TWI798217B - 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 that is excellent in balance between swelling and extensibility when producing a polarizing film, does not cause cracks when producing a thin polarizing film, exhibits high polarizing performance, and has less unevenness in chromaticity A polarizing film, and a polarizing film and a polarizing plate using the polyvinyl alcohol-based film, and a method for manufacturing the polyvinyl alcohol-based film are provided. When the polyvinyl alcohol-based film of the present invention is cut out from the central part in the width direction, a rectangular first sample of 40 mm in the width direction (TD) x 270 mm in the length direction (MD) is immersed in water at 30°C for 30 seconds. The elongation W _MD30 in the longitudinal direction of the portion of 250 mm in the longitudinal direction before immersion is 30 mm to 50 mm, and the first rectangle of 270 mm in the width direction (TD) x 40 mm in the length direction (MD) cut out from the central part in the width direction 2 When the sample is immersed in water at 30°C for 300 seconds, the elongation in the width direction W _TD300 of the portion 250 mm in the width direction before immersion is 15 mm to 60 mm.

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, firstly, an aqueous solution of polyvinyl alcohol-based resin is casted into a casting mold such as a casting drum or an endless belt to form a film, and then the film obtained by this film formation is peeled from the casting mold, and then cast using a roller or the like. Manufactured while transporting in the flow direction (MD) and drying with a hot roll or 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. Moreover, 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. . In addition, the above stretching step is to stretch the dyed film along the flow direction (MD) to align the dichroic dyes in the polyvinyl alcohol 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 order 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), adjust the elongation in the longitudinal direction (MD) to a specific range when immersed in water at 30°C for 30 seconds, and adjust the elongation in the width direction when immersed in water at 30°C for 300 seconds A method of adjusting the elongation of (TD) 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. 2016/093259

[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). Conversely, the addition of a water swelling aid disturbs the alignment state of the polymer and tends to make it 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 (M D) 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.

The technology disclosed in the above-mentioned Patent Document 5, although the polyvinyl alcohol-based film with a thickness of about 45 μm used in the examples has a certain degree of improvement effect on the swelling properties of the polarizing film, it is difficult to apply it to the polarizing film. In the case of further thinning, polyvinyl alcohol-based films with a film thickness of 40 μm or less are not satisfactory for improving swelling properties or elongation at the time of polarizing film production.

Therefore, under such a background, the present invention provides a polyvinyl alcohol-based film, which can obtain a good balance between swelling and extensibility during the manufacture of polarizing films, and will not crack when manufacturing thin polarizing films, exhibiting high polarized light. The present invention provides a polarizing film with 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. [Means to solve the problem]

As a result of a series of in-depth studies conducted by the inventors of this case, they found that the longitudinal direction (MD ) and the elongation in the width direction (TD) when immersed in water at 30°C for 300 seconds, if the elongation in the width direction (TD) when immersed in water at 30°C for 300 seconds is The conventional polyvinyl alcohol-based film is smaller, and it can obtain a good balance between swelling and elongation during the production of polarizing films, and it will not crack when producing thin polarizing films, showing high polarizing performance and polarized light with less uneven chromaticity membrane.

That is, the first gist of the present invention is a polyvinyl alcohol-based film, which is a long strip-shaped polyvinyl alcohol-based film with a thickness of 40 μm or less. For the first rectangular sample of 40 mm in the width direction (TD) x 270 mm in the longitudinal direction (MD), when the first sample is immersed in water at 30°C for 30 seconds, the two ends of the longitudinal direction (MD) are excluded before immersion. For the part of 250mm, the elongation W _MD30 in the longitudinal direction (MD) is 30mm to 50mm; for the width direction (TD) 270mm x length direction (MD) cut from the central part of the width direction of the polyvinyl alcohol film For a 40 mm rectangular second sample, when the second sample is immersed in water at 30°C for 300 seconds, the portion of 250 mm excluding both ends in the width direction (TD) before immersion, the width direction (TD) The elongation of W _TD300 is above 15mm and below 60mm.

