JP2018013810A - Method of manufacturing polarizing film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a polarizing film, which reduces generation of folds and wrinkles of polyvinyl alcohol-based films.SOLUTION: A method of manufacturing a polarizing film comprises sequentially performing swelling treatment and dying treatment on a polyvinyl alcohol-based film. The swelling treatment involves passing the polyvinyl alcohol-based film sequentially through n (n is a natural number) pieces of swelling tanks while stretching the film. The swelling treatment is applied such that an initial width W of the polyvinyl alcohol-based film, a final width X of the polyvinyl alcohol-based film measured when coming out of the n-th swelling tank, and a cumulative stretch ratio A through all the swelling tanks satisfy -0.14≤(W-X)/W/A≤0.05.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a method for producing a polarizing film.

  Conventionally, as a manufacturing method of a polarizing film, there exists a thing described in Unexamined-Japanese-Patent No. 2006-267153 (patent document 1). In this method for producing a polarizing film, a polyvinyl film is subjected to a swelling treatment, a dyeing treatment, and an immobilization treatment in this order to produce a polarizing film. And it includes the procedure of sequentially immersing the polyvinyl alcohol film in a plurality of swelling treatment tanks, and the temperature of the solution in the downstream swelling tank is higher than the solution in the upstream swelling tank by more than 7 ° C. By setting to, a polarizing film having uniform optical characteristics is obtained.

JP 2006-267153 A

  By the way, when it tried to manufacture a polarizing film with the manufacturing method of the said conventional polarizing film, it discovered that there existed the following problem. That is, folding and wrinkles are generated in the polarizing film, thereby causing uneven dyeing in the polarizing film. As a result of intensive studies, the inventor of the present application has found that folds and wrinkles are generated in the polyvinyl alcohol film during the swelling treatment.

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

In order to solve the above problems, the method for producing a polarizing film of the present invention comprises:
A method of producing a polarizing film by sequentially performing a swelling treatment and a dyeing treatment on a polyvinyl alcohol film,
The swelling treatment is performed by sequentially passing through the n (where n is a natural number) swelling tanks while stretching the polyvinyl alcohol film.
In the swelling treatment, the initial width of the polyvinyl alcohol film is W, the final width of the polyvinyl alcohol film when leaving the n-th swelling tank is X, and the cumulative draw ratio in all the swelling tanks is A. When
−0.14 ≦ (W−X) /W/A≦0.05 is satisfied.

  According to the method for producing a polarizing film of the present invention, −0.14 ≦ (W−X) /W/A≦0.05 is satisfied, and therefore, in the polyvinyl alcohol film after the swelling treatment, the end portion is not folded. Generation and generation of wrinkles in the center can be reduced. As a result, it is possible to reduce uneven dyeing of the polyvinyl alcohol film in the dyeing process.

Moreover, in one embodiment of the manufacturing method of the polarizing film,
-0.12 ≦ (W−X) /W/A≦0.02 is satisfied.

  According to the embodiment, since −0.12 ≦ (W−X) /W/A≦0.02 is satisfied, in the polyvinyl alcohol film after the swelling treatment, the occurrence of folding at the end and the central portion The generation of wrinkles can be further reduced.

  Moreover, in one Embodiment of the manufacturing method of a polarizing film, the said swelling tank is two pieces.

  According to the embodiment, since there are two swelling tanks, the polyvinyl alcohol film can be smoothly swelled and stretched.

Moreover, 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 transport direction of the polyvinyl alcohol film is equal to or lower than the temperature of the k-th (1 ≦ k ≦ (n−1)) swelling tank.

  According to the embodiment, since the temperature of the nth swelling tank is equal to or lower than the temperature of the kth swelling tank, the neck-in can be advanced without applying a draw ratio in the low temperature nth swelling tank. It is preferable in terms of tension and optical characteristics.

  Moreover, in one Embodiment of the manufacturing method of a polarizing film, the initial width W of the said polyvinyl alcohol-type film is 400 mm or more.

  According to the embodiment, since the initial width W of the polyvinyl alcohol film is 400 mm or more, the occurrence of folding and wrinkles can be effectively reduced in a wide polyvinyl alcohol film.

