Nylon 6 resin and manufacturing method thereof

Abstract

The present invention provides: a nylon 6 resin obtained from chemical recycling, said nylon 6 resin having a color tone equivalent to that of a nylon 6 resin produced using an original epsilon-caprolactam; and a method for producing the nylon 6 resin. The nylon 6 resin according to the present invention contains chemically recycled nylon 6, and contains 1 mass% or less of a peak other than nylon 6 in a region of 6.5 ppm to 13.0 ppm (inclusive) under 1H NMR.

Description

Technical Field

[0001] The present invention relates to a resin containing nylon 6 after chemical recycling and a method for manufacturing the same. Background Art

[0002] Polyamides are raw materials widely used in clothing or industrial applications such as fiber products or resin products. Due to the increasing attention to sustainable development represented by the Sustainable Development Goals (SDGs), recycling based on recycling is being promoted. As a method for recycling polyamides, a thermal recycling method, a material recycling method, and a chemical recycling method are known. Among them, the chemical recycling method decomposes polyamide resin into raw material monomers and then recovers them, which can be reused as raw materials for polymers. Therefore, it is an industrially useful recycling method.

[0003] In polyamides, even when nylon 6 is manufactured using ε-caprolactam derived from petroleum raw materials, since its polymerization reaction is an equilibrium reaction, generally an extraction process for removing monomer / oligomer components after polymerization is required. Industrially, in order to reduce raw material loss and reduce the drainage load, generally the recovered monomer / oligomer components are depolymerized and reused. In terms of effectively utilizing the recovery / reuse cycle, nylon 6 has an advantage over other polyamides.

[0004] For example, Patent Document 1 describes a recycling method for chemically recycling a dustproof suit, and Patent Document 2 describes a recycling method for chemically recycling a clothing product made of nylon 6 fiber. This method describes that assuming chemical recycling from the product design stage, by making each raw material in the product mainly nylon 6, mixing of impurities of other resins such as polyurethane or polyester can be minimized, and thus a high-purity monomer raw material can be obtained.

[0005] In addition, Patent Document 3 describes a method for recycling a clothing product made of nylon 6 as follows: by limiting the content of a water repellent and titanium oxide to a certain amount or less, ε-caprolactam as a monomer can be recovered without equipment failure during depolymerization. It is described that by controlling the mixing ratio of substances that hinder the depolymerization process of reducing nylon products to ε-caprolactam as a raw material, depolymerization can be carried out without clogging the distillation line.

[0006] Furthermore, Patent Document 4 describes a method as follows: recycling is carried out by performing a pretreatment of heating in an aqueous alkali solution from a nylon 6 product containing one or more resin components as impurities.

[0007] Prior Art Documents

[0008] Patent Documents

[0009] Patent Document 1: Japanese Patent Laid-Open No. 7-331514

[0010] Patent Document 2: Japanese Patent Laid-Open No. 7-310205

[0011] Patent Document 3: Japanese Patent Laid-Open No. 2009-227960

[0012] Patent Document 4: Japanese Patent Laid-Open No. 2008-179816 Summary of the Invention

[0013] Problems to be Solved by the Invention

[0014] However, in the methods of Patent Documents 1 and 2, since the design limits the use of resins or components other than nylon 6, the purity of the ε-caprolactam obtained by chemical recycling becomes high. However, in addition to the limited applicability of the original applicable products, recycling is also required to prevent mixing with other products, resulting in extremely limited chemical recycling. Furthermore, it cannot be applied to the chemical recycling of general nylon 6 products already existing in the market.

[0015] In addition, in the method of Patent Document 3, by focusing on substances that hinder the depolymerization of nylon 6 products and restricting their ratios, the purity of the ε-caprolactam quality becomes high. However, in addition to the need to screen products that do not contain resins other than nylon 6, the content of water repellents or titanium oxide in the products must be chemically analyzed for quantification. Therefore, it is not practical to apply it to general nylon 6 products, and its industrial use is also extremely limited.

[0016] Furthermore, in the method of Patent Document 4, resins other than nylon 6 that can chemically reduce the quality of ε-caprolactam after depolymerization can be removed. However, in addition to the need to treat high-concentration alkali at high temperature, other components that are dissolved also need to be drained as waste liquid, imposing a large load on the wastewater treatment process. Therefore, it is difficult to increase the quantity and apply it to industrial uses.

