Regenerated polyester resin composition and molded article thereof

Abstract

The present invention relates to a regenerated polyester resin composition comprising regenerated dimethyl terephthalate prepared from waste polyester and a molded article thereof. Specifically, according to one embodiment of the present invention, since the regenerated polyester resin composition comprises a regenerated polyester resin comprising a repeating unit derived from a diol component and a repeating unit derived from regenerated dimethyl terephthalate (rDMT); a hindered phenol type main antioxidant; and a phosphorus-based or sulfur-based auxiliary antioxidant, so that the crystallinity, heat resistance and volatility resistance can be improved. Therefore, when a molded article for a vehicle headlamp is prepared using the regenerated polyester resin composition, excellent performance can be exhibited.

Description

Technical Field

[0001] This invention relates to a recycled polyester resin composition comprising recycled dimethyl terephthalate prepared from waste polyester and its molded articles thereof. Background Technology

[0002] Polyester, with its excellent mechanical strength, heat resistance, transparency, and gas barrier properties, is widely used as a material for beverage filling containers, packaging films, audio-visual films, and industrial materials such as medical fibers and tire cords. In particular, polyester sheets or plates have good transparency and excellent mechanical strength, and are therefore widely used as raw materials for shells, boxes, partitions, shelves, panels, packaging materials, building materials, and interior and exterior materials.

[0003] Therefore, a massive amount of plastic waste, including polyester, is generated globally each year at levels that are difficult to manage. Recently, countries worldwide have established regulations and plans for recycling waste plastic resources (including waste polyester). Physical or chemical methods are used to recycle waste polyester. Physical recycling methods cannot guarantee purity and are therefore not widely used. In chemical recycling methods, the ester bonds of waste polyester are broken to depolymerize it. Reactions such as glycolysis, hydrolysis, methanololysis, and ammonolysis can be used.

[0004] In recent years, waste polyester is no longer simply recycled; instead, research is focused on improving the quality of polyester products manufactured from recycled raw materials. For example, there have been attempts to recover waste polyethylene terephthalate (PET) through glycolysis to prepare recycled polyester resins other than PET. However, this reaction uses excess ethylene glycol and has a long reaction time, resulting in a large number of byproducts. Furthermore, when recovering PET through methanol hydrolysis to prepare recycled polyester resins other than PET, there is a significant deterioration in the performance of the final resin and products using it, leading to a decline in quality.

[0005] Meanwhile, examples of polyester products include materials used in vehicle headlights or lamps. Vehicle headlights include a reflector for focusing and guiding light emitted from a light source forward, and a bezel for housing the reflector. The bezel and reflector are made by depositing metal onto a substrate surface, requiring complex design and high gloss. Manufacturing such complex molded parts requires materials with high flowability. That is, by using materials with high flowability, it is possible to produce high-quality molded parts without unformed portions, even in complex mold structures. In recent years, polybutylene terephthalate (PBT) resin has been used as a material to meet the high flowability and smoothness requirements of molded parts such as automotive headlights due to its fast crystallization speed, short molding cycle, and excellent flowability, making it easy to achieve complex shapes. However, with the increasing number of light sources and electronic components in the functional parts of the headlight bezel and reflector, heat sources become more diverse, and designs become more complex. The multiple heat sources and complex structure of the headlight can lead to temperature differences between the inside and outside of the headlight, potentially causing thermal decomposition of the headlight component materials and increasing the likelihood of the components becoming cloudy. Therefore, the required physical properties of resins used as materials are gradually increasing.

[0006] Therefore, research is focused on developing recycled polyester resins and products using these resins, where the final resins prepared from recycled polyester resins and the products produced from them do not deteriorate in performance, achieving excellent quality. At the same time, the recycling process of waste polyester does not require the use of excessive alcohols or glycols, minimizing the formation of byproducts.

[0007] For example, Korean Patent Publication No. 2011-0080260 discloses a method for chemically recycling polyester. This method is easily used to produce fine fibers, functional yarns, etc., and is carried out through the following steps: depolymerizing waste polyester and ethylene glycol to prepare an oligomer solution, contacting the oligomer solution with an ion exchange resin to remove the catalyst in the oligomer solution, passing the oligomer solution after catalyst removal through a decolorizing agent to remove pigments and other colored substances in the oligomer solution, and performing polycondensation on the solution.

[0008] [Existing technical documents]

[0009] (Patent Document 1) Korean Patent Publication No. 2011-0080260. Summary of the Invention

[0010] Technical issues

[0011] Therefore, the present invention aims to provide a recycled polyester resin composition and its molded articles, which, by including recycled dimethyl terephthalate, can minimize the formation of by-products during the depolymerization of waste polyester and can produce recycled dimethyl terephthalate with high purity and excellent processability, while also possessing excellent physical properties.

[0012] Technical solution

[0013] According to one embodiment of the present invention, a recycled polyester resin composition comprises a recycled polyester resin containing repeating units derived from a diol component and repeating units derived from recycled dimethyl terephthalate (rDMT); a hindered phenolic primary antioxidant; and a phosphorus or sulfur secondary antioxidant; wherein, in the recycled polyester resin, when the crystalline area is calculated in X-ray diffraction (XRD) analysis according to Equation 1 below for the separation of crystalline diffraction peaks appearing in the 2θ value range of 0° to 50° by single-peak fitting, the crystalline area value is 20% or more.

[0014] [Equation 1]

[0015] Crystalline area (%) = (Area of ​​crystalline region) / (Area of ​​crystalline region + Area of ​​amorphous region) × 100

[0016] A molded article according to another embodiment of the present invention is prepared from the recycled polyester resin composition.

[0017] Beneficial effects of the present invention

[0018] Since the recycled polyester resin composition according to one embodiment of the present invention comprises a recycled polyester resin containing repeating units derived from a diol component and repeating units derived from recycled dimethyl terephthalate (rDMT); a hindered phenolic primary antioxidant; and a phosphorus or sulfur secondary antioxidant, it is able to improve crystallinity, heat resistance and volatility resistance.

[0019] Typically, recycled dimethyl terephthalate (rDMT) prepared from waste polyester has low purity due to impurities generated from side reactions with reagents used in the depolymerization process. Therefore, attempts have been made to improve purity through methods such as fractionation, but these methods are inefficient in terms of cost, hindering commercial application, and also have limitations in purity improvement.

[0020] Since the recycled polyester resin composition according to one embodiment of the present invention contains recycled dimethyl terephthalate obtained from depolymerized waste polyester and has excellent color, purity and crystallinity, it exhibits excellent performance in terms of crystallinity, heat resistance and volatility resistance.

[0021] Specifically, recycled dimethyl terephthalate (DMT) is prepared through the following steps: crystallizing a depolymerized composition obtained from depolymerized waste polyester at low temperature; separating the solid and liquid phases of the crystallized slurry; and drying, washing, and purifying the product, thereby achieving excellent performance in terms of color, purity, and crystallinity. More specifically, in the method for preparing recycled DMT, the content of ethylene glycol byproducts or terephthalate derivatives such as monomethyl terephthalate (MHT) formed by side reactions during the process is low, in addition to the required DMT. Therefore, when used as a raw material for various polymers, it can improve color characteristics and purity, and enhance quality. Furthermore, since high-purity recycled DMT can be obtained in the method for preparing recycled DMT, its processing performance is excellent. In addition, due to the low content of environmentally impactful ethylene glycol byproducts, it is environmentally friendly.

[0022] Therefore, since this recycled polyester resin is prepared using rDMT, which has excellent purity, crystallinity, and color properties, it exhibits superior performance in properties such as chromaticity (color b and color L), melting point (Tm), enthalpy of fusion, heat distortion temperature, and crystallinity. Thus, products composed solely of recycled polyester resin, without being mixed with commercially available polyester resin, also possess excellent quality.

[0023] Furthermore, the aforementioned high-performance recycled polyester resin is used in conjunction with hindered phenolic primary antioxidants and phosphorus or sulfur-based auxiliary antioxidants, while controlling the content of each component. Therefore, when using recycled polyester resin compositions with these properties to manufacture molded articles (more specifically, retaining rings or reflectors) for vehicle headlights, excellent performance can be achieved. Attached Figure Description

[0024] Figure 1 The X-ray diffraction (XRD) analysis results of resins A, D, E, H, and I are shown.

[0025] Figures 2 to 6 The peaks separated by deconvolution of the X-ray diffraction peaks of resins A, D, E, H and I using the single-peak fitting method are shown respectively.

[0026] Best way to carry out the invention

[0027] The present invention will be described in detail below. The present invention is not limited to the content disclosed below; it can be modified in various forms without altering its essence.

[0028] In this specification, unless otherwise expressly stated, when a component is described as "containing" a certain element, it should be understood that it may also contain other elements, rather than excluding other elements.

[0029] Unless otherwise stated, all numerical values ​​and expressions used in this document relating to component quantities, reaction conditions, etc., should be understood as being modified by the term “about”.

[0030] In this specification, the terms "first," "second," etc., are used to describe the components. However, these components should not be limited by these terms. These terms are only used to distinguish one component from another.

[0031] In this specification, a unit or group "derived from" a specific component refers to a portion of that component that is retained in the final product through a chemical reaction such as polymerization. This portion may exist in a form that is partially modified during the reaction or combined with other components. For example, the chains constituting a polymer may contain units or groups derived from at least one monomer.

[0032] Recycled polyester resin composition

[0033] According to one embodiment of the present invention, a recycled polyester resin composition comprises a recycled polyester resin containing repeating units derived from a diol component and repeating units derived from recycled dimethyl terephthalate (rDMT); a hindered phenolic primary antioxidant; and a phosphorus or sulfur secondary antioxidant; wherein, in the recycled polyester resin, when calculating the crystalline and amorphous regions obtained by separating crystalline diffraction peaks appearing in the 2θ value range of 0° to 50° by single-peak fitting method according to Equation 1 above in X-ray diffraction (XRD) analysis, the crystalline area value is 20% or more.

[0034] According to ASTM D1238, the melt flow index (MI) of this recycled polyester resin composition, measured at 250°C and 2.16 kg, can be 60 g / 10 min or more. For example, according to ASTM D1238, the melt flow index (MI) of this recycled polyester resin composition, measured at 250°C and 2.16 kg, can be 60.5 g / 10 min or more, 61 g / 10 min or more, 62 g / 10 min or more, 65 g / 10 min or more, 70 g / 10 min or more, 72 g / 10 min or more, 76 g / 10 min or more, 80 g / 10 min or more, 85 g / 10 min or more, or 90 g / 10 min or more.

[0035] According to ASTM D638, the tensile strength of this recycled polyester resin composition may be 45 MPa or more. For example, according to ASTM D638, the tensile strength of this recycled polyester resin composition may be 46 MPa or more, 48 MPa or more, 49 MPa or more, 50 MPa or more, 52 MPa or more, 55 MPa or more, 57 MPa or more, or 58 MPa or more.

[0036] According to ASTM D648, the heat distortion temperature (HDT) of this recycled polyester resin composition measured under a low load of 0.45 MPa can be 175°C or higher. For example, according to ASTM D648, the HDT of this recycled polyester resin composition measured under a low load of 0.45 MPa can be 176°C or higher, 178°C or higher, 180°C or higher, 181°C or higher, 182°C or higher, 183°C or higher, 185°C or higher, 186°C or higher, or 188°C or higher.

[0037] The TVOC peak area of ​​the recycled polyester resin composition, as determined by gas chromatography / mass spectrometry (GC / MS), can be 80 area / g or less. For example, the TVOC peak area of ​​the recycled polyester resin composition, as determined by gas chromatography / mass spectrometry (GC / MS), can be 65 area / g or less, 60 area / g or less, 55 area / g or less, 50 area / g or less, 48 ​​area / g or less, 46 area / g or less, 44 area / g or less, 41 area / g or less, or 40 area / g or less.

