Method for producing powdered polyamide

Abstract

A production method of a powdery polyamide according to the present invention includes: step 1 for heating and dissolving a polyamide resin composition in a metal chloride-containing alcoholic solution containing a metal chloride and an alcohol to obtain a heated polyamide solution; step 2 for diluting the heated polyamide solution with the alcohol to obtain an alcohol-diluted solution; and step 3 for cooling the alcohol-diluted solution to precipitate the powdery polyamide. In the aforesaid step 1, the ratio by mass of the metal chloride is 23-35 mass% inclusive relative to 100 mass% of the metal chloride-containing alcoholic solution. In the aforesaid step 1, the heated polyamide solution contains 0.2-2.5 mol inclusive of water per mol of the metal chloride. In the aforesaid step 2, the heated polyamide solution is diluted without lowering the temperature thereof below 50°C.

Description

[Technical Field]

[0001] This invention relates to a method for producing powdered polyamide. In particular, the present invention (I) relates to a method for producing powdered polyamide. Preferably, it relates to a method for producing powdered polyamide with reduced waste liquid volume and energy usage. The present invention (II) relates to a method for producing recycled polyamide with reduced waste liquid volume. The present invention (III) relates to a method for producing recycled polyamide. More specifically, it relates to a method for producing recycled polyamide using a polyamide base fabric coated with silicone or the like as a raw material. The present invention (IV) relates to a methanol composition that can be used as a solvent with low metal corrosiveness and high polyamide solubility, a method for producing a polyamide composition using the same, a polyamide composition, and a powder. The present invention (V) relates to a method for producing polyamide. The present invention (VI) relates to a method for producing polyamide, a method for producing polyethylene terephthalate, and a method for producing polyamide and polyethylene terephthalate. The present invention (VII) relates to a method for producing recycled polyamide. More specifically, it relates to a method for producing recycled polyamide using a polyamide base fabric coated with urethane or the like as a raw material. [Background technology]

[0002] Regarding the present invention (I), polyamides, including nylon 6 and nylon 66, which are representative engineering plastics, have heat resistance and good mechanical properties, and are widely used in fibers, automobile parts, electrical product parts, etc., and are one of the irreplaceable materials in modern society.

[0003] In recent years, technological developments have been made regarding the recycling of plastics with the aim of conserving resources and achieving carbon neutrality, and polyamides are no exception.

[0004] Recycling can be broadly divided into two types: material recycling, which involves re-pelletizing molded polyamides, and chemical recycling, which reuses monomers through depolymerization. While material recycling raises concerns about unstable quality because the polymer degradation and additives contained in the molded product remain in the recycled polymer, it does not involve chemical reactions and requires fewer auxiliary materials, thus requiring less resources and energy. Therefore, material recycling is chosen when the use is fixed and the product is to be recycled. Furthermore, even before implementing chemical recycling, the process of removing additives and coatings from processed and used polyamides recovered from factories and markets goes through a similar process to material recycling to recover clean polyamides. Thus, material recycling technology is also a useful technology for chemical recycling. Furthermore, the particle properties of the resulting polyamide vary depending on the application. For example, to prevent scattering during powder handling, a large particle size is preferable, while from the viewpoint of processability and mixability with additives, uniform particles with a small particle size distribution are preferable. Technologies to control these properties are also required.

[0005] Furthermore, with respect to the present invention (II), polyamides, including nylon 6 and nylon 66, which are representative engineering plastics, possess heat resistance and good mechanical properties, and are widely used in fibers, automobile parts, and electrical product components, making them one of the irreplaceable materials in modern society.

[0006] In recent years, technological developments have been made regarding the recycling of plastics with the aim of conserving resources and achieving carbon neutrality, and polyamides are no exception.

[0007] Recycling methods are broadly classified into two types: material recycling, which involves re-pelletizing molded products, and chemical recycling, which involves depolymerizing polymers to reuse monomers. Material recycling raises concerns about unstable quality because the degradation of the polymer and additives contained in the molded product are carried over to the recycled polymer. However, it has the advantage of reducing resource and energy input because it does not involve chemical reactions and requires fewer auxiliary materials. Therefore, material recycling is chosen when the product is to be recycled for a fixed purpose. Furthermore, before implementing chemical recycling, processed and / or used polyamide molded products collected from factories or markets undergo a process to recover clean polyamide by removing additives, coatings, etc., similar to material recycling. Therefore, material recycling technology is also a useful technology for carrying out chemical recycling.

[0008] Physical methods for removing impurities from used polyamide molded articles to achieve a clean state include methods such as crushing the recovered molded articles and then separating them by specific gravity (Patent Document 1). Although this method can separate impurities with little energy, it is difficult to separate them if the polyamide and impurities are strongly bound together, for example, by mixing, bonding, and / or adhering. There are also methods that dissolve some or all of the unwanted impurities with a solvent and remove them. However, impurities are generally added to or coated onto the polyamide, and some or all of them are located inside the polyamide structure, making it difficult to completely dissolve the impurities with a solvent and separate them from the polyamide structure.

[0009] Another method involves dissolving the polyamide in the molded product with a solvent, removing insoluble impurities, and then precipitating and recovering the polyamide by some means. However, solvents capable of dissolving polyamide include strong acids such as formic acid and sulfuric acid, as well as expensive solvents such as HFIP, and many are not suitable for industrial use. An example of a solvent suitable for industrial use is the dissolution and recovery method using ethylene glycol (Patent Document 2). However, this method requires a very high temperature reaction, raising concerns about glycolysis of the polyamide, and also requires the complete removal and drying of the solvent from the sherbet-like solid, thus requiring a lot of energy in addition to the heating during the reaction. Therefore, as a method that can be carried out at low temperatures using general-purpose raw materials, there is also a method of dissolution using a calcium chloride solution of alcohol. For example, a method has been proposed in which a cloth-like polyamide molded product coated with silicone is treated with a methanol solution of calcium chloride to dissolve the polyamide, and then diluted with a large amount of water or methanol to obtain the target polyamide as a powder (Patent Document 3).

[0010] Furthermore, with respect to the present invention (III), polyamides, including nylon 6 and nylon 66, which are representative engineering plastics, possess heat resistance and good mechanical properties, and are widely used in fibers, automobile parts, electrical product parts, etc., making them one of the irreplaceable materials in modern society. Among these, nylon 66 is of particularly high importance in applications where heat resistance and durability in harsh environments are required.

[0011] In recent years, technological developments have been made regarding the recycling of plastics with the aim of conserving resources and achieving carbon neutrality, and polyamides are no exception.

[0012] Recycling is broadly classified into material recycling, which involves re-pelletizing once-formed materials, and chemical recycling, which involves reusing monomers through depolymerization. Although there are concerns that the quality of recycled polymers may not be stabilized in material recycling because the polymers in molded products deteriorate and the added components remain in the recycled polymers as they are, since it does not involve chemical reactions and requires few auxiliary raw materials, less resources and energy are required, so material recycling is selected when the application is fixed and circulated. Also, even before implementing chemical recycling, when removing additives, coatings, etc. from processed and used polyamides recovered from factories or the market, a process of recovering clean polyamides is required as in material recycling, so material recycling technology is also a useful technology for performing chemical recycling. As described above, since there are various contaminants in processed and used polyamides, it is necessary to change the recovery method depending on the application. The applications of polyamides are diverse, but one of the applications of nylon 66 is automotive applications where high safety is required. For example, it is used for parts around the engine that require high heat resistance and for the base fabric of airbags that require durability at the time of rupture. Among them, the base fabric of airbags is less deteriorated and suitable for material recycling. Not only used airbags but also scraps generated when parts are cut during the manufacture and sewing of the base fabric for airbags can be targets for recycling. Generally, the base fabric of an airbag is made by spinning nylon 66, weaving it into a woven fabric, and coating it with a silicone resin. Therefore, in order to materially recycle the airbag base fabric, it is necessary to separate this coating from nylon 66.

[0013] Regarding the present invention (IV), polyamides such as polyamide 6 and polyamide 66, which are typical engineering plastics, have heat resistance and good mechanical properties and are widely used in fibers, automotive parts, electrical product parts, etc., and are one of the materials that cannot be replaced in modern society.

[0014] In recent years, technological developments have been made regarding the recycling of plastics for the purpose of resource conservation and carbon neutrality, and polyamides are no exception. In particular, polyamide 66 (polyhexamethylene adipamide), which is one of the polyamides, has a large production volume and is one of the polyamides that should be preferentially recycled.

[0015] Recycling is broadly classified into material recycling, which involves re-pelletizing once-molded products, and chemical recycling, which involves reusing monomers through depolymerization. Although there are concerns that the quality may not be stabilized in material recycling because the degradation of the polymer contained in the molded product and the added components remain in the recycled polymer as they are, since it does not involve a chemical reaction and requires less auxiliary raw materials, less resources and energy are required, so material recycling is selected for cases where the use is fixed and circulated. Also, before implementing chemical recycling, when removing additives, coatings, etc. from processed and used polyamides recovered from factories or the market, a process of recovering clean polyamides is carried out in the same way as in material recycling, so material recycling technology is also a useful technology for carrying out chemical recycling.

[0016] Physical methods for making used polyamides clean by removing their contaminants include methods such as separating by specific gravity after crushing the recovered materials (Patent Document 1). Although this method can separate with less energy, it is difficult to separate when the polyamide and the contaminants are strongly bonded by mixing, joining, adhesion, etc., such as the coating of an airbag. Also, there is a method of dissolving and removing some or all of the unnecessary contaminants with a solvent. However, generally, contaminants are often added or applied to the polyamide, and some or all of them are present inside the structure of the polyamide, and it is difficult to dissolve all the contaminants.

[0017] Another method involves dissolving the polyamide in a solvent, removing impurities as insoluble matter, and then precipitating and recovering the polyamide by some means. However, many solvents used to dissolve polyamide are not suitable for industrial use, such as highly corrosive strong acids like formic acid and sulfuric acid, or hard-to-find solvents like HFIP. An example of a solvent that is easily usable industrially is the dissolution and recovery method using ethylene glycol (Patent Document 2). However, this method requires a very high temperature reaction, raising concerns about glycolysis of the polyamide, and also requires the complete removal and drying of the solvent from the sherbet-like solid, thus requiring a lot of energy in addition to the heating during the reaction. Therefore, as a method using low temperatures and readily available raw materials, there is also the method of dissolving with an alcohol solution of a metal chloride such as calcium chloride. For example, Patent Document 3 describes a method in which a polyamide cloth coated with silicone is treated with a methanol solution of calcium chloride to dissolve the polyamide, and the desired polyamide is obtained as a powder by diluting it with a large amount of water or methanol. While this method is considered very useful for recovering polyamides, calcium chloride methanol solution is highly corrosive, easily corroding common metals such as carbon steel and stainless steels like SUS304 and SUS316. Therefore, it cannot be used as a material for polyamide dissolution equipment utilizing calcium chloride methanol solution. Instead, it is necessary to use nickel-based alloys with high chlorine corrosion resistance, such as ALLOY C276, or equipment treated with non-metallic glass lining, rubber lining, or fluorine lining. In terms of material availability and processability, it is necessary to use readily available, general-purpose materials.

[0018] Furthermore, with respect to the present invention (V), polyamide resins exhibit excellent properties and are therefore used in the manufacture of various machines and parts, such as automobiles, machinery, and electrical and electronic components. In particular, polyamide resins are widely used as molding materials for sliding parts such as gears, cams, and bearings because of their excellent mechanical properties and wear resistance.

[0019] In recent years, technological developments have been made regarding the recycling of plastics with the aim of conserving resources and achieving carbon neutrality, and polyamides are no exception.

[0020] Recycling can be broadly divided into two types: material recycling, which involves re-pelletizing molded materials, and chemical recycling, which involves reusing monomers through depolymerization. While material recycling raises concerns about unstable quality because degraded polymers and additives from molded products remain in the recycled polymer, it does not involve chemical reactions and requires few auxiliary materials, thus requiring less resources and energy. Therefore, material recycling is chosen when the product is intended for a fixed use and is to be recycled. Furthermore, even before implementing chemical recycling, if additives, coatings, etc., are removed from processed and used polyamide-containing materials recovered from factories and markets, the process of recovering clean polyamide is carried out in the same way as material recycling. Therefore, material recycling technology is also a useful technology for carrying out chemical recycling.

[0021] For example, to prevent scattering when handling powder, it is preferable that the particle size is large, and from the viewpoint of processability and mixability with additives, it is preferable that the particles are uniform with a small particle size distribution. Technologies to control these are required. For example, one physical method for cleaning used polyamide by removing impurities is to dissolve the polyamide in a solvent, remove the impurities as insoluble matter, and then precipitate and recover the polyamide by some method. However, many solvents used to dissolve polyamide, such as strong acids like formic acid and sulfuric acid, or expensive solvents like HFIP, are not suitable for industrial use. An example of a solvent that is easy to use industrially is the dissolution and recovery method using ethylene glycol (Patent Document 2). However, the recovery method in Patent Document 2 requires a reaction at a very high temperature, which raises concerns about glycolysis of polyamide. Furthermore, since the solvent used must be completely removed and dried from the sherbet-like solid, it is thought that a lot of energy is required in addition to the heating during the reaction.

[0022] Therefore, as a method using low temperatures and readily available raw materials, there is also a method of dissolving the polyamide using a calcium chloride solution of alcohol. For example, Patent Document 3 discloses a method in which a polyamide cloth coated with silicone is treated with a methanol solution of calcium chloride to dissolve the polyamide, and the desired polyamide is obtained as a powder by diluting it with a large amount of water or methanol. However, while the method described in Patent Document 3 can obtain powdered polyamide, when diluted with a large amount of solvent, the precipitation rate changes due to changes in the dilution ratio over time, resulting in a wide particle size distribution. Conversely, adding the polyamide solution to a large amount of solvent is expected to reduce the particle size distribution, but increasing the dilution ratio to the point where compositional changes can be ignored requires a large amount of solvent, which poses a significant economic and environmental burden.

[0023] Furthermore, as a method for controlling precipitation without increasing the dilution ratio, there is a method such as recrystallization, which involves diluting with an aqueous methanol solution while heated and then allowing precipitation to occur through cooling, as described in Patent Document 4. However, the technology described in Patent Document 4 only examined the conditions for obtaining porous powder, and did not describe the crystallization conditions for obtaining good powder or the changes in particle size distribution due to that crystallization, so the optimal conditions remained unclear.

[0024] Furthermore, with respect to the present invention (VI), polyamide resins and polyethylene terephthalate resins exhibit excellent properties and are therefore used in the manufacture of various machines and parts, such as automobiles, machinery, and electrical and electronic components. Among these, polyamide resins are particularly excellent in mechanical properties and wear resistance, and are therefore widely used as molding materials for sliding parts such as gears, cams, and bearings.

[0025] In recent years, technological developments have been made regarding the recycling of plastics with the aim of conserving resources and achieving carbon neutrality, and polyamides and polyethylene terephthalate are no exception.

[0026] Recycling can be broadly divided into two types: material recycling, which involves re-pelletizing molded materials, and chemical recycling, which involves reusing monomers through depolymerization. While material recycling raises concerns about unstable quality because degraded polymers and additives from molded products remain in the recycled polymer, it does not involve chemical reactions and requires few auxiliary materials, thus requiring less resources and energy. Therefore, material recycling is chosen when the product is intended for a fixed use and is to be recycled. Furthermore, even before implementing chemical recycling, if additives, coatings, etc., are removed from processed and used polyamide-containing materials recovered from factories and markets, the process of recovering clean polyamide is carried out in the same way as material recycling. Therefore, material recycling technology is also a useful technology for carrying out chemical recycling.

[0027] As mentioned above, processed and used polyamides contain various impurities, so the recovery method needs to be changed depending on the application. Polyamides have a wide range of applications, but one application of nylon 66 is in the automotive industry where high safety is required. For example, it is used in engine components that require high heat resistance and in the base fabric of airbags that require durability when ruptured. Among these, the base fabric of airbags deteriorates less and is particularly suitable for material recycling. Not only used airbags, but also scraps generated when parts are cut off during the manufacturing and sewing of airbag base fabrics can be recycled.

[0028] Generally, the base fabric for airbags is made by spinning nylon 66 and polyethylene terephthalate, and then weaving them together either individually or partially mixed together to form a woven fabric. Therefore, in order to recycle airbag base fabric, it is necessary to separate the polyamide from the polyethylene terephthalate.

[0029] Here, physical methods for removing impurities from polyamide containing impurities to obtain a clean state include methods such as crushing the recovered material and then separating it by specific gravity (Patent Document 1). Although this method allows for separation with minimal energy, it is difficult to separate polyamide from airbag base fabrics where the polyamide and impurities are strongly bound together through mixing, bonding, or adhesion.

[0030] Furthermore, there are methods for dissolving and removing unwanted contaminants such as silicone using a solvent, either partially or completely (see, for example, Patent Document 6). However, since the silicone has permeated the polyamide fibers, silicone resin remains in the recovered polyamide. Furthermore, the recovered polyamide is recovered in the form of shredded cloth. Used airbags and manufacturing scraps come in various shapes, and it is difficult to reuse them in their original form or in the form of fiber scraps obtained by cutting them. Also, even if they are melted down and reused, they are unsuitable for feeding into extruders and other equipment.

[0031] Conversely to the method described above, another possible approach is to first dissolve the polyamide in a solvent, remove any impurities as insoluble matter, and then precipitate and recover the polyamide using some method. However, many solvents used to dissolve polyamides, such as strong acids like formic acid and sulfuric acid, or expensive solvents like HFIP, are not suitable for industrial use, raising concerns about the decomposition of polyethylene terephthalate. An example of a solvent that is easy to use industrially is a dissolution and recovery method using ethylene glycol (Patent Document 2). However, this method requires a very high temperature reaction, raising concerns about glycolysis of polyamide and polyethylene terephthalate. Furthermore, since the solvent used must be completely removed and dried from the sherbet-like solid state, it is thought that a great deal of energy will be required in addition to the heating during the reaction.

[0032] Therefore, as a method that uses low temperatures and readily available raw materials, there is also a method of dissolving alcohol in a calcium chloride solution. For example, Patent Document 3 describes a method for obtaining the desired polyamide as a powder by treating a polyamide cloth coated with silicone with a methanol solution of calcium chloride, dissolving the polyamide, and then diluting it with a large amount of water or methanol. However, problems became apparent when the silicone-coated polyamide base fabric was actually dissolved using the method described in Patent Document 3. Patent Document 3 states that it is preferable to use calcium chloride dihydrate, which has high polyamide solubility, or to add water equivalent to the hydrate in addition to anhydrous calcium chloride, and the reason for this is that the solubility of polyamide is high in that composition.

[0033] Furthermore, with respect to the present invention (VII), polyamides, including nylon 6 and nylon 66, which are representative engineering plastics, possess heat resistance and good mechanical properties, and are widely used in fibers, automobile parts, electrical product parts, etc., making them irreplaceable materials in modern society. Among these, nylon 66 is of particularly high importance in applications where heat resistance and durability in harsh environments are required.

[0034] In recent years, technological developments have been made regarding the recycling of plastics with the aim of conserving resources and achieving carbon neutrality, and polyamides are no exception.

[0035] Recycling can be broadly divided into two types: material recycling, which involves re-pelletizing molded polyamides, and chemical recycling, which reuses monomers through depolymerization. While material recycling raises concerns about unstable quality because the polymer degradation and additives contained in the molded product remain in the recycled polymer, it does not involve chemical reactions and requires fewer auxiliary materials, thus requiring less resources and energy. Therefore, material recycling is chosen when the use is fixed and the product is to be recycled. Furthermore, even before implementing chemical recycling, the process of removing additives and coatings from processed and used polyamides recovered from factories and markets goes through a similar process to material recycling to recover clean polyamides. Thus, material recycling technology is also a useful technology for chemical recycling. As mentioned above, processed and used polyamides contain various impurities, so the recovery method needs to be changed depending on the application. Polyamides have a wide range of applications, but one application of nylon 66 is in the automotive industry where high safety is required. For example, it is used in engine components that require high heat resistance and as the base fabric for airbags that require durability when ruptured. Among these, the base fabric for airbags deteriorates less and is particularly suitable for material recycling. Not only used airbags, but also scraps generated when parts are cut off during the manufacturing and sewing of airbag base fabrics can be recycled. Generally, the base fabric of airbags is made from spun and woven nylon 66, which is then coated with resin. Therefore, in order to recycle the airbag base fabric, it is necessary to separate this coating from the nylon 66. [Prior art documents] [Patent Documents]

[0036] [Patent Document 1] Patent No. 5841598 [Patent Document 2] Japanese Patent Publication No. 2018-172618 [Patent Document 3] Patent No. 5110704 [Patent Document 4] Japanese Patent Application Publication No. 60-233129 [Patent Document 5] Japanese Patent Application Publication No. 62-218421 [Patent Document 6] Patent No. 7024037 [Overview of the Initiative] [Problems that the invention aims to solve]

[0037] The present invention aims to efficiently produce powdered polyamide.

[0038] Regarding the present invention (I), physical methods for removing impurities from used polyamide to a clean state include methods of crushing the recovered material and then separating it by specific gravity (Patent Document 1). Although this method allows for separation with little energy, it is difficult to separate polyamide and impurities if they are strongly bound together by mixing, joining, or bonding. There are also methods of dissolving some or all of the unwanted impurities with a solvent and removing them. However, impurities are generally added to or coated on the polyamide, and some or all of them are located inside the polyamide structure, making it difficult to dissolve all of the impurities, and the resulting polyamide is in a crushed state, making it difficult to adequately control its shape, size, etc.

[0039] Another possible method involves dissolving the polyamide in a solvent, removing impurities as insoluble matter, and then precipitating and recovering the polyamide by some means. However, many solvents used to dissolve polyamide are not suitable for industrial use, such as strong acids like formic acid and sulfuric acid, or expensive solvents like HFIP. An example of a solvent that is easily usable industrially is the dissolution and recovery method using ethylene glycol (Patent Document 2). However, this method requires a reaction at a very high temperature, raising concerns about glycolysis of the polyamide. Furthermore, since the solvent used must be completely removed and dried from the sherbet-like solid, it is thought that a lot of energy is required in addition to the heating during the reaction.

[0040] Therefore, as a method using low temperatures and readily available raw materials, there is also a method of dissolving the polyamide using a calcium chloride solution of alcohol. For example, Patent Document 3 describes a method in which a polyamide cloth coated with silicone is treated with a methanol solution of calcium chloride to dissolve the polyamide, and the desired polyamide is obtained as a powder by diluting it with a large amount of water or methanol. When we investigated a method for producing polyamide powder using elution with a metal chloride alcohol solution, assuming industrial production, we found that while it is indeed possible to obtain polyamide powder free of impurities such as silicone, there are significant problems with industrial implementation. The polyamide powder precipitated from the solvent contains a large amount of solvent during precipitation, and the solvent that has penetrated the solid cannot be easily removed even by filtration or centrifugation. As a result, it is necessary to wash the powder repeatedly with large amounts of washing solvent to remove impurities such as metal chlorides from the solid. Furthermore, drying the powder after washing to remove the solvent also requires a large amount of energy, which is another problem. After diligently investigating this phenomenon, we determined that the cause of the large amount of solvent was the porosity of the particles. A method for controlling the porosity of polyamide is described in Patent Document 4. Patent Document 4 describes an invention in which porous particles can be obtained by dissolving polyamide in a metal chloride methanol solution, adding a methanol aqueous solution with a limited range of water to the heated polyamide solution, and then cooling and precipitating it. Dilution with methanol is given as an example of suppressing porosity, and the invention emphasizes that the solvent conditions for precipitation are important. Based on this invention, we conducted an investigation to suppress porosity, but although there was some suppression effect, porous solids were still obtained, and no significant effect was observed. From the standpoint of particle size control, although the method described in Patent Document 3 can obtain powdered polyamide, when diluted with a large amount of solvent, the precipitation rate changes due to changes in the dilution ratio over time, resulting in a broad particle size distribution. Conversely, adding the polyamide solution to a large amount of solvent is expected to reduce the particle size distribution, but if the dilution ratio is increased to the point where compositional changes can be ignored, a large amount of solvent is required, resulting in a significant economic and environmental burden.

[0041] One method for controlling precipitation without increasing the dilution ratio is recrystallization, which involves diluting with a methanol aqueous solution under heating and then cooling to precipitate, as described in Patent Document 4. However, Patent Document 4 only discusses the conditions for obtaining porous powder and does not describe the crystallization conditions for obtaining good powder or the changes in particle size distribution due to crystallization, so the optimal conditions remain unclear.

[0042] Furthermore, Patent Document 5 describes a method for obtaining powder by dissolving polyamide at a high temperature of 130°C or higher under pressure and slowly cooling it at 3-20°C / hr. However, even at this temperature, there is a concern that polyamide may decompose slightly due to alcohol, and that additives may leach out from impurities, so high-temperature processing is undesirable. In addition, slow cooling takes a long time, making it unsuitable as an industrial process.

[0043] Therefore, an object of the present invention (I) is to provide a method for producing powdered polyamide that suppresses porosity and reduces the amount of solvent contained, thereby reducing the amount of waste liquid and the energy required for drying. Furthermore, it is preferable to provide a method for producing powdered polyamide that has a large particle size and a small particle size distribution in a short time.

[0044] In relation to the present invention (II), the polyamide recovered from the polyamide molded article is molded again after adjusting the composition of additives, etc., so it is desirable that it be free of impurities. If the impurities are organic compounds, washing with a washing solution such as an organic solvent is necessary, and for washing inorganic compounds, washing with water and / or a washing solution containing water is preferred. In particular, when the dissolution process is carried out with a methanol solution of calcium chloride, the calcium chloride used as the solvent, potassium and other metals such as copper which are additives to the polyamide must be thoroughly removed in the washing process, and considering their solubility, it is preferable to wash the polyamide with water in the end.

[0045] The present inventors attempted to recover polyamide using the method described in Patent Document 3, which involves treating a polyamide molded article with a methanol solution of calcium chloride. Although the polyamide was recovered, they found that a specific phenomenon occurred during filtration. Specifically, the precipitated polyamide contained a large amount of solvent (including water, methanol, and calcium chloride methanol solution). The amount of impurities that can be removed in a single wash is determined by the dilution ratio obtained by diluting the solvent contained in the precipitated polyamide with the washing solution. Therefore, if the amount of solvent contained in the precipitated polyamide is large, the amount of washing solution (typically water) must also be increased proportionally, and as a result, the efficiency of impurity removal is greatly reduced.

[0046] Furthermore, removing the solution (especially water) that has penetrated and stabilized within the polyamide particles by heating and vacuum drying requires a great deal of energy, and the increasing amount of solution contained in the polyamide particles places a very significant burden on the process.

[0047] Therefore, an object of the present invention (II) is to provide a method for producing recycled polyamide with reduced waste liquid volume.

[0048] Regarding the present invention (III), physical methods for removing impurities from polyamide containing impurities to a clean state include methods of crushing the recovered material and then separating it by specific gravity (Patent Document 1). Although this method allows for separation with little energy, it is difficult to separate the polyamide and impurities in the case of airbag base fabrics where the polyamide and impurities are strongly bound together by mixing, joining, or bonding.

[0049] Furthermore, there are methods to dissolve and remove some or all of unwanted contaminants such as silicone using a solvent (for example, Patent Document 6). However, since the silicone is impregnated into the polyamide fibers, silicone resin remains in the recovered polyamide. Also, the recovered polyamide is recovered in the form of crushed cloth. Used airbags and manufacturing scraps come in various shapes, and it is difficult to reuse them as they are, or in the form of fiber scraps obtained by cutting them. Moreover, even if they are melted and reused, they are unsuitable for feeding into extruders and the like.

[0050] Conversely to the method described above, another possible method involves dissolving the polyamide in a solvent, removing impurities as insoluble matter, and then precipitating and recovering the polyamide by some means. However, many solvents used to dissolve polyamide are not suitable for industrial use, such as strong acids like formic acid and sulfuric acid, or expensive solvents like HFIP. An example of a solvent that is easily usable industrially is the dissolution and recovery method using ethylene glycol (Patent Document 2). However, this method requires a reaction at a very high temperature, raising concerns about glycolysis of the polyamide. Furthermore, since the solvent used must be completely removed and dried from the sherbet-like solid, it is thought that a lot of energy is required in addition to the heating during the reaction.

[0051] Therefore, as a method using low temperatures and readily available raw materials, there is also a method of dissolving the polyamide using a calcium chloride solution of alcohol. For example, Patent Document 3 describes a method in which a polyamide cloth coated with silicone is treated with a methanol solution of calcium chloride to dissolve the polyamide, and the desired polyamide is obtained as a powder by diluting it with a large amount of water or methanol. However, problems became apparent when the silicone-coated polyamide base fabric was actually dissolved using the method described in Patent Document 3. Patent Document 3 states that it is preferable to use calcium chloride dihydrate, which has high solubility for polyamide, or to add water equivalent to the hydrate in addition to anhydrous calcium chloride, and the reason for this is that the solubility of polyamide is high in that composition.

