KR102543171B1 - Polyvinyl alcohol-based film and polarizing film using the same, polarizing plate, and manufacturing method of the polyvinyl alcohol-based film - Google Patents

Abstract

A polyvinyl alcohol-based film having a thickness of 5 to 60 μm, a width of 2 m or more, and a length of 2 km or more, and the intersection angle θ (°) between the orientation axis (slow axis) and the width direction (TD direction) is 20° or less, and the intersection angle θ It is a polyvinyl alcohol-based film with a deviation Δθ (°) of 20 ° or less. For this reason, it is possible to obtain a polarizing film having excellent stretchability at the time of producing the polarizing film and having high polarization performance and less color unevenness. In particular, it becomes possible to provide a polyvinyl alcohol-based film that does not break even when producing a thin polarizing film.

Description

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

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

Conventionally, a polyvinyl alcohol-based film has been used for many applications as a film having excellent transparency, and a polarizing film is one of its useful uses. Such a polarizing film is used as a basic component of a liquid crystal display, and in recent years, its use has been expanded to devices requiring high quality and high reliability.

Among these, a polarizing film having excellent optical properties is required in accordance with high luminance, high definition, large area, and thickness reduction of screens such as liquid crystal TVs and multifunctional portable terminals. Specifically, it is a further improvement in polarization degree and elimination of color unevenness.

Generally, a polyvinyl alcohol-based film is produced by a continuous casting method from an aqueous solution of a polyvinyl alcohol-based resin. Specifically, an aqueous solution of polyvinyl alcohol-based resin is cast on a cast mold such as a cast drum or endless belt to form a film, and after the film formed is peeled off from the cast mold, a nip roll or the like is used to move the flow direction (MD direction). ), while drying using a hot roll or floating dryer. In such a conveyance step, since the formed film is pulled in the flow direction (MD direction), the polyvinyl alcohol-based polymer is easily oriented in the MD direction, and the orientation axis (slow axis) of the obtained polyvinyl alcohol-based film軸)) is often directed toward MD. If the orientation in the MD direction is too large, the in-plane retardation of the polyvinyl alcohol-based film increases and finally the polarization performance of the polarizing film is deteriorated. Conversely, in the width direction (TD direction) of the formed film, shrinkage stress dependent on Poisson's ratio and shrinkage stress due to dehydration are generated, so using such stress in the TD direction can cause polyvinyl alcohol-based polymers to be It is also possible to orientate in the degree TD direction. In this case, the orientation axis of the obtained polyvinyl alcohol-based film is directed between the MD direction and the TD direction, and the in-plane retardation tends to be reduced. In addition, an orientation axis is also called an optical axis.

On the other hand, in general, a polarizing film is manufactured by swelling a polyvinyl alcohol-based film, which is the original material, with water (including warm water), dyeing it with a dichroic dye such as iodine, and stretching it. Such a stretching step is a step of highly orienting the dichroic dye in the film by stretching the dyed film in the flow direction (MD direction). It is necessary to have good stretchability.

In addition, a case in which the order of the stretching process and the dyeing process is reversed from the above in the manufacture of a polarizing film is also being implemented. That is, it is a case in which a polyvinyl alcohol-based film, which is a raw material, is swollen with water (including warm water) and then stretched and dyed with a dichroic dye such as iodine. The alcohol-based film needs to have good stretchability in the MD direction.

In addition, in recent years, in order to reduce the thickness of the polarizing film, the polyvinyl alcohol-based film has also been reduced in thickness. What used to have a thickness of about 60 μm is now about 45 μm in thickness, and is expected to be less than 30 μm in recent years. Such a thin film had a problem of productivity, such as being broken by stretching when producing a polarizing film.

As a method of improving stretchability, for example, a method of specifying the ratio between the speed of the cast drum when forming a film and the final film winding speed (see, for example, Patent Document 1), a film formed with a cast drum A method in which the film is subsequently suspended and dried (for example, see Patent Document 2) and a method for controlling the tension state in the drying step of the formed film (for example, see Patent Document 3) have been proposed. In addition, polyvinyl alcohol-based films with reduced in-plane retardation have been proposed (see Patent Documents 4 and 5, for example). In addition, a polyvinyl alcohol-based film having an optical axis inclination (orientation angle) within a specific range has been proposed (see Patent Document 6, for example).

Patent Document 1 JP 2001-315141A Patent Document 2 JP 2001-315142A Patent Document 3 JP 2002-79531A 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 above patent literature, it is insufficient to improve the stretchability in producing a polarizing film.

Patent Document 1 specifies the degree of stretching (tension state) in the MD direction when producing a polyvinyl alcohol-based film, but if stretching in the TD direction is not taken into account, the in-plane retardation of the polyvinyl alcohol-based film can be reduced. It is not possible, and it is also insufficient to improve the stretchability at the time of producing a polarizing film. In general, it is difficult to stretch a polyvinyl alcohol-based film stretched in the MD direction in the MD direction when producing a polarizing film. That is, pulling the polyvinyl alcohol-based polymer oriented in the MD direction back to the MD direction is difficult because the molecular chain is forcibly stretched. Conversely, it is relatively easy to pull a 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 polarizing film cannot be stretched uniformly in the MD direction during manufacture. In Patent Document 1, there is an example in which the polyvinyl alcohol-based film is not stretched as much in the MD direction (an example in which it is not stretched) when producing a polyvinyl alcohol-based film, but only the shrinkage stress dependent on the Poisson's ratio and the shrinkage stress due to dehydration can be used in the TD direction. There is a problem that the polymer orientation cannot be sufficiently homogenized. That is, unless the polymer is stretched to some extent in the TD direction or at least the width direction is not fixed, a uniform orientation state of the polymer in the TD direction cannot be obtained.

