JP5512335B2 - Manufacturing method of polarizing film - Google Patents

Description

  The present invention relates to a method for producing a polarizing film used in an image display device such as a liquid crystal display device, an electroluminescence (EL) display device, a plasma display (PD), and a field emission display (FED).

  Conventionally, a polarizing film in which a dichroic dye is adsorbed and oriented on a polyvinyl alcohol film has been used. That is, an iodine polarizing film using iodine as a dichroic dye, a dye polarizing film using a dichroic dye as a dichroic dye, and the like are known. These polarizing films are usually used as polarizing plates by laminating a protective film such as triacetyl cellulose via an adhesive made of an aqueous solution of a polyvinyl alcohol resin on at least one surface, preferably both surfaces of the polarizing film. (LCD), for example, used for liquid crystal televisions, personal computer monitors, mobile phone display screens, etc.

As a method for producing a polarizing film, a nip roll and a guide roll are used, and after the polyvinyl alcohol film is immersed in water and swollen, it is dyed with the dichroic dye, stretched, and then iodine is formed into the film. In order to fix it, a method is known in which a polyvinyl alcohol film is treated with boric acid (crosslinking treatment), washed with water and then dried. At this time, the film is stretched by giving a peripheral speed difference to the nip rolls before and after the treatment bath, the film transport direction is changed by the guide rolls, and the film is introduced into and taken out of the treatment liquid.
Further, in recent years, along with the increase in size, function and brightness of liquid crystal display devices, the polarizing film used for the liquid crystal display device is also required to increase in optical properties and in-plane uniformity at the same time. However, in order to obtain a large polarizing film, it is necessary to uniaxially stretch a wide original film, but this is actually a very difficult process, and at the same time, in-plane uniformity. Optical characteristics tend to deteriorate. Further, when the in-plane optical characteristics are not uniform, display unevenness occurs when the image display device is formed.

In order to solve the above problems, Patent Document 1 discloses that a polyvinyl alcohol film is dyed with a dyeing solution containing iodine having a dichroic property, crosslinked with a crosslinking agent, and at least in the above step. Production of a polarizing film that is stretched using a pair of rolls and that has two or more baths containing the crosslinking agent and stretches at a stretch ratio higher than the stretch ratio of the first bath. A method has been proposed. However, this method has a problem that the film shrinks after stretching, the film thickness increases, and the film width further decreases.
On the other hand, Patent Document 2 discloses that a wide film can be produced by reducing the distance between the stretches during the stretching process in the wet stretching process of the film. However, the method of Patent Document 2 has a problem that the film is easily broken when stretched, and therefore the processing stability is poor.

JP 2001-290026 A JP 2008-241909 A

  The main problem to be solved by the present invention is to provide a method for producing a more uniform and thin polarizing film having excellent processing stability.

  As a result of intensive studies to solve the above-mentioned problems, the inventors of the present invention before or during the process of treating the polyvinyl alcohol film in the order of swelling treatment, dyeing treatment, boric acid treatment, washing treatment, and drying treatment. In the manufacturing method of the polarizing film which performs axial stretching, it has a boric acid treatment process of three or more steps, and utilizes the difference in peripheral speed between two nip rolls after the third step of the boric acid treatment process, and A high-stretching process step of uniaxial stretching of 1.5 times or more is provided through at least one guide roll, and the residence time of the film from the upstream nip roll to the first guide roll in this step is 4 seconds or less And a slitting process for removing both ends of the film after the cleaning process, wherein the difference between the maximum and minimum film thickness is 5 μm. If the slit is made to be lower, the film thickness of the polarizing film is uniform by reducing the film breakage while widening the polarizing film being stretched and further cutting and removing both ends of the film in the slitting process. The present inventors have found a new fact that it can be realized and have completed the present invention.

