TW201841718A - Polyvinyl alcohol film, polarizing film and polarizing plate, and polyvinyl alcohol film production method - Google Patents

Abstract

A polyvinyl alcohol film which has an excellent balance of swelling properties and stretching properties during polarizing film manufacture, does not result in rupture during thin polarizing film production, and enables obtaining a polarizing film that exhibits high polarization performance and has few color irregularities, a polarizing film and polarizing plate using said polyvinyl alcohol film, and a polyvinyl alcohol film production method are provided. This polyvinyl alcohol film is such that when a first sample, cut out from the center in the width direction and having a rectangular shape of 40mm in the width direction (TD) by 270 mm in the length direction (MD), is immersed in 30 DEG C water for 30 seconds, the amount of elongation WMD30 in the length direction of a portion that is 250 mm in the length direction prior to immersion is 30-50 mm, and, when a second sample, cut out from the center in the width direction and having a rectangular shape of 270 mm in the width direction (TD) by 40 mm in the length direction (MD), is immersed in 30 DEG C water for 300 seconds, the amount of elongation WTD300 in the width direction of a portion that is 250 mm in the width direction prior to immersion is 15-60 mm.

Description

Production method of polyvinyl alcohol film, polarizing film, polarizing plate, and polyvinyl alcohol film

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

Conventionally, a polyvinyl alcohol-based film has been used in many applications as a film having excellent transparency. One of such useful applications is a polarizing film. This polarizing film is used as a basic constituent element of a liquid crystal display. In recent years, its use has expanded to devices requiring high quality and high reliability.

In such a case, a polarizing film having excellent optical characteristics has been required along with the increase in brightness, high definition, large area, and thinness of a screen of a liquid crystal television or a multifunctional portable terminal. The specific requirements are to further improve the polarization or eliminate chromaticity unevenness.

Generally, 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, an aqueous solution of a polyvinyl alcohol resin is cast into a casting mold such as a casting drum or an endless belt to form a film, and then the film obtained from the film is peeled from the casting mold, and a roll is used. It is manufactured by conveying in the flow direction (MD) and drying it using a hot roll or a floating dryer. In the transporting step, since the film obtained by the film formation is stretched in the flow direction (MD), the polyvinyl alcohol polymer is easily aligned in the flow direction (MD).

On the other hand, in general, a polyvinyl alcohol-based film, which is a roll of polarizing film, is first swelled with water (including warm water), and then dyed with a dichroic dye such as iodine. The polarizing film is produced by stretching. Furthermore, it is important in the above swelling step to quickly swell the polyvinyl alcohol-based film in the thickness direction, and to uniformly swell the polyvinyl alcohol-based film in the above-mentioned dyeing step so that the dye can be smoothly dipped into the film. . In addition, the above-mentioned stretching step is a step of stretching the dyed film along the flow direction (MD) and orienting the dichroic dye in the polyvinyl alcohol film to a high degree. In order to improve the polarization performance of the polarizing film, It is important that in the stretching step, the polyvinyl alcohol-based film made into the raw material roll needs to exhibit good stretchability in the flow direction (MD).

In addition, there are cases where the order of the stretching step and the dyeing step in the manufacture of a polarizing film is reversed from the above. That is, a polyvinyl alcohol-based film that is a raw material roll is first swelled with water (including warm water) and then 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 exhibits good swelling property in the thickness direction and good extensibility in the flow direction (MD).

In addition, in recent years, in order to reduce the thickness of a polarizing film, there has been a reduction in thickness of a polyvinyl alcohol-based film used as a raw material roll. However, this thin film has productivity problems such as cracking due to elongation during manufacturing of the polarizing film.

As a method for improving the swelling property of a polyvinyl alcohol-based film, for example, a method of adding a polyhydric alcohol to a polyvinyl alcohol-based resin as a water swelling aid has been proposed (for example, refer to Patent Document 1). In addition, as a method for improving the stretchability of a polyvinyl alcohol-based film, for example, a method has been proposed in which the ratio of the speed of a casting drum during film formation to the final polyvinyl alcohol-based film winding speed is set to a specific value. (For example, refer to Patent Document 2), a method of drying a film by suspending the film after forming a film by a casting drum (for example, refer to Patent Document 3), and a method of controlling the degree of stretching in a film drying step (For example, refer to Patent Document 4) The lengthwise (MD) elongation when immersed in 30 ° C water for 30 seconds is adjusted to a specific range, and the width direction when immersed in 30 ° C water for 300 seconds (TD) The method of adjusting the amount of elongation to a specific range (for example, refer to patent document 5). [Prior Art Literature] [Patent Literature]

[Patent Document 1] JP 2001-302867 [Patent Document 2] JP 2001-315141 [Patent Document 3] JP 2001-315142 [Patent Document 4] JP 2002-79531 Bulletin [Patent Document 5] International Publication No. 2016/093259

[Problems to be Solved by the Invention]

However, for the thin polyvinyl alcohol-based film described above, the improvement of the swelling property is not satisfactory with the method of Patent Document 1 described above, and with the methods of Patent Documents 2 to 5 described above, for the production of polarizing films The improvement in extensibility is not satisfactory.

That is, the technology disclosed in the aforementioned Patent Document 1 can improve the swelling properties of the entire polyvinyl alcohol-based film, but 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 production. Extensibility in flow direction (MD). On the contrary, the addition of the water swelling aid causes the alignment state of the polymer to be disturbed, and uniform extension in the flow direction (MD) tends to be difficult.

Although the technique disclosed in the above Patent Document 2 sets the degree of elongation (stretched state) in the flow direction (MD) during the production of the polyvinyl alcohol-based film to a specific level, the elongation in the width direction (TD) is not considered at the same time. , It is unsatisfactory in terms of improving the extensibility when manufacturing a polarizing film.

