KR20190018419A - A polyvinyl alcohol film, a production method thereof, and a polarizing film using the polyvinyl alcohol film - Google Patents

Abstract

A polyvinyl alcohol film excellent in dyeability as a disc of polarizing film and capable of producing a polarizing film excellent in polarization performance with high productivity, a method for producing the same, and a polarizing film using the polyvinyl alcohol film are provided. The polyvinyl alcohol film of the present invention is characterized in that the contact angle θ _1S with respect to n-hexadecane after 1 second from the contact of the droplets of n-hexadecane is 5 to 13 °.

Description

A polyvinyl alcohol film, a production method thereof, and a polarizing film using the polyvinyl alcohol film

The present invention relates to a polyvinyl alcohol film excellent in durability as a raw material of a polarizing film and capable of producing a polarizing film excellent in polarization performance with high productivity, a method for producing the same, and a polarizing film employing the polyvinyl alcohol film .

Conventionally, a polyvinyl alcohol-based film is produced by dissolving a polyvinyl alcohol-based resin in a solvent such as water and adding a plasticizer such as glycerin or an additive such as a surfactant to prepare a stock solution for film-forming, And is dried by using a metal heating roll or the like. The polyvinyl alcohol-based film thus produced is used for many applications as a film having excellent transparency and dyeability, and polarizing films are one useful application thereof.

The polarizing film is produced by dyeing and stretching a polyvinyl alcohol-based film, which becomes a raw material, with a dye such as iodine. For example, a polyvinyl alcohol film is swollen with water (including hot water), followed by dyeing with iodine, stretching to arrange iodine molecules, crosslinking with a crosslinking agent such as boric acid to maintain the stretched state, And drying. Each of the steps of water swelling, dyeing, stretching, and boric acid crosslinking may be changed in sequence or a plurality of steps may be simultaneously carried out.

Such a polarizing film is used as a basic component part of a liquid crystal display device such as a portable information terminal or a television. In recent years, a polarizing film having a high light transmittance and a high degree of polarization has been demanded due to high brightness and high definition of liquid crystal display. In addition, as a result of a large screen or thinning of a liquid crystal TV or the like, A polarizing film is required.

In order to meet such a demand, a thin polyvinyl alcohol-based film having excellent dyability and a wide width and a long length is needed. When the dyability of the polyvinyl alcohol-based film is low, a sufficient degree of polarization can not be obtained, and polarization unevenness tends to occur easily. This tendency was particularly remarkable in the production of a thin polarizing film.

In order to improve the dyeability of a polyvinyl alcohol-based film, a polyvinyl alcohol-based film having a specific periodic structure has been proposed (see, for example, Patent Document 1). In addition, a polyvinyl alcohol-based film containing a specific surfactant has been proposed (see, for example, Patent Documents 2, 3 and 4). Further, a method of controlling the bath temperature in the swelling process has been proposed (see, for example, Patent Documents 5 and 6).

(Patent Document 1) JP 2006-188655 A (Patent Document 2) JP 2005-206809 A (Patent Document 3) JP 2005-206810 A (Patent Document 4) JP 2006-188656 A (Patent Document 5) JP 2006-065309 A (Patent Document 6) JP 2014-197050 A

However, in the technique described in Patent Document 1, the dyeability in the inside of the film is improved, but the dyeability in the vicinity of the surface of the film is sometimes insufficient, and there is room for improvement in that point. In addition, in the technologies described in the above Patent Documents 2, 3 and 4, the added surfactant bleeds out on the surface of the film, so that sufficient dyeability can not be obtained, and there is room for improvement in this respect. In the techniques described in Patent Documents 5 and 6, even if the swelling degree can be controlled by the bath temperature, there is a problem that the dye can not be uniformly adsorbed unless the dyeability of the polyvinyl alcohol film itself as a disc is good.

Accordingly, the present invention provides a polyvinyl alcohol-based film excellent in dyeability under such a background, which can obtain a polarizing film having a high degree of polarization and a polarization unevenness even when the film is wide and long and thin .

Therefore, the inventors of the present invention have found that polyvinyl alcohol films whose surface has specific wettability solve the above problems as a result of repeated studies in view of such circumstances. And, the present inventors have found that the specific wettability can be specified by the contact angle to n-hexadecane. Further, the present inventors have also attempted to measure the contact angle with water, but since the polyvinyl alcohol film is hydrophilic and water swellable, the wettability can not be specified because it can not be stably measured accurately.

That is, the first aspect of the present invention is a polyvinyl alcohol-based film characterized in that the contact angle θ _1S to n-hexadecane is 1 to 5 ° after 1 second from the contact of droplets of n-hexadecane.

A second aspect of the present invention is a method for producing a polyvinyl alcohol-based film of the first aspect, comprising a preparing step of preparing an aqueous solution of a polyvinyl alcohol-based resin, and a step of continuously preparing an aqueous solution of the polyvinyl alcohol- And a drying step of drying the film after peeling off the film from the casting mold. The present invention also provides a method for producing a polyvinyl alcohol-based film.

The third point of the present invention is a polarizing film in which the polyvinyl alcohol film is used.

The polyvinyl alcohol film of the first aspect of the present invention has a contact angle θ _{1S of 5} to 13 ° with respect to n-hexadecane after 1 second from the contact of droplets of n-hexadecane. This indicates that the surface of the polyvinyl alcohol-based film has a specific wettability. Therefore, the polyvinyl alcohol-based film is excellent in dyeability when the polarizing film is produced. When the polyvinyl alcohol-based film is used, the polarizing film having a high degree of polarization and having no staining unevenness can be obtained.

In particular, when the difference δθ _1S = | θ _1S -θ _1S '| between the contact angle θ _1S of the first surface and the contact angle θ _1S' of the second surface on both surfaces of the film is within 2 °, the polarizing film is manufactured The same dyeing property can be obtained on both sides of the film, and a polarizing film having no uneven dyeing can be obtained.

Further, a difference Δθ = | θ _0S- θ _1S | between the contact angle θ _1S and the contact angle θ _0S with respect to the n-hexadecane after 0.1 second from the contact of the droplet of the n-hexadecane on each surface of the film on both surfaces of the film, Is in the range of 3 to 7 DEG, the swelling property and the dyeability at the time of producing the polarizing film can be more appropriately adjusted, and a polarizing film free from uneven dyeing can be obtained.