That is, the manufacturing method of the polarizing film of this invention has the following structures.
(1) In a manufacturing method of a polarizing film in which uniaxial stretching is performed before or during a process in which a polyvinyl alcohol-based film is processed in the order of swelling treatment, dyeing treatment, boric acid treatment, washing treatment, and drying treatment, three or more steps are continuous. A boric acid treatment process to be performed, and at the third and subsequent stages of the boric acid treatment process, a peripheral speed difference between two nip rolls is used, and at least one uniaxial stretching is performed through at least one guide roll. A slit that removes both ends in the width direction of the film after the cleaning process, with a high-stretching process step in which the residence time of the film from the nip roll on the inlet side to the guide roll is 4 seconds or less. A method for producing a polarizing film, characterized in that a step is provided and slitting is performed so that the difference between the maximum and minimum film thicknesses is 5 μm or less. (1) characterized in that uniaxial stretching is performed using a difference in peripheral speed between the upstream nip roll arranged in the liquid and the downstream nip roll arranged in the air in the film conveying direction. The manufacturing method of the polarizing film of description.
(3) The manufacturing method of the polarizing film as described in (1) or (2) whose guide roll is a sponge rubber roll or a rubber roll in the said high extending | stretching process process.
(4) From (1), the sponge rubber roll has a sponge hardness of 20 to 60 degrees on a JIS Shore C scale, a surface roughness of 10 to 30 S, and a coefficient of dynamic friction in water with the treated film of 0.3 to 0.8. (3) The manufacturing method of the polarizing film in any one of.
(5) The hardness of the rubber roll is 50 to 90 degrees on a JIS Shore A scale, the surface roughness is 0.4 to 2.0 S, and the coefficient of dynamic friction in water with the treated film is 0.3 to 0.8 (1) The manufacturing method of the polarizing film in any one of (3).
(6) The production method according to any one of (1) to (5), wherein a draw ratio in the high draw treatment step is 1.7 times or more and a total draw ratio is 5.5 times or more and 6.5 times or less.
(7) A fourth boric acid treatment step is provided after the high stretching treatment step, and uniaxial stretching is performed at 1.05 times or more in the step, according to any one of (1) to (6) Manufacturing method.
(8) The production according to any one of (1) to (7), wherein the boric acid concentration in the fourth boric acid treatment step is lower than the boric acid concentration in the third boric acid treatment step. Method.

  The method for producing a polarizing film of the present invention can produce a polarizing film with little breakage during stretching, a thin film thickness, and a uniform thickness.

It is the schematic which shows the high extending | stretching process process in this invention. It is a schematic diagram which shows the change of the thickness in the width direction of the polarizing film performed by this invention.

(Production method of polarizing film)
Hereinafter, the present invention will be described in detail.
Examples of the polyvinyl alcohol-based resin that forms the polyvinyl alcohol-based film in the present invention include those obtained by saponifying a polyvinyl acetate-based resin. The degree of saponification is about 85 mol% or more, preferably about 90 mol% or more, more preferably about 99 mol% to 100 mol%. Polyvinyl acetate resins include polyvinyl acetate, which is a homopolymer of vinyl acetate, and copolymers of vinyl acetate and other monomers copolymerizable therewith, such as ethylene-vinyl acetate copolymer. Examples include coalescence. Examples of other copolymerizable monomers include unsaturated carboxylic acids, olefins, vinyl ethers, and unsaturated sulfonic acids. The degree of polymerization of the polyvinyl alcohol resin is about 1000 to 10000, preferably about 1500 to 5000.

These polyvinyl alcohol resins may be modified. For example, polyvinyl formal modified with aldehydes, polyvinyl acetal, polyvinyl butyral, and the like may be used. Usually, an unstretched film of a polyvinyl alcohol-based resin film having a thickness of about 20 μm to 100 μm, preferably about 30 μm to 80 μm is used as a starting material for manufacturing a polarizing film. Industrially, the width of the film is practically about 1500 mm to 6000 mm.
The unstretched film is processed in the order of swelling treatment, dyeing treatment, boric acid treatment (crosslinking treatment), water washing treatment, and finally dried to obtain a polyvinyl alcohol polarizing film having a thickness of, for example, about 5 to 50 μm. is there.

