TWI748089B - Method for manufacturing polyvinyl alcohol film, polarizing film, polarizing plate and polyvinyl alcohol film - Google Patents

Abstract

The present invention provides a polyvinyl alcohol-based film, which can obtain a good balance of swelling and extensibility during the manufacture of a polarizing film, and will not crack during the manufacture of a thin polarizing film, exhibiting high polarization performance and less chromaticity unevenness A polarizing film, a polarizing film and a polarizing plate using the polyvinyl alcohol-based film, and a manufacturing method of the polyvinyl alcohol-based film are provided. The polyvinyl alcohol-based film of the present invention is an elongated polyvinyl alcohol-based film with a thickness of 5-60 μm, and is characterized in that the birefringence in the longitudinal direction (MD) of the _{first side is Δn MDA} , and the birefringence of the second side is Δn MDA. When the birefringence in the longitudinal direction (MD) is Δn _MDB and the birefringence in the center of the thickness direction is Δn _MDC , all the following formulas (A)～(C) are met; 1.0≦Δn _MDA /Δn _MDB ≦1.5･･ ･(A) Δn _MDB -Δn _MDC ≧0.2×10 ^-3 ･･･(B) Δn _MDA ≧3.0×10 ^-3 ･･･(C).

Description

Method for manufacturing polyvinyl alcohol film, polarizing film, polarizing plate and polyvinyl alcohol film

The present invention relates to a polyvinyl alcohol-based film that can be used as a material for forming a polarizing film with excellent dyeability, high polarization and less chromaticity unevenness, and to a polarizing film using the polyvinyl alcohol-based film and Polarizing plate, and manufacturing method of the polyvinyl alcohol-based film.

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

Under such circumstances, along with the high brightness, high definition, large area, and thinning of screens of LCD TVs and multifunctional portable terminals, polarizing films with excellent optical properties are required. The specific requirement is to further improve the degree of polarization or eliminate the unevenness of chromaticity.

Generally speaking, polyvinyl alcohol-based films are produced by continuous casting using an aqueous solution of polyvinyl alcohol-based resin as a material. Specifically, first, an aqueous solution of polyvinyl alcohol resin is cast to a casting mold such as a casting drum or endless belt to form a film, and then the film obtained by the film is peeled from the casting mold, and then a roll is used It is transported in the direction of flow (MD) and dried using a hot roll or floating dryer. In the above-mentioned transportation 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, generally speaking, the raw material of the polarizing film, namely the polyvinyl alcohol-based film, is first swelled with water (including warm water), and then dyed with dichroic dyes such as iodine. The polarizing film is produced by stretching. Moreover, 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 penetrated into the film. . In addition, the above-mentioned stretching step is a step of stretching the dyed film along the flow direction (MD) so that the dichroic dye in the polyvinyl alcohol film is aligned to a high degree. In order to improve the polarization performance of the polarizing film, What is important is that in this 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 also cases in which the sequence of the stretching step and the dyeing step is reversed from the above in the manufacture of polarizing film. That is, a case where a polyvinyl alcohol-based film that will be 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 polarization performance of the polarizing film, it is important that the polyvinyl alcohol film of the raw material roll exhibits good swelling properties in the thickness direction and good extensibility in the flow direction (MD).

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

Regarding the 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, with regard to methods for improving the extensibility of polyvinyl alcohol-based films, for example, it has been proposed that the ratio of the speed of the casting drum during film formation to the final winding speed of the polyvinyl alcohol-based film is set to a specific value. (For example, refer to Patent Literature 2). After forming a film by a casting drum, the film is suspended and dried (for example, refer to Patent Literature 3). The degree of stretching is controlled in the drying step of the film formed by the film. The method (for example, refer to Patent Document 4) is a method of controlling the birefringence of the surface layer and the core layer to 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 No. [Patent Document 5] Japanese Patent Laid-Open No. 2005-324355

[The problem to be solved by the invention]

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

That is, the technique disclosed in Patent Document 1 mentioned above can improve the swelling properties of the entire polyvinyl alcohol-based film, but it does not take into account the alignment state of the polyvinyl alcohol-based polymer, and it is difficult to efficiently improve the polarizing film manufacturing process. Extensibility in the direction of flow (MD). On the contrary, the addition of the water swelling auxiliary agent disturbs the alignment state of the polymer, and it tends to become difficult to extend uniformly in the direction of flow (MD).

The technique disclosed in Patent Document 2 mentioned above sets the degree of elongation in the flow direction (MD) (stretching condition) at the time of producing the polyvinyl alcohol-based film to a specific level, but if the elongation in the width direction (TD) is not considered at the same time , It is unsatisfactory to improve the extensibility of the polarizing film during manufacture.

Although the technique disclosed in Patent Document 3 can uniformly dry the film formed into the film, it cannot control the alignment of the polymer, and is unsatisfactory in terms of improving the swelling or extensibility during the production of the polarizing film. In addition, the technique disclosed in Patent Document 4 mentioned above can make the film thickness of the polyvinyl alcohol film uniform, but cannot control the alignment of the polymer. In terms of improving the swelling or extensibility during the production of the polarizing film, it is not Unsatisfactory.

The technology disclosed in Patent Document 5 mentioned above, although the polyvinyl alcohol-based film with a thickness of about 75 μm used in the examples can exhibit high extensibility, it is considered that the specific surface layer and core layer correspond to the birefringence system In the above-mentioned thick polyvinyl alcohol-based film, it is difficult to apply to the further thinning of the polarizing film. In the polyvinyl alcohol-based film with a film thickness of 60μm or less, the swelling or extensibility of the polarizing film during the production The improvement is unsatisfactory.

Therefore, the present invention provides a polyvinyl alcohol film under such a background, which can obtain a good balance of swelling and extensibility during the manufacture of polarizing film, and will not crack during the manufacture of thin polarizing film, showing high polarization. It provides a polarizing film with performance and less chromaticity unevenness, 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]

The inventors of this case have repeated the results of a series of studies using this situation as a guide, and found that in a polyvinyl alcohol-based film, if the birefringence of the two sides of the film is made close, the birefringence inside the film is higher than that of the two sides of the film. The birefringence is smaller, and the birefringence on both sides of the film is larger than before, and the balance of swelling and extensibility during the manufacture of polarizing film can be obtained. It will not break during the manufacture of thin polarizing film and exhibit high polarization performance. And a polarizing film with less chromaticity unevenness.

