Method for manfacturing polarizing film and polyvinyl alcohol-based film

Abstract

The present invention aims to provide a method for manufacturing a polarizing film capable of manufacturing a polarizing film in a stable process and a polyvinyl alcohol-based film. A method for manufacturing a polarizing film according to one embodiment is a method for manufacturing a polarizing film while conveying a polyvinyl alcohol-based film, comprising an immersion process in which a long polyvinyl alcohol-based film is immersed in a treatment solution, and in the immersion process, the variation 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 solution is 0.5% or less.

Description

Technology Field

[0001] The present invention relates to a method for manufacturing a polarizing film and a polyvinyl alcohol-based film. Background Technology

[0002] As described in Patent Documents 1 and 2, a polarizing film is manufactured by performing treatments such as swelling, dyeing, crosslinking, stretching, washing, and drying on a polyvinyl alcohol-based film. In the treatment of the polyvinyl alcohol-based film, the polyvinyl alcohol-based film may be immersed in a treatment solution. For example, in the swelling treatment, the polyvinyl alcohol-based film is immersed in water, which is the treatment solution. Prior art literature

[0003] [Patent Document 1] Japanese Patent Publication No. 2016-48382 [Patent Document 2] Japanese Patent Publication No. 2017-102438 The problem to be solved

[0004] In the conventional manufacturing of polarizing films, film breakage or the like occurred, which sometimes resulted in unstable production processes.

[0005] Therefore, the present invention aims to provide a method for manufacturing a polarizing film capable of manufacturing a polarizing film in a stable process and a polyvinyl alcohol-based film. means of solving the problem

[0006] The inventors of the present invention discovered that when manufacturing a polarizing film, if the variation range of the width change rate before and after immersion is too large, the film breaks. Therefore, the following method for manufacturing a polarizing film was completed.

[0007] A method for manufacturing a polarizing film according to one aspect of the present invention is a method for manufacturing a polarizing film while conveying a polyvinyl alcohol-based film, comprising an immersion process in which the polyvinyl alcohol-based film is immersed in a treatment solution, and in the immersion process, the variation 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 solution is 0.5% or less.

[0008] In the above manufacturing method, the variation range (%) of the width change rate (%) in the width direction of the polyvinyl alcohol-based film during the immersion process is 0.5% or less. In this case, since the variation range is small, breakage of the film does not easily occur during the manufacturing of the polarizing film, so the polarizing film can be manufactured in a stable process.

[0009] In the above immersion process, the polyvinyl alcohol-based film may be immersed in the treatment solution while applying a constant tension using a nip roll before and after immersion in the treatment solution.

[0010] In the above immersion process, the polyvinyl alcohol-based film may be immersed in the treatment solution while maintaining a constant ratio of the rotational speed of the nip roll before and after immersion in the treatment solution.

[0011] The above immersion process may be performed during the swelling treatment of the polyvinyl alcohol-based film. The swelling treatment is performed during the initial stage of manufacturing the polarizing film. Therefore, the width of the polyvinyl alcohol-based film is prone to change during the swelling treatment. For this reason, it is effective to perform the swelling treatment during the above immersion process.

[0012] The above width change rate is calculated by the following formula (1), and the above fluctuation range may be calculated by the following formula (2).

[0013] Change in width = |(W2-W1) / W1| × 100···(1)

[0014] Variation range = Maximum value of change in width - Minimum value of change in width...(2)

[0015] (In Equation (1), W1 [mm] represents the width of the polyvinyl alcohol-based film before immersion in the treatment solution, and W2 [mm] represents the width of the polyvinyl alcohol-based film after immersion in the treatment solution. In Equation (2), the maximum value and the minimum value of the width change rate are each values ​​when the width change rate is calculated continuously for 60 seconds or more.)

[0016] According to another aspect of the present invention, a polyvinyl alcohol-based film is immersed in water based on conditions including a predetermined temperature and a predetermined immersion time while conveying a long polyvinyl alcohol-based film, wherein the variation range (%) of the width change rate (%) in the width direction of the polyvinyl alcohol-based film before and after immersion is 0.5% or less, the predetermined temperature is a temperature selected in the range of 15℃ to 40℃, the predetermined immersion time is an immersion time selected in the range of 20 seconds to 120 seconds, and the variation range (%) 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 acquired continuously for 60 seconds or more.

[0017] The above polyvinyl alcohol-based film is used, for example, in the manufacture of a polarizing film. A method for manufacturing a polarizing film includes an immersion process in which a long polyvinyl alcohol-based film is immersed in a processing solution. When the above immersion process is performed using the above polyvinyl alcohol-based film, the variation 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 processing solution is likely to be 0.5% or less. In this case, since the variation range is small, breakage of the film does not easily occur during the manufacture of the polarizing film, and the polarizing film can be manufactured in a stable process.

[0018] The above variation range (%) may be the variation range in the case where the polyvinyl alcohol-based film is conveyed while maintaining a tension selected in the range of 5 N / m to 100 N / m, and is immersed in water based on conditions including the above predetermined temperature and the above predetermined immersion time.

[0019] The above variation range (%) may be the variation range in the case where the polyvinyl alcohol-based film is conveyed while maintaining the rotational speed ratio of the nip roll before and after immersion in the water at a rotational speed ratio selected within the range of 1.1 to 4.0, based on conditions including the above predetermined temperature and the above predetermined immersion time.

[0020] The above fluctuation range (%) may be 0.3% or less.

[0021] The length of the above polyvinyl alcohol-based film in the long direction is, for example, 1000 m or more. Effects of the invention

[0022] According to the present invention, a polarizing film can be manufactured in a stable process. Brief explanation of the drawing

[0023] FIG. 1 is a schematic diagram illustrating a method for manufacturing a polarizing film according to one embodiment. Figure 2 is a diagram illustrating an immersion process provided by a method for manufacturing a polarizing film. Figure 3 is a diagram illustrating an example of a method for obtaining the width change rate and the variation width. Specific details for implementing the invention

[0024] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the drawings, identical or equivalent parts are denoted by the same reference numerals, and redundant descriptions are omitted. The dimensional ratios in the drawings do not necessarily correspond to those described.

[0025] (First embodiment)

[0026] As a first embodiment, a method for manufacturing a polarizing film is described. FIG. 1 is a schematic diagram illustrating an example of a method for manufacturing a polarizing film according to one embodiment of the present invention.