  According to the method for producing a polarizing film of the present invention, since −0.14 ≦ (W−X) /W/A≦0.05 is satisfied, folding of the polyvinyl alcohol film and generation of wrinkles can be reduced.

It is a simplified lineblock diagram showing one embodiment of a polarizing film manufacturing device of the present invention. It is explanatory drawing explaining one Embodiment of the polarizing film manufacturing method of this invention.

  Hereinafter, the present invention will be described in detail with reference to the illustrated embodiments.

  FIG. 1 is a simplified configuration diagram showing an embodiment of a polarizing film manufacturing apparatus of the present invention. As shown in FIG. 1, the polarizing film manufacturing apparatus 5 includes two swelling tanks 11 and 12 that swell a polyvinyl alcohol film 2 (hereinafter referred to as a PVA film 2), two swelling tanks 11, 12 includes a dyeing tank 20 that performs a dyeing process on the PVA film 2 that has passed through 12, and stretching rollers 61 and 62 that extend the PVA film 2 that passes through the swelling tanks 11 and 12. The number of swelling tanks is not two, but may be one or three or more.

  In the polarizing film manufacturing method, the polarizing film 3 is manufactured by sequentially performing a swelling process and a dyeing process on the PVA-based film 2. The swelling treatment is performed by sequentially passing the PVA film 2 through the two swelling tanks 11 and 12 while stretching. As shown in FIG. 2, in the swelling treatment, the initial width of the PVA-based film 2 is W, the final width of the PVA-based film 2 when leaving the second swelling tank 12 is X, and in all the swelling tanks 11 and 12 When the cumulative draw ratio is A, −0.14 ≦ (W−X) /W/A≦0.05 is satisfied. In addition, a polarizing film manufacturing method is not limited to the structure of the polarizing film manufacturing apparatus 5 shown in FIG. 1, It can implement.

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

  According to the polarizing film manufacturing method, −0.14 ≦ (W−X) /W/A≦0.05 is satisfied, and therefore, in the PVA film 2 after the swelling treatment, the occurrence of folding of the end portion and the central portion The generation of wrinkles can be reduced. As a result, uneven dyeing of the PVA film 2 in the dyeing process can be reduced.

  On the other hand, when the above relational expression (W−X) / W / A is lower than −0.14 which is the lower limit value, the PVA film 2 becomes soft, and when exiting the swelling tanks 11 and 12, PVA The frequency with which folding occurs at the end of the system film 2 increases. On the other hand, when the relational expression (W-X) / W / A exceeds 0.05 which is the upper limit value, the PVA film 2 becomes too hard and does not spread well in the swelling tanks 11 and 12, and the PVA system The frequency of occurrence of wrinkles in the center of the film 2 increases. And when a fold and wrinkle generate | occur | produce in the swelling tanks 11 and 12, the coloring unevenness will arise in the generation | occurrence | production part of a fold or wrinkle, and a yield will worsen. Moreover, when a fold is severe, it may become a factor of the fracture | rupture of the PVA-type film 2 in conveyance.

  In short, the present inventor has a neck-in behavior that varies depending on the temperature, residence time, and draw ratio when the PVA film 2 is swollen, but by specifying the neck-in rate per unit of the integral draw ratio, It has been found that the frequency of folding of the film 2 is reduced to improve the yield and to suppress the breakage of the PVA film 2 being conveyed.

  Preferably, −0.12 ≦ (W−X) /W/A≦0.02 is satisfied. Thereby, in the PVA-type film 2 after a swelling process, generation | occurrence | production of the folding of an edge part and generation | occurrence | production of the wrinkle of a center part can be reduced further.

  Preferably, there are two swelling tanks. Thereby, swelling and extending | stretching of the PVA-type 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 transport direction of the PVA film 2 is kth (1 ≦ k ≦ (n−1)). It is below the temperature of the swelling tank. That is, the temperature of the most downstream swelling tank in the transport direction is equal to or lower than the temperature of other swelling tanks.
Thus, since the temperature of the n-th swelling tank is equal to or lower than the temperature of the k-th swelling tank, in the n-th swelling tank having a low temperature, the neck-in can be advanced without applying a draw ratio, It is preferable in terms of tension and optical characteristics.

