KR102535102B1 - Process for producing polarizing film and apparatus for producing polarizing film - Google Patents

Abstract

[PROBLEMS] It is an object of the present invention to provide a method for producing a polarizing film having high optical properties despite a reduced boron content, and an apparatus for producing the same.
[Solution] A method for producing a polarizing film having a boron content of 2.0 to 3.5% by weight from a polyvinyl alcohol-based resin film, comprising: a dyeing step of dyeing the polyvinyl alcohol-based resin film with a dichroic dye; and the dyeing step A crosslinking step of immersing the subsequent polyvinyl alcohol-based resin film in a crosslinking bath composed of an aqueous solution of a crosslinking agent containing a boron compound for crosslinking treatment, and the polyvinyl alcohol-based resin film after the crosslinking step has a thickness of more than 2 μm and 4 μm A polarizing film including an electromagnetic wave irradiation step of irradiating electromagnetic waves in which the ratio of infrared radiant energy of the following wavelengths is 25% or more of the total radiant energy, and a cleaning step of washing the polyvinyl alcohol-based resin film after irradiating the electromagnetic waves. manufacturing method.

Description

Manufacturing method and manufacturing apparatus of polarizing film {PROCESS FOR PRODUCING POLARIZING FILM AND APPARATUS FOR PRODUCING POLARIZING FILM}

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

A polarizing plate is widely used as a polarizing element or the like in image display devices such as liquid crystal display devices. As a polarizing plate, a structure in which a transparent resin film (protective film or the like) is bonded to one or both surfaces of a polarizing film using an adhesive or the like is common.

The polarizing film is immersed in a dyeing bath containing a dichroic dye such as iodine, followed by a treatment in which a raw film made of polyvinyl alcohol-based resin is immersed in a crosslinking bath containing a crosslinking agent such as boric acid, etc. In addition, it is manufactured by uniaxially stretching the film at any stage. Uniaxial stretching includes dry stretching performed in air and wet stretching performed in a liquid such as the dyeing bath and crosslinking bath described above.

A crosslinked polarizing film tends to shrink when heated and may not have sufficient durability. In Japanese Unexamined Patent Publication No. 2013-148806 (Patent Document 1), it is described that a polarizing film having excellent durability is provided by lowering the boron content of the polarizing film to 1 to 3.5% by weight.

Patent Document 1: Japanese Unexamined Patent Publication No. 2013-148806

However, in a polarizing film, when the boron content is reduced, a sufficient degree of crosslinking may not be obtained and the optical properties may decrease. An object of this invention is to provide the manufacturing method of the polarizing film which has high optical characteristics in spite of the boron content rate being reduced, and its manufacturing apparatus. Moreover, it aims at providing the novel polarizing film obtained by the manufacturing method of such a polarizing film.

This invention provides the manufacturing method, manufacturing apparatus, and polarizing film of the polarizing film shown below.

[1] A method for producing a polarizing film having a boron content of 2.0 to 3.5% by weight from a polyvinyl alcohol-based resin film,

A dyeing step of dyeing the polyvinyl alcohol-based resin film with a dichroic dye;

A crosslinking step of immersing the polyvinyl alcohol-based resin film after the dyeing step in a crosslinking bath composed of an aqueous solution of a crosslinking agent containing a boron compound for crosslinking treatment;

An electromagnetic wave irradiation step of irradiating the polyvinyl alcohol-based resin film after the crosslinking step with electromagnetic waves having an infrared radiant energy ratio of 25% or more of the total radiant energy having a wavelength of more than 2 μm and less than 4 μm;

A method for producing a polarizing film including a washing step of washing the polyvinyl alcohol-based resin film after irradiating the electromagnetic waves.

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

[3] [1] or [2] further comprising a liquid removal step of removing the aqueous solution adhering to the surface of the polyvinyl alcohol-based resin film after the crosslinking treatment and before irradiating the electromagnetic wave; The manufacturing method of the polarizing film described in.

[4] The method for producing a polarizing film according to any one of [1] to [3], wherein the electromagnetic wave irradiation step is performed within 5 seconds after the polyvinyl alcohol-based resin film is taken out of the crosslinking bath.

[5] In the crosslinking step, any one of [1] to [4], wherein the crosslinking bath is composed of an aqueous solution of a crosslinking agent containing 1.5 parts by weight or more and 3 parts by weight or less of the boron compound with respect to 100 parts by weight of water. The manufacturing method of the polarizing film described in.

[6] A manufacturing device for producing a polarizing film having a boron content of 2.0 to 3.5% by weight from a polyvinyl alcohol-based resin film,

A dyeing unit for dyeing the polyvinyl alcohol-based resin film with a dichroic dye;

a cross-linking portion for cross-linking treatment by immersing the polyvinyl alcohol-based resin film after the dyeing treatment in a cross-linking bath comprising an aqueous solution of a cross-linking agent containing a boron compound;

an electromagnetic wave irradiation unit for irradiating the polyvinyl alcohol-based resin film after the crosslinking treatment with electromagnetic waves having a ratio of infrared radiant energy having a wavelength of more than 2 μm to 4 μm or less of 25% or more of the total radiant energy;

A polarizing film manufacturing apparatus comprising a cleaning unit for cleaning the polyvinyl alcohol-based resin film after being irradiated with the electromagnetic waves.

[7] A polarizing film in which a polyvinyl alcohol-based resin film is dyed with a dichroic dye,

The boron content is 2.0 to 3.5% by weight,

The visibility correction single transmittance is 42.0% or more,

The visibility correction polarization degree is 99.990% or more,

The polarizing film whose ratio A 480 /A 600 between the absorbance A ₄₈₀ in the direction of the absorption axis at a wavelength of 480 nm and the absorbance A ₆₀₀ in the direction of the absorption _axis at a wavelength of ₆₀₀ nm is 0.75 or more and 1.00 or less.

ADVANTAGE OF THE INVENTION According to this invention, although the boron content rate is reduced, the manufacturing method of the polarizing film which has high optical characteristics and its manufacturing apparatus can be provided. Further, according to the present invention, a polarizing film having a low boron content and excellent optical properties can be provided.

1 is a cross-sectional view schematically showing an example of a method for manufacturing a polarizing film according to the present invention and a polarizing film manufacturing apparatus used therefor.
2 is a diagram showing a radiant energy spectrum for each type of electromagnetic wave irradiator.

