Recycled polyester resin and method for producing recycled polyester resin

Abstract

To provide a copolyester resin using a recycled polyester raw material as a raw material.SOLUTION: There is provided a recycled polyester which is a polyester resin containing 80 mass% or more of a component derived from a recycled polyester raw material and satisfies all of the following (1) to (4). (1) The polyester resin contains an organic phosphorus compound having 2 or more ester-forming functional groups and a content of phosphorus atoms in the polyester resin is 1000 to 10000 ppm, (2) when a total amount of all glycol components is defined as 100 mol%, a content of ethylene glycol is 80 mol% or more and a content of diethylene glycol is 4 mol% or less, (3) carboxyl end group concentration is 40 equivalent / t or less and (4) an average pressure increase rate is 0.6 MPa / h or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a novel flame-retardant recycled polyester resin and a method for producing the same. In particular, the present invention relates to a recycled polyester resin produced using 80% by mass or more of components derived from recycled polyester raw materials, including used polyester products and unused polyester resin generated in the process of producing polyester products, which has a low level of foreign matter contamination and can be processed into various molded products in the same way as virgin polyester resin, and a method for producing the same. [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 flow 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] Various methods have been proposed for recycling recycled polyester raw materials, including a method in which methanol is added to PET scraps to decompose them into dimethylene terephthalate (hereinafter sometimes referred to as "DMT") and ethylene glycol (hereinafter sometimes referred to as "EG") (Patent Document 1), a method in which EG is added to PET scraps to depolymerize them, and then methanol is added to recover DMT (Patent Document 2), and a method in which PET scraps are depolymerized with EG to form oligomers, which are then used in a polycondensation reaction (Patent Document 3).

[0005] Furthermore, when recycling PET bottles that have already been used as products, problems can arise, such as additives added to the polyester resin and items attached to the bottle itself, such as caps (aluminum, polypropylene, polyethylene), inner stoppers and liners (polypropylene, polyethylene), labels (paper, resins such as polystyrene, ink), adhesives, and printing ink. As a pre-treatment for the recycling process, collected PET bottles are first put through a vibrating sieve to remove sand, metal, etc. The PET bottles are then washed, and colored bottles are separated before being roughly crushed. Labels and other materials are then removed using air separation. Aluminum pieces from caps and other materials are then removed and the PET bottle pieces are finely crushed. Components such as adhesives, proteins, and mold are removed using high-temperature alkaline washing, and heterogeneous components such as polypropylene and polyethylene are separated based on their specific gravity.

[0006] However, even after these steps, it has been difficult to completely separate non-polyester resins, particularly those mentioned above, such as polypropylene, polyethylene, and polystyrene, from PET resin. Therefore, even if recycled polyester resin is obtained using the recycling methods described in Patent Documents 1 to 3, the foreign matter derived from the non-polyester resin cannot be sufficiently removed, the amount of foreign matter mixed in cannot be sufficiently reduced, and a product with the same quality as virgin polyester resin cannot be obtained. Furthermore, the methods described in Patent Documents 1 to 3 require large costs for the installation, operation, and maintenance of recovery equipment, and there is room for improvement in terms of practicality.

[0007] Furthermore, the invention described in Patent Document 4 describes a method in which polyester waste is depolymerized with ethylene glycol, filtered through a filter with an average mesh size of 10 to 50 μm, and then repolymerized. It is also shown that the resulting recycled polyester resin contains little foreign matter and is easy to process. However, even with this method, the amount of foreign matter derived from non-polyester resins as described above is not sufficiently removed, and the amount of foreign matter is not sufficiently reduced.

[0008] In particular, when attempting to produce fibers by melt spinning polyester resin, the amount of contaminants present significantly affects productivity. In the melt spinning process, resin is extruded through a small-diameter nozzle, and the extruded filaments are collected on a roller. If necessary, they are stretched and heat-treated, and then wound up. In this case, if resin containing contaminants is used, thread breakage is likely to occur in all of the melt spinning, stretching, heat treatment, and winding processes, making stable production difficult. This problem becomes even more pronounced when attempting to produce finer fibers.

[0009] Furthermore, due to growing awareness of environmental issues, there is an increasing demand for recycled polyester resins that use a high percentage of recycled raw materials. In recycled polyester resins that use 80% or more recycled raw materials, or even 100% recycled raw materials, the problem of foreign matter contamination as described above becomes more pronounced, and the resins also have poor thermal stability, which naturally makes it more difficult to obtain fine fibers by melt spinning.

[0010] 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 polyesters, but from the viewpoints of performance and productivity, a method of copolymerizing a flame retardant during polyester production is common. Phosphorus compounds are considered advantageous as flame retardant substances used for this purpose from the viewpoints of flame retardancy, cost, environmental pollution, and safety. However, no polyester resins have yet been proposed that have been copolymerized with such phosphorus compounds to impart flame retardancy and that have performance equivalent to that of virgin polyester, even when made from recycled polyester. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Special Publication No. 42-8855 [Patent Document 2] Japanese Patent Publication No. 48-62732 [Patent Document 3] Japanese Patent Application Publication No. 60-248646 [Patent Document 4] Japanese Patent Application Laid-Open No. 2005-171138 Summary of the Invention [Problem to be solved by the invention]

[0012] The present invention aims to solve the above problems and provide a recycled polyester resin containing 80% by mass or more of components derived from recycled polyester raw materials, including used polyester products or scraps generated in the process of manufacturing polyester resins and products, which has flame retardancy and performance equivalent to that of virgin polyester resins and can be used to manufacture polyester products in various forms. It also aims to provide a production method by which such a recycled polyester resin of the present invention can be obtained. [Means for solving the problem]

[0013] The present inventors have conducted extensive research in light of the problems of the prior art and have discovered that by using recycled polyester raw materials and manufacturing them through a specific manufacturing process, it is possible to obtain recycled polyester resin with a low amount of foreign matter mixed in and having performance and flame retardancy equivalent to that of virgin polyester resin, thereby completing the present invention.

[0014] That is, the present invention is summarized as follows (i) to (iv).

[0015] (i) A recycled polyester resin containing 80% by mass or more of components derived from at least one recycled polyester raw material, i.e., a) used polyester products and b) unused polyester resins generated in the process of manufacturing polyester products, and characterized in that the recycled polyester resin satisfies all of the following (1) to (4): (1) An organic phosphorus compound having two or more ester-forming functional groups is contained, and the content of phosphorus atoms in the polyester resin is 1,000 to 10,000 ppm by mass; (2) When the total amount of all glycol components is 100 mol%, ethylene glycol is 80 mol% or more and diethylene glycol is 4 mol% or less, (3) The carboxyl end group concentration is 40 equivalents / t or less, (4) The average pressure rise rate is 0.6 MPa / h or less (wherein the average pressure rise rate is a value calculated by the following procedure: a pressure rise tester including an extruder and a pressure sensor is used, a stainless steel filter (nominal mesh size: 1400 mesh, weave: twill weave, vertical mesh: 165 mesh, horizontal mesh: 1400 mesh, vertical wire diameter: 0.07 mm, horizontal wire diameter: 0.04 mm, filtration particle size: 12 μm) is set at the tip of the extruder, polyester resin is melted in the extruder at 300°C, and the melt is extruded from the filter at a discharge rate of 29.0 g / min. The pressure value at the start of extrusion is defined as the "initial pressure value (MPa)," and the pressure value at the point when extrusion has been continued for 12 hours thereafter is defined as the "final pressure value (MPa)." Based on these pressure values, the average pressure rise rate is calculated using the following formula A: Average pressure rise rate (MPa / h) = (final pressure value - initial pressure value) / 12) A) (ii) A molded product containing the recycled polyester resin described in (i). (c) Fibers containing the recycled polyester resin described in (a). (iv) A method for producing a recycled polyester resin using at least one recycled polyester raw material, which is a) a used polyester product and b) an unused polyester resin generated in the process of producing a polyester product, and which is characterized by including all of the following steps (1) to (4): (1) a step of adding ethylene glycol, an organophosphorus compound having two or more ester-forming functional groups, and a recycled polyester raw material so that the molar ratio of total glycol components / total acid components is 1.05 to 1.40, and performing depolymerization under heat treatment conditions of 245 to 280°C to obtain a depolymerized polymer having a melt viscosity of 10 to 1500 mPa s; (2) passing the depolymerized product through a filter having a filtration particle size of 10 to 25 μm to recover the filtrate; (3) A step of adding a polycondensation catalyst to the filtrate and kneading to obtain a reaction product. (4) A step of subjecting the reaction product to a polycondensation reaction of the depolymerization at a temperature of 250°C or higher and a reduced pressure of 1.0 hPa or lower. [Effects of the Invention]

