Para-aramid fibers and methods for producing the same

Abstract

The present invention relates to a para-aramid fiber and a method for producing the same. The para-aramid fiber has a large crystal size and a high degree of crystallinity, and therefore exhibits excellent tensile properties.

Description

【Technical Field】 【0001】 The present invention relates to para-aramid fibers and a method for producing the same. 【Background Art】 【0002】 Aramid fibers composed of an aromatic dicarboxylic acid component and an aromatic diamine component, particularly para-aramid fibers such as poly(p-phenylene terephthalamide) (PPTA) fibers, are widely used in industrial applications, medical applications, etc. because of their excellent strength, elastic modulus, and heat resistance. However, the mechanical properties such as the strength and elastic modulus of the fibers are still not sufficient for the applications in which they are used, and efforts to provide fibers with more excellent physical properties have been continuously attempted. 【Summary of the Invention】 【Problems to be Solved by the Invention】 【0003】 The present invention provides para-aramid fibers and a method for producing the same. 【Means for Solving the Problems】 【0004】 Hereinafter, para-aramid fibers and a method for producing the same according to specific embodiments of the invention will be described. 【0005】 According to an embodiment of the invention, there is provided a para-aramid fiber including a plurality of monofilaments, having a crystallinity of 67% or more, a crystal size based on the 110 plane of 5.8 to 7.0 nm, a total fineness of 200 to 1,600 de, and a tensile strength of 22 g / d or more. 【0006】 According to another embodiment of the invention, a method for producing para-aramid fibers is provided, comprising the steps of: filtering reaction raw materials to remove impurities; adding an aromatic diamine to a mixed solvent containing an organic solvent and an inorganic salt to form a slurry; adding an aromatic diacyl halide to a reactor containing the slurry in three or more installments and reacting them to form a para-aramid polymer; and spinning a spinning dope containing the para-aramid polymer to produce fibers, wherein in the step of forming the polymer, the temperature difference of the cooling water between the inlet and outlet for cooling the reactor during the primary and secondary additions of the aromatic diacyl halide is controlled to be within 50°C. 【0007】 Unless otherwise specified herein, physical properties such as tensile properties and microstructure measurements of para-aramid fibers are measured values ​​for fibers obtained after normal spinning, coagulation, and drying, and are measured values ​​for fibers in a state where no heat treatment process, which can be added to the fiber manufacturing method, has been performed. 【0008】 The inventors of the present invention completed this invention by discovering through experiments that when using a para-aramid polymer produced through a specific polymerization method, it is possible to provide para-aramid fibers that have a large crystal size and high degree of crystallinity and exhibit excellent tensile properties. 【0009】 The following describes in detail the method for producing the para-aramid fibers (hereinafter simply referred to as the 'production method') and the para-aramid fibers produced therefrom. 【0010】 In the above manufacturing method, the amount of residual inorganic impurities in the final polymer is minimized through the step of removing impurities from the reaction raw materials, thereby providing para-aramid fibers with excellent mechanical strength. 【0011】 The reaction raw materials include an organic solvent, an inorganic salt, an aromatic diamine, and an aromatic diacid halide. In the step of filtering the reaction raw materials to remove impurities, at least one of the listed reaction raw materials can be filtered to remove the impurities contained in that raw material. For example, in the step of filtering the reaction raw materials to remove impurities, the organic solvent, inorganic salt, aromatic diamine, and aromatic diacid halide can each be filtered to prepare reaction raw materials from which impurities have been removed. 【0012】 In the step of filtering the reaction raw materials to remove impurities, the reaction raw materials can be filtered using a filter with a diameter of 0.01 to 1.0 μm, 0.03 to 0.7 μm, or 0.05 to 0.5 μm. The diameter may also be the length of the long axis of the filter's filtration holes. By using a filter with such a diameter, the content of inorganic impurities in the reaction system can be reduced to 1 ppm or less. Furthermore, by using a filter with the aforementioned diameter, the content of inorganic impurities in the polymerized polymer can be reduced to 50 ppb or less. The lower limit of the inorganic impurity content may be 0 ppb or higher. 【0013】 The order in which the step of filtering the reaction raw materials to remove impurities is performed is not particularly limited. Specifically, the step of filtering the reaction raw materials to remove impurities can be performed before the step of forming the slurry, or during the step of forming the slurry. For example, if the step of filtering the reaction raw materials to remove impurities is performed during the step of forming the slurry, a mixed solvent containing an organic solvent and an inorganic salt can be prepared, filtered to prepare the mixed solvent, and then an aromatic diamine, which has been filtered separately to remove impurities, can be added to the mixed solvent to form the slurry. 