JP7061712B2 - Method for manufacturing polarizing film and polyvinyl alcohol-based film - Google Patents

Description

The present invention relates to a method for producing a polarizing film and a polyvinyl alcohol-based film.

As described in Patent Documents 1 and 2, the polarizing film is produced by subjecting a polyvinyl alcohol-based film to, for example, a treatment such as swelling, dyeing, crosslinking, stretching, washing, and drying. In the treatment of the polyvinyl alcohol-based film, the polyvinyl alcohol-based film may be immersed in the treatment liquid. For example, in the swelling treatment, a polyvinyl alcohol-based film is immersed in water, which is a treatment liquid.

Japanese Unexamined Patent Publication No. 2016-48382 Japanese Unexamined Patent Publication No. 2017-102438

In the conventional production of a polarizing film, the film may be broken and the production process may not be stable.

Therefore, an object of the present invention is to provide a method for producing a polarizing film and a polyvinyl alcohol-based film capable of producing a polarizing film in a stable process.

The inventors of the present application have found that when the polarizing film is manufactured, if the fluctuation range of the width change rate before and after the immersion is too large, the film breaks. Therefore, the following method for manufacturing a polarizing film was completed.

The method for producing a polarizing film according to one aspect of the present invention is a method for producing a polarizing film while transporting a polyvinyl alcohol-based film, in which the polyvinyl alcohol-based film is put into a treatment liquid on a long polyvinyl alcohol-based film. The dipping step is provided, and in the dipping step, the fluctuation range (%) of the width change rate (%) in the width direction of the polyvinyl alcohol-based film before and after being immersed in the treatment liquid is determined. It is 0.5% or less.

In the above manufacturing method, the fluctuation width (%) of the width change rate (%) in the width direction of the polyvinyl alcohol-based film in the dipping step is 0.5% or less. In this case, since the fluctuation range is small, the film is less likely to break during the production of the polarizing film, and the polarizing film can be produced in a stable process.

In the dipping step, the polyvinyl alcohol-based film may be immersed in the treatment liquid while applying a constant tension by using the nip roll before and after the immersion in the treatment liquid.

In the dipping step, the polyvinyl alcohol-based film may be immersed in the treatment liquid while maintaining a constant rotation speed ratio of the nip roll before and after the immersion in the treatment liquid.

The dipping step may be performed in the swelling treatment for the polyvinyl alcohol-based film. The swelling treatment is carried out in the early stages of manufacturing the polarizing film. Therefore, the width of the polyvinyl alcohol-based film is likely to change during the swelling treatment. Therefore, it is effective to carry out the swelling treatment in the dipping step.

The width change rate may be calculated by the formula (1), and the width fluctuation width may be calculated by the formula (2).
Width change rate = | (W2-W1) / W1 | × 100 ... (1)
Fluctuation width = maximum value of width change rate-minimum value of width change rate ... (2)
In the formula (1), W1 [mm] represents the width of the polyvinyl alcohol-based film before being immersed in the treatment liquid, and W2 [mm] is the polyvinyl alcohol after being immersed in the treatment liquid. Represents the width of the system film. In equation (2), the maximum value of the width change rate and the minimum value of the width change rate are the values when the width change rate is continuously calculated for 60 seconds or longer.)

The polyvinyl alcohol-based film according to another aspect of the present invention is immersed in water under conditions including a predetermined temperature and a predetermined immersion time while transporting a long polyvinyl alcohol-based film. The fluctuation range (%) of the width change rate (%) in the width direction of the polyvinyl alcohol-based film before and after is 0.5% or less, and the predetermined temperature is a temperature selected from the range of 15 ° C to 40 ° C. The predetermined immersion time is the immersion time selected from the range of 20 seconds to 120 seconds, and the fluctuation range (%) is the width when the width change rate is continuously acquired for 60 seconds or more. It is the difference between the maximum value of the rate of change and the minimum value of the rate of change.

The polyvinyl alcohol-based film is used, for example, in the production of a polarizing film. The method for producing a polarizing film includes a dipping step of immersing a long polyvinyl alcohol-based film in a treatment liquid. When the dipping step is performed using the polyvinyl alcohol-based film, the fluctuation range of the width change rate (%) in the width direction of the polyvinyl alcohol-based film before and after the polyvinyl alcohol-based film is immersed in the treatment liquid (%). %) Is likely to be 0.5% or less. In this case, since the fluctuation range is small, the film is less likely to break during the production of the polarizing film, and the polarizing film can be produced in a stable process.

The fluctuation range (%) includes the predetermined temperature and the predetermined immersion time while transporting the polyvinyl alcohol-based film while maintaining the tension selected from the range of 5 N / m to 100 N / m. And, it may be the fluctuation range when it is immersed in the above water.

The fluctuation range (%) is such that the polyvinyl alcohol-based film is conveyed in a state where the rotation speed ratio of the nip roll before and after immersion in water is maintained at the rotation speed ratio selected within the range of 1.1 to 4.0. However, it may have a fluctuation range when immersed in the water under the conditions including the predetermined temperature and the predetermined immersion time.

The fluctuation range (%) may be 0.3% or less.

The length of the polyvinyl alcohol-based film in the long direction is, for example, 1000 m or more.

According to the present invention, the polarizing film can be manufactured in a stable process.

FIG. 1 is a schematic diagram for explaining a method for manufacturing a polarizing film according to an embodiment. FIG. 2 is a drawing for explaining a dipping process included in the method for manufacturing a polarizing film. FIG. 3 is a drawing for explaining an example of a method of acquiring a width change rate and a fluctuation width.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference numerals, and duplicate description will be omitted. The dimensional ratios in the drawings do not always match those described.

(First Embodiment)
As the first embodiment, a method for manufacturing a polarizing film will be described. FIG. 1 is a schematic diagram illustrating an example of a method for manufacturing a polarizing film according to an embodiment of the present invention.

In the first embodiment, while transporting a long polyvinyl alcohol-based film 2 (hereinafter, simply referred to as “film 2”), the film 2 being transported is subjected to swelling treatment, dyeing treatment, cross-linking treatment, stretching treatment, and drying. By applying the treatment, the polarizing film 4 is manufactured. The stretching treatment may be applied to the film 2 during any one treatment (for example, a crosslinking treatment) or in parallel while performing a plurality of treatments.

The material of the film 2 may be any known polyvinyl alcohol-based resin used for producing a polarizing film, and is preferably a saponified polyvinyl alcohol-based resin. The range of the degree of saponification is preferably 80.0 to 100.0 mol%, more preferably 90.0 to 99.5 mol%, and 93.0 to 99.5 mol%. Is even more preferable. The degree of saponification is a numerical value defined by the formula: degree of saponification (mol%) = (number of hydroxyl groups) / (number of hydroxyl groups + number of acetic acid groups) × 100, and is defined by JIS K 6726 (1994). It can be obtained by the method used. The average degree of polymerization of the polyvinyl alcohol-based resin is preferably 100 to 10000, more preferably 1000 to 10000. The average degree of polymerization is a numerical value obtained by the method defined by JIS K 6726 (1994).

