TWI716479B - Polyvinyl alcohol-based film and manufacturing method of polarizing film, polarizing plate and polyvinyl alcohol-based film using the polyvinyl alcohol-based film - Google Patents

Abstract

The present invention is a polyvinyl alcohol-based film with a thickness of 5-60 μm, a width of 2m or more, and a length of 2km or more, and is characterized by satisfying the following formulas (1) and (2): (1) In-plane retardation Rxy≦30nm; 2) The thickness direction retardation Rth≧90nm; where the in-plane retardation Rxy (nm) and the thickness direction retardation Rth (nm) are determined by making the refractive index in the width direction (TD direction) of the polyvinyl alcohol film nx, the refractive index in the longitudinal direction (MD direction) is ny, the refractive index in the thickness direction is nz, and the thickness is d (nm), the values calculated by the following formulas (A) and (B): (A) Rxy(nm)=|nx-ny|×d(nm); (B)Rth(nm)=[(nx+ny)/2-nz]×d(nm).

Description

Polyvinyl alcohol-based film and manufacturing method of polarizing film, polarizing plate and polyvinyl alcohol-based film using the polyvinyl alcohol-based film

The present invention relates to a polyvinyl alcohol-based film, in particular to a polyvinyl alcohol-based film that can obtain a polarizing film with excellent dyeability, high polarization and less color unevenness, and a polarizing film using the polyvinyl alcohol-based film , The manufacturing method of polarizing plate and polyvinyl alcohol 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 component of liquid crystal displays. In recent years, its use in equipment requiring high quality and high reliability is expanding.

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

Generally, the polyvinyl alcohol-based 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 is peeled from the casting mold, the nip roll is used 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 transportation 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, and the optical axis (late phase) of the obtained polyvinyl alcohol-based film The axis) often faces the MD direction. If the alignment in the MD direction is too large, the in-plane phase difference of the polyvinyl alcohol-based film will increase, which will eventually lead to a decrease in the polarization performance of the polarizing film. Conversely, in the width direction (TD direction) of the film obtained by forming the film, there will be shrinkage stress that depends on Poisson's ratio and shrinkage stress due to dehydration. Therefore, if the stress in the TD direction is used , Can also make the polyvinyl alcohol-based polymer have a certain degree of alignment in the TD direction. At this time, the optical axis of the obtained polyvinyl alcohol-based film is oriented between the MD direction and the TD direction, and the in-plane phase difference tends to decrease.

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), and then 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 direction of travel (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, in the production of polarizing films, there are cases where the sequence of the stretching step and the dyeing step is reversed. That is, a case where the polyvinyl alcohol-based film, which is the raw material roll, 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 Polarization performance, 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 when manufacturing the polarizing film.

As a method of improving swelling properties, for example, a method of adding a polyol 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 stretchability, for example, a method of specifying the ratio of the speed of the casting drum to the final winding speed of the film when the film is formed into a film (for example, refer to Patent Document 2), the film is formed by the casting drum A method of suspending and drying (for example, refer to Patent Document 3), and a method of controlling the stretching condition of a film obtained by film formation in the drying step (for example, refer to Patent Document 4). In addition, some have proposed a polyvinyl alcohol-based film with reduced in-plane retardation (for example, refer to Patent Documents 5 and 6). [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 Application Publication No. 2006-291173 [Patent Document 6] Japanese Patent Application Publication No. 2007-137042

[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 swellability can be improved, the alignment state of the polyvinyl alcohol-based polymer is not considered, and it is difficult to improve the extensibility during the production of the polarizing film. On the contrary, there is a tendency that the alignment state of the polymer is disturbed due to the addition of a water swelling agent, and uniform stretching tends not to be performed.

