Method of producing polyamide, method of producing polyethylene terephthalate, and method of producing polyamide and polyethylene terephthalate

Abstract

To provide a method of producing a polyamide capable of recovering the polyamide and / or polyethylene terephthalate from a mixture of the polyamide and the polyethylene terephthalate with high efficiency and high yield, a method of producing polyethylene terephthalate, and a method of producing a polyamide and polyethylene terephthalate.SOLUTION: A method of producing a polyamide for recovering the polyamide from a mixture of the polyamide and polyethylene terephthalate includes: a process of mixing the mixture with a metal chloride alcohol solution including a metal chloride and alcohol to obtain a polyamide solution with the polyamide dissolved; and a process of subjecting the polyamide solution to separation and recovery.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a method for producing polyamide, a method for producing polyethylene terephthalate, and a method for producing polyamide and polyethylene terephthalate. [Background technology]

[0002] Polyamide resins and polyethylene terephthalate resins have excellent properties and are therefore used in the manufacture of various machines and parts, such as in the manufacture of automobiles, machines, electrical and electronic parts, etc. Among these, polyamide resins are particularly excellent in mechanical properties and abrasion resistance and are therefore widely used as molding materials for sliding parts such as gears, cams, and bearings.

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

[0004] Recycling can be broadly divided into material recycling, in which materials that have already been molded are re-pelletized, and chemical recycling, in which monomers are reused through depolymerization. With material recycling, there are concerns that quality may not be stable because degraded polymers and added components contained in molded products remain in the recycled polymer. However, since no chemical reactions are involved and few auxiliary raw materials are required, less resources and energy are required. Therefore, material recycling is chosen when recycling with a fixed use. Furthermore, even before carrying out chemical recycling, when additives, coatings, etc. are removed from processed or used polyamide-containing materials collected from factories or markets, a process of recovering clean polyamide is carried out, just like in material recycling, and therefore material recycling technology is also useful for carrying out chemical recycling.

[0005] 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 of the applications of nylon 66 is in automobiles, where high safety is required. For example, it is used in engine parts that require high heat resistance, and in airbag base fabrics that require durability in the event of a rupture. Among them, airbag base fabrics are least susceptible to deterioration and are suitable for material recycling. Not only used airbags, but also scraps generated when cutting out parts during the manufacture and sewing of airbag base fabrics can be recycled.

[0006] Generally, the base fabric for airbags is made by spinning nylon 66 and polyethylene terephthalate and weaving each of them separately or partially mixing them together to form a woven fabric. Therefore, in order to recycle the airbag base fabric, it is necessary to separate the polyamide and polyethylene terephthalate.

[0007] Here, examples of physical methods for removing impurities from polyamide containing impurities to make it in a clean state include a method in which the recovered material is crushed and then separated by specific gravity (Patent Document 1). Although this method requires little energy to separate the impurities, it is difficult to separate them from airbag fabrics, in which the polyamide and impurities are strongly bound together through mixing, bonding, adhesion, etc.

[0008] There is also a method of removing impurities such as unnecessary silicone by dissolving them partially or entirely with a solvent (eg, Patent Document 2). However, since the silicone is infiltrated into the polyamide fibers, the silicone resin remains in the recovered polyamide. The recovered polyamide is also in the form of crushed cloth. Used airbags and scraps from manufacturing have various shapes, and it is difficult to reuse them as they are, or in the form of fiber waste obtained by cutting them. In addition, even if they are melted and reused, they are not suitable for feeding into an extruder, etc.

[0009] Conversely to the above-mentioned method, it is also possible to consider a method in which the polyamide is first dissolved in a solvent, impurities are removed as insoluble matter, and then the polyamide is precipitated by some method and recovered. However, many of the solvents that dissolve polyamides are unsuitable for industrial use; for example, they are strong acids such as formic acid or sulfuric acid, or expensive solvents such as HFIP, and there is a concern that the polyethylene terephthalate may decompose. An example of the use of a solvent that is easy to use industrially is a dissolution and recovery method using ethylene glycol (Patent Document 3). However, this method requires a very high-temperature reaction, which raises concerns about glycolysis of polyamide and polyethylene terephthalate. In addition, it is necessary to distill and dry the sherbet-like solid to remove all of the solvent used, which is likely to require a lot of energy in addition to the heating required during the reaction.

