Recycled polyester resin and method for producing recycled polyester resin

Abstract

To provide a recycled polyester raw material derived from used polyester products, or a copolymer polyester resin with a recycled polyester raw material derived from wastes generated in a process of manufacturing a polyester resin and products as a raw material.SOLUTION: A polyester resin containing a recycled polyester raw material is characterized by satisfying all the following (1) to (5). (1) When a total amount of all acid components constituting the polyester is set to 100 mol%, 80 to 98 mol% is terephthalic acid, 1 to 10 mol% is isophthalic acid, and (2) the number of foreign matter of a particle diameter of 50 μm or larger present in a sheet of 1 m2 is 200 pieces or smaller of a sheet when produced into a film thickness of 0.2 mm, (3) a haze is 2% or smaller, (4) a retention rate of the intrinsic viscosity before and after melting when melted 30 minutes at a temperature of 300°C is 85% or larger, and (5) a carboxyl terminal group concentration is 40 equivalent / t or smaller.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] Furthermore, there are many recycled materials in the market that are made from PET bottles that have once been used in products, but most of these recycled materials are mainly made of polyethylene terephthalate. There is almost no practice of collecting products that use copolymer polyester and using them as recycled materials.

[0006] On the other hand, in the production of plastic bottles and the like, the so-called blow molding method is adopted, in which molten plasticized resin is extruded through a die orifice to form a cylindrical parison, which is then sandwiched between molds and air is blown into it, due to its ease of molding, high productivity, and relatively low equipment costs for molding machines, molds, etc. Even in such blow-molded products, the use of recycled polyester resins is being considered from the perspective of environmental issues.

[0007] However, because crystallization is likely to occur during blow molding, even if molding is possible, there is a problem that whitening occurs and transparency becomes insufficient. Therefore, in order to improve transparency, polyester resins in which polyethylene terephthalate is copolymerized with other monomer components have been proposed (see, for example, Patent Document 1).

[0008] Thus, there is a great demand for copolymer polyester resins made from recycled polyester raw materials in various molded products, but no copolymer polyester resin has yet been obtained that can be sufficiently freed from various inorganic foreign matter and that can be used to produce various high-quality products similar to those produced from virgin polyester resins. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Patent No. 6297351 Summary of the Invention [Problem to be solved by the invention]

[0010] The present invention aims to solve the above-mentioned problems and to provide a recycled polyester resin that is a copolymer polyester resin made from recycled polyester raw materials derived from used polyester products or recycled polyester raw materials derived from scraps generated in the process of producing polyester resins and products, and that can be used to produce polyester products in various forms. It also aims to provide a production method by which such a recycled polyester resin of the present invention can be obtained.

[0011] The present inventors have conducted extensive research in light of the problems of the prior art and have discovered that by using recycled polyester raw materials and treating them in a specific manner, it is possible to obtain recycled polyester resins that contain less foreign matter and have thermal stability similar to that of virgin polyester resins, thereby completing the present invention. [Means for solving the problem]

[0012] That is, the present invention relates to the following recycled polyester resin and a method for producing the same. (A) A polyester resin containing at least one recycled polyester raw material, which is a) a used polyester product and b) an unused polyester generated in the process of manufacturing a polyester product, A recycled polyester resin characterized by satisfying all of the following (1) to (5): (1) When the total amount of all acid components constituting the polyester is taken as 100 mol %, 80 to 98 mol % is terephthalic acid and 1 to 10 mol % is isophthalic acid, (2) 1 m of sheet when a sheet with a film thickness of 0.2 mm is produced 2 The number of foreign particles with a particle size of 50 μm or more per unit area is 200 or less, (3) Haze is 2% or less; (4) The retention of intrinsic viscosity before and after melting when melted at a temperature of 300°C for 30 minutes is 85% or more, (5) The carboxyl end group concentration is 40 equivalents / t or less. (ii) Molded products containing the recycled polyester resin described in (i). (c) 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 in that the method for producing a recycled polyester resin described in (a) is characterized by carrying out the following steps (1) to (4) in order. (1) A process of removing metal foreign matter from recycled polyester raw materials using a metal detector; (2) A process of removing foreign matter from the recycled polyester raw material by passing it through an air classifier; (3) A step of melting the recycled polyester raw material in an extruder, wherein the temperature near the inlet of the recycled polyester raw material in the extruder is set to 290 to 280°C, the temperature near the outlet is set to 270 to 260°C, and the temperature difference between the temperature near the inlet and the temperature near the outlet is set to 20 to 25°C; (4) A process to remove foreign matter by passing the recycled polyester raw material through a filter with a filtration particle size of 10 to 25 μm. [Effects of the Invention]