[0052] However, when we actually attempted to dissolve the polyamide using a polyamide base fabric, a problem became apparent: the recovery rate was low. Even when trying to dissolve polyamide at a saturation solubility of about 23% in the given solvent composition, if the base fabric had a certain surface area, it was impossible to dissolve and recover all of the polyamide due to the fabric sticking together or wrapping around itself. The dissolved supernatant was also cloudy and, although fluid, could not be considered fully dissolved. To increase the yield, one method is to crush the base fabric beforehand, but in that case, tiny fragments of silicone resin would disperse in the liquid, making their recovery from the solution extremely difficult.

[0053] The object of the present invention (III) is to provide a method for efficiently producing recycled polyamide from a silicone-coated polyamide base fabric in high yield.

[0054] With respect to the present invention (IV), the object of the present invention (IV) is to provide a solvent that has low metal corrosiveness and high solubility of polyamides.

[0055] With respect to the present invention (V), as described above, the techniques of Patent Documents 2 to 4 had room for further improvement as a method for recovering polyamide with high efficiency and high yield.

[0056] Furthermore, as described in Patent Document 3, when polyamide is dissolved using an alcohol-based calcium chloride solution, it is common practice to precipitate the polyamide, recover it, and then wash the recovered polyamide. However, when washing the recovered polyamide, it is preferable to avoid excessive washing from the standpoint of manufacturing efficiency, cost, and environmental considerations. On the other hand, if the recovered polyamide is not washed sufficiently, there is a problem in that some of the polyamide melts due to metal chlorides adhering to the polyamide after washing, and then solidifies during subsequent drying.

[0057] Therefore, an object of the present invention (V) is to provide a method for producing polyamide that allows for the recovery of polyamide with high efficiency and high yield, and that enables the production of high-quality polyamide without excessive washing.

[0058] With respect to the present invention (VI), as described above, the techniques of Patent Documents 1 to 3 and 6 had room for further improvement as a method for recovering polyamide with high efficiency and high yield.

[0059] Furthermore, when the airbag base fabric is a mixture of polyamide and polyethylene terephthalate, the base fabric has a certain surface area, and due to the base fabric sticking together or wrapping around itself, it is difficult to efficiently recover the polyamide and polyethylene terephthalate, resulting in a low recovery rate. To increase the yield, one could consider crushing the base fabric beforehand, but this would complicate the process, and there was also the concern that polyethylene terephthalate fragments would disperse in the liquid, making recovery extremely difficult.

[0060] Therefore, an object of the present invention (VI) is to provide a method for producing polyamide, a method for producing polyethylene terephthalate, and a method for producing polyamide and polyethylene terephthalate, which can recover polyamide and / or polyethylene terephthalate from a mixture of polyamide and polyethylene terephthalate with high efficiency and high yield.

[0061] Regarding the present invention (VII), physical methods for removing impurities from polyamide containing impurities to a clean state include methods of crushing the recovered material and then separating it by specific gravity (Patent Document 1). Although this method can separate the materials with little energy, it is difficult to separate them in the case of airbag base fabrics where the polyamide and impurities are strongly bound together by mixing, joining, or bonding.

[0062] Furthermore, there are methods to dissolve and remove some or all of the unwanted coating resin and other impurities using a solvent (for example, Patent Document 6). However, since the coating resin is impregnated into the polyamide fibers, the coating resin remains in the recovered polyamide. Also, the recovered polyamide is recovered in the form of crushed cloth. Used airbags and manufacturing scraps come in various shapes, and it is difficult to reuse them as they are, or in the form of fiber scraps obtained by cutting them. Moreover, even if they are melted and reused, they are unsuitable for feeding into extruders and the like.

[0063] Conversely to the method described above, another possible method involves dissolving the polyamide in a solvent, removing impurities as insoluble matter, and then precipitating and recovering the polyamide by some means. However, many solvents used to dissolve polyamide are not suitable for industrial use, such as strong acids like formic acid and sulfuric acid, or expensive solvents like HFIP. An example of a solvent that is easily usable industrially is the dissolution and recovery method using ethylene glycol (Patent Document 2). However, this method requires a reaction at a very high temperature, raising concerns about glycolysis of the polyamide. Furthermore, since the solvent used must be completely removed and dried from the sherbet-like solid, it is thought that a lot of energy is required in addition to the heating during the reaction.

[0064] Therefore, as a method using low temperatures and readily available raw materials, there is also a method of dissolving the polyamide using a calcium chloride solution of alcohol. For example, Patent Document 3 describes a method in which a polyamide cloth coated with a coating resin is treated with a methanol solution of calcium chloride to dissolve the polyamide, and the desired polyamide is obtained as a powder by diluting it with a large amount of water or methanol. However, problems became apparent when the resin-coated polyamide base fabric was actually dissolved using the method described in Patent Document 3. Patent Document 3 states that it is preferable to use calcium chloride dihydrate, which has high solubility for polyamide, or to add water equivalent to the hydrate in addition to anhydrous calcium chloride, and the reason for this is that the solubility of polyamide is high in that composition.

[0065] However, when we actually attempted to dissolve the polyamide using polyamide fabric, a problem became apparent: the recovery rate was low. Even when trying to dissolve polyamide at a saturation solubility of about 23% in the solvent composition, if the fabric had a certain surface area, it was impossible to dissolve and recover all of the polyamide due to the fabric sticking together or wrapping around itself. The supernatant after dissolution was also cloudy and, although fluid, could not be considered fully dissolved. To increase the yield, one method is to crush the fabric beforehand, but in that case, tiny fragments of the coating resin would disperse in the liquid, making their recovery from the solution extremely difficult.

[0066] The object of the present invention (VII) is to provide a method for efficiently producing recycled polyamide in high yield from a urethane-coated polyamide base fabric. [Means for solving the problem]

[0067] With respect to the present invention (I), we diligently pursued research using an approach different from the prior art, and surprisingly, we discovered that the solution composition during dissolution has a greater influence on porosity than the composition during precipitation. We found that by setting the solution composition during dissolution within a specific range, we could suppress the porosity of the polyamide powder and significantly reduce the amount of solvent contained during precipitation, thus completing the invention.

[0068] In other words, the present invention (I) is as follows: [1] Step 1: A step to obtain a heated polyamide solution by heating and dissolving the polyamide resin composition in a metal chloride alcohol solution containing metal chloride and alcohol. Step 2: A step of diluting the heated polyamide solution with alcohol to obtain an alcoholic diluted solution, and Step 3: A step of cooling the alcohol dilution to precipitate the powdered polyamide. Includes, In step 1, the mass ratio of metal chloride to 100% by mass of the metal chloride alcohol solution is 23% by mass or more and 35% by mass or less; in step 1, the heated polyamide solution contains 0.2 moles or more and 2.5 moles of water per mole of metal chloride; and in step 2, the heated polyamide solution is diluted without lowering its temperature below 50°C. A method for producing powdered polyamide, characterized by the following features. [2] Step 1: A step to obtain a heated polyamide solution by heating and dissolving the polyamide resin composition in a metal chloride alcohol solution containing metal chloride and alcohol. Step 2: A step of diluting the heated polyamide solution with alcohol to obtain an alcoholic diluted solution, and Step 3: A step of cooling the alcohol dilution to precipitate the powdered polyamide. Includes, In step 1, the mass ratio of metal chloride to 100% by mass of the metal chloride alcohol solution is 23% by mass or more and 35% by mass or less; in step 1, the heated polyamide solution contains 0.2 moles or more and 2.5 moles of water per mole of metal chloride; and in step 2, the mass of polyamide precipitated is 1% by mass or less of the total mass of polyamide contained in the heated polyamide solution. A method for producing powdered polyamide, characterized by the following features. [3] A method for producing recycled polyamide using a polyamide resin composition containing a polyamide coated with a silicone resin as a raw material, The process includes a dissolution step in which the polyamide is dissolved to obtain a polyamide solution by mixing a metal chloride alcohol solution containing metal chloride and alcohol with the polyamide resin composition. In the dissolution step, the mass percentage of polyamide in the polyamide solution is 5 to 15% by mass. A method for producing recycled polyamide, characterized by the following features. [4] A methanol composition containing 5-25% of a metal chloride, 0.001-1% of the same metal hydroxide, and 0.001-5% of water. [5] A method for producing polyamide, comprising recovering polyamide from a mixture containing at least polyamide and polyethylene terephthalate, The process involves mixing the aforementioned mixture with a metal chloride alcohol solution containing metal chlorides and alcohols to obtain a polyamide solution in which the polyamide is dissolved, The process of separating and recovering the polyamide solution, A method for producing polyamide, characterized by containing the following: [6] A method for producing recycled polyamide using a mixture containing a polyamide coated with urethane resin as a raw material, The process includes a dissolution step in which a polyamide is dissolved by mixing a metal chloride alcohol solution containing a metal chloride and an alcohol with the aforementioned mixture to obtain a polyamide solution. In the dissolution step, the mass percentage of polyamide in the polyamide solution is 5 to 15% by mass. A method for producing recycled polyamide, characterized by the following features. [7] The method for producing powdered polyamide according to [1] or [2], further comprising step 4: washing the powdered polyamide obtained in step 3 once or more times with a solvent. [8] The method for producing powdered polyamide according to [7], wherein the solvent used for the initial washing in step 4 is the same alcohol used in step 1. [9] A method for producing powdered polyamide according to [1] or [2], wherein the heating and dissolving temperature in step 1 is 60°C or higher and 80°C or lower.

[10] The method for producing powdered polyamide according to [1] or [2], further comprising step 5: heating the powdered polyamide precipitated in step 3 to obtain heated powdered polyamide.

[11] A method for producing powdered polyamide according to

[10] , further comprising step 6: a step of washing the solid obtained by solid-liquid separation of the heated powdered polyamide obtained in step 5, after step 5.

[12] A method for producing powdered polyamide according to [1] or [2], wherein the polyamide resin composition comprises a polyamide coated with a silicone resin, and the concentration of the polyamide in the heated polyamide solution in step 1 is 5 to 15% by mass.

[13] A method for producing powdered polyamide according to [1] or [2], wherein the polyamide resin composition comprises a polyamide coated with a silicone resin, and the viscosity of the heated polyamide solution in step 1 at 25°C is 10 to 20,000 mPa·s.

[14] A metal chloride alcohol solution having a metal chloride concentration of 23% by mass or more and 35% by mass or less, and containing 0.001 to 1% by mass of a hydroxide of the same metal as the metal contained in the metal chloride, and 0.001 to 10% by mass of water.

[15] The method for producing powdered polyamide according to [1] or [2], wherein the metal chloride alcohol solution has a metal chloride concentration of 23% by mass or more and 35% by mass or less, and contains 0.001 to 1% by mass of a hydroxide of the same metal as the metal contained in the metal chloride and 0.001 to 10% by mass of water.

[16] A method for producing powdered polyamide according to [1] or [2], wherein the powdered polyamide contains 0.001 to 1500 ppm of calcium atoms and the molar content of halogen atoms is less than 1 relative to the molar content of calcium atoms.

[17] A method for producing powdered polyamide according to [1] or [2], wherein the polyamide resin composition comprises at least polyamide and polyethylene terephthalate.

[18] A method for producing powdered polyamide according to [1] or [2], comprising the polyamide resin composition having a polyamide coated with a urethane resin.

[19] After steps 1-3 described above Step 7: A step to recover the precipitated powdered polyamide, Step 8: A washing step to wash the recovered powdered polyamide, Step 9: A drying step in which the washed powdered polyamide is heated and dried, Includes, The method for producing powdered polyamide according to [1] or [2], wherein the amount of metal chloride adhering to the powdered polyamide after heating and drying in step 9 is 20 parts by mass or less per 100 parts by mass of the powdered polyamide.

[0069] Furthermore, with respect to the present invention (II), the inventors, as a result of diligent research, investigated various methods to reduce the amount of solvent contained in the precipitated polyamide in order to reduce the amount of washing solution. As a result, they discovered that the precipitated polyamide can be modified by heat treatment of the polyamide precipitated from a calcium chloride methanol solution, and thus completed the present invention (II). In the present invention (II), since the amount of solvent contained in the precipitated polyamide during washing is small, the amount of liquid required for washing can be reduced.

[0070] In other words, the present invention (II) is as follows: [1] A method for producing recycled polyamide, (i) Dissolve the polyamide in a calcium chloride methanol solution to obtain the dissolved polyamide A step to obtain a solution containing, (ii) Precipitate the dissolved polyamide from the solution containing the dissolved polyamide. Then, the process of obtaining precipitated polyamide, (iii) A step of heating the precipitated polyamide to obtain heated polyamide, call (iv) A step of washing the heated polyamide with a washing solution to obtain regenerated polyamide. Manufacturing method including; [2] In step (iii), the precipitated polyamide is used in step (ii) The manufacturing method described in [1], which involves heating in the aforementioned solution at the time; [3] In step (ii), the precipitated polyamide is separated from the solution used for precipitation. After obtaining a solid containing polyamide, the obtained solid was washed with an additional washing solution. The manufacturing method according to [1], wherein the polyamide is heated in step (iii) above; [4] The manufactured according to any one of [1] to [3], wherein the recycled polyamide is in powder form. Construction method. [5] The method for producing the product according to [1], wherein the polyamide is polyhexamethylene adipamide; [6] In step (ii), add a poor solvent to the solution containing the dissolved polyamide. Afterward, the dissolved polyamide is precipitated from the solution to obtain the precipitated polyamide. The manufacturing method described in any one of items [1] to [5]; [7] In step (ii), an additional solvent is added to the solution containing the dissolved polyamide. Without adding anything, the dissolved polyamide is precipitated from the solution, and the precipitated polyamide A manufacturing method described in any one of items [1] to [5] to obtain [the product]; [8] The cleaning solution in step (iv) is water, any one of [1] to [7] Manufacturing method as described in the section; [9] The additional washing solution in step (ii) is methanol, [3]~[8 The manufacturing method described in any one of the items of ].

[0071] Furthermore, with respect to the present invention (III), we conducted thorough research on a method for recovering polyamide using a calcium chloride methanol solution and discovered that the factor causing a decrease in recovery efficiency is the increase in viscosity due to the dissolution of polyamide. As a result, we found that processing with the composition with the highest solubility is not necessarily the solution composition that recovers polyamide (e.g., nylon 66) in high yield. Through further investigation of the dissolution composition, we found that metal chlorides other than calcium chloride can be used, and that by controlling the polyamide or the viscosity of the solution after dissolution, the yield of regenerated polyamide can be increased, thus completing the invention.

[0072] In other words, the present invention (III) is as follows: [1] A method for producing recycled polyamide using a polyamide resin composition containing a polyamide coated with a silicone resin as a raw material, The process includes a dissolution step in which the polyamide is dissolved to obtain a polyamide solution by mixing a metal chloride alcohol solution containing metal chloride and alcohol with the polyamide resin composition. In the dissolution step, the mass percentage of polyamide in the polyamide solution is 5 to 15% by mass. A method for producing recycled polyamide, characterized by the following features. [2] A method for producing recycled polyamide using a polyamide resin composition containing a polyamide coated with a silicone resin as a raw material, The process includes a dissolution step in which the polyamide is dissolved to obtain a polyamide solution by mixing a metal chloride alcohol solution containing metal chloride and alcohol with the polyamide resin composition. In the dissolution step, the viscosity of the polyamide solution at 25°C is 10 to 20,000 mPa·s. A method for producing recycled polyamide, characterized by the following features. [3] The manufacturing method according to [1] or [2], wherein the temperature at which the polyamide resin composition and the metal chloride alcohol solution are mixed in the dissolution step is 30 to 90°C. [4] The method for producing the polyamide according to any one of [1] to [3], wherein the polyamide is an aliphatic polyamide. [5] The manufacturing method according to any one of [1] to [4], wherein the metal chloride is zinc chloride or calcium chloride. [6] The manufacturing method according to [5], wherein the metal chloride is calcium chloride. [7] The manufacturing method according to any one of [1] to [6], wherein the alcohol is methanol. [8] The manufacturing method according to any one of [1] to [7], wherein the polyamide is nylon 66. [9] The manufacturing method according to any one of [1] to [8], wherein the metal chloride alcohol solution is a solution produced by separating polyamide from a metal chloride alcohol solution obtained by dissolving polyamide from a polyamide base fabric.

[10] The method for producing a metal chloride alcohol solution according to [9], wherein the metal chloride alcohol solution is a concentrated solution obtained after separating the polyamide.

[0073] Furthermore, with respect to the present invention (IV), we have diligently investigated methods for suppressing the corrosion of metals such as the material of dissolution equipment using metal chloride alcohol solutions such as calcium chloride methanol solution. The mechanism of metal corrosion by metal chlorides such as calcium chloride is due to the destabilization of the passivation state by chloride ions, and raising the pH is a common method to suppress this. Therefore, it is easy to consider adding a basic compound soluble in methanol to raise the pH, but for example, if sodium hydroxide is added as a base soluble in methanol, the chloride ions and sodium hydroxide react, and the resulting sodium chloride does not dissolve in methanol, so it precipitates. Such sodium chloride particles do not mix well with the solvent, so they tend to remain in gaps in the equipment, causing a localized increase in chloride ion concentration and making crevice corrosion more likely, which should be avoided. In addition, the overall concentration of metal chlorides such as calcium chloride decreases, so the solubility of polyamide also decreases. From this perspective, after examining various bases, we discovered that when a hydroxide of the same metal as the metal chloride (hereinafter referred to as "hydroxide of the same metal"), such as calcium hydroxide, is added, the corrosiveness of the polyamide can be significantly reduced without reducing its solubility, thus completing Invention (IV).

[0074] In other words, the present invention (IV) is as follows: [1] A methanol composition containing 5-25% of a metal chloride, 0.001-1% of the same metal hydroxide, and 0.001-5% of water. [2] The methanol composition according to [1], further comprising a polyamide dissolved in a methanol composition as a solvent. [3] The methanol composition according to [1] or [2], wherein the metal chloride is zinc chloride and the hydroxide of the same metal is zinc hydroxide. [4] The methanol composition according to [1] or [2], wherein the metal chloride is calcium chloride and the hydroxide of the same metal is calcium hydroxide. [5] A method for producing a polyamide composition, comprising the steps of: dissolving a raw material polyamide composition in a solvent to obtain a polyamide solution; and separating the polyamide from the obtained polyamide solution, wherein the solvent for dissolving the raw material polyamide composition is the methanol composition described in [1] or [2]. [6] The method for producing the polyamide composition according to [5], wherein the polyamide composition comprises polyhexamethylene adipamide. [7] A polyamide composition obtained by the method described in [5], which contains 0.001 to 1000 ppm of metal atoms and has a molar content of halogen atoms of less than 2 relative to the molar content of metal atoms. [8] The polyamide composition according to [7], which contains 0.001 to 1000 ppm of metal atoms and has a molar content of halogen atoms that is less than 1 relative to the molar content of metal atoms. [9] The polyamide composition according to [7], wherein the metal atom is a zinc atom or a calcium atom.

[10] The polyamide composition according to [7], further comprising polyhexamethylene adipamide.

[11] A powder containing the polyamide composition described in [7].

[0075] Furthermore, with respect to the present invention (V), the inventors, as a result of diligent research, have found that by heating and dissolving a polyamide resin composition in a metal chloride alcohol solution containing metal chlorides and alcohols to obtain a heated polyamide solution, then precipitating and recovering the polyamide from the heated polyamide solution, and then washing and drying the recovered polyamide, the amount of metal chloride adhering to the polyamide after heating and drying can be controlled to 20 parts by mass or less per 100 parts by mass of the polyamide, thereby suppressing the adhesion of the recovered polyamide without excessive washing, and thus completing the present invention (V).

[0076] The present invention (V) is based on the above findings, and its gist is as follows. [1] Step 1: A dissolution step in which the polyamide resin composition is heated and dissolved in a metal chloride alcohol solution containing metal chlorides and alcohols to obtain a heated polyamide solution, Step 2: A recovery step in which polyamide is precipitated from the heated polyamide solution and recovered, Step 3: A washing step to wash the recovered polyamide, Step 4: A drying step in which the washed polyamide is heated and dried, Includes, A method for producing polyamide, characterized in that the amount of metal chloride adhering to the polyamide after heating and drying in step 4 is 20 parts by mass or less per 100 parts by mass of the polyamide. [2] The method for producing polyamide according to [1], characterized in that the washing step is a control step for controlling the amount of metal chloride after heating and drying. [3] The method for producing polyamide according to [1] or [2], characterized in that the temperature at which the material is heated and melted in step 1 is 30 to 90°C. [4] A method for producing polyamide according to any one of [1] to [3], characterized in that the polyamide concentration in the heated polyamide solution is 5 to 15% by mass. [5] A method for producing polyamide according to any one of [1] to [4], characterized in that the metal chloride is zinc chloride or calcium chloride. [6] A method for producing a polyamide according to any one of [1] to [5], further comprising a confirmation step of measuring the amount of metal chloride attached to the polyamide and confirming whether or not it is within the range. [7] The method for producing polyamide according to [6], characterized in that the confirmation step is carried out by taking a portion of the washed polyamide after the washing in step 3. [8] The method for producing polyamide according to [6], characterized in that the step of confirming whether the amount of metal chloride attached to the polyamide is within the range is performed by taking a portion of the polyamide after heating and drying in step 4. [9] A method for producing a polyamide according to any one of [6] to [8], characterized in that if the amount of metal chloride attached to the polyamide exceeds 20 parts by mass per 100 parts by mass of the polyamide, a second washing step is performed to wash the polyamide again.

[0077] Furthermore, with respect to the present invention (VI), the inventors have found that by mixing a mixture of polyamide and polyethylene terephthalate with a metal chloride alcohol solution containing a metal chloride and an alcohol, and dissolving and separating the polyamide, the polyamide and / or polyethylene terephthalate can be recovered from the mixture, and the efficiency and yield of the separation and recovery can also be improved, thus completing the present invention (VI).

[0078] The present invention (VI) is based on the above findings, and its gist is as follows. [1] A method for producing polyamide, comprising recovering polyamide from a mixture containing at least polyamide and polyethylene terephthalate, The process involves mixing the aforementioned mixture with a metal chloride alcohol solution containing metal chlorides and alcohols to obtain a polyamide solution in which the polyamide is dissolved, The process of separating and recovering the polyamide solution, A method for producing polyamide, characterized by containing the following: [2] A method for producing polyethylene terephthalate, comprising recovering polyethylene terephthalate from a mixture containing at least polyamide and polyethylene terephthalate, The process involves mixing the aforementioned mixture with a metal chloride alcohol solution containing metal chlorides and alcohols to obtain a polyamide solution in which at least the polyamide is dissolved, The process of separating and recovering the polyethylene terephthalate, A method for producing polyethylene terephthalate, characterized by containing the following: [3] A method for producing polyamide and polyethylene terephthalate, comprising recovering polyamide and polyethylene terephthalate from a mixture of polyamide and polyethylene terephthalate, The process involves mixing the aforementioned mixture with a metal chloride alcohol solution containing metal chloride and alcohol to obtain a polyamide solution in which the polyamide is dissolved, A step of separating and recovering the polyamide solution and the polyethylene terephthalate, A method for producing polyamide and polyethylene terephthalate, characterized by containing the following: [4] The manufacturing method according to [1], [2], or [3], characterized in that the mixed material is a woven fabric. [5] The manufacturing method according to [4], characterized in that the woven fabric is an airbag component. [6] The manufacturing method according to any one of [1] to [5], characterized in that the temperature at which the mixture is mixed with the metal chloride alcohol solution is 30 to 90°C. [7] The manufacturing method according to any one of [1] to [6] above, characterized in that the metal chloride is zinc chloride or calcium chloride.

[0079] Furthermore, regarding the present invention (VII), after diligently studying a method for recovering polyamide using a calcium chloride methanol solution, we discovered that the factor causing a decrease in recovery efficiency is the increase in viscosity due to the dissolution of polyamide. As a result, we found that processing with the composition with the highest solubility is not necessarily the solution composition that recovers polyamide (e.g., nylon 66) in high yield. Through further investigation of the dissolution composition, we found that metal chlorides other than calcium chloride can be used, and that by controlling the polyamide or the viscosity of the solution after dissolution, the yield of regenerated polyamide can be increased, thus completing the invention (VII).

[0080] In other words, the present invention (VII) is as follows: [1] A method for producing recycled polyamide using a mixture containing a polyamide coated with urethane resin as a raw material, The process includes a dissolution step in which a polyamide is dissolved by mixing a metal chloride alcohol solution containing a metal chloride and an alcohol with the aforementioned mixture to obtain a polyamide solution. In the dissolution step, the mass percentage of polyamide in the polyamide solution is 5 to 15% by mass. A method for producing recycled polyamide, characterized by the following features. [2] A method for producing recycled polyamide using a mixture containing a polyamide coated with urethane resin as a raw material, The process includes a dissolution step in which a polyamide is dissolved by mixing a metal chloride alcohol solution containing a metal chloride and an alcohol with the aforementioned mixture to obtain a polyamide solution. In the dissolution step, the viscosity of the polyamide solution at 25°C is 10 to 20,000 mPa·s. A method for producing recycled polyamide, characterized by the following features. [3] The manufacturing method according to [1] or [2], wherein the temperature at which the mixture and the metal chloride alcohol solution are mixed in the dissolution step is 30 to 90°C. [4] The method for producing the polyamide according to any one of [1] to [3], wherein the polyamide is an aliphatic polyamide. [5] The manufacturing method according to any one of [1] to [4], wherein the metal chloride is zinc chloride or calcium chloride. [6] The manufacturing method according to [5], wherein the metal chloride is calcium chloride. [7] The manufacturing method according to any one of [1] to [6], wherein the alcohol is methanol. [8] The manufacturing method according to any one of [1] to [7], wherein the polyamide is nylon 66. [9] The manufacturing method according to any one of [1] to [8], wherein the metal chloride alcohol solution is a solution produced by separating polyamide from a metal chloride alcohol solution obtained by dissolving polyamide from a polyamide base fabric.

[10] The method for producing a metal chloride alcohol solution according to [9], wherein the metal chloride alcohol solution is a concentrated solution obtained after separating the polyamide. [Effects of the Invention]

[0081] According to the present invention (I), powdered polyamide can be produced efficiently. The present invention (I) provides a method for producing powdered polyamide that suppresses porosity and reduces the amount of solvent contained, thereby reducing the amount of waste liquid and the energy required for drying. Furthermore, it is preferable to provide a method for producing powdered polyamide with a large particle size and a small particle size distribution in a short time. With respect to the present invention (II), according to the present invention (II), a method for producing recycled polyamide with reduced waste liquid volume can be provided. ru. With respect to the present invention (III), the present invention (III) provides a method for efficiently producing a polyamide base fabric from a silicone-coated polyamide base fabric in high yield. With respect to the present invention (IV), according to the present invention (IV), a solvent that is less corrosive and capable of dissolving polyamides can be provided. With respect to the present invention (V), the present invention (V) provides a method for producing polyamide that allows for the recovery of polyamide with high efficiency and high yield, and that enables the production of high-quality polyamide without excessive washing. With respect to the present invention (VI), according to the present invention (VI), it is possible to provide a method for producing polyamide, a method for producing polyethylene terephthalate, and a method for producing polyamide and polyethylene terephthalate, which can recover polyamide and / or polyethylene terephthalate from a mixture of polyamide and polyethylene terephthalate with high efficiency and high yield. With respect to the present invention (VII), the present invention (VII) provides a method for efficiently producing a polyamide base fabric from a urethane-coated polyamide base fabric in high yield. [Modes for carrying out the invention]

[0082] The embodiments for carrying out the present invention (hereinafter simply referred to as "this embodiment") will be described in detail below.

[0083] [Invention (I)] The present invention (I) will be described below. In the present invention (I), the conditions of the present invention (II) to (VII) may be incorporated as appropriate. The method for producing powdered polyamide according to this embodiment (I) includes the steps of: step 1: heating and dissolving a polyamide resin composition in a metal chloride alcohol solution containing a metal chloride and an alcohol to obtain a heated polyamide solution; step 2: diluting the heated polyamide solution with alcohol to obtain an alcohol dilution; and step 3: cooling the alcohol dilution to precipitate powdered polyamide, wherein in step 1, the mass ratio of metal chloride to 100% by mass of the metal chloride alcohol solution is 23% by mass or more and 35% by mass or less; in step 1, the heated polyamide solution contains 0.2 moles or more and 2.5 moles of water per mole of metal chloride; and in step 2, the heated polyamide solution is diluted without lowering its temperature below 50°C. Furthermore, another method for producing powdered polyamide according to this embodiment (I) includes the steps of: step 1: heating and dissolving a polyamide resin composition in a metal chloride alcohol solution containing a metal chloride and an alcohol to obtain a heated polyamide solution; step 2: diluting the heated polyamide solution with alcohol to obtain an alcohol dilution; and step 3: cooling the alcohol dilution to precipitate powdered polyamide, wherein in step 1, the mass ratio of metal chloride to 100% by mass of the metal chloride alcohol solution is 23% by mass or more and 35% by mass or less; in step 1, the heated polyamide solution contains 0.2 moles or more and 2.5 moles of water per mole of metal chloride; and in step 2, the mass of polyamide precipitated is 1% by mass or less of the total mass of polyamide contained in the heated polyamide solution. The manufacturing method of this embodiment may consist only of steps 1 to 3, or it may include other steps.

