KR20090109264A - Method for recovering of dyeing solution from waste solution for polarizing film and method for preparing polarizing film using the recovered dyeing solution - Google Patents

Abstract

PURPOSE: A method for collecting dyeing liquid from waste water and a manufacturing method for the polarizing film are provided to reduce treatment cost of industrial waste, and to offer environment-friendly effects by recycling chemical materials. CONSTITUTION: A method for collecting dyeing liquid from wastewater comprises the following steps of; condensing polyvinyl alcohol resin and organic compounds included in waste liquid; accelerating cohesion of the compound by putting the wastewater in low temperature; separating the dyeing liquid, the polyvinyl alcohol resin or organic materials after filtering the wastewater; filtering the separated dyeing liquid secondarily; and collecting the filtered dyeing liquid.

Description

METHOD FOR RECOVERING OF DYEING SOLUTION FROM WASTE SOLUTION FOR POLARIZING FILM AND METHOD FOR PREPARING POLARIZING FILM USING THE RECOVERED DYEING SOLUTION}

The present invention relates to a method for recovering a dye solution from a waste liquid generated as a large amount of waste in a manufacturing process of a polarizing film and a method for producing a polarizing film by recycling the recovered dye solution.

The polarizing plate used in a liquid crystal display device (LCD) is a protective film represented by a polarizing film (or 'polarizer') and a triacetyl cellulose (TAC) film on one or both sides of the polarizing film. It has a laminated multilayer structure.

In general, a polarizing film is mainly used in which a dichroic dye is adsorbed and oriented on a uniaxially stretched polyvinyl alcohol (PVA) resin film. Such a polarizing film includes a step of uniaxially stretching a polyvinyl alcohol-based resin film, a step of dyeing a polyvinyl alcohol-based resin film with a dichroic dye to adsorb the dichroic dye, and a polyvinyl alcohol-based resin adsorbed with a dichroic dye. It manufactures via the process of processing a film with aqueous solution of boric acid, and the process of washing with water.

Looking at the manufacturing process of the polarizing film in detail, first, the polyvinyl alcohol-based resin film is uniaxially stretched using a method of stretching between rolls having different circumferential speeds or stretching using a thermal roll. In order to dye a monoaxially stretched polyvinyl alcohol-based resin film with a dichroic dye, for example, a method of dipping and dyeing the polyvinyl alcohol-based resin film in an aqueous solution containing a dichroic dye can be used. At this time, an iodine or a dichroic dye is used as a dichroic dye. A polarizing film is obtained by immersing a polyvinyl alcohol-based resin film dyed in a dichroic dye in a boric acid-containing aqueous solution, crosslinking, washing with water and drying.

The polarizing film prepared by the above process has some special optical characteristics depending on the solute of the compound (or 'dye') used in the stretching, dyeing or washing process. That is, a difference occurs in the reaction between the PVA film and the solute according to the concentration of the dye solution, which causes a difference in the performance of the polarizing film.

On the other hand, the dyeing liquid used in the manufacturing process of the polarizing film is composed of organic matter such as PVA resin in the stretching, dyeing or washing process, glycerin used to prevent sticking during storage of the polarizing film and various impurities adsorbed in the process. When the stain is used, when the stain is used, organic matter is adsorbed on the polarizing film, which causes a problem of product defects.

However, until now, no suitable method for removing organic matter from the dyeing solution used in polarizing film production has been proposed, and the used dyeing solution is treated as a waste solution. A significant amount of these dyes are treated as industrial waste, which increases secondary costs such as waste disposal costs in addition to production costs, and chemicals such as iodine, dichroic dyes or boric acid in the dyeings cause environmental problems. Environmental regulations are becoming stricter. In particular, PVA, an organic substance, is a hardly degradable polymer that is soluble in water, which inevitably increases the chemical oxygen demand (COD) load of the waste liquid, and is hardly treated by biological processes by bacteria. If released into the water, the balance of water quality and ecosystems in public waters will be disrupted, making the regulations more stringent. Therefore, there is a demand for a method for recycling the dyeing solution by removing PVA and various other organic substances from the waste solution generated in a considerable amount in the manufacturing process of the polarizing film.