[0027] In the first embodiment, a polarizing film (4) is manufactured by transporting a long polyvinyl alcohol-based film (2) [hereinafter simply referred to as "film (2)") and performing swelling treatment, dyeing treatment, crosslinking treatment, stretching treatment, and drying treatment on the film (2) while it is being transported. The stretching treatment may be performed on the film (2) during any one of the treatments (e.g., crosslinking treatment) or in parallel while performing multiple treatments.

[0028] The material of the film (2) may be a known polyvinyl alcohol-based resin used in the manufacture of polarizing films, 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 even more preferably 93.0 to 99.5 mol%. 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 can be obtained by the method specified in JIS K 6726 (1994). The average degree of polymerization of the polyvinyl alcohol-based resin is preferably 100 to 10000, and more preferably 1000 to 10000. The average degree of polymerization is a numerical value that can be obtained according to the method specified in JIS K 6726 (1994).

[0029] 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, 30000 m or less, and preferably 20000 m or less. An example of the length of the film (2) in the width direction (a direction perpendicular 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.

[0030] The film (2) is not particularly limited and can be manufactured by known methods such as melt extrusion and solvent casting. For example, the film (2) can be obtained by coating a polyvinyl alcohol-based resin solution onto a base film composed of a thermoplastic resin [polyolefin-based resin, (meth)acrylic-based resin, etc.], performing film molding by drying the resin solution, and peeling the obtained film (2) from the base film.

[0031] The above-mentioned substrate film may have a primer layer provided as needed. The thickness of the substrate film can be appropriately determined, but is preferably 1 μm to 500 μm, and more preferably 1 μm to 300 μm. The width and length of the substrate film can be appropriately determined according to the size of the film (2) to be intended.

[0032] A polyvinyl alcohol-based resin solution can be obtained by dissolving the aforementioned polyvinyl alcohol-based resin in water, alcohol, etc. The viscosity of the solution is preferably 500 cps to 10,000 cps, more preferably 1,000 cps to 7,000 cps, and even more preferably 1,000 cps to 5,000 cps.

[0033] The coating of the polyvinyl alcohol-based resin solution can be appropriately selected from known methods such as roll coating methods like gravure coating and die coating methods. The film thickness of the polyvinyl alcohol-based resin solution to be coated can be, for example, 50 μm to 1000 μm.

[0034] The above drying can be carried out with the resin temperature typically ranging from 30°C to 200°C and the drying time ranging from 2 minutes to 24 hours. In cases where the film thickness of the polyvinyl alcohol-based resin solution to be coated is thick, the moisture may be removed by drying with hot air at 80°C or higher for 1 to 10 minutes, and then dried with hot air at 30°C to less than 50°C.

[0035] The coating, drying, and peeling of the film (2) from the base film of the above polyvinyl alcohol-based resin solution can be performed continuously while conveying the base film.

[0036] In the above drying process, 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 conveying direction of the base film (the elongation direction of the base film). In the above drying process, tension may be applied in the elongation direction so that the dimensional change rate of the base film in the elongation direction before and after drying exceeds 0%, that is, so that plastic deformation occurs. The dimensional change rate may be 0.01% or more, or 0.1% or more. Furthermore, it is preferable that the dimensional change rate in the drying process be 5% or less, and more preferable that it be 1% or less.

[0037] The thickness of the obtained film (2) may be 5 μm to 100 μm. In addition, the width of the polyvinyl alcohol-based resin layer [film (2)] after drying may be 400 mm to 5000 mm.

[0038] FIG. 1 illustrates a case in which a film (2) is prepared as a disc roll (6), and a polarizing film (4) is obtained by performing each treatment on the film (2) unwound from the disc roll (6). When the film (2) is manufactured by the above method (melt extrusion method, solvent casting method, etc.), for example, the film (2) manufactured by the above method (melt extrusion method, solvent casting method, etc.) may be continuously conveyed, and each of the above treatments may be performed during the conveyance.

[0039] Based on the form illustrated in FIG. 1, an example of a method for manufacturing a polarizing film (4) is described. First, a schematic of a manufacturing apparatus (10) for a polarizing film (4) is described. The manufacturing apparatus (10) comprises a plurality of nip rolls (11), a plurality of guide rolls (12), a swelling treatment unit (131), a dyeing treatment unit (132), a crosslinking treatment unit (133), a washing treatment unit (134), and a drying treatment unit (135).

[0040] A plurality of nip rolls (11) and a plurality of guide rolls (12) constitute a transport mechanism for the film (2). By appropriately arranging the plurality of nip rolls (11) and the plurality of guide rolls (12), a transport path for the film (2) is formed.

[0041] The swelling treatment section (131) is a section that performs swelling treatment on the film (2). The swelling treatment section (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 section (131), swelling treatment is performed on the film (2). In the first embodiment, a transport path for the film immersing the film (2) in the treatment liquid is formed by a nip roll (11) and two guide rolls (12) arranged before and after the film (2) is immersed in the treatment liquid.

[0042] The above swelling treatment is performed for purposes such as removing foreign substances from the surface of the film (2), removing plasticizers from the film (2), providing ease of dyeing in subsequent processes, and plasticizing the film (2). The conditions for the swelling treatment can be determined within a range that can achieve these purposes, and also within a range where problems such as extreme dissolution or devitrification of the film (2) do not occur. In the swelling treatment section (131), the swelling treatment is performed by immersing the film (2) in a treatment solution, for example, at a temperature of 10°C to 50°C, preferably 15°C to 40°C. The time of the swelling treatment (immersion time) is approximately 5 seconds to 300 seconds, preferably 20 seconds to 120 seconds. An example of the treatment solution in the swelling treatment section (131) is water. Therefore, the swelling treatment can also serve as a water washing treatment for the film (2).

[0043] The dyeing treatment section (132) is a section that performs a dyeing treatment on the film (2). The dyeing treatment section (132) has a treatment tank in which a treatment solution for dyeing treatment is stored. By immersing the film (2) in the treatment solution of the dyeing treatment section (132), a dyeing treatment is performed on the film (2). In the first embodiment, a conveying path for the film immersed in the treatment solution is formed by a nip roll (11) and two guide rolls (12) arranged before and after the film (2) is immersed in the treatment solution.

