JP2023083360A - Polyvinyl alcohol-based film, polarizing film and polarizing plate and method for producing polyvinyl alcohol-based film - Google Patents

Abstract

To provide: a polyvinyl alcohol-based film which is capable of obtaining a polarizing film which has excellent balance between swellability and extensibility during producing a polarizing film, causes no breakage during producing a thin polarizing film, exhibits high polarizing performance and has less color unevenness; a polarizing film and a polarizing plate using the polyvinyl alcohol-based film; and a method for producing the polyvinyl alcohol-based film.SOLUTION: There is provided a polyvinyl alcohol-based film in which when a rectangular first sample of 40 mm in the width direction (TD)×270 mm in the length direction (MD) cut from the central part in the width direction is immersed in water at 30°C for 30 seconds, the elongation amount WMD30 in the length direction at a portion of 250 mm in the length direction before immersion is 30 mm or more and 50 mm or less and when a rectangular second sample of 270 mm in the width direction (TD)×40 mm in the length direction (MD) cut from the central part in the width direction is immersed in water at 30°C for 300 seconds, the elongation amount WTD300 in the width direction at a portion of 250 mm in the width direction before immersion is 15 mm or more and 60 mm or less.SELECTED DRAWING: None

Description

The present invention provides a polyvinyl alcohol-based film that has excellent dyeability and serves as a material for forming a polarizing film with a high degree of polarization and little color unevenness, a polarizing film and a polarizing plate using the polyvinyl alcohol-based film, and the polyvinyl alcohol The present invention relates to a method for producing an alcohol-based film.

BACKGROUND ART Conventionally, polyvinyl alcohol-based films have been used in many applications as films with excellent transparency, and one of the useful applications thereof is a polarizing film. The polarizing film is used as a basic component of a liquid crystal display, and in recent years, its use has expanded to equipment that requires high quality and high reliability.

Under these circumstances, a polarizing film with excellent optical properties is required as the screens of liquid crystal televisions, multifunctional mobile terminals, etc. become brighter, have higher definition, have a larger area, and are thinner. The specific requirements are further improvement of the degree of polarization and elimination of color unevenness.

In general, a polyvinyl alcohol film is produced by a continuous casting method using an aqueous solution of a polyvinyl alcohol resin as a material. Specifically, first, an aqueous solution of a polyvinyl alcohol-based resin is cast onto a cast mold such as a cast drum or an endless belt to form a film, and then the film formed is peeled off from the cast mold. , while conveying in the machine direction (MD) using nip rolls or the like, and drying using hot rolls, a floating dryer, or the like. In the conveying step, the formed film is pulled in the machine direction (MD), so the polyvinyl alcohol-based polymer tends to be oriented in the machine direction (MD).

On the other hand, in general, a polarizing film is made by first swelling a polyvinyl alcohol-based film, which is the original film, with water (including hot water), then dyeing it with a dichroic dye such as iodine, and then stretching it. Manufactured by
What is important in the swelling step is to quickly swell the polyvinyl alcohol film in the thickness direction, and to uniformly swell the polyvinyl alcohol film so that the dye can smoothly enter the inside of the film in the dyeing step. That is.
In addition, the stretching step is a step of stretching the dyed film in the machine direction (MD) to highly orient the dichroic dye in the polyvinyl alcohol film. Therefore, in this stretching step, it is important that the polyvinyl alcohol-based film, which is the original fabric, exhibits good stretchability in the machine direction (MD).

In the production of the polarizing film, the order of the stretching process and the dyeing process is sometimes reversed. That is, in this case, the original polyvinyl alcohol film is first swelled with water (including warm water), then stretched, and then dyed with a dichroic dye such as iodine. In this case as well, what is important for improving the polarizing performance of the polarizing film is that the raw polyvinyl alcohol film exhibits good swelling properties in the thickness direction and good stretchability in the machine direction (MD). is to show

Furthermore, in recent years, in order to make the polarizing film thinner, the original polyvinyl alcohol-based film has also been made thinner. However, the thin film has productivity problems such as breakage due to stretching during production of the polarizing film.

As a method for improving the swelling properties of polyvinyl alcohol-based films, for example, a method of adding a polyhydric alcohol as a water swelling aid to a polyvinyl alcohol-based resin has been proposed (see, for example, Patent Document 1).
In addition, as a method of improving the stretchability of the polyvinyl alcohol film, for example, a method of specifying the ratio of the speed of the cast drum when forming the film and the final winding speed of the polyvinyl alcohol film (for example, patent see Document 2), a method of floating and drying the film after film formation on a cast drum (see, for example, Patent Document 3), and a method of controlling the degree of tension in the drying process of the formed film (see, for example, Patent Document 4). ), the amount of elongation in the length direction (MD) when immersed in water at 30 ° C. for 30 seconds is adjusted to a specific range, and the elongation in the width direction (TD) when immersed in water at 30 ° C. for 300 seconds. has been proposed to adjust to a specific range (see, for example, Patent Document 5).

JP-A-2001-302867 Japanese Patent Application Laid-Open No. 2001-315141 Japanese Patent Application Laid-Open No. 2001-315142 Japanese Unexamined Patent Application Publication No. 2002-79531 WO2016/093259

However, for the thin polyvinyl alcohol-based film, the method of Patent Document 1 is insufficient to improve the swelling property, and the methods of Patent Documents 2 to 5 do not improve the stretchability during the production of the polarizing film. Insufficient to improve.

That is, in the technique disclosed in Patent Document 1, even if the swelling property of the entire polyvinyl alcohol-based film can be improved, the orientation state of the polyvinyl alcohol-based polymer is not taken into consideration. It is difficult to efficiently improve drawability in the MD). Conversely, the addition of the water-swelling aid tends to disturb the orientation of the polymer, making uniform stretching in the machine direction (MD) difficult.

The technique disclosed in Patent Document 2 above specifies the degree of stretching (pulling condition) in the machine direction (MD) when producing a polyvinyl alcohol film, but also considers stretching in the width direction (TD). Otherwise, it is insufficient to improve the stretchability during the production of the polarizing film.