That is, the first gist of the present invention is a polyvinyl alcohol-based film, which is a long-form polyvinyl alcohol-based film with a thickness of 5 to 60 μm, and is characterized in that the birefringence in the longitudinal direction of the first side of the film is When the ratio is Δn _MDA , the birefringence in the longitudinal direction of the second surface of _{the film is Δn MDB} , and the birefringence in the center of the thickness direction of the film is Δn _MDC , all of the following formulas (A) to (C) are met ; 1.0≦Δn _MDA /Δn _MDB ≦1.5･･･(A) Δn _MDB -Δn _MDC ≧0.2×10 ^-3 ･･･(B) Δn _MDA ≧3.0×10 ^-3 ･･･(C).

In addition, the second gist of the present invention is a polarizing film characterized by using the above-mentioned polyvinyl alcohol-based film. In addition, the third gist of the present invention is a polarizing plate characterized by including the polarizing film and a protective film provided on at least one side of the polarizing film.

Furthermore, 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 from an aqueous solution of a polyvinyl alcohol resin by a continuous casting method; and a drying and stretching step to form the film The film produced by the film is transported along the flow direction (MD), and the film is continuously dried and continuously stretched; it is characterized in that the produced polyvinyl alcohol film conforms to the following formulas (A) to (C) All: 1.0≦Δn _MDA /Δn _MDB ≦1.5･･･(A) Δn _MDB -Δn _MDC ≧0.2×10 ^-3 ･･･(B) Δn _MDA ≧3.0×10 ^-3 ･･･(C) This formula In (A)～(C), Δn _MDA represents the birefringence of the flow direction (MD) of _{the first side of the polyvinyl alcohol-based film, and Δn MDB} represents the flow of the second side of the polyvinyl alcohol-based film The birefringence in the direction (MD), Δn _MDC represents the birefringence in the center of the thickness direction of the polyvinyl alcohol-based film. [Effects of the invention]

The polyvinyl alcohol film of the present invention conforms to all the above formulas (A) to (C), so it has excellent swelling and extensibility during the production of the polarizing film. Even if it is made thin, it is used in the production of thin polarizing films. In the middle, there is still no rupture. In addition, if this polyvinyl alcohol-based film is used, a polarizing film that exhibits high polarization performance and has less chromaticity unevenness can be obtained.

Furthermore, the birefringence in the width direction (TD) perpendicular to the length direction (MD) of the first side of the polyvinyl alcohol-based film is Δn _TDA and perpendicular to the length direction (MD) of the second side of the film When the birefringence in the width direction (TD) is Δn _TDB , if it meets at least one of the following formulas (D) and (E), the swelling and extensibility during the production of the polarizing film can be better, and the performance Better polarizing film; Δn _MDA /Δn _TDA ≦1.0･･･(D) Δn _MDB /Δn _TDB ≦1.0･･･(E).

Especially when the thickness of the above-mentioned polyvinyl alcohol-based film is 5 to 45 μm, a polarizing film with more improved swelling and extensibility during the production of the polarizing film and more improved performance can be obtained.

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

Furthermore, the manufacturing method of the polyvinyl alcohol-based film of the present invention includes: a film forming step, which is used to form a film by a continuous casting method; and a drying and stretching step, the film formed by the film is transported along the flow direction (MD) , While performing continuous drying and continuous stretching on the film; therefore, in combination with the manufacturing conditions in these steps, the above-mentioned polyvinyl alcohol-based film of the present invention with a specific birefringence can be obtained.

In particular, in the drying and stretching steps, when the film formed by the film is stretched 1.05 to 1.3 times in the width direction (TD), the birefringence can be appropriately obtained, and the swelling and stretchability of the polarizing film during the production of the film can be improved. Excellent polyvinyl alcohol film.

In addition, in the drying and stretching step, after the film formed as described above is temporarily stretched more than 1.3 times in the width direction (TD), and the size is reduced so that the final width direction stretch magnification becomes 1.3 times or less, the above can be alleviated. The stress of the film produced by the film. Therefore, even if the film obtained by the above-mentioned film formation is thin, the film can still be prevented from breaking.

Next, the present invention will be explained in detail. The polyvinyl alcohol-based film of the present invention is a long-length polyvinyl alcohol-based film with a thickness of 5-60 μm, and is characterized in that the birefringence in the longitudinal direction (MD) of the first side of the film is Δn _MDA , When the birefringence in the longitudinal direction (MD) of the second surface (the other side) of _{the film is Δn MDB} and the birefringence in the center of the thickness direction of the film is Δn _MDC , the following formula (A )～(C)All; 1.0≦Δn _MDA /Δn _MDB ≦1.5･･･(A) Δn _MDB -Δn _MDC ≧0.2×10 ^-3 ･･･(B) Δn _MDA ≧3.0×10 ^-3 ･･･ (C).

The thickness of the polyvinyl alcohol film of the present invention needs to be 5 to 60 μm, preferably 5 to 50 μm from the viewpoint of thinning of the polarizing film, 5 to 45 μm from the viewpoint of avoiding cracking, and more preferably 10 to 40 μm. If the above-mentioned thickness is too thin, it will easily break during the production of the polarizing film described later, which is less desirable, and if it is too thick, the tension required for stretching will increase, which is less desirable.

_{In the above-mentioned polyvinyl alcohol-based film, the value (Δn MDA} /Δn _MDB ) obtained by dividing the birefringence in the longitudinal direction (MD) of the first surface by the birefringence in the longitudinal direction (MD) of the second surface ) Need to be 1.0≦Δn _MDA /Δn _MDB ≦1.5, preferably 1.0≦Δn _MDA /Δn _MDB ≦1.4, especially 1.0≦Δn _MDA /Δn _MDB ≦1.3, more preferably 1.0≦Δn _MDA /Δn _MDB ≦1.2 . If _{the value of Δn MDA} /Δn _MDB is too large, the difference in physical properties between the two sides of the polyvinyl alcohol-based film becomes larger, and the polyvinyl alcohol-based film is easily bent in water, and the object of the invention cannot be achieved. In addition, in the present invention, in the birefringence in the longitudinal direction (MD) of both sides of the polyvinyl alcohol-based film, the larger value is Δn _MDA and the smaller value is Δn _MDB .

The difference between the birefringence of the single side of the film on the side with the smaller birefringence and the birefringence of the central part in the thickness direction of the film (Δn _MDB- Δn _MDC ) needs to be Δn _MDB- Δn _MDC ≧0.2× 10 ^-3 , preferably Δn _MDB -Δn _MDC ≧0.3×10 ^-3 , especially Δn _{MDB -Δn MDC} ≧0.4×10 ^-3 . If _{the value of Δn MDB-} Δn _MDC is too small, the stretchability of the polyvinyl alcohol-based film will deteriorate, and the object of the invention will not be achieved. In addition, the upper limit of the above-mentioned Δn _MDB -Δn _MDC ^{is usually 10×10 -3} (preferably 9.0×10 ^-3 ). If the value of the above-mentioned Δn _MDB -Δn _MDC is too large, the film may be It is prone to partially produce white turbidity and unevenness.

