JP2018032026A - Method and device for manufacturing polarizing film, and the polarizing film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a polarizing film in which variation in polarizing film characteristics is reduced, and a device for manufacturing the same.SOLUTION: The method for manufacturing a polarizing film from a polyvinyl alcohol resin film comprises: a dyeing step for dyeing the polyvinyl alcohol resin film with a dichroic dye; a crosslinking step for crosslinking the polyvinyl alcohol resin film after the dyeing step with a crosslinking agent; an electromagnetic wave irradiation step for irradiating the polyvinyl alcohol resin film after the crosslinking step with electromagnetic waves including infrared rays; and a cleaning step for cleaning the polyvinyl alcohol resin film after the irradiation with the electromagnetic waves. In the electromagnetic wave irradiation step, an irradiated heat amount of the electromagnetic waves per unit volume of the polyvinyl alcohol resin film has a distribution in the width direction.SELECTED DRAWING: Figure 1

Description

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

  Conventionally, in the manufacturing method of a polarizing film, various devices have been made to improve the characteristics of the polarizing film. In JP 2013-148806 A (Patent Document 1), by providing a primary drying step of drying a polyvinyl alcohol-based resin film between the boric acid treatment step and the water washing step, the transmitted light can have a favorable hue. It is described that it can, i.e., close to neutral gray.

JP 2013-148806 A

  The present inventors cut out a sample from the polarizing film and measured the characteristics, and even if the sample was cut out from the polarizing film obtained by the same manufacturing method, the problem is that the characteristics may vary greatly depending on the sample. It came. An object of this invention is to provide the manufacturing method of the polarizing film which reduces the dispersion | variation in the characteristic of a polarizing film, and its manufacturing apparatus. Moreover, an object of this invention is to provide the polarizing film with the uniform characteristic of the width direction.

This invention provides the manufacturing method of a polarizing film, a manufacturing apparatus, and a polarizing film shown below.
[1] A method for producing a polarizing film 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 crosslinking the polyvinyl alcohol-based resin film after the dyeing step with a crosslinking agent;
An electromagnetic wave irradiation step of irradiating the polyvinyl alcohol-based resin film after the crosslinking step with an electromagnetic wave containing infrared;
A washing step of washing the polyvinyl alcohol-based resin film after irradiating the electromagnetic wave,
The said electromagnetic wave irradiation process WHEREIN: The manufacturing method of a polarizing film with which the irradiation heat amount per unit volume of the said electromagnetic wave of the said polyvinyl alcohol-type resin film has distribution in the width direction.

  [2] In the electromagnetic wave irradiation step, the irradiation heat amount per unit volume of the electromagnetic wave in the first region including the center and not including the end in the width direction of the polyvinyl alcohol-based resin film includes the end and includes the center. The manufacturing method of the polarizing film as described in [1] which is larger than the irradiation heat amount per unit volume of the electromagnetic wave in the second region.

[3] In the infrared electromagnetic wave irradiation step, the irradiation heat amount of the electromagnetic wave infrared light in the first region 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 manufacturing method of the polarizing film of description.

  [4] In any one of [1] to [3], in the electromagnetic wave irradiation step, an electromagnetic wave having a ratio of infrared radiation energy of a wavelength of more than 2 μm and not more than 4 μm is 25% or more of the total radiation energy. The manufacturing method of the polarizing film of description.

  [5] The method for producing a polarizing film according to any one of [1] to [4], wherein the crosslinking agent includes a boron compound.

  [6] The polarizing film according to any one of [1] to [5], wherein the crosslinking step is a step of immersing the polyvinyl alcohol-based resin film in a crosslinking bath made of an aqueous solution of the crosslinking agent. Production method.

  [7] The polarizing film according to [6], 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. Manufacturing method.