[0010] Therefore, there is a method of dissolving the calcium chloride in an alcohol solution, which is a low-temperature method using a general-purpose raw material. For example, Patent Document 4 describes a method in which a silicone-coated polyamide cloth is treated with a methanol solution of calcium chloride to dissolve the polyamide, and then the polyamide is diluted with a large amount of water or methanol to obtain the desired polyamide as a powder. However, problems became apparent when actually dissolving a silicone-coated polyamide base fabric using the method described in Patent Document 4. Patent Document 4 describes that it is preferable to use calcium chloride dihydrate, which has high solubility for polyamide, or to add an amount of water equivalent to the hydrate in addition to calcium chloride anhydride, because the solubility of polyamide in this composition is high. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Patent No. 5841598 [Patent Document 2] Patent No. 7024037 [Patent Document 3] JP 2018-172618 A [Patent Document 4] Patent No. 5110704 Summary of the Invention [Problem to be solved by the invention]

[0012] Thus, the techniques of Patent Documents 1 to 4 have room for further improvement as methods for recovering polyamide with high efficiency and high yield.

[0013] Furthermore, when the base fabric of an airbag is a mixture of polyamide and polyethylene terephthalate, the base fabric has a certain area, and the base fabrics tend to stick to each other or wrap around each other, making it difficult to efficiently recover the polyamide and polyethylene terephthalate, resulting in a low recovery rate. In order to increase the yield, it is possible to crush the base fabric beforehand, but in that case, there is a problem that the work becomes complicated and that the polyethylene terephthalate fragments are dispersed in the liquid, making recovery very difficult.

[0014] Therefore, an object of the present invention is to provide a method for producing polyamide, a method for producing polyethylene terephthalate, and a method for producing polyamide and polyethylene terephthalate, which are capable of recovering polyamide and / or polyethylene terephthalate highly efficiently and in high yield from a mixture of polyamide and polyethylene terephthalate. [Means for solving the problem]

[0015] The inventors have discovered that by mixing a mixture of polyamide and polyethylene terephthalate with a metal chloride alcohol solution containing a metal chloride and alcohol and dissolving and separating the polyamide, it is possible to recover polyamide and / or polyethylene terephthalate from the mixture and to increase the efficiency and yield during separation and recovery, thereby completing the present invention.

[0016] The present invention has been made based on the above findings, and the gist of the present invention is as follows. [1] A method for producing a polyamide, comprising recovering a polyamide from a mixture containing at least a polyamide and a polyethylene terephthalate, comprising the steps of: mixing the mixture with a metal chloride alcohol solution containing a metal chloride and an alcohol to obtain a polyamide solution in which the polyamide is dissolved; A step of separating and recovering the polyamide solution; A method for producing a polyamide, comprising: [2] A method for producing polyethylene terephthalate, comprising recovering polyethylene terephthalate from a mixture containing at least polyamide and polyethylene terephthalate, comprising the steps of: mixing the mixture with a metal chloride alcohol solution containing a metal chloride and an alcohol to obtain a polyamide solution in which at least the polyamide is dissolved; A step of separating and recovering the polyethylene terephthalate; A method for producing polyethylene terephthalate, comprising the steps of: [3] A method for producing polyamide and polyethylene terephthalate, comprising recovering polyamide and polyethylene terephthalate from a mixture of polyamide and polyethylene terephthalate, comprising the steps of: mixing the mixture with a metal chloride alcohol solution containing a metal chloride and an 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, comprising the steps of: [4] The manufacturing method described in [1], [2] or [3] above, characterized in that the mixture is a woven fabric. [5] The manufacturing method described in [4] above, characterized in that the woven fabric is an airbag material. [6] The method for producing a metal chloride according to any one of [1] to [5] above, wherein the mixture and the alcohol solution of the metal chloride are mixed at a temperature of 30 to 90° C. [7] The method according to any one of [1] to [6] above, wherein the metal chloride is zinc chloride or calcium chloride. Effect of the Invention

[0017] According to the present invention, 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 are capable of recovering polyamide and / or polyethylene terephthalate highly efficiently and in high yield from a mixture of polyamide and polyethylene terephthalate. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Hereinafter, an embodiment for carrying out the present invention (hereinafter, referred to as "the present embodiment") will be described in detail. Note that the present embodiment is an example for explaining the present invention, and the present invention is not limited to the embodiment. In other words, the present invention can be modified in various ways without departing from the gist of the present invention.