[0044] The treatment solution of the dyeing treatment unit (132) in the first embodiment is an aqueous solution of a dichroic pigment, and in the dyeing treatment, the film (2) is dyed with the dichroic pigment. The dyeing treatment with a conventional dichroic pigment is performed for purposes such as adsorbing the dichroic pigment onto the film (2). The treatment conditions are determined according to the desired optical properties within a range that can achieve such purposes and within a range that does not cause problems such as extreme dissolution or devitrification of the film (2). Examples of dichroic pigments used for dyeing are iodine and dichroic dyes.

[0045] When iodine is used as a dichroic pigment, the dyeing treatment is performed by immersing the film (2) for 10 to 600 seconds, preferably 30 to 300 seconds, in an aqueous solution containing 0.003 to 0.2 parts by weight of iodine and 0.1 to 10 parts by weight of potassium iodide per 100 parts by weight of water, for example, at a temperature of 10°C to 50°C, preferably 15°C to 40°C. Instead of potassium iodide, other iodides, such as zinc iodide, may be used. Other iodides may be used in combination with potassium iodide. In addition, compounds other than iodides, boric acid, zinc chloride, cobalt chloride, etc., may be coexisted. A treatment solution containing 0.003 parts by weight or more of iodine per 100 parts by weight of water can be considered as a treatment solution for dyeing.

[0046] When a dichroic dye is used as a dichroic pigment, for example, a dyeing treatment is performed by immersing the film (2) in an aqueous solution containing 0.001 parts by weight to 0.1 parts by weight of the dichroic dye per 100 parts by weight of water at a temperature of 20°C to 80°C, preferably 30°C to 60°C, for 10 seconds to 600 seconds, preferably 20 seconds to 300 seconds. The aqueous solution of the dichroic dye used may contain dyeing aids, etc., or may contain inorganic salts such as sodium sulfate, surfactants, etc. Only one type of dichroic dye may be used, or two or more types of dichroic dyes may be used in combination depending on the desired color.

[0047] The crosslinking treatment section (133) is a section that performs crosslinking treatment on the film (2). The crosslinking treatment section (133) has a treatment tank in which a treatment solution for crosslinking treatment is stored. By immersing the film (2) in the treatment solution of the crosslinking treatment section (133), crosslinking treatment is performed on the film (2). In the first embodiment, a transport path for the film immersing the film (2) in the treatment solution is formed by a nip roll (11) and two guide rolls (12) arranged before and after the film (2) is immersed in the treatment solution.

[0048] Crosslinking treatment is a treatment performed for purposes such as water resistance or color adjustment [preventing the film (2) from turning bluish].

[0049] The treatment solution used in the crosslinking treatment unit (133) is, for example, an aqueous solution containing 1 to 10 parts by weight of boric acid per 100 parts by weight of water. When the dichroic pigment used in the dyeing treatment is iodine, the treatment solution used in the crosslinking treatment unit (133) preferably contains an iodide in addition to boric acid, and the amount is, for example, 1 to 30 parts by weight per 100 parts by weight of water. Examples of iodides include potassium iodide and zinc iodide. Compounds other than iodides, zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, sodium sulfate, etc. may also be coexisted.

[0050] In the cross-linking treatment in the cross-linking treatment section (133), the concentration of boric acid and iodide and the temperature of the treatment solution can be appropriately changed according to the purpose.

[0051] For example, when the purpose of the crosslinking treatment is to make the film water resistant through crosslinking, and the swelling treatment, dyeing treatment, and crosslinking treatment are performed in this order on a polyvinyl alcohol-based resin film, the crosslinking agent-containing solution of the treatment solution is, for example, an aqueous solution with a concentration of boric acid / iodide / water = 3 to 10 / 1 to 20 / 100 by weight ratio. If necessary, other crosslinking agents such as glyoxal or glutaraldehyde may be used instead of boric acid, or boric acid and other crosslinking agents may be used in combination. The temperature of the treatment solution when immersing the film (2) is typically about 50°C to 70°C, preferably 53°C to 65°C, and the immersion time of the film (2) is typically about 10 seconds to 600 seconds, preferably 20 seconds to 300 seconds, more preferably 20 seconds to 200 seconds. When dyeing and crosslinking treatments are performed in this order on a film (2) that has been stretched in advance before swelling treatment, the temperature of the treatment solution is typically 50°C to 85°C, preferably 55°C to 80°C.

[0052] The purpose of the crosslinking treatment is color adjustment, and for example, when iodine is used as a dichroic pigment, a crosslinking agent-containing solution with a weight ratio of boric acid / iodide / water = 1 to 5 / 3 to 30 / 100 can be used as the treatment solution. The temperature of the treatment solution when immersing the film (2) is typically about 10 to 45°C, and the immersion time of the film (2) is typically about 1 to 300 seconds, preferably 2 to 100 seconds.

[0053] The cleaning treatment unit (134) is a part that performs cleaning treatment on the film (2) after crosslinking treatment. The cleaning treatment unit (134) has a treatment tank in which a treatment solution for cleaning treatment is stored. By immersing the film (2) in the treatment solution of the cleaning treatment unit (134), cleaning treatment is performed on the film (2). In the first embodiment, a conveying path for the film immersing the film (2) in the treatment solution is formed by a nip roll (11) and two guide rolls (12) arranged before and after the film (2) is immersed in the treatment solution. Examples of the treatment solution for cleaning treatment include water, an aqueous solution containing potassium iodide, and an aqueous solution containing boric acid. The temperature of the treatment solution is typically about 2°C to 40°C, and the treatment time (immersion time) is typically about 2 seconds to 120 seconds.

[0054] The drying treatment unit (135) is a part that performs a drying treatment on the film (2). In the first embodiment, the drying treatment unit (135) is a drying device. In the drying treatment unit (135), the film (2) that has been cleaned in the cleaning treatment unit (134) is introduced, and the film (2) is dried while passing through the drying treatment unit (135). In the first embodiment, a transport path for the film that dries the film (2) in the drying device is formed by nip rolls (11) arranged before and after the drying treatment unit (135). Guide rolls (12) may be appropriately arranged within the drying treatment unit (135) to support and transport the film (2). Drying by the drying treatment unit (135) is performed for, for example, 30 seconds to 600 seconds within the drying treatment unit (135) which is maintained at a temperature of, for example, 40°C to 100°C. In FIG. 1, a drying treatment unit (135) is schematically shown. The drying treatment unit (135) is not particularly limited as long as it can dry moisture attached to the film (2), and may be a known unit commonly used in the manufacture of polarizing films.

