Polyester resins and polyester containers produced therefrom

Abstract

The present invention relates to a polyester resin comprising repeating units derived from polymerized raw materials, which comprises recycled bis(2-hydroxyethyl) terephthalate, a polyester preform prepared therefrom, and a polyester container manufactured therefrom. The polyester resin has a controlled acetaldehyde (AA) content, thereby preventing leaching of acetaldehyde (AA), and provides a polyester container having excellent heat resistance, weather resistance, and color properties.

Description

Technical Field

[0001] This invention relates to a polyester resin having excellent heat resistance and controllable acetaldehyde (AA) content, and to a polyester container made from the polyester resin having excellent heat resistance, weather resistance, color characteristics, etc. Background Technology

[0002] Among polymers, polyester resins are widely used as materials for beverage containers, various packaging films, and various internal and external components due to their excellent heat resistance, transparency, gas barrier properties, and high mechanical strength.

[0003] Various products made from this polyester resin are discarded as waste after use, causing serious environmental problems. Therefore, technologies for recycling polyester waste containing polyester resin are attracting attention.

[0004] Meanwhile, polyester resin is prepared by loading polymeric raw materials into a reactor and carrying out polycondensation reactions, solid-state polymerization reactions, etc. In this case, acetaldehyde (AA) is formed as a byproduct during the reaction, and it may remain in the polyester resin even after separation and purification steps.

[0005] If beverage containers are made using polyester resins containing residual acetaldehyde (AA), the taste of the beverage contained in the container may be altered, thus reducing its palatability. To address this, a technique has been proposed to suppress the formation of acetaldehyde (AA) by adding additives, such as amine compounds, to the polymerization step of the polyester resin to minimize the residual acetaldehyde (AA) in the polyester resin.

[0006] However, the use of this additive produces new, undesirable byproducts, making it difficult to ensure the performance of the polyester resin and also limiting the ability to control the residual acetaldehyde (AA) content to the required level. Summary of the Invention

[0007] Technical issues

[0008] In recent years, in order to address the environmental problem that is becoming the biggest concern, a technology has been proposed to recycle polyester waste by chemically depolymerizing polyester waste to obtain recycled polymer raw materials and using them to prepare polyester resin (recycled polyester resin).

[0009] However, the inventors have discovered that impurities leading to acetaldehyde (AA) formation accumulate in the recycled polymer raw materials obtained through the depolymerization step; therefore, the polyester resin prepared using it has a high acetaldehyde (AA) content, which has an adverse effect on it.

[0010] To address this problem, the inventors conducted various studies. As a result, it has been found that the content of specific impurities (e.g., HA-esters, DEG-esters, BHET oligomers, etc.) contained in the recycled polymer raw materials can be minimized when they are used to prepare polyester resins.

[0011] Therefore, one object of the present invention is to provide a polyester resin that can improve environmental issues and has the desired physical properties while minimizing the content of residual acetaldehyde (AA), although additives are not used alone as in the prior art.

[0012] Furthermore, another object of the present invention is to provide a polyester preform made of polyester resin.

[0013] Furthermore, another object of the present invention is to provide a polyester container made of polyester resin and a method thereof.

[0014] Solution to the problem

[0015] To achieve the above objectives, the present invention provides a polyester resin comprising repeating units derived from a polymerizing raw material comprising recycled bis(2-hydroxyethyl) terephthalate, wherein the acetaldehyde (AA) content is 25 ppm or lower when the preform obtained by molding the polyester resin at a temperature of 290°C is analyzed by gas chromatography (GC).

[0016] In addition, the present invention also provides a polyester preform made of polyester resin.

[0017] In addition, the present invention also provides a polyester container made of polyester resin.

[0018] Furthermore, the present invention provides a method for preparing a polyester container, the method comprising first molding a polyester resin at a temperature of 250°C to 300°C to produce a polyester preform; and second molding the polyester preform.

[0019] Beneficial effects of the invention

[0020] In this invention, polyester resin is prepared by using recycled polymeric raw materials that minimize acetaldehyde (AA) formation during the polymerization reaction step or molding step of the polyester resin. Therefore, a polyester resin can be provided that improves environmental performance and exhibits excellent heat resistance, thermal stability, color properties, etc., while having a very low acetaldehyde (AA) content.

[0021] Furthermore, in this invention, polyester containers are prepared using polyester resin. Therefore, a polyester container (e.g., a bottle for cold or hot drinks) can be provided that has excellent heat resistance, weather resistance, color characteristics, etc., and does not cause problems due to acetaldehyde (AA). Detailed Implementation

[0022] Best Implementation of the Invention

[0023] The present invention will now be described in detail. However, the invention is not limited to the disclosure given below, but can be modified in various ways without altering the spirit of the invention.

[0024] In this specification, the term "comprising" is intended to specify a particular feature, region, step, method, element, and / or component. Unless otherwise expressly stated, the presence or addition of any other feature, region, step, method, element, and / or component is not excluded.

[0025] Throughout this specification, the terms "first," "second," etc., are used to describe various components. However, these components should not be limited by these terms. These terms are used to distinguish one element from another.

[0026] Unless otherwise stated, all figures and expressions used herein relating to component quantities, reaction conditions, etc., should be understood as being modified by the term “about”.

[0027] In this specification, singular expressions are also interpreted to include plural expressions, unless the context otherwise requires.

[0028] Polyester resin

[0029] The polyester resin according to the invention is a recycled polyester resin prepared using a polymeric raw material comprising recycled bis(2-hydroxyethyl) terephthalate (r-BHET). It comprises repeating units derived from the polymeric raw material, and when the preform obtained by molding the polyester resin at a temperature of 290°C is analyzed by gas chromatography (GC), the acetaldehyde (AA) content is 25 ppm or less.