【0014】 On the other hand, in the step of forming the slurry, an inorganic salt can be added to the organic solvent to produce a mixed solvent in order to increase the degree of polymerization of the para-aramid polymer. 【0015】 The inorganic salt contained in the mixed solvent may include alkali metal halides or alkaline earth metal halides. For example, the inorganic salt may include one or more selected from the group consisting of CaCl2, LiCl, NaCl, KCl, LiBr, and KBr. Such an inorganic salt may be present in an amount of 0.01 to 15% by weight, 0.05 to 13% by weight, 0.1 to 11% by weight, or 1 to 10% by weight, based on the total weight of the mixed solvent. 【0016】 The organic solvent contained in the mixed solvent may include one or more selected from the group consisting of N-methyl-2-pyrrolidone, N,N-dimethylacetamide, hexamethylphosphoamide, N,N,N',N'-tetramethylurea, N,N-dimethylformamide, and dimethyl sulfoxide. The organic solvent may be included in an amount equal to the remainder after excluding the inorganic salt, based on the total weight of the mixed solvent. 【0017】 In the step of forming the slurry, the mixed solvent and the aromatic diamine can be mixed so that the aromatic diamine content in the slurry is 0.5 to 10% by weight. 【0018】 As the aromatic diamine, one or more selected from the group consisting of p-phenylenediamine, 4,4'-oxydianiline, 2,6-naphthalenediamine, 1,5-naphthalenediamine, and 4,4'-diaminobenzanilide may be used. 【0019】 Next, in the step of forming the para-aramid polymer, an aromatic diacid halide can be added to the previously produced slurry and reacted to produce the para-aramid polymer. 【0020】 As the aromatic diacid halide, one or more selected from the group consisting of terephthaloyl dichloride, [1,1'-biphenyl]-4,4'-dicarbonyl dichloride, 4,4'-oxybis(benzoyl chloride), naphthalene-2,6-dicarbonyl dichloride, and naphthalene-1,5-dicarbonyl dichloride can be used. 【0021】 Since the aromatic diacid halide reacts with the aromatic diamine in a molar ratio of 1:1, the molar ratio of the aromatic diacid halide to the aromatic diamine may be about 0.9 to 1.1. 【0022】 The polymerization reaction between the aromatic diamine and the aromatic diacid halide proceeds at a high rate along with heat generation. Therefore, conventionally, a part of the aromatic diacid halide was added first to carry out preliminary polymerization, and then the remaining aromatic diacid halide was added to minimize the difference in the degree of polymerization between the finally obtained polymers. 【0023】 In the manufacturing method according to the other embodiment, by using reaction raw materials from which impurities have been removed one step further than the conventionally used method and controlling the charging conditions and charging method of the reaction raw materials, not only is the difference in the degree of polymerization between polymers small, but it is also possible to provide para-aramid fibers having large crystal size and high crystallinity. 【0024】 Specifically, in the manufacturing method according to the other embodiment, instead of the method of adding the conventional aromatic diacid halide in two portions, the aromatic diacid halide is added in three or more divided portions. When the primary and secondary additions of the aromatic diacid halide are made, the temperature difference of the cooling water entering and leaving the reactor is controlled within 50°C, so that para-aramid fibers having the desired large crystal size and high crystallinity can be provided. 【0025】 Specifically, in the step of forming the polymer, a reactor into which cooling water can enter and leave is used. 【0026】 In the step of forming the slurry, the slurry may be produced in a reactor or in another container other than the reactor and then charged into the reactor. 【0027】 In the step of forming the polymer, the aromatic diacid halide is added to the reactor containing the slurry in three or more divided portions. In particular, the aromatic diacid halide can be added in the first and second times while the temperature difference of the cooling water at the inlet and outlet of the cooling water in the reactor is controlled within 0°C to 50°C. 【0028】 More specifically, when adding the aromatic diacid halide for the first time, the temperature difference of the cooling water at the inlet and outlet of the cooling water can be controlled to 0°C to 50°C, 0°C to 40°C, 0°C to 35°C or 0°C to 30°C. 【0029】 Also, when adding the aromatic diacid halide for the second time, the temperature difference of the cooling water at the inlet and outlet of the cooling water can be controlled to 0°C to 50°C, 0°C to 40°C, 0°C to 35°C or 0°C to 30°C. 【0030】 In order to control the temperature difference of the cooling water at the inlet and outlet of the cooling water within 50°C, the stirring speed of the reactor can be adjusted to 10 to 1000 rpm, 10 to 900 rpm, 10 to 700 rpm or 10 to 500 rpm while the cooling water in the reactor is circulating. 【0031】 The content of the aromatic diacid halide added for the first time can be adjusted to 20 to 40 mol% or 25 to 35 mol% with respect to the total content of the aromatic diacid halide to be added. Within such a range, a prepolymer having a molecular chain of appropriate length can be formed. 【0032】 After adding the aromatic diacid halide for the first time, stirring can be carried out at a temperature of 0°C to 45°C for 1 minute to 30 minutes or about 5 minutes to 15 minutes to perform prepolymerization. 