JP6953804B2 - Polyvinyl alcohol-based film, its manufacturing method, and polarizing film - Google Patents

Description

The present invention relates to a polyvinyl alcohol-based film. More specifically, the present invention is a polyvinyl alcohol-based film which is thin and has excellent stretchability, and is a polyvinyl alcohol-based film capable of obtaining a flexible polarizing film having no color unevenness. , And a method for producing the same, and a polarizing film obtained by using the polyvinyl alcohol-based film.

In recent years, the development of organic EL displays has been remarkable, and they have begun to be widely used in smartphones, tablets, televisions, in-vehicle panels, and the like. Furthermore, it is expected as a next-generation display that can be made lighter and thinner, curved surface display, and more flexible, which is difficult to achieve with liquid crystal displays. Such an organic EL display is equipped with a polarizing film to prevent reflection of external light and / or internal light, and the polarizing film is also required to be thin and flexible, and to be foldable and foldable. ing.

In general, a polarizing film is formed by swelling a polyvinyl alcohol-based film, which is a raw material, with water (including warm water), dyeing it with iodine, stretching it to align iodine molecules, and boric acid cross-linking to align the iodine molecules. Is used. Boric acid cross-linking tends to increase the rigidity of the polarizing film and decrease the flexibility. Further, when a protective film such as triacetyl cellulose is attached to one side or both sides, the rigidity is increased and it tends to be difficult to bend or fold. No matter how flexible the organic EL device is, if the antireflection film is not flexible, only a flat display can be obtained. In order to improve such flexibility, it is strongly desired to reduce the thickness of the polarizing film. The polarizing film is also called a polarizing film or a polarizer.

In order to reduce the thickness of the polarizing film, it is essential to reduce the thickness of the polyvinyl alcohol-based film, which is the raw material, and high stretchability is required. Conventionally, polyvinyl alcohol-based films have a thickness of about 60 μm, but it is expected that 45 μm or less will become the mainstream in the future. Usually, the stretching ratio at the time of producing a polarizing film is about 4 to 7 times, and a flexible polarizing film having a thickness of 20 μm or less is produced by stretching at a high magnification using a polyvinyl alcohol-based film having a thickness of 45 μm or less. It becomes possible.

On the other hand, the polyvinyl alcohol-based film, which is the raw material, is generally produced from an aqueous solution of the raw material polyvinyl alcohol-based resin by a continuous casting method. Specifically, an aqueous solution of a polyvinyl alcohol-based resin is spilled into a cast mold such as a cast drum or an endless belt, the obtained film is peeled from the cast mold, and then the metal is conveyed in the length direction (MD direction). It is produced by drying with a heating roll and, if necessary, heat-treating with a floating dryer or the like. In such a transporting step, since the film is pulled in the MD direction, the polyvinyl alcohol-based polymer is likely to be oriented in the MD direction, and if the orientation is too large, the stretchability of the polyvinyl alcohol-based film in the MD direction is lowered. Finally, the polarization performance of the polarizing film will deteriorate.

As a method for thinning the polarizing film, for example, a method for producing a polarizing film in which a polyvinyl alcohol layer formed on a thermoplastic resin film is stretched has been proposed (see, for example, Patent Document 1). As a method for improving the stretchability of a polyvinyl alcohol-based film, a polyvinyl alcohol-based film in which Young's modulus (tensile elastic modulus) is reduced to 20 MPa or less by electromagnetic wave irradiation has been proposed (see, for example, Patent Document 2). Further, a method for producing an aqueous solution of a polyvinyl alcohol-based resin having no undissolved substance has also been proposed (see, for example, Patent Document 3).

Japanese Unexamined Patent Publication No. 2014-32361 Japanese Unexamined Patent Publication No. 2013-97232 JP-A-2002-60495

However, even with the method of the above patent document, it has been difficult to reduce the thickness of the polarizing film.
In Patent Document 1, a polyvinyl alcohol layer having a thickness of about 6 μm is stretched about 6 times to produce a polarizing film having a thickness of about 3 μm. During the stretching step, the polyvinyl alcohol layer and / or a thermoplastic resin film is produced. There was a problem that it broke.

