TWI712620B - Polyvinyl alcohol-based film, manufacturing method of polyvinyl alcohol-based film, polarizing film and polarizing plate - Google Patents

Abstract

The present invention provides a polyvinyl alcohol-based film that can obtain a polarizing film with less thickness variation and excellent polarization characteristics, and provides a polarizing film. The polyvinyl alcohol-based film is a polyvinyl alcohol-based film with a thickness of 5-60 μm, a width of 2 m or more, and a length of 2 km or more; it is characterized in that the coefficient of variation of the thickness of the entire film is 1% or less.

Description

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

The present invention relates to a polyvinyl alcohol film. More specifically, it relates to a polyvinyl alcohol-based film that can obtain a polarizing film with less thickness variation and excellent polarization characteristics, and a method for producing the polyvinyl alcohol-based film, a polarizing film, and a polarizing plate.

Conventionally, a polyvinyl alcohol-based film is produced by dissolving a polyvinyl alcohol-based resin in a solvent such as water to prepare a stock solution, forming a film by a solution casting method (casting method), and drying it using a metal heating roller or the like. The polyvinyl alcohol-based film obtained in this manner is used in various applications as a film having excellent transparency and dyeability, and one of its useful applications includes a polarizing film. The polarizing film is used as a basic component of a liquid crystal display. In recent years, machines requiring high-level and high reliability and their use are expanding.

Among these, as the screens of liquid crystal televisions and the like become larger, it is necessary to have a higher level of flatness than conventional products, a wide, long and thin polarizing film, and a polyvinyl alcohol-based film that becomes the original roll. When the polyvinyl alcohol film is not flat due to the thickness variation, the thickness variation of the polarizing film also becomes larger, and the in-plane uniformity of the polarization performance is insufficient, and the assembled liquid crystal cell generates stress, which causes the deformation and durability of the liquid crystal cell itself. The reduction. As for countermeasures against such problems, for example, it has been proposed to use a polyvinyl alcohol-based film with a thickness variation in the TD direction (width direction) of 0.5 μm/mm or less for the production of polarizing films (for example, refer to Patent Document 1 .). In addition, in order to suppress the thickness variation, a method of forming a polyvinyl alcohol-based film using a mold and a metal roll in a specific positional relationship has been proposed (for example, refer to Patent Document 2). [Patent Literature]

[Patent Document 1] Japanese Patent Application Publication No. 2002-31720 [Patent Document 2] Japanese Patent Application Publication No. 2002-144355

[Problem to be Solved by the Invention] However, we believe that although the thickness variation in the TD direction in the aforementioned Patent Document 1 is 0.5 μm or less per 1 mm in length, it is at most the variation value in the length 1 mm, and in particular, the full width is In the case of a wide film of 2 m or more, the variation value will increase significantly. Furthermore, in the case of a long film with a total length of 2km or more, the thickness variation in the TD direction will be further increased. In addition, if only the thickness variation in the TD direction is reduced, when the film is rolled out from a polyvinyl alcohol-based film roll to produce a polarizing film, due to the thickness variation in the MD direction (flow direction: longitudinal direction), such as dyeing, It is difficult to process uniformly in the steps of stretching and boric acid treatment, and there will be a problem that the in-plane polarization of the polarizing film becomes uneven.

In the example of Patent Document 2, although the thickness variation in the TD direction of the film is 1.5μm, the thickness of the film is 75μm. It is difficult to cope with the thinning of the polarizing film. If the thickness is less than 60μm, it may not be guaranteed. The problem of sufficient thickness accuracy. In addition, when the thickness of the film is 30 μm, if the thickness variation of the film is 1.5 μm, the thickness variation coefficient is about 0.8%. Also, as in the case of Patent Document 1, if only the thickness variation in the TD direction is reduced, when the film is unrolled from a polyvinyl alcohol-based film roll to produce a polarizing film, due to the thickness variation in the MD direction, such as dyeing It is difficult to uniformly process the steps of, stretching and boric acid treatment, and there will be a problem that the in-plane polarization of the polarizing film becomes uneven.

In addition, when the thickness of the polyvinyl alcohol-based film varies greatly and is uneven, it will be difficult to wind up on a roll. When the film absorbs moisture during storage and transportation, the fluctuations will increase, and most of it will have to be destroyed before the polarizing film is manufactured. The problem with the film.

Therefore, under these backgrounds, the present invention aims to provide a polyvinyl alcohol-based film that can obtain a polarizing film with less thickness variation and excellent polarization characteristics, and a method for manufacturing the polyvinyl alcohol-based film, and polarizing films and polarizing plates. . [Means to solve the problem]

As a result of diligent research by the inventors in view of these circumstances, they focused on the film thickness of the polyvinyl alcohol-based film, and found that by controlling the coefficient of variation to make it smaller, a polarizing film with excellent polarization characteristics can be obtained. invention.