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: 40mm in the width direction cut out from the central part of the width direction of the obtained polyvinyl alcohol-based film × For a rectangular first sample of 270 mm in the flow direction, when the first sample is immersed in water at 30°C for 30 seconds, the portion of 250 mm excluding both ends in the longitudinal direction before immersion is the elongation in the longitudinal direction W _MD30 is 30mm to 50mm; and for the second sample cut out from the central part of the width direction of the polyvinyl alcohol-based film, which is a rectangle of 270mm in the width direction x 40mm in the flow direction, put the second sample in water at 30°C After 300 seconds of immersion, the elongation in the width direction W _TD300 of the portion of 250 mm excluding both ends in the width direction before immersion is 15 mm to 60 mm. [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, because the above-mentioned elongation W _MD30 and width in the longitudinal direction (MD) when immersed in water at 30°C for a specific time The above-mentioned elongation W _TD300 in the direction (TD) is within a specific range, so the swelling and extensibility of the polarizing film are excellent during manufacture, even if it is made thin (thickness below 40 μm), it is used in the manufacture of thin polarizing films , no cracking will occur. In addition, when the polyvinyl alcohol-based film is used, a polarizing film exhibiting high polarizing performance and having little chromaticity unevenness can be obtained.

Especially when the width of the said polyvinyl alcohol-type film is 2 m or more, the productivity of the polarizing film using this polyvinyl-alcohol-type film improves.

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 according to the present invention includes: a film forming step of forming a film by continuous casting; Continuous drying and continuous stretching are carried out on the film; therefore, combined with the manufacturing conditions in these steps, the elongation W _MD30 in the longitudinal direction (MD) and the elongation in the width direction can be obtained when immersed in water at 30°C for a specific time (TD) The said polyvinyl-alcohol-type film of this invention which becomes the said elongation W _TD300 of a specific range.

In particular, 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), it is appropriate to obtain the above-mentioned elongation W _MD30 and elongation W _TD300 . A polyvinyl alcohol-based film with better swelling and stretchability.

In addition, in the above-mentioned drying and stretching step, after temporarily stretching the film obtained by the above-mentioned film formation more than 1.3 times in the width direction (TD), shrink the size so that the final stretching ratio in the width direction (TD) becomes 1.3 times or less. In some cases, the stress on the film obtained by the above-mentioned film production can be relieved. Therefore, even if the film obtained by the above-mentioned film production is thin, the film can be prevented from cracking.

Next, 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 exhibits specific characteristics in the longitudinal direction (MD) and width direction (TD) after being immersed in water at 30°C. Elongation. That is, for a rectangular first sample of 40 mm in the width direction (TD) x 270 mm in the longitudinal direction (MD) cut out from the central portion of the polyvinyl alcohol-based film in the width direction, the first sample was immersed in water at 30°C After 30 seconds, the elongation W _MD30 in the longitudinal direction is 30 mm or more and 50 mm or less for the portion of 250 mm excluding both ends in the longitudinal direction before dipping. In addition, a rectangular second sample of 270 mm in the width direction (TD) x 40 mm in the longitudinal direction (MD) cut out from the central portion of the polyvinyl alcohol-based film in the width direction was immersed in water at 30°C. At 300 seconds, the elongation W _TD300 in the width direction is 15 mm or more and 60 mm or less for the portion of 250 mm excluding both ends in the width direction before dipping.

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 5-40 μm, and from the viewpoint of avoiding cracks, it is preferably 10-40 μm, more preferably 10-40 μm. 38 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 elongation in the longitudinal direction (MD) and width direction (TD) in a specific range after immersion in 30°C water as described above. With this controlled elongation, when the above-mentioned polyvinyl alcohol-based film is made into a very thin thickness of 40 μm or less, it has excellent performance.

The amount of elongation in the longitudinal direction (MD) is controlled so that when the above-mentioned first sample is immersed in water at 30°C for 30 seconds, the portion of 250 mm in the longitudinal direction excluding both ends of the longitudinal direction before immersion is controlled as described above. The amount of elongation W _MD30 in (MD) is 30 mm or more and 50 mm or less. The elongation W _MD30 in the longitudinal direction (MD) is preferably 31mm≦W _MD30 ≦48mm, especially 32mm≦W _MD30 ≦45mm, and more preferably 33mm≦W _MD30 ≦43mm. If the value of W _MD30 is too small, the extensibility of the polarizing film described later will be deteriorated, so the purpose of the present invention cannot be achieved. In addition, if the value of W _MD30 is too large, relaxation will occur during the production of the polarizing film, and wrinkles will occur Or crease, so can't reach the purpose of the present invention.