Although the breaking elongation can be improved by the technique disclosed in Patent Document 2, the electron beam irradiator has a large equipment load, and only a polyvinyl alcohol-based film having a thickness of 50 μm or more is described in the examples in recent years. Further improvements have been requested in order to meet the demand for thinner polarizing films.

Although the undissolved material can be reduced by the technique disclosed in Patent Document 3, the polyvinyl alcohol-based resin tends to be decomposed due to the high temperature, and the saponification degree of the polyvinyl alcohol-based resin tends to change.

The required characteristics of the polarizing film for liquid crystal display and the polarizing film for organic EL are slightly different. A polarizing film for a liquid crystal display is required to have a high degree of polarization, and as described above, a polarizing film for an organic EL is required to have a degree of polarization required for antireflection, but to be more flexible. .. That is, a polarizing film for a liquid crystal display is required to have a degree of polarization of 99.9% or more, and in order to achieve such a degree of polarization, a polyvinyl alcohol-based resin having a high molecular weight and a high average saponification degree is required. A degree of polarization of 98% or more is sufficient for the polarizing film for use, and an appropriate molecular weight and an average degree of saponification for achieving flexibility are prioritized. However, the requirements for quality such as color unevenness are the same, the manufacturing process of the polarizing film is the same, and it is strictly prohibited to reduce the manufacturing yield. For example, it is necessary to avoid a situation in which a polyvinyl alcohol-based resin is eluted in a stretching tank or a boric acid cross-linking tank and contaminates the inside of the tank, and it is necessary to set an appropriate molecular weight and average saponification degree.

Therefore, the present invention provides a polyvinyl alcohol-based film that is a thin polyvinyl alcohol-based film but has excellent stretchability during manufacturing of a polarizing film, and can obtain a thin polarizing film with less color unevenness. The purpose is to do.

However, as a result of diligent research in view of such circumstances, the present inventors have found that a thin-film polyvinyl alcohol-based film obtained from a specific polyvinyl alcohol-based resin and which exhibits a specific elongation at break has been obtained. The present invention has been completed by finding a solution to the above problems.

That is, the gist of the present invention is that a polyvinyl alcohol having a weight average molecular weight of 120,000 to 160,000 and an average saponification degree of 99.0 to 99.9 mol% is produced from a polyvinyl alcohol-based resin and has a thickness of 45 μm or less. It is an alcohol-based film, which is a polyvinyl alcohol-based film characterized by having a breaking elongation of 6 times or more when a tensile test is performed in an environment of 23 ° C. and 50% RH according to JIS K7127: 1999.

The present invention also provides a method for producing the polyvinyl alcohol-based film and a polarizing film obtained by using the polyvinyl alcohol-based film.

The polyvinyl alcohol-based film of the present invention is thin but has excellent stretchability during production of a polarizing film, does not break even when a thin polarizing film is manufactured, and provides a polarizing film with high productivity and less color unevenness. be able to.

Hereinafter, the present invention will be described in detail.
The polyvinyl alcohol-based film of the present invention is produced from a polyvinyl alcohol-based resin having a weight average molecular weight of 120,000 to 160,000 and an average saponification degree of 99.0 to 99.9 mol% and having a thickness of 45 μm or less. It is a polyvinyl alcohol-based film and has a breaking elongation of 6 times or more when a tensile test is performed in an environment of 23 ° C. and 50% RH according to JIS K7127: 1999.

The weight average molecular weight of the polyvinyl alcohol-based resin needs to be 120,000 to 160,000, preferably 130,000 to 160,000 in terms of degree of polarization, and particularly preferably 135,000 to 160,000. More preferably, it is 135,000 to 150,000, and particularly preferably 135,000 to 145,000 in terms of stretchability. 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 saponification degree of the polyvinyl alcohol-based resin needs to be 99.0 to 99.9 mol%, and in terms of the degree of polarization, it is particularly preferably 99.0 to 99.7 mol%, and more preferably stretched. In terms of sex, it is 99.1 to 99.5%. The average saponification degree is measured according to JIS K 6726.