A second aspect of the present invention is a method for producing a polyvinyl alcohol-based film, comprising the steps of preparing an aqueous solution of a polyvinyl alcohol-based resin, a film-forming step of continuously forming a film of the prepared aqueous solution in a casted state, Since the film is peeled off from the cast mold and then dried, it is possible to continuously produce a polyvinyl alcohol film in the flow direction (MD).

Particularly, in the preparation process, the aqueous solution of the polyvinyl alcohol-based resin in which 0.01 to 0.1 wt% of a higher fatty acid amide compound having 10 to 30 carbon atoms is blended with the polyvinyl alcohol-based resin is heated to 100 to 150 캜 , It is possible to obtain the polyvinyl alcohol-based film of the first feature, which is excellent in the solubility of the above-mentioned higher fatty acid amide-based compound and in peelability from the cast form of the film thus formed and excellent in transparency .

Among them, in the case of decomposing 10 to 90% by weight of the above-mentioned higher fatty acid amide compound in the preparation process, a polyvinyl alcohol film easy to set the contact angle to n-hexadecane within the above range can be obtained .

In the preparation process, when the time taken to prepare the aqueous solution of the polyvinyl alcohol-based resin is 5 to 40 hours, a polyvinyl alcohol film excellent in controllability of the contact angle with respect to n-hexadecane can be obtained .

When the polyvinyl alcohol-based film has a thickness of 5 to 45 탆, the polarizing film can be thinned.

Since the polarizing film of the third aspect of the present invention uses the above-mentioned polyvinyl alcohol film, it has an effect that it has a high degree of polarization and can be free from uneven dyeing.

Hereinafter, the present invention will be described in detail.

The polyvinyl alcohol film of the present invention is characterized in that the contact angle? _1S with respect to n-hexadecane after 1 second from the contact of the droplets of n-hexadecane is 5 to 13 °.

Here, the contact angle is generally, liquid-drops of polyvinyl alcohol-based film from immediately after contact with the surface to change with time, but stabilized in a few seconds, in the present invention, the contact angle θ _1S after one second from enemy contact liquid as described above, certain Value.

 In addition, the above-mentioned contact angles were obtained by using a polyvinyl alcohol-based film having a humidity of 23 占 폚 and 50% RH for 24 hours and not touching or rubbing the portion to be tested of the film surface, / 2 method) is the contact angle for n-hexadecane.

The contact angle can be measured easily by using a commercially available contact angle measuring device. If n-hexadecane is used, the contact angle can be measured continuously and precisely from immediately after contact. In addition, intermittent measurement of 0.1 second pieces is also possible, and the contact angle can be varied with time.

The polyvinyl alcohol film can be produced by a continuous casting method using an aqueous solution of a polyvinyl alcohol-based resin containing specific surfactants and prepared under specific conditions, as will be described later in detail.

The polyvinyl alcohol film is formed into a polarizing film through a process such as swelling, dyeing, boric acid crosslinking, stretching, washing, and drying.

As described above, the polyvinyl alcohol-based film of the present invention needs to have a contact angle θ _{1S of 5} to 13 ° after 1 second from the contact of liquid droplets of n-hexadecane to the surface of the film, preferably 7 to 12 ° , Particularly preferably 8 to 11 deg. The value of the contact angle? _1S is a value of the entire surface of the polyvinyl alcohol film.

That is, there is no need to control the contact angle of a polyvinyl alcohol film used in a polarizing film while a thin polarizing film having a large width and a long length is required. Accordingly, the inventors of the present invention have found that, in order to obtain a thin, wide and long polarizing film having an optimal dyeability, the contact angle of the polyvinyl alcohol film of the disc may be set to a specific range smaller than the conventional one. Specifically, it has been found that, when the contact angle? _1S to n-hexadecane is made smaller than that of the conventional one, a polarizing film excellent in dyeability in the production of a polarizing film and free from dyeing unevenness is obtained.

However, when the contact angle? _1S is too small, organic components other than iodine are likely to enter the surface of the polyvinyl alcohol film in the dyeing step performed in water because of the high lipophilicity of the polyvinyl alcohol film. Therefore, uneven dyeing easily occurs and the object of the present invention can not be achieved. For example, an organic component such as a low molecular weight polyvinyl alcohol-based resin, a plasticizer and a surfactant in the polyvinyl alcohol-based film eluted in the swelling process is subjected to transport of the polyvinyl alcohol-based film, The film is carried into the dyeing tank continuously and unevenly penetrates into the surface of the polyvinyl alcohol film in the dyeing step, so that uniform adsorption of iodine tends to be hindered.

On the contrary, if the contact angle? _1S is too large, the adsorption of iodine is not stabilized, resulting in uneven dyeing, and the object of the present invention can not be achieved.

In addition, such &thetas; _1S satisfies the above-described range even when either of the two surfaces (front and back surfaces) of the polyvinyl alcohol film is measured.

In the present invention, the both sides of the polyvinyl alcohol-based film, one surface (first surface), the contact angle θ _1S and the contact angle θ _{1S 'with} the difference δθ _1S (= the other surface (second surface) of the | ? _{1S -} ? _{1S '} |) is preferably within 2 °, particularly preferably within 1.5 °, and more preferably within 1 °.

If the value of delta [theta] _1S is too large, adsorption of iodine on both surfaces of the polyvinyl alcohol-based film becomes uneven, so that uneven dyeing tends to occur in the polarizing film.

The contact angles? _1S and? _{1S '} are values measured on both sides of the polyvinyl alcohol film at the same point.

In the present invention, the contact angle? _0S after 0.1 second from the contact of the droplet of n-hexadecane and the contact angle? S after 1 second from the contact, which are measured on one side (first side) of the polyvinyl alcohol film, the difference between _{θ 1S Δθ (= | θ 0S} -θ 1S |) is a 3~7 ° which is preferred, and preferably 3.5~6.5 °, more preferably 4~6 °.

If the value of ?? is too small, the dyeability of the polyvinyl alcohol-based film tends to decrease. On the other hand, if the value is too large, the wettability to the liquid tends to fluctuate greatly and a certain degree of swelling in the swelling process can not be obtained, , There is a tendency that uneven dyeing is likely to occur.

It is also preferable that such a value of DELTA [theta] satisfies the above-described range even when measured on either side of the polyvinyl alcohol-based film.

