JP2005202386A - Method for manufacturing polarizing film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing a polarizing film which is ameliorated in dyeing unevenness and is excellent in the intra-surface uniformity of polarization performance (polarization degree and single substance transmittance). <P>SOLUTION: The method for manufacturing the polarizing film comprises incorporating a surfactant into an iodine dyeing liquid during an iodine dyeing process at the time of manufacturing the polarizing film by subjecting a polyvinyl alcohol-based film to iodine dyeing. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for producing a polarizing film using a polyvinyl alcohol film (hereinafter abbreviated as PVA), and more specifically, in the plane of polarization performance (polarization degree, single transmittance) with improved dyeing unevenness. The present invention relates to a method for producing a polarizing plate film having excellent uniformity.

In recent years, liquid crystal display devices have been used in desktop electronic computers, electronic watches, automobile and mechanical instruments, televisions, notebook computers, mobile phones, and the like, and the demand for polarizing plates has increased accordingly.
Such a polarizing plate is generally constituted by adhering a protective film to both surfaces or one surface of a polarizing film having polarizing ability via an adhesive layer. Currently known typical PVA polarizing films include those in which iodine is dyed and adsorbed on PVA films and those in which organic dyes are dyed and adsorbed. Among them, iodine is dyed and adsorbed. The polarizing film is preferably used because the polarizing performance is particularly excellent.
In this way, as a polarizing film in which a dichroic material such as iodine or an organic dye is dyed and adsorbed on a PVA film, an aqueous solution of PVA is formed, and this is uniaxially stretched and dyed or dyed. After being uniaxially stretched, a material that has been subjected to a durability treatment with a boron compound is preferably used, and as a protective film, a cellulose acetate film is excellent in optical transparency, non-orientation, etc. Has been.
Recently, high-quality and high-reliability devices have been developed, especially for large-screen liquid crystal displays, etc., and the required physical properties associated with this increase in size, in-plane uniformity, etc. There is a strong demand for improvement.

Under such circumstances, there has been a demand for a polarizing film that is more excellent in in-plane uniformity of polarization performance, and one of them is improvement of display unevenness due to uneven dyeing. As a method for producing a polarizing film for the purpose of improving such display unevenness, a dye having a dichroic property or a dye bath having an iodine concentration of 0.02 wt% or more, and the temperature of the dye bath is 15 ° C. or more and 50 ° C. or less. A method has been proposed in which the draw ratio in the bath is 5 times or less and the solution in the bath is dyed while being stirred. (For example, refer to Patent Document 1).
JP 2001-290025 A

However, the technique disclosed in the publication is still not satisfactory, and even though it seems that the uniformity is apparently normal in the normal state, there is a problem that uneven coloring becomes apparent especially when used under high temperature and high humidity. In-plane uniformity of polarization performance due to uneven dyeing is inferior, and further improvements have been required to obtain higher quality and higher optical properties.
Therefore, an object of the present invention is to provide a method for producing a polarizing film having excellent in-plane uniformity of polarization performance with improved dyeing unevenness under such a background.

  However, as a result of intensive investigations in view of such circumstances, the present inventors have included a surfactant in the iodine dyeing solution in the iodine dyeing step in producing a polarizing film by dyeing a PVA film with iodine. The present invention was completed by finding out that the above object was met.

  In the present invention, in producing a polarizing film by dyeing a PVA-based film with iodine, by adding a surfactant to the iodine dyeing solution in the iodine dyeing process, dyeing unevenness under normal conditions and high temperature and high humidity can be improved. A polarizing film excellent in in-plane uniformity of polarization performance can be obtained, and the obtained polarizing film is useful as a polarizing film used in a liquid crystal display device having a large area and high display quality.