[8] A manufacturing apparatus for manufacturing a polarizing film 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 for cross-linking the polyvinyl alcohol-based resin film after the dyeing treatment with a cross-linking agent;
An electromagnetic wave irradiation part for irradiating the polyvinyl alcohol-based resin film after the crosslinking treatment with an electromagnetic wave containing infrared;
A washing section for washing the polyvinyl alcohol-based resin film after being irradiated with the electromagnetic wave,
The said electromagnetic wave irradiation part is a manufacturing apparatus of the polarizing film which irradiates the said electromagnetic wave so that the irradiation heat amount per unit volume of the said electromagnetic wave of the said polyvinyl alcohol-type resin film has distribution in the width direction.

[9] The method for producing a polarizing film according to [2] or [3], wherein in the electromagnetic wave irradiation step, only the first region is irradiated with electromagnetic waves.
[10] The method for producing a polarizing film according to [9], wherein the width of the first region with respect to the entire width of the polyvinyl alcohol-based resin film is 60 to 90%.
[11] The average value of iodine (I) content at 10 measurement points in the width direction is 1.35% by mass or more, and the maximum content of iodine (I) at the 10 measurement points The difference between the value and the minimum value is 0.60% by mass or less,
The ten measurement points are polarizing films, each being a measurement point included in a section obtained by dividing the entire width in the width direction into ten equal parts.
[12] The polarizing film according to [11], wherein an average content of iodine (I) at the 10 measurement points is 1.65% by mass or more.

  ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method and manufacturing apparatus of a polarizing film which reduce the variation in the characteristic of a polarizing film can be provided. Moreover, according to this invention, the polarizing film with the uniform characteristic of the width direction 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. 3 is a graph in which measured values of Py in Example 1, Comparative Example 1 and Comparative Example 2 are plotted. 6 is a graph in which b values of orthogonal hues of Example 1, Comparative Example 1, and Comparative Example 2 are plotted.

<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 is, for example, about 400 to 6000 mm, preferably 2000 mm or more. In particular, when the width of the raw film is 2000 mm or more, the production method of the present invention is effective because the characteristics in the width direction of the polarizing film are likely to vary. 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.

  When the present inventors examined the variation in the characteristic of a polarizing film, they acquired the knowledge that the variation is easy to produce in the width direction. The present inventors have further studied, and after the crosslinking treatment and before the washing treatment, by performing an electromagnetic wave irradiation step to irradiate the film with an electromagnetic wave to be described later, the polarizing film has characteristics in the width direction. As a result, the present inventors have found that the variation of the above can be suppressed.

  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. Although the density | concentration of the crosslinking agent in a crosslinking solution is not limited to this, It is preferable to exist in the range of 1-20 weight%, and it is more preferable that it is 6-15 weight%.

  The crosslinking liquid can be an aqueous solution containing, for example, about 1 to 10 parts by weight of boric acid with respect to 100 parts by weight of water. When the dichroic dye used in the dyeing treatment is iodine, the crosslinking liquid preferably contains iodide in addition to boric acid. The amount is, for example, 1 to 30 parts by weight with respect to 100 parts by weight of water. It can be. 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 = 3 to 10/1 to 20/100 by weight ratio. As needed, it may replace with boric acid and may use another crosslinking agent, and may use boric acid and another crosslinking agent together. 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 as long as they are within the above range. 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.

  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. From the electromagnetic wave irradiation part, the electromagnetic wave is irradiated so that the irradiation heat quantity per unit volume of the polyvinyl alcohol resin film to be irradiated has a distribution in the width direction.

  As an example of the distribution in the width direction, the polyvinyl alcohol-based resin film is a first region that includes the center and does not include the end portion in the width direction, and the second region that is located on both sides of the first region and includes the end portion and does not include the center. It can be divided into regions, and the amount of irradiation heat per unit volume of electromagnetic waves can be different between the first region and the second region. When the first region and the second region divided as described above are compared, there is a tendency that optical characteristics such as hue tend to vary. In the electromagnetic wave irradiation step, the variation in optical characteristics can be suppressed by making the irradiation heat amount per unit volume of the electromagnetic wave in the first region larger than the irradiation heat amount per unit volume of the electromagnetic wave in the second region. The difference in the amount of irradiation heat can be selected as appropriate. For example, the amount of irradiation heat in the first region may be selected to be twice or more that in the second region, or the first region may be irradiated with electromagnetic waves. And the second region may not be irradiated with electromagnetic waves.

