Regenerated all-aromatic polyamide fibers, and method for producing the same

Abstract

This invention provides a highly durable and functional recycled all-aromatic polyamide fiber, and a method for producing the same. [Solution] A recovered fiber structure containing meta-type all-aromatic polyamide fibers, para-type all-aromatic polyamide fibers, and conductive fibers is dissolved in an amide-based solvent. In this solution, 10 to 25% by mass of meta-type all-aromatic polyamide polymer is dissolved to produce an all-aromatic polyamide dope. This dope is then used for spinning to obtain regenerated all-aromatic polyamide fibers.

Description

[Technical Field]

[0001] The present invention relates to a method for producing recycled whole-aromatic polyamide fibers containing a very small amount of alloy other than meta-type whole-aromatic polyamide fibers by redissolving and spinning a fibrous structure composed of meta-type whole-aromatic polyamide fibers and other fibers. [Background technology]

[0002] It has been well known that all-aromatic polyamides, conventionally produced from aromatic diamines and aromatic dicarboxylic acid dihalides, exhibit excellent heat resistance and flame retardancy. Among such all-aromatic polyamides, meta-type all-aromatic polyamides (hereinafter sometimes referred to as meta-aramids), represented by polymetaphenylene isophthalamide, are particularly useful as heat-resistant and flame-retardant fibers. These properties enable their use in applications such as protective clothing and other disaster prevention and safety garments, as well as in industrial applications such as filters and electronic components. Such meta-type all-aromatic polyamide fibers are mostly manufactured as staple fibers, which are then processed into fabrics and spun yarns for use in a variety of applications.

[0003] On the other hand, when disposing of meta-type all-aromatic polyamide fibers during brand changes at manufacturing sites, incineration or other disposal methods are not possible due to chemical stability and flame retardancy. Therefore, landfill disposal is common, and given that these fibers are used as industrial fibers, the large amount of all-aromatic polyamide fiber waste poses a significant environmental burden, which is a problem.

[0004] Several methods have been reported for recycling meta-type all-aromatic polyamide fibers to address the problems described above. For example, as shown in Patent Document 1, a method has been reported for producing all-aromatic polyamide dope from molded articles containing discarded aramid fibrils.

[0005] On the other hand, as described above, instead of using aramid fibrils, methods have also been reported for producing aramid-doped materials by dissolving meta-type fully aromatic polyamide fibers in an amide-based solvent containing an inorganic salt, as described in Patent Documents 2 to 5. Similarly, with regard to blended yarns and woven fabrics, the environmental impact of disposal, such as scraps of fabric cut during the creation of protective clothing, is also a problem.

[0006] For example, Patent Document 6 describes a method for obtaining regenerated fully aromatic polyamide fibers by sulfuric acid spinning after treating a fabric containing meta-type fully aromatic polyamide, para-type fully aromatic polyamide, and a conductive material with sulfuric acid. However, in this manufacturing method, sulfuric acid remains inside the regenerated fully aromatic polyamide fibers, resulting in low yarn strength and room for improvement. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 7-286061 [Patent Document 2] Patent No. 5193439 [Patent Document 3] Japanese Patent Publication No. 2006-241271 [Patent Document 4] Japanese Patent Publication No. 2006-241264 [Patent Document 5] Patent No. 7267821 [Patent Document 6] Special Publication No. 2023-507132 [Overview of the project] [Problems that the invention aims to solve]

[0008] The object of the present invention is to provide a highly strong and functional recycled all-aromatic polyamide fiber, and a method for producing the same. [Means for solving the problem]

[0009] The inventors of the present invention conducted diligent research to solve the above problems and discovered that, in the production of recycled whole aromatic polyamide fibers, by simultaneously dissolving a small amount of other fiber alloys when redissolving meta-type whole aromatic polyamide fibers, high strength and functionality can be imparted, thus completing the present invention.