Hereinafter, the present invention will be specifically described.
The PVA resin used as a raw material for the PVA film used in the present invention is usually produced by saponifying polyvinyl acetate obtained by polymerizing vinyl acetate, but the present invention is not necessarily limited to this, and a small amount Unsaturated carboxylic acids (including salts, esters, amides, nitriles, etc.), olefins having 2 to 30 carbon atoms (ethylene, propylene, n-butene, isobutene, etc.), vinyl ethers, unsaturated sulfonates, etc., vinyl acetate It may be a modified polyvinyl alcohol-based resin containing a component copolymerizable with the. In addition to this modification, a polyvinyl alcohol-based resin containing a silyl group may be used. Polyvinyl alcohol may be post-modified using a silylating agent, or a silyl group-containing olefinically unsaturated monomer and vinyl acetate may be used together. Examples thereof include a method of saponifying a copolymer obtained by polymerization. Examples of the silyl group-containing olefinically unsaturated monomer include vinyl silane and (meth) acrylamide-alkyl silane.

The viscosity average degree of polymerization in the PVA-based resin is not particularly limited, but is preferably 1000 to 5000, particularly 1200 to 5000, and more preferably 1400 to 4500. When the viscosity average degree of polymerization is less than 1000, sufficient polarizing performance cannot be obtained when a polarizing film is used, and when it exceeds 5000, stretching is difficult and industrial production is difficult and undesirable.
The viscosity average degree of polymerization is measured according to JIS K 6726.
Furthermore, the saponification degree of the PVA-based resin is preferably 80 mol% or more, particularly 85 to 100 mol%, more preferably 98 to 100 mol%. If the degree of saponification is less than 80 mol%, a sufficient polarizing performance cannot be obtained when a polarizing film is obtained, which is not preferable.

The PVA resin may include one or more commonly used plasticizers such as glycerin, diglycerin, triglycerin, ethylene glycol, triethylene glycol, polyethylene glycol, etc. 30 wt% or less, preferably 3 to 25 wt%, more preferably 5 to 20 wt%. When the plasticizer exceeds 30% by weight, the film strength is inferior, which is not preferable.
More preferably, in order to improve the releasability from the substrate (roll, belt, etc.) at the time of film formation, one or more of various release agents are 5% by weight or less based on the PVA resin, Preferably it is 0.001 to 3weight%, More preferably, it is also possible to contain 0.001 to 2weight%. When the release agent exceeds 5% by weight, poor appearance of the film surface or blocking between the films is not preferable.

  As a method for producing a polarizing film using the PVA-based resin, a PVA-based resin aqueous solution is prepared, and the aqueous solution is cast from a T-type slit die onto a drum-type roll to form a film, followed by drying. In general, a method of producing a polarizing film by giving a polarizing performance by subjecting the raw film to dyeing / stretching and the like is then common.

When preparing an aqueous PVA resin solution, water, dimethyl sulfoxide (DMSO), N-methylpyrrolidone, glycerin, ethylene glycol, propylene glycol, diethylene glycol, triethylene glycol, tetraethylene glycol, trimethylolpropane and other polyhydric alcohols , Amines such as ethylenediamine and diethylenetriamine, and mixtures thereof.
The concentration of the PVA resin in the PVA resin aqueous solution is practically 5 to 50% by weight.

Next, the PVA-based resin aqueous solution is cast from a T-type slit die onto a drum-type roll to form a film.
The material of such a drum-type roll is not particularly limited, but usually stainless steel is preferably used, and the surface of the roll is preferably metal-plated to prevent damage. As the type of metal plating, for example, chrome plating, nickel plating, galvanization, etc. are suitably used, which can be used alone or in combination of two or more kinds of multilayers, particularly the ease of surface smoothing and its durability. From this point, the outermost surface is preferably chrome plating. The surface of the drum is desirably kept smooth, and the surface roughness is desirably 3S or less, particularly 0.5S or less.

The temperature of the drum-type roll at the time of film formation is practically 50 to 120 ° C., and peels from the roll when the moisture content of the film reaches about 5 to 30% by weight. Subsequently, drying is performed using a single or multi-stage roll, preferably alternating drying of the front and back surfaces of the film is continued using a multi-stage roll, and after drying, an unstretched PVA-based film is formed.
If necessary, after drying, heat treatment and humidity control are performed, and the PVA film is obtained by being wound around a core tube in a roll state. The film thickness of the obtained PVA film is preferably 10 to 100 μm, more preferably 20 to 90 μm, and particularly preferably 30 to 80 μm. When the film thickness is less than 10 μm, stretching is difficult, and when it exceeds 100 μm, the film thickness accuracy decreases. It is not preferable.
The width of the film is arbitrary, and is generally about 50 cm to 4 m. However, in the case of a wide film that is strongly demanded by the recent market, 2 m or more, preferably 2.5 m or more, particularly 3 m or more is useful. The length of the film is also arbitrary, about 1000 m to 10000 m.