The length of the film 2 in the long direction is, for example, 1000 m or more. When the length of the film 2 in the long direction is 1000 m or more, the length of the film 2 in the long direction is, for example, 30,000 m or less, preferably 20,000 m or less. An example of the length of the film 2 in the width direction (direction orthogonal to the long direction) is 1300 mm to 5000 mm. An example of the thickness of the film 2 is 10 μm to 100 μm.

The film 2 is not particularly limited and can be produced by a known method such as a melt extrusion method or a solvent casting method. For example, the film 2 is formed by applying a polyvinyl alcohol-based resin solution on a base film made of a thermoplastic resin (polyolefin resin, (meth) acrylic resin, etc.) and drying the resin solution. It can be obtained by performing molding and peeling the obtained film 2 from the base film.

The substrate film may be provided with a primer layer, if necessary. The thickness of the base film can be appropriately determined, but is preferably 1 μm to 500 μm, more preferably 1 μm to 300 μm. The width and length of the base film can be appropriately determined according to the size of the target film 2.

The polyvinyl alcohol-based resin solution can be obtained by dissolving the above-mentioned polyvinyl alcohol-based resin in water, alcohol or the like. The viscosity of the solution is preferably 500 cps to 10000 cps, more preferably 1000 cps to 7000 cps, still more preferably 1000 cps to 5000 cps.

The coating of the polyvinyl alcohol-based resin solution can be appropriately selected from known methods such as a roll coating method such as gravure coating; a die coating method; The film thickness of the solution of the polyvinyl alcohol-based resin to be coated can be, for example, 50 μm to 1000 μm.

The drying can be carried out at a resin temperature of usually 30 ° C. to 200 ° C. and a drying time of 2 minutes to 24 hours. If the film thickness of the polyvinyl alcohol-based resin solution to be applied is thick, dry it with hot air of 80 ° C or higher for 1 to 10 minutes to remove some water, and then dry it with hot air of 30 ° C to less than 50 ° C. You can also let it.

The coating of the polyvinyl alcohol-based resin solution, drying, and peeling of the film 2 from the base film can be continuously performed while transporting the base film.

In the above drying, a tension of 45 N or more per 1 m in the width direction of the base film may be applied to the base film in the transport direction of the base film (long direction of the base film). In the above drying, the dimensional change rate in the long direction of the base film before and after drying may be stretched by more than 0%, that is, tension may be applied in the long direction so that plastic deformation occurs. The dimensional change rate may be 0.01% or more, or 0.1% or more. Further, the dimensional change rate in the drying step is preferably 5% or less, and more preferably 1% or less.

The thickness of the obtained film 2 can be 5 μm to 100 μm. The width of the polyvinyl alcohol-based resin layer (film 2) after drying can be 400 mm to 5000 mm.

FIG. 1 illustrates a case where a film 2 is prepared as an original roll 6 and the film 2 unwound from the original roll 6 is subjected to each treatment to obtain a polarizing film 4. When the film 2 is manufactured by the above method (melt extrusion method, solvent casting method, etc.), for example, the film 2 produced by the above method (melt extrusion method, solvent casting method, etc.) is continuously conveyed and the film 2 is conveyed. Each of the above-mentioned treatments may be carried out during transportation.

An example of a method for manufacturing the polarizing film 4 will be described based on the form shown in FIG. First, the outline of the manufacturing apparatus 10 for the polarizing film 4 will be described. The manufacturing apparatus 10 includes a plurality of nip rolls 11, a plurality of guide rolls 12, a swelling treatment unit 13 ₁ , a dyeing treatment unit ₁₃₂ , a cross-linking treatment unit 133 _, a cleaning treatment unit 134, and a drying treatment unit ₁₃ . ₅ and.

The plurality of nip rolls 11 and the plurality of guide rolls 12 form a transport mechanism for the film 2. By appropriately arranging the plurality of nip rolls 11 and the plurality of guide rolls 12, the transport path of the film 2 is configured.

The swelling treatment unit 13 ₁ is a portion for performing a swelling treatment on the film 2. The swelling treatment unit ₁₃₁ has a treatment tank in which a treatment liquid for swelling treatment is stored. By immersing the film 2 in the treatment liquid of the swelling treatment unit ₁₃₁ , the swelling treatment is performed on the film 2. In the first embodiment, the nip roll 11 and the two guide rolls 12 arranged before and after the film 2 is immersed in the treatment liquid form a transport path for the film for immersing the film 2 in the treatment liquid.

The swelling treatment is performed for the purpose of removing foreign matter on the surface of the film 2, removing the plasticizer in the film 2, imparting easy dyeability in a subsequent step, and plasticizing the film 2. The conditions for the swelling treatment can be determined within a range in which these objectives can be achieved and within a range in which defects such as extreme dissolution and devitrification of the film 2 do not occur. In the swelling treatment unit ₁₃₁ , the swelling treatment is performed by immersing the film 2 in a treatment liquid having a temperature of, for example, 10 ° C to 50 ° C, preferably 15 ° C to 40 ° C. The swelling treatment time (immersion time) is about 5 seconds to 300 seconds, preferably about 20 seconds to 120 seconds. An example of the treatment liquid in the swelling treatment unit ₁₃₁ is water. Therefore, the swelling treatment can also serve as a washing treatment of the film 2.

The dyeing treatment unit 132 is a portion for dyeing the film ₂ . _The dyeing treatment unit 132 has a treatment tank in which a treatment liquid for a dyeing treatment is stored. By immersing the film ₂ in the treatment liquid of the dyeing treatment unit 132, the film 2 is dyed. In the first embodiment, the nip roll 11 and the two guide rolls 12 arranged before and after the film 2 is immersed in the treatment liquid form a transport path for the film for immersing the film 2 in the treatment liquid.

The treatment liquid contained in the dyeing treatment unit 132 in the first embodiment is an aqueous solution of a dichroic dye, and in the dyeing treatment, the film ₂ is dyed with the dichroic dye. The usual dyeing treatment with a dichroic dye is performed for the purpose of adsorbing the dichroic dye on the film 2. The treatment conditions are determined according to the desired optical characteristics within a range in which such an object can be achieved and within a range in which defects such as extreme dissolution and devitrification of the film 2 do not occur. Examples of dichroic dyes used for dyeing are iodine and dichroic dyes.

