Recycled polyester resin and method for producing recycled polyester resin

Abstract

To provide a copolyester resin made from recycled polyester raw materials.SOLUTION: A polyester resin contains components derived from recycled polyester raw materials, satisfying all of the following (1)-(5): (1) of all the acid components, 70 mol% or more is terephthalic acid and 30 mol% or less is an aliphatic dicarboxylic acid component or an aliphatic lactone, (2) glycol components constituting the polyester include ethylene glycol, 1,4-butanediol and diethylene glycol, with the molar ratio of ethylene glycol and 1,4-butanediol of 80 / 20-30 / 70, (3) of all the glycol components, the total amount of ethylene glycol and 1,4-butanediol is 80-99 mol% and diethylene glycol is 0.5-4 mol%, (4) the level of carboxyl end groups is 35 eq / t or less, and (5) the average pressure rise rate is 0.6 MPa / h or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to a novel recycled polyester resin and a method for producing the recycled polyester resin. In particular, this invention relates to a recycled polyester resin and a method for producing the same, which is manufactured using recycled polyester raw materials derived from used polyester products as well as recycled polyester raw materials derived from unused polyester generated in the process of manufacturing polyester products, which has a low amount of foreign matter contamination and can be processed into various molded articles in the same way as virgin polyester resin. [Background technology]

[0002] Polyethylene terephthalate (hereinafter sometimes abbreviated as PET) is widely used in fibers, films, molded products such as PET bottles, etc., due to its high melting point, chemical resistance, and relatively low cost. These polyester products inevitably generate waste during the manufacturing or processing stages, and are often disposed of after use. However, incineration generates high heat, causing significant damage to incinerators and shortening their lifespan. On the other hand, if not incinerated, they will remain almost indefinitely because they do not decompose.

[0003] In recent years, it has become a serious problem that used polyester products, such as plastic containers discarded as waste, flow into the ocean via rivers, are broken down into microplastics by waves or currents, and accumulate in the bodies of marine organisms, becoming concentrated in the food chain and negatively impacting marine ecosystems. As a result, there is a global movement to reduce the amount of plastic used and switch to biodegradable plastics.

[0004] From the perspective of these environmental issues, recycling is being carried out in various ways 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 to collect products that have been discarded after entering the market and reuse them as raw materials. In particular, in recent years, textile products bearing the Eco Mark, which certifies that a certain recycling rate has been achieved, have become widespread.

[0005] Various methods have been proposed for recycling polyester waste generated during the manufacturing process or used polyester products as recycled polyester raw materials. For example, methods such as adding methanol to PET waste to decompose it into dimethylene terephthalate (hereinafter sometimes referred to as "DMT") and ethylene glycol (hereinafter sometimes referred to as "EG") (Patent Document 1), adding EG to PET waste to depolymerize it, and then adding methanol to recover DMT (Patent Document 2), and depolymerizing PET waste with EG to form an oligomer, which is then used in a polycondensation reaction (Patent Document 3) have been proposed.

[0006] Incidentally, impurities that become problematic when recycling PET bottles and other products once they have been manufactured include various additives added to the polyester resin, as well as components attached to the bottle itself, such as a) caps (aluminum, polypropylene, polyethylene), b) stoppers, c) liners (polypropylene, polyethylene), d) labels (paper, polystyrene or other resins, ink), e) adhesives, and f) printing inks.

[0007] Generally, the pretreatment for the recycling process involves passing the collected PET bottles through a vibrating sieve to remove sand, metal, etc. Then, the PET bottles are washed, colored bottles are separated, and then coarsely crushed. Labels and other components are then removed by air separation. Furthermore, aluminum fragments originating from caps, etc., are removed, and the PET bottle fragments are finely crushed. High-temperature alkaline washing is performed to remove components such as adhesives, proteins, and mold, and a process is carried out to separate different components such as polypropylene and polyethylene based on differences in specific gravity.

[0008] However, even after going through these processes, it is difficult to completely separate and remove non-polyester resins, particularly polypropylene, polyethylene, and polystyrene, from PET resin.

[0009] For example, even if one attempts to manufacture recycled polyester resin using the recycling methods described in Patent Documents 1 to 4, the removal of foreign matter originating from non-polyester resins may not be sufficient, and the amount of foreign matter contamination may not be sufficiently reduced, making it difficult to obtain a product with the same quality as virgin polyester resin. If the amount of foreign matter contamination is not sufficiently reduced in this way, the pressure increase rate of the filtration filter in the spinning or film-making process will be too fast, making long-term continuous operation impossible and resulting in very poor processing operability. Moreover, methods such as those described in Patent Documents 1 to 3 incur significant costs for the installation, operation, and maintenance of the recovery equipment, and there is room for improvement in terms of practicality.

[0010] Furthermore, Patent Document 5 describes a direct blow-molded hollow product made of a copolymerized polyester resin containing 90-40 mol% ethylene-2,6-naphthalate units and 10-60 mol% ethylene isophthalate units, which is shown to have excellent gas barrier properties and transparency. However, such copolymerized polyester resins have a high melting point, making molding at low temperatures impossible, and the resulting molded products lack flexibility. Moreover, recycled materials are not used as the polyester resins that form such blow-molded products, and the use of recycled polyester resins is being considered from an environmental perspective.

[0011] Furthermore, polyester resin is used in textiles, and hot-melt binder fibers are widely used to bond fibers that make up fillings for pillows and bedding, quilting, and mattresses. Copolymerized polyester resins are widely used for such binder fibers. In addition to the main fibers, the use of recycled polyester resin is also being considered for binder fibers that serve as adhesive components.

[0012] Thus, there is a great demand for copolymer polyester resins that use recycled polyester raw materials and possess performance suitable for various applications in molded products and textile products. However, a copolymer polyester resin that can adequately remove not only various inorganic substances but also foreign substances derived from non-polyester resins, and that can produce various products of the same high quality as virgin polyester resins, has yet to be obtained. [Prior art documents] [Patent Documents]

[0013] [Patent Document 1] Special Publication No. 42-8855 [Patent Document 2] Japanese Patent Application Publication No. 48-62732 [Patent Document 3] Japanese Patent Application Publication No. 60-248646 [Patent Document 4] Japanese Patent Publication No. 2005-171138 [Patent Document 5] Japanese Patent Application Publication No. 5-008283 [Overview of the project] [Problems that the invention aims to solve]

[0014] The present invention aims to solve the above problems and provide a low-melting-point recycled polyester resin that can be used in the manufacture of various types of polyester products, which is a copolymer polyester resin made from recycled polyester raw materials derived from used polyester products, or recycled polyester raw materials derived from waste generated in the process of manufacturing polyester resins and products. Furthermore, the present invention aims to provide a method for producing such a recycled polyester resin. [Means for solving the problem]

[0015] In light of the problems of the prior art, the inventors conducted extensive research and, as a result, discovered that a polyester resin obtained by using recycled polyester raw materials and employing a specific manufacturing method can achieve the above objective, thus completing the present invention.