[0017] Therefore, an object of the present invention is to provide a recycled nylon 6 resin and a method for manufacturing the same, which have the same hue as nylon products manufactured using ε-caprolactam not obtained through recycling when chemically recycling a large number of nylon 6 products already existing in the market industrially.

[0018] Technical Means for Solving the Problems

[0019] The present invention adopts the following structure to achieve the above object.

[0020] (1) A nylon 6 resin comprising nylon 6 after chemical recycling, in 1In nuclear magnetic resonance (NMR), the region above 6.5 ppm and below 13.0 ppm contains less than 1% by mass of peaks other than nylon 6.

[0021] (2) The nylon 6 resin according to (1) above contains, in 1 a substance other than nylon 6 that has a peak in the region above 6.5 ppm and below 13.0 ppm under 1H NMR, and the substance has a benzene ring structure.

[0022] (3) A method for manufacturing a nylon 6 resin, which is a method for manufacturing the nylon 6 resin according to (1) or (2) above, includes depolymerizing a recycled nylon 6 product as a raw material to recover ε-caprolactam and refining and polymerizing the ε-caprolactam, and the ratio of the polyester resin in the recycled nylon 6 product is 5% by mass or less.

[0023] Effects of the Invention

[0024] By the present invention, a nylon 6 resin after chemical recycling having the same hue as a so-called virgin type nylon 6 resin that has not undergone chemical recycling can be provided. Detailed Description of the Invention

[0025] Hereinafter, the present invention will be described in detail.

[0026] In addition, in this specification, "mass" and "weight" have the same meaning.

[0027] The nylon 6 resin of the present invention contains nylon 6 after chemical recycling, and in 1 1H NMR, the region above 6.5 ppm and below 13.0 ppm contains less than 1% by mass of peaks other than nylon 6. The nylon 6 resin of the present invention is preferably 95% by mass or more of nylon 6, more preferably 97% by mass or more of nylon 6, and still more preferably 99% by mass or more of nylon 6.

[0028] The nylon 6 resin of the present invention is suitably in the range of 2.0 to 4.0 in terms of the relative viscosity of a 98% sulfuric acid solution. To the extent that the object of the present invention is not hindered, the nylon 6 resin may also contain additives such as titanium oxide and heat-resistant agents.

[0029] The nylon 6 resin of the present invention is in 1 1H NMR, the region above 6.5 ppm and below 13.0 ppm contains less than 1% by mass of peaks other than nylon 6. The peaks other than nylon 6 are more preferably 0.7% by mass or less, and still more preferably 0.5% by mass or less. On the other hand, regarding the lower limit, it is preferably 0.1% by mass or more. That is, in1 In the 1H NMR spectrum, in the region above 6.5 ppm and below 13.0 ppm, peaks other than those of nylon 6 are preferably included in the range of 0.1% by mass or more and 1% by mass or less. 1 In the 1H NMR spectrum, the region above 6.5 ppm and below 13.0 ppm is a region where peaks of multiple bonds or hydrogen atoms bonded to aromatic groups that affect the resin color tone can be confirmed. If the peaks contained in this region are 1% by mass or less, a nylon 6 resin with good color tone can be obtained. As substances other than nylon 6 that can be confirmed in the peaks in this region, substances having a benzene ring structure can be cited. Particularly preferably, the content of substances having a benzene ring structure is controlled. If a large amount of substances having a benzene ring structure is contained, there is a concern that the color tone of the obtained nylon 6 resin deteriorates. As a substance having a benzene ring structure, for example, terephthalic acid can be cited.

[0030] In the present invention 1 The 1H NMR can be measured by any method. For example, deuterated hexafluoroisopropanol (HFIP) (containing tetramethylsilane (TMS)) is dissolved in resin particles, and 1 the 1H NMR is measured. As long as it is a solvent that dissolves nylon 6, other deuterated solvents can also be used. The integral ratio is calculated based on the peaks attributed to each component, and the component amount is calculated. The amount of components other than nylon 6 in the present invention is calculated based on the area ratio of the 4H peak derived from terephthalic acid at 8 ppm to 8.5 ppm and the 2H peak derived from nylon 6 at 3 ppm to 3.5 ppm. As long as it is a peak that does not interfere with other peaks and can be identified, it is not limited to the above peaks.