_{The birefringence (Δn MDA} ) of one side of the film on the side with the larger birefringence should be Δn _MDA ≧3.0×10 ^-3 , preferably Δn _MDA ≧3.2×10 ^-3 , especially Δn _MDA ≧3.5×10 ^-3 , further preferably Δn _MDA ≧4.0×10 ^-3 . If _{the value of Δn MDA} is too small, the film is likely to be broken during the production of the polarizing film described later, and the object of the present invention cannot be achieved. In addition, _{the upper limit of Δn MDA} is usually 10×10 ^-3 (preferably 9.0×10 ^-3 ). If _{the value of Δn MDA} is too large, the stretching tension required during the production of the polarizing film described later tends to become too high.

In the present invention, in terms of the method of controlling the above formulas (A) to (C), it is preferable that in the method for producing the polyvinyl alcohol-based film by the continuous casting method described later, the film is formed by casting. The obtained film is peeled from the casting mold and then stretched in the width direction (TD). At this time, the conditions in other steps will be adjusted appropriately according to the stretching conditions in the width direction (TD) (stretching ratio, ambient temperature during stretching, stretching time, etc.). The conditions include, for example, the chemical structure of the polyvinyl alcohol-based resin that forms the material of the polyvinyl alcohol-based film, the type or amount of plasticizer, and the film-forming conditions of the film (the temperature of the casting mold, etc.) ), drying conditions (temperature, time) for drying the film obtained by forming the film, the conveying speed in the flow direction (MD) of the film obtained by the film forming, etc. At least one of these conditions is matched with the extension condition in the width direction (TD) to control the formulas (A) to (C).

The values of Δn _MDA , Δn _MDB and Δn _{MDC in} the present invention can be measured, for example, by the following method. In addition, _{the measurement positions of these Δn MDA} , Δn _MDB and Δn _MDC are within the area of 50 mm×50 mm of the polyvinyl alcohol-based film.

[ _{Measurement method of Δn MDA} , Δn _MDB , Δn _MDC ] (1) Cut out MD from the center of the PVA film at any position in the flow direction (MD) of the PVA film ×TD=5mm×10mm small pieces. Then, both sides of the thin piece were clamped with a 100 μm thick PET (polyethylene terephthalate) film, and then clamped and installed in a slicer device with a wooden frame. (2) Then, the above-mentioned cut pieces are sliced at intervals of 10 μm parallel to the flow direction (MD) of the pieces to prepare observation slices (MD×TD=5mm×10 μm). (3) Then, in such a way that the slice surface can be observed, put the slice upside down and place it on the glass slide, cover the slide with a cover glass and tricresyl phosphate (refractive index: 1.557), and use a two-dimensional light The flexibility evaluation system "PA-micro" (manufactured by Photonic Lattice, Inc.) measures the retardation. (4) With the phase retardation distribution of the slice displayed on the measurement screen of "PA-micro", a vertical line X is drawn on the surface of the above-mentioned polyvinyl alcohol-based film by transversely cutting through the slice, and on the line X Perform line segment analysis on the above to obtain the phase retardation distribution data in the thickness direction of the slice. In addition, the observation system was performed using a 40x objective lens, and the average value of the phase retardation with a line width of 3 pixels was adopted. (5) Divide the obtained phase retardation distribution data in the thickness direction of the slice by the thickness of the slice 10μm to obtain the birefringence distribution in the thickness direction of the slice, and make the maximum values of the birefringence near the two sides of the slice be respectively _{The birefringence Δn MDA} and Δn _MDB on both sides of the slice. In addition, as mentioned above, at this time, the larger value is set to Δn _MDA , and the smaller value is set to Δn _MDB . In addition, let the birefringence of the central portion of the slice in the thickness direction be Δn _MDC .

In addition, the polyvinyl alcohol-based film of the present invention has a birefringence in the width direction (TD) perpendicular to the flow direction (MD) of the first surface of the film as Δn _TDA and the same as the second surface of the film. When the birefringence in the direction of flow (MD) perpendicular to the width direction (TD) of the surface is Δn _TDB , it is more in line with at least one of the following formulas (D) and (E) to reduce the chromaticity unevenness of the polarizing film The view is more ideal. Δn _MDA /Δn _TDA ≦1.0･･･(D) Δn _MDB /Δn _TDB ≦1.0･･･(E)

[ _{Measurement method of Δn TDA} and Δn _TDB ] (1) At any position in the flow direction (MD) of the polyvinyl alcohol film, cut out MD×TD= from the center part of the width direction (TD) of the polyvinyl alcohol film Small pieces of 10mm×5mm in size. Then, the two sides of the thin piece were clamped with a PET film with a thickness of 100 μm, and it was clamped and installed in a slicer device with a wooden frame. (2) Then, the above-mentioned cut pieces were sliced parallel to the width direction (TD) of the thin pieces at intervals of 10 μm to prepare observation slices (MD×TD=10 μm×5 mm). (3) Then, in such a way that the slice surface can be observed, put the slice upside down and place it on the glass slide, cover the slide with a cover glass and tricresyl phosphate (refractive index: 1.557), and use a two-dimensional light The elasticity evaluation system "PA-micro" (manufactured by Photonic Lattice, Inc.) measures the phase delay of slices. (4) With the phase retardation distribution of the slice displayed on the measurement screen of "PA-micro", a vertical line X is drawn on the surface of the above-mentioned polyvinyl alcohol-based film by transversely cutting through the slice, and on the line X Perform line segment analysis on the above to obtain the phase retardation distribution data in the thickness direction of the slice. In addition, the observation system was performed using a 40x objective lens, and the average value of the phase retardation with a line width of 3 pixels was adopted. (5) Divide the obtained phase retardation distribution data in the thickness direction of the slice by the thickness of the slice 10μm to obtain the birefringence distribution in the thickness direction of the slice, and make the maximum values of the birefringence near the two sides of the slice be respectively _{The birefringence Δn TDA} and Δn _TDB on both sides of the slice. In addition, as mentioned above, at this time, the larger value is set to Δn _TDA , and the smaller value is set to Δn _TDB .

Here, the manufacturing method of the polyvinyl alcohol-based film of the present invention will be described in the order of steps.

