Method for producing a wholly aromatic polyamide solution

Abstract

To provide a manufacturing method of a wholly aromatic amide solution which shows high solubility property capable of dissolving aramid fibers such as waste aramid fibers without using an inorganic salt and an aprotic polar organic solvent and excellent process stabilization property.SOLUTION: A wholly aromatic polyamide fiber having a single fiber fineness of 10dtex or under is brought into contact with an ionic liquid at a mass ratio of 0.5:99.5 to 10:90 to give a mixture, then the mixture is kneaded under a shear stress while heating at 60°C or over.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a wholly aromatic polyamide (hereinafter, sometimes referred to as "aramid") solution, and more particularly to a method for producing an aramid solution by redissolving aramid fibers in a solvent in order to effectively reuse aramid fibers. [Background technology]

[0002] Taking advantage of their high strength, high modulus, and chemical resistance, aramid fibers are used in industrial materials, functional clothing, etc. However, when disposing of these aramid fiber products, incineration or other methods are extremely difficult due to their chemical stability and flame retardancy, so they are generally disposed of by landfilling, and the large amount of aramid fiber waste that is used as an industrial fiber poses a significant environmental burden, which has become a problem.

[0003] Furthermore, in recent years, demand for high-performance fiber products has been required to grow sustainably, and calls for recycling have been increasing in the textile industry. Against this background, in order to make effective use of aramid fiber, a method of recycling by redissolving discarded aramid fiber in a solvent to make a polymer solution (dope) has been studied.

[0004] For example, Japanese Patent Application Laid-Open No. 2006-241624 discloses a method of redissolving aramid fibers by contacting and mixing fiber waste generated in a process with N-methyl-pyrrolidone (NMP) containing an inorganic salt such as calcium chloride, and then subjecting the mixture to shear stress.

[0005] However, the chloride ions in the calcium chloride used in this method damage the non-conductive coating made up of oxygen and chromium on the surface of stainless steel pipes, reaching the stainless steel substrate, causing an anodic reaction in which iron, chromium, nickel, and other elements in the stainless steel substrate are ionized. Meanwhile, at the cathode nearby, dissolved oxygen undergoes a reduction reaction. It is believed that the chloride ions then replace the oxygen that makes up the coating, accelerating its destruction.

[0006] Damage to this coating can lead to corrosion of the pipes, which can then lead to leakage of the chemicals inside the pipes, which can lead to explosions and fires. Therefore, a solvent that does not use inorganic salts was sought, but strong acids and strong alkalis were thought to be such solvents, and although they were capable of dissolving fibers, industrial feasibility was extremely low when considering the corrosiveness of the pipes and workability.

[0007] In addition, Japanese Patent Application Laid-Open No. 2009-40871 describes an aramid solution in which poorly soluble para-aramid is dissolved using a quaternary ammonium salt and an aprotic polar solvent. However, this method is not suitable for industrial use because the concentration at which the para-wholly aromatic polyamide dissolves is extremely low and hydrogen fluoride and the like may be generated.

[0008] Furthermore, WO2015 / 158866 proposes the use of ionic liquids as a partial solubility solvent as an alternative solvent. However, even with these solvents, the solubility is low, and it is extremely difficult to prepare a dope from discarded aramid fibers and then re-coagulate it to obtain solids such as fibers or films. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-241624 [Patent Document 2] Japanese Patent Application Laid-Open No. 2009-40871 [Patent Document 3] WO2015 / 158866 Summary of the Invention [Problem to be solved by the invention]

[0010] An object of the present invention is to solve the problems in the prior art and to provide a method for producing a wholly aromatic amide solution which exhibits high solubility capable of dissolving aramid fibers such as discarded aramid fibers without using an inorganic salt or an aprotic polar organic solvent, and which is excellent in process stability. [Means for solving the problem]

[0011] As a result of intensive research into solving the above-mentioned problems, the inventors have found that the above-mentioned problems can be solved by contacting and mixing wholly aromatic polyamide fibers with an ionic liquid, and then kneading the resulting mixture under shear stress, thereby completing the present invention.