With the technique disclosed in Patent Document 3, although the formed film can be dried uniformly, it is not possible to control the orientation of the polymer, and it is not sufficient to improve the swelling property and stretchability during the production of the polarizing film. be.
Further, in the technique disclosed in Patent Document 4, although the film thickness of the polyvinyl alcohol film can be made uniform, it is not possible to control the orientation of the polymer. inadequate.

In the technique disclosed in Patent Document 5, in the polyvinyl alcohol-based film having a thickness of about 45 μm used in the examples, although there is a certain improvement effect on the swelling property at the time of manufacturing the polarizing film, the polarizing film is further improved. It is difficult to reduce the film thickness, and in thin polyvinyl alcohol films having a thickness of 40 μm or less, it is insufficient to improve the swelling property and stretchability during the production of the polarizing film.

In view of this background, the present invention provides an excellent balance between swelling property and stretchability during the production of a polarizing film, no breakage during the production of a thin polarizing film, high polarizing performance, and excellent color polarizing performance. Provided are a polyvinyl alcohol-based film capable of obtaining a polarizing film with little unevenness, a polarizing film and a polarizing plate using the polyvinyl alcohol-based film, and a method for producing the polyvinyl alcohol-based film.

The present inventors have made intensive studies in view of such circumstances, and found that a long polyvinyl alcohol film having a thickness of 40 μ or less was immersed in water at 30 ° C. for 30 seconds. and the amount of elongation in the width direction (TD) when immersed in water at 30 ° C. for 300 seconds. When it is made smaller than conventional polyvinyl alcohol films, it has a good balance between swelling property and stretchability during the production of the polarizing film, does not break even during the production of the thin polarizing film, exhibits high polarizing performance, and has little color unevenness. It was found that a polarizing film can be obtained.

That is, the present invention is a long polyvinyl alcohol film having a thickness of 40 μm or less, and a rectangle of width direction (TD) 40 mm × length direction (MD) 270 mm cut from the width direction central part of the polyvinyl alcohol film For the first sample, when this first sample is immersed in water at 30 ° C. for 30 seconds, the length direction (MD) elongation in the 250 mm portion excluding both ends in the length direction (MD) before immersion W _MD30 is 30 mm or more and 50 mm or less, and a rectangular second sample of width direction (TD) 270 mm × length direction (MD) 40 mm cut from the width direction central part of the polyvinyl alcohol film is immersed in water at 30° C. for 300 seconds, and the amount of elongation W _TD300 in the width direction (TD) at a portion of 250 mm excluding both ends in the width direction (TD) before immersion is 15 mm or more and 60 mm or less. is the first gist.

A second aspect of the present invention is a polarizing film using the polyvinyl alcohol film. Further, a third aspect is a polarizing plate comprising the polarizing film and a protective film provided on at least one side of the polarizing film.

Then, a film-forming step of forming a film from an aqueous solution of a polyvinyl alcohol-based resin by a continuous casting method, and continuously drying and stretching the film while conveying the film in the flow direction. A method for producing a polyvinyl alcohol film comprising drying and stretching steps, wherein a rectangular first sample of 40 mm in the width direction × 270 mm in the machine direction cut out from the central part in the width direction of the polyvinyl alcohol film to be produced is prepared. When one sample is immersed in water at 30°C for 30 seconds, the amount of elongation W _MD30 in the length direction at a portion of 250 mm excluding both ends in the length direction before immersion is 30 mm or more and 50 mm or less. For a rectangular second sample of 270 mm in the width direction × 40 mm in the flow direction cut out from the central part of the polyvinyl alcohol-based film in the width direction, when this second sample is immersed in water at 30 ° C. for 300 seconds, the width direction before immersion A fourth aspect is a method for producing a polyvinyl alcohol film, characterized in that the widthwise elongation W _TD300 in a 250 mm portion excluding both ends is set to 15 mm or more and 60 mm or less.

The polyvinyl alcohol film of the present invention is a long polyvinyl alcohol film having a thickness of 40 μm or less, and when immersed in water at 30 ° C. for a specific period of time, the above elongation amount W _MD30 in the length direction (MD) and Since the amount of elongation W _TD300 in the width direction (TD) is within a specific range, the polarizing film is excellent in swelling property and stretchability at the time of manufacturing. Even if it is used for manufacturing a polarizing film, it is possible to prevent breakage from occurring. Furthermore, by using the polyvinyl alcohol film, it is possible to obtain a polarizing film exhibiting high polarizing performance and little color unevenness.

In particular, when the width of the polyvinyl alcohol film is 2 m or more, the productivity of the polarizing film using the polyvinyl alcohol film is improved.

Further, the polarizing film of the present invention uses the polyvinyl alcohol-based film, so that it exhibits high polarizing performance and little color unevenness.

Furthermore, since the polarizing film of the present invention is used, the polarizing plate of the present invention exhibits high polarizing performance and little color unevenness.

The method for producing a polyvinyl alcohol-based film of the present invention includes a film forming step by a continuous casting method, and continuous drying and continuous stretching of the film while conveying the formed film in the machine direction. Since it is provided with a drying and stretching step to be applied, the manufacturing conditions in each step are combined, and when immersed in water at 30 ° C. for a specific time, the above elongation amount W _MD30 It is possible to obtain the polyvinyl alcohol film of the present invention in which the amount of elongation W _TD300 in the width direction (TD) falls within a specific range.

In particular, in the drying/stretching step, when the film formed above is stretched 1.05 to 1.3 times in the width direction (TD), the amount of elongation W _MD30 and the amount of elongation W _TD300 are suitable, and the polarized light It is possible to obtain a polyvinyl alcohol-based film having excellent swelling properties and stretchability during film production.

Further, in the drying/stretching step, the film formed above is temporarily stretched by more than 1.3 times in the width direction (TD), and then the final stretch ratio in the width direction (TD) is 1.3 times. When the dimension is shrunk to 3 times or less, the stress applied to the formed film can be relaxed. Therefore, even if the formed film is thin, breakage of the film can be avoided.

