodium content of 1800 ppm was obtained.

[0066] 60 kg of the polyvinyl alcohol resin wet cake is placed in a dissolving can equipped with Max-blend type wings (manufactured by Sumitomo Heavy Industries), 3.6 kg of glycerin as a plasticizer, and 36 g of polyoxyethylene alkylamino ether as a release agent. And 20 kg of water were added, and steam was blown from the bottom of the can. When the internal resin temperature reached 50 ° C., stirring (rotation speed: 5 rpm) was performed.
When the temperature reached 00 ° C., the inside of the system was pressurized and heated up to 150 ° C., and then the blowing of steam was stopped (total of 75 kg of steam blowing), and the mixture was stirred for 30 minutes (rotation speed: 20 rpm).
After m) and uniform dissolution, a 35% concentration aqueous solution of a polyvinyl alcohol-based resin (including a plasticizer and a release agent as a solid content) was obtained by adjusting the concentration.

Next, the aqueous solution of the polyvinyl alcohol resin (liquid temperature: 147 ° C.) was supplied from a gear pump (P1) to a twin screw extruder (manufactured by Toshiba Machine Co., Ltd.), defoamed, and then discharged from a gear pump (P2). . The conditions of the gear pump (P1), the twin-screw extruder (A), and the gear pump (P2) are as follows.

Gear pump (P1) Number of gears: 2 gears Size: 50 cc / rev (discharge amount per rotation) Inlet pressure: 4.5 kg / cm ²

Twin screw extruder (A) Screw outer diameter: 35 mm Screw L / D: 40 (L: length, D: diameter) Extruder tip pressure: 50 kg / cm ² Revolution: 300 rpm C1 / C2 (vent) / C3 / C4 / C5 = 150/1
35/110/105/105

Gear pump (P2) Inlet pressure: 50 kg / cm ² Discharge amount: 46.9 kg / hr Number of gears: 2 gears Size: 50 cc / rev (discharge amount per rotation) Number of revolutions: 14.1 rpm Gear pump (P2) No bubbles or the like were observed in the discharged polyvinyl alcohol-based resin aqueous solution.

The aqueous polyvinyl alcohol resin solution discharged from the gear pump (P2) was cast on a drum-type roll from a T-shaped slit die (a straight manifold die having a width of 450 mm) to form a film. The conditions for such casting film formation are as follows. Drum type roll Diameter (R1): 3200 mm, width:
1000mm Rotation speed: 8m / min Surface temperature: 90 ° C Resin temperature at T-type slit die exit: 97 ° C

Then, drying was performed while the front and back surfaces of the obtained film were alternately brought into contact with a drying roll under the following conditions. (It was a condition satisfying the expression (2).) Drying roll Diameter (R2): 600 mm, width: 1
000 mm Number (n): 6 Rotation speed: 8 m / min Surface temperature: 75 ° C.

Thereafter, according to Example 1, further heat treatment (conditions: floating dryer (140 ° C., length 6)
m)) and humidity control (condition: Fludex), and a polyvinyl alcohol-based film (F-2) (width 400 m)
m, thickness 75 μm). The obtained polyvinyl alcohol-based film (F-2) has a refractive index (nx) in the longitudinal direction of the film of 1.5272, a refractive index (ny) in the width direction of the film of 1.5275, and a refractive index (nz) in the thickness direction of the film. ) Was 1.5260, which satisfied the expression (1). Further, in the same manner as in Example 1, the polarizing film (H-2)
(A single transmittance of 41.5% and a degree of polarization of 99.9%).
The same evaluation as in Example 1 was performed for the obtained polarizing film.

Comparative Example 1 An aqueous polyvinyl alcohol-based resin solution (liquid temperature: 147 ° C.) obtained in the same manner as in Example 1 was supplied from a gear pump (P1) to a twin-screw extruder (manufactured by Toshiba Machine Co., Ltd.), and defoamed. After doing
It was discharged from the gear pump (P2). Gear pump (P2)
No bubbles or the like were observed in the discharged polyvinyl alcohol-based resin aqueous solution.

The aqueous polyvinyl alcohol resin solution discharged from the gear pump (P2) was cast on a drum-type roll from a T-shaped slit die (a straight manifold die having a width of 450 mm) to form a film. The conditions for such casting film formation are as follows. Drum type roll Diameter (R1): 3200 mm, width:
1000mm Rotation speed: 8m / min Surface temperature: 90 ° C Resin temperature at T-type slit die outlet: 98 ° C

Then, the film was dried while the front and back surfaces of the obtained film were alternately brought into contact with a drying roll under the following conditions. (The conditions did not satisfy the expression (2).) Drying roll Diameter (R2): 320 mm, width: 1
000 mm Number (n): 3 Rotation speed: 8 m / min Surface temperature: 80 ° C.