[0016] In other words, the present invention relates to the following recycled polyester resin and a method for producing the same. 1. A recycled polyester resin comprising components derived from at least one recycled polyester raw material, a) used polyester products and b) unused polyester generated in the process of manufacturing polyester products, characterized in that it satisfies all of the following (1) to (5). (1) When the total amount of all acidic components is 100 mol%, 70 mol% or more is terephthalic acid, and 30 mol% or less is an aliphatic dicarboxylic acid component or an aliphatic lactone. (2) The glycol component constituting the polyester contains ethylene glycol, 1,4-butanediol, and diethylene glycol, and the molar ratio of ethylene glycol to 1,4-butanediol is 80 / 20 to 30 / 70. (3) When the total amount of all glycol components is 100 mol%, the total amount of ethylene glycol and 1,4-butanediol is 80-99 mol%, and diethylene glycol is 0.5-4 mol%, (4) The carboxyl terminal group concentration is 35 equivalents / t or less, (5) The average pressure increase rate is 0.6 MPa / h or less (provided that the average pressure increase rate is a value calculated by the following procedure: using a pressure increase tester including an extruder and a pressure sensor, set a stainless steel filter (nominal size mesh: 1400 mesh, weaving method: twilled dutch weave, warp mesh: 165 mesh, weft mesh: 1400 mesh, warp wire diameter: 0.07 mm, weft wire diameter: 0.04 mm, filtration particle size: 12 μm) at the tip of the extruder, melt a polyester resin at 300°C with the extruder, and when the melt is extruded at a discharge rate of 29.0 g / min from the filter, taking the pressure value at the start of extrusion as "initial pressure value (MPa)" and the pressure value at the time point after continuous extrusion for 12 hours as "final pressure value (MPa)", the average pressure increase rate is calculated by the following formula A based on these pressure values: Average pressure increase rate (MPa / h) = (final pressure value - initial pressure value) / 12)···A) 2. The recycled polyester resin according to Item 1, which has a melting point of 150 to 200°C. 3. A molded article containing the recycled polyester resin according to Item 1 or 2. 4. A fiber containing the recycled polyester resin according to Item 1 or 2. 5. A method for producing a polyester resin comprising a component derived from at least one recycled polyester raw material selected from a) used polyester products and b) unadopted polyester generated in the process of producing polyester products, the method comprising the following steps (1) to (3): (1) a step of adding the raw material to a mixture containing ethylene terephthalate oligomer and ethylene glycol such that the molar ratio of total glycol components to 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 depolymerized product, (2) a step of passing the reaction product through a filter having a filtration particle size of 10 to 25 μm and recovering a filtrate, (3) A step of adding an aliphatic dicarboxylic acid or an aliphatic lactone, and 1,4-butanediol to the filtrate, performing depolymerization under heat treatment conditions of 220 to 255°C, then adding a polymerization catalyst, and subjecting the depolymerized product to a polycondensation reaction at a temperature of 220 to 255°C under a reduced pressure of 1.0 hPa or less Effects of the Invention

[0017] The recycled polyester resin of the present invention is excellent in thermal stability because it uses a high proportion of at least one recycled polyester raw material selected from a) used polyester products and b) non-adopted polyester generated in the process of producing polyester products, has a small amount of foreign matter contamination, and the carboxyl end group concentration and the like are controlled within a specific range.

[0018] Therefore, for example, in a process of obtaining fibers by melt spinning, continuous operation over a relatively long period of time can be achieved, and fibers having the same characteristic values as those obtained when using virgin polyester resin can be produced with good productivity.

[0019] Furthermore, although it is a recycled polyester resin, it is a copolymerized polyester resin containing a copolymerization component and has a low melting point, so that molded articles such as bottles requiring transparency can be molded at low temperature, and it can also be suitably used for fiber applications requiring adhesiveness. Mode for Carrying Out the Invention

[0020] Hereinafter, the present invention will be described in detail. 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 of a) used polyester products and b) unused polyester generated in a process of producing polyester products. These components form part of the polyester constituting the resin of the present invention.

[0021] Examples of used polyester products as described in a) above include polyester molded products (including fibers) that have been on the market and then collected after use. Typical examples include containers or packaging materials such as PET bottles.

[0022] Unused polyester generated in the process of manufacturing the polyester products described in b) above is polyester that did not make it into a product. Examples include resin pellets that do not meet specifications, materials that are no longer needed during molding, fragments that are cut during molding, waste generated during molding or processing, cut pieces of transitional products generated when a brand name is changed, and cut pieces of prototypes or defective products.

[0023] The forms of a) and b) described above are not limited, and may be further processed by crushing, cutting, or other methods to form pellets as needed, or they may be melted and then formed into pellets. A) and b) described above may be used individually, or a mixture of both may be used.

[0024] Furthermore, the recycled polyester raw materials in a) and b) above may be either crystalline or amorphous. Therefore, for example, amorphous polyester scrap pellets that have not been heat-treated, heat-treated crystalline pellets, or a mixture of crystalline and amorphous pellets can be used. In the present invention, it is particularly preferable to use crystalline recycled polyester raw materials in order to prevent the pellets from fusing together when being placed in a can or during the depolymerization reaction. Therefore, materials from a) or b) above that have been crystallized by heat treatment (crystallized pellets, etc.) can be suitably used.

[0025] Furthermore, the properties of the recycled polyester raw materials described in a) and b) above are not limited; they may remain in the forms described in a) and b), or they may be processed further by cutting, crushing, etc. to obtain shredded pieces, crushed material (powder), etc., or solid forms such as molded bodies (pellets, etc.) formed from these. More specifically, examples include pellets obtained by cooling and cutting molten polyester waste, and shredded pieces obtained by finely cutting polyester molded products such as PET bottles. In addition, they may also be in liquid form obtained by dispersing or dissolving the above-mentioned shredded pieces, crushed material (powder), etc., in a solvent. When manufacturing polyester products using these raw materials, they may be melted at a temperature above their melting point and added to the can as a molten liquid if necessary.

[0026] The recycled polyester resin of the present invention (the present invention resin) contains components derived from at least one recycled polyester raw material, a) used polyester products and b) unused polyester generated in the process of manufacturing polyester products. Preferably, the content of the components is 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 unused polyester decreases. The upper limit of the above content is not particularly limited, but according to the manufacturing method of the present invention described later, it is possible to easily obtain recycled polyester resin with a recycled polyester raw material content of 40 to 80% by mass.

[0027] In the present invention, when the total amount of all acidic components constituting the polyester is taken as 100 mol%, 70 mol% or more is terephthalic acid, and 30 mol% or less is aliphatic dicarboxylic acid or aliphatic lactone. The acidic component is mainly terephthalic acid, with aliphatic dicarboxylic acid or aliphatic lactone as a copolymer component. However, the present invention also includes resins that do not contain aliphatic dicarboxylic acid or aliphatic lactone as a copolymer component.

[0028] Aliphatic dicarboxylic acids or aliphatic lactones have the effect of lowering the melting point of the resin of the present invention. The copolymerization amount of aliphatic dicarboxylic acids or aliphatic lactones is 30 mol% or less, and more preferably 20 mol% or less. If the copolymerization amount of aliphatic dicarboxylic acids or aliphatic lactones exceeds 30 mol%, the melting point becomes too low (below 150°C), and the heat resistance and other properties decrease, which is undesirable. On the other hand, it is preferable that the aliphatic dicarboxylic acids or aliphatic lactones are contained (copolymerized) in an amount of 5 mol% or more, and if it is less than 5 mol%, the effect of lowering the melting point becomes poor.

[0029] Specific examples of aliphatic dicarboxylic acid components include adipic acid, azelaic acid, sebacic acid, dodecanediic acid, hexadecanedioic acid, and eicosanedioic acid. Aliphatic lactones include lactones having 4 to 11 carbon atoms and homopolymers or copolymers of two or more of these, with ε-caprolactone and δ-barrelactone being particularly preferred aliphatic lactones.

[0030] In the resin of the present invention, acid components other than terephthalic acid, aliphatic dicarboxylic acids, and aliphatic lactones include phthalic acid, 5-sodium sulfisophthalic acid, phthalic anhydride, naphthalenedicarboxylic acid, and two or more of these may be used in combination, or ester-forming derivatives of these acids may be used.