[0038] Furthermore, according to Equation 2 below, the haze variation of the recycled polyester resin composition can be 5 or less.

[0039] [Equation 2]

[0040] Haze change = |H1–H2|

[0041] In Equation 2, H1 is the haze measured before fogging evaluation of particles prepared using the recycled polyester resin composition at 130°C for 5 hours, according to the DIN 75201-A test method; it is a unitless value. H2 is the haze caused by the gas formed during the fogging evaluation of particles prepared using the recycled polyester resin composition at 130°C for 5 hours, according to the DIN 75201-A test method; it is a unitless value.

[0042] For example, according to Equation 2 above, the haze variation of the recycled polyester resin composition can be 4.5 or less, 4 or less, 3.5 or less, 3 or less, 2.9 or less, 2.8 or less, 2.7 or less, 2.5 or less, or 2.2 or less.

[0043] Furthermore, when granules prepared using this recycled polyester resin composition are dried under reduced pressure at 50°C for 15 hours in a nitrogen atmosphere using a differential scanning calorimeter (DSC, TA instrument), and then heated from 30°C to 240°C at a rate of 10°C / min, and when the conditions are changed from nitrogen to air at a conversion rate of 20 ml / min, the exothermic oxidation time measured after holding at 240°C for 60 minutes can be 10 minutes or more. For example, this exothermic oxidation time can be 10.5 minutes or more, 11 minutes or more, 12 minutes or more, 13 minutes or more, 15 minutes or more, 17 minutes or more, 17.5 minutes or more, 20 minutes or more, 25 minutes or more, 35 minutes or more, 50 minutes or more, or 60 minutes or more.

[0044] Furthermore, the melting point of this recycled polyester resin composition, measured during a second scan using a differential scanning calorimeter, can be 210°C or higher, and the enthalpy of fusion (ΔHm) can be 38 J / g or higher. For example, the melting point can be 215°C or higher, 218°C or higher, 220°C or higher, 222°C or higher, or 225°C or higher, and 300°C or lower, 280°C or lower, 260°C, or 240°C or lower. The enthalpy of fusion (ΔHm) can be 39.5 J / g or higher, 40 J / g or higher, 40.5 J / g or higher, 41 J / g or higher, 41.3 J / g or higher, 42 J / g or higher, 42.5 J / g or higher, 43 J / g or higher, 43.2 J / g or higher, or 43.5 J / g or higher.

[0045] Recycled polyester resin

[0046] A recycled polyester resin composition according to one embodiment of the present invention comprises a recycled polyester resin containing repeating units derived from a diol component and repeating units derived from recycled dimethyl terephthalate (rDMT).

[0047] The recycled polyester resin may contain repeating units derived from one or more diol components; and repeating units derived from one or more acid components.

[0048] The recycled polyester resin can be a homopolymer or copolymer resin. For example, the recycled polyester resin can be polybutylene terephthalate (PBT) resin, which is a homopolymer resin containing 1,4-butanediol as a constitutive diol component and recycled dimethyl terephthalate as a constitutive acid component. As another example, the recycled polyester resin can be a copolymer resin containing 1,4-butanediol and an additional diol as constitutive diol components and recycled dimethyl terephthalate and an additional acid as constitutive acid components. The additional diol and acid components may be added separately in the esterification and / or polycondensation steps, which will be described in detail below in the method for preparing the recycled polyester resin.

[0049] According to one embodiment of the present invention, the recycled polyester resin comprises repeating units derived from a diol component.

[0050] The diol component may comprise at least one selected from the group consisting of: 1,3-propanediol, 1,4-cyclohexanediol, 2-methyl-1,3-propanediol, 2-methylene-1,3-propanediol, 2-ethyl-1,3-propanediol, 2-isopropyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol, 2,3-butanediol, 3-methyl-1,5-pentanediol, 3-methyl-2,4-pentanediol, 1,6-hexanediol, 1,2-cyclohexanediol, 1,4-cyclohexanediol, diethylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylenediol, polyhexamethylenediol, copolymers of ethylene oxide and tetrahydrofuran, polypropylene glycol ethylene oxide adducts, polycarbonate diol, polyneoprene glycol, poly-3-methylpentanediol, and poly-1,5-pentanediol.

[0051] Recycled dimethyl terephthalate can be obtained by depolymerizing waste polyester. Alternatively, recycled dimethyl terephthalate can be prepared by first depolymerizing waste polyester to obtain recycled bis(2-hydroxyethyl) terephthalate (rBHET), and then depolymerizing it. The method for preparing recycled dimethyl terephthalate will be described in detail below.

[0052] Traditionally, recycled terephthalates prepared from waste polyester suffer from poor physical properties, such as color characteristics, and low purity, making them difficult to use alone as an acid component in polyester resins. However, the recycled polyester resin according to one embodiment of the present invention is prepared using this recycled terephthalate; therefore, even with an increased content of recycled terephthalate compared to conventional methods, the resin still ensures sufficient physical properties, resulting in excellent quality. Therefore, the recycled polyester resin according to one embodiment of the present invention may contain only recycled terephthalate, or it may contain recycled terephthalate and another acid component to enhance physical properties and other characteristics.

[0053] The acid component may contain at least one selected from the group consisting of: adipic acid, sebacic acid, succinic acid, isodecylsuccinic acid, maleic acid, fumaric acid, glutaric acid, azelaic acid, 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid, diphenyldicarboxylic acid, 4,4'-stilbenedicarboxylic acid, 2,5-furandicarboxylic acid, and 2,5-thiophenedicarboxylic acid.

[0054] The purity of regenerated dimethyl terephthalate can reach 90% or more. For example, the purity of regenerated dimethyl terephthalate can be obtained by measuring the peak area using ultra-high performance liquid chromatography (UPLC) and then calculating its fraction (%) relative to the total peak area. The purity can be 91% or more, 93% or more, 95% or more, 97% or more, 98% or more, 99% or more, 99.5% or more, or 99.9% or more.

[0055] Specifically, 0.01 g of sample was dissolved in a mixture of 20 ml methanol and a 0.3% phosphoric acid distilled aqueous solution. Peak areas were determined using ultra-high performance liquid chromatography (UPLC), and the percentage (%) of each peak area relative to the total peak area was calculated to determine purity, components formed by side reactions, components formed other than the target product DMT, and their concentrations. In this case, dilution may be performed according to the mobile phase and flow rate.

[0056] Furthermore, the APHA chromaticity value of regenerated dimethyl terephthalate can be 120 or less. For example, according to ASTM-D1209, regenerated dimethyl terephthalate can be dissolved in dimethylformamide at a 10% weight concentration, placed in an analytical container made of quartz with an optical path length of 10 mm, and then measured using a colorimeter in transmission mode. The APHA chromaticity value can be 105 or less, 100 or less, 93 or less, 90 or less, 85 or less, 65 or less, or 55 or less. APHA (American Public Health Association) is a color-coded scale indicating the level of contamination in a liquid. The lower the value, the closer it is to the color of pure water (colorless). Because regenerated dimethyl terephthalate has APHA chromaticity values ​​that meet the above range, it has high purity and low contamination, and therefore excellent quality.

[0057] According to one embodiment of the present invention, in X-ray diffraction (XRD) analysis, when calculating the crystalline and amorphous regions of the recycled polyester resin obtained by separating the crystalline diffraction peaks appearing in the 2θ value range of 0° to 50° by single-peak fitting method according to the following Equation 1, the crystalline area value is 20% or more.

[0058] [Equation 1]

[0059] Crystalline area (%) = (Area of ​​crystalline region) / (Area of ​​crystalline region + Area of ​​amorphous region) × 100

[0060] Here, the crystallization area value (%) refers to the percentage (%) of the crystalline region area relative to the total area measured in the X-ray diffraction (XRD) analysis of the polyester resin, where the total area is the sum of the areas of the crystalline and amorphous regions. According to the present invention, the area of ​​each region used as the basis for calculating the crystallization area value (%) is obtained by separating the peaks measured in the 2θ range of 0° to 50° in the X-ray diffraction (XRD) analysis of the polyester resin using a single-peak fitting method. The area of ​​each region can be calculated as an integral value of the crystalline or amorphous region, respectively. Because the crystalline components are regularly arranged in three-dimensional space, X-rays are scattered in a certain direction when they collide with the diffraction surface; therefore, the diffraction peaks of the crystalline region appear as high and narrow peaks. In contrast, because the amorphous components are randomly arranged, they are scattered in multiple directions; therefore, the peaks of the amorphous region appear gradually over a wider 2θ range (see...). Figures 2 to 6 ).

[0061] According to Equation 1 above, the larger the crystallization area value, specifically the higher the proportion of each crystallization area separated by the single-peak fitting method, the better the crystallinity of the resin. Furthermore, the mechanical strength, heat resistance, and chemical resistance of the resin can also be improved. However, as crystallinity increases, the bond strength decreases at temperatures below the melting point (Tm), which may limit the application of the resin; therefore, controlling the performance within an appropriate range is crucial.

[0062] For example, the crystalline area value of the recycled polyester resin according to Equation 1 above can be 20.5% or more, 21% or more, 21.5% or more, 22% or more, 22.5% or more, 23% or more, 25% or more, 26% or more, 27% or more, 29% or more, 30% or more, 31% or more, 33% or more, or 33.5% or more. Because the crystalline area value of the recycled polyester resin according to Equation 1 above meets the above range, it possesses ideal properties such as mechanical properties, heat resistance, chemical resistance, and adhesive strength, and has excellent crystallinity, thus making it suitable for a variety of applications.

[0063] The XRD analysis according to Equation 1 above can be wide-angle X-ray diffraction (WAXD) analysis, and can be performed by taking WAXD plate images using a Rigaku SmartLab X-ray diffractometer. In the above WAXD analysis, measurement data corrected for polarization factor, absorption factor, and air scattering can be used to perform deconvolution and separation of amorphous component regions in X-ray diffraction (XRD) analysis. Using the integral value of the diffraction peak in the crystalline region within the 2θ angle range of 0° to 50° and the scattering intensity value of the amorphous region, the crystalline area value (%) can be calculated according to Equation 1 above.

[0064] Furthermore, the difference in crystallization area values ​​calculated by the recycled polyester resin according to Equation 3 below can be negative.

[0065] [Equation 3]

[0066] Difference in crystallization area = Ca1 – Ca2

[0067] In Equation 3, Ca1 is the crystallization area value of polyester resin containing repeating units derived from dimethyl terephthalate (virgin DMT) calculated according to Equation 1 above, which is a unitless value; Ca2 is the crystallization area value of recycled polyester resin containing repeating units derived from recycled dimethyl terephthalate (rDMT) calculated according to Equation 1 above, which is a unitless value.

[0068] Specifically, Ca1 is the crystallization area value calculated according to Equation 1 above for polyester resin containing repeating units derived from commercially available dimethyl terephthalate rather than recycled dimethyl terephthalate prepared from waste polyester, and is a unitless value. For example, Ca1 can be 20 or more, 20.5 or more, 21 or more, 21.5 or more, or 22 or more.

[0069] Ca2 is the crystallization area value calculated according to Equation 1 above for recycled polyester resin containing repeating units derived from recycled dimethyl terephthalate prepared from waste polyester, and it is a unitless value. For example, as mentioned above, Ca2 can be 20.5 or more, 21 or more, 21.5 or more, 22 or more, 22.5 or more, 23 or more, 25 or more, 25.5 or more, 27 or more, 29 or more, 30 or more, 31.5 or more, 32 or more, or 33.5 or more.

