JP2018032025A - Method and device for manufacturing polarizing film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a polarizing film having high optical characteristics even though a boron content rate is reduced, and a device for manufacturing the same.SOLUTION: The method for manufacturing, from a polyvinyl alcohol resin film, a polarizing film having a boron content rate of 2.0-3.5 wt.% comprises: a dyeing step for dyeing the polyvinyl alcohol resin film with a dichroic dye; a crosslinking step for immersing the polyvinyl alcohol resin film after the dyeing step in a crosslinking bath including an aqueous solution of a crosslinking agent containing a boron compound and performing a crosslinking treatment on the polyvinyl alcohol resin film; an electromagnetic wave irradiation step for irradiating the polyvinyl alcohol resin film after the crosslinking step, with electromagnetic waves in which infrared rays having wavelengths of more than 2 μm and 4 μm or less have a radiation energy percentage of 25% or more of total radiation energy; and a cleaning step for cleaning the polyvinyl alcohol resin film after the irradiation with the electromagnetic waves.SELECTED DRAWING: Figure 1

Description

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

  A polarizing plate is widely used as a polarizing element in an image display device such as a liquid crystal display device. As a polarizing plate, the thing of the structure which bonded the transparent resin film (protective film etc.) on the single side | surface or both surfaces of the polarizing film using the adhesive agent etc. is common.

  The polarizing film is mainly immersed in a dye bath containing a dichroic dye such as iodine, and then immersed in a cross-linking bath containing a cross-linking agent such as boric acid, with respect to the raw film made of polyvinyl alcohol resin. The film is produced by uniaxially stretching the film at any stage. Uniaxial stretching includes dry stretching in which stretching is performed in the air and wet stretching in which stretching is performed in a liquid such as the dyeing bath and the crosslinking bath.

  The cross-linked polarizing film tends to shrink when heated and may not have sufficient durability. Japanese Patent Application Laid-Open No. 2013-148806 (Patent Document 1) describes that a polarizing film has a low boron content of 1 to 3.5% by weight and provides a polarizing film excellent in durability.

JP 2013-148806 A

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

  The present invention provides the following polarizing film manufacturing method, manufacturing apparatus, and polarizing film.

[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 made of an aqueous solution of a crosslinking agent containing a boron compound;
An electromagnetic wave irradiation step of irradiating the polyvinyl alcohol-based resin film after the cross-linking step with an electromagnetic wave having a ratio of infrared radiation energy of a wavelength of more than 2 μm to 4 μm or less being 25% or more of the total radiation energy;
A cleaning step of cleaning the polyvinyl alcohol-based resin film after being irradiated with the electromagnetic wave.

[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 resin film. .

  [3] The method according to [1] or [2], further including 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 of description.

  [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 drawn from the crosslinking bath.

  [5] In the crosslinking step, the crosslinking bath comprises 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 of any one of Claims 1.

[6] A production 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 portion for dyeing the polyvinyl alcohol-based resin film with a dichroic dye;
A cross-linked portion that undergoes a cross-linking treatment by immersing the polyvinyl alcohol-based resin film after the dyeing treatment in a cross-linking bath made of 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 an electromagnetic wave in which the ratio of the infrared radiation energy having a wavelength of more than 2 μm to 4 μm or less is 25% or more of the total radiation energy;
And a cleaning unit for cleaning the polyvinyl alcohol-based resin film after being irradiated with the electromagnetic wave.

[7] A polarizing film dyeing a polyvinyl alcohol resin film with a dichroic dye,
The boron content is 2.0 to 3.5% by weight,
Visibility corrected single transmittance is 42.0% or more,
Visibility correction polarization degree is 99.990% or more,
The ratio _A 480 _{/ A 600} absorption axis direction of the absorbance _{A 600} in the absorption axis direction of the absorbance _{A 480} and wavelength 600nm at a wavelength of 480nm is 0.75 to 1.00, a polarizing film.

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

It is sectional drawing which shows typically an example of the manufacturing method of the polarizing film which concerns on this invention, and a polarizing film manufacturing apparatus used for it. It is a figure which shows the radiant energy spectrum for every kind of electromagnetic wave irradiation device.

<Production method of polarizing film>
In the present invention, the polarizing film is one in which a dichroic dye (iodine or dichroic dye) is adsorbed and oriented on a uniaxially stretched polyvinyl alcohol 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 resin can be, for example, a copolymer of vinyl acetate, which is a homopolymer of vinyl acetate, or a copolymer of vinyl acetate and another monomer copolymerizable therewith. 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 1000 to 10000, preferably about 1500 to 5000.

  These polyvinyl alcohol resins may be modified. For example, polyvinyl formal modified with aldehydes, polyvinyl acetal, polyvinyl butyral, and the like may be used.

In the present invention, an unstretched polyvinyl alcohol-based resin film (raw fabric) 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, and even more preferably 30 μm or less is used as a starting material for manufacturing a polarizing film. Film).
As a result, it is possible to obtain a thin polarizing film whose market demand is increasing. The width of the raw film is not particularly limited and can be, for example, about 400 to 6000 mm. The original fabric film is prepared, for example, as a roll (raw fabric roll) of a long unstretched polyvinyl alcohol resin film.

  In addition, the polyvinyl alcohol resin film used in the present invention may be laminated on a base film that supports the film, that is, the polyvinyl alcohol resin film is laminated on the base film. It may be prepared as a laminated film with a 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 surface of the base film and then drying it.

