Recycled polyester fiber and method for producing the same

Abstract

To provide a recycled polyester fiber consisting of a resin composition obtained by adding a phosphorous compound into polyester resin including a recycled polyester raw material, the recycled polyester fiber having small unevenness of fineness even if being a long fiber of thin fineness and an equivalent characteristic value to that of a polyester fiber obtained by melt spinning using virgin polyester resin.SOLUTION: A recycled polyester fiber including a recycled polyester raw material satisfies all the following (1) to (3): (1) including an organic phosphorous compound having 2 or more ester formable functional groups and containing 1000-10000 mass ppm of phosphorous atoms; (2) being a long fiber having single fiber fineness of 0.2-10 dtex, the number of filaments of 40-320, and the total fineness of 20-300 dtex; and (3) having a variability rate in fiber diameter of 5% or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a novel flame-retardant recycled polyester fiber, which is a recycled polyester fiber made from recycled polyester raw materials derived from used polyester products as well as recycled polyester raw materials derived from unused polyester generated in the process of manufacturing polyester products, and a method for producing the recycled polyester fiber. [Background technology]

[0002] Polyethylene terephthalate (hereinafter sometimes abbreviated as PET) has a high melting point, is chemical resistant, and is relatively low cost, so it is widely used in fibers, films, and molded products such as PET bottles. These polyester products inevitably generate waste during the manufacturing and processing stages, and are often disposed of after use, but if they are incinerated, the high heat generated will severely damage the incinerator and shorten its lifespan, while if they are not incinerated, they will remain in the furnace almost indefinitely because they do not decompose. In recent years, plastic containers and other polyester products that have been used and discarded as garbage have been found to be flowing into the ocean via rivers. These microplastics are broken down into small pieces by the action of waves and tidal currents, and accumulate in the bodies of marine organisms. These plastics are concentrated in the food chain, adversely affecting the marine ecosystem, and plastics have become a major cause of marine pollution. This has led to a global movement to reduce the amount of plastic used and to switch to biodegradable plastics.

[0003] From the perspective of reducing the amount of plastic products used and from the perspective of environmental issues, various methods of recycling resources are being used. Regarding polyester products, methods are being considered for recycling polyester waste generated during the manufacturing process and for recovering products that have been discarded after being sold on the market and reusing them as raw materials. In particular, in recent years, textile products that have been awarded the Eco Mark, which is certified as achieving a certain recycling rate, have become popular.

[0004] Furthermore, in recent years, there has been an increasing demand for flame-retardant synthetic fibers and various plastic products from the perspective of fire prevention. Various attempts have been made to impart flame retardancy to polyester, but from the standpoints of performance and productivity, the most common method is to copolymerize a flame retardant-imparting substance during polyester production. Phosphorus compounds are considered advantageous as flame retardant-imparting substances for this purpose from the standpoints of flame retardancy, cost, environmental pollution, and safety. It has been disclosed that flame retardancy can be achieved by blending specific phosphorus compounds into polyester fibers (e.g., Patent Document 1). However, no polyester fibers have yet been proposed that contain such phosphorus compounds and have flame retardancy equivalent to that of fibers made from virgin polyester, even though they are made from recycled polyester.

[0005] In other words, recycled polyester raw materials themselves, unlike virgin polyester raw materials, contain a large amount of foreign matter and are poor in uniformity. However, the addition of a phosphorus compound further deteriorates the uniformity of the resin. Therefore, when a polyester resin composition containing a phosphorus compound in a recycled polyester raw material is melt-spun, thread breakage during spinning is likely to occur, resulting in poor operability. Therefore, when obtaining long fibers, the more complex the fiber shape or the finer the fiber size, the greater the influence of foreign matter, making thread breakage more likely and making production difficult. In addition, the obtained fibers tend to have large unevenness in fineness and are prone to have poor mechanical properties such as strength and elongation, as well as poor thermal stability. As a result, products such as woven and knitted fabrics made from such fibers are of poor quality, and when dyed, yarn irregularities such as dye irregularities occur. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent Publication No. 2016-108706 Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention aims to solve the above problems and to provide a recycled polyester fiber made from a resin composition in which a phosphorus compound is added to a polyester resin made from recycled polyester raw materials derived from used polyester products or recycled polyester raw materials derived from scraps generated in the process of producing polyester resins and products, the recycled polyester fiber having little fineness unevenness even when made into a fine long fiber and having properties equivalent to those of polyester fibers obtained by melt spinning using virgin polyester resin. It also aims to provide a production method by which such a recycled polyester fiber of the present invention can be obtained. [Means for solving the problem]

