Method for manufacturing decolored wholly aromatic polyamide fiber

Abstract

To provide a method for decoloring a wholly aromatic polyamide fiber colored with a disperse dye or pigment by using a process liquid for decoloration including a specific ionic liquid and an aprotic organic solvent.SOLUTION: A wholly aromatic polyamide fiber colored with a disperse dye or pigment is subjected to decoloration treatment by bringing the fiber into contact with an imidazolium-based ionic liquid containing an alkyl group with a carbon number of 5 or less in a molecule, and an aprotic organic solvent at a treatment temperature of 100-130°C for 3-5 hours.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method for producing a bleached wholly aromatic polyamide fiber, and more specifically, to a method for bleaching a wholly aromatic polyamide fiber colored with a disperse dye or a pigment, using a bleaching treatment liquid containing an imidazolium-based ionic liquid and an aprotic organic solvent. [Background technology]

[0002] Fully aromatic polyamide fibers (hereinafter also referred to as aramid fibers) are utilized for industrial material applications and functional clothing, taking advantage of their characteristics such as high strength, high elastic modulus, and chemical resistance. Furthermore, in recent years, the demand for high-performance fiber products has been required to grow sustainably, and calls for recycling have been increasing in the textile industry as well. Against this background, in order to effectively utilize aramid fibers, there is a demand for the reuse of discarded waste fibers for industrial material applications and functional clothing, and / or fiber waste generated in the process of manufacturing and processing aramid fibers. In order to meet such demands, for example, recovery techniques for recycling aramid fiber products (see Patent Document 1) are known.

[0003] However, currently, aramid fiber products are usually colored with pigments, and in order to reuse the recovered aramid fibers or to reuse them as a dope for aramid fibers, it is necessary to remove the pigments in the fibers to some extent and decolorize them, but it is difficult to say that an efficient decolorization method has been developed at present.

[0004] Among current decolorization techniques for chemical fibers, there is a method that uses a non-chlorine solvent in consideration of the environmental load (see Patent Document 2). In this method, the polyester fiber to be treated is entirely immersed in the solvent to remove the pigment from the fiber. However, in this method, the fiber is constantly in contact with the solvent, and when the dissolved pigment becomes saturated in the solvent, the pigment adheres to the fiber again, which is a problem. Therefore, in order to completely decolorize the fiber, it is necessary to repeatedly immerse the fiber in fresh solvent every time the dye in the solvent becomes saturated, which requires the use of a large amount of solvent, and in addition, it has not yet been examined whether such a method can be applied to aramid fibers. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 2023-507132 [Patent Document 2] U.S. Patent No. 7,959,807 Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to solve the problems in the conventional technology and to provide a method for decolorizing wholly aromatic polyamide fibers colored with a disperse dye or pigment by using a decolorizing treatment liquid containing a specific ionic liquid and an aprotic organic solvent. [Means for solving the problem]

[0007] As a result of intensive studies to solve the above problems, the present inventors have found that when dyed or material-colored (hereinafter sometimes referred to as "spun-dyed") aramid fibers are brought into contact with a decolorizing treatment liquid obtained by mixing an ionic liquid and an organic solvent and mixed under shear stress, the colored aramid fibers can be decolorized to a state close to that before coloring, and have completed the present invention.