The above-mentioned Patent Document 2 specifies the degree of extension in the MD direction (stretching condition) during the production of the polyvinyl alcohol-based film, but if the extension in the TD direction is not also considered, the in-plane retardation of the polyvinyl alcohol-based film cannot be reduced. Moreover, the improvement of the extensibility during the manufacture of the polarizing film is still insufficient. In general, in the production of a polarizing film, it is difficult to stretch a polyvinyl alcohol-based film that has been stretched in the MD direction and then stretch it in the MD direction. That is, it is difficult to stretch the polyvinyl alcohol polymer that has been aligned 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 polymer alignment 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 that depends on Poisson's ratio and dehydration The shrinkage stress may cause the 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, and the extensibility 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 the extensibility and swelling properties 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 extensibility and swelling properties of the polarized film cannot be improved. enough. In the techniques disclosed in Patent Documents 5 and 6, although the in-plane retardation of the polyvinyl alcohol-based film can be reduced and uniformly manufactured, the retardation in the thickness direction is not mentioned. There is room for improvement in terms of extensibility and swelling properties.

Therefore, under such a background, the present invention provides: a polyvinyl alcohol-based film that can obtain a polarizing film with excellent swelling and extensibility during the production of a polarizing film, high polarization performance, and less color unevenness, especially : A polyvinyl alcohol film that does not break during the manufacture of a thin polarizing film. It also provides: a polarizing film composed of the polyvinyl alcohol film and a method for manufacturing a polarizing plate and a polyvinyl alcohol film. [Means to solve the problem]

In view of this situation, the inventors of the present case have conducted intensive studies and found that the polyvinyl alcohol-based film with in-plane retardation (Rxy) and thickness-direction retardation (Rth) within a specific range has swelling during the production of polarized films It has excellent properties and extensibility, 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 having a thickness of 5 to 60 μm, a width of 2 m or more, and a length of 2 km or more, and is characterized by satisfying the following formulas (1) and (2): (1) plane Inner retardation Rxy≦30nm (2) Thickness direction retardation Rth≧90nm where in-plane retardation Rxy(nm) and thickness direction retardation Rth(nm) are related to the width direction (TD) of the polyvinyl alcohol film The refractive index in the direction) is nx, the refractive index in the longitudinal direction (MD direction) is ny, the refractive index in the thickness direction is nz, and the thickness is d (nm), respectively, calculated by the following formulas (A) and (B) Value: (A)Rxy(nm)=|nx-ny|×d(nm) (B)Rth(nm)=[(nx+ny)/2-nz]×d(nm)

In particular, a polyvinyl alcohol-based film characterized by the deviation ΔRxy of the in-plane retardation Rxy in the width direction (TD direction) of 5 nm or less is the second gist of the present invention.

In addition, a polyvinyl alcohol-based film characterized by the deviation ΔRth of the thickness direction retardation Rth in the width direction (TD direction) of 30 nm or less is regarded as the third gist of the present invention.

Moreover, when measuring the swelling degree of the film after immersing in water at 30°C for 15 minutes, the swelling degree X (%) in the width direction (TD direction), the swelling degree Y (%) in the length direction (MD direction), and the thickness The swelling degree Z (%) of the direction is a polyvinyl alcohol film satisfying Z≧1.1X and Z≧1.1Y as the fourth gist of the present invention.

Among them, 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 as the fifth gist of the present invention.

In addition, a polyvinyl alcohol-based film characterized by a thickness of 5 to 30 μm is the sixth gist of the present invention.

In addition, the present invention provides a polarizing film characterized by using the aforementioned polyvinyl alcohol-based film as the seventh feature.

