Polarizing film manufacturing method and manufacturing device

Abstract

The present invention provides a method and apparatus for manufacturing a polarizing film capable of manufacturing a polarizing film having a uniform shrinkage force in the width direction. The method includes a stretching step in which a polyvinyl alcohol-based resin film is stretched between a pair of nip rollers while being conveyed. In the stretching step, when the width of the nip roller on the upstream side of the pair of nip rollers in the film conveying direction is set to A [mm], the width of the nip roller on the downstream side of the pair of nip rollers in the film conveying direction is set to B [mm], and the width of the polyvinyl alcohol-based resin film that is about to contact the downstream nip roller in the film conveying direction is set to C [mm], 3.0 ≤ Y < 7.0 [where Y = (A + B + C) / C] is satisfied.

Description

Technical Field

[0001] The present invention relates to a method and apparatus for manufacturing a polarizing film. Background Art

[0002] For example, Patent Documents 1 and 2 propose methods for producing polarizing films.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2017-149052

[0006] Patent Document 2: Japanese Patent Application Publication No. 2017-105970 Summary of the Invention

[0007] Problems to be solved by the invention

[0008] An object of the present invention is to provide a method and apparatus for producing a polarizing film, which are capable of producing a polarizing film having a uniform shrinkage force in the width direction of the polarizing film.

[0009] Means for solving problems

[0010] The present invention provides the following polarizing film manufacturing apparatus and manufacturing method.

[0011] [1] A method for producing a polarizing film, comprising a stretching step of stretching a polyvinyl alcohol-based resin film between a pair of nip rollers while conveying the film,

[0012] In the stretching treatment step, when the width of the nip roller on the upstream side in the film conveying direction of the pair of nip rollers is A [mm], the width of the nip roller on the downstream side in the film conveying direction is B [mm], and the width of the polyvinyl alcohol-based resin film that is about to come into contact with the nip roller on the downstream side in the film conveying direction is C [mm], the following formula (1) is satisfied:

[0013] 3.0≤Y<7.0 (1)

[0014] [Wherein, Y=(A+B+C) / C].

[0015] [2] The method for producing a polarizing film according to [1], wherein A [mm] and C [mm] satisfy the following formula (2):

[0016] 1.0<A / C<3.0 (2).

[0017] [3] The method for producing a polarizing film according to [1] or [2], wherein B [mm] and C [mm] satisfy the following formula (3):

[0018] 1.0<B / C<3.0 (3).

[0019] [4] The method for producing a polarizing film according to any one of [1] to [3], wherein:

[0020] It also includes the following steps:

[0021] The unwinding process is to unwind a long strip of polyvinyl alcohol resin film from the raw material roll;

[0022] a swelling treatment step of immersing the polyvinyl alcohol-based resin film after the unwinding step in a swelling bath and then pulling it out;

[0023] a dyeing treatment step of immersing the polyvinyl alcohol-based resin film after the swelling treatment step in a dyeing bath and then pulling it out; and

[0024] In a cross-linking treatment step, the dyed polyvinyl alcohol resin film is immersed in a cross-linking bath and then pulled out.

[0025] The stretching treatment step is performed in at least one of the swelling treatment step, the dyeing treatment step, and the cross-linking treatment step.

[0026] [5] The method for producing a polarizing film according to [4], wherein the stretching treatment step is performed during the cross-linking treatment step.

[0027] [6] The method for manufacturing a polarizing film according to [5], wherein the cross-linking treatment process includes: a first cross-linking treatment process, immersing the polyvinyl alcohol-based resin film after dyeing treatment in a first cross-linking bath and then pulling it out; and a second cross-linking treatment process, immersing the polyvinyl alcohol-based resin film after the first cross-linking treatment process in a second cross-linking bath and then pulling it out, and the stretching treatment process is implemented in the second cross-linking treatment process.

[0028] [7] A polarizing film manufacturing device, comprising:

[0029] a guide roller for conveying the long polyvinyl alcohol-based resin film along a film conveyance path while unwinding the long polyvinyl alcohol-based resin film from a raw material roll; and

[0030] A pair of nip rollers are used to stretch the unwound polyvinyl alcohol resin film.

[0031] When the width of the nip roller disposed on the upstream side of the film transport path is A [mm], the width of the nip roller disposed on the downstream side of the film transport path is B [mm], and the width of the polyvinyl alcohol-based resin film that is about to come into contact with the nip roller disposed on the downstream side of the film transport path is C [mm], the following formula (4) is satisfied:

[0032] 3.0≤Y<7.0 (4)

[0033] [Wherein, Y=(A+B+C) / C].

[0034] [8] The polarizing film manufacturing apparatus according to [7], wherein A [mm] and C [mm] satisfy the following formula (5):

[0035] 1.0<A / C<3.0 (5).

[0036] [9] The polarizing film manufacturing apparatus according to [7] or [8], wherein B [mm] and C [mm] satisfy the following formula (6):

[0037] 1.0<B / C<3.0 (6).

[0038]

[10] The polarizing film manufacturing apparatus according to any one of [7] to [9], wherein a bath for performing a swelling treatment, a bath for performing a dyeing treatment, and a bath for performing a cross-linking treatment are sequentially provided on the film transport path.

[0039] The pair of nip rollers is provided at the inlet and the outlet of at least one of the baths.

[0040]

[11] The polarizing film manufacturing apparatus according to

[10] , wherein the pair of nip rollers are provided at the inlet and outlet of the bath for performing the crosslinking treatment.

[0041]

[12] A polarizing film manufacturing device according to

[11] , wherein the bath for implementing the cross-linking treatment comprises a first cross-linking bath and a second cross-linking bath in sequence from the upstream side of the film conveying path, and the pair of clamping rollers are provided at the inlet and outlet of the second cross-linking bath.

[0042] Effects of the Invention

[0043] According to the present invention, a method and apparatus for producing a polarizing film capable of producing a polarizing film having uniform shrinkage force in the width direction can be provided. In addition, the polarizing film obtained using the method and apparatus for producing a polarizing film of the present invention has excellent thickness uniformity and optical properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1This is a schematic diagram schematically showing an example of a method for producing a polarizing film.

[0045] Figure 2 This is a flowchart showing a method for producing a polarizing film.

[0046] Figure 3 It is a cross-sectional view schematically showing an example of an apparatus for producing a polarizing film.

