WO2017056580A1 - Method for producing polarizing film, polarizing film, and polarizing plate - Google Patents

Abstract

The purpose of the invention is to produce, with excellent productivity, a polarizing film with little unevenness in polarization by solving problems related to folding and creases throughout all of the steps for producing the polarizing film. Disclosed is a method for producing a polarizing film through: (1) a step for unwinding a polyvinyl alcohol-based film from a roll and transporting the film in the horizontal direction; (2) a water-swelling step; (3) a dyeing step; (4) a drawing step; and (5) a boric acid crosslinking step. Before and/or after one of the steps (2) to (4), a gas is blown onto both edges, in the width direction, of the film according to the following condition (a), to prevent curling of the film. Condition (a): the angle θ1 formed between the gas blowing direction and the surface of the film is from 5 to 80°.

Description

Manufacturing method of polarizing film, polarizing film and polarizing plate

The present invention relates to a method for producing a polarizing film, a polarizing film and a polarizing plate used in a liquid crystal display device (hereinafter sometimes abbreviated as LCD), and more specifically, a polyvinyl alcohol film as a raw material. The present invention relates to a method for producing a polarizing film dyed with iodine, a polarizing film produced by the production method, and a polarizing plate using the polarizing film.

LCDs are used in portable information terminals, liquid crystal televisions, desktop electronic calculators, electronic watches, personal computers, word processors, automobile and machine instruments, etc., and polarizing plates are used in this LCD. As the polarizing plate, one in which a protective film such as triacetyl cellulose is laminated on one side or both sides of a polarizing film made of a polyvinyl alcohol film to which iodine or a dichroic dye is adsorbed and oriented is brightly used. In order to provide an LCD having a high contrast, a polarizing plate having a high transmittance and a high degree of polarization is required.

The polarizing film described above, for example, is obtained by swelling a polyvinyl alcohol film with water (including warm water), dyeing with iodine, stretching to arrange iodine molecules, and boric acid to maintain the stretched state. It is produced by crosslinking with a crosslinking agent such as This manufacturing process is continuously performed while unwinding the polyvinyl alcohol film from the roll and transporting it in the horizontal direction using a winder or a nip roll.

However, in the manufacturing process of water swelling, dyeing, stretching, boric acid crosslinking, and drying, the film absorbs water or dehydrates and curls, and folds and wrinkles occur at the end in the width direction of the film. There was a problem that it could not be manufactured. In particular, when the film is thin, there is a problem that the film breaks due to such folds and wrinkles and the production is interrupted. Furthermore, such a defect at the edge also affects the inside of the polarizing film, thereby degrading the polarizing performance of the entire polarizing film, making it difficult to uniformly attach the polarizing plate to the liquid crystal cell, and the color of the liquid crystal display image. It was the cause of unevenness and white spots.

In recent years, with the enlargement of screens of liquid crystal televisions and the like, a polarizing film that is wider and thinner than conventional products is required.
In order to reduce such folds and wrinkles, a method of applying a constant tension in the width direction of the film by a drying process has been proposed (for example, see Patent Document 1). Moreover, the method of injecting water from a nozzle to the both ends of the width direction of the film currently running underwater is proposed (for example, refer to patent documents 2).

JP 2006-189560 A Japanese Patent Laid-Open No. 7-247378

However, although the disclosed technique of Patent Document 1 can avoid creases and wrinkles in the drying process, the film may be folded or wrinkled in any of the steps of water swelling, dyeing, stretching, and boric acid crosslinking before the drying process. If it occurs, there is a problem that it cannot be transported to the drying process in the first place.
Moreover, although the disclosed technique of Patent Document 2 can avoid folding and wrinkles in water, it cannot prevent folding and wrinkles that occur in the air.
Therefore, the present invention aims to solve the problem of folding and wrinkles in the entire manufacturing process of the polarizing film, and to manufacture a polarizing film with high productivity and little polarization unevenness.

Therefore, the present invention provides the following aspects of the invention.
[Method for producing polarizing film]
1) A method for producing a polarizing film comprising a step of unwinding a polyvinyl alcohol film from a roll and transferring it horizontally, 2) a water swelling step, 3) a dyeing step, 4) a stretching step, and 5) a boric acid crosslinking step. There,
Before and / or after any of the steps 2) to 4), a gas is blown to both ends of the film in the width direction under the following condition a to prevent curling of the film: Production method.
Condition a) The angle θ1 formed between the gas blowing direction and the film surface is 5 to 80 °.