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

In addition, the present invention provides a method for producing a polyvinyl alcohol-based film, which is to form a film by a continuous casting method with an aqueous solution of a polyvinyl alcohol-based resin, and after peeling from the casting mold, it is transported in the traveling direction (MD direction). While continuously drying and stretching in the width direction (TD direction), a polyvinyl alcohol-based film is obtained, which is characterized in that the polyvinyl alcohol-based film satisfies the following formulas (1) and (2) as the ninth point; (1) side Internal phase difference Rxy≦30nm; (2) Thickness direction phase difference Rth≧90nm; Here the in-plane phase difference Rxy(nm) and the thickness direction phase difference Rth(nm) are related to the width direction of the polyvinyl alcohol-based film The refractive index in the (TD direction) is nx, and the refractive index in the traveling direction (MD direction) is ny; when the refractive index in the thickness direction is nz and the thickness is d (nm), the following formulas (A) and (B) are respectively calculated The obtained value: (A)Rxy(nm)=|nx-ny|×d(nm); (B)Rth(nm)=[(nx+ny)/2-nz]×d(nm).

In particular, a method for producing a polyvinyl alcohol-based film characterized by being stretched 1.05 to 1.3 times in the width direction (TD direction) of the film is the tenth gist of the present invention.

In addition, a method for producing a polyvinyl alcohol-based film characterized by successively stretching in the width direction (TD direction) of the film is the eleventh gist of the present invention. [Effects of Invention]

The polyvinyl alcohol-based film of the present invention can provide a polarizing film with excellent swelling and extensibility during the manufacture of a polarizing film, even if a thin polarizing film is manufactured, it will not break, and exhibit a polarizing film with high polarization performance and less color unevenness. In addition, the swelling and extensibility of the polarizing film of the present invention depends on the alignment state of the polyvinyl alcohol-based polymer in the film, especially the alignment state in the thickness direction, so by controlling the alignment state index That is, phase difference improves swelling and extensibility.

The present invention will be explained in detail below. The polyvinyl alcohol film of the present invention has a thickness of 5 to 60 μm, a width of 2 m or more, and a length of 2 km or more, and has the following characteristics. In detail, an aqueous solution of a polyvinyl alcohol 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), and satisfies the physical property values of both the following formulas (1) and (2). Even if only one of the physical properties is satisfied, the purpose of the invention cannot be achieved. (1) In-plane retardation Rxy≦30nm; (2) Thickness direction retardation Rth≧90nm; Here in-plane retardation Rxy(nm) and thickness direction retardation Rth(nm) are related to the polyvinyl alcohol-based film When the refractive index in the width direction (TD direction) is nx, the refractive index in the traveling direction (MD direction) is ny, the refractive index in the thickness direction is nz, and the thickness is d (nm), the following formulas (A), (B) Calculated value: (A)Rxy(nm)=|nx-ny|×d(nm); (B)Rth(nm)=[(nx+ny)/2-nz]×d( nm).

The above equations (1) and (2) will be described. Equation (1) specifies the general in-plane phase difference, which is within the scope of the known technology. The in-plane phase difference Rxy (nm) of the polyvinyl alcohol-based film of the present invention must be 30 nm or less, preferably 20 nm or less, and particularly preferably 15 nm or less. If the in-plane phase difference Rxy exceeds the upper limit, the polarizing film tends to have uneven color, which is less desirable.

In the present invention, the shift ΔRxy of the in-plane phase difference Rxy in the width direction (TD direction) is preferably 5 nm or less, particularly preferably 3 nm or less, and even more preferably 2 nm or less. If the deviation ΔRxy is too large, the polarizing film tends to have uneven color.

Then, the formula (2) specifies the retardation in the thickness direction, and the biggest feature of the present invention is that the retardation Rth (nm) in the thickness direction is a positive value and a larger value greater than 90 nm. That is, in the polyvinyl alcohol film of the present invention, it has a chemical structure in which the polymer chains are mainly aligned in the plane direction and are easily swollen in the thickness direction. The thickness direction retardation Rth(nm) must be 90nm or more, preferably 100nm or more, and 110~200nm is particularly preferred. If the thickness direction retardation Rth (nm) is smaller than the lower limit value, the swelling property in the thickness direction will be lowered and less ideal. If it is too large, the surface alignment of the polymer chains will be strong and the polarizing film will face the surface direction ( MD direction and TD direction) tend to be difficult to extend.

