JP7129766B2 - Manufacturing method and manufacturing apparatus for polarizing film - Google Patents

Description

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

A polarizing plate is widely used as a polarizing element or the like in an image display device such as a liquid crystal display device. A polarizing plate generally has a structure in which a transparent resin film (protective film or the like) is laminated on one or both sides of a polarizing film using an adhesive or the like.

The polarizing film is mainly made by immersing a raw film made of polyvinyl alcohol resin in a dyeing bath containing a dichroic dye such as iodine, and then immersing it in a cross-linking bath containing a cross-linking agent such as boric acid. It is manufactured by subjecting the film to uniaxial stretching at some stage while applying processing such as stretching. Uniaxial stretching includes dry stretching in the air and wet stretching in a liquid such as the above-mentioned dyeing bath or cross-linking bath.

Conventionally, in the method for producing a polarizing film, various measures have been taken to improve the properties of the polarizing film. In Japanese Patent Application Laid-Open No. 2013-148806 (Patent Document 1), a primary drying step for drying a polyvinyl alcohol resin film is provided between a boric acid treatment step and a water washing step, thereby making transmitted light a good hue. In other words, it is possible to approach a neutral gray.

In Japanese Patent Application Laid-Open No. 59-094706 (Patent Document 2), a polarizing film having a small shrinkage rate and good flatness is obtained by performing a fixing treatment by irradiating far infrared rays having a wavelength of 1 μm or more. It is stated that

JP 2013-148806 A JP-A-59-094706

In addition to the hue, shrinkage ratio, and flatness described above, there are various properties required for polarizing films, and optical properties indexed by single transmittance and degree of polarization are important properties. A cross-linking treatment using a cross-linking agent such as boric acid to fix a dichroic dye such as iodine is also one of the methods that can improve water resistance and optical properties.

In the method described in Patent Document 1, although a cross-linking treatment is performed, it is not clear whether the optical properties of the polarizing film can be further improved by performing the primary drying step. In the method described in Patent Document 2, cross-linking treatment is not performed, and the results show that the degree of polarization decreases by performing the step of irradiating far infrared rays (Table 1 of Patent Document 2 Comparison of the degree of polarization of the examples in which the indicated immobilization treatment method is "before treatment" and "far infrared rays").

An object of the present invention is to provide a method for producing a polarizing film that can further improve the optical properties of the polarizing film, and an apparatus for producing the same, in the method for producing a polarizing film that performs a cross-linking treatment.

The present invention provides the following manufacturing method and manufacturing apparatus for a polarizing film.
[1] A method for producing a polarizing film from a polyvinyl alcohol resin film, comprising:
A dyeing step of dyeing the polyvinyl alcohol resin film with a dichroic dye;
A cross-linking step of cross-linking the polyvinyl alcohol-based resin film after the dyeing treatment with a cross-linking agent;
an electromagnetic wave irradiation step of irradiating the polyvinyl alcohol-based resin film after the cross-linking treatment with an electromagnetic wave in which the ratio of the radiant energy of infrared rays with a wavelength of more than 2 μm and 4 μm or less in the total radiant energy is 25% or more of the total radiant energy;
and a washing step of washing the polyvinyl alcohol-based resin film after being irradiated with the electromagnetic waves.

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

[3] The method for producing a polarizing film according to [1] or [2], wherein the cross-linking agent contains a boron compound.

[4] The method for producing a polarizing film according to any one of [1] to [3], wherein the cross-linking step is a step of immersing the polyvinyl alcohol-based resin film in a cross-linking bath containing an aqueous solution of the cross-linking agent. .

[5] The polarizing film according to [4], further comprising a liquid removing step of removing the aqueous solution adhering to the surface of the polyvinyl alcohol-based resin film after the cross-linking treatment and before the electromagnetic wave irradiation. manufacturing method.

[6] The method for producing a polarizing film according to [4] or [5], wherein the electromagnetic wave irradiation step is performed within 5 seconds after the polyvinyl alcohol-based resin film is pulled out from the cross-linking bath.

[7] A manufacturing apparatus for manufacturing a polarizing film from a polyvinyl alcohol resin film,
A dyeing unit that dyes the polyvinyl alcohol-based resin film with a dichroic dye;
A cross-linking unit that cross-links the polyvinyl alcohol-based resin film after the dyeing process with a cross-linking agent;
an electromagnetic wave irradiation unit that irradiates the polyvinyl alcohol-based resin film after the cross-linking treatment with an electromagnetic wave in which the proportion of the radiant energy of infrared rays having a wavelength of more than 2 μm and 4 μm or less is 25% or more of the total radiant energy;
A manufacturing apparatus for a polarizing film, comprising: a washing unit for washing the polyvinyl alcohol-based resin film after being irradiated with the electromagnetic wave.

ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method and manufacturing apparatus of a polarizing film which can improve the optical characteristic of a polarizing film can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS It is sectional drawing which shows typically an example of the manufacturing method of the polarizing film which concerns on this invention, and a polarizing film manufacturing apparatus used therewith. FIG. 4 is a diagram showing radiant energy spectra for each type of electromagnetic wave irradiator;

<Method for producing polarizing film>
In the present invention, the polarizing film is a uniaxially stretched polyvinyl alcohol resin film in which a dichroic dye (iodine or dichroic dye) is adsorbed and oriented. The polyvinyl alcohol-based resin that constitutes the polyvinyl alcohol-based resin film is usually obtained by saponifying a polyvinyl acetate-based resin. The degree of saponification is generally about 85 mol% or more, preferably about 90 mol% or more, more preferably about 99 mol% or more. The polyvinyl acetate-based resin may be, for example, polyvinyl acetate, which is a homopolymer of vinyl acetate, or a copolymer of vinyl acetate and other monomers copolymerizable therewith. Examples of other copolymerizable monomers include unsaturated carboxylic acids, olefins, vinyl ethers, unsaturated sulfonic acids and the like. The degree of polymerization of the polyvinyl alcohol resin is generally about 1000-10000, preferably about 1500-5000.

