TWI789390B - Polyvinyl alcohol-based film, polarizing film, polarizing plate, and method for producing polyvinyl alcohol-based film - Google Patents

Abstract

The present invention provides a polyvinyl alcohol-based film, which can achieve a good balance between swelling and extensibility during the production of polarizing films, does not cause cracks during the production of thin polarizing films, exhibits high polarizing performance, and has uneven chromaticity The present invention provides a polarizing film and a polarizing plate using the polyvinyl alcohol-based film, and the above-mentioned polyvinyl alcohol-based film. The polyvinyl alcohol-based film of the present invention is a strip-shaped polyvinyl alcohol-based film with a thickness of 40 μm or less, and is characterized in that: when immersed in water at 30°C for 5 minutes, the degree of swelling (S _A ), swelling in the width direction Swelling degree (S _X ), swelling degree in the longitudinal direction (S Y ); the swelling degree (S _B ) when it is stretched in water at 30°C at a speed of 0.12m/min to 3 times the extension ratio (S _B ) conforms to the following formula (1)~(3). 190%≦S _A ≦230%･･･(1) 220%≦S _B ≦310%･･･(2) 1.01≦S _Y /S _X ≦1.20･･･(3)

Description

Polyvinyl alcohol-based film, polarizing film, polarizing plate, and method for producing polyvinyl alcohol-based film

The present invention relates to a polyvinyl alcohol-based film as a material for forming a polarizing film having excellent dyeability, high degree of polarization, and less unevenness in chromaticity, and to a polarizing film and a polarizing film using the polyvinyl alcohol-based film. Plate, and the manufacturing method of this polyvinyl alcohol-based film.

Conventionally, polyvinyl alcohol-based films have been used in many applications as films excellent in transparency, and one of such useful applications is a polarizing film. The polarizing film is used as a basic component of liquid crystal displays, and in recent years, its use has expanded to equipment requiring high quality and high reliability.

Under such circumstances, along with the increase in luminance, high definition, large area, and thinning of the screens of liquid crystal televisions and multifunctional portable terminals, polarizing films with excellent optical characteristics are required. Its specific requirement is to further improve the degree of polarization or eliminate the unevenness of chromaticity.

In general, a polyvinyl alcohol-based film is produced by a continuous casting method using an aqueous solution of a polyvinyl alcohol-based resin as a material. Specifically, first, a film is formed by casting an aqueous solution of a polyvinyl alcohol-based resin into a casting mold such as a casting drum or an endless belt. Manufactured while being transported in the flow direction (MD) and dried using a hot roll or a floating dryer. In the above conveying step, since the film obtained by the above-mentioned film formation is stretched along the flow direction (MD), the polyvinyl alcohol-based polymer is easily aligned along the flow direction (MD).

On the other hand, in general, the raw material of the polarizing film, that is, a polyvinyl alcohol-based film, is first swollen with water (including warm water), then dyed with a dichroic dye such as iodine, and then dyed with a dichroic dye such as iodine. A polarizing film is produced by stretching. Also, it is important to rapidly swell the polyvinyl alcohol-based film in the thickness direction in the above-mentioned swelling step, and to swell the polyvinyl-alcohol-based film uniformly in the above-mentioned dyeing step so that the dye can smoothly penetrate into the film. internal. In addition, the above-mentioned stretching step is a step of stretching the dyed film along the flow direction (MD) to align the dichroic dyes in the polyvinyl alcohol-based film to a high degree. In order to improve the polarizing performance of the polarizing film, It is important that in this stretching step, the polyvinyl alcohol-based film made into the raw material roll exhibits good stretchability in the flow direction (MD).

In addition, there are cases in which the sequence of the stretching step and the dyeing step is reversed to the above in the production of polarizing film. That is, a polyvinyl alcohol-based film that is a raw material roll is first swollen with water (including warm water), stretched, and then dyed with a dichroic dye such as iodine. Even in this case, in order to improve the polarizing performance of the polarizing film, it is important that the polyvinyl alcohol-based film of the raw material roll exhibit good swelling properties in the thickness direction and good elongation in the flow direction (MD).

In addition, in recent years, in order to reduce the thickness of the polarizing film, there are some people who want to reduce the thickness of the polyvinyl alcohol-based film of the raw material roll. However, this thin film has problems in productivity such as cracking due to stretching during production of the polarizing film.

As a method of improving the swelling property of a polyvinyl alcohol-based film, for example, a method of adding a polyhydric alcohol as a water swelling aid to a polyvinyl alcohol-based resin has been proposed (for example, refer to Patent Document 1). In addition, as a method of improving the stretchability of a polyvinyl alcohol-based film, for example, a method has been proposed in which the ratio of the speed of the casting drum at the time of film formation to the winding speed of the final polyvinyl alcohol-based film is set to a specific value. (For example, refer to Patent Document 2), a method of drying the film by suspending the film after forming a film by casting a drum (for example, refer to Patent Document 3), a method of controlling the degree of stretching in the drying step of the film obtained by film formation (For example, refer to Patent Document 4), a film having a thickness of 40 μm or less and a swelling degree before and after stretching in 30° C. water falls within a specific range (for example, refer to Patent Document 5). [Prior Art Document] [Patent Document]

[Patent Document 1] Japanese Patent Application Publication No. 2001-302867 [Patent Document 2] Japanese Patent Application Publication No. 2001-315141 [Patent Document 3] Japanese Patent Application Publication No. 2001-315142 [Patent Document 4] Japanese Patent Application Publication No. 2002-79531 Publication No. [Patent Document 5] International Publication No. 2014/050697

[Problem to be Solved by the Invention]

However, for the above-mentioned thin polyvinyl alcohol-based film, the improvement of the above-mentioned swelling property is unsatisfactory in terms of the method of the above-mentioned patent document 1, and the method of the above-mentioned patent documents 2 to 5 is not satisfactory for the production of the polarizing film. The improvement of extensibility is not satisfactory.

That is, the technology disclosed in the above-mentioned Patent Document 1, even if it can improve the swelling property of the polyvinyl alcohol-based film as a whole, does not take into account the alignment state of the polyvinyl alcohol-based polymer, and it is difficult to efficiently improve the orientation of the polarizing film during manufacture. Extensibility in flow direction (MD). On the contrary, the addition of the water swelling aid disturbs the alignment state of the polymer, and it tends to become difficult to stretch uniformly in the flow direction (MD).

In the technology disclosed in the above-mentioned Patent Document 2, although the degree of stretching (stretch state) in the flow direction (MD) is set to a specific level when producing a polyvinyl alcohol-based film, if the stretching in the width direction (TD) is not considered at the same time, , it is unsatisfactory in terms of improving the extensibility of the polarizing film during manufacture.

The technique disclosed in Patent Document 3 mentioned above can evenly dry the obtained film, but it cannot control the alignment of polymers, and it is unsatisfactory in terms of improving swelling or extensibility during polarizing film production. In addition, although the technology disclosed in the above-mentioned Patent Document 4 can make the thickness of the polyvinyl alcohol-based film uniform, it cannot control the alignment of the polymer. Unsatisfactory.

