TWI693248B - Method for manufacturing polarizing film, polarizing film and polarizing plate - Google Patents

Abstract

The purpose of the present invention is to solve the problem of bending or wrinkling in all the manufacturing steps of the polarizing film, so as to manufacture a polarizing film with good productivity and less polarization unevenness. A method for manufacturing a polarizing film, comprising: 1) a step of rolling out a polyvinyl alcohol-based film from a roller and transporting it in a horizontal direction, 2) a water swelling step, 3) a dyeing step, 4) an extension step, and 5) boric acid cross It is characterized by: before and/or after any of the steps 2) to 4), the liquid is sprayed on both ends in the width direction of the film to prevent the film from curling.

Description

Method for manufacturing polarizing film, polarizing film and polarizing plate

The present invention relates to a method of manufacturing a polarizing film used in a liquid crystal display device (hereinafter sometimes referred to as LCD.), a polarizing film, and a polarizing plate. A method for manufacturing the obtained polarizing film, a polarizing film manufactured by the manufacturing method, and a polarizing plate using the polarizing film.

The LCD is used in mobile information terminals, LCD TVs, desktop electronic computers, electronic clocks, personal computers, word processors, automobile or mechanical instruments, etc., and a polarizing plate is used for the LCD. As for the polarizing plate, it is generally used by laminating a protective film such as cellulose triacetate on one or both sides of a polarizing film composed of a polyvinyl alcohol film obtained by aligning iodine or a dichroic dye. In addition, in order to provide a bright, high-contrast LCD, a polarizing plate having both high transmittance and high polarization is required.

The above polarizing film is, for example, a polyvinyl alcohol-based film swelled with water (including warm water), dyed with iodine, and stretched to arrange iodine molecules, and cross-linked by boric acid or the like to maintain the stretched state. The agent is made by crosslinking and drying. This manufacturing step involves unwinding the polyvinyl alcohol-based film from a roll and using a winder or a roll to carry it continuously in a horizontal direction.

However, in the manufacturing steps of water swelling, dyeing, elongation, boric acid crosslinking, and drying, the film curls due to water absorption or dehydration, resulting in folds or wrinkles at the ends in the width direction of the film, so there is no good productivity The problem of manufacturing polarizing film. Especially when the film is thin, there is also a problem that the film is broken due to the bending or wrinkling, and the production is interrupted. Furthermore, the problem of the end part also has an influence on the inside of the polarizing film, so that the polarizing performance of the entire polarizing film is degraded, or the polarizing plate is difficult to be uniformly mounted on the liquid crystal cell, resulting in uneven color of the liquid crystal display image or White dots and other reasons.

In recent years, with the enlargement of screens such as LCD TVs, there has been a demand to further widen thin polarizing films compared to conventional products. Among them, it is necessary to eliminate the problem of bending or wrinkling at the ends.

In order to reduce this bending or wrinkling, a method of applying a certain tension in the width direction of the film by drying treatment has been proposed (for example, refer to Patent Document 1.). In addition, a method of spraying water from a shower head to both ends in the width direction of a film in water transportation is proposed (for example, refer to Patent Document 2.).

[Prior Technical Literature]

[Patent Literature]

[Patent Document 1] Japanese Unexamined Patent Publication No. 2006-189560

[Patent Document 2] Japanese Patent Laid-Open No. 7-247378

However, in the technique disclosed in the above Patent Document 1, although bending or wrinkling in the drying process step can be avoided, there are still any steps such as water swelling, dyeing, elongation, and boric acid crosslinking before the drying step If the film is bent or wrinkled, it cannot be transported to the drying step first.

In addition, in the technique disclosed in Patent Document 2 above, although bending or wrinkling in water can be avoided, bending or wrinkling in air cannot be prevented.

Therefore, the object of the present invention is to solve the problem of bending or wrinkling in all the manufacturing steps of the polarizing film, so as to manufacture a polarizing film with good productivity and less polarization unevenness.

Therefore, the present invention provides the following aspects of the invention.

[Manufacturing method of polarizing film]

A method for manufacturing a polarizing film, comprising: 1) a step of rolling out a polyvinyl alcohol-based film from a roller and transporting it in a horizontal direction, 2) a water swelling step, 3) a dyeing step, 4) an extension step, and 5) boric acid cross It is characterized by: before and/or after any one of the steps 2) to 4), the liquid is sprayed on both ends in the width direction of the film to prevent the film from curling.

[Polarizing film]

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

[Polarizer]

A polarizing plate is characterized by being provided with a protective film on at least one side of the polarizing film of the present invention.