Next, the manufacturing method of the polarizing film using a PVA-type film is demonstrated.
In the present invention, it is preferable to produce a polarizing film by passing a PVA film at least in the order of a water washing step, an iodine dyeing step, and a boron compound treatment step, and between the water washing step and the iodine dyeing step, the PVA film It is also preferable to provide a swelling step that swells the film in terms of preventing wrinkling due to excessive swelling of the PVA film.
As a method for producing a polarizing film, for example, after washing the above PVA-based film (after further swelling if necessary), the film is stretched and immersed in an iodine dyeing solution for dyeing, or stretching and dyeing are performed simultaneously. There is a method of performing or stretching by dyeing with an iodine dyeing solution and then immobilizing with a boron compound. In addition, there are methods such as drawing in a washing step and swelling step, or drawing in a solution of a boron compound after dyeing, etc., and can be selected and used as appropriate. In particular, at least during dyeing and / or a boron compound Stretching during the treatment is preferable from the viewpoint of improving optical performance. Furthermore, any step may be performed twice or more as required.

  Stretching is wet stretching or dry stretching, and it is desirable to stretch 3 to 10 times, preferably 3.5 to 8 times in a uniaxial direction. In particular, it is more preferable to carry out by wet stretching. At this time, the film may be slightly stretched in the direction perpendicular to the above (stretching to prevent shrinkage in the width direction or more). The temperature condition during stretching is desirably selected from 40 to 170 ° C. Furthermore, the draw ratio may be finally set in the above range, and the drawing operation may be performed not only in one stage but also in any stage of the manufacturing process.

In the washing step, it is preferable to wash the PVA film using water at about 15 to 40 ° C., and in the swelling step, about 20 to 40 ° C. containing a crosslinking agent such as water or a small amount of boric acid. It is preferable to swell the PVA film by treating in a water bath.
Next, an iodine-potassium iodide aqueous solution is usually used as the iodine staining solution in the iodine staining step. The iodine concentration is 0.1-2.0 g / l, and the potassium iodide concentration is 10-100 g / l. The weight ratio of iodine / potassium iodide is suitably 20-100. The temperature of the iodine staining solution is preferably 5 to 50 ° C. In addition to the water solvent, a small amount of an organic solvent compatible with water may be contained. Further, a crosslinking agent such as boric acid may be contained. Any means such as dipping, coating, spraying, etc. can be applied as the contact means.

  In the present invention, in order to obtain a polarizing film having uniform polarization performance in a large area with improved dyeing unevenness, the greatest feature is that the iodine dyeing solution contains a surfactant when the PVA film is dyed with iodine. It is what.

  There are no particular limitations on the type of surfactant, but anionic surfactants are preferred, and carboxylate types such as fatty acid soaps, N-acyl amino acids and salts thereof, polyoxyethylene alkyl ester carboxylates, and acylated peptides. Alkylbenzene sulfonate, alkyl naphthalene sulfonate, naphthalene sulfonic acid salt formalin polycondensate, melamine sulfonic acid salt formalin condensate, dialkyl sulfosuccinic acid ester salt, sulfosuccinic acid alkyl disalt, polyoxyethylene alkyl sulfosuccinic acid di Salts, alkyl sulfoacetates, α-olefin sulfonates, N-acylmethyl taurates, sulfonates such as dimethyl-5-sulfoisophthalate sodium, sulfated oils, higher alkyl sulfates, polyoxyethylene Alkylue Tersulfate, higher alcohol ethoxysulfate, polyoxyethylene alkylphenyl ether sulfate, sulfate salt type such as monoglyculate, polyoxyethylene alkyl ether phosphate, polyoxyethylene alkylphenyl ether phosphate, alkyl phosphoric acid Examples thereof include phosphate ester salt types such as salts. Among them, sulfate type anionic surfactants such as alkyl sulfates, polyoxyethylene alkyl ether sulfates, polyoxyethylene alkylphenyl ether sulfates, higher fatty acid alkanolamide sulfates and the like perform uniform dyeing. This is preferable.

