Polyamide solid production method, polyamide solid, and polyamide fiber production method

Abstract

The purpose of the present invention is to provide a method for producing a polyamide solid having few black spots. This polyamide solid production method is characterized by comprising: a step 1 for dissolving a first polyamide solid serving as a starting material in a solvent to obtain a polyamide solution; a step 2 for removing insoluble matter contained in the polyamide solution to obtain an insoluble matter-removed polyamide solution; a step 3 for precipitating and recovering a polyamide from the insoluble matter-removed polyamide solution; and a step 4 for molding the polyamide recovered at step 3 at a temperature lower than the melting point of the polyamide to obtain a second polyamide solid.

Description

Method for producing polyamide solid, polyamide solid, and method for producing polyamide fiber

[0001] The present invention relates to a method for producing a polyamide solid, a polyamide solid, and a method for producing a polyamide fiber.

[0002] Polyamides, including nylon 6 and nylon 66, are representative engineering plastics that have excellent heat resistance and mechanical properties. They are widely used in textiles, automobile parts, electrical appliance parts, and more, and are one of the irreplaceable materials in modern society.

[0003] Japanese Patent Application Laid-Open No. 2004-143242

[0004] Polyamides can develop black spots during heating, such as during melting, during manufacturing. These black spots can impair the appearance of molded products, reduce their strength, and cause clogging during melt molding and spinning, reducing continuous productivity. Therefore, there has been a need to reduce the number of black spots. Since black spots remain solid even when polyamide is melted or dissolved in a solvent to form a liquid, one possible method for removing them is to separate the solid from the liquid using a filter. However, if the polyamide is melt-extruded after filtering to obtain pellets, the black spots increase again. Furthermore, if polyamide is dissolved in a solvent and then separated into solids, it becomes powder. Conventional polyamide molding equipment is designed for solids such as pellets, making it difficult to handle powders. However, if powdered polyamide is remelted and pelletized, the black spots increase again. Furthermore, powdered polyamides easily absorb moisture, requiring strict drying, storage, and management.

[0005] As a method for suppressing black spots, a method of adding polyphenylene ether to polyamide and melt-kneading it is known (Patent Document 1). However, the method of Patent Document 1 only produces a composition containing a mixed resin with polyphenylene ether, so further improvement is required. Therefore, we have investigated a method for producing a polyamide solid that does not necessarily require the addition of additives.

[0006] An object of the present invention is to provide a method for producing a polyamide solid with fewer black spots.

[0007] That is, the present invention is as follows: [1] A method for producing a polyamide solid, comprising the following steps: Step 1: dissolving a first polyamide solid, which is a raw material, in a solvent to obtain a polyamide solution, Step 2: removing insoluble matter contained in the polyamide solution to obtain an insoluble matter-removed polyamide solution, Step 3: precipitating and recovering polyamide from the insoluble matter-removed polyamide solution, and Step 4: molding the polyamide recovered in Step 3 at a temperature below the melting point of the polyamide to obtain a second polyamide solid. [2] The method for producing a polyamide solid according to [1], wherein in Step 4, the polyamide is compression-molded or extrusion-granulated to obtain a second polyamide solid in the form of a green compact. [3] The method for producing a polyamide solid according to [1] or [2], wherein, when a solution obtained by dissolving the second polyamide solid in a solvent is filtered through a separation material having a pore size of 10 μm, the number of insoluble particles having a major axis of 200 μm or less remaining on the separation material is 50,000 or less per 1 g of the second polyamide solid, and no insoluble particles having a major axis larger than 200 μm are present. [4] The method for producing a polyamide solid according to any one of [1] to [3], wherein, when a solution obtained by dissolving the second polyamide solid in a solvent is filtered through a separation material having a pore size of 10 μm, the mass of insoluble particles remaining on the separation material is 0.5 ppm by mass or less relative to 100% by mass of the second polyamide solid. [5] The method for producing a polyamide solid according to any one of [1] to [4], wherein the solvent used to dissolve the first polyamide solid in step 1 is an alcohol solution of a metal chloride. [6] The method for producing a polyamide solid according to [3] or [4], wherein the solvent used to dissolve the second polyamide solid is an alcohol solution of a metal chloride. [7] The method for producing a polyamide solid according to [4], wherein the mass of the insoluble matter is calculated based on the specific gravity of the second polyamide solid by optically measuring the volume of the insoluble matter remaining on a separation material. [8] A polyamide solid, wherein, when a solution of the polyamide solid in a solvent is filtered and separated using a separation material with a pore size of 10 μm, the number of insoluble matter having a major axis of 200 μm or less remaining on the separation material is 50,000 or less per 1 g of the polyamide solid, and no insoluble matter having a major axis of more than 200 μm is present.[9] A polyamide solid, wherein when a solution of a polyamide solid in a solvent is filtered using a separation material with a pore size of 10 μm, the mass of insoluble matter remaining on the separation material is 0.5 ppm by mass or less relative to 100% by mass of the polyamide solid.

[10] A method for producing a polyamide fiber using the polyamide solid according to [8] as a raw material.

[11] A method for producing a polyamide fiber using the polyamide solid according to [9] as a raw material.

[12] A method for producing a polyamide fiber, comprising the following steps: Step 1: dissolving a first polyamide solid as a raw material in a solvent to obtain a polyamide solution, Step 2: removing insoluble matter contained in the polyamide solution to obtain an insoluble matter-removed polyamide solution, Step 3: precipitating and recovering polyamide from the insoluble matter-removed polyamide solution, Step 4: molding the polyamide recovered in Step 3 at a temperature below the melting point of the polyamide to obtain a second polyamide solid, and Step 5: melt-spinning the second polyamide solid as a raw material.

[13] The method for producing a polyamide fiber according to

[12] , wherein in step 4, the polyamide is compression-molded or extrusion-granulated to obtain a second polyamide solid that is a green compact.

[14] The method for producing a polyamide fiber according to

[12] or

[13] , wherein the second polyamide solid contains 5,000 ppm by mass or less of compounds having an amide bond and a molecular weight of 1,000 or less.

[15] The method for producing a polyamide fiber according to

[12] or

[13] , wherein the solvent for dissolving the first polyamide solid in step 1 is an alcohol solution of a metal chloride.

[16] A polyamide solid containing 5,000 ppm by mass or less of compounds having an amide bond and a molecular weight of 1,000 or less.

[17] The polyamide solid according to

[16] , which is a green compact.

[18] A polyamide fiber containing 5,000 ppm by mass or less of compounds having an amide bond and a molecular weight of 1,000 or less.

[0008] The method for producing a polyamide solid of the present invention has the above-mentioned configuration, and therefore can produce a polyamide solid with few black spots.

[0009] Hereinafter, an embodiment of the present invention (hereinafter simply referred to as "the present embodiment") will be described in detail.

[0010] [Method for Producing Polyamide Solid] The method for producing a polyamide solid of this embodiment includes at least the following steps 1 to 4: Step 1: dissolving a first polyamide solid, which is a raw material, in a solvent to obtain a polyamide solution, Step 2: removing insoluble matter contained in the polyamide solution to obtain an insoluble matter-removed polyamide solution, Step 3: precipitating and recovering polyamide from the insoluble matter-removed polyamide solution, and Step 4: molding the polyamide recovered in step 3 at a temperature below the melting point of the polyamide to obtain a second polyamide solid. The method for producing a polyamide solid of this embodiment may consist of only steps 1 to 4 above, or may further include other steps.

[0011] The present inventors have found that when polyamide is used as a spinning raw material, using polyamide in powder form (e.g., particles with a major axis of less than 1 mm) can result in thread breakage due to air entrapment, etc. They have also found that thread breakage during spinning can be prevented by removing insoluble matter from the polyamide and then molding the polyamide to form pellets (e.g., particles with a major axis of 1 mm or more). Furthermore, they have found that molding the polyamide to obtain pellets at a temperature below its melting point can suppress the occurrence of black spots in the pellets, resulting in a raw polyamide with excellent appearance and strength. The polyamide solid obtained by the method for producing a polyamide solid of this embodiment is particularly suitable for use as a spinning raw material.

[0012] <Step 1> (First Polyamide Solid) The first polyamide solid may be a solid consisting of polyamide alone, or may further contain other components.