[0070] The difference in crystallization area values ​​according to Equation 3 above can be -0.5 or less, -1 or less, -2 or less, -3 or less, -4 or less, -5 or less, -6 or less, -7 or less, -8 or less, -9.5 or less, -10 or less, -11 or less, or -12 or less. Since the difference in crystallization area values ​​according to Equation 3 satisfies the above range, it exhibits superior crystallinity compared to polyester resins containing commercially available dimethyl terephthalate but not recycled dimethyl terephthalate.

[0071] Furthermore, based on the total molar number of glycol component residues, the total content (molar percentage) of ethylene glycol residues and diethylene glycol residues in the recycled polyester resin can be 5 mol% or less. Specifically, the recycled polyester resin may contain ethylene glycol residues. More specifically, the recycled polyester resin may contain ethylene glycol residues and diethylene glycol residues. For example, the polyester resin may contain ethylene glycol residues and diethylene glycol residues in a content that, based on the total molar number of glycol component residues, is 3.5 mol% or less, 2.5 mol% or less, 2 mol% or less, 1.8 mol% or less, or 1.5 mol% or less, and is 0.01 mol% or more, 0.02 mol% or more, 0.03 mol% or more, 0.05 mol% or more, or 0.1 mol% or more.

[0072] The intrinsic viscosity of the recycled polyester resin at 35°C can be from 0.5 dl / g to 1.5 dl / g. For example, the intrinsic viscosity of the recycled polyester resin at 35°C can be from 0.55 dl / g to 1.35 dl / g, 0.65 dl / g to 1.3 dl / g, 0.7 dl / g to 1.2 dl / g, 0.72 dl / g to 1.14 dl / g, 0.55 dl / g to 1.1 dl / g, or 0.6 dl / g to 0.7 dl / g.

[0073] The chromaticity b of the recycled polyester resin may be 12 or lower. For example, the chromaticity b of the recycled polyester resin may be 10 or less, 9 or less, 8.5 or less, 8.1 or less, 7.5 or less, or 7 or less, and greater than 0, 1 or more, 2 or more, 2.5 or more, or 3 or more.

[0074] The chromaticity L of the recycled polyester resin can be 70 or more. For example, the chromaticity L of the recycled polyester resin can be 72 or more, 75 or more, 78 or more, 80 or more, 81 or more, 82 or more, or 83 or more.

[0075] Color characteristics are defined by a color coordinate system established by the International Commission on Illumination (CIE), in which color is represented by three parameters: L (lightness), a (complementary color from green to red), and b (complementary color from yellow to blue). These parameters can be measured using a colorimeter.

[0076] Furthermore, the melting point of the recycled polyester resin, measured during a second scan using a differential scanning calorimeter, can be 210°C or higher, and the enthalpy of fusion (ΔHm) can be 38 J / g or higher. For example, the melting point can be 215°C or higher, 218°C or higher, 220°C or higher, 222°C or higher, or 225°C or higher, and 300°C or lower, 280°C or lower, 260°C, or 240°C or lower. The enthalpy of fusion (ΔHm) can be 39.5 J / g or higher, 40 J / g or higher, 40.5 J / g or higher, 41 J / g or higher, 41.3 J / g or higher, 42 J / g or higher, 42.5 J / g or higher, 43 J / g or higher, 43.2 J / g or higher, or 43.5 J / g or higher.

[0077] Specifically, the enthalpy of fusion can be determined by drying the recycled polyester resin under reduced pressure at 50°C for 15 hours, melting it at 260°C, rapidly cooling it to 30°C, and then scanning it using a differential scanning calorimeter at a heating rate of 10°C / min. In this case, the enthalpy of fusion can be determined by using a scanning calorimeter to measure the enthalpy of fusion through the first scan (1... st (scan) or second scan (2) nd The enthalpy of fusion is measured by a second scan. In this specification, the measurement is performed by a second scan.

[0078] In the heat flow curve obtained by scanning, the first endothermic temperature is the glass transition temperature (Tg), the exothermic temperature measured after the glass transition temperature (Tg) is the crystallization temperature (Tc), and the endothermic temperature measured after the crystallization temperature (Tc) is the melting point (Tm). In addition, the integral value at the melting point (Tm) is calculated as the enthalpy of fusion (ΔHm).

[0079] Furthermore, according to ASTM D648, the heat deflection temperature (HDT) of recycled polyester resin measured under a low load of 0.48 MPa can be 90°C or higher. For example, the HDT can be 92°C or higher, 94.5°C or higher, 95°C or higher, 96°C or higher, 98°C or higher, 98.4°C or higher, 99°C or higher, 99.3°C or higher, 99.5°C or higher, 100°C or higher, or 101°C or higher.

[0080] Main antioxidants

[0081] A recycled polyester resin composition according to one embodiment of the present invention comprises a primary antioxidant.

[0082] The primary antioxidant can be a phenolic antioxidant. This phenolic antioxidant prevents oxidation of the recycled polyester resin composition and also acts as a heat stabilizer. There are no particular limitations on the type of phenolic antioxidant; various commercially available phenolic antioxidants can be used. As a specific example, a recycled polyester resin composition according to one embodiment of the present invention comprises a hindered phenolic primary antioxidant.

[0083] For example, the primary antioxidant may comprise tetra[methylene-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]methane, octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, phenylpropionic acid, 3,5-bis(1,1-dimethylethyl)-4-hydroxy, alkyl esters (wherein the alkyl group has 7 or 9 carbon atoms), triethylene glycol-bis-3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionate, tris(3,5-di-tert-butyl-4-hydroxybenzyl)isocyanurate, 1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene, or combinations thereof.

[0084] The recycled polyester resin composition may contain 0.001 to 0.3 parts by weight of a major antioxidant relative to 100 parts by weight of the recycled polyester resin. For example, the content of the major antioxidant may be 0.002 to 0.3 parts by weight, 0.005 to 0.3 parts by weight, 0.01 to 0.3 parts by weight, 0.01 to 0.25 parts by weight, 0.02 to 0.2 parts by weight, or 0.05 to 0.1 parts by weight relative to 100 parts by weight of the recycled polyester resin.

[0085] When the content of the main antioxidant meets the above range, the recycled polyester resin composition and its molded articles can advantageously minimize discoloration or gas generation caused by high-temperature thermal decomposition, thereby ensuring excellent appearance. If the content is below the above range, oxidation may occur at high temperatures, leading to deterioration of physical properties. If the content exceeds the above range, antioxidant decomposition products may migrate to the surface under prolonged high-temperature conditions, resulting in poor performance in fogging assessment.

[0086] The effect of antioxidants on the thermal stability of polyester resins at high temperatures can be verified by the oxidation induction time (OIT). Many organic compounds, including polymers, readily undergo oxidation reactions even at low temperatures in the presence of oxygen. However, some substances, when exposed to isothermal conditions, exhibit an induction period during which they do not react with oxygen. This period is called the oxidation induction time (OIT). After this induction period, the reaction rate with oxygen increases. In other words, OIT represents information about the oxidative stability of a substance. The time at which the exothermic reaction begins, defined as the OIT, is determined by rapidly heating to the desired temperature using differential scanning calorimetry (DSC) in a nitrogen atmosphere and maintaining stability, followed by switching to an oxygen atmosphere and maintaining an isothermal state.

[0087] Co-oxidants

[0088] A recycled polyester resin composition according to one embodiment of the present invention comprises an auxiliary antioxidant. Specifically, a recycled polyester resin composition according to one embodiment of the present invention comprises a phosphorus-based or sulfur-based auxiliary antioxidant.

[0089] For example, phosphorus antioxidants may contain 3,9-bis(2,4-dicumylphenoxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane, bis(2,6-di-tert-butyl-4-methylphenyl)pentaerythritol diphosphite, bis(2,4-di-tert-butylphenyl)pentaerythritol diphosphite, tetra(2,4-di-tert-butylphenyl)4,4'-biphenyl diphosphite, or combinations thereof.

[0090] In addition, sulfur-based antioxidants may include, for example, dilauryl 3,3'-thiodipropionate, dimyristyl 3,3'-thiodipropionate, distearate 3,3'-thiodipropionate, lauryl stearate 3,3'-thiodipropionate, pentaerythritol tetra(3-lauryl thiopropionate) or combinations thereof.

[0091] The recycled polyester resin composition may contain 0.001 to 0.2 parts by weight of an auxiliary antioxidant relative to 100 parts by weight of the recycled polyester resin. For example, the content of the auxiliary antioxidant may be 0.002 to 0.2 parts by weight, 0.005 to 0.2 parts by weight, 0.01 to 0.2 parts by weight, or 0.02 to 0.18 parts by weight relative to 100 parts by weight of the recycled polyester resin.

[0092] When the content of the auxiliary antioxidant meets the above range, the recycled polyester resin composition and its molded articles can advantageously minimize discoloration or gas generation caused by high-temperature thermal decomposition, thereby ensuring excellent appearance. If the content is below the above range, oxidation may occur at high temperatures, leading to deterioration of physical properties. If the content exceeds the above range, antioxidant decomposition products may migrate to the surface under prolonged high-temperature conditions, resulting in poor performance in fogging assessment.

[0093] Wax-based lubricants

[0094] A recycled polyester resin composition according to one embodiment of the present invention may contain a wax-based lubricant.

[0095] Using wax-based lubricants helps ensure the release properties of products made from recycled polyester resin compositions during injection molding.

[0096] The wax may contain at least one of fatty acid ester lubricants and montan-based lubricants.

[0097] Fatty acid ester lubricants may contain at least one selected from the group consisting of: fatty acid esters of alcohols or polyols, hardened oils, butyl stearate, glyceryl monostearate, pentaerythritol tetrastearate, stearyl stearate, ester waxes, and alkyl phosphates.

[0098] Lignite wax lubricants may contain at least one of lignite ester wax and lignite metal salt. The saponification value of the lignite ester wax may be from 20 mg KOH / g to 300 mg KOH / g, or from 50 mg KOH / g to 250 mg KOH / g. When lignite ester wax with a saponification value within the above range is used, the recycled polyester resin composition and its molded articles may exhibit excellent miscibility and release properties.

[0099] Specifically, the recycled polyester resin composition may include a waxy lubricant comprising at least one selected from the group consisting of fatty acid esters, fatty acid amides, polyethylene waxes, plant waxes, and mineral waxes.

[0100] The content of the waxy lubricant relative to 100 parts by weight of recycled polyester resin can be from 0.001 parts by weight to 0.2 parts by weight. For example, the content of the waxy lubricant relative to 100 parts by weight of recycled polyester resin can be from 0.002 parts by weight to 0.2 parts by weight, 0.005 parts by weight to 0.2 parts by weight, 0.01 parts by weight to 0.18 parts by weight, 0.02 parts by weight to 0.15 parts by weight, 0.05 parts by weight to 0.15 parts by weight, 0.05 parts by weight to 0.12 parts by weight, or 0.05 parts by weight to 0.1 parts by weight.

[0101] When the content of the wax-based lubricant meets the above-mentioned range, the recycled polyester resin composition and its molded articles can exhibit excellent miscibility and release properties. If the content exceeds the above-mentioned range, the anti-volatilization properties of the recycled polyester resin composition and its molded articles may be poor.

[0102] In addition, the recycled polyester resin composition may contain at least one additive selected from the group consisting of: flame retardants, nucleating agents, coupling agents, fillers, plasticizers, impact modifiers, lubricants, antibacterial agents, release agents, inorganic additives, UV stabilizers, antistatic agents, pigments, and dyes.

