KR20220012192A - Method for manfacturing polarizing film and polyvinyl alcohol-based film - Google Patents

Abstract

The purpose of the present invention is to provide a manufacturing method of a polarizing film which can manufacture a polarizing film in a stable process and a polyvinyl alcohol-based film. The manufacturing method of the polarizing film while conveying the polyvinyl alcohol-based film comprises an immersion process of immersing a long polyvinyl alcohol-based film in a treatment solution, wherein in the immersion process, the variation (%) of a width change rate (%) in a 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

The manufacturing method and polyvinyl alcohol-type film of a polarizing film TECHNICAL FIELD

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

A polarizing film is manufactured by performing processes, such as swelling, dyeing|staining, crosslinking, extending|stretching, washing|cleaning, drying, to a polyvinyl alcohol-type film to a polyvinyl alcohol-type film, as it describes in patent documents 1 and 2, for example. In the process to the said polyvinyl alcohol-type film, a polyvinyl alcohol-type film may be immersed in a process liquid. For example, in a swelling process, a polyvinyl alcohol-type film is immersed in the water which is a process liquid.

[Patent Document 1] Japanese Patent Laid-Open No. 2016-48382 [Patent Document 2] Japanese Patent Laid-Open No. 2017-102438

In manufacture of the conventional polarizing film, the fracture|rupture of a film etc. may generate|occur|produce, and a production process may not be stable.

Then, this invention aims at providing the manufacturing method of a polarizing film which can manufacture a polarizing film in a stable process, and a polyvinyl alcohol-type film.

The inventors of this application discovered that the fracture|rupture of a film generate|occur|produced, when the fluctuation range of the rate of width change in the said immersion before and behind was too large at the time of manufacture of a polarizing film. Then, the manufacturing method of the following polarizing films was completed.

A method of manufacturing a polarizing film according to an aspect of the present invention is a method of manufacturing a polarizing film while conveying a polyvinyl alcohol-based film, wherein the polyvinyl alcohol-based film is immersed in a treatment solution in a long polyvinyl alcohol-based film. An immersion step is provided, wherein in the immersion step, the variation (%) 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% is below.

In the said manufacturing method, in the said immersion process, the fluctuation range (%) of the width change rate (%) of the width direction of a polyvinyl alcohol-type film is 0.5 % or less. In this case, since the said fluctuation range is small, a fracture|rupture does not easily generate|occur|produce in a film during manufacture of a polarizing film, and a polarizing film can be manufactured in a stable process.

In the said immersion process, you may immerse the said polyvinyl alcohol-type film in the said processing liquid, providing fixed tension|tensile_strength using the nip roll in the immersion to the said processing liquid before and behind.

In the said immersion process, you may immerse the said polyvinyl alcohol-type film in the said processing liquid, maintaining constant the rotational speed ratio of the nip roll before and behind immersion to the said processing liquid.

The said immersion process may be performed by the swelling process with respect to the said polyvinyl alcohol-type film. A swelling process is performed in the initial stage of manufacture of a polarizing film. Therefore, the width of the polyvinyl alcohol-based film tends to change in the swelling treatment. Therefore, in the said immersion process, it is effective to perform a swelling process.

The said width change rate may be computed by following formula (1), and the said fluctuation range may be computed by following formula (2).

Width change rate =|(W2-W1)/W1|×100...(1)

Variation width = maximum value of width change rate - minimum value of width change rate... (2)

(in formula (1), W1 [mm] represents the width of the polyvinyl alcohol-based film before being immersed in the treatment solution, and W2 [mm] is the width of the polyvinyl alcohol-based film after being immersed in the treatment solution In formula (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 calculated for 60 seconds or more.)

The polyvinyl alcohol-based film according to another aspect of the present invention is immersed in water based on conditions including a predetermined temperature and a predetermined immersion time while conveying a long polyvinyl alcohol-based film. The variation (%) of the width change rate (%) in the width direction of the polyvinyl alcohol-based film before and after is 0.5% or less, the predetermined temperature is a temperature selected from the range of 15°C to 40°C, and the predetermined immersion time is 20 It is an immersion time selected from the range of seconds to 120 seconds, and 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 more.

The polyvinyl alcohol-based film is used, for example, in the production of a polarizing film. The manufacturing method of a polarizing film has the immersion process of immersing a long polyvinyl alcohol-type film in a process liquid. When the immersion process is performed using the polyvinyl alcohol-based film, the width of change (%) 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 likely to be 0.5% or less. In this case, since the said fluctuation range is small, a fracture|rupture does not easily generate|occur|produce in a film during manufacture of a polarizing film, and a polarizing film can be manufactured in a stable process.

The fluctuation range (%) is based on conditions including the predetermined temperature and the 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 As a result, the fluctuation range in the case of immersion in the water may be sufficient.

The fluctuation range (%) is while conveying the polyvinyl alcohol-based film while maintaining the rotation speed ratio of the nip roll before and after immersion in water at a rotation speed ratio selected within the range of 1.1 to 4.0. The fluctuation range in the case of immersion in the water based on the conditions including the predetermined temperature and the predetermined immersion time may be sufficient.

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

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

ADVANTAGE OF THE INVENTION According to this invention, a polarizing film can be manufactured by a stable process.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic diagram for demonstrating the manufacturing method of the polarizing film which concerns on one Embodiment.
It is a figure for demonstrating the immersion process with which the manufacturing method of a polarizing film is equipped.
It is a figure for demonstrating an example of the acquisition method of a width change rate and a fluctuation|variation width.

EMBODIMENT OF THE INVENTION Hereinafter, embodiment of this invention is described with reference to drawings. In the drawings, the same reference numerals are attached to the same or corresponding parts, and overlapping explanations are omitted. Dimensional ratios in the drawings do not necessarily coincide with those described.

(First embodiment)

As 1st Embodiment, the manufacturing method of a polarizing film is demonstrated. BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic diagram explaining an example of the manufacturing method of the polarizing film which concerns on one Embodiment of this invention.