In the present invention, the "width direction of the film" is generally a direction approximately perpendicular to the longitudinal direction of the strip-shaped film. Especially in the polyvinyl alcohol-based film rolled out from the roll and transported in the horizontal direction, it is about The direction perpendicular to the transport direction of the film usually refers to the direction when the distance between the two edges of the film is the shortest.

In the present invention, the width direction of the film is called "TD direction", and the transport direction of the film is called "MD direction".

In the following, the polyvinyl alcohol-based film is also simply referred to as "film".

According to the manufacturing method of the polarizing film of the present invention, the liquid is sprayed on the width direction of the polyvinyl alcohol-based film before and/or after any of 2) water swelling step, 3) dyeing step and 4) stretching step The two ends of the film prevent the film from curling, so the entire surface of the film can be kept flat and can avoid bending or wrinkling.

With the manufacturing method of the present invention, a widened and thin polarizing film can be manufactured with good productivity, and a polarizing film having uniform polarization degree from the center to the end of the polarizing film can be obtained. Furthermore, the widening and thinning polarizing plate can be easily manufactured, and the color unevenness or white point of the liquid crystal display image can be reduced.

PVA film: polyvinyl alcohol film

θ1(°): the angle formed between the spraying direction and the surface of the film

θ2(°): the angle between the direction when the spraying direction is projected perpendicularly on the surface of the polyvinyl alcohol-based film and the transport direction of the polyvinyl alcohol-based film

Distance A: The distance between the liquid surface of the water swelling tank and the roller a

Distance B: distance between roller a and roller b

[FIG. 1] FIG. 1 is a diagram schematically showing the liquid spraying position in the 1) raw material roll unwinding step, 2) water swelling step, and 3) dyeing step.

[FIG. 2] FIG. 2 is a diagram schematically showing the distance A between the liquid surface of the water swelling tank and the roller a between the water swelling step and 3) the dyeing step, and the distance B between the roller a and the roller b.

[FIG. 3A] FIG. 3A is a diagram showing a spray pattern when a liquid is sprayed on the surface of a polyvinyl alcohol-based film (PVA film).

[FIG. 3B] FIG. 3B is a diagram showing a spraying state when a liquid is sprayed on the back surface of a polyvinyl alcohol-based film (PVA film).

[FIG. 4] FIG. 4 is a diagram showing the angle θ1 between the spray direction and the surface of the film when the liquid is sprayed on the surface or the back of the polyvinyl alcohol-based film.

[Figure 5] Figure 5 shows the direction when the liquid is sprayed on the surface or back of the polyvinyl alcohol-based film, and the spraying direction is perpendicularly projected on the surface of the polyvinyl alcohol-based film and the transport direction of the polyvinyl alcohol-based film. Figure of the angle θ2.

[Figure 6] Figure 6 shows the angle θ1 between the spray direction and the film surface when spraying liquid on the surface or back of the PVA film, and when the spray direction is projected perpendicularly on the surface of the PVA film The angle θ2 formed by the direction of the direction and the transport direction of the polyvinyl alcohol-based film.

[FIG. 7] FIG. 7 is a diagram showing an example of a spray pattern when a liquid is sprayed on a polyvinyl alcohol-based film.

Hereinafter, the composition of the present invention will be described in detail, but these are examples of desired implementations, and the present invention is not limited to these contents.

The manufacturing method of the polarizing film of the present invention is through 1) the step of winding out the polyvinyl alcohol-based film from the roll and transporting it in the horizontal direction, 2) the water swelling step, 3) the dyeing step, 4) the stretching step, and 5) boric acid Crosslinking step to produce polarizing film. Among them, 1) the step of winding the polyvinyl alcohol-based film out of the roll and transporting it in the horizontal direction is also referred to as 1) the step of rolling out the raw material roll.

The polyvinyl alcohol-based film used in the above-mentioned 1) raw material roll-out step is obtained by forming the polyvinyl alcohol-based resin into a film and winding it on a roll.

The polyvinyl alcohol-based resin used in the polyvinyl alcohol-based film is usually an unmodified polyvinyl alcohol-based resin, that is to say, the polyvinyl acetate obtained by polymerizing vinyl acetate is used for saponification. A resin produced. The polyvinyl alcohol-based film used in the present invention is not necessarily limited to this, and vinyl acetate and a small amount (for example, 10 mol% or less, preferably 5 mol% or less) of vinyl acetate can be used. A polyvinyl alcohol resin obtained by saponification of a copolymer of components of ester copolymerization. The components that can be copolymerized with vinyl acetate include, for example, unsaturated carboxylic acids (for example, including salts, esters, amides, and nitriles), and olefins having 2 to 30 carbon atoms (for example, ethylene, propylene, and n-butyl) Ene, isobutylene, etc.), vinyl ethers, unsaturated sulfonates, etc. In addition, a modified polyvinyl alcohol-based resin obtained by chemically modifying the saponified hydroxyl group can also be used.

