KR20180074673A - POLYVINYLLLICOHOLE FILM, POLARIZING FILM, POLARIZING PLATE, AND METHOD FOR PRODUCING POLYVINYLLOHOLYE-BASED FILM - Google Patents

Abstract

(° C.) of an orientation axis (slow axis) and a transverse direction (TD direction) of 20 ° or less and a cross angle θ Is a polyvinyl alcohol-based film having a deviation &thetas; (DEG) of 20 DEG or less. Therefore, a polarizing film having a high polarizing performance and a low color unevenness can be obtained because of excellent extensibility at the time of polarizing film production. It is possible to provide a polyvinyl alcohol-based film which does not break even when the thin polarizing film is produced.

Description

POLYVINYLLLICOHOLE FILM, POLARIZING FILM, POLARIZING PLATE, AND METHOD FOR PRODUCING POLYVINYLLOHOLYE-BASED FILM

The present invention relates to a polyvinyl alcohol film, particularly a polyvinyl alcohol 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 film And a method for producing a polyvinyl alcohol-based film.

Background Art [0002] Conventionally, a polyvinyl alcohol-based film has been used for many applications as a film having excellent transparency, and polarizing films are 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 high-quality and highly reliable apparatus has been expanding.

Of these, a polarizing film having excellent optical characteristics is required in accordance with a high luminance, 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 polyvinyl alcohol polymer is easily oriented in the MD direction because it is pulled in the flow direction (MD direction) in the film thus formed in such a carrying process, the orientation axis of the obtained polyvinyl alcohol film Axis) are often oriented in the MD direction. 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 orientation 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. The orientation axis is also called an optical axis.

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

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 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. Conventionally, a thickness of about 60 占 퐉 is now about 45 占 퐉 in thickness, and it is expected to be 30 占 퐉 or less in recent years. 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 stretchability, for example, a method of specifying the ratio between the speed of the cast drum and the final film winding speed at the time of film formation (see, for example, Patent Document 1) (Refer to Patent Document 2, for example), and a method of controlling the tensile state in the drying process of a film formed thereon (see, for example, Patent Document 3) has been proposed. In addition, a polyvinyl alcohol-based film having a reduced in-plane retardation has been proposed (for example, see Patent Documents 4 and 5). A polyvinyl alcohol-based film having a tilt (orientation angle) of an optical axis within a specific range has been proposed (see, for example, Patent Document 6).

Patent Document 1 JP 2001-315141A Patent Document 2 JP 2001-315142A Patent Document 3 JP 2002-79531 A Patent Document 4 JP 2006-291173A Patent Document 5 JP 2007-137042A Patent Document 6 WO 2009 / 028141A

However, even with the method of the patent document, it is insufficient to improve the stretchability in the production of the polarizing film.

Patent Document 1 specifies the degree of stretching (tensile 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 it is insufficient to improve 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 makes it difficult to stretch the molecular chains forcibly. 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 Literature 1 discloses an example in which the polyvinyl alcohol film is not stretched in the MD direction at the time of producing the polyvinyl alcohol film. However, the shrinkage stress due to the Poisson's ratio and the shrinkage stress due to dehydration are not sufficient in the TD direction There is a problem that the polymer orientation can not be sufficiently made uniform. That is, unless the polymer 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.

In the technique disclosed in Patent Document 2, the film after film formation can be dried uniformly, but the orientation of the polymer can not be controlled and it is insufficient to improve the stretchability in the production of the polarizing film.

In the technique disclosed in Patent Document 3, the film thickness of the polyvinyl alcohol film can be made uniform, but the orientation of the polymer can not be controlled and it is insufficient to improve the stretchability in the production of the polarizing film.

Although the in-plane retardation of the polyvinyl alcohol film can be reduced in the above-described Patent Documents 4 and 5, the polymer is only randomly oriented, and if the in-plane retardation is not reduced in a uniformly aligned state, It is insufficient to improve the continuity of poetry, and there is room for improvement in that respect.