[0016] The recycled polyester resin of the present invention contains 80% by mass or more of a component derived from at least one recycled polyester raw material, i.e., a) used polyester products and b) unused polyester resins generated in the process of manufacturing polyester products, but the amount of foreign matter mixed in is low, and the carboxyl end group concentration and diethylene glycol content satisfy specific ranges, resulting in excellent thermal stability. Furthermore, the inclusion of a phosphorus compound also provides excellent flame retardancy. This enables relatively long-term continuous operation in processes for obtaining fibers by melt spinning, sheets or films by film formation, and molded products such as bottles, enabling the production of flame-retardant products in various forms with high productivity. Furthermore, the method for producing the recycled polyester resin of the present invention does not require complicated steps or equipment, and it is possible to obtain the recycled polyester resin of the present invention with good operability and low cost, which has great practical advantages. DETAILED DESCRIPTION OF THE INVENTION

[0017] The present invention will be described in detail below. The recycled polyester resin of the present invention (hereinafter sometimes referred to as the resin of the present invention) contains 80% by mass or more of components derived from at least one recycled polyester raw material, i.e., a) used polyester products and b) unused polyester resins generated in the process of manufacturing polyester products.

[0018] 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 resin 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 and defective products.

[0019] 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. 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 fusion between pellets during charging into the reactor or during the depolymerization reaction. Therefore, materials a) or b) above that have been crystallized by heat treatment (crystallized pellets, etc.) can be preferably used.

[0020] The properties of the recycled polyester raw materials in 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 charged into a can as a melt, if necessary.

[0021] Since the object of the present invention is to obtain a recycled polyester resin with a high usage rate of recycled polyester raw materials, the recycled polyester resin of the present invention contains 80% by mass or more, and preferably 85% by mass or more, of components derived from recycled polyester raw materials, which are at least one of a) and b) above. The recycled polyester resin of the present invention can be obtained by the production method of the present invention described below, but it is also possible to easily obtain a recycled polyester resin that is 100% derived from recycled polyester raw materials, i.e., is composed only of recycled raw materials.

[0022] The resin 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 the content of phosphorus atoms in the polyester resin is 1000 to 10000 ppm. As the phosphorus compound (Y), a compound represented by the following formula (1) is preferred in terms of reactivity in the polycondensation reaction, residual rate of the organic phosphorus compound, etc.

[0023] [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.

[0024] 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.

[0025] [ka]

[0026] By including the phosphorus compound so that the content of phosphorus atoms in the polyester resin is 1000 to 10000 ppm, flame retardancy can be imparted to the polyester resin, and flame-retardant molded articles and fibers can be obtained. The content of phosphorus atoms in the polyester resin is 1000 to 10000 ppm, and more preferably 2000 to 7000 ppm.

[0027] If the phosphorus atom content is less than 1,000 ppm, the flame retardancy will be poor, whereas if the phosphorus atom content is more than 10,000 ppm, the resin will be amorphous, which will easily cause blocking and fusion during high-temperature drying, making it impossible to use in spinning or molding processes.

[0028] The content of phosphorus atoms in the polyester resin can be adjusted to fall within the above range by adjusting the amount of the phosphorus compound (Y) contained in the polyester resin. In the present invention, methods for incorporating the phosphorus compound (Y) into the polyester resin include copolymerizing the phosphorus compound (Y) during polymerization to obtain the recycled polyester resin, and blending the phosphorus compound (Y) into the recycled polyester resin after it is obtained. More specific methods will be described in detail in the explanation of the production method.

[0029] The acid component (100 mol%) of the resin of the present invention preferably contains 80 to 98 mol% of terephthalic acid, more preferably 85 to 97 mol%. If the terephthalic acid content is less than 80 mol%, the resin composition tends to have low crystallinity and become amorphous. On the other hand, if the terephthalic acid content exceeds 98 mol%, the amount of phosphorus atoms copolymerized (content) decreases when a phosphorus compound is copolymerized, resulting in a reduced flame retardant effect.

[0030] Examples of acid components other than terephthalic acid and phosphorus compounds in the resin 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.

[0031] In the resin of the present invention, when the total amount of all glycol components is taken as 100 mol %, ethylene glycol accounts for 80 mol % or more of all glycol components, and preferably 90 mol % or more. If the ethylene glycol content is less than 80 mol %, the resulting polyester resin will have poor crystallinity and heat resistance.

[0032] Furthermore, when the total amount of all glycol components in the resin of the present invention is taken as 100 mol %, the diethylene glycol content is preferably 4 mol % or less, and more preferably 3 mol % or less. In particular, the resin of the present invention obtained by the production method of the present invention uses ethylene glycol as one of the raw materials, and diethylene glycol may be generated as a by-product during this process. The resin of the present invention has a small amount of diethylene glycol as a by-product, and since the diethylene glycol content is 4 mol % or less, it has excellent thermal stability. This makes it possible to produce molded products such as fibers, injection-molded articles, various blow-molded articles, sheets, and films with good productivity. The lower limit of the diethylene glycol content can be, for example, about 0.5 mol %, but is not limited to this.

[0033] Furthermore, examples of diol components other than ethylene glycol and diethylene glycol in the total glycol components in the 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.

[0034] The resin of the present invention contains a polycondensation catalyst and various additives that are added depending on the application. First, the polycondensation catalyst may be, but is not limited to, at least one of germanium compounds, antimony compounds, titanium compounds, cobalt compounds, zinc compounds, tin compounds, etc. Among these, it is particularly preferable to use at least one of germanium compounds and antimony compounds. When the transparency of the resulting recycled polyester resin is important, it is preferable to use a germanium compound. As each of the above compounds, oxides, inorganic acid salts, organic acid salts, halides, sulfides, etc. of germanium, antimony, titanium, cobalt, etc. may be used.

[0035] The amount of the polycondensation catalyst used is not particularly limited, but for example, it is 1×10 -5 It is preferable that the amount is 6×10 mol or more, and among these, 6×10 -5 The upper limit of the amount used is, for example, 1 × 10 -3 It can be on the molar level, but is not limited to this.

[0036] In addition, since the polycondensation catalyst contained in the recycled polyester raw material may also act as a catalyst during the polycondensation reaction, it is preferable to take into consideration the type and content of the polycondensation catalyst contained in the recycled polyester raw material when adding the polycondensation catalyst in the polycondensation step.

[0037] Examples of various additives that can be added depending on the application include fatty acid esters that can adjust the melt viscosity, hindered phenol-based antioxidants, phosphorus compounds that can suppress thermal decomposition of the resin, color adjusters that can improve the appearance of the resin, titanium compounds that improve the whiteness of the resin, and crystal nucleating agents that improve the crystallinity of the resin.

[0038] Examples of fatty acid esters include beeswax (a mixture mainly composed of myricyl palmitate), stearyl stearate, behenyl behenate, stearyl behenate, glycerin monopalmitate, glycerin monostearate, glycerin distearate, glycerin tristearate, pentaerythritol monopalmitate, pentaerythritol monostearate, pentaerythritol distearate, pentaerythritol tristearate, pentaerythritol tetrastearate, and dipentaerythritol hexastearate. Among these, glycerin monostearate, pentaerythritol tetrastearate, and dipentaerythritol hexastearate are preferred. These can be used alone or in combination of two or more.