<Method for producing polarizing film>

In the present invention, in the polarizing film, a dichroic dye (iodine or dichroic dye) is adsorbed and oriented on a polyvinyl alcohol-based resin film uniaxially stretched. The polyvinyl alcohol-based resin constituting the polyvinyl alcohol-based resin film is usually obtained by saponifying polyvinyl acetate-based resin. The saponification degree is usually about 85 mol% or more, preferably about 90 mol% or more, and more preferably about 99 mol% or more. The polyvinyl acetate-based resin may be, for example, a copolymer of vinyl acetate and another monomer copolymerizable therewith other than polyvinyl acetate which is a homopolymer of vinyl acetate. As another monomer which can be copolymerized, unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids etc. are mentioned, for example. The degree of polymerization of the polyvinyl alcohol-based resin is usually about 1000 to 10000, preferably about 1500 to 5000.

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

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

Accordingly, it is possible to obtain a thin polarizing film for which market demand is gradually increasing. The width of the raw film is not particularly limited, and may be, for example, about 400 to 6000 mm. The raw film is prepared, for example, as a roll (original roll) of a long unstretched polyvinyl alcohol-based resin film.

Further, the polyvinyl alcohol-based resin film used in the present invention may be laminated on a base film supporting the same, that is, the polyvinyl alcohol-based resin film is a base film and a polyvinyl alcohol-based resin film laminated thereon. It may be prepared as a laminated film of and. In this case, the polyvinyl alcohol-based resin film can be produced by, for example, coating a coating solution containing the polyvinyl alcohol-based resin on at least one surface of the base film and then drying the film.

As the base film, for example, a film made of a thermoplastic resin can be used. As a specific example, it is a film composed of a light-transmitting thermoplastic resin, preferably an optically transparent thermoplastic resin, such as chain polyolefin-based resins (polypropylene-based resins, etc.) and cyclic polyolefin-based resins (norbornene-based resins, etc.). polyolefin resin; cellulosic resins such as triacetyl cellulose and diacetyl cellulose; polyester-based resins such as polyethylene terephthalate and polybutylene terephthalate; polycarbonate-based resin; (meth)acrylic resins such as methyl methacrylate resins; polystyrene-based resin; polyvinyl chloride-based resins; Acrylonitrile·butadiene·styrene type resin; Acrylonitrile styrene type resin; polyvinyl acetate-based resin; polyvinylidene chloride-based resins; polyamide-based resin; polyacetal-based resins; Modified polyphenylene ether type resin; polysulfone-based resins; polyethersulfone-based resins; polyarylate-based resins; polyamideimide-based resins; It may be a polyimide-based resin or the like.

After the polarizing film is transported continuously along the film transport path of the polarizing film manufacturing apparatus while unwinding the long raw film described above from the raw film roll, and immersed in the treatment liquid (hereinafter also referred to as “treatment bath”) accommodated in the treatment tank, It can manufacture continuously as a long polarizing film by performing a drying process after performing the predetermined|prescribed processing process to draw|draw. Here, the treatment step is not limited to a method of immersing the film in a treatment bath as long as it is a method of treating the film by contacting the treatment liquid, and a method of treating the film by adhering the treatment liquid to the surface of the film by spraying, dripping, dropping, etc. even good When the treatment step is performed by immersing the film in a treatment bath, the number of treatment baths in which one treatment step is performed is not limited to one, and one treatment step may be completed by sequentially immersing the film in two or more treatment baths. .

Examples of the treatment liquid include a swelling liquid, a dyeing liquid, a crosslinking liquid, and a washing liquid. And, as the above treatment step, a swelling step in which a swelling liquid is brought into contact with a raw film to perform a swelling process, a dyeing process in which a dyeing solution is brought into contact with a film after swelling treatment and a dyeing process is performed, and a crosslinking liquid is contacted with a film after dyeing treatment crosslinking step of performing crosslinking treatment, and washing step of performing washing treatment by bringing a washing liquid into contact with the film after crosslinking treatment. In addition, between these series of treatment steps (namely, before and after any one or more treatment steps and/or during any one or more treatment steps), a wet or dry uniaxial stretching treatment is performed. Other processing steps may be added as needed.

In the present invention, after the crosslinking treatment and before the washing treatment, an electromagnetic wave irradiation step described below is performed to irradiate the film with electromagnetic waves. By performing the electromagnetic wave irradiation step, a polarizing film having excellent optical properties can be obtained even at a low boron content.

Hereinafter, an example of a method for manufacturing a polarizing film according to the present invention will be described in detail with reference to FIG. 1 . 1 is a cross-sectional view schematically showing an example of a method for manufacturing a polarizing film according to the present invention and a polarizing film manufacturing apparatus used therefor. The polarizing film manufacturing apparatus shown in FIG. 1 conveys the raw (unstretched) film 10 made of polyvinyl alcohol-based resin along the film conveying route while continuously unwinding it from the original roll 11, thereby conveying the film conveying route. A swelling bath (swelling liquid accommodated in the swelling tank) 13, a dyeing bath (dyeing liquid accommodated in the dyeing tank) 15, a first crosslinking bath (first crosslinking liquid accommodated in the crosslinking tank) 17a, The second crosslinking bath (second crosslinking liquid contained in the crosslinking tank) 17b and the washing bath (washing liquid contained in the washing tank) 19 are sequentially passed through, and finally through the drying furnace 21. The obtained polarizing film 23 can be conveyed to the next polarizing plate manufacturing process (process of bonding a protective film to one surface or both surfaces of the polarizing film 23) as it is, for example. Arrows in Fig. 1 indicate the transport direction of the film.

In the description of FIG. 1, "treatment tank" is a general term including a swelling tank, dyeing tank, crosslinking tank, and washing tank, and "treatment liquid" is a general term including swelling liquid, dyeing liquid, crosslinking liquid, and washing liquid, and " Treatment bath” is a general term including a swelling bath, a dyeing bath, a crosslinking bath, and a washing bath. The swelling bath, dyeing bath, crosslinking bath, and washing bath constitute the swelling portion, dyeing portion, crosslinking portion, and washing portion in the manufacturing apparatus of the present invention, respectively.

