KR20190008213A - A polyvinyl alcohol film, a production method thereof, and a polarizing film using the polyvinyl alcohol film - Google Patents

Abstract

A polyvinyl alcohol film capable of obtaining a polarizing film having a high degree of polarization and a small degree of unevenness with excellent extensibility at the time of production of the polarizing film, particularly a polyvinyl alcohol film which does not break even when the thin polarizing film is produced, And a polarizing film using the polyvinyl alcohol-based film. The polyvinyl alcohol-based film of the present invention is a polyvinyl alcohol-based film having a length of 4 km or more, and has a tensile modulus X (MPa) of 5 to 12 MPa in the longitudinal direction (MD) do.

Description

A polyvinyl alcohol film, a production method thereof, and a polarizing film using the polyvinyl alcohol film

The present invention relates to a polyvinyl alcohol film, particularly, a polyvinyl alcohol film which has excellent stretchability and can obtain a polarizing film having a high degree of polarization and few stains, a method for producing the film, and a polarizing film using the polyvinyl alcohol film will be.

BACKGROUND ART [0002] Recently, the development of a liquid crystal display device is remarkable and widely used in smart phones, tablets, personal computers, liquid crystal TVs, projectors, vehicle panels and the like. A polarizing film is used for such a liquid crystal display device, and as the polarizing film, an iodine or a dichromatic dye is adsorbed and oriented on a polyvinyl alcohol film. In recent years, a thin, polarized film that has a higher degree of polarization than that of conventional quality, has no unevenness, and has a wide width and is required to have a high definition, high luminance, large size, and thinness. The polarizing film in the present invention is also called a polarizing film or a polarizer.

In general, the polarizing film is produced by unwinding a polyvinyl alcohol film as a raw material from a roll, swelling the film with water (including hot water) while conveying it in the flow direction (MD) Dyed with a dye and stretched. In such a stretching process, the film after stretching in the flow direction (MD) is stretched to highly orient the dichroic dye in the film. In order to improve the degree of polarization of the polarizing film, the polyvinyl alcohol- MD), it is necessary to have good stretchability.

As the order of polarizing film production, cases in which stretching and dyeing are opposite are also carried out. That is, in the case of a polyvinyl alcohol film which is a disc, the film is swollen with water (including hot water), followed by stretching and dyed with a dichroic dye such as iodine. However, in such a case, in order to improve the polarization degree of the polarizing film , It is necessary that the polyvinyl alcohol-based film has good stretchability in the flow direction (MD). For example, when the stretching tension is too large, the stretching can not be performed at a predetermined stretching ratio, and the dichroic dye is not sufficiently oriented, so that the degree of polarization tends not to be improved. On the contrary, when the stretching tension is too small, orientation of the dichroic dye is unstable even when stretched to a predetermined stretching magnification, and there is a tendency that unevenness occurs in the polarizing film.

On the other hand, the polyvinyl alcohol film as a master is generally produced by continuous casting from an aqueous solution of a polyvinyl alcohol-based resin as a raw material. Concretely, an aqueous solution of a polyvinyl alcohol-based resin is cast in a casting mold such as a cast drum or an endless belt, and the film thus formed is peeled off from the casting mold and is transported in the flow direction (MD) Roll, and then heat-treating the film using a floating dryer or the like as necessary. In such a transporting step, the film formed is stretched in the flow direction (MD), so that the polyvinyl alcohol-based polymer is easy to be oriented in the flow direction (MD). If the orientation is too large, the flow of the polyvinyl alcohol- The stretching property in the direction (MD) is lowered, and finally the polarization performance of the polarizing film is lowered.

In recent years, in order to make the polarizing film thinner, the polyvinyl alcohol-based film is also thinned. Conventionally, the thickness of the polyvinyl alcohol-based film was about 60 占 퐉, and now it is about 45 占 퐉 in thickness. Is expected to be. Such a thin polyvinyl alcohol-based film has problems of productivity such as being broken by stretching when the polarizing film is produced.

As a method for improving the stretchability of a polyvinyl alcohol-based film, for example, a method in which the ratio of the speed of the cast drum to the final film winding speed at the time of film formation of the polyvinyl alcohol film is set to a specific ratio (for example, (See, for example, Patent Document 2), a method of controlling the tensile state in the drying process of the polyvinyl alcohol film (see, for example, Patent Document 1), a method of suspending the film after casting with a cast drum , Patent Document 3) has been proposed.

In addition, a polyvinyl alcohol film (for example, see Patent Document 4) in which the in-plane retardation is reduced (see Patent Document 4) or a polyvinyl alcohol film (for example, For example, Patent Document 5), and a polyvinyl alcohol film (see Patent Document 6, for example) in which the Young's modulus (tensile elastic modulus) is reduced to 20 MPa or less by electromagnetic wave irradiation.

Patent Document 1 JP 2001-315141 A Patent Document 2 JP 2001-315142 A Patent Document 3 JP 2002-79531 A Patent Document 4 JP 2006-291173 A Patent Document 5 JP 2002-30164 A Patent Document 6 JP 2013-97232 A

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

The starting technique of Patent Document 1 specifies the degree of stretching (tensile state) in the flow direction (MD) when the polyvinyl alcohol film is produced, but if the drying conditions and the heat treatment conditions are not taken into consideration, The stretchability of the film is not sufficiently improved.