Although the technique disclosed in the above Patent Document 3 can uniformly dry the film obtained by film formation, the orientation of the polymer cannot be controlled, and the swelling property or extensibility during the manufacture of the polarizing film is not satisfactory. In addition, although the technology disclosed in the above Patent Document 4 can make the thickness of the polyvinyl alcohol-based film uniform, it is impossible to control the orientation of the polymer. In terms of improving the swelling property or extensibility of the polarizing film, Unsatisfactory.

Although the technology disclosed in the aforementioned Patent Document 5 has a certain degree of improvement in swelling properties during the manufacture of polarizing films, the polyvinyl alcohol-based films having a thickness of about 45 μm used in the examples are difficult to correspond to polarizing films. In the case of further thinning, a polyvinyl alcohol-based film having a film thickness of 40 μm or less is not satisfactory in improving the swelling property or extensibility during the production of a polarizing film.

Therefore, the present invention is to provide a polyvinyl alcohol film under such a background, which can obtain a good balance between the swelling property and the extensibility when manufacturing a polarizing film, and it will not crack when manufacturing a thin polarizing film, and exhibit high polarization. A polarizing film having high performance and low color unevenness, and a polarizing film and a polarizing plate using the polyvinyl alcohol-based film, and a method for manufacturing the polyvinyl alcohol-based film. [Means for solving problems]

The inventors of this case conducted a series of in-depth studies based on such circumstances, and found that the length direction (MD) of a polyvinyl alcohol-based film with a thickness of 40 μm or less and a long shape when immersed in 30 ° C water for 30 seconds (MD The relationship between the elongation of) and the elongation in the width direction (TD) when immersed in 30 ° C water for 300 seconds, if the elongation in the width (TD) direction when immersed in 30 ° C water for 300 seconds Conventional polyvinyl alcohol-based films are smaller and can achieve excellent balance between swelling properties and extensibility during the manufacture of polarizing films, and will not crack when manufacturing thin polarizing films, exhibiting polarized light with high polarization performance and less color unevenness. membrane.

That is, the first gist of the present invention is a polyvinyl alcohol-based film, which is a thin polyvinyl alcohol-based film having a thickness of 40 μm or less, and which is cut from a central portion in the width direction of the polyvinyl alcohol-based film. When the first sample of the rectangular shape with a width direction (TD) of 40mm × length direction (MD) of 270mm is immersed in water at 30 ° C for 30 seconds, both ends of the length direction (MD) are not included before immersion. For the 250mm portion, the elongation in the longitudinal direction (MD) W _MD30 is 30mm or more and 50mm or less; for the width direction (TD) 270mm × length direction (MD) cut out from the central portion of the width direction of the polyvinyl alcohol film When the second sample of the 40 mm rectangle is immersed in water at 30 ° C for 300 seconds, the 250 mm portion of the width direction (TD) is not included before the immersion, and the width direction (TD) The elongation W _TD300 is 15mm to 60mm.

In addition, a second gist of the present invention is a polarizing film using the polyvinyl alcohol-based film described above. 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 side of the polarizing film.

In addition, the 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 of an aqueous solution of a polyvinyl alcohol-based resin by a continuous casting method; a drying and stretching step, The film obtained from the film is continuously dried and continuously stretched while being conveyed in the flow direction. It is characterized in that it is 40 mm in width direction cut from the central portion of the width direction of the produced polyvinyl alcohol film × The 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 the longitudinal end portions before the immersion becomes the longitudinal extension W _MD30 is 30mm or more and 50mm or less; and for the second sample of a rectangular shape of 270mm in width and 40mm of flow direction cut from the center of the width direction of the produced polyvinyl alcohol film, the second sample is placed in water at 30 ° C When immersed for 300 seconds, the portion of 250 mm excluding both ends in the width direction before the immersion becomes the elongation in the width direction. W _TD300 is 15 mm or more and 60 mm or less. [Effect of the invention]

The polyvinyl alcohol-based film of the present invention is a strip-shaped polyvinyl alcohol-based film having 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 in a specific range, so it has excellent swelling and elongation properties during the manufacture of polarizing films. Even if it is made thin (thickness less than 40 μm), it is used for the manufacture of thin polarizing films. No cracks will occur. Moreover, when this polyvinyl-alcohol-type film is used, a polarizing film which exhibits high polarization performance and has little chromaticity unevenness can be obtained.

In particular, when the width of the polyvinyl alcohol-based film is 2 m or more, the productivity of a polarizing film using the polyvinyl alcohol-based film is improved.

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 less color unevenness.

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

In addition, the method for producing a polyvinyl alcohol-based film of the present invention includes: a film-forming step, which is performed by a continuous casting method; a drying and stretching step, while the film obtained by the film-forming is conveyed along the flow direction, The film is subjected to continuous drying and continuous stretching; therefore, in combination with the manufacturing conditions in these steps, the above-mentioned elongation W _MD30 and width direction of the length direction (MD) when immersed in water at 30 ° C for a specific time can be obtained. The above-mentioned elongation amount W _TD300 of (TD) becomes the above-mentioned polyvinyl alcohol-based film of the present invention in a specific range.

In particular, in the above-mentioned drying and stretching steps, when the film obtained by the above-mentioned film is stretched in the width direction (TD) by 1.05 to 1.3 times, the above-mentioned elongation W _MD30 and elongation W _TD300 can be obtained appropriately. Manufacture of polarizing film It is a polyvinyl alcohol-based film with better swelling properties and elongation at the time.

In addition, in the above-mentioned drying and stretching steps, after the film obtained by the above-mentioned film formation is temporarily extended in the width direction (TD) by more than 1.3 times, the shrinkage dimension makes the final width direction (TD) extension ratio to 1.3 times or less. In this case, it is possible to reduce the stress to which the thin film obtained by the above film formation is subjected. Therefore, even if the thin film obtained by the above-mentioned film formation is thin, cracking of the thin film can still be avoided.

