TWI737640B - Method for manufacturing polyvinyl alcohol-based film for manufacturing polarizing film, polarizing film using the polyvinyl alcohol-based film, polarizing plate, and polyvinyl alcohol-based film for manufacturing polarizing film - Google Patents

Abstract

The present invention is a polyvinyl alcohol-based film used to manufacture polarizing films, with a thickness of 5-60μm, a width of 2m or more, and a length of 2km or more. It is characterized in that the polyvinyl alcohol-based film is immersed in water at 30°C for 15 minutes , The swelling degree X (%) in the width direction (TD direction) and the swelling degree Y (%) in the length direction (MD direction) satisfy the following conditions (1) and (2): (1) 110≦Y≦140; (2) 1.01≦Y/X≦1.2.

Description

Method for manufacturing polyvinyl alcohol-based film for manufacturing polarizing film, polarizing film using the polyvinyl alcohol-based film, polarizing plate, and manufacturing method for polyvinyl alcohol-based film for manufacturing polarizing film

The present invention relates to polyvinyl alcohol-based films (hereinafter sometimes referred to as "polyvinyl alcohol-based films") used to manufacture polarizing films, and in particular, to obtain excellent dyeability, high degree of polarization, and less color unevenness. A method for manufacturing a polyvinyl alcohol-based film of a polarizing film, and a polarizing film using the polyvinyl alcohol-based film, a polarizing plate, and a polyvinyl alcohol-based film for manufacturing the polarizing film.

Conventionally, polyvinyl alcohol-based films have been used in many applications as films with excellent transparency, and one of its effective applications includes polarizing films. This polarizing film is used as a basic constituent element of a liquid crystal display. In recent years, its use in equipment requiring high quality and high reliability is expanding.

Among these, with the high brightness, high definition, large area, and thinning of the screens of LCD TVs, multifunctional portable terminals, etc., polarizing films with excellent polarization performance are required. Specifically, the system improves the degree of polarization and solves color unevenness.

Generally, the polyvinyl alcohol-based film used for manufacturing the polarizing film is manufactured from an aqueous solution of a polyvinyl alcohol-based resin by a continuous casting method. Specifically, an aqueous solution of polyvinyl alcohol-based resin is cast on a casting mold such as a casting drum, endless belt, etc. to form a film, and after the film formed by the film is peeled from the casting mold, the use of a nip roll is equivalent to It is transported in the direction of travel (MD direction), and is manufactured while drying using a hot roller and a floating dryer. In this transport step, the film formed by the film is stretched in the traveling direction (MD direction), so the polyvinyl alcohol-based polymer is easily aligned in the MD direction.

On the other hand, generally, a polarizing film is produced by swelling a polyvinyl alcohol-based film, which is a raw material roll, in water (including warm water), dyeing it with a dichroic dye such as iodine, and stretching. In this swelling step, the polyvinyl alcohol-based film must be rapidly swelled in the thickness direction. In addition, it must be uniformly swollen during the dyeing step so that the dye can smoothly penetrate the inside of the film. In addition, the stretching step is a step in which the dyed film is stretched in the traveling direction (MD direction) so that the dichroic dye in the film is highly aligned. In order to improve the polarization performance of the polarizing film, it becomes the polyvinyl alcohol of the raw material roll. The mesangium must have good extensibility in the MD direction.

In addition, there are also cases in which the sequence of the stretching step and the dyeing step is reversed in the manufacturing of the polarizing film. That is, a case where the raw material roll, which is a polyvinyl alcohol-based film, is swelled in water (including warm water) and then stretched and dyed with a dichroic dye such as iodine. However, even in this case, in order to improve the polarizing film For polarizing properties, the polyvinyl alcohol-based film must still have good swelling properties in the thickness direction and good extensibility in the MD direction.

In addition, due to the thinning of the polarizing film in recent years, the thickness of the polyvinyl alcohol-based film has also been reduced. This thin film has productivity problems such as breakage due to stretching during the production of the polarizing film.

As a method of improving swelling properties, 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). As a method of improving the extensibility, for example, a method of specifying the ratio of the speed of the casting drum to the final film winding speed when the film is formed into a film (for example, refer to Patent Document 2), the film is formed by the casting drum The method of drying by suspending (for example, refer to Patent Document 3), and the method of controlling the stretching state of the film obtained by film formation in the drying step (for example, refer to Patent Document 4). [Prior Technical Documents] [Patent Documents]

[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 Bulletin

[Problem to be Solved by the Invention] However, even with the method of the above-mentioned patent document, the improvement of swelling and elongation at the time of the production of the polarizing film is still insufficient.

In the technique disclosed in Patent Document 1, even if the swelling properties of the polyvinyl alcohol-based film as a whole can be improved, the alignment state of the polyvinyl alcohol-based polymer is not considered, and the direction of travel during the production of the polarizing film is effectively improved. Extensibility (MD direction) is difficult. Conversely, there is a tendency that the alignment state of the polymer is disturbed due to the addition of the water swelling agent, and uniform extension in the direction of travel (MD direction) becomes difficult.

The above-mentioned Patent Document 2 specifies the degree of extension in the MD direction (stretching condition) when producing a polyvinyl alcohol-based film, but if the extension in the TD direction is not also considered, the improvement of the extensibility during the production of the polarizing film is still insufficient. Generally speaking, it is difficult to extend the polyvinyl alcohol-based film aligned in the MD direction in the MD direction during the production of the polarizing film. That is, it is difficult to stretch the polyvinyl alcohol polymer that has been aligned in the MD direction in the MD direction to forcibly elongate the molecular chain. Conversely, it is easier to stretch the polyvinyl alcohol-based polymer aligned in the TD direction in the MD direction. However, if the alignment of the polymer in the TD direction is not uniform, the polarizing film cannot be stretched uniformly in the MD direction during manufacture. In Patent Document 2, during the production of polyvinyl alcohol-based films, although there is an example (unstretched example) that does not extend to such an extent in the MD direction, only the above-mentioned shrinkage stress depends on the Poisson's ratio. In addition to the shrinkage stress caused by dehydration, there is a problem that the polymer alignment in the TD direction cannot be fully homogenized. That is, if it does not extend to a certain extent in the TD direction, or at least the width direction is not fixed, a uniform alignment state of the polymer in the TD direction cannot be obtained. The extensibility in the MD direction in the manufacturing of the improved polarizing film is insufficient. And there is no description about the orientation in the thickness direction, and the swelling property during the production of the polarizing film cannot be controlled.

In the technique disclosed in Patent Document 3, although the film after film formation can be uniformly dried, the alignment of the polymer cannot be controlled, and the improvement of swelling and extensibility during the production of the polarizing film is still insufficient. In the technique disclosed in Patent Document 4, although the film thickness of the polyvinyl alcohol-based film can be made uniform, the alignment of the polymer cannot be controlled, and the swelling and extensibility of the polarizing film cannot be improved. enough.

