Nylon 6 fiber, recycled polyhexamethylene amide resin particles, and methods for manufacturing the same.

Abstract

This invention relates to a nylon 6 fiber, recycled polyhexamethylene amide resin particles, and a method for manufacturing the same. The nylon 6 fiber is characterized in that: at least 20% by weight of the fiber is recycled nylon 6; the molecular weight distribution of the nylon 6, as determined by GPC, i.e., the weight average molecular weight (Mw) / number average molecular weight (Mn) ratio is 3.4 or less, and the z-average molecular weight (Mz) / weight average molecular weight (Mw) ratio is 1.6 or less. Recycled nylon 6 fibers are provided with good operability.

Description

Technical Field

[0001] This invention relates to nylon 6 fibers using recycled polyhexamethylene amide resin particles, and more particularly to recycled polyhexamethylene amide resin particles suitable for the manufacture of recycled nylon 6 fibers with good operability. Background Technology

[0002] Polyamide fibers, represented by polycaproamide or polyhexamethylene adipamide, are used not only in clothing but also in interior decoration, vehicle interiors, and industrial applications due to their excellent mechanical properties and dimensional stability.

[0003] However, from the perspective of resource-recycling-based environmental protection, polyhexylamide faces the following challenges: its raw material is petroleum, which is not biodegradable and thus becomes industrial waste. Against this backdrop, efforts are being made to actively recycle polyamides, such as polyhexylamide, manufactured from petroleum resources, to make them suitable for resource recycling.

[0004] For example, a type of recycled polyamide filament mainly for industrial use has been proposed. It is made by melting and filtering polyamide fiber scraps or polymer scraps generated in the filament making process to obtain recycled polyamide resin, and then blending the recycled polyamide resin into 5% to 80% by mass. It has an irregular or hollow cross section, and the total fineness is 500 dtex to 3000 dtex, and the single filament fineness is 5 dtex to 50 dtex (Patent Document 1).

[0005] In addition, as a method for manufacturing polyamide short fibers containing recycled polyamide, the following manufacturing method has been proposed: after melting and filtering polyamide fiber scraps or polymer scraps generated in the spinning process to obtain recycled polyamide resin particles, the particles are filtered again using a spinning die during melt spinning (Patent Document 2).

[0006] In addition, the following manufacturing method is proposed: crushing polyhexamethylene hexamethylenediamide fiber scraps coated with spinning oil → washing (de-oiling) → dehydration → melting to obtain material recycling polyamide resin particles, and then performing melt spinning to obtain material recycling polyamide fibers (Patent Document 3).

[0007] Existing technical documents

[0008] Patent documents

[0009] Patent Document 1: Japanese Patent Application Publication No. 2013-155454

[0010] Patent Document 2: Japanese Patent Application Publication No. 2009-84767

[0011] Patent Document 3: Japanese Patent Application Publication No. 2020-2336 Summary of the Invention

[0012] The problem that the invention aims to solve

[0013] However, although the recycled polyamide filaments with irregular or hollow cross-sections described in Patent Document 1 contain polymer debris in the waste materials used in material recycling, it is difficult to remove oligomer components, which are the source of spinning die fouling, from the polymer debris. As a result, the obtained recycled polyamide resin contains a large amount of oligomer components, leading to spinning die fouling and frequent filament breakage. In fact, when more than 80% by mass of recycled polyamide resin is formulated, foreign matter contained in the recycled polyamide resin causes component leakage or abnormal ejection as the internal pressure of the spinning assembly (pack) increases. It is inferred that part of the ejection abnormality is caused by oligomer components.

[0014] Furthermore, the polyamide polymers described in Patent Document 1, primarily suitable for industrial applications, often use high-viscosity (high-molecular-weight) polymers to ensure shape accuracy or to meet high strength requirements. Although the waste materials used in material recycling also contain polymer scraps, it is difficult to remove low-molecular-weight impurities from these scraps, resulting in a large amount of low-molecular-weight impurities in the obtained recycled polyamide polymers. When developing recycled polyamide polymers, primarily for industrial applications, for clothing applications—specifically, when manufacturing polyamide long fibers with a total fineness of 200 dtex or less and a single filament fineness of 0.2 dtex to 10 dtex—the fiber surface area is larger compared to the fineness range used in industrial applications. Therefore, there are more residual low-molecular-weight impurities, significantly impacting yarn production and raw yarn properties. From a yarn production perspective, recycled polyamide polymers, in addition to containing residual low-molecular-weight impurities, are prone to thickening and thermal degradation due to thermal processes, and also contain a large amount of high-molecular-weight impurities. This leads to the following issues: reduced strength and elongation, deviation in amino-terminated group content, resulting in filament breakage and poor high-pass yield during advanced processing; and color difference during dyeing, making it difficult to meet the stringent fabric appearance inspection standards required for clothing applications.

[0015] Patent Document 2's method for manufacturing recycled polyamide short fibers does not remove the oil, oligomer components, or other contaminants adhering to the fiber or polymer scraps used as raw materials for recycled polyamide resin particles. Furthermore, similar to Patent Document 1, since removing oligomer components from polymer scraps is inherently difficult, the resulting recycled polyamide resin particles contain a large amount of oligomer components, leading to spinning die fouling and numerous fiber breakages. Additionally, the reduced strength and elongation caused by residual low-molecular-weight impurities result in fiber breakage during higher-level processing, leading to poor high-level throughput.

[0016] While the method for manufacturing recycled polyamide fibers described in Patent Document 3 also involves a degreasing process for polyamide fiber scraps and is effective in removing foreign matter caused by the oiling agent, it is insufficient in removing oligomer components contained in the polyamide fiber scraps. As a result, the obtained recycled polyamide resin particles contain a large amount of oligomer components. Although long fibers are obtained in the high-speed winding area and are at a level suitable for melt spinning, issues such as die fouling caused by oligomer components occur, and fiber breakage increases with the number of spinning days. From the viewpoint of long-term continuous manufacturing, it is difficult to use for the manufacture of polyamide fibers.

[0017] The objective of this invention is to solve the aforementioned problems and provide recycled polyvinyl acetate resin particles that are difficult to remove to a limit in the prior art, particularly suitable for the easy manufacture of recycled nylon 6 fibers. Furthermore, the objective is to provide a nylon 6 fiber that, through the use of the recycled polyvinyl acetate resin, provides recycled nylon fibers with fewer low-molecular-weight or high-molecular-weight impurities, and provides high-quality textile fabrics with the same filament properties as virgin-type nylon 6 fibers, excellent high-pass permeability.

[0018] Technical means to solve the problem

[0019] The present invention employs the following structure to achieve the aforementioned objective.

[0020] (1) A nylon 6 fiber, characterized in that: more than 20% by weight of the fiber is nylon 6 after material recycling, and the dispersion ratio of the molecular weight distribution obtained by gel permeation chromatography (GPC), the weight average molecular weight (Mw) / number average molecular weight (Mn) is less than 3.4, and the z-average molecular weight (Mz) / weight average molecular weight (Mw) is less than 1.6.

[0021] (2) The nylon 6 fiber according to (1) is characterized in that: the total fineness is 3dtex to 200dtex, the single filament fineness is 0.2dtex to 10dtex, and the coefficient of variation (CV)% of the continuous strength elongation product is less than 3.5.

[0022] (3) The nylon 6 fiber according to (1) or (2) is characterized in that the yellowness index (YI) value is less than 15.

[0023] (4) Nylon 6 fiber according to any one of (1) to (3), characterized in that: the amount of oligomer content in the nylon 6 resin particles after material recycling is less than 1.5% by weight.

[0024] (5) A material for recycling polyhexamethylene amide resin particles, wherein the amount of oligomer content detected by hot water extraction is less than 1.5% by weight.

[0025] (6) The material recycles polyhexamethylene amide resin particles according to (5), wherein the filtration pressure rise rate is less than 2.0 MPa / hour.

[0026] (7) A method for manufacturing recycled polyhexamethylene amide resin particles, wherein the recycled polyhexamethylene amide resin particles according to (5) are manufactured by cutting the fiber scraps generated in the manufacturing process of polyhexamethylene amide fibers, immersing the cut fiber scraps in hot water at a temperature above 50°C, melting, filtering and spraying the fiber scraps, cooling the sprayed polyhexamethylene amide resin with water and cutting it into particles, and then immersing the polyhexamethylene amide resin particles in hot water at a temperature above 50°C.

[0027] (8) The method for manufacturing recycled polyhexamethylene amide resin particles according to (7) wherein, in the process of melting, filtering and spraying the fiber scraps, the spraying is performed after more than two filtration processes.

