Polyester resin containing recycled bis(2-hydroxyethyl) terephthalate, and articles containing polyester resin.

Abstract

A polyester resin according to one embodiment contains recycled bis(2-hydroxyethyl) terephthalate obtained by depolymerization of waste polyester, and the acetaldehyde content is controlled to be within a predetermined range. The polyester resin according to this embodiment has excellent qualities such as heat resistance and color while being polymerized using recycled monomers. In addition, an article containing the polyester resin according to this embodiment is provided.

Description

Detailed description of the invention

[0001] [Technical field] The present invention relates to a polyester resin containing recycled bis(2-hydroxyethyl) terephthalate and articles containing the same.

[0002] [Background technology] Polyester is widely used as a material for beverage filling containers, packaging films, audio and video films, etc., thanks to its excellent mechanical strength, heat resistance, transparency, and gas barrier properties. In addition, polyester is widely produced worldwide as an industrial material 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 a raw material for cases, boxes, partitions, shelves, panels, packaging materials, building materials, interior and exterior materials, etc.

[0003] As a result, the waste of plastics such as polyester is generated at an uncontrollable level globally every year. Recently, countries around the world have been developing rules and plans for recycling waste plastic resources, including waste polyester. For example, there are attempts to use recycled resins in packaging materials used in various fields at a certain proportion or higher. Physical or chemical methods are used to recycle waste polyester, but physical recycling methods cannot guarantee purity and are therefore not widely used.

[0004] In chemical regeneration methods, the ester bonds of waste polyester are cleaved and depolymerized. Reactions such as glycolysis, hydrolysis, methanolysis, and aminolysis are used. Among these, glycolysis involves decomposing waste polyester by adding glycols such as ethylene glycol or diethylene glycol at high temperatures. A reaction product mainly containing bis(2-hydroxyethyl) terephthalate (BHET) is obtained. Bis(2-hydroxyethyl) terephthalate may be used as a raw material for preparing polyester resin after crystallization or purification.

[0005] However, the bis(2-hydroxyethyl) terephthalate thus regenerated may contain reagents or solvents used in various chemical steps during the depolymerization of waste polyester, or by-products formed by side reactions with them. These impurities may remain in trace amounts even after several purifications. In particular, acetaldehyde is formed as a by-product during the polycondensation reaction used to prepare polyester resins. When polymerization is carried out using regenerated monomers, there has been a problem in that side reactions are further exacerbated by impurities, reducing the quality of the polyester resin, such as its heat resistance and color.

[0006] In addition, thermoplastic polyester resins are widely used in the manufacture of beverage containers due to their excellent stability against heat and oxygen. However, acetaldehyde, a by-product, can alter the flavor of beverages stored in the containers and negatively affect their taste. Therefore, research is being conducted to control raw materials and process conditions in order to minimize acetaldehyde formation in methods for preparing polyester resins.

[0007] [Prior art document] [Patent Document 1] Korean Patent Application Publication No. 2022-0068991

[0008] [Disclosure of the Invention] [Technical issues] In the case of recycled polyester resins using monomers such as recycled bis(2-hydroxyethyl) terephthalate, there are concerns that side reactions may be increased compared to virgin resins. However, no research has been conducted to reduce acetaldehyde formation in recycled polyester resins.

[0009] In addition, research has been conducted to reduce the amount of acetaldehyde in polyester resins using new additives. However, when new additives are added, the amount of the additive must be controlled during the process, which presents a problem in that it degrades the properties of the resulting polyester resin.

[0010] Therefore, the object of the present invention is to provide a polyester resin having excellent qualities such as heat resistance and color by controlling the acetaldehyde content to a specific range while polymerizing using recycled monomers.

[0011] [Means of solving the problem] According to one aspect of the present invention, a polyester resin is provided which contains recycled bis(2-hydroxyethyl) terephthalate (BHET) obtained by depolymerization of waste polyester, and which has an acetaldehyde content of 1 ppm or less.

[0012] According to another aspect of the present invention, an article comprising a polyester resin is provided.

[0013] [Advantageous effects of the invention] The polyester resin according to the present invention contains bis(2-hydroxyethyl) terephthalate obtained by the depolymerization of waste polyester, and by controlling the acetaldehyde content within a specific range, it possesses excellent qualities such as heat resistance and color.

[0014] [Best mode for carrying out the invention] In this specification, the terms used to refer to each component are used to distinguish them from one another and are not intended to limit the scope of the embodiments. In addition, in this specification, singular expressions are interpreted as encompassing plural expressions unless otherwise specified in the context.

[0015] In this specification, terms such as "1," "2," etc., are used to describe various components. However, components should not be limited by these terms. The terms are used for the purpose of distinguishing one element from another.

[0016] In this specification, the term “including” is intended to specify a particular characteristic, area, step, process, element, and / or component. Unless otherwise specifically stated, it does not exclude the presence or addition of any other characteristic, area, step, process, element, and / or component.

[0017] The molecular weights of the compounds or polymers described herein, such as number-average molecular weights or weight-average molecular weights, are, as is well known, relative masses based on carbon-12. While the units of relative mass are not specified, they may be understood as molar masses (g / mol) of the same value, if necessary.

[0018] In this specification, a "derivative" of a specific compound refers to a compound obtained by partially transforming the compound through a chemical reaction or by combining the compound with other components, thereby containing the main part of the compound.

[0019] In this specification, units or groups "derived from" specific components refer to a portion of the components contained in the final product through a chemical reaction such as polymerization. The units or groups may exist in a modified form or in combination with other components during the reaction. For example, units or groups derived from at least one monomer or oligomer are contained in the chains constituting the polymer.

[0020] In the numerical ranges that limit the size and physical properties of components, etc., described herein, if numerical ranges limited only by an upper limit and numerical ranges limited only by a lower limit are separately exemplified, it should be understood that numerical ranges combining these upper and lower limits are also included in the exemplary range of the present invention.

[0021] Polyester resin According to one aspect of the present invention, there is provided a polyester resin comprising recycled bis(2-hydroxyethyl) terephthalate (BHET) obtained by depolymerization of waste polyester, wherein the content of acetaldehyde is 1 ppm or less.

[0022] The polyester resin of the present invention is a polyester resin regenerated by chemical recycling of waste polyester.

[0023] Specifically, since the polyester resin of the present invention is polymerized using recycled BHET, the polymer chain contains repeating units derived from recycled BHET.

[0024] The content of recycled BHET in the polyester resin of the present invention may be 1% by weight or more, 5% by weight or more, 10% by weight or more, 30% by weight or more, 50% by weight or more, 70% by weight or more, or 90% by weight or more. In addition, the content of recycled BHET may be 100% by weight or less, 99% by weight or less, 80% by weight or less, 60% by weight or less, 40% by weight or less, or 20% by weight or less.

[0025] As an example, recycled bis(2-hydroxyethyl) terephthalate may be used in an amount of 10% by weight to 99% by weight based on the weight of the polyester resin.

[0026] In the polyester resin according to one embodiment of the present invention, the content of acetaldehyde is 1 ppm or less.

[0027] Specifically, the content of acetaldehyde in the polyester resin may be less than 1 ppm, 0.9 ppm or less, 0.8 ppm or less, 0.7 ppm or less, 0.6 ppm or less, 0.5 ppm or less, 0.4 ppm or less, 0.3 ppm or less, or 0.2 ppm or less. On the other hand, the lower limit of the acetaldehyde content in the polyester resin is not particularly limited, and may be, for example, 0 ppm or more, more than 0 ppm, 0.001 ppm or more, 0.01 ppm or more, or 0.1 ppm or more.

[0028] The acetaldehyde content may be based on the weight of the polyester resin (i.e., ppmw) of the acetaldehyde content.

[0029] Acetaldehyde is a compound having the formula CH3CHO and is contained in resins.

[0030] The acetaldehyde content can be measured, for example, by LC-UV (liquid chromatography using a UV detector). Specifically, a sample is prepared by adding 1 g of polyester resin to 10 ml of a mixture of acetonitrile and deionized water (50:50 by volume), and then the acetaldehyde content is measured by LC-UV. More specifically, UV-LC may be performed using a UV detector at a wavelength of 363 nm under conditions of a column temperature of 35°C, a sample volume of 20 μl, and a flow rate of 0.8 ml / min.

[0031] The polyester resin according to the present invention contains bis(2-hydroxyethyl) terephthalate obtained by the depolymerization of waste polyester, and by controlling the acetaldehyde content within a specific range, it possesses excellent qualities such as heat resistance and color.

[0032] In particular, the color change of polyester resins is controlled to a specific range, even when stored under high temperature and high humidity conditions.

