TWI761361B - Method and apparatus for manufacturing polarizing film - Google Patents

Abstract

The present invention is to provide a method and apparatus for manufacturing polarizing film; the method for manufacturing polarizing film is capable of further improving optical characteristics of a polarizing film by performing crosslinking treatment in the manufacturing method of the polarizing film.

The method of the present invention is a method for manufacturing a polarizing film from a polyvinyl alcohol-based resin film, comprising: a dyeing step of dyeing the polyvinyl alcohol-based resin film with a dichroic dye; a crosslinking step of subjecting the polyvinyl alcohol-based resin film subjected to the dyeing treatment to a crosslinking treatment with a crosslinking agent; an electromagnetic wave irradiating step of irradiating the polyvinyl alcohol-based resin film after the crosslinking treatment with an electromagnetic wave having a ratio of radiant energy of infrared rays of more than 2 μm to 4 μm or less of 25 % or more; and a washing step of washing the polyvinyl alcohol-based resin film irradiated with the electromagnetic wave.

Description

Manufacturing method and manufacturing apparatus of polarizing film

The present invention relates to a method for producing a polarizing film from a polyvinyl alcohol-based resin film, and a production apparatus.

Polarizing plates are widely used as polarizing elements and the like in video display devices such as liquid crystal display devices. Generally, as a polarizing plate, a transparent resin film (protective film etc.) is laminated on one side or both sides of a polarizing film using an adhesive or the like.

The polarizing film is mainly immersed in a dyeing bath containing dichroic dyes such as iodine, and then immersed in a crosslinking bath containing a crosslinking agent such as boric acid, etc. The film is produced by uniaxially extending the film at any stage. The uniaxial stretching includes dry stretching in which stretching is performed in air, and wet stretching in which stretching is performed in liquids such as the above-mentioned dyeing bath and cross-linking bath.

Conventionally, in the manufacturing method of a polarizing film, various efforts have been made in order to improve the characteristics of the polarizing film. Japanese Patent Laid-Open No. 2013-148806 (Patent Document 1) describes that a primary drying step for drying a polyvinyl alcohol-based resin film is provided between the boric acid treatment step and the water washing step. In this step, the transmitted light can be made into a good hue, that is, it can be close to neutral gray.

Japanese Patent Application Laid-Open No. 59-094706 (Patent Document 2) describes that by irradiating far infrared rays having a wavelength of 1 μm or more and performing immobilization treatment, a polarizing film having a small shrinkage rate and good flatness can be obtained.

[Prior Art Literature] [Patent Literature]

Patent Document 1: Japanese Patent Laid-Open No. 2013-148806.

Patent Document 2: Japanese Patent Laid-Open No. 59-094706.

The properties required for polarizing films include various properties in addition to the aforementioned hue, shrinkage rate, and flatness, and important properties include optical properties using monomer transmittance and degree of polarization as indicators. Crosslinking treatment using a crosslinking agent such as boric acid in order to fix dichroic dyes such as iodine is also one of the methods for improving water resistance and improving optical properties.

In the method described in Patent Document 1, although the crosslinking treatment is performed, it is still unclear whether the optical properties of the polarizing film can be further improved by performing the drying step once. In the method described in Patent Document 2, no crosslinking treatment was performed, and the step of irradiating far-infrared rays resulted in a decrease in the degree of polarization (the immobilization treatment method shown in Table 1 of Patent Document 2 was a comparison "before treatment"). ” and “far-infrared” examples of the degree of polarization).

The object of the present invention is to provide a kind of manufacture of polarizing film The method and the manufacturing apparatus thereof, and the aforementioned manufacturing method of the polarizing film, are used in the manufacturing method of the polarizing film subjected to the cross-linking treatment, which can further improve the optical properties of the polarizing film.

The present invention provides a manufacturing method and a manufacturing apparatus of the polarizing film shown below.

[1] A method for producing a polarizing film, comprising: producing a polarizing film from a polyvinyl alcohol-based resin film, comprising: a dyeing step of dyeing the polyvinyl alcohol-based resin film with a dichroic dye; The above-mentioned polyvinyl alcohol-based resin film is subjected to a cross-linking step of cross-linking treatment with a cross-linking agent, and after the above-mentioned cross-linking step, the polyvinyl alcohol-based resin film is irradiated with infrared rays with wavelengths exceeding 2 μm and 4 μm in total radiation energy. The electromagnetic wave irradiation step of the electromagnetic wave whose radiation energy ratio is 25% or more of the total radiation energy, and the cleaning step of cleaning the polyvinyl alcohol-based resin film after irradiating the electromagnetic wave.

[2] The method for producing a polarizing film according to [1], wherein, in the step of irradiating electromagnetic waves, the heat of irradiation of the electromagnetic waves is 100 J/cm ³ or more and 50 kJ/cm ³ per unit volume of the polyvinyl alcohol-based resin film. the following.

[3] The method for producing a polarizing film according to [1] or [2], wherein the crosslinking agent contains a boron compound.

[4] The method for producing a polarizing film according to any one of [1] to [3], wherein the crosslinking step is formed by immersing the polyvinyl alcohol-based resin film in an aqueous solution of the crosslinking agent step of the cross-linking bath.

[5] The method for producing a polarizing film according to [4], which further comprises a deliquoring step for removing the aqueous solution adhering to the surface of the polyvinyl alcohol-based resin film after the crosslinking treatment and before the irradiation of the electromagnetic wave step.

[6] The method for producing a polarizing film according to [4] or [5], wherein the electromagnetic wave irradiation step is performed within 5 seconds after the polyvinyl alcohol-based resin film is pulled out from the crosslinking bath.

[7] An apparatus for producing a polarizing film, which produces a polarizing film from a polyvinyl alcohol-based resin film, comprising: a dyeing section for dyeing the polyvinyl alcohol-based resin film with a dichroic dye, The cross-linked portion of the polyvinyl alcohol-based resin film that is cross-linked with a cross-linking agent, and the polyvinyl alcohol-based resin film after the cross-linking step is irradiated with radiation energy of infrared rays with wavelengths exceeding 2 μm and 4 μm or less. The electromagnetic wave irradiation part of the electromagnetic wave whose ratio is 25% or more of the total radiation energy, and the cleaning part which washes the polyvinyl alcohol-based resin film after irradiating the electromagnetic wave.

According to the present invention, the optical characteristics of the polarizing film can be provided. A manufacturing method and a manufacturing apparatus of a polarizing film with improved properties.