[0028] The effects of the invention

[0029] According to the present invention, a material-recycled nylon 6 fiber is provided, which provides a high-quality garment fabric with the same filament properties as virgin nylon 6 fiber, excellent high-pass yield, and superior quality. Additionally, a material-recycled polyhexamethylene resin particle is provided that removes oligomer components from the recycled polyhexamethylene resin particles to a limit, particularly suitable for the easy manufacture of material-recycled polyhexamethylene fibers. Detailed Implementation

[0030] The present invention will now be described in detail.

[0031] The nylon 6 fiber of the present invention is a nylon 6 fiber characterized in that: 20% by weight or more of the fiber is nylon 6 after material recycling, and the dispersion ratio of the molecular weight distribution of nylon 6 obtained by GPC determination, i.e., the weight average molecular weight (Mw) / number average molecular weight (Mn) is 3.4 or less, and the z-average molecular weight (Mz) / weight average molecular weight (Mw) is 1.6 or less.

[0032] The nylon 6 fiber of the present invention is a polyhexamethylene amide fiber (hereinafter referred to as nylon 6 fiber) made by blending 20% ​​or more of the fiber with a low oligomer content of 1.5% or less of recycled polyhexamethylene amide resin. From the viewpoint of the increasing awareness of environmental protection in recent years, it is preferable to make nylon 6 fiber by blending 50% to 100% of the fiber with recycled polyhexamethylene amide resin.

[0033] Regarding the molecular weight distribution of the nylon 6 fibers of the present invention, the weight average molecular weight (Mw) / number average molecular weight (Mn) is 3.4 or less, and the z-average molecular weight (Mz) / weight average molecular weight (Mw) is 1.6 or less. By setting these ranges, a high-quality garment fabric with the same raw filament properties as virgin nylon 6 fibers and excellent high-pass permeability can be obtained.

[0034] The number-average molecular weight (Mn), weight-average molecular weight (Mw), and z-average molecular weight (Mz) molecular weight distributions described in this invention are determined by gel permeation chromatography (GPC). Specifically, a GPC instrument is used as the apparatus, and one Showa Denko "Shodex HEIP-G" column and two Showa Denko "Shodex HEIP-606M" columns are used as the columns. The determination solvent is 5 mM hexafluoroisopropanol with added sodium trifluoroacetate. The standard sample uses 3 mg of Showa Denko polymethyl methacrylate (PMMA) and 3 mg of nylon 6 fiber. After stable stirring at room temperature, the solution is filtered through a 0.45 μm filter and adjusted. The molecular weight distribution of the adjusted solution is determined under the following conditions: column temperature 40°C, flow rate 0.2 ml / min, and Showa Denko "RI-104" refractive index detector.

[0035] The weight-average molecular weight (Mw) / number-average molecular weight (Mn) of the nylon 6 fiber of the present invention is 3.4 or less. The weight-average molecular weight (Mw) / number-average molecular weight (Mn) is an indicator of the diffusion of low molecular weight components; the smaller the value, the fewer the impurities originating from monomers / oligomers. By setting it within the aforementioned range, the same raw filament properties as virgin nylon 6 fibers can be obtained, the continuous strength-elongation product and the CV% of the continuous strength-elongation product are improved, and nylon 6 fibers with excellent high-pass throughput can be obtained. If Mw / Mn exceeds 3.4, the CV% of the continuous strength-elongation product increases, which can cause filament breakage and other problems during high-pass processing, starting from points with locally low strength-elongation products, resulting in poor high-pass throughput. Preferably, it is 2.9 to 3.2.

[0036] The z-average molecular weight (Mz) / weight average molecular weight (Mw) of the nylon 6 fiber of the present invention is 1.6 or less. The z-average molecular weight (Mz) / weight average molecular weight (Mw) is an indicator of the diffusion of high molecular weight components; the smaller the value, the less high molecular weight components are present. By setting it within the aforementioned range, the raw filament properties are equivalent to those of virgin nylon 6 fiber, the formation of heat-degrading substances is suppressed, the CV% of amino-terminal groups is improved, and high-quality garment fabrics with no color difference during dyeing can be obtained. If Mz / Mw exceeds 1.6, a large amount of heat-degrading substances are generated, thus increasing the CV% of amino-terminal groups, resulting in color difference during dyeing and a poor appearance in the garment fabric. Furthermore, there is a tendency for a decrease in continuous strength-elongation product and an increase in CV%, which can easily cause filament breakage during advanced processing, leading to a deterioration in high-level throughput. Preferably, it is 1.55 to 1.58.

[0037] The preferred amount of amino-terminal groups in the nylon 6 fibers of the present invention is 3.5 × 10⁻⁶. -5 mol / g or higher. Preferably 4.0 × 10⁻⁶. -5 mol / g~5.5×10 -5 mol / g. By setting this range, excellent color development can be obtained with common dyes (acid dyes) and methods (atmospheric pressure dyeing) used in dyeing processes. Furthermore, the CV% of the amount of amino-terminal groups, which represents the deviation of the amount of amino-terminal groups in the fiber length direction, is preferably 4.0% or less. By setting this range, high-quality garment fabrics with no color difference during dyeing can be obtained regardless of color matching.

[0038] The total fineness of the nylon 6 fibers of the present invention is preferably 3 dtex to 200 dtex, more preferably 10 dtex to 150 dtex. By setting it within the range, even when using recycled polyvinyl amide resin particles, the same raw filament properties or quality as virgin nylon 6 fibers can be obtained, and a woven fabric with a suitable hand feel for clothing applications can be obtained.

[0039] The nylon 6 fiber of the present invention preferably has a single filament fineness of 0.2 dtex to 10 dtex, more preferably 0.4 dtex to 5 dtex. By setting it within the range described above, even when using recycled polyvinyl amide resin particles, the same raw filament properties or quality as virgin nylon 6 fiber can be obtained, resulting in a woven fabric with a suitable hand feel for clothing applications.

[0040] The CV% of the continuous strength-elongation product of the nylon 6 fibers of the present invention is preferably 3.5% or less. A lower CV% indicates a smaller deviation in the tensile strength-elongation curve along the fiber length direction. By setting it within this range, there are no weak fibers with locally low strength-elongation products, resulting in no fiber breakage during high-level processing and stable high-level throughput. Furthermore, since the fiber structure is also stable, high-quality garment fabrics without dyeing color differences can be obtained regardless of color matching.

[0041] Furthermore, the average value of the continuous strength-elongation product is preferably 6.4 or higher. By setting it to this range, no wire breakage is observed during high-level processing, resulting in stable high-level throughput. Moreover, the minimum value of the continuous strength-elongation product is preferably 5.5 or higher. The lower the minimum value, the more likely points with locally low strength-elongation products become weak wire sections, making wire breakage more likely from these points. By setting it to this range, no wire breakage is observed even during high-level processing, resulting in stable high-level processing performance.

[0042] The continuous strength-elongation product described in this invention involves measuring fiber samples 50 times using a "tensilon" (registered trademark) manufactured by Orientec (stock) Co., Ltd., according to Japanese Industrial Standards (JIS) L1013 (2010), under constant elongation conditions, a clamping interval of 50 cm, and a tensile speed of 50 cm / min, and plotting a tensile strength-elongation curve (total length 25 m). Strength is determined from the point on the tensile strength-elongation curve showing the maximum strength, and elongation is determined from the elongation rate showing the maximum strength. Strength is defined as the value obtained by dividing the maximum strength by the total fineness. The strength-elongation product is calculated using the following formula, and the minimum and average values ​​of each of the 50 measurements are calculated, and the CV% is calculated using the following formula.

[0043] Continuous strength-stretch product = Strength [cN / dtex] × (1 + Elongation [%] / 100)

[0044] CV% = (Standard deviation of continuous strength-elongation product) / (Average value of continuous strength-elongation) × 100.

[0045] The hue (YI value) of the nylon 6 fiber of the present invention is preferably 15 or less. Polyamide is a polymer that is easily oxidized and is characterized by its susceptibility to oxidation and yellowing when exposed to oxygen in the air under heat. Typically, polyamide shavings generated during the fiber manufacturing process are mostly heated and yellow to varying degrees. If the YI value exceeds 15, even if the oxidation deterioration is not to the extent of poor fiber physical properties, yellowing can sometimes significantly limit its applications. By controlling it to the aforementioned range, it can be used in woven fabrics for clothing without application limitations.

[0046] The YI value is determined by winding the obtained nylon 6 fibers onto a plastic sheet and using a multi-light source spectrophotometer (manufactured by Suga Testing Equipment Co., Ltd.).