[0019] <Production method of 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 the present embodiment (hereinafter sometimes simply referred to as "the production method of the present embodiment") are methods for producing polyamide and / or polyethylene terephthalate, in which polyamide and / or polyethylene terephthalate are recovered from a mixture of polyamide and polyethylene terephthalate, and include a step of mixing the mixture with a metal chloride alcohol solution containing a metal chloride and alcohols to obtain a polyamide solution in which the polyamide is dissolved, and a step of separating and recovering the polyamide solution and / or the polyethylene terephthalate.

[0020] (mixture of polyamide and polyethylene terephthalate) First, the mixture used in the manufacturing method of this embodiment will be described. The mixture used as the material of the manufacturing method of the present embodiment is a mixture of polyamide and polyethylene terephthalate. Note that the mixture may contain at least polyamide and polyethylene terephthalate, and may contain other components as necessary. The other components are not particularly limited, but include components that cover the mixture of polyamide and polyethylene terephthalate, components to be applied, etc. Examples of the components to be applied include resins, such as silicone resins and urethane resins, but are not limited thereto. Examples of the components to be applied include lubricating oils, etc.

[0021] Here, the shape, etc. of the mixture is not particularly limited, but in terms of being able to enjoy the effects of the present invention more effectively, it is preferably a woven fabric (water jet loom, air jet loom, rapier loom, airbag base fabric, etc.), and more preferably an airbag member. When the mixture is a high-density woven fabric such as an airbag fabric, the fibers made of the polyamide and the fibers made of the polyethylene terephthalate are entangled, making it difficult to separate them sufficiently using conventional separation methods. On the other hand, in the present embodiment, the polyamide and / or polyethylene terephthalate can be recovered from the mixture by dissolving and separating the polyamide, so that even if the mixture is a woven fabric, the polyamide and / or polyethylene terephthalate can be recovered with high efficiency and high yield.

[0022] ·polyamide As the polyamide, a polymer polymerized through an amide bond, such as a polycondensation product of a diamine compound and a dicarboxylic acid compound, or a ring-opening polymerization product of a cyclic lactam, can be used. The diamine compound is not particularly limited, but examples thereof include ethylenediamine, trimethylenediamine, tetramethylenediamine, pentamethylenediamine, hexamethylenediamine, nonanediamine, methylpentanediamine, and p-phenylenediamine. The dicarboxylic acid compound is not particularly limited, but examples thereof include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, sebacic acid, terephthalic acid, and isophthalic acid. The cyclic lactam is not particularly limited, but examples thereof include ε-caprolactam, undecane lactam, and lauryllactam. The combination of the diamine compound, the dicarboxylic acid compound, and the cyclic lactam compound is not particularly limited, and a plurality of types of each compound may be used in combination. Polyhexamethylene adipamide (e.g., polyhexamethylene adipamide composed of hexamethylene diamine and adipic acid) has high solubility and is suitable for the method for producing polyamide of this embodiment.

[0023] The method for measuring the particle size and particle size distribution of the powdered polyamide is not particularly limited, but examples thereof include a laser diffraction method, a laser scattering method, a centrifugal sedimentation method, a particle tracking method, and a dynamic scattered light method.