[0103] The recycled polyester resin composition may contain 0.01 to 3 parts by weight of additives relative to 100 parts by weight of recycled polyester resin. For example, the total amount of additives may be 0.02 to 2.5 parts by weight, 0.03 to 2 parts by weight, 0.05 to 1.5 parts by weight, 0.1 to 1.2 parts by weight, 0.2 to 1 part by weight, or 0.5 to 1 part by weight.

[0104] Molded products

[0105] A molded article according to another embodiment of the present invention is prepared from the recycled polyester resin composition.

[0106] Because the molded products are made from recycled polyester resin compositions, they possess excellent crystallinity, heat resistance, and volatility resistance.

[0107] The molded article may be a molded article used for vehicle headlights, but is not limited to this.

[0108] As a specific example, the molded article can be in granular form obtained by melt extruding a recycled polyester resin composition using a twin-screw extruder at a temperature of 200°C to 300°C or 220°C to 260°C.

[0109] Method for preparing recycled dimethyl terephthalate

[0110] A method for preparing recycled dimethyl terephthalate according to another embodiment of the present invention comprises depolymerizing waste polyester to obtain a depolymerized composition; and crystallizing the resulting depolymerized composition.

[0111] Waste polyester can be obtained by crushing or melting waste polyester products. For example, waste polyester can be obtained by crushing used and recycled polyester products or processing them into granules (post-consumer recycled materials; PCR), or by polyester waste such as defective products or waste that may be generated in the molding of polyester films, fibers, containers, etc. (post-industrial recycled materials; PIR), but is not limited to these. As a specific example, waste polyester can be waste polyethylene terephthalate (waste PET).

[0112] In addition, waste polyester can be cut or crushed to sizes of 1mm to 30mm, 2mm to 25mm, or 3mm to 20mm to improve the process efficiency of the depolymerization step, and can be made into recycled polyester chips by washing and drying.

[0113] For example, the intrinsic viscosity (IV) of waste polyester may be greater than 0.3 dl / g, 0.35 dl / g or more, 0.4 dl / g or more, or 0.45 dl / g or more, and is 1.1 dl / g or less, 1.0 dl / g or less, or 0.9 dl / g or less.

[0114] A method for preparing recycled dimethyl terephthalate according to another embodiment of the present invention comprises depolymerizing waste polyester to obtain a depolymerized composition.

[0115] This depolymerization may include alcoholysis. Specifically, alcoholysis can be carried out using alcohols, more specifically, monohydric or dihydric alcohols. Furthermore, this depolymerization may include glycolysis. Specifically, glycolysis can be carried out using ethylene glycol.

[0116] Furthermore, depolymerization can be carried out at temperatures ranging from 80°C to 240°C. For example, depolymerization can be carried out at temperatures ranging from 85°C to 235°C, 90°C to 225°C, or 90°C to 220°C.

[0117] According to one embodiment of the present invention, depolymerization can be performed in one step or in two steps, namely, first depolymerization and second depolymerization.

[0118] As a specific example, depolymerization can be carried out through alcoholysis of waste polyester, or by first depolymerizing the waste polyester to generate recycled di(2-hydroxyethyl) terephthalate (rBHET), followed by a second depolymerization of rBHET. More specifically, the first depolymerization can be achieved through glycolysis using ethylene glycol, while the second depolymerization can be achieved through alcoholysis using alcohols.

[0119] For example, waste polyester and methanol are added to a first high-pressure reactor, an alcoholysis catalyst is added thereto, and alcoholysis can be carried out with all connections of the first high-pressure reactor sealed.

[0120] As another example, waste polyester, ethylene glycol, and anhydrous zinc acetate can be added to a stainless steel reactor for a first depolymerization via glycolysis to obtain solid rBHET. Subsequently, solid rBHET and methanol are added to a first high-pressure reactor, an alcoholysis catalyst is added, and a second depolymerization can be carried out via alcoholysis with all connections of the first high-pressure reactor sealed to obtain solid rDMT.

[0121] Alcohololysis can be carried out for 2 to 5 hours at temperatures ranging from 80°C to 240°C and pressures ranging from 2 to 60 bar. For example, alcohololysis can be carried out for 2.5 to 5 hours, 2.5 to 4 hours, or 3 to 5 hours at temperatures ranging from 80°C to 235°C, 85°C to 230°C, or 90°C to 230°C, and pressures ranging from 2 to 60 bar, 3 to 60 bar, 4 to 60 bar, 3 to 20 bar, 3 to 15 bar, 35 to 60 bar, 40 to 60 bar, or 50 to 60 bar.

[0122] Alcohololysis can be carried out by adding an alcoholysis catalyst. Alcohololysis can proceed smoothly as a non-catalytic reaction, eliminating the need for a catalyst and making it environmentally friendly. Especially when the waste polyester contains a high content of insoluble metals, non-catalytic reactions may be more advantageous for efficient treatment and impurity removal. Furthermore, for energy consumption considerations, an alcoholysis catalyst can be added to enhance processability by increasing reaction activity.

[0123] The alcoholysis catalyst can be a metal acetate, alkali metal salt, or hydroxyl salt.

[0124] More specifically, the alcoholysis catalyst may contain at least one cation selected from the group consisting of alkali metal ions such as Li + Na + K + and Cs + Alkaline earth metal ions such as Be 2+ Mg 2+ Ca 2+ and Ba 2+ Ammonium ions, such as NH4+ 4+ and NR 4+ (where R is an alkyl group), and Zn 2+ Or at least one anion selected from the group consisting of: OH- - OR - (where R is an alkyl group), HCO3 - CO3 2- Benzoate ions (C7H5O2) - ), 4-alkoxycarbonylbenzoate ion, acetate ion and terephthalate ion. R can be an alkyl group having 1 to 10 carbon atoms or an alkyl group having 1 to 5 carbon atoms.

[0125] For example, the alcoholysis catalyst may contain at least one selected from the group consisting of: Zn(OAc)2, Co(OAc)2, Mn(OAc)2, Mg(OAc)2, Ca(OAc)2, Ba(OAc)2, LiOAc, NaOAc, KOAc, Zn(OAc)2·2H2O, Co(OAc)2·4H2O, Pb(OAc)2, Mn(OAc)2·4H2O, Mg(OAc)2·4H2O, Pd(OAc)2, Ti(OBu)4, Ti(OiPr)4, GeO2, Al(OiPr)3, Na2CO3, K2CO3, dibutyltin(IV) oxide, stannous octoate, titanium phosphate, and terephthalic acid.

[0126] The amount of alcoholysis catalyst added can be from 10 ppm to 10,000 ppm, depending on the total weight of the waste polyester. For example, when depolymerization is carried out in one step, the amount of alcoholysis catalyst added relative to the total weight of the waste polyester can be 10 ppm to 9,000 ppm, 50 ppm to 8,000 ppm, 100 ppm to 6,000 ppm, 250 ppm to 3,500 ppm, 300 ppm to 2,000 ppm, 500 ppm to 1,500 ppm, or 600 ppm to 1,200 ppm.

[0127] Furthermore, the amount of alcoholysis catalyst added relative to the total weight of rBHET can be from 10 ppm to 10,000 ppm. For example, when depolymerization is carried out in two steps and the depolymerization corresponding to the alcoholysis reaction is the second depolymerization, the amount of alcoholysis catalyst added relative to the total weight of the intermediate product (specifically rBHET) generated by the first depolymerization can be from 10 ppm to 9,000 ppm, 50 ppm to 8,000 ppm, 100 ppm to 6,000 ppm, 250 ppm to 3,500 ppm, 300 ppm to 2,000 ppm, or 300 ppm to 1,500 ppm.

[0128] Furthermore, glycolysis can be carried out at temperatures ranging from 160°C to 240°C. For example, glycolysis can be performed by raising the temperature inside the reactor to 170°C to 220°C, 175°C to 210°C, or 185°C to 200°C.

[0129] A method for preparing recycled dimethyl terephthalate according to another embodiment of the present invention comprises crystallizing the resulting depolymerized composition.

[0130] The crystallization step can be carried out by cooling the depolymerized composition to 25°C to 60°C and stirring at a low speed of 10 rpm to 30 rpm or by letting it stand for 1 hour to 6 hours. For example, the crystallization step can be carried out by cooling the depolymerized composition to 25°C to 55°C, 30°C to 60°C, or 40°C to 55°C and stirring at a low speed of 10 rpm to 25 rpm or 10 rpm to 20 rpm, or by letting it stand for 1 hour to 5 hours or 2 hours to 4 hours.

[0131] More specifically, since the crystallization step under the above conditions is carried out after depolymerization, a depolymerized composition in slurry form can be obtained. As a specific example, since the crystallization step under the above conditions is carried out after alcoholysis depolymerization, an alcoholysis composition in slurry form can be obtained. The slurry-form depolymerized composition may contain solid-phase regenerated dimethyl terephthalate (rDMT), excess unreacted methanol, a small amount of liquid-phase dissolved regenerated dimethyl terephthalate (rDMT), ethylene glycol derivatives generated from side reactions, polyester oligomers, methanol-terminated oligomers, etc.

[0132] In this case, the depolymerization composition obtained by the crystallization step may contain ethylene glycol derivatives generated by the side reaction, as well as terephthalic acid and terephthalate derivatives generated in addition to the target product DMT or BHET, wherein each component and its content can be analyzed by ultra-high performance liquid chromatography (UPLC).

[0133] Furthermore, after depolymerization is complete, the components used in depolymerization can be recovered through stratification or fractional distillation. For example, methanol used in alcoholysis or ethylene glycol used in glycolysis can be recovered through stratification or fractional distillation.

[0134] In addition, ethylene glycol derivatives may be generated as byproducts during the depolymerization step.

[0135] Based on the total weight of recycled dimethyl terephthalate, the content of ethylene glycol derivatives may be 5% by weight or less. For example, ethylene glycol derivatives may comprise ethylene glycol and diethylene glycol, and based on the total weight of recycled dimethyl terephthalate, the content of ethylene glycol derivatives may be 4% by weight or less, 3.5% by weight or less, 3% by weight or less, 2.5% by weight or less, or 2% by weight or less, and may be 0.1% by weight or more, 0.2% by weight or more, 0.3% by weight or more, or 0.5% by weight or more.

[0136] In addition, terephthalic acid and terephthalate derivatives may be generated as byproducts during the depolymerization step.

[0137] Terephthalate derivatives do not contain dimethyl terephthalate, but may be at least one selected from the group consisting of: dimethyl isophthalate (DMI), monomethyl terephthalate (MHT), 1-(2-hydroxyethyl)4-methyl terephthalate (HEMT), ethyl methyl terephthalate (EMT), mono(hydroxyethyl) terephthalate (MHET), 2-hydroxyethyl[2-(2-hydroxyethoxy)ethyl] terephthalate (HEHDET) and bis[2-(2-hydroxyethoxy)ethyl] terephthalate (BDHET), but are not limited thereto.

[0138] In this case, based on the total weight of recycled dimethyl terephthalate, the content of terephthalic acid and terephthalate derivatives may be 10% by weight or less. For example, based on the total weight of recycled dimethyl terephthalate, the content of terephthalic acid and terephthalate derivatives may be 9% by weight or less, 8% by weight or less, 6.5% by weight or less, 5% by weight or less, 3% by weight or less, 1.5% by weight or less, or 1% by weight or less.