As a method for removing the conventional PVA, Korean Patent No. 083754 (registered as 2007.12.3.) Discloses a method of treating wastewater containing PVA by biological treatment using activated sludge method after chemical treatment through salting method. It is. However, the use of such a method has the disadvantage that the consumption of the drug and the sludge generated by the chemical treatment is large, takes a very long time for biological treatment, and requires a large installation space, the burden on the facility cost is quite large.

 Korean Laid-Open Patent Publication No. 1998-057625 (published on Sep. 25, 1999) discloses a method of irradiating an electron beam to a wastewater containing PVA resin to decompose PVA, and then adding a flocculant to adsorb, aggregate and precipitate the decomposed PVA. have. However, in order to irradiate an electron beam, an expensive electromagnetic emission device is required, and a high radiation dose is required, so there is a problem in terms of economy.

An object of the present invention is to provide a method for recovering a dye solution from the waste liquid generated in a considerable amount as waste in the manufacturing process of the polarizing film.

In another aspect, the present invention is to provide a method for producing a polarizing film by recycling the recovered dye solution.

In order to achieve the above object, the present inventors have intensively studied, and when the dye solution is regenerated from waste liquids generated in the manufacturing process of the polarizing film, that is, waste liquid contaminated with organic substances such as PVA resin, glycerin and various impurities In addition, it is possible to reduce the generation amount and the treatment cost of the waste liquid by a simple method, and confirm that the recovered dye solution can be used again in the manufacture of the polarizing film, thereby completing the present invention.

The present invention provides a method for recovering the dye solution from the waste liquid generated in the polarizing film manufacturing process.

In another aspect, the present invention provides a method for producing a polarizing film by recycling the recovered dye solution.

According to the present invention, by recovering the dye solution from the waste liquid generated as a large amount of waste in the manufacturing process of the polarizing film, it is possible to recycle chemicals causing environmental problems such as dichroic dyes such as iodine and boric acid, which is not only environmentally friendly but also industrial. It is possible to reduce the amount of waste generated and to reduce its disposal cost. In addition, it is possible to recover the dyeing solution using a simple method such as agglomeration and filtration, and can be used again in the manufacturing process of the polarizing film by correcting the recovered dyeing solution is more economical, it is also possible to improve the manufacturing yield of the polarizing film. .

The present invention relates to a method for recovering a dye solution from a waste liquid generated as a large amount of waste in a manufacturing process of a polarizing film and a method for producing a polarizing film by recycling the recovered dye solution.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

The method for recovering the dye solution of the present invention is characterized in that the waste solution generated in the polarizing film manufacturing process is used as a raw material.

In general, the polarizing film is a process of uniaxially stretching a polyvinyl alcohol-based resin film, dyeing the stretched polyvinyl alcohol-based resin film with a dichroic dye to adsorb the dichroic dye, and polyvinyl alcohol with a dichroic dye adsorbed. It manufactures through the process of processing a system resin film with aqueous boric acid solution, and the process of washing with water after the process by the said boric acid aqueous solution.

The polyvinyl alcohol-based resin constituting the polarizing film can be obtained by saponifying a polyvinyl acetate-based resin. As an example of polyvinyl acetate type resin, the copolymer etc. of vinyl acetate and the other monomer copolymerizable with this besides the polyvinyl acetate which is a homopolymer of vinyl acetate are mentioned. As another monomer copolymerizable with vinyl acetate, unsaturated carboxylic acid, unsaturated sulfonic acid, olefins, vinyl ether, acrylamide which has an ammonium group, etc. are mentioned, for example. The saponification degree of the polyvinyl alcohol-based resin is usually about 85 to 100 mol%, preferably 98 mol% or more. The polyvinyl alcohol-based resin may also be modified. For example, polyvinyl formal or polyvinyl acetal modified with aldehydes may be used.

The process of uniaxially stretching the polyvinyl alcohol resin film may be performed before dyeing, may be performed simultaneously with dyeing, or may be performed after dyeing. When the uniaxial stretching is performed after dyeing, it may be performed before boric acid treatment, or may be performed during boric acid treatment. Of course, it is also possible to uniaxially stretch in these several steps. In uniaxial stretching, a circumferential speed may be uniaxially stretched between different rolls, and you may uniaxially stretch using a thermal roll. Moreover, it may be dry stretching, such as extending | stretching in air | atmosphere, or wet extending | stretching which extends in the state swelled with a solvent may be sufficient.