[0047] The nylon 6 fiber of this invention can be suitably used in woven fabrics for clothing. As a woven fabric for clothing, it can be used in a wide range of fields such as outerwear and underwear.

[0048] The polyhexamethylene amide in this invention is a type of polyamide in which hydrocarbons are linked to the main chain via amide bonds. The caprolactam unit constituting the polyhexamethylene amide comprises 90 mol% or more, preferably 95 mol% or more. Other structural components are not particularly limited without impairing the effects of this invention. Examples include: undecanolactam and dodecanolactam constituting polyundecanoamide, polydodecanoamide, etc.; and salts formed by the equimolar bonding of dicarboxylic acids and diamines constituting polytetramethylenehexadiamide, polypentamethylenehexadiamide, polypentamethylenedecanedamide, polyhexamethylenehexadiamide, polyhexamethylenedecanedamide, polyhexamethylenedodecanoamide, polyhexamethylenetridecanoamide, etc.

[0049] The recycled polyhexamethylene amide resin particles of the present invention are obtained by melting polyhexamethylene amide waste. Other recycling methods are also known, such as chemically recycled polyhexamethylene amide resin particles obtained by depolymerizing polyhexamethylene amide waste into caprolactam and then repolymerizing the caprolactam obtained through depolymerization. However, since the depolymerization and repolymerization process is extremely complex, the quality management of the obtained polyhexamethylene amide resin particles is extremely difficult.

[0050] The amount of oligomer content in the recycled polyhexamethylene amide resin particles of the present invention, as detected by hot water extraction, is 1.5% by weight or less. Preferably, it is 1.0% by weight or less. By setting the amount of oligomer content to this range, the generation of oligomer content when manufacturing recycled polyhexamethylene amide fibers (hereinafter referred to as nylon 6 fibers) using the particles is suppressed. Therefore, there are fewer fiber breaks caused by oligomer content (such as spinning die fouling), and nylon 6 fibers can be manufactured with good operability. In addition, since there is less spinning die fouling, the periodic cleaning of the spinning die surface, which is carried out in long-term continuous manufacturing, can also be extended. When the amount of oligomer content detected by hot water extraction exceeds 1.5% by weight, more oligomer content is generated when manufacturing nylon 6 fibers using the particles. Therefore, there are more fiber breaks caused by oligomer content (such as spinning die fouling), resulting in difficulty in manufacturing nylon 6 fibers with good operability.

[0051] In order to set the molecular weight distribution on the low molecular weight side of the nylon 6 fiber of the present invention, i.e., the weight average molecular weight (Mw) / number average molecular weight (Mn) to be 3.4 or less, it can be controlled by using recycled polyhexamethylene amide resin particles with an oligomer content of 1.5% or less.

[0052] The filtration pressure rise rate of the recycled polyhexamethylene amide resin particles of the present invention is preferably 2.0 MPa / hour or less. More preferably, it is 1.0 MPa / hour or less. Details of the filtration pressure rise rate described herein are as described in Example B. Filtration Pressure Rise Rate (Resin Particles) described later. If the filtration pressure rise rate is 2.0 MPa / hour or less, the pressure rise inside the spinning assembly during the manufacture of nylon 6 fibers is suppressed, thus reducing spinning troubles such as assembly leakage or abnormal ejection, and enabling the manufacture of nylon 6 fibers with good operability.

[0053] The relative viscosity (ηr) of the recycled polyhexamethylene amide resin particles of the present invention, obtained with 98% sulfuric acid, is preferably 2.2 to 3.8. More preferably, it is 2.5 to 3.5. If the relative viscosity (ηr) of 98% sulfuric acid is 2.2 or higher, the nylon 6 fibers can be ejected from the spinning die at an appropriate melt viscosity during manufacturing, thus making it difficult to produce monofilament fineness deviations or Uster unevenness (U%) abnormalities in the nylon 6 fibers. In addition, the strength of the nylon 6 fibers can be maintained. If the relative viscosity (ηr) of 98% sulfuric acid is 3.8 or lower, the filaments ejected from the spinning die can be well drawn onto the rollers during manufacturing of nylon 6 fibers, enabling stable manufacturing of nylon 6 fibers.

[0054] The preferred amount of amino-terminal groups in the recycled polyhexamethylene amide resin particles of the present invention is 2.0 × 10⁻⁶. -5mol / g~10×10 -5 mol / g. More preferably, 3.0 × 10⁻⁶ mol / g. -5 mol / g~9.0×10 -5 mol / g. If the amount of amino-terminal group is 2.0 × 10⁻⁶ mol / g. - 5 If the concentration is above mol / g, the dyeability of nylon 6 fibers can be ensured when dyeing them with acid dyes or gold-containing dyes. If the amino-terminal group content is 10 × 10⁻⁶, the dyeability of nylon 6 fibers can be guaranteed. -5 If the viscosity is below mol / g, there will be no extreme viscosity changes during the manufacture of nylon 6 fibers, and nylon 6 fibers can be manufactured stably.

[0055] Typically, titanium dioxide is used as a matting agent for polyamide fibers. The recycled polyvinyl acetate resin particles of the present invention may also contain titanium dioxide as a matting agent. The titanium dioxide content in the recycled polyvinyl acetate resin particles of the present invention can be suitably set within a range that does not impair the effects of the present invention; a preferred range is 0% by weight to 20% by weight.

[0056] Without impairing the effects of the present invention, the recycled polyhexamethylene amide resin particles of the present invention may contain various additives in addition to the aforementioned titanium dioxide. Examples of such additives include stabilizers such as manganese compounds, flame retardants, conductivity imparting agents, and fibrous reinforcing agents.

[0057] The recycled polyhexamethylene amide resin particles of the present invention can be operated in the same way as so-called plain polyhexamethylene amide resin particles that have not been recycled. They can certainly be used in fiber manufacturing, and are also suitable for various processing methods such as film processing or injection molding. In particular, the recycled polyhexamethylene amide resin particles of the present invention remove oligomer components to the limit, which is especially effective from an operability point of view when used for melt spinning of fine fibers and other materials where manufacturing is very demanding.

[0058] The following describes the manufacturing method of the recycled polyhexamethylene amide resin particles and the recycled nylon 6 fibers of the present invention.

[0059] The polyhexamethylene amide waste used in the manufacture of the recycled polyhexamethylene amide resin particles of the present invention includes polyhexamethylene amide fiber scraps generated during the fiber manufacturing process. Regarding the recycling of polyamide materials, as described in Patent Document 1 or Patent Document 2, polymer scraps generated during the fiber manufacturing process are usually used together. However, polyhexamethylene amide generates a large amount of oligomer components when melted. Therefore, when melting polyhexamethylene amide for material recycling, it is extremely important to remove these oligomer components beforehand. As described later, hot water extraction is performed to remove the oligomer components before melting the scraps for material recycling. During the hot water extraction process, the larger the specific surface area of ​​the scraps, the more efficiently the oligomer components are removed. Comparing the shapes of polymer scraps and fiber scraps, polymer scraps are mostly blocky and have a smaller specific surface area than fiber scraps, making it difficult to efficiently remove oligomer components from polymer scraps. Of course, it would be possible to cut, crush, or otherwise reduce the polymer scraps to the size of fiber scraps, but this is impractical.

[0060] The polyhexamethylene amide fiber scraps used in the manufacture of the recycled polyhexamethylene amide resin particles of the present invention are fiber scraps generated during the fiber manufacturing process. Among these, there are fiber scraps (washing scraps) generated from the time the spinning die is installed until the fiber product is collected as a drum package or the like, or fiber scraps (broken fiber scraps) generated due to fiber breakage failures in the spinning or stretching process, or scraps (product scraps) with abnormal material content or that are unqualified in the final form of the fiber product such as a drum package. Any type of fiber scrap can be used.

[0061] As described above, the recycled polyhexamethylene amide resin particles of the present invention may also contain various additives such as titanium dioxide. For example, in order to set the titanium dioxide content to a desired range, the titanium dioxide content in the polyhexamethylene amide fiber scraps used in the manufacturing process must be known. To ensure the content is known, it is important not to mix polyhexamethylene amide fiber scraps with different titanium dioxide contents during recycling. However, considering the fiber manufacturing process, it can be difficult to handle shavings or broken fibers. In such cases, it is sufficient to use product scraps that are easy to distinguish from polyhexamethylene amide fiber scraps with different titanium dioxide contents. Furthermore, if the titanium dioxide content in the recycled polyhexamethylene amide resin particles of the present invention is insufficient solely by the titanium dioxide content contained in the fiber scraps, titanium dioxide may be added.