In the first embodiment, while conveying a long polyvinyl alcohol-based film 2 (hereinafter simply referred to as “film 2”), swelling treatment, dyeing treatment, crosslinking treatment, The polarizing film 4 is manufactured by performing an extending|stretching process and a drying process. The stretching treatment may be performed on the film 2 during any one treatment (eg, crosslinking treatment) or in parallel while performing a plurality of treatments.

The material of the film 2 should just be a well-known polyvinyl alcohol-type resin used for manufacture of a polarizing film, and it is preferable that it is saponified polyvinyl alcohol-type resin. It is preferable that it is 80.0-100.0 mol%, and, as for the range of saponification degree, it is more preferable that it is 90.0-99.5 mol%, It is still more preferable that it is 93.0-99.5 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 acetate groups) × 100, and can be obtained by the method prescribed in JIS K 6726 (1994). have. 100-10000 are preferable and, as for the average degree of polymerization of polyvinyl alcohol-type resin, 1000-10000 are more preferable. An average degree of polymerization is a numerical value which can be calculated|required according to the method set by JISK6726 (1994).

The length of the film 2 in the long direction is, for example, 1000 m or more. When the length in the long direction of the film 2 is 1000 m or more, the length in the long direction of the film 2 is, for example, 30000 m or less, preferably 20000 m or less. The example of the length of the width direction (direction orthogonal to a long direction) of the film 2 is 1300 mm - 5000 mm. An example of the thickness of the film 2 is 10 mu m to 100 mu m.

The film 2 is not specifically limited, It can manufacture by well-known methods, such as a melt extrusion method and a solvent casting method. For example, the film 2 is formed by coating a polyvinyl alcohol-based resin solution on a base film composed of a thermoplastic resin (polyolefin-based resin, (meth)acrylic-based resin, etc.) and drying the resin solution to form a film. It can be obtained by performing and peeling the obtained film (2) from a base film.

The said base film can provide a primer layer as needed. Although the thickness of a base film can be determined suitably, 1 micrometer - 500 micrometers are preferable, and 1 micrometer - 300 micrometers are more preferable. The width and length of the base film can be appropriately determined according to the size of the target film 2 .

The polyvinyl alcohol-type resin solution can be obtained by melt|dissolving the above-mentioned polyvinyl alcohol-type resin with water, alcohol, etc. The viscosity of the solution is preferably 500 cps to 10000 cps, more preferably 1000 cps to 7000 cps, and still more preferably 1000 cps to 5000 cps.

Coating of polyvinyl alcohol-type resin solution can be suitably selected from well-known methods, such as roll coating methods, such as gravure coating, and a die-coating method. The film thickness of the polyvinyl alcohol-type resin solution to be coated can be 50 micrometers - 1000 micrometers, for example.

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

Coating of the said polyvinyl alcohol-type resin solution, drying, and peeling of the film 2 from a base film can be performed continuously, conveying a base film.

Said drying WHEREIN: With respect to a base film, you may provide the tension|tensile_strength of 45 N or more per length 1m of the width direction of a base film in the conveyance direction (long direction of a base film) of a base film. Said drying WHEREIN: The dimensional change rate in the elongate direction of the base film before and behind drying may extend exceeding 0 %, ie, you may apply tension|tensile_strength in the elongate direction so that plastic deformation may occur. 0.01 % or more may be sufficient as the dimensional change rate, and 0.1 % or more may be sufficient as it. Moreover, it is preferable that it is 5 % or less, and, as for the dimensional change rate in a drying process, it is more preferable that it is 1 % or less.

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.

In FIG. 1, the case where the film 2 is prepared as the raw roll 6, each process is performed to the film 2 unwound from the raw roll 6, and the polarizing film 4 is obtained is shown. When the film 2 is produced 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, Each of the above-described processes may be performed during conveyance.

An example of the manufacturing method of the polarizing film 4 is demonstrated based on the aspect shown in FIG. First, the outline of the manufacturing apparatus 10 of the polarizing film 4 is demonstrated. The manufacturing apparatus 10 includes a plurality of nip rolls 11 , a plurality of guide rolls 12 , a swelling treatment section 13 ₁ , a dyeing treatment section 13 ₂ , a crosslinking treatment section 13 ₃ , and washing _A processing unit 134 and a drying processing unit ₁₃₅ are provided.

The some nip roll 11 and the some guide roll 12 comprise the conveyance mechanism of the film 2 . The conveyance path|route of the film 2 is comprised by arrange|positioning the some nip roll 11 and the some guide roll 12 suitably.

The swelling processing part 13 ₁ is a part which performs a swelling process on the film 2 . The swelling processing unit 13 ₁ has a processing tank in which the processing liquid for the swelling processing is stored. A swelling process is performed to the film 2 by immersing the film 2 in the processing liquid which the swelling processing part 13 ₁ has. In the first embodiment, a film in which the film 2 is immersed in the processing liquid by the nip roll 11 and the two guide rolls 12 arranged before and after the film 2 is immersed in the processing liquid. of the transport path is formed.

The said swelling treatment is performed for the objective of foreign material removal on the surface of the film 2, plasticizer removal in the film 2, provision of dyeing easiness in a post process, plasticization of the film 2, etc. Conditions for the swelling treatment can be determined within a range that can achieve these objects and within a range in which problems such as extreme dissolution of the film 2 and devitrification do not occur. In the swelling treatment section 13 ₁ , the swelling treatment is performed by immersing the film 2 in, for example, a treatment liquid having a temperature of 10°C to 50°C, preferably 15°C to 40°C. The time (immersion time) of a swelling process is about 5 second - 300 second, Preferably they are about 20 second - 120 second. An example of the processing liquid in the swelling processing unit 13 ₁ is water. Therefore, the swelling treatment can also serve as the water washing treatment of the film 2 .