Here, the method for producing the polyvinyl alcohol-based film of the present invention will be described.

The method for producing a polyvinyl alcohol-based film of the present invention comprises the steps of (A) preparing an aqueous solution of a polyvinyl alcohol-based resin (a film-forming solution), (2) preparing a film by continuously discharging and preparing the prepared aqueous solution, A step (B), and a drying step (C) for peeling the formed film from the cast mold and then drying it. Further, it is preferable that a heat treatment step (D) for heat-treating the dried film as required is provided.

[Preparation process (A)]

First, the process (A) for preparing the polyvinyl alcohol-based resin aqueous solution will be described in detail.

As the polyvinyl alcohol-based resin to be used in the present invention, a resin produced by saponifying polyvinyl alcohol-based resin which is unmodified, that is, 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 of vinyl acetate can be used. Examples of the component copolymerizable with vinyl acetate include unsaturated carboxylic acids (including salts, esters, amides, nitriles, etc.), olefins having 2 to 30 carbon atoms (e.g., Butene, isobutene, etc.), vinyl ethers, and unsaturated sulfonic acid salts. It is also possible to use a modified polyvinyl alcohol-based resin obtained by chemically modifying a hydroxyl group after saponification.

As the polyvinyl alcohol-based resin, a polyvinyl alcohol-based resin having a 1,2-diol structure in the side chain may also be used. Such a polyvinyl alcohol-based resin having a 1,2-diol structure in the side chain can be obtained by, for example, (i) saponifying a copolymer of vinyl acetate and 3,4-diacetoxy-1-butene, ) Saponifying and decarboxylating a copolymer of vinyl acetate and vinylethylene carbonate, (iii) saponifying and removing a copolymer of vinyl acetate and 2,2-dialkyl-4-vinyl-1,3-dioxolane (Iv) a method of saponifying a copolymer of vinyl acetate and glycerin monoaryl ether, and 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 more preferably 120,000 to 260,000. When the weight average molecular weight is too small, the degree of polarization of the polarizing film tends to decrease. When the weight average molecular weight is too large, the stretching at the time of polarizing film tends to be difficult. The weight average molecular weight of the polyvinyl alcohol resin is a weight average molecular weight measured by the GPC-MALS method.

The average saponification degree of the polyvinyl alcohol-based resin used in the present invention is preferably 98 mol% or more, particularly preferably 99 mol% or more, more preferably 99.5 mol% or more, particularly preferably 99.8 mol% or more to be. 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 in accordance with JIS K 6726.

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

Then, the polyvinyl alcohol-based resin is washed with water and dehydrated using a centrifugal separator or the like to obtain a polyvinyl alcohol-based resin wet cake having a moisture content of 50% by weight or less. If the moisture content is too large, it tends to be difficult to obtain the desired aqueous solution concentration.

The polyvinyl alcohol-based resin wet cake is dissolved in hot water or hot water to adjust the polyvinyl alcohol-based resin aqueous solution.

The method of preparing the polyvinyl alcohol-based resin aqueous solution is not particularly limited, and examples thereof include a method of preparing by using a heated multi-screw extruder, and a method of preparing by using a dissolving can having an upflow and downward circulation flow- . In the latter method, the polyvinyl alcohol-based resin wet cake is put into the dissolving can, and water vapor is blown into the dissolving can to dissolve and prepare an aqueous solution of a desired concentration.

In the present invention, the latter is preferable from the viewpoint of improving the light transmittance of the polarizing film, and the temperature of the aqueous solution during preparation is preferably 100 to 150 캜. Of course, since the temperature is higher than the boiling point of water under atmospheric pressure, such preparation is carried out by pressurization.

In the polyvinyl alcohol-based resin aqueous solution, it is preferable that a plasticizer or a surfactant is contained, if necessary, in addition to the polyvinyl alcohol-based resin in view of the film formability of the polyvinyl alcohol-based film.

Examples of the plasticizer used in the present invention include glycerin, diglycerin, triglycerin, ethylene glycol, triethylene glycol, polyethylene glycol, trimethylol propane and the like. Of these, glycerin is preferable from the viewpoint of low cost.

When glycerin is used, the blending amount of the polyvinyl alcohol-based resin is preferably 5 to 15% by weight, particularly preferably 6 to 13% by weight, and more preferably 7 to 12%. When the blending amount is too small, the water swelling property of the polyvinyl alcohol-based film tends to be lowered, while if it is too much, the dyeability of the polyvinyl alcohol-based film tends to be lowered.

Examples of the surfactant used in the present invention include at least one surfactant selected from nonionic, anionic, and cationic surfactants. Among them, a nonionic surfactant is preferred from the viewpoint of compatibility with a polyvinyl alcohol-based resin aqueous solution.

Examples of the nonionic surfactant include polyoxyethylenehexyl ether, polyoxyethylene heptyl ether, polyoxyethylene octyl ether, polyoxyethylene nonyl ether, polyoxyethylene decyl ether, polyoxyethylene dodecyl ether, polyoxyethylene Ethylene tetradecyl ether, polyoxyethylene hexadecyl ether, polyoxyethylene octadecyl ether, polyoxyethylene eicosyl ether, polyoxyethylene oleyl ether, palm oil reduced alcohol ethylene oxide adduct, bovine fat reduced alcohol ethylene oxide adduct, etc. Polyoxyethylene alkyl ethers;

Polyoxyethylene laurylamine, hydroxyethyl lauryl amine, polyoxyethylene hexylamine, polyoxyethylene heptylamine, polyoxyethylene octylamine, polyoxyethylene nonylamine, polyoxyethylene decylamine, polyoxyethylene dodecylamine, polyoxyethylene tetradecylamine , Polyoxyethylene alkylamine such as polyoxyethylene hexadecylamine, polyoxyethylene octadecylamine, polyoxyethylene oleoylamine, and polyoxyethylene eicosylamine;

But are not limited to, amides such as amide, caproic acid amide, enanthate amide, caprylic acid amide, pelargonic acid amide, capric acid amide, undecyl acid amide, lauric acid amide, tridecyl acid amide, myristic acid amide, But are not limited to, lactic acid amide, stearic acid amide, stearic acid amide, stearic acid amide, nonadecyl acid amide, arachic acid amide, hexamic acid amide, behenic acid amide, tricosyl acid amide, lignoceric acid amide, Higher fatty acid amides;