10‧‧‧Material film composed of polyvinyl alcohol resin

11‧‧‧Material Roller

13‧‧‧Swelling bath

15‧‧‧Dyeing Bath

17a‧‧‧First Crosslinking Bath

17b‧‧‧Second Crosslinking Bath

19‧‧‧Cleaning bath

21‧‧‧Drying furnace

23‧‧‧Polarizing film

30 to 48, 60, 61‧‧‧Guide Roller

50 to 52, 53a, 53b, 54, 55‧‧‧ nip roll

71‧‧‧Electromagnetic wave irradiation section

Fig. 1 is a cross-sectional view schematically showing an example of a method for producing a polarizing film of the present invention and an example of a polarizing film producing apparatus used therefor.

Fig. 2 shows the radiation energy spectrum of various types of electromagnetic wave irradiators.

<Manufacturing method of polarizing film>

The polarizing film in the present invention is a dichroic dye (iodine or dichroic dye) adsorbed and aligned on a uniaxially stretched polyvinyl alcohol-based resin film. The polyvinyl alcohol-based resin constituting the polyvinyl alcohol-based resin film is usually obtained by saponifying a polyvinyl acetate-based resin. The degree of saponification is usually about 85 mol% or more, preferably about 90 mol% or more, more preferably about 99 mol% or more. The polyvinyl acetate-based resin may be, for example, a copolymer of vinyl acetate and other monomers copolymerizable therewith, in addition to polyvinyl acetate which is a vinyl acetate homopolymer. Examples of other copolymerizable monomers include unsaturated carboxylic acids, olefins, vinyl ethers, and unsaturated sulfonic acids. The degree of polymerization of the polyvinyl alcohol-based resin is usually about 1,000 to 10,000, preferably about 1,500 to 5,000.

These polyvinyl alcohol-based resins can be modified, and for example, polyvinyl formal, polyvinyl acetal, polyvinyl butyral, etc. modified with aldehydes can also be used.

In the present invention, as a starting material for producing a polarizing film, An unstretched polyvinyl alcohol-based resin film (raw material film) having a thickness of 65 μm or less (eg, 60 μm or less), preferably 50 μm or less, more preferably 35 μm or less, and still more preferably 30 μm or less, is used.

Thereby, a thin-film polarizing film with increasing market requirements can be obtained. The width of the raw material film is not particularly limited, for example, it may be about 400 to 6000 mm. For the raw material film, for example, a roll (raw material roll) of a long unstretched polyvinyl alcohol-based resin film can be prepared.

In addition, the polyvinyl alcohol-based resin film used in the present invention may be one that is laminated on a supporting base film, that is, a laminated film of a base film and a polyvinyl alcohol-based resin film laminated thereon may be prepared, and as the polyvinyl alcohol-based resin film. 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 on at least one side of the base film, and then drying.

As the base film, for example, a film made of a thermoplastic resin can be used. As a specific example, it is a light-transmitting thermoplastic resin, preferably a film made of an optically transparent thermoplastic resin, such as a chain polyolefin-based resin (polypropylene-based resin, etc.), a cyclic polyolefin-based resin Polyolefin-based resins such as (norbornene-based resins, etc.); cellulose-based resins such as cellulose triacetate and cellulose diacetate; polyethylene terephthalate, polybutylene terephthalate Polycarbonate resins; (meth)acrylic resins such as methyl methacrylate resins; Polystyrene resins; Polyvinyl chloride resins; Acrylonitrile/butadiene / Styrenic resin; Acrylonitrile / Styrenic resin; Polyvinyl acetate resin; Polyvinylidene chloride resin; Polyamide resin; Polyacetal resin; Modified polyphenylene ether resin; Polyethylene Polyester resin; Polyether resin; Polyarylate resin; Polyamide imide resin; Polyimide resins, etc.

The polarizing film is continuously conveyed along the film conveying path of the polarizing film manufacturing apparatus while pulling out the above-mentioned long raw material film from the raw material roll, and is immersed in a treatment liquid (hereinafter also referred to as a "treatment bath") accommodated in a treatment tank. Post-drawing is performed, and a drying step is performed after performing a predetermined processing step, whereby a long polarizing film can be continuously manufactured. In addition, the treatment step is not limited to a method of immersing the film in a treatment bath as long as the treatment step is a method of contacting the film with the treatment liquid, and may be a method of treating the film by attaching the treatment liquid to the film surface by spraying, flowing, dripping, or the like. method. When the treatment step is performed by immersing the film in the treatment bath, the treatment bath for performing one treatment step is not limited to one, and one treatment step may be completed by sequentially immersing the film in two or more treatment baths.

As said process liquid, a swelling liquid, a dyeing liquid, a crosslinking liquid, a washing|cleaning liquid etc. are mentioned, for example. Next, the above-mentioned treatment steps include, for example, a swelling step in which a raw film is brought into contact with a swelling liquid to perform a swelling treatment, a dyeing step in which the film after the swelling treatment is brought into contact with a dyeing liquid to perform a dyeing treatment, and a film after the dyeing treatment is brought into contact and crosslinking A cross-linking step for performing cross-linking treatment with a liquid, and a cleaning step for performing a cleaning treatment by contacting the film after the cross-linking treatment with a cleaning liquid. Furthermore, wet or dry uniaxial stretching can be performed between the series of processing steps (ie, before and after any one or more processing steps and/or during any one or more processing steps). Other processing steps may be added as required.

In the present invention, the step of irradiating the film with electromagnetic waves, which will be described later, is performed after the crosslinking treatment and before the washing treatment. By performing the electromagnetic wave irradiation step, the optical properties of the obtained polarizing film can be improved.

Hereinafter, an example of the manufacturing method of the polarizing film of this invention is demonstrated in detail, referring FIG. 1. FIG. FIG. 1 is a cross-sectional view schematically showing an example of a manufacturing method of a polarizing film of the present invention and an example of a polarizing film manufacturing apparatus used therein. The polarizing film manufacturing apparatus shown in FIG. 1 is configured such that a raw (unstretched) film 10 made of a polyvinyl alcohol-based resin is continuously drawn out by a raw roll 11 while being conveyed along the film The path is conveyed by passing through the swelling bath (swelling liquid accommodated in the swelling tank) 13, the dyeing bath (the dyeing liquid accommodated in the dyeing tank) 15, the first cross-linking bath (accommodating the The first cross-linking liquid in the cross-linking tank) 17a, the second cross-linking bath (the second cross-linking liquid in the cross-linking tank) 17b, and the cleaning bath (the cleaning liquid in the cleaning tank) ) 19, and finally pass through the drying oven 21. The obtained polarizing film 23 can be directly conveyed, for example, to the following polarizing plate manufacturing step (step of attaching a protective film to one side or both sides of the polarizing film 23 ). Arrows in Fig. 1 indicate the film conveying direction.