[0013] According to the present invention, it is possible to provide a recycled polyester resin that can be used to produce polyester products of various types, using recycled polyester raw materials derived from used polyester products or recycled polyester raw materials derived from polyester waste generated in the process of producing polyester resins and products.

[0014] In particular, the present invention utilizes a high proportion of at least one recycled polyester raw material, including a) used polyester products and b) unused polyesters generated during the polyester product manufacturing process, while minimizing the amount of foreign matter mixed in and controlling the carboxyl end group concentration within a specific range, thereby providing a recycled polyester resin with excellent thermal stability and heat resistance. As a result, the process for obtaining molded articles enables relatively long-term continuous operation, enabling the production of various types of products with properties equivalent to those obtained using virgin polyester resin with high productivity. Furthermore, because the recycled polyester resin is a copolymer polyester resin containing a copolymer component, it can be suitably used for molded articles such as bottles that require transparency.

[0015] According to the method for producing recycled polyester resin of the present invention, it is possible to efficiently and reliably produce recycled polyester resin that has a low amount of foreign matter mixed in, has high thermal stability, and is suitable for use in molded products such as bottles. DETAILED DESCRIPTION OF THE INVENTION

[0016] The present invention will be described in detail below. The recycled polyester resin of the present invention (the resin of the present invention) contains at least one recycled polyester raw material, which is a) a used polyester product and b) unused polyester generated in the process of manufacturing a polyester product. These raw materials constitute a part of the polyester that constitutes the resin of the present invention.

[0017] Examples of used polyester products of 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 and packaging materials such as PET bottles. Among these, polyester products using polyester resins copolymerized with isophthalic acid are preferred.

[0018] The unadopted polyester generated in the process of manufacturing polyester products (b) above is polyester that did not reach the stage of commercialization, such as off-specification resin pellets, materials no longer needed during molding, fragments cut during molding, scraps (polyester scraps) generated during molding or processing, cut pieces of transitional products generated when changing brands, cut pieces of prototypes or defective products, etc. Among these, polyester resins copolymerized with isophthalic acid are preferred.

[0019] The above a) and b) are not limited in their form, and may be pelletized by further processing such as pulverization or cutting as necessary, or may be melted and pelletized. The above a) and b) may be used alone or as a mixture of the two.

[0020] 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.

[0021] The properties of the recycled polyester raw materials in a) and b) above are not limited, and may be in the form of a) and b) above as is, or may be in the form of cut pieces or crushed material (powders) obtained by further processing such as cutting or crushing, or in solid forms such as molded bodies (pellets, etc.) obtained by molding these. More specific 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.

[0022] 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, 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 manufacturing 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 up to 100% by mass.

[0023] In the resin of the present invention, when the total amount of all acid components constituting the polyester is taken as 100 mol %, 80 to 98 mol % is terephthalic acid and 1 to 10 mol % is isophthalic acid. In other words, the acid components are mainly terephthalic acid and copolymerized with isophthalic acid. The copolymerization amount of isophthalic acid must be 1 to 10 mol%, and preferably 2 to 8 mol%. By copolymerizing 1 to 10 mol% of isophthalic acid, the crystallization rate of the polyester resin can be adjusted to suit various molding processes, and whitening due to crystallization during molding can be prevented. The melting point of the resulting recycled polyester resin is preferably 235 to 250°C.

