TW201815918A - Method for manufacturing polarizing film, manufacturing apparatus and polarizing film - Google Patents

Abstract

An object of the present invention is to provide a method for manufacturing polarizing film that reduces variations in properties of polarizing film, and an apparatus for manufacturing the same. A solution for resolving the object is a method for manufacturing a polarizing film from a polyvinyl alcohol-based resin film, which comprises: 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 rays, and a washing step of washing the polyvinyl alcohol-based resin film having been irradiated with the electromagnetic wave; wherein in the electromagnetic wave irradiation step, the amount of heat irradiated per unit volume of the electromagnetic wave in the polyvinyl alcohol-based resin film has a distribution in the width direction.

Description

   Manufacturing method, manufacturing device and polarizing film of polarizing film   

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

The polarizing plate is widely used as a polarizing element in an image display device such as a liquid crystal display device. A polarizing plate is generally constituted by bonding a transparent resin film (protective film, etc.) to one or both sides of the polarizing film using an adhesive or the like.

The polarizing film is mainly a immersion film composed of a polyvinyl alcohol-based resin, and is immersed in a dyeing bath containing a dichroic pigment containing iodine and the like, and then immersed in a crosslinking bath containing a crosslinking agent containing boric acid and the like Processing, etc., and the film is produced by uniaxial stretching at any one time. Uniaxial stretching refers to dry stretching in the air and wet stretching in liquids such as the dyeing bath and cross-linking bath.

Conventionally, in the manufacturing method of a polarizing film, various methods are considered in order to improve the characteristic of a polarizing film. Japanese Patent Application Laid-Open No. 2013-148806 (Patent Document 1) describes a method of providing a primary drying step for drying a polyvinyl alcohol-based resin film between a boric acid treatment step and a water washing step, thereby making it possible to improve the penetration of light. Hue, that is, close to the content of neutral gray.

    [Prior technical literature]         [Patent Literature]    

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

When the present inventors cut a sample from a polarizing film and measured the characteristics, they found that even when a sample is cut from a polarizing film obtained by the same manufacturing method, there is a problem that the characteristics may be greatly different depending on the sample. . An object of the present invention is to provide a method for producing a polarizing film that reduces the variation in characteristics of the polarizing film, and an apparatus for producing the same. Another object of the present invention is to provide a polarizing film with uniform characteristics in the width direction.

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

[1] A method for manufacturing a polarizing film, which is a method for manufacturing a polarizing film from a polyvinyl alcohol-based resin film, comprising the following steps: a dyeing step of dyeing the polyvinyl alcohol-based resin film with a dichroic dye, A cross-linking step of cross-linking the polyvinyl alcohol-based resin film after the dyeing step with a cross-linking agent, and an electromagnetic wave irradiation step of irradiating electromagnetic waves including infrared rays on the polyvinyl alcohol-based resin film after the crosslinking step And a washing step of washing the polyvinyl alcohol-based resin film after the electromagnetic wave is irradiated; in the electromagnetic wave irradiation step, the irradiation heat of the electromagnetic wave per unit volume of the polyvinyl alcohol-based resin film is in a width direction With distribution.

[2] The method for producing a polarizing film according to [1], wherein in the electromagnetic wave irradiation step, in the width direction of the polyvinyl alcohol-based resin film, the first region including the center and not including the end portion is included in the first region. The radiation heat per unit volume of the electromagnetic wave is greater than the radiation heat per unit volume of the electromagnetic wave in the second region including the end portion and excluding the center.

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

[4] The method for producing a polarizing film according to any one of [1] to [3], wherein in the electromagnetic wave irradiation step, the radiated energy of infrared rays having a wavelength exceeding 2 μm and having a wavelength of 4 μm or less in the electromagnetic wave irradiation step The ratio is more than 25% of the total radiation energy.

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

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

[7] The method for producing a polarizing film according to [6], further comprising: removing the aqueous solution attached to a surface of the polyvinyl alcohol-based resin film after the crosslinking treatment and before the electromagnetic wave is irradiated.液 步骤。 Liquid steps.

[8] A manufacturing apparatus for a polarizing film, which is a manufacturing apparatus for manufacturing a polarizing film from a polyvinyl alcohol-based resin film, and includes a dyeing section that dyes the polyvinyl alcohol-based resin film with a dichroic dye, and A crosslinking agent that cross-links the polyvinyl alcohol-based resin film after the dyeing treatment, and irradiates an electromagnetic wave including infrared rays to the electromagnetic wave-irradiation portion of the polyvinyl alcohol-based resin film after the crosslinking treatment; And a cleaning section for cleaning the polyvinyl alcohol-based resin film after the electromagnetic wave is irradiated; the electromagnetic wave irradiating section is configured to radiate heat of the electromagnetic wave per unit volume of the polyvinyl alcohol-based resin film in a width direction; Method, irradiating the electromagnetic wave.

[9] The method for producing a polarizing film according to [2] or [3], wherein in the electromagnetic wave irradiation step, electromagnetic waves are irradiated only to the first region.

[10] The method for producing a polarizing film according to [9], wherein a width of the first region is 60 to 90% with respect to a full width of the polyvinyl alcohol-based resin film.

[11] A polarizing film, the average value of the content of iodine (I) at 10 measurement points in the width direction is 1.35 mass% or more, and the maximum and minimum values of the content of iodine (I) at the 10 measurement points The difference in the values is 0.60% by mass or less; the above-mentioned 10 measurement points are measurement points included in an interval that divides the full width in the width direction into 10 equal divisions.

[12] The polarizing film according to [11], wherein the average value of the content of iodine (I) at the above 10 measurement points is 1.65% by mass or more.

According to the present invention, it is possible to provide a manufacturing method and a manufacturing apparatus of a polarizing film that reduce variation in characteristics of the polarizing film. In addition, according to the present invention, a polarizing film with uniform characteristics in the width direction can be provided.

10‧‧‧ embryonic membrane made of polyvinyl alcohol resin

11‧‧‧ embryo membrane roll

13‧‧‧Swelling bath

15‧‧‧ Dyeing bath

17a‧‧‧The first cross-linking bath

17b‧‧‧ 2nd Crosslinking Bath

19‧‧‧washing bath

21‧‧‧ drying furnace

23‧‧‧Polarizing Film

30 to 48, 60, 61‧‧‧ guide rollers

50 to 52, 53a, 53b, 54, 55, ‧‧‧ rolls

71‧‧‧ electromagnetic wave irradiation section

FIG. 1 is a cross-sectional view schematically showing an example of a method for producing a polarizing film of the present invention and a device for producing a polarizing film used in the method.

Fig. 2 is a graph showing the radiation energy spectra of different types of electromagnetic wave irradiators.

FIG. 3 is a graph in which the measured values of Py in Example 1, Comparative Example 1, and Comparative Example 2 are plotted.

FIG. 4 is a graph plotting b values of orthogonal hue of Example 1, Comparative Example 1, and Comparative Example 2. FIG.

    <Manufacturing method of polarizing film>    

In the present invention, a polarizing film-based dichroic dye (iodine or dichroic dye) is adsorbed and aligned on a uniaxially stretched polyvinyl alcohol-based resin film. The polyvinyl alcohol-based resin constituting the polyvinyl alcohol-based resin film is usually obtained by saponifying a polyvinyl acetate resin. The saponification degree is usually about 85 mol% or more, preferably about 90 mol% or more, and particularly preferably about 99 mol% or more. The polyvinyl acetate-based resin may be, for example, a copolymer of vinyl acetate and other monomers copolymerizable with the vinyl acetate, in addition to polyvinyl acetate, which is a homopolymer of vinyl acetate. Examples of other copolymerizable monomers include unsaturated carboxylic acids, olefins, vinyl ethers, and unsaturated sulfonic acids. The degree of polymerization of the polyvinyl alcohol-based resin is usually about 1,000 to 10,000, and preferably about 1500 to 5,000.