[0024] Examples of the polyamide include polycaproamide (nylon 6), polyhexamethylene adipamide (nylon 66), polytetramethylene adipamide (nylon 46), polytetramethylene sebacamide (nylon 410), polypentamethylene adipamide (nylon 56), polypentamethylene sebacamide (nylon 510), polyhexamethylene sebacamide (nylon 610), polyhexamethylene dodecamide (nylon 612), polydecamethylene adipamide (nylon 106), polydecamethylene sebacamide (nylon 1010), Polydecamethylene dodecamide (nylon 1012), polyundecane amide (nylon 11), polydodecanamide (nylon 12), polycaproamide / polyhexamethylene adipamide copolymer (nylon 6 / 66), polycaproamide / polyhexamethylene terephthalamide copolymer (nylon 6 / 6T), polyhexamethylene adipamide / polyhexamethylene terephthalamide copolymer (nylon 66 / 6T), polyhexamethylene adipamide / polyhexamethylene isophthalamide copolymer (nylon 66 / 6I), polyhexamethylene Polyhexamethylene terephthalamide / Polyhexamethylene isophthalamide copolymer (Nylon 6T / 6I), Polyhexamethylene terephthalamide / Polyundecane amide copolymer (Nylon 6T / 11), Polyhexamethylene terephthalamide / Polydodecane amide copolymer (Nylon 6T / 12), Polyhexamethylene adipamide / Polyhexamethylene terephthalamide / Polyhexamethylene isophthalamide copolymer (Nylon 66 / 6T / 6I), Polyxylylene adipamide (Nylon XD6), Polyxylylene sebacamide (Nylon XD10), Examples of such copolymers 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 addition, the symbol " / " indicates a copolymer. These polyamides may be used alone 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 already generally known, and is usually produced by polycondensation of hexamethylenediamine and adipic acid. Alternatively, polyamide 66 may be a copolymer containing at least one monomer unit selected from the group consisting of lactam, aminocarboxylic acid, and a combination of other diamine and dicarboxylic acid in an amount of less than 30% by mass based on the total mass of all monomer units.

[0025] These polyamides may be commercially available or may be produced by a known method. The method for producing the polyamide is not particularly limited, but examples thereof include a method for ring-opening polymerization of lactam, a method for self-condensation of ω-aminocarboxylic acid, and a method for condensing diamine and dicarboxylic acid.

[0026] Furthermore, the polyamide has a value [NH 2 It is preferable that [NH 2 When the ratio of [COOH] / [COOH] is within the above range, the interaction between the surface of the glass fiber and the polyamide terminal becomes sufficiently large during melt kneading, and the physical properties of the obtained composition become sufficiently high. 1 It can be measured using H-NMR.

[0027] The polyamide may be composed of only polyamide, or may be a polyamide resin composition containing the polyamide and other components. For example, impurities such as other resins and metals may be mixed, attached, or applied to the polyamide as other components. The mass ratio of the polyamide relative to 100% by mass of the polyamide is preferably 30 to 100% by mass, more preferably 70% by mass or more, even more preferably 80% by mass or more, still more preferably 85% by mass or more, and particularly preferably 100% by mass, from the viewpoint of obtaining a powdered polyamide having a larger particle size and a smaller particle size distribution in a short period of time.

[0028] In addition, when impurities other than the polyamide are contained, a process of separating the polyamide from the impurities may be included. The method of separation is not particularly limited, but if the impurities are insoluble in the polyamide resin composition in a dissolved state, they can be separated by methods such as filtration, centrifugation, and sedimentation. If the impurities are dissolved in the solvent together with the polyamide, separation by extraction in the dissolved state, membrane separation, electrodialysis, etc., or a method of washing after precipitating the polyamide in a precipitation step described later can be considered.

[0029] ·Polyethylene terephthalate The polyethylene terephthalate (PET) constituting the mixture generally has the following structure: [ka]

[0030] In the mixture, the polyethylene terephthalate may be present as fibrous PET, which can be obtained by further solid-state polymerization and spinning of PET resin.

[0031] The polyethylene terephthalate may be composed of only polyethylene terephthalate, or may be a polyethylene terephthalate resin composition containing the polyethylene terephthalate and other components. For example, impurities such as other resins and metals may be mixed, attached, or applied to the polyethylene terephthalate as other components.

[0032] (Step of Obtaining Polyamide Solution) The manufacturing method of this embodiment includes a step of mixing the mixture with a metal chloride alcohol solution containing a metal chloride and alcohols to obtain a polyamide solution in which the polyamide is dissolved. This process allows only the polyamide to be melt-separated from the mixture of the polyamide and polyethylene terephthalate, facilitating the subsequent recovery of the polyamide and / or the polyethylene terephthalate. In addition, since only the polyamide can be melt-separated by simply mixing the mixture with a predetermined alcoholic solution of a metal chloride, the polyamide and / or the polyethylene terephthalate can be recovered efficiently and in high yield.

[0033] The metal chloride alcohol solution used to dissolve the polyamide contains a metal chloride and an alcohol, and may further contain components other than the metal chloride and the alcohol, if necessary. In particular, from the viewpoint of the solubility of the polyamide, the total mass ratio of the metal chloride and the alcohols to 100 mass% of the metal chloride alcohol solution is preferably 80 mass% or more, more preferably 90 mass% or more, and even more preferably 100 mass%.

