Polyester resin mixture, method for preparing same, and polyester film prepared therefrom

Abstract

The present invention relates to a polyester resin mixture comprising a polyester copolymer prepared using recycled monomers; a method for preparing the polyester resin mixture; and a polyester film prepared by the method, wherein the polyester resin mixture has excellent extrusion properties (processability) and can therefore provide a polyester film with excellent physical properties and / or quality.

Description

Detailed Description of the Invention

[0001] [Technical field] The present invention relates to a polyester resin mixture comprising a polyester copolymer prepared using recycled monomers, a method for preparing the polyester resin mixture, and a polyester film prepared from the polyester resin mixture. [Background technology]

[0002] Among polymers, polyesters are used as materials in various fields due to their excellent mechanical strength, heat resistance, transparency, and gas barrier properties. In particular, polyester films or plates have good transparency and excellent mechanical strength, and are therefore widely used for cases, boxes, partitions, shelves, panels, packaging materials, building materials, interior materials, exterior materials, etc.

[0003] As a result, plastic waste, including polyester, is produced worldwide every year at levels that are difficult to manage. In recent years, various countries around the world have created regulations and systems for recycling waste plastic resources, including waste polyester.

[0004] Methods for recycling waste polyester include physical methods, which recycle the waste polyester through processes such as crushing and melting, and chemical methods, which recycle the waste polyester through a depolymerization process that breaks the ester bonds of the waste polyester.

[0005] Although various attempts have been made to recycle waste polyester by physical or chemical methods, there are limitations in achieving polyesters with good physical properties due to the presence of foreign substances in the waste polyester. In particular, polyesters prepared using recycled monomers obtained by depolymerization of waste polyester have poor extrudability (processability) and transparency due to the side reaction products (e.g., DEG esters) formed during the depolymerization process, thus limiting their use.

[0006] [Prior art document] [Patent documents] [Patent Document 1] Korean Patent Publication No. 2013-0041205

[0007] [DISCLOSURE OF THE INVENTION] [Technical challenges] The inventors have conducted various investigations to solve the above-mentioned conventional problems, and as a result, it has been found that when a polyester copolymer is prepared using recycled monomers, the types and amounts of recycled monomers and raw material monomers are optimized to obtain a polyester copolymer, and the polyester copolymer is mixed with polyethylene terephthalate, a polyester resin mixture having significantly improved extrudability (processability) can be obtained.

[0008] It is therefore an object of the present invention to provide a polyester resin blend, and a method for preparing the polyester resin blend, comprising a polyester copolymer and polyethylene terephthalate prepared using recycled monomers, and having controlled extrudability.

[0009] Additionally, another object of the present invention is to provide a polyester film prepared from a polyester resin mixture and a method for preparing the polyester film.

[0010] [Means for solving the problem] In order to solve the above-mentioned problems, the present invention provides a polyester resin mixture containing a polyester copolymer including a repeating unit (a) derived from a recycled monomer, a repeating unit (b) derived from a dicarboxylic acid compound, and a repeating unit (c) derived from a diol compound, and polyethylene terephthalate, wherein when extruded to a thickness of 1 mm, the polyester resin mixture satisfies the following equation 1: [Equation 1] Extrusion coefficient = A / 10 7 The present invention provides a polyester resin mixture having an extrudability coefficient of 6 or less according to the above.

[0011] In Equation 1, A is the quantitative analysis of oligomers (area / g) determined by gas chromatography (GC) analysis of the polyester copolymer.

[0012] Additionally, the present invention provides a method for preparing a polyester resin mixture, comprising: feeding a recycled monomer, a dicarboxylic acid compound, and a diol compound to a reactor; and supplying the resulting mixture at a pressure of 0 to 10.0 kgf / cm. 2 and a temperature of 150 to 300°C to obtain a reactant; subjecting the reactant to a polycondensation reaction to obtain a polyester copolymer; and mixing the polyester copolymer with polyethylene terephthalate.

[0013] Additionally, the present invention provides a polyester film prepared from the polyester resin mixture.

[0014] Additionally, the present invention provides a method for preparing a polyester film, the method comprising the steps of: preparing an unstretched sheet from a polyester resin mixture; and stretching the unstretched sheet. [Advantageous effects of the invention] The polyester resin mixture according to the present invention has an extrudability coefficient controlled within a specific range, and therefore, when various articles are manufactured using the polyester resin mixture, contamination of process equipment is prevented, while excellent extrudability (processability), transparency, heat shrinkability (stretchability), etc. Therefore, the present invention can provide articles (e.g., polyester films) having excellent physical properties and / or quality, even when a polyester copolymer prepared using recycled monomers is used. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a cross-sectional view of a polyester film according to one embodiment of the present invention.

[0016] [Best Mode for Carrying Out the Invention] The present invention will be described in detail below. The present invention in this specification is not limited to the disclosure given below, but can be modified in various forms as long as the gist of the present invention is not changed.

[0017] As used herein, the term "comprising" is intended to specify certain features, regions, steps, processes, elements, and / or components. Unless specifically stated to the contrary, this does not exclude the presence or addition of any other features, regions, steps, processes, elements, and / or components.

[0018] All numbers and expressions used herein relating to quantities of ingredients, reaction conditions, and the like, should be understood to be modified by the term "about," unless otherwise indicated.

[0019] Polyester Resin Mixture The present invention provides a polyester resin blend that has controlled extrudability and can therefore produce polyester articles with excellent physical properties, even when the recycled content is high. Specifically, the polyester resin blend includes a polyester copolymer including repeating units (a) derived from recycled monomers, repeating units (b) derived from a dicarboxylic acid compound, and repeating units (c) derived from a diol compound, and polyethylene terephthalate, which are described as follows:

[0020] Here, the term "derived from" may mean that a particular moiety or unit originating from a particular compound is contained in the result obtained by a chemical reaction of that particular compound.