When iodine is used as the dichroic dye, for example, at a temperature of 10 ° C to 50 ° C, preferably 15 ° C to 40 ° C, and with respect to 100 parts by weight of water, iodine is added in an amount of 0.003 parts to 0.2 parts by weight. The dyeing treatment is performed by immersing the film 2 in an aqueous solution containing 0.1 parts by weight to 10 parts by weight of potassium iodide for 10 seconds to 600 seconds, preferably 30 seconds to 300 seconds. Other iodides, such as zinc iodide, may be used in place of potassium iodide. Other iodides may be used in combination with potassium iodide. Further, compounds other than iodide, boric acid, zinc chloride, cobalt chloride and the like may coexist. Any treatment liquid containing 0.003 parts by weight or more of iodine with respect to 100 parts by weight of water can be regarded as a treatment liquid for dyeing.

When a dichroic dye is used as the dichroic dye, for example, at a temperature of 20 ° C to 80 ° C, preferably 30 ° C to 60 ° C, and 0.001 weight of the dichroic dye with respect to 100 parts by weight of water. The dyeing treatment is performed by immersing the film 2 in an aqueous solution containing 10 parts to 0.1 parts by weight for 10 seconds to 600 seconds, preferably 20 seconds to 300 seconds. The aqueous solution of the bicolor dye to be used may contain a dyeing aid or the like, or may contain an inorganic salt such as sodium sulfate, a surfactant or the like. Only one kind of dichroic dye may be used, or two or more kinds of dichroic dyes may be used in combination depending on the desired hue.

The cross-linking processing unit ₁₃₃ is a portion for performing a cross-linking treatment on the film 2. The cross _- linking treatment unit 133 has a treatment tank in which a treatment liquid for the cross-linking treatment is stored. By immersing the film 2 in the treatment liquid contained in the cross-linking treatment unit 133 _, the cross-linking treatment is performed on the film 2. In the first embodiment, the nip roll 11 and the two guide rolls 12 arranged before and after the film 2 is immersed in the treatment liquid form a transport path for the film for immersing the film 2 in the treatment liquid.

The cross-linking treatment is a treatment performed for the purpose of making the film water resistant by cross-linking and adjusting the hue (preventing the film 2 from becoming bluish, etc.).

The treatment liquid used in the crosslinking treatment unit 133 is _, for example, an aqueous solution containing about 1 part by weight to 10 parts by weight of boric acid with respect to 100 parts by weight of water. When the dichroic dye used in the dyeing treatment is iodine, the treatment liquid used in the cross _- linking treatment unit 133 preferably contains iodide in addition to boric acid, and the amount thereof is based on 100 parts by weight of water. For example, it is 1 part by weight to 30 parts by weight. Examples of the iodide include potassium iodide and zinc iodide. Compounds other than iodide, zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, sodium sulfate and the like may coexist.

In the cross-linking treatment in the cross _- linking treatment unit 133, the concentrations of boric acid and iodide and the temperature of the treatment liquid can be appropriately changed depending on the purpose.

For example, when the purpose of the crosslinking treatment is to make the polyvinyl alcohol-based resin film water resistant by crosslinking, and the polyvinyl alcohol-based resin film is subjected to a swelling treatment, a dyeing treatment, and a crosslinking treatment in this order, the crosslinking agent-containing liquid of the treatment liquid has, for example, a concentration by weight. It is an aqueous solution of boric acid / iodide / water = 3 to 10/1 to 20/100 in ratio. If necessary, other cross-linking agents such as glyoxal or glutaraldehyde may be used instead of boric acid, or boric acid and other cross-linking agents may be used in combination. The temperature of the treatment liquid when the film 2 is immersed is usually about 50 ° C. to 70 ° C., preferably 53 ° C. to 65 ° C., and the immersion time of the film 2 is usually about 10 seconds to 600 seconds, preferably about 10 seconds to 600 seconds. It is 20 seconds to 300 seconds, more preferably 20 seconds to 200 seconds. When the film 2 previously stretched before the swelling treatment is subjected to the dyeing treatment and the crosslinking treatment in this order, the temperature of the treatment liquid is usually about 50 ° C. to 85 ° C., preferably 55 ° C. to 80 ° C.

The purpose of the cross-linking treatment is to adjust the hue. For example, when iodine is used as the dichroic dye, a cross-linking agent-containing liquid having a concentration of boric acid / iodide / water = 1 to 5/3 to 30/100 in weight ratio. Can be used as a treatment liquid. The temperature of the treatment liquid when the film 2 is immersed is usually about 10 to 45 ° C., and the immersion time of the film 2 is usually about 1 to 300 seconds, preferably about 2 to 100 seconds.

The cleaning treatment unit 134 is a portion for performing a cleaning treatment on the film ₂ after _the crosslinking treatment. The cleaning processing unit ₁₃₄ has a processing tank in which a processing liquid for cleaning processing is stored. By immersing the film ₂ in the treatment liquid contained in the cleaning treatment unit 134, the film 2 is subjected to the cleaning treatment. In the first embodiment, the nip roll 11 and the two guide rolls 12 arranged before and after the film 2 is immersed in the treatment liquid form a transport path for the film for immersing the film 2 in the treatment liquid. Examples of the treatment liquid in the cleaning treatment include water, an aqueous solution containing potassium iodide, and an aqueous solution containing boric acid. The temperature of the treatment liquid is usually about 2 ° C. to 40 ° C., and the treatment time (immersion time) is usually about 2 seconds to 120 seconds.

The drying treatment unit ₁₃₅ is a portion for drying the film 2. In the first embodiment, the drying processing unit ₁₃₅ is a drying device. The film ₂ cleaned by the cleaning processing unit 134 is carried into the drying processing unit 135, and the film ₂ is dried while the film ₂ passes through the drying processing unit 135. In the first embodiment, the nip rolls ₁₁ arranged before and after the drying treatment unit 135 form a transport path for the film for immersing the film 2 in the treatment liquid. A guide roll 12 may be appropriately arranged in the drying processing unit ₁₃₅ in order to support and convey the film 2. Drying by the drying processing unit ₁₃₅ is performed for about 30 seconds to about 600 seconds in the drying processing unit ₁₃₅ kept at a temperature of about 40 ° C. to 100 ° C. FIG. 1 _{schematically} shows the drying processing unit 135. The drying treatment unit ₁₃₅ is not particularly limited as long as it can dry the moisture adhering to the film 2, and may be a known one that is usually used in the production of a polarizing film.

In the manufacturing apparatus 10, a stretching process is performed in which the film 2 is uniaxially stretched by utilizing the difference in rotation speed between at least two nip rolls 11 (upstream side nip roll 11 and downstream side nip roll 11) in the plurality of nip rolls 11. In this case, the two nip rolls 11 that contribute to the uniaxial stretching process function as the stretching process section.