【0033】 Next, in order to control the temperature difference of the cooling water at the inlet and outlet of the cooling water within 50°C again, the stirring speed of the reactor can be adjusted to 10 to 1000 rpm, 10 to 900 rpm, 10 to 700 rpm or 10 to 500 rpm while the cooling water in the reactor is circulating. 【0034】 The content of the aromatic diacid halide added in the second stage can be adjusted to 20-75 mol%, 40-75 mol%, or 50-70 mol% of the total content of the aromatic diacid halides added. Within this range, polymers can be formed that provide fibers with large crystal size and high crystallinity while minimizing the difference in the degree of polymerization between polymers. 【0035】 After adding the aromatic diacid halide in the second step, polymerization can be carried out by stirring at a temperature of 0°C to 45°C for 1 to 30 minutes or 5 to 15 minutes. 【0036】 Subsequently, the remaining aromatic diacid halide content can be added in one or more fractional additions, and then additional polymerization can be carried out to finally produce a para-aramid polymer. This additional polymerization can be carried out by stirring at a temperature of 0°C to 45°C for 5 minutes to 1 hour or 10 minutes to 40 minutes. 【0037】 After the step of forming the polymer, one or more of the following steps can be performed, regardless of the order described: separating the generated polymer from the polymerization reaction system, washing the polymer, neutralizing the polymer, and pulverizing the polymer. 【0038】 The para-aramid polymer may have an intrinsic viscosity of 4.0 dl / g or more, 5.0 dl / g or more, or 5.3 dl / g or more, and 9.0 dl / g or less. 【0039】 Furthermore, the para-aramid polymer may have an intrinsic viscosity deviation of 1.0 dl / g or less, 0.9 dl / g or less, or 0.8 dl / g or less. Since a smaller intrinsic viscosity deviation of the para-aramid polymer is advantageous, the lower limit of the intrinsic viscosity deviation may be 0 dl / g or greater. 【0040】 The deviation in intrinsic viscosity can be determined by dividing the para-aramid polymer, after washing and drying, into three groups using standard sieves with mesh sizes of 1 mm and 2 mm, respectively: a group with mesh sizes of 2 mm or more, a group with mesh sizes of 1 mm or more but less than 2 mm, and a group with mesh sizes of less than 1 mm. After measuring the intrinsic viscosity of each group, the difference between the maximum and minimum values ​​of the average intrinsic viscosity of the three groups can be calculated. 【0041】 Since the para-aramid polymer is manufactured from reaction raw materials from which impurities have been removed, the amount of residual inorganic impurities in the polymer may be very small or nonexistent. For example, the content of inorganic impurities in the polymer may be 50 ppb or less. 【0042】 The para-aramid polymer may be poly(para-phenylene terephthalamide), poly(4,4'-benzanilide terephthalamide), poly(para-phenylene-4,4'-biphenylene-dicarbonylamide), poly(para-phenylene-2,6-naphthalenedicarbonylamide), or copolymers thereof. For example, the para-aramid polymer may be poly(para-phenylene terephthalamide). 【0043】 On the other hand, in the step of manufacturing the fibers, the spinning dope containing the polymer produced in the step of forming the polymer is spun to provide the fibers. 【0044】 As the solvent for the spinning dope, sulfuric acid having a concentration of 97-102% by weight can be used. Chlorosulfuric acid or fluorosulfuric acid can also be used as the solvent instead of sulfuric acid. 【0045】 The viscosity of the spinning dope used to manufacture fibers increases as the concentration of para-aramid polymer in the spinning dope increases. However, when the concentration of para-aramid polymer exceeds the critical concentration, the viscosity of the spinning dope decreases rapidly. At this point, the spinning dope changes from optical isotropy to optical anisotropy without forming a solid phase. Optical anisotropic dope can provide high-strength para-aramid fibers without a separate drawing process due to its structural and functional properties. Therefore, it is preferable that the concentration of para-aramid polymer in the spinning dope exceeds the critical concentration, but if the concentration is excessively high, the viscosity of the spinning dope may become excessively low. Thus, the spinning dope can contain para-aramid polymer in an amount of 10 to 25% by weight relative to the total weight of the spinning dope. 【0046】 In the stage of manufacturing the aforementioned fibers, a spinning process can be carried out to spin the spinning dope. 【0047】 In the aforementioned spinning process, the spinning dope can be spun into a filament form through air gap wet spinning. 【0048】 The aforementioned air-gap wet spinning method involves providing an air gap between the spinneret and the surface of the coagulation bath. Through this air-gap wet spinning method, the spinning dope can be spun through the spinneret, across the air gap, into a coagulation bath containing the coagulation solution. 【0049】 In the aforementioned spinning process, the thickness of the fiber can be controlled by the pressure and spinning speed during the extrusion of the spinning dope through the spinneret. 【0050】 The spinneret may be provided with a plurality of holes through which the spinning dope can be spun. 【0051】 Specifically, the spinneret can be equipped with 50 to 3000, 100 to 2000, 120 to 1500, or 500 to 1200 holes. Within this range, it is possible to provide para-aramid fibers that have a large crystal size and high crystallinity and exhibit excellent tensile properties. 