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

In the disclosed technology of Patent Document 3, the film thickness of the polyvinyl alcohol-based film can be made uniform, but the orientation of the polymer cannot be controlled, and thus it is insufficient to improve the stretchability when producing the polarizing film.

In the disclosed technology of Patent Documents 4 and 5, although the in-plane retardation of the polyvinyl alcohol-based film can be reduced, the polymer is only randomly oriented, and the polarizing film is manufactured if the in-plane retardation is not reduced in a uniform orientation state. It is insufficient to improve the stretchability of the poem, and there is room for improvement in that respect.

The technology disclosed in Patent Document 6 is a polyvinyl alcohol-based film in which the orientation angle in the width direction of the film is 45 to 135 ° in the longitudinal direction, but the angle range widens as half of the entire direction is occupied, controlling the orientation of the polymer It's hard to say that there is. The narrowest range of orientation angles in the examples is 54 degrees, and the deviation of orientation angles is large. If it fluctuates to this extent, the stretchability fluctuates in the width direction, and color unevenness tends to occur in the obtained polarizing film. In addition, the technique of the present disclosure controls the orientation angle with the peripheral speed ratio of the dry roll, but in this manufacturing method, the properties of the film tend to fluctuate in the longitudinal direction, and the orientation angle is within the above range over the entire length, or the stretchability is It is unknown whether it is constant (there is no description of the film length in the examples, and the measurement is only one place in the long direction). Moreover, the thickness of the film in an Example is 75 micrometers, and it is difficult to respond to the recent thinning request.

Therefore, in the present invention, under this background, the polyvinyl alcohol-based film, in particular, a thin polarizing film, which has excellent polarization performance and has excellent polarization performance during production of a polarizing film under this background, can obtain a polarizing film with little color unevenness. To provide a polyvinyl alcohol-based film, and to provide a polarizing film and a polarizing plate containing such a polyvinyl alcohol-based film, and a method for producing the polyvinyl alcohol-based film.

Therefore, the inventors of the present invention have studied intensively in view of such circumstances, and as a result, a polyvinyl alcohol-based film having a thickness of 5 to 60 μm, a width of 2 m or more, and a length of 2 km or more is obtained. ), the cross angle θ (°), and the deviation Δθ (°) of the cross angle θ are within a specific range, and the polyvinyl alcohol-based film has excellent stretchability when producing a polarizing film, so that a thin polarizing film can be produced with good yield, It has been found that a polarizing film obtained using such a polyvinyl alcohol-based film has high polarizing performance and is a polarizing film with little color unevenness.

That is, the first aspect of the present invention is a polyvinyl alcohol-based film having a thickness of 5 to 60 μm, a width of 2 m or more, and a length of 2 km or more, and the intersection angle θ (°) between the orientation axis (slow axis) and the width direction (TD direction) is A polyvinyl alcohol-based film characterized in that the deviation Δθ (°) of the intersection angle θ is 20° or less.

In particular, when the refractive index in the width direction (TD direction) is nx and the refractive index in the direction perpendicular thereto (MD direction) is ny, the birefringence ΔNxy, which is a value calculated by the following formula (A), is 0.001 or less Poly, characterized in that A vinyl alcohol-based film is the second gist of the present invention.

(A) ΔNxy=|nx-ny|

In addition, a polyvinyl alcohol-based film characterized in that the thickness of the polyvinyl alcohol-based film is 5 to 30 μm as a third aspect of the present invention.

Further, the present invention makes a polarizing film characterized by using the polyvinyl alcohol-based film described above as a fourth gist.

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

And the present invention is a polyvinyl alcohol-based resin solution provided with a step of forming a film by a continuous casting method, and a step of continuously drying and stretching while conveying in the flow direction (MD direction) after peeling from the cast mold. A method for producing a vinyl alcohol-based film, wherein the polyvinyl alcohol-based film produced has an orientation axis (slow axis) and a width direction (TD direction) intersection angle θ (°) of 20 ° or less, and a deviation of the intersection angle θ Δθ A sixth aspect is a method for producing a polyvinyl alcohol-based film characterized in that (°) is 20° or less.

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

In addition, after the film is temporarily stretched beyond 1.3 times in the width direction (TD direction), it is dimensionally shrunk so that the final stretch ratio in the width direction (TD direction) is 1.3 times or less. A film manufacturing method is the eighth aspect of the present invention.

The polyvinyl alcohol-based film of the present invention has excellent stretchability during production of a polarizing film, does not break even when producing a thin polarizing film, exhibits high polarization performance, and can provide a polarizing film with low color unevenness.