In the technique disclosed in Patent Document 2, the film after film formation can be uniformly dried, but the tensile modulus can not be controlled and the stretchability of the polyvinyl alcohol film at the time of polarizing film production is not improved sufficiently.

Although the film thickness of the film can be made uniform in the technique disclosed in Patent Document 3, the stretchability of the polyvinyl alcohol film during the production of the polarizing film is not improved sufficiently because the tensile elastic modulus can not be controlled.

Although the in-plane retardation of the film can be reduced in the technique disclosed in Patent Document 4, there is room for improvement in terms of control of the tensile modulus and improvement of the stretchability of the polyvinyl alcohol film at the time of polarizing film production. Further, in the manufacturing method of the present disclosure, the film after drying (70 ° C) or heat treatment (120 ° C) is once cooled to 50 ° C or lower and heated again to 50-100 ° C However, the heating process is troublesome and there is room for improvement from the viewpoint of productivity.

In the technique disclosed in Patent Document 5, although the tensile elongation of the polyvinyl alcohol film can be stabilized, the tensile elastic modulus itself is not controlled, and the stretchability of the polyvinyl alcohol film at the time of producing the polarizing film is not sufficiently improved.

Although the tensile elastic modulus can be reduced in the technique disclosed in the Patent Document 6, the tensile modulus is preferably reduced to 13.8 to 17.8 MPa in the examples and 27 MPa in the comparative examples not irradiated with electromagnetic waves.

In addition, in the examples of the above-mentioned Patent Documents 1 to 6, only a polyvinyl alcohol film having a thickness of 50 占 퐉 or more is described, and further improvement is demanded in order to cope with recent demand for thinning.

Therefore, the present invention is to provide a polyvinyl alcohol film excellent in stretchability at the time of producing a polarizing film under such a background, a polyvinyl alcohol film capable of obtaining a polarizing film having a high degree of polarization and less stain, And a polarizing film using the polyvinyl alcohol film. The present invention also provides a polarizing film using the polyvinyl alcohol film.

Accordingly, the present inventors have conducted intensive studies in view of such circumstances, and as a result, have found that the length of the flow direction (MD) is not less than a specific length, and the tensile elastic modulus in the flow direction (longitudinal direction, MD) It was found that the polyvinyl alcohol-based film is excellent in stretchability at the time of producing the polarizing film, and that the thin polarizing film can be produced with good yield. It has been found that a polarizing film obtained by using such a polyvinyl alcohol-based film has a high degree of polarization and becomes a polarizing film with less unevenness.

That is, the first point of the present invention is a polyvinyl alcohol-based film having a length of 4 km or more and a tensile modulus X (MPa) in the longitudinal direction (MD) of 5 to 12 MPa in a state where the moisture content of the film is 9 wt% Is a polyvinyl alcohol-based film.

In a second aspect of the present invention, there is provided a process for producing a polyvinyl alcohol-based resin, which comprises a film-forming step of forming an aqueous solution of a polyvinyl alcohol-based resin by continuous casting, a drying step of drying the film thus formed, and a heat- The method for producing a polyvinyl alcohol-based film according to the first aspect of the present invention is characterized in that the film-forming film is dried at a temperature of 100 ° C or higher in the drying step, and the heat- And then heating the film to 60 to 99 占 폚.

The third aspect of the present invention is a polarizing film characterized in that the polyvinyl alcohol film of the first aspect is used.

The polyvinyl alcohol film of the first aspect of the present invention has a tensile modulus X of 5 to 12 MPa in the longitudinal direction (MD) in a state where the water content is 9% by weight, so that the film has excellent stretchability in the production of the polarizing film, There is an effect that breakage can be prevented from occurring in the case of manufacturing.

Particularly when the thickness D of the film is 5 to 25 占 퐉 and the thickness D (占 퐉) and the tensile elastic modulus X (MPa) satisfy the following formula (1), the improvement of the rupture resistance It is possible to achieve the effect.

0.4? X / D? 0.6 (1)

Among them, the tensile elastic modulus Y (MPa) in the width direction (TD) and the tensile elastic modulus X (MPa) in the length direction (MD) in the state that the moisture content of the film is 9 wt% satisfy the following formula , It is possible to improve the stretchability at the time of producing the polarizing film.

0.7? Y / X? 1.3 (2)

In addition, when the tensile strength F in the longitudinal direction (MD) is 100 MPa or more, it is possible to prevent the thin polarizing film from being broken when it is produced.

(3), where ny is the refractive index in the longitudinal direction (MD), ny is the refractive index in the width direction (TD), nz is the refractive index in the thickness direction, and D When the retardation Rth is in the range of 80 to 140 nm, the swelling property in the thickness direction can be optimized and the elongation at the time of polarizing film production can be appropriately adjusted.

Rth = {(nx + ny) / 2-nz} x 1000 x D (3)

When the width of the film is 4 m or more, the productivity can be improved.