[0024] If the copolymerization amount of isophthalic acid is less than 1 mol%, the crystallization rate of the resin composition becomes so fast that when molded, the molded product crystallizes and turns white, resulting in poor transparency.On the other hand, if the copolymerization amount of isophthalic acid exceeds 10 mol%, the melting point becomes low and the heat resistance becomes poor.

[0025] The proportion of terephthalic acid in the acid component is 80 to 98 mol%, and the proportion of terephthalic acid is preferably 85 to 97 mol%. If the proportion of terephthalic acid is less than 80 mol%, the crystallinity of the resin composition decreases and it tends to become amorphous. On the other hand, if the proportion of terephthalic acid exceeds 98 mol%, the amount of isophthalic acid copolymerized decreases, making it difficult to achieve the effects obtained by copolymerizing isophthalic acid in various products.

[0026] Examples of acid components other than terephthalic acid and isophthalic acid in the resin of the present invention include phthalic acid, phthalic anhydride, naphthalenedicarboxylic acid, adipic acid, sebacic acid, 1,4-cyclohexanedicarboxylic acid, dodecanedioic acid, and other dimer acids, as well as trimellitic anhydride, trimellitic acid, pyromellitic acid, 1,4-cyclohexanedicarboxylic acid, sebacic acid, and dimer acids. Two or more of these may be used in combination, and ester-forming derivatives of these acids may also be used.

[0027] 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 is likely to have poor crystallinity and heat resistance.

[0028] In the resin of the present invention, examples of diol components other than ethylene glycol in the total glycol components include neopentyl glycol, 1,4-butanediol, 1,2-propylene glycol, 1,5-pentanediol, 1,3-propanediol, 1,6-hexamethylenediol, diethylene glycol, 1,4-cyclohexanedimethanol, dimer diol, butylethylpropanediol, (2-methyl-1,3-propanediol, trimethylolpropane, glycerin, pentaerythritol, and ethylene oxide adducts of bisphenol A or bisphenol S.

[0029] The resin of the present invention has the above-mentioned composition and also has the following characteristic values. (a) 1 m of sheet when a sheet with a film thickness of 0.2 mm is produced 2 The number of foreign particles with a particle size of 50 μm or more per unit area is 200 or less, (b) a haze of 2% or less; (c) The retention of the intrinsic viscosity before and after melting when melted at a temperature of 300°C for 30 minutes is 85% or more, (d) The concentration of carboxyl terminal groups is 40 equivalents / t 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.

[0030] First, the resin of the present invention has the characteristic value (a) of the thickness of 1 m of the sheet when a sheet having a thickness of 0.2 mm is produced. 2 The number of foreign particles having a particle size of 50 μm or more per unit area is 200 or less. It is particularly preferable that the number of foreign particles is 160 or less. The lower limit of the number of foreign particles can be, for example, about 50 or more, but is not limited to this.

[0031] If the number of foreign particles exceeds 200, the transparency of the resulting molded product will be impaired due to the foreign particles themselves or due to the occurrence of spherulites with the foreign particles as nuclei. Examples of such foreign matter that may arise from the use of recycled polyester raw materials include foreign matter derived from materials other than polyester, such as polystyrene and polyolefin, foreign matter derived from catalysts, and powder-like or froth-like high-melting-point foreign matter adhering to the surface of recycled polyester raw materials.

[0032] The method for measuring the number of foreign particles in the resin of the present invention is to prepare a sheet having a thickness of 0.2 mm under the conditions of an extruder temperature of 260 to 290°C, a rotation speed of 130 rpm, a winder temperature of 30 to 50°C, and a rotation speed of 2 m / min, using a fish eye counter (gel counter) manufactured by Optical Control Systems. 2 It detects and measures the number of foreign particles with a particle size of 50 μm or more per unit area.