[0033] According to one embodiment, the polyester resin may have ΔCol-b in the range of -1 to +1 according to the following formula 1. ΔCol-b = Col-b[10D] - Col-b[0D] In the formula, Col-b[10D] is the b value in the Hunter Lab color space measured after storing the polyester resin at 50°C and 60%RH for 10 days, and Col-b[0D] is the b value in the Hunter Lab color space measured for the polyester resin before storage.

[0034] For example, ΔCol-b may be in the range of -1 or greater, -0.8 or greater, -0.6 or greater, -0.4 or greater, or -0.2 or greater, and 1 or less, 0.8 or less, 0.6 or less, 0.4 or less, or 0.2 or less. Specifically, ΔCol-b may be in the range of -0.8 to 0.8, -0.6 to 0.6, -0.4 to 0.4, or -0.2 to 0.2.

[0035] Furthermore, according to the present invention, by adjusting the content and properties of the ethylene glycol component and recycled BHET component constituting the polyester resin, it is possible to provide a polyester resin with enhanced quality, such as heat resistance.

[0036] In particular, the heat resistance index of the polyester resin, calculated from the mole fraction of the ethylene glycol component among the diol components constituting the polyester resin, which is related to the properties and weight fraction of the recycled BHET component, can be adjusted to a specific range.

[0037] According to one embodiment, the heat resistance index of the resin is calculated using the mole fraction of ethylene glycol in the diol components constituting the polyester resin as a parameter. The heat resistance index of the resin may be adjusted to a specific range. The heat resistance index of the resin is a numerical value related to the ethylene glycol content constituting the polyester resin. If the heat resistance index of the resin is adjusted, it is possible to suppress the deterioration of the heat resistance of the polyester resin even when a large amount of recycled BHET is used.

[0038] Specifically, the polyester resin may have a resin heat resistance index of 2.0 or less, calculated by the following formula (Ia). The heat resistance index of the resin = mole fraction of ethylene glycol × 0.02 (Ia) In the formula, the mole fraction of ethylene glycol is the content (mol%) of the ethylene glycol component based on the total number of moles of diol components contained in the polyester resin.

[0039] In equation (Ia), the heat resistance index is calculated using only numerical values, excluding the units of the parameters.

[0040] For example, the heat resistance index of the resin may be 2.0 or less, 1.8 or less, 1.6 or less, 1.4 or less, 1.2 or less, 1.0 or less, 0.8 or less, or 0.6 or less. In addition, the heat resistance index of the resin may be 0 or more, 0.1 or more, 0.2 or more, 0.3 or more, 0.4 or more, or 0.5 or more. As a specific example, the heat resistance index of the resin may be 0 to 2.0 or 0.1 to 2.0.

[0041] According to another embodiment, the regenerated heat resistance index is calculated using the properties and weight fraction of the regenerated BHET component used in the polymerization of the polyester resin as parameters. The regenerated heat resistance index may be adjusted to a specific range. The regenerated heat resistance index is the heat resistance index attributable to the regenerated BHET used in the polymerization of the polyester resin. When the regenerated heat resistance index is adjusted, it can be controlled to have a heat resistance level similar to that of a resin polymerized from virgin monomers.

[0042] Specifically, the polyester resin may have a regenerative heat resistance index of 7.0 or less, calculated by the following formula (Ib). Regeneration heat resistance index = (r-BHET TDI) × weight fraction of r-BHET × 2 (Ib) In the formula, the weight fraction of r-BHET is the content (by weight) of recycled BHET based on the total weight of the polyester resin, and the r-BHET TDI is defined by the following formula when recycled BHET is analyzed using high-performance liquid chromatography (HPLC). r-BHET TDI = [DEG-ester-1] + [DEG-ester-2] × 2 + exp^[HA-ester] In the formula, DEG-ester-1 is the peak area fraction (%) of 2-hydroxyethyl[2-(2-hydroxyethoxy)ethyl]terephthalate, DEG-ester-2 is the peak area fraction (%) of bis[2-(2-hydroxyethoxy)ethyl]benzene-1,4-dicarboxylate, and HA-ester is the peak area fraction (%) of 2-hydroxyethyl(2-acetoxyethyl)terephthalate.

[0043] Here, the regeneration heat resistance index is calculated using only the numerical values, excluding the units of these parameters.

[0044] For example, the regeneration heat resistance index may be 7.0 or less, 6.0 or less, 5.0 or less, 4.0 or less, 3.0 or less, 2.0 or less, or 1.0 or less. In addition, the regeneration heat resistance index may be 0 or more, 0.1 or more, 0.2 or more, 0.3 or more, 0.4 or more, or 0.5 or more. As a specific example, the regeneration heat resistance index may be between 0 and 7.0 or between 0.1 and 7.0.

[0045] According to another embodiment, the combined heat resistance index is calculated using the resin's heat resistance index and the recycled heat resistance index as parameters. The combined heat resistance index may be adjusted to a specific range. By adjusting the combined heat resistance index, it is possible to more effectively control the heat resistance of the polyester resin, as it comprehensively considers the quality and quantity of recycled BHET and the ethylene glycol content in the polyester resin.

[0046] Specifically, the polyester resin has a combined heat resistance index of 9.0 or less, calculated by the following formula (I). Combined heat resistance index = Resin heat resistance index + Recycled heat resistance index (I) In the formulas, the heat resistance index of the resin is calculated using formula (Ia) above, and the regeneration heat resistance index is calculated using formula (Ib) above.

[0047] For example, the combined heat resistance index may be 9.0 or less, 8.0 or less, 7.0 or less, 6.0 or less, 5.0 or less, 4.0 or less, 3.0 or less, or 2.0 or less. In addition, the combined heat resistance index may be 0 or more, 0.1 or more, 0.2 or more, 0.3 or more, 0.4 or more, or 0.5 or more. As a specific example, the combined heat resistance index may be 0 to 9.0 or 0.1 to 9.0.

[0048] Since the bis(2-hydroxyethyl) terephthalate used in the preparation of the polyester resin of the present invention has a structure in which two ethylene glycols and one terephthalic acid are bonded together, the polyester resin of the present invention may contain repeating units derived from ethylene glycol and terephthalic acid.

[0049] As described above, the polyester resin of the present invention contains dicarboxylic acid components and diol components as monomer components (polymer building blocks) constituting the polyester resin. These components may originate from the initially supplied bis(2-hydroxyethyl) terephthalate and monomers supplied additionally for the preparation of the polyester resin.

[0050] The polyester resin may contain at least one comonomer selected from dicarboxylic acids and diols. Therefore, the polyester resin may be a copolymerized polyester resin.

[0051] For example, the dicarboxylic acid component may further include aromatic dicarboxylic acid components other than terephthalic acid, aliphatic dicarboxylic acid components, or mixtures thereof. Dicarboxylic acids other than terephthalic acid may be used in an amount of 1% to 30% by weight, based on the total weight of the dicarboxylic acid components.

[0052] The aromatic dicarboxylic acid component may be an aromatic dicarboxylic acid having 8 to 20 carbon atoms, preferably 8 to 14 carbon atoms, or a mixture thereof. Examples of aromatic dicarboxylic acids include, but are not limited to, isophthalic acid, naphthalenedicarboxylic acids such as 2,6-naphthalenedicarboxylic acid, diphenyldicarboxylic acid, 4,4'-stilbenedicarboxylic acid, 2,5-franzicarboxylic acid, and 2,5-thiophenedicarboxylic acid.

[0053] The aliphatic dicarboxylic acid component may be an aliphatic dicarboxylic acid having 4 to 20 carbon atoms, preferably 4 to 12 carbon atoms, or a mixture thereof. Examples of aliphatic dicarboxylic acids include, but are not limited to, linear, branched, or cyclic aliphatic dicarboxylic acid components, such as cyclohexanedicarboxylic acids including 1,4-cyclohexanedicarboxylic acid and 1,3-cyclohexanedicarboxylic acid, phthalic acid, sebacic acid, succinic acid, isodecylsuccinic acid, maleic acid, fumaric acid, adipic acid, glutaric acid, azelaic acid, etc.

[0054] As a specific example, the dicarboxylic acid may be at least one selected from the group consisting of isophthalic acid, dimethyl isophthalate, phthalic acid, dimethyl phthalate, phthalic anhydride, 2,6-naphthalenedicarboxylic acid, dimethyl 2,6-naphthalenedicarboxylic acid, diphenyldicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, dimethyl 1,4-cyclohexanedicarboxylic acid, dimethyl 1,3-cyclohexanedicarboxylic acid, sebacic acid, succinic acid, isodecylsuccinic acid, maleic acid, maleic anhydride, fumaric acid, adipic acid, glutaric acid, and azelaic acid.