[0021] Additionally, the term "recycled component" may refer to a component derived from a monomer or polymer obtained by decomposition, depolymerization, reprocessing, or repolymerization of waste plastics by physical or chemical methods. Specifically, the recycled component may refer to at least one component selected from the group consisting of recycled bis-2-hydroxyethyl terephthalate (recycled BHET), recycled ethylene glycol (recycled EG), recycled cyclohexanedimethanol (recycled CHDM), recycled terephthalic acid (recycled TPA), recycled isophthalic acid (recycled IPA), recycled dimethyl terephthalate (recycled DMT), recycled dimethyl isophthalate (recycled DMI), mechanically recycled polyethylene terephthalate (mechanically recycled PET), and chemically recycled polyethylene terephthalate (chemically recycled PET).

[0022] Polyester Copolymer The polyester copolymer according to the present invention comprises a repeating unit (a) derived from a recycled monomer, a repeating unit (b) derived from a dicarboxylic acid compound, and a repeating unit (c) derived from a diol compound. In other words, the polyester copolymer according to the present invention is obtained by an esterification reaction and / or polycondensation reaction of the recycled monomer, the dicarboxylic acid compound, and the diol compound.

[0023] The recycled monomer forming the repeating unit (a) is not particularly limited as long as it is a monomer obtained from waste plastics (e.g., waste polyester). Specifically, the recycled monomer forming the repeating unit (a) may be recycled bis-2-hydroxyethyl terephthalate (recycled BHET, r-BHET). More specifically, r-BHET may be obtained by depolymerization of waste polyesters (e.g., waste PET, waste PETG) using chemical methods such as glycolysis, hydrolysis, methanolysis, and aminolysis. Because r-BHET obtained by the depolymerization method has high purity, polyester resin mixtures containing polyester copolymers prepared using it may have excellent extrudability (processability), transparency, stretchability, and the like.

[0024] The repeating unit (a) may be contained in an amount of 1 wt % or more, 5 wt % or more, 10 wt % or more, 30 wt % or more, 50 wt % or more, 70 wt % or more, or 90 wt % or more (e.g., 1 to 95 wt %, 3 to 80 wt %, 5 to 75 wt %, or 7 to 70 wt %) based on the total weight of the polyester copolymer. Specifically, the polyester copolymer may contain repeating units (a) derived from r-BHET. r-BHET ) may be contained in an amount of 7% by weight or more, 10% by weight or more, 30% by weight or more, or 50% by weight or more (e.g., 1 to 95% by weight, 3 to 80% by weight, 5 to 75% by weight, 7 to 70% by weight) based on the total weight of the polyester copolymer. Because the repeating unit (a) is contained in the above-mentioned content range, even when recycled monomers are used, a polyester resin mixture having excellent extrudability (processability), stretchability, etc. can be obtained.

[0025] The dicarboxylic acid compound forming the repeating unit (b) is not particularly limited. Specifically, the dicarboxylic acid compound may be a compound containing at least one selected from the group consisting of terephthalic acid, isophthalic acid, dimethyl isophthalate, phthalic acid, dimethyl terephthalate, dimethyl phthalate, phthalic anhydride, 2,6-naphthalenedicarboxylic acid, dimethyl 2,6-naphthalenedicarboxylate, diphenyldicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, dimethyl 1,4-cyclohexanedicarboxylate, dimethyl 1,3-cyclohexanedicarboxylate, sebacic acid, succinic acid, isodecylsuccinic acid, maleic acid, maleic anhydride, fumaric acid, adipic acid, glutaric acid, and azelaic acid. More specifically, the dicarboxylic acid compound may be at least one selected from the group consisting of terephthalic acid, isophthalic acid, dimethyl isophthalate, and dimethyl terephthalate.

[0026] In addition, the dicarboxylic acid compound may contain a recycled monomer derived from waste plastic. Specifically, the dicarboxylic acid compound may be a compound containing at least one selected from the group consisting of recycled terephthalic acid (recycled TPA), recycled isophthalic acid (recycled IPA), recycled dimethyl isophthalate (recycled DMI), and recycled dimethyl terephthalate (recycled DMT).

[0027] The repeat unit (b) may be contained in an amount of 0 to 50 wt%, greater than 0 to 25 wt%, 1 to 15 wt%, 1 to 10 wt%, or 1 to 5 wt%, based on the total weight of the polyester copolymer.

[0028] The diol compound forming the repeating unit (c) is not particularly limited. Specifically, the diol compound may be isosorbide, ethylene 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 The diol compound may be at least one selected from the group consisting of 1,4-cyclohexanediol, diethylene glycol, cyclohexanedimethanol (e.g., 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, or 1,4-cyclohexanedimethanol), and cyclohexanedimethanol derivatives (e.g., 4-(hydroxymethyl)cyclohexylmethyl-4-(hydroxymethyl)cyclohexanecarboxylic acid or 4-(4-(hydroxymethyl)cyclohexylmethoxymethyl)cyclohexylmethanol). More specifically, the diol compound may be at least one selected from the group consisting of ethylene glycol, diethylene glycol, 1,4-cyclohexanedimethanol, 4-(hydroxymethyl)cyclohexylmethyl-4-(hydroxymethyl)cyclohexanecarboxylic acid, and 4-(4-(hydroxymethyl)cyclohexylmethoxymethyl)cyclohexylmethanol.

[0029] In addition, the diol compound may contain a recycled monomer derived from waste plastics. Specifically, the diol compound may be a compound containing at least one selected from the group consisting of recycled ethylene glycol (recycled EG) and recycled cyclohexanedimethanol (recycled CHDM).

[0030] The repeat unit (c) may be contained in an amount of 0 to 50 wt%, greater than 0 to 25 wt%, 1 to 15 wt%, or 1 to 5 wt%, based on the total weight of the polyester copolymer.