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

In the present invention, as a starting material for polarizing film production, an unstretched polyvinyl alcohol-based resin film (original film film) is used.
This makes it possible to obtain a thin polarizing film for which market demand is increasing. The width of the raw film is not particularly limited, and can be, for example, about 400 to 6000 mm. The original film is prepared, for example, as a roll of a long unstretched polyvinyl alcohol-based resin film (original roll).

The polyvinyl alcohol-based resin film used in the present invention may be laminated on a substrate film that supports it. It may be prepared as a laminated film with a polyvinyl alcohol-based resin film. In this case, the polyvinyl alcohol-based resin film can be produced, for example, by applying a coating liquid containing the polyvinyl alcohol-based resin to at least one surface of the substrate film and then drying.

As the base film, for example, a film made of a thermoplastic resin can be used. A specific example is a film composed of a translucent thermoplastic resin, preferably an optically transparent thermoplastic resin, such as a linear polyolefin resin (polypropylene resin, etc.), a cyclic polyolefin resin Polyolefin resins such as (norbornene resins, etc.); Cellulose resins such as triacetyl cellulose and diacetyl cellulose; Polyester resins such as polyethylene terephthalate and polybutylene terephthalate; Polycarbonate resins; (meth)acrylic resin; polystyrene resin; polyvinyl chloride resin; acrylonitrile-butadiene-styrene resin; acrylonitrile-styrene resin; polyvinyl acetate resin; polyvinylidene chloride resin; polyamide resin; Resin; Modified polyphenylene ether-based resin; Polysulfone-based resin; Polyethersulfone-based resin; Polyarylate-based resin; Polyamideimide-based resin;

The polarizing film is produced by unwinding the long raw film from the raw roll and continuously conveying it along the film conveying route of the polarizing film manufacturing apparatus, and processing liquid contained in the processing tank (hereinafter referred to as A long polarizing film can be continuously produced by carrying out a drying step after carrying out a predetermined treatment step of immersing the film in a "treatment bath" and drawing it out. The treatment process is not limited to the method of immersing the film in the treatment bath as long as it is a method of contacting the film with the treatment solution, and the treatment solution is attached to the film surface by spraying, flowing, dripping, or the like. It may also be a method of processing the film by allowing the When the treatment step is performed by immersing the film in a treatment bath, the treatment bath in which one treatment step is performed is not limited to one. One processing step may be completed.

Examples of the treatment liquid include a swelling liquid, a dyeing liquid, a cross-linking liquid, a washing liquid, and the like. Then, as the above-mentioned treatment steps, a swelling step of contacting a swelling liquid to the raw film to perform a swelling treatment, a dyeing step of contacting a dyeing solution to the film after the swelling treatment and performing a dyeing process, and a dyeing process after the dyeing process Examples include a cross-linking step in which a cross-linking solution is brought into contact with the film and a cleaning step in which a cleaning solution is brought into contact with the film after the cross-linking treatment. In addition, between these series of treatment steps (that is, before and after any one or more treatment steps and/or during any one or more treatment steps), wet or dry uniaxial stretching treatment is performed. Other processing steps may be added as desired.

In the present invention, after the cross-linking treatment and before the washing treatment, the electromagnetic wave irradiation step, which will be described later, is performed to irradiate the film with an electromagnetic wave. By performing the electromagnetic wave irradiation step, the optical properties of the obtained polarizing film can be improved.

Hereinafter, an example of the method for producing a polarizing film according to the present invention will be described in detail with reference to FIG. FIG. 1 is a cross-sectional view schematically showing an example of a polarizing film manufacturing method and a polarizing film manufacturing apparatus used therein according to the present invention. The polarizing film manufacturing apparatus shown in FIG. 1 continuously unwinds a raw (unstretched) film 10 made of a polyvinyl alcohol-based resin from a raw roll 11 and conveys it along a film conveying route, thereby producing a film. A swelling bath (swelling liquid contained in the swelling tank) 13, a dyeing bath (dyeing liquid contained in the dyeing tank) 15, and a first cross-linking bath (first Crosslinking liquid) 17a, second crosslinking bath (second crosslinking liquid contained in crosslink tank) 17b, and washing bath (washing liquid contained in washing tank) 19 are sequentially passed, and finally pass through drying oven 21. It is configured to allow The obtained polarizing film 23 can be conveyed as it is to the next polarizing plate manufacturing step (the step of laminating a protective film on one side or both sides of the polarizing film 23), for example. The arrows in FIG. 1 indicate the transport direction of the film.

In the explanation of FIG. 1, "treatment tank" is a generic term including swelling tank, dyeing tank, cross-linking tank and washing tank, and "treatment liquid" is a generic term including swelling liquid, dyeing liquid, cross-linking liquid and washing liquid. , "treatment bath" is a generic term including swelling baths, dyeing baths, cross-linking baths and washing baths. The swelling bath, dyeing bath, cross-linking bath and cleaning bath respectively constitute the swelling section, dyeing section, cross-linking section and cleaning section in the manufacturing apparatus of the present invention.