【0052】 Only by adjusting the diameter of the holes formed in the spinneret to an appropriate size can the molecular orientation on the surface and inside of the filament be fully improved. From this perspective, the diameter of the holes in the spinneret can be adjusted to 100 μm or less, while being 50 μm or more. 【0053】 In the spinning process, the spinning dope can be spun at a spinning speed of 80 m / min or more and 800 m / min or less. 【0054】 Specifically, the spinning dope can be spun at spinning speeds of 80-800 m / min, 100-800 m / min, 300-800 m / min, 500-700 m / min, 550-660 m / min, 580-650 m / min, 580-640 m / min, or 590-610 m / min. Within this range, it is possible to provide para-aramid fibers that have a large crystal size and high crystallinity and exhibit excellent tensile properties. 【0055】 The dope spun through the aforementioned spinneret is obtained as an unsolidified filament in which sulfuric acid is distributed on a matrix in which para-aramid polymers are uniformly distributed. Such an unsolidified filament can be solidified by passing through an air gap and into a solidification tank containing a solidification solution. 【0056】 The air gap may be an air layer or an inert gas layer. For example, the air gap may be a nitrogen layer supplied with dry nitrogen (dry N2). The length of the air gap can be adjusted from 0.1 to 15 cm. 【0057】 The doped yarn, spun from the spinneret and passing through an air gap, forms a filament as it passes through the solidification tank, with the sulfuric acid inside being removed. If the sulfuric acid is removed too rapidly from the filament surface, the surface may solidify before the sulfuric acid contained inside has had a chance to escape, resulting in poor uniformity between the inside and outside of the filament. Therefore, it is preferable that the solidification liquid placed in the solidification tank be an aqueous sulfuric acid solution containing sulfuric acid. 【0058】 Specifically, the coagulation solution placed in the coagulation tank may be an aqueous sulfuric acid solution obtained by adding sulfuric acid to water. In addition, monohydric alcohols such as methanol, ethanol, or propanol; dihydric alcohols such as ethylene glycol or propylene glycol; or trihydric alcohols such as glycerol may be added to the coagulation solution as needed. 【0059】 The temperature of the solidifying solution is preferably 1 to 10°C. If the temperature of the solidifying solution is excessively low, sulfuric acid may not escape easily from the filament. If the temperature of the solidifying solution is excessively high, sulfuric acid may escape rapidly from the filament, reducing the uniformity of the filament. 【0060】 A solidification tube may be formed at the bottom of the solidification tank. The solidification tube is connected to the solidification tank, and a number of nozzles may be formed in the solidification tube. In this case, the nozzles are connected to a predetermined jet device, and the solidified liquid sprayed from the jet device is sprayed onto the filament passing through the solidification tube via the nozzles. Preferably, the number of nozzles are aligned so that the solidified liquid is sprayed symmetrically onto the filament. The spray angle of the solidified liquid is preferably 0 to 85° with respect to the axial direction of the filament, and a spray angle of 20 to 40° is particularly suitable in commercial production processes. 【0061】 In the stage of manufacturing the aforementioned fibers, following the solidification step, a water washing step may be performed to remove any remaining sulfuric acid from the solidified filaments. 【0062】 The washing step can be carried out by spraying water, or a mixed solution of water and an alkaline solution, onto the solidified filament. 【0063】 The washing process can be carried out in multiple stages. For example, the solidified filament can be first washed with a 0.1 to 1.5% by weight aqueous caustic solution, followed by a second washing with a dilute aqueous caustic solution. 【0064】 In the stage of manufacturing the aforementioned fibers, following the coagulation and washing steps, a drying step may be performed to adjust the moisture content remaining in the filaments. 【0065】 The drying process can be carried out by adjusting the time the filament is in contact with the heated drying roll, or by adjusting the temperature of the drying roll. 【0066】 The monofilaments constituting the para-aramid fibers ultimately obtained can have a fineness of 1.0 to 2.5 de (denier). 【0067】 Furthermore, the para-aramid fiber comprises a plurality of monofilaments and can have a total fineness of 200-1,600 de, 200-400 de, 800-1,000 de, 1,000-1,100 de, or 1,400-1,600 de. 【0068】 Para-aramid fibers produced by this manufacturing method have a large crystal size, exhibit high crystallinity and orientation, and can demonstrate excellent tensile properties. 【0069】 The para-aramid fibers can have an increased crystal size when manufactured by the above manufacturing method. 【0070】 For example, the para-aramid fiber may have a crystal size (crystal dimensions) based on the (110) plane of 5.8 nm or more, 5.9 nm or more, 6.0 nm or more, or 6.2 nm or more, and may also be 7.0 nm or less, 6.8 nm or less, or 6.6 nm or less. Furthermore, the para-aramid fiber may have a crystal size (crystal dimensions) based on the (200) plane of 5.0 nm or more, 5.5 nm or more, or 5.6 nm or more, and may also be 6.5 nm or less, 6.4 nm or less, or 6.2 nm or less. 