[0031] From the viewpoint of extrudability of the polyester resin mixture, the repeating unit (c) may contain the repeating unit (c1) derived from diethylene glycol in an amount of 0 to 30 mol%, greater than 0 to 25 mol%, 1 to 20 mol%, 3 to 18 mol%, 5 to 16 mol%, or 7 to 15 mol%, based on the total number of moles of the repeating unit (c). In addition, the repeating unit (c) may contain the repeating unit (c2) derived from cyclohexanedimethanol (1,4-cyclohexanedimethanol) in an amount of 0 to 45 mol%, greater than 0 to 40 mol%, 1 to 35 mol%, 3 to 35 mol%, 5 to 34 mol%, 10 to 33 mol%, or 13 to 33 mol%, based on the total number of moles of the repeating unit (c). Additionally, the repeating unit (c) may contain repeating units (c3) derived from a cyclohexanedimethanol derivative in an amount of 0 to 25 mol%, greater than 0 to 20 mol%, 0.5 to 20 mol%, 1 to 10 mol%, or 3 to 5 mol%, based on the total number of moles of the repeating unit (c). Additionally, the repeating unit (c) may contain repeating units (c4) derived from neopentyl glycol in an amount of 0 to 45 mol%, greater than 0 to 30 mol%, 1 to 25 mol%, or 5 to 20 mol%, based on the total number of moles of the repeating unit (c).

[0032] The polyester copolymer according to the present invention may have an intrinsic viscosity of about 0.45 to 1.2 dl / g, about 0.55 to 1.0 dl / g, about 0.60 to 1.0 dl / g, or about 0.60 to 0.9 dl / g when dissolved in orthochlorophenol at a concentration of 1.2 g / dl for 15 minutes at 150° C. and measured at 35° C. When the intrinsic viscosity is within the above range, the polyester copolymer has a (suitable) molecular weight required to have excellent mechanical properties, and can be uniformly mixed with polyethylene terephthalate under mild pressure and temperature conditions to facilitate molding of the polyester resin mixture.

[0033] Polyethylene terephthalate The polyethylene terephthalate according to the present invention may be obtained by a commonly known esterification reaction and / or polycondensation reaction of a diol compound and a dicarboxylic acid compound. Each of the diol compound and the dicarboxylic acid compound may be a virgin monomer or a recycled monomer. In addition, the polyethylene terephthalate may be obtained by a process such as pulverization and melting of waste polyethylene terephthalate collected after use.

[0034] Specifically, the polyethylene terephthalate may be one or more selected from the group consisting of mechanically recycled polyethylene terephthalate (mechanically recycled PET, MR-PET), chemically recycled polyethylene terephthalate (chemically recycled PET, CR-PET), and virgin polyethylene terephthalate (virgin PET).

[0035] Additionally, the polyethylene terephthalate may be crystalline polyethylene terephthalate. Specifically, the polyethylene terephthalate may be polyethylene terephthalate having a crystallization temperature (Tc) of 190°C or less, 180°C or less, or 170°C or less (e.g., 130 to 170°C).

[0036] From the viewpoints of extrudability, stretchability, etc., the polyester resin mixture according to the present invention may have a weight ratio of the polyester copolymer to polyethylene terephthalate of 1:99 to 99:1, a weight ratio of 5:95 to 95:5, a weight ratio of 10:90 to 90:10, a weight ratio of 15:85 to 85:15, or a weight ratio of 20:80 to 80:20. If a polyester resin mixture is extruded to a thickness of 1 mm, the following equation 1 [Equation 1] Extrusion coefficient = A / 10 7 The extrudability factor according to may be 6 or less.

[0037] In Equation 1, A is the quantitative analysis of oligomers (area / g) determined by gas chromatography (GC) analysis of the polyester copolymer.

[0038] The oligomer in the definition of A may refer to a polymer having a molecular weight of 1,000 g / mol or less (specifically, 500 to 1,000 g / mol).

[0039] In the polyester resin mixture according to the present invention, when the extrudability coefficient according to Equation 1 is controlled to 6 or less, it is possible to minimize the plate-out phenomenon of the roll during extrusion and the generation of outgassing. Therefore, when a polyester article is produced using the polyester resin mixture according to the present invention, it is possible to obtain a polyester article (e.g., polyester film) having excellent physical properties (e.g., heat shrinkage rate) while preventing contamination of processing equipment.

[0040] Specifically, the lower the extrudability coefficient, the better the extrudability (processability). The polyester resin mixture according to the present invention may have an extrudability coefficient of 5.0 or less, 4.5 or less, 4.0 or less, 3.5 or less, 3.0 or less, 2.0 or less, or 1.0 or less. More specifically, the polyester resin mixture may have an extrudability coefficient of 0.1 to 6.0, 0.15 to 5.0, 0.2 to 4.5, 0.25 to 4.0, 0.3 to 3.5, 0.3 to 3.0, 0.4 to 2.0, or 0.5 to 1.0.

[0041] The polyester resin mixture according to the present invention may contain recycled components in an amount of 30% by weight or more, based on the total weight of the polyester resin mixture. Specifically, the polyester resin mixture may contain the recycled components as defined above in an amount of 30 to 90% by weight, 30 to 88% by weight, 33 to 85% by weight, or 35 to 80% by weight. Even if the polyester resin mixture according to the present invention contains a relatively high content of recycled components, it still contains a polyester copolymer prepared by optimizing the types and amounts of recycled monomers and raw material monomers. Therefore, the polyester resin mixture according to the present invention ensures the required levels of extrudability, stretchability, etc., and can be used to produce polyester articles with excellent physical properties and / or quality.

[0042] Process for preparing polyester resin blends The present invention provides a method for preparing the above-mentioned polyester resin mixture. Specifically, the method for preparing the polyester resin mixture according to the present invention includes feeding recycled monomers, a dicarboxylic acid compound, and a diol compound to a reactor, and applying a pressure of 0 to 10.0 kgf / cm 2 and a temperature of 150 to 300°C to obtain a reactant; subjecting the reactant to a polycondensation reaction to obtain a polyester copolymer; and mixing the polyester copolymer with polyethylene terephthalate.

[0043] The step of obtaining the reactants may be carried out by supplying each monomer to a reactor and carrying out an esterification reaction (transesterification reaction) under specific reaction conditions. The details regarding the recycled monomer, dicarboxylic acid compound, and diol compound supplied to the reactor are the same as those regarding the polyester resin mixture.