  The polarizing film of the present invention is a polyvinyl alcohol uniaxially stretched film obtained by adsorbing and orienting a dichroic dye, and there are roughly two production methods as the production method. One is a method in which a polyvinyl alcohol film is uniaxially stretched in air or an inert gas, followed by solution treatment in the order of swelling treatment, dyeing treatment, boric acid treatment and water washing treatment, followed by drying. In the second method, an unstretched polyvinyl alcohol film is subjected to a solution treatment in the order of swelling treatment, dyeing treatment, boric acid treatment, and water washing treatment with an aqueous solution. This is a method of performing uniaxial stretching and finally drying.

In the present invention, as a stretching method, a known method can be adopted, and stretching between rolls in which stretching is performed with a peripheral speed difference between two nip rolls that transport a film, as described in Japanese Patent No. 2731813. There are a hot roll stretching method and a tenter stretching method. The order of the steps is basically as described above, but there are no restrictions on the number of treatment baths or treatment conditions.
Needless to say, a process not described in the above process can be freely inserted for another purpose. As an example of this step, after boric acid treatment, immersion treatment with an aqueous iodide solution not containing boric acid (iodide treatment) or immersion treatment with an aqueous solution containing zinc chloride not containing boric acid (zinc treatment), The slit process etc. which cut and remove the both ends of a film after the washing process and make the film thickness more uniform are mentioned.

(Swelling process)
The swelling treatment is performed for the purpose of removing foreign substances on the film surface, removing the plasticizer in the film, imparting easy dyeability in the next step, and plasticizing the film. The treatment conditions are determined within a range in which these objects can be achieved and within a range in which problems such as extreme dissolution and devitrification of the base film do not occur. When the film previously stretched in the gas is swollen, for example, the film is immersed in an aqueous solution of about 20 to 70 ° C., preferably about 30 to 60 ° C. The immersion time of the film is about 30 to 300 seconds, more preferably about 60 to 240 seconds. In order to swell the unstretched raw film from the beginning, the film is immersed in an aqueous solution of about 10 to 50 ° C., preferably about 20 to 40 ° C., for example. The immersion time of the film is about 30 to 300 seconds, more preferably about 60 to 240 seconds.

  In the swelling process, problems such as film swelling in the width direction and wrinkling of the film are likely to occur, so known widening such as widening roll (expander roll), spiral roll, crown roll, cross guider, bend bar, tenter clip It is preferable to transport the film while removing wrinkles of the film with an apparatus. In order to stabilize the film transport in the bath, the water flow in the swelling bath is controlled with an underwater shower, or an EPC device (Edge Position Control device: a device that detects the edge of the film and prevents meandering of the film) It is also useful to use these together. In this step, since the film swells and expands in the running direction of the film, it is preferable to take measures such as controlling the speed of the transport roll before and after the treatment tank in order to eliminate the slack of the film in the transport direction. In addition to pure water, the swelling treatment bath used is boric acid (described in JP-A-10-153709), chloride (described in JP-A-06-281816), inorganic acid, inorganic salt, water-soluble An aqueous solution to which an organic solvent, alcohol or the like is added in an amount of about 0.01 to 10% by weight can also be used.

(Dyeing process)
The dyeing step with the dichroic dye is performed for the purpose of adsorbing and orienting the dichroic dye on the film. The treatment conditions are determined within a range in which these objects can be achieved and within a range in which problems such as extreme dissolution and devitrification of the base film do not occur. When iodine is used as the dichroic dye, for example, at a temperature of about 10 ° C. to 45 ° C., preferably about 20 ° C. to 35 ° C., and in a weight ratio, iodine / KI / water = about 0.003 to 0.2 / The immersion treatment is performed at a concentration of about 0.1 to 10/100 for about 30 seconds to 600 seconds, preferably about 60 seconds to 300 seconds. Instead of potassium iodide, other iodides such as zinc iodide may be used. In addition, the other iodide but it may also be used in combination with potassium iodide. Further, compounds other than iodide, such as boric acid, zinc chloride, cobalt chloride, etc. may coexist. When boric acid is added, it is distinguished from the following boric acid treatment in that it contains iodine. Any dye containing about 0.003 parts by weight or more of iodine with respect to 100 parts by weight of water can be regarded as a dyeing tank.