In the technology disclosed in the above-mentioned Patent Document 5, polyvinyl alcohol with high stretchability can be obtained by preventing wrinkles during stretching by making a polyvinyl alcohol-based film whose swelling degree is a specific value before and after stretching in water at 30°C. It is a thin film, but the wrinkles during swelling cannot be controlled, and it is not satisfactory in terms of manufacturing a polarizing film with excellent uniformity. In addition, the polyvinyl alcohol-based film is unsatisfactory in terms of productivity due to the need for a long-time heat-and-moisture treatment.

Therefore, under such background, the present invention provides a polyvinyl alcohol-based film, which can achieve a good balance between swelling and extensibility during the manufacture of polarizing films, and will not cause cracks when manufacturing thin polarizing films, showing high A polarizing film having a polarizing performance and less unevenness in chromaticity, a polarizing film and a polarizing plate using the polyvinyl alcohol-based film, and a method for producing the polyvinyl alcohol-based film are provided. [Means to solve the problem]

As a result of a series of studies conducted by the inventors of this case, it was found that in a long polyvinyl alcohol-based film with a thickness of 40 μm or less and a mass-based swelling degree of 190-230%, if the length direction ( Adjust the ratio of the swelling degree of the dimensional basis of MD) to the swelling degree of the dimensional basis of the width direction (TD) to a specific range, and adjust the swelling degree of the mass standard after stretching in water to a specific range to obtain a polarizing film The balance between swelling and extensibility during manufacture is excellent, and no cracks will occur during the manufacture of thin polarizing films. It is a polarizing film that exhibits high polarizing performance and less unevenness in chromaticity.

That is, the first gist of the present invention is a polyvinyl alcohol-based film with a thickness of 40 μm or less and in a long strip shape, characterized by meeting the following formulas (1)~(3): 190%≦ _SA ≦230% ･･･(1) 220%≦S _B ≦310%･･･(2) 1.01≦S _Y /S _X ≦1.20･･･(3) [In the formula (1), S _A means that the polyethylene Swelling degree based on mass when the alcohol-based film is immersed in water at ₃₀ °C for 5 minutes; Swelling degree based on mass when performing uniaxial stretching so that the stretching ratio becomes 3 times; In the formula (3), S _X represents the width direction (TD) when the polyvinyl alcohol-based film is immersed in water at 30°C for 5 minutes Swelling degree based on the dimension, S _Y represents the swelling degree based on the dimension in the longitudinal direction (MD) when this polyvinyl-alcohol-type film was immersed in the water of 30 degreeC for 5 minutes. ]

Moreover, the 2nd gist of this invention is a polarizing film characterized by using the said polyvinyl-alcohol-type film. In addition, a third gist of the present invention is a polarizing plate including the polarizing film and a protective film provided on at least one surface of the polarizing film.

Furthermore, a fourth gist of the present invention is a method for producing a polyvinyl alcohol-based film comprising: a film forming step of forming a film from an aqueous solution of a polyvinyl alcohol-based resin by continuous casting; a drying and stretching step of forming the film The film obtained from the film is conveyed along the flow direction, and the film is continuously dried and continuously stretched; it is characterized in that the produced polyvinyl alcohol film meets the following formula (1)~(3): 190%≦S _A ≦230%･･･(1) 220%≦S _B ≦310%･･･(2) 1.01≦S _Y /S _X ≦1.20･･･(3) [In the formula (1), S _A represents The swelling degree of the mass _basis when the polyvinyl alcohol-based film was immersed in water at 30°C for 5 minutes; Swelling degree on a mass basis when one-axis stretching is carried out at a fraction of the stretching speed so that the stretching ratio becomes 3 times; In the formula (3), S _X represents the width when the polyvinyl alcohol film is immersed in water at 30°C for 5 minutes The swelling degree based on the size of the direction (TD), S _Y represents the swelling degree based on the size of the longitudinal direction (MD) when the polyvinyl alcohol-based film is immersed in water at 30° C. for 5 minutes. ] [Effect of Invention]

The polyvinyl alcohol-based film of the present invention is a strip-shaped polyvinyl alcohol-based film with a thickness of 40 μm or less and a mass-based swelling degree ( _SA ) of 190-230%. The ratio of the swelling degree (S _Y ) to the swelling degree (S _X ) of the dimension standard in the width direction (TD) (S _Y /S _X ) is within a specific range, and the swelling degree of the mass standard after being stretched in water (S _B ) is within a specific range, so the swelling and extensibility of the polarizing film are excellent when it is manufactured. Even if it is made thin (thickness below 40 μm), it is used in the manufacture of a thin polarizing film without cracking. In addition, when this polyvinyl alcohol-based film is used, a polarizing film exhibiting high polarizing performance and having little chromaticity unevenness can be obtained.

In addition, since the polarizing film of the present invention uses the above-mentioned polyvinyl alcohol-based film, it exhibits high polarizing performance and has little chromaticity unevenness.

In addition, since the polarizing plate of the present invention uses the above-mentioned polarizing film, it exhibits high polarizing performance and has little chromaticity unevenness.

Furthermore, the method for producing a polyvinyl alcohol-based film of the present invention includes the following steps: a film forming step of forming a film by a continuous casting method; a drying and stretching step of transporting the film obtained by the film production along the flow direction, Continuous drying and continuous stretching are performed on the film; therefore, combining the manufacturing conditions in these steps, the above-mentioned polyvinyl alcohol-based film of the present invention conforming to the above-mentioned formulas (1)-(3) can be obtained.

Especially in the above-mentioned drying and stretching steps, when the film obtained by the above-mentioned film formation is stretched 1.05 to 1.3 times in the width direction (TD), S _A , S _B , S _Y /S in the above formulas (1) to (3) When each value of _X is appropriate, a polyvinyl alcohol-based film having better swelling properties and extensibility at the time of polarizing film production can be obtained.

In addition, in the above-mentioned drying and stretching step, after temporarily stretching the film obtained by the above-mentioned film formation in the width direction (TD) more than 1.3 times, shrink the size so that the final stretching ratio in the width direction becomes 1.3 times or less, which can alleviate the stress caused by the above-mentioned production. The stress applied to the thin film obtained by the film. Therefore, even if the thin film obtained by the above-mentioned film formation is thin, the crack of the film can be avoided.

