KR20180072674A - POLYVINYLLOHOLOR FILM, POLARIZING MEMBRANE USING THE SAME, POLARIZING PLATE AND METHOD FOR PRODUCING POLYVINYL VOLUME LIQUID FILM - Google Patents

Abstract

When the refractive index in the width direction (TD 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) in the polyvinyl alcohol film, (A) and (B), respectively.
(A) Rxy (nm) = | nx-ny | xd (nm)
(B) Rth (nm) = {(nx + ny) / 2-nz}

Description

POLYVINYLLOHOLOR FILM, POLARIZING MEMBRANE USING THE SAME, POLARIZING PLATE AND METHOD FOR PRODUCING POLYVINYL VOLUME LIQUID FILM

The present invention relates to a polyvinyl alcohol-based film, particularly to a polyvinyl alcohol-based film having excellent dyeability and high polarization degree and capable of obtaining a polarizing film having less color unevenness and a polarizing film, a polarizing plate, and a polarizing film using the polyvinyl alcohol- And a method for producing a polyvinyl alcohol-based film.

Background Art [0002] Conventionally, a polyvinyl alcohol film has been used in many applications as a film having excellent transparency, and a polarizing film is one useful application. Such a polarizing film is used as a basic constituent element of a liquid crystal display, and in recent years, its use as a device which requires high quality and high reliability has been expanded.

Of these, a polarizing film having excellent optical characteristics is demanded in accordance with a high brightness, a high definition, a large screen, and a thinness of a screen of a liquid crystal TV or a multi-function portable terminal. Concretely, it is a further improvement of the polarization degree and resolution of color unevenness.

Generally, a polyvinyl alcohol-based film is produced from an aqueous solution of a polyvinyl alcohol-based resin by a continuous casting method. Specifically, the film is cast by casting an aqueous solution of a polyvinyl alcohol-based resin into a casting mold such as a cast drum or an endless belt, and the film thus formed is peeled off from the casting mold. Thereafter, ), And drying using a heat roll or a floating dryer. Since the film thus formed is pulled in the flow direction (MD direction) in such a conveying step, the polyvinyl alcohol-based polymer is liable to be oriented in the MD direction, and the optical axis of the obtained polyvinyl alcohol- There are a lot of directions. If the orientation in the MD direction is too large, the in-plane retardation of the polyvinyl alcohol-based film increases, and the polarization performance of the polarizing film finally decreases. Conversely, shrinkage stress due to Poisson's ratio and shrinkage stress due to dehydration are generated in the width direction (TD direction) of the film thus formed. Therefore, when such stress in the TD direction is used, the polyvinyl alcohol- It is also possible to orient it in the TD direction. In this case, the optical axis of the obtained polyvinyl alcohol-based film is oriented between the MD direction and the TD direction, and the in-plane retardation tends to be reduced.

On the other hand, in general, a polarizing film is produced by swelling a polyvinyl alcohol film as a raw material thereof with water (including hot water), then dyeing the film with a dichroic dye such as iodine and stretching. In such a swelling step, it is necessary to rapidly swell the polyvinyl alcohol-based film in the thickness direction. In addition, it is necessary to uniformly swell the dye so that the dye penetrates into the film smoothly in the dyeing step.

In the stretching process, the film after the dyeing is stretched in the flow direction (MD direction) to highly orient the dichroic dye in the film. In order to improve the polarizing performance of the polarizing film, the polyvinyl alcohol- It is necessary to have a good stretchability in the direction

In addition, a case where the order of the stretching process and the dyeing process in the polarizing film production are opposite to those described above is also carried out. That is, in the case of swelling a polyvinyl alcohol film as a disc with water (including hot water), stretching it and dying it with a dichroic dye such as iodine. In such a case, in order to improve the polarizing performance of the polarizing film, It is necessary for the alcoholic film to have good swelling properties in the thickness direction and also to have good stretchability in the MD direction.

In addition, in recent years, in order to make the polarizing film thinner, the polyvinyl alcohol film is also thinned. Such a thin film has problems of productivity such as breakage by stretching when the polarizing film is produced.

As a method for improving the swelling property, there has been proposed, for example, a method of adding a polyhydric alcohol to a polyvinyl alcohol-based resin as a water swelling auxiliary (for example, see Patent Document 1). As a method for improving the stretchability, for example, there is a method of specifying the ratio between the speed of the cast drum at the time of film formation and the final film winding speed (see, for example, Patent Document 2) There has been proposed a method of suspending a film (for example, refer to Patent Document 3), and a method of controlling a tensile state in a drying process of a film formed (see, for example, Patent Document 4). In addition, a polyvinyl alcohol-based film in which the in-plane retardation is reduced has been proposed (see, for example, Patent Documents 5 and 6).

Patent Document 1 JP2001-302867A Patent Document 2 JP2001-315141A Patent Document 3 JP2001-315142A Patent Document 4 JP2002-79531A Patent Document 5 JP2006-291173A Patent Document 6 JP2007-137042A

However, even with the method of the patent document, it is insufficient to improve the swelling property and the stretchability at the time of producing the polarizing film.

Even if the swelling property can be improved, the orientation state of the polyvinyl alcohol-based polymer is not taken into consideration in the technique disclosed in Patent Document 1, and it is difficult to improve the stretchability at the time of producing the polarizing film. On the contrary, by the addition of the water swelling agent, the orientation of the polymer is disturbed and uniform drawing can not be performed.

Patent Document 2 specifies the degree of stretching (pulling state) in the MD direction when the polyvinyl alcohol film is produced, but if the stretching in the TD direction is not taken into account, the in-plane retardation of the polyvinyl alcohol film is reduced And is insufficient for improving the stretchability in the production of the polarizing film. In general, it is difficult to stretch a polyvinyl alcohol-based film stretched in the MD direction in the MD direction at the time of producing the polarizing film. That is, pulling the polyvinyl alcohol-based polymer oriented in the MD direction again in the MD direction is difficult because the molecular chains are forcibly stretched. On the contrary, it is relatively easy to pull the polyvinyl alcohol-based polymer oriented in the TD direction in the MD direction. However, if the orientation of the polymer in the TD direction is not uniform, the film can not be stretched uniformly in the MD direction during the production of the polarizing film. Patent Document 2 discloses an example in which the polyvinyl alcohol film is not stretched as much in the MD direction as in the case of producing a polyvinyl alcohol film. However, the shrinkage stress due to the Poisson's ratio and the shrinkage stress due to dehydration are not sufficient There is a problem that the polymer orientation can not be sufficiently made uniform. That is, unless the film is stretched to some extent in the TD direction or at least fixed in the width direction, a uniform orientation state of the polymer in the TD direction can not be obtained, which is insufficient for improving the stretchability in the polarizing film production. Further, there is no description about the orientation in the thickness direction, and the swelling property at the time of producing the polarizing film is not controlled.

