JP6834956B2 - A polyvinyl alcohol-based film, a method for producing the same, and a polarizing film using the polyvinyl alcohol-based film. - Google Patents

Description

INDUSTRIAL APPLICABILITY According to the present invention, a polyvinyl alcohol-based film having less elution of impurities into water and less likely to curl even when immersed in water, a polyvinyl alcohol-based film capable of obtaining a polarizing film having particularly high polarization performance with high productivity, and a polyvinyl alcohol-based film. The present invention relates to the production method thereof and a polarizing film using the polyvinyl alcohol-based 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. A polarizing film is used in such a liquid crystal display device, and as the polarizing film, a polyvinyl alcohol-based film in which iodine is adsorbed and oriented is mainly used. In recent years, with the increase in definition, brightness, and size of screens, there is a need for a wide and long polarizing film that has better polarization performance than conventional products, has no color unevenness, and is wide and long.

In general, the polarizing film is formed by unwinding a polyvinyl alcohol-based film, which is the raw material, from a roll, swelling it with water (including warm water) while transporting it in the flow direction (MD direction), and then dyeing with iodine and iodine. It is manufactured through steps such as stretching for orientation and boric acid cross-linking 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 step, if impurities are eluted from the polyvinyl alcohol-based film and the swelling tank is contaminated, the contamination will diffuse to the entire post-process. Even in the dyeing step and the boric acid cross-linking step, if impurities are eluted from the polyvinyl alcohol-based film, not only the polarization performance of the obtained polarizing film deteriorates, but also a great deal of labor is required for filtering and exchanging the chemical solution used in each step. It will be. Examples of 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 have a degree of polarization. There was a tendency to easily form a low molecular weight iodine complex. Further, in the swelling step, if breaks or wrinkles occur at both ends of the polyvinyl alcohol-based film in the width direction (TD direction), not only the transport becomes difficult, but also the film tends to break during stretching.

On the other hand, a polyvinyl alcohol-based film, which is 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, an aqueous solution of a polyvinyl alcohol-based resin is discharged and cast on a cast mold such as a cast drum or an endless belt to peel the film formed from the cast mold, and then the film is conveyed in the flow direction (MD direction). However, it is produced by drying using a plurality of metal heating rolls. Among these steps, the drying step is an important step for controlling the amount of resin eluted from the polyvinyl alcohol-based film and for the swelling characteristics of the polyvinyl alcohol-based film. That is, if the drying in the drying step is insufficient, the amount of resin eluted during the production of the polarizing film increases, and at the same time, the polyvinyl alcohol-based film is likely to be broken or wrinkled in the swelling step, and conversely, the drying is excessive. And the swelling rate in the swelling tank tends to decrease. Further, if there is a difference in characteristics between the front surface and the back surface of the film formed in the drying step, it tends to curl in the swelling step.

As a method for improving the above problems, for example, a polyvinyl alcohol-based film in which the amount of polyvinyl alcohol-based resin eluted in water is reduced has been proposed (see, for example, Patent Document 1). Further, a polyvinyl alcohol-based 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) or a film having a thickness of 50 μm or less and immersed in water at 30 ° C. for 30 seconds. A polyvinyl alcohol-based film having a curl angle of 200 ° or less has been proposed (see, for example, Patent Document 3). Further, a method for producing a polyvinyl alcohol-based film under specific drying conditions has been proposed (see, for example, Patent Document 4). Here, the curl angle is the angle formed by the flat portion of the polyvinyl alcohol-based film and the tangential direction of the edge portion of the curled portion in the width direction (TD direction) of the polyvinyl alcohol-based film [FIG. 2 (b). ) Refer to the symbol α].

Japanese Unexamined Patent Publication No. 2009-22246 Japanese Unexamined Patent Publication No. 2001-315140 International Publication No. 2014/208537 Japanese Unexamined Patent Publication No. 2011-156874

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

In the disclosed technique of Patent Document 1, the eluent concentration of the polyvinyl alcohol-based resin is 10 to 50 ppm when a 10 cm × 10 cm square polyvinyl alcohol-based film is immersed in 1 liter of water at 50 ° C. for 4 hours. When converted to 1 m ^{2 of} film, as much as 1,000 to 5,000 ppm / m ^{2 of} polyvinyl alcohol-based resin will elute, and in order to produce a polarizing film with high production efficiency in response to the recent demand for polarizing films. , It is necessary to further reduce the elution amount of the polyvinyl alcohol-based resin.

In the technique disclosed in Patent Document 2, the curl angle 180 ° is in a bent state, the curl angle 90 ° is in a wrinkled state, and the curl angle 45 ° is in a greatly warped state. It is necessary to reduce the curl angle. In particular, in order to meet the wide and long length required for polarizing films in recent years, it is necessary to further reduce the curl angle in the wide and long polyvinyl alcohol-based film.

In the technique disclosed in Patent Document 3, the curl angle when immersed in water at 30 ° C. for 30 seconds is set to 200 ° or less to suppress breakage during stretching to some extent, but in particular, a polarizing film due to an increase in line speed in recent years. It is necessary to further reduce the curl angle in order to cope with the improvement of productivity.

The technique disclosed in Patent Document 4 can certainly reduce the retardation of the polyvinyl alcohol-based film by setting the contact time between the film and each of the thermal rolls to 1 to 6 seconds, but the polyvinyl alcohol-based during the production of the polarizing film In order to reduce the amount of resin eluted, there is room for improvement in terms of further control of drying conditions.

Therefore, in the present invention, under such a background, it is a polyvinyl alcohol-based film capable of obtaining a polarizing film having excellent controllability and swelling characteristics of the elution amount of the polyvinyl alcohol-based resin at the time of manufacturing the polarizing film and excellent polarization performance. Therefore, the amount of polyvinyl alcohol-based 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, and swelling during polarizing film manufacturing. Provided are a polyvinyl alcohol-based film that is less likely to break or wrinkle in the process, a method for producing the same, and a polarizing film using the polyvinyl alcohol-based film.

However, as a result of intensive studies in view of such circumstances, the present inventors have found that the amount of polyvinyl alcohol-based resin eluted in water at a specific temperature is small and the curl angle measured under specific water immersion conditions is small. It has been found that the above-mentioned problems can be solved and a high-performance polarizing film can be manufactured with high productivity by manufacturing a polarizing film using the above.

That is, the first gist of the present invention is that 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 short side direction measured under the condition A below. It is a polyvinyl alcohol-based film characterized by having 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-based 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 whole test piece is immersed in water at 30 ° C. for 10 seconds while the test piece provided with 5 g of a heavy stone is supported and suspended at the center of the second edge portion in the long side direction of the test piece. ..