[0010] Thus, according to the present invention, A recycled all-aromatic polyamide fiber characterized by comprising 1.90 to 95% by mass of meta-type all-aromatic polyamide, 3 to 7% by mass of para-type all-aromatic polyamide, and 1 to 3% by mass of a conductive material, and having a tensile breaking strength of 4.0 cN / dtex or more. 2. The electrical resistance of recycled all-aromatic polyamide fibers is 10 12 The recycled all-aromatic polyamide fiber described in item 1 above, having a density of Ω / cm or less. 3. A method for producing regenerated whole-aromatic polyamide fibers, characterized by dissolving 10 to 25% by mass of a meta-type whole-aromatic polyamide polymer in a solution obtained by dissolving a recovered fiber structure containing meta-type whole-aromatic polyamide fibers, para-type whole-aromatic polyamide fibers, and conductive fibers in an amide-based solvent, and then spinning the fibers using the dope. And, 4. A method for producing recycled whole aromatic polyamide fibers according to item 3 above, wherein the recovered fiber structure comprises 1 to 40% by mass of meta-type whole aromatic polyamide fibers, 0.5 to 2% by mass of para-type whole aromatic polyamide fibers, and 0.1 to 0.3% by mass of conductive fibers. It will be provided. [Effects of the Invention]

[0011] According to the present invention, a regenerated all-aromatic polyamide polymer solution suitable for functionality can be obtained by the method described above, and by using it, a regenerated all-aromatic polyamide fiber with high strength and functionality can be easily provided. [Modes for carrying out the invention]

[0012] The components constituting the regenerated wholly aromatic polyamide fiber of the present invention are not only meta-type wholly aromatic polyamides, but also include para-type wholly aromatic polyamide fiber alloys, and are composed of a meta-type aromatic diamine component and a meta-type wholly aromatic dicarboxylic acid component.

[0013] Particularly preferably used in the present invention is a consumer using a fiber made of a meta-type wholly aromatic polyamide having a metaphenylene isophthalamide unit as a main component from the viewpoints of mechanical properties, heat resistance, and flame retardancy. As the meta-type wholly aromatic polyamide composed of a metaphenylene isophthalamide unit, it is preferable that the metaphenylene isophthalamide unit is 90 mol% or more of all repeating units, and the para-type wholly aromatic polyamide unit is 1 to 10 mol% or less of all repeating units.

[0014] And, as the meta-type aromatic diamine component of the meta-type wholly aromatic polyamide serving as the raw material of the regenerated wholly aromatic polyamide fiber of the present invention, metaphenylenediamine, 3,4'-diaminodiphenyl ether, 3,4'-diaminodiphenyl sulfone, etc., and derivatives having substituents such as halogen and an alkyl group having 1 to 3 carbon atoms on these aromatic rings, for example, 2,4-toluylenediamine, 2,6-toluylenediamine, 2,4-diaminobenzene chloride, 2,6-diaminobenzene chloride, etc. can be exemplified. Among them, it is preferable that it is a mixed diamine containing 80 mol% or more of metaphenylenediamine and 1 mol% or more of paraphenylenediamine.

[0015] Examples of the raw material of the meta-type aromatic dicarboxylic acid component constituting the meta-type wholly aromatic polyamide include, for example, meta-type aromatic dicarboxylic acid halides. Examples of the meta-type aromatic dicarboxylic acid halides include isophthalic acid chlorides such as isophthalic acid chloride and isophthalic acid bromide, and derivatives having substituents such as halogen and alkoxy groups having 1 to 3 carbon atoms in these aromatic rings, such as 3-chloroisophthalic acid chloride. Among them, isophthalic acid chloride itself, or a mixed carboxylic acid halide containing 85 mol% or more, preferably 90 mol% or more, particularly preferably 95 mol% or more of isophthalic acid chloride is preferred.

[0016] In the present invention, a recovered fiber structure mainly composed of fibers made of the above meta-type wholly aromatic polyamide is used. Here, the recovered fiber structure refers to fibers obtained in an intermediate process during the production of meta-type wholly aromatic polyamide fibers, having a crystallinity of 10% or less, spun yarns containing meta-type wholly aromatic polyamide fibers, rovings containing meta-type wholly aromatic polyamide fibers, fabrics containing meta-type wholly aromatic polyamide fibers, clothing containing meta-type wholly aromatic polyamide fibers, etc., which are fiber structures mainly containing meta-type wholly aromatic polyamide fibers at 80 to 95% by mass, para-type wholly aromatic polyamide fibers at 2 to 15% by mass, and conductive fibers at 0.1 to 5% by mass.

[0017] Examples of the para-type wholly aromatic polyamide fibers include conventionally known para-type wholly aromatic polyamide fibers, such as "Kevlar" (registered trademark) of DuPont in the United States, "Twaron" (registered trademark), "Technora" (registered trademark) of Teijin Limited, etc.