[0013] The polyamide may be a polymer formed by polymerization through an amide bond, such as a polycondensation of a diamine compound and a dicarboxylic acid compound or a ring-opening polymerization of a cyclic lactam. Examples of the diamine compound include, but are not limited to, ethylenediamine, trimethylenediamine, tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, nonanediamine, methylpentanediamine, and p-phenylenediamine. Examples of the dicarboxylic acid compound include, but are not limited to, oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, sebacic acid, terephthalic acid, and isophthalic acid. Examples of the cyclic lactam include, but are not limited to, ε-caprolactam, undecanelactam, and lauryllactam. The combination of the diamine compound, dicarboxylic acid compound, and cyclic lactam compound is not particularly limited, and multiple types of each compound may be used in combination. Polyhexamethylene adipamide (for example, polyhexamethylene adipamide made from hexamethylenediamine and adipic acid) has high solubility and is suitable for the manufacturing method of this embodiment.

[0014] Examples of the polyamide include polycaproamide (nylon 6), polyhexamethylene adipamide (nylon 66), polytetramethylene adipamide (nylon 46), polytetramethylene sebacamide (nylon 410), polypentamethylene adipamide (nylon 56), polypentamethylene sebacamide (nylon 510), polyhexamethylene sebacamide (nylon 610), polyhexamethylene dodecamide (nylon 612), polydecamethylene adipamide (nylon 106), polydecamethylene sebacamide (nylon 1010), poly Lidecamethylene dodecamide (Nylon 1012), polyundecaneamide (Nylon 11), polydodecanamide (Nylon 12), polycaproamide / polyhexamethylene adipamide copolymer (Nylon 6 / 66), polycaproamide / polyhexamethylene terephthalamide copolymer (Nylon 6 / 6T), polyhexamethylene adipamide / polyhexamethylene terephthalamide copolymer (Nylon 66 / 6T), polyhexamethylene adipamide / polyhexamethylene isophthalamide copolymer (Nylon 66 / 6I), polyhexamethylene Terephthalamide / Polyhexamethylene isophthalamide copolymer (Nylon 6T / 6I), Polyhexamethylene terephthalamide / Polyundecaneamide copolymer (Nylon 6T / 11), Polyhexamethylene terephthalamide / Polydodecanamide copolymer (Nylon 6T / 12), Polyhexamethylene adipamide / Polyhexamethylene terephthalamide / Polyhexamethylene isophthalamide copolymer (Nylon 66 / 6T / 6I), Polyxylylene adipamide (Nylon XD6), Polyxylylene sebacamide (Nylon XD10), Poly Examples thereof include polyhexamethylene terephthalamide / polypentamethylene terephthalamide copolymer (nylon 6T / 5T), polyhexamethylene terephthalamide / poly-2-methylpentamethylene terephthalamide copolymer (nylon 6T / M5T), polypentamethylene terephthalamide / polydecamethylene terephthalamide copolymer (nylon 5T / 10T), polynonamethylene terephthalamide (nylon 9T), polydecamethylene terephthalamide (nylon 10T), and polydodecamethylene terephthalamide (nylon 12T).The symbol " / " indicates a copolymer. These polyamides may be used singly or in combination. Among these, it is preferable to use one selected from the group consisting of polyamide 6, polyamide 66, polyamide 46, polyamide 610, and polyamide 612, with polyamide 66 being particularly preferable. Polyamide 66 itself is a commonly known polyamide resin, typically produced by polycondensation of hexamethylenediamine and adipic acid. Alternatively, polyamide 66 may be a copolymer containing less than 30% by mass of at least one monomer unit selected from the group consisting of lactams, aminocarboxylic acids, and combinations of other diamines and dicarboxylic acids, based on the total mass of all monomer units.

[0015] These polyamides may be commercially available or may be produced by known methods. Specific methods for producing polyamides are not particularly limited, but examples thereof include ring-opening polymerization of lactams, self-condensation of ω-aminocarboxylic acids, and condensation of diamines and dicarboxylic acids.

[0016] Furthermore, the polyamide has a value obtained by dividing the amount of amino terminal groups by the amount of carboxy terminal groups [NH ２ ] / [COOH] is preferably 0.5 or more and 0.9 or less. ２ When the ratio of [COOH] / [COOH] is within the above range, the interaction between the surface of the glass fiber and the polyamide terminal becomes sufficiently large during melt kneading, and the physical properties of the resulting composition become sufficiently high. １ It can be measured using H-NMR.

[0017] The mass ratio of the polyamide relative to 100% by mass of the first polyamide solid is preferably 70 to 100% by mass, more preferably 80 to 99% by mass, even more preferably 90 to 98% by mass, and may even be 100% by mass. The polyamide solid may contain one or more types of polyamide. The resin component of the first polyamide solid is preferably polyamide alone, and the polyamide content is preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 99% by mass or more, relative to 100% by mass of the resin component. For example, impurities such as other resins or metals may be mixed, adhered, or coated onto the polyamide. If impurities other than the polyamide are present, a step of separating the polyamide from the impurities may be included. The separation method is not particularly limited; however, if the impurities are insoluble in the dissolved polyamide resin composition, they can be separated by methods such as filtration, centrifugation, or sedimentation. When the polyamide dissolves in the solvent, possible methods include separation by extraction in the dissolved state, membrane separation, electrodialysis, or the like, or washing after precipitating the polyamide.

[0018] The first polyamide solid is not particularly limited as long as it is a polyamide solid, and examples thereof include pellets, powder, pulverized pieces, granules, fibers, cloth, etc. The shape of the polyamide solid is also not particularly limited, and examples thereof include spheres, cylinders, polygonal pillars, fibers, etc.

[0019] (Solvent) Examples of the solvent include a metal chloride alcohol solution, a fluorine-based solvent such as hexafluoroisopropanol or trifluoroethanol, or an acidic solution such as formic acid or sulfuric acid, and the like, with a metal chloride alcohol solution being preferred. The metal chloride alcohol solution contains a metal chloride and a first alcohol, and may further contain other components. In particular, from the viewpoint of the solubility of polyamide, the total mass ratio of the metal chloride and the first alcohol to 100% by mass of the metal chloride alcohol solution is preferably 80% by mass or more, more preferably 90% by mass or more.

[0020] Examples of the first alcohol include methanol, ethanol, linear or branched propanol, linear or branched butanol, ethylene glycol, propylene diol, butane diol, and other diols, and combinations thereof. Among these, from the viewpoint of the solubility of polyamide, methanol, ethanol, or combinations thereof are preferred, and methanol is more preferred. The first alcohol may be one type or a combination of multiple types.

[0021] The mass ratio of the metal chloride relative to 100 mass% of the metal chloride alcohol solution is preferably 10 to 50 mass%, more preferably 15 to 35 mass%. If the mass ratio is less than 10 mass%, the amount of polyamide dissolved is small, requiring a large amount of solvent. If the mass ratio exceeds 35 mass%, the metal chloride is likely to remain undissolved and become mixed in as an impurity. If the mass ratio is 15 to 35 mass%, the solubility of the polyamide and the thickening caused by the metal chloride are well balanced, allowing for more efficient production of polyamide solids.

[0022] Examples of the metal chloride include zinc chloride, magnesium chloride, and calcium chloride, with zinc chloride and calcium chloride being preferred, and calcium chloride being most preferred. The metal chloride may be one type or a combination of multiple types. The mass ratio of water in the metal chloride alcohol solution is preferably 30 mass% or less, more preferably 15 mass% or less, and even more preferably 10 mass% or less. The metal chloride alcohol solution is preferably a solution in which the metal chloride is calcium chloride and the first alcohol is methanol.

[0023] In the step 1, when the first polyamide solid is dissolved in the solvent, the mass ratio of the first polyamide solid to 100 parts by mass of the solvent is preferably 5 to 15 parts by mass, more preferably 7 to 13 parts by mass, from the viewpoints of the solubility of the polyamide and handleability such as viscosity after dissolution.

[0024] In step 1, the first polyamide solid is preferably stirred after being dissolved in the solvent. The stirring temperature is preferably 30 to 90°C, more preferably 50 to 80°C, from the viewpoint of suppressing thermal degradation of the polyamide and decomposition due to the solvent and water contained therein, and suppressing further generation of black spots. The stirring time is preferably 5 minutes to 100 hours, more preferably 1 to 20 hours, and even more preferably 5 to 15 hours.