[0031] On the other hand, the glycol component in the resin of the present invention includes ethylene glycol (hereinafter sometimes abbreviated as EG), 1,4-butanediol (hereinafter sometimes abbreviated as BD), and diethylene glycol (hereinafter sometimes abbreviated as DEG). When the total amount of all glycol components is 100 mol%, the total amount of EG and BD is 80 to 99 mol%, and preferably 90 mol% or more. If the content of both components is less than 80 mol%, the resulting polyester resin will have inferior crystallinity and heat resistance.

[0032] The molar ratio of the two (EG / BD) is preferably 80 / 20 to 30 / 70, with 70 / 30 to 40 / 60 being particularly desirable. If the ratio deviates from this range, the melting point of the resulting polyester resin will be high (exceeding 200°C). Furthermore, the crystallinity of the polyester resin will deteriorate, tetrahydrofuran will be formed during the polycondensation reaction, and the thermal stability of the polyester will worsen. As a result, blow molding cannot be performed at low temperatures, and even if blow molding is performed at high temperatures, resin drawdown will occur, making molding difficult, or resulting in molded products with uneven thickness. When used as a binder fiber, the high melting point means that sufficient thermal adhesion cannot be obtained with low-temperature heat treatment, while high-temperature heat treatment causes thermal decomposition and a decrease in strength.

[0033] Furthermore, in the resin of the present invention, when the total amount of all glycol components is 100 mol%, the diethylene glycol content is 0.5 to 4 mol%, and preferably 0.5 to 3 mol%. In particular, in the resin of the present invention obtained by the manufacturing method of the present invention, ethylene glycol is used as one of the raw materials, and diethylene glycol may be produced as a by-product. The resin of the present invention has a small amount of by-product diethylene glycol, and because the diethylene glycol content is 0.5 to 4 mol%, it has excellent thermal stability. For this reason, it is possible to obtain molded products such as fibers, injection molded articles and various blow molded articles, sheets, and films with high productivity.

[0034] Furthermore, in the resin of the present invention, diol components other than ethylene glycol, 1,4-butanediol, and diethylene glycol in the total glycol components can be, for example, neopentyl glycol, 1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, dimergol, ethylene oxide adduct of bisphenol S, ethylene oxide adduct of bisphenol A, etc.

[0035] While not limited to specific types, at least one of the following can be used as the polycondensation catalyst: for example, germanium compounds, antimony compounds, titanium compounds, and cobalt compounds. Among these, at least one titanium compound and a germanium compound is particularly preferred. When 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, and sulfides of germanium, antimony, titanium, and cobalt.

[0036] The amount of polycondensation catalyst used is not particularly limited, but for example, 2 × 10⁻¹⁶ per mole of the acid component of the resulting polyester resin -5 It is preferable to have a mole / unit or higher, and among those, 5 × 10 -5 It is more preferable to use a value of moles / unit or more. The upper limit of the above usage amount is, for example, 5 × 10 -4 It can be expressed as approximately moles / unit, but is not limited to this.

[0037] Furthermore, since polymerization catalysts contained in recycled polyester raw materials may also act as catalysts during the polycondensation reaction, it is preferable to consider the type and amount of polymerization catalyst contained in the recycled polyester raw materials when adding polymerization catalysts in the polycondensation process.

[0038] Furthermore, during the polycondensation reaction, if necessary, fatty acid esters, hindered phenol-based antioxidants, phosphorus compounds that can suppress the thermal decomposition of the resin, and titanium dioxide to improve whiteness can be added in conjunction with the polycondensation catalyst mentioned above.

[0039] 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 individually or in combination of two or more.

[0040] 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), and tri Ethylene glycol-bis[3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionate], 3,9-bis{2-[3-(3-t-butyl-4-hydroxy-5-methylphenyl)propionyloxy]-1,1'-dimethylethyl}-2,4,8,10-tetraoxaspiro[5,5]undecane, etc., are used, but tetrakis[methylene-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate]methane is preferred in terms of effectiveness and cost. These can be used individually or in combination of two or more.

[0041] Examples of phosphorus compounds that can be used include phosphorous acid, phosphoric acid, trimethyl phosphite, triphenyl phosphite, tridecyl phosphite, trimethyl phosphate, tridecyl phosphate, and triphenyl phosphate. These can be used individually or in combination of two or more.

[0042] Titanium dioxide is commonly used as a matting agent and white pigment for polyester, but the addition of an appropriate amount of titanium dioxide to the resin of the present invention is preferable because it improves the whiteness of the fibers and allows for the acquisition of woven or knitted fabrics with good color tones. The amount of titanium dioxide to be added is preferably 0.05 to 5 parts by mass per 100 parts by mass of copolymerized polyester.

[0043] The resin of the present invention has the above-described composition and the characteristic values ​​shown below. (i) The carboxyl terminal group concentration is 35 equivalents / t or less. (b) Average boosting rate is 0.6 MPa / h or less The resin of the present invention having these characteristic values ​​can be obtained by the manufacturing method of the present invention described later.

[0044] The resin of the present invention has a carboxyl terminal group concentration of 35 equivalents / t or less, preferably 32 equivalents / t or less, and most preferably 30 equivalents / t or less, as a characteristic value of (a). By setting the carboxyl terminal group concentration to 35 equivalents / t or less, it has excellent heat resistance, and it is possible to obtain molded products with excellent heat resistance by various molding methods. The lower limit of the carboxyl terminal group concentration can be, for example, about 5 equivalents / t, but is not limited to this.

[0045] The resin of the present invention has a characteristic value (b) in which the average pressure increase rate, measured by the following method, is 0.6 MPa / h or less, preferably 0.5 MPa / h or less, and more preferably 0.4 MPa / h or less. The average pressure increase rate in the present invention is an indicator of the amount of foreign matter derived from various inorganic materials and foreign matter derived from non-polyester resins, and the smaller the average pressure increase rate, the smaller the amount of foreign matter. By having an average pressure increase rate of 0.6 MPa / h or less, a polyester resin with a small amount of foreign matter can be obtained, making it possible to obtain molded products and fibers with high productivity in blow molding and fiber manufacturing. The lower limit of the average pressure increase rate can be, for example, about 0.01 MPa / h, but is not limited to this.

[0046] The method for measuring the average pressure increase rate involves using a pressure test machine including an extruder and a pressure sensor. A stainless steel filter (nominal mesh size: 1400 mesh, weave: twill weave, warp mesh: 165 mesh, weft mesh: 1400 mesh, warp wire diameter: 0.07 mm, weft wire diameter: 0.04 mm, filtration particle size: 12 μm) is set at the tip of the extruder. Polyester resin is melted at 300°C in the extruder, and the molten material is extruded from the filter at a discharge rate of 29.0 g / min. The pressure value applied to the filter at the start of extrusion is defined as the "initial pressure value (MPa)," and the pressure value after continuous extrusion for 12 hours is defined as the "final pressure value (MPa)." Based on these pressure values, the average pressure increase rate is calculated using the following formula A. Average pressure increase rate (MPa / h) = (Final pressure value - Initial pressure value) / 12) ... A)

[0047] By employing the manufacturing method described later, the resin of the present invention can reduce the amount of foreign matter derived from various inorganic materials and foreign matter derived from non-polyester resins, making it possible to achieve a characteristic value of (b), the average pressure increase rate measured by a pressure increase tester, of 0.6 MPa / h or less.

[0048] Furthermore, the resin of the present invention has the property (c) of having a melting point of 150 to 200°C, preferably 150 to 190°C, and even more preferably 150 to 175°C. By setting the melting point within the above range, when used as a binder fiber, the melting point is lower than that of ordinary polyester resin, which allows for a lower heat treatment temperature during bonding and also results in good heat adhesion. When obtaining molded products such as bottles, molding can be done at low temperatures.