[0055] The diol component may further contain other diol components as comonomers besides ethylene glycol. The comonomer may include, for example, at least one selected from the group consisting of diethylene glycol, cyclohexanedimethanol, cyclohexanedimethanol derivatives, and isosorbide.

[0056] Diethylene glycol can contribute to enhancing the transparency and impact resistance of polyester resins. For example, diethylene glycol may be used in amounts ranging from 0.1 mol% to 50 mol%, based on the total number of moles of the diol.

[0057] Cyclohexanedimethanol (e.g., 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, and 1,4-cyclohexanedimethanol) can contribute to enhancing the transparency and impact resistance of the resulting polyester resin. For example, cyclohexanedimethanol may be used in amounts of 5 mol% to 90 mol%, based on the total number of moles of the diol component. The cyclohexanedimethanol derivative may be 4-(hydroxymethyl)cyclohexylmethyl-4-(hydroxymethyl)cyclohexanecarboxylate or 4-(4-(hydroxymethyl)cyclohexylmethoxymethyl)cyclohexylmethanol. The cyclohexanedimethanol derivative may be used in amounts of 0.1 mol% to 25 mol%, based on the total number of moles of the diol component.

[0058] Isosorbide can enhance the processability of the final polyester resin. While the transparency and impact resistance of polyester resins are enhanced by the diol components of cyclohexanedimethanol and ethylene glycol, the shear fluidization properties should be improved and the crystallization rate should be delayed for processability. However, achieving this effect with cyclohexanedimethanol and ethylene glycol alone is difficult. Therefore, if isosorbide is used as the diol component, the shear fluidization properties are improved and the crystallization rate is delayed while maintaining transparency and impact resistance. As a result, the processability of the resulting polyester resin can be improved. Preferably, isosorbide may be used in an amount of 0.1 mol% to 70 mol%, based on the total number of moles of the diol components.

[0059] As a specific example, the diol may be at least one selected from the group consisting of isosorbide, neopentyl glycol, 1,2-propanediol, 1,3-propanediol, 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, 1,4-butanediol, 2,3-butanediol, 3-methyl-1,5-pentanediol, 3-methyl-2,4-pentanediol, 1,6-hexanediol, 1,2-cyclohexanediol, 1,4-cyclohexanediol, diethylene glycol, 4-(hydroxymethyl)cyclohexylmethyl-4-(hydroxymethyl)cyclohexanecarboxylate, and 4-(4-(hydroxymethyl)cyclohexylmethoxymethyl)cyclohexylmethanol.

[0060] As mentioned above, in addition to recycled BHET, monomers commonly used in the polymerization of polyester resins (virgin monomers) can be used in the preparation of polyester resins.

[0061] In addition, at least one recycled monomer obtained by depolymerization of waste polyester may be used in the preparation of polyester resin in addition to recycled BHET. The "recycled monomer" may be a monomer obtained by decomposing, depolymerizing, reprocessing, or repolymerizing waste plastics such as waste polyester by physical or chemical methods, or a polymerization raw material that contains or is derived from a monomer. Such recycled monomers can be obtained directly from waste plastics such as waste polyester by known methods, or they can be purchased and used commercially.

[0062] As a specific example, at least one recycled monomer may be selected from the group consisting of recycled dicarboxylic acids, recycled dicarboxylic acid derivatives, recycled diols, and recycled diol derivatives. More specifically, the polyester resin may contain at least one recycled monomer selected from the group consisting of recycled ethylene glycol, recycled 1,4-cyclohexanedimethanol, recycled diethylene glycol, recycled neopentyl glycol, recycled isosorbide, recycled terephthalic acid, recycled dimethyl terephthalate, recycled isophthalic acid, and recycled dimethyl isophthalate. However, the types of recycled monomers that can be used in the present invention are not limited to these. Any recycled monomer that can be used in the preparation of a polyester resin can be used. Such recycled monomers may be incorporated into the polyester resin by completely replacing virgin monomers. Alternatively, recycled monomers and virgin monomers may be incorporated together in a certain ratio in the polyester resin.

[0063] Polyester resins may also include catalysts used in the polymerization reaction for their preparation. For example, a polyester resin may contain at least one catalyst selected from metal oxides and acetates. The metal contained in the catalyst may be selected from the group consisting of antimony (Sb), titanium (Ti), germanium (Ge), manganese (Mn), cobalt (Co), tin (Sn), and calcium (Ca).

[0064] Regenerated bis(2-hydroxyethyl) terephthalate The polyester resin according to the present invention contains recycled bis(2-hydroxyethyl) terephthalate (BHET).

[0065] Bis(2-hydroxyethyl) terephthalate (BHET) is an ester of two ethylene glycol molecules and one terephthalic acid molecule. For example, BHET is a compound formed as an intermediate in methods for preparing polyesters such as polyethylene terephthalate (PET) by polymerization of ethylene glycol and terephthalic acid or its ester.

[0066] On the other hand, recycled bis(2-hydroxyethyl) terephthalate (referred to as recycled BHET) obtained by the depolymerization of waste polyester as described above may contain reagents or solvents used in various chemical steps during the depolymerization of waste polyester, or by-products formed by side reactions with them. Therefore, BHET recycled by a general depolymerization process contains organic and inorganic impurities in addition to BHET as the main component, and thus the purity of recycled BHET is not high.

[0067] However, the recycled bis(2-hydroxyethyl) terephthalate used in the preparation of the polyester resin in this invention has excellent purity and quality despite being obtained by the depolymerization of waste polyester.

[0068] The purity of regenerated BHET can be measured using liquid chromatography or other methods. Specifically, the purity of regenerated BHET can be calculated by measuring the fraction (%) of the peak area of ​​BHET within the total peak area in the spectrum obtained using high-performance liquid chromatography (HPLC).

[0069] Regenerated bis(2-hydroxyethyl) terephthalate may have a peak area fraction of 95% or more of bis(2-hydroxyethyl) terephthalate when measured by high-performance liquid chromatography (HPLC). For example, the peak area fraction of bis(2-hydroxyethyl) terephthalate may be 95% or more, 97% or more, 98% or more, 99% or more, or 99.5% or more, specifically 95% to 100% or 97% to 100%.

[0070] On the other hand, recycled bis(2-hydroxyethyl) terephthalate may also contain compounds other than BHET, specifically BHET analogs, BHET oligomers (e.g., dimers, trimers), esters, acetates, etc.

[0071] Specifically, when measured by high-performance liquid chromatography (HPLC), recycled bis(2-hydroxyethyl) terephthalate may have a peak area fraction of oligomers, such as dimers or more, totaling 2.0% or less. More specifically, the peak area fraction of oligomers, such as dimers or more, may be 1.5% or less, 1.0% or less, or 0.5% or less.

[0072] Generally, bis(2-hydroxyethyl) terephthalate regenerated by the depolymerization of waste polyester resin contains oligomeric substances such as dimers and trimers, which function as factors that impair the quality of the product, along with by-products derived from diethylene glycol (DEG) formed at high depolymerization temperatures.

[0073] In addition, acetates (e.g., zinc acetate), which are primarily used as catalysts in glycolysis, react with ethylene glycol during depolymerization to convert to hydroxyethyl acetate (HA). HA has a boiling point similar to that of ethylene glycol, which is primarily used as a solvent, and therefore is not easily filtered out as an impurity during the recovery and reuse of ethylene glycol. As a result, HA accumulates as the process is repeated, forming a byproduct.

[0074] As shown in the reaction scheme 1 below, acetic acid (AcOH), which is mainly derived from metal acetate salts used as catalysts, can react with ethylene glycol (EG) to produce acetate compounds such as 2-hydroxyethyl acetate (HA) and water (H2O).

[0075] [ka]

[0076] In addition, as shown in Reaction Scheme 2 below, 2-hydroxyethyl acetate (HA) can be converted to ester compounds such as 2-hydroxyethyl (2-acetoxyethyl) terephthalate (HAET) and ethylene glycol (EG) through transesterification with bis(2-hydroxyethyl) terephthalate (BHET).

[0077] [ka]

[0078] Recycled bis(2-hydroxyethyl) terephthalate has a peak area fraction of 1.0% or less of acetate-based ester compounds when measured by high-performance liquid chromatography (HPLC). Specifically, recycled bis(2-hydroxyethyl) terephthalate may have a peak area fraction of 0.7% or less, 0.5% or less, 0.3% or less, or 0.2% or less of acetate-based ester compounds when measured by high-performance liquid chromatography (HPLC). On the other hand, the lower limit of the peak area fraction of acetate-based ester compounds is not particularly limited, but may be 0% or more, 0.001% or more, 0.01% or more, or 0.1% or more in total. The acetate-based ester compound may be a 2-hydroxyethyl acetate ester compound. Specifically, the acetate ester compound may include at least one selected from the group consisting of 2-hydroxyethyl (2-acetoxyethyl) terephthalate (HAET), 2-acetoxyethyl [2-(2-hydroxyethoxy)ethyl] terephthalate, and 2-hydroxyethyl [2-[2-(2-hydroxyethoxy)ethoxy]ethyl] terephthalate. More specifically, the acetate ester compound may include 2-hydroxyethyl (2-acetoxyethyl) terephthalate.