[0008] The present inventors have conducted extensive research in light of the problems of the prior art and have found that recycled polyester fibers having the same properties and flame retardancy as those produced using virgin polyester resins can be obtained by producing recycled polyester fibers using a specific production process, thereby completing the present invention.

[0009] That is, the present invention is summarized as follows (i) to (iii). (i) A recycled polyester fiber containing at least one recycled polyester raw material from a) used polyester products and b) unused polyester generated in the process of manufacturing polyester products, characterized in that the recycled polyester fiber satisfies all of the following (1) to (3): (1) An organic phosphorus compound having two or more ester-forming functional groups and a phosphorus atom content of 1,000 to 10,000 ppm by mass. (2) A long fiber with a single fiber fineness of 0.2 to 10 dtex, a filament count of 40 to 320, and a total fineness of 20 to 300 dtex. (3) The fluctuation rate of the fiber diameter is 5% or less. (ii) The regenerated polyester fiber according to (1), having a single fiber fineness of 0.2 to 10 dtex. (c) A method for producing recycled polyester fibers, which comprises melt-kneading at least one recycled polyester raw material selected from a) used polyester products and b) unused polyesters generated in the process of producing polyester products, and an organophosphorus compound having two or more ester-forming functional groups in an extruder, passing the mixture through a metering pump and melt-spinning the mixture through a melt-spinning nozzle equipped with a spinneret, cooling the spun fiber in a cooling cylinder, and taking it up with a take-up roller, wherein the temperature during melt-kneading in the extruder is a, the temperature of the metering pump is b, the temperature of the melt-spinning nozzle is c, and the temperature of the cooling cylinder is d, and the temperatures a to d satisfy the following conditions: a is 280-290℃ b is a+5~a+10℃ c is 310-320℃ d is C-150 to C-50°C [Effects of the Invention]

[0010] The recycled polyester fiber of the present invention is made from at least one recycled polyester raw material selected from a) used polyester products and b) unused polyester generated in the process of manufacturing polyester products, and further contains a phosphorus compound. However, melt spinning can be performed with good spinning operability, and therefore, recycled polyester fibers with little unevenness in fineness can be obtained even in the case of fine long fibers. Therefore, the recycled polyester fiber of the present invention has properties equivalent to those of fibers obtained using virgin polyester resin, and the resulting woven or knitted fabrics are less likely to develop dye spots when dyed and have excellent flame retardancy, making them suitable for use in a variety of applications including clothing and interior decoration.

[0011] Furthermore, according to the method for producing the recycled polyester fiber of the present invention, the recycled polyester fiber of the present invention can be obtained with good operability, which is a great practical advantage. DETAILED DESCRIPTION OF THE INVENTION

[0012] The present invention will be described in detail below. The regenerated polyester fiber of the present invention (the fiber of the present invention) comprises at least one recycled polyester raw material selected from a) used polyester products and b) unused polyester generated in the process of manufacturing polyester products.

[0013] Examples of used polyester products in the above category a) include polyester molded products (including fibers) that were once on the market and then collected after use. Typical examples include containers such as PET bottles and packaging materials. The unadopted polyester generated in the manufacturing process of polyester products mentioned in b) above is polyester that did not reach the stage of commercialization. Examples include resin pellets that do not meet specifications, materials that are no longer needed during molding, fragments cut during molding, scraps generated during molding or processing, cut-off pieces of transitional products generated when changing brands, and cut-off pieces of prototypes or defective products.