[0049] Next, the method for manufacturing the resin of the present invention will be described. The manufacturing method of the present invention includes steps (1) to (3), and it is important to perform the steps shown in (1) to (3) in order. (1) A step of obtaining a reaction product containing a depolymer by adding the recycled polyester raw material to a mixture containing ethylene terephthalate oligomer and ethylene glycol, so that the molar ratio of total glycol component to total acid component is 1.05 to 1.30, and carrying out depolymerization under heat treatment conditions of 245 to 280°C. (2) A step of passing the reaction product through a filter with a particle size of 10 to 25 μm and collecting the filtrate, (3) Add an aliphatic dicarboxylic acid or aliphatic lactone, or 1,4-butanediol to the filtrate, depolymerize under heat treatment conditions of 220 to 255°C, add a polymerization catalyst, and carry out a polycondensation reaction of the depolymer at a temperature of 220 to 255°C and under reduced pressure of 1.0 hPa or less.

[0050] First, in the depolymerization step (1), the recycled polyester raw material is added to a mixture containing ethylene terephthalate oligomer and ethylene glycol so that the molar ratio of total glycol component to total acid component 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 the depolymer.

[0051] Ethylene terephthalate oligomer and ethylene glycol can both be known or commercially available. They can also be manufactured by known manufacturing methods.

[0052] In particular, as the ethylene terephthalate oligomer, for example, an esterification reaction product of ethylene glycol and terephthalic acid can be suitably used. Furthermore, the number-average degree of polymerization of the ethylene terephthalate oligomer is not limited, but can be, for example, around 2 to 20.

[0053] The amount of the mixture of ethylene terephthalate oligomer and ethylene glycol (hereinafter sometimes referred to as mixture E) is preferably about 20.0 to 80.0% by mass, and more preferably 30.0 to 70.0% by mass, of 100% by mass of the final recycled polyester resin.

[0054] If the amount of mixture E is less than the above, when the recycled polyester raw material is added, it is more likely to cause blocking among the recycled polyester raw materials, which places an excessive load on the agitator and is therefore undesirable. On the other hand, if the amount of mixture E is greater than the above range, no particular problems occur in the depolymerization reaction, but the recycling rate of the ultimately obtained recycled polyester resin becomes low, which is undesirable.

[0055] In step (1), it is preferable to add ethylene terephthalate oligomer, ethylene glycol, and recycled polyester raw material in the following proportions (totaling 100 parts by mass): preferably 5 to 55 parts by mass of ethylene terephthalate oligomer, 1 to 15 parts by mass of ethylene glycol, and 40 to 80 parts by mass of recycled polyester raw material.

[0056] In particular, the amount of ethylene glycol added is preferably 2 to 18% by mass, and more preferably 3 to 17% by mass, relative to 100% by mass of ethylene terephthalate oligomer, in order to allow the depolymerization reaction to proceed sufficiently. If the amount of ethylene glycol added exceeds 18% by mass, the ethylene terephthalate oligomer is likely to solidify in the reactor, and the reaction may not be able to continue.

[0057] When mixing ethylene terephthalate oligomer and ethylene glycol, there are no particular limitations, but for example, it is preferable to add ethylene glycol to the ethylene terephthalate oligomer. Furthermore, when adding, it is preferable to stir the mixture while ensuring that the temperature of the contents is uniform in order to prevent the oligomer from solidifying.

[0058] In step (1), when adding recycled polyester raw material to the mixture of ethylene terephthalate oligomer and ethylene glycol, depolymerization is carried out under heat treatment conditions of 245 to 280°C while stirring so that the molar ratio of total glycol components to total acid components is 1.05 to 1.30.

[0059] The polyester raw material is added so that the molar ratio of total glycol components to total acid components is 1.05 to 1.30. The molar ratio is particularly preferably 1.10 to 1.28, and among these, 1.12 to 1.25 is preferable. If the molar ratio of total glycol components to total acid components is outside the above range, the resulting recycled polyester resin will have a diethylene glycol content exceeding 4 mol%, will not satisfy the carboxyl end group concentration specified in this invention, and will also have a higher average pressurization rate. This is because, when the molar ratio of total glycol components to total acid components during the depolymerization reaction is outside the above range, the precipitation of various inorganic substances and foreign substances derived from non-polyester resins does not occur efficiently, so these foreign substances cannot be effectively filtered out in the filtration step, and foreign substances tend to precipitate after the polycondensation step. As a result, the recycled polyester resin will have a high average pressurization rate and poor thermal stability (high carboxyl end group concentration and high diethylene glycol content).

[0060] In the manufacturing 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, whereas in the present invention, the depolymerization reaction of the recycled polyester raw material is carried out in the presence of a mixture containing ethylene terephthalate oligomer and ethylene glycol, and the recycled polyester raw material is added so that the molar ratio of the total glycol component to the total acid component of the oligomer and recycled polyester raw material is within the above range, and the depolymerization reaction is carried out.

[0061] By performing step (1) as described above, not only various inorganic substances but also foreign substances derived from non-polyester resins are efficiently precipitated, so that these foreign substances can be completely filtered out in step (2). Then, in the polycondensation step of step (3), it becomes possible to obtain a recycled polyester resin in which the carboxyl terminal group concentration and diethylene glycol content are below a specified amount, and the amount of foreign substances is low.

[0062] Furthermore, by depolymerizing recycled polyester raw materials in the presence of ethylene terephthalate oligomer and ethylene glycol, the depolymerization reaction can proceed at lower temperatures compared to when depolymerization is performed using recycled polyester raw materials alone. This represents a significant advantage when implemented on an industrial scale.

[0063] In the manufacturing method of the present invention, it is desirable that the recycled polyester raw material is not decomposed into monomers by the above-mentioned depolymerization reaction, but rather decomposed into oligomers with approximately 5 to 20 repeating units. 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.

[0064] The reactor used in the production method of the present invention can be a commonly used esterification reactor in terms of capacity and the shape of the stirring blades, but it is preferable that it has a structure that includes a distillation column to prevent aliphatic diols from distilling out of the system in order to efficiently advance the depolymerization reaction.

[0065] When adding recycled polyester raw materials, it is preferable to do so under atmospheric pressure while stirring, and it is even more preferable to add them after purging them with a small amount of inert gas (generally nitrogen gas).

[0066] The reaction temperature during depolymerization in step (1) is preferably set to a reactor temperature of 245 to 280°C, and more preferably to a temperature of 255 to 275°C. If the reaction temperature during depolymerization is below 245°C, the reactants solidify, the operability deteriorates, and even if recycled polyester resin is obtained, the carboxyl end group concentration tends to become too high. If the reaction temperature exceeds 280°C, the carboxyl end group concentration and the amount of diethylene glycol in the obtained recycled polyester resin become too high.

[0067] Furthermore, the reaction time for depolymerization (reaction time from the end of the input of recycled polyester raw materials) is preferably within 4 hours, and more preferably within 2 hours from the viewpoint of suppressing deterioration of the polyester's color tone.

[0068] In step (2), the reaction product containing the depolymer that underwent the depolymerization reaction in step (1) is passed through a filter with a particle size of 10 to 25 μm to collect 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 substances derived from non-polyester resins are efficiently precipitated. By passing the filtrate through a filter with a particle size of 10 to 25 μm, the precipitated foreign substances are filtered out, and a filtrate with a low amount of foreign matter contamination can be obtained.

[0069] Using filters with a particle size larger than 25 μm prevents sufficient removal of impurities from the polymer, resulting in a higher concentration of impurities in the resulting recycled polyester resin. Therefore, spinning with such resin can lead to increased nozzle pack pressure and thread breakage. On the other hand, using filters with a particle size smaller than 10 μm is prone to clogging by impurities, shortening the filter life, resulting in cost disadvantages and reduced operability.