That is, the first gist of the present invention relates to a polyvinyl alcohol-based film, which 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; it is characterized in that the coefficient of variation of the thickness of the entire film is 1% or less.

In addition, the second gist of the present invention relates to a method for producing a polyvinyl alcohol-based film, which is to discharge an aqueous solution of a polyvinyl alcohol-based resin from a T-shaped slit die onto a rotating cast drum. A film is formed and continuously dried to obtain a polyvinyl alcohol-based film; it is characterized in that the coefficient of variation of the thickness of the entire film is 1% or less. Furthermore, the third gist of the present invention relates to a polarizing film composed of the polyvinyl alcohol-based film. Furthermore, the fourth gist of the present invention relates to a polarizing plate, which is formed by providing a protective film on at least one side of the polarizing film. [Effects of Invention]

The polyvinyl alcohol film of the present invention can obtain a polarizing film with excellent polarization characteristics due to its excellent thickness accuracy, and is particularly suitable for use as the original roll of a thin and long polarizing film, and the degree of polarization can be uniform in the plane. Polarizing film.

The polyvinyl alcohol film of the present invention is a polyvinyl alcohol film having a thickness of 5-60 μm, a width of 2 m or more, and a length of 2 km or more, and is characterized in that the coefficient of variation of the thickness of the entire film is 1% or less.

Here, the above-mentioned coefficient of variation is obtained by the following method. <Measurement method> First, the thickness of the polyvinyl alcohol-based film is measured at any point.・The flow direction (MD direction) is measured using the "Spectral Interference Film Thickness Gauge SI-T80" manufactured by KEYENCE at 0.3mm steps at the center and both ends in the width direction (TD direction). 60,000 points.・The measurement in the TD direction uses the "Continuous Film Thickness Gauge TOF-5R01" manufactured by Sanbun Electric Co., and measures 4000 points at three locations at the front end, center, and end in the MD direction. Then, for the measured value of the above thickness, calculate the standard deviation according to the following formula.

[Number 1] Standard deviation (SD)=√ (Σ (xi-x) ² /(n-1)) x: average value xi: value at the i-th point n: number of samples

Finally, calculate the coefficient of variation according to the following formula. Coefficient of Variation (C.V.)=100×S.D./x

In addition, in the present invention, "the entire surface of the film" refers to the measurement of the full length and the full width. Specifically, in the MD direction, it refers to at least three places between the center and both ends. In the TD direction, it is also the center and both ends. At least 3 places in the department.

For the polyvinyl alcohol film of the present invention, it is necessary that the coefficient of variation of the thickness obtained by the above method is 1% or less, preferably 0.7% or less, particularly preferably 0.5% or less, and more preferably 0.4% or less. If the coefficient of variation of the thickness is greater than 1%, the performance of the polarizing film will deteriorate and the purpose of the invention will not be achieved. In addition, the lower limit of the coefficient of variation of the thickness is usually 0.01%, preferably 0.05%, and particularly preferably 0.1%.

The above-mentioned polyvinyl alcohol-based film of the present invention is preferably prepared by discharging an aqueous solution of a polyvinyl alcohol-based resin from a T-shaped slot die onto a rotating casting drum to form a film, and then drying it continuously.

As for the polyvinyl alcohol-based resin, an unmodified polyvinyl alcohol-based resin is usually used, that is, a resin obtained by saponifying polyvinyl acetate obtained by polymerizing vinyl acetate. If necessary, a resin obtained by saponifying a copolymer of vinyl acetate and a small amount (for example, 10 mol% or less, 5 mol% or less) of a component copolymerizable with vinyl acetate can also be used. Components that can be copolymerized with vinyl acetate, for example, unsaturated carboxylic acids (for example, including salts, esters, amides, nitriles, etc.), olefins with 2 to 30 carbon atoms (for example, ethylene, propylene, n-butene) , Isobutylene, etc.), vinyl ethers, unsaturated sulfonates, etc. In addition, modified polyvinyl alcohol-based resins obtained by chemically modifying saponified hydroxyl groups can also be used.

In addition, as a polyvinyl alcohol-based resin, it can also be used for a polyvinyl alcohol-based resin having a 1,2-diol structure in the side chain. The polyvinyl alcohol resin having a 1,2-diol structure in the side chain, for example, can be saponified by (i) a copolymer of vinyl acetate and 3,4-diethoxy-1-butene The method of (ii) saponification and decarboxylation of the copolymer of vinyl acetate and vinyl ethylene carbonate, (iii) the method of combining vinyl acetate with 2,2-dialkyl-4-vinyl-1,3 -The method of saponification and deketalization of the copolymer of dioxolane, (iv) the method of saponifying the copolymer of vinyl acetate and glycerol monoallyl ether, etc.

