TW201815558A - Method and apparatus for manufacturing polarizing film - Google Patents

Abstract

The present invention provides a method for manufacturing polarizing film capable of obtaining a polarizing film having high optical characteristics despite even if the boron content is reduced, and a manufacturing apparatus thereof. The method for manufacturing a polarizing film having a boron content of 2.0 to 3.5% by weight 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 immersing the polyvinyl alcohol-based resin film after the dyeing step in a crosslinking bath composed of an aqueous solution of a crosslinking agent containing a boron compound to crosslink the polyvinyl alcohol resin film; an electromagnetic wave irradiation step of irradiating the polyvinyl alcohol-based resin film after the crosslinking step with an electromagnetic wave in which the ratio of radiant energy of infrared radiation with a wavelength of more than 2 [mu]m to 4 [mu]m or less with respect to the total radiant energy is 25% or more; and a washing step of washing the polyvinyl alcohol-based resin film having been irradiated with the electromagnetic wave.

Description

   Manufacturing method and manufacturing device of polarizing film   

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

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

The polarizing film is mainly processed by dipping a raw material film made of a polyvinyl alcohol resin in a dyeing bath containing a dichroic pigment such as iodine, and then by dipping in a crosslinking bath containing a crosslinking agent such as boric acid. The film was produced by uniaxially stretching the film at any stage. Uniaxial stretching includes dry stretching in air and wet stretching in liquids such as the dyeing bath and cross-linking bath.

The cross-linked polarizing film is liable to shrink if heated, and may have insufficient durability. Japanese Patent Application Laid-Open No. 2013-148806 (Patent Document 1) discloses that the boron content of the polarizing film is as low as 1 to 3.5% by weight, and a polarizing film having excellent durability can be provided.

    [Prior technical literature]         [Patent Literature]    

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

However, if the content of boron in the polarizing film is lowered, a sufficient degree of crosslinking may not be obtained and the optical characteristics may be lowered. An object of the present invention is to provide a method for manufacturing a polarizing film having high optical characteristics even if the boron content is reduced, and a manufacturing apparatus therefor. Moreover, it aims at providing the novel polarizing film obtained by the manufacturing method of such a polarizing film.

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

[1] A method for manufacturing a polarizing film, which is a polarizing film having a boron content of 2.0 to 3.5% by weight from a polyvinyl alcohol-based resin film, and includes: a dyeing step in which the aforementioned polyvinyl alcohol-based resin film is two-colored The dye is dyed; the cross-linking step is performed by dipping the polyvinyl alcohol-based resin film after the dyeing step in a cross-linking bath composed of an aqueous solution containing a cross-linking agent of a boron compound to perform a cross-linking treatment; electromagnetic wave irradiation Step: the polyvinyl alcohol-based resin film is irradiated with an electromagnetic wave after the cross-linking step, and the ratio of the radiant energy of the infrared ray with a wavelength exceeding 2 μm to 4 μm is 25% or more of the total radiant energy; and a washing step Is to wash the polyvinyl alcohol-based resin film after irradiating the electromagnetic wave.

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

[3] The method for producing a polarizing film according to [1] or [2], further including a liquid removing step, which is performed before the electromagnetic wave is irradiated after the cross-linking treatment, and then adheres to the polyvinyl alcohol-based system. The aforementioned aqueous solution on the surface of the resin film is removed.

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

[5] The method for producing a polarizing film according to any one of [1] to [4], wherein in the cross-linking step, the cross-linking bath contains 1.5 parts by weight or more of 100 parts by weight of water 3 An aqueous solution of the cross-linking agent of the boron compound described below in parts by weight.

[6] An apparatus for producing a polarizing film, which is a polarizing film having a boron content of 2.0 to 3.5% by weight based on a polyvinyl alcohol resin film, and includes: a dyeing section that divides the aforementioned polyvinyl alcohol resin film into two The chromatic pigment is subjected to a dyeing treatment; the cross-linking section is to perform a cross-linking treatment by dipping the polyvinyl alcohol-based resin film after the dyeing treatment in a cross-linking bath composed of an aqueous solution containing a cross-linking agent of a boron compound; The irradiating part is irradiated with the electromagnetic wave by the polyvinyl alcohol-based resin film after the cross-linking treatment, and the ratio of the radiant energy of the infrared ray with a wavelength exceeding 2 μm to 4 μm is 25% or more of the total radiant energy; It is to wash the polyvinyl alcohol-based resin film after the electromagnetic wave is irradiated.

[7] A polarizing film, which is a polarizing film obtained by dyeing a polyvinyl alcohol-based resin film with a dichroic pigment, wherein the boron content is 2.0 to 3.5% by weight, and the visual acuity correction monomer transmission rate is 42.0% above, depending on the degree of polarization sensitivity correction than 99.990%, and the ratio a ₄₈₀ absorbance a 600nm wavelength of the absorbance a of the absorption axis direction of the absorption axis direction ₆₀₀ of 480nm in wavelength of ₄₈₀ / a ₆₀₀ of 0.75 to 1.00.

According to the present invention, it is possible to provide a method and a device for producing a polarizing film having high optical characteristics even if the boron content is reduced. Furthermore, according to the present invention, a polarizing film having a low boron content and excellent optical characteristics can be provided.

10‧‧‧ Raw material film made of polyvinyl alcohol resin

11‧‧‧ Raw Rolls

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 ...

