Method for manufacturing polarizing film and apparatus for manufacturing polarizing film

Abstract

Provided is a method for producing a polarizing film in which uneven dyeing is inhibited. The present invention is a method for producing a polarizing film for a polarizing film made of a polyvinyl alcohol-based resin film, the method comprising, in this order: a first treatment step of bringing the polyvinyl alcohol-based resin film into contact with a first treatment liquid; and a conveying step of conveying the polyvinyl alcohol-based resin film while the polyvinyl alcohol-based resin film is in contact with a roller having at least one of a recessed portion having a depth of 0.03 mm or more and 0.9 mm or less and a protruded portion having a height of 0.03 mm or more and 0.9 mm or less on a surface that comes into contact with the polyvinyl alcohol-based resin film, the first treatment liquid containing iodine.

Description

TECHNICAL FIELD

[0001] The present application relates to a method for manufacturing a polarizing film and an apparatus for manufacturing a polarizing film, which are used for manufacturing a polarizing film from a polyvinyl alcohol-based resin film. BACKGROUND

[0002] Conventionally, it is known that a polarizing film is obtained by adsorbing a dichroic dye such as iodine to a polyvinyl alcohol-based resin film subjected to uniaxial stretching and orienting the dichroic dye. For example, Japanese Patent Application Publication No. 2001-141926 (Patent Literature 1) discloses that a polarizing film is manufactured by sequentially performing dyeing treatment of dyeing a polyvinyl alcohol-based resin film with a dichroic dye, cross-linking treatment of treating the polyvinyl alcohol-based resin film with a cross-linking agent, and film drying treatment, and performing stretching treatment on the polyvinyl alcohol-based resin film during the manufacturing process.

[0003] In Japanese Patent Application Publication No. 2012-173477 (Patent Literature 2), it is described that a polarizing sheet is less likely to be scratched by using a grooved metal guide roll in the conveyance of the resin film. In Japanese Patent Application Publication No. 2000-147252 (Patent Literature 3), it is described that a polarizing film is less likely to be broken by using a spiral rubber roll in the conveyance of the polarizing film.

[0004] PRIOR ART DOCUMENTS

[0005] PATENT LITERATURE

[0006] Patent Literature 1: Japanese Patent Application Publication No. 2001-141926

[0007] Patent Literature 2: Japanese Patent Application Publication No. 2012-173477

[0008] Patent Literature 3: Japanese Patent Application Publication No. 2000-147252 SUMMARY

[0009] PROBLEMS TO BE SOLVED BY THE INVENTION

[0010] A polarizing film is industrially produced by applying a manufacturing method in which a long polyvinyl alcohol-based resin film is continuously conveyed along a film conveyance path of a polarizing film manufacturing apparatus while being sequentially dipped in each tank on the conveyance path for performing the above-described dyeing treatment and cross-linking treatment, and the like. In the conveyance of the film, it is preferable that the conveyance speed of the film coincides with the rotation speed of the guide roll from the viewpoint of protecting the surface of the film. A film in a wet state is particularly likely to be damaged by contact with a roll. For example, it is known that although the grip of the film can be improved by roughening the surface of the guide roll as described in Patent Literatures 2 and 3, uneven dyeing is observed when a high-transmittance polarizing film is manufactured using this method.

[0011] In view of the above actual situation, the present application aims to provide a manufacturing method and manufacturing apparatus for a polarizing film that suppresses the occurrence of dye unevenness in the polarizing film.

[0012] Means for solving the problem

[0013] The present application provides a manufacturing method and manufacturing apparatus for a polarizing film as shown below.

[0014] [1] A manufacturing method for a polarizing film, which is a manufacturing method for a polarizing film made of a polyvinyl alcohol-based resin film,

[0015] The manufacturing method successively has: a first treatment step of bringing the polyvinyl alcohol-based resin film into contact with a first treatment liquid; and a conveyance step of conveying the polyvinyl alcohol-based resin film in a state where the first treatment liquid is interposed therebetween, in contact with a roll,

[0016] The first treatment liquid contains iodine,

[0017] The roll has at least one of a recessed portion having a depth of 0.03 mm or more and 0.9 mm or less and a protruded portion having a height of 0.03 mm or more and 0.9 mm or less on a surface in contact with the polyvinyl alcohol-based resin film.

[0018] [2] The manufacturing method for a polarizing film according to [1], wherein the first treatment liquid contains boric acid.

[0019] [3] The manufacturing method for a polarizing film according to [1] or [2], further having a second treatment step of bringing the polyvinyl alcohol-based resin film into contact with a second treatment liquid different from the first treatment liquid.

[0020] [4] The manufacturing method for a polarizing film according to any one of [1] to [3], wherein the roll is a sponge roll.

[0021] [5] The manufacturing method for a polarizing film according to any one of [1] to [4], wherein the polarizing film has a visible light corrected monomer transmittance of 43% or more.

[0022] [6] An apparatus for manufacturing a polarizing film from a polyvinyl alcohol-based resin film,

[0023] The apparatus has:

[0024] a first treatment bath that contains a first treatment liquid,

[0025] a roll disposed in the first treatment bath, and

[0026] a conveyance path through the roll,

[0027] The first treatment liquid contains iodine,

[0028] The polyvinyl alcohol-based resin film is carried along the conveyance path, immersed in the first treatment bath,

[0029] The roll has at least one of a recess having a depth of 0.03 mm or more and 0.9 mm or less and a projection having a height of 0.03 mm or more and 0.9 mm or less on a surface in contact with the polyvinyl alcohol-based resin film.

[0030] Effects of Invention

[0031] According to the present application, it is possible to provide a manufacturing method of a polarizing film in which formation of dyeing unevenness is suppressed. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 (a) is a plan view and (b) is a sectional view schematically showing a roll having a recess and a projection.

[0033] Figure 2 (b) is a sectional view schematically showing an example of a polarizing film manufacturing apparatus used in the manufacturing method of the present embodiment.

[0034] Figure 3 (b) is a sectional view schematically showing an example of a polarizing film manufacturing apparatus used in the manufacturing method of the present embodiment.

