Method for preparing regenerated polyester yarn by using waste fabric

Abstract

The present invention relates to a method for producing a regenerated polyester yarn using a waste fabric, and provides a method for producing a regenerated polyester yarn by adding a specific chain extender to a regenerated polyester resin in which a waste fabric made of a polyester yarn is melted to prevent a decrease in viscosity of the melted regenerated polyester resin. The physical properties of the regenerated polyester resin are adjusted by adding a low-melting-point admixture (alloy agent) having a low melting point and crystallinity thereto, thereby improving the extrudability (operability) in a melt spinning process for the regenerated polyester yarn; the present invention relates to a method for producing a regenerated polyester yarn using a waste fabric, which is capable of producing a regenerated polyester yarn using a waste fabric and having physical properties equivalent to those of a virgin polyester yarn.

Description

Technical Field

[0001] The present invention relates to a method for preparing recycled polyester yarn using waste fabric. More specifically, the present invention relates to a method for preparing recycled polyester yarn using waste fabric, which can prevent a decrease in viscosity by adding a chain extender to recycled polyester resin obtained by melting waste fabric made of polyester yarn, and can improve extrudability in the process of melt-spinning recycled polyester yarn and have physical properties equivalent to those of virgin polyester yarn by adding a low-melting-point mixture for adjusting the physical properties of the recycled polyester resin. Background Art

[0002] The demand for synthetic resin, which is a general-purpose polymer in the form of plastic, is increasing as various product groups in modern society. Such synthetic resin can be mass-produced, but it can also be discarded in large quantities. In this regard, the environmental pollution caused by industrialization, that is, the problem of non-degradable waste, has reached a level that seriously threatens its treatment cost and ecosystem.

[0003] In response, in terms of environmental protection and resource reuse, as people's attention to the use of degradable synthetic resin or the reuse of waste synthetic resin gradually increases, efforts are not only being made to implement the separate discharge of plastics and reduce the use of disposable plastics, but also to construct an efficient plastic recycling process while continuously conducting research on significantly reducing carbon generation and producing environmentally friendly recycled plastics with high quality.

[0004] Among them, polyester resin is not only the most widely used synthetic fiber material due to its excellent mechanical properties, chemical stability, high melting point, etc., but also a commercially important polymer as a material for various plastic products. It is mainly made of polyethylene terephthalate (PET) in the form of fibers or sheets and is applied to clothing, films, bottles, containers, optical elements, etc. Due to its excellent processability, transparency, heat resistance, and electrical properties, and good dimensional stability at high temperatures, people are constantly trying to improve physical properties and production efficiency by synthesizing PET with high degree of polymerization and low carboxyl content in a shorter time.

[0005] So far, many methods have been proposed to crush, granulate, and process polyester fibers or fabrics into polyester chips, and then melt the chips and use them to produce new fibers in polyester fabrics. However, typical recycling methods for reuse may have many problems related to production efficiency and economy due to expensive hydrolysis agents, environmental pollution such as wastewater discharge, expensive energy use, and complex process conditions.

[0006] As described above, as a method for recycling waste polyester, the method of preparing polyester chips by simply extruding waste polyester has a narrow range of applicable products due to reasons such as color discoloration, foreign matter mixing, and viscosity reduction. Therefore, there is a problem that it is not suitable as a fiber material. In addition, in the method of recycling by depolymerizing waste polyester, since it is necessary to mix and melt waste polyester with ethylene glycol for depolymerization, although the physical properties of the recycled polyester are excellent, there are serious problems such as low production efficiency, high recycling cost, color deterioration and dyeing defects caused by long-term depolymerization.

[0007] As a representative prior art for preparing recycled polyester yarns by such physical and / or chemical methods, Korean Patent Publication No. 10-2010-0087578 discloses a recycled polyester fiber and a method for preparing the same, including the following steps: melting recycled polyester recovered from fibers, films, bottle moldings, etc.; filtering foreign substances or coarse inorganic particles, denatured resins, etc. using a filter of the molten material; extruding the filtered melt into recycled polyester pellets; drying the recycled polyester pellets and mixing them with ordinary polyester, and melt-kneading in a twin-screw extruder; and spinning the melt-kneaded material.