  When a water-soluble dichroic dye is used as the dichroic dye, for example, at a temperature of about 20 ° C. to 80 ° C., preferably about 30 ° C. to 70 ° C., and a weight ratio of dichroic dye / water = about 0.001. The immersion treatment is performed at a concentration of about 0.1 / 100 for about 30 seconds to 600 seconds, preferably about 60 seconds to 300 seconds. The aqueous solution of the dichroic dye to be used may have a dyeing assistant or the like, and may contain, for example, an inorganic salt such as sodium sulfate, a surfactant or the like. The dichroic dye may be used alone, or two or more dichroic dyes may be used at the same time.

  As described above, the film may be stretched in a dyeing tank. Stretching is performed by a method of giving a peripheral speed difference between the nip rolls before and after the dyeing tank. Similarly to the swelling step, a widening roll (expander roll), a spiral roll, a crown roll, a cross guider, a bend bar, and the like can be installed in the dyeing bath and / or at the bath entrance / exit.

(Boric acid treatment process)
The boric acid treatment is performed by immersing a polyvinyl alcohol film dyed with a dichroic dye in an aqueous solution containing about 1 to 10 parts by weight of boric acid with respect to 100 parts by weight of water. When the dichroic dye is iodine, it is preferable to contain about 1 to 30 parts by weight of iodide.
Examples of iodide include potassium iodide and zinc iodide. Further, compounds other than iodide, for example, zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, but it may also be allowed to coexist, such as sodium sulfate.
This boric acid treatment is carried out for water resistance, hue adjustment (preventing bluishness, etc.) by crosslinking, and the like. In the case of water resistance by cross-linking, a cross-linking agent such as glyoxal or glutaraldehyde can be used in addition to or together with boric acid, if necessary.
In addition, the boric acid treatment for water resistance may be referred to by names such as water resistance treatment, crosslinking treatment, and immobilization treatment. In addition, boric acid treatment for hue adjustment may be referred to by a name such as complementary color treatment or re-dyeing treatment.

This boric acid treatment is performed by appropriately changing the concentrations of boric acid and iodide and the temperature of the treatment bath according to the purpose.
The boric acid treatment for water resistance and the boric acid treatment for hue adjustment are not particularly distinguished, but are carried out under the following conditions.
When the raw film is swollen, dyed or treated with boric acid, and the boric acid treatment is aimed at water resistance by crosslinking, about 3 to 10 parts by weight of boric acid and 100% by weight of iodide, iodide Is carried out at a temperature of about 50 ° C. to 70 ° C., preferably about 53 ° C. to 65 ° C. The immersion time is usually about 10 to 600 seconds, preferably 20 to 300 seconds, more preferably 20 to 200 seconds.
In addition, when dye | staining and boric-acid treatment the film extended | stretched previously, the temperature of a boric-acid treatment bath is about 50 to 85 degreeC normally, Preferably it is about 55 to 80 degreeC.

After the boric acid treatment for water-resistant, but it may also be made of boric acid treatment for the hue adjustment. For example, when the dichroic dye is iodine, a boric acid treatment bath containing about 1 to 5 parts by weight of boric acid and about 3 to 30 parts by weight of iodide for 100 parts by weight of water is used for this purpose. And is usually performed at a temperature of about 10 ° C to 45 ° C. The immersion time is usually about 1 to 300 seconds, preferably 2 to 100 seconds.

These boric acid treatment rather it may also be carried out in multiple steps, the present invention is carried out in three or more steps. In this case, the aqueous solution composition and temperature of each boric acid treatment tank to be used may be the same or different within the above range. Also, boric acid treatment for the water-resistant, but it may also be subjected to boric acid treatment for the hue adjustment plurality of steps.

(Cleaning process)
After the boric acid treatment, washing treatment (water washing treatment) is performed. The washing treatment is performed, for example, by immersing a polyvinyl alcohol film treated with boric acid for water resistance and / or color tone adjustment in water, spraying water as a shower, or combining immersion and spraying. The water temperature in the water washing treatment is usually about 2 to 40 ° C., and the immersion time is preferably about 2 to 120 seconds.
Thereafter, the polyvinyl alcohol film is washed and dried in a drying oven at a temperature of about 40 to 100 ° C. for about 60 to 600 seconds to obtain a polarizing film.
In addition, although this invention mentions later, the slit process which cut | disconnects both ends for making the film thickness of a polarizing film more uniform is provided after a washing | cleaning process process.