[0033] The resin of the present invention has a characteristic value (b) of 2% or less, preferably 1% or less, of haze measured by the following method. The lower limit of the haze can be, for example, about 0.1% or more, but is not limited thereto. The haze in the present invention is an index of the number of spherulites caused by various foreign matters, and the smaller the haze, the less foreign matter is mixed in. The haze is measured by molding a 5 mm thick molded plate in an injection molding machine at a temperature of 260 to 290°C and a mold temperature of 20°C, and then measuring the haze using a haze measuring device (Nippon Denshoku Industries Co., Ltd. Haze Meter SH-7000).

[0034] The resin of the present invention has the characteristic value (c) of having a retention of intrinsic viscosity before and after melting when melted at a temperature of 300° C. for 30 minutes of 85% or more, preferably 90% or more. If the retention rate of the intrinsic viscosity is less than 85%, the thermal stability of the polyester resin will be low, and the intrinsic viscosity will decrease when molded, resulting in poor properties such as impact resistance and strength / elongation of the resulting molded product.

[0035] The intrinsic viscosity of the resin of the present invention is preferably 0.35 to 0.80, more preferably 0.45 to 0.70, as measured at 20°C using a mixture of equal masses of phenol and tetrachloroethane as a solvent.

[0036] The resin of the present invention has the characteristic value (d) of a carboxyl terminal group concentration of 40 equivalents / t or less, preferably 35 equivalents / t or less, and more preferably 30 equivalents / t or less. The resin of the present invention has a carboxyl terminal group concentration of 40 equivalents / t or less, and therefore has excellent heat resistance, making it possible to obtain fibers and molded articles with excellent heat resistance by various methods. If the carboxyl end group concentration exceeds 40 equivalents / ton, the thermal stability of the resulting polyester resin will be reduced, the performance of the polyester will be reduced by heat treatment during molding, and the properties of the resulting molded product, such as impact resistance and strength / elongation, will be inferior.

[0037] Next, a method for producing the resin of the present invention will be described. In the production method of the present invention, it is important to carry out the steps (1) to (4) in order. (1) A process of removing metal foreign matter from recycled polyester raw materials using a metal detector; (2) A process of removing foreign matter from recycled polyester raw materials by passing them through a precision air classifier; (3) A step of melting the recycled polyester raw material in an extruder, wherein the temperature near the inlet of the recycled polyester raw material in the extruder is set to 290 to 280°C, the temperature near the outlet is set to 270 to 260°C, and the temperature difference between the temperature near the inlet and the temperature near the outlet is set to 20 to 25°C; (4) A process to remove foreign matter by passing the recycled polyester raw material through a filter with a filtration particle size of 10 to 25 μm.

[0038] First, in the step (1) of removing metallic foreign matter using a metal detector, the recycled polyester raw material is subjected to removal of metallic foreign matter using a commercially available metal detector. A preferred metal detector is one that uses a magnet, and examples of such a method include attaching a magnetic bar to the piping used to blow the recycled polyester raw material to the step (2) to remove metallic foreign matter. If the metal-derived foreign matter is not removed, the heat stability of the polyester will be reduced, the impact resistance of the molded product will be low, and the number of foreign matters will be large, resulting in low transparency when molded.

[0039] In the next step (2), foreign matter is removed by passing the material through an air classifier. The recycled polyester raw material from step (1) is further purified using an air classifier. Examples of air classifiers that can be used include gravity classifiers, inertial classifiers, and centrifugal classifiers. Commercially available air classifiers are available, but it is preferable to use a classifier capable of precise classification. For example, a double-cylinder classifier manufactured by Sanko Air Equipment Co., Ltd. is used. By using an air classifier, powder and froth-like foreign matter adhering to the surface of recycled polyester raw materials can be separated using a nitrogen or air stream. The powder and froth-like foreign matter adhering to the chip surface often has a high melting point, and if it is left adhering without being removed using an air classifier, it will not melt during molding, resulting in molded products with poor transparency.