[0012] That is, according to the present invention, 1. A method for producing a wholly aromatic polyamide solution, comprising contacting wholly aromatic polyamide fibers having a single fiber fineness of 10 dtex or less with an ionic liquid in a mass ratio of 0.5:99.5 to 10:90 to form a mixture, and then kneading the mixture under shear stress while heating it to 60°C or higher; 2. A method for producing a wholly aromatic polyamide solution according to item 1 above, wherein the wholly aromatic polyamide is a para-type wholly aromatic copolyamide composed of an acid component and a diamine component, containing terephthalic acid dichloride (hereinafter referred to as the first component) as the acid component and paraphenylenediamine (hereinafter referred to as the second component) and any one of 3,3'-oxydiphenylenediamine, 3,4'-oxydiphenylenediamine, and 4,4'-oxydiphenylenediamine, or a mixture thereof (hereinafter referred to as the third component) as the diamine component, and wherein the molar ratio of the second component to the third component in the diamine component is 20 / 80 to 80 / 20; 3. The ionic liquid has a solubility parameter δt of 37 (J / cm) by the molecular contribution method. 3 ) 1 / 2 3. The method for producing a wholly aromatic polyamide solution according to 1 or 2 above, wherein the imidazolium-based ionic liquid is an imidazolium-based ionic liquid; 4. The method for producing a wholly aromatic polyamide solution according to 3 above, wherein the ionic liquid is at least one selected from the group consisting of combinations of 1-ethyl-3-methylimidazolium acetate, 1-ethyl-3-methylimidazolium trifluoroacetate, 1-ethyl-3-methylimidazolium methylphosphonate, 1-ethyl-3-methylimidazolium chloride, and 1-butyl-3-methylimidazolium chloride. 5. The ionic liquid has a solubility parameter δt of 27 (J / cm) by the molecular contribution method. 3 ) 1 / 2 3. A method for producing a wholly aromatic polyamide solution according to 1 or 2 above, wherein the phosphonium-based ionic liquid is the above-mentioned phosphonium-based ionic liquid. 6. The method for producing a wholly aromatic polyamide solution according to 5 above, wherein the ionic liquid is at least one selected from the group consisting of a combination of tributyl(ethyl)phosphonium diethylphosphate and tributyl(methyl)phosphonium dimethylphosphate. 7. The method for producing a wholly aromatic polyamide solution according to 5 above, wherein the polymer concentration in the wholly aromatic polyamide solution is 5% by mass or less. and, 8. A method for producing wholly aromatic polyamide fibers, characterized in that the wholly aromatic polyamide solution according to 1 above is used as a dope for wet spinning. is provided. [Effects of the Invention]

[0013] According to the present invention, a wholly aromatic polyamide solution having excellent solution stability can be obtained by redissolving discarded aramid fibers such as para-type wholly aromatic polyamide fibers in an ionic liquid, and this wholly aromatic polyamide solution can be used as a dope for wet spinning to obtain regenerated wholly aromatic polyamide fibers.

[0014] Furthermore, spinning is possible without using aprotic polar solvents, simplifying the solvent recovery process, which contributes greatly to reducing the environmental impact and is extremely valuable in terms of recycling waste resources. DETAILED DESCRIPTION OF THE INVENTION

[0015] The present invention will be described in detail below.

[0016] <Fully aromatic polyamide> The wholly aromatic polyamide of the present invention is a para-type wholly aromatic copolyamide composed of an acid chloride component and a diamine component, and particularly preferably a para-type wholly aromatic copolyamide composed of an acid chloride component and a diamine component, which contains terephthalic acid dichloride (hereinafter referred to as the first component) as the acid chloride component and paraphenylenediamine (hereinafter referred to as the second component) and one of 3,3'-oxydiphenylenediamine, 3,4'-oxydiphenylenediamine, or 4,4'-oxydiphenylenediamine, or a mixture thereof (hereinafter referred to as the third component), as the diamine component, and in which the molar ratio of the second component to the third component in the diamine component is 20 / 80 to 80 / 20. Technora (manufactured by Teijin Limited) is an example of a fiber made from such wholly aromatic polyamide that has already been industrialized.

[0017] These fibers are generated as waste yarn during the manufacturing process, or are mixed and used as spun yarn or filament for textiles and knitted fabrics, and then discarded. The waste yarn and waste products thus generated are remelted.