[0035] EXPLANATION OF REFERENCE NUMERALS

[0036] 10: raw material film containing a polyvinyl alcohol-based resin, 11: raw material roll, 13: swelling bath, 14: dyeing bath, 15: crosslinking bath, 16: complementary color bath, 17: cleaning bath, 21: drying furnace, 23: polarizing film, 30 to 32, 34 to 36, 38 to 40, 42 to 46: guide roll, 50 to 52, 53a, 53b, 54 to 55: nip roll. DETAILED DESCRIPTION

[0037] Hereinafter, with reference to the drawings, a manufacturing method of a polarizing film (hereinafter also referred to as "the manufacturing method of the present embodiment") of one embodiment of the present application will be described. However, the present application is not limited to this embodiment.

[0038] [Manufacturing method of polarizing film]

[0039] The manufacturing method of the present embodiment is a manufacturing method of a polarizing film for producing a polarizing film from a polyvinyl alcohol-based resin film. Specifically, it sequentially has: a first treatment step of bringing the above polyvinyl alcohol-based resin film into contact with a first treatment liquid; and a conveyance step of conveying the above polyvinyl alcohol-based resin film in a state of being interposed with the above first treatment liquid to a roller. The above treatment liquid contains iodine. In addition, the above roller has at least one of a recessed portion having a depth of 0.03 mm or more and 0.9 mm or less and a protruded portion having a height of 0.03 mm or more and 0.9 mm or less on a surface in contact with the above polyvinyl alcohol-based resin film. By having such a recessed portion or a protruded portion, the adhesion of the film can be improved. In addition, such a recessed portion or a protruded portion is less likely to be a cause of dyeing unevenness of the film.

[0040] In the present specification, the recessed portion refers to a region that is recessed compared to the surroundings, and is preferably a region that the polyvinyl alcohol-based resin film does not contact. The shape of the recessed portion is not limited, and examples include a circular recessed portion, a rectangular recessed portion, and the like in which the length of a straight line reaching the maximum length (the longest length) and the length of a straight line reaching the shortest length (the shortest length) among straight lines connecting the shapes of the recessed portion are the same degree, and a groove-like recessed portion in which the longest length and the shortest length are different. The groove-like recessed portion can be formed over the entire circumference of the roller. The width of the recessed portion is, for example, 0.3 mm or more and 50 mm or less. The depth of the recessed portion of the roller used in the manufacturing method of the present embodiment is 0.03 mm or more and 0.9 mm or less.

[0041] In the present specification, the protruded portion refers to a region that is protruded compared to the surroundings, and is preferably a region that the polyvinyl alcohol-based resin film contacts with stronger pressure than other regions. The shape of the protruded portion is not limited, and examples include a circular protruded portion, a rectangular protruded portion, and the like in which the length of a straight line reaching the maximum length (the longest length) and the length of a straight line reaching the shortest length (the shortest length) among straight lines connecting the shapes of the protruded portion are the same degree, and a convex portion in which the longest length and the shortest length are different. The convex portion can be formed over the entire circumference of the roller. The width of the protruded portion is, for example, 0.3 mm or more and 50 mm or less. The height of the protruded portion of the roller used in the manufacturing method of the present embodiment is 0.03 mm or more and 0.9 mm or less.

[0042] The recessed portion or the protruded portion can be one or a plurality. The area of the shape of the recessed portion or the protruded portion is not limited, and is, for example, 0.03 mm 2 0.07 mm or more, 1 mm or more, and 2 mm or more 2 1 mm or more, and 2 mm or more 2 1 mm or more, and 2 mm or more. When the area of the shape of the recessed portion or the protruded portion is less than 1 mm 2In the case where the recessed portions or the protruded portions are present, it is preferable that a plurality of recessed portions or protruded portions are present. For the total area of the outer shape of the recessed portions having a depth of 0.03 mm or more and 0.9 mm or less and the protruded portions having a height of 0.03 mm or more and 0.9 mm or less, it is 0.1% or more of the surface area of the roll from the viewpoint of maintaining the gripping property of the film, and it is preferably 1% or more, and for example, it is 30% or less, and it is preferably 20% or less.

[0043] The roll preferably has a recessed portion having a depth of 0.3 mm or more and 0.9 mm or less, or a protruded portion having a height of 0.3 mm or more and 0.9 mm or less on the surface in contact with the polyvinyl alcohol-based resin film, and does not have a recessed portion having a depth of more than 0.9 mm, or a protruded portion having a height of more than 0.9 mm. By using such a roll, it is possible to improve the gripping property of the film while suppressing the dyeing unevenness of the film.

[0044] Although the details of the factor that forms the dyeing unevenness in the polarizing film are not clear, it is presumed that it is because the processing liquid that makes the dyeing property uneven is easily left in the recessed portion or the protruded portion or in the vicinity thereof.

[0045] In the present embodiment, after the polyvinyl alcohol-based resin film is contacted with the first processing liquid containing iodine in the first processing step, the obtained polyvinyl alcohol-based resin film is conveyed in a state where the first processing liquid is interposed therebetween using a roll having a recessed portion having a depth of 0.3 mm or more and 0.9 mm or less, or a protruded portion having a height of 0.3 mm or more and 0.9 mm or less, whereby it is possible to suppress the dyeing unevenness.

[0046] In the present specification, the depth of the recessed portion means the maximum value of the difference between the surface of the recessed portion and the height of the surface other than the recessed portion and the protruded portion in the periphery of the recessed portion. In the present specification, the height of the protruded portion means the maximum value of the difference between the surface of the protruded portion and the height of the surface other than the protruded portion and the recessed portion in the periphery of the protruded portion. Figure 1 (a) is a plan view schematically showing a roll used in the method of the present embodiment and having a recessed portion in the region in contact with the polyvinyl alcohol-based resin film, Figure 1 (b) shows Figure 1 (b) shows Figure 1 (b) shows Figure 1 In the roll 60 shown in (a) and (b), the recessed portion 61 is present in the region in contact with the polyvinyl alcohol-based resin film. For the recessed portion 61, the depth D is 0.03 mm or more and 0.9 mm or less.

[0047] The kind of the roll used in the above conveying step is not particularly limited, and for example, it can be a guide roll that supports one face of the film as a free roll, or it can be a pair of rolls (nip rolls or the like) that sandwiches the film. The shape of the roll is not limited, and for example, a spiral roll, a crown roll, or the like can be given.