The second gist of the present invention is a film-forming step of continuously discharging and casting an aqueous solution of a polyvinyl alcohol-based resin into a cast mold to form a film, and peeling the film-formed film from the cast mold. A method for producing a polyvinyl alcohol-based film according to the first gist, which comprises a drying step of drying the film-formed film, wherein the film-forming film is dried in the drying step. This is a method for producing a polyvinyl alcohol-based film, which is carried out by alternately bringing the front surface and the back surface of the film into contact with a plurality of metal heating rolls.

The third gist of the present invention is a polarizing film in which the polyvinyl alcohol-based film of the first gist is used.

Since the polyvinyl alcohol-based film of the first gist of the present invention has a small amount of polyvinyl alcohol-based resin eluted with water at a specific temperature and a small curl angle measured under specific water immersion conditions, even during the production of a polarizing film. , The amount of polyvinyl alcohol-based resin eluted can be reduced, and the curl angle can be reduced. Therefore, it is possible to produce a polarizing film having excellent polarization performance with high productivity.

In particular, under the condition A, when the immersion time of the test piece is 2 minutes and the measured curl angle in the short side direction is 40 ° or less, the swelling step during the production of the polarizing film is further enhanced. It is possible to prevent breakage from occurring, and it is possible to further prevent breakage during manufacturing of the polarizing film. Therefore, it is possible to produce a polarizing film having better polarization performance with higher productivity.

When the polyvinyl alcohol-based film is a long film, the long side of the test piece is in the length direction of the film, and the short side is in the width direction of the film, the curl angle is increased. It can be made smaller, and the occurrence of the above-mentioned folds at both ends in the width direction can be further suppressed during the production of the polarizing film. Therefore, it is possible to produce a polarizing film having excellent polarization performance with higher productivity.

Further, 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, so that the swelling tank is contaminated in the production of the polarizing film. Since the number can be reduced, the polarization performance of the polarizing film to be manufactured 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 area of the polarizing film can be increased.

The second gist of the present invention, the method for producing a polyvinyl alcohol-based film, is to dry the film-formed film by alternately contacting the front surface and the back surface of the film-formed film with a plurality of metal heating rolls. , The dry state of the front surface and the back surface of the formed film can be appropriately controlled. As a result, it is possible to produce the polyvinyl alcohol-based film of the first gist, which is excellent in suppressing the elution amount of the polyvinyl alcohol-based resin and suppressing the curl angle at the time of producing 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 rolls in which the film peeled from the cast mold comes into contact with the 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 produced polyvinyl alcohol-based film is D (μm), and n is an integer of 1 or more and P or less, Tn × Sn. When Σ (Tn × Sn) representing the sum of the above satisfies the following formula (1), it is possible to further suppress the elution amount of the polyvinyl alcohol-based resin during the production of the polarizing film.
75 ≦ Σ (Tn × Sn) / D ≦ 110 ・ ・ ・ (1)

Further, the total number of the metal heating rolls used in the drying step is P, the surface temperature of the metal heating rolls in which the film peeled from the cast mold comes into contact at the xth position is Tx (° C.), and the film is The surface temperature of the y-th contacting metal heating roll is Ty (° C.), the contact time between the x-th metal heating roll and the film is Sx (seconds), and the y-th metal heating roll and the film. When the contact time is Sy (seconds), x is an odd number of 1 or more and P or less, and y is an even number of 2 or more and P or less, Σ (Tx × Sx) representing the sum of Tx × Sx and Ty. When Σ (Ty × Sy), which represents the sum of × Sy, satisfies the following equation (2), it has an effect that 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 rolls in which the film peeled from the cast mold comes into contact at the xth position is Tx (° C.), and the film is The surface temperature of the y-th contacting metal heating roll is Ty (° C.), the contact time between the x-th metal heating roll and the film is Sx (seconds), and the y-th 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 of 1 or more and P or less, and y is an even number of 2 or more and P or less, Tx × Sx. When Σ (Tx × Sx) representing the total and Σ (Ty × Sy) representing the total of Ty × Sy satisfy the following equation (3), the curl angle at the time of manufacturing the polarizing film is further reduced. It has the effect of being able to.
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 above drying step around a core tube in a roll shape, and the film wound body is wrapped in a steam barrier film and has an atmosphere of 25 to 30 ° C. When it is stored at a temperature for 5 days or more, it has an effect that the occurrence of curl during the production of the polarizing film can be further reduced.

Since the polyvinyl alcohol-based film of the first gist of the present invention is used for the polarizing film of the third gist of the present invention, it has an effect of being excellent in polarization performance.

It is explanatory drawing which shows typically the method of contacting a formed film with a metal heating roll and drying. (A) is an explanatory diagram schematically showing the measurement conditions of the curl angle, and (b) is an explanatory diagram showing the curl angle.

The present invention will be described in detail below.
When the polyvinyl alcohol-based film of the present invention was subjected to an elution test under the condition of being immersed in water at 50 ° C. for 1 minute, the elution amount of the polyvinyl alcohol-based resin was 900 ppm / m ² or less, and the following A The curl angle in the short side direction measured under the 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-based film in an arbitrary direction, and the first edge portion in the long side direction of the test piece. A test piece equipped with a weight stone having a mass of 5 g attached to the center of the test piece is supported and suspended at the center of the second edge portion in the long side direction of the test piece, and the whole test piece is held at 30 ° C. Conditions for immersion in water for 10 seconds.

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

Then, the polyvinyl alcohol-based film is formed into a polarizing film through a swelling step, a dyeing step, a boric acid cross-linking step, a stretching step, and the like. Here, as described above, the polyvinyl alcohol-based film has a small elution amount of the polyvinyl alcohol-based resin with respect to water at a specific temperature of 900 ppm / m ² or less, and the curl angle measured under specific water immersion conditions is 135 °. It is as small as the following. Therefore, during the production of the polarizing film, the polarizing film manufacturing equipment is not contaminated, and breakage and wrinkles are less likely to occur in the swelling process. As a result, the productivity of the polarizing film is high, and the obtained polarizing film has excellent polarization 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. The lower limit of the elution amount of the polyvinyl alcohol-based resin is usually 1 ppm / m ² .
In general, the polyvinyl alcohol-based film is immersed in warm water at around 50 ° C. for about 1 minute during the production of the polarizing film. Therefore, in the present invention, the immersion condition of 50 ° C. for 1 minute was used as an index.
The elution amount (ppm / m ² ) in the present invention is calculated by dividing the elution concentration (ppm) by the area (m ² ) of the test piece actually subjected to the elution test and converting it to 1 m ^2. ..