[0040] Furthermore, in the step (3) of melting the recycled polyester raw material in the extruder, the temperature near the inlet of the recycled polyester raw material in the extruder is set to 290 to 280°C, the temperature near the outlet is set to 270 to 260°C, and the temperature difference between the temperature near the inlet and the temperature near the outlet is set to 20 to 25°C.

[0041] This step is important in the production method of the present invention. In step (3), it is presumed that the foreign matter present in the recycled polyester raw material becomes in a state where it is easily precipitated as foreign matter, with substances derived from the catalyst metal acting as nuclei. Therefore, in the next step (4), it becomes possible to remove the foreign matter from the recycled polyester raw material that could not be removed in steps (1) and (2), and the resin of the present invention that satisfies the above-mentioned characteristic values ​​can be obtained.

[0042] First, when the recycled polyester raw material is fed into the extruder, it is melted at a temperature of 290-280°C, and the temperature inside the extruder is gradually lowered, so that substances derived from the catalyst metal melted in the resin act as nuclei and facilitate the precipitation of foreign matter. At this time, it is important to melt the material by setting the temperature near the extruder outlet to 270-260°C and the temperature difference between the temperature near the inlet and the temperature near the outlet to 20-25°C.

[0043] The temperature near the inlet of the extruder must be set in the range of 290 to 280° C. If this temperature is less than 280° C., the above-mentioned precipitation of foreign matter does not proceed, whereas if this temperature exceeds 290° C., decomposition of the polyester resin tends to proceed, the carboxyl terminal group concentration increases, and the thermal stability becomes poor.

[0044] The residence time of the recycled polyester raw material in the extruder is preferably 10 minutes or less, and more preferably 5 minutes or less from the viewpoint of suppressing the concentration of carboxyl terminal groups and suppressing deterioration in the color tone of the polyester.

[0045] The foreign matter precipitated in step (3) is removed in step (4). In step (4), the recycled polyester raw material is passed through a filter with a filtration particle size of 10 to 25 μm to remove the foreign matter. If a filter with a filtration particle size larger than 25 μm is used, the foreign matter in the precipitated resin cannot be sufficiently removed, and the number of foreign matter particles exceeds 200. On the other hand, if a filter with a filtration particle size smaller than 10 μm is used, the filter is prone to clogging with foreign matter, shortening the filter life, which is cost-inefficient and also worsens operability.

[0046] Furthermore, the filter that can be used in step (4) of the present invention may be a general filter, such as a screen changer type filter, a leaf disc filter, or a candle type sintered filter.

[0047] From the viewpoint of environmental issues, molded articles containing the resin of the present invention preferably contain the resin of the present invention in an amount of 30% by mass or more, more preferably 40% by mass or more, and even more preferably 50% by mass or more. The resin of the present invention has little foreign matter, excellent thermal stability, and performance equivalent to that of virgin polyester resin, so there is no problem in using it in a molded article at 100% by mass. Examples of molded articles include blow molded articles, injection molded articles, sheets, films, etc. obtained by blow molding, injection molding, stretching, etc., and fibers (multifilament yarn, monofilament yarn, long fiber, short fiber) can be obtained by melt spinning. [Example]

[0048] 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 recycled 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.

[0049] (d) Number of foreign objects The measurement was carried out by the above-mentioned method. (e) Haze 1 Using the obtained recycled polyester resin, a 5 mm thick molded plate was molded in an injection molding machine (manufactured by Nissei Plastic Industrial Co., Ltd., model name: PS-20) under conditions of a temperature of 260 to 290°C and a mold temperature of 20°C, and the turbidity was measured using a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., model name: SH-7000) and recorded as the average value for 20. The smaller this value, the better the transparency, and a value of 2% or less was determined to be excellent transparency. (f) Haze 2 Sample pieces (20 pieces) were cut out from the obtained container, and the turbidity was measured using a haze meter (manufactured by Nippon Denshoku Industries Co., Ltd., model name: SH-7000) and recorded as the average value of n=20. The smaller this value, the better the transparency, and a value of 2% or less was determined to be excellent transparency.