[0018] [Remelt] The fiber waste to be fed into the remelting process is preferably cut into long fibers, short fibers, etc. for ease of handling in a kneader. The fiber length is preferably less than 50 mm, more preferably 0.5 to 30 mm, and even more preferably 0.5 to 10 mm.

[0019] The cutting method is to use a guillotine cutter, a rotary cutter, a fiber cutter for wool, or the like. The fineness of the fibers used must be 10 dtex or less, preferably in the range of 0.5 to 10 dtex. If the fineness is more than 10 dtex, the fibers will not dissolve completely and tend to remain.

[0020] When cutting, moisture can be added to prevent scattering, but it must be dried before dissolving. It is preferable to control the moisture content to within 10% at temperatures above 100°C. If it is above 10%, it will not dissolve properly, which is not recommended.

[0021] For redissolving, 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.

[0022] To dissolve the ionic liquid, the ionic liquid is introduced into a mixer, and the wholly aromatic polyamide fiber yarn or cut yarn, or powdered wholly aromatic polyamide polymer is dispersed in the ionic liquid while heating and kneading under shear stress. The heating temperature must be 60°C or higher. A temperature of 80°C or higher is more preferable, as this can shorten the dissolution time.

[0023] Traditionally, solvents such as N-methyl-pyrrolidone (NMP) and N,N-dimethylacetamide (DMAC) have been used, but NMP has been identified as being reproductively toxic, and DMAC has been identified as being reproductively toxic and carcinogenic, and so ionic liquids have been expected to be an alternative solvent.

[0024] Ionic liquids are ionic liquids with cations such as imidazolium, pyridinium, pyrrolidinium, quaternary ammonium, and quaternary phosphonium, and with counterions such as halides, acetates, phosphates, phosphonates, sulfates, hydrogen sulfates, tetrafluoroborate, bis(trifluorosulfonyl)imides, and hexafluorophosphates. All of these can be modified with alkyl or aromatic groups, making it possible to adjust the balance between cations and anions.

[0025] In the case of ion pairs between atomic ions, such as sodium chloride, the ions are not localized, resulting in a high ionic bond strength and a high melting point. On the other hand, ionic liquids have localized ions within the molecule, resulting in a low ionic bond strength and a low melting point. Furthermore, they are considered to be less volatile and safer than molecular solvents.

[0026] As mentioned above, when using a solvent such as NMP, it is necessary to use an inorganic salt such as calcium chloride in combination. It is known that corrosion progresses inside pipes when chloride ions are present. The theoretical background for this is the local battery model, in which pitting corrosion progresses locally inside pipes due to electron transfer similar to that of a carbamide battery.

[0027] In this model, a passive film is formed on the stainless steel surface with oxygen and chromium (Cr), but chloride ions cause the film to break down. As a result, the area where the film breaks down becomes the anode, and the other becomes the cathode. M + nH2O → M(OH) n-1 +H + (M: metal atom) This reaction occurs, which is the main cause of the pH drop. Initially, Cr is the main component, but after the passive film is destroyed, Fe Fe → Fe 2+ +2e - The ionization of iron proceeds as shown below. The generated electrons become free electrons and undergo the following reaction with dissolved oxygen and water in the cathode area, other than the area where the insulating film is broken down. 1 / 2O2+H2O+2e - →2OH - , 2H + +2e - →H2 This consumes electrons. The dissolved iron ions form rust such as Fe(OH)2, Fe(OH)3, FeOOH, and Fe2O3 on the metal surface, and corrosion progresses.

[0028] As a result of examining the ionic liquid used in the present invention to dissolve the wholly aromatic polyamide, the solubility parameter according to the molecular contribution method was found to be 37 (J / cm 3 ) 1 / 2 The above imidazolium-based ionic liquids are one example of preferred ionic liquids.