The disclosed technique of Patent Document 6 is a polyvinyl alcohol film whose orientation angle in the width direction of the film is 45 to 135 degrees with respect to the longitudinal direction, but the angular range is wider as it occupies half of all directions, It is hard to say that. The range of the alignment angle in the embodiment is the narrowest at 54 deg., And the deviation of the alignment angle is large. If the film is shaken to such a large extent, the stretchability is shaken in the width direction, and color unevenness tends to occur in the resulting polarizing film. In addition, although the present disclosure technique is to control the orientation angle with the peripheral speed ratio of the drying roll, such a production method is disadvantageous in that the characteristics of the film tend to fluctuate in the longitudinal direction, and the orientation angle is within the above range over the entire length, The constant ground is unknown (in the example, there is no film length substrate, only one measurement in the long direction). In addition, the thickness of the film in the examples is 75 mu m, and it is difficult to cope with the demand for thinning in recent years.

Accordingly, in the present invention, a polyvinyl alcohol-based film capable of obtaining a polarizing film having a high polarizing performance and excellent in polarizing performance at the time of production of a polarizing film under such a background and having less color unevenness, To provide a polarizing film and a polarizing plate including such a polyvinyl alcohol film, and a method of producing a polyvinyl alcohol film.

Accordingly, the present inventors have conducted intensive studies in view of such circumstances. As a result, they have found that 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 the deviation of the crossing angle [Delta] [theta] ([Delta] [theta]) in the specific range are excellent in the stretchability at the time of producing the polarizing film, and 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 film has a high polarization performance and becomes a polarizing film with less color unevenness.

That is, the first aspect of the present invention is a polyvinyl alcohol-based 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 is characterized in that an intersection angle? (?) Of an orientation axis (slow axis) 20 DEG or less, and the deviation [Delta] [theta] (DEG) of the crossing angle [theta] is 20 DEG or less.

Particularly, when the refractive index in the width direction (TD direction) is nx and the refractive index in the direction (MD direction) perpendicular thereto is ny, the value of birefringence DELTA Nxy, which is a value calculated by the following formula (A) The vinyl alcohol-based film is the second object of the present invention.

(A)? Nxy = | nx-ny |

The third 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 占 퐉.

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

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

The present invention also provides a process for producing a polyvinyl alcohol-based resin, comprising: a step of forming an aqueous solution of a polyvinyl alcohol-based resin by a continuous casting method; and a step of continuously drying and stretching while being transported in the flow direction (MD direction) Wherein the polyvinyl alcohol film to be produced has an angle of intersection &thetas; (degrees) of an orientation axis (slow axis) and a width direction (TD direction) of 20 DEG or less and a deviation DELTA &thetas; (°) of the polyvinyl alcohol-based film is 20 ° or less.

Particularly, a method for producing a polyvinyl alcohol-based film is characterized in that the film is stretched 1.05 to 1.3 times in the transverse direction (TD direction) of the film.

The film is stretched beyond 1.3 times in transverse direction (TD direction) of the film, and then shrinkage is performed so that the final stretching magnification in the transverse direction (TD direction) is 1.3 times or less. The polyvinyl alcohol system The method for producing the film is the eighth aspect of the present invention.

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

Further, the present invention improves the stretchability by controlling the orientation axis because the stretching property upon production of the polarizing film depends on the orientation state of the polyvinyl alcohol-based polymer in the film.

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 占 퐉, a width of 2 m or more, and a length of 2 km or more and is a polyvinyl alcohol film having a crossing angle? (Deg.) Between the orientation axis (slow axis) Is 20 DEG or less, and the deviation DELTA &thetas; (DEG) of the crossing angle &thetas; is 20 DEG or less.

The thickness of the polyvinyl alcohol film of the present invention is 5 to 60 占 퐉, preferably 5 to 45 占 퐉, particularly preferably 5 to 30 占 퐉, particularly preferably 5 to 20 占 퐉, from the viewpoint of thinning of the polarizing film . The thickness of such a polyvinyl alcohol-based film is adjusted by the resin concentration in the polyvinyl alcohol-based resin aqueous solution, the cast amount, the ejection amount (ejection speed), the draw ratio, and the like.

The width of the polyvinyl alcohol-based film of the present invention is 2 m or more, preferably 2 to 6 m from the viewpoint of avoiding breakage.