The present invention will now be described in detail.
The polyvinyl alcohol-based film of the present invention is a long polyvinyl alcohol-based film having a thickness of 40 μm or less, and when immersed in water at 30 ° C., it has a specific length direction (MD) and width direction (TD). Indicates the amount of elongation. That is, a rectangular first sample of 40 mm in the width direction (TD) × 270 mm in the length direction (MD) cut from the width direction central portion of the polyvinyl alcohol film was immersed in water at 30 ° C. for 30 seconds. At this time, the amount of elongation W _MD30 in the length direction in the 250 mm portion excluding both ends in the length direction before immersion is 30 mm or more and 50 mm or less. Furthermore, a rectangular second sample of 270 mm in the width direction (TD) × 40 mm in the length direction (MD) cut from the width direction central portion of the polyvinyl alcohol film was immersed in water at 30 ° C. for 300 seconds. At this time, the amount of elongation W _TD300 in the width direction in a portion of 250 mm excluding both ends in the width direction before immersion is 15 mm or more and 60 mm or less.

The thickness of the polyvinyl alcohol-based film of the present invention must be as thin as 40 μm or less, preferably 5 to 40 μm from the viewpoint of thinning the polarizing film, and particularly preferably to avoid breakage. The point is 10 to 40 μm, more preferably 10 to 38 μm.
If the thickness of the polyvinyl alcohol-based film is too thick, the tension increases during stretching in the process of manufacturing the polarizing film, which will be described later, which is not preferable. If the thickness is too thin, it tends to be easily broken during the production of the polarizing film.

That is, in the polyvinyl alcohol film of the present invention, as described above, the elongation in the length direction (MD) and width direction (TD) when immersed in water at 30° C. was controlled to be within a specific range. It is. This controlled elongation allows the polyvinyl alcohol film to have excellent performance as a very thin film having a thickness of 40 μm or less.

The amount of elongation in the length direction (MD) is, as described above, when the first sample is immersed in water at 30 ° C. for 30 seconds, in a 250 mm portion excluding both longitudinal ends before immersion The amount of elongation W _MD30 in the length direction (MD) is controlled to be 30 mm or more and 50 mm or less. The amount of elongation W _MD30 in the longitudinal direction (MD) is preferably 31 mm≦W _MD30 ≦48 mm, particularly preferably 32 mm≦W _MD30 ≦45 mm, and still more preferably 33 mm≦W _MD30 ≦43 mm.
If the value of W _MD30 is too small, the stretchability during the production of the polarizing film, which will be described later, is deteriorated, _so that the object of the present invention cannot be achieved. The object of the present invention cannot be achieved because sagging occurs and wrinkles and folds occur.

As described above, the amount of elongation in the width direction (TD) is the width direction ( TD) is controlled so that the amount of elongation W _TD300 is 15 mm or more and 60 mm or less. The amount of elongation W _TD300 in the width direction (TD) is preferably 16 mm≦W _TD300 ≦55 mm, particularly preferably 17 mm≦W _TD300 ≦50 mm, further preferably 18 mm≦W _TD300 ≦45 mm.
If the value of W _TD300 is too small, uneven dyeing occurs during the production of the polarizing film, making it impossible to achieve _the object of the present invention. The object of the present invention cannot be achieved because it spreads too much in the direction and wrinkles and folds occur.

In the present invention, as a method for controlling the W _MD30 and W _TD300 , in the method for producing the polyvinyl alcohol film by the continuous casting method described later, after peeling the film formed by the cast mold from the cast mold, A method of stretching in the width direction (TD) is preferred. In this case, the conditions in other steps are appropriately adjusted according to the stretching conditions in the width direction (TD) (stretch ratio, ambient temperature during stretching, stretching time, etc.). The conditions include, for example, the chemical structure of the polyvinyl alcohol-based resin that is the material for forming the polyvinyl alcohol-based film, the type and amount of the plasticizer added, the film-forming conditions (cast mold temperature, etc.), and the film-forming conditions. Drying conditions (temperature, time) for drying the formed film, transport speed of the formed film in the machine direction (MD), and the like can be mentioned. At least one of these conditions and the stretching condition in the width direction (TD) are combined to control the W _MD30 and W _TD300 .

The values of W _MD30 and W _TD300 in the present invention are measured, for example, by the following methods. The measurement positions of W _MD30 and W _TD300 are within a 500 mm×500 mm area of the polyvinyl alcohol film.

[Measurement method of W _MD30 ]
A first rectangular sample of 40 mm in the width direction (TD)×270 mm in the length direction (MD) is cut out from the central portion of the polyvinyl alcohol-based film in the width direction. Next, marked lines were drawn with an oil-based ink (with a line thickness of 0.3 mm) 10 mm inside each edge in the longitudinal direction (MD) of the first sample. The portions outside the marked lines at both ends are sandwiched by commercially available clips (chuck width: 40 mm, mass: 7.3 g), and one of the clips is fixed with a rod-shaped jig. After confirming that the distance between the gauge lines is 250 mm, put the first sample with the clip in pure water stored in a cylindrical transparent water tank and adjusted to 30 ° C. The first sample is quickly immersed with the long side vertical (vertical). Immediately after the immersion, the rod-shaped jig is hooked on the top of the water tank to fix the long side of the first sample vertically (perpendicularly). After that, a metal ruler is immersed in water, and the distance between gauge marks is measured 30 seconds after the first sample is immersed. The amount of elongation (W _MD30 ) (unit: mm) is calculated by subtracting the original distance between the gauge lines (250 mm) from the measured value read in increments of 0.5 mm.