For example, a stretching process may be performed in which the uniaxial stretching process is performed by utilizing the difference in rotational speed between the nip roll ₁₁ arranged before the crosslinking processing section 133 and the nip roll ₁₁ arranged after the crosslinking processing section 133. In this case, since the stretching treatment is performed in parallel with the cross-linking treatment, the cross-linking treatment unit ₁₃₃ also functions as the stretching treatment unit. The stretching treatment is also effective for suppressing the occurrence of wrinkles in the film 2.

In addition to mainly performing stretching treatment using two nip rolls 11 arranged before and after one processing section (for example, the cross _- linking treatment section 133 described above), gradually stretching using another nip roll 11 Further treatment may be performed.

The manufacturing apparatus 10 may separately have a stretching treatment unit for performing the stretching treatment. In this case, the stretching treatment section is arranged, for example, in the subsequent stage of the crosslinking treatment section 133 ₍ for example, between the crosslinking treatment section ₁₃₃ and the cleaning treatment section ₁₃₄ ).

The manufacturing apparatus 10 may have a plurality of treatment units of at _least one of a swelling treatment unit 13 ₁ , a dyeing treatment unit ₁₃₂ , a cross-linking treatment unit 133 _, a cleaning treatment unit ₁₃₄ , and a drying treatment unit 135. For example, the manufacturing apparatus 10 may include a plurality of cross _- linking processing units 133. The manufacturing apparatus 10 may include a stretching processing unit.

An example of a method for manufacturing the polarizing film 4 using the manufacturing apparatus 10 will be described. First, the film 2 is unwound from the original roll 6. The unwound film 2 is conveyed in the elongated direction of the film 2 along a conveying path formed by the plurality of nip rolls 11 and the plurality of guide rolls 12. An example of the transport speed may be 1 m / min to 60 m / min, or 1.5 m / min to 50 m / min. The transport path of the film 2 is provided with a swelling treatment unit ₁₃₁ , a dyeing treatment unit 132, a cross _- linking treatment unit 133 _, a cleaning treatment unit ₁₃₄ , and a drying treatment unit 135 from the raw fabric roll ₆ side. Further, as described above, at least two nip rolls 11 also have a function as a stretching processing unit. Therefore, by transporting the film 2 along the transport path, the film 2 is subjected to a swelling treatment, a dyeing treatment, a cross-linking treatment, a cleaning treatment, a drying treatment, and a stretching treatment. As a result, the linear polarization characteristic is imparted to the film 2, and the polarizing film 4 is obtained.

The swelling treatment, dyeing treatment, cross-linking treatment and cleaning treatment are carried out by immersing the film 2 in the treatment liquid. Therefore, the method for producing the polarizing film 4 includes a plurality of dipping steps (steps of dipping the film 2 in the treatment liquid). In other words, in the plurality of dipping steps, a swelling treatment, a dyeing treatment, a cross-linking treatment and a cleaning treatment are carried out. In the method for producing the polarizing film 4 of the first embodiment, at least one of the plurality of dipping steps corresponding to the swelling treatment, the dyeing treatment, the cross-linking treatment, and the cleaning treatment is described with reference to FIG. (Hereinafter, for convenience of explanation, it is referred to as "immersion step A").

FIG. 2 is a schematic diagram for explaining the dipping step A. FIG. 2 schematically shows a state in which the treatment liquid 8 is stored in the treatment tank and the film 2 is immersed in the treatment liquid 8 while being conveyed. The treatment liquid 8 is a treatment liquid corresponding to the treatment carried out in the dipping step A among the swelling treatment, the dyeing treatment, the crosslinking treatment and the cleaning treatment. Similar to each processing section shown in FIG. 1, the transport path of the film 2 is formed by the nip roll 11 and the two guide rolls before and after the treatment liquid 8. In the transport path, the nip roll 11 through which the film 2 before being immersed in the treatment liquid 8 passes is referred to as a nip roll 11 _UP , and the nip roll 11 through which the film 2 passes after the film 2 is immersed in the treatment liquid 8 is referred to as a nip roll 11 _DOWN. Also called.

In the dipping step A, the film 2 can be immersed in the treatment liquid while maintaining the tension applied to the film 2.

The tension in the dipping step A is usually 3 N / m to 2000 N / m, preferably 5 N / m to 1500 N / m. When the dipping step is a swelling step, it is more preferably 3 N / m to 200 N / m, still more preferably 5 N / m to 100 N / m.

In the dipping step A, for example, the nip roll 11 _UP and the nip roll 11 _DOWN shown in FIG. 2 may be used to apply a constant tension to the film 2. For example, a constant tension can be applied by adjusting the rotation speed of the nip roll 11 _UP and the rotation speed of the nip roll 11 _DOWN . By applying a constant tension in this way, the film 2 can be immersed in the treatment liquid 8 while maintaining the tension.

In order to adjust the tension, for example, the tension may be detected by a tension detector. As the tension detector, a commercially available one can be used. For example, tension is detected by a principle such as a differential transformer method or a strain gauge method. The tension is continuously monitored by the tension detector. For example, the detected tension value is sent to the control system. In the control system, when the detected tension value deviates from the set value, the amount is measured and a signal is sent to the drive device (for example, a servo motor) that drives the nip roll 11 _DOWN to control the drive, and the tension value is changed. Try to keep it constant.

In the dipping step A, the film 2 may be immersed in the processing liquid while maintaining a constant rotation speed ratio of the nip roll before and after the immersion in the treatment liquid 8. The rotation speed ratio is the ratio of the rotation speed of the nip roll 11 _UP before being immersed in the treatment liquid 8 and the rotation speed of the nip roll 11 _DOWN after being immersed in the treatment liquid 8. In this way, by immersing the film 2 in the treatment liquid while maintaining the rotation speed ratio constant, the film 2 can be immersed in the treatment liquid while maintaining the tension.

In the dipping step A, the following condition α is satisfied.
<Condition α>
The fluctuation width (%) of the width change rate (%) in the width direction of the film 2 before and after the film 2 is immersed in the treatment liquid 8 is 0.5% or less.

In one embodiment, the width change rate and the fluctuation range are calculated by the formulas (1) and (2).
Width change rate = | (W2-W1) / W1 | × 100 ... (1)
Fluctuation width = maximum value of width change rate-minimum value of width change rate ... (2)
In the formula (1), W1 [mm] represents the width of the film 2 before being immersed in the treatment liquid 8, and W2 [mm] represents the width of the film 2 after being immersed in the treatment liquid 8.
In the equation (2), the maximum value of the width change rate and the minimum value of the width change rate are values when the width change rate is continuously acquired, for example, for a certain period of time.
The fixed period is, for example, 60 seconds or longer, preferably 1 hour or longer, and more preferably 24 hours or longer. The upper limit of the fixed period is the time when the dipping step A is carried out with respect to the total length of the film 2, and can be determined by the total length of the film 2 and the transport speed. For example, the upper limit is 200 hours.