Polyoxyethylene stearic acid amide, polyoxyethylene stearic acid amide, polyoxyethylene stearic acid amide, polyoxyethylene stearic acid amide, polyoxyethylene stearic acid amide, polyoxyethylene stearic acid amide, polyoxyethylene lauric acid amide, Polyoxyethylene stearic acid amide, polyoxyethylene stearic acid amide, polyoxyethylene stearic acid amide, polyoxyethylene stearic acid amide, polyoxyethylene stearic acid amide, polyoxyethylene stearic acid amide, polyoxyethylene stearic acid amide, Nonadecyl acid amide, nonadecyl acid amide, polyoxyethylene aralkyl amide, polyoxyethylene heptalic acid amide, polyoxyethylene behenic acid amide, polyoxyethylene tricosylic acid amide, polyoxyethylene lignoceric acid amide, , Polyoxyethylene montanic acid amide, polyoxyethylene mellitol Polyoxyethylene higher fatty acid amides, such as acid amide, polyoxyethylene oleic acid amide;

N-ethanols such as N-ethanol undecyl acid amide, N-ethanol lauric acid amide, N-ethanol tridecyl acid amide, N-ethanol myristin acid amide, N-ethanol pentadecyl acid amide, N-ethanol palmitic acid amide, Butanedioic acid amide, N-ethanedicarboxylic acid amide, N-ethanedicarboxylic acid amide, N-ethanedicarboxylic acid amide, N- N-alkanol higher fatty acid amides such as ethanol lignoceric acid amide, N-ethanol serotinic acid amide, N-ethanol montanic acid amide, N-ethanol maleic acid amide and N-ethanol oleic acid amide;

N, N-diethanol undecyl acid amide, N, N-diethanol lauric acid amide, N, N-diethanol tridecyl acid amide, N, N, N-diethanolamidecarboxylic acid amide, N, N-diethanolmalonic acid amide, N, N-diethanol stearic acid amide, N, N-diethanol nonadecyl acid amide, N, N, N-diethanolic behenic acid amide, N, N-diethanol tricoxylic acid amide, N, N-diethanol lignoceric acid amide, N, N-diethanolhexanoic acid amide, N, N-dialkanol higher fatty acid amides such as N-diethanololactinamide, N, N-diethanolmonocarbonamide, N, N-diethanolmalonic acid amide and N, N-diethanol oleic acid amide;

Amine oxides such as dimethyl lauryl amine oxide, dimethyl stearyl amine oxide and dihydroxy ethyl lauryl amine oxide; and the like.

Of these, higher fatty acid amides, polyoxyethylene higher fatty acid amides, N-alkanol higher fatty acid amides, N-alkoxylated fatty acid amides, and N-alkoxylated fatty acid amides are preferable from the viewpoint of setting the contact angle of polyvinyl alcohol- , And N-dialkanol higher fatty acid amide, and particularly preferably a higher fatty acid amide compound having 10 to 30 carbon atoms from the viewpoint of solubility, more preferably from 15 to 20 carbon atoms Of higher fatty acid amide compounds. The above-mentioned polyoxyethylene alkyl ether and polyoxyethylene alkylamine are preferably used in combination with the higher fatty acid amide compound.

These higher fatty acid amide compounds may be used alone or in combination of two or more.

The compounding amount (total amount) of the higher fatty acid amide compound in the polyvinyl alcohol-based resin aqueous solution is preferably 0.01 to 0.1% by weight, particularly preferably 0.02 to 0.07% by weight, based on the polyvinyl alcohol-based resin. When the blending amount is too small, the peeling property of the film from the cast surface tends to be lowered, while when it is too much, the film tends to become opaque.

From the viewpoint of easily setting the contact angle of the polyvinyl alcohol-based film of the present invention with respect to n-hexadecane within the above-specified specific range of the objective, 10 to 90 wt% of the higher fatty acid amide-based compound compounded in the polyvinyl alcohol- %, More preferably from 20 to 80% by weight, and still more preferably from 30 to 70% by weight.

Such decomposition amount is determined by using an analytical method such as liquid chromatography mass spectrometry (LC / MS) or gas chromatography mass spectrometry (GC / MS), after the preparation, the residual amount of the higher fatty acid amide compound in the aqueous solution Can be calculated.

The product obtained by the decomposition and the above-mentioned higher fatty acid amide compound remaining unreacted are combined to influence the surface state of the polyvinyl alcohol-based film to be produced, so that the contact angle with respect to n-hexadecane falls within the above- do.

Such decomposition amount can be controlled by the preparation temperature and the preparation time (time taken for preparation). The preparation temperature is the temperature of the aqueous solution of the polyvinyl alcohol-based resin when it is prepared in a state in which the higher fatty acid amide compound is contained, and is set at a relatively high temperature in the present invention. The preparation temperature is preferably 100 to 150 占 폚 as described above, but particularly preferably 110 to 145 占 폚, and more preferably 120 to 140 占 폚. The preparation time is a time taken for preparation of the aqueous solution of the polyvinyl alcohol-based resin, more specifically, the time taken for containing the higher fatty acid amide compound, and is set to a relatively long time in the present invention. The preparation time is preferably 1 to 50 hours, particularly preferably 5 to 40 hours, and more preferably 10 to 30 hours.

The resin concentration of the polyvinyl alcohol-based resin aqueous solution, which is the stock solution for film formation thus obtained, is preferably 5 to 60% by weight, particularly preferably 8 to 50% by weight, and more preferably 10 to 40% by weight. If the concentration of such a resin is too low, the production load tends to be lowered because the drying load becomes large. If the resin concentration is too high, the viscosity tends to become too high, and uniform flexibility tends to become impossible.

[Film forming step (B)]

Next, the film forming step (B) will be described in detail.

The polyvinyl alcohol-based resin aqueous solution is degassed first. As the defoaming method, there can be mentioned defoaming by a multi-screw extruder having a static deformation or a vent, etc. As the multi-screw extruder having a vent, a twin-screw extruder usually having a vent is used.

After the defoaming treatment, the polyvinyl alcohol-based resin aqueous solution is introduced into the T-shaped slit die by a predetermined amount from the viewpoint of wide elongation and uniformity of the film thickness, and is discharged and softened to the cast mold, and is formed by the casting method.