[0014] The above a) and b) are not limited in their form, and may be pelletized by further processing such as pulverization or cutting as necessary, or may be melted and pelletized. The above a) and b) may be used alone or as a mixture of the two.

[0015] The recycled polyester raw materials a) and b) above may be either crystalline or amorphous. Therefore, for example, pellets of amorphous polyester waste that have not been heat-treated, crystalline pellets that have been heat-treated, or a mixture of crystalline and amorphous pellets can be used. In the present invention, it is preferable to use crystalline recycled polyester raw materials, particularly for the purpose of preventing the pellets from fusing together when being introduced into the device. Therefore, materials a) or b) above that have been crystallized by heat treatment (crystallized pellets, etc.) can be preferably used.

[0016] The properties of the recycled polyester raw materials a) and b) above are not limited, and may be in the form of a) and b) above, or may be in the form of cut pieces, crushed material (powders), etc. obtained by further processing such as cutting and crushing, as well as solid forms such as molded bodies (pellets, etc.) obtained by molding these. More specifically, examples include pellets obtained by cooling and cutting melted polyester waste, and cut pieces obtained by finely cutting polyester molded products such as PET bottles. Alternatively, the recycled polyester raw materials may be in the form of a liquid obtained by dispersing or dissolving the cut pieces, crushed material (powders), etc. in a solvent. When producing polyester products using these raw materials, they can be melted at a temperature above their melting point and introduced into the device as a melt, as needed.

[0017] The regenerated polyester fiber of the present invention preferably contains 40% by mass or more, and more preferably 50% by mass or more, of the recycled polyester raw material, which is at least one of the above a) and b). If the content of recycled polyester raw materials is less than 40% by mass, the objective of considering environmental issues cannot be achieved. There is no particular upper limit to the content of recycled polyester raw materials, but according to the production method of the present invention described below, it is possible to easily obtain a recycled polyester resin with a recycled polyester raw material content of 40 to 100% by mass.

[0018] The regenerated polyester fiber of the present invention contains an organic phosphorus compound having two or more ester-forming functional groups (hereinafter, sometimes referred to as phosphorus compound (Y)), and has a phosphorus atom content of 1,000 to 10,000 ppm. As the phosphorus compound (Y), a compound represented by the following formula (1) is preferred in terms of the residual rate of the organic phosphorus compound, etc. [ka] where R1 represents an alkyl group or aryl group having 1 to 12 carbon atoms, R2 represents an alkyl group, aryl group, or monohydroxyalkyl group having 1 to 18 carbon atoms, or a cyclic structure connected via R1, or a hydrogen atom, R3 represents an alkyl group, aryl group, or monohydroxyalkyl group having 1 to 18 carbon atoms, or a hydrogen atom, A represents a divalent or higher hydrocarbon group, and n represents the valence of A minus 1.

[0019] Preferred specific examples of the organophosphorus compound represented by the above formula (1) include those represented by the following structural formulas (a) to (d). Among them, the compound represented by structural formula (a) is particularly preferred in terms of flame retardancy. These may be used as they are or in the form of esterified products. [ka] By including the phosphorus compound in the polyester fiber so that the phosphorus atom content is 1000 to 10000 ppm, flame retardancy can be imparted to the polyester fiber, and various flame-retardant textile products can be obtained. The content of phosphorus atoms in the fiber is 1000 to 10000 ppm, and more preferably 2000 to 7000 ppm.

[0020] If the content of phosphorus atoms in the recycled polyester fiber is less than 1,000 ppm, the flame retardancy will be poor. On the other hand, if the content of phosphorus atoms exceeds 10,000 ppm, the melting point of the polymer will decrease, causing yarn breakage during spinning and reducing operability. In addition, the resulting recycled polyester fiber will have low strength and a high rate of variation in fiber diameter.