The weight average molecular weight of the polyvinyl alcohol resin is preferably 100,000 to 300,000, particularly preferably 110,000 to 280,000, and more preferably 120,000 to 260,000. If the weight average molecular weight is too small, it will tend to be difficult to obtain sufficient optical performance when the polyvinyl alcohol-based resin is formed into an optical film; if it is too large, it may become difficult to stretch when the polyvinyl alcohol-based film is made into a polarizing film. tendency. In addition, the weight average molecular weight of the said polyvinyl alcohol-type resin is the weight average molecular weight measured by GPC-MALS method.

The average saponification degree of the polyvinyl alcohol resin used in the present invention is generally preferably 98 mol% or more, 99 mol% or more is particularly preferred, 99.5 mol% or more is more preferred, and 99.8 mol% or more is particularly preferred. If the average saponification is too small, there is a tendency that sufficient optical performance cannot be obtained when the polyvinyl alcohol-based film is formed into a polarizing film. Here, the average degree of saponification in the present invention is measured in accordance with JIS K 6726.

The polyvinyl alcohol-based resin used in the present invention may also be used with two or more different modified substances, weight average molecular weight, average saponification degree, and the like.

The polyvinyl alcohol-based resin aqueous solution is prepared using the above-mentioned polyvinyl alcohol-based resin, and the aqueous solution is cast on a rotating casting drum (roller type roll), and a film is formed by a casting method and dried, thereby continuously manufacturing the polyvinyl alcohol of the present invention The thin film can be produced by the following steps, for example. (A) The thin film is formed by a casting method. (B) Heat and dry the formed film. (C) After cutting the dried film, it is wound on a roll.

Hereinafter, the above-mentioned step (A) will be described. In step (A), it is preferable to wash the above-mentioned polyvinyl alcohol-based resin with a solvent such as water, and use a centrifugal separator for dehydration to form a polyvinyl alcohol-based resin wet cake with a moisture content of 50% by weight or less. . If the water content is too large, it will tend to be difficult to achieve the desired concentration of the aqueous solution. This polyvinyl alcohol-based resin wet cake is dissolved in warm water or hot water to prepare a polyvinyl alcohol-based resin aqueous solution.

The preparation method of the polyvinyl alcohol-based resin aqueous solution is not particularly limited. For example, it can be prepared using a heated multi-axis extruder, and the polyvinyl alcohol-based resin solution can also be added to a dissolving tank equipped with a vertical circulation flow generating type stirring blade. Wet the resin cake and blow water vapor into the tank to dissolve and prepare an aqueous solution of the desired concentration.

In addition to the polyvinyl alcohol resin, the aqueous solution of polyvinyl alcohol resin contains glycerin, diglycerin, triglycerin, ethylene glycol, triethylene glycol, polyethylene glycol, trimethylolpropane, etc. as necessary. Generally used The plasticizer; nonionic, anionic, or cationic surfactants are preferred in terms of film-forming properties of polyvinyl alcohol-based films.

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 more preferably 20 to 50% by weight. If the resin concentration is too low, the drying load will increase and the productivity will tend to decrease. If it is too high, the viscosity will become too high and it will tend to be difficult to dissolve uniformly.

Then, the obtained polyvinyl alcohol-based resin aqueous solution is subjected to defoaming treatment. As far as defoaming methods are concerned, methods such as static defoaming and defoaming using a multi-axis extruder can be cited. The multi-screw extruder is not particularly limited as long as it is a multi-screw extruder with vent holes, and a twin-screw extruder with vent holes is generally used.

After the defoaming treatment, the polyvinyl alcohol-based resin aqueous solution is quantitatively introduced into the T-shaped slit die successively, and discharged and cast onto a rotating casting drum, and a film is formed by a casting method.

The temperature of the polyvinyl alcohol resin aqueous solution at the exit of the T-shaped slit die is preferably 80-100°C, and 85-98°C is particularly preferred. If the temperature of the polyvinyl alcohol-based resin aqueous solution is too low, the flow will tend to be poor, and if it is too high, there will be a tendency to foam.

The viscosity of the polyvinyl alcohol-based resin aqueous solution is preferably 50 to 200 Pa·s during discharge, and particularly preferably 70 to 150 Pa·s. If the viscosity of the aqueous solution is too low, the flow will tend to be poor, and if it is too high, the casting will tend to become difficult.

The discharge speed of the polyvinyl alcohol resin aqueous solution discharged from the T-shaped slit die to the casting drum is preferably 0.5-5 m/min, 0.8-4 m/min is particularly preferable, and 1-3 m/min is more preferable. If the discharge rate is too slow, productivity tends to decrease, and if it is too fast, casting tends to become difficult.

In addition, the flight time of the polyvinyl alcohol-based resin aqueous solution from the T-slot die outlet to reaching the surface of the casting drum is preferably 0.1 to 0.7 seconds, and considering the relaxation of tensile stress and compressive stress described later, it is 0.2 to 0.6 The second is particularly good, considering that it can avoid the shape deformation caused by the environment described later, 0.2 to 0.4 seconds is more preferable. If the flight time is too short or too long, the thickness variation tends to increase.

