KR102484819B1 - Method for producing polarizing film, apparatus for producing the same, and polarizing film - Google Patents

Abstract

An object of this invention is to provide the manufacturing method of the polarizing film which reduces the nonuniformity of a polarizing film characteristic, and its manufacturing apparatus.
The above object is a method for producing a polarizing film from a polyvinyl alcohol-based resin film, a dyeing step of dyeing the polyvinyl alcohol-based resin film with a dichroic dye, and the polyvinyl alcohol-based resin film after the dyeing step. A crosslinking step of crosslinking treatment with a crosslinking agent, an electromagnetic wave irradiation step of irradiating electromagnetic waves including infrared rays to the polyvinyl alcohol-based resin film after the crosslinking step, and washing of washing the polyvinyl alcohol-based resin film after irradiating the electromagnetic wave step, wherein in the electromagnetic wave irradiation step, the irradiation heat amount per unit volume of the electromagnetic wave of the polyvinyl alcohol-based resin film has a distribution in a width direction.

Description

Polarizing film manufacturing method, manufacturing apparatus, and polarizing film

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

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

The polarizing film is immersed in a dyeing bath containing dichroic dyes such as iodine, and then immersed in a crosslinking bath containing a crosslinking agent such as boric acid. In addition, it is manufactured by uniaxially stretching the film at any stage. Uniaxial stretching includes dry stretching performed in air and wet stretching performed in a liquid such as the dyeing bath and crosslinking bath described above.

Conventionally, in the manufacturing method of a polarizing film, various things are devised in order to improve the characteristic of a polarizing film. In Japanese Unexamined Patent Publication No. 2013-148806 (Patent Document 1), by providing a primary drying step of drying a polyvinyl alcohol-based resin film between a boric acid treatment step and a water washing step, transmitted light can be made into a good color, that is, neutral gray It is described that it can be close to .

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

When the present inventors cut out a sample from a polarizing film and measured characteristics, even if it is a sample cut out from the polarizing film obtained by the same manufacturing method, it came to the problem that characteristics may differ greatly depending on a sample. An object of this invention is to provide the manufacturing method of the polarizing film which reduces the nonuniformity of a polarizing film characteristic, and its manufacturing apparatus. Furthermore, an object of the present invention is to provide a polarizing film having uniform characteristics in the width direction.

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

[1] As a method for producing a polarizing film from a polyvinyl alcohol-based resin film,

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

A crosslinking step of crosslinking the polyvinyl alcohol-based resin film after the dyeing step with a crosslinking agent;

An electromagnetic wave irradiation step of irradiating electromagnetic waves including infrared rays to the polyvinyl alcohol-based resin film after the crosslinking step;

A cleaning step of cleaning the polyvinyl alcohol-based resin film after irradiating the electromagnetic waves;

In the electromagnetic wave irradiation step, the irradiation heat amount per unit volume of the electromagnetic wave of the polyvinyl alcohol-based resin film has a distribution in the width direction.

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

[3] In the infrared electromagnetic wave irradiation step, in [2], the radiation heat amount of the electromagnetic wave infrared rays in the first region is 100 J/cm 3 or more and 50 kJ/cm 3 or less per unit volume of the polyvinyl alcohol-based resin film. A method for producing the polarizing film described above.

[4] Described in any one of [1] to [3], in the electromagnetic wave irradiation step, irradiating electromagnetic waves in which the ratio of infrared radiant energy of a wavelength of more than 2 μm to 4 μm or less is 25% or more of the total radiant energy A method for producing a polarizing film.

[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 step of immersing the polyvinyl alcohol-based resin film in a crosslinking bath composed of an aqueous solution of the crosslinking agent. .

[7] The polarizing film according to [6], which further includes a liquid removal step of removing the aqueous solution adhering to the surface of the polyvinyl alcohol-based resin film after the crosslinking treatment and before irradiating the electromagnetic wave. manufacturing method.

[8] As a manufacturing apparatus for manufacturing a polarizing film from a polyvinyl alcohol-based resin film,

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

A cross-linking portion for cross-linking the polyvinyl alcohol-based resin film after the dyeing treatment with a cross-linking agent;

an electromagnetic wave irradiation unit for irradiating electromagnetic waves including infrared rays to the polyvinyl alcohol-based resin film after the crosslinking treatment;

A cleaning unit for cleaning the polyvinyl alcohol-based resin film after irradiating the electromagnetic waves,

The electromagnetic wave irradiation unit irradiates the electromagnetic wave so that the irradiation heat per unit volume of the electromagnetic wave of the polyvinyl alcohol-based resin film has a distribution in a width direction.