[0021] The content of phosphorus atoms in the polyester fiber can be adjusted to fall within the above range by adjusting the amount of the phosphorus compound (Y) contained in the polyester fiber. In the present invention, an example of a method for incorporating the phosphorus compound (Y) into polyester fibers is a method in which the phosphorus compound (Y) is blended with a recycled polyester resin containing the above-mentioned recycled polyester raw material. More specific methods will be described in detail in the explanation of the production method.

[0022] The polyester resin constituting the recycled polyester fiber of the present invention preferably has terephthalic acid as the main acid component. Specifically, when the total acid components are taken as 100 mol%, the acid content is preferably 90 mol% or more, and more preferably 92 to 98 mol%.

[0023] Examples of the dicarboxylic acid component other than terephthalic acid in the polyester fiber of the present invention include isophthalic acid, phthalic acid, 5-sodium sulfoisophthalic acid, phthalic anhydride, naphthalenedicarboxylic acid, adipic acid, sebacic acid, and dimer acid. Two or more of these may be used in combination, and ester-forming derivatives of these acids may also be used.

[0024] The polyester resin constituting the recycled polyester fiber of the present invention preferably has a glycol component mainly composed of ethylene glycol, and specifically, when the total glycol components are taken as 100 mol %, the glycol component is preferably 90 mol % or more, and more preferably 95 to 98 mol %.

[0025] Furthermore, examples of the diol component other than ethylene glycol that can be used in the polyester resin of the present invention include neopentyl glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, diethylene glycol, dimer diol, an ethylene oxide adduct of bisphenol S, and an ethylene oxide adduct of bisphenol A.

[0026] The polyester fiber of the present invention has the above-mentioned composition and also has the characteristic values ​​shown in (2) and (3) above, and particularly preferably has the characteristic values ​​shown in (4) and (5) below.

[0027] The fiber of the present invention is a long fiber having the characteristic value (2) of a single fiber fineness of 0.2 to 10 dtex, a filament count of 40 to 320, and a total fineness of 20 to 200 dtex. Even if the single fiber fineness is 0.5 dtex or less, it is possible to obtain a fiber having the strength and elongation shown in (5) with good operability.

[0028] The fiber of the present invention preferably has the characteristic values ​​(5) of a fiber strength of 1.5 cN / dtex or more and an elongation of 150% or less. The fiber of the present invention may be either a drawn yarn or an undrawn yarn. In the case of a drawn yarn, the strength is preferably 2 cN / dtex or more and an elongation of 20 to 60%, and in the case of an undrawn yarn (including a highly oriented undrawn yarn), the strength is preferably 2 cN / dtex or more and an elongation of 50 to 150%.

[0029] Furthermore, the fiber of the present invention has a characteristic value (3) of 5% or less in fiber diameter variation. The fiber diameter variation refers to the degree of variation in fiber diameter. The fiber diameter variation is preferably 5% or less, and more preferably 3% or less. If the fiber diameter variation exceeds 5%, the resulting filaments will have poor uniformity, which may cause streaks or the like when dyed. In addition, there is a high possibility that broken yarns will increase during spinning, resulting in poor operability. The fiber diameter fluctuation rate referred to in the present invention is measured using a KET-80V / Type C (Keisoki Kogyo Co., Ltd.) under the conditions of a sample speed of 25 m / min, a sample length of 100 m, a twister rotation speed of 3000 rpm, and a measurement mode of 1 / 2INERT.

[0030] As for the characteristic value (4), it is preferable that the fiber of the present invention has no detectable crystallization temperature when cooled from 310°C to 25°C at a rate of 20°C / min in differential scanning calorimetry. If a crystallization temperature is detected under the above conditions, various foreign matter acts as a crystal nucleus and crystallization occurs, indicating poor thermal stability. When thermal stability is poor, woven or knitted fabrics obtained using the fiber of the present invention are prone to dye spots when dyed. Furthermore, when the crystallization temperature is detected under the above conditions, it is highly likely that crystals will be generated in the fiber during the spinning process, and that these crystals will become foreign matter and cause yarn breakage. It is also highly likely that the rate of variation in the fiber diameter of the obtained fiber will increase.