In the present invention, the test piece (second test piece: polyvinyl alcohol-based film) to be subjected to the above dissolution test is assumed to be humidity-controlled at 23 ° C. and 50% RH for 24 hours or more. It should be noted that such humidity control conditions are general environmental conditions applied to various tests of plastic films, and are conditions for adjusting the moisture content in the polyvinyl alcohol-based film to the equilibrium moisture content in such an environment. is there. Usually, by such humidity control, the water content in the test piece is adjusted to about 10%. The test piece after humidity control is promptly subjected to the dissolution test.
The humidity control before the test is also applied to the dissolution test at 30 ° C., which will be described later.

Further, the polyvinyl alcohol-based film of the present invention preferably has an elution amount of the polyvinyl alcohol-based 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, and more preferably 30 ppm / m ² or less in terms 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 step during the production of the polarizing film, the polyvinyl alcohol-based film is swelled with warm water at around 30 ° C. for several minutes. Therefore, in the present invention, the immersion condition is 30 ° C. for 2 minutes as described above. Was also used as an index. Examples of the method for reducing the elution amount in the immersion at 30 ° C. for 2 minutes are the same as the method described in the case of the immersion at 50 ° C. for 1 minute.

Further, the polyvinyl alcohol-based film of the present invention needs to have a curl angle of 135 ° or less, particularly preferably 90 ° or less, still more preferably 45 ° or less, as measured under the condition A.
If the curl angle is larger than 135 °, creases and wrinkles are likely to occur during the production of the polarizing film, and the object of the present invention cannot be achieved.

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

Further, the polyvinyl alcohol-based 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 piece is 2 minutes under the condition A. It is 30 ° or less, more preferably 20 ° or less. If the curl angle is too large, breakage occurs in the swelling step during the production of the polarizing film, and breakage tends to occur easily during transportation of the polyvinyl alcohol-based film.

In general, the polyvinyl alcohol-based film is swollen for several minutes in warm water at around 30 ° C. during the production of the polarizing film. Therefore, in the present invention, the curl angle at 30 ° C. for 2 minutes was also taken into consideration for the measurement.

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

Here, the method for producing the polyvinyl alcohol-based film of the present invention will be described.
That is, the method for producing a polyvinyl alcohol-based film of the present invention includes a film-forming step of continuously ejecting and casting an aqueous solution of a polyvinyl alcohol-based resin into a cast mold to form a film, and the cast-type film. A method for producing a polyvinyl alcohol-based film, which comprises a drying step of drying the film-formed film after peeling from the film, wherein the drying of the film-formed film in the drying step is the surface of the film-formed film. And the back surface are alternately brought into contact with a plurality of metal heating rolls. The production method of the present invention has the greatest feature in the setting conditions of the drying process.

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

As the polyvinyl alcohol-based resin used in the present invention, an unmodified polyvinyl alcohol-based 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 vinyl acetate and a copolymerizable component may be used. it can. Examples of the component copolymerizable with vinyl acetate include unsaturated carboxylic acids (including, for example, salts, esters, amides, nitriles, etc.) and olefins having 2 to 30 carbon atoms (for example, ethylene, propylene, n-butene). , Isobutene, etc.), vinyl ethers, unsaturated sulfonates, etc. Further, a modified polyvinyl alcohol-based resin obtained by chemically modifying the hydroxyl group after saponification can also be used.

Further, as the polyvinyl alcohol-based resin, a polyvinyl alcohol-based resin having a 1,2-diol structure in the side chain can also be used. The polyvinyl alcohol-based resin having a 1,2-diol structure in the side chain is, for example, (i) a method for saponifying a copolymer of vinyl acetate and 3,4-diacetoxy-1-butene, (ii) acetate. A method for saponifying and decarbonizing a copolymer of vinyl and vinyl ethylene carbonate, (iii) saponifying and decarbonating a copolymer of vinyl acetate and 2,2-dialkyl-4-vinyl-1,3-dioxolane. It can be obtained by a method of ketalization, (iv) a method of saponifying a copolymer of vinyl acetate and glycerin monoallyl ether, or the like.

The weight average molecular weight of the polyvinyl alcohol-based resin is preferably 100,000 to 300,000, particularly preferably 110,000 to 280,000, and even 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 manufacturing of the polarizing film tends to be difficult. The weight average molecular weight of the polyvinyl alcohol-based resin is the weight average molecular weight measured by the GPC-MALS method.

The average degree of saponification of the polyvinyl alcohol-based resin used in the present invention is usually preferably 98 mol% or more, particularly preferably 99 mol% or more, still more preferably 99.5 mol% or more, and particularly preferably 99. 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 degree of saponification in the present invention is measured according to JIS K 6726.

As the polyvinyl alcohol-based resin used in the present invention, two or more kinds having different modified species, modified amounts, weight average molecular weight, average saponification degree and the like may be used in combination.

Then, using the polyvinyl alcohol-based resin, an aqueous solution to be a film-forming stock solution is prepared.
That is, it is preferable that the polyvinyl alcohol-based resin is first washed with water and dehydrated using a centrifuge or the like to obtain a polyvinyl alcohol-based resin wet cake having a water content of 50% by weight or less. If the water content is too high, it tends to be difficult to obtain the desired aqueous solution concentration.
The polyvinyl alcohol-based resin wet cake is dissolved in warm water or hot water to prepare a polyvinyl alcohol-based resin aqueous solution.

The method for preparing the polyvinyl alcohol-based resin aqueous solution is not particularly limited, and for example, it may be prepared using a heated multi-screw extruder, and the dissolution can provided with the vertical circulation flow generation type stirring blade is described above. It is also possible to add the above-mentioned polyvinyl alcohol-based resin wet cake and blow steam into the can to dissolve and prepare an aqueous solution having a desired concentration.

In addition to polyvinyl alcohol-based resins, polyvinyl alcohol-based resin aqueous solutions include commonly used plasticizers such as glycerin, diglycerin, triglycerin, ethylene glycol, triethylene glycol, polyethylene glycol, and trimethylolpropane, and nonionic properties. , Anionic, and cationic surfactants are preferably contained in terms of film-forming property of the polyvinyl alcohol-based film.

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

First, the obtained polyvinyl alcohol-based resin aqueous solution is defoamed. Examples of the defoaming method include static defoaming and defoaming with 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 the T-shaped slit die in a fixed amount, discharged and cast on a rotating cast drum, and formed by a continuous casting method.

