KR102093539B1 - Method for producing polarizing film - Google Patents

Abstract

[Problem] A method for manufacturing a polarizing film with reduced occurrence of cuts and wrinkles in a polyvinyl alcohol-based film is provided.
[Solution] A method of producing a polarizing film by sequentially performing a swelling treatment and a dyeing treatment on a polyvinyl alcohol-based film, and the swelling treatment sequentially passes through n swelling tanks (n is a natural number) while stretching the polyvinyl alcohol-based film. In the swelling treatment, the initial width of the polyvinyl alcohol-based film is W, the final width of the polyvinyl alcohol-based film when exiting the n-th swelling tank is X, and the integrated draw ratio in all the swelling baths is A. When it does, -0.14≤ (WX) /W/A≤0.05 is satisfied.

Description

Manufacturing method of polarizing film {METHOD FOR PRODUCING POLARIZING FILM}

The present invention relates to a method of manufacturing a polarizing film.

Conventionally, as a manufacturing method of a polarizing film, there is one described in Japanese Patent Laid-Open No. 2006-267153 (Patent Document 1). In the manufacturing method of this polarizing film, a swelling process, a dyeing process, and an immobilization process are sequentially performed on a polyvinyl alcohol-type film, and a polarizing film is manufactured. And, it includes a procedure of sequentially immersing the polyvinyl alcohol-based film in a plurality of swelling treatment tanks, and the solution in the downstream swelling tank is set to be higher than the solution in the upstream swelling tank so that the liquid temperature becomes greater than 7 ° C. A polarizing film having optical properties has been obtained.

Patent Document 1: Japanese Patent Publication No. 2006-267153

However, it has been found that there are the following problems when attempting to manufacture a polarizing film by the conventional method of manufacturing a polarizing film. That is, cut marks and wrinkles are generated in the polarizing film, and accordingly, dyeing unevenness is generated in the polarizing film. As a result of earnestly examining the inventors of the present application, it has been found that swelling treatment causes cut marks and wrinkles on the polyvinyl alcohol-based film.

Then, the subject of this invention is providing the manufacturing method of the polarizing film which reduced the generation | occurrence | production of the cut and wrinkles of a polyvinyl alcohol-type film.

In order to solve the above problems, the method of manufacturing the polarizing film of the present invention,

A method for producing a polarizing film by sequentially performing a swelling treatment and a dyeing treatment on a polyvinyl alcohol-based film,

The swelling treatment is performed by sequentially passing n (n is a natural number) swelling tank while stretching the polyvinyl alcohol-based film,

In the swelling treatment, the initial width of the polyvinyl alcohol-based film is W, and the final width of the polyvinyl alcohol-based film when exiting the n-th swelling tank is X, and the cumulative stretching ratio in all the swelling baths is A When you do

-0.14 ≤ (W-X) / W / A ≤ 0.05.

According to the manufacturing method of the polarizing film of the present invention, since -0.14≤ (WX) /W/A≤0.05 is satisfied, in the polyvinyl alcohol-based film after the swelling treatment, occurrence of cut marks and wrinkles in the center part Can be reduced. As a result, dyeing unevenness of the polyvinyl alcohol-based film in the dyeing treatment can be reduced.

In addition, in one embodiment of the manufacturing method of the polarizing film,

-0.12≤ (W-X) /W/A≤0.02.

According to the above embodiment, since -0.12≤ (WX) /W/A≤0.02 is satisfied, in the polyvinyl alcohol-based film after the swelling treatment, it is possible to further reduce the occurrence of cut marks and wrinkles at the center. have.

In addition, in one embodiment of the manufacturing method of a polarizing film, there are two said swelling tanks.

According to the above embodiment, since there are two swelling tanks, it is possible to swell and stretch the polyvinyl alcohol-based film smoothly.

In addition, in one embodiment of the manufacturing method of the polarizing film,

n is 2 or more,

The temperature of the n-th swelling tank in the conveying direction of the polyvinyl alcohol-based film is equal to or less than the temperature of the k-th (1≤k≤ (n-1)) swelling tank.