[0030] Acetaldehyde (AA) is a substance with adverse effects and can be formed during the polymerization or molding steps of polyester resin. In this invention, the acetaldehyde (AA) content in the preform obtained through the polyester resin molding step is controlled within a specific range, namely 25 ppm or lower, thereby solving the aforementioned problems caused by acetaldehyde (AA).

[0031] For example, when the preform obtained by molding the polyester resin at a temperature of 290°C is analyzed by gas chromatography (GC), the acetaldehyde (AA) content in the preform may be less than 25 ppm, 24 ppm or less, less than 24 ppm, 23 ppm or less, 22 ppm or less, 21 ppm or less, 20 ppm or less, 19 ppm or less, 18 ppm or less, 17 ppm or less, 16 ppm or less, or 15 ppm or less (specifically, 0 ppm to 25 ppm, greater than 0 ppm to less than 25 ppm, 0.01 ppm to 24 ppm, 0.05 ppm to 20 ppm, or 0.1 ppm to 18 ppm).

[0032] Meanwhile, the polymerization raw materials can be recycled polymeric materials obtained through the depolymerization of waste polyester. Depolymerization can be carried out through physical depolymerization or chemical depolymerization. Specifically, it can be carried out through a glycolysis reaction that breaks down the ester bonds of waste polyester by reacting it with glycol compounds (e.g., ethylene glycol, diethylene glycol, etc.).

[0033] For example, a reactant (first reactant) can be obtained by first depolymerizing waste polyester with an ethylene glycol-based compound at 180°C to 200°C (specifically, 180°C to 195°C, 180°C to 190°C, or 180°C to 185°C), and then a reactant (second reactant) can be obtained by second depolymerizing the thus obtained reactant with an ethylene glycol-based compound at 150°C to 170°C (150°C to 165°C, 150°C to 160°C, or 150°C to 155°C), and then separated and purified.

[0034] There are no particular limitations on the steps for separating and purifying the reactants (second reactants), but it may include steps such as cooling and solid-liquid separation, treatment with ion exchange resins, cooling crystallization, pressure filtration, and distillation.

[0035] Specifically, in the cooling and solid-liquid separation process, the reactants (second reactants) are cooled by vacuum flash evaporation (at 100°C to 135°C and 15 Torr to 200 Torr), followed by solid-liquid separation using a filter aid. As a result, the reactants (second reactants) can be converted into liquid reactants. With the proceeding of the cooling and solid-liquid separation steps, solid impurities such as particles and insoluble organic matter contained in the reactants (second reactants) are removed, thereby improving the yield and purity of the polymerization feedstock.

[0036] Treatment with ion exchange resins can be carried out by passing the liquid reactants through the ion exchange resin or by adding the ion exchange resin to the liquid reactants. As these steps are performed, ionic impurities contained in the liquid reactants can be removed to obtain reactants of high purity (third reactant). The ion exchange resins used in the treatment can be known cation exchange resins, anion exchange resins, amphoteric ion exchange resins, chelating resins, or combinations thereof.

[0037] Cooling crystallization can be carried out by cooling the reactants (third reactant) to form a crystalline product. There are no particular limitations on the temperature at which the reactants (third reactant) are cooled, but it can specifically be 70°C or lower, 60°C or lower, 50°C or lower, 40°C or lower, 30°C or lower, or 25°C or lower, and can also be 0°C or higher, 5°C or higher, 10°C or higher, 15°C or higher, or 20°C or higher. As cooling crystallization proceeds, a crystalline product in which impurities (e.g., acetate compounds, diethylene glycol ester compounds, etc.) have been effectively removed can be obtained.

[0038] Pressure filtration can be performed by filtering the crystallized products using a Nutsche filter or a filter press. There are no particular limitations on the pressure and temperature for pressure filtration of the crystallized products, but the pressure can be from 0.1 bar to 21 bar, 0.5 bar to 10 bar, or 1 bar to 5 bar, and the temperature can be from 5°C to 35°C, 10°C to 30°C, or 15°C to 25°C. When pressure filtration is performed, a reactant (the fourth reactant) can be obtained with impurities (e.g., acetate compounds, diethylene glycol ester compounds, BHET dimers, BHET trimers, etc.) effectively removed.

[0039] Distillation can be performed by first distilling the reactant (the fourth reactant) under vacuum distillation, followed by a second distillation by thin-film evaporation. As distillation proceeds, a material is obtained in which impurities (e.g., BHET dimers, BHET trimers, etc.) have been effectively removed, while unreacted diol compounds (e.g., ethylene glycol, diethylene glycol, etc.) have been removed (recovered).

[0040] The material obtained through the separation and purification steps can be subjected to additional steps as needed, such as filtration and drying, thereby obtaining the polymer raw material of the present invention.

[0041] In this invention, reactants can refer to the products obtained through each step.

[0042] The polymerization raw material obtained through the above steps can have high purity by minimizing impurities, while also having a high content of recovered bis(2-hydroxyethyl) terephthalate (hereinafter referred to as "r-BHET").

[0043] Specifically, when measured by high performance liquid chromatography (HPLC), the polymer feedstock may have a peak area fraction of 95% or higher for bis(2-hydroxyethyl) terephthalate, which may indicate that the polymer feedstock has high purity and contains r-BHET. For example, when measured by high-performance liquid chromatography (HPLC), the peak area fraction of bis(2-hydroxyethyl) terephthalate in the polymer raw material can be 95.3% or greater, 95.5% or greater, 95.8% or greater, 96% or greater, 96.2% or greater, 96.5% or greater, 96.7% or greater, 97% or greater, 97.2% or greater, 97.5% or greater, 97.8% or greater, 98% or greater, 98.2% or greater, 98.5% or greater, 99% or greater, 99.5% or greater, or 100% (specifically, 95% to 100%, 95.5% to 99.5%, 96% to 99%, or 97% to 98.5%). Because the polyester resin according to the invention is prepared using polymer raw materials with high purity and containing r-BHET, it can have excellent heat resistance, color characteristics, etc., while improving environmental protection.