[0008] That is, according to the present invention, 1. A method for producing a bleached wholly aromatic polyamide fiber, comprising contacting a wholly aromatic polyamide fiber colored with a disperse dye or pigment with a bleaching treatment liquid containing an imidazolium-based ionic liquid containing an alkyl group having 5 or less carbon atoms in the molecule and an aprotic organic solvent, and bleaching the wholly aromatic polyamide fiber at a treatment temperature of 100°C to 130°C for 3 to 5 hours, thereby making the color difference ΔE of the wholly aromatic polyamide fiber before and after the bleaching treatment 13 or less in accordance with JIS Z 8729:2013; 2. A method for producing a bleached wholly aromatic polyamide fiber according to the above item 1, wherein the wholly aromatic polyamide fiber is a para-type wholly aromatic copolyamide or a meta-type wholly aromatic copolyamide composed of an acid chloride component and a diamine component, the acid chloride component containing terephthalic acid dichloride (hereinafter referred to as the first component), the diamine component containing paraphenylenediamine or metaphenylenediamine (hereinafter referred to as the second component), and at least one diamine (hereinafter referred to as the third component) selected from the group consisting of 3,3'-oxydiphenylenediamine, 3,4'-oxydiphenylenediamine, and 4,4'-oxydiphenylenediamine, and the molar ratio of the second component to the third component in the diamine component is 20 / 80 to 80 / 20; 3. The method for producing bleached wholly aromatic polyamide fibers according to 1 or 2 above, wherein the imidazolium ionic liquid is 1-ethyl-3-methylimidazolium chloride or 1-butyl-3-methylimidazolium chloride. 4. The method for producing a bleached wholly aromatic polyamide fiber according to 1 or 2 above, wherein the aprotic organic solvent is a plant-derived organic solvent. And, 5. The method for producing bleached wholly aromatic polyamide fibers according to the above 1 or 2, wherein the aprotic organic solvent is γ-valerolactone. is provided. Effect of the Invention

[0009] By using the method for producing bleached wholly aromatic polyamide fibers of the present invention, dyes and pigments can be easily bleached from the fibers by bleaching treatment, making it possible to provide recyclable wholly aromatic polyamide fiber products. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The present invention will be described in detail below.

[0011] <Fully aromatic polyamide> The wholly aromatic polyamide used in the present invention is a para-type wholly aromatic polyamide or a meta-type wholly aromatic polyamide composed of an acid chloride component and a diamine component, and in particular, it is preferable that the wholly aromatic polyamide is a para-type wholly aromatic copolyamide or a meta-type wholly aromatic copolyamide which contains terephthalic acid dichloride (hereinafter referred to as the first component) as the acid chloride component, and contains paraphenylenediamine or metaphenylenediamine (hereinafter referred to as the second component) as the diamine component, and at least one diamine (hereinafter referred to as the third component) selected from the group consisting of 3,3'-oxydiphenylenediamine, 3,4'-oxydiphenylenediamine, and 4,4'-oxydiphenylenediamine, and in which the molar ratio of the second component to the third component in the diamine component is 20 / 80 to 80 / 20.

[0012] To produce the above-mentioned para-type wholly aromatic copolyamide fibers, the concentration of the para-type wholly aromatic copolyamide is adjusted with NMP, and the polymer solution is used as a spinning dope. The polymer solution is discharged from a spinneret and extruded into an aqueous NMP solution through an air gap in a coagulation step, followed by a heat drawing step, a washing step, and a dry heat treatment step. In this manner, the para-type wholly aromatic copolyamide fibers can be obtained by a conventionally known method.

[0013] In addition, in order to produce the above-mentioned meta-type wholly aromatic copolyamide fiber, a spinning dope having a polymer concentration of 15 to 20 mass% is produced using the meta-type wholly aromatic copolyamide in a spinning solution preparation step, and the dope is discharged from a spinneret in a coagulation step, followed by a hot drawing step, a washing step, and a dry heat treatment step, so that the meta-type wholly aromatic copolyamide fiber can be obtained by a conventionally known method.

[0014] Among these wholly aromatic polyamide fibers, Technora (registered trademark, manufactured by Teijin Limited) and Teijin Conex (registered trademark, manufactured by Teijin Limited) are examples of fibers that have already been industrialized.

[0015] <Pigments and dyes> The pigment and disperse dye used in the present invention are not particularly limited, and conventionally known pigments and disperse dyes can be used. It is preferable to include at least one type selected from the group consisting of iron oxide-based (red), Co-based or Al-based (blue), and carbon black (black) disperse pigments.

[0016] Furthermore, pigments other than iron oxide (red), Co or Al (blue), and carbon black (black) dispersed pigments such as titanium oxide and zinc may be used in combination as long as the pigment retains its color to an extent that does not cause problems in the decolorization treatment described below.