The flight time can be adjusted by adjusting the discharge speed from the T-shaped slit mold 1, the distance A from the discharge port 1a of the T-shaped slit mold 1 to the surface of the casting drum 2 (ground point P), and the T-shaped slit mold 1. Adjust the lip opening of the lipstick and the viscosity of the polyvinyl alcohol-based resin aqueous solution (see Figure 1).

In the present invention, in order to reduce the thickness variation of the obtained polyvinyl alcohol-based film, it is preferable to set the time to relax the shape deformation accompanying stress release and the time to avoid the shape deformation caused by the environment as much as possible.

Regarding the former, for example, when the polyvinyl alcohol-based resin aqueous solution 3 is discharged vertically from above to the apex of the rotating casting drum 2, the newly discharged polyvinyl alcohol-based resin aqueous solution 3 generates tensile stress on the casting drum side R, and the free surface Compressive stress is generated on the side S (refer to FIG. 2). If the aqueous solution is grounded to the casting drum 2 in a short period of time, the difference between the two stresses will cause the thickness to vary. However, even if the viscosity of the polyvinyl alcohol resin aqueous solution 3 is relatively high, if the stress relaxation time is set appropriately, the thickness can be reduced. The impact of changes. The lower limit of the flight time of the present invention can be set in consideration of the time for the stress relaxation.

The diameter of the casting drum is preferably 2-5m, particularly preferably 2.4-4.5m, and even more preferably 2.8-4m. If the diameter is too small, the drying length will be insufficient and the speed will tend to be difficult to achieve, and if the diameter is too large, the transportability will tend to decrease.

The width of the casting drum is preferably at least 2m, particularly preferably at least 3m, more preferably at least 4m, and particularly preferably 5-6m. If the width of the casting drum is too small, the productivity tends to decrease.

The rotation speed of the casting drum is preferably 3-50m/min, 4-40m/min is particularly preferred, and 5~35m/min is more preferred. If the rotation speed is too slow, the productivity will tend to decrease, and if it is too fast, the drying will tend to be insufficient.

The surface temperature of the casting drum is preferably 40-99°C, particularly preferably 60-97°C. If the surface temperature is too low, there will be a tendency for poor drying, and if it is too high, there will be a tendency for foaming.

Next, the above step (B) will be described. Step (B) is a step of heating and drying the formed film.

The drying of the film formed in the casting drum is performed by alternately contacting the surface and back of the film with a plurality of hot rollers. The surface temperature of the heat roller is usually 40 to 150°C, preferably 50 to 140°C. If the surface temperature is too low, there will be a tendency for poor drying, and if it is too high, there will be a tendency for excessive drying to cause poor appearance such as undulation. In addition, as for the heat roller, for example, a roller having a diameter of 0.2 to 2 m on which a hard chromium plating treatment or a mirror surface treatment has been applied to the surface is preferable, and usually 2 to 30, preferably 10 to 25, are used for drying.

In the present invention, it is preferable to heat-treat the film after drying by a heat roller. The heat treatment temperature is preferably 60-150°C, particularly preferably 70-140°C. If the heat treatment temperature is too low, the water resistance of the polyvinyl alcohol-based film may decrease, which may cause retardation oscillations. If the heat treatment temperature is too high, the extensibility during the production of the polarizing film may decrease. The heat treatment method includes, for example, a method of contacting a high-temperature heat roller, a method of using a floating dryer, and the like.

The film after drying and optionally heat treatment undergoes the above step (C) to become a product (the polyvinyl alcohol film of the present invention). Step (C) is a step of cutting both ends of the film and winding it up on a roll.

In addition, up to this point, the method of preparing a polyvinyl alcohol-based resin aqueous solution, casting the aqueous solution on a rotating casting drum (roller type roll), forming a film by a casting method, and drying to produce a polyvinyl alcohol-based film has been described. It is also possible to cast the polyvinyl alcohol-based resin aqueous solution onto a resin film or metal belt, and form a film and dry it.

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

The polyvinyl alcohol-based film of the present invention must have a thickness of 5-60 μm. Considering thinness, 5-50 μm is particularly preferred, and 5-30 μm is more preferred, and 10-30 μm is particularly preferred for avoiding cracking.

It is necessary for the polyvinyl alcohol film of the present invention to have a width of 2 m or more. Considering a larger area, it is particularly preferably 3 m or more, and considering avoiding breakage, it is more preferably 4-6 m.

It is necessary for the polyvinyl alcohol film of the present invention to have a length of 2 km or more. Considering a larger area, 3 km or more is particularly preferable, and 4 km or more is more preferable. In addition, the upper limit of the length of the film, considering the avoidance of breakage, is preferably 50km or less, 40km or less is particularly preferred, and 30km or less is more preferred.