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

In the present invention, the starting material for the production of a polarizing film is a non-stretched polyvinyl alcohol-based material having a thickness of 65 μm or less (for example, 60 μm or less), preferably 50 μm or less, particularly preferably 35 μm or less, and more preferably 30 μm or less. Resin film (embryonic membrane). Thereby, a polarizing film of a thin film with an increasing market demand can be obtained. The width of the embryonic membrane is not particularly limited, and may be, for example, 400 to 6000 mm, and preferably 2000 mm or more. In particular, when the width of the embryonic membrane is 2000 mm or more, the characteristics in the width direction of the polarizing film are likely to change, so the manufacturing method of the present invention is more effective. For the germ membrane system, for example, a roll of a polyvinyl alcohol-based resin film having a long shape and no stretch (embryonic membrane roll) is prepared.

In addition, the polyvinyl alcohol-based resin film used in the present invention may be a substrate film laminated thereon, that is, the polyvinyl alcohol-based resin film may be used as a substrate film and a polyethylene layered thereon. A laminated film of an alcohol-based resin film is prepared. In this case, the polyvinyl alcohol-based resin film can be produced by, for example, applying a coating solution containing a polyvinyl alcohol-based resin to at least one side 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 are light-transmitting thermoplastic resins, preferably films made of optically transparent thermoplastic resins, for example, chain polyolefin resins (such as polypropylene resins) and cyclic polyolefin resins ( (Pinene resin, etc.) polyolefin resins; cellulose triacetate, cellulose diacetate cellulose resins; polyethylene terephthalate, polybutylene terephthalate polyester Resins; polycarbonate resins; (meth) acrylic resins like methyl methacrylate resins; polystyrene resins; polyvinyl chloride resins; acrylonitrile-butadiene-styrene resins; Acrylonitrile-styrene resin; Polyvinyl acetate resin; Polyvinylidene chloride resin; Polyamine resin; Polyacetal resin; Modified polyphenylene ether resin; Polyfluorene resin; Polyether Fluorene resin; polyarylate resin; polyfluorene amine imine resin; polyfluorene resin.

The polarizing film is subjected to the following predetermined processing steps, that is, the long embryonic film is rolled out from the embryonic film roll while being continuously conveyed along the film conveying path of the polarizing film manufacturing apparatus, and is immersed in and accommodated in After the processing liquid of the processing tank (hereinafter also referred to as "processing bath") is pulled out, a drying step is performed, whereby a long polarizing film can be continuously manufactured. The processing step may be any method in which the processing liquid is brought into contact with the film for processing, and is not limited to a method of immersing the film in a processing bath. The processing liquid may be adhered to the surface of the film by spraying, inflowing, dropping, etc. To process the film. When the processing step is implemented by immersing the film in a processing bath, the processing bath for performing one processing step is not limited to one, and the film may be sequentially dipped in two or more processing baths to complete one. Processing steps.

Examples of the treatment liquid system include a swelling liquid, a dyeing liquid, a crosslinking liquid, a cleaning liquid, and the like. In addition, the above treatment steps are exemplified: a swelling step in which a swelling solution is brought into contact with the embryonic membrane to perform a swelling treatment, a dyeing step in which a dyeing solution is brought into contact with the swelling-treated film to perform a dyeing treatment, and a crosslinking solution is brought into contact with the dyeing treatment And a cleaning step of performing a crosslinking treatment on the film, and a cleaning step of contacting the cleaning solution with the film after the crosslinking treatment. In addition, between these series of processing steps (that is, before and / or during any one or more processing steps and / or during any one or more processing steps), uniaxial stretching is applied by wet or dry processing. Other processing steps can be added as needed.

When the inventors of the present invention examined the variation of the characteristics of the polarizing film, they found that the variation easily occurs in the width direction. The present inventors further studied and found that after the cross-linking treatment and before the cleaning treatment, by performing the electromagnetic wave irradiation step described below after irradiating the film with electromagnetic waves, the variation in characteristics in the width direction of the polarizing film can be suppressed. this invention.

An example of a method for manufacturing a polarizing film of the present invention will be described in detail below with reference to FIG. 1. FIG. 1 is a cross-sectional view schematically showing an example of a method for producing a polarizing film of the present invention and an apparatus for producing a polarizing film used in the method. The polarizing film manufacturing apparatus shown in FIG. 1 rolls an embryonic film (unstretched film) 10 composed of a polyvinyl alcohol resin continuously from the embryonic film roll 11 while conveying it along the film conveying path, and borrows This sequentially passes the swelling bath (swelling solution contained in the swelling tank) provided on the membrane transport path, the dyeing bath (staining solution contained in the dyeing tank) 15, and the first crosslinking bath (storing in the crosslinking tank). The first cross-linking liquid in the inside) 17a, the second cross-linking bath (the second cross-linking liquid contained in the cross-linking tank) 17b, and the washing bath (the cleansing liquid contained in the cleaning tank) 19, and finally pass through the drying furnace 21 constructs. For example, the obtained polarizing film 23 can be directly transported to a subsequent step of manufacturing a polarizing plate (a step of attaching a protective film to one or both sides of the polarizing film 23). The arrows in Fig. 1 show the transport direction of the film.

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

In addition to the above-mentioned processing bath, the film transport path of the polarizing film manufacturing device can also be arranged at an appropriate position: guide rollers 30 to 48, 60, 61 that can support the film to be transported or further change the film transport direction, or It is constructed by pressing and holding the film to be transported, and applying a driving force formed by the rotation to the film, or by further changing the film transport direction of the rolls 50 to 55. Guide rollers or rolls can be placed before and after each treatment bath or in the treatment bath, whereby the film can be introduced and immersed in the treatment bath, and the film can be pulled out of the treatment bath [refer to Figure 1]. For example, by providing one or more guide rollers in each processing bath and transporting the film along these guide rollers, the film can be immersed in each processing bath.

The polarizing film manufacturing apparatus shown in FIG. 1 is configured by arranging rolls (rolls 50 to 54) before and after each processing bath, thereby forming in any one or more processing baths between the rolls disposed before and after the processing bath. The peripheral speed is different, and the roll-to-roll stretching which performs the uniaxial stretching in the longitudinal direction is performed.

In the polarizing film manufacturing apparatus shown in FIG. 1, an electromagnetic wave irradiation section 71 is arranged on a transport path located downstream of the second crosslinking bath 17 b and upstream of the cleaning bath 19 to perform an electromagnetic wave irradiation step. Each processing step is described below.

    (Swelling step)    

The swelling step is performed for the purpose of removing impurities on the surface of the embryonic membrane 10, removing plasticizers in the embryonic membrane 10, imparting easy dyeability, and achieving plasticization of the embryonic membrane 10. The processing conditions are determined within a range in which the purpose can be achieved without causing extreme dissolution or devitrification of the germ membrane 10.