[0044] The amount of recycled monomer fed to the reactor may be 1 to 95 wt%, 3 to 80 wt%, 5 to 75 wt%, or 7 to 70 wt%, based on the total weight of the composition (slurry) for preparing the polyester copolymer. In addition, the amount of dicarboxylic acid compound fed to the reactor may be 0 to 50 wt%, greater than 0 to 25 wt%, 0 to 15 wt%, 1 to 10 wt%, or 1 to 5 wt%, based on the total weight of the composition (slurry) for preparing the polyester copolymer. In addition, the amount of diol compound fed to the reactor may be 0 to 50 wt%, 1 to 35 wt%, 2 to 30 wt%, 3 to 25 wt%, 4 to 20 wt%, or 4 to 15 wt%, based on the total weight of the composition (slurry) for preparing the polyester copolymer.

[0045] On the other hand, additives such as, for example, catalysts, stabilizers, colorants, crystallizing agents, antioxidants, and branching agents may be further added to the reactor to promote the esterification and / or polycondensation reactions and to enhance the physical properties of the resulting polyester copolymer.

[0046] The catalyst may be sodium and magnesium methylates; acetates, borates, or fatty acid salts of Zn, Cd, Mn, Co, Ca, and Ba; and oxides or hydrates of Mg, Pb, Mn, Ti, Zn, Sb, and Ge.

[0047] As the stabilizer, phosphorus compounds such as phosphoric acid, trimethyl phosphate, and triethyl phosphate may be used.

[0048] As colorants, organic compounds such as cobalt-based compounds, anthraquinone-based compounds, perinone-based compounds, azo-based compounds, and methine-based compounds (e.g., cobalt acetate, cobalt propionate, Clarient's Polysynthren Blue RLS toner, and Clarient's Solvaperm Red BB toner) may be used.

[0049] As the crystallizing agent, a crystal nucleating agent, an ultraviolet absorber, a polyolefin resin, a polyamide resin, or the like may be used.

[0050] As the antioxidant, a hindered phenol compound, a phosphite compound, a thioether compound, or the like may be used.

[0051] As the branching agent, trimellitic anhydride, trimethylolpropane, trimellitic acid, or the like may be used.

[0052] The esterification reaction is carried out at a temperature of about 200 to 300°C, about 230 to 280°C, about 230 to 265°C, or about 245 to 255°C, and at a pressure of 0 to 10.0 kgf / cm 2 (0 to 7,355.6 mmHg), over 0 to 5.0 kgf / cm 2 (over 0~3,677.8mmHg), 0.1~3.0kgf / cm 2 (73.6 to 2,206.7 mmHg), or 1.0 to 3.0 kgf / cm 2 In addition, the transesterification reaction may be carried out at a temperature of 150 to 270°C or 180 to 260°C and a pressure of 0 to 5.0 kgf / cm. 2 (0~3,677.8mmHg), over 0~5.0kgf / cm 2 (over 0 to 3,677.8 mmHg), or 0.1 to 3.0 kgf / cm 2 Pressures of 73.6 to 2,206.7 mmHg (73.6 to 2,206.7 mmHg) may be used. 2 Pressure in mmHg refers to gauge pressure, pressure in mmHg refers to absolute pressure.

[0053] The esterification reaction (transesterification reaction) may be carried out in a batch or continuous manner. The recycled monomer, the dicarboxylic acid compound, and the diol compound may each be added to the reactor separately or in the form of a mixed slurry.

[0054] The step of obtaining the polyester copolymer may be carried out by polycondensing the reaction product obtained by the esterification reaction. Specifically, the polycondensation may be carried out for 1 to 24 hours at a temperature of 150 to 300°C and a reduced pressure of 600 to 0.01 mmHg.

[0055] The mixing step may be carried out by mixing the polyester copolymer obtained by the polycondensation reaction with the polyethylene terephthalate prepared in advance. The mixing step may be carried out by a conventionally known method.

[0056] Polyester film The present invention provides a polyester film prepared from a polyester resin mixture. Specifically, the polyester film according to the present invention comprises a polyester copolymer including a repeating unit (a) derived from a recycled monomer, a repeating unit (b) derived from a dicarboxylic acid compound, and a repeating unit (c) derived from a diol compound, and polyethylene terephthalate, and when the mixture is extruded to a thickness of 1 mm, the extrudability coefficient according to the above-mentioned equation 1 is 6 or less. Because the polyester film according to the present invention is prepared from the above-mentioned polyester resin mixture, it can exhibit high transparency and the required heat shrinkage rate (target heat shrinkage rate) even when the content of recycled components is high.

[0057] Specifically, the polyester film according to the present invention has a haze of 5% or less, 4% or less, 3% or less, 2.5% or less, 2% or less, or 1% or less (e.g., 0 to 2%) based on a film thickness of 50 μm, as measured in accordance with ASTM D1003-97, thereby exhibiting high transparency.

[0058] In addition, the polyester film according to the present invention has a low shrinkage initiation temperature of 65°C or less, and therefore, when used in the production of heat-shrinkable labels for PET containers, can be molded with excellent quality without causing clouding or deformation of the PET container. Specifically, the polyester film according to the present invention has a maximum shrinkage rate at 95°C of 30% or more, 40% or more, 50% or more, 55% or more, 60% or more, 65% or more, 70% or more, or 75% or more (e.g., 55 to 85%), and therefore can be effectively used as a heat-shrinkable film.

[0059] The polyester film according to the present invention may have a single-layer structure or a multi-layer structure. Specifically, referring to FIG. 1a, the polyester film (10) according to the present invention may have a single-layer structure consisting of only a resin layer (11) made of the above-mentioned polyester resin mixture. In addition, referring to FIG. 1b, the polyester film (10) according to the present invention may have a multi-layer structure including a base layer (11) and at least one resin layer (12, 13). Here, the structure in which at least one resin layer (12, 13) is laminated to the base layer (11) is not limited to that shown in FIG. 1b; in various structures, at least one resin layer may be laminated on both the top and bottom of the base layer (11).