Generally, it is said that the polyvinyl alcohol-based resin used for the polarizing film for liquid crystals is preferably one having a high molecular weight and a high average saponification degree in terms of improving the degree of polarization. Certainly, in order to secure a degree of polarization of 99% or more, a molecular weight of 120,000 or more is required, and an average saponification degree of 99.0 mol% or more is required. However, if the molecular weight exceeds 160,000 or the average saponification degree exceeds 99.9 mol%, the stretchability of the polyvinyl alcohol-based film is lowered, so that it tends to be unsuitable for a polarizing film for organic EL.

The thickness of the polyvinyl alcohol-based film of the present invention needs to be 45 μm or less, and is preferably 30 to 45 μm in terms of avoiding breakage during the production of the polarizing film.
The thickness is adjusted by the resin concentration in the polyvinyl alcohol-based resin aqueous solution, the discharge amount to the cast mold (discharge rate), the draw ratio, and the like.

According to JIS K7127: 1999 of the polyvinyl alcohol-based film of the present invention, the breaking elongation when a tensile test is performed in an environment of 23 ° C. and 50% RH needs to be 6 times or more, and the polarizing film must be thin. In terms of conversion, it is preferably 6.1 times or more, and particularly preferably 6.2 times or more. Generally, the upper limit of elongation at break is 7 times.

In the polyvinyl alcohol-based film of the present invention, the polyvinyl alcohol-based resin that elutes when the film is immersed in water at 60 ° C. for 5 minutes ^{is preferably 20,000 ppm / m 2} or less, particularly preferably 15,000 ppm. It is / m ² or less, more preferably 10,000 ppm / m ² or less.
If the amount of the polyvinyl alcohol-based resin eluted under such immersion conditions is too large, the eluted polyvinyl alcohol-based resin contaminates the chemical solution in the polarizing film manufacturing process, and the frequency of exchanging the chemical solution and the frequency of cleaning the inside of the tank tend to increase. be. In the present invention, considering that the step of producing the polarizing film is several tens of degrees Celsius for several minutes, the amount of elution with water at 60 ° C. for 5 minutes was used as an index.

Examples of the method for reducing the amount of elution include a method for adjusting the weight average molecular weight and the degree of saponification of the raw material polyvinyl alcohol-based resin, and a method for sufficiently drying and / or heat-treating the polyvinyl alcohol-based film.

Further, in the polyvinyl alcohol-based film of the present invention, the polyvinyl alcohol-based resin that elutes when the film is immersed in water at 30 ° C. for 2 minutes ^{is preferably 50 ppm / m 2} or less, particularly preferably 40 ppm / m. ^{It is 2} or less, more preferably 30 ppm / m ² or less. If the amount of the polyvinyl alcohol-based resin eluted under such immersion conditions is too large, the eluted polyvinyl alcohol-based resin tends to contaminate the swelling tank in the swelling step of producing the polarizing film, and the quality of the polarizing film tends to deteriorate. In the present invention, considering that the swelling step is at around 30 ° C. for several minutes, the amount of elution with water at 30 ° C. for 2 minutes is used as an index.

The above-mentioned dissolution test ^{may be carried out using a film having an area of 1 m 2} as a test piece, but a film having a smaller size is dipped, and the area of the actually dipped film is ^{converted into 1 m 2} to obtain m. ^It may be the elution amount per 2. When using a film of such a small size, especially for dissolution test at low temperature, that is a plurality dipping, the total area of the actual soaked film was area terms of 1 m ^2, the elution amount per m ² preferable. For example, 5 sheets of film of 10cm square (total area 0.05 m ²⁾ when immersed, can be obtained elution concentration elution amount (ppm) 20 times to (ppm / m ^2).