[0018] Furthermore, the conductive fibers mentioned above include conventionally known conductive fibers, such as acrylic or polyester conductive yarns in which conductive metals or carbon black are incorporated into chemical fibers, or the surface of the fibers is coated with metal, or metal fibers made from metals such as stainless steel. Specifically, examples include Kuraray Trading's "Kuracarbo" (registered trademark), Seiren's "Metaflex" (registered trademark), Teijin Limited's carbon fiber "Tenax" (registered trademark), Toray Industries, Inc.'s "Luana" (registered trademark), Mitsubishi Chemical's "Corebrid" (registered trademark), and Unitika Trading's "Megana" (registered trademark).

[0019] Furthermore, in addition to meta-type total aromatic polyamide fibers, para-type total aromatic polyamide fibers, and conductive fibers, other fibers included in the recovered fiber structure may include flame-retardant rayon fibers, flame-retardant polyester fibers, and flame-retardant fibers such as modacrylic. However, among these fibers, it is preferable to remove those that cannot be dissolved in amide-based solvents from the recovered fiber structure beforehand, or to remove them by filtration in a later spinning solution preparation step.

[0020] The recycled whole-aromatic polyamide fibers of the present invention are manufactured using a recovered fiber structure mainly composed of meta-type whole-aromatic polyamide fibers, as described above, through the following processes: spinning solution preparation, spinning and coagulation, washing, wet (boiling water) stretching, dry heat treatment, and heat stretching.

[0021] In the spinning solution preparation process, the recovered fiber structure, mainly composed of meta-type total aromatic polyamide fibers, is dissolved in a solvent to prepare the spinning solution (dope). For the preparation of the spinning solution, an amide-based solvent is usually used, and examples of such solvents include N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), and dimethylacetamide (DMAc). Dimethyl sulfoxide (DMSO), an aprotic polar solvent, is also an example. Of these, NMP or DMAc is preferred from the viewpoint of solubility and handling safety.

[0022] Here, the ratio of the recovered fiber structure to the total spinning solution is preferably 0.5 to 10.5% by mass. If this ratio falls outside the above range, problems such as poor dissolution of the recovered fiber structure may occur. Furthermore, it is preferable that the spinning solution contains inorganic salts such as calcium chloride, lithium chloride, and magnesium chloride in an amount ranging from 1.0 to 3.0% by mass.

[0023] In this invention, it is important to completely dissolve the meta-type total aromatic polyamide fibers when preparing the spinning solution. Undissolved meta-type total aromatic polyamide is difficult to identify visually because it is transparent, but it can be identified using a polarizing microscope.

[0024] When producing recycled whole-aromatic polyamide fibers, it is ideal to use 100% meta-type whole-aromatic polyamide fibers as raw materials. However, if a small amount of para-type whole-aromatic polyamide fibers are included, it becomes unnecessary to filter out and remove the para-type whole-aromatic polyamide fibers, which are insoluble under the solubility conditions of the meta-type whole-aromatic polyamide fibers. Moreover, by creating a dope containing a small amount of para-type whole-aromatic polyamide fiber alloy, it is surprisingly possible to increase the tensile breaking strength of the recycled whole-aromatic polyamide fibers.

[0025] In other words, if 100% meta-type total aromatic polyamide fibers are used as raw materials, since they are recycled fibers, sorting is first required to determine whether or not they can be used as raw materials, and even after sorting, there is a possibility that yarn cannot be drawn from them. One possible benefit is that the spinnability will also improve as the strength increases.

[0026] In the present invention, when preparing the spinning solution, it is preferable to dissolve 10 to 25% by mass of an unused meta-type total aromatic polyamide polymer, different from the meta-type total aromatic polyamide constituting the fiber structure, in a spinning solution containing a fiber structure made of meta-type total aromatic polyamide fibers dissolved in a solvent, thereby adjusting the concentration and weight-average molecular weight.

[0027] When unused meta-type fully aromatic polyamide polymers are used in combination, it is preferable that the unused meta-type fully aromatic polyamide polymers have the same composition as the meta-type fully aromatic polyamide fibers described above, and that their weight-average molecular weight is 600,000 or more. Any polymerization method may be used to obtain the unused meta-type fully aromatic polyamide polymers.