Referring to FIG. 1, in the swelling step, the germ membrane 10 is continuously rolled out from the germ membrane roll 11 while being transported along the film transport path, and the germ membrane 10 is immersed in the swelling bath 13 for a predetermined time, and then pulled out. Implementation. In the example shown in FIG. 1, from the time when the germ film 10 is rolled out to the time when the swelling bath 13 is immersed, the germ film 10 is transported along a film transport path constructed by the guide rollers 60 and 61 and the roller 50. In the swelling process, the film is transported along a film transport path constructed by the guide rollers 30 to 32 and the roll 51.

The swelling liquid of the swelling bath 13 can be used in addition to pure water: boric acid (Japanese Patent Application Laid-Open No. 10-153709) and chloride (Japanese Patent Application Laid-Open No. 06-281816) are added in a range of about 0.01 to 10% by weight. Bulletin), inorganic acids, inorganic salts, water-soluble organic solvents, alcohols, etc.

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

In the swelling treatment, a problem that the germ membrane 10 swells in the width direction tends to cause the film to wrinkle. One way to transport the film while removing the wrinkles is to use rolls with expansion functions such as expansion rollers, spiral rollers, and convex rollers, or cloth guides, curved stick openers, and tenter clips. Other pliers-like widening devices are used as guide rollers 30, 31 and / or 32. Another means to suppress the generation of wrinkles can be stretched. For example, a uniaxial stretching treatment can be applied to the swelling bath 13 by utilizing the difference in peripheral speed between the roll 50 and the roll 51.

In the swelling process, since the film also swells and expands in the transport direction of the film, in order to eliminate the sag of the film in the transport direction when the film is not actively stretched, it is preferable to use, for example, control Means such as the speed of the front and rear rolls 50, 51. In addition, for the purpose of stabilizing the transport of the membrane in the swelling bath 13, the water flow in the swelling bath 13 is controlled by rinsing in water, or an EPC device (Edge Position Control device: detects the end of the film and prevents the Snake device) etc. are also useful.

In the example shown in FIG. 1, the film pulled out from the swelling bath 13 is sequentially introduced into the dyeing bath 15 through the guide roller 32, the roll 51, and the guide roller 33.

    (Dyeing step)    

The dyeing step is performed for the purpose of adsorbing and aligning a dichroic dye to a polyvinyl alcohol-based resin film or the like after the swelling treatment. The processing conditions are determined within a range in which the purpose can be achieved, and in the range where no extreme dissolution or loss of devitrification of the membrane is generated. Referring to FIG. 1, the dyeing process can be carried along the film conveying path constructed by the rolls 51, the guide rolls 33 to 36 and the roll 52, and the swelling-treated film is immersed in the dyeing bath 15 (accommodated in the The treatment solution of the dyeing tank), and then pulled out for implementation. In order to improve the dyeability of the dichroic pigment, the film provided to the dyeing step is preferably a film subjected to at least a certain degree of uniaxial stretching treatment, or is preferably uniaxially stretched during the dyeing treatment. The treatment is used to replace the uniaxial stretching treatment before the dyeing treatment, or in addition to the uniaxial stretching treatment before the dyeing treatment, the uniaxial stretching treatment is also performed during the dyeing treatment.

When iodine is used as the dichroic pigment, the dyeing liquid of the dyeing bath 15 can be, for example, an aqueous solution having a concentration in a weight ratio of iodine / potassium iodide / water = about 0.003 to 0.3 / about 0.1 to 10/100. 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 by the point that boron is included. If the aqueous solution contains 100 parts by weight of water and about 0.003 parts by weight or more of iodine, the dye bath 15 can be considered. The temperature of the dyeing bath 15 when the film is impregnated is usually about 10 to 45 ° C, preferably about 10 to 40 ° C, particularly preferably about 20 to 35 ° C, and the time of the film soaking is usually about 30 to 600 seconds, preferably about 60 to 300 seconds.

When a water-soluble dichroic dye is used as the dichroic dye, for example, an aqueous solution of the dichroic dye / water = approximately 0.001 to 0.1 / 100 can be used as the coloring solution of the dyeing bath 15 in a weight ratio. In the dyeing bath 15, dyeing auxiliary agents and the like can coexist, and for example, an inorganic salt such as sodium sulfate and a surfactant can be contained. A dichroic dye may be used individually by 1 type, or may use 2 or more types of dichroic dyes in combination. The temperature of the dyeing bath 15 when the film is immersed, for example, about 20 to 80 ° C, preferably about 30 to 70 ° C, and the immersion time of the film is usually about 30 to 600 seconds, preferably about 60 to 300 seconds.

As described above, in the dyeing step, the film can be uniaxially stretched in the dyeing bath 15. The uniaxial stretching of the film can be performed by a method such as forming a peripheral speed difference between the rolls 51 and the rolls 52 arranged in the front and rear of the dyeing bath 15.

In the dyeing process, the same as the swelling process, in order to remove the wrinkles of the film and transport the polyvinyl alcohol-based resin film, a roll having a widening function such as an expansion roll, a spiral roll, a convex roll, or a guide cloth can be used. Device, bent stick opener, other tentering device like tenter clamp, as the guide rollers 33, 34, 35 and / or 36. Another method for suppressing the generation of wrinkles is the same as the swelling treatment, and a stretching treatment can be applied.

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

    (Crosslinking step)    

The crosslinking step is a treatment performed for the purpose of achieving water resistance or hue adjustment (to prevent the film from being blue, etc.), etc., depending on the crosslinking. In the example shown in FIG. 1, two cross-linking baths are provided as cross-linking baths for performing the cross-linking step, and the first cross-linking step for the purpose of water resistance is performed in the first cross-linking bath 17a. The second crosslinking step 17b is performed in the second crosslinking bath 17b for the purpose of hue adjustment. Referring to FIG. 1, the first cross-linking step is carried along a film conveying path constructed by the roll 52, the guide rolls 37 to 40, and the roll 53 a, and the dyed film is dipped in the first time for a predetermined time The cross-linking bath 17a (the first cross-linking liquid contained in the cross-linking tank) is then pulled out and implemented. The second cross-linking step is carried along the film transport path constructed by the rolls 53a, the guide rolls 41 to 44 and the rolls 53b, and the film after the first cross-linking step is immersed in the second cross-linking at a predetermined time. The bath 17b (the second cross-linking liquid stored in the cross-linking tank) is then pulled out to carry out. Hereinafter, when the cross-linking bath is referred to, both the first cross-linking bath 17a and the second cross-linking bath 17b are included, and when the cross-linking liquid is referred to, the first cross-linking liquid and the second cross-linking liquid are included.

As the crosslinking solution, a solution in which a crosslinking agent is dissolved in a solvent can be used. Examples of the cross-linking agent include boron compounds such as boric acid and borax, or glyoxal and glutaraldehyde. These may be used singly or in combination of two or more. As the solvent, for example, water may be used, and it may further contain an organic solvent compatible with water. Although the concentration of the crosslinking agent in the crosslinking solution is not limited thereto, it is preferably in the range of 1 to 20% by weight, and particularly preferably 6 to 15% by weight.

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

In the cross-linking treatment, the concentrations of boric acid and iodide, and the temperature of the cross-linking bath 17 may be appropriately changed according to the purpose. For example, when the purpose of the cross-linking treatment is the first cross-linking solution that is water-resistant based on the cross-linking, the concentration may be boric acid / iodide / water = 3 to 10/1 to 20/100 by weight ratio. Aqueous solution. If necessary, other cross-linking agents can be used instead of boric acid, or boric acid can be used in combination with other cross-linking agents. The temperature of the first cross-linking bath 17a when the film is impregnated is usually about 50 to 70 ° C, preferably 53 to 65 ° C. The immersion time of the film is usually 10 to 600 seconds, preferably 20 to 300 seconds, particularly preferably For 20 to 200 seconds. In addition, when the polyvinyl alcohol-based resin film stretched in advance before the swelling treatment is sequentially subjected to a dyeing treatment and a first crosslinking treatment, the temperature of the first crosslinking bath 17a is usually about 50 to 85 ° C, preferably 55 to 80 ° C.

