Recycled polyester resin and method for producing recycled polyester resin

Abstract

To provide a copolymerized polyester resin produced from recycled polyester resin as raw material.SOLUTION: A polyester resin comprising a component derived from recycled polyester resin as raw material satisfies all the following conditions (1) to (4): (1) relative to 100 mol% of total amount of total acid components, 77 to 97.5 mol% of terephthalic acid, 0.5 to 5 mol% of aromatic dicarboxylic acid having a metal sulfonate group, and 2 to 18 mol% of aliphatic dicarboxylic acid having 5 to 10 carbon atoms, (2) relative to 100 mol% of total amount of total glycol components, 80 mol% or more of ethylene glycol, and 6.5 mol% or less of diethylene glycol, (3) carboxyl end group content: 40 equivalent / t or less, and (4) average pressure rise rate: 0.6 MPa / h or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a novel recycled polyester resin and a method for producing the same. In particular, the present invention relates to a recycled polyester resin produced 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 producing polyester products, which has a low amount of foreign matter mixed in 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, making it widely used in fibers, films, plastic bottles, and other molded products. These polyester products inevitably generate waste during the manufacturing and processing stages, and are often disposed of after use. However, when incinerated, the high heat generated causes significant damage to the incinerator and shortens its lifespan. On the other hand, when not incinerated, it does not decompose and remains semi-permanently.

[0003] 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, where they are broken down into small pieces by the action of waves or tidal currents and accumulate in the bodies of marine organisms as microplastics. These microplastics then accumulate in the food chain, adversely affecting the marine ecosystem. Plastics have become a major cause of marine pollution, and there is growing concern around the world that plastics are a major cause of marine pollution, leading to a movement to reduce their use and switch to biodegradable plastics.

[0004] In light of these environmental issues, various methods of recycling are being used to reuse resources. Regarding polyester products, such as PET, in addition to recycling the polyester waste generated during the manufacturing process, methods are being considered for collecting products that were once on the market and discarded 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 widespread.

[0005] Polyester fibers are widely used due to their excellent physical properties, weather resistance, chemical resistance, and wash-and-wear properties. Various methods have been used to impart high color development to polyester fibers with cationic dyes, such as copolymerizing aromatic dicarboxylic acids having metal sulfonate groups, or to impart atmospheric dyeability, such as copolymerizing diol components (e.g., 1,4-butanediol or polyalkylene glycol) or aliphatic dicarboxylic acids (e.g., adipic acid or sebacic acid). Even for such cationic dyeable polyester fibers, the use of recycled polyester resins has been considered from the perspective of environmental concerns.

[0006] However, because recycled polyester is processed into various products, used, and then recovered, the regenerated polyester fibers obtained from recycled polyester are prone to coloring and discoloration. Furthermore, recycled polyester has large variations in physical properties such as melt viscosity, molecular weight, and crystallinity, and the physical properties are not stable between lots. Therefore, the performance of the obtained fibers is poor in uniformity, and when dyed, color spots occur within the product and color differences occur between packaging units.

[0007] Various methods have been proposed for recycling polyester using polyester scraps generated in the manufacturing process or recovered used polyester products as raw materials for recycled polyester. For example, a method of adding methanol 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 of adding EG to PET scraps to depolymerize them, and then adding methanol to recover DMT (Patent Document 2), and a method of depolymerizing PET scraps with EG to form oligomers, which are then used in a polycondensation reaction (Patent Document 3) have been proposed.

[0008] Incidentally, impurities that can become a problem when recycling PET bottles and other products include various additives added to the polyester resin, as well as items attached to the bottle itself, such as a) caps (aluminum, polypropylene, polyethylene), b) inner stoppers, c) liners (polypropylene, polyethylene), d) labels (paper, resins such as polystyrene, ink), e) adhesives, and f) printing ink.

[0009] Typically, as a pre-treatment step for the recycling process, collected PET bottles are passed through a vibrating screen to remove sand, metal, etc. The PET bottles are then washed, and colored bottles are separated before being roughly crushed. Labels and other contaminants are then removed by air separation. Furthermore, aluminum fragments from caps and other materials are removed and the PET bottle fragments are finely crushed. High-temperature alkaline washing is then used to remove components such as adhesives, proteins, and mold, and different components such as polypropylene and polyethylene are separated based on differences in specific gravity. However, even after these processes, it is difficult to completely separate and remove non-polyester resins, particularly polypropylene, polyethylene, polystyrene, etc., from PET resin.

[0010] For example, even if attempts are made to produce recycled polyester resin using the recycling methods described in Patent Documents 1 to 4, the removal of non-polyester resin-derived foreign matter is insufficient, and the amount of foreign matter is not sufficiently reduced, making it difficult to obtain a product with the same quality as virgin polyester resin. If the amount of foreign matter is not sufficiently reduced, the pressure rise rate of the filtration filter in the spinning or film-forming process is high, making long-term continuous operation impossible and significantly reducing processing operability. Furthermore, the methods described in Patent Documents 1 to 3 require significant costs for the installation, operation, and maintenance of the recovery equipment, leaving room for improvement in terms of practicality. [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] As described above, a method for obtaining recycled polyester resin from which not only various inorganic substances but also foreign substances derived from non-polyester resins have been sufficiently removed and from which various products can be obtained in the same way as virgin polyester resin has not yet been developed.