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 therefor.

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

<Manufacturing method of polarizing film>

The polarizing film in the present invention is a polyvinyl alcohol-based resin film that is uniaxially stretched, and is adsorbed and aligned with a dichroic pigment (iodine or dichroic dye). 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, and more preferably about 99 mol% or more. The polyvinyl acetate-based resin may be, for example, a copolymer of vinyl acetate and other monomers copolymerizable therewith, in addition to polyvinyl acetate, which is a 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, preferably about 1500 to 5,000.

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

In the present invention, as a starting material for manufacturing a polarizing film, an unstretched polyvinyl alcohol 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 more preferably 30 μm or less is used. System resin film (raw material film).

In this way, a thin film polarizing film that is increasingly required by the market can be obtained. The width of the raw material film is not particularly limited, and may be, for example, about 400 to 6000 mm. As the raw material film, for example, a roll (raw material roll) of a long unstretched polyvinyl alcohol-based resin film can be prepared.

In addition, the polyvinyl alcohol-based resin film used in the present invention may be a substrate film laminated on a supporting substrate film, that is, a laminated film of a substrate film and a polyvinyl alcohol-based resin film laminated thereon may be prepared, and As this polyvinyl alcohol-based resin film. In this case, the polyvinyl alcohol-based resin film can be produced, for example, by 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. As a specific example, a light-transmitting thermoplastic resin is preferably a film made of an optically transparent thermoplastic resin, and may be, for example, a chain polyolefin resin (such as a polypropylene resin) or a cyclic polyolefin resin. (Norbornene-based resins) and other polyolefin-based resins; cellulose triacetate and cellulose diacetate-based cellulose resins; polyethylene terephthalate, polybutylene terephthalate Polyester resins such as; polycarbonate resins; (meth) acrylic resins such as methyl methacrylate resins; polystyrene resins; polyvinyl chloride resins; acrylonitrile / butadiene / Styrene resin; acrylonitrile / styrene resin; polyvinyl acetate resin; polyvinylidene chloride resin; polyamide resin; polyacetal resin; modified polyphenylene ether resin; Fluorene resin; polyether fluorene resin; polyarylate resin; polyfluorene amine imine resin; polyfluorene resin.

The polarizing film is continuously conveyed along the film conveying path of the polarizing film manufacturing device while the long raw film is pulled out from the raw material roll, and is immersed in a processing liquid (hereinafter also referred to as a "processing bath") stored in a processing tank. It is then pulled out, and a drying step is performed after performing a predetermined processing step, whereby a long polarizing film can be continuously manufactured. In addition, the processing step is not limited to a method of immersing a film in a processing bath as long as the film is brought into contact with a processing solution, and may be a method of processing the film by attaching the processing liquid to the surface of the film by spraying, flowing down, or dropping. method. When the processing step is performed by immersing the film in a processing bath, the processing bath performing one processing step is not limited to one, and the film may be sequentially immersed in two or more processing baths to complete one processing step.

Examples of the treatment liquid include a swelling liquid, a dyeing liquid, a crosslinking liquid, and a cleaning liquid. Next, as the above-mentioned treatment steps, for example, a swelling step in which a raw film is brought into contact with a swelling solution to perform a swelling treatment, a dyeing step in which a swelling-treated film is brought into contact with a dyeing liquid to perform a dyeing treatment, and a film after the dyeing treatment is brought into contact with cross-linking A cross-linking step for performing a cross-linking treatment with liquid, and a washing step for subjecting the film after the cross-linking treatment to a cleaning solution to perform a washing treatment. Furthermore, a wet or dry uniaxial stretching process may be performed between such a series of processing steps (that is, before or after any one or more processing steps and / or during any one or more processing steps). Other processing steps can be added as needed.

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

An example of a method for manufacturing the 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 therefor. The polarizing film manufacturing apparatus shown in FIG. 1 is structured as follows: The raw material (unstretched) film 10 made of a polyvinyl alcohol resin is continuously pulled out of the raw material roll 11 while being conveyed along the film. Path transfer, so as to sequentially pass through the swelling bath (swelling solution stored in the swelling tank) provided on the film transfer path 13, the dyeing bath (staining solution stored in the dyeing tank) 15, the first cross-linking bath (storage The first cross-linking liquid in the cross-linking tank) 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 wash tank) ) 19, and finally pass through the drying furnace 21. The obtained polarizing film 23 can be directly transported, for example, to the following polarizing plate manufacturing step (a step of laminating a protective film on one or both sides of the polarizing film 23). The arrow in FIG. 1 shows the film conveyance direction.

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

In addition to the above-mentioned processing bath, the film transfer path of the polarizing film manufacturing device can be configured as follows: guide rollers 30 to 48, 60, and 61 that can support the film to be transferred or further change the film transfer direction; can be pressed, clamped The nip rollers 50 to 55 that hold the transported film and can give a driving force to the film through its rotation, or can further change the film transport direction are arranged at appropriate positions. The guide rollers or nip rollers can be arranged before and after each processing bath or in the processing baths, whereby the film can be introduced and immersed in the processing bath, and pulled out from the processing bath [refer to FIG. 1]. For example, one or more guide rollers may be provided in each processing bath, and a film may be conveyed along these guide rollers, whereby a film may be immersed in each processing bath.