The dyeing process part 132 is a part which performs dyeing process on the film ₂ . _The dyeing process part 132 has the process tank in which the process liquid for dyeing process was stored. A dyeing process is performed to the film 2 by immersing the film ₂ in the processing liquid which the dyeing|staining processing part 132 has. In the first embodiment, a film in which the film 2 is immersed in the processing liquid by the nip roll 11 and the two guide rolls 12 arranged before and after the film 2 is immersed in the processing liquid. of the transport path is formed.

The processing liquid which the dyeing|staining process part 132 in 1st Embodiment has is the aqueous solution of a dichroic dye, and by a dyeing process, the film ₂ is dyed with a dichroic dye. The dyeing process by a normal dichroic dye is performed for the objective of making the film 2 adsorb|suck a dichroic dye. The treatment conditions are determined according to the desired optical properties within a range that can achieve this purpose and within a range where problems 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 using iodine as a dichroic dye, for example, at a temperature of 10°C to 50°C, preferably 15°C to 40°C, 0.003 parts by weight to 0.2 parts by weight of iodine and potassium iodide with respect to 100 parts by weight of water A dyeing process is performed by immersing the film 2 in the aqueous solution containing 0.1 weight part - 10 weight part for 10 second - 600 second, Preferably it is 30 second - 300 second. Instead of potassium iodide, another iodide, such as zinc iodide, may be used. You may use another iodide together with potassium iodide. Further, a compound other than iodide, boric acid, zinc chloride, cobalt chloride, or the like may coexist. If it is a treatment solution containing 0.003 parts by weight or more of iodine with respect to 100 parts by weight of water, it can be regarded as a treatment solution 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 parts by weight to 0.1 parts by weight of the dichroic dye with respect to 100 parts by weight of water. The dyeing process is performed by immersing the film 2 in the aqueous solution to be used for 10 seconds to 600 seconds, preferably for 20 seconds to 300 seconds. The aqueous solution of the dichroic dye to be used may contain the dyeing aid etc., and may contain the inorganic salt like sodium sulfate, surfactant, etc. Only one type of dichroic dye may be used and two or more types of dichroic dyes may be used together according to a desired color.

The crosslinking processing section 133 is a portion that performs a crosslinking treatment on the film ₂ . _The crosslinking processing unit 133 has a processing tank in which the processing liquid for the crosslinking processing is stored. Crosslinking treatment is performed on the film 2 by immersing the film ₂ in the treatment liquid of the crosslinking treatment section 133 . In the first embodiment, a film in which the film 2 is immersed in the processing liquid by the nip roll 11 and the two guide rolls 12 arranged before and after the film 2 is immersed in the processing liquid. of the transport path is formed.

The crosslinking treatment is a treatment performed for the purpose of water resistance by crosslinking or color adjustment (preventing the film 2 from turning bluish, etc.).

_The treatment liquid used in the crosslinking treatment section 133 is, for example, an aqueous solution containing 1 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 crosslinking treatment section 133 preferably contains iodide in addition to boric acid, and the amount is, for example, ₁ weight per 100 parts by weight of water. parts to 30 parts by weight. Potassium iodide, zinc iodide, etc. are mentioned as an iodide. You may make it coexist with compounds other than iodide, zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, sodium sulfate, etc.

_In the crosslinking treatment in the crosslinking treatment unit 133 , the concentrations of boric acid and iodide and the temperature of the treatment liquid can be appropriately changed according to the purpose.

For example, when the purpose of the crosslinking treatment is water resistance by crosslinking, and the polyvinyl alcohol-based resin film is subjected to swelling treatment, dyeing treatment and crosslinking treatment in this order, the crosslinking agent-containing solution of the treatment solution is, for example, in a concentration by weight ratio. It is an aqueous solution of rhoboric acid/iodide/water = 3 to 10/1 to 20/100. 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 processing liquid at the time of immersing the film 2 is about 50 degreeC - 70 degreeC normally, Preferably it is 53 degreeC - 65 degreeC, and the immersion time of the film 2 is about 10 seconds - about 600 seconds normally. , Preferably it is 20 second - 300 second, More preferably, it is 20 second - 200 second. When the dyeing treatment and the crosslinking treatment are performed in this order on the film 2 stretched in advance before the swelling treatment, the temperature of the treatment liquid is usually about 50°C to 85°C, preferably 55°C to 80°C.

When the purpose of the crosslinking treatment is color adjustment, for example, when iodine is used as the dichroic dye, a crosslinking agent-containing solution having a concentration of boric acid/iodide/water = 1 to 5/3 to 30/100 in a weight ratio can be used as the treatment solution. . The temperature of the processing liquid at the time of immersing the film 2 is about 10-45 degreeC normally, and the immersion time of the film 2 is about 1-300 second normally, Preferably it is 2-100 second.

The washing process part 134 is a part which performs a washing process on the film ₂ after a crosslinking process. _The cleaning processing unit 134 has a processing tank in which a processing liquid for cleaning processing is stored. The washing process is performed on the film 2 by immersing the film ₂ in the process liquid which the washing|cleaning process part 134 has. In the first embodiment, a film in which the film 2 is immersed in the treatment liquid by the nip roll 11 and the two guide rolls 12 disposed before and after the film 2 is immersed in the treatment liquid. of the transport path is formed. As a processing liquid in a washing|cleaning process, the aqueous solution containing water, the aqueous solution containing potassium iodide, and boric acid is mentioned. 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 processing part 135 is a part which performs a drying processing on the film ₂ . In the first embodiment, the drying processing unit ₁₃₅ is a drying apparatus. _In the drying processing unit 135 , the film ₂ washed in the washing processing unit 134 is carried in, and while the film ₂ passes through the drying processing unit 135 , the film 2 is dried. . In 1st Embodiment, the conveyance path|route of the film which dries the film 2 with a drying apparatus is formed with the nip roll ₁₁ arrange|positioned before and behind the drying process part 135. In order to support and convey the film ₂ in the drying processing part 135, the guide roll 12 may be arrange|positioned suitably. Drying by the drying processing unit 135 is performed, for example, _in the drying processing unit 135 maintained at a temperature of 40°C to 100°C, for example, for ₃₀ seconds to 600 seconds. _In FIG. 1, the drying process part 135 is shown typically. The dry processing part 135 will not be specifically limited if the water|moisture content adhering to the film ₂ can be dried, Manufacture of a polarizing film WHEREIN: A well-known thing used normally may be sufficient as it.