[0139] Furthermore, the rDMT ultimately prepared by depolymerization may contain inorganic compounds. For example, the final rDMT may contain at least one inorganic compound selected from the group consisting of: antimony-containing compounds, germanium-containing compounds, titanium-containing compounds, zinc-containing compounds, cobalt-containing compounds, tin-containing compounds, aluminum-containing compounds, magnesium, sodium salts, potassium salts, phosphorus-containing compounds, and sulfur-containing compounds. These inorganic compounds may be derived from waste polyester or may be additional components added during the depolymerization process. Based on the total weight of the rDMT, the content of inorganic compounds may be from 10 ppm to 500 ppm, 30 ppm to 400 ppm, 50 ppm to 350 ppm, or 100 ppm to 300 ppm.

[0140] According to one embodiment of the present invention, the method for preparing regenerated dimethyl terephthalate may further include at least one step selected from the group consisting of a solid-liquid separation step, a drying step, a washing step, and a purification step.

[0141] For example, washing and purification steps can be performed after the crystallization step, or solid-liquid separation, washing, and purification steps can be performed after the crystallization step.

[0142] More specifically, after the crystallization step, solid-liquid separation, drying, washing, and purification steps can be performed sequentially. As a specific example, the depolymerized composition obtained through the crystallization step can be separated into solid and liquid, and then dried and washed to obtain a wet cake-like rDMT. The washed wet cake-like rDMT can be purified to obtain solid rDMT.

[0143] Solid-liquid separation can be performed using a centrifuge. Specifically, the solid rDMT or rBHET contained in the depolymerization composition can be separated from the liquid components (such as ethylene glycol and methanol) introduced during depolymerization through solid-liquid separation. Specifically, solid-liquid separation can be performed using a centrifuge at 1000 rpm to 4000 rpm, 1500 rpm to 3500 rpm, or 2000 rpm to 3000 rpm.

[0144] The drying step can be carried out at temperatures ranging from 85°C to 130°C. For example, the drying step can be performed at temperatures ranging from 90°C to 120°C, 95°C to 110°C, or 95°C to 105°C.

[0145] Washing can be performed three or more times using mixtures of alcohol and / or water, protic solvents such as isopropanol and acetic acid, or aprotic solvents such as acetone, dichloromethane, chloroform, tetrahydrofuran (THF), and toluene. Residual pigments or yellow impurities produced during pigment decomposition during hydrolysis can be effectively removed by washing, thereby improving color properties.

[0146] The purification step can be carried out by fractional distillation at temperatures ranging from 170°C to 240°C and under reduced pressure of 100 Torr or less. For example, the purification step can be carried out by fractional distillation at temperatures ranging from 175°C to 235°C, 180°C to 225°C, or 190°C to 220°C, and under reduced pressure of 100 Torr or less, 80 Torr or less, or 60 Torr or less. Furthermore, the purification step may further include cooling to room temperature after fractional distillation.

[0147] Methods for preparing recycled polyester resin

[0148] According to another embodiment of the present invention, a method for preparing recycled polyester resin comprises depolymerizing waste polyester to prepare recycled dimethyl terephthalate (rDMT); mixing the rDMT with a diol component and subjecting the mixture to an esterification reaction to prepare recycled bis(4-hydroxybutyl) terephthalate (rBHBT); and subjecting the rBHBT to a polycondensation reaction to prepare recycled polyester resin, wherein, in the recycled polyester resin, when calculating the crystalline and amorphous regions obtained by separating the crystalline diffraction peaks appearing in the 2θ value range of 0° to 50° using the single-peak fitting method according to Equation 1 above in X-ray diffraction (XRD) analysis, the crystalline area value is 20% or more.

[0149] The steps for depolymerizing waste polyester to prepare recycled dimethyl terephthalate are as described above.

[0150] Details of the diol component are as described above. rDMT forms residues of bis(4-hydroxybutyl) terephthalate or its oligomers through esterification with the diol. More specifically, rBHBT or its oligomers can constitute the polymer chain of the ultimately prepared polyester resin.

[0151] Esterification reactions can be carried out at temperatures of 165°C or higher, 170°C or higher, 180°C or higher, or 190°C or higher, and can be carried out at temperatures of 225°C or lower, 220°C or lower, 215°C or lower, 210°C or lower, or 205°C or lower. For example, esterification reactions can be carried out at temperatures of 170°C or higher to facilitate the removal of the byproduct methanol; they can also be carried out at temperatures 10°C lower than the boiling point of the glycol to reduce the loss of the glycol to be substituted. As a specific example, the esterification reaction of 1,4-butanediol with rDMT can be carried out at temperatures between 170°C and 220°C.

[0152] Furthermore, esterification reactions can occur at pressures above atmospheric pressure (0 kg / cm²). 2 Up to 10kg / cm 2 (0 mmHg to 7355.6 mmHg), 0 kg / cm 2 Up to 5kg / cm 2 (0 to 3677.8 mmHg) or 0 kg / cm 2 Up to 2.0 kg / cm 2 The esterification reaction is carried out under pressure of 0 to 1471.1 mmHg. Furthermore, the esterification reaction can be carried out for 1 to 24 hours, 1 to 10 hours, or 1 to 6 hours.

[0153] The polycondensation reaction can be carried out at temperatures ranging from 150°C to 300°C, 200°C to 290°C, 240°C to 280°C, or 260°C to 280°C. Furthermore, the polycondensation reaction can be carried out under reduced pressure conditions ranging from 0.01 mmHg to 600 mmHg, 0.05 mmHg to 300 mmHg, or 0.1 mmHg to 100 mmHg. Moreover, the polycondensation reaction can be carried out for the desired time until the target intrinsic viscosity is reached. For example, it can be carried out for 1 hour to 24 hours, 1 hour to 10 hours, or 1 hour to 4 hours. When the polycondensation process conditions meet the above ranges, the diol, as a byproduct of the polycondensation reaction, can be efficiently removed from the system.

[0154] At the start of the polycondensation reaction, the stirring speed can be set to a higher value. As the polycondensation reaction proceeds, if the stirring power decreases due to the increase in the viscosity of the reactants or if the temperature of the reactants rises above the set temperature, the stirring speed can be adjusted accordingly.

[0155] In addition, diol or acid components may be added during the esterification and / or polycondensation steps.

[0156] The diol component may comprise at least one selected from the group consisting of: 1,3-propanediol, 1,4-cyclohexanediol, 2-methyl-1,3-propanediol, 2-methylene-1,3-propanediol, 2-ethyl-1,3-propanediol, 2-isopropyl-1,3-propanediol, 2,2-dimethyl-1,3-propanediol, 2,3-butanediol, 3-methyl-1,5-pentanediol, 3-methyl-2,4-pentanediol, 1,6-hexanediol, 1,2-cyclohexanediol, 1,4-cyclohexanediol, diethylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylenediol, polyhexamethylenediol, copolymers of ethylene oxide and tetrahydrofuran, polypropylene glycol ethylene oxide adducts, polycarbonate diol, polyneoprene glycol, poly-3-methylpentanediol, and poly-1,5-pentanediol.

[0157] The acid component may contain at least one selected from the group consisting of: adipic acid, sebacic acid, succinic acid, isodecylsuccinic acid, maleic acid, fumaric acid, glutaric acid, azelaic acid, 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid, diphenyldicarboxylic acid, 4,4'-stilbenedicarboxylic acid, 2,5-furandicarboxylic acid, and 2,5-thiophenedicarboxylic acid.

[0158] In addition, catalysts and / or stabilizers may be added during esterification and polycondensation reactions.

[0159] For example, catalysts used in esterification reactions can be methoxides of sodium and magnesium; acetates, borates, fatty acid salts, and carbonates of zinc, cadmium, manganese, cobalt, calcium, and barium; metallic magnesium; and oxides of lead, zinc, antimony, germanium, and titanium.

[0160] In addition, the catalysts used in the polycondensation reaction can be, for example, titanium-based catalysts, such as tetraethyl titanate, acetyl tripropyl titanate, tetrapropyl titanate, tetrabutyl titanate, polybutyl titanate, 2-ethylhexyl titanate, octyl glycol titanate, titanyl lactate, triethanolamine titanate, acetylacetone titanate, ethyl acetoacetate titanate, isostearyl titanate, titanium dioxide, titanium dioxide / silica copolymer, titanium dioxide / zirconium dioxide copolymer; germanium-based catalysts such as germanium dioxide and its copolymers; or tin-based catalysts, such as monobutyltin oxide, dibutyltin oxide, and monobutyl hydroxytin oxide.

[0161] In addition, stabilizers can be phosphorus compounds, such as phosphoric acid, trimethyl phosphate and triethyl phosphate, but are not limited to these.

[0162] A method for preparing polyester resin according to another embodiment of the present invention may further include carrying out a solid-state polymerization reaction. For example, solid-state polymerization may be carried out after a polycondensation reaction at a temperature of 190°C to 230°C, under vacuum conditions of 0.2 Torr to 2.0 Torr, or in a nitrogen atmosphere.

[0163] Method for preparing recycled polyester resin compositions

[0164] A method for preparing a recycled polyester resin composition according to another embodiment of the present invention comprises mixing a recycled polyester resin comprising repeating units derived from a diol component and repeating units derived from recycled dimethyl terephthalate (rDMT); a hindered phenolic primary antioxidant; and a phosphorus or sulfur secondary antioxidant.

[0165] According to another embodiment, a waxy lubricant may be further added during the mixing step. This waxy lubricant comprises at least one selected from the group consisting of fatty acid esters, fatty acid amides, polyethylene wax, plant waxes, and mineral waxes. According to another embodiment, at least one additive may be further added during the mixing step. This additive is selected from the group consisting of flame retardants, nucleating agents, coupling agents, fillers, plasticizers, impact modifiers, lubricants, antibacterial agents, release agents, inorganic additives, UV stabilizers, antistatic agents, pigments, and dyes.

[0166] The mixing amount of each component can be appropriately adjusted according to the content in the recycled polyester resin composition of the above example.

[0167] Furthermore, the recycled polyester resin composition can be processed into granules after mixing. For example, the recycled polyester resin composition is fed into an extruder to remove volatile gases under reduced pressure, and then the composition can be prepared into granules at about 200°C to 300°C using a pelletizer.

[0168] Invention Embodiments

[0169] The present invention will now be described in further detail with reference to the following embodiments. However, these embodiments are only for illustrating the present invention, and the scope of the present invention is not limited thereto.

[0170] Preparation of Regenerated Dimethyl Terephthalate (rDMT)

[0171] Preparation Example 1

[0172] 120g of waste polyethylene terephthalate (waste PET) and 400g of methanol were added to a first high-pressure reactor with a capacity of 1 liter, followed by the addition of 120mg of Zn(OAC)2·2H2O as an alcoholysis catalyst (1000ppm relative to the total weight of waste PET).

[0173] Subsequently, all connections to the first high-pressure reactor were tightened and sealed, and the temperature was raised to 220°C within one hour. Stirring was maintained at 220°C and 58 bar for 3 hours to implement depolymerization via alcoholysis. After alcoholysis, the mixture was cooled to room temperature and crystallized by slow stirring at 10 to 20 rpm for 2 hours to obtain an alcoholysis composition in slurry form. In this case, the alcoholysis composition contains solid recycled dimethyl terephthalate (rDMT), excess unreacted methanol, and ethylene glycol derivatives generated from the side reaction.

[0174] Subsequently, the alcoholysis composition was centrifuged for solid-liquid separation, dried in an oven at 100°C, and washed three or more times with methanol to obtain rDMT in wet cake form. The washed rDMT in wet cake form was fractionated at 205°C under reduced pressure below 100 Torr and cooled to room temperature to obtain further purified solid rDMT. Under these conditions, ultra-high performance liquid chromatography (UPLC) was used to analyze the components and contents of the ethylene glycol derivatives generated in the side reactions, or the terephthalic acid and terephthalate derivatives generated in addition to the desired product DMT (see Table 2 below).