The polarizing film manufacturing apparatus shown in FIG. 1 is provided with nip rollers (nip rollers 50 to 54) before and after each processing bath, so that roll extension can be performed in any one or more treatment baths. A peripheral speed difference is applied between the nip rolls before and after the treatment bath, and longitudinal uniaxial stretching is performed.

In the polarizing film manufacturing apparatus shown in FIG. 1, an electromagnetic wave irradiation section 71 is disposed on a transport path downstream of the second cross-linking bath 17 b and upstream of the cleaning bath 19, and performs an electromagnetic wave irradiation step. Each step is described below.

(Swelling step)

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

Referring to FIG. 1, the swelling step may be performed by continuously pulling the raw material film 10 through the raw material roll 11 while conveying the raw material film 10 along the film conveying path, soaking the raw material film 10 in the swelling bath 13 for a predetermined time, Then pull it out. In the example of FIG. 1, the raw material film 10 is conveyed along the film conveyance path constructed by the guide rollers 60 and 61 and the nip roller 50 between the raw material film 10 being pulled out and immersed in the swelling bath 13. In the swelling process, the film is transported along the film transport path constructed by the guide rollers 30 to 32 and the nip roller 51.

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

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

In the swelling treatment, a problem that the raw material film 10 swells in the width direction and wrinkles are formed in the film easily occurs. As a method for removing the wrinkles and transporting the film, a roll having a widening function such as an expansion roll, a spiral roll, or a crown roll may be used for the guide rolls 30, 31, and / or 32. Or use other widening devices such as cross guides, bending rods, and tenter clips. Another method to suppress the occurrence of wrinkles is to perform an extension treatment. For example, a uniaxial stretching process can be performed in the swelling bath 13 using the peripheral speed difference of the nip roll 50 and the nip roll 51.

In the swelling process, the film also swells and expands in the film conveying direction. Therefore, in the case where the film is not actively stretched, in order to eliminate the film slack in the conveying direction, it is preferable to take control of the nip rollers 50 arranged before and after the swelling bath 13, for example. , 51 speed and other methods. In addition, for the purpose of transporting the film in the stabilization swelling bath 13, the water flow in the swelling bath 13 is controlled by a flush bath in water, or an EPC device (Edge Position Control device: a device that detects the end of the film and prevents the film from meandering), etc. It's useful.

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

(Dyeing step)

The purpose of performing the dyeing step is to adsorb the polyvinyl alcohol-based resin film after swelling treatment, and to align the dichroic pigment. The processing conditions are determined within a range in which the object can be achieved without causing defects such as extreme dissolution or devitrification of the membrane. Referring to FIG. 1, the dyeing step can be carried along the film conveying path constructed by the nip rollers 51, guide rollers 33 to 36, and nip rollers 52, and the swelled film is processed in the dyeing bath 15 (the treatment stored in the dyeing tank) Liquid) is immersed for a predetermined time and then pulled out. In order to improve the dyeability of the dichroic pigment, the film used in the dyeing step is preferably a film that is subjected to at least a certain degree of uniaxial stretching treatment, or it is preferable to replace the uniaxial stretching treatment before the dyeing treatment, or otherwise. In addition to the uniaxial stretching process, the uniaxial stretching process is performed during the dyeing process.

When using iodine as a dichroic pigment, an aqueous solution having a concentration of, for example, a weight ratio of iodine / potassium iodide / water = about 0.003 to 0.3 / about 0.1 to 10/100 can be used in the dyeing liquid of the dyeing bath 15. Instead of potassium iodide, other iodides such as zinc iodide may be used, or potassium iodide may be used in combination with other iodides. In addition, compounds other than iodide may be coexisted, such as boric acid, zinc chloride, and cobalt chloride. When boric acid is added, it can be distinguished from the crosslinking treatment described later by the point containing iodine, and it can be regarded as dyeing bath 15 as long as the aqueous solution contains about 0.003 parts by weight or more of iodine. The temperature of the dyeing bath 15 when the film is impregnated is usually about 10 to 45 ° C, preferably 10 to 40 ° C, more preferably 20 to 35 ° C. The impregnation time of the film is usually about 30 to 600 seconds, preferably 60 to 300 seconds.

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

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

In the dyeing process, in order to remove the wrinkles of the film and convey the polyvinyl alcohol-based resin film in the same manner as the swelling process, an extension roller, a spiral roller, a convex roller, or the like is used for the guide rollers 33, 34, 35, and / or 36 The roller with widening function can also use other widening devices such as cross guide rollers, bending rods, and tenter clips. As with the swelling treatment, another method for suppressing the occurrence of wrinkles is the extension treatment.

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

(Crosslinking step)

The purpose of performing the cross-linking step is to make the cross-linking resistant to water or adjust the color tone (to prevent the film from appearing blue, etc.). In the example shown in FIG. 1, two cross-linking baths are used as cross-linking baths for performing the cross-linking step. The first cross-linking step performed for the purpose of water resistance is performed in the first cross-linking bath 17a to adjust the color tone as The second crosslinking step performed for the purpose is performed in the second crosslinking bath 17b. Referring to FIG. 1, the first cross-linking step can be carried along the film conveying path constructed by the nip roller 52, the guide rollers 37 to 40 and the nip roller 53 a, and the dyed film is transferred to the first cross-linking bath 17 a. (The first cross-linking solution contained in the cross-linking tank) is immersed for a predetermined time, and then pulled out for implementation. The second cross-linking step can be carried along the film transport path constructed by the nip rollers 53a, guide rollers 41 to 44 and nip rollers 53b. The film after the first cross-linking step is placed in the second cross-linking bath 17b (contained in The second crosslinking liquid in the crosslinking tank) is immersed for a predetermined time, and then pulled out for implementation. Hereinafter, when the cross-linking bath is referred to, it includes both the first cross-linking bath 17a and the second cross-linking bath 17b. When it is referred to as the cross-linking liquid, both the first cross-linking liquid and the second cross-linking liquid are included.