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

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 thickness of 5 to 60 μm, a width of 2 m or more, and a length of 2 km or more, and the intersection angle θ (°) between the orientation axis (slow axis) and the width direction (TD direction) is 20° or less, and the deviation Δθ (°) of the intersection angle θ is 20° or less.

The thickness of the polyvinyl alcohol-based film of the present invention is 5 to 60 μm, preferably 5 to 45 μm, particularly preferably 5 to 30 μm, particularly preferably 5 to 20 μm from the viewpoint of thinning 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 amount of ejection in a cast type (discharge speed), the stretching 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 viewpoint of increasing the area, and particularly preferably 3 to 50 km from the viewpoint of transport weight.

In the present invention, the intersection angle θ (°) between the orientation axis (slow axis) and the width direction (TD direction) needs to be 20° or less, preferably 15° or less, particularly preferably 10° or less, and still more preferably 5° or less, more preferably 2° or less. If such an intersection angle θ (°) exceeds the upper limit, the stretchability in the MD direction at the time of manufacturing the polarizing film is reduced, and the object of the present invention cannot be achieved. In addition, the lower limit of the normal intersection angle θ (°) is 0°.

In the present invention, the deviation Δθ (°) of the intersection angle θ must be 20° or less, preferably 10° or less, particularly preferably 5° or less, and still more preferably 3° or less. If the deviation Δθ (°) of the intersection angle θ is too large, color unevenness occurs in the polarizing film, and the object of the present invention cannot be achieved. In addition, normally, the lower limit of the deviation Δθ (°) of the intersection angle θ is 0°.

In the present invention, the birefringence ΔNxy is preferably 0.001 or less, particularly preferably 0.0008 or less, still more preferably 0.0006 or less, and particularly preferably 0.0005 or less. If such birefringence ΔNxy is too large, color unevenness tends to occur in the polarizing film.

In addition, ΔNxy here 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. In addition, the product (|nx−ny|×d) of the birefringence ΔNxy and the thickness d (nm) of the film is the in-plane retardation (nm).

In the present invention, as a method for controlling the cross angle θ (°), the deviation Δθ (°) of the cross angle θ, and the birefringence ΔNxy, from the viewpoint of precise control of the cross angle θ (°), the film peeled from the cast mold is separated in the width direction (TD direction) is preferred. In addition, a method of adjusting the drying conditions of the aqueous solution, a method of adjusting the chemical structure of the polyvinyl alcohol-based resin, and the like may be mentioned.

Here, the manufacturing method of the polyvinyl alcohol-based 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 polyvinyl alcohol resin aqueous solution will be described.

As the polyvinyl alcohol-based resin constituting the polyvinyl alcohol-based film in the present invention, an unmodified polyvinyl alcohol-based resin, that is, a resin produced by saponifying polyvinyl acetate obtained by polymerization of 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 vinyl acetate and a copolymerizable component may be used. Examples of components copolymerizable with vinyl acetate include unsaturated carboxylic acids (eg, salts, esters, amides, nitriles, etc.), olefins having 2 to 30 carbon atoms (eg, ethylene, propylene, n- butene, isobutene, etc.), vinyl ethers, unsaturated sulfonic acid salts, and the like. These can be used alone or in combination of two or more. In addition, a modified polyvinyl alcohol-based resin obtained by chemically modifying a hydroxyl group after saponification can also be used.

Moreover, as polyvinyl alcohol-type resin, the polyvinyl alcohol-type resin which has a 1, 2- diol structure in a side chain can also be used. Such a polyvinyl alcohol-based resin having a 1,2-diol structure in the side chain is, for example, (i) a method of saponifying a copolymer of vinyl acetate and 3,4-diacetoxy-1-butene, (ii) ) Saponification and decarboxylation of a copolymer of vinyl acetate and vinylethylene carbonate, (iii) Saponification and decarboxylation of a copolymer of vinyl acetate and 2,2-dialkyl-4-vinyl-1,3-dioxolane It can be obtained by deaeration, (iv) saponification of 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 still more preferably 120,000 to 260,000. If such a weight average molecular weight is too small, it tends to be difficult to obtain sufficient optical performance when using the polyvinyl alcohol-based resin as an optical film, and if it is too large, it tends to be difficult to stretch the polyvinyl alcohol-based film when producing a polarizing film. there is. In addition, the weight average molecular weight of the said polyvinyl alcohol-type resin is a weight average molecular weight measured by the GPC-MALS method.

The average degree of saponification of the polyvinyl alcohol-based resin used in the present invention is usually 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. am. If the average degree of saponification is too small, sufficient optical performance tends not to be obtained when a polyvinyl alcohol-based film is used as a polarizing film.

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

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

In the polyvinyl alcohol-based resin aqueous solution, in addition to the polyvinyl alcohol-based resin, if necessary, generally used plasticizers such as glycerin, diglycerin, triglycerin, ethylene glycol, triethylene glycol, polyethylene glycol, and trimethylolpropane, and nonionic , It is preferable from the viewpoint of film forming property to contain at least one surfactant of anionic and cationic nature. These may be used alone or in combination of two or more.

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

Next, the obtained polyvinyl alcohol-based resin aqueous solution is degassed. Methods, such as stationary defoaming and defoaming by a multi-screw extruder, are mentioned as a defoaming method. The multi-screw extruder may be a multi-screw extruder with a vent, and a twin-screw extruder with a vent is usually used.