In addition to the treatment bath, the film conveyance route of the polarizing film manufacturing device includes guide rolls 30 to 48, 60, 61 capable of supporting the conveyed film or changing the film conveyance direction, and pressing/pressing the conveyed film. It can be constructed by arranging nip rolls 50 to 55 at appropriate positions, which can be pinched and can impart a driving force by rotation thereof to the film, or can further change the film transport direction. Guide rolls and nip rolls can be placed 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 taken out of the treatment bath (see Fig. 1). For example, the film can be immersed in each treatment bath by installing one or more guide rolls in each treatment bath and conveying the film along these guide rolls.

In the polarizing film manufacturing apparatus shown in FIG. 1 , nip rolls are disposed before and after each treatment bath (nip rolls 50 to 54), thereby providing nip rolls disposed before and after any one or more treatment baths. It is possible to perform stretching between rolls in which longitudinal uniaxial stretching is performed with a circumferential speed difference therebetween.

In the polarizing film production apparatus shown in FIG. 1 , an electromagnetic wave irradiation unit 71 is disposed on a conveyance path downstream of the second crosslinking bath 17b and upstream of the cleaning bath 19, and the electromagnetic wave irradiation step is performed. Hereinafter, each process is demonstrated.

(swelling process)

The swelling step is performed for purposes such as removal of foreign matter on the surface of the raw film 10, removal of plasticizers in the raw film 10, provision of easy dyeing properties, plasticization of the raw film 10, and the like. The processing conditions are determined within a range in which the object can be achieved and in a range in which problems such as extreme melting of the raw film 10 or loss of transparency are not caused.

Referring to FIG. 1, in the swelling step, the raw film 10 is continuously unwound from the raw roll 11, conveyed along the film conveyance path, and the raw film 10 is immersed in the swelling bath 13 for a predetermined time It can be carried out by doing and then withdrawing. In the example of FIG. 1, the raw film 10 is immersed in the swelling bath 13 after unwinding the raw film 10 by the guide rolls 60, 61 and the nip roll 50. It is conveyed along the constructed film conveyance route. In the swelling process, it is conveyed along the film conveyance path constructed by the guide rolls 30 to 32 and the nip rolls 51.

As the swelling liquid of the swelling bath 13, besides pure water, boric acid (Japanese Patent Laid-Open No. 10-153709), chloride (Japanese Patent Laid-Open No. 06-281816), inorganic acids, inorganic salts, water-soluble organic solvents, alcohols It is also possible to use an aqueous solution in which eg.

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 film 10 is preferably about 10 to 300 seconds, more preferably about 20 to 200 seconds. In the case where the raw film 10 is a polyvinyl alcohol-based resin film previously stretched in a substrate, 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 film 10 is preferably about 30 to 300 seconds, more preferably about 60 to 240 seconds.

In the swelling treatment, the problem that the raw film 10 swells in the width direction and wrinkles enter the film is likely to occur. As one means for conveying the film while removing these wrinkles, a roll having a widening function such as an expander roll, a spiral roll, or a crown roll is used for the guide rolls 30, 31 and/or 32, or Examples include the use of other widening devices such as cloth guiders, bend bars and tenter clips. Another means for suppressing the occurrence of wrinkles is to perform stretching treatment. For example, the uniaxial stretching process can be performed in the swelling bath 13 using the difference in circumferential speed between the nip rolls 50 and the nip rolls 51 .

In the swelling treatment, since the film swells and expands also in the conveying direction of the film, when the film is not actively stretched, in order to eliminate the sagging of the film in the conveying direction, for example, a nip disposed before and after the swelling bath 13 It is preferable to provide means such as controlling the speed of the rolls 50 and 51. In addition, for the purpose of stabilizing the transport of the film in the swelling bath 13, the water flow in the swelling bath 13 is controlled by an underwater shower, or an EPC device (Edge Position Control device: detects the end of the film to prevent meandering of the film) It is also useful to use a device to prevent it) or the like in combination.

In the example shown in FIG. 1 , the film taken out from the swelling bath 13 passes through the guide rolls 32, nip rolls 51, and guide rolls 33 in sequence and is introduced into the dyeing bath 15.

(dyeing process)

The dyeing step is performed for the purpose of adsorbing and orienting the dichroic dye to the polyvinyl alcohol-based resin film after the swelling treatment. Treatment conditions are determined within a range where the object can be achieved, and within a range where problems such as extreme dissolution of the film or loss of transparency do not occur. Referring to Figure 1, the dyeing process is conveyed along the film conveyance path built by the nip rolls 51, guide rolls 33 to 36 and nip rolls 52, and the film after swelling treatment is dyed bath 15 ) (treatment liquid contained in a dyeing tank) for a predetermined time, and then taken out. In order to enhance the dyeability of the dichroic dye, the film used in the dyeing step is preferably a film subjected to at least a certain degree of uniaxial stretching treatment, or instead of uniaxial stretching treatment before dyeing treatment or in addition to uniaxial stretching treatment before dyeing treatment , It is preferable to perform uniaxial stretching treatment at the time of dyeing treatment.

When iodine is used as the 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 in weight ratio can be used for the dyeing solution of the dyeing bath 15. Instead of potassium iodide, other iodides such as zinc iodide may be used, or potassium iodide and other iodides may be used in combination. In addition, compounds other than iodide, such as boric acid, zinc chloride, cobalt chloride, and the like may coexist. When boric acid is added, it is distinguished from the crosslinking treatment described later in that iodine is included, and if the aqueous solution contains about 0.003 parts by weight or more of iodine with respect to 100 parts by weight of water, it can be regarded as a dyeing bath 15. can The temperature of the dyeing bath 15 when the film is immersed 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 30 to 600 °C. seconds, preferably 60 to 300 seconds.

In the case of using a water-soluble dichroic dye as the dichroic dye, for example, an aqueous solution having a concentration of dichroic dye/water = about 0.001 to 0.1/100 in weight ratio can be used for the dyeing solution of the dyeing bath 15. The dyeing bath 15 may coexist with a dyeing aid or the like, and may contain, for example, an inorganic salt such as sodium sulfate or a surfactant. As for the dichroic dye, only 1 type may be used independently, and two or more types of dichroic dye may be used together. The temperature of the dyeing bath 15 at the time of immersing the film is, for example, about 20 to 80°C, preferably about 30 to 70°C, and the immersion time of the film is usually about 30 to 600 seconds, preferably about 60 to 300 seconds. am.

As described above, in the dyeing process, the film can be uniaxially stretched in the dyeing bath 15. Uniaxial stretching of the film can be performed by a method such as giving a difference in circumferential speed between the nip rolls 51 and 52 disposed before and after the dyeing bath 15.