[0048] In addition, the material thereof is not limited, and a sponge roller, a rubber roller, a wooden roller, or a metal roller, etc. can be used, however, from the viewpoint of the gripping property, a sponge roller in which the surface of the roller is subjected to a foaming treatment, a micro groove roller in which the surface of the roller is subjected to a groove cutting process, etc. are preferably used. By using a roller having an excellent gripping property, the PVA-based resin film can be prevented from slipping over the surface of the roller, and the formation of a scratch on the surface of the PVA-based resin film can be suppressed.

[0049] As the material of the sponge of the sponge roller, for example, a polyurethane resin, a silicone-based resin, a polyvinyl chloride-based resin, etc. can be given, and a polyurethane resin is preferably used.

[0050] Due to the above-mentioned first treatment step, the first treatment liquid is present on the surface of the film. Thus, the film which has contacted the first treatment liquid is transported in the transport step in a state in which the first treatment liquid is present on the surface thereof, i.e., in a state in which the first treatment liquid is interposed. As the roller in the transport step, a roller in the first treatment bath, a roller which is disposed in the first treatment bath in a state in which at least a part thereof is immersed in the first treatment liquid, a roller which the film first contacts after the film is taken out of the first treatment bath, etc. can be given.

[0051] The first treatment bath herein is a treatment bath which accommodates a treatment liquid containing iodine, and for example, a dyeing bath described later is given. In addition, in the case where the cross-linking liquid and the complementary liquid contain iodine, the cross-linking bath and the complementary bath can be given. The treatment bath which conforms to the first treatment bath can be one, or two or more. Hereinafter, the manufacturing method of the present embodiment will be described in detail.

[0052] 〔Polyvinyl alcohol-based resin film〕

[0053] The polarizing film can be obtained, for example, by adsorbing a dichroic dye (iodine, a dichroic dye, etc.) to a polyvinyl alcohol-based resin film subjected to uniaxial stretching and orienting the dichroic dye. The polyvinyl alcohol-based resin film refers to a film containing a polyvinyl alcohol-based resin, and for example, a saponified polyvinyl acetate-based resin, etc. can be given. As the polyvinyl acetate-based resin, in addition to polyvinyl acetate which is a homopolymer of vinyl acetate, a copolymer of vinyl acetate and another monomer which can be copolymerized therewith (for example, an ethylene-vinyl acetate copolymer), etc. can be given. As the other monomer which can be copolymerized, for example, an unsaturated carboxylic acid, an olefin, a vinyl ether, an unsaturated sulfonic acid, etc. can be given. The degree of polymerization of the polyvinyl alcohol-based resin is usually about 1000 to 10000, and is preferably about 1500 to 5000. The degree of saponification is usually 85 mol% or more, and is preferably 90 mol% or more, and more preferably 99 to 100 mol%. These polyvinyl alcohol-based resins can be modified, and for example, a polyvinyl formal, a polyvinyl acetal, a polyvinyl butyral, etc. modified by an aldehyde can be used.

[0054] As the polyvinyl alcohol-based resin film which becomes a starting material in the production method of the present embodiment, an unstretched polyvinyl alcohol-based resin film (raw material film) having a thickness of 80 μm or less, preferably 60 μm or less, more preferably 45 μm or less, further preferably 30 μm or less can be used. Thereby, a thin polarizing film which is increasingly in demand in the market can be obtained. The width of the raw material film is not particularly limited, and for example, is 400 mm or more and 8000 mm or less, preferably 2000 mm or more and 5500 mm or less. The thickness of the unstretched polyvinyl alcohol-based resin film can be 10 μm or more, or 20 μm or more. The raw material film can be prepared, for example, in the form of a roll of an unstretched polyvinyl alcohol-based resin film (raw material roll). Note that the unstretched polyvinyl alcohol-based resin film (raw material film) is generally supplied in the form of a roll of film.

[0055] The above polyvinyl alcohol-based resin film can be laminated to a base film which supports it. That is, the polyvinyl alcohol-based resin film can be prepared in the form of a laminated film of a base film and a polyvinyl alcohol-based resin film laminated thereon. In this case, the polyvinyl alcohol-based resin film can be produced, for example, by applying a coating liquid containing a polyvinyl alcohol-based resin to at least one face of the base film and then drying the coating liquid.

[0056] As the base film, for example, a film containing a thermoplastic resin can be used. As specific examples, it can be a film formed of a thermoplastic resin having light transmittance, preferably an optically transparent thermoplastic resin, such as a polyolefin-based resin such as a chain polyolefin-based resin (polypropylene-based resin or the like), a cyclic polyolefin-based resin (norbornene-based resin or the like); a cellulose-based resin such as triacetyl cellulose, diacetyl cellulose; a polyester-based resin such as polyethylene terephthalate, polybutylene terephthalate; a polycarbonate-based resin; a (meth)acrylic-based resin such as a methyl methacrylate-based resin; a polystyrene-based resin; a polyvinyl chloride-based resin; an acrylonitrile-butadiene-styrene-based resin; an acrylonitrile-styrene-based resin; a polyvinyl acetate-based resin; a polyvinylidene chloride-based resin; a polyamide-based resin; a polyacetal-based resin; a modified polyphenylene ether-based resin; a polysulfone-based resin; a polyethersulfone-based resin; a polyarylate-based resin; a polyamide-imide-based resin; a polyimide-based resin, and the like.

[0057] 〔Treatment step〕

[0058] The production method of the present embodiment is a production method of a polarizing film produced from a polyvinyl alcohol-based resin film. Hereinafter, the series of production processes from the polyvinyl alcohol-based resin film to the production of the polarizing film in the present specification will be described using the term "treatment process". That is, the production method of the present embodiment can produce a polarizing film from a polyvinyl alcohol-based resin film by performing one or more treatment processes. As the above one or more treatment processes, for example, swelling process, dyeing process, crosslinking process (boric acid process), color compensation process, and washing process, and the like, in which various treatments such as swelling, dyeing, crosslinking, color compensation, and washing, and the like, are performed on the above polyvinyl alcohol-based resin film can be exemplified.