[film formation process]

After the degassing treatment, the polyvinyl alcohol-based resin aqueous solution is introduced into a T-shaped slit die in a fixed amount, discharged and cast on a rotating cast drum, and formed into a film by a general casting method according to a conventional method. Especially, the continuous casting method is preferable from a viewpoint of productivity.

The continuous casting method is, for example, a method of forming a film by discharging and casting an aqueous solution of polyvinyl alcohol-based resin onto a cast mold such as a cast drum, endless belt, or resin film that rotates with a T-shaped slit die. After being peeled off from the cast mold, the formed film is continuously dried with a hot roll or the like while being transported in the flow direction (MD direction), and finally wound up on a roll as a polyvinyl alcohol film to become a product.

The resin temperature of the polyvinyl alcohol-based resin aqueous solution at the outlet of the T-shaped slit die is preferably 80 to 100°C, particularly preferably 85 to 98°C. If the resin temperature of such a polyvinyl alcohol-based resin aqueous solution is too low, flow failure tends to occur, and if it is too high, it tends to foam.

The viscosity of such an aqueous polyvinyl alcohol-based resin solution at the time of discharge is preferably 50 to 200 Pa·s, and particularly preferably 70 to 150 Pa·s. If the viscosity of such an aqueous solution is too low, flow failure tends to occur, and if the viscosity is too high, casting tends to be difficult.

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

If such a discharge speed is too slow, productivity tends to decrease, and if it is too fast, casting tends to be difficult.

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

If such a diameter is too small, the speed tends to be difficult to rise because the drying section on the cast drum is shortened, and if it is too large, transportability tends to decrease.

The width of such a cast drum is preferably 4 m or more, particularly preferably 4.5 m or more, still more preferably 5 m or more, and 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 3 to 50 m/min, particularly preferably 4 to 40 m/min, and still more preferably 5 to 35 m/min.

If such a rotation speed is too slow, productivity tends to decrease, and if it is too fast, drying tends to be insufficient.

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

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

[Formed film]

The moisture content of the film formed as described above [film before stretching in the width direction (TD direction)] is preferably 0.5 to 15% by weight, particularly preferably 1 to 13% by weight, and still more preferably 2 to 12% by weight %am. Even if such a moisture content is too low or too high, orientation of the target polymer, that is, expression of the target intersection angle θ (°) tends to be difficult.

In order to adjust such a moisture content, when the moisture 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), conversely, in the width direction (TD direction) ) When the water content of the film before stretching is too low, it is preferable to adjust humidity before stretching in the width direction (TD direction). More preferably, it adjusts the conditions of a drying process so that a moisture content may fall into the said range.

Although such drying can be carried out by a known method using a heating roll or an infrared heater, etc., in the present invention, it is preferable to carry out the drying with a plurality of heating rolls, particularly preferably the temperature of the heating rolls is 40 to 150 ° C. More preferably, it is 50-140 degreeC. Moreover, for adjustment of moisture content, a humidity control area can also be provided before extending|stretching to the width direction (TD direction).

[Conveyance/stretching process]

Then, the film formed into a film as described above and the moisture content is prepared is continuously or intermittently stretched in the width direction (TD direction) while conveying it in the flow direction (MD direction).

There is no need to particularly stretch the film formed in the present invention in the flow direction (MD direction), and it is sufficient to convey the film at a pulling tension that does not warp the film. As a matter of course, neck-in (shrinkage) dependent on Poisson's ratio occurs in the flow direction (MD direction) due to stretching in the width direction (TD direction), and dehydration shrinkage also occurs in the flow direction (MD direction) during drying. Because of this shrinkage, even if the rotational speed of the conveying roll or the heating roll is constant, tension suitable for the flow direction (MD direction) can be obtained, and complicated rotational speed control as in Patent Document 1 or Patent Document 6 is unnecessary. From a manufacturing point of view, it is preferable that the dimensions in the flow direction (MD direction) are constant, and the dimensional change rate in the flow direction (MD direction) before and after stretching in the width direction (TD direction) is preferably 0.8 to 1.2, particularly preferably is 0.9 to 1.1.

The transport 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 still more preferably 8 to 20 m/min. If such a conveyance speed is too slow, productivity tends to decrease, and if it is too fast, the deviation Δθ (°) of the crossing angle θ tends to increase.

The method of simultaneously conveying the formed film in the flow direction (MD direction) and stretching in the width direction (TD direction) is not particularly limited. For example, by holding both ends of the film in the width direction with a plurality of clips, It is preferable to carry out conveying and extending|stretching simultaneously. In such a case, the arrangement of the clips at each end is preferably at a pitch of 200 mm or less, particularly preferably at a pitch of 100 mm or less, and more preferably at a pitch of 50 mm or less.

If the pitch of such a clip is too wide, there is a tendency that the film after stretching is bent or the variation Δθ (°) of the crossing angle θ of the obtained polyvinyl alcohol-based film increases. In addition, the holding position of the clip (the front end of the clip) is preferably 100 mm or less from both ends in the width direction of the formed film. When the clamping position (tip end) of the clip is excessively positioned toward the center in the film width direction, the end portion of the film to be destroyed tends to increase and the width of the product tends to narrow.