[0008] In addition, Korean Patent No. 10-1197724 discloses a method for preparing recycled polyester yarns using waste polyester, characterized by including the following steps: depolymerization, mixing waste polyester flakes with ethylene glycol (EG) at a molar ratio of 1.0:0.1 to 1.0, pressurizing with nitrogen (N2) to 1.5 to 2.5 kg / cm 2 , stirring and melting at 10 to 50 rpm for 3 to 4 hours, and then pressurizing the molten mixture with nitrogen (N2) to 2.0 to 2.5 kg / cm 2 , and depolymerizing for 1.0 to 2.0 hours while stirring at 245 to 260 °C at 30 to 70 rpm to generate bis(2-hydroxyethyl) terephthalate (BHET); filtering, removing foreign substances from the bis(2-hydroxyethyl) terephthalate (BHET) generated by the depolymerization process through a filter of 600 to 2000 mesh; polycondensation, polymerizing the bis(2-hydroxyethyl) terephthalate (BHET) under a vacuum state to generate polyester; preparing recycled polyester chips, preparing the recycled polyester prepared by the polycondensation process into chips; mixing the chips, mixing the recycled polyester chips according to color; spinning, spinning the recycled polyester chips and preparing partially oriented yarns (POY: partially oriented yarn); and a draw texturing process, using the partially oriented yarns to prepare draw textured yarns (DTY: draw textured yarn).

[0009] In addition, Korean Patent No. 10-2183241 discloses a recycled polyester fiber with excellent spinnability and a method for preparing the same, which is characterized by including the following steps: melting, melting waste polyester; first filtration, filtering the molten polyester using a mesh filter; second filtration, secondarily filtering the filtered polyester using a candle filter; and fibrillation, spinning the secondarily filtered polyester to perform fibrillation.

[0010] In addition, referring to Korean Published Patent No. 10-22-0034027, a multicomponent fiber includes: a first component containing polyester (at least 80 wt% of the polyester is recycled polyester) and having a melting point MP1; and a second component containing polyester (at least 80 wt% of the polyester is recycled polyester) and having a melting point MP2. As a multicomponent fiber where MP2 is less than or equal to MP1, the second component is polyester and a melting point reducing additive, and the melting point reducing additive uses a diol.

[0011] The supply sources for reusing polyester waste fabrics can be classified as: (1) pre-consumer supply sources, which reuse wastes such as scraps generated in the preparation processes of raw yarns, fabrics, shoes, and other items; (2) post-consumer supply sources, which reuse the recycled products after the use purposes of products such as clothes, automotive interiors, and household items are completed. In the present invention, a method for obtaining high-quality environmentally friendly recycled polyester yarns from the supply sources of (1) and (2) has been developed. Summary of the Invention

[0012] Technical Problem

[0013] An object of the present invention is to provide a method for preparing a recycled polyester yarn using waste fabrics, which adds a specific chain extender to a recycled polyester resin obtained by melting waste fabrics made of polyester yarns to prevent a decrease in the viscosity of the molten recycled polyester resin, and adjusts the physical properties of the recycled polyester resin by adding a low melting point alloy agent with a lower melting point and crystallinity, thereby not only improving the extrudability (operability) in the process of melt spinning the recycled polyester yarn but also having physical properties equivalent to those of virgin polyester yarns.

[0014] Technical Solution

[0015] The method for preparing recycled polyester yarn using waste fabric according to the present invention includes: a first step of recovering waste fabric made of polyester yarn and removing impurities; a second step of cutting and pulverizing the waste fabric from which the impurities have been removed; a third step of putting the pulverized waste fabric into a compounding machine, melting it at a temperature of 230 to 270 °C to obtain recycled polyester resin, and then extruding a melt of carbonyl bis-caprolactam (CBC: Carbonylbis caprolactam) added in a range of 0.5 to 2 parts by weight with respect to 100 parts by weight of the molten recycled polyester resin as a chain extender to prepare recycled polyester pellets; a fourth step of drying the recycled polyester pellets; and a fifth step of putting the dried recycled polyester pellets into a spinning machine and performing melt spinning at a temperature condition of 260 to 320 °C.

[0016] According to a preferred embodiment of the present invention, it is characterized in that, in the third step, copolyester (CoPET: Copolyester) as a low-melting-point alloy agent is further added in a range of 2 to 10 parts by weight with respect to 100 parts by weight of the molten recycled polyester resin, and the density of the copolyester (CoPET: Copolyester) is 1.2 to 1.4 g / cm 3 , and the melting point is 123 to 133 °C.

[0017] Thus, it is characterized in that the tensile strength of the recycled polyester yarn is 0.55 to 0.65 kgf / cm 2 , and the elongation at break is 20 to 32%.