  The ratio of the width of the first region and the value obtained by adding the widths of the two second regions can be, for example, in the range of 10: 1 to 1:10. Such a ratio can be selected according to the situation of variation in characteristics to be improved.

  The variation in the optical characteristics is that the treatment liquid is more likely to enter from the end face than the surface of the polyvinyl alcohol-based resin film in each treatment step described above, and the amount of treatment liquid intrusion differs between the vicinity of the end and the center. It is predicted that one of the factors is the difference between the two. Moreover, it is estimated that it is one factor that the thickness varies in the width direction due to stretching, and that the degree of treatment in each treatment process varies depending on the thickness. Examining such factors, the polyvinyl alcohol-based resin film is not limited to the method of dividing the “second region / first region / second region” in the width direction as described above. It may be divided so that one or more regions exist between the one region and the second region, and the irradiation heat amount per unit volume of the electromagnetic wave may be different for each region.

As a method of irradiating electromagnetic waves so as to have a distribution in the width direction,
i) The amount of radiant heat of electromagnetic waves radiated from the electromagnetic wave irradiation unit is distributed in the width direction.
ii) A part of the electromagnetic wave emitted from the electromagnetic wave irradiation part is absorbed by a mask or the like so that the electromagnetic wave is distributed in the width direction.

  As an example of the specific method of i), the electromagnetic wave emission region (heater heating unit) of the electromagnetic wave irradiation unit 71 corresponds to only a part of the width direction of the polyvinyl alcohol-based resin film. Electromagnetic wave is irradiated to the position corresponding to, and the electromagnetic wave is not irradiated to the position not corresponding to the electromagnetic wave radiation area, or the irradiation heat amount of the electromagnetic wave is reduced (the irradiation light may be irradiated by spreading), in the width direction The electromagnetic wave is irradiated so as to have a distribution.

  The present invention was completed based on the knowledge that irradiation of electromagnetic waves including infrared rays can affect characteristics such as optical characteristics of the polarizing film. In particular, the optical characteristics can be further improved by irradiating an electromagnetic wave in which 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 of the total radiant energy. In one embodiment of the present invention, the amount of irradiation heat per unit volume of the electromagnetic wave in the first region is adjusted to be larger than the amount of heat irradiation per unit volume of the electromagnetic wave in the second region. Variations can be suppressed. At the same time, it is possible to improve the hue so as to approach the neutral gray as a whole. Optical characteristics such as hue are characteristics that cause variations in the width direction and that lower the characteristics of the first region compared to the characteristics of the second region.

  On the other hand, when the electromagnetic wave irradiation is effective for the characteristic in which the characteristic of the first region is higher than the characteristic of the second region, unlike the above-described characteristic, the variation in the characteristic is improved. Therefore, the variation in characteristics can be improved by adjusting the amount of irradiation heat per unit volume of the electromagnetic wave in the second region to be larger than the amount of heat irradiation per unit volume of the electromagnetic wave in the first region. Moreover, when the characteristic which acts with the wavelength of electromagnetic waves changes, you may make it adjust the distribution of irradiation heat amount for every wavelength range.

  From the viewpoint of improving the variation in optical characteristics such as hue, the electromagnetic wave used in the electromagnetic wave irradiation step is preferably such that the ratio of infrared radiation energy having a wavelength of more than 2 μm and less than 4 μm is 25% or more of the total radiation energy, More preferably, it is 28% or more, More preferably, it is 35% or more. By irradiating such an electromagnetic wave on the film so as to have a distribution in the width direction, it is possible to further improve variations in optical characteristics such as hue of the obtained polarizing film. Further, the upper limit value of the ratio of the radiant energy of infrared rays having a wavelength of more than 2 μm and not more than 4 μm is not particularly limited, but for example 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 step, the optical characteristics of the polarizing film can be effectively improved by irradiating the electromagnetic wave in which 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 of the total radiant energy. Although the mechanism is not clear, 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 crosslinked film, and the polarization film It is presumed that optical characteristics and the like can be improved.