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

The crosslinking treatment may be performed a plurality of times, usually 2 to 5 times. At this time, 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 achieving water resistance based on the cross-linking and the cross-linking treatment for adjusting hue can be performed in a plurality of steps, respectively.

It is also possible to apply a uniaxial stretching treatment in the first cross-linking bath 17a using the peripheral speed difference between the roll 52 and the roll 53a. In addition, it is also possible to apply a uniaxial stretching treatment to the second crosslinking bath 17b by utilizing the peripheral speed difference between the rolls 53a and 53b.

In the cross-linking treatment, the same as the swelling treatment, in order to remove the wrinkles of the film and transport the polyvinyl alcohol-based resin film, a roll having a widening function such as an expansion roll, a spiral roll, a convex roll, or a guide cloth can be used. Device, bent stick opener, other tentering devices such as tenter clamps, as the guide rollers 38, 39, 40, 41, 42, 43 and / or 44. Another method for suppressing the generation of wrinkles is the same as the swelling treatment, and a stretching treatment can be applied.

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

    (Cleaning step)    

The example shown in FIG. 1 includes a cleaning step after the crosslinking step. The cleaning treatment is performed for the purpose of removing excess boric acid or iodine from the polyvinyl alcohol resin film. The washing step may be performed by immersing the polyvinyl alcohol-based resin film after the crosslinking treatment in the washing bath 19. In the cleaning step, the step of immersing the film in the cleaning bath 19 can also be replaced by spraying the cleaning solution onto the membrane by showering, or using the dipping and spraying of the cleaning bath to the cleaning bath 19 together.

FIG. 1 shows an example when a polyvinyl alcohol-based resin film is immersed in a cleaning bath 19 to perform a cleaning process. The temperature of the cleaning bath 19 in the cleaning process 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, for the purpose of removing the wrinkles of the film and transporting the polyvinyl alcohol-based resin film, an expansion roller such as an expansion roller, a spiral roller, or a convex roller, or a cloth guide device or a bending device can be used. As a guide roller 45, 46, 47, and / or 48, other tentering devices such as a stick opener and a tenter clamp are used. In addition, in the film cleaning process, a stretching process may be performed in order to suppress the occurrence of wrinkles.

    (Stretching step)    

As described above, the embryonic membrane 10 is applied between the above-mentioned series of processing steps (that is, before and after any one or more processing steps and / or during any one or more processing steps), and is uniaxially applied by wet or dry processing. Stretch processing. A specific method of uniaxial stretching may be, for example, forming a peripheral speed difference between two rolls constituting a film conveying path (for example, two rolls arranged before and after a processing bath), and performing roll uniaxial stretching between rolls. Stretching, or hot-roll stretching, tenter stretching, etc. described in Japanese Patent No. 2731813 is preferably stretching between rolls. The uniaxial stretching step may be performed multiple times from the embryonic membrane 10 to the time when the polarizing film 23 is obtained. As described above, the stretching treatment is also advantageous for suppressing the occurrence of wrinkles in the film.

The final cumulative stretching ratio of the polarizing film 23 based on the embryonic film 10 is usually about 4.5 to 7 times, preferably 5 to 6.5 times. The stretching step may be performed in any processing step. When the stretching processing is performed in two or more processing steps, the stretching step may be performed in any processing step.

    (Electromagnetic wave irradiation step)    

In the apparatus shown in FIG. 1, the film is pulled out from the second cross-linking bath 17b, and after passing through the roller 53b and before being immersed in the cleaning bath 19, the film is irradiated with electromagnetic waves (electromagnetic wave irradiation step). In the device shown in FIG. 1, electromagnetic waves are irradiated from the electromagnetic wave irradiation section 71. From the electromagnetic wave irradiation section, electromagnetic wave irradiation is performed so that the irradiation heat per unit volume of the polyvinyl alcohol-based resin film to be irradiated has a distribution in the width direction.

As an example of the distribution in the width direction, in the width direction, it can be divided into a first region including a center and not including an end portion, and a second region located on both sides of the first region and including an end and not including a center. In addition, in the first region and the second region, the amount of heat radiated by electromagnetic waves per unit volume is different. When comparing the first region and the second region that are distinguished as described above, the optical characteristics of equal colors tend to easily change. In the electromagnetic wave irradiation step, it is possible to suppress variations in optical characteristics by setting the irradiation heat amount per unit volume of electromagnetic waves in the first region to be larger than the irradiation heat amount per unit volume of electromagnetic waves in the second region. The difference in irradiation heat can be appropriately selected. For example, the irradiation heat in the first area can be more than twice that in the second area, or the first area can be irradiated with electromagnetic waves instead of the second area. Irradiation.

The ratio of the width of the first region to the value obtained by adding the widths of the two second regions can be set in a range of, for example, 10: 1 to 1:10. This ratio can be selected in accordance with the fluctuation conditions of the characteristics to be improved.

One of the factors that can change the optical characteristics is that in each of the above-mentioned processing steps, the treatment liquid is easier to infiltrate from the end surface than the surface of the polyvinyl alcohol-based resin film, so that the infiltration amount of the treatment liquid is near the end portion. There is a difference in the vicinity of the central part, which results in a difference in the degree of processing. In addition, one of the factors can be presumed to be that the thickness changes in the width direction upon stretching, and the processing degree in each processing step varies depending on the thickness. When examining this factor, it is not limited to the method of dividing the polyvinyl alcohol-based resin film into the "second region / first region / second region" in the width direction as described above, and it can also be divided into the first region and the There is more than one region between the second regions, and the irradiation heat of the electromagnetic wave per unit volume in each region is different.

Methods for radiating electromagnetic waves in a manner having a distribution in the width direction include: i) radiating the energy of electromagnetic waves radiated from the electromagnetic wave irradiating portion in the width direction, and ii) irradiating the electromagnetic waves The electromagnetic wave has a distribution pattern in the width direction, and a part or the like is absorbed by a mask or the like.

As an example of the specific method of i) described above, the electromagnetic wave irradiation area (heater heating portion) of the electromagnetic wave irradiation portion 71 can correspond to only a part of the width direction of the polyvinyl alcohol-based resin film, thereby irradiating the electromagnetic wave to The position of the electromagnetic wave radiating area, and at a position that does not correspond to the electromagnetic wave radiating area, the irradiation energy is not irradiated or the irradiation energy of the electromagnetic wave is reduced (sometimes, it is irradiated by the irradiation light diffusion), so as to have a distribution in the width direction Way to irradiate electromagnetic waves.

The present inventors have found that the irradiation of electromagnetic waves including infrared rays can affect the optical characteristics and the like of polarizing films, and thus completed the present invention. In particular, by radiating an electromagnetic wave having a ratio of radiant energy of infrared rays having a wavelength of more than 2 μm and less than 4 μm to 25% or more of the total radiant energy, the optical characteristics can be further improved. In one aspect of the present invention, by adjusting the irradiation heat amount per unit volume of electromagnetic waves in the first region to be larger than the irradiation heat amount per unit volume of electromagnetic waves in the second region, it is possible to suppress variations in optical characteristics of equal color. . In addition, at the same time, the hue can be improved to be close to neutral gray as a whole. As a characteristic that varies in the width direction, the characteristic of the first region is lower than the characteristic of the second region, and it is an optical characteristic that is colored and equal.