Then, the present invention will be described in detail. The polyvinyl alcohol-based film of the present invention is a strip-shaped polyvinyl alcohol-based film with a thickness of 40 μm or less, and is characterized in that it meets the following formulas (1)~(3): 190%≦ _SA ≦230%･･ ･(1) 220%≦S _B ≦310%･･･(2) 1.01≦S _Y /S _X ≦1.20･･･(3) [In the formula (1), S _A means that the polyvinyl alcohol system The swelling degree of the mass _basis when the film is immersed in water at 30°C for 5 minutes; ) at a stretching speed of 1-axis stretching so that the stretching ratio becomes 3 times the mass-based swelling degree; in this formula (3), S _X represents the width when the polyvinyl alcohol-based film is immersed in water at 30°C for 5 minutes The swelling degree based on the size of the direction (TD), S _Y represents the swelling degree based on the size of the longitudinal direction (MD) when the polyvinyl alcohol-based film is immersed in water at 30° C. for 5 minutes. ]

The thickness of the polyvinyl alcohol-based film of the present invention needs to be very thin, less than 40 μm. From the viewpoint of thinning the polarizing film, it is preferably 5 to 40 μm, and from the viewpoint of avoiding cracks, it is especially preferably 10 to 40 μm, more preferably 10 ~30 μm. If the thickness of the above-mentioned polyvinyl alcohol-based film is too thick, the tension at the time of stretching in the production process of the polarizing film described later will become high, which is not preferable. Moreover, when it is too thin, there exists a tendency for it to crack easily at the time of manufacture of a polarizing film.

That is, the polyvinyl alcohol-based film of the present invention controls the above-mentioned specific degree of swelling when immersed in water at 30° C. within a specific range as described above. With this controlled swelling degree, when the above-mentioned polyvinyl alcohol-based film is made into a very thin thickness of 40 μm or less, it has excellent performance.

Furthermore, as mentioned above, the polyvinyl alcohol-based film of the present invention controls the swelling degree (S _A ) based on mass when immersed in water at 30°C for 5 minutes so that it is 190%≦ _SA ≦230%. The swelling degree (S _A ) of the quality standard is preferably 195%≦ _SA ≦225%, especially preferably 195%≦ _SA ≦220%. If the value of the above-mentioned swelling degree ( _SA ) is too small, the extensibility of the polarizing film described later is reduced, so the purpose of the present invention cannot be achieved. If the value of the above-mentioned swelling degree ( _SA ) is too large, the Wrinkles are generated in the swelling step during manufacture, and uneven chromaticity is likely to occur in the polarizing film, so the object of the present invention cannot be achieved.

The swelling degree (S _A ) above is an index showing the water retention capacity of the polyvinyl alcohol-based film when immersed in water. The mass is divided by the mass after immersion and dried at 105° C. for 16 hours, and is obtained in the form of a percentage. For example, it can be measured by the method in the examples described later.

In addition, as mentioned above, the polyvinyl alcohol-based film of the present invention is uniaxially stretched in water at 30°C at a stretching speed of 0.12m/min (240%/min) so that the stretching ratio becomes 3 times the swelling of the mass basis. degree (S _B ), making it 220%≦S _B ≦310%. The swelling degree (S _B ) of the quality standard is preferably 225%≦S _B ≦300%, especially preferably 230%≦S _B ≦280%, especially preferably 230%≦S _B ≦260%. If the value of the swelling degree (S _B ) is too small, the purpose of the present invention cannot be achieved because the extensibility of the polarizing film described later will be poor. If the value of the swelling degree (S _B ) is too large, the Swelling during film production and wrinkles in the dyeing process are likely to cause uneven chromaticity in the polarizing film, so the purpose of the present invention cannot be achieved.

The above swelling degree (S _B ) is an index indicating the water retention capacity of the polyvinyl alcohol-based film after stretching it in water at 30°C to 3 times the stretching ratio. The mass after stretching in water at 30°C at a stretching speed of 0.12m/min (240%/min) to 3 times the stretching ratio, divided by the mass after stretching and drying at 105°C for 16 hours, and calculated as a percentage , can be measured, for example, by the method in the examples described later. In general, when a polarizing film is produced from a polyvinyl alcohol-based film, after swelling and dyeing are performed at 30° C., the film is introduced into a high-temperature stretching tank. Since the polyvinyl alcohol-based film is stretched less than 3 times in the swelling and dyeing steps, the above-mentioned swelling degree (S _B ) when stretching in water to 3 times the stretching ratio is determined by the stretchability of the film in a high-temperature stretching tank. index.

In addition, as mentioned above, the polyvinyl alcohol-based film of the present invention controls the swelling degree (S X ) based on the size of the width direction (TD) when immersed in water at 30°C for 5 minutes, and the degree of swelling (S _X ) of the film after immersion in water at 30°C for 5 minutes. The degree of swelling (S _Y ) of the dimension basis in the longitudinal direction (MD) at the minute meets the relationship of 1.01≦S _Y /S _X ≦1.20. The ratio (S _Y /S _X ) is preferably 1.03≦S _Y /S _X ≦1.18, especially 1.05≦S _Y /S _X ≦1.15. If the value of the above-mentioned ratio (S _Y /S _X ) is too small, then because the extensibility of the polarizing film described later becomes worse, the purpose of the present invention cannot be achieved. If the value of the above-mentioned ratio (S _Y /S _X ) is too large, Then, because wrinkles are generated in the swelling step during the manufacture of the polarizing film, uneven chromaticity is likely to occur in the polarizing film, so the object of the present invention cannot be achieved.

The above-mentioned swelling degree (S _X and S _Y ) is an index indicating the extension of the polyvinyl alcohol-based film when immersed in water, which can be obtained by immersing the polyvinyl alcohol-based film directly (without stretching) in water at 30°C for 5 minutes Dimensions in the longitudinal direction (MD) and width direction (TD) are respectively divided by the dimensions before immersion in water, and obtained in the form of percentage, for example, can be measured by the method in the examples described later.

In the present invention, in the method of controlling the above-mentioned formulas (1) to (3), in the production method of the above-mentioned polyvinyl alcohol-based film by the continuous casting method described later, the film obtained by casting and molding A method in which the film is stretched in the width direction (TD) after peeling from the casting mold is preferable. At this time, the conditions in other steps are appropriately adjusted according to the stretching conditions in the width direction (TD) (stretching ratio, ambient temperature during stretching, stretching time, etc.). Such conditions include, for example, the chemical structure of the polyvinyl alcohol-based resin that is the forming material of the above-mentioned polyvinyl alcohol-based film, the type or amount of the plasticizer, the film-forming conditions of the above-mentioned film (the temperature of the casting mold, etc.) ), the drying conditions (temperature, time) for drying the film obtained above, the conveying speed of the film obtained above in the flow direction (MD), etc. The above-mentioned formulas (1)-(3) are controlled by combining at least one of these conditions with the above-mentioned elongation condition in the width direction (TD).

In addition, the measurement position of the degree of swelling ( _SA , S _B , S _X , S _Y ) in the above formulas (1) to (3) is within the area of 500mm×500mm of the polyvinyl alcohol-based film.