Also in the dyeing treatment, in order to convey the polyvinyl alcohol-based resin film while removing wrinkles of the film similarly to the swelling treatment, the guide rolls 33, 34, 35 and/or 36 are provided with expander rolls, spiral rolls, crown rolls, and the like. A roll having a widening function may be used, or another widening device such as a cloth guider, a bend bar, or a tenter clip may be used. Another means for suppressing the occurrence of wrinkles is to perform the stretching treatment similarly to the swelling treatment.

In the example shown in FIG. 1 , the film taken out from the dyeing bath 15 passes through the guide rolls 36, nip rolls 52 and guide rolls 37 in sequence and is introduced into the crosslinking bath 17.

(Crosslinking process)

The crosslinking step is a treatment performed for purposes such as water resistance by crosslinking or color adjustment (preventing a film from becoming bluish). In the example shown in Fig. 1, two cross-linking baths are arranged as cross-linking baths for performing the cross-linking step, and the first cross-linking step for water resistance is performed in the first cross-linking bath 17a for the purpose of color adjustment. The second crosslinking step performed by the above process is performed in the second crosslinking bath 17b. Referring to FIG. 1, in the first crosslinking step, the nip roll 52, the guide rolls 37 to 40, and the nip roll 53a are transported along the film conveyance path, and the first crosslinking bath 17a It can be carried out by immersing the film after dyeing treatment in (the first crosslinking liquid contained in the crosslinking tank) for a predetermined time, and then pulling it out. In the second crosslinking step, the second crosslinking bath 17b (the second It can be implemented by immersing the film after the first crosslinking step in a crosslinking liquid) for a predetermined time and then pulling it out. Hereinafter, the cross-linking bath includes both the first cross-linking bath 17a and the second cross-linking bath 17b, and the cross-linking liquid includes both the first cross-linking liquid and the second cross-linking liquid.

As the crosslinking liquid, a solution in which a crosslinking agent is dissolved in a solvent can be used. As a crosslinking agent, boron compounds, such as boric acid and borax, glyoxal, glutaraldehyde, etc. are mentioned, for example. One type may be sufficient as these, and they may use two or more types together. As the solvent, for example, water can be used, but an organic solvent compatible with water may be further included. The concentration of the cross-linking agent in the cross-linking liquid, the temperature of the cross-linking bath, the immersion time of the film, and the number of cross-linking baths in which the film is immersed are not particularly limited, and a polarizing film having a boron content of 2.0 to 3.5% by weight is selected appropriately. You can get it. As the crosslinking liquid, for example, an aqueous solution containing 1 to 10 parts by weight of a boron compound such as boric acid can be used with respect to 100 parts by weight of water, and it is preferable to use an aqueous solution containing 1.5 to 3 parts by weight. 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 of iodide can be, for example, 1 to 30 parts by weight based on 100 parts by weight of water. As iodide, potassium iodide, zinc iodide, etc. are mentioned. In addition, compounds other than iodide, such as zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, sodium sulfate, etc. may coexist.

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 crosslinking liquid, in which the purpose of the crosslinking treatment is water resistance by crosslinking, it may be an aqueous solution having a concentration of boric acid/iodide/water = 1 to 10/1 to 30/100 in weight ratio. The temperature of the first crosslinking bath 17a when immersing the film is usually about 50 to 70°C, preferably about 53 to 65°C, and the immersion time of the film is usually about 10 to 600 seconds, preferably about 20 to 300°C. seconds, more preferably 20 to 200 seconds.

Further, when the dyeing treatment and the first crosslinking treatment are performed in this order on the polyvinyl alcohol-based resin film stretched in advance before the swelling treatment, the temperature of the first crosslinking bath 17a is usually about 50 to 85° C., preferably is 55 to 80 ° C.

In the second crosslinking liquid for the purpose of color adjustment, for example, when iodine is used as a dichroic dye, boric acid/iodide/water = 1 to 5/3 to 30/100 in concentration by weight ratio can be used. The temperature of the second crosslinking bath 17b when immersing the film 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 crosslinking treatment may be performed a plurality of times, and is usually performed 2 to 5 times. In this case, the composition and temperature of each crosslinking bath used may be the same or different. The crosslinking treatment for waterproofing by crosslinking and the crosslinking treatment for color adjustment may be performed in a plurality of steps, respectively.

The uniaxial stretching treatment may be performed in the first crosslinking bath 17a using the difference in circumferential speed between the nip rolls 52 and the nip rolls 53a. In addition, the uniaxial stretching treatment may be performed in the second crosslinking bath 17b using the difference in circumferential speed between the nip rolls 53a and the nip rolls 53b.

Also in the crosslinking treatment, in order to convey the polyvinyl alcohol-based resin film while removing wrinkles of the film similarly to the swelling treatment, guide rolls 38, 39, 40, 41, 42, 43 and/or 44 are provided with expander rolls and spirals. A roll having a widening function such as a roll or crown roll may be used, or another widening device such as a cloth guider, a bend bar, or a tenter clip may be used. Another means for suppressing the occurrence of wrinkles is to perform the stretching treatment similarly to the swelling treatment.

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

(cleaning process)

In the example shown in FIG. 1, the cleaning process after the crosslinking process is included. Washing treatment is performed for the purpose of removing chemicals such as excess boric acid and iodine adhering to the polyvinyl alcohol-based resin film. The washing process is performed by immersing the crosslinked polyvinyl alcohol-based resin film in the washing bath 19, for example. Further, the cleaning step may be performed by spraying the film with a cleaning liquid as a shower instead of immersing the film in the cleaning bath 19, or by using a combination of immersion in the cleaning bath 19 and spraying of the cleaning liquid.

FIG. 1 shows an example in which a polyvinyl alcohol-based resin film is immersed in a cleaning bath 19 to perform cleaning treatment. 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. What is necessary is just to select washing process conditions suitably so that the boron content rate of the finally obtained polarizing film may become 2.0-3.5 mass %.

In addition, in the washing process, for the purpose of conveying the polyvinyl alcohol-based resin film while removing wrinkles, the guide rolls 45, 46, 47 and/or 48 are provided with a widening function such as an expander roll, a spiral roll, and a crown roll. It is possible to use a roll having a width, or to use another widening device such as a cloth guider, a bend bar, or a tenter clip. Further, in the film cleaning treatment, a stretching treatment may be performed in order to suppress the occurrence of wrinkles.