  FIG. 2 shows a radiant energy spectrum for each type of electromagnetic wave irradiator. Moreover, Table 1 shows the ratio which occupies for the total radiant energy of the radiant energy of the electromagnetic wave of each wavelength range (it represents with the range of wavelength xmicrometer) for every kind of electromagnetic wave irradiation device. 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. By adjusting the arrangement method of a plurality of electromagnetic wave irradiators, irradiation having a distribution in the width direction can be performed. 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. It is preferable to select a plurality of electromagnetic wave irradiators so that the total radiation energy is 25% or more. 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. For example, the first area is irradiated with electromagnetic waves from both sides, and the second area is irradiated with electromagnetic waves from only one side, so that the amount of irradiation heat per unit volume in the width direction has a distribution. May be.

  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 25-90 degreeC, and it is more preferable that it is maintained at 30-80 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 characteristics of the polarizing film, in the region of maximum irradiation heat in the width direction, it is preferably 100 J / cm ³ or more, more preferably 500 J / cm ³ or more, 1000 J / cm ³ More preferably, it is the above. In addition, from the viewpoint of suppressing deterioration of the film due to a temperature rise, the irradiation heat amount of electromagnetic waves per unit volume of the film is preferably 10 kJ / cm ³ or less in the region where the maximum irradiation heat amount is obtained in the width direction. more preferably cm ³ or less, still more preferably 3000 J / cm ³ or less. 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. The region having the maximum irradiation heat amount in the width direction can be, for example, the first region including the center and not including the end portion.

  In the present invention, by performing the electromagnetic wave irradiation step before the cleaning treatment, variations in the characteristics of the obtained polarizing film can be suppressed. 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 cross-linking of boric acid and the like because it can proceed more effectively.

  From the viewpoint of suppressing variations in optical properties, the irradiation with electromagnetic waves 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 the extraction from the crosslinking bath to the irradiation of the electromagnetic wave, the more the optical characteristics of the polarizing film by the irradiation of the electromagnetic wave 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.

  In addition, the present inventors have obtained knowledge that the iodine (I) content tends to vary in the width direction of the polarizing film. The variation in the content of iodine (I) in the polarizing film causes variations in optical characteristics such as single transmittance and variations in durability. The inventors of the present invention have made extensive studies, and in the electromagnetic wave irradiation step, by making the irradiation heat amount per unit volume of the electromagnetic wave in the first region larger than the irradiation heat amount per unit volume of the electromagnetic wave in the second region, The knowledge that the variation in content of iodine (I) can be suppressed was obtained. For example, it is possible to suppress the variation in the content of iodine (I) by irradiating only the first region with electromagnetic waves. Based on the width of the entire polyvinyl alcohol-based resin film, the width of the first region can be, for example, 5 to 95%, preferably 40 to 90%, and more preferably 60 to 90%. In the electromagnetic wave irradiation process aiming at suppressing the variation in the content of iodine (I), the above description of the electromagnetic wave irradiation process aiming at suppressing the characteristic variation is applied. In one embodiment, the first region is a region centered on the center of the polyvinyl alcohol-based resin film, and the second region having the same length in the width direction is located on both sides in the width direction of the first region. The first area and the second area are divided.

(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.

(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 the above-mentioned method, the polarizing film in which the variation in the characteristics in the width direction is suppressed can be obtained. The visibility corrected single transmittance Ty of the obtained polarizing film is preferably 40 to 47%, more preferably 41 to 45% in consideration of the balance with the visibility corrected polarization degree Py. The visibility correction polarization degree Py is preferably 99.9% or more, more preferably 99.95% or more, and a larger value is more preferable.