[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, for the polyvinyl alcohol-based resin constituting the polyvinyl alcohol-based film, an unmodified polyvinyl alcohol-based resin is usually used, that is, polyvinyl acetate obtained by polymerizing vinyl acetate is saponified to obtain Manufactured resin. The resin obtained by saponifying a copolymer of vinyl acetate and a small amount (usually less than 10 mol%, preferably less than 5 mol%) of components copolymerizable with vinyl acetate can also be used according to needs. As for the components that can be copolymerized with vinyl acetate, for example, unsaturated carboxylic acids (for example, including salts, esters, amides, nitriles, etc.), olefins with 2 to 30 carbon atoms (for example, ethylene, propylene, normal Butene, isobutylene, etc.), vinyl ethers, unsaturated sulfonates, etc. These can be used singly or in combination of two or more kinds. In addition, modified polyvinyl alcohol resins obtained by chemically modifying saponified hydroxyl groups can also be used.

Furthermore, as for the polyvinyl alcohol-based resin, a polyvinyl alcohol-based resin having a 1,2-diol structure in the side chain can also be used. The polyvinyl alcohol resin having a 1,2-diol structure in the side chain can be obtained by the following methods, for example (i) combining vinyl acetate with 3,4-diethoxy-1-butanol The method of saponifying the copolymer of olefin, (ii) the method of saponifying and decarboxylating the copolymer of vinyl acetate and vinyl ethylene carbonate, (iii) the method of combining vinyl acetate with 2,2-dialkyl-4- The method of saponifying and deketalizing the copolymer of vinyl-1,3-dioxolane, (iv) the method of saponifying the copolymer of vinyl acetate and glycerol 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 polyvinyl alcohol-based resin is made into an optical film. If it is too large, it tends to be difficult to stretch the polyvinyl alcohol-based film during the production of a polarizing film. . In addition, the weight average molecular weight of the above-mentioned polyvinyl alcohol-based resin is the weight average molecular weight measured according to the GPC-MALS method.

The average saponification degree of the polyvinyl alcohol resin used in the present invention is generally 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, there is a tendency that sufficient optical performance cannot be obtained when the polyvinyl alcohol-based film is made into a polarizing film. Here, in the present invention, the average saponification degree is measured according to JIS K 6726.

Regarding the polyvinyl alcohol-based resin used in the present invention, two or more modified substances, modified amount, weight average molecular weight, average saponification degree, and other different ones can also be used in combination.

In addition to the polyvinyl alcohol-based resin, the polyvinyl alcohol-based resin aqueous solution should also contain glycerin, diglycerin, triglycerin, ethylene glycol, triethylene glycol, and polyethylene in consideration of film-forming properties. Generally used plasticizers such as glycols and trimethylolpropane, or surfactants of at least one of nonionic, anionic, and cationic. These can be used alone or in combination of two or more kinds.

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 further preferably 20 to 50% by weight. If the resin concentration of the above-mentioned aqueous solution is too low, because the drying load is large, the productivity tends to decrease. 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 defoaming treatment. As for the defoaming method, methods such as defoaming by standing defoaming or a multi-axis extruder can be cited. As far as the multi-axis extruder is concerned, as long as it is a multi-axis extruder with vent holes, a biaxial extruder with vent holes is usually 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 preferable and productivity is considered. The point of view is particularly suitable for continuous casting.

In this continuous casting method, for example, the aqueous solution of the polyvinyl alcohol-based resin is continuously discharged from a T-slot mold and poured into a casting mold such as a rotating casting drum, endless belt, and resin film to form a film. Here, the film forming method in the case where the casting mold is a casting drum is explained.

The temperature of the polyvinyl alcohol resin aqueous solution at the outlet of the T-slot die is preferably 80-100°C, especially 85-98°C. If the temperature of the polyvinyl alcohol-based resin aqueous solution is too low, the flow tends to become poor, and if it is too high, it tends to foam.

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

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

The diameter of the casting drum is preferably 2 to 5 m, particularly preferably 2.4 to 4.5 m, and further preferably 2.8 to 4 m. If the diameter of the casting drum is too small, the drying length will be insufficient and the speed will not be easy to increase. If it is too large, the transportability will tend to decrease.

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

The rotation speed of the casting drum is preferably 5-50 m/min, particularly preferably 6-40 m/min, and further preferably 7-35 m/min. If the above-mentioned rotation speed is too slow, there is a tendency for productivity to decrease, and if it is too fast, there is a tendency for insufficient drying.

The surface temperature of the above casting drum is preferably 40-99°C, especially 60-95°C. If the surface temperature is too low, it will tend to become poorly dried, and if it is too high, it will tend to foam.

In this way, the film forming step is performed. Furthermore, the film obtained by this film formation is peeled from the said casting drum, and is conveyed along the flow direction (MD). The water content of the film obtained by the above-mentioned 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. If the water content is too low or too high, it will tend to be difficult to exhibit the intended swelling or extensibility.

[Drying and stretching step] Regarding the adjustment of the above-mentioned moisture content, when the moisture content of the film before stretching in the width direction (TD) is too high, it is advisable to dry the film before stretching in the width direction (TD), on the contrary 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-mentioned range.

The above-mentioned drying system is continuously performed. The 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 the temperature of the heating roller is particularly preferably 40 to 150°C, and more preferably 50°C. ～140℃. In addition, in order to adjust the moisture content, a humidity control area may be provided before extending in the width direction (TD).

In the present invention, the film obtained by film formation does not need to be particularly stretched in the flow direction (MD), and it is sufficient as long as it is transported under a stretching tension to the extent that the film does not bend. Of course, due to the extension in the width direction (TD), neck-in depending on the Poisson's ratio (Poisson's ratio) will occur in the flow direction (MD), and also in the flow direction (MD) during drying. Syneresis. Because of this shrinkage, 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 the complicated rotation speed control as in Patent Document 2 is not required. Considering the manufacturing point of view, the size of the film in the direction of flow (MD) should be constant, especially before and after the stretching in the width direction (TD), the rate of dimensional change in the direction of flow (MD) is 0.8-1.2, especially 0.9 ~ 1.1.

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

The method of conveying the film in the direction of flow (MD) and extending in the width direction (TD) of the film obtained at the same time is not particularly limited. Ideal for transportation and extension. At this time, the arrangement of the clamps at each end is preferably at an interval of 200mm or less, particularly preferably at an interval of 100mm or less, and further preferably at an interval of 50mm or less. If the interval between the clamps is too wide, the stretched film will deform, and the in-plane uniformity of the obtained polyvinyl alcohol-based film in the width direction of both ends will tend to decrease. In addition, the holding position of the jig (the front end of the jig) is preferably 100 mm or less from both ends in the width direction of the film obtained by film formation. If the clamping position (front end) of the clamp is too close to the central part 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 stretching 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 magnification in the width direction (TD) is too high or too low, the in-plane uniformity tends to decrease.