[0044] According to the present invention, when analyzing the polymerization raw materials by high performance liquid chromatography (HPLC), the peak area fraction of acetate esters (HA-esters) can be 1.0% or less. Acetate esters may include 2-hydroxyethyl (2-acetoxyethyl) terephthalate, which is a substance that causes the formation of acetaldehyde (AA) and has an adverse effect; therefore, controlling its content is important.

[0045] Specifically, acetate compounds can be byproducts of acetate esters, which act as catalysts in the depolymerization of waste polyester via glycolysis. That is, referring to reaction scheme 1 below, acetic acid derived from the acetate ester used as a catalyst can react with ethylene glycol (EG) to produce acetate-based compounds, such as 2-hydroxyethyl acetate (HA) and water (H₂O). In this case, 2-hydroxyethyl acetate (HA) has a similar boiling point to ethylene glycol (EG); therefore, it is not easily filtered out as an impurity during the removal (recovery) of ethylene glycol (EG). As a result, byproducts such as acetate compounds accumulate as the process continues. Specifically, referring to reaction scheme 2 below, 2-hydroxyethyl acetate (HA) can undergo a transesterification reaction with bis(2-hydroxyethyl) terephthalate (BHET) to produce ester compounds, such as 2-hydroxyethyl(2-acetoxyethyl) terephthalate (HAET) and ethylene glycol (EG).

[0046] [Reaction Scheme 1]

[0047] [Reaction Scheme 2]

[0048] Acetate compounds, such as 2-hydroxyethyl (2-acetoxyethyl) terephthalate (HAET), accumulate during the depolymerization step, resulting in polymer raw materials with high residual acetate content. When polymer raw materials with high residual acetate content are used to prepare polyester resins or polyester preforms, acetaldehyde (AA) can be formed as a byproduct of the polymerization reaction or molding step. As a result, polyester resins or polyester preforms containing a relatively high acetaldehyde (AA) content can be prepared.

[0049] However, in this invention, when preparing polyester resin, polymer raw materials in which the content of acetate ester (HA-ester) compounds (which are impurities that cause the formation of acetaldehyde (AA)) is controlled within a specific range are used.

[0050] Specifically, when measured by high performance liquid chromatography (HPLC), the peak area fraction of acetate (HA-ester) compounds in the polymerization feedstock can be 0.9% or less, 0.8% or less, 0.7% or less, 0.6% or less, 0.5% or less, 0.45% or less, 0.4% or less, 0.35% or less, 0.3% or less, 0.25% or less, or 0.24% or less (e.g., 0% to 1.0%, greater than 0% to 0.5%, 0.01% to 0.4%, or 0.1% to 0.3%).

[0051] Furthermore, according to the present invention, when the polymerization raw materials are analyzed by high performance liquid chromatography (HPLC), the total peak area fraction of the diethylene glycol ester compounds can be 2.0% or less. In the step of depolymerizing waste polyester via glycolysis, the diethylene glycol ester compounds can be generated through an transesterification reaction between diethylene glycol and bis(2-hydroxyethyl) terephthalate (BHET). The diethylene glycol ester compounds may specifically include 2-hydroxyethyl[2-(2-hydroxyethoxy)ethyl] terephthalate (DEG-ester-1) represented by Formula 1 and bis[2-(2-hydroxyethoxy)ethyl]phenyl-1,4-dicarboxylic acid ester (DEG-ester-2) represented by Formula 2.

[0052] [Formula 1]

[0053] [Equation 2]

[0054] Specifically, when measured by high-performance liquid chromatography (HPLC), the total peak area fraction of diethylene glycol ester (DEG ester) compounds in the polymer feedstock according to the present invention (e.g., the peak area fraction of DEG-ester-1 and the peak area fraction of DEG-ester-2) can be 1.9% or less, 1.8% or less, 1.7% or less, 1.6% or less, 1.5% or less, 1.4% or less, 1.3% or less, 1.2% or less, 1.1% or less, 1.0% or less, 0.95% or less, 0.9% or less, 0.7% or less, or 0.6% or less. For example, the total peak area fraction of diethylene glycol ester compounds (DEG-esters) can be 0% to 2.0%, greater than 0% to 1.5%, greater than 0% to 1.0%, greater than 0% to 0.8%, greater than 0% to 0.7%, or 0.01% to 0.55%.

[0055] According to the present invention, when measured by high-performance liquid chromatography (HPLC), the total peak area fraction of oligomers, such as dimers or higher oligomers, in the polymerization raw material can be 1.0% or less. Specifically, the dimers or higher oligomers can be dimers of bis(2-hydroxyethyl) terephthalate (BHET), trimers of bis(2-hydroxyethyl) terephthalate (BHET), or combinations thereof. The oligomers can have a molecular weight of 2,000 g / mol or less (e.g., 1,000 to 2,000 g / mol).

[0056] Specifically, when measured by high-performance liquid chromatography (HPLC), the total peak area fraction of dimers or higher oligomers in the polymeric raw materials according to the present invention (e.g., the peak area fraction of BHET dimer and the peak area fraction of BHET trimer) can be less than 1.0%, 0.8% or less, 0.6% or less, 0.55% or less, 0.5% or less, 0.45% or less, 0.4% or less, 0.35% or less, or 0.3% or less. For example, the total peak area fraction of dimers or higher oligomers can be 0% to 1.0%, greater than 0% to 0.9%, greater than 0% to 0.7%, 0.01% to 0.5%, 0.05% to 0.45%, 0.1% to 0.4%, or 0.1% to 0.35%.

[0057] Meanwhile, as the content of diethylene glycol ester compounds in the polymerization raw materials increases, the melting point (T) of the polyester resin also increases. m The melting point (T) decreases linearly. mAcetate compounds are an indicator of heat resistance. They act as terminators that inhibit polymer chain growth. The heat resistance of polyester resins decreases exponentially with increasing content of acetate compounds in the polymerizing raw materials. Using this relationship, a correlation can be derived to predict the heat resistance of polyester resins prepared using polymerizing raw materials (specifically, recycled bis(2-hydroxyethyl) terephthalate).