[0013] In particular, when attempting to produce fibers using polyester resin through melt spinning, the amount of foreign matter contamination and thermal stability have a significant impact on 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 a resin with a high level of foreign matter contamination or poor thermal stability is used, thread breakage is likely to occur during the melt spinning, stretching, heat treatment, and winding processes, making stable production difficult.

[0014] This problem becomes more pronounced when attempting to produce finer fibers. For example, it has not yet been realized to produce ultrafine fibers, particularly those with a single fiber fineness of 0.5 dtex or less, by melt-spinning recycled polyester resin produced from polyester waste or the like.

[0015] Therefore, a main object of the present invention is to solve the above problems and to provide a recycled polyester resin that is made from recycled polyester raw materials derived from used polyester products or recycled polyester raw materials derived from scraps and the like generated in the process of producing polyester resins and products, and that is copolymerized with an aromatic dicarboxylic acid having a metal sulfonate group, and that is particularly suitable for obtaining cationic dyeable polyester fibers. [Means for solving the problem]

[0016] As a result of extensive research in light of the problems of the prior art, the present inventors have discovered that polyester resins obtained by using recycled polyester raw materials and employing a specific manufacturing method contain a small amount of foreign matter and are recycled polyester resins having thermal stability similar to that of virgin polyester resins, and have thus completed the present invention.

[0017] That is, the present invention relates to the following recycled polyester resin and a method for producing the same. 1. A polyester resin containing a component derived from at least one recycled polyester raw material, i.e., a) used polyester products and b) unused polyester generated in the process of manufacturing polyester products, characterized in that the recycled polyester resin satisfies all of the following (1) to (4): (1) When the total amount of all acid components constituting the polyester is 100 mol%, 77 to 100 mol% 97 mole % is terephthalic acid; 1.0 up to 5 mol % is an aromatic dicarboxylic acid having a metal sulfonate group, and 2 to 18 mol % is an aliphatic dicarboxylic acid having 5 to 10 carbon atoms; (2) When the total amount of all glycol components is 100 mol%, ethylene glycol accounts for 80 mol% or more and diethylene glycol accounts for 6.5 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) 2. Fibers containing the recycled polyester resin described in item 1 above. 3. 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) unused polyester generated in the process of producing a polyester product, characterized by comprising the following steps (1) to (3): The method of claim 1 A method for producing recycled polyester resin. (1) Ethylene terephthalate oligomer, ethylene glycol, carbon number 5 to 1 0 adding the raw materials to a mixture containing the aliphatic dicarboxylic acid in an amount such that the molar ratio of total glycol components / total acid components becomes 1.05 to 1.30, and performing depolymerization under heat treatment conditions of 245 to 280°C to obtain a reaction product containing a depolymerization product; (2) passing the reaction product through a filter having a filtration particle size of 10 to 25 μm to recover the filtrate; (3) adding an aromatic dicarboxylic acid having a metal sulfonate group and a polymerization catalyst to the filtrate, and carrying out a polycondensation reaction of the depolymerization at a temperature of 260°C or higher and a reduced pressure of 1.0 hPa or lower; A method for producing a recycled polyester resin, comprising: [Effects of the Invention]

[0018] The recycled polyester resin of the present invention contains at least one recycled polyester raw material, i.e., a) used polyester products and b) unused polyesters generated in the process of manufacturing polyester products, but contains little foreign matter, has a carboxyl end group concentration and a diethylene glycol content that satisfy specific ranges, and has excellent thermal stability. Therefore, for example, in a process for obtaining fibers by melt spinning, continuous operation over a relatively long period of time is possible, and ultrafine fibers with a single fiber fineness of 0.5 dtex or less can be produced with good productivity.

[0019] Furthermore, since the recycled polyester resin of the present invention is obtained by copolymerizing a specific amount of aromatic dicarboxylic acid having a metal sulfonate group, the resulting fiber is dyeable with cationic dyes under normal pressure conditions, and has excellent mechanical properties and good dyeability equivalent to those of fibers made from virgin polyester resin (no color spots within the product or color differences between packaging units).

[0020] Furthermore, according to the method for producing the recycled polyester resin of the present invention, it is possible to obtain the recycled polyester resin of the present invention having a copolymerization component with good operability and low cost without requiring complicated steps or equipment, and this has great practical advantages. DETAILED DESCRIPTION OF THE INVENTION

[0021] The present invention will be described in detail below. The recycled polyester resin of the present invention (the resin of the present invention) contains components derived from at least one recycled polyester raw material, i.e., a) used polyester products and b) unused polyester generated in the process of manufacturing polyester products. These components constitute part of the polyester that constitutes the resin of the present invention.

[0022] 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.

[0023] 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 (polyester scraps) generated during molding and processing, cut-up materials of transitional products generated when changing brands, and cut-up materials of prototypes and defective products.

[0024] 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.

[0025] 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.

[0026] 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 pulverization, or in 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 (dispersion or solution) 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.

[0027] The recycled polyester resin of the present invention (the resin of the present invention) contains a component derived from at least one recycled polyester raw material, i.e., a) used polyester products and b) unused polyester generated in the process of manufacturing polyester products. The content of the component in the resin of the present invention is preferably 40% by mass or more, and more preferably 50% by mass or more. If the content is less than 40% by mass, the recycling rate of the unused polyester decreases. There is no particular upper limit to the content, 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 80% by mass.