The draw ratio 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 still more preferably 1.1 to 1.2 times. Even if the draw ratio in the width direction (TD direction) is too high or too low, the deviation Δθ (°) of the crossing angle θ tends to increase.

Such a continuous stretching step in the width direction (TD direction) may be one step (one time) or may be multiple steps (multiple times) such that the total draw ratio is within the range of the draw ratio (also referred to as sequential drawing). For example, after one-step stretching, simple conveyance with a fixed width direction (TD direction) may be performed, followed by second-step extension. Particularly, in the case of a thin film, simple conveyance with fixed width is also possible. By inserting the process, the stress relief of the film is made and it becomes possible to avoid breakage.

In the case of inserting a conveyance step of fixed width, it is also possible to make the fixed width narrower than the width after one-step stretching. Since the film immediately after stretching tends to shrink for stress relaxation and shrinkage due to dehydration also occurs, it is possible to narrow the fixed width to such a shrinkage width. However, if it is narrowed to more than the shrinkage width, it is not preferable because waviness occurs in the film.

Although it is preferable to carry out such a stretching process after a drying process of a film, it is carried out before at least one of the drying process of a film, during a drying process, and after a drying process.

As a preferred embodiment of the present invention, a method in which a formed film is temporarily stretched beyond 1.3 times in the width direction (TD direction) and then dimensionally shrunk so that the final stretch ratio in the width direction (TD direction) is 1.05 to 1.3 times. can be used. In such a case, the film may be simply conveyed with a fixed width of a stretch ratio of 1.05 to 1.3 after temporarily stretching beyond 1.3 times. By this method, stress relief of the film is achieved, and it becomes possible to avoid breakage, especially in the case of a thin film.

Stretching in the width direction (TD direction) of the film formed in the present invention is preferably performed at 50 to 150°C. The temperature for such stretching is particularly preferably 60 to 140°C, and still more preferably 70 to 130°C. Even if the stretching temperature is too low or too high, the deviation Δθ (°) of the crossing angle θ tends to increase. In the case of successive stretching, the stretching temperature may be changed in each stretching step.

The stretching time for the film formed in the present invention when stretching in the width direction (TD direction) is preferably 2 to 60 seconds, particularly preferably 5 to 45 seconds, and still more preferably 10 to 30 seconds. If the stretching time is too short, the film tends to break easily, and if the stretching time is too long, the equipment load tends to increase. When sequential stretching is performed, such stretching time may be changed in each stretching step.

In the present invention, after stretching in the width direction (TD direction) of the formed film, heat treatment may be performed with a floating dryer or the like, if necessary. The temperature of such heat treatment is preferably 60 to 200°C, particularly preferably 70 to 150°C.

If the heat treatment temperature is too low, the dimensional stability tends to deteriorate, and conversely, if the heat treatment temperature is too high, the stretchability during production of the polarizing film tends to deteriorate.

Further, 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, and conversely, if the heat treatment time is too long, the stretchability during production of the polarizing film tends to decrease.

[Polyvinyl alcohol-based film]

In this way, the polyvinyl alcohol-based film of the present invention can be obtained.

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

Hereinafter, a method for producing a polarizing film obtained using the polyvinyl alcohol-based film of the present invention will be described.

[Method for producing polarizing film]

The polarizing film of the present invention is manufactured through processes such as unwinding the polyvinyl alcohol-based film from a roll and transporting it in a horizontal direction, followed by swelling, dyeing, crosslinking with boric acid, stretching, washing, and drying.

The swelling process is carried out before the dyeing process. In the swelling step, stains on the surface of the polyvinyl alcohol-based film can be cleaned, and swelling of the polyvinyl alcohol-based film also has an effect of preventing color unevenness and the like. Water is usually used as the treatment liquid in the swelling step. When the main component of the treatment liquid is water, a small amount of additives such as an iodide compound and a surfactant, alcohol, and the like may be included. The temperature of the swelling bath is usually about 10 to 45°C, and the immersion time in the swelling bath is usually about 0.1 to 10 minutes.

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

A boric acid bridge|crosslinking process is performed using boron compounds, such as boric acid and borax. The boron compound is used in the form of an aqueous solution or a water-organic solvent mixture at a concentration of about 10 to 100 g/L, and it is preferable to coexist potassium iodide in the solution from the viewpoint of stabilization of polarization performance. The temperature at the time of treatment is preferably about 30 to 70° C., and the treatment time is preferably about 0.1 to 20 minutes, and if necessary, stretching may be performed during treatment.

In the stretching step, it is preferable to stretch the film 3 to 10 times in a uniaxial direction, preferably 3.5 to 6 times. At this time, a slight stretching (stretching to the extent of preventing shrinkage in the width direction or higher) may also be performed in a direction perpendicular to the stretching direction. As for the temperature at the time of extending|stretching, 40-170 degreeC is preferable. In addition, what is necessary is just to finally set a draw ratio in the said range, and extending|stretching operation can also be performed several times with respect to a manufacturing process not only once.