On the other hand, unlike the above characteristics, the characteristics with respect to the first region are higher than those with the second region. When electromagnetic wave irradiation is effective, in order to improve the variation of the characteristics, the second region is changed The amount of radiation heat per unit volume of the electromagnetic waves is adjusted to be greater than the amount of radiation heat per unit volume of the electromagnetic waves in the first region, which can improve the change in characteristics. In addition, when the applied characteristics are different due to the different wavelengths of the electromagnetic waves, the distribution of the irradiation heat can be adjusted for each wavelength region.

From the viewpoint of improving the variation of the optical characteristics of equal color, the ratio of the radiant energy of the infrared wave used in the electromagnetic wave irradiation step to a wavelength exceeding 2 μm and a wavelength of 4 μm or less is preferably 25% or more of the total radiant energy. It is more preferably 28% or more, and more preferably 35% or more. Such an electromagnetic wave is irradiated on the film in a manner having a distribution in the width direction, whereby the variation of the optical characteristics of the obtained polarizing film having the same color can be improved. In addition, the upper limit value of the ratio of the radiant energy of infrared rays exceeding 2 μm and having a wavelength of 4 μm or less is not particularly limited, and is, for example, 80% or less. Generally, an electromagnetic wave having a wavelength of 0.75 μm to 1000 μm is referred to as infrared rays.

In the electromagnetic wave irradiation step, the mechanism that can effectively improve the optical characteristics of the polarizing film by irradiating electromagnetic waves with a ratio of the radiation energy of infrared rays exceeding 2 μm and a wavelength of 4 μm or less to 25% or more of the total radiation energy is not clear, but It is speculated that by immobilizing molecules in the film excited by infrared light having a wavelength exceeding 2 μm and less than 4 μm, the immobilization of dichroic pigments such as iodine in the film after the cross-linking treatment can be promoted, and the polarization can be improved. Optical characteristics of the film, etc.

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

As shown in Table 1, short-wavelength infrared heaters (heat source temperature 2200 ° C), high-speed reaction medium-wavelength infrared heaters (heat source temperature 1600 ° C), carbon heaters (heat source temperature 1200 ° C), carbon heaters (heat source temperature 950 ° C) ), Medium-wavelength infrared heater (heat source temperature 900 ° C), since the ratio of the radiant energy of infrared rays with a wavelength exceeding 2 μm and less than 4 μm is 25% or more of the total radiant energy, it can be preferably used as an electromagnetic wave irradiation unit 71 electromagnetic wave irradiator. The electromagnetic wave irradiation section 71 may be configured by one electromagnetic wave irradiator, or may be configured by a plurality of electromagnetic wave irradiators. It is also possible to irradiate in a manner having a distribution in the width direction by adjusting the arrangement method of the plurality of electromagnetic wave irradiators. When composed of a plurality of electromagnetic wave irradiators, it is preferable that the radiation energy of infrared rays with a wavelength exceeding 2 μm and less than 4 μm emitted from the plurality of electromagnetic wave irradiators becomes a plurality of electromagnetic wave irradiators. Select a plurality of electromagnetic wave irradiators in such a way that the total radiation energy of the emitted electromagnetic waves is more than 25%. In addition, in FIG. 1, the electromagnetic wave irradiating section 71 is configured so that electromagnetic waves are irradiated to only one side of the film. However, a plurality of electromagnetic wave irradiators may be arranged so as to irradiate electromagnetic waves from both sides of the film. For example, electromagnetic waves may be irradiated from both sides in the first region, and electromagnetic waves may be irradiated from only one side in the second region, so that the radiation heat per unit volume in the width direction may be distributed.

In the electromagnetic wave irradiation step, the electromagnetic wave is preferably irradiated from the upper side in a direction perpendicular to the film surface. In addition, the distance between the electromagnetic wave emitting port of the electromagnetic wave irradiator in the electromagnetic wave irradiation section 71 and the film is preferably 2 to 40 cm, and more preferably 5 to 20 cm. However, the distance is preferably selected in consideration of the radiation energy of the electromagnetic wave radiated from the electromagnetic wave irradiator, or the surface temperature of the film. The temperature of the surface of the film during electromagnetic wave irradiation is preferably maintained at 25 to 90 ° C, and more preferably 30 to 80 ° C.

In the electromagnetic wave irradiation step, the irradiation heat of the electromagnetic wave per unit volume of the film can be generally set to be 100 J / cm ³ or more and 50 kJ / cm ³ or less. From the viewpoint of the optical characteristics of the polarizing film to enhance the view in the width direction of the largest irradiated area of the heat, it is preferable to 100J / cm ³ or more, and particularly preferably set to 500J / cm ³ or more, more preferably set to 1000J / cm ³ or more. In addition, from the viewpoint of suppressing the degradation of the film due to temperature rise, the irradiation heat per unit volume of the film is preferably set to 10 kJ / cm ³ or less, more preferably 5000 J / cm ³ or less, and more preferably 3000 J / cm ³ or less. Generally, the water content of the film is reduced in proportion to the amount of radiation of electromagnetic waves. Since the electromagnetic wave irradiation step of the present invention is not for the purpose of reducing the amount of water in the film, the amount of radiation can be appropriately selected, preferably within the above range. Choose appropriately. The area that has the largest amount of radiated heat in the width direction may be, for example, the first area including the center and not including the end portion.

In the present invention, by performing the electromagnetic wave irradiation step before the cleaning treatment, it is possible to suppress the variation of the characteristics of the obtained polarizing film. The electromagnetic wave irradiation step may be performed on the film immersed in at least one cross-linking bath. As shown in FIG. 1, it is not limited to the film immersion in all the cross-linking baths. That is, in the example shown in FIG. 1, an electromagnetic wave irradiation step may be performed on the film immersed in the first crosslinking bath and before the second crosslinking bath, or the film after immersed in the second crosslinking bath. The electromagnetic wave irradiation step is performed. However, by this electromagnetic wave irradiation step, the cross-linking of boric acid taken into the film can be performed by immersion in the crosslinking bath. It is preferable to efficiently perform cross-linking of boric acid and the like.

From the viewpoint of suppressing changes in optical characteristics, the electromagnetic wave irradiation is preferably performed within 10 seconds, and more preferably within 5 seconds, after the film is pulled out from the crosslinking bath. The shorter the time from when the cross-linking bath is drawn until the electromagnetic wave is irradiated, the more the optical characteristics of the polarizing film can be improved by the electromagnetic wave irradiation. In the electromagnetic wave irradiation step, the number of water molecules adhering to the surface of the film is preferably smaller. This is because when water molecules exist on the surface of the film, the water molecules on the surface of the film absorb infrared rays, which reduces the excitation effect of molecular motion in the film caused by electromagnetic wave irradiation. Shortly after being pulled out from the cross-linking bath, since the cross-linking liquid adheres to the surface of the film, it is preferable to provide a means for removing the liquid before the electromagnetic wave irradiation step. In Fig. 1, the roller 53b also has a function of a liquid removing means for removing the cross-linking liquid attached to the surface of the film. In addition to the liquid removing means, in addition to the roll, a means for blowing air to the film to remove the liquid, or a scraper that contacts the film to remove the liquid can also be used.