[0029] When an imidazolium-based ionic liquid is used, the imidazolium ion acts as a corrosion inhibitor. On the anode side, water contacts the metal surface, promoting the destruction of the chloride ion passivation film. However, when imidazolium ions are present, the imidazolium ion forms micelles with water, chloride ions, etc., forming a film on the metal surface, suppressing the generation of metal ions. On the cathode side, water attached to the metal surface and dissolved oxygen form metal hydroxides. When imidazolium ions are present, the π electrons of the imidazolium group donate electrons to the vacant d orbitals of metal atoms on the metal surface, displacing the water on the surface with the imidazolium ion, forming a film of imidazolium ions. Therefore, when an imidazolium-based ionic liquid is used as a process fluid, the imidazolium group acts as a corrosion inhibitor, making corrosion less likely to occur. The use of imidazolium-based ionic liquids is preferred because it ensures the dissolution of aromatic polyamide resins and process stability.

[0030] The cationic species of the ionic liquid is preferably an imidazolium ion in which R1 in molecular formula (1) is a methyl group and R2 is an alkyl group having from 1 to 10 carbon atoms. More preferably, the number of carbon atoms is from 2 to 8. If the number of carbon atoms exceeds 10, the viscosity becomes too high, and the viscosity of the obtained wholly aromatic polyamide solution becomes too high, which is not preferred.

[0031] [ka]

[0032] Examples of anion species in ionic liquids include halides such as F, Cl, and Br, acetate ions, alkyl phosphate ions, and alkyl phosphonate ions. Of these, acetate ions are preferred. These cation species and anion species may be combined (separated by a space between the cation species and the anion species) in any combination. However, suitable combinations include one or more of 1-ethyl-3-methylimidazolium acetate, 1-ethyl-3-methylimidazolium trifluoroacetate, 1-ethyl-3-methylimidazolium methylphosphonate, and 1-butyl-3-methylimidazolium chloride. Of these, the combination with 1-ethyl-3-methylimidazolium acetate is particularly preferred from the viewpoints of solubility and viscosity of the resulting wholly aromatic polyamide solution.

[0033] Further investigation into the ionic liquid used in the present invention that dissolves the wholly aromatic polyamide revealed that the solubility parameter was 27 (J / cm 3 ) 1 / 2 The above phosphonium-based ionic liquids are another preferred ionic liquid.

[0034] The cationic species of the ionic liquid is preferably a phosphonium ion in which R1 in molecular formula (2) is a methyl group or an ethyl group, and R2, R3, and R4 are alkyl groups having from 1 to 10 carbon atoms. If the number of carbon atoms exceeds 10, the viscosity becomes too high, and the viscosity of the resulting wholly aromatic polyamide solution becomes too high, which is not preferred.

[0035] [ka]

[0036] Examples of anion species include halides such as F, Cl, and Br, acetate ions, alkyl phosphate ions, and alkyl phosphonate ions. Of these, acetate ions are preferred. While any combination of these cations and anions may be used, combinations of one or more of tributyl(ethyl)phosphonium diethylphosphate, tributyl(methyl)phosphonium dimethylphosphate, and trihexyl(tetradecyl)phosphonium chloride are preferred. Of these, the combination of tributyl(ethyl)phosphonium diethylphosphate is particularly preferred from the standpoints of solubility and viscosity of the resulting wholly aromatic polyamide solution.

[0037] The mass ratio of the wholly aromatic polyamide to the ionic liquid is 0.5:99.5 to 10:90. If the mass ratio of the wholly aromatic polyamide is less than 0.5 mass%, when the wholly aromatic polyamide solution is used as a spinning dope, it cannot be collected as thread. If the mass ratio of the wholly aromatic polyamide is more than 10 mass%, the viscosity becomes too high and it cannot be used as a spinning dope. The mass ratio of the wholly aromatic polyamide to the ionic liquid is preferably 0.5:99.5 to 8:92, and more preferably 0.5:99.5 to 5:95.

[0038] In particular, when an ionic liquid with a low solubility parameter according to the molecular contribution method, such as the above-mentioned phosphonium-based ionic liquid, is used, the preferred mass ratio of wholly aromatic polyamide to ionic liquid is 0.5:99.5 to 5:95.

[0039] The preferred viscosity range of the wholly aromatic polyamide solution obtained by the present invention is 1 to 250 (Pa·s) at 100°C and a shear rate of 250 to 1500 (1 / s). It is more preferably 10 to 250 (Pa·s). If the viscosity is higher than 250 (Pa·s), the extrudability may be poor during spinning, which is not preferred. On the other hand, if the viscosity is lower than 1 (Pa·s), the spinnability may be poor, which is not preferred.