Hereinafter, a method for producing a polyvinyl alcohol-based film of the present invention will be described.
Generally, a polyvinyl alcohol-based film is obtained by forming an aqueous solution of a polyvinyl alcohol-based resin by a continuous casting method and drying the obtained film. However, in the present invention, an aqueous solution of a polyvinyl alcohol-based resin is added. It is preferably prepared by pressure melting.

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. 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.

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.

The polyvinyl alcohol-based resin is dissolved in warm water or hot water to prepare an aqueous solution of the polyvinyl alcohol-based resin. In addition to the polyvinyl alcohol-based resin, the aqueous solution of the polyvinyl alcohol-based resin includes glycerin, diglycerin, and triglycerin. , Ethylene glycol, triethylene glycol, polyethylene glycol, trimethylolpropane, and other commonly used plasticizers, as well as polyvinyl alcohol-based, nonionic, anionic, and / or cationic surfactants. It is preferable in terms of film forming property.

In the present invention, the amount of the plasticizer or surfactant in the polyvinyl alcohol-based film is preferably 30% by weight or less, particularly preferably 20% by weight or less, still more preferably 15% by weight, from the viewpoint of reducing the elution amount. It is as follows.

To prepare the polyvinyl alcohol-based resin aqueous solution, first, the polyvinyl alcohol-based resin is 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. Is preferable. 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.

In the present invention, the wet cake, and if necessary, a plasticizer or a surfactant are put into a melting can equipped with a vertical circulation flow generating stirring blade, and steam is blown into the melting can to melt while pressurizing. And it is preferable to prepare an aqueous solution having a desired concentration.
The pressure at the time of such pressure dissolution is not particularly limited, but is preferably about 0.1 to 1 MPa.

The temperature at the time of pressure dissolution is preferably 100 to 150 ° C, particularly preferably 105 to 140 ° C, and even more preferably 110 to 130 ° C. If the dissolution temperature at the time of such pressure dissolution is too low, undissolved matter tends to remain, and if it is too high, the saponification degree is excessively increased and the stretchability is lowered, and decomposition products are generated to generate water. The amount of polyvinyl alcohol-based resin eluted into the resin tends to increase.

The dissolution time at the time of pressure dissolution is preferably 1 to 60 minutes, particularly preferably 2 to 40 minutes, and even more preferably 3 to 30 minutes. If the dissolution time is too short, undissolved substances tend to remain, and if it is too long, the degree of saponification increases excessively and the stretchability decreases, and decomposition products are generated to increase the amount of elution into water. Tend to do. After dissolution, a part of the liquid in the dissolution can is withdrawn, the concentration is measured using a process refractive index meter, and water is added or evaporated to obtain a desired concentration to adjust the concentration.

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 production capacity of the polyvinyl alcohol-based film tends to decrease, and if it is too high, the viscosity tends to be high and it tends to be difficult to transfer the liquid.

The polyvinyl alcohol-based film of the present invention is continuously formed by discharging and casting the above-mentioned aqueous solution of the polyvinyl alcohol-based resin into a rotating cast mold, forming a film by a casting method, and drying and heat-treating the obtained film. It can be manufactured in, for example, by the following steps.
(A) A step of forming a film by a continuous casting method.
(B) A step of heating, drying, and heat-treating the obtained film, if necessary.

Here, examples of the cast type include a cast drum (drum type roll), an endless belt, a resin film type, etc., but the cast drum is used because of its excellent width, length, and film thickness uniformity. Is preferable.
Hereinafter, the case where the cast type is a cast drum will be described.

The 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 such an aqueous solution is too low, it tends to cause poor flow, and if it is too high, it tends to be difficult to spill.

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 2 m / min, particularly preferably 0.2 to 1.5 m / min, and even more preferably 0.2 to 1.5 m / min. It is 0.3 to 1 m / min. If the discharge rate is too slow, the productivity tends to decrease, and if it is too fast, the salivation tends to be difficult.