[0017] Dyeing with pigments is carried out by adding a dispersing pigment at the stage of fiber production of the above-mentioned para-type wholly aromatic copolyamide or meta-type wholly aromatic copolyamide. Dyeing with dispersing dyes may be carried out in any state of the above-mentioned meta-type wholly aromatic copolyamide fiber products or para-type wholly aromatic copolyamide fiber products in the form of thread, cotton, woven fabric, knitted fabric, nonwoven fabric, etc., or in the form of sewn products such as clothes, bags, sacks, tents, curtains, futons, and sheets. In both cases of meta-type wholly aromatic copolyamide fiber products and para-type wholly aromatic copolyamide fiber products, it is preferable to use cationic dyes. The dyeing density may be any color from light to dark, and the dyeing hue may be any color such as red, blue, yellow, green, or black.

[0018] <Bleaching treatment> The method for bleaching wholly aromatic polyamide fibers of the present invention is characterized in that wholly aromatic polyamide fibers colored with a disperse dye or pigment are brought into contact with a bleaching treatment liquid that is a mixture of an ionic liquid and an aprotic organic solvent, and mixed under shear stress to perform a bleaching treatment. Here, it is essential that an imidazolium-based ionic liquid is used as the ionic liquid.

[0019] Ionic liquids can be classified into imidazolium-based cations and chloride-based counter ions, and both can be modified with alkyl or aromatic groups, making it possible to adjust the balance between cations and anions.

[0020] In the case of ion pairs between atomic ions such as sodium chloride, the ions are not localized, so the ionic bond strength is high, resulting in crystals with a high melting point. On the other hand, those used as ionic liquids have ions localized within the molecules, so the ionic bond strength is low and the melting point is low. In addition, they are considered to be less volatile and safer than molecular solvents.

[0021] The cationic species of the imidazolium ionic liquid used in the present invention is exemplified by imidazolium ions in which R1 in the molecular formula (1) is a methyl group and R2 is an alkyl group having 1 to 5 carbon atoms. Imidazolium ions in which R2 is an alkyl group having 2 to 4 carbon atoms are more preferred. Groups with more than 5 carbon atoms become solid and are not preferred for aramid fiber decolorization treatment. Cl is preferred as the anionic species.

[0022] [ka]

[0023] Any combination of these cations and anions may be used (hereinafter, a space will be inserted between the cation species and the anion species to distinguish them), but in the case of para-type wholly aromatic polyamides, from the standpoint of solubility and the proportion of ionic liquid (cost), 1-ethyl-3-methylimidazolium chloride or 1-butyl-3-methylimidazolium chloride is preferred, and 1-ethyl-3-methylimidazolium chloride is particularly preferred.

[0024] The aprotic organic solvent used in the present invention is a solvent that does not have a proton-donating group such as a hydroxyl group, which is made of an organic compound, and examples of such solvents include ethyl carbonate, propyl carbonate, ethyl fluorocarbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, 1,2-butylene carbonate, dimethyl sulfone, ethyl methyl sulfone, diethyl sulfone, dipropyl sulfone, sulfolane, dimethyl sulfide, diethyl sulfide, diisopropyl sulfide, dimethyl sulfoxide, diethyl sulfoxide, diethyl ether, propyl ether, isopropyl ether, dibutyl ether, diisobutyl ether, cyclopentyl methyl ether, tetrahydrofuran, 2-methyl ... Examples of the dimethyl lactone include tetrahydrofuran, 2,5-dimethyltetrahydrofuran, dioxane, dihydrolevoglucosenone, α-angelica lactone, γ-butyrolactone, γ-valerolactone, γ-caprolactone, γ-heptanolactone, γ-octanolactone, γ-nonalactone, γ-decanolactone, δ-valerolactone, δ-hexanolactone, δ-octanolactone, δ-decanolactone, δ-tetradecanolactone, ε-caprolactone, ε-decanolactone, dimethylisosorbide, acetone, methyl ethyl ketone, methyl isobutyl ketone, diisobutyl ketone, cyclopentanone, and cyclohexanone. Of these, γ-valerolactone is preferred.