[0059] Specifically, the swelling process is a process in which a swelling liquid is brought into contact with the above raw material film to perform swelling treatment. The dyeing process is a process in which a dyeing liquid is brought into contact with the polyvinyl alcohol-based resin film after the swelling treatment (hereinafter also referred to as "swollen film") to perform dyeing treatment. The crosslinking process (boric acid process) is a process in which a crosslinking liquid is brought into contact with the polyvinyl alcohol-based resin film after the dyeing treatment (hereinafter also referred to as "dyed film") to perform crosslinking treatment. The color compensation process is a process in which a color compensation liquid is brought into contact with the polyvinyl alcohol-based resin film after the crosslinking treatment (hereinafter also referred to as "crosslinked film") to perform color adjustment treatment. Further, the washing process is a process in which washing treatment is performed by bringing a washing liquid into contact with the polyvinyl alcohol-based resin film after the color adjustment treatment (hereinafter also referred to as "color corrected film") to remove excess boric acid, iodine, and the like, adhered in the above crosslinking process, color compensation process, and the like. The above one or more treatment processes are not limited to the above processes as long as they exert the effects of the present application, and other processes can be included. The above one or more treatment processes can also appropriately combine the above processes and other processes.

[0060] The above treatment processes preferably include an operation of uniaxially stretching the polyvinyl alcohol-based resin film before or in any of the above swelling process and the like. For example, a process in which the uniaxial stretching of the unstretched raw material film is performed in air or a non-reactive gas (dry stretching) and then the swelling process, dyeing process, crosslinking process, color compensation process, and washing process are sequentially performed can be exemplified. Alternatively, a process in which the swelling process, dyeing process, crosslinking process, color compensation process, and washing process are sequentially performed using the unstretched raw material film and the uniaxial stretching of the polyvinyl alcohol-based resin film is performed in a wet manner before or in the above crosslinking process can be exemplified.

[0061] Hereinafter, the production method of the present embodiment will be exemplified while referring to Figure 2 , and thus a specific description will be given. Figure 2 is a cross-sectional view schematically showing an example of a polarizing film production apparatus used in the production method of the present embodiment.

[0062] Figure 2The polarizing film manufacturing apparatus shown can continuously wind up a raw material (unstretched) film 10 containing polyvinyl alcohol resin from a raw material roll 11 and transport it along a film transport path, sequentially passing it through a swelling bath (swelling liquid contained in a swelling tank) 13, a dyeing bath (dyeing liquid contained in a dyeing tank) 14, a crosslinking bath (crosslinking liquid contained in a crosslinking tank) 15, a color-correcting bath (color-correcting liquid contained in a color-correcting tank) 16, and a cleaning bath (cleaning liquid contained in a cleaning tank) 17 provided on the film transport path, thereby performing the swelling process, dyeing process, crosslinking process, color-correcting process, and cleaning process in sequence. Furthermore, as shown below, the raw material (unstretched) film 10 that has passed through the above-mentioned treatment baths is finally passed through a drying oven 21, thereby obtaining a polarizing film 23. Then, the polarizing film manufacturing apparatus can transport the polarizing film 23 directly, for example, to the following polarizing plate manufacturing process (the process of attaching a protective film to one or both sides of the polarizing film 23). Figure 2 The arrows indicate the direction of membrane transport.

[0063] exist Figure 2 In the description, "processing tank" is a general term encompassing swelling tank, dyeing tank, crosslinking tank, color-correcting tank, and cleaning tank; "processing solution" is a general term encompassing swelling solution, dyeing solution, crosslinking solution, color-correcting solution, and cleaning solution; and "processing bath" is a general term encompassing swelling bath, dyeing bath, crosslinking bath, color-correcting bath, and cleaning bath. The swelling bath, dyeing bath, crosslinking bath, color-correcting bath, and cleaning bath respectively constitute the swelling section, dyeing section, crosslinking section, color-correcting section, and cleaning section of the aforementioned polarization film manufacturing apparatus.

[0064] The film transport path of the polarizing film manufacturing apparatus is constituted by arranging the aforementioned processing baths, guide rollers 30-32, 34-36, 38-40, 42-46, and clamping rollers 50-52, 53a, 53b, and 54-55 at appropriate locations. The guide rollers 30-32, 34-36, 38-40, and 42-46 can support the transported film and can change the film transport direction. The clamping rollers 50-52, 53a, 53b, and 54-55 can press and clamp the film transported along the aforementioned film transport path, imparting a rotational driving force to the film and can change the film transport direction. The guide rollers and clamping rollers can be arranged before, after, and within each processing bath, thereby enabling the introduction, immersion, and removal of the film from the processing bath. For example, by providing one or more guide rollers in each processing bath and transporting the film along these guide rollers, the film can be immersed in each processing bath.

[0065] The polarizing film manufacturing apparatus has clamping rollers 50-52, 53a, 53b, and 54 arranged before and after each processing bath. This allows for inter-roll stretching in any one or more processing baths, i.e., longitudinal uniaxial stretching by setting a circumferential speed difference between the clamping rollers arranged before and after the processing bath. Each process will be described below.

[0066] <Swelling process>

[0067] The swelling process is performed for the purpose of removing foreign matter from the surface of the raw material film 10, removing a plasticizer from the raw material film 10, imparting easy dyeability, plasticizing the raw material film 10, and the like. The treatment conditions are determined in a range in which the above-mentioned purposes can be achieved and in which no undesirable conditions such as extreme dissolution and devitrification of the raw material film 10 occur.

[0068] In the above-mentioned swelling process, the raw material film 10 is continuously wound out from the raw material roll 11 while being transported along a film transport path, is immersed in the swelling bath 13 for a prescribed time, and is then pulled out as a swollen film, whereby the swelling treatment can be performed. As the swelling liquid used in the swelling bath, in addition to pure water, an aqueous solution in which boric acid (Japanese Patent Laid-Open No. 10-153709), chloride (Japanese Patent Laid-Open No. 06-281816), inorganic acid, inorganic salt, water-soluble organic solvent, alcohol, or the like is added in a range of 0.01 to 10 mass% can be used.

[0069] The temperature of the swelling bath 13 is, for example, about 10 to 70°C, preferably about 15 to 50°C, and more preferably about 15 to 35°C. The immersion time of the raw material film 10 is preferably about 10 to 600 seconds, and more preferably about 15 to 300 seconds.

[0070] In the above-mentioned swelling treatment, since the raw material film 10 swells in the width direction, a problem of forming a wrinkle in the swollen film is easily caused. As one method for transporting the swollen film while removing the wrinkle, a known roll having a spread function, a known spread device, or the like can be used. Another method for suppressing the generation of a wrinkle is to perform a stretching treatment. For example, a uniaxial stretching treatment can be performed in the swelling bath 13 by utilizing the difference in circumferential speed of the pinch rollers 50 and 51.