(stretching process)

As described above, the raw film 10 is uniaxially stretched in a wet or dry manner between the series of treatment steps (that is, before and after any one or more treatment steps and/or during any one or more treatment steps). A specific method of the uniaxial stretching treatment is, for example, between two nip rolls constituting the film conveyance path (for example, two nip rolls disposed before and after the treatment bath) to perform longitudinal uniaxial stretching by adding a difference in circumferential speed between the rolls, Japanese patent It may be hot roll stretching, tenter stretching, or the like as described in Publication No. 2731813, preferably inter-roll stretching. The uniaxial stretching process can be performed over several times until the polarizing film 23 is obtained from the raw film 10 . As described above, the stretching treatment is also advantageous in suppressing wrinkles in the film.

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

(electromagnetic wave irradiation process)

In the apparatus shown in FIG. 1 , after the film is taken out from the second crosslinking step 17b and passed through the nip rolls 53b, and before being immersed in the washing bath 19, the film is irradiated with electromagnetic waves (electromagnetic waves irradiation process) is performed. In the device shown in FIG. 1 , electromagnetic waves are irradiated from the electromagnetic wave irradiation unit 71 . In the electromagnetic wave used in the electromagnetic wave irradiation process of the present invention, the ratio of infrared radiant energy having a wavelength of more than 2 μm to 4 μm or less is 25% or more of the total radiant energy, preferably 28% or more, and more preferably 35 more than % By irradiating the film with such electromagnetic waves, the optical properties of the resulting polarizing film can be improved. In addition, with respect to electromagnetic waves used in the present invention, the upper limit of the ratio of infrared radiant energy having a wavelength of more than 2 μm and less than or equal to 4 μm is not particularly limited, but is, for example, 80% or less. In general, electromagnetic waves with a wavelength of 0.75 μm to 1000 μm are called infrared rays.

In the electromagnetic wave irradiation process, the mechanism by which the optical properties of the polarizing film can be improved by irradiating electromagnetic waves in which the ratio of infrared radiant energy of a wavelength of more than 2 μm to 4 μm or less is 25% or more of the total radiant energy is not clear, but 2 It is estimated that the optical properties of the polarizing film can be improved by accelerating the immobilization of dichroic dyes such as iodine in the crosslinked film by molecular motion in the film excited by infrared rays with a wavelength of more than 4 μm and not more than 4 μm. .

2 shows a spectrum of radiant energy for each type of electromagnetic wave irradiator. In addition, Table 1 shows the ratio of the radiant energy of electromagnetic waves in each wavelength region (expressed as a range of wavelength x μm) to the total radiant energy for each type of electromagnetic wave irradiator. The electromagnetic wave irradiator shown in FIG. 2 and Table 1 is a halogen heater (heat source temperature: 2600° C.), a short-wavelength infrared heater (heat source temperature: 2200° C.), a high-speed response mid-wavelength infrared heater (heat source temperature: 1600° C.), a carbon heater (heat source temperature: 1200° C.) ), a carbon heater (heat source temperature: 950°C), and a mid-wavelength infrared heater (heat source temperature: 900°C).

As shown in Table 1, short-wavelength infrared heater (heat source temperature 2200 ° C.), high-speed response mid-wavelength infrared heater (heat source temperature 1600 ° C.), carbon heater (heat source temperature 1200 ° C.), carbon heater (heat source temperature 950 ° C.), medium-wavelength The infrared heater (heat source temperature: 900° C.) is suitably used as an electromagnetic wave irradiator constituting the electromagnetic wave irradiation unit 71 because the ratio of infrared radiant energy with a wavelength of more than 2 μm to 4 μm or less is 25% or more of the total radiant energy. can The electromagnetic wave irradiation unit 71 may be constituted by a single electromagnetic wave irradiator, or may be constituted by a plurality of electromagnetic wave irradiators. When it is composed of several electromagnetic wave irradiators, 25% or more of the total radiant energy of the electromagnetic waves emitted from the multiple electromagnetic wave irradiators is 25% or more Choose as many microwave irradiators as possible. In Fig. 1, the electromagnetic wave irradiation unit 71 is configured so that only one side of the film is irradiated with electromagnetic waves, but a plurality of electromagnetic wave irradiators may be arranged so that electromagnetic waves are irradiated from both sides of the film. The electromagnetic wave irradiation unit 71 is preferably configured so that electromagnetic waves are irradiated to the entire width direction of the polyvinyl alcohol-based resin film to be irradiated.

In the electromagnetic wave irradiation step, electromagnetic waves are preferably irradiated from above in a direction perpendicular to the film surface. Further, the distance between the electromagnetic wave spinneret of the electromagnetic wave irradiator in the electromagnetic wave irradiator 71 and the film is preferably 2 to 40 cm, and more preferably 5 to 20 cm. However, it is preferable to select this distance appropriately in consideration of the amount of radiant energy of electromagnetic waves emitted from the electromagnetic wave irradiator, the temperature of the surface of the film, and the like. The temperature of the surface of the film during electromagnetic wave irradiation is preferably maintained at 30 to 90°C, and more preferably at 40 to 80°C.

In the electromagnetic wave irradiation step, the irradiation heat amount of electromagnetic waves per unit volume of the film can be 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. From the viewpoint of suppressing deterioration of the film due to temperature rise, the irradiation heat amount of electromagnetic waves per unit volume of the film is preferably 10 kJ/cm 3 or less, more preferably 5000 J/cm 3 or less, and 3000 J/cm 3 or less. more preferable Normally, the moisture content of the film decreases in proportion to the amount of heat irradiated with electromagnetic waves, but the purpose of the electromagnetic wave irradiation step of the present invention is not to reduce the amount of moisture in the film, and the amount of heat irradiation can be appropriately selected. Select appropriately within the range.

In this invention, the optical characteristic of the polarizing film obtained can be improved by performing an electromagnetic wave irradiation process before a washing process. The electromagnetic wave irradiation step may be performed on the film after being immersed in at least one cross-linking bath, and as shown in Fig. 1, it is not limited to being performed on the film after being immersed in all of the cross-linking baths. That is, in the example shown in Fig. 1, the electromagnetic wave irradiation step may be performed on the film after being immersed in the first crosslinking bath and before being immersed in the second crosslinking bath, or the film after being immersed in the second crosslinking bath may be subjected to electromagnetic wave irradiation. You may perform an irradiation process. However, since crosslinking of the boric acid introduced into the film can be promoted by immersing in the crosslinking bath in the electromagnetic wave irradiation step, performing the electromagnetic wave irradiation step on the film after all the immersion in the crosslinking bath is more effective in reducing the crosslinking of boric acid. It is preferable because it can advance effectively.