[0055] In the manufacturing apparatus (10), a stretching process is performed to uniaxially stretch the film (2) using the difference in rotational speed between at least two nip rolls (11) [upstream nip roll (11) and downstream nip roll (11)] among a plurality of nip rolls (11). In this case, the two nip rolls (11) contributing to the uniaxial stretching process function as stretching processing units.

[0056] For example, a stretching treatment may be performed by utilizing the difference in rotational speed between the nip roll (11) placed in front of the crosslinking treatment section (133) and the nip roll (11) placed behind the crosslinking treatment section (133). In this case, since the stretching treatment is performed in parallel with the crosslinking treatment, the crosslinking treatment section (133) also functions as a stretching treatment section. The stretching treatment is also effective for suppressing the occurrence of wrinkles in the film (2).

[0057] In addition to performing mainly stretching treatment using two nip rolls (11) positioned before and after one processing unit [e.g., the aforementioned cross-linking processing unit (133)], it is also possible to perform further stretching treatment gradually using another nip roll (11).

[0058] The manufacturing device (10) may have a separate stretching treatment unit for performing stretching treatment. In this case, the stretching treatment unit is positioned, for example, at the rear end of the cross-linking treatment unit (133) [for example, between the cross-linking treatment unit (133) and the cleaning treatment unit (134)].

[0059] The manufacturing device (10) may have multiple processing units among at least one of a swelling treatment unit (131), a dyeing treatment unit (132), a crosslinking treatment unit (133), a washing treatment unit (134), and a drying treatment unit (135). For example, the manufacturing device (10) may have multiple crosslinking treatment units (133). The manufacturing device (10) may also have a stretching treatment unit.

[0060] An example of a method for manufacturing a polarizing film (4) using the above-described manufacturing device (10) is described. First, the film (2) is unwound from the disc roll (6). The unwound film (2) is conveyed along a conveying path formed by a plurality of nip rolls (11) and a plurality of guide rolls (12) in the elongation direction of the film (2). Examples of conveying speeds may be 1 m / min to 60 m / min or 1.5 m / min to 50 m / min. In the conveying path of the film (2), a swelling treatment section (131), a dyeing treatment section (132), a crosslinking treatment section (133), a cleaning treatment section (134), and a drying treatment section (135) are provided from the side of the disc roll (6). In addition, as described above, at least two nip rolls (11) also function as a stretching treatment section. Accordingly, by conveying the film (2) along the conveying path, swelling treatment, dyeing treatment, crosslinking treatment, washing treatment and drying treatment are performed on the film (2), and stretching treatment is performed. By doing so, linear polarization characteristics are imparted to the film (2), and a polarizing film (4) is obtained.

[0061] The above swelling treatment, dyeing treatment, crosslinking treatment, and washing treatment are performed by immersing the film (2) in a treatment solution. Accordingly, the method for manufacturing a polarizing film (4) has a plurality of immersion processes [a process of immersing the film (2) in a treatment solution]. In other words, in the plurality of immersion processes, the swelling treatment, dyeing treatment, crosslinking treatment, and washing treatment are performed. The method for manufacturing a polarizing film (4) of the first embodiment performs at least one of the plurality of immersion processes corresponding to the swelling treatment, dyeing treatment, crosslinking treatment, and washing treatment as an immersion process (hereinafter referred to as "immersion process A" for convenience of explanation) as described using FIG. 2.

[0062] FIG. 2 is a schematic diagram for explaining immersion process A. FIG. 2 schematically illustrates a state in which a treatment liquid (8) is stored in a treatment tank and a film (2) is immersed while being conveyed to the treatment liquid (8). The treatment liquid (8) is a treatment liquid corresponding to the treatment performed in immersion process A among swelling treatment, dyeing treatment, crosslinking treatment, and washing treatment. Similar to each treatment section shown in FIG. 1, the conveying path of the film (2) is formed by a nip roll (11) and two guide rolls (12) before and after the treatment liquid (8). In the conveying path, the nip roll (11) through which the film (2) passes before being immersed in the treatment liquid (8) is the nip roll (11 UP (Illegible) and the nip roll (11) through which the film (2) passes after the film (2) is immersed in the treatment solution (8) is called the nip roll (11 DOWN It is also called ).

[0063] In immersion process A, the film (2) can be immersed in the treatment solution while maintaining the tension applied to the film (2).

[0064] The tension in immersion process A is typically 3 N / m to 2000 N / m, and preferably 5 N / m to 1500 N / m. When the immersion process is a swelling process, it is more preferably 3 N / m to 200 N / m, and even more preferably 5 N / m to 100 N / m.

[0065] In immersion process A, for example, the nip roll (11) shown in FIG. 2 UP ) and nip roll (11 DOWN A constant tension may be applied to the film (2) using a nip roll (11 UP The rotational speed of ) and the nip roll (11 DOWN By adjusting the rotation speed in ), constant tension can be applied. In this way, by applying constant tension, the film (2) can be immersed in the treatment solution (8) while maintaining tension.

[0066] To adjust the tension, the tension may be detected, for example, by a tension detector. Commercially available tension detectors may be used. For example, tension is detected by principles such as a differential transformer type or a distortion gauge type. The tension is continuously monitored by the tension detector. For example, the detected tension value is sent to a control system. In the control system, if the detected tension value deviates from a set value, the amount is measured, and the nip roll (11 DOWN A signal is sent to a driving device (e.g., a servo motor) that drives the device to control the drive and maintain the tension value at a constant level.

[0067] In immersion process A, the film (2) may be immersed in the treatment solution while maintaining a constant ratio of the rotational speed of the nip roll before and after immersion in the treatment solution (8). The above rotational speed ratio is the nip roll (11) before immersion in the treatment solution (8). UP The rotational speed of ) and the nip roll (11) after being immersed in the processing liquid (8) DOWNIt is the ratio of the rotational speed of ). In this way, by immersing the film (2) in the treatment solution while maintaining the above rotational speed ratio constant, the film (2) can be immersed in the treatment solution while maintaining tension.

[0068] In immersion process A, the following condition α is satisfied.

[0069] <Condition α>

[0070] The variation range (%) of the width change rate (%) in the width direction of the film (2) before and after the film (2) is immersed in the treatment solution (8) is 0.5% or less.