In the manufacturing apparatus 10, using the rotational speed difference of the at least two nip rolls 11 (the upstream nip roll 11 and the downstream nip roll 11) in the some nip roll 11, The extending|stretching process which uniaxially stretches the film 2 is performed. In this case, the two nip rolls 11 contributing to the said uniaxial stretching process function as an extending|stretching part.

For example, you may perform the extending|stretching process of uniaxially extending|stretching using the rotational speed difference of the nip roll 11 arrange|positioned in front of the bridge|crosslinking process part 13 ₃ , and the nip roll 11 arrange|positioned behind the bridge|crosslinking process part 13 ₃ . In this case, since an extending|stretching process is performed in parallel with a crosslinking process, the bridge|crosslinking process part ₁₃₃ also functions as an extending|stretching process part. The stretching treatment is effective also in order to suppress the generation of wrinkles in the film 2 .

In addition to mainly performing the stretching treatment using the two nip rolls 11 disposed before and after one treatment section (eg, the crosslinking treatment section 13 ₃ described above), the drawing treatment is gradually performed using the other nip rolls 11 . may be further performed.

The manufacturing apparatus 10 may have an extending|stretching process part for performing an extending|stretching process separately. _In this case, the stretching processing unit is disposed, for example, at the rear end of the crosslinking processing unit 133 (eg, between the crosslinking processing unit ₁₃₃ and the washing processing unit ₁₃₄ ).

The manufacturing apparatus 10 may have a plurality of processing units of at least one of the swelling processing unit _{13 1} , the dyeing processing unit 13 ₂ , the crosslinking processing unit 13 ₃ , the washing processing unit ₁₃₄ , and the drying processing unit 135 . good. For example, the manufacturing apparatus 10 may be provided with the bridge|crosslinking process part 13 ₃ in multiple numbers. The manufacturing apparatus 10 may be equipped with the extending|stretching process part.

An example of the manufacturing method of the polarizing film 4 using the said manufacturing apparatus 10 is demonstrated. First, the film 2 is unwound from the original roll 6 . The unrolled film 2 is conveyed in the elongate direction of the film 2 along the conveyance path formed by the some nip roll 11 and the some guide roll 12. 1 m/min - 60 m/min may be sufficient as the example of a conveyance speed, and 1.5 m/min - 50 m/min may be sufficient as it. In the conveyance route of the film 2, from the raw roll 6 side, the swelling processing unit 13 ₁ , the dyeing processing unit 13 ₂ , the crosslinking processing unit 13 ₃ , the washing processing unit ₁₃₄ , and the drying processing unit ₁₃₅ . ) is provided. Moreover, as mentioned above, the at least two nip rolls 11 also have a function as an extending|stretching part. Therefore, by conveying the film 2 along a conveyance route, while a swelling process, a dyeing|staining process, a crosslinking process, a washing process, and a drying process are performed to the film 2, an extending|stretching process is performed. Thereby, linearly polarized light characteristic is provided to the film 2, and the polarizing film 4 is obtained.

The above-mentioned swelling treatment, dyeing treatment, crosslinking treatment and washing treatment are performed by immersing the film 2 in a treatment solution. Therefore, the manufacturing method of the polarizing film 4 has a some immersion process (the process of immersing the film 2 in a process liquid). In other words, a swelling process, a dyeing process, a crosslinking process, and a washing process are performed in the said some immersion process. The immersion process which the manufacturing method of the polarizing film 4 of 1st Embodiment demonstrates using FIG. 2 an at least 1 immersion process among a some immersion process corresponding to a swelling process, a dyeing process, a crosslinking process, and a washing process. (Hereinafter, for convenience of description, it is called "immersion process A").

It is a schematic diagram for demonstrating the immersion process A. In FIG. 2 , the processing liquid 8 is stored in the processing tank, and the state which is immersed while conveying the film 2 in the processing liquid 8 is shown typically. The treatment liquid 8 is a treatment liquid corresponding to the treatment performed in the immersion step A among the swelling treatment, the dyeing treatment, the crosslinking treatment, and the washing treatment. Similar to each processing unit shown in FIG. 1 , the conveyance path of the film 2 is formed by the nip roll 11 in front and back of the processing liquid 8 and the two guide rolls 12 . In the conveyance path, the nip roll 11 through which the film 2 before being immersed in the processing liquid 8 passes is called a nip roll _11UP , and the film 2 is immersed in the processing liquid 8 after The nip roll 11 through which the film 2 passes is also called nip roll _11DOWN .

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

The tension|tensile_strength in immersion process A is 3 N/m - 2000 N/m normally, Preferably they are 5 N/m - 1500 N/m. When an immersion process is a swelling process, More preferably, they are 3 N/m - 200 N/m, More preferably, they are 5 N/m - 100 N/m.

In the immersion process A, you may apply constant tension| _{tensile_strength} to the film 2 using nip roll 11UP and nip roll _11DOWN shown in FIG. 2, for example. For example, a constant tension can be provided by adjusting the rotation speed of the nip roll 11 _UP and the rotation speed in the nip roll 11 _DOWN . In this way, by providing a constant tension, the film 2 can be immersed in the treatment liquid 8 while maintaining the tension.

To adjust the tension, the tension may be detected, for example, by a tension detector. As the tension detector, a commercially available one can be used. For example, the tension is detected by the principle of a differential transformer method, a strain gauge method, or the like. 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 a drive device (eg, a servomotor, etc.) that drives the nip roll 11 _DOWN to control the drive, and the tension value is to keep it constant.