The amount of elongation in the width direction (TD) is controlled as described above so that when the above-mentioned second sample is immersed in water at 30°C for 300 seconds, the elongation in the width direction (TD) of the portion of 250 mm excluding both ends in the width direction before immersion is ) The elongation W _TD300 is 15 mm or more and 60 mm or less. The elongation W _TD300 in the width direction (TD) is preferably 16mm≦W _TD300 ≦55mm, especially preferably 17mm≦W _TD300 ≦50mm, more preferably 18mm≦W _TD300 ≦45mm. If the value of above-mentioned W _TD300 is too small, non-uniform dyeing will occur when the polarizing film is manufactured, so the purpose of the present invention cannot be achieved, and if the value of W _TD300 is too large in addition, the film is too wide in the width direction when the polarizing film is manufactured Wrinkles or creases are produced, so the purpose of the present invention cannot be achieved.

In the present invention, regarding the method of controlling the above-mentioned _WMD30 and _WTD300 , in the production method of the above-mentioned polyvinyl alcohol-based film by the continuous casting method described later, the film obtained by casting the molded film is cast from the The method of stretching in the width direction (TD) after peeling off the casting mold is ideal. At this time, the conditions of 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 in the flow direction (MD) of the film obtained above, etc. The aforementioned W _MD30 and W _TD300 are controlled by combining at least one of these conditions with the aforementioned stretching condition in the width direction (TD).

The above-mentioned _WMD30 and _WTD300 values of the present invention are measured, for example, by the following method. In addition, the measurement positions of these W _MD30 and W _TD300 are within the area of 500 mm x 500 mm of the polyvinyl alcohol-based film.

[Measuring method of W _MD30 ] A rectangular first sample of 40 mm in the width direction (TD) x 270 mm in the length direction (MD) is cut out from the central portion of the polyvinyl alcohol-based film in the width direction. Then, draw marking lines with oil-based ink (thickness of the line is 0.3 mm) at 10 mm inward from both ends of the first sample in the longitudinal direction (MD). From the marked lines at both ends, clamp the outer part with commercially available clamps (clamp width 40mm, mass 7.3g), and one of the above clamps is fixed with a rod-shaped jig. After confirming that the distance between the marking lines is 250mm, quickly make the long side of the above-mentioned first sample vertical (vertical) in such a way that the entire first sample held by the above-mentioned jig is immersed in water until it is stored in the cylinder Shaped transparent water tank and adjust the temperature to pure water at 30°C. Immediately after dipping, hang and fix the rod-shaped jig above the upper part of the water tank so that the long side of the above-mentioned first sample is vertical (vertical). Thereafter, a metal ruler was immersed in water, and the distance between the marking lines 30 seconds after the start of immersion of the above-mentioned first sample was measured. The elongation (W _MD30 ) (unit: mm) was calculated by subtracting the original distance between marking lines (250 mm) from the measured value read with a scale of 0.5 mm.

[Measuring method of W _TD300 ] A second sample of a rectangle of 270 mm in the width direction (TD) and 40 mm in the length direction (MD) was cut out from the central portion of the polyvinyl alcohol-based film in the width direction. Then, mark lines were drawn with oil-based ink (line thickness: 0.3 mm) at 10 mm inward from both ends of the second sample in the width direction (TD). From the marked lines at both ends, clamp the outer part with commercially available clamps (clamp width 40mm, mass 7.3g), and one of the above clamps is fixed with a rod-shaped jig. After confirming that the distance between the marking lines is 250 mm, quickly make the long side of the second sample held vertically (vertical) and immerse it in the cylinder in such a way that the entire second sample held by the above-mentioned jig is immersed in water. Shaped transparent water tank and adjust the temperature to pure water at 30°C. Immediately after dipping, hang and fix the above-mentioned stick-shaped jig on the upper part of the water tank so that the long side of the above-mentioned second sample is vertical (vertical). Thereafter, a metal ruler was immersed in water, and the distance between the marked lines of the second sample was measured 300 seconds after the start of immersion. The elongation (W _TD300 ) (unit: mm) was calculated by subtracting the original distance between marking lines (250 mm) from the measured value read with a scale of 0.5 mm.

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 aqueous solution of the polyvinyl alcohol-based resin 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. 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 as needed. 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, particularly preferably 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 during production of 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, and if it is too high, the viscosity becomes too high, and it tends to become difficult to dissolve uniformly.

Then, the obtained polyvinyl alcohol-based resin aqueous solution was subjected to defoaming treatment. As the defoaming method, methods such as static defoaming or multi-screw extruder defoaming can be mentioned. As for the multi-screw extruder, as long as it is a multi-screw extruder having a vent hole, a twin-screw extruder having a vent hole is usually used.

[Film-making process] 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. From the point of view, it is especially suitable for continuous casting method.