Since the process for producing a polyvinyl alcohol-based film according to the second aspect of the present invention comprises a specific drying process and a heat treatment process, the polyvinyl alcohol-based film of the first aspect, which is excellent in stretchability and rupture resistance in polarizing film production Can be produced.

Since the polarizing film of the third aspect of the present invention uses the polyvinyl alcohol-based film of the first aspect, it exhibits a high degree of polarization and has an effect of reducing the number of irregularities.

Hereinafter, the present invention will be described in detail.

The polyvinyl alcohol-based film of the present invention is a polyvinyl alcohol-based film having a length of 4 km or more, and has a tensile modulus X of 5 to 12 MPa in the longitudinal direction (MD) measured with the moisture content of the film being 9 wt% do.

The polyvinyl alcohol film is formed as a polarizing film through a swelling process, a stretching process and the like, while being transported in the longitudinal direction (MD). Here, it is preferable that the polyvinyl alcohol film has a specific length (4 km or more) and the longitudinal direction (MD) measured with the water content of the polyvinyl alcohol-based film being 9% by weight is a specific tensile modulus X 12 MPa), the polyvinyl alcohol-based film is excellent in stretchability at the time of producing the polarizing film, and even when a thin polarizing film is produced, no breakage occurs. Then, the obtained polarizing film exhibits a high degree of polarization and also has less unevenness.

First, the tensile modulus of elasticity of the polyvinyl alcohol film of the present invention will be described.

The tensile modulus in the present invention is a value measured under an environment of 20 占 폚 and 65% RH in accordance with JIS K 7127: 1999. The tensile modulus is also called Young's modulus or tensile modulus.

The moisture content in the present invention is a value calculated from the weight before and after drying the polyvinyl alcohol film at a temperature of 105 ° C. for 16 hours by a dryer and is defined as A before the drying and B after drying Is calculated by the following equation.

Water content (% by weight) = 100 x (A-B) / A

As described above, although the polyvinyl alcohol-based film is stretched after swelling in the production process of the polarizing film, it is difficult to accurately and stably measure the tensile elastic modulus after swelling. In the present invention, in consideration of the fact that the moisture content of the polyvinyl alcohol-based film provided for the polarizing film production is several percent, the tensile elastic modulus at a water content of 9 wt%, which is easy to control by humidity control, is taken as an index.

The humidity control method is not particularly limited. For example, when a relatively dry polyvinyl alcohol film immediately after production is humidified for several hours to several hours under an environment of 20 ° C and 65% RH, a humidity close to the equilibrium moisture content The moisture content can be stabilized by weight%. In the present invention, the term "moisture content 9 wt%" means "moisture content is in the range of 9.0 wt% ± 0.5 wt%", and within this range, the tensile modulus largely does not change most. Since the moisture content in the film varies with the equilibrium moisture content depending on the environmental humidity, a test piece having a moisture content of 9 wt% is quickly provided for measurement of the tensile modulus.

In the present invention, the in-plane variation ΔX (MPa) of the tensile modulus X in the longitudinal direction (MD) and the tensile elastic modulus Y (MPa) in the width direction (TD) in the state where the moisture content is 9 wt% The in-plane deviation? Y (MPa) is preferably 5 MPa or less, particularly preferably 3 MPa or less, more preferably 2 MPa or less.

If such in-plane deviation [Delta] X and in-plane deviation [Delta] Y are too large, there is a tendency that unevenness in drawing occurs during the production of the polarizing film, and unevenness occurs in the polarizing film.

Here, the method for producing the polyvinyl alcohol-based film of the present invention will be described. That is, the method for producing a polyvinyl alcohol-based film of the present invention comprises a film-forming step (A) for forming an aqueous solution of a polyvinyl alcohol-based resin by a continuous casting method, a drying step (B) for drying the film- And a heat treatment step (C) for heat-treating the dried film, wherein the temperature for drying the film formed in the drying step (B) is 100 占 폚 or higher, The heat treatment step (C) is characterized in that the dried film is cooled to 50 캜 or lower and then heated at 60 to 99 캜.

[Film forming step (A)]

First, the film forming step (A) will be described in detail.

As the polyvinyl alcohol-based resin used in the present invention, a resin produced by saponifying polyvinyl alcohol-based resin that is unmodified, that is, polyvinyl acetate obtained by polymerizing vinyl acetate is usually used. If necessary, a resin obtained by saponifying a copolymer of vinyl acetate and a small amount (usually 10 mol% or less, preferably 5 mol% or less) of a copolymerizable component 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., Butene, isobutene, etc.), vinyl ethers, and unsaturated sulfonate salts. It is also possible to use a modified polyvinyl alcohol-based resin obtained by chemically modifying a hydroxyl group after saponification.

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) ) Saponifying and decarboxylating a copolymer of vinyl acetate and vinylethylene carbonate, (iii) saponifying and removing 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 monoaryl 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, the degree of polarization of the polarizing film tends to decrease. When the weight-average molecular weight is too large, the stretching at the time of producing the polarizing film of the polyvinyl alcohol-based film tends to become difficult. 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. If the average degree of saponification is too small, the degree of polarization of the polarizing film tends to decrease.