The resin temperature at the outlet of the T-shaped slit die is preferably 80 to 100 占 폚, particularly preferably 85 to 99 占 폚. If the resin temperature is too low, flow defects tend to occur. If too high, the resin tends to foam.

The viscosity of the aqueous solution of the polyvinyl alcohol-based resin is preferably from 50 to 200 Pa · s, particularly preferably from 70 to 150 Pa · s at the time of discharging. When the viscosity of such an aqueous solution is too low, flow deficiency tends to occur.

The discharge speed of the aqueous solution discharged from the T-shaped slit die to the cast mold is preferably 0.1 to 5 m / min, particularly preferably 0.2 to 4 m / min, and more preferably 0.3 to 3 m / min. If the discharge speed is too late, the productivity tends to decrease. If the discharge speed is too high, the flexibility tends to become difficult.

In casting, it is preferable to use a casting drum as the casting mold from the viewpoints of greatly increasing the length, length, uniformity of the film thickness, and the like. As the cast drum, generally, a surface of stainless steel (SUS) containing iron as a main component is subjected to metal plating to prevent scratches. Examples of the metal plating include chromium plating, nickel plating, and zinc plating, and they are used alone or in a laminated structure of two or more layers. Among these, from the viewpoint of durability of the drum surface, it is preferable that the outermost surface is chromium-plated.

The width of the cast drum is preferably 4 m or more, and more preferably 5 m or more. If the width of the cast drum is too small, it tends to be difficult to obtain a wide film.

The rotation speed of the cast drum is preferably 1 to 50 m / min, particularly preferably 2 to 40 m / min, and more preferably 3 to 35 m / min. If the rotation speed is too slow, productivity tends to decrease, and if it is too fast, drying tends to be insufficient.

The surface temperature of the cast drum is preferably 50 to 100 캜, particularly preferably 60 to 97 캜. When the surface temperature is too low, drying tendency tends to be poor, while when it is too high, the aqueous solution tends to foam.

The film is thus formed.

In this embodiment, a casting drum (drum-shaped roll) is used as a casting mold for use in film formation. However, a casting drum may be changed to use a endless belt or the like for film formation. It is preferable to use a cast drum from the viewpoint of improvement in film thickness and uniformity of film thickness.

[Drying step (C)]

Next, the drying step (C) will be described in detail. The drying step (C) is a step of heating and drying the formed film by bringing it into contact with a plurality of metal heating rolls (hereinafter simply referred to as " thermal rolls ").

Drying of the film formed by the cast drum is performed by peeling off the cast drum and then alternately bringing the surface and the back of the film into contact with a plurality of heat rolls. The surface temperature of the thermal roll is not particularly limited, but is usually 40 to 150 캜, preferably 50 to 140 캜. When the surface temperature is too low, drying tends to become defective. When the surface temperature is too high, it becomes too dry and tends to cause appearance defects such as waves.

[Heat Treatment Step (D)]

Next, the heat treatment step (D) will be described in detail. The heat treatment step (D) is a step of heat-treating the dried film. This heat treatment step (D) is an optional step which is carried out if necessary.

Examples of the heat treatment method include a method of blowing hot air on both sides of a film using a floating dryer or a method of irradiating near infrared rays on both sides of a film by using an infrared lamp, .

The heat treatment temperature is preferably 70 to 150 占 폚, particularly preferably 80 to 140 占 폚. When the heat treatment temperature is too low, the water resistance of the polyvinyl alcohol-based film tends to become insufficient. When the heat treatment temperature is too high, the stretchability upon production of the polarizing film tends to decrease. The heat treatment temperature means the temperature of the blowing hot air when the floating dryer is used, and the temperature of near infrared rays to be irradiated when the infrared lamp is used. The heat treatment time is not particularly limited, but in the case of using a floating dryer, it is preferably 10 to 100 seconds, particularly preferably 20 to 80 seconds.

[Polyvinyl alcohol film]

After the drying step (C), if necessary, the film subjected to the heat treatment step (D) becomes a polyvinyl alcohol-based film of the present invention having both end portions in the width direction (TD) slit and long in the flow direction (MD). This polyvinyl alcohol-based film is wound on a core tube in the form of a roll, thereby being produced as a film.

The polyvinyl alcohol film of the present invention thus obtained has a contact angle with respect to n-hexadecane within a specific range as described above. The difference between the contact angle and the conventional polyvinyl alcohol-based film is that, as described above, it depends on the product resulting from the decomposition of the higher fatty acid amide compound in the film and the higher fatty acid amide compound remaining without decomposition And it does not depend on the surface roughness of the film. The surface of the polyvinyl alcohol film of the present invention is smoothened to the same as the surface of the conventional polyvinyl alcohol film, and the surface roughness (Ra) of these films is in the range of 1 to 50 nm.

The width of the polyvinyl alcohol film is preferably 4 m or more from the viewpoint of widening the polarizing film, particularly preferably 4.5 m or more from the standpoint of further widening, and more preferably 4.5 to 7 m to be.

The length of the polyvinyl alcohol-based film is preferably 4 km or more from the viewpoint of enlargement of the polarizing film, and particularly preferably 4.5 to 50 km from the viewpoint of the transport weight, more preferably 4.5 km or more from the view point of the deck face.

The thickness of the polyvinyl alcohol film is preferably 5 to 45 占 퐉, more preferably 5 to 30 占 퐉, and still more preferably 10 to 30 占 퐉 in view of avoiding breakage, Mu m.

The polyvinyl alcohol film preferably has an in-plane retardation of 50 nm or less, particularly preferably 40 nm or less, and more preferably 30 nm or less, from the viewpoint of dyeability at the time of producing a polarizing film.

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

[Polarizing film production method]

The polarizing film of the present invention is produced by loosening the above polyvinyl alcohol film from the above-mentioned film and transporting it in the horizontal direction, and by swelling, dyeing, boric acid crosslinking, stretching, washing, drying and the like.

The swelling process is carried out before the dyeing process. In addition to being able to clean the surface of the polyvinyl alcohol film by the swelling process, the polyvinyl alcohol film is also swollen to prevent uneven dyeing. In the swelling process, water is usually used as the treatment liquid. If the main component is water, the treatment liquid may contain a small amount of an additive such as an iodide compound, a surfactant, or an alcohol. The temperature of the swelling bath is usually about 10 to 45 DEG C, and the immersion time in the swelling bath is usually about 0.1 to 10 minutes.