[0018] The recycled polyester yarn obtained by the preparation method of the present invention, by adding a specific chain extender to the recycled polyester resin obtained by melting waste fabric made of polyester yarn, has the effect of preventing a decrease in the viscosity of the recycled polyester resin, and by adding a low-melting-point alloy agent with a lower melting point and crystallinity to adjust the physical properties of the recycled polyester resin, it can not only improve the extrudability (operability) in the process of melt spinning the recycled polyester yarn, but also has the effect of making it have physical properties equivalent to those of virgin polyester yarn.

[0019] The present invention can simply recycle polyester yarn from waste fabric by combining the above-mentioned chemical and physical melt mixing methods, thereby having the advantages of reducing costs by virtue of low cost and high production efficiency, and preventing environmental pollution by reusing a large amount of waste resources. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a figure presenting and showing the surface state of the recycled polyester yarn prepared by the method according to the first preferred embodiment of the present invention in the form of a photograph.

[0021] Figure 2 This is a figure presenting and showing the surface state of the recycled polyester yarn prepared by the method according to the second preferred embodiment of the present invention in the form of a photograph.

[0022] Figure 3 This is a figure presenting and showing the surface state of the virgin polyester yarn in the form of a photograph.

[0023] Best Mode

[0024] Hereinafter, a method for preparing recycled polyester yarn using waste fabrics according to the present invention will be described. The purpose is to enable those of ordinary skill in the technical field to which the present invention pertains to easily implement the present invention, and it does not mean to limit the technical idea and scope of the present invention thereby.

[0025] Generally, polyester resin is a general term for high molecular compounds having an ester bond (-CO-O-) through the polycondensation of polybasic acids and polyhydric alcohols, which may include thermoplastic saturated polyesters and thermosetting unsaturated polyesters. Among them, polyester synthetic fibers belonging to the former mix terephthalic acid and ethylene glycol and heat them, and while reducing the pressure of the resulting substance, polymerization is carried out to prepare polyethylene terephthalate (PET).

[0026] The polyester resin is classified into unsaturated polyester resins, alkyd resins, polyester synthetic fibers, etc. In the present invention, as polyester synthetic fibers, it refers to waste fabrics composed of polyethylene terephthalate (PET), where polyethylene terephthalate is a thermoplastic saturated polyester that is most widely used in the fiber field and is widely used as an industrial material.

[0027] Due to the advantages of excellent mechanical and physical properties, durability, and recyclability, the market for polyethylene terephthalate (PET) is in a further expanding trend. In the present invention, the core theme is to establish vertical integration and one-stop process conditions from the raw yarns and fabric wastes generated in the process to the fabric products, while ensuring environmental protection technologies.

[0028] In the conventional methods for recycling polyester, there are hydrolysis methods that use water to reduce it to monomer or oligomer phases, glycolysis methods that use diols such as ethylene glycol or propylene glycol, methanolysis methods that use methanol, etc. However, these chemical methods not only have problems such as low economy and productivity due to the need to use high-cost additives, environmental pollution such as wastewater discharge, and high-cost energy costs and complex process conditions caused by heat treatment for improving fiber crystallinity in some cases, but also imply problems such as color deterioration and poor dyeing of fibers caused by long-term depolymerization.

[0029] Therefore, the present invention can regenerate a large amount of low-cost and high-quality polyester yarns from waste fabrics through a melt mixing method that combines chemical and physical methods, thereby achieving cost reduction while having environmental protection advantages with high economy and production efficiency.

[0030] As a method for preparing recycled polyester yarns using waste fabrics, the present invention includes: a first step of recovering waste fabrics made of polyester yarns and removing impurities; a second step of cutting and pulverizing the waste fabrics from which the impurities have been removed; a third step of putting the pulverized waste fabrics into a compounding machine, melting at a temperature of 230 to 270 °C to obtain recycled polyester resin, and then extruding a melt of carbonyl bis caprolactam (CBC) as a chain extender in a range of 0.5 to 2 parts by weight with respect to 100 parts by weight of the molten recycled polyester resin to prepare recycled polyester pellets; a fourth step of drying the recycled polyester pellets; and a fifth step of putting the dried recycled polyester pellets into a spinning machine and performing melt spinning at a temperature condition of 260 to 320 °C.