[0047] Figure 4 It is a cross-sectional view schematically showing an example of a cross-linking bath of an apparatus for producing a polarizing film.

[0048] Description of Reference Numerals

[0049] 1, 2 clamping rollers, 1a, 1b, 2a, 2b rollers, 3 polyvinyl alcohol resin film, 10 raw material film, 11 raw material roll, 13 swelling bath, 15 dyeing bath, 17 cross-linking bath, 17a first cross-linking bath, 17b second cross-linking bath, 19 cleaning tank, 21 drying oven, 23 polarizing film, 30-50 guide rollers, 51-57 clamping rollers. DETAILED DESCRIPTION

[0050] The following describes embodiments of the present invention with reference to the accompanying drawings. However, the present invention is not limited to the following embodiments. In all the following drawings, the proportions of the components are appropriately adjusted to facilitate understanding, and the proportions of the components shown in the drawings are not necessarily consistent with the proportions of the actual components.

[0051] <Polarizing Film Manufacturing Method>

[0052] The method for producing a polarizing film according to one embodiment of the present invention includes a stretching step of stretching a polyvinyl alcohol-based resin film between a pair of nip rolls while conveying the film.

[0053] [Polyvinyl alcohol-based resin film]

[0054] A resin obtained by saponifying a polyvinyl acetate resin can be used as the polyvinyl alcohol resin for forming the polyvinyl alcohol resin film. As the polyvinyl acetate resin, in addition to polyvinyl acetate as a homopolymer of vinyl acetate, copolymers of vinyl acetate and other monomers copolymerizable therewith can also be exemplified. Other monomers copolymerizable with vinyl acetate include, for example, unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids, (meth)acrylamides having ammonium groups, and the like. The saponification degree of the polyvinyl alcohol resin is generally about 85 mol% or more, preferably about 90 mol% or more, and more preferably about 99 mol% or more. The so-called "(meth)acrylic" in this specification refers to at least one selected from acrylic acid and methacrylic acid. The same applies to "(meth)acryloyl".

[0055] The polyvinyl alcohol-based resin may be modified. For example, polyvinyl formal, polyvinyl acetal, polyvinyl butyral, etc. modified with aldehydes may be used.

[0056] The average degree of polymerization of the polyvinyl alcohol resin is preferably 100 to 10,000, more preferably 1,500 to 8,000, and even more preferably 2,000 to 5,000. The average degree of polymerization of the polyvinyl alcohol resin can be determined in accordance with JIS K 6726 (1994). If the average degree of polymerization is less than 100, it is difficult to obtain preferred polarization performance, while if it is greater than 10,000, the film processability may be poor.

[0057] The width of the polyvinyl alcohol-based resin film as the raw material film is, for example, 300 mm or more and 5000 mm or less.

[0058] The thickness of the polyvinyl alcohol-based resin film as the raw material film is, for example, approximately 10 μm to 50 μm. From the viewpoint of making the thickness of the polarizing film 15 μm or less, the thickness is preferably 40 μm or less, and more preferably 30 μm or less.

[0059] [Stretching process]

[0060] The stretching step is a step of stretching the polyvinyl alcohol-based resin film between a pair of nip rolls while conveying it. The stretching step may be uniaxial stretching. The stretching step may be dry stretching performed in mid-air, wet stretching performed in a treatment bath described below, or both. The stretching step may be inter-roll stretching, in which a circumferential speed difference is established between the pair of nip rolls to perform uniaxial stretching in the film conveyance direction.

[0061] The stretching ratio based on the original film (the cumulative stretching ratio when the stretching treatment is performed in two or more stages) is about 3 times or more and 8 times or less. In order to impart good polarization characteristics, the stretching ratio is preferably 4 times or more, more preferably 5 times or more.

[0062] Figure 1 This is a schematic diagram showing a stretching process. When the width of the nip roller 1 on the upstream side in the film conveying direction of the nip rollers 1 and 2 forming a pair of nip rollers is set to A [mm] (hereinafter also referred to as the upstream nip roller width A), the width of the nip roller 2 on the downstream side in the film conveying direction is set to B [mm] (hereinafter also referred to as the downstream nip roller width B), and the width of the polyvinyl alcohol-based resin film 3 that is about to contact the nip roller 2 on the downstream side in the film conveying direction is set to C [mm] (hereinafter also referred to as the PVA width C), the following formula (1) is satisfied:

[0063] 3.0≤Y<7.0 (1)

[0064] [Wherein, Y=(A+B+C) / C].

[0065] The nip roll is usually formed of two rolls. Figure 1 In the embodiment, the nip roller 1 is formed by two rollers 1a and 1b, and the nip roller 2 is formed by two rollers 2a and 2b. The widths of the two rollers forming the nip roller may be the same or different from each other.

[0066] During the stretching process, by satisfying the above formula (1), the shrinkage force and thickness deviation of the resulting polarizing film in the width direction are reduced, and it is easy to obtain excellent visibility-corrected single transmittance Ty (hereinafter also referred to as transmittance Ty) and visibility-corrected single polarization degree Py (hereinafter also referred to as polarization degree Py). In this specification, the width direction of the polarizing film is a direction perpendicular to the film conveyance direction, that is, a direction perpendicular to the absorption axis of the polarizing film.

[0067] Y in the above formula (1) is preferably 3.1 or greater, more preferably 3.3 or greater, and even more preferably 3.5 or greater. Y in the above formula (1) is preferably 6.9 or less, more preferably 6.7 or less, even more preferably 6.5 or less, and particularly preferably 6.3 or less.

[0068] The upstream nip roller width A is, for example, 300 mm to 3600 mm. If the widths of the two rollers forming the upstream nip roller are different, the shorter roller width is defined as the upstream nip roller width A.

[0069] The downstream nip roller width B is, for example, 300 mm to 3100 mm. If the widths of the two downstream nip rollers are different, the width of the shorter roller is defined as the downstream nip roller width B.

[0070] The upstream side nip roller width A [mm] and the downstream side nip roller width B [mm] may be the same or different.

[0071] The PVA width C is, for example, not less than 300 mm and not more than 3000 mm.

[0072] From the viewpoint of uniformity of shrinkage force and thickness in the width direction of the polarizing film, the upstream nip roller width A and the PVA width C preferably further satisfy the following formula (2):

[0073] 1.0<A / C<3.0 (2).