[0040] In the present invention, the above-mentioned wet spinning can be carried out using a wholly aromatic polyamide solution prepared using the above-mentioned ionic liquid. Water or alcohols can be used as the coagulation liquid for wet spinning, and a mixture of the ionic liquid with water or alcohols can also be recovered.

[0041] In conventional technology, a wholly aromatic polyamide is dissolved in a spinning solution using N-methylpyrrolidone (NMP) and calcium chloride as an inorganic salt. When this is used as a spinning dope and spun using water as a poor solvent, recovering the NMP as the solvent requires distillation to volatilize the water and extraction and removal of calcium chloride from the NMP, which requires a great deal of energy. However, when the ionic liquid of the present invention is used, N-methylpyrrolidone (NMP) and inorganic salts are not used, and therefore, for example, a membrane separation method can be adopted. [Example]

[0042] 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. In addition, each physical property in the examples was measured by the following methods.

[0043] (1) Observation of undissolved parts using a microscope The obtained wholly aromatic polyamide solution was left standing overnight, after which the upper solution was removed by decantation, and the lower solution was collected for microscopic observation. If the viscosity was too high to allow decantation, the upper solution was removed with a spatula or the like, and the lower solution was collected for microscopic observation. The collected solution was sandwiched between glass plates, and the dissolved wholly aromatic polyamide solution was observed under a microscope at 200x magnification to confirm whether or not there was any undissolved material. The same observation was made three times, and the dissolution was judged according to the following criteria. Dissolution: There was no undissolved matter with a length of 100 μm or more, and the fiber waste was completely dissolved. Partially dissolved: Although there was a small amount of undissolved material over 100 μm in length, the fiber waste was almost completely dissolved. Not dissolved: There were many undissolved pieces with a length of 100 μm or more, and the fiber waste could not be dissolved.

[0044] (2) Calculation of solubility parameters The calculation was carried out using the molecular contribution method proposed by Fedor.

[0045] 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 and dissolved in equimolar amounts. Terephthalic acid dichloride was weighed and added to this diamine solution in an amount approximately equimolar to the total molar amount of the diamines. After the reaction was completed, the mixture was neutralized with calcium hydroxide to obtain a fully aromatic polyamide solution.

[0046] The solution was used as a spinning dope as is, and discharged from a spinneret with a hole diameter of 0.3 mm and 100 manifolds, and spun into an aqueous solution of 30% NMP through an air gap of approximately 10 mm. The dope was then washed with water, dried, stretched 10 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. Of the fibers produced by this method, fiber waste (single filament fineness 1.5 dtex) that could not be used in products due to abnormal fineness was cut into 3 mm pieces using a guillotine cutter and used for remelting.

[0047] [Remelt] Fiber scraps cut into 3 mm pieces were dried for 2 hours at 120°C. 4,700 g of 1-ethyl-3-methylimidazolium acetate and 300 g of the dried fiber scraps were placed in a planetary mixer and kneaded for 1 hour under shear stress while heating at 80°C in a nitrogen atmosphere. The dissolved fiber waste is sometimes referred to as a polymer. In the case of Example 1, the polymer concentration was 6% by mass. When the obtained wholly aromatic polyamide solution was observed under an optical microscope, it was confirmed that there were no undissolved particles with a length of 100 μm or more, and that the fiber waste had been dissolved.

[0048] <Example 2> [Aramid fiber manufacturing] The same operations as in Example 1 were carried out except that the single filament fineness of the obtained aramid fiber was 8 dtex (fiber waste: 9 dtex). [Remelt] The same procedure as in Example 1 was carried out. When the obtained wholly aromatic polyamide solution was observed under an optical microscope, it was confirmed that there were no undissolved particles with a length of 100 μm or more, and that the fiber waste had been dissolved.

[0049] Example 3 [Aramid fiber manufacturing] The same procedure as in Example 1 was carried out except that the cut length of the fiber waste was set to 20 to 30 mm. [Remelt] The same procedure as in Example 1 was carried out. When the obtained wholly aromatic polyamide solution was observed under an optical microscope, it was confirmed that there were no undissolved particles with a length of 100 μm or more, and that the fiber waste had been dissolved.