[0062] The manufacturing process of the recycled polyhexamethylene amide resin particles of the present invention includes the following steps: cutting fiber scraps; impregnating fiber scraps in hot water; melting, filtering, and spraying the fiber scraps; water cooling and cutting the sprayed resin; and impregnating the resin particles in hot water. Each step will be described below.

[0063] Polyhexamethylene amide fiber scraps generated during the fiber manufacturing process, whether wash scraps, broken fiber scraps, or product scraps, are all cut before being supplied to the hot water impregnation and dewatering processes. This is because it facilitates the handling of the fiber scraps when supplying them to the hot water impregnation, dewatering processes, or subsequent melting, filtering, and spraying processes. If the fiber scraps are not cut to an appropriate length, they will become entangled during the dewatering process, preventing proper dewatering. Furthermore, the supply of fiber scraps to the melting section will be impaired when supplying them to the melting hopper, resulting in poor melting. The cutting length of the polyhexamethylene amide fiber scraps should be set appropriately based on the dewatering machine or melting equipment, ideally between approximately 0.1m and 1.0m.

[0064] Furthermore, among the shavings, broken filaments, and product shavings, shavings and broken filaments can sometimes have fibers fused together to form clumps. Since the specific surface area of ​​this type of shaving is smaller than that of fiber shavings, it is impossible to efficiently remove the oligomer components through hot water extraction. Therefore, when using shavings or broken filaments, clump-shaped shavings should be removed beforehand by screening. If such screening removal is difficult, only product shavings may be used.

[0065] The cut fiber scraps are then subjected to an immersion and dehydration process in hot water. Polyhexylamide generates a large amount of oligomer components through melting. Therefore, when melting polyhexylamide and recycling the material, it is extremely important to remove these oligomer components beforehand. This is achieved by immersing the scraps in hot water before melting and recycling, thereby extracting and removing the oligomer components. The temperature of the hot water used for immersion is 50°C to 90°C, preferably 70°C to 90°C.

[0066] By setting the hot water temperature within the aforementioned range, oligomer components can be efficiently removed from the fiber debris. As a result, recycled polyvinyl acetate resin granules with an oligomer content of 1.5% by weight or less can be manufactured, and the weight average molecular weight (Mw) / number average molecular weight (Mn) of the obtained nylon 6 fibers can be controlled to 3.4 or less. When the hot water temperature is below 50°C, oligomer components cannot be efficiently removed from the fiber debris, making it difficult to manufacture recycled polyvinyl acetate resin granules with an oligomer content of 1.5% by weight or less. Up to 90°C, the higher the hot water temperature, the more efficiently oligomer components can be removed from the fiber debris; however, even when the hot water temperature exceeds 90°C, the removal efficiency of oligomer components does not increase further. Regarding the degreasing process for polyamide fiber debris described in Patent Document 3, the washing (extraction) temperature is unclear. It is effective in removing foreign matter caused by oiling agents, but insufficient for removing oligomer components contained in the polyamide fiber debris. As a result, the obtained recycled polyamide resin granules contain a large amount of oligomer components.

[0067] Regarding the liquor ratio when immersing the cut fiber scraps in hot water, it should be set appropriately based on factors such as the extraction equipment or the production batch size when recycling polyamide resin particles. The ratio can be approximately 1:3 to 1:10, calculated as the weight of fiber scraps to the weight of hot water. The liquor ratio described here is the weight ratio of hot water to the weight of fiber scraps. For example, if the hot water volume is 3 kg relative to 1 kg of fiber scraps, the liquor ratio is 1:3.

[0068] The preferred immersion time for soaking the cut fiber scraps in hot water is 20 to 60 minutes, and more preferably 30 to 60 minutes. If the immersion time is 20 minutes or longer, oligomer components can be efficiently removed from the fiber scraps. As a result, recycled polyvinyl amide resin particles with an oligomer content of 1.5% by weight or less can be manufactured, and the weight average molecular weight (Mw) / number average molecular weight (Mn) of the obtained nylon 6 fibers can be controlled to 3.4 or less. Up to 60 minutes, the longer the immersion time, the more efficiently oligomer components can be removed from the fiber scraps; however, even if the immersion time exceeds 60 minutes, the removal efficiency of oligomer components will not increase further.

[0069] When immersed in hot water, the large surface area of ​​the fiber fragments allows yellowing caused by contact with oxygen in the water to progress rapidly. Furthermore, the progression of yellowing caused by thermal processes in nylon 6 fibers is also relatively fast in polyamides. Therefore, it is preferable to add a reducing agent to the extraction water to decompose dissolved oxygen and inhibit yellowing. The reducing agent can be any compound that can control the YI value of nylon 6 fibers to 15 or less. Hydrazine hydrate, hydrazine carbonate, and other similar compounds are preferred.

[0070] The reducing agent is preferably added at a rate of 0.003% to 0.01% by weight relative to the amount of water extracted. By setting it to 0.003% by weight or more, the YI value can be controlled to be preferably 15 or less.

[0071] After hot water extraction, the fiber scraps are rinsed and then dehydrated. Dehydration should be carried out until the moisture content of the fiber scraps is 5% to 15% by weight.

[0072] The fiber scraps extracted from hot water are then fed into the melting, filtration, and extrusion processes. Melting methods include pressure melters and extruders; either method can produce recycled polyvinyl acetate resin granules. Furthermore, the extruder can be either a single-shaft or a two-shaft type. The preferred melting temperature for melting the fiber scraps is 240°C to 300°C. If the melting temperature is above 240°C, there is no unmelted material, and there are no malfunctions such as increased filtration pressure in the melting system, allowing for stable production of recycled polyvinyl acetate resin granules. If the melting temperature is below 300°C, thermal degradation of the recycled polyvinyl acetate resin granules can be suppressed, and the z-average molecular weight (Mz) / weight average molecular weight (Mw) of the obtained nylon 6 fibers can be controlled to below 1.6.

[0073] It is extremely important to filter the fiber scraps simultaneously during the melting process. By filtering along with the melting, foreign matter can be removed from the recycled polyhexamethylene amide resin particles. As a result, the pressure rise within the spinning assembly during the manufacture of recycled polyhexamethylene amide fibers is suppressed. Therefore, spinning failures such as assembly leakage or abnormal ejection are reduced, and recycled polyhexamethylene amide fibers can be manufactured with good operability. Regarding the filter, a filter with a filtration accuracy of 5μm to 50μm is preferred. If the filtration accuracy is 5μm or higher, there is no pressure rise caused by filter blockage in the melting system, and the fiber scraps can be melted stably. If the filtration accuracy is 50μm or lower, foreign matter can be removed from the recycled polyhexamethylene amide resin particles. Regarding the filter, any type of filter, such as a metal mesh type, a metal nonwoven type, or a metal short fiber type, can be used as long as filtration can be performed normally.

[0074] The recycled polyvinyl amide resin particles of the present invention are also used in melt spinning, where the manufacturing process is very strict, such as high-speed winding of fine fibers. Therefore, it is preferable to filter to the limit to remove foreign matter from the recycled polyvinyl amide resin particles to the maximum extent. To remove foreign matter to the maximum extent, it is sufficient to make the mesh of the filter finer. However, if the mesh of the filter is simply made finer, when melting fiber scraps containing a large amount of additives such as titanium dioxide, pressure rises may occur in the melt system due to filter blockage, making it difficult to melt the fiber scraps stably. In such cases, it is preferable to perform filtration in two or more stages. When filtration is performed in two or more stages, the mesh of the filter is gradually made finer to improve the filtration accuracy. For example, when filtration is performed in two stages, it is sufficient to use a filter with a mesh size of 10 μm to 50 μm for the first filtration and a filter with a mesh size of 5 μm to 20 μm that is finer than the first filtration for the second filtration. When filtration is performed in two or more stages, two or more filters can be installed in a single melting system. Alternatively, the particles can be temporarily granulated after melting and filtration, and then melted and filtered again.

[0075] The melting and filtration time is 3 minutes / kg or less. A time of 3 minutes / kg or less can suppress the thermal degradation of recycled polyvinyl amide resin particles due to the thermal process during melting and filtration, allowing the z-average molecular weight (Mz) / weight average molecular weight (Mw) of the obtained nylon 6 fibers to be controlled to 1.6 or less. Furthermore, it can suppress the viscosity increase associated with the thermal process and control the CV% of amino-terminal groups along the fiber length direction to 4.0% or less.

[0076] The molten, filtered material is recycled into granules of polyhexamethylene amide resin and ejected from the die. During ejection from the die, to efficiently perform hot water extraction of the polyhexamethylene amide resin particles (described later), it is preferable to eject the particles with a diameter of 1 mm to 3 mm.