[0031] A method for manufacturing the nylon 6 resin of the present invention will be described.

[0032] The method for manufacturing the nylon 6 resin of the present invention includes a case where a nylon 6 recycled product is depolymerized to recover ε-caprolactam, and the recovered ε-caprolactam is refined and polymerized, and the ratio of the polyester resin in the nylon 6 recycled product is set to 5% by mass or less. The nylon 6 recycled product refers to pre-consumer waste and / or post-consumer waste. Each waste is not limited to the following. For example, pre-consumer waste includes scouring waste, broken filament waste, and extrusion waste in the filament making process, and post-consumer waste includes recycled clothing products, fishing nets, ropes, etc.

[0033] The depolymerization carried out in the present invention can be any method. The nylon 6 recycled product is melted by heating and depolymerized. At this time, a catalyst can be used, and it can be carried out either in the absence of water (dry method) or in the presence of water (wet method).

[0034] The pressure during depolymerization can be any one of reduced pressure, normal pressure, and increased pressure. The depolymerization temperature is preferably 100°C to 400°C, more preferably 200°C to 350°C, and still more preferably 220°C to 300°C. If the temperature is too low, the recycled nylon 6 product will not melt and the depolymerization rate will slow down. If the temperature is too high, the monomer of nylon 6 (i.e., ε-caprolactam) will decompose, resulting in a decrease in the purity of the recycled ε-caprolactam.

[0035] In the case of using a catalyst, an acid catalyst or a base catalyst, etc. is used. Examples of the acid catalyst include: phosphoric acid, boric acid, sulfuric acid, organic acids, organic sulfonic acids, solid acids, and salts thereof. In addition, examples of the base catalyst include: basic hydroxides, basic salts, alkaline earth metal hydroxides, alkaline earth metal salts, organic bases, solid bases, etc. Preferably, examples include: phosphoric acid, boric acid, organic acids, basic hydroxides, basic salts, etc. Still more preferably, examples include: phosphoric acid, sodium phosphate, potassium phosphate, sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, sodium bicarbonate, potassium bicarbonate, etc.

[0036] Relative to the recycled nylon 6 product, the catalyst amount is preferably used in an amount of 0.01% by mass to 50% by mass. More preferably, it is 0.01% by mass to 20% by mass, and still more preferably, it is 0.5% by mass to 10% by mass. If the catalyst amount is too small, the reaction rate will slow down. If the catalyst amount is too large, side reactions will increase and the catalyst cost will increase, which is economically disadvantageous.

[0037] In the case of wet depolymerization, relative to the recycled nylon 6 product, the amount of water is preferably 0.1 times by mass to 50 times by mass. More preferably, it is 0.5 times by mass to 20 times by mass, and still more preferably, it is 1 time by mass to 10 times by mass. If the amount of water is too small, the reaction rate will slow down. If the amount of water is too large, the concentration of the aqueous solution of the recycled ε-caprolactam will decrease.

[0038] In the depolymerized nylon 6 recycled product, it is desirable that other resin components such as polyurethane or polyester are less. Relative to the nylon 6 recycled product, the resin component other than nylon 6 is preferably 5% by mass or less, more preferably 3% by mass or less, and the lower limit is preferably 1% by mass or more. If the nylon 6 recycled product with other resins attached or attached is decomposed by depolymerization, there are concerns as follows: the purity of the recovered ε-caprolactam is reduced, and at the same time, the viscosity of the molten raw material during depolymerization increases or the catalyst is deactivated, resulting in a reduction in the recovery rate of ε-caprolactam. In particular, if polyethylene terephthalate, which is representative of polyester resins, is included, problems may also occur in the operation of the recycling device, such as the sublimation of terephthalic acid by-produced during depolymerization and the blockage of the pipes of the depolymerization equipment. Therefore, in the present invention, the ratio of the polyester resin in the nylon 6 recycled product is set to 5% by mass or less. The ratio of the polyester resin is preferably 3% by mass or less, and preferably 1% by mass or more. That is, the ratio of the polyester resin is preferably set to 1% by mass or more and 5% by mass or less.