The electromagnetic wave irradiation is preferably performed within 10 seconds, and more preferably within 5 seconds after the film is taken out of the crosslinking bath. The shorter the time from being taken out of the crosslinking bath to the electromagnetic wave irradiation, the more the optical properties of the polarizing film by electromagnetic wave irradiation can be improved. In the electromagnetic wave irradiation step, it is preferable that the number of water molecules adhering to the surface of the film is small. This is because when water molecules exist on the surface of the film, the water molecules on the surface of the film absorb infrared rays, thereby reducing the excitation effect of molecular motion in the film by electromagnetic wave irradiation. Since the crosslinking liquid adheres to the surface of the film immediately after being taken out of the crosslinking bath, it is preferable to provide liquid removal means to remove it before the electromagnetic wave irradiation step. In FIG. 1 , the nip rolls 53b also function as liquid removal means for removing the crosslinking liquid adhering to the surface of the film. As liquid removal means, you may use, besides a nip roll, a means for blowing air into a film to remove liquid, a scraper for contacting the film to perform liquid removal, or the like.

When the film processing speed is high from the viewpoint of economy, specifically, when the processing speed is set to a high processing speed of 10 to 100 m/min, the electromagnetic wave irradiation time is short, and the irradiation heat amount may be insufficient. As a response to this, by installing several electromagnetic wave irradiators in parallel, a sufficient amount of irradiation heat can be obtained.

(drying process)

It is preferable to perform the process of drying a polyvinyl alcohol-type resin film after a washing|cleaning process. Drying of the film is not particularly limited, but may be performed using a drying furnace 21 as in the example shown in FIG. 1 . The drying furnace 21 may include, for example, a hot air dryer. 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 a polyvinyl alcohol-type resin film can also be performed using a far-infrared heater. The thickness of the polarizing film 23 obtained as described above is, for example, about 5 to 30 μm.

The obtained polarizing film may be rolled up sequentially on a winding roll to form a roll, or may be directly used in a polarizing plate manufacturing step (a step of laminating a protective film or the like on one or both surfaces of a polarizing film) without being wound up.

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

Processing other than the above processing may be added. Examples of treatments that can be added are immersion treatment in an iodide aqueous solution not containing boric acid (complementary color treatment), which is performed after the crosslinking step, and immersion treatment in an aqueous solution containing zinc chloride or the like without boric acid (zinc processing) included.

<Polarizing film>

By producing a polarizing film by the above method,

i) the boron content is 2.0 to 3.5% by weight;

ii) the visibility correction single transmittance (Ty) is 42.0% or more;

iii) a visibility correction polarization degree (Py) of 99.990% or more;

iv) A polarizing film in which the ratio A ₄₈₀ / A 600 of the absorbance A ₄₈₀ in the direction of the absorption axis of the polarizing film at a wavelength of 480 nm and the absorbance A ₆₀₀ in the direction of the absorption axis of the polarizing film at a wavelength of ₆₀₀ nm is 0.75 or more and 1.00 or less You can get it.

When the boron content rate of a polarizing film is the same as said i), shrinkage force becomes what was suppressed. As for the boron content rate of a polarizing film, it is more preferable that it is 2.0-3.0 weight%. The shrinkage force of the polarizing film is preferably 3.8 N/2 mm or less, more preferably 3.5 N/2 mm or less. The boron content and shrinkage force of the polarizing film here are measured according to the description in the section of Examples described later.

In general, high optical properties can be obtained by setting the boron content of the polarizing film as high as, for example, 3.8% by weight or more. However, it is difficult to obtain excellent optical properties while reducing the boron content of the polarizing film as in i) above. In the production method of the present invention, a polarizing film having excellent optical properties that satisfies ii) and iii) while satisfying i) can be obtained by having an electromagnetic wave irradiation step. The visibility-corrected single transmittance (Ty) and the visibility-corrected polarization degree (Py) of the polarizing film here are measured according to the description in the section of Examples described later.

In addition, in the manufacturing method of the present invention, as the electromagnetic wave used in the electromagnetic wave irradiation step, the ratio of infrared radiant energy having a wavelength of more than 2 μm and less than 4 μm is 25% or more of the total radiant energy, so that the characteristics of iv) above It is possible to obtain a polarizing film having an excellent color close to neutral gray that satisfies . If A ₄₈₀ /A ₆₀₀ is less than 0.75, bluish color is strong, and if A ₄₈₀ /A ₆₀₀ exceeds 1.00, red color is strong. In suppressing redness, it is more preferable that A ₄₈₀ /A ₆₀₀ is 0.90 or less. That is, according to the manufacturing method of the present invention, a polarizing film having excellent optical properties can be obtained by reducing the boron content of the polarizing film as in i) to suppress shrinkage while simultaneously satisfying the properties of ii) to iv).

<Polarizer>

A polarizing plate can be obtained by bonding a protective film to at least one surface of the polarizing film manufactured as described above via an adhesive. Examples of protective films include films made of acetyl cellulose-based resins such as triacetyl cellulose and diacetyl cellulose; films made of polyester resins such as polyethylene terephthalate, polyethylene naphthalate and polybutylene terephthalate; polycarbonate-based resin films, cycloolefin-based resin films; acrylic resin film; A film made of a chain olefin resin of a polypropylene resin is exemplified.

In order to improve the adhesion between the polarizing film and the protective film, surface treatment such as corona treatment, flame treatment, plasma treatment, ultraviolet irradiation, primer coating treatment, saponification treatment is performed on the bonding surface of the polarizing film and/or the protective film, also good Examples of the adhesive used for bonding the polarizing film and the protective film include an active energy ray curable adhesive such as an ultraviolet curable adhesive, an aqueous solution of a polyvinyl alcohol-based resin, an aqueous solution in which a crosslinking agent is mixed therein, and a water-based adhesive such as a urethane emulsion adhesive. can be heard The UV-curable adhesive may be a mixture of an acrylic compound and a radical photopolymerization initiator, or a mixture of an epoxy compound and a photocationic polymerization initiator. 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 may be used together as an initiator.