  The b value of the orthogonal hue of the obtained polarizing film is preferably −3.0 to +0.5, and more preferably −2.0 to 0. With such a value, the orthogonal hue does not shift excessively to blue and becomes neutral gray. In addition, when b values of orthogonal hues are measured at a plurality of points in the width direction at arbitrary positions in the length direction, it is preferable that variations in the measured values are small. Specifically, the measurement points at both ends in the width direction are determined to be at a distance of 0.5 to 50 mm from the end of the film so that the adjacent measurement points are equidistant between the measurement points at both ends. When the remaining 13 measurement points are determined and b values of orthogonal hues are measured at a total of 15 measurement points, the standard deviation is preferably 0.2 or less, and 0.1 or less. Is more preferable. Further, the difference between the maximum value and the minimum value of the b value of the orthogonal hue is preferably 0.7 or less, and more preferably 0.5 or less. The b value of the orthogonal hue is measured in accordance with the description in the example section described later. According to one embodiment of the present invention, it is possible to obtain a polarizing film in which the standard deviation of the b value of the orthogonal hue is 0.2 or less. The b values of Ty, Py, and orthogonal hue are measured by the following method.

The polarizing film was measured for MD transmittance and TD transmittance in the wavelength range of 380 to 780 nm using a spectrophotometer with an integrating sphere [“V7100” manufactured by JASCO Corporation], 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 are 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 correction single transmittance (Ty), the visibility correction polarization degree (Py), and the b value of the orthogonal hue are obtained.

Moreover, according to the above-mentioned method, the content of iodine (I) at 10 measurement points in the width direction satisfies the following conditions i) and ii) at the same time, and there is little variation in the content of iodine (I). A polarizing film can be obtained.
i) The average content of iodine (I) at 10 measurement points is 1.35% by mass or more.
ii) The difference between the maximum value and the minimum value of the iodine (I) content at 10 measurement points is 0.60% by mass or less.
The 10 measurement points are not limited as long as the measurement points are included in each of the sections obtained by dividing the entire width in the width direction into 10 parts, and 10 measurement points satisfying the conditions i) and ii) at the same time. If there is a combination, the polarizing film satisfies the conditions i) and ii) at the same time. Usually, the content of iodine (I) does not fluctuate greatly in each region in which the entire width in the width direction is divided into 10 equal parts. Therefore, the conditions of i) and ii) described above are applied to any combination of 10 points. If not satisfied, it can be considered that there is no combination of 10 points that simultaneously satisfy the conditions i) and ii). In addition, content (mass%) of iodine (I) in a polarizing film is based on the analysis result by a fluorescent X ray analysis as described in an Example.

  According to the above-mentioned method, it is possible to obtain a polarizing film having an average iodine concentration at 10 measurement points of 1.65% by mass or more, further 1.70% by mass or more and satisfying the above condition i). it can. Furthermore, according to the above method, the difference between the maximum value and the minimum value of iodine concentration at 10 measurement points is 0.50% by mass or less, further 0.45% by mass or less, and the above condition ii) is satisfied. A polarizing film that satisfies the requirements can also be obtained. The width | variety of the polarizing film of this invention is 50 mm-5000 mm, for example, Preferably it is 150 mm-4000 mm.

  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.

<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 width of 550 mm and 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 / 3.8 / 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 / 3.8 / 100 (weight ratio) in 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, with respect to the film having a width of 280 mm that has been drawn out from the second crosslinking bath 17b and passed through the nip roll 53b, the film is disposed at the center in the width direction of the film so as to be substantially parallel to the width direction of the film. Irradiation length (length in the width direction of the heater heating part) 230 mm electromagnetic wave irradiator (fast response medium wavelength infrared heater (FRMW heater), product name: Golden 8 Medium-wave fast response twin tube emitter, manufactured by Heraeus, heat source temperature An electromagnetic wave radiation outlet was disposed at a position 5 cm away from the surface of the film at 1600 ° C. and a maximum energy density of 150 kW / m ² ), and the electromagnetic wave was irradiated at an output of 50% with respect to the maximum irradiation output of the electromagnetic wave irradiation device.