[0039] Examples of hindered phenol antioxidants include 2,6-di-t-butyl-4-methylphenol, n-octadecyl-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate, tetrakis[methylene-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate]methane, tris(3,5-di-t-butyl-4-hydroxybenzyl)isocyanurate, 4,4'-butylidenebis-(3-methyl-6-t-butylphenol), ... Examples of suitable compounds include ethylene glycol-bis[3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionate] and 3,9-bis{2-[3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionyloxy]-1,1'-dimethylethyl}-2,4,8,10-tetraoxaspiro[5,5]undecane, but tetrakis[methylene-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate]methane is preferred from the standpoint of effectiveness and cost. These compounds can be used alone or in combination of two or more.

[0040] The phosphorus compound may be any compound other than the phosphorus compound (Y) described above, such as phosphorous acid, phosphoric acid, trimethyl phosphite, triphenyl phosphite, tridecyl phosphate, trimethyl phosphate, triethyl phosphate, tridecyl phosphate, or triphenyl phosphate. These compounds may be used alone or in combination of two or more. The content of these compounds is such that the phosphorus atom content in the polyester resin is within the range of 1,000 to 10,000 ppm.

[0041] Examples of the color tone adjuster include cobalt compounds such as cobalt acetate, manganese compounds such as manganese acetate, anthraquinone dye compounds, copper phthalocyanine compounds, etc. Among these, cobalt acetate is preferred from the viewpoints of polycondensation catalyst activity, physical properties of the resulting polyester resin, and cost. Furthermore, it is preferable that the dye contains a blue dye, a red dye, a purple dye, or the like, since this results in a good color tone.

[0042] Examples of dyes include blue dyes such as SOLVENT BLUE 104, SOLVENT BLUE 122, and SOLVENT BLUE 45, red dyes such as SOLVENT RED 111, SOLVENT RED 179, SOLVENT RED 195, SOLVENT RED 135, PIGMENT RED 263, and VATRED 41, and violet dyes such as DESPERSE VIOLET 26, SOLVENT VIOLET 13, SOLVENT VIOLET 37, and SOLVENT VIOLET 49. Among these, preferred are SOLVENT BLUE 104, SOLVENT BLUE 45, SOLVENT RED 179, SOLVENT RED 195, SOLVENT RED 135, and SOLVENT VIOLET 49, which do not contain halogens that can easily cause equipment corrosion, have relatively good heat resistance at high temperatures, and have excellent color development. These can be used alone or in combination of two or more.

[0043] As the titanium compound, titanium oxide is preferably used. Titanium oxide is generally used as a matting agent or white pigment for polyester resins, but adding an appropriate amount of titanium oxide to the resin of the present invention is preferable because it improves the whiteness of the fibers when made into fibers and allows for the production of woven or knitted fabrics with good color tone. The amount of titanium oxide added is preferably 0.05 to 5 parts by mass per 100 parts by mass of the polyester resin.

[0044] Examples of nucleating agents include carbon black, calcium carbonate, synthetic silicic acid and silicates, zinc oxide, hysite clay, kaolin, basic magnesium carbonate, mica, talc, quartz powder, diatomaceous earth, dolomite powder, titanium oxide, zinc oxide, antimony oxide, barium sulfate, calcium sulfate, alumina, calcium silicate, boron nitride, etc.; low-molecular-weight organic compounds having a metal salt of a carboxyl group; high-molecular-weight organic compounds having a metal salt of a carboxyl group; and high-molecular-weight organic compounds. Among these, mica, talc, and high-molecular-weight organic compounds are preferred. These can be used alone or in combination of two or more.

[0045] The resin of the present invention has the above-mentioned composition and also has the following characteristic values. (a) Carboxyl end group concentration is 40 equivalents / t or less (b) The average pressure rise rate measured by a pressure rise tester is 0.6 MPa / h or less. The resin of the present invention having these characteristic values ​​can be obtained by the production method of the present invention described below.

[0046] First, the resin of the present invention has the characteristic value (a) of a carboxyl terminal group concentration of 40 equivalents / t or less, preferably 30 equivalents / t or less, and more preferably 25 equivalents / t or less. The resin of the present invention has a carboxyl terminal group concentration of 40 equivalents / t or less, and therefore has excellent heat resistance, making it possible to produce molded products with excellent heat resistance with good productivity using various molding methods.

[0047] The intrinsic viscosity of the recycled polyester resin of the present invention is not particularly limited, but is usually preferably about 0.44 to 0.80. The intrinsic viscosity (IV) is measured at a temperature of 20°C using a mixture of equal masses of phenol and tetrachloroethane as a solvent.

[0048] The resin of the present invention has a characteristic value (b) of an average pressure increase rate of 0.6 MPa / h or less, preferably 0.5 MPa / h or less, and more preferably 0.4 MPa / h or less, as measured by the following method. The average pressure increase rate in the present invention is an index of the amount of foreign matter derived from various inorganic substances or non-polyester resins, with a lower average pressure increase rate indicating a lower amount of foreign matter. The lower limit of the average pressure increase rate can be, for example, about 0.01 MPa / h, but is not limited to this.

[0049] The average pressure rise rate was measured using a pressure rise tester including an extruder and a pressure sensor. A stainless steel filter (nominal mesh size: 1400 mesh, weave: twill weave, vertical mesh: 165 mesh, horizontal mesh: 1400 mesh, vertical wire diameter: 0.07 mm, horizontal wire diameter: 0.04 mm, filtration particle size: 12 μm) was attached to the tip of the extruder. The polyester resin was melted in the extruder at 300°C, and the melt was extruded from the filter at a discharge rate of 29.0 g / min. The pressure value at the start of extrusion was defined as the "initial pressure value (MPa)," and the pressure value at the end of 12 continuous hours of extrusion was defined as the "final pressure value (MPa)." The average pressure rise rate was calculated based on these pressure values ​​using the following formula A. Average pressure rise rate (MPa / h) = (final pressure value - initial pressure value) / 12) A)

[0050] By employing the production method described below, the resin of the present invention can reduce the amount of foreign matter derived from various inorganic substances and foreign matter derived from non-polyester resins, thereby suppressing the by-production of diethylene glycol and making it possible to obtain a recycled polyester resin that satisfies the characteristic values ​​(a) and (b).

[0051] The method for producing the resin of the present invention will be described. Methods for incorporating the phosphorus compound (Y) into the polyester resin include a method in which the phosphorus compound (Y) is copolymerized during polymerization to obtain the recycled polyester resin (hereinafter, sometimes referred to as Production Method 1), and a method in which the phosphorus compound (Y) is blended into the recycled polyester resin after it is obtained (hereinafter, sometimes referred to as Production Method 2).

[0052] [Manufacturing method 1] First, a description will be given of the above-mentioned Production Method 1. By Production Method 1, a phosphorus compound can be copolymerized into the acid component that constitutes the polyester resin. In the production method 1 of the present invention, it is important to carry out the steps (1) to (4) in this order. (1) a step of adding ethylene glycol, an organophosphorus compound having two or more ester-forming functional groups, and a recycled polyester raw material so that the molar ratio of total glycol components / total acid components is 1.05 to 1.40, and performing depolymerization under heat treatment conditions of 245 to 280°C to obtain a depolymerized product having a melt viscosity of 10 to 1500 mPa s; (2) passing the depolymerized product through a filter having a filtration particle size of 10 to 25 μm to recover the filtrate; (3) A step of adding a polycondensation catalyst to the filtrate and kneading to obtain a reaction product. (4) A step of subjecting the reaction product to a polycondensation reaction of the depolymerization at a temperature of 250°C or higher and a reduced pressure of 1.0 hPa or lower.

[0053] First, in the depolymerization step (1), ethylene glycol, an organophosphorus compound having two or more ester-forming functional groups, and recycled polyester raw materials are added so that the molar ratio of total glycol components to total acid components is 1.05 to 1.40, and depolymerization is carried out under heat treatment conditions of 245 to 280°C to obtain a depolymerized product with a melt viscosity of 10 to 1500 mPa·s. In the production method of the present invention, the melt viscosity of the depolymerized polymer is a value measured at the heat treatment temperature during depolymerization, and is measured using a Brookfield VISCO METER DV2T melt viscometer.