The continuous casting method is, for example, a method of continuously discharging the aqueous solution of the above-mentioned polyvinyl alcohol-based resin from a T-shaped slot die and casting (casting) 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, flow 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 polyvinyl alcohol-based resin aqueous solution is too low, the flow tends to be poor, and if it is too high, casting (casting) tends to be 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 (casting) tends to become difficult.

The diameter of the above 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 above-mentioned 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 particularly 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 transport 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, drying tends to be insufficient.

There is no particular limitation on the method of carrying out the conveyance of the film in the flow direction (MD) and the extension in the width direction (TD) of the film obtained 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 distance between the above-mentioned clips is too wide, the film after stretching will be deformed, and the in-plane uniformity of the obtained polyvinyl alcohol-based film will tend 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 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 which the width direction (TD) is fixed 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 equipment load 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. If the heat treatment time is too short, the dimensional stability tends to decrease, and conversely, if 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. The thickness of the polyvinyl alcohol-based film of the present invention is as mentioned above, and it needs to be very thin to be 40 μm or less. 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. 10~38μm.

The width of the polyvinyl alcohol-based film of the present invention is preferably more than 2 m, especially 2-7 m, more preferably 3-6 m from the viewpoint of avoiding cracks.

The length of the polyvinyl alcohol-based film of the present invention is preferably 2 km or more, especially 3 km or more from the viewpoint of large area, and more preferably 3 to 50 km from the viewpoint of transportation weight.

The polyvinyl alcohol-based film of the present invention has excellent extensibility, so it is particularly suitable for use as a raw material roll for polarizing films.

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 and transporting it in the horizontal direction, and undergoing 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. As long as the main component of the above-mentioned treatment liquid is water, a small amount of additives such as iodine compound, surfactant, alcohol, 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 also 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 processing should be about 30~70°C, and the processing time should be about 0.1~20 minutes. In addition, the processing can also be extended 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 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 luminance 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, polymethylmethacrylate, 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.

In addition, the measurement and evaluation of the properties (W _MD30 , W _TD300 ) of the polyvinyl alcohol-based film and the properties of the polarizing film (polarization degree, monomer transmittance, chromaticity unevenness) in the examples and comparative examples described later are as follows proceed in the manner described.

[Measuring method of W _MD30 ] A rectangular first sample of 40 mm in the width direction (TD) x 270 mm in the length direction (MD) is cut out from the central portion of the polyvinyl alcohol-based film in the width direction. Then, mark lines were drawn with oil-based ink (the thickness of the line is 0.3 mm) at 10 mm inward from both ends of the 270 mm long of the first sample. From the marked lines at both ends, clamp the outer part with commercially available clamps (clamp width 40mm, mass 7.3g), and one of the clamps is fixed with a rod-shaped jig. After confirming that the distance between the marking lines is 250 mm, quickly make the long side of the first sample vertical (vertical) and immerse it in a cylindrical shape in such a way that the entire first sample with the jig installed is immersed in water. In a transparent water tank and adjust the temperature to pure water at 30°C. Immediately after dipping, hang the rod-shaped jig on the upper part of the water tank and fix it so that the long side of the above-mentioned first sample is vertical (vertical). Thereafter, a metal ruler was immersed in water, and the distance between the marking lines 30 seconds after the start of immersion of the above-mentioned first sample was measured. The elongation (W _MD30 ) (unit: mm) was calculated by subtracting the original distance between marking lines (250 mm) from the measured value read with a scale of 0.5 mm.

[Measuring method of W _TD300 ] A second sample of a rectangle of 270 mm in the width direction (TD) and 40 mm in the length direction (MD) was cut out from the central portion of the polyvinyl alcohol-based film in the width direction. Then, at 10 mm inward from both ends of the 270 mm length of the second sample, mark lines were drawn with oil-based ink (the thickness of the line is 0.3 mm). From the marked lines at both ends, clamp the outer part with commercially available clamps (clamp width 40mm, mass 7.3g), and one of the clamps is fixed with a rod-shaped jig. After confirming that the distance between the marking lines is 250 mm, quickly make the long side of the second sample vertical (vertical) and immerse it in a cylindrical shape in such a way that the entire second sample with the jig installed is immersed in water. A transparent water tank and adjust the temperature to pure water at 30°C. Immediately after dipping, hang the rod-shaped jig on the upper part of the water tank and fix it so that the long side of the above-mentioned second sample is vertical (vertical). Thereafter, a metal ruler was immersed in water, and the distance between the marked lines of the second sample was measured 300 seconds after the start of immersion. The elongation (W _TD300 ) (unit: mm) was calculated by subtracting the original distance between marking lines (250 mm) from the measured value read with a scale of 0.5 mm.