[0058] Specifically, when measured by high performance liquid chromatography (HPLC), the polymeric raw material according to the present invention can have a thermal performance degradation index (TDI) of 6.0 or less, as defined in Equation 1 below.

[0059] [Equation 1]

[0060] TDI = [DEG-ester-1] + ([DEG-ester-2] × 2) + exp^[HA-ester]

[0061] In Equation 1, 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-dicarboxylic acid ester, and HA-ester is the peak area fraction (%) of 2-hydroxyethyl(2-acetoxyethyl) terephthalate, where only values ​​excluding the units of these parameters are used for calculation.

[0062] Specifically, when the thermal performance degradation index (TDI) expressed by Equation 1 is 6.0 or less, the heat resistance of the polyester resin can be more effectively prevented from deteriorating during the preparation of the polyester resin due to DEG-ester-1, DEG-ester-2, and HA-ester. For example, the thermal performance degradation index (TDI) can be 5.5 or less, 5.0 or less, 4.8 or less, 4.5 or less, 4.3 or less, or 4.0 or less (specifically, 0 to 5.5, 0.5 to 5.0, or 1.0 to 4.0).

[0063] According to the present invention, when a solution (sample polymerization raw material solution) dissolved in dimethylformamide at a concentration of 25% by weight is measured, the polymerization raw material can have a yellow index (YID) of 5.0 or lower. Specifically, the yellow index (YID) can be 4.5 or lower, 4.3 or lower, 4.0 or lower, 3.8 or lower, 3.5 or lower, 3.3 or lower, 3.0 or lower, 2.5 or lower, 2.3 or lower, 2.1 or lower, 2.0 or lower, 1.7 or lower, 1.5 or lower, or 1.3 or lower. The polyester resin according to the present invention can have excellent color properties (e.g., transparency) because it is prepared using a polymerization raw material with a controlled yellow index (YID).

[0064] According to the present invention, the polyester resin can have a high glass transition temperature (T0). g ) and high melting point (T m This results in excellent heat resistance. For example, when measured by differential scanning calorimetry (DSC), polyester resins can exhibit a glass transition temperature (T0) of 80°C or higher. g Specifically, it can be 80.5°C or higher, 81°C or higher, 81.5°C or higher, 82°C or higher, or 82.5°C or higher (e.g., 80°C to 85°C or 80.5°C to 83°C). Furthermore, when measured by differential scanning calorimetry (DSC), the polyester resin can have a melting point of 240°C or higher (T). m Specifically, it can be 245°C or higher, 250°C or higher, 255°C or higher, 255.5°C or higher, 256.5°C or higher, 257°C or higher, or 257.5°C or higher (e.g., 255°C to 260°C or 257°C to 258°C).

[0065] According to the present invention, the polyester resin may have a very low content of diethylene glycol (DEG), which, along with acetaldehyde (AA), is considered an impurity. Specifically, the content of diethylene glycol (DEG) in the polyester resin, as measured by gas chromatography (GC), may be 2.0% by weight or less. More specifically, it may be 1.8% by weight or less, 1.5% by weight or less, 1.3% by weight or less, 1.0% by weight or less, 0.9% by weight or less, 0.8% by weight or less, 0.7% by weight or less, or 0.6% by weight or less (e.g., 0% by weight to 2.0% by weight, greater than 0% by weight to 1.5% by weight, or 0.1% by weight to 1.0% by weight).

[0066] Polyester resins can possess excellent color properties (e.g., transparency). Specifically, when measuring colors L, a, and b using the CIE LAB index, and when calculating the L–b value from the measurement results, the L–b value can be greater than 80, 82 or greater, 83 or greater, 84 or greater, 85 or greater, 86 or greater, 87 or greater, 88 or greater, or 89 or greater (e.g., 81 to 90 or 85 to 89.5). The CIE LAB index is a color space coordinate system defined by the CIE (International Commission on Illumination). The L value represents lightness (0-100; 0 for black, 100 for white), the a value represents green-red (+ for red and - for green, with 0 as the reference), and the b value represents yellow-blue (+ for yellow and - for blue, with 0 as the reference).

[0067] Polyester resins can have intrinsic viscosity (IV) controlled within a specific range, resulting in excellent processability. Specifically, the intrinsic viscosity (solid phase IV) of the polyester resin can be 0.75 dl / g to 0.85 dl / g, 0.76 dl / g to 0.84 dl / g, 0.77 dl / g to 0.83 dl / g, or 0.78 dl / g to 0.82 dl / g.

[0068] Polyester preform

[0069] The polyester preform according to the present invention is prepared from the above-described polyester resin. For example, the polyester preform can be a polyester injection molded article obtained by injection molding the above-described polyester resin. Since the polyester preform is prepared using the above-described polyester resin, it can have a very low acetaldehyde content and an intrinsic viscosity (IV) similar to that of the polyester resin, and therefore has excellent thermal stability.

[0070] Specifically, when the aforementioned polyester resin is molded at a temperature of 290°C to prepare a polyester preform, and when the polyester preform is analyzed by gas chromatography (GC), the acetaldehyde (AA) content of the polyester preform can be 25 ppm or lower. For example, the acetaldehyde (AA) content of the polyester preform can be less than 25 ppm, 24 ppm or lower, less than 24 ppm, 23 ppm or lower, 22 ppm or lower, 21 ppm or lower, 20 ppm or lower, 19 ppm or lower, 18 ppm or lower, 17 ppm or lower, 16 ppm or lower, or 15 ppm or lower (specifically, 0 ppm to 25 ppm, above 0 ppm to below 25 ppm, 0.01 ppm to 24 ppm, 0.05 ppm to 20 ppm, or 0.1 to 18 ppm).