[0079] In addition, recycled bis(2-hydroxyethyl) terephthalate may have a total peak area fraction of 2.0% or less of diethylene glycol (DEG) ester compounds when measured by high-performance liquid chromatography (HPLC). For example, the total peak area fraction of diethylene glycol (DEG) ester compounds may be 1.5% or less, 1% or less, or 0.5% or less. On the other hand, the lower limit of the peak area fraction of diethylene glycol (DEG) ester compounds is not particularly limited, but may be 0% or more, 0.001% or more, 0.01% or more, or 0.1% or more. The diethylene glycol ester compounds may include 2-hydroxyethyl[2-(2-hydroxyethoxy)ethyl] terephthalate and bis[2-(2-hydroxyethoxy)ethyl]benzene-1,4-dicarboxylate. These are represented by the following formulas 1 and 2, respectively.

[0080] [ka]

[0081] According to one embodiment, recycled bis(2-hydroxyethyl) terephthalate (BHET) has a peak area fraction of 2.5% or less of 2-hydroxyethyl[2-(2-hydroxyethoxy)ethyl]terephthalate (first diethylene glycol ester) when measured by high-performance liquid chromatography (HPLC). Specifically, the peak area fraction of 2-hydroxyethyl[2-(2-hydroxyethoxy)ethyl]terephthalate measured by HPLC may be 2.0% or less, 1.5% or less, 1.0% or less, or 0.5% or less.

[0082] According to another embodiment, regenerated bis(2-hydroxyethyl) terephthalate (BHET) has a peak area fraction of 0.5% or less of bis[2-(2-hydroxyethoxy)ethyl]benzene-1,4-dicarboxylate (second diethylene glycol ester) when measured by high-performance liquid chromatography (HPLC). Specifically, the peak area fraction of bis[2-(2-hydroxyethoxy)ethyl]benzene-1,4-dicarboxylate measured by HPLC may be 0.2% or less, more specifically, 0.15% or less, 0.1% or less, or 0.05% or less.

[0083] In this invention, the content of acetate ester compounds and diethylene glycol ester compounds in recycled bis(2-hydroxyethyl) terephthalate is adjusted to specific levels. Therefore, it is possible to prevent the deterioration of heat resistance properties due to these compounds during the polymerization of recycled polyester resin.

[0084] As the content of diethylene glycol ester compounds in recycled bis(2-hydroxyethyl) terephthalate increases, the heat resistance, such as the melting point, of the final polymer resin decreases linearly. Acetate ester compounds act as binding agents that inhibit polymer chain growth. As their content increases, the heat resistance of the final polymer resin decreases exponentially. This relationship can be used to derive a correlation and predict the heat resistance of polymers prepared using recycled bis(2-hydroxyethyl) terephthalate.

[0085] For example, recycled bis(2-hydroxyethyl) terephthalate may have a thermal property drop index (TDI) of 6.0 or less, 5.0 or less, or 4.0 or less, specifically 3.0 or less, as defined by the following formula, when measured by high-performance liquid chromatography (HPLC). r-BHET TDI = [DEG-ester-1] + [DEG-ester-2] × 2 + exp^[HA-ester] In the formula, DEG-ester-1 is the peak area fraction (%) of 2-hydroxyethyl[2-(2-hydroxyethoxy)ethyl]terephthalate, DEG-ester-2 is the peak area fraction (%) of bis[2-(2-hydroxyethoxy)ethyl]benzene-1,4-dicarboxylate, and HA-ester is the peak area fraction (%) of 2-hydroxyethyl(2-acetoxyethyl)terephthalate. TDI is calculated using only the numerical values, excluding the units of these parameters.

[0086] Specifically, if the thermal degradation index (TDI) defined by the above formula is 3.0 or less, it is possible to more effectively prevent the deterioration of heat resistance caused by these compounds during the polymerization of recycled polyester resin. More specifically, the thermal degradation index (TDI) may be 2.5 or less or 2.0 or less. Alternatively, the thermal degradation index (TDI) may be 0 to 3.0, 0 to 2.5, 0.5 to 3.0, 1.0 to 3.0, or 0.5 to 2.5.

[0087] In addition, recycled bis(2-hydroxyethyl) terephthalate may have a peak area fraction of monohydroxyethyl terephthalate (MHET) of 2% or less, 1.5% or less, 1% or less, or 0.5% or less when measured by high-performance liquid chromatography (HPLC).

[0088] In addition, the total residual ethylene glycol content in recycled bis(2-hydroxyethyl) terephthalate may be 1% by weight or less, 0.9% by weight or less, 0.5% by weight or less, or 0.3% by weight or less, based on the weight ratio detected by gas chromatography analysis. More specifically, the residual ethylene glycol content in recycled bis(2-hydroxyethyl) terephthalate may be 0.5% by weight or less. More specifically, the residual ethylene glycol content in recycled bis(2-hydroxyethyl) terephthalate may be 0.2% by weight or less, 0.15% by weight or less, or 0.1% by weight or less.

[0089] As described above, the bis(2-hydroxyethyl) terephthalate used in the preparation of polyester resin according to the present invention is a recycled monomer obtained by the depolymerization of waste polyester, and has high purity and a low content of impurities such as diethylene glycol ester.

[0090] According to one embodiment, a method for preparing recycled bis(2-hydroxyethyl) terephthalate according to the present invention comprises: (a) depolymerizing waste polyester by glycolysis to obtain a crude bis(2-hydroxyethyl) terephthalate solution; (b) cooling the crude bis(2-hydroxyethyl) terephthalate solution to crystallize the solution; and (c) performing solid-liquid separation of the crystallized product using a pressure filter.

[0091] Specifically, the depolymerization in step (a) may include (1) subjecting the waste polyester to depolymerization at a temperature of 180°C to 200°C by a first glycolysis reaction to obtain a first reactant, and (2) subjecting the first reactant to depolymerization at a temperature of 150°C to 170°C by a second glycolysis reaction to obtain a second reactant.

[0092] In addition, the pressure filter in step (c) may be a Nutsche filter or a filter press. Furthermore, acetate compounds and diethylene glycol-based compounds may be removed by the pressure filter in step (c).

[0093] Recycled bis(2-hydroxyethyl) terephthalate may be prepared by further carrying out the step of removing unreacted glycol by distillation.

[0094] In addition, recycled bis(2-hydroxyethyl) terephthalate may be prepared by further carrying out thin-film evaporation under reduced pressure, and at least one of dissolution in water and adsorption-crystallization.

[0095] Since low-weight organic substances, including acetic acid, are removed during the purification process by cold crystallization and pressure filtration, the content of by-products such as acetate ester compounds or diethylene glycol ester compounds can be effectively controlled. Method for preparing polyester resin A method for preparing a polyester resin according to the present invention comprises polymerizing the polyester resin using recycled bis(2-hydroxyethyl) terephthalate (BHET) obtained by depolymerization of waste polyester.

[0096] The polyester resin according to the present invention may be prepared by further adding terephthalic acid or its derivatives and / or ethylene glycol to recycled bis(2-hydroxyethyl) terephthalate. In addition, the polyester resin may be prepared as a copolymer by further adding a comonomer selected from other dicarboxylic acids and / or diols.

[0097] In polymerization, the esterification reaction (Step 1) and the polycondensation reaction (Step 2) may be carried out sequentially.

[0098] The esterification reaction may be carried out in the presence of an esterification catalyst. For example, a zinc-based compound may be used. Specific examples of zinc-based catalysts include zinc acetate, zinc acetate hydrate, zinc chloride, zinc sulfate, zinc sulfide, zinc carbonate, zinc citrate, zinc gluconate, or mixtures thereof.

[0099] Esterification reactions, for example, at 0 kgf / cm² 2 ~10.0 kgf / cm² 2 The reaction may be carried out at a pressure of 0 kg / cm² and a temperature of 150°C to 300°C. The esterification reaction conditions may be appropriately adjusted according to the inherent properties of the resulting polyester, the ratio of each component, or the process conditions. Specifically, the pressure in the esterification reaction may be 0 kg / cm². 2 ~5.0 kg / cm 2 More specifically, 0.1 kg / cm³ 2 ~3.0 kg / cm2 This is also acceptable. In addition, the temperature in the esterification reaction may be 200°C to 270°C, more specifically 240°C to 260°C.