  As the base film, for example, a film made of a thermoplastic resin can be used. Specific examples include a film made of a light-transmitting thermoplastic resin, preferably an optically transparent thermoplastic resin, such as a chain polyolefin resin (polypropylene resin, etc.), a cyclic polyolefin resin, and the like. Polyolefin resins such as (norbornene resins); cellulose resins such as triacetyl cellulose and diacetyl cellulose; polyester resins such as polyethylene terephthalate and polybutylene terephthalate; polycarbonate resins; methyl methacrylate resins (Meth) acrylic resins; polystyrene resins; polyvinyl chloride resins; acrylonitrile / butadiene / styrene resins; acrylonitrile / styrene resins; polyvinyl acetate resins; polyvinylidene chloride resins; polyamide resins; It may be a polyimide resin or the like; Li acetal resins; modified polyphenylene ether resin; polysulfone resins; poly (ether sulfone) resins; polyarylate resin; polyamide-imide resin.

  The polarizing film, while unwinding the above-described long original film from the original roll, is continuously conveyed along the film conveying path of the polarizing film manufacturing apparatus, and the processing liquid (hereinafter, It can be continuously produced as a long polarizing film by carrying out a drying step after carrying out a predetermined treatment step that is drawn after being immersed in a “treatment bath”. The treatment process is not limited to the method of immersing the film in the treatment bath as long as the treatment solution is brought into contact with the film, and the treatment solution is adhered to the film surface by spraying, flowing down, dropping, or the like. And a method of processing the film. When the treatment step is performed by a method of immersing the film in the treatment bath, the treatment bath for performing one treatment step is not limited to one, and the film is sequentially immersed in two or more treatment baths. One processing step may be completed.

  Examples of the treatment liquid include swelling liquid, dyeing liquid, crosslinking liquid, and cleaning liquid. And as said process process, the swelling process which makes a swelling liquid contact a raw fabric film, and the dyeing process which makes a dyeing process contact the dyeing | staining liquid on the film after a swelling process, and after a dyeing process Examples include a crosslinking step in which a crosslinking solution is brought into contact with the film to perform a crosslinking treatment and a washing step in which a washing solution is brought into contact with the film after the crosslinking treatment to perform a washing treatment. In addition, a uniaxial stretching process is performed in a wet or dry manner between these series of processing steps (that is, 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 necessary.

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

  Hereinafter, an example of the manufacturing method of the polarizing film which concerns on this invention is demonstrated in detail, referring FIG. Drawing 1 is a sectional view showing typically an example of the manufacturing method of the polarizing film concerning the present invention, and the polarizing film manufacturing device used for it. The polarizing film manufacturing apparatus shown in FIG. 1 transports a raw fabric (unstretched) film 10 made of polyvinyl alcohol resin along a film transport path while continuously unwinding from a raw fabric roll 11. A swelling bath (swelling liquid accommodated in the swelling tank) 13 provided on the transport path, a dyeing bath (dyeing liquid accommodated in the dyeing tank) 15, a first cross-linking bath (first accommodated in the cross-linking tank). Cross-linking liquid) 17a, second cross-linking bath (second cross-linking liquid accommodated in the cross-linking tank) 17b, and cleaning bath (cleaning liquid accommodated in the cleaning tank) 19 are sequentially passed, and finally passed through the drying furnace 21. It is configured to let you. The obtained polarizing film 23 can be conveyed, for example, to the next polarizing plate production step (step of bonding a protective film on one or both sides of the polarizing film 23) as it is. The arrow in FIG. 1 has shown the conveyance direction of the film.

  In the description of FIG. 1, “treatment tank” is a generic name including a swelling tank, a dyeing tank, a crosslinking tank, and a washing tank, and “treatment liquid” is a generic name that includes a swelling liquid, a staining liquid, a crosslinking liquid, and a washing liquid. The “treatment bath” is a generic term including a swelling bath, a dyeing bath, a crosslinking bath and a washing bath. The swelling bath, the dyeing bath, the crosslinking bath, and the washing bath respectively constitute a swelling part, a dyeing part, a crosslinking part, and a washing part in the production apparatus of the present invention.

  The film transport path of the polarizing film manufacturing apparatus includes guide rolls 30 to 48, 60, 61 that can support the film to be transported or can further change the film transport direction in addition to the processing bath, and the film to be transported. Can be constructed by placing nip rolls 50 to 55 at appropriate positions, which can press and hold the film and apply a driving force by rotation thereof to the film, or can further change the film conveyance direction. Guide rolls and nip rolls can be arranged before and after each treatment bath or in the treatment bath, whereby the film can be introduced and immersed in the treatment bath and drawn out from the treatment bath (see FIG. 1). For example, by providing one or more guide rolls in each treatment bath and transporting the film along these guide rolls, the film can be immersed in each treatment bath.

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

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

(Swelling process)
The swelling step is performed for the purpose of removing foreign matters on the surface of the original film 10, removing the plasticizer in the original film 10, imparting easy dyeability, and plasticizing the original film 10. The processing conditions are determined within a range in which the object can be achieved and within a range in which problems such as extreme dissolution and devitrification of the raw film 10 do not occur.

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

  As the swelling liquid of the swelling bath 13, in addition to pure water, boric acid (JP-A-10-153709), chloride (JP-A-06-281816), inorganic acid, inorganic salt, water-soluble organic solvent, alcohol It is also possible to use an aqueous solution to which a kind or the like is added in the range of about 0.01 to 10% by weight.