[0031] The fiber of the present invention has the above-mentioned properties and is also resistant to deformation at a temperature of 310°C and a shear rate of 1000 s -1 It is preferable that the melt viscosity at 2000 kJ / min is 50 to 100 Pa·s.

[0032] Although the fiber of the present invention is made from recycled polyester as a raw material, it can satisfy the above characteristic values ​​(1) to (5) by the manufacturing method described below, even if the single yarn fineness is small.

[0033] The method for producing the fiber of the present invention will be described. In the production method of the present invention, at least one recycled polyester raw material (hereinafter sometimes simply referred to as recycled polyester raw material) consisting of a) used polyester products and b) unused polyesters generated in the process of producing polyester products is melt-kneaded with an organic phosphorus compound having two or more ester-forming functional groups in an extruder. First, the following methods (a) and (b) can be used as a method for blending the recycled polyester raw material with the phosphorus compound (Y).

[0034] (a) Direct blending of recycled polyester raw materials with phosphorus compounds (b) A method of blending recycled polyester raw materials with polyester resin (master resin) containing a high concentration of phosphorus compounds. In both of the manufacturing methods (a) and (b), for example, a batch blending method can be employed in which a screw-type extruder is used to simultaneously add the recycled polyester raw material and the phosphorus compound or a master resin containing a phosphorus compound, and then melt and knead the mixture; or a separate blending method can be employed in which the recycled polyester raw material is melted and kneaded, and then the phosphorus compound or a master resin containing a phosphorus compound is fed from another feed port of the extruder, and then melted and kneaded.

[0035] The production method of the present invention involves blending the recycled polyester raw material with the phosphorus compound (Y) as described above, melt-kneading the mixture in an extruder, passing the mixture through a metering pump, melt-spinning the mixture from a melt-spinning nozzle equipped with a spinneret, and cooling the spun fiber in a cooling cylinder and taking it up with a take-up roller. The temperature during melt-kneading in the extruder is defined as a, the temperature of the metering pump as b, the temperature of the melt spinning nozzle as c, and the temperature of the cooling cylinder as d, and the temperatures a to d must satisfy the following conditions. a is 280-290℃ b is a+5~a+10℃ c is 310-320℃ d is C-150 to C-50°C

[0036] By satisfying the above conditions, temperatures a and b allow the extruder and metering pump to be relatively low, at 300°C or below. On the other hand, by setting the temperature of the melt spinning nozzle (c) at 310-320°C, it is possible to melt impurities in the polyester resin while suppressing thermal decomposition of the resin and keeping the melt viscosity low, thereby consistently obtaining fine-fineness fibers. Furthermore, by setting the temperature of the cooling cylinder 50-150°C, especially 80-130°C, lower than the temperature of the melt spinning nozzle, uniform cooling is possible, resulting in fibers with small fineness variations and sufficient yarn quality.

[0037] If the temperatures a to d do not satisfy the above conditions, foreign matter in the resin will not melt and the melt viscosity cannot be lowered, making it difficult to consistently obtain fine fibers, and the obtained fibers will have many uneven finenesses and insufficient yarn quality. In the case of a fiber obtained by melt spinning without melting the foreign matter in the resin, the crystallization temperature is detected in differential scanning calorimetry when the temperature is lowered from 310°C to 25°C at a rate of 20°C / min. In other words, the characteristic value (4) of the fiber of the present invention is not satisfied.

[0038] In the case of drawn yarn, the melt-spun fiber produced by the above-mentioned production method is wound up at a spinning speed of 500 to 2500 m / min. The obtained undrawn yarn is drawn in a drawing device at a drawing temperature of 20 to 200°C and a draw ratio of 1.1 to 5.0, and then wound up to obtain the drawn yarn. Undrawn yarn (highly oriented undrawn yarn) can be obtained by winding up melt-spun fibers at a spinning speed of 2500 to 8000 m / min.