The washing step is performed by immersing the polyvinyl alcohol-based film in, for example, water or an iodide aqueous solution such as potassium iodide, and can remove precipitates generated on the surface of the film. The potassium iodide concentration in the case of using potassium iodide aqueous solution is preferably about 1 to 80 g/L. The temperature during the washing treatment is usually 5 to 50°C, preferably 10 to 45°C. The treatment time is usually from 1 to 300 seconds, preferably from 10 to 240 seconds. Further, washing with water and washing with an aqueous solution of potassium iodide may be appropriately combined.

In the drying step, for example, the film is dried in the air at 40 to 80°C for 1 to 10 minutes.

Further, the degree of polarization of the polarizing film is preferably 99.5% or higher, more preferably 99.8% or higher. When the degree of polarization is too low, there is a tendency that the contrast in the liquid crystal display cannot be secured.

In addition, the degree of polarization is generally determined by the light transmittance (H ₁₁ ) measured for the wavelength λ in a state in which two polarizing films are stacked so that their alignment directions are in the same direction, and the direction in which the orientation directions of the two polarizing films are orthogonal to each other. It is calculated according to the following formula from the light transmittance (H ₁ ) measured for the wavelength λ in a state where they are overlapped as much as possible.

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

Further, the single transmittance of the polarizing film of the present invention is preferably 42% or more. If such a single transmittance is too low, there is a tendency that high luminance of the liquid crystal display cannot be achieved. The single transmittance is a value obtained by measuring the light transmittance of a single polarizing film using a spectrophotometer.

Hereinafter, the manufacturing method of the polarizing plate of this invention using the polarizing film of this invention is demonstrated.

The polarizing film of the present invention is very suitable for producing a polarizing plate with less staining and excellent polarization performance.

[Method for producing polarizing plate]

The polarizing plate of the present invention is produced by bonding an optically isotropic resin film as a protective film to one or both surfaces of the polarizing film of the present invention through an adhesive. As the protective film, for example, cellulose triacetate, cellulose diacetate, polycarbonate, polymethyl methacrylate, cycloolefin polymer, cycloolefin copolymer, polystyrene, polyethersulfone, polyarylene ester, poly-4-methyl Films or sheets, such as pentene and polyphenylene oxide, are mentioned.

The bonding method is carried out by a known method, but, for example, after uniformly applying a liquid adhesive composition to a polarizing film, a protective film, or both, bonding them together and crimping, heating or irradiation with active energy rays It is carried out by doing

Alternatively, a polarizing plate may be obtained by applying a curable resin such as a urethane-based resin, an acrylic resin, or a urea resin to one or both surfaces of the polarizing film and curing to form a cured layer. In this way, the cured layer serves as a substitute for the protective film, and thinning can be achieved.

The polarizing film and polarizing plate using the polyvinyl alcohol-based film of the present invention have excellent polarizing performance and can be used in portable information terminals, PCs, televisions, projectors, signage, electronic desk calculators, electronic clocks, word processors, electronic papers, game machines, and video devices. , cameras, photo albums, thermometers, audio devices, liquid crystal display devices such as instruments for automobiles and machinery, sunglasses, anti-glare glasses, 3D glasses, wearable displays, antireflection layers for display elements (CRT, LCD, organic EL, electronic paper, etc.) , optical communication devices, medical devices, building materials, toys, etc. are preferably used.

(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 as long as the gist thereof is not exceeded.

In addition, "part" in the examples means a weight basis.

In addition, the characteristics of the polyvinyl alcohol-based film (crossing angle between the orientation axis and the width direction, birefringence deviation of the crossing angle) and the characteristics of the polarizing film (polarization degree, single transmittance, unevenness) in the following Examples and Comparative Examples Measurement and Evaluation was performed as follows.

<measurement conditions>

[intersection angle θ (°) between the orientation axis (slow axis) and the width direction (TD direction), deviation Δθ (°) of the intersection angle θ, and birefringence ΔNxy]

A test piece having a length of 4 cm and a width of 4 cm was cut from the central portion and both ends in the width direction of the obtained polyvinyl alcohol film (inside 10 cm from the film edge), and a retardation measuring device ("KOBRA-WR" manufactured by Oji Keishoku Instruments Co., Ltd.) ) was used, and the cross angle θ (°) between the orientation axis (slow axis) and the width direction (TD direction), the deviation Δθ (°) of the cross angle θ, and the birefringence ΔNxy (nm) at 590 nm were measured. Such measurement was performed for the central part and the front end/terminal part of the polyvinyl alcohol-based film in the direction of flow (MD direction) (within 10 m from each end of the film).

[polarization degree (%), single transmittance (%)]

A test piece with a length of 4 cm and a width of 4 cm was cut from the center and both ends in the width direction of the obtained polarizing film (inside 10 cm from the film end), and the degree of polarization (%) was measured using an automatic polarizing film measuring device (manufactured by Nippon Bunko Co., Ltd.: VAP7070). and single transmittance (%) were measured. This measurement was performed for the central part and the tip/terminal part of the flow direction (MD direction) of the polarizing film (10 m inside each film end of the polarizing film's tip and end).