In the description of Fig. 1, "treatment tank" is a general term including swelling tank, dyeing tank, cross-linking tank and cleaning tank, and "treatment liquid" is a general term including swelling liquid, dyeing liquid, cross-linking liquid and cleaning liquid , "Treatment bath" is a general term including swelling bath, dyeing bath, cross-linking bath and cleaning bath. The swelling bath, the dyeing bath, the crosslinking bath, and the washing bath constitute the swelling part, the dyeing part, the crosslinking part, and the washing part, respectively, in the manufacturing apparatus of the present invention.

The film conveyance path of the polarizing film manufacturing apparatus can be constituted by, in addition to the above-mentioned treatment bath, the following modes: guide rollers 30 to 48, 60, 61 which can support the conveyed film or further change the film conveying direction; Holding the conveyed film and imparting driving force to the film through its rotation, or further The nip rolls 50 to 55, which can change the direction of film conveyance, are arranged at appropriate positions. Guide rolls or nip rolls can be arranged before and after each treatment bath or in the treatment bath, whereby the film can be introduced into and immersed in the treatment bath, and pulled out from the treatment bath [see Fig. 1]. For example, one or more guide rolls can be provided in each treatment bath, and the film can be immersed in each treatment bath by conveying the film along these guide rolls.

In the polarizing film manufacturing apparatus shown in Fig. 1, nip rolls (nip rolls 50 to 54) are arranged before and after each treatment bath, whereby stretching between rolls can be performed in any one or more treatment baths. A rotational speed difference was applied between the nip rolls before and after the treatment bath, and longitudinal uniaxial stretching was performed.

In the polarizing film manufacturing apparatus shown in FIG. 1, the electromagnetic wave irradiation part 71 is arrange|positioned in the conveyance path which flows down the 2nd crosslinking bath 17b and the washing bath 19 flows up, and performs an electromagnetic wave irradiation process. Each step is explained below.

(swelling step)

The purpose of performing the swelling step is to remove foreign matter on the surface of the raw material film 10 , remove the plasticizer in the raw material film 10 , impart easy dyeability, and plasticize the raw material film 10 . The processing conditions are determined in a range in which the object can be achieved, and in a range in which the raw material film 10 does not suffer from extreme dissolution or devitrification.

Referring to FIG. 1, the swelling step can be carried out by: immersing the raw material film 10 in the swelling bath 13 for a predetermined time while continuously pulling out the raw material film 10 by the raw material roll 11 while conveying the raw material film 10 along the film conveying path, Then pull out. In the example of FIG. 1, the raw material film 10 is conveyed along the film conveyance path constructed by the guide rolls 60 and 61 and the nip roll 50 between the extraction of the raw material film 10 and the immersion in the swelling bath 13. In the swelling treatment, the film is transported along the film transport path constructed by the guide rolls 30 to 32 and the nip roll 51 .

As the swelling liquid of the swelling bath 13, besides pure water, boric acid (Japanese Unexamined Patent Publication No. 10-153709), chlorides (Japanese Unexamined Patent Publication No. 06-281816 ), Aqueous solutions of inorganic acids, inorganic salts, water-soluble organic solvents, alcohols, etc.

The temperature of the swelling bath 13 is, for example, about 10 to 50°C, preferably about 10 to 40°C, and more preferably about 15 to 30°C. The immersion time of the raw material film 10 is preferably about 10 to 300 seconds, more preferably about 20 to 200 seconds. In addition, when the raw material film 10 is a polyvinyl alcohol-based resin film previously stretched in gas, the temperature of the swelling bath 13 is, for example, about 20 to 70°C, preferably about 30 to 60°C. The immersion time of the raw material film 10 is preferably about 30 to 300 seconds, more preferably about 60 to 240 seconds.

During the swelling treatment, the raw material film 10 is likely to swell in the width direction to form wrinkles in the film. As one method for removing the wrinkles and conveying the film, the guide rollers 30, 31, and/or 32 may use rolls having a widening function, such as expansion rolls, spiral rolls, and crown rolls. Or use other widening devices such as cross guiders, curved bars, tenter clips, or the like. Another method for suppressing wrinkle generation is to perform a stretching treatment. For example, the uniaxial stretching treatment can be performed in the swelling bath 13 by utilizing the difference in rotational speed between the nip roll 50 and the nip roll 51 .

In the swelling treatment, the film also swells and expands in the film conveying direction. Therefore, in order to eliminate film slack in the conveying direction when the film is not actively stretched, it is preferable to employ, for example, control the nip rolls 50 arranged before and after the swelling bath 13. , 51 speed and other methods. In addition, for the purpose of stabilizing the film transfer in the swelling bath 13, the water flow in the swelling bath 13 is controlled by bathing in water, or a combination of It is useful to use an EPC device (Edge Position Control device: a device that detects the end of the membrane and prevents the membrane from meandering).

In the example shown in FIG. 1 , the film drawn from the swelling bath 13 passes through the guide roll 32 , the nip roll 51 , and the guide roll 33 in this order, and is introduced into the dyeing bath 15 .

(Dyeing step)

The purpose of the dyeing step is to adsorb, align the dichroic dye, and the like to the polyvinyl alcohol-based resin film after the swelling treatment. The treatment conditions are determined within a range within which the purpose can be achieved, and within a range where defects such as extreme dissolution and devitrification of the film do not occur. Referring to FIG. 1, the dyeing step can be carried out along the film conveying path constructed by the nip rolls 51, the guide rolls 33 to 36, and the nip rolls 52, and the film after the swelling treatment can be placed in the dyeing bath 15 (treatment in the dyeing tank). liquid) is immersed for a predetermined time, and then pulled out. In order to improve the dyeability of the dichroic dye, the film to be used in the dyeing step is preferably a film subjected to at least a certain degree of uniaxial stretching treatment, or is preferably a uniaxial stretching treatment in place of the dyeing treatment, or in addition to the dyeing treatment. In addition to the uniaxial stretching treatment, the uniaxial stretching treatment is performed during the dyeing treatment.