[0039] Furthermore, the fibers may be those which have been wound up without being drawn as described above and then false-twisted at a processing speed of 100 to 700 m / min and a draw ratio of 1.10 to 1.30.The production method of the present invention makes it possible to obtain polyester fibers which are less prone to yarn breakage in any of the steps, such as melt spinning and drawing, and which have good productivity, excellent mechanical properties and thermal stability, and little unevenness in fineness. [Example]

[0040] The present invention will now be described in detail with reference to examples, in which the measurement and evaluation methods for various properties and the like are as follows. (a) Melt viscosity The obtained recycled polyester fiber was subjected to a flow test using a flow tester "CFT-500" (Shimadzu Corporation) under the following conditions: polyester resin residence time: 1 minute, measurement temperature: 310°C, shear rate: 1000 sec -1 The measurements were carried out under the condition of a die diameter of 0.5 mm x 2 mm. (b) Phosphorus atom content in polyester fiber The obtained regenerated polyester fiber was dissolved in a mixed solvent of deuterated trifluoroacetic acid and deuterated chloroform in a volume ratio of 1 / 11, and 1H-NMR was measured using a JEOL JNM-ECZ400R / S1 NMR apparatus. The content was determined from the integrated intensity of the proton peak of each component in the obtained chart. (c) Cooling crystallization temperature The obtained regenerated polyester fiber was measured using a PerkinElmer differential scanning calorimeter DSC-7 in a nitrogen stream at a temperature range of 25 to 310°C and a temperature decrease rate of 20°C / min. (d) Variation rate of fiber diameter Using the obtained recycled polyester fiber, the measurement and calculation were carried out by the above-mentioned method. (e) Textile manufacturing operability (yarn cuts) Regarding the number of times of yarn breakage during the melt spinning process, less than three times per ton of spinning amount was rated as pass (◯), and three or more times was rated as fail (×). (f) Fiber fineness The single fiber fineness of the obtained regenerated polyester fiber was measured according to JIS L1015 8.5.1 Method B. (g) Fiber strength and elongation The obtained recycled polyester fiber was used to measure the value at which the yarn broke using a tensile tester AG-100G manufactured by Shimadzu Corporation in accordance with JIS L1013, with a gripping distance of 500 mm and a pulling speed of 500 mm / min. (h) Stained spots The obtained recycled polyester fibers were cylindrically knitted using a cylindrical knitting machine manufactured by Koike Machinery Manufacturing Co., Ltd. (300 needles, 3.5 inch diameter), and dyed under the conditions described below. The presence or absence of dye spots on the cylindrical knitted fabric after dyeing was visually inspected and evaluated on the following two-level scale. Dyeing conditions: Dyeing was carried out in a conventional manner using a dye solution of 1.0% omf Terasil Navy Blue SGL (dye for raw yarn, manufactured by Ciba Specialty Chemicals) at a bath ratio of 1:50 at 130°C for 30 minutes. ○: No staining spots ×: Dye spots occurred (i) Flame retardant The cylindrical knitted fabric obtained during the dye spot evaluation was used to evaluate flame retardancy using the limiting oxygen index (LOI) in accordance with JIS K 7201 A2. An LOI value of 26% or more was considered to pass the flame retardancy test.