[0028] Furthermore, it is preferable that the unused meta-type all-aromatic polyamide polymer be used in an amount of 20 to 100% by mass relative to the meta-type all-aromatic polyamide fibers constituting the fiber structure. The above mass ratio must be determined by the weight-average molecular weight of the meta-type all-aromatic polyamide fibers constituting the fiber structure used, and it is preferable to adopt a mass ratio that will yield sufficient fibers in the spinning process described later.

[0029] Furthermore, in order to obtain sufficient spinnability and fiber strength in the spinning process described later, it is preferable that the weight-average molecular weight of both the meta-type all-aromatic polyamide fibers constituting the fiber structure and the meta-type all-aromatic polyamide polymer mixed therewith be 500,000 or more. If the meta-type all-aromatic polyamide polymer is not mixed, depending on the weight-average molecular weight of the meta-type all-aromatic polyamide fibers constituting the fiber structure, problems may arise such as insufficient strength due to poor stretching, or unstable spinning that prevents production.

[0030] Furthermore, the preparation of a meta-type all-aromatic polyamide polymer solution is also affected by the form of the meta-type all-aromatic polyamide fiber product when it is dissolved. For example, in the case of tow, it is difficult to dissolve if it is longer than 5 cm square, so it is preferable to cut it to a size smaller than that.

[0031] The concentration of meta-type total aromatic polyamide in the spinning solution should be selected appropriately from the viewpoint of the solidification rate in the subsequent spinning and solidification process and the solubility of the meta-type total aromatic polyamide. In addition, the concentration of the inorganic salt is preferably 1.0 to 3.0% by mass.

[0032] The resulting meta-type all-aromatic polyamide spinning solution is spun into a coagulation solution and coagulated in the spinning and coagulation process. The spinning apparatus is not particularly limited, and conventionally known wet spinning apparatuses can be used. As long as it can perform stable wet spinning, there is no particular need to limit the number of spinning holes and the arrangement of the spinneret. For example, a multi-hole spinneret for staple fibers with 10 to 30,000 holes and a spinning hole diameter of 0.03 to 0.2 mm may be used. Furthermore, the doping temperature during spinning from the spinneret is suitable in the range of 20 to 90°C, but is particularly preferred at 70 to 90°C.

[0033] The coagulation bath used to obtain the regenerated fully aromatic polyamide fibers of the present invention is an aqueous solution containing 30% by mass, preferably 35-45% by mass, of inorganic salts such as calcium chloride, lithium chloride, and magnesium chloride, and 1-20% by mass, preferably 3-15% by mass, of an amide solvent, and is used at a temperature of 50-90°C. Although a method using an aqueous solution of an amide solvent that substantially does not contain inorganic salts is also known, stable spinning is impossible with such a coagulation solution, or yarn with sufficient strength cannot be obtained.

[0034] The resulting coagulated yarn is thoroughly washed in an aqueous washing bath and sent to the wet stretching process. Typically, wet stretching is performed in a boiling water stretching bath, and the stretching ratio is appropriately 1.5 to 5.0 times, more preferably in the range of 2.0 to 3.5 times. In the present invention, by performing wet stretching within this range and increasing the molecular chain orientation, the breaking strength of the final obtained fiber can be ensured.

[0035] Preferably, a dry heat treatment step is performed on the fibers that have undergone the above washing and wet stretching process. In the dry heat treatment process, the fibers that have been washed and stretched in the washing and wet stretching process described above are subjected to dry heat treatment at a range of preferably 100 to 250°C, and more preferably 100 to 200°C. Here, the dry heat treatment is not particularly limited, but it is preferable to perform it under constant length conditions. The temperature of the dry heat treatment described above refers to the set temperature of the fiber heating means, such as a hot plate or heating roller.

[0036] In the present invention, the fibers that have undergone the dry heat treatment process described above are subjected to a heat stretching process. In the heat stretching process, stretching is carried out while applying heat treatment at 300 to 380°C. A stretching ratio of 1.2 to 5.0 times is appropriate, and more preferably in the range of 1.5 to 3.5 times.