Therefore, under such a background, the present invention provides: polyvinyl alcohol for the production of polarizing films that can obtain polarizing films with excellent swelling and extensibility during the production of polarizing films, high polarizing properties and less color unevenness Films, in particular, provide: polyvinyl alcohol-based films for the production of polarizing films that will not break during the manufacture of thin polarizing films, and also provide: polyvinyl alcohol-based films for the production of polarizing films Polarizing film, polarizing plate, and manufacturing method of polyvinyl alcohol-based film for manufacturing polarizing film. [Means to solve the problem]

In view of the situation, the inventors of the present case have conducted in-depth studies and found that the ratio of the swelling degree X (%) in the width direction (TD direction) to the swelling degree Y (%) in the traveling direction (MD direction) is within a specific range. The polyvinyl alcohol-based film has excellent swelling properties and extensibility during the production of the polarizing film, and the polarizing film obtained by using the polyvinyl alcohol-based film has high polarization performance and less color unevenness.

That is, the first gist of the present invention is: a polyvinyl alcohol-based film for producing a polarizing film, which has a thickness of 5-60 μm, a width of 2m or more, and a length of 2km or more, and is characterized in that the polyvinyl alcohol-based film is 30 When immersed in water at ℃ for 15 minutes, the swelling degree X (%) in the width direction (TD direction) and the swelling degree Y (%) in the length direction (MD direction) satisfy the following conditions (1) and (2): ( 1)110≦Y≦140; (2)1.01≦Y/X≦1.2.

In particular, when the polyvinyl alcohol-based film is immersed in water at 30°C for 15 minutes, the degree of swelling Z (%) in the thickness direction meets the following condition (3) as the polyvinyl alcohol-based film used to manufacture the polarizing film The second gist of the present invention: (3) 140≦Z≦170.

In addition, the characteristics are the deviation ΔX (%) of the swelling degree X (%) in the width direction (TD direction), the deviation ΔY (%) of the swelling degree Y (%) in the length direction (MD direction), and the thickness direction The deviation ΔZ (%) of the swelling degree Z (%) is within 5% of the polyvinyl alcohol-based film used to manufacture the polarizing film as the third gist of the present invention.

Furthermore, a polyvinyl alcohol-based film for producing a polarizing film characterized by satisfying the following conditions (4) and (5) is regarded as the fourth gist of the present invention: (4) In-plane retardation Rxy (nm): 100~ 200nm; (5) The crossing angle θ(°) between the alignment axis, that is, the slow axis and the width direction, that is, the TD direction, is 20° or less; where the in-plane phase difference Rxy(nm) is in the polyvinyl alcohol-based film , The refractive index in the width direction (TD direction) is nx, the refractive index in the length direction (MD direction) is ny, and the thickness is d(nm), the value calculated by the following formula (A): (A)Rxy(nm) )=|nx-ny|×d(nm).

In particular, a polyvinyl alcohol-based film for producing a polarizing film characterized by the deviation ΔRxy (nm) of the in-plane phase difference Rxy (nm) in the width direction (TD direction) of 10 nm or less is the fifth gist of the present invention.

Among them, a polyvinyl alcohol-based film for producing a polarizing film characterized by a deviation Δθ (°) of the crossing angle θ (°) of 10° or less is the sixth gist of the present invention.

In addition, a polyvinyl alcohol-based film for producing a polarizing film characterized by a thickness of 5 to 30 μm is regarded as the seventh gist of the present invention.

In addition, the present invention has a polarizing film characterized by using the aforementioned polyvinyl alcohol-based film for manufacturing the polarizing film as the eighth aspect.

In addition, the present invention takes a polarizing plate characterized by comprising the above-mentioned polarizing film and a protective film provided on at least one side of the above-mentioned polarizing film as the ninth gist.

Furthermore, the present invention provides a method for producing a polyvinyl alcohol-based film for producing a polarizing film, which is to form a film with an aqueous solution of a polyvinyl alcohol-based resin by a continuous casting method, and after peeling from the casting mold, move it in the direction of travel (MD direction) The polyvinyl alcohol-based film is obtained by conveying, continuously drying and stretching in the width direction (TD direction), which is characterized in that when the polyvinyl alcohol-based film is immersed in water at 30°C for 15 minutes, The swelling degree X (%) in the width direction (TD direction) and the swelling degree Y (%) in the traveling direction (MD direction) satisfy the following conditions (1) and (2) as the tenth key: (1) 110≦Y ≦140; (2) 1.01≦Y/X≦1.2.

In particular, a method for producing a polyvinyl alcohol-based film for producing a polarizing film characterized by stretching in the width direction (TD direction) at a stretching ratio of 1.05 to 1.5 times is the eleventh gist of the present invention.

In addition, a production method of a polyvinyl alcohol-based film for producing a polarizing film characterized by extending in the width direction (TD direction) at 50 to 150°C is the twelfth gist of the present invention.

Furthermore, a method for producing a polyvinyl alcohol-based film for producing a polarizing film characterized by the water content of the film before stretching in the width direction (TD direction) is 0.5 to 15% by weight is the 13th gist of the present invention.

Among them, it is characterized by temporarily extending more than 1.3 times in the width direction (TD direction), and then shrinking its size so that the final width direction (TD direction) stretch ratio becomes 1.05~1.5 times to make polarizing film The manufacturing method of the polyvinyl alcohol-based film is the 14th gist of the present invention.

In addition, a method for producing a polyvinyl alcohol-based film for the production of a polarizing film characterized by the dimensional change rate of the film in the direction of travel (MD direction) before and after stretching in the width direction (TD direction) is 0.8 to 1.0 as the present invention The fifteenth keynote. [Effects of Invention]

The polyvinyl alcohol-based film used to manufacture the polarizing film of the present invention can provide excellent swelling and extensibility during the manufacture of the polarizing film, and will not break even when the thin polarizing film is manufactured, and exhibits high polarization performance and less color unevenness. Polarizing film. In addition, the present invention is based on the technical idea of improving the swelling property and extensibility during the production of the polarizing film by increasing the swelling property of the polyvinyl alcohol-based film in the traveling direction (MD direction).

The present invention will be described in detail below. The polyvinyl alcohol-based film for producing a polarizing film of the present invention has a thickness of 5-60 μm, a width of 2 m or more, and a length of 2 km or more, and has the following characteristics. Specifically, an aqueous solution of a polyvinyl alcohol-based resin is formed into a film by a continuous casting method. After the film formed by the film is peeled from the casting mold, it is continuously conveyed in the traveling direction (MD direction). It is obtained by drying and stretching in the width direction (TD direction).

The degree of swelling X (%) in the width direction (TD direction) and the degree of swelling in the traveling direction (MD direction) of the polyvinyl alcohol film produced by the above method of the present invention when immersed in water at 30°C for 15 minutes Y (%) is a physical property value that satisfies both of the following conditions (1) and (2). This is the characteristic of the present invention. Even if only one of the physical properties is satisfied, the purpose of the invention cannot be achieved. (1)110≦Y≦140; (2)1.01≦Y/X≦1.2.