[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) , Measured polarization (%) and monomer transmittance (%).

[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 illumination of 14,000 lux (lx), observe the optical chromaticity unevenness in the 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 degree of saponification of 99.8 mol%, and 2,500kg of water as a plasticizer in a 5,000L dissolution tank 105 kg of glycerin and 0.25 kg of polyoxyethylene laurylamine as a surfactant were heated up to 150° C. for pressure dissolution while stirring, and an 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 casted. ) to a casting drum with a surface temperature of 80°C 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 described later. 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, 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. 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 except that it was transported. 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 (casting) to a casting drum with a surface temperature of 88°C to form a film. In the same manner as in Example 1, a film (width 2 m, thickness 45 μm) having a moisture content of 10% by weight was formed. Then, in the same manner as in Example 1, after stretching 1.1 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 2.2m. Transported to obtain a polyvinyl alcohol-based film (2.2 m in width, 38 μm in thickness, and 2 km in length). Table 1 shows the characteristics of the obtained polyvinyl alcohol-based film. 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.

<Comparative Example 1> In Example 1, a polyvinyl alcohol-based film was obtained in the same manner as in Example 1 except that the obtained film was not stretched in the width direction (TD) using a stretcher ( Width 2m, thickness 30μm, length 2km). The properties of the obtained polyvinyl alcohol-based film are shown in Table 1 below. In addition, using the above-mentioned polyvinyl alcohol-based film, a polarizing film and a polarizing plate were produced in the same manner as in Example 1, but creases or wrinkles were formed in the 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 known that the elongation in the longitudinal direction (MD) obtained when the polyvinyl alcohol-based film is immersed in water at 30°C for 30 seconds and the elongation in the width direction when immersed in water at 30°C for 300 seconds The polarizing films of the polyvinyl alcohol-based films of Examples 1 to 3 whose elongation of (T D) all meet the above specified ranges are uniform polarizing films with high polarizing properties and no uneven chromaticity. On the other hand, it can be seen that the polarizing film obtained from the polyvinyl alcohol-based film of Comparative Example 1 whose elongation in the width direction (TD) is larger than the above-mentioned specific range has poor polarization characteristics and also has uneven chromaticity.

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 (7)

A polyvinyl alcohol-based film, which has a thickness of 40 μm or less and is in the shape of a strip, characterized in that: a rectangular first cut out from the central part of the polyvinyl alcohol-based film in the width direction of 40 mm in the width direction × 270 mm in the length direction For the sample, when the first sample is immersed in water at 30°C for 30 seconds, the elongation in the longitudinal direction W _MD30 of the portion of 250 mm excluding both ends in the longitudinal direction before immersion is 30 mm to 50 mm; and for Cut out a second sample of a rectangle of 270 mm in the width direction x 40 mm in the length direction from the central part of the polyvinyl alcohol-based film in the width direction, and immerse the second sample in water at 30°C for 300 seconds. The elongation W _TD300 in the width direction is not less than 15 mm and not more than 50 mm, including the portion of 250 mm at both ends in the width direction. The polyvinyl alcohol-based film as claimed in claim 1, wherein the polyvinyl alcohol-based film has a width of 2 m or more. A polarizing film, characterized in that it uses the polyvinyl alcohol film as described in item 1 or 2 of the scope of the patent application. A polarizing plate, characterized in that it has a polarizing film as described in item 3 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 the film-forming Direction conveying, while carrying out continuous drying and continuous stretching of the film; It is characterized in that: for the first rectangle of width direction 40mm × flow direction 270mm cut out from the central part of the width direction of the polyvinyl alcohol-based film For the sample, when the first sample is immersed in water at 30°C for 30 seconds, the elongation W _MD30 in the longitudinal direction of the portion of 250 mm excluding both ends in the longitudinal direction before immersion is 30 mm to 50 mm; and for Cut out the second sample of the rectangular width direction 270mm x flow direction 40mm from the central part of the width direction of the obtained polyvinyl alcohol-based film, and immerse the second sample in water at 30°C for 300 seconds, before immersion The portion of 250 mm not including both ends in the width direction is the elongation W _TD300 in the width direction of 15 mm or more and 50 mm or less. A method for producing a polyvinyl alcohol-based film as claimed in claim 5, wherein, in the drying and stretching steps, the film obtained by film formation 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 5 or 6 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.