[0070] Furthermore, while any general filter can be used in step (2) of the present invention, examples include screen changer filters, leaf disc filters, and candle-type sintered filters.

[0071] In the production method of the present invention, the required amount of aliphatic dicarboxylic acid or aliphatic lactone, or 1,4-butanediol is added to the filtrate obtained through step (2) above, and a depolymerization reaction is carried out at a reaction temperature of 220 to 255°C. In other words, in the production method of the present invention, a depolymerization reaction is carried out in step (1), and then another depolymerization reaction is carried out in step (3).

[0072] If the depolymerization temperature after adding 1,4-butanediol is below 220°C, the reaction will not only be slow, but there is also a risk that the oligomer will solidify. Furthermore, if the temperature exceeds 255°C, 1,4-butanediol will decompose during the reaction to form tetrahydrofuran, and a polyester resin with the desired butanediol ratio cannot be obtained.

[0073] Furthermore, a polymerization catalyst is added, and the polycondensation reaction is carried out at a temperature of 220-255°C under reduced pressure of 1.0 hPa or less. It is preferable to use the polymerization catalyst described above, but the amount added should be 5 × 10⁻¹⁰ per mole of the acid component constituting the polyester. -5 It is preferable to have a value of 6 × 10⁻¹⁰ or higher, and among these, 6 × 10⁻¹⁰ -5 It is more preferable to have a concentration of moles / unit or higher.

[0074] Furthermore, during the polycondensation reaction, fatty acid esters, hindered phenol antioxidants, phosphorus compounds, and titanium dioxide can also be added in conjunction with the polymerization catalyst mentioned above.

[0075] Then, the polycondensation reaction is carried out in a polycondensation reactor at a temperature of 220-255°C and under reduced pressure of 1.0 hPa or less. If the polycondensation reaction temperature is below 220°C, or if the pressure during the polycondensation reaction exceeds 1.0 hPa, the polycondensation reaction time will be prolonged, resulting in lower productivity.

[0076] If the polycondensation reaction temperature exceeds 255°C, 1,4-butanediol decomposes during the reaction to form tetrahydrofuran, making it impossible to obtain a polyester resin with the desired ratio of 1,4-butanediol. Similarly, thermal decomposition increases the concentration of carboxyl terminal groups, which is undesirable.

[0077] The intrinsic viscosity of the recycled polyester resin of the present invention obtained by the polycondensation reaction described above is not particularly limited, but is usually preferably 0.44 to 0.80.

[0078] The resin of the present invention may contain various additives other than those described above, such as polymerization catalysts, antioxidants, and phosphorus compounds, as long as they do not impair its effects. Various additives may be included, such as manganese compounds including manganese acetate, anthraquinone dye compounds, and copper phthalocyanine compounds, in order to suppress discoloration caused by thermal decomposition of the polyester resin.

[0079] The resin of the present invention can be used to obtain various products, and can be suitably used in, for example, fibers, molded articles, films, and the like.

[0080] In the case of molded articles containing the resin of the present invention, they can be manufactured by applying various molding methods such as press molding, extrusion molding, pressure molding, and blow molding using raw materials containing the resin of the present invention. This makes it possible to provide various parts, including containers. The resin of the present invention has properties similar to virgin polyester resin and is particularly suitable for the manufacture of blow-molded articles because it has excellent thermal stability. Therefore, a method for manufacturing a molded article that includes the step of obtaining a parison from a molten raw material containing the resin of the present invention and the step of blowing gas into the parison can be suitably adopted. This makes it possible to manufacture molded articles such as containers.

[0081] As described above, the resin of the present invention exhibits excellent thermal stability due to its diethylene glycol content and carboxyl terminal group concentration being below a specific amount. Therefore, when obtaining molded products as described above, thickness variations are less likely to occur, and molded products with high uniformity can be obtained with good operability. Furthermore, as described above, the resin of the present invention has an average pressurization rate of 0.6 MPa / h or less and contains a small amount of foreign matter. Foreign matter present in the resin is thought to include inorganic substances and foreign matter derived from non-polyester resins, but the low amount of these foreign matter allows for the production of molded products with a good surface appearance and excellent impact resistance and strength. Furthermore, since the resin of the present invention has a low melting point of 150 to 200°C, it is possible to mold various molded products at low temperatures, which is advantageous in terms of cost.

[0082] In the case of molded products, including 0.1 to 1.0% by mass of a hindered phenol-based antioxidant can prevent a decrease in intrinsic viscosity and deterioration of color after molding.

[0083] As described above, the resin of the present invention has a relatively low content of foreign matter and possesses properties equivalent to those of virgin polyester resin. Therefore, problems such as yarn breakage are less likely to occur in any of the processes, including melt spinning, stretching / heat treatment, and winding, and polyester fibers can be obtained with high productivity.

[0084] The fibers of the present invention containing the resin of the present invention may be monofilaments, multifilaments, or any other type, and may also be long fibers, short fibers, or any other type. Fibers containing the resin of the present invention can be manufactured by conventional melt spinning and drawing.

[0085] Because the resin of the present invention has a low melting point of 150 to 200°C, it can be used as a binder fiber or a heat-fusible fiber. In addition to fully melted binder fibers using only the resin of the present invention, core-sheath type binder fibers or heat-fusible fibers may also be used in which the resin of the present invention is used only in the sheath portion. Furthermore, the resin of the present invention may be used in only one of the two components of a composite fiber bonded side by side. The other component in such a composite fiber may be appropriately selected according to the required fiber properties and application.

[0086] In fiber manufacturing, it is generally more difficult to produce multifilaments. However, with the fiber of the present invention, for example, a multifilament can be produced having characteristic values ​​such as a single filament fineness of 0.3 to 30 decitex, a single filament 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%.

[0087] When the fibers of the present invention are short fibers, for example, fibers with characteristic values ​​of 0.5 to 25.0 decitex fineness, 0.1 to 6.0 cN / decitex strength, and 20 to 600% elongation can be obtained. As described above, the resin of the present invention has excellent thermal stability because the carboxyl end group concentration is below a specific amount. Therefore, when obtaining short fibers as described above, single-fiber fusion in the spinning and drawing processes is suppressed, so variations in single-fiber fineness are less likely to occur, and fibers with high uniformity can be obtained with good operability. Furthermore, in the case of short fibers used for wet nonwoven fabric applications, since single-fiber fusion in the spinning and drawing processes is suppressed, fibers with good single-fiber dispersibility in water can be obtained.

[0088] Furthermore, as described above, the resin of the present invention has an average pressure increase rate of 0.6 MPa / h or less and contains a small amount of foreign matter. Foreign matter present in the resin is thought to include inorganic substances and foreign matter derived from non-polyester resins, but the low amount of these foreign matter improves the quality and strength of products such as nonwoven fabrics obtained when the fibers of the present invention are used as binder fibers.

[0089] The nonwoven fabric obtained when the fibers of the present invention are used as binder fibers may be dry or wet, and the basis weight of the nonwoven fabric is not particularly limited. As for the method of nonwoven fabric formation, the low-melting-point polyester resin (resin of the present invention) constituting the fibers of the present invention acts as a heat-bonding component, and the fibers are integrated by heat bonding. However, the constituent fibers may be three-dimensionally entangled before heat bonding.

[0090] Nonwoven fabrics obtained using the fibers of the present invention as binder fibers may contain fibers other than the fibers of the present invention. For example, a nonwoven fabric containing fibers made of polyester resin with a higher melting point than the resin of the present invention may be used.