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

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

The discharge rate of the polyvinyl alcohol-based resin aqueous solution discharged from the T-type slit die to the cast drum is preferably 0.1 to 5 m / min, particularly preferably 0.2 to 4 m / min, and even more preferably 0. It is 3 to 3 m / min. If the discharge rate is too slow, the productivity tends to decrease, and if it is too fast, the flow tends to be difficult.

As the cast drum, a drum made of stainless steel (SUS) containing iron as a main component and having a metal plating applied to prevent scratches is usually used. Examples of the metal plating include chrome plating, nickel plating, zinc plating and the like, and these are used alone or in layers of two or more layers. Of these, the outermost surface is preferably chrome-plated from the viewpoint of durability of the drum surface.

The diameter of such a cast drum is preferably 2 to 5 m, particularly preferably 2.4 to 4.5 m, and even more preferably 2.8 to 4 m. If the diameter is too small, the drying length tends to be insufficient and the speed tends to be low, and if it is too large, the transportability tends to decrease.

The width of such a cast drum is preferably 4 to 7 m, 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 rotation speed of the cast drum is preferably 3 to 50 m / min, particularly preferably 4 to 40 m / min, and even more preferably 5 to 35 m / min. If the rotation speed is too slow, the productivity tends to decrease, and if it is too fast, the peelability when the film-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, still more preferably 60 to 97 ° C, particularly preferably 70 to 96 ° C, and particularly preferably 80 to 95 ° C. Is. If the surface temperature is too low, the peelability when peeling the film obtained by forming the film from the cast mold tends to decrease, and if it is too high, foaming tends to occur.

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

[Drying process]
Next, the drying step of heating and drying the peeled film (film-formed film) will be described in detail.

In such a drying step, as shown in FIG. 1, while transporting the film F peeled from the cast drum D in the flow direction (MD direction), a plurality of metal heating rolls alternately cover the front surface and the back surface of the film F. (Hereinafter, it is simply referred to as "heat roll".) It is brought into contact with R1 to R7 and dried. Note that FIG. 1 shows a case where seven thermal rolls R1 to R7 are used. Further, in FIG. 1, reference numeral C indicates a T-shaped slit die, and reference numeral E indicates a 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 surface surface of which is hard chrome-plated or mirror-treated and have a diameter of 0.2 to 2 m. The number of rolls is usually 2 to 30, preferably 10 to 25. In the present invention, a heat roll whose surface temperature is heated to 40 ° C. or higher and whose temperature is adjusted is referred to as a heat roll.

As described above, in this drying step, one of the major features of the present invention is that the front surface and the back surface of the film peeled from the cast drum are alternately brought into contact with a plurality of heat rolls to be dried. As a result, as described above, the dry state of the front surface and the back surface of the peeled film is appropriately controlled, and the polyvinyl alcohol-based film produced through this drying step has the elution amount of the polyvinyl alcohol-based resin and the elution amount. It can be assumed that the curl angle is reduced.

Here, a method of more optimizing the control of the dry state of the front surface and the back surface of the peeled film and further reducing the elution amount and curl angle of the polyvinyl alcohol-based resin will be described.

In the present invention, the total number of the heat rolls used in the drying step is P, and the surface temperature of the heat rolls in which the film peeled from the cast drum comes into contact with the nth is Tn (° C.), and the nth heat thereof. When the contact time between the roll and the film is Sn (seconds), the thickness of the produced polyvinyl alcohol film is D (μm), and n is an integer of 1 or more and P or less, it represents the sum of Tn × Sn. It is preferable that Σ (Tn × Sn) satisfies the following equation (1).
75 ≦ Σ (Tn × Sn) / D ≦ 110 ・ ・ ・ (1)

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

Here, Σ (Tn × Sn) is a value obtained by obtaining the value of Tn × Sn for all the 1st to Pth thermal rolls and adding them all together. The value of Σ (Tn × Sn) / D is (70 ×) when, for example, the total number of heat rolls is 3, the thickness D of the produced polyvinyl alcohol-based film is 20 μm, and the drying conditions are as follows. 6 + 80 × 7 + 90 × 8) ÷ 20 = 85.
The surface temperature of the _first heat roll T 1 = 70 ° C., and the contact time between the first heat roll and the film S ₁ = 6 seconds.
-The surface temperature of the second heat roll T ₂ = 80 ° C., and the contact time between the second heat roll and the film S ₂ = 7 seconds.
-The surface temperature of the third heat roll T ₃ = 90 ° C., and the 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, and conversely, if it is too large, the swelling property tends to increase. Tends to decline. As shown by the above formulas (1) to (1 ″), the thicker the produced polyvinyl alcohol-based film, the larger the thermal energy required for drying.

The contact time between the thermal roll and the film means the contact time between any one point on the film surface and each thermal roll. The contact time can be controlled by changing the outer diameter and arrangement of the heat rolls even if the film transport speed is constant.

In the present invention, the surface temperature Tn of all the thermal rolls used is preferably 40 to 150 ° C., particularly preferably 50 to 140 ° C., still more preferably 60 to 130 ° C., and particularly preferably 70 to 120 ° C. Is.
If the surface temperature of the thermal roll is too low, drying tends to be insufficient, and if the surface temperature Tn of the thermal roll is too high, crystallization of the polyvinyl alcohol-based resin proceeds, and the swelling property during the production of the polarizing film is uniform. Tends to disappear.

In the present invention, the contact time Sn between each thermal roll and the film is preferably 1 to 60 seconds, particularly preferably 2 to 30 seconds, still 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.

Further, in the present invention, the total number of the heat rolls used in the drying step is P, and the surface temperature of the heat rolls in which the film peeled from the cast mold comes into contact with the xth (odd number) is Tx (° C.). ), The surface temperature of the thermal roll in which the film contacts the y-th (even-numbered) is Ty (° C.), the contact time between the x-th (odd-numbered) thermal roll and the film is Sx (seconds), y. When the contact time between the third (even-numbered) heat roll and the film is Sy (seconds), Σ (Tx × Sx) representing the sum of Tx × Sx and Σ (Ty × Sy) representing the sum of Ty × Sy. ) Satisfies the following formula (2).
Σ (Ty × Sy) <Σ (Tx × Sx) ・ ・ ・ (2)

Particularly preferably, the following formula (2') is satisfied, and more preferably, the following formula (2 ″) is satisfied.
Σ (Ty × Sy) <0.9 × Σ (Tx × Sx) ・ ・ ・ (2')
0.8 x Σ (Tx x Sx) <Σ (Ty x Sy) <0.9 x Σ (Tx x Sx) ... (2'')

For example, when the total number of heat rolls is 3 and the drying conditions are as follows, the value of the above Σ (Tx × Sx) is 70 × 6 + 90 × 8 = 1140, and the above Σ (Ty × Sy). The value is 80 x 7 = 560.
The surface temperature of the _first heat roll T 1 = 70 ° C., and the contact time between the first heat roll and the film S ₁ = 6 seconds.
-The surface temperature of the second heat roll T ₂ = 80 ° C., and the contact time between the second heat roll and the film S ₂ = 7 seconds.
-The surface temperature of the third heat roll T ₃ = 90 ° C., and the 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-based film tends to curl easily in the swelling step during the production of the polarizing film. On the contrary, even if Σ (Ty × Sy) is excessively small, the polyvinyl alcohol-based film tends to curl in the opposite direction. That is, the purpose of the above formula (2) is that the surface of the film-formed film in contact with the cast mold is usually in contact with the even-numbered heat rolls, so that the amount of heat received from the even-numbered heat rolls is an odd-numbered number. The purpose is to equalize the amount of heat supplied to both sides of the film by making it less than the amount of heat received from the heat roll.