[0100] The esterification reaction may be carried out in batches or continuously. Each of the raw materials may be supplied separately, but it is preferable to supply the raw materials in the form of a slurry containing a mixture of the diol component, the dicarboxylic acid component, and regenerated BHET. In addition, a slurry may be prepared by dissolving a diol component such as isosorbide, which is solid at room temperature, in water or ethylene glycol, and then mixing it with a dicarboxylic acid component such as terephthalic acid. Alternatively, isosorbide may be melted at 60°C or higher, and then mixed with a dicarboxylic acid component such as terephthalic acid and other diol components to prepare a slurry. In addition, water may be added to the mixed slurry to help increase the fluidity of the slurry.

[0101] The polycondensation reaction may be carried out, for example, by reacting the esterification reaction product at a temperature of 150°C to 300°C and under reduced pressure of 0.01 mmHg to 600 mmHg for 1 to 24 hours. The polycondensation reaction can produce polyester resins with relatively low molecular weight by melt polymerization. In addition, polyester resins with relatively high molecular weight may be produced by solid-phase polymerization after melt polymerization.

[0102] The temperature in the polycondensation reaction may be 150°C to 300°C, specifically 200°C to 290°C, and more specifically 260°C to 280°C. In addition, the pressure in the polycondensation reaction may be 0.01 mmHg to 600 mmHg, specifically 0.05 mmHg to 200 mmHg, and more specifically 0.1 mmHg to 100 mmHg. When reduced pressure conditions are used in the polycondensation reaction, glycol, a byproduct of the polycondensation reaction, can be removed from the system. If the pressure in the polycondensation reaction exceeds the range of 0.01 mmHg to 600 mmHg, the removal of the byproduct may be insufficient. In addition, if the temperature in the polycondensation reaction is lower than 150°C, glycol as a byproduct of the reaction cannot be effectively removed from the system, and therefore the intrinsic viscosity of the final reaction product is low, resulting in a decrease in the physical properties of the final polyester resin. If the temperature during the polycondensation reaction exceeds 300°C, the likelihood of yellowing of the final polyester resin increases. In addition, the polycondensation reaction may be carried out for the necessary period, for example, over an average residence time of 1 to 24 hours, until the intrinsic viscosity of the final reaction product reaches an appropriate level.

[0103] In addition, the polycondensation reaction may be carried out in the presence of a polycondensation catalyst. The polycondensation catalyst may be, for example, a titanium-based compound, a germanium-based compound, an antimony-based compound, an aluminum-based compound, a tin-based compound, or a mixture thereof. Examples of titanium-based compounds include tetraethyl titanate, acetyl tripropyl titanate, tetrapropyl titanate, tetrabutyl titanate, 2-ethylhexyl titanate, octylene glycol titanate, lactate titanate, triethanolamine titanate, acetyl acetonate titanate, ethyl acetoacetate titanate, isostearyl titanate, titanium dioxide, etc. Examples of germanium-based compounds include germanium dioxide, germanium tetrachloride, germanium ethylene glycol oxide, germanium acetate, or a mixture thereof. Preferably, germanium dioxide can be used. Both crystalline and amorphous germanium dioxide may be used, and those soluble in glycol may also be used. The amount of polycondensation catalyst used may be such that the amount of titanium element is about 1 to 100 ppm, more preferably about 1 to 50 ppm, relative to the weight of the polyester resin.

[0104] In addition to the polycondensation catalyst, stabilizers, colorants, crystallizers, antioxidants, branching agents, etc., may be used. The timing of adding these additives is not particularly limited and they may be added at any time during the polyester resin preparation step.

[0105] As stabilizers, phosphorus-based compounds such as phosphoric acid, trimethyl phosphate, triethyl phosphate, and triethyl phosphonoacetate may be commonly used. The amount of compound added may be 10 to 200 ppm relative to the weight of the polyester resin, based on the amount of phosphorus. In addition, common colorants such as cobalt acetate and cobalt propionate may be exemplified as colorants added to enhance the color of the polyester resin. The amount of colorant added may be 10 to 200 ppm relative to the weight of the polyester resin, based on the amount of cobalt. If necessary, anthraquinone-based compounds, perinone-based compounds, azo-based compounds, methine-based compounds, etc., may be used as organic colorants. Commercially available toners such as Clarient's Polysynthren Blue RLS or Clarient's Solva Perm Red BB may be used. The amount of organic compound colorant added may be adjusted to 0 to 50 ppm, based on the weight of the polyester resin. Crystallizing agents may be exemplified as crystallizing agents such as crystal nucleating agents, ultraviolet absorbers, polyolefin resins, and polyamide resins. Hindered phenol-based antioxidants, phosphite-based antioxidants, thioether-based antioxidants, or mixtures thereof may be exemplified as antioxidants. Conventional branching agents having three or more functional groups, such as trimellitic anhydride, trimethylolpropane, trimellitic acid, or mixtures thereof, may also be exemplified as branching agents.

[0106] The intrinsic viscosity of the polyester resin at 35°C may be 0.5 dl / g or more, 0.6 dl / g or more, or 0.7 dl / g or more, and may also be 1.2 dl / g or less, 1.1 dl / g or less, 1.0 dl / g or less, or 0.9 dl / g or less. For example, the polyester resin may have an intrinsic viscosity of 0.5 dl / g to 1.2 dl / g at 35°C. Specifically, the polyester resin is dissolved in ortho-chlorophenol (OCP) at 100°C at a concentration of 0.12%, and the intrinsic viscosity is measured using an Ubbelohde viscometer at a thermostat at 35°C.

[0107] The polyester resin according to the present invention contains bis(2-hydroxyethyl) terephthalate obtained by the depolymerization of waste polyester, and by controlling the acetaldehyde content to a specific range, it possesses excellent qualities such as heat resistance and color. Specifically, acetaldehyde is formed as a byproduct during the polycondensation reaction for the preparation of the polyester resin. If acetate ester compounds are present in the recycled bis(2-hydroxyethyl) terephthalate, acetaldehyde formation can increase during the polycondensation procedure. However, since the polyester resin of the present invention is prepared using recycled bis(2-hydroxyethyl) terephthalate with a controlled content of acetate ester compounds, acetaldehyde formation during the polycondensation procedure can be suppressed.

[0108] The polyester resin according to the present invention has excellent qualities such as heat resistance and color, and therefore can be used in the production of products in various fields.

[0109] Accordingly, the present invention provides an article comprising the polyester resin described above. For example, the article may be a container, a blow, a film, a sheet, or a profile.

[0110] Specific examples of containers include cosmetic containers and food containers.

[0111] Blow molding refers to the material used to obtain hollow plastic molded parts by blow molding. Specific examples of blow molding include injection blow molding and extrusion blow molding.

[0112] Specific examples of films include heat-shrinkable films and inflation films.

[0113] A profile refers to a continuous extruded plastic product, excluding sheets and films. Profiles may be manufactured by general extrusion molding methods and may have, for example, a tubular or channel shape.

[0114] Mode of the invention Hereafter, preferred embodiments of the present invention will be presented for the purpose of understanding the present invention. However, the following examples are provided solely to aid in a brief understanding of the present invention, and the scope of the present invention is not limited by these examples.

[0115] <Method for preparing regenerated BHET> Preparation example: r-BHET A1 1,000 g of waste polyester resin, 2,000 g of ethylene glycol, and 5.0 g of anhydrous zinc acetate were added to a first reactor made of stainless steel (SUS). The temperature inside the reactor was raised to 180°C, and depolymerization (first glycolysis) was carried out for 2 hours. The reactant obtained in this way (first reactant) was transferred to a second reactor and cooled to 150°C. An additional 2,000 g of ethylene glycol was added, and depolymerization (second glycolysis) was carried out for 2 hours while maintaining the reactor temperature at 150°C.

[0116] The reactant obtained in this manner (second reactant) was cooled to 120°C by vacuum flashing, 16 g of a filter aid (Celite® 545) was added, and then solid-liquid separation was performed by pressure filtration. The separated liquid reactant was passed through a column packed with ion exchange resin (Bonlite BC107(H)) to remove ionic impurities and a mixture containing bis(2-hydroxyethyl) terephthalate and ethylene glycol (third reactant) was obtained.

[0117] The mixture (third reactant) was cooled to room temperature over 2 hours while being stirred at 100 rpm in a 10-liter crystallizer equipped with a cooling water circulation jacket. A pressurized Nutsch filter (jacketed type, filtration area 0.2 m²) was used. 2 Using a pressure of 3 bar, the obtained crystallization product was separated into solid and liquid to obtain the BHET cake (fourth reactant).