[W _TD300 measurement method]
A second rectangular sample of 270 mm in the width direction (TD)×40 mm in the length direction (MD) is cut out from the central portion in the width direction of the polyvinyl alcohol-based film. Next, marked lines were drawn with oil-based ink (line thickness: 0.3 mm) 10 mm inside each edge in the width direction (TD) of the second sample. The portions outside the marked lines at both ends are sandwiched by commercially available clips (chuck width: 40 mm, mass: 7.3 g), and one of the clips is fixed with a rod-shaped jig. After confirming that the distance between the gauge lines is 250 mm, put the second sample with the clip in pure water stored in a cylindrical transparent water tank and adjusted to 30 ° C. Immediately, the second sample is immersed with the long side vertical (vertical). Immediately after the immersion, the rod-shaped jig is hooked on the top of the water tank to fix the second sample so that the long side of the second sample is vertical. Thereafter, a metal ruler is immersed in water, and the distance between gauge marks is measured 300 seconds after the second sample is immersed. The amount of elongation (W _TD300 ) (unit: mm) is calculated by subtracting the original distance between the gauge lines (250 mm) from the measured value read in increments of 0.5 mm.

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

[Film material]
First, the polyvinyl alcohol resin used in the present invention and the polyvinyl alcohol resin aqueous solution thereof will be described.
In the present invention, the polyvinyl alcohol-based resin constituting the polyvinyl alcohol-based film is usually an unmodified polyvinyl alcohol-based resin, that is, a resin produced by saponifying polyvinyl acetate obtained by polymerizing vinyl acetate. 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 component copolymerizable with vinyl acetate may be used. can. Components copolymerizable with vinyl acetate include, for example, unsaturated carboxylic acids (including salts, esters, amides, nitriles, etc.), olefins having 2 to 30 carbon atoms (eg, ethylene, propylene, n-butene, , isobutene, etc.), vinyl ethers, unsaturated sulfonates, and the like. These can be used alone or in combination of two or more. Modified polyvinyl alcohol-based resins obtained by chemically modifying hydroxyl groups after saponification can also be used.

As the polyvinyl alcohol-based resin, a polyvinyl alcohol-based resin having a 1,2-diol structure in a side chain can also be used. The polyvinyl alcohol resin having a 1,2-diol structure in the side chain can be obtained, for example, by (i) saponifying a copolymer of vinyl acetate and 3,4-diacetoxy-1-butene, (ii) acetic acid (iii) saponifying and decarboxylating 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, further preferably 120,000 to 260,000. If the weight-average molecular weight is too small, sufficient optical performance tends to be difficult to obtain when the polyvinyl alcohol-based resin is used as an optical film. tend to become The weight average molecular weight of the polyvinyl alcohol-based resin is the 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 generally preferably 98 mol% or more, particularly preferably 99 mol% or more, still more preferably 99.5 mol% or more, particularly preferably 99.5 mol% or more. 8 mol % or more. If the average degree of saponification is too small, there is a tendency that sufficient optical performance cannot be obtained when the polyvinyl alcohol film is used as a polarizing film.
Here, the average degree of saponification in the present invention is measured according to JIS K6726.

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

In addition to the polyvinyl alcohol resin, the polyvinyl alcohol resin aqueous solution may contain commonly used plasticizing agents such as glycerin, diglycerin, triglycerin, ethylene glycol, triethylene glycol, polyethylene glycol, trimethylolpropane, etc., if necessary. From the viewpoint of film-forming properties, it is preferable to contain a surfactant or at least one of nonionic, anionic, and cationic surfactants. These can be used alone or in combination of two or more.

The resin concentration of the polyvinyl alcohol resin aqueous solution thus obtained is preferably 15 to 60% by weight, particularly preferably 17 to 55% by weight, further preferably 20 to 50% by weight. If the resin concentration of the aqueous solution is too low, the drying load tends to increase, resulting in a decrease in production capacity.

Next, the obtained polyvinyl alcohol-based resin aqueous solution is defoamed. Examples of defoaming methods include static defoaming and defoaming using a multi-screw extruder. As the multi-screw extruder, any multi-screw extruder having a vent may be used, and a twin-screw extruder having a vent is usually used.

[Film forming process]
The polyvinyl alcohol film of the present invention is produced by a casting method or a melt extrusion method. It is a continuous casting method from the point of view of quality.

The continuous casting method is, for example, a film formation by continuously discharging and casting the aqueous solution of the polyvinyl alcohol resin from a T-shaped slit die to a casting mold such as a rotating cast drum, endless belt, or resin film. It is a way to
Here, the film forming process when the cast mold is a cast drum will be described.

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

The viscosity of the polyvinyl alcohol-based resin aqueous solution is preferably 50 to 200 Pa s at the time of ejection (at the preferred temperature of 80 to 100 ° C.), particularly preferably 70 to 150 Pa (at the particularly preferred temperature of 85 to 98 ° C.). · s.
If the viscosity of the polyvinyl alcohol-based resin aqueous solution is too low, it tends to flow poorly, and if it is too high, casting tends to be difficult.

The discharge speed of the polyvinyl alcohol resin aqueous solution discharged from the T-type slit die onto the cast drum is preferably 0.2 to 5 m/min, particularly preferably 0.4 to 4 m/min, and more preferably 0.4 m/min. 6 to 3 m/min.
If the ejection speed is too slow, productivity tends to decrease, and if it is too fast, casting tends to be difficult.

The diameter of the casting drum is preferably 2-5 m, particularly preferably 2.4-4.5 m, more preferably 2.8-4 m.
If the diameter is too small, the dry length tends to be insufficient and the speed tends to be difficult to achieve.

The width of the casting 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 7 m.
If the width of the cast drum is too small, productivity tends to decrease.

The rotational speed of the cast drum is preferably 5 to 50 m/min, particularly preferably 6 to 40 m/min, further preferably 7 to 35 m/min.
If the rotational speed is too slow, the productivity tends to decrease, and if it is too fast, the drying tends to be insufficient.

The surface temperature of the cast drum is preferably 40 to 99°C, particularly preferably 60 to 95°C.
If the surface temperature is too low, there is a tendency to cause poor drying, and if it is too high, there is a tendency for foaming to occur.

Thus, the film forming process is performed. Then, the formed film is separated from the cast drum and transported in the machine direction (MD).
The water content of the formed film is preferably 0.5 to 15% by weight, particularly preferably 1 to 13% by weight, further preferably 2 to 12% by weight. If the moisture content is too low or too high, it tends to be difficult to achieve the desired swelling properties and stretchability.