The above conditions (1) and (2) can be achieved, for example, by stretching in the width direction (TD direction) of the film obtained by forming the film. In this case, the stretching ratio is preferably 1.05 to 1.5 times, and 1.1 to 1.45 times. Especially good, 1.2~1.4 times better. If the extension ratio in the width direction (TD direction) is too low or too high, there will be control and phase difference of the swelling degree X (%) in the width direction (TD direction) and the swelling degree Y (%) in the traveling direction (MD direction) It tends to be difficult to control, and the swelling property and extensibility of the polarizing film during the production of the polarizing film tend to decrease.

The condition (1) specifies the degree of swelling Y (%) in the direction of travel (MD direction), which is within the scope of the known technology. The swelling degree Y (%) must be 110% or more and 140% or less, preferably 115% or more and 135% or less, preferably 120% or more and 130% or less. If the swelling degree Y (%) does not reach the lower limit, the extensibility during the manufacture of the polarizing film will be lowered, which is not ideal. On the contrary, if the swelling degree Y (%) exceeds the upper limit, the polarization degree of the polarizing film will be lowered, which is not ideal.

Condition (2) specifies the ratio (Y/X) of the swelling degree Y (%) in the traveling direction (MD direction) to the swelling degree X (%) in the width direction (TD direction). The biggest feature of the present invention is that the degree of swelling Y (%) in the traveling direction (MD direction) is greater than the degree of swelling X (%) in the width direction (TD direction) in a specific range. In conventional polyvinyl alcohol-based films, this ratio is often 1 or less. This is because the molecular chains of polyvinyl alcohol polymers are usually aligned in the direction of travel (MD direction) and are not easy to swell in this direction.

The ratio (Y/X) of the swelling degree Y (%) in the traveling direction (MD direction) to the swelling degree X (%) in the width direction (TD direction) must meet the condition (2) 1.01≦Y/X≦1.2, preferably The following conditions (2') are met, and the following conditions (2'') are particularly preferred: (2') 1.03≦Y/X≦1.15; (2”) 1.05≦Y/X≦1.1. If the Y/X does not reach the lower limit, the extensibility of the polarizing film during manufacture will be insufficient and less ideal. On the contrary, if the Y/X exceeds the upper limit, the degree of polarization of the polarizing film will decrease and become less desirable.

In addition, when the polyvinyl alcohol film of the present invention is immersed in water at 30°C for 15 minutes, the degree of swelling Z (%) in the thickness direction should preferably satisfy the following condition (3), and it is particularly preferred that the following condition (3') is satisfied. It is even better if the following conditions (3'') are met: (3)140≦Z≦170 (3')143≦Z≦169 (3'')145≦Z≦168

The swelling degree Z (%) in the present invention is based on the swelling degree X (%) in the width direction (TD direction), the swelling degree Y (%) in the traveling direction (MD direction), and the weight of the film after immersion and the immersion The weight of the film after drying is calculated according to the following formula. Swelling degree Z(%)=1000000×weight after immersion(g)/weight after drying(g)/X/Y

If the above-mentioned swelling degree Z (%) is too low, the swelling property during the production of the polarizing film will tend to decrease. On the contrary, if it is too high, the polarization degree of the polarizing film will tend to decrease. The degree of swelling Z (%) can be clearly seen from the conditions (1), (2), and (3), which is larger than the degree of swelling in the width direction (TD direction) and the degree of swelling in the traveling direction (MD direction). This is because the molecular chain of the polyvinyl alcohol polymer becomes a chemical structure that is mainly aligned in the plane direction and is easy to swell in the thickness direction. Due to this chemical structure, the polyvinyl alcohol-based film can be quickly and uniformly swelled in the swelling step during the production of the polarizing film.

In addition, the deviation ΔX(%) of the swelling degree X (%) in the width direction (TD direction) of the polyvinyl alcohol film of the present invention, and the deviation ΔY (%) of the swelling degree Y (%) in the traveling direction (MD direction) %), and the deviation ΔZ (%) of the swelling degree Z (%) in the thickness direction are all within 5%, preferably within 4%, and even better within 3%. If the shift is too large, the polarizing film tends to have uneven color.

In addition, in the present invention, as a method for satisfying the conditions (1), (2), and (3), in addition to performing the film peeled from the casting mold in the width direction (TD direction) as in the present invention In addition to the method of stretching, a method of adjusting the drying conditions of the polyvinyl alcohol-based resin aqueous solution, a method of adjusting the chemical structure of the polyvinyl alcohol-based resin, and the like can also be cited.

In addition, the polyvinyl alcohol-based film produced by the above method preferably satisfies the physical property values of both the following conditions (4) and (5): (4) In-plane retardation Rxy(nm): 100~200nm; 5) The intersection angle θ (°) between the alignment axis (slow phase axis) and the width direction (TD direction) is 20° or less. Here the in-plane retardation Rxy (nm) is based on the fact that in the polyvinyl alcohol film, the refractive index in the width direction (TD direction) is nx, the refractive index in the traveling direction (MD direction) is ny, and the thickness is d (nm) When the value is calculated by the following formula (A): (A) Rxy(nm)=|nx-ny|×d(nm).

The in-plane phase difference Rxy (nm) is particularly preferably 110 to 180 nm, and even more preferably 130 to 170 nm. If the in-plane retardation Rxy (nm) is too small, the extensibility in the MD direction during the production of the polarizing film will tend to decrease, and if it is too large, the color of the polarizing film will tend to be uneven.

The shift ΔRxy (nm) of the in-plane retardation Rxy (nm) in the width direction (TD direction) is preferably 10 nm or less, particularly preferably 5 nm or less, and more preferably 3 nm or less. If the deviation ΔRxy is too large, the polarizing film tends to have uneven color.

The intersection angle θ (°) between the alignment axis (slow phase axis) and the width direction (TD direction) is preferably 20° or less, particularly preferably 10° or less, and even more preferably 5° or less. If the crossing angle θ (°) is too large, the stretchability in the MD direction during the production of the polarizing film tends to decrease.

The offset Δθ(°) of the crossing angle θ(°) in the width direction (TD direction) is preferably 10° or less, particularly preferably 5° or less, and more preferably 3° or less. If the deviation Δθ (°) is too large, the polarizing film tends to have uneven color.

In addition, as a method of controlling the above-mentioned in-plane retardation Rxy (nm) and crossing angle θ (°), in addition to the method of extending the film peeled from the casting mold in the width direction (TD direction) as in the present invention It can also include: a method of adjusting the drying conditions of the aqueous solution, a method of adjusting the chemical structure of the polyvinyl alcohol-based resin, and the like.