[0031] First, the first step, as a process for recovering waste fabrics made of polyester yarns and removing impurities, is a process of cleaning and removing foreign substances from by-products generated during the preparation of raw yarns and fabrics, or scraps generated during the preparation process of shoes or clothing, or waste fabrics made of polyester yarns used in clothes and automotive interiors. The second step is a process of cutting the waste fabrics from which the impurities have been removed into an average size of 1 to 10 mm or less and pulverizing them. The first step and the second step can be regarded as conventional preparation steps for obtaining recycled polyester resin in a molten state.

[0032] Next, the third step involves the following process: The shredded waste fabric is put into a compounding machine, melted at a temperature of 230 - 270 °C to obtain recycled polyester resin, and then, a melt of carbonyl biscaprolactam (CBC) as a chain extender is added in the range of 0.5 - 2 parts by weight relative to 100 parts by weight of the molten recycled polyester resin and extruded to prepare recycled polyester pellets.

[0033] In the present invention, in order to prevent the phenomenon that the molecular chains of the polyester resin are partially broken due to the melting of the waste fabric made of polyester yarn, resulting in a decrease in the viscosity of the naturally melted recycled polyester resin, 0.5 - 2 parts by weight of carbonyl bis caprolactam (CBC) as a chain extender is added. This is based on the principle that the chain extension reaction is caused by the reaction of the alcohol and carboxylic acid at the chain ends of the polyester resin, thereby increasing the inherent viscosity.

[0034] The process for preparing the recycled polyester pellets preferably uses a conventional vent-type extruder, etc. As described above, while maintaining the extrusion pressure uniformly, foreign matters or coarse inorganic particles, denatured resins, etc. are filtered using a filter, and then the molten recycled polyester resin recovered is extruded, cooled, and cut in a strand form to produce granular recycled polyester pellets.

[0035] At this time, in the third step, 2 - 10 parts by weight of copolyester (CoPET) as a low-melting-point alloy agent is further added relative to 100 parts by weight of the molten recycled polyester resin to adjust the melting point, so that the defective rate during melt spinning can be reduced to less than 2%, thereby improving production efficiency.

[0036] As described above, in the present invention, as a low-melting-point alloy agent, by adding 2 - 10 parts by weight of copolyester (CoPET), the melting point and crystallinity of the molten recycled polyester are reduced to improve operability (extrudability). This is because conventional polyester (polyethylene terephthalate) is a crystalline polymer with excellent transparency, toughness, rigidity, heat resistance, etc., having a melting point (Tm) of 250 °C and a glass transition temperature (Tg) of about 70 °C. Therefore, it is also difficult to control the crystallization of the recycled polyester resin used in the present invention only through processing conditions such as heating / cooling and stretching.

[0037] The copolyester (CoPET: Copolyester) appropriately reduces the melting point and crystallinity of the recycled polyester resin by adding 2 to 10 parts by weight of a resin with a density of 1.2 to 1.4 g / cm 3 and a melting point adjusted to the range of 123 to 133 °C, so as to not only improve the extrusion formability of the recycled polyester yarn, but also prepare a recycled polyester yarn with physical properties equivalent to those of virgin polyester yarn.

[0038] The test results for the typical properties of the copolyester (CoPET: Copolyester) are as follows [Table 1].

[0039] [Table 1]

[0040] Physical properties Unit Test results Test method Viscosity index <![CDATA[cm 3 / g]]> 80-88 DIN 53 728 Melting point (DSC) ℃ 123-133 DIN 53 765 Glass transition temperature (DSC) ℃ 0 DIN 53 765 Softening point (ring and ball method) ℃ 140±20 DIN ISO 4625 Melt flow rate (at 160 °C) g / 10 min 30±5 DIN ISO 1133 (21.6 N) Melt viscosity (at 160 °C) Pa·s 330±50 (parallel plates method) Pot life s 8-15 Degussa method Tensile strength <![CDATA[N / mm 2 > 25±5 DIN EN ISO 527-1 / 3 Density <![CDATA[g / cm 3 > 1.3±0.1 DIN 53 479

[0041] *DSC: Differential scanning calorimetry

[0042] *DIN: Deutsche Industric Normen

[0043] For reference, the copolyester is a polyester obtained by polycondensation of two or more dibasic acids, diols or hydroxy acids. Compared with the copolyester, a polyester composed of only a single structural unit is called a homopolyester. The copolyester is not simply a mechanical mixture of two or more homopolyesters, but is formed by bonding each structural unit to each other through an ester bond, and is prepared by a polycondensation reaction in the same way as the components (dibasic acid and diol) of the polyester. The melting point and crystallinity of the copolyester are lower than those of the homopolyester of the components.

