WO2017204271A1

WO2017204271A1 - Polyvinyl alcohol-based film, production method therefor, and polarization film using polyvinyl alcohol-based film

Info

Publication number: WO2017204271A1
Application number: PCT/JP2017/019450
Authority: WO
Inventors: 学花島; 御手洗　宏志; 早川　誠一郎
Original assignee: 日本合成化学工業株式会社
Priority date: 2016-05-27
Filing date: 2017-05-25
Publication date: 2017-11-30
Also published as: TW202118612A; KR102400929B1; TWI721171B; TWI757067B; CN109312085A; TW201815544A; JP6834956B2; CN109312085B; JPWO2017204271A1; CN114437385A; KR20190013765A

Abstract

Provided are: a polyvinyl alcohol-based film that, when immersed in water, is able to reduce the elution amount of a polyvinyl alcohol-based resin, and is unlikely to become curled; a method for producing said polyvinyl alcohol-based film; and a polarization film using said polyvinyl alcohol-based film. The polyvinyl alcohol-based film according to the present invention is characterized in that, when immersed in 50°C water for one minute, the elution amount of a polyvinyl alcohol-based resin is not more than 900 ppm/m², and the curl angle measured under condition (A) in the short side direction is not more than 135°. (A) A condition in which a test object, comprising a 10 cm (long side) × 5 cm (short side) rectangular test piece cut out in a given direction from the polyvinyl alcohol-based film and a weight having a mass of 5 g and being attached to the center of a first longitudinal end section of the test piece, is suspended while being supported at the center of a second longitudinal end section of the test piece, and is entirely immersed in 30°C water for 10 seconds.

Description

POLYVINYL ALCOHOL FILM, PROCESS FOR PRODUCING THE SAME, AND POLARIZING FILM USING THE POLYVINYL ALCOHOL FILM

The present invention relates to a polyvinyl alcohol-based film that is less likely to elute impurities into water and that does not curl even when immersed in water, in particular, a polyvinyl alcohol-based film that can obtain a polarizing film having high polarization performance with high productivity, and The present invention relates to a production method and a polarizing film using the polyvinyl alcohol film.

In recent years, the development of liquid crystal display devices has been remarkable, and they are widely used in smartphones, tablets, personal computers, liquid crystal televisions, projectors, in-vehicle panels, and the like. Such a liquid crystal display device uses a polarizing film. As the polarizing film, a film obtained by adsorbing and orienting iodine on a polyvinyl alcohol film is mainly used. In recent years, with the increase in screen definition, brightness, and size, there has been a need for polarizing films that are more excellent in polarization performance than conventional products, have no color unevenness, and are wide and long.

In general, a polarizing film is a raw material polyvinyl alcohol film that is unwound from a roll and swelled with water (including warm water) while being conveyed in the flow direction (MD direction), and then stained with iodine and iodine. It is manufactured through steps such as stretching for orientation and boric acid crosslinking for fixing the orientation state. The defects that occur during these steps greatly reduce the productivity of the polarizing film. For example, in the swelling process, when impurities are eluted from the polyvinyl alcohol film and the swelling tank is contaminated, the contamination is diffused throughout the subsequent process. Even in the dyeing process and boric acid crosslinking process, if impurities are eluted from the polyvinyl alcohol film, the polarizing performance of the obtained polarizing film is deteriorated, and a great amount of labor is required for filtration and replacement of chemicals used in each process. It will be. Such impurities include low molecular weight polyvinyl alcohol resins (including oligomers) present in the polyvinyl alcohol film. In particular, low molecular weight substances having a molecular weight of 50,000 or less are easily eluted in water, and the degree of polarization. There was a tendency to form a low molecular weight iodine complex that lowers. In the swelling process, if folds or wrinkles are generated at both ends in the width direction (TD direction) of the polyvinyl alcohol film, not only conveyance becomes difficult, but the film tends to break during stretching.

On the other hand, a polyvinyl alcohol-based film as a raw material is generally produced by dissolving a polyvinyl alcohol-based resin as a raw material in water and using such an aqueous solution (film-forming stock solution) by a continuous casting method. Specifically, a film formed by discharging and casting an aqueous solution of a polyvinyl alcohol-based resin onto a cast mold such as a cast drum or an endless belt is peeled from the cast mold, and then conveyed in the flow direction (MD direction). However, it is manufactured by drying using a plurality of metal heating rolls. Among these processes, the drying process is an important process for controlling the elution amount of the resin from the polyvinyl alcohol film and the swelling property of the polyvinyl alcohol film. That is, if the drying in the drying process is insufficient, the resin eluted during the production of the polarizing film increases, and at the same time, the polyvinyl alcohol film tends to be broken or wrinkled in the swelling process, and conversely, the drying is excessive. And the swelling speed in the swelling tank tends to decrease. In addition, if there is a difference in characteristics between the front and back surfaces of the film formed in the drying process, the film tends to curl in the swelling process.

As a method for improving the above problem, for example, a polyvinyl alcohol film in which the amount of the polyvinyl alcohol resin eluted into water is reduced has been proposed (for example, see Patent Document 1). Further, a polyvinyl alcohol film having a curl angle of 180 ° or less when immersed in water at 30 ° C. for 5 minutes (see, for example, Patent Document 2), a thickness of 50 μm or less, and immersed in water at 30 ° C. for 30 seconds. A polyvinyl alcohol film having a curl angle of 200 ° or less has been proposed (see, for example, Patent Document 3). Moreover, the manufacturing method of the polyvinyl alcohol-type film by specific drying conditions is proposed (for example, refer patent document 4). Here, the curl angle is an angle formed by the plane portion of the polyvinyl alcohol film and the tangential direction of the edge portion of the curled portion in the width direction (TD direction) of the polyvinyl alcohol film [FIG. ))].

JP 2009-212462 A JP 2001-315140 A International Publication No. 2014/208537 JP 2011-156874 A

However, even with the technique of the above-mentioned patent document, it is insufficient to control the elution amount of the polyvinyl alcohol-based resin and improve the swelling characteristics at the time of manufacturing the polarizing film.

In the disclosed technique of Patent Document 1, the concentration of the eluate of the polyvinyl alcohol resin is 10 to 50 ppm when a 10 cm × 10 cm square polyvinyl alcohol film is immersed in 1 liter of water at 50 ° C. for 4 hours. When converted to 1 m ^{2 of} film, polyvinyl alcohol resin of 1,000 to 5,000 ppm / m ² is eluted, and in order to produce a polarizing film with high production efficiency according to the recent demand for polarizing films. Further reduction of the elution amount of the polyvinyl alcohol resin is necessary.

In the disclosed technique of Patent Document 2, the curl angle 180 ° is a folded state, the curl angle 90 ° is a wrinkled state, and the curl angle 45 ° is a greatly warped state. It is necessary to reduce the curl angle. In particular, in order to cope with the increase in width and length required for a polarizing film in recent years, it is necessary to further reduce the curl angle in a wide and long polyvinyl alcohol film.

In the technique disclosed in Patent Document 3, although the curl angle when immersed in water at 30 ° C. for 30 seconds is set to 200 ° or less, breakage during stretching can be suppressed to some extent. In order to cope with the improvement in productivity, it is necessary to further reduce the curl angle.

The disclosed technique of the above-mentioned patent document 4 can reduce the retardation of the polyvinyl alcohol film by setting the contact time between the film and each heat roll to 1 to 6 seconds. In order to reduce the resin elution amount, there is room for improvement in terms of further control of drying conditions.

Therefore, in the present invention, in such a background, the polyvinyl alcohol film is excellent in controllability and swelling property of the elution amount of the polyvinyl alcohol resin during the production of the polarizing film, and can obtain a polarizing film excellent in polarizing performance. In addition, the amount of polyvinyl alcohol resin eluted when immersed in water can be reduced, the polarizing film manufacturing equipment is not contaminated, and it is difficult to curl even when immersed in water. Disclosed are a polyvinyl alcohol film that is less likely to be broken or wrinkled in the process, a method for producing the same, and a polarizing film using the polyvinyl alcohol film.