[0071] In one embodiment, the width change rate and the variation range are calculated by the following equations (1) and (2).

[0072] Change in width = |(W2-W1) / W1| × 100···(1)

[0073] Variation range = Maximum value of change in width - Minimum value of change in width...(2)

[0074] In equation (1), W1 [mm] represents the width of the film (2) before it is immersed in the treatment solution (8), and W2 [mm] represents the width of the film (2) after it is immersed in the treatment solution (8).

[0075] In Equation (2), the maximum and minimum values ​​of the width change rate are the values ​​obtained when the width change rate is acquired continuously, for example, over a certain period.

[0076] The above specified period is, for example, 60 seconds or more, preferably 1 hour or more, more preferably 24 hours or more. The upper limit of the specified period is the time when immersion process A is performed over the entire length of the film (2), and can be determined by the entire length of the film (2) and the transport speed. For example, the upper limit is 200 hours.

[0077] The width W1 of the film (2) before the film (2) is immersed in the treatment solution (8) is, for example, the width of the film (2) at position x1 as shown in FIG. 2. In FIG. 2, position x1 is where the film (2) is nip roll (11 UP It is the position after passing through the ). The width W2 of the film (2) after the film (2) is immersed in the treatment solution (8) is, for example, the width of the film (2) at position x2 shown in FIG. 2. Position x2 is where the film (2) passes through the nip roll (11 DOWN Indicates the position after passing through ).

[0078] In order to obtain (or calculate) the above width change rate and variation width, the manufacturing device (10) may have two width measuring devices (30) and a calculation unit (40) as shown in FIG. 3 for a treatment tank that performs immersion process A.

[0079] An example of a method for obtaining the width change rate and variation width using a width measuring device (30) and a calculation unit (40) is described. Hereinafter, the series of processes from measuring widths W1 and W2 to obtaining the width change rate and variation width may be collectively referred to as the "monitoring process."

[0080] Each of the two width measuring devices (30) is a device that continuously measures the width of the film (2). One of the two width measuring devices (30) is a width measuring device that measures the width W1 of the film (2) before the film (2) is immersed in the treatment liquid (8) [hereinafter, "width measuring device (30 UP [referred to as )”], and the other of the two width measuring devices (30) is a measuring device for measuring the width W2 of the film (2) after the film (2) is immersed in the treatment liquid (8) [hereinafter, “width measuring device (30 DOWN It is called )".

[0081] Width measuring instrument (30 UP ) and width measuring instrument (30 DOWNEach of the two end detection units (31) has two end detection units. 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 a detection unit that detects the other end (2b) [the end opposite to the end (2a)] in the width direction of the film (2). Each end detection unit (31) detects the end of the film (2), for example, optically and non-contactually. Each end detection unit (31) is configured to acquire an image of the end to be detected and the vicinity thereof. For example, the end detection unit (31) may have an imaging unit such as a camera.

[0082] The output unit (40) is a width measuring device (30 UP Based on the detection results of the two end detection units (31) having ), the width W1 is calculated, and the width measuring device (30 DOWN Based on the detection results of the two end detection units (31) having ), the width W2 is calculated. For example, the calculation unit (40) is a width measuring device (30 UP Width W1 and width W2 are calculated by determining the position of the ends (2a, 2b) based on the detection results (e.g., image data) of the two end detection units (31) having )

[0083] The calculation unit (40) calculates the width change rate from width W1, width W2 and Equation (1), and also calculates the variation width from Equation (2).

[0084] In the first embodiment, the width W1 may be measured at position x1, and then the width W2 may be measured at the point when the film location where the width W1 was measured is returned to position x2, or the width W1 at position x1 and the width W2 at position x2 may be measured at the same timing (i.e., simultaneously). The "same timing" may have a slight discrepancy within a range that does not deviate from the spirit of the present invention. Although not particularly limited by the return speed, the time difference between the measurement time at position x1 and the measurement time at position x2 may be within 1 minute, within 30 seconds, within 20 seconds, or within 10 seconds.

[0085] It is preferable to carry out the monitoring process through automation. In the first embodiment, in order to efficiently implement automation, it is preferable to measure the width W1 at position x1 and the width W2 at position x2 at the same timing.

[0086] The above condition α can be realized by adjusting, for example, the temperature of the treatment solution (8), the immersion time (treatment time), the tension applied to the film (2), etc.

[0087] In the monitoring process, if the variation range exceeds 0.5%, the width change rate can be adjusted to satisfy the above condition α by adjusting each processing condition, etc. according to the processing in which the monitoring process is being performed. For example, to satisfy the above condition α, the temperature of the processing solution (8), the immersion time (processing time), the tension applied to the film (2), etc., may be adjusted, or the film (2) used in the manufacture of the polarizing film (4) may be changed. More specifically, in the monitoring process during the swelling treatment, if the width change rate is small, the variation range can be reduced by means such as raising the temperature of the processing solution, lowering the tension, or extending the processing time, while if the width change rate is large, the variation range can be reduced by means such as lowering the temperature of the processing solution, raising the tension, or shortening the processing time. When the immersion of the film (2) in the crosslinking process into the treatment solution is carried out as immersion process A and a monitoring process is carried out, the range of variation can be adjusted by the content of the crosslinking agent or the arrangement of the guide rolls, in addition to the above-mentioned manufacturing conditions (temperature, tension, treatment time).

[0088] The method for manufacturing a polarizing film (4) includes an immersion process A that satisfies the above condition α. ​​Therefore, in the immersion process A, even when the film (2) is immersed in the treatment solution (8), the variation range of the width change rate of the film (2) is 0.5% or less. In this case, since the variation range of the film (2) is small, it is difficult for the film (2) to break, for example, during the immersion process A or in a process after the immersion process A. As a result, the polarizing film (4) can be manufactured stably. Since the variation range of the film (2) is small, defects and appearance defects caused by width change can be reduced. As a result, a polarizing film (4) of good quality can be manufactured.