[0044] It is known that the copolyester has the use of improving the dyeability of polyester fibers. For example, by adding an appropriate amount of isophthalic acid to polyethylene terephthalate (PET) to form a copolyester, the dyeability can be significantly improved. The present invention is based on the fact that by directly adding a copolyester that acts as a low-melting alloy agent with a lower melting point and crystallinity, not only can the physical properties of the polyester resin be adjusted and the extrusion property of the recycled polyester yarn be improved through a melt spinning process, but also physical properties equivalent to those of virgin polyester can be obtained.

[0045] In this regard, melting point reducing additives for reducing the melting point of existing polyesters may include plasticizers, etc., in order to produce a copolyester with a lower melting point by subjecting recycled polyester to ethylene glycol modification or replacing a predetermined proportion of terephthalic acid with isophthalic acid, or by modifying the polymer chain to have a lower melting point (refer to Korean Patent Publication No. 10-2022-0034027, prior art document 4). In the present invention, in order to improve the disadvantages such as pollutants and economy generated by the above-described chemical modification methods, by ensuring a process technology based on a physical method of adding a copolyester (CoPET: Copolyester) as a low melting point mixture in a range of 2 to 10 parts by weight, it was confirmed that the viscosity of the molten polyester can be adjusted.

[0046] The fourth step is a process of drying the recycled polyester pellets. For example, vacuum drying can be carried out under hot air or reduced pressure conditions to remove the moisture in the obtained recycled polyester pellets.

[0047] Finally, the fifth step is a process of melt spinning at a temperature of 260 to 320 °C after putting the dried recycled polyester pellets into a spinning machine. The object of the present invention is to prepare recycled polyester yarns using 100% of the recycled polyester pellets. Optionally, of course, the recycled polyester masterbatch pellets can be supplied to a metering device according to a pre-designed mixing ratio, and then polyester pellets prepared by polymerizing and solid-phase polymerizing conventional high-purity raw materials are metered according to the mixing ratio. Through a hopper, the spinning rate is controlled in a twin extruder, which is a melt extruder with excellent uniform mixing performance, and polyester yarns containing recycled polyester pellets are prepared through melting, extrusion, and cooling and solidification.

[0048] Hereinafter, a method for preparing recycled polyester yarns using waste fabrics according to the present invention will be specifically described, and the present invention will be described through preferred embodiments that can be easily implemented by those of ordinary skill in the technical field to which the present invention pertains. Detailed Description of the Invention

[0049]

Examples

[0050] 1. Preparation of recycled polyester pellets

[0051] ○ First step: After recovering waste fabrics such as fabrics, clothing, and shoe scraps made of polyester yarns, foreign matter sieving and impurity removal were carried out.

[0052] ○ Second step: The waste fabrics from which the impurities were removed were cut using a crusher and crushed to a size of 10 mm or less.

[0053] ○ Third step: Put the shredded waste fabric into a compounding machine, melt it at a temperature of 230 - 270 °C to obtain recycled polyester resin, and then add carbonyl bis caprolactam (CBC: Carbonyl bis caprolactam) as a chain extender in the range of 0.5 - 2 parts by weight relative to 100 parts by weight of the molten recycled polyester resin and add copolyester (CoPET: Copolyester) as a low melting point alloy agent in the range within 2 - 10 parts by weight, and extrude the melt to prepare recycled polyester pellets.

[0054] ○ Fourth step: Dry the recycled polyester pellets with hot air.

[0055] 2. Preparation of recycled polyester yarns

[0056] A. Preparation of monofilament yarn (150 denier)

[0057] ○ Step 5-1: Put the recycled polyester pellets prepared in the fourth step into a spinning extruder, and melt and extrude them at a temperature of 260 °C - 300 °C (operating speed: 200 m / min). Cool the filaments produced through the die of the extruder with water at a temperature of 25 - 40 °C and stretch the obtained filaments, and then cure the stretched filaments in a heating cavity and wind them up to make polyester monofilament yarn with a fineness of 50 - 350 denier.

[0058] B. Preparation of multifilament yarn (50 denier / filament)

[0059] ○ Step 5-2: Put the thermoplastic polyurethane pellets prepared in the fourth step into a spinning extruder, and carry out melt extrusion at a temperature of 260 - 320 °C. Aggregate the filaments produced through the die of the extruder according to the number of filaments, and carry out air cooling at 25 - 40 °C, stretch the obtained filaments and wind up the stretched filaments to make polyester multifilament yarn with a single filament fineness of 50 denier / filament or less.