[0077] The recycled polyhexamethylene amide resin ejected from the die is then used for water cooling and cutting processes. The water cooling of the recycled polyhexamethylene amide resin is sufficient to cool it to a level that allows for easy cutting. The cutting of the recycled polyhexamethylene amide resin can be performed using known methods; however, for efficient hot water extraction of the polyhexamethylene amide resin particles (described later), it is preferable to cut them into lengths of 1 mm to 4 mm.

[0078] The recycled polyhexylamide resin granules are subjected to an impregnation process in hot water. Polyhexylamide generates a large amount of oligomer components through melting. Therefore, when melting polyhexylamide and recycling the material, it is extremely important to remove these oligomer components. After granulation, the granules are also impregnated in hot water to extract and remove the oligomer components. The hot water temperature for impregnation is 50°C to 90°C, preferably 70°C to 90°C. By setting the hot water temperature within this range, recycled polyhexylamide resin granules with an oligomer content of 1.5% by weight or less can be manufactured, and the weight average molecular weight (Mw) / number average molecular weight (Mn) of the obtained nylon 6 fibers can be controlled to 3.4 or less. It is difficult to manufacture recycled polyhexylamide resin granules with an oligomer content of 1.5% by weight or less when the hot water temperature is below 50°C. Before the hot water temperature reaches 90°C, the higher the hot water temperature, the more efficiently the oligomer components can be discharged from the recycled polyhexamethylene amide resin particles. However, even if the hot water temperature exceeds 90°C, the discharge efficiency of the oligomer components will not increase further.

[0079] Regarding the bath ratio when immersing recycled polyhexamethylene amide resin particles in hot water, it is appropriate to set it according to the extraction equipment or the production batch when manufacturing recycled polyhexamethylene amide resin particles, as long as it is easy to extract oligomer components from the recycled polyhexamethylene amide resin particles. The ratio can be approximately 1:3 to 1:10 based on the particle weight to the hot water weight.

[0080] Regarding the immersion time when immersing recycled polyvinyl acetate resin particles in hot water, 20 to 60 minutes is preferred, and more preferably 30 to 60 minutes. If the immersion time is 20 minutes or longer, oligomer components can be efficiently removed from the recycled polyvinyl acetate resin particles, resulting in the production of recycled polyvinyl acetate resin particles with an oligomer content of 1.5% by weight or less. Up to 60 minutes, the longer the immersion time, the more efficiently oligomer components can be removed from the recycled polyvinyl acetate resin particles; however, even if the immersion time exceeds 60 minutes, the removal efficiency of oligomer components does not further improve.

[0081] When immersing in hot water, it is preferable to add a reducing agent in the same way as when immersing in fiber scraps.

[0082] The nylon 6 fiber of the present invention is manufactured through a manufacturing process comprising a mixing device for metering and mixing recycled polyhexamethylene amide resin particles and virgin polyhexamethylene amide resin particles, drying to adjust to a specified moisture content, and including conventional melt spinning, cooling, oiling, and stretching. The melt spinning device used in the present invention can be either an extruder-type spinning machine or a pressure melt spinning machine. When a colorant is added, particles formed by mixing master particles with a high concentration of colorant with base particles can be fed into the spinning machine, or the particles can be metered and fed simultaneously above the spinning machine. Alternatively, the colorant can be added directly to the spinning machine in powder or liquid form.

[0083] The nylon 6 fiber of the present invention is obtained by melting recycled polyhexamethylene amide resin particles and virgin polyhexamethylene amide resin particles together in a specific ratio, and then spinning the mixture through a spinning die. In particular, in order to control the molecular weight distribution on the high molecular weight side, i.e., the z-average molecular weight (Mz) / weight average molecular weight (Mw), to be below 1.6, the moisture content of the resin particles and the filtration conditions are appropriately set during melt spinning. Details are described below.

[0084] Regarding the polyhexamethylene amide resin particles used in the manufacture of the nylon 6 fiber of the present invention, the moisture content of the resin particles is adjusted to 600 ppm to 1000 ppm during the drying process. Preferably, it is 700 ppm to 900 ppm. It is known that polyhexamethylene amide resin polymers undergo polymerization reactions due to retention during melt spinning, resulting in increased viscosity and decreased amino-terminal group content. Therefore, by setting the moisture content of the polyhexamethylene amide resin particles to 600 ppm to 1000 ppm and controlling the polymerization equilibrium reaction, the increase in viscosity of the polymer retained in the spinning tubing can be suppressed, and the decrease in amino-terminal group content can be suppressed. With the increase in polymer viscosity, thermal degradation products are easily generated; therefore, the z-average molecular weight (Mz) / weight average molecular weight (Mw) can be controlled to 1.6 or less. In addition, the deviation in the amount of amino-terminal groups that accompanies the increase in viscosity can also be suppressed, thus obtaining high-quality woven fabrics for clothing with no color difference during dyeing. When the moisture content of the polyhexamethylene amide resin particles is less than 600 ppm, the viscosity of the polymer retained in the spinning tubing gradually increases, thereby increasing the z-average molecular weight (Mz) / weight average molecular weight (Mw) and the CV% of the amino-terminal group content. If the particle moisture content exceeds 1000 ppm, it promotes the hydrolysis of the polymer retained in the spinning tubing, causing an extreme decrease in polymer viscosity and deviation, making stable spraying impossible, and increasing the CV% of the continuous strength-elongation product. During high-level processing, this can lead to filament breakage starting from points with locally low strength-elongation products, resulting in poor high-level throughput.

[0085] In the manufacture of nylon 6 fibers according to the present invention, the melt spinning temperature is preferably between 240°C and 300°C. By setting the temperature within this range, stable spinning can be achieved, and thermal degradation of the polymer can be suppressed.

[0086] The melt spinning assembly used in the manufacture of nylon 6 fibers of the present invention is a melt spinning assembly that is at least configured with a spinning die, a pressure plate, a filter, and a sand filter layer or a rectifier plate. Between the filter and the sand filter layer or rectifier plate, a sintered filter containing short metal fibers with a cross-section having a generally polygonal shape is used as the filter.

[0087] Nylon 6 fibers undergo a thermal process during the remelting of polyamide fiber scraps or polymer scraps generated in the fiber manufacturing process to form recycled polyvinyl amide resin particles, resulting in the formation of polymer thermal degradation products. While these polymer thermal degradation products are removed as much as possible during the resin particle manufacturing stage, they may remain in the resin particles. For example, in the case of recycled polyamide crimped fibers described in Patent Document 1, the presence of residual thermal degradation products causes color difference in the dyeing process due to deviations in the amount of amino-terminated groups in the woven fabrics used for clothing as intended by this invention.

[0088] To further refine the thermally degraded polymer and reduce the molecular weight distribution on the high molecular weight side, it is necessary to improve the filtration accuracy of the filter, sand filter layer, or rectifier plate constituting the melt spinning assembly. Therefore, a sintered filter comprising short metal fibers with a generally polygonal shape is used as the filter. By using this component, the short metal fibers can be intertwined, further improving filtration or dispersibility. As a generally polygonal shape, a cross-sectional shape with acute angles is preferred. This is because thermally modifying the acute-angle portion of the cross-section allows for fine dispersion of the thermally degraded polymer through collision. Furthermore, by setting the cross-sectional shape to acute angles, the thermally modified gelled polymer can be further finely subdivided. Additionally, the filtration accuracy of the sintered filter containing the short metal fibers also depends on the ejection rate, ranging from 5 μm to 20 μm. By setting the filtration accuracy of the sintered filter containing the short metal fibers within this range, the thermally degraded polymer can be finely dispersed, and the z-average molecular weight (Mz) / weight average molecular weight (Mw) can be controlled to be 1.6 or less.

[0089] When the filtration accuracy exceeds 20 μm, solid foreign matter that is not completely discharged during the recycling of polyhexamethylene amide resin particles in the manufacturing process is not adequately filtered and is ejected as part of the fiber. This results in a z-average molecular weight (Mz) / weight average molecular weight (Mw) exceeding 1.6, and the locations of these solid foreign matter create locally low strength-elongation products, increasing the CV% of continuous strength-elongation. This can cause fiber breakage and poor high-pass permeability during advanced processing. Furthermore, the filterability and dispersibility within the melt spinning assembly decrease, and the CV% of amino-terminal groups increases due to the generation of thermal degradation products, leading to color differences in dyeing.

[0090] The nylon 6 fiber of the present invention can be spun using a conventional die with a specified number of nozzles and a nozzle diameter and length that can be stably ejected, designed according to the target fineness and filament count.