[0118] The BHET cake was transferred to a 10-liter distillation apparatus and reheated to 130°C. Vacuum distillation was carried out under stepwise reduced pressure conditions from 760 Tor to 0.8 Tor to recover the unreacted ethylene glycol. The reactant from which the ethylene glycol had been removed (the fifth reactant) was subjected to thin-film evaporation at 220°C and 0.08 Tor in a thin-film evaporator (VTA VKL70-4S) to obtain 1,040 g of product from which dimers and oligomers had been removed. Subsequently, for adsorption and crystallization, 1,040 g of the above product and 3,120 g of distilled water were placed in a 10-liter glass reactor and dissolved at a temperature of 70°C. Then, 5.2 g of activated carbon was added thereto, followed by stirring for 30 minutes, and the mixture was filtered. The filtrate was cooled to room temperature for crystallization, filtered, and dried in a vacuum oven. As a result, 1,980 g of regenerated bis(2-hydroxyethyl) terephthalate was obtained.

[0119] Preparation example: r-BHET A2 Regenerated bis(2-hydroxyethyl) terephthalate was obtained by repeating the same procedure as the preparation example of r-BHET A1, except that the reaction time for the first glycolysis reaction was adjusted to 1 hour.

[0120] Preparation example: r-BHET A3 Instead of a pressurized Nutche filter, use a filter press (filtration area 0.4m²). 2 Regenerated bis(2-hydroxyethyl) terephthalate was obtained by repeating the same procedure as the preparation example of r-BHET A1, except that filtration was performed using a filtration plate (4ea) under a pressure of 18 bar.

[0121] Preparation example: r-BHET A4 Recycled bis(2-hydroxyethyl) terephthalate was obtained by repeating the same procedure as the preparation example of r-BHET A1, except that waste polyester fibers were used as waste polyester resin.

[0122] Preparation example: r-BHET A5 Regenerated bis(2-hydroxyethyl) terephthalate was obtained by repeating the same procedure as the preparation example of r-BHET A1, except that adsorption-crystallization was not performed after thin film evaporation.

[0123] Preparation example: r-BHET A6 Regenerated bis(2-hydroxyethyl) terephthalate was obtained by repeating the same procedure as in the preparation example of r-BHET A4.

[0124] Preparation example: r-BHET A7 Regenerated bis(2-hydroxyethyl) terephthalate was obtained by repeating the same procedure as in the preparation example of r-BHET A1.

[0125] Preparation example: r-BHET B1 Regenerated bis(2-hydroxyethyl) terephthalate was obtained by repeating the same procedure as the preparation example of r-BHET A1, except that the temperature in the first glycolysis reaction was adjusted to 210°C and the temperature in the second glycolysis reaction was adjusted to 250°C.

[0126] Preparation example: r-BHET B2 Regenerated bis(2-hydroxyethyl) terephthalate was obtained by repeating the same procedure as the preparation example of r-BHET A1, except that the cooling crystallization and pressurized Nutsch filter steps were omitted.

[0127] Test example (1) High-performance liquid chromatography (HPLC) Approximately 0.01 g of recycled bis(2-hydroxyethyl) terephthalate was diluted with approximately 20 ml of methanol and analyzed by high-performance liquid chromatography (HPLC) (model: Waters e2695, column: C18 (4.6 × 250 mm), 5 μm, UV detector: 242 nm, injection volume: 10 μl, eluent (gradient) A: H2O + H3PO4, B: acetonitrile). Subsequently, the peak area fraction (%) of the following components within the total peak area of ​​the HPLC was obtained. MHET: Monohydroxyethyl terephthalate BHET: Bis(2-hydroxyethyl) terephthalate DEG-Ester-1: 2-Hydroxyethyl[2-(2-Hydroxyethoxy)ethyl]terephthalate DEG-Ester-2: Bis[2-(2-hydroxyethoxy)ethyl]benzene-1,4-dicarboxylate HA-Ester: 2-Hydroxyethyl (2-Acetoxyethyl) Terephthalate Dimer: BHET dimer Trimer: BHET trimer

[0128] (2) Gas chromatography (GC) 0.1 g of recycled bis(2-hydroxyethyl) terephthalate was dissolved in 10 ml of CHCl3, filtered through a 0.45 μm filter, and measured by GC. Model: Agilent 7890B Column: DB-624 (30m x 0.25mm x 1.4μm) Oven temperature: 60°C (2 minutes) ~ 10°C / min ~ 200°C (0 minutes) ~ 20°C / min ~ 260°C (5 minutes) Injector temperature: 250℃ Detector temperature: 250℃ Flow rate: 1.5ml / min (N2), split ratio: 1 / 50

[0129] (3) TDI Regenerated bis(2-hydroxyethyl) terephthalate was subjected to HPLC analysis in the same manner as in Section (1) above. The thermal degradation index (TDI), defined by the following formula, was then calculated. TDI = [DEG-ester-1] + [DEG-ester-2] × 2 + exp^[HA-ester] In the formula, DEG-ester-1 is the peak area fraction (%) of 2-hydroxyethyl[2-(2-hydroxyethoxy)ethyl] terephthalate, DEG-ester-2 is the peak area fraction (%) of bis[2-(2-hydroxyethoxy)ethyl] benzene-1,4-dicarboxylate, and HA-ester is the peak area fraction (%) of 2-hydroxyethyl(2-acetoxyethyl) terephthalate. TDI was calculated using only the numerical values of these parameters, excluding their units.

[0130] The results are shown in the table below.

[0131]

Table 1

[0132]

Table 2

[0133] <Preparation of polyester resin> Example 1 A reactor equipped with a column and a cooler capable of cooling with water was charged with recycled bis(2-hydroxyethyl) terephthalate (r-BHET A1, 6,273.5 g), terephthalic acid (TPA, 4,100.0 g), ethylene glycol (EG, 612.5 g), 1,4-cyclohexanedimethanol (CHDM, 1,067.0 g), isosorbide (ISB, 288.5 g), diethylene glycol (DEG, 72.1 g), Ti catalyst (0.4 g), phosphoric acid (10.0 g), blue toner (0.010 g), and red toner (0.005 g).

[0134] Thereafter, nitrogen was injected into the reactor to 1.0 kgf / cm 2The reactor was pressurized to a pressure higher than atmospheric pressure (absolute pressure: 1,495.6 mmHg). The reactor temperature was then raised to 220°C over 90 minutes, maintained at 220°C for 2 hours, and then raised again to 260°C over 2 hours. The esterification reaction was then carried out at 260°C, while visually observing the mixture in the reactor, until the mixture became clear. During this procedure, byproducts were discharged from the column and condenser. Upon completion of the esterification reaction, the nitrogen in the pressurized reactor was released to the outside, reducing the pressure in the reactor to atmospheric pressure, and the mixture in the reactor was then transferred to a reactor capable of reacting under vacuum.

[0135] Next, the reactor pressure was reduced from atmospheric pressure to 5 Torre (absolute pressure: 5 mmHg) over 30 minutes. Simultaneously, the reactor temperature was raised to 265°C over 1 hour, and the polycondensation reaction was carried out while maintaining the reactor pressure at 1 Torre (absolute pressure: 1 mmHg) or less. At the start of the polycondensation reaction, the stirring speed may be set high. As the polycondensation reaction progresses, the stirring force weakens due to the increase in viscosity of the reactants, or the temperature of the reactants rises above the set temperature, in which case the stirring speed can be appropriately adjusted as needed. The polycondensation reaction was carried out until the intrinsic viscosity (IV) of the mixture (molten) in the reactor reached 0.70 dl / g. Once the intrinsic viscosity of the mixture in the reactor reached the desired level, the mixture was then discharged from the reactor to form strands, solidified with a coolant, and then granulated to have an average weight of approximately 12-14 mg.

[0136] The granules were allowed to crystallize at 150°C for 1 hour, and then supplied to a solid-phase polymerization reactor. While nitrogen flowed at a rate of 50 L / min, the reactor temperature was raised from room temperature to 200°C at a rate of 40°C / hour. While maintaining the temperature, solid-phase polymerization was carried out until the intrinsic viscosity (IV) of the granules in the reactor reached 1.00 dl / g, yielding approximately 10 kg of polyester resin.

[0137] Example 2 Recycled bis(2-hydroxyethyl) terephthalate (r-BHET A2, 11,936.1g), 1,4-cyclohexanedimethanol (CHDM, 1,353.4g), diethylene glycol (DEG, 137.2g), Ge catalyst (6.4g), blue toner (0.030g), and red toner (0.015g) were added, and the esterification reaction was carried out at a pressure of 2.0 kgf / cm² above atmospheric pressure. 2 The procedure was repeated as in Example 1, except that it was carried out at a higher pressure and a temperature of 260°C, the polycondensation reaction was carried out at a temperature of 275°C until the intrinsic viscosity (IV) reached 0.65 dl / g, and solid-phase polymerization was not performed, to obtain approximately 10 kg of polyester resin.