[Polarizing film]
The polarizing film manufactured by the manufacturing method of the polarizing film of this invention.

〔Polarizer〕
A polarizing plate comprising a protective film provided on at least one surface of the polarizing film of the present invention.

In the present invention, the “film width direction” is generally a direction substantially perpendicular to the longitudinal direction of the belt-like film. In particular, in a polyvinyl alcohol film unwound from a roll and transferred in the horizontal direction, the direction is substantially perpendicular to the film transfer direction, and typically the distance between both edges of the film is the shortest. The direction.
In the present invention, the width direction of the film is referred to as “TD direction”, and the transfer direction of the film is referred to as “MD direction”.
Hereinafter, the polyvinyl alcohol film is also simply referred to as “film”.

According to the method for producing a polarizing film of the present invention, both ends of the polyvinyl alcohol film in the width direction before and / or after any of the steps 2) water swelling step, 3) dyeing step, and 4) stretching step. Since the film is blown under a predetermined condition to prevent curling of the film, the entire surface of the film can be kept flat, and folding and wrinkles can be avoided.

By the production method of the present invention, a wide, long and thin polarizing film can be produced with high productivity, and a polarizing film having a uniform degree of polarization from the center to the end of the polarizing film can be obtained. Furthermore, it is possible to easily produce a wide, long and thin polarizing plate, and to reduce color unevenness and white spots in a liquid crystal display image.

FIG. 1 is a diagram schematically showing locations of air blowing in 1) a raw fabric unwinding step, 2) a water swelling step, and 3) a dyeing step. FIG. 2 is a diagram schematically showing the distance A between the liquid level of the water swelling tank and the roll a and the distance B between the roll a and the roll b between 2) the water swelling process and 3) the dyeing process. FIG. 3A is a diagram showing a spraying mode when a liquid is sprayed on the surface of a polyvinyl alcohol film (PVA film). FIG. 3B is a diagram showing a spraying mode when a liquid is sprayed on the back surface of a polyvinyl alcohol film (PVA film). FIG. 4 is a diagram showing an angle θ1 formed by the blowing direction and the surface of the film when air is blown onto the front or back surface of the polyvinyl alcohol film. FIG. 5 shows the angle θ2 formed between the direction when the blowing direction is perpendicularly projected onto the surface of the polyvinyl alcohol film and the transfer direction of the polyvinyl alcohol film when air is blown onto the front or back surface of the polyvinyl alcohol film. FIG. FIG. 6 shows the angle θ1 formed between the blowing direction and the surface of the film when air is blown on the front or back surface of the polyvinyl alcohol film, and the direction when the blowing direction is vertically projected onto the surface of the polyvinyl alcohol film. It is a figure which shows angle (theta) 2 which makes with the transfer direction of an alcoholic film. FIG. 7 is a diagram showing an example of a spraying mode when air is sprayed on a polyvinyl alcohol film.

Hereinafter, the configuration of the present invention will be described in detail, but these show examples of desirable embodiments, and the present invention is not limited to these contents.

In the method for producing a polarizing film of the present invention, 1) a step of unwinding a polyvinyl alcohol film from a roll and transferring it horizontally, 2) a water swelling step, 3) a dyeing step, 4) a stretching step, and 5) boric acid A polarizing film is manufactured through a crosslinking step. In addition, 1) The process which unwinds a polyvinyl alcohol-type film from a roll and transfers it to a horizontal direction is also called 1) original fabric unwinding process below.
The polyvinyl alcohol film used in the above 1) raw roll unwinding step is a film obtained by forming a polyvinyl alcohol resin into a film and wound up on a roll.

As the polyvinyl alcohol resin used for the polyvinyl alcohol film, an unmodified polyvinyl alcohol resin, that is, a resin produced by saponifying polyvinyl acetate obtained by polymerizing vinyl acetate is usually used. The polyvinyl alcohol film used in the present invention is not necessarily limited thereto, and can be copolymerized with vinyl acetate and a small amount (for example, 10 mol% or less, preferably 5 mol% or less) of vinyl acetate. A polyvinyl alcohol-based resin obtained by saponifying a copolymer with a component can also be used. Examples of components copolymerizable with vinyl acetate include unsaturated carboxylic acids (including salts, esters, amides, nitriles, etc.), and olefins having 2 to 30 carbon atoms (eg, ethylene, propylene, n-butene). , Isobutene, etc.), vinyl ethers, unsaturated sulfonates and the like. Moreover, the modified polyvinyl alcohol-type resin obtained by chemically modifying the hydroxyl group after saponification can also be used.