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

[Membrane Material] First, the polyvinyl alcohol resin and its aqueous solution used in the present invention will be described. In the present invention, as the polyvinyl alcohol-based resin constituting the polyvinyl alcohol-based film, an unmodified polyvinyl alcohol-based resin is generally used, that is, a polyvinyl acetate obtained by polymerization of vinyl acetate is used for saponification. The resin obtained. Resins obtained by saponification of a copolymer of vinyl acetate and a small amount (usually less than 10 mol%, preferably less than 5 mol%) capable of copolymerizing with vinyl acetate can also be used according to needs. Examples of components that can be copolymerized with vinyl acetate include: unsaturated carboxylic acids (including, for example, salts, esters, amides, nitriles, etc.); olefins with 2 to 30 carbon atoms (e.g., ethylene, propylene, n-butene, etc.) , Isobutylene, etc.); vinyl ethers; unsaturated sulfonates, etc. In addition, modified polyvinyl alcohol-based resins obtained by chemically modifying saponified hydroxyl groups can also be used. These can be used individually or in combination of 2 or more types.

In addition, as a polyvinyl alcohol-based resin, it can also be used for a polyvinyl alcohol-based resin having a 1,2-diol structure in the side chain. The polyvinyl alcohol resin having a 1,2-diol structure in the side chain can be obtained by the following method, for example: (i) Combining vinyl acetate with 3,4-diethoxy-1-butene The method of saponifying the copolymer of ethylene; (ii) the method of saponifying and decarboxylating the copolymer of vinyl acetate and ethylene ethylene carbonate; (iii) the method of combining vinyl acetate with 2,2-dialkyl-4-ethylene The method of saponification and deketalization of the copolymer of base-1,3-dioxolane; (iv) the method of saponifying the copolymer of vinyl acetate and glycerol monoallyl ether, etc.

The weight average molecular weight of the polyvinyl alcohol resin is preferably 100,000 to 300,000, preferably 110,000 to 280,000, and even more preferably 120,000 to 260,000. If the weight average molecular weight is too small, it will be difficult to obtain sufficient optical performance when using a polyvinyl alcohol-based resin as an optical film. If it is too large, it may become difficult to stretch when using a polyvinyl alcohol-based film to produce a polarizing film. The tendency. In addition, the weight average molecular weight of the above-mentioned polyvinyl alcohol-based resin is measured by the GPC-MALS method.

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

As the polyvinyl alcohol-based resin used in the present invention, two or more types of modified species, modified amount, weight average molecular weight, average saponification degree, and other different ones may also be used in combination.

As far as the aqueous solution of polyvinyl alcohol resin is concerned, in addition to containing polyvinyl alcohol resin, if necessary, it may contain glycerin, diglycerin, triglycerin, ethylene glycol, triethylene glycol, polyethylene glycol, and triethylene glycol. In the case of commonly used plasticizers such as methyl propane, or at least one of nonionic, anionic, and cationic surfactants, it is preferable to consider film forming properties. These can be used individually or in combination of 2 or more types.

The resin concentration of the polyvinyl alcohol-based resin aqueous solution obtained in this way is preferably 15-60% by weight, particularly preferably 17-55% by weight, and even more preferably 20-50% by weight. If the resin concentration of the aqueous solution is too low, the drying load will increase and the productivity will tend to decrease. If it is too high, the viscosity will become too high and it will tend to be difficult to dissolve uniformly.

Then, the obtained polyvinyl alcohol-based resin aqueous solution is subjected to a defoaming treatment. Examples of defoaming methods include: static defoaming, defoaming using a multi-screw extruder, and the like. As the multi-axis extruder, if it is a multi-axis extruder with vent holes, a bi-axis extruder with vent holes is usually used.

[Film forming step] After the defoaming treatment, a certain amount of the polyvinyl alcohol-based resin aqueous solution is successively introduced into the T-shaped slot mold, discharged and cast on a rotating casting drum, and the film is formed by a continuous casting method.

The continuous casting method in the present invention refers to, for example, a method of spitting out an aqueous solution of a polyvinyl alcohol resin from a T-slot mold and casting it on a casting mold such as a rotating casting drum, an endless belt, and a resin film to form a film. After the film formed by the film is peeled from the casting mold, it is conveyed in the advancing direction (MD direction) and continuously dried with a hot roll. For example, it may be heat-treated with a floating dryer.

The resin temperature of the polyvinyl alcohol resin aqueous solution at the outlet of the T-slot die is preferably 80~100℃, and 85~98℃ is particularly good. If the resin temperature of the polyvinyl alcohol-based resin aqueous solution is too low, there will be a tendency for poor flow, and if it is too high, there will be a tendency for foaming.

The viscosity of the polyvinyl alcohol-based resin aqueous solution is preferably 50~200Pa･s when spitting out, especially 70~150Pa･s. If the viscosity of the aqueous solution is too low, the flow will tend to be poor, and if it is too high, the casting will tend to become difficult.

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

The diameter of the casting drum is preferably 2~5m, 2.4~4.5m is particularly preferred, and 2.8~4m is even better. If the diameter is too small, the drying zone on the casting drum will be shortened and the speed will tend to be difficult to increase. If the diameter is too large, the transportability will tend to decrease.

The width of the casting drum is preferably 4m or more, particularly preferably 4.5m or more, more preferably 5m or more, and particularly preferably 5-6m. If the width of the casting drum is too small, productivity tends to decrease.

The rotation speed of the casting drum is preferably 3~50m/min, 4~40m/min is particularly preferred, and 5~35m/min is even more preferred. If the 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 casting drum is preferably 40~99℃, and 60~95℃ is particularly good. If the surface temperature is too low, there will be a tendency for poor drying, and if it is too high, there will be a tendency for foaming.

[Film obtained by film forming] The film [film before stretching in the width direction (TD direction)] obtained by forming the film as described above preferably has a moisture content of 0.5 to 15% by weight, and 1 to 13% by weight. Preferably, it is 2-12% by weight and even more preferably. Regardless of whether the water content is too low or too high, the alignment of the target polymer, that is, the display of the target swelling degree and extensibility tends to be difficult.

In order to adjust the moisture content, when the moisture content of the film before stretching in the width direction (TD direction) is too high, it is advisable to dry the film before stretching in the width direction (TD direction). Conversely, when the film is stretched in the width direction (TD direction). When the moisture content of the film before stretching is too low, it is advisable to adjust the humidity before stretching in the width direction (TD direction). It is more preferable to adjust the conditions of the drying step so that the moisture content falls within the above-mentioned range.

The drying can be carried out by a known method using heating rollers, infrared heaters, etc. In the present invention, multiple heating rollers are ideally used. The temperature of the heating rollers is particularly preferably 40~150℃, and even more preferably 50~120℃ . In addition, in order to adjust the moisture content, a humidity control zone may be provided before extending in the width direction (TD direction).

[Conveying and stretching steps] Then, while the film is formed as described above and the water content is adjusted, the film is conveyed in the traveling direction (MD direction), and continuously or intermittently in the width direction (TD direction) extend.

In the present invention, it is not necessary to particularly stretch the film formed into the film in the advancing direction (MD direction), and it is sufficient to carry it with a stretching tension such that the film does not bend. Of course, due to the extension in the width direction (TD direction), the shrinkage depends on Poisson's ratio in the travel direction (MD direction), and syneresis also occurs in the travel direction (MD direction) during drying, so The film shrinks slightly in the direction of travel (MD direction).