[0074] A / C in the above formula (2) is preferably 1.1 or more, more preferably 1.2 or more. A / C in the above formula (2) is preferably 2.9 or less, more preferably 2.7 or less, further preferably 2.6 or less, and particularly preferably 2.5 or less.

[0075] From the viewpoint of uniformity of shrinkage force and thickness in the width direction of the polarizing film, the upstream nip roller width B and the PVA width C preferably further satisfy the following formula (3):

[0076] 1.0<B / C<3.0 (3).

[0077] The B / C in the above formula (3) is preferably 1.1 or more, more preferably 1.2 or more. The B / C in the above formula (3) is preferably 2.9 or less, more preferably 2.7 or less, further preferably 2.6 or less, and particularly preferably 2.5 or less.

[0078] Figure 1 Although not shown in the drawings, one or more guide rollers may be used between the pair of nip rollers 1 and 2 to support the film.

[0079] [One embodiment of a method for producing a polarizing film]

[0080] The manufacturing method of the polarizing film may also include the following steps: a rolling-out step, rolling out a long strip of polyvinyl alcohol resin film from the original material roll; a swelling treatment step, immersing the polyvinyl alcohol resin film after the rolling-out step in a swelling bath and then pulling it out; a dyeing treatment step, immersing the polyvinyl alcohol resin film after the swelling treatment step in a dyeing bath and then pulling it out; and a cross-linking treatment step, immersing the polyvinyl alcohol resin film after the dyeing treatment in a cross-linking bath and then pulling it out.

[0081] The stretching step may be performed in any one or more of the swelling step, the dyeing step, and the cross-linking step. Furthermore, other stretching treatments may be performed in addition to the aforementioned stretching steps. Examples of the other stretching treatments include inter-roll stretching, hot roll stretching, and tenter stretching, in addition to the aforementioned stretching treatments.

[0082] The above steps can be continuously carried out by continuously conveying the polyvinyl alcohol-based resin film as the raw film along a film conveying path of the polarizing film manufacturing apparatus. The film conveying path is equipped with equipment (treatment tanks, furnaces, etc.) for carrying out the steps in the order in which they are carried out.

[0083] The film transport path can be constructed by placing the aforementioned equipment in appropriate locations, along with guide rollers, nip rollers, and the like. For example, guide rollers can be placed before or after, or within, the treatment baths described below, allowing the film to be introduced into, immersed in, and removed from the treatment baths. More specifically, two or more guide rollers can be installed in each treatment bath, and the film can be transported along these guide rollers, thereby immersing the film in each treatment bath.

[0084] Regarding the method for manufacturing the polarizing film, referring to Figure 2 A more detailed description will be given at the same time. Figure 2 The manufacturing method shown includes: a rolling-out step S10, rolling out a long strip of polyvinyl alcohol-based resin film from a raw material roll; a swelling treatment step S20, immersing the polyvinyl alcohol-based resin film after the rolling-out step in a swelling bath and then pulling it out; a dyeing treatment step S30, immersing the polyvinyl alcohol-based resin film after the swelling treatment step in a dyeing bath and then pulling it out; and a cross-linking treatment step S40, immersing the polyvinyl alcohol-based resin film after the dyeing treatment in a cross-linking bath and then pulling it out; a cleaning step S50, immersing the film after the cross-linking treatment step S40 in a cleaning tank; and a drying step S60 after the cleaning step S50.

[0085] As described above, the polyvinyl alcohol-based resin film may be subjected to the stretching treatment step in one or more stages of the polarizing film production process, more specifically, in one or more stages from the swelling treatment step S20 to the crosslinking treatment step S40 .

[0086] [Unwinding process]

[0087] For example, the polyvinyl alcohol resin film as the raw material film can be prepared in the form of a long unstretched or stretched polyvinyl alcohol resin film roll (wound product). In this case, the polarizing film is also obtained in the form of a long strip. In the unwinding step S10, the long polyvinyl alcohol resin film can be unwound from the raw material roll using an unwinding device. The unwound polyvinyl alcohol resin film is continuously transported along the film transport path.

[0088] [Swelling treatment process]

[0089] Swelling treatment is a treatment performed as needed for the purpose of removing foreign matter, removing plasticizers, imparting dyeability, and plasticizing the polyvinyl alcohol-based resin film as a base film. Specifically, it can be performed by immersing the polyvinyl alcohol-based resin film in a bath for performing swelling treatment (hereinafter also referred to as a swelling bath) containing a treatment liquid containing water. The film may be immersed in a single swelling bath or in two or more swelling baths in sequence.

[0090] The stretching treatment step may be performed before the swelling treatment, during the swelling treatment, or before and during the swelling treatment.

[0091] The treatment liquid contained in the swelling bath may be water (for example, pure water), or an aqueous solution to which a water-soluble organic solvent such as alcohol is added.

[0092] The temperature of the treatment liquid contained in the swelling bath during immersion of the membrane is usually about 10 to 70° C., preferably about 15 to 50° C., and the membrane immersion time is usually about 10 to 600 seconds, preferably about 20 to 300 seconds.

[0093] The swelling treatment step may include a tank for performing a water washing treatment for washing the polyvinyl alcohol-based resin film before performing the swelling treatment (hereinafter also referred to as a water washing treatment tank).

[0094] [Dyeing process]

[0095] The dyeing process in this step is performed to cause the polyvinyl alcohol-based resin film to adsorb a dichroic pigment and orient the dichroic pigment. Specifically, it can be performed by immersing the polyvinyl alcohol-based resin film in a bath for dyeing (hereinafter referred to as a dyeing bath) containing a treatment solution containing a dichroic pigment. The film can be immersed in a single dyeing bath or in two or more dyeing baths in sequence. For example, when immersed in two dyeing baths in sequence, the steps are sometimes referred to as the first dyeing process step and the second dyeing process step, starting from the upstream side in the film transport direction.

[0096] In order to improve the dyeing properties of the dichroic dye, the film subjected to the dyeing process may be subjected to at least some degree of stretching. Alternatively, the stretching process may be performed during the dyeing process instead of the stretching process before the dyeing process, or in addition to the stretching process before the dyeing process, the stretching process may be performed during the dyeing process.