Also, as the polyvinyl alcohol resin, a polyvinyl alcohol resin having a 1,2-diol structure in the side chain can be used. Such a polyvinyl alcohol resin having a 1,2-diol structure in the side chain includes, for example, (i) a method for saponifying a copolymer of vinyl acetate and 3,4-diacetoxy-1-butene, and (ii) acetic acid. A method of saponifying and decarboxylating a copolymer of vinyl and vinylene carbonate; (iii) saponifying and decarboxylating a copolymer of vinyl acetate and 2,2-dialkyl-4-vinyl-1,3-dioxolane. It is obtained by a method of ketalization, (iv) a method of saponifying a copolymer of vinyl acetate and glyceryl monoallyl ether, or the like.

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 from the viewpoint of optical performance and stretchability.
The average saponification degree of the polyvinyl alcohol-based resin is usually preferably 98 mol% or more, particularly preferably 99 mol% or more, more preferably 99.5 mol% or more, particularly preferably from the viewpoint of optical performance. It is 99.8 mol% or more.

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

The polyvinyl alcohol film used in the present invention prepares a polyvinyl alcohol resin aqueous solution using the above polyvinyl alcohol resin, and discharges and flows the aqueous solution to a cast mold such as a cast drum, a cast belt, and a cast resin film. It is manufactured by rolling and forming a film, winding it on a roll after drying.

In addition to polyvinyl alcohol-based resins, polyvinyl alcohol-based resin aqueous solutions include plastics commonly used such as glycerin, diglycerin, triglycerin, ethylene glycol, triethylene glycol, polyethylene glycol, and trimethylol propane as necessary. It is preferable from the viewpoint of film forming property to contain an agent and a nonionic, anionic, and / or cationic surfactant.

The resin concentration of the aqueous polyvinyl alcohol resin solution is preferably 10 to 60% by weight, particularly preferably 15 to 55% by weight, and further preferably 20 to 50% by weight.

The temperature of the aqueous polyvinyl alcohol resin solution when discharged into a cast mold is preferably 80 to 100 ° C., particularly preferably 85 to 98 ° C. The discharge rate of the aqueous polyvinyl alcohol resin solution discharged into the cast mold is preferably 0.1 to 5 m / min, particularly preferably 0.2 to 4 m / min, and more preferably 0.3 to 3 m. / Min.

The surface temperature of a cast mold such as a cast drum is preferably 40 to 99 ° C, particularly preferably 60 to 95 ° C.
The film formed in the cast mold is dried by conveying the film while the front surface and the back surface of the film are alternately brought into contact with the outer peripheral portions of a plurality of heat rolls. After drying with a hot roll, the film may be heat treated. The heat treatment is preferably performed at 60 to 150 ° C., particularly preferably 80 to 130 ° C.
Before winding the film on a roll, both ends of the film may be cut off with slits.

The thickness of the polyvinyl alcohol film is preferably 5 to 60 μm from the viewpoint of thinning the polarizing film, more preferably 5 to 30 μm from the viewpoint of further thinning, from the viewpoint of avoiding breakage. Particularly preferably, the thickness is 10 to 30 μm.
The width of the polyvinyl alcohol film is preferably 3 m or more, more preferably 4 m or more from the viewpoint of increasing the area, and particularly preferably 4 to 6 m from the viewpoint of avoiding breakage.
Moreover, it is preferable that the length of a polyvinyl alcohol-type film is 4 km or more, More preferably, it is 4.5 km or more from the point of enlargement, Preferably it is 5 km or more.
The upper limit of the length of the film is preferably 50 km or less, particularly preferably 40 km or less, and further preferably 30 km or less from the viewpoint of avoiding breakage.

In the production method of the present invention, before and / or after any one of the above-mentioned 2) water swelling step, 3) dyeing step, and 4) stretching step, gas is given to both ends in the width direction of the film to be conveyed. To prevent the film from curling.
4) After the stretching step 5) After the boric acid crosslinking step and after the subsequent 6) drying step, it is possible to spray the gas, but in this step, the film becomes hard due to crosslinking and drying. Folds and wrinkles are unlikely to occur and the effect of spraying is not significant.