[0084] The compounds used in the manufacturing method of this embodiment will be described.

[0085] <Polyamide> The polyamides mentioned above can be polymers polymerized by amide bonds, such as those obtained by polycondensation of diamine compounds and dicarboxylic acid compounds, or by ring-opening polymerization of cyclic lactams. The above-mentioned diamine compounds are not particularly limited, but include ethylenediamine, trimethylenediamine, tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, nonanediamine, methylpentanediamine, and p-phenylenediamine. The above-mentioned dicarboxylic acid compounds are not particularly limited, but include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, sebacic acid, terephthalic acid, and isophthalic acid. Examples of the above-mentioned cyclic lactams include, but are not limited to, ε-caprolactam, undecanlactam, and lauryllactam. The combination of the above-mentioned diamine compound, dicarboxylic acid compound, and cyclic lactam compound is not particularly limited, and multiple types of compounds may be used in combination for each type. Polyhexamethylene adipamide, consisting of hexamethylenediamine and adipic acid, has high solubility and is suitable for the powdering process.

[0086] While there are no particular limitations on the method for measuring the particle size and particle size distribution of powdered polyamide, examples include laser diffraction, laser scattering, centrifugal sedimentation, particle tracking, and dynamic scattering.

[0087] <Polyamide resin composition> The polyamide resin composition may contain additives intended to produce effects during use and processing in its final application. Examples of additives include, but are not limited to, heat stabilizers, pigments, dyes, and plasticizers. Each additive may be an inorganic salt or an organic compound. The above polyamide resin composition may contain polyamide coated with a resin other than polyamide. Examples of coating resins, though not limited to polyolefin resins, include polyolefin resins, polyurethanes, acrylic resins, silicone resins, and RFL (resorcinol-formaldehyde-latex) adhesives. From the viewpoint of separability, it is preferable to include polyamide coated with a silicone resin. The composition may consist solely of polyamide coated with a silicone resin, or it may further contain other components. In particular, from the viewpoint of the production efficiency of powdered polyamide, the mass ratio of polyamide coated with silicone resin is preferably 30 to 100% by mass, more preferably 60% by mass or more, even more preferably 70% by mass or more, and especially preferably 80% by mass or more, based on 100% by mass of the polyamide resin composition.

[0088] The above-mentioned silicone resin is not particularly limited, but examples include methyl silicone and phenyl silicone resin. It may be a mixture of these resins, or a mixture of each raw material that has been cured.

[0089] The polyamide coated with silicone resin may also have other coatings in addition to the silicone resin. The type of other coating is not particularly limited, but examples include polyethylene, polypropylene, polyester, and fluororesin. It is preferable that the coating is insoluble in the metal chloride alcohol solution used for dissolution. Polyamide coated with silicone resin may be recycled polyamide raw material, such as process scraps and waste from molded products such as fibers, automotive parts, and electrical product parts, which use polyamide as a raw material. Specifically, this includes process scraps and waste from clothing, airbags, tire cords, engine compartment and intake system parts, fuel system parts, connectors, fishing nets, and UD tape. The composition of the RFL adhesive is not particularly limited; any RFL adhesive used for bonding polyamide fibers and rubber, commonly used in tire cords, may be used. Polyamides coated with polyurethane or acrylic resin include base fabrics used in clothing, and the types of polyurethane and acrylic resins are not particularly limited.

[0090] The above polyamide resin composition may also contain sewing thread. The material of the sewing thread is not particularly limited, but it is preferable that it be made of the same polyamide as the base fabric, as this can be recovered as recycled polyamide.

[0091] The above polyamide resin composition may consist solely of the above polyamide, or it may contain the above polyamide and other components. For example, other resins, metals, or other impurities may be mixed with, attached to, or coated on the polyamide as other components. The mass ratio of the polyamide to 100% by mass of the polyamide resin composition is preferably 30 to 100% by mass, more preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 85% by mass or more, and particularly preferably 100% by mass, from the viewpoint of polyamide recovery rate. If impurities other than polyamide are present, the process may include a step to separate the polyamide from these impurities. The separation method is not particularly limited, but if the impurities are insoluble while the polyamide resin composition is dissolved, they can be separated by methods such as filtration, centrifugation, or sedimentation. If the impurities dissolve together with the polyamide in the solvent, methods such as extraction separation in the dissolved state, membrane separation, electrodialysis, or washing after precipitating the polyamide in the precipitation step described later can be considered.

[0092] The above polyamide resin composition may contain at least polyamide and polyethylene terephthalate. Furthermore, it may contain other components. Other components include coating components and coating components for polyamide and polyethylene terephthalate mixtures. Coating components include resins, such as silicone resins and urethane resins. Coating components include lubricants. Regarding the shape of the polyamide resin composition containing polyamide and polyethylene terephthalate, it is preferable that it be a woven fabric (water jet loom, air jet loom, rapier loom, airbag base fabric, etc.) and more preferably an airbag component, in order to better enjoy the effects of the present invention. In the case of a high-density woven fabric such as an airbag base fabric, the fibers made of polyamide and the fibers made of polyethylene terephthalate are intertwined, making it difficult to separate them sufficiently with conventional separation methods. On the other hand, in this embodiment, by dissolving and separating the polyamide, polyamide and / or polyethylene terephthalate can be recovered from the mixture of polyamide and polyethylene terephthalate, and even in the case of a woven fabric, polyamide and / or polyethylene terephthalate can be recovered with high efficiency and high yield.

[0093] Examples of polyethylene terephthalate (PET) mentioned above include resins having the following structure. [ka] The polyethylene terephthalate described above may consist solely of polyethylene terephthalate, or it may be a polyethylene terephthalate resin composition containing the polyethylene terephthalate and other components. For example, impurities such as other resins or metals may be mixed, attached to, or coated onto the polyethylene terephthalate as other components. The polyethylene terephthalate mentioned above may be included in the polyamide resin composition as fibrous PET. This fibrous PET can be obtained by further solid-phase polymerization and spinning of the PET resin. Furthermore, since polyethylene terephthalate is insoluble in the metal chloride alcohol solution described later, only the polyamide can be melted and separated in step 1. Therefore, by simply mixing a polyamide resin composition containing polyamide and polyethylene terephthalate with a predetermined metal chloride alcohol solution, the polyamide and polyethylene terephthalate can be separated efficiently and in high yield, and the polyamide can be recovered. Polyethylene terephthalate can be separated and recovered if it remains undissolved. One method for separating and recovering the polyethylene terephthalate is to remove the undissolved polyethylene terephthalate remaining in the heated polyamide solution by filtration or other means.

[0094] The above polyamide resin composition preferably contains a polyamide coated with a urethane resin. From the viewpoint of the manufacturing efficiency of powdered polyamide, the mass ratio of polyamide coated with urethane resin is preferably 30 to 100% by mass, more preferably 60% by mass or more, even more preferably 70% by mass or more, and particularly preferably 80% by mass or more, based on 100% by mass of the polyamide resin composition. Polyurethane resin is obtained by the reaction of a polyol component and a polyisocyanate component. Examples of the polyol component include polycarbonate polyol, polyester polyol, and polyether polyol. The above-mentioned urethane resin is not particularly limited, but examples include polyester-based polyurethane resins, polyether-based polyurethane resins, and polycarbonate-based polyurethane resins. The urethane resin may also be given a crosslinking agent consisting of epoxy, melamine, polyfunctional isocyanate, etc., a carbodiimide-based hydrolysis inhibitor, phenols, aromatic amine antioxidants, ultraviolet absorbers such as salicylic acid-based, benzophenone-based, and benzotriazole-based derivatives, and a flame retardant such as thiourea. The polyamide coated with urethane resin may also have other coatings in addition to the urethane resin. The type of other coating is not particularly limited, but examples include polyethylene, polypropylene, polyester, fluororesin, and silicone resin. It is preferable that the coating does not dissolve in the metal chloride alcohol solution used for dissolution. It is preferable that the coating resin does not contain silicone resin. Polyamide coated with urethane resin may be recycled polyamide raw material, such as process scraps and waste from molded products such as fibers, automobile parts, and electrical product parts, which use polyamide as a raw material. Specifically, this includes process scraps and waste from clothing, airbags, tire cords, engine compartment, intake system, and fuel system parts, connectors, fishing nets, and UD tape. Methods for separating the urethane resin include scooping it out of the molten layer, filtration, centrifugation, and sedimentation, and these may be combined. Since fine fragments of the urethane resin may be generated during the heating and melting of polyamide, it is preferable to remove these fine fragments by filtration or a method combined with filtration. It is preferable to remove any other coatings on the polyamide coated with urethane resin at the same time as the urethane resin. Since the separated urethane resin and other coatings have a polyamide-containing solution attached to them, it is preferable to wash them and recover the polyamide-containing solution. The solvent for washing is not particularly limited, but calcium chloride methanol solution is preferred. The washing method is not particularly limited, but examples include stirring washing in a tank reactor or flow washing in a filter.

[0095] <Metal chloride alcohol solution> The above metal chloride alcohol solution contains a metal chloride and an alcohol, and may further contain a hydroxide of the same metal as the above metal chloride, or other components. In particular, from the viewpoint of polyamide solubility, the total mass ratio of the metal chloride and the alcohol to 100% by mass of the metal chloride alcohol solution is preferably 80% by mass or more, and more preferably 90% by mass or more.

[0096] Examples of the alcohols mentioned above include methanol, ethanol, linear or branched propanol, linear or branched butanol, and combinations thereof. Of these, methanol, ethanol, or combinations thereof are preferred from the viewpoint of polyamide solubility, with methanol being more preferred.

[0097] The mass ratio of metal chloride to 100% by mass of the above metal chloride alcohol solution is preferably 23 to 35% by mass, more preferably 25 to 33% by mass, and particularly preferably 27 to 31% by mass. If the mass ratio is less than 23% by mass, the amount of polyamide that can be dissolved will be small, and a large amount of solvent will be required. If it exceeds 35% by mass, the metal chloride is more likely to remain undissolved and be introduced as an impurity.

[0098] Examples of the above-mentioned metal chlorides include zinc chloride, magnesium chloride, and calcium chloride, with zinc chloride and calcium chloride being preferred, and calcium chloride being the most preferred. The above-mentioned metal chlorides can be added as anhydrous or hydrated forms. The mass percentage of water in the above metal chloride alcohol solution is preferably 30% by mass or less, more preferably 15% by mass or less, and even more preferably 10% by mass or less, and it is particularly preferable that it contains no water.

[0099] The above metal chloride alcohol solution may be a solution containing alcohol, a metal chloride, a hydroxide of the same metal as the above metal chloride (which may be referred to as "hydroxide of the same metal" in this specification), and water. Examples of metals that constitute the hydroxide of the above-mentioned metal include zinc (i.e., the metal chloride is zinc chloride, and the hydroxide of the same metal is zinc hydroxide) and calcium (i.e., the metal chloride is calcium chloride, and the hydroxide of the same metal is calcium hydroxide), with calcium being preferred. The concentration of the hydroxide of the above-mentioned metal is preferably 0.001 to 1% by mass, more preferably 0.001 to 0.1% by mass, and even more preferably 0.001 to 0.01% by mass, based on 100% by mass of the metal chloride alcohol solution. The hydroxide of the metal does not need to be completely dissolved in an alcohol such as methanol, and it is acceptable if some of it is not dissolved. The mass ratio of water to 100% by mass of the above metal chloride alcohol solution is preferably 0.001 to 10% by mass, more preferably 0.001 to 5% by mass, even more preferably 0.001 to 1% by mass, and particularly preferably 0.01 to 0.1% by mass.

[0100] Each step in the manufacturing method of this embodiment will be described.

[0101] <Step 1: Step to obtain a heated polyamide solution> The polyamide resin composition is dissolved using a metal chloride alcohol solution. In step 1 above, the polyamide resin composition and the metal chloride alcohol solution are mixed and heated to dissolve them.

[0102] The temperature at which the material melts is not particularly limited, but it is preferably 30 to 90°C, and more preferably 60 to 80°C. It may also be 40 to 60°C. If the temperature is too low, melting will be slow, and if it exceeds 90°C, the temperature will be higher than the boiling point, which is undesirable from the viewpoint of corrosiveness and decomposition. During step 1 described above, the temperature may be constant or may be varied within the above range.

[0103] Dissolution can be carried out using either a batch or continuous method. In the batch process, stirring is not particularly limited, but it is preferable. Stirring improves the dissolution rate of the polyamide. In a continuous flow system, the solvent can be continuously passed through the solid, or the solution can be circulated. Circulation is preferable because it reduces the amount of solvent used.

[0104] The shape of the container used when heating and dissolving the above polyamide resin composition and the metal chloride alcohol solution is not particularly limited, and any shape such as a tank type or a circulating type may be used. Furthermore, the material of these containers and piping is not particularly limited, but examples include SUS316, SUS316L, SUS329J4L, and SUS444. These materials may also be treated with lining, coating, or other processes, such as glass, fluororesin, rubber, and epoxy, with glass and fluororesin being preferred from the viewpoint of corrosion resistance. If lining or coating is applied, the material of the container and piping itself can be selected without considering corrosiveness.

[0105] The heating and dissolution time is not particularly limited, but is preferably between 5 minutes and 100 hours.

[0106] The mass ratio of the polyamide resin composition to the metal chloride alcohol solution used in step 1 is not particularly limited, but is preferably 5 to 15% by mass, and more preferably 7 to 13% by mass. If it is less than 5% by mass, too much solvent is required, and if it exceeds 15% by mass, the viscosity becomes high, leading to a longer dissolution time and deterioration of handling properties. Furthermore, for the same reasons as above, the mass percentage of polyamide in the heated polyamide solution is preferably 5 to 15% by mass, and more preferably 7 to 13% by mass. The above-mentioned heated polyamide solution preferably contains 0.2 to 2.5 moles of water per mole of metal chloride, more preferably 0.5 to 2.0 moles, and even more preferably 1 to 1.5 moles, from the viewpoint of suppressing the liquid content of the precipitate obtained by crystallization. Although the principle is not clear, it is thought that the presence of water during dissolution affects the state of hydrogen bonding of the polyamide in the metal chloride alcohol solution and plays a role in regulating the microscopic solubility and dispersibility that cannot be evaluated by the macroscopic dissolution state. If the amount is less than 0.2 moles, the dispersibility of calcium chloride in alcohol decreases and it becomes difficult for it to interact with the polyamide, and if it is more than 2.5 moles, it is thought that the polyamide does not disperse uniformly in the solution because polyamide has low solubility in water. When the above polyamide resin composition includes a polyamide coated with a silicone resin, the mass percentage of polyamide in 100% by mass of the above heated polyamide solution is preferably 5 to 15% by mass, and more preferably 7 to 13% by mass. If it is less than 5% by mass, too much solvent is required, and if it exceeds 15% by mass, the viscosity becomes high, leading to a longer dissolution time and deterioration of handling properties. When the above polyamide resin composition includes a polyamide coated with a silicone resin, the viscosity of the heated polyamide solution at 25°C is preferably 10 to 20,000 mPa·s, more preferably 10 to 10,000 mPa·s, and even more preferably 10 to 3,000 mPa·s. Although a higher viscosity indicates a higher polymer concentration, the dissolution efficiency of the polyamide decreases due to factors such as adhesion to the base fabric.

[0107] When the above polyamide resin composition includes a polyamide coated with a silicone resin, the method for separating the silicone resin from the heated polyamide solution is not particularly limited, but examples include scooping the silicone resin from the dissolved layer, filtration, centrifugation, and sedimentation, and these may be combined. Since fine fragments of silicone may be generated during the heated dissolution of the polyamide, it is preferable to remove these fine fragments by filtration or a method combined with filtration. It is preferable to remove any other polyamide coatings coated on the silicone resin at the same time as the silicone resin. Since the separated silicone resin and other coatings have a polyamide-containing solution attached to them, it is preferable to wash them and recover the polyamide-containing solution. The solvent for washing is not particularly limited, but calcium chloride methanol solution is preferred. The washing method is not particularly limited, but examples include stirring washing in a tank reactor or flow washing in a filter.

[0108] The heated polyamide solution obtained in step 1 is preferably used continuously in step 2.

[0109] <Step 2: Step to obtain the alcohol dilution> Step 2 is the process of diluting the heated polyamide solution obtained in Step 1 with alcohol. The alcohol used in step 2 may be methanol, ethanol, linear or branched propanol, linear or branched butanol, or a combination thereof. From the viewpoint of ease of recovery when reusing the solvent, it is preferable that the alcohol used is the same as the alcohol contained in the metal chloride alcohol solution described above.

[0110] This document describes in detail the method for diluting a heated polyamide solution. A dilution ratio of 1.5 to 5 times with alcohol is preferred. In this specification, the dilution ratio is defined as the value obtained by dividing the mass of the alcohol-diluted solution by the mass of the polyamide heat-dissolved solution at the time of dissolution. In this case, even if precipitation occurs in the alcohol-diluted solution after dilution, the weight including the precipitate is taken as the mass of the alcohol-diluted solution after dilution. If the dilution ratio is less than 1.5 times, the amount of polyamide precipitated is small and the particles do not grow sufficiently, resulting in a small particle size. If the dilution ratio is greater than 5 times, precipitation is more likely to occur during dilution, resulting in a wider particle size distribution.

[0111] In step 2, from the viewpoint of suppressing the liquid content of the precipitate obtained by crystallization, it is preferable to dilute the polyamide heated solution so that its temperature does not fall below 50°C. Although the principle is not clear, it is thought that by maintaining a high temperature during the dilution stage, rapid precipitation can be avoided and the properties of the precipitate can be made uniform from the initial to the final stages of precipitation. The temperature at which the solution is diluted with alcohol is not particularly limited, but 30 to 90°C is preferred. If diluted at a temperature lower than 30°C, the particle size will decrease due to precipitation during dilution. If diluted at a temperature higher than 90°C, uneven precipitation is likely to occur due to the evaporation and condensation of alcohol near the liquid surface, making it difficult to control the particle size distribution. The temperature from the production of the above-mentioned heated polyamide solution to obtaining the above-mentioned alcohol dilution solution is preferably within ±10°C of the above-mentioned heating and dissolving temperature in step 1, and more preferably within ±5°C, from the viewpoint of obtaining a powdered polyamide with larger particle size and a smaller particle size distribution in a short time.

[0112] The dilution rate of the alcohol is not particularly limited, but it is preferable to add it at a rate that does not cause rapid changes in concentration or temperature during dilution, thus preventing the precipitation of polyamide.

[0113] The amount of polyamide precipitated during dilution (i.e., the mass of polyamide precipitated in step 2) is preferably 1% by mass or less, and more preferably less than 1% by mass, relative to the total mass of polyamide contained in the heated polyamide solution obtained in step 1. The polyamide precipitated during dilution and the polyamide precipitated during cooling have different microscopic separation mechanisms when they precipitate from the solvent, and as the amount of polyamide precipitated during dilution increases, the liquid content of the precipitate increases. Furthermore, because these particles are generated due to a rapid change in composition, particle size control is not possible, and if there are many particles present, particle size control in the cooling precipitation process described later becomes difficult.

[0114] The temperature of the alcohol used for dilution is not particularly limited, but it is preferably between 15 and 90°C. Below 15°C, localized precipitation is likely to occur during dilution, and above 90°C, the temperature is higher or closer to the boiling point of the alcohol, requiring processing under pressure.

[0115] The water content of the alcohol used for dilution is not particularly limited, but is preferably 0.005 to 50% by mass, and more preferably 0.005 to 1% by mass. If the water content is too high, the polyamide will precipitate rapidly because the aqueous solution has lower solubility. Since the precipitation properties differ depending on the type of polyamide, the amount of water can be changed within the above range depending on the polyamide.

[0116] There are no particular restrictions on the dilution method. Either batch or continuous dilution is acceptable. In the case of batch processing, stirring is not particularly limited, but it is preferable. Stirring ensures uniform temperature and concentration.

[0117] The shape of the container used to dilute the above-mentioned polyamide heated solution with the above-mentioned alcohol is not particularly limited, and any shape such as a tank type or a circulating type may be used. The same container as in step 1 may be used. Furthermore, the material of these containers and piping is not particularly limited, but examples include SUS316, SUS316L, SUS329J4L, and SUS444. In addition, the surface of these materials may be treated with lining, coating, etc., and examples include glass, fluororesin, rubber, and epoxy, with glass and fluororesin being preferred from the viewpoint of corrosion resistance. If lining or coating is applied, the material of the container and piping itself can be selected without considering corrosiveness.

[0118] <Step 3: Precipitation of powdered polyamide> Step 3 is a step in which the alcohol dilution obtained in Step 2 is cooled to precipitate the polyamide.

[0119] When cooling the above alcohol dilution, stirring is preferable. Stirring ensures uniform temperature and concentration, making particle size control easier. It is preferable to stir under conditions that minimize particle breakage and shearing, depending on the equipment and method used.

[0120] 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. Below 10°C / Hr, the cooling time is long, and above 100°C / Hr, rapid precipitation results in smaller particle sizes. The particle size can be controlled by changing the cooling rate.

[0121] The temperature after cooling is not particularly limited, but it is preferable that it be at least 10°C lower than the temperature at the time of dilution. If the temperature difference is less than 10°C, precipitation will be minimal and particle growth will be difficult.

[0122] It is preferable to recover the precipitated solid by solid-liquid separation. The method of solid-liquid separation is not particularly limited, but examples include filtration, centrifugation, and sedimentation. Either batch or continuous operation is acceptable for any of these methods.

[0123] It is preferable to wash the solid obtained by solid-liquid separation with a solvent. The washing solvent is not particularly limited, but it is preferable to use a solvent that has a composition similar to the liquid portion at the time of precipitation, a good solvent, or a solvent that can dissolve metal chlorides, etc. Methanol, ethanol and other alcohols and water are preferred, and combinations thereof may also be used.

[0124] The washing method is not particularly limited and includes batch washing, continuous washing by flowing a washing solvent through a solid-liquid separation device such as a filter or centrifuge, and methods combining these.

[0125] After washing, the polyamide can be dried to obtain powdered polyamide by removing the washing solvent by heating and / or reduced pressure.

[0126] In the manufacturing method of this embodiment, it is preferable to include a step 4 in which the powdered polyamide obtained in step 3 is washed once or more times with a solvent. The washing may be done once or multiple times. Of the above cleaning processes, the solvent used for the first cleaning is preferably the same alcohol used in step 1, from the viewpoint of cleaning efficiency and reuse of raw materials. That is, it is preferable that the solvent is the same alcohol contained in the metal chloride alcohol solution in step 1. The solution contained in the polyamide after crystallization contains the metal chloride used during dissolution. By using the same alcohol as used in step 1, the filtrate from the filtration after crystallization and the cleaning solution can be combined and concentrated to reuse the solution as a dissolution, thereby reducing the amount of metal chloride waste. Furthermore, using a different solvent results in a significant change in the affinity between the polyamide and the solvent, leading to a decrease in cleaning efficiency.

[0127] In the manufacturing method of this embodiment, it is preferable to include step 5, in which the powdered polyamide obtained in step 3 is heated to obtain heated powdered polyamide. By heating and modifying the precipitated powdered polyamide solid, the content of the solvent (typically a metal chloride alcohol solution such as a calcium chloride methanol solution) in the powdered polyamide solid can be reduced. Step 5 may be performed after Step 4, meaning that the powdered polyamide washed in Step 4 is heated. Alternatively, the powdered polyamide heated in Step 4 may be washed after obtaining the powdered polyamide heated in Step 5. Step 5 described above may be step (iii) of the present invention (II) described later.

[0128] The heating in step 5 described above may be carried out in air or in an inert gas. In addition to heating, drying may be performed, or drying may occur in conjunction with heating. For example, after washing the powdered polyamide in step 4, the powdered polyamide may be heated and dried in step 5.

[0129] While not intending to be bound by any particular theory, it is believed that heating modifies the powdered polyamide as follows: During precipitation, the powdered polyamide is assumed to swell while the solvent (typically a metal chloride alcohol solution such as calcium chloride methanol solution) has permeated it. Heating in this state is thought to dry out the metal chloride alcohol solution, and / or reduce the voids that held the metal chloride alcohol solution. Therefore, the amount of remaining metal chloride alcohol solution can be reduced, and furthermore, the efficiency of impurity removal during subsequent washing is also thought to be improved.

[0130] The heating temperature in step 5 described above is not particularly limited, but for example, it is between 20°C and 100°C. If the heating temperature is too low, the modification effect will be low, and if the heating temperature is too high, solid fusion will occur due to the solution, making it difficult to handle.

[0131] While there are no particular limitations on the stirring during heating in step 5 above, stirring is preferable in order to avoid localized heating.

[0132] The pressure during heating in step 5 above is not particularly limited; it may be heated under pressure, or under reduced pressure. Heating at a pressure below atmospheric pressure is preferable because it allows the solvent (typically a metal chloride alcohol solution such as calcium chloride methanol solution) to be distilled off, reducing the amount of remaining metal chloride alcohol solution, and further improving the efficiency of impurity removal during subsequent washing.

[0133] In the manufacturing method of this embodiment, it is preferable to include a step 6 in which the heated powdered polyamide obtained in step 5 is subjected to solid-liquid separation, and the solid obtained by solid-liquid separation is washed. The method of solid-liquid separation is not particularly limited, but examples include filtration, centrifugation, and sedimentation. A washing solution is added to the solid obtained by solid-liquid separation to dissolve and remove impurities.

[0134] Examples of the above-mentioned cleaning solution include water, as well as alcohols such as ethanol, n-propanol, and isopropanol, and these may be used in combination. Depending on the type of impurity, acids such as hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, and acetic acid, and bases such as sodium hydroxide, potassium hydroxide, sodium carbonate, and sodium bicarbonate may also be added to the cleaning solution. To avoid residue after cleaning, it is preferable to perform the final wash with water, and most preferably to perform all washes with water.

[0135] The amount of cleaning solution used in step 6 described above is not particularly limited, but it is preferable to determine the amount of cleaning solution so that the amount of remaining impurities after cleaning is reduced to the target amount.

[0136] The cleaning method in step 6 described above is not particularly limited and may include, for example, a batch cleaning method performed the required number of times, a continuous cleaning method in which the cleaning solution is passed through a filter or centrifuge with the solid inside, and a method combining these.

[0137] After washing, drying may be performed as needed. For example, if a polyamide solid is obtained by washing with water, the water is removed from the solid by heating and / or reduced pressure to obtain a dry solid.

[0138] The manufacturing method of this embodiment involves, after steps 1 to 3, Step 7: A step to recover the precipitated powdered polyamide, Step 8: A washing step in which the recovered polyamide powder is washed, Step 9: A drying step in which the powdered polyamide after washing is heated and dried, Includes, A preferred method is one in which the amount of metal chloride adhering to the powdered polyamide after heating and drying in step 9 is 20 parts by mass or less per 100 parts by mass of the powdered polyamide recovered in step 7.

[0139] The polyamide manufacturing method of this embodiment may further include a recovery step (step 7) after step 3 to recover the precipitated powdered polyamide. For example, the powdered polyamide washed in step 4 may be recovered, the powdered polyamide heated in step 5 may be recovered, or the powdered polyamide after washing the solid obtained by solid-liquid separation in step 6 may be recovered.

[0140] The manufacturing method of this embodiment preferably includes a washing step (step 8) for washing the powdered polyamide recovered in step 7. This step makes it possible to remove impurities such as metal chlorides from the polyamide recovered in step 7. The washing solution used in step 8 is not particularly limited, but for example, a solution with the same composition as the liquid portion at the time of precipitation, a good solvent, and a solvent capable of dissolving calcium chloride, etc., can be used. Additional washing solutions used here include, for example, water and alcohols such as methanol, ethanol, n-propanol, and isopropanol. The additional washing solution is preferably methanol. Washing may be performed multiple times as needed. The cleaning method is not particularly limited and includes batch cleaning, continuous cleaning by flowing water through a solid-liquid separation device such as a filter or centrifuge, and methods combining these. Furthermore, it is preferable that step 8 is a control step that controls the amount of metal chloride after heating and drying in step 9, which will be described later. The amount of metal chloride after drying in step 9 can be controlled by adjusting the type and concentration of the cleaning solution, the cleaning time, etc., so that the amount of metal chloride after drying in step 9 falls within a specific range.

[0141] The manufacturing method of this embodiment may include a step (step 9) in which the polyamide washed in step 8 is dried by heating. In step 9, the washing solvent is removed from the washed polyamide by distillation, and the polyamide can be obtained as a dry solid.