[0097] The dichroic pigment may be iodine or a dichroic organic dye. Specific examples of the dichroic organic dye include Red BR, Red LR, Red R, Pink LB, Rubine BL, Bordeaux GS, Sky Blue LG, Lemon Yellow, Blue BR, Blue 2R, Navy RY, Green LG, Violet LB, Violet B, Black H, Black B, Black GSP, Yellow 3G, Yellow R, Orange LR, Orange 3R, Scarlet GL, Scarlet KGL, Congo Red, Brilliant Violet BK, Supra Blue G, Supra Blue GL, Supra Orange GL, Direct Sky Blue, Direct Fast Orange S, Fast Black. The dichroic pigment may be used alone or in combination of two or more.

[0098] When using iodine as the dichroic pigment, the treatment solution of holding in the dye bath can use the aqueous solution that contains iodine and potassium iodide.Also can replace potassium iodide and use other iodides such as zinc iodide, also can use potassium iodide and other iodides.In addition, also can coexist the compound beyond the iodide, for example boric acid, zinc chloride, cobalt chloride etc.When adding boric acid, be different from the cross-linking treatment described later in comprising iodine this point.The content of iodine in the above-mentioned aqueous solution is usually more than 0.01 mass parts and below 1 mass parts in per 100 mass parts water.In addition, the content of iodides such as potassium iodide is usually more than 0.5 mass parts and below 20 mass parts in per 100 mass parts water.

[0099] The temperature of the treatment liquid contained in the dyeing bath when immersing the film is usually 10°C or higher and 45°C or lower, preferably 10°C or higher and 40°C or lower, more preferably 20°C or higher and 35°C or lower, and the immersion time of the film is usually 30 seconds or higher and 600 seconds or lower, preferably 60 seconds or higher and 300 seconds or lower.

[0100] When a dichroic organic dye is used as the dichroic pigment, the treatment liquid contained in the dye bath can be an aqueous solution containing the dichroic organic dye. The content of the dichroic organic dye in the aqueous solution is usually 1×10-4 parts by mass or more and 10 parts by mass or less, preferably 1×10 -3 The dye bath may contain at least one part by mass and no more than 1 part by mass. Dyeing auxiliaries, such as inorganic salts such as sodium sulfate and surfactants, may also be present in the dye bath. A single dichroic organic dye may be used alone, or two or more may be used in combination. The temperature of the treatment liquid contained in the dye bath during immersion of the film is, for example, from 20°C to 80°C, preferably from 30°C to 70°C. The immersion time of the film is generally from 30 seconds to 600 seconds, preferably from 60 seconds to 300 seconds.

[0101] [Cross-linking treatment process]

[0102] The cross-linking treatment of the polyvinyl alcohol-based resin film after the dyeing treatment process with a cross-linking agent is a treatment performed for the purpose of water resistance and color tone adjustment by cross-linking. Specifically, it can be a treatment process in which the film after the dyeing treatment process is immersed in a treatment solution contained in a bath containing a cross-linking agent for implementing the cross-linking treatment (hereinafter also referred to as a cross-linking bath). The film can be immersed in one cross-linking bath or in two or more cross-linking baths in sequence. A stretching treatment process can be performed during the cross-linking treatment. For example, when immersed in two cross-linking baths in sequence, sometimes the first cross-linking treatment process and the second cross-linking treatment process are referred to as the first cross-linking treatment process and the second cross-linking treatment process from the upstream side in the film transport direction.

[0103] As cross-linking agent, boric acid, glyoxal, glutaraldehyde etc. can be enumerated, preferably boric acid is used. It is also possible to use two or more cross-linking agents in combination. The content of boric acid in the treatment solution accommodated in the cross-linking bath is usually 0.1 mass part or more and 15 mass parts or less per 100 mass parts of water, preferably 1 mass part or more and 10 mass parts or less. When the dichroic pigment is iodine, the treatment solution accommodated in the cross-linking bath preferably also contains iodide on the basis of containing boric acid. The content of iodide in the treatment solution accommodated in the cross-linking bath is usually 0.1 mass part or more and 15 mass parts or less per 100 mass parts of water, preferably 5 mass parts or more and 12 mass parts or less. As iodide, potassium iodide, zinc iodide etc. can be enumerated. In addition, compounds other than iodide, such as zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, sodium sulfate etc. can also be coexisted in the cross-linking bath.

[0104] The temperature of the treatment liquid contained in the crosslinking bath during immersion of the film is usually 50°C to 85°C, preferably 50°C to 70°C, and the immersion time of the film is usually 10 seconds to 600 seconds, preferably 20 seconds to 300 seconds.

[0105] When two or more crosslinking baths are used, the composition and temperature of the treatment solution contained in each crosslinking bath may be the same or different. The treatment solution contained in the crosslinking bath may have a concentration and temperature of the crosslinking agent, iodide, etc. that is appropriate for the purpose of impregnating the polyvinyl alcohol-based resin film. The crosslinking treatment for water resistance and the crosslinking treatment for color adjustment (color correction) may be performed separately in multiple steps (e.g., multiple baths).

[0106] In general, when both a cross-linking treatment for water resistance using cross-linking and a cross-linking treatment for color tone adjustment (color correction) are implemented, the tank (color correction tank) for implementing the cross-linking treatment for color tone adjustment (color correction) is arranged in the rear section. The temperature of the treatment liquid contained in the color correction tank is, for example, 10°C or more and 55°C or less, preferably 20°C or more and 50°C or less. The content of the cross-linking agent in the treatment liquid contained in the color correction tank is, for example, 1 part by mass or more and 5 parts by mass or less per 100 parts by mass of water. The content of the iodide in the treatment liquid contained in the color correction tank is, for example, 3 parts by mass or more and 30 parts by mass or less per 100 parts by mass of water.

[0107] From the perspective of shrinkage force and thickness uniformity in the width direction of the polarizing film, it is preferred to perform the stretching treatment step during the cross-linking treatment step, and it is more preferred to perform the stretching treatment step during either the swelling treatment step or the color correction treatment step in addition to the cross-linking treatment step. In a case where the cross-linking treatment step includes a first cross-linking treatment step of immersing the dyed polyvinyl alcohol-based resin film in a first cross-linking bath and then pulling it out, and a second cross-linking treatment step of immersing the polyvinyl alcohol-based resin film after the first cross-linking treatment step in a second cross-linking bath and then pulling it out, it is preferred to perform the stretching treatment step during the second cross-linking treatment step.