(Uniaxial stretching)
The present invention has three or more successive boric acid treatment steps having at least one guide roll, and in the third and subsequent stages of the boric acid treatment step, an upstream nip roll and a downstream side of the film transport direction are provided. Between the nip rolls, uniaxial stretching is performed by a wet stretching method in a boric acid-containing aqueous solution using the difference in peripheral speed between the two nip rolls.

A high stretching treatment step is provided after the third stage of the boric acid treatment step. FIG. 1 shows the high-stretching step. As shown in FIG. 1, a boric acid treatment tank 4 containing a boric acid-containing aqueous solution 11 is a nip roll installed on the upstream side in the conveyance direction of the polyvinyl alcohol film 1. 2, a nip roll 2 ′ installed on the downstream side, and a guide roll 3 installed between them.
The nip rolls 2 and 2 'are used to uniaxially stretch the polyvinyl alcohol film 1 by utilizing the peripheral speed difference between them. At this time, the upstream nip roll 2 sandwiches and stretches the polyvinyl alcohol film 1 in the liquid of the boric acid-containing aqueous solution 11 and the downstream nip roll 2 ′ in the air above the boric acid-containing aqueous solution 11. It is configured as follows. The guide roll 3 is also immersed in the liquid.
In the present invention, the uniaxial stretching between the nip rolls 2 and 2 'is 1.5 times or more, preferably 1.5 to 2.7 times, more preferably 1.7 to 2.5 times.
The residence time of the film from the nip roll 2 on the upstream side in the film conveyance direction to the contact with the guide roll 3 in the high stretching process is 4 seconds or less.

Further, the film residence time T from the upstream nip roll 2 toward the guide roll 3 in the high-stretching process step (precisely from the contact point between the rolls) is 4 seconds or less. Is preferred. This is because when the film residence time is 4 seconds or longer, the film thickness becomes thin and the film may break. The residence distillation time T that is 0.5 to 3 seconds, more preferably. In order to adjust the residence time T to 4 seconds or less, for example, the film conveyance speed may be controlled, or the distance between the nip roll 2 and the guide roll 3 may be adjusted.

In the high stretching treatment step of the present invention, the film is immersed in the boric acid- containing aqueous solution 11 while performing a high stretching treatment, so that the nip roll 2 on the upstream side in the film transport direction is in the boric acid-containing aqueous solution 11 and downstream. The nip rolls 2 'on the side are preferably installed in the air. In addition, although it does not specifically limit, In order to lengthen the immersion time of the film, the guide roll 3 is also preferably in the liquid.

  As the guide roll 3 used in the present invention, a sponge rubber roll or a rubber roll is used.

  As the sponge roll, the hardness of the sponge is 20 to 60 degrees, more preferably 25 to 50 degrees on the JIS Shore C scale measured by the test method of JIS K 6301, and the surface roughness is JIS B 0601 (surface roughness). Expressed by an average interval S between the local peaks of the curve, it is about 10-30S, more preferably about 15-25S, and the coefficient of dynamic friction with the treated film in water is 0.3-0.8, more preferably 0.4- It is preferably 0.8.

  When the guide roll is a rubber roll, the hardness of the rubber roll is 50 to 90 degrees on the JIS Shore A scale, more preferably 70 to 80 degrees, and the surface roughness is a roughness curve of JIS B 0601 (surface roughness). Expressed in terms of an average interval S between the local peaks of 0.1 to 5S, more preferably 0.5 to 1S, and a coefficient of dynamic friction in water with the treated film of 0.3 to 0.8, more preferably 0.4 to It is preferably 0.8.

  For example, when a stainless steel roll is used as the guide roll in the treatment liquid, slipping occurs, the film restraining force is reduced, and the effect of uniaxial stretching is weakened.