In the technique disclosed in Patent Document 3, the film after film formation can be uniformly dried, but the orientation of the polymer can not be controlled, and it is insufficient to improve the stretchability and swelling property at the time of producing the polarizing film.

In the technique disclosed in Patent Document 4, although the film thickness of the polyvinyl alcohol-based film can be made uniform, it can not control up to the orientation of the polymer, and is insufficient for improving the stretchability and swelling property at the time of producing the polarizing film.

Although the in-plane retardation of the polyvinyl alcohol-based film can be reduced and made uniform, the retardation in the thickness direction is not mentioned in the disclosure of the Patent Documents 5 and 6, so that the stretching property and the swelling property There is room for improvement from the perspective.

Therefore, in the present invention, in the production of a polyvinyl alcohol-based film, particularly a thin polarizing film, which is excellent in swelling property and stretching property at the time of production of a polarizing film under such a background and has a high polarizing performance and in which a polarizing film having less color unevenness can be obtained, And a method for producing a polarizing film, a polarizing plate, and a polyvinyl alcohol-based film, which comprises such a polyvinyl alcohol-based film.

Therefore, the present inventors have conducted intensive studies in view of such circumstances, and as a result, they have found that a polyvinyl alcohol film having in-plane retardation (Rxy) and thickness direction retardation (Rth) in a specific range exhibits swellability and stretchability And it was found that a polarizing film obtained by using such a polyvinyl alcohol film has a high polarization performance and also a polarizing film with less color unevenness.

That is, the first aspect of the present invention is a polyvinyl alcohol film having a thickness of 5 to 60 탆, a width of 2 m or more, and a length of 2 km or more, and satisfying the following formulas (1) and (2) to be.

(1) In-plane retardation Rxy? 30 nm

(2) Thickness phase difference Rth? 90 nm

In the polyvinyl alcohol film, the refractive index in the width direction (TD direction) is nx, the refractive index in the longitudinal direction (MD direction) is ny, the refractive index in the thickness direction (refractive index in the thickness direction) (N), and d (nm) is the thickness, respectively.

(A) Rxy (nm) = | nx-ny | xd (nm)

(B) Rth (nm) = {(nx + ny) / 2-nz}

Particularly, the polyvinyl alcohol-based film is characterized in that the deviation? Rxy of the in-plane retardation Rxy in the width direction (TD direction) is 5 nm or less.

The third aspect of the present invention is a polyvinyl alcohol film characterized in that the deviation? Rth in the thickness direction retardation Rth in the width direction (TD direction) is 30 nm or less.

The swelling degree X (%) in the width direction (TD direction), the swelling degree Y (%) in the length direction (MD direction), the swelling degree Z (%) Satisfies Z? 1.1 X and Z? 1.1 Y. The fourth aspect of the present invention is a polyvinyl alcohol film.

Among them, the deviation ΔX (%) of the swelling degree X (%) in the width direction (TD direction), the deviation ΔY (%) of the swelling degree Y (%) in the lengthwise direction (MD direction) And the deviation? Z (%) of the film thickness (%) is within 5% in all cases.

The sixth aspect of the present invention is a polyvinyl alcohol-based film characterized in that the thickness of the polyvinyl alcohol-based film is 5 to 30 탆.

Further, the present invention is a polarizing film characterized in that the polyvinyl alcohol film is used.

The present invention also provides a polarizing plate characterized by comprising a polarizing film and a protective film provided on at least one surface of the polarizing film.

The present invention also relates to a process for continuously drying a polyvinyl alcohol resin aqueous solution by a continuous casting method, a step of peeling off from a cast mold while being conveyed in a flow direction (MD direction) ), Characterized in that the polyvinyl alcohol film to be produced satisfies the following formulas (1) and (2): (1) a method of producing a polyvinyl alcohol film As the ninth point.

(1) In-plane retardation Rxy? 30 nm

(2) Thickness phase difference Rth? 90 nm

Herein, the in-plane retardation Rxy (nm) and the thickness direction retardation Rth (nm) are nx, ny, nz in the transverse direction (TD direction) , And d (nm) is the thickness, respectively, calculated by the following formulas (A) and (B).

(A) Rxy (nm) = | nx-ny | xd (nm)

(B) Rth (nm) = {(nx + ny) / 2-nz}

Particularly, a method for producing a polyvinyl alcohol-based film, which is characterized in that the stretching is performed at 1.05 to 1.3 times in the transverse direction (TD direction) of the film, is a tenth aspect of the present invention.

The method for producing a polyvinyl alcohol-based film is characterized in that the film is stretched in the transverse direction (TD direction).

The polyvinyl alcohol-based film of the present invention is excellent in swelling property and stretchability at the time of production of a polarizing film, and can provide a polarizing film exhibiting high polarization performance without causing breakage even when a thin polarizing film is produced, and having less color unevenness.

Further, since the swelling property and the stretching property at the time of production of the polarizing film depend on the orientation state of the polyvinyl alcohol-based polymer in the film, particularly the orientation state in the thickness direction, the present invention can control the retardation, It is to improve divinity.

Hereinafter, the present invention will be described in detail.

The polyvinyl alcohol film of the present invention is a polyvinyl alcohol film having a thickness of 5 to 60 탆, a width of 2 m or more, and a length of 2 km or more and having the following characteristics. Specifically, an aqueous solution of a polyvinyl alcohol-based resin is formed by a continuous casting method, and the film thus formed is peeled off from the cast mold and then dried and conveyed continuously in the transverse direction (TD direction) , And is a polyvinyl alcohol-based film characterized by satisfying both physical properties of the following formulas (1) and (2). Even if only one property value is satisfied, the object of the present invention is not achieved.

(1) In-plane retardation Rxy? 30 nm

(2) Thickness phase difference Rth? 90 nm

Herein, the in-plane retardation Rxy (nm) and the thickness direction retardation Rth (nm) are nx, ny, nz in the transverse direction (TD direction) , And d (nm) is the thickness, respectively, calculated by the following formulas (A) and (B).