[0071] In the above-mentioned swelling treatment, since the film also swells and expands in the transport direction of the film, in order to eliminate the relaxation of the film in the transport direction without actively stretching the raw material film, for example, a method of controlling the speed of the pinch rollers 50 and 51 disposed before and after the swelling bath 13, or the like is preferably adopted. In addition, for the purpose of stabilizing the film transport in the swelling bath 13, it is also useful to control the water flow in the swelling bath 13 by using a sprayer, or to use an EPC device (Edge Position Control device: a device for detecting the end of the film and preventing the meandering of the film), or the like.

[0072] Figure 2 In the illustrated example, the swollen film pulled out from the swelling bath 13 is introduced into the dyeing bath 14 in order through the guide roller 32 and the pinch roller 51.

[0073] <Staining Process>

[0074] The staining process is performed for the purpose of adsorbing a dichroic pigment such as iodine to the polyvinyl alcohol-based resin film after the swelling treatment, and orienting the dichroic pigment, etc. The treatment conditions are determined within a range in which the above purpose can be achieved, and in which no undesirable conditions such as extreme dissolution and devitrification of the film occur. In the staining process, the swollen film after the swelling treatment is transported along the film transport path formed by the nip rollers 51, the guide rollers 34 to 35, and the nip rollers 52, immersed in the staining bath 14 for a prescribed time, and then pulled out as a stained film, whereby the staining treatment can be performed. In order to improve the staining property of the dichroic pigment, the swollen film supplied to the staining process is preferably a film on which at least some degree of uniaxial stretching treatment has been performed, and it is preferable to perform the uniaxial stretching treatment at the time of the staining treatment instead of the uniaxial stretching treatment before the staining treatment, or to perform the uniaxial stretching treatment at the time of the staining treatment in addition to the uniaxial stretching treatment before the staining treatment.

[0075] It is preferable to use iodine as the dichroic pigment, and as the staining solution used in the staining bath 14, for example, an aqueous solution having a concentration of iodine / potassium iodide / water = 0.003 to 1 / 0.1 to 20 / 100 by mass ratio can be used. Instead of potassium iodide, other iodides such as zinc iodide can also be used, and potassium iodide and other iodides can also be used in combination. In addition, compounds other than iodides, such as boric acid, zinc chloride, cobalt chloride, etc. can also coexist. In the case where boric acid is added, the staining solution differs from the cross-linking solution described later in that it contains a dichroic pigment. In this specification, in the case where an aqueous solution contains 0.003 mass parts or more of a dichroic pigment with respect to 100 mass parts of water, the above aqueous solution can be regarded as a staining solution. The temperature of the staining bath 14 at the time of immersion of the swollen film is usually about 10 to 45°C, preferably 10 to 40°C, and more preferably 20 to 35°C, and the immersion time of the swollen film is usually about 20 to 600 seconds, and preferably 30 to 300 seconds.

[0076] As described above, in the staining process, uniaxial stretching of the swollen film can be performed in the staining bath 14. The uniaxial stretching of the swollen film can be performed by providing a difference in circumferential speed between the nip rollers 51 and 52 disposed before and after the staining bath 14.

[0077] In the above staining treatment, in order to transport the polyvinyl alcohol-based resin film while removing wrinkles, as with the above swelling treatment, a publicly known roller having a spreading function can be used as the above guide rollers 34, 35, 36, or a publicly known spreading device can be provided. Another method for suppressing the generation of wrinkles is to perform stretching treatment, as with the swelling treatment.

[0078] Figure 2 In the example shown, the stained film pulled out of the staining bath 14 is introduced into the cross-linking bath 15 in order through the guide roller 36 and the nip roller 52.

[0079] One embodiment of the dyeing step

[0080] In one embodiment of the dyeing step, the dyeing step is the first treatment step, and the dyeing liquid is the first treatment liquid. In this embodiment, Figure 2 At least one of the guide rollers 34, 35, and 36 illustrated is a roller (hereinafter also referred to as "first roller") having at least one of a recess with a depth of 0.03 mm or more and 0.9 mm or less and a protrusion with a height of 0.03 mm or more and 0.9 mm or less on a surface in contact with the polyvinyl alcohol-based resin film. Figure 2 In the embodiment, the first roller contacts the polyvinyl alcohol-based resin film while the dyeing liquid is interposed therebetween and conveys the polyvinyl alcohol-based resin film, and on the surface in contact with the polyvinyl alcohol-based resin film, does not have a recess with a depth greater than 0.9 mm or a protrusion with a height greater than 0.9 mm. According to the production method of this embodiment, it is possible to suppress the case where the polarizing film is formed with dyeing unevenness.

[0081] In the production method of the present embodiment, the dyeing step is not limited to the method exemplified above as long as the effect of the present application can be obtained, and all changes can be made in the meaning equivalent to the scope of the technical solution claimed and within the scope. Furthermore, in the production method of the present embodiment, the treatment step as the first treatment step is not limited to the case where the step is the dyeing step, but can be a treatment step in which the treatment liquid contained in the treatment bath contains iodine. For example, the cross-linking step and the complementary color step can be applicable. In these cases, it is also possible to provide a polarizing film that does not have observation failure due to dyeing unevenness. In a production method having a plurality of treatment steps in which different treatment liquids are used in each treatment step, at least one of the treatment steps can be the first treatment step, and the other treatment steps can be a second treatment step different from the first treatment step. The treatment liquid of a different composition from the first treatment liquid used in the second treatment step is set as a second treatment liquid.

[0082] In the case where the cross-linking step and the complementary color step are the first treatment step, the description regarding the conveying step of one embodiment of the dyeing step described above can be applied to the conveying step in these treatment steps.

[0083] < Cross-linking step >

[0084] The cross-linking step is performed for the purpose of imparting water resistance to the dyed film described above. The cross-linking step described above can be performed once or a plurality of times. In the cross-linking step, the dyed film conveyed along the film conveying path constructed by the nip roller 52, the guide rollers 38 to 40, and the nip roller 53a is immersed in the cross-linking bath 15 for a prescribed time and then pulled out as a cross-linked film, whereby the cross-linking treatment can be performed.