As a cross-linking solution, it can be used for a solution in which a cross-linking agent is dissolved in a solvent. Examples of the crosslinking agent include boron compounds such as boric acid and borax, glyoxal, and glutaraldehyde. These may be one type or two or more types may be used in combination. As the solvent, for example, water may be used, and an organic solvent having compatibility with water may be contained. The concentration of the cross-linking agent in the cross-linking solution, the temperature of the cross-linking bath, the film immersion time, and the number of cross-linking baths of the immersion film are not particularly limited, and can be appropriately selected from these to obtain the boron content ratio. It is a polarizing film of 2.0 to 3.5% by weight. As the crosslinking solution, for example, an aqueous solution containing 1 to 10 parts by weight of a boron compound such as boric acid with respect to 100 parts by weight of water can be used, and an aqueous solution containing 1.5 to 3 parts by weight is preferably used. When the dichroic dye used for the dyeing treatment is iodine, the crosslinking solution preferably contains iodide in addition to boric acid, and the amount of iodide may be, for example, 1 to 30 parts by weight relative to 100 parts by weight of water. Examples of the iodide include potassium iodide and zinc iodide. In addition, compounds other than iodide may be coexisted, such as zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, and sodium sulfate.

In the crosslinking treatment, the concentrations of boric acid and iodide, and the temperature of the crosslinking bath 17 can be appropriately changed according to the purpose. For example, when the first cross-linking solution whose cross-linking purpose is to be water-resistant by cross-linking, the concentration may be an aqueous solution of boric acid / iodide / water = 1 to 10/1 to 30/100 in terms of weight ratio. The temperature of the first crosslinking 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 about 10 to 600 seconds, preferably 20 to 300 seconds, more 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 cross-linking liquid for the purpose of adjusting color tone, for example, when iodine is used as a dichroic dye, the concentration in terms of weight ratio may be boric acid / iodide / water = 1 to 5/3 to 30/100. The temperature of the second crosslinking bath 17b when the film is impregnated is usually about 10 to 45 ° C, and the impregnation 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. The cross-linking treatment for achieving water resistance through cross-linking and the cross-linking treatment for adjusting color tone may be performed in a plurality of steps, respectively.

A uniaxial stretching process can be performed in the 1st crosslinking bath 17a by the peripheral speed difference of the nip roll 52 and the nip roll 53a. In addition, a uniaxial stretching treatment may be performed in the second cross-linking bath 17b by utilizing a difference in peripheral speed between the nip rollers 53a and 53b.

In the cross-linking treatment, similar to the swelling treatment, in order to remove the wrinkles of the film and transport the polyvinyl alcohol-based resin film, an extension roller or a spiral roller may be used for the guide rollers 38, 39, 40, 41, 42, 43, and / or 44 Rollers with widening functions such as, convex rollers, and other widening devices such as cross guide rollers, bending rods, and tenter clips can also be used. As with the swelling treatment, another method for suppressing the occurrence of wrinkles is a stretching treatment.

In the example shown in FIG. 1, the film drawn from the second cross-linking bath 17 b is sequentially introduced into the washing bath 19 through the guide roller 44 and the nip roller 53 b.

(Washing step)

The example shown in Fig. 1 includes a washing step after the crosslinking step. The purpose of the cleaning treatment is to remove excess boric acid, iodine, and other agents attached to the polyvinyl alcohol resin film. The washing step is performed, for example, by immersing the cross-linked polyvinyl alcohol-based resin film in the washing bath 19. In addition, instead of the step of dipping the film in the washing bath 19, the washing step may be performed by spraying the film with the washing liquid as a rinsing bath, or by using the dipping and washing liquid of the washing bath 19 in combination. Spraying.

FIG. 1 shows an example in which a polyvinyl alcohol-based resin film is immersed in a washing bath 19 and subjected to a washing treatment. 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. The conditions of the washing treatment may be appropriately selected so that the boron content of the finally obtained polarizing film is 2.0 to 3.5% by mass.

In addition, in the cleaning process, for the purpose of removing wrinkles and conveying the polyvinyl alcohol-based resin film, the guide rollers 45, 46, 47, and / or 48 can be widened by using expansion rollers, spiral rollers, convex rollers, or the like. Functional rollers can also use other widening devices such as cross guide rollers, bending rods, and tenter clips. In addition, the film washing process may be extended to suppress the occurrence of wrinkles.