When iodine is used as a dichroic dye, for example, an aqueous solution having a concentration of iodine/potassium iodide/water=about 0.003 to 0.3/about 0.1 to 10/100 by weight can be used in the dyeing solution of the dyeing bath 15 . Other iodides such as zinc iodide may be used in place of potassium iodide, or potassium iodide and other iodides may be used in combination. Moreover, compounds other than iodide, for example, boric acid, zinc chloride, cobalt chloride, etc. may coexist. When adding boric acid, it can be distinguished from the crosslinking treatment described later by the point containing iodine, and an aqueous solution containing about 0.003 parts by weight or more of iodine can be regarded as dyeing bath 15 with respect to 100 parts by weight of water. Dyeing when dipping film The temperature of the bath 15 is usually about 10 to 45°C, preferably 10 to 40°C, more preferably 20 to 35°C, and the immersion time of the film is usually about 30 to 600 seconds, preferably 60 to 300 seconds.

When a water-soluble dichroic dye is used as the dichroic dye, an aqueous solution having a concentration of, for example, dichroic dye/water=about 0.001 to 0.1/100 by weight can be used in the dyeing solution of the dyeing bath 15 . The dyeing bath 15 may coexist with dyeing auxiliaries and the like, and may contain, for example, inorganic salts such as sodium sulfate, surfactants, and the like. Only one type of dichroic dye may be used alone, or two or more types of dichroic dye may be used in combination. The temperature of the dyeing bath 15 when dipping the film is, for example, about 20 to 80°C, preferably 30 to 70°C, and the immersion time of the film is usually about 30 to 600 seconds, preferably about 60 to 300 seconds.

In the dyeing step as described above, the uniaxial extension of the film may be performed in the dyeing bath 15 . The uniaxial stretching of the film can be performed by a method such as applying a rotational speed difference between the nip rolls 51 and 52 disposed before and after the dyeing bath 15 .

In the dyeing treatment, similarly to the swelling treatment, in order to remove the wrinkles of the film and convey the polyvinyl alcohol-based resin film, the guide rollers 33, 34, 35, and/or 36 may be provided with an expansion roller, a spiral roller, a convex roller, or the like. The rolls with the widening function can also use other widening devices such as cross guide rolls, bending rods, and tenter clips. Similar to the swelling treatment, another method for suppressing the occurrence of wrinkles is to perform a stretching treatment.

In the example shown in FIG. 1 , the film drawn from the dyeing bath 15 passes through the guide roll 36 , the nip roll 52 , and the guide roll 37 in this order, and is introduced into the crosslinking bath 17 .

(crosslinking step)

The cross-linking step is carried out for the purpose of water resistance or color tone adjustment by cross-linking (to prevent the film from appearing blue, etc.) and so on. In the example shown in Fig. 1, two cross-linking baths are arranged as the cross-linking baths for the cross-linking step. The first cross-linking step for water resistance is performed in the first cross-linking bath 17a, and the color tone is adjusted as The second cross-linking step performed for the purpose is performed in the second cross-linking bath 17b. Referring to FIG. 1, the first cross-linking step can be carried out along the film conveying path constructed by the nip rolls 52, the guide rolls 37 to 40, and the nip roll 53a, and the dyed film is placed in the first cross-linking bath 17a. (The 1st crosslinking liquid accommodated in a crosslinking tank) is immersed for a predetermined time, and it pulls out and implements. In the second cross-linking step, the film after the first cross-linking step can be transferred to the second cross-linking bath 17b (stored in The second cross-linking liquid of the cross-linking tank) is immersed for a predetermined time, and then pulled out and implemented. Hereinafter, when it calls a crosslinking bath, it contains both the 1st crosslinking bath 17a and the 2nd crosslinking bath 17b, When it calls a crosslinking liquid, it also contains both a 1st crosslinking liquid and a 2nd crosslinking liquid.

The cross-linking solution can be used in a solution in which the cross-linking agent is dissolved in the solvent. As a crosslinking agent, boron compounds, such as boric acid and borax, glyoxal, glutaraldehyde, etc. are mentioned, for example. These may be one type or two or more types may be used in combination. As a solvent, for example, water can be used, and an organic solvent having compatibility with water may also be contained. The concentration of the crosslinking agent in the crosslinking solution is preferably in the range of 1 to 20% by weight, more preferably 6 to 15% by weight, but not limited thereto.

The cross-linking liquid can be an aqueous solution containing boric acid, for example, about 1 to 10 parts by weight relative to 100 parts by weight of water. When the dichroic dye used in the dyeing treatment is iodine, the crosslinking solution preferably contains iodide in addition to boric acid, and the amount may be, for example, 1 to 30 parts by weight relative to 100 parts by weight of water. Examples of the iodide include potassium iodide, zinc iodide, and the like. In addition, chemicals other than iodide may coexist Compounds, such as zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, sodium sulfate, etc.

In the crosslinking treatment, the concentrations of boric acid and iodide and the temperature of the crosslinking bath 17 can be appropriately changed according to the purpose. For example, in the case of the first cross-linking liquid whose purpose of cross-linking is to achieve water resistance by cross-linking, the concentration may be an aqueous solution of boric acid/iodide/water=3 to 10/1 to 20/100 in weight ratio. Other cross-linking agents may be used in place of boric acid as required, or boric acid and other cross-linking agents may be used in combination. The temperature of the first cross-linking bath 17a when the film is dipped is usually about 50 to 70°C, preferably 53 to 65°C, and the immersion time of the film is usually about 10 to 600 seconds, preferably 20 to 300 seconds, more preferably for 20 to 200 seconds. Moreover, when the dyeing treatment and the first cross-linking treatment are sequentially performed on the polyvinyl alcohol-based resin film stretched before the swelling treatment, the temperature of the first cross-linking bath 17a is usually about 50 to 85° C., preferably 55 to 85° C. 80°C.

For example, when iodine is used as a dichroic dye in the second cross-linking liquid for the purpose of adjusting the color tone, the concentration of boric acid/iodide/water=1 to 5/3 to 30/100 by weight can be used. The temperature of the second crosslinking bath 17b when the film is dipped is usually about 10 to 45°C, and the immersion time of the film is usually about 1 to 300 seconds, preferably 2 to 100 seconds.

The cross-linking treatment may be performed a plurality of times, usually 2 to 5 times. At this time, the composition and temperature of each crosslinking bath to be used may be the same or different as long as they are within the above-mentioned ranges. The cross-linking treatment for achieving water resistance through cross-linking and the cross-linking treatment for adjusting the color tone may be performed in plural steps, respectively.

The difference in rotation speed between the nip roller 52 and the nip roller 53a can be used in the first Uniaxial stretching treatment is performed in the crosslinking bath 17a. Moreover, the uniaxial stretching process may be performed in the 2nd crosslinking bath 17b using the rotational speed difference of the nip roll 53a and the nip roll 53b.