[0089] It is effective for immersion process A to be performed during the swelling treatment. The swelling treatment is a treatment performed upstream (initial stage of the manufacturing process) among a plurality of treatments performed sequentially on the film (2) as shown in FIG. 1. Therefore, since the width of the film (2) is prone to change during the swelling treatment, the quality of the manufactured polarizing film (4) is improved by performing the immersion process A during the swelling treatment. In addition, the film (2) is difficult to break during the swelling treatment and subsequent treatments. When immersion process A is performed during the swelling treatment, the temperature of the treatment solution (e.g., water) is preferably 15°C to 40°C, and the immersion time is preferably 20 seconds to 120 seconds.

[0090] As described above, the immersion process A satisfying condition α may be carried out in at least one of the plurality of immersion processes corresponding to swelling treatment, dyeing treatment, crosslinking treatment and washing treatment.

[0091] (Second embodiment)

[0092] As a second embodiment, a long polyvinyl alcohol-based film (2) is described. In the second embodiment as well, 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.

[0093] The film (2) is a film that satisfies the following condition β.

[0094] <Condition β>

[0095] When the above polyvinyl alcohol-based film is transported and the film (2) is immersed in water at a predetermined temperature and a predetermined immersion time, the film (2) has a variation range (%) of the width change rate (%) in the width direction before and after immersion of 0.5% or less.

[0096] In order to further suppress color non-uniformity of the polarizing film manufactured using the film (2), the variation range (%) in condition β is preferably 0.3% or less.

[0097] The above-mentioned predetermined temperature is a temperature selected in the range of 15℃ to 40℃, and the above-mentioned predetermined immersion time is an immersion time selected in the range of 20 seconds to 120 seconds.

[0098] The above width change rate (%) can be calculated, for example, in the same way as the above formula (1). The water in the description regarding the above condition β corresponds to the treatment liquid (8) in the immersion process A of the first embodiment.

[0099] The above fluctuation range (%) is the difference between the maximum value of the width change rate and the minimum value of the width change rate when the above width change rate is acquired continuously for 60 seconds or more.

[0100] Under the above condition β, the polyvinyl alcohol-based film is conveyed with the tension typically kept constant or with the ratio of the nip roll's rotational speed before and after immersion in water kept constant. When conveying the polyvinyl alcohol-based film with the tension typically kept constant, the tension is maintained at a level selected within the range of 5 N / m to 100 N / m. When conveying the polyvinyl alcohol-based film with the ratio of the rotational speed before and after immersion in water kept constant, the rotational speed ratio is maintained at a level selected within the range of 1.1 to 4.0. The rotational speed ratio is the ratio of the rotational speed of the nip roll before immersion in water to the rotational speed of the nip roll after immersion in water.

[0101] For example, in the immersion process A described using FIG. 2, the treatment solution (8) is water, and the film (2) is immersed in the treatment solution (8) at the predetermined temperature and predetermined immersion time. By calculating the variation range (%) of the width change rate (%) in the same manner as in the immersion process A, it can be verified whether the film (2) satisfies condition β. As described above, when the film (2) is conveyed while the tension is kept constant or while the rotational speed ratio before and after immersion in water is kept constant, the method of keeping the tension constant or the method of keeping the rotational speed ratio before and after immersion in water constant can be done in the same manner as in the immersion process A.

[0102] The above film (2) can be manufactured, for example, by adjusting the manufacturing conditions to satisfy the above condition β, such as by melt extrusion or solvent casting. In addition, when the above film (2) is prepared by a method including the process of coating and drying the aforementioned polyvinyl alcohol-based resin solution, it is easier to prepare a film that satisfies the above condition β, so it is preferable to dry it at a temperature of 30°C or higher and less than 50°C for 30 minutes or more.

[0103] In the case of manufacturing a polarizing film (4) using a film (2) that satisfies condition β, if swelling treatment is performed by, for example, by performing an immersion process (immersion process A) that satisfies condition α, a high-quality polarizing film can be obtained. In addition, since the film (2) is unlikely to break during the manufacturing of the polarizing film (4), the polarizing film (4) can be manufactured stably.

[0104] This point is explained in detail based on Example 1, Example 2, and Comparative Example 1. In Example 1, Example 2, and Comparative Example 1, a polyvinyl alcohol-based film is prepared. For convenience of explanation, the polyvinyl alcohol-based film prepared in Example 2 and Comparative Example 1, along with Example 1, is referred to as "film (2)".

[0105] [Example 1]

[0106] <Manufacturing of film (2)>

[0107] (Production of the base film)

[0108] A polypropylene containing a nucleating agent was produced by mixing 1% by weight of a nucleating agent containing high-density polyethylene with homopolypropylene, which is a homopolymer of propylene (Sumitomo MonoBrene (registered trademark) FLX80E4 manufactured by Sumitomo Chemical Co., Ltd., melting point Tm=163℃). From this and a random copolymer of propylene / ethylene containing about 5% by weight of ethylene units, "Sumitomo MonoBrene (registered trademark) W151," a polypropylene-based laminated film with a three-layer structure was produced by co-extrusion molding using a multilayer extrusion molding machine, wherein a resin layer containing the polypropylene containing the nucleating agent was disposed on both sides of a resin layer containing "Sumitomo MonoBrene (registered trademark) W151," and this was used as a base film. The total thickness of this substrate film was 100 μm, and the thickness ratio of each layer (polypropylene containing nucleating agent / W151 / polypropylene containing nucleating agent) was 3 / 4 / 3.

[0109] (Preparation of coating solution)

[0110] Polyvinyl alcohol powder ("Z-200" manufactured by Nihongo Seigaku Kogyo Co., Ltd., average molecular weight 1100, average degree of saponification 99.5 mol%) was dissolved in hot water at 95°C to prepare an aqueous polyvinyl alcohol solution with a concentration of 3 wt%. A crosslinking agent ("Sumiresin (registered trademark) 650" manufactured by Sumitomo Chemical Co., Ltd.) was mixed into the obtained aqueous solution in a ratio of 1 wt part per 2 wt parts of polyvinyl alcohol to prepare a coating solution for forming a primer layer.

[0111] In addition, polyvinyl alcohol powder ("PVA124" manufactured by Kuraray Co., Ltd., average degree of polymerization 2400, average degree of saponification 98.0–99.0 mol%) was dissolved in hot water at 95°C to prepare a polyvinyl alcohol-based coating solution for forming a resin layer, which is an aqueous polyvinyl alcohol solution with a concentration of 8 wt%.