[Example]

Hereinafter, the present invention will be described more specifically by showing examples, but the present invention is not limited by these examples.

<Example 1>

The polarizing film of Example 1 was manufactured from the polyvinyl alcohol-type resin film using the manufacturing apparatus shown in FIG. Specifically, a long polyvinyl alcohol (PVA) raw film with a thickness of 60 μm [trade name “Kurare Vinylon VF-PE#6000” manufactured by Kuraray Co., Ltd., average degree of polymerization 2400, degree of saponification of 99.9 mol% or more] from a roll It was conveyed continuously while unwinding, and was immersed in a swelling bath made of pure water at 30°C for a residence time of 79 seconds (swelling step). Thereafter, the film taken out from the swelling bath was immersed in a dyeing bath at 30°C containing iodine in a ratio of potassium iodide/boric acid/water to 1/0.3/100 (weight ratio) at a residence time of 123 seconds (dyeing step). Subsequently, the film taken out from the dyeing bath was immersed in a first crosslinking bath at 53°C in which potassium iodide/boric acid/water was 11/2.0/100 (weight ratio) at a residence time of 44 seconds, and then potassium iodide/boric acid/water It was immersed in the 40 degreeC 2nd crosslinking bath of 11/2.0/100 (weight ratio) with a residence time of 6 seconds (crosslinking process). In the dyeing process and the crosslinking process, longitudinal uniaxial stretching was performed by inter-roll stretching in a bath. The total stretching ratio based on the raw film was 5.65 times.

Next, with respect to the film taken out from the second crosslinking bath 17b and passed through the nip roll 53b, an electromagnetic wave irradiator (mid-wave infrared heater (MW heater), product name: Golden 8 Medium-wave twin tube emitter, Heraeus) Manufacturing, using a heat source temperature of 900 ° C and a maximum energy density of 60 kW / ㎡), place an electromagnetic wave spinneret at a location 5 cm away from the surface of the film, and irradiate electromagnetic waves at 50% of the maximum irradiation output of the electromagnetic wave irradiator did. The irradiation heat amount of electromagnetic waves per unit volume of the film was 490 J/cm 3 . In addition, the irradiation heat amount of electromagnetic waves per unit volume of the film was calculated by the following formula.

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

The output (%) represents the ratio (%) of the actually irradiated output to the maximum irradiation output of the electromagnetic wave irradiator.

After being taken out of the second cross-linking bath 17b, the time taken for the film to be conveyed and reach the irradiation position of the electromagnetic wave irradiator to be irradiated with electromagnetic waves was 5 seconds.

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

<Examples 2 to 6, Comparative Examples 3 and 4>

In the electromagnetic wave irradiation step, the type of electromagnetic wave irradiator, the output (%), the amount of radiation heat of electromagnetic waves per unit volume of the film, and the number of parts by weight of boric acid with respect to 100 parts by weight of water in the first crosslinking bath and the second crosslinking bath are shown in Table 2 and A polarizing film was obtained in the same way as in Example 1 except for the same points. The thickness of all the obtained polarizing films was 23 micrometers. As an electromagnetic wave irradiator, a halogen heater (product name: direct-type halogen heater lamp QIR, manufactured by Ushio Lighting Co., Ltd., heat source temperature 2600 ° C, maximum energy density 300 kW / ㎡), short-wavelength infrared heater (SW heater) (product name: Golden 8 Short -wave twin tube emitter, manufactured by Heraeus, heat source temperature 2200℃, maximum energy density 200 kW/㎡), high-speed response mid-wave infrared heater (FRMW heater) (product name: Golden 8 Medium-wave fast response twin tubu emitter, Heraeus) Manufacturing, heat source temperature 1600℃, maximum energy density 150 kW/㎡), medium-wave infrared heater (MW heater) (product name: Golden 8 Medium-wave twin tube emitter, manufactured by Heraeus, heat source temperature 900℃, maximum energy density 60 kW /㎡) was used.

<Comparative Examples 1, 2, 5>

A polarizing film was prepared in the same manner as in Example 1 except that the electromagnetic wave irradiation step was not performed and the number of parts by weight of boric acid with respect to 100 parts by weight of water in the first crosslinking bath and the second crosslinking bath was changed as shown in Table 2. got it The thickness of all the obtained polarizing films was 23 micrometers.

[Evaluation of polarizing film]

(a) measurement of single transmittance and degree of polarization

For the polarizing films obtained in each Example and each Comparative Example, MD transmittance and TD transmittance in the wavelength range of 380 to 780 nm were measured using a spectrophotometer ["V7100" manufactured by Nippon Bunko Co., Ltd.] having an integrating sphere. Measured, the following formula:

Single transmittance (%)=(MD+TD)/2

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

Based on this, the single transmittance and polarization degree at each wavelength were calculated.

The "MD transmittance" is the transmittance when the direction of polarized light emitted from the Glen Thomson prism and the transmittance axis of the polarizing film sample are made parallel, and is represented by "MD" in the above formula. In addition, the "TD transmittance" is the transmittance when the direction of the polarized light emitted from the Glen Thomson prism and the transmission axis of the polarizing film sample are orthogonal, and is represented by "TD" in the above formula. Concerning the obtained single transmittance and polarization degree, visibility correction is performed with a two-degree field of view (C light source) of JIS Z 8701: 1999 "Color display method-XYZ color system and X ₁₀ Y ₁₀ Z ₁₀ color system", and the visibility corrected single transmittance (Ty ) and visibility correction polarization (Py) were obtained. Table 2 shows the calculation results of the visibility-corrected single transmittance (Ty) and the visibility-corrected polarization degree (Py).

(b) Measurement of absorbance of polarizing film

Measurement was performed using a spectrophotometer ["V7100" manufactured by Nippon Bunko Co., Ltd.] having an integrating sphere. Specifically, using the TD transmittances TD ₄₈₀ and TD ₆₀₀ at a wavelength of 480 nm and a wavelength of 600 nm, the following formula:

A ₄₈₀ = - log ₁₀ (TD ₄₈₀ /100)

A ₆₀₀ = - log ₁₀ (TD ₆₀₀ /100)

Based on this, absorbance A ₄₈₀ at a wavelength of 480 nm and absorbance A ₆₀₀ at a wavelength of 600 nm were calculated. Table 2 shows the absorbance A ₄₈₀ , the absorbance A ₆₀₀ , and the calculated value of the ratio A ₄₈₀ /A ₆₀₀ calculated based on these values.