[color unevenness]

A test piece with a length of 30 cm and a width of 30 cm was cut from the center and both ends in the width direction of the obtained polarizing film (inside 10 cm from the film end), and two polarizing plates in a crossed Nicol state (single transmittance: 43.5%, polarization degree: 99.9%) were prepared. After being sandwiched at an angle of 45°, the optical unevenness was observed in transmission mode using a light box having a surface roughness of 14,000 lx, and evaluated according to the following criteria.

(Evaluation standard)

○・・・no stain

△・・・slightly stained

×・・・stained

Such evaluation was performed for the central part and the tip/terminal part of the polarizing film in the direction of flow (MD direction) (inside 10 m from each film end of the polarizing film's front end and terminal end).

<Example 1>

(Production of polyvinyl alcohol-based film)

In a 5,000 L dissolving can, 1,000 kg of a polyvinyl alcohol-based resin having a weight average molecular weight of 142,000 and a degree of saponification of 99.8 mol%, 2,500 kg of water, 105 kg of glycerin as a plasticizer and 0.25 kg of polyoxyethylene laurylamine as a surfactant were added while stirring. The temperature was raised to 150°C, dissolution was performed under pressure, and an aqueous solution of polyvinyl alcohol-based resin having a resin concentration of 25% by weight was obtained by adjusting the concentration. Then, after supplying the polyvinyl alcohol-based resin aqueous solution to a twin-screw extruder to degas, the temperature of the aqueous solution is set to 95 ° C., and discharged from the T-shaped slit die discharge port to a rotating cast drum (discharge speed 2.5 m / min) and casting So it was unveiled. The formed film is peeled off from the cast drum (film width: 2.1 m) and dried while being transported in the flow direction (MD direction) while bringing the front and back surfaces of the film into contact with a total of 10 hot rolls alternately to obtain a moisture content of 10 weight % of the film (width 2 m, thickness 60 μm) was obtained. Next, the left and right ends of the film were held at a clip pitch of 45 mm, and the film was stretched 1.1 times in the width direction (TD direction) at 120 ° C. using a stretching machine while conveying the film in the flow direction (MD direction) at a speed of 8 m / min. A polyvinyl alcohol-based film (width 2.2 m, thickness 55 μm, length 2 km) was obtained. The characteristics of the obtained polyvinyl alcohol-based film are as shown in Table 1.

(Production of polarizing film and polarizing plate)

The obtained polyvinyl alcohol-based film was continuously fed out from the roll and stretched 1.7 times in the flow direction (MD direction) while being immersed in a water bath at a water temperature of 30°C to swell while conveying in a horizontal direction. Then, it is immersed in an aqueous solution at 30 ° C. consisting of 0.5 g / L of iodine and 30 g / L of potassium iodide, and then stretched 1.6 times in the flow direction (MD direction) while dyeing, followed by 40 g / L of boric acid and 30 g / L of potassium iodide. It was uniaxially stretched 2.1 times in the flow direction (MD direction) while being immersed in an aqueous solution (50°C) and crosslinked with boric acid. Finally, washing was performed 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 5.8 times. No breakage occurred during such manufacture, and the characteristics of the obtained polarizing film are shown in Table 2. A polyvinyl alcohol aqueous solution was used as an adhesive on both sides of the polarizing film obtained above, and a triacetyl cellulose film having a film thickness of 40 μm was bonded together and dried at 70° C. to obtain a polarizing plate.

<Example 2>

A polyvinyl alcohol-based film (2.2 m in width, 55 μm in thickness) 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) at 110 ° C. using a stretching machine. , length 2 km) was obtained. The characteristics of the obtained polyvinyl alcohol-based film are as shown in Table 1.

In addition, a polarizing film and a polarizing plate were obtained in the same manner as in Example 1 using the polyvinyl alcohol-based film. The characteristics of the obtained polarizing film are as shown in Table 2.

<Example 3>

In Example 1, the discharge speed at the time of film formation was set to 0.8 m/min, and a film having a water content of 5% by weight (width 2 m, thickness 20 μm) was stretched 1.2 times in the width direction (TD direction) at 120 ° C. using a stretching machine. A polyvinyl alcohol-based film (2.4 m in width, 17 μm in thickness, 2 km in length) was obtained in the same manner as in Example 1 except for the above. The characteristics of the obtained polyvinyl alcohol-based film are as shown in Table 1.

In addition, a polarizing film and a polarizing plate were obtained in the same manner as in Example 1 using the polyvinyl alcohol-based film. Although the original polyvinyl alcohol-based film was thin, no breakage occurred in the stretching process at the time of producing the polarizing film. The characteristics of the obtained polarizing film are as shown in Table 2.

<Example 4>

In Example 1, the discharge speed at the time of film formation was 0.8 m/min, and a film (2 m wide, 20 μm thick) with a water content of 5% by weight was stretched 1.4 times in the width direction (TD direction) at 120 ° C. using a stretching machine. After that, a polyvinyl alcohol-based film (2.4 m in width, 17 μm in thickness, 2 km in length) was obtained in the same manner as in Example 1, except that it was contracted by stress relaxation to a fixed width of 2.4 m (equivalent to 1.2-fold stretching). The characteristics of the obtained polyvinyl alcohol-based film are as shown in Table 1.