  The content of the surfactant is preferably 0.1 ppm to 1000 ppm, more preferably 0.5 to 500 ppm, particularly preferably 1 to 200 ppm, and most preferably 3 to 200 ppm with respect to the iodine dyeing solution. If it is less than 0.1 ppm, the effect of improving the unevenness of dyeing hardly appears, and if it exceeds 1000 ppm, the iodine dyeing solution is not preferred because it causes foaming unevenness, and a protective film is bonded to the liquid crystal display device. When it is used, it is not preferable because sufficient durability tends not to be obtained.

  Moreover, in this invention, in addition to making surfactant contain in an iodine dyeing | staining liquid, you may contain surfactant in said water washing process and / or swelling process. The type of the surfactant is not particularly limited, and examples thereof include the same as those described above. Among them, anionic surfactants are preferable, and alkyl sulfate salts, polyoxyethylene alkyl ether sulfates, polyoxyethylene alkyls are particularly preferable. Sulfate ester type anionic surfactants such as phenyl ether sulfate and higher fatty acid alkanolamide sulfate are preferable in that a uniform polarizing film can be obtained.

Next, the iodine dyed PVA-based film is then fixed with a boron compound. As the boron compound, boric acid and borax are practical. The boron compound is used in the form of an aqueous solution or a water-organic solvent mixture at a concentration of about 0.3 to 2 mol / l, and it is practically desirable that a small amount of potassium iodide coexists in the solution.
As a treatment method, a dipping method is desirable, but of course, a coating method and a spraying method can also be implemented. The temperature during the treatment is preferably about 40 to 70 ° C., and the treatment time is preferably about 1 to 20 minutes. It is also preferable to perform a stretching operation during the treatment, if necessary.
In the present invention, a surfactant may be added to the boron compound aqueous solution in the fixing treatment step using the boron compound. The type of the surfactant is not particularly limited, and examples thereof include the same as those described above. Among them, anionic surfactants are preferable, and alkyl sulfate salts, polyoxyethylene alkyl ether sulfates, polyoxyethylene alkyls are particularly preferable. Sulfate ester type anionic surfactants such as phenyl ether sulfate and higher fatty acid alkanolamide sulfate are preferable in that a uniform polarizing film can be obtained.

Thus, the polarizing film of the present invention can be obtained, but it can also be used as a polarizing plate by laminating and bonding an optically isotropic polymer film or sheet as a protective film on one or both sides thereof.
Examples of the protective film include films or sheets of cellulose triacetate, cellulose diacetate, polycarbonate, polymethyl methacrylate, polystyrene, polyethersulfone, polyarylene ester, poly-4-methylpentene, polyphenylene oxide, and the like.

  In addition, instead of the protective film, such a polarizing film may be laminated by applying a curable resin such as a urethane resin, an acrylic resin, or a urea resin on one or both sides instead of the protective film.

  Further, such a polarizing film (or a protective film or a curable resin laminated on at least one surface thereof) is formed on one surface of the polarizing film, if necessary, by a generally known method. In some cases, it may be put to practical use. Examples of the pressure-sensitive adhesive layer include acrylic acid esters such as butyl acrylate, ethyl acrylate, methyl acrylate, 2-ethylhexyl acrylate, and α-monoolefin carboxylic acids such as acrylic acid, maleic acid, itaconic acid, methacrylic acid. Copolymers with acids, crotonic acid, etc. (including those added with vinyl monomers such as acrylonitrile, vinyl acetate, and styrene) do not interfere with the polarization characteristics of the polarizing film. Although it is particularly preferable, it is not limited to this, and any pressure-sensitive adhesive having transparency can be used. For example, a polyvinyl ether type or a rubber type may be used.