[0091] The melt-spun filaments are cooled and solidified by cold air, then coated with an oiling agent and drawn to a rotating traction roller at a specified traction speed. The traction speed is preferably 300 m / min to 4000 m / min. The drawn filaments typically continue to extend. Alternatively, the filaments can be temporarily wound up as unextended yarn and then extended in other processes; or temporarily wound up the extended yarn and then wound up in other processes.

[0092] The nylon 6 fibers of the present invention are preferably stretched in the range of 1.0 to 4.0 times the elongation ratio, and stretched in such a way that the elongation is 30% to 100%.

[0093] Example

[0094] The present invention will now be specifically described through examples, but the invention is not limited to these examples. Furthermore, the methods for measuring the characteristic values ​​in the examples are as follows.

[0095] A. Oligomer content

[0096] (1) After crushing the resin particles, use a 35-mesh (420μm opening) and a 115-mesh (125μm opening) metal mesh filter to sieve them and separate the powder that passes through the 35-mesh filter and is retained in the 115-mesh filter.

[0097] (2) After drying the powder obtained in (1) to a moisture content of less than 0.03% by weight, weigh approximately 3g (W1).

[0098] (3) Use more than 10L of boiling water to extract the powder weighed in (2) for 4 hours.

[0099] (4) The powder obtained in (3) is washed with water and dried until the moisture content is less than 0.03% by weight, and then weighed (W2).

[0100] (5) It is calculated from W1 and W2 by the following formula.

[0101] Oligomer content (wt%) = (W1-W2) / W1×100.

[0102] B. Filtration pressure rise rate (resin particles)

[0103] (1) Regarding the temperature of the resin particle melting section of the melt tester used to confirm the filter pressure rise rate, the melting section heater is set to 280°C, the insulation cylinder heater is set to 285°C, and the die preheating is set to 260°C.

[0104] (2) The filter used is a DF40D (40φ) (model: NF2M-5C3 (with aluminum wheel)) manufactured by Nippon Seiki Co., Ltd. Furthermore, regarding the mesh size, it is equivalent to a cutoff of 5μm, and the actual filter diameter is 30φ.

[0105] (3) Spray resin particles dried to a moisture content of less than 0.03% by weight at a rate of 4 g / min.

[0106] (4) Confirm the filter pressure (MPa) (P1) 1 hour after the start of spraying.

[0107] (5) Confirm the filtration pressure (MPa) (P2) 3 hours after the start of spraying.

[0108] (6) Calculated from P1 and P2 using the following formula.

[0109] Filtration pressure rise rate (MPa / hour) = (P2-P1) / 2.

[0110] C. Relative viscosity (ηr) of 98% sulfuric acid

[0111] 0.25 g of resin particles were dissolved in 100 ml of 98% sulfuric acid to obtain 1 g of solution. The flow time (T1) at 25°C was measured using an Ostwald viscometer. The flow time (T2) of 98% sulfuric acid alone was then measured. The ratio of T1 to T2, i.e., T1 / T2, was set as the relative viscosity (ηr) of 98% sulfuric acid.

[0112] D. Amin-terminal group amount

[0113] Prepare a solution by dissolving 1 g of resin particles or fibers in 50 mL of a phenol / ethanol mixture (phenol / ethanol = 83.5 / 16.5) at 25°C with shaking. Neutralize and titrate the solution with 0.02N-hydrochloric acid to determine the amount of 0.02N-hydrochloric acid required for the titration. Alternatively, neutralize and titrate only the phenol / ethanol mixture with 0.02N-hydrochloric acid to determine the amount of 0.02N-hydrochloric acid required for the titration. Then, calculate the amount of amino-terminal groups per ton of resin particles or fibers based on the difference.

[0114] The amount of amino-terminal groups of the fiber was sampled from five equal parts of the outermost and innermost layers of the fiber encapsulation, and the CV% was calculated using the following formula.

[0115] CV% = (Standard deviation of amino-terminal group) / (Average value of amino-terminal group) × 100.

[0116] E. Number of wire breaks

[0117] The number of fiber breaks is used in the example described later, "Manufacturing of Polyhexamethylene Acrylamide Fiber (Melt Spinning)". Evaluation was conducted using 5 tons or more of polyhexamethylene amide resin particles, and the number of fiber breaks per ton was determined. Furthermore, a number of fiber breaks of 2.0 times / ton or less was considered acceptable.

[0118] F. Time until the wire breaks

[0119] In the example described later, "Manufacturing of Polyhexamethylene Fiber (Melt Spinning)," the average time from the start of winding to the occurrence of filament breakage was measured for each spinning assembly (N number = 12).

[0120] G. Filtration pressure rise rate (melt spinning)

[0121] The filtration pressure rise rate is the rate at which the spinning assembly in the example described later, <Manufacturing of Polyhexamethylene Fiber (Melting Spinning)>, is measured. The molten polymer is passed through the assembly for at least 5 consecutive days, and the filtration pressure rise rate is determined for each day.

[0122] H. Total fineness, monofilament fineness

[0123] For fibers, based on JIS L1013 (2010) 8.3.1 positive fineness a) Method A, a measuring machine manufactured by Zhongshan Electric Industry (Co., Ltd. was used. An initial load of 0.45 mN / dtex (displayed fineness × 0.45 mN / dtex) was applied, and the measurement was performed with a specified filament length of 100 m, which was set as the total fineness. The fineness of a single filament was calculated by dividing the fineness by the filament count.

[0124] I. Continuous Strength Extensibility Product, CV%

[0125] For the fiber, in a temperature-controlled chamber with an air temperature of 20°C and a humidity of 65%, using "tensilon" (registered trademark) manufactured by Orientec (stock), 50 measurements were performed (total length 25m) according to JIS L1013 (2010), under constant elongation conditions, a clamping interval of 50cm, and a stretching speed of 50cm / min. Tensile strength was determined from the point showing maximum strength on the tensile strength-elongation curve, and elongation was determined from the elongation at which maximum strength was achieved. Furthermore, strength was defined as the value obtained by dividing the maximum strength by the total fineness. The strength-elongation product was calculated using the following formula, and the minimum and average values ​​of the 50 measurements were calculated to determine the CV%.

[0126] Continuous strength-stretch product = Strength [cN / dtex] × (1 + Elongation [%] / 100)

[0127] CV% = (Standard deviation of strength-elongation product) / (average strength-elongation product) × 100.

[0128] J. Number average molecular weight (Mn), weight average molecular weight (Mw), z-average molecular weight (Mz)

[0129] Molecular weight distribution was determined by gel permeation chromatography (GPC). Specifically, a GPC instrument was used, and one Showa Denko "Shodex HEIP-G" column and two Showa Denko "Shodex HEIP-606M" columns were used. The solvent was 5 mM hexafluoroisopropanol with added sodium trifluoroacetate. The standard sample was 3 mg of Showa Denko polymethyl methacrylate (PMMA), with 3 mg of fiber added. After stable stirring at room temperature, the solution was filtered through a 0.45 μm filter and adjusted. The molecular weight distribution was determined using a Showa Denko "RI-104" refractive index detector at a column temperature of 40°C, a flow rate of 0.2 ml / min.

[0130] The following shows the definitions of each average molecular weight. Here, Mi is the molecular weight at each dissolution position of the GPC curve obtained through molecular weight correction, and Ni is the number of molecules.

[0131] Number average molecular weight Mn Mn=Σ(Ni×Mi) / ΣNi

[0132] Weight-average molecular weight Mw Mw=Σ(Ni×Mi2) / Σ(Ni×Mi)

[0133] The average molecular weight is Mz = Σ(Ni×Mi3) / Σ(Ni×Mi2).

[0134] Dispersion ratio Mw / Mn

[0135] Dispersion ratio Mz / Mw

[0136] Mn is the average value related to low molecular weight components, and Mz is the average value related to high molecular weight components. Additionally, Mw / Mn is an indicator of diffusion towards the low molecular weight side, and Mz / Mw is an indicator of diffusion towards the high molecular weight side.

[0137] K. Moisture content

[0138] Add resin particles into a micro moisture meter and allow the moisture to vaporize at 230°C for 30 minutes. Read the moisture value and set the measured value as the moisture rate.

[0139] L.YI value

[0140] Regarding the YI value, the obtained nylon 6 fiber was wound onto a plastic board and measured three times using a multi-light source spectrophotometer (manufactured by Suga Testing Equipment Co., Ltd.), and the value was calculated based on the average value.

[0141] M. Product quality (based on dyeing color difference and poor silk properties, resulting in stripe quality)

[0142] The dyeing color difference, stripe quality, and luster of the fabric are confirmed through visual inspection by experienced inspectors, and scoring is conducted in the following three stages. A comprehensive evaluation of the product quality is then performed based on the combined score of quality and luster.