However, as a result of intensive studies in view of such circumstances, the present inventors have found that a polyvinyl alcohol-based film having a small curl angle measured under specific water immersion conditions with a small elution amount of the polyvinyl alcohol-based resin with respect to water at a specific temperature. The present inventors have found that when a polarizing film is produced using a glass, the above-mentioned problems can be solved and a high-performance polarizing film can be produced with high productivity.

That is, the first gist of the present invention is that the elution amount of the polyvinyl alcohol resin when immersed in water at 50 ° C. for 1 minute is 900 ppm / m ² or less, and the short side direction is measured under the following condition A. The polyvinyl alcohol film has a curl angle of 135 ° or less.
(A) A rectangular test piece having a long side of 10 cm and a short side of 5 cm cut out from the polyvinyl alcohol film in an arbitrary direction, and a mass attached to the center of the first edge portion in the long side direction of the test piece A condition in which the entire test body is immersed in water at 30 ° C. for 10 seconds in a state where a test body provided with 5 g of weight is supported and suspended at the center of the second end edge in the long side direction of the test piece. .

Further, the second gist of the present invention is that a film forming step of continuously discharging and casting an aqueous solution of a polyvinyl alcohol resin into a cast mold to form a film, and peeling the formed film from the cast mold. Then, the manufacturing method of the polyvinyl alcohol-type film of the said 1st summary provided with the drying process which dries the film formed, Comprising: Drying of the film formed in the said drying process formed the said film It is a manufacturing method of the polyvinyl alcohol-type film characterized by performing by making the front surface and back surface of a film contact a some metal heating roll alternately.

And the 3rd summary of this invention is a polarizing film in which the polyvinyl-alcohol-type film of the said 1st summary is used.

The polyvinyl alcohol film according to the first aspect of the present invention has a small amount of polyvinyl alcohol resin eluted with respect to water at a specific temperature and a small curl angle measured under specific water immersion conditions. The amount of elution of the polyvinyl alcohol resin can be reduced, and the curl angle can be reduced. Therefore, the effect that a polarizing film excellent in polarization performance can be produced with high productivity is exhibited.

In particular, in the condition A, when the immersion time of the test specimen is 2 minutes and the measured curl angle in the short side direction is 40 ° or less, the swelling process during the production of the polarizing film is further increased. Breakage can hardly occur, and breakage when manufacturing a polarizing film can be further prevented. Therefore, the effect that the polarizing film which is excellent in polarization performance can be manufactured with higher productivity is produced.

In addition, when the polyvinyl alcohol film is a long film, the long side of the test piece is the length direction of the film, and the short side is the width direction of the film, the curl angle is more It can be made small, and the occurrence of the above-described folds at both ends in the width direction can be further suppressed during the production of the polarizing film. Therefore, the effect that a polarizing film excellent in polarization performance can be produced with higher productivity is exhibited.

Furthermore, when the elution amount of the polyvinyl alcohol-based resin when immersed in water at 30 ° C. for 2 minutes is 50 ppm / m ² or less, the elution amount is small. Since it can reduce more, there exists an effect that the polarization performance of the polarizing film to manufacture can be improved.

When the thickness is 20 to 60 μm, the length is 5 km or more, and the width is 4 m or more, the polarizing film can be increased in area.

The method for producing a polyvinyl alcohol film according to the second aspect of the present invention is to dry the formed film by bringing the front and back surfaces of the formed film alternately into contact with a plurality of metal heating rolls. The dried state of the front and back surfaces of the formed film can be controlled appropriately. As a result, it is possible to produce the polyvinyl alcohol film according to the first aspect, which is excellent in suppressing the elution amount of the polyvinyl alcohol resin and suppressing the curl angle during the production of the polarizing film.

In particular, the total number of the metal heating rolls used in the drying step is P, and the surface temperature of the metal heating roll with which the film peeled off from the cast mold contacts nth is Tn (° C.), the nth When the contact time between the metal heating roll and the film is Sn (seconds), the thickness of the manufactured polyvinyl alcohol film is D (μm), and n is an integer between 1 and P, Tn × Sn When Σ (Tn × Sn) representing the sum of the above satisfies the following formula (1), the elution amount of the polyvinyl alcohol-based resin during the production of the polarizing film can be further suppressed.
75 ≦ Σ (Tn × Sn) / D ≦ 110 (1)

In addition, the total number of the metal heating rolls used in the drying step is P, the surface temperature of the metal heating roll that the film peeled from the cast mold contacts xth is Tx (° C.), and the film is The surface temperature of the metal heating roll in contact with the yth is Ty (° C.), the contact time between the xth metal heating roll and the film is Sx (seconds), the yth metal heating roll and the film Σ (Tx × Sx) representing the sum of Tx × Sx, where Ty is a contact time of Sy (seconds), x is an odd number from 1 to P, y is an even number from 2 to P When Σ (Ty × Sy) representing the sum of × Sy satisfies the following formula (2), the curl angle at the time of manufacturing the polarizing film can be further suppressed.
Σ (Ty × Sy) <Σ (Tx × Sx) (2)

Further, the total number of the metal heating rolls used in the drying step is P, the surface temperature of the metal heating roll that the film peeled from the cast mold contacts xth is Tx (° C.), and the film is The surface temperature of the metal heating roll in contact with the yth is Ty (° C.), the contact time between the xth metal heating roll and the film is Sx (seconds), the yth metal heating roll and the film When the contact time is Sy (seconds), the surface temperature of the cast mold is T ₀ (° C.), x is an odd number from 1 to P, and y is an even number from 2 to P, Tx × Sx When Σ (Tx × Sx) representing the sum and Σ (Ty × Sy) representing the sum of Ty × Sy satisfy the following formula (3), the curl angle at the time of manufacturing the polarizing film is further reduced. The effect of being able to Achieve the.
Σ (Ty × Sy) + T ₀ ≦ Σ (Tx × Sx) ≦ Σ (Ty × Sy) + T ₀ × 10 (3)

Then, a film wound body is produced by winding the film dried in the drying step around a core tube in a roll shape, and the film wound body is wrapped with a water vapor barrier film, and an atmosphere of 25 to 30 ° C. When stored at a temperature for 5 days or more, there is an effect that the occurrence of curling during the production of the polarizing film can be further reduced.

The polarizing film according to the third aspect of the present invention has the effect that the polarizing performance is excellent since the polyvinyl alcohol film according to the first aspect is used.

It is explanatory drawing which shows typically the method of making the formed film contact a metal heating roll, and drying it. (A) is explanatory drawing which shows typically the measurement conditions of a curl angle, (b) is explanatory drawing which shows a curl angle.

The present invention is described in detail below.
When the polyvinyl alcohol film of the present invention was subjected to a dissolution test under the condition of being immersed in water at 50 ° C. for 1 minute, the dissolution amount of the polyvinyl alcohol resin was 900 ppm / m ² or less, and the following A The curl angle in the short side direction measured under conditions is 135 ° or less.
(A) A rectangular test piece (first test piece) having a long side of 10 cm and a short side of 5 cm cut out from the polyvinyl alcohol film in an arbitrary direction, and a first edge portion in the long side direction of the test piece In a state where a test body having a weight of 5 g attached to the center of the test piece is supported and hung at the center of the second end edge in the long side direction of the test piece, the entire test body is 30 ° C. Conditions for immersion in water for 10 seconds.

As described above, the polyvinyl alcohol-based film in which the elution amount and the curl angle of the polyvinyl alcohol-based resin are reduced is obtained by adopting a specific method for the drying process in the process of manufacturing the polyvinyl alcohol-based film by the continuous casting method. can get. That is, as will be described later, in the drying step, the film formed in a cast mold is alternately brought into contact with a plurality of metal heating rolls to dry the formed film. Thereby, the dry state of the surface and the back surface of the film formed above is appropriately controlled, and the polyvinyl alcohol film produced through the drying process has the above-described elution amount and curl angle of the polyvinyl alcohol resin. Is reduced.

And the said polyvinyl alcohol-type film is formed in a polarizing film through a swelling process, a dyeing | staining process, a boric-acid bridge | crosslinking process, a extending process, etc. Here, as described above, the polyvinyl alcohol-based film has an elution amount of the polyvinyl alcohol-based resin with respect to water at a specific temperature as low as 900 ppm / m ² or less, and a curl angle measured under specific water immersion conditions is 135 °. The following is a small one. Therefore, at the time of manufacturing the polarizing film, the polarizing film manufacturing equipment is not contaminated, and folding and wrinkles are hardly generated in the swelling process. As a result, the productivity of the polarizing film is high, and the obtained polarizing film is excellent in polarizing performance.