  Furthermore, various functional layers can be provided on one side of the polarizing film (or polarizing plate). Examples of the functional layer include an antiglare layer, a hard coat layer, an antireflection layer, a half reflection layer, a reflective layer, and a phosphorescent layer. , A diffusion layer, an electroluminescence layer, a viewing angle widening layer, a brightness enhancement layer, and the like. Furthermore, it is also possible to combine two or more kinds, for example, an antiglare layer and an antireflection layer, a phosphorescent layer and a reflective layer, A combination of a phosphorescent layer and a half reflection layer, a phosphorescent layer and a light diffusion layer, a phosphorescent layer and an electroluminescence layer, a half reflection layer and an electroluminescence layer, and the like can be given. However, it is not limited to these.

Hereinafter, the present invention will be specifically described with reference to examples.
In the examples, “parts” and “%” are based on weight unless otherwise specified.

Example 1
Using a PVA resin having a viscosity average polymerization degree of 2600 and a saponification degree of 99.7 mol%, a 35% concentration PVA resin aqueous solution (with respect to the PVA resin, 10% glycerin as a plasticizer, polyoxyethylene alkylamino (Containing 0.1% ether), cast the aqueous solution with a drum-type roll from a T-type slit die, dry to a moisture content of 10%, and heat-treat at 120 ° C. for 3 minutes. The PVA film (width: 3.0 m, film thickness: 75 μm) having a moisture content of 4% was obtained as a film roll by conditioning the humidity and winding it around the core tube.

  Next, the obtained PVA film was unwound at 1.25 m / min, washed and swollen in a washing tank (24 ° C.), and then an iodine staining tank having a sodium dodecyl sulfate concentration of 5 ppm with respect to the iodine staining solution ( The film was immersed in 20 ° C., an iodine concentration of 0.2 g / l, and a potassium iodide concentration of 60 g / l), and uniaxially stretched 1.4 times. Subsequently, it was immersed in a boric acid bath (50 ° C., iodine concentration 0.0012 g / l, potassium iodide concentration 30 g / l, boric acid concentration 47 g / l), and the immobilization treatment was performed while uniaxially stretching 2.5 times. After performing uniaxial stretching of 5.0 times in total, it was dried with a dryer at 40 ° C. to obtain a polarizing film.

  A cellulose triacetate film was bonded to both surfaces of the obtained polarizing film using a PVA adhesive to obtain a polarizing plate.

(Dyeing unevenness evaluation method)
The obtained polarizing plate was sandwiched between two polarizing plates in a crossed Nicol state (single transmittance 43.5%, polarization degree 99.9%) at an angle of 45 °, and then the surface illuminance of 14,000 lux was obtained in a dark room. Using a light box, staining unevenness was observed in the transmission mode and evaluated according to the following criteria.
○ ・ ・ ・ No dyeing unevenness × ・ ・ ・ With dyeing unevenness

(Dyeing unevenness evaluation method after durability test)
An adhesive layer (25 μm thick) is provided on one side of the obtained polarizing plate, and after bonding to a glass plate, left for 20 days at 60 ° C. and 90% RH, then two polarizing plates in a crossed Nicol state (single unit) After being sandwiched at an angle of 45 ° between the transmittance of 43.5% and the degree of polarization of 99.9%, using a light box with a surface illuminance of 14,000 lux in a dark room, the staining unevenness was observed in the transmission mode. Evaluated by criteria.
○ ・ ・ ・ No dyeing unevenness × ・ ・ ・ With dyeing unevenness

Example 2
A polarizing film was obtained in the same manner as in Example 1 except that 80 ppm of polyoxyethylene dodecyl ether sodium sulfate was used instead of 5 ppm of sodium dodecyl sulfate, and the same evaluation as in Example 1 was performed.