As described above, in the polyvinyl alcohol film of the present invention, the coefficient of variation of the thickness of the entire film is less than 1%, and the coefficient of variation of the thickness of the film in the direction of flow (MD direction) takes into account the polarization performance of the polarizing film. It is preferably 0.7% or less, particularly preferably 0.6% or less, and more preferably 0.5% or less. In addition, the coefficient of variation of the thickness in the width direction (TD direction), considering the polarization performance of the polarizing film, is preferably 0.7% or less, 0.6% or less is particularly preferred, and 0.5% or less is more preferred. Here, when the thickness of the polyvinyl alcohol-based film is thin, the degree of polarization in the flow direction tends to become uneven in the production of the polarizing film, and the thickness accuracy in the flow direction (MD direction) of the original roll becomes important.

The thickness variation coefficient of the present invention will be described in detail.

The coefficient of variation of film thickness depends on the smoothness of the casting drum, the uniform rotation of the casting drum, the uniformity of the opening of the T-slot die, the discharge accuracy of the polyvinyl alcohol resin aqueous solution, and the polyvinyl alcohol resin aqueous solution The discharge angle toward the casting drum, the time and distance until the polyvinyl alcohol-based resin aqueous solution is grounded to the casting drum, the stable contact between the polyvinyl alcohol-based resin aqueous solution and the casting drum, the drying conditions in the casting drum or the subsequent hot roller, etc. Among them, stable contact between the polyvinyl alcohol-based resin aqueous solution and the casting roll is important, and if the contact line (contact line) moves back and forth in the MD direction, the thickness of the film will vary in the MD direction. In addition, if the contact line wobbles in the TD direction, the thickness of the film will fluctuate in the TD direction. In order to stabilize the antenna, the method of adjusting the following [I] to [V] is effective and preferable.

[I] "The flying distance A (refer to Fig. 1) of the polyvinyl alcohol-based resin aqueous solution from the discharge port 1a of the T-shaped slit mold 1 to the surface of the casting drum 2 (ground point P)." The longer the flying distance A is, The polyvinyl alcohol-based resin aqueous solution is more susceptible to the rotation of the casting drum 2 or the influence of the ambient air flow, so the distance from the outlet 1a to the casting drum 2 is preferably as close as possible. In the present invention, the shortest distance B from the discharge port 1a of the T-shaped slot die 1 to the surface (grounding point P) of the casting drum 2 is preferably 2 mm or less, 1.5 mm or less is particularly preferable, and 1 mm or less is more preferable. If the shortest distance B is too large, the thickness variation of the film tends to increase.

[II] "The discharging direction D of the polyvinyl alcohol-based resin aqueous solution from the T-shaped slit mold 1 to the casting drum 2 (refer to Figure 3)." The polyvinyl alcohol-based resin aqueous solution is discharged from above until it touches the casting drum 2, due to gravity If dripping occurs, the contact line is easily confused. For example, when the tangent of the casting drum 2 at the grounding point P is parallel to the discharge direction D, the discharge liquid (a polyvinyl alcohol-based resin aqueous solution) drops due to gravity and it is difficult to smoothly ground. In the present invention, the discharge direction D from the T-shaped slit die 1 toward the casting drum 2 (the direction facing the lip surface inside the T-shaped slit die) D, and the discharge port 1a connecting the T-shaped slit die 1 and the casting drum 2 The angle θ formed by the plane E of the central axis C is preferably 40° or less, preferably 1-30°, more preferably 2-20°, and particularly preferably 3-10°. If the angle θ is too large, the thickness variation of the film tends to increase.

[III] "Air knife and/or air chamber." A general method used to forcibly stabilize the contact wire in resin extrusion molding. As for the air knife or air chamber, a known method can be used.

[IV] "The levelness of the T-shaped slit die." Since the width of the film formed by the film is 2m or more, the width of the T-shaped slit die is also 2m or more. In this case, the influence of gravity cannot be ignored. The T-shaped slit die uses a high-rigidity material. At the same time, in order to prevent the central part of the T-shaped slit die from bending in the width direction, the method of lifting it is effective. In the present invention, it is better to lift the T-shaped slit die with one or more suspension parts. Specifically, the bending of the central part of the T-shaped slit die in the width direction due to gravity should be 0.3mm or less Preferably, 0.2 mm or less is particularly preferable, and 0.1 mm or less is more preferable. In order to reduce the amount of bending, methods such as increasing the number of suspensions and changing the hanging position can be cited.

[V] "The amount of displacement in the space of the casting drum." Of course, when the casting drum seems to sway in space, the spit from the T-shaped slot mold cannot be grounded stably. In the present invention, the shaking of the rotating casting drum up and down, front and back (MD direction), and left and right (TD direction) are preferably ±50 μm or less, preferably ±40 μm or less, and more preferably ±30 μm or less. If the shaking is too large, the thickness variation of the film tends to increase. In order to reduce the shaking of the casting drum, methods such as reducing the weight of the casting drum and improving the rotation accuracy of the motor can be cited.

The polyvinyl alcohol-based film of the present invention has excellent thickness accuracy, and can be suitably used as a polyvinyl alcohol-based film for optics, and is particularly preferably used as a raw roll for a polarizing film.