[0028] When the total amount of all acid components constituting the polyester is taken as 100 mol %, the resin of the present invention comprises 77 to 97.5 mol % of terephthalic acid, 0.5 to 5 mol % of an aromatic dicarboxylic acid having a metal sulfonate group, and 2 to 18 mol % of an aliphatic dicarboxylic acid having 5 to 10 carbon atoms. By copolymerizing appropriate amounts of an aromatic dicarboxylic acid having a metal sulfonate group and an aliphatic dicarboxylic acid having 5 to 10 carbon atoms, dyeability with cationic dyes under normal pressure conditions can be imparted to the polyester resin.

[0029] If the content (copolymerization amount) of aromatic dicarboxylic acid having a metal sulfonate group is less than 0.5 mol%, the dyeing sites (number of reactive groups that react with the cationic dye) of the cationic dye in the entire polymer are insufficient, and when the resulting polyester copolymer is made into fibers, sufficient dyeing performance tends to be insufficient, which is undesirable. On the other hand, if the content exceeds 5 mol%, the melt viscosity of the polyester tends to be too high in the polycondensation step, making it difficult to sufficiently increase the degree of polymerization, which is undesirable. As a result, the material strength, such as the yarn strength when made into fibers, tends to decrease.

[0030] Examples of aromatic dicarboxylic acids having a metal sulfonate group include 5-sodium sulfoisophthalic acid, 5-potassium sulfoisophthalic acid, 5-lithium sulfoisophthalic acid, sodium sulfonaphthalenedicarboxylic acid, sodium sulfophenyldicarboxylic acid, and 5-sodium sulfoterephthalic acid, and in the present invention, 5-sodium sulfoisophthalic acid is preferably used in terms of color development with cationic dyes, operability during melt spinning, and cost. Furthermore, these acids may be used as they are, or ester-forming derivatives may be used, and in terms of operability, etc., esters with ethylene glycol are preferably used.

[0031] If the content (copolymerization amount) of the aliphatic dicarboxylic acid having 5 to 10 carbon atoms is less than 2 mol%, the dyeability with cationic dyes under normal pressure dyeing when the copolymerized polyester is made into a fiber becomes insufficient. On the other hand, if the content of the aliphatic dicarboxylic acid component exceeds 18 mol%, the thermal stability of the copolymerized polyester decreases, and the yarn strength when made into a fiber becomes low.

[0032] Examples of the aliphatic dicarboxylic acid having 5 to 10 carbon atoms include glutaric acid, adipic acid, pimelic acid, suberic acid, and sebacic acid. In the present invention, adipic acid is preferably used from the viewpoints of operability and cost during melt spinning.

[0033] The proportion of terephthalic acid in the acid component is 77 to 97.5 mol%, and preferably 85 to 90 mol%. If the proportion of terephthalic acid is less than 77 mol%, the crystallinity of the resin composition will decrease, and the melting point will be lowered, resulting in poor operability in melt spinning and drawing. On the other hand, if the proportion of terephthalic acid exceeds 97.5 mol%, the amount of copolymerization of aromatic dicarboxylic acid having a metal sulfonate group and aliphatic dicarboxylic acid having 5 to 10 carbon atoms will decrease, resulting in a reduced effect on cationic dye dyeability under normal pressure conditions.

[0034] In the resin of the present invention, examples of acid components other than terephthalic acid, aromatic dicarboxylic acid having a metal sulfonate group, and aliphatic dicarboxylic acid having 5 to 10 carbon atoms include isophthalic acid, phthalic acid, phthalic anhydride, naphthalenedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, dodecanedioic acid, and dimer acids, and two or more of these may be used in combination, or ester-forming derivatives of these acids may be used.

[0035] 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 % 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.

[0036] 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 (copolymerization amount) is 6.5 mol % or less, and preferably 1.0 to 5 mol %. In particular, in the resin of the present invention obtained by the production method of the present invention, ethylene glycol is used 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 by limiting the diethylene glycol content to 6.5 mol % or less, excellent thermal stability can be obtained. Therefore, even fibers with a small single yarn fineness can be obtained with good productivity.

[0037] In the resin of the present invention, examples of diol components other than ethylene glycol and diethylene glycol in the total glycol components include neopentyl glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexamethylenediol, 1,4-cyclohexanedimethanol, dimer diol, and ethylene oxide adducts of bisphenol A or bisphenol S.

[0038] The polymerization catalyst may be, but is not limited to, at least one of a germanium compound, an antimony compound, a titanium compound, a cobalt compound, and the like. Among these, at least one of a germanium compound and an antimony compound is particularly used. When the transparency of the resulting recycled polyester resin is important, it is preferable to use a germanium compound. Examples of the above compounds include oxides, inorganic acid salts, organic acid salts, halides, sulfides, and the like of germanium, antimony, titanium, cobalt, and the like.

[0039] The amount of the polymerization catalyst used is not particularly limited, but for example, it is 5×10 -5 It is preferable to set the concentration to 6×10 moles / unit or more. -5 The upper limit of the amount used is, for example, 1 × 10 -3 It can be about mole / unit, but is not limited to this.

[0040] In addition, since the polymerization 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 polymerization catalyst contained in the recycled polyester raw material when adding the polymerization catalyst in the polycondensation step.

[0041] During the polycondensation reaction, if necessary, the following may be added in addition to the above-mentioned polymerization catalyst: an alkali metal compound capable of suppressing the by-production of diethylene glycol; an alkaline earth metal compound capable of generating fine internal particles generated by the reaction during polymerization; a fatty acid ester capable of adjusting the melt viscosity; a hindered phenol-based antioxidant; a phosphorus compound capable of suppressing thermal decomposition of the resin; or titanium oxide for improving whiteness.