In the cross-linking treatment, similarly to the swelling treatment, in order to remove the wrinkles of the film and convey the polyvinyl alcohol-based resin film, the guide rollers 38, 39, 40, 41, 42, 43 and/or 44 can be equipped with expansion rollers, spiral Rolls with widening functions such as rolls and convex rolls can also be used with other widening devices such as cross guide rolls, bending rods, and tenter clips. Similar to the swelling treatment, another method for suppressing the occurrence of wrinkles is to perform a stretching treatment.

In the example shown in FIG. 1, the film drawn from the second crosslinking bath 17b passes through the guide roll 44 and the nip roll 53b in this order, and is introduced into the cleaning bath 19.

(cleaning step)

The example shown in Fig. 1 includes a washing step after the crosslinking step. The purpose of the cleaning treatment is to remove chemicals such as excess boric acid and iodine adhering to the polyvinyl alcohol-based resin film. The cleaning step is performed by, for example, immersing the cross-linked polyvinyl alcohol-based resin film in the cleaning bath 19 . Furthermore, instead of the step of immersing the film in the cleaning bath 19, the cleaning step may be performed by spraying the film with the cleaning solution as a shower, or by using the immersion in the cleaning bath 19 and the cleaning solution in combination. by spraying.

FIG. 1 shows an example in which a polyvinyl alcohol-based resin film is immersed in a cleaning bath 19 and subjected to a cleaning process. The temperature of the cleaning bath 19 in the cleaning treatment is usually about 2 to 40° C., and the immersion time of the film is usually about 2 to 120 seconds.

In addition, washing process to remove wrinkles and convey poly For the purpose of vinyl alcohol-based resin film, guide rollers 45, 46, 47 and/or 48 can be used with a widening function such as a spreading roll, a spiral roll, a convex roll, or a cross guide roll or a curved bar. , tenter clips and other widening devices. In addition, a stretching treatment for suppressing the occurrence of wrinkles may be performed in the film cleaning treatment.

(extension step)

As described above, the raw material film 10 is subjected to wet or dry uniaxial stretching treatment between the above-mentioned series of processing steps (ie, before and after any one or more processing steps and/or during any one or more processing steps). The specific method of the uniaxial stretching treatment can be, for example, applying a rotational speed difference between two nip rolls (for example, two nip rolls arranged before and after the treatment bath) that constitute the film conveying path to perform longitudinal uniaxial stretching between rolls, such as in Japan. The hot roll stretching, tenter stretching, and the like described in Patent No. 2731813 are preferably inter-roll stretching. The uniaxial stretching step may be performed a plurality of times between obtaining the polarizing film 23 from the raw material film 10 . As described above, the stretching treatment is also advantageous for suppressing the occurrence of wrinkles in the film.

Based on the raw material film 10 , the final cumulative stretching ratio of the polarizing film 23 is usually about 4.5 to 7 times, preferably 5 to 6.5 times. The extension step may be performed in any of the treatment steps, and when the extension treatment is performed in two or more treatment steps, the extension treatment may be performed in any of the treatment steps.

(Electromagnetic wave irradiation step)

In the apparatus shown in FIG. 1, after the film is pulled out from the second crosslinking step 17b and passed through the nip rolls 53b, the film is irradiated with electromagnetic waves before being immersed in the cleaning bath 19 (electromagnetic wave irradiation step). In the apparatus shown in FIG. 1 , the electromagnetic wave is irradiated by the electromagnetic wave irradiation unit 71 . The electromagnetic wave used in the electromagnetic wave irradiation step of the present invention has a ratio of infrared radiation energy with wavelengths exceeding 2 μm and below 4 μm: More than 25% of the total radiation energy, preferably more than 28%, more preferably more than 35%. By irradiating the film with such electromagnetic waves, the optical properties of the obtained polarizing film can be improved. Moreover, although the upper limit of the ratio of infrared radiation energy of the wavelength exceeding 2 micrometers and 4 micrometers or less is not specifically limited about the electromagnetic wave used in this invention, for example, it is 80% or less. Usually electromagnetic waves with wavelengths from 0.75μm to 1000μm are called infrared rays.

In the electromagnetic wave irradiation step, by irradiating electromagnetic waves with a wavelength of more than 2 μm and less than 4 μm in which the radiation energy ratio is 25% or more of the total radiation energy, the mechanism by which the optical properties of the polarizing film can be improved is not clear, but it is presumed to be due to Molecular movement in the film is stimulated by infrared rays with wavelengths exceeding 2 μm and below 4 μm, which can promote the immobilization of dichroic dyes such as iodine in the cross-linked film, and improve the optical properties of the polarizing film.

Figure 2 shows the radiation energy spectrum of various types of electromagnetic wave irradiators. In addition, Table 1 shows the ratio of the electromagnetic wave radiation energy to the total radiation energy in each wavelength region (represented by the range of wavelength x μm) of various types of electromagnetic wave irradiators. The electromagnetic wave irradiators shown in Fig. 2 and Table 1 are halogen heaters (heat source temperature 2600°C), short-wavelength infrared heaters (heat source temperature 2200°C), fast-reaction medium-wavelength infrared heaters (heat source temperature 1600°C), carbon Heater (heat source temperature 1200°C), carbon heater (heat source temperature 950°C), and mid-wavelength infrared heater (heat source temperature 900°C).

As shown in Table 1, short-wavelength infrared heaters (heat source temperature 2200°C), fast-reaction mid-wavelength infrared heaters (heat source temperature 1600°C), carbon heaters (heat source temperature 1200°C), carbon heaters (heat source temperature 950°C) ), and the middle-wavelength infrared heater (heat source temperature of 900°C), the proportion of infrared radiation energy with wavelengths exceeding 2 μm and below 4 μm is more than 25% of the total radiation energy, so it can be suitably used in the electromagnetic wave irradiator constituting the electromagnetic wave irradiation part 71. The electromagnetic wave irradiation unit 71 may be constituted by one electromagnetic wave irradiator, or may be constituted by a plurality of electromagnetic wave irradiators. When it is composed of a plurality of electromagnetic wave irradiators, a plurality of electromagnetic wave irradiators are selected so that the infrared radiation energy of wavelengths exceeding 2 μm and 4 μm or less radiated by the plurality of electromagnetic wave irradiators is the total amount of electromagnetic waves radiated by the plurality of electromagnetic wave irradiators. More than 25% of the radiant energy. In addition, although the electromagnetic wave irradiation part 71 is comprised so that only one surface of a film may irradiate an electromagnetic wave in FIG. 1, a plurality of electromagnetic wave irradiators may be arrange|positioned so that an electromagnetic wave may be irradiated to both surfaces of a film. It is preferable that the electromagnetic wave irradiation part 71 is comprised so that the whole width direction of the polyvinyl-alcohol-type resin film of irradiation object may be irradiated with an electromagnetic wave.