  Preferably, the initial width W of the PVA film 2 is 400 mm or more. Thereby, in wide PVA-type film 2, generation | occurrence | production of a fold and a wrinkle can be reduced effectively.

  Hereinafter, a polarizing film manufacturing apparatus and a polarizing film manufacturing method are demonstrated in detail.

(Polarizing film manufacturing equipment)
As shown in FIG. 1, the polarizing film manufacturing apparatus 5 includes first and second swelling tanks 11 and 12 that perform a swelling process, a dyeing tank 20 that performs a dyeing process, and a conveying path of the PVA film 2. It has the bridge | crosslinking tank 30 which performs a crosslinking process, the water washing tank 40 which performs a water-washing process, and the drying furnace 50 which performs a drying process. The PVA film 2 is fed out from the raw roll 1 and passes through the first and second swelling tanks 11 and 12, the dyeing tank 20, the crosslinking tank 30, the washing tank 40, and the drying furnace 50 in order. A polarizing film 3 is obtained. In FIG. 1, one dyeing tank 20, one crosslinking tank 30, and one water washing tank 40 are provided, but a plurality of tanks may be provided as necessary. Although two swelling tanks 11 and 12 are provided, one or three or more tanks may be provided.

  As shown in FIGS. 1 and 2, the polarizing film manufacturing apparatus 5 is disposed between the feed roller 60 disposed upstream of the first swelling tank 11, and the first swelling tank 11 and the second swelling tank 12. A first stretching roller 61 and a second stretching roller 62 disposed downstream of the second swelling tank 12. The delivery roller 60 delivers the PVA film 2 to the first swelling tank 11. The first stretching roller 61 stretches the PVA film 2 that passes through the first swelling tank 11. For example, the number of rotations of the first stretching roller 61 is made larger than the number of rotations of the sending roller 60, and the PVA film 2 is stretched by being pulled in the transport direction. The second stretching roller 62 stretches the PVA film 2 that passes through the second swelling tank 12. For example, the number of rotations of the second stretching roller 62 is made larger than the number of rotations of the first stretching roller 61, and the PVA film 2 is stretched by being pulled in the transport direction.

  The stretching of the PVA film 2 by the first and second stretching rollers 61 and 62 is such that the initial width of the PVA film 2 when passing through the feed roller 60 is W, and the PVA film 2 when leaving the second swelling tank 12. -0.14 ≦ (W−X) / W where X is the final width of A, and A is the cumulative draw ratio of the first and second swelling tanks 11 and 12 by the first and second stretching rollers 61 and 62. It is controlled so as to satisfy /A≦0.05. Preferably, the stretching of the PVA film 2 by the first and second stretching rollers 61 and 62 is controlled so as to satisfy −0.12 ≦ (W−X) /W/A≦0.02. Therefore, in the PVA film 2 after the swelling treatment, it is possible to reduce the occurrence of folding at the end and the generation of wrinkles at the center. It is preferable that the temperature of the 1st swelling tank 12 is below the temperature of the 1st swelling tank 11, By this, in the 2nd swelling tank 12 with low temperature, neck-in can be advanced without applying a draw ratio. In terms of tension and optical properties, it becomes favorable. Since there are two swelling tanks 11 and 12, the PVA film 2 can be smoothly swelled and stretched.

(PVA film)
The polyvinyl alcohol resin that forms the PVA film is usually obtained by saponifying a polyvinyl acetate 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%. 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. In addition to the above ethylene, examples of other copolymerizable monomers include unsaturated carboxylic acids, olefins other than ethylene, vinyl ethers, and unsaturated sulfonic acids. The degree of polymerization of the polyvinyl alcohol-based resin is usually about 1000 to 10,000, preferably about 1500 to 5,000.