In addition to the treatment bath, the film transport path of the polarizing film manufacturing apparatus includes guide rolls 30 to 48, 60, 61 that support the film to be transported or can change the film transport direction, and the film to be transported. It can be constructed by arranging nip rolls 50 to 55 at appropriate positions that can press and hold the and can apply a driving force to the film by its rotation, or can further change the film conveying direction. Guide rolls and nip rolls can be arranged before, after, or in each treatment bath, so that the film can be introduced into, immersed in, and pulled 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 transporting the film along these guide rolls.

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

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

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

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

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

The temperature of the swelling bath 13 is, for example, about 10 to 50.degree. C., preferably about 10 to 40.degree. C., more preferably about 15 to 30.degree. The immersion time of the original film 10 is preferably about 10 to 300 seconds, more preferably about 20 to 200 seconds. Further, when the original film 10 is a polyvinyl alcohol resin film stretched in advance in gas, the temperature of the swelling bath 13 is, for example, about 20 to 70.degree. C., preferably about 30 to 60.degree. The immersion time of the original film 10 is preferably about 30 to 300 seconds, more preferably about 60 to 240 seconds.

In the swelling treatment, the raw film 10 tends to swell in the width direction, causing wrinkles in the film. As one means for transporting the film while removing the wrinkles, a roll having a widening function such as an expander roll, a spiral roll, or a crown roll is used as the guide rolls 30, 31 and/or 32, or a cross guider or bend bar is used. , using other widening devices such as tenter clips. Another means for suppressing the occurrence of wrinkles is to apply a stretching treatment. For example, the uniaxial stretching process can be performed in the swelling bath 13 by utilizing the peripheral speed difference between the nip rolls 50 and 51 .

In the swelling process, the film swells and expands also in the transport direction of the film. Therefore, if the film is not actively stretched, it is placed, for example, before and after the swelling bath 13 in order to eliminate the slack of the film in the transport direction. It is preferable to take measures such as controlling the speed of the nip rolls 50 and 51 . In addition, for the purpose of stabilizing the film transport in the swelling bath 13, the water flow in the swelling bath 13 is controlled by a water shower, or an EPC device (Edge Position Control device: detects the edge of the film and controls the meandering of the film. It is also useful to use a device that prevents

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

(Dyeing process)
The dyeing step is performed for the purpose of adsorbing and orienting the dichroic dye on the polyvinyl alcohol-based resin film after the swelling treatment. The processing conditions are determined within a range in which the object can be achieved and in which problems such as extreme dissolution or devitrification of the film do not occur. Referring to FIG. 1, in the dyeing process, the film is conveyed along a film conveying path constructed by nip roll 51, guide rolls 33 to 36 and nip roll 52, and the film after swelling is stored in dyeing bath 15 (dyeing tank). It can be carried out by immersing the substrate in the treatment solution for a predetermined period of time and then withdrawing it. In order to enhance the dyeability of the dichroic dye, the film subjected to the dyeing process is preferably a film that has been uniaxially stretched to at least some degree, or instead of the uniaxial stretching process before the dyeing process, or In addition to the uniaxial stretching treatment before the dyeing treatment, it is preferable to perform the uniaxial stretching treatment during the dyeing treatment.

When iodine is used as the dichroic dye, the dyeing solution of the dyeing bath 15 has, for example, a concentration by weight of iodine/potassium iodide/water=about 0.003 to 0.3/about 0.1 to 10/ Aqueous solutions that are 100 can be used. Instead of potassium iodide, other iodides such as zinc iodide may be used, or potassium iodide and other iodides may be used in combination. Compounds other than iodide, such as boric acid, zinc chloride, and cobalt chloride, may coexist. When boric acid is added, it is distinguished from the cross-linking treatment described later in that it contains iodine. can be regarded as 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 film immersion time is usually 30 to 600 seconds. degree, preferably 60 to 300 seconds.

When a water-soluble dichroic dye is used as the dichroic dye, the dyeing solution in the dyeing bath 15 has a concentration by weight of the dichroic dye/water=about 0.001 to 0.1/100, for example. Aqueous solutions can be used. The dyeing bath 15 may contain a dyeing assistant or the like, and may contain, for example, an inorganic salt such as sodium sulfate or a surfactant. Only one type of dichroic dye may be used alone, or two or more types 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., and the immersion time of the film is usually about 30 to 600 seconds, preferably about 60 to 300 seconds. be.

As described above, in the dyeing process, the film may be uniaxially stretched in the dyeing bath 15 . The uniaxial stretching of the film can be performed by a method such as creating a peripheral speed difference between the nip rolls 51 and 52 arranged before and after the dyeing bath 15 .

In the dyeing process as well as in the swelling process, the guide rolls 33, 34, 35 and/or 36 are provided with expander rolls, spiral rolls, crown rolls, etc., in order to convey the polyvinyl alcohol resin film while removing wrinkles of the film. Rolls with a widening function can be used, or other widening devices such as cross guiders, bend bars, tenter clips can be used. Another means for suppressing the occurrence of wrinkles is to apply stretching treatment, as in the case of swelling treatment.

In the example shown in FIG. 1, the film drawn from dyeing bath 15 passes through guide roll 36, nip roll 52, and guide roll 37 in sequence and is introduced into cross-linking bath 17. In the example shown in FIG.