In addition, the polyvinyl alcohol-based resin 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 can be saponified by, for example, (i) copolymerization of vinyl acetate and 3,4-diethyloxy-1-butene Method, (ii) Method of saponification and decarbonation of copolymer of vinyl acetate and vinyl ethylene carbonate, (iii) Method of vinyl acetate and 2,2-dialkyl-4-vinyl-1, The method of saponification and deketalization of the copolymer of 3-dioxolane, (iv) The method of saponification of the copolymer of vinyl acetate and glycerol monoallyl ether, etc. are obtained.

From the viewpoint of optical performance or extensibility, the weight average molecular weight of the polyvinyl alcohol-based resin is preferably 100,000 to 300,000, especially 110,000 to 280,000, and further preferably 120,000 to 260,000.

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

For the polyvinyl alcohol resin used in the present invention, two or more different modifiers, modifiers, weight average molecular weight, and average saponification degree may be used in combination.

The polyvinyl alcohol-based film used in the present invention is a polyvinyl alcohol-based resin aqueous solution prepared by using the polyvinyl alcohol-based resin, and the aqueous solution is discharged and cast in a casting mold such as a casting drum, casting belt, casting resin film, etc. The film is formed, dried, and wound around a roll for manufacturing.

In the aqueous solution of polyvinyl alcohol-based resin, in view of film-forming properties, in addition to the polyvinyl alcohol-based resin, it contains glycerin, diglycerin, triglycerin, ethylene glycol, triethylene glycol, polyethylene glycol, Plasticizers generally used such as trimethylolpropane, or nonionic, anionic, and/or cationic surfactants are preferred.

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

The temperature of the polyvinyl alcohol-based resin aqueous solution discharged from the casting mold is preferably 80 to 100°C, and particularly preferably 85 to 98°C. In addition, the discharge speed of the polyvinyl alcohol-based resin aqueous solution discharged into the casting 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 casting molds such as casting drums should be 40~99℃, especially 60~95℃.

The film obtained by casting and molding the film is dried by bringing the front and back surfaces of the film and the peripheral portions of the multiple heat rollers into contact with each other while contacting each other. After drying by hot roller, the film can also be heat treated. For heat treatment, it is suitable for 60 ~ 150 ℃, especially suitable for 80 ~ 130 ℃.

Before winding the film around the roll, the two ends of the film can be cut by slitting.

The thickness of the polyvinyl alcohol-based film is preferably 5 to 60 μm in view of thinning of the polarizing film, especially 5 to 30 μm in view of thinning, and 10 to 30 μm in view of avoiding breakage.

In addition, the width of the polyvinyl alcohol-based film is preferably 3 m or more, and the viewpoint of larger area is particularly preferably 4 m or more, and the viewpoint of avoiding breakage is more preferably 4-6 m.

In addition, the length of the polyvinyl alcohol-based film is preferably 4 km or more, and in view of large area, it is particularly preferably 4.5 km or more, and more preferably 5 km or more.

Among them, the upper limit of the length of the film is considered to be less than 50km, especially 40km or less, and more preferably 30km or less.

The manufacturing method of the present invention prevents spraying of liquid on both ends in the width direction of the transported film before and/or after any of the above 2) water swelling step, 3) dyeing step, and 4) extension step The film is curled.

Although after 4) the extension step 5) after the boric acid cross-linking step or after the 6) drying step, liquid spraying can also be carried out, but in these steps, the film becomes difficult to produce because of the high hardness of the cross-linking or drying Bending or wrinkling, the effect of spraying is not significant.

For the time point of liquid spraying, in the above 2) water swelling step, 3) dyeing step, and 4) extension step, considering the viewpoint of avoiding bending, it is preferable to 2) after the water swelling step, and/or 3) After the dyeing step, from the viewpoint of avoiding wrinkles, it is particularly preferable to 2) after the water swelling step, and from the viewpoint of the flattening of the polarizing film, more preferably 2) after the water swelling step and within 10 seconds.

The surface of the film to be sprayed is not particularly limited, and the surface, the back surface, and both surfaces can be sprayed. Generally, the polyvinyl alcohol-based resin aqueous solution is discharged and cast in a casting mold such as a casting belt to form a film, and is continuously dried to obtain a polyvinyl alcohol-based film as a raw material roll. In this drying, many times The condition of the two sides cannot be completely the same, and there is often a case where the moisture on one side is low or the degree of crystallization is high. As a matter of course, since the surface with less moisture is easy to absorb water and extend, in the 2) water swelling step or 3) dyeing step of polarizing film manufacturing, the film tends to curl toward the other side. This situation is effective in the present invention for spraying liquid at both ends of the other side in the curling direction.