Further, in the present invention, when the surface temperature of the cast type is T ₀ (° C.), Σ (Tx × Sx) representing the sum of Tx × Sx and Σ (Ty × Sy) representing the sum of Ty × Sy. It is preferable that the following formula (3) is satisfied.
Σ (Ty × Sy) + T ₀ ≦ Σ (Tx × Sx) ≦ Σ (Ty × Sy) + T ₀ × 10 ・ ・ ・ (3)

Particularly preferably, the following formula (3') is satisfied, and more 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-based film tends to curl immediately after being immersed in water in the swelling step during the production of the polarizing film. That is, the purpose of the above equation (3) is that the surface of the film that is in contact with the cast mold generally contacts the even-numbered heat rolls, so that the amount of heat received from the cast mold and the even-numbered heat rolls is an odd-numbered one. The purpose is to make the amount of heat received from the heat roll equal to that of the amount of heat supplied to both sides of the film.

The moisture content of the dried film is preferably 10% by weight or less, particularly preferably 1 to 9% by weight, and even more preferably 2 to 8% by weight. If the water content is too high, the finally obtained polyvinyl alcohol-based 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 of both sides of the film can be made uniform. Examples of such a heat treatment method include a method of blowing hot air on both sides of the film using a floating dryer and a method of irradiating both sides of the film with near infrared rays using an infrared lamp.
The 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 when the heat treatment method is a method of irradiating near infrared rays with the infrared lamp. , Means its 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. The heat treatment method is a method that does not use a heat roll.

[Polyvinyl alcohol film]
After the drying step, the heat treatment is performed as necessary to obtain the polyvinyl alcohol-based film of the present invention which is long in the flow direction (MD direction). This polyvinyl alcohol-based film is produced as a film-wrapped 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 wrap the film-wrapped body with a water vapor barrier film to obtain a package, 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 longer, particularly preferably 15 days or longer, and even more preferably 15 to 60 days. If the storage period is too short, curling tends to occur during immersion in water. 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 or a roll stocker.

Although it is not clear why the above-mentioned storage reduces the curl during immersion in water, the above-mentioned storage makes the water content of the polyvinyl alcohol-based film constant in the plane and in the thickness direction, and the temperature is higher than room temperature. It is presumed that this is because the stress in the in-plane and thickness directions of the polyvinyl alcohol-based film is relaxed. Therefore, if the storage temperature is outside the above range, it is presumed that unevenness in moisture content and uneven stress will occur, which is not preferable.

The length of the polyvinyl alcohol-based 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-based film of the present invention is preferably 4 m or more in terms of widening the polarizing film, particularly preferably 5 m or more, and more preferably 5 to 6 m in terms of avoiding breakage during the production of the polarizing film. Is.

The polyvinyl alcohol-based 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. It is ~ 60 μm, more preferably 30-60 μm from the viewpoint of avoiding breakage.

Further, in the polyvinyl alcohol-based film of the present invention, it is preferable that the intersection angle θ between the orientation axis (slow phase axis) and the width direction (TD direction) of the film is 45 ° or less. When the crossing angle θ exceeds 45 °, it tends to curl in the width direction (TD direction) at the time of swelling. It is expected that such a phenomenon occurs because water absorption enters the gaps between the polymers, not in the orientation direction of the polymers. That is, when the orientation direction of the polymer is the length direction (MD direction), the swelling is more likely to occur in the width direction (TD direction) than in the target length direction (MD direction).

Further, in the polyvinyl alcohol-based film of the present invention, the refractive index in the length direction (MD direction) is nx, the refractive index in the width direction (TD direction) is ny, the refractive index in the thickness direction is nz, and the thickness is D ( When μm), the phase difference Rth (nm) in the thickness direction of the film calculated by the following formula (4) is preferably 100 nm or more, particularly preferably 110 nm or more, and further preferably 110 to 200 nm. is there. If the phase difference Rth is too small, it tends to curl during swelling. It is expected that such a phenomenon is because when the phase difference Rth is small, the orientation of the polymer chain in the thickness direction becomes strong and smooth swelling in the thickness direction is hindered. On the contrary, even if the phase difference Rth is too large, the plane orientation of the polymer chain is strong, so that smooth swelling in the plane direction tends to be hindered.
Rth = {(nx + ny) /2-nz} x 1000 x D ... (4)

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

Further, in the above embodiment, as a method of reducing the elution amount of the polyvinyl alcohol-based resin, in the drying step of the process of producing the polyvinyl alcohol-based film by the continuous casting method, the surface of the film formed by the cast mold is used. Although the method of appropriately controlling the dry state of the front surface and the back surface of the film-formed film by bringing the back surface into contact with a plurality of metal heating rolls alternately is adopted, another method may be adopted. .. For example, a method of adjusting the molecular weight and saponification degree of a polyvinyl alcohol-based resin as a raw material, a method of cleaning a polyvinyl alcohol-based resin to improve its purity, a method of adding a surfactant to an aqueous solution of a polyvinyl alcohol-based resin, and polyvinyl. Examples thereof include a method of controlling the degree of crystallinity and orientation of the polymer in the step of forming a film using an alcohol-based resin aqueous solution, and a method of controlling the dry state of the formed film.

Further, in the above embodiment, as a method of reducing the curl angle, the front surface and the back surface of the film formed by the cast mold are alternately alternately formed in the drying step of the process of producing the polyvinyl alcohol-based film by the continuous casting method. Although a method of appropriately controlling the dry state of the front surface and the back surface of the film-formed film by contacting with a plurality of metal heating rolls is adopted, other methods may be adopted. For example, a method of controlling the orientation state of the polymer in the process of forming a film using a polyvinyl alcohol-based resin aqueous solution, a method of improving the thickness accuracy during film formation, a method of controlling the dry state of the formed film, and the like. 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 elutes less when immersed in water and the curl angle is reduced.