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

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

[11] The average value of the iodine (I) content at 10 measurement points in the width direction is 1.35 mass% or more, and the difference between the maximum and minimum iodine (I) content at the 10 measurement points is 0.60 mass% below,

The 10 measuring points are measuring points each included in 10 equal divisions of the total width in the width direction of the polarizing film.

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

ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method and manufacturing apparatus of a polarizing film which reduce nonuniformity of a polarizing film property can be provided. In addition, according to the present invention, it is possible to provide a polarizing film having uniform characteristics in the width direction.

1 is a cross-sectional view schematically showing an example of a method for manufacturing a polarizing film according to the present invention and a polarizing film manufacturing apparatus used therefor.
2 is a diagram showing a radiant energy spectrum for each type of electromagnetic wave irradiator.
3 is a graph plotting measured values of Py in Example 1, Comparative Example 1, and Comparative Example 2.
4 is a graph plotting b values of orthogonal colors of Example 1, Comparative Example 1, and Comparative Example 2.

<Method for producing polarizing film>

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

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

In the present invention, as a starting material for producing a polarizing film, unstretched polyvinyl having a thickness of 65 μm or less (for example, 60 μm or less), preferably 50 μm or less, more preferably 35 μm or less, still more preferably 30 μm or less An alcohol-based resin film (raw film) is used. Accordingly, it is possible to obtain a thin polarizing film for which market demand is gradually increasing. The width of the raw film is not particularly limited, and is, for example, about 400 to 6000 mm, preferably 2000 mm or more. In particular, since the properties of the polarizing film in the width direction tend to become non-uniform when the width of the raw film is 2000 mm or more, the manufacturing method of the present invention is effective. The raw film is prepared, for example, as a roll (raw material roll) of a long unstretched polyvinyl alcohol-based resin film.

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

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

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

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

When the present inventors examined nonuniformity of polarizing film properties, they obtained the knowledge that nonuniformity tends to occur in the width direction. The present inventors further studied and found out that nonuniformity in width direction characteristics of a polarizing film can be suppressed by performing an electromagnetic wave irradiation step described later in which the film is irradiated with electromagnetic waves after the crosslinking treatment and before the washing treatment, arrived at the present invention.

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

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

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

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

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

(swelling process)

The swelling process is performed for purposes such as removal of foreign matter on the surface of the raw film 10, removal of plasticizers in the raw film 10, provision of discoloration, plasticization of the raw film 10, and the like. The processing conditions are determined within a range that can achieve the above object and within a range that does not cause problems such as extreme dissolution of the raw film 10 or loss of transparency.

1, the swelling process is carried out along the film transport path while continuously unwinding the raw film 10 from the raw material roll 11, immersing the raw film 10 in the swelling bath 13 for a predetermined time, , which can then be carried out by withdrawing. 1, the raw film 10 is constructed by the guide rolls 60 and 61 and the nip roll 50 between the unwinding of the raw film 10 and the immersion in the swelling bath 13. It is transported along the designated film transport path. In the swelling process, it is conveyed along the film conveyance path constructed by the guide rolls 30 to 32 and the nip rolls 51.

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

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

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

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

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

(dyeing process)

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

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

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

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

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

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

(Crosslinking process)

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

As the crosslinking liquid, a solution in which a crosslinking agent is dissolved in a solvent can be used. As a crosslinking agent, boron compounds, such as boric acid and borax, glyoxal, glutaraldehyde, etc. are mentioned, for example. One type may be sufficient as these, and they may use two or more types together. As the solvent, for example, water can be used, but an organic solvent compatible with water may be further included. The concentration of the crosslinking agent in the crosslinking solution is not limited thereto, but is preferably in the range of 1 to 20% by weight, more preferably 6 to 15% by weight.

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

In the crosslinking treatment, the concentrations of boric acid and iodide and the temperature of the crosslinking bath 17 can be appropriately changed according to the purpose. For example, in the case of the first crosslinking liquid, in which the purpose of the crosslinking treatment is water resistance by crosslinking, it may be an aqueous solution having a concentration of boric acid/iodide/water = 3 to 10/1 to 20/100 in weight ratio. If necessary, other crosslinking agents may be used instead of boric acid, or boric acid and other crosslinking agents may be used in combination. The temperature of the first crosslinking bath 17a when immersing the film is usually about 50 to 70°C, preferably about 53 to 65°C, and the immersion time of the film is usually about 10 to 600 seconds, preferably about 20 to 300°C. seconds, more preferably 20 to 200 seconds. Further, when the dyeing treatment and the first crosslinking treatment are performed in this order on the polyvinyl alcohol-based resin film stretched in advance before the swelling treatment, the temperature of the first crosslinking bath 17a is usually about 50 to 85° C., preferably is 55 to 80 ° C.