【0071】 The crystal size is determined by analysis of the X-ray diffraction pattern, and for more detailed measurement methods, please refer to the methods described in the test examples below. Furthermore, the para-aramid fibers can have a high degree of crystallinity when manufactured by the above manufacturing method. 【0072】 Specifically, the para-aramid fiber may have a crystallinity of 67% or more, 68% or more, 68.5% or more, 69% or more, 70% or more, 71% or more, 72% or more, or 72.5% or more, but may also be 78% or less, 75% or less, or 73% or less. 【0073】 The aforementioned crystallinity was determined by analysis of the X-ray diffraction pattern, and for more detailed measurement methods, please refer to the methods described in the test examples below. 【0074】 The para-aramid fibers produced by the manufacturing method described above can exhibit a high degree of orientation. That is, the para-aramid fibers can have a high degree of orientation and a small orientation angle. 【0075】 For example, the para-aramid fiber may have an orientation angle of 2° or more, 5° or more, or 7° or more with respect to the (110) plane, and may be 12° or less, 11° or less, 10.5° or less, 10° or less, 9.5° or less, 9.3° or less, 9.1° or less, or 9.0° or less. Also, the para-aramid fiber may have an orientation angle of 2° or more, 5° or more, or 8° or more with respect to the (200) plane, and may be 13° or less, 12° or less, 11.5° or less, 11.2° or less, 11° or less, 10.5° or less, or 10.3° or less. 【0076】 The orientation angle mentioned above is the orientation angle analyzed from the X-ray diffraction pattern, and for more detailed measurement methods, please refer to the methods described in the test examples below. 【0077】 The para-aramid fibers can have their crystalline parameters minimized by being manufactured by the aforementioned manufacturing method. 【0078】 As an example, the para-aramid fiber may have crystalline defects of 1.00% or more, or 1.30% or more, and may also have 1.85% or less, 1.80% or less, 1.70% or less, or 1.60% or less. 【0079】 The aforementioned crystal defects were analyzed from the X-ray diffraction pattern, and for more detailed measurement methods, please refer to the methods described in the test examples below. 【0080】 The aforementioned para-aramid fibers can exhibit excellent tensile properties due to their large crystal size and high degree of crystallinity. 【0081】 For example, the para-aramid fiber may have a tensile strength of 22 g / d or more, 22.5 g / d or more, 23 g / d or more, 23.5 g / d or more, 24 g / d or more, or 25 g / d or more, and may be 30 g / d or less, or 28 g / d or less. Furthermore, the para-aramid fiber may have a Young's modulus of 750 g / d or more, 760 g / d or more, 780 g / d or more, 790 g / d or more, 800 g / d or more, or 810 g / d or more, while being 900 g / d or less, 880 g / d or less, or 860 g / d or less. The para-aramid fiber may have an elongation of 2.0% or more, 2.5% or more, 3.0% or more, 3.1% or more, 3.2% or more, 3.3% or more, or 3.4% or more, and may be 4.5% or less, or 4.0% or less. 【0082】 The aforementioned tensile properties, such as tensile strength, Young's modulus, and elongation, were measured using the ASTM D885 standard test method for a sample with a twist multiplier of 1.1. For more detailed measurement methods, please refer to the test examples described later. [Effects of the Invention] 【0083】 Para-aramid fibers according to one embodiment of the invention exhibit excellent tensile properties due to their large crystal size and high degree of crystallinity. [Modes for carrying out the invention] 【0084】 The function and effects of the invention will be explained in more detail below through specific embodiments of the invention. However, these are presented as examples of the invention and do not limit the scope of the invention's rights in any way. [Examples] 【0085】 <Test Example 1: Evaluation of Physical Properties of Para-Aramid Polymers> The physical properties of the para-aramid polymers obtained from the synthesis examples below were measured by the method described below. 【0086】 (1) Intrinsic viscosity measurement The intrinsic viscosity of the polymer was measured by the following formula 1. 【0087】 [Formula 1] IV = ln(η) rel ) / C 【0088】 In equation 1 above, ln is the natural logarithm function, C is the concentration of the polymer solution (a solution in which 0.5 g of polymer is dissolved in 100 mL of 98 wt% sulfuric acid), and the relative viscosity (η) rel This is the ratio of the flow time between the polymer solution and the solvent, measured at 30°C using a capillary viscometer. 【0089】 (2) Measurement of intrinsic viscosity deviation After washing and drying, the polymers were separated into three groups using standard sieves with mesh sizes of 1 mm and 2 mm, respectively: a group of 2 mm or larger, a group of 1 mm to less than 2 mm, and a group of less than 1 mm. 【0090】 After measuring the intrinsic viscosity of each group, the difference between the maximum and minimum average intrinsic viscosity for the three groups was calculated to determine the intrinsic viscosity deviation of the polymers. 【0091】 (3)Inorganic impurity content The inorganic impurity content in para-aramid polymers was measured by the following method: After completely decomposing a 1g sample by acid treatment, the concentration of ionized and residual inorganic impurities in the sample was measured using an inductively coupled plasma atomic emission spectrophotometer. 【0092】 <Synthesis Example 1: Production of Para-aramid Polymer (PPTA-1)> As reaction raw materials, N-methyl-2-pyrrolidone (NMP), CaCl2, p-phenylenediamine (PPD), and terephthaloyl chloride (TPC) were passed through a filter with a diameter of 0.1 μm to remove impurities from the reaction raw materials. 