Elution amount of the polyvinyl alcohol resin, in terms of pollution avoidance of the polarizing film manufacturing facility, is preferably 800 ppm / m ² or less, particularly preferably not more than 700 ppm / m ^2, the elution of such a polyvinyl alcohol resin If the amount is too large, the polarizing film manufacturing equipment is contaminated and the object of the present invention cannot be achieved. Moreover, the lower limit of the elution amount of the polyvinyl alcohol-based resin is usually 1 ppm / m ² .
In general, since the polyvinyl alcohol film is immersed in warm water around 50 ° C. for about 1 minute when manufacturing the polarizing film, the immersion condition of 50 ° C. for 1 minute is used as an index in the present invention.
Further, the elution amount (ppm / m ² ) in the present invention is obtained by dividing the elution concentration (ppm) by the area (m ² ) of the test piece actually subjected to the elution test and converted to 1 m ^2. .

In the present invention, the test piece (second test piece: polyvinyl alcohol film) subjected to the dissolution test is conditioned at 23 ° C. and 50% RH for 24 hours or more. Such humidity conditioning conditions are general environmental conditions applied to various tests of plastic films, and are conditions for adjusting the moisture content in the polyvinyl alcohol film to the equilibrium moisture content in such an environment. is there. Normally, the moisture content in the test piece is adjusted to about 10% by such humidity control. The test piece after humidity conditioning is immediately subjected to the dissolution test.
The humidity control before the test is also applied in the elution test at 30 ° C. described later.

Furthermore, the polyvinyl alcohol film of the present invention preferably has an elution amount of the polyvinyl alcohol resin of 50 ppm / m ² or less when immersed in water at 30 ° C. for 2 minutes. The elution amount of the polyvinyl alcohol-based resin is particularly preferably 40 ppm / m ² or less, more preferably 30 ppm / m ² or less, from the viewpoint of avoiding contamination of the swelling tank in the production of the polarizing film. The lower limit of the elution amount is usually 1 ppm / m ² .
In general, in the swelling process during the production of the polarizing film, since the polyvinyl alcohol film is swollen for several minutes in warm water around 30 ° C., in the present invention, as described above, the immersion condition of 30 ° C. for 2 minutes is used. Was also an indicator. The method for reducing the amount of elution in the immersion at 30 ° C. for 2 minutes is the same as the method described in the case of immersion at 50 ° C. for 1 minute.

In the polyvinyl alcohol film of the present invention, the curl angle measured under the condition A is required to be 135 ° or less, particularly preferably 90 ° or less, and more preferably 45 ° or less.
If the curl angle is larger than 135 °, the film is likely to be broken or wrinkled during the production of the polarizing film, and the object of the present invention cannot be achieved.

Generally, when a polyvinyl alcohol film is immersed in water, it curls greatly immediately after the immersion, and the curling is eased with the immersion time. Therefore, in the present invention, it is immersed for 10 seconds immediately after being immersed in warm water at 30 ° C. The curl angle at that time was used as an index.

Furthermore, the polyvinyl alcohol film of the present invention preferably has a curl angle in the short side direction of 40 ° or less, particularly preferably, when the immersion time of the test specimen is 2 minutes under the condition A. 30 ° or less, more preferably 20 ° or less. If the curl angle is too large, breakage occurs in the swelling process during the production of the polarizing film, and breakage tends to occur during the transportation of the polyvinyl alcohol film.

In general, since a polyvinyl alcohol film is swollen for several minutes in warm water around 30 ° C. during the production of a polarizing film, the present invention was measured by paying attention to the curl angle at 30 ° C. for 2 minutes.

Here, a test piece (first test piece: test piece under the condition A) used for the measurement of the curl angle is cut out from the long polyvinyl alcohol film. The cutting direction may be any direction, and is not particularly limited, but is cut out in a direction in which the long side of the test piece coincides with the film length direction (MD direction) and the short side corresponds to the film width direction (TD direction). It is preferable from the viewpoint of further reducing the curl angle and further suppressing the occurrence of the bending during the production of the polarizing film.

Here, the manufacturing method of the polyvinyl alcohol-type film of this invention is demonstrated.
That is, the method for producing a polyvinyl alcohol-based film of the present invention comprises a film-forming step of continuously discharging and casting an aqueous solution of a polyvinyl alcohol-based resin into a cast mold, and forming the film thus formed into the cast mold. And then drying the formed film, and then drying the formed film in the drying step, wherein the film is dried on the surface of the formed film. And the back surface are alternately brought into contact with a plurality of metal heating rolls. And in the manufacturing method of this invention, there exists the biggest characteristic in the setting conditions of the said drying process.

[Film forming process]
First, the film forming process will be described in detail.

As the polyvinyl alcohol resin used in the present invention, an unmodified polyvinyl alcohol resin, that is, a resin produced by saponifying polyvinyl acetate obtained by polymerizing vinyl acetate is usually used. If necessary, a resin obtained by saponifying a copolymer of vinyl acetate and a small amount (usually 10 mol% or less, preferably 5 mol% or less) of a copolymerizable component with vinyl acetate may be used. it can. Examples of components copolymerizable with vinyl acetate include unsaturated carboxylic acids (including salts, esters, amides, nitriles, etc.), and olefins having 2 to 30 carbon atoms (eg, ethylene, propylene, n-butene). , Isobutene, etc.), vinyl ethers, unsaturated sulfonates and the like. Moreover, the modified polyvinyl alcohol-type resin obtained by chemically modifying the hydroxyl group after saponification can also be used.

Also, as the polyvinyl alcohol resin, a polyvinyl alcohol resin having a 1,2-diol structure in the side chain can be used. Such a polyvinyl alcohol resin having a 1,2-diol structure in the side chain includes, for example, (i) a method of saponifying a copolymer of vinyl acetate and 3,4-diacetoxy-1-butene, and (ii) acetic acid. A method of saponifying and decarboxylating a copolymer of vinyl and vinyl ethylene carbonate; (iii) saponifying and decarboxylating a copolymer of vinyl acetate and 2,2-dialkyl-4-vinyl-1,3-dioxolane. It is obtained by a method of ketalization, (iv) a method of saponifying a copolymer of vinyl acetate and glycerol monoallyl ether, or the like.

The weight average molecular weight of the polyvinyl alcohol resin is preferably 100,000 to 300,000, particularly preferably 110,000 to 280,000, and more preferably 120,000 to 260,000. If the weight average molecular weight is too small, the degree of polarization of the polarizing film tends to decrease, and if it is too large, stretching during the production of the polarizing film tends to be difficult. The weight average molecular weight of the polyvinyl alcohol resin is a weight average molecular weight measured by GPC-MALS method.

The average saponification degree of the polyvinyl alcohol resin used in the present invention is usually preferably 98 mol% or more, particularly preferably 99 mol% or more, further preferably 99.5 mol% or more, and particularly preferably 99.mol%. It is 8 mol% or more. If the average degree of saponification is too small, the degree of polarization of the polarizing film tends to decrease.
Here, the average saponification degree in the present invention is measured according to JIS K 6726.

As the polyvinyl alcohol resin used in the present invention, two or more kinds having different modified species, modified amount, weight average molecular weight, average saponification degree, etc. may be used in combination.

And the aqueous solution used as the film-forming stock solution is prepared using the said polyvinyl alcohol-type resin.
That is, first, the polyvinyl alcohol resin is preferably washed with water and dehydrated using a centrifuge or the like to obtain a polyvinyl alcohol resin wet cake having a water content of 50% by weight or less. When the water content is too large, it tends to be difficult to obtain a desired aqueous solution concentration.
Such polyvinyl alcohol resin wet cake is dissolved in warm water or hot water to prepare a polyvinyl alcohol resin aqueous solution.

The method for preparing the polyvinyl alcohol-based resin aqueous solution is not particularly limited. For example, the polyvinyl alcohol-based resin aqueous solution may be prepared by using a heated multi-screw extruder. The polyvinyl alcohol resin wet cake thus prepared is charged, and water vapor is blown into the can to prepare an aqueous solution having a desired concentration and dissolution.