In the present invention, the deviation ΔRth of the thickness direction retardation Rth in the width direction (TD direction) is preferably 30 nm or less, particularly preferably 20 nm or less, and even more preferably 10 nm or less. If the deviation ΔRth is too large, the polarizing film tends to have uneven color.

In addition, in order to satisfy the formulas (1) and (2), 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 is also possible to include: adjusting the drying conditions of the aqueous solution The method of adjusting the chemical structure of the polyvinyl alcohol resin, etc.

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

[Film 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, 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 as needed. 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 (such as ethylene, propylene, n-butene) , 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 vinyl acetate; (ii) The method of saponifying and decarboxylating the copolymer of vinyl acetate and ethylene vinyl 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, particularly 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 properties when using polyvinyl alcohol-based resin as an optical film. If the weight-average molecular weight 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 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 saponification degree 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 the like may 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 contains glycerin, diglycerin, triglycerin, ethylene glycol, triethylene glycol, polyethylene glycol, trihydroxy 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 defoaming treatment. Examples of defoaming methods include: static defoaming, defoaming using a multi-screw extruder, and the like. As the multi-shaft extruder, if it is a multi-shaft extruder with vent holes, a bi-axial 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 introduced into the T-shaped slot mold successively, discharged and cast on the rotating casting drum, and the film is formed by the continuous casting method.

The continuous casting method in the present invention refers to, for example, a method in which an aqueous solution of a polyvinyl alcohol resin is ejected from a T-slot die and cast on a casting mold such as a rotating casting drum, endless belt, and 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 roller. 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, it will tend to have poor flow, and if it is too high, it will tend to foam.

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 be difficult.

The discharging speed of the polyvinyl alcohol 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 better. If the rotation speed is too slow, productivity tends to decrease, and if it is too fast, drying tends to become insufficient.

The surface temperature of the casting drum is preferably 40~99℃, especially 60~95℃. 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 0.5-15% by weight, and 1-13% 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, there is a tendency that the alignment of the target polymer, that is, the expression of the target phase difference will become 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). 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 better to adjust the conditions of the drying step so that the moisture content falls within the above 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 preferably used. The temperature of the heating rollers is particularly preferably 40~150℃, and even more preferably 50~140℃ . 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 forming the film as described above and adjusting the moisture content, the film is conveyed in the traveling direction (MD direction), and in the width direction (TD direction) in a continuous and intermittent manner. At least one way to 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), necking depending on Poisson's ratio occurs in the traveling direction (MD direction), and syneresis also occurs in the traveling direction (MD direction) during drying. Due to the contraction, even if the rotation speed of the conveying roller and the heating roller is fixed, an appropriate tension can be obtained in the traveling direction (MD direction), and the complicated rotation speed control as in Patent Document 2 is not required. In addition, from the viewpoint of manufacturability, the size of the film in the traveling direction (MD direction) is preferably fixed.

In addition, while the film formed by the film is transported in the traveling direction (MD direction), stretching in both the traveling direction (MD direction) and the width direction (TD direction) will disturb the alignment of the polymer and cannot be displayed The phase difference in the in-plane and thickness direction as a target is less ideal. In particular, it is not suitable to extend to the extent that the dimensions in the direction of travel (MD direction) stretch.

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 preferred. If the conveying speed is too slow, the productivity tends to decrease, and if it is too fast, the color unevenness tends to increase.

There are no particular restrictions on the method of carrying the film obtained by film formation in the traveling direction (MD direction) and extending in the width direction (TD direction) at the same time. For example, the two ends of the film in the width direction are held by multiple 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 forming the film. If the gripping 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 narrow.

In the present invention, the stretch magnification in the width direction (TD direction) is preferably 1.05 to 1.3 times, 1.05 to 1.25 times is particularly preferable, and 1.1 to 1.2 times is even more preferable. Even if the stretch magnification in the width direction (TD direction) is too high or too low, the in-plane phase difference tends to increase.