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 having a thickness of 40 μm or less. When immersed in water at 30 ° C., it exhibits specific characteristics in the longitudinal direction (MD) and width direction (TD). Elongation. That is, a rectangular first sample having a width direction (TD) of 40 mm and a length direction (MD) of 270 mm cut from a central portion in the width direction of the polyvinyl alcohol-based film was immersed in water at 30 ° C. When 30 seconds have _elapsed , before the immersion, the length of the longitudinal direction W _MD30 is not more than 30 mm and not more than 50 mm at a portion excluding 250 mm at both ends in the length direction. In addition, a rectangular second sample having a width direction (TD) of 270 mm and a length direction (MD) of 40 mm cut out from the central portion in the width direction of the polyvinyl alcohol-based film was immersed in water at 30 ° C. At 300 seconds, before the immersion, the width of 250 mm at both ends in the width direction is not included, and the width extension elongation W _TD300 is 15 mm or more and 60 mm or less.

The thickness of the polyvinyl alcohol film of the present invention needs to be very thin, which is 40 μm or less. From the viewpoint of thinning the polarizing film, it is preferably 5 to 40 μm. From the viewpoint of avoiding cracking, it is preferably 10 to 40 μm, and more preferably 10 to 38 μm. If the thickness of the polyvinyl alcohol-based film is too thick, the tension during stretching in the manufacturing process of a polarizing film described later becomes high, which is not desirable. Moreover, if it is too thin, it tends to be easily broken when manufacturing a polarizing film.

That is, the polyvinyl alcohol-based film of the present invention has the elongation in the length direction (MD) and the width direction (TD) when immersed in water at 30 ° C as described above, within a specific range. With the controlled elongation, the polyvinyl alcohol-based film is excellent in performance when it is made to a thickness of 40 μm or less.

As described above, the amount of elongation in the lengthwise direction (MD) is controlled such that when the first sample is immersed in water at 30 ° C for 30 seconds, the lengthwise direction of the portion that does not include the 250mm ends of the lengthwise direction before the immersion is performed. The (MD) elongation amount W _MD30 is 30 mm or more and 50 mm or less. The elongation in the longitudinal direction (MD) W _{MD30 is} preferably 31 mm ≦ W _MD30 ≦ 48 mm, especially 32 mm ≦ W _MD30 ≦ 45 mm, and more preferably 33 mm ≦ W _MD30 ≦ 43 mm. If the _size of the W _MD30 is too small, the extensibility during the production of the polarizing film described below will be deteriorated, so the purpose of the present invention will not be achieved. In addition, if the size of the W _MD30 is too large, the polarizing film will be loosened and wrinkles will be produced. Or creases, so the purpose of the invention cannot be achieved.

The elongation in the width direction (TD) is as described above. When the second sample is immersed in water at 30 ° C for 300 seconds, the width direction (TD The elongation amount 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, particularly preferably 17mm ≦ W _TD300 ≦ 50mm, and further preferably 18mm ≦ W _TD300 ≦ 45mm. If the _size of the W _TD300 is too small, uneven dyeing will occur during the manufacture of the polarizing film, so the purpose of the invention cannot be achieved. In addition, if the size of the W _TD300 is too large, the film will be too wide in the width direction when the polarizing film is manufactured, and Wrinkles or creases are generated, so the purpose of the present invention cannot be achieved.

In the present invention, as for the method of controlling the W _MD30 and W _TD300 , in a method for producing the polyvinyl alcohol-based film by a continuous casting method described later, a film obtained by casting a film is obtained from the film. The method of extending in the width direction (TD) after peeling the casting mold is preferable. At this time, the conditions of the other steps may be appropriately adjusted according to the stretching conditions in the width direction (TD) (elongation magnification, ambient temperature during stretching, stretching time, etc.). The conditions include, for example, the chemical structure of a polyvinyl alcohol-based resin that is a material for forming the polyvinyl alcohol-based film, the type or amount of a plasticizer, and the film-forming conditions of the film (temperature of a casting mold, etc.). ), Drying conditions (temperature, time) for drying the thin film obtained from the film formation, a conveyance speed in the flow direction (MD) of the thin film obtained from the film formation, and the like. At least one of these conditions is matched with the extension condition of the width direction (TD) to control the W _MD30 and W _TD300 .

The _radon of the W _MD30 and W _TD300 of the present invention is measured by, for example, the following method. In addition, the measurement positions of these W _MD30 and W _TD300 are within a region of 500 mm × 500 mm of the polyvinyl alcohol-based film.

[W _MD30 Measurement Method] A rectangular first sample having a width direction (TD) of 40 mm and a length direction (MD) of 270 mm was cut out from the central portion in the width direction of the polyvinyl alcohol film. Then, mark the lines with oil-based ink (the thickness of the line is 0.3 mm) at 10 mm inward from the both end edges in the longitudinal direction (MD) of the first sample. A commercially available jig (width of chuck 40 mm, mass 7.3 g) was used to clamp the outer part from the marked lines at both ends, and one of the above jigs was fixed with a rod-shaped jig. After confirming that the distance between the markings is 250 mm, the first sample held by the jig is immersed in water, and the long side of the first sample is immediately vertical (vertical) and immersed in a cylinder. Pure water in a transparent water tank with a temperature of 30 ° C. Immediately after the dipping, the rod-shaped jig was hung on the upper part of the water tank and fixed so that the long side of the first sample was vertical (vertical). Thereafter, a metal ruler was immersed in water, and the distance between the ruled lines 30 seconds after the start of the immersion of the first sample was measured. The length (W _MD30 ) (unit: mm) was calculated by subtracting the original distance between the marked lines (250 mm) from the measurement 读 出 read on a 0.5 mm scale.