In the immersion process A, you may make the film 2 immerse in the process liquid, maintaining the rotational speed ratio of the nip roll before and behind immersion to the process liquid 8 constant. The said rotation speed ratio is ratio of the rotation speed of the nip roll _11UP before being immersed in the processing liquid 8, and the rotation speed of the nip roll _11DOWN after being immersed in the processing liquid 8. As described above, by immersing the film 2 in the treatment liquid while maintaining the rotational speed ratio constant, the film 2 can be immersed in the treatment liquid while maintaining the tension.

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

<Condition α>

The fluctuation width (%) of the width change rate (%) of the width direction of the film 2 before and after the film 2 is immersed in the processing liquid 8 is 0.5 % or less.

In one embodiment, the width change rate and the fluctuation width are calculated by the following formulas (1) and (2).

Width change rate =|(W2-W1)/W1|×100...(1)

Variation width = maximum value of width change rate - minimum value of width change rate... (2)

In formula (1), W1 [mm] represents the width of the film 2 before immersion in the treatment solution 8, and W2 [mm] represents the width of the film 2 after immersion in the treatment solution 8 indicates.

In Formula (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 fixed period, respectively.

The predetermined period is, for example, 60 seconds or longer, preferably 1 hour or longer, and more preferably 24 hours or longer. The upper limit of a fixed period is time when the immersion process A is implemented with respect to the full length of the film 2, and can be determined with the full length of the film 2, and a conveyance 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. 2 . 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. 2 . Position x2 represents the position after the film 2 has passed through the nip roll 11 _DOWN .

In order to acquire (or calculate) the said width change rate and fluctuation range, the manufacturing apparatus 10 has two width measuring devices 30 and the calculation part 40 shown in FIG. 3 with respect to the processing tank which implements the immersion process A. may have

An example of the width change rate and the acquisition method of the change width using the width measuring device 30 and the calculation part 40 is demonstrated. Hereinafter, a series of steps from the measurement of the width W1 and the width W2 to the acquisition of the rate of change of the width and the width of variation may be collectively referred to as a "monitoring process".

Each of the two width measuring instruments 30 is a device for continuously measuring the width of the film 2 . One of the two width measuring instruments 30 is a width measuring instrument for measuring the width W1 of the film 2 before the film 2 is immersed in the treatment liquid 8 (hereinafter referred to as "width measuring instrument 30 _UP ") ], and the other of the two width measuring instruments 30 is a measuring instrument for measuring the width W2 of the film 2 after the film 2 is immersed in the treatment liquid 8 [hereinafter referred to as “width measuring instrument 30 _DOWN )” called '].

Each of the width gauge 30 _UP and the width gauge 30 _DOWN has two end detection units 31 . One of the two edge detection parts 31 is a detection part which detects the one edge part 2a in the width direction of the film 2, and the other edge part 2b in the width direction of the film 2 is the other side. It is a detection part which detects [the end opposite to the said end part 2a]. Each end detection unit 31 detects an end of the film 2 , for example, optically and non-contact. Each edge detection part 31 should just be comprised so that the image of the edge part to be detected and its vicinity can be acquired. For example, the edge part detection part 31 may have an imaging part, 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 measurement unit 30 _UP and the width measurement unit 30 _DOWN has two edge detection units ( 31), the width W2 is calculated. For example, the calculation part 40 specifies the position of the edge parts 2a, 2b based on the detection result (for example, image data) of the two edge part detection parts 31 which the width measurement device _30UP has, by specifying the width Calculate W1 and width W2.

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

In the first embodiment, the width W1 is measured at the position x1, and then, the width W2 may be measured at the time when the film location where the width W1 is measured is conveyed to the position x2, and the width W1 is measured 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). In the "same timing", slight deviations may occur within a range that does not deviate from the spirit of the present invention. Although it does not specifically limit with the conveyance speed, either, the time difference between the measurement time at the said position x1 and the measurement time at the position x2 may be less than about 1 minute, may be less than 30 seconds, may be less than 20 seconds, may be less than 10 seconds. good.

It is preferable to automate (automation) and implement a monitoring process. In the first embodiment, in order to perform automation efficiently, 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.

Monitoring in the monitoring step WHEREIN: When the fluctuation range exceeds 0.5 %, the width change rate can be adjusted so that the said condition (alpha) may be satisfied by adjusting each processing condition etc. according to the process which is implementing the monitoring process. For example, the temperature of the treatment liquid 8, the immersion time (treatment time), the tension applied to the film 2, etc. may be adjusted so as to satisfy the above condition α, or used for the production of the polarizing film 4 The existing film 2 may be replaced. More specifically, in the monitoring step at the time of the swelling treatment, when the rate of change in width is small, the fluctuation range 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 range can be reduced by means such as lowering the temperature of the processing liquid, increasing the tension, or shortening the processing time. When the monitoring step is performed while performing the immersion of the film 2 in the treatment liquid in the crosslinking step as the immersion step A, the content of the crosslinking agent and the guide roll The fluctuation range can also be adjusted by arrangement or the like.

The manufacturing method of the polarizing film 4 has the immersion process A which satisfy|fills the said condition (alpha). Therefore, in the immersion process A, even if the film 2 is immersed in the process liquid 8, the fluctuation range of the width change rate of the film 2 is 0.5 % or less. In this case, since the fluctuation range of the film 2 is small, for example, the film 2 is hard to fracture|rupture during the immersion process A or in the process after immersion process A. As a result, the polarizing film 4 can be manufactured stably. Since the fluctuation range of the film 2 is small, defects resulting from the width change and poor appearance can be reduced. As a result, the polarizing film 4 with good quality can be manufactured.

It is effective that the immersion process A is implemented in a swelling process. As shown in FIG. 1, a swelling process is a process performed on the upstream side (initial stage in a manufacturing process) among several processes implemented with respect to the film 2 in order. Therefore, in a swelling process, since the width|variety of the film 2 changes easily, the quality improvement of the manufactured polarizing film 4 is attained by the said immersion process A being implemented by a swelling process. Further, during and after the swelling treatment, the film 2 is hardly fractured. When immersion process A is implemented by a swelling process, 15 to 40 degreeC is preferable, for example, and, as for the temperature of a processing liquid (for example, water), 20 second - 120 second are preferable for immersion time.