Hereinafter, the manufacturing method of the polarizing film obtained using the polyvinyl alcohol film of this invention is demonstrated.

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

The swelling step is implemented before the dyeing step. The swelling step not only cleans the stains on the surface of the polyvinyl alcohol-based film, but also has the effect of preventing uneven dyeing by swelling the polyvinyl alcohol-based film. In the swelling step, water is usually used as the treatment liquid. As long as the main component of the treatment liquid is water, a small amount of additives such as iodine compounds and surfactants, alcohol, etc. may be added. 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 step is performed by contacting the film with a liquid containing iodine or a dichroic dye. Usually, an aqueous solution of iodine-potassium iodide is used, and the concentration of iodine is 0.1-2g/L, and the concentration of potassium iodide is 1-100g/L. The dyeing time is about 30 to 500 seconds, which is more practical. The temperature of the treatment bath is preferably 5-50°C. In addition to water solvents, the aqueous solution may also contain a small amount of organic solvents that are compatible with water.

The boric acid crosslinking step is performed using boron compounds such as boric acid or borax. The boron compound is used in the form of an aqueous solution or a water-organic solvent mixture and a concentration of about 10 to 100 g/L. When potassium iodide is coexisted in the liquid, it is preferable to stabilize the polarization performance. The temperature during the treatment is preferably about 30 to 70°C, and the treatment time is preferably about 0.1 to 20 minutes. Moreover, the stretching operation may be performed during the treatment when necessary.

The extension step should preferably extend 3-10 times in the uniaxial direction, preferably 3.5-6 times. At this time, even if a slight extension is performed in the direction at right angles to the extension direction (the degree of preventing shrinkage in the width direction, or the extension of more than this degree). The temperature during stretching is preferably 40 to 170°C. Furthermore, as long as the stretching magnification is finally set to the above-mentioned range, the stretching operation is not only performed in a single stage, but may be performed in a stage within an arbitrary range of the manufacturing process.

The washing step is performed by, for example, immersing the polyvinyl alcohol-based film in water or an iodide aqueous solution such as potassium iodide to remove precipitates generated on the surface of the film. The potassium iodide concentration when using the potassium iodide aqueous solution can be 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. In addition, washing with water and washing with potassium iodide aqueous solution may be suitably combined.

The drying step may be performed in the air at 40 to 80°C for 1 to 10 minutes.

In addition, the degree of polarization of the polarizing film is preferably 99.5% or more, more preferably 99.8% or more. If the polarization is too low, there is a tendency that the contrast of the liquid crystal display cannot be ensured. In addition, the degree of polarization is generally determined by the light transmittance (H ₁₁ ) measured at the wavelength λ in a state where two polarizing films are superimposed so that their alignment directions become the same direction, and when the two polarizing films are superimposed to make The light transmittance (H ₁ ) measured at the wavelength λ in the state where the alignment directions are perpendicular to each other is calculated according to the following formula. [(H ₁₁ -H ₁ )/(H ₁₁ +H ₁ )] ^1/2

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

In this way, the polarizing film of the present invention can be obtained, and the polarizing film of the present invention is suitable for manufacturing a polarizing plate with less uneven dyeing. Hereinafter, the manufacturing method of the polarizing plate of the present invention will be described.

The polarizing film of the present invention is formed by bonding an optically isotropic resin film as a protective film to one or both sides of the polarizing plate via an adhesive. As the protective film, for example, cellulose triacetate, cellulose diacetate, polycarbonate, polymethyl methacrylate, cyclic olefin polymer, cyclic olefin copolymer, polystyrene, polyether block, polyarylene Films or sheets of base ester, poly-4-methylpentene, polyphenylene ether, etc.

The bonding method can be performed by a known technique. For example, a liquid adhesive composition is uniformly coated on a polarizing film, a protective film, or both, and then the two are bonded and press-bonded by heating or irradiation. Active energy rays.

In order to make the film into a thin film, a curable resin such as urethane resin, acrylic resin, or urea resin may be applied to one or both sides of the polarizing film instead of the protective film, and then cured to form a polarizing plate.

The polarizing film and polarizing plate obtained according to the present invention have excellent thickness variation coefficient, no dyeing unevenness and excellent in-plane uniformity of polarization performance, and can be ideally used in portable information terminals, personal computers, televisions, and projectors , Sign boards, electronic desktop computers, electronic clocks, word processors, electronic paper, game consoles, video cameras, cameras, photo albums, thermometers, audio, automotive or mechanical measuring instruments such as liquid crystal display devices, sunglasses, Anti-glare glasses, stereo glasses, wearable displays, display elements (CRT, LCD, organic EL, electronic paper, etc.) with reflection reduction layer, optical communication equipment, medical equipment, construction materials, toys, etc. [Example]

Hereinafter, the present invention will be explained more specifically with examples, but the present invention is not limited to the following examples as long as it does not exceed the gist. In addition, "parts" and "%" in the examples mean weight basis. The various physical properties are obtained as follows.