[W _TD300 measurement method] A second sample having a rectangular shape with a width direction (TD) of 270 mm and a length direction (MD) of 40 mm was cut from the central portion in the width direction of the polyvinyl alcohol film. Then, mark the lines with oil-based ink (the thickness of the line is 0.3 mm) at 10 mm inward from both end edges in the width direction (TD) of the second sample. A commercially available jig (width of chuck 40 mm, mass 7.3 g) was used to clamp the outer part from the marked lines at both ends, and one of the above jigs was fixed with a rod-shaped jig. After confirming that the distance between the marked lines is 250 mm, the second sample held by the jig is immersed in water so that the long side of the second sample is vertically (vertically) immersed and stored in a cylinder. Pure water in a transparent water tank with a temperature of 30 ° C. Immediately after the dipping, the rod-shaped jig was hung on the upper part of the water tank and fixed so that the long side of the second sample was vertical (vertical). Thereafter, a metal ruler was immersed in water, and the distance between the ruled lines 300 seconds after the start of the immersion of the second sample was measured. Subtract the original distance between the marked lines (250mm) from the measurement 读 出 read at 0.5mm scale to calculate the elongation (W _TD300 ) (unit is mm).

Here, the manufacturing method of the polyvinyl-alcohol-type film of this invention is demonstrated 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 for the polyvinyl alcohol-based resin constituting the polyvinyl alcohol-based film, an unmodified polyvinyl alcohol-based resin is generally used, that is, polyvinyl acetate obtained by polymerizing vinyl acetate is saponified to Manufacturing resin. A resin obtained by saponifying a copolymer of vinyl acetate with a small amount (usually 10 mol% or less, preferably 5 mol% or less) of a copolymerizable component with vinyl acetate can also be used according to demand. Examples of the components copolymerizable with vinyl acetate include, for example, unsaturated carboxylic acids (for example, salts, esters, amidines, nitriles, etc.) and olefins having 2 to 30 carbon atoms (for example, ethylene, propylene, n- (Butene, isobutylene, etc.), vinyl ethers, unsaturated sulfonates, etc. These can be used alone or in combination of two or more. In addition, a modified polyvinyl alcohol-based resin obtained by chemically modifying a saponified hydroxyl group may also be used.

In addition, as the polyvinyl alcohol-based resin, a polyvinyl alcohol-based resin having a 1,2-diol structure in a side chain can also be used. The polyvinyl alcohol-based resin having a 1,2-diol structure in the side chain can be obtained by the following methods and the like, for example, (i) vinyl acetate and 3,4-diethoxyl-1-butene Method for saponification of copolymer, (ii) method for saponification and decarboxylation of copolymer of vinyl acetate and vinyl ethylene carbonate, (iii) method of vinyl acetate and 2,2-dialkyl-4-ethylene A method for saponification and deketalization of a copolymer of -1,3-dioxolane, and (iv) a method for saponification of a copolymer of vinyl acetate and glycerol monoallyl ether.

The weight average molecular weight of the polyvinyl alcohol 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, sufficient optical properties tend to be difficult to obtain when the polyvinyl alcohol-based resin is made into an optical film. If the weight-average molecular weight is too large, extension of the polarizing film of the polyvinyl alcohol-based film becomes difficult. The tendency. The weight average molecular weight of the polyvinyl alcohol-based resin is a weight average molecular weight measured by a GPC-MALS method.

The average saponification degree of the polyvinyl alcohol-based resin used in the present invention is usually preferably 98 mol% or more, more preferably 99 mol% or more, further preferably 99.5 mol% or more, and particularly preferably 99.8 mol% or more. . If the average saponification degree is too small, when the polyvinyl alcohol-based film is made into a polarizing film, there is a tendency that sufficient optical performance cannot be obtained. Here, the average saponification degree in the present invention is measured in accordance with JIS K 6726.

In the polyvinyl alcohol-based resin used in the present invention, two or more types of modified substances, modified amounts, weight average molecular weight, average saponification degree, and the like may be used in combination.

In addition to the polyvinyl alcohol resin, the polyvinyl alcohol resin aqueous solution should contain glycerol, diglycerol, triglycerol, ethylene glycol, triethylene glycol, and polyethylene glycol from the viewpoint of film-forming properties in accordance with the demand. Glycol, trimethylolpropane, and other commonly used plasticizers, or nonionic, anionic, and cationic surfactants. These can be used alone or in combination of two or more.

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 productivity tends to decrease due to a large drying load. If it is too high, the viscosity becomes too high, and it tends to be difficult to dissolve uniformly.

Then, the obtained polyvinyl alcohol-based resin aqueous solution is subjected to a defoaming treatment. Examples of the defoaming method include a method for defoaming by standing still defoaming or a multi-axis extruder. As for the multi-axis extruder, any multi-axis extruder having a vent hole may be used, and a biaxial extruder having a vent hole is generally used.

[Film-forming step] The polyvinyl alcohol-based film of the present invention is produced by a casting method or a melt extrusion method. In the present invention, considering the viewpoints of transparency, thickness accuracy, and surface smoothness, the casting method is preferred, and productivity is considered. From this viewpoint, the continuous casting method is particularly suitable.

This continuous casting method is, for example, a method of continuously discharging an aqueous solution of the polyvinyl alcohol-based resin from a T-slot die and casting the film to a rotating casting drum, endless belt, resin film, or the like. Here, a film forming method when the casting mold is a casting drum will be described.

The temperature of the polyvinyl alcohol-based resin aqueous solution at the exit of the T-slot die is preferably 80 to 100 ° C, and particularly preferably 85 to 98 ° C. When the temperature of the said polyvinyl alcohol-type resin aqueous solution is too low, there exists a tendency for a poor flow, and when it is too high, there exists a tendency for foaming.

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

The discharge speed of the polyvinyl alcohol-based resin aqueous solution discharged from the T-slot die to the casting drum should preferably be 0.2 to 5 m / min, particularly preferably 0.4 to 4 m / min, and more preferably 0.6 to 3 m / min. If the above discharge speed 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 should be 2 ~ 5m, especially 2.4 ~ 4.5m, and further preferably 2.8 ~ 4m. If the diameter is too small, the drying length tends to be insufficient and it is difficult to increase the speed. If it is too large, the transportability tends to decrease.