【0093】 Under a nitrogen atmosphere, a mixed solvent consisting of NMP as an organic solvent and CaCl2 as an inorganic salt in a weight ratio of 92:8 was placed in a reactor, and PPD was added to the slurry until the concentration of PPD in the slurry reached 5% by weight to produce a slurry. 【0094】 Next, TPC equivalent to 30 mol% of the molar amount of PPD was added to the reactor, which had been cooled to 30°C, and the reaction was allowed to proceed for 10 minutes. During this time, the stirring speed of the reactor was adjusted to approximately 200 rpm to control the temperature difference of the cooling water between the inlet and outlet to approximately 20°C. 【0095】 Subsequently, TPC equivalent to 60 mol% of the molar amount of PPD was added to the reactor, which had been cooled again to 30°C, and the reaction was allowed to proceed for 30 minutes. During this time, the stirring speed of the reactor was adjusted to approximately 200 rpm to control the temperature difference between the cooling water inlet and outlet to approximately 20°C. 【0096】 Finally, TPC equivalent to 10 mol% of the molar amount of PPD was added to a reactor cooled to 30°C, and the reaction was carried out for 30 minutes to produce a para-aramid polymer. 【0097】 To the solution containing the para-aramid polymer, water and NaOH were added to neutralize the acid. Next, the para-aramid polymer was pulverized, and the polymerization solvent contained in the para-aramid polymer was extracted using water. The polymer was then dehydrated and dried to finally obtain PPTA-1. 【0098】 The intrinsic viscosity of the PPTA-1 produced in this manner was 5.4 dl / g, and the inorganic impurity content in the polymer was 48 ppb. Furthermore, using standard sieves with mesh sizes of 1 mm and 2 mm, the PPTA-1 was classified into three groups: one with a mesh size of 2 mm or more, one with a mesh size between 1 mm and 2 mm, and one with a mesh size of less than 1 mm. After measuring the intrinsic viscosity of each group, the intrinsic viscosity deviation, calculated by the difference between the maximum and minimum average intrinsic viscosities for the three groups, was 0.85 dl / g. 【0099】 <Synthesis Example 2: Production of Para-aramid Polymer (PPTA-2)> Under a nitrogen atmosphere, a mixed solvent consisting of NMP as an organic solvent and CaCl2 as an inorganic salt in a weight ratio of 86:14 was placed in a reactor, and PPD was added to the slurry until the concentration of PPD in the slurry reached 3% by weight, thereby producing a slurry. 【0100】 Next, TPC equivalent to 30 mol% of the molar amount of PPD was added to the reactor, which had been cooled to 0°C, and the reaction was carried out at 5°C for 30 minutes. 【0101】 After 30 minutes, the temperature difference between the cooling water inlet and outlet was 65°C. TPC equivalent to 60 mol% of the molars of PPD was added to the reactor, and the mixture was reacted at 5°C for 20 minutes. Then, TPC equivalent to 10 mol% of the molars of PPD was added to the reactor, and the mixture was reacted at 5°C for 5 minutes to produce a para-aramid polymer. 【0102】 To the solution containing the para-aramid polymer, water and NaOH were added to neutralize the acid. Next, the para-aramid polymer was pulverized, and the polymerization solvent contained in the para-aramid polymer was extracted using water. The polymer was then dehydrated and dried to finally obtain PPTA-2. 【0103】 The intrinsic viscosity of the PPTA-2 produced in this manner was 5.4 dl / g, and the inorganic impurity content in the polymer was 3150 ppb. Furthermore, using standard sieves with mesh sizes of 1 mm and 2 mm, the PPTA-2 was classified into three groups: one with a mesh size of 2 mm or more, one with a mesh size of 1 mm or more but less than 2 mm, and one with a mesh size of less than 1 mm. After measuring the intrinsic viscosity of each group, the intrinsic viscosity deviation, calculated by the difference between the maximum and minimum average intrinsic viscosities of the three groups, was 1.3 dl / g. 【0104】 <Example 1: Production of para-aramid fibers> A spinning dope was prepared by dissolving PPTA-1 obtained from Synthesis Example 1 in 99.8% by weight sulfuric acid at a concentration of 19% by weight relative to the total weight of the spinning dope. 【0105】 The aforementioned spinning dope was spun at a speed of 650 m / min through a spinneret with 133 holes, and the resulting filament was solidified in a solidification tank via an air gap. 【0106】 The solidified filament was washed with water to remove any remaining sulfuric acid, etc., and then dried and wound up to obtain a para-aramid fiber with a monofilament fineness of 1.47 de and a total fineness of 213 de. 【0107】 <Example 2: Production of para-aramid fibers> A spinning dope was prepared by dissolving PPTA-1 obtained from Synthesis Example 1 in 99.8% by weight sulfuric acid at a concentration of 19% by weight relative to the total weight of the spinning dope. 【0108】 The aforementioned spinning dope was spun at a speed of 620 m / min through a spinneret with 665 holes, and the resulting filament was solidified in a solidification tank via an air gap. 【0109】 The solidified filament was washed with water to remove any remaining sulfuric acid, etc., and then dried and wound to obtain a para-aramid fiber with a monofilament fineness of 1.43 de and a total fineness of 988 de. 