[0175] Subsequently, the filtrate remaining after filtering solid rDMT was added to a separate flask, and excess unreacted methanol and ethylene glycol (EG) formed by the side reaction were recovered using a fractionation apparatus.

[0176] Preparation Example 2

[0177] 1000g of waste polyethylene terephthalate (PET), 4000g of ethylene glycol, and 3.5g of anhydrous zinc acetate were added to a reactor made of stainless steel (SUS). The internal temperature of the reactor was raised to 196°C, and the first depolymerization was carried out through alcoholysis for 4 hours.

[0178] Subsequently, the first depolymerization composition was cooled to 30°C and crystallized by stirring at 10 to 20 rpm for 2 hours. The final product was a slurry containing recycled bis(2-hydroxyethyl) terephthalate (rBHET) and excess ethylene glycol (EG).

[0179] Subsequently, the slurry was centrifuged for solid-liquid separation and washed twice with distilled water. Residual solvent was removed using an 80°C oven, yielding approximately 1000 g of solid rBHET. Under these conditions, ultra-high performance liquid chromatography (UPLC) was used to analyze the components and contents of ethylene glycol derivatives generated in the side reactions, as well as terephthalic acid and terephthalate derivatives generated excluding the desired product, bis(2-hydroxyethyl) terephthalate (rBHET), (see Table 2 below).

[0180] Subsequently, the filtrate remaining after filtering the solid rBHET was added to a separate flask, and excess unreacted ethylene glycol (EG) was recovered using a fractionation apparatus.

[0181] Subsequently, 150g of solid rBHET and 400g of methanol were added to a first high-pressure reactor with a capacity of 1 liter, and then 45mg of Zn(OAC)2·2H2O was added as an alcoholysis catalyst (300ppm relative to the total weight of rBHET).

[0182] Subsequently, all connections to the first high-pressure reactor were tightened and sealed, and the temperature was raised to 90°C within one hour. The mixture was stirred for 5 hours while maintaining the temperature at 90°C and the pressure at 3 bar to carry out the second depolymerization via alcoholysis. After alcoholysis, the mixture was cooled to room temperature and allowed to stand for 4 hours to obtain a second depolymerization composition in slurry form. In this case, the second depolymerization composition contained solid recycled dimethyl terephthalate (rDMT), excess unreacted methanol, and ethylene glycol derivatives generated from the side reaction.

[0183] Subsequently, the second depolymerization composition was centrifuged for solid-liquid separation, dried in an oven at 100°C, and washed with methanol at least three times to obtain rDMT in wet cake form. The washed rDMT in wet cake form was fractionated at 205°C under reduced pressure (below 100 Torr) and cooled to room temperature to obtain further purified solid rDMT. Under these conditions, ultra-high performance liquid chromatography (UPLC) was used to analyze the components and contents of the ethylene glycol derivatives generated in the side reactions, or the terephthalic acid and terephthalate derivatives generated in addition to the desired product DMT (see Table 2 below).

[0184] Subsequently, the filtrate remaining after filtering solid rDMT was added to a separate flask, and excess unreacted methanol and ethylene glycol (EG) formed by the side reaction were recovered using a fractionation apparatus.

[0185] Preparation Example 3

[0186] 1000g of waste polyethylene terephthalate (PET), 4000g of ethylene glycol, and 3.5g of anhydrous zinc acetate were added to a reactor made of stainless steel (SUS). The internal temperature of the reactor was raised to 196°C, and the first depolymerization was carried out through alcoholysis for 4 hours.

[0187] Subsequently, the first depolymerization composition was cooled to 30°C and crystallized by stirring at 10 to 20 rpm for 2 hours. The final product was a slurry containing recycled bis(2-hydroxyethyl) terephthalate (rBHET) and excess ethylene glycol (EG).

[0188] Subsequently, the slurry was centrifuged for solid-liquid separation and washed twice with distilled water. Residual solvent was removed using an 80°C oven, yielding approximately 1000 g of solid rBHET. Under these conditions, ultra-high performance liquid chromatography (UPLC) was used to analyze the components and contents of ethylene glycol derivatives generated in the side reactions, as well as terephthalic acid and terephthalate derivatives generated excluding the desired product, bis(2-hydroxyethyl) terephthalate (rBHET), (see Table 2 below).

[0189] Subsequently, the filtrate remaining after filtering the solid rBHET was added to a separate flask, and excess unreacted ethylene glycol (EG) was recovered using a fractionation apparatus.

[0190] Subsequently, 150g of solid rBHET and 400g of methanol were added to a first high-pressure reactor with a capacity of 1 liter, and then 45mg of Zn(OAC)2·2H2O was added as an alcoholysis catalyst (300ppm relative to the total weight of rBHET).

[0191] Subsequently, all connections to the first high-pressure reactor were tightened and sealed, and the temperature was raised to 220°C within one hour. The mixture was stirred for three hours while maintaining the temperature at 220°C and the pressure at 58 bar to carry out the second depolymerization via alcoholysis. After alcoholysis, the mixture was cooled to room temperature and allowed to stand for three hours to obtain a second depolymerization composition in slurry form. In this case, the second depolymerization composition contained solid recycled dimethyl terephthalate (rDMT), excess unreacted methanol, and ethylene glycol derivatives generated from the side reaction.

[0192] Subsequently, the second depolymerization composition was added to a centrifuge for solid-liquid separation and dried in an oven at 100°C to obtain solid rDMT. Under these conditions, ultra-high performance liquid chromatography (UPLC) was used to analyze the components and contents of the ethylene glycol derivatives generated in the side reactions, or the terephthalic acid and terephthalate derivatives generated in addition to the desired product DMT (see Table 2 below).

[0193] Subsequently, the filtrate remaining after filtering solid rDMT was added to a separate flask, and excess unreacted methanol and ethylene glycol (EG) formed by the side reaction were recovered using a fractionation apparatus.

[0194] Preparation Example 4

[0195] 1000g of waste polyethylene terephthalate (PET), 4000g of ethylene glycol, and 3.5g of anhydrous zinc acetate were added to a reactor made of stainless steel (SUS). The internal temperature of the reactor was raised to 196°C, and the first depolymerization was carried out through alcoholysis for 4 hours.

[0196] Subsequently, the first depolymerization composition was cooled to 30°C and crystallized by stirring at 10 to 20 rpm for 2 hours. The final product was a slurry containing recycled bis(2-hydroxyethyl) terephthalate (rBHET) and excess ethylene glycol (EG).

[0197] Subsequently, the slurry was centrifuged for solid-liquid separation and washed twice with distilled water. Residual solvent was removed using an 80°C oven, yielding approximately 1000 g of solid rBHET. Under these conditions, ultra-high performance liquid chromatography (UPLC) was used to analyze the components and contents of ethylene glycol derivatives generated in the side reactions, as well as terephthalic acid and terephthalate derivatives generated excluding the desired product, bis(2-hydroxyethyl) terephthalate (rBHET), (see Table 2 below).

[0198] Subsequently, 150g of solid rBHET and 400g of methanol were added to a first high-pressure reactor with a capacity of 1 liter, and then 150mg of Zn(OAC)2·2H2O was added as an alcoholysis catalyst (1,000ppm relative to the total weight of rBHET).

[0199] Subsequently, all connections to the first high-pressure reactor were tightened and sealed, and the temperature was raised to 220°C within one hour. The mixture was stirred for three hours while maintaining the temperature at 220°C and the pressure at 58 bar to carry out the second depolymerization via alcoholysis. After alcoholysis, the mixture was cooled to room temperature and allowed to stand for three hours to obtain a second depolymerization composition in slurry form. In this case, the second depolymerization composition contained solid recycled dimethyl terephthalate (rDMT), excess unreacted methanol, and ethylene glycol derivatives generated from the side reaction.

[0200] Subsequently, the second depolymerization composition was subjected to a first fractionation at 60°C and 500 mmHg, a second fractionation at 170°C and 300 mmHg, and a third fractionation at 200°C and 60 mmHg to obtain solid rDMT. Under these conditions, ultra-high performance liquid chromatography (UPLC) was used to analyze the components and contents of the ethylene glycol derivatives generated in the side reactions, or the terephthalic acid and terephthalate derivatives generated in addition to the desired product DMT (see Table 2 below).

[0201] Subsequently, the filtrate remaining after filtering solid rDMT was added to a separate flask, and excess unreacted methanol and ethylene glycol (EG) formed by the side reaction were recovered using a fractionation apparatus.

[0202] Experimental Example 1-1: Ultra-High Performance Liquid Chromatography (UPLC)

[0203] The purity of rDMT obtained in Preparation Examples 1 to 4 and rBHET obtained in Preparation Example 2 were determined by ultra-high performance liquid chromatography (UPLC). The composition and content of ethylene glycol derivatives generated by side reactions or terephthalic acid or terephthalic ester derivatives other than the desired products DMT or BHET were also analyzed.

[0204] Specifically, according to the mobile phase and flow rate conditions listed in Table 1, 0.01 g of sample was dissolved in 20 ml of a mixture of methanol and a 0.3% phosphoric acid distilled aqueous solution. Peak areas were determined using ultra-high performance liquid chromatography (UHPLC) (manufacturer: Waters, model: ACQUITY UPLC H-Class Systems), and the percentage (%) of each peak area relative to the total peak area was calculated to determine purity, side reaction components, components formed other than the target product DMT, and their concentrations. In this case, commercially available DMT (manufacturer: SK Chemicals, model: SKYDMT) is shown as a control group in Table 2.

[0205] Table 1

[0206]

[0207] Experimental Examples 1-2: APHA Colorimetric Values

[0208] The rDMT obtained in Preparation Examples 1 to 4 and the rBHET obtained in Preparation Example 2 were subjected to APHA (American Public Health Association) colorimetric values ​​according to ASTM-D1209. Specifically, according to ASTM-D1209, rDMT and rBHET were dissolved in dimethylformamide solvent to prepare 10% by weight solutions, which were then placed in a quartz analytical container with an optical path length of 10 mm. The APHA colorimetric values ​​were measured using a colorimeter (model: ColorEye7000A).

[0209] Table 2

[0210]

[0211] As can be seen from Table 2 above, the rDMTs prepared in Preparation Examples 1 and 2 according to one embodiment of the present invention have a high purity of 95% or higher and excellent transparency, with APHA color values ​​of 85 or lower. In particular, Preparation Examples 1 and 2 exhibit excellent purity and crystallinity due to their low content of ethylene glycol and diethylene glycol. Since they contain low amounts of terephthalic acid derivatives (e.g., monomethyl terephthalate, MHT) in addition to the target DMT, they are suitable as raw materials for various polymers.

[0212] Furthermore, Preparation Example 3, which did not undergo a methanol washing process, showed a low purity of less than 90%. Preparation Example 4, which used a conventional fractionation method, showed very low transparency, an APHA color value of 125, and very low purity of only about 68%.

[0213] Preparation of recycled polyester resin

[0214] Resin A

[0215] Step (1): Prepare regenerated bis(4-hydroxybutyl) terephthalate (rBHBT) via transesterification.

[0216] 3068 g of 1,4-butanediol (BD) as the diol component, 4407 g of rDMT (prepared in Preparation Example 1) as the acid component, and 2 g of tetrabutyl titanate (TBT) as the transesterification catalyst were added to a 1-liter transesterification reactor equipped with a water-cooled fractionating column and a condenser. The pressure inside the reactor was adjusted to 0.1 kg / cm² by introducing nitrogen gas. 2 The temperature was increased while maintaining pressure and stirring. The transesterification reaction was carried out at a maintained temperature of 200°C. During this process, methanol, as a byproduct, was discharged through a fractionating column and condenser during the transesterification reaction. The transesterification reaction continued until methanol discharge ceased, thereby obtaining a transesterification composition containing rBHBT and its oligomers. After the transesterification reaction was completed, nitrogen gas in the pressurized reactor was released to the outside, reducing the pressure inside the reactor to atmospheric pressure.