The above-mentioned stretching in the width direction (TD) is performed continuously. This continuous stretching may be one stage (1 time) or multiple stages (several times) (also called successive stretching) so that the total stretching ratio falls within the above-mentioned stretching ratio range. For example, after the continuous stretching in the first stage is performed, simple transportation of the width direction (TD) fixation is performed, and then the continuous stretching after the second stage is performed. Especially in the case of a thin film, after the first stage of continuous stretching, by inserting a simple transport step with a fixed width, the stress of the film can be relieved and breakage can be avoided. When inserting a transport step with a fixed width, the fixed width can also be narrower than the width after continuous extension in the first stage. The film just after stretching is easy to shrink due to the relaxation of the stress, and shrinkage accompanied by dehydration will also occur. The fixed width can be narrowed to this shrinkage width. However, if it is narrower than the shrinking width, it is not ideal because the film will bend. The above-mentioned continuous stretching is preferably carried out after the drying step of the film as described above, but it can also be carried out at least one of the steps before, during, and after the drying step of the film.

According to an ideal form of the present invention, a film can be used to temporarily stretch more than 1.3 times in the width direction (TD) of the film obtained by forming the film, and then shrink the size so that the final stretch 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 with a fixed width of 1.05 to 1.3 times the stretching ratio. By this method, the stress of the film can be alleviated, especially in the case of thin films, and cracks can be avoided.

In the present invention, the stretching in the width direction (TD) of the film obtained by forming the film is preferably performed 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 ambient temperature during the stretching is too low or too high, the in-plane uniformity tends to decrease. When performing successive extensions, the ambient temperature during extension can be changed at each extension stage.

In the present invention, the stretching time in the width direction (TD) of the film obtained by forming the film is preferably 2 to 60 seconds, particularly preferably 5 to 45 seconds, and more preferably 10 to 30 seconds. If the extension time is too short, the film tends to break easily, while if it 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 formed by the film is stretched in the width direction (TD), the two sides of the film can be heat-treated by means of a floating dryer or the like as required. The temperature of the heat treatment is preferably 60 to 200°C, especially 70 to 150°C. In addition, the heat treatment by the floating dryer is a process of blowing hot air, and the heat treatment temperature means the temperature of the blowing hot air. If the heat treatment temperature is too low, the dimensional stability tends to be easily reduced. On the contrary, if it is too high, the extensibility during the production of the polarizing film tends to be reduced. In addition, the heat treatment time is preferably 1 to 60 seconds, particularly preferably 5 to 30 seconds. If the heat treatment time is too short, the dimensional stability tends to decrease, and if it is too long, the extensibility 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 is obtained. This polyvinyl alcohol-based film is long in the flow direction (MD) and is wound around a core tube into a roll shape to produce a film wound body. The thickness of the polyvinyl alcohol film of the present invention needs to be 5-60 μm as mentioned above, and it is preferably 5-50 μm from the viewpoint of thinning the polarizing film, and from the viewpoint of avoiding cracking, it is particularly preferably 5 to 45 μm, and further preferably 10 to 40μm.

The width of the polyvinyl alcohol-based film of the present invention is preferably 2m or more, and in view of avoiding breakage, it is particularly preferably 2-6m.

The length of the polyvinyl alcohol-based film of the present invention is preferably 2 km or more, and in view of large area, it is particularly preferably 3 km or more, and in view of transport weight, it is more preferably 3 to 50 km.

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

Next, the manufacturing method of obtaining a polarizing film using the polyvinyl alcohol-based film of the present invention will be described.

[Method for manufacturing polarizing film] The polarizing film of the present invention draws the above-mentioned polyvinyl alcohol-based film from the above-mentioned film winding body and transports it in a horizontal direction, and undergoes the steps of swelling, dyeing, boric acid cross-linking, stretching, washing, drying, etc. To make it.

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 it also has the effect of preventing uneven dyeing by swelling the polyvinyl alcohol-based film. In the swelling step, water is usually used as the treatment liquid. As long as the main component of the above-mentioned treatment liquid is water, a small amount of additives such as iodine compounds and surfactants, alcohols, etc. may also be added. The temperature of the swelling bath is usually about 10 to 45°C, and the immersion time in the swelling bath is usually about 0.1 to 10 minutes.

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

The boric acid cross-linking step is performed using a boron compound such as boric acid or 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 to 100 g/L. From the viewpoint of stable polarization performance, it is ideal to make potassium iodide coexist in the liquid. The temperature during treatment should be around 30-70°C, and the treatment time should be around 0.1-20 minutes. In addition, extension operations can also be carried out during treatment according to needs.

The stretching step is preferably to stretch the polyvinyl alcohol-based film in the uniaxial direction [flow direction (MD)] by 3-10 times, more preferably by 3.5-6 times. At this time, it does not matter if some extension is also performed in the direction perpendicular to the extension direction (the degree to prevent contraction in the width direction (TD), or more than that). The temperature during extension should be 40～70℃. Furthermore, the stretching magnification may be finally set within the above-mentioned range, and the stretching operation is not limited to one stage (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 iodide such as potassium iodide, and the precipitates generated on the surface of the polyvinyl alcohol-based film can be removed. When using potassium iodide aqueous solution, the potassium iodide concentration is about 1 to 80 g/L. The temperature during the cleaning treatment is usually 5 to 50°C, preferably 10 to 45°C. The treatment time is usually 1 to 300 seconds, preferably 10 to 240 seconds. In addition, it is also possible to appropriately combine water washing and washing with potassium iodide aqueous solution.

The drying step is performed, for example, by drying the 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, more preferably 99.8% or more. If the polarization is too low, there will be a tendency that the contrast in the liquid crystal display cannot be ensured. _{In addition, it is generally based on the light transmittance (H 11} ) measured at the wavelength λ when the two polarizing films are stacked so that the alignment direction is the same direction, and the two polarizing films are stacked so that the alignment direction is _{The light transmittance (H 1} ) is measured at the wavelength λ in the state in the directions perpendicular to each other, and the degree of polarization is calculated according to the following formula. Polarization (%)=[(H ₁₁ -H ₁ )/(H ₁₁ +H ₁ )] ^1/2

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

Next, the manufacturing method of the polarizing plate of the present invention using the polarizing film of the present invention will be described. The polarizing film of the present invention is suitable for manufacturing polarizing plates with less chromaticity unevenness and excellent polarization performance.

[Method for manufacturing polarizing plate] The polarizing plate of the present invention is manufactured by bonding an optically isotropic resin film as a protective film to one or both sides of the polarizing film of the present invention via an adhesive. As for the protective film, for example, cellulose triacetate, cellulose diacetate, polycarbonate, polymethyl methacrylate, cyclic olefin polymer, cyclic olefin copolymer, polystyrene, polyether block, poly stretch Film or sheet of aryl ester, 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, and then bonding the two together and crimping, and It is performed by heating or irradiating active energy rays.