[0085] As the cross-linking liquid, a solution in which a cross-linking agent is dissolved in a solvent can be used. As the cross-linking agent, for example, boron compounds such as boric acid, borax, glyoxal, glutaraldehyde, and the like can be cited. They can be used singly or in combination of two or more. As the solvent, for example, water can be used, and an organic solvent compatible with water can also be contained. The concentration of the cross-linking agent in the cross-linking liquid is preferably in the range of 0.1 to 15% by mass, more preferably 1 to 12% by mass, but is not limited thereto.

[0086] In the cross-linking treatment, other cross-linking agents can be used instead of boric acid, or boric acid and other cross-linking agents can be used in combination, as needed. The temperature of the cross-linking bath at the time of impregnation of the dyed film is usually about 20 to 85°C, preferably 30 to 70°C, and the impregnation time of the dyed film is usually about 10 to 600 seconds, preferably 20 to 300 seconds. In addition, in the case where the polyvinyl alcohol-based resin film which has been stretched in advance before the swelling treatment is subjected to the dyeing treatment and the cross-linking treatment in this order, the temperature of the cross-linking bath is usually 50°C or higher, preferably 50 to 85°C.

[0087] The cross-linking treatment can be performed once or a plurality of times. In this case, the composition and the temperature of the cross-linking bath used can be the same or different, as long as they are within the above-described ranges. In addition, uniaxial stretching treatment can be performed in the cross-linking bath using the difference in the peripheral speed of each nip roller.

[0088] In the cross-linking treatment, in order to convey the polyvinyl alcohol-based resin film while removing wrinkles, a publicly known roller having a spreading function can be used as the guide roller 38, 39, 40, or a publicly known spreading device can be provided, as in the swelling treatment. Another method for suppressing the generation of wrinkles is to perform stretching treatment, as in the swelling treatment.

[0089] Figure 2 In the illustrated example, the cross-linked film drawn out of the cross-linking bath 15 is introduced into the color correction bath 16 in this order via the guide roller 40 and the nip roller 53a.

[0090] < Color Correction Process >

[0091] The color correction process is performed for the purpose of adjusting the color tone of the cross-linked film. In the color correction process, the cross-linked film conveyed along the film conveying path formed by the nip roller 53a, the guide rollers 42 to 44, and the nip roller 53b is immersed in the color correction bath 16 for a prescribed time, and then drawn out as a color corrected film, whereby the color correction treatment can be performed. The temperature of the color correction bath at the time of immersion of the cross-linked film is usually about 20 to 65°C, and the immersion time of the cross-linked film is usually about 1 to 300 seconds, preferably 2 to 100 seconds.

[0092] Uniaxial stretching treatment can also be performed in the color correction bath 16 using the difference in the peripheral speed of each of the nip rollers 53a, 53b disposed before and after the color correction bath 16. Figure 2In the illustrated example, the color correction film drawn out of the complementary bath 16 is introduced along a film conveying path into a cleaning bath 17 used in a cleaning process described below.

[0093] <Stretching Process>

[0094] Here, as described above, the polyvinyl alcohol-based resin film is preferably subjected to uniaxial stretching treatment in a wet or dry manner during a series of treatment processes (i.e., before and after any of the one or more treatment processes and / or in any one or more of the treatment processes). The specific method of uniaxial stretching treatment can be, for example, inter-roller stretching in which a circumferential speed difference is provided between two nip rollers (e.g., two nip rollers disposed before and after the treatment bath) that constitute the film conveying path, heat roller stretching like that described in Japanese Patent No. 2731813, tenter stretching, or the like, and is preferably inter-roller stretching. The uniaxial stretching process can be performed multiple times during the period from the raw film of the polyvinyl alcohol-based resin film as the starting material to the obtaining of the polarizing film. The stretching treatment is also effective for suppressing the generation of wrinkles in the film.

[0095] The final cumulative stretching ratio of the polarizing film based on the raw film is generally about 3.5 to 7 times, and is preferably 4 to 6.5 times. The stretching process can be performed in any of the treatment processes, and in the case where stretching treatment is performed in two or more treatment processes, the stretching treatment can also be performed in any of the treatment processes.

[0096] <Cleaning Process>

[0097] The purpose of the cleaning process is to remove excess chemical agents such as boric acid and iodine that adhere to the film in the above-described crosslinking process, complementary process, and the like. For example Figure 2 In the cleaning bath 17 of the polarizing film manufacturing apparatus illustrated, the color correction film after the above-described complementary process can be conveyed along a film conveying path constructed from guide rollers 45 and 46 provided inside the cleaning bath 17 and two nip rollers 53b and 54 disposed before and after the cleaning bath 17, while being subjected to cleaning treatment. The first nip roller 53b and the second nip roller 54 function as water removal rollers, and thus excess chemical agents such as boric acid and iodine that adhere to the color correction film can be cleaned and removed.

[0098] In the above-described cleaning process, for the purpose of conveying the polyvinyl alcohol-based resin film while removing wrinkles, a publicly known roller having a spread function can be used as the guide rollers 45 and 46, or a publicly known spread device can be provided, as in the swelling process and the like. In addition, in the cleaning process, stretching treatment can also be performed in order to suppress the generation of wrinkles.

[0099] As the cleaning liquid used in the cleaning step, water, and the conventionally known cleaning liquid used in cleaning of such a polyvinyl alcohol-based resin film can be used. The temperature range of the cleaning liquid used in the cleaning step can also be set to the same temperature range as in the past (for example, 2 to 60°C). Note that in the case where the cleaning liquid is removed from the above film after the cleaning step, as the cleaning liquid removal mechanism, for example, a mechanism having a nip roller 54 and blowing air to the above film in addition to the nip roller to remove the liquid can be used; a squeegee, a suction roller, a water removal roller, or the like that removes the liquid in contact with the above film.