[0112] (Painting and drying)

[0113] While continuously conveying the base film in the long direction, corona treatment was performed on one side thereof. Subsequently, a coating solution for the primer layer was continuously applied to the corona-treated surface using a micro-gravure coater, and by drying at 60°C for 3 minutes, a primer layer with a thickness of 0.2 μm was formed on one side thereof. Subsequently, while conveying the film in the long direction, a coating solution for forming the polyvinyl alcohol-based resin layer was continuously applied to each primer layer using a comma coater, and dried for 5 minutes using hot air at 80°C. After that, by completely drying using hot air at 30°C, a polyvinyl alcohol-based resin layer with an average thickness of 30 μm was formed on the primer layer, and wound onto an axis to obtain a disc roll of a laminated film having a base film and a film (2) laminated on the base film. The length of the laminated film wound on the disc roll was 5000 m, and the width of the laminated film was 800 mm. The laminated film constituting the disc roll was formed by laminating the film (2) onto the base film. As a result, as shown in Table 1, a film (2) with a width of 800 mm, a thickness (average thickness) of 30 μm, and a length of 5000 m could be obtained.

[0114]

[0115] <Manufacturing of Polarizing Films>

[0116] The film (2) was unraveled while peeling the base film from the laminated film, and as a swelling treatment (swelling process), it was immersed for 30 seconds in a swelling treatment tank containing pure water at 30°C while applying a tension of 10 N / m. Next, as a dyeing treatment, it was immersed for 60 seconds in a dyeing treatment tank containing an aqueous solution at 30°C containing iodine and potassium iodide, and uniaxial stretching was performed up to 2.2 times. Then, it was immersed in a boric acid treatment tank containing an aqueous solution at 55°C with a weight ratio of potassium iodide / boric acid / water of 12 / 4.4 / 100 to perform water resistance treatment, and uniaxial stretching was performed until the cumulative stretching ratio from the disc roll became 5.5 times. Next, the polarizing film was prepared by immersing it in a tank containing an aqueous boric acid solution at 40°C, then immersing it in a washing treatment tank containing pure water at 12°C, and then drying it at 70°C for 3 minutes using a drying oven.

[0117] In Example 1, while conveying the film (2), the width of the film (2) was continuously measured over the entire length of the film (2) before and after the swelling process. The width of the film (2) was calculated by irradiating LED light onto both ends of the film (2) conveyed on the rolls of nip rolls installed before and after the swelling treatment tank (at positions x1 and x2 in the example of FIG. 2), measuring the positions of both ends of the film from the difference in brightness between the film (2) and the rolls, and calculating the width from the measured positions. The timing of the width measurement before and after the swelling treatment tank was the same. Additionally, since FIG. 2 is a schematic diagram for explaining the immersion process, the film (2) is separated from the roll at position x2; however, in Example 1, since a dyeing treatment is performed following the swelling treatment as described above, the film was partially caught on the roll at position x2 as well. In addition, the variation range was calculated as the difference between the maximum and minimum values ​​among the width change rates calculated sequentially according to the width of the film (2) measured continuously in this manner. The results of the variation range calculation are as shown in Table 2. Table 2 also shows the conditions in the swelling process. The width change rate and variation range were calculated using Equation (1) and Equation (2).

[0118] In the manufacture of the polarizing film in Example 1, as shown in Table 2, no breakage of the film (2) occurred.

[0119] <Evaluation of Color Non-uniformity>

[0120] The manufactured polarizing film was placed in a dark room in a cross-Nicol state relative to a linear polarizing filter. Subsequently, 6000 cd / m² 2The backlight was irradiated onto the polarizing film through the linear polarizing filter, and the color non-uniformity of the polarizing film was observed visually. Then, the level (intensity) of the color non-uniformity was determined in three stages, “1,” “2,” and “3,” through visual sensory evaluation. Evaluation “1” indicates the weakest non-uniformity, evaluation “3” indicates the strongest non-uniformity, and evaluation “2” indicates an intermediate between evaluation “1” and evaluation “3.” In the sensory evaluation, the color non-uniformity was evaluated in three stages as described above by comparing it with a sample of a level determined according to the level (intensity) of the color non-uniformity. The polarizing film prepared in Example 1 was evaluated as “1.”

[0121] [Example 2]

[0122] In Example 2, a disc roll of a laminated film having a base film and a film (2) laminated on the base film was manufactured in the same manner as in 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) in Example 1, as shown in Table 1 above. In Example 2, the film (2) was unwound while peeling the base film from the laminated film, and a polarizing film was manufactured in the same manner as in Example 1, except that as a swelling treatment (swelling process), the film (2) was immersed for 20 seconds in a swelling treatment tank containing pure water at 35°C while applying a tension of 15 N / m.

[0123] In the manufacture of the polarizing film in Example 2, as shown in Table 2, no breakage of the film (2) occurred.

[0124] <Evaluation of Color Non-uniformity>

[0125] The color non-uniformity of the manufactured polarizing film was evaluated in the same way as in Example 1. The evaluation result of the polarizing film manufactured in Example 2 was “2”.

[0126] In Example 2 as in Example 1, the width of the film (2) was measured before and after the swelling process, and the variation range was calculated. The results of the variation range calculation were as shown in Table 2.

[0127] [Comparative Example 1]

[0128] In Comparative Example 1, a film (2) was prepared in the same manner as in Example 1, except that the coating solution for forming the polyvinyl alcohol-based resin layer was dried for 15 minutes using hot air at 100°C. Specifically, a disc roll of a laminated film having a base film and a film (2) laminated on the base film was prepared. 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) in Example 1, as shown in Table 1 above. The film (2) was unwound while peeling the base film from the disc roll prepared in this way, and a polarizing film was prepared in the same manner as in Example 1.

[0129] In the manufacture of the polarizing film in Comparative Example 1, as shown in Table 2, breakage of the film (2) occurred. In Comparative Example 1, after breakage occurred once in the film (2), the polarizing film was manufactured by unwinding the film (2) again from the same disc roll. In Comparative Example 2, breakage occurred twice until the film (2) was used for 2000 m.

[0130] <Evaluation of Color Non-uniformity>

[0131] The color non-uniformity of the manufactured polarizing film was evaluated in the same way as in Example 1. The evaluation result of the polarizing film manufactured in Comparative Example 1 was “3”.