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

[Film Material] First, the polyvinyl alcohol-based resin used in the present invention and the polyvinyl alcohol-based resin aqueous solution will be described. In the present invention, as the polyvinyl alcohol-based resin constituting the polyvinyl alcohol-based film, an unmodified polyvinyl alcohol-based resin, that is, polyvinyl acetate obtained by polymerizing vinyl acetate, is generally used Manufactured resin. If necessary, a resin obtained by saponifying a copolymer of vinyl acetate and a small amount (usually less than 10 mol%, preferably less than 5 mol%) of a component that can be copolymerized with vinyl acetate can also be used. In terms of components that can be copolymerized with vinyl acetate, for example, unsaturated carboxylic acids (such as salts, esters, amides, nitriles, etc.), olefins with 2 to 30 carbons (such as ethylene, propylene, n- butene, isobutene, etc.), vinyl ethers, unsaturated sulfonates, etc. These can be used individually or in combination of 2 or more types. In addition, a modified polyvinyl alcohol-based resin obtained by chemically modifying a saponified hydroxyl group can also be used.

Moreover, the polyvinyl-alcohol-type resin which has a 1, 2-diol structure in a side chain can also be used for a polyvinyl-alcohol-type resin. The polyvinyl alcohol-based resin having a 1,2-diol structure in the side chain can be obtained by the following method, such as (i) combining vinyl acetate with 3,4-diacetyloxy-1-butene (ii) Saponification and decarboxylation of a copolymer of vinyl acetate and vinyl ethylene carbonate, (iii) Vinyl acetate and 2,2-dialkyl-4-ethylene (iv) A method of saponifying a copolymer of vinyl acetate and glycerin monoallyl ether.

The weight average molecular weight of the polyvinyl alcohol-based resin is preferably 100,000 to 300,000, especially 110,000 to 280,000, and further preferably 120,000 to 260,000. If the weight average molecular weight is too small, it tends to be difficult to obtain sufficient optical performance when the polyvinyl alcohol-based resin is made into an optical film, and if it is too large, it may become difficult to stretch the polyvinyl alcohol-based film when producing a polarizing film. tendency. In addition, the weight average molecular weight of the said polyvinyl alcohol-type resin is the weight average molecular weight measured by the GPC-MALS method.

The average degree of saponification of the polyvinyl alcohol-based resin used in the present invention is usually preferably at least 98 mol%, more preferably at least 99 mol%, further preferably at least 99.5 mol%, especially preferably at least 99.8 mol% . When the average degree of saponification is too small, sufficient optical performance tends not to be obtained when the polyvinyl alcohol-based film is used as a polarizing film. Here, in the present invention, the average degree of saponification is measured in accordance with JIS K 6726.

The polyvinyl alcohol-based resin used in the present invention may be used in combination of two or more modified substances, modified amounts, weight average molecular weights, and average saponification degrees.

In the polyvinyl alcohol-based resin aqueous solution, in addition to polyvinyl alcohol-based resins, it is better to include glycerin, diglycerin, triglycerin, ethylene glycol, triethylene glycol, polyethylene glycol, etc. Commonly used plasticizers such as glycols and trimethylolpropane, or at least one of nonionic, anionic, and cationic surfactants. These can be used individually or in combination of 2 or more types.

The resin concentration of the polyvinyl alcohol-based resin aqueous solution obtained in this way is preferably 15 to 60% by weight, particularly preferably 17 to 55% by weight, and more preferably 20 to 50% by weight. If the resin concentration of the above-mentioned aqueous solution is too low, the drying load tends to be large, so the productivity tends to decrease. If it is too high, the viscosity becomes too high, and uniform dissolution tends to be difficult.

Then, the obtained polyvinyl alcohol-based resin aqueous solution was subjected to defoaming treatment. As the defoaming method, methods such as defoaming by static defoaming or multi-screw extruder are mentioned. As for the multi-screw extruder, any multi-screw extruder having a vent hole may be used, and a twin-screw extruder having a vent hole is generally used.

[Film-making step] The polyvinyl alcohol-based film of the present invention is produced by casting or melt extrusion. In the present invention, the casting method is preferred in consideration of transparency, thickness accuracy, and surface smoothness. Considering productivity From the point of view, it is especially suitable for continuous casting.

The continuous casting method is, for example, a method in which the aqueous solution of the polyvinyl alcohol-based resin is continuously discharged from a T-shaped slot die and cast to a casting mold such as a rotating casting drum, an endless belt, or a resin film to form a film. Here, the film production method in the case where the casting mold is a casting drum will be described.

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

The viscosity of the above-mentioned polyvinyl alcohol-based resin aqueous solution is preferably 50-200 Pa･s when discharged (at the above-mentioned ideal temperature of 80-100°C), and (at the above-mentioned particularly ideal temperature of 85-98°C) is preferably 70~150Pa･s. If the viscosity of the aqueous polyvinyl alcohol-based resin solution is too low, flow tends to be poor, and if it is too high, casting tends to become difficult.

The discharge speed of the polyvinyl alcohol-based resin aqueous solution discharged from the T-shaped slot die to the casting drum is preferably 0.2-5 m/min, especially 0.4-4 m/min, and more preferably 0.6-3 m/min. If the discharge rate is too slow, productivity tends to decrease, and if it is too fast, casting tends to become difficult.

The diameter of the above-mentioned casting drum is preferably 2~5m, especially 2.4~4.5m, more preferably 2.8~4m. If the above-mentioned diameter is too small, the dry length tends to be insufficient, making it difficult to increase the speed, and if it is too large, the transportability tends to decrease.

The width of the casting drum is preferably at least 4m, especially at least 4.5m, more preferably at least 5m, particularly preferably at least 5-7m. If the width of the casting drum is too small, productivity tends to decrease.

The rotational speed of the above-mentioned casting drum is preferably 5-50 m/min, especially 6-40 m/min, more preferably 7-35 m/min. If the above-mentioned 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 casting drum is preferably 40-99°C, especially 60-95°C. If the above-mentioned surface temperature is too low, drying tends to be poor, and if it is too high, foaming tends to occur.

In this manner, the film forming step was performed. And the film obtained by this film formation is peeled off from the said casting drum, and is conveyed along the flow direction (MD). The moisture content of the film obtained by the above film production is preferably 0.5 to 15% by weight, particularly preferably 1 to 13% by weight, and more preferably 2 to 12% by weight. If the above moisture content is too low or too high, it tends to be difficult to exhibit the intended swelling property or extensibility.

[Drying and Stretching Steps] Regarding the adjustment of the above moisture content, if the moisture content of the film before stretching in the width direction (TD) is too high, it is preferable to dry the film before stretching in the width direction (TD). When the moisture content of the film before stretching in the width direction (TD) is too low, it is preferable to adjust the humidity before stretching in the width direction (TD). It is more desirable to adjust the conditions of the drying step so that the moisture content falls within the above-mentioned range.

The above-mentioned drying system is carried out continuously. This continuous drying can be carried out by using known methods such as heating rollers or infrared heaters. In the present invention, it is preferable to use a large number of heating rollers, especially the temperature of the heating rollers is 40-150°C, and more preferably 50°C. ~140°C. In addition, in order to adjust the moisture content, a humidity control zone can be provided before extending in the width direction (TD).