[0138] Example 3 Recycled bis(2-hydroxyethyl) terephthalate (r-BHET A3, 8,472.8g), terephthalic acid (TPA, 2,373.1g), ethylene glycol (EG, 177.3g), 1,4-cyclohexanedimethanol (CHDM, 960.7g), diethylene glycol (DEG, 347.9g), CHDM derivative (containing 4-(hydroxymethyl)cyclohexylmethyl-4-(hydroxymethyl)cyclohexanecarboxylate and 4-(4-(hydroxymethyl)cyclohexylmethoxymethyl)cyclohexylmethanol in a 1:3 molar ratio, 347.9g), Ge catalyst (6.4g), Ti catalyst (0.5g), blue toner (0.040g), and red toner (0.010g) were added, and the esterification reaction was carried out at a pressure of 0.5 kgf / cm² above atmospheric pressure. 2 The procedure was repeated as in Example 1, except that it was carried out at a higher pressure and a temperature of 260°C, the polycondensation reaction was carried out at a temperature of 275°C until the intrinsic viscosity (IV) reached 0.75 dl / g, and solid-phase polymerization was not performed, to obtain approximately 10 kg of polyester resin.

[0139] Example 4 Recycled bis(2-hydroxyethyl) terephthalate (r-BHET A4, 2,220.3g), terephthalic acid (TPA, 5,804.2g), ethylene glycol (EG, 9.0g), 1,4-cyclohexanedimethanol (CHDM, 3,776.2g), isosorbide (ISB, 1,701.6g), diethylene glycol (DEG, 319.1g), Ti catalyst (0.4g), phosphoric acid (3.0g), blue toner (0.015g), and red toner (0.005g) were added, and the esterification reaction was carried out at a pressure of 1.0 kgf / cm² higher than atmospheric pressure. 2 The procedure was repeated as in Example 1, except that it was carried out at a higher pressure and a temperature of 265°C, the polycondensation reaction was carried out at a temperature of 280°C until the intrinsic viscosity (IV) reached 0.75 dl / g, and solid-phase polymerization was not performed, to obtain approximately 10 kg of polyester resin.

[0140] Example 5 Recycled bis(2-hydroxyethyl) terephthalate (r-BHET A5, 4,739.6g), terephthalic acid (TPA, 4,646.3g), ethylene glycol (EG, 1,793.2g), 1,4-cyclohexanedimethanol (CHDM, 1,679.4g), CHDM derivative (containing 4-(hydroxymethyl)cyclohexylmethyl-4-(hydroxymethyl)cyclohexanecarboxylate and 4-(4-(hydroxymethyl)cyclohexylmethoxymethyl)cyclohexylmethanol in a 1:3 molar ratio, 204.3g), Ge catalyst (12.8g), Ti catalyst (0.9g), blue toner (0.006g), and red toner (0.002g) were added, and the esterification reaction was carried out at a pressure of 2 kgf / cm² higher than atmospheric pressure. 2 The procedure was repeated as in Example 1, except that the reaction was carried out at a higher pressure and a temperature of 255°C, the polycondensation reaction was carried out at a temperature of 285°C until the intrinsic viscosity (IV) reached 0.80 dl / g, and solid-phase polymerization was not performed, to obtain approximately 10 kg of polyester resin.

[0141] Example 6 Recycled bis(2-hydroxyethyl) terephthalate (r-BHET A6, 12,510.4g), terephthalic acid (TPA, 430.3g), ethylene glycol (EG, 225.0g), CHDM derivative (containing 4-(hydroxymethyl)cyclohexylmethyl-4-(hydroxymethyl)cyclohexanecarboxylate and 4-(4-(hydroxymethyl)cyclohexylmethoxymethyl)cyclohexylmethanol in a 1:3 molar ratio, 227.1g), Ge catalyst (12.8g), Ti catalyst (0.9g), blue toner (0.006g), and red toner (0.002g) were added, and the esterification reaction was carried out at a pressure of 2 kgf / cm² higher than atmospheric pressure. 2 The procedure was repeated as in Example 1, except that the reaction was carried out at a higher pressure and a temperature of 255°C, the polycondensation reaction was carried out at a temperature of 285°C until the intrinsic viscosity (IV) reached 0.80 dl / g, and solid-phase polymerization was not performed, to obtain approximately 10 kg of polyester resin.

[0142] Example 7 Recycled bis(2-hydroxyethyl) terephthalate (r-BHET A7, 8,660.5g), terephthalic acid (TPA, 2,425.7g), isophthalic acid (IPA, 5,660.0g), ethylene glycol (EG, 100.7g), 1,4-cyclohexanedimethanol (CHDM, 1,402.8g), isosorbide (ISB, 474.1g), diethylene glycol (DEG, 355.6g), Ti catalyst (0.9g), phosphoric acid (1.0g), blue toner (0.020g), and red toner (0.010g) were added, and the esterification reaction was carried out at a pressure of 3.0 kgf / cm² higher than atmospheric pressure. 2 The procedure was repeated as in Example 1, except that it was carried out at a higher pressure and a temperature of 260°C, the polycondensation reaction was carried out at a temperature of 275°C until the intrinsic viscosity (IV) reached 0.65 dl / g, and solid-phase polymerization was not performed, to obtain approximately 10 kg of polyester resin.

[0143] Comparative Example 1 Recycled bis(2-hydroxyethyl) terephthalate (r-BHET B1, 5,968.0g), terephthalic acid (TPA, 3,900.4g), ethylene glycol (EG, 874.1g), 1,4-cyclohexanedimethanol (CHDM, 1,353.4g), Ge catalyst (12.8g), blue toner (0.020g), and red toner (0.010g) were added, and the esterification reaction was carried out at a pressure of 0.5 kgf / cm² higher than atmospheric pressure. 2 The procedure was repeated as in Example 1, except that it was carried out at a higher pressure and a temperature of 260°C, the polycondensation reaction was carried out at a temperature of 280°C until the intrinsic viscosity (IV) reached 0.70 dl / g, and solid-phase polymerization was not performed, to obtain approximately 10 kg of polyester resin.

[0144] Comparative Example 2 Recycled bis(2-hydroxyethyl) terephthalate (r-BHET B2, 10,037.5g), terephthalic acid (TPA, 1,640.0g), ethylene glycol (EG, 2,143.8g), 1,4-cyclohexanedimethanol (CHDM, 1,067.0g), diethylene glycol (DEG, 72.1g), Ti catalyst (0.4g), blue toner (0.015g), and red toner (0.005g) were added, and the esterification reaction was carried out at a pressure of 1 kgf / cm² higher than atmospheric pressure. 2 The same procedure as in Example 1 was repeated, except that the reaction was carried out at a higher pressure and a temperature of 265°C, the polycondensation reaction was carried out at a temperature of 270°C until the intrinsic viscosity (IV) reached 0.70 dl / g, and the solid-phase polymerization was carried out at a temperature of 200°C until the intrinsic viscosity (IV) reached 0.90 dl / g, to obtain approximately 10 kg of polyester resin.

[0145] The types and content of recycled BHET used in the examples and comparative examples, as well as the amount of comonomers, are summarized in the table below.

[0146] [Table 3]

[0147] [Table 4]

[0148] Test example (1) Heat resistance index The heat resistance index of the polyester resin obtained in each of the examples and comparative examples was calculated as follows. a. Heat resistance index of resins The heat resistance index of the resin was calculated according to the following formula (Ia). The heat resistance index of the resin = mole fraction of ethylene glycol × 0.02 (Ia) In the formula, the mole fraction of ethylene glycol is the content (mol%) of the ethylene glycol component based on the total number of moles of diol components contained in the polyester resin. b.Recycled heat resistance index The regeneration heat resistance index was calculated according to the following formula (Ib). Regeneration heat resistance index = (r-BHET TDI) × weight fraction of r-BHET × 2 (Ib) In the formula, the weight fraction of r-BHET is the content (weight %) of recycled BHET based on the total weight of the polyester resin, and r-BHET TDI is the TDI value of recycled BHET calculated in the above test example. c. Combined heat resistance index The combined heat resistance index was calculated using the heat resistance index of the resin and the regeneration heat resistance index obtained above. Combined heat resistance index = Resin heat resistance index + Recycled heat resistance index (I)

[0149] (2) ΔCol-b The color changes of the polyester resins obtained in the examples and comparative examples were measured in high-temperature and high-humidity environments. a.Initial Col-b Reflectance data for polyester resin pellets was acquired using Hunter Lab's Color Flex EZ with an Illuminuteant D65 at an observer angle of 2°. The b-value in the Hunter Lab color space was calculated using the software color analyzer. b. Col-b after storage in a high-temperature, high-humidity environment Each polyester resin was stored at 50°C and 60% RH for 10 days. The b-value in the Hunter Lab color space was calculated using the same method as described above. c. ΔCol-b ΔCol-b was calculated according to the following formula. ΔCol-b = Col-b[10D] - Col-b[0D] In the formula, Col-b[10D] is the b value in the Hunter Lab color space measured after storing the polyester resin at 50°C and 60%RH for 10 days, and Col-b[0D] is the b value in the Hunter Lab color space measured for the polyester resin before storage.