(Crosslinking step)
The cross-linking step is a process performed for the purpose of water resistance by cross-linking, hue adjustment (preventing the film from becoming bluish, etc.). In the example shown in FIG. 1, two cross-linking baths are arranged as cross-linking baths for carrying out the cross-linking step. A cross-linking step is performed in the second cross-linking bath 17b. Referring to FIG. 1, in the first cross-linking step, the film is transported along a transport path constructed by nip roll 52, guide rolls 37 to 40 and nip roll 53a, and first cross-linking bath 17a (the first cross-linking bath accommodated in the cross-linking bath). 1 cross-linking solution) after the dyeing treatment is immersed for a predetermined time and then pulled out. In the second cross-linking step, the film is transported along the film transport path constructed by the nip roll 53a, the guide rolls 41 to 44, and the nip roll 53b, and the second cross-linking bath 17b (the second cross-linking liquid contained in the cross-linking tank) is first It can be carried out by immersing the film after the cross-linking process for a predetermined time and then withdrawing it. Hereinafter, the term "cross-linking bath" includes both the first cross-linking bath 17a and the second cross-linking bath 17b, and the term "cross-linking liquid" includes both the first cross-linking liquid and the second cross-linking liquid.

As the cross-linking liquid, a solution obtained by dissolving a cross-linking agent in a solvent can be used. Examples of cross-linking agents include boron compounds such as boric acid and borax, glyoxal, and glutaraldehyde. One of these may be used, or two or more of them may be used in combination. As a solvent, for example, water can be used, but an organic solvent compatible with water may be included. The concentration of the cross-linking agent in the cross-linking solution is, but not limited to, preferably in the range of 1 to 20 wt %, more preferably 6 to 15 wt %.

The cross-linking liquid may be an aqueous solution containing, for example, about 1 to 10 parts by weight of boric acid per 100 parts by weight of water. When the dichroic dye used in the dyeing treatment is iodine, the cross-linking liquid preferably contains iodide in addition to boric acid, and the amount thereof is, for example, 1 to 30 parts by weight with respect to 100 parts by weight of water. can be Examples of iodides include potassium iodide and zinc iodide. Compounds other than iodides, such as zinc chloride, cobalt chloride, zirconium chloride, sodium thiosulfate, potassium sulfite, sodium sulfate, etc., may coexist.

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

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

The cross-linking treatment may be performed multiple times, usually 2 to 5 times. In this case, the composition and temperature of each cross-linking bath used may be the same or different within the above ranges. The cross-linking treatment for water resistance by cross-linking and the cross-linking treatment for hue adjustment may be performed in a plurality of steps.

The uniaxial stretching treatment can also be performed in the first cross-linking bath 17a by utilizing the peripheral speed difference between the nip rolls 52 and 53a. Also, the uniaxial stretching treatment can be performed in the second cross-linking bath 17b by utilizing the peripheral speed difference between the nip rolls 53a and 53b.

In the cross-linking treatment, as in the swelling treatment, the guide rolls 38, 39, 40, 41, 42, 43 and/or 44 are provided with expander rolls and spiral rolls in order to convey the polyvinyl alcohol resin film while removing wrinkles of the film. , crown rolls, or other widening devices such as cross guiders, bend bars, tenter clips, etc. can be used. Another means for suppressing the occurrence of wrinkles is to apply stretching treatment, as in the case of swelling treatment.

In the example shown in FIG. 1, the film pulled out from the second cross-linking bath 17b passes through the guide roll 44 and the nip roll 53b in order and is introduced into the washing bath 19. In the example shown in FIG.

(Washing process)
The example shown in FIG. 1 includes a washing step after the cross-linking step. The cleaning treatment is performed for the purpose of removing excess chemicals such as boric acid and iodine adhering to the polyvinyl alcohol-based resin film. The cleaning step is performed by, for example, immersing the crosslinked polyvinyl alcohol-based resin film in the cleaning bath 19 . The cleaning step is performed by spraying the film with the cleaning solution as a shower instead of immersing the film in the cleaning bath 19, or by combining immersion in the cleaning bath 19 and spraying the cleaning solution. can also

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

Also in the cleaning process, for the purpose of conveying the polyvinyl alcohol resin film while removing wrinkles, the guide rolls 45, 46, 47 and/or 48 are rolls having a widening function such as expander rolls, spiral rolls and crown rolls. can be used, or other widening devices such as cross guiders, bend bars, tenter clips can be used. Further, in the film washing treatment, a stretching treatment may be applied to suppress the generation of wrinkles.

(Stretching process)
As described above, the raw film 10 is uniaxially stretched wet or dry during 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). It is processed. A specific method of uniaxial stretching treatment is, for example, between two nip rolls (for example, two nip rolls arranged before and after the treatment bath) that constitute the film conveying path, and longitudinal uniaxial stretching is performed by applying a peripheral speed difference between the rolls. Stretching can be hot roll stretching or tenter stretching as described in Japanese Patent No. 2731813, preferably stretching between rolls. The uniaxial stretching process can be performed multiple times from raw film 10 to polarizing film 23 . As described above, the stretching treatment is also advantageous in suppressing the generation of wrinkles in the film.

The final cumulative draw ratio of the polarizing film 23 based on the original film 10 is usually about 4.5 to 7 times, preferably 5 to 6.5 times. The stretching process may be carried out in any treatment process, and even when the stretching treatment is carried out in two or more treatment processes, the stretching treatment may be carried out in any treatment process.