The width W1 of the film 2 before the film 2 is immersed in the treatment liquid 8 is, for example, the width of the film 2 at the position x1 as shown in FIG. In FIG. 2, the position x1 is the position after the film 2 has passed through the nip roll 11 _UP . The width W2 of the film 2 after the film 2 is immersed in the treatment liquid 8 is, for example, the width of the film 2 at the position x2 shown in FIG. The position x2 indicates the position after the film 2 has passed through the nip roll 11 _DOWN .

In order to acquire (or calculate) the width change rate and the fluctuation width, the manufacturing apparatus 10 has two width measuring instruments 30 shown in FIG. 3 and a calculation unit 40 for the processing tank in which the immersion step A is performed. May have.

An example of a method of acquiring the width change rate and the volatility using the width measuring device 30 and the calculation unit 40 will be described. Hereinafter, a series of steps from the measurement of the width W1 and the width W2 to the acquisition of the width change rate and the volatility may be collectively referred to as a “monitoring step”.

Each of the two width measuring instruments 30 is a device that continuously measures the width of the film 2. One of the two width measuring instruments 30 is a width measuring instrument (hereinafter referred to as "width measuring instrument 30 _UP ") for measuring the width W1 of the film 2 before the film 2 is immersed in the treatment liquid 8. The other of the two width measuring instruments 30 is a measuring instrument (hereinafter referred to as "width measuring instrument 30 _DOWN ") for measuring the width W2 of the film 2 after the film 2 is immersed in the treatment liquid 8. ..

Each of the width measuring instrument 30 _UP and the width measuring instrument 30 _DOWN has two end detection units 31. One of the two end detection units 31 is a detection unit that detects one end 2a in the width direction of the film 2, and the other is the other end 2b (with the end 2a) in the width direction of the film 2. It is a detection unit that detects the opposite end). Each end detection unit 31 detects the end of the film 2, for example, optically and non-contactly. Each end detection unit 31 may be configured to be able to acquire an image of the end to be detected and its vicinity. For example, the end detection unit 31 may have an image pickup unit such as a camera.

The calculation unit 40 calculates the width W1 based on the detection results of the two end detection units 31 of the width measuring device 30 _UP , and the detection result of the two end detection units 31 of the width measuring device 30 _DOWN . The width W2 is calculated based on. For example, the calculation unit 40 identifies the positions of the ends 2a and 2b based on the detection results (for example, image data) of the two end detection units 31 possessed by the width measuring device 30 _UP , thereby performing the width W1 and the width W1 and The width W2 is calculated.

The calculation unit 40 calculates the width change rate from the width W1, the width W2, and the formula (1), and calculates the fluctuation width from the formula (2).

In the first embodiment, the width W1 may be measured at the position x1, and then the width W2 may be measured when the film portion where the width W1 is measured is conveyed to the position x2, or the width W1 at the position x1. And the width W2 at the position x2 may be measured at the same timing (that is, at the same time). The "same timing" may have a slight deviation within a range that does not deviate from the gist of the present invention. Although not particularly limited depending on the transport speed, the time difference between the measurement at the position x1 and the measurement at the position x2 may be about 1 minute or less, 30 seconds or less, or 20 seconds. It may be within 10 seconds.

The monitoring process is preferably carried out by automation. In the first embodiment, in order to efficiently carry out automation, it is preferable to measure the width W1 at the position x1 and the width W2 at the position x2 at the same timing.

The above condition α can be realized, for example, by adjusting the temperature of the treatment liquid 8, the immersion time (treatment time), the tension applied to the film 2, and the like.

In the monitoring in the monitoring process, when the fluctuation range exceeds 0.5%, the width changes so as to satisfy the above condition α by adjusting each processing condition etc. according to the processing in which the monitoring process is performed. The rate can be adjusted. For example, the temperature of the treatment liquid 8, the immersion time (treatment time), the tension applied to the film 2, and the like may be adjusted so as to satisfy the above condition α, or the polarizing film 4 may be manufactured. The film 2 may be replaced. More specifically, in the monitoring step during the swelling treatment, when the width change rate is small, the fluctuation width can be reduced by means such as raising the temperature of the treatment liquid, lowering the tension, or lengthening the treatment time. On the other hand, when the width change rate is large, the fluctuation width can be reduced by means such as lowering the temperature of the treatment liquid, increasing the tension, and shortening the treatment time. When the film 2 is immersed in the treatment liquid in the cross-linking step as the dipping step A and the monitoring step is carried out, in addition to the above manufacturing conditions (temperature, tension, treatment time), the content of the cross-linking agent and the guide roll The fluctuation range can also be adjusted by the arrangement of the above.

The method for producing the polarizing film 4 includes a dipping step A that satisfies the above condition α. Therefore, in the dipping step A, even if the film 2 is immersed in the treatment liquid 8, the fluctuation range of the width change rate of the film 2 is 0.5% or less. In this case, since the volatility of the film 2 is small, the film 2 is less likely to break, for example, during the dipping step A or in a step after the dipping step A. As a result, the polarizing film 4 can be stably manufactured. Since the volatility of the film 2 is small, defects and poor appearance due to the width change can be reduced. As a result, a high-quality polarizing film 4 can be manufactured.

It is effective that the dipping step A is carried out in the swelling treatment. As shown in FIG. 1, the swelling treatment is a treatment performed on the upstream side (initial stage in the manufacturing process) among a plurality of treatments sequentially performed on the film 2. Therefore, since the width of the film 2 is likely to change in the swelling treatment, the quality of the manufactured polarizing film 4 can be improved by performing the dipping step A in the swelling treatment. Further, the film 2 is less likely to break during the swelling treatment and the subsequent treatments. When the dipping step A is carried out by the swelling treatment, the temperature of the treatment liquid (for example, water) is preferably 15 ° C. to 40 ° C., and the dipping time is preferably 20 seconds to 120 seconds.

As described above, the dipping step A satisfying the condition α may be carried out in at least one dipping step among a plurality of dipping steps corresponding to the swelling treatment, the dyeing treatment, the cross-linking treatment and the cleaning treatment.

(Second Embodiment)
As a second embodiment, a long polyvinyl alcohol-based film 2 will be described. Also in the second embodiment, the polyvinyl alcohol-based film 2 is simply referred to as “film 2”. Examples of the material, length, and thickness of the film 2 according to the second embodiment are the same as those of the first embodiment.

The film 2 is a film that satisfies the following condition β.
<Condition β>
When the film 2 is immersed in water at a predetermined temperature and a predetermined immersion time while transporting the polyvinyl alcohol-based film, the fluctuation width (%) of the width change rate (%) of the film 2 in the width direction before and after the immersion is (%). Is a film having a value of 0.5% or less.
The fluctuation range (%) under the condition β is preferably 0.3% or less from the viewpoint of further suppressing color unevenness of the polarizing film produced by using the film 2.