In order to dye the stretched polyvinyl alcohol-based resin film with a dichroic dye, for example, the polyvinyl alcohol-based resin film can be immersed in an aqueous solution containing a dichroic dye. As a dichroic dye, an iodine and a dichroic dye are used specifically. In addition, the polyvinyl alcohol-based resin film is preferably immersed in water before dyeing treatment.

When using iodine as a dichroic dye, the method of immersing and dyeing a polyvinyl alcohol-type resin film in the aqueous solution containing iodine and potassium iodide can be used normally. The content of iodine in the aqueous solution is usually about 0.01 to 1 part by weight based on 100 parts by weight of distilled water, and the content of potassium iodide is about 0.5 to 20 parts by weight based on 100 parts by weight of distilled water. The temperature of the aqueous solution used for dyeing is about 20-40 degreeC normally, and the immersion time (dyeing time) in aqueous solution is about 20-1,800 second normally.

Moreover, when using a dichroic dye as a dichroic dye, the method of immersing and dyeing a polyvinyl alcohol-type resin film in the aqueous solution containing a water-soluble dichroic dye can be used normally. The content of the dichroic dye in the aqueous solution is usually about 0.01 to 1 part by weight based on 100 parts by weight of distilled water, and the content of potassium iodide is usually about 1 x 10 ^-4 to 10 parts by weight based on 100 parts by weight of distilled water, preferably Is about 1 x 10 ^-3 to 1 part by weight. This aqueous solution may contain inorganic salts, such as sodium sulfate, as a dyeing adjuvant. The temperature of the dye aqueous solution used for dyeing is about 20-80 degreeC normally, and the immersion time (dyeing time) in aqueous solution is about 10-1,800 second normally.

The boric acid treatment after dyeing with a dichroic dye can be performed by immersing the dyed polyvinyl alcohol-based resin film in an aqueous solution containing boric acid. The content of boric acid in the boric acid-containing aqueous solution is usually about 2 to 15 parts by weight, preferably about 5 to 12 parts by weight with respect to 100 parts by weight of water. When iodine is used as the dichroic dye, the boric acid-containing aqueous solution preferably contains potassium iodide. The amount of potassium iodide in the boric-acid containing aqueous solution is about 0.1-15 weight part normally with respect to 100 weight part of water, Preferably it is about 5-12 weight part. Immersion time in boric-acid containing aqueous solution is about 60 to 1,200 second normally, Preferably it is about 150 to 600 second, More preferably, it is about 200 to 400 second. The temperature of the boric-acid containing aqueous solution is 50 degreeC or more normally, Preferably it is 50-85 degreeC, More preferably, it is 60-80 degreeC.

The polyvinyl alcohol-based resin film after boric acid treatment is usually washed with water. A water washing process can be performed by immersing the polyvinyl alcohol-type resin film treated with boric acid, for example in water. The temperature of the water in a water washing process is about 5-40 degreeC normally, and immersion time is about 1 to 120 second normally. After water washing, a polarizing film can be obtained by performing a drying process. Drying process can be normally performed using a hot-dryer or a far-infrared heater. The temperature of a drying process is about 30-100 degreeC normally, Preferably it is 50-80 degreeC. The drying treatment time is usually about 60 to 600 seconds, preferably about 120 to 600 seconds.

The waste solution for producing a polarizing film is a solution to be treated as waste after being used in the stretching, dyeing or washing process as described above, a dyeing solution containing a dichroic dye, boric acid and distilled water, a PVA resin dissolved in a dyeing solution during the process, and It is a solution containing organic matter outside. In particular, the waste liquid contains a large amount of PVA resin. Moreover, plasticizer organic substances, such as glycerin contained at the time of processing of a raw material PVA film, are also included.

The method for recovering the dye solution from the waste film manufacturing waste solution may include a first step of agglomerating an organic material and a polyvinyl alcohol resin contained in the waste solution; A second step of accelerating aggregation by leaving the waste liquid at a low temperature; A third step of separating the aggregated polyvinyl alcohol resin and the organic material and the dyeing solution by primary filtration of the waste liquid having been aggregated; A fourth step of secondary filtration of the separated dye solution; And a fifth step of recovering the filtered dye solution.

Hereinafter, with reference to the accompanying drawings will be described in detail.

1 is a process chart showing a regeneration method of a polarizing film manufacturing waste according to an embodiment of the present invention.