When the film processing speed is set to a high speed from an economical point of view, 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 irradiation heat may become insufficient. In response to this, by arranging a plurality of electromagnetic wave irradiators in parallel, sufficient radiation heat can be obtained.

In addition, the present inventors have found that the content of iodine (I) tends to change easily in the width direction of the polarizing film. The change in the iodine (I) content of the polarizing film is the cause of changes in optical characteristics such as the transmittance of monomers, and changes in durability. The present inventors have conducted intensive studies and found that by setting the irradiation heat per unit volume of electromagnetic waves in the first region to be larger than the irradiation heat per unit volume of electromagnetic waves in the second region, iodine (I ) Changes in content. For example, by irradiating electromagnetic waves only in the first region, it is possible to suppress fluctuations in the iodine (I) content. The width of the first region can be set to, for example, 5 to 95%, preferably 40 to 90%, and more preferably 60 to 90% based on the entire width of the polyvinyl alcohol-based resin film. In the electromagnetic wave irradiation step for the purpose of suppressing the fluctuation of the iodine (I) content, the above-mentioned explanation of the electromagnetic wave irradiation step for the purpose of suppressing the change of the characteristic may also be applied. In one form, the first region is located in a region centered on the center of the polyvinyl alcohol resin film, and the second region is equal in length in the width direction. The second region is located on both sides in the width direction of the first region. The first area and the second area.

    (Drying step)    

After the washing step, it is preferable to perform a treatment for drying the polyvinyl alcohol-based resin film. There is no particular limitation on the drying of the film, and the drying furnace 21 can be used as in the example shown in FIG. 1. The drying temperature is, for example, about 30 to 100 ° C, and the drying time is, for example, about 30 to 600 seconds. The process of drying a polyvinyl alcohol-type resin film can also be performed using a far-infrared heater. The thickness of the polarizing film 23 obtained in the above manner is, for example, about 5 to 30 μm.

    (Other processing steps for polyvinyl alcohol resin film)    

Processing other than the above processing may be added. Examples of additional treatments include: immersion treatment (color correction treatment) in which an iodide aqueous solution containing no boric acid is immersed after crosslinking treatment; and immersion treatment in an aqueous solution containing no boric acid and containing zinc chloride. (Zinc treatment).

    <Polarizing film>    

According to the method described above, a polarizing film with suppressed variation in characteristics in the width direction can be obtained. The obtained visual sensitivity correction monomer transmittance Ty of the obtained polarizing film, taking into consideration the balance of the visual sensitivity correction polarization Py, is preferably 40 to 47%, and particularly preferably 41 to 45%. The visual sensitivity correction polarization Py is preferably 99.9% or more, particularly preferably 99.95% or more. The larger the value, the better.

The b value of the orthogonal hue of the obtained polarizing film is preferably -3.0 to +0.5, and even more preferably -2.0 to 0. By setting this value, the orthogonal hue does not shift excessively to blue, but appears neutral gray. In addition, when the b value of the orthogonal hue is measured at a plurality of points in the width direction at an arbitrary position in the length direction, it is preferable that the variation in the measured value is small. Specifically, the measurement points at both ends in the width direction are determined at a distance of 0.5 to 50 mm from the end of the film, and between the measurement points at both ends so that the adjacent measurement points are equally spaced. When determining the remaining 13 measurement points and measuring the b value of the orthogonal hue with a total of 15 measurement points, the standard deviation is preferably 0.2 or less, and more preferably 0.1 or less. 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 of the items in the examples described later. According to one aspect of the present invention, a polarizing film having a standard value of b of orthogonal hue of 0.2 or less can be obtained. The b values of Ty, Py, and orthogonal hue are measured by the following methods.

For the polarizing film, the MD transmittance and TD transmittance in the range of wavelengths from 380 to 780 nm were measured using a spectrophotometer with a integrating sphere ["V7100" manufactured by JASCO Corporation] and according to the following formula: Cell penetration rate (%) = (MD + TD) / 2

Polarization (%) = {(MD-TD) / (MD + TD)} × 100 to calculate the monomer transmittance and polarization at each wavelength.

The "MD transmittance" is the transmittance when the direction of polarized light emitted from Glan-Thompsonson is parallel to the transmission axis of a polarizing film sample, and is expressed in the above formula as "MD". In addition, the "TD transmittance" is a transmittance when the direction of polarized light emitted from Glan-Thomson 稜鏡 is orthogonal to the transmission axis of a polarizing film sample. ". The obtained unit transmittance and polarization degree were measured in accordance with JIS Z8701: 1999 "Color display method-XYZ color system and X ₁₀ Y ₁₀ Z ₁₀ color system" with a 2 degree field of view (C light source). The visual sensitivity is corrected, and the b values of the visual sensitivity correction single transmittance (Ty), the visual sensitivity correction polarization (Py), and the orthogonal hue are obtained.

In addition, according to the method described above, a polarizing film with little variation in the iodine (I) content in which the iodine (I) content at the ten measurement points in the width direction simultaneously meets the conditions i) and ii) below can be obtained.

i) The average value of the content of iodine (I) at 10 measurement points is 1.35 mass% or more.

ii) The difference between the maximum value and the minimum value of the content of iodine (I) at 10 measurement points is 0.60% by mass or less.

The above 10 measurement points are not particularly limited as long as they are included in the interval that divides the full width in the width direction into 10 equal divisions. If there are conditions that simultaneously satisfy the conditions i) and ii) above A combination of 10 points is a polarizing film that satisfies the conditions i) and ii). Generally, in each region that divides the full width in the width direction into 10 equal parts, the content of iodine (I) does not change significantly. Therefore, for any combination of 10 points, the In the case of conditions, it can be considered that there is no combination of 10 points that simultaneously satisfy the conditions of i) and ii). The content (% by mass) of iodine (I) in the polarizing film is an analysis result based on fluorescent X-ray analysis, as described in the examples.

According to the above method, if the average value of the iodine concentration at 10 measurement points is 1.65% by mass or more, and further 1.70% by mass or more, a polarizing film that satisfies the condition i) can be obtained. Furthermore, according to the method described above, if the difference between the maximum value and the minimum value of iodine concentration at 10 measurement points is 0.50% by mass or less, and further 0.45% by mass or less, a polarizing film that satisfies the condition ii) can be obtained. The width of the polarizing film of the present invention is, for example, 50 mm to 5000 mm, and preferably 150 to 4000 mm.

The obtained polarizing film can also be configured as a roll that is sequentially wound on a winding roll, or directly provided to the polarizing plate production step without winding (a protective film or the like is laminated on one or both sides of the polarizing film) The steps).

    <Polarizer>    

A polarizing plate can be obtained by bonding a protective film on at least one side of the polarizing film manufactured above through an adhesive. Examples of the protective film include a film composed of cellulose triacetate or cellulose diacetate resin such as cellulose diacetate; polyethylene terephthalate, polyethylene naphthalate, and polyterephthalate. Films made of polyester resins such as succinate; polycarbonate resin films and cycloolefin resin films; acrylic resin films; films made of polypropylene resins and chain polyolefin resins .