[0071] In addition, the polyester preform can have an intrinsic viscosity (IV) of 0.75 dl / g to 0.82 dl / g, specifically 0.75 dl / g to 0.81 dl / g, 0.76 dl / g to 0.80 dl / g, or 0.76 dl / g to 0.79 dl / g.

[0072] According to the present invention, the intrinsic viscosity (IV) of the polyester preform is determined according to the following Equation 2. V The variation in intrinsic viscosity (IV) can be 0.05 dl / g or less. Specifically, the variation in intrinsic viscosity (IV) can be 0.05 dl / g or less. VThe variation can be less than 0.05 dl / g, 0.04 dl / g or less, 0.03 dl / g or less, 0.02 dl / g or less, or 0.01 dl / g or less (e.g., 0.01 dl / g to 0.05 dl / g, 0.01 dl / g to 0.04 dl / g, or 0.01 dl / g to 0.03 dl / g). Due to the intrinsic viscosity (IV... V Within the above range, thermal stability can be ensured when polyester preforms are prepared by molding polyester resin.

[0073] [Equation 2]

[0074] IV V = IV1 – IV2

[0075] In Equation 2, IV1 is the intrinsic viscosity of the polyester resin, and IV2 is the intrinsic viscosity of the polyester preform (specifically, the preform obtained by molding the polyester resin at a temperature of 290°C).

[0076] Polyester containers

[0077] The polyester container according to the present invention is made from the above-described polyester resin. Because the polyester container is made using the above-described polyester resin, it has excellent heat resistance, weather resistance, color characteristics (transparency), etc., while minimizing the release of acetaldehyde (AA) from the polyester container.

[0078] In particular, because polyester containers are made using polyester resin with acetaldehyde (AA) content controlled to a minimum, they are suitable for both cold and hot drinks.

[0079] Furthermore, according to the present invention, based on the following Equation 3, the polyester container can have a color variation of 2 or less (C V Specifically, color (C) V The variation can be less than 2, 1.9 or less, 1.8 or less, 1.7 or less, 1.6 or less, 1.5 or less, 1.4 or less, 1.3 or less, 1.2 or less, 1.1 or less, or 1.0 or less (e.g., 0 to less than 2, greater than 0 to 1.9, or 0.5 to 1.5). Because the color change (CV) is within the above range, color change of the polyester container can be prevented even when the polyester container is stored under high temperature and humid conditions.

[0080] [Equation 3]

[0081] C V = C1 – C2

[0082] In Equation 3, C1 is the difference (L1-b1) between the color L value (L1) and color b value (b1) of the polyester container (initial polyester container), and C2 is the difference (L2-b2) between the color L value (L2) and color b value (b2) of the polyester container obtained after placing the polyester container (initial polyester container) in a constant temperature and humidity oven at 50°C and 60% relative humidity for 500 hours.

[0083] Method for preparing polyester containers

[0084] Furthermore, the present invention provides a method for preparing a polyester container, the method comprising first molding a polyester resin at a temperature of 250°C to 300°C to produce a polyester preform; and second molding the polyester preform.

[0085] The temperature at which the polyester resin is first molded to prepare the polyester preform can be specifically 260°C to 295°C, 270°C to 295°C, or 280°C to 290°C.

[0086] The first molding can be carried out by known injection molding, extrusion molding or vacuum molding, and is preferably carried out by injection molding.

[0087] The second molding process involves shaping the polyester container, which can preferably be done via blow molding. Blow molding can be performed using known methods.

[0088] Invention Model

[0089] The invention will be described in more detail below with reference to embodiments. However, these embodiments are for illustrative purposes only, and the invention is not limited thereto.

[0090] <Preparation of Polymer Raw Materials>

[0091] [Preparation Example 1]

[0092] 1,000 g of waste polyester resin, 2,000 g of ethylene glycol, and 5.0 g of zinc acetic anhydride were charged into a first reactor made of stainless steel (SUS). The temperature inside the first reactor was raised to 180°C, and a first depolymerization (first glycolysis reaction) was carried out for 2 hours to obtain the first reactant. The first reactant obtained therefrom was transferred to a second reactor and cooled to 150°C. Then, 2,000 g of ethylene glycol was further fed into the second reactor, and a second depolymerization (second glycolysis reaction) was carried out for 2 hours, while the temperature inside the second reactor was maintained at 150°C to obtain the second reactant.

[0093] The second reactant obtained therefrom was cooled to 120°C by vacuum flash evaporation, and 16 g of filter aid (Celite) was added to it.TM 545), followed by pressure filtration (solid-liquid separation) to obtain a liquid reactant. The liquid reactant is then passed through a column packed with ion exchange resin (Bonlite BC107(H)) to remove ionic impurities contained in the liquid reactant, thereby obtaining a third reactant containing bis(2-hydroxyethyl) terephthalate (BHET) and ethylene glycol.

[0094] The third reactant was loaded into a 10-liter crystallizer equipped with a cooling water circulation jacket and stirred at 100 rpm for 2 hours, then cooled to room temperature for crystallization. A pressurized Nutsche filter (jacketed type, 0.2 m² filtration area) was used. 2 The crystalline product obtained by crystallization was subjected to solid-liquid separation under a pressure of 3 bar to obtain BHET filter cake as the fourth reactant.

[0095] The BHET cake was transferred to a 10-liter distillation apparatus and reheated to 130°C. Vacuum distillation was performed under progressively reduced pressure from 760 Torr to 0.8 Torr to remove (recover) unreacted ethylene glycol. The fifth reactant, with unreacted ethylene glycol removed, was then subjected to thin-film evaporation in a thin-film evaporator (VTA VKL70-4S) at 220°C and 0.08 Torr to obtain 1,040 g of the resulting material with dimers or higher oligomers removed.