[0142] Furthermore, in the polyamide manufacturing method of this embodiment, it is preferable that the amount of metal chloride adhering to the polyamide after heating and drying in step 9 is 20 parts by mass or less per 100 parts by mass of the polyamide. Regarding the washing of the recovered polyamide as described above, while it is preferable to avoid excessive washing from the standpoint of manufacturing efficiency, cost, and environmental considerations, there was also the problem that if the recovered polyamide was not washed sufficiently, some of the polyamide would melt due to metal chlorides adhering to it after washing, and then solidify during subsequent drying. Therefore, by keeping the amount of metal chloride adhering to the polyamide after heating and drying in step 9 to 20 parts by mass or less per 100 parts by mass of the polyamide obtained in step 9, the metal chloride concentration can be kept within a range that suppresses the melting of the polyamide. In addition, it is preferable to keep the amount of metal chloride adhering to the polyamide after heating and drying in step 9 to 0.01 parts by mass or more per 100 parts by mass of the polyamide, as this avoids the need for excessive washing. From a similar viewpoint, the amount of metal chloride adhering to the polyamide after heating and drying in step 9 is preferably 0.01 to 10 parts by mass, and more preferably 0.01 to 5 parts by mass, per 100 parts by mass of the polyamide. The method for measuring the amount of metal chloride attached to the polyamide after heating and drying in step 9 above is not particularly limited, but examples include sampling a portion and measuring it by 1) X-ray fluorescence analysis after drying, 2) heating and decomposing it with nitric acid and then measuring it with ICP-AES, or 3) extracting the metal chloride with water and measuring it with ion chromatography. The amount of metal chloride adhering to the polyamide after heating and drying in step 9 can be measured either after heating and drying in step 9, or after washing the polyamide in step 8 as described above. For measuring the amount of the above-mentioned metal chlorides, known methods can be used as appropriate.

[0143] From the viewpoint of reusing the metal chloride alcohol solution, the manufacturing method of this embodiment may further include a step of concentrating the metal chloride alcohol solution. For example, the metal alcohol solution containing metal chloride and alcohol obtained in the polyamide recovery process described above may be concentrated and reused. Examples of the concentration methods mentioned above include concentration by heating.

[0144] As described above, according to the manufacturing method of this embodiment, when dissolving and precipitating polyamides useful as engineering plastics to produce powdered polyamides, by setting the content of metal chloride and water in the metal chloride alcohol solution used to dissolve the polyamide within a specific range, and by setting the dilution temperature or the amount of precipitation during dilution within a specific range, it is possible to reduce the liquid content of the precipitated polyamide and provide a method for producing powdered polyamides that reduces the amount of washing solvent and drying energy.

[0145] <Powdered polyamide> The powdered polyamide obtained by the manufacturing method of this embodiment has a large particle size and a small particle size distribution. The median diameter of the above-mentioned powdered polyamide is preferably 20 μm or more, and more preferably 30 to 70 μm. The above-mentioned median diameter can be measured by the method described in the examples below. The particle size distribution of the above powdered polyamide is the value obtained by raising 10 to the power of S using the following formula (1) S The span is preferably 5 or less, more preferably 4 or less, and even more preferably 3 or less. S=log(d90 / d10) / log(d50) ···(1) (Here, in equation (1) above, dn (where n represents 10, 50, or 90) refers to the particle size at which the number of particles smaller than dn accounts for n% of the total number of particles, when the particle size distribution of the above-mentioned polyamide powder is measured by laser diffraction and scattering.) The above particle size distribution can be measured by the method described in the examples below.

[0146] The above-mentioned powdered polyamide may contain metal atoms and halogen atoms. The above-mentioned metal atoms include metal atoms derived from the metal chloride and / or the hydroxide of the same metal contained in the above-mentioned metal chloride alcohol solution. For example, zinc atoms and calcium atoms are examples, with calcium atoms being preferred. The above-mentioned powdered polyamide preferably contains 0.001 to 1500 ppm of calcium atoms, and the molar content of halogen atoms is less than 1 relative to the molar content of calcium atoms. The metal atom content in the above-mentioned powdered polyamide is preferably 0.001 to 1500 ppm, more preferably 0.001 to 1000 ppm, even more preferably 0.001 to 700 ppm, and particularly preferably 0.001 to 500 ppm. The calcium atom content in the above-mentioned powdered polyamide is preferably 0.001 to 1500 ppm, more preferably 0.001 to 1000 ppm, even more preferably 0.001 to 700 ppm, and particularly preferably 0.001 to 500 ppm. The ratio of the molar content of halogen atoms (e.g., moles / L) to the molar content of metal atoms (e.g., moles / L) in the above-mentioned powdered polyamide (molar content of halogen atoms / molar content of metal atoms) is preferably less than 2, more preferably less than 1, and even more preferably less than 0.5.

[0147] Elements not derived from silicon and polyamide may be contained in the powdered polyamide, but are not limited to calcium and zinc (e.g., in the form of calcium compounds, zinc compounds). The amount of calcium contained in the powdered polyamide is preferably 1500 ppm or less, more preferably 1000 ppm or less, even more preferably 700 ppm or less, and particularly preferably 500 ppm or less, as determined by X-ray fluorescence analysis. The amount of zinc contained in the powdered polyamide is preferably 1500 ppm or less, more preferably 1000 ppm or less, even more preferably 700 ppm or less, and particularly preferably 500 ppm or less, as determined by X-ray fluorescence analysis. While calcium and zinc have little effect on clogging during spinning, these compounds readily absorb water. When they dissolve powdered polyamide while still containing water, hydrolysis occurs, reducing the molecular weight and decreasing the durability of the molded product.

[0148] (Spinning of polyamide fibers) In melt spinning, the spinning temperature is preferably between 290°C and 310°C. Setting the spinning temperature to 310°C or lower is preferable because it suppresses the thermal decomposition of the polyamide, 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 preferable because it allows the polyamide to exhibit sufficient melt fluidity, resulting in uniform discharge volume between discharge holes and enabling high-magnification stretching.

[0149] In the melt spinning process, the residence time (the time from when the polyamide resin is melted until it is extruded from the spinneret) should be as short as possible. A residence time of 30 minutes or less is preferable, 15 minutes or less is more preferable, and 0.5 minutes to 7 minutes is even more preferable. A short residence time is preferable because the amount of cyclopentanones in the polymer increases at the melting temperature.

[0150] For thermal stability in high-temperature, high-humidity environments, it is preferable to add a copper compound to the polyamide so that the copper concentration is 1 to 500 ppm, and more preferably 30 to 500 ppm. This effectively suppresses the deterioration of mechanical performance even when exposed to high-temperature, high-humidity environments for extended periods or to environments with high ozone content. Below 30 ppm of copper, the heat resistance strength retention rate decreases, while above 500 ppm, the strength decreases.

[0151] 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 halogen compound. Examples of metal halogen 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 or colorimetric methods.

[0152] While not limited to the following, organic antioxidants such as hindered phenol antioxidants, sulfur antioxidants, and phosphorus antioxidants, as well as heat stabilizers, light stabilizers such as hindered amine, benzophenone, and imidazole antioxidants, and UV absorbers may be added as stabilizers. The amount to be added should be selected appropriately, but it can be added at a concentration of 1 to 1000 ppm relative to the polyamide. These additives may be used individually or in combination.

[0153] Furthermore, in the melt spinning process, it is preferable to use a single-screw or double-screw extruder in the melting section. This extruder allows the polyamide resin to be guided to polymer piping, a gear pump, and a spinning pack while applying appropriate pressure.

[0154] Furthermore, filtering the polyamide resin with a metal fiber nonwoven fabric filter or sand before it is extruded from the spinneret is preferable because it stabilizes the spinning operation. The shape of the spinneret hole in the spinneret should be selected according to the cross-sectional shape of the single fiber that makes up the filament to be manufactured. The spun yarn from the spinneret is solidified with cooling air, a process lubricant is applied, the yarn is taken up, stretched, and heat-treated to obtain polyamide fibers.

[0155] The oil adhesion rate of polyamide fibers is preferably 0.5 to 1.5 wt%. If the oil adhesion rate is 1.5 wt% or less, there is almost no difficulty in the weft yarn flying away due to stickiness (tackiness), and the single yarn convergence is not too good beyond what would occur due to entanglement, reducing the apparent cross-sectional area and preventing the air or water, which are the weft yarn transport media, from losing their weft yarn transport power, 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.

[0156] (Polyamide base fabric) In weaving, looms such as water jet looms, air jet looms, and rapier looms can be used. The base fabric for airbags is a high-density fabric, and in the warping and weaving processes, it is preferable to increase the warp tension to ensure good process passability. By setting the warp tension higher during weaving and creating effective reed beating conditions, a high-density fabric is formed.

[0157] Woven fabrics can have the process oils from the polyamide fibers washed off during the scouring process. The scouring process can be performed using hot water or pressurized hot water, and the processing can be a single-stage process or a multi-stage process of two or more stages. It is also preferable to apply a conventionally known scouring agent to perform the scouring.

[0158] It is preferable to heat-set the fabric in a heat-setting process. The heat-setting temperature is preferably between 110°C and 200°C, and the heat-setting time can be appropriately selected within the range of 0.1 minutes to 30 minutes. It is also preferable to dry the fabric while tensing it so that its shrinkage force is maintained at a predetermined level during the heat-setting process. Heat-setting the fabric helps to stabilize the processability of the subsequent resin coating process.

[0159] The fabric after the refining process may be subjected to a drying treatment as necessary before the heat setting process. The drying temperature is preferably in the range of 80°C or higher and 130°C or lower, more preferably 100°C or higher and 120°C or lower. Also, the treatment time is preferably appropriately selected within the range of 0.1 minute or longer and 30 minutes or shorter. The drying may be performed in a relaxed state or a tense state of the fabric.

[0160] The polyamide base fabric can be used for the non-coated base fabric after the heat setting process, or it may be coated with a coating agent such as silicon or urethane, or heat laminated with a thin film or the like.

[0161] As a method of coating the fabric surface, after immersing the fabric in a resin solution tank, a method of forming and homogenizing the excess resin using a mangle, a vacuum, or a coating knife, a bar coating method such as a comma coater, a method of spraying the resin using a spray device or a forming device, etc. can be adopted. Among these, from the viewpoint of uniformly and thinly applying the resin, the knife coating method is preferred.

[0162] The coating amount is 5 g / m 2 or more and 100 g / m 2 or less, more preferably 10 g / m 2 or more and 70 g / m 2 or less, even more preferably 15 g / m 2 or more and 30 g / m 2 or less. With a coating amount of 5 g / m 2 or more, the required airtightness can be obtained. On the other hand, with a coating amount of 100 g / m 2 or less, the coated fabric has flexibility, good storage properties, and the weight of the entire bag can be suppressed.

[0163] <Airbag> The airbag can be appropriately selected from commonly used airbags such as the driver's seat, passenger seat, side (including inflatable curtain), and rear seat. The cut shape of the airbag bag body can be any of circular, oval, elliptical, rectangular, polygonal, or a combination thereof, as long as it satisfies the desired deployment shape. The seam shapes include a single straight line or multiple parallel straight lines, zigzag, combined use of straight line and zigzag, straight line and oblique line, etc. The sewing method can also be commonly used ones such as plain sewing and double loop sewing, and the sewing pitch can be selected from the range of 20 to 60 stitches / 10 cm. Also, the sewing thread thickness can be selected from 420d to 3000d, and commercially available sewing threads such as polyamide fiber, polyester fiber, vinylon-based fiber, aramid-based fiber, and glass fiber can be used as the thread material.

[0164] [Invention (II)] Hereinafter, Invention (II) will be described. In Invention (II), the conditions of Invention (I) (III) to (VII) can be appropriately incorporated. Invention (II) relates to a method for producing regenerated polyamide by precipitating polyamide dissolved in a solvent. This production method is characterized by including a step of washing the precipitated polyamide with a washing liquid after heating it.

[0165] The method for producing regenerated polyamide according to Invention (II) is (i) a step of dissolving polyamide in a calcium chloride methanol solution to obtain a solution containing the dissolved polyamide, (ii) a step of precipitating the dissolved polyamide from the solution containing the dissolved polyamide to obtain the precipitated polyamide, (iii) a step of heating the precipitated polyamide to obtain the heated polyamide, and (iv) a step of washing the heated polyamide with a washing liquid to obtain regenerated polyamide is included.

[0166] In this specification, the term "method for producing recycled polyamide" is synonymous with and interchangeable with terms such as "method for recovering polyamide," "method for isolating polyamide," "method for purifying polyamide," and "method for regenerating polyamide." In this invention, polyamide is recovered, isolated, and / or purified from polyamide molded articles, specifically processed or used polyamide molded articles, for the purpose of reuse. Therefore, in this specification, the term "recycled polyamide" refers to polyamide obtained through such processing.

[0167] <Polyamide> In this specification, polyamides include polymers polymerized by amide bonds, such as those obtained by polycondensation of diamine compounds and dicarboxylic acid compounds, and those obtained by ring-opening polymerization of cyclic lactams. Polyamides include those having only an aliphatic skeleton, those having only an aromatic skeleton, and those having both an aliphatic and an aromatic skeleton. In the production method of the present invention, the polyamide preferably has only an aliphatic skeleton.

[0168] The diamine compounds are not particularly limited, but examples include ethylenediamine, trimethylenediamine, tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, nonanediamine, methylpentanediamine, and p-phenylenediamine.

[0169] Dicarboxylic acid compounds are not particularly limited, but examples include oxalic acid, succinic acid, glutaric acid, adipic acid, sebacic acid, terephthalic acid, and isophthalic acid.

[0170] Cyclic lactams are not particularly limited, but examples include ε-caprolactam, undecanelactam, and lauryllactam.

[0171] The combinations of diamine compounds, dicarboxylic acid compounds, and cyclic lactam compounds are not particularly limited, and multiple types of compounds may be used in combination for each type.

[0172] The polyamide is preferably polyhexamethylene adipamide. Polyhexamethylene adipamide, composed of hexamethylenediamine and adipic acid, has high solubility and is suitable for the process of the manufacturing method of the present invention. Furthermore, due to its high solubility, it is also easy to powderize.

[0173] <Process (i): Dissolution process of polyamide> In this step, polyamide is dissolved in a calcium chloride methanol solution to obtain a solution containing the dissolved polyamide. In this step, the polyamide is dissolved using a calcium chloride methanol solution, and the polyamide dissolution process is performed.

[0174] The concentration of calcium chloride in the calcium chloride methanol solution is not particularly limited, but is, for example, 10% to 25% by weight, preferably 12% to 22% by weight, and more preferably 15% to 20% by weight. If the concentration of calcium chloride in the calcium chloride methanol solution is too low, the amount of polyamide that can be dissolved will be small, and a large amount of solvent will be required. On the other hand, if the concentration of calcium chloride in the calcium chloride methanol solution is too high, calcium chloride is likely to remain undissolved and easily become an impurity.

[0175] The calcium chloride methanol solution may further contain solvents other than methanol. Examples of solvents other than methanol include, but are not limited to, water, and alcohols such as ethanol, n-propanol, and isopropanol. If the calcium chloride methanol solution contains such solvents, then the solution containing the dissolved polyamide will also contain these solvents.

[0176] The calcium chloride used as a raw material for the calcium chloride methanol solution is preferably anhydrous because the solubility of the polyamide decreases when water is mixed in, but it is possible to mix in dihydrate as long as the solubility is within an acceptable range.

[0177] When dissolving calcium chloride, heating may or may not be used. The heating temperature is not particularly limited, but for example, it is preferably between 20°C and 100°C, and more preferably between 25°C and 80°C. Below 20°C, the dissolution rate decreases, and above 100°C, the decomposition reaction proceeds, and the yield decreases.

[0178] The dissolution of calcium chloride may be carried out in either a batch or continuous manner. In the batch method, stirring may or may not be performed, but stirring is preferable. Stirring improves the dissolution rate of the polyamide solid. In the continuous method, the solvent may be continuously passed over the solid, or the solution may be circulated, but from the viewpoint of reducing the amount of solvent used, circulating the solution is preferable.

[0179] The shape of the container used to dissolve calcium chloride is not particularly limited; any shape, such as a tank type or a circulating type, may be used.

[0180] There are no particular limitations on the dissolution time, but it can range from, for example, 5 minutes to 48 hours.

[0181] In this process, the concentration of polyamide relative to the solvent (specifically, calcium chloride methanol solution) is not particularly limited, but is, for example, 1 to 20%, preferably 5 to 15%. If the concentration of polyamide relative to the solvent is too low, too much solvent will be required, while if the concentration of polyamide relative to the solvent is too high, the viscosity will increase and dissolution will take a long time.

[0182] The polyamide molded article to be subjected to dissolution, specifically, a processed polyamide molded article or a used polyamide molded article, etc., may be composed of only polyamide or may contain impurities. The impurities are, for example, other resins and metals. The polyamide to be subjected to dissolution may be in a state where such impurities are mixed, adhered, and / or coated. However, when impurities coexist, if necessary, the polyamide and the impurities are separated. The method of separation is not particularly limited. In a state where the polyamide is dissolved, if the impurities are unnecessary, they can be separated by methods such as filtration, centrifugation, and sedimentation separation. When the impurities are dissolved in the solvent together with the polyamide, for example, separation by extraction separation, membrane separation, and electrodialysis in a dissolved state can be performed, or it is possible to wash after precipitating the polyamide in the precipitation step described later.

[0183] <Step (ii): Precipitation step> In this step, the dissolved polyamide obtained in step (i) is precipitated from the solution containing the dissolved polyamide to obtain precipitated polyamide. In this step, the precipitated polyamide solid content may be separated from the solution.

[0184] The method of precipitating the dissolved polyamide from the solution is not particularly limited, but several precipitation methods are possible depending on the dissolved state.

[0185] When dissolved by heating, precipitation by cooling using the temperature dependence of the solubility of polyamide is conceivable. In this case, without adding an additional solvent to the solution containing the dissolved polyamide, the dissolved polyamide is precipitated from the solution to obtain precipitated polyamide.

[0186] If the temperature dependence of the solubility during dissolution is small, the polyamide may be precipitated by lowering its solubility by mixing it with a poor solvent. In this case, the poor solvent is added to a solution containing the dissolved polyamide, and then the dissolved polyamide is precipitated from the solution to obtain the precipitated polyamide. The poor solvent is not particularly limited, but examples include water and alcohols such as ethanol, n-propanol, and isopropanol. The method of adding the poor solvent to the polyamide may be either adding the polyamide solution to the poor solvent or adding the polyamide to the poor solvent, and the addition rate, temperature, and stirring rate during addition are not particularly limited.

[0187] If the temperature dependence of solubility during dissolution is small, the solubility of polyamide can also be reduced by lowering the concentration of calcium chloride.

[0188] As described above, in this process, the precipitated polyamide solids may be separated from the solution before the subsequent heating step. Examples of solid-liquid separation methods include filtration, centrifugation, and sedimentation. Either batch or continuous separation methods may be used.

[0189] The solid content obtained by solid-liquid separation may be washed with an additional washing liquid. Specifically, the precipitated polyamide is separated from the solution at the time of precipitation to obtain a solid content containing polyamide, and after the obtained solid content is washed with an additional washing liquid, in step (iii), the polyamide may be heated. The additional washing liquid is not particularly limited, and for example, a solution having the composition of the liquid portion at the time of precipitation, a good solvent, and a solvent capable of dissolving calcium chloride or the like is used. The additional washing liquid used here is, for example, water and alcohols such as methanol, ethanol, n-propanol, and isopropanol. The additional washing liquid is preferably methanol. The washing may be performed a plurality of times as necessary. Also, when it is necessary to remove the additional washing liquid by reduced pressure in the heating step described later, the additional washing liquid used for washing preferably has a boiling point of less than 100 °C. If the boiling point of the additional washing liquid is too high, the energy required to remove the washing liquid will increase.

[0190] <Step (iii): Heating step> In this step, the precipitated polyamide obtained in step (ii) is heated to obtain a heated polyamide. The precipitated polyamide solid content is heated and modified to reduce the content of the solvent (typically, a calcium chloride methanol solution) in the polyamide solid content.

[0191] In step (ii), if the solid content of the precipitated polyamide has not been separated from the solution, in this step, the solid content is heated in the solution. That is, the polyamide precipitated in step (ii) is heated in the solution at the time of precipitation in step (ii).

[0192] Also, in step (ii), when the precipitated solid content is separated from the solution at the time of precipitation, the heating is performed, for example, in air or an inert gas. In the heating of this step, drying may be performed in addition to heating, or drying may be performed along with heating. For example, as described above, in step (ii), the precipitated polyamide is separated from the solution at the time of precipitation to obtain a solid content containing polyamide, and after the obtained solid content is washed with an additional washing liquid, in this step, the polyamide may be heated.

[0193] While not intending to be bound by any particular theory, it is thought that heating modifies the polyamide as follows: During precipitation, it is assumed that the polyamide swells while the solvent (typically calcium chloride methanol solution) is permeated into it. By heating in this state, the solvent, the calcium chloride methanol solution, dries out, and / or the voids that held the calcium chloride methanol solution shrink. Therefore, it is thought that liquids such as washing solutions are less likely to re-permeate the polyamide, reducing the amount of residual calcium chloride methanol solution, and further improving the efficiency of impurity removal during the subsequent washing (step (iv)).

[0194] The heating temperature is not particularly limited, but for example, it is between 20°C and 100°C. If the heating temperature is too low, the modification effect will be low, and if the heating temperature is too high, the solid will fuse with the solution, making it difficult to handle.

[0195] While there are no particular limitations on stirring during heating, it is preferable to stir in order to avoid localized heating.

[0196] The pressure during heating is not particularly limited; heating may be done under pressure, or under reduced pressure. When solid-liquid separation is performed in step (ii), heating at a pressure below atmospheric pressure is preferable because the solvent (typically calcium chloride methanol solution) is distilled off, which increases the efficiency of the washing described later (step (iv)).

[0197] <Process (iv): Washing Process> In this step, the heated polyamide obtained in step (iii) is washed with a washing solution to obtain regenerated polyamide. In other words, this step is a step for washing the modified polyamide solids.

[0198] If solid-liquid separation is not performed in step (ii), and the precipitated solution is heated, solid-liquid separation should be performed first. The method of solid-liquid separation is not particularly limited, but examples include filtration, centrifugation, and sedimentation. A washing solution is added to the solid obtained by solid-liquid separation to dissolve and remove impurities.

[0199] Examples of washing solutions used in this process include water and alcohols such as ethanol, n-propanol, and isopropanol, which may be used in combination. Depending on the type of impurity, acids such as hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, and acetic acid, and bases such as sodium hydroxide, potassium hydroxide, sodium carbonate, and sodium bicarbonate may also be added to the washing solution. To avoid residue after washing, the final wash is preferably performed with water, and it is most preferable to perform all washes with water. In other words, in a preferred embodiment, the washing solution in step (iv) is water.

[0200] The amount of cleaning solution used in this process is not particularly limited, but it is preferable to determine the amount of cleaning solution so that the amount of remaining impurities after cleaning is reduced to the target amount.

[0201] The cleaning method in this process is not particularly limited and may include, for example, batch cleaning as many times as needed, continuous cleaning by flowing cleaning solution through a filter or centrifuge with the solid inside, or a combination of these methods.

[0202] After washing, drying may be performed as needed. For example, if a polyamide solid is obtained by washing with water, the water is removed from the solid by heating and / or reduced pressure to obtain a dry solid.

[0203] The recycled polyamide obtained in this process is a solid, preferably in powder form.

[0204] As described above, according to the present invention, the amount of wastewater generated in the washing process (e.g., the water washing process), which is essential for removing impurities during the recycling of polyamides useful as engineering plastics, can be reduced. Furthermore, it is believed that the amount of energy required during drying can be reduced by reducing the amount of wastewater. Therefore, it is expected that the amount of energy required for the polyamide recycling process can be reduced, thereby reducing the burden on the process.

[0205] [Invention (III)] The present invention (III) will now be described. In the present invention (III), the conditions of the present invention (I) to (II) and (IV) to (VII) may be incorporated as appropriate.

[0206] The method for producing recycled polyamide according to this embodiment (III) is a method for producing recycled polyamide using a polyamide resin composition containing polyamide coated with a silicone resin as a raw material, and includes a dissolution step in which the polyamide is dissolved to obtain a polyamide solution by mixing the polyamide resin composition with a metal chloride alcohol solution containing a metal chloride and an alcohol, wherein the mass percentage of polyamide in the polyamide solution in the dissolution step is 5 to 15% by mass. Another embodiment (III) of the method for producing recycled polyamide is a method for producing recycled polyamide using a polyamide resin composition containing polyamide coated with a silicone resin as a raw material, and includes a dissolution step in which the polyamide is dissolved to obtain a polyamide solution by mixing the polyamide resin composition with a metal chloride alcohol solution containing metal chloride and alcohol, wherein the viscosity of the polyamide solution at 25°C is 10 to 20,000 mPa·s. The manufacturing method of this embodiment (III) may be a method for producing recycled polyamide, for example, which involves a step of dissolving and extracting polyamide from a silicone-coated polyamide base fabric using a metal chloride alcohol solution with controlled moisture content.

[0207] The compounds used in the manufacturing method of this embodiment (III) will be described.

[0208] <Polyamide resin composition> In this embodiment, the polyamide can be a polymer polymerized by amide bonds, such as a polymer obtained by polycondensation of a diamine compound and a dicarboxylic acid compound, or a polymer obtained by ring-opening polymerization of a cyclic lactam. The above-mentioned diamine compounds are not particularly limited, but include ethylenediamine, trimethylenediamine, tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, nonanediamine, methylpentanediamine, and p-phenylenediamine. The above-mentioned dicarboxylic acid compounds are not particularly limited, but include oxalic acid, glutaric acid, adipic acid, sebacic acid, terephthalic acid, and isophthalic acid. Examples of the above-mentioned cyclic lactams include, but are not limited to, ε-caprolactam, undecanlactam, and lauryllactam. The combination of the above-mentioned diamine compound, dicarboxylic acid compound, and cyclic lactam compound is not particularly limited, and multiple types of compounds may be used in combination for each type. Among these, aliphatic polyamides are preferred from the viewpoint of high solubility in metal chloride alcohol solutions (e.g., calcium chloride methanol), and nylon 66 is the most preferred.

[0209] The above polyamide resin composition includes a polyamide coated with a silicone resin. The composition may consist solely of a polyamide coated with a silicone resin, or it may further contain other components. In particular, from the viewpoint of the manufacturing efficiency of recycled polyamide, the mass ratio of polyamide coated with silicone resin is preferably 30 to 100% by mass, more preferably 60% by mass or more, even more preferably 70% by mass or more, and especially preferably 80% by mass or more, based on 100% by mass of the polyamide resin composition.

[0210] The above-mentioned silicone resin is not particularly limited, but examples include methyl silicone and phenyl silicone resin. It may be a mixture of these resins, or a mixture of each raw material that has been cured.

[0211] The polyamide coated with silicone resin may also have other coatings in addition to the silicone resin. The type of other coating is not particularly limited, but examples include polyethylene, polypropylene, polyester, and fluororesin. It is preferable that the coating is insoluble in the metal chloride alcohol solution used for dissolution. Polyamide coated with silicone resin may be recycled polyamide raw material, such as process scraps and waste from molded products such as fibers, automotive parts, and electrical product parts, which use polyamide as a raw material. Specifically, this includes process scraps and waste from clothing, airbags, tire cords, engine compartment and intake system parts, fuel system parts, connectors, fishing nets, and UD tape.

[0212] The above polyamide resin composition may also contain sewing thread. The material of the sewing thread is not particularly limited, but it is preferable that it be made of the same polyamide as the base fabric, as this can be recovered as recycled polyamide.

[0213] <Metal chloride alcohol solution> For dissolving polyamide, a metal chloride alcohol solution is used. The above metal chloride alcohol solution contains a metal chloride and an alcohol, and may also contain other components. In particular, the total mass ratio of the metal chloride and the 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, and even more preferably 100% by mass.

[0214] The above-mentioned metal chlorides are not particularly limited, but examples include zinc chloride, magnesium chloride, and calcium chloride, with zinc chloride and calcium chloride being preferred, and calcium chloride being the most preferred. The metal chloride used as a raw material may be in anhydrous or hydrated form.

[0215] The mass ratio of the metal chloride to 100% by mass of the above metal chloride alcohol solution is preferably 10 to 25% by mass. If it is less than 10% by mass, the amount of polyamide that can be dissolved will be small, and a large amount of solvent will be required. If it exceeds 25% by mass, the metal chloride is likely to remain undissolved and is more likely to be mixed in as an impurity.

[0216] The amount of water in the above metal chloride alcohol solution is not particularly limited, but it is preferably 4 moles or less of water per mole of metal chloride in the solution.

[0217] Examples of the alcohols mentioned above include methanol, ethanol, n-propanol, and 2-propanol. Among these, methanol is preferred from the viewpoint of polyamide solubility.

[0218] The method for mixing the above metal chloride and alcohol is not particularly limited, but stirring is preferable if it is done in a batch process. Although calcium chloride will dissolve even without stirring, it takes time and localized variations in composition may occur.

[0219] The metal chloride alcohol solution used for dissolving the polyamide is preferably a solution produced by separating the polyamide from the metal chloride alcohol solution in which the polyamide was dissolved from the polyamide base fabric. If the concentration and composition change during the separation and recovery of the polyamide, separation from unwanted components by extraction or distillation, concentration by distillation, or concentration adjustment by adding metal chloride and / or alcohol may be performed. For example, the metal chloride alcohol solution from which the polyamide was separated may be concentrated and used in the production method of this embodiment. Since alcohol and metal chloride are not discarded, the environmental impact is small, and the recovery rate is improved because the polyamide remaining in the supernatant during the separation and recovery of the polyamide can be recovered again.