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

The boric acid crosslinking process is carried out using a boron compound such as boric acid or borax. The boron compound is used at a concentration of about 10 to 100 g / L in the form of an aqueous solution or a mixture of water and an organic solvent, and it is preferable that potassium iodide coexists in the liquid from the viewpoint of stabilization of the polarization performance. The temperature for the treatment is preferably about 30 to 70 占 폚, and the treatment time is preferably about 0.1 to 20 minutes, and if necessary, the stretching operation may be carried out during the treatment.

The stretching step is preferably stretched by 3 to 10 times, preferably by 3.5 to 6 times in a uniaxial direction (flow direction (MD)). At this time, it is also possible to perform a slight stretching (a degree of preventing the shrinkage in the width direction (TD), or a stretching further) in the direction perpendicular to the stretching direction. The temperature at the time of stretching is preferably 30 to 170 占 폚. The stretching magnification may be set to the above range, and the stretching operation may be performed not only once but also several times in the polarizing film producing step.

The cleaning step is carried out, for example, by immersing the polyvinyl alcohol film in an aqueous iodide solution such as water or potassium iodide, and the precipitates generated on the surface of the polyvinyl alcohol film can be removed. When potassium iodide aqueous solution is used, the concentration of potassium iodide is about 1 to 80 g / L. The temperature at the time of the washing treatment is usually 5 to 50 占 폚, preferably 10 to 45 占 폚. The treatment time is usually from 1 to 300 seconds, preferably from 10 to 240 seconds. The washing with water and the washing with aqueous potassium iodide solution may be carried out in appropriate combination.

The drying step is carried out, for example, by drying the polyvinyl alcohol-based film at 40 to 80 DEG C for 1 to 10 minutes in the atmosphere.

Thus, the polarizing film of the present invention can be obtained. The polarization degree of such a polarizing film is preferably not less than 99.8%, more preferably not less than 99.9%. When the degree of polarization is too low, the contrast in the liquid crystal display tends to decrease.

The polarization degree is generally set such that the two polarizing films are aligned so that their alignment directions are in the same direction, and the light transmittance (H ₁₁ ) measured at the wavelength? Is calculated from the light transmittance (H ₁ ) measured at the wavelength? In the overlapping state according to the following formula.

Polarization degree = [(H ₁₁ -H ₁ ) / (H ₁₁ + H ₁ )] ^1/2

The polarizing film of the present invention preferably has a single transmittance of 44% or more. If such a simple mass transmittance is too low, the brightness of the liquid crystal display tends to be unable to be achieved.

The mass transmittance is a value obtained by measuring the light transmittance of the single polarizing film by using a spectrophotometer.

[Polarizing plate production method]

The thus obtained polarizing film is used in the production of a polarizing plate. That is, the polarizing plate is produced by laminating and bonding an optically isotropic polymer film or sheet as a protective film to one side or both sides of the polarizing film. As the protective film, for example, cellulose triacetate, cellulose diacetate, polycarbonate, polymethyl methacrylate, cycloolefin polymer, cycloolefin copolymer, polystyrene, polyether sulfone, polyallylene ester, , Polyphenylene oxide, and the like.

The bonding method is carried out by a known method. For example, a liquid adhesive composition is uniformly applied to a polarizing film, a protective film, or both, and the two are adhered to each other by compression, .

It is also possible to apply a curable resin such as a urethane resin, an acrylic resin, or a urea resin to one surface or both surfaces of the polarizing film and cure it to form a cured layer, thereby forming a polarizing plate. In this case, the cured layer becomes a substitute for the protective film, and the thin film can be formed.

The polarizing film and the polarizing plate using the polyvinyl alcohol film of the present invention are excellent in the polarizing performance and can be used in portable information terminals, PCs, televisions, projectors, signage, electronic tabletop calculators, electronic clocks, word processors, An antireflection layer for a display device (CRT, LCD, organic EL, electronic paper and the like), a liquid crystal display device such as a camera, a photo album, a thermometer, audio, instrument of an automobile or a machine, a sunglass, Optical communication equipment, medical equipment, building materials, toys, and the like.

(Example)

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 unless the gist thereof is exceeded.

The properties (the decomposition amount of the higher fatty acid amide compound) of the polyvinyl alcohol-based resin solution in the following Examples and Comparative Examples, the characteristics of the polyvinyl alcohol-based film (contact angle with respect to n-hexadecane) The measurement and evaluation of the characteristics (staining unevenness, degree of polarization, and unit transmittance) were carried out as follows.

<Measurement Conditions>

(1) Degradation amount (% by weight) of high fatty acid amide compound

A 10 g sample was taken from the polyvinyl alcohol-based resin solution after preparation, and the higher fatty acid amide compound was dissolved in methanol (11 mL cell) by use of Accelerated Solvent Extraction using ASE-200 (11 mL cell) / Water (9/1). The solid content after the extraction was dried and weighed to determine the content A (g) of the polyvinyl alcohol resin. On the other hand, the extract was concentrated and dissolved in methanol to give a sample of 10 mL of liquid chromatography mass spectrometry (LC / MS), and the content B (g) of the higher fatty acid amide compound was measured by the following measuring apparatus and measuring conditions .

(Liquid chromatography)

Device: Agilent Technologies HP1100 from Agilent

Column: YMC-Pack ODS-A 150 占 3.0 mm? 5 占 퐉, column temperature 30 占 폚

Moving layer: 10 mM AcONH4 / MeOH = 25/75 (0 min)? 5/95 (15-30 min), flow rate 0.4 mL / min

(Mass analysis)

Apparatus: Thermo Electron LCQ Deca XP Max

Measurement mode: Positive ion mode

MS detector: Full-scan (m / z 100-2000) & MS / MS

(% By weight) of the higher fatty acid amide compound relative to the polyvinyl alcohol resin was calculated from the content B (g) of the obtained higher fatty acid amide compound and the content A (g) of the polyvinyl alcohol resin, Respectively.

Residual amount (% by weight) = 100 x B (g) / A (g)

Subsequently, from the residual amount (% by weight) of the higher fatty acid amide compound and the compounding amount (% by weight) of the higher fatty acid amide compound to the polyvinyl alcohol resin, the decomposition amount of the higher fatty acid amide compound Weight%) was calculated.