In the electromagnetic wave irradiation step, the electromagnetic wave is preferably irradiated from the upper side in the vertical direction with respect to the film surface. Moreover, in the electromagnetic wave irradiation part 71, the distance between the electromagnetic wave radiation opening of the electromagnetic wave irradiator and the film is preferably 2 to 40 cm, more preferably 5 to 20 cm. However, it is preferable that this distance is appropriately selected and performed in consideration of the radiation energy amount of the electromagnetic wave radiated from the electromagnetic wave irradiator, the temperature of the film surface, and the like. The film surface temperature at the time of electromagnetic wave irradiation is preferably maintained at 30 to 90°C, and more preferably maintained at 40 to 80°C.

In the electromagnetic wave irradiation step, the electromagnetic wave irradiation heat amount per unit volume of the film is usually 100 J/cm ³ or more and 50 kJ/cm ³ or less. From the viewpoint of improving the optical properties of the polarizing film, it is preferably 100 J/cm ³ or more, more preferably 500 J/cm ³ or more, and still more preferably 1000 J/cm ³ or more. In addition, from the viewpoint of suppressing deterioration of the film due to temperature rise, the radiation heat amount of the electromagnetic wave per unit volume of the film is preferably 10 kJ/cm ³ or less, more preferably 5000 J/cm ³ or less, and still more preferably 3000 J/cm 3 ³ or less. Usually, the reduction of the moisture content of the film is proportional to the heat of irradiation of electromagnetic waves, but the purpose of the electromagnetic wave irradiation step of the present invention is not to reduce the moisture content of the film, so the heat of irradiation can be appropriately selected, preferably within the above-mentioned range. .

In the present invention, the electromagnetic wave irradiation step is performed before the cleaning step, whereby the optical properties of the obtained polarizing film can be improved. The electromagnetic wave irradiation step may be performed only on the film after immersion in at least one cross-linking bath, and as shown in FIG. 1 , it is not limited to be performed on the film after immersion in all cross-linking baths. That is, in the example shown in FIG. 1, the electromagnetic wave irradiation step may be performed on the film after immersion in the first crosslinking bath and before the immersion in the second crosslinking bath, and the electromagnetic wave irradiation may be performed on the film after immersion in the second crosslinking bath. step. However, through the electromagnetic wave irradiation step and immersion in the cross-linking bath, the boric acid entering the film can be cross-linked. Therefore, the electromagnetic wave irradiation step for the film immersed in all the cross-linking baths can more effectively carry out the boric acid cross-linking. better.

The irradiation of electromagnetic waves is preferably performed within 10 seconds after the film is pulled out from the crosslinking bath, and more preferably within 5 seconds. The optical properties of the polarizing film by electromagnetic wave irradiation can be further improved as the time taken from the crosslinking bath to irradiate the electromagnetic wave is shorter. Moreover, in the electromagnetic wave irradiation process, it is preferable that there are few water molecules adhering to the film surface. If there is water on the membrane surface molecules, the water molecules on the surface of the membrane will absorb infrared rays, thus reducing the effect of stimulating the movement of molecules in the membrane by electromagnetic wave irradiation. Since the crosslinking liquid adheres to the film surface after being pulled out from the crosslinking bath, it is preferable to provide a liquid removal method for removing it before the electromagnetic wave irradiation step. In Fig. 1, the nip roll 53b also functions as a liquid removal method for removing the crosslinking liquid adhering to the film surface. In addition to the nip rolls, there is a method of removing liquid by blowing air on the film, and a doctor blade or the like for removing liquid by contacting the film can also be used.

From an economical point of view, if the film processing speed is high, specifically, when the processing speed is 10 to 100 m/min as the high processing speed, the electromagnetic wave irradiation time is short and the irradiation heat is insufficient. In this corresponding method, a plurality of electromagnetic wave irradiators are installed in parallel, whereby sufficient irradiation heat can be obtained.

(drying step)

It is preferable to perform the process of drying a polyvinyl-alcohol-type resin film after a washing|cleaning process. The drying of the film is not particularly limited, and it can be performed using the drying furnace 21 in the example shown in FIG. 1 . As the drying furnace 21, for example, a hot air dryer can be used. The drying temperature is, for example, about 30 to 100° C., and the drying time is, for example, about 30 to 600 seconds. The treatment of drying the polyvinyl alcohol-based resin film can be performed using a far-infrared heater. The thickness of the polarizing film 23 obtained in the above manner is, for example, about 5 to 30 μm.

Considering the balance with the sensitivity-corrected polarization degree Py, the sensitivity-corrected monomer transmittance Ty of the obtained polarizing film is preferably 40 to 47%, more preferably 41 to 45%. The viewing sensitivity correction polarization degree Py is preferably 99.9% or more, more preferably 99.95% or more, and the larger the value, the better. Sensitivity correction of polarizing film The larger the monomer transmittance Ty is, the larger the optical property improvement effect obtained by the present invention is. Therefore, it is particularly advantageous in the present invention to manufacture a polarizing film having a visibility correction monomer transmittance Ty of 41% or more, further 42% or more, and further 43% or more. According to the present invention, for example, a polarizing film having Ty of 43% or more and Py of 99.994% or more can be obtained. Ty and Py can be measured according to the description of the following examples.

The obtained polarizing film can be sequentially wound into a winding roll to form a roll shape, or it can be directly supplied to the polarizing plate manufacturing step (steps such as layering a protective film on one side or two areas of the polarizing film) without being wound.

(Other processing steps for polyvinyl alcohol-based resin film)

Processing other than the above processing can be added. Examples of additional treatments include immersion in an aqueous solution of iodide that does not contain boric acid (color correction treatment) after the crosslinking step, and immersion in an aqueous solution containing zinc chloride or the like without boric acid (zinc treatment).

<Polarizer>

A polarizing plate can be obtained by bonding a protective film to at least one side of the polarizing film manufactured by the above method via an adhesive. Examples of the protective film include films made of cellulose acetate-based resins such as cellulose triacetate or cellulose diacetate; polyethylene terephthalate, polyethylene naphthalate, and polyethylene terephthalate. Films composed of polyester resins such as butylene formate; polycarbonate resin films, cycloolefin resin films; acrylic resin films; polypropylene resins and chain olefin resins.