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

The crosslinking treatment may be performed a plurality of times, and is usually performed 2 to 5 times. In this case, the composition and temperature of each crosslinking bath to be used may be the same or different as long as they are within the above ranges. The crosslinking treatment for waterproofing by crosslinking and the crosslinking treatment for color adjustment may be performed in a plurality of steps, respectively.

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

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

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

(cleaning process)

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

1 shows an example in which a polyvinyl alcohol-based resin film is immersed in a cleaning bath 19 to perform cleaning treatment. The temperature of the washing bath 19 in the washing treatment is usually about 2 to 40°C, and the immersion time of the film is usually about 2 to 120 seconds.

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

(stretching process)

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

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

(electromagnetic wave irradiation process)

In the apparatus shown in FIG. 1, after the film is taken out from the second crosslinking step 17b and passed through the nip rolls 53b, and before being immersed in the washing bath 19, the film is irradiated with electromagnetic waves (electromagnetic wave irradiation). process) is performed. In the device shown in FIG. 1 , electromagnetic waves are irradiated from the electromagnetic wave irradiation unit 71 . From the electromagnetic wave irradiation unit, the electromagnetic wave is irradiated 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, a polyvinyl alcohol-based resin film is disposed in the width direction in a first region including a center and not including an edge, and located on both sides of the first region, including an edge and not including a center. It is divided into the second region, and the irradiation heat per unit volume of electromagnetic waves is different in the first region and the second region. When the first area and the second area are contrasted as described above, non-uniformity in optical properties such as color tends to occur easily. In the electromagnetic wave irradiation step, the non-uniformity of the optical properties can be suppressed by setting the radiated heat amount per unit volume of the electromagnetic waves in the first region to be greater than the radiated heat amount per unit volume of the electromagnetic waves in the second region. The difference in the amount of irradiation can be appropriately selected, for example, the amount of heat irradiation in the first area may be selected so that it is twice or more than the amount of heat irradiated in the second area, or the first area is irradiated with electromagnetic waves, and the second area is Electromagnetic waves may not be irradiated.

The ratio of the width of the first region to the sum of the widths of the two second regions can be, for example, in the range of 10:1 to 1:10. Such a ratio can be selected according to the situation of non-uniformity of characteristics to be improved.

The non-uniformity of the optical properties is such that in each of the above-described treatment steps, the treatment liquid penetrates more easily from the end surface than from the surface of the polyvinyl alcohol-based resin film, resulting in a difference in the amount of penetration of the treatment liquid near the end and near the center, which affects the degree of treatment. Differences are predicted to be a factor. In addition, it is predicted that one factor is that nonuniformity in thickness occurs in the width direction due to stretching, and a difference in processing degree in each processing step occurs depending on the thickness. Examining these factors, the polyvinyl alcohol-based resin film is not limited to the method of dividing the polyvinyl alcohol-based resin film into "second region/first region/second region" as described above in the width direction, and the first region and the second region It is also possible to divide the two regions so that one or more regions exist between the two regions, and the irradiation heat amount per unit volume of the electromagnetic waves may be different for each region.

As a method of irradiating electromagnetic waves to have a distribution in the width direction,

i) having a distribution in the width direction of the radiant heat of the electromagnetic waves emitted from the electromagnetic wave irradiation unit;

ii) Absorbing a part of the electromagnetic waves emitted from the electromagnetic wave irradiation unit so as to have a distribution in the width direction with a mask or the like.

As an example of the specific method of i), the electromagnetic wave radiation area (heater heating unit) of the electromagnetic wave irradiation unit 71 corresponds to only a part of the width direction of the polyvinyl alcohol-based resin film, so that the electromagnetic wave radiation area corresponds to the electromagnetic wave radiation area. is irradiated, and the electromagnetic waves are not irradiated to positions that do not correspond to the electromagnetic wave radiation area, or the radiation heat amount of the electromagnetic waves is reduced (in some cases, the irradiation light is irradiated by widening), so that the electromagnetic waves are irradiated so as to have a distribution in the width direction. .