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

In the present invention, the intersecting angle? (Degrees) between the orientation axis (slow axis) and the width direction (TD direction) is required to be 20 degrees or less, preferably 15 degrees or less, particularly preferably 10 degrees or less, 5 DEG or less, and still more preferably 2 DEG or less. If such an intersection angle? (°) exceeds the upper limit value, the elongation in the MD direction at the time of production of the polarizing film is lowered and the object of the present invention can not be achieved. Further, the lower limit value of the normal crossing angle? (0) is 0 占.

Further, in the present invention, the deviation ?? (?) Of the crossing angle? Is required to be 20 占 or less, preferably 10 占 or less, particularly preferably 5 占 or less, more preferably 3 占 or less. If the deviation ?? (?) Of such a crossing angle? Is too large, the polarizing film may have color unevenness, and the object of the present invention can not be achieved. Further, the lower limit value of the deviation ?? (?) Of the normal crossing angle? Is 0 占.

In the present invention, the birefringence ΔNxy is preferably 0.001 or less, particularly preferably 0.0008 or less, more preferably 0.0006 or less, particularly preferably 0.0005 or less. When the birefringence ΔNxy is too large, color irregularity tends to occur in the polarizing film.

Here,? Nxy is a numerical value calculated by | nx-ny | when the refractive index in the width direction (TD direction) is nx and the refractive index in the flow direction (MD direction) is ny. The product (| nx-ny | xd) of the birefringence ΔNxy and the film thickness d (nm) is the in-plane retardation (nm).

In the present invention, as a method of controlling the deviation? (), The deviation ?? () and the birefringence? Nxy of the crossing angle?, The film peeled from the casting mold in terms of precise control of the crossing angle? (TD direction) is preferred. A method of controlling the drying condition of the aqueous solution, a method of controlling the chemical structure of the polyvinyl alcohol-based resin, and the like.

Here, the method for producing the polyvinyl alcohol film of the present invention will be described in the order of steps.

[Film material]

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

As the polyvinyl alcohol-based resin constituting the polyvinyl alcohol-based film in the present invention, a resin prepared by saponifying polyvinyl alcohol-based resin obtained by polymerizing non-modified polyvinyl alcohol resin, that is, polyvinyl 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. They can be used with poison or with two or more. 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, ) 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 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. If 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. If it is too large, it tends to be difficult to stretch the polyvinyl alcohol- have. The weight average molecular weight of the polyvinyl alcohol resin is a weight average molecular weight measured by the GPC-MALS method.

The average degree of saponification of the polyvinyl alcohol 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, still more 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 aqueous solution is introduced into the T-shaped slit die by a predetermined amount and discharged and cast on a rotating casting drum, and is formed by a general casting method according to an ordinary method. Among them, the continuous cast method is preferable from the viewpoint of productivity.

The continuous casting method is a method in which an aqueous solution of a polyvinyl alcohol-based resin is cast and cast by casting such as cast drums, endless belts, and resin films, which are rotated in a T-shaped slit die. The film thus formed is peeled off from the cast mold, and is continuously dried by a heat roll or the like while being conveyed in the flow direction (MD direction), and is finally wound on a roll as a polyvinyl alcohol-based film to be a product.

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 the 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 a polyvinyl alcohol-based resin aqueous solution is preferably from 50 to 200 Pa · s at the time of discharging, and particularly preferably from 70 to 150 Pa · s. 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, more preferably 0.6 to 3 m / min to be.

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 low, 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, it tends to be difficult to obtain the desired orientation of the polymer, that is, the intended cross angle? (°).

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

[Carrying / Stretching Process]

Then, the film formed as described above and stretched in the transverse direction (TD direction) is continuously or intermittently stretched while conveying the film having the moisture content adjusted in the flow direction (MD direction).