[0025] The concentration of the ionic liquid in the decolorizing treatment liquid obtained by mixing the ionic liquid with the aprotic organic solvent is preferably 0.05 to 10 mass%, particularly preferably 0.1 to 1 mass%. If the concentration of the ionic liquid is less than 0.05 mass%, the decolorizing effect may be insufficient, whereas if the concentration of the ionic liquid exceeds 10 mass%, the wholly aromatic polyamide fiber may be dissolved, and it is also disadvantageous in terms of cost.

[0026] In the present invention, the wholly aromatic polyamide fiber colored with a disperse dye or pigment is brought into contact with the above-mentioned bleaching treatment liquid and mixed under shear stress to perform the bleaching treatment, and the treatment temperature at that time must be 100 to 130° C., and preferably 120 to 130° C. If the temperature is below 100° C., sufficient bleaching cannot be achieved, while if the treatment temperature exceeds 130° C., the polyamide fiber will gel.

[0027] The decolorization treatment time must be between 3 and 5 hours. If the treatment time is less than 3 hours, the decolorization effect is weak and the decolorization treatment cannot be performed sufficiently. On the other hand, if the treatment time exceeds 5 hours, gelation of the fibers occurs and the decolorization treatment cannot be performed sufficiently.

[0028] In the present invention, aprotic organic solvents derived from plants can also be used as the aprotic organic solvent. The aprotic organic solvents derived from plants are organic compounds synthesized from raw materials derived from plants (sugar / starch biomass, lignocellulosic biomass including cellulose, hemicellulose, lignin, etc.), and natural products produced by animals, plants, and microorganisms. There is no difference in physical properties such as molecular weight and thermal properties (melting point, boiling point) between solvents derived from plants and solvents derived from fossils. Therefore, biomass degree is generally used to distinguish between them.

[0029] The biomass degree is a value obtained by measuring the content of carbon derived from biomass by measuring radioactive carbon (14C, half-life 5730 years). 14N is converted to 14C by high-energy cosmic rays in the upper atmosphere, and carbon dioxide in the atmosphere contains a certain amount of 14C. Carbon dioxide is fixed in plants as carbohydrates by photosynthesis, so plants contain the same amount of 14C. On the other hand, fossil-derived petroleum does not substantially contain 14C, so carbon derived from plants and carbon derived from fossils can be distinguished. ASTM D6866 and the like are commonly known methods for measuring the biomass degree. Therefore, the organic solvent derived from animals and plants of the present invention can also be distinguished by extracting the organic solvent in the polymer solution and then measuring the biomass degree.

[0030] In the present invention, it is preferable to cut long fibers, short fibers, etc., before use because they are easy to handle in a kneader. The preferred fiber length is 40 mm or less, and the shorter the fiber length, the greater the contact area with the solvent, making it preferable. The cutting method is to cut the fibers using a guillotine cutter, a rotary cutter, a fiber cutter for wool, etc.

[0031] When cutting, moisture can be added to prevent scattering, but it is necessary to dry it before dissolving. It is preferable to control the moisture content to within 10% under temperature conditions of 100°C or higher. If it is more than 10%, it will not dissolve properly, which is not recommended.

[0032] For the decolorization treatment, a known mixer can be used, such as a single-shaft mixer, a ribbon mixer, a planetary mixer, etc. Among these, it is preferable to select a planetary mixer.

[0033] In the decolorization treatment, the ionic liquid and the aprotic organic solvent are charged into a mixer, and then the wholly aromatic polyamide fiber yarn or cut yarn, and the powdered wholly aromatic polyamide polymer are dispersed in the decolorization treatment liquid, and the decolorization treatment is carried out at the treatment temperature and for the treatment time described above.