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 stretching ratio falls within the range of the aforementioned stretching ratio (also called successive stretching). For example, after the stretching in the first stage is performed, a simple transport of fixing the width direction (TD direction) may be performed, and then the stretching after the second stage may be performed. Especially in the case of thin films, by inserting a simple transfer step with a fixed width, the stress of the film can be relaxed and breakage can be avoided. When inserting a transfer 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 implemented after the drying step of the film, but it may be implemented separately at least at a time point before the drying step of the film and after the drying step, or it may be implemented in the drying step.

As an ideal form of the present invention, it can be used to temporarily stretch more than 1.3 times in the width direction (TD direction) of the film obtained by forming the film, and then use the final stretching ratio in the width direction (TD direction) to become 1.05~ A method of shrinking its size by 1.3 times. At this time, after stretching more than 1.3 times temporarily, the film can be simply transported with a fixed width of 1.05 to 1.3 times the stretching ratio. With this method, the stress of the film can be relaxed, especially in the case of a thin film, breakage can be avoided.

In the present invention, the stretching temperature of the film obtained by forming the film in the width direction (TD direction) is preferably 50 to 150°C, particularly preferably 60 to 140°C, and even more preferably 70 to 130°C. Even if the stretching temperature is too low or too high, the in-plane phase difference tends to increase. When performing successive extensions, the extension temperature can also be changed at each extension stage.

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 extension time is too short, the film tends to break easily, and 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.

As an ideal form of the present invention, after stretching in the width direction (TD direction) at a lower temperature, the width direction (TD direction) is fixed for simple transportation, and then the second stage width direction is carried out at a higher temperature. (TD direction) extension method. Specifically, the first stage is preferably carried out at 50°C or higher, preferably 50 to 130°C, and the second stage is preferably carried out at 80°C or higher, and more preferably 80 to 150°C. With this method, drying can be performed smoothly to become a uniform polymer alignment, and the desired in-plane and thickness direction retardation can be exhibited.

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 temperature of this heat treatment is preferably 60~200℃, especially 70~150℃. 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. Moreover, 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 tends to decrease. Conversely, if the heat treatment time is too long, the extensibility during the production of the polarizing film tends to decrease.

[Polyvinyl alcohol-based film] In this way, the polyvinyl alcohol-based film of the present invention is obtained, and finally it is wound on a roll to become a product. The thickness of the polyvinyl alcohol-based film is preferably 5 to 60 μm from the viewpoint of thinning of the polarizing film, 5 to 45 μm is particularly preferable from the viewpoint of further thinning, and 5 to 30 μm is more preferable, and 5 to avoid breakage. ~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 of the present invention is very effective as a raw material roll film of a 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 the above-mentioned polyvinyl alcohol-based film extracted from a roll and transferred horizontally, and then subjected to the steps of water swelling, dyeing, boric acid crosslinking, stretching, washing, drying, etc. manufacture.

From the viewpoint of controlling the swelling degree of the polyvinyl alcohol-based film, the water swelling step is usually performed at about 30°C for 0.1 to 15 minutes.

In this water swelling step, the degree of swelling of the polyvinyl alcohol film of the present invention is: 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 (%), The degree of swelling Y (%) in the direction of travel (MD direction) and the degree of swelling Z (%) in the thickness direction satisfy Z≧1.1X and Z≧1.1Y, which is ideal. Z≧1.2X and Z≧1.2Y are particularly preferred. Z≧1.3X and Z≧1.3Y are even better. By setting the swelling degree Z (%) in the thickness direction to be greater than the swelling degree X (%) in the width direction (TD direction) and the swelling degree Y (%) in the traveling direction (MD direction), the swelling speed can be increased and It is ideal to reduce the color unevenness of the polarizing film.

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

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℃. 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 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 coexists 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.