[Drying/stretching process]
For adjusting the moisture content, if the moisture content of the film before stretching in the width direction (TD) is too high, it is preferable to dry the film before stretching in the width direction (TD). If the moisture content of the film before stretching in the TD) is too low, it is preferable to condition the film before stretching in the width direction (TD). Particularly preferably, the conditions of the drying process are adjusted so that the water content is within the above range.

The drying is performed continuously. This continuous drying can be carried out by a known method using a heating roll, an infrared heater, or the like. to 150°C, more preferably 50 to 140°C. In addition, a humidity conditioning area may be provided before stretching in the width direction (TD) to adjust the moisture content.

In the present invention, it is not necessary to particularly stretch the formed film in the machine direction (MD), and it is sufficient to convey the film with a tensile tension that does not bend the film. As a matter of course, stretching in the width direction (TD) causes neck-in depending on the Poisson's ratio in the machine direction (MD), and dehydration shrinkage also occurs in the machine direction (MD) during drying. Due to these shrinkages, even if the rotational speeds of the transport roll and the heating roll are constant, an appropriate tension can be obtained in the flow direction (MD), and the complicated control of the rotational speed as in Patent Document 2 is unnecessary. From the manufacturing point of view, it is preferable that the dimension of the film in the machine direction (MD) is constant, and particularly preferably, the dimensional change rate in the machine direction (MD) is 0.8 before and after stretching in the width direction (TD). to 1.2, particularly preferably 0.9 to 1.1.

The conveying speed of the formed film in the machine direction (MD) is preferably 5 to 30 m/min, particularly preferably 7 to 25 m/min, further preferably 8 to 20 m/min. If the conveying speed is too slow, productivity tends to decrease, and if it is too fast, drying tends to be insufficient.

The method of conveying the formed film in the machine direction (MD) and stretching it in the width direction (TD) at the same time is not particularly limited. Therefore, it is preferable to carry out the transport and the stretching at the same time. In this case, the arrangement of the clips at each end preferably has a pitch of 200 mm or less, particularly preferably a pitch of 100 mm or less, more preferably a pitch of 50 mm or less.
If the pitch of the clips is too wide, the stretched film tends to flex, and the in-plane uniformity of the resulting polyvinyl alcohol film tends to deteriorate. Moreover, the clamping position of the clip (tip of the clip) is preferably 100 mm or less from both edges in the width direction of the formed film. If the clamping position (tip) of the clip is located too close to the center in the width direction of the film, the film ends to be discarded increase and the width of the product tends to become narrow.

The draw ratio in the width direction (TD) in the present invention is preferably 1.05 to 1.3 times, particularly preferably 1.05 to 1.25 times, more preferably 1.1 to 1.2 times. is. If the draw ratio in the width direction (TD) is too high or too low, the in-plane uniformity tends to decrease.

The stretching in the width direction (TD) is performed continuously. This continuous drawing may be performed in one step (once) or in multiple steps (multiple times) so that the total draw ratio is within the range of the above draw ratio (also called sequential drawing). For example, after performing the first stage of continuous stretching, simple transport with a fixed width direction (TD) may be performed, and then the second and subsequent stages of continuous stretching may be performed. In particular, in the case of a thin film, by inserting a simple width-fixed conveying process after the first stage of continuous stretching, the stress of the film can be relaxed and breakage can be avoided. .
When inserting a width-fixed conveying step, the fixed width can be narrower than the width after the first stage of continuous stretching. Since the film immediately after being stretched tends to shrink due to stress relaxation and also shrinks due to dehydration, it is possible to narrow the fixed width to the shrinkage width. However, if the width is narrowed beyond the shrinkage width, the film will be bent, which is not preferable.
As described above, the continuous stretching is preferably performed after the film drying process, but it is performed at least one of before the film drying process, during the drying process, and after the drying process.

As a preferred embodiment of the present invention, after temporarily stretching the film in the width direction (TD) by more than 1.3 times, the final stretch ratio in the width direction (TD) is 1.05. A method of dimensional shrinkage to 1.3 times can be used.
In this case, the film may be temporarily stretched over 1.3 times and then simply conveyed at a fixed width of 1.05 to 1.3 stretch ratio. This method provides stress relaxation of the film and makes it possible to avoid breakage, especially in the case of thin films.

In the present invention, the transverse direction (TD) stretching of the formed film is preferably carried out at an ambient temperature of 50 to 150°C. The ambient temperature during the stretching is particularly preferably 60 to 140°C, more preferably 70 to 130°C. If the ambient temperature during the stretching is too low or too high, the in-plane uniformity tends to decrease. In the case of sequential stretching, the ambient temperature during the stretching may be changed at each stage of stretching.

In the present invention, the stretching time in the width direction (TD) of the formed film 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, and if it is too long, the equipment load tends to increase. In the case of sequential stretching, the stretching time may be changed at each stretching step.

In the present invention, after stretching the formed film in the width direction (TD), if necessary, both sides of the film may be heat-treated with a floating dryer or the like. The temperature of this heat treatment is preferably 60 to 200°C, particularly preferably 70 to 150°C. The heat treatment by the floating dryer is a process of blowing hot air, and the heat treatment temperature means the temperature of the hot air.
If the heat treatment temperature is too low, the dimensional stability tends to decrease, and if it is too high, stretchability tends to decrease during the production of the polarizing film.
Also, 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 if it is too long, the stretchability tends to decrease during the production of the polarizing film.

[Polyvinyl alcohol film]
Thus, the polyvinyl alcohol film of the present invention is obtained. This polyvinyl alcohol-based film is long in the machine direction (MD), and is produced as a film roll by being wound around a core tube in the form of a roll.
As described above, the thickness of the polyvinyl alcohol film of the present invention must be very thin, 40 μm or less, and preferably 5 to 40 μm from the viewpoint of thinning the polarizing film. Particularly preferably, it is 10 to 40 μm, more preferably 10 to 38 μm in terms of avoiding breakage.