[0034] <Evaluation of bleaching effect> The wholly aromatic polyamide fiber was subjected to Lab color space optical measurement using a color difference meter before and after coloring and bleaching treatment (based on JIS Z 8729:2013). The value of L is 100, which indicates white, and 0, which indicates black. The value of a is 100, which indicates magenta, and 0, which indicates green. The value of b is 100, which indicates yellow, and 0, which indicates blue. In order to say that bleaching has been performed sufficiently, the color difference ΔE between the color of the dyed fiber after the bleaching treatment as described below and the color of the fiber before it was dyed must be 13 or less, and preferably 10 or less. Here, the color difference ΔE is calculated according to the CIE1976LAB ΔE=√(ΔL 2 +Δa 2 +Δb 2 ), light source D65, 10° field of view. EXAMPLES

[0035] The present invention will be described in detail below with reference to examples and comparative examples, but the scope of the present invention is not limited to the following examples and comparative examples.

[0036] [Reference example 1] [Aramid fiber manufacturing] N-methyl-pyrrolidone (NMP) was placed in a reaction vessel, and p-phenylenediamine and 3,4'-diaminodiphenyl ether were weighed out and dissolved in equimolar amounts. Terephthalic acid dichloride was weighed out and added to this diamine solution in an amount approximately equimolar to the total molar amount of diamines. After the reaction was completed, the mixture was neutralized with calcium hydroxide to obtain a fully aromatic polyamide solution. At this time, the mass concentration of the fully aromatic polyamide polymer was adjusted to 6% relative to the fully aromatic polyamide solution.

[0037] The solution was used as a spinning dope, extruded from a spinneret with 1000 holes and a diameter of 1.2 mm, and extruded through an air gap of 3 to 10 mm into an aqueous NMP solution with a mass concentration of 30% and solidified. The dope was then washed with water, dried, stretched 6 times at 500°C, and wound up to obtain a wholly aromatic polyamide fiber (copolyparaphenylene-3,4'-oxydiphenylene-terephthalamide fiber) with a single fiber fineness of 1.67 dtex. The Lab value of the obtained fiber according to JIS Z 8729:2013 is shown in Table 1.

[0038] [Example 1] [Aramid fiber manufacturing] The same procedure as in Reference Example 1 was carried out, except that the wholly aromatic polyamide solution and the red pigment (iron oxide) were blended in a mass ratio of 6:1.5 and used as the spinning dope. Among the fibers produced by the above method, fiber waste (single filament fineness 1.5 dtex) that could not be used for products due to abnormal fineness was cut into 3 mm pieces using a guillotine cutter and used for decolorization treatment.

[0039] [Bleaching treatment] The fiber scraps cut into 3 mm pieces were dried for 2 hours at 120° C. 1,880 g of 1-ethyl-3-methylimidazolium chloride, 2,820 g of γ-valerolactone, totaling 4,700 g, and 300 g of the dried fiber scraps were added to a planetary mixer and kneaded under shear stress at 100° C. for 5 hours in a nitrogen atmosphere. When the solid matter was filtered from the kneaded solution, the fiber was found to be almost orange with a slight reddish tinge. Next, the L ab value of the bleached fiber was measured, and the color difference ΔE from the fiber before dyeing obtained in Reference Example 1 was calculated. The results of the bleaching effect are shown in Table 1.

[0040] [Evaluation of decolorization effect] The ΔE ratio between before and after the bleaching treatment was 9.08, which was confirmed to be less than 13, and the bleaching effect was observed.

[0041] [Example 2] [Aramid fiber manufacturing] The same operations as in Example 1 were carried out, except that the pigment was a blue pigment (chromium oxide / aluminum) and the mass ratio of the wholly aromatic polyamide solution to the blue pigment was 6:1.5.

[0042] [Bleaching treatment] The same procedure was carried out as in Example 1. The Lab value of the bleached fiber was measured, and the color difference ΔE from the fiber before and after dyeing obtained in Reference Example 1 was calculated. The results of the bleaching effect are shown in Table 1.