[0060] When the polyester film according to the present invention has a multi-layer structure, each layer is prepared from the above-mentioned polyester resin mixture, and the content ratio of the polyester copolymer and the polyethylene terephthalate contained in each layer may be adjusted.

[0061] Specifically, in forming the base layer (11) from the above-mentioned polyester resin mixture containing polyethylene terephthalate and a polyester copolymer, the base layer (11) may contain a polyester resin mixture containing polyethylene terephthalate and the polyester copolymer in a weight ratio of 1:99 to 50:50. Therefore, the base layer (11) may contain polyethylene terephthalate and the polyester copolymer in a weight ratio of 1:99 to 50:50, specifically, a weight ratio of 2:98 to 45:55, a weight ratio of 3:97 to 35:65, or a weight ratio of 5:95 to 25:75.

[0062] Additionally, in forming the at least one resin layer (12, 13) from the above-described polyester resin mixture containing polyethylene terephthalate and a polyester copolymer, the at least one resin layer (12, 13) may contain a polyester resin mixture containing polyethylene terephthalate and a polyester copolymer in a weight ratio of 10:90 to 99:1. Thus, the at least one resin layer (12, 13) may contain polyethylene terephthalate and a polyester copolymer in a weight ratio of 10:90 to 99:1, specifically, a weight ratio of 10:90 to 85:15, a weight ratio of 10:90 to 80:20, or a weight ratio of 10:90 to 75:25.

[0063] When the base layer (11) and the at least one resin layer (12, 13) each contain polyethylene terephthalate and polyester copolymer in the weight ratio described above, it is possible to realize a polyester film that has excellent physical properties such as transparency and heat shrinkage, even if the recycled content is high.

[0064] Specifically, the content of recycled components in the polyester film according to the present invention may be 30% by weight or more, 50% by weight or more, or 70% by weight or more (e.g., 30 to 75% by weight) based on the total weight of the polyester film. In addition, the content of polyethylene terephthalate in the polyester film according to the present invention may be 5% by weight or more, 15% by weight or more, or 30% by weight or more (e.g., 5 to 35% by weight) based on the total weight of the polyester film.

[0065] On the other hand, the polyester film according to the present invention may be a uniaxially or biaxially stretched film. As a result, the polyester film according to the present invention can be excellent in transparency, heat shrinkability, thickness uniformity, etc. Specifically, the polyester film according to the present invention may be a film uniaxially stretched 1.5 to 6 times, 1.6 to 5.8 times, or 1.8 to 5.5 times in the transverse direction (TD). In addition, the polyester film according to the present invention may be a film uniaxially stretched 1.1 to 5 times, 1.2 to 4.9 times, or 1.5 to 4.5 times in the machine direction (MD). In addition, the polyester film according to the present invention may be a film biaxially stretched 1.5 to 6 times, 1.6 to 5.8 times, or 1.8 to 5.5 times in the transverse direction (TD) and 1.1 to 5 times, 1.2 to 4.9 times, or 1.5 to 4.5 times in the machine direction (MD).

[0066] Method for preparing polyester film The present invention provides a method for preparing the above-mentioned polyester film. Specifically, the method for preparing the polyester film according to the present invention includes the steps of preparing an unstretched sheet from a polyester resin mixture, the polyester resin mixture comprising a polyester copolymer including a repeating unit (a) derived from a recycled monomer, a repeating unit (b) derived from a dicarboxylic acid compound, and a repeating unit (c) derived from a diol compound, and polyethylene terephthalate, wherein the mixture has an extrudability factor of 6 or less according to the above-mentioned Equation 1 when extruded to a thickness of 1 mm; and stretching the unstretched sheet.

[0067] The step of preparing an unstretched sheet may be carried out by extruding the polyester resin mixture described above. Here, when the polyester film has a multilayer structure, polyester resin mixtures for forming each layer are prepared and co-extruded to prepare an unstretched sheet. The extrusion of the polyester resin mixture may be carried out at a temperature range of about 230 to 310°C, about 240 to 300°C, or about 250 to 290°C.

[0068] The step of stretching the unstretched sheet may be carried out by uniaxial stretching or biaxial stretching. Uniaxial stretching refers to stretching the unstretched sheet in either the machine direction (MD) or the transverse direction (TD) of the unstretched sheet. Biaxial stretching may be carried out by stretching the unstretched sheet in the machine direction (MD) and the transverse direction (TD) simultaneously or sequentially.

[0069] The stretch ratio of the unstretched sheet in the machine direction (MD) may be 1.1 to 5, 1.2 to 4.9, or 1.5 to 4.5. In addition, the stretch ratio of the unstretched sheet in the transverse direction (TD) may be 1.5 to 6, 1.6 to 5.8, or 1.8 to 5.5. When the stretch ratios in each of the machine direction (MD) and transverse direction (TD) are within the above-mentioned ranges, a polyester film having a uniform thickness and a required shrinkage can be obtained.

[0070] If necessary, the film obtained by stretching may be further subjected to commonly known heat setting, relaxation and cooling steps. [Mode of Invention] The present invention will be described in more detail below with reference to the following embodiments, but these examples are provided for illustrative purposes only and the present invention is not limited to these examples.

[0071] <Preparation of Polyester Copolymer> [Polymerization Example 1] A 10-liter reactor equipped with a water-coolable column and condenser was charged with recycled bis-2-hydroxyethyl terephthalate (r-BHET, 1,471.5 g), terephthalic acid (TPA, 2,043.6 g), ethylene glycol (EG, 373.8 g), 1,4-cyclohexanedimethanol (CHDM, 826.4 g), and diethylene glycol (DEG, 211.1 g), followed by the addition of titanium dioxide (TiO, 1.0 g) as a catalyst, phosphoric acid (1.5 g) as a stabilizer, and blue toner (0.006 g) and red toner (0.004 g) as colorants.