[0143] M-1. Dyeing color difference, stripe quality

[0144] 2 points: No color difference or streaks in the dyeing process, indicating excellent quality.

[0145] 1 point: Although there are slight color differences and streaks in the dyeing, there are no problems when using it as a product.

[0146] 0 points: It has defects such as color difference or stripes in the dyeing process and cannot be used as a product.

[0147] M-2. Color

[0148] 2 points: The target color is clearly visible, indicating excellent quality.

[0149] 1 point: The color development is slightly poor, but there is no problem when it is used as a product.

[0150] 0 points: Poor color development, unsuitable for use as a product.

[0151] M-3. Product Quality (Overall Evaluation)

[0152] A: Products scoring 3-4 are qualified.

[0153] C: Products scoring 0-2 points are considered substandard.

[0154] N. High-level passability

[0155] The following criteria are used to evaluate the number of machine stops caused by yarn breakage when using a water jet loom to weave 10 bolts (1000m / bol) of plain weave fabric at a machine speed of 750 rpm and a weft yarn length of 1620 mm.

[0156] A: Less than 2 times

[0157] B: More than 2 times but less than 6 times

[0158] C: More than 6 times

[0159] Set A and B as high-pass-through-qualified.

[0160] <Manufacturing of virgin polyhexamethylene amide resin particles without recycling>

[0161] (Refer to Example 1)

[0162] In a polymerization tank, a 90 wt% aqueous solution of caprolactam was added, along with acetic acid as a polymerization modifier at a ratio of 0.002 mol / L relative to 1 mol of caprolactam, and titanium dioxide as an additive at a ratio of 0.3 wt% relative to the polyhexamethylenetetramine produced. Polymerization was then carried out by stirring and heating the raw materials under a closed system. When the pressure inside the tank reached 1 MPa, water vapor was distilled off and maintained at this pressure. When the internal liquid temperature reached 250°C, the pressure inside the tank was gradually reduced to atmospheric pressure over 70 minutes. At this point, the internal liquid temperature was 260°C. Subsequently, while maintaining the internal liquid temperature at 260°C, nitrogen was allowed to flow in the gas phase of the tank for 60 minutes to complete the polymerization. After polymerization, the molten polyhexamethylenetetramine was extruded from the bottom of the polymerization tank in a gut-like manner. After water cooling, it was cut into granules using a pelletizer. The oligomer components were extracted from the granules using hot water.

[0163] <Manufacturing of recycled polyhexamethylene amide resin particles>

[0164] (Examples 1-5, Comparative Example 3, Comparative Example 5)

[0165] From the coil packaging containing 0.3% by weight of polyhexamethylene amide fiber, after recovering coil packaging with abnormal weight or failing product screening, the polyhexamethylene amide fiber is cut into 0.1m to 1.0m pieces.

[0166] The cut polyhexamethylene amide fiber scraps were placed into the extraction tank, and hot water at the temperatures shown in Table 1 was added at a bath ratio of 1:5 (fiber scrap weight: hot water weight). The hot water was maintained at the temperatures shown in Table 1, and the scraps were soaked for 30 minutes while circulating the hot water using a circulation pump. The fiber scraps were then rinsed and dehydrated to a moisture content of 5% to 15% by weight.

[0167] The dehydrated fiber scraps were melted at 260°C using a pressure melter, and the molten polymer was fed into a single-shaft extruder. The extruder was set to a melting temperature of 260°C and a front-end pressure of 8 MPa while melting was performed, and the polymer was filtered using a metal nonwoven filter with the filtration precision shown in Table 1. The filtered molten polymer was ejected from the die and water-cooled and temporarily granulated. This was then used for a second melting and filtration process, with the melting temperature set to 260°C and the front-end pressure maintained at 8 MPa in the single-shaft extruder, and the polymer was filtered using a metal nonwoven filter with the filtration precision shown in Table 1. The ejection rate was adjusted to ensure the total melting and filtration time was as shown in Table 1. The filtered molten polymer was ejected from the die and water-cooled and granulated to obtain recycled polyhexamethylene amide resin granules with a diameter of 1.2 mm and a length of 2.0 mm.

[0168] The obtained recycled polyhexamethylene amide resin particles were added to an extraction tank, and hot water at the temperatures shown in Table 1 was added at a bath ratio of 1:5 (particle weight: hot water weight). The hot water temperature shown in Table 1 was maintained, and the mixture was soaked for 30 minutes while circulating the hot water using a circulation pump.

[0169] The oligomer content, filtration pressure rise rate, 98% sulfuric acid relative viscosity (ηr), and amino-terminal group content of the obtained recycled polyhexamethylene amide resin particles are shown in Table 1.

[0170] (Example 6, Example 7)

[0171] Except for not performing a second melting and filtration, the process was carried out in the same manner as in Example 1 to obtain recycled polyhexamethylene amide resin particles with a diameter of 1.2 mm and a length of 2.0 mm. Furthermore, in Example 7, front-end pressure fluctuations occurred during melting in the extruder, and leakage of molten polymer in the melting system was also observed.

[0172] The oligomer content, filtration pressure rise rate, 98% sulfuric acid relative viscosity (ηr), and amino-terminal group content of the obtained recycled polyhexamethylene amide resin particles are shown in Table 1.

[0173] (Comparative Example 1)

[0174] Except for using polymer scraps of polyhexamethylene amide containing 0.3% by weight of titanium dioxide as waste, the process was carried out in the same manner as in Example 1 to obtain recycled polyhexamethylene amide resin particles with a diameter of 1.2 mm and a length of 2.0 mm. Furthermore, the polymer scraps of polyhexamethylene amide were not larger than 50 mm square, and polymer scraps larger than 50 mm square were cut to a size of 50 mm square or less.

[0175] The oligomer content, filtration pressure rise rate, 98% sulfuric acid relative viscosity (ηr), and amino-terminal group content of the obtained recycled polyhexamethylene amide resin particles are shown in Table 1.

[0176] (Comparative Example 2)

[0177] Except for not performing hot water extraction of the fiber scraps used as waste, the process was carried out in the same manner as in Example 1 to obtain recycled polyhexamethylene amide resin particles with a diameter of 1.2 mm and a length of 2.0 mm.

[0178] The oligomer content, filtration pressure rise rate, 98% sulfuric acid relative viscosity (ηr), and amino-terminal group content of the obtained recycled polyhexamethylene amide resin particles are shown in Table 1.

[0179] (Comparative Example 4)

[0180] Except for not performing hot water extraction of the recycled polyhexamethylene amide resin particles, the process was carried out in the same manner as in Example 1 to obtain recycled polyhexamethylene amide resin particles with a diameter of 1.2 mm and a length of 2.0 mm.

[0181] The oligomer content, filtration pressure rise rate, 98% sulfuric acid relative viscosity (ηr), and amino-terminal group content of the obtained recycled polyhexamethylene amide resin particles are shown in Table 1.

[0182] <Manufacturing of Polyhexamethylene Fiber (Nylon 6 Fiber) (Melt Spinning)>

[0183] (Refer to Example 1, Examples 1 to 7, Comparative Examples 1 to 5)

[0184] The obtained polyhexamethylene amide resin particles were dried to a moisture content of less than 300 ppm and then placed into a melting system at a temperature of 260°C in a spin block (spinning insulation box). The melt was then melted using a pressure melter at a melting temperature of 265°C. The molten polymer was then introduced into a spinning assembly containing a 10 μm metal nonwoven filter and a spinning die with 4 groups of 10 round holes (totaling 40 holes). The polymer was ejected at a rate of 59 g / min from each spinning assembly.

[0185] The gas generated around the spinning die is forcibly removed by a suction wind speed of 25 m / min. After the fiber filaments are cooled by cold air at a temperature of 18°C ​​and a speed of 30 m / min, oil is supplied through an oil supply device, and entanglement is formed through an entanglement nozzle device. Nylon 6 fibers with a fineness of 33 dtex and a length of 10 are manufactured at a winding speed of 4500 m / min.

[0186] The number of fiber breaks, the time until fiber breakage, and the rate of increase in filtration pressure of the spinning assembly during the manufacturing of nylon 6 fibers are shown in Table 1.

[0187] [Table 1]

[0188]

[0189] As is evident from the results in Table 1, the material recycled polyhexamethylene amide resin particles of the present invention exhibit a remarkably significant effect from the viewpoint of producing material recycled nylon 6 fibers with good operability, compared to the previous material recycled polyhexamethylene amide resin particles.