The first step is to aggregate the organic matter and the PVA resin contained in the waste liquid. In more detail, a coagulant is added to the waste liquid to agglomerate the PVA resin with organic substances such as glycerin and various impurities.

As the flocculant, a large amount of PVA resin contained in the waste liquid and a polymer organic material having a property of adsorbing and precipitating various other organic substances and metal salts can be used, and the use of metal salts can increase the removal efficiency in a later process. It is more preferable in that it exists.

Specific examples of the polymer organic material may include polyacrylamide or polyamide.

In addition, the metal salts include aluminum salts and iron salts, preferably aluminum sulfate, ferrous sulfate, ferric sulfate, and ferric chloride. These etc. can be mentioned, These can be used individually or in combination of 2 or more types.

The flocculant may be used in excess so as to aggregate all the PVA resin and other organic substances contained in the waste liquid. For example, it is 0.001-5 weight part with respect to 100 weight part of waste liquid, More preferably, it is 0.01-2 weight part. In the above content range, impurities other than the dye solution in the waste liquid can be removed efficiently and economically, and are more preferable because no load is applied to the step after the aggregation.

The aggregation can be carried out at room temperature.

The second step is to accelerate the coagulation of the PVA resin and other organic matter by leaving the waste liquid in which the coagulant is added in the first step at a low temperature.

Acceleration of the aggregation is preferably carried out at a low temperature of 20 ℃ or less, more preferably 10 to 18 ℃. When the acceleration temperature is 20 ° C. or less, the solubility of PVA resin and other organic substances dissolved in the waste liquid can be adjusted low, thereby accelerating aggregation. In addition, when the acceleration temperature exceeds 20 ℃, the acceleration effect is insignificant, which is inefficient in the process.

The aging is preferably performed for 1 to 48 hours, more preferably 5 to 15 hours.

The third step is a step of primary filtration of the waste liquid in which the aggregation is completed in the second step. Through this step, the aggregated PVA resin and other organic matter and the dyeing solution are separated, and a part of the flocculant used in the first step is also removed.

For the primary filtration, a filter having an average diameter in the range of 1 micron, which is usually used for removing PVA resin aggregates, can be used.

The third step may be carried out at 20 ℃ or less, preferably 10 to 18 ℃. In the case of the temperature range, the aggregate can be maintained at a temperature similar to that of the accelerated aggregation of the second step, so that the aggregate can be separated more efficiently.

The fourth step is to remove the remaining coagulant by secondary filtration of the dye solution separated in the third step.

The dyeing solution separated in the third step contains a large amount of the coagulant introduced in the first step. When the dyeing solution is recycled to the manufacturing process of the polarizing film, the remaining coagulant becomes an impurity to deteriorate the quality of the final product. There is a problem that causes a defect.

The secondary filtration is preferably performed using a nano filter. Generally, metal ion forms that can be removed using nanofilters are known as materials having an atomic weight of about 200 or more, but are not generalized to date. Recently, with the development of nanotechnology, the use of nanofilters in the separation, concentration and softening processes in the fine chemical field is increasing, and nanofilters are also used in the purification process to effectively separate a large amount of salts from dye and pigment manufacturing processes. The membrane is being used.

The nanofilter preferably has an average diameter of pores of about 0.001 to 0.01 μm. In the case where the average diameter range is used, the flocculant can be removed more efficiently, and thus the quality of the final product can be prevented when the separated dye solution is recycled to the manufacturing process of the polarizing film.

The kind of said nanofilter is not specifically limited, A commercially available product can also be used. Specific examples include Filmtec products such as NF90-2540, NF90-4040, NF90-400, NF200-400, NF270-400, NF270-2540, NF270-4040, NF-400, CK2540FF, CK4040FF, CK8040F, CK8040N, Duraslick NF2540, Duraslick NF4040, Duraslick NF8040, HL2514T, HL2514TF, HL2540FF, HL2540TF, HL3218T, HL3308T, HL4014TF, HL4021TF, HL4040FF, HL4040FF-CERT, HL40FF, DHL8040F, DHL8040 And Osmonics products such as DK8040C, DL2540F, DL4040F, DL8040F, DL2540C, DL4040C, DL8040C, Duracid NF2540C, Duracid NF4040C, and Duracid NF8040C. Of these, Duracid-based products are preferred.

The fourth step is preferably performed at a temperature of 10 to 40 ℃, preferably 10 to 20 ℃ and 100 to 700 psig.