Decomposition amount (% by weight) = 100 x {blending amount (% by weight) - remaining amount (% by weight)} /

(2) Contact angle against n-hexadecane (°)

A test piece of 10 cm x 10 cm was cut out from the obtained polyvinyl alcohol film and humidity-conditioned at 23 DEG C and 50% RH for 24 hours. Then, using JIS-R3257 (1999) using a portable contact angle PCA-1 manufactured by Kyowa Interface Science Co., , The contact angle with respect to n-hexadecane at 23 DEG C and 50% RH was measured (&amp;thetas; / 2 method). The droplet volume of n-hexadecane is 1 l. The contact angle after 0.1 second after the contact between the droplet and the film was measured to? _0S (?) And after one second after the elapse of time, and the value after one second was defined as? _1S (?). The measurement was made on both sides of the surface of the polyvinyl alcohol film that was in contact with the cast drum and the opposite side was the back surface.

(3) Uneven dyeing

A test piece having a length of 30 cm and a width of 30 cm was cut out from the obtained polarizing film and sandwiched between two polarizing plates in a crossed Nicol state (having a single light transmittance of 43.5% and a polarization degree of 99.9%) at an angle of 45 °. The dyed unevenness was observed in the transmission mode using a light box and evaluated according to the following criteria.

(Evaluation standard)

○ · · · There is no dyeing stain on the front

△ ... Less than 20% of the area has uneven dyeing

× · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · ·

(4) Polarization degree (%), unit transmittance (%)

A sample having a length of 4 cm and a width of 4 cm was cut out from the obtained polarizing film and the degree of polarization (%) and the unit transmissivity (%) were measured using an automatic polarizing film measuring apparatus (VAP7070, manufactured by Nippon Bunkou Co., Ltd.).

&Lt; Example 1 &gt;

(Production of polyvinyl alcohol film)

1,000 kg of a polyvinyl alcohol resin having a weight average molecular weight of 142,000, a saponification degree of 99.9 mol%, 2,500 kg of water, 105 kg of glycerin as a plasticizer, and N, N-diethanol lauric acid amide 16, carbon number 16) (0.03% by weight based on the polyvinyl alcohol-based resin) was added and steam was added thereto while stirring to form a polyvinyl alcohol-based resin aqueous solution having a resin concentration of 25% by weight. The preparation temperature of such a preparation is 140 ° C and the preparation time is 20 hours. The residual amount of N, N-diethanol lauric acid amide in the obtained aqueous solution was measured and found to be 0.009% by weight with respect to the polyvinyl alcohol resin, and the decomposition amount of the higher fatty acid amide compound was 70% by weight.

Subsequently, the polyvinyl alcohol-based resin aqueous solution was fed to a twin-screw extruder and defoamed. Thereafter, the temperature of the aqueous solution was adjusted to 95 占 폚, and discharged from a T-shaped slit discharge port into a rotating casting drum at a discharge speed of 1.8 m / I made it. The film thus formed was peeled off from the cast drum, and the surface and back of the film were alternately brought into contact with a total of ten heat rolls while drying. Then, hot air of 140 DEG C was blown from both sides of the peeled film and heat treatment was performed. Then, both ends in the width direction (TD) were slit to obtain a polyvinyl alcohol film (thickness 45 m, width 5 m, length 5 km). The properties of the obtained polyvinyl alcohol-based film are shown in Table 1 below. Finally, the polyvinyl alcohol-based film was wound on a core tube in the form of a roll to obtain a film recommended body.

(Production of polarizing film)

The resulting polyvinyl alcohol-based film was unwound from the above-mentioned film and stretched 1.7 times in the flow direction (MD) while being swollen by immersing in a water bath at 30 ° C while conveying in the horizontal direction. Subsequently, the resultant was immersed in an aqueous solution of 30 g / l of iodine and 30 g / l of iodine and stretched 1.6 times in the flow direction (MD) while dyeing. Then, an aqueous solution of boric acid of 40 g / L and potassium iodide of 30 g / (50 占 폚) and uniaxially stretched 2.1 times in the flow direction (MD) while crosslinking the boric acid. Finally, the film was washed with an aqueous solution of potassium iodide and dried at 50 DEG C for 2 minutes to obtain a polarizing film having a total draw ratio of 5.7 times. The properties of the obtained polarizing film are shown in Table 1 below.

&Lt; Example 2 &gt;

A polyvinyl alcohol film was obtained in the same manner as in Example 1 except that the preparation time was changed to 10 hours in Example 1. The properties of the obtained polyvinyl alcohol-based film 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 1 below.

&Lt; Example 3 &gt;

In Example 1, a polyvinyl alcohol-based film was obtained in the same manner as in Example 1 except that the preparation temperature was set at 120 캜. The properties of the obtained polyvinyl alcohol-based film 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 1 below.

<Example 4>

In Example 1, a polyvinyl alcohol-based film was obtained in the same manner as in Example 1 except that the preparation temperature was set at 100 캜. The properties of the obtained polyvinyl alcohol-based film 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 1 below.

&Lt; Example 5 &gt;

A polyvinyl alcohol-based film was obtained in the same manner as in Example 1 except that 0.5 kg of N, N-diethanol lauric acid amide (compounding amount to polyvinyl alcohol-based resin: 0.05 wt%) was used in Example 1 . The properties of the obtained polyvinyl alcohol-based film 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 1 below.

&Lt; Example 6 &gt;

In Example 1, 0.3 kg of N, N-diethanol lauric acid amide (0.03% by weight based on the polyvinyl alcohol-based resin) was added and 0.1 kg of stearic acid amide (carbon number 18) 0.01% by weight) was used instead of the polyvinyl alcohol-based film. The properties of the obtained polyvinyl alcohol-based film 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 1 below. The residual amount of N, N-diethanol lauric acid amide and stearic acid amide in the resulting aqueous solution was measured and found to be 0.021% by weight and 0.002% by weight for the polyvinyl alcohol-based resin, (Total value of N, N-diethanol lauric acid amide and stearic acid amide) was 42% by weight.