[0042] Examples of alkali metal compounds include hydroxides, organic carboxylates, alcoholates, inorganic weak acid salts, etc., and specific examples include hydroxides of sodium, potassium, and lithium, aliphatic carboxylates such as acetates, methylates, ethylates, carbonates, and borates. Among these, sodium acetate and lithium acetate are particularly preferred because they are highly effective in suppressing the by-production of diethylene glycol. The amount of alkali metal compound added is 5 × 10 per mole of the total acid components of the polyester. -4 ~3×10 -3 Within this range, the amount of diethylene glycol produced as a by-product can be suppressed.

[0043] Examples of alkaline earth metal compounds include hydroxides, organic carboxylates, alcoholates, inorganic weak acid salts, etc. Specific examples include hydroxides of beryllium, magnesium, calcium, strontium, barium, and radium, aliphatic carboxylates such as acetates, methylates, ethylates, carbonates, borates, etc. Among these, magnesium acetate and calcium acetate are preferably used because they are widely available.

[0044] 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.

[0045] 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.

[0046] Examples of phosphorus compounds that can be used include phosphorous acid, phosphoric acid, trimethyl phosphite, triphenyl phosphite, tridecyl phosphite, trimethyl phosphate, triethyl phosphate, tridecyl phosphate, and triphenyl phosphate. These compounds can be used alone or in combination of two or more.

[0047] Titanium oxide is generally used as a matting agent or white pigment for polyester, and adding an appropriate amount of titanium oxide to the resin of the present invention is preferable because it improves the whiteness of the fiber when made into a fiber and enables the production of a fabric with a 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 copolymer polyester.

[0048] 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 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.

[0049] 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 5 to 35 equivalents / t. The resin of the present invention has a carboxyl end group concentration of 40 equivalents / t or less, and therefore has excellent thermal stability, allowing fibers with small single yarn fineness to be obtained with good operability, and also has excellent yarn quality (strength, etc.) and dyeability. Excellent dyeability means that there is no color unevenness within the product or color difference between packaging units.

[0050] The resin of the present invention has the 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 indicator of the amount of foreign matter derived from various inorganic substances and foreign matter derived from non-polyester resins, with a lower average pressure increase rate indicating a lower amount of foreign matter. By having an average pressure increase rate of 0.6 MPa / h or less, it becomes possible to produce fibers having a single fiber fineness of 0.5 decitex or less, for example, by melt spinning. The lower limit of the average pressure increase rate can be, for example, about 0.01 MPa / h, but is not limited to this. If the average pressure increase rate exceeds 0.6 MPa / h, the amount of foreign matter increases, making melt spinning difficult and resulting in a decrease in yarn quality and performance, and also resulting in poor dyeability, similar to when the carboxyl end group concentration becomes too high.

[0051] 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)

[0052] By employing the production method described below, the amount of foreign matter derived from various inorganic substances and foreign matter derived from non-polyester resins can be reduced in the resin of the present invention, and therefore the average pressure increase rate measured by a pressure increase tester, which is the characteristic value of (b), can be reduced to 0.6 MPa / h or less.

[0053] The intrinsic viscosity of the recycled polyester resin of the present invention is not particularly limited, but is preferably about 0.35 to 0.80. The intrinsic viscosity is measured at 20°C using an equal weight mixture of phenol and tetrachloroethane as a solvent.

[0054] Next, a method for producing the resin of the present invention will be described. The production method of the present invention includes the steps (1) to (3), and it is preferable to carry out the steps (1) to (3) in this order. (1) a step of adding the raw materials to a mixture containing ethylene terephthalate oligomer, ethylene glycol, and an aliphatic dicarboxylic acid having 5 to 15 carbon atoms so that the molar ratio of total glycol components / total acid components is 1.05 to 1.30, and performing depolymerization under heat treatment conditions of 245 to 280°C to obtain a reaction product containing a depolymerization product; (2) passing the reaction product through a filter having a filtration particle size of 10 to 25 μm to recover the filtrate; (3) adding an aromatic dicarboxylic acid having a metal sulfonate group and a polymerization catalyst to the filtrate, and carrying out a polycondensation reaction at a temperature of 250°C or higher and under a reduced pressure of 1.0 hPa or lower;

[0055] First, in the depolymerization step (1), a recycled polyester raw material is added to a mixture containing ethylene terephthalate oligomer, ethylene glycol, and an aliphatic dicarboxylic acid having 5 to 15 carbon atoms so that the molar ratio of total glycol components / total acid components is 1.05 to 1.30, and depolymerization is carried out under heat treatment conditions of 245 to 280°C to obtain a reaction product containing a depolymerization product.

[0056] The ethylene terephthalate oligomer, ethylene glycol, and aliphatic dicarboxylic acid having 5 to 15 carbon atoms may be any known or commercially available product, or may be produced by known production methods.

[0057] In particular, the ethylene terephthalate oligomer may be, for example, an esterification reaction product of ethylene glycol and terephthalic acid. The number-average degree of polymerization of the ethylene terephthalate oligomer is not limited, but may be, for example, about 2 to 20.