  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 PVA film having a thickness of 20 to 100 μm, preferably 30 to 80 μm, is used as a starting material for manufacturing a polarizing film. Note that a stretched PVA-based film that has been stretched in advance may be used. In general, when a PVA film having a thickness of 75 μm or less is used, folding and wrinkling are likely to occur. In particular, when the thickness is 65 μm or less, folding and wrinkling are prominent. In the present embodiment, even when a PVA-based film with such a small thickness difference is used, the occurrence of folding and wrinkles can be reduced. The initial width W of the PVA film is 400 mm or more, and industrially, 1500 mm to 6000 mm is practical. In this embodiment, even when such a wide PVA film is used, the occurrence of folding and wrinkles can be reduced.

(Swelling treatment)
The swelling treatment is performed for the purpose of removing foreign matter on the surface of the PVA film, removing the plasticizer in the PVA film, imparting easy dyeability in a subsequent process, and plasticizing the PVA film. The conditions for the swelling treatment are determined within a range in which these objects can be achieved, and in a range in which problems such as extreme dissolution and devitrification of the PVA film do not occur. A swelling process is performed by immersing an unstretched PVA-type film in the processing bath of temperature 10-50 degreeC, for example, Preferably 15-45 degreeC. When there are a plurality of swelling tanks, the temperature of the most downstream swelling tank in the conveyance direction is preferably equal to or lower than the temperature of the other swelling tank, and the temperature difference between the swelling tank on the most downstream side in the conveyance direction and the other swelling tank is preferably 0 to 20 ° C, more preferably 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 the PVA film swell in the width direction and wrinkles into the PVA film are likely to occur. It is preferable to transport the PVA film while removing wrinkles of the film. For the purpose of stabilizing the transport of PVA film in the bath, the water flow in the swelling bath is controlled with an underwater shower, or the edge of the PVA film is detected by an EPC device (Edge Position Control device: It is also useful to use a device for preventing meandering in combination. In this process, since the PVA film swells and expands in the transport direction of the PVA film, for example, in order to eliminate the slack of the PVA film in the transport direction, for example, rollers 60, 61, It is preferable to take measures such as controlling the speed of 62. Specifically, the initial width of the PVA-based film 2 is W, the final width of the PVA-based film 2 when leaving the second swelling tank 12 is X, and the cumulative stretching ratio in the first and second swelling tanks 11 and 12 is When A, −0.14 ≦ (W−X) /W/A≦0.05 (preferably −0.12 ≦ (W−X) /W/A≦0.02) is satisfied. The speed of the rollers 60, 61, 62 is controlled. Thereby, in the PVA-type film 2 after a swelling process, generation | occurrence | production of the folding of an edge part and generation | occurrence | production of the wrinkle of a center part can be reduced. In addition, it is preferable that the temperature of the 2nd swelling tank 12 shall be below the temperature of the 1st swelling tank 11, and by this, in the 2nd swelling tank 12 with low temperature, a neck-in can be advanced without applying a draw ratio. Thus, the tension and optical characteristics are improved. Since there are two swelling tanks 11 and 12, the PVA film 2 can be smoothly swelled and stretched.

  The treatment bath used in the swelling tanks 11 and 12 is an aqueous solution to which boric acid, chloride, other inorganic acids, other inorganic salts and the like are added in an amount of 0.01 to 10% by weight in addition to pure water. Can be. However, in the swelling tanks 11 and 12, pure water having substantially no dissolved component is preferably used.

(Dyeing process)
The dyeing process is performed for the purpose of adsorbing the dichroic dye on the PVA film. The processing conditions are determined within a range in which such an object can be achieved, and in a range in which problems such as extreme dissolution and devitrification of the PVA film do not occur.