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 difficult to obtain, and if it is too large, the transportability tends to decrease.

The width of such a cast drum is preferably 4 m or more, particularly preferably 4.5 m or more, still more preferably 5 m or more, and particularly preferably 5 to 7 m. If the width of the cast drum is too small, productivity tends to decrease.

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 obtained by forming the film is peeled from the cast drum tends to decrease.

The surface temperature of such a cast drum is preferably 50 to 99 ° C, more preferably 60 to 90 ° C, and particularly preferably 65 to 85 ° C. If the surface temperature is too low, the peelability when the film obtained by forming the film is peeled from the cast drum tends to decrease, and if it is too high, foaming tends to occur.

Thus, the film is formed and the obtained film is peeled off from the cast drum.

Next, the step (B) will be described. The step (B) is a step of heating the obtained film, drying it, and heat-treating it if necessary.

The film peeled off from the cast drum is conveyed in the length direction (MD direction) and dried by alternately bringing the front surface and the back surface of the film into contact with a plurality of metal heating rolls. The metal heating roll is, for example, a roll having a diameter of 0.2 to 2 m whose surface is hard chrome-plated or mirror-treated, and it is preferable to dry using usually 2 to 30 rolls, preferably 10 to 25 rolls. ..

The drying temperature is preferably 50 to 150 ° C, particularly preferably 60 to 140 ° C, still more preferably 70 to 130 ° C, and particularly preferably 80 to 120 ° C. If the drying temperature is too low, it tends to cause poor drying, and if it is too high, it tends to cause poor appearance such as swell.

The drying time is preferably 10 to 100 seconds, particularly preferably 20 to 90 seconds, still more preferably 30 to 80 seconds, and particularly preferably 40 to 70 seconds. If the drying time is too short, it tends to cause poor drying, and if it is too long, it tends to cause poor appearance such as swelling.

After drying with a metal heating roll, the film may be heat treated. Examples of the heat treatment method include a method of performing with a floating dryer, a method of cooling to about room temperature after drying and then contacting the heat roll with a high temperature again, and a method of irradiating both sides of the film with near infrared rays using an infrared lamp. However, among these, the method of using a floating dryer is preferable in that heat treatment can be performed uniformly.

When the heat treatment is performed, the temperature is preferably 70 to 150 ° C, particularly preferably 80 to 140 ° C, and even more preferably 90 to 130 ° C. If the heat treatment temperature is too low, the water resistance of the film tends to be insufficient, and if it is too high, the stretchability during the production of the polarizing film tends to decrease.

The heat treatment time is not particularly limited, but when a floating dryer is used, it is preferably 10 to 120 seconds, particularly preferably 20 to 90 seconds, and even more preferably 30 to 60 seconds. If the heat treatment time is too short, the water resistance of the film tends to be insufficient, and conversely, if the heat treatment time is too long, the productivity tends to decrease.

The film that has been dried and heat-treated as necessary is slit at both ends of the film and wound up on a roll to form a product (polyvinyl alcohol-based film).

The width of the polyvinyl alcohol-based film thus obtained is preferably 4 m or more in terms of increasing the area of the polarizing film, and particularly preferably 4 to 6 m in terms of avoiding fracture.

The length of the polyvinyl alcohol-based film is preferably 4 km or more in terms of increasing the area of the polarizing film, and particularly preferably 4 to 50 km in terms of transport weight.

Thus, the polyvinyl alcohol-based film of the present invention can be obtained.
Since the polyvinyl alcohol-based film of the present invention has excellent stretchability, it is preferably used as a raw material for a thin polarizing film, and particularly preferably used as a raw material for an antireflection film of a flexible organic EL display.