Examples of the liquid to be sprayed include liquids such as water (including warm water), methanol, ethanol, isopropanol, acid/alkaline water, dyeing liquid, glycerin aqueous solution, and various chemical aqueous solutions. Among these, in view of not having a bad influence on the performance of the polarizing film, liquids such as water and dyeing liquid are preferred, and in view of the simplicity of the device, water is particularly preferred. When using water, the water temperature should preferably be 10-50°C, especially 20-40°C.

In addition, as for the sprayed liquid, a liquid in a water vapor state may also be used. In view of not adversely affecting the performance of the polarizing film or the simplicity of the device, it is preferably water in a water vapor state. The liquid in the water vapor state is also referred to as "water vapor" for short.

Here, the meaning of water vapor generally means that the liquid is artificially turned into a mist, which is a tiny droplet. The particle size of water vapor is usually from submicron to hundreds of microns. The particle size of the water vapor used in the present invention is preferably 1 to 500 μm, particularly preferably 2 to 100 μm, and further preferably 3 to 50 μm. If the particle size of the water vapor is too large, there is a tendency to produce uneven spraying. If it is too small, it is difficult to control the spraying pressure, or it may be scattered and have a tendency to adversely affect the environment.

The spraying of water vapor can be carried out using a water vapor distribution device which is commercially available. As for the water vapor distributing device, a fluid method in which a compressed liquid is sprayed from a spray head by a pump may be cited, or a water vapor formed by conflicting the compressed liquid and compressed air may be sprayed. For the two-fluid system, in the present invention, considering the simplicity of the equipment, the one-fluid system is preferred. From the viewpoint of spraying effect, the flow rate of water vapor during spraying should be 0.01~1L/min, especially 0.1~0.5L/min.

In addition, the shape of the water vapor ejected from the shower head may be dot-shaped, linear, circular, elliptical, etc. In the present invention, the spray effect is preferably circular. Although the spray angle is not particularly limited, the spray effect is preferably 1 to 90°. Among them, when using liquids other than water, plastic nozzles with excellent corrosion resistance should be used.

Hereinafter, the present invention will be described by taking an example of one of the ideal embodiments of the present invention in the case where liquid spray is performed after the 2) water swelling step.

In general, from the viewpoint of controlling the swelling degree of the polyvinyl alcohol-based film, 2) the water swelling step is preferably 10 to 45°C, especially 20 to 35°C, and immersed in water for 0.1 to 10 minutes, especially 0.5 ~5 points. Among them, the water may contain a small amount of additives such as iodinated compounds, surfactants, alcohol, and the like.

For example, as shown in FIG. 1, the polyvinyl alcohol-based film that has been wound into the roll is rolled out from the roller and transported in the horizontal direction. The water swelling of the polyvinyl alcohol-based film is performed by the 2) water swelling step. After that, the polyvinyl alcohol-based film taken out of the water-swelling tank is transported to the dyeing tank via a roller, and the polyvinyl alcohol-based film is dyed by the 3) dyeing step.

In the present invention, the liquid spraying at both ends of the film is as described above, and the liquid spraying is ideal for the film between the steps of 2) the water swelling step and 3) the dyeing step. Bends or wrinkles are most likely to occur between the steps. Once the films are attached to each other by bending or wrinkles, they cannot be easily peeled off. In addition, when bending or wrinkling occurs in this step, because the steps 2) and 3) are the initial steps of polarizing film manufacturing, it will have a significant impact on the subsequent steps. The specific position of spraying is ideal, for example, just after taking out from the water swelling tank in the step 2) water swelling step, and immediately after the frontmost roller a. Among them, the position and direction of spraying are schematically indicated by arrows in FIG. 1.

In the present invention, as shown in FIG. 2, the distance A from the water swelling tank of the step 2) water swelling step to the contact with the foremost roller a is preferably 1 m or less, particularly preferably from the foremost roller a to The distance B to the roller b before the dyeing tank is also 1 m or less. If the distance A is too long, there is a tendency for bending or wrinkling to increase. Among them, the distance A from the water swelling tank to the roller a represents the shortest distance from the liquid surface of the water swelling tank to the roller a, and the distance B from the front roller a to the roller b before the dyeing tank represents the roller The shortest distance between a and roller b.