Total final extension Shin ratio in the present invention, 5.5 to 6.5 times, preferably in the range of 5.6 to 6.3 times.

  In the present invention, after the high stretching treatment step, a fourth boric acid treatment step is provided in order to further reduce the thickness of the polarizing film and to improve the performance of the polarizing film. It is good to carry out uniaxial stretching more than 0.05 times, more preferably more than 1.07 times. This step is preferably provided before the polarizing film cleaning step.

  The boric acid concentration in the fourth boric acid treatment step after the high stretching treatment step is preferably lower than the concentration in the third boric acid treatment step, and by treatment with a boric acid-containing aqueous solution having a low boric acid concentration. By adjusting the amount of boron in the film, the film thickness and width of the film can be adjusted. When the concentration is high, the boric acid-containing aqueous solution is easily fixed on the film.

In each step after the stretching treatment, tension control may be performed so that the tension of the film becomes substantially constant.
When the above-described iodide treatment or zinc treatment is performed after the boric acid treatment, tension control is also performed for these steps.

Tension in each of the process rather than good may be the same, but it may also be different.
The tension to the film in the tension control is not particularly limited, and is appropriately set within a range of about 150 N / m to 2000 N / m, preferably about 600 N / m to 1500 N / m per unit width. When the tension is less than about 150 N / m, the film is likely to be wrinkled. On the other hand, if the tension exceeds about 2000 N / m, problems such as film breakage and shortened life due to bearing wear occur. The tension per unit width is calculated from the film width near the entrance of the process and the tension value of the tension detector.
In addition, when tension control is performed, there are cases where the film is inevitably slightly stretched or shrunk, but in the present invention, this is not included in the stretching process.

In this invention, the slit process which cuts and removes the both ends of a film is provided after the washing process process of a film. This slit process is a process for making a polarizing film into a more uniform film thickness, and although not particularly limited, it is cut and removed by a method such as an air cutter or spraying high-pressure water.
The slit process can be performed either before or after the cleaning process.

(Film thickness)
FIG. 2 shows a polarizing film manufactured using a conventional technique that does not have a high-stretching process in the present invention, with the polarizing film thickness being the vertical axis and the width direction of the film being the horizontal axis. When B is represented by B, their thickness distribution is schematically shown. Moreover, L has shown the width | variety of the film after cut | disconnecting at the slit process.
As is clear from FIG. 2, the film A obtained by the production method of the present invention is thinner than the film B and has a substantially uniform thickness except for both ends. Therefore, in the manufacturing method of the present invention, the (maximum value−minimum value) of the film thickness after slitting can be set to a range of 5 μm or less, and the product yield is also improved because it is wide.
On the other hand, even if the film B is slit with the same slit width (L) as the film A, the film thickness after the slit (maximum value−minimum value) exceeds 5 μm and the entire thickness is also increased. ing.
In the present invention, a uniform film having a thin film thickness can be produced by the high stretching process.

A polarizing plate is obtained by bonding a protective film with an adhesive on at least one side of the polarizing film thus produced.
As the protective film, for example, a film made of an acetyl cellulose resin such as triacetyl cellulose or diacetyl cellulose, a film made of a polyester resin such as polyethylene terephthalate, polyethylene naphthalate or polybutylene terephthalate, or a film made of a polycarbonate resin , A film made of a cycloolefin resin, an acrylic resin film, and a polypropylene film.

  In order to improve the adhesiveness between the adhesive and the polarizing film and / or protective film, the polarizing film and / or protective film may be subjected to corona treatment, flame treatment, plasma treatment, ultraviolet irradiation, primer coating treatment, saponification treatment, etc. A surface treatment may be applied.

  EXAMPLES Next, although an Example is given and this invention is demonstrated concretely, this invention is not restrict | limited at all by these Examples.