[0025] In the step 1, only the first polyamide solid and the solvent may be mixed, or other components may be mixed in. The ratio of the total mass of the first polyamide solid and the solvent to 100 parts by mass of all components added in the step 1 is preferably 90 parts by mass or more. In the step 1, the first polyamide solid, the solvent, and the other components may be added all at once or in multiple portions.

[0026] <Step 2> The step 2 may be carried out immediately after the step 1, or may be carried out after the polyamide solution obtained in the step 1 has been temporarily stored.

[0027] Methods for removing insoluble matters contained in the polyamide solution include filtration, centrifugation, sedimentation, and the like.

[0028] The filter used for the above filtration is preferably a filter made of polyethylene, polypropylene, polyester, polysulfone, polyethersulfone, polycarbonate, polystyrene, a cellulose derivative, an ethylene vinyl alcohol polymer, polyvinyl chloride, polylactic acid, polyurethane, polyphenylene sulfide, polyimide, polyvinylidene fluoride, polytetrafluoroethylene, or an acrylic resin, and from the viewpoint of filter stability, a polytetrafluoroethylene filter is more preferred.

[0029] The pore size of the filter used for the filtration is preferably 5 to 30 μm, more preferably 7 to 20 μm, even more preferably 8 to 15 μm, and particularly preferably 9 to 11 μm, from the viewpoint of easily removing black spots of a size that may affect physical properties.

[0030] The thickness of the filter used for the above filtration may be 0.1 to 3 mm.

[0031] The temperature during the filtration is preferably 10 to 80°C, more preferably 20 to 70°C, from the viewpoint of preventing thermal deterioration of the polyamide and efficiently removing insoluble matters.

[0032] The filtration is preferably pressure filtration, and the pressure during filtration is preferably 0.01 to 1 MPa from the viewpoint of filtration efficiency.

[0033] The filtration may be performed once or multiple times. Furthermore, filtration may be combined with a method for removing other insoluble matters.

[0034] After the filtration, a solvent may be added to the filter, and the solution that has passed through the filter may be mixed with the initial filtrate to obtain a polyamide solution from which insoluble matter has been removed. The solvent is preferably the same as the solvent used to dissolve the first polyamide solid when producing the polyamide solution. The amount of solvent added to the filter may be 0.01 to 0.5 times, or even 0.05 to 0.3 times, the mass of the polyamide solution initially added to the filter. A filter aid may also be present.

[0035] <Step 3> The step 3 may be carried out immediately after the step 2, or may be carried out after the insoluble matter-removed polyamide solution obtained in the step 2 has been temporarily stored.

[0036] Examples of methods for precipitating and recovering polyamide from the insoluble matter-removed polyamide solution include a method of diluting the insoluble matter-removed polyamide solution with a poor solvent followed by crystallization (crystallization), and a method of dropping the insoluble matter-removed polyamide solution into a large amount of poor solvent to precipitate (resedimentation).

[0037] (Crystallization) A method for recovering polyamide from the insoluble matter-removed polyamide solution by crystallization will be described.

[0038] Examples of poor solvents for diluting the insoluble matter-removed polyamide solution include water; chloroform; second alcohols such as alcohols such as methanol, ethanol, linear or branched propanol, and linear or branched butanol, and diols such as ethylene glycol, propylene diol, and butanediol; and combinations thereof. When the solvent in step 1 is a metal chloride alcohol solution, the poor solvent is preferably the same alcohol as the first alcohol contained in the metal chloride alcohol solution, from the viewpoint of facilitating solvent reuse. The poor solvent refers to a poor solvent for polyamide, and may be, for example, a solvent that, when 100 g of solvent is added to 1 g of polyamide (e.g., nylon 66) and stirred at 20°C for 1 hour, dissolves 0.05 g or less of polyamide in the solution.

[0039] The dilution ratio with the poor solvent is preferably 1 to 20 times, more preferably 2 to 10 times. Here, the dilution ratio is defined as the mass of the diluted solution (i.e., the total mass of the insoluble matter-removed polyamide solution and the poor solvent) divided by the mass of the insoluble matter-removed polyamide solution. In this case, even if precipitates are present in the diluted solution, the mass of the diluted solution includes the mass of the precipitates. If the dilution ratio is 1 time or more, particles grow, allowing the production of polyamide with a larger particle size. Furthermore, if the dilution ratio is 20 times or less, a polyamide with a narrow particle size distribution can be produced.

[0040] Dilution with a poor solvent may be carried out while heating. The temperature during dilution may be constant or may be changed within the following range. The temperature during dilution with a poor solvent is not particularly limited, but is preferably from the melting point of the solvent to 90°C. Dilution at a temperature exceeding 90°C is likely to cause non-uniform precipitation due to evaporation and condensation of the poor solvent near the liquid surface.

[0041] The dilution method is not particularly limited. Either a batch method or a continuous method may be used. In the case of a batch method, stirring is not particularly limited, but stirring is preferred. Stirring makes the temperature and concentration uniform.

[0042] After diluting the insoluble matter-removed polyamide solution with a poor solvent, the polyamide may be further precipitated by cooling. Stirring is preferred during cooling. Stirring makes the temperature and concentration uniform, facilitating particle size control. Depending on the equipment and method used for stirring, stirring is preferably performed under conditions that minimize particle destruction and shearing. The cooling rate is not particularly limited, but is preferably 10 to 100°C / Hr, more preferably 20 to 70°C / Hr, and even more preferably 40 to 68°C / Hr.

[0043] (Reprecipitation) A method of dropping the above-mentioned insoluble matter-removed polyamide solution into a poor solvent for precipitation will be described.

[0044] Examples of the poor solvent into which the insoluble matter-removed polyamide solution is dropped include water, chloroform, second alcohols such as alcohols such as methanol, ethanol, linear or branched propanol, linear or branched butanol, and diols such as ethylene glycol, propylene diol, butane diol, and combinations thereof. When the solvent in step 1 is a metal chloride alcohol solution, from the viewpoint of facilitating the reuse of the solvent, it is preferable that the poor solvent be the same alcohol as the first alcohol contained in the metal chloride alcohol solution.

[0045] From the viewpoint of polyamide yield and recovery efficiency, the mass of the poor solvent is preferably 1 to 2.5 times, more preferably 1 to 2 times, and even more preferably 1 to 1.5 times the mass of the insoluble matter-removed polyamide solution to be added. In recovering compounds by reprecipitation, using a large excess of poor solvent relative to the added solution usually results in a higher yield and improved filterability. However, in reprecipitation of polyamide using a solution in which polyamide is dissolved in a metal chloride alcohol solution, it has been found that dilution with a large excess of poor solvent significantly deteriorates filterability, and the filtration time increases, significantly reducing recovery efficiency. Furthermore, unlike conventional reprecipitation, when the ratio of poor solvent to polyamide is within the above range, particle properties are improved and filterability is dramatically improved. Furthermore, the yield is also good, and polyamide can be obtained efficiently.

[0046] The rate at which the insoluble matter-removed polyamide solution is added to the poor solvent is not particularly limited, and the appropriate rate varies depending on the type and amount of poor solvent. It is preferable that precipitation occurs immediately after addition; adding at such a high rate that precipitation is delayed after addition is undesirable because it deteriorates the filterability of the resulting solid. The rate of addition may be constant or may be changed during the addition. When the rate is changed during the addition, it is preferable to change it within the above range.

[0047] The addition may be continuous or divided into several portions. When the addition is divided into several portions, different poor solvents may be added, or the same poor solvent may be used. When the addition is divided into several portions, it is preferable that the addition speed in each addition is within the above range.

[0048] From the viewpoint of reprecipitation efficiency, the temperature of the poor solvent when the insoluble matter-removed polyamide solution is added is preferably not more than 10° C. higher than the temperature of the insoluble matter-removed polyamide solution to be added, more preferably not more than 5° C. higher, and even more preferably not more than 1° C. higher. The temperature may be within a range of room temperature (e.g., 20° C.) ±5° C.

[0049] To increase the purity, reprecipitation may be carried out multiple times. The multiple reprecipitations may be carried out under the same conditions or under different conditions.