In addition, in a series of steps, the tension between the rollers should be 1-100N/m. If the tension between the rollers is too large, there is a tendency to break easily; on the contrary, if the tension is too small, there is a tendency to increase bending or wrinkling.

In addition, from the viewpoint of productivity, the transport speed of the film from the 2) water swelling step to the 3) dyeing step is preferably 1 m/min or more, particularly preferably 1.5 m/min or more, and further preferably 2 m/min or more.

When spraying liquid, it is ideal to use a spray head to spray liquid on one or both sides of both ends of the film in the width direction. At this time, as shown in FIG. 3A, liquid may be ejected on the surface of the film, or as shown in FIG. 3B, liquid may be ejected on the back of the film, or liquid may be ejected on both sides of the film. The spray head is not particularly limited, and a well-known spray head such as a dot spray head, a linear spray head, and a surface spray head can be used. In view of controlling the spray position, it is preferably a dot spray. The spray head system can be provided with multiple spray heads of the same type, and multiple types of spray heads can also be combined.

The position of the nozzle is shown in Figure 2. From the viewpoint of avoiding the bending of the film, the film should be from the water swelling groove in the 2) water swelling step to the contact with the roller a for transportation to avoid wrinkling of the film From the viewpoint of pleats, the distance from the outlet of the water swelling tank to the shower head is preferably within 1 m, and from the viewpoint of the flatness of the film, the distance from the transport roller a to the shower head is preferably within 0.5 m. Among them, the distance from the outlet of the water swelling tank to the spray head, and the distance from the transport roller a to the spray head are the shortest distances.

In addition, the distance between the nozzle and the film surface is preferably 1-100 mm in view of avoiding the bending of the film, and 2-50 mm in view of avoiding the wrinkle of the film. The distance between the nozzle and the film surface represents the shortest distance, specifically, the distance between the nozzle and the film surface in a direction perpendicular to the film surface.

In the present invention, from the viewpoint of the effect of preventing curling, what is important is the spray flow rate and spray angle.

The flow velocity of spraying should be 0.01~5m/sec, especially 0.02~3m/sec, further preferably 0.03~2m/sec. If the flow rate is too slow, there is a tendency for the effect of preventing curling to decrease, and if the flow rate is too fast, there is a tendency for the film to be undulated easily.

When projecting the liquid spray direction perpendicular to the film surface, in other words when looking at the film surface in a direction perpendicular to the film surface, the liquid spray direction is not parallel to the film width direction (TD direction) or film transport direction (MD Direction) is ideal. Therefore, the spray angle of the liquid should not only include the angle θ1 between the spray direction of the liquid and the surface of the film, but also include the direction when the spray direction of the liquid is projected perpendicularly on the surface of the film and the transport direction (MD direction) of the film The angle θ2 (refer to Figures 4 to 6).

Among them, in FIG. 6, the transport direction of the film is defined as the x-axis, the width direction of the film is defined as the y-axis, the direction perpendicular to the film surface is defined as the z-axis, and the film surface is defined as the xy surface, which is perpendicular to the film surface And the plane parallel to the width direction of the film is defined as the yz plane, and the plane perpendicular to the film plane and parallel to the transport direction of the film is defined as the xz plane.

The angle θ1 between the spraying direction of the liquid and the surface of the film is preferably 5 to 80°, particularly preferably 10 to 70°, and further preferably 20 to 60°. If the spray angle θ1 is too low, there is a tendency for the effect of preventing curling to fall, and if it is too high, there is a tendency for the film to easily rise and fall.

In addition, the angle θ2 formed by the direction when the spray direction of the liquid is projected perpendicularly on the surface of the film and the transport direction (MD direction) of the film is preferably 5 to 175°, particularly preferably 20 to 90°, and further preferably 30 ~60°. If the spray angle θ2 is too low, there is a tendency for the effect of preventing curling to fall, and if it is too high, there is a tendency for the film to wrinkle.

As shown in FIG. 7, when multiple spray heads are used, even if all of them are the same, the spray flow rate and spray angle may be different for each spray head. As for the method in which the spray flow rate and spray angle of each spray head are different, for example, from the upstream to the downstream of the film transport direction (MD direction), the spray flow rate is gradually reduced, or the spray angle θ1 is gradually lowered Angle and other methods.

By this method, the polyvinyl alcohol-based film is transported to the subsequent 3) dyeing step or 4) stretching step without bending or wrinkling.