[0050] (g) Intrinsic viscosity retention rate 5 g of the obtained recycled polyester resin was placed in a test tube, the inside of the test tube was substituted with a nitrogen atmosphere, and the test tube containing the resin was set in a heater at 300°C. After 30 minutes of heat treatment, the test tube was removed and the intrinsic viscosity of the resin before and after the heat treatment was measured, and the retention rate was calculated using the following formula. Intrinsic viscosity retention rate (%) = (Intrinsic viscosity after heating / Intrinsic viscosity before heating) x 100 (h) Formability The thickness of the body of the resulting containers (100 samples) was measured, and those with a difference in thickness between the thickest and thinnest parts of up to 0.30 mm were deemed to have passed. Depending on the number of samples that passed, the containers were evaluated in two stages as follows: 〇: Number of passing samples is 95 or more ×: Number of passing samples is 94 or less (i) Impact resistance (h) Molded products (100 samples) that passed the moldability evaluation were filled with 340 ml of tap water and dropped once on a P tile from a height of 200 cm, with the bottom and side facing downwards. The number of molded products that did not break was used to evaluate impact resistance. If 90 or more samples were dropped, the impact resistance was evaluated as good. 〇: 90 or more passing samples ×: The number of acceptable samples is 89 or less.

[0051] Example 1 100 kg of recycled polyester raw material (unused polyester resin (pellet-like polyester waste) generated in the process of manufacturing polyester resin, in which 4 mol% of isophthalic acid (IPA) is copolymerized when the total amount of all acid components is 100 mol%)) was passed through an air transfer pipe installed inside the air classifier using a 13,000 gauss magnet bar with 3 magnet bars in 1 row x 3 rows as a metal detector. In this case, a double cylindrical air classifier manufactured by Sanko Air Equipment Co., Ltd. was used as the air classifier. Next, the recycled polyester raw material was introduced into an extruder. At this time, the temperature near the inlet for the recycled polyester raw material of the extruder was set to 285°C, the temperature near the outlet was set to 265°C, and the temperature difference between the temperature near the inlet and the temperature near the outlet was set to 20°C, and the recycled polyester raw material was melted. Then, the recycled polyester raw material was passed through a metering pump and a 20 μm filter to obtain a recycled polyester resin. [Blow molded products] The recycled polyester resin was chipped and dried, and then extruded at 260°C using a direct blow molding machine (manufactured by Tahara) to form a cylindrical parison. While the parison was still softened, it was clamped in a mold to form a bottom, and then blown into a bottle. When the parison reached a diameter of 3 cm and a length of 25 cm, the bottom was formed and blown to obtain a 350 ml hollow container (direct blow molded product).

[0052] Examples 2 to 7, Comparative Examples 1 to 9 A recycled polyester resin was obtained in the same manner as in Example 1, except that the type of recycled polyester raw material (copolymerization amount of isophthalic acid), the presence or absence of a metal detector, the presence or absence of an air classifier, the extruder temperature, and the filter filtration particle size were changed. A blow-molded article was obtained in the same manner as in Example 1 using the obtained recycled polyester resin.

[0053] Table 1 shows the property values ​​of the polyester resins obtained in Examples 1 to 7 and Comparative Examples 1 to 9, and the evaluation results of the haze value, moldability, and impact resistance of the blow-molded products.