[0220] The following describes each step in the manufacturing method of this embodiment.

[0221] <Process 1 Melting process> The above dissolution step involves mixing a polyamide resin composition containing silicone-coated polyamide (for example, silicone-coated polyamide base fabric) with a metal chloride alcohol solution to dissolve the polyamide. By mixing the polyamide resin composition with the metal chloride alcohol solution, the polyamide dissolves from the silicone-coated polyamide in the polyamide resin composition. In this specification, a solution obtained by mixing the above polyamide resin composition and the above metal chloride alcohol solution is referred to as "polyamide dissolution." The polyamide dissolution contains dissolved polyamide, silicone that coated the polyamide, etc. By separating the coating material such as silicone from the polyamide dissolution, a "solution containing polyamide" can be obtained. The shape of the polyamide base fabric used for dissolution is not particularly limited. It may be added in its original form as scraps from the base fabric manufacturing process or as used airbags, or it may be cut according to the size of the dissolution equipment.

[0222] The temperature at which the above polyamide resin composition and the above metal chloride alcohol solution are mixed is not particularly limited, but is preferably 30 to 90°C, more preferably 40 to 90°C, and even more preferably 40 to 60°C. Dissolution is slow below 30°C, and above 90°C the temperature is higher than the boiling point, which is undesirable from the viewpoint of corrosiveness and decomposition.

[0223] Dissolution can be carried out using either a batch or continuous method. In the batch process, stirring is not particularly limited, but it is preferable. Stirring improves the dissolution rate of the polyamide solid. In a continuous flow system, the solvent can be continuously passed through the solid, or the solution can be circulated. Circulation is preferable because it reduces the amount of solvent used.

[0224] The shape of the container used in the above dissolution process is not particularly limited; any shape, such as a tank type or a circulating type, may be used.

[0225] The time for mixing the polyamide resin composition and the metal chloride alcohol solution is not particularly limited, but it is preferably between 5 minutes and 100 hours.

[0226] The mass percentage of polyamide in the above polyamide solution (100% by mass) is preferably 5 to 15% by mass, and more preferably 7 to 13% by mass. If it is less than 5% by mass, too much solvent is required, and if it exceeds 15% by mass, the viscosity becomes high, leading to a longer dissolution time and poor handling. Furthermore, the mass percentage of polyamide in a 100% mass solution containing the above-mentioned polyamide is preferably 5 to 15% by mass, and more preferably 7 to 13% by mass. If it is less than 5% by mass, too much solvent is required, and if it exceeds 15% by mass, the viscosity becomes high, leading to longer mixing times and poor handling.

[0227] The viscosity of the above polyamide solution at 25°C is preferably 10 to 20,000 mPa·s, more preferably 10 to 10,000 mPa·s, and even more preferably 10 to 3,000 mPa·s. While higher viscosity indicates a higher polymer concentration, it reduces the dissolution efficiency of the polyamide due to factors such as adhesion to the base fabric. Furthermore, the viscosity of the solution containing the polyamide at 25°C is preferably 10 to 20,000 mPa·s, more preferably 10 to 10,000 mPa·s, and even more preferably 10 to 3,000 mPa·s.

[0228] The method for separating the silicone resin from the polyamide solution is not particularly limited, but examples include scooping the silicone resin from the dissolved layer, filtration, centrifugation, and sedimentation separation, and these may be combined. Since fine fragments of silicone may be generated during the dissolution of polyamide, it is preferable to remove these fine fragments by filtration or a method combined with filtration.

[0229] It is preferable to remove any other polyamide coatings coated on the silicone resin at the same time as the silicone resin. Since the separated silicone resin and other coatings have a polyamide-containing solution attached to them, it is preferable to wash them and recover the polyamide-containing solution. The solvent for washing is not particularly limited, but calcium chloride methanol solution is preferred. The washing method is not particularly limited, but examples include stirring washing in a tank reactor or flow washing in a filter.

[0230] <Polyamide recovery process> The polyamide recovery step described above is a step of recovering polyamide from a solution containing polyamide, from which the silicone resin obtained in the dissolution step has been removed. While polyamide may be recovered from the above-mentioned polyamide solution, it is preferable to recover the polyamide from the polyamide-containing solution after removing any coatings such as silicone resin, in order to further improve recovery efficiency.

[0231] One method for recovering polyamide from a polyamide-containing solution is to precipitate the polyamide. While there are no particular limitations on the method for precipitation of polyamide from the polyamide-containing solution, several precipitation methods are possible depending on the dissolved state. If the polyamide is dissolved by heating, precipitation by cooling, utilizing the temperature dependence of the polyamide's solubility, can be considered. In this case, the dissolved polyamide is precipitated from the solution without adding any additional solvent, thereby obtaining the precipitated polyamide.

[0232] If the temperature dependence of solubility during dissolution is small, the solubility of the polyamide may be reduced and precipitated by mixing the polyamide-containing solution with a poor solvent. In this case, the poor solvent is added to the solution containing the dissolved polyamide, and then the dissolved polyamide is precipitated from the solution to obtain the precipitated polyamide. The poor solvent is not particularly limited, but examples include water and alcohols such as ethanol, n-propanol, and isopropanol. The method of adding the poor solvent to the polyamide may be either adding the polyamide-containing solution to the poor solvent, or adding the poor solvent to the polyamide-containing solution, and the addition rate, temperature, and stirring rate during addition are not particularly limited. The amount of poor solvent added is not particularly limited, but it is preferably 0.5 to 50 times the mass of the solution containing the polyamide, and more preferably 1 to 10 times the mass. A smaller amount of poor solvent added results in a lower recovery rate, while a larger amount of poor solvent added results in a larger solution volume, requiring more time and energy for processing.

[0233] If the temperature dependence of solubility during dissolution is small, the solubility of polyamide can also be reduced by lowering the concentration of calcium chloride. The method of adding methanol to lower the concentration of calcium chloride is not particularly limited, but it may be either by adding methanol to the solution containing the polyamide, or by adding methanol to the solution containing the polyamide, and the rate of addition, temperature, and stirring speed during addition are not particularly limited.

[0234] There are no particular restrictions on the shape of the container; any shape, such as a tank type or a circulating type, may be used.

[0235] The precipitated polyamide is preferably recovered by solid-liquid separation. Examples of solid-liquid separation methods include filtration, centrifugation, and sedimentation. Either batch or continuous methods may be used.

[0236] The polyamide obtained by solid-liquid separation is preferably washed with a solvent. The washing solution is not particularly limited, but for example, a solution with the same composition as the liquid portion at the time of precipitation, a good solvent, and a solvent that can dissolve calcium chloride, etc., can be used. Additional washing solutions used here include, for example, water and alcohols such as methanol, ethanol, n-propanol, and isopropanol. Methanol is preferred as the additional washing solution. Washing may be performed multiple times as needed.

[0237] The washing method is not particularly limited and includes batch washing, continuous washing by flowing water through a solid-liquid separation device such as a filter or centrifuge, and methods combining these. After washing, the polyamide can be dried to obtain powdered polyamide by removing the washing solvent by heating and / or reduced pressure.

[0238] As described above, this embodiment provides a method for producing recycled polyamide in high yield from a composition in which polyamide, useful as an engineering plastic, is coated with silicone.

[0239] <Process for concentrating the metal chloride alcohol solution> From the viewpoint of reusing the metal chloride alcohol solution, the manufacturing method of this embodiment may further include a step of concentrating the metal chloride alcohol solution. For example, the metal alcohol solution containing metal chloride and alcohol obtained in the polyamide recovery process described above may be concentrated and reused. Examples of the concentration methods mentioned above include concentration by heating.

[0240] <Recycled polyamide> The shape of the recycled polyamide produced by the manufacturing method of this embodiment is not particularly limited, and examples include polyamide that has been melted during recycling and formed into pellets, polyamide that has been dissolved in a solvent and then precipitated into a powder, and tablet-shaped polyamide produced by agglomerating the powder according to handling conditions. The above-mentioned recycled polyamide can be used as a raw material for polyamide fibers, polyamide base fabrics, airbags, and the like.

[0241] (Spinning of polyamide fibers) In melt spinning, the spinning temperature is preferably between 290°C and 310°C. Setting the spinning temperature to 310°C or lower is preferable because it suppresses the thermal decomposition of the polyamide, 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 preferable because it allows the polyamide to exhibit sufficient melt fluidity, resulting in uniform discharge volume between discharge holes and enabling high-magnification stretching.

[0242] In the melt spinning process, the residence time (the time from when the polyamide resin is melted until it is extruded from the spinneret) should be as short as possible. A residence time of 30 minutes or less is preferable, 15 minutes or less is more preferable, and 0.5 minutes to 7 minutes is even more preferable. A short residence time is preferable because the amount of cyclopentanones in the polymer increases at the melting temperature.

[0243] For thermal stability in high-temperature, high-humidity environments, it is preferable to add a copper compound to the polyamide so that the copper concentration is 1 to 500 ppm, and more preferably 30 to 500 ppm. This effectively suppresses the deterioration of mechanical performance even when exposed to high-temperature, high-humidity environments for extended periods or to environments with high ozone content. Below 30 ppm of copper, the heat resistance strength retention rate decreases, while above 500 ppm, the strength decreases.

[0244] 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 halogen compound. Examples of metal halogen 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 or colorimetric methods.

[0245] While not limited to the following, organic antioxidants such as hindered phenol antioxidants, sulfur antioxidants, and phosphorus antioxidants, as well as heat stabilizers, light stabilizers such as hindered amine, benzophenone, and imidazole antioxidants, and UV absorbers may be added as stabilizers. The amount to be added should be selected appropriately, but it can be added at a concentration of 1 to 1000 ppm relative to the polyamide. These additives may be used individually or in combination.

[0246] Furthermore, in the melt spinning process, it is preferable to use a single-screw or double-screw extruder in the melting section. This extruder allows the polyamide resin to be guided to polymer piping, a gear pump, and a spinning pack while applying appropriate pressure.

[0247] Furthermore, filtering the polyamide resin with a metal fiber nonwoven fabric filter or sand before it is extruded from the spinneret is preferable because it stabilizes the spinning operation. The shape of the spinneret hole in the spinneret should be selected according to the cross-sectional shape of the single fiber that makes up the filament to be manufactured. The yarn spun from the spinneret is solidified with cooling air, a process lubricant is applied, the yarn is taken up, stretched, and heat-treated to obtain polyamide fibers.

[0248] The oil adhesion rate of polyamide fibers is preferably 0.5 to 1.5 wt%. If the oil adhesion rate is 1.5 wt% or less, there is almost no difficulty in the weft yarn flying away due to stickiness (tackiness), and the single yarn convergence is not too good beyond what would occur due to entanglement, reducing the apparent cross-sectional area and preventing the air or water, which are the weft yarn transport media, from losing their weft yarn transport power, 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.

[0249] (Polyamide base fabric) In weaving, looms such as water jet looms, air jet looms, and rapier looms can be used. The base fabric for airbags is a high-density fabric, and in the warping and weaving processes, it is preferable to increase the warp tension to ensure good process passability. By setting the warp tension higher during weaving and creating effective reed beating conditions, a high-density fabric is formed.

[0250] Woven fabrics can have the process oils from the polyamide fibers washed off during the scouring process. The scouring process can be performed using hot water or pressurized hot water, and the processing can be a single-stage process or a multi-stage process of two or more stages. It is also preferable to apply a conventionally known scouring agent to perform the scouring.

[0251] It is preferable to heat-set the fabric in a heat-setting process. The heat-setting temperature is preferably between 110°C and 200°C, and the heat-setting time can be appropriately selected within the range of 0.1 minutes to 30 minutes. It is also preferable to dry the fabric while tensing it so that its shrinkage force is maintained at a predetermined level during the heat-setting process. Heat-setting the fabric helps to stabilize the processability of the subsequent resin coating process.

[0252] The fabric after the scouring process may be dried before the heat setting process, if necessary. The drying temperature is preferably in the range of 80°C to 130°C, and more preferably in the range of 100°C to 120°C. The drying time is preferably selected as appropriate, between 0.1 minutes and 30 minutes. Drying may be carried out in a relaxed or taut state.

[0253] Polyamide base fabrics can be used as uncoated base fabrics after undergoing a heat-setting process, but they can also be coated with coating agents such as silicone or urethane, or heat-laminated with thin films.

[0254] Methods for coating the surface of a woven fabric include immersing the fabric in a resin solution bath and then shaping and homogenizing the excess resin using a mangle, vacuum, or coating knife; bar coating methods such as comma coaters; and spraying the resin using a spray device or forming device. Of these, knife coating is preferred from the viewpoint of applying the resin uniformly and in small amounts.

[0255] The coating amount is 5g / m². 2 More than 100g / m 2 The following is more preferable: 10 g / m 2 More than 70g / m 2 The following is more preferably 15 g / m 2 More than 30g / m 2 The following is true: 5g / m 2 The required airtightness can be achieved with the above application amount. On the other hand, 100g / m 2 The following application amounts allow the coated fabric to be flexible, improve storage capacity, and reduce the overall weight of the bag.

[0256] <Airbag> The airbags can be appropriately selected from among the commonly used airbags for the driver's seat, passenger seat, side seats (including inflatable curtains), rear seats, etc. The cut shape of the airbag bag can be circular, oval, elliptical, rectangular, polygonal, or a combination thereof, as long as it satisfies the required deployment shape. Stitch shapes include single straight lines, multiple parallel straight lines, zigzag patterns, combinations of straight and zigzag patterns, and straight and diagonal lines. Standard stitching methods such as lockstitch and double chain stitch are acceptable, and the stitch pitch can be selected from a range of 20 to 60 stitches per 10cm. The thread thickness can be selected from 420d to 3000d, and commercially available threads made from materials such as polyamide, polyester, vinylon, aramid, and glass fibers can be used.

[0257] [Invention (IV)] The present invention (IV) will now be described. In the present invention (IV), the conditions of the present invention (I) to (III) and (V) to (VII) may be incorporated as appropriate. The present invention (IV) relates to a solvent that is less corrosive and capable of dissolving polyamides.

[0258] <Low-corrosive solvent (methanol composition)> The solvent in the present invention (IV) is a methanol composition containing a metal chloride, a hydroxide of the same metal, and water, each at a predetermined concentration. The concentration of metal chloride in this solvent is 5-25%, preferably 10-23%, and more preferably 15-22%. The concentration of metal chloride is specified as the weight concentration relative to the entire methanol composition. The lower the concentration of metal chloride, the lower the solubility of polyamide. The solubility of metal chloride in methanol is 25%, and excess metal chloride absorbs moisture, increasing the water content in the methanol composition and consequently decreasing the solubility of polyamide. Furthermore, the mass ratio of the metal chloride to 100% by mass of the above solvent is preferably 23 to 35% by mass, more preferably 25 to 33% by mass, and particularly preferably 27 to 31% by mass. The metals constituting the metal chloride and the hydroxide of the same metal are not particularly limited, but examples include zinc (i.e., the metal chloride is zinc chloride and the hydroxide of the same metal is zinc hydroxide) and calcium (i.e., the metal chloride is calcium chloride and the hydroxide of the same metal is calcium hydroxide), with calcium being preferred. The metal chloride used in preparing the solvent is preferably an anhydrous form, but a hydrate may also be used as long as it maintains the solubility of the polyamide. The solvent in this invention contains a hydroxide of the metal as a base that reduces corrosion by metal chlorides. Because the solvent in this invention contains a hydroxide of the metal, metal corrosivity can be reduced without decreasing the solubility of the polyamide in the metal chloride methanol solution. The concentration of the metal hydroxide is 0.001 to 1%, preferably 0.001 to 0.1%, and more preferably 0.001 to 0.01%. The concentration of the metal hydroxide is defined as the weight concentration of the metal hydroxide relative to the entire methanol composition. The metal hydroxide does not need to be completely dissolved in methanol; it may be partially undissolved. The mass ratio of water to 100% by mass of the above metal chloride alcohol solution is preferably 0.001 to 10% by mass, more preferably 0.001 to 5% by mass, even more preferably 0.001 to 1% by mass, and particularly preferably 0.01 to 0.1% by mass. In this embodiment, the metal chloride alcohol solution preferably has a metal chloride concentration of 23% by mass or more and 35% by mass or less, and contains 0.001 to 1% of a hydroxide of the same metal as the metal contained in the metal chloride and 0.001 to 10% of water.

[0259] <Polyamide-containing solution> Furthermore, the methanol composition may be a polyamide-containing solution further containing polyamide dissolved in the methanol composition as a solvent. Such a polyamide-containing solution can reduce corrosiveness.

[0260] <Polyamide> In this invention, polyamide refers to polymers polymerized by amide bonds, such as those obtained by polycondensation of a diamine compound and a dicarboxylic acid compound, or by ring-opening polymerization of a cyclic lactam.

[0261] The diamine compounds are not particularly limited, but examples include hexamethylenediamine, nonanediamine, methylpentanediamine, and p-phenylenediamine.

[0262] The dicarboxylic acid compounds are not particularly limited, but examples include adipic acid, sebacic acid, terephthalic acid, and isophthalic acid.

[0263] Examples of cyclic lactams, though not particularly limited, include ε-caprolactam, undecanlactam, and lauryllactam.

[0264] The combination of diamine compounds, dicarboxylic acid compounds, and cyclic lactam compounds is not particularly limited, and multiple types of compounds may be used in combination for each type. Polyhexamethylene adipamide, composed of hexamethylenediamine and adipic acid, is suitable due to its high solubility.

[0265] While the polyamide is not particularly limited, examples include those containing aliphatic polyamides such as polyamide 66 (polyhexamethylene adipamide), polyamide 6, polyamide 610, polyamide 6T, and polyamide 6I. Polyamides containing aliphatic polyamides are preferred, and those containing polyamide 66 (polyhexamethylene adipamide) are most preferred.

[0266] <Method for producing polyamide composition> The following describes in detail a method for producing a polyamide composition using the low-corrosive solvent of the present invention, but the following description is not intended to limit the method for producing the polyamide composition.

[0267] <Step 1: Dissolution of polyamide> Step 1 is the process of dissolving the raw material polyamide composition, which will be the raw material for polyamide.

[0268] The solvent used to dissolve the raw material polyamide composition is the low-corrosion solvent described above.

[0269] The dissolution temperature is not particularly limited, but it is preferably between 40 and 90°C, and more preferably between 40 and 60°C or lower. Below 40°C, dissolution is slow, and above 90°C, the temperature is higher than the boiling point, which is undesirable from the viewpoint of corrosiveness and decomposition.

[0270] Dissolution can be carried out using either a batch or continuous method. In the batch process, stirring is not particularly limited, but it is preferable. Stirring improves the dissolution rate of the polyamide solid. In a continuous flow system, the solvent can be continuously passed through the solid, or the solution can be circulated. Circulation is preferable because it reduces the amount of solvent used.

[0271] There are no particular restrictions on the shape of the container; any shape, such as a tank type or a circulating type, may be used.

[0272] The dissolution time is not particularly limited, but it is preferably between 5 minutes and 100 hours.

[0273] The concentration of polyamide in the solvent is not particularly limited, but it is preferably 5-15%, and more preferably 7-13%. If it is less than 5%, too much solvent is required, and if it exceeds 15%, the viscosity becomes high, leading to a longer dissolution time and poor handling.

[0274] The raw material polyamide composition used for dissolution may consist solely of polyamide, or it may contain impurities such as other resins or metals mixed in, attached to, or coated. If impurities other than polyamide are present, a process to separate the polyamide from these impurities is necessary. The separation method is not particularly limited, but if the impurities are not needed while the polyamide is dissolved, they can be separated by methods such as filtration, centrifugation, or sedimentation. If the impurities dissolve together with the polyamide in the solvent, methods such as extraction separation in the dissolved state, membrane separation, electrodialysis, or washing after precipitating the polyamide in the precipitation process described later can be considered.

[0275] <Step 2: Dilution Step> Step 2 is an optional step in which the polyamide dissolved in the solvent in Step 1 is diluted with methanol.

[0276] This document describes in detail the method for diluting polyamide solutions. A methanol dilution ratio of 1.5 to 5 times is preferred. In this specification, the dilution ratio is defined as the value obtained by dividing the weight of the polyamide solution after dilution by the weight of the polyamide solution at the time of dissolution. In this case, even if precipitation occurs in the polyamide solution after dilution, the weight including the precipitate is considered to be the weight of the polyamide solution after dilution. If the dilution ratio is less than 1.5, the amount of polyamide precipitated is small and the particles do not grow sufficiently, resulting in a small particle size. If the dilution ratio is greater than 5 times, precipitation is more likely to occur during dilution, resulting in a wider particle size distribution. The temperature at which the solution is diluted with methanol is not particularly limited, but 40-90°C is preferred. Dilution at temperatures lower than 40°C is prone to precipitation. Dilution at temperatures above 90°C is prone to uneven precipitation due to the volatilization and condensation of methanol near the liquid surface, making it difficult to control the particle size distribution. The dilution rate of methanol is not particularly limited, but it is preferable to add it at a rate that does not cause rapid changes in concentration or temperature during dilution, thus preventing the precipitation of polyamide. The temperature of the methanol used for dilution is not particularly limited, but it is preferably between 15 and 90°C. Below 15°C, localized precipitation is likely to occur during dilution, and above 90°C, the temperature is higher than the boiling point of methanol, requiring processing under pressure. The water content of the methanol used for dilution is not particularly limited, but it is preferably 0.005 to 1%. If the water content is too high, the polyamide will precipitate rapidly because the aqueous solution has lower solubility. There are no particular restrictions on the dilution method. Either batch or continuous dilution is acceptable. In the case of batch processing, stirring is not particularly limited, but it is preferable. Stirring ensures uniform temperature and concentration.

[0277] There are no particular restrictions on the shape of the container; any shape, such as a tank type or a circulating type, may be used.

[0278] <Process 3 Separation process (cooling precipitation process)> Step 3 is the step of separating the polyamide from the polyamide solution. Separation of the polyamide may be performed, for example, by precipitation of the polyamide by cooling the polyamide solution and solid-liquid separation of the precipitated solid polyamide from the polyamide solution. There are no particular restrictions on the cooling method; either batch or continuous cooling is acceptable. In batch processing, there are no particular limitations on whether or not stirring is performed, but stirring is preferable. Stirring ensures uniform temperature and concentration. It is preferable to stir under conditions that minimize particle breakage and shearing, depending on the equipment and method used.

[0279] The cooling rate is not particularly limited, but 10 to 100°C / Hr is preferred, and 20 to 50°C / Hr is more preferred. Below 10°C / Hr, the cooling time is long, and at cooling rates above 100°C / Hr, rapid precipitation results in smaller particle sizes. The particle size can be controlled by changing the cooling rate. While there are no particular limitations on the cooling temperature, it is preferable that it be at least 10°C lower than the dilution temperature. If the temperature difference is less than 10°C, precipitation will be minimal and particle growth will be difficult. It is preferable to recover the precipitated solid by solid-liquid separation. The method of solid-liquid separation is not particularly limited, but examples include filtration, centrifugation, and sedimentation. Either batch or continuous operation is acceptable for any of these methods. It is preferable to wash the solid obtained by solid-liquid separation with a solvent. The washing solvent is not particularly limited, but it is preferable to use a solution with a composition similar to the liquid portion at the time of precipitation, a good solvent, or a solvent that can dissolve metal chlorides, etc. As washing solvents, alcohols such as methanol and ethanol, and water are preferred. The washing method is not particularly limited and includes batch washing, continuous washing by flowing water through a solid-liquid separation device such as a filter or centrifuge, and methods combining these. After washing, the polyamide can be dried to obtain a polyamide composition by removing the washing solvent by heating and / or reduced pressure. In the method for producing the polyamide composition of the present invention, the polyamide composition may be obtained as a powder (powdered polyamide composition).

[0280] <Polyamide composition> The polyamide composition obtained by the production method of the present invention may include aliphatic polyamides such as polyamide 66 (polyhexamethylene adipamide), polyamide 6, polyamide 610, polyamide 6T, and polyamide 6I as the polyamide, but it is preferable that it contains aliphatic polyamides, and it is most preferable that it contains polyamide 66 (polyhexamethylene adipamide). The polyamide composition obtained by the production method of the present invention may also contain metal atoms and halogen atoms. The metal atoms are metal atoms derived from metal chlorides and / or hydroxides of the same metal contained in the low-corrosive solvent (methanol composition) used in the production method of the present invention, and examples include zinc atoms and calcium atoms, with calcium atoms being preferred. The metal atom content of the polyamide composition obtained by the production method of the present invention is preferably 0.001 to 1000 ppm, more preferably 0.001 to 700 ppm, and even more preferably 0.001 to 500 ppm. The molar content of halogen atoms in the polyamide composition obtained by the manufacturing method of the present invention is preferably less than 2, more preferably less than 1, and even more preferably less than 0.5 relative to the molar content of metal atoms. The polyamide composition obtained by the manufacturing method of the present invention may be in powder form.

[0281] <Uses of polyamide compositions> The polyamide composition obtained by the manufacturing method of the present invention can be used as a material for polyamide fibers. By spinning the polyamide fibers, recycled fibers can be obtained. By weaving the recycled fibers of this embodiment, recycled woven fabric can be obtained. The recycled woven fabric of this embodiment can be used as a polyamide base fabric for recycled airbags.

[0282] <Spinning of polyamide fibers> In melt spinning, the spinning temperature is preferably between 290°C and 310°C. Setting the spinning temperature to 310°C or lower is preferable because it suppresses the thermal decomposition of the polyamide, 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 preferable because it allows the polyamide to exhibit sufficient melt fluidity, resulting in uniform discharge volume between discharge holes and enabling high-magnification stretching.

[0283] In the melt spinning process, the residence time (the time from when the polyamide resin is melted until it is extruded from the spinneret) should be as short as possible. A residence time of 30 minutes or less is preferable, 15 minutes or less is more preferable, and 0.5 minutes to 7 minutes is even more preferable. A short residence time is preferable because the amount of cyclopentanones in the polymer increases at the melting temperature.

[0284] For thermal stability in high-temperature, high-humidity environments, it is preferable to add a copper compound to the polyamide so that the copper concentration is 1 to 500 ppm, and more preferably 30 to 500 ppm. By doing so, even if the product of the present invention is left in a high-temperature, high-humidity environment for a long time, or exposed to an environment with a large amount of ozone for a long period of time, the deterioration of its mechanical performance is extremely effectively suppressed. If the copper content is less than 30 ppm, the heat resistance strength retention rate decreases, and if the amount added exceeds 500 ppm, the strength decreases.

[0285] 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 halogen compound. Examples of metal halogen 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 or colorimetric methods.

[0286] While not limited to the following, organic antioxidants such as hindered phenol antioxidants, sulfur antioxidants, and phosphorus antioxidants, as well as heat stabilizers, light stabilizers such as hindered amine, benzophenone, and imidazole antioxidants, and UV absorbers may be added as stabilizers. The amount to be added should be selected appropriately, but it can be added at a concentration of 1 to 1000 ppm relative to the polyamide. These additives may be used individually or in combination.

[0287] Furthermore, in the melt spinning process, it is preferable to use a single-screw or double-screw extruder in the melting section. This extruder allows the polyamide resin to be guided to polymer piping, a gear pump, and a spinning pack while applying appropriate pressure.

[0288] Furthermore, filtering the polyamide resin with a metal fiber nonwoven fabric filter or sand before it is extruded from the spinneret is preferable because it stabilizes the spinning operation. The shape of the spinneret hole in the spinneret should be selected according to the cross-sectional shape of the single fiber that constitutes the filament to be manufactured. The yarn spun from the spinneret is solidified with cooling air, a process lubricant is applied, the yarn is taken up, stretched, and heat-treated to obtain the polyamide fiber used in the present invention.

[0289] The oil adhesion rate of polyamide fibers is preferably 0.5 to 1.5 wt%. If the oil adhesion rate is 1.5 wt% or less, there is almost no difficulty in the weft yarn flying away due to stickiness (tackiness), and the single yarn convergence is not too good beyond what would occur due to entanglement, reducing the apparent cross-sectional area and preventing the air or water, which are the weft yarn transport media, from losing their weft yarn transport power, 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.

[0290] <Polyamide base fabric> In weaving, looms such as water jet looms, air jet looms, and rapier looms can be used. The base fabric for airbags is a high-density fabric, and in the warping and weaving processes, it is preferable to increase the warp tension to ensure good process passability. By setting the warp tension higher during weaving and creating effective reed beating conditions, a high-density fabric is formed. Woven fabrics can have the process oils from the polyamide fibers washed off during the scouring process. The scouring process can be performed using hot water or pressurized hot water, and the processing can be a single-stage process or a multi-stage process of two or more stages. It is also preferable to apply a conventionally known scouring agent to perform the scouring. It is preferable to heat-set the fabric in a heat-setting process. The heat-setting temperature is preferably between 110°C and 200°C, and the heat-setting time can be appropriately selected within the range of 0.1 minutes to 30 minutes. It is also preferable to dry the fabric while tensing it so that its shrinkage force is maintained at a predetermined level during the heat-setting process. Heat-setting the fabric helps to stabilize the processability of the subsequent resin coating process. The fabric after the scouring process may be dried before the heat setting process, if necessary. The drying temperature is preferably in the range of 80°C to 130°C, and more preferably in the range of 100°C to 120°C. The drying time is preferably selected as appropriate, between 0.1 minutes and 30 minutes. Drying may be carried out in a relaxed or taut state.