The width of the polyvinyl alcohol film of the present invention is preferably 2 m or more, particularly preferably 2 to 7 m, more preferably 3 to 6 m in terms of avoiding breakage.

The length of the polyvinyl alcohol-based film of the present invention is preferably 2 km or more, particularly preferably 3 km or more in terms of increasing the area, and more preferably 3 to 50 km in terms of transportation weight.

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

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

[Method for producing polarizing film]
The polarizing film of the present invention is produced by unwinding the polyvinyl alcohol film from the film roll, conveying it in the horizontal direction, and subjecting it to swelling, dyeing, cross-linking with boric acid, stretching, washing, drying, and the like.

The swelling step is performed before the dyeing step. By the swelling process, stains on the surface of the polyvinyl alcohol film can be cleaned, and the swelling of the polyvinyl alcohol film also has the effect of preventing uneven dyeing. In the swelling step, water is usually used as the treatment liquid. The treatment liquid may contain a small amount of an iodide compound, an additive such as a surfactant, alcohol, etc., as long as the main component is water. 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 the polyvinyl alcohol film into contact with a liquid containing iodine or a dichroic dye. Usually, an iodine-potassium iodide aqueous solution is used, and an iodine concentration of 0.1 to 2 g/L and a potassium iodide concentration of 1 to 100 g/L are suitable. A dyeing time of about 30 to 500 seconds is practical. The temperature of the treatment bath is preferably 5-50°C. The aqueous solution may contain a small amount of an organic solvent compatible with water in addition to the water solvent.

The boric acid cross-linking step is performed using a boron compound such as boric acid or borax. The boron compound is used in the form of an aqueous solution or a water-organic solvent mixture at a concentration of about 10 to 100 g/L, and potassium iodide is preferably coexistent in the liquid from the viewpoint of stabilizing the polarizing performance. The treatment temperature is preferably about 30 to 70° C., and the treatment time is preferably about 0.1 to 20 minutes. If necessary, a stretching operation may be performed during the treatment.

In the stretching step, the polyvinyl alcohol film is preferably stretched 3 to 10 times, preferably 3.5 to 6 times in the uniaxial direction [machine direction (MD)]. At this time, the film may be slightly stretched in the direction perpendicular to the stretching direction [stretching to such an extent that shrinkage in the width direction (TD) is prevented or more]. The temperature during stretching is preferably 40 to 70°C. Furthermore, the stretching ratio may be finally set within the above range, and the stretching operation may be performed not only in one step (once) but also multiple times in the polarizing film manufacturing process.

The washing step is carried out by, for example, immersing the polyvinyl alcohol film in water or an aqueous solution of iodide such as potassium iodide to remove deposits generated on the surface of the polyvinyl alcohol film. When a potassium iodide aqueous solution is used, the potassium iodide concentration is 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 1 to 300 seconds, preferably 10 to 240 seconds. Note that washing with water and washing with an aqueous solution of potassium iodide may be appropriately combined.

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

Also, the degree of polarization of the polarizing film is preferably 99.5% or more, more preferably 99.8% or more. If the degree of polarization is too low, there is a tendency that the contrast in the liquid crystal display cannot be ensured.
In addition, the degree of polarization is generally measured in a state where two polarizing films are superimposed so that their orientation directions are in the same direction, and the light transmittance (H ₁₁ ) measured at the wavelength λ, and the two polarized light It is calculated according to the following formula from the light transmittance (H ₁ ) measured at the wavelength λ in a state in which the films are stacked so that the orientation directions are perpendicular to each other.
Degree of polarization (%)=[(H ₁₁ −H ₁ )/(H ₁₁ +H ₁ )] ^1/2

Furthermore, the single transmittance of the polarizing film of the present invention is preferably 42% or more. If the single transmittance is too low, there is a tendency that the liquid crystal display cannot achieve high brightness.
Single transmittance is a value obtained by measuring the light transmittance of a single polarizing film using a spectrophotometer.

A method for manufacturing the polarizing plate of the present invention using the polarizing film of the present invention will be described below.
The polarizing film of the present invention is suitable for producing a polarizing plate with little color unevenness and excellent polarizing performance.

[Method for producing polarizing plate]
The polarizing plate of the present invention is produced by laminating an optically isotropic resin film as a protective film on one or both sides of the polarizing film of the present invention via an adhesive. Examples of protective films include films of cellulose triacetate, cellulose diacetate, polycarbonate, polymethyl methacrylate, cycloolefin polymer, cycloolefin copolymer, polystyrene, polyethersulfone, polyarylene ester, poly-4-methylpentene, polyphenylene oxide, and the like. Or you can get a sheet.

The lamination method is performed by a known method. For example, a liquid adhesive composition is uniformly applied to the polarizing film, the protective film, or both, and then the two are laminated and pressure-bonded, followed by heating or It is performed by irradiating with active energy rays.

A curable resin such as a urethane resin, an acrylic resin, or a urea resin may be applied to one or both sides of the polarizing film and cured to form a cured layer, thereby forming a polarizing plate. By doing so, the hardening layer serves as a substitute for the protective film, and a thin film can be achieved.

The polarizing film and polarizing plate using the polyvinyl alcohol-based film of the present invention have excellent polarizing performance, and are used in personal digital assistants, personal computers, televisions, projectors, signage, electronic desk calculators, electronic clocks, word processors, electronic paper, and game machines. , videos, cameras, photo albums, thermometers, audio, liquid crystal display devices such as automobiles and machinery instruments, sunglasses, anti-glare glasses, stereoscopic glasses, wearable displays, display elements (CRT, LCD, organic EL, electronic paper etc.), optical communication equipment, medical equipment, building materials, toys and the like.

EXAMPLES The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the examples described below as long as the gist of the present invention is not exceeded.

Then, the properties (W _MD30 , W _TD300 ) of the polyvinyl alcohol film and the properties of the polarizing film (degree of polarization, single transmittance, color unevenness) in Examples and Comparative Examples described later were measured and evaluated as follows. rice field.