[0091] An example of a method for manufacturing dry nonwoven fabric is given. When mixing with other fibers other than the fibers of the present invention, the other fibers are prepared and weighed in any proportion. The proportion of the fibers of the present invention when mixing can be appropriately selected according to the required characteristics of the nonwoven fabric, and is preferably about 10 to 90% by mass. The weighed constituent fibers are fed into a carding machine and defibrated to produce a dry web. The obtained web is subjected to a heat bonding treatment in a continuous heat treatment machine that performs hot air treatment at a temperature at which the low melting point polyester resin melts or softens, and a dry nonwoven fabric is obtained in which the constituent fibers are integrated by heat bonding.

[0092] In the manufacturing method of the wet-laid nonwoven fabric, when mixing with other fibers other than the fibers of the present invention, the other fibers are prepared and weighed in any desired proportion. The proportion of the fibers of the present invention when mixing can be appropriately selected according to the required characteristics of the nonwoven fabric, and is preferably about 10 to 90% by mass. After stirring and defibration processes using a weighed pulp disintegrator, a wet-laid web is produced in a paper machine. The obtained web is subjected to a heat bonding treatment in a continuous heat treatment machine that performs hot air treatment at a temperature at which the low-melting-point polyester resin melts or softens, thereby obtaining a wet-laid nonwoven fabric in which the constituent fibers are integrated by heat bonding. [Examples]

[0093] Next, the present invention will be specifically described using examples. The measurement and evaluation methods for various characteristic values ​​in the examples are as follows. (a) Intrinsic viscosity The obtained recycled polyester resin is used as a solvent, and measurements are taken at a temperature of 20°C. (b) Composition of polyester resin The obtained polyester resin was dissolved in a mixed solvent of deuterated hexafluoroisopropanol and deuterated chloroform in a volume ratio of 1:11. The 1H-NMR spectrum was measured using a JEOL JNM-ECZ400R / S1 NMR spectrometer, and the types and contents of copolymer components were determined from the integrated intensities of the proton peaks of each component in the resulting chart. (c) Carboxyl-terminal group concentration The obtained recycled polyester resin was dissolved in 10 ml of benzyl alcohol, 10 ml of chloroform was added to this solution, and then the result was obtained by titration with a 1 / 10 N potassium hydroxide benzyl alcohol solution.

[0094] (d) Average boost rate The obtained polyester resin is melted at 300°C in an extruder, and a stainless steel twill weave 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, viscosity resistance coefficient (m-1): 2.60 × 10⁷, inertia resistance coefficient: 5.14 × 10⁻⁶, manufactured by Kamijo Seiki Co., Ltd.) is set as a filter at the tip of the extruder, and a reinforcing material (stainless steel plain weave wire mesh (nominal mesh size)) is set on the back (downstream side) of it After laminating a 40-mesh, plain weave, 0.21mm diameter (manufactured by Kamijo Seiki Co., Ltd.) filter, the polymer discharge rate was set to 29.0 g / min, and the filter pressure was measured using a pressure booster tester; an Asahi Gauge "MES-Y44D" detector. The pressure boost test using the above-mentioned pressure booster tester was performed continuously for 12 hours, and the average pressure boost rate was calculated from the initial pressure value (MPa) at the start of the pressure boost test (the minimum pressure between 5 and 10 minutes after the polyester resin begins to pass through the filter is defined as the initial pressure) and the final pressure value (MPa) after 12 hours using the following formula. Average pressure increase rate (MPa / h) = (Final pressure value - Initial pressure value) / 12 (e) Melting point (Tm) Measurements were taken using a PerkinElmer DSC-7 differential scanning calorimeter in a nitrogen atmosphere, within a temperature range of 25-280°C, and with a heating / cooling rate of 20°C / min.

[0095] (f) Formability The thickness of the body of the obtained containers (100 samples) was measured, and those with a difference of 0.30 mm or less between the thickest and thinnest parts were considered acceptable. Based on the number of samples that passed, the following two-stage evaluation was performed. ○: Number of passing samples is 95 or more ×: Number of acceptable samples is 94 or less (g) haze Twenty sample pieces were cut from the obtained containers, and their turbidity was measured using a MODEL 1001DP turbidimeter manufactured by Nippon Denshoku Industries Co., Ltd. (air: haze 0%). The average value of n(n) 20 was used. A smaller value indicates better transparency, and a value of 6% or less was judged to be excellent transparency.

[0096] (h) Operability of short fiber manufacturing (cut yarn) If the number of yarn breaks during 24 hours of continuous melt spinning was 3 or less per day / spindle, and there was no single-yarn adhesion during the drawing process, it was marked as "○". Otherwise, it was marked as "×". (i) The properties of short fibers (strength, elongation) Using the obtained short fibers, the strength and elongation were measured in accordance with JIS L-1015 using a Shimadzu Autograph AG-50KNI with a gripping distance of 20 cm and a tensile speed of 20 cm. (j) Strong non-woven fabric The obtained nonwoven fabric was cut into 150 mm strips in the MD direction and 50 mm strips in the CD direction. The MD strength was measured using an Autograph (Shimadzu AG-50KNI) under conditions of a tensile speed of 100 mm / min and a chuck distance of 100 mm. The sample size was n=5. The tensile strength of the obtained nonwoven fabric was evaluated in the following two stages. ○: Tensile strength of 1500 cN or more ×: Tensile strength less than 1500 cN

[0097] (k) Operability of long fiber manufacturing (cut yarn) If the number of filament cuts per spindle during 24 hours of continuous melt spinning was 3 or less, and there was no single-fiber adhesion during the drawing process, it was marked as "○". Otherwise, it was marked as "×". (l) Long fiber yarn properties (strength, elongation) Using the obtained long fibers, the strength and elongation were measured in accordance with JIS L-1013 using a Shimadzu Autograph DSS-500 with a gripping distance of 25 cm and a tensile speed of 30 cm.

[0098] 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 under conditions of 250°C and 50 hPa to obtain ethylene terephthalate oligomer (number average degree of polymerization: 5) with an esterification reaction rate of 95%. 49.0 parts by mass of ethylene terephthalate oligomer were placed in the esterification reactor, and then, while the reactor's stirrer was running, 6.0 parts by mass of ethylene glycol (EG) were added. Once the internal temperature of the esterification reactor (hereinafter referred to as the "ES can") stopped decreasing, 45.0 parts by mass of recycled polyester raw material (pellets of polyester waste generated in the process of manufacturing polyester resin) were added quantitatively via a rotary valve over a period of approximately 2 hours. At this time, 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 1.21. Then, the depolymerization reaction was carried out for 1 hour under heat treatment conditions of 260°C. The resulting depolymer was then pumped into the polycondensation reactor (hereinafter referred to as the PC can) through a candle filter with a mesh size of 20 μm placed between the esterification reactor and the polycondensation reactor. Then, 60.7 parts by mass of 1,4-butanediol (1,4-BD) and 8.2 parts by mass of ε-caprolactone as an aliphatic lactone were added to the PC can, and the depolymerization reaction was carried out for 1 hour under heat treatment conditions of 240°C. Subsequently, 4.0 × 10⁻⁶ tetrabutyl titanate was added as a polymerization catalyst. -4 After adding mol / unit, the PC can was reduced in pressure for 60 minutes, and then a polycondensation reaction was carried out at a final pressure of 0.5 hPa and a temperature of 240°C for 3 hours to obtain a polyester resin (intrinsic viscosity: 0.60).

[0099] [Blow molded product] The obtained polyester resin was chipped and dried. Then, using a direct blow molding machine (manufactured by Tahara Corporation), the resin was extruded at an extrusion temperature of 230°C to form a cylindrical parison. While the parison was still soft, it was sandwiched in a mold to form the bottom, and then blow-molded to form a bottle. At this point, the parison had a diameter of 3 cm and a length of 25 cm when the bottom was formed and blow-molded to obtain a hollow container (direct blow-molded product) with an average wall thickness of 1 mm in the body, an inner diameter of 3.5 cm, a height of 15 cm, and a capacity of 150 cc.