[0043] [Evaluation of decolorization effect] The ΔE between before and after coloring was 10.30, which was confirmed to be less than 13, and the bleaching effect was observed.

[0044] [Example 3] [Aramid fiber manufacturing] The same operations as in Example 1 were carried out, except that the pigment was a black pigment (carbon black) and the mass ratio of the wholly aromatic polyamide solution to the black pigment was 6:1.5.

[0045] [Bleaching treatment] The same procedure was carried out as in Example 1. The Lab value of the bleached fiber was measured, and the color difference ΔE from the fiber before and after dyeing obtained in Reference Example 1 was calculated. The results of the bleaching effect are shown in Table 1.

[0046] [Evaluation of decolorization effect] The ΔE between before and after coloring was 12.53, which was confirmed to be less than 13, and the bleaching effect was observed.

[0047] [Example 4] [Aramid fiber manufacturing] The same procedure as in Example 1 was carried out.

[0048] [Bleaching treatment] The same procedure as in Example 1 was repeated except that 1-butyl-3-methylimidazolium chloride was used as the ionic liquid. When the solid matter was filtered from the kneaded solution, the fibers were almost gray. The Lab value of the bleached fibers was measured, and the color difference ΔE from the fibers before and after dyeing obtained in Reference Example 1 was calculated. The results of the bleaching effect are shown in Table 1.

[0049] [Evaluation of decolorization effect] The ΔE between before and after coloring was 12.68, which was confirmed to be less than 13, and the decolorization was effective.

[0050] [Example 5] [Aramid fiber manufacturing] The same procedure as in Example 1 was carried out.

[0051] [Bleaching treatment] The same procedure as in Example 1 was repeated except that 1-ethyl-3-methylimidazolium chloride was used as the ionic liquid. When the solid matter was filtered from the kneaded solution, the fibers were almost gray. The Lab value of the bleached fibers was measured, and the color difference ΔE from the fibers before and after dyeing obtained in Reference Example 1 was calculated. The results of the bleaching effect are shown in Table 1.

[0052] [Evaluation of decolorization effect] The ΔE between before and after coloring was 12.97, which was confirmed to be less than 13, and the bleaching effect was observed.

[0053] [Comparative Example 1] [Aramid fiber manufacturing] The same procedure as in Example 3 was followed.

[0054] [Bleaching treatment] The same procedure as in Example 1 was carried out except that the kneading temperature was 50°C. When the solid matter was filtered from the solution after kneading, the solution remained colorless and transparent. The Lab value of the fiber after bleaching was measured, and the color difference ΔE from the fiber before bleaching obtained in Reference Example 1 was calculated. The measurement results of the bleaching effect are shown in Table 1.

[0055] [Evaluation of decolorization effect] The ΔE between before and after the bleaching treatment was 53.33, showing no bleaching effect.

[0056] [Comparative Example 2] [Aramid fiber manufacturing] The same procedure as in Example 3 was followed.

[0057] [Bleaching treatment] The same procedure as in Example 1 was repeated except that 1-hexyl-3-methylimidazolium chloride was used as the ionic liquid. When we tried to filter the solid matter from the solution after kneading, the fiber scraps were dissolved and could not be separated from the solution. Therefore, it was not possible to measure the color difference ΔE between the fiber before coloring and the fiber after bleaching. The measurement results of the bleaching effect are shown in Table 1.

[0058] [Comparative Example 3] [Aramid fiber manufacturing] The same procedure as in Example 3 was followed.

[0059] [Bleaching treatment] The same procedure as in Example 1 was carried out except that the kneading temperature was 140°C. When we tried to filter the solid matter from the solution after kneading, the fiber scraps gelled and could not be separated from the solution. Therefore, it was not possible to measure the color difference ΔE between the fiber before coloring and the fiber after bleaching. The measurement results of the bleaching effect are shown in Table 1.

[0060] [Comparative Example 4] [Aramid fiber manufacturing] The same procedure as in Example 3 was followed.