The stretching step is to perform 3-10 times the film in the uniaxial direction, preferably 3.5-6 times the extension. At this time, even if a slight extension is performed in the direction perpendicular to the extension direction (the extent of preventing the shrinkage 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, for example, can be implemented by immersing the membrane in water, potassium iodide and other iodide aqueous solution to remove the precipitates generated on the surface of the membrane. The potassium iodide concentration when using the 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.

For example, the drying step is 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% or more, more preferably 99.5% 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 composed of 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 at the wavelength of 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.

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, Film or sheet of polyarylene ester, poly(4-methylpentene), polyphenylene ether, etc.

The bonding method is implemented by a known method, for example, by uniformly coating the liquid adhesive composition on the polarizing film, the protective film, or both, and then bonding the two together to perform pressure bonding, heating, Or irradiate active energy rays to implement.

In addition, curable resins such as urethane resins, acrylic resins, and urea resins may be coated on one side or both sides of the polarizing film, and cured to form a hardened layer to serve 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 electronic clocks , Word processors, electronic paper, game consoles, video recorders, cameras, photo albums, thermometers, stereos, automobiles, machinery and other liquid crystal display devices, sunglasses, anti-glare glasses, stereo glasses, wearable displays, Anti-reflection layers for display elements (CRT, LCD, organic EL, electronic paper, etc.), optical communication equipment, medical equipment, construction 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.

<Measurement conditions> In addition, the characteristics of the polyvinyl alcohol-based film in the following examples and comparative examples (in-plane retardation, thickness-direction retardation, in-plane retardation shift, thickness-direction retardation, etc.) were implemented as follows: Measurement and evaluation of deviation, swelling degree, swelling degree deviation) and characteristics of polarizing film (polarization degree, monomer transmittance, color unevenness). [In-plane retardation Rxy (nm), thickness direction retardation Rth (nm)] Cut out the length from the center part in the width direction of the obtained polyvinyl alcohol film and the left and right ends (inside 10 cm from the edge of the film) For the test piece of 4 cm×width 4 cm, the in-plane phase difference Rxy (nm) and thickness direction phase difference Rth (nm) at 590 nm were measured using a phase difference measuring device (manufactured by Oji Measuring Instruments Co., Ltd. "KOBRA-WR"). <Measurement conditions for Rth> Incident angle: 50° Inclination center axis: Slow phase axis Average refractive index: Value measured with Abbe refractometer

[Offset of in-plane retardation ΔRxy (nm)] Among the in-plane retardation Rxy (nm) between the center part in the width direction and the left and right ends obtained from the above measurement, the difference between the maximum value and the minimum value is taken as the phase The deviation of the difference ΔRxy (nm).

[Deflection of the thickness direction retardation ΔRth(nm)] Among the thickness direction retardation Rth(nm) between the center part in the width direction and the left and right ends obtained from the above measurement, the difference between the maximum value and the minimum value is taken as the thickness The deviation of the directional phase difference ΔRth(nm).

[Swelling degree (%)] From the center part and the left and right ends of the obtained polyvinyl alcohol-based film in the width direction, one film each with a width of 100 mm × a length of 100 mm was cut out, and immersed in water at 30°C for 15 minutes. Swelling. 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 and the left and right ends of the polyvinyl alcohol-based film in the width direction. One film each with a width of 100 mm and a length of 100 mm is cut out and immersed in water at 30°C for 15 minutes. After swelling, the membrane was taken out, and the membrane was unfolded and placed on the filter paper (5A). Then overlap the filter paper (5A) on the membrane, and place a 150mm×150mm×4mm (4.4×10 ^-2 g/mm ² ) SUS plate on it for 5 seconds to remove adhering water on the membrane surface. Quickly put this film into a weighing bottle to measure the weight, and set it as the "weight after immersion". The above operation is performed 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 put into 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 (%)] Among the swelling degrees in the width direction and the left and right ends obtained by the above measurement, the difference between the maximum value and the minimum value is taken as the swelling in the width direction (TD direction) Degree X (%) deviation ΔX (%), travel direction (MD direction) swelling degree Y (%) deviation ΔY (%), thickness direction swelling degree Z (%) deviation ΔZ (%) .