[0054] The ethylene glycol and the organophosphorus compound having two or more ester-forming functional groups to be added to the recycled polyester raw material may be those obtained by known methods or commercially available products.

[0055] In step (1), when the recycled polyester raw material is added to ethylene glycol and an organophosphorus compound having two or more ester-forming functional groups, depolymerization is carried out under heat treatment conditions of 245 to 280°C while stirring so that the molar ratio of total glycol components / total acid components becomes 1.05 to 1.40, and a depolymerization with a melt viscosity of 10 to 1500 mPa·s is obtained. This step is important in the production method of the present invention. That is, in the present invention, the depolymerization of the recycled polyester raw material is carried out in the presence of ethylene glycol and an organic phosphorus compound, and at this time, the ethylene glycol, the organic phosphorus compound, and the recycled polyester raw material are all charged in such a way that the molar ratio of the total glycol components / total acid components is 1.05 to 1.40, and then the depolymerization is carried out.

[0056] The amount of recycled polyester raw material added (amount added) is preferably 65 parts by mass or more, more preferably 70 parts by mass or more, even more preferably 80 parts by mass or more, and most preferably 85 parts by mass or more, when the total amount added is 100 parts by mass. The total amount of ethylene glycol and organic phosphorus compound added is preferably 5 to 20 parts by mass, more preferably 7 to 15 parts by mass, when the total amount added is 100 parts by mass. If the amounts of ethylene glycol and organic phosphorus compound added are less than the above, the recycled polyester raw materials are likely to block with each other when they are added, which is undesirable because it places an excessive load on the mixer.

[0057] When the content of components derived from recycled polyester raw materials in the recycled polyester resin obtained by the production method of the present invention is 80% by mass or more, depolymerization may be carried out by adding ethylene terephthalate oligomer in addition to ethylene glycol, an organic phosphorus compound, and the recycled polyester raw materials in step (1).When adding ethylene terephthalate oligomer, it is also necessary to adjust the molar ratio of total glycol components / total acid components to 1.05 to 1.40.

[0058] As the ethylene terephthalate oligomer, for example, an esterification reaction product of ethylene glycol and terephthalic acid can be suitably used. The number average degree of polymerization of the ethylene terephthalate oligomer is not limited, but can be, for example, about 2 to 20.

[0059] In the step (1), it is important that the melt viscosity of the depolymerization obtained by the above depolymerization is 10 to 1500 mPa·s. By adjusting the molar ratio of total glycol components / total acid components during depolymerization and obtaining a depolymerization product with a melt viscosity of 10 to 1500 mPa·s, not only the various inorganic substances contained in the recycled polyester raw material but also non-polyester resin-derived impurities can be efficiently precipitated, making it possible to filter out all of these impurities in step (2).

[0060] In the step (3) of adding and kneading the polycondensation catalyst and various additives depending on the application, the polycondensation catalyst and various additives can be kneaded uniformly without agglomeration. As a result, in the polycondensation reaction of step (4), it is possible to obtain a recycled polyester resin having the characteristic values ​​of the present invention, namely, the diethylene glycol content (copolymerization amount) and the carboxyl terminal group concentration, which are below a specific amount, and which has a low amount of foreign matter mixed in.

[0061] In the step (1) of the present invention, it is desirable that the recycled polyester raw material is not decomposed into monomers by the depolymerization reaction described above, but is decomposed into oligomers having about 5 to 20 repeating units.

[0062] If the molar ratio of total glycol components / total acid components during the depolymerization reaction is outside the above range, the resulting recycled polyester resin will not satisfy at least one of the carboxyl terminal group concentration and diethylene glycol content specified in the present invention, and will also have a high average pressure rise rate. This is because, when the molar ratio of total glycol components / total acid components during the depolymerization reaction is outside the above range, precipitation of various inorganic substances and non-polyester resin-derived foreign matter in the recycled polyester raw material does not occur efficiently, making it impossible to filter out these foreign matters completely in step (2), and foreign matter precipitates after the polycondensation reaction in step (4), resulting in a recycled polyester resin with a high average pressure rise rate.

[0063] Furthermore, in the depolymerization reaction step (1), if the melt viscosity of the resulting depolymerization product is less than 10 mPa·s, the viscosity will be too low, which will lead to leakage from the joint between the piping and the filter during the filtration of foreign matter, resulting in poor filtration efficiency, insufficient filtration of foreign matter, and reduced productivity.On the other hand, if the melt viscosity of the depolymerization product exceeds 1500 mPa·s, the viscosity will be too high, which will increase the load on the stirring blades during the depolymerization reaction and further increase the pressure during the filtration of foreign matter, resulting in reduced productivity.

[0064] In the production method of the present invention, the reactor used in step (1) may be a commonly used esterification reactor with no particular problem in terms of volume or shape of stirring blades. However, in order to efficiently proceed with the depolymerization reaction, it is preferable that the reactor has a structure equipped with a distillation column that prevents ethylene glycol from being distilled out of the system. When the recycled polyester raw material is charged, it is preferably stirred under normal pressure, and more preferably charged in a state purged with a small amount of inert gas (generally nitrogen gas).

[0065] Furthermore, when the depolymerization reaction is carried out using an esterification reactor, it is preferable to employ a method in which the depolymerization reaction is carried out in multiple batches by adding the recycled polyester raw material and ethylene glycol, or a method in which the recycled polyester raw material is added little by little to ethylene glycol.

[0066] When carrying out the depolymerization reaction, a melt extruder may be used instead of an esterification reactor. In the method using a melt extruder, the polymer is sealed and extruded inside the extruder, so there is no contact with air (especially oxygen), and therefore no oxidative decomposition of the polymer occurs, and problems such as color deterioration and a decrease in viscosity of the molten polymer due to an increase in carboxyl end groups do not occur. Moreover, when a melt extruder is used, the reaction can be carried out under any pressure condition, including atmospheric pressure, elevated pressure, and reduced pressure. The melt extruder may be either a single-screw extruder or a twin-screw extruder, but it is preferable to use a twin-screw extruder since the above-mentioned advantages can be more easily obtained.

[0067] Furthermore, when using a melt extruder in step (1), supplying ethylene glycol into the extruder allows the depolymerization reaction to proceed within the extruder. Adding ethylene glycol to the recycled polyester raw material while passing it through the melt extruder facilitates lowering the viscosity, allowing for smoother discharge from the nozzle. Changing the pressure conditions to lower the viscosity also allows for a lower melt temperature (the temperature of the depolymerization reaction) in the melt extruder.

[0068] The melt viscosity of the depolymerization product can be controlled within the range of the present invention by appropriately adjusting the molar ratio of total glycol components / total acid components, heat treatment temperature, heat treatment time, pressure, etc. during depolymerization.

[0069] The reaction temperature during depolymerization in step (1) is preferably set at an internal temperature of the reactor or melt extruder in the range of 245 to 280°C, and more preferably at an internal temperature of 250 to 280°C. If the reaction temperature during depolymerization is less than 245°C, a long heat treatment time is required to reduce the melt viscosity of the depolymer to 1500 mPa s or less, which reduces operability and results in the obtained recycled polyester resin exhibiting a worse color tone and a higher diethylene glycol content and carboxyl end group concentration. On the other hand, if the reaction temperature exceeds 280°C, the melt viscosity of the depolymerization product becomes too low, and the diethylene glycol content and carboxyl terminal group concentration of the obtained recycled polyester resin become high. The reaction time during depolymerization (the reaction time from the end of the addition of the recycled polyester raw material) is preferably within 4 hours, and more preferably within 2 hours from the viewpoints of suppressing the amount of diethylene glycol by-product and suppressing deterioration in the color tone of the polyester.