According to the above-described embodiment, since the temperature of the n-th swelling tank is lower than or equal to the temperature of the k-th swelling tank, in the n-th swelling tank having a low temperature, the neck-in can proceed without applying a stretching magnification, and the surface of the tension and optical properties Is preferred.

In addition, in one embodiment of the manufacturing method of the polarizing film, the initial width W of the polyvinyl alcohol-based film is 400 mm or more.

According to the above embodiment, since the initial width W of the polyvinyl alcohol-based film is 400 mm or more, it is possible to effectively reduce the occurrence of cut marks and wrinkles in the wide polyvinyl alcohol-based film.

According to the manufacturing method of the polarizing film of the present invention, since -0.14≤ (W-X) /W/A≤0.05 is satisfied, it is possible to reduce the occurrence of cuts and wrinkles in the polyvinyl alcohol-based film.

1 is a simplified configuration diagram showing an embodiment of a polarizing film production apparatus of the present invention.
It is explanatory drawing explaining one Embodiment of the manufacturing method of the polarizing film of this invention.

Hereinafter, it demonstrates in detail by embodiment which shows this invention.

1 is a simplified configuration diagram showing an embodiment of a manufacturing apparatus for a polarizing film of the present invention. As shown in FIG. 1, the polarizing film production apparatus 5 has two swelling tanks 11 and 12 that swell the polyvinyl alcohol-based film 2 (hereinafter referred to as PVA-based film 2). ), A dyeing tank 20 for dyeing the PVA-based film 2 passed through the two swelling tanks 11 and 12, and a PVA-based film 2 passing through the swelling tanks 11 and 12. It has stretching rollers 61 and 62 for stretching. At this time, the number of swelling tanks may be one or three or more, not two.

In the polarizing film manufacturing method, the swelling treatment and the dyeing treatment are sequentially performed on the PVA-based film 2 to produce the polarizing film 3. The swelling treatment is performed by sequentially passing the two swelling tanks 11 and 12 while stretching the PVA-based film 2. As shown in Fig. 2, in the swelling treatment, the initial width of the PVA-based film 2 is W, and the final width of the PVA-based film 2 when exiting the second swelling tank 12 is X, all When the integrated draw ratio in the swelling tanks 11 and 12 is A, -0.14 ≤ (WX) / W / A ≤ 0.05 is satisfied. At this time, the polarizing film manufacturing method can be performed without being limited to the configuration of the polarizing film manufacturing apparatus 5 shown in FIG. 1.

The method of stretching the PVA-based film 2 by the swelling treatment is performed by applying tension in the conveying direction to the PVA-based film 2 using, for example, stretching rollers 61 and 62.

According to the polarizing film manufacturing method, since -0.14≤ (WX) /W/A≤0.05 is satisfied, in the PVA-based film 2 after the swelling treatment, it is possible to reduce the occurrence of cut marks and wrinkles at the center. have. As a result, dyeing unevenness of the PVA-based film 2 in the dyeing treatment can be reduced.

On the other hand, when the relational formula (WX) / W / A is below the lower limit of -0.14, when the PVA-based film 2 becomes soft and exits the swelling tanks 11 and 12, the PVA-based film 2 The frequency of cut marks at the end increases. On the other hand, when the relational formula (WX) / W / A exceeds the upper limit of 0.05, the PVA-based film 2 becomes too hard and does not spread well in the swelling tanks 11 and 12, and the PVA-based film 2 ), The frequency of wrinkles in the center increases. In addition, when cut marks or wrinkles are generated in the swelling tanks 11 and 12, dye stains are formed on the cut marks or wrinkles, resulting in poor yield. In addition, when the cut marks are severe, the PVA-based film 2 being transported may be a factor for breaking.

In short, the inventor of the present application, when swelling the PVA-based film 2, differs in the neck-in behavior depending on the temperature, residence time, and draw ratio, but by defining the ratio of the neck-in per unit of the integrated draw ratio, the PVA-based film ( It has been found that the frequency of cut marks in 2) is reduced, and there is an effect of improving yield or suppressing the breakage of the PVA-based film 2 being transported.