[0039] In order to control the content of other resin components such as polyester resin to 5% by mass or less, for example, there are: a method of physically removing parts containing other resin components, a method of chemically separating and removing other resin components by dissolving them in a good solvent, etc.

[0040] The method for recovering ε-caprolactam carried out in the present invention is not particularly limited and can be any method. For example, in the case of dry depolymerization, the generated ε-caprolactam is distilled out from the depolymerization reaction device by vacuum distillation and recovered. ε-Caprolactam can also be extracted by vacuum distillation after the depolymerization reaction is completed. It can also be continuously extracted while the depolymerization reaction is in progress. In addition, in the case of wet depolymerization, the generated ε-caprolactam is distilled out from the depolymerization reaction device together with water, and an aqueous solution of ε-caprolactam is recovered. ε-Caprolactam can also be extracted by vacuum distillation after the depolymerization reaction is completed. It can also be continuously extracted while the depolymerization reaction is in progress.

[0041] As a method for refining the recovered ε-caprolactam, for example, there are: a method of precisely distilling the recovered ε-caprolactam, a method of performing vacuum distillation by adding a small amount of sodium hydroxide, a method of performing activated carbon treatment, a method of performing ion exchange treatment, a method of performing recrystallization, etc., and these refining methods can be combined.

[0042] Regarding the degree of coloring of ε-caprolactam obtained by depolymerization carried out in the present invention, a 50% by mass aqueous solution of ε-caprolactam is placed in a 10 mm long quartz cell, and the transmittance based on water at a wavelength of 290 nm is measured using a spectrophotometer. Generally, the higher the transmittance, the lower the degree of coloring. If the degree of coloring of ε-caprolactam is low, the hue of nylon 6 resin can be reduced. The transmittance of the 50% by mass aqueous solution of ε-caprolactam is preferably 30% or more, more preferably 50% or more. The higher the transmittance, the more preferable, and thus there is no particular limitation on the upper limit.

[0043] The polymerization carried out in the present invention can be any method. For example, an 80% to 95% by mass aqueous solution of ε-caprolactam that has been recovered and refined is introduced into a stainless steel autoclave (polymerization reaction apparatus). After the inside of the polymerization reaction apparatus is sealed with nitrogen, the temperature is raised over 1 to 3 hours until the internal pressure of the polymerization reaction apparatus reaches 0.8 MPa to 1.2 MPa. While maintaining the pressure, a polymerization reaction is carried out at 240°C to 260°C for 1 to 2 hours. Thereafter, the pressure inside the polymerization reaction apparatus is released, and polymerization is further carried out for 1 to 2 hours under a nitrogen stream. Then, the obtained polymer is extruded in a strand shape, cooled / cut, and pellets are obtained. Subsequently, the obtained pellets are transferred to an atmospheric pressure container containing 5 to 20 times the amount of hot water relative to the amount of pellets, and left to stand at a water temperature of 90°C to 100°C for 12 to 24 hours. After extracting unreacted monomer or oligomer components, a dehydration treatment is carried out.

[0044] Examples

[0045] Hereinafter, examples are given to more specifically illustrate the present invention.

[0046] 〔Measurement method〕

[0047] <Transmittance>

[0048] The obtained ε-caprolactam and purified water are mixed to obtain a 50% by mass aqueous solution of ε-caprolactam, which is placed in a 10 mm long quartz cell, and the transmittance based on water at a wavelength of 290 nm is measured using a spectrophotometer and expressed in terms of hue.

[0049] <Yellowness index (YI)>

[0050] The YI value of the resin pellets is measured using a color computer manufactured by Suga Test Instruments Co., Ltd. The measurement method is carried out in accordance with Japanese Industrial Standards (JIS) specification K7105 (Test method for optical properties of plastics).

[0051] <Component amount of peaks other than nylon 6>

[0052] Dissolve 1 mg of the resin particles in 0.4 mL of deuterated HFIP, and measure using an ECA - 400 manufactured by JEOL Ltd. 1 1H NMR. Based on the peaks attributed to each component, calculate the component amount of substances other than nylon 6 in the region of 6.5 ppm or more and 13.0 ppm or less.