[0070] In step (2), the depolymerized product from step (1) is passed through a filter with a filtration size of 10 to 25 μm to filter out foreign matter. As described above, by performing the depolymerization under the conditions of step (1) to obtain a depolymerized product with a melt viscosity within a specific range, even when a large amount of recycled polyester raw material is used, not only various inorganic substances contained in these raw materials but also foreign matter derived from non-polyester resins is efficiently precipitated. Therefore, by passing the depolymerized product through a filter with a filtration size of 10 to 25 μm, all of the precipitated foreign matter can be captured by the filter, and a filtrate with a low amount of foreign matter can be obtained. If a filter with a filtration particle size larger than 25 μm is used, foreign matter in the depolymerization cannot be sufficiently removed, resulting in a large amount of foreign matter in the resulting recycled polyester resin. Therefore, when such a resin is used for spinning, pressure buildup in the nozzle pack and broken fibers occur. On the other hand, if a filter with a filtration particle size smaller than 10 μm is used, clogging by foreign matter easily occurs, shortening the filter life, resulting in cost disadvantages and poor operability.

[0071] Furthermore, filters that can be used in step (2) of the production method of the present invention may be ordinary filters without any particular problems, and examples thereof include screen changer type filters, leaf disc filters, and candle type sintered filters.

[0072] In step (3) of the production method of the present invention, the polycondensation catalyst as described above is added to the filtrate obtained through step (2) and kneaded to obtain a reaction product. In step (3), it is preferable that additives to be added depending on various applications are also added together with the polycondensation catalyst and kneaded. The additives to be added depending on various applications can be those described above. The temperature at which the kneading is carried out in the step (3) is preferably within a range of ±10° C. of the temperature at which the polycondensation reaction is carried out in the step (4).

[0073] Next, in step (4), the reaction product obtained in step (3) is subjected to a polycondensation reaction in a polycondensation reaction tank at a temperature of 250° C. or higher and under a reduced pressure of 1.0 hPa or lower. If the polycondensation reaction temperature is less than 250°C or the pressure during the polycondensation reaction exceeds 1.0 hPa, the polycondensation reaction time will be long, resulting in poor productivity or the polycondensation reaction will not proceed, making it impossible to obtain recycled polyester resin. The polycondensation reaction temperature is more preferably 270° C. or higher. However, if the polycondensation reaction temperature is too high, the polymer will be colored due to thermal decomposition, the color tone will deteriorate, and the amount of terminal groups (COOH) will increase due to thermal decomposition. Therefore, in the present invention, the upper limit of the polycondensation reaction temperature is preferably 285° C. or lower. The intrinsic viscosity of the recycled polyester resin (prepolymer) obtained here is preferably 0.44 to 0.80.

[0074] [Manufacturing method 2] Next, we will explain the above-mentioned Production Method 2. Production Method 2 is a method in which a recycled polyester resin is obtained and then a phosphorus compound (Y) is blended therewith, and at this time, the following methods (a) and (b) can be adopted. (a) Direct blending of phosphorus compounds into recycled polyester resin (b) A method of blending recycled polyester resin with polyester resin (master resin) containing a high concentration of phosphorus compounds. The recycled polyester resin used in manufacturing method 2 is a recycled polyester resin containing a component derived from at least one recycled polyester raw material, i.e., a) used polyester product and b) unused polyester resin generated in the process of manufacturing polyester products, and preferably contains 80 mol% or more of ethylene glycol, 4 mol% or less of diethylene glycol, a carboxyl terminal group concentration of 40 equivalents / t or less, and an average pressure increase rate of 0.6 MPa / h or less, when the total amount of all glycol components is 100 mol%. It is preferable to use the recycled polyester resin described in Japanese Patent Application No. 2021-132793 as such a recycled polyester resin, and it is preferably obtained by the manufacturing method of recycled polyester resin described in the same application.

[0075] In addition, in the manufacturing method (b), when considering the global environment, it is preferable to use the recycled polyester resin described in the above-mentioned Patent Application No. 2021-132793 as the polyester resin used for the master resin.

[0076] In both manufacturing methods (i) and (ii), a lump-blending method can be used in which, for example, a screw-type extruder is used to simultaneously add the recycled polyester resin and a phosphorus compound or a master resin containing a phosphorus compound to the recycled polyester resin obtained by the manufacturing method for recycled polyester resin described in Patent Application No. 2021-132793, and the mixture is melted and kneaded to form pellets; or a separate blending method can be used in which, after the recycled polyester resin is melted and kneaded, a master resin containing a phosphorus compound or a phosphorus compound is supplied from another supply port of the extruder, and the mixture is melted and kneaded to form pellets.

[0077] The resin of the present invention can be used to obtain molded articles (blow molded articles, injection molded articles, sheets, films, etc.) by employing blow molding, injection molding, stretching methods, etc., and can also be used to obtain fibers by melt spinning.

[0078] In both molded articles containing the resin of the present invention and fibers containing the resin of the present invention, the content of the resin of the present invention is preferably 50% by mass or more of the resin constituting the molded article or fiber, more preferably 60% by mass or more, even more preferably 80% by mass or more, and most preferably 100% by mass. If the proportion of the resin of the present invention in the resin constituting the molded article or fiber is less than 50% by mass, the rate of use of recycled raw materials will be low, making it difficult to produce environmentally friendly products.

[0079] In the case of molded products, the inclusion of 0.1 to 1.0 mass % of a hindered phenol-based antioxidant can prevent a decrease in intrinsic viscosity and deterioration of color tone after molding.

[0080] In the case of fibers containing the resin of the present invention, the fibers can be produced, for example, by a production method including a step of melting and spinning a raw material containing the resin of the present invention. This makes it possible to produce ultrafine fibers with a single fiber fineness of 0.8 dtex or less (preferably 0.6 to 0.3 dtex). The spinning method can be carried out under known conditions.

[0081] As described above, the resin of the present invention has a relatively low content of foreign matter and has properties equivalent to those of virgin polyester resin, and therefore, yarn breakage is unlikely to occur in any of the melt spinning, drawing / heat treatment, and winding steps, and polyester fibers can be obtained with good productivity.

[0082] The fiber of the present invention containing the resin of the present invention may be, for example, either a monofilament or a multifilament, and may be either a long fiber or a short fiber.

[0083] Furthermore, in the production of fibers, it is generally more difficult to produce multifilaments, but the fibers of the present invention can be multifilaments having characteristic values ​​such as a single yarn fineness of 0.3 to 30 decitex, a single yarn count of 2 to 300, a total fineness of 5 to 350, a strength of 1 to 5 cN / decitex, and an elongation of 10 to 400%. As described above, the resin of the present invention has excellent thermal stability due to the diethylene glycol content and carboxyl end group concentration being below specific levels, so that when the above-mentioned long fibers are produced, thickness variations are unlikely to occur, and highly uniform fibers can be produced with good operability.

[0084] Furthermore, as described above, the resin of the present invention has an average pressure increase rate of 0.6 MPa / h or less and has a low amount of foreign matter mixed in. Foreign matter present in the resin is expected to be inorganic matter or foreign matter derived from non-polyester resins, but the low amount of such foreign matter makes it possible to efficiently obtain ultrafine fibers having a single fiber fineness of 1.0 dtex or less, especially 0.6 dtex or less.

[0085] When the fibers of the present invention are short fibers, they can have, for example, properties such as a single filament fineness of 0.1 to 25.0 dtex, a strength of 0.1 to 6.0 cN / dtex, and an elongation of 20 to 500%. As described above, the resin of the present invention has excellent thermal stability due to the diethylene glycol content and carboxyl end group concentration being below specific levels. Therefore, when producing short fibers such as those described above, single filament fusion during the spinning and drawing processes is suppressed, which reduces variation in single filament fineness and allows for the production of highly uniform fibers with good operability. Furthermore, because single filament fusion during the spinning and drawing processes is suppressed, single filament dispersibility in water is improved when used in wetlaid nonwoven fabric applications.