The predetermined temperature is a temperature selected from the range of 15 ° C. to 40 ° C., and the predetermined immersion time is a immersion time selected from the range of 20 seconds to 120 seconds.
The width change rate (%) can be calculated in the same manner as in the above equation (1), for example. The water in the description regarding the above condition β corresponds to the treatment liquid 8 in the dipping step A of the first embodiment.
The fluctuation width (%) is the difference between the maximum value of the width change rate and the minimum value of the width change rate when the width change rate is continuously acquired for 60 seconds or longer.
Under the above condition β, the polyvinyl alcohol-based film is usually conveyed in a state where the tension is constant or a state where the rotation speed ratio of the nip roll before and after immersion in water is constant. When the polyvinyl alcohol-based film is conveyed with a constant tension, it is usually kept at a tension selected from the range of 5 N / m to 100 N / m. When the polyvinyl alcohol-based film is transported in a state where the rotation speed ratio before and after immersion in water is constant, it is usually maintained at a rotation speed ratio selected in the range of 1.1 to 4.0. .. The rotation speed ratio is the ratio of the rotation speed of the nip roll before being immersed in water to the rotation speed of the nip roll after being immersed in water.

For example, in the dipping step A described with reference to FIG. 2, the treatment liquid 8 is water, the film 2 is immersed in the treatment liquid 8 at the predetermined temperature and the predetermined dipping time, and the width is the same as in the case of the dipping step A. By calculating the fluctuation range (%) of the rate of change (%), it can be verified whether or not the film 2 satisfies the condition β. As described above, when the film 2 is conveyed in a state where the tension is constant or the rotation speed ratio is constant before and after immersion in water, a method for keeping the tension constant or the rotation before and after immersion in water. The method for keeping the speed ratio constant may be the same as in the case of the immersion step A.

The film 2 can be manufactured by, for example, a melt extrusion method, a solvent casting method, or the like by adjusting the production conditions so as to satisfy the above condition β. When the film 2 is prepared by a method including a step of applying and drying the above-mentioned polyvinyl alcohol-based resin solution, it is easy to prepare a film satisfying the above-mentioned condition β, and the temperature is 30 ° C. or higher and lower than 50 ° C. It is preferable to dry at the temperature of 30 minutes or more.

When the polarizing film 4 is manufactured using the film 2 satisfying the condition β, for example, when the swelling treatment is performed by performing the dipping step (immersing step A) satisfying the condition α, a high-quality polarizing film can be obtained. Can be done. Further, since the film 2 is not easily broken during the production of the polarizing film 4, the polarizing film 4 can be stably produced.

This point will be specifically described with reference to Example 1, Example 2, and Comparative Example 1. In Example 1, Example 2, and Comparative Example 1, a polyvinyl alcohol-based film is produced. For convenience of explanation, the polyvinyl alcohol-based film produced in Example 2 and Comparative Example 1 together with Example 1 is referred to as “film 2”.

[Example 1]
<Manufacturing of film 2>
(Preparation of base film)
Homopolypropylene (Sumitomo Chemical Co., Ltd. "Sumitomo Noblen (registered trademark) FLX80E4", melting point Tm = 163 ° C.), which is a homopolymer of propylene, is mixed with 1% by weight of a nucleating agent made of high-density polyethylene. Polypropylene containing a nucleating agent was prepared. From this and the propylene / ethylene random copolymer "Sumitomo Noblen (registered trademark) W151" containing about 5% by weight of ethylene unit, "Sumitomo Noblen (registered trademark)" was produced by coextrusion using a multi-layer extruder. A long polypropylene-based laminated film having a three-layer structure in which the resin layer made of polypropylene containing a nucleating agent was arranged on both sides of the resin layer made of "W151" was prepared and used as a base film. The total thickness of this base film was 100 μm, and the thickness ratio of each layer (polypropylene containing a nucleating agent / W151 / polypropylene containing a nucleating agent) was 3/4/3.

(Adjustment of coating liquid)
Polyvinyl alcohol powder (“Z-200” manufactured by Nippon Synthetic Chemical Industry Co., Ltd., average molecular weight 1100, average saponification degree 99.5 mol%) is dissolved in hot water at 95 ° C. to prepare a polyvinyl alcohol aqueous solution with a concentration of 3% by weight. It was adjusted. A cross-linking agent (“Smiley Resin (registered trademark) 650” manufactured by Sumitomo Chemical Co., Ltd.) was mixed with 2 parts by weight of polyvinyl alcohol in the obtained aqueous solution to prepare a coating liquid for forming a primer layer. ..

Further, polyvinyl alcohol powder (“PVA124” manufactured by Kuraray Co., Ltd., average degree of polymerization 2400, average degree of polymerization 98.0-99.0 mol%) was dissolved in hot water at 95 ° C. to make polyvinyl alcohol having a concentration of 8% by weight. A coating liquid for forming a polyvinyl alcohol-based resin layer, which is an aqueous solution, was prepared.

(Coating and drying)
While the base film was continuously conveyed in the long direction, one side thereof was subjected to corona treatment. Then, the above-mentioned primer layer coating liquid was continuously applied to the corona-treated surface using a microgravure coater, and dried at 60 ° C. for 3 minutes to form a primer layer having a thickness of 0.2 μm on one surface. .. The coating liquid for forming the polyvinyl alcohol-based resin layer was continuously applied onto each primer layer using a comma coater while the film was continuously conveyed in the long direction, and dried with hot air at 80 ° C. for 5 minutes. I let you. Then, by completely drying with hot air at 30 ° C., a polyvinyl alcohol-based resin layer having an average thickness of 30 μm was formed on the primer layer, wound around a shaft, and laminated on the base film and the base film. An original roll of a laminated film having film 2 was obtained. The length of the laminated film wound on the original roll was 5000 m, and the width of the laminated film was 800 mm. The laminated film constituting the raw fabric roll was formed by laminating the film 2 on the base film. Therefore, as shown in Table 1, a film 2 having a width of 800 mm, a thickness (average thickness) of 30 μm, and a length of 5000 m was obtained.