In addition, a polarizing film and a polarizing plate were obtained in the same manner as in Example 1 using the polyvinyl alcohol-based film. Although the original polyvinyl alcohol-based film was thin, no breakage occurred in the stretching process at the time of producing the polarizing film. The characteristics of the obtained polarizing film are as shown in Table 2.

<Comparative Example 1>

Polyvinyl Alcohol A based film (width 2 m, thickness 60 μm, length 2 km) was obtained. The characteristics of the obtained polyvinyl alcohol-based film are as shown in Table 1.

In addition, a polarizing film and a polarizing plate were obtained in the same manner as in Example 1 using the polyvinyl alcohol-based film. The characteristics of the obtained polarizing film are as shown in Table 2.

<Comparative Example 2>

Polyvinyl polyvinyl An alcohol-based film (width 2 m, thickness 20 μm, length 2 km) was obtained. The properties of the obtained polyvinyl alcohol-based film are shown in Table 1.

In addition, an attempt was made to manufacture a polarizing film in the same manner as in Example 1 using the polyvinyl alcohol-based film, but breakage occurred during stretching in the boric acid crosslinking step. The properties of the leading end of the polarizing film obtained are shown in Table 2. .

From the results of the above Examples and Comparative Examples, the intersection angle θ (°) of the orientation axis (slow axis) and the width direction (TD direction) and the deviation Δθ (°) of the intersection angle θ are all 20° or less, which is a feature of the present invention. The polarizing films of Examples 1 to 4 obtained from the polyvinyl alcohol-based film of had a high degree of polarization and had no color unevenness. On the other hand, the polarizing films of Comparative Examples 1 and 2 obtained from polyvinyl alcohol-based films in which the intersection angle θ (°) between the orientation axis (slow axis) and the width direction (TD direction) exceeds 20° were inferior in polarization degree and color It can be seen that stains are also observed.

In addition, the polyvinyl alcohol-based films of Examples 1 to 4 obtained by the production method of the present invention have a cross angle θ (°) that is stable in both the width direction (TD direction) and the flow direction (MD direction), and the orientation of the polymer is sufficiently It can be seen that it is controlled.

In addition, it can be seen that the thin polyvinyl alcohol-based films of Examples 3 and 4 also provide polarizing films having excellent polarization degree and no color unevenness.

Although the specific form in this invention was shown in the said Example, the said Example is only a mere illustration and is not interpreted limitedly. Various modifications obvious to those skilled in the art are expected to fall within the scope of the present invention.

The polarizing film and polarizing plate using the polyvinyl alcohol-based film of the present invention have excellent polarizing performance and can be used in portable information terminals, PCs, televisions, projectors, signage, electronic desk calculators, electronic clocks, word processors, electronic papers, game machines, and video devices. , liquid crystal display devices such as cameras, photo albums, thermometers, audio devices, instruments for automobiles and machinery, sunglasses, anti-glare glasses, stereoscopic glasses, wearable displays, antireflection layers for display elements (CRT, LCD, organic EL, electronic paper, etc.), It is preferably used in optical communication devices, medical devices, building materials, toys, and the like.

Claims (8)

A polyvinyl alcohol-based film having a thickness of 5 to 60 μm, a width of 2 m or more and a length of 2 km or more,
The intersection angle θ (°) between the orientation axis (ie, the slow axis) and the width direction (ie, the TD direction) is 20° or less, and the deviation Δθ (°) of the intersection angle θ is 10° or less. Characterized by a polyvinyl alcohol-based film. The method of claim 1,
When the refractive index in the width direction (ie, TD direction) is nx and the refractive index in the direction perpendicular thereto (ie, MD direction) is ny, birefringence ΔNxy, which is a value calculated by the following formula (A), is 0.001 or less. A polyvinyl alcohol-based film.
(A) ΔNxy=|nx-ny| According to claim 1 or 2,
The polyvinyl alcohol-based film, characterized in that the thickness of the polyvinyl alcohol-based film is 5 to 30㎛. A polarizing film characterized by using the polyvinyl alcohol-based film according to claim 1 or 2. A polarizing plate comprising the polarizing film according to claim 4 and a protective film provided on at least one surface of the polarizing film. Polyvinyl alcohol comprising a step of forming a film from an aqueous solution of polyvinyl alcohol-based resin by a continuous casting method, and a step of continuously drying and stretching while transporting an aqueous solution of polyvinyl alcohol-based resin in a flow direction (ie, MD direction) after peeling from the cast mold A method for producing a film based on polyvinyl alcohol, wherein the polyvinyl alcohol-based film produced has an intersection angle θ (°) of an orientation axis (ie, slow axis) and a width direction (ie, TD direction) of 20 ° or less, and further, the intersection angle θ A method for producing a polyvinyl alcohol-based film, characterized in that the deviation Δθ (°) is 10 ° or less. The method of claim 6,
A method for producing a polyvinyl alcohol-based film characterized in that the film is stretched 1.05 to 1.3 times in the width direction (ie, TD direction). According to claim 6 or 7,
Polyvinyl characterized in that the film is temporarily stretched beyond 1.3 times in the width direction (ie, TD direction) and then dimensionally shrunk so that the final draw ratio in the width direction (ie, TD direction) becomes 1.05 to 1.3 times. A method for producing an alcohol-based film.