[0041] Example 1 (Manufacturing of long fibers) PET bottle scraps were used as the recycled polyester raw material, and polyethylene terephthalate resin containing 30% by mass of the phosphorus compound of structural formula (a) was used as the master resin. 20 parts by mass of master resin were used for 100 parts by mass of PET bottle scraps, and these were fed into an extruder at 285°C. After passing through a metering pump at 293°C, a spinneret with 84 holes and a hole diameter of 0.15 mm was used, at 315°C. The spun yarn was passed through an oiling device to apply oil to a coating amount of 0.5% by mass, then focused with a focusing guide, entangled, and then taken up with a roller at a spinning speed of 2900 m / min and wound on a winding machine. The resulting filament (highly oriented undrawn yarn) had a density of 45 dtex / 84 f. At this time, the temperature a during melt-kneading in the extruder was 285° C., the temperature b of the metering pump was 295° C., the temperature c of the melt spinning nozzle was 315° C., and the temperature d of the cooling cylinder was 215° C. In addition, the polyester resin obtained by melt-kneading in the extruder had a recycled raw material content of 80% by mass.

[0042] Example 2 Continuous fibers were obtained in the same manner as in Example 1, except that the single fiber fineness was changed to that shown in Table 1.

[0043] Examples 3 and 4, Comparative Examples 1 and 2 Long fibers were obtained in the same manner as in Example 1, except that the amount of master resin per 100 parts by mass of PET bottle scraps was changed to that shown in Table 1.

[0044] Examples 5 to 8, Comparative Examples 3 to 9 Long fibers were obtained in the same manner as in Example 1, except that the temperature a during melt-kneading in the extruder, the temperature b of the metering pump, the temperature c of the melt spinning nozzle, and the temperature d of the cooling cylinder were changed to those shown in Table 1.

[0045] Example 9 PET bottle scraps were used as the recycled polyester raw material. The polyester raw material and the phosphorus compound were fed into an extruder at 285°C so that 6 parts by mass of the phosphorus compound represented by structural formula (a) was used per 100 parts by mass of the recycled polyester raw material. The mixture was passed through a metering pump at 293°C and then into a spinneret with a temperature of 315°C, 84 holes, and a hole diameter of 0.15 mm. The spun yarn was passed through an oiling device to apply oil to a 0.5% by mass coating amount, then focused with a focusing guide, entangled, and then taken up with a roller at a spinning speed of 2900 m / min and wound on a winding machine. The resulting fiber (highly oriented undrawn yarn) had a density of 45 dtex / 84 f. At this time, the temperature a during melt-kneading in the extruder was 285° C., the temperature b of the metering pump was 293° C., the temperature c of the melt-spinning nozzle was 315° C., and the temperature d of the cooling cylinder was 215° C. The polyester resin obtained by melt-kneading in the extruder had a recycled raw material content of 100% by mass.

[0046] Examples 10 and 11, Comparative Examples 10 and 11 Long fibers were obtained in the same manner as in Example 9, except that the amount of the phosphorus compound represented by structural formula (a) added was changed to that shown in Table 1 relative to 100 parts by mass of PET bottle scraps.

[0047] Table 1 shows the property values ​​of the recycled polyester fibers obtained in Examples 1 to 11 and Comparative Examples 1 to 11, evaluation of spinning operability, and evaluation of the obtained long fibers. [Table 1]

[0048] As is clear from Table 1, in Examples 1 to 11, recycled polyester fibers were obtained with good spinning operability, and the obtained recycled polyester fibers (long fibers) satisfied all of the above conditions (1) to (3). Therefore, the obtained continuous fibers have flame retardancy, are free of unevenness in fineness, and have excellent mechanical properties. Therefore, the tubular knitted fabrics made from these recycled polyester fibers have excellent quality and are free of uneven dyeing.