[0037] The regenerated fully aromatic polyamide fiber of the present invention obtained by the above method comprises 90-95% by mass of meta-type fully aromatic polyamide, 3-7% by mass of para-type fully aromatic polyamide, and 1-3% by mass of conductive material, and its tensile breaking strength must be 4.0 cN / dtex or higher, more preferably 4.0-6.0 cN / dtex. Furthermore, the elongation at break is preferably 20% or higher. Furthermore, the heat shrinkage rate of the undrawn yarn is preferably 10% or less. Furthermore, the single fiber fineness is preferably 0.5-15.0 dtex, more preferably 1.4-2.5 dtex. If the single fiber fineness is less than 0.5 dtex or greater than 15 dtex, the process passability is poor and stable spinning cannot be achieved. Furthermore, the limiting oxygen index (LOI) is preferably 26 or higher. Furthermore, the electrical resistance value is 10 12 It is preferable that the density is Ω / cm or less. [Examples]

[0038] 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. The physical properties in the examples and comparative examples were measured by the methods described below.

[0039] [Single yarn fineness] Measurements were performed in accordance with JIS L 1015, using Method A for true fineness, and the results are expressed as apparent fineness.

[0040] [Breaking strength, elongation] The tensile strength was measured using a tensile testing machine (Instron, model: 5565) in accordance with JIS L 1015 under the following conditions. (Measurement conditions) Grip spacing: 20mm Initial load: 0.044cN / dtex(1 / 20gf / dtex) Tensile speed: 20 mm / min

[0041] [Degree of crystallinity] Wide-angle X-ray scattering (WAXS) is a non-destructive technique for measuring the crystallinity of fibers. In WAXS, a diffraction pattern is formed, and the crystallinity is measured from this pattern and expressed as crystallinity (CI). CI is defined as the ratio of the area of ​​crystalline peaks to the total area after deconvolution of crystalline peaks from a broad amorphous region in the XRD pattern. CI takes a value between 0 and 1, i.e., 0 for a perfectly amorphous sample and 1 for a perfectly crystalline sample. Measurements were performed using a PANalytical X'Pert MPD diffractometer equipped with a curved graphite monochromator that generates Cu K-α radiation (wavelength = 1.5418). Measurement conditions: 0.5-degree divergent slit, 0.5-degree anti-scatter grid and 0.3 mm receiving slit, and 45 kV, 40 mA generator settings. Data were collected in a reflection configuration. The diffraction scan range was 2θ = 4 to 40 degrees with a step size of 0.05 degrees. During measurement, the sample is rotated at a rate of 5 seconds per step and 2 seconds per rotation.

[0042] [Limited Oxygen Index (LOI)] Flame retardancy was determined by calculating the LOI value in accordance with the JIS K-7201 LOI measurement method. An LOI value of 26 or higher is considered to indicate superior flame retardancy.

[0043] [Electrical resistance value] The electrical resistance value was determined in accordance with the electrical resistance measurement method of JIS L 1094. 12 An electrical resistance value of Ω / cm or less is considered to be excellent.

[0044] [Composition of regenerated fibers] The composition of the regenerated fibers was determined by dissolving the spun regenerated fibers in NMP to return them to a doped state, then purging them in air or with He gas, and quantifying the conductive material using X-ray fluorescence based on a calibration curve. Conductive materials that could not be identified by X-ray fluorescence were quantified by thermogravimetric analysis (TGA). Furthermore, using the above-mentioned dope, quantitative measurements of meta-type and para-type total aromatic polyamides were performed in NMP solution.

[0045] [Example 1] 6.5% by mass of a recovered fiber structure containing 93% by mass of meta-type all-aromatic polyamide fibers, 5% by mass of para-type all-aromatic polyamide fibers, and 2% by mass of acrylic conductive yarn was cut to a length of 5 cm, and dissolved by treatment with 75.5% by mass of N-methyl-2-pyrrolidone (NMP) and 3.0% by mass of calcium chloride at 60-80°C for 10 hours. 15% by mass of the meta-type all-aromatic polymer was added to the polymer cooled to room temperature (40°C), stirred, and then dissolved at 80°C for 30 minutes to obtain a transparent polymer solution (all-aromatic polyamide polymer solution).

[0046] This polymer solution was heated to 89°C and used as the spinning stock. The yarn was extruded from a spinneret with a circular nozzle having a pore size of 0.12 mm and 100 pores into a 70°C coagulation bath for spinning. The composition of this coagulation bath was 35% by mass of calcium chloride, 3% by mass of NMP, and the remaining 62% by mass of water. The yarn was passed through the bath at a speed of 5.0 m / min with an immersion length (effective coagulation bath length) of 120 cm, and then withdrawn into the air.