[0034] Examples of the alcohols include methanol, ethanol, linear or branched propanol, linear or branched butanol, and combinations thereof. Among them, from the viewpoint of the solubility of polyamide, methanol, ethanol, or combinations thereof are preferred, and methanol is more preferred. The alcohols may also contain various diols as necessary.

[0035] The mass ratio of the metal chloride to the 100 mass% alcohol solution of the metal chloride is preferably 10 to 50 mass%, more preferably 15 to 25 mass%. If the mass ratio is less than 10 mass%, the amount of polyamide dissolved is small, and a large amount of solvent is required. If the mass ratio is more than 50 mass%, the metal chloride is likely to remain undissolved and is likely to be mixed in as an impurity.

[0036] The metal chloride includes zinc chloride, magnesium chloride, calcium chloride, etc., with zinc chloride and calcium chloride being preferred, and calcium chloride being most preferred. The metal chloride is preferably anhydrous. If water is mixed in, the solubility of the polyamide decreases. However, a hydrate (for example, dihydrate of calcium chloride) may be mixed in as long as the solubility is within an acceptable range. The mass ratio of water in the metal chloride is preferably 30 mass % or less, more preferably 1 mass % or less, further preferably 0.1 mass % or less, and it is particularly preferable that the metal chloride contains no water.

[0037] 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. If the temperature is too low, dissolution will be slow, and if the temperature exceeds 90° C., the temperature will be higher than the boiling point, which is undesirable from the viewpoints of corrosiveness and decomposability. The temperature may be constant or may be varied within the range.

[0038] The polyamide may be dissolved in either a batch system or a continuous system. In the case of the batch method, the stirring is not particularly limited, but stirring is preferred, as stirring increases the dissolution rate of the polyamide. In the case of a continuous system, the solvent may be continuously passed through the solid, or the solution may be circulated. Circulation is preferred because it allows the amount of solvent used to be reduced.

[0039] The shape of a container used when mixing the mixture of polyamide and polyethylene terephthalate with the alcohol solution of a metal chloride and dissolving the polyamide is not particularly limited, and any shape such as a tank type or a circulation type may be used.

[0040] The dissolution time of the polyamide is not particularly limited, but is preferably 5 minutes to 100 hours.

[0041] In the step of obtaining the polyamide solution, the mass ratio of the polyamide in the mixture to the metal chloride alcohol solution is not particularly limited, but is preferably 3 to 15 mass%, more preferably 5 to 13 mass%. If it is less than 3 mass%, too much solvent is required, and if it exceeds 15 mass%, the viscosity of the polyamide solution increases, prolonging the dissolution time and deteriorating operability.

[0042] (Step of separating and recovering polyamide solution) The method for producing polyamide, and the method for producing polyamide and polyethylene terephthalate according to the present embodiment further includes a step of separating and recovering the polyamide solution after the step of obtaining the polyamide solution. By this step, the polyamide contained in the polyamide solution can be separated and recovered from the polyethylene terephthalate that remains undissolved.

[0043] The method for separating and recovering the polyamide solution is not particularly limited, and the polyamide alone can be separated and recovered by removing the polyethylene terephthalate that remains undissolved in the polyamide solution by filtration or the like.

[0044] The step of separating and recovering the polyamide solution may be carried out after the step of obtaining the polyamide solution, and may be carried out after the step of obtaining an alcohol dilution solution, which will be described later. For example, the polyamide solution may be diluted at a high temperature, separated in a state where the polyamide does not precipitate, and then cooled to recover the polyamide.

[0045] In the manufacturing method of this embodiment, from the viewpoint of reusing the metal chloride alcohol solution, the metal chloride alcohol solution can be further concentrated. For example, the metal alcohol solution containing the metal chloride and the alcohol obtained in the polyamide recovery step may be concentrated and reused. Examples of the concentration method include concentration by heating.

[0046] (Process for separating and recovering polyethylene terephthalate) The method for producing polyethylene terephthalate and the method for producing polyamide and polyethylene terephthalate according to the present embodiment further includes a step of separating and recovering the polyethylene terephthalate after the step of obtaining the polyamide solution. By this step, the polyethylene terephthalate remaining undissolved can be separated and recovered from the polyamide contained in the polyamide solution.