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-based resin is preferably washed with a solvent such as water and dehydrated using a centrifugal separator or the like to obtain a polyvinyl alcohol-based resin wet cake having a moisture content of 50% by weight or less. If the moisture content is too large, it tends to be difficult to obtain a desired aqueous solution concentration.

The polyvinyl alcohol-based resin wet cake is dissolved in hot water or hot water to prepare a polyvinyl alcohol-based resin aqueous solution.

The method of preparing the polyvinyl alcohol-based resin aqueous solution is not particularly limited, and for example, it may be prepared by using a heated multi-screw extruder, or by adding to the molten can having the upper and lower circulation flow- A vinyl alcohol based resin wet cake may be put in and water vapor may be blown into the can to dissolve and prepare an aqueous solution of a desired concentration.

The aqueous solution of the polyvinyl alcohol resin may contain, in addition to the polyvinyl alcohol resin, a commonly used plasticizer such as glycerin, diglycerin, triglycerin, ethylene glycol, triethylene glycol, polyethylene glycol and trimethylolpropane, , And cationic is preferable from the viewpoint of the film formability of the polyvinyl alcohol-based film.

The preferred plasticizer is glycerin. The content of the plasticizer in the polyvinyl alcohol-based resin aqueous solution is preferably 1 to 20% by weight.

The surfactant is preferably a polyoxyethylene alkylamine or a higher fatty acid alkanolamide. The content of the surfactant in the polyvinyl alcohol resin aqueous solution is preferably 0.01 to 1% by weight.

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 defoaming by a multi-screw extruder having a static deformation or a vent. As the multiaxial extruder having a vent, a twin-screw extruder having a vent is usually used.

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

The viscosity of such a polyvinyl alcohol-based resin aqueous solution is preferably from 50 to 200 Pa · s, particularly preferably from 70 to 150 Pa · s, at the time of discharging. 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 0.1 to 3.0 m / min, particularly preferably 0.2 to 2.5 m / min, more preferably 0.3 to 2.0 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 length tends to be insufficient, and the speed tends to be difficult to come out. 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 such a cast drum is preferably 1 to 30 m / min, particularly preferably 2 to 25 m / min, and more preferably 3 to 20 m / min. If the rotation speed is too slow, the productivity tends to decrease. If the rotation speed is too fast, the dehydration tends to become insufficient.

The surface temperature of such a cast drum is preferably 40 to 99 占 폚, more preferably 50 to 90 占 폚, and particularly preferably 55 to 80 占 폚. When the surface temperature is too low, defective dewatering tends to occur, while when it is too high, foaming tends to occur.

In this way, the film-forming step (A) is carried out and the film thus formed is peeled off from the casting drum.

[Drying step (B)]

Next, the drying step (B) will be described in detail. This drying step (B) is a step of heating and drying the film thus formed.

The film peeled off from the cast drum (the film thus formed) is transported in the direction of flow (MD) using a nip roll or the like, and is dried by alternately contacting the surface and the back surface of the film with a plurality of heat rolls. The heat roll is preferably a roll having a diameter of 0.2 to 2 m, for example, hard chrome plated or mirror-finished on its surface, and is preferably dried using 2 to 30 rolls, preferably 10 to 25 rolls.

The drying temperature (the temperature at which the formed film is dried) is preferably 100 占 폚 or higher, particularly preferably 100 to 120 占 폚, more preferably 100 to 115 占 폚, particularly preferably 100 to 110 占 폚. If the drying temperature is too low, the drying tendency tends to become defective. If the drying temperature is too high, the appearance tends to cause defects such as waves. The drying temperature in the present invention is the surface temperature of the hot roll, which is the highest temperature among the heat rolls used.

The drying time is not particularly limited, but is usually 1 to 60 seconds, preferably 2 to 50 seconds, particularly preferably 3 to 40 seconds, more preferably 4 to 30 seconds. When the drying time is too short, the drying tendency tends to become poor. When the drying time is too long, there is a tendency to cause appearance defects such as waves.

The drying time in the present invention means the contact time between the hot roll at the highest temperature and the film formed. When a plurality of hot rolls having the highest temperature are used, the contact time with the hot roll Lt; / RTI >

The moisture content of the dried film is preferably 5% by weight or less, particularly preferably 0.1 to 4% by weight, more preferably 0.2 to 3% by weight, particularly preferably 0.3 to 2.5% by weight. If the moisture content is too high, the polyvinyl alcohol-based film finally obtained tends to be inferior in drying.

[Heat treatment step (C)]

Next, the heat treatment step (C) will be described in detail. This heat treatment step (C) is a step of heat-treating the dried film. Such a heat treatment step is generally an arbitrary step that is made as necessary, but in the present invention, it is an essential step for controlling the tensile modulus of elasticity. That is, in this heat treatment step (C), the film dried at 100 占 폚 or higher in the drying step (B) is once cooled to 50 占 폚 or lower (the temperature of the dried film itself) The tensile modulus of elasticity is set in a desired range to improve the stretchability in the production of the polarizing film.