  When iodine is used as the dichroic dye, for example, iodine is 0.003 to 0.2 parts by weight and iodine at a temperature of 10 to 50 ° C., preferably 20 to 40 ° C., and 100 parts by weight of water. The dyeing treatment is performed by immersing in an aqueous solution containing 0.1 to 10 parts by weight of potassium halide for 10 to 600 seconds, preferably 30 to 200 seconds. Instead of potassium iodide, other iodides such as zinc iodide may be used. Other iodides may be used in combination with potassium iodide. Furthermore, compounds other than iodide, such as boric acid, zinc chloride, cobalt chloride, etc. may coexist. Even when boric acid is added, it is distinguished from the subsequent boric acid treatment in that it contains iodine. Any bath containing 0.003 parts by weight or more of iodine with respect to 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 the dichroic dye, the dichroic dye is used at a temperature of, for example, 20 to 80 ° C., preferably 30 to 60 ° C., and 100 parts by weight of water. The dyeing treatment is performed by immersing in an aqueous solution containing 001 to 0.1 parts by weight for 10 to 600 seconds, preferably 20 to 300 seconds. The aqueous solution of the dichroic dye to be used may contain a dyeing assistant or the like, and may contain, for example, an inorganic salt such as sodium sulfate or a surfactant. Only one type of dichroic dye may be used, or two or more types of dichroic dyes may be used in combination according to the desired hue.

  In the dyeing process, as in the swelling process, an expander roll, a spiral roll, a crown roll, a cross guider, a bend bar, and the like may be appropriately installed in the dyeing bath and / or at the bath entrance / exit. In this dyeing process, uniaxial stretching can be simultaneously performed in the machine direction.

(Crosslinking treatment)
The crosslinking treatment is performed by immersing the PVA film dyed with the dichroic dye in an aqueous solution containing boric acid. The boric acid content in this aqueous solution is usually about 1 to 10 parts by weight per 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 with respect to 100 parts by weight of water. Examples of iodide include potassium iodide and zinc iodide. In addition, compounds other than iodide, such as zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, sodium sulfate, etc. may coexist.

  The cross-linking treatment is carried out for water resistance, hue adjustment (preventing bluishness, etc.) by cross-linking 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 crosslinking treatment for water resistance may be referred to by a name such as water resistance treatment or immobilization treatment. In some cases, the crosslinking treatment for hue adjustment is referred to as a complementary color treatment, a re-dyeing treatment, or the like.

  The crosslinking 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 crosslinking treatment for water resistance and the crosslinking treatment for adjusting the hue are not particularly distinguished, but are carried out under the following conditions. When swelling treatment is performed using an unstretched PVA-based film, followed by dyeing treatment and crosslinking treatment, and the crosslinking treatment aims at water resistance, boric acid is added to 100 parts by weight of water. A boric acid treatment bath containing 10 to 10 parts by weight and 1 to 20 parts by weight of iodide is used, and is usually performed 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, and more preferably 20 to 200 seconds. In addition, when performing a swelling process using the PVA-type film extended | stretched previously, and performing a dyeing process and a crosslinking process after that, the temperature of a boric-acid treatment bath is 50-85 degreeC normally, Preferably it is 55-80 degreeC.

  You may perform the crosslinking process for hue adjustment after the crosslinking process for water resistance. For example, when the dichroic dye is iodine, for the purpose of adjusting the hue, a boric acid treatment bath containing 1 to 5 parts by weight of boric acid and 3 to 30 parts by weight of iodide for 100 parts by weight of water is used. It is usually used at a temperature of 10 ° C to 45 ° C. The immersion time is usually 1 to 300 seconds, preferably 2 to 100 seconds.

  These cross-linking treatments may be performed a plurality of times and are usually performed 2 to 5 times in many cases. 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. The boric acid treatment for water resistance and the boric acid treatment for hue adjustment may be performed in a plurality of steps, respectively.

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

(Washing treatment)
After the crosslinking treatment, it is usually subjected to a water washing treatment. The water washing treatment is performed, for example, by immersing a PVA film treated with boric acid for water resistance and / or hue adjustment in water, spraying water as a shower, or using both immersion and spraying. 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.

(Drying process)
The PVA-based film after the water washing treatment is usually guided to a drying furnace and subjected to a 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 a plurality of drying furnaces are provided, the temperatures of the respective drying furnaces may be the same or different. When drying through multiple drying furnaces in order, the temperature should be increased sequentially from the front stage of the drying furnace to the rear stage of the drying furnace so that wrinkles do not enter the PVA film due to rapid drying. A gradient is preferred.