  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. Moreover, when the raw fabric 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 film 10 is preferably about 30 to 300 seconds, more preferably about 60 to 240 seconds.

  In the swelling treatment, the problem that the original film 10 swells in the width direction and the film is wrinkled easily occurs. As one means for conveying the film while removing the 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, a cross guider, a bend bar. Or using other widening devices such as tenter clips. Another means for suppressing the generation of wrinkles is to perform stretching. For example, the uniaxial stretching process can be performed in the swelling bath 13 by utilizing the peripheral speed difference between the nip roll 50 and the nip roll 51.

  In the swelling treatment, the film swells and expands in the film conveyance direction. Therefore, when the film is not actively stretched, for example, it is disposed before and after the swelling bath 13 in order to eliminate the sag of the film in the conveyance direction. It is preferable to take measures such as controlling the speed of the nip rolls 50 and 51. In addition, for the purpose of stabilizing the film transport 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: detecting the edge of the film to meander the film. It is also useful to use a device for preventing the above in combination.

  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 order 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 on the polyvinyl alcohol-based resin film after the swelling treatment. The processing conditions are determined within a range in which the object can be achieved and in a range in which defects such as extreme dissolution and devitrification of the film do not occur. Referring to FIG. 1, in the dyeing step, the film after the swelling treatment is conveyed along the film conveyance path constructed by the nip roll 51, the guide rolls 33 to 36 and the nip roll 52, and the film after the swelling treatment is accommodated in the dye bath 15 (dye tank). In the treatment liquid) for a predetermined time and then withdrawing. In order to enhance the dyeability of the dichroic dye, the film subjected to the dyeing process is preferably a film subjected to at least some uniaxial stretching treatment, or instead of the uniaxial stretching treatment before the dyeing treatment, or In addition to the uniaxial stretching process before the dyeing process, it is preferable to perform the uniaxial stretching process during the dyeing process.

  When iodine is used as the dichroic dye, the concentration of the dyeing solution in the dyeing bath 15 is, for example, iodine / potassium iodide / water = about 0.003-0.3 / about 0.1-10 / weight by weight. An aqueous solution of 100 can be used. 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, for example, 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 terms of containing iodine. If the aqueous solution contains about 0.003 parts by weight or more of iodine with respect to 100 parts by weight of water, the dyeing bath 15 Can be considered. The temperature of the dyeing bath 15 when dipping the film is usually about 10 to 45 ° C., preferably 10 to 40 ° C., more preferably 20 to 35 ° C., and the dipping time of the film is usually 30 to 600 seconds. Degree, preferably 60 to 300 seconds.

  When a water-soluble dichroic dye is used as the dichroic dye, the concentration of the dyeing solution in the dyeing bath 15 is, for example, dichroic dye / water by weight ratio of about 0.001 to 0.1 / 100. An aqueous solution can be used. This dyeing bath 15 may contain a dyeing assistant or the like, and may contain, for example, an inorganic salt such as sodium sulfate or a surfactant. Only one dichroic dye may be used alone, or two or more dichroic dyes 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 dipping time of the film is usually about 30 to 600 seconds, preferably about 60 to 300 seconds. is there.

  As described above, the film can be uniaxially stretched in the dyeing bath 15 in the dyeing process. Uniaxial stretching of the film can be performed by a method of making a peripheral speed difference between the nip roll 51 and the nip roll 52 arranged before and after the dyeing bath 15.

  In the dyeing process, as in the swelling process, in order to convey the polyvinyl alcohol resin film while removing the wrinkles of the film, an expander roll, a spiral roll, a crown roll, etc. are provided on the guide rolls 33, 34, 35 and / or 36. A roll having a widening function can be used, or another widening device such as a cross guider, a bend bar, or a tenter clip can be used. Another means for suppressing the generation of wrinkles is to perform a stretching process as in the swelling process.

  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 order and is introduced into the crosslinking bath 17.

(Crosslinking process)
The crosslinking step is a treatment performed for the purpose of water resistance and hue adjustment (such as preventing the film from being bluish) by crosslinking. In the example shown in FIG. 1, two crosslinking baths are arranged as crosslinking baths for performing the crosslinking step, and the first crosslinking step for the purpose of water resistance is performed in the first crosslinking bath 17a, and the second is performed for the purpose of hue adjustment. The crosslinking step is performed in the second crosslinking bath 17b. Referring to FIG. 1, the first crosslinking step is conveyed along a film conveyance path constructed by the nip roll 52, the guide rolls 37 to 40, and the nip roll 53 a, and the first crosslinking bath 17 a (the first bridge accommodated in the crosslinking tank). (1 crosslinking liquid) can be carried out by immersing the film after dyeing treatment for a predetermined time and then pulling it out. The second crosslinking step is conveyed along the film conveyance path constructed by the nip roll 53a, the guide rolls 41 to 44, and the nip roll 53b, and the first crosslinking bath 17b (second crosslinking liquid accommodated in the crosslinking tank) is first. It can be carried out by immersing the film after the crosslinking step for a predetermined time and then pulling it out. Hereinafter, the term “crosslinking bath” includes both the first crosslinking bath 17a and the second crosslinking bath 17b, and the term “crosslinking solution” includes both the first crosslinking solution and the second crosslinking solution.