The present invention may further include the step of adding a chelating agent to the waste liquid between the third step and the fourth step in order to more easily remove the metal salt used as the flocculant in the first step.

Metal ions used as the flocculant, particularly aluminum or iron, may not be completely removed using only nanofilters. Although the separation mechanism of the nanofilter has not been clearly identified until now, considering that the principle of the filter is separation by size, when the chelating agent is added, the coagulant in the metal ion state to be removed is surrounded by the chelating agent. As the size increases, it is determined that the nanofilter is easily removed during filtration.

The chelating agent is preferably a compound containing a sulfone group (-SO ₃ H) or a carboxy group (-COOH) as a functional group, or a compound containing a hydroxyketone group.

Specific examples of the compound containing a sulfone group or a carboxyl group include sulfosalicylic acid, salicylic acid, benzenesulfonic acid, sulfopicolinic acid, 3-sulfo-4-pyridinecarboxylic acid, 4-sulfo-3-pyridinecarboxylic acid, and sulfo And phthalic acid. Specific examples of the compound containing the hydroxyketone group include pyrogelol red, pyrocatechol violet, 2-hydroxycyclohexanone, 1- (1-hydroxycyclohexyl) ethanone, 3-hydroxy-3-phenyl-2-butanone, 2-hydroxycyclodecanone, 4-hydroxy-2,2,5,5-tetramethyl-3-hexanone, 1-hydroxy-1- Methyl-2 (1H) -naphthalenone, 2-hydroxycyclodecanone, 1-hydroxy-1,1-diphenylacetone, etc. are mentioned, These can be used individually or in combination of 2 or more types. Of these, sulfosalicylic acid, picolinic acid, pyrocatechol violet and the like are particularly preferable.

The chelating agent is preferably used in an amount of 1.5 parts by weight or less, more preferably 1 to 1.5 parts by weight based on 1 part by weight of the flocculant. Within this content range, the flocculant can be removed economically and effectively without causing secondary contamination of the final dye solution by the chelating agent.

The fifth step is to recover the second filtered dye solution in the fourth step.

The recovered dye solution may have a total organic carbon concentration of 30 ppm or less. The dye solution containing the PVA resin and the organic material in the same concentration does not cause a defect of the final product even when recycled to the manufacturing process of the polarizing film.

The present invention provides a method for producing a polarizing film by recycling the recovered dye solution.

The recovered dye solution is a solution having a total organic carbon concentration of 30 ppm or less, and may be used as it is, and may be used by correcting the concentration of the dichroic dye and boric acid.

Hereinafter, preferred examples are provided to aid the understanding of the present invention, but the following examples are merely for exemplifying the present invention, and various changes and modifications within the scope and spirit of the present invention are apparent to those skilled in the art. Naturally, such modifications and variations fall within the scope of the appended claims.

In the following Examples and Comparative Examples, "%" and "parts" indicating contents are by weight unless otherwise specified.

<Example 1-3, Comparative Example 1-2. Recovery of Dye Solution from Polarizing Film Waste

Example 1

The waste liquid used in the process of manufacturing a polarizing film using iodine was collect | recovered. 1 part of ferric sulfate, a coagulant, was added to 100 parts by weight of the collected waste liquid to agglomerate the PVA resin and other organic materials, and this was stored at 15 ° C. for 12 hours to accelerate aggregation. After the aggregation was completed, the waste solution was first filtered using a filter to remove the aggregated PVA resin and other organic substances, and then, the dye solution was recovered by secondary filtration at 20 ° C. and 600 psig using a nanofilter (Duracid NF4040C).

Example 2

1 part of sulfosalicylic acid, which is a chelating agent, was added to the first filtered dye solution, followed by the same method as Example 1 except for filtering using a nanofilter.

Example 3

The same process as in Example 1 was conducted except that 1 part of aluminum sulfate was added as a flocculant.

Comparative Example 1

The step of accelerating aggregation at low temperature was carried out in the same manner as in Example 1 except that instead of storing for 12 hours at 30 ℃.

Comparative Example 2

The same process as in Example 1 was carried out except that the second filtration step was not performed using the nanofilter.

<Example 4-6 and Comparative Example 3-4. Manufacturing Polarizing Film Using Recovered Dye Solution>

After correcting the concentrations of iodine and boric acid in the dye solution recovered in Examples 1 to 3 and Comparative Examples 1 to 2, using this to prepare a polarizing film by a conventional manufacturing method.