(A) Rxy (nm) = | nx-ny | xd (nm)

(B) Rth (nm) = {(nx + ny) / 2-nz}

The above equations (1) and (2) will be described.

Equation (1) specifies general in-plane retardation, but is within the scope of the known art. The in-plane retardation Rxy (nm) of the polyvinyl alcohol-based film of the present invention is required to be 30 nm or less, preferably 20 nm or less, and particularly preferably 15 nm or less. When the in-plane retardation Rxy exceeds the upper limit value, color irregularity easily occurs in the polarizing film, which is not preferable.

In the present invention, the deviation? Rxy of the in-plane retardation Rxy in the width direction (TD direction) is preferably 5 nm or less, particularly preferably 3 nm or less, and more preferably 2 nm or less.

When the deviation DELTA Rxy is too large, color unevenness tends to occur in the polarizing film.

Next, the equation (2) specifies the phase difference in the thickness direction, and the greatest feature of the present invention is that the thickness direction retardation Rth (nm) is a positive value and 90 nm or more. That is, in the polyvinyl alcohol-based film of the present invention, the polymer chain is oriented mainly in the plane direction, and has a chemical structure which tends to swell in the thickness direction. The thickness direction retardation Rth (nm) is required to be 90 nm or more, preferably 100 nm or more, particularly preferably 110 to 200 nm. If the thickness direction retardation Rth (nm) is smaller than the lower limit value, the swelling property in the thickness direction is lowered, which is undesirable. If the thickness direction retardation Rth (nm) is too small, ) Tends to be difficult to elongate.

In the present invention, the deviation? Rth in the thickness direction retardation Rth in the width direction (TD direction) is preferably 30 nm or less, particularly preferably 20 nm or less, more preferably 10 nm or less. If such a deviation? Rth is too large, there is a tendency that the polarizing film tends to be uneven.

Further, in order to satisfy the formulas (1) and (2), besides the method of stretching the film peeled from the cast mold like the present invention in the width direction (TD direction), a method of controlling the drying condition of the aqueous solution, And a method of controlling the chemical structure of the resin.

Here, the production method of the polyvinyl alcohol film of the present invention will be described in more detail in the order of the process.

[Film material]

First, the polyvinyl alcohol resin and its aqueous solution used in the present invention will be described.

As the polyvinyl alcohol-based resin constituting the polyvinyl alcohol-based film in the present invention, a resin produced by saponification of an unmodified polyvinyl alcohol-based resin, that is, polyvinyl acetate obtained by polymerizing vinyl acetate, is used. If necessary, a resin obtained by saponifying a copolymer of vinyl acetate and a component capable of copolymerizing with a small amount (usually 10 mol% or less, preferably 5 mol% or less) of vinyl acetate can be used. Examples of the component copolymerizable with vinyl acetate include unsaturated carboxylic acids (including salts, esters, amides, nitriles, etc.), olefins having 2 to 30 carbon atoms (e.g., ethylene, propylene, n -Butene, isobutene, etc.), vinyl ethers, and unsaturated sulfonic acid salts. It is also possible to use a modified polyvinyl alcohol-based resin obtained by chemically modifying a hydroxyl group after saponification. These may be used alone or in combination of two or more.

As the polyvinyl alcohol-based resin, a polyvinyl alcohol-based resin having a 1,2-diol structure in the side chain may also be used. Such a polyvinyl alcohol-based resin having a 1,2-diol structure in the side chain can be obtained by, for example, (i) saponifying a copolymer of vinyl acetate and 3,4-diacetoxy-1-butene, (Ii) a method of saponifying and decarboxylating a copolymer of vinyl acetate and vinylethylene carbonate, (iii) saponifying and copolymerizing a copolymer of vinyl acetate and 2,2-dialkyl-4-vinyl-1,3-dioxolane, (Iv) a method of saponifying a copolymer of vinyl acetate and glycerin monoallyl ether, and the like.

The weight average molecular weight of the polyvinyl alcohol-based resin is preferably 100,000 to 300,000, particularly preferably 110,000 to 280,000, and more preferably 120,000 to 260,000. When the weight-average molecular weight is too small, it tends to be difficult to obtain sufficient optical performance when the polyvinyl alcohol-based resin is used as an optical film. When the polyvinyl alcohol-based resin is too large, stretching is difficult There is a tendency to disappear. The weight average molecular weight of the polyvinyl alcohol resin is a weight average molecular weight measured by the GPC-MALS method.

The average saponification degree of the polyvinyl alcohol-based resin used in the present invention is preferably 98 mol% or more, particularly preferably 99 mol% or more, more preferably 99.5 mol% or more, particularly preferably 99.8 mol% or more to be. When the average degree of saponification is too small, sufficient optical performance tends not to be obtained when a polarizing film is used as the polyvinyl alcohol-based film.

Here, the average degree of saponification in the present invention is measured in accordance with JIS K 6726.

As the polyvinyl alcohol-based resin to be used in the present invention, two or more kinds of modified species, modified amount, weight average molecular weight, average saponification degree and the like may be used in combination.

The polyvinyl alcohol resin aqueous solution may contain, in addition to the polyvinyl alcohol-based resin, a commonly used plasticizer such as glycerin, diglycerin, triglycerin, ethylene glycol, triethylene glycol, polyethylene glycol, trimethylolpropane, It is preferable to include at least one surfactant of anionic and cationic in view of film formability. These may be used alone or in combination of two or more.

The resin concentration of the polyvinyl alcohol-based resin solution thus obtained is preferably 15 to 60% by weight, particularly preferably 17 to 55% by weight, and more preferably 20 to 50% by weight. If the concentration of the resin in such an aqueous solution is too low, the production load tends to decrease because the drying load becomes large. If the resin concentration is too high, the viscosity tends to become too high and uniform dissolution becomes impossible.

Then, the resulting polyvinyl alcohol-based resin aqueous solution is defoamed. Examples of the defoaming method include a defoaming method using a static deformation or a multi-screw extruder. The multi-screw extruder may be a multi-screw extruder having a vent, and a twin-screw extruder usually having a vent is used.

[Film forming process]

After the defoaming treatment, the polyvinyl alcohol-based resin solution is introduced into the T-shaped slit die by a predetermined amount, and is discharged and cast on the rotating casting drum, and is formed by the continuous casting method.