The present invention was completed based on the discovery that irradiation of electromagnetic waves including infrared rays can affect properties such as optical properties of a polarizing film. In addition, the optical characteristics can be further improved by irradiating electromagnetic waves having a ratio of infrared radiant energy of 25% or more of the total radiant energy, especially having a wavelength of more than 2 μm and 4 μm or less. In one embodiment of the present invention, non-uniformity in optical properties such as color can be suppressed by adjusting the amount of radiated heat per unit volume of electromagnetic waves in the first region to be greater than the amount of radiated heat per unit volume of electromagnetic waves in the second region. can Also, at the same time, the color can be enhanced to approach neutral gray as a whole. Non-uniformity occurs in the width direction, and as a characteristic in which the characteristics of the first region are lower than those of the second region, there are optical characteristics such as color.

On the other hand, unlike the above characteristics, when electromagnetic wave irradiation is effective for characteristics in which the characteristics of the first region are higher than those of the second region, in order to improve the non-uniformity of these characteristics, in the second region It is possible to improve the non-uniformity of characteristics by adjusting the radiated heat amount per unit volume of the electromagnetic waves in the first region to be greater than the radiated heat amount per unit volume of the electromagnetic waves in the first region. In addition, in the case where the characteristics that act according to the wavelength of the electromagnetic wave are different, the distribution of the amount of irradiation heat may be adjusted for each wavelength region.

From the viewpoint of improving the non-uniformity of optical properties such as color, the electromagnetic waves used in the electromagnetic wave irradiation process preferably have a wavelength of more than 2 μm and not more than 4 μm. , More preferably, it is 28% or more, and even more preferably, it is 35% or more. By irradiating the film with such electromagnetic waves to have a distribution in the width direction, non-uniformity in optical properties such as color of the obtained polarizing film can be further improved. In addition, the upper limit of the ratio of the radiant energy of infrared rays having a wavelength of more than 2 μm and not more than 4 μm is not particularly limited, but is, for example, 80% or less. In general, electromagnetic waves with a wavelength of 0.75 μm to 1000 μm are called infrared rays.

In the electromagnetic wave irradiation process, by irradiating electromagnetic waves in which the ratio of infrared radiant energy of a wavelength of more than 2 μm to 4 μm or less is 25% or more of the total radiant energy, the mechanism that can effectively improve the optical properties of the polarizing film is not clear. , Molecular motion in the film excited by infrared rays having a wavelength of more than 2 μm and not more than 4 μm promotes the immobilization of dichroic dyes such as iodine in the crosslinked film, thereby improving the optical properties of the polarizing film, etc. guessed

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

As shown in Table 1, short-wavelength infrared heater (heat source temperature 2200 ° C), high-speed response mid-wavelength infrared heater (heat source temperature 1600 ° C), carbon heater (heat source temperature 1200 ° C), carbon heater (heat source temperature 950 ° C), medium-wavelength Since the infrared heater (heat source temperature: 900° C.) has a ratio of infrared radiant energy of a wavelength exceeding 2 μm to 4 μm or less of the total radiant energy of 25% or more, it can be suitably used as an electromagnetic wave irradiator constituting the electromagnetic wave irradiation unit 71. there is. The electromagnetic wave irradiation unit 71 may be composed of one electromagnetic wave irradiator, or may be composed of several electromagnetic wave irradiators. By adjusting the arrangement method of a plurality of electromagnetic wave irradiators, it is also possible to perform irradiation having a distribution in the width direction. If it is composed of several electromagnetic wave irradiators, the radiant energy of infrared rays having a wavelength of more than 2 μm and less than 4 μm emitted from the multiple electromagnetic wave irradiators is 25% or more of the total radiation energy of the electromagnetic waves emitted from the multiple electromagnetic wave irradiators. It is desirable to select several microwave irradiators. In FIG. 1, the electromagnetic wave irradiation unit 71 is configured so that only one side of the film is irradiated with electromagnetic waves, but a plurality of electromagnetic wave irradiators may be arranged so that electromagnetic waves are irradiated from both sides of the film. For example, the first region may be irradiated with electromagnetic waves from both sides, and the second region may be irradiated with electromagnetic waves from only one side, so that the radiation amount per unit volume in the width direction is distributed.

In the electromagnetic wave irradiation step, electromagnetic waves are preferably irradiated from above in a direction perpendicular to the film surface. Further, the distance between the electromagnetic wave spinneret of the electromagnetic wave irradiator in the electromagnetic wave irradiator 71 and the film is preferably 2 to 40 cm, and more preferably 5 to 20 cm. However, it is preferable to select this distance appropriately in consideration of the amount of radiant energy of electromagnetic waves emitted from the electromagnetic wave irradiator, the temperature of the surface of the film, and the like. The temperature of the surface of the film during electromagnetic wave irradiation is preferably maintained at 25 to 90°C, more preferably at 30 to 80°C.