[0050] (Solid-liquid separation) The precipitated solid is preferably recovered by solid-liquid separation. The method of solid-liquid separation is not particularly limited, but examples include filtration, centrifugation, sedimentation, etc. Either method may be a batch method or a continuous method.

[0051] The solid obtained by solid-liquid separation is preferably washed with a solvent. The washing solvent is preferably an alcohol such as methanol or ethanol, or water, or a combination thereof.

[0052] The washing method is not particularly limited, and examples thereof include a batch washing method, a continuous washing method in which a washing solvent is passed through a solid-liquid separator such as a filter or a centrifugal separator, and a combination thereof.

[0053] After washing, the polyamide is dried and solidified by distilling off the washing solvent under heating and / or reduced pressure, thereby obtaining a powdery polyamide.

[0054] <Step 4> The step 4 may be carried out immediately after the step 3, or may be carried out after the polyamide recovered in the step 3 has been temporarily stored.

[0055] Methods for obtaining the second polyamide solid include, for example, compression molding and extrusion granulation. The second polyamide solid is preferably a solid obtained as a powder compact by compression molding or extrusion granulation of the powder polyamide recovered in step 3. The second polyamide solid is preferably a powder compact obtained by pressing the polyamide powder without melting it. A polyamide powder powder compact can be formed by compression molding or extrusion granulation without heating. From the perspective of forming the second polyamide solid into a powder compact, the number of particles of 2 mm or less in the particles (granulation raw material) obtained in step 3 preferably accounts for 90% or more of the total number of particles, and preferably the number of particles of 1 mm or less accounts for 90% or more of the total number of particles. The particle size may be controlled by controlling the conditions for precipitation and solvent removal, or may be pulverized, sieved, or the like after solvent removal. The porosity within the second polyamide solid is preferably 20% or less, more preferably 15% or less, and even more preferably 10% or less, from the viewpoints of the strength of the solid and the suppression of bubbles when the solid is melted. On the other hand, a polyamide solid with too low a porosity may be in a molten state (heat generation due to local friction, etc.) due to some influence, raising concerns about deterioration. From this perspective, a porosity of 3% or more is preferable. While there are no particular limitations on the method for measuring the porosity, examples include mercury intrusion porosimetry and gas adsorption pore analysis. The porosity referred to here is the value obtained by dividing the pore volume in the polyamide solid by the volume of the polyamide solid, expressed as a percentage.

[0056] In the production method using extrusion granulation, for example, the granulation raw material containing the polyamide recovered in step 3 and other additives as needed is fed into an extrusion granulator, and the extrudate is cut and pelletized to produce a granulated product. Examples of the other additives include water, organic solvents, etc. Compounds having a boiling point equal to or lower than the boiling point of water are preferred, as they can be removed in the drying step of the pellets before the spinning step.

[0057] The temperature at which the polyamide recovered in step 3 is molded (for example, the temperature during extrusion granulation) is, from the viewpoint of suppressing the occurrence of black spots, a temperature below the melting point of the polyamide recovered in step 3, and is preferably 200° C. or lower, more preferably 20 to 150° C. It is acceptable for the temperature to deviate from the above temperature range locally and / or for a short period of time due to frictional heat during the molding process or the like.

[0058] Examples of extrusion granulators include screw-type extrusion granulators, roll-type extrusion granulators, disc pelleter-type extrusion granulators, pellet mill-type extrusion granulators, basket-type extrusion granulators, blade-type extrusion granulators, oscillating-type extrusion granulators, gear-type extrusion granulators, and ring die-type extrusion granulators.

[0059] The size of the second polyamide solid can be controlled by adjusting various parameters of the extrusion granulator. For example, in the case of a disc pelletizer, the size can be controlled by adjusting the disc rotation speed, etc.

[0060] The above-mentioned extrusion granulation is preferably performed using water and / or an organic solvent, from the viewpoint of reducing the load on the extrusion granulation apparatus and enabling a high processing speed. Water is preferred as the binder for wet granulation, from the viewpoint of eliminating the need for explosion-proof equipment. The mass of water added is preferably 5% by mass or more, more preferably 7% by mass or more, relative to 100% by mass of polyamide. Considering that the second polyamide solid will be used as a spinning raw material, it is preferable that it does not contain a binder at the time of use, and the binder is preferably volatile and added in an amount that is easy to remove after molding. From this viewpoint, the upper limit of the amount added is preferably 25% by mass or less, more preferably 15% by mass or less. When wet granulation is performed, it is preferable that the water and / or organic solvent used in wet granulation be removed after granulation. Methods for removing the water and / or organic solvent after granulation include, for example, drying at a temperature of 60 to 100°C under atmospheric or reduced pressure, or flowing an inert gas such as nitrogen through the mixture.

[0061] [Characteristics of the Second Polyamide Solid] The second polyamide solid is prepared by stirring 1 g of the second polyamide solid and 30 g of a solvent (e.g., a 20 wt % calcium chloride methanol solution) at 60°C for 12 hours, filtering the resulting solution under pressure (e.g., pressure filtration at a pressure of 0.01 MPa) using a separation material with a pore size of 10 μm (e.g., a PTFE membrane filter with a pore size of 10 μm), filtering 30 g of a solvent (e.g., an alcohol solution of a metal chloride such as a 20 wt % calcium chloride methanol solution) under pressure (e.g., pressure filtration at a pressure of 0.01 MPa), passing 100 g of methanol through the solution, and then vacuum drying at 50°C. Preferably, the number of insoluble particles with a major axis of 200 μm or less remaining on the separation material is 50,000 or less per 1 g of the second polyamide solid, and no insoluble particles with a major axis greater than 200 μm are present. The number of insoluble particles having a major axis of 200 μm or less remaining on the separation material is preferably 40,000 or less per gram of the second polyamide solid, more preferably 20,000 or less. Preferably, no insoluble particles having a major axis of more than 100 μm are present on the separation material, and preferably no insoluble particles having a major axis of more than 50 μm are present on the separation material. Note that the insoluble particles remaining on the separation material in the above-mentioned measurement method may be insoluble particles that could not be removed in the above-mentioned step 2, or insoluble particles such as black spots that occurred during molding to obtain the second polyamide solid.

[0062] The second polyamide solid is prepared by stirring 1 g of the second polyamide solid and 30 g of a solvent (e.g., a 20 wt % calcium chloride methanol solution) at 60°C for 12 hours, and then filtering the resulting solution under pressure (e.g., pressure filtration under a pressure of 0.01 MPa) using a separation material with a pore size of 10 μm (e.g., a PTFE membrane filter with a pore size of 10 μm), filtering 30 g of a solvent (e.g., an alcohol solution of a metal chloride such as a 20 wt % calcium chloride methanol solution) under pressure (e.g., pressure filtration under a pressure of 0.01 MPa), passing 100 g of methanol through the solution, and then vacuum drying at 50°C. The mass of insoluble matter remaining on the separation material is preferably 0.5 mass ppm or less, more preferably 0.4 mass ppm or less, and even more preferably 0.2 mass ppm or less, relative to 100 mass% of the second polyamide solid. The mass of the insoluble matter remaining on the separation material can be obtained by optically measuring the volume of the insoluble matter remaining on the separation material and calculating the mass of the insoluble matter based on the specific gravity of the second polyamide solid. Note that the insoluble matter remaining on the separation material in the above-mentioned measurement method may be insoluble matter that could not be removed in the above step 2, or insoluble matter such as black spots that occurred during molding to obtain the second polyamide solid.

[0063] [Polyamide Solid] The polyamide solid of the present embodiment may be, for example, the second polyamide solid obtained by the production method of the present embodiment described above, or may be a polyamide solid obtained by another method.