<Manufacturing of polarizing film>
The film 2 was unwound while peeling the base film from the laminated film, and was immersed in a swelling treatment tank containing pure water at 30 ° C. for 30 seconds while applying a tension of 10 N / m as a swelling treatment (swelling step). Next, as a dyeing treatment, uniaxial stretching was performed up to 2.2 times while immersing in a dyeing treatment tank containing an aqueous solution of iodine and potassium iodide at 30 ° C. for 60 seconds, and potassium iodide / boric acid / water was weighted. While immersing in a boric acid treatment tank containing a 55 ° C aqueous solution of 12 / 4.4 / 100 to make it water resistant, uniaxial stretching is performed until the cumulative stretching ratio from the raw roll becomes 5.5 times. gone. Subsequently, it is immersed in a tank containing a 40 ° C boric acid aqueous solution, then immersed in a cleaning treatment tank containing 12 ° C pure water, and then dried in a drying oven at 70 ° C for 3 minutes to form a polarizing film. Manufactured.

In Example 1, the width of the film 2 was continuously measured over the entire length of the film 2 before and after the swelling step while the film 2 was conveyed. The width of the film 2 is such that the film 2 conveyed on the rolls of the nip rolls provided before and after the swelling treatment tank (in the example of FIG. 2 at the positions x1 and the position x2) has LEDs on both ends of the film. After irradiating with light, the positions of both ends of the film were measured from the difference in brightness of the reflected light between the film 2 and the roll, and the position was calculated from the measured positions. The timing of measuring the width before and after the swelling treatment tank was the same. Since FIG. 2 is a schematic diagram for explaining the dipping process, the film 2 is separated from the roll at the position x2, but in the first embodiment, the swelling treatment is followed by the dyeing treatment. Therefore, the film partially rested on the roll even at the position x2. Further, the fluctuation width was calculated as the difference between the maximum value and the minimum value of the width fluctuation rates sequentially calculated according to the width of the film 2 measured continuously in this way. The calculation results of the fluctuation range are shown in Table 2. Table 2 also shows the conditions in the swelling step. The width volatility and fluctuation width were calculated using equations (1) and (2).

In the production of the polarizing film in Example 1, as shown in Table 2, no breakage of the film 2 occurred.

<Evaluation of color unevenness>
The produced polarizing film was placed in a cross Nicol state with respect to the linear polarizing filter in a dark room. Then, a backlight of 6000 cd / m ² was applied to the polarizing film through the linear polarizing filter, and the color unevenness of the polarizing film was visually observed. Then, the level (intensity) of the color unevenness was determined by a visual sensory inspection in three stages of "1", "2", and "3". Evaluation "1" indicates the weakest unevenness, evaluation "3" indicates the strongest unevenness, and evaluation "2" indicates an intermediate between evaluation "1" and evaluation "3". There is. In the above sensory test, the color unevenness was evaluated in three stages as described above by comparing with the level sample sample determined according to the level (intensity) of the color unevenness. The polarizing film produced in Example 1 was evaluated as "1".

[Example 2]
In Example 2, the original roll of the laminated film having the base film and the film 2 laminated on the base film was produced in the same manner as in the case of Example 1. The width, thickness and length of the film 2 obtained in Example 2 were the same as the width, thickness and length of the film 2 of Example 1 as shown in Table 1 above. In Example 2, the film 2 is unwound while peeling the base film from the laminated film, and as a swelling treatment (swelling step), 20 is applied to a swelling treatment tank containing pure water at 35 ° C. with a tension of 15 N / m. A polarizing film was produced in the same manner as in Example 1 except that it was immersed for a second.

In the production of the polarizing film in Example 2, as shown in Table 2, no breakage of the film 2 occurred.

<Evaluation of color unevenness>
The color unevenness of the produced polarizing film was evaluated in the same manner as in Example 1. The evaluation result of the polarizing film produced in Example 2 was "2".

In Example 2, as in Example 1, the width of the film 2 was measured before and after the swelling step, and the fluctuation width was calculated. The calculation results of the fluctuation range are shown in Table 2.

[Comparative Example 1]
In Comparative Example 1, the film 2 was produced in the same manner as in Example 1 except that the coating liquid for forming the polyvinyl alcohol-based resin layer was dried with hot air at 100 ° C. for 15 minutes. Specifically, a raw fabric roll of a laminated film having a base film and a film 2 laminated on the base film was manufactured. The width, thickness and length of the film 2 obtained in Comparative Example 1 were the same as the width, thickness and length of the film 2 of Example 1 as shown in Table 1 above. The film 2 was unwound while peeling the base film from the raw roll produced in this way, and a polarizing film was produced in the same manner as in Example 1.

In the production of the polarizing film in Comparative Example 1, the film 2 was broken as shown in Table 2. In Comparative Example 1, after the film 2 was broken once, the polarizing film was manufactured while the film 2 was unwound again from the same raw fabric roll. In Comparative Example 2, two breaks occurred before the film 2 was used for 2000 m.

<Evaluation of color unevenness>
The color unevenness of the produced polarizing film was evaluated in the same manner as in Example 1. The evaluation result of the polarizing film produced in Comparative Example 1 was "3".

In Comparative Example 1, as in Example 1, the width of the film 2 was measured before and after the swelling step, and the fluctuation width was calculated. The calculation results of the fluctuation range are shown in Table 2. Table 2 also shows the conditions in the swelling process. In Table 2, 0.69 (%) was the fluctuation range until the first break occurred, and 0.75% was the fluctuation range until the second break occurred.

In Examples 1 and 2, as described above, the width of the film 2 before and after the swelling treatment was continuously measured over the entire length of the film 2, and the fluctuation width was calculated. Therefore, the fluctuation range of Example 1 and Example 2 was the difference between the maximum value of the width change rate and the minimum value of the width change rate when the width change rate was continuously acquired for 60 seconds or longer. As described above, pure water was used for the swelling treatment. Therefore, the immersion of the film 2 in pure water in the swelling treatment corresponds to the immersion of the film 2 under the condition β. As shown in Table 2, the films 2 produced in Examples 1 and 2 were obtained from the fluctuation width (%) calculated from the measurement results of the conditions and widths of the swelling steps of Examples 1 and 2. The condition β was satisfied. Further, the swelling steps of Examples 1 and 2 corresponded to the dipping step A satisfying the condition α. On the other hand, from the fluctuation width (%) calculated from the conditions of the swelling step of Comparative Example 1 and the measurement result of the width, the film 2 produced in Comparative Example 1 did not satisfy the condition β, and the film 2 of Comparative Example 1 did not satisfy the condition β. The swelling step did not meet the condition α.

In Examples 1 and 2 in which the swelling treatment is performed by performing the dipping step A satisfying the condition α, the film 2 is less likely to break during the production of the polarizing film, so that the polarizing film can be stably produced. In Examples 1 and 2, since the film 2 satisfies the condition β, it is easy to carry out the dipping step A.

From the results of Examples 1 and 2 shown in Table 2, it can be understood that the color unevenness is further suppressed when the fluctuation range (%) is 0.3% or less.

The embodiment of the present invention has been described above. However, the present invention is not limited to the above-described embodiment, and is intended to include the scope indicated by the claims, as well as all meanings and scope equivalent to the scope of the claims. Changes are intended to be included.