In addition to polyvinyl alcohol resins, polyvinyl alcohol resin aqueous solutions include commonly used plasticizers such as glycerin, diglycerin, triglycerin, ethylene glycol, triethylene glycol, polyethylene glycol, trimethylolpropane, and nonionic properties. It is preferable from the viewpoint of the film-forming property of the polyvinyl alcohol film to contain at least one surfactant, anionic and cationic.

The resin concentration of the aqueous polyvinyl alcohol resin solution thus obtained is preferably 15 to 60% by weight, particularly preferably 17 to 55% by weight, and further preferably 20 to 50% by weight. If the resin concentration of such an aqueous solution is too low, the drying load increases and the production capacity tends to decrease. If it is too high, the viscosity becomes too high and uniform dissolution tends to be difficult.

First, the obtained polyvinyl alcohol resin aqueous solution is defoamed. Examples of the defoaming method include stationary defoaming and defoaming using a multi-screw extruder having a vent. As the multi-screw extruder having a vent, a twin-screw extruder having a vent is usually used.

After the defoaming treatment, the polyvinyl alcohol-based resin aqueous solution is introduced into a T-shaped slit die by a certain amount, discharged and cast on a rotating cast drum, and formed into a film by a continuous casting method.

The temperature of the polyvinyl alcohol resin aqueous solution at the exit of the T-shaped slit die is preferably 80 to 100 ° C., particularly preferably 85 to 98 ° C. If the temperature of the aqueous polyvinyl alcohol resin solution is too low, it tends to cause poor flow, and if it is too high, it tends to foam.

The viscosity of the polyvinyl alcohol-based resin aqueous solution is preferably 50 to 200 Pa · s, particularly preferably 70 to 150 Pa · s at the time of discharge. When the viscosity of the aqueous solution is too low, the flow tends to be poor, and when it is too high, casting tends to be difficult.

The discharge speed of the aqueous polyvinyl alcohol resin solution discharged from the T-type slit die onto the cast drum is preferably 0.1 to 5 m / min, particularly preferably 0.2 to 4 m / min, and more preferably 0.8. 3 to 3 m / min. If the discharge speed is too slow, the productivity tends to decrease, and if it is too fast, casting tends to be difficult.

As the cast drum, usually, a surface of stainless steel (SUS) whose main component is iron is plated with metal to prevent scratches. Examples of the metal plating include chrome plating, nickel plating, galvanization, and the like, and these are used alone or in a laminate of two or more layers. Among these, it is preferable that the outermost surface is chrome plating from the viewpoint of durability of the drum surface.

The diameter of the cast drum is preferably 2 to 5 m, particularly preferably 2.4 to 4.5 m, and further preferably 2.8 to 4 m. If the diameter is too small, the drying length is insufficient and the speed tends not to be obtained, and if it is too large, the transportability tends to decrease.

The width of the cast drum is preferably 4 to 7 m, and particularly preferably 5 to 6 m. If the width of the cast drum is too narrow, the productivity tends to decrease, and if it is too wide, the equipment load tends to increase.

The rotational speed of the cast drum is preferably 3 to 50 m / min, particularly preferably 4 to 40 m / min, and further preferably 5 to 35 m / min. If the rotational speed is too slow, the productivity tends to decrease. If the rotational speed is too fast, the peelability when the formed film is peeled from the cast mold tends to decrease.

The surface temperature of such a cast drum is preferably 40 to 99 ° C., more preferably 50 to 98 ° C., further preferably 60 to 97 ° C., particularly preferably 70 to 96 ° C., and particularly preferably 80 to 95 ° C. It is. When the surface temperature is too low, the peelability when the film obtained by film formation is peeled off from the cast mold tends to be lowered, and when it is too high, the film tends to be foamed.

Thus, the film forming step is performed, and the formed film is peeled off from the cast drum.

[Drying process]
Subsequently, the said drying process which heats and dries the said peeled film (film formed film) is demonstrated in detail.

In this drying process, as shown in FIG. 1, while conveying the film F peeled from the cast drum D in the flow direction (MD direction), the front and back surfaces of the film F are alternately heated by a plurality of metal heating rolls. (Hereinafter, it is simply referred to as “hot roll”.) Dry by contacting with R1 to R7. FIG. 1 shows a case where seven heat rolls R1 to R7 are used. Moreover, in FIG. 1, the code | symbol C shows the T-type slit die, and the code | symbol E has shown the free roll.
The heat rolls R1 to R7 are not particularly limited as long as they are made of a metal having a heating function, but are preferably rolls having a diameter of 0.2 to 2 m with a hard chrome plating treatment or a mirror finish treatment. The number of rolls is usually 2 to 30, preferably 10 to 25. In the present invention, a roll whose surface temperature is heated to 40 ° C. or higher and whose temperature is adjusted is referred to as a hot roll.

Thus, in this drying step, it is one of the major features of the present invention that the front and back surfaces of the film peeled off from the cast drum are alternately brought into contact with a plurality of hot rolls for drying. Thereby, as described above, the dried state of the surface and the back surface of the peeled film is appropriately controlled, and the polyvinyl alcohol film produced through this drying step has an elution amount of the polyvinyl alcohol resin and The curl angle can be reduced.

Here, a method for more appropriately controlling the dry state of the front and back surfaces of the peeled film and further reducing the elution amount and curl angle of the polyvinyl alcohol resin will be described.

In the present invention, the total number of the heat rolls used in the drying step is P, the surface temperature of the heat roll at which the film peeled off from the cast drum contacts nth is Tn (° C.), and the nth heat When the contact time of the roll and the film is Sn (seconds), the thickness of the polyvinyl alcohol film to be produced is D (μm), and n is an integer of 1 to P, the total of Tn × Sn is expressed. It is preferable that Σ (Tn × Sn) satisfies the following formula (1).
75 ≦ Σ (Tn × Sn) / D ≦ 110 (1)

It is particularly preferable to satisfy the following formula (1 ′), more preferably to satisfy the following formula (1 ″), and particularly preferably to satisfy the following formula (1 ″ ′).
76 ≦ Σ (Tn × Sn) / D ≦ 100 (1 ′)
78 ≦ Σ (Tn × Sn) / D ≦ 92 (1 ″)
80 ≦ Σ (Tn × Sn) / D ≦ 90 (1 ′ ″)

Here, Σ (Tn × Sn) is a value obtained by calculating the value of Tn × Sn for all the 1st to Pth heat rolls and adding them together. The value of Σ (Tn × Sn) / D is, for example, when the total number of hot rolls is 3, the thickness D of the manufactured polyvinyl alcohol film is 20 μm, and the drying conditions are as follows: 6 + 80 × 7 + 90 × 8) ÷ 20 = 85.
The surface temperature T _{1 of the first} heat roll = 70 ° C. The contact time S ₁ between the first heat roll and the film is 6 seconds.
· Second surface temperature T ₂ = 80 ° C. in a hot roll, contact time between the second heated roll and the film S ₂ = 7 seconds.
- third of the surface temperature T ₃ = 90 ° C. in a hot roll, contact time between the third heat roll and the film S ₃ = 8 seconds.

If the value of Σ (Tn × Sn) / D is too small, the elution of the polyvinyl alcohol-based resin into water tends to increase in the swelling step during the production of the polarizing film. There is a tendency to decrease. As shown by the above formulas (1) to (1 '' '), the greater the thickness of the polyvinyl alcohol film produced, the greater the heat energy required for drying.

The contact time between the heat roll and the film means the contact time between any one point in the film plane and each heat roll. Such a contact time can be controlled by changing the outer diameter and arrangement of each heat roll even if the film conveyance speed is constant.

In the present invention, the surface temperature Tn of all the hot rolls used is preferably 40 to 150 ° C., particularly preferably 50 to 140 ° C., more preferably 60 to 130 ° C., and particularly preferably 70 to 120 ° C. It is.
If the surface temperature of such a heat roll is too low, drying tends to be insufficient, and if the surface temperature Tn of the heat roll is too high, the crystallization of the polyvinyl alcohol-based resin proceeds and the swellability during the production of the polarizing film is uniform. There is a tendency to disappear.