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

  Examples of the present invention will be described below, but the present invention is not limited to these examples. Table 1 shows the effect when the unstretched PVA film (thickness: 60 μm) was processed under different conditions in the first to seventh examples and the first and second comparative examples.

  Conditions include neck-in (W−X) / W, integrated draw ratio A, temperature of the first and second swelling tanks [° C.], and relational expression (W−X) / W / A. Effects include folding of the end of the PVA film, wrinkles at the center of the PVA film, and frequency of breakage of the PVA film [times / h].

  When the relational expression is within the range of −0.14 to 0.05, “◯” is indicated, and when the relational expression is outside the range of −0.14 to 0.05, “x” is indicated. 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 end folding could be reduced to 1 mm at each end. There are no wrinkles in the center. The breaking frequency is 0 times per hour.

  In the second embodiment, the relational expression is -0.118. At this time, end folding does not occur. There are no wrinkles in the center. The breaking frequency is 0 times per hour.

  In the third embodiment, the relational expression is -0.099. At this time, end folding does not occur. There are no wrinkles in the center. The breaking frequency is 0 times per hour.

  In the fourth embodiment, the relational expression is -0.062. At this time, end folding does not occur. There are no wrinkles in the center. The breaking frequency is 0 times per hour.

  In the fifth embodiment, the relational expression is -0.005. At this time, end folding does not occur. There are no wrinkles in the center. The breaking frequency is 0 times per hour.

  In the sixth embodiment, the relational expression is 0.016. At this time, end folding does not occur. There are no wrinkles in the center. The breaking frequency is 0 times per hour.

  In the seventh embodiment, the relational expression is 0.048. At this time, end folding does not occur. The wrinkles at the center could be reduced to one row. The breaking frequency is 0 times per hour.

  In the first comparative example, the relational expression is −0.150. At this time, end folding occurs at both ends of 2 mm, which is outside the allowable range. There are no wrinkles in the center. The breaking frequency is 0.33 times per hour.

  In the second comparative example, the relational expression is 0.059. At this time, end folding does not occur. There are three rows of wrinkles in the center, which is outside the allowable range. The breaking frequency 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 folding or wrinkle at the center, and there is no problem of breakage frequency. On the other hand, in the first and second comparative examples, the relational expression is out of the range of −0.14 to 0.05, there are problems of end folding and central wrinkles, and there is also a problem of breaking frequency. In particular, in the second to sixth embodiments, the relational expression is in the range of -0.12 to 0.02, and the end folding and the central wrinkle are not generated at all.

DESCRIPTION OF SYMBOLS 1 Original fabric roll 2 PVA-type film 3 Polarizing film 5 Polarizing film manufacturing apparatus 11 1st swelling tank 12 2nd swelling tank 20 Dyeing tank 30 Crosslinking tank 40 Washing tank 50 Drying furnace 60 Feeding roller 61 1st extending | stretching roller 62 2nd extending | stretching roller

Claims (5)

A method of producing a polarizing film by sequentially performing a swelling treatment and a dyeing treatment on a polyvinyl alcohol film,
The swelling treatment is performed by sequentially passing through the n (where n is a natural number) swelling tanks while stretching the polyvinyl alcohol film.
In the swelling treatment, the initial width of the polyvinyl alcohol film is W, the final width of the polyvinyl alcohol film when leaving the n-th swelling tank is X, and the cumulative draw ratio in all the swelling tanks is A. When
A method for producing a polarizing film satisfying −0.14 ≦ (W−X) /W/A≦0.05.   The manufacturing method of the polarizing film of Claim 1 which satisfy | fills -0.12 <= (W-X) / W / A <= 0.02.   The method for producing a polarizing film according to claim 1, wherein the number of swelling tanks is two. n is 2 or more,
The temperature of the nth swelling tank of the conveyance direction of the said polyvinyl alcohol-type film is any one of Claim 1 to 3 below the temperature of the kth (1 <= k <= (n-1)) swelling tank. The manufacturing method of the polarizing film of description.   The manufacturing method of the polarizing film as described in any one of Claim 1 to 4 whose initial width W of the said polyvinyl alcohol-type film is 400 mm or more.

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