[Example 1]
Polyvinyl alcohol film 1 (Kurarevinilon VF-PS # 7500, polymerization degree 2,400, saponification degree 99.9 mol% or more) having a thickness of 75 μm and a width of 450 mm is kept in pure water at 30 ° C. so that the film does not loosen The film was sufficiently swollen by immersing the film in a tension state. Next, uniaxial stretching was performed while immersing in an aqueous solution of iodine / potassium iodide / water at a weight ratio of 0.02 / 1.5 / 100. Thereafter, as the first boric acid treatment step, the total draw ratio from the original fabric is 2.32 while immersing in a 55 ° C. aqueous solution of potassium iodide / boric acid / water 12 / 4.2 / 100 by weight. Uniaxial stretching was performed until doubling. Next, as a second boric acid treatment step, uniaxial stretching was performed until the integrated draw ratio from the original fabric was 2.69 times while being immersed in a boric acid-containing aqueous solution having the same composition and temperature. Next, as a high-stretching step, using a boric acid treatment tank 4 filled with a boric acid-containing aqueous solution 11 having the same composition and temperature, as a guide roll 3, a sponge guide roll (the hardness of the sponge is 25 degrees on the JIS Shore C scale). The film was stretched 2.06 times due to the difference in peripheral speed between the in-liquid nip roll 2 and the in-air nip roll 2 ′ through a density of 0.42 g / cm ³ and a surface roughness of 20S. At this time, the residence time T (immersion time) between the submerged nip roll 2 and the guide roll 3 was 3 seconds. Then, after immersing in a 40 ° C. boric acid-containing aqueous solution having the same composition, followed by washing with pure water at 5 ° C. for 8 seconds and drying at 70 ° C. for 3 minutes, both ends are slit by 40 mm and a polarizing film having a width of 210 mm Got. The maximum thickness of the obtained polarizing film was 25.9 μm, the minimum was 23.5 μm, and the difference between the maximum and minimum was 2.4 μm.
In the following examples and comparative examples, the width of the polarizing film after the slit process is adjusted to 210 mm.

[Example 2]
In the high stretching treatment step, the same as in Example 1 except that the residence time T (immersion time) of the film 1 to the nip roll 2 and the guide roll 3 in the liquid was 1.5 seconds and the slit width after drying was 46 mm. Thus, a polarizing film was obtained. The maximum thickness of the obtained polarizing film was 25.7 μm, the minimum was 23.4 μm, and the difference between the maximum and the minimum was 2.3 μm.

Example 3
Example 1 except that uniaxial stretching was performed by setting the cumulative stretching ratio before the high stretching treatment step to 2.35 times, the stretching ratio in the high stretching step to 2.35 times, and the slit width after drying to 49 mm. A polarizing film was obtained in the same manner. The maximum thickness of the obtained polarizing film was 24.7 μm, the minimum was 22.6 μm, and the difference between the maximum and minimum was 2.1 μm.

Example 4
Example 1 except that uniaxial stretching was performed by setting the cumulative stretching ratio before the high stretching treatment step to 3.27 times, the stretching ratio in the high stretching step to 1.70 times, and the slit width after drying to 33 mm. A polarizing film was obtained in the same manner. The maximum thickness of the obtained polarizing film was 28.0 μm, the minimum was 24.0 μm, and the difference between the maximum and minimum was 4.0 μm.

Example 5
The guide roll 3 in the high stretching process is a guide roll made of NBR rubber having a rubber hardness of 80 degrees on a JIS Shore C scale, a density of 1.3 g / cm ³ , and a surface roughness of 0.6 S. A polarizing film was obtained in the same manner as in Example 1 except that the slit width was 39 mm. The maximum thickness of the obtained polarizing film was 26.2 μm, the minimum was 23.3 μm, and the difference between the maximum and minimum was 2.9 μm.

Example 6
In the boric acid treatment step after the high-stretching treatment step, uniaxial stretching was performed 1.07 times with a 40 ° C. aqueous solution having a chemical composition of 9 / 2.9 / 100 in weight ratio of potassium iodide / boric acid / water. A polarizing film was obtained in the same manner as in Example 1 except that the slit width after drying was changed to 30 mm. The maximum thickness of the obtained polarizing film was 24.8 μm, the minimum was 22.2 μm, and the difference between the maximum and minimum was 2.6 μm.