In the above 2) water swelling step, 3) dyeing step, and 4) stretching step, the gas is sprayed from the viewpoint of avoiding breakage, 2) after the water swelling step, and / or 3) dyeing step. After the water swelling step, particularly preferably 2) after the water swelling step, more preferably 2) within the range of 10 seconds after the water swelling step.

The surface of the film to be sprayed is not particularly limited, and can be sprayed on the front surface, the back surface, and both surfaces. Generally, a polyvinyl alcohol film as a raw material is obtained by discharging and flowing an aqueous solution of a polyvinyl alcohol resin into a cast mold such as a cast belt and continuously drying the film. In such drying, the states on both sides are often not exactly the same, and the moisture on one side is often low or the degree of crystallinity is high. As a matter of course, since the surface with little moisture absorbs water and tends to stretch, the film tends to curl on the opposite surface side in the 2) water swelling process and 3) dyeing process in the production of the polarizing film. In such a case, in the present invention, it is effective to spray gas on both ends on the opposite surface side in the curl direction.

The gas to be blown includes gases such as air, nitrogen, oxygen, water vapor, and inert gas. Among these, air or water vapor is preferable in that it does not adversely affect the performance of the polarizing film, and air is more preferable in terms of simplicity of equipment. When air is used, the temperature is preferably 10 to 50 ° C., particularly preferably 20 to 40 ° C.

Hereinafter, the present invention will be described as an example of a preferred embodiment of the present invention, taking as an example the case where 2) air is blown after the water swelling step.

Generally, 2) the water swelling step is 10 to 45 ° C., preferably 20 to 35 ° C. for 0.1 to 10 minutes, preferably 0.5 to 5 in terms of controlling the degree of swelling of the polyvinyl alcohol film. Dipped in water for a minute. The water may contain a small amount of an iodide compound, an additive such as a surfactant, alcohol and the like.
For example, as shown in FIG. 1, a polyvinyl alcohol film wound on a roll is unwound from the roll and transferred in the horizontal direction. 1) A polyvinyl alcohol film fed into a water swelling tank through an unwinding step. 2) The water swelling of the polyvinyl alcohol film is performed by the water swelling step. Thereafter, the polyvinyl alcohol film pulled up from the water swelling tank is transferred to a dyeing tank through a roll, and 3) the polyvinyl alcohol film is dyed in a dyeing step.

In the present invention, it is preferable that the air is blown onto both ends of the film, as described above, between 2) the water swelling process and 3) the dyeing process. Breaks and wrinkles are most likely to occur between these processes, and once the films are stuck together with the breaks or wrinkles, they are not easily peeled off. In addition, when a crease or wrinkle occurs between the processes, the processes 2) and 3) are the first processes for manufacturing the polarizing film, so the influence on the subsequent processes is significant. The specific position of spraying is, for example, 2) Immediately after coming out of the water swelling tank in the water swelling step and immediately after the first roll a. In addition, the position and direction of spraying are schematically shown by arrows in FIG.

In the present invention, as shown in FIG. 2, it is preferable that the distance A until the film exits the water swelling tank in 2) the water swelling step and comes into contact with the first roll a is 1 m or less. This is a case where the distance B from the roll a to the roll b just before the dyeing tank is 1 m or less. If the distance A is too long, there is a tendency for folds and wrinkles to increase. The distance A from the water swelling tank to the roll a represents the shortest distance from the liquid surface of the water swelling tank to the roll a, and the distance B from the first roll a to the roll b just before the dyeing tank is the same as that of the roll a. This represents the shortest distance between the roll b.
The tension between the rolls in the series of steps is preferably 1 to 100 N / m. If the tension between the rolls is too large, it tends to break, and conversely if it is too small, it tends to increase creases and wrinkles.
Furthermore, the transfer speed of the film from 2) the water swelling process to 3) the dyeing process is preferably 1 m / min or more, particularly preferably 1.5 m / min or more, more preferably 2 m from the viewpoint of productivity. / Min or more.

When spraying with air, it is preferable to discharge air to one or both sides of the both ends in the width direction of the film using a nozzle. At this time, as shown in FIG. 3A, air may be discharged to the surface of the film, as shown in FIG. 3B, air may be discharged to the back surface of the film, or air is discharged to both surfaces of the film. May be. Such nozzles are not particularly limited, and known nozzles such as point discharge nozzles, line discharge nozzles, and surface discharge nozzles can be used, but point discharge is preferable from the viewpoint of controlling the spray position. A plurality of the same types of nozzles may be installed, or a plurality of types of nozzles may be combined.