When the method for producing the polarizing film includes the cleaning treatment in the cleaning processing unit 134 as shown in FIG. ₁ , in the cleaning treatment, a method of spraying the treatment liquid as a shower, a method of using dipping and spraying in combination, or the like is used. The film 2 may be washed.

The method for measuring the width of the film 2 is not particularly limited to the exemplified method. For example, the width may be measured by a measuring device such as a laser displacement meter or an LED displacement meter. The entire film 2 may be photographed with a camera or the like, and the width may be calculated from the obtained image. As shown in FIG. 3, in the method of acquiring the positions of the end portions 2a and 2b of the film 2, a device for measuring the positions of the end portions 2a and 2b may be arranged at each of the end portions 2a and 2b of the film 2. Therefore, it is preferable from the viewpoint of installation space and equipment management (maintenance and inspection, etc.).

The stretching treatment in the stretching treatment unit is not limited to the wet stretching method, and a dry stretching method may be adopted. In the above-described embodiment, the order of the processes exemplified for producing the polarizing film may be appropriately changed or combined without departing from the spirit of the present invention. The number of processing tanks possessed by each processing unit may be one or a plurality.

The above-described embodiment and various modifications may be appropriately combined without departing from the spirit of the present invention.

2 ... film (polyvinyl alcohol-based film), 4 ... polarizing film, 8 ... treatment liquid, 11 ... nip roll.

Claims (10)

It is a method of manufacturing a polarizing film while transporting a polyvinyl alcohol-based film.
It is equipped with a dipping step of immersing a long polyvinyl alcohol-based film in the treatment liquid.
In the dipping step, the fluctuation range (%) of the width change rate (%) in the width direction of the polyvinyl alcohol-based film before and after being immersed in the treatment liquid is 0.5% or less. ,
The dipping step is performed in a swelling treatment for the polyvinyl alcohol-based film.
The width change rate is calculated by the equation (1).
The fluctuation range is calculated by the equation (2).
In the swelling treatment, at least one of the temperature of the treatment liquid, the immersion time, and the tension applied to the polyvinyl alcohol-based film is adjusted so that the fluctuation range is 0.5% or less.
Method for manufacturing a polarizing film.
Width change rate = | (W2-W1) / W1 | × 100 ... (1)
Fluctuation width = maximum value of width change rate-minimum value of width change rate ... (2)
(In the formula (1), W1 [mm] represents the width of the polyvinyl alcohol-based film before being immersed in the treatment liquid, and W2 [mm] is the polyvinyl alcohol after being immersed in the treatment liquid. Represents the width of the system film. In Eq. (2), the maximum value of the width change rate and the minimum value of the width change rate are the values when the width change rate is continuously acquired for 60 seconds or more.) In the dipping step, the polyvinyl alcohol-based film is immersed in the treatment liquid while applying a constant tension by using a nip roll before and after the immersion in the treatment liquid.
The method for manufacturing a polarizing film according to claim 1. In the dipping step, the polyvinyl alcohol-based film is immersed in the treatment liquid while maintaining a constant rotation speed ratio of the nip roll before and after the immersion in the treatment liquid.
The method for manufacturing a polarizing film according to claim 1. It is a long polyvinyl alcohol-based film as a raw fabric.
When the polyvinyl alcohol-based film is transported and immersed in water under conditions including a predetermined temperature and a predetermined immersion time, the width change rate in the width direction of the polyvinyl alcohol-based film before and after the immersion ( %) Fluctuation range (%) is 0.5% or less,
The predetermined temperature is a temperature selected from the range of 15 ° C to 40 ° C.
The predetermined soaking time is a soaking time selected from the range of 20 seconds to 120 seconds.
The width change rate is calculated by the equation (3).
The fluctuation range is calculated by the equation (4).
Polyvinyl alcohol film.
Width change rate = | (W2a-W1a) / W1a | × 100 ... (3)
Fluctuation width = maximum value of width change rate-minimum value of width change rate ... (4)
(In the formula (3), W1a [mm] represents the width of the polyvinyl alcohol-based film before being immersed in the water, and W2a [mm] is the polyvinyl alcohol-based film after being immersed in the water. In the equation (4), the maximum value of the width change rate and the minimum value of the width change rate are the values when the width change rate is continuously acquired for 60 seconds or more.) The fluctuation range (%) includes the predetermined temperature and the predetermined immersion time while transporting the polyvinyl alcohol-based film while maintaining the tension selected from the range of 5 N / m to 100 N / m. It is the fluctuation range when immersed in the water.
The polyvinyl alcohol-based film according to claim 4 . With respect to the fluctuation range (%), the polyvinyl alcohol-based film is conveyed in a state where the rotation speed ratio of the nip roll before and after immersion in water is maintained at a rotation speed ratio selected within the range of 1.1 to 4.0. However, it is the fluctuation range when immersed in the water under the conditions including the predetermined temperature and the predetermined immersion time.
The polyvinyl alcohol-based film according to claim 4 . The fluctuation range (%) is 0.3% or less.
The polyvinyl alcohol-based film according to any one of claims 4 to 6 . The length of the polyvinyl alcohol-based film in the long direction is 1000 m or more.
The polyvinyl alcohol-based film according to any one of claims 4 to 7 . A method for producing a polarizing film while transporting the polyvinyl alcohol-based film according to any one of claims 4 to 8.
A dipping step of immersing the polyvinyl alcohol-based film in the treatment liquid is provided.
In the dipping step, the fluctuation range (%) of the width change rate (%) in the width direction of the polyvinyl alcohol-based film before and after being immersed in the treatment liquid is 0.5% or less. ,
The dipping step is performed in a swelling treatment for the polyvinyl alcohol-based film.
The width change rate in the dipping step is calculated by the formula (5).
The fluctuation range in the dipping step is calculated by the formula (6).
Method for manufacturing a polarizing film.
The width change rate in the dipping step = | (W2-W1) / W1 | × 100 ... (5)
The fluctuation width in the dipping step = the maximum value of the width change rate-the minimum value of the width change rate ... (6)
(In the formula (5), W1 [mm] represents the width of the polyvinyl alcohol-based film before being immersed in the treatment liquid, and W2 [mm] is the polyvinyl alcohol after being immersed in the treatment liquid. Represents the width of the system film. In the formula (6), the maximum value of the width change rate and the minimum value of the width change rate are the values when the width change rate in the dipping step is continuously acquired for 60 seconds or more. be) In the swelling treatment, at least one of the temperature of the treatment liquid, the soaking time, and the tension applied to the polyvinyl alcohol-based film is adjusted so that the fluctuation range in the dipping step is 0.5% or less. do,
The method for manufacturing a polarizing film according to claim 9.

Images