[0047] The coagulated yarn was washed in two aqueous washing baths, with a total immersion time of 230 seconds. The water temperatures for the two aqueous washing baths were 20°C and 30°C, respectively. Next, the washed yarn was stretched to 2.5 times its original length in boiling water at 90°C, and then immersed in warm water at 95°C for 40 seconds for washing.

[0048] Next, the material was wound onto a roller with a surface temperature of 170°C and subjected to dry heat treatment, and then stretched to 1.5 times its original size on a hot plate with a surface temperature of 340°C to obtain regenerated fully aromatic polyamide fibers. The resulting fiber comprises 99 mass of meta-type total aromatic polyamide, 0.6 mass% of para-type total aromatic polyamide, and 0.4 mass% of conductive material. It has a single fiber fineness of 2.1 dtex, a tensile breaking strength of 4.1 cN / dtex, an elongation at break of 50%, a standard deviation of breaking strength of 0.5 cN / dtex, a LOI value of 29, a heat shrinkage rate of 5.5% for uncurled yarn, and an electrical resistance of 10. 12 The value was Ω / cm.

[0049] [Example 2] Recycled whole-aromatic polyamide fibers were produced in the same manner as in Example 1, except that the recovered fiber structure was changed to a fiber structure containing 90% by mass of meta-type whole-aromatic polyamide fibers, 5% by mass of para-type whole-aromatic polyamide fibers, 3% by mass of flame-retardant rayon fibers, and 2% by mass of acrylic conductive yarn.

[0050] The resulting fiber comprises 99% by mass of meta-type fully aromatic polyamide, 0.5% by mass of para-type fully aromatic polyamide, and 0.5% by mass of conductive material. It has a single fiber fineness of 2.1 dtex, a tensile breaking strength of 4.0 cN / dtex, an elongation at break of 50%, a standard deviation of breaking strength of 0.4 cN / dtex, a LOI value of 29, a heat shrinkage rate of 5.0% for uncurled yarn, and an electrical resistance of 10. 12 The value was Ω / cm.

[0051] [Example 3] In Example 1, the recovered fiber structure was changed to a recovered fiber structure composed of 40% by mass of meta-type all-aromatic polyamide fiber, 2% by mass of para-type all-aromatic polyamide fiber, 56% by mass of flame-retardant rayon, and 2% by mass of acrylic conductive yarn. This fiber structure was treated with N-methyl-2-pyrrolidone (NMP) and 3.0% by mass of calcium chloride at 60-80°C for 10 hours to dissolve it. The flame-retardant rayon, which was an insoluble material, was filtered through a 200-mesh filter. 19% by mass of meta-type all-aromatic polymer was added to the polymer cooled to room temperature (40°C), stirred, and then dissolved at 80°C for 30 minutes to obtain a transparent polymer solution (all-aromatic polyamide polymer solution). The procedure was carried out in the same manner as in Example 1, except that a transparent polymer solution (all-aromatic polyamide polymer solution) was obtained. Regenerated all-aromatic polyamide fiber was produced.

[0052] The resulting fiber comprises 99.2% by mass of meta-type total aromatic polyamide, 0.4% by mass of para-type total aromatic polyamide, and 0.4% by mass of conductive material. The single fiber fineness is 2.2 dtex, the tensile breaking strength is 4.1 cN / dtex, the elongation at break is 55%, the standard deviation of the breaking strength is 0.4 cN / dtex, the LOI value is 29, the heat shrinkage rate of the uncurled yarn is 5.0%, and the electrical resistance is 10 12 The value was Ω / cm.

[0053] [Example 4] Recycled whole aromatic polyamide fibers were produced in the same manner as in Example 1, except that the recovered fiber structure was changed to a fiber structure containing 93% by mass of meta-type whole aromatic polyamide fibers, 5% by mass of para-type whole aromatic polyamide fibers, and 2% by mass of polyester conductive yarn.

[0054] The resulting fiber comprises 99% by mass of meta-type total aromatic polyamide, 0.5% by mass of para-type total aromatic polyamide, and 0.5% by mass of conductive material. It has a single fiber fineness of 2.1 dtex, a tensile breaking strength of 4.2 cN / dtex, an elongation at break of 53%, a standard deviation of breaking strength of 0.3 cN / dtex, a LOI value of 29, a heat shrinkage rate of 4.5% for uncurled yarn, and an electrical resistance of 10. 12 The value was Ω / cm.