In the electromagnetic wave irradiation step, the irradiation heat amount of electromagnetic waves per unit volume of the film can be usually 100 J/cm 3 or more and 50 kJ/cm 3 or less. From the viewpoint of improving the optical properties of the polarizing film, in the region where the irradiation heat amount is the largest in the width direction, it is preferably 100 J/cm 3 or more, more preferably 500 J/cm 3 or more, and still more preferably 1000 J/cm 3 or more. desirable. Further, from the viewpoint of suppressing deterioration of the film due to temperature rise, the irradiation heat amount of electromagnetic waves per unit volume of the film is preferably 10 kJ/cm 3 or less in a region where the irradiation heat amount is the maximum in the width direction, and is 5000 J /cm 3 or less is more preferable, and 3000 J/cm 3 or less is still more preferable.

Normally, the amount of moisture in the film decreases in proportion to the amount of heat irradiated with electromagnetic waves. However, since the purpose of the electromagnetic wave irradiation step of the present invention is not to reduce the amount of moisture in the film, the amount of heat irradiation can be appropriately selected, preferably as described above. Select appropriately within the range. The region having the maximum irradiation heat amount in the width direction can be, for example, the above-described first region including the center and not including the end portions.

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

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

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

Furthermore, the inventors of the present invention obtained the knowledge that nonuniformity tends to occur easily in the content of iodine (I) in the width direction of the polarizing film. The non-uniformity of the iodine (I) content in the polarizing film causes non-uniformity in optical properties such as monolithic transmittance, non-uniformity in durability, and the like. The present inventors repeatedly studied intensively and, in the electromagnetic wave irradiation step, increased the irradiation heat amount per unit volume of electromagnetic waves in the first region than the irradiation heat amount per unit volume of electromagnetic waves in the second region, so that iodine (I ), it was found that the non-uniformity of the content can be suppressed. For example, by irradiating only the first region with electromagnetic waves, non-uniformity in iodine (I) content can be suppressed. Based on the width of the entire polyvinyl alcohol-based resin film, the width of the first region can be, for example, 5 to 95%, preferably 40 to 90%, and more preferably 60 to 90%. Also in the electromagnetic wave irradiation step for the purpose of suppressing non-uniformity in the iodine (I) content, the above description of the electromagnetic wave irradiation step for the purpose of suppressing non-uniformity in properties is applied. In one aspect, the first region is a region centered on the center of the polyvinyl alcohol-based resin film, and the first region and the second region having the same length in the width direction are located on both sides of the first region in the width direction. 2 areas are separated.

(drying process)

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

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

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

<Polarizing film>

By the method described above, a polarizing film in which non-uniformity in width direction properties is suppressed can be obtained. It is preferable that it is 40 to 47 %, and, as for the visibility correction|amendment monolithic transmittance Ty of the obtained polarizing film, considering the balance with the visibility correction|amendment polarization degree Py, it is more preferable that it is 41 to 45 %. The visibility correction polarization degree Py is preferably 99.9% or more, more preferably 99.95% or more, and a larger value is preferable.

It is preferable that it is -3.0 to +0.5, and, as for the b-value of orthogonal hue of the polarizing film obtained, it is more preferable that it is -2.0 to 0. With this value, the orthogonal hue does not shift excessively to blue, and becomes neutral gray. Further, when the b values of orthogonal hues are measured at a plurality of points in the width direction at arbitrary positions in the length direction, it is preferable that the non-uniformity of the measured values is small. Specifically, the measurement points at both ends in the width direction are determined at positions at a distance of 0.5 to 50 mm from the end of the film, and the remaining 13 measurement points are determined so that adjacent measurement points are equally spaced between measurement points at both ends. Thus, when the b values of orthogonal hues are measured at a total of 15 measurement points, the standard deviation is preferably 0.2 or less, more preferably 0.1 or less. Further, the difference between the maximum value and the minimum value of b 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 according to the description in the section of Examples described later. According to one aspect of the present invention, a polarizing film having the standard deviation of b values of orthogonal colors of 0.2 or less can be obtained. Ty, Py, and the b value of orthogonal color are measured by the following method.

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

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

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

Calculate the monolithic transmittance and polarization degree at each wavelength based on .

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

Further, according to the method described above, the iodine (I) content at 10 measurement points in the width direction simultaneously satisfies the following conditions i) and ii), a polarizing film with little non-uniformity in the iodine (I) content can be obtained.