In order to improve the adhesion between the polarizing film and the protective film, corona treatment, flame treatment, Plasma treatment, UV irradiation, primer coating treatment, saponification treatment and other surface treatments. Examples of the adhesive used for bonding the polarizing film and the protective film include active energy ray-curable adhesives such as ultraviolet curable adhesives, aqueous solutions of polyvinyl alcohol-based resins, or aqueous solutions in which crosslinking agents are blended, and Water-based adhesives such as urethane-based emulsion adhesives. The ultraviolet curable adhesive can be a mixture of an acrylic compound and a photo-radical polymerization initiator, or a mixture of an epoxy compound and a photo-cationic polymerization initiator, and the like. Moreover, a cationically polymerizable epoxy compound and a radically polymerizable acrylic compound may be used together, and a photocationic polymerization initiator and a photoradical polymerization initiator as initiators may be used together.

[Example]

Hereinafter, the present invention will be further specifically described with reference to examples, but the present invention is not limited to these examples.

<Example 1>

Using the manufacturing apparatus shown in FIG. 1, the polarizing film of Example 1 was manufactured from the polyvinyl alcohol-type resin film. Specifically, a long polyvinyl alcohol (PVA) raw material film with a thickness of 60 μm [trade name "Kuraray Vinylon VF-PE#6000" manufactured by Kuraray Co., Ltd., average degree of polymerization 2400, degree of saponification 99.9 mol% or more) It was continuously conveyed while being pulled out from a roll, and was immersed in a swelling bath containing pure water at 30°C for a residence time of 79 seconds (swelling step). After that, the film pulled out from the swelling bath was dipped in a dyeing bath containing iodine at 30° C. in a ratio of 1/0.3/100 (weight ratio) of 3 potassium iodide/boric acid/water for a residence time of 123 seconds (dyeing step). Next, the film was pulled out from the dyeing bath, and the first cross-linking bath at 53°C was 11/3.8/100 (weight ratio) of potassium iodide/boric acid/water for a residence time. Immersion was performed for 44 seconds, followed by immersion in a second crosslinking bath at 40° C. of potassium iodide/boric acid/water of 11/3.8/100 (weight ratio) for a residence time of 6 seconds (crosslinking step). In the dyeing step and the cross-linking step, longitudinal uniaxial stretching is performed by stretching between rolls in a bath. The total stretching ratio based on the raw material film was 65 times.

Next, an electromagnetic wave irradiator (medium wavelength infrared heater (MW heater), product name: Golden 8 Medium-wave twin tube emitter, Heraeus Co., Ltd.) was used for the film drawn from the second crosslinking bath 17b and passed through the nip roll 53b. Heat source temperature 900°C, maximum energy density 60kW/m ² ), the electromagnetic wave radiation port was arranged at a position 5cm away from the film surface, and the electromagnetic wave was irradiated at 50% of the maximum radiation output of the electromagnetic wave irradiator. The radiation heat of electromagnetic waves per unit volume of the film was 490 J/cm ³ . In addition, the irradiated heat amount of the electromagnetic wave per unit volume of the film was calculated by the following formula.

(Electromagnetic wave irradiation heat per unit volume of film)={(maximum energy density)×(heater heating part surface area)×output (%)/(electromagnetic wave irradiation area)}×(electromagnetic wave irradiation time)÷(film thickness)

Output (%) refers to the ratio (%) of the actual irradiated output to the maximum irradiated output of the electromagnetic wave irradiator.

After pulling out from the 2nd crosslinking bath 17b, the time required from conveying a film until reaching the irradiation position of an electromagnetic wave irradiator and irradiating an electromagnetic wave is 5 seconds.

The film irradiated with electromagnetic waves was immersed in a cleaning bath 19 containing pure water at 5° C. for a residence time of 3 seconds (cleaning step). Then, the polarizing film was obtained by drying the film at a temperature of 60° C. and an absolute humidity of 11 g/cm ³ in the drying furnace 21 . The thickness of the obtained polarizing film was 23 μm.

<Examples 2 to 4, Comparative Example 2>

In the electromagnetic wave irradiation step, the type of electromagnetic wave irradiator, the output (%), and the amount of electromagnetic wave irradiation heat per unit volume of the film are shown in Table 2, except that the same procedure as in Example 1 was performed to obtain a polarizing film. The thicknesses of the obtained polarizing films were all 23 μm. As the electromagnetic wave irradiator, any one of the following was used: a halogen heater (product name: straight tube halogen heating lamp QIR, manufactured by USHIO LIGHTING Co., Ltd., heat source temperature 2600°C, maximum energy density 300kW/m ² ), Short-wavelength infrared heater (SW heater) (product name: Golden 8 Short-wave twin tube emitter, manufactured by Heraeus, heat source temperature 2200°C, maximum energy density 200kW/m ² ), fast-response medium-wavelength infrared heater (FRMW Heater) (product name: Golden 8 Medium-wave fast response twin tubu emitter, manufactured by Heraeus, heat source temperature 1600°C, maximum energy density 150kW/m ² ), mid-wavelength infrared heater (Mw heater) (product name: Golden 8 Medium-wave twin tube emitter, manufactured by Heraeus, heat source temperature 900°C, maximum energy density 60kW/m ² ).

<Comparative Example 1>

A polarizing film was obtained in the same manner as in Example 1 except that the electromagnetic wave irradiation step was not performed.

The thickness of the obtained polarizing film was 23 μm.

<Example 5>

A long polyvinyl alcohol (PVA) raw material film with a thickness of 20 μm (trade name “Kuraray poval film VF-PE # 2000” manufactured by Kuraray Co., Ltd., average degree of polymerization 2400, degree of saponification 99.9 mol% or more) was passed through a roller. Continuously conveying while pulling out, 4.1 times the single axis of the dry type The stretching was carried out by immersion in a swelling bath containing pure water at 30° C. for a residence time of 40 seconds while being kept in a taut state (swelling step). Then, the film pulled out from the swelling bath was immersed in a dyeing bath containing iodine at 6/100 (weight ratio) of potassium iodide/water at 28° C. with a residence time of 30 seconds (dyeing step). Thereafter, the film drawn from the dyeing bath was immersed in a 67°C crosslinking bath of potassium iodide/boric acid/water of 15/5.5/100 (weight ratio) with a residence time of 120 seconds (crosslinking step). In the dyeing step and the cross-linking step, longitudinal uniaxial stretching is further performed by stretching between rolls in the bath. The total stretching ratio based on the raw material film was 4.59 times.