As shown in FIG. 2, the position of the nozzle is preferably from the point of avoiding the breakage of the film until the film comes out of the water swelling tank in the water swelling step and comes into contact with the transport roll a. Preferably, the distance from the outlet of the water swelling tank to the nozzle is within 1 m from the viewpoint of avoiding wrinkles of the film, and more preferably, within 0.5 m from the transport roll a to the nozzle from the viewpoint of film flatness. Is the distance. The distance from the outlet of the water swelling tank to the nozzle and the distance from the transport roll a to the nozzle each represent the shortest distance.
The distance between the nozzle and the film surface is preferably 1 to 100 mm in terms of avoiding film breakage, and particularly preferably 2 to 50 mm in terms of avoiding film wrinkles. is there. The distance between the nozzle and the film surface represents the shortest distance, and specifically represents the distance between the nozzle and the film surface in a direction perpendicular to the film surface.

In the present invention, the spraying flow velocity and the spraying angle are important in terms of curling prevention effects.
The spraying flow rate is preferably 0.1 to 10 m / sec. Particularly preferred is 0.2 to 5 m / sec, and even more preferred is 0.3 to 3 m / sec. If the flow rate is too slow, the effect of preventing curling tends to decrease, and if the flow rate is too fast, the film tends to swell.

When the air blowing direction is vertically projected onto the film surface, in other words, when the film surface is viewed in a direction perpendicular to the film surface, the air blowing direction is the film width direction (TD direction) or the film transport direction (MD Direction). Therefore, preferably, the air blowing angle includes not only the angle θ1 formed by the air blowing direction and the film surface, but also the direction when the air blowing direction is vertically projected on the film surface and the film transport direction. The angle θ2 formed with the (MD direction) is included (see FIGS. 4 to 6).
In FIG. 6, the film transport direction is the x-axis, the film width direction is the y-axis, the direction perpendicular to the film surface is the z-axis, the film surface is the xy surface, and the surface is perpendicular to the film surface. The plane parallel to the width direction is the yz plane, and the plane perpendicular to the film plane and parallel to the film transfer direction is the xz plane.

The angle θ1 formed by the air blowing direction and the film surface is preferably 5 to 80 °, particularly preferably 10 to 70 °, and further preferably 20 to 60 °. If the spray angle θ1 is too low, the effect of preventing curling tends to decrease, and if it is too high, the film tends to be swelled.
In addition, the angle θ2 formed by the direction when the air blowing direction is vertically projected onto the film surface and the film transport direction (MD direction) is preferably 5 to 175 °, particularly preferably 20 to 90 °. More preferably, it is 30 to 60 °. If the spray angle θ2 is too low, the effect of preventing curling tends to decrease, and if it is too high, wrinkles tend to occur on the film.
As shown in FIG. 7, when a plurality of nozzles are used, the flow velocity and the spray angle of the spraying may be the same for all nozzles or may be different for each nozzle. As a method different for each nozzle, for example, the spraying flow rate is gradually set lower from the upstream side to the downstream side in the film transfer direction (MD direction), or the spraying angle θ1 is gradually lowered. A method is mentioned.

When using a gas other than air, the conditions described above are preferable for the nozzle used, the arrangement of the nozzles, the spraying flow rate, and the spraying angle.

By such a method, the polyvinyl alcohol film is transferred to the following 3) dyeing step and 4) stretching step in a state where there is no break or wrinkle.

The polarizing film of the present invention is 1) after the unwinding step, 2) the water swelling step, 3) the dyeing step, 4) the stretching step, 5) the boric acid crosslinking step, and if necessary, the washing step and the drying step. It is manufactured through processes such as Such manufacturing steps are not necessarily performed in the order of 2) to 5), and a plurality of steps may be appropriately combined. For example, 2) the stretching process may be performed simultaneously with 2) the water swelling process, 2) after the water swelling process, 3) the stretching process may be performed with the dyeing process, and 2) the water swelling process. And 3) After the dyeing step, 5) The boric acid crosslinking step and 4) the stretching step may be performed, 2) the water swelling step, 3) the dyeing step, and 5) the boric acid crosslinking step. A stretching process may be performed.

Hereinafter, 2) Steps after water swelling will be described.