【0110】 <Example 3: Production of para-aramid fibers> A spinning dope was prepared by dissolving PPTA-1 obtained from Synthesis Example 1 in 99.8% by weight sulfuric acid at a concentration of 20% by weight relative to the total weight of the spinning dope. 【0111】 The aforementioned spinning dope was spun at a speed of 600 m / min through a spinneret with 665 holes, and the resulting filament was solidified in a solidification tank via an air gap. 【0112】 The solidified filament was washed with water to remove any remaining sulfuric acid, etc., and then dried and wound to obtain a para-aramid fiber having a monofilament fineness of 1.50 de and a total fineness of 1022 de. 【0113】 <Example 4: Production of para-aramid fibers> A spinning dope was prepared by dissolving PPTA-1 obtained from Synthesis Example 1 in 99.8% by weight sulfuric acid at a concentration of 19% by weight relative to the total weight of the spinning dope. 【0114】 The aforementioned spinning dope was spun at a speed of 650 m / min through a spinneret with 1000 holes, and the resulting filament was solidified in a solidification tank via an air gap. 【0115】 The solidified filament was washed with water to remove any remaining sulfuric acid, etc., and then dried and wound to obtain a para-aramid fiber with a monofilament fineness of 1.54 de and a total fineness of 1550 de. 【0116】 <Comparative Example 1: Production of Para-aramid Fibers> A spinning dope was prepared by dissolving PPTA-2 obtained from Synthesis Example 2 in 99.8% by weight sulfuric acid at a concentration of 19% by weight relative to the total weight of the spinning dope. 【0117】 The aforementioned spinning dope was spun at a speed of 600 m / min through a spinneret with 1000 holes, and the resulting filament was solidified in a solidification tank via an air gap. 【0118】 The solidified filament was washed with water to remove any remaining sulfuric acid, etc., and then dried and wound up to obtain a para-aramid fiber with a monofilament fineness of 1.49 de and a total fineness of 1527 de. 【0119】 For reference, when the spinning speed of PPTA-2 obtained from Synthesis Example 2 was the same as that of Example 4, the general physical properties were inferior. Therefore, it was manufactured to have the same level of fineness as the para-aramid fiber of Example 4, and the spinning speed was adjusted to a speed optimized for PPTA-2 obtained from Synthesis Example 2. 【0120】 <Test Example 2: Evaluation of Physical Properties of Para-Aramid Fibers> The physical properties of the para-aramid fibers obtained from the above examples and comparative examples were measured by the method described below, and the results are shown in Table 1. 【0121】 (1) Denier (de) Fineness is expressed as denier (de), which is the weight (g) of 9000m of yarn, and was measured according to ASTM D1577. 【0122】 (2) Tensile properties Para-aramid fibers produced through the examples and comparative examples were cut to a length of 250 mm and twisted with TM (twist multiplier) 1.1 to prepare samples, which were then stored for 14 hours at a relative humidity of 55% and a temperature of 23°C. 【0123】 Next, the sample was mounted on an Instron Engineering Corp. (Canton, Mass) tester according to the ASTM D885 standard test method. One end of the fiber was fixed, and the initial load was set to 1 / 30 g of the fineness (fineness × 1 / 30 g). The other end was then pulled at a speed of 25 mm / min, and the tensile load (g) and elongation (strain) at which the fiber broke were measured. The strength (g / d) was obtained by dividing the measured tensile load by the fineness, and Young's modulus was determined from the slope of the stress-deformation curve of the para-aramid fiber obtained under the tensile load measurement conditions. 【0124】 (3) X-ray diffraction (XRD) analysis The microstructure of para-aramid fibers produced by the examples and comparative examples was analyzed using X-ray diffraction patterns. 【0125】 Para-aramid fibers produced according to the examples and comparative examples were cut to a length of 20-30 mm, arranged as evenly as possible, and then attached to a holder to prepare the samples. The prepared samples were placed on a sample attachment so that the β-position was 0°. After warming up the XRD measuring instrument, the voltage and current were gradually increased to the measurement conditions of 50 kV and 180 mA, and the equatorial pattern was measured. The main measurement conditions were then set as follows. 【0126】 Goniometer, Continuous scan mode, Scan angle range: 10~40°, Scan speed: 2. 【0127】 The 2θ positions of two peaks, located between 20-21° and 22-23°, were measured in the scanned profile. The measured profile was then processed using a multi-peak separation method program. 【0128】 After specifying a straight background from 2θ 15 to 35°, the two crystal peaks were separated to obtain the X-ray diffraction pattern. 【0129】 i) Crystal size (apparent crystal size; ACS) Using the aforementioned X-ray diffraction patterns, the apparent crystal size (ACS) for each crystal plane when K is 1 was determined by Scherrer's equation, using the factors [2θ Position, Intensity, Full Width at Half Maximum (FWHM)]. Here, the apparent crystal size (ACS) represents the average size of the crystals in that plane. 【0130】 ii) Crystallinity (Xc) Using the aforementioned X-ray diffraction pattern, the degree of crystallinity was determined by the ratio of crystalline peaks to amorphous peaks. 【0131】 iii) Orientation angle (OA) After performing an azimuthal scan at each plane of the aforementioned X-ray diffraction pattern, the orientation angle was determined by calculating the full width at half maximum (FWHM) of each peak. 