As described above, the immersion step A satisfying the condition α may be performed in at least one immersion step among a plurality of immersion steps corresponding to the swelling treatment, the dyeing treatment, the crosslinking treatment, and the washing treatment.

(Second embodiment)

As 2nd Embodiment, the elongate polyvinyl alcohol-type film 2 is demonstrated. Also in 2nd Embodiment, the polyvinyl alcohol-type film 2 is simply called "film 2". Examples of the material, length, and thickness of the film 2 according to the second embodiment are the same as in the case of the first embodiment.

The film 2 is a film which satisfies the following conditions (beta).

<condition β>

When the film 2 is immersed in water at a predetermined temperature and a predetermined immersion time while conveying the polyvinyl alcohol-based film, the fluctuation width (%) of the width change rate (%) of the film 2 before and after immersion ) is 0.5% or less.

From a viewpoint of suppressing further the color nonuniformity of the polarizing film manufactured using the film 2, the said fluctuation range (%) in condition (beta) becomes like this. Preferably it is 0.3 % or less.

The predetermined temperature is a temperature selected from the range of 15°C to 40°C, and the predetermined immersion time is an immersion time selected from the range of 20 seconds to 120 seconds.

The width change rate (%) may be calculated, for example, in the same manner as in Equation (1). Water in the description relating to the condition β corresponds to the treatment liquid 8 in the immersion step A of the first embodiment.

The 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 width change rate is continuously acquired for 60 seconds or more.

The said condition (beta) WHEREIN: The said polyvinyl alcohol-type film is normally conveyed in the state which made tension|tensile_strength constant, or the state which made the rotational speed ratio of the nip roll in water before and behind constant. When conveying the said polyvinyl alcohol-type film in the state which made tension|tensile_strength constant, let it be the state which maintained the tension|tensile_strength normally selected from the range of 5 N/m - 100 N/m. When conveying the said polyvinyl alcohol-type film in the state which made the rotation speed ratio in water before and behind immersion constant, let it be the state hold|maintained at the rotation speed ratio normally selected within the range of 1.1-4.0. The said rotation speed ratio is ratio of the rotation speed of the nip roll before being immersed in water, and the rotation speed of the nip roll after being immersed in water.

For example, in the immersion process A demonstrated using FIG. 2, the process liquid 8 is water, and the film 2 is immersed in the process liquid 8 at the said predetermined temperature and predetermined immersion time, In the case of immersion process A By doing the same as with and calculating the variation width (%) of the width change rate (%), it can be verified whether the film 2 is a film satisfying the condition β. As described above, when the film 2 is conveyed in a state in which the tension is constant or in a state in which the rotational speed ratio before and after immersion in water is constant, the method of making the tension constant or The method of making the said rotation speed ratio in immersion before and behind constant can be carried out similarly to the case of the immersion process A.

The film 2 can be produced, for example, by melt extrusion, solvent casting, or the like, by adjusting production conditions to satisfy the above condition β. In addition, when the film 2 is prepared by a method including the step of coating and drying the above-described polyvinyl alcohol-based resin solution, it is easy to prepare a film satisfying the above condition β, at 30° C. or higher. , drying at a temperature of less than 50° C. for at least 30 minutes is preferred.

In the case of manufacturing the polarizing film 4 using the film 2 which satisfies the condition β, for example, when a swelling treatment is performed by performing an immersion step (immersion step A) satisfying the condition α, a polarizing film with good quality can be obtained Moreover, since the film 2 is hard to fracture|rupture during manufacture of the polarizing film 4, the polarizing film 4 can be manufactured stably.

This point is concretely demonstrated based on Example 1, Example 2, and Comparative Example 1. In Example 1, Example 2, and Comparative Example 1, a polyvinyl alcohol-based film was prepared. For convenience of explanation, the polyvinyl alcohol-based films produced in Example 2 and Comparative Example 1 along with Example 1 are referred to as “film (2)”.

[Example 1]

<Production of film 2>

(Production of base film)

1 wt% of a nucleating agent containing high-density polyethylene is blended with homopolypropylene, a homopolymer of propylene (“Sumitomobrene (registered trademark) FLX80E4” manufactured by Sumitomo Chemical Co., Ltd., melting point Tm = 163° C.) , polypropylene containing a nucleating agent was prepared. From this and a random copolymer of propylene/ethylene containing about 5% by weight of ethylene units “Sumitomonobrene (registered trademark) W151”, by co-extrusion using a multi-layer extrusion molding machine, “Sumitomonobrene (registered trademark)” A long polypropylene-based laminated film having a three-layer structure in which a resin layer containing polypropylene containing the nucleating agent is disposed on both sides of a resin layer containing “trademark) W151” was prepared as a base film. The total thickness of this base film was 100 micrometers, and the thickness ratio (polypropylene/W151/polypropylene containing a nucleating agent containing a nucleating agent) of each layer was 3/4/3.

(Preparation of coating solution)

Polyvinyl alcohol powder (“Z-200” manufactured by Nippon Kosei Chemicals Co., Ltd., average molecular weight 1100, average degree of saponification 99.5 mol%) was dissolved in hot water at 95° C., and a polyvinyl alcohol aqueous solution having a concentration of 3 wt. prepared. A coating solution for forming a primer layer was prepared by mixing 1 part by weight of a crosslinking agent (“Sumirez Resin (registered trademark) 650” manufactured by Sumitomo Chemical Co., Ltd.) to the obtained aqueous solution with respect to 2 parts by weight of polyvinyl alcohol.

In addition, polyvinyl alcohol powder ("PVA124" manufactured by Kuraray Corporation, average degree of polymerization 2400, average degree of saponification of 98.0 to 99.0 mol%) is dissolved in hot water at 95°C, and polyvinyl alcohol aqueous solution having a concentration of 8% by weight of polyvinyl alcohol A coating liquid for forming a vinyl alcohol-based resin layer was prepared.