The irradiation heat amount of electromagnetic waves per unit volume in a region having a width of 230 mm centering on the center in the width direction of the film (a region having a width of 82% with respect to the total width) was 1020 J / cm ³ . On the other hand, since the irradiation length of the electromagnetic wave irradiator was shorter than the length in the width direction of the film, the electromagnetic wave was not irradiated near the end of the film. The irradiation heat quantity of the electromagnetic wave per unit volume in the 0 mm region from the end of the film was 0 J / cm ³ . In addition, the irradiation heat amount of the electromagnetic wave per unit film volume was calculated by the following formula.
(Irradiation heat amount 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.

<Comparative Example 1>
A polarizing film was obtained in the same manner as in Example 1 except that the electromagnetic wave irradiation step was not performed. The thickness of the obtained polarizing film was 23 μm.

<Comparative example 2>
With respect to the film that has passed from the second crosslinking bath 17b and passed through the nip roll 53b, the irradiation length in the width direction of the film (of the heater heating section) is arranged at the center in the width direction of the film so as to be substantially parallel to the width direction of the film. Electromagnetic irradiator with a length of 400 mm (fast response medium wavelength infrared heater (FRMW heater), product name: Golden 8 Medium-wave fast response twin tube emitter, manufactured by Heraeus, heat source temperature 1600 ° C., maximum energy density 150 kW / M ² ), and a polarizing film was obtained in the same manner as in Example 1 except that the electromagnetic wave was irradiated at an output of 40%. In the entire region in the width direction of the film, the heat of irradiation of electromagnetic waves per unit volume was 820 J / cm ³ . The thickness of the obtained polarizing film was 23 μm.

[Evaluation of Polarizing Films of Example 1, Comparative Example 1 and Comparative Example 2]
(A) Measurement of polarization degree and b value of orthogonal hue For the polarizing films obtained in Example 1, Comparative Example 1 and Comparative Example 2, 15 measurement points in the width direction were determined at arbitrary positions in the longitudinal direction. Then, based on the above method, the visibility correction polarization degree (Py) and the b value of the orthogonal hue were obtained. The 15 measurement points are determined so that the measurement points at both ends in the width direction are at a distance of 10 mm from the end of the film, and the adjacent measurement points are equally spaced between the measurement points at both ends. The remaining 13 measurement points were determined, and the visibility correction polarization degree (Py) and the b value of the orthogonal hue were obtained at a total of 15 measurement points (measurement points 1 to 15). Table 2 shows the measurement results.

  FIG. 3 is a graph in which the measurement results of Py shown in Table 2 are plotted. FIG. 4 is a graph plotting measurement results of b values of orthogonal hues shown in Table 2. Table 3 shows the results of calculating the average value of the visibility correction polarization degree (Py) and the orthogonal hue b value, the standard deviation, and the difference between the maximum value and the minimum value based on the measurement results shown in Table 2.

  As shown in Table 3, in the polarizing film of Example 1, the b value variation of the orthogonal hue in the width direction was reduced as compared with Comparative Examples 1 and 2, and Py was larger and orthogonal than Comparative Example 1. The b value of the hue was small and the optical properties were excellent.

<Example 2>
The polarizing film of Example 2 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 width of 2590 mm and a thickness of 45 μm [trade name “Kuraray Vinylon VF-PE # 4500” 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 28 ° C. for a residence time of 56 seconds (swelling step). Thereafter, the film drawn out from the swelling bath is immersed in a dyeing bath at 30 ° C. containing iodine in which potassium iodide / boric acid / water is 1.5 / 0.3 / 100 (weight ratio) for a residence time of 80 seconds. (Dyeing process). Next, the film drawn from the dyeing bath is immersed in a first crosslinking bath at 55.5 ° C. in which potassium iodide / boric acid / water is 11.3 / 2.9 / 100 (weight ratio) with a residence time of 34 seconds. Subsequently, it was immersed in a second crosslinking bath at 40 ° C. in which potassium iodide / boric acid / water was 12/4/100 (weight ratio) with a residence time of 5 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 5.89 times.