[0100] [Manufacturing of short fibers] A 560-pore, 0.35mm-diameter spinneret was used to form the core of polyethylene terephthalate with an intrinsic viscosity of 0.70 and the resulting polyester resin into the sheath. Melt spinning was performed at a spinning temperature of 270°C and a spinning speed of 790 m / min, with a discharge rate of 312 g / min, a core-sheath mass ratio of 50 / 50. The obtained undrawn yarn was gathered to form an 80ktex tow and drawn at a drawing temperature of 60°C and a draw ratio of 3.5 times. Then, mechanical crimping was applied using a push-type crimper, and the fibers were cut to a length of 51 mm to obtain a heat-adhesive core-sheath composite fiber with a fineness of 2.2 dtex.

[0101] [Preparation of dry-laid nonwoven fabric] Unitika Regular Polyester Fiber <121> 1.7T51mm fibers were blended at a ratio of 70% by mass and the resulting heat-adhesive core-sheath composite fiber at 30% by mass. The basis weight of the nonwoven fabric after heat treatment was 50 g / m². 2 To achieve this, fibers were fed into a carding machine (SC-500DI3HC, manufactured by Yamato Kiko) to create a web. Subsequently, a continuous heat treatment machine (NFD-500E2, manufactured by Tsujii Dyeing Machinery Co., Ltd.) was used to process the web at an airflow of 57 m³. 3 Dry nonwoven fabric was prepared by heat treatment under the conditions of / min at 190°C for 1 minute.

[0102] Examples 2-8, Comparative Examples 1-12 [Recycled polyester resin] The depolymerization reaction (first step) was carried out in the same manner as in Example 1, except that the amounts of ethylene terephthalate oligomer, ethylene glycol, and recycled polyester raw material added during the depolymerization reaction (first step), the G / A ratio, and the heat treatment temperature were changed to those shown in Table 1. Furthermore, polyester resin was produced in the same manner as in Example 1, except that the filtration particle size of the filter in the filtrate recovery process, the amount of ε-caprolactone and 1,4-BD added during the depolymerization reaction (second time) and the heat treatment temperature, and the heat treatment temperature in the polycondensation reaction process were changed to those shown in Table 1. [Blow molded product] Using the obtained polyester resin, blow molding was performed in the same manner as in Example 1, except that the extrusion temperature of the direct blow molding machine was changed to that shown in Table 1, to obtain a blow-molded product. [Manufacturing of short fibers] A heat-adhesive core-sheath composite fiber was obtained in the same manner as in Example 1, except that the obtained polyester resin was used for the sheath portion. [Preparation of dry-laid nonwoven fabric] A dry-laid nonwoven fabric was prepared in the same manner as in Example 1, except that the obtained heat-adhesive core-sheath type composite fiber was used.

[0103] [Manufacturing of long fibers] Example 9 The recycled polyester resin obtained in Example 1 was extruded through a 12-hole nozzle at a spinning temperature of 285°C, with polyethylene terephthalate with an intrinsic viscosity of 0.74 as the sheath and polyethylene terephthalate with an intrinsic viscosity of 0.74 as the core. Partially oriented yarn was collected at a spinning speed of 3000 m / min. The obtained partially oriented yarn was stretched at a first roller temperature of 70°C, a heat setting temperature of 130°C, and a stretch ratio of 1.84 times to obtain a heat-adhesive core-sheath composite multifilament (long fiber) of 26 dtex 12 filaments.

[0104] Examples 10-12 Long fibers were obtained in the same manner as in Example 9, except that the recycled polyester resin obtained in Examples 2 to 4 was used for the sheath portion.

[0105] Example 13 [Manufacturing of short fibers] Using a spinneret with 560 holes and a hole diameter of 0.35 mm, melt spinning was performed with a discharge rate of 312 g / min, a core-to-sheath mass ratio of 50 / 50, a spinning temperature of 272 °C, and a spinning speed of 790 m / min, with polyethylene terephthalate with an intrinsic viscosity of 0.70 as the core and the polyester resin obtained in Example 3 as the sheath. The resulting undrawn yarn was gathered to form a 50 ktex tow and drawn at a drawing temperature of 74 °C and a draw ratio of 3.4 times. Next, after applying an oil, the tow was squeezed to a moisture content of approximately 18 mass%, cut to a length of 5 mm with a drum cutter, and obtained a heat-adhesive core-sheath type composite short-cut fiber with a fineness of 2.2 dtex. [Preparation of wet-laid nonwoven fabrics] Next, the obtained heat-adhesive core-sheath type composite short-cut fiber is used as a binder fiber, and the main fiber is a short-cut fiber made of polyethylene terephthalate with a single fiber fineness of 1.6 dtex and a length of 5 mm (manufactured by Unitika Corporation). <n801>Using 1.6T5), the mixture was dispersed in water with a binder fiber / main fiber (mass ratio) of 40 / 60, and a formed web was obtained using a cylinder paper machine. Thereafter, using a continuous heat treatment machine (manufactured by Tsujii Dyeing Machine Industry Co., Ltd., model NFD-500E2), an air volume of 57m 3 / min, heat treatment was performed under conditions of 200°C×1 min to prepare a wet-laid nonwoven fabric.

[0106] Example 14 [Method for producing short fibers] Using only the polyester resin obtained in Example 3, melt spinning was performed using a spinneret with 120 holes and a hole diameter of 0.6 mm under the conditions of a discharge rate of 210 g / min, a spinning temperature of 270°C, and a spinning speed of 850 m / min. The obtained undrawn yarn was converged to form a tow of 80 ktex, and drawn under the conditions of a drawing temperature of 60°C and a draw ratio of 4.0 times. Next, after imparting mechanical crimping with a push-type crimper, it was cut to a fiber length of 51 mm to obtain heat-adhesive short fibers with a fineness of 5.5 dtex. [Preparation of dry-laid nonwoven fabric] A dry-laid nonwoven fabric was produced in the same manner as in Example 1, except that the obtained heat-adhesive short fibers were used as binder fibers.

[0107] Example 15 [Method for producing short fibers] Using only the polyester resin obtained in Example 3, melt spinning was performed using a spinneret with 720 holes and a hole diameter of 0.25 mm under the conditions of a discharge rate of 350 g / min, a spinning temperature of 275°C, and a spinning speed of 850 m / min. The obtained undrawn yarn was converged to form a 50 ktex tow, and drawn under the conditions of a drawing temperature of 50°C and a draw ratio of 3.8 times. Next, after applying an oil agent, the tow was squeezed so that the moisture content thereof was about 18% by mass, cut to a length of 5 mm with a drum cutter, to obtain heat-adhesive shortcut fibers with a fineness of 1.7 dtex. [Preparation of wet-laid nonwoven fabric] A wet-laid nonwoven fabric was produced in the same manner as in Example 13, except that the obtained heat-adhesive shortcut fibers were used as binder fibers.

[0108] Table 1 shows the property values ​​of the polyester resins, blow-molded products, and evaluation results of the short fibers obtained in Examples 1-8 and Comparative Examples 1-12. Table 2 shows the evaluation results of the long fibers obtained in Examples 9-12, and Table 3 shows the evaluation results of the short fibers and nonwoven fabrics obtained in Examples 13-15.