[0060] As described above, the specific spinning conditions, the content of the chain extender and the low melting point alloy agent in the process of preparing the recycled polyester yarn are adjusted within the scope defined in the present invention according to the physical properties of the recycled polyester resin or the type of the required recycled polyester yarn, thereby establishing the technology of the preparation process of the recycled polyester yarn using waste fabric.

[0061]

Experimental Example

[0062] The recycled polyester yarns (CBC 1 phr, CoPET 3 phr) prepared according to the embodiments are spun through a common profiled spinneret, thereby preparing draw textured yarns (DTY) based on 150 d / 48 f (Example ①, Figure 1 ), 150 d / 96 f (Example ②, Figure 2 ). In order to compare them with virgin polyester yarns (Comparative Example, Figure 3 ), the relative physical properties such as tensile strength, elongation at break, and unit weight were evaluated several times, and the results are as follows [Table 2]. The results show that, as shown in the photos of Figure 1 and Figure 2 , the surface state of the recycled polyester yarns is also as good as that of the virgin polyester yarns shown in Figure 3 .

[0063]

Table 2

[0064]

[0065] As shown in the above [Table 2], in Example ① and Example ②, the recycled polyester yarns prepared by containing CBC 1 phr and CoPET 3 phr can exhibit properties equal to or above those of virgin polyester yarns in terms of tensile strength. In addition, since the elongation at break is increased by about 10 - 30% and the unit weight is reduced by about 5 - 10%, not only can lightweight products be produced, but also no problems such as defective rates in the spinning process are found. Furthermore, the recycled polyester yarns prepared based on Example ① and Example ② are expected to produce fiber products with overall physical properties superior to those of virgin polyester yarns of the same level or above, so they have the advantages of being able to seek the stability and economy of raw material supply and demand.

[0066] Industrial Applicability

[0067] The recycled polyester yarns prepared from waste fabrics according to the present invention have the advantages of environmental protection and reduction of defective rates in the preparation process. Therefore, they are applicable not only to the fabric fields required for various shoes, clothing, bags, etc. that require uniform color performance and durability, but also to a variety of uses such as sports goods, daily necessities, and industrial products like synthetic leather and plastic products.

[0068] Bibliography

[0069]

Prior Art Documents

[0070] (Patent Document 1) Korean Patent Publication No. 10 - 2010 - 0087578 (Publication Date: August 5, 2010)

[0071] (Patent Document 2) Korean Patent Gazette No. 10-1197724 (Publication Date: November 06, 2012)

[0072] (Patent Document 3) Korean Patent Gazette No. 10-2183241 (Publication Date: November 26, 2020)

[0073] (Patent Document 4) Korean Patent Publication Gazette No. 10-2022-0034027 (Publication Date: March 17, 2022)

Claims

1. A preparation method of regenerated polyester yarn using waste fabrics, characterized in that, Including: The first step is to recycle waste fabrics made of polyester yarns and remove impurities; The second step is to cut and crush the waste fabrics from which the impurities have been removed; The third step is to put the crushed waste fabrics into a compounding machine, melt them at a temperature of 230 to 270 °C to obtain recycled polyester resin, and then extrude a melt of caproyl lactam as a chain extender added in a range of 0.5 to 2 parts by weight relative to 100 parts by weight of the molten recycled polyester resin to prepare recycled polyester pellets; The fourth step is to dry the recycled polyester pellets; And The fifth step is to put the dried recycled polyester pellets into a spinning machine and carry out melt spinning at a temperature condition of 260 to 320 °C.

2. The method for preparing recycled polyester yarns from waste fabrics according to claim 1, characterized in that In the third step, a copolyester as a low melting point mixture is further added in a range of 2 to 10 parts by weight relative to 100 parts by weight of the molten recycled polyester resin.

3. The method for preparing recycled polyester yarns from waste fabrics according to claim 2, characterized in that The density of the copolyester is 1.2 to 1.4 g / cm 3 , and the melting point is 123 to 133 °C.

4. The method for preparing recycled polyester yarns from waste fabrics according to claim 1, characterized in that The tensile strength of the regenerated polyester yarn is 0.55 to 0.65 kgf / cm 2 , and the elongation at break is 20 to 32%.

5. A recycled polyester yarn made from waste fabrics produced by using the preparation method according to any one of claims 1 to 4.

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