(coating and drying)

The single surface was corona-treated, conveying a base film continuously in a long direction. Subsequently, the coating solution for the primer layer was continuously coated on the corona-treated surface using a micro-gravure coater, and a primer layer having a thickness of 0.2 μm was formed on one side by drying at 60° C. for 3 minutes. Subsequently, the coating solution for forming a polyvinyl alcohol-based resin layer was continuously coated on each primer layer using a comma coater while the film was conveyed in a long direction, and dried using hot air at 80° C. for 5 minutes. Thereafter, by drying completely using hot air at 30° C., a polyvinyl alcohol-based resin layer having an average thickness of 30 μm is formed on the primer layer, wound on a shaft, and laminated on the base film and the base film (2) A raw roll of laminated film having The length of the laminated|multilayer film wound on the original roll was 5000 m, and the width|variety of the laminated|multilayer film was 800 mm. The laminated|multilayer film which comprises a raw roll was formed by laminating|stacking the film 2 on a 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.

<Production of polarizing film>

The film 2 was released while peeling the base film from the laminated film, and as a swelling treatment (swelling step), it was immersed for 30 seconds while applying a tension of 10 N/m to a swelling treatment tank containing 30° C. pure water. Next, as a dyeing treatment, uniaxial stretching is performed up to 2.2 times while being immersed in a dyeing treatment tank containing an aqueous solution at 30° C. containing iodine and potassium iodide for 60 seconds, and potassium iodide/boric acid/water is 12/4.4/100 by weight Uniaxial stretching was performed until the cumulative draw ratio from the original roll became 5.5 times while immersing in a boric acid treatment tank containing an aqueous solution of phosphorus at 55° C. and waterproofing treatment. Subsequently, after being immersed in a bath containing an aqueous boric acid solution at 40°C, immersed in a washing treatment bath containing pure water at 12°C, and then dried at 70°C for 3 minutes using a drying furnace to prepare a polarizing film.

In Example 1, the width of the film 2 was continuously measured over the entire length of the film 2 before and after the said swelling process, conveying the film 2. The width of the film 2 is about the film 2 conveyed on the roll which the nip roll provided before and behind the said swelling treatment tank has (in the example of FIG. 2, in the position of a position x1 and a position x2), both ends of a film was irradiated with LED light, and the position of both ends of the film was measured from the difference in luminance of the reflected light in the film 2 and the roll, and it was calculated from the measured position. The measurement timing of the width|variety in the front and back of the said swelling processing tank was the same. In addition, in Fig. 2, since it is a schematic diagram for explanation of the immersion process, the film 2 is separated from the roll at the position of position x2, but in Example 1, since the swelling treatment is followed by the dyeing treatment as described above, the position Even at the x2, the film was partially caught on the roll. In addition, the fluctuation range was computed as the difference between the maximum value and the minimum value among the width change rates sequentially calculated according to the width|variety of the film 2 measured continuously in this way. The calculation result of the fluctuation range is shown in Table 2. Table 2 also shows the conditions in the swelling step. The width change rate and the fluctuation range were calculated using Equations (1) and (2).

In manufacture of the said polarizing film in Example 1, as shown in Table 2, the fracture|rupture of the film 2 did not arise.

<Evaluation of color unevenness>

The prepared polarizing film was placed in a cross nicol state with respect to a linear polarizing filter in a dark room. Then, the backlight of 6000 cd/m< ² > was irradiated to the polarizing film through the said linear polarizing filter, and the color nonuniformity of the polarizing film was observed visually. And the level (strength) of color nonuniformity was judged by the sensory examination by visual observation in 3 steps of "1", "2", and "3". Evaluation "1" shows that the nonuniformity is the weakest, evaluation "3" shows the thing with the strongest nonuniformity, and evaluation "2" shows the middle of evaluation "1" and evaluation "3". In the sensory test, the color nonuniformity was evaluated in three stages as described above by comparing it with a level sample sample determined according to the level (intensity) of the color nonuniformity. The polarizing film manufactured in Example 1 was evaluation "1".

[Example 2]

In Example 2, it carried out similarly to the case of Example 1, and produced the raw roll of the laminated|multilayer film which has a base film and the film 2 laminated|stacked on the base film. The width, thickness, and length of the film (2) obtained in Example 2 were the same as those of the film (2) of Example 1, as shown in Table 1 above. In Example 2, the film 2 is released while peeling the base film from the laminated film, and as a swelling treatment (swelling step), while applying a tension of 15 N/m to a swelling treatment tank containing pure water at 35° C. 20 A polarizing film was manufactured in the same manner as in Example 1, except that it was immersed for a second.

In manufacture of the said polarizing film in Example 2, as shown in Table 2, the fracture|rupture of the film 2 did not generate|occur|produce.

<Evaluation of color unevenness>

The color nonuniformity of the manufactured polarizing film was carried out similarly to Example 1, and it evaluated. The evaluation result of the polarizing film manufactured in Example 2 was "2".

Also in Example 2, similarly to Example 1, the width|variety of the film 2 was measured before and behind a swelling process, and the fluctuation range was computed. The calculation result of the fluctuation range is shown in Table 2.

[Comparative Example 1]

In Comparative Example 1, a film (2) was manufactured in the same manner as in Example 1, except that the coating solution for forming a polyvinyl alcohol-based resin layer was dried for 15 minutes using hot air at 100°C. Specifically, the raw roll of the laminated|multilayer film which has a base film and the film 2 laminated|stacked on the base film was manufactured. The width, thickness, and length of the film (2) obtained in Comparative Example 1 were the same as those 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 prepared in this way, and it carried out similarly to Example 1, and manufactured the polarizing film.

In manufacture of the said polarizing film in the comparative example 1, as shown in Table 2, the fracture|rupture of the film 2 generate|occur|produced. In the comparative example 1, after a breakage generate|occur|produced in the film 2 once, the polarizing film was manufactured, unwinding the film 2 again from the same raw material roll. In Comparative Example 2, two fractures occurred until the film 2 was used for 2000 m.