  As the crosslinking liquid, a solution in which a crosslinking agent is dissolved in a solvent can be used. Examples of the crosslinking agent include boron compounds such as boric acid and borax, glyoxal, and glutaraldehyde. One kind of these may be used, or two or more kinds may be used in combination. As the solvent, for example, water can be used, but an organic solvent compatible with water may be further included. The concentration of the crosslinking agent in the crosslinking liquid, the temperature of the crosslinking bath, the immersion time of the film, and the number of crosslinking baths in which the film is immersed are not particularly limited. By appropriately selecting these, the boron content is 2.0. A polarizing film of ˜3.5% by weight can be obtained. 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 an aqueous solution containing 1.5 to 3 parts by weight is preferably used. . When the dichroic dye used in the dyeing treatment is iodine, the crosslinking liquid preferably contains iodide in addition to boric acid. The amount of iodide is, for example, 1 to 30 with respect to 100 parts by weight of water. It can be a weight part. Examples of iodide include potassium iodide and zinc iodide. In addition, compounds other than iodide, for example, zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, sodium sulfate and the like may coexist.

In the crosslinking treatment, the concentration of boric acid and iodide and the temperature of the crosslinking bath 17 can be appropriately changed depending on the purpose. For example, in the case of the first crosslinking liquid whose purpose of crosslinking treatment is water resistance by crosslinking, it can be an aqueous solution having a concentration of boric acid / iodide / water = 1 to 10/1 to 30/100 by weight ratio. The temperature of the first crosslinking bath 17a when dipping the film is usually about 50 to 70 ° C, preferably 53 to 65 ° C, and the dipping time of the film is usually about 10 to 600 seconds, preferably 20 to 300 seconds. More preferably, it is 20 to 200 seconds.
Moreover, when performing the dyeing | staining process and the 1st bridge | crosslinking process in this order with respect to the polyvinyl alcohol-type resin film previously extended | stretched before the swelling process, the temperature of the 1st bridge | crosslinking bath 17a is about 50-85 degreeC normally, Preferably it is 55-55. 80 ° C.

  In the second crosslinking liquid for the purpose of adjusting the hue, for example, when iodine is used as the dichroic dye, the concentration is boric acid / iodide / water = 1 to 5/3 to 30/100 by weight ratio. can do. The temperature of the second crosslinking bath 17b when dipping the film is usually about 10 to 45 ° C., and the dipping 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 cross-linking treatment for water resistance by cross-linking and the cross-linking treatment for hue adjustment may be performed in a plurality of steps, respectively.

  A uniaxial stretching process can also be performed in the first cross-linking bath 17a using a difference in peripheral speed between the nip roll 52 and the nip roll 53a. Moreover, the uniaxial stretching process can also be performed in the second cross-linking bath 17b by utilizing the peripheral speed difference between the nip roll 53a and the nip roll 53b.

  In the cross-linking treatment, an expander roll and a spiral roll are provided on the guide rolls 38, 39, 40, 41, 42, 43 and / or 44 in order to convey the polyvinyl alcohol resin film while removing the wrinkles of the film as in the swelling treatment. A roll having a widening function such as a crown roll can be used, or another widening apparatus such as a cross guider, a bend bar, or a tenter clip can be used. Another means for suppressing the generation of wrinkles is to perform a stretching process as in the swelling process.

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

(Washing process)
The example shown in FIG. 1 includes a cleaning step after the crosslinking step. The washing treatment is performed for the purpose of removing excess chemicals such as boric acid and iodine adhering to the polyvinyl alcohol resin film. The cleaning step is performed, for example, by immersing a crosslinked polyvinyl alcohol resin film in the cleaning bath 19. In addition, it replaces with the process of immersing a film in the washing | cleaning bath 19, and a washing | cleaning process is performed by spraying a washing | cleaning liquid with respect to a film as a shower, or using the immersion to the washing bath 19 and spraying of a washing | cleaning liquid together. You can also.

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

  In the cleaning process, a roll having a widening function such as an expander roll, a spiral roll, or a crown roll in the guide rolls 45, 46, 47, and / or 48 for the purpose of transporting the polyvinyl alcohol resin film while removing wrinkles. Or other widening devices such as cross guiders, bend bars, and tenter clips. In the film cleaning process, a stretching process may be performed in order to suppress generation of wrinkles.

(Stretching process)
As described above, the raw film 10 is uniaxially stretched wet or dry during the series of processing steps (that is, before and after any one or more processing steps and / or during any one or more processing steps). It is processed. A specific method of the uniaxial stretching process is, for example, between rolls that perform longitudinal uniaxial stretching with a peripheral speed difference between two nip rolls (for example, two nip rolls arranged before and after the treatment bath) constituting the film conveyance path. Stretching, hot roll stretching as described in Japanese Patent No. 2731813, tenter stretching, and the like, and inter-roll stretching is preferred. The uniaxial stretching step can be performed a plurality of times before the polarizing film 23 is obtained from the raw film 10. As described above, the stretching treatment is also advantageous for suppressing the generation of wrinkles on the film.

  The final cumulative draw ratio of the polarizing film 23 on the basis of the original fabric 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 process, and in the case where the stretching process is performed in two or more treatment processes, the stretching process may be performed in any treatment process.