In the present invention, the film obtained by forming the film does not need to be stretched in the flow direction (MD) in particular, and it is sufficient to transport the film with a stretching tension that does not bend the film. Of course, due to the extension in the width direction (TD), neck-in (neck-in) depending on Poisson's ratio (Poisson's ratio) will occur in the flow direction (MD), and it will also occur in the flow direction (MD) during drying. Syneresis. Due to these shrinkages, even if the rotational speed of the conveying roller or the heating roller is constant, an appropriate tension can be obtained in the flow direction (MD), and there is no need for complicated rotational speed control like the above-mentioned Patent Document 2. Considering the manufacturing point of view, the size of the flow direction (MD) of the film should be constant, especially before and after stretching in the width direction (TD), the dimensional change rate of the flow direction (MD) is 0.8~1.2, especially preferably 0.9 ~1.1.

The conveying speed of the film obtained by film production in the flow direction (MD) is preferably 5-30 m/min, especially 7-25 m/min, and further preferably 8-20 m/min. If the transport speed is too slow, productivity tends to decrease, and if it is too fast, in-plane uniformity tends to decrease.

There is no particular limitation on the method of carrying out the conveyance of the film obtained by filming in the flow direction (MD) and the extension in the width direction (TD) at the same time. Ideal for transport and extension. At this time, the arrangement of the jigs at each end is preferably at a distance of 200 mm or less, particularly preferably at a distance of 100 mm or less, and more preferably at a distance of 50 mm or less. If the interval between the above-mentioned clips is too wide, the stretched film tends to be deformed, and the in-plane uniformity of the obtained polyvinyl alcohol-based film tends to decrease. In addition, the gripping position of the jig (the front end of the jig) is preferably 100 mm or less from both edges in the width direction of the film obtained by film production. If the clamping position (front end) of the jig is too close to the center of the film in the width direction, the end of the film to be discarded will increase and the width of the product will tend to narrow.

The elongation ratio in the width direction (TD) of the present invention is preferably 1.05 to 1.3 times, especially 1.05 to 1.25 times, and further preferably 1.1 to 1.2 times. If the elongation ratio in the width direction (TD) is too high or too low, the in-plane uniformity tends to decrease.

The stretching in the width direction (TD) is carried out continuously. This continuous stretching may be performed in one step (once) or in multiple steps (several times) (also referred to as sequential stretching) so that the total stretching ratio falls within the range of the above stretching ratio. For example, after performing continuous stretching in the first stage, simple conveyance in a fixed width direction (TD) may be performed, and then continuous stretching after the second stage may be performed. Especially in the case of thin films, after the continuous stretching of the first stage, by inserting a simple conveying step with a fixed width, the stress of the film can be relaxed and cracks can be avoided. When inserting a conveying step with a fixed width, the fixed width can also be narrower than the width after continuous stretching in the first stage. The film immediately after stretching is easy to shrink due to stress relaxation, and also shrinks with dehydration, so the fixed width can be narrowed to the width of such shrinkage. However, if it is narrower than the shrinkage width, it is not ideal because the film will be deformed. The continuous stretching described above is preferably performed after the drying step of the film, but may be performed at least one of before, during, and after the drying step of the film.

With regard to an ideal form of the present invention, it is possible to use a film that is temporarily stretched more than 1.3 times in the width direction (TD) of the film obtained by film production, and then shrinks in size so that the final stretching ratio in the width direction (TD) becomes 1.05 to 1.3 times. method. At this time, after temporarily stretching more than 1.3 times, the film can be simply transported at a fixed width of 1.05 to 1.3 times the stretching ratio. By means of this method, the stress of the film can be relaxed, especially in the case of thin films, and cracking can be avoided.

In the present invention, stretching in the width direction (TD) of the film obtained by film formation is preferably carried out at an ambient temperature of 50 to 150°C. The ambient temperature during the stretching is particularly preferably 60-140°C, more preferably 70-130°C. If the above-mentioned ambient temperature during stretching is too low or too high, the in-plane uniformity will tend to decrease. When successive stretching is carried out, the ambient temperature during the above-mentioned stretching can be changed in each stretching stage.

In the present invention, the stretching time of the film obtained in the width direction (TD) is preferably 2 to 60 seconds, especially 5 to 45 seconds, and further preferably 10 to 30 seconds. If the stretching time is too short, the film tends to be easily cracked, and conversely, if it is too long, the load on the equipment tends to increase. When performing successive extensions, the above-mentioned extension time can be changed in each extension stage.

In the present invention, after the formed film is stretched in the width direction (TD), both sides of the film may be heat-treated with a floating dryer or the like as required. The heat treatment temperature is preferably 60-200°C, especially 70-150°C. In addition, the above-mentioned heat treatment by the floating dryer is a treatment of spraying hot air, and the heat treatment temperature means the temperature of the above-mentioned sprayed hot air. When the above-mentioned heat treatment temperature is too low, the dimensional stability tends to decrease easily, and conversely, when it is too high, the extensibility at the time of polarizing film production tends to decrease. In addition, the heat treatment time is preferably 1 to 60 seconds, especially 5 to 30 seconds. When the heat treatment time is too short, the dimensional stability tends to decrease, and conversely, when it is too long, the elongation at the time of polarizing film production tends to decrease.

[Polyvinyl Alcohol-Based Film] In this way, the polyvinyl alcohol-based film of the present invention can be obtained. The polyvinyl alcohol-based film is long in the flow direction (MD), and is wound around a core tube in a roll shape to produce a film roll. As mentioned above, the thickness of the polyvinyl alcohol-based film of the present invention needs to be very thin below 40 μm. From the viewpoint of thinning the polarizing film, it is preferably 5 to 40 μm, and from the viewpoint of avoiding cracks, it is more preferably 10 to 40 μm. Further, It should be 10~38μm.

The width of the polyvinyl alcohol-based film of the present invention is preferably 2 m or more, and is particularly preferably 2 to 6 m from the viewpoint of avoiding cracks.

The length of the polyvinyl alcohol-based film of the present invention is preferably at least 2 km, and particularly preferably at least 3 km from the viewpoint of increasing the area. From the point of view of transport weight, it is more suitable to be 3~50km.

The polyvinyl alcohol-based film of the present invention is particularly ideal for use as a raw material roll for polarizing films because of its excellent stretchability.

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

[Manufacturing method of polarizing film] The polarizing film of the present invention is obtained by pulling out the above-mentioned polyvinyl alcohol-based film from the above-mentioned film winding body, transporting it in the horizontal direction, and going through steps such as swelling, dyeing, boric acid cross-linking, stretching, washing, and drying. to manufacture.

The swelling step is performed before the dyeing step. Swelling process can clean the dirt on the surface of the polyvinyl alcohol-based film, and also has the effect of preventing uneven dyeing by swelling the polyvinyl alcohol-based film. In the swelling step, water is generally used as a treatment liquid. The main component of the above-mentioned treatment solution is water, and a small amount of additives such as iodine compounds, surfactants, alcohols, etc. may be added. The temperature of the swelling bath is usually about 10~45°C, and the time of immersion in the swelling bath is usually about 0.1~10 minutes.