Next, with respect to the film having a width of 1290 mm that has been drawn out from the second crosslinking bath 17b and passed through the nip roll 53b, the film is disposed at the center in the width direction of the film so as to be substantially parallel to the width direction of the film. Irradiation length (length in the width direction of the heater heating part) 830 mm electromagnetic wave irradiator (fast response medium wavelength infrared heater (FRMW heater), product name: Golden 8 Medium-wave fast response twin tube emitter, manufactured by Heraeus, heat source temperature An electromagnetic wave emission port was arranged at a position 5 cm away from the surface of the film at 1600 ° C. and a maximum energy density of 150 kW / m ² ), and an electromagnetic wave was irradiated at an output of 65%.

The irradiation heat amount of electromagnetic waves per unit volume in a region of 830 mm in width centering on the center in the width direction of the film (region having a width of 64% with respect to the total width) was 2310 J / cm ³ . On the other hand, since the irradiation length of the electromagnetic wave irradiator was shorter than the length in the width direction of the film, the electromagnetic wave was not irradiated near the end of the film. The irradiation heat quantity of the electromagnetic wave per unit volume in the 0 mm region from the end of the film was 0 J / cm ³ . In addition, the irradiation heat amount of the electromagnetic wave per unit film volume was calculated by the following formula.
(Irradiation heat amount 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 10 ° C. for a residence time of 5 seconds (cleaning step). Thereafter, the film was dried at a temperature of 88 ° C. in the drying furnace 21 to obtain a polarizing film. The obtained polarizing film had a thickness of 18 μm and a width of 1080 mm.

<Example 3>
A polarizing film was obtained in the same manner as in Example 2, except that the output was 35% and the electromagnetic wave irradiation heat amount in the electromagnetic wave irradiation step was 1240 J / cm ³ . The obtained polarizing film had a thickness of 18 μm and a width of 1080 mm.

<Comparative Example 3>
A polarizing film was obtained in the same manner as in Example 2 except that the electromagnetic wave irradiation step was not performed. The obtained polarizing film had a thickness of 18 μm and a width of 1080 mm.

[Evaluation of polarizing films of Example 2, Example 3 and Comparative Example 3]
(B) Measurement of Content of Iodine (I) About the polarizing films obtained in Example 2, Example 3 and Comparative Example 3, at arbitrary positions in the longitudinal direction, 10 measurement points (measurement points in the width direction) 1-10) was determined, and the iodine concentration was measured at each measurement point based on the following method. The 10 measurement points are determined so that the measurement points at both ends in the width direction are at a distance of 10 mm from the end of the film, and the adjacent measurement points are equally spaced between the measurement points at both ends. The remaining 8 measurement points were determined. The determined ten measurement points are measurement points included in each section of the width 108 mm obtained by dividing the total width 1080 mm in the width direction into ten equal parts.

The iodine (I) content was measured by fluorescent X-ray analysis.
Measuring device: X-ray fluorescence analyzer (device name: AXIOS, manufactured by PANalytical)
X-ray light source: Rh
Output: 30kV, 100mA
Measurement diameter: 27mmφ
Measurement method: 0.15 g of a polarizing film was collected so as to include each measurement point, each sample was dissolved in 20 ml of pure water, sealed, heated to 90 ° C., and the polarizing film was dissolved to obtain a measurement solution. The measurement result was compared with a calibration curve prepared with a standard solution, and the iodine concentration in the solution was calculated. From the obtained iodine concentration, it was converted into the weight of the polarizing film and defined as the iodine content (mass%). Table 4 shows the measurement results.