In addition, a polarizing film may be coated with curable resin such as urethane resin, acrylic resin, urea resin, etc., on one side or both sides of the polarizing film, and cured to form a hardened layer to form a polarizing plate. By producing in this way, the hardened layer can replace the protective film, and thinning can be achieved.

The polarizing film and polarizing plate using the polyvinyl alcohol film of the present invention have excellent polarizing properties, and can be ideally used in portable information terminal equipment, computers, TVs, projectors, signage, desktop computers, electronic clocks, and documents 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 components (CRT , LCD, organic EL, electronic paper, etc.) anti-reflection coatings, optical fiber communication equipment, medical equipment, building materials, toys, etc. [Example]

Next, examples are given to explain the present invention more specifically, but the present invention is not limited to the examples described later unless it goes beyond the gist.

In addition, the characteristics of the polyvinyl alcohol-based films (Δn _MDA , Δn _MDB , Δn _MDC , Δn _TDA , Δn _TDB ) and the characteristics of the polarizing film (polarization degree, monomer transmittance, chromaticity) in the following Examples and Comparative Examples The measurement and evaluation of non-uniformity) and the characteristics of the polarizing plate (light leakage resistance) were carried out as follows.

[ _{Measurement method of Δn MDA} , Δn _MDB , Δn _MDC ] (1) Cut out MD from the center of the PVA film at any position in the flow direction (MD) of the PVA film ×TD=5mm×10mm small pieces. Then, both sides of the thin piece were clamped with a 100 μm thick PET (polyethylene terephthalate) film, and then clamped and installed in a slicer device with a wooden frame. (2) Then, the above-mentioned cut pieces are sliced at intervals of 10 μm parallel to the flow direction (MD) of the pieces to prepare observation slices (MD×TD=5mm×10 μm). (3) Then, in such a way that the slice surface can be observed, put the slice upside down and place it on the glass slide, cover the slide with a cover glass and tricresyl phosphate (refractive index: 1.557), and use a two-dimensional light The elasticity evaluation system "PA-micro" (manufactured by Photonic Lattice, Inc.) measures the phase delay. (4) With the phase retardation distribution of the slice displayed on the measurement screen of "PA-micro", a vertical line X is drawn on the surface of the above-mentioned polyvinyl alcohol-based film by transversely cutting through the slice, and on the line X Perform line segment analysis on the above to obtain the phase retardation distribution data in the thickness direction of the slice. In addition, the observation system was performed using a 40x objective lens, and the average value of the phase retardation with a line width of 3 pixels was adopted. (5) Divide the obtained phase retardation distribution data in the thickness direction of the slice by the thickness of the slice 10μm to obtain the birefringence distribution in the thickness direction of the slice, and make the maximum values of the birefringence near the two sides of the slice be respectively _{The birefringence Δn MDA} and Δn _MDB on both sides of the slice. In addition, as mentioned above, at this time, the larger value is set to Δn _MDA , and the smaller value is set to Δn _MDB . In addition, suppose the birefringence of the central part in the thickness direction of the slice is Δn _MDC .

[ _{Measurement method of Δn TDA} and Δn _TDB ] (1) At any position in the flow direction (MD) of the polyvinyl alcohol film, cut out MD×TD= from the center part of the width direction (TD) of the polyvinyl alcohol film Small pieces of 10mm×5mm in size. Then, the two sides of the thin piece were clamped with a PET film with a thickness of 100 μm, and then it was clamped and installed in a slicer device with a wooden frame. (2) Then, the above-mentioned cut pieces were sliced parallel to the width direction (TD) of the thin pieces at intervals of 10 μm to prepare observation slices (MD×TD=10 μm×5 mm). (3) Then, in such a way that the slice surface can be observed, put the slice upside down and place it on the glass slide, cover the slide with a cover glass and tricresyl phosphate (refractive index: 1.557), and use a two-dimensional light The elasticity evaluation system "PA-micro" (manufactured by Photonic Lattice, Inc.) measures the phase delay of slices. (4) With the phase retardation distribution of the slice displayed on the measurement screen of "PA-micro", a vertical line X is drawn on the surface of the above-mentioned polyvinyl alcohol-based film by transversely cutting through the slice, and on the line X Perform line segment analysis on the above to obtain the phase retardation distribution data in the thickness direction of the slice. In addition, the observation system was performed using a 40x objective lens, and the average value of the phase retardation with a line width of 3 pixels was adopted. (5) Divide the obtained phase retardation distribution data in the thickness direction of the slice by the thickness of the slice 10μm to obtain the birefringence distribution in the thickness direction of the slice, and make the maximum values of the birefringence near the two sides of the slice be respectively _{The birefringence Δn TDA} and Δn _TDB on both sides of the slice. In addition, as mentioned above, at this time, the larger value is set to Δn _TDA , and the smaller value is set to Δn _TDB .

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

[Color non-uniformity] A test piece of length 30cm×width 30cm was cut out from the central part of the obtained polarizing film in the width direction, and two polarizing plates in a cross-polarized state were sandwiched at an angle of 45° (single transmittance 43.5 % And 99.9%), use a light box with a surface illuminance of 14,000 lux (lx) to observe the optical chromaticity unevenness in the transmission mode, and evaluate it based on the following criteria. (Evaluation criteria) ○･･･No chromaticity unevenness △･･･Slight chromaticity unevenness ×･･･Clearly chromaticity unevenness

[Light Leak Resistance] An acrylic adhesive layer (thickness 25μm) was placed on one side of the obtained polarizer to produce a polarizer with an adhesive layer. The polarizing plate was bonded to the glass plate so that the absorption axis became 45 degrees, and then the polarizing plate was bonded to the other side of the glass plate to form a cross-polarized arrangement to prepare a sample for evaluating light leakage resistance. In addition, the size of the polarizing plate test piece was used by punching out 20 cm×15 cm from the above-mentioned sample for light leakage resistance evaluation. The sample was left in an environment of 80°C for 500 hours, and light leakage was visually observed, and the evaluation was performed based on the following criteria. (Evaluation criteria) ○･･･Although light leakage occurred at the end of the four sides of the polarizing plate test piece, it was not noticeable. ×･･･Strong light leakage occurred at the end of the 4 sides of the polarizing plate test piece.