Preferably, -0.12≤ (W-X) /W/A≤0.02 is satisfied. Accordingly, in the PVA-based film 2 after the swelling treatment, it is possible to further reduce the occurrence of cut marks at the ends and wrinkles at the center.

Preferably, there are two swelling tanks. Thereby, the swelling and extending | stretching of the PVA system film 2 can be performed smoothly.

Preferably, the number of swelling tanks is n (n is a natural number of 2 or more), and the temperature of the nth swelling tank in the conveying direction of the PVA-based film 2 is the kth (1 ≦ k ≦ (n-1)) temperature of the swelling tank. Is below. That is, the temperature of the most downstream swelling tank in the conveying direction is below the temperature of other swelling tanks.

As described above, since the temperature of the n-th swelling tank is lower than or equal to the temperature of the k-th swelling tank, in the n-th swelling tank having a low temperature, neck-in can proceed without applying a stretching ratio, which is preferable in terms of tension and optical properties. .

Preferably, the initial width W of the PVA-based film 2 is 400 mm or more. Thereby, in the wide PVA-based film 2, it is possible to effectively reduce the occurrence of cut marks and wrinkles.

Hereinafter, a polarizing film manufacturing apparatus and a polarizing film manufacturing method will be described in more detail.

(Polarizing film manufacturing apparatus)

As shown in FIG. 1, the polarizing film manufacturing apparatus 5 is provided with the 1st and 2nd swelling tanks 11 and 12 which perform swelling process along the conveyance path of the PVA system film 2, and the dyeing process. It has a dyeing tank 20 to perform, a crosslinking tank 30 to perform crosslinking treatment, a water washing tank 40 to perform water washing treatment, and a drying furnace 50 to perform drying treatment. The PVA-based film 2 is released from the disc roll 1, and the first and second swelling tanks 11 and 12, a dyeing tank 20, a crosslinking tank 30, and a water washing tank 40 ) And sequentially through the drying furnace 50, the polarizing film 3 can be obtained. Here, although the dyeing tank 20, the crosslinking tank 30, and the water washing tank 40 are respectively provided in FIG. 1, a plurality of tanks may be provided as necessary. Although two sets of swelling tanks 11 and 12 are provided, one or three or more sets may be provided.

1 and 2, the polarizing film production apparatus 5 includes a delivery roller 60 disposed upstream of the first swelling tank 11, a first swelling tank 11 and a second swelling It has a first stretching roller 61 disposed between the jaws 12 and a second stretching roller 62 disposed downstream of the second swelling tank 12. The delivery roller 60 delivers the PVA-based film 2 to the first swelling tank 11. The first stretching roller 61 stretches the PVA-based film 2 passing through the first swelling tank 11. For example, the rotational speed of the first stretching roller 61 is made larger than the rotational speed of the delivery roller 60, and the PVA-based film 2 is stretched by pulling in the conveying direction. The second stretching roller 62 stretches the PVA-based film 2 passing through the second swelling tank 12. For example, the rotation speed of the second stretching roller 62 is made larger than the rotation speed of the first stretching roller 61, and the PVA-based film 2 is stretched by pulling in the conveying direction.

The stretching of the PVA-based film 2 by the first and second stretching rollers 61 and 62 is the initial width of the PVA-based film 2 when passing through the delivery roller 60 W, and the second swelling tank The final width of the PVA-based film 2 when exiting (12) is the integrated stretching magnification in the first and second swelling tanks (11, 12) by X, the first and second stretching rollers (61, 62). When A is set to A, it is controlled to satisfy -0.14 ≤ (WX) / W / A ≤ 0.05. Preferably, the stretching of the PVA-based film 2 by the first and second stretching rollers 61 and 62 is controlled to satisfy -0.12 ≤ (W-X) / W / A ≤ 0.02. Therefore, in the PVA-based film 2 after the swelling treatment, it is possible to reduce the occurrence of cut marks at the ends and the occurrence of wrinkles at the center. It is preferable that the temperature of the first swelling tank 12 is equal to or less than the temperature of the first swelling tank 11, and accordingly, in the second swelling tank 12 having a low temperature, the neck-in can proceed without applying a stretching ratio. It is good in terms of tension and optical properties. Since there are two swelling tanks 11 and 12, the swelling and stretching of the PVA-based film 2 can be performed smoothly.