(Electromagnetic wave irradiation process)
In the apparatus shown in FIG. 1, after the film is withdrawn from the second cross-linking step 17b and passed through the nip rolls 53b, the film is irradiated with electromagnetic waves (electromagnetic wave irradiation step) before being immersed in the cleaning bath 19. is done. In the apparatus shown in FIG. 1, electromagnetic waves are emitted from the electromagnetic wave emitting unit 71 . In the electromagnetic wave used in the electromagnetic wave irradiation step of the present invention, the proportion of infrared radiant energy with a wavelength of more than 2 μm and 4 μm or less is 25% or more, preferably 28% or more, more preferably 35% or more of the total radiant energy. is. By irradiating the film with such an electromagnetic wave, the optical properties of the obtained polarizing film can be improved. In addition, regarding the electromagnetic wave used in the present invention, 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. Generally, electromagnetic waves with wavelengths of 0.75 μm to 1000 μm are called infrared rays.

In the electromagnetic wave irradiation step, the mechanism by which the optical properties of the polarizing film can be improved by irradiating with an electromagnetic wave in which the proportion of the radiant energy of infrared rays with a wavelength of more than 2 μm and 4 μm or less is 25% or more of the total radiant energy is not clear. However, molecular motion in the film excited by infrared rays with 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 and improves the optical properties of the polarizing film. presumed to be able to

FIG. 2 shows the radiant energy spectrum for each type of electromagnetic wave irradiator. Table 1 shows the ratio of the radiant energy of electromagnetic waves in each wavelength range (expressed in the range of wavelength x μm) to the total radiant energy for each type of electromagnetic wave irradiator. The electromagnetic wave irradiation devices shown in FIG. 1200° C.), a carbon heater (heat source temperature 950° C.), and a medium wavelength infrared heater (heat source temperature 900° C.).

As shown in Table 1, short wavelength infrared heater (heat source temperature 2200 ° C), fast response medium wavelength infrared heater (heat source temperature 1600 ° C), carbon heater (heat source temperature 1200 ° C), carbon heater (heat source temperature 950 ° C), medium The wavelength infrared heater (heat source temperature 900° C.) is suitably used as an electromagnetic wave irradiator constituting the electromagnetic wave irradiator 71 because the ratio of the radiant energy of infrared rays with a wavelength of 2 μm to 4 μm is 25% or more of the total radiant energy. be able to. The electromagnetic wave irradiator 71 may be composed of one electromagnetic wave irradiator, or may be composed of a plurality of electromagnetic wave irradiators. In the case where the system consists of a plurality of electromagnetic wave irradiators, the radiant energy of infrared rays with a wavelength of more than 2 μm and 4 μm or less emitted from the plurality of electromagnetic wave irradiators is the same as that of the electromagnetic waves radiated from the plurality of electromagnetic wave irradiators. A plurality of electromagnetic wave irradiators are selected to account for 25% or more of the total radiant energy. In FIG. 1, the electromagnetic wave irradiator 71 is configured to irradiate only one surface of the film with electromagnetic waves, but a plurality of electromagnetic wave irradiators are arranged so that electromagnetic waves are radiated from both sides of the film. You may It is preferable that the electromagnetic wave irradiation unit 71 is configured to irradiate the entire width direction of the polyvinyl alcohol resin film to be irradiated with the electromagnetic wave.

In the electromagnetic wave irradiation step, it is preferable that the electromagnetic wave is irradiated from above in the direction perpendicular to the film surface. Further, the distance between the electromagnetic wave emitting port of the electromagnetic wave emitting device and the film in the electromagnetic wave emitting section 71 is preferably 2 to 40 cm, more preferably 5 to 20 cm. However, it is preferable that this distance is appropriately selected in consideration of the amount of radiant energy of the electromagnetic wave radiated from the electromagnetic wave irradiator, the temperature of the film surface, and the like. The temperature of the film surface during electromagnetic wave irradiation is preferably maintained at 30 to 90.degree. C., more preferably 40 to 80.degree.

In the electromagnetic wave irradiation step, the irradiation heat amount of the electromagnetic wave per unit volume of the film can be usually set to 100 J/cm ³ or more and 50 kJ/cm ³ or less. From the viewpoint of improving the optical properties of the polarizing film, it is preferably 100 J/cm ³ or more, more preferably 500 J/cm ³ or more, and even more preferably 1000 J/cm ³ or more. In addition, from the viewpoint of suppressing deterioration of the film due to temperature rise, the radiation heat quantity of electromagnetic waves per unit volume of the film is preferably 10 kJ/cm ³ or less, more preferably 5000 J/cm ³ or less, more preferably 3000 J/cm 3 or less. cm ³ or less is more preferable.
Normally, the water content of the film decreases in proportion to the amount of heat irradiated by the electromagnetic wave, but the electromagnetic wave irradiation step of the present invention is not intended to reduce the water content of the film, so the heat amount of irradiation is appropriately selected. It is preferably selected as appropriate within the above range.