[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 of the obtained polarizing film in the width direction, and the two polarizing plates in the cross-polarized state were clamped at an angle of 45° (single transmittance of 43.5% After the polarization degree is between 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 film) 1,000 kg of polyvinyl alcohol resin with a weight average molecular weight of 142,000 and a saponification degree 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 resin concentration of 25% by weight of polyvinyl alcohol resin Aqueous solution. Then, the polyvinyl alcohol-based resin aqueous solution was supplied to a biaxial extruder for defoaming, and the temperature of the aqueous solution was set to 95°C, and the solution was discharged from the T-slot die discharge port (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 off from the casting roll, and conveyed in the advancing direction (MD direction), while 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 conveyed in the advancing direction (MD direction) at a speed of 8m/min. Using a stretcher at 120°C in the width direction (TD direction) 1.1 Stretched twice to obtain a polyvinyl alcohol film (width 2.2 m, thickness 55 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 it is immersed in a water tank with a water temperature of 30°C to swell and move 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 traveling direction (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 crosslinking, 2.1 times uniaxial stretching is performed in the traveling direction (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 the production, and the characteristics of the obtained polarizing film are shown in Table 3. 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 by the film was stretched 1.05 times in the width direction (TD direction) at 75°C using a stretching machine, and then stretched in the width direction (TD direction) at 120°C Except for stretching to 1.05 times (total stretching ratio of 1.1 times), it was carried out in the same manner as in Example 1 to obtain a polyvinyl alcohol-based film (width 2.2 m, thickness 55 μm, length 2 km). 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.

<Example 3> In Example 1, the discharge speed during film formation was set to 1.3 m/min, and a film (width 2 m, thickness 30 μm) with a moisture content of 7 wt% was performed in the width direction (TD direction) 1.1 Except for double stretching, the same procedure as in Example 1 was carried out to obtain a polyvinyl alcohol-based film (width 2.2 m, thickness 27 μm, length 2 km). 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.

<Example 4> 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) at 1.2 Except for double stretching, the same procedure as in Example 1 was carried out to obtain a polyvinyl alcohol-based film (width 2.4 m, thickness 17 μm, length 2 km). 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.

<Example 5> 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) 1.1 After double-stretching, it was transported with a fixed width of 2.2m (equivalent to 1.1-fold stretch), and then 1.1-fold stretched in the width direction (TD direction) (total stretch magnification 1.2 times), except that it was the same as Example 1 Proceed to obtain a polyvinyl alcohol-based film (width 2.4 m, thickness 17 μm, length 2 km). 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 both ends of the film formed by the film were not clamped by a clamp, and were transported at a speed of 8 m/min in the traveling direction (MD direction) and heated at 120°C. Except for this, it carried out similarly to Example 1, and obtained the polyvinyl alcohol-type film (width 2m, thickness 60 μm, 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 4, the both ends of the film formed by the film were not clamped by a clamp, and were transported at a speed of 8m/min in the traveling direction (MD direction) and heated at 120°C. Except for this, it carried out similarly to Example 4, and obtained the polyvinyl alcohol type film (width 2m, thickness 20 micrometers, 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-mentioned examples and comparative examples, it is known that the in-plane phase difference (Rxy) and the thickness-direction phase difference (Rth) are obtained from polyvinyl alcohol-based films that satisfy the ranges specified by the aforementioned formulas (1) and (2). The polarizing films of Examples 1 to 5 have high polarization and no color unevenness. On the other hand, obtained from Comparative Examples 1 and 2 of polyvinyl alcohol-based films in which the in-plane retardation (Rxy) and the thickness direction retardation (Rth) are outside the ranges specified by the aforementioned formulas (1) and (2) Polarizing film, its degree of polarization is poor and color unevenness is observed.