[0108] [Cleaning process]

[0109] The cleaning process in this step is a treatment performed as needed to remove excess crosslinking agents, dichroic pigments, and other chemicals attached to the polyvinyl alcohol-based resin film. It involves using a water-containing cleaning solution to clean the polyvinyl alcohol-based resin film after the crosslinking process. Specifically, the film after the crosslinking process can be immersed in a treatment solution (cleaning solution) contained in a cleaning tank. The film can be immersed in a single cleaning tank or in two or more cleaning tanks in sequence. Alternatively, the cleaning process can be a treatment in which the cleaning solution is sprayed onto the polyvinyl alcohol-based resin film after the crosslinking process in the form of a spray liquid, or a combination of the above-mentioned immersion and spraying.

[0110] The cleaning liquid may be water (eg, pure water) or an aqueous solution to which a water-soluble organic solvent such as alcohol is added. The temperature of the cleaning liquid may be, for example, about 5° C. or higher and 40° C. or lower.

[0111] The cleaning step S50 is an optional step and may be omitted, or the cleaning process may be performed in the drying step S60 as described later. It is preferable to perform the drying step S60 on the film after the cleaning step S50.

[0112] [Drying process]

[0113] The drying step S60 is a zone for drying the polyvinyl alcohol-based resin film after the cleaning step S50. The polyvinyl alcohol-based resin film after the cleaning step S50 is continuously conveyed while being introduced into the drying step S60 to perform a drying treatment, thereby obtaining a polarizing film.

[0114] The drying process is carried out using a drying mechanism (heating mechanism) for the film. A suitable example of a drying mechanism is a drying oven. The drying oven is preferably a drying oven capable of controlling the temperature inside the oven. The drying oven is, for example, a hot air oven capable of increasing the temperature inside the oven by supplying hot air, etc. In addition, the drying process using the drying mechanism may be a process in which the polyvinyl alcohol-based resin film after the cleaning step S50 is closely attached to one or more heating bodies having a convex curved surface, or a process in which a heater is used to heat the film.

[0115] Examples of the heating element include a roller having an internal heat source (e.g., a heat medium such as warm water, an infrared heater), and a roller capable of raising the surface temperature (e.g., a guide roller also serving as a heated roller). Examples of the heater include an infrared heater, a halogen heater, and a flat plate heater.

[0116] The drying temperature (eg, the temperature inside the drying furnace, the surface temperature of the hot roller, etc.) is usually 30° C. to 100° C., preferably 50° C. to 90° C. The drying time is not particularly limited, but is, for example, 30 seconds to 600 seconds.

[0117] [Other processing steps]

[0118] As another treatment step, for example, a color correction treatment step of immersing the film in an aqueous iodide solution not containing boric acid, which is performed after the cross-linking treatment, may be mentioned.

[0119] Through the above steps, a polarizing film in which a dichroic dye is adsorbed and oriented on a uniaxially stretched polyvinyl alcohol-based resin film can be obtained.

[0120] The obtained polarizing film may be directly conveyed to the subsequent polarizing plate production step (step of laminating a thermoplastic resin film to one or both surfaces of the polarizing film), for example.

[0121] [Polarizing film]

[0122] The thickness of the polarizing film can be, for example, 4 μm or more and 40 μm or less, preferably 4 μm or more and 30 μm or less, and more preferably 4 μm or more and 24 μm or less.

[0123] The shrinkage force of the polarizing film may be, for example, 1.0 N to 10.0 N, preferably 1.0 N to 5.0 N, and more preferably 1.0 N to 4.0 N.

[0124] The deviation of the shrinkage force in the width direction of the polarizing film may be, for example, 0.3 N or less, and preferably 0.25 N or less. In this specification, the deviation of the shrinkage force in the width direction refers to the difference in shrinkage force between the center portion and the end portions in the width direction.

[0125] The transmittance Ty of the polarizing film may be, for example, 40% or more, and is usually 50.0% or less, and may be, for example, less than 50.0% or 49.0% or less.

[0126] The deviation of the transmittance Ty in the width direction of the polarizing film may be, for example, 2.0% or less, and preferably 1.0% or less. In this specification, the deviation of the transmittance Ty in the width direction refers to the difference between the maximum and minimum values ​​of the transmittance Ty in the width direction.

[0127] The polarization degree Py of the polarizing film may be, for example, 99.00% or more, preferably 99.90% or more, and is usually 100% or less, for example, less than 100%.

[0128] The deviation of the polarization degree Py in the width direction of the polarizing film may be, for example, 0.1% or less, preferably 0.01% or less. In this specification, the deviation of the polarization degree Py in the width direction refers to the difference between the maximum and minimum values ​​of the polarization degree Py in the width direction.

[0129] The thickness, shrinkage force, transmittance Ty, and polarization degree Py of the polarizing film can be measured according to the method described in the section of Examples below.

[0130] <Polarizing Film Manufacturing Apparatus>

[0131] Another embodiment of the present invention includes a polarizing film manufacturing apparatus comprising a guide roller for unwinding a long polyvinyl alcohol-based resin film from a raw material roll while conveying the polyvinyl alcohol-based resin film along a film conveyance path, and a pair of pinch rollers for stretching the unwound polyvinyl alcohol-based resin film. The description of the polyvinyl alcohol-based resin film, the raw material roll, the film conveyance path, the guide roller, the stretching process, and the pair of pinch rollers is the same as that of the aforementioned polarizing film manufacturing method.

[0132] When the width of the nip roller arranged on the upstream side of the film transport path is A [mm] (hereinafter also referred to as the upstream nip roller width A), the width of the nip roller arranged on the downstream side of the film transport path is B [mm] (hereinafter also referred to as the downstream nip roller width B), and the width of the polyvinyl alcohol-based resin film that is about to come into contact with the nip roller arranged on the downstream side of the film transport path is C [mm] (hereinafter also referred to as the PVA width C), the following formula (4) is satisfied:

[0133] 3.0≤Y<7.0 (4)

[0134] [Wherein, Y=(A+B+C) / C].

[0135] In a polarizing film manufacturing apparatus, by satisfying the above formula (4), the shrinkage force and thickness variation in the width direction of the obtained polarizing film are reduced, and excellent transmittance Ty and polarization degree Py tend to be easily obtained.

[0136] In the above formula (4), Y is preferably 3.1 or greater, more preferably 3.3 or greater, and even more preferably 3.5 or greater. In the above formula (4), Y is preferably 6.9 or less, more preferably 6.7 or less, even more preferably 6.5 or less, and particularly preferably 6.3 or less.