Examples of the cooling method include, for example, a natural cooling method in which the material is left to cool naturally, and a method in which cold air is blown out.

Examples of the heating method include a method of blowing hot air with a floating dryer, a method of contacting with a hot roll, and the like. In the present invention, a method using a floating dryer is preferable from the viewpoint of stabilizing the tensile elastic modulus.

The heating temperature is preferably 65 to 95 占 폚, particularly preferably 70 to 90 占 폚, and more preferably 70 to 80 占 폚. When the heating temperature is too low, the tensile modulus tends to decrease. When the heating temperature is too high, the tensile modulus tends to increase. The heating temperature in the present invention means the temperature of the hot air when the heating method blows hot air through the floating dryer. When the heating method is a method of contacting the hot roll, Means the surface temperature of the roll.

The heating time is not particularly limited, but in the case of using a floating dryer, the heating time is preferably 10 to 120 seconds, particularly preferably 20 to 90 seconds, and more preferably 30 to 60 seconds. If the heating time is too short, the tensile modulus tends to increase. When the heating time is too long, the productivity tends to decrease.

The moisture content of the film after heating is preferably from 0.1 to 2% by weight, particularly preferably from 0.2 to 1.7% by weight, more preferably from 0.3 to 1.5% by weight. When the moisture content is too low, water swelling at the time of producing the polarizing film tends to become difficult. On the other hand, when the moisture content is too high, the polyvinyl alcohol-based film finally obtained tends to be inferior in drying.

As described above, the drying process (B) and the heat treatment process (C) have been described. However, in the manufacturing method of the present invention, the temperature balance between the two processes is important and the drying temperature in the drying process (B) It is more preferable to select a relatively low temperature in such a temperature range, and it is particularly preferable that the heating temperature in the heat treatment step (C) is less than 100 占 폚, which is the boiling point of water.

[Polyvinyl alcohol film]

It is possible to obtain the polyvinyl alcohol-based film of the present invention which is long in the flow direction (MD) through the drying step (B) and the heat treatment step (C). The polyvinyl alcohol film is slit on both ends thereof and wound in a roll form on the core pipe.

The width of the polyvinyl alcohol film of the present invention thus obtained is preferably 4 m or more from the viewpoint of productivity improvement, and more preferably 4 to 6 m from the standpoint of avoiding breakage.

The length of the polyvinyl alcohol film of the present invention is presumed to be 4 km or more, preferably 5 km or more from the viewpoint of the polarizing film and correspondingly large area of the liquid crystal screen, and particularly preferably 5 ~ 50km.

The thickness D of the polyvinyl alcohol film is preferably 30 占 퐉 or less from the viewpoint of thinning of the polarizing film, particularly preferably 25 占 퐉 or less from the viewpoint of further thinning, more preferably 5 to 25 占 퐉, Particularly preferably 5 to 20 占 퐉.

Such a thickness D (占 퐉) is adjusted by the resin concentration in the polyvinyl alcohol-based resin aqueous solution, the amount of the resin to be cast into the cast mold (ejection speed), the draw ratio and the like.

In the polyvinyl alcohol film of the present invention, when the thickness D of the film is 5 to 25 占 퐉, the tensile modulus X (占 퐉) in the flow direction (MD) measured with the thickness D (占 퐉) (MPa) preferably satisfies the following formula (1) from the viewpoint of improving the rupture resistance at the time of producing the polarizing film.

0.4? X / D? 0.6 (1)

Particularly preferably, the following formula (1 ') is satisfied from the viewpoint of improvement in stretchability at the time of producing the polarizing film.

0.45? X / D? 0.55 (1 '

In the polyvinyl alcohol film of the present invention, the tensile modulus of elasticity Y (MPa) in the transverse direction (TD) in a state where the water content is 9% by weight satisfies the following formula (2) from the viewpoint of improvement in stretchability at the time of producing the polarizing film .

0.7? Y / X? 1.3 (2)

Particularly preferably, the following formula (2 ') is satisfied from the viewpoint of improvement in stretchability at the time of producing the polarizing film.

0.75? Y / X? 1.1 (2 '

If the value of Y / X is too small, the elongation in the flow direction (MD) of the polarizing film production time tends to decrease. On the other hand, if it is too large, the stretching property tends not to be stabilized.

The tensile strength F (MPa) of the polyvinyl alcohol-based film of the present invention in the flow direction (MD) in the state where the water content is 9 wt% is preferably 100 MPa or more, and particularly preferably 110 MPa or more. When the tensile strength F (MPa) is too small, breakage tends to occur at the time of producing a thin polarizing film. The upper limit value of the tensile strength F (MPa) is usually 200 MPa.

In the polyvinyl alcohol film of the present invention, when the refractive index in the longitudinal direction (MD) is nx, the refractive index in the width direction (TD) is ny, the refractive index in the thickness direction is nz, and the thickness is D It is preferable that the retardation Rth (nm) in the thickness direction calculated in (3) is 80 to 140 nm. More preferably 85 to 130 nm, and further preferably 90 to 120 nm. If the retardation Rth (nm) in the thickness direction is too small, the swelling property in the thickness direction tends to decrease. If the retardation Rth (nm) in the thickness direction is too large, the planar orientation of the polymer chains is strong, have.