<Evaluation of color unevenness>

The color nonuniformity of the manufactured polarizing film was carried out similarly to Example 1, and it evaluated. The evaluation result of the polarizing film manufactured by the comparative example 1 was "3".

Also in the comparative example 1, similarly to Example 1, the width|variety of the film 2 was measured before and behind a swelling process, and the fluctuation range was computed. The calculation result of the fluctuation range is 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 fracture occurred, and 0.75% was the fluctuation range until the second fracture occurred.

In Example 1 and Example 2, the width|variety of the film 2 before and behind a swelling treatment was continuously measured over the full length of the film 2, and the fluctuation range was computed as mentioned above. Therefore, the fluctuation range of Example 1 and Example 2 was the difference between the maximum value of the width change rate at the time of acquiring the width change rate continuously for 60 second or more, and the minimum value of the width change rate. As described above, pure water was used in the swelling treatment. Therefore, immersion of the film 2 to the pure water in the said swelling process corresponds to immersion of the film 2 in condition (beta). As shown in Table 2, from the fluctuation range (%) calculated from the measurement result of the conditions and width of the swelling process of Examples 1 and 2, the films 2 prepared in Examples 1 and 2 were subjected to condition β was satisfied. In addition, the swelling process of Example 1 and Example 2 corresponded to the immersion process A which satisfy|fills condition (alpha). On the other hand, from the fluctuation range (%) calculated from the measurement result of the conditions and width of the swelling process of Comparative Example 1, the film 2 prepared in Comparative Example 1 did not satisfy the condition β, and the swelling process of Comparative Example 1 was The condition α was not satisfied.

And in Example 1 and Example 2 which performed the swelling process by performing the immersion process A which satisfy|fills condition (alpha), since the film 2 is hard to fracture|rupture during manufacture of a polarizing film, a polarizing film can be manufactured stably . In Example 1 and Example 2, since the film 2 satisfy|fills the condition (beta), it is easy to implement the immersion process A.

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

As mentioned above, embodiment of this invention is described. However, this invention is not limited to the said embodiment, While it is intended that the range shown by a claim is included, it is intended that the meaning and equivalent of a claim and all the changes within the range are included. .

When the manufacturing method of a polarizing film has the washing process in the washing process part 134 as shown in FIG. ₁ , in a washing process, the method of spraying a process liquid with a shower, or the method of using immersion and spraying together The film 2 may be washed by such a method.

The measuring method of the width|variety of the film 2 is not specifically limited to the illustrated method. For example, the width may be measured with a measuring instrument such as a laser displacement gauge or an LED displacement gauge. 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 ends 2a and 2b of the film 2, the positions of the ends 2a, 2b are measured at the ends 2a, 2b of the film 2, respectively. Since what is necessary is just to arrange|position the apparatus to do, it is preferable from a viewpoint of installation space and apparatus management (maintenance inspection, etc.).

The extending|stretching process in an extending|stretching part is not limited to the wet extending|stretching method, A dry extending|stretching method may be employ|adopted. In the above-mentioned embodiment, the order of the process illustrated in order to manufacture a polarizing film may be suitably changed or combined in the range which does not deviate from the meaning of this invention. One may be sufficient as the number of the processing tank which each processing part has, and multiple may be sufficient as it.

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)

A method for producing a polarizing film while conveying a polyvinyl alcohol-based film, the method comprising:
An immersion step of immersing a long polyvinyl alcohol-based film in a treatment solution,
In the immersion step, the variation (%) of the width change rate (%) of the polyvinyl alcohol-based film in the width direction before and after the polyvinyl alcohol-based film is immersed in the treatment solution is 0.5% or less
A method for manufacturing a polarizing film. The method according to claim 1, wherein in the immersion step, the polyvinyl alcohol-based film is immersed in the treatment liquid while applying a constant tension using a nip roll before and after immersion in the treatment liquid.
A method for manufacturing a polarizing film. The method according to claim 1, wherein in the immersion 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 immersion in the treatment liquid.
A method for manufacturing a polarizing film. The method according to any one of claims 1 to 3, wherein the immersion step is performed in the swelling treatment of the polyvinyl alcohol-based film.
A method for manufacturing a polarizing film. 5. The method according to any one of claims 1 to 4,
The width change rate is calculated by the following formula (1),
The fluctuation range is calculated by the following formula (2)
A method for producing a polarizing film:
Width change rate =|(W2-W1)/W1|×100...(1)
Variation width = maximum value of width change rate - minimum value of width change rate... (2)
(in formula (1), W1 [mm] represents the width of the polyvinyl alcohol-based film before being immersed in the treatment solution, and W2 [mm] is the width of the polyvinyl alcohol-based film after being immersed in the treatment solution In formula (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.) The width in the width direction of the polyvinyl alcohol-based film before and after the immersion when it is immersed in water based on conditions including a predetermined temperature and a predetermined immersion time while conveying a long polyvinyl alcohol-based film The variation (%) of the rate of change (%) is 0.5% or less,
The predetermined temperature is a temperature selected from the range of 15 ℃ ~ 40 ℃,
The predetermined immersion time is an immersion time selected from the range of 20 seconds to 120 seconds,
The 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 width change rate is continuously acquired for 60 seconds or more
Polyvinyl alcohol-based film. The method according to claim 6, wherein the variation (%) is the predetermined temperature and the 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. Based on the condition including
Polyvinyl alcohol-based film. The polyvinyl alcohol system according to claim 6, wherein the variation (%) is 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. It is the fluctuation range in the case where it is made to immerse in the said water based on the conditions including the said predetermined temperature and the said predetermined|prescribed immersion time while conveying a film
Polyvinyl alcohol-based film. The method according to any one of claims 6 to 8, wherein the fluctuation range (%) is 0.3% or less.
Polyvinyl alcohol-based film. 10. The method according to any one of claims 6 to 9, wherein the length in the long direction of the polyvinyl alcohol-based film is 1000 m or more.
Polyvinyl alcohol-based film.

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