[0137] The upstream nip roller width A is, for example, 300 mm to 3600 mm. If the widths of the two rollers forming the upstream nip roller are different, the shorter roller width is defined as the upstream nip roller width A.

[0138] The downstream nip roller width B is, for example, 300 mm to 3100 mm. If the widths of the two downstream nip rollers are different, the width of the shorter roller is defined as the downstream nip roller width B.

[0139] The upstream side nip roller width A [mm] and the downstream side nip roller width B [mm] may be the same or different.

[0140] The PVA width C is, for example, not less than 300 mm and not more than 3000 mm.

[0141] From the viewpoint of shrinkage force, the upstream nip roller width A and the PVA width C preferably satisfy the following formula (5):

[0142] 1.0<A / C<3.0 (5).

[0143] In the above formula (5), A / C is preferably 1.1 or greater, more preferably 1.2 or greater. The right side of the above formula (5) is preferably 2.9 or less, more preferably 2.7 or less, further preferably 2.6 or less, and particularly preferably 2.5 or less.

[0144] From the perspective of shrinkage force, the upstream nip roller width B and the PVA width C preferably satisfy the following formula (6):

[0145] 1.0<B / C<3.0 (6).

[0146] In the above formula (6), B / C is preferably 1.1 or more, more preferably 1.2 or more. In the above formula (6), B / C is preferably 2.9 or less, more preferably 2.7 or less, further preferably 2.6 or less, and particularly preferably 2.5 or less.

[0147] In a polarizing film manufacturing apparatus, a pair of nip rollers may be disposed at the inlet and outlet of one or more treatment baths (tanks such as swelling baths, dyeing baths, crosslinking baths, and cleaning baths, which are located along a film transport path and contain treatment liquids for treating polyvinyl alcohol-based resin films, are collectively referred to as treatment baths). This allows for inter-roll stretching, which is uniaxial stretching along the film transport direction, to be performed in one or more treatment baths by providing a circumferential speed difference between nip rollers disposed before and after the treatment baths.

[0148] [One embodiment of a polarizing film manufacturing apparatus]

[0149] The polarizing film manufacturing apparatus includes, along the film transport path, a bath for performing a swelling treatment, a bath for performing a dyeing treatment, and a bath for performing a crosslinking treatment. A pair of nip rollers for performing a stretching treatment may be provided at the inlet and outlet of any one or more of these baths. The swelling treatment, dyeing treatment, and crosslinking treatment are described in the aforementioned polarizing film manufacturing method.

[0150] Below, in reference Figure 3 At the same time, the manufacturing device of the polarizing film of the present invention is described in more detail. Figure 3 The polarizing film manufacturing apparatus shown is constructed as follows: a raw (unstretched) film 10 containing a polyvinyl alcohol-based resin is continuously unwound from a raw material roll 11 while being transported along a film transport path. The film 10 passes sequentially through a swelling bath 13, a dyeing bath 15, a cross-linking bath 17, and a cleaning bath 19 provided on the film transport path, and finally passes through a drying furnace 21. The resulting polarizing film 23 can be directly transported to a subsequent polarizing plate production step (a step of laminating a protective film to one or both sides of the polarizing film 23), for example. Figure 3 The arrow in the figure indicates the direction in which the film is transported.

[0151] It should be noted that although Figure 3 Although an example is given in which one treatment bath (swelling bath 13, dyeing bath 15, cross-linking bath 17, and cleaning bath 19) is provided, two or more treatment baths of any one type may be provided as needed.

[0152] The pair of nip rollers may be, for example, a combination of the nip rollers 51 and 52 , a combination of the nip rollers 52 and 53 , a combination of the nip rollers 53 and 54 , or the like.

[0153] The film transport path of a polarizing film manufacturing apparatus can be constructed by, in addition to arranging the aforementioned treatment baths at appropriate locations, also arranging guide rollers 30-50, which can support the film being transported or change the film's transport direction; and nip rollers 51-55, which can press and clamp the film being transported, impart a driving force to the film through its rotation, or change the film's transport direction. Guide rollers and nip rollers can be placed before and after each treatment bath, as well as within the treatment bath, to facilitate the introduction, immersion, and removal of the film from the treatment bath. For example, by placing one or more guide rollers in each treatment bath and conveying the film along these guide rollers, the film can be immersed in each treatment bath.

[0154] The swelling treatment can be performed by continuously unwinding the raw film 10 from the raw material roll 11 while conveying it along a film conveyance path, immersing the raw film 10 in a swelling bath 13 (containing a treatment solution) for a predetermined time, and then pulling it out. During the swelling treatment, the raw film 10 is conveyed along a film conveyance path constructed by the nip rollers 51 and 52 and the guide rollers 30 to 34.

[0155] During the swelling process, the raw film 10 tends to swell in the width direction, causing wrinkles to form within the film. One method for conveying the film while removing these wrinkles is to use at least one of the guide rollers 30-34, such as a spreader roller, a twisted roller, or a mid-height roller, with a width-expanding function. Alternatively, other width-expanding devices such as a cloth guide (Japanese: cross guide), a bending roller, or a tenter clip can be used. Furthermore, using the clamping rollers 51 and 52 for stretching tends to suppress the formation of wrinkles.

[0156] When the film is stretched in the swelling bath 13 , it can be stretched by, for example, providing a peripheral speed difference between the nip rolls 51 and 52 disposed at the inlet and outlet of the swelling bath 13 .

[0157] During the swelling treatment, the film also swells and expands in the direction of film transport. Therefore, in order to eliminate film slack in the transport direction without actively stretching the film, it is preferable to adopt methods such as controlling the speed of the nip rollers 51 and 52 arranged before and after the swelling bath 13. Furthermore, to stabilize the transport of the film in the swelling bath 13, it is also useful to control the water flow in the swelling bath 13 using a water sprayer or to use an EPC device (Edge Position Control: a device that detects the ends of the film and prevents it from meandering).

[0158] Figure 3 In the example shown, the film drawn out from the swelling bath 13 passes through the nip roller 52 and the guide roller 35 in sequence and is then introduced into the dyeing bath 15 .

[0159] The dyeing process can be carried out by immersing the swollen film in a dye bath 15 (containing a treatment solution) for a predetermined period of time while conveying the film along a film conveying path formed by nip rollers 52 and 53 and guide rollers 35 to 39, and then withdrawing the film. To improve the dyeing properties of the dichroic dye, the film provided to the dyeing process is preferably stretched to at least some extent, or more preferably, stretched during the dyeing process in addition to or in addition to the stretching process before the dyeing process.