Rth = {(nx + ny) / 2-nz} x 1000 x D (3)

In the above-described embodiment, a method of producing a polyvinyl alcohol-based film by using a cast drum (drum-shaped roll) as the casting type is described, but a cast belt or a resin film is used as the casting type And the like.

Since the polyvinyl alcohol-based film of the present invention is excellent in stretchability, it is particularly preferably used as a disk for a polarizing film.

Here, a method for producing a polarizing film obtained by using the polyvinyl alcohol film of the present invention will be described.

[Polarizing film production method]

The polarizing film of the present invention is produced by loosening the polyvinyl alcohol film from the roll and transferring it in the horizontal direction, and by swelling, dyeing, boric acid crosslinking, stretching, washing, drying and the like.

The swelling process is carried out before the dyeing process. In addition to being able to clean the surface of the polyvinyl alcohol film by the swelling process, the polyvinyl alcohol film is also swollen to prevent uneven dyeing. As the treatment liquid in the swelling process, water is usually used. If the main component is water, the treatment liquid may contain a small amount of an additive such as an iodide compound, a surfactant, or an alcohol. The temperature of the swelling bath is usually about 10 to 45 DEG C, and the immersion time in the swelling bath is usually about 0.1 to 10 minutes.

The dyeing step is carried out by bringing a polyvinyl alcohol-based 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 in the form of an aqueous solution or a water-organic solvent mixture at a concentration of about 10 to 100 g / L, and potassium iodide is preferably allowed to coexist in the liquid from the viewpoint of stabilizing 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.

The stretching step is preferably stretched by 3 to 10 times, preferably by 3.5 to 6 times in one axis direction (flow direction (MD)). At this time, it is also possible to perform a slight stretching (a degree of preventing the shrinkage in the width direction (TD) or more) in the direction perpendicular to the stretching direction. The temperature at the time of stretching is preferably 30 to 170 캜. The stretching magnification may be set to the above range, and the stretching operation may be performed not only once but also several times in the polarizing film producing step.

In the present invention, as described above, the stretching tension in such a stretching step needs to be in an appropriate range. That is, when the stretching tension is too large, the stretching can not be performed at a predetermined stretching magnification, and the dichroic dye is not sufficiently oriented, so that the degree of polarization tends not to be improved. On the contrary, when the stretching tension is too small, orientation of the dichroic dye is unstable even when stretched to a predetermined stretching ratio, and there is a tendency that unevenness occurs in the polarizing film.

Generally, since the stretching tension is set for each thickness in the polarizing film producing step, it is difficult to generalize the preferable range, but it is preferable to reduce the stretching tension by at least 1% in comparison with the same thickness, 1 to 3 percent.

The cleaning process is carried out, for example, by immersing the polyvinyl alcohol film in an aqueous iodide solution such as water or potassium iodide, and the precipitates generated on the surface of the polyvinyl alcohol film can be removed. When potassium iodide aqueous solution is used, the concentration of potassium iodide is 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 from 1 to 300 seconds, preferably from 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 step is carried out, for example, by drying the polyvinyl alcohol-based film at 40 to 80 DEG C for 1 to 10 minutes in the atmosphere.

Thus, the polarizing film of the present invention is obtained. The degree of polarization of the polarizing film of the present invention is preferably 99.5% or more, and more preferably 99.8% or more. When the degree of polarization is too low, the contrast in the liquid crystal display tends to be insufficient.

In addition, the degree of polarization is usually in the overlapped state where the two polarizing films of the orientation direction to be in the same direction, the luminous transmittance to the wavelength λ (H _11), and two polarizing films, the orientation of direction are orthogonal to each other (H ₁ ) measured with respect to the wavelength? In accordance with the following formula.

Polarization degree = [(H ₁₁ -H ₁ ) / (H ₁₁ + H ₁ )] ^1/2

The polarizing film of the present invention has a simple transmittance of preferably 42% or more, and more preferably 43% 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.

The polarizing film of the present invention is excellent in the degree of polarization and is therefore very suitable for producing a polarizing plate free from unevenness.

Here, a method for producing a polarizing plate using the polarizing film of the present invention will be described.

[Polarizing plate production method]

The polarizing plate is produced by bonding a resin film, which is optically isotropic, to one side or both sides of the polarizing film of the present invention as an optical protective film through an adhesive. Examples of the protective film include cellulose triacetate, cellulose diacetate, polycarbonate, polymethyl methacrylate, cycloolefin polymer, cycloolefin copolymer, polystyrene, polyether sulfone, polyarylene 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 then the two are adhered to each other, .

It is also possible to apply a curable resin such as a urethane resin, an acrylic resin, or a urea resin to one side or both sides of the polarizing film, and cure to form a cured layer, thereby forming 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 or the polarizing plate using the polyvinyl alcohol film of the present invention is excellent in the polarizing performance and can be used for a portable information terminal, a PC, a television, a projector, a signage, an electronic tabletop calculator, an electronic clock, a word processor, An antireflection layer for a display device (a CRT, an LCD, an organic EL, an electronic paper, etc.), an optical communication device, a liquid crystal display device such as a camera, a photo album, a thermometer, 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.