[0291] Polyamide base fabrics can be used as uncoated base fabrics after undergoing a heat-setting process, but they can also be coated with coating agents such as silicone or urethane, or heat-laminated with thin films.

[0292] Methods for coating the surface of a woven fabric include immersing the fabric in a resin solution bath and then using a mangle, vacuum, or coating knife to form and homogenize the excess resin; bar coating methods such as comma coaters; and spraying the resin using a spray device or forming device. Of these, knife coating is preferred from the viewpoint of applying the resin uniformly and in small amounts.

[0293] The coating amount is 5g / m². 2 More than 100g / m 2 The following is more preferable: 10 g / m 2 More than 70g / m 2 The following is more preferably 15 g / m 2 More than 30g / m 2 The following is true: 5g / m 2 The required airtightness can be achieved with the above application amount. On the other hand, 100g / m 2 The following application amounts allow the coated fabric to be flexible, improve storage capacity, and reduce the overall weight of the bag.

[0294] <Airbag> The airbags can be appropriately selected from among the commonly used airbags for the driver's seat, passenger seat, side seats (including inflatable curtains), rear seats, etc. The cut shape of the airbag bag can be circular, oval, elliptical, rectangular, polygonal, or a combination thereof, as long as it satisfies the required deployment shape. Stitch shapes include single straight lines, multiple parallel straight lines, zigzag patterns, combinations of straight and zigzag patterns, and straight and diagonal lines. Standard stitching methods such as lockstitch and double chain stitch are acceptable, and the stitch pitch can be selected from a range of 20 to 60 stitches per 10cm. The thread thickness can be selected from 420d to 3000d, and commercially available threads made from materials such as polyamide, polyester, vinylon, aramid, and glass fibers can be used.

[0295] As described above, the present invention provides a solvent capable of dissolving polyamides with low corrosiveness, which can also be used to dissolve and precipitate polyamides useful as engineering plastics in order to produce powdered polyamides.

[0296] [Invention (V)] The present invention (V) will now be described. In the present invention (V), the conditions of the present invention (I) to (IV) and (VI) to (VII) may be incorporated as appropriate. <Method for producing polyamide> The method for producing polyamide according to this embodiment (V) (hereinafter sometimes referred to as "the method for producing polyamide according to this embodiment" or "the method according to this embodiment") is Step 1: A dissolution step in which a polyamide resin composition is heated and dissolved in a metal chloride alcohol solution containing metal chlorides and alcohols to obtain a heated polyamide solution, Step 2: A recovery step in which polyamide is precipitated from the heated polyamide solution and recovered, Step 3: A washing step to wash the recovered polyamide, Step 4: A drying step in which the washed polyamide is heated and dried, Includes. The manufacturing method of this embodiment may consist only of steps 1 to 4, or it may include other steps as well.

[0297] (polyamide) First, the polyamide and polyamide resin composition used in the manufacturing method of this embodiment will be described.

[0298] The polyamide can be a polymer polymerized by amide bonds, such as one obtained by polycondensation of a diamine compound and a dicarboxylic acid compound, or one obtained by ring-opening polymerization of a cyclic lactam. The aforementioned diamine compound is not particularly limited, but examples include ethylenediamine, trimethylenediamine, tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, nonanediamine, methylpentanediamine, and p-phenylenediamine. The dicarboxylic acid compound is not particularly limited, but examples include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, sebacic acid, terephthalic acid, and isophthalic acid. The cyclic lactams mentioned above are not particularly limited, but include ε-caprolactam, undecanlactam, and lauryllactam. The combination of the diamine compound, the dicarboxylic acid compound, and the cyclic lactam compound is not particularly limited, and multiple types of compounds may be used in combination for each type. Polyhexamethylene adipamide (for example, polyhexamethylene adipamide consisting of hexamethylenediamine and adipic acid) has high solubility and is suitable for the polyamide production method of this embodiment.

[0299] Furthermore, examples of the polyamides include polycaproamide (nylon 6), polyhexamethylene adipamide (nylon 66), polytetramethylene adipamide (nylon 46), polytetramethylene sebaamide (nylon 410), polypentamethylene adipamide (nylon 56), polypentamethylene sebaamide (nylon 510), polyhexamethylene sebaamide (nylon 610), polyhexamethylene dodecamide (nylon 612), polydecamethylene adipamide (nylon 106), polydecamethylene sebaamide (nylon 1010), Polydecamethylene dodecamide (Nylon 1012), Polyundecaneamide (Nylon 11), Polydodecaneamide (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 Polyhexamethylene terephthalamide / polyhexamethylene isophthalamide copolymer (nylon 6T / 6I), polyhexamethylene terephthalamide / polyundecaneamide copolymer (nylon 6T / 11), polyhexamethylene terephthalamide / polydodecaneamide copolymer (nylon 6T / 12), polyhexamethylene adipamide / polyhexamethylene terephthalamide / polyhexamethylene isophthalamide copolymer (nylon 66 / 6T / 6I), polyxylylene adipamide (nylon XD6), polyxylylene sebaamide (nylon XD10), Examples 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).In this context, " / " indicates a copolymer. These polyamides may be used individually or in combination of two or more. 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 as the polyamide, and it is particularly preferable to use polyamide 66. Polyamide 66 itself is a polyamide resin that is already generally known and is usually 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 lactam, aminocarboxylic acid, and combinations of other diamines and dicarboxylic acids, based on the total mass of all monomer units.

[0300] Furthermore, these polyamides may be commercially available or manufactured using known methods. Specific methods for producing polyamides are not particularly limited, but examples include methods of ring-opening polymerization of lactams, methods of self-condensation of ω-aminocarboxylic acids, and methods of condensation of diamines and dicarboxylic acids.

[0301] Furthermore, it is preferable that the polyamide has a value [NH2] / [COOH] obtained by dividing the amount of amino-terminal groups by the amount of carboxy-terminal groups, which is 0.5 or more and 0.9 or less. When [NH2] / [COOH] is within the above range, the interaction between the surface of the glass fibers and the polyamide ends becomes sufficiently large during melt kneading, and the physical properties of the resulting composition become sufficiently high. The amount of amino-terminal groups and carboxy-terminal groups are, for example, 1 This can be measured using 1H-NMR.

[0302] Furthermore, the polyamide may consist solely of polyamide, or it may be used as a polyamide resin composition containing the polyamide and other components. For example, the polyamide may have other impurities such as other resins or metals mixed in, attached to, or coated as other components. The mass ratio of the polyamide to 100% by mass of the polyamide resin composition is preferably 30 to 100% by mass, more preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 85% by mass or more, and particularly preferably 100% by mass, from the viewpoint of obtaining a powdered polyamide with larger particle size and a smaller particle size distribution in a short time.

[0303] Furthermore, if impurities other than the polyamide are present, the process may include a step to separate the polyamide from these impurities. The separation method is not particularly limited, but if the impurities are insoluble in the dissolved polyamide resin composition, they can be separated by methods such as filtration, centrifugation, or sedimentation. If the impurities dissolve together with the polyamide in the solvent, methods such as extraction separation in the dissolved state, membrane separation, electrodialysis, or washing after precipitating the polyamide in the precipitation step described later can be considered.

[0304] (Step 1: Process for obtaining a heated polyamide solution) Furthermore, the recovery method of this embodiment includes a dissolution step (step 1) in which the polyamide resin composition is heated and dissolved in a metal chloride alcohol solution containing metal chlorides and alcohols to obtain a heated polyamide solution. This process allows for the melt-separation of only the polyamide from the polyamide resin composition, thereby facilitating the subsequent recovery of the polyamide. Furthermore, since the polyamide can be melted and separated simply by mixing the polyamide resin composition with a predetermined metal chloride alcohol solution, the polyamide can be recovered efficiently and in high yield.

[0305] The metal chloride alcohol solution used for heating and dissolving the polyamide contains metal chlorides and alcohols. Furthermore, other components besides metal chlorides and alcohols may be included as needed. In particular, from the viewpoint of the solubility of the polyamide, the total mass ratio of the metal chloride and the alcohols to 100% by mass of the metal chloride alcohol solution is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 100% by mass.

[0306] Examples of the aforementioned alcohols include methanol, ethanol, linear or branched propanol, linear or branched butanol, and combinations thereof. Of these, methanol, ethanol, or combinations thereof are preferred from the viewpoint of polyamide solubility, with methanol being more preferred. In addition, the aforementioned alcohols may also include various diols as needed.

[0307] The mass ratio of the metal chloride to 100% by mass of the metal chloride alcohol solution is preferably 10 to 50% by mass, and more preferably 15 to 25% by mass. If the mass ratio is less than 10% by mass, the amount of polyamide that can be dissolved is small, and a large amount of solvent is required. If it exceeds 50% by mass, the metal chloride tends to remain undissolved and is more likely to be mixed in as an impurity.

[0308] Examples of the aforementioned metal chlorides include zinc chloride, magnesium chloride, and calcium chloride, with zinc chloride and calcium chloride being preferred, and calcium chloride being the most preferred. The metal chloride is preferably in an anhydrous form. The solubility of the polyamide decreases if water is mixed in. However, hydrates (for example, dihydrates of calcium chloride) may be mixed in as long as the solubility is within an acceptable range. The mass percentage of water in the metal chloride is preferably 30% by mass or less, more preferably 1% by mass or less, and even more preferably 0.1% by mass or less, and it is particularly preferable that it contains no water at all.

[0309] Furthermore, while there are no particular limitations on the temperature at which the material is heated and melted, it is preferably 30 to 90°C, and more preferably 40 to 60°C, from the viewpoint of solubility and other factors. Note that if the temperature is too low, melting will be slow, and if it exceeds 90°C, the temperature will be higher than the boiling point, which is undesirable from the viewpoint of corrosiveness and decomposition. The temperature may be constant, or it may be varied within the specified range.

[0310] The dissolution of the polyamide can be carried out in either a batch or continuous manner. In the batch process, stirring is not particularly limited, but it is preferable. Stirring improves the dissolution rate of the polyamide. In a continuous flow system, the solvent can be continuously passed through the solid, or the solution can be circulated. Circulation is preferable because it reduces the amount of solvent used.

[0311] The shape of the container used when heating and dissolving the polyamide is not particularly limited, and any shape such as a tank type or a circulating type may be used.

[0312] The dissolution time of the polyamide is not particularly limited, but is preferably between 5 minutes and 100 hours.

[0313] In step 1, the mass ratio of the polyamide resin composition to the metal chloride alcohol solution is not particularly limited, but is preferably 3 to 15% by mass, and more preferably 5 to 13% by mass. If it is less than 3% by mass, too much solvent is required, and if it exceeds 15% by mass, the viscosity of the heated polyamide solution increases, leading to a longer dissolution time and deterioration of handling properties.

[0314] (Step 2: Polyamide precipitation and recovery process) The method for producing polyamide according to this embodiment further includes a recovery step (step 2) after step 1, in which polyamide is precipitated from the heated polyamide solution and recovered. This process allows for the separation and recovery of the polyamide contained in the heated polyamide solution.

[0315] The method for precipitating the heated polyamide solution is not particularly limited. For example, the polyamide can be precipitated by cooling the heated polyamide solution.

[0316] The step of separating and recovering the heated polyamide solution may be performed after the dissolution step to obtain the heated polyamide solution, or after the step of obtaining the alcohol dilution solution, which will be described later.

[0317] There are no particular restrictions on the cooling method; either batch or continuous cooling is acceptable. In batch processing, there are no particular limitations on whether or not stirring is performed, but stirring is preferable. Stirring ensures uniform temperature and concentration. It is preferable to stir under conditions that minimize particle breakage and shearing, depending on the equipment and method used.

[0318] The cooling rate is not particularly limited, but 10 to 100°C / Hr is preferred, and 20 to 50°C / Hr is more preferred. Below 10°C / Hr, the cooling time is long, and at cooling rates above 100°C / Hr, rapid precipitation results in smaller particle sizes. The particle size can be controlled by changing the cooling rate. While there are no particular limitations on the cooling temperature, it is preferable that it be at least 10°C lower than the dilution temperature. If the temperature difference is less than 10°C, precipitation will be minimal and particle growth will be difficult. It is preferable to recover the precipitated solid by solid-liquid separation.

[0319] The method of solid-liquid separation is not particularly limited, but examples include filtration, centrifugation, and sedimentation. Either batch or continuous operation is acceptable for any of these methods. It is preferable to wash the solid obtained by solid-liquid separation with a solvent. The washing solvent is not particularly limited, but it is preferable to use a solution with a composition similar to the liquid portion at the time of precipitation, a good solvent, or a solvent that can dissolve metal chlorides, etc.

[0320] If the temperature dependence of the solubility during dissolution is small, the solubility of the heated polyamide solution may be reduced and precipitated by mixing it with a poor solvent for the polyamide. In this case, the poor solvent is added to the solution containing the dissolved polyamide, and then the dissolved polyamide is precipitated from the solution to obtain the precipitated polyamide. The poor solvent is not particularly limited, but examples include water and alcohols such as ethanol, n-propanol, and isopropanol. The method of adding the poor solvent to the polyamide may be either adding a solution containing the polyamide to the poor solvent, or adding the poor solvent to a solution containing the polyamide, and the rate of addition, temperature, and stirring speed during addition are not particularly limited. The amount of the poor solvent added is not particularly limited, but it is preferably 0.5 to 50 times the mass of the solution containing the polyamide, and more preferably 1 to 10 times the mass. A smaller amount added results in a lower recovery rate, while a larger amount added results in a larger solution volume, requiring more time and energy for processing.

[0321] Furthermore, if the temperature dependence of the solubility during dissolution is small, the solubility of the polyamide can also be reduced by lowering the concentration of calcium chloride. The method of adding methanol to lower the concentration of calcium chloride is not particularly limited, but it may be either adding the solution containing the polyamide to methanol, or adding methanol to the solution containing the polyamide, and the addition rate, temperature, and stirring rate during addition are not particularly limited. Furthermore, there are no particular restrictions on the shape of the container; any shape, such as a tank type or a circulating type, may be used.

[0322] (Step 3: Washing process of polyamide) The method for producing polyamide according to this embodiment further includes a washing step (step 3) in which the polyamide recovered in step 2 is washed. This process allows for the removal of impurities such as metal chlorides from the recovered polyamide.

[0323] The washing solution used in the washing is not particularly limited, but for example, a solution with the same composition as the liquid portion at the time of precipitation, a good solvent, and a solvent capable of dissolving calcium chloride, etc., can be used. Additional washing solutions used here include, for example, water and alcohols such as methanol, ethanol, n-propanol, and isopropanol. The additional washing solution is preferably methanol. Washing may be performed multiple times as needed.

[0324] The cleaning method is not particularly limited and includes batch cleaning, continuous cleaning by flowing water through a solid-liquid separation device such as a filter or centrifuge, and methods combining these.

[0325] Furthermore, it is preferable that step 3 is a control step that controls the amount of metal chloride after drying in step 4, which will be described later. The amount of metal chloride after drying in step 4 described below can be controlled by adjusting the type and concentration of the cleaning solution, the cleaning time, etc., so that the amount of metal chloride after drying in step 4 described below falls within a specific range.

[0326] (Step 4: Heat drying process of polyamide) The method for producing polyamide according to this embodiment further includes a drying step of heating and drying the polyamide after washing. This process allows the washing solvent to be removed from the washed polyamide by distillation, resulting in a dry solid and thus obtaining the polyamide.

[0327] Furthermore, in the polyamide manufacturing method of this embodiment, the amount of metal chloride adhering to the polyamide after heating and drying in step 4 is set to 20 parts by mass or less per 100 parts by mass of the polyamide. Regarding the washing of the recovered polyamide, while it is preferable to avoid excessive washing from the viewpoints of manufacturing efficiency, cost, and environmental considerations, there was also the problem that if the recovered polyamide was not washed sufficiently, some of the polyamide would melt due to metal chlorides adhering to it after washing, and then solidify during subsequent drying. Therefore, by keeping the amount of metal chloride adhering to the polyamide after heating and drying in step 4 to 20 parts by mass or less per 100 parts by mass of the polyamide, the metal chloride concentration can be kept within a range that can suppress the melting of the polyamide. In addition, it is preferable to keep the amount of metal chloride adhering to the polyamide after heating and drying in step 4 to 0.01 parts by mass or more per 100 parts by mass of the polyamide, as this can avoid excessive washing. From a similar viewpoint, the amount of metal chloride adhering to the polyamide after heating and drying in step 4 is preferably 0.01 to 10 parts by mass, and more preferably 0.01 to 5 parts by mass, per 100 parts by mass of the polyamide.

[0328] The method for measuring the amount of metal chloride attached to the polyamide after heating and drying in step 4 is not particularly limited, but examples include sampling a portion and measuring it by 1) X-ray fluorescence analysis after drying, 2) heating and decomposing it with nitric acid and then measuring it by ICP-AES, or 3) extracting the metal chloride with water and measuring it by ion chromatography.

[0329] The amount of metal chloride adhering to the polyamide after heating and drying in step 4 can be measured either after heating and drying in step 4, or after washing the polyamide in step 3 as described above. For measuring the amount of the aforementioned metal chloride, known methods can be used as appropriate.

[0330] (Measuring and confirming the amount of metal chloride, second cleaning process) Furthermore, the method for producing polyamide according to this embodiment preferably further includes a confirmation step of measuring the amount of metal chloride attached to the polyamide after heating and drying in step 4 and confirming whether or not it is within a predetermined range (20 parts by mass or less per 100 parts by mass of the polyamide). This process allows us to confirm the amount of metal chlorides adhering to the polyamide after heating and drying, and to adjust the washing and other conditions as appropriate.

[0331] For example, if the amount of metal chloride adhering to the polyamide after washing in step 3 or after heat drying in step 4 is checked and it is less than 0.01 parts by mass per 100 parts by mass of polyamide, there is a possibility that the washing in step 3 is excessive, and the washing conditions (washing time, washing solution concentration, etc.) can be relaxed. On the other hand, if the amount of metal chloride adhering to the polyamide after washing in step 3 or after heat drying in step 4 exceeds 20 parts by mass per 100 parts by mass of polyamide, it is considered that there is a large amount of metal chloride adhering to the polyamide after washing, which may cause solidification after heat drying, and a second washing step can be performed to wash it again.

[0332] Furthermore, confirmation that the amount of metal chloride attached to the polyamide is within the range can be done by taking a sample of the washed polyamide after the washing in step 3, or by taking a sample of the polyamide after the heating and drying in step 4, and measuring the amount of metal chloride attached to the polyamide.

[0333] (Recovered polyamide) The shape of the recovered polyamide is not particularly limited and can be in the form of pellets made by melting the polyamide, powder made by dissolving it in a solvent and then precipitating it, or tablet-shaped products made by agglomerating the powder according to the handling conditions.

[0334] The powdered polyamide obtained by the manufacturing method of this embodiment has a large particle size and a small particle size distribution. The median diameter of the aforementioned powdered polyamide is preferably 20 μm or more, and more preferably 30 to 70 μm. The above median diameter can be measured by the method described in the examples below. The particle size distribution of the aforementioned powdered polyamide is the value obtained by raising 10 to the power of S using the following formula (1) S The span is preferably 5 or less, more preferably 4 or less, and even more preferably 3 or less. S=log(d90 / d10) / log(d50) ···(1) (Here, in equation (1) above, dn (where n represents 10, 50, or 90) refers to the particle size at which the number of particles smaller than dn accounts for n% of the total number of particles, when the particle size distribution of the above-mentioned polyamide powder is measured by laser diffraction and scattering.) The above particle size distribution can be measured by the method described in the examples below.

[0335] Furthermore, the obtained polyamide can be melt-spun to produce polyamide fibers. In melt spinning, the spinning temperature is preferably between 290°C and 310°C. Setting the spinning temperature to 310°C or lower is preferable because it suppresses the thermal decomposition of the polyamide, 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 preferable because it allows the polyamide to exhibit sufficient melt fluidity, resulting in uniform discharge volume between discharge holes and enabling high-magnification stretching.

[0336] In the melt spinning process, the residence time (the time from when the polyamide resin is melted until it is extruded from the spinneret) should be as short as possible. A residence time of 30 minutes or less is preferable, 15 minutes or less is more preferable, and 0.5 minutes to 7 minutes is even more preferable. A short residence time is preferable because the amount of cyclopentanones in the polymer increases at the melting temperature.

[0337] For thermal stability in high-temperature, high-humidity environments, it is preferable to add a copper compound to the polyamide so that the copper concentration is 1 to 500 ppm, and more preferably 30 to 500 ppm. This effectively suppresses the deterioration of mechanical performance even when exposed to high-temperature, high-humidity environments for extended periods or to environments with high ozone content. However, if the copper content is less than 30 ppm, the heat resistance strength retention rate decreases, and if the copper content exceeds 500 ppm, the strength decreases.

[0338] 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 halogen compound. Examples of metal halogen 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 or colorimetric methods.

[0339] While not limited to the following, organic antioxidants such as hindered phenol antioxidants, sulfur antioxidants, and phosphorus antioxidants, as well as heat stabilizers, light stabilizers such as hindered amine, benzophenone, and imidazole antioxidants, and UV absorbers may be added as stabilizers. The amount to be added should be selected appropriately, but it can be added at a concentration of 1 to 1000 ppm relative to the polyamide. These additives may be used individually or in combination.

[0340] Furthermore, in the melt spinning process, it is preferable to use a single-screw or double-screw extruder in the melting section. This extruder allows the polyamide resin to be guided to polymer piping, a gear pump, and a spinning pack while applying appropriate pressure.

[0341] Furthermore, filtering the polyamide resin with a metal fiber nonwoven fabric filter or sand before it is extruded from the spinneret is preferable because it stabilizes the spinning operation. The shape of the spinneret hole in the spinneret should be selected according to the cross-sectional shape of the single fiber that makes up the filament to be manufactured. The spun yarn from the spinneret is solidified with cooling air, a process lubricant is applied, the yarn is taken up, stretched, and heat-treated to obtain polyamide fibers.

[0342] Furthermore, filtering the polyamide resin with a metal fiber nonwoven fabric filter or sand before it is extruded from the spinneret is preferable because it stabilizes the spinning operation. The shape of the spinneret hole in the spinneret should be selected according to the cross-sectional shape of the single fiber that makes up the filament to be manufactured. The spun yarn from the spinneret is solidified with cooling air, a process lubricant is applied, the yarn is taken up, stretched, and heat-treated to obtain polyamide fibers.

[0343] Furthermore, it is preferable that the oil adhesion rate of the polyamide fibers be 0.5 to 1.5 wt%. If the oil adhesion rate is 1.5 wt% or less, there is almost no difficulty in the weft yarn flying away due to stickiness (tackiness), and the single yarn convergence is not too good beyond what would occur due to entanglement, reducing the apparent cross-sectional area and preventing the air or water, which are the weft yarn transport media, from losing their weft yarn transport power, 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.

[0344] (Polyamide base fabric) Furthermore, the polyamide obtained by the manufacturing method of this embodiment can be melt-spun to form a polyamide base fabric. In weaving, looms such as water jet looms, air jet looms, and rapier looms can be used. The base fabric for airbags is a high-density fabric, and in the warping and weaving processes, it is preferable to increase the warp tension to ensure good process passability. By setting the warp tension higher during weaving and creating effective reed beating conditions, a high-density fabric is formed.

[0345] Woven fabrics can have the process oils from the polyamide fibers washed off during the scouring process. The scouring process can be performed using hot water or pressurized hot water, and the processing can be a single-stage process or a multi-stage process of two or more stages. It is also preferable to apply a conventionally known scouring agent to perform the scouring.

[0346] It is preferable to heat-set the fabric in a heat-setting process. The heat-setting temperature is preferably between 110°C and 200°C, and the heat-setting time can be appropriately selected within the range of 0.1 minutes to 30 minutes. It is also preferable to dry the fabric while tensing it so that its shrinkage force is maintained at a predetermined level during the heat-setting process. Heat-setting the fabric helps to stabilize the processability of the subsequent resin coating process. The fabric after the scouring process may be dried before the heat setting process, if necessary. The drying temperature is preferably in the range of 80°C to 130°C, and more preferably in the range of 100°C to 120°C. The drying time is preferably selected as appropriate, between 0.1 minutes and 30 minutes. Drying may be carried out in a relaxed or taut state.

[0347] Polyamide base fabrics can be used as uncoated base fabrics after undergoing a heat-setting process, but they can also be coated with coating agents such as silicone or urethane, or heat-laminated with thin films. Methods for coating the surface of a woven fabric include immersing the fabric in a resin solution bath and then shaping and homogenizing the excess resin using a mangle, vacuum, or coating knife; bar coating methods such as comma coaters; and spraying the resin using a spray device or forming device. Of these, knife coating is preferred from the viewpoint of applying the resin uniformly and in small amounts. The coating amount is 5g / m². 2 More than 100g / m 2 The following is more preferable: 10 g / m 2 More than 70g / m 2 The following is more preferably 15 g / m 2 More than 30g / m 2 The following is true: 5g / m 2 The required airtightness can be achieved with the above application amount. On the other hand, 100g / m 2 The following application amounts allow the coated fabric to be flexible, improve storage capacity, and reduce the overall weight of the bag.

[0348] [Invention (VI)] The present invention (VI) will now be described. In the present invention (VI), the conditions of the present invention (I) to (V) and (VII) may be incorporated as appropriate. <Method for producing polyamide and / or polyethylene terephthalate> The method for producing polyamide, the method for producing polyethylene terephthalate, and the method for producing polyamide and polyethylene terephthalate according to this embodiment (VI) (hereinafter sometimes simply referred to as "the method of this embodiment") are methods for producing polyamide and / or polyethylene terephthalate, which recover polyamide and / or polyethylene terephthalate from a mixture of polyamide and polyethylene terephthalate, comprising the steps of: mixing the mixture with a metal chloride alcohol solution containing metal chlorides and alcohols to obtain a polyamide solution in which the polyamide is dissolved; and separating and recovering the polyamide solution and / or the polyethylene terephthalate.

[0349] (A mixture of polyamide and polyethylene terephthalate) First, the impurities used in the manufacturing method of this embodiment will be described. The mixture used as a material in the manufacturing method of this embodiment is a mixture of polyamide and polyethylene terephthalate. The mixture only needs to contain at least polyamide and polyethylene terephthalate, and may contain other components as needed. Other components are not particularly limited, but include components that coat the polyamide and polyethylene terephthalate mixture, and components that are applied to it. Examples of coating components include resins, such as silicone resins and urethane resins, but are not limited to these. Examples of applied components include lubricating oils.

[0350] Here, the shape of the mixed material is not particularly limited, but it is preferable that it be a woven fabric (water jet loom, air jet loom, rapier loom, airbag base fabric, etc.) and more preferably an airbag component, in order to better enjoy the effects of the present invention. When the mixed material is a high-density woven fabric such as an airbag base fabric, the polyamide fibers and polyethylene terephthalate fibers become entangled, making it difficult to separate them sufficiently using conventional separation methods. On the other hand, in this embodiment, polyamide and / or polyethylene terephthalate can be recovered from the mixed material by dissolving and separating the polyamide. Therefore, even if the mixed material is a woven fabric, polyamide and / or polyethylene terephthalate can be recovered with high efficiency and high yield.

[0351] ·polyamide The polyamide can be a polymer polymerized by amide bonds, such as one obtained by polycondensation of a diamine compound and a dicarboxylic acid compound, or one obtained by ring-opening polymerization of a cyclic lactam. The aforementioned diamine compound is not particularly limited, but examples include ethylenediamine, trimethylenediamine, tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, nonanediamine, methylpentanediamine, and p-phenylenediamine. The dicarboxylic acid compound is not particularly limited, but examples include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, sebacic acid, terephthalic acid, and isophthalic acid. The cyclic lactams mentioned above are not particularly limited, but include ε-caprolactam, undecanlactam, and lauryllactam. The combination of the diamine compound, the dicarboxylic acid compound, and the cyclic lactam compound is not particularly limited, and multiple types of compounds may be used in combination for each type. Polyhexamethylene adipamide (for example, polyhexamethylene adipamide consisting of hexamethylenediamine and adipic acid) has high solubility and is suitable for the polyamide production method of this embodiment.

[0352] While there are no particular limitations on the method for measuring the particle size and particle size distribution of powdered polyamide, examples include laser diffraction, laser scattering, centrifugal sedimentation, particle tracking, and dynamic scattering.