The continuous casting method in the present invention is a method of forming a film by discharging and casting an aqueous solution of a polyvinyl alcohol-based resin into a casting mold such as a cast drum, endless belt, resin film or the like rotating in a T-shaped slit die to be. The film thus formed is peeled off from the cast mold and then continuously dried with a heat roll while being conveyed in the flow direction (MD direction), for example, may be heat-treated with a floating dryer.

The resin temperature of the polyvinyl alcohol-based resin solution at the outlet of the T-shaped slit die is preferably 80 to 100 占 폚, particularly preferably 85 to 98 占 폚.

When the resin temperature of such a polyvinyl alcohol-based resin aqueous solution is too low, flow defects tend to occur. When the resin temperature is too high, foaming tends to occur.

The viscosity of such an aqueous solution of a polyvinyl alcohol-based resin is preferably from 50 to 200 Pa · s, more preferably from 70 to 150 Pa · s, in the case of a sheet.

If the viscosity of such an aqueous solution is too low, the flow tends to become defective. If the viscosity is too high, casting tends to be difficult.

The discharge speed of the polyvinyl alcohol-based resin solution discharged from the T-shaped slit die to the cast drum is preferably 0.2 to 5 m / min, particularly preferably 0.4 to 4 m / min, and more preferably 0.6 to 3 m / min.

If the discharge speed is too low, productivity tends to decrease, and if it is too fast, casting becomes difficult.

The diameter of such a cast drum is preferably 2 to 5 m, particularly preferably 2.4 to 4.5 m, and more preferably 2.8 to 4 m.

If the diameter is too small, the drying section on the casting drum is shortened, so that the speed tends to increase. When the diameter is too large, the transportability tends to decrease.

The width of such a cast drum is preferably 4 m or more, particularly preferably 4.5 m or more, more preferably 5 m or more, particularly preferably 5 to 6 m.

If the width of the cast drum is too small, productivity tends to decrease.

The rotation speed of the casting drum is preferably 3 to 50 m / min, particularly preferably 4 to 40 m / min, and more preferably 5 to 35 m / min.

If the rotation speed is too slow, the productivity tends to decrease. If the rotation speed is too fast, the drying tends to be insufficient.

The surface temperature of such a cast drum is preferably 40 to 99 占 폚, particularly preferably 60 to 95 占 폚.

If the surface temperature is too low, drying tends to be poor, and if it is too high, it tends to foam.

[Coated film]

The water content of the film thus formed (film before stretching in the width direction (TD direction)] is preferably 0.5 to 15% by weight, particularly preferably 1 to 13% by weight, more preferably 2 to 12% %to be. Even if the water content is too low or too high, the orientation of the desired polymer, that is, the intended phase difference, tends to become difficult.

When the water content of the film before stretching in the width direction (TD direction) is too high, it is preferable to dry the film before stretching in the width direction (TD direction), and conversely, Direction is too low, it is preferable that the moisture content is adjusted before stretching in the width direction (TD direction). More preferably, the conditions of the drying process are adjusted so that the water content falls within the above range.

Such a drying can be carried out by a known method using a heating roll or an infrared heater, but in the present invention, it is preferable to carry out drying with a plurality of heating rolls, particularly preferably the temperature of the heating roll is 40 to 150 DEG C, More preferably 50 to 140 占 폚. Further, because of the adjustment of the water content, a humidity control area may be provided before stretching in the width direction (TD direction).

[Carrying / Stretching Process]

The film thus formed and stretched in at least one of the continuous and intermittent directions in the transverse direction (TD direction) while conveying the film having the water content prepared in the above manner in the flow direction (MD direction).

It is not necessary to stretch the film formed in the present invention particularly in the flow direction (MD direction), and it is sufficient to carry the film with a pulling tension sufficient for not bending the film. Naturally, shrinkage occurs in the flow direction (MD direction) depending on the Poisson's ratio by stretching in the width direction (TD direction), and dehydration shrinkage also occurs in the flow direction (MD direction) during drying. Due to such shrinkage, a suitable tension is obtained in the flow direction (MD direction) even if the rotating speed of the conveying roll or the heating roll is constant, and control of the complicated rotational speed as in Patent Document 2 is unnecessary. Further, it is preferable that the dimension in the film flow direction (MD direction) is constant from a manufacturing standpoint.

In addition, stretching in both the flow direction (MD direction) and the width direction (TD direction) while conveying the formed film in the flow direction (MD direction) disturbs the orientation of the polymer, It is not preferable because a phase difference can not be expressed. In particular, stretching is not preferable as the dimension in the flow direction (MD direction) increases.

The preferred range of the conveying speed in the flow direction (MD direction) of the film-formed film is 5 to 30 m / min, particularly preferably 7 to 25 m / min, and more preferably 8 to 20 m / min. If the conveying speed is too low, the productivity tends to decrease. If the conveying speed is too high, the color unevenness tends to increase.

There are no particular limitations on the method of carrying the formed film in the transport direction (MD direction) and stretching in the transverse direction (TD direction) at the same time. For example, And it is preferable to simultaneously carry out and stretch. In such a case, the arrangement of the clips at each end is preferably 200 mm or less in pitch, particularly preferably 100 mm or less in pitch, and more preferably 50 mm or less in pitch.

If the pitch of the clips is too wide, there is a tendency that the film after stretching is bent or the thickness of both ends in the width direction of the obtained polyvinyl alcohol film becomes uneven and the phase difference unevenness increases. It is preferable that the clamping position of the clip (the tip of the clip) is 100 mm or less at both ends in the width direction of the film formed. If the clamping position (distal end) of the clip is located too far toward the center in the width direction of the film, the end of the film to be destroyed is increased, and the product width tends to be narrowed.

The stretching magnification in the width direction (TD direction) in the present invention is preferably 1.05 to 1.3 times, particularly preferably 1.05 to 1.25 times, and more preferably 1.1 to 1.2 times.

If the stretching magnification in the width direction (TD direction) is too high or too low, the in-plane retardation tends to increase.

The continuous stretching process in the width direction (TD direction) may be one step (one time), and may be a plurality of steps (plural times) (also called continuous stretching) so that the total stretching magnification falls within the range of the stretching magnification. For example, it is also possible to carry out a simple conveyance in which the width direction (TD direction) is fixed after the stretching in one step, and then the stretching in the second step and the subsequent steps can be carried out. Particularly, in the case of a thin film, by merely inserting a conveying step of fixed width, the stress of the film is relaxed, and breakage can be avoided.