The dyeing step is performed by bringing the 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 suitably 0.1~2g/L, and the concentration of potassium iodide is suitably 1~100g/L. The dyeing time is practically about 30 to 500 seconds. The temperature of the treatment bath should be 5~50℃. In addition to the water solvent, the aqueous solution may contain a small amount of an organic solvent compatible with water.

The boric acid crosslinking step is performed using boric acid or boron compounds such as borax. The boron compound is in the form of an aqueous solution or a water-organic solvent mixture, and is used at a concentration of about 10~100g/L. From the viewpoint of stable polarizing performance, it is ideal to coexist potassium iodide in the liquid. The temperature during treatment should be about 30~70°C, and the treatment time should be about 0.1~20 minutes. In addition, it can also be extended during the treatment according to the needs.

In the extending step, the polyvinyl alcohol-based film is preferably extended 3 to 10 times along one axis [flow direction (MD)], more preferably 3.5 to 6 times. In this case, there is no problem in stretching slightly (to prevent shrinkage in the width direction (TD) or more) in a direction perpendicular to the stretching direction. The temperature during stretching should be 40~70°C. Furthermore, the stretching ratio may be set within the above-mentioned range at the end, and the stretching operation is not limited to only one step (one time), and may be performed several times in the polarizing film manufacturing step.

The cleaning step is performed, for example, by immersing the polyvinyl alcohol-based film in water or an aqueous solution of an iodide such as potassium iodide, so that precipitates generated on the surface of the polyvinyl alcohol-based film can be removed. When potassium iodide aqueous solution is used, the concentration of potassium iodide is about 1~80g/L. The temperature during cleaning is usually 5~50°C, preferably 10~45°C. The processing time is usually 1-300 seconds, preferably 10-240 seconds. In addition, washing with water and washing with an aqueous solution of potassium iodide may be performed in combination as appropriate.

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

In addition, the degree of polarization of the polarizing film is preferably above 99.5%, more preferably above 99.8%. If the polarization is too low, there is a tendency that the contrast in a liquid crystal display cannot be ensured. In addition, in general, the light transmittance (H 11 ) obtained by measuring at wavelength λ when two polarizing films are stacked so that their alignment directions are in the same direction, and the light transmittance (H ₁₁ ) obtained when two polarizing films are stacked so that their alignment directions It is the light transmittance (H ₁ ) measured at the wavelength λ in the state of mutually perpendicular directions, and the degree of polarization is calculated according to the following formula. Degree of polarization (%)=[(H ₁₁ -H ₁ )/(H ₁₁ +H ₁ )] ^1/2

In addition, the single transmittance of the polarizing film of the present invention is preferably 42% or more. When the single transmittance is too low, there is a tendency that the high brightness of the liquid crystal display cannot be achieved. The monomer transmittance is the value obtained by measuring the light transmittance of the polarizing film monomer with a spectrophotometer.

Hereinafter, the manufacturing method of the polarizing plate of this invention using the polarizing film of this invention is demonstrated. The polarizing film of the present invention is suitable for manufacturing a polarizing plate with less chromaticity unevenness and excellent polarizing performance.

[Manufacturing method of polarizing plate] The polarizing plate of the present invention is produced by laminating an optically isotropic resin film as a protective film on one or both sides of the polarizing film of the present invention through an adhesive. As for the protective film, examples include cellulose triacetate, cellulose diacetate, polycarbonate, polymethyl methacrylate, cycloolefin polymer, cycloolefin copolymer, polystyrene, polyether Films or sheets of aryl esters, poly-4-methylpentene, polyphenylene ether, etc.

The bonding method can be carried out by a known method, for example, by uniformly coating the liquid adhesive composition on the polarizing film, the protective film, or both, bonding the two together and crimping them, and This is performed by heating or irradiating active energy rays.

In addition, a curable resin such as urethane resin, acrylic resin, and urea resin can be coated on one or both sides of the polarizing film, and cured to form a cured layer to form a polarizing plate. By manufacturing in this way, the above-mentioned cured layer can replace the above-mentioned protective film, and thinning can be achieved.

Polarizing films and polarizing plates using the polyvinyl alcohol-based film of the present invention have excellent polarizing properties and can be ideally used in portable information terminal equipment, computers, televisions, projectors, billboards, desktop computers, electronic clocks, and documents Processors, electronic paper, game consoles, video recorders, cameras, photo frames, thermometers, audio, liquid crystal display devices such as automotive or mechanical instruments, sunglasses, anti-glare glasses, three-dimensional glasses, wearable displays, display components (CRT , LCD, organic EL, electronic paper, etc.) anti-reflection layer, optical fiber communication equipment, medical equipment, building materials, toys, etc. [Example]

Hereinafter, although an Example is given and this invention is demonstrated more concretely, this invention is not limited to the Example mentioned later unless the summary is exceeded.

Furthermore, the properties of the polyvinyl alcohol-based films [swelling degree ( _SA , S _B , S _X , S _Y ) and the properties of the polarizing film (polarization degree, monomer transmittance, chromaticity) in Examples and Comparative Examples described later Inhomogeneity)] measurement and evaluation were carried out as follows.

[Measurement method of the above-mentioned swelling degree ( _SA ) of polyvinyl alcohol-based film] Cut out a rectangle of 10 cm in the width direction (TD) and 20 cm in the flow direction (MD) from the central part of the width direction of the polyvinyl alcohol-based film The film-like sample was further cut into strips with a width of 3 mm and a length of 20 cm. After that, these strip-shaped first samples were directly immersed in 1,000 g of water at 30°C. After soaking for 30 minutes, take out the strip-shaped first sample, and use a centrifuge to perform centrifugal dehydration at 3,000 rpm for 5 minutes, and measure the mass "N" after dehydration (total of all the strip-shaped first samples). Then, after drying the strip-shaped first sample with a dryer at 105°C for 16 hours, measure the mass "M" (total of all the strip-shaped first samples), and calculate the swelling degree (S _A ). In addition, the same measurement was performed 3 times, and the average value was used. Swelling degree (S _A ) (%)=100×N/M

[Measurement method of the above-mentioned swelling degree (S _B ) of polyvinyl alcohol-based film] Cut out a rectangle of 5 cm in the width direction (TD) and 15 cm in the flow direction (MD) from the central part of the width direction of the polyvinyl alcohol-based film For the second sample, clamp the two ends of the second sample in the flow direction (MD) with the chucks so that the distance between the chucks is 5 cm, then immerse it in water at 30°C, and immediately put it in the water with A stretching speed of 0.12m/min (240%/min) was used for uniaxial stretching to triple the stretching ratio (the distance between the above-mentioned chucks of the second sample after stretching was 15cm). After stretching, take the above-mentioned second sample out of the water, and within 1 minute in an environment with a temperature of 20°C and a relative humidity of 65%RH, use filter paper to wipe off the moisture on the surface of the second sample after stretching, and measure the moisture content of the second sample. Quality "L". Then, after drying the second sample with a dryer at 105°C for 16 hours, measure the mass "K", and calculate the swelling degree (S _B ) after stretching in water at 30°C to 3 times the extension ratio by the following formula. In addition, the same measurement was performed 5 times, and the average value was used. Swelling degree (S _B ) (%)=100×L/K