[0096] Subsequently, for adsorption-crystallization, 1,040 g of the obtained material and 3,120 g of distilled water were placed in a 10-liter glass reactor and dissolved at 70°C. Then, 5.2 g of activated carbon was added, followed by stirring for 30 minutes and filtration. Next, the filtrate was cooled to room temperature to allow crystallization, filtered again, and dried in a vacuum oven to obtain 1,980 g of polymerization feedstock (polymer feedstock solution) containing recovered bis(2-hydroxyethyl) terephthalate (r-BHET).

[0097] [Preparation Example 2]

[0098] Except for adjusting the reaction time of the first glycolysis reaction from 2 hours to 1 hour, the same steps as in Example 1 were repeated to obtain a polymerization feedstock (polymer feedstock solution) containing recovered bis(2-hydroxyethyl) terephthalate (r-BHET).

[0099] [Preparation Example 3]

[0100] In addition to using a filter press (filtration area 0.4m²) 2In addition to filtering with filter plate 4ea at 18 bar instead of a pressurized Nutsche filter, the same steps as in Example 1 were repeated to obtain a polymerization feedstock (polymer feedstock solution) containing recovered bis(2-hydroxyethyl) terephthalate (r-BHET).

[0101] [Preparation Example 4]

[0102] Except for using waste polyester fiber instead of waste polyester resin, the same steps as in Example 1 were repeated to obtain a polymerization feedstock (polymer feedstock solution) containing recycled bis(2-hydroxyethyl) terephthalate (r-BHET).

[0103] [Preparation Example 5]

[0104] Except that no adsorption-crystallization is performed after film evaporation, the same steps as in Example 1 are repeated to obtain a polymerization feedstock (polymer feedstock solution) containing recovered bis(2-hydroxyethyl) terephthalate (r-BHET).

[0105] [Comparative Preparation Example 1]

[0106] Except for adjusting the temperature of the first glycolysis reaction from 180°C to 210°C and the temperature of the second glycolysis reaction from 150°C to 250°C, the same steps as in Example 1 were repeated to obtain a polymerization feedstock (polymer feedstock solution) containing recovered bis(2-hydroxyethyl) terephthalate (r-BHET).

[0107] [Comparative Preparation Example 2]

[0108] Except for the Nutsche filter step which does not involve cooling crystallization and pressurization, the same steps as in Example 1 are repeated to obtain a polymerization feedstock (polymer feedstock solution) containing recovered bis(2-hydroxyethyl) terephthalate (r-BHET).

[0109] [Test Example 1]

[0110] The polymer raw materials obtained above were all tested using the following methods. The results are shown in Table 1 below.

[0111] (1) High Performance Liquid Chromatography (HPLC)

[0112] Approximately 0.01 g of sample (polymerization feedstock) was diluted in 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). The peak area fractions (%) of the following components in the total HPLC peak area were then obtained.

[0113] - MHET: Monohydroxyethyl terephthalate

[0114] - BHET: Bis(2-hydroxyethyl) terephthalate, - DEG-Ester-1: 2-Hydroxyethyl[2-(2-hydroxyethoxy)ethyl] terephthalate - DEG-Ester-2: Bis[2-(2-hydroxyethoxy)ethyl]phenyl-1,4-dicarboxylic acid ester - HA-ester: 2-hydroxyethyl (2-acetoxyethyl) terephthalate - Dimer: BHET dimer - Trimer: BHET trimer

[0115] (2) Gas chromatography (GC)

[0116] Approximately 0.1 g of sample was diluted in approximately 10 ml of CHCl3, processed through a 0.45 μm filter, and then measured by gas chromatography (GC).

[0117] Model: Agilent 7890B

[0118] - Column: DB-624 (30 m × 0.25 mm × 1.4 µm)

[0119] - Oven temperature: 60°C (2 minutes) - 10°C / minute - 200°C (0 minutes) - 20°C / minute - 260°C (5 minutes)

[0120] -Injection temperature: 250°C

[0121] - Detector temperature: 250°C

[0122] - Flow rate: 1.5 ml / min (N2), split ratio: 1 / 50

[0123] (3) TDI

[0124] HPLC analysis was performed using the test method described in section (1) above, and the thermal performance degradation index (TDI) was calculated as expressed by Equation 1 below.

[0125] [Equation 1]

[0126] TDI = [DEG-ester-1] + ([DEG-ester-2] × 2) + exp^[HA-ester]

[0127] In Equation 1, 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-dicarboxylic acid ester, and HA-ester is the peak area fraction (%) of 2-hydroxyethyl(2-acetoxyethyl) terephthalate. In Equation 1, only values ​​excluding the units of these parameters are used for calculation. Here, exp^ represents the exponential function (e^).

[0128] (4) Melting point (Tm)

[0129] The melting point was measured when the temperature was increased from 30°C to 280°C at a rate of 20°C / min using a differential scanning calorimeter (DSC, TA Instruments Q20).

[0130] (5) Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES)

[0131] 0.3 g of sample (polymer raw material) was ultrasonically treated and diluted with ultrapure water. The content of inorganic substances (ppm) was measured using ICP-AES (Model 5100 of Agilent) (detection limit 5 ppm).

[0132] (6) Yellow Index (YID)

[0133] At room temperature, the sample (polymer raw material) was dissolved in dimethylformamide at a concentration of 25% by weight to prepare a solution. The prepared solution was allowed to stand for 30 minutes, after which its yellow index was measured. Specifically, transmittance data were obtained using a Hunter Lab ColorFlex EZ with an Illuminant D65 at an observer angle of 2°. The yellowness index (YID) value was calculated using the color analyzer in the software.

[0134] [Table 1]

[0135] Referring to Table 1 above, the polymerization raw materials of Preparation Examples 1 to 5 according to the present invention have a total HPLC peak area fraction of 2.0% or less of diethylene glycol esters (DEG-ester-1, DEG-ester-2) and a total HPLC peak area fraction of 1.0% or less of acetate esters (HA-esters), while the contents of other impurities (MHET, dimers, trimers) or residual EG are very low. Furthermore, their melting points (T0) are low. m It has excellent yellow index (YID) and yellow index.