<Example 1> (Production of polyvinyl alcohol-based film) In a 5,000L dissolving tank, 1,000 kg of polyvinyl alcohol-based resin with a weight average molecular weight of 142,000 and a saponification degree of 99.8 mol%, and 2,500 kg of water were added as a plasticizer 105kg of glycerin, and 0.25kg of polyoxyethylene laurylamine as a surfactant, were heated to 150°C while stirring, and dissolved under pressure. By adjusting the concentration, an aqueous solution of a polyvinyl alcohol-based resin with a resin concentration of 25% by weight was obtained. Then, the polyvinyl alcohol-based resin aqueous solution was supplied to the biaxial extruder for defoaming, the temperature of the aqueous solution was set to 95°C, and the solution was discharged from the T-slot die outlet (discharge speed 1.3m/min) and poured onto the surface The film is formed on a casting drum with a temperature of 80°C. The film obtained by forming the film was peeled off from the casting drum, conveyed in the flow direction (MD), and dried while alternately contacting the surface and the back surface of the film with a total of 10 hot rolls. Thereby, a film (width 2 m, thickness 30 μm) with a moisture content of 7 wt% was obtained. Then, the left and right ends of the above film were clamped with clamps with a clamp spacing of 45mm, and the film was transported along the flow direction (MD) at a speed of 8m/min, while using a stretching machine at 80°C along the width direction (TD ) After stretching 1.2 times, the film was transported 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 as shown in Table 1 below. Finally, this polyvinyl alcohol-based film was wound around a core tube into a roll shape to obtain a film wound body.

(Production of polarizing film and polarizing plate) The obtained polyvinyl alcohol-based film is drawn from the above-mentioned film winding body, transported in the horizontal direction, and immersed in a water tank with a water temperature of 30°C to make it swell and flow direction (MD ) Extend 1.7 times. During the swelling step, the film did not produce creases or wrinkles. Then, while immersing in a 30°C aqueous solution composed of 0.5 g/L of iodine and 30 g/L of potassium iodide, dyeing is carried out while extending 1.6 times in the flow direction (MD direction), and then immersed in 40 g/L of boric acid and 30 g/L of potassium iodide. In the aqueous solution (50°C) of the composition, the boric acid cross-linking edge is uniaxially stretched along the flow direction (MD direction), and the stretch is 2.1 times. Finally, it was washed with potassium iodide aqueous solution and dried at 50°C for 2 minutes to obtain a polarizing film with a total stretching ratio of 5.8 times. No cracks occurred during the production of the polarizing film. In addition, the characteristics of the obtained polarizing film are as shown in Table 1 below. 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 pasted, and dried at 70° C. to obtain a polarizing plate. The characteristics of the obtained polarizing plate are as shown in Table 1 below.

<Example 2> In Example 1, the stretching machine was used to stretch 1.4 times in the width direction (TD) at 80°C, and the stress was relieved at 130°C to shrink to a fixed width of 2.4m (equivalent to stretching 1.2 times) Except that it was transported, a polyvinyl alcohol-based film (width 2.4 m, thickness 25 μm, length 2 km) was obtained in the same manner as in Example 1. The characteristics of the obtained polyvinyl alcohol-based film are as shown in Table 1 below. In addition, using the above-mentioned polyvinyl alcohol-based film, a polarizing film and a polarizing plate were obtained in the same manner as in Example 1. In the swelling step during the production of the polarizing film, no creases or wrinkles occurred in the above-mentioned polyvinyl alcohol-based film, and no cracks occurred. The characteristics of the obtained polarizing film and polarizing plate are as shown in Table 1 below.

<Example 3> In Example 1, the discharge speed during film formation was 0.8m/min, and a film with a water content of 5% by weight (width 2m, thickness 20μm) was formed using a stretching machine at 80°C in the width direction (TD) After being stretched 1.4 times, it was transported by shrinking it to a fixed width of 2.4 m (equivalent to stretching 1.2 times) by relaxing the stress at 130°C. Except for this, a polyvinyl alcohol system was obtained in the same manner as in Example 1. Film (width 2.4m, thickness 17μm, length 2km). The obtained polyvinyl alcohol-based film is as shown in Table 1. In addition, using the above-mentioned polyvinyl alcohol-based film, a polarizing film and a polarizing plate were obtained in the same manner as in Example 1. In the swelling step during the production of the polarizing film, no creases or wrinkles occurred in the above-mentioned polyvinyl alcohol-based film, and no cracks occurred. The characteristics of the obtained polarizing film and polarizing plate are as shown in Table 1 below.

<Example 4> In Example 1, the polyvinyl alcohol-based resin aqueous solution was discharged (discharge speed 2.5 m/min) and poured into a casting drum with a surface temperature of 90°C to form a film. The film obtained by forming the film was peeled from the casting drum, and conveyed in the flow direction (MD), and dried while alternately contacting the front and back surfaces of the film with a total of 10 hot rolls. Thus, a film (width 2 m, thickness 60 μm) with a moisture content of 10% by weight was obtained. Then, the left and right ends of the above-mentioned film were clamped with clamps with a clamp spacing of 45mm, and the film was transported along the flow direction (MD) at a speed of 8m/min, while using a stretching machine at 80°C along the width direction (TD ) Except for extending 1.1 times, in the same manner as in Example 1, a polyvinyl alcohol-based film (width 2.2 m, thickness 55 μm, length 2 km) was obtained. The properties of the obtained polyvinyl alcohol-based film are as shown in Table 1 below. In addition, using the above-mentioned polyvinyl alcohol-based film, a polarizing film and a polarizing plate were obtained in the same manner as in Example 1. In the swelling step during the production of the polarizing film, no creases or wrinkles occurred in the above-mentioned polyvinyl alcohol-based film, and no cracks occurred. The characteristics of the obtained polarizing film and polarizing plate are as shown in Table 1 below.

<Example 5> In Example 1, the polyvinyl alcohol-based resin aqueous solution was discharged (discharge speed 1.9 m/min) and poured onto a casting drum with a surface temperature of 88°C to form a film. The film obtained by forming the film was peeled from the casting drum, and conveyed in the flow direction (MD), and dried while alternately contacting the front and back surfaces of the film with a total of 10 hot rolls. Thus, a film (width 2 m, thickness 45 μm) with a moisture content of 10% by weight was obtained. Then, the left and right ends of the above-mentioned film were clamped with clamps with a clamp spacing of 45mm, and the film was transported along the flow direction (MD) at a speed of 8m/min, while using a stretching machine at 80°C along the width direction (TD ) After being stretched 1.4 times, the film was contracted to a fixed width of 2.4 m (equivalent to stretching 1.2 times) at 135°C by relaxing the stress. Except for this, the same method as in Example 1 was carried out to obtain a polyvinyl alcohol-based Film (width 2.4m, thickness 34μm, length 2km). The properties of the obtained polyvinyl alcohol-based film are as shown in Table 1 below. In addition, using the above-mentioned polyvinyl alcohol-based film, a polarizing film and a polarizing plate were obtained in the same manner as in Example 1. In the swelling step during the production of the polarizing film, no creases or wrinkles occurred in the above-mentioned polyvinyl alcohol-based film, and no cracks occurred. The characteristics of the obtained polarizing film and polarizing plate are as shown in Table 1 below.