In the case of inserting a conveying step of fixed width, the fixing width may be narrower than the width after the one-step stretching. Since the film immediately after stretching is likely to shrink for stress relaxation and contraction is caused by dehydration, it is possible to narrow the fixing width to these shrinkage widths. However, if the film is narrowed beyond the shrinkage width, the film may be bent, which is not preferable.

Such a stretching step is preferably carried out after the drying step of the film, but may be carried out at least either before the film drying step or after the drying step, or may be carried out during the drying step.

As a preferred embodiment of the present invention, there is a method of temporally shrinking the film so that the stretching magnification in the final width direction (TD direction) is 1.05 to 1.3 times in the transverse direction (TD direction) Can be used. In such a case, the film may be simply transported at a fixed width of 1.05 to 1.3 at a stretching magnification after being stretched beyond 1.3 times. By such a method, the stress relaxation of the film is achieved, and in particular, in the case of a thin film, breakage can be avoided.

The stretching temperature in the transverse direction (TD direction) of the film formed in the present invention is preferably 50 to 150 占 폚, particularly preferably 60 to 140 占 폚, and more preferably 70 to 130 占 폚. Even if such a drawing temperature is too low or too high, the in-plane retardation tends to increase. In the case of performing sequential stretching, the stretching temperature may be changed at each stretching step.

The stretching time in the transverse direction (TD direction) of the film formed in the present invention is preferably 2 to 60 seconds, particularly preferably 5 to 45 seconds, and more preferably 10 to 30 seconds. If the stretching time is too short, the film tends to be broken. On the other hand, if the stretching time is too long, the equipment load tends to increase. In the case of the sequential stretching, such stretching time may be changed in each stretching step.

As a preferred form of the present invention, the stretching in the transverse direction (TD direction) is performed at a relatively low temperature, the stretching in the transverse direction (TD direction) is fixed, Is carried out. Concretely, it is preferable to carry out the first stage at 50 ° C or higher, more preferably 50 to 130 ° C, and the second stage at 80 ° C or higher, more preferably 80 to 150 ° C. By such a method, drying can proceed smoothly and homogeneous polymer alignment can be achieved, and desired phase difference in the in-plane and thickness directions can be expressed.

In the present invention, after the film is stretched in the transverse direction (TD direction), it may be subjected to heat treatment with a floating dryer or the like. The temperature of the heat treatment is preferably 60 to 200 占 폚, particularly preferably 70 to 150 占 폚.

When the heat treatment temperature is too low, the dimensional stability tends to deteriorate. On the other hand, if the heat treatment temperature is too high, the elongation at the time of producing the polarizing film tends to decrease.

The heat treatment time is preferably 1 to 60 seconds, particularly preferably 5 to 30 seconds. If the heat treatment time is too short, the dimensional stability tends to decrease. On the other hand, if the heat treatment time is too long, the elongation at the time of producing the polarizing film tends to be lowered.

[Polyvinyl alcohol film]

Thus, the polyvinyl alcohol-based film of the present invention can be obtained, and finally the product is wound on a roll to become a product. The thickness of such a polyvinyl alcohol-based film is 5 to 60 占 퐉 from the viewpoint of thinning of the polarizing film, particularly preferably 5 to 45 占 퐉, more preferably 5 to 30 占 퐉 in view of further thinning, From the viewpoint of avoidance. The thickness of such a polyvinyl alcohol-based film is adjusted by the resin concentration in the polyvinyl alcohol-based resin aqueous solution, the discharge amount (discharge speed) into the cast mold, the draw ratio, and the like.

The width of such a polyvinyl alcohol-based film is 2 m or more, particularly preferably 3 m or more from the standpoint of large-area enlargement, and more preferably 4 to 6 m from the viewpoint of avoiding breakage.

The length of such a polyvinyl alcohol-based film is 2 km or more, particularly preferably 3 km or more from the standpoint of large-scale surface area, and more preferably 3 to 50 km from the viewpoint of transportation weight.

The polyvinyl alcohol-based film of the present invention is very useful as a original film of a polarizing film. Hereinafter, a polarizing film made of the above-mentioned polyvinyl alcohol-based film and a manufacturing method of the polarizing plate will be described.

[Polarizing film production method]

The polarizing film in the present invention is produced by continuously exposing the polyvinyl alcohol film from the roll, transporting it in the horizontal direction, and performing processes such as swelling, dyeing, boric acid crosslinking, stretching, washing and drying.

The water swelling process is usually carried out at about 30 DEG C for 0.1 to 15 minutes from the viewpoint of controlling the degree of swelling of the polyvinyl alcohol-based film.

In the water swelling process, the degree of swelling of the polyvinyl alcohol-based film of the present invention is measured by swelling degree X (%) in the width direction (TD direction), MD The swelling degree Y (%) in the thickness direction and the swelling degree Z (%) in the thickness direction in the thickness direction are preferably Z? 1.1X and Z? 1.1Y, more preferably Z? 1.2X, Y, more preferably Z? 1.3X, and Z? 1.3Y. By increasing the degree of swelling Z (%) in the thickness direction to be larger than the degree of swelling X (%) in the width direction (TD direction) and the degree Y of swelling in the flow direction (MD direction), the swelling speed is improved, Can be reduced.

The deviation ΔX (%) of the swelling degree X (%) in the width direction (TD direction), the deviation ΔY (%) of the swelling degree Y (%) in the flow direction It is preferable that all of Z (%) is within 5%, particularly preferably within 4%, and more preferably within 3%. If such a deviation is too large, color irregularity tends to occur in the polarizing film.

The dyeing process is carried out by bringing the film into contact with a liquid containing iodine or a dichroic dye. Usually, an aqueous solution of iodine-potassium iodide is used, the concentration of iodine is 0.1 to 2 g / L, and the concentration of potassium iodide is preferably 1 to 100 g / L. Dyeing time is practically about 30 to 500 seconds. The temperature of the treatment bath is preferably 5 to 50 占 폚. The aqueous solution may contain a small amount of an organic solvent compatible with water in addition to the water solvent.

The boric acid crosslinking process is carried out using a boron compound such as boric acid or borax. The boron compound is used at a concentration of about 10 to 100 g / L in the form of an aqueous solution or a water-organic solvent mixture, and it is preferable that potassium iodide coexists in the liquid from the viewpoint of stabilization of the polarization performance. The temperature for the treatment is preferably about 30 to 70 占 폚, and the treatment time is preferably about 0.1 to 20 minutes, and if necessary, the stretching operation may be carried out during the treatment.