[0058] The amount of ethylene terephthalate oligomer, a mixture containing ethylene terephthalate and an aliphatic dicarboxylic acid having 5 to 15 carbon atoms (hereinafter sometimes referred to as mixture E) is preferably about 20 to 80 mass % of the final recycled polyester resin (100 mass %), and more preferably 30 to 70 mass %. If the amount of ethylene terephthalate oligomer is less than the above range, the recycled polyester raw material is likely to block with itself when the recycled polyester raw material is added, which is undesirable because it places an excessive load on the mixer. On the other hand, if the amount of ethylene terephthalate oligomer is greater than the above range, no particular problems will arise in the depolymerization reaction, but the recycling rate of the finally obtained recycled polyester resin will be undesirably low.

[0059] In step (1), the proportions of the ethylene terephthalate oligomer, ethylene glycol, aliphatic dicarboxylic acid having 5 to 15 carbon atoms, and recycled polyester raw material added can be varied as appropriate depending on the copolymerization amount of the polyester resin to be ultimately obtained, but are generally preferably added in the following proportions (total of 100 parts by mass): 5 to 50 parts by mass of ethylene terephthalate oligomer, 1 to 18 parts by mass of ethylene glycol, 1 to 20 parts by mass of aliphatic dicarboxylic acid having 5 to 15 mol% of carbon atoms, and 40 to 60 parts by mass of recycled polyester raw material. In particular, the amount of ethylene glycol added is preferably 1 to 18% by mass, more preferably 3 to 15% by mass, relative to 100% by mass of the ethylene terephthalate oligomer, in order to sufficiently promote the depolymerization reaction. If the amount of ethylene glycol added exceeds 18% by mass, the ethylene terephthalate oligomer tends to solidify in the reactor, and the subsequent reaction may not be able to continue.

[0060] In the case of adding ethylene glycol or an aliphatic dicarboxylic acid having 5 to 15 mol% of carbon atoms to the ethylene terephthalate oligomer in the mixture E, it is preferable to make the temperature of the contents uniform while rotating the stirrer before adding the ethylene glycol or the aliphatic dicarboxylic acid having 5 to 15 mol% of carbon atoms in order to prevent the oligomer from solidifying.

[0061] In step (1), when the recycled polyester raw material is added to mixture E, the depolymerization reaction 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 1.30.

[0062] In the production method of the present invention, this step is important. That is, in conventional methods using recycled polyester raw materials, depolymerization is carried out using only the recycled polyester raw material, but in the present invention, the depolymerization reaction of the recycled polyester raw material is carried out in the presence of ethylene terephthalate oligomer, an aliphatic dicarboxylic acid having 5 to 15 mol% of carbon atoms, and ethylene glycol, and the recycled polyester raw material is added such that the molar ratio of ethylene terephthalate oligomer, ethylene glycol, the aliphatic dicarboxylic acid having 5 to 15 carbon atoms, and all of the components of the recycled polyester raw material is 1.05 to 1.30 (total glycol components / total acid components), and the depolymerization reaction is carried out.

[0063] By carrying out the above-described step (1), not only various inorganic substances but also foreign substances derived from non-polyester resins are efficiently precipitated, and these foreign substances can be completely filtered out in the filtration step (2).Then, in the polycondensation reaction in step (3), it becomes possible to obtain a recycled polyester resin having the characteristic values of the present invention, such as the diethylene glycol content (copolymerization amount) and the carboxyl terminal group concentration, which are not more than specific amounts, and which contains relatively little foreign substances.

[0064] Furthermore, by depolymerizing recycled polyester raw materials in the presence of ethylene terephthalate oligomer, ethylene glycol, and an aliphatic dicarboxylic acid having 5 to 15 carbon atoms, the presence of copolymerization components makes it possible to proceed with the depolymerization reaction at a lower temperature than when depolymerization is performed using only recycled polyester raw materials, which is a great advantage when carried out on an industrial scale.

[0065] In the production method of the present invention, it is desirable that the recycled polyester raw material is not decomposed into monomers by the depolymerization reaction, but rather into oligomers having repeating units of about 5 to 20. By controlling the depolymerization reaction in this way, not only various inorganic substances but also foreign substances derived from non-polyester resins are efficiently precipitated, making it possible to remove a larger amount of foreign substances.

[0066] 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 foreign matter derived from non-polyester resins does not occur efficiently, making it impossible to filter out these foreign matters completely in step (2), and foreign matters precipitate after the polycondensation reaction in step (3), resulting in a recycled polyester resin with a high average pressure rise rate.

[0067] The reactor used in the production method of the present invention 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 in which a distillation column is attached so as not to distill ethylene glycol 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).

[0068] The reaction temperature during depolymerization in step (1) is preferably set at an internal reactor temperature in the range of 245 to 280°C, more preferably 255 to 275°C. If the reaction temperature during depolymerization is less than 245°C, the reaction product solidifies, resulting in poor operability. Even if a recycled polyester resin is obtained, the diethylene glycol content and carboxyl terminal group concentration will be too high. If the reaction temperature exceeds 280°C, the diethylene glycol content and carboxyl terminal group concentration of the resulting recycled polyester resin will be too high.

[0069] The depolymerization reaction time (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 reaction product containing the depolymerized product from step (1) is passed through a filter with a filtration size of 10 to 25 μm to recover the filtrate. As described above, by carrying out the depolymerization reaction under the conditions of step (1), not only various inorganic substances but also foreign matter derived from non-polyester resins is efficiently precipitated. Therefore, by passing the product through a filter with a filtration size of 10 to 25 μm, the precipitated foreign matter can be filtered out, and a depolymer containing little foreign matter can be obtained.