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

The polarizing film of the present invention is produced by unwinding the polyvinyl alcohol-based film from a roll, transferring it 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 the 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. The dyeing time is practically about 30 to 500 seconds. The temperature of the treatment bath is preferably 5 to 50 ° C. The aqueous solution may contain a small amount of an organic solvent compatible with water in addition to the 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 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 4 to 10 times, preferably 5 to 8 times in the uniaxial direction. At this time, a slight stretching (stretching to the extent of preventing shrinkage in the width direction or more) may be performed in the direction perpendicular to the stretching direction. The temperature at the time of stretching is preferably 40 to 170 ° C. Further, the stretching ratio may be finally set in the above range, and the stretching operation may be performed not only in one step but also in any range of the 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 precipitates generated on the surface of the film can be removed. When an aqueous potassium iodide solution is used, the potassium iodide concentration may be about 1 to 80 g / L. The temperature during the cleaning treatment is usually 5 to 50 ° C, preferably 10 to 45 ° C. The processing time is usually 1 to 300 seconds, preferably 10 to 240 seconds. In addition, washing with water and washing with an aqueous solution of potassium iodide may be performed in an appropriate combination.

The drying step may be carried out in the air at 40 to 80 ° C. for 1 to 10 minutes.

The degree of polarization of the polarizing film is preferably 98% or more, more preferably 99% or more. If the degree of polarization is too low, the antireflection effect in the organic EL display tends to decrease.
_{The degree of polarization is generally the light transmittance (H 11} ) measured at wavelength λ and the two polarizations 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.
[(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, particularly preferably 43% or more. If the single transmittance is too low, it tends to be impossible to achieve high brightness of the organic EL display.
The simple substance transmittance is a value obtained by measuring the light transmittance of a single polarizing film using a spectrophotometer.

Thus, the polarizing film of the present invention can be obtained, and the polarizing film of the present invention is suitable for producing a polarizing plate having a thin shape and no color unevenness.
Hereinafter, the method for producing the polarizing plate of the present invention will be described.

The polarizing film of the present invention is formed by laminating an optically isotropic resin film as a protective film on one side or both sides thereof via an adhesive to form a polarizing plate. Examples of the protective film include films such as cellulose triacetate, cellulose diacetate, polycarbonate, polymethylmethacrylate, cycloolefin polymer, cycloolefin copolymer, polystyrene, polyether sulfone, polyarylene ester, poly-4-methylpentene, and polyphenylene oxide. 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 heat or activate. It is done by irradiating with energy rays.

Further, for the purpose of thinning the polarizing film, a curable resin such as a urethane resin, an acrylic resin, or a urea resin is applied to one or both sides of the protective film instead of the protective film, and the polarizing film is cured to form a polarizing plate. You can also do it.

Since the polarizing film or polarizing plate made of the polyvinyl alcohol-based film of the present invention is thin and has no color unevenness, it is a portable information terminal, a personal computer, a television, a projector, a signage, an electronic desk computer, an electronic clock, a word processor, an electronic paper, a game. 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 antireflection layers for (paper, etc.), optical communication equipment, medical equipment, building materials, toys, and the like.

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 of the present invention is not exceeded.
In the example, "part" and "%" mean the weight standard.

<Measurement conditions>
(1) Weight average molecular weight of polyvinyl alcohol-based resin Measured by the GPC-MALS method under the following conditions.
Equipment: Gel permeation chromatograph Multi-angle light scattering photometer Configuration pump: Waters 515
Detector: Differential refractometer Waters RI-2410 type (sensitivity: 128 x)
Multi-angle light scattering detector Wyatt Technology DAWN EOS
Column: Tosoh Corporation TSK-gel-GMPW _XL 2 bottles, G2500PW _XL 1 bottle Solvent: 0.1M Sodium nitrate aqueous solution Flow velocity: 0.7 mL / min Temperature: 23 ° C
Sample preparation: 5 mL of the solvent was added to 5 mg of the sample, and the mixture was stirred at about 90 ° C. for 2 hours (sample concentration: about 0.1%). After visually confirming that it was dissolved, filtration was performed using a 0.45 μm filter.
Injection volume: 0.2 ml
Refractive index concentration change (dn / dc): 0.1593 ml / g

(2) Average saponification degree (mol%) of polyvinyl alcohol-based resin
Measured according to JIS K 6726.