[0150] (3) LC-UV The acetaldehyde content (ppm) in the polyester resins obtained in each of the examples and comparative examples was measured by LC-UV (liquid chromatography using a UV detector) analysis as follows. Specifically, the acetaldehyde content may refer to the acetaldehyde content based on the weight of the polyester resin (i.e., ppmw).

[0151] Samples were prepared by adding 1 g of each polyester resin to 10 ml of a mixture of acetonitrile and deionized water (50:50 by volume). 200 μl of acidified 2,3-dinitrophenylhydrazine (2,3-DNPH) was then added, and the mixture was stirred at 37°C for 1 hour. Column: Quasar C18 5μm Column temperature: 35℃ Sample volume: 20 μl Diluent: Mixture of acetonitrile and deionized water Flow rate: 0.8ml / min Detector: UV, 363nm Acetaldehyde quantification was calibrated using a standard range of 0.05–20 mg / l. 2 If the value was 0.995 or higher, the calibration model was judged to be valid.

[0152] (4) Intrinsic viscosity The polyester resins prepared in the examples were dissolved in ortho-chlorophenol (OCP) at a concentration of 0.12% at 100°C, and their intrinsic viscosity (IV, dl / g) was measured using an Ubbelohde viscometer at a thermostat of 35°C. As a result, it was confirmed that all polyester resins obtained in the examples had an intrinsic viscosity in the range of 0.5 dl / g to 1.2 dl / g at 35°C.

[0153] The test results are shown in the table below.

[0154] [Table 5]

[0155] [Table 6]

[0156] As can be seen from the test results above, the polyester resins of Examples 1 to 7 had excellent heat resistance and color quality, while the acetaldehyde content was controlled within a specific range even when recycled monomers were used. In contrast, the polyester resins of Comparative Examples 1 and 2 had acetaldehyde content outside the desirable range and had poor heat resistance and color quality.

Claims

1. A polyester resin containing recycled bis(2-hydroxyethyl) terephthalate (BHET) obtained by depolymerization of waste polyester, wherein the acetaldehyde content is 1 ppm or less.

2. The following formula: ΔCol-b=Col-b[10D]-Col-b[0D] [In the formula, Col-b[10D] is the b value in the Hunter Lab color space measured after storing the polyester resin at 50°C and 60% R.H. for 10 days.] Col-b[0D] is the b value in the Hunter Lab color space measured for polyester resin before storage. The polyester resin according to claim 1, having ΔCol-b in the range of -1 to +1.

3. The following equation (Ia): The heat resistance index of the resin = mole fraction of ethylene glycol × 0.02 (Ia) [In the formula, the mole fraction of ethylene glycol is the content (mol%) of the ethylene glycol component based on the total number of moles of diol components contained in the polyester resin.] The resin has a heat resistance index of 2.0 or less, calculated by [the specified method]. The heat resistance index is calculated using only numerical values, excluding the units of the parameters. The polyester resin according to claim 1.

4. The following formula (Ib): Regeneration heat resistance index = (r - BHET TDI) × weight fraction of r - BHET × 2 (Ib) [In the formula, the weight fraction of r-BHET is the content (weight %) of recycled BHET based on the total weight of the polyester resin.] The r-BHET TDI is given by the following formula when regenerated BHET is analyzed using high-performance liquid chromatography (HPLC): r-BHET TDI = [DEG-ester-1] + [DEG-ester-2] × 2 + exp^[HA-ester] (In the formula, DEG-ester-1 is the peak area fraction (%) of 2-hydroxyethyl[2-(2-hydroxyethoxy)ethyl]terephthalate, DEG-ester-2 is the peak area fraction (%) of bis[2-(2-hydroxyethoxy)ethyl]benzene-1,4-dicarboxylate, and HA-ester is the peak area fraction (%) of 2-hydroxyethyl(2-acetoxyethyl)terephthalate.) [defined by] It has a regeneration heat resistance index of 7.0 or less calculated by [the method], The regeneration heat resistance index is calculated using only numerical values, excluding the units of these parameters. The polyester resin according to claim 3.

5. The following equation (I): Combined heat resistance index = Resin heat resistance index + Recycled heat resistance index (I) [In the formulas, the heat resistance index of the resin is calculated using formula (Ia) above, and the regeneration heat resistance index is calculated using formula (Ib) above.] The polyester resin according to claim 4, having a combined heat resistance index of 9.0 or less calculated by [the specified method].

6. The polyester resin according to claim 1, wherein the recycled bis(2-hydroxyethyl) terephthalate, when measured by high-performance liquid chromatography (HPLC), has a peak area fraction of 95% or more of bis(2-hydroxyethyl) terephthalate and a peak area fraction of 2.5% or less of 2-hydroxyethyl[2-(2-hydroxyethoxy)ethyl] terephthalate.

7. When the recycled bis(2-hydroxyethyl) terephthalate is measured by high-performance liquid chromatography (HPLC), the following formula is obtained: TDI = [DEG-ester-1] + [DEG-ester-2] × 2 + exp^[HA-ester] [In the formula, DEG-ester-1 is the peak area fraction (%) of 2-hydroxyethyl[2-(2-hydroxyethoxy)ethyl]terephthalate, DEG-ester-2 is the peak area fraction (%) of bis[2-(2-hydroxyethoxy)ethyl]benzene-1,4-dicarboxylate, and HA-ester is the peak area fraction (%) of 2-hydroxyethyl(2-acetoxyethyl)terephthalate] It has a Thermal Degradation Index (TDI) of 3.0 or less, as defined by [the formula], and the TDI is calculated using only the numerical values, excluding the units of these parameters. The polyester resin according to claim 1.

8. The polyester resin according to claim 1, wherein the recycled bis(2-hydroxyethyl) terephthalate, when measured by high-performance liquid chromatography (HPLC), has a peak area fraction of 1.0% or less of acetate ester compounds and a total peak area fraction of 2.0% or less of diethylene glycol ester compounds.

9. The acetate ester compound comprises 2-hydroxyethyl (2-acetoxyethyl) terephthalate, The diethylene glycol ester compound comprises 2-hydroxyethyl[2-(2-hydroxyethoxy)ethyl]terephthalate and bis[2-(2-hydroxyethoxy)ethyl]benzene-1,4-dicarboxylate. The polyester resin according to claim 8.

10. It contains at least one comonomer selected from dicarboxylic acids and diols as a component, The dicarboxylic acid is at least one selected from the group consisting of isophthalic acid, dimethyl isophthalate, phthalic acid, dimethyl phthalate, phthalic anhydride, 2,6-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid dimethyl, diphenyldicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid dimethyl, 1,3-cyclohexanedicarboxylic acid dimethyl, sebacic acid, succinic acid, isodecyl succinic acid, maleic acid, maleic anhydride, fumaric acid, adipic acid, glutaric acid, and azelaic acid. The diol is at least one selected from the group consisting of isosorbide, neopentyl glycol, 1,2-propanediol, 1,3-propanediol, 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, 1,4-butanediol, 2,3-butanediol, 3-methyl-1,5-pentanediol, 3-methyl-2,4-pentanediol, 1,6-hexanediol, 1,2-cyclohexanediol, 1,4-cyclohexanediol, diethylene glycol, 4-(hydroxymethyl)cyclohexylmethyl-4-(hydroxymethyl)cyclohexanecarboxylate, and 4-(4-(hydroxymethyl)cyclohexylmethoxymethyl)cyclohexylmethanol. The polyester resin according to claim 1.

11. The polyester resin according to claim 1, comprising at least one recycled monomer selected from the group consisting of recycled ethylene glycol, recycled 1,4-cyclohexanedimethanol, recycled diethylene glycol, recycled neopentyl glycol, recycled isosorbide, recycled terephthalic acid, recycled dimethyl terephthalate, recycled isophthalic acid, and recycled dimethyl isophthalate.

12. The polyester resin according to claim 1, having an intrinsic viscosity of 0.5 dl / g to 1.2 dl / g at 35°C.

13. An article comprising the polyester resin described in claim 1.

14. The article according to claim 13, which is a container, blow, film, sheet, or profile.

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