Here, a method for producing a polarizing film obtained by using the polyvinyl alcohol-based film of the present invention will be described.

[Manufacturing method of polarizing film]
The polarizing film of the present invention is produced by feeding the polyvinyl alcohol-based film from the film-wrapped body, transporting the film in the horizontal direction, and performing steps such as swelling, dyeing, boric acid cross-linking, stretching, washing, and drying.

The swelling step is performed before the dyeing step. In addition to being able to clean the dirt on the surface of the polyvinyl alcohol-based film by the swelling step, there is also an effect of preventing uneven dyeing and the like by swelling the polyvinyl alcohol-based film. In the swelling step, water is usually used as the treatment liquid. If the main component of the treatment liquid is water, a small amount of an iodide compound, additives such as a surfactant, alcohol and the like may be contained. 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 contacting a polyvinyl alcohol-based film with a liquid containing iodine or a dichroic dye. Usually, an aqueous solution of iodine-potassium iodide is used, and an iodine concentration of 0.1 to 2 g / L and a potassium iodide concentration of 1 to 100 g / L are suitable. It is practical that the dyeing time is 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 water solvent.

The boric acid cross-linking step is carried out 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 at the time of treatment is preferably about 30 to 70 ° C., the treatment time is preferably about 0.1 to 20 minutes, and if necessary, a stretching operation may be performed during the treatment.

In the stretching step, it is preferable to stretch 3 to 10 times, preferably 3.5 to 6 times in the uniaxial direction [flow direction (MD direction)]. At this time, a slight stretching [stretching to the extent of preventing shrinkage in the width direction (TD direction) or more] may be performed in the direction perpendicular to the stretching direction. The temperature at the time of stretching is preferably 30 to 170 ° C. Further, the stretching ratio may be finally set in the above range, and the stretching operation may be performed not only once but also a plurality of times in the polarizing film manufacturing process.

The washing step is performed by immersing the polyvinyl alcohol-based film in, for example, an aqueous solution of iodide such as water or potassium iodide, and the precipitate generated on the surface of the polyvinyl alcohol-based film can be removed. When an aqueous potassium iodide solution is used, the potassium iodide concentration is about 1 to 80 g / L. The temperature during the cleaning 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. The washing with water and the washing with an aqueous potassium iodide solution may be performed in an appropriate combination.

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

Thus, the polarizing film of the present invention is obtained. The degree of polarization 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, it tends to be impossible to secure the contrast in the liquid crystal display.
_{The degree of polarization is generally the light transmittance (H 11} ) measured at wavelength λ and the two polarized light in a state where two polarizing films are superposed so that their orientation directions are the same. It is calculated according to the following formula from _{the light transmittance (H 1} ) measured at the wavelength λ in a state where the films are superposed so that the orientation directions are orthogonal to each other.
Polarization = [(H ₁₁ −H ₁ ) / (H ₁₁ + H ₁ )] ^1/2

Further, the simple substance 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 simple substance 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, a method for manufacturing a polarizing plate using the polarizing film of the present invention will be described.

[Manufacturing 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 films of cellulose triacetate, cellulose diacetate, polycarbonate, polymethylmethacrylate, cycloolefin polymer, cycloolefin copolymer, polystyrene, polyether sulfone, polyarylene ester, poly-4-methylpentene, polyphenylene oxide and the like. Or you can give a sheet.

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

Further, a curable resin such as a urethane resin, an acrylic resin, or a urea resin may be applied to one or both sides of the polarizing film and cured to form a cured layer to form a polarizing plate. In this way, the cured layer can replace the protective film and can be thinned.

The polarizing film or polarizing plate using the polyvinyl alcohol-based film of the present invention has excellent polarization performance, and is used for portable information terminals, personal computers, televisions, projectors, signage, electronic desk computers, electronic clocks, word processors, electronic paper, and games. Liquid crystal displays such as machines, videos, cameras, photo albums, thermometers, audio, automobile and mechanical instruments, sunglasses, anti-glare glasses, stereoscopic glasses, wearable displays, display elements (CRT, LCD, organic EL, electronic) It is preferably used for anti-reflection layers for paper, etc., optical communication equipment, medical equipment, building materials, toys, etc.

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

Then, the measurement and evaluation of the characteristics of the polyvinyl alcohol-based film (elution amount of polyvinyl alcohol-based resin, curl angle) and the characteristics of the polarizing film (polarization degree, single transmittance, color unevenness) in the following Examples and Comparative Examples are as follows. I went like this.

<Measurement conditions>
[Elution amount of polyvinyl alcohol resin (ppm / m ² )]
The obtained polyvinyl alcohol-based film was humidity-controlled at 23 ° C. and 50% RH for 24 hours, and then a 100 mm × 100 mm (0.01 m ² ) test piece (the second test piece) was cut out and 1 L of ion-exchanged water was used. Was immersed in 50 ° C. for 1 minute to obtain an eluate. After mixing 10 mL of a coloring reagent (ion-exchanged water 500 g, potassium iodide 7.4 g, iodine 0.65 g, boric acid 10.6 g) with 10 mL of the eluate at room temperature (25 ° C.), a spectrophotometer (Shimadzu Seisakusho Co., Ltd.) Manufactured by: UV-3100PC), the absorbance at a wavelength of 690 nm was measured, the concentration (ppm) of the polyvinyl alcohol-based resin was calculated from the calibration curve prepared in advance, and the area was converted to the elution amount (ppm / m ² ). did.
In the same manner as 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-based film. At this time, the long side of the test piece was defined as the length direction (MD direction) of the film, and the short side was defined as the width direction (TD direction) of the film. Then, as shown in FIG. 2A, the center of the lower end edge of the test piece 1 in the long side direction is centered on the (first) clip (Kokuyo's "eyeball clip pole bean"; mouth width 20 mm; mass 2). .1g) It was sandwiched between 2a, and the wire 2b was wound around the clip 2a. The clip 2a and the wire 2b were used to form a weight stone 2 having a total mass of 5 g, and a test body composed of the test piece 1 and the weight stone 2 was prepared. After that, the center of the upper end edge of the test piece 1 in the long side direction was sandwiched between the (second) clips (same as above) 3a, and the string 3b was tied to the clip 3a (hanging consisting of the clip 3a and the string 3b). The lowering jig 3 was attached to the central portion of the upper end edge of the test piece 1 in the long side direction). Next, the test body with the clip 3a was suspended by the string 3b, and the entire test body was immersed in water 4a at 30 ° C. in the water tank 4. Then, as shown in FIG. 2 (b), the curl angle α (°) in the short side direction (width direction) at the time when 10 seconds and 2 minutes have passed from the immersion is the upper part of the water tank 4 (not shown). It was visually observed from. In FIG. 2B, the weight stone 2, the hanging jig 3, and the water tank 4 are not shown in order to make the configuration easy to understand. Further, the curl angle α is an angle formed by the flat surface portion of the test piece 1 and the tangential direction of the edge portion of the curled portion in the short side direction.