In order to improve the adhesion between the polarizing film and the protective film, the bonding surface of the polarizing film and / or the protective film may be subjected to corona treatment, flame treatment, plasma treatment, ultraviolet irradiation, primer coating treatment, saponification treatment, etc. Surface treatment. Examples of the adhesive used for the bonding of the polarizing film and the protective film include an active energy ray-curable adhesive such as an ultraviolet-curable adhesive, an aqueous solution of a polyvinyl alcohol resin, or a cross-linking agent prepared here. Aqueous solution, urethane-based emulsification adhesive, water-based adhesive. The ultraviolet-curable adhesive may be a mixture of an acrylic compound and a photoradical polymerization initiator, or a mixture of an epoxy compound and a photocationic polymerization initiator. In addition, a cationic polymerizable epoxy compound and a radical polymerizable acrylic compound may be used in combination, and a photocationic polymerization initiator and a photoradical polymerization initiator may be used in combination as the initiator.

    (Example)    

The following is a more detailed description of the present invention by showing examples, but the present invention is not limited to these examples.

    <Example 1>    

The polarizing film of Example 1 was produced from a polyvinyl alcohol-based resin film using the production apparatus shown in FIG. 1. Specifically, a long polyvinyl alcohol (PVA) embryo membrane having a width of 550 mm and a thickness of 60 μm was rolled out from a roll [Kuraray Vinylon VF-PE # 6000, a trade name manufactured by Kuraray Co., Ltd., and the average degree of polymerization was 2400. , Saponification degree of 99.9 mol% or more], continuously transported, and immersed in a swelling bath made of pure water at 30 ° C for a retention time of 79 seconds (swelling step). The film pulled out from the swelling bath was then immersed in a dyeing bath containing potassium iodide / boric acid / water at a temperature of 1 / 0.3 / 100 (weight ratio) at 30 ° C. (dyeing step) at a retention time of 123 seconds. Next, the film pulled out from the dyeing bath was immersed in a first cross-linking bath at 53 ° C with potassium iodide / boric acid / water 11 / 3.8 / 100 (weight ratio) for a retention time of 44 seconds, followed by immersion for a retention time of 6 seconds. The second cross-linking bath (cross-linking step) was performed at 40 ° C where potassium iodide / boric acid / water was 11 / 3.8 / 100 (weight ratio). In the dyeing step and the crosslinking step, longitudinal uniaxial stretching is performed by stretching between rolls in a bath. The total stretching ratio based on the embryonic membrane was set to 5.65 times.

Then, the irradiation length in the film width direction of the central portion of the width direction of the film was drawn so as to be approximately parallel to the width direction of the film drawn from the second crosslinking bath 17b and passed through the roller 53b with a width of 280 mm. (The length in the width direction of the heater heating portion) An electromagnetic wave irradiator (FRMW heater) with a high speed of 230 mm, product name: Golden 8 Medium-wave fast response twin tube emitter, manufactured by Heraeus, The heat source temperature is 1600 ° C and the maximum energy density is 150 kW / cm ² ). An electromagnetic wave emitting port is arranged at a distance of 5 cm from the surface of the film, and the electromagnetic wave is irradiated with a maximum irradiation output of 50%.

The radiated heat per unit volume of electromagnetic waves in a 230 mm wide area (with respect to a width area of 82% of the full width) centered on the center in the width direction of the film was 1020 J / cm ³ . On the other hand, since the irradiation length of the electromagnetic wave irradiator is shorter than the length in the width direction of the film, electromagnetic waves are not irradiated near the end of the film. The irradiation heat per unit volume of electromagnetic waves in a region of 0 mm from the end of the film was 0 J / cm ³ . The amount of radiation of electromagnetic waves per unit volume of the film is calculated by the following formula. (Radiation heat per unit volume of the electromagnetic wave of the film) = ((maximum energy density) × (surface area of the heater heating section) × output (%) / (electromagnetic wave irradiation area)) × (electromagnetic wave irradiation time) ÷ (film thickness)

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

The time required after the second cross-linking bath 17b was pulled out until the film was transported and reached the irradiation position of the electromagnetic wave irradiator and the electromagnetic wave was irradiated 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 retention time of 3 seconds (cleaning step). Then, the film was dried in a drying furnace 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 by performing the same operation 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>    

For the film drawn from the second cross-linking bath 17b and passed through the roller 53b, the irradiation length in the film width direction (heater heating section) arranged at the center of the width direction of the film approximately parallel to the width direction of the film is used The length in the width direction) is an electromagnetic wave irradiator (FRMW heater with high-speed response, 400mm), product name: Golden 8 Medium-wave fast response twin tube emitter, manufactured by Heraeus, heat source temperature 1600 ° C, The maximum energy density was 150 kW / cm ² ), and irradiation of electromagnetic waves was performed at an output of 40%. The same operation as in Example 1 was performed to obtain a polarizing film. In the entire area in the width direction of the film, the irradiation heat of the electromagnetic wave per unit volume of the electromagnetic wave 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 b value of polarization and orthogonal hue    

For the polarizing films obtained in Example 1, Comparative Example 1, and Comparative Example 2, 15 measurement points were determined in the width direction at any position in the length direction, and the visual sensitivity correction polarization degree was obtained according to the above method ( Py) and the b value of the orthogonal hue. The 15-point measurement points are determined at the two ends in the width direction at a distance of 10 mm from the end of the film, and between the two measurement points so that adjacent measurement points are equally spaced. In this way, the remaining 13 measurement points are determined, and a total of 15 measurement points (measurement points 1 to 15) are used to obtain the b value of the visual sensitivity correction polarization (Py) and the orthogonal hue. 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 b values of the orthogonal hue shown in Table 2. Table 3 shows the results of the visual sensitivity correction polarization (Py) and the average, standard deviation, and difference between the maximum and minimum values of the b-values of the orthogonal hue based on the measurement results shown in Table 2.

As shown in Table 3, the change in b value of the orthogonal hue in the width direction of the polarizing film of Example 1 is lower than that of Comparative Examples 1 and 2, and Py is larger than that of Comparative Example 1. In addition, the value of b value of the orthogonal hue is small, and has excellent optical characteristics.

    <Example 2>    

The polarizing film of Example 2 was manufactured from a polyvinyl alcohol-based resin film using the manufacturing apparatus shown in FIG. 1. Specifically, a strip-shaped polyvinyl alcohol (PVA) embryo membrane having a width of 2590 mm and a thickness of 45 μm was rolled out from a roll [Kuraray Vinylon VF-PE # 4500, trade name manufactured by Kuraray Co., Ltd., and an average degree of polymerization was 2400 , Saponification degree of 99.9 mol% or more], continuously transported, and immersed in a swelling bath composed of pure water at 28 ° C for a retention time of 56 seconds (swelling step). Then, the film pulled out from the swelling bath was immersed in a 30 ° C dyeing bath containing potassium iodide / boric acid / water at a weight ratio of 1.5 / 0.3 / 100 (weight ratio) at a retention time of 80 seconds (dyeing step). Next, the film pulled out from the dyeing bath was immersed in a first cross-linking bath at 55.5 ° C. with potassium iodide / boric acid / water 11.3 / 2.9 / 100 (weight ratio) for a retention time of 34 seconds, followed by immersion for a retention time of 5 seconds. The second crosslinking bath (cross-linking step) was performed at 40 ° C with potassium iodide / boric acid / water at 12/4/100 (weight ratio). In the dyeing step and the crosslinking step, longitudinal uniaxial stretching is performed by stretching between rolls in a bath. The total stretching ratio based on the embryonic membrane was set to 5.89 times.