3) The dyeing step is performed by bringing the film into contact with a liquid containing iodine or a dichroic dye. Usually, an iodine-potassium iodide aqueous solution is used. The iodine concentration is suitably 0.1-2 g / L, and the potassium iodide concentration is 1-100 g / L. The dyeing time is practically about 30 to 500 seconds. The temperature of the treatment bath is preferably 5 to 50 ° C. The aqueous solution may contain a small amount of an organic solvent compatible with water in addition to the aqueous solvent. As the contact means, any means such as dipping, coating, spraying and the like can be applied.

4) The stretching step is a step of stretching 3 to 10 times in a uniaxial direction, and it is particularly preferable to stretch 3.5 to 6 times. At this time, the film may be slightly stretched (stretching to prevent shrinkage in the width direction or more) in a direction perpendicular to the stretching direction. The temperature during stretching is preferably selected from a temperature range of 30 to 170 ° C. Furthermore, the draw ratio may be finally set within the above range, and the drawing operation may be performed not only in one stage but also in any stage of the manufacturing process.

5) The boric acid crosslinking 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 it is desirable to allow a small amount of potassium iodide to coexist in the solution from the viewpoint of stabilizing the polarization performance. The treatment temperature is preferably about 30 to 70 ° C., and the treatment time is preferably about 0.1 to 20 minutes.

Thereafter, the film may be washed. The precipitate generated on the surface of the film can be removed by the washing treatment. The cleaning treatment is performed, for example, by immersing a polyvinyl alcohol film in an aqueous iodide solution such as water or potassium iodide. When using an aqueous potassium iodide solution, the concentration of potassium iodide may 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, you may perform combining water washing | cleaning and washing | cleaning by potassium iodide aqueous solution suitably. Moreover, you may give a drying process to the said film after that.
The drying step may be performed in the atmosphere at 40 to 80 ° C. for 1 to 10 minutes.

The polarization degree of the polarizing film thus obtained is preferably 99.8% or more, more preferably 99.9% or more. If the degree of polarization is too low, there is a tendency that the contrast in the liquid crystal display cannot be secured.
Note that the degree of polarization is generally the light transmittance (H ₁₁ ) measured at the wavelength λ in the state where two polarizing films are overlapped so that their orientation directions are the same direction, and the two polarizing films. It is calculated according to the following equation from the light transmittance (H ₁ ) measured at the wavelength λ in a state where the films are superposed so that the orientation directions are orthogonal to each other.
[(H ₁₁ −H ₁ ) / (H ₁₁ + H ₁ )] ^1/2

Further, the single transmittance of the polarizing film of the present invention is preferably 42% or more. If the single transmittance is too low, it tends to be impossible to achieve high brightness of the liquid crystal display.
The single transmittance is a value obtained by measuring the light transmittance of a single polarizing film using a spectrophotometer.

The width of the polarizing film of the present invention is preferably 1 m or more, preferably 1.3 m or more from the viewpoint of increasing the area, and particularly preferably 1.5 m or more from the viewpoint of further increasing the area. From the viewpoint of avoiding breakage, it is more preferably 1.5 to 2.5 m.

The thickness of the polarizing film of the present invention is preferably 15 μm or less, particularly preferably 10 μm or less from the viewpoint of further thinning, more preferably 2 to 9 μm, particularly preferably from the viewpoint of avoiding breakage. Is 3 to 8 μm.

Since the polarizing film of the present invention thus obtained has little polarization unevenness, it is suitable for producing a high-performance polarizing plate.
Hereinafter, the manufacturing method which manufactures a polarizing plate from the polarizing film of this invention is demonstrated.

The polarizing film of the present invention is bonded to one side or both sides of an optically isotropic resin film as a protective film via an adhesive to form a polarizing plate. 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 a sheet | seat is mentioned.

The bonding method is performed by a known method. For example, after a liquid adhesive composition is uniformly applied to a polarizing film, a protective film, or both, the two are bonded and pressure-bonded, and heating or active energy is applied. This is done by irradiating a line.

In addition, for the purpose of thinning the polarizing film, instead of the protective film, a curable resin such as urethane resin, acrylic resin, urea resin or the like is applied to one side or both sides of the protective film and cured to obtain a polarizing plate. You can also

The polarizing film and polarizing plate obtained by the present invention are excellent in polarization performance, such as portable information terminals, personal computers, televisions, projectors, signage, electronic desk calculators, electronic watches, word processors, electronic paper, game machines, videos, cameras. , Photo albums, thermometers, audio, liquid crystal display devices such as automobile and machinery instruments, sunglasses, anti-glare glasses, stereoscopic glasses, wearable displays, reflection for display elements (CRT, LCD, organic EL, electronic paper, etc.) It is preferably used for a prevention layer, an optical communication device, a medical device, a building material, a toy and the like.

Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to the following examples unless it exceeds the gist.

<Measurement conditions>
About the polarizing film obtained by the Example and the comparative example, polarization degree (%) was measured as follows.
The polarization degree of the obtained polarizing film at the central part and both ends (each 10 cm from the end) in the width direction was measured using RETS-1100A manufactured by Otsuka Electronics Co., Ltd.

<Example 1>
(Manufacture of polyvinyl alcohol film)
Polyvinyl alcohol resin with a weight average molecular weight of 142,000, saponification degree of 99.8 mol%, 1000 kg of water, 2500 kg of water and 100 kg of glycerin as a plasticizer are added, and the temperature is raised to 140 ° C. with stirring to adjust the resin concentration to 25% by weight. To obtain a uniformly dissolved polyvinyl alcohol-based resin aqueous solution.
Next, the polyvinyl alcohol-based resin aqueous solution is supplied to a twin-screw extruder having a vent and defoamed, and then the aqueous solution temperature is set to 95 ° C., and a cast drum having a surface temperature of 90 ° C. from the T-type slit die discharge port, The film was cast by casting at a discharge speed of 0.6 m / min.
Next, the obtained film was dried with a plurality of hot rolls, subjected to heat treatment at 120 ° C. for 3 minutes using a floating dryer, and cut into a 4 m width with a slit. Finally, it is wound on an aluminum core tube having an outer diameter of 17 cm, an inner diameter of 16 cm, and a length of 4.4 m, thereby forming a strip-like polyvinyl alcohol film having a moisture content of 2 wt% (width 4 m, length 5 km, thickness 15 μm). A film roll wound around the core tube was obtained.

(Manufacture of polarizing film)
While the obtained polyvinyl alcohol film was unwound from a roll and transferred in the horizontal direction [1) Raw roll unwinding step], the film was stretched in the transfer direction while being immersed in hot water in a water swelling tank and swollen (25 (2) Water swelling step].
The film is pulled up from the water swelling tank, and the two ends of the film are transported in the horizontal direction at a transfer speed of 1 m / min between two horizontally disposed rolls (distance between rolls 1 m, tension between rolls 20 N / m). Then, air (23 ° C.) was blown from the upper side with a nozzle to prevent curling. The air blowing conditions are as follows.
Nozzle: Adjust hose made by MISUMI Nozzle position: 1 m from the outlet of the water swelling tank
Nozzle position (height): 5mm from the top of the film
Spraying flow velocity: 3m / sec Spraying angle θ1: 30 °
Spray angle θ2: 45 °

The obtained film was stretched in the transfer direction while being immersed and dyed in an aqueous solution composed of 0.9 g / L of iodine and 30 g / L of potassium iodide (0.5 minutes at 28 ° C., 1.6 times stretching ratio). ) [3) Dyeing step].
Next, it was immersed in an aqueous solution having a composition of boric acid 25 g / L and potassium iodide 30 g / L, and uniaxially stretched in the transport direction while crosslinking with boric acid (55 ° C. for 1 minute, stretch ratio 2.0 times) [5] Boric acid crosslinking step].
Thereafter, the film was washed with an aqueous potassium iodide solution and dried to obtain a polarizing film having a total draw ratio of 5.4 times (width 1.8 m, thickness 7 μm). The obtained polarizing film was not broken or wrinkled, and no breakage occurred over a length of 12 km. Table 1 shows the polarization characteristics of the obtained polarizing film.

(Manufacture of polarizing plates)
A triacetyl cellulose film (TAC film) with a thickness of 40 μm was bonded to both surfaces of the obtained polarizing film using a polyvinyl alcohol-based aqueous solution as an adhesive, and dried at 50 ° C. to obtain a polarizing plate. Polarization unevenness was not observed in the obtained polarizing plate.

<Example 2>
In Example 1, a polarizing film was obtained in the same manner as in Example 1 except that the air blowing angle θ1 was set to 60 °. About the obtained polarizing film, evaluation similar to Example 1 was performed. The evaluation results are shown in Table 1. Further, a polarizing plate was obtained in the same manner as in Example 1. Polarization unevenness was not observed in the obtained polarizing plate.