[0064] The polyamide solid of this embodiment is prepared by stirring 1 g of polyamide solid and 30 g of a solvent (e.g., a 20 wt % calcium chloride methanol solution) at 60°C for 12 hours, and then filtering the resulting solution under pressure (e.g., pressure filtration at a pressure of 0.01 MPa) using a separation material with a pore size of 10 μm (e.g., a PTFE membrane filter with a pore size of 10 μm), filtering 30 g of a solvent (e.g., an alcohol solution of a metal chloride such as a 20 wt % calcium chloride methanol solution) under pressure (e.g., pressure filtration at a pressure of 0.01 MPa), passing 100 g of methanol through the solution, and then vacuum drying at 50°C. Preferably, the number of insoluble particles with a major axis of 200 μm or less remaining on the separation material is 50,000 or less per 1 g of the polyamide solid, and no insoluble particles with a major axis greater than 200 μm are present. The number of insoluble particles having a major axis of 200 μm or less remaining on the separation material is preferably 40,000 or less per gram of the polyamide solid, more preferably 20,000 or less. Preferably, no insoluble particles having a major axis of more than 200 μm are present on the separation material, and more preferably no insoluble particles having a major axis of more than 50 μm are present. Polyamide fibers can be produced using the polyamide solid as a raw material.

[0065] The polyamide solid of this embodiment is prepared by stirring 1 g of polyamide solid and 30 g of a solvent (e.g., a 20 wt % calcium chloride methanol solution) at 60°C for 12 hours, and then filtering the resulting solution under pressure (e.g., pressure filtration at a pressure of 0.01 MPa) using a separation material with a pore size of 10 μm (e.g., a PTFE membrane filter with a pore size of 10 μm), filtering 30 g of a solvent (e.g., an alcohol solution of a metal chloride such as a 20 wt % calcium chloride methanol solution) under pressure (e.g., pressure filtration at a pressure of 0.01 MPa), passing 100 g of methanol through the solution, and then vacuum drying at 50°C. The mass of insoluble matter remaining on the separation material is preferably 0.5 ppm by mass or less, more preferably 0.4 ppm by mass or less, and even more preferably 0.2 ppm by mass or less, relative to 100% by mass of the polyamide solid. The mass of the insoluble matter remaining on the separation material can be obtained by optically measuring the volume of the insoluble matter remaining on the separation material and calculating the mass of the insoluble matter based on the specific gravity of the polyamide solid. Polyamide fibers can be produced using the second polyamide solid as a raw material.

[0066] In the second polyamide solid of this embodiment, the mass proportion of compounds having an amide bond and a molecular weight of 1,000 or less per 100% by mass of the polyamide solid is preferably 5,000 ppm by mass or less, more preferably 3,000 ppm by mass or less, and even more preferably 2,000 ppm by mass or less. Compounds having a molecular weight of 1,000 or less are known to volatilize at high temperatures and high surface areas during spinning, causing problems with deposition on spinning equipment, etc., and therefore it is preferable to reduce their content. Examples of compounds having a molecular weight of 1,000 or less and having an amide bond include oligomers formed by decomposition (e.g., hydrolysis) of polyamide. These oligomers may be either linear or cyclic, and may contain diamines, dicarboxylic acids, lactams, etc., that constitute the main polyamide component. GPC is preferably used as a method for quantifying molecular weights of 1,000 or less, as it allows simultaneous analysis of compounds having multiple molecular weights. For example, the molecular weight distribution can be determined using GPC equipped with a differential refractometer, and the concentration of components with a molecular weight of 1000 or less can be calculated from the ratio of the area with a molecular weight of 1000 or less to the total area. Among compounds having an amide bond with a molecular weight of 1000 or less, particularly highly volatile compounds are cyclic compounds composed of one or two monomer molecules (hereinafter referred to as cyclic monomers). For example, in the case of PA6, ε-caprolactam can be used, and in the case of PA66, 1,8-diazacyclotetradecane-2,7-dione (a cyclic condensation compound of hexamethylenediamine and adipic acid) can be used. The mass proportion of cyclic monomers in 100% by mass of polyamide solids is preferably 1000 ppm by mass or less, more preferably 200 ppm by mass or less, and even more preferably 100 ppm by mass or less. Methods for quantifying cyclic monomers are not particularly limited, but examples include LC. For example, the polyamide solid material may be analyzed using an LC equipped with a differential refractometer, a UV detector, a mass spectrum detector, etc., and quantified by a calibration curve method based on the peak area of ​​the corresponding component. The polyamide solid material having a mass proportion of 5000 mass ppm or less of the compound having an amide bond and a molecular weight of 1000 or less is preferably in the form of a compressed powder.The present inventors have discovered that conventional polyamide fiber production methods result in the accumulation of deposits within the melt spinning apparatus, reducing production efficiency. They have also discovered that these deposits are low-molecular-weight components of polyamide (e.g., oligomers) and that these low-molecular-weight components are contained in pellets produced by melt pelletizing, which are used as the raw material for spinning. The mechanisms by which the low-molecular-weight components are generated are thought to be that they are produced as by-products during polymerization and that the low-molecular-weight components are produced by hydrolysis due to moisture adhering to the pellets produced by melt pelletizing. The production method of this embodiment produces polyamide solids, which are the raw material for melt-proofing, by molding them at a temperature below the melting point of polyamide. This results in fewer low-molecular-weight components, less deposits accumulating within the spinning apparatus, and superior production efficiency for polyamide fibers.

[0067] [Method for Producing Polyamide Fibers] The method for producing polyamide fibers of this embodiment preferably uses the second polyamide solid obtained by the above-described method for producing polyamide fibers of this embodiment as a raw material. The method for producing polyamide fibers of this embodiment preferably includes the following steps 1 to 5: Step 1: Dissolving the first polyamide solid as a raw material in a solvent to obtain a polyamide solution; Step 2: Removing insoluble matter from the polyamide solution to obtain an insoluble-matter-removed polyamide solution; Step 3: Precipitating and recovering polyamide from the insoluble-matter-removed polyamide solution; Step 4: Molding the polyamide recovered in step 3 at a temperature below the melting point of the polyamide to obtain a second polyamide solid; and Step 5: Melt-spinning the second polyamide solid as a raw material. Steps 1 to 4 include the steps described above.

[0068] (Spinning of polyamide fiber) The second polyamide solid can be used as a raw material for spinning (preferably melt spinning) to form a polyamide fiber. The spinning temperature in melt spinning is preferably 290°C or higher and 310°C or lower. Setting the spinning temperature to 310°C or lower is preferred because thermal decomposition of the polyamide can be suppressed, more preferably 300°C or lower, and even more preferably 295°C or lower. On the other hand, a spinning temperature of 290°C or higher is preferred because the polyamide exhibits sufficient melt fluidity, the discharge amount between the nozzles is made uniform, and high-magnification drawing is possible.

[0069] The shorter the residence time in the melt spinning step (the time from when the polyamide resin is melted until it is discharged from the spinneret), the better. The residence time is preferably 30 minutes or less, more preferably 15 minutes or less, and even more preferably 0.5 minutes to 7 minutes. A short residence time is preferable because cyclopentanones in the polymer increase at the melting temperature.

[0070] To ensure thermal stability in high-temperature, high-humidity environments, it is preferable to add a copper compound to the polyamide (e.g., the polyamide contained in the second polyamide solid) so that the copper concentration is 1 to 500 ppm by mass, more preferably 30 to 500 ppm by mass. This effectively prevents deterioration of mechanical performance, even when the polyamide is left in a high-temperature, high-humidity environment for a long period of time or exposed to an environment containing a large amount of ozone for a long period of time. If the copper content is less than 30 ppm by mass, the heat strength retention rate decreases, and if the amount added exceeds 500 ppm by mass, the strength decreases. The method for adding the copper compound is not particularly limited, but examples include a method in which the copper compound is impregnated into the polyamide during washing in step 3, a method in which the copper compound is added in the form of a copper compound solution during solvent removal and then the solvent is distilled off, and a method in which the copper compound is mixed with the solvent added during granulation.

[0071] The copper compound is not particularly limited in type, and for example, organic copper salts such as copper acetate, or copper halides such as cuprous chloride and cupric chloride can be preferably used. It is more preferable to use the copper compound in combination with a metal halide compound. Examples of metal halide compounds include potassium iodide, potassium bromide, and potassium chloride. Preferred combinations in this embodiment are cuprous iodide and potassium iodide, and copper acetate and potassium iodide. The copper content in the polyamide can be measured by atomic absorption spectrometry, colorimetry, or the like.

[0072] Stabilizers that may be added include, but are not limited to, organic antioxidants such as hindered phenol antioxidants, sulfur-based antioxidants, and phosphorus-based antioxidants, heat stabilizers, light stabilizers such as hindered amines, benzophenones, and imidazoles, and ultraviolet absorbers. The amount of additive may be selected appropriately, and can be added in an amount of 1 to 1,000 ppm by mass based on the polyamide. These additives may be used singly or in combination of several types.