In the present invention, the contact time Sn between each hot roll and the film is preferably 1 to 60 seconds, particularly preferably 2 to 30 seconds, more preferably 3 to 20 seconds, and particularly preferably 4 to 10 seconds. If the contact time Sn is too short, drying tends to be insufficient, and if the contact time Sn is too long, the equipment load tends to increase.

Furthermore, in this invention, the total number of the said heat rolls used for the said drying process is P piece, The surface temperature of the said heat roll which the film peeled from the said casting mold contacts xth (odd number) is set to Tx (degreeC). ), The surface temperature of the heat roll contacting the y-th (even number) film is Ty (° C.), the contact time between the x-th (odd number) heat roll and the film is Sx (seconds), and y Σ (Tx × Sx) representing the sum of Tx × Sx and Σ (Ty × Sy) representing the sum of Ty × Sy, where Sy (seconds) is the contact time between the second (even number) heat roll and the film. It is preferable that the following formula (2) is satisfied.
Σ (Ty × Sy) <Σ (Tx × Sx) (2)

Particularly preferably, the following formula (2 ′) is satisfied, and further preferably, the following formula (2 ″) is satisfied.
Σ (Ty × Sy) <0.9 × Σ (Tx × Sx) (2 ′)
0.8 × Σ (Tx × Sx) <Σ (Ty × Sy) <0.9 × Σ (Tx × Sx) (2 ″)

For example, when the total number of heat rolls is three and the drying conditions are as follows, the value of Σ (Tx × Sx) is 70 × 6 + 90 × 8 = 1140, and the value of Σ (Ty × Sy) The value is 80 × 7 = 560.
The surface temperature T _{1 of the first} heat roll = 70 ° C. The contact time S ₁ between the first heat roll and the film is 6 seconds.
· Second surface temperature T ₂ = 80 ° C. in a hot roll, contact time between the second heated roll and the film S ₂ = 7 seconds.
- third of the surface temperature T ₃ = 90 ° C. in a hot roll, contact time between the third heat roll and the film S ₃ = 8 seconds.

When Σ (Ty × Sy) exceeds Σ (Tx × Sx), the polyvinyl alcohol film tends to curl in the swelling process during the production of the polarizing film. Conversely, even if Σ (Ty × Sy) is excessively small, the polyvinyl alcohol film tends to curl in the reverse direction. That is, the purpose of the above formula (2) is that the surface of the film formed that is in contact with the cast mold is normally in contact with the even-numbered heat roll. The amount of heat supplied to both sides of the film is made equal to less than the amount of heat received from the heat roll.

Furthermore, in the present invention, when the surface temperature of the cast mold is T ₀ (° C.), Σ (Tx × Sx) representing the sum of Tx × Sx and Σ (Ty × Sy) representing the sum of Ty × Sy. And preferably satisfy the following formula (3).
Σ (Ty × Sy) + T ₀ ≦ Σ (Tx × Sx) ≦ Σ (Ty × Sy) + T ₀ × 10 (3)

Particularly preferably, the following formula (3 ′) is satisfied, and further preferably, the following formula (3 ″) is satisfied.
Σ (Ty × Sy) + T ₀ × 2 ≦ Σ (Tx × Sx) ≦ Σ (Ty × Sy) + T ₀ × 6 (3 ′)
Σ (Ty × Sy) + T ₀ × 3 ≦ Σ (Tx × Sx) ≦ Σ (Ty × Sy) + T ₀ × 4 (3 ″)

If the value of Σ (Tx × Sx) is too small or too large, the polyvinyl alcohol film tends to curl immediately after immersion in water in the swelling process during the production of the polarizing film. That is, the purpose of the above formula (3) is that the surface that is in contact with the cast mold of the film is in contact with the even-numbered heat roll, so the amount of heat received from the cast mold and the even-numbered heat roll is The purpose is to make the amount of heat supplied from both sides of the film substantially equal to the amount of heat received from the heat roll.

The moisture content of the dried film is preferably 10% by weight or less, particularly preferably 1 to 9% by weight, and more preferably 2 to 8% by weight. If the moisture content is too high, the finally obtained polyvinyl alcohol film tends to be poorly dried.

In the present invention, it is preferable to heat-treat the dried film, and it is particularly preferable to heat-treat from both sides of the film in that the dried state on both sides of the film can be made uniform. Examples of the heat treatment method include a method of blowing hot air on both surfaces of the film using a floating dryer, and a method of irradiating near infrared rays on both surfaces of the film using an infrared lamp.
Such a heat treatment temperature is preferably 50 to 150 ° C., particularly preferably 70 to 130 ° C. The heat treatment temperature means the temperature of the hot air when the heat treatment method is a method of blowing hot air with the floating dryer, and the heat treatment method is a method of irradiating near infrared light with the infrared lamp. , That means the near infrared temperature. The heat treatment time is not particularly limited, but when a floating dryer is used, it is preferably 10 to 100 seconds, and particularly preferably 20 to 80 seconds. Note that the heat treatment method does not use a heat roll.

[Polyvinyl alcohol film]
The said heat processing is performed after the said drying process as needed, and the polyvinyl alcohol-type film of this invention long in a flow direction (MD direction) is obtained. This polyvinyl alcohol film is produced into a film winding body by slitting both ends in the width direction (TD direction) and winding it around a core tube in a roll shape.

In the present invention, it is preferable to obtain a package by packaging the film winding body with a water vapor barrier film, and store the package at an atmospheric temperature of 25 to 30 ° C. for 5 days or more. The storage period is particularly preferably 10 days or more, particularly preferably 15 days or more, and further preferably 15 to 60 days. If the storage period is too short, curling during water immersion tends to occur. On the contrary, if the storage period is too long, the production of the polarizing film tends to be delayed. The storage method is not particularly limited, and examples thereof include a method using a constant temperature and humidity chamber and a roll stocker.

The reason why curling during water immersion is reduced by the above storage is not clear, but the above-mentioned storage makes the moisture content in the plane and thickness direction of the polyvinyl alcohol film constant, and a temperature higher than room temperature. It is presumed that the stress in the plane and thickness direction of the polyvinyl alcohol film is relaxed. Therefore, when the storage temperature is outside the above range, it is estimated that moisture content unevenness or stress unevenness occurs, which is not preferable.

The length of the polyvinyl alcohol film of the present invention thus obtained is preferably 5 km or more from the viewpoint of increasing the area of the polarizing film, and particularly preferably 5 to 50 km from the viewpoint of transport weight.

The width of the polyvinyl alcohol film of the present invention is preferably 4 m or more from the viewpoint of widening the polarizing film, particularly preferably 5 m or more, and more preferably 5 to 6 m from the viewpoint of avoiding breakage during the production of the polarizing film. It is.

In addition, the polyvinyl alcohol film of the present invention preferably has a thickness of 10 to 75 μm, preferably 10 to 60 μm from the viewpoint of thinning, and particularly preferably 20 from the viewpoint of reducing retardation. From 60 to 60 μm, more preferably from 30 to 60 μm from the viewpoint of avoiding breakage.

In the polyvinyl alcohol film of the present invention, the crossing angle θ between the film orientation axis (slow axis) and the width direction (TD direction) is preferably 45 ° or less. When the crossing angle θ exceeds 45 °, there is a tendency to curl in the width direction (TD direction) during swelling. Such a phenomenon is expected to occur because water absorption occurs not in the orientation direction of the polymer but in a gap between the polymers. That is, when the orientation direction of the polymer is the length direction (MD direction), swelling is more likely to occur in the width direction (TD direction) than in the intended length direction (MD direction).

Furthermore, the polyvinyl alcohol film of the present invention has a refractive index in the length direction (MD direction) of nx, a refractive index in the width direction (TD direction) of ny, a refractive index in the thickness direction of nz, and a thickness of D ( μm), the thickness direction retardation Rth (nm) calculated by the following formula (4) is preferably 100 nm or more, particularly preferably 110 nm or more, more preferably 110 to 200 nm. is there. If the phase difference Rth is too small, it tends to curl during swelling. Such a phenomenon is expected because, when the phase difference Rth is small, the alignment of the polymer chain in the thickness direction becomes strong, and smooth swelling in the thickness direction is inhibited. Conversely, even if the phase difference Rth is too large, the surface orientation of the polymer chain is strong, so that smooth swelling in the surface direction tends to be hindered.
Rth = {(nx + ny) / 2−nz} × 1000 × D (4)

In the above embodiment, the method for producing a polyvinyl alcohol film has been described by taking as an example the case where a cast drum (drum roll) is used as a cast mold. However, a cast belt or a resin film is used as a cast mold. It is also possible to manufacture.