[0160] During the dyeing process, similar to the swelling process, in order to convey the polyvinyl alcohol-based resin film while removing wrinkles from the film, at least one of the guide rollers 35 to 39 may be a roller with a width-expanding function, such as a spreader roller, a twisted roller, or a mid-height roller, or another width-expanding device such as a cloth guide, a bending roller, or a tenter clip. Furthermore, when the nip rollers 52 and 53 are used for stretching, the formation of wrinkles tends to be suppressed.

[0161] When the film is stretched in the dye bath 15 , it can be stretched by providing a peripheral speed difference between the nip rolls 52 and 53 respectively disposed at the inlet and outlet of the dye bath 15 .

[0162] The film drawn out from the dyeing bath 15 passes through the nip roller 53 and the guide roller 40 in sequence and is then introduced into the cross-linking bath 17 .

[0163] The crosslinking treatment can be carried out by transporting the film along the film transport path constructed by the nip rollers 53 and 54 and the guide rollers 40 to 44, immersing the dyed film in the crosslinking bath 17 (the treatment liquid contained in the crosslinking bath) for a predetermined time, and then pulling it out.

[0164] Alternatively, the stretching treatment may be performed in the crosslinking bath 17 by utilizing the difference in peripheral speed between the nip rollers 53 and 54, which are respectively arranged at the inlet and outlet of the bath for performing the crosslinking treatment. From the viewpoint of shrinkage force in the width direction of the polarizing film and thickness uniformity, it is preferable to perform the stretching treatment step in the crosslinking bath 17.

[0165] The cross-linking bath 17 can be Figure 4 As shown, the film transport path is composed of a first crosslinking bath 17a and a second crosslinking bath 17b in order from the upstream side. When the crosslinking bath 17 is composed of the first crosslinking bath 17a and the second crosslinking bath 17b, it is preferable to perform the stretching treatment using a pair of nip rollers 56 and 57 arranged at the inlet and outlet of the second crosslinking bath 17b. Figure 4 In the figure, the pinch roller 56 is a pinch roller on the inlet side, and the pinch roller 57 is a pinch roller on the outlet side.

[0166] During the crosslinking treatment, similar to the swelling treatment, in order to convey the polyvinyl alcohol-based resin film while removing wrinkles from the film, at least one of the guide rollers 40 to 44 may be a roll with a width-expanding function, such as a spreader roller, a twisted roller, or a mid-height roller, or another width-expanding device, such as a cloth guide, a bending roller, or a tenter clip. Furthermore, when the nip rollers 53 and 54 are used for stretching, the formation of wrinkles tends to be suppressed.

[0167] The film drawn out from the crosslinking bath 17 passes through the nip roller 54 and the guide roller 45 in sequence and is then introduced into the cleaning tank 19. During the cleaning process, in order to remove wrinkles while conveying the polyvinyl alcohol-based resin film, at least one of the guide rollers 45 to 49 may be a roller having a width-expanding function such as a spreader roller, a twisted roller, or a medium-high roller, or other width-expanding devices such as a cloth guide, a bending roller, or a tenter clip may be used.

[0168] After the washing treatment, it is preferred to dry the polyvinyl alcohol resin film. There is no particular limitation on the drying of the film, and for example, Figure 3 As shown, a drying oven 21 is used.

[0169] The method for producing a polarizing film may include other treatment baths. Examples of other treatment baths include a color correction treatment bath for treating with an iodide aqueous solution not containing boric acid after the crosslinking treatment.

[0170] Example

[0171] The present invention will be described in further detail below using Examples. "%" and "parts" in the Examples refer to mass % and mass parts unless otherwise specified.

[0172] (1) Shrinkage force of polarizing film

[0173] In such a way that the slow axis of the polarizing film is aligned with the long side, the polarizing film is cut into rectangles with a short side of 2 mm and a long side of 50 mm from the center and the end in the width direction using a super cutter (manufactured by Ogino Seiki Mfg. Co., Ltd.) to prepare test pieces. The shrinkage force of the test piece is measured using a thermomechanical analyzer (manufactured by SII Nanotechnology Co., Ltd., model TMA / 6100). The measurement is carried out in a constant size mode (the distance between the chucks is set to 10 mm). After the test piece is placed in a room at 20°C for a sufficient time, the temperature setting of the sample room is raised from 20°C to 80°C in 10 minutes. After the temperature is raised, the temperature of the sample room is set to maintain at 80°C. After the temperature is raised and placed for another 4 hours, the shrinkage force of the test piece in the long side direction is measured in an environment of 80°C.

[0174] In this measurement, the static load was set to 0 mN, and a probe made of SUS was used as a jig. The difference in contraction force between the center and the end portions was determined as the deviation.

[0175] (2) Visibility Correction Single Transmittance Ty and Visibility Correction Polarization Py of Polarizing Film

[0176] A measurement sample was prepared by laminating an alkali-free glass plate (Corning's "EAGLE XG" product, 0.7 mm thick) to the polarizing film via a (meth)acrylic adhesive layer. This sample was placed in a spectrophotometer equipped with an integrating sphere (JASCO Corporation's "V7100," 2-degree field of view, illuminant C) to measure the transmittance Ty and polarization index Py. The sample was positioned so that incident light was incident from the side opposite to the alkali-free glass plate.

[0177] It should be noted that the transmittance Ty and polarization degree Py are defined by the following formulas:

[0178] Transmittance (λ) = 0.5 × (Tp(λ) + Tc(λ))

[0179] Degree of polarization (λ)=100×(Tp(λ)-Tc(λ)) / (Tp(λ)+Tc(λ))

[0180] Tp(λ) is the transmittance (%) measured using the relationship between incident linearly polarized light of wavelength λnm and parallel Nicol prisms, and Tc(λ) is the transmittance (%) measured using the relationship between incident linearly polarized light of wavelength λnm and orthogonal Nicol prisms.

[0181] The transmittance Ty and polarization degree Py are values ​​obtained by correcting the single transmittance (λ) and polarization degree (λ) obtained at each wavelength using a 2-degree field of view (illuminant C) according to JIS Z 8701. Ty and Py were measured at 5 nm intervals within the wavelength range of 380 to 780 nm.