[0047] The method for separating and recovering the polyethylene terephthalate is not particularly limited, and the polyethylene terephthalate that remains undissolved in the polyamide solution can be removed by filtration or the like to perform separation and recovery.

[0048] The step of separating and recovering the polyethylene terephthalate may be carried out after the step of obtaining the polyamide solution, and may be carried out after the step of obtaining an alcohol dilution solution, which will be described later.

[0049] (Polyamide precipitation and recovery process) In addition, in the production method of the present embodiment, after the step of obtaining the polyamide solution or after the step of separating and recovering the polyamide solution and / or the polyethylene terephthalate, It is preferable that the method further comprises the step of precipitating and recovering the polyamide.

[0050] The polyamide may be recovered from the polyamide solution. From the viewpoint of further improving recovery efficiency, however, it is preferable to recover the polyamide after precipitating the polyamide from the polyamide solution.

[0051] The method for recovering the polyamide from the solution containing the polyamide includes a method for precipitating the polyamide. The method for precipitating the polyamide from the solution containing the polyamide is not particularly limited, but several precipitation methods are possible depending on the dissolved state of the polyamide. When the polyamide is dissolved by heating, it is possible to precipitate the polyamide by cooling, taking advantage of the temperature dependency of the solubility of the polyamide. In this case, the dissolved polyamide is precipitated from the solution containing the dissolved polyamide without adding an additional solvent to the solution, thereby obtaining a precipitated polyamide.

[0052] In the case where the temperature dependency of the solubility during dissolution is small, the solution containing the polyamide may be mixed with a poor solvent for the polyamide to reduce the solubility and cause precipitation. In this case, a 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 thereof include water and alcohols such as ethanol, n-propanol, and isopropanol. The method of adding the poor solvent to the polyamide may be either a method of adding a solution containing the polyamide to the poor solvent, or a method of adding a poor solvent to the solution containing the polyamide, and the addition speed, temperature, stirring speed, etc. during addition are not particularly limited. The amount of poor solvent added is not particularly limited, but is preferably 0.5 to 50 times the mass of the polyamide-containing solution, and more preferably 1 to 10 times the mass. The smaller the amount added, the lower the recovery rate, and the larger the amount added, the larger the amount of solution becomes, requiring more time and energy for treatment.

[0053] When the temperature dependency of the solubility during dissolution is small, the solubility of the polyamide can also be reduced by reducing the concentration of calcium chloride. The method of adding methanol to reduce the concentration of calcium chloride is not particularly limited, but may be either a method of adding a solution containing the polyamide to methanol or a method of adding methanol to a solution containing the polyamide, and the addition speed, temperature, stirring speed, etc. during addition are not particularly limited. The shape of the container is not particularly limited, and any shape such as a tank type or a circulation type may be used.

[0054] The precipitated polyamide is preferably recovered by solid-liquid separation. Examples of the solid-liquid separation method include filtration, centrifugation, and sedimentation. Either method may be used in a batch or continuous manner.

[0055] The polyamide obtained by solid-liquid separation is preferably washed with a solvent. The washing liquid is not particularly limited, but for example, a solution having the composition of the liquid portion during precipitation, a good solvent, and a solvent capable of dissolving calcium chloride and the like are 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. Washing may be performed multiple times as necessary.

[0056] The washing method is not particularly limited, and examples thereof include a batch washing method, a continuous washing method in which a solid is placed in a solid-liquid separation device such as a filter or a centrifugal separator and water is passed through the solid, and a combination of these methods. After washing, the polyamide can be dried and solidified by distilling off the washing solvent through heating and / or reduced pressure to obtain a powdered polyamide.

[0057] The shape of the recovered polyamide is not particularly limited, and examples thereof include polyamide melted and formed into pellets, polyamide dissolved in a solvent and then precipitated into a powder, and powder agglomerated in accordance with handling conditions to form tablets.