In the present invention, it is not necessary to particularly stretch the film in the flow direction (MD direction), and it is enough to carry the film with a pulling tension to such an extent that the film is not warped. 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 complicated rotational speeds as in Patent Documents 1 and 6 is not required. From the viewpoint of production, the dimension in the flow direction (MD direction) is preferably constant, particularly preferably the dimensional change ratio in the flow direction (MD direction) before and after stretching in the width direction (TD direction) is 0.8 to 1.2, Lt; / RTI >

The transporting speed of the formed film in the flow direction (MD direction) is preferably 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 late, the productivity tends to decrease. If the conveying speed is too fast, the deviation ?? (?) Of the crossing angle tends to increase.

There is no particular limitation on the method of carrying the formed film in the flow direction (MD direction) and the stretching in the width direction (TD direction) at the same time. For example, It is preferable to perform carrying and stretching at the same time. In such a case, the arrangement of the clips on 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 deviation ?? (degrees) of the crossing angle? Of the obtained polyvinyl alcohol film increases. It is preferable that the clip holding position (distal end portion of the clip) is 100 mm or less from both ends in the width direction of the film formed. If the gripping position (distal end) of the clip is located excessively at the central portion in the film width direction, the end portion of the film to be destroyed tends to increase 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. Even when the stretching ratio in the width direction (TD direction) is too high or too low, the deviation ?? (?) Of the crossing angle? 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 (multiple times) (also called continuous stretching) so that the total stretching magnification falls within the range of the stretching magnification. For example, after the stretching in one step, the stretching after the second step may be carried out by carrying out simple carrying with the width direction (TD direction) fixed. Particularly, in the case of a thin film, By inserting the process, stress relaxation of the film is made possible, 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. The film immediately after stretching is liable to shrink for stress relaxation and shrinkage accompanying dehydration also occurs so that it is possible to narrow the fixing width to such shrinkage width. 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 it is carried out before at least one of the drying step of the film, the drying step and the drying step.

As a preferred form of the present invention, there is a method of temporally shrinking the film so that the stretching magnification in the final transverse 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 temporarily stretched beyond 1.3 times. By such a method, stress relaxation of the film is achieved, and in particular, in the case of a thin film, breakage can be avoided.

The stretching in the transverse direction (TD direction) to the film formed in the present invention is preferably performed at 50 to 150 캜. Such a stretching temperature is particularly preferably 60 to 140 占 폚, and more preferably 70 to 130 占 폚. Even if the drawing temperature is too low or too high, the deviation ?? (?) Of the crossing angle? 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. Conversely, if it 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.

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 drier or the like, if necessary. The temperature of the heat treatment is preferably 60 to 200 占 폚, particularly preferably 70 to 150 占 폚.

If the heat treatment temperature is too low, the dimensional stability tends to be lowered. On the other hand, if the temperature is too high, the stretching property upon production of the polarizing film tends to be lowered.

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.

The polyvinyl alcohol film of the present invention is particularly preferably used as a disk for a polarizing film because of its excellent stretchability.

Hereinafter, 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 transferring the polyvinyl alcohol film from the roll in the horizontal direction and 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 process is carried out by bringing the film into contact with a liquid containing iodine or a dichroic dye. Normally, an aqueous solution of iodine-iodine potassium 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 finally 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 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 film can be removed. When potassium iodide aqueous solution is used, the concentration of potassium iodide is preferably 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 an aqueous solution of potassium iodide may be suitably combined.

For example, the film is dried in the air at 40 to 80 DEG C for 1 to 10 minutes.

The degree of polarization of the polarizing film 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 generally expressed by the relationship between the light transmittance (H ₁₁ ) measured with respect to the wavelength? And the direction in which the orientation directions of the two polarizing films are orthogonal to each other in a state in which two polarizing films are superimposed so that their alignment directions are the same Is calculated in accordance with the following equation from the light transmittance (H ₁ ) measured with respect to the wavelength?

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

The single transmittance of the polarizing film of the present invention is preferably 42% 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.

Hereinafter, 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 unevenness and excellent polarization performance.

[Polarizing plate production method]

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. 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,

For example, a liquid adhesive composition is uniformly applied to a polarizing film, a protective film, or both, and then both are adhered to each other, followed by pressing and heating and irradiation 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 side or both sides of the polarizing film, and cure it 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 cameras, photo albums, thermometers, audio, instrumentation of automobiles and machinery, sunglasses, anti-glare glasses, stereoscopic glasses, wearable displays, , 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.