[0190] In Comparative Example 1, because polymer scraps were used as waste, the resulting recycled polyhexamethylene amide resin particles had a higher oligomer content. Consequently, the number of filament breaks during melt spinning increased, resulting in poor operational stability. The filament breaks were caused by die fouling due to the oligomer content, and the time to filament breakage was shorter compared to the Example, necessitating frequent cleaning of the die surface.

[0191] In Comparative Examples 2 and 3, due to insufficient hot water extraction of the fiber scraps used as waste, the resulting recycled polyhexamethylene amide resin particles had a higher oligomer content. Consequently, the number of filament breaks during melt spinning increased, resulting in poor operational stability. The filament breaks were caused by die fouling due to the oligomer content, and the time to filament breakage was shorter compared to the examples, necessitating frequent cleaning of the die surface.

[0192] In Comparative Examples 4 and 5, the hot water extraction of the recycled polyhexamethylene amide resin particles was insufficient, resulting in a higher oligomer content in the particles. Consequently, the number of filament breaks during melt spinning increased, leading to poor operational stability. The filament breaks were caused by die fouling due to the oligomer content, and the time to filament breakage was shorter compared to the examples, necessitating frequent cleaning of the die surface.

[0193] (Example 8)

[0194] The proportion of recycled polyhexamethylene amide resin particles used was set to 100% by weight. A spinning assembly was used, comprising a spinning die (20 holes x 3 groups, totaling 60 holes), a pressure plate, a filter, and sand filter media. The filter was a short-fiber metal filter, consisting of stainless steel short fibers with a generally polygonal cross-section, a length of 1.0 mm to 3.0 mm, an equivalent diameter of 30 μm to 60 μm, and an aspect ratio of 10 to 100 (filtration accuracy 10 μm). The recycled polyhexamethylene amide resin particles obtained in Example 8 were dried to a moisture content of 800 ppm and then placed in a melting system at a spinning box (spinning insulation box) at a temperature of 260°C. Melting was performed using a pressure melter at a melting temperature of 265°C. The molten polymer was introduced into the spinning assembly and extruded at a rate of 30 g / min per spinning assembly.

[0195] The gas generated around the spinning die is forcibly removed by a suction wind speed of 25 m / min. After the fiber filaments are cooled by cold air at a temperature of 18°C ​​and a speed of 30 m / min, oil is supplied through an oil supply device, and entanglement is formed through an entanglement nozzle device. Nylon 6 fibers with 26 dtex 20 filaments are manufactured at a winding speed of 4000 m / min.

[0196] The properties of the obtained nylon 6 fibers are shown in Table 2.

[0197] <Textile Manufacturing>

[0198] Using a water-jet loom, 10 rolls (1000m / roll) of plain weave fabric were woven at a loom speed of 750rpm and a weft yarn length of 1620mm. The high passability and product quality are shown in Table 2.

[0199] (Comparative Examples 6 to 9)

[0200] By changing the hot water temperature of the fiber scraps, the melting temperature, the melting and filtration time, and the hot water temperature of the resin particles as shown in Table 2, recycled polyhexamethylene amide resin particles were manufactured in the same manner as in Example 1.

[0201] The manufacture of nylon 6 fibers was carried out in the same manner as in Example 8. The results are shown in Table 2.

[0202] (Example 9)

[0203] The spray rate was adjusted to achieve a melting and filtration time of 2 minutes / kg. The recycled polyhexamethylene amide resin particles of Example 6 were obtained by filtering only once using a metal short fiber filter with a filtration accuracy of 20 μm. These particles were then used to manufacture nylon 6 fibers in the same manner as in Example 8. The results are shown in Table 2.

[0204] [Table 2]

[0205] [Table 2]

[0206]

[0207] (Examples 10-11, Comparative Examples 10-11)

[0208] Except for adjusting the moisture content of the resin particles in the drying process as shown in Table 3 to manufacture nylon 6 fibers, the process was carried out in the same manner as in Example 8. The results are shown in Table 3.

[0209] (Comparative Example 12)

[0210] Except for adjusting the filtration precision of the metal short fiber filter to manufacture nylon 6 fibers as shown in Table 3, the process was carried out in the same manner as in Example 8. The results are shown in Table 3.

[0211] (Comparative Example 13)

[0212] The process was carried out in the same manner as in Example 8, except that the filter was replaced with a metal nonwoven filter with a filtration accuracy of 10 μm to manufacture the nylon 6 fibers. The results are shown in Table 3.

[0213] [Table 3]

[0214] [Table 3]

[0215]

[0216] (Examples 12-13)

[0217] Except for adjusting the proportion of recycled polyhexamethylene amide resin particles used to manufacture nylon 6 fibers as shown in Table 4, the process was carried out in the same manner as in Example 8. The results are shown in Table 4.

[0218] (Example 14)

[0219] The ejection rate was adjusted to 43 g / min for each melt spinning assembly, and 52 dtex 34 nylon 6 fibers were manufactured using a spinning die (34 holes × 2 sets, totaling 68 holes). Otherwise, the process was carried out in the same manner as in Example 8. The results are shown in Table 4.

[0220] (See Example 2 for reference)

[0221] The virgin polyhexamethylene amide resin particles obtained in Reference Example 1 were used. After drying the particles to a moisture content of less than 300 ppm, they were placed in a melting system at a temperature of 260°C in a spinning box (spinning insulation box), and melted using a pressure melter at a melting temperature of 265°C. The molten polymer was then introduced into a spinning assembly containing a 10 μm filtration precision metal nonwoven filter and a spinning die with 20 holes × 3 groups (60 holes in total), and ejected at a rate of 30 g / min per spinning assembly. Gas generated around the spinning die was forcibly removed using a suction velocity of 25 m / min. After cooling the fiber filaments with cold air at a temperature of 18°C ​​and a velocity of 30 m / min, oil was supplied through an oil supply device, and entanglement was formed through an entanglement nozzle device. Nylon 6 fibers with a length of 26 dtex 20 were manufactured at a winding speed of 4000 m / min. The results are shown in Table 4.

[0222] [Table 4]

[0223] [Table 4]

[0224]

[0225] (Examples 15-17, Comparative Example 14)

[0226] When the cut polyhexamethylene amide fiber scraps were fed into the extraction tank, and when the obtained recycled polyhexamethylene amide resin particles were fed into the extraction tank, hydrazine monohydrate (manufactured by Tokyo Chemical Industry Co., Ltd.) as a reducing agent was added relative to the hot water, as shown in Table 5. Otherwise, the recycled polyhexamethylene amide resin particles were manufactured in the same manner as in Example 1.

[0227] The manufacture of nylon 6 fibers was carried out in the same manner as in Example 8, producing nylon 6 fibers with a length of 26 dtex 20. The results are shown in Table 5.

[0228] [Table 5]

[0229] [Table 5]

[0230]

Claims

1. A nylon 6 fiber, characterized in that: More than 20% by weight of the fiber is recycled nylon 6. The amount of oligomer in the resin particles of the recycled nylon 6 detected by hot water extraction is less than 1.5% by weight, and the dispersion ratio of the molecular weight distribution, i.e., weight average molecular weight Mw / number average molecular weight Mn, is less than 3.4, and the z-average molecular weight Mz / weight average molecular weight Mw is less than 1.

6. The molecular weight distribution is obtained by gel permeation chromatography.

2. The nylon 6 fiber according to claim 1, characterized in that: The total fineness is 3 dtex to 200 dtex, the single filament fineness is 0.2 dtex to 10 dtex, and the coefficient of variation of the continuous strength elongation product is less than 3.5%.

3. The nylon 6 fiber according to claim 1 or 2, characterized in that: The yellowness index value is below 15.

4. A material for recycling polyhexamethylene amide resin particles, wherein the amount of oligomer content detected by hot water extraction is less than 1.5% by weight.

5. The material recyclable polyhexamethylene amide resin particles according to claim 4, wherein the filtration pressure rise rate is less than 2.0 MPa / hour.

6. A method for manufacturing recycled polyhexamethylene amide resin particles, wherein the recycled polyhexamethylene amide resin particles as described in claim 4 are manufactured by cutting the fiber scraps generated in the manufacturing process of polyhexamethylene amide fibers, immersing the cut fiber scraps in hot water at a temperature above 50°C, melting, filtering, and spraying the fiber scraps, cooling the sprayed polyhexamethylene amide resin with water and cutting it into particles, and then immersing the polyhexamethylene amide resin particles in hot water at a temperature above 50°C.

7. The method for manufacturing recycled polyhexamethylene amide resin particles according to claim 6, wherein in the process of melting, filtering and spraying the fiber scraps, the spraying is performed after two or more filtration processes.

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