(3) Elongation at break (double)
The obtained polyvinyl alcohol-based film was humidity-controlled for 24 hours in a constant temperature and humidity chamber at 23 ° C. and 50% RH, and then a 120 mm × 15 mm test piece was cut out. Using "AG-IS)", according to JIS K7127: 1999 (tensile speed 1000 mm / min, chuck distance 50 mm), MD (length direction) breaking elongation (in the length direction) in an environment of 23 ° C. and 50% RH. Double) was measured.

(4) Elution amount of polyvinyl alcohol-based resin (ppm / m ² )
The obtained polyvinyl alcohol-based film is humidity-controlled for 24 hours in a constant temperature and humidity chamber at 23 ° C. and 50% RH, and then one 100 mm × 100 mm (0.01 m ² ) test piece is cut out and 1 L of ion-exchanged water is used. Was immersed in 60 ° C. for 5 minutes to obtain an eluate. After mixing 10 mL of the color-developing 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, a spectrophotometer (UV-3100PC manufactured by Shimadzu Corporation). ) Was used to measure the absorbance at a wavelength of 690 nm, the concentration (ppm) of the polyvinyl alcohol-based resin was calculated from the calibration curve prepared in advance, and the elution amount (ppm / m ² ) was obtained by converting the area.
The elution amount (ppm / ppm) when 150 pieces of 100 mm × 100 mm (0.01 m ² ) test pieces were cut out and immersed for 2 minutes at 30 ° C. in the same manner as above except that ^{all the test pieces (1.5 m 2 in total) were immersed.} m ² ) was calculated.

(5) Polarization degree (%), simple substance transmittance (%)
A test piece having a length of 4 cm and a width of 4 cm was cut out from the central portion and both ends of the obtained polarizing film in the width direction (10 cm inside from the film edge), and an automatic polarizing film measuring device (manufactured by JASCO Corporation: Using VAP7070), the degree of polarization (%) and the single transmittance (%) were measured.

(6) 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 ends (10 cm inside from the film edge) of the obtained polarizing film in the width direction, and two polarized light in a cross-nicoled state. After sandwiching it between plates (single transmittance 43.5%, polarization degree 99.9%) at an angle of 45 °, using a light box with a surface illuminance of 14,000 lux, optical color unevenness in transmission mode Was observed and evaluated according to the following criteria.
(Evaluation criteria)
○ ・ ・ ・ No color unevenness was observed × ・ ・ ・ Color unevenness was observed

<Example 1>
(Preparation of polyvinyl alcohol film)
Put 1,000 kg of polyvinyl alcohol-based resin having a weight average molecular weight of 142,000 and an average saponification degree of 99.1 mol%, 2,500 kg of water, and 100 kg of glycerin as a plasticizer in a dissolution can, and heat and pressurize while stirring. , 120 ° C. for 1 hour. After such pressure dissolution, the concentration was adjusted to a resin concentration of 25% to obtain a uniformly dissolved polyvinyl alcohol-based resin aqueous solution.
Next, the polyvinyl alcohol-based resin aqueous solution is supplied to a twin-screw extruder having a vent to defoam, and then discharged from a T-shaped slit die discharge port to a rotating cast drum (discharge speed 1.9 m / min). The film was cast and formed. The film is peeled off from the cast drum, dried (80 to 120 ° C.) while alternately contacting the front surface and the back surface of the film with 20 metal heating rolls, and then heat-treated at 120 ° C. for 30 seconds using a floating dryer. Was done. Finally, both ends were slit and wound on a roll to obtain a polyvinyl alcohol-based film having a thickness of 45 μm, a width of 5 m, and a length of 5 km. The characteristics of the obtained polyvinyl alcohol-based film are shown in Table 1.