In the present invention, the optical properties of the obtained polarizing film can be improved by performing the electromagnetic wave irradiation step before the washing treatment. 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. is not limited to That is, in the example shown in FIG. 1, the electromagnetic wave irradiation step may be performed on the film after being immersed in the first cross-linking bath and before being immersed in the second cross-linking bath. You may perform an electromagnetic wave irradiation process with respect to the film after making it immerse in. However, in the electromagnetic wave irradiation step, the immersion in the cross-linking bath allows the cross-linking of the boric acid incorporated into the film to proceed, so the electromagnetic wave irradiation step is performed on the film that has been completely immersed in the cross-linking bath. This is preferable because it allows the crosslinking of boric acid to proceed more effectively.

Irradiation with electromagnetic waves is preferably carried out within 10 seconds, more preferably within 5 seconds, after the film is pulled out of the crosslinking bath. The shorter the time from the drawing out of the cross-linking bath to the irradiation with the electromagnetic wave, the more improved the optical properties of the polarizing film by the irradiation with the electromagnetic wave. In addition, 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 are present on the surface of the film, the water molecules on the film surface absorb infrared rays, thereby reducing the effect of excitation of molecular motion in the film by electromagnetic wave irradiation. Since the cross-linking liquid adheres to the surface of the film immediately after being pulled out from the cross-linking bath, it is preferable to provide a liquid removing means for removing this before the electromagnetic wave irradiation step. In FIG. 1, the nip roll 53b also functions as liquid removing means for removing the cross-linking liquid adhering to the surface of the film. As the liquid removing means, in addition to the nip rolls, a means for removing the liquid by blowing air onto the film, a scraper for removing the liquid by contacting the film, or the like may be used.

If the film processing speed is high from the viewpoint of economy, specifically, if the processing speed is as high as 10 to 100 m / min, the electromagnetic wave irradiation time will be short, and the irradiation heat amount may be insufficient. . By installing a plurality of electromagnetic wave irradiators in parallel as a countermeasure, a sufficient amount of irradiation heat can be obtained.

(Drying process)
After the washing step, it is preferable to carry out a treatment for drying the polyvinyl alcohol-based resin film. Drying of the film is not particularly limited, but can be performed using a drying oven 21 as in the example shown in FIG. The drying oven 21 may be equipped with, for example, a hot air dryer. The drying temperature is, for example, about 30 to 100° C., and the drying time is, for example, about 30 to 600 seconds. The treatment for drying the polyvinyl alcohol-based resin film can also be performed using a far-infrared heater. The thickness of the polarizing film 23 obtained as described above is, for example, about 5 to 30 μm.

The visibility-corrected single transmittance Ty of the resulting polarizing film is preferably 40 to 47%, more preferably 41 to 45%, in consideration of the balance with the visibility-corrected polarization degree Py. The visibility correction polarization degree Py is preferably 99.9% or more, more preferably 99.95% or more, and the larger the value, the more preferable. The greater the luminosity correction single transmittance Ty of the polarizing film, the greater the effect of improving the optical properties obtained by the present invention. Therefore, the present invention is particularly advantageous in producing a polarizing film having a luminosity correction single transmittance Ty of 41% or more, further 42% or more, and furthermore 43% or more. According to the present invention, for example, a polarizing film having Ty of 43% or more and Py of 99.994% or more can be obtained. Ty and Py are measured according to the description in the Examples section below.

The obtained polarizing film may be sequentially wound on a winding roll to form a roll, or may be directly subjected to the polarizing plate manufacturing step (the step of laminating a protective film or the like on one or both sides of the polarizing film) without being wound. can also

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

<Polarizing plate>
A polarizing plate can be obtained by bonding a protective film to at least one surface of the polarizing film produced as described above via an adhesive. Protective films include, for example, films made of acetylcellulose-based resins such as triacetylcellulose and diacetylcellulose; films made of polyester-based resins such as polyethylene terephthalate, polyethylene naphthalate and polybutylene terephthalate; polycarbonate-based resin films, cyclo Olefin-based resin films; acrylic-based resin films; and films made of linear olefin-based resins such as polypropylene-based resins.

In order to improve the adhesion between the polarizing film and the protective film, the bonding surface of the polarizing film and/or the protective film is subjected to corona treatment, flame treatment, plasma treatment, ultraviolet irradiation, primer coating treatment, saponification treatment, etc. may be treated. As the adhesive used for bonding the polarizing film and the protective film, an active energy ray-curable adhesive such as an ultraviolet-curable adhesive, an aqueous solution of a polyvinyl alcohol-based resin, or an aqueous solution in which a cross-linking agent is added thereto. and water-based adhesives such as urethane-based emulsion adhesives. The UV-curable adhesive may be a mixture of an acrylic compound and a photoradical polymerization initiator, a mixture of an epoxy compound and a photocationic polymerization initiator, or the like. Moreover, a cationic polymerizable epoxy compound and a radically polymerizable acrylic compound can be used together, and a photocationic polymerization initiator and a photoradical polymerization initiator can be used together as initiators.

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

<Example 1>
A polarizing film of Example 1 was manufactured from a polyvinyl alcohol-based resin film using the manufacturing apparatus shown in FIG. Specifically, a long polyvinyl alcohol (PVA) raw film with a thickness of 60 μm [trade name “Kuraray Vinylon VF-PE#6000” manufactured by Kuraray Co., Ltd., average polymerization degree 2400, saponification degree 99.9 mol % or more] was continuously conveyed while being unwound from a roll, and immersed in a swelling bath made of pure water at 30° C. for a residence time of 79 seconds (swelling step). After that, the film pulled out from the swelling bath was immersed in a dyeing bath at 30°C containing iodine in which potassium iodide/boric acid/water was 1/0.3/100 (weight ratio) for a residence time of 123 seconds ( dyeing process). The film withdrawn from the dyeing bath was then immersed in a first cross-linking bath of 11/3.8/100 (weight ratio) of potassium iodide/boric acid/water at 53° C. for a residence time of 44 seconds followed by , potassium iodide/boric acid/water in a ratio of 11/3.8/100 (weight ratio) at 40° C. for a residence time of 6 seconds (crosslinking step). In the dyeing process and the cross-linking process, longitudinal uniaxial stretching was performed by stretching between rolls in a bath. The total draw ratio based on the raw film was 5.65 times.