The width of the above-mentioned casting drum is preferably 4 m or more, particularly preferably 4.5 m or more, further preferably 5 m or more, and particularly preferably 5 to 7 m. If the width of the casting drum is too small, productivity tends to decrease.

The rotation speed of the casting drum is preferably 5 to 50 m / min, especially 6 to 40 m / min, and more preferably 7 to 35 m / min. If the rotation speed is too slow, productivity tends to decrease, and if it is too fast, drying tends to be insufficient.

The surface temperature of the casting drum is preferably 40 to 99 ° C, and particularly preferably 60 to 95 ° C. If the surface temperature is too low, drying tends to become poor, and if it is too high, foaming tends to occur.

The film formation step is performed in this manner. Moreover, the film obtained by this film formation is peeled from the said casting drum, and is conveyed along a flow direction (MD). The moisture content of the film obtained by the above film formation is preferably 0.5 to 15% by weight, particularly preferably 1 to 13% by weight, and further preferably 2 to 12% by weight. When the water content is too low or too high, the swelling property or elongation property tends to be difficult to exhibit.

[Drying and stretching steps] Regarding the adjustment of the moisture content described above, 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 advisable 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 range.

The drying is performed continuously. This continuous drying can be performed by using a known method such as a heating roller or an infrared heater. In the present invention, it is preferable to use a large number of heating rollers, and it is particularly preferable that the temperature of the heating roller is 40 to 150 ° C, and more preferably 50 ° C. ~ 140 ° C. In addition, in order to adjust the moisture content, a humidity control region may be provided before extending in the width direction (TD).

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

The transport speed of the thin film obtained from the film in the direction of flow (MD) should be 5-30 m / min, especially 7-25 m / min, and more preferably 8-20 m / min. If the conveying speed is too slow, productivity tends to decrease, and if it is too fast, drying tends to be insufficient.

There are no particular limitations on the method of transporting the film in the flow direction (MD) and extending it in the width direction (TD), which is obtained by film formation at the same time. For example, the two ends of the film in the width direction are held by several clamps, and Ideal for delivery and extension. At this time, the arrangement of the clamps at each end should be 200mm or less, especially 100mm or less, and 50mm or less. If the interval between the clamps is too wide, the stretched film tends to deform and the in-plane uniformity of the obtained polyvinyl alcohol-based film tends to decrease. In addition, the clamping position of the jig (the front end of the jig) should be 100 mm or less from the both ends of the film in the width direction. If the clamping position (front end portion) of the jig is located too close to the central portion in the width direction of the film, the end portion of the film to be discarded will increase, and the width of the product will tend to narrow.

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

The extension in the width direction (TD) is performed continuously. This continuous stretching may be one stage (one time) or multiple stages (several times) (also referred to as successive stretching) so that the total stretching magnification falls within the range of the above-mentioned stretching magnification. For example, after the continuous stretching in the first stage, a simple transportation in which the width direction (TD) is fixed is performed, and then, the continuous stretching after the second stage may be performed. In the case of a thin film, after carrying out the continuous stretching in the first stage, by inserting a simple width-fixing transport step, the stress of the film can be relaxed and cracks can be avoided. When inserting a fixed-width shipping step, the fixed width can also be narrower than the width after continuous extension in the first stage. The film immediately after stretching is easy to shrink due to stress relaxation, and shrinkage accompanied by dehydration also occurs, so the fixed width can be narrowed to the width of such shrinkage. However, if it is narrower than the width of the shrinkage, it is less desirable because the film is deformed. The continuous stretching described above is preferably performed after the drying step of the film, but may also be performed at least one of before, during, and after the drying step of the film.

According to an ideal form of the present invention, after the width direction (TD) of the film obtained along the film is temporarily extended more than 1.3 times, the shrinkage dimension can be used to make the final width direction (TD) extension ratio to 1.05 to 1.3 times. method. At this time, after temporarily extending more than 1.3 times, the film may be simply transported with a fixed width of 1.05 to 1.3 times the extension ratio. By this method, the stress of the film can be relaxed, especially in the case of a thin film, and cracking can be avoided.

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

In the present invention, the elongation time when extending the width direction (TD) of the film obtained from the film is preferably 2 to 60 seconds, particularly preferably 5 to 45 seconds, and further preferably 10 to 30 seconds. If the elongation time is too short, the film tends to be easily cracked. On the contrary, if the elongation time is too long, the equipment load tends to increase. When performing successive extensions, the above extension time can be changed at each extension stage.

In the present invention, after the film obtained by film formation is extended in the width direction (TD), both sides of the film may be heat-treated by a floating dryer or the like according to demand. The temperature of the heat treatment is preferably 60 to 200 ° C, and particularly preferably 70 to 150 ° C. In addition, the above-mentioned heat treatment by a floating dryer is a treatment of blowing hot air, and the heat treatment temperature is a meaning of the temperature of the blowing hot air. If the heat treatment temperature is too low, the dimensional stability tends to decrease. On the contrary, if the heat treatment temperature is too high, the stretchability at the time of manufacturing the polarizing film tends to decrease. In addition, the heat treatment time should be 1 to 60 seconds, and particularly 5 to 30 seconds. If the heat treatment time is too short, the dimensional stability tends to decrease, while if it is too long, the stretchability at the time of production of the polarizing film tends to decrease.

[Polyvinyl alcohol-based film] In this manner, the polyvinyl alcohol-based film of the present invention can be obtained. This polyvinyl alcohol-based film is made of a long film in the direction of flow (MD) and is wound around a core tube to form a roll shape to produce a film roll. The thickness of the polyvinyl alcohol-based film of the present invention is as described above, and needs to be very thin at 40 μm or less. The viewpoint of thinning the polarizing film is preferably 5 to 40 μm, and the viewpoint of avoiding cracking is more preferably 10 to 40 μm, and more preferably 10 ~ 38μm.