Moreover, in the said embodiment, as a method of reducing the elution amount of the said polyvinyl alcohol-type resin, in the drying process of the process which manufactures a polyvinyl-alcohol-type film by the continuous casting method, the surface of the film formed with the cast type | mold, Although the back surface is alternately brought into contact with a plurality of metal heating rolls, the method of appropriately controlling the dry state of the surface and the back surface of the film formed is adopted, but other methods may be adopted. . For example, a method for adjusting the molecular weight and saponification degree of a polyvinyl alcohol resin as a raw material, a method for improving the purity by washing the polyvinyl alcohol resin, a method for adding a surfactant to an aqueous solution of a polyvinyl alcohol resin, polyvinyl Examples thereof include a method for controlling the crystallinity and orientation of the polymer in the step of forming a film using an alcohol-based resin aqueous solution, and a method for controlling the dry state of the formed film.

Further, in the above embodiment, as a method of reducing the curl angle, the surface and the back surface of the film formed with the cast mold are alternately used in the drying process in the process of producing the polyvinyl alcohol film by the continuous casting method. Although the method which controls appropriately the dry state of the surface and back surface of the film formed by making it contact with a some metal heating roll was employ | adopted, you may employ | adopt another method. For example, a method for controlling the orientation state of the polymer in the step of forming a film using a polyvinyl alcohol resin aqueous solution, a method for improving the thickness accuracy during film formation, a method for controlling the dry state of the formed film, etc. can give.

The polyvinyl alcohol-based film of the present invention is particularly preferably used as a raw material for a polarizing film because the polyvinyl alcohol-based resin is hardly eluted when immersed in water and the curl angle is reduced.

Here, the manufacturing method of the polarizing film obtained using the polyvinyl alcohol-type film of this invention is demonstrated.

[Method for producing polarizing film]
The polarizing film of the present invention is produced through steps such as swelling, dyeing, boric acid crosslinking, stretching, washing, and drying by feeding the polyvinyl alcohol film out of the film winding body and transporting it in the horizontal direction.

The swelling process is performed before the dyeing process. In addition to being able to clean the surface of the polyvinyl alcohol film by the swelling step, there is also an effect of preventing uneven dyeing by swelling the polyvinyl alcohol film. In the swelling step, water is usually used as the treatment liquid. As long as the main component is water, the treatment liquid may contain a small amount of an additive such as an iodide compound, a surfactant, alcohol, and the like. The temperature of the swelling bath is usually about 10 to 45 ° C., and the immersion time in the swelling bath is usually about 0.1 to 10 minutes.

The dyeing step is performed by bringing a liquid containing iodine or a dichroic dye into contact with the polyvinyl alcohol film. Usually, an iodine-potassium iodide aqueous solution is used. The iodine concentration is suitably 0.1-2 g / L, and the potassium iodide concentration is 1-100 g / L. The dyeing time is practically about 30 to 500 seconds. The temperature of the treatment bath is preferably 5 to 50 ° C. The aqueous solution may contain a small amount of an organic solvent compatible with water in addition to the aqueous solvent.

The boric acid crosslinking step is performed using a boron compound such as boric acid or borax. The boron compound is used in the form of an aqueous solution or a water-organic solvent mixture at a concentration of about 10 to 100 g / L, and it is preferable that potassium iodide coexists in the solution from the viewpoint of stabilizing the polarization performance. The temperature during the treatment is preferably about 30 to 70 ° C., and the treatment time is preferably about 0.1 to 20 minutes. If necessary, the stretching operation may be performed during the treatment.

The stretching step is preferably performed 3 to 10 times, preferably 3.5 to 6 times in a uniaxial direction [flow direction (MD direction)]. At this time, a slight stretching (stretching to prevent shrinkage in the width direction (TD direction) or more) may also be performed in the direction perpendicular to the stretching direction. The temperature during stretching is preferably 30 to 170 ° C. Furthermore, the stretching ratio may be finally set within the above range, and the stretching operation may be performed not only once but plural times in the polarizing film manufacturing process.

The washing step is performed, for example, by immersing the polyvinyl alcohol film in an aqueous iodide solution such as water or potassium iodide, and the deposits generated on the surface of the polyvinyl alcohol film can be removed. When using an aqueous potassium iodide solution, the potassium iodide concentration is about 1 to 80 g / L. The temperature during the washing treatment is usually 5 to 50 ° C., preferably 10 to 45 ° C. The treatment time is usually 1 to 300 seconds, preferably 10 to 240 seconds. In addition, you may perform combining water washing | cleaning and washing | cleaning by potassium iodide aqueous solution suitably.

In the drying step, for example, the polyvinyl alcohol film is dried in the atmosphere at 40 to 80 ° C. for 1 to 10 minutes.

Thus, the polarizing film of the present invention is obtained. The polarization degree of the polarizing film of the present invention is preferably 99.8% or more, more preferably 99.9% or more. If the degree of polarization is too low, there is a tendency that the contrast in the liquid crystal display cannot be secured.
The degree of polarization is generally determined by the light transmittance (H ₁₁ ) measured at the wavelength λ and the two polarized films in a state where two polarizing films are overlapped so that the orientation directions thereof are the same. It is calculated according to the following equation from the light transmittance (H ₁ ) measured at the wavelength λ in a state where the films are superposed so that the alignment directions are orthogonal to each other.
Polarization degree = [(H ₁₁ −H ₁ ) / (H ₁₁ + H ₁ )] ^1/2

Further, the single transmittance of the polarizing film of the present invention is preferably 42% or more, more preferably 43% or more. If the single transmittance is too low, it tends to be impossible to achieve high brightness of the liquid crystal display.
The single transmittance is a value obtained by measuring the light transmittance of a single polarizing film using a spectrophotometer.

The polarizing film of the present invention is suitable for producing a polarizing plate having excellent degree of polarization and no color unevenness.
Here, the manufacturing method of the polarizing plate using the polarizing film of this invention is demonstrated.

[Production method of polarizing plate]
The polarizing plate is produced by laminating an optically isotropic resin film as a protective film on one or both sides of the polarizing film of the present invention via an adhesive. Examples of the protective film include cellulose triacetate, cellulose diacetate, polycarbonate, polymethyl methacrylate, cycloolefin polymer, cycloolefin copolymer, polystyrene, polyethersulfone, polyarylene ester, poly-4-methylpentene, polyphenylene oxide, and the like. Or a sheet.

The bonding method is performed by a known method. For example, after a liquid adhesive composition is uniformly applied to a polarizing film, a protective film, or both, the two are bonded and pressure-bonded. It is performed by irradiating active energy rays.

Also, a polarizing plate can be formed by applying a curable resin such as urethane resin, acrylic resin, urea resin or the like to one or both surfaces of the polarizing film and curing to form a cured layer. If it does in this way, the said hardened layer becomes a substitute of the said protective film, and can attain thinning.

Polarizing films and polarizing plates using the polyvinyl alcohol film of the present invention are excellent in polarizing performance, such as portable information terminals, personal computers, televisions, projectors, signage, electronic desk calculators, electronic watches, word processors, electronic paper, games. Machines, videos, cameras, photo albums, thermometers, audio, liquid crystal display devices such as automobile and machinery instruments, sunglasses, anti-glare glasses, stereoscopic glasses, wearable displays, display elements (CRT, LCD, organic EL, electronic It is preferably used for an antireflection layer for paper and the like, an optical communication device, a medical device, a building material, a toy and the like.

Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples as long as the gist thereof is not exceeded.

The measurement and evaluation of the properties of the polyvinyl alcohol film (elution amount of polyvinyl alcohol resin, curl angle) and the properties of the polarizing film (polarization degree, single transmittance, color unevenness) in the following examples and comparative examples are as follows. I went as follows.