[0353] Furthermore, examples of the polyamides include polycaproamide (nylon 6), polyhexamethylene adipamide (nylon 66), polytetramethylene adipamide (nylon 46), polytetramethylene sebaamide (nylon 410), polypentamethylene adipamide (nylon 56), polypentamethylene sebaamide (nylon 510), polyhexamethylene sebaamide (nylon 610), polyhexamethylene dodecamide (nylon 612), polydecamethylene adipamide (nylon 106), polydecamethylene sebaamide (nylon 1010), Polydecamethylene dodecamide (Nylon 1012), Polyundecaneamide (Nylon 11), Polydodecaneamide (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 Polyhexamethylene terephthalamide / polyhexamethylene isophthalamide copolymer (nylon 6T / 6I), polyhexamethylene terephthalamide / polyundecaneamide copolymer (nylon 6T / 11), polyhexamethylene terephthalamide / polydodecaneamide copolymer (nylon 6T / 12), polyhexamethylene adipamide / polyhexamethylene terephthalamide / polyhexamethylene isophthalamide copolymer (nylon 66 / 6T / 6I), polyxylylene adipamide (nylon XD6), polyxylylene sebaamide (nylon XD10), Examples 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).In this context, " / " indicates a copolymer. These polyamides may be used individually or in combination of two or more. 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 as the polyamide, and it is particularly preferable to use polyamide 66. Polyamide 66 itself is a polyamide resin that is already generally known and is usually 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 lactam, aminocarboxylic acid, and combinations of other diamines and dicarboxylic acids, based on the total mass of all monomer units.

[0354] Furthermore, these polyamides may be commercially available or manufactured using known methods. Specific methods for producing polyamides are not particularly limited, but examples include methods of ring-opening polymerization of lactams, methods of self-condensation of ω-aminocarboxylic acids, and methods of condensation of diamines and dicarboxylic acids.

[0355] Furthermore, it is preferable that the polyamide has a value [NH2] / [COOH] obtained by dividing the amount of amino-terminal groups by the amount of carboxy-terminal groups, which is 0.5 or more and 0.9 or less. When [NH2] / [COOH] is within the above range, the interaction between the surface of the glass fibers and the polyamide ends becomes sufficiently large during melt kneading, and the physical properties of the resulting composition become sufficiently high. The amount of amino-terminal groups and carboxy-terminal groups are, for example, 1 This can be measured using 1H-NMR.

[0356] Furthermore, the polyamide may consist solely of polyamide, or it may be a polyamide resin composition containing the polyamide and other components. For example, other resins, metals, or other impurities may be mixed, attached to, or coated onto the polyamide as other components. The mass ratio of polyamide to 100% by mass of the aforementioned polyamide is preferably 30 to 100% by mass, more preferably 70% by mass or more, even more preferably 80% by mass or more, even more preferably 85% by mass or more, and particularly preferably 100% by mass, from the viewpoint of obtaining a powder polyamide with larger particle size and a smaller particle size distribution in a short time.

[0357] Furthermore, if impurities other than the polyamide are present, the process may include a step to separate the polyamide from these impurities. The separation method is not particularly limited, but if the impurities are insoluble in the dissolved polyamide resin composition, they can be separated by methods such as filtration, centrifugation, or sedimentation. If the impurities dissolve together with the polyamide in the solvent, methods such as extraction separation in the dissolved state, membrane separation, electrodialysis, or washing after precipitating the polyamide in the precipitation step described later can be considered.

[0358] • Polyethylene terephthalate The polyethylene terephthalate (PET) constituting the aforementioned mixture typically has the following structure. [ka]

[0359] Furthermore, in the aforementioned mixture, the polyethylene terephthalate may exist as fibrous PET. This fibrous PET can be obtained by further solid-phase polymerization and spinning of PET resin.

[0360] The polyethylene terephthalate may consist solely of polyethylene terephthalate, or it may be a polyethylene terephthalate resin composition containing polyethylene terephthalate and other components. For example, other resins, metals, or other impurities may be mixed, attached to, or coated onto the polyethylene terephthalate as other components.

[0361] (Step to obtain a polyamide solution) Furthermore, the manufacturing method of this embodiment includes the step of mixing the mixture with a metal chloride alcohol solution containing metal chlorides and alcohols to obtain a polyamide solution in which the polyamide is dissolved. This process allows for the melt-separation of only the polyamide from the mixture of polyamide and polyethylene terephthalate, thereby facilitating the subsequent recovery of the polyamide and / or polyethylene terephthalate. Furthermore, since the polyamide can be melt-separated simply by mixing the mixture with a predetermined metal chloride alcohol solution, the polyamide and / or polyethylene terephthalate can be recovered efficiently and in high yield.

[0362] The metal chloride alcohol solution used to dissolve the polyamide contains metal chlorides and alcohols. Furthermore, other components besides metal chlorides and alcohols may be included as needed. In particular, from the viewpoint of the solubility of the polyamide, the total mass ratio of the metal chloride and the alcohols to 100% by mass of the metal chloride alcohol solution is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably 100% by mass.

[0363] Examples of the aforementioned alcohols include methanol, ethanol, linear or branched propanol, linear or branched butanol, and combinations thereof. Of these, methanol, ethanol, or combinations thereof are preferred from the viewpoint of polyamide solubility, with methanol being more preferred. In addition, the aforementioned alcohols may also include various diols as needed.

[0364] The mass ratio of the metal chloride to 100% by mass of the metal chloride alcohol solution is preferably 10 to 50% by mass, and more preferably 15 to 25% by mass. If the mass ratio is less than 10% by mass, the amount of polyamide that can be dissolved is small, and a large amount of solvent is required. If it exceeds 50% by mass, the metal chloride tends to remain undissolved and is more likely to be mixed in as an impurity.

[0365] Examples of the aforementioned metal chlorides include zinc chloride, magnesium chloride, and calcium chloride, with zinc chloride and calcium chloride being preferred, and calcium chloride being the most preferred. The metal chloride is preferably in an anhydrous form. The solubility of the polyamide decreases if water is mixed in. However, hydrates (for example, dihydrates of calcium chloride) may be mixed in as long as the solubility is within an acceptable range. The mass percentage of water in the metal chloride is preferably 30% by mass or less, more preferably 1% by mass or less, and even more preferably 0.1% by mass or less, and it is particularly preferable that it contains no water at all.

[0366] Furthermore, in the step of obtaining the polyamide solution, the temperature at which the mixture is mixed with the metal chloride alcohol solution is preferably 30 to 90°C, and more preferably 40 to 60°C. Note that if the temperature is too low, dissolution will be slow, and if it exceeds 90°C, the temperature will be higher than the boiling point, which is undesirable from the viewpoint of corrosiveness and decomposition. The temperature may be constant, or it may be varied within the specified range.

[0367] The dissolution of the polyamide can be carried out in either a batch or continuous manner. In the batch process, stirring is not particularly limited, but it is preferable. Stirring improves the dissolution rate of the polyamide. In a continuous flow system, the solvent can be continuously passed through the solid, or the solution can be circulated. Circulation is preferable because it reduces the amount of solvent used.

[0368] The shape of the container used when mixing the mixture of polyamide and polyethylene terephthalate with a metal chloride alcohol solution to dissolve the polyamide is not particularly limited, and any shape such as a tank type or a circulating type may be used.

[0369] The dissolution time of the polyamide is not particularly limited, but is preferably between 5 minutes and 100 hours.

[0370] In the step of obtaining the polyamide solution, the mass ratio of the polyamide in the mixed material to the metal chloride alcohol solution is not particularly limited, but is preferably 3 to 15% by mass, and more preferably 5 to 13% by mass. If it is less than 3% by mass, too much solvent is required, and if it exceeds 15% by mass, the viscosity of the polyamide solution increases, leading to a longer dissolution time and deterioration of handling properties.

[0371] (Process for separating and recovering the polyamide solution) The method for producing polyamide according to this embodiment, and the method for producing polyamide and polyethylene terephthalate, further include a step of separating and recovering the polyamide solution after the step of obtaining the polyamide solution. This process allows for the separation and recovery of the polyamide contained in the polyamide solution from the undissolved polyethylene terephthalate.

[0372] The method for separating and recovering the polyamide solution is not particularly limited. The polyamide can be separated and recovered by removing the undissolved polyethylene terephthalate remaining in the polyamide solution by filtration or the like.

[0373] The step of separating and recovering the polyamide solution may be performed after the step of obtaining the polyamide solution, or after the step of obtaining the alcohol dilution solution described later. For example, the solution may be diluted at a high temperature to separate the polyamide before it precipitates, and then cooled to recover the polyamide.

[0374] Furthermore, in the manufacturing method of this embodiment, the metal chloride alcohol solution can be further concentrated from the viewpoint of reusing the metal chloride alcohol solution. For example, the metal alcohol solution containing metal chloride and alcohol obtained in the polyamide recovery step may be concentrated and reused. Examples of such concentration methods include concentration by heating.

[0375] (Process for separating and recovering polyethylene terephthalate) The method for producing polyethylene terephthalate according to this embodiment, and the method for producing polyamide and polyethylene terephthalate, further include a step of separating and recovering the polyethylene terephthalate after the step of obtaining the polyamide solution. This process allows for the separation and recovery of undissolved polyethylene terephthalate from the polyamide contained in the polyamide solution.

[0376] The method for separating and recovering the polyethylene terephthalate is not particularly limited, and the polyethylene terephthalate remaining undissolved in the polyamide solution can be separated and recovered by filtration or the like.

[0377] The step of separating and recovering the polyethylene terephthalate may be performed after the step of obtaining the polyamide solution, or after the step of obtaining the alcohol dilution solution, which will be described later.

[0378] (Polyamide precipitation and recovery process) Furthermore, the manufacturing method of this embodiment includes the step of obtaining the polyamide solution, or the step of separating and recovering the polyamide solution and / or the polyethylene terephthalate, Preferably, the process further includes a step of precipitating and recovering the polyamide.

[0379] While polyamide may be recovered from the aforementioned polyamide solution, it is preferable to recover the polyamide after precipitating it from the polyamide solution, from the viewpoint of further improving recovery efficiency.

[0380] One method for recovering polyamide from the aforementioned solution containing polyamide is to precipitate the polyamide. The method for precipitation of polyamide from the aforementioned solution containing polyamide is not particularly limited, but several precipitation methods are possible depending on the dissolved state. If the polyamide is dissolved by heating, precipitation by cooling, utilizing the temperature dependence of the polyamide's solubility, can be considered. In this case, the dissolved polyamide is precipitated from the solution without adding any additional solvent, thereby obtaining the precipitated polyamide.

[0381] If the temperature dependence of the solubility during dissolution is small, the solubility of the polyamide may be reduced and precipitated by mixing the polyamide-containing solution with a poor solvent. In this case, the poor solvent is added to the solution containing the dissolved polyamide, and then the dissolved polyamide is precipitated from the solution to obtain the precipitated polyamide. The poor solvent is not particularly limited, but examples include water and alcohols such as ethanol, n-propanol, and isopropanol. The method of adding the poor solvent to the polyamide may be either adding the polyamide-containing solution to the poor solvent, or adding the poor solvent to the polyamide-containing solution, and the addition rate, temperature, and stirring rate during addition are not particularly limited. The amount of poor solvent added is not particularly limited, but it is preferably 0.5 to 50 times the mass of the solution containing the polyamide, and more preferably 1 to 10 times the mass. A smaller amount of poor solvent added results in a lower recovery rate, while a larger amount of poor solvent added results in a larger solution volume, requiring more time and energy for processing.

[0382] If the temperature dependence of solubility during dissolution is small, the solubility of polyamide can also be reduced by lowering the concentration of calcium chloride. The method of adding methanol to lower the concentration of calcium chloride is not particularly limited, but it may be either by adding methanol to the solution containing the polyamide, or by adding methanol to the solution containing the polyamide, and the rate of addition, temperature, and stirring speed during addition are not particularly limited. Furthermore, there are no particular restrictions on the shape of the container; any shape, such as a tank type or a circulating type, may be used.

[0383] Furthermore, the precipitated polyamide is preferably recovered by solid-liquid separation. Examples of solid-liquid separation methods include filtration, centrifugation, and sedimentation. Either batch or continuous methods may be used for any of these methods.

[0384] The polyamide obtained by solid-liquid separation is preferably washed with a solvent. The washing solution is not particularly limited, but for example, a solution with the same composition as the liquid portion at the time of precipitation, a good solvent, and a solvent that can dissolve calcium chloride, etc., can be used. Additional washing solutions used here include, for example, water and alcohols such as methanol, ethanol, n-propanol, and isopropanol. Methanol is preferred as the additional washing solution. Washing may be performed multiple times as needed.

[0385] The washing method is not particularly limited and includes batch washing, continuous washing by flowing water through a solid-liquid separation device such as a filter or centrifuge, and methods combining these. After washing, the polyamide can be dried to obtain powdered polyamide by removing the washing solvent by heating and / or reduced pressure.

[0386] The shape of the recovered polyamide is not particularly limited and can be in the form of pellets made by melting the polyamide, powder made by dissolving it in a solvent and then precipitating it, or tablet-shaped products made by agglomerating the powder according to the handling conditions.

[0387] (Spinning of polyamide fibers) Furthermore, the obtained polyamide can be melt-spun to produce polyamide fibers. In melt spinning, the spinning temperature is preferably between 290°C and 310°C. Setting the spinning temperature to 310°C or lower is preferable because it suppresses the thermal decomposition of the polyamide, 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 preferable because it allows the polyamide to exhibit sufficient melt fluidity, resulting in uniform discharge volume between discharge holes and enabling high-magnification stretching.

[0388] In the melt spinning process, the residence time (the time from when the polyamide resin is melted until it is extruded from the spinneret) should be as short as possible. A residence time of 30 minutes or less is preferable, 15 minutes or less is more preferable, and 0.5 minutes to 7 minutes is even more preferable. A short residence time is preferable because the amount of cyclopentanones in the polymer increases at the melting temperature.

[0389] For thermal stability in high-temperature, high-humidity environments, it is preferable to add a copper compound to the polyamide so that the copper concentration is 1 to 500 ppm, and more preferably 30 to 500 ppm. This effectively suppresses the deterioration of mechanical performance even when exposed to high-temperature, high-humidity environments for extended periods or to environments with high ozone content. However, if the copper content is less than 30 ppm, the heat resistance strength retention rate decreases, and if the copper content exceeds 500 ppm, the strength decreases.

[0390] 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 halogen compound. Examples of metal halogen 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 or colorimetric methods.

[0391] While not limited to the following, organic antioxidants such as hindered phenol antioxidants, sulfur antioxidants, and phosphorus antioxidants, as well as heat stabilizers, light stabilizers such as hindered amine, benzophenone, and imidazole antioxidants, and UV absorbers may be added as stabilizers. The amount to be added should be selected appropriately, but it can be added at a concentration of 1 to 1000 ppm relative to the polyamide. These additives may be used individually or in combination.

[0392] Furthermore, in the melt spinning process, it is preferable to use a single-screw or double-screw extruder in the melting section. This extruder allows the polyamide resin to be guided to polymer piping, a gear pump, and a spinning pack while applying appropriate pressure.

[0393] Furthermore, filtering the polyamide resin with a metal fiber nonwoven fabric filter or sand before it is extruded from the spinneret is preferable because it stabilizes the spinning operation. The shape of the spinneret hole in the spinneret should be selected according to the cross-sectional shape of the single fiber that makes up the filament to be manufactured. The yarn spun from the spinneret is solidified with cooling air, a process lubricant is applied, the yarn is taken up, stretched, and heat-treated to obtain polyamide fibers.

[0394] Furthermore, filtering the polyamide resin with a metal fiber nonwoven fabric filter or sand before it is extruded from the spinneret is preferable because it stabilizes the spinning operation. The shape of the spinneret hole in the spinneret should be selected according to the cross-sectional shape of the single fiber that makes up the filament to be manufactured. The yarn spun from the spinneret is solidified with cooling air, a process lubricant is applied, the yarn is taken up, stretched, and heat-treated to obtain polyamide fibers.

[0395] [Invention (VII)] The present invention (VII) will now be described. In the present invention (VII), the conditions of the present invention (I) to (VI) may be incorporated as appropriate. The method for producing recycled polyamide according to this embodiment (VII) is a method for producing recycled polyamide using a mixture containing polyamide coated with urethane resin as a raw material, and includes a dissolution step in which the polyamide is dissolved in a polyamide solution by mixing the mixture with a metal chloride alcohol solution containing metal chloride and alcohol, wherein the mass percentage of polyamide in the polyamide solution in the dissolution step is 5 to 15% by mass. Another embodiment (VII) of the method for producing recycled polyamide is a method for producing recycled polyamide using a mixture containing polyamide coated with urethane resin as a raw material, and includes a dissolution step in which the polyamide is dissolved to obtain a polyamide solution by mixing the mixture with a metal chloride alcohol solution containing metal chloride and alcohol, wherein the viscosity of the polyamide solution at 25°C is 10 to 20,000 mPa·s. The manufacturing method of this embodiment (VII) may be a method for producing recycled polyamide, for example, which involves a step of dissolving and extracting polyamide from a urethane-coated polyamide base fabric using a metal chloride alcohol solution with controlled moisture content.

[0396] The compounds used in the manufacturing method of this embodiment (VII) will be described below.

[0397] <Mixture> (polyamide) The polyamides mentioned above can be polymers polymerized by amide bonds, such as those obtained by polycondensation of diamine compounds and dicarboxylic acid compounds, or by ring-opening polymerization of cyclic lactams. The above-mentioned diamine compounds are not particularly limited, but include ethylenediamine, trimethylenediamine, tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, nonanediamine, methylpentanediamine, and p-phenylenediamine. The above-mentioned dicarboxylic acid compounds are not particularly limited, but include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, sebacic acid, terephthalic acid, and isophthalic acid. Examples of the above-mentioned cyclic lactams include, but are not limited to, ε-caprolactam, undecanlactam, and lauryllactam. The combination of the above-mentioned diamine compound, dicarboxylic acid compound, and cyclic lactam compound is not particularly limited, and multiple types of compounds may be used in combination for each type. Polyhexamethylene adipamide (nylon 66) (for example, polyhexamethylene adipamide consisting of hexamethylenediamine and adipic acid) has high solubility and is suitable for the polyamide production method of this embodiment.

[0398] The above mixture contains polyamide coated with urethane resin. The mixture may consist only of polyamide coated with urethane resin, or it may also contain other components. In particular, from the viewpoint of the manufacturing efficiency of recycled polyamide, the mass ratio of polyamide coated with urethane resin is preferably 30 to 100% by mass, more preferably 60% by mass or more, even more preferably 70% by mass or more, and especially preferably 80% by mass or more, based on 100% by mass of the mixture.

[0399] Polyurethane resin is obtained by the reaction of a polyol component and a polyisocyanate component. Examples of the polyol component include polycarbonate polyol, polyester polyol, and polyether polyol. The above-mentioned urethane resin is not particularly limited, but examples include polyester-based polyurethane resins, polyether-based polyurethane resins, and polycarbonate-based polyurethane resins. The urethane resin may also be given a crosslinking agent consisting of epoxy, melamine, polyfunctional isocyanate, etc., a carbodiimide-based hydrolysis inhibitor, phenols, aromatic amine antioxidants, ultraviolet absorbers such as salicylic acid-based, benzophenone-based, and benzotriazole-based derivatives, and a flame retardant such as thiourea.

[0400] The polyamide coated with urethane resin may also have other coatings in addition to the urethane resin. The type of other coating is not particularly limited, but examples include polyethylene, polypropylene, polyester, and fluororesin. It is preferable that the coating does not dissolve in the metal chloride alcohol solution used for dissolution. It is preferable that the coating resin does not contain silicone resin. Polyamide coated with urethane resin may be recycled polyamide raw material, such as process scraps and waste from molded products such as fibers, automobile parts, and electrical product parts, which use polyamide as a raw material. Specifically, this includes process scraps and waste from clothing, airbags, tire cords, engine compartment, intake system, and fuel system parts, connectors, fishing nets, and UD tape.

[0401] The above mixture may also contain sewing thread. The material of the sewing thread is not particularly limited, but it is preferable that it be the same polyamide as the base fabric, as it can be recovered as recycled polyamide.

[0402] <Metal chloride alcohol solution> For dissolving polyamide, a metal chloride alcohol solution is used. The above metal chloride alcohol solution contains a metal chloride and an alcohol, and may also contain other components. In particular, the total mass ratio of the metal chloride and the 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, and even more preferably 100% by mass.

[0403] The above-mentioned metal chlorides are not particularly limited, but examples include zinc chloride, magnesium chloride, and calcium chloride, with zinc chloride and calcium chloride being preferred, and calcium chloride being the most preferred. The metal chloride used as a raw material may be in anhydrous or hydrated form.

[0404] The mass ratio of the metal chloride to 100% by mass of the above metal chloride alcohol solution is preferably 10 to 25% by mass. If it is less than 10% by mass, the amount of polyamide that can be dissolved will be small, and a large amount of solvent will be required. If it exceeds 25% by mass, the metal chloride is likely to remain undissolved and is more likely to be mixed in as an impurity.

[0405] The amount of water in the above metal chloride alcohol solution is not particularly limited, but it is preferably 4 moles or less of water per mole of metal chloride in the solution.

[0406] Examples of the alcohols mentioned above include methanol, ethanol, n-propanol, and 2-propanol. Among these, methanol is preferred from the viewpoint of polyamide solubility.

[0407] The method for mixing the above metal chloride and alcohol is not particularly limited, but stirring is preferable if it is done in a batch process. Although calcium chloride will dissolve even without stirring, it takes time and localized variations in composition may occur.

[0408] The metal chloride alcohol solution used for dissolving the polyamide is preferably a solution produced by separating the polyamide from the metal chloride alcohol solution in which the polyamide was dissolved from the polyamide base fabric. If the concentration and composition change during the separation and recovery of the polyamide, separation from unwanted components by extraction or distillation, concentration by distillation, or concentration adjustment by adding metal chloride and / or alcohol may be performed. For example, the metal chloride alcohol solution from which the polyamide was separated may be concentrated and used in the production method of this embodiment. Since alcohol and metal chloride are not discarded, the environmental impact is small, and the recovery rate is improved because the polyamide remaining in the supernatant during the separation and recovery of the polyamide can be recovered again.

[0409] The following describes each step in the manufacturing method of this embodiment.

[0410] <Process 1 Melting process> The above dissolution step involves mixing a mixture containing urethane-coated polyamide (for example, urethane-coated polyamide base fabric) with a metal chloride alcohol solution to dissolve the polyamide. By mixing the above mixture with the metal chloride alcohol solution, the polyamide dissolves from the urethane-coated polyamide in the mixture. In this specification, the solution obtained by mixing the above mixture and the above metal chloride alcohol solution is referred to as "polyamide dissolution." The polyamide dissolution contains dissolved polyamide, urethane that coated the polyamide, etc. By separating the coating material such as urethane from the polyamide dissolution, a "solution containing polyamide" can be obtained. The shape of the polyamide base fabric used for dissolution is not particularly limited. It may be added in its original form as scraps from the base fabric manufacturing process or as used airbags, or it may be cut according to the size of the dissolution equipment.

[0411] The temperature at which the above mixture and the above metal chloride alcohol solution are mixed is not particularly limited, but is preferably 30 to 90°C, more preferably 40 to 90°C, and even more preferably 40 to 60°C. Dissolution is slow below 30°C, and above 90°C the temperature is higher than the boiling point, which is undesirable from the viewpoint of corrosiveness and decomposition.

[0412] Dissolution can be carried out using either a batch or continuous method. In the batch process, stirring is not particularly limited, but it is preferable. Stirring improves the dissolution rate of the polyamide solid. In a continuous flow system, the solvent can be continuously passed through the solid, or the solution can be circulated. Circulation is preferable because it reduces the amount of solvent used.

[0413] The shape of the container used in the above dissolution process is not particularly limited; any shape, such as a tank type or a circulating type, may be used.

[0414] The time for mixing the mixture with the metal chloride alcohol solution is not particularly limited, but it is preferably between 5 minutes and 100 hours.

[0415] The mass percentage of polyamide in the above polyamide solution (100% by mass) is preferably 5 to 15% by mass, and more preferably 7 to 13% by mass. If it is less than 5% by mass, too much solvent is required, and if it exceeds 15% by mass, the viscosity becomes high, leading to a longer dissolution time and poor handling. Furthermore, the mass percentage of polyamide in a 100% mass solution containing the above-mentioned polyamide is preferably 5 to 15% by mass, and more preferably 7 to 13% by mass. If it is less than 5% by mass, too much solvent is required, and if it exceeds 15% by mass, the viscosity becomes high, leading to longer mixing times and poor handling.

[0416] The viscosity of the above polyamide solution at 25°C is preferably 10 to 20,000 mPa·s, more preferably 10 to 10,000 mPa·s, and even more preferably 10 to 3,000 mPa·s. While higher viscosity indicates a higher polymer concentration, it reduces the dissolution efficiency of the polyamide due to factors such as adhesion to the base fabric. Furthermore, the viscosity of the solution containing the polyamide at 25°C is preferably 10 to 20,000 mPa·s, more preferably 10 to 10,000 mPa·s, and even more preferably 10 to 3,000 mPa·s.

[0417] The method for separating the urethane resin from the polyamide solution is not particularly limited, but examples include scooping the urethane resin from the dissolved layer, filtration, centrifugation, and sedimentation separation, and these may be combined. Since fine fragments of the urethane resin may be generated during the dissolution of polyamide, it is preferable to remove these fine fragments by filtration or a method combined with filtration.

[0418] It is preferable to remove any other coatings on the polyamide coated with urethane resin at the same time as the urethane resin. Since the separated urethane resin and other coatings have a polyamide-containing solution attached to them, it is preferable to wash them and recover the polyamide-containing solution. The solvent for washing is not particularly limited, but calcium chloride methanol solution is preferred. The washing method is not particularly limited, but examples include stirring washing in a tank reactor or flow washing in a filter.

[0419] <Polyamide recovery process> The polyamide recovery step described above is a step of recovering polyamide from a solution containing polyamide, from which the urethane resin obtained in the dissolution step has been removed. While polyamide may be recovered from the above-mentioned polyamide solution, it is preferable to recover the polyamide from the polyamide-containing solution after removing any coatings such as urethane resin, in order to further improve recovery efficiency.

[0420] One method for recovering polyamide from a polyamide-containing solution is to precipitate the polyamide. While there are no particular limitations on the method for precipitation of polyamide from the polyamide-containing solution, several precipitation methods are possible depending on the dissolved state. If the polyamide is dissolved by heating, precipitation by cooling, utilizing the temperature dependence of the polyamide's solubility, can be considered. In this case, the dissolved polyamide is precipitated from the solution without adding any additional solvent, thereby obtaining the precipitated polyamide.

[0421] If the temperature dependence of solubility during dissolution is small, the solubility of the polyamide may be reduced and precipitated by mixing the polyamide-containing solution with a poor solvent. In this case, the poor solvent is added to the solution containing the dissolved polyamide, and then the dissolved polyamide is precipitated from the solution to obtain the precipitated polyamide. The poor solvent is not particularly limited, but examples include water and alcohols such as ethanol, n-propanol, and isopropanol. The method of adding the poor solvent to the polyamide may be either adding the polyamide-containing solution to the poor solvent, or adding the poor solvent to the polyamide-containing solution, and the addition rate, temperature, and stirring rate during addition are not particularly limited. The amount of poor solvent added is not particularly limited, but it is preferably 0.5 to 50 times the mass of the solution containing the polyamide, and more preferably 1 to 10 times the mass. A smaller amount of poor solvent added results in a lower recovery rate, while a larger amount of poor solvent added results in a larger solution volume, requiring more time and energy for processing.

[0422] If the temperature dependence of solubility during dissolution is small, the solubility of polyamide can also be reduced by lowering the concentration of calcium chloride. The method of adding methanol to lower the concentration of calcium chloride is not particularly limited, but it may be either by adding methanol to the solution containing the polyamide, or by adding methanol to the solution containing the polyamide, and the rate of addition, temperature, and stirring speed during addition are not particularly limited.

[0423] There are no particular restrictions on the shape of the container; any shape, such as a tank type or a circulating type, may be used.

[0424] The precipitated polyamide is preferably recovered by solid-liquid separation. Examples of solid-liquid separation methods include filtration, centrifugation, and sedimentation. Either batch or continuous methods may be used.

[0425] The polyamide obtained by solid-liquid separation is preferably washed with a solvent. The washing solution is not particularly limited, but for example, a solution with the same composition as the liquid portion at the time of precipitation, a good solvent, and a solvent that can dissolve calcium chloride, etc., can be used. Additional washing solutions used here include, for example, water and alcohols such as methanol, ethanol, n-propanol, and isopropanol. Methanol is preferred as the additional washing solution. Washing may be performed multiple times as needed.

[0426] The washing method is not particularly limited and includes batch washing, continuous washing by flowing water through a solid-liquid separation device such as a filter or centrifuge, and methods combining these. After washing, the polyamide can be dried to obtain powdered polyamide by removing the washing solvent by heating and / or reduced pressure.

[0427] As described above, this embodiment provides a method for producing recycled polyamide in high yield from a mixture of polyamide, which is useful as an engineering plastic, coated with urethane.

[0428] <Process for concentrating the metal chloride alcohol solution> From the viewpoint of reusing the metal chloride alcohol solution, the manufacturing method of this embodiment may further include a step of concentrating the metal chloride alcohol solution. For example, the metal alcohol solution containing metal chloride and alcohol obtained in the polyamide recovery process described above may be concentrated and reused. Examples of the concentration methods mentioned above include concentration by heating.