[0217] Step (2): Prepare recycled polyester resin through polycondensation reaction

[0218] The transesterification composition obtained in step (1) was added to a polycondensation reactor. The reactor pressure was then reduced from atmospheric pressure to 5.0 Torr (absolute pressure: 5 mmHg) over 30 minutes. Simultaneously, the reactor temperature was increased to 245°C over 1 hour, and the polycondensation reaction was carried out while maintaining a reactor pressure of 1.0 Torr (absolute pressure: 1.0 mmHg) or less. Under these conditions, the stirring speed was set to a high value at the start of the polycondensation reaction. As the polycondensation reaction proceeded, the diol component, as a byproduct, was discharged from the reactor. The stirring speed was adjusted appropriately when the viscosity of the mixture in the reactor increased, leading to a decrease in stirring power, or when the temperature of the mixture rose above the set temperature. The polycondensation reaction continued until the intrinsic viscosity (IV) of the mixture (melt) in the reactor reached 1.14 dl / g. When the intrinsic viscosity of the mixture in the reactor reached the desired level, the mixture was discharged from the reactor to form strips, which were then cured with a coolant and pelletized to obtain polyester resin with an average weight of approximately 12 mg to 14 mg. Thus, 5000 g of recycled polyester (rPBT) resin was obtained.

[0219] Resin B

[0220] The transesterification reaction was carried out in the same manner as in Example 1, except that the rDMT prepared in Preparation Example 2 was used instead of the rDMT prepared in Preparation Example 1 in step (1). The polycondensation reaction was carried out in the same manner as in Example 1 until the intrinsic viscosity (IV) in the reactor in step (2) reached 0.98 dl / g, thereby obtaining 5000g of recycled polyester (rPBT) resin.

[0221] Resin C

[0222] Polycondensation was carried out in the same manner as in Example 1 until the intrinsic viscosity (IV) in the reactor in step (2) reached 0.72 dl / g, thereby obtaining 5000g of recycled polyester (rPBT) resin.

[0223] Resin D

[0224] The transesterification reaction was carried out in the same manner as in Example 1, except that commercially available DMT (manufacturer: SK Chemicals, model: SKYDMT) was used instead of the rDMT prepared in Preparation Example 1 in step (1). The polycondensation reaction was carried out in the same manner as in Example 1 until the intrinsic viscosity (IV) in the reactor reached 1.11 dl / g in step (2), thereby obtaining 5000g of virgin polyester (PBT) resin.

[0225] Resin E

[0226] The transesterification reaction was carried out in the same manner as in Example 1, except that the rDMT prepared in Preparation Example 3 was used instead of the rDMT prepared in Preparation Example 1 in step (1). The polycondensation reaction was carried out in the same manner as in Example 1 until the intrinsic viscosity (IV) in the reactor in step (2) reached 1.1 dl / g, thereby obtaining 5000g of recycled polyester (rPBT) resin.

[0227] Resin F

[0228] The transesterification reaction was carried out in the same manner as in Example 1, except that the rDMT prepared in Preparation Example 4 was used instead of the rDMT prepared in Preparation Example 1 in step (1). The polycondensation reaction was carried out in the same manner as in Example 1 until the intrinsic viscosity (IV) in the reactor in step (2) reached 0.9 dl / g, thereby obtaining 5000g of recycled polyester (rPBT) resin.

[0229] Resin G

[0230] The transesterification reaction was carried out in the same manner as in Example 1, except that 2836 g of 1,4-butanediol (BD) was used as the diol component in step (1), and 2852 g of rDMT prepared in Preparation Example 4 and 1600 g of rBHET prepared in Preparation Example 2 were used as the acid component. The polycondensation reaction was carried out in the same manner as in Example 1 until the intrinsic viscosity (IV) in the reactor reached 0.83 dl / g in step (2), thereby obtaining 5000 g of recycled polyester (rPBT) resin.

[0231] Resin H

[0232] The transesterification reaction was carried out in the same manner as in Example 1, except that 1783 g of 1,4-butanediol (BD) was used as the diol component in step (1), and 6287 g of rBHET obtained in Preparation Example 2 was used as the acid component. The polycondensation reaction was carried out in the same manner as in Example 1 until the intrinsic viscosity (IV) in the reactor reached 0.81 dl / g in step (2), thereby obtaining 5000 g of recycled polyester (rPBT) resin.

[0233] Resin I

[0234] The transesterification reaction was carried out in the same manner as in Example 1, except that 1286 g of 1,4-butanediol (BD) was used as the diol component in step (1), and 7257 g of rBHET obtained in Preparation Example 2 was used as the acid component. The polycondensation reaction was carried out in the same manner as in Example 1 until the intrinsic viscosity (IV) in the reactor reached 0.78 dl / g in step (2), thereby obtaining 5000 g of recycled polyester (rPBT) resin.

[0235] Experimental Example 2-1: Wide-angle X-ray diffraction (WAXD) analysis

[0236] Wide-angle X-ray diffraction plate photography was performed on resins A through I using a Rigaku SmartLab X-ray diffractometer. The imaging conditions were as follows.

[0237] - X-ray generator: 3kW (copper target)

[0238] -θ-θ goniometer with horizontal sample mounting stage

[0239] - Detector: D / teX Ultra250

[0240] -Application Software: PDXL

[0241] -ICDD Database PDF-2

[0242] For WAXD analysis, calibrated data were used, with the measured data corrected for polarization factor, absorption factor, and air scattering. The basic parameter (FP) method of the Bruker TOPAS fitting program was employed for deconvolution via single-line fitting. Crystalline and amorphous peaks within the 2θ angle range of 0° to 50° were separated from the wide-angle X-ray diffraction (WAXD) pattern obtained from X-ray diffraction (XRD) analysis, and the area and area percentage of each peak were calculated (see [link to relevant documentation]). Figures 2 to 6 According to Equation 1 below, the crystallization area value (%) corresponding to the area of ​​each obtained peak was calculated.

[0243] [Equation 1]

[0244] Crystalline area (%) = (Area of ​​crystalline region) / (Area of ​​crystalline region + Area of ​​amorphous region) × 100

[0245] Figure 1 The X-ray diffraction (XRD) analysis results of resins A, D, E, H, and I are shown. Figure 1 As shown, recycled polyester resin A exhibits strong diffraction peaks at angles (2θ, Bragg) of 9°, 15.9°, 17.2°, 20.6°, 23.4°, and 25.1° due to its crystal structure. These peaks correspond to diffraction planes (001), (011), (010), (110), (100), and (111), and are associated with the α-crystal form of PBT. However, the recycled polyester resins prepared in Comparative Examples 2, 5, and 6 exhibit lower crystallinity due to shifts in the position of the peak angles corresponding to each diffraction plane or a reduction in peak area.

[0246] Experimental Example 2-2: Chromaticity b and chromaticity L

[0247] The colorimetric b and L values ​​of resins A to I were measured using a colorimeter, which are the color characteristics.

[0248] Specifically, each recycled polyester resin was prepared into a sample with a width of 30 mm, a length of 30 mm, and a thickness of 6 mm using a hot press. Transmission data were acquired under a D65 light source at a 2° viewing angle, and the data were processed using a color analysis device in Grams / 32 software to measure the chromaticity b-value and chromaticity b-value in Hunter Lab space.

[0249] Experimental Example 2-3: Intrinsic Viscosity

[0250] Resins A through I were dissolved in o-chlorophenol (OCP) at a concentration of 0.12% at 150°C to prepare solutions. The intrinsic viscosity was measured using an Ubbelohde viscometer in a constant temperature bath at 35°C. Specifically, the viscosity tube temperature was maintained at 35°C, and the time required for the solvent to pass through a specific cross-section of the viscosity tube (outflow time) and the time required for the solution to pass through were measured to obtain the specific viscosity, and the intrinsic viscosity was calculated accordingly.

[0251] Experimental Examples 2-4: Tm and ΔHm

[0252] The melting point (Tm) and enthalpy of fusion (ΔHm) of resins A to I were determined using a differential scanning calorimeter (DSC, TA instrument).

[0253] Specifically, each recycled polyester resin was dried under reduced pressure at 50°C for 15 hours, melted at 260°C, and then rapidly cooled to 30°C. A differential scanning calorimeter was used to scan the resin at a heating rate of 10°C / min. In this case, the first scan (1...) can be used to determine the optimal temperature range for the recycled polyester resin. st (scan) or second scan (2) nd The enthalpy of fusion is measured by scanning. In the test example, the measurement is performed by a second scan.

[0254] In the heat flow curve obtained by scanning, the first endothermic temperature is the glass transition temperature (Tg), the exothermic temperature measured after the glass transition temperature (Tg) is the crystallization temperature (Tc), and the endothermic temperature measured after the crystallization temperature (Tc) is the melting point (Tm). In addition, the integral value at the melting point (Tm) is calculated as the enthalpy of fusion (ΔHm).

[0255] Experimental Example 2-5: Heat Deflection Temperature (HDT) (1)

[0256] Resins A to I were prepared according to ASTM D648, and their heat distortion temperature was determined using a Toyo Seiki 6M-2 tester under a low load of 0.48 MPa.

[0257] Experimental Example 2-6: 1 H-NMR

[0258] Resins A through I were dissolved in CDCl3 solvent at a concentration of 3 mg / ml, and their concentrations were measured using a nuclear magnetic resonance spectrometer (JEOL Ltd., 600 MHz FT-NMR) at 25°C. 1 H-NMR spectrum. By analysis 1 H-NMR spectra, based on the total molar number of residues from all diols (ethylene glycol, diethylene glycol, triethylene glycol, butanediol, etc.), calculate the content (molar percentage) of ethylene glycol residues and the total content of diethylene glycol residues.

[0259] Table 3

[0260]

[0261]

[0262] As can be seen from Table 3 above, since resins A to C are all prepared using rDMT with excellent purity, crystallinity and color characteristics, they exhibit outstanding performance in terms of color properties such as color b and color L, melting point (Tm), enthalpy of fusion, heat distortion temperature and crystallinity.

[0263] More specifically, resins A to C, as measured by Equation 1, have a crystallization area of ​​20% or more, and compared to resin D, which uses commercially available dimethyl terephthalate instead of recycled dimethyl terephthalate, the difference in crystallization area calculated by Equation 3 is 5.8 or more, demonstrating excellent crystallinity. Furthermore, based on the total molar number of glycols and their derivatives, the total content of ethylene glycol residues and diethylene glycol residues in resins A to C is 5 mol% or less, demonstrating excellent purity and crystallinity.

[0264] Furthermore, resins E, F, and G, which use rDMT with a purity of less than 90% alone or rDMT and rBHET together as acid components, and resins H and I, which use rBHET alone, have crystallization area values ​​calculated according to Equation 1 of 20% or less, which are lower than those of resin D, which uses commercially available dimethyl terephthalate instead of recycled dimethyl terephthalate. Therefore, resins G to I exhibit poorer performance in terms of color (e.g., chroma b and chroma L), melting point (Tm), enthalpy of fusion, and heat distortion temperature.