(PVA-based film)

The polyvinyl alcohol-based resin forming the PVA-based film is usually obtained by saponifying a polyvinyl acetate-based resin. The saponification degree of the polyvinyl alcohol-based resin is usually 85 mol% or more, preferably 90 mol% or more, and more preferably 99 to 100 mol%. Examples of the polyvinyl acetate-based resin 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 of the other copolymerizable monomers include unsaturated carboxylic acids, olefins other than ethylene, vinyl ethers, and unsaturated sulfonic acids, in addition to the above ethylene. The degree of polymerization of the polyvinyl alcohol-based resin is usually 1000 to 10000, preferably about 1500 to 5000.

These polyvinyl alcohol-based resins may be modified, for example, polyvinyl formal modified with aldehydes, polyvinyl acetal, polyvinyl butyral, and the like can be used. Usually, an unstretched PVA-based film having a thickness of 20 to 100 µm, preferably 30 to 80 µm, is used as a starting material for the production of the polarizing film. Moreover, you may use the extending | stretching PVA system film to which extending | stretching process was previously performed. When a PVA-based film having a thickness of 75 µm or less is generally used, it is easy to cause cuts and wrinkles. Particularly, when it is 65 µm or less, occurrence of cuts and wrinkles becomes remarkable. In this embodiment, even if a PVA-based film having such a small thickness difference is used, it is possible to reduce the occurrence of cut marks and wrinkles. The initial width W of the PVA-based film is 400 mm or more, and industrially, 1500 mm to 6000 mm are practical. In this embodiment, even if such a wide PVA-based film is used, the occurrence of cut marks and wrinkles can be reduced.

(Swelling treatment)

The swelling treatment is performed for the purpose of removing foreign substances on the surface of the PVA-based film, removing the plasticizer in the PVA-based film, imparting dichroism in a subsequent step, or plasticizing the PVA-based film. The conditions of the swelling treatment are determined in a range in which these objects can be achieved, and in a range in which problems such as extreme dissolution of the PVA-based film and loss of transparency do not occur. The swelling treatment is performed by immersing the unstretched PVA-based film in a treatment bath at a temperature of 10 to 50 ° C, preferably 15 to 45 ° C, for example. When there are several swelling tanks, the temperature of the most downstream swelling tank in the conveying direction is preferably equal to or less than the temperature of other swelling tanks, and the temperature difference between the most downstream swelling tank and other swelling tanks is preferably 0 to 20 ° C. , More preferably, it is 5 to 10 ° C. The swelling treatment time is about 5 to 300 seconds, preferably about 20 to 240 seconds.