Moreover, it is not suitable to extend in the direction of travel (MD direction) to the extent that the dimensions in the direction of travel (MD direction) can stretch. Before and after the extension in the width direction (TD direction), the dimensional change rate in the travel direction (MD direction) is preferably 0.8~1.0, particularly preferably 0.9~1.0, and even more preferably 0.95~1.0. If the dimensional change rate is too small or too large, the deviation of the swelling degree tends to increase, and the alignment of the target polymer, that is, the development of the target swelling degree tends to become difficult.

The ideal range of the conveying speed of the film obtained by film formation in the traveling direction (MD direction) is 5-30m/min, 7-25m/min is particularly preferred, and 8-20m/min is even more preferable. If the conveying speed is too slow, the productivity tends to decrease, and if it is too fast, the color unevenness of the polarizing film tends to increase.

There are no particular restrictions on the method of simultaneously carrying the film obtained by film formation in the traveling direction (MD direction) and extending in the width direction (TD direction). For example, the two ends of the film in the width direction are held by a plurality of clamps. It is ideal to carry out handling and extension at the same time. At this time, the arrangement of the clamps at the respective ends is preferably 200mm or less, particularly preferably 100mm or less, and even more preferably 50mm or less. If the distance between the clamps is too wide, the stretched film may be bent, or the thickness of both ends in the width direction of the obtained polyvinyl alcohol-based film may become uneven and the retardation may become uneven. In addition, the holding position of the jig (the tip of the jig) is preferably 100 mm or less from both ends in the width direction of the film formed by the film. If the clamping position (front end) of the clamp is too positioned at the center of the film width direction, the end of the film to be discarded will increase and the product width will tend to be narrow.

The polyvinyl alcohol-based film system specified in the present invention can be achieved by stretching in the width direction (TD direction) of the film obtained by forming the film as described above. The stretching ratio at this time is preferably 1.05~1.5 times , 1.1~1.45 times is particularly good, 1.15~1.4 times is even better, 1.2~1.3 times is particularly good. Even if the stretching ratio in the width direction (TD direction) is too low or too high, the swelling and extensibility during the production of the polarizing film tend to decrease.

The continuous stretching step in the width direction (TD direction) may be one stage (1 time) or multiple stages (multiple times) so that the total stretch magnification falls within the range of the above stretch magnification (also referred to as successive stretch). For example, after performing the first stage of stretching, a simple conveyance that fixes the width direction (TD direction) may be performed, and then the second stage and subsequent stretching may be performed. Especially in the case of a thin film, by inserting this simple transport step, the stress of the film can be relaxed and breakage can be avoided. When inserting a transport step with a fixed width, the fixed width can also be set to be narrower than the width after the first stage of extension. The stretched film tends to shrink due to stress relaxation and also shrinks with dehydration. Therefore, the fixed width can be set as narrow as the shrinkage width. However, if it is narrower than the shrinkage width, it is not ideal because the film will bend. This stretching step is preferably carried out after the drying step of the film, but it may be carried out separately at least at a time point before the drying step of the film and after the drying step, or it may be carried out in the drying step.

As an ideal form of the present invention, it can also be used to temporarily stretch more than 1.3 times in the width direction (TD direction) of the film, and then make the final stretch ratio in the width direction (TD direction) 1.05~1.5 times. The method of shrinking size. 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 1.5 times the stretching ratio. With this method, the stress of the film can be relaxed, especially in the case of a thin film to avoid breakage.

In the present invention, the stretching of the film obtained by forming the film in the width direction (TD direction) is preferably carried out at 50 to 150°C, particularly preferably at 60 to 140°C, and even more preferably at 70 to 130°C. Even if the stretching temperature is too low or too high, the stretchability tends to decrease during the production of the polarizing film. When performing successive extensions and intermittent extensions, the extension temperature can also be changed at each extension stage, and the temperature gradient can also be set during extension.

In the present invention, the elongation time of the film obtained by forming the film in the width direction (TD direction) is preferably 2 to 60 seconds, particularly preferably 5 to 45 seconds, and more preferably 10 to 30 seconds. good. If the elongation time is too short, the film tends to break easily. On the contrary, if it is too long, the equipment load tends to increase. When implementing successive extensions, the extension time can also be changed at each extension stage.

In the present invention, after the film formed by the film is stretched in the width direction (TD direction), heat treatment may be performed with a floating dryer or the like. The heat treatment temperature is preferably 60~200°C, 70~150°C is particularly preferred, and 100~140°C is even more preferred. If the heat treatment temperature is too low, the dimensional stability tends to be easily reduced. On the contrary, if the heat treatment temperature 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, and 5 to 30 seconds is particularly preferred. If the heat treatment time is too short, the dimensional stability will tend to decrease. Conversely, if the heat treatment time is too long, the swelling and elongation during the production of the polarizing film will tend to decrease.

[Polyvinyl alcohol-based film for producing a polarizing film] In this way, the polyvinyl alcohol-based film for producing a polarizing film of the present invention is obtained, and it is finally wound on a roll to become a product. The thickness of the polyvinyl alcohol-based film is preferably 5-60μm from the viewpoint of in-plane retardation. From the viewpoint of thinning of the polarizing film, it is particularly preferably 5~45μm, and even more preferably 5-30μm, from the viewpoint of avoiding breakage. 10~20μm is particularly good. The thickness of the polyvinyl alcohol-based film is adjusted by the resin concentration in the polyvinyl alcohol-based resin aqueous solution, the discharge amount (discharge rate) to the casting mold, the stretching ratio, and the like.

The width of the polyvinyl alcohol-based film is preferably 2 m or more, particularly preferably 3 m or more in view of increasing the area, and 4 to 6 m or more in view of avoiding breakage.

The length of the polyvinyl alcohol-based film is preferably 2 km or more, particularly preferably 3 km or more from the viewpoint of increasing the area, and more preferably 3 to 50 km from the viewpoint of transport weight.

The polyvinyl alcohol-based film for producing the polarizing film of the present invention is very effective as a raw material roll film of the polarizing film. Hereinafter, a method for manufacturing a polarizing film and a polarizing plate composed of the polyvinyl alcohol-based film will be described.

[Method for manufacturing polarizing film] The polarizing film of the present invention is produced by transferring the above-mentioned polyvinyl alcohol-based film from a roller in a horizontal direction, and undergoing steps such as swelling, dyeing, boric acid crosslinking, stretching, washing, and drying.

The swelling step is implemented before the dyeing step. The swelling step not only can clean the dirt on the surface of the polyvinyl alcohol-based film, but 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. If the main component of the treatment liquid is water, a small amount of additives such as iodinated compounds, surfactants, and alcohols can 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.