Next, the film passed through the nip roll 53b was pulled out from the second cross-linking bath 17b, and was irradiated with an electromagnetic wave irradiator (medium wavelength infrared heater (MW heater), product name: Golden 8 Medium-wave twin tube emitter, manufactured by Heraeus, Using a heat source temperature of 900° C. and a maximum energy density of 60 kW/m ² ), an electromagnetic wave emission port is placed at a position 5 cm away from the surface of the film, and electromagnetic waves are irradiated at an output of 50% of the maximum irradiation output of the electromagnetic wave irradiation device. did. The radiation heat amount of the electromagnetic wave per unit volume of the film was 490 J/cm ³ . In addition, the irradiation heat amount of the electromagnetic wave per film unit volume was calculated by the following formula.
(Irradiation heat amount of electromagnetic wave per unit volume of film) = {(maximum energy density) × (surface area of heater heating part) × output (%) / (electromagnetic wave irradiation area)} × (electromagnetic wave irradiation time) ÷ (film thickness)
The output (%) indicates the ratio (%) of the actual irradiation output to the maximum irradiation output of the electromagnetic wave irradiation device.
After being pulled out of the second cross-linking bath 17b, the time required for the film to be transported, reach the irradiation position of the electromagnetic wave irradiator, and 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 retention time of 3 seconds (cleaning step). Thereafter, the film was dried in a drying oven 21 at a temperature of 60° C. and an absolute humidity of 11 g/cm ³ to obtain a polarizing film. The thickness of the obtained polarizing film was 23 μm.

<Examples 2 to 4, Comparative Example 2>
A polarizing film was obtained in the same manner as in Example 1, except that in the electromagnetic wave irradiation step, the type of electromagnetic wave irradiator, the output (%), and the irradiation heat amount of the electromagnetic wave per unit volume of the film were as shown in Table 2. The thickness of the obtained polarizing film was 23 μm. As an electromagnetic wave irradiator, a halogen heater (product name: straight tube halogen heater lamp QIR, manufactured by Ushio Lighting Co., Ltd., heat source temperature 2600 ° C., maximum energy density 300 kW / m ² ), short wavelength infrared heater (SW heater). (Product name: Golden 8 Short-wave twin tube emitter, manufactured by Heraeus, heat source temperature 2200 ° C., maximum energy density 200 kW / m ² ), fast response medium wavelength infrared heater (FRMW heater) (product name: Golden 8 Medium-wave Fast response twin tube emitter, Heraeus, heat source temperature 1600°C, maximum energy density 150 kW/m ² ), medium wavelength infrared heater (MW heater) (Product name: Golden 8 Medium-wave twin tube emitter, Heraeus, heat source A temperature of 900° C. and a maximum energy density of 60 kW/m ² ) were used.

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

<Example 5>
A long polyvinyl alcohol (PVA) raw film with a thickness of 20 μm [trade name “Kuraray Poval Film VF-PE #2000” manufactured by Kuraray Co., Ltd., average degree of polymerization 2400, degree of saponification 99.9 mol% or more]. While being unwound from the roll and continuously conveyed, it was uniaxially stretched by a dry method to 4.1 times, and further immersed in a swelling bath made of pure water at 30 ° C. for a residence time of 40 seconds while maintaining the tension ( swelling process). After that, the film pulled out from the swelling bath was immersed in a 28° C. dyeing bath containing iodine with a potassium iodide/water ratio of 6/100 (weight ratio) for a residence time of 30 seconds (dyeing step). Next, the film pulled out from the dyeing bath was immersed in a crosslinking bath containing potassium iodide/boric acid/water at a weight ratio of 15/5.5/100 (weight ratio) at 67°C for a residence time of 120 seconds (crosslinking step). . In the dyeing and cross-linking steps, longitudinal uniaxial stretching was further performed by stretching between rolls in a bath. The total draw ratio based on the raw film was 4.59 times.

Next, the film passed through the nip rolls was pulled out from the cross-linking bath, and an electromagnetic wave irradiator (medium wavelength infrared heater (MW heater), product name: Golden 8 Medium-wave twin tube emitter, manufactured by Heraeus, heat source temperature 900 ° C. , a maximum energy density of 60 kW/m ² ), an electromagnetic wave emission port was placed at a position 4 cm away from the surface of the film, and electromagnetic waves were irradiated at an output of 30%. The radiation heat amount of the electromagnetic waves per unit volume of the film was 960 J/cm ³ . After the film was pulled out from the cross-linking bath, it took 5 seconds until the film was transported, reached the irradiation position of the electromagnetic wave irradiator, and was irradiated with the electromagnetic wave.

The film irradiated with electromagnetic waves was immersed in a cleaning bath made of pure water at 15° C. for a residence time of 3 seconds (cleaning step). Thereafter, the film was dried in a drying oven at a temperature of 40° C. and an absolute humidity of 11 g/cm ³ to obtain a polarizing film. The thickness of the obtained polarizing film was 8 μm.