In the swelling treatment, problems such as swelling of the PVA-based film in the width direction and wrinkles in the PVA-based film are likely to occur, so that the PVA is used as a known expansion device such as expander roll, spiral roll, crown roll, cloth guider, bend bar, etc. It is preferable to convey the PVA-based film while removing wrinkles of the system film. For the purpose of stabilizing the conveyance of the PVA-based film in the bath, the water flow in the swelling bath is controlled by an underwater shower, or the edge position control device (EPC device) detects the end of the PVA-based film to prevent meandering of the PVA-based film. It is also useful to use a device) together. In this step, since the PVA-based film swells and expands also in the conveying direction of the PVA-based film, in order to eliminate the looseness of the PVA-based film in the conveying direction, for example, rollers 60 before and after the swelling tanks 11 and 12 , 61, 62). Specifically, the initial width of the PVA-based film 2 is W, and the final width of the PVA-based film 2 when exiting the second swelling tank 12 is X, the first, and the second swelling tanks 11 and 12. When the integrated stretching magnification in) is A, the rollers 60, 61, and so as to satisfy -0.14≤ (WX) /W/A≤0.05 (preferably -0.12≤ (WX) /W/A≤0.02). 62) to control the speed. In this way, in the PVA-based film 2 after the swelling treatment, it is possible to reduce the occurrence of cuts at the ends and the occurrence of wrinkles at the center. Moreover, it is preferable to make the temperature of the 2nd swelling tank 12 less than the temperature of the 1st swelling tank 11, and accordingly, in the 2nd swelling tank 12 with a low temperature, it is neck-in without applying a draw ratio. It can advance, and it becomes favorable in terms of tension and optical properties. Since there are two swelling tanks 11 and 12, the swelling and stretching of the PVA-based film 2 can be performed smoothly.

The treatment bath used in the swelling tanks 11 and 12 may be an aqueous solution in which, in addition to pure water, boric acid, chloride, other inorganic acids, and other inorganic salts are added in a range of 0.01 to 10% by weight. However, in these swelling tanks 11 and 12, pure water substantially free of soluble components is preferably used.

(Dyeing treatment)

The dyeing treatment is performed for the purpose of adsorbing a dichroic dye onto a PVA-based film. Treatment conditions are determined in a range that can achieve this purpose, and in a range in which problems such as extreme dissolution of PVA-based films and loss of transparency do not occur.

When using iodine as a dichroic dye, for example, at a temperature of 10 to 50 ° C, preferably 20 to 40 ° C, and 0.003 to 0.2 parts by weight of iodine and 0.1 to 10 parts by weight of potassium iodide with respect to 100 parts by weight of water The dyeing treatment is performed by immersing in an aqueous solution for 10 to 600 seconds, preferably 30 to 200 seconds. Other iodide, such as zinc iodide, may be used instead of potassium iodide. Further, other iodide may be used in combination with potassium iodide. Further, compounds other than iodide, such as boric acid, zinc chloride, and cobalt chloride, may coexist. Even when boric acid is added, it differs from the subsequent boric acid treatment in that it contains iodine. A bath containing at least 0.003 parts by weight of iodine per 100 parts by weight of water can be regarded as a dyeing bath.

On the other hand, when a water-soluble dichroic dye is used as a dichroic dye, for example, at a temperature of 20 to 80 ° C, preferably 30 to 60 ° C, the dichroic dye is contained in an amount of 0.001 to 0.1 parts by weight based on 100 parts by weight of water. The dyeing treatment is performed by immersion in an aqueous solution to be performed for 10 to 600 seconds, preferably 20 to 300 seconds. The aqueous solution of the dichroic dye to be used may contain a dyeing aid or the like, for example, an inorganic salt such as sodium sulfate, or a surfactant. Only one type of dichroic dye may be used, and two or more types of dichroic dyes may be used in combination depending on the desired color.

Also in the dyeing treatment, an expander roll, a spiral roll, a crown roll, a cloth guider, a bend bar, etc. may be appropriately provided in the dyeing bath and / or in the bath entrance as in the swelling process. In this dyeing treatment, it is possible to uniaxially stretch in the machine direction at the same time.

(Crosslinking)

The crosslinking treatment is performed by immersing the PVA-based film dyed with a dichroic dye in an aqueous solution containing boric acid. The content of boric acid in this aqueous solution is usually about 1 to 10 parts by weight with respect to 100 parts by weight of water. When the dichroic dye is iodine, it is preferable to contain 1 to 30 parts by weight of iodide relative to 100 parts by weight of water. Potassium iodide, zinc iodide, etc. are mentioned as iodide. Further, compounds other than iodide, such as zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, sodium sulfate and the like may coexist.