In the following Examples and Comparative Examples, the characteristics (polarizing degree, unitary transmittance, unevenness) of the characteristics of the polyvinyl alcohol film (crossing angle in the orientation axis and width direction and deviation angle birefringence) Evaluation was carried out as follows.

<Measurement Conditions>

(A), a deviation Δθ (°) of the crossing angle θ, and a birefringence ΔNxy] in the widthwise direction (TD direction)

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 both end portions (inside 10 cm from the film end), and the film was measured with a retardation measuring apparatus ("KOBRA-WR" ), The crossing angle? (?) Between the orientation axis (slow axis) and the width direction (TD direction), the deviation ?? (degrees) at the crossing angle? And the birefringence? Nxy (nm) at 590 nm were measured. This measurement was performed on the center portion and the tip portion / end portion (within 10 m from each end of the film) in the flow direction (MD direction) of the polyvinyl alcohol film.

[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 both ends (taken 10 cm inward from the end of the film), and the degree of polarization (%) was measured using an automatic polarizing film measuring apparatus (VAP7070, manufactured by Nippon Bunkou Co., And the mass transmittance (%) were measured. This measurement was carried out for the central part of the polarizing film in the flow direction (MD direction) and for the tip end / terminal end (10 m inside the tip of the polarizing film and at each end of the terminal).

[Uneven color]

A test piece having a length of 30 cm and a width of 30 cm was cut from the central portion in the width direction of the obtained polarizing film and both ends (10 cm inward from the end of the film) to obtain a polarizing plate having two polarizing plates in crossed Nicol state (having a single light transmittance of 43.5% and a polarization degree of 99.9% , And then optical stains were observed in a 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

△ · · · There is faint smudge

× · · With dirt

Such evaluations were performed on the central portion in the flow direction (MD direction) of the polarizing film and the tip portion / terminal portion (making 10m inside from the tip of the polarizing film and from each end of the terminal).

&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 added to 5,000 L of the dissolution can while stirring The temperature was raised to 150 DEG C, followed by 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-based resin aqueous solution was fed to a twin-screw extruder and defoamed. Thereafter, the temperature of the aqueous solution was adjusted to 95 占 폚, and discharged from a T-shaped slit die discharge port into a rotating casting drum (discharging speed: 2.5 m / min) . The film thus formed was peeled from the cast drum (film width: 2.1 m) and conveyed in the flow direction (MD direction) while the surface and back of the film were alternately brought into contact with a total of ten heat rolls, % Of a film (2 m in width, 60 탆 in thickness). Subsequently, the film was stretched 1.1 times in the transverse direction (TD direction) at 120 DEG C using a stretching machine while sandwiching both right and left ends of the film at a clip pitch of 45 mm and conveying the film in the flow direction (MD direction) at a speed of 8 m / 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 Table 1.

(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 swelled by being immersed in a water bath at a 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, 40 g / L of boric acid and 30 g / Was immersed in an aqueous solution (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 2. [ 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;

A polyvinyl alcohol film (width: 2.2 m, thickness: 55 m, thickness: 55 m) was produced in the same manner as in Example 1 except that the film formed in Example 1 was stretched 1.1 times in the width direction (TD direction) , Length 2 km). The properties of the obtained polyvinyl alcohol-based film are shown in Table 1.

Using the polyvinyl alcohol film, a polarizing film and a polarizing plate were obtained in the same manner as in Example 1. The properties of the obtained polarizing film are shown in Table 2.

&Lt; Example 3 &gt;

(2 m in width and 20 m in thickness) having a moisture content of 5% by weight was stretched 1.2 times in the transverse direction (TD direction) at 120 캜 using a stretching machine at a discharge speed of 0.8 m / , A polyvinyl alcohol film (width 2.4 m, thickness 17 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 Table 1.

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. The properties of the obtained polarizing film are shown in Table 2.