[0053] (Example 1)

[0054] In 420 g of a nylon 6 recycled product containing 21 g of a polyester resin, charge 16.8 g of a 75 mass% phosphoric acid aqueous solution containing phosphoric acid as a depolymerization catalyst into a depolymerization device, and heat to 260 °C under a nitrogen atmosphere.

[0055] Stop nitrogen, blow superheated steam into the depolymerization device at an introduction rate of 500 g / hour to start the reaction, react at 260 °C for 10 hours, recover and cool the steam containing ε - caprolactam continuously distilled from the depolymerization device to obtain an ε - caprolactam aqueous solution.

[0056] For the obtained ε - caprolactam aqueous solution, distill off water and concentrate it through an evaporator under reduced pressure conditions of about 70 °C and 3.3 kPa, then transfer it to a 1000 ml Houben flask.

[0057] Add 5.3 g of a 40 mass% sodium hydroxide aqueous solution thereto, and further concentrate it under reduced pressure conditions of about 100 °C and 3.3 kPa. Subsequently, under reduced pressure distillation of ε - caprolactam under reduced pressure conditions of about 160 °C and 0.7 kPa, 335 g of refined ε - caprolactam is obtained. The transmittance of a 50 mass% ε - caprolactam aqueous solution is 37%.

[0058] Add water to the ε - caprolactam to prepare a 90 mass% ε - caprolactam aqueous solution, put it into a polymerization tank, stir it in a closed state while heating, and when the pressure in the tank reaches 1 MPa, distill out steam and maintain the pressure. When the internal liquid temperature reaches 250 °C, gradually reduce the pressure in the tank to reach atmospheric pressure within 70 minutes. The internal liquid temperature at this time is 260 °C. Thereafter, while maintaining the internal liquid temperature at 260 °C, allow nitrogen to flow in the gas phase part of the tank for 60 minutes to complete the polymerization.

[0059] After the polymerization is completed, extrude the molten nylon 6 from the bottom of the polymerization tank in a strand shape, cool it with water, and cut it with a pelletizer to form particles. For the particles, extract impurities of low molecular weight substances with hot water to obtain nylon 6 resin particles obtained by chemical recycling.

[0060] For the obtained resin particles, the component amount and hue YI of substances having peaks other than nylon 6 in the region of 6.5 ppm or more and 13.0 ppm were measured. The results are shown in Table 1.

[0061] (Example 2, Example 3, Comparative Example 1)

[0062] As shown in Table 1, the amount of polyester resin in the nylon 6 recycled product was changed, and other than that, it was carried out in the same manner as in Example 1.

[0063] (Reference Example 1)

[0064] Polymerization was carried out using the original type of ε-caprolactam as a raw material, and other than that, it was carried out in the same manner as in Example 1.

[0065] [Table 1]

[0066]

[0067] According to Table 1, compared with Comparative Example 1, Examples 1 to 3 can obtain a nylon 6 resin having a hue close to that of Reference Example 1, and the nylon 6 resin is a newly produced nylon 6 resin rather than a recycled material.

[0068] Although the present invention has been described in detail using specific forms, it is obvious to those skilled in the art that various changes and modifications can be made without departing from the intention and scope of the present invention. In addition, this application is based on a Japanese patent application (Japanese Patent Application No. 2022-191333) filed on November 30, 2022, the entire content of which is incorporated herein by reference.

Claims

1. A nylon 6 resin comprising nylon 6 after chemical recycling, which contains 1% by mass or less of peaks other than nylon 6 in the region above 6.5 ppm and below 13.0 ppm under 1 1H nuclear magnetic resonance.

2. The nylon 6 resin according to claim 1, comprising a substance other than nylon 6 having a peak in the region of 6.5 ppm or more and 13.0 ppm or less under 1H nuclear magnetic resonance, and the substance has a benzene ring structure. 1 ​ 3. A method for manufacturing nylon 6 resin, which is the method for manufacturing nylon 6 resin according to claim 1 or 2, including the case of depolymerizing a recycled nylon 6 product as a raw material to recover ε-caprolactam and refining and polymerizing the ε-caprolactam, wherein the ratio of polyester resin in the recycled nylon 6 product is 5% by mass or less.

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