[0072] Next, nitrogen was injected into the reactor to apply pressure to the reactor, and the pressure was increased by 2.0 kgf / cm from atmospheric pressure. 2 The temperature was increased (absolute pressure: 2,231.1 mmHg). The temperature of the reactor was then increased to 220°C over 90 minutes, maintained at 220°C for 2 hours, and then the temperature was increased again to 260°C over 2 hours. Thereafter, the esterification reaction was carried out at a temperature of 260°C while visually observing the mixture in the reactor until it became transparent. During this procedure, by-products were discharged through a column and a condenser. Upon completion of the esterification reaction, the nitrogen in the pressurized reactor was released to the outside, and the pressure in the reactor was reduced to atmospheric pressure. The mixture in the reactor was then transferred to a 7-liter reactor capable of reaction under reduced pressure.

[0073] The reactor pressure was then reduced from atmospheric pressure to 5 torr (5 mmHg absolute) over 30 minutes. Simultaneously, the reactor temperature was increased to 265°C over 1 hour, and the polycondensation reaction was carried out while maintaining the reactor pressure at 1 torr (1 mmHg absolute) or less. A high stirring speed may be set at the start of the polycondensation reaction. As the polycondensation reaction progresses, if the stirring force weakens due to an increase in the viscosity of the reactants, or if the temperature of the reactants rises above the set temperature, the stirring speed may be adjusted accordingly. The polycondensation reaction was carried out until the intrinsic viscosity (IV) of the mixture (melt) in the reactor reached 0.70 dL / g. When the intrinsic viscosity of the mixture in the reactor reached the desired level, the mixture was discharged from the reactor to form strands. The strands were solidified using a cooling liquid and then granulated to prepare polyester copolymers with an average weight of approximately 12-14 mg.

[0074] [Polymerization Example 2] A 10-liter reactor equipped with a water-cooled column and a condenser was charged with recycled bis-2-hydroxyethyl terephthalate (r-BHET, 2,944.0 g), terephthalic acid (TPA, 1,130.0 g), ethylene glycol (EG, 26.2 g), and 1,4-cyclohexanedimethanol (CHDM, 839.8 g), followed by the addition of titanium dioxide (TiO, 1.0 g) as a catalyst, phosphoric acid (1.5 g) as a stabilizer, and cobalt acetate (0.7 g) as a colorant.

[0075] Next, nitrogen was injected into the reactor to apply pressure to the reactor, and the pressure was increased by 1.0 kgf / cm from atmospheric pressure. 2 The temperature was increased (absolute pressure: 1,495.6 mmHg). The temperature of the reactor was then increased to 220°C over 90 minutes and maintained at 220°C for 2 hours, and then the temperature was increased again to 255°C over 2 hours. Thereafter, the esterification reaction was carried out at a temperature of 255°C while visually observing the mixture in the reactor until it became transparent. During this procedure, by-products were discharged through a column and a condenser. Upon completion of the esterification reaction, the nitrogen in the pressurized reactor was released to the outside, and the pressure in the reactor was reduced to atmospheric pressure. The mixture in the reactor was then transferred to a 7-liter reactor capable of reaction under reduced pressure.

[0076] The reactor pressure was then reduced from atmospheric pressure to 5 torr (5 mmHg absolute) over 30 minutes. Simultaneously, the reactor temperature was increased to 285°C over 1 hour, and the polycondensation reaction was carried out while maintaining the reactor pressure at 1 torr (1 mmHg absolute) or less. A high stirring speed may be set at the beginning of the polycondensation reaction. As the polycondensation reaction progresses, if the stirring force weakens due to an increase in the viscosity of the reactants, or if the temperature of the reactants rises above the set temperature, the stirring speed may be adjusted accordingly. The polycondensation reaction was carried out until the intrinsic viscosity (IV) of the mixture (melt) in the reactor reached 0.75 dL / g. When the intrinsic viscosity of the mixture in the reactor reached the desired level, the mixture was discharged from the reactor to form strands. The strands were solidified using a cooling liquid and then granulated to prepare polyester copolymers with an average weight of approximately 12-14 mg.

[0077] [Polymerization Example 3] A 10-liter reactor equipped with a water-coolable column and condenser was charged with recycled bis-2-hydroxyethyl terephthalate (r-BHET, 3,653.7 g), terephthalic acid (TPA, 713.2 g), 1,4-cyclohexanedimethanol (CHDM, 564.9 g), and diethylene glycol (DEG, 336.6 g), followed by the addition of titanium dioxide (TiO, 1.0 g) as a catalyst, phosphoric acid (1.5 g) as a stabilizer, and blue toner (0.008 g) and red toner (0.004 g) as colorants.

[0078] Next, nitrogen was injected into the reactor to apply pressure to the reactor, and the pressure was increased by 2.0 kgf / cm from atmospheric pressure. 2The temperature was increased (absolute pressure: 2,231.1 mmHg). The temperature of the reactor was then increased to 220°C over 90 minutes and maintained at 220°C for 2 hours, and then the temperature was increased again to 255°C over 2 hours. Thereafter, the esterification reaction was carried out at a temperature of 255°C while visually observing the mixture in the reactor until it became transparent. During this procedure, by-products were discharged through a column and a condenser. Upon completion of the esterification reaction, the nitrogen in the pressurized reactor was released to the outside, and the pressure in the reactor was reduced to atmospheric pressure. The mixture in the reactor was then transferred to a 7-liter reactor capable of reaction under reduced pressure.

[0079] The reactor pressure was then reduced from atmospheric pressure to 5 torr (5 mmHg absolute) over 30 minutes. Simultaneously, the reactor temperature was increased to 285°C over 1 hour, and the polycondensation reaction was carried out while maintaining the reactor pressure at 1 torr (1 mmHg absolute) or less. A high stirring speed may be set at the start of the polycondensation reaction. As the polycondensation reaction progresses, if the stirring force weakens due to an increase in the viscosity of the reactants, or if the temperature of the reactants rises above the set temperature, the stirring speed may be adjusted accordingly. The polycondensation reaction was carried out until the intrinsic viscosity (IV) of the mixture (melt) in the reactor reached 0.70 dL / g. When the intrinsic viscosity of the mixture in the reactor reached the desired level, the mixture was discharged from the reactor to form strands. The strands were solidified using a cooling liquid and then granulated to prepare polyester copolymers with an average weight of approximately 12-14 mg.