[0109] [Table 1]

[0110] [Table 2]

[0111] [Table 3]

[0112] As is clear from Table 1, the recycled polyester resins obtained in Examples 1 to 8 were obtained by the manufacturing method of the present invention, and therefore the amount of carboxyl-terminated groups, the diethylene glycol content, and the average pressurization rate were within the range specified in the present invention. For this reason, blow-molded products and short fibers could be obtained with the same ease of operation as with virgin polyester resin. Furthermore, the blow-molded products were free of haze and of high quality, and the nonwoven fabrics obtained using heat-adhesive core-sheath composite short fibers with recycled polyester resin in the sheath portion had high strength.

[0113] Furthermore, as is clear from Table 2, the recycled polyester resin obtained in Examples 1-4 was used for the sheath portion, and heat-adhesive core-sheath type composite multifilaments (long fibers) were obtained with good operability. In addition, the obtained long fibers had no practical problems in terms of both strength and elongation.

[0114] Furthermore, as is clear from Table 3, in Example 13, recycled polyester resin was used in the sheath portion, and heat-adhesive core-sheath composite short fibers were obtained with good operability. In addition, the wet-laid nonwoven fabric obtained using the heat-adhesive core-sheath composite short fibers had high strength. Moreover, as in Examples 14-15, heat-adhesive short fibers could also be obtained with good operability when recycled polyester resin was used as a single component. Furthermore, the dry-laid and wet-laid nonwoven fabrics obtained using the heat-adhesive short fibers had high strength.

[0115] On the other hand, in Comparative Example 1, the G / A ratio during the depolymerization reaction was high at 1.40, resulting in a high diethylene glycol content, a high carboxyl terminal group concentration, and a high average pressure increase rate. Consequently, thermal decomposition occurred when the fibers were formed, leading to poor operability, inferior yarn quality of the resulting fibers, and low nonwoven fabric strength. Furthermore, the molded product exhibited thickness variations, a high amount of foreign matter, and poor haze. In Comparative Example 2, the heat treatment temperature during depolymerization was high at 290°C, resulting in high diethylene glycol content and carboxyl terminal group concentration. Consequently, thermal decomposition occurred when the fibers were formed, leading to poor operability, inferior yarn quality, and low nonwoven fabric strength. Furthermore, thickness variations were observed in the molded products. In Comparative Example 3, the filtration particle size of the candle filter placed between the ES can and the PC can was high at 30 μm, resulting in a large amount of foreign matter contamination and a high average pressure increase rate. Consequently, when the fibers were produced, frequent pressure increase in the nozzle pack and thread breakage worsened operability, and the resulting fibers had poor quality. Furthermore, the molded products also had a high amount of foreign matter, resulting in poor haze.

[0116] In Comparative Example 4, the amount of aliphatic lactone added was high at 29.2 parts by mass, resulting in a high aliphatic lactone content of 35 mol%, and a low melting point of the polyester resin at 132°C. Consequently, thermal decomposition occurred when the fibers were formed, leading to poor operability, inferior yarn quality of the resulting fibers, and low nonwoven fabric strength. Furthermore, thermal decomposition occurred during molding of the molded product, resulting in uneven thickness. In Comparative Example 5, the amount of 1,4-butanediol added was high at 187 parts by mass, resulting in a high 1,4-butanediol content of 73.2 mol%, which raised the resin's melting point to over 200°C. When formed into a nonwoven fabric, thermal bonding was insufficient, resulting in low nonwoven fabric strength. Furthermore, whitening of the molded product was observed during blow molding, and the haze was poor. In addition, molding at a high extrusion temperature caused thermal decomposition of the resin, resulting in uneven thickness in the molded product. In Comparative Example 6, the amount of 1,4-butanediol added was small (12.2 parts by mass), resulting in a low 1,4-butanediol content of 17.7 mol%, which caused the melting point of the polyester resin to exceed 200°C. As a result, when formed into a nonwoven fabric, thermal bonding was insufficient, and the nonwoven fabric strength was low. Furthermore, the high extrusion temperature during molding caused thermal decomposition of the resin, resulting in uneven thickness in the molded product.

[0117] In Comparative Example 7, the heat treatment temperature during the depolymerization reaction in step (1) was low at 230°C, causing the reactants to solidify and preventing the acquisition of polyester resin. In Comparative Example 8, the polycondensation reaction temperature was low at 210°C, so the polycondensation reaction did not proceed and polyester resin could not be obtained. In Comparative Example 9, the heat treatment temperature during the depolymerization reaction in step (3) was too high, resulting in high diethylene glycol content and carboxyl terminal group concentration. Consequently, thermal decomposition occurred when the fibers were formed, leading to poor operability, inferior yarn quality, and low nonwoven fabric strength. Furthermore, thickness variations were observed in the molded product.

[0118] In Comparative Example 10, the G / A ratio during the depolymerization reaction was low at 1.02, resulting in a high concentration of carboxyl terminal groups and a high average pressure increase rate. Consequently, thermal decomposition occurred when the fibers were formed, leading to poor operability, inferior yarn quality, and low nonwoven fabric strength. Furthermore, the molded product had a high amount of foreign matter, resulting in poor haze. In Comparative Example 11, the reaction temperature in the polycondensation reaction was high at 265°C, resulting in high diethylene glycol content and carboxyl terminal group concentration. Consequently, thermal decomposition occurred when the fibers were formed, leading to poor operability, inferior yarn quality, and low nonwoven fabric strength. Furthermore, thickness variations were observed in the molded product. In Comparative Example 12, the filtration particle size of the candle filter placed between the ES can and the PC can was low at 5 μm, which caused clogging and poor operability, making it impossible to obtain polyester resin.

Claims

1. a) a used polyester product and b) a polyester resin containing 40% by mass or more of a component derived from at least one recycled polyester raw material of unused polyester generated in the process of manufacturing polyester products, characterized in that it satisfies all of the following (1) to (6). (1) When the total amount of all acidic components is 100 mol%, 70 mol% or more is terephthalic acid, and 30 mol% or less is an aliphatic dicarboxylic acid component or an aliphatic lactone. (2) The glycol component constituting the polyester includes ethylene glycol, 1,4-butanediol and diethylene glycol, and the molar ratio of ethylene glycol to 1,4-butanediol is 80 / 20 to 30 / 70. (3) When the total amount of all glycol components is 100 mol%, the total amount of ethylene glycol and 1,4-butanediol is 80 to 99 mol%, and diethylene glycol is 0.5 to 4 mol%, (4) The carboxyl terminal group concentration is 35 equivalents / t or less, (5) The average pressure increase rate is 0.6 MPa / h or less (however, the average pressure increase rate is a value calculated by the following procedure: Using a pressure test machine including an extruder and a pressure sensor, a stainless steel filter (nominal mesh size: 1400 mesh, weave: twill weave, warp mesh: 165 mesh, weft mesh: 1400 mesh, warp wire diameter: 0.07 mm, weft wire diameter: 0.04 mm, filtration particle size: 12 μm) is set at the tip of the extruder, polyester resin is melted at 300°C in the extruder, and the pressure value applied to the filter when the molten material is extruded at a discharge rate of 29.0 g / min is defined as the pressure value at the start of extrusion as the "initial pressure value (MPa)" and the pressure value after extrusion has been continued for 12 hours as the "final pressure value (MPa)", the average pressure increase rate is calculated using the following formula A based on these pressure values: Average pressure increase rate (MPa / h) = (Final pressure value - Initial pressure value) / 12) ... A) (6) a) Used polyester products and b) At least one recycled polyester raw material consisting of terephthalic acid and ethylene glycol is a polyester made from unused polyester generated in the process of manufacturing polyester products.

2. The recycled polyester resin according to claim 1, wherein the melting point is 150 to 200°C.

3. A molded article containing the recycled polyester resin described in claim 1 or 2.

4. A fiber containing the recycled polyester resin described in claim 1 or 2.

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