[0049] On the other hand, the recycled polyester fiber obtained in Comparative Example 1 had a phosphorus atom content as low as 670 ppm by mass, and therefore the flame retardancy of the obtained fiber was low. The recycled polyester fiber obtained in Comparative Example 2 had a high phosphorus atom content of 11,090 ppm by mass, resulting in a low melting point, which resulted in yarn breakage during spinning and poor operability. As a result, the resulting recycled polyester fiber had low strength, a high rate of variation in fiber diameter, and dyeing spots. In Comparative Example 3, the extruder temperature was as low as 275°C, so that foreign matter in the resin did not melt, and the obtained recycled polyester fiber had a temperature-lowering crystallization temperature that was detected by differential scanning calorimetry, and the rate of variation in fiber diameter was large. As a result, dyeing spots were also observed. In Comparative Example 4, the extruder temperature was as high as 295°C, which caused thermal decomposition, leading to yarn breakage during spinning and poor operability. As a result, the resulting recycled polyester fiber had low strength, a high rate of variation in fiber diameter, and dyeing spots. In Comparative Example 5, the temperature of the metering pump was as low as 285°C, so that foreign matter in the resin did not melt, and the obtained recycled polyester fiber had a temperature-low crystallization temperature that was detected by differential scanning calorimetry, and the rate of variation in fiber diameter was large. As a result, dyeing spots were also observed. In Comparative Example 6, the temperature of the metering pump was as high as 305°C, which caused thermal decomposition, leading to yarn breakage during spinning and poor operability. As a result, the resulting recycled polyester fiber had low strength, a high rate of variation in fiber diameter, and dyeing spots. In Comparative Example 7, the nozzle temperature was low at 295°C, so that foreign matter in the resin did not melt, and the obtained recycled polyester fiber had a crystallization temperature that could be detected by differential scanning calorimetry, and the fiber diameter had a large variation rate. As a result, dyeing spots were also observed. In Comparative Example 8, the nozzle temperature was as high as 325°C, which caused thermal decomposition, leading to yarn breakage during spinning and poor operability. As a result, the recycled polyester fiber obtained had low strength, a high rate of variation in fiber diameter, and dyeing spots. In Comparative Example 9, the temperature of the cooling cylinder was as low as 215°C, so that the foreign matter in the resin did not melt, and the obtained recycled polyester fiber had a temperature-lowering crystallization temperature that was detected by differential scanning calorimetry, and the rate of variation in fiber diameter was large. As a result, dyeing spots were also observed. The recycled polyester fiber obtained in Comparative Example 10 had a phosphorus atom content as low as 650 ppm by mass, and therefore the flame retardancy of the obtained fiber was low. The recycled polyester fiber obtained in Comparative Example 11 had a high phosphorus atom content of 11,370 ppm by mass, resulting in a low melting point, which resulted in yarn breakage during spinning and poor operability. As a result, the resulting recycled polyester fiber had low strength, a high rate of variation in fiber diameter, and dyeing spots.

Claims

1. A recycled polyester fiber containing 40% by mass or more of at least one recycled polyester raw material selected from a) used polyester products and b) unused polyesters generated in the process of manufacturing polyester products, and characterized in that the recycled polyester fiber satisfies all of the following (1) to (3): (1) An organic phosphorus compound having two or more ester-forming functional groups and represented by any one of the following structural formulas (a) to (d), in which the phosphorus atom content is 1,000 to 10,000 ppm by mass. (2) A long fiber having a single fiber fineness of 0.2 to 10 dtex, a filament count of 40 to 320, and a total fineness of 20 to 300 dtex. (3) The fluctuation rate of the fiber diameter is 5% or less. 【Chemical 1】

2. 2. The regenerated polyester fiber according to claim 1, having a strength of 1.5 cN / dtex or more and an elongation of 150% or less.

3. 1. A method for producing recycled polyester fibers, comprising the steps of melt-kneading at least one recycled polyester raw material selected from a) used polyester products and b) unused polyesters generated in the process of producing polyester products, and an organophosphorus compound having two or more ester-forming functional groups in an extruder, passing the mixture through a metering pump and melt-spinning the mixture through a melt-spinning nozzle equipped with a spinneret, cooling the spun fiber in a cooling cylinder, and taking it up with a take-up roller; wherein the temperature during melt-kneading in the extruder is a, the temperature of the metering pump is b, the temperature of the melt-spinning nozzle is c, and the temperature of the cooling cylinder is d, and the temperatures a to d satisfy the following conditions: a is 280 to 290°C b is a+5 to a+10°C c is 310 to 320°C d is c-150 to c-50°C

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