[0054] [Table 1]

[0055] As is clear from the results in Table 1, the recycled polyester resins obtained in Examples 1 to 7 had the foreign matter count, haze, intrinsic viscosity retention, and carboxyl terminal group concentration within the ranges specified in the present invention. Therefore, hollow containers obtained from these recycled polyester resins had good moldability and were also excellent in haze value and impact resistance. On the other hand, in Comparative Example 1, the recycled polyester resin obtained did not pass through a metal detector, so it contained metal-derived foreign matter and had poor thermal stability, resulting in a high concentration of carboxyl end groups, a low retention rate of intrinsic viscosity, a large number of foreign matters, and poor haze.The molded product also had uneven thickness, poor moldability, haze, and low impact resistance. In Comparative Example 2, the recycled polyester resin obtained did not pass through a precision classifier, so it contained high-melting-point impurities, had a large amount of impurities, and had poor haze. The molded product also had uneven thickness, poor moldability, poor haze, and low impact resistance. In Comparative Example 3, the temperature directly below the resin inlet of the extruder was high, so the resulting recycled polyester resin had poor thermal stability, a high carboxyl end group concentration, and low intrinsic viscosity retention. It also contained catalyst-derived impurities, resulting in a large amount of impurities and poor haze. The molded product also had uneven thickness, poor moldability, poor haze, and low impact resistance. In Comparative Example 4, the temperature immediately adjacent to the nozzle of the extruder was low, so the resin solidified in the extruder, and no resin could be obtained. In Comparative Example 5, the temperature gradient of the extruder was low at the resin inlet and high near the nozzle, so that catalyst-derived impurities were not precipitated and remained contained in the resin. The resulting recycled polyester resin had a high carboxyl end group concentration and low intrinsic viscosity retention. It also contained catalyst-derived impurities, resulting in a large amount of impurities and poor haze. The molded product also had uneven thickness, poor moldability, haze, and low impact resistance. In Comparative Example 6, the openings of the filter were too small to allow the resin to pass through the extruder, and therefore the resin could not be obtained. In Comparative Example 7, the filter had large openings, so catalyst-derived impurities remained in the resin. The resulting recycled polyester resin had a high carboxyl end group concentration and low intrinsic viscosity retention. The resin also contained catalyst-derived impurities, resulting in a large amount of impurities and poor haze. The molded product also had uneven thickness, poor moldability, poor haze, and low impact resistance. The recycled polyester resin of Comparative Example 8 had a low content of isophthalic acid, and therefore had high crystallinity, which caused crystallization in the molded product and resulted in poor haze. The recycled polyester resin of Comparative Example 9 had a high isophthalic acid content, which resulted in low heat resistance, a high carboxyl end group concentration, and a low intrinsic viscosity retention. The molded product also had uneven thickness and poor moldability and impact resistance.

Claims

[Claim 1] A method for producing a recycled polyester resin comprising at least one recycled polyester raw material consisting of a) used polyester products and b) unused polyesters generated in the process of producing polyester products, the method satisfying all of the following (1) to (5), characterized by carrying out the following steps (1) to (4) in order: Recycled polyester resin (1) When the total amount of all acid components constituting the polyester is taken as 100 mol%, 80 to 98 mol% is terephthalic acid, 1 to 10 mol% is isophthalic acid, and when the total amount of all glycol components is taken as 100 mol%, 80 mol% or more is ethylene glycol; (2) 1 m of sheet when a sheet with a film thickness of 0.2 mm is produced ２ The number of foreign matters having a particle size of 50 μm or more per unit area is 200 or less, (3) Haze is 2% or less; (4) The retention of the intrinsic viscosity before and after melting when melted at a temperature of 300°C for 30 minutes is 85% or more; (5) The concentration of carboxyl terminal groups is 40 equivalents / t or less. process (1) a step of removing metal foreign matter from recycled polyester raw materials using a metal detector; (2) removing foreign matter from the recycled polyester raw material by passing it through an air classifier; (3) A step of melting the recycled polyester raw material in an extruder, wherein the temperature near the inlet of the recycled polyester raw material in the extruder is set to 290 to 280°C, the temperature near the outlet is set to 270 to 260°C, and the temperature difference between the temperature near the inlet and the temperature near the outlet is set to 20 to 25°C; (4) A process of removing foreign matter by passing the recycled polyester raw material through a filter with a filtration particle size of 10 to 25 μm.

Images