[0071] If a filter with a filtration particle size larger than 25 μm is used, foreign matter in the polymer 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 threads occur. On the other hand, if a filter with a filtration particle size smaller than 10 μm is used, it is prone to clogging with foreign matter and the filter life is shortened, which is cost-effective and also reduces operability.

[0072] Furthermore, filters that can be used in step (2) of the present invention may be any common type, and examples thereof include screen changer type filters, leaf disc filters, and candle-type sintered filters.

[0073] In the production method of the present invention, the aromatic dicarboxylic acid having a metal sulfonate group and a polymerization catalyst as described above are added to the filtrate obtained through the above step (2), and a polycondensation reaction is carried out at a temperature of 260°C or higher and under a reduced pressure of 1.0 hPa or less.

[0074] The amount of the aromatic dicarboxylic acid having a metal sulfonate group added is preferably 0.5 to 5 mol % when the total amount of all acid components constituting the polyester is taken as 100 mol %.

[0075] It is preferable to use the above-mentioned polymerization catalysts, and the amount of these to be added is 5×10 -5 It is preferable to set the concentration to 6×10 moles / unit or more. -5 It is more preferable to set it to mol / unit or more. Furthermore, during the polycondensation reaction, alkali metal compounds, alkaline earth metal compounds, fatty acid esters, hindered phenol-based antioxidants, phosphorus compounds, and titanium oxide may be added in addition to the above-mentioned polymerization catalyst.

[0076] Then, in the polycondensation reaction tank, the polycondensation reaction is carried out at a temperature of 260°C or higher and under a reduced pressure of 1.0 hPa or lower. If the polycondensation reaction temperature is lower than 260°C or the pressure during the polycondensation reaction exceeds 1.0 hPa, the polycondensation reaction time becomes long, resulting in poor productivity. 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, resulting in a deterioration in color tone, and the amount of terminal groups (COOH) will also increase due to thermal decomposition. Therefore, in the present invention, the upper limit of the polycondensation reaction temperature is preferably 285° C. or lower.

[0077] The resin of the present invention may contain various additives other than the above-mentioned additives such as polymerization catalyst, antioxidant, phosphorus compound, etc., as long as the effects of the resin are not impaired. As various additives, additives such as manganese compounds such as manganese acetate, anthraquinone dye compounds, copper phthalocyanine compounds, etc. may be contained in order to suppress coloration due to thermal decomposition of the polyester resin.

[0078] The various products obtainable using the resin of the present invention are not particularly limited as long as they contain the resin of the present invention, and can be suitably used in the form of, for example, fibers, molded articles, films, etc.

[0079] 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.

[0080] 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.

[0081] 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. Furthermore, the fiber of the present invention containing the resin of the present invention is not particularly limited in the shape of the single fiber that constitutes the fiber, and may have not only a round cross section but also an irregular cross section such as a polygonal cross section. Furthermore, not only may the single fiber be formed entirely from the resin of the present invention, but the fiber may also be a composite fiber of the resin of the present invention and a polyester resin other than the resin of the present invention (such as a virgin polyester resin or a polyester resin containing another copolymer component). Examples of composite fibers include core-sheath, side-by-side, and sea-island types.

[0082] Generally, in fiber production, it is more difficult to produce multifilaments, but the fiber of the present invention uses the resin of the present invention, which has properties equivalent to those of virgin polyester, and therefore can be made into multifilaments having properties 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 / dtex, and an elongation of 10 to 400%. Among these, ultrafine fibers, which are more difficult to produce, can also be obtained.

[0083] 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 amounts. Therefore, when producing the long fibers described above, thickness variations are unlikely to occur, and highly uniform fibers can be efficiently produced. Furthermore, as described above, the resin of the present invention has an average pressure increase rate of 0.6 MPa / h or less, and is low in foreign matter. The low level of foreign matter makes it possible to produce ultrafine fibers with good operability.

[0084] Furthermore, the resin of the present invention can be dyed with cationic dyes under normal pressure conditions by copolymerizing an aromatic dicarboxylic acid component having a metal sulfonate group with an aliphatic dicarboxylic acid component having 5 to 10 carbon atoms. Since the resin has properties equivalent to those of fibers obtained from virgin polyester resin, when dyed, no color spots occur within the product or color differences occur between packaging units, and the dyeability is also excellent. [Example]

[0085] 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) 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. (b) Composition of polyester resin 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. (c) 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.

[0086] (d) 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 7 A 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

[0087] (e) Melting point The measurements were carried out using a PerkinElmer DSC-7 differential scanning calorimeter in a nitrogen stream at a temperature range of 25 to 280°C and a heating rate of 20°C / min. (f) Glass transition temperature The measurements were carried out using a PerkinElmer DSC-7 differential scanning calorimeter in a nitrogen stream at a temperature range of 25 to 280°C and a heating rate of 20°C / min.