(Electromagnetic wave irradiation process)
In the apparatus shown in FIG. 1, the film is drawn from the second crosslinking step 17b, passes through the nip roll 53b, and is then immersed in the cleaning bath 19 before being irradiated with electromagnetic waves (electromagnetic wave irradiation step). Is done. In the apparatus shown in FIG. 1, an electromagnetic wave is irradiated from the electromagnetic wave irradiation unit 71. In the electromagnetic wave used in the electromagnetic wave irradiation step of the present invention, the ratio of the radiant energy of infrared rays having a wavelength of more than 2 μm and not more than 4 μm is 25% or more, preferably 28% or more, more preferably 35% or more. It is. By irradiating the film with such an electromagnetic wave, the optical properties of the obtained polarizing film can be improved. Moreover, although the upper limit of the ratio of the radiant energy of infrared rays with a wavelength of more than 2 μm and 4 μm or less is not particularly limited, for example, it is 80% or less. Usually, an electromagnetic wave having a wavelength of 0.75 μm to 1000 μm is referred to as infrared light.

  In the electromagnetic wave irradiation process, the mechanism that can improve the optical characteristics of the polarizing film by irradiating the electromagnetic wave whose ratio of the radiant energy of infrared rays with a wavelength of more than 2 μm and less than 4 μm is 25% or more of the total radiant energy is not clear. Although it is not, the molecular motion in the film excited by infrared rays with a wavelength of more than 2 μm and less than 4 μm promotes the fixation of dichroic dyes such as iodine in the cross-linked film and improves the optical properties of the polarizing film It is assumed that it can be made.

  FIG. 2 shows a radiant energy spectrum for each type of electromagnetic wave irradiator. Table 1 shows the ratio of the radiant energy of the electromagnetic wave in each wavelength region (expressed in the 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 includes a halogen heater (heat source temperature 2600 ° C.), a short wavelength infrared heater (heat source temperature 2200 ° C.), a fast response medium wavelength infrared heater (heat source temperature 1600 ° C.), a carbon heater (heat source temperature). 1200 ° C.), carbon heater (heat source temperature 950 ° C.), and medium wavelength infrared heater (heat source temperature 900 ° C.).

  As shown in Table 1, short wavelength infrared heater (heat source temperature 2200 ° C), fast response medium wavelength infrared heater (heat source temperature 1600 ° C), carbon heater (heat source temperature 1200 ° C), carbon heater (heat source temperature 950 ° C), medium The wavelength 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 the radiant energy of infrared rays having a wavelength of more than 2 μm and less than 4 μm is 25% or more of the total radiant energy. be able to. The electromagnetic wave irradiation unit 71 may be configured by one electromagnetic wave irradiator or may be configured by a plurality of electromagnetic wave irradiators. In the case of being constituted by a plurality of electromagnetic wave irradiators, infrared radiation energy of a wavelength of 2 μm or more and 4 μm or less radiated from the plurality of electromagnetic wave irradiators is applied to the electromagnetic waves radiated from the plurality of electromagnetic wave irradiators. A plurality of electromagnetic wave irradiators are selected so as to be 25% or more of the total radiation energy. Moreover, in FIG. 1, although the electromagnetic wave irradiation part 71 is comprised so that electromagnetic waves may be irradiated only to one surface of a film, several electromagnetic wave irradiation device is arrange | positioned so that electromagnetic waves may be irradiated from both surfaces of a film May be. It is preferable that the electromagnetic wave irradiation part 71 is comprised so that electromagnetic waves may be irradiated to the whole width direction area of the polyvinyl alcohol-type resin film to be irradiated.

  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, it is preferable that the distance between the electromagnetic wave radiation | emission port of the electromagnetic wave irradiation device and the film in the electromagnetic wave irradiation part 71 is 2-40 cm, and it is further more preferable that it is 5-20 cm. However, this distance is preferably selected while appropriately selecting in consideration of the amount of radiant energy of the electromagnetic wave radiated from the electromagnetic wave irradiator, the temperature of the film surface, and the like. It is preferable that the temperature of the film surface at the time of electromagnetic wave irradiation is maintained at 30-90 degreeC, and it is more preferable that it is maintained at 40-80 degreeC.

In the electromagnetic wave irradiation step, the irradiation heat amount of the electromagnetic wave 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 further preferably 1000 J / cm ³ or more. In addition, the heat of irradiation 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, from the viewpoint of suppressing deterioration of the film due to temperature rise. More preferably, it is not more than cm ³ .
Usually, the amount of moisture in the film decreases in proportion to the amount of heat applied to the electromagnetic wave. However, since the electromagnetic wave irradiation process of the present invention is not intended to reduce the amount of water in the film, the amount of heat applied is appropriately selected. Preferably, it selects suitably within the said 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 crosslinking bath, and is performed on the film after being immersed in all the crosslinking baths as shown in FIG. It is not limited to. 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 second crosslinking bath. You may perform an electromagnetic wave irradiation process with respect to the film after making it soak in. However, since the crosslinking of boric acid incorporated in the film can be promoted by immersing in the crosslinking bath by the electromagnetic wave irradiation step, the electromagnetic wave irradiation step is performed on the film that has been immersed in all the crosslinking baths. It is preferable to carry out the crosslinking because the crosslinking of boric acid can proceed more effectively.