[0050] Example 4 [Aramid fiber manufacturing] The same procedure as in Example 1 was carried out. [Remelt] The same procedure as in Example 1 was carried out except that 4,500 g of 1-ethyl-3-methylimidazolium acetate and 500 g of dried fiber waste were added to the planetary mixer. When the obtained wholly aromatic polyamide solution was observed under an optical microscope, it was confirmed that there were no undissolved particles with a length of 100 μm or more, and that the fiber waste had been dissolved.

[0051] <Example 5> [Aramid fiber manufacturing] The same procedure as in Example 1 was carried out. [Remelt] The same procedure as in Example 1 was carried out except that 4,975 g of 1-ethyl-3-methylimidazolium acetate and 25 g of dried drawn waste fiber were charged into the planetary mixer. When the obtained wholly aromatic polyamide solution was observed under an optical microscope, it was confirmed that there were no undissolved particles with a length of 100 μm or more, and that the fiber waste had been dissolved.

[0052] Example 6 [Aramid fiber manufacturing] The same procedure as in Example 1 was carried out. [Remelt] The same procedure as in Example 1 was carried out except that 1-ethyl-3-methylimidazolium methylphosphonate was used instead of 1-ethyl-3-methylimidazolium acetate. When the obtained wholly aromatic polyamide solution was observed under an optical microscope, it was confirmed that there were no undissolved particles with a length of 100 μm or more, and that the fiber waste had been dissolved.

[0053] <Comparative Example 1> [Aramid fiber manufacturing] The same procedure as in Example 1 was carried out except that the single yarn fineness of the obtained aramid fiber was 18 dtex (fiber waste: 19 dtex). [Remelt] The same procedure as in Example 1 was carried out. When the obtained wholly aromatic polyamide solution was observed under an optical microscope, it was found that many undissolved particles having a length of 100 μm or more were present, and the fiber waste could not be dissolved.

[0054] <Comparative Example 2> [Aramid fiber manufacturing] The same procedure as in Example 1 was carried out. [Remelt] The same procedure as in Example 1 was carried out except that 4,300 g of 1-ethyl-3-methylimidazolium acetate and 700 g of dried drawn waste fiber were charged into the planetary mixer. When the obtained wholly aromatic polyamide solution was observed under an optical microscope, it was found that many undissolved particles having a length of 100 μm or more were present, and the fiber waste could not be dissolved.

[0055] Example 7 [Aramid fiber manufacturing] The same procedure as in Example 1 was carried out. [Remelt] The same procedure as in Example 1 was repeated, except that 1-ethyl-3-methylimidazolium trifluoroacetate was used instead of 1-ethyl-3-methylimidazolium acetate. When the obtained wholly aromatic polyamide solution was observed under an optical microscope, it was found that a small amount of undissolved matter having a length of 100 μm or more was found, but the fiber waste was almost completely dissolved. The results of Examples 1 to 7 and Comparative Examples 1 and 2 are shown in Table 1.

[0056] [Table 1]

[0057] Example 8 [Aramid fiber manufacturing] The same procedure as in Example 1 was carried out. [Remelt] Fiber waste cut into 3 mm pieces was dried for 2 hours at 120°C. 4,700 g of tributyl(ethyl)phosphonium diethylphosphate and 300 g of dried drawn waste fiber were placed in a planetary mixer and kneaded under shear stress at 120°C for 1 hour in a nitrogen atmosphere. When the obtained wholly aromatic polyamide solution was observed under an optical microscope, it was confirmed that there were no undissolved particles with a length of 100 μm or more, and that the fiber waste had been dissolved.

[0058] Example 9 [Aramid fiber manufacturing] The same procedure as in Example 1 was carried out except that the single yarn fineness was set to 9 dtex. [Remelt] Fiber waste cut into 3 mm pieces was dried for 2 hours at 120°C. 4,700 g of tributyl(ethyl)phosphonium diethylphosphate and 300 g of dried drawn waste fiber were placed in a planetary mixer and kneaded under shear stress at 80°C for 1 hour in a nitrogen atmosphere. When the obtained wholly aromatic polyamide solution was observed under an optical microscope, it was confirmed that there were no undissolved particles with a length of 100 μm or more, and that the fiber waste had been dissolved.