[0058] (Polyamide fiber spinning) The resulting polyamide can also be melt spun to produce polyamide fibers. The spinning temperature in melt spinning is preferably 290° C. or higher and 310° C. or lower. Setting the spinning temperature to 310° C. or lower is preferable because thermal decomposition of the polyamide can be suppressed, more preferably 300° C. or lower, and even more preferably 295° C. or lower. On the other hand, a spinning temperature of 290° C. or higher is preferable because the polyamide exhibits sufficient melt fluidity, the discharge amount between the discharge holes is uniform, and high-magnification drawing is possible.

[0059] The shorter the residence time in the melt spinning process (the time from when the polyamide resin is melted until it is discharged from the spinneret), the better. The residence time is preferably 30 minutes or less, more preferably 15 minutes or less, and even more preferably 0.5 minutes to 7 minutes. A short residence time is preferable because cyclopentanones in the polymer increase at the melting temperature.

[0060] For thermal stability in high temperature and high humidity environments, it is preferable to add a copper compound so that the copper concentration relative to the polyamide is 1 to 500 ppm, more preferably 30 to 500 ppm. By doing so, even if the polyamide is left in a high temperature and high humidity environment for a long time or exposed to an environment containing a large amount of ozone for a long time, the deterioration of mechanical properties 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.

[0061] The copper compound is not particularly limited in type, and for example, an organic copper salt such as copper acetate, or a copper halide such as cuprous chloride or cupric chloride can be preferably used. The copper compound is more preferably used in combination with a metal halide compound. Examples of the metal halide compound include potassium iodide, potassium bromide, and potassium chloride. The preferred combinations in this embodiment are cuprous iodide and potassium iodide, and copper acetate and potassium iodide. The copper content in the polyamide can be measured by atomic absorption spectrometry, colorimetry, or the like.

[0062] As a stabilizer, organic antioxidants such as hindered phenol antioxidants, sulfur antioxidants, and phosphorus antioxidants, heat stabilizers, light stabilizers such as hindered amines, benzophenones, and imidazoles, and ultraviolet absorbers may be added, although not limited thereto. An appropriate amount may be selected, and 1 to 1000 ppm may be added to the polyamide. These additives may be used alone or in combination of several kinds.

[0063] In the melt spinning process, a single-screw or twin-screw extruder is preferably used in the melting section, which can apply an appropriate pressure to the polyamide resin while guiding it to the polymer pipe, gear pump, and spinning pack.

[0064] In addition, it is preferable to filter the polyamide resin using a metal fiber nonwoven fabric filter, sand, or the like before it is discharged from the spinneret, since this stabilizes the spinning operation. The shape of the nozzle holes in the spinneret may be selected according to the cross-sectional shape of the single fibers constituting the filaments to be produced. The yarn spun from the spinneret is solidified with cooling air, a process oil is applied, and the yarn is taken up, stretched, and heat-treated to obtain polyamide fiber.

[0065] In addition, it is preferable to filter the polyamide resin using a metal fiber nonwoven fabric filter, sand, or the like before it is discharged from the spinneret, since this stabilizes the spinning operation. The shape of the nozzle holes in the spinneret may be selected according to the cross-sectional shape of the single fibers constituting the filaments to be produced. The yarn spun from the spinneret is solidified with cooling air, a process oil is applied, and the yarn is taken up, stretched, and heat-treated to obtain polyamide fiber. EXAMPLES

[0066] The present invention will be described below with reference to specific examples and comparative examples, but the present invention is not limited to the following examples.

[0067] (Airbag fabric) In the following examples and comparative examples, an airbag fabric was used as a mixture of polyamide and polyethylene terephthalate. This airbag fabric is a woven fabric made of polyamide fiber (nylon 66 fiber) and polyethylene terephthalate fiber, and the weight ratio of the polyamide fiber to the polyethylene terephthalate fiber is 99: 1. This airbag fabric was cut into a size of 50 mm x 50 mm and used as a sample.

[0068] [Example 1] 10 g of airbag fabric and 100 g of 20 wt% calcium chloride methanol solution were added to a 300 mL glass bottle containing a stirrer, and the bottle was placed in a 60°C water bath and stirred with a magnetic stirrer for 12 hours to dissolve the polyamide. The polyamide solution was passed through a stainless steel mesh with a mesh size of 1 mm and a stainless steel mesh with a mesh size of 500 μm to remove the undissolved polyethylene terephthalate woven fabric. The resulting polyethylene terephthalate was washed with methanol and dried to obtain 0.095 g (95% yield relative to the polyethylene terephthalate in the fabric). The solution containing the recovered polyamide was transferred to a 1000 mL beaker, and 500 g of methanol was added while stirring. The resulting precipitate was collected by filtration using a 1 μm membrane filter. The solid after filtration was thoroughly washed with water. The washed solid was heated and dried in a vacuum dryer at 40 degrees, yielding 9.8 g of regenerated polyamide (99% yield relative to the polyamide in the base fabric).