Next, an electromagnetic wave irradiator (medium wavelength infrared heater (MW heater), product name: Golden 8 Medium-wave twin tube emitter, manufactured by Heraeus, Inc., heat source temperature) was used for the film drawn from the crosslinking bath and passed through the nip rolls. 900° C., maximum energy density of 60 kW/m ² ), the electromagnetic wave radiation port was arranged at a position 4 cm away from the film surface, and the electromagnetic wave was irradiated with an output of 30%. The radiation heat of the electromagnetic wave per unit volume of the film was 960 J/cm ³ . After pulling out from the crosslinking bath, the time required until the conveyed film reached the irradiation position of the electromagnetic wave irradiator and irradiated the electromagnetic wave was 5 seconds.

The film irradiated with electromagnetic waves was immersed in a cleaning bath containing pure water at 15° C. for a residence time of 3 seconds (cleaning step). Then, the inside of the drying furnace was set to a temperature of 40° C. and an absolute humidity of 11 g/cm ³ , and the film was dried to obtain a polarizing film. The thickness of the obtained polarizing film was 8 micrometers.

<Example 6>

A polarizing film was obtained in the same manner as in Example 5, except that in the electromagnetic wave irradiation step, the output (%) of the electromagnetic wave irradiator and the electromagnetic wave irradiation heat amount per unit volume of the film were shown in Table 3. The thickness of the obtained polarizing film was 8 μm.

<Comparative Example 3>

A polarizing film was obtained in the same manner as in Example 5 except that the electromagnetic wave irradiation step was not performed. The thickness of the obtained polarizing film was 8 μm.

[Evaluation of polarizing film]

(a) Measurement of monomer transmittance, degree of polarization, and b value of orthogonal hue For the polarizing films obtained in each Example and each Comparative Example, a spectrophotometer with an integrating sphere (“V7100” manufactured by Nippon Shoko Co., Ltd.) was used. , measure the MD transmittance and TD transmittance in the wavelength range of 380 to 780 nm, and calculate the monomer transmittance and polarization degree in each wavelength according to the following formula.

Monomer penetration rate (%)=(MD+TD)/2

Polarization (%)={(MD-TD)/(MD+TD)}×100

"MD transmittance" refers to the transmittance when the polarizing direction of the Glan-Thomson fluoride is parallel to the transmission axis of the polarizing film sample, and is expressed as "MD" in the above formula. In addition, "TD transmittance" refers to the transmittance when the polarizing direction of the Glan-Thomson ion beam is perpendicular to the transmission axis of the polarizing film sample, and is expressed as "TD" in the above formula. The obtained monomer transmittance and polarization degree are corrected by penetrating the 2-degree field of view (C light source) of JIS Z 8701:1999 "Color Representation Method - XYZ Color System and X ₁₀ Y ₁₀ Z ₁₀ Color System", Then find the b value of the visible sensitivity corrected single transmittance (Ty), the visible sensitivity corrected polarization degree (Py) and the orthogonal hue. Table 2 and Table 3 show the calculation results of the sensitivity-corrected single transmittance (Ty), the sensitivity-corrected polarization degree (Py), the b value of the orthogonal hue, and the polarization degree at a wavelength of 480 nm and a wavelength of 600 nm.

As shown in Table 2, compared with the polarizing films of Comparative Examples 1 to 4, the polarizing films of Examples 1 and 2 have almost the same transmittance (Ty) of the visual sensitivity correction monomer, but the degree of polarization is higher, which is more excellent the optical properties. Also, as shown in Table 3, compared with the polarizing film of Comparative Example 3, the polarizing films of Examples 5 and 6 have almost the same sensitivity correction monomer transmittance (Ty), but have a higher degree of polarization and have more excellent the optical properties.

10‧‧‧Material film composed of polyvinyl alcohol resin

11‧‧‧Material Roller

13‧‧‧Swelling bath

15‧‧‧Dyeing Bath

17a‧‧‧First Crosslinking Bath

17b‧‧‧Second Crosslinking Bath

19‧‧‧Cleaning bath

21‧‧‧Drying furnace

23‧‧‧Polarizing film

30 to 48, 60, 61‧‧‧Guide Roller

50 to 52, 53a, 53b, 54, 55‧‧‧ nip roll

71‧‧‧Electromagnetic wave irradiation section

Claims (8)

A method for producing a polarizing film, comprising: a dyeing step of dyeing the polyvinyl alcohol-based resin film with a dichroic dye; The crosslinking step of crosslinking the vinyl alcohol-based resin film with a crosslinking agent, and the radiation energy ratio of the polyvinyl alcohol-based resin film irradiated with infrared rays with wavelengths exceeding 2 μm and 4 μm or less after the above-mentioned cross-linking treatment is the total radiation energy The electromagnetic wave irradiation step of 25% or more of the electromagnetic wave, and the cleaning step of cleaning the polyvinyl alcohol-based resin film after the electromagnetic wave irradiation. The method for producing a polarizing film according to claim 1, wherein in the step of irradiating electromagnetic waves, the heat of irradiation of the electromagnetic waves is 100 J/cm ³ or more and 50 kJ/cm ³ per unit volume of the polyvinyl alcohol-based resin film. the following. The method for producing a polarizing film according to claim 1 or 2, wherein the crosslinking agent contains a boron compound. The method for producing a polarizing film according to claim 1 or 2, wherein the cross-linking step is a cross-linking step obtained by immersing the polyvinyl alcohol-based resin film in an aqueous solution of the cross-linking agent. The steps of the combined bath. According to the manufacturing method of the polarizing film described in item 4 of the scope of application, the After the said crosslinking process, before the said electromagnetic wave irradiation, the liquid removal process which removes the said aqueous solution adhering to the surface of the said polyvinyl alcohol-type resin film is further included. The method for producing a polarizing film according to claim 4, wherein the electromagnetic wave irradiation step is performed within 5 seconds after the polyvinyl alcohol-based resin film is pulled out from the crosslinking bath. The method for producing a polarizing film according to claim 5, wherein the electromagnetic wave irradiation step is performed within 5 seconds after the polyvinyl alcohol-based resin film is pulled out from the cross-linking bath. A manufacturing apparatus for a polarizing film, which manufactures a polarizing film from a polyvinyl alcohol-based resin film, and includes: a dyeing section for dyeing the polyvinyl alcohol-based resin film with a dichroic dye, and the polyvinyl alcohol-based resin film after the dyeing treatment. The cross-linked portion of the vinyl alcohol-based resin film cross-linked with a cross-linking agent and the polyvinyl alcohol-based resin film after the aforementioned cross-linking treatment are irradiated with infrared rays with wavelengths exceeding 2 μm and 4 μm. The proportion of the radiation energy is total radiation The electromagnetic wave irradiation part of the electromagnetic wave of 25% or more of energy, and the cleaning part which washes the said polyvinyl alcohol-type resin film after the said electromagnetic wave irradiation.

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