  As shown in Table 4, in Examples 2 and 3, the average value of the content of iodine (I) is 1.35% by mass or more, and the content of iodine (I) at 10 measurement points A polarizing film having a difference between the maximum value and the minimum value of 0.60% by mass or less was obtained.

  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 (12)

A method for producing a polarizing film 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 crosslinking the polyvinyl alcohol-based resin film after the dyeing step with a crosslinking agent;
An electromagnetic wave irradiation step of irradiating the polyvinyl alcohol-based resin film after the crosslinking step with an electromagnetic wave containing infrared;
A washing step of washing the polyvinyl alcohol-based resin film after irradiating the electromagnetic wave,
The said electromagnetic wave irradiation process WHEREIN: The manufacturing method of a polarizing film with which the irradiation heat amount per unit volume of the said electromagnetic wave of the said polyvinyl alcohol-type resin film has distribution in the width direction.   In the electromagnetic wave irradiation step, the irradiation heat amount per unit volume of the electromagnetic wave in the first region including the center and not including the end in the width direction of the polyvinyl alcohol-based resin film includes the end and does not include the center. The manufacturing method of the polarizing film of Claim 1 which is larger than the irradiation heat amount per unit volume of the said electromagnetic wave in a area | region. ^3. The polarized light according to claim 2, wherein, in the infrared electromagnetic wave irradiation step, the heat radiation amount of the electromagnetic wave infrared ray in the first region is 100 J / cm ³ or more and 50 kJ / cm ³ or less per unit volume of the polyvinyl alcohol-based resin film. A method for producing a film.   The polarizing film according to any one of claims 1 to 3, wherein in the electromagnetic wave irradiation step, an electromagnetic wave having a ratio of infrared radiation energy having a wavelength of more than 2 µm and not more than 4 µm is 25% or more of the total radiation energy. Production method.   The said crosslinking agent is a manufacturing method of the polarizing film of any one of Claims 1-4 containing a boron compound.   The said crosslinking process is a manufacturing method of the polarizing film of any one of Claims 1-5 which is a process of immersing the said polyvinyl alcohol-type resin film in the crosslinking bath which consists of the aqueous solution of the said crosslinking agent.   The manufacturing method of the polarizing film of Claim 6 which further includes the liquid removal process of removing the said aqueous solution adhering to the surface of the said polyvinyl alcohol-type resin film after the said crosslinking process and before irradiating the said electromagnetic wave. . A manufacturing apparatus for manufacturing a polarizing film 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 for cross-linking the polyvinyl alcohol-based resin film after the dyeing treatment with a cross-linking agent;
An electromagnetic wave irradiation part for irradiating the polyvinyl alcohol-based resin film after the crosslinking treatment with an electromagnetic wave containing infrared;
A washing section for washing the polyvinyl alcohol-based resin film after being irradiated with the electromagnetic wave,
The said electromagnetic wave irradiation part is a manufacturing apparatus of the polarizing film which irradiates the said electromagnetic wave so that the irradiation heat amount per unit volume of the said electromagnetic wave of the said polyvinyl alcohol-type resin film has distribution in the width direction.   The manufacturing method of the polarizing film of Claim 2 or 3 which irradiates an electromagnetic wave only to the said 1st area | region in the said electromagnetic wave irradiation process.   The manufacturing method of the polarizing film of Claim 9 whose width | variety of the said 1st area | region with respect to the full width of the said polyvinyl alcohol-type resin film is 60 to 90%. The average value of iodine (I) content at 10 measurement points in the width direction is 1.35% by mass or more, and the maximum and minimum values of iodine (I) content at the 10 measurement points The difference in value is 0.60% by mass
The ten measurement points are polarizing films, each being a measurement point included in a section obtained by dividing the entire width in the width direction into ten equal parts. The polarizing film of Claim 11 whose average value of content of iodine (I) in the 10 measurement points is 1.65% by mass or more.