[Polarization (%), Elementary transmittance (%)]
A test piece having a length of 4 cm and a width of 4 cm is cut out from the central portion and both side ends (10 cm inside from each end of both side ends of the polarizing film) in the width direction (TD direction) of the obtained polarizing film, and is automatically polarized. The degree of polarization (%) and the single transmittance (%) were measured using a film measuring device (manufactured by JASCO Corporation: VAP7070). Such measurements were performed on the central portion and the tip / end portion (10 m inside from each end of the tip and end of the polarizing film) in the length direction (MD direction) of the polarizing film.

〔Color unevenness〕
A test piece having a length of 30 cm and a width of 30 cm was cut out from the central portion and both end side portions (10 cm inside from each end of both side ends of the polarizing film) of the obtained polarizing film in the width direction (TD direction), and cross Nicol. After sandwiching it at an angle of 45 ° between the two polarizing plates in the state (single transmittance 43.5%, polarization degree 99.9%), using a light box with a surface illuminance of 14,000 lp, a transmission mode The optical color unevenness was observed with the following criteria and evaluated according to the following criteria. Such measurements were performed on the central portion and the tip / end portion (10 m inside from each end of both side ends of the polarizing film) in the length direction (MD direction) of the polarizing film.
(Evaluation criteria)
○ ・ ・ ・ There was no color unevenness.
× ... There was color unevenness.
Such evaluation was performed for the central portion and the tip / end portion (10 m inside from each end of the tip and end of the polarizing film) in the length direction (MD direction) of the polarizing film.

<Example 1> (Preparation of polyvinyl alcohol-based film)
Add 2,000 kg of polyvinyl alcohol-based 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, and heat the temperature to 140 ° C. while stirring to dissolve under pressure. After that, the concentration was adjusted to a resin concentration of 25% by weight to obtain a uniformly dissolved polyvinyl alcohol-based resin aqueous solution. Next, the above polyvinyl alcohol-based resin aqueous solution is supplied to a twin-screw extruder having a vent to defoam, then the aqueous solution temperature is set to 95 ° C., and a cast drum (surface temperature 92 ° C.) is rotated from a T-shaped slit die discharge port. ) Was discharged (discharge rate 2.5 m / min) and cast to form a film. The formed film was peeled off from the cast drum, and the front surface and the back surface (contact surface with the cast drum) of the film were dried while being alternately contacted with a total of 15 heat rolls. The drying conditions [see the above formulas (1) to (3)] are as shown in Table 1 below. Next, using a floating dryer, hot air at 120 ° C. was blown from both sides of the peeled film to perform heat treatment to obtain a polyvinyl alcohol-based film having a thickness of 60 μm. Finally, by slitting both ends of the polyvinyl alcohol-based film in the width direction (TD direction) and winding it around the core tube in a roll shape, the film wound body (dimensions of the polyvinyl alcohol-based film: width 5 m, length). 5 km) was obtained.

(Storage of polyvinyl alcohol film)
Then, the film-wrapped body was double-wrapped with a water vapor barrier film and packaged to obtain a package. As the water vapor barrier film, a laminated film of an aluminum-deposited polyester film (polyethylene terephthalate film in which aluminum was vapor-deposited at 50 nm, 12 μm thickness) and a polyethylene film (25 μm thickness) was used. Next, the package was stored in a roll stocker having an atmospheric temperature of 26 ° C. for 15 days. The characteristics of the polyvinyl alcohol-based film after storage are shown in Table 1 below.

(Manufacturing of polarizing film)
The obtained polyvinyl alcohol-based film is unwound from the film-wrapped body, transported in the horizontal direction using a transport roll, and first immersed in a water tank having a water temperature of 30 ° C. to swell and flow in the flow direction (MD direction). ) Was stretched 1.7 times. Next, it was immersed in an aqueous solution of iodine (0.5 g / L and potassium iodide) at 28 ° C. and stained, and stretched 1.6 times in the flow direction (MD direction) in 0.5 minutes. Then, it was immersed in an aqueous solution of 40 g / L of boric acid and 30 g / L of potassium iodide at 50 ° C., and uniaxially stretched 2.1 times in the flow direction (MD direction) in 1 minute while cross-linking borate. 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 characteristics of the obtained polarizing film are shown in Table 2 below.

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

<Example 3>
In Example 1, the discharge rate of 2.5 m / min was set to 1.9 m / min, and the film wound body (polyvinyl alcohol-based film) was produced in the same manner as in Example 1 except that the film was manufactured under the conditions shown in Table 1 below. Dimensions: thickness 45 μm, width 5 m, length 5 km) were obtained. Further, the film-wrapped body was stored in the same manner as in Example 1. The characteristics of the polyvinyl alcohol-based film after storage are shown in Table 1 below. Further, a polarizing film was obtained in the same manner as in Example 1. The characteristics of the obtained polarizing film are shown in Table 2 below.

<Example 4>
In Example 1, the discharge rate of 2.5 m / min was set to 1.3 m / min, and the film wound body (polyvinyl alcohol-based film) was produced in the same manner as in Example 1 except that the film was manufactured under the conditions shown in Table 1 below. Dimensions: thickness 30 μm, width 5 m, length 5 km) were obtained. Further, the film-wrapped body was stored in the same manner as in Example 1. The characteristics of the polyvinyl alcohol-based film after storage are shown in Table 1 below. Further, a polarizing film was obtained in the same manner as in Example 1. The characteristics of the obtained polarizing film are shown in Table 2 below.

<Comparative example 1>
A film wound body (dimensions of polyvinyl alcohol-based film: thickness 60 μm, width 5 m, length 5 km) was obtained in the same manner as in Example 1 except for the production under the conditions shown in Table 1 below. Further, the film-wrapped body was stored in the same manner as in Example 1. The characteristics of the polyvinyl alcohol-based film after storage are shown in Table 1 below. Further, a polarizing film was obtained in the same manner as in Example 1. The characteristics of the obtained polarizing film are shown in Table 2 below.
When the chemical solution in the boric acid cross-linking tank was visually confirmed after the polarizing film was manufactured, cloudiness was observed, and the circulation filter of the chemical solution was clogged.