In the stretching step, the film is preferably stretched in the uniaxial direction by 3 to 10 times, preferably by 3.5 to 6 times. At this time, a slight stretching (a degree of preventing the stretching in the width direction or further stretching) may also be performed in the direction perpendicular to the stretching direction. The temperature at the time of stretching is preferably from 40 to 170 캜. The stretching magnification may be set within the above range, and the stretching operation may be performed not only once but also several times in the manufacturing process.

The cleaning step is carried out, for example, by immersing the film in an aqueous iodide solution such as water or potassium iodide, and the precipitate generated on the surface of the film can be removed. When potassium iodide aqueous solution is used, the concentration of potassium iodide should be about 1 to 80 g / L. The temperature at the time of the washing treatment is usually 5 to 50 占 폚, preferably 10 to 45 占 폚. The treatment time is usually 1 to 300 seconds, preferably 10 to 240 seconds. The washing with water and the washing with aqueous potassium iodide solution may be carried out in appropriate combination.

The drying process is performed, for example, by drying the film at 40 to 80 DEG C for 1 to 10 minutes in the atmosphere.

Although the polarizing film can be obtained in this way, the degree of polarization of such a polarizing film is preferably 99% or more, and more preferably 99.5% or more. When the degree of polarization is too low, the contrast in the liquid crystal display tends to decrease. Generally, the degree of polarization is determined by the relationship between the light transmittance (H ₁₁ ) measured for the wavelength? And the transmittance (H ₁₁ ) of the two polarizing films measured in the direction of the alignment direction of the two polarizing films And the light transmittance (H ₁ ) measured with respect to the wavelength? In accordance with the following formula.

Degree of polarization = _{[(H 11 -H 1) / (} H 11 + H 1) ] ^{/ 2}

The polarizing film of the present invention preferably has a single transmittance of 44% or more. If such a simple mass transmittance is too low, the brightness of the liquid crystal display tends to be unable to be achieved.

The mass transmittance is a value obtained by measuring the light transmittance of the single polarizing film by using a spectrophotometer.

Next, a method for producing a 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 very suitable for producing a polarizing plate having less color unevenness and excellent polarization performance.

The polarizing plate of the present invention is produced by bonding an optically isotropic resin film as a protective film to 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, polyethersulfone, polyallylene ester, And films or sheets such as polyethylene, polypropylene, polyethylene, polypropylene, polyethylene, polypropylene, polyethylene, polypropylene,

The bonding method is carried out by a known method. For example, a liquid adhesive composition is uniformly applied to a polarizing film, a protective film, or both, and the two are adhered to each other, pressed and heated and irradiated with an active energy ray .

It is also possible to apply a curable resin such as a urethane resin, an acrylic resin, or a urea resin to one surface or both surfaces of the polarizing film and cure the same to form a cured layer to form a polarizing plate. In this case, the cured layer becomes a substitute for the protective film, and the thin film can be formed.

The polarizing film and the polarizing plate using the polyvinyl alcohol film of the present invention are excellent in the polarizing performance and can be used in portable information terminals, PCs, televisions, projectors, signage, electronic tabletop calculators, electronic clocks, word processors, (CRT, LCD, organic EL, electronic paper, etc.), liquid crystal display devices such as liquid crystal display devices such as liquid crystal display devices, video cameras, photo albums, thermometers, audio devices, instrumentation of automobiles and machinery, sunglasses, , Optical communication equipment, medical equipment, building materials, toys, and the like.

(Example)

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples unless the gist thereof is exceeded.

In the examples, " part " means weight basis.

<Measurement Conditions>

In the following Examples and Comparative Examples, the characteristics (in-plane retardation, retardation in thickness direction, deviation in in-plane retardation, deviation in thickness direction retardation, , The unit transmittance, and the color unevenness) were measured and evaluated as follows.

[In-plane retardation Rxy (nm), thickness direction retardation Rth (nm)]

 A test piece having a length of 4 cm and a width of 4 cm was cut from the center portion in the width direction of the obtained polyvinyl alcohol film and the both left and right end portions (10 cm inward from the film end), and a retardation measurement device ("KOBRA-WR" Manufactured by Mitsui Chemicals, Inc.) was used, and the in-plane retardation Rxy (nm) and the thickness direction retardation Rth (nm) at 590 nm were measured.

&Lt; Measurement conditions of Rth &

Angle of incidence: 50 °

Slope center axis: Ground axis

Average refractive index: Measured using Abbe's refractometer

[Variation in in-plane retardation? Rxy (nm)]

The difference between the maximum value and the minimum value was taken out from the in-plane retardation Rxy (nm) of the central portion in the width direction and the in-plane retardation Rxy (nm) at both ends in the width direction.

[Deviation of thickness direction retardation? Rth (nm)]

The difference between the maximum value and the minimum value was taken out of the thickness direction retardation Rth (nm) of the center portion and the left and right end portions in the width direction obtained in the above measurement, and the deviation in thickness direction retardation? Rth (nm) was determined.

[Swelling degree (%)]

Each of the films having a width of 100 mm and a length of 100 mm was cut out from the center portion in the width direction of the obtained polyvinyl alcohol-based film and both the left and right ends thereof, and the film was swelled by immersion in water at 30 캜 for 15 minutes. The swelling degree X (%) in the width direction (TD direction) and the swelling degree Y (%) in the flow direction (MD direction) were calculated from the dimensions before and after immersion according to the following formula. The swelling degree Z (%) in the thickness direction was obtained by cutting one film having a width of 100 mm and a length of 100 mm from the center portion in the width direction and the left and right end portions of the polyvinyl alcohol film in one piece and immersing the film in water at 30 캜 for 15 minutes, The film was taken out and the film spread on the filter paper 5A. Again, the filter paper 5A was overlaid on the film, and an SUS plate of 150 mm x 150 mm x 4 mm (4.4 x ^10-2 g / mm &lt; ² &gt;) was placed thereon for 5 seconds to remove the adhered water on the surface of the film. This film was quickly put into a weighing bottle and its weight was measured. This weight was defined as &quot; weight after immersion &quot;. The above operation was performed in an environment of 23 ° C and 50% RH.

Then, the film was allowed to stand in a dryer at 105 DEG C for 16 hours to remove water in the film, and then the film was taken out and quickly put into a weighing bottle to measure the weight, and this was regarded as &quot; weight after drying &quot;. Then, according to the following formula, the swelling degree Z (%) in the thickness direction was calculated.