[0080] [Polymerization Example 4] A 10-liter reactor equipped with a water-cooled column and condenser was charged with recycled bis-2-hydroxyethyl terephthalate (r-BHET, 1,777.6 g), terephthalic acid (TPA, 1,895.5 g), ethylene glycol (EG, 1,347.4 g), 1,4-cyclohexanedimethanol (CHDM, 265.2 g), diethylene glycol (DEG, 242.0 g), and a CHDM derivative (4-(hydroxymethyl)cyclohexylmethyl-4-(hydroxymethyl)cyclohexanecarboxylic acid and 4-(4-(hydroxymethyl)cyclohexylmethoxymethyl)cyclohexylmethanol in a 1:3 molar ratio, 345.5 g), followed by the addition of germanium dioxide (GeO, 1.0 g) as a catalyst, phosphoric acid (1.5 g) as a stabilizer, and blue toner (0.020 g) and red toner (0.008 g) as colorants.

[0081] Next, nitrogen was injected into the reactor to apply pressure to the reactor, and the pressure was increased by 0.5 kgf / cm from atmospheric pressure. 2 The temperature was increased (absolute pressure: 1,127.8 mmHg). The temperature of the reactor was then increased to 220°C over 90 minutes, maintained at 220°C for 2 hours, and then the temperature was increased again to 260°C over 2 hours. Thereafter, the esterification reaction was carried out at a temperature of 260°C while visually observing the mixture in the reactor until it became transparent. During this procedure, by-products were discharged through a column and a condenser. Upon completion of the esterification reaction, the nitrogen in the pressurized reactor was released to the outside, and the pressure in the reactor was reduced to atmospheric pressure. The mixture in the reactor was then transferred to a 7-liter reactor capable of reaction under reduced pressure.

[0082] The reactor pressure was then reduced from atmospheric pressure to 5 torr (5 mmHg absolute) over 30 minutes. Simultaneously, the reactor temperature was increased to 275°C over 1 hour, and the polycondensation reaction was carried out while maintaining the reactor pressure at 1 torr (1 mmHg absolute) or less. A high stirring speed may be set at the start of the polycondensation reaction. As the polycondensation reaction progresses, if the stirring force weakens due to an increase in the viscosity of the reactants, or if the temperature of the reactants rises above the set temperature, the stirring speed may be adjusted accordingly. The polycondensation reaction was carried out until the intrinsic viscosity (IV) of the mixture (melt) in the reactor reached 0.83 dL / g. When the intrinsic viscosity of the mixture in the reactor reached the desired level, the mixture was discharged from the reactor to form strands. The strands were solidified using a cooling liquid and then granulated to prepare polyester copolymers with an average weight of approximately 12-14 mg.

[0083] [Polymerization Example 5] A 10-liter reactor equipped with a water-cooled column and condenser was charged with recycled bis-2-hydroxyethyl terephthalate (r-BHET, 3,222.7 g), dimethyl terephthalate (DMT, 1,158.3 g), ethylene glycol (EG, 127.3 g), 1,4-cyclohexanedimethanol (CHDM, 618.0 g), and diethylene glycol (DEG, 272.4 g), followed by the addition of Mn(II) acetate tetrahydrate (1.5 g) and antimony trioxide (SbO, 1.8 g) as catalysts, phosphoric acid (1.5 g) as a stabilizer, and cobalt acetate (0.7 g) as a colorant.

[0084] Next, nitrogen was injected into the reactor to apply pressure to the reactor, and the pressure was increased by 0.1 kgf / cm from atmospheric pressure. 2The temperature was increased (absolute pressure: 833.6 mmHg). The temperature of the reactor was then increased to 220°C over 90 minutes, maintained at 220°C for 2 hours, and then the temperature was increased again to 240°C over 2 hours. Thereafter, the esterification reaction was carried out at a temperature of 240°C while visually observing the mixture in the reactor until it became transparent. During this procedure, by-products were discharged through a column and a condenser. Upon completion of the esterification reaction, the nitrogen in the pressurized reactor was released to the outside, and the pressure in the reactor was reduced to atmospheric pressure. The mixture in the reactor was then transferred to a 7-liter reactor capable of reaction under reduced pressure.

[0085] The reactor pressure was then reduced from atmospheric pressure to 5 torr (5 mmHg absolute) over 30 minutes. Simultaneously, the reactor temperature was increased to 265°C over 1 hour, and the polycondensation reaction was carried out while maintaining the reactor pressure at 1 torr (1 mmHg absolute) or less. A high stirring speed may be set at the start of the polycondensation reaction. As the polycondensation reaction progresses, if the stirring force weakens due to an increase in the viscosity of the reactants, or if the temperature of the reactants rises above the set temperature, the stirring speed may be adjusted accordingly. The polycondensation reaction was carried out until the intrinsic viscosity (IV) of the mixture (melt) in the reactor reached 0.75 dL / g. When the intrinsic viscosity of the mixture in the reactor reached the desired level, the mixture was discharged from the reactor to form strands. The strands were solidified using a cooling liquid and then granulated to prepare polyester copolymers with an average weight of approximately 12-14 mg.

[0086] [Polymerization Example 6] A 10-liter reactor equipped with a water-cooled column and condenser was charged with recycled bis-2-hydroxyethyl terephthalate (r-BHET, 522.0 g), terephthalic acid (TPA, 2,759.9 g), isophthalic acid (IPA, 341.1 g), ethylene glycol (EG, 127.3 g), 1,4-cyclohexanedimethanol (CHDM, 852.8 g), and a CHDM derivative (4-(hydroxymethyl)cyclohexylmethyl-4-(hydroxymethyl)cyclohexanecarboxylic acid and 4-(4-(hydroxymethyl)cyclohexylmethoxymethyl)cyclohexylmethanol in a 1:3 molar ratio, 350.5 g), followed by the addition of germanium dioxide (GeO, 1.0 g) as a catalyst, phosphoric acid (1.5 g) as a stabilizer, and blue toner (0.012 g) and red toner (0.004 g) as colorants.