[0429] <Recycled polyamide> The shape of the recycled polyamide produced by the manufacturing method of this embodiment is not particularly limited, and examples include polyamide that has been melted during recycling and formed into pellets, polyamide that has been dissolved in a solvent and then precipitated into a powder, and tablet-shaped polyamide produced by agglomerating the powder according to handling conditions. The above-mentioned recycled polyamide can be used as a raw material for polyamide fibers, polyamide base fabrics, airbags, and the like.

[0430] (Spinning of polyamide fibers) The above-mentioned recycled polyamide fibers can be spun to form a polyamide base fabric. In melt spinning, the spinning temperature is preferably between 290°C and 310°C. Setting the spinning temperature to 310°C or lower is preferable because it suppresses the thermal decomposition of the polyamide, 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 preferable because it allows the polyamide to exhibit sufficient melt fluidity, resulting in uniform discharge volume between discharge holes and enabling high-magnification stretching.

[0431] In the melt spinning process, the residence time (the time from when the polyamide resin is melted until it is extruded from the spinneret) should be as short as possible. A residence time of 30 minutes or less is preferable, 15 minutes or less is more preferable, and 0.5 minutes to 7 minutes is even more preferable. A short residence time is preferable because the amount of cyclopentanones in the polymer increases at the melting temperature.

[0432] For thermal stability in high-temperature, high-humidity environments, it is preferable to add a copper compound to the polyamide so that the copper concentration is 1 to 500 ppm by mass, and more preferably 30 to 500 ppm by mass. By doing so, the deterioration of mechanical performance is very effectively suppressed even when left in high-temperature, high-humidity environments for long periods of time, or when exposed to environments with high ozone content for long periods of time. If the copper content is less than 30 ppm by mass, the heat resistance strength retention rate decreases, and if the amount added exceeds 500 ppm by mass, the strength decreases.

[0433] 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 halogen compound. Examples of metal halogen 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 or colorimetric methods.

[0434] While not limited to the following, organic antioxidants such as hindered phenol antioxidants, sulfur antioxidants, and phosphorus antioxidants, as well as heat stabilizers, light stabilizers such as hindered amine, benzophenone, and imidazole antioxidants, and UV absorbers may be added as stabilizers. The amount to be added should be selected appropriately, but it can be added at a rate of 1 to 1000 ppm by mass relative to the polyamide. These additives may be used individually or in combination of several types.

[0435] Furthermore, in the melt spinning process, it is preferable to use a single-screw or double-screw extruder in the melting section. This extruder allows the polyamide resin to be guided to polymer piping, a gear pump, and a spinning pack while applying appropriate pressure.

[0436] Furthermore, filtering the polyamide resin with a metal fiber nonwoven fabric filter or sand before it is extruded from the spinneret is preferable because it stabilizes the spinning operation. The shape of the spinneret hole in the spinneret should be selected according to the cross-sectional shape of the single fiber that makes up the filament to be manufactured. The yarn spun from the spinneret is solidified with cooling air, a process lubricant is applied, the yarn is taken up, stretched, and heat-treated to obtain polyamide fibers.

[0437] The oil adhesion rate of polyamide fibers is preferably 0.5 to 1.5 wt%. If the oil adhesion rate is 1.5 wt% or less, there is almost no difficulty in the weft yarn flying away due to stickiness (tackiness), and the single yarn convergence is not too good beyond what would occur due to entanglement, reducing the apparent cross-sectional area and preventing the air or water, which are the weft yarn transport media, from losing their weft yarn transport power, 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.

[0438] (Polyamide base fabric) In weaving, looms such as water jet looms, air jet looms, and rapier looms can be used. The base fabric for airbags is a high-density fabric, and in the warping and weaving processes, it is preferable to increase the warp tension to ensure good process passability. By setting the warp tension higher during weaving and creating effective reed beating conditions, a high-density fabric is formed.

[0439] Woven fabrics can have the process oils from the polyamide fibers washed off during the scouring process. The scouring process can be performed using hot water or pressurized hot water, and the processing can be a single-stage process or a multi-stage process of two or more stages. It is also preferable to apply a conventionally known scouring agent to perform the scouring.

[0440] It is preferable to heat-set the fabric in a heat-setting process. The heat-setting temperature is preferably between 110°C and 200°C, and the heat-setting time can be appropriately selected within the range of 0.1 minutes to 30 minutes. It is also preferable to dry the fabric while tensing it so that its shrinkage force is maintained at a predetermined level during the heat-setting process. Heat-setting the fabric helps to stabilize the processability of the subsequent resin coating process.

[0441] The fabric after the scouring process may be dried before the heat setting process, if necessary. The drying temperature is preferably in the range of 80°C to 130°C, and more preferably in the range of 100°C to 120°C. The drying time is preferably selected as appropriate, between 0.1 minutes and 30 minutes. Drying may be carried out in a relaxed or taut state.

[0442] Polyamide base fabrics can be used as uncoated base fabrics after undergoing a heat-setting process, but they can also be coated with coating agents such as silicone or urethane, or heat-laminated with thin films.

[0443] Methods for coating the surface of a woven fabric include immersing the fabric in a resin solution bath and then shaping and homogenizing the excess resin using a mangle, vacuum, or coating knife; bar coating methods such as comma coaters; and spraying the resin using a spray device or forming device. Of these, knife coating is preferred from the viewpoint of applying the resin uniformly and in small amounts.

[0444] The coating amount is 5g / m². 2 More than 100g / m 2 The following is more preferable: 10 g / m 2 More than 70g / m 2 The following is more preferably 15 g / m 2 More than 30g / m 2 The following is true: 5g / m 2 The required airtightness can be achieved with the above application amount. On the other hand, 100g / m 2 The following application amounts allow the coated fabric to be flexible, improve storage capacity, and reduce the overall weight of the bag.

[0445] <Airbag> The airbags can be appropriately selected from among the commonly used airbags for the driver's seat, passenger seat, side seats (including inflatable curtains), rear seats, etc. The cut shape of the airbag bag can be circular, oval, elliptical, rectangular, polygonal, or a combination thereof, as long as it satisfies the required deployment shape. Stitch shapes include single straight lines, multiple parallel straight lines, zigzag patterns, combinations of straight and zigzag patterns, and straight and diagonal lines. Standard stitching methods such as lockstitch and double chain stitch are acceptable, and the stitch pitch can be selected from a range of 20 to 60 stitches per 10cm. The thread thickness can be selected from 420d to 3000d, and commercially available threads made from materials such as polyamide, polyester, vinylon, aramid, and glass fibers can be used. [Examples]

[0446] The present invention will be described in more detail below using examples, but the present invention is not limited to these examples.

[0447] An embodiment of the present invention (I) will be described below.

[0448] The analytical methods used in the examples and comparative examples are as follows:

[0449] <Particle size distribution> (1) Particle size distribution measuring device Measuring device: MT3300EX (Microtrac MRB) Transparency: Transparent Solvent: Water Distribution: Volume Based on the analysis results, the median diameter is expressed as the particle size. The median diameter refers to the particle size at which the number of particles larger than or smaller than the median diameter is equal for a given powder. Furthermore, if the value derived by the following general formula (1) is denoted as S, then "10 S The numerical value represented by is used as the span and is shown as an indicator of particle size distribution. The closer this value is to 1, the narrower the particle size distribution. S=log(d90 / d10) / log(d50) ···(1) (Here, in equation (1) above, dn (where n represents 10, 50, or 90) refers to the particle size at which the number of particles smaller than dn accounts for n% of the total number of particles, when the particle size distribution of the obtained powdered polyamide is measured by laser diffraction and scattering.) Note that d50 is the median diameter.

[0450] [Example 1] In a 300 mL three-necked flask containing a stirring bar, 10 g of polyamide 66 pellets and 100 g of 25 wt% calcium chloride methanol solution (25.0 g calcium chloride, 8.1 g water (moles of water / moles of calcium chloride = 2)) were added. The flask was placed in an 80°C oil bath and the polyamide 66 was dissolved by stirring with a magnetic stirrer for 12 hours to obtain a heated polyamide solution. The viscosity of the obtained heated polyamide solution at 25°C was 4200 mPa·s. The heated polyamide solution was diluted by adding 220.0 g of methanol while stirring. The internal temperature was maintained above 65°C during the addition. After adding methanol, the flask was removed from the oil bath and cooled. After 1 hour, when the temperature reached 30°C, stirring was stopped and the solid precipitate was recovered by pressure filtration using a 10 μm membrane filter. The weight of the wet filtration material was 43 g. 50 g of methanol was added to the filter and pressure filtration was performed again. The amount of calcium chloride in the filtrate was analyzed by ion chromatography, and the amount of calcium chloride remaining in the polyamide was calculated. The process of adding methanol and calculating the remaining calcium chloride was repeated, and washing was stopped when the remaining amount was less than 1000 ppm. There were 7 washes, and the amount of washing solution was 350 g. The mass of the washing solution (g) relative to the mass (g) of the raw material polyamide 66 pellets (g) was 35. The solid precipitate after washing was heated and dried in a vacuum dryer at 80°C to obtain 9.8 g of powdered polyamide 66 (yield 98.0%). The energy required for drying, calculated from the amount of solvent contained, was 3.6 kJ per 1 g of polyamide 66. The amount of solution (g) contained in the powdered polyamide per 1 g of the obtained powdered polyamide 66 was 3.3.

[0451] [Examples 2-8][Comparative Examples 1-4] The results of performing the same procedure as in Example 1, except that the metal chloride alcohol solution was composed as shown in Table 1, are shown in Table 1.

[0452] [Table 1]

[0453] [Example 9] In a 300 mL three-necked flask containing a stirring bar, 10 g of polyamide 66 pellets and 100 g of 25 wt% calcium chloride methanol solution (25.0 g calcium chloride, 8.1 g water (moles of water / moles of calcium chloride = 2)) were added. The flask was placed in an 80°C oil bath and the polyamide 66 was dissolved by stirring with a magnetic stirrer for 12 hours to obtain a heated polyamide solution. The viscosity of the obtained heated polyamide solution at 25°C was 4200 mPa·s. The heated polyamide solution was diluted by adding 220.0 g of methanol while stirring. During the addition, the internal temperature decreased to 45°C. At this time, the supernatant was sampled and the content of precipitated polyamide was calculated to be 0.7% by weight of the polyamide 66 used as the raw material. After the addition of methanol, the flask was removed from the oil bath and cooled. After one hour, stirring was stopped when the temperature reached 30°C, and the solid precipitate was recovered by pressure filtration using a 10 μm membrane filter. The weight of the wet filtrate was 43 g. 50 g of methanol was added to the filter, and pressure filtration was performed again. The amount of calcium chloride in the filtrate was analyzed by ion chromatography, and the amount of calcium chloride remaining in the polyamide was calculated. The process of adding methanol and calculating the amount of calcium chloride remaining was repeated, and washing was stopped when the amount was less than 1000 ppm. The number of washes was 6, and the amount of washing solution was 300 g. The solid precipitate after washing was heated and dried in a vacuum dryer at 80°C to obtain 9.8 g of powdered polyamide 66 (yield 98.0%). The energy required for drying, calculated from the amount of solvent contained, was 3.6 kJ per g of polyamide 66.

[0454] [Example 10] In a 300 mL three-necked flask containing a stirring bar, 10 g of polyamide 6 pellets and 100 g of 25 wt% calcium chloride methanol solution (25.0 g calcium chloride, 8.1 g water (moles of water / moles of calcium chloride = 2)) were added. The flask was placed in an 80°C oil bath and the polyamide 6 was dissolved by stirring with a magnetic stirrer for 12 hours to obtain a heated polyamide solution. The viscosity of the obtained heated polyamide solution at 25°C was 2500 mPa·s. The heated polyamide solution was diluted by adding an aqueous methanol solution (150.0 g methanol, 60.0 g water) while stirring. The internal temperature was maintained above 65°C during the addition. After adding the aqueous methanol solution, the flask was removed from the oil bath and cooled. After 1 hour, when the temperature reached 30°C, stirring was stopped, and the solid precipitate was recovered by pressure filtration using a 10 μm membrane filter. The weight of the wet filtration material was 41 g. 50 g of methanol was added to the filter, and pressure filtration was performed again. The amount of calcium chloride in the filtrate was analyzed by ion chromatography, and the amount of calcium chloride remaining in the polyamide was calculated. The process of adding methanol and calculating the amount of calcium chloride remaining was repeated, and washing was stopped when the remaining amount was less than 1000 ppm. The number of washes was 6, and the amount of washing solution was 300 g. The solid precipitate after washing was heated and dried in a vacuum dryer at 80°C to obtain 9.8 g of powdered polyamide 66 (yield 98.0%). The energy required for drying, calculated from the amount of solvent contained, was 3.4 kJ per g of polyamide 66.

[0455] [Example 11] In a 300 mL three-necked flask containing a stirring bar, 10 g of polyamide 66 pellets and 100 g of 25 wt% calcium chloride ethanol solution (25.0 g calcium chloride, 8.1 g water (moles of water / moles of calcium chloride = 2)) were added. The flask was placed in an 80°C oil bath and the polyamide 66 was dissolved by stirring with a magnetic stirrer for 12 hours to obtain a heated polyamide solution. The viscosity of the obtained heated polyamide solution at 25°C was 4100 mPa·s. The heated polyamide solution was diluted by adding 220.0 g of ethanol while stirring. The internal temperature was maintained above 65°C during the addition. After adding ethanol, the flask was removed from the oil bath and cooled. After 1 hour, stirring was stopped when the temperature reached 30°C, and the solid precipitate was recovered by pressure filtration using a 10 μm membrane filter. The weight of the wet filtration material was 44 g. 50 g of methanol was added to the filter, and pressure filtration was performed again. The amount of calcium chloride in the filtrate was analyzed by ion chromatography, and the remaining amount of calcium chloride in the polyamide was calculated. The process of adding ethanol and calculating the remaining calcium chloride was repeated, and washing was stopped when the remaining amount was less than 1000 ppm. The washing was performed 6 times, and the amount of washing solution was 300 g. The solid precipitate after washing was heated and dried in a vacuum dryer at 80°C to obtain 9.8 g of powdered polyamide 66 (yield 98.0%). The energy required for drying, calculated from the amount of solvent contained, was 3.6 kJ per g of polyamide 66.

[0456] [Example 12] In a 300 mL three-necked flask containing a stirring bar, 10 g of polyamide 66 pellets and 100 g of 25 wt% calcium chloride methanol solution (25.0 g calcium chloride, 8.1 g water (moles of water / moles of calcium chloride = 2)) were added. The flask was placed in an 80°C oil bath and the polyamide 66 was dissolved by stirring with a magnetic stirrer for 12 hours to obtain a heated polyamide solution. The viscosity of the obtained heated polyamide solution at 25°C was 4200 mPa·s. The heated polyamide solution was diluted by adding 220.0 g of methanol while stirring. The internal temperature was maintained above 65°C during the addition. After adding methanol, the flask was removed from the oil bath and cooled. After 1 hour, when the temperature reached 30°C, stirring was stopped and the solid precipitate was recovered by pressure filtration using a 10 μm membrane filter. The weight of the wet filtration material was 43 g. 50 g of water was added to the filter and pressure filtration was performed again. The amount of calcium chloride in the filtrate was analyzed by ion chromatography, and the remaining amount of calcium chloride in the polyamide was calculated. The process of adding water and calculating the remaining calcium chloride was repeated, and washing was stopped when the remaining amount was less than 1000 ppm. There were 7 washes, and the amount of washing solution was 350 g. After replacing the solvent with methanol to facilitate drying, the solid precipitate was heated and dried in a vacuum dryer at 80°C to obtain 9.8 g of powdered polyamide 66 (yield 98.0%). The energy required for drying, calculated from the amount of solvent contained, was 3.6 kJ per g of polyamide 66.

[0457] [Reference example 1] 400 g of calcium chloride methanol solution, obtained by mixing all of the filtrate and washing solution from Example 1, was weighed into a 1 L flask and concentrated using a rotary evaporator to obtain 100 g of concentrate. The resulting solution contained 24.9 g of calcium chloride and 8.7 g of water (moles of water / moles of calcium chloride = 2.1), and can be used as a calcium chloride methanol solution for dissolving polyamides.

[0458] [Reference example 2] 450 g of calcium chloride methanol solution, obtained by mixing all the filtrate and washing solution from Example 12, was weighed into a 1 L flask and concentrated using a rotary evaporator to obtain 100 g of concentrate. The resulting solution was an aqueous solution containing 24.9 g of calcium chloride, with a methanol content of 1.2%. Since the water used for washing has a higher boiling point than methanol, the concentrate could not be used to dissolve the polyamide.

[0459] [Example 13] In a 300 mL three-necked flask containing a stirring bar, 10 g of polyamide 66 pellets and 100 g of 25 wt% calcium chloride methanol solution (25.0 g calcium chloride, 8.1 g water (moles of water / moles of calcium chloride = 2)) were added. The flask was placed in an 80°C oil bath and the polyamide 66 was dissolved by stirring with a magnetic stirrer for 12 hours to obtain a heated polyamide solution. The viscosity of the obtained heated polyamide solution at 25°C was 4200 mPa·s. The heated polyamide solution was diluted by adding 220.0 g of methanol while stirring. The internal temperature was maintained above 65°C during the addition. After adding methanol, the flask was removed from the oil bath and cooled. After 1 hour, when the temperature reached 30°C, stirring was stopped and the solid precipitate was recovered by pressure filtration using a 10 μm membrane filter. The weight of the wet filtration material was 43 g. 50 g of methanol was added to the filter and pressure filtration was performed again. The amount of calcium chloride in the filtrate was analyzed by ion chromatography, and the residual amount of calcium chloride in the polyamide was calculated to be 10% by mass. The solid precipitate after washing was heated and dried in a vacuum dryer at 80°C to obtain 9.8 g of powdered polyamide 66 (yield 98.0%). The energy required for drying, calculated from the amount of solvent present, was 3.6 kJ per g of polyamide 66.

[0460] [Example 14] In a 300 mL three-necked flask containing a stirring bar, 10 g of polyamide 66 pellets and 100 g of 25 wt% calcium chloride methanol solution (25.0 g calcium chloride, 8.1 g water (moles of water / moles of calcium chloride = 2)) were added. The flask was placed in an 80°C oil bath and the polyamide 66 was dissolved by stirring with a magnetic stirrer for 12 hours to obtain a heated polyamide solution. The viscosity of the obtained heated polyamide solution at 25°C was 4200 mPa·s. 220.0 g of methanol was added to the heated polyamide solution while stirring. The internal temperature was maintained above 65°C during the addition. After adding methanol, the flask was removed from the oil bath and cooled. After 1 hour, stirring was stopped when the temperature reached 30°C, and the solid precipitate was recovered by pressure filtration using a 10 μm membrane filter. The weight of the wet filtration material was 43 g. The calcium chloride content after filtration was 25.8% by mass. When the washed solid precipitate was heated and dried in a vacuum dryer at 80°C, the dried solid was found to be a solid mass formed from the powder. The energy required for drying, calculated from the amount of solvent contained, was 3.6 kJ per gram of polyamide 66.

[0461] [Example 15] In a 300 mL three-necked flask containing a stirring bar, 11 g of airbag base fabric (10 g of polyamide 66, 1 g of silicone coating) and 100 g of 25 wt% calcium chloride methanol solution (25.0 g of calcium chloride, 8.1 g of water (moles of water / moles of calcium chloride = 2)) were added. The flask was placed in an 80°C oil bath and the polyamide 66 was dissolved by stirring with a magnetic stirrer for 12 hours to obtain a heated polyamide solution. Insoluble matter was separated from the obtained heated polyamide solution through a 200 mesh stainless steel mesh and pressure filtered through a 10 μm pore size membrane filter. The viscosity of the obtained solution at 25°C was 4100 mPa·s. The heated polyamide solution was diluted by adding 220.0 g of methanol while stirring. The internal temperature was maintained above 65°C during the addition. After adding the solution, the mixture was removed from the oil bath and cooled. After 1 hour, when the temperature reached 30°C, stirring was stopped, and the solid precipitate was recovered by pressure filtration using a 10 μm membrane filter. The weight of the wet filtrate was 43 g. 50 g of methanol was added to the filter, and pressure filtration was performed again. The amount of calcium chloride in the filtrate was analyzed by ion chromatography, and the amount of calcium chloride remaining in the polyamide was calculated. The process of adding methanol and calculating the amount of calcium chloride remaining was repeated, and washing was stopped when the remaining amount was less than 1000 ppm. The number of washes was 6, and the amount of washing solution was 300 g. The solid precipitate after washing was heated and dried in a vacuum dryer at 80°C to obtain 9.8 g of powdered polyamide 66 (yield 98.0%). The energy required for drying, calculated from the amount of solvent contained, was 3.6 kJ per g of polyamide 66.

[0462] [Example 16] In a 300 mL three-necked flask containing a stirring bar, 18 g of airbag base fabric (16.4 g of polyamide 66, 1.6 g of silicone coating) and 100 g of 25 wt% calcium chloride methanol solution (25.0 g of calcium chloride, 8.1 g of water (moles of water / moles of calcium chloride = 2)) were added. The flask was placed in an 80°C oil bath and the polyamide 66 was dissolved by stirring with a magnetic stirrer for 12 hours to obtain a heated polyamide solution. Insoluble matter was separated from the obtained solution through a 200 mesh stainless steel mesh and pressure filtered through a 10 μm pore size membrane filter. The viscosity of the obtained solution at 25°C was 43000 mPa·s. The heated polyamide solution was diluted by adding 220.0 g of methanol while stirring. The internal temperature was maintained above 65°C during the addition. After adding methanol, the flask was removed from the oil bath and cooled. After one hour, stirring was stopped when the temperature reached 30°C, and the solid precipitate was recovered by pressure filtration using a 10 μm membrane filter. The weight of the wet filtrate was 34 g. 50 g of methanol was added to the filter, and pressure filtration was performed again. The amount of calcium chloride in the filtrate was analyzed by ion chromatography, and the amount of calcium chloride remaining in the polyamide was calculated. The process of adding methanol and calculating the amount of calcium chloride remaining was repeated, and washing was stopped when the remaining amount was less than 1000 ppm. The number of washes was 6, and the amount of washing solution was 300 g. The solid precipitate after washing was heated and dried in a vacuum dryer at 80°C to obtain 10.1 g of powdered polyamide 66 (yield 61.6%). The energy required for drying, calculated from the amount of solvent contained, was 3.5 kJ per g of polyamide 66.

[0463] [Reference example 3] 25.0 g of calcium chloride, 8.1 g of water, and 67 g of methanol were weighed into a 200 mL glass bottle containing a stirring bar, and the mixture was stirred to obtain a homogeneous solution. Further, 0.01 g of calcium hydroxide was added and stirred to obtain a cloudy solution. A SUS316 mesh was placed in the glass bottle and immersed at room temperature for 100 hours. The supernatant remained colorless and transparent.

[0464] [Reference example 4] 25.0 g of calcium chloride, 8.1 g of water, and 67 g of methanol were weighed into a 200 mL glass bottle containing a stirring bar, and the mixture was stirred to obtain a homogeneous solution. Further, 0.1 g of calcium hydroxide was added and stirred to obtain a cloudy solution. A SUS316 mesh was placed in the glass bottle and immersed at room temperature for 100 hours. The supernatant was yellow in color.

[0465] [Example 17] In a 300 mL three-necked flask containing a stirring bar, 10 g of polyamide 66 pellets and 100 g of the solution prepared in Reference Example 3 (25.0 g calcium chloride, 8.1 g water (moles of water / moles of calcium chloride = 2)) were added. The flask was placed in an 80°C oil bath and the polyamide 66 was dissolved by stirring with a magnetic stirrer for 12 hours to obtain a heated polyamide solution. The viscosity of the obtained heated polyamide solution at 25°C was 4200 mPa·s. The heated polyamide solution was diluted by adding 220.0 g of methanol while stirring. The internal temperature was maintained above 65°C during the addition. After adding methanol, the flask was removed from the oil bath and cooled. After 1 hour, when the temperature reached 30°C, stirring was stopped and the solid precipitate was recovered by pressure filtration using a 10 μm membrane filter. The wet filtrate weighed 43 g. 50 g of methanol was added to the filter, and pressure filtration was performed again. The amount of calcium chloride in the filtrate was analyzed by ion chromatography, and the amount of calcium chloride remaining in the polyamide was calculated. The process of adding methanol and calculating the amount of calcium chloride remaining was repeated, and washing was stopped when the remaining amount was less than 1000 ppm. The number of washes was 6, and the amount of washing solution was 300 g. The solid precipitate after washing was heated and dried in a vacuum dryer at 80°C to obtain 9.8 g of powdered polyamide 66 (yield 98.0%). The obtained polyamide was white. The calcium content was 500 ppm by mass, and the molar content of halogen atoms was 0.02 times the molar content of calcium. The energy required for drying, calculated from the amount of solvent contained, was 3.6 kJ per g of polyamide 66.

[0466] [Example 18] In a 300 mL three-necked flask containing a sti...

Claims

1. Step 1: A step to obtain a heated polyamide solution by heating and dissolving the polyamide resin composition in a metal chloride alcohol solution containing calcium chloride and alcohol. Step 2: A step of diluting the heated polyamide solution with alcohol to obtain an alcoholic diluted solution, and Step 3: A step of cooling the alcohol dilution to precipitate the powdered polyamide. Includes, In step 1, the mass ratio of calcium chloride to 100% by mass of the metal chloride alcohol solution is 23% by mass or more and 31% by mass or less; in step 1, the heated polyamide solution contains 0.2 moles or more and 2.0 moles of water per mole of calcium chloride; and in step 2, the heated polyamide solution is diluted without lowering its temperature below 50°C. A method for producing powdered polyamide, characterized by the following features.

2. Step 1: A step to obtain a heated polyamide solution by heating and dissolving the polyamide resin composition in a metal chloride alcohol solution containing calcium chloride and alcohol. Step 2: A step of diluting the heated polyamide solution with alcohol to obtain an alcoholic diluted solution, and Step 3: A step of cooling the alcohol dilution to precipitate the powdered polyamide. Includes, In step 1, the mass ratio of calcium chloride to 100% by mass of the metal chloride alcohol solution is 23% by mass or more and 31% by mass or less; in step 1, the heated polyamide solution contains 0.2 moles or more and 2.0 moles of water per mole of calcium chloride; and in step 2, the mass of the polyamide precipitated is 1% by mass or less of the total mass of the polyamide contained in the heated polyamide solution. A method for producing powdered polyamide, characterized by the following features.

3. The method for producing powdered polyamide according to claim 1 or 2, further comprising step 4: washing the powdered polyamide obtained in step 3 once or more times with a solvent.

4. The method for producing powdered polyamide according to claim 3, wherein the solvent used for the initial washing in step 4 is the same alcohol used in step 1.

5. The method for producing powdered polyamide according to claim 1 or 2, wherein the heating and melting temperature in step 1 is 60°C or higher and 80°C or lower.

6. The method for producing powdered polyamide according to claim 1 or 2, further comprising step 5: heating the powdered polyamide precipitated in step 3 to obtain heated powdered polyamide.

7. The method for producing powdered polyamide according to claim 6, further comprising step 6: a step of washing the solid obtained by solid-liquid separation of the heated powdered polyamide obtained in step 5, after step 5.

8. The method for producing powdered polyamide according to claim 1 or 2, wherein the polyamide resin composition comprises a polyamide coated with a silicone resin, and the concentration of the polyamide in the heated polyamide solution in step 1 is 5 to 15% by mass.

9. A method for producing powdered polyamide according to claim 1 or 2, wherein the polyamide resin composition comprises a polyamide coated with a silicone resin, and the viscosity of the heated polyamide solution in step 1 at 25°C is 10 to 20,000 mPa·s.

10. The method for producing powdered polyamide according to claim 1 or 2, wherein the metal chloride alcohol solution has a calcium chloride concentration of 23% by mass or more and 31% by mass or less, and contains 0.001 to 1% by mass of a hydroxide of the same metal as the metal contained in the calcium chloride and 0.001 to 10% by mass of water.

11. A method for producing a powdered polyamide according to claim 1 or 2, wherein the powdered polyamide contains 0.001 to 1500 ppm of calcium atoms and the molar content of halogen atoms is less than 1 relative to the molar content of calcium atoms.

12. The method for producing powdered polyamide according to claim 1 or 2, wherein the polyamide resin composition comprises at least polyamide and polyethylene terephthalate.

13. A method for producing powdered polyamide according to claim 1 or 2, wherein the polyamide resin composition comprises a polyamide coated with a urethane resin.

14. After steps 1 to 3 above Step 7: A step to recover the precipitated powdered polyamide, Step 8: A washing step to wash the recovered powdered polyamide, Step 9: A drying step in which the washed powdered polyamide is heated and dried, Includes, The method for producing powdered polyamide according to claim 1 or 2, wherein the amount of calcium chloride adhering to the powdered polyamide after heating and drying in step 9 is 20 parts by mass or less per 100 parts by mass of the powdered polyamide.

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