(c) MD contraction force

From the obtained polarizing film, a measurement sample having a width of 2 mm and a length of 10 mm with the long side in the direction of the absorption axis (MD, stretching direction) was cut out. The long side direction that occurs when this sample is set in a thermomechanical analyzer (TMA) "EXSTAR-6000" manufactured by SI Nanotechnology Co., Ltd., and maintained at 80 ° C. for 4 hours while maintaining constant dimensions. (Absorption axis direction, MD) shrinkage force (MD shrinkage force) was measured. Table 2 shows the measured contractile force values.

(d) boron content of polarizing film

After adding 0.2 g of the polarizing film to 170 ml of pure water and completely dissolving at 95°C, 30 g of a mannitol aqueous solution (12.5% by weight) was added to obtain a sample solution for measurement. Sodium hydroxide aqueous solution (1 mol/l) was added dropwise until the sample solution for measurement reached the neutralization point, and the boron content (% by weight) in the polyvinyl alcohol-based resin film was calculated from the dropwise amount by the following formula:

Boron content (% by weight) = 1.08 × sodium hydroxide aqueous solution dropping amount (ml) / weight (g) of polarizing film

was calculated from Table 2 shows the measured boron content values.

As shown in Table 2, the polarizing films of Examples 1 to 6,

i) the boron content is 2.0 to 3.5% by weight;

ii) the visibility correction single transmittance Ty is 42.0% or more;

iii) the visibility correction polarization Py is 99.990% or more;

iv) The ratio A 480/A 600 of the absorbance A ₄₈₀ in the direction of the absorption axis of the polarizing film at a wavelength of 480 nm and the absorbance A ₆₀₀ in the direction of the absorption axis of the polarizing film at a wavelength of ₆₀₀ nm was _0.75 or more and 1 or less. In addition, the contraction force was suppressed by satisfying the above i), and there was no problem in color by satisfying the above iv). The polarizing film of Comparative Example 1 did not undergo an electromagnetic wave irradiation process and had a low value of visibility correction polarization degree (Py).

Since the polarizing film of Comparative Example 2 did not satisfy the above condition i), the shrinkage force was large. In the polarizing film of Comparative Example 3, the value of A ₄₈₀ /A ₆₀₀ exceeded 1, and the reddish color was strong. In Comparative Examples 4 and 5, the value of the visibility correction polarization degree (Py) was low because the boron content was not sufficient.

10: original film made of polyvinyl alcohol-based resin, 11: original roll, 13: swelling bath, 15: dyeing bath, 17a: first crosslinking bath, 17b: second crosslinking bath, 19: washing bath, 21: drying furnace, 23: polarizing film, 30 to 48, 60, 61: guide roll, 50 to 52, 53a, 53b, 54, 55: nip roll, 71: electromagnetic wave irradiation unit.

Claims (7)

A method for producing a polarizing film having a boron content of 2.0 to 3.5% by weight from a polyvinyl alcohol-based resin film,
A dyeing step of dyeing the polyvinyl alcohol-based resin film with a dichroic dye;
A crosslinking step of immersing the polyvinyl alcohol-based resin film after the dyeing step in a crosslinking bath composed of an aqueous solution of a crosslinking agent containing a boron compound for crosslinking treatment;
An electromagnetic wave irradiation step of irradiating the polyvinyl alcohol-based resin film after the crosslinking step with electromagnetic waves having an infrared radiant energy ratio of 25% or more of the total radiant energy having a wavelength of more than 2 μm and less than 4 μm;
A cleaning step of cleaning the polyvinyl alcohol-based resin film after irradiating the electromagnetic waves;
The method of manufacturing a polarizing film further comprising a liquid removal step of removing the aqueous solution adhering to the surface of the polyvinyl alcohol-based resin film after the crosslinking treatment and before irradiating the electromagnetic wave. The method of manufacturing a polarizing film according to claim 1, wherein in the electromagnetic wave irradiation step, the irradiation heat amount of the electromagnetic wave is 100 J/cm 3 or more and 50 kJ/cm 3 or less per unit volume of the polyvinyl alcohol-based resin film. The method for producing a polarizing film according to claim 1 or 2, wherein the electromagnetic wave irradiation step is performed within 5 seconds after the polyvinyl alcohol-based resin film is taken out of the crosslinking bath. The polarizing film according to claim 1 or 2, wherein in the crosslinking step, the crosslinking bath is made of an aqueous solution of a crosslinking agent containing 1.5 parts by weight or more and 3 parts by weight or less of the boron compound with respect to 100 parts by weight of water. method. A manufacturing apparatus for producing a polarizing film having a boron content of 2.0 to 3.5% by weight from a polyvinyl alcohol-based resin film,
A dyeing unit for dyeing the polyvinyl alcohol-based resin film with a dichroic dye;
a cross-linking portion for cross-linking treatment by immersing the polyvinyl alcohol-based resin film after the dyeing treatment in a cross-linking bath comprising an aqueous solution of a cross-linking agent containing a boron compound;
an electromagnetic wave irradiation unit for irradiating the polyvinyl alcohol-based resin film after the crosslinking treatment with electromagnetic waves having a ratio of infrared radiant energy having a wavelength of more than 2 μm to 4 μm or less of 25% or more of the total radiant energy;
A cleaning unit for cleaning the polyvinyl alcohol-based resin film after irradiating the electromagnetic waves,
The manufacturing apparatus of a polarizing film further comprising a removing means for removing the aqueous solution adhering to the surface of the polyvinyl alcohol-based resin film after the crosslinking treatment and before irradiating the electromagnetic wave. A polarizing film in which a polyvinyl alcohol-based resin film is dyed with a dichroic dye,
The boron content is 2.0 to 3.5% by weight,
The visibility correction single transmittance is 42.0% or more,
The visibility correction polarization degree is 99.990% or more,
A polarizing film in which the ratio A 480 _/ A 600 of the absorbance A ₄₈₀ in the direction of the absorption axis at a wavelength of 480 nm and the absorbance A ₆₀₀ of the polarizing film in the direction of the absorption axis at a wavelength of ₆₀₀ nm is 0.75 or more and 1.00 or less. delete

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