[Measurement method of the above-mentioned swelling degree (S _X and S _Y ) of polyvinyl alcohol-based film] Cut from the central part of the polyvinyl alcohol-based film in the width direction to 10 cm in the width direction (TD), and in the flow direction (MD) The third sample of 10cm square is placed on a flat glass plate, and the width direction (TD) and flow direction (MD) of the third sample are measured with a vernier caliper. Then, soak the above-mentioned third sample in the ion-exchange water tank adjusted to 30°C for 5 minutes, take it out and place it on a flat glass plate immediately, and measure the width direction (TD) and The size in the flow direction (MD) is calculated by the following formula to calculate the degree of swelling (S _X and S _Y ). In addition, the above-mentioned operations were carried out in an environment of 23° C. and 50% RH. Swelling degree (S _X ) (%)=(TD size after immersion/TD size before immersion)×100 Swelling degree (S _Y )(%)=(MD size after immersion/MD size before immersion size)×100

[Polarization degree (%), monomer transmittance (%)] Cut out a test piece with a length of 4 cm x a width of 4 cm from the central part of the obtained polarizing film in the width direction, and use an automatic polarizing film measuring device (VAP7070 manufactured by JASCO Corporation) The polarization degree (%) and the monomer transmittance (%) were measured.

[Non-uniform chromaticity] Cut out a test piece with a length of 30 cm x a width of 30 cm from the central part of the obtained polarizing film in the width direction, and sandwich two polarizing plates in a crossed polarization state at an angle of 45° (single transmittance 43.5 %, polarization degree 99.9%), use a light box with a surface illuminance of 14,000 lux (lx), observe optical chromaticity unevenness in transmission mode, and evaluate according to the following criteria. (Evaluation criteria) ○...No color unevenness △...Slight color unevenness ×...Definitely have color unevenness

<Example 1> (Preparation of polyvinyl alcohol-based film) Add 1,000kg of polyvinyl alcohol-based resin with a weight average molecular weight of 142,000 and a saponification degree of 99.8 mol%, and 2,500kg of water as a plasticizer in a 5,000L dissolution tank. 105kg of glycerin and 0.25kg of polyoxyethylene laurylamine as a surfactant were heated up to 150°C while stirring to dissolve under pressure, and the aqueous solution of polyvinyl alcohol-based resin with a resin concentration of 25% by weight was obtained by adjusting the concentration. Then, after supplying this aqueous solution of polyvinyl alcohol-based resin to a twin-screw extruder for defoaming, the temperature of the aqueous solution was set at 95° C., and it was discharged from a discharge port of a T-shaped slot die (discharge speed 1.3 m/min) and cast onto the surface. The casting drum at 80°C was used for film formation. The film obtained by this film formation was peeled off from the casting drum, and was dried while being transported in the flow direction (MD) while bringing the front and back sides of the film into contact with a total of 10 hot rolls alternately. Thereby, a film (width 2 m, thickness 30 μm) having a moisture content of 7% by weight was obtained. Then, the left and right ends of the above-mentioned film are clamped by clamps with a clamp distance of 45 mm, and the film is transported along the flow direction (MD) at a speed of 8 m/min. ) after being stretched 1.2 times, the film was conveyed in a dryer at 130° C. with a fixed width of 2.4 m to obtain a polyvinyl alcohol-based film (width 2.4 m, thickness 25 μm, length 2 km). The properties of the obtained polyvinyl alcohol-based film are shown in Table 1 below. Finally, the polyvinyl alcohol-based film is wound around a core tube in a roll shape to obtain a film roll.

(Production of Polarizing Film and Polarizing Plate) The obtained polyvinyl alcohol-based film was pulled out from the above-mentioned film winding body, conveyed in the horizontal direction, immersed in a water tank with a water temperature of 30°C to swell, and flowed in the direction of flow (MD) ) extended by 1.7 times. During this swelling step, the film did not crease or wrinkle. Then, dyeing is carried out while dipping in an aqueous solution at 30°C consisting of 0.5 g/L iodine and 30 g/L potassium iodide, extending 1.6 times in the flow direction (MD), and dipping in 40 g/L boric acid and 30 g/L potassium iodide The boric acid cross-linking is carried out in the aqueous solution (50°C) of the composition, and one-axis extension is carried out along the flow direction (MD), and the extension is 2.1 times. Finally, wash with potassium iodide aqueous solution, and dry at 50° C. for 2 minutes to obtain a polarizing film with a total extension ratio of 5.8 times. No cracks occurred during the production of this polarizing film. In addition, the characteristic of the obtained polarizing film is as shown in Table 1 mentioned later. A polyvinyl alcohol aqueous solution was used as an adhesive on both sides of the polarizing film obtained above, and a triacetyl cellulose film with a film thickness of 40 μm was bonded together, and dried at 70° C. to obtain a polarizing plate.

<Example 2> In Example 1, after stretching 1.4 times in the width direction (TD) at 80°C using a stretching machine, it was shrunk to a fixed width of 2.4m (equivalent to 1.2 times stretching) at 130°C by relaxing the stress. Except for transporting, a polyvinyl alcohol-based film (2.4 m in width, 25 μm in thickness, and 2 km in length) was obtained in the same manner as in Example 1. The properties of the obtained polyvinyl alcohol-based film are as shown in Table 1 below. Moreover, using the said polyvinyl-alcohol-type film, it carried out similarly to Example 1, and obtained the polarizing film and the polarizing plate. In the swelling step during the production of the polarizing film, the above-mentioned polyvinyl alcohol-based film did not generate creases or wrinkles, and did not crack. The properties of the obtained polarizing film are shown in Table 1 described later.

<Example 3> In Example 1, the polyvinyl alcohol-based resin aqueous solution was discharged (discharge speed 1.9m/min) and cast onto a casting drum with a surface temperature of 88°C to form a film. 1 In the same manner, a film with a moisture content of 10% by weight (width 2 m, thickness 45 μm) was formed. Then, in the same manner as in Example 1, after stretching 1.2 times in the width direction (TD) using a stretcher at 80°C, the film obtained by the above-mentioned film production was placed in a dryer at 135°C with a fixed width of 2.4m. It was transported to obtain a polyvinyl alcohol-based film (2.4 m in width, 35 μm in thickness, and 2 km in length). The properties of the obtained polyvinyl alcohol-based film are as shown in Table 1 below. Moreover, using the said polyvinyl-alcohol-type film, it carried out similarly to Example 1, and obtained the polarizing film and the polarizing plate. In the swelling step during the production of the polarizing film, the above-mentioned polyvinyl alcohol-based film did not generate creases or wrinkles, and did not crack. The properties of the obtained polarizing film are shown in Table 1 described later.