【0132】 iv) Crystal defects (paracrystalline parameter; g II ) Para-aramid fibers produced according to the examples and comparative examples were cut to lengths of 20-30 mm, arranged as evenly as possible, and then attached to a holder to prepare the samples. The prepared samples were placed in a sample attachment so that the β-position was 0°. After warming up the XRD measuring instrument, the voltage and current were gradually increased to the measurement conditions of 50 kV and 180 mA, and the meridional pattern was measured. The main measurement conditions were then set as follows. 【0133】 Goniometer, Continuous scan mode, Scan angle range: 10~40°, Scan speed: 0.5 [Step / scan time is sufficient to allow sufficient beam exposure time to achieve 2,000 CPS because the peak intensity is small]. 【0134】 The 2θ position of the peak ((002) plane) shown between 10 and 15° was measured in the scanned profile. The paracrystalline parameter was derived by substituting the measured profile into the Hosemann equation in Equation 2 below. 【0135】 [Formula 2] JPEG0007875890000001.jpg24164 【0136】 In equation 2 above, δs is the dispersion of the diffraction peak, L is the crystal size, d is the lattice plane spacing, and m is the order of the diffraction peak. 【0137】 [Table 1] 【0138】 *The crystal sizes in Table 1 above refer to the crystal size based on the (110) plane and the crystal size based on the (200) plane, and the orientation angles refer to the orientation angle based on the (110) plane and the orientation angle based on the 200 plane. 【0139】 Referring to Table 1 above, it can be confirmed that para-aramid fibers according to one embodiment can be provided as high-quality para-aramid fibers of various grades by being formed from para-aramid polymers produced using reaction raw materials from which impurities have been removed, and by controlling the input conditions and methods of the reaction raw materials. 【0140】 Specifically, comparing Examples 1, 2, and 4 and Comparative Example 1, which provide standard tenacity aramid fibers with a strength of approximately 20-24 g / d, it was confirmed that Examples 1, 2, and 4 exhibit larger crystal size, higher crystallinity, and higher orientation compared to Comparative Example 1, and also have superior Young's modulus. 【0141】 Furthermore, Example 3, which provides high-tenacity aramid fibers with a strength of 25 g / d or more, also exhibits large crystal size, high crystallinity, and high orientation, confirming excellent tensile properties.

Claims

[Claim 1] A para-aramid fiber containing multiple monofilaments, The aforementioned para-aramid fiber has a crystallinity of 71% or more. The crystal size relative to the (110) plane (110 plane) is 5.8 to 6.8 nm. The total fineness is 200 to 1,600 denier, the tensile strength is 22 g / d or more, and the Young's modulus is 880 g / d or less. Para-aramid fibers containing a para-aramid polymer in which the content of inorganic impurities within the polymer is 50 ppb or less. [Claim 2] The para-aramid fiber according to claim 1, comprising a para-aramid polymer having an intrinsic viscosity of 4.0 to 9.0 dl / g. [Claim 3] The para-aramid fiber according to claim 1, comprising a para-aramid polymer having an intrinsic viscosity deviation of 1.0 dl / g or less. [Claim 4] The para-aramid fiber according to claim 1, wherein the (200) plane (200 plane) reference crystal size is 5.0 to 6.5 nm. [Claim 5] The para-aramid fiber according to claim 1, wherein the degree of crystallinity is 71 to 78%. [Claim 6] The para-aramid fiber according to claim 1, wherein the orientation angle relative to the (110) plane (110 plane) is 2 to 12°. [Claim 7] The para-aramid fiber according to claim 1, wherein the orientation angle relative to the (200) plane (200 plane) is 2 to 13°. [Claim 8] The para-aramid fiber according to claim 1, wherein the crystal defect content is 1.00 to 1.85%. [Claim 9] The para-aramid fiber according to claim 1, wherein the Young's modulus is 750 to 880 g / d. [Claim 10] The para-aramid fiber according to claim 1, having an elongation of 2 to 4%. [Claim 11] A method for producing para-aramid fibers according to claim 1, A step in which the reaction raw materials are filtered to remove impurities; A step of forming a slurry by adding an aromatic diamine to a mixed solvent containing an organic solvent and an inorganic salt; The steps include: adding aromatic diacid halides to the reactor containing the slurry in three or more fractional amounts and reacting them to form a para-aramid polymer; and The process includes the step of spinning a spinning dope containing the aforementioned para-aramid polymer to produce fibers, A method for producing para-aramid fibers, wherein, in the step of forming the polymer, the temperature difference of the cooling water between the inlet and outlet for cooling the reactor is controlled to within 50°C during the primary and secondary addition of the aromatic diacid halide. [Claim 12] A method for producing para-aramid fibers according to claim 11, wherein the reaction raw material is filtered using a filter having a diameter of 0.01 to 1.0 μm. [Claim 13] The method for producing para-aramid fibers according to claim 11, wherein the stirring speed of the reactor is adjusted to 10 to 1000 rpm when the aromatic diacid halide is added as a primary. [Claim 14] The method for producing para-aramid fibers according to claim 11, wherein the stirring speed of the reactor is adjusted to 10 to 1000 rpm when the aromatic diacid halide is added as a secondary component.

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