Width of swelling X (%) = 100 占 Width in TD direction after immersion (mm) / Width in mm in TD before immersion (mm)

Width of swelling Y (%) = 100 占 Width in MD direction after immersion (mm) / Width in MD direction before immersion (mm)

Swelling degree Z (%) = 1000000 Weight after immersion (g) / Weight after drying (g) / X / Y

[Variation (%) of swelling degree]

(%) Of the swelling degree X (%) in the width direction (TD direction), the flow direction (MD direction) of the swelling degree X (%) Of the degree of swelling Y (%) and the degree of swelling Z (%) in the thickness direction.

[Polarization degree (%), unit transmittance (%)]

A test piece having a length of 4 cm and a width of 4 cm was cut from the central portion in the width direction of the obtained polarizing film and the degree of polarization (%) and the unit transmissivity (%) were measured using an automatic polarizing film measuring apparatus (VAP7070, manufactured by Nippon Bunko).

[Uneven color]

A test piece having a length of 30 cm and a width of 30 cm was cut out from the central portion in the width direction of the obtained polarizing film and sandwiched between two polarizing plates in a crossed Nicol state (having a single light transmittance of 43.5% and a polarization degree of 99.9% , A light box with a surface roughness of 14,000 lx was used to observe optical color unevenness in a transmission mode, and evaluation was made according to the following criteria.

(Evaluation standard)

○ · · · No color stain

△ · · · There is faint smudge

× · · With dirt

&Lt; Example 1 &gt;

(Production of polyvinyl alcohol film)

1,000 kg of a polyvinyl alcohol resin having a weight average molecular weight of 142,000, a saponification degree of 99.8 mol%, 2,500 kg of water, 105 kg of glycerin as a plasticizer and 0.25 kg of polyoxyethylene laurylamine as a surfactant were placed in a 5,000 L dissolution can, , The solution was heated up to 150 DEG C and subjected to pressure melting, and an aqueous solution of a polyvinyl alcohol-based resin having a resin concentration of 25 wt% was obtained by adjusting the concentration. Subsequently, the polyvinyl alcohol resin aqueous solution was fed to a twin-screw extruder and defoamed. Thereafter, the temperature of the aqueous solution was set to 95 占 폚, and the sheet was discharged from the T-shaped slit die discharge port into a rotating casting drum at a discharge speed of 2.5 m / Casting and casting. The formed film was peeled off from the cast drum and dried while being conveyed in the flow direction (MD direction) while alternately contacting the surface and the back of the film with a total of ten heat rolls. Thus, a film having a moisture content of 10% by weight (2 m wide and 60 m thick) was obtained. Subsequently, the film was stretched 1.1 times in the transverse direction (TD direction) at 120 DEG C using a stretching machine while the film was conveyed at a speed of 8 m / min in the flow direction (MD direction) with the left and right ends of the film held at a clip pitch of 45 mm, And a polyvinyl alcohol film (width 2.2 m, thickness 55 m, length 2 km) was obtained. The characteristics of the obtained polyvinyl alcohol-based film are shown in Tables 1 and 2.

(Preparation of Polarizing Film and Polarizing Plate)

The obtained polyvinyl alcohol film was continuously fed out from the roll and stretched 1.7 times in the flow direction (MD direction) while being swollen by immersing in a water bath at a water temperature of 30 캜 while being transported in the horizontal direction. Subsequently, the resultant was immersed in an aqueous solution of 30 g / l of iodine and 0.5 g / l of potassium iodide and stretched 1.6 times in the flow direction (MD direction) while dyeing. Subsequently, a composition of 40 g / L of boric acid and 30 g / L of potassium iodide (50 占 폚), and uniaxially stretched 2.1 times in the flow direction (MD direction) while crosslinking the boric acid. Finally, the film was washed with an aqueous solution of potassium iodide and dried at 50 DEG C for 2 minutes to obtain a polarizing film having a total draw ratio of 5.8 times. No breakage occurred during the production, and the characteristics of the obtained polarizing film were as shown in Table 3. [ Using a polyvinyl alcohol aqueous solution as an adhesive on both surfaces of the polarizing film obtained above, a triacetylcellulose film having a thickness of 40 탆 was laminated and dried at 70 캜 to obtain a polarizing plate.

&Lt; Example 2 &gt;

The film formed in Example 1 was stretched 1.05 times in the width direction (TD direction) at 75 DEG C using a stretching machine, and then stretched 1.05 times (total stretching ratio 1.1 times) in the width direction (TD direction) at 120 DEG C , A polyvinyl alcohol film (width 2.2 m, thickness 55 m, length 2 km) was obtained in the same manner as in Example 1. The characteristics of the obtained polyvinyl alcohol-based film are shown in Tables 1 and 2. Using the above polyvinyl alcohol film, a polarizing film and a polarizing plate were obtained in the same manner as in Example 1. Properties of the obtained polarizing film are as shown in Table 3. &lt; tb &gt; &lt; TABLE &gt;

&Lt; Example 3 &gt;

Example 1 was repeated except that the film (width 2 m, thickness 30 탆) having a moisture content of 7% by weight was stretched 1.1 times in the width direction (TD direction) at a discharge speed of 1.3 m / , A polyvinyl alcohol film (width 2.2 m, thickness 27 m, length 2 km) was obtained. The characteristics of the obtained polyvinyl alcohol-based film are shown in Tables 1 and 2.

Using the polyvinyl alcohol film, a polarizing film and a polarizing plate were obtained in the same manner as in Example 1. Although the original polyvinyl alcohol film was thin, no breakage occurred in the stretching process at the time of producing the polarizing film. Properties of the obtained polarizing film are as shown in Table 3. &lt; tb &gt; &lt; TABLE &gt;

<Example 4>

Example 1 was repeated except that the film (width 2 m, thickness 20 탆) having a water content of 5% by weight was stretched 1.2 times in the width direction (TD direction) at a discharge speed of 0.8 m / , A polyvinyl alcohol film (width 2.4 m, thickness 17 m, length 2 km) was obtained. The characteristics of the obtained polyvinyl alcohol-based film are shown in Tables 1 and 2.