Then, the irradiation length in the film width direction of the central portion of the width direction of the film, which is approximately parallel to the width direction of the film, is drawn from the second crosslinking bath 17b and passed through the roll 53b with a width of 1290 mm. (The length in the width direction of the heater heating section) An electromagnetic wave irradiator (FRMW heater with a high-speed response) of 830 mm, product name: Golden 8 Medium-wave fast response twin tube emitter, manufactured by Heraeus, The heat source temperature is 1600 ° C and the maximum energy density is 150 kW / cm ² ). An electromagnetic wave radiation port is arranged at a distance of 5 cm from the surface of the film, and the electromagnetic wave is irradiated with an output of 65%.

The heat radiation amount per unit volume of the electromagnetic wave per unit volume in a region of 830 mm in width (64% of the full width relative to the center of the width direction of the film) was 2310 J / cm ³ . On the other hand, since the irradiation length of the electromagnetic wave irradiator is shorter than the length in the width direction of the film, electromagnetic waves are not irradiated near the end of the film. The irradiation heat per unit volume of electromagnetic waves in a region of 0 mm from the end of the film was 0 J / cm ³ . The amount of radiation of electromagnetic waves per unit volume of the film is calculated by the following formula. (Radiation heat per unit volume of the electromagnetic wave of the film) = ((maximum energy density) × (surface area of the heater heating section) × output (%) / (electromagnetic wave irradiation area)) × (electromagnetic wave irradiation time) ÷ (film thickness)

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

The time required after the second cross-linking bath 17b was pulled out until the film was transported and reached the irradiation position of the electromagnetic wave irradiator and the electromagnetic wave was irradiated was 5 seconds.

The film after being irradiated with electromagnetic waves was immersed in a cleaning bath 19 made of pure water at 10 ° C. for a retention time of 5 seconds (cleaning step). Then, the film was dried in a drying furnace 21 at a temperature of 88 ° C 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 by performing the same operation as in Example 2 except that the output was set to 35% and the electromagnetic wave irradiation heat in the electromagnetic wave irradiation step was set to 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 by performing the same operation 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) Determination of iodine (I) content    

For the polarizing films obtained in Example 2, Example 3, and Comparative Example 3, the measurement points (measurement points 1 to 10) of 10 points in the width direction were determined at arbitrary positions in the length direction, and each measurement was performed according to the following method. Spot the iodine concentration. The measurement points of 10 points are determined at the two ends in the width direction at a distance of 10 mm from the end of the film, and between the measurement points at both ends so that the adjacent measurement points are equally spaced. Way to determine the remaining 8 measurement points. The determined measurement point is a measurement point included in each section that divides the full width 1080 mm in the width direction into 10 equal-width 108 mm sections.

The content of iodine (I) was measured by fluorescent X-ray analysis.

Measuring device: fluorescent X-ray analysis device (device name: AXIOS, manufactured by PANalytical)

X-ray light source: Rh

Output: 30kV, 100mA

Measuring diameter: 27mm

Measurement method: Collect 0.15 g of a polarizing film so as to include each measurement point, dissolve each sample in 20 ml of pure water, seal, and heat to 90 ° C. to dissolve the polarizing film to prepare a measurement solution. The measurement result is compared with a calibration curve prepared from a standard solution to calculate the iodine concentration in the solution. The weight of the polarizing film was converted from the obtained iodine concentration, and it was set 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) was 1.35 mass% or more, and the maximum and minimum values of the content of iodine (I) at 10 measurement points were obtained. The difference is a polarizing film of 0.60% by mass or less.

Claims (12)

    A method for manufacturing a polarizing film is a method for manufacturing a polarizing film from a polyvinyl alcohol-based resin film, comprising the following steps: a dyeing step of dyeing the polyvinyl alcohol-based resin film with a dichroic dye, and crosslinking A crosslinking step of crosslinking the polyvinyl alcohol-based resin film after the dyeing step, irradiating an electromagnetic wave including infrared rays to the electromagnetic wave irradiation step of the polyvinyl alcohol-based resin film after the crosslinking step, and A washing step of washing the polyvinyl alcohol-based resin film after the electromagnetic wave is irradiated; in the electromagnetic wave irradiation step, a radiation amount of the electromagnetic wave per unit volume of the polyvinyl alcohol-based resin film has a distribution in a width direction.         The method for manufacturing a polarizing film according to item 1 of the scope of patent application, wherein in the electromagnetic wave irradiation step, in the width direction of the polyvinyl alcohol-based resin film, the first region including the center and not including the end portion is included in the The radiation heat per unit volume of the electromagnetic wave is greater than the radiation heat per unit volume of the electromagnetic wave in the second region including the end portion and excluding the center.     The method for manufacturing a polarizing film according to item 2 of the scope of the patent application, wherein in the infrared electromagnetic wave irradiation step, the amount of heat radiated by the electromagnetic wave infrared rays in the first region is per unit volume of the polyvinyl alcohol-based resin film. It is 100 J / cm ³ or more and 50 kJ / cm ³ or less.     The method for manufacturing a polarizing film according to any one of claims 1 to 3, wherein in the above electromagnetic wave irradiation step, a ratio of radiant energy of infrared rays having a wavelength of more than 2 μm and less than 4 μm in the electromagnetic wave irradiation step More than 25% of the total radiation energy.         The method for producing a polarizing film according to any one of claims 1 to 4, wherein the crosslinking agent contains a boron compound.         The method for producing a polarizing film according to any one of claims 1 to 5, wherein the cross-linking step is a cross-linking in which the polyvinyl alcohol-based resin film is immersed in an aqueous solution of the cross-linking agent. Bath steps.         The method for manufacturing a polarizing film according to item 6 of the patent application scope, further comprising: removing the aqueous solution attached to the surface of the polyvinyl alcohol-based resin film after the cross-linking treatment and before the electromagnetic wave is irradiated.液 步骤。 Liquid steps.         An apparatus for manufacturing a polarizing film, which is a manufacturing apparatus for manufacturing a polarizing film from a polyvinyl alcohol-based resin film, and includes a dyeing section that dyes the polyvinyl alcohol-based resin film with a dichroic dye, and a cross-linking agent. A cross-linking section for cross-linking the polyvinyl alcohol-based resin film after the dyeing treatment, irradiating an electromagnetic wave including infrared rays to the electromagnetic wave-irradiating section of the polyvinyl alcohol-based resin film after the cross-linking treatment, and irradiating A cleaning section for cleaning the polyvinyl alcohol-based resin film after the electromagnetic wave; the electromagnetic wave irradiating section is such that the irradiation heat of the electromagnetic wave per unit volume of the polyvinyl alcohol-based resin film is distributed in a width direction, The above electromagnetic waves are irradiated.         The method of manufacturing a polarizing film according to item 2 or 3 of the scope of the patent application, wherein in the electromagnetic wave irradiation step, the electromagnetic wave is irradiated only to the first region.         The method of manufacturing a polarizing film according to item 9 of the scope of patent application, wherein the width of the first region is 60 to 90% with respect to the full width of the polyvinyl alcohol-based resin film.         A polarizing film having an average value of iodine (I) content at 10 measurement points in a width direction of 1.35 mass% or more, and a difference between a maximum value and a minimum value of the iodine (I) content at the 10 measurement points It is 0.60% by mass or less; the above-mentioned 10 measurement points are measurement points included in a section that divides the full width in the width direction into 10 equal divisions.         The polarizing film according to item 11 of the scope of the patent application, wherein the average value of the content of iodine (I) at the above 10 measurement points is 1.65% by mass or more.