<Measurement conditions>
[Elution amount of polyvinyl alcohol resin (ppm / m ² )]
The obtained polyvinyl alcohol film was conditioned at 23 ° C. and 50% RH for 24 hours, and then a 100 mm × 100 mm (0.01 m ² ) test piece (second test piece) was cut out and 1 L of ion-exchanged water. Was immersed for 1 minute at 50 ° C. to obtain an eluate. After mixing 10 mL of this eluate with 10 mL of a coloring reagent (ion exchange water 500 g, potassium iodide 7.4 g, iodine 0.65 g, boric acid 10.6 g) at room temperature (25 ° C.), a spectrophotometer (Shimadzu Corporation) (Manufactured by: UV-3100PC), the absorbance at a wavelength of 690 nm was measured, the concentration (ppm) of the polyvinyl alcohol resin was calculated from a calibration curve prepared in advance, and the elution amount (ppm / m ² ) was calculated by converting the area. did.
In the same manner as described above, the elution amount (ppm / m ² ) when immersed at 30 ° C. for 2 minutes was determined.

[Curl angle (°)]
A test piece (the first test piece) having a long side of 10 cm and a short side of 5 cm was cut out from the obtained polyvinyl alcohol film. At this time, the long side of the test piece was the length direction (MD direction) of the film, and the short side was the width direction (TD direction) of the film. Then, as shown in FIG. 2 (a), the center of the lower edge of the test piece 1 in the long side direction is the (first) clip ("Kokuyo's" eyeball clip pea "); mouth width 20mm; mass 2 .1g) The wire 2b was wound around the clip 2a. Using these clips 2 a and wire 2 b, the weight of total weight 5 g was changed to a weight 2, and a test body composed of the test piece 1 and the weight 2 was prepared. Thereafter, the center of the upper edge of the test piece 1 in the long side direction is sandwiched between the (second) clip (same as above) 3a, and the string 3b is tied to the clip 3a (the suspension composed of the clip 3a and the string 3b). The lowering jig 3 was attached to the center of the upper edge of the test piece 1 in the long side direction). Next, the entire test body was immersed in 30 ° C. water 4a in the water tank 4 in a state where the test body with the clip 3a was suspended by the string 3b. Then, the curl angle α (°) in the short side direction (width direction) at the time when 10 seconds have passed and 2 minutes have passed since the immersion, as shown in FIG. 2 (b), the upper part of the water tank 4 (not shown). To observe visually. In FIG. 2 (b), the above-described heavy stone 2, the hanging jig 3, and the water tank 4 are not shown for easy understanding of the configuration. Further, the curl angle α is an angle formed by the plane portion of the test piece 1 and the tangential direction of the edge of the curled portion in the short side direction.

[Degree of polarization (%), single transmittance (%)]
A test piece 4 cm long x 4 cm wide was cut out from the center and both side ends (10 cm inside from both ends of the polarizing film) in the width direction (TD direction) of the obtained polarizing film. The degree of polarization (%) and single transmittance (%) were measured using a film measuring apparatus (manufactured by JASCO Corporation: VAP7070). Such measurement was performed for the central portion in the length direction (MD direction) of the polarizing film and the front end / terminal portion (10 m inside from each end of the front end and the end of the polarizing film).

〔Color unevenness〕
From the central part and both end side parts of the polarizing film obtained in the width direction (TD direction) (10 cm inside from each end on both sides of the polarizing film), a 30 cm long × 30 cm wide test piece was cut out and crossed Nicol After being sandwiched between the two polarizing plates (single transmittance 43.5%, polarization degree 99.9%) at an angle of 45 °, using a light box with a surface illumination of 14,000 lx, a transmission mode The optical color unevenness was observed and evaluated according to the following criteria. Such measurement was performed for the central portion in the length direction (MD direction) of the polarizing film and the front end portion / terminal portion (10 m inside from each end on both side ends of the polarizing film).
(Evaluation criteria)
○: There was no color unevenness.
X: There was uneven color.
Such evaluation was performed for the central portion and the tip / terminal portion (the inner side of each end of the polarizing film, 10 m from the end of the polarizing film) in the length direction (MD direction) of the polarizing film.

<Example 1> (Preparation of polyvinyl alcohol film)
2,000 kg of polyvinyl alcohol resin having a weight average molecular weight of 142,000 and a saponification degree of 99.8 mol%, 5,000 kg of water, and 220 kg of glycerin as a plasticizer are added, heated to 140 ° C. with stirring and dissolved under pressure. Then, the concentration was adjusted to a resin concentration of 25% by weight to obtain a uniformly dissolved polyvinyl alcohol resin aqueous solution. Next, the polyvinyl alcohol-based resin aqueous solution is supplied to a twin-screw extruder having a vent and defoamed, and then the temperature of the aqueous solution is set to 95 ° C., and the cast drum (surface temperature 92 ° C.) is rotated from the T-type slit die discharge port. ) Were discharged (discharge speed 2.5 m / min) and cast to form a film. The formed film was peeled from the cast drum, and dried while the front surface and the back surface (contact surface with the cast drum) of the film were alternately brought into contact with a total of 15 hot rolls. Drying conditions [see the above formulas (1) to (3)] are as shown in Table 1 below. Next, using a floating dryer, heat treatment was performed by blowing hot air at 120 ° C. from both sides of the peeled film to obtain a polyvinyl alcohol film having a thickness of 60 μm. Finally, by slitting both ends of the polyvinyl alcohol film in the width direction (TD direction) and winding it around the core tube in a roll shape, the film winding body (dimension of the polyvinyl alcohol film: width 5 m, length 5 km) was obtained.

(Storage of polyvinyl alcohol film)
And the said film winding body was wrapped twice with the water vapor | steam barrier film, and was packaged, and the packaging body was obtained. As the water vapor barrier film, a laminated film of an aluminum vapor-deposited polyester film (a polyethylene terephthalate film vapor-deposited with 50 nm of aluminum, 12 μm thickness) and a polyethylene film (25 μm thickness) was used. Next, the package was stored for 15 days in a roll stocker with an ambient temperature of 26 ° C. The characteristics of the polyvinyl alcohol film after storage are shown in Table 1 below.

(Manufacture of polarizing film)
The obtained polyvinyl alcohol film is unwound from the film winding body and transported in the horizontal direction using a transport roll. First, the film is immersed in a water bath with a water temperature of 30 ° C. and swollen in 2 minutes (MD direction). ) Was stretched 1.7 times. Next, the film is stretched 1.6 times in the flow direction (MD direction) in 0.5 minutes while being immersed and dyed in a 28 ° C. aqueous solution composed of 0.5 g / L of iodine and 30 g / L of potassium iodide. Subsequently, the film was immersed in a 50 ° C. aqueous solution of 40 g / L boric acid and 30 g / L potassium iodide, and uniaxially stretched 2.1 times in the flow direction (MD direction) in 1 minute while crosslinking with boric acid. Finally, it was washed with an aqueous potassium iodide solution and dried at 50 ° C. for 2 minutes to obtain a polarizing film having a total draw ratio of 5.8 times. The properties of the obtained polarizing film are shown in Table 2 below.

<Example 2>
A film winding body (size of polyvinyl alcohol film: thickness 60 μm, width 5 m, length 5 km) was obtained in the same manner as in Example 1 except that the production was performed under the conditions shown in Table 1 below. Further, the film winding body was stored in the same manner as in Example 1. The characteristics of the polyvinyl alcohol film after storage are shown in Table 1 below. Further, a polarizing film was obtained in the same manner as in Example 1. The properties of the obtained polarizing film are shown in Table 2 below.

<Example 3>
In Example 1, a film wound body (polyvinyl alcohol film) was prepared in the same manner as in Example 1 except that the discharge rate was 2.5 m / min and the production was performed under the conditions shown in Table 1 below. Dimension: thickness 45 μm, width 5 m, length 5 km). Further, the film winding body was stored in the same manner as in Example 1. The characteristics of the polyvinyl alcohol film after storage are shown in Table 1 below. Further, a polarizing film was obtained in the same manner as in Example 1. The properties of the obtained polarizing film are shown in Table 2 below.

<Example 4>
In Example 1, the film winding body (polyvinyl alcohol film) was prepared in the same manner as in Example 1 except that the discharge rate was 2.5 m / min and the condition shown in Table 1 below was set to 1.3 m / min. Dimension: thickness 30 μm, width 5 m, length 5 km). Further, the film winding body was stored in the same manner as in Example 1. The characteristics of the polyvinyl alcohol film after storage are shown in Table 1 below. Further, a polarizing film was obtained in the same manner as in Example 1. The properties of the obtained polarizing film are shown in Table 2 below.