[0055] [Comparative Example 1] Recycled whole aromatic polyamide fibers were produced in the same manner as in Example 1, except that the recovered fiber structure was changed to a recovered fiber structure composed of 100% by mass of meta-type whole aromatic polyamide fibers.

[0056] The resulting fiber contains 100% by mass of meta-type total aromatic polyamide, with a single fiber fineness of 2.1 dtex, tensile breaking strength of 3.0 cN / dtex, elongation at break of 45%, standard deviation of breaking strength of 1.7 cN / dtex, LOI value of 29, heat shrinkage of uncurled yarn of 7.0%, and electrical resistance of 10 14 The strength was Ω / cm. The recovered fiber structure, composed solely of meta-type all-aromatic polyamide fibers, was highly likely to contain weak threads, and the presence of these weak threads in the dope reduced the tensile breaking strength.

[0057] [Comparative Example 2] In Example 1, regenerated wholly aromatic polyamide fibers were produced in the same manner as in Example 1, except that the recovered fiber structure was changed to a recovered fiber structure composed of 40% by mass of meta-type wholly aromatic polyamide fibers and 60% by mass of flame-retardant rayon.

[0058] The obtained fibers consisted of 100% by mass of meta-type wholly aromatic polyamide, had a single fiber fineness of 2.1 dtex, a tensile breaking strength of 2.9 cN / dtex, an elongation at break of 43%, a standard deviation of breaking strength of 1.9 cN / dtex, a LOI value of 31, a heat shrinkage rate of unshrunk yarn of 7.0%, and an electrical resistance value of 10 14 Ω / cm.

[0059] [Comparative Example 3] In Example 1, regenerated wholly aromatic polyamide fibers were produced in the same manner as in Example 1, except that the recovered fiber structure containing 93% by mass of meta-type wholly aromatic polyamide fibers, 5% by mass of para-type wholly aromatic polyamide fibers, and 2% by mass of acrylic conductive yarn was dissolved in sulfuric acid.

[0060] The obtained fibers consisted of 93% by mass of meta-type wholly aromatic polyamide, 5% by mass of para-type wholly aromatic polyamide, and 2% by mass of acrylic, had a single fiber fineness of 2.1 dtex, a tensile breaking strength of 3.2 cN / dtex, an elongation at break of 32%, a standard deviation of breaking strength of 5.8 cN / dtex, a LOI value of 31, a heat shrinkage rate of unshrunk yarn of 7.0%, and an electrical resistance value of 10 14 Ω / cm. [Industrial Applicability]

[0061] According to the present invention, a recovered fiber structure containing meta-type all-aromatic polyamide fibers, para-type all-aromatic polyamide fibers, and conductive yarn is dissolved in an amide-based solvent, then 10 to 25% by mass of meta-type all-aromatic polyamide polymer is dissolved to produce a meta-type all-aromatic polyamide dope, and this dope is used again to spin yarn, thereby providing a regenerated all-aromatic polyamide fiber. Therefore, the present invention not only makes a significant contribution to reducing environmental impact, but also has high industrial applicability and extremely high industrial value.

Claims

1. A recycled whole-aromatic polyamide fiber comprising 90 to 99.98% by mass of meta-type whole-aromatic polyamide, 0.01 to 7% by mass of para-type whole-aromatic polyamide, and 0.01 to 3% by mass of a conductive material, characterized in that its tensile breaking strength is 4.0 cN / dtex or higher.

2. The electrical resistance of recycled whole aromatic polyamide fibers is 10 １２ The recycled total aromatic polyamide fiber according to claim 1, wherein the density is Ω / cm or less.

3. A method for producing regenerated whole aromatic polyamide fibers, characterized by dissolving 10 to 25% by mass of a meta-type whole aromatic polyamide polymer in a solution obtained by dissolving a recovered fiber structure containing meta-type whole aromatic polyamide fibers, para-type whole aromatic polyamide fibers, and conductive fibers in an amide-based solvent, thereby producing a whole aromatic polyamide dope, and spinning using the dope.

4. A method for producing recycled whole aromatic polyamide fibers according to claim 3, wherein the recovered fiber structure comprises 30 to 95% by mass of meta-type whole aromatic polyamide fibers, 2 to 15% by mass of para-type whole aromatic polyamide fibers, and 0.1 to 5% by mass of conductive fibers.