[0059] Example 10 [Aramid fiber manufacturing] The same procedure as in Example 1 was carried out except that the cut length of the fiber waste (single filament fineness 1.5 dtex) was set to 20 to 30 mm. [Remelt] Fiber scraps cut into 20-30 mm pieces were dried for 2 hours at 120°C. 4,700 g of tributyl(ethyl)phosphonium diethylphosphate and 300 g of the dried fiber scraps were placed in a planetary mixer and kneaded under shear stress at 80°C for 1 hour in a nitrogen atmosphere. When the obtained wholly aromatic polyamide solution was observed under an optical microscope, it was confirmed that there were no undissolved particles with a length of 100 μm or more, and that the fiber waste had been dissolved.

[0060] Example 11 [Aramid fiber manufacturing] The same procedure as in Example 1 was carried out. [Remelt] Fiber waste cut to 3 mm (single filament fineness 1.5 dtex) was dried for 2 hours at 120°C. 4,500 g of tributyl(ethyl)phosphonium diethylphosphate and 500 g of the dried fiber waste were placed in a planetary mixer and kneaded under shear stress at 120°C for 1 hour in a nitrogen atmosphere. When the obtained wholly aromatic polyamide solution was observed under an optical microscope, it was confirmed that there were no undissolved particles with a length of 100 μm or more, and that the fiber waste had been dissolved.

[0061] Example 12 [Aramid fiber manufacturing] The same procedure as in Example 1 was carried out. [Remelt] Fiber waste cut to 3 mm (single filament fineness 1.5 dtex) was dried for 2 hours at 120°C. 4,700 g of tributyl(methyl)phosphonium diethylphosphate and 300 g of the dried fiber waste were placed in a planetary mixer and kneaded under shear stress at 120°C for 1 hour in a nitrogen atmosphere. When the obtained wholly aromatic polyamide solution was observed under an optical microscope, it was confirmed that there were no undissolved particles with a length of 100 μm or more, and that the fiber waste had been dissolved.

[0062] Example 13 [Aramid fiber manufacturing] The same procedure as in Example 1 was carried out. [Remelt] Fiber waste cut to 3 mm (single filament fineness 1.5 dtex) was dried for 2 hours at 120°C. 4,750 g of trihexyl(tetradecyl)phosphonium chloride and 250 g of the dried fiber waste were placed in a planetary mixer and kneaded under shear stress at 120°C for 1 hour in a nitrogen atmosphere. When the obtained wholly aromatic polyamide solution was observed under an optical microscope, it was confirmed that there were no undissolved particles with a length of 100 μm or more, and that the fiber waste had been dissolved.

[0063] <Comparative Example 3> [Aramid fiber manufacturing] The same procedure as in Example 1 was carried out. [Remelt] Fiber waste cut into 3 mm pieces was dried for 2 hours at 120°C. 4,300 g of tributyl(ethyl)phosphonium diethylphosphate and 700 g (14 wt%) of dried drawn waste fiber were placed in a planetary mixer and kneaded under shear stress at 120°C for 1 hour in a nitrogen atmosphere. When the obtained wholly aromatic polyamide solution was observed under an optical microscope, it was found that many undissolved particles having a length of 100 μm or more were present, and the fiber waste could not be dissolved.

[0064] <Comparative Example 4> [Aramid fiber manufacturing] The same procedure as in Example 1 was carried out. [Remelt] Fiber scraps cut into 3 mm pieces were dried for 2 hours at 120°C. 4,990 g of tributyl(ethyl)phosphonium diethylphosphate and 10 g (0.2 wt%) of the dried fiber scraps were placed in a planetary mixer and kneaded under shear stress at 120°C for 1 hour in a nitrogen atmosphere. When the obtained wholly aromatic polyamide solution was observed under an optical microscope, no undissolved matter with a length of 100 μm or more was found, and the fiber scraps were dissolved. However, the concentration of the wholly aromatic polyamide solution was too low, and when the solution was used as a spinning dope, it did not coagulate and could not be collected as a thread.