In this swelling step, the degree of swelling of the polyvinyl alcohol-based film of the present invention is as described above. When the degree of swelling of the film is measured after being immersed in water at 30°C for 15 minutes, the degree of swelling in the width direction (TD direction) X( %) and the degree of swelling Y (%) in the direction of travel (MD direction). Physical property values satisfying both of the following conditions (1) and (2): (1)110≦Y≦140; (2)1.01≦Y/ X≦1.2.

In addition, as described above, it is desirable that the degree of swelling Z (%) in the thickness direction satisfies the following condition (3): (3) 140≦Z≦170.

The dyeing step is performed by contacting the film with a liquid containing iodine or a dichroic dye. Usually, an aqueous solution of iodine-potassium iodide is used. The concentration of iodine is 0.1~2g/L, and the concentration of potassium iodide is 1~100g/L. The dyeing time is about 30 to 500 seconds, which is practical. The temperature of the treatment bath should be 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 implemented using boron compounds such as boric acid and borax. The boron compound is used in the form of an aqueous solution or a water-organic solvent mixture with a concentration of about 10 to 100 g/L. If potassium iodide is coexisted in the solution, it is preferable to stabilize the polarization performance. The temperature during the treatment is about 30~70°C, and the treatment time is preferably about 0.1~20 minutes, and extension operations can also be implemented during the treatment if necessary.

In the stretching step, the film is stretched 3-10 times in the uniaxial direction, preferably 3.5-6 times stretched. At this time, even if a slight extension is performed in a direction at right angles to the extension direction (the extent of preventing contraction in the width direction or the extension beyond that). The temperature during extension should be 40~170℃. In addition, the stretching magnification may be finally set in the aforementioned range, and the stretching operation may be performed not only once, but also multiple times in the manufacturing step.

The cleaning step can be implemented by immersing the polyvinyl alcohol-based film in water, potassium iodide, or other iodide aqueous solution, to remove precipitates generated on the surface of the film, for example. The potassium iodide concentration when using potassium iodide aqueous solution is about 1 to 80 g/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 a potassium iodide aqueous solution can also be appropriately combined and implemented.

The drying step is for example implemented: drying the film in the air at 40-80° C. for 1-10 minutes.

In this way, a polarizing film can be obtained, and the degree of polarization of the polarizing film is preferably 99.5% or more, particularly preferably 99.8% or more. If the polarization is too low, the contrast in the liquid crystal display tends to decrease. _{In addition, in general, the degree of polarization is determined by the light transmittance (H 11} ) measured at the wavelength λ when the two polarizing films are stacked so that their alignment directions are in the same direction, and the light transmittance (H 11) measured by the two polarized films. _{The light transmittance (H 1} ) measured at the wavelength λ when the films are superimposed in such a way that the alignment directions are perpendicular to each other 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 44% 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.

Then, 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 a polarizing plate with less color unevenness and excellent polarization performance.

[Method for manufacturing polarizing plate] The polarizing plate of the present invention is produced by bonding an optically isotropic resin film that is a protective film on one or both sides of the polarizing film of the present invention through an adhesive. As the protective film, for example, cellulose triacetate, cellulose diacetate, polycarbonate, polymethyl methacrylate, cycloolefin polymer, cycloolefin copolymer, polystyrene, polyether agglomerate, Films or sheets of polyarylene ester, poly(4-methylpentene), polyphenylene ether, etc.

The bonding method is implemented by a well-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 to perform pressure bonding, heating, Or irradiate active energy rays to implement.

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

The polarizing film and polarizing plate using the polyvinyl alcohol-based film of the present invention have excellent polarizing performance and are suitable for use in portable information terminals, personal computers, televisions, projectors, logo plates, desktop computers, and electronics Clocks, word processors, electronic paper, game consoles, video recorders, cameras, photo albums, thermometers, stereos, automotive and mechanical instruments, etc. LCD devices, sunglasses, anti-glare glasses, stereo glasses, wearable displays , Display components (CRT, LCD, organic EL, electronic paper, etc.) anti-reflection layer, optical communication equipment, medical equipment, building materials, toys, etc. [Example]

Hereinafter, the present invention will be explained more specifically with examples, but the present invention is not limited to the following examples as long as it does not exceed the gist. In addition, "parts" in the examples means weight basis.

In addition, the characteristics of the polyvinyl alcohol-based film in the following examples and comparative examples (swelling degree, swelling degree deviation, in-plane retardation, in-plane retardation deviation, alignment axis and width direction The measurement and evaluation of the cross angle, dimensional change rate) and the characteristics of the polarizing film (polarization, monomer transmittance, color unevenness). <Measurement conditions> [Swelling degree of polyvinyl alcohol-based film (%)] From the center and left and right ends of the obtained polyvinyl alcohol-based film in the width direction, cut out one film each with a width of 100 mm and a length of 100 mm, and It was immersed in water at 30°C for 15 minutes to swell it. From the dimensions before and after immersion, the swelling degree X (%) in the width direction (TD direction) and the swelling degree Y (%) in the traveling direction (MD direction) are calculated according to the following formula. The degree of swelling in the thickness direction Z(%) is cut out from the center part and the left and right ends of the polyvinyl alcohol-based film in the width direction, each with a width of 100mm × a length of 100mm, and immersed in water at 30°C for 15 minutes. After it swells, take out the membrane, unfold the membrane and place it on the filter paper (5A), then overlay the filter paper (5A) on the membrane, and place 150mm×150mm×4mm (4.4×10 ^-2 g/mm) on it ² ) Remove the attached water on the surface of the film on the SUS board for 5 seconds. Quickly put the film into a weighing bottle to measure the weight, and set it as the "weight after immersion". The above operation is carried out in an environment of 23°C and 50%RH. Then, the film was placed in a dryer at 105°C for 16 hours to remove moisture from the film. After that, the film was taken out and quickly placed in a weighing bottle to measure the weight, and set it as the "weight after drying". Then calculate the swelling degree Z (%) in the thickness direction according to the following formula. Swelling degree X(%)=100×width in TD direction after immersion (mm)/width in TD direction before immersion (mm) Swelling degree Y(%)=100×width in MD direction after immersion (mm)/ Width in the MD direction before immersion (mm) Swelling degree Z (%) = 1000000 × weight after immersion (g) / weight after drying (g) / X/Y

[Deviation of swelling degree (%)] The value of swelling degree X (%) in the width direction (TD direction) obtained from the above measurement (3 points between the center and the left and right ends), taking the maximum and minimum values The difference of is defined as the deviation ΔX (%) of the degree of swelling in the width direction (TD direction). Similarly, the deviation ΔY (%) of the degree of swelling in the traveling direction (MD direction) and the deviation ΔZ (%) of the degree of swelling in the thickness direction are obtained.