Then, according to Example 1, further heat treatment (condition: floating dryer (140 ° C., length 6)
m)) and humidity control (condition: Fludex), and a polyvinyl alcohol-based film (F-3) (width 400 m)
m, thickness 75 μm). The obtained polyvinyl alcohol-based film (F-3) has a refractive index (nx) in the longitudinal direction of the film of 1.5217, a refractive index (ny) in the width direction of the film of 1.5218, and a refractive index (nz) in the thickness direction of the film. ) Was 1.5050, which did not satisfy the expression (1). Further, in the same manner as in Example 1, the polarizing film (H-
3) (Single transmittance 41.0%, degree of polarization 99.8%) was obtained. The same evaluation as in Example 1 was performed for the obtained polarizing film.

Comparative Example 2 An aqueous polyvinyl alcohol-based resin solution (liquid temperature: 147 ° C.) obtained in the same manner as in Example 1 was supplied from a gear pump (P1) to a twin-screw extruder (manufactured by Toshiba Machine Co., Ltd.), and defoamed. After doing
It was discharged from the gear pump (P2). Gear pump (P2)
No bubbles or the like were observed in the discharged polyvinyl alcohol-based resin aqueous solution.

The polyvinyl alcohol-based resin aqueous solution discharged from the gear pump (P2) was cast on a drum type roll from a T-shaped slit die (a straight manifold die having a width of 450 mm) to form a film. The conditions for such casting film formation are as follows. Drum type roll Diameter (R1): 2500 mm, width:
1000mm Rotation speed: 8m / min Surface temperature: 90 ° C Resin temperature at T-type slit die outlet: 95 ° C

Then, the film was dried while the front and back surfaces of the obtained film were alternately brought into contact with a drying roll under the following conditions. (The conditions did not satisfy the expression (2).) Drying roll Diameter (R2): 320 mm, width: 1
000 mm Number (n): 26 Rotation speed: 8 m / min Surface temperature: 75 ° C.

Thereafter, according to Example 1, further heat treatment (condition: floating dryer (140 ° C., length 6)
m)) and humidity control (condition: Fludex), and a polyvinyl alcohol-based film (F-4) (width 400 m)
m, thickness 75 μm). The obtained polyvinyl alcohol-based film (F-4) had a refractive index (nx) of 1.5287 in the film longitudinal direction, a refractive index (ny) of 1.5285 in the film width direction, and a refractive index (nz) of the film thickness direction. ) Was 1.5284, which did not satisfy the expression (1). Further, in the same manner as in Example 1, the polarizing film (H-
4) (Single transmittance 41.0%, degree of polarization 99.8%) was obtained. The same evaluation as in Example 1 was performed for the obtained polarizing film. Table 1 shows the evaluation results of the examples and the comparative examples.

[0082]

[0083]

The polyvinyl alcohol-based film of the present invention is a polyvinyl alcohol-based film that satisfies the above formula (1). Therefore, preferably, an aqueous solution of a polyvinyl alcohol-based resin is cast on a drum-type roll to form a film. The relationship between the diameter of the drum type roll (R1) and the diameter of the drying roll (R2) in producing the polyvinyl alcohol-based film by drying the film while alternately contacting the front and back surfaces of the film with a plurality of drying rolls. Is adjusted under the condition that satisfies the above formula (2) to produce a polyvinyl alcohol-based film. Therefore, polyvinyl alcohol for producing a polarizing film having excellent in-plane uniformity of polarization performance (degree of polarization, single transmittance). It becomes an alcohol-based film.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) // B29K 29:00 B29K 29:00 B29L 7:00 B29L 7:00 C08L 29:04 C08L 29:04 F Term (reference) 2H049 BA02 BA26 BA27 BB27 BB28 BB29 BB33 BB43 BB51 BC03 BC09 BC10 BC22 2H091 FA08X FA08Y FA08Z FB02 FC01 KA01 KA10 LA16 4F071 AA29 AF31 BB02 BB06 BC01 4F205 AA19 AG02 GB02 GF24

Claims (3)

[Claims] 1. A polyvinyl resin wherein the refractive index (nx) in the longitudinal direction of the film, the refractive index (ny) in the width direction of the film, and the refractive index (nz) in the thickness direction of the film satisfy the following formula (1). Alcohol-based film. 0.0003 ≦ (nx + ny) /2−nz≦0.01 (1) 2. A polyvinyl alcohol-based resin aqueous solution is cast on a drum-type roll to form a film, and the film is dried while alternately contacting the front surface and the back surface with a plurality of drying rolls to form a polyvinyl alcohol-based film. In manufacturing
Drum-type roll diameter (R1) and drying roll diameter (R
The method for producing a polyvinyl alcohol-based film according to claim 1, wherein the relationship with (2) is adjusted under a condition satisfying the following expression (2). 0.5 ≦ nxR2 / R1 ≦ 3.0 (2) (where n represents the number of drying rolls and is an integer of 2 to 30) 3. A polarizing film comprising the polyvinyl alcohol-based film according to claim 1.