[0086] When the fibers of the present invention are short fibers, they may be mechanically crimped short fibers for dry nonwoven fabrics with a fiber length of 30 to 100 mm, or they may be non-mechanically crimped short fibers for wet nonwoven fabrics with a fiber length of 3 to 20 mm that are treated with a hydrophilic oil.

[0087] Furthermore, as described above, the resin of the present invention has an average pressure increase rate of 0.6 MPa / h or less and has a low amount of foreign matter mixed in. Foreign matter present in the resin is expected to be inorganic matter or foreign matter derived from non-polyester resins, but the low amount of such foreign matter improves the quality and strength of products such as nonwoven fabrics obtained using the fiber of the present invention.

[0088] Furthermore, because the resin of the present invention has excellent thermal stability and a low amount of foreign matter, flow drawing can be performed in the drawing process, and ultrafine fibers with a single fiber fineness of 0.1 to 0.03 dtex can be obtained. Flow drawing involves drawing at a temperature between the glass transition temperature and the temperature-raised crystallization temperature of the resin used, making it possible to reduce the fiber diameter while suppressing the orientation of the undrawn fibers. For more stable flow drawing, it is desirable to draw in a medium at a temperature 10°C or more higher than the glass transition temperature of the polyester used. Furthermore, it is preferable to use water or steam as the medium, and more preferably, drawing is performed in warm water at a temperature of 80°C to less than 110°C or in moist heat at less than 110°C.

[0089] Furthermore, lubricant particles may be added during melt spinning of the fibers, provided that the effects of the present invention are not impaired. The lubricant is preferably inactive to polyester, and examples thereof include titanium oxide, silica, calcium carbonate, barium sulfate, and aluminum oxide. Titanium oxide is particularly preferred from the viewpoints of smoothness and particle size distribution. Adding a lubricant can further suppress fusion of single filaments during the spinning and drawing processes, thereby improving the dispersibility of single filaments in water when used for wetlaid nonwoven fabrics. The lubricant may be added at any stage of the composite fiber spinning process. Examples of the addition method include the masterbatch method and the liquid color method. However, the masterbatch method is preferred due to the stability during melt spinning and the ease of handling the colored pigment. When the masterbatch method is used, examples include a method in which the raw material pellets are metered and mixed and then melt-spun, and a method in which separately molten polymers are metered and mixed and then spun. Either method may be used.

[0090] The fibers (short fibers) of the present invention can be suitably used for nonwoven fabric applications, and nonwoven fabrics obtained using the fibers of the present invention may consist solely of the fibers of the present invention or may contain fibers other than the fibers of the present invention. For example, a nonwoven fabric may be made using the fibers of the present invention as the main fiber and fibers made of a polyester resin having a lower melting point than the resin of the present invention as the binder fiber.

[0091] The nonwoven fabric obtained using the fiber of the present invention may be dry-laid or wet-laid, and the basis weight of the nonwoven fabric is not particularly limited. When the fiber of the present invention is used as the main fiber, the nonwoven fabric may be in the form of a thermal-bonded nonwoven fabric, a needle-punched nonwoven fabric, an air-laid nonwoven fabric, a spunlace nonwoven fabric, or a wet-laid nonwoven fabric (papermaking). Since the fiber of the present invention contains a phosphorus compound, it has high flame retardancy, and the nonwoven fabric using the fiber of the present invention can be suitably used for the interior materials of automobiles and the like that are used in high-temperature regions.

[0092] An example of a method for producing a drylaid nonwoven fabric is given below. In this example, a drylaid nonwoven fabric is obtained by mixing the fiber of the present invention as the main fiber with binder fibers other than the fiber of the present invention. The ratio of the fiber of the present invention to the binder fiber when mixing can be selected according to the required properties of the nonwoven fabric, but the ratio of the fiber of the present invention is preferably about 10 to 90% by mass. These fibers (fibers that will become the constituent fibers) are fed into a carding machine and defibrated to produce a drylaid web. The obtained web is subjected to a thermal bonding treatment in a continuous heat treatment machine that performs a hot air treatment at a temperature at which the resin that makes up the binder fiber melts or softens, resulting in a drylaid nonwoven fabric in which the constituent fibers are integrated by thermal bonding.

[0093] An example of a method for producing a wetlaid nonwoven fabric is given below. As with drylaid nonwoven fabrics, the fibers of the present invention are used as the main fibers and are mixed with binder fibers other than the fibers of the present invention to obtain a wetlaid nonwoven fabric. The ratio of the fibers of the present invention to the binder fibers when mixed can be selected appropriately depending on the required properties of the nonwoven fabric, but the ratio of the fibers of the present invention is preferably about 10 to 90% by mass. These fibers (fibers that will become the constituent fibers) are agitated and defibrated using a pulp disintegrator, and then a wetlaid web is produced using a papermaking machine. The resulting web is subjected to a thermal bonding treatment in a continuous heat treatment machine that performs hot air treatment at a temperature at which the resin that makes up the binder fibers melts or softens, resulting in a wetlaid nonwoven fabric in which the constituent fibers are integrated by thermal bonding. [Example]

[0094] 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 of depolymerized polymer The depolymerization product obtained in the production step (1) was measured using a Brookfield VISCO METER DV2T melt viscometer at the same temperature as the heat treatment temperature during depolymerization. (b) Intrinsic viscosity The obtained recycled polyester resin is used, and the measurement is carried out at a temperature of 20°C using an equal mass mixture of phenol and tetrachloroethane as a solvent. (c) Composition of polyester resin and phosphorus atom content The obtained polyester resin 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 type and content of copolymerized components were determined from the integrated intensity of the proton peaks of each component in the obtained chart. (d) Carboxyl end group concentration 0.1 g of the resulting recycled polyester resin was dissolved in 10 ml of benzyl alcohol, and 10 ml of chloroform was added to the solution, followed by titration with a 1 / 10 N potassium hydroxide benzyl alcohol solution to determine the content.

[0095] (e) Average pressure rise rate measured by a pressure rise tester The obtained recycled polyester resin was melted at 300°C in an extruder, and a stainless steel twill weave filter (nominal mesh size: 1400 mesh, weaving method: twill weave, vertical mesh: 165 mesh, horizontal mesh: 1400 mesh, vertical wire diameter: 0.07 mm, horizontal wire diameter: 0.04 mm, filtration particle size: 12 μm, viscous resistance coefficient (m -1 ): 2.60 x 10 7A filter (Kamijo Seiki Co., Ltd., inertial resistance coefficient: 5.14 × 10) was set in place, and a reinforcing material (stainless steel plain weave wire mesh (nominal mesh size: 40 mesh, weave: plain weave, wire diameter: 0.21 mm, Kamijo Seiki Co., Ltd.) was layered on the back (downstream side) of the filter. The polymer discharge rate was set to 29.0 g / min, and the filter pressure was measured using a pressure rise tester (ASAHI GAGE ​​MES-Y44D type detector). The pressure rise test using the pressure rise tester was performed continuously for 12 hours, and the average pressure rise rate was calculated using the following formula from the initial pressure value (MPa) at the start of the pressure rise test (the minimum pressure value between 5 and 10 minutes after the polyester resin began to pass through the filter was defined as the initial pressure) and the final pressure value (MPa) after 12 hours had elapsed. Average pressure rise rate (MPa / h) = (final pressure value - initial pressure value) / 12

[0096] (f) Melting point, glass transition temperature The obtained recycled polyester resin was measured using a PerkinElmer differential scanning calorimeter (Diamond DSC) in a nitrogen stream at a temperature range of 25°C to 280°C, a temperature increase (decrease) rate of 20°C / min, and a sample weight of 8 mg. (g) Fiber manufacturing operability (yarn cut) The operability was evaluated based on the number of times that yarn breaks occurred during the melt spinning process. A yarn breakage rate of less than three times per ton of spinning was evaluated as pass (○), and a yarn breakage rate of three or more times was evaluated as fail (×). (h) Single fiber fineness Measurement was performed according to JIS L1015 8.5.1 Method B. (i) Texture of nonwoven fabric The texture of the resulting nonwoven fabric was visually evaluated according to the following two-level scale. ○: The distribution of constituent fibers is uniform and there are very few irregularities. ×: The distribution of constituent fibers is uneven and spots are noticeable (j) Flame retardancy of nonwoven fabrics The flame retardancy of the obtained nonwoven fabric was evaluated by limiting oxygen index (LOI) in accordance with JIS K 7201 A2, with the LOI value preferably being 26% or more.