The polarizing film of the present invention is subjected to the steps of 1) rolling out the raw material, followed by 2) water swelling step, 3) dyeing step, 4) extension step, 5) boric acid cross-linking step, cleaning step or drying step as required And manufacture. The 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) water swelling step and 4) elongation step, 2) water swelling step can also be performed at the same time, 3) dyeing step and 4) extension step, 2) water swelling step and 3) dyeing step can also be performed At the same time, 5) boric acid cross-linking step and 4) extension step can also be performed in 2) water swelling step, 3) dyeing step, 5) boric acid cross-linking step, and 4) extension step.

The following describes the steps after 2) water swelling.

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

4) The extension step is a step that preferably extends 3 to 10 times along one axis, and particularly preferably 3.5 to 6 times. At this time, a slight extension may also be performed along the direction formed at a right angle to the extension direction (the degree of shrinkage in the width direction is prevented or extended). The temperature during extension is desirably selected from the temperature range of 30 to 170°C. In addition, the stretching magnification may be set to the above-mentioned range at the end, and the stretching operation is not limited to one stage, and may be performed at a stage of any range of the manufacturing steps.

5) The boric acid cross-linking step is performed using boron compounds such as boric acid and borax. The boron compound is used in the form of an aqueous solution or a water-organic solvent mixed solution with a concentration of about 10 to 100 g/L. When a small amount of potassium iodide coexists in the liquid, it is ideal from the viewpoint of stabilizing the polarization performance. The temperature during treatment should be about 30~70℃, and the treatment time should be about 0.1~20 minutes.

After that, the above-mentioned film can be subjected to a cleaning process. By the cleaning process, the precipitates generated on the surface of the film can be removed. The cleaning treatment is performed, for example, by immersing the polyvinyl alcohol-based film in an aqueous iodide solution such as water or potassium iodide. When using an aqueous solution of potassium iodide, the concentration of potassium iodide may be about 1 to 80 g/L. The temperature during the cleaning process is usually 5 to 50°C, preferably 10 to 45°C. The processing time is usually 1 to 300 seconds, preferably 10 to 240 seconds. Among them, water washing and washing with an aqueous potassium iodide solution can be appropriately combined. In addition, the above-mentioned film may be subjected to a drying step thereafter.

The drying step can be carried out in the air at 40~80℃ for 1~10 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 with the LCD cannot be ensured.

Among them, generally speaking, the light transmittance (H ₁₁ ) is measured at a wavelength λ when two polarizing films are stacked so that their alignment directions are in the same direction, and when two polarizing films are stacked The light transmittance (H ₁ ) measured at the wavelength λ in a 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

In addition, 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 the brightness of the liquid crystal display cannot be increased.

The monomer transmittance is a value obtained by measuring the light transmittance of the polarizing film monomer using a spectrophotometer.

The width of the polarizing film of the present invention is preferably 1 m or more, the viewpoint of larger area is preferably 1.3 m or more, the viewpoint of larger area is particularly preferable to be 1.5 m or more, and the viewpoint of avoiding breakage is considered, further preferably 1.5 to 2.5 m.

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

The polarizing film of the present invention thus obtained is suitable for manufacturing a high-performance polarizing plate because of less uneven polarization.

Hereinafter, a method for manufacturing a polarizing plate from the polarizing film of the present invention will be described.

The polarizing film of the present invention is a polarizing plate formed by bonding an optically isotropic resin film as a protective film to an adhesive on one or both sides thereof. As for the protective film, for example, cellulose triacetate, cellulose diacetate, polycarbonate, polymethyl methacrylate, cycloolefin polymer, cycloolefin copolymer, polystyrene, polyether sulfone, polyimide Films or sheets of aryl esters, poly-4-methylpentene, polyphenylene ether, etc.

The bonding method is carried out by a known method, for example, after uniformly coating the liquid adhesive composition on the polarizing film, the protective film, or both, the two are bonded together and pressed together, by heating or It is performed by irradiating active energy rays.

In addition, for the purpose of thinning the polarizing film, instead of the above protective film, a hardening resin such as urethane-based resin, acrylic resin, urea resin, etc. may be coated on one or both sides of the protective film and cured to become a polarizing plate. .

The polarizing film or polarizing plate obtained by the present invention has excellent polarizing performance and can be ideally used in mobile information terminal equipment, computers, televisions, projectors, billboards, desktop electronic computers, electronic clocks, word processors, electronic paper, Liquid crystal display devices such as game consoles, video recorders, cameras, photo frames, thermometers, stereos, automobile or mechanical instruments, sunglasses, anti-glare glasses, stereo glasses, wearable displays, display elements (CRT, LCD, organic EL, Electronic paper, etc.) anti-reflection layer, optical fiber communication equipment, medical equipment, building materials, toys, etc.

[Example]

The following examples are given to explain the present invention more specifically. The present invention is not limited to the following examples within the scope not exceeding the gist thereof.