[0136] In particular, the thermal performance degradation index (TDI) of the polymer raw materials used in Examples 1 to 5 was 5.0 or less, and the content of HA-ester was very low. Therefore, when used to prepare polyester resins, it is expected that polyester resins with excellent heat resistance and minimized acetaldehyde (AA) content can be produced.

[0137] <Preparation of Polyester Resin>

[0138] [Example 1]

[0139] 2,775 g of the polymerization raw material (a solution containing r-BHET) from Preparation Example 1, 0.8 g of antimony trioxide as a catalyst, 0.6 g of triethyl phosphate as a stabilizer, and 0.4 g of cobalt acetate as a colorant were charged into a 7-liter reactor capable of reaction under vacuum. The reactor temperature was then raised to 190°C over 2 hours. When the temperature reached 190°C, the reactor pressure was reduced from atmospheric pressure to 20 Torr over 30 minutes. Simultaneously, the reactor temperature was raised to 280°C over 1 hour, and polycondensation was carried out while the reactor pressure was maintained at 1 Torr or lower. At the start of the polycondensation reaction, the stirring speed was set very high. As the polycondensation reaction proceeded, the stirring speed was adjusted appropriately as the stirring capacity decreased due to the increase in reactant viscosity or the reactant temperature rose above the set temperature. The polycondensation reaction was carried out until the intrinsic viscosity (IV) of the mixture (melt) in the reactor reached 0.64 dl / g. Subsequently, when the intrinsic viscosity (IV) of the mixture inside the reactor reaches the desired level, the mixture is then discharged outside the reactor to form strips, which are solidified with a coolant and then granulated to have an average weight of about 12 mg to 14 mg.

[0140] Next, the granular product was placed at 150°C for 1 hour to crystallize, and then loaded into a 20-liter reactor for solid-state polymerization. Nitrogen gas was then introduced into the solid-state polymerization reactor at a rate of 50 liters / minute. Under these conditions, the temperature of the solid-state polymerization reactor was increased from room temperature to 140°C at a rate of 40°C / hour and maintained at 140°C for 3 hours. Then, the temperature was increased to 220°C at a rate of 40°C / hour, and solid-state polymerization was carried out at 220°C. Solid-state polymerization continued until the intrinsic viscosity (IV) of the granular product reached 0.81 dl / g to prepare polyester resin (recycled polyester resin).

[0141] [Examples 2 to 5]

[0142] Except for using the polymerization raw materials of Preparation Examples 2 to 5 respectively, polyester resin (recycled polyester resin) was obtained by carrying out the same polymerization reaction steps as in Example 1.

[0143] [Comparative Examples 1 and 2]

[0144] Except for using the polymerization raw materials of Comparative Preparation Examples 1 and 2 respectively, polyester resin (recycled polyester resin) was obtained by carrying out the same polymerization reaction steps as in Example 1.

[0145] <Preparation of Polyester Resin>

[0146] [Production Examples 1 to 5]

[0147] The polyester resins obtained in Examples 1 to 5 were dried in a vacuum oven at 150°C and 1 tor or less for 10 hours. First, transparent preforms weighing 50 grams were prepared by injection molding using a Nissei ASB150 injection molding machine at a temperature of 290°C, a mold cooling time of 6 seconds, and a total cycle time of 20 seconds.

[0148] Using the LB01E bottle forming machine manufactured by Krupp, at 7 kg / cm 2 Primary pressure, 25 kg / cm 2 The preform thus prepared is heated under secondary pressure and an infrared lamp heater heating time of 26.5 seconds. The polyester bottle is then manufactured by bottle forming (secondary blow molding) with a thermal equilibrium time of 8 seconds and the preform temperature set at 112°C-120°C before bottle forming.

[0149] [Compare Production Examples 1 and 2]

[0150] Except for using the polyester resins obtained in Comparative Examples 1 and 2 respectively, polyester bottles were manufactured using the same steps as in Production Example 1.

[0151] [Test Example 2]

[0152] The polyester resin and polyester bottles obtained above were tested using the following methods. The results are shown in Table 2 below.

[0153] (1) Intrinsic viscosity (IV)

[0154] At 150°C, the sample (polyester resin or polyester preform) was dissolved in o-chlorophenol (OCP) at a concentration of 1.2 g / dl to obtain a solution, and the intrinsic viscosity was measured using an Ubbelohde viscometer. Specifically, the temperature of the viscous tube was maintained at 35°C, and the specific viscosity was obtained by measuring the time required for the solvent to pass through a specific internal cross-section of the viscous tube (outflow time) and the time required for the solution to pass through, which was used to calculate the intrinsic viscosity.

[0155] (2) Glass transition temperature (T) g ) and melting point (T m )

[0156] The glass transition temperature (Tg) of the samples (polyester resin or polyester preform) was measured using a differential scanning calorimeter (DSC, Q20 type, TA instrument). Specifically, each sample was placed in an aluminum pan and heated to 290°C at a rate of 10°C / min, held at 290°C for 5 minutes, and then cooled to 30°C at a rate of -300°C / min. The glass transition temperature (Tg) was then measured from the heat flux obtained when the temperature was increased to 280°C at a rate of 10°C / min. g ) and melting temperature (T) m ).

[0157] (3) Gas chromatography (GC)

[0158] Each sample (polyester resin or polyester preform) was analyzed by gas chromatography (GC, Agilent 7890B) to determine the content of residual DEG and acetaldehyde (AA). In this case, polyester resin samples were prepared by pulverizing each polyester resin using a pulverizer and ammonolyzing 2 g of the pulverized polyester resin with hydrazine hydrate. Additionally, polyester preform samples were prepared by cutting each polyester preform to collect 3.0 g of preform, pulverizing it using a cryogenic pulverizer, filtering it through a 30-mesh filter, placing 1 g of preform in a vial, sealing it, and heating it at 150°C for 40 minutes.