[0065] Example 14 [Aramid fiber manufacturing] The same procedure as in Example 1 was carried out except that the fiber waste (single filament fineness 1.5 dtex) was cut into 50 mm pieces using a guillotine cutter. [Remelt] Fiber waste cut into 50 mm pieces was dried for 2 hours at 120°C. 4,700 g of tributyl(ethyl)phosphonium diethylphosphate and 300 g of the dried fiber waste were placed in a planetary mixer and kneaded under shear stress at 120°C for 1 hour in a nitrogen atmosphere. When the obtained wholly aromatic polyamide solution was observed under an optical microscope, it was found that a small amount of undissolved matter having a length of 100 μm or more was found, but the fiber waste was almost completely dissolved.

[0066] <Comparative Example 5> [Aramid fiber manufacturing] The same procedure as in Example 1 was carried out. [Remelt] Fiber waste cut into 3 mm pieces was dried for 2 hours at 120°C. 4,700 g of trihexyl(tetradecyl)phosphonium chloride and 300 g of dried drawn waste fiber were placed in a planetary mixer and kneaded under shear stress at 55°C for 1 hour in a nitrogen atmosphere. When the obtained wholly aromatic polyamide solution was observed under an optical microscope, it was found that many undissolved particles having a length of 100 μm or more were present, and the fiber waste could not be dissolved. The results of Examples 8 to 14 and Comparative Examples 3 to 5 are shown in Table 2.

[0067] [Table 2] [Industrial Applicability]

[0068] According to the present invention, there is provided a method for producing a wholly aromatic amide solution which exhibits high solubility capable of dissolving aramid fibers such as discarded aramid fibers and is excellent in process stability, without using an inorganic salt or an aprotic polar organic solvent. Therefore, the present invention has high industrial applicability and extremely great industrial value.

Claims

1. A method for producing a wholly aromatic polyamide solution, comprising contacting wholly aromatic polyamide fibers having a single fiber fineness of 10 dtex or less with an ionic liquid in a mass ratio of 0.5:99.5 to 10:90 to form a mixture, and then kneading the mixture under shear stress while heating it to 60°C or higher.

2. 2. The method for producing a wholly aromatic polyamide solution according to claim 1, wherein the wholly aromatic polyamide is a para-type wholly aromatic copolyamide composed of an acid component and a diamine component, and the acid component is terephthalic acid dichloride (hereinafter referred to as the first component), and the diamine component is paraphenylenediamine (hereinafter referred to as the second component) and one of 3,3'-oxydiphenylenediamine, 3,4'-oxydiphenylenediamine, or 4,4'-oxydiphenylenediamine, or a mixture thereof (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. The ionic liquid has a solubility parameter δt of 37 (J / cm ３ ) １／２ The method for producing a wholly aromatic polyamide solution according to claim 1 or 2, wherein the imidazolium-based ionic liquid is the above-mentioned imidazolium-based ionic liquid.

4. 4. The method for producing a wholly aromatic polyamide solution according to claim 3, wherein the ionic liquid is at least one selected from the group consisting of 1-ethyl-3-methylimidazolium acetate, 1-ethyl-3-methylimidazolium trifluoroacetate, 1-ethyl-3-methylimidazolium methylphosphonate, 1-ethyl-3-methylimidazolium chloride, and 1-butyl-3-methylimidazolium chloride.

5. The ionic liquid has a solubility parameter δt of 27 (J / cm) by the molecular contribution method. ３ ) １／２ The method for producing a wholly aromatic polyamide solution according to claim 1 or 2, wherein the phosphonium-based ionic liquid is the above-mentioned phosphonium-based ionic liquid.

6. 6. The method for producing a wholly aromatic polyamide solution according to claim 5, wherein the ionic liquid is at least one selected from the group consisting of tributyl(ethyl)phosphonium diethylphosphate and tributyl(methyl)phosphonium dimethylphosphate.

7. The method for producing a wholly aromatic polyamide solution according to claim 5, wherein the mass ratio of the wholly aromatic polyamide to the ionic liquid is 0.5:99.5 to 5:

95.

8. A method for producing wholly aromatic polyamide fibers, comprising using the wholly aromatic polyamide solution according to claim 1 as a dope for wet spinning.

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