The crosslinking treatment is carried out for water resistance by color crosslinking, color adjustment (preventing blue light, and the like). In the case of water resistance by crosslinking, if necessary, crosslinking agents such as glyoxal and glutaraldehyde can also be used in addition to or together with boric acid. In addition, crosslinking treatment for water resistance may be referred to as water resistance treatment or immobilization treatment. In addition, the crosslinking treatment for color adjustment is sometimes referred to as a complementary color treatment or a re-dyeing treatment.

The crosslinking treatment is performed by appropriately changing the concentration of boric acid and iodide and the temperature of the treatment bath according to the purpose. The crosslinking treatment for water resistance and the crosslinking treatment for color adjustment are not particularly distinguished, but are carried out under the following conditions. When the swelling treatment is performed using an unstretched PVA-based film, followed by dyeing treatment and crosslinking treatment, and when the crosslinking treatment is intended for water resistance, boric acid is 3 to 10 weights per 100 parts by weight of water. Part, using a boric acid treatment bath containing 1 to 20 parts by weight of iodide, is usually carried out at a temperature of 50 to 70 ° C, preferably 53 to 65 ° C. The immersion time is usually about 10 to 600 seconds, preferably 20 to 300 seconds, more preferably 20 to 200 seconds. At this time, when a swelling treatment is performed using a pre-stretched PVA-based film and thereafter dyeing treatment and crosslinking treatment, the temperature of the boric acid treatment bath is usually 50 to 85 ° C, preferably 55 to 80 ° C.

After the crosslinking treatment for water resistance, a crosslinking treatment for color adjustment may be performed. For example, when the dichroic dye is iodine, for the purpose of color adjustment, using a boric acid treatment bath containing 1 to 5 parts by weight of boric acid and 3 to 30 parts by weight of iodide with respect to 100 parts by weight of water, usually 10 ° C It is performed at a temperature of ~ 45 ° C. The immersion time is usually 1 to 300 seconds, preferably 2 to 100 seconds.

These crosslinking treatments may be performed multiple times, and are usually performed 2 to 5 times. In this case, the composition and temperature of the aqueous solution of each boric acid treatment tank to be used may be the same or different within the above range. The boric acid treatment for water resistance and the boric acid treatment for color adjustment may be performed in a plurality of processes, respectively.

The final integrated stretching magnification of the stretching of the polarizing film in this embodiment is usually 4.5 to 7 times, preferably 5 to 6.5 times.

(Flush treatment)

After the crosslinking treatment, it is usually sent to a water washing treatment. The water washing treatment is performed by, for example, immersing the PVA-based film in which boric acid treatment is carried out for water resistance and / or color adjustment, by spraying water as a shower, or by dipping and spraying together. The water temperature in the water washing treatment is usually about 2 to 40 ° C, and the immersion time is preferably 2 to 120 seconds.

(Dry treatment)

The PVA-based film after the water washing treatment is usually guided to a drying furnace and subjected to drying treatment. This drying treatment is performed by passing it through a drying furnace maintained at a temperature of 40 to 100 ° C, preferably 50 to 100 ° C, for about 30 to 600 seconds. There may be a plurality of drying furnaces, and when multiple drying furnaces are provided, the temperatures of each drying furnace may be the same or different. When drying is performed by sequentially passing through a plurality of drying furnaces, it is preferable to apply a temperature gradient so that the temperature increases sequentially from the front end of the drying furnace to the rear end of the drying furnace so that wrinkles do not enter the PVA-based film by rapid drying.

A polarizing film is manufactured through the above process. Although a detailed description is omitted, a transparent protective film is then bonded to at least one side of the polarizing film to produce a polarizing plate.

[Example]

Hereinafter, examples of the present invention will be described, but the present invention is not limited by these examples. Table 1 shows the effects of the unstretched PVA-based films (thickness of 60 µm) treated under different conditions in the first to seventh examples and the first and second comparative examples.

As conditions, there are neck-in (W-X) / W, integrated stretching magnification A, temperature [° C] of the first and second swelling tanks, and relational expression (W-X) / W / A. As effects, there are cuts in the end of the PVA-based film, wrinkles in the center of the PVA-based film, and the frequency of breakage (times / h) of the PVA-based film.