  The electromagnetic wave irradiation is preferably performed within 10 seconds after the film is drawn out from the crosslinking bath, and more preferably within 5 seconds. The shorter the time from extraction from the crosslinking bath to irradiation of electromagnetic waves, the more the optical properties of the polarizing film by electromagnetic irradiation can be improved. In addition, in the electromagnetic wave irradiation process, it is preferable that there are few water molecules adhering to the surface of a film. This is because, when water molecules are present on the surface of the film, the water molecules on the film surface absorb infrared rays, thereby reducing the excitation effect of molecular motion in the film due to electromagnetic wave irradiation. Immediately after being drawn out from the crosslinking bath, since the crosslinking liquid adheres to the surface of the film, it is preferable to provide a liquid removing means for removing this before the electromagnetic wave irradiation step. In FIG. 1, the nip roll 53b also functions as a liquid removal means for removing the crosslinking liquid adhering to the film surface. As the liquid removal means, in addition to the nip roll, a means for removing liquid by blowing air onto the film, a scraper for removing liquid by contact with the film, or the like may be used.

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

(Drying process)
It is preferable to perform the process which dries a polyvinyl alcohol-type resin film after a washing | cleaning process. The drying of the film is not particularly limited, but can be performed using a drying furnace 21 as in the example shown in FIG. The drying furnace 21 can be provided with, 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 treatment for drying the polyvinyl alcohol-based 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 wound into a roll by sequentially winding it on a take-up roll, or provided as it is to the polarizing plate preparation step (step of laminating a protective film or the like on one or both sides of the polarizing film) without taking up. You can also.

(Other processing steps for polyvinyl alcohol resin film)
Processing other than the processing described above can also be added. Examples of treatments that can be added include immersion treatment (complementary color treatment) in an aqueous iodide solution that does not contain boric acid, and immersion treatment in an aqueous solution that does not contain boric acid and contains zinc chloride, etc. (zinc) Processing).

<Polarizing film>
By producing a polarizing film by the above method,
i) the boron content is 2.0-3.5 wt%,
ii) Visibility correction single transmittance (Ty) is 42.0% or more iii) Visibility correction polarization degree (Py) is 99.990% or more,
The ratio _A 480 _{/ A 600} absorption axis direction of the absorbance _{A 600} of the polarizing film in the absorption axis direction of the absorbance _{A 480} and wavelength 600nm of the polarizing film in iv) Wavelength 480nm is 0.75 to 1.00, a polarizing film Can be obtained.

  When the boron content of the polarizing film is as described in i) above, the shrinkage force is suppressed. The boron content of the polarizing film is more preferably 2.0 to 3.0% by weight. The contraction force of the polarizing film is preferably 3.8 N / 2 mm or less, and more preferably 3.5 N / 2 mm or less. Here, the boron content and shrinkage force of the polarizing film are measured in accordance with the description in the section of Examples described later.

  In general, high optical characteristics can be obtained by increasing the boron content of the polarizing film to be, 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). In the production method of the present invention, by having an electromagnetic wave irradiation step, it is possible to obtain a polarizing film having excellent optical characteristics that satisfies the above ii) and iii) while satisfying the above i). Here, the visibility-corrected single transmittance (Ty) and the visibility-corrected polarization degree (Py) of the polarizing film are measured in accordance with the description in the example section described later.

In the production method of the present invention, the electromagnetic wave used in the electromagnetic wave irradiation step is an electromagnetic wave having a ratio of infrared radiant energy having a wavelength of more than 2 μm and not more than 4 μm that is 25% or more of the total radiant energy. A polarizing film having excellent hue close to neutral gray that satisfies the characteristics can be obtained. If A ₄₈₀ / A ₆₀₀ is less than 0.75, the bluish color is strong, and if A ₄₈₀ / A ₆₀₀ exceeds 1.00, the red color becomes strong. In order to suppress redness, A ₄₈₀ / A ₆₀₀ is more preferably 0.90 or less. That is, by the production method of the present invention, a polarizing film having excellent optical properties that simultaneously satisfies the properties ii) to iv) while suppressing the shrinkage force by reducing the boron content of the polarizing film as in the above i). Can be obtained.

<Polarizing plate>
A polarizing plate can be obtained by bonding a protective film via an adhesive on at least one surface of the polarizing film produced as described above. As the protective film, for example, a film made of an acetyl cellulose resin such as triacetyl cellulose or diacetyl cellulose; a film made of a polyester resin such as polyethylene terephthalate, polyethylene naphthalate and polybutylene terephthalate; a polycarbonate resin film, a cyclo Examples include olefin resin films; acrylic resin films; and films made of polypropylene-based chain olefin resins.

  Surfaces such as corona treatment, flame treatment, plasma treatment, ultraviolet irradiation, primer coating treatment, saponification treatment, etc. on the polarizing film and / or protective film bonding surface in order to improve the adhesion between the polarizing film and the protective film Processing may be performed. As an adhesive used for laminating a polarizing film and a protective film, an active energy ray curable adhesive such as an ultraviolet curable adhesive, an aqueous solution of a polyvinyl alcohol resin, or an aqueous solution in which a crosslinking agent is blended. And water-based adhesives such as urethane emulsion adhesives. The ultraviolet curable adhesive may be a mixture of an acrylic compound and a photo radical polymerization initiator, a mixture of an epoxy compound and a photo cationic polymerization initiator, or the like. Alternatively, a cationic polymerizable epoxy compound and a radical polymerizable acrylic compound may be used in combination, and a photo cationic polymerization initiator and a photo radical polymerization initiator may be used in combination as an initiator.