[0097] Example 1 [Recycled polyester resin] 36.0 parts by mass of recycled polyester raw material (recycled PET flakes made from used products) were charged into an esterification reactor, followed by 2.7 parts by mass of ethylene glycol while the esterification reactor's agitator was running. Once the internal temperature of the esterification reactor (hereafter referred to as the "ES can") had stopped decreasing, 54.0 parts by mass of recycled polyester raw material (recycled PET flakes made from used products) were added in a fixed amount over approximately 30 minutes, followed by an additional 5.3 parts by mass of the phosphorus compound represented by structural formula (a) and 2.0 parts by mass of ethylene glycol. At this time, the recycled polyester raw material was added so that the molar ratio of total glycol components / total acid components (hereinafter, sometimes referred to as G / A) was 1.13. The depolymerization reaction was then carried out under heat treatment conditions at 260°C for 1 hour, yielding a depolymerization product with a melt viscosity of 50 mPa·s at 260°C. The obtained depolymerization was then pumped into a polycondensation reactor (hereinafter referred to as a PC can) through a candle filter with a mesh size of 20 μm, which was set between the esterification reactor and the polycondensation reactor. At this time, the depolymerization was passed through the filter, and the filtrate was collected. In a PC can, antimony trioxide was added to the filtrate as a polycondensation catalyst at a concentration of 2.0 × 10 -4 mol and titanium oxide were added so that the total amount was 0.37 parts by mass, and the mixture was kneaded at a temperature of 275°C to obtain a reaction product. Next, the PC can was decompressed and after 60 minutes, a polycondensation reaction was carried out at a final pressure of 0.5 hPa and a temperature of 275°C for 4 hours to obtain a recycled polyester resin (intrinsic viscosity: 0.64). [Fiber manufacturing] The resulting recycled polyester resin was melt-spun using a spinneret with 2160 holes and a hole diameter of 0.16 mm at a throughput rate of 312 g / min, a spinning temperature of 297°C, and a spinning speed of 1176 m / min. The number of yarn breaks during melt spinning was 1.5 times / ton. The resulting undrawn yarn was converged to form a 50 ktex tow, which was then stretched at a stretching temperature of 70°C and a stretch ratio of 3.2. After stretching, the tow was heat-set on a heat drum at 199°C. An oil solution mainly composed of potassium lauryl phosphate was then sprayed onto the tow, which was then heated with a heating roller at 170°C. The tow was then heated with steam and introduced into a press-type crimper to impart crimping. The tow was then cooled on a cooling conveyor without being heat-treated in a dryer, and cut to 32 mm lengths to obtain short fibers. [Production of nonwoven fabric] The obtained staple fibers were used as the main fibers, and core-sheath type heat-fused fibers manufactured by Unitika Ltd. (short fibers consisting of a core made of polyethylene terephthalate and a sheath made of copolymer polyester with a melting point of 110°C, with a single fiber fineness of 2.2 dtex and a fiber length of 51 mm) were used as the binder fibers. The mass ratio of main fiber / binder fiber was 80 / 20, and a card web (basis weight 100 g / m 2 ) was prepared at a temperature of 150°C and an air volume of 38 m 2 / min, treatment time 1 minute, heat treatment in a hot air dryer, basis weight 100g / m 2 A nonwoven fabric was produced.

[0098] Examples 2 to 13, Comparative Examples 1 to 10 [Recycled polyester resin] The depolymerization reaction was carried out in the same manner as in Example 1, except that the amounts of ethylene terephthalate oligomer, ethylene glycol, phosphorus compound, and recycled polyester raw material added during the depolymerization reaction, G / A, and heat treatment temperature were changed to those shown in Table 1. In addition, recycled polyester resins were produced in the same manner as in Example 1, except that the filtration particle size of the filter in the step of recovering the filtrate and the heat treatment temperature in the polymerization reaction step were changed to those shown in Table 1. [Fiber manufacturing] Short fibers were produced in the same manner as in Example 1 using the obtained recycled polyester resins (Examples 2 to 13, Comparative Examples 1 to 9). [Production of nonwoven fabric] A nonwoven fabric was produced in the same manner as in Example 1 using the obtained short fibers.

[0099] Table 1 shows the operability and properties of the recycled polyester resins and short fibers obtained in Examples 1 to 8 and Comparative Examples 1 to 3 and 6 to 8, and evaluations of the nonwoven fabrics.

[0100] [Table 1]

[0101] Example 14 [Recycled polyester resin] 36.4 parts by mass of recycled polyester raw material (recycled PET flakes made from used products) was charged into an esterification reactor, and then 3.6 parts by mass of ethylene glycol was added while the esterification reactor's agitator was running. Once the internal temperature of the esterification reactor (hereinafter referred to as the "ES can") stopped dropping, 54.5 parts by mass of recycled polyester raw material (recycled PET flakes made from used products) was added in a fixed amount over approximately 30 minutes, and then an additional 5.5 parts by mass of ethylene glycol was added. At this time, the recycled polyester raw material was added so that the molar ratio of total glycol components / total acid components (hereinafter sometimes referred to as "G / A") was 1.31. The depolymerization reaction was then carried out under heat treatment conditions at 260°C for 1 hour, yielding a depolymerization product with a melt viscosity of 50 mPa·s at 260°C. The obtained depolymerization was then pumped into a polycondensation reactor (hereinafter referred to as a PC can) through a candle filter with a mesh size of 20 μm, which was set between the esterification reactor and the polycondensation reactor. At this time, the depolymerization was passed through the filter, and the filtrate was collected. In a PC can, the filtrate is added with 1.0 × 10 antimony trioxide as a polycondensation catalyst for 1 mole of the acid component of the polyester resin. -4mol, and 0.2 × 10 cobalt acetate as a color adjuster. -4 mol and 0.23 parts by mass of titanium oxide were added and kneaded at a temperature of 275°C to obtain a reaction product. Next, the PC can was decompressed and after 60 minutes, a polycondensation reaction was carried out at a final pressure of 0.5 hPa and a temperature of 275°C for 2.5 hours to obtain a recycled polyester resin (A) (intrinsic viscosity: 0.65). Next, the recycled polyester resin (A) and the phosphorus compound represented by structural formula (a) were fed into an extruder at a temperature of 290°C so that 5.3 parts by mass of the phosphorus compound were used per 100 parts by mass of the obtained recycled polyester resin (A), and a polyester resin with an intrinsic viscosity of 0.62 was obtained. [Fiber manufacturing] Short fibers were produced in the same manner as in Example 1 using the obtained recycled polyester resin. [Production of nonwoven fabric] A nonwoven fabric was produced in the same manner as in Example 1 using the obtained short fibers.

[0102] Examples 15 and 16, Comparative Examples 11 and 12 [Recycled polyester resin] Recycled polyester resins were produced in the same manner as in Example 14, except that the amount of the phosphorus compound added relative to 100 parts by mass of the obtained recycled polyester resin (A) was changed to that shown in Table 2. [Fiber manufacturing] Short fibers were produced in the same manner as in Example 14 using the obtained recycled polyester resins (Examples 15 and 16, Comparative Examples 11 and 12). [Production of nonwoven fabric] Using the resulting short fibers, a nonwoven fabric was produced in the same manner as in Example 14.

[0103] Table 2 shows the operability and property values ​​of the recycled polyester resins and short fibers obtained in Examples 14 to 16 and Comparative Examples 11 and 12, and evaluations of the nonwoven fabrics.