[0073] In the melt spinning step, a single-screw or twin-screw extruder is preferably used in the melting section, which allows the polyamide resin to be guided to a polymer pipe, a gear pump, and a spinning pack while applying an appropriate pressure to the polyamide resin.

[0074] In addition, filtering the polyamide resin using a metal fiber nonwoven filter, sand, or the like before it is discharged from the spinneret is preferable because it stabilizes the spinning operation. The shape of the spinneret holes may be selected depending on the cross-sectional shape of the single fibers that constitute the filaments to be produced. The spun yarn from the spinneret is solidified with cooling air, a process oil is applied, and the yarn is taken up, stretched, and heat-treated to obtain a polyamide fiber.

[0075] The oil adhesion rate of the polyamide fiber is preferably 0.5 to 1.5 wt%. If the oil adhesion rate is 1.5 wt% or less, the weft yarn hardly has difficulty flying due to stickiness (tackiness), and the weft yarn transport medium, air or water, does not lose its weft transport force due to a reduction in apparent cross-sectional area caused by the single yarn bundle being too good compared to the single yarn bundle caused by entanglement, resulting in good weaving stability. On the other hand, if the oil adhesion rate is 0.5 wt% or more, the weft yarn is supplied smoothly due to an appropriate friction reduction effect, resulting in excellent productivity without weaving stoppages.

[0076] The polyamide fiber preferably contains 5,000 ppm by mass or less of compounds having an amide bond and a molecular weight of 1,000 or less. The mass proportion of compounds having an amide bond and a molecular weight of 1,000 or less in the polyamide fiber can be measured by the method described above. The mass proportion of cyclic monomers in 100% by mass of polyamide solids is preferably 1,000 ppm by mass or less, more preferably 200 ppm by mass or less, and even more preferably 100 ppm by mass or less.

[0077] (Polyamide base fabric) In weaving, a water jet loom, an air jet loom, a rapier loom, or the like can be used as a loom. The airbag base fabric is a high-density woven fabric, and it is preferable to increase the warp tension in the warping process and the weaving process to produce a fabric with good processability. A high-density woven fabric is formed by setting the warp tension high in weaving and creating effective beating conditions.

[0078] The woven fabric can be subjected to a scouring process to wash off the process oil from the polyamide fiber. The scouring process can be performed using warm water or hot compressed water, and the treatment process may be a one-stage or multi-stage treatment consisting of two or more stages. It is also preferable to perform scouring by applying a conventionally known scouring agent.

[0079] The woven fabric is preferably heat-set in a heat-setting step. The heat-setting temperature is preferably 110°C or higher and 200°C or lower, and the heat-setting time may be appropriately selected from the range of 0.1 minutes to 30 minutes. In the heat-setting step, the woven fabric is preferably dried under tension so that the shrinkage force of the fabric is maintained at a predetermined force. Heat-setting the woven fabric stabilizes the processability of the subsequent resin application step.

[0080] The woven fabric after the scouring step may be subjected to a drying treatment as needed before the heat setting step. The drying temperature is preferably in the range of 80°C to 130°C, more preferably 100°C to 120°C. The treatment time is preferably selected appropriately from 0.1 minutes to 30 minutes. The drying may be performed with the woven fabric in a relaxed state or in a tensioned state.

[0081] Polyamide base fabric can be used as an uncoated base fabric after being subjected to a heat setting process, but it may also be coated with a coating agent such as silicone or urethane, or heat laminated with a thin film.

[0082] Methods for coating the surface of a woven fabric include immersing the fabric in a resin solution bath and then removing excess resin by mangling, vacuuming, or even using a coating knife, bar coating using a comma coater, or spraying the resin using a spray device or forming device. Of these, knife coating is preferred from the viewpoint of applying a small amount of resin uniformly.

[0083] The coating amount is 5 g / m ２ More than 100g / m ２ It is preferable that the content is 10 g / m or less, and more preferably 10 g / m ２ 70g / m or more ２ More preferably 15 g / m or less ２ 30g / m or more ２ 5 g / m or less ２ The required airtightness can be obtained with an application amount of 100 g / m or more. ２ At the following application amounts, the coated fabric is flexible, easy to store, and the overall weight of the bag is reduced.

[0084] (Airbag) The airbag may be selected from commonly used airbags for the driver's seat, passenger seat, side (including inflatable curtains), rear seat, etc., and the cut shape of the airbag body may be circular, oval, elliptical, rectangular, polygonal, or a combination of these, as long as it satisfies the desired deployed shape. Stitch shapes include a single straight line or multiple parallel straight lines, zigzag, a combination of straight and zigzag, or straight and diagonal lines. Commonly used stitching methods, such as lockstitch and double chainstitch, may be used, and the stitch pitch may be selected from a range of 20 to 60 stitches per 10 cm. The thread thickness may be selected from a range of 420d to 3000d, and commercially available threads such as polyamide fiber, polyester fiber, vinylon fiber, aramid fiber, and glass fiber may be used.

[0085] The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples.

[0086] Example 1: 300 g of polyamide 66 pellets (Leona 1300S, Asahi Kasei Corporation, melting point 265°C) and 3 kg of 20 wt% calcium chloride methanol solution were added to a 5 L glass bottle containing a stirrer, placed in a 60°C water bath, and stirred with a magnetic stirrer for 12 hours to dissolve the polyamide 66, yielding a polyamide solution. The polyamide solution was then pressure-filtered through a pressure filter equipped with a 10 μm pore size PTFE membrane filter at 30°C and 0.01 MPa to obtain a filtrate. After filtration, 300 g of 20 wt% calcium chloride methanol solution was added to the pressure filter and pressure-filtered. This was combined with the previous filtrate to yield 3.56 kg of insoluble-removed polyamide solution. The recovered insoluble-removed polyamide solution was transferred to a 40 L stainless steel reactor equipped with a stirring blade, and 10.7 kg of methanol was added while stirring to obtain a polyamide (polyamide 66) solid precipitate. The resulting solid precipitate was collected by filtration using a 10 μm membrane filter. The filtered solid precipitate was thoroughly washed with water. The washed solid precipitate was dried by heating in a vacuum dryer at 80°C, yielding 296 g (yield 98.7%) of powdered polyamide 66. The same method was repeated to produce 2 kg of powdered polyamide. 200 g of water was added to 2 kg of the resulting powdered polyamide 66 and kneaded. The resulting kneaded mixture was pelleted using a disc pelletizer (F-5, manufactured by Dalton Co., Ltd.) to obtain 1,881 g of cylindrical polyamide molded bodies with an outer diameter of 3 mm and a length of 6 mm. No heating was performed during molding, but the maximum internal temperature during molding was 70°C. The product was dried by heating in a vacuum dryer at 80°C, yielding 1,787 g of polyamide molded bodies. The mass proportion of components having amide bonds and a molecular weight of 1,000 or less, determined by GPC, was 3,000 ppm by mass. On the other hand, the mass proportion of the cyclic monomer (1,8-diazacyclotetradecane-2,7-dione) quantified by LC method was 15 ppm by mass. The obtained polyamide molded product was dissolved under the conditions described below, and the membrane filter was observed under a microscope to count the number of insoluble particles with a major axis of 200 μm or less. The number of insoluble particles was found to be 12,000 particles / g PA66. Furthermore, there was no insoluble particle with a major axis of more than 200 μm on the membrane filter.The mass ratio of insoluble matter remaining on the membrane filter was 0.05 ppm by mass relative to 100% by mass of the polyamide molded product. All of the insoluble matter confirmed on the membrane filter was black foreign matter. Melt spinning was performed using 1 kg of the obtained polyamide molded product in a small spinning machine. This was performed continuously for 8 hours, and the volatile components were collected in water and analyzed by LC / MS. The amount of low molecular weight compounds was 50 ppm by mass relative to the polyamide. The mass ratio of components having an amide bond and a molecular weight of 1,000 or less, determined by GPC, was 2,900 ppm by mass. Meanwhile, the mass ratio of the cyclic monomer (1,8-diazacyclotetradecane-2,7-dione) quantified by LC / MS was 58 ppm by mass. The extrusion pressure increase during spinning was 0.1 MPa after 3 hours and 0.2 MPa after 8 hours.