[How to measure W _MD30 ]
A first rectangular sample of 40 mm in the width direction (TD)×270 mm in the length direction (MD) was cut out from the central portion in the width direction of the polyvinyl alcohol-based film. Then, marking lines were drawn with an oil-based ink (thickness of line: 0.3 mm) inside each 10 mm from both ends of the first sample having a length of 270 mm. The portions outside the marked lines at both ends were sandwiched by commercially available clips (chuck width: 40 mm, mass: 7.3 g), and one clip was fixed with a rod-shaped jig. After confirming that the distance between the gauge lines is 250 mm, quickly put the first sample with the clip in pure water stored in a cylindrical transparent water tank and adjusted to 30 ° C so that the whole is submerged in water. The long side of the first sample was immersed vertically (perpendicularly). Immediately after the immersion, a rod-shaped jig was hooked on the top of the water tank to fix the long side of the first sample vertically. Thereafter, a metal ruler was immersed in water, and the distance between gauge lines was measured 30 seconds after the first sample was immersed. An elongation amount (W _MD30 ) (unit: mm) was calculated by subtracting the original distance between gauge lines (250 mm) from the measured value read in increments of 0.5 mm.

[W _TD300 measurement method]
A second rectangular sample of 270 mm in the width direction (TD)×40 mm in the length direction (MD) was cut out from the central portion of the polyvinyl alcohol-based film in the width direction. Next, on the second sample, a 270 mm length, 10 mm from each end, a marked line was drawn with an oil-based ink (with a line thickness of 0.3 mm). The portions outside the marked lines of both ends are sandwiched by commercially available clips (chuck width: 40 mm, mass: 7.3 g), and one clip is fixed with a rod-shaped jig. After confirming that the distance between the gauge lines is 250 mm, quickly put the second sample with the clip in pure water stored in a cylindrical transparent water tank and adjusted to 30 ° C so that the whole is submerged in water. The long side of the second sample was immersed vertically (vertically). Immediately after the immersion, a rod-shaped jig was hooked on the top of the water tank to fix the long side of the second sample vertically. Thereafter, a metal ruler was immersed in water, and the distance between gauge lines was measured 300 seconds after the second sample was immersed. The elongation amount (W _TD300 ) (unit: mm) was calculated by subtracting the original distance between the gauge lines (250 mm) from the measured value read at 0.5 mm intervals.

[Polarization degree (%), single transmittance (%)]
A test piece having a length of 4 cm and a width of 4 cm was cut out from the central portion of the obtained polarizing film in the width direction, and an automatic polarizing film measurement device (manufactured by JASCO Corporation: VAP7070) was used to measure the degree of polarization (%) and the single transmittance. The rate (%) was measured.

〔Color unevenness〕
A test piece having a length of 30 cm and a width of 30 cm was cut out from the central portion in the width direction of the obtained polarizing film, and two polarizing plates in a crossed Nicol state (single transmittance 43.5%, degree of polarization 99.9%). After sandwiching it between the two at an angle of 45°, using a light box with a surface illuminance of 14,000 lx, optical color unevenness was observed in transmission mode and evaluated according to the following criteria.
(Evaluation criteria)
A: There was no color unevenness.
Δ: Slight color unevenness was observed.
x: Distinct color unevenness was observed.

<Example 1>
(Preparation of polyvinyl alcohol film)
In a 5,000 L dissolving can, 1,000 kg of polyvinyl alcohol 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 polyoxyl as a surfactant. 0.25 kg of ethylene lauryl amine was added, and the temperature was raised to 150° C. while stirring to perform pressure dissolution. Next, the polyvinyl alcohol-based resin aqueous solution is supplied to a twin-screw extruder and defoamed, then the temperature of the aqueous solution is set to 95 ° C., and the surface temperature is discharged from the T-shaped slit die outlet to a cast drum having a surface temperature of 80 ° C. (discharge speed 1.3 m/min) and casting to form a film. The formed film was peeled off from the cast drum, and dried while being transported in the machine direction (MD) while bringing the front and back surfaces of the film into contact with a total of 10 hot rolls alternately. As a result, a film (width 2 m, thickness 30 μm) with a water content of 7% by weight was obtained. Next, the left and right ends of the film are clamped by clips with a clip pitch of 45 mm, and the film is transported in the machine direction (MD) at a speed of 8 m / min while being stretched in the width direction (TD) at 80 ° C. using a stretching machine. After being stretched 1.2 times, the film was transported in a dryer at a fixed width of 2.4 m and at 130° C. to obtain a polyvinyl alcohol film (width 2.4 m, thickness 25 μm, length 2 km). The properties of the obtained polyvinyl alcohol film were as shown in Table 1 below. Finally, the polyvinyl alcohol-based film was wound around a core tube in the form of a roll to obtain a film-wound body.

(Preparation of polarizing film and polarizing plate)
The obtained polyvinyl alcohol film was unwound from the film roll and stretched 1.7 times in the machine direction (MD) while being transported in the horizontal direction and immersed in a water tank at a water temperature of 30° C. to swell. During the swelling process, no creases or wrinkles occurred in the film. Then, the sheet was immersed in an aqueous solution containing 0.5 g/L of iodine and 30 g/L of potassium iodide at 30° C. and stretched 1.6 times in the machine direction (MD) while being dyed. The film was immersed in an aqueous solution (50° C.) having a composition of L and 30 g/L of potassium iodide and uniaxially stretched 2.1 times in the machine direction (MD) while cross-linking with boric acid. Finally, the film was washed with an aqueous solution of potassium iodide and dried at 50° C. for 2 minutes to obtain a polarizing film with a total draw ratio of 5.8. No breakage occurred during the production of this polarizing film. The properties of the obtained polarizing film were as shown in Table 1 below.
A 40 μm-thick triacetyl cellulose film was attached to both surfaces of the polarizing film obtained above using an aqueous polyvinyl alcohol solution as an adhesive, and dried at 70° C. to obtain a polarizing plate.