[In-plane phase difference Rxy (nm), in-plane phase difference offset ΔRxy (nm), alignment axis (late axis) and width direction (TD direction) crossing angle θ (°) and crossing angle θ offset Δθ(°)] A test piece of length 4cm×width 4cm was cut out from the center part in the width direction of the obtained polyvinyl alcohol-based film and the left and right ends (inside 10cm from the edge of the film), and a phase difference measuring device was used ( "KOBRA-WR" manufactured by Oji Measuring Instruments Co., Ltd.) measures the in-plane phase difference Rxy (nm) and the intersection angle θ (°) between the alignment axis (slow phase axis) and the width direction (TD direction). In addition, among the in-plane phase difference Rxy (nm) between the center part in the width direction and the left and right end parts obtained by the above measurement, the difference between the maximum value and the minimum value is taken as the deviation of the in-plane phase difference ΔRxy (nm) ). In addition, among the crossing angle θ (°) between the center part and the left and right end parts in the width direction obtained by the above measurement, the difference between the maximum value and the minimum value is taken as the offset Δθ (°) of the crossing angle θ (°) ).

[Dimensional change rate] Before extending in the width direction (TD direction), mark (2 points) at the distance of lm in the travel direction (MD direction) of the strange pen. After extending in the width direction (TD direction), measure the distance L(m) between the two points with a vernier caliper, and calculate the size change rate according to the following formula: Size change rate=L(m)/l(m).

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

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

<Example 1> (Production of polyvinyl alcohol-based film) 1,000 kg of polyvinyl alcohol-based resin with a weight average molecular weight of 142,000 and a degree of saponification of 99.8 mol%, 2,500 kg of water, 105 kg of glycerin as a plasticizer, and an interface 0.25 kg of polyoxyethylene laurylamine as the active agent is put into a 5,000L dissolution tank, and the temperature is raised to 150°C under stirring to perform pressure dissolution, and the concentration is adjusted to obtain a polyvinyl alcohol resin with a resin concentration of 25% by weight Aqueous solution. Then, the aqueous solution of the polyvinyl alcohol-based resin was supplied to a biaxial extruder for defoaming, and the temperature of the aqueous solution was set to 95°C, and the solution was discharged from the discharge port of the T-slot die (discharge speed 2.5m/min) and cast on the rotary The casting roller is used to make the film. The film obtained by forming the film was peeled from the casting roll, and while being conveyed in the advancing direction (MD direction), the surface and the back surface of the film were alternately contacted with a total of 10 heating rollers to perform drying. Thereby, 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 film were clamped with a clamp pitch of 45mm, and the film was transported in the advancing direction (MD direction) at a speed of 8m/min, while using a stretcher to carry out 1.2 in the width direction (TD direction) at 120°C. Fold extension. Before and after the extension in the width direction (TD direction), the dimensional change rate in the traveling direction (MD direction) was 0.96. Finally, heat treatment was performed at 120°C for 10 seconds to obtain a polyvinyl alcohol-based film (width 2.4 m, thickness 50 μm, length 2 km). The characteristics of the obtained polyvinyl alcohol-based film are shown in Table 1 and Table 2.

(Production of polarizing film and polarizing plate) The obtained polyvinyl alcohol-based film is taken from the roll and transported in the horizontal direction, while immersing it in a water tank with a water temperature of 30°C and swelling, it moves in the direction of travel (MD Direction) 1.7 times extension. Then, it was immersed in a 30°C aqueous solution composed of 0.5 g/L of iodine and 30 g/L of potassium iodide for dyeing, and stretched 1.6 times in the direction of travel (MD direction), and then immersed in 40 g/L of boric acid. , In a 30g/L potassium iodide aqueous solution (50°C), while performing boric acid cross-linking, 2.1 times uniaxially stretched in the direction of travel (MD direction). 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 fracture occurred during this manufacturing. The characteristics of the obtained polarizing film are shown in Table 2. A polyvinyl alcohol aqueous solution was used as an adhesive to bond a triacetyl cellulose film with a film thickness of 40 μm on both sides of the polarizing film obtained above, and dried at 70° C. to obtain a polarizing plate.

<Example 2> In Example 1, the film formed into a film was stretched 1.4 times in the width direction (TD direction) at 120°C using a stretching machine, and then a fixed width of 2.4m (equivalent to 1.2 times stretching) Except for conveying, it carried out similarly to Example 1, and obtained the polyvinyl alcohol-type film (width 2.4m, thickness 50 micrometers, length 2km). Before and after the extension in the width direction (TD direction), the dimensional change rate in the travel direction (MD direction) was 0.96. The characteristics of the obtained polyvinyl alcohol-based film are shown in Table 1 and Table 2. In addition, using this polyvinyl alcohol-based film, the same procedure as in Example 1 was carried out to obtain a polarizing film and a polarizing plate. No fracture occurred during this manufacturing. The characteristics of the obtained polarizing film are shown in Table 2.

<Example 3> In Example 1, the discharge rate during film formation was set to 0.8 m/min, and a film (width 2 m, thickness 20 μm) with a moisture content of 5 wt% was performed in the width direction (TD direction) of 1.4 After double-stretching, it was conveyed with a fixed width of 2.6 m (corresponding to 1.3-fold stretch), except that it was carried out in the same manner as in Example 1 to obtain a polyvinyl alcohol-based film (width 2.6 m, thickness 15 μm, length 2 km). Before and after the extension in the width direction (TD direction), the dimensional change rate in the traveling direction (MD direction) was 0.98. The characteristics of the obtained polyvinyl alcohol-based film are shown in Table 1 and Table 2. In addition, using this polyvinyl alcohol-based film, the same procedure as in Example 1 was carried out to obtain a polarizing film and a polarizing plate. Although the polyvinyl alcohol-based film of the raw material roll is thin, it did not break during the stretching step during the production of the polarizing film. The characteristics of the obtained polarizing film are shown in Table 3.

<Comparative Example 1> In Example 1, the film obtained by forming the film was not stretched in the width direction (TD direction) using a stretching machine, but it was carried out in the same manner as in Example 1 to obtain poly Vinyl alcohol film (width 2m, thickness 60μm, length 2km). The characteristics of the obtained polyvinyl alcohol-based film are shown in Table 1 and Table 2. In addition, using this polyvinyl alcohol-based film, the same procedure as in Example 1 was carried out to obtain a polarizing film and a polarizing plate. The characteristics of the obtained polarizing film are shown in Table 3.

<Comparative Example 2> In Example 3, the film obtained by forming the film was not stretched in the width direction (TD direction) using a stretching machine, and it was carried out in the same manner as in Example 3 to obtain a poly Vinyl alcohol film (width 2m, thickness 20μm, length 2km). The characteristics of the obtained polyvinyl alcohol-based film are shown in Table 1 and Table 2. In addition, using this polyvinyl alcohol-based film, the same procedure as in Example 1 was carried out to obtain a polarizing film and a polarizing plate. The characteristics of the obtained polarizing film are shown in Table 3.