The properties (water content, tensile modulus, tensile strength, stretching tension in the direction of the thickness, stretching tension) of the polyvinyl alcohol film in the following examples and comparative examples and characteristics (polarization degree, unit transmittance, unevenness) Were measured and evaluated as follows.

<Measurement Conditions>

[Water content (% by weight)]

A test piece of 100 mm x 100 mm was cut out from the obtained polyvinyl alcohol film and the weight B (g) after the initial weight A (g) and the weight B (g) after drying for 16 hours at an ambient temperature of 105 캜 by a dryer, (% By weight).

Water content (% by weight) = 100 x (A-B) / A

[Tensile modulus (MPa), tensile strength F (MPa)]

A 120 mm x 15 mm test piece was cut out from the obtained polyvinyl alcohol film and conditioned in a thermostatic hygrostat at 20 deg. C and 65% RH such that the water content was 9% by weight. + -. 0.5% by weight. Tensile modulus X of the flow direction (MD) in an environment of 20 占 폚 and 65% RH in accordance with JIS K 7127: 1999 (tensile speed 1000 mm / minute, chuck distance 50 mm) (MPa) and the tensile elastic modulus Y (MPa) in the transverse direction (TD) were measured. The tensile strength F (MPa) was measured in the flow direction (MD).

[Directional phase difference Rth (nm) of thickness]

A test piece having a length of 4 cm and a width of 4 cm was cut from the center portion and the both end portions (10 cm inward from the film end) of the obtained polyvinyl alcohol film in the width direction (TD) and measured with a retardation measuring apparatus ("KOBRA-WR" Manufactured by Oji Scientific Co., Ltd.), the retardation Rth (nm) in the thickness direction at 590 nm was measured.

&Lt; Measurement conditions of Rth &

Angle of incidence: 50 °

Slope center axis: Ground axis

Average refractive index: Measured using Abbe's refractometer

[Stretching tension (N)]

A test piece having a length of 50 mm x width (width direction (TD)) of 35 mm in length (MD) was cut from the obtained polyvinyl alcohol film and stretched in the longitudinal direction MD so that the distance between the chucks was 20 mm. (34 mm) in the longitudinal direction (MD) while being immersed in hot water at 25 占 폚 for 60 seconds, and then stretched in the longitudinal direction (占 퐉) in the dyeing solution at 28 占 폚. (MD) and 1.6 times (54.4 mm) in the longitudinal direction (MD) and 2.05 times (111.5 mm) in the longitudinal direction (MD) in the boric acid solution at 55 占 폚. The compositions of the dyeing solution and the boric acid solution used are as follows.

Dyeing solution: Iodine 0.9 g / L, potassium iodide 30 g / L

Boric acid solution: 30 g / L of potassium iodide, 25 g / L of boric acid

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

A test piece having a length of 4 cm and a width of 4 cm was cut from the center portion of the obtained polarizing film in the width direction (TD) and both side ends (10 cm inside from both ends of the polarizing film), and the polarizing film was measured with an automatic polarizing film measuring apparatus (%) And a unit transmittance (%) were measured using a spectrophotometer (manufactured by Usha Co., Ltd., VAP7070). This measurement was performed on the central portion of the polarizing film in the flow direction MD and on the tip portion / terminal portion (10 m inward from each end of the polarizing film and each end of the polarizing film).

〔stain〕

A test piece having a length of 30 cm and a width of 30 cm was cut from the central portion of the obtained polarizing film in the width direction TD and the both side ends (10 cm inward from each end of both side ends of the polarizing film) to obtain two polarizing plates (43.5% in terms of the unit transmittance and 99.9% in the degree of polarization) at an angle of 45 [deg.], The optical stain was observed in the transmission mode using a light box with a surface illuminance of 14,000 lx and evaluated according to the following criteria.

(Evaluation standard)

○ · · · No staining

× · · With dirt

This evaluation was carried out with respect to the central portion of the polarizing film in the flow direction MD and the tip portion / terminal portion (10 m inward from each end of the polarizer film and each end of the polarizer film).

&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 degree of saponification of 99.8 mol%, 2,500 kg of water and 120 kg of glycerin as a plasticizer were placed and heated to 140 캜 with stirring to adjust the concentration to 25 wt% To obtain a dissolved polyvinyl alcohol-based resin aqueous solution. Subsequently, the polyvinyl alcohol resin aqueous solution was fed to a twin-screw extruder having a vent and defoamed. Thereafter, the temperature of the aqueous solution was set at 95 占 폚, and the sheet was discharged from a T-shaped slit die discharge port into a rotating casting drum at a discharge speed of 0.8 m / ) And casting. The formed film was peeled off from the cast drum, and the surface and back of the film were dried while alternately contacting with 20 heat rolls. The drying temperature (surface temperature of the hot roll at the highest temperature) was 120 占 폚, and the drying time (cumulative time of contact between the hot roll at the highest temperature and the film) was 12 seconds. Subsequently, the dried film was naturally cooled, the temperature of the film itself was once cooled to 40 占 폚, heated by a hot air of 75 占 폚 for 60 seconds from both sides of the film using a floating dryer, To obtain a polyvinyl alcohol film (thickness 20 m, width 5 m, length 5 km). Finally, both ends of the polyvinyl alcohol-based film were slit and wound in roll form on a core tube. The properties of the obtained polyvinyl alcohol film are shown in Table 1 below.