[0088] (g) Runability of filament manufacturing (cut yarn) If the number of yarn breakages during 24 hours of continuous melt spinning was 3 times or less per day per spindle and there was no single yarn breakage during the drawing process, the result was marked as "○", and otherwise marked as "×". (h) Thread quality According to JIS L-1013, strength and elongation were measured using an autograph DSS-500 manufactured by Shimadzu Corporation at a gripping distance of 10 cm and a pulling speed of 10 cm. (i) Dyeability (L value after dyeing) The obtained multifilament yarn was knitted into a cylindrical knitted fabric using a knitting machine (manufactured by Koike Kikai Seisakusho, number of needles: 300, diameter of kettle: 3.5 inches). The resulting cylindrical knit fabric was scoured at 60°C for 20 minutes, then dyed at 100°C for 60 minutes under normal pressure under the dyeing conditions described below and air-dried. Next, a small pin tenter was used to heat-set the fabric at 150°C for 1 minute, after which a four-ply sample piece was prepared. The L value of this sample piece was measured using a color difference meter to evaluate its dyeability. The lower the L value, the darker the color of the fiber, and the better the dyeability. An L value of 35 or less was considered acceptable. The 30 dyed cylindrical knitted fabrics were visually inspected for the presence or absence of dye streaks or dye spots, and the number of non-defective fabrics having neither dye streaks nor dye spots was counted and evaluated as follows: 〇: 27 or more good quality items ×: The number of good products is 26 or less (Dyeing conditions) Dye: Astrazon Blue 0.5% omf Leveling agent: acetic acid 0.2mL / L Sodium acetate 0.2g / L Bath ratio: 1:50

[0089] Example 1 [Recycled polyester resin] A slurry of terephthalic acid (TPA) and ethylene glycol (EG) (TPA / EG molar ratio = 1 / 1.6) was supplied to an esterification reactor and reacted at a temperature of 250°C and a pressure of 50 hPa to obtain ethylene terephthalate oligomer (number average degree of polymerization: 5) with an esterification reaction rate of 95%. 41.5 parts by mass of ethylene terephthalate oligomer was charged into an esterification reactor, followed by the addition of 2.0 parts by mass of adipic acid and 4.5 parts by mass of ethylene glycol (EG) as aliphatic dicarboxylic acids to obtain a mixture E. Thereafter, 52 parts by mass of recycled polyester raw material (pelletized polyester waste generated in the process of producing polyester resin) was added via a rotary valve over a period of approximately 2 hours. At this time, the recycled polyester raw material was added so that the molar ratio of total glycol components to total acid components (hereinafter sometimes referred to as G / A) was 1.17. Thereafter, a depolymerization reaction was carried out under heat treatment conditions of 260°C for 1 hour. The obtained depolymerization product was then pressure-fed to a polycondensation reactor (hereinafter referred to as a PC can) through a candle filter with a mesh size of 20 μm set between the esterification reactor and the polycondensation reactor, and then mixed with 3.6 parts by mass of diethylene glycol ester of 5-sodium sulfoisophthalic acid as an aromatic dicarboxylic acid component having a metal sulfonate group, 0.05 parts by mass of titanium oxide, and 2.0 × 10 parts by mass of antimony trioxide as a polymerization catalyst. -4 mol / unit, germanium dioxide 5.0 × 10 -4 mol / unit, 0.4 × 10 cobalt acetate as a cobalt compound -4 mol / unit, triethyl phosphate 8.5 × 10 -4 mol / unit, and lithium acetate as an alkali metal compound is 1.5 × 10 -3 mol / unit, magnesium acetate as alkaline earth metal compound is 12.2 × 10 -4 The PC can was then decompressed and after 60 minutes, the melt polymerization reaction was carried out at a final pressure of 0.5 hPa and a temperature of 280°C for 3 hours, yielding a polyester resin with an intrinsic viscosity of 0.52 (which was then extruded into chips in the usual way).

[0090] [Production of Long Fibers] The resulting polyester resin was dried and then spun at a spinning temperature of 273°C using a spinneret with 48 nozzles, followed by cooling and oil application while winding at a speed of 1395 m / min to obtain an undrawn yarn, which was then drawn at a draw ratio of 2.5, a roll heater temperature of 80°C, a plate heater temperature of 150°C, and a drawing speed of 600 m / min, followed by winding to obtain an 84 dtex / 48 filament multifilament yarn (drawn yarn).

[0091] Examples 2 to 10, Comparative Examples 1 to 11 [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, adipic acid, 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, polyester resins were produced in the same manner as in Example 1, except that the filtration particle size of the filter used in the filtrate recovery step, the heat treatment temperature in the polymerization reaction step, and the amounts of 5-sodium sulfoisophthalic acid diethylene glycol ester and lithium acetate added were changed as shown in Table 1. [Fiber manufacturing] Using the obtained polyester resin, a multifilament yarn was obtained in the same manner as in Example 1.

[0092] Example 11 (Example of obtaining ultrafine fibers) A 45 decitex / 84 filament multifilament yarn (drawn yarn) was obtained in the same manner as in Example 1, except that the recycled polyester resin obtained in Example 2 was used and a spinneret (hole diameter 0.15 mm, number of holes 84) was used.

[0093] Example 12 Melt spinning and drawing were carried out in the same manner as in Example 11, except that the recycled polyester resin obtained in Example 6 was used, to obtain a multifilament yarn having a fineness of 45 dtex.

[0094] Comparative Examples 12 to 13 When melt spinning was carried out in the same manner as in Example 11 using the recycled polyester resins obtained in Comparative Examples 1 and 2, single yarn breakage and broken yarns frequently occurred during spinning, and multifilament yarn could not be obtained.

[0095] Table 1 shows the property values of the recycled polyester resins obtained in Examples 1 to 10 and Comparative Examples 1 to 11, and the property values and evaluation results of the multifilament yarns obtained in Examples 1 to 12, Comparative Examples 1 to 2, and 4 to 9.