Example 3
In Example 1, using a PVA resin having a viscosity average polymerization degree of 4000 and a saponification degree of 99.7 mol%, a 25% concentration PVA resin aqueous solution (10% glycerin as a plasticizer, A PVA film having a width of 3.3 m and a film thickness of 75 μm was obtained in the same manner except that 0.1% polyoxyethylene alkylamino ether was prepared).
Next, the obtained PVA film was unwound at 1.25 m / min, washed in a water washing tank (24 ° C.), and subsequently a swelling tank having a sodium dodecyl sulfate concentration of 2 ppm with respect to the aqueous solution (30 ° C., boric acid concentration). 0.01 g / l), the polyoxyethylene dodecyl ether sodium sulfate concentration is 20 ppm with respect to the iodine dyeing solution (20 ° C., iodine concentration 0.22 g / l, potassium iodide concentration 60 g / l). l) and uniaxially stretching 1.4 times. Subsequently, it was immersed in a boric acid bath (50 ° C., iodine concentration 0.0012 g / l, potassium iodide concentration 30 g / l, boric acid concentration 47 g / l), and the immobilization treatment was performed while uniaxially stretching 2.5 times. After performing uniaxial stretching of 5.0 times in total, it was dried with a dryer at 40 ° C. to obtain a polarizing film.
Evaluation similar to Example 1 was performed about the obtained polarizing film.

Example 4
The PVA-based film obtained in Example 1 was uniaxially stretched 2.7 times under an atmosphere of 120 ° C., and the polyoxyethylene dodecyl ether sodium sulfate concentration was 150 ppm with respect to the iodine dyeing solution while maintaining the tension state. After dyeing by immersion in an iodine staining tank (20 ° C., iodine concentration 0.2 g / l, potassium iodide concentration 30 g / l), boric acid tank (55 ° C., iodine concentration 0.001 g / l, iodination) Dipping in a potassium concentration of 40 g / l and boric acid concentration of 60 g / l), performing immobilization treatment while performing uniaxial stretching of 2 times, and after performing uniaxial stretching of total 6.0 times, using a dryer at 40 ° C. It dried and the polarizing film was obtained.
Evaluation similar to Example 1 was performed about the obtained polarizing film.

Comparative Example 1
In Example 1, it carried out similarly except not adding sodium dodecyl sulfate to an iodine dyeing tank, the polarizing film was obtained, and evaluation similar to Example 1 was performed.

Comparative Example 2
In Example 1, without adding sodium dodecyl sulfate to the iodine dyeing tank, the iodine aqueous solution in the iodine dyeing tank was stirred using the water flow of 2 m / sec while preventing the water flow from directly contacting the film. The polarizing film was obtained, and the same evaluation as in Example 1 was performed.
The results of Examples and Comparative Examples are shown in Table 1.

  The polarizing film obtained by the production method of the present invention has optical characteristics excellent in in-plane uniformity without optical color unevenness due to dyeing unevenness, electronic desk calculator, electronic clock, word processor, personal computer, Monitors, LCD TVs, personal digital assistants, liquid crystal display devices such as automobile and machinery instruments, sunglasses, anti-glare glasses, stereoscopic glasses, reflection reduction layers for display elements (CRT, LCD, etc.), medical equipment, building materials It is very useful for toys.

Claims (7)

  A method for producing a polarizing film, comprising producing a polarizing film by iodine-staining a polyvinyl alcohol film, wherein an iodine dyeing solution in the iodine dyeing step contains a surfactant.   The method for producing a polarizing film according to claim 1, wherein the polarizing film is produced by passing a polyvinyl alcohol film in the order of at least a washing step, an iodine staining step, and a boron compound treatment step.   The method for producing a polarizing film according to claim 1 or 2, wherein the content of the surfactant is 0.1 to 1000 ppm with respect to the iodine dyeing solution.   The method for producing a polarizing film according to claim 1, wherein the surfactant is an anionic surfactant.   5. The method for producing a polarizing film according to claim 4, wherein the anionic surfactant is a sulfate ester type anionic surfactant.   The method for producing a polarizing film according to any one of claims 1 to 5, wherein a swelling step for swelling the polyvinyl alcohol film is provided between the water washing step and the iodine dyeing step. The method for producing a polarizing film according to claim 6, wherein a surfactant is contained in the swelling liquid during the swelling step.