(Manufacturing of polarizing film)
The obtained polyvinyl alcohol-based film was unwound from the roll, transported in the horizontal direction using a transport roll, and first, the film was immersed in a water tank having a water temperature of 30 ° C. to swell and stretched 2.0 times in 2 minutes. Next, it was immersed in an aqueous solution of iodine (0.9 g / L) and potassium iodide (30 g / L) at 28 ° C. and stretched 1.6 times in 0.5 minutes while dyeing, followed by boric acid (25 g / L). It was immersed in an aqueous solution of potassium iodide at 60 ° C. and uniaxially stretched 2.2 times while boric acid cross-linking. Finally, the mixture was washed with an aqueous potassium iodide solution and dried at 50 ° C. for 2 minutes to obtain a polarizing film (thickness 14 μm) having a total draw ratio of 7.0 times. No breakage occurred during the production of such a polarizing film. The characteristics of the obtained polarizing film are shown in Table 2.

<Example 2, Comparative Examples 1 and 2>
A polyvinyl alcohol-based film and a polarizing film were obtained in the same manner as in Example 1 except for the production under the conditions shown in Table 1. The characteristics of the obtained polyvinyl alcohol-based film are shown in Table 1, and the characteristics of the obtained polarizing film are shown in Table 2.
In Comparative Example 1, an attempt was made to produce a polarizing film in the same manner as in Example 1, but fracture occurred during stretching in the boric acid cross-linking step. Further, in Comparative Example 2, when the chemical solution in the boric acid cross-linking tank was visually confirmed after the polarizing film was produced, precipitates due to elution of the polyvinyl alcohol-based resin were observed.

Since the polyvinyl alcohol-based films of Examples 1 and 2 were within the specific range of the present invention, a polarizing film having excellent polarization performance was obtained, whereas the polyvinyl alcohol-based films of Comparative Examples 1 and 2 were Since it is outside the specific range of the present invention, it can be seen that a polarizing film having excellent polarization performance could not be obtained.

Since the polarizing film or polarizing plate made of the polyvinyl alcohol-based film of the present invention is thin and has no color unevenness, it is a portable information terminal, a personal computer, a television, a projector, a signage, an electronic desk computer, an electronic clock, a word processor, an electronic paper, a game. 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 antireflection layers for (paper, etc.), optical communication equipment, medical equipment, building materials, toys, and the like.

Claims (7)

A polyvinyl alcohol-based film having a weight average molecular weight of 120,000 to 160,000 and an average saponification degree of 99.0 to 99.9 mol%, which is a polyvinyl alcohol-based film having a thickness of 45 μm or less and having a thickness of 45 μm or less. K7127: A polyvinyl alcohol-based film having a breaking elongation of 6 times or more when subjected to a tensile test in an environment of 23 ° C. and 50% RH according to 1999. The polyvinyl alcohol-based film according to claim 1, wherein the amount of the polyvinyl alcohol-based resin eluted when the polyvinyl alcohol-based film is immersed in water at 60 ° C. for 5 minutes is 20,000 ppm / m ^{2 or less.} The polyvinyl alcohol-based film according to claim 1 or 2, wherein the amount of the polyvinyl alcohol-based resin eluted when the polyvinyl alcohol-based film is 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 3, wherein the film has a width of 4 m or more and a length of 4 km or more. An aqueous solution of a polyvinyl alcohol-based resin having a weight average molecular weight of 120,000 to 160,000 and an average saponification degree of 99.0 to 99.9 mol% is discharged and spilled into a cast mold to form a film, and dried. The polyvinyl alcohol-based film according to any one of claims 1 to 4, which is a method for producing a polyvinyl alcohol-based film, which is obtained by preparing an aqueous solution of a polyvinyl alcohol-based resin at 110 to 130 ° C. A method for producing an alcohol-based film. A polarizing film obtained by using the polyvinyl alcohol-based film according to any one of claims 1 to 4. The polarizing film according to claim 6, wherein the polarizing film is an antireflection film for organic EL.