<Comparative Example 2> (corresponding to Example 1 of Patent Document 3)
In Example 1, the film winding body (polyvinyl alcohol type) was produced in the same manner as in Example 1 except that the discharge rate was set to 1.9 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) were obtained. Further, the film-wrapped body was stored in the same manner as in Example 1. The characteristics of the polyvinyl alcohol-based 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 discontinued due to breakage at the end of the film in the swelling step. 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 discharge rate of 2.5 m / min was set to 1.3 m / min, and the film wound body (polyvinyl alcohol-based film) was produced in the same manner as in Example 1 except that the film was manufactured under the conditions shown in Table 1 below. Dimensions: thickness 30 μm, width 5 m, length 5 km) were obtained. Further, the film-wrapped body was stored in the same manner as in Example 1. The characteristics of the polyvinyl alcohol-based film after storage are shown in Table 1 below. Further, an attempt was made to produce a polarizing film in the same manner as in Example 1, but a polarizing film could not be obtained because a break occurred at the edge of the film in the swelling step and a break occurred in the subsequent stretching step.

<Comparative example 4>
In Example 1, the discharge rate was set to 2.1 m / min, and a total of 18 thermal rolls were used to manufacture the film under the conditions shown in Table 1 below. A film wound body (dimensions of polyvinyl alcohol-based film: thickness 50 μm, width 5 m, length 5 km) was obtained. Further, the film-wrapped body was stored in the same manner as in Example 1. The characteristics of the polyvinyl alcohol-based film after storage are shown in Table 1 below.
Further, an attempt was made to produce a polarizing film in the same manner as in Example 1, but a polarizing film could not be obtained because a break occurred at the edge of the film in the swelling step and a break occurred in the subsequent stretching step.

In the polyvinyl alcohol-based films of Examples 1 to 4, since the amount of resin eluted in water and the curl angle when immersed in water are within the range specified in the present application, the polarizing film has good productivity, excellent polarization performance, and no color unevenness. was gotten. On the other hand, in the polyvinyl alcohol-based film of Comparative Example 1, since the amount of resin eluted in water is out of the range specified in the present application, it can be seen that the obtained polarizing film is inferior in polarization performance and has color unevenness. Further, in the polyvinyl alcohol films of Comparative Examples 2 to 4, a wide and long polarizing film could not be obtained because the curl angle at the time of immersion in water was out of the range specified in the present application.

Although the specific embodiments of the present invention have been shown in the above examples, the above examples are merely examples and are not to be interpreted in a limited manner. Various variations apparent to those skilled in the art are intended to be within the scope of the present invention.

The polarizing film or polarizing plate using the polyvinyl alcohol-based film of the present invention has excellent polarization performance, and is used for portable information terminals, personal computers, televisions, projectors, signage, electronic desk computers, electronic clocks, word processors, electronic paper, and games. Liquid crystal displays such as machines, videos, cameras, photo albums, thermometers, audio, automobile and mechanical instruments, sunglasses, anti-glare glasses, stereoscopic glasses, wearable displays, display elements (CRT, LCD, organic EL, electronic) It is preferably used for anti-reflection layers for paper, etc., optical communication equipment, medical equipment, building materials, toys, etc.

Claims (12)

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 condition A below is 135 ° or less. A polyvinyl alcohol-based 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-based 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 whole test piece is immersed in water at 30 ° C. for 10 seconds while the test piece provided with 5 g of a heavy stone is supported and suspended at the center of the second edge portion in the long side direction of the test piece. .. The polyvinyl alcohol-based film according to claim 1, wherein the curl angle in the short side direction measured is 40 ° or less when the immersion time of the test piece is 2 minutes under the condition A. The invention according to claim 1 or 2, wherein the polyvinyl alcohol-based film is a long film, the long side of the test piece is in the length direction of the film, and the short side is in the width direction of the film. Polyvinyl alcohol-based film. The polyvinyl alcohol-based film according to any one of claims 1 to 3, wherein 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 polyvinyl alcohol-based film according to any one of claims 1 to 4, wherein the 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 process in which an aqueous solution of a polyvinyl alcohol-based resin is continuously discharged and cast into a cast mold to form a film, and the film-formed film is peeled from the cast mold and then dried to dry the film-formed film. The method for producing a polyvinyl alcohol-based film according to any one of claims 1 to 5, which comprises a step, wherein the drying of the film-formed film in the drying step is the surface of the film-formed film. A method for producing a polyvinyl alcohol-based film, which 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, and the surface temperature of the metal heating rolls in which the film peeled from the cast mold comes into contact with the nth is Tn (° C.), and the nth metal thereof. When the contact time between the heated roll and the film is Sn (seconds), the thickness of the polyvinyl alcohol film produced is D (μm), and n is an integer of 1 or more and P or less, the total of Tn × Sn. The method for producing a polyvinyl alcohol-based film according to claim 6, wherein Σ (Tn × Sn) representing the above satisfies the following formula (1).
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 rolls in which the film peeled from the cast mold comes into contact at the xth position is Tx (° C.), and the film is the yth position. The surface temperature of the metal heating roll that comes into contact with the film is Ty (° C.), the contact time between the xth 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 x is an odd number of 1 or more and P or less, and the y is an even number of 2 or more and P or less, Σ (Tx × Sx) representing the sum of Tx × Sx and Ty × Sy The method for producing a polyvinyl alcohol-based film according to claim 6 or 7, wherein Σ (Ty × Sy) representing the sum of the above satisfies the following formula (2).
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 rolls in which the film peeled from the cast mold comes into contact at the xth position is Tx (° C.), and the film is the yth position. The surface temperature of the metal heating roll that comes into contact with the film is Ty (° C.), the contact time between the xth 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 type is T ₀ (° C), x is 1 or more and an odd number of P or less, and y is 2 or more and an even number of P or less, the sum of Tx × Sx is calculated. The invention according to any one of claims 6 to 8, wherein Σ (Tx × Sx) representing and Σ (Ty × Sy) representing the sum of Ty × Sy satisfy the following formula (3). A method for producing a polyvinyl alcohol-based 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 above drying step into a core tube in a roll shape, and the film wound body is wrapped in a water vapor barrier film at an atmospheric temperature of 25 to 30 ° C. The method for producing a polyvinyl alcohol-based film according to any one of claims 6 to 9, wherein the film is stored for 5 days or more. A polyvinyl alcohol-based film produced by the method for producing a polyvinyl alcohol-based film according to any one of claims 6 to 10. A polarizing film according to any one of claims 1 to 5 and 11, wherein the polyvinyl alcohol-based film is used.

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