[0087] Example 2 2 kg of powdered polyamide was produced in the same manner as in Example 1, except that the filter used to filter the polyamide solution was changed to a PTFE membrane filter with a pore size of 100 μm. 200 g of water was added to 2 kg of the resulting powdered polyamide 66 and kneaded. The resulting kneaded mixture was pelleted using a disc pelletizer (F-5, manufactured by Dalton Co., Ltd.) to obtain 1,880 g of cylindrical polyamide molded bodies with an outer diameter of 3 mm and a length of 6 mm. No heating was performed during molding, but the maximum internal temperature during molding was 70°C. The mixture was heated and dried in a vacuum dryer at 80°C to obtain 1,787 g of polyamide molded bodies. The mass proportion of components having an amide bond and a molecular weight of 1,000 or less, as determined by GPC, was 2,980 ppm by mass. Meanwhile, the mass proportion of the cyclic monomer (1,8-diazacyclotetradecane-2,7-dione), as determined by LC, was 16 ppm by mass. The resulting polyamide molded product was dissolved under the following conditions, and the membrane filter was observed under a microscope to count the number of insoluble particles with a major axis of 200 μm or less. The number of insoluble particles was 60,000 particles / g PA66. Furthermore, no insoluble particles with a major axis greater than 200 μm remained on the membrane filter. The mass ratio of insoluble particles remaining on the membrane filter was 0.25 ppm by mass relative to 100% by mass of the polyamide molded product. All insoluble particles observed on the membrane filter were black foreign matter. Melt spinning was performed using 1 kg of the resulting polyamide molded product using a small spinning machine. This was performed continuously for 8 hours, and the volatile components were collected in water and analyzed by LC / MS. The amount of low-molecular-weight compounds was 50 ppm by mass relative to the polyamide. The content of amide-bonded components with a molecular weight of 1,000 or less, as determined by GPC, was 3,000 ppm by mass. On the other hand, the mass proportion of the cyclic monomer (1,8-diazacyclotetradecane-2,7-dione) determined by LC / MS was 78 ppm by mass. The increase in extrusion pressure during spinning was 0.2 MPa after 3 hours and 0.34 MPa after 8 hours.

[0088] Example 3: 300 g of polyamide 66 pellets (Leona 1300S, Asahi Kasei Corporation, melting point 265°C) and 3 kg of HFIP (hexafluoroisopropanol) were added to a 5 L glass bottle containing a stirrer, placed in a 60°C water bath, and stirred with a magnetic stirrer for 12 hours to dissolve the polyamide 66, yielding a polyamide solution. The polyamide solution was then pressure-filtered through a pressure filter equipped with a 10 μm pore size PTFE membrane filter at a temperature of 30°C and a pressure of 0.01 MPa to obtain a filtrate. 300 g of HFIP was added to the pressure filter after filtration, and pressure-filtered. This was combined with the previous filtrate to obtain 3.56 kg of insoluble matter-removed polyamide solution. The recovered insoluble matter-removed polyamide solution was transferred to a 5 L stainless steel reactor equipped with a stirring blade and a condenser connected to a vacuum pump by a hose, and the HFIP was distilled off under reduced pressure and heating while stirring. The solids accumulated at the bottom were scraped out and heated and dried in a vacuum dryer at 80°C, yielding 294 g (yield 98.0%) of powdered polyamide. The same method was repeated to produce 2 kg of powdered polyamide. 200 g of water was added to 2 kg of the obtained powdered polyamide 66 and kneaded. The obtained powder was pelleted using a disc pelletizer (F-5, manufactured by Dalton Co., Ltd.) to obtain 1,881 g of cylindrical polyamide molded bodies with an outer diameter of 3 mm and a length of 6 mm. No heating was performed during molding, but the maximum internal temperature during molding was 70°C. The mixture was heated and dried in a vacuum dryer at 80°C, yielding 1,787 g of polyamide molded bodies. The mass proportion of components having an amide bond and a molecular weight of 1,000 or less, determined by GPC, was 10,000 ppm by mass. On the other hand, the mass proportion of the cyclic monomer (1,8-diazacyclotetradecane-2,7-dione) quantified by LC / MS was 9,000 ppm by mass. The obtained polyamide molded product was dissolved under the conditions described below, and the membrane filter was observed under a microscope to count the number of insoluble particles with a major axis of 200 μm or less. The number of insoluble particles was 13,000 particles / g PA66. Furthermore, there was no insoluble particle with a major axis greater than 200 μm on the membrane filter. Furthermore, the mass proportion of the insoluble particles remaining on the membrane filter was 0.06 ppm by mass relative to 100% by mass of the polyamide molded product.All of the insoluble matter confirmed on the membrane filter was black foreign matter. Melt spinning was performed using 1 kg of the obtained polyamide molded body in a small spinning machine. The spinning was performed continuously for 8 hours, and the volatile components were collected in water and analyzed by LC / MS. The amount of low molecular weight compounds was 800 ppm by mass relative to the polyamide. The mass proportion of components having an amide bond and a molecular weight of 1,000 or less, determined by GPC, was 11,000 ppm by mass. Meanwhile, the mass proportion of the cyclic monomer (1,8-diazacyclotetradecane-2,7-dione) quantified by LC / MS was 9,900 ppm by mass. The extrusion pressure increase during spinning was 0.1 MPa after 3 hours and 0.21 MPa after 8 hours.

[0089] (Comparative Example 1) Polyamide 66 pellets (Leona 1300S, Asahi Kasei Corporation, melting point 265°C) were melted and pelletized using an extruder set at 280°C to obtain pellets. The mass proportion of components having an amide bond and a molecular weight of 1000 or less, as determined by GPC, was 35,000 ppm by mass. Meanwhile, the mass proportion of cyclic monomers (1,8-diazacyclotetradecane-2,7-dione) quantified by LC / MS was 10,800 ppm by mass. The obtained pellets were dissolved under the conditions described below, and the membrane filter was observed under a microscope under the conditions described below. The number of insoluble particles with a major axis of 200 μm or less was counted, resulting in a number of insoluble particles of 120,000 particles / g PA66. In addition, insoluble particles with a maximum major axis of 230 μm were present on the membrane filter. The mass ratio of insoluble matter remaining on the membrane filter was 0.7 ppm by mass relative to 100% by mass of the polyamide molded body. All of the insoluble matter confirmed on the membrane filter was black foreign matter. Using 1 kg of the resulting pellets, melt spinning was performed using a small spinning machine. This was performed continuously for 8 hours, and the volatile components were collected in water and analyzed by LC / MS. The amount of low molecular weight compounds was 1,200 ppm by mass relative to the polyamide. The mass ratio of components having an amide bond and a molecular weight of 1,000 or less, determined by GPC, was 36,000 ppm by mass. Meanwhile, the mass ratio of the cyclic monomer (1,8-diazacyclotetradecane-2,7-dione) quantified by LC / MS was 9,900 ppm by mass. The extrusion pressure increase during spinning was 0.6 MPa after 3 hours and 2.0 MPa after 8 hours.

[0090] Comparative Example 2: The same procedure as in Example 1 was repeated, except that filtration to remove insoluble matter was not performed, to obtain 2 kg of powdered polyamide. 200 g of water was added to 2 kg of the obtained powdered polyamide 66 and kneaded. The obtained powder was pelleted using a disk pelletizer (F-5, manufactured by Dalton Co., Ltd.) to obtain 1,881 g of cylindrical polyamide molded products with an outer diameter of 3 mm and a length of 6 mm. Heating was not performed during molding, but the maximum internal temperature during molding was 70°C. Heat drying in a vacuum dryer at 80°C yielded 1,787 g of polyamide molded products. The mass proportion of components having an amide bond and a molecular weight of 1,000 or less, as determined by GPC, was 3,000 ppm by mass. Meanwhile, the mass proportion of the cyclic monomer (1,8-diazacyclotetradecane-2,7-dione), as quantified by LC / MS, was 15 ppm by mass. The resulting polyamide molded product was dissolved under the following conditions, and the membrane filter was observed under a microscope under the following conditions. The number of insoluble particles with a major axis of 200 μm or less was counted. The number of insoluble particles was 100,000 particles / g PA66. Furthermore, there were no insoluble particles with a major axis greater than 200 μm on the membrane filter. The mass ratio of insoluble particles remaining on the membrane filter was 0.4 ppm by mass relative to 100% by mass of the polyamide molded product. All insoluble particles observed on the membrane filter were black foreign matter. Melt spinning was performed using 1 kg of the resulting polyamide molded product using a small spinning machine. This was performed continuously for 8 hours, and the volatile components were collected in water and analyzed by LC / MS. The amount of low molecular weight compounds was 50 ppm by mass relative to the polyamide. The mass ratio of components having amide bonds and a molecular weight of 1,000 or less, determined by GPC, was 2,900 ppm by mass. On the other hand, the mass proportion of the cyclic monomer (1,8-diazacyclotetradecane-2,7-dione) determined by LC / MS was 80 ppm by mass. The increase in extrusion pressure during spinning was 0.4 MPa after 3 hours and 1.8 MPa after 8 hours.