[0104] [Table 2]

[0105] Example 17 [Recycled polyester resin] 70 parts by mass of the recycled polyester resin (A) obtained in Example 14 and 30 parts by mass of the phosphorus compound represented by structural formula (a) were fed into an extruder at a temperature of 290°C to obtain recycled polyester resin (B) containing 30% by mass of the phosphorus compound. Subsequently, 80 parts by mass of recycled polyester resin (A) and 20 parts by mass of recycled polyester resin (B) were fed into an extruder at a temperature of 290°C to obtain a polyester resin with an intrinsic viscosity of 0.62. [Fiber manufacturing] Short fibers were produced in the same manner as in Example 1 using the obtained recycled polyester resin. [Production of nonwoven fabric] A nonwoven fabric was produced in the same manner as in Example 1 using the obtained short fibers.

[0106] Examples 18 and 19, Comparative Examples 13 and 14 [Recycled polyester resin] Recycled polyester resins were produced in the same manner as in Example 17, except that the blending ratio of recycled polyester resin (A) and recycled polyester resin (B) was changed to that shown in Table 3. [Fiber manufacturing] Short fibers were produced in the same manner as in Example 17 using the obtained recycled polyester resins (Examples 18 and 19, Comparative Examples 13 and 14). [Production of nonwoven fabric] Using the resulting short fibers, a nonwoven fabric was produced in the same manner as in Example 17.

[0107] Example 20 [Recycled polyester resin] A polyester resin having an intrinsic viscosity of 0.62 was obtained in the same manner as in Example 17, except that a virgin polyester resin [polyethylene terephthalate (MA-6101-3 manufactured by Unitika Ltd.)] was used instead of the recycled polyester resin (A) when obtaining recycled polyester resin (B) in Example 17. [Fiber manufacturing] Using the obtained recycled polyester resin, short fibers were produced in the same manner as in Example 17. [Production of nonwoven fabric] Using the resulting short fibers, a nonwoven fabric was produced in the same manner as in Example 17.

[0108] Table 3 shows the operability and property values ​​of the recycled polyester resins and short fibers obtained in Examples 17 to 20 and Comparative Examples 13 to 14, and evaluations of the nonwoven fabrics.

[0109] [Table 3]

[0110] As is clear from Tables 1 to 3, the recycled polyester resins obtained in Examples 1 to 20 had phosphorus atom contents, carboxyl terminal group concentrations, diethylene glycol contents, and average pressure rise rates within the ranges specified in the present invention. Therefore, excellent operability in obtaining short fibers and excellent flame retardancy were obtained.

[0111] On the other hand, in Comparative Example 1, the phosphorus atom content was as low as 740 ppm by mass, and therefore the obtained fiber had poor flame retardancy. In Comparative Example 2, the reaction temperature during depolymerization was as high as 287°C, resulting in a high diethylene glycol content and a high carboxyl end group concentration. As a result, thermal decomposition occurred during fiber formation, which deteriorated operability, resulted in a high heat shrinkage rate for the obtained fiber, and the texture of the nonwoven fabric was poor. In Comparative Example 3, the melt viscosity of the depolymerized polymer obtained in the depolymerization step was too high, making it difficult to pass through the filter in the filtration step, and the product could not proceed to the next step. In Comparative Example 4, the melt viscosity of the depolymerized polymer obtained in the depolymerization step was too low, so that the filtrate leaked when passing through the filter in the filtration step, and the product could not proceed to the next step. In Comparative Example 5, the candle filter provided between the ES can and the PC can had a low particle size of 5 μm, which caused clogging in the filtration process, making it impossible to obtain a polyester resin. In Comparative Example 6, the filtration particle size of the candle filter installed between the ES can and the PC can was as high as 30 μm, resulting in a large amount of foreign matter being mixed in and a high average pressure increase rate. As a result, when the resulting fiber was made, the nozzle pack pressure increased and yarn breakage occurred frequently, which deteriorated operability and resulted in poor formation of the nonwoven fabric.

[0112] In Comparative Example 7, the G / A ratio during depolymerization was as low as 1.05, which resulted in insufficient depolymerization and insufficient removal of foreign matter, resulting in a high average pressure rise rate. Furthermore, the carboxyl end group concentration was high, which resulted in thermal decomposition during fiber formation, deteriorating operability and resulting in poor formation of the nonwoven fabric. In Comparative Example 8, the content of phosphorus atoms was as high as 10,980 ppm by mass, resulting in a resin with low crystallinity, which caused fusion during drying and could not be used for the fiber process.

[0113] In Comparative Example 9, the reaction temperature during depolymerization was as low as 240° C., which resulted in solidification of the polyester oligomer during the depolymerization reaction and prevented the production of a polyester resin. The heat treatment temperature in the depolymerization step was low, and the melt viscosity of the depolymer obtained in the depolymerization step was too high, making it difficult to pass through a filter in the filtration step, and the product could not proceed to the next step. In Comparative Example 10, the polycondensation temperature was as low as 240° C., so that the polycondensation reaction did not proceed and a polyester resin could not be obtained. In Comparative Example 11, the content of phosphorus atoms was as low as 730 ppm by mass, and therefore the flame retardancy of the obtained fiber was low. In Comparative Example 12, the content of phosphorus atoms was as high as 11,060 ppm by mass, resulting in a resin with low crystallinity, which caused fusion during drying and could not be used for the fiber process. In Comparative Example 13, the content of phosphorus atoms was as low as 630 ppm by mass, and therefore the flame retardancy of the obtained fiber was low. In Comparative Example 14, the content of phosphorus atoms was as high as 11,040 ppm by mass, resulting in a resin with low crystallinity, which caused fusion during drying and could not be used for the fiber process.

Claims

[Claim 1] A method for producing a recycled polyester resin that satisfies all of the following (i) to (iv), using at least one recycled polyester raw material from a) used polyester products and b) unused polyester resin generated in the process of producing polyester products, and that contains 80 mass% or more of components derived from the recycled polyester raw material, and that is characterized by including all of the following steps (1) to (4): [Recycled polyester resin] (A) The polyester resin contains an organic phosphorus compound having two or more ester-forming functional groups, and the content of phosphorus atoms in the polyester resin is 1,000 to 10,000 ppm by mass; (b) When the total amount of all glycol components is 100 mol%, ethylene glycol is 80 mol% or more and diethylene glycol is 4 mol% or less, (c) the carboxyl terminal group concentration is 40 equivalents / t or less; (D) The average pressure rise rate is 0.6 MPa / h or less (wherein the average pressure rise rate is a value calculated by the following procedure: a pressure rise tester including an extruder and a pressure sensor is used, a stainless steel filter (nominal mesh size: 1400 mesh, weave: twill weave, vertical mesh: 165 mesh, horizontal mesh: 1400 mesh, vertical wire diameter: 0.07 mm, horizontal wire diameter: 0.04 mm, filtration particle size: 12 μm) is attached to the tip of the extruder, a polyester resin is melted in the extruder at 300° C., and the melt is extruded from the filter at a discharge rate of 29.0 g / min. The pressure value at the start of extrusion is defined as the "initial pressure value (MPa)," and the pressure value at the time of subsequent continuous extrusion for 12 hours is defined as the "final pressure value (MPa)." The average pressure rise rate is calculated based on these pressure values ​​using the following calculation formula A: Average pressure increase rate (MPa / h) = (final pressure value - initial pressure value) / 12) ... A) [Process] (1) a step of adding ethylene glycol, an organic phosphorus compound having two or more ester-forming functional groups, and a recycled polyester raw material so that the molar ratio of total glycol components / total acid components is 1.05 to 1.40, and performing depolymerization under heat treatment conditions of 245 to 280°C to obtain a depolymerized polymer having a melt viscosity of 10 to 1,500 mPa s; (2) passing the depolymerized product through a filter having a filtration particle size of 10 to 25 μm to recover the filtrate; (3) A step of adding a polycondensation catalyst to the filtrate and kneading the mixture to obtain a reaction product. (4) A step of subjecting the reaction product to a polycondensation reaction of the depolymerization at a temperature of 250° C. or higher and a reduced pressure of 1.0 hPa or lower.

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