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

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

In addition, the 10 measurement points are not limited as long as they are each included in a section in which the total width in the width direction is divided into 10 equal parts, and if a combination of 10 points simultaneously satisfying the conditions of i) and ii) exists, the above A polarizing film that simultaneously satisfies the conditions of i) and ii). Normally, the content of iodine (I) does not fluctuate greatly in each area where the total width in the width direction is divided into 10 equal parts, so the conditions of i) and ii) above for any combination of 10 points is not satisfied, it can be considered that there is no combination of 10 points that simultaneously satisfies the above conditions i) and ii). Moreover, content (mass %) of iodine (I) in a polarizing film is based on the analysis result by fluorescence X-ray analysis as described in the Example.

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

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

<Polarizer>

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

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

[Example]

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

<Example 1>

The polarizing film of Example 1 was manufactured from the polyvinyl alcohol-type resin film using the manufacturing apparatus shown in FIG. Specifically, a long polyvinyl alcohol (PVA) raw film with a width of 550 nm and a thickness of 60 μm [trade name “Kurare Vinylon VF-PE # 6000” manufactured by Kuraray, average degree of polymerization 2400, degree of saponification 99.9 mol% or more ] was continuously conveyed while being unwound from the roll, and was immersed in a swelling bath made of pure water at 30°C with a residence time of 79 seconds (swelling step). Thereafter, the film taken out from the swelling bath was immersed in a dyeing bath at 30°C containing iodine in a ratio of potassium iodide/boric acid/water to 1/0.3/100 (weight ratio) at a residence time of 123 seconds (dyeing step). Subsequently, the film taken out from the dyeing bath was immersed in a first crosslinking bath at 53° C. containing potassium iodide/boric acid/water in a ratio of 11/3.8/100 (weight ratio) at a residence time of 44 seconds, and then potassium iodide/boric acid/water It was immersed in the 40 degreeC 2nd crosslinking bath of 11/3.8/100 (weight ratio) with a residence time of 6 seconds (crosslinking process). In the dyeing step and the crosslinking step, longitudinal uniaxial stretching was performed by inter-roll stretching in a bath. The total draw ratio based on the fabric film was 5.65 times.

Next, with respect to the film having a width of 280 mm that was taken out from the second cross-linking bath 17b and passed through the nip rolls 53b, the center portion in the width direction of the film was arranged so as to be substantially parallel to the width direction of the film. 230 mm irradiation length (width direction of heater heating part) electromagnetic wave irradiator (fast response medium-wave infrared heater (FRMW heater), product name: Golden 8 Medium-wave fast response twin tube emitter, manufactured by Heraeus, heat source temperature 1600 ℃ , maximum energy density of 150 kW/m2), the electromagnetic wave spinneret was placed 5 cm away from the surface of the film, and electromagnetic waves were irradiated at 50% of the maximum irradiation output of the electromagnetic wave irradiator.

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

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

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

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

The film irradiated with electromagnetic waves was immersed in a cleaning bath 19 made of pure water at 5° C. for a residence time of 3 seconds (cleaning step). Thereafter, within the drying furnace 21, the film was dried 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 micrometers.

<Comparative Example 1>

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

<Comparative Example 2>

For the film taken out from the second crosslinking bath 17b and passed through the nip roll 53b, the irradiation length in the width direction of the film (heater heating Length in the width direction of the part) 400 mm electromagnetic wave irradiator (Fast Response Medium Wave Infrared Heater (FRMW Heater), product name: Golden 8 Medium-wave fast response twin tube emitter, manufactured by Heraeus, heat source temperature 1600℃, maximum energy density 150 kW /m 2 ) was used, and a polarizing film was obtained in the same manner as in Example 1 except that electromagnetic waves were irradiated at an output of 40%. In the entire area of the film in the width direction, the amount of heat irradiation of electromagnetic waves per unit volume was 820 J/cm 3 . The thickness of the obtained polarizing film was 23 micrometers.

[Evaluation of polarizing films of Example 1, Comparative Example 1 and Comparative Example 2]

(a) Measurement of polarization degree and b value of orthogonal color

Regarding the polarizing films obtained in Example 1, Comparative Example 1, and Comparative Example 2, at an arbitrary position in the longitudinal direction, 15 measurement points were determined in the width direction, based on the method described above, the visibility correction polarization degree (Py ) and the b value of the orthogonal color was obtained. In addition, as for the 15 measurement points, the measurement points at both ends in the width direction are determined as positions at a distance of 10 mm from the end of the film, and the remaining 13 measurement points are equally spaced between the measurement points at both ends so that adjacent measurement points are equally spaced. was determined, and the visibility corrected polarization degree (Py) and the b value of the orthogonal color at a total of 15 measurement points (measurement points 1 to 15) were obtained. Table 2 shows the measurement results.