[Comparative Example 1]
In the high stretching treatment step, the same as in Example 2 except that the residence time T (immersion time) between the submerged nip roll 2 and the guide roll 3 on the inlet side was 5 seconds and the slit width after drying was 25 mm. A polarizing film was obtained. The maximum thickness of the obtained polarizing film was 29.8 μm, the minimum was 24.7 μm, and the difference between the maximum and the minimum was 5.1 μm.

[Comparative Example 2]
Example 1 except that uniaxial stretching was performed with the integrated stretching ratio before the high stretching treatment step being 4.16 times, the stretching ratio in the high stretching step being 1.33 times, and the slit width after drying being 22 mm. A polarizing film was obtained in the same manner. The maximum thickness of the obtained polarizing film was 31.5 μm, the minimum was 25.6 μm, and the difference between the maximum and minimum was 5.9 μm.

[Comparative Example 3]
A polarizing film was obtained in the same manner as in Example 1 except that the guide roll 3 in the high stretching treatment step was a stainless steel guide roll and the slit width after drying was 24 mm. The maximum thickness of the obtained polarizing film was 28.8 μm, the minimum was 23.5 μm, and the difference between the maximum and minimum was 5.3 μm.

上記した表１より、膜厚の最大と最小の差は、実施例３が最小となり、比較例２が最大となった。 The results of Examples 1 to 5 and Comparative Examples 1 and 2 described above are shown below.

From Table 1 described above, the difference between the maximum and minimum film thicknesses was the minimum in Example 3 and the maximum in Comparative Example 2.

DESCRIPTION OF SYMBOLS 1 Polyvinyl alcohol film, 2, 2 'nip roll 3 Guide roll, 4 Boric acid processing tank, 11 Boric acid containing aqueous solution T Residence time, L Film width after cutting

Claims (8)

In the method for producing a polarizing film in which uniaxial stretching is performed before or during the process of treating the polyvinyl alcohol film in the order of swelling treatment, dyeing treatment, boric acid treatment, washing treatment, and drying treatment,
It has three or more stages of boric acid treatment steps, and after the third step of the boric acid treatment step, the difference in peripheral speed between the two nip rolls is used and 1.5 at least through one guide roll. A high stretching treatment step for performing uniaxial stretching not less than twice and not more than 2.7 times is provided, and the residence time of the film from the nip roll on the inlet side to the guide roll in the step is not less than 0.5 seconds and not more than 4 seconds,
The total draw ratio of the polarizing film obtained after the drying treatment is 5.5 times or more and 6.5 times or less,
Furthermore, the manufacturing method of the polarizing film characterized by providing the slit process which removes the width direction both ends of a film after a washing process, and performing a slit so that the maximum and minimum difference of a film thickness may be 5 micrometers or less. In the high stretching process, cormorants rows uniaxially stretching utilizing the peripheral speed difference of the deployed film toward the upstream side nip rolls and disposed in the air on the downstream side nip roll in the liquid 請 Motomeko The manufacturing method of the polarizing film of 1.   The method for producing a polarizing film according to claim 1, wherein in the high stretching treatment step, the guide roll is a sponge rubber roll or a rubber roll.   The polarized light according to claim 3, wherein the sponge rubber roll has a sponge hardness of 20 to 60 degrees on a JIS Shore C scale, a surface roughness of 10 to 30S, and a coefficient of dynamic friction in water with a treated film of 0.3 to 0.8. A method for producing a film.   The hardness of the rubber roll is 50 to 90 degrees on a JIS Shore A scale, the surface roughness is 0.4 to 2.0 S, and the dynamic friction coefficient in water with the treated film is 0.3 to 0.8. A method for producing a polarizing film. The production method according to any one of claims 1 to 5, wherein a draw ratio in the high-stretching treatment step is 1.7 times or more and the total draw ratio is 5.6 times or more and 6.3 times or less. Fourth boric acid treatment provided a method according to uniaxial stretching of more than 1.05 times the one from the row cormorants請 Motomeko 1 6 in the step after the high stretching process. The manufacturing method according to claim 7 , wherein the boric acid concentration in the fourth boric acid treatment step is lower than the boric acid concentration in the third boric acid treatment step.

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