Test Example

In order to determine the degree of organic matter removal of the dye solution recovered in Examples 1 to 3 and Comparative Examples 1 to 2, the total organic carbon (TOC) concentration was measured, and the results are shown in Table 1 below. In addition, it measured through the total organic carbon concentration of the waste liquid before recovery, and compared the result. At this time, the total organic carbon meter used was a TOC-V CPH model of SHIMADZU.

division Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Waste TOC (ppm) 25 19 22 230 70 800

In addition, the defective rate by the organic material on the surface of the polarizing film prepared in Examples 4 to 6 and Comparative Examples 3 to 4 was measured, and the results are shown in Table 2 below. At this time, the polarizing film manufactured using the general dye solution was also measured by the same method (reference example), and the results were compared.

division Example 4 Example 5 Example 6 Comparative Example 3 Comparative Example 4 Reference Example Defective rate 0.1% or less 0.1% or less 0.1% or less 1.0% 1.7% 0.1% or less

As shown in Tables 1 and 2, according to the present invention, a dye solution having a low concentration of PVA resin and other organic matters could be easily recovered from the polarizing film manufacturing waste solution. In addition, it was confirmed that the polarizing film prepared by recycling the recovered dye solution showed a surface similar to that of the polarizing film manufactured using a general dye solution.

1 is a process chart showing a regeneration method of a polarizing film manufacturing waste according to an embodiment of the present invention.

Claims (16)

A method for recovering the dye solution from the waste liquid generated in the polarizing film manufacturing process. The method of claim 1, wherein the waste liquid is a solution containing a compound used in the stretching, dyeing or washing process of the polarizing film. The method of claim 2, wherein the waste liquid is a dye solution containing a dichroic dye, boric acid, and distilled water, and a solution containing a polyvinyl alcohol resin and an organic substance. The method of claim 1, further comprising: coagulating the organic material with the polyvinyl alcohol resin included in the waste liquid; A second step of accelerating aggregation by leaving the waste liquid at a low temperature; A third step of separating the aggregated polyvinyl alcohol resin and the organic material and the dyeing solution by primary filtration of the waste liquid having been aggregated; A fourth step of secondary filtration of the separated dye solution; And a fifth step of recovering the filtered dye solution. 5. The method of claim 4, wherein the flocculation of the first step is performed by introducing at least one flocculant selected from the group consisting of aluminum sulfate, ferrous sulfate, ferric sulfate, and ferric chloride. The method of claim 4, wherein the second step is performed at a low temperature of 20 ° C. or less. The method of claim 4, wherein the second step is performed at 10 to 18 ° C. 6. The method of claim 4, wherein the third step is performed at 20 ° C. or lower. 5. The method of claim 4, further comprising adding a chelating agent to the waste liquid between the third and fourth steps. The method of claim 9, wherein the chelating agent is sulfosalicylic acid, salicylic acid, benzenesulfonic acid, sulfopicolinic acid, 3-sulfo-4-pyridinecarboxylic acid, 4-sulfo-3-pyridinecarboxylic acid, sulfophthalic acid, pyrogelol Red, pyrocatechol violet, 2-hydroxycyclohexanone, 1- (1-hydroxycyclohexyl) ethanone, 3-hydroxy-3-phenyl-2-butanone, 2-hydroxycyclodecanone, 4-hydroxy-2,2,5,5-tetramethyl-3-hexanone, 1-hydroxy-1-methyl-2 (1H) -naphthalenone, 2-hydroxycyclodecanone and 1-hydroxy At least one selected from the group consisting of oxy-1,1-diphenylacetone. The method of claim 9, wherein the chelating agent is added at 1.5 parts by weight or less based on 1 part by weight of the flocculant. The method of claim 4, wherein the fourth step is performed using a nanofilter having an average diameter of pores of 0.001 to 0.01 μm. The method of claim 4, wherein the fourth step is performed at 10 to 40 ° C. and 100 to 700 psig. The method according to claim 1, wherein the concentration of the total organic carbon in the recovered dye solution is 30 ppm or less. A method for producing a polarizing film by recycling the dye solution recovered by any one of claims 1 to 14. The method of claim 15, comprising correcting the concentration of dichroic dye and boric acid in the recovered dye solution.

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