<Example 2>
In Example 1, after stretching 1.4 times in the width direction (TD) at 80 ° C. using a stretching machine, it was shrunk by stress relaxation to a fixed width of 2.4 m (equivalent to 1.2 times stretching) at 130 ° C. and conveyed. A polyvinyl alcohol film (width 2.4 m, thickness 25 μm, length 2 km) was obtained in the same manner as in Example 1 except that The properties of the obtained polyvinyl alcohol film were as shown in Table 1 below.
Furthermore, a polarizing film and a polarizing plate were obtained in the same manner as in Example 1 using the polyvinyl alcohol film. In the swelling process during the production of the polarizing film, the polyvinyl alcohol-based film was neither bent nor wrinkled, nor was it broken. The properties of the obtained polarizing film were as shown in Table 1 below.

<Example 3>
In Example 1, the procedure was repeated except that the polyvinyl alcohol resin aqueous solution was discharged onto a cast drum having a surface temperature of 88° C. (discharging speed: 1.9 m/min) and cast to form a film. A film (width 2 m, thickness 45 μm) was formed. Then, in the same manner as in Example 1, after stretching 1.1 times in the width direction (TD) at 80°C using a stretching machine, the film formed above was dried in a dryer at 135°C with a fixed width of 2.2 m. It was transported to obtain a polyvinyl alcohol film (width 2.2 m, thickness 38 µm, length 2 km). The properties of the obtained polyvinyl alcohol film were as shown in Table 1.
Furthermore, a polarizing film and a polarizing plate were obtained in the same manner as in Example 1 using the polyvinyl alcohol film. In the swelling process during the production of the polarizing film, the polyvinyl alcohol-based film was neither bent nor wrinkled, nor was it broken. The properties of the obtained polarizing film were as shown in Table 1 below.

<Comparative Example 1>
In Example 1, a polyvinyl alcohol film (2 m wide, 30 μm thick, 2 km in length). The properties of the obtained polyvinyl alcohol film were as shown in Table 1 below.
Furthermore, when a polarizing film and a polarizing plate were produced in the same manner as in Example 1 using the polyvinyl alcohol film, folds and wrinkles occurred in the film during the swelling process. The properties of the obtained polarizing film were as shown in Table 1 below.

From the results of the above examples and comparative examples, the amount of elongation in the length direction (MD) when the polyvinyl alcohol film was immersed in water at 30 ° C. for 30 seconds, and the width direction when immersed in water at 30 ° C. for 300 seconds The polarizing films obtained from the polyvinyl alcohol-based films of Examples 1 to 3, which satisfy the above-mentioned specific ranges in terms of both the elongation amount of (TD), have high polarizing properties and are uniform without color unevenness. I know there is.
On the other hand, the polarizing film obtained from the polyvinyl alcohol-based film of Comparative Example 1, in which the amount of elongation in the width direction (TD) is greater than the range specified above, has poor polarizing properties and color unevenness is observed. I understand.

Although specific embodiments of the present invention have been described in the above examples, the above examples are merely illustrative and should not be construed as limiting. Various modifications apparent to those skilled in the art are intended to be within the scope of the invention.

The polarizing film made of the polyvinyl alcohol-based film of the present invention has excellent polarizing performance, and is used for personal digital assistants, personal computers, televisions, projectors, signage, electronic desk calculators, electronic clocks, word processors, electronic paper, game machines, videos, Cameras, photo albums, thermometers, audio equipment, liquid crystal display devices for automobiles and machinery instruments, sunglasses, anti-glare glasses, stereoscopic glasses, wearable displays, display elements (CRT, LCD, organic EL, electronic paper, etc.) It is preferably used for reflection reducing layers, optical communication equipment, medical equipment, building materials, toys and the like.

Claims (7)

A long polyvinyl alcohol film having a thickness of 40 μm or less,
For the first rectangular sample of 40 mm in the width direction × 270 mm in the length direction cut out from the central part in the width direction of the polyvinyl alcohol-based film,
When the first sample is immersed in water at 30° C. for 30 seconds, the lengthwise elongation W _MD30 in the 250 mm portion excluding both ends in the length direction before immersion is 30 mm or more and 50 mm or less,
And, for a rectangular second sample of 270 mm in the width direction × 40 mm in the length direction cut out from the center part in the width direction of the polyvinyl alcohol film,
When the second sample is immersed in water at 30° C. for 300 seconds, the widthwise elongation W _TD300 in a portion of 250 mm excluding both ends in the width direction before immersion is 15 mm or more and 60 mm or less. alcoholic film. 2. The polyvinyl alcohol film according to claim 1, wherein the width of said polyvinyl alcohol film is 2 m or more. A polarizing film comprising the polyvinyl alcohol film according to claim 1 . A polarizing plate comprising the polarizing film according to claim 3 and a protective film provided on at least one side of the polarizing film. A film-forming process in which an aqueous solution of a polyvinyl alcohol-based resin is formed into a film by a continuous casting method, and a drying and continuous stretching of the film while conveying the film in the flow direction. A method for producing a polyvinyl alcohol film comprising a stretching step,
For the first rectangular sample of 40 mm in the width direction × 270 mm in the flow direction cut out from the center part in the width direction of the polyvinyl alcohol film to be manufactured,
When the first sample is immersed in water at 30° C. for 30 seconds, the longitudinal elongation W _MD30 in a 250 mm portion excluding both longitudinal ends before immersion is 30 mm or more and 50 mm or less,
And, for a rectangular second sample of 270 mm in the width direction × 40 mm in the flow direction cut out from the center part in the width direction of the polyvinyl alcohol film to be produced,
When the second sample is immersed in water at 30°C for 300 seconds, the amount of stretching W _TD300 in the width direction at a portion of 250 mm excluding both ends in the width direction before immersion is 15 mm or more and 60 mm or less. A method for producing a polyvinyl alcohol film. 6. The method for producing a polyvinyl alcohol film according to claim 5, wherein in the drying/stretching step, the formed film is stretched 1.05 to 1.3 times in the width direction. In the drying/stretching step, the formed film is temporarily stretched in the width direction by more than 1.3 times, and then dimensionally contracted so that the final stretch ratio in the width direction is 1.3 times or less. 7. The method for producing a polyvinyl alcohol film according to claim 5 or 6, characterized in that