<Example 3>
In Example 1, a polarizing film was obtained in the same manner as in Example 1 except that the air blowing angle θ2 was set to 135 °. About the obtained polarizing film, evaluation similar to Example 1 was performed. The evaluation results are shown in Table 1. Further, a polarizing plate was obtained in the same manner as in Example 1. Polarization unevenness was not observed in the obtained polarizing plate.

<Example 4>
In Example 1, a polarizing film was obtained in the same manner as in Example 1 except that water vapor was blown instead of air.
About the obtained polarizing film, evaluation similar to Example 1 was performed. The evaluation results are shown in Table 1. Further, a polarizing plate was obtained in the same manner as in Example 1. Polarization unevenness was not observed in the obtained polarizing plate.

<Comparative Example 1>
In Example 1, the production of the polarizing film was started in the same manner as in Example 1 except that the spraying was not performed. However, 2) After the water swelling step, folds and wrinkles were observed at both ends of the film, and when a polarizing film having a length of 1 km was produced, breakage occurred in the dyeing tank. Table 1 shows the polarization characteristics of the obtained part. In addition, since the fracture occurred, the polarizing plate could not be manufactured.

As shown in Table 1, according to the method for producing a polarizing film of the present invention, a long polarizing film can be obtained without folds or wrinkles. In addition, since the degree of polarization is high not only in the central part of the polarizing film but also at both ends in the width direction, a polarizing film having a uniform degree of polarization from the central part to the end part of the polarizing film can be obtained. Furthermore, it is possible to easily produce a wide, long and thin polarizing plate, and to reduce color unevenness and white spots in a liquid crystal display image.

The polarizing film of the present invention is a portable information terminal, personal computer, TV, projector, signage, electronic desk calculator, electronic clock, word processor, electronic paper, game machine, video, camera, photo album, thermometer, audio, automobile and machine. Liquid crystal display devices such as various instruments, sunglasses, anti-glare glasses, stereoscopic glasses, wearable displays, antireflection layers for display elements (CRT, LCD, organic EL, electronic paper, etc.), optical communication equipment, medical equipment, building materials Used for toys.

PVA film: polyvinyl alcohol-based film θ1 (°): angle formed by spraying direction and film surface θ2 (°): direction when the spraying direction is perpendicularly projected onto the surface of the polyvinyl alcohol-based film and transfer of the polyvinyl alcohol-based film Angle formed by direction Distance A: Distance between the liquid level of the water swelling tank and roll a Distance B: Distance between roll a and roll b

Claims (10)

1. 1) A method for producing a polarizing film comprising a step of unwinding a polyvinyl alcohol film from a roll and transferring it horizontally, 2) a water swelling step, 3) a dyeing step, 4) a stretching step, and 5) a boric acid crosslinking step. There,
   Before and / or after any of the steps 2) to 4), a polarizing film is characterized in that gas is blown to both end portions in the width direction of the film under the following condition a) to prevent the film from curling. Manufacturing method.
   Condition a) The angle θ1 formed between the gas blowing direction and the film surface is 5 to 80 °.
2. 2. The method for producing a polarizing film according to claim 1, wherein the gas is sprayed under the following condition b).
   Condition b) The angle θ2 formed by the direction in which the gas blowing direction is perpendicularly projected onto the surface of the film and the film transfer direction is 5 to 175 °.
3. 3. The method for producing a polarizing film according to claim 1, wherein the gas is sprayed after 2) the water swelling step.
4. The method for producing a polarizing film according to any one of claims 1 to 3, wherein the gas is air or water vapor.
5. 5. The method for producing a polarizing film according to claim 1, wherein the gas is sprayed at a flow rate of 0.1 to 10 m / sec.
6. 6. The method for producing a polarizing film according to claim 1, wherein the transfer speed of the film from the 2) water swelling step to the 3) dyeing step is 1 m / min or more.
7. 7. The method for producing a polarizing film according to claim 1, wherein the polarizing film has a thickness of 15 μm or less.
8. 8. The method for producing a polarizing film according to claim 1, wherein the width of the polarizing film is 1 m or more.
9. A polarizing film produced by the method for producing a polarizing film according to any one of claims 1 to 8.
10. A polarizing plate comprising a protective film provided on at least one side of the polarizing film according to claim 9.

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