<Measurement conditions>

For the polarizing films obtained in Examples and Comparative Examples, the degree of polarization (%) was measured in the following manner.

Using Otsuka Electronics Co., Ltd. product: RETS-1100A, the polarization degree of the obtained central portion of the polarizing film in the width direction and both ends (a position of 10 cm from each end) was measured.

<Example 1>

(Manufacture of polyvinyl alcohol film)

1000kg of polyvinyl alcohol resin with a weight average molecular weight of 142000, a saponification degree of 99.8 mol%, 1000kg of water, 2500kg of water, and 100kg of glycerin as a plasticizer were added, and the temperature was raised to 140°C while stirring, and the concentration was adjusted to adjust the resin concentration to 25% by weight To obtain a uniformly dissolved aqueous solution of polyvinyl alcohol resin.

Next, after the polyvinyl alcohol-based resin aqueous solution was supplied to a biaxial extruder having a vent hole and defoamed, the temperature of the aqueous solution was 95°C, and it was cast from the T-slot die discharge hole at a discharge speed of 0.6 m/min. The film was formed on a casting drum with a surface temperature of 90°C.

Next, the obtained film was dried with a plurality of hot rollers, heat-treated at 120° C. for 3 minutes using a floating dryer, and slit to a width of 4 m by slitting. Finally, by winding an aluminum core tube with an outer diameter of 17 cm, an inner diameter of 16 cm, and a length of 4.4 m, a band-shaped polyvinyl alcohol-based film with a moisture content of 2% by weight (width 4 m, length 5 km, and thickness 15 μm) was obtained ) Film roll wound around the core tube.

(Manufacture of polarizing film)

The obtained polyvinyl alcohol-based film is rolled out from the roll and transported in the horizontal direction [1) Raw material roll-out step], and immersed in the warm water of the water swelling tank to swell, extending in the transport direction (at 25 ℃, 1 minute, elongation ratio 1.7 times) [2) Water swelling step].

Take out the film from the water swelling tank, between two horizontally arranged rollers (the distance between the rollers is 1m, the tension between the rollers is 20N/m), and transport it in the horizontal direction at a transport speed of 2m/min. Both ends of the film are sprayed with water (23°C) from above by a spray head to prevent curling. The spraying conditions of this water are as follows.

Nozzle: Adjustable hose made by MISUMI Corporation

Nozzle position: 1m away from the outlet of the water swelling tank

Nozzle position (height): 5mm from the top surface of the film

Spray velocity: 0.1m/s

Spray angle θ1: 30°

Spray angle θ2: 45°

Dip the obtained film in an aqueous solution composed of 0.9 g/L of iodine and 30 g/L of potassium iodide and dye it, and then extend it in the direction of transport (at 28° C., 0.5 minutes, extension ratio of 1.6 times) [3) Dyeing step] .

Next, while being immersed in an aqueous solution composed of 25 g/L boric acid and 30 g/L potassium iodide to carry out boric acid cross-linking, uniaxial extension was carried out in the direction of transport (55° C., 1 minute, extension ratio 2.0 times) [5) Boric acid cross-linking step] .

After that, by washing with an aqueous potassium iodide solution and drying, a polarizing film (1.8 m in width and 7 μm in thickness) with a total elongation ratio of 5.4 times was obtained. The obtained polarizing film had no bending or wrinkling, and no breakage occurred across the length of 12km. The polarization characteristics of the obtained polarizing film are shown in Table 1.

(Manufacture of polarizing plates)

On both surfaces of the obtained polarizing film, a polyvinyl alcohol-based aqueous solution was used as an adhesive, and a triacetyl cellulose film (TAC film) with a thickness of 40 μm was bonded, and dried at 50° C. to become a polarizing plate. No polarization unevenness was observed in the obtained polarizing plate.

<Example 2~4>

A polarizing film was obtained in the same manner as in Example 1 except that the spraying conditions of Example 1 were set to the conditions shown in Table 1. The obtained polarizing film had no folds or wrinkles, and there was no breakage across the length of 12km. The obtained polarizing film was evaluated in the same manner as in Example 1. The evaluation results are shown in Table 1. Further, a polarizing plate was obtained in the same manner as in Example 1. No polarization unevenness was observed in the obtained polarizing plate.

<Example 5>

A polarizing film was obtained in the same manner as in Example 1 except that the water in Example 1 was changed to a water vapor state. The spraying conditions of the water vapor are as follows.

Print head: HITJET print head made by Spraying Systems Co.