<Example 6>
A polarizing film was obtained in the same manner as in Example 5, except that in the electromagnetic wave irradiation step, the output (%) of the electromagnetic wave irradiator and the amount of irradiation heat of the electromagnetic wave per unit volume of the film were as shown in Table 3. The thickness of the obtained polarizing film was 8 μm.

<Comparative Example 3>
A polarizing film was obtained in the same manner as in Example 5, except that the electromagnetic wave irradiation step was not performed.
The thickness of the obtained polarizing film was 8 μm.

[Evaluation of polarizing film]
(a) Measurement of single transmittance, degree of polarization, and b value of orthogonal hue For the polarizing films obtained in each example and each comparative example, a spectrophotometer with an integrating sphere ["V7100" manufactured by JASCO Corporation] Measure the MD transmittance and TD transmittance in the wavelength range of 380 to 780 nm using
Single transmittance (%) = (MD + TD) / 2
Degree of polarization (%) = {(MD-TD) / (MD + TD)} x 100
Single transmittance and degree of polarization at each wavelength were calculated based on.

"MD transmittance" is the transmittance when the direction of polarized light emitted from the Glan-Thompson prism is parallel to the transmission axis of the polarizing film sample, and is expressed as "MD" in the above formula. The "TD transmittance" is the transmittance when the direction of the polarized light emitted from the Glan-Thompson prism is perpendicular to the transmission axis of the polarizing film sample, and is represented by "TD" in the above formula. Regarding the obtained single transmittance and degree of polarization, visibility correction was performed using a 2-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”. Then, the luminosity-corrected single transmittance (Ty), the luminosity-corrected polarization degree (Py), and the b value of the orthogonal hue were obtained. Tables 2 and 3 show the luminosity correction single transmittance (Ty), the luminosity correction degree of polarization (Py), the b value of the orthogonal hue, and the calculation results of the degree of polarization at wavelengths of 480 nm and 600 nm.

As shown in Table 2, the polarizing films of Examples 1 to 4 have almost the same luminosity correction single transmittance (Ty) as the polarizing films of Comparative Examples 1 and 2, but the degree of polarization is It was higher and had better optical properties. Further, as shown in Table 3, the polarizing films of Examples 5 and 6 had substantially the same luminosity correction single transmittance (Ty) as the polarizing film of Comparative Example 3, but the degree of polarization was It was higher and had better optical properties.

10 raw film made of polyvinyl alcohol-based resin, 11 raw roll, 13 swelling bath, 15 dyeing bath, 17a first cross-linking bath, 17b second cross-linking bath, 19 cleaning bath, 21 drying furnace, 23 polarizing film, 30 ~ 48, 60, 61 guide rolls, 50 to 52, 53a, 53b, 54, 55 nip rolls, 71 electromagnetic wave irradiation section.

Claims (5)

A method for producing a polarizing film from a polyvinyl alcohol resin film,
A dyeing step of dyeing the polyvinyl alcohol resin film with a dichroic dye;
A cross-linking step of cross-linking the polyvinyl alcohol-based resin film after the dyeing treatment with a cross-linking agent;
an electromagnetic wave irradiation step of irradiating the polyvinyl alcohol-based resin film after the cross-linking treatment with an electromagnetic wave in which the ratio of the radiant energy of infrared rays having a wavelength of more than 2 μm and 4 μm or less is 25% or more of the total radiant energy;
a cleaning step of cleaning the polyvinyl alcohol-based resin film after being irradiated with the electromagnetic wave ,
The cross-linking step is a step of immersing the polyvinyl alcohol-based resin film in a cross-linking bath containing an aqueous solution of the cross-linking agent,
A method for producing a polarizing film, further comprising a liquid removal step of removing the aqueous solution adhering to the surface of the polyvinyl alcohol-based resin film after the cross-linking treatment and before the electromagnetic wave irradiation . The method for producing a polarizing film according to claim 1, wherein in the electromagnetic wave irradiation step, the amount of heat applied by the electromagnetic wave is 100 J/ ^cm3 or more and 50 kJ/ ^cm3 or less per unit volume of the polyvinyl alcohol resin film. The method for producing a polarizing film according to claim 1 or 2, wherein the cross-linking agent contains a boron compound. The method for producing 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 resin film is pulled out of the cross-linking bath. A manufacturing apparatus for manufacturing a polarizing film from a polyvinyl alcohol resin film,
A dyeing unit that dyes the polyvinyl alcohol-based resin film with a dichroic dye;
A cross-linking unit that cross-links the polyvinyl alcohol-based resin film after the dyeing process with a cross-linking agent;
an electromagnetic wave irradiation unit that irradiates the polyvinyl alcohol-based resin film after the cross-linking treatment with an electromagnetic wave in which the proportion of the radiant energy of infrared rays having a wavelength of more than 2 μm and 4 μm or less is 25% or more of the total radiant energy;
a cleaning unit for cleaning the polyvinyl alcohol-based resin film after being irradiated with the electromagnetic wave,
In the cross-linking part, the polyvinyl alcohol-based resin film is immersed in a cross-linking bath containing an aqueous solution of the cross-linking agent,
The apparatus for producing a polarizing film, further comprising removing means for removing the aqueous solution adhering to the surface of the polyvinyl alcohol-based resin film after the cross-linking treatment and before the electromagnetic wave is applied .

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