[0061] [Bleaching treatment] The same procedure as in Example 1 was carried out, except that the kneading time was changed to 2 hours. When the solid matter was filtered from the kneaded solution, the solvent system remained colorless and transparent. The Lab value of the fiber after bleaching was measured, and the color difference ΔE from the fiber before bleaching obtained in Reference Example 1 was calculated. The results of the bleaching effect are shown in Table 1.

[0062] [Evaluation of decolorization effect] The ΔE between before and after the bleaching treatment was 53.33, showing no bleaching effect.

[0063] [Comparative Example 5] [Aramid fiber manufacturing] The same procedure as in Example 3 was followed.

[0064] [Bleaching treatment] The same procedure as in Example 1 was carried out, except that the kneading time was 8 hours. When we tried to filter the solid matter from the solution after kneading, the fiber scraps gelled and could not be separated from the solution. Therefore, it was not possible to measure the color difference ΔE between the fiber before coloring and the fiber after bleaching. The measurement results of the bleaching effect are shown in Table 1.

[0065] [Comparative Example 6] [Aramid fiber manufacturing] The same procedure as in Example 3 was followed.

[0066] [Bleaching treatment] The same procedure as in Example 1 was repeated except that ethanol was used instead of the ionic liquid. When the solid matter was filtered from the kneaded solution, the solvent system remained colorless and transparent. The Lab value of the fiber after bleaching was measured, and the color difference ΔE from the fiber before bleaching obtained in Reference Example 1 was calculated. The results of the bleaching effect are shown in Table 1.

[0067] [Evaluation of decolorization effect] The ΔE between before and after the bleaching treatment was 53.33, showing no bleaching effect.

[0068] [Table 1] [Industrial Applicability]

[0069] According to the present invention, there is provided a method for decolorizing wholly aromatic polyamide fibers colored with a disperse dye or pigment by using a decolorizing treatment liquid containing a specific ionic liquid and an aprotic organic solvent, which makes it possible to reuse colored aramid fiber products and colored fiber waste generated during the manufacturing process, and thus has extremely great industrial value.

Claims

1. A method for producing a bleached wholly aromatic polyamide fiber, comprising contacting a wholly aromatic polyamide fiber colored with a disperse dye or pigment with a bleaching treatment liquid containing an imidazolium-based ionic liquid containing an alkyl group having 5 or less carbon atoms in the molecule, and an aprotic organic solvent, and subjecting the wholly aromatic polyamide fiber to a bleaching treatment at a treatment temperature of 100°C to 130°C for 3 to 5 hours, thereby making the color difference ΔE of the wholly aromatic polyamide fiber before and after the bleaching treatment 13 or less in accordance with JIS Z 8729:2013.

2. 2. The method for producing a bleached wholly aromatic polyamide fiber according to claim 1, wherein the wholly aromatic polyamide fiber is a para-type wholly aromatic copolyamide or a meta-type wholly aromatic copolyamide composed of an acid chloride component and a diamine component, the acid chloride component containing terephthalic acid dichloride (hereinafter referred to as the first component), the diamine component containing paraphenylenediamine or metaphenylenediamine (hereinafter referred to as the second component), and at least one diamine selected from the group consisting of 3,3'oxydiphenylenediamine, 3,4'oxydiphenylenediamine, and 4,4'oxydiphenylenediamine (hereinafter referred to as the third component), and the molar ratio of the second component to the third component in the diamine component is 20 / 80 to 80 / 20.

3. 3. The method for producing bleached wholly aromatic polyamide fibers according to claim 1, wherein the imidazolium-based ionic liquid is 1-ethyl-3-methylimidazolium chloride or 1-butyl-3-methylimidazolium chloride.

4. 3. The method for producing bleached wholly aromatic polyamide fibers according to claim 1, wherein the aprotic organic solvent is an organic solvent derived from a plant.

5. 3. The method for producing bleached wholly aromatic polyamide fibers according to claim 1, wherein the aprotic organic solvent is γ-valerolactone.

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