Nozzle position: 1m away from the outlet of the water swelling tank

Nozzle position (height): 5mm from the top surface of the film

Spray velocity: 0.1m/s

Spray angle θ1: 30°

Spray angle θ2: 45°

Water vapor particle size: 20μm

Water and gas flow: 0.2L/min

The obtained polarizing film was evaluated in the same manner as in Example 1. The evaluation results are shown in Table 1. Further, a polarizing plate was obtained in the same manner as in Example 1. No polarization unevenness was observed in the obtained polarizing plate.

<Examples 6 to 8>

A polarizing film was obtained in the same manner as in Example 5 except that the spraying conditions in Example 5 were set to the conditions shown in Table 1. The obtained polarizing film had no folds or wrinkles, and there was no breakage across a length of 12 km. against The obtained polarizing film was evaluated in the same manner as in Example 1. The evaluation results are shown in Table 1. Further, a polarizing plate was obtained in the same manner as in Example 1. No polarization unevenness was observed in the obtained polarizing plate.

<Comparative Example 1>

The polarizing film was started in the same manner as in Example 1 except that Example 1 was not sprayed. However, 2) After the water swelling step, folds or wrinkles were observed at both ends of the film, and when a polarizing film with a length of 1 km was produced, breakage occurred in the dyeing tank. The polarization characteristics of the obtained part are shown in Table 1. Among them, the polarizing plate cannot be manufactured because of fracture.

As shown in Table 1, according to the method of manufacturing a polarizing film of the present invention, a polarizing film that grows without bending or wrinkling can be obtained. In addition, since not only the central portion of the polarizing film, but also the polarization degree at the end in the width direction is high, a polarizing film having uniform polarization degree from the central portion to both ends of the polarizing film can be obtained. Furthermore, the widening and thinning polarizing plate can be easily manufactured, which can reduce the uneven color or white point of the liquid crystal display image.

[Industry availability]

The polarizing film of the present invention can be used in mobile information terminal equipment, computers, televisions, projectors, billboards, desktop computers, electronic clocks, word processors, electronic paper, game consoles, video recorders, cameras, photo frames, thermometers , Anti-reflection layer for optical devices such as audio, automobile, or mechanical instruments, sun glasses, anti-glare glasses, stereo glasses, wearable displays, display elements (CRT, LCD, organic EL, electronic paper, etc.), optical fiber communication equipment , Medical equipment, building materials, toys, etc.

Claims (13)

A method for manufacturing a polarizing film, comprising: 1) a step of rolling out a polyvinyl alcohol-based film from a roller and transporting it in a horizontal direction, 2) a water swelling step, 3) a dyeing step, 4) an extension step, and 5) boric acid cross It is characterized by: before and/or after any one of the steps 2) to 4), the liquid is sprayed on the end in the width direction of the film to prevent the film from curling. For example, the method for manufacturing a polarizing film according to item 1 of the patent application, wherein the spraying of the liquid is performed after the 2) water swelling step. For example, in the method of manufacturing a polarizing film according to item 1 or 2 of the patent application, the angle between the spray direction of the liquid and the surface of the film is 5 to 80°. For example, the method for manufacturing a polarizing film according to item 1 or 2 of the patent application, wherein the angle between the direction when the spraying direction of the liquid is vertically projected on the surface of the film and the transport direction of the film is 5 to 175°. For example, the method for manufacturing a polarizing film according to item 1 or 2 of the patent application, wherein the spraying of the liquid is performed at a flow rate of 0.01 to 5 m/sec. For example, the method of manufacturing a polarizing film according to item 1 or 2 of the patent application, in which the liquid system is water or dyeing liquid. For example, the method for manufacturing a polarizing film according to item 1 or 2 of the patent application, in which the liquid system is a liquid in a water vapor state. For example, the method of manufacturing a polarizing film according to item 7 of the patent application, in which the liquid system in the water vapor state is formed by spraying the compressed liquid by spraying from the nozzle. For example, the method for manufacturing a polarizing film according to item 7 of the patent application, wherein the particle size of the water vapor in the liquid in the water vapor state is 1 to 500 μm. For example, the method for manufacturing a polarizing film according to item 7 of the patent application, wherein the flow rate of the liquid in a water vapor state is 0.01 to 1 L/min. For example, the method for manufacturing a polarizing film according to item 1 or 2 of the patent application, wherein the transport speed of the film from the 2) water swelling step to the 3) dyeing step is 1 m/min or more. For example, the method for manufacturing a polarizing film according to item 1 or 2 of the patent application, wherein the thickness of the polarizing film is 15 μm or less. For example, the method for manufacturing a polarizing film according to item 1 or 2 of the patent application, wherein the width of the polarizing film is 1 m or more.

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