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

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 electronic clocks , Word processors, electronic paper, game consoles, video recorders, cameras, photo albums, thermometers, stereos, automobiles, machinery and other liquid crystal display devices, sunglasses, anti-glare glasses, stereo glasses, wearable displays, Anti-reflection layers for display elements (CRT, LCD, organic EL, electronic paper, etc.), optical communication equipment, medical equipment, construction materials, toys, etc.

no

Claims (11)

A polyvinyl alcohol-based film with a thickness of 5-60μm, a width of 2m or more, and a length of 2km or more, and is characterized by satisfying the following formulas (1) and (2): (1) In-plane retardation Rxy≦30nm; (2) Thickness The directional phase difference Rth≧90nm; where the in-plane phase difference Rxy(nm) and the thickness direction phase difference Rth(nm) are caused by making 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 MD direction is ny, the refractive index in the thickness direction is nz, and the thickness is d (nm), the values calculated by the following formulas (A) and (B): (A)Rxy(nm )=|nx-ny|×d(nm); (B)Rth(nm)=[(nx+ny)/2-nz]×d(nm). For example, the polyvinyl alcohol-based film of the first item in the scope of patent application, the deviation ΔRxy of the in-plane phase difference Rxy in the width direction, that is, the TD direction, is 5 nm or less. For example, the polyvinyl alcohol-based film of the first or second item in the scope of patent application, the deviation ΔRth of the thickness direction retardation Rth in the width direction, that is, the TD direction, is 30 nm or less. For example, when the polyvinyl alcohol film of the first or second item of the patent application is immersed in water at 30°C for 15 minutes, the swelling degree of the film is measured, the swelling degree X (%) in the width direction, that is, the TD direction, and the length direction are also That is, the degree of swelling Y (%) in the MD direction and the degree of swelling Z (%) in the thickness direction satisfy Z≧1.1X and Z≧1.1Y. For example, the polyvinyl alcohol film in the fourth item of the scope of patent application, the width direction is the offset of the swelling degree X (%) in the TD direction ΔX (%), and the length direction is the swelling degree Y (%) in the MD direction The deviation ΔY (%) and the deviation ΔZ (%) of the swelling degree Z (%) in the thickness direction are both within 5%. For example, the polyvinyl alcohol film of item 1 or 2 of the scope of patent application has a thickness of 5-30μm. A polarizing film, which is characterized by using a polyvinyl alcohol-based film as in any one of items 1 to 6 in the scope of patent application. A polarizing plate, which is characterized by having: the polarizing film of item 7 in the scope of patent application; and a protective film provided on at least one side of the polarizing film. A method for manufacturing polyvinyl alcohol-based film, which is to form a film using a continuous casting method with an aqueous solution of a polyvinyl alcohol-based resin. After being peeled from the casting mold, the film is continuously dried while being transported in the direction of travel, that is, in the MD direction. And extending in the width direction, that is, in the TD direction to obtain a polyvinyl alcohol-based film, which is characterized in that: the polyvinyl alcohol-based film satisfies the following formulas (1) and (2): (1) in-plane retardation Rxy≦30nm; 2) The thickness direction retardation Rth≧90nm; where the in-plane retardation Rxy (nm) and the thickness direction retardation Rth (nm) are determined by making the width direction of the polyvinyl alcohol film, that is, the refractive index in the TD direction nx, the direction of travel, that is, the refractive index in the MD direction is ny, the refractive index in the thickness direction is nz, and the thickness is d (nm), the values calculated by the following formulas (A) and (B) respectively: (A) Rxy(nm)=|nx-ny|×d(nm); (B)Rth(nm)=[(nx+ny)/2-nz]×d(nm). For example, the method for manufacturing a polyvinyl alcohol-based film in the scope of the patent application, which stretches 1.05 to 1.3 times in the width direction of the film, that is, the TD direction. For example, the manufacturing method of the polyvinyl alcohol-based film of the 9th or 10th item of the scope of patent application, which implements successive extension in the width direction of the film, that is, the TD direction.