(Production of polarizing film)

The obtained polyvinyl alcohol film was unrolled from the roll, conveyed horizontally using a conveying roll, and first stretched 1.7 times in the flow direction (MD) for 1 minute while being immersed in a water bath at 25 캜 and swelled. Subsequently, the resultant was immersed in an aqueous solution at 28 占 폚 consisting of 0.9 g / L of iodine and 30 g / L of potassium iodide and stretched 1.6 times in the flow direction (MD) for 0.5 minutes while dyeing. Then, 25 g / L of boric acid and 30 g / L and uniaxially stretched 2.0 times in the flow direction (MD) while crosslinking the boric acid. Finally, the film was washed with an aqueous solution of potassium iodide and dried at 50 ° C for 2 minutes to obtain a polarizing film having a total draw ratio of 5.6 times. No breakage occurred during the production of such a polarizing film. The properties of the obtained polarizing film are shown in Table 2 below.

&Lt; Example 2, Comparative Example 1 &gt;

A polyvinyl alcohol film and a polarizing film were obtained in the same manner as in Example 1 except that the film was produced under the conditions shown in Table 1 below. The characteristics of the resulting polyvinyl alcohol film are shown in Table 1, and the properties of the obtained polarizer film are shown in Table 2 below.

In Comparative Example 1, a polarizing membrane was produced in the same manner as in Example 1, but fracture occurred during drawing in the boric acid crosslinking step. The properties shown in Table 2 are characteristics of the polarizing film front end portion barely obtained.

The polyvinyl alcohol films of Examples 1 and 2 had a high degree of polarization of the obtained polarizing film and no unevenness because the value of the tensile elastic modulus was within the specific range of the present invention. On the contrary, the polyvinyl alcohol film of Comparative Example 1 had a tensile modulus Is outside the specific range of the present invention, it is easy to break, and it can be seen that the resulting polarizing film is inferior to the degree of polarization and has unevenness.

In the same manner as in Example 1, a polyvinyl alcohol film having a length of 4 km and a length of 10 km was produced. Also in the case of the polyvinyl alcohol film having such a length, the same tendency as in Examples 1 and 2 was obtained.

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 or the polarizing plate using the polyvinyl alcohol film of the present invention is excellent in the polarizing performance and can be used for a portable information terminal, a PC, a television, a projector, a signage, an electronic tabletop calculator, an electronic clock, a word processor, , Antireflection layers for display devices (CRT, LCD, organic EL, electronic paper, etc.), optical communication devices (such as liquid crystal display devices such as photo albums, thermometers, audio, instrumentation of automobiles and machinery, sunglasses, , Medical equipment, building materials, toys, and the like.

Claims (8)

A polyvinyl alcohol-based film having a length of 4 km or more and a tensile modulus X of 5 to 12 MPa in a longitudinal direction (MD) in a state where the moisture content of the film is 9% by weight. The method according to claim 1,
Wherein the thickness D of the film is 5 to 25 占 퐉 and the thickness D (占 퐉) and the tensile elastic modulus X (MPa) satisfy the following formula (1).
0.4? X / D? 0.6 (1) The method according to claim 1 or 2,
The tensile elastic modulus Y (MPa) in the transverse direction (TD) and the tensile elastic modulus X (MPa) in the longitudinal direction (MD) in the state that the moisture content of the film is 9 wt% satisfy the following formula (2) A polyvinyl alcohol-based film.
0.7? Y / X? 1.3 (2) 4. The method according to any one of claims 1 to 3,
Wherein a tensile strength F in the longitudinal direction (MD) is 100 MPa or more. 5. The method according to any one of claims 1 to 4,
The retardation Rth in the thickness direction calculated by the following equation (3), where ny is the refractive index in the longitudinal direction MD, ny is the refractive index in the width direction TD, nz is the refractive index in the thickness direction, Is in the range of 80 to 140 nm.
Rth = {(nx + ny) / 2-nz} x 1000 x D (3) 6. The method according to any one of claims 1 to 5,
Wherein the film has a width of 4 m or more. A process for producing a film according to any one of claims 1 to 6, which comprises a film forming step of forming an aqueous solution of a polyvinyl alcohol-based resin by a continuous casting method, a drying step of drying the film thus formed, and a heat treatment step of heat- , Wherein the film-forming film is dried at a temperature of 100 占 폚 or higher in the drying step, and the heat-treating step is a step of cooling the dried film to 50 占 폚 or lower , And heating the polyvinyl alcohol-based film at 60 to 99 占 폚. A polarizing film characterized in that the polyvinyl alcohol film according to any one of claims 1 to 6 is used.