(Extended steps)

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

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

(Electromagnetic wave irradiation step)

In the apparatus shown in FIG. 1, after the film is pulled out from the second crosslinking step 17b and passed through the nip roller 53b, the film is irradiated with electromagnetic waves before being immersed in the washing bath 19 (electromagnetic wave irradiation step). In the apparatus shown in FIG. 1, an electromagnetic wave is irradiated by the electromagnetic wave irradiation section 71. In the electromagnetic wave irradiation step of the present invention, the ratio of the infrared radiation energy of the electromagnetic wave system with a wavelength exceeding 2 μm and less than 4 μm is 25% or more of the total radiation energy, preferably 28% or more, and more preferably 35% or more. By irradiating the film with such an electromagnetic wave, the optical characteristics of the obtained polarizing film can be improved. The upper limit of the ratio of the infrared radiation energy exceeding a wavelength of 2 μm to 4 μm is not particularly limited for the electromagnetic wave used in the present invention, but it is, for example, 80% or less. Generally, electromagnetic waves with a wavelength of 0.75 μm to 1000 μm are called infrared rays.

In the electromagnetic wave irradiation step, the mechanism of improving the optical characteristics of the polarizing film is not clear by irradiating electromagnetic waves having an infrared radiation energy ratio of more than 2 μm and a wavelength of less than 4 μm to a total radiation energy of more than 25%, but it is estimated that Molecules in the film excited by infrared rays with a wavelength of 2 μm and less than 4 μm promote the fixation of dichroic pigments such as iodine in the cross-linked film, thereby improving the optical characteristics of the polarizing film.

Figure 2 shows the radiation energy spectrum of various types of electromagnetic wave irradiators. In addition, Table 1 shows the ratio of the electromagnetic wave radiation energy to the total radiation energy in each wavelength region (expressed in the range of wavelength x μm) of various types of electromagnetic wave irradiators. The electromagnetic wave irradiators shown in Figure 2 and Table 1 are halogen heaters (heat source temperature 2600 ° C), short-wavelength infrared heaters (heat source temperature 2200 ° C), fast-response medium-wavelength infrared heaters (heat source temperature 1600 ° C), 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 heaters (heat source temperature 2200 ° C), fast-response medium-wavelength infrared heaters (heat source temperature 1600 ° C), carbon heaters (heat source temperature 1200 ° C), and carbon heaters (heat source temperature 950 ℃), and medium-wavelength infrared heater (heat source temperature 900 ° C), because the ratio of the infrared radiation energy of the wavelength exceeding 2 μm and less than 4 μm is 25% or more of the total radiation energy, it can be applied as an electromagnetic wave irradiator constituting the electromagnetic wave irradiation section 71. 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. In the case of a plurality of electromagnetic wave irradiators, the plurality of electromagnetic wave irradiators are selected so that the infrared radiation energy of a wavelength exceeding 2 μm and less than 4 μm emitted by the plurality of electromagnetic wave irradiators is the total of the electromagnetic waves emitted by the plurality of electromagnetic wave irradiators More than 25% of the radiated energy. In the first figure, the electromagnetic wave irradiating unit 71 is configured to irradiate electromagnetic waves to only one side of the film, but a plurality of electromagnetic wave irradiators may be arranged to irradiate electromagnetic waves to both sides of the film. The electromagnetic wave irradiation section 71 is preferably configured to irradiate the entire area in the width direction of the polyvinyl alcohol-based resin film to be irradiated with electromagnetic waves.

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. In addition, in the electromagnetic wave irradiating section 71, the distance between the electromagnetic wave emitting port of the electromagnetic wave irradiator and the film is preferably 2 to 40 cm, and more preferably 5 to 20 cm. However, the distance is preferably appropriately selected and performed in consideration of the amount of radiated energy of electromagnetic waves radiated from the electromagnetic wave irradiator, the temperature of the film surface, and the like. The temperature of the film surface during electromagnetic wave irradiation is preferably maintained at 30 to 90 ° C, and more preferably maintained at 40 to 80 ° C.

In the electromagnetic wave irradiation step, the electromagnetic wave irradiation heat per unit volume of the film may be generally 100 J / cm ³ or more and 50 kJ / cm ³ or less. In the viewpoint of improving the optical characteristics of the polarizing film, it is preferably 100J / cm ³ or more, more preferably 500J / cm ³ or more, and more preferably 1000J / cm ³ or more. From the viewpoint of suppressing the deterioration of the film due to temperature rise, the radiation heat of the electromagnetic wave per unit volume of the film is preferably 10 kJ / cm ³ or less, more preferably 5000 J / cm ³ or less, and still more preferably 3000 J / cm. ³ or less. Generally, the reduction of the moisture content of the film is proportional to the amount of heat irradiated by the electromagnetic waves. However, the purpose of the electromagnetic wave irradiation step of the present invention is not to reduce the amount of moisture of the film. Therefore, the amount of heat radiated can be appropriately selected, and it is preferable to appropriately select within the above range .

In the present invention, by performing the electromagnetic wave irradiation step before the cleaning process, the optical characteristics of the obtained polarizing film can be improved. The electromagnetic wave irradiation step may be performed on the film immersed in at least one crosslinking bath. As shown in FIG. 1, it is not limited to the film immersed in all the crosslinking 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 cross-linking bath and before the second cross-linking bath, or the film immersed in the second cross-linking bath may be subjected to electromagnetic wave irradiation. step. However, through the electromagnetic wave irradiation step, the boric acid entering the film due to immersion in the cross-linking bath can be cross-linked. Therefore, the electromagnetic wave irradiation step on the film that has been immersed in all the cross-linking baths can more effectively cross-link the boric acid. Better.