[0091] [Evaluation] (GPC method) 10 mg of the polyamide molded product was dissolved in 10 mL of the following eluent, and GPC measurement was performed under the following conditions to measure the mass ratio of compounds having an amide bond and a molecular weight of 1,000 or less relative to 100 mass% of the amide molded product. Note that low molecular weight compounds refer to compounds with a molecular weight of 1,000 or less. Measurement equipment: HLC-8320GPC (manufactured by Tosoh Corporation) Column: TSKgel GMHHR-H(S) x 3 (4.6 mm I.D. x 15 cm) (manufactured by Tosoh Corporation) Eluent: HFIP (Na trifluoroacetate-5 mmol / L) Flow rate: 0.175 mL / min Column temperature: 40°C Detector: Differential refractometry (built into the analytical equipment) Standard substance: PMMA (LC / MS method) Measurement equipment: ACQUITY UPLC H-Class (manufactured by Waters Corporation) Column: ACQUITY UPLC HSS T3 1.8 μm 2.0 x 100 mm (manufactured by Waters Corporation) Eluent: A: 0.1% formalic acid-H ２ O, B: 0.1% formalic acid-AcCN 0 → 10 min A: 98% → 0% 10 → 15 min A: 0% 15 → 15.1 min A: 0 → 98% 15.1 → 25 min A: 98% Flow rate: 0.4 mL / min Column temperature: 30°C Detector: Single quadrupole mass spectrometer SQD2 (Waters) Ionization method: ESI Quantitative method: Calibration curve method

[0092] (Analysis of Insoluble Matter on Filter) 1 g of the obtained polyamide molded product and 30 g of a 20 wt % calcium chloride methanol solution were added to a 100 mL glass bottle containing a stirrer and stirred at 60 °C for 12 hours to dissolve the product, yielding a polyamide solution. The mixture was filtered under pressure at 0.01 MPa through a pressure filter equipped with a 10 μm pore size PTFE membrane filter. 30 g of a 20 wt % calcium chloride methanol solution was added to the filtered pressure filter and filtered under pressure at 0.01 MPa. Further, 100 g of methanol was passed through the filter thoroughly to wash out the calcium chloride methanol solution. The membrane filter was removed and dried in a vacuum dryer at 50 °C. The dried membrane filter was observed using a microscope (Keyence Corporation, VHX7000) under the following conditions, and the major axis and number of insoluble matter on the membrane filter were analyzed. The major axis of the insoluble matter refers to the longest diameter of each insoluble matter calculated by automatic analysis (automatic area measurement (particle measurement)). It is preferable to adjust the light unevenness appropriately depending on the brightness during measurement. A portion without obvious contamination (such as fibers from the product bag) is selected, and the average value of three measurements is used. - Observation conditions - Observation area is approximately 300,000 μm ２ The field of view was set at a magnification such that the black particles within the observation range were analyzed automatically as described above. Based on the major axis, each insoluble particle was assumed to be a sphere, and its volume was calculated. The weight was then calculated using the specific gravity of the polyamide (1.14 for polyamide 66). The color of the insoluble particles was determined visually by observing the image under the above conditions.

[0093]

[0094] The polyamide solid produced by the method for producing a polyamide solid of the present invention has few black spots and can be used as polyamide fibers for airbags and the like.

Claims

1. A method for producing a polyamide solid, comprising the following steps: step 1: dissolving a first polyamide solid as a raw material in a solvent to obtain a polyamide solution; step 2: removing insoluble matter contained in the polyamide solution to obtain an insoluble matter-removed polyamide solution; step 3: precipitating and recovering polyamide from the insoluble matter-removed polyamide solution; and step 4: molding the polyamide recovered in step 3 at a temperature below the melting point of the polyamide to obtain a second polyamide solid.

2. The method for producing a polyamide solid according to claim 1, wherein in step 4, the polyamide is compression molded or extrusion granulated to obtain a second polyamide solid which is a green compact.

3. A method for producing a polyamide solid according to claim 1, wherein, when a solution obtained by dissolving said second polyamide solid in a solvent is filtered and separated using a separation material having a pore size of 10 μm, the number of insoluble particles having a major axis of 200 μm or less remaining on the separation material is 50,000 or less per 1 g of said second polyamide solid, and no insoluble particles having a major axis of more than 200 μm exist.

4. A method for producing a polyamide solid according to claim 1, wherein when a solution obtained by dissolving the second polyamide solid in a solvent is filtered and separated using a separation material having a pore size of 10 μm, the mass of insoluble matter remaining on the separation material is 0.5 ppm by mass or less relative to 100% by mass of the second polyamide solid.

5. The method for producing a polyamide solid according to any one of claims 1 to 3, wherein the solvent for dissolving the first polyamide solid in step 1 is an alcohol solution of a metal chloride.

6. The method for producing a polyamide solid according to claim 3 or 4, wherein the solvent for dissolving the second polyamide solid is an alcohol solution of a metal chloride.

7. A method for producing a polyamide solid according to claim 4, wherein the mass of the insoluble matter is calculated by optically measuring the volume of the insoluble matter remaining on the separation material and based on the specific gravity of the second polyamide solid matter.

8. A polyamide solid, in which when a solution obtained by dissolving a polyamide solid in a solvent is filtered and separated using a separation material having a pore size of 10 μm, the number of insoluble particles having a major axis of 200 μm or less remaining on the separation material is 50,000 or less per 1 g of the polyamide solid, and no insoluble particles having a major axis larger than 200 μm are present.

9. A polyamide solid, in which when a solution obtained by dissolving a polyamide solid in a solvent is filtered and separated using a separation material having a pore size of 10 μm, the mass of insoluble matter remaining on the separation material is 0.5 ppm by mass or less relative to 100% by mass of the polyamide solid.

10. A method for producing polyamide fibers using the polyamide solid material according to claim 8 as a raw material.

11. A method for producing polyamide fibers using the polyamide solid material according to claim 9 as a raw material.

12. A method for producing polyamide fibers, comprising the following steps: step 1: dissolving a first polyamide solid as a raw material in a solvent to obtain a polyamide solution; step 2: removing insoluble matter contained in the polyamide solution to obtain an insoluble matter-removed polyamide solution; step 3: precipitating and recovering polyamide from the insoluble matter-removed polyamide solution; step 4: molding the polyamide recovered in step 3 at a temperature below the melting point of the polyamide to obtain a second polyamide solid; and step 5: melt spinning the second polyamide solid as a raw material.

13. The method for producing polyamide fibers according to claim 12, wherein in step 4, the polyamide is compression molded or extrusion granulated to obtain a second polyamide solid body which is a green compact.

14. The method for producing polyamide fibers according to claim 12 or 13, wherein the mass ratio of the compound having an amide bond and a molecular weight of 1,000 or less in the second polyamide solid is 5,000 ppm by mass or less.

15. The process according to claim 12 or 13, wherein the solvent for dissolving the first polyamide solid in step 1 is an alcohol solution of a metal chloride.

16. A polyamide solid, in which the mass ratio of a compound having an amide bond and a molecular weight of 1,000 or less is 5,000 ppm by mass or less.

17. The polyamide solid according to claim 16, which is in the form of a compact.

18. Polyamide fiber, in which the mass ratio of a compound having an amide bond and a molecular weight of 1,000 or less is 5,000 ppm by mass or less.

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