3 is a graph plotting the measurement results of Py shown in Table 2. Fig. 4 is a graph plotting measurement results of b values of orthogonal colors shown in Table 2; Table 3 shows the results of calculating the difference between the average value, standard deviation, and maximum and minimum values of the visibility correction polarization degree (Py) and the orthogonal color b value, based on the measurement results shown in Table 2.

As shown in Table 3, in the polarizing film of Example 1, the unevenness of the b-value of the orthogonal color in the width direction is reduced compared to Comparative Examples 1 and 2, and the Py is larger than that of Comparative Example 1, and the b-value of the orthogonal color is reduced. The value of was small and had excellent optical properties.

<Example 2>

The polarizing film of Example 2 was manufactured from the polyvinyl alcohol-type resin film using the manufacturing apparatus shown in FIG. Specifically, a long polyvinyl alcohol (PVA) raw film with a width of 2590 mm and a thickness of 45 μm [trade name “Kurare Vinylon VF-PE # 4500” manufactured by Kuraray, average degree of polymerization 2400, degree of saponification 99.9 mol% above] was continuously transported while being unwound from the roll, and immersed in a swelling bath made of pure water at 28°C for a residence time of 56 seconds (swelling step). Thereafter, the film taken out from the swelling bath was immersed in a 30°C dyeing bath containing iodine in a ratio of potassium iodide/boric acid/water of 1.5/0.3/100 (weight ratio) at a residence time of 80 seconds (dyeing step). Subsequently, the film taken out from the dyeing bath was immersed in a first crosslinking bath at 55.5°C in which potassium iodide/boric acid/water was 11.3/2.9/100 (weight ratio) at a residence time of 34 seconds, and then potassium iodide/boric acid/water It was immersed in the 40 degreeC 2nd crosslinking bath of 12/4/100 (weight ratio) with a residence time of 5 seconds (crosslinking process). In the dyeing process and the crosslinking process, longitudinal uniaxial stretching was performed by inter-roll stretching in a bath. The total draw ratio based on the raw film was 5.89 times.

Then, with respect to the film having a width of 1290 mm that was taken out from the second crosslinking bath 17b and passed through the nip rolls 53b, the center portion in the width direction of the film was arranged so as to be substantially parallel to the width direction of the film. 830 mm irradiation length (length in the width direction of the heater heating part) (high-speed response mid-wave infrared heater (FRMW heater), product name: Golden 8 Medium-wave fast response twin tube emitter, manufactured by Heraeus, heat source temperature 1600 ° C) , maximum energy density of 150 kW/m2), the electromagnetic wave spinneret was placed 5 cm away from the surface of the film, and electromagnetic waves were irradiated with an output of 65%.

The irradiation heat amount of electromagnetic waves per unit volume in an area with a width of 830 mm centered on the center in the width direction of the film (an area with a width of 64% of the total width) was 2310 J/cm 3 . On the other hand, since the irradiation length of the electromagnetic wave irradiator was shorter than the length in the width direction of the film, electromagnetic waves were not irradiated near the end of the film. The radiation heat amount of the electromagnetic waves per unit volume in the 0 mm region from the end of the film was 0 J/cm 3 . In addition, the irradiation heat amount of electromagnetic waves per film unit volume was calculated by the following formula.

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

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

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

The film irradiated with electromagnetic waves was immersed in a cleaning bath 19 made of pure water at 10° C. for a residence time of 5 seconds (cleaning step). Then, within the drying furnace 21, the film was dried at the temperature of 88 degreeC, and the polarizing film was obtained. The obtained polarizing film had a thickness of 18 µm and a width of 1080 mm.

<Example 3>

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

<Comparative Example 3>

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

[Evaluation of the polarizing films of Example 2, Example 3 and Comparative Example 3]

(b) measurement of iodine (I) content

Regarding the polarizing films obtained in Example 2, Example 3 and Comparative Example 3, in an arbitrary position in the longitudinal direction, 10 measurement points (measurement points 1 to 10) were determined in the width direction, and the following method was performed at each measurement point. Based on the iodine concentration was measured. In addition, as for the 10 measurement points, the measurement points at both ends in the width direction are determined to be positions at a distance of 10 mm from the end of the film, and between the measurement points at both ends, the remaining 8 points are set so that adjacent measurement points are spaced at equal intervals. The measuring point was determined. The determined 10 measurement points are measurement points included in each section of a width of 108 mm obtained by dividing the entire width of 1080 mm in the width direction into 10 equal parts.