<Example 4> In Example 1, the polyvinyl alcohol-based resin aqueous solution was discharged (discharge speed 1.9m/min) and cast onto a casting drum with a surface temperature of 88°C to form a film. In the same manner as in Example 1, a film with a moisture content of 10% by weight (width 2 m, thickness 45 μm) was formed. Then, in the same manner as in Example 1, after stretching 1.4 times in the width direction (TD) at 80°C using a stretching machine, it was shrunk to a fixed width of 2.4m (equivalent to stretching 1.2 times) at 135°C by relaxing the stress. , and a polyvinyl alcohol-based film (width 2.4 m, thickness 34 μm, length 2 km) was obtained. The properties of the obtained polyvinyl alcohol-based film are shown in Table 1 below. Moreover, using the said polyvinyl-alcohol-type film, it carried out similarly to Example 1, and obtained the polarizing film and the polarizing plate. In the swelling step during the production of the polarizing film, the above-mentioned polyvinyl alcohol-based film did not generate creases or wrinkles, and did not crack. The properties of the obtained polarizing film are shown in Table 1 below.

<Comparative example 1> In Example 1, a polyvinyl alcohol-type resin aqueous solution was discharged (1.3 m/min discharge speed), and cast|cast to the casting drum whose surface temperature was 80 degreeC, and film-forming was performed. The obtained film was heat-treated at 130° C. using a floating dryer, and was obtained in the same manner as in Example 1, except that stretching in the width direction (TD) using a stretcher was not carried out. Polyvinyl alcohol-based film (2 m in width, 30 μm in thickness, and 2 km in length). The properties of the obtained polyvinyl alcohol-based film are shown in Table 1 below. In addition, when a polarizing film and a polarizing plate were produced in the same manner as in Example 1 using the polyvinyl alcohol-based film, creases or wrinkles were generated in the polyvinyl alcohol-based film in the swelling step. The properties of the obtained polarizing film are shown in Table 1 described later.

<Comparative example 2> In Example 1, the polyvinyl alcohol-type resin aqueous solution was discharged (1.3 m/min discharge speed), and it cast|cast to the casting drum whose surface temperature was 80 degreeC, and film-formed. The obtained film was heat-treated at 120° C. using a floating dryer, and was obtained in the same manner as in Example 1, except that stretching in the width direction (TD) using a stretcher was not carried out. Polyvinyl alcohol-based film (2 m in width, 30 μm in thickness, and 2 km in length). The properties of the obtained polyvinyl alcohol-based film are shown in Table 1 below. In addition, when a polarizing film and a polarizing plate were produced in the same manner as in Example 1 using the polyvinyl alcohol-based film, creases or wrinkles were generated in the polyvinyl alcohol-based film in the swelling step. The properties of the obtained polarizing film are shown in Table 1 below.

【Table 1】

From the results of the above Examples and Comparative Examples, it can _{be seen from the degree of swelling (S A ) when the polyvinyl alcohol-based film is immersed in water at 30°C, the degree of swelling (S B )} when it is stretched three times in one axis at 30°C, Polarizing films obtained from the polyvinyl alcohol-based films of Examples 1 to 4, which represent the swelling degrees (S _X and S _Y ) of the extension of the film after immersion in 30°C water, all conforming to the above formulas (1) to (3), It is a uniform polarizing film with high polarizing properties and no uneven chromaticity. On the other hand, it can be seen that the polyvinyl alcohol-based films of Comparative Example 1 and Comparative Example 2 that do not satisfy the formula (3) have poor polarization characteristics, and uneven chromaticity is also observed.

Although the specific aspect of this invention was shown in the said Example, the said Example is a mere illustration and does not have a limiting meaning. Various changes obvious to those skilled in the art are intended to be included within the scope of the present invention. [industrial availability]

The polarizing film system composed of the polyvinyl alcohol film of the present invention has excellent polarizing performance, and can be ideally used in portable information terminal equipment, computers, televisions, projectors, billboards, desktop computers, electronic clocks, word processors, Electronic paper, game consoles, video recorders, cameras, photo frames, thermometers, audio, liquid crystal display devices such as automotive or mechanical instruments, sunglasses, anti-glare glasses, three-dimensional glasses, wearable displays, display components (CRT, LCD, Organic EL, electronic paper, etc.), optical fiber communication equipment, medical equipment, building materials, toys, etc.

Claims (6)

A polyvinyl alcohol-based film, which has a thickness of 40 μm or less and is elongated, and is characterized in that it meets the following formulas (1)~(3): 190%≦S _A ≦230%･･･(1) 220%≦S _B ≦310%･･･(2) 1.01≦S _Y /S _X ≦1.20･･･(3) In the formula (1), S _A means that the polyvinyl alcohol film was immersed in water at 30℃ for 5 In the formula (2), S _B represents the uniaxial stretching of the polyvinyl alcohol-based film in water at 30°C at a stretching speed of 0.12m/min so that the stretching ratio becomes 3 times Swelling degree based on mass; In the formula (3), S _X represents the swelling degree based on the size of the width direction when the polyvinyl alcohol-based film is immersed in water at 30° C. for 5 minutes, and S _Y represents the polyethylene Swelling degree based on dimensions in the longitudinal direction when the alcohol-based film is immersed in water at 30°C for 5 minutes. A polarizing film, characterized in that it uses the polyvinyl alcohol-based film as described in item 1 of the scope of the patent application. A polarizing plate, characterized in that it has a polarizing film as described in item 2 of the scope of the patent application, and a protective film provided on at least one side of the polarizing film. A method for producing a polyvinyl alcohol-based film, comprising: a film-forming step of forming a film from an aqueous solution of a polyvinyl alcohol-based resin by continuous casting; a drying and stretching step of flowing the film obtained by film-forming The film is transported in the direction of continuous drying and continuous stretching; it is characterized in that the manufactured polyvinyl alcohol film meets the following formulas (1)~(3): 190%≦ _SA ≦230%･･･(1 ) 220%≦S _B ≦310%･･･(2) 1.01≦S _Y /S _X ≦1.20･･･(3) In the formula (1), S _A means that the polyvinyl alcohol-based film is kept at 30℃ The mass-based swelling degree when immersed in water for 5 minutes; In the formula (2), S _B represents the extension ratio of the polyvinyl alcohol-based film in 30°C water at a stretching speed of 0.12m/min. Swelling degree based on mass when it becomes 3 times; In this formula (3), S _X represents the swelling degree based on dimension in the width direction when the polyvinyl alcohol-based film is immersed in water at 30°C for 5 minutes, and S _Y It shows the swelling degree based on the size of the longitudinal direction when this polyvinyl-alcohol-type film was immersed in 30 degreeC water for 5 minutes. A method for producing a polyvinyl alcohol-based film as claimed in claim 4 of the patent application, wherein, in the drying and stretching steps, the film obtained by forming the film is stretched 1.05 to 1.3 times in the width direction. A method for producing a polyvinyl alcohol-based film as claimed in claim 4 or 5 of the patent application, wherein, in the drying and stretching step, the film obtained by making the film is temporarily stretched by more than 1.3 times in the width direction, and then shrunk. The dimensions are such that the stretch ratio in the final width direction is 1.3 times or less.