&Lt; Example 7 &gt;

In Example 1, 0.3 kg of N, N-diethanol lauric acid amide (0.03% by weight based on the polyvinyl alcohol-based resin) was added and 0.2 kg of polyoxyethylene dodecylamine (average carbon number 28) (polyvinyl alcohol 0.02% by weight based on the total weight of the resin) was also used as the polyvinyl alcohol-based film. The properties of the obtained polyvinyl alcohol-based film 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 1 below.

Further, the amount of polyoxyethylene dodecylamine remaining in the obtained aqueous solution was measured and found to be 0.02% by weight based on the polyvinyl alcohol resin, and no decomposition was observed. The remaining amount of N, N-diethanol lauric acid amide was measured and found to be 0.009% by weight based on the polyvinyl alcohol-based resin, and the content of the higher fatty acid amide compound (N, N-diethanol lauric acid amide alone) The decomposition amount was 70% by weight.

&Lt; Example 8 &gt;

In Example 1, a polyvinyl alcohol film was obtained in the same manner as in Example 1 except that the film thickness was changed to 30 탆 at a discharge speed of 1.25 m / min. The properties of the obtained polyvinyl alcohol-based film 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 1 below.

&Lt; Comparative Example 1 &

A polyvinyl alcohol-based film was obtained in the same manner as in Example 1 except that the preparation temperature was changed to 160 캜. The properties of the obtained polyvinyl alcohol-based film are shown in Table 2 below. Further, a polarizing film was obtained in the same manner as in Example 1. Properties of the obtained polarizing film are shown in Table 2 below.

&Lt; Comparative Example 2 &

In Example 1, 0.2 kg of polyoxyethylene dodecylamine (amount based on the amount of polyvinyl alcohol-based resin to be mixed with polyvinyl alcohol-based resin) was used instead of 0.3 kg of N, N-diethanol lauric acid amide 0.02% by weight) was used instead of the polyvinyl alcohol-based film. The properties of the obtained polyvinyl alcohol-based film are shown in Table 2 below. Further, a polarizing film was obtained in the same manner as in Example 1. Properties of the obtained polarizing film are shown in Table 2 below.

 The residual amount of polyoxyethylene dodecylamine in the obtained aqueous solution was measured and found to be 0.02% by weight based on the polyvinyl alcohol resin, and no decomposition was confirmed.

&Lt; Comparative Example 3 &

A polyvinyl alcohol film was obtained in the same manner as in Example 1 except that the preparation temperature was 100 ° C and the preparation time was 1 hour. The properties of the obtained polyvinyl alcohol-based film are shown in Table 2 below. In the same manner as in Example 1, a polarizing film was obtained. The characteristics of the resulting polarizing film were as shown in Table 2 below.

Since the polyvinyl alcohol films of Examples 1 to 8 had a contact angle with respect to n-hexadecane within the specific range of the present invention, the polarizing films using these polyvinyl alcohol films had no staining unevenness, . On the other hand, since the polyvinyl alcohol films of Comparative Examples 1 to 3 are outside the specific range of the present invention, it is understood that the polarizing films using these polyvinyl alcohol films are uneven in dyeing and poor in polarization performance.

The polarization degree is 99.84% or more in Examples 1 to 8 and 99.75 to 99.76 in Comparative Examples 1 to 3. This difference is not significant in the numerical value, but the difference is that when the polarizing film is used in a liquid crystal display, The first to eighth embodiments have a great advantage.

Although the embodiment has been described in the concrete form of the present invention, the embodiment is merely an example and is not to be construed as limiting. Various modifications apparent to those skilled in the art are expected to be within the scope of the present invention.

The polarizing film or the polarizing plate using the polyvinyl alcohol film of the present invention is excellent in the polarizing performance and can be used as an electronic tablet calculator, an electronic clock, a word processor, a PC, a portable information terminal, a television, a projector, a cinematograph, , Antireflection films for display devices (CRT, LCD, organic EL, electronic paper, etc.), liquid crystal display devices such as cameras, photo albums, thermometers, audio, instrumentation of automobiles and machinery, sunglasses, anti- Optical communication equipment, medical equipment, building materials, toys, optical communication equipment, medical equipment, building materials, toys, and the like.

Claims (11)

hexadecane and the contact angle? _1S with respect to the n-hexadecane after 1 second from the contact of the liquid droplets of n-hexadecane is 5 to 13 占 The polyvinyl alcohol- The method according to claim 1,
And the contact angle θ of the first side _1S of the film on both sides, the contact angle θ of the second surface of the _{1S, 1S} with the difference δθ = | θ -θ _{1S 1S '|} is based polyvinyl alcohol, characterized in that less than 2 ° film. The method according to claim 1 or 2,
The difference between the contact angle θ _1S and the contact angle θ _0S with respect to the n-hexadecane after 0.1 second from the contact of the droplet of the n-hexadecane is Δθ = | θ _0S- θ _1S | Lt; RTI ID = 0.0 &gt; 7 C. &lt; / RTI &gt; A process for producing a polyvinyl alcohol film as set forth in any one of claims 1 to 3, comprising the steps of preparing an aqueous solution of a polyvinyl alcohol-based resin, a step of forming a film by continuously casting the prepared aqueous solution into a cast mold And a drying step of peeling the formed film from the cast mold and then drying the film. The method of claim 4,
In the preparation step, the aqueous solution of the polyvinyl alcohol-based resin is prepared by adding an aqueous solution containing 0.01 to 0.1 wt% of a higher fatty acid amide compound having 10 to 30 carbon atoms to the polyvinyl alcohol-based resin at 100 to 150 캜 Wherein the polyvinyl alcohol-based film is obtained by preparing a polyvinyl alcohol-based film. The method of claim 5,
Wherein in the preparation step, 10 to 90% by weight of the higher fatty acid amide compound is dissolved in the polyvinyl alcohol-based film. The method according to any one of claims 4 to 6,
Wherein the time required for preparation of the aqueous solution of the polyvinyl alcohol-based resin in the preparation step is 5 to 40 hours. A polyvinyl alcohol film produced by the process for producing a polyvinyl alcohol film according to any one of claims 4 to 7. The method according to any one of claims 1 to 3, 8,
A polyvinyl alcohol film characterized by being used for producing a polarizing film. The method according to any one of claims 1 to 3, 8, and 9,
And the thickness of the polyvinyl alcohol film is 5 to 45 mu m. A polarizing film characterized by using the polyvinyl alcohol film according to any one of claims 1 to 3 and 8 to 10.