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

Measuring device: Fluorescent X-ray analyzer (device name: AXIOS, manufactured by PANalytical)

X-ray source: Rh

Output: 30 kV, 100 mA

Measuring diameter: 27 mmφ

Measurement method: 0.15 g of polarizing film was taken so as to include each measuring point, each sample was dissolved in 20 ml of pure water, sealed, heated to 90°C to dissolve the polarizing film, and used as a measurement solution. The measurement result was compared with a calibration curve prepared with a standard solution, and the iodine concentration in the solution was calculated. From the obtained iodine concentration, it was converted into the polarizing film weight, and it was set as iodine content (mass %). Table 4 shows the measurement results.

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

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

Claims (12)

As a method for producing a polarizing film from a polyvinyl alcohol-based resin film,
A dyeing step of dyeing the polyvinyl alcohol-based resin film with a dichroic dye;
A crosslinking step of crosslinking the polyvinyl alcohol-based resin film after the dyeing step with a crosslinking agent;
An electromagnetic wave irradiation step of irradiating electromagnetic waves including infrared rays to the polyvinyl alcohol-based resin film after the crosslinking step;
A cleaning step of cleaning the polyvinyl alcohol-based resin film after irradiating the electromagnetic waves;
In the electromagnetic wave irradiation step, in the width direction of the polyvinyl alcohol-based resin film, the amount of radiation heat per unit volume of the electromagnetic waves in the first region including the center but not including the edges is A method for producing a polarizing film, which is greater than the irradiation heat amount per unit volume of the electromagnetic waves in the second region that does not contain. delete The polarized light according to claim 1, wherein in the infrared electromagnetic wave irradiation step, an irradiation heat amount of the infrared electromagnetic wave in the first region is 100 J/cm 3 or more and 50 kJ/cm 3 or less per unit volume of the polyvinyl alcohol-based resin film. How to make a film. The method for producing a polarizing film according to claim 1 or 3, wherein in the electromagnetic wave irradiation step, electromagnetic waves having a ratio of infrared radiant energy having a wavelength of more than 2 μm to 4 μm or less of 25% or more of the total radiant energy are irradiated. The method for manufacturing a polarizing film according to claim 1 or 3, wherein the crosslinking agent includes a boron compound. The method for producing a polarizing film according to claim 1 or 3, wherein the crosslinking step is a step of immersing the polyvinyl alcohol-based resin film in a crosslinking bath composed of an aqueous solution of the crosslinking agent. The method for producing a polarizing film according to claim 6, further comprising a liquid removal step of removing the aqueous solution adhering to the surface of the polyvinyl alcohol-based resin film after the crosslinking treatment and before irradiating the electromagnetic waves. A manufacturing apparatus for manufacturing a polarizing film from a polyvinyl alcohol-based resin film,
A dyeing unit for dyeing the polyvinyl alcohol-based resin film with a dichroic dye;
A cross-linking portion for cross-linking the polyvinyl alcohol-based resin film after the dyeing treatment with a cross-linking agent;
an electromagnetic wave irradiation unit for irradiating electromagnetic waves including infrared rays to the polyvinyl alcohol-based resin film after the crosslinking treatment;
A cleaning unit for cleaning the polyvinyl alcohol-based resin film after irradiating the electromagnetic waves,
In the electromagnetic wave irradiation unit, in the width direction of the polyvinyl alcohol-based resin film, the amount of radiation heat per unit volume of the electromagnetic waves in the first region including the center and not including the end portion includes the end portion and includes the center portion The apparatus for producing a polarizing film, wherein the electromagnetic wave is irradiated so as to be greater than the irradiation heat amount per unit volume of the electromagnetic wave in a second region where the polarization film is not applied. The method for producing a polarizing film according to claim 1 or 3, wherein in the electromagnetic wave irradiation step, only the first region is irradiated with electromagnetic waves. The method of manufacturing a polarizing film according to claim 9, wherein the width of the first region is 60% to 90% of the total width of the polyvinyl alcohol-based resin film. The average value of the iodine (I) content at 10 measuring points in the width direction is 1.35 mass% or more, and the difference between the maximum and minimum iodine (I) content at the 10 measuring points is 0.60 mass% or less,
The 10 measuring points are measuring points each included in 10 equal divisions of the total width in the width direction of the polarizing film. The polarizing film according to claim 11, wherein the average value of the iodine (I) content at the 10 measurement points is 1.65% by mass or more.

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