The width of the polyvinyl alcohol-based film of the present invention is preferably 2 m or more, and from the viewpoint of avoiding cracking, it is particularly preferably 2 to 7 m, and more preferably 3 to 6 m.

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

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

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 that the polyvinyl alcohol film is pulled out from the film roll and transported in a horizontal direction, and is subjected to steps such as swelling, dyeing, boric acid crosslinking, stretching, cleaning, and drying. To manufacture.

The swelling step is performed before the dyeing step. The swelling step can clean the dirt on the surface of the polyvinyl alcohol-based film, and also has effects such as preventing uneven dyeing by swelling the polyvinyl alcohol-based film. In the swelling step, water is usually used as the treatment liquid. The treatment liquid may be water as long as the main component, 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 into the swelling bath is usually about 0.1 ~ 10 minutes.

The dyeing step is performed by contacting a polyvinyl alcohol-based film with a liquid containing iodine or a dichroic dye. Generally, an aqueous solution of iodine-potassium iodide is used, and the concentration of iodine is suitably 0.1 to 2 g / L, and the concentration of potassium iodide is suitably 1 to 100 g / L. The dyeing time is practically about 30 to 500 seconds. The temperature of the treatment bath should be 5 ~ 50 ℃. In addition to an aqueous solvent, the aqueous solution may contain a small amount of an organic solvent compatible with water.

The boric acid crosslinking step is performed using a boron compound such as boric acid or borax. The boron compound is used in the form of an aqueous solution or a mixed solution of water and an organic solvent, and is used at a concentration of about 10 to 100 g / L. From the viewpoint of stable polarization performance, it is desirable 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, it can also be extended during processing according to demand.

The extending step is preferably to extend the polyvinyl alcohol-based film in the direction of one axis [flow direction (MD)] by 3 to 10 times, more preferably 3.5 to 6 times. At this time, it is also possible to perform a slight extension (a degree of preventing shrinkage in the width direction (TD), or an extension thereof or more) in a direction perpendicular to the extension direction. The temperature during stretching should be 40 ~ 70 ℃. Further, the stretching magnification may be set within the above range at the end, and the stretching operation is not limited to one stage (once), and may be performed several times in the step of manufacturing the polarizing film.

The washing step is performed, for example, by immersing a polyvinyl alcohol-based film in water or an aqueous solution of an iodide such as potassium iodide to remove precipitates generated on the surface of the polyvinyl alcohol-based film. When using potassium iodide aqueous solution, the concentration of potassium iodide is about 1 ~ 80g / L. The temperature during cleaning is usually 5 ~ 50 ℃, preferably 10 ~ 45 ℃. The processing time is usually 1 to 300 seconds, preferably 10 to 240 seconds. In addition, water washing and washing with an aqueous potassium iodide solution may be appropriately combined.

The drying step is performed, for example, by drying a polyvinyl alcohol-based film in air at 40 to 80 ° C. for 1 to 10 minutes.

In addition, the degree of polarization of the polarizing film is preferably 99.5% or more, and more preferably 99.8% or more. If the degree of polarization is too low, there is a tendency that the contrast in a liquid crystal display cannot be secured. In addition, generally, the light transmittance (H ₁₁ ) measured at a wavelength λ in a state where two polarizing films are superposed so that their alignment directions are the same direction, and the orientation direction is superposed by two polarizing films is superposed. The light transmittance (H ₁ ) measured at a wavelength λ in a state perpendicular to each other, and the degree of polarization was calculated according to the following formula. Polarization (%) = [(H ₁₁ -H ₁ ) / (H ₁₁ + H ₁ )] ^1/2

In addition, it is preferable that the single-body transmittance of the polarizing film of the present invention is 42% or more. If the single transmittance is too low, there is a tendency that the high brightness of the liquid crystal display cannot be achieved. The unit transmittance is a value obtained by measuring the light transmittance of a polarizing film unit using 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 bonding one or both sides of the polarizing film of the present invention with an optically isotropic resin film as a protective film through an adhesive. As the protective film, for example, cellulose triacetate, cellulose diacetate, polycarbonate, polymethyl methacrylate, cyclic olefin polymer, cyclic olefin copolymer, polystyrene, polyether, polyimide Films or sheets of aryl esters, poly-4-methylpentene, polyphenylene ether, etc.

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

In addition, a polarizing film may be prepared by coating a curable resin such as a urethane resin, an acrylic resin, or a urea resin on one or both sides of the polarizing film and curing it to form a hardened layer. By producing in this way, the hardened layer can replace the protective film and can be made into a thin film.

The polarizing film and polarizing plate using the polyvinyl alcohol film of the present invention are excellent in polarizing performance, and can be ideally used in portable information terminal equipment, computers, televisions, projectors, kanbans, desktop electronic computers, electronic clocks, documents Processors, electronic paper, game consoles, video recorders, cameras, photo frames, thermometers, audio, automotive, or mechanical instrumentation and other liquid crystal display devices, sunglasses, anti-glare glasses, stereo glasses, wearable displays, display elements (CRT , LCD, organic EL, electronic paper, etc.) anti-reflection layer, optical fiber communication equipment, medical equipment, building materials, toys, etc. [Example]

Hereinafter, the present invention will be described more specifically by exemplifying examples. The present invention is not limited to the examples described below without departing from the gist thereof.

In _addition , the measurement and evaluation of the characteristics (W _MD30 , W _TD300 ) of the polyvinyl alcohol film and the characteristics (polarization, monomer transmittance, and chromaticity unevenness) of the polarizing film in the examples and comparative examples described below are as follows: The way described.