  EXAMPLES Hereinafter, although an Example is shown and this invention is demonstrated further more concretely, this 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 having a thickness of 60 μm [trade name “Kuraray Vinylon VF-PE # 6000” manufactured by Kuraray Co., Ltd., average polymerization degree 2400, saponification degree 99.9 mol % Or more] was continuously conveyed while being unwound from the roll, and immersed in a swelling bath made of pure water at 30 ° C. for a residence time of 79 seconds (swelling step). Thereafter, the film drawn out from the swelling bath was immersed in a dye bath at 30 ° C. containing iodine having a potassium iodide / boric acid / water ratio of 1 / 0.3 / 100 (weight ratio) with a residence time of 123 seconds ( Dyeing process). The film drawn from the dyeing bath is then immersed in a first crosslinking bath at 53 ° C. having a potassium iodide / boric acid / water ratio of 11 / 2.0 / 100 (weight ratio) with a residence time of 44 seconds, followed by Then, it was immersed in a second crosslinking bath at 40 ° C. in which potassium iodide / boric acid / water was 11 / 2.0 / 100 (weight ratio) for a residence time of 6 seconds (crosslinking step). In the dyeing process and the crosslinking process, longitudinal uniaxial stretching was performed by stretching between rolls in a bath. The total draw ratio based on the original film was 5.65 times.

Next, an electromagnetic wave irradiator (medium wavelength infrared heater (MW heater), product name: Golden 8 Medium-wave twin tube emitter, manufactured by Heraeus Co., Ltd.) with respect to the film drawn out from the second crosslinking bath 17b and passed through the nip roll 53b. Using a heat source temperature of 900 ° C. and a maximum energy density of 60 kW / m ² ), an electromagnetic wave emission port is placed at a position 5 cm away from the surface of the film, and the electromagnetic wave is irradiated at an output of 50% with respect to 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 the electromagnetic wave per unit film volume was calculated by the following formula.
(Radiation heat of electromagnetic wave per unit volume of film) = {(maximum energy density) × (heater heating part surface area) × output (%) / (electromagnetic wave irradiation area)} × (electromagnetic wave irradiation time) ÷ (film thickness)
The output (%) indicates the ratio (%) of the actually irradiated output with respect to the maximum irradiation output of the electromagnetic wave irradiator.
After the film was drawn out from the second crosslinking bath 17b, the time required for the film to be transported to reach the irradiation position of the electromagnetic wave irradiator and to be irradiated with the electromagnetic wave 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). Thereafter, the film was dried in a drying oven 21 at a temperature of 60 ° C. and an absolute humidity of 11 g / cm ³ to obtain a polarizing film. The thickness of the obtained polarizing film was 23 μm.

<Examples 2 to 6, Comparative Examples 3 and 4>
In the electromagnetic wave irradiation step, Table 2 shows the types of electromagnetic wave irradiators, the output (%), the heat of irradiation of electromagnetic waves per unit volume of film, and the parts by weight of boric acid with respect to 100 parts by weight of water in the first and second crosslinking baths. A polarizing film was obtained in the same manner as in Example 1 except for the points as shown. Each of the obtained polarizing films had a thickness of 23 μm. As the electromagnetic wave irradiator, halogen heater (product name: straight tube type halogen heater lamp QIR, manufactured by Ushio Lighting Co., Ltd., heat source temperature 2600 ° C., maximum energy density 300 kW / m ² ), short wavelength infrared heater (SW heater) (Product name: Golden 8 Short-tube twin tube emitter, manufactured by Heraeus, heat source temperature 2200 ° C., maximum energy density 200 kW / m ² ), fast response medium wavelength infrared heater (FRMW heater) (Product name: Golden 8 Medium-wave fast response twin tubu emitter, Heraeus Co., the heat source temperature 1600 ° C., the maximum energy density 150 kW ^{/ m} 2), medium wavelength infrared heater (MW heater) (product name: Golden 8 Me ium-wave twin tube emitter, Heraeus Co., the heat source temperature 900 ° C., with either a maximum energy density 60kW / ^{m 2).}

<Comparative Examples 1, 2, 5>
Polarized light in the same manner as in Example 1 except that the electromagnetic wave irradiation step was not performed and the parts by weight of boric acid with respect to 100 parts by weight of water in the first and second crosslinking baths were as shown in Table 2. A film was obtained. Each of the obtained polarizing films had a thickness of 23 μm.

[Evaluation of polarizing film]
(A) Measurement of single transmittance and degree of polarization About the polarizing film obtained in each example and each comparative example, using a spectrophotometer with an integrating sphere ["V7100" manufactured by JASCO Corporation], a wavelength of 380 to 380 The MD transmittance and TD transmittance in the range of 780 nm were measured, and the following formula:
Single transmittance (%) = (MD + TD) / 2
Degree of polarization (%) = {(MD−TD) / (MD + TD)} × 100
Based on the above, the single transmittance and the degree of polarization at each wavelength were calculated.