(1) Thickness The thickness of the MD and TD directions of the polyvinyl alcohol-based film is measured.・The flow direction (MD direction) is measured using the "Spectral Interference Film Thickness Gauge SI-T80" manufactured by KEYENCE, with a 0.3mm step on the center and both ends of the width direction (TD direction) (inside 20 cm from both ends) ) Measure 60,000 points at 3 places.・The measurement in the TD direction uses the "Continuous Film Thickness Gauge TOF-5R01" manufactured by Sanbun Electric Co., and measures 4000 points at three locations at the front end, center, and end in the MD direction.

(2) Thickness variation coefficient Use the measured value of the above thickness to calculate according to the following formula.

[Number 2] Coefficient of Variation (CV)=100×SD/x "Standard Deviation (SD)=√(Σ(xi-x) ² /(n-1)) x: mean value xi: value n at the i-th point ：Number of samples"

(3) Polarization degree (%) From the center part of the obtained polarizing film in the width direction, a strip sample with an extension direction of 200 mm × a width direction of 40 mm was cut out, and "RETS-1100A" manufactured by Otsuka Electronics Co., Ltd. was used in the extension direction. The degree of polarization at 10 points is measured with a pitch of 10 mm.

<Example 1> (Production of polyvinyl alcohol-based film) 1000kg of polyvinyl alcohol-based resin with a weight average molecular weight of 142,000 and a saponification degree of 99.8 mol%, 2000kg of water, and 100kg of glycerin as a plasticizer were added, and the temperature was raised while stirring. At 150°C, the concentration was adjusted to 25% of the resin concentration to obtain a uniformly dissolved aqueous solution of polyvinyl alcohol resin. Then, the polyvinyl alcohol-based resin aqueous solution was supplied to a biaxial extruder and defoamed, and the temperature of the aqueous solution was set to 95°C, and the solution was cast from the T-slot die outlet to the rotating casting drum at a discharge speed of 2.5 m/min. Film making. The shortest distance from the outlet of the T-shaped slit die to the surface of the casting drum is 2mm, from the T-shaped slit die toward the ejection direction of the casting drum (the direction facing the lip surface inside the T-shaped slit die), and the connecting T-shaped slit The angle formed by the slot die outlet and the plane of the central axis of the casting drum is 15° (refer to Table 1). Then, the obtained film is peeled from the casting drum, and dried with a hot roll and heat treatment with a floating dryer. Then, both ends were cut so that the width became 4 m, and a polyvinyl alcohol-based film was obtained. The properties of the obtained polyvinyl alcohol-based film are shown in Table 2.

Then, using the polyvinyl alcohol-based film obtained above, a polarizing film was obtained according to the following procedures, and the following evaluation was performed. The evaluation results are shown in Table 3.

(Production of polarizing film) The obtained polyvinyl alcohol-based film was stretched to 1.7 times while being immersed in a water tank with a water temperature of 25°C. Then it was immersed in a 28°C aqueous solution composed of 0.5g/L of iodine and 30 g/L of potassium iodide while extending to 1.6 times, and then immersed in an aqueous solution (55°C) of 40g/L of boric acid and 30g/L of potassium iodide, At the same time, the boric acid treatment was performed while uniaxially stretched to 2.1 times. Then, it was washed with a potassium iodide aqueous solution and dried to obtain a polarizing film with a total stretching ratio of 5.8 times. The polarization characteristics of the obtained polarizing film are shown in Table 3.

<Examples 2, 3, 5 to 7, Comparative Examples 1 to 4> Except that the film forming conditions in Example 1 were changed as shown in Table 1, the same procedure as in Example 1 was carried out to obtain polyvinyl alcohol A thin film, and further, a polarizing film was obtained in the same manner as in Example 1. The same evaluations as in Example 1 were performed for the obtained polyvinyl alcohol-based film and polarizing film. The evaluation results are shown in Table 2 and Table 3.

<Example 4> The film forming conditions in Example 1 were changed as shown in Table 1, and an air knife (height 5mm, angle 90°) was installed on the top of the aqueous solution when the aqueous solution was discharged. Except that air was discharged from an air knife at a pressure of 10 kPa to stabilize the antenna, the same procedure as in Example 1 was carried out to obtain a polyvinyl alcohol-based film, and further, a polarizing film was obtained in the same manner as in Example 1. About the obtained polyvinyl alcohol-based film and the polarizing film, the same evaluation as Example 1 was performed. The evaluation results are shown in Table 2 and Table 3.