[Table 1]

[Table 2]

[table 3]

From the results of the above examples and comparative examples, it can be seen that the ratio of the swelling degree X (%) in the width direction (TD direction) to the swelling degree Y (%) in the traveling direction (MD direction) satisfies the aforementioned condition (1) The polarizing film of Examples 1 to 3 of the polyvinyl alcohol-based film in the range specified by (2) and (2) has a high degree of polarization and no color unevenness. In contrast, the ratio of the degree of swelling X (%) in the width direction (TD direction) to the degree of swelling Y (%) in the traveling direction (MD direction) is within the range specified in the aforementioned conditions (1) and (2) The polarizing films of Comparative Examples 1 and 2 of the other polyvinyl alcohol-based films had poor polarization and color unevenness was also observed.

It can also be seen that: derived from the in-plane phase difference (Rxy), and the intersection angle θ(°) between the alignment axis (late axis) and the width direction (TD direction) satisfies the aforementioned conditions (4) and (5). The polarizing film of Examples 1 to 3 of the polyvinyl alcohol-based film in the range of, which has a high degree of polarization and no color unevenness. On the other hand, it is derived from the in-plane phase difference (Rxy) and the intersection angle θ(°) between the alignment axis (late axis) and the width direction (TD direction) specified in the aforementioned conditions (4) and (5) The polarizing films of Comparative Examples 1 and 2 of the polyvinyl alcohol-based film outside the range had poor polarization and color unevenness was also observed.

The above-mentioned embodiments have disclosed specific forms of the present invention, but the above-mentioned embodiments are only examples and are not interpreted as limiting. Various changes that are obvious to those with ordinary knowledge in the technical field are all intended to be included in the scope of the present invention. [Industrial Utilization]

The polarizing film and polarizing plate using the polyvinyl alcohol-based film of the present invention have excellent polarizing performance and are suitable for use in portable information terminals, personal computers, televisions, projectors, logo plates, desktop computers, and electronics Clocks, word processors, electronic paper, game consoles, video recorders, cameras, photo albums, thermometers, stereos, automotive and mechanical instruments, etc. LCD devices, sunglasses, anti-glare glasses, stereo glasses, wearable displays , Display components (CRT, LCD, organic EL, electronic paper, etc.) anti-reflection layer, optical communication equipment, medical equipment, building materials, toys, etc.

Claims (14)

A polyvinyl alcohol-based film used to manufacture polarizing films, with a thickness of 5-60μm, a width of 2m or more, and a length of 2km or more. That is, the degree of swelling X (%) in the TD direction and the degree of swelling Y (%) in the longitudinal direction, which is the MD direction, satisfy the following conditions (1) and (2) and simultaneously satisfy the following conditions (4) and (5) ：(1)110≦Y≦140; (2)1.03≦Y/X≦1.2; (4) In-plane phase difference Rxy(nm): 100~200nm; (5) Alignment axis, that is, the slow axis and the width direction That is, the intersection angle θ (°) in the TD direction is 20° or less; here the in-plane phase difference Rxy (nm) is to make the width direction of the polyvinyl alcohol film, that is, the refractive index in the TD direction nx, and the length When the refractive index in the direction, that is, the MD direction, is ny and the thickness is d (nm), the value calculated by the following formula (A): (A) Rxy (nm)=|nx-ny|×d(nm). For example, the polyvinyl alcohol-based film used to manufacture polarizing films in the first item of the scope of patent application, where the polyvinyl alcohol-based film is immersed in water at 30°C for 15 minutes, the swelling degree Z (%) in the thickness direction satisfies the following Condition (3): (3) 140≦Z≦170. For example, the polyvinyl alcohol film used in the first or second item of the scope of patent application for the production of polarizing film, the width direction is the offset of the swelling degree X (%) in the TD direction, and the length direction is the MD direction. The deviation ΔY (%) of the swelling degree Y (%) and the deviation ΔZ (%) of the swelling degree Z (%) in the thickness direction are both within 5%. For example, the polyvinyl alcohol-based film used to manufacture the polarizing film in the first or second item of the scope of patent application, the deviation ΔRxy (nm) of the in-plane phase difference Rxy (nm) in the width direction, that is, the TD direction, is 10 nm or less. For example, the polyvinyl alcohol film used to manufacture the polarizing film in item 1 or 2 of the scope of patent application, the deviation Δθ(°) of the crossing angle θ(°) is less than 10°. For example, the thickness of the polyvinyl alcohol film used to manufacture the polarizing film in the first or second item of the scope of patent application is 5-30μm. A polarizing film, which is characterized by using a polyvinyl alcohol-based film for manufacturing a polarizing film as in any one of items 1 to 6 in the scope of the patent application. A polarizing plate, which is characterized by having: a polarizing film as claimed in item 7 of the scope of patent application; and a protective film arranged on at least one side of the polarizing film. A method for manufacturing polyvinyl alcohol-based films for the production of polarizing films. An aqueous solution of polyvinyl alcohol-based resin is formed by continuous casting. After being peeled from the casting mold, it is transported in the direction of travel, that is, in the MD direction. , While continuously drying and stretching in the width direction, that is, the TD direction, a polyvinyl alcohol-based film is obtained, It is characterized in that when the polyvinyl alcohol-based film is immersed in water at 30°C for 15 minutes, the swelling degree X (%) in the width direction, that is, the TD direction, and the swelling degree Y (%) in the direction of travel, that is the MD direction, satisfy The following conditions (1) and (2) and the following conditions (4) and (5) are met at the same time: (1) 110≦Y≦140; (2) 1.03≦Y/X≦1.2; (4) In-plane phase Difference Rxy(nm): 100~200nm; (5) The intersection angle θ(°) between the alignment axis, that is, the slow axis and the width direction, that is, the TD direction, is less than 20°; here the in-plane phase difference Rxy(nm), When the width direction of the polyvinyl alcohol film is nx, the refractive index in the MD direction is ny, and the thickness is d (nm), it can be calculated by the following formula (A) The value of: (A)Rxy(nm)=|nx-ny|×d(nm). For example, the manufacturing method of the polyvinyl alcohol-based film used to manufacture the polarizing film in the 9th item of the scope of patent application is stretched at a stretching ratio of 1.05 to 1.5 times in the width direction, that is, the TD direction. For example, the manufacturing method of the polyvinyl alcohol-based film used to manufacture the polarizing film of the 9th or 10th item of the scope of patent application is to implement the extension in the width direction, that is, the TD direction at 50~150°C. For example, the method for manufacturing a polyvinyl alcohol film for manufacturing a polarizing film in the 9th or 10th patent application, the water content of the film before stretching in the width direction, that is, in the TD direction, is 0.5-15% by weight. For example, the manufacturing method of the polyvinyl alcohol film used to manufacture the polarizing film of the 9th or 10th patent application, which temporarily extends more than 1.3 times in the width direction, that is, the TD direction, and then the final width direction, that is, the TD direction. The extension ratio becomes 1.05~1.5 times to shrink the size. For example, the manufacturing method of the polyvinyl alcohol-based film used to manufacture the polarizing film in the 9th or 10th item of the scope of patent application, before and after the extension in the width direction, that is, the TD direction, the dimensional change rate in the direction of travel of the film, that is, in the MD direction 0.8~1.0.