[0069] [Example 2] 10 g of airbag fabric and 200 g of 10 wt% zinc chloride methanol solution were added to a 300 mL glass bottle containing a stirrer, and the bottle was placed in a 60°C water bath and stirred with a magnetic stirrer for 50 hours to dissolve the polyamide. The polyamide solution was passed through a stainless steel mesh with a mesh size of 1 mm and a stainless steel mesh with a mesh size of 500 μm to remove the undissolved polyethylene terephthalate woven fabric. The resulting polyethylene terephthalate was washed with methanol and dried to obtain 0.095 g (95% yield relative to the polyethylene terephthalate in the fabric). The solution containing the recovered polyamide was transferred to a 1000 mL beaker, and 500 g of methanol was added while stirring. The resulting precipitate was filtered and recovered using a 1 μm membrane filter. The solid after filtration was thoroughly washed with water. The washed solid was heated and dried in a vacuum dryer at 40 degrees, yielding 9.5 g of regenerated polyamide (95% yield relative to the polyamide in the base fabric).

[0070] [Comparative Example 1] 10 g of airbag fabric and 200 g of concentrated sulfuric acid were added to a 300 mL glass bottle containing a stirrer, and the bottle was placed in a 100°C oil bath and stirred with a magnetic stirrer for 24 hours to dissolve the polyamide. The polyamide solution was passed through a Hastelloy mesh with 1 mm openings and a Hastelloy mesh with 500 μm openings in an attempt to remove the undissolved polyethylene terephthalate woven fabric, but all of it had dissolved. The solution containing the recovered polyamide was transferred to a 2000 mL beaker, and 1500 g of water was added while stirring in an ice bath. The resulting precipitate was filtered and recovered using a 1 μm membrane filter. The filtered solid was thoroughly washed with water. The washed solid was heated and dried in a vacuum dryer at 40 degrees, yielding 8.8 g (89% yield relative to the polyamide in the base fabric). The filtrate was analyzed to determine the decrease in yield, and decomposition products such as adipic acid and hexamethylenediamine were confirmed. [Industrial Applicability]

[0071] According to the present invention, 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 are capable of recovering polyamide and / or polyethylene terephthalate highly efficiently and in high yield from a mixture of polyamide and polyethylene terephthalate.

Claims

1. A method for producing a polyamide, comprising recovering a polyamide from a mixture containing at least a polyamide and a polyethylene terephthalate, the method comprising the steps of: mixing the mixture with a metal chloride alcohol solution containing a metal chloride and an alcohol to obtain a polyamide solution in which the polyamide is dissolved; A step of separating and recovering the polyamide solution; A method for producing a polyamide, comprising:

2. A method for producing polyethylene terephthalate, comprising recovering polyethylene terephthalate from a mixture containing at least polyamide and polyethylene terephthalate, comprising the steps of: mixing the mixture with a metal chloride alcohol solution containing a metal chloride and an alcohol to obtain a polyamide solution in which at least the polyamide is dissolved; A step of separating and recovering the polyethylene terephthalate; A method for producing polyethylene terephthalate, comprising the steps of:

3. A method for producing polyamide and polyethylene terephthalate, comprising recovering polyamide and polyethylene terephthalate from a mixture of polyamide and polyethylene terephthalate, the method comprising the steps of: mixing the mixture with a metal chloride alcohol solution containing a metal chloride and an 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, comprising the steps of:

4. The method according to claim 1, 2 or 3, characterized in that the mixture is a woven fabric.

5. The method of claim 4, wherein the woven fabric is an airbag material.

6. 4. The method according to claim 1, 2 or 3, wherein the mixture and the alcohol solution of metal chloride are mixed at a temperature of 30 to 90° C.

7. 4. The method according to claim 1, 2 or 3, wherein the metal chloride is zinc chloride or calcium chloride.

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