[W _MD30 Measurement Method] A rectangular first sample having a width direction (TD) of 40 mm and a length direction (MD) of 270 mm was cut out from the central portion in the width direction of the polyvinyl alcohol film. Then, mark the line with oil-based ink (the thickness of the line is 0.3 mm) at 10 mm inward from both ends of the 270 mm length of the first sample. From the marked lines at both ends, a commercially available clamp (width of chuck 40 mm, mass 7.3 g) is used to clamp the outer portion, and one of the clamps is fixed with a rod-shaped jig. After confirming that the distance between the marked lines is 250 mm, the first sample with the jig installed is immersed in water, and the long side of the first sample is immediately vertical (vertical) and immersed in a cylindrical shape. In a transparent water tank, adjust the temperature to 30 ° C in pure water. Immediately after the dipping, the rod-shaped jig was hung on the upper part of the water tank and fixed so that the long side of the first sample was vertical (vertical). Thereafter, a metal ruler was immersed in water, and the distance between the ruled lines 30 seconds after the start of the immersion of the first sample was measured. The length (W _MD30 ) (unit: mm) was calculated by subtracting the original distance between the marked lines (250 mm) from the measurement 读 出 read on a 0.5 mm scale.

[W _TD300 measurement method] A second sample having a rectangular shape with a width direction (TD) of 270 mm and a length direction (MD) of 40 mm was cut from the central portion in the width direction of the polyvinyl alcohol film. Then, mark the line with oil-based ink (the thickness of the line is 0.3 mm) at 10 mm inward from both ends of the 270 mm length of the second sample. From the marked lines at both ends, a commercially available clamp (width of chuck 40 mm, mass 7.3 g) is used to clamp the outer portion, and one of the clamps is fixed with a rod-shaped jig. After confirming that the distance between the marked lines is 250 mm, the second sample with the jig installed is immersed in water so that the long side of the second sample is vertically (vertically) immersed and stored in a cylindrical shape. In a transparent water tank, adjust the temperature to pure water at 30 ° C. Immediately after the dipping, the rod-shaped jig was hung on the upper part of the water tank and fixed so that the long side of the second sample was vertical (vertical). Thereafter, a metal ruler was immersed in water, and the distance between the marking lines of the second sample 300 seconds after the start of the immersion was measured. Subtract the distance (250mm) between the standard lines from the measurement 读 出 read at 0.5mm scale to calculate the elongation (W _TD300 ) (unit is mm).

[Polarity (%), monomer transmittance (%)] A 4 cm × 4 cm test piece was cut out from the central portion in the width direction of the obtained polarizing film, and an automatic polarizing film measuring device (VAP7070 manufactured by JASCO Corporation) was used. , Measure the polarization (%) and transmittance (%) of the monomer.

[Color unevenness] Cut out a test piece with a length of 30cm × width of 30cm from the central part in the width direction of the obtained polarizing film, and sandwich two polarizing plates in the orthogonal polarization state at an angle of 45 ° (transmittance of 43.5 monomer %, Polarization degree 99.9%), using a light box with a surface illuminance of 14,000 lux (lx), the optical chromaticity unevenness was observed in the transmission mode, and evaluated according to the following criteria. (Evaluation criteria) ○ ... No chromaticity unevenness △ ... Slightly uneven chromaticity × ... Clearly chromaticity unevenness

<Example 1> (Production of polyvinyl alcohol-based film) A 5,000 L dissolution tank was charged with a polyvinyl alcohol-based resin having a weight average molecular weight of 142,000 and a saponification degree of 99.8 mol%, 1,000 kg of water, and 2,500 kg as a plasticizer. 105 kg of glycerin and 0.25 kg of polyoxyethylene laurylamine as a surfactant were heated to 150 ° C. while being stirred to dissolve under pressure, and an aqueous solution of a polyvinyl alcohol resin having a resin concentration of 25% by weight was obtained by adjusting the concentration. Then, this polyvinyl alcohol-based resin aqueous solution was supplied to a biaxial extruder for defoaming, and the temperature of the aqueous solution was set to 95 ° C., and was discharged from a T-slot die discharge port (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 from the film formation was peeled from the casting drum, and was conveyed in the flow direction (MD), and the film was dried while bringing the surface and the back surface of the film into contact with a total of 10 heat rollers. 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 film were clamped with a clamp having a clamp pitch of 45 mm, and the film was transported at a speed of 8 m / min along the flow direction (MD). ) After being stretched 1.2 times, the film was transported in a dryer having a fixed width of 2.4 m at 130 ° C. to obtain a polyvinyl alcohol-based film (2.4 m in width, 25 μm in thickness, and 2 km in length). The properties of the obtained polyvinyl alcohol-based film are as shown in Table 1 described later. This polyvinyl alcohol-based film was wound around a core tube into a roll shape at the end, and a film wound body was obtained.

(Production of polarizing film and polarizing plate) The obtained polyvinyl alcohol-based film was pulled out from the above-mentioned film roll, transported in a horizontal direction, dipped in a water tank at a water temperature of 30 ° C to swell, and along the flow direction (MD ) Extended 1.7 times. During this swelling step, the film did not have creases or wrinkles. Then, while immersed in an aqueous solution at 30 ° C. consisting of 0.5 g / L of iodine and 30 g / L of potassium iodide to dye, extend 1.6 times along the flow direction (MD), and then immerse in 40 g / L of boric acid and 30 g / L of potassium iodide. Boric acid cross-linking was carried out in an aqueous solution (50 ° C.) having the composition, and one-axis extension was performed along the flow direction (MD), and the extension was 2.1 times. Finally, it was washed with an aqueous potassium iodide solution and dried at 50 ° C. for 2 minutes to obtain a polarizing film with a total stretching ratio of 5.8 times. No cracking occurred during the production of this polarizing film. The characteristics of the obtained polarizing film are as shown in Table 1 described later. On both sides of the polarizing film obtained above, a polyvinyl alcohol aqueous solution was used as an adhesive, and a triethylammonium cellulose film having a film thickness of 40 μm was bonded and dried at 70 ° C. to obtain a polarizing plate.