Using the above polyvinyl alcohol film, a polarizing film and a polarizing plate were obtained in the same manner as in Example 1. Although the original polyvinyl alcohol film was thin, no breakage occurred in the stretching process at the time of producing the polarizing film. Properties of the obtained polarizing film are as shown in Table 3. &lt; tb &gt; &lt; TABLE &gt;

&Lt; Example 5 &gt;

(2 m in width and 20 m in thickness) having a moisture content of 5% by weight was stretched 1.1 times in the width direction (TD direction) at a discharge speed of 0.8 m / min at the time of film formation in Example 1, Except that a polyvinyl alcohol film (having a width of 2.4 m and a thickness of 2.4 m) was produced in the same manner as in Example 1, except that the polyvinyl alcohol film was transported in a transverse direction (direction corresponding to 1.1 times elongation) 17 m, length 2 km). The characteristics of the obtained polyvinyl alcohol-based film are shown in Tables 1 and 2.

Using the polyvinyl alcohol film, a polarizing film and a polarizing plate were obtained in the same manner as in Example 1. Although the original polyvinyl alcohol film was thin, no breakage occurred in the stretching process at the time of producing the polarizing film. Properties of the obtained polarizing film are as shown in Table 3. &lt; tb &gt; &lt; TABLE &gt;

&Lt; Comparative Example 1 &

The same procedure as in Example 1 was repeated except that both ends of the film formed in Example 1 were heated at 120 占 폚 while being conveyed at a speed of 8 m / min in the flow direction (MD direction) Vinyl alcohol film (width 2 m, thickness 60 m, length 2 km). The characteristics of the obtained polyvinyl alcohol-based film are shown in Tables 1 and 2.

Using the polyvinyl alcohol film, a polarizing film and a polarizing plate were obtained in the same manner as in Example 1. Properties of the obtained polarizing film are as shown in Table 3. &lt; tb &gt; &lt; TABLE &gt;

&Lt; Comparative Example 2 &

Except that both ends of the film formed in Example 4 were heated at 120 占 폚 while being conveyed at a speed of 8 m / min in the flow direction (MD direction) without sandwiching the both ends of the film with a clip, Vinyl alcohol film (width 2 m, thickness 20 m, length 2 km). The characteristics of the obtained polyvinyl alcohol-based film are shown in Tables 1 and 2.

Using the polyvinyl alcohol film, a polarizing film and a polarizing plate were obtained in the same manner as in Example 1. Properties of the obtained polarizing film are as shown in Table 3. &lt; tb &gt; &lt; TABLE &gt;

From the results of the above Examples and Comparative Examples, it was confirmed that the films of Examples 1 to 5 (obtained from polyvinyl alcohol films satisfying the ranges specified by the above-mentioned formulas (1) and (2) Of the polarizing film had a high degree of polarization and also had no color unevenness. On the other hand, the polarizing films of Comparative Examples 1 and 2, which are obtained from a polyvinyl alcohol film whose in-plane retardation Rxy and thickness direction retardation Rth are outside the ranges specified by the above-mentioned formulas (1) and (2) It can be seen that dirt is also observed.

Although the embodiment has been described in the concrete form of the present invention, the embodiment is merely an example and is not to be construed as limiting. Various modifications that are obvious to those skilled in the art are expected to be within the scope of the present invention.

The polarizing film and the polarizing plate using the polyvinyl alcohol film of the present invention are excellent in the polarizing performance and can be used in portable information terminals, PCs, televisions, projectors, signage, electronic tabletop calculators, electronic clocks, word processors, (CRT, LCD, organic EL, electronic paper, etc.), liquid crystal display devices such as liquid crystal display devices such as liquid crystal display devices, video cameras, photo albums, thermometers, audio devices, instrumentation of automobiles and machinery, sunglasses, , Optical communication equipment, medical equipment, building materials, toys, and the like.

Claims (11)

A polyvinyl alcohol film having a thickness of 5 to 60 占 퐉, a width of 2 m or more, and a length of 2 km or more, and satisfying the following formulas (1) and (2).
(1) In-plane retardation Rxy? 30 nm
(2) Thickness phase difference Rth? 90 nm
Herein, the in-plane retardation Rxy (nm) and the thickness direction retardation Rth (nm) of the polyvinyl alcohol film are nx and ny, respectively, in the width direction (TD direction) (A) and (B) when the refractive index in the thickness direction is nz and the thickness is d (nm).
(A) Rxy (nm) = | nx-ny | xd (nm)
(B) Rth (nm) = {(nx + ny) / 2-nz} The method according to claim 1,
And the deviation? Rxy of the in-plane retardation Rxy in the width direction (i.e., the TD direction) is 5 nm or less. The method according to claim 1 or 2,
And the deviation? Rth of the thickness direction retardation Rth in the width direction (i.e., the TD direction) is 30 nm or less. 4. The method according to any one of claims 1 to 3,
The swelling degree X (%) in the width direction (i.e., the TD direction), the swelling degree Y (%) in the longitudinal direction (i.e., the MD direction) And the swelling degree Z (%) satisfies Z? 1.1X and Z? 1.1Y. The method of claim 4,
The deviation ΔY (%) of the swelling degree Y (%) in the longitudinal direction (that is, the MD direction) and the swelling degree Y (%) of the swelling degree X And the deviation Z (%) of Z (%) is all within 5%. 6. The method according to any one of claims 1 to 5,
Wherein the polyvinyl alcohol-based film has a thickness of 5 to 30 占 퐉. A polarizing film characterized in that the polyvinyl alcohol film described in any one of claims 1 to 6 is used. A polarizing plate comprising: the polarizing film according to claim 7; and a protective film provided on at least one surface of the polarizing film. (That is, in the TD direction) while continuously conveying in the flow direction (that is, in the MD direction) after the step of forming the aqueous solution of the polyvinyl alcohol-based resin by the continuous casting method, And a step of stretching the polyvinyl alcohol-based film,
Wherein the polyvinyl alcohol film to be produced satisfies the following formulas (1) and (2).
(1) In-plane retardation Rxy? 30 nm
(2) Thickness phase difference Rth? 90 nm
Herein, the in-plane retardation Rxy (nm) and the thickness direction retardation Rth (nm) are nx, ny, and ny, respectively, when the refractive index of the polyvinyl alcohol film in the width direction (A) and (B), respectively, where nz is the refractive index of the film, and d (nm) is the thickness.
(A) Rxy (nm) = | nx-ny | xd (nm)
(B) Rth (nm) = {(nx + ny) / 2-nz} The method of claim 9,
Wherein the stretching is performed in the width direction of the film (i.e., in the TD direction) by 1.05 to 1.3 times. The method according to claim 9 or 10,
And the stretching is effected in the transverse direction of the film (i.e., in the TD direction).