[0182] (3)Thickness of polarizing film

[0183] The thickness of the polarizing film in the width direction (direction perpendicular to the film feed direction) was measured at multiple points using a digital micrometer "MH-15M" manufactured by Nikon Corporation. The difference between the maximum and minimum values ​​was defined as the deviation, and the improvement rate was calculated according to the following formula.

[0184] Improvement rate [%] = [(variation of Comparative Example 1 - deviation of Example) / deviation of Comparative Example 1] × 100

[0185] <Example 1>

[0186] A long polyvinyl alcohol-based resin film (raw material width: 550 mm, average polymerization degree: approximately 2400, saponification degree: 99.9 mol% or more, thickness: 30 μm) was continuously conveyed and, while applying tension, was sequentially immersed in the following baths [1] to [4] to stretch the film in the conveying direction. The film was then washed with pure water and dried to obtain a long polarizing film in which iodine was adsorbed and oriented on the uniaxially stretched polyvinyl alcohol film.

[0187] When stretching is performed between a pair of nip rollers in the second crosslinking bath of [4], the width of the nip roller on the inlet side (upstream side in the film transport direction) of the second crosslinking bath (nip roller width A) is 900 mm, the width of the nip roller on the outlet side (downstream side in the film transport direction) is 900 m, and the width of the polyvinyl alcohol-based resin film immediately before contacting the nip roller on the outlet side (PVA width C) is 355 nm. (A+B+C) / C=6.1.

[0188] [1] Swelling bath: pure water at 40°C;

[0189] [2] Dye bath: A solution containing iodine and potassium iodide;

[0190] [3] First crosslinking bath: an aqueous solution containing potassium iodide and boric acid;

[0191] [4] Second cross-linking bath: an aqueous solution containing potassium iodide and boric acid.

[0192] Table 1 shows the shrinkage force, optical performance, and improvement rate of thickness variation of the obtained polarizing film.

[0193] <Examples 2 to 5, Comparative Example 1>

[0194] A polarizing film was produced in the same manner as in Example 1 except that the raw material width of the long polyvinyl alcohol-based resin film, the nip roll widths A and B, and the PVA width C were set to the values ​​shown in Table 1.

[0195] The results are shown in Table 1.

[0196] [Table 1]

[0197]

Claims

1. A method for producing a polarizing film, comprising a stretching step of stretching a polyvinyl alcohol-based resin film between a pair of nip rollers while conveying the film. In the stretching treatment step, when the width of the nip roller on the upstream side in the film conveying direction among the pair of nip rollers is set to A, the width of the nip roller on the downstream side in the film conveying direction is set to B, and the width of the polyvinyl alcohol-based resin film that is about to come into contact with the nip roller on the downstream side in the film conveying direction is set to C, the following formula (1) is satisfied: 3.0≤Y＜7.0　　　　　　（1） In the formula, let Y = (A + B + C) / C, The units of A, B, and C are mm.

2. The method for manufacturing a polarizing film according to claim 1, wherein: A and C satisfy the following formula (2): 1.0<A / C<3.0 (2) The units of A and C are mm.

3. The method for producing a polarizing film according to claim 1 or 2, wherein: The B and the C satisfy the following formula (3): 1.0<B / C<3.0 (3) The units of B and C are mm.

4. The method for producing a polarizing film according to claim 1 or 2, wherein: It also includes the following steps: The unwinding process is to unwind a long strip of polyvinyl alcohol resin film from the raw material roll; a swelling treatment step of immersing the polyvinyl alcohol-based resin film after the unwinding step in a swelling bath and then pulling it out; a dyeing treatment step of immersing the polyvinyl alcohol-based resin film after the swelling treatment step in a dyeing bath and then pulling it out; as well as In a cross-linking treatment step, the dyed polyvinyl alcohol resin film is immersed in a cross-linking bath and then pulled out. The stretching treatment step is performed in at least one of the swelling treatment step, the dyeing treatment step, and the cross-linking treatment step.

5. The method for manufacturing a polarizing film according to claim 4, wherein: The stretching treatment step is performed during the cross-linking treatment step.

6. The method for manufacturing a polarizing film according to claim 5, wherein: The cross-linking treatment process includes: a first cross-linking treatment step of immersing the dyed polyvinyl alcohol-based resin film in a first cross-linking bath and then pulling it out; and In the second cross-linking treatment step, the polyvinyl alcohol-based resin film after the first cross-linking treatment step is immersed in a second cross-linking bath and then pulled out. The stretching step is performed in the second cross-linking step.

7. A polarizing film manufacturing device, comprising: a guide roller for conveying the long polyvinyl alcohol-based resin film along a film conveyance path while unwinding the long polyvinyl alcohol-based resin film from a raw material roll; and A pair of nip rollers are used to stretch the unwound polyvinyl alcohol resin film. When the width of the nip roller arranged on the upstream side of the film transport path is A, the width of the nip roller arranged on the downstream side of the film transport path is B, and the width of the polyvinyl alcohol-based resin film about to come into contact with the nip roller arranged on the downstream side of the film transport path is C, the following formula (4) is satisfied: 3.0≤Y＜7.0　　　　　　（4） In the formula, let Y = (A + B + C) / C, The units of A, B, and C are mm.

8. The polarizing film manufacturing apparatus according to claim 7, wherein: A and C satisfy the following formula (5): 1.0<A / C<3.0 (5) The units of A and C are mm.

9. The polarizing film manufacturing apparatus according to claim 7 or 8, wherein: The B and the C satisfy the following formula (6): 1.0<B / C<3.0 (6) The units of B and C are mm.

10. The polarizing film manufacturing apparatus according to claim 7 or 8, wherein: A bath for performing a swelling treatment, a bath for performing a dyeing treatment, and a bath for performing a cross-linking treatment are sequentially provided on the film transport path. The pair of nip rollers is provided at the inlet and the outlet of any one or more of the baths.

11. The polarizing film manufacturing apparatus according to claim 10, wherein: The pair of nip rollers are provided at the inlet and outlet of the bath for performing the cross-linking treatment.

12. The polarizing film manufacturing apparatus according to claim 11, wherein: The bath for performing the crosslinking treatment includes a first crosslinking bath and a second crosslinking bath in order from the upstream side of the film transport path. The pair of nip rollers are provided at the inlet and outlet of the second cross-linking bath.

Images