[0265] Preparation of recycled polyester resin particles

[0266] Examples 1 to 5 and Comparative Examples 1 to 8

[0267] The components shown in Table 4 below were uniformly mixed as shown in Tables 5 and 6 to prepare a resin composition. The resin composition was automatically metered and fed into the hopper of a twin-screw extruder (extruder diameter 40 mm, length-to-diameter ratio: 40). Volatile gases were removed under reduced pressure, and the composition was pelletized at approximately 250°C using a pelletizer. In this case, information on the components used in the examples and comparative examples is shown in Table 4 below. The values ​​shown in Tables 5 and 6 below are parts by weight.

[0268] Table 4

[0269]

[0270] Table 5

[0271]

[0272] Table 6

[0273]

[0274] Experimental Example 3-1: Heat Distortion Temperature (HDT) (2)

[0275] The recycled polyester resin particles prepared in Examples 1 to 6 and Comparative Examples 1 to 7 were made into samples according to ASTM D648. After aging and crystallizing in a hot air oven at 110°C for 12 hours, the heat distortion temperature was measured using a Toyo Seiki 6M-2 tester under a low load of 0.45 MPa.

[0276] Experimental Example 3-2: Melt Flow Index (MI)

[0277] The recycled polyester resin particles prepared in Examples 1 to 6 and Comparative Examples 1 to 7 were tested according to ASTM D1238 at 250°C and 2.16 kg to determine their melt flow index (MI).

[0278] Test Example 3-3: Tensile Strength

[0279] The tensile strength (MPa) of the recycled polyester resin particles prepared in Examples 1 to 6 and Comparative Examples 1 to 7 was determined according to ASTM D638.

[0280] Experimental Examples 3-4: Assessment of Total Volatile Organic Compounds (TVOC)

[0281] The total volatile organic compounds in the recycled polyester resin particles prepared in Examples 1 to 6 and Comparative Examples 1 to 7 were quantitatively determined by headspace gas chromatography / mass spectrometry (HS-GC / MS).

[0282] (1) Sample pretreatment

[0283] Take about 0.1g of sample and place it in a headspace vial (20ml), seal it with a clamp, and then perform the determination.

[0284] (2) Headspace (HS) device conditions

[0285] (i) Model: Triplus 500 (Thermo Fisher Scientific)

[0286] (ii) Incubation temperature: 130℃

[0287] (iii) Incubation time: 300 minutes

[0288] (iv) Circuit temperature: 200℃

[0289] (v) Circulation volume: 1 ml

[0290] (vi) Injection time: 0.5 minutes

[0291] (vii) Injection mode: Standard

[0292] (3) Gas chromatography / mass spectrometry (GC / MS) device conditions

[0293] (i) Model: Thermo Fisher 13010 / ISQ7000

[0294] (ii) Column: DB-5MS (60m × 0.32mm × 1.0μm)

[0295] (iii) Oven temperature: 40℃ (5 minutes) - 10℃ / minute - 300℃ (5 minutes)

[0296] (iv) Circuit temperature: 200℃

[0297] (v) Split ratio: 1:30

[0298] (vi) Flow rate: 1.5 ml / min (constant flow)

[0299] (vii) Ion source and transfer line temperature: 250℃

[0300] (viii) Quality range: 29-300

[0301] Experimental Example 3-5: Fogging Test

[0302] The recycled polyester resin particles prepared in Examples 1 to 6 and Comparative Examples 1 to 7 were subjected to fogging tests according to the DIN 75201-A test method.

[0303] 15g of particles were placed in a 100mm diameter, 20mm high glass petri dish (thickness: 2mm), and covered with a 120mm diameter, 20mm high glass petri dish (thickness: 2mm). The dish was then heated on a 130°C hot plate for 5 hours. The haze was measured before and after heating in the glass petri dish used as the cover, and the change in haze due to volatile gas deposition on the glass plate was calculated (|haze before heating - haze after heating|). A haze assessment was performed based on this. In this case, the haze (%) was measured using a NDH5000 from Nippon Denshoku. The haze change was calculated according to Equation 2 below.

[0304] [Equation 2]

[0305] Haze change = |H1–H2|

[0306] In Equation 2, H1 is the haze measured before the fogging assessment at 130℃ for 5 hours, which is a value without units; H2 represents the haze affected by the gas formed during the fogging assessment at 130℃ for 5 hours, which is a value without units.

[0307] Experimental Examples 3-6: Evaluation of Oxidation Induction Time (OIT)

[0308] The time of the exothermic oxidation reaction of the recycled polyester resin particles prepared in Examples 1 to 6 and Comparative Examples 1 to 7 was measured to evaluate the oxidation induction period.

[0309] Specifically, after drying the particles under reduced pressure at 50°C for 15 hours, they were heated from 30°C to 240°C in a nitrogen atmosphere using a differential scanning calorimeter (DSC, TA instrument) at a heating rate of 10°C / min. Subsequently, the conditions were switched from nitrogen to air at a switching rate of 20 ml / min, and the time for the exothermic oxidation reaction was measured while maintaining a constant temperature of 240°C for 60 minutes.

[0310] Experimental Example 3-7: Injection Molding Flow Marks

[0311] The recycled polyester resin granules prepared in Examples 1-6 and Comparative Examples 1-7 were injection molded into sheets with dimensions of 120mm × 120mm × 2T to prepare molded articles. The surface appearance of the molded articles was visually observed, and they were rated as × or ○ based on whether streaky flow marks were observed.

[0312] Table 7

[0313]

[0314] Table 8

[0315]

[0316] As can be seen from Tables 7 and 8, the recycled polyester resin particles of Examples 1 to 6 all meet the required numerical ranges in terms of melt flow index (mi), tensile strength, and heat distortion temperature, and also perform excellently in the evaluation of characteristics such as TVOC, fogging, oxidation induction time, and injection flow marks. Specifically, the recycled polyester resin particles of Examples 1 to 6 achieve equivalent or higher performance than Comparative Example 1, which was prepared using resin D made from commercially available dimethyl terephthalate instead of recycled dimethyl terephthalate.

Claims

1. A recycled polyester resin composition comprising: a recycled polyester resin comprising repeating units derived from a diol component and repeating units derived from recycled dimethyl terephthalate (rDMT); a hindered phenolic primary antioxidant; and a phosphorus or sulfur secondary antioxidant; in, In the recycled polyester resin, when calculating the crystalline and amorphous regions obtained by separating the crystalline diffraction peaks appearing in the 2θ value range of 0° to 50° by the single-peak fitting method in X-ray diffraction (XRD) analysis according to the following Equation 1, the crystalline area value is 20% or more. [Equation 1] Crystallization area (%) = (Crystallization area) / (Crystallization area + Amorphous area) × 100.

2. The recycled polyester resin composition of claim 1, wherein, relative to 100 parts by weight of the recycled polyester resin, the recycled polyester resin composition comprises 0.001 parts by weight to 0.3 parts by weight of a primary antioxidant and 0.001 parts by weight to 0.2 parts by weight of a secondary antioxidant.

3. The recycled polyester resin composition of claim 1, wherein the recycled polyester resin composition further comprises a waxy lubricant, the waxy lubricant comprising at least one selected from the group consisting of fatty acid esters, fatty acid amides, polyethylene waxes, plant waxes and mineral waxes.

4. The recycled polyester resin composition of claim 3, wherein the content of the waxy lubricant is from 0.001 parts by weight to 0.2 parts by weight relative to 100 parts by weight of the recycled polyester resin.

5. The recycled polyester resin composition of claim 1, wherein the recycled polyester resin composition further comprises at least one additive selected from the group consisting of: flame retardants, nucleating agents, coupling agents, fillers, plasticizers, impact modifiers, lubricants, antibacterial agents, mold release agents, inorganic additives, ultraviolet stabilizers, antistatic agents, pigments, and dyes.

6. The recycled polyester resin composition of claim 1, wherein, according to ASTM D1238, the melt flow index (MI) of the recycled polyester resin composition, measured at 250°C and 2.16 kg, is 60 g / 10 min or more. According to ASTM D638, the tensile strength is 45 MPa or more, and According to ASTM D648, the heat distortion temperature (HDT) measured under a low load of 0.45 MPa is 175°C or higher.

7. The recycled polyester resin composition of claim 1, wherein the TVOC peak area of ​​the recycled polyester resin composition, as determined by gas chromatography / mass spectrometry (GC / MS), is 80 area / g or less.

8. The recycled polyester resin composition of claim 1, wherein the haze variation of the recycled polyester resin composition is 5 or less according to Equation 2 below: [Equation 2] Haze change = |H1–H2| In Equation 2, H1 is the haze measured before fogging evaluation of particles prepared using the aforementioned recycled polyester resin composition at 130°C for 5 hours, according to DIN 75201-A test method. It is a unitless value. H2 is the haze caused by the gas formed during a fogging assessment of particles prepared using the aforementioned recycled polyester resin composition at 130°C for 5 hours, according to the DIN 75201-A test method. It is a numerical value excluding units.

9. The recycled polyester resin composition of claim 1, wherein, When particles prepared using the recycled polyester resin composition are dried under reduced pressure at 50°C for 15 hours in a nitrogen atmosphere using a differential scanning calorimeter (DSC, TA instrument) and then heated from 30°C to 240°C at a rate of 10°C / min, and when the conditions are changed from nitrogen to air at a conversion rate of 20 ml / min, the time of exothermic oxidation measured at 240°C for 60 minutes is 10 minutes or more.

10. The recycled polyester resin composition of claim 1, wherein the difference in the crystallization area values ​​of the recycled polyester resin is negative according to Equation 3 below: [Equation 3] Difference in crystallization area = Ca1 – Ca2 In Equation 3, Ca1 is the crystallization area value of the polyester resin containing repeating units derived from dimethyl terephthalate, calculated according to Equation 1 above. This value is a unitless numerical value. Ca2 is the crystallization area value calculated according to Equation 1 above from recycled polyester resin containing repeating units derived from recycled dimethyl terephthalate (rDMT), and it is a unitless value.

11. The recycled polyester resin composition of claim 10, wherein the difference in the crystallization area values ​​according to Equation 3 above is -0.5 or less.

12. The recycled polyester resin composition of claim 1, wherein the total content of ethylene glycol residues and diethylene glycol residues in the recycled polyester resin is 5 mol% or less, based on the total molar number of glycol component residues.

13. The recycled polyester resin composition of claim 1, wherein the recycled dimethyl terephthalate has a purity of 90% or more and an APHA color value of 120 or less.

14. The recycled polyester resin composition of claim 1, wherein the recycled dimethyl terephthalate is prepared by depolymerizing waste polyester.

15. The recycled polyester resin composition of claim 1, wherein the recycled dimethyl terephthalate is prepared by first depolymerizing waste polyester to obtain recycled bis(2-hydroxyethyl) terephthalate (rBHET), and then performing a second depolymerization.

16. The recycled polyester resin composition of claim 1, wherein the recycled polyester resin has a melting point of 210°C or higher and an enthalpy of fusion (ΔHm) of 38 J / g or more when measured by a differential scanning calorimeter during a second scan.

17. The recycled polyester resin composition of claim 1, wherein the recycled polyester resin has an intrinsic viscosity of 0.5 dl / g to 1.5 dl / g at 35°C, a chromaticity b of 12 or less, and a chromaticity L of 70 or more.

18. The recycled polyester resin composition of claim 1, wherein the recycled polyester resin composition has a melting point of 210°C or higher and an enthalpy of fusion (ΔHm) of 38 J / g or more when measured by a differential scanning calorimeter during a second scan.

19. The recycled polyester resin composition of claim 1, wherein the recycled polyester resin has a heat distortion temperature (HDT) of 90°C or higher when measured under a low load of 0.48 MPa, according to ASTM D648.

20. A molded article, said molded article being prepared from the recycled polyester resin composition of claim 1.

21. The molded article of claim 20, wherein the molded article is a molded article for a vehicle headlight.

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