When the relational expression is within the range of -0.14 to 0.05, it is represented by "○", and when the relational expression is outside the range of -0.14 to 0.05, it is represented by "x". The first to seventh examples are "○", and the first and second comparative examples are "x".

Specifically, in the first embodiment, the relational expression is -0.139. At this time, the cut marks at the ends could be reduced to 1 mm at both ends. There was no wrinkles in the center. The rupture frequency is 0 times per hour.

In the second embodiment, the relational expression is -0.118. At this time, no cut marks were generated at the ends. There was no wrinkles in the center. The rupture frequency is 0 times per hour.

In the third embodiment, the relational expression is -0.099. At this time, no cut marks were generated at the ends. There was no wrinkles in the center. The rupture frequency is 0 times per hour.

In the fourth embodiment, the relational expression is -0.062. At this time, no cut marks were generated at the ends. There was no wrinkles in the center. The rupture frequency is 0 times per hour.

In the fifth embodiment, the relational expression is -0.005. At this time, no cut marks were generated at the ends. There was no wrinkles in the center. The rupture frequency is 0 times per hour.

In the sixth embodiment, the relational expression is 0.016. At this time, no cut marks were generated at the ends. There was no wrinkles in the center. The rupture frequency is 0 times per hour.

In the seventh embodiment, the relational expression is 0.048. At this time, no cut marks were generated at the ends. The wrinkles at the center could be reduced to one line. The rupture frequency is 0 times per hour.

In the first comparative example, the relational expression is -0.150. At this time, the cut marks at the ends occur at 2 mm each at both ends, and are outside the allowable range. There was no wrinkles in the center. The frequency of breakage is 0.33 times per hour.

In the second comparative example, the relational expression is 0.059. At this time, no cut marks were generated at the ends. There are three lines of wrinkles in the central part, which are outside the allowable range. The frequency of breaks is 0.17 times per hour.

Therefore, in the first to seventh embodiments, the relational expression is in the range of -0.14 to 0.05, and there is no problem of end cuts or wrinkles at the center, and there is no problem of breaking frequency. On the other hand, in the first and second comparative examples, the relational expression is outside the range of -0.14 to 0.05, and there is a problem of end cuts and wrinkles at the center, and there is also a problem of breaking frequency. In particular, in the second to sixth embodiments, the relational expression was in the range of -0.12 to 0.02, so that no end cut marks and central wrinkles were generated.

1: Disc roll, 2: PVA-based film, 3: Polarizing film, 5: Polarizing film manufacturing apparatus, 11: First swelling tank, 12: Second swelling tank, 20: Dyeing tank, 30: Crosslinking tank, 40: Water Washing tank, 50: drying furnace, 60: delivery roller, 61: first stretching roller, 62: second stretching roller

Claims (5)

A method for producing a polarizing film by sequentially performing a swelling treatment and a dyeing treatment on a polyvinyl alcohol-based film,
The swelling treatment is performed by unscrewing the polyvinyl alcohol-based film from the disc roll and sequentially passing n (n is a natural number) swelling tank while stretching in the conveying direction,
In the swelling treatment, the initial width of the polyvinyl alcohol-based film is W, the final width of the polyvinyl alcohol-based film when exiting the n-th swelling tank is X, and the total stretching ratio in all the swelling baths is A When you do
The manufacturing method of a polarizing film which satisfies -0.14≤ (WX) /W/A≤0.05. The method of claim 1, wherein -0.12 ≤ (W-X) / W / A ≤ 0.02. The method for manufacturing a polarizing film according to claim 1 or 2, wherein the swelling tank is two. The method according to claim 1 or 2, n is 2 or more,
The temperature of the n-th swelling tank in the conveying direction of the polyvinyl alcohol-based film is a k-th (1 ≦ k ≦ (n-1)) swelling tank temperature or lower. The method of claim 1 or 2, wherein the initial width (W) of the polyvinyl alcohol-based film is 400 mm or more.

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