<Comparative Example 1>
A film winding body (size of polyvinyl alcohol film: thickness 60 μm, width 5 m, length 5 km) was obtained in the same manner as in Example 1 except that the production was performed under the conditions shown in Table 1 below. Further, the film winding body was stored in the same manner as in Example 1. The characteristics of the polyvinyl alcohol film after storage are shown in Table 1 below. Further, a polarizing film was obtained in the same manner as in Example 1. The properties of the obtained polarizing film are shown in Table 2 below.
In addition, when the chemical | medical solution of the boric-acid crosslinking tank was confirmed visually after manufacture of a polarizing film, cloudiness was seen and clogging had generate | occur | produced in the circulation filter of a chemical | medical solution.

<Comparative Example 2> (corresponding to Example 1 of Patent Document 3)
In Example 1, the film winding body (polyvinyl alcohol type) was prepared in the same manner as in Example 1 except that the discharge rate was 2.5 m / min and the production was performed under the conditions shown in Table 1 below. Film dimensions: thickness 45 μm, width 5 m, length 5 km). Further, the film winding body was stored in the same manner as in Example 1. The characteristics of the polyvinyl alcohol film after storage are shown in Table 1 below. Further, the production of the polarizing film was started in the same manner as in Example 1, but the production was stopped because the film edge was broken in the swelling process. The characteristics of the obtained portion (tip portion) of the polarizing film are shown in Table 2 below.

<Comparative Example 3>
In Example 1, the film winding body (polyvinyl alcohol film) was prepared in the same manner as in Example 1 except that the discharge rate was 2.5 m / min and the condition shown in Table 1 below was set to 1.3 m / min. Dimension: thickness 30 μm, width 5 m, length 5 km). Further, the film winding body was stored in the same manner as in Example 1. The characteristics of the polyvinyl alcohol film after storage are shown in Table 1 below. Furthermore, an attempt was made to produce a polarizing film in the same manner as in Example 1. However, a fold occurred at the end of the film in the swelling process, and a rupture occurred in the subsequent stretching process, so that the polarizing film was not obtained.

<Comparative Example 4>
In Example 1, the discharge speed was 2.5 m / min, 2.1 m / min, and the production was performed under the conditions shown in Table 1 below using a total of 18 heat rolls. A film winding body (size of polyvinyl alcohol film: thickness 50 μm, width 5 m, length 5 km) was obtained. Further, the film winding body was stored in the same manner as in Example 1. The characteristics of the polyvinyl alcohol film after storage are shown in Table 1 below.
Furthermore, an attempt was made to produce a polarizing film in the same manner as in Example 1. However, a fold occurred at the end of the film in the swelling process, and a rupture occurred in the subsequent stretching process, so that the polarizing film was not obtained.

Since the polyvinyl alcohol film of Examples 1 to 4 has a resin elution amount in water and a curl angle when immersed in water within the specific range of the present application, the polarizing film has excellent productivity and polarization performance and no color unevenness. was gotten. On the other hand, since the polyvinyl alcohol film of Comparative Example 1 has a resin elution amount in water outside the specific range of the present application, it can be seen that the obtained polarizing film is inferior in polarization performance and has color unevenness. In addition, since the polyvinyl alcohol films of Comparative Examples 2 to 4 had a curl angle when immersed in water outside the specific range of the present application, a wide and long polarizing film could not be obtained.

In the above embodiments, specific forms in the present invention have been described. However, the above embodiments are merely examples and are not construed as limiting. Various modifications apparent to those skilled in the art are contemplated to be within the scope of this invention.

Claims

The elution amount of the polyvinyl alcohol-based resin when immersed in water at 50 ° C. for 1 minute is 900 ppm / m 2 or less, and the curl angle in the short side direction measured under the following condition A is 135 ° or less. A polyvinyl alcohol film characterized by
(A) A rectangular test piece having a long side of 10 cm and a short side of 5 cm cut out from the polyvinyl alcohol film in an arbitrary direction, and a mass attached to the center of the first edge portion in the long side direction of the test piece A condition in which the entire test body is immersed in water at 30 ° C. for 10 seconds in a state where a test body provided with 5 g of weight is supported and suspended at the center of the second end edge in the long side direction of the test piece. .
2. The polyvinyl alcohol film according to claim 1, wherein under the condition A, the curl angle in the short side direction is 40 ° or less when the immersion time of the specimen is 2 minutes.
3. The polyvinyl alcohol film is a long film, the long side of the test piece is the length direction of the film, and the short side is the width direction of the film. Polyvinyl alcohol film.
The polyvinyl alcohol film according to any one of claims 1 to 3, wherein an elution amount of the polyvinyl alcohol resin when immersed in water at 30 ° C for 2 minutes is 50 ppm / m 2 or less.
5. The polyvinyl alcohol film according to claim 1, wherein the polyvinyl alcohol film has a thickness of 20 to 60 μm, a length of 5 km or more, and a width of 4 m or more.
A film forming step of continuously discharging and casting an aqueous solution of a polyvinyl alcohol resin into a cast mold to form a film, and drying the formed film after peeling the formed film from the cast mold A method for producing a polyvinyl alcohol film according to any one of claims 1 to 5, comprising drying a film formed on the surface of the film formed in the drying step. A method for producing a polyvinyl alcohol film, wherein the method is carried out by alternately contacting the back surface with a plurality of metal heating rolls.
The total number of the metal heating rolls used in the drying step is P, the surface temperature of the metal heating roll with which the film peeled from the cast mold contacts nth is Tn (° C.), and the nth metal When the contact time between the heating roll and the film is Sn (seconds), the thickness of the manufactured polyvinyl alcohol film is D (μm), and n is an integer between 1 and P, the total of Tn × Sn The Σ (Tn × Sn) representing the formula satisfies the following formula (1): The method for producing a polyvinyl alcohol film according to claim 6.
75 ≦ Σ (Tn × Sn) / D ≦ 110 (1)
The total number of the metal heating rolls used in the drying step is P, the surface temperature of the metal heating roll with which the film peeled from the cast mold contacts xth is Tx (° C.), and the film is yth The surface temperature of the metal heating roll in contact with Ty (° C.), the contact time between the x-th metal heating roll and the film is Sx (seconds), and the contact between the y-th metal heating roll and the film Σ (Tx × Sx) representing the sum of Tx × Sx and Ty × Sy, where time is Sy (seconds), x is an odd number from 1 to P and y is an even number from 2 to P The Σ (Ty × Sy) representing the sum of the above satisfies the following formula (2): The method for producing a polyvinyl alcohol film according to claim 6 or 7.
Σ (Ty × Sy) <Σ (Tx × Sx) (2)
The total number of the metal heating rolls used in the drying step is P, the surface temperature of the metal heating roll with which the film peeled from the cast mold contacts xth is Tx (° C.), and the film is yth The surface temperature of the metal heating roll in contact with Ty (° C.), the contact time between the x-th metal heating roll and the film is Sx (seconds), and the contact between the y-th metal heating roll and the film When the time is Sy (seconds), the surface temperature of the cast mold is T 0 (° C.), x is an odd number between 1 and P, and y is an even number between 2 and P, the total of Tx × Sx is The Σ (Tx × Sx) that represents and the Σ (Ty × Sy) that represents the sum of Ty × Sy satisfy the following formula (3): Of manufacturing polyvinyl alcohol film .
Σ (Ty × Sy) + T 0 ≦ Σ (Tx × Sx) ≦ Σ (Ty × Sy) + T 0 × 10 (3)
A film wound body is produced by winding the film dried in the drying step around a core tube in a roll shape, and the film wound body is wrapped with a water vapor barrier film at an ambient temperature of 25 to 30 ° C. The method for producing a polyvinyl alcohol film according to any one of claims 6 to 9, wherein the polyvinyl alcohol film is stored for 5 days or more.
A polyvinyl alcohol film produced by the method for producing a polyvinyl alcohol film according to any one of claims 6 to 10.
A polarizing film using the polyvinyl alcohol film according to any one of claims 1 to 5 and 11.