<Example 4>

(2 m in width and 20 m in thickness) having a moisture content of 5% by weight was stretched 1.4 times in the transverse direction (TD direction) at 120 캜 using a stretching machine at a film forming rate of 0.8 m / (Width 2.4 m, thickness 17 m, length 2 km) was obtained in the same manner as in Example 1, except that the film was shrunk by stress relaxation up to a fixing width of 2.4 m (corresponding to 1.2 times stretching). The characteristics of the obtained polyvinyl alcohol-based film are shown in Table 1.

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. The properties of the obtained polarizing film are shown in Table 2.

&Lt; Comparative Example 1 &

The procedure of 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) Based film (width 2 m, thickness 60 m, length 2 km). The characteristics of the obtained polyvinyl alcohol-based film are shown in Table 1.

Using the polyvinyl alcohol film, a polarizing film and a polarizing plate were obtained in the same manner as in Example 1. The properties of the obtained polarizing film are shown in Table 2.

&Lt; Comparative Example 2 &

The procedure of Example 3 was repeated except that the both ends of the film formed in Example 3 were heated at 120 占 폚 while being conveyed at a speed of 8 m / min in the flow direction (MD direction) An alcohol film (width 2 m, thickness 20 m, length 2 km) was obtained. The properties of the obtained polyvinyl alcohol-based film are shown in Table 1.

The polarizing film was prepared in the same manner as in Example 1 except that the polyvinyl alcohol film was used, but fracture occurred during the stretching in the boric acid crosslinking step. The properties of the obtained polarizing film front end were as shown in Table 2 .

It can be seen from the results of the above Examples and Comparative Examples that the cross angle θ (°) between the orientation axis (slow axis) and the width direction (TD direction) and the deviation Δθ Of the polarizing films of Examples 1 to 4 obtained with the polyvinyl alcohol film of the present invention had a high degree of polarization and no color unevenness. On the other hand, the polarizing films of Comparative Examples 1 and 2, which are obtained from a polyvinyl alcohol film having an intersecting angle? (°) of more than 20 degrees between the orientation axis (slow axis) and the width direction (TD direction) It can be seen that dirt is also observed.

In addition, the polyvinyl alcohol films of Examples 1 to 4 obtained by the production method of the present invention are stable in the transverse direction (TD direction) and in the flow direction (MD direction) It can be seen that it is being controlled.

It can also be seen from the thin polyvinyl alcohol films of Examples 3 and 4 that a polarizing film excellent in the degree of polarization and having no color unevenness can be 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 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, Reflective coatings for display devices (CRT, LCD, organic EL, electronic paper, etc.), liquid crystal display devices such as cameras, photo albums, thermometers, audio, instrumentation of automobiles and machinery, sunglasses, anti-glare glasses, stereoscopic glasses, wearable displays, Optical communication equipment, medical equipment, building materials, toys, and the like.

Claims (8)

A thickness of 5 to 60 mu m, a width of 2 m or more, and a length of 2 km or more,
(°) of the orientation axis (that is, the slow axis) and the width direction (that is, the TD direction) is 20 ° or less and the deviation ?? Is a polyvinyl alcohol-based film. The method according to claim 1,
The birefringence ΔNxy which is a value calculated by the following formula (A) is 0.001 or less when the refractive index in the width direction (ie, the TD direction) is nx and the refractive index in the direction perpendicular to the direction (ie, the MD direction) is ny A polyvinyl alcohol-based film.
(A)? Nxy = | nx-ny | The method according to claim 1 or 2,
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 3 is used. A polarizing film according to claim 4, and a protective film provided on at least one side of the polarizing film. A step of forming an aqueous solution of a polyvinyl alcohol based resin by a continuous casting method, and a step of continuously drying and stretching while being conveyed in the flow direction (i.e., the MD direction) after peeling from the cast type, Wherein the polyvinyl alcohol film to be produced has an angle of intersection &amp;thetas; (degrees) in the transverse direction (TD direction) with the orientation axis (i.e., the slow axis) Wherein the deviation ?? (?) Is 20 占 or less. The method of claim 6,
Is stretched 1.05 to 1.3 times in the transverse direction of the film (i.e., the TD direction). The method according to claim 6 or 7,
(I.e., the TD direction) is 1.3 times or less in the transverse direction (i.e., the TD direction) of the film after transiently stretching it over 1.3 times, A method for producing an alcoholic film.