[0132] In Comparative Example 1, just as in Example 1, the width of the film (2) was measured before and after the swelling process, and the variation range was calculated. The results of the variation range calculation were as shown in Table 2. Table 2 also indicates the conditions during the swelling process. 0.69 (%) in Table 2 was the variation range until the first break occurred, and 0.75% was the variation range until the second break occurred.

[0133]

[0134] 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 variation range was calculated. Accordingly, the variation range of Examples 1 and 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 acquired continuously for 60 seconds or more. As described above, pure water was used in the swelling treatment. Therefore, the immersion of the film (2) in pure water during the swelling treatment corresponds to the immersion of the film (2) under condition β. As shown in Table 2, based on the variation range (%) calculated from the swelling process conditions and width measurement results of Examples 1 and 2, the film (2) produced in Examples 1 and 2 satisfied condition β. Furthermore, the swelling process of Examples 1 and 2 corresponded to immersion process A satisfying condition α. Meanwhile, from the variation range (%) calculated from the measurement results of the conditions and width of the swelling process of Comparative Example 1, the film (2) manufactured in Comparative Example 1 did not satisfy condition β, and the swelling process of Comparative Example 1 did not satisfy condition α.

[0135] In addition, in Examples 1 and 2, in which swelling treatment is performed by carrying out an immersion process A satisfying condition α, the film (2) is less likely to break during the manufacture of the polarizing film, so the polarizing film can be manufactured stably. In Examples 1 and 2, since the film (2) satisfies condition β, it is easy to carry out the immersion process A.

[0136] From the results of Examples 1 and 2 shown in Table 2, it can be understood that color non-uniformity is further suppressed by having a variation range (%) of 0.3% or less.

[0137] The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiments, but is intended to include the scope defined by the claims, and is also intended to include all modifications within the meaning and scope equivalent to the claims.

[0138] In the case where the manufacturing method of the polarizing film includes a cleaning treatment in the cleaning treatment unit (134) as shown in FIG. 1, the cleaning treatment may be performed by spraying the treatment liquid as a shower, or by using a method that combines immersion and spraying, etc.

[0139] The method for measuring the width of the film (2) is not specifically limited to the method described above. For example, the width may be measured using 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 for obtaining the position of the ends (2a, 2b) of the film (2), a device for measuring the position of the ends (2a, 2b) is placed at each of the ends (2a, 2b) of the film (2), which is desirable in terms of installation space and equipment management (maintenance, inspection, etc.).

[0140] The stretching treatment in the stretching treatment section is not limited to a wet stretching method, but may also employ a dry stretching method. In the above-described embodiment, the sequence of treatments exemplified for manufacturing a polarizing film may be appropriately modified or combined within a range that does not deviate from the spirit of the present invention. The number of treatment tanks in each treatment section may be one or multiple.

[0141] The above embodiments and various modifications may be appropriately combined within the scope of not departing from the spirit of the present invention. Explanation of the symbols

[0142] 2 : Film (polyvinyl alcohol-based film) 4: Polarizing film 8 : Treatment solution 11: Nip Roll

Claims

Claim 1 A method for manufacturing a polarizing film while conveying a polyvinyl alcohol-based film, comprising an immersion process in which a long polyvinyl alcohol-based film is immersed in a treatment solution, wherein in the immersion process, the variation 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 solution is 0.5% or less, wherein the width change rate is calculated by the following formula (1), and the variation range is calculated by the following formula (2), wherein the immersion process is a method for manufacturing a polarizing film that is performed in a swelling treatment of the polyvinyl alcohol-based film: width change rate = |(W2-W1) / W1| × 100···(1) Variation range = maximum value of width change rate - minimum value of width change rate···(2) (wherein in formula (1), W1 [mm] represents the width of the polyvinyl alcohol-based film before immersion in the treatment solution, W2 [mm] represents the width of the polyvinyl alcohol-based film after immersion in the treatment solution. In Equation (2), the maximum and minimum values ​​of the width change rate are the values ​​obtained when the width change rate is acquired continuously for 60 seconds or more. Claim 2 A method for manufacturing a polarizing film according to claim 1, wherein in the immersion process, the polyvinyl alcohol-based film is immersed in the treatment solution while applying a constant tension using a nip roll before and after immersion in the treatment solution. Claim 3 A method for manufacturing a polarizing film according to claim 1, wherein in the immersion process, the polyvinyl alcohol-based film is immersed in the treatment solution while maintaining a constant ratio of the rotational speed of the nip roll before and after immersion in the treatment solution. Claim 4 delete Claim 5 delete Claim 6 When a long polyvinyl alcohol-based film is conveyed and immersed in water based on conditions including a predetermined temperature and a predetermined immersion time, the variation range (%) of the width change rate (%) in the width direction of the polyvinyl alcohol-based film before and after immersion is 0.5% or less, the width change rate is calculated by the following formula (1), and the variation range is calculated by the following formula (2), the predetermined temperature is a temperature selected in the range of 15℃ to 40℃, the predetermined immersion time is an immersion time selected in the range of 20 seconds to 120 seconds, and the variation range (%) 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 acquired continuously for 60 seconds or more. Polyvinyl alcohol-based film: Width change rate = |(W2-W1) / W1| × 100···(1) Variation range = Maximum value of width change rate - Minimum value of width change rate···(2) (Formula (1) Among them, W1 [mm] represents the width of the polyvinyl alcohol-based film before immersion in the treatment solution, and W2 [mm] represents the width of the polyvinyl alcohol-based film after immersion in the treatment solution.) Claim 7 In claim 6, the above variation range (%) is the variation range when the polyvinyl alcohol-based film is immersed in water based on conditions including the above predetermined temperature and the above predetermined immersion time while conveying the polyvinyl alcohol-based film while maintaining a tension selected in the range of 5 N / m to 100 N / m. Claim 8 In claim 6, the above variation range (%) is the variation range when the polyvinyl alcohol-based film is immersed in water based on conditions including the above predetermined temperature and the above predetermined immersion time, while conveying the polyvinyl alcohol-based film while maintaining the rotational speed ratio of the nip roll before and after immersion in water at a rotational speed ratio selected within the range of 1.1 to 4.

0. Claim 9 A polyvinyl alcohol-based film according to any one of claims 6 to 8, wherein the variation range (%) is 0.3% or less. Claim 10 A polyvinyl alcohol-based film according to any one of claims 6 to 8, wherein the length in the longitudinal direction of the polyvinyl alcohol-based film is 1000 m or more.

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