【Table 1】

【Table 2】

【table 3】

Although the polyvinyl alcohol-based films of Examples 1 to 7 are thin, wide and long, the thickness variation coefficient of either the MD direction or the TD direction is 1% or less. Therefore, the degree of polarization of the obtained polarizing film is In contrast, the polyvinyl alcohol-based films of Comparative Examples 1 to 4 have a large variation coefficient of thickness, and the degree of polarization of the obtained polarizing film is not uniform in the plane. In addition, it was found that by adjusting the shortest distance (mm) from the discharge port of the T-shaped slit die to the surface of the casting drum, the direction from the T-shaped slit die to the ejection direction of the casting drum (the direction facing the lip surface inside the T-shaped slit die) ) And the angle (°) formed by the plane connecting the outlet of the T-shaped slit die and the central axis of the casting drum, and the use of an air knife, etc., to produce a polyvinyl alcohol film with a small thickness variation coefficient.

The above-mentioned embodiment shows the specific form of the present invention, but the above-mentioned embodiment is only an illustration, and is not a limited interpretation. For those with ordinary knowledge in this technical field, various obvious modifications are still intended to be included in the scope of the present invention. [Industrial availability]

The polarizing film and polarizing plate obtained according to the present invention have excellent thickness variation coefficient and excellent in-plane uniformity of polarization performance. They can be ideally used in portable information terminals, personal computers, televisions, projectors, sign boards, and electronics. Desktop computers, electronic clocks, word processors, electronic paper, game consoles, video cameras, cameras, photo albums, thermometers, stereos, automotive or mechanical measuring instruments such as liquid crystal display devices, sunglasses, anti-glare glasses, stereo Reflection reduction layers for glasses, wearable displays, display elements (CRT, LCD, organic EL, electronic paper, etc.), optical communication equipment, medical equipment, building materials, toys, etc.

1‧‧‧T-shaped slit die 1a‧‧‧T-shaped slit die outlet 2‧‧‧Casting drum 3‧‧‧Polyvinyl alcohol resin aqueous solution A‧‧‧The flying distance of the polyvinyl alcohol resin aqueous solution from the outlet 1a of the T-shaped slit die 1 to the surface of the casting drum 2 (grounding point P) B‧‧‧The shortest distance from the outlet 1a of the T-shaped slot die 1 to the surface of the casting drum 2 (grounding point P) C‧‧‧Central axis of casting drum 2 D‧‧‧From the T-shaped slit mold 1 to the direction of the casting drum 2 (the direction facing the lip surface of the T-shaped slit mold) E‧‧‧The plane connecting the outlet 1a of the T-shaped slit die 1 and the central axis C of the casting drum 2 P‧‧‧Ground point R‧‧‧Casting drum side S‧‧‧free side θ‧‧‧The discharge direction from the T-shaped slit die 1 to the casting drum 2 (the direction facing the lip surface of the T-shaped slit die) D, and the outlet 1a connecting the T-shaped slit die 1 and the casting drum 2 The angle formed by the plane E of the central axis C

Fig. 1 is an explanatory diagram showing the state (flight time) of the polyvinyl alcohol-based resin aqueous solution discharged from the T-slot die discharge port toward the surface of the casting drum. Fig. 2 is an explanatory diagram showing the landed state of the polyvinyl alcohol-based resin aqueous solution toward the surface of the casting drum. Fig. 3 is an explanatory diagram showing the direction in which the polyvinyl alcohol-based resin aqueous solution is discharged from the T-shaped slot die toward the casting drum.

Claims (7)

A polyvinyl alcohol-based film, a polyvinyl alcohol-based film with a thickness of 5-60μm, a width of 2m or more, and a length of 2km or more; it is characterized in that the coefficient of variation of the thickness of the entire film is less than 1%; the polyvinyl alcohol-based film The coefficient of variation of the thickness in the flow direction (MD direction) is 0.7% or less. For example, the polyvinyl alcohol-based film in the first item of the scope of patent application, wherein the thickness of the polyvinyl alcohol-based film is 30 μm or less. A method for producing a polyvinyl alcohol-based film, which is obtained by spitting out an aqueous solution of a polyvinyl alcohol-based resin from a T-shaped slit die onto a rotating cast drum to form a film, and then continuously drying it. Polyvinyl alcohol-based film; characterized in that: the coefficient of variation of the thickness of the entire film is less than 1%; the coefficient of variation of the thickness of the polyvinyl alcohol-based film in the flow direction (MD direction) is less than 0.7%; from the T type The slit mold faces the ejection direction of the casting drum (the direction facing the lip surface inside the T-shaped slit die), and the plane connecting the T-shaped slit die outlet and the center axis of the casting drum is formed The angle is 40° or less. For example, the manufacturing method of polyvinyl alcohol-based film in the third item of the scope of patent application, wherein the shortest distance from the T-shaped slit die to the surface of the casting roller is 2mm or less. For example, the manufacturing method of the polyvinyl alcohol-based film of the third or fourth patent application, wherein the touch line of the aqueous solution grounded to the casting drum is stabilized by an air knife. A polarizing film is composed of a polyvinyl alcohol-based film such as item 1 or 2 of the scope of patent application. A polarizing plate is formed by arranging a protective film on at least one side of the polarizing film as in item 6 of the scope of patent application.

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