Irradiation of electromagnetic waves is preferably performed within 10 seconds after the film is pulled out of the cross-linking bath, and more preferably within 5 seconds. The shorter the time from when the cross-linking bath is drawn until the electromagnetic wave is irradiated, the further the optical characteristics of the polarizing film caused by the electromagnetic wave irradiation can be further improved. In the electromagnetic wave irradiation step, it is preferable that there are fewer water molecules attached to the surface of the film. If there are water molecules on the surface of the film, the water molecules on the surface of the film will absorb infrared rays, so the effect of stimulating the movement of molecules in the film by electromagnetic wave irradiation will be reduced. The cross-linking liquid will adhere to the film surface after being pulled out from the cross-linking bath, so it is preferable to set a liquid removing method to remove it before the electromagnetic wave irradiation step. In Fig. 1, the nip roller 53b also has a function of a liquid removal method for removing the cross-linking liquid adhered to the film surface. In addition to the nip roller, there is a method for removing liquid by blowing air on the film, and a doctor blade or the like may be used to remove the liquid by contacting the film.

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

(Drying step)

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

The obtained polarizing film may be sequentially wound into a rolled roll and formed into a roll form, or may be directly supplied to a polarizing plate manufacturing step (such as a single-sided or two-area layer protective film step of the polarizing film) without winding.

(Other processing steps for polyvinyl alcohol resin film)

Processing other than the above processing can be added. Examples of the additional treatment include: treatment after dipping in an aqueous iodide solution that does not contain boric acid (color correction treatment); and treatment that does not include boric acid but contains an aqueous solution such as zinc chloride (zinc treatment).

<Polarizing film>

By manufacturing the polarizing film by the above method, a polarizing film that satisfies the following requirements: i) boron content of 2.0 to 3.5% by weight, ii) visual sensitivity-corrected monomer transmittance (Ty) of 42.0% or more, iii) visual sensitivity correcting the degree of polarization (Py) of 99.990% or more, an absorbance a ₄₈₀ iv) the absorption axis direction of the polarizing film of 480nm wavelength to the absorption axis direction of the absorbance a 600nm wavelength of the polarizing film ₆₀₀ ratio a ₄₈₀ / a ₆₀₀ It is 0.75 or more and 1.00 or less.

When the boron content of the polarizing film is as described in i) above, it is possible to reduce the shrinkage force. The boron content of the polarizing film is more preferably 2.0 to 3.0% by weight. The shrinkage force of the polarizing film is preferably 3.8 N / 2 mm or less, and more preferably 3.5 N / 2 mm or less. The boron content rate and shrinkage force of the polarizing film here are measured according to the methods described in the examples described later.

Generally, by setting the boron content of the polarizing film to be, for example, 3.8% by weight or more, high optical characteristics can be obtained. However, it is difficult to obtain excellent optical characteristics while the boron content of the polarizing film is as low as i) described above. In the manufacturing method of the present invention, by having an electromagnetic wave irradiation step, a polarizing film that satisfies the above i) and satisfies the above ii) and the above iii) can be obtained. The visual sensitivity-corrected monomer transmittance (Ty) and the visual sensitivity-corrected polarization (Py) of the polarizing film herein are measured according to the methods described in the examples described later.

Furthermore, in the manufacturing method of the present invention, as the electromagnetic wave used in the electromagnetic wave irradiation step, by using an electromagnetic wave having a wavelength of more than 2 μm and a wavelength of 4 μm or less, the ratio of the radiation energy is 25% or more of the total radiation energy. A polarizing film that satisfies the above-mentioned characteristics iv) and has an excellent hue close to neutral gray was obtained. When A ₄₈₀ / A _{600 is} less than 0.75, blue is strong, and when A ₄₈₀ / A _{600 is} more than 1.00, red is strong. In order to suppress red, A ₄₈₀ / A _{600 is} preferably 0.90 or less. That is, by the manufacturing method of the present invention, it is possible to obtain a polarizing film having excellent optical characteristics while reducing the boron content of the polarizing film as described in i) above while suppressing the shrinkage force, and satisfying the characteristics of ii) to iv) above. .

<Polarizer>

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

In order to improve the adhesion between the polarizing film and the protective film, the surface of the polarizing film and / or the protective film can be subjected to corona treatment, flame treatment, plasma treatment, ultraviolet irradiation, primer coating treatment, saponification treatment, etc. deal with. Examples of the adhesive used for bonding the polarizing film and the protective film include an active energy ray-curable adhesive such as a UV-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-based emulsion adhesives. The ultraviolet curing type 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. Moreover, 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 an initiator.

    [Example]    

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

<Example 1>

The polarizing film of Example 1 was manufactured from a polyvinyl alcohol-based resin film using the manufacturing apparatus shown in FIG. 1. Specifically, a long polyvinyl alcohol (PVA) raw material film with a thickness of 60 μm [Kuraray Co., Ltd.'s trade name "Kuraray Vinylon VF-PE # 6000", an average degree of polymerization of 2400, and a degree of saponification of 99.9 mole% or more] It was continuously conveyed while being pulled out from the roll, and immersed in a swelling bath containing pure water at 30 ° C. for a residence time of 79 seconds (swelling step). Thereafter, the film pulled out from the swelling bath was immersed in a iodine-containing 30 ° C dyeing bath with potassium iodide / boric acid / water of 1 / 0.3 / 100 (weight ratio) for a retention time of 123 seconds (dyeing step). Next, the film pulled out from the dyeing bath was immersed in a 53 ° C first crosslinking bath with potassium iodide / boric acid / water at 11 / 2.0 / 100 (weight ratio) for a retention time of 44 seconds, followed by potassium iodide / boric acid / water as The second cross-linking bath at 40 ° C. of 11 / 2.0 / 100 (weight ratio) was impregnated with a retention time of 6 seconds (cross-linking step). In the dyeing step and the cross-linking step, longitudinal uniaxial stretching is performed by stretching between rolls in a bath. The total stretch ratio based on the raw film is 5.65 times.