“MD transmittance” is the transmittance when the direction of polarized light emitted from the Glan-Thompson prism is parallel to the transmission axis of the polarizing film sample, and is represented by “MD” in the above formula. The “TD transmittance” is the transmittance when the direction of polarized light emitted from the Glan-Thompson prism is orthogonal to the transmission axis of the polarizing film sample, and is represented by “TD” in the above formula. About the obtained single transmittance and degree of polarization, visibility correction is performed by 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”. The visibility corrected single transmittance (Ty) and the visibility corrected polarization degree (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 The measurement was performed using a spectrophotometer with an integrating sphere [“V7100” manufactured by JASCO Corporation]. 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 the above, the absorbance A _{480 at a} wavelength of ₄₈₀ nm and the absorbance A ₆₀₀ at a wavelength of 600 nm were calculated. Table 2 shows the absorbance A ₄₈₀ , absorbance A ₆₀₀ , and calculated values of the ratio A ₄₈₀ / A ₆₀₀ calculated based on these values.

(C) MD shrinkage force From the obtained polarizing film, a measurement sample having a width of 2 mm and a length of 10 mm with the absorption axis direction (MD, stretching direction) as the long side was cut out. The long side generated when this sample is set in the thermomechanical analyzer (TMA) “EXSTAR-6000” manufactured by SII Nanotechnology, Inc. and kept at 80 ° C. for 4 hours while keeping the dimensions constant. The contraction force (MD contraction force) in the direction (absorption axis direction, MD) was measured. Table 2 shows the measured contractile force values.

(D) Boron content of polarizing film After adding 0.2 g of polarizing film to 170 ml of pure water and completely dissolving at 95 ° C., 30 g of aqueous mannitol solution (12.5 wt%) was added to the sample solution for measurement and did. A sodium hydroxide aqueous solution (1 mol / l) is dropped until the sample solution for measurement reaches the neutralization point, and the boron content (% by weight) in the polyvinyl alcohol-based resin film is calculated from the amount added by the following formula:
Boron content (% by weight) = 1.08 × amount of sodium hydroxide aqueous solution dropped (ml) / weight of polarizing film (g)
Calculated from Table 2 shows the measured boron content values.

As shown in Table 2, the polarizing films of Examples 1 to 6 are
i) the boron content is 2.0-3.5 wt%,
ii) Visibility correction single transmittance Ty is 42.0% or more iii) Visibility correction polarization degree Py is 99.990% or more,
The ratio _A 480 _{/ A 600} absorption axis direction of the absorbance _{A 600} of the polarizing film in the absorption axis direction of the absorbance _{A 480} and wavelength 600nm of the polarizing film in iv) Wavelength 480nm was 0.75 or more and 1 or less. Further, the contraction force was suppressed by satisfying the above i), and there was no problem in the hue by satisfying the above iv). The polarizing film of Comparative Example 1 did not carry out the electromagnetic wave irradiation step, and had a low value of the visibility correction polarization degree (Py).
The polarizing film of Comparative Example 2 had a large shrinkage force because it did not satisfy the above i). In the polarizing film of Comparative Example 3, the value of A ₄₈₀ / A ₆₀₀ exceeded 1 and the redness was strong. In Comparative Examples 4 and 5, since the boron content was not sufficient, the value of the visibility correction polarization degree (Py) was low.

  DESCRIPTION OF SYMBOLS 10 Original fabric film which consists of polyvinyl alcohol-type resin, 11 Original fabric roll, 13 Swelling bath, 15 Dye bath, 17a 1st crosslinking bath, 17b 2nd crosslinking bath, 19 Washing bath, 21 Drying furnace, 23 Polarizing film, 30- 48, 60, 61 Guide roll, 50-52, 53a, 53b, 54, 55 Nip roll, 71 Electromagnetic wave irradiation part.

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 made of an aqueous solution of a crosslinking agent containing a boron compound;
An electromagnetic wave irradiation step of irradiating the polyvinyl alcohol-based resin film after the cross-linking step with an electromagnetic wave having a ratio of infrared radiation energy of a wavelength of more than 2 μm to 4 μm or less being 25% or more of the total radiation energy;
A cleaning step of cleaning the polyvinyl alcohol-based resin film after being irradiated with the electromagnetic wave. 2. The method for producing 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 polarized light according to claim 1, further comprising a liquid removal step of removing the aqueous solution adhering to the surface of the polyvinyl alcohol-based resin film before the irradiation with the electromagnetic wave after the crosslinking treatment. A method for producing a film.   The said electromagnetic wave irradiation process is a manufacturing method of the polarizing film of any one of Claims 1-3 performed within 5 second, after pulling out the said polyvinyl alcohol-type resin film from the said crosslinking bath.   5. The crosslinking process according to claim 1, wherein in the crosslinking step, the crosslinking bath comprises 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 of description. A production 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 portion for dyeing the polyvinyl alcohol-based resin film with a dichroic dye;
A cross-linked portion that undergoes a cross-linking treatment by immersing the polyvinyl alcohol-based resin film after the dyeing treatment in a cross-linking bath made of 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 an electromagnetic wave in which the ratio of the infrared radiation energy having a wavelength of more than 2 μm to 4 μm or less is 25% or more of the total radiation energy;
And a cleaning unit for cleaning the polyvinyl alcohol-based resin film after being irradiated with the electromagnetic wave. A polarizing film dyeing a polyvinyl alcohol resin film with a dichroic dye,
The boron content is 2.0 to 3.5% by weight,
Visibility corrected single transmittance is 42.0% or more,
Visibility correction polarization degree is 99.990% or more,
The ratio _A 480 _{/ A 600} absorbance _{A 600} of the polarizing film in the absorption axis direction of the absorbance _{A 480} and wavelength 600nm at a wavelength of 480nm is 0.75 to 1.00, a polarizing film.