[0100] <Other Step: For example, Drying Step>

[0101] The production method of the present embodiment can include a step other than the above-described respective processing steps. As the other step, for example, a drying step can be cited. The drying step is a step of performing a process of drying the polyvinyl alcohol-based resin film after the cleaning step. The drying method in the above-described drying step is not particularly limited, and, for example, hot air drying can be performed using a drying furnace 21 as shown in FIG. 1. In this case, the drying temperature is, for example, about 30 to 100°C, and the drying time is, for example, about 30 to 600 seconds. The process of drying the polyvinyl alcohol-based resin film can also be performed using a far infrared heater. The polarizing film can be produced as described above. The thickness of the polarizing film is, for example, about 5 to 50 μm. Figure 3

[0102] < Polarizing Film>

[0103] With the production method of the present embodiment, a polarizing film in which the formation of a striped dye unevenness on the surface is suppressed can be obtained. The visibility correction monomer transmittance Ty of the above-described polarizing film is preferably 43 to 50%, more preferably 43 to 49%, and further preferably 44 to 48% in consideration of the balance with the visibility correction degree of polarization Py. The visibility correction degree of polarization Py is preferably 90.0% or more, and more preferably 98.0% or more at any position in the width direction.

[0104] The visibility correction monomer transmittance (Ty) and the visibility correction degree of polarization (Py) can be found using the following measurement method. First, the MD transmittance and the TD transmittance in the range of wavelengths of 380 to 780 nm are measured for the above-described polarizing film using a spectrophotometer with an integrating sphere ("V7100" manufactured by Japan Spectroscopic Co., Ltd.), and the monomer transmittance and the degree of polarization at each wavelength are calculated based on the following formulas:

[0105] Monomer transmittance (%) = (MD + TD) / 2

[0106] Degree of polarization (%) = {(MD - TD) / (MD + TD)} x 100

[0107] ​The "MD transmittance" herein refers to the transmittance when the direction of polarized light emitted from a Glan-Thomson prism is parallel to the transmission axis of the polarizing film sample, and is represented by "MD" in the above formula. In addition, the "TD transmittance" refers to the transmittance when the direction of polarized light emitted from a Glan-Thomson prism is orthogonal to the transmission axis of the polarizing film sample, and is represented by "TD" in the above formula. Then, for the above monomer transmittance and degree of polarization, the visibility is corrected based on JIS Z 8701: 1999 "Method of Expression of Color - XYZ Color System and X 10 Y 10 Z 10 The visibility-corrected monomer transmittance (Ty) and the visibility-corrected degree of polarization (Py) can be obtained.

[0108] The width of the polarizing film is, for example, 50 mm or more and 5,000 mm or less, and is preferably 500 mm or more and 4,000 mm or less. The polarizing film can be wound on a winding roll to be in a roll shape, or can be directly supplied to a process of producing a polarizing plate without being wound (a process of laminating a protective film or the like on one side or both sides of the polarizing film).

[0109] < Polarizing plate >

[0110] The polarizing plate can be obtained by adhering a protective film to at least one side of the polarizing film produced as described above with an adhesive. As the protective film, for example, a film containing an acetylcellulose-based resin such as triacetylcellulose and diacetylcellulose; a film containing a polyester-based resin such as polyethylene terephthalate, polyethylene naphthalate, and polybutylene terephthalate; a polycarbonate-based resin film; a cyclic olefin-based resin film; an acrylic resin film; and a film containing a chain olefin-based resin such as a polypropylene-based resin can be given.

[0111] In order to improve the adhesion between the polarizing film and the protective film, a surface treatment such as a corona treatment, a flame treatment, a plasma treatment, ultraviolet irradiation, a primer coating treatment, a saponification treatment, or the like can be performed on the adhering surface of the polarizing film and / or the protective film. As the adhesive used in the adhesion of the polarizing film and the protective film, a living energy ray-curable adhesive such as an ultraviolet-curable adhesive, an aqueous solution of a polyvinyl alcohol-based resin, or an aqueous solution in which a crosslinking agent is incorporated, a water-based adhesive such as a urethane-based emulsion adhesive, or the like can be given.

[0112] Example

[0113] Hereinafter, the present application will be further described in detail using examples, but the present application is not limited by the following examples.

[0114] (Preparation of guide roll A-1)

[0115] A guide roll A-1 having a diameter of 70 mm and a width of 600 mm and having no recesses and protrusions on the surface was prepared.

[0116] (Preparation of guide roll A-2)

[0117] A sponge roll having the same size as the guide roll A-1 prepared above and having a large number of approximately circular recesses on the surface was prepared as a guide roll A-2. The 10 recesses included in an arbitrary area of the surface of the guide roll A-2 had a depth of 0.2 to 0.5 mm and an average of 0.3 mm, and an area of 0.03 to 0.20 mm 2 and an average of 0.07 mm 2 . The recesses occupied 15% of the surface of the roll.

[0118] (Preparation of guide rolls B-1, B-2, B-3, B-4, B-5)

[0119] A plurality of groovelike recesses having a depth d [mm] and a width w [mm] and extending around the entire circumference were formed on the surface of the guide roll A-2 at intervals g [mm] in the width direction to prepare guide rolls B-1, B-2, B-3, B-4, and B-5. The respective depths d, widths w, and intervals g are shown in Table 1. Depth d [mm] A schematic view showing a cross section of the guide roll B-4 is shown.

[0120] [Table 1]

[0121] Width w [mm] Spacing g [mm] Guide roller B-1 Guide roller B-2 0.05 1 30 Guide roller B-3 0.05 20 30 Guide roller B-4 0.1 20 30 Guide roller B-5 0.3 20 30 Figure 2 1.0 20 30

[0122] (Example 1)

[0123] A polarizing film 23 was continuously produced from a long polyvinyl alcohol film (PVA-based resin film 10) using a production apparatus similar to that shown in ​ . The polyvinyl alcohol film used was a polyvinyl alcohol film having a thickness of 60 μm, and the polyvinyl alcohol constituting the film had a saponification degree of 99.9 mol% or more and an average polymerization degree of 2400. Two guide rolls A-2 were disposed in the dyeing bath 14.

[0124] (a) Swelling treatment step

[0125] The PVA-based resin film 10 was continuously unwound from the unwinding roll 11 while being immersed in the swelling bath 13 to which pure water was added at 30°C, and the film was subjected to 1.5-fold inter-roll stretching (uniaxial stretching in the longitudinal direction) by setting a difference in circumferential speed between the nip rolls 50 and 51 in such a manner that the film was not relaxed, to perform swelling treatment.