<Example 2> In Example 1, after using a stretcher to stretch 1.4 times in the width direction (TD) at 80 ° C, it was contracted to a fixed width of 2.4m at 130 ° C by relaxing the stress (equivalent to 1.2 times the extension). A polyvinyl alcohol-based film (a width of 2.4 m, a thickness of 25 μm, and a length of 2 km) 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 described later. A polarizing film and a polarizing plate were obtained in the same manner as in Example 1 using the polyvinyl alcohol-based film. In the swelling step at the time of manufacturing the polarizing film, the polyvinyl alcohol-based film did not generate creases or wrinkles, and did not crack. The characteristics of the obtained polarizing film are as shown in Table 1 described later.

<Example 3> In Example 1, a polyvinyl alcohol-based resin aqueous solution was discharged (discharge rate 1.9 m / min) and casted to a casting drum having a surface temperature of 88 ° C to perform film formation. In the same manner as in Example 1, a film (width 2 m, thickness 45 μm) having a water content of 10% by weight was formed. Then, in the same manner as in Example 1, using a stretcher to stretch 1.1 times in the width direction (TD) at 80 ° C, the film obtained by the above film formation was dried in a dryer at a fixed width of 2.2m at 135 ° C. It was transported to obtain a polyvinyl alcohol-based film (2.2 m in width, 38 μm in thickness, and 2 km in length). The characteristics of the obtained polyvinyl alcohol-based film are shown in Table 1. A polarizing film and a polarizing plate were obtained in the same manner as in Example 1 using the polyvinyl alcohol-based film. In the swelling step at the time of manufacturing the polarizing film, the polyvinyl alcohol-based film did not generate creases or wrinkles, and did not crack. The characteristics of the obtained polarizing film are as shown in Table 1 described later.

<Comparative Example 1> In the same manner as in Example 1, except that the obtained film was not stretched in the width direction (TD) using a stretcher, a polyvinyl alcohol-based film was obtained ( (Width 2m, thickness 30μm, length 2km). The properties of the obtained polyvinyl alcohol-based film are as shown in Table 1 below. A polarizing film and a polarizing plate were produced in the same manner as in Example 1 using the polyvinyl alcohol-based film, and in the swelling step, creases or wrinkles were generated in the film. The characteristics of the obtained polarizing film are as shown in Table 1 below.

【Table 1】

From the results of the above Examples and Comparative Examples, it is known that the lengthwise (MD) elongation when the polyvinyl alcohol film is immersed in water at 30 ° C for 30 seconds and the width direction when immersed in water at 30 ° C for 300 seconds. (TD) The polarizing films of the polyvinyl alcohol-based thin films of Examples 1 to 3 whose elongation amounts conform to the above-mentioned specific ranges are uniform polarizing films having high polarization characteristics and no chromaticity unevenness. On the other hand, it can be seen that the polarizing film of the polyvinyl alcohol-based film of Comparative Example 1 having a larger elongation in the width direction (TD) than the specific range described above has poor polarizing characteristics, and at the same time, uneven chromaticity was observed.

Although the specific form of this invention was shown in the said Example, the said Example is a mere example, and does not have a limited meaning. Various changes apparent to those skilled in the art are intended to be included within the scope of the present invention. [Industrial availability]

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

Claims (7)

A polyvinyl alcohol-based film having a thickness of 40 μm or less and having a long shape, is characterized in that it is a first rectangular shape of a rectangular shape of 40 mm in width and 270 mm in length that is cut out from a central portion in 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, before the immersion, the length of the longitudinal direction W _MD30 is not more than 30mm and not more than 50mm, and the portion of the length 250mm is not included. A rectangular second sample having a width of 270 mm and a length of 40 mm cut from the central portion in the width direction of the polyvinyl alcohol-based film. When the second sample was immersed in water at 30 ° C for 300 seconds, it was not affected before immersion. Including 250mm portions at both ends in the width direction, the widthwise extension amount W _TD300 is 15 mm or more and 60 mm or less. For example, the polyvinyl alcohol-based film according to item 1 of the patent application scope, wherein the width of the polyvinyl alcohol-based film is 2 m or more. A polarizing film characterized in that a polyvinyl alcohol-based film such as item 1 or 2 of the scope of patent application is used. A polarizing plate is characterized in that it comprises a polarizing film as in item 3 of the scope of patent application, and a protective film provided on at least one side of the polarizing film. A method for manufacturing a polyvinyl alcohol-based film, comprising: a film-forming step of forming a film of an aqueous solution of a polyvinyl alcohol-based resin by a continuous casting method; and a drying and stretching step of the film obtained from the film-making process while flowing The film is conveyed in the direction, and the film is continuously dried and continuously stretched. It is characterized in that it is the first rectangular rectangle of 40 mm in width and 270 mm in flow direction cut from the central portion of the width direction of the polyvinyl alcohol film produced. For the sample, when the first sample is immersed in water at 30 ° C for 30 seconds, the portion of 250 mm excluding both ends in the length direction before immersion becomes the elongation in the length direction. W _MD30 is 30 mm or more and 50 mm or less; A rectangular second sample having a width of 270 mm and a flow direction of 40 mm cut out from the central portion in the width direction of the obtained polyvinyl alcohol-based film. When the second sample was immersed in water at 30 ° C for 300 seconds, the sample was immersed before immersion. The part that does not include 250 mm at both ends in the width direction becomes the elongation in the width direction. W _TD300 is 15 mm or more and 60 mm or less. For example, in the method for manufacturing a polyvinyl alcohol-based film according to item 5 of the patent application scope, in the drying and stretching steps, the film obtained by forming the film is extended by 1.05 to 1.3 times in the width direction. For example, in the method for manufacturing a polyvinyl alcohol-based film in the scope of application for a patent No. 5 or 6, in the drying and stretching steps, the film obtained by the film formation is temporarily extended more than 1.3 times in the width direction, and then shrinks. The size is such that the final magnification in the width direction is 1.3 times or less.