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

(Irradiation heat of the electromagnetic wave per unit volume of the film) = ((maximum energy density) × (surface area of the heater heating section) × output (%) / (electromagnetic wave irradiation area)) × (electromagnetic wave irradiation time) ÷ (film thickness)

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

After being pulled out from the second cross-linking bath 17b, the time required to transport the film to the irradiation position of the electromagnetic wave irradiator and irradiate the electromagnetic wave was 5 seconds.

The film irradiated with electromagnetic waves was immersed in a washing bath 19 containing pure water at 5 ° C. for a retention time of 3 seconds (washing step). Thereafter, 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.

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

In the electromagnetic wave irradiation step, the type, output (%) of the electromagnetic wave irradiator, the amount of electromagnetic wave irradiation heat per unit volume of the film, and the weight fraction of boric acid relative to 100 weight parts of water in the first crosslinking bath and the second crosslinking bath are set. As shown in Table 2, a polarizing film was obtained in the same manner as in Example 1 except for this point. The thickness of the obtained polarizing films was 23 μm. As an electromagnetic wave irradiator, a halogen heater (product name: straight-tube halogen heater lamp QIR, manufactured by Shiyo Lighting Co., Ltd., heat source temperature 2600 ° C, maximum energy density 300kW / m ² ), short-wavelength infrared Heater (SW heater) (product name: Golden 8 Short-wave twin tube emitter, manufactured by Heraeus, heat source temperature 2200 ° C, maximum energy density 200kW / m ² ), high-speed reaction medium wavelength infrared heater (FRMW heater) (Product name: Golden 8 Medium-wave fast response twin tubu emitter, manufactured by Heraeus, heat source temperature 1600 ° C, maximum energy density 150kW / m ² ), medium wavelength infrared heater (MW heater) (product name: Golden 8 Medium -wave twin tube emitter, manufactured by Heraeus, with a heat source temperature of 900 ° C and a maximum energy density of 60 kW / m ² ).

<Comparative Examples 1, 2, 5>

Except for the point that the electromagnetic wave irradiation step was not performed, and the weight parts of boric acid with respect to 100 weight parts of water with respect to 100 weight parts of water were set to the points shown in Table 2, it was the same as in Example 1. The polarizing film was obtained by applying it on the ground. The thickness of the obtained polarizing film was 23 μm.

[Evaluation of Polarizing Film]

(a) Measurement of monomer transmittance and polarization

For the polarizing films obtained in each of the Examples and Comparative Examples, a spectrophotometer with an integrating sphere ["V7100" manufactured by JASCO Corporation] was used to measure the MD transmittance and TD transmittance in the range of 380 to 780 nm. , Calculate the monomer transmittance and polarization at each wavelength according to the following formula.

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

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

"MD transmittance" refers to the transmittance when the polarization direction of the polarized light emitted by Gran-Thomson is parallel to the transmission axis of the polarizing film sample, and it is expressed as "MD" in the above formula. The "TD transmittance" refers to the transmittance when the direction of polarization of the polarized light emitted by Glan-Thomson is perpendicular to the transmission axis of the polarizing film sample, and is expressed as "TD" in the above formula. The obtained monomer transmittance and polarization degree are corrected for visual sensitivity from the 2-degree field of view (C light source) of JIS Z 8701: 1999 "color representation method-XYZ color system and X ₁₀ Y ₁₀ Z ₁₀ color system", and Obtain the visual sensitivity correction unit transmittance (Ty) and visual sensitivity correction polarization (Py). Table 2 shows the calculation results of the visual sensitivity correction unit transmittance (Ty) and the visual sensitivity correction polarization (Py).

(b) Measurement of absorbance of polarizing film

It was performed using a spectrophotometer with an integrating sphere [Japanese V-Separation Co., Ltd. "V7100"]. Specifically, the TD transmittances TD ₄₈₀ and TD ₆₀₀ at a wavelength of 480 nm and a wavelength of 600 nm are used according to the following formula: A ₄₈₀ = -log ₁₀ (TD _480/100 )

_{A 600 = -log 10 (TD 600} /100) to calculate the wavelength of 480nm and wavelength of 600nm absorbance A ₄₈₀ absorbance of A _600. Table 2 shows the calculated values of the absorbance A ₄₈₀ , the absorbance A ₆₀₀ , and the ratio A ₄₈₀ / A ₆₀₀ calculated based on these values.

(c) MD contraction force

From the obtained polarizing film, a measurement sample having a width of 2 mm and a length of 10 mm with the absorption axis direction (MD, extension direction) as the long side was cut. This sample was set in SII NanoTechnology Co., Ltd.'s thermomechanical analysis device (TMA) "EXSTAR-6000", and the long-side direction (absorption axis direction, MD) generated when the sample was held at 80 ° C for 4 hours was maintained at a fixed size. Contraction force (MD contraction force). Table 2 shows the measured values of the shrinkage force.