[0096] [Table 1]

[0097] As is clear from Table 1, the recycled polyester resins obtained in Examples 1 to 10 had carboxyl terminal group amounts, diethylene glycol contents, and average pressure rise rates within the ranges specified in the present invention. Therefore, multifilament yarns could be obtained with good spinning operability. The fibers obtained in Examples 1 to 12 were excellent in properties such as strength and elongation, and had uniform dyeability by normal pressure dyeing. Among them, the fibers obtained in Examples 11 and 12 had a single yarn fineness of less than 0.6 dtex, but were obtained with good spinning operability and had excellent properties and dyeability equivalent to those of the fibers obtained in Examples 1 to 10.

[0098] On the other hand, in Comparative Example 1, the amount of 5-Na sulfoisophthalic acid diethylene glycol ester added was as low as 0.8 parts by mass, and therefore the amount of copolymerization of 5-Na sulfoisophthalic acid in the obtained recycled polyester resin was as low as 0.5 mol %, and therefore the obtained fiber had poor dyeability. In Comparative Example 2, the heat treatment temperature during depolymerization was as high as 285°C, and the resulting recycled polyester resin had a high diethylene glycol content and a high carboxyl end group concentration. As a result, thermal decomposition occurred when the polyester resin was made into fibers, which deteriorated operability and resulted in poor dyeability of the resulting fibers. In Comparative Example 3, the filtration particle size of the candle filter provided between the ES can and the PC can was as low as 5 μm, so clogging occurred and a polyester resin could not be obtained.

[0099] In Comparative Example 4, the filtration particle size of the candle filter placed between the ES can and the PC can was as high as 30 μm, so the obtained recycled polyester resin contained a large amount of foreign matter and had a high average pressure increase rate. As a result, when the resin was made into fibers, the nozzle pack pressure increased and yarn breakage occurred frequently, which deteriorated operability and resulted in poor strength and dyeability of the obtained fibers. In Comparative Example 5, the G / A ratio during the depolymerization reaction was as low as 1.01, and therefore the resulting recycled polyester resin had a high carboxyl end group concentration and a high average pressure rise rate. As a result, thermal decomposition occurred when the polyester resin was made into fibers, which deteriorated operability and resulted in fibers with poor strength and dyeability. In Comparative Example 6, the G / A ratio during the depolymerization reaction was as high as 1.35, and the resulting recycled polyester resin had a high diethylene glycol content. As a result, the crystallinity and thermal stability were low, the carboxyl end group concentration was high, and the operability deteriorated when the resulting fiber was made, and the resulting fiber had poor strength and dyeability.

[0100] In Comparative Example 7, the amount of adipic acid added was low at 1.0 part by mass, so the amount of adipic acid copolymerized in the obtained recycled polyester resin was low at 1.4 mol %, and the obtained fiber had poor dyeability. In Comparative Example 8, the amount of 5-Na diethylene glycol sulfoisophthalate added was as high as 9.5 parts by mass, which resulted in an excessively high melt viscosity during the polycondensation step, making it impossible to sufficiently increase the degree of polymerization. As a result, the resulting recycled polyester resin had a high diethylene glycol content and a high concentration of carboxyl end groups, which resulted in poor operability when made into fibers, and the resulting fibers were inferior in both yarn quality and dyeability. In Comparative Example 9, the amount of adipic acid added was as high as 20.0 parts by mass, and therefore the resulting recycled polyester resin had a high adipic acid content of 27.3 mol %, which resulted in low thermal stability, a high diethylene glycol content, and a high carboxyl end group concentration. This resulted in poor operability when made into fibers, and the resulting fibers were poor in both yarn quality and dyeability.

[0101] In Comparative Example 10, the heat treatment temperature during depolymerization was as low as 240° C., so the reaction product solidified and a polyester resin could not be obtained. In Comparative Example 11, the polycondensation reaction temperature was as low as 250° C., so the polycondensation reaction did not proceed and a polyester resin could not be obtained.

Claims

1. A recycled polyester resin comprising a component derived from at least one recycled polyester raw material, i.e., a) used polyester products and b) unused polyester 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) When the total amount of all acid components constituting the polyester is taken as 100 mol %, 77 to 97 mol % is terephthalic acid, 1.0 to 5 mol % is an aromatic dicarboxylic acid having a metal sulfonate group, and 2 to 18 mol % is an aliphatic dicarboxylic acid having 5 to 10 carbon atoms; (2) When the total amount of all glycol components is 100 mol%, ethylene glycol accounts for 80 mol% or more and diethylene glycol accounts for 6.5 mol% or less; (3) The carboxyl terminal 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, 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).

2. A fiber containing the recycled polyester resin according to claim 1.

3. A method for producing a recycled polyester resin according to claim 1, characterized in that the method comprises the following steps (1) to (3): a) using 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 the method comprises the following steps (1) to (3): (1) A process of adding recycled polyester raw material to a mixture containing ethylene terephthalate oligomer, ethylene glycol, and aliphatic dicarboxylic acid having 5 to 10 carbon atoms so that the molar ratio of total glycol components / total acid components is 1.05 to 1.30, and performing depolymerization under heat treatment conditions of 245 to 280°C to obtain a reaction product containing a depolymerization product. (2) A step of passing the reaction product through a filter having a filtration particle size of 10 to 25 μm and recovering the filtrate. (3) A step of adding an aromatic dicarboxylic acid having a metal sulfonate group and a polymerization catalyst to the filtrate and carrying out a polycondensation reaction of the depolymerization at a temperature of 260°C or higher and a reduced pressure of 1.0 hPa or lower.

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