[0159] (4) Polyester resin color (L–b)

[0160] The colors L, a, and b of each sample (polyester resin) were measured using a colorimeter (CR-410, Konica Minolta) based on the CIE LAB index. The L–b values ​​were calculated based on the results.

[0161] (5) Polyester container color (L–b)

[0162] The chromaticity and luminance of each polyester container sample were measured using a Varian Cary 5 UV / Vis / NIR spectrophotometer equipped with a diffuse reflection attachment. Specifically, the label panel portion of each polyester container was cut to prepare a specimen 30 mm wide and 30 mm long. For this specimen, the transmittance data (based on the CIE LAB index) of the D65 illuminant at an observer angle of 2° was obtained and processed using a color analyzer in Grams / 32 software to calculate the color values ​​L, a, and b. Based on the results, the L–b value was calculated. Furthermore, the color change (C) was calculated using the following Equation 3. V ).

[0163] [Equation 3]

[0164] C V = C1 – C2

[0165] In Equation 3, C1 is the difference (L1-b1) between the color L value (L1) and color b value (b1) of the polyester container (initial polyester container sample), and C2 is the difference (L2-b2) between the color L value (L2) and color b value (b2) of the polyester container (initial polyester container sample) obtained after placing it in a constant temperature and humidity oven at 50°C and 60% relative humidity for 500 hours.

[0166] [Table 2]

[0167] [Table 3]

[0168] Referring to Tables 2 and 3 above, the polyester resins of Examples 1 to 5 according to the present invention exhibit excellent heat resistance due to their high glass transition temperature and high melting point, while having very low contents of residual diethylene glycol (DEG) and acetaldehyde (AA) as a byproduct, making them suitable for manufacturing polyester containers (e.g., beverage bottles). Furthermore, during the preparation of polyester preforms from the polyester resins, the intrinsic viscosity (IV1-IV2) shows almost no change, indicating excellent thermal stability and guaranteed color characteristics.

[0169] Furthermore, the polyester containers of Production Examples 1 to 5 according to the present invention show almost no change in color characteristics even under high temperature and high humidity conditions, which indicates excellent heat resistance and weather resistance.

[0170] Conversely, the polyester resins of Comparative Examples 1 and 2 exhibit poor heat resistance due to their low glass transition temperature and low melting point, and their high content of residual diethylene glycol (DEG) and acetaldehyde (AA) as a byproduct makes them unsuitable for manufacturing polyester containers. This can be attributed to the use of the low-purity polymer raw materials of Comparative Examples 1 and 2 in the preparation of the polyester resins of Comparative Examples 1 and 2, respectively.

Claims

1. A polyester resin comprising repeating units derived from a polymerizing raw material comprising recycled bis(2-hydroxyethyl) terephthalate, wherein the acetaldehyde (AA) content is 25 ppm or less when a preform obtained by molding the polyester resin at a temperature of 290°C is analyzed by gas chromatography (GC).

2. The polyester resin according to claim 1, wherein when the polymer raw materials are analyzed by high performance liquid chromatography (HPLC), the peak area fraction of bis(2-hydroxyethyl) terephthalate is 95% or greater, and the peak area fraction of acetate compounds is 1.0% or less.

3. The polyester resin according to claim 2, wherein the acetate compound includes 2-hydroxyethyl (2-acetoxyethyl) terephthalate.

4. The polyester resin according to claim 1, wherein when the polymer raw material is analyzed by high performance liquid chromatography (HPLC), the total peak area fraction of the diethylene glycol ester compounds is 2.0% or less.

5. The polyester resin according to claim 1, wherein when measured in a solution of the polymeric raw material dissolved in dimethylformamide at a concentration of 25% by weight, the yellow index (YID) of the polymeric raw material is 5.0 or lower.

6. The polyester resin according to claim 1, wherein the thermal performance degradation index (TDI) is 6.0 or less when the polymer raw material is analyzed by high performance liquid chromatography (HPLC), as defined in Equation 1 below: [Equation 1] TDI = [DEG-ester-1] + ([DEG-ester-2] × 2) + exp^[HA-ester] In Equation 1, 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-dicarboxylic acid ester, and HA-ester is the peak area fraction (%) of 2-hydroxyethyl(2-acetoxyethyl) terephthalate, where only values ​​excluding the units of these parameters are used for calculation.

7. The polyester resin according to claim 1, wherein the content of diethylene glycol (DEG) is 2.0% by weight or less when the polyester resin is analyzed by gas chromatography (GC).

8. A polyester preform prepared from a polyester resin according to any one of claims 1 to 7.

9. The polyester preform according to claim 8, wherein its intrinsic viscosity (IV) is determined according to the following Equation 2. V The change was 0.05 dl / g or less: [Equation 2] IV V = IV1 – IV2 In Equation 2, IV1 is the intrinsic viscosity of the polyester resin, and IV2 is the intrinsic viscosity of the polyester preform.

10. A polyester container made from a polyester resin according to any one of claims 1 to 7.

11. The polyester container according to claim 10, having a color variation of 2 or less according to the following equation 3 (C V ): [Equation 3] C V = C1 – C2 In Equation 3, C1 is the difference (L1-b1) between the color L value (L1) and color b value (b1) of the polyester container, and C2 is the difference (L2-b2) between the color L value (L2) and color b value (b2) of the polyester container obtained after placing the polyester container in a constant temperature and humidity oven at 50°C and 60% relative humidity for 500 hours.

12. A method for preparing a polyester container, comprising first molding a polyester resin according to any one of claims 1 to 7 at a temperature of 250°C to 300°C to produce a polyester preform, and second molding the polyester preform.

13. The method for preparing a polyester container according to claim 12, wherein the first molding is injection molding and the second molding is blow molding.

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