(d) Boron content of polarizing film

0.2 g of a polarizing film was added to 170 ml of pure water, and after completely dissolving at 95 ° C., 30 g of an aqueous mannitol solution (12.5% by weight) was added as a sample solution for measurement. Until the measurement sample solution reaches the neutralization point, a sodium hydroxide aqueous solution (1 mol / l) was dropped, and the boron content rate (% by weight) in the polyvinyl alcohol resin film was calculated from the dropped amount according to the following formula.

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

Table 2 shows the values of the boron content ratios measured.

As shown in Table 2, the polarizing films of Examples 1 to 6 satisfy: i) a boron content of 2.0 to 3.5% by weight, ii) visual sensitivity correction monomer transmittance Ty is 42.0% or more, iii) visual sensitivity correction polarization Py of 99.990% or more, the absorption axis direction of the absorbance a absorbance a ₄₈₀ iv) the absorption axis direction of the polarizing film of 480nm wavelength and 600nm wavelength of the polarizing film a ₆₀₀ ratio of ₄₈₀ / a ₆₀₀ is 0.75 to 1 or less . In addition, by satisfying the above-mentioned i), the contraction force can be suppressed, and when the above-mentioned iv) is satisfied, the hue is not a problem. The polarizing film of Comparative Example 1 did not carry out the electromagnetic wave irradiation step, and the value of the corrected polarization degree (Py) of the visual sensitivity was lower.

Since the polarizing film of Comparative Example 2 did not satisfy i) above, the shrinking force was large. The polarizing film A ₄₈₀ / A ₆₀₀ of Comparative Example 3 had a value of more than 1, so the red color was stronger. Comparative Examples 4 and 5 had insufficient boron content, so the value of visual sensitivity correction polarization (Py) was lower.

Claims (7)

    A method for manufacturing a polarizing film is to produce a polarizing film having a boron content of 2.0 to 3.5% by weight from a polyvinyl alcohol-based resin film, and includes: a dyeing step of performing the aforementioned polyvinyl alcohol-based resin film with a dichroic pigment Dyeing treatment; cross-linking step, wherein the polyvinyl alcohol-based resin film after the aforementioned dyeing step is dipped in a cross-linking bath composed of an aqueous solution containing a cross-linking agent of a boron compound to perform a cross-linking treatment; The aforementioned polyvinyl alcohol-based resin film after the aforementioned cross-linking step is irradiated with electromagnetic waves, and the ratio of the radiant energy of infrared rays having a wavelength exceeding 2 μm to 4 μm in the electromagnetic waves is more than 25% of the total radiant energy; The polyvinyl alcohol-based resin film was washed after the electromagnetic wave was irradiated.     The method for manufacturing a polarizing film according to item 1 of the scope of the patent application, wherein in the electromagnetic wave irradiation step, the irradiation energy of the electromagnetic wave is 100 J / cm ³ or more and 50 kJ per unit volume of the polyvinyl alcohol-based resin film. / cm ³ or less.     According to the method for manufacturing a polarizing film described in item 1 or 2 of the scope of the patent application, the method further includes a liquid removing step. The liquid removing step is irradiated with the aforementioned electromagnetic wave before the cross-linking treatment, and then adheres to the polyvinyl alcohol-based resin film. The aforementioned aqueous solution is removed from the surface.         The method for manufacturing a polarizing film according to any one of claims 1 to 3, wherein the electromagnetic wave irradiation step is performed within 5 seconds after the polyvinyl alcohol-based resin film is pulled out of the crosslinking bath. .         The method for manufacturing a polarizing film according to any one of claims 1 to 4 in the scope of the patent application, wherein, in the cross-linking step, the cross-linking bath is composed of 1.5 parts by weight or more and 3 parts by weight with respect to 100 parts by weight of water. The following is an aqueous solution of the cross-linking agent of the boron compound.         A polarizing film manufacturing device is a device for producing a polarizing film having a boron content of 2.0 to 3.5% by weight from a polyvinyl alcohol-based resin film, and includes a dyeing section for converting the aforementioned polyvinyl alcohol-based resin film to a dichroic pigment Performing the dyeing treatment; the cross-linking unit is a cross-linking treatment by dipping the polyvinyl alcohol-based resin film after the dyeing treatment in a cross-linking bath composed of an aqueous solution containing a cross-linking agent of a boron compound; an electromagnetic wave irradiation unit, The aforementioned polyvinyl alcohol-based resin film after the aforementioned cross-linking treatment is irradiated with electromagnetic waves, and the ratio of the radiant energy of the infrared rays having a wavelength exceeding 2 μm to 4 μm is 25% or more of the total radiant energy; The polyvinyl alcohol-based resin film after washing the electromagnetic wave is washed.     A polarizing film is a polarizing film obtained by dyeing a polyvinyl alcohol-based resin film with a dichroic pigment. The boron content is 2.0 to 3.5% by weight, and the transmissivity of the visual sensitivity correction monomer is 42.0% or more. The sensitivity correction polarization is 99.990% or more. The ratio A ₄₈₀ / A ₆₀₀ of the absorbance A ₄₈₀ in the absorption axis direction at a wavelength of ₄₈₀ nm to the absorbance A ₆₀₀ of a polarizing film at a wavelength of 600 nm is 0.75 or more and 1.00 or less.