[0126] (b) Dyeing treatment step

[0127] Then, in order to perform the first dyeing treatment, the PVA-based resin film 10 that has passed through the nip roller 51 was immersed in a dyeing bath 14 of iodine / potassium iodide / water (mass ratio) 0.03 / 1.0 / 100 at 30°C for 120 seconds. In this dyeing treatment, 1.5-fold inter-roller stretching (uniaxial stretching in the longitudinal direction) was performed by setting a difference in peripheral speed between the nip rollers arranged before and after the dyeing bath 14.

[0128] 〔c〕 Cross-linking treatment step and color compensation treatment step

[0129] Then, in order to perform the cross-linking treatment for the purpose of water resistance, the PVA-based resin film 10 that has passed through the nip roller 52 was immersed in a cross-linking bath 15 of potassium iodide / boric acid / water (mass ratio) 10 / 5 / 100 at 55°C for 30 seconds. In this cross-linking treatment, 2.0-fold inter-roller stretching (uniaxial stretching in the longitudinal direction) was performed by setting a difference in peripheral speed between the nip rollers. Then, the PVA-based resin film 10 after the cross-linking treatment was immersed in a color compensation bath 16 of potassium iodide / boric acid / water (mass ratio) 10 / 5 / 100 at 40°C for 15 seconds (color compensation treatment). In this color compensation treatment, 1.2-fold inter-roller stretching (uniaxial stretching in the longitudinal direction) was performed by setting a difference in peripheral speed between the nip rollers.

[0130] Subsequently, the PVA-based resin film 10 after the color compensation treatment was immersed in a washing bath 17 to which pure water was added at 15°C, and then was passed through a drying furnace 21, whereby the PVA-based resin film 10 was dried at 70°C for 3 minutes, to produce a polarizing film 23.

[0131] (Example 2)

[0132] In the polarizing film production apparatus, the two guide rollers arranged in the dyeing bath 14 were replaced with the guide roller B-1 instead of the guide roller A-2, and otherwise, the polarizing film 23 was produced in the same manner as in Example 1.

[0133] (Example 3)

[0134] In the polarizing film production apparatus, the two guide rollers arranged in the dyeing bath 14 were replaced with the guide roller B-2 instead of the guide roller A-2, and otherwise, the polarizing film 23 was produced in the same manner as in Example 1.

[0135] (Example 4)

[0136] In the polarizing film production apparatus, the two guide rollers arranged in the dyeing bath 14 were replaced with the guide roller B-3 instead of the guide roller A-2, and otherwise, the polarizing film 23 was produced in the same manner as in Example 1.

[0137] (Example 5)

[0138] In the manufacturing apparatus of the polarizing film, for the two guide rollers disposed in the dyeing bath 14, the guide roller B-4 was used instead of the guide roller A-2, and otherwise the polarizing film 23 was produced in the same manner as in Example 1.

[0139] (Comparative Example 1)

[0140] In the manufacturing apparatus of the polarizing film, for the two guide rollers disposed in the dyeing bath 14, the guide roller A-1 was used instead of the guide roller A-2, and otherwise the polarizing film 23 was produced in the same manner as in Example 1.

[0141] (Comparative Example 2)

[0142] In the manufacturing apparatus of the polarizing film, for the two guide rollers disposed in the dyeing bath 14, the guide roller B-5 was used instead of the guide roller A-2, and otherwise the polarizing film 23 was produced in the same manner as in Example 1.

[0143] (Evaluation)

[0144] For the polarizing films produced in Examples 1 to 5 and Comparative Examples 1 and 2, the visibility-corrected monomer transmittance Ty was measured, and in addition, the rotation property of the guide roller and the dyeing unevenness were evaluated based on the following criteria by visual observation. The visibility-corrected monomer transmittance Ty of the polarizing films produced in Examples 1 to 5 and Comparative Examples 1 and 2 was 44.0% in each case. In Table 2, the evaluation results are shown.

[0145] <Rotation property of guide roller>

[0146] A: The roller rotates at the same speed as the film.

[0147] B: The roller rotates without stopping although slower than the flow of the film.

[0148] C: The roller occasionally stops although the film is flowing.

[0149] D: The roller stops although the film is flowing.

[0150] <Dyeing unevenness>

[0151] A: No dyeing unevenness was observed.

[0152] B: Dyeing unevenness was faintly confirmed, but not to a problematic level.

[0153] C: Dyeing unevenness was clearly observed.

[0154] [Table 2]

[0155]

[0156] From the results shown in Table 2, it was found that, in the dyeing bath, for Examples 1 to 5 in which the guide roller having the recess with a depth of 0.9 mm or less was used, dyeing unevenness at a problematic level was not observed. In addition, in Examples 1 to 5, the case where the guide roller was completely stopped like Comparative Example 1 was suppressed in terms of the rotation property of the guide roller.

Claims

1. A method for manufacturing a polarizing film, comprising a method for manufacturing a polarizing film by forming a polarizing film from a polyvinyl alcohol-based resin film. The manufacturing method comprises, in sequence: The first processing step involves contacting the polyvinyl alcohol-based resin film with the first processing solution; and In the conveying process, the polyvinyl alcohol resin film is conveyed in contact with rollers while being sandwiched between the first treatment liquid. The first treatment solution contains iodine. The roller has a recess with a depth of 0.03 mm or more and 0.9 mm or less on the surface that contacts the polyvinyl alcohol resin film.

2. The method for manufacturing a polarizing film according to claim 1, wherein, The first treatment solution contains boric acid.

3. The method for manufacturing a polarizing film according to claim 1 or 2, further comprising a second processing step. In the second processing step, the polyvinyl alcohol resin film is brought into contact with a second processing solution that is different from the first processing solution.

4. The method for manufacturing a polarizing film according to claim 1 or 2, wherein, The roller is a sponge roller.

5. The method for manufacturing a polarizing film according to claim 1 or 2, wherein, The polarizing film has a visibility correction monomer transmittance of over 43%.

6. An apparatus for manufacturing a polarizing film from a polyvinyl alcohol-based resin film. The device has: The first treatment bath containing the first treatment solution, Rollers and rollers configured in the first processing bath The conveying path through the rollers, The first treatment solution contains iodine. The polyvinyl alcohol-based resin film is transported along the transport path and impregnated in the first treatment bath. The roller has a recess with a depth of 0.03 mm or more and 0.9 mm or less on the surface that contacts the polyvinyl alcohol resin film.

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