<Comparative Example 1> In Example 1, the polyvinyl alcohol-based resin aqueous solution was discharged (discharge speed 3.1 m/min) and poured onto a casting drum with a surface temperature of 93°C to form a film. The film obtained by forming the film was heat-treated with a heat-treatment roll with a surface temperature of 105°C, without performing the stretching in the width direction (TD) using a stretching machine. In the same manner as in Example 1, the water-containing film was obtained. Polyvinyl alcohol film with a rate of 2.6% by weight (width 2m, thickness 75μm, length 2km). The characteristics of the obtained polyvinyl alcohol-based film are as shown in Table 1 below. In addition, using the above-mentioned polyvinyl alcohol-based film, a polarizing film and a polarizing plate were obtained in the same manner as in Example 1. The characteristics of the obtained polarizing film and the polarizing plate were as shown in Table 1 below, and light leakage was confirmed when the 80°C heat resistance test was conducted.

<Comparative Example 2> In Example 1, the film formed into a film was heat-treated with a heat-treatment roll with a surface temperature of 105°C, and the stretching in the width direction (TD) using a stretching machine was not performed. In the same manner as in Example 1, a polyvinyl alcohol-based film (width 2 m, thickness 30 μm, and length 2 km) with a moisture content of 1% by weight was obtained. The characteristics of the obtained polyvinyl alcohol-based film are as shown in Table 1 below. In addition, when the above-mentioned polyvinyl alcohol-based film was used to produce a polarizing film and a polarizing plate in the same manner as in Example 1, creases or wrinkles were generated in the film in the swelling step. The characteristics of the obtained polarizing film and polarizing plate are as shown in Table 1 below.

【Table 1】

_{From the results of the above-mentioned examples and comparative examples, it is known that the birefringence Δn MDA in} the flow direction (MD) of the first side of the polyvinyl alcohol-based film and the birefringence Δn in the flow direction (MD) of the second side are derived from the polyvinyl alcohol-based film. _MDB , the birefringence Δn of the central part in the thickness direction. _MDC conforms to all formulas (A) to (C). The polarizing film of the polyvinyl alcohol film of Examples 1 to 5 has high polarization characteristics and less chromaticity unevenness. , It is a uniform and excellent polarizing film. On the other hand, the polarizing plate obtained from the polyvinyl alcohol-based film of Comparative Example 1 having a film thickness of 75 μm caused strong light leakage during the heat resistance test. In addition, the polyvinyl alcohol-based film of Comparative Example 2 that does not conform to the formula (C) has poor polarization characteristics, and at the same time, unevenness in chromaticity is observed.

In summary, it can be seen that the polyvinyl alcohol-based film with a film thickness of less than 60μm can obtain a uniform polarizing film with high polarization characteristics, no uneven chromaticity, and resistance to light leakage by conforming to formulas (A) ~ (C). Polarizing plate with good performance.

In the above-mentioned embodiment, the specific aspect of the present invention is shown, but the above-mentioned embodiment is only a mere example and does not have a limited meaning. Various changes that are obvious to those having ordinary knowledge in the technical field are all intended to be included in the scope of the present invention. [Industrial Utilization]

The polarizing film composed of the polyvinyl alcohol-based film of the present invention has excellent polarization 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, automotive or mechanical instruments and other liquid crystal display devices, sunglasses, anti-glare glasses, stereo glasses, wearable displays, display components (CRT, LCD, Organic EL, electronic paper, etc.) anti-reflection coatings, optical fiber communication equipment, medical equipment, construction materials, toys, etc.

Claims (7)

A polyvinyl alcohol-based film, a strip of polyvinyl alcohol-based film with a thickness of 5~45μm, characterized in that the birefringence in the longitudinal direction of the first side of _{the film is △n MDA} and the first side of the film is When the birefringence in the length direction of the two sides is △n _MDB and the birefringence in the center of the thickness direction of the film is △n _MDC , all of the following formulas (A) ~ (C) are met; 1.0<△n _MDA / △n _MDB ≦1.5…(A) △n _MDB -△n _MDC ≧0.2×10 ^-3 …(B) △n _MDA ≧3.0×10 ^-3 …(C). For example, the polyvinyl alcohol-based film of item 1 of the scope of the patent application, wherein the birefringence in the width direction perpendicular to the length direction of the first side of the polyvinyl alcohol-based film is Δn _TDA and the film’s When the birefringence in the width direction perpendicular to the length direction of the second surface is △n _TDB , it meets at least one of the following formulas (D) and (E); △n _MDA /△n _TDA ≦1.0...(D ) △n _MDB /△n _TDB ≦1.0...(E). A polarizing film characterized by using a polyvinyl alcohol-based film such as item 1 or 2 in the scope of the patent application. A polarizing plate, which is characterized by being provided with a polarizing film as in item 3 of the scope of patent application, and a protective film arranged on at least one side of the polarizing film. A method for manufacturing a polyvinyl alcohol-based film such as the first or second item of the scope of the patent application, comprising: a film forming step, which is a continuous casting method for an aqueous solution of a polyvinyl alcohol-based resin; and a drying and stretching step, The film produced by the film is transported along the flow direction while continuously drying and continuous stretching is performed on the film; it is characterized in that the produced polyvinyl alcohol-based film meets all of the following formulas (A) to (C): 1.0<△n _MDA /△n _MDB ≦1.5…(A) △n _MDB -△n _MDC ≧0.2×10 ^-3 …(B) △n _MDA ≧3.0×10 ^-3 …(C) This formula (A) In ~(C), △n _MDA represents the birefringence in the flow direction of the first side of the polyvinyl alcohol film, and △n _MDB represents the birefringence in the flow direction of the second side of the polyvinyl alcohol film The ratio, Δn _MDC represents the birefringence of the central part in the thickness direction of the polyvinyl alcohol-based film. For example, the method for producing a polyvinyl alcohol-based film of item 5 in the scope of the patent application, wherein, in the drying and stretching step, the film obtained by forming the film is stretched 1.05 to 1.3 times in the width direction. For example, the method for manufacturing a polyvinyl alcohol film of item 5 or 6 of the scope of the patent application, wherein in the drying and stretching step, the film obtained by forming the film is temporarily stretched more than 1.3 times in the width direction, and then shrinks in size Make the final stretch magnification in the width direction 1.3 times or less.