[0087] Next, nitrogen was injected into the reactor to apply pressure to the reactor, and the pressure was increased by 1.0 kgf / cm from atmospheric pressure. 2 The temperature was increased (absolute pressure: 1,495.6 mmHg). The temperature of the reactor was then increased to 220°C over 90 minutes and maintained at 220°C for 2 hours, and then the temperature was increased again to 255°C over 2 hours. Thereafter, the esterification reaction was carried out at a temperature of 255°C while visually observing the mixture in the reactor until it became transparent. During this procedure, by-products were discharged through a column and a condenser. Upon completion of the esterification reaction, the nitrogen in the pressurized reactor was released to the outside, and the pressure in the reactor was reduced to atmospheric pressure. The mixture in the reactor was then transferred to a 7-liter reactor capable of reaction under reduced pressure.

[0088] The reactor pressure was then reduced from atmospheric pressure to 5 torr (5 mmHg absolute) over 30 minutes. Simultaneously, the reactor temperature was increased to 285°C over 1 hour, and the polycondensation reaction was carried out while maintaining the reactor pressure at 1 torr (1 mmHg absolute) or less. A high stirring speed may be set at the start of the polycondensation reaction. As the polycondensation reaction progresses, if the stirring force weakens due to an increase in the viscosity of the reactants, or if the temperature of the reactants rises above the set temperature, the stirring speed may be adjusted accordingly. The polycondensation reaction was carried out until the intrinsic viscosity (IV) of the mixture (melt) in the reactor reached 0.70 dL / g. When the intrinsic viscosity of the mixture in the reactor reached the desired level, the mixture was discharged from the reactor to form strands. The strands were solidified using a cooling liquid and then granulated to prepare polyester copolymers with an average weight of approximately 12-14 mg.

[0089] [Polymerization Example 7] A 10-liter reactor equipped with a water-coolable column and condenser was charged with recycled bis-2-hydroxyethyl terephthalate (r-BHET, 1,432.4 g), dimethyl terephthalate (DMT, 2,813.3 g), neopentyl glycol (NPG, 187.3 g), and diethylene glycol (DEG, 294.1 g), followed by the addition of germanium dioxide (GeO, 1.0 g) and titanium dioxide (TiO, 1.0 g) as catalysts, phosphoric acid (1.5 g) as a stabilizer, and blue toner (0.006 g) and red toner (0.004 g) as colorants.

[0090] Next, nitrogen was injected into the reactor to apply pressure to the reactor, and the pressure was increased by 0.5 kgf / cm from atmospheric pressure. 2The temperature was increased (absolute pressure: 1,127.8 mmHg). The temperature of the reactor was then increased to 220°C over 90 minutes, maintained at 220°C for 2 hours, and then the temperature was increased again to 260°C over 2 hours. Thereafter, the esterification reaction was carried out at a temperature of 260°C while visually observing the mixture in the reactor until it became transparent. During this procedure, by-products were discharged through a column and a condenser. Upon completion of the esterification reaction, the nitrogen in the pressurized reactor was released to the outside, and the pressure in the reactor was reduced to atmospheric pressure. The mixture in the reactor was then transferred to a 7-liter reactor capable of reaction under reduced pressure.

[0091] The reactor pressure was then reduced from atmospheric pressure to 5 torr (5 mmHg absolute) over 30 minutes. Simultaneously, the reactor temperature was increased to 275°C over 1 hour, and the polycondensation reaction was carried out while maintaining the reactor pressure at 1 torr (1 mmHg absolute) or less. A high stirring speed may be set at the start of the polycondensation reaction. As the polycondensation reaction progresses, if the stirring force weakens due to an increase in the viscosity of the reactants, or if the temperature of the reactants rises above the set temperature, the stirring speed may be adjusted accordingly. The polycondensation reaction was carried out until the intrinsic viscosity (IV) of the mixture (melt) in the reactor reached 0.79 dL / g. When the intrinsic viscosity of the mixture in the reactor reached the desired level, the mixture was discharged from the reactor to form strands. The strands were solidified using a cooling liquid and then granulated to prepare polyester copolymers with an average weight of approximately 12-14 mg.

[0092] [Comparative Polymerization Example 1] A 10-liter reactor equipped with a water-cooled column and condenser was charged with terephthalic acid (TPA, 3,419.2 g), ethylene glycol (EG, 2,617.9 g), and diethylene glycol (DEG, 150.4 g), followed by the addition of germanium dioxide (GeO, 1.0 g) as a catalyst and phosphoric acid (1.5 g) as a stabilizer.

[0093] Next, nitrogen was injected into the reactor to apply pressure to the reactor, and the pressure was increased by 1.0 kgf / cm from atmospheric pressure.2 The temperature was increased (absolute pressure: 1,495.6 mmHg). The temperature of the reactor was then increased to 220°C over 90 minutes, maintained at 220°C for 2 hours, and then the temperature was increased again to 265°C over 2 hours. Thereafter, the esterification reaction was carried out at a temperature of 265°C while visually observing the mixture in the reactor until it became transparent. During this procedure, by-products were discharged through a column and a condenser. Upon completion of the esterification reaction, the nitrogen in the pressurized reactor was released to the outside, and the pressure in the reactor was reduced to atmospheric pressure. The mixture in the reactor was then transferred to a 7-liter reactor capable of reaction under reduced pressure.

[0094] The reactor pressure was then reduced from atmospheric pressure to 5 torr (5 mmHg absolute) over 30 minutes. Simultaneously, the reactor temperature was increased to 275°C over 1 hour, and the polycondensation reaction was carried out while maintaining the reactor pressure at 1 torr (1 mmHg absolute) or less. A high stirring speed may be set at the start of the polycondensation reaction. As the polycondensation reaction progresses, if the stirring force weakens due to an increase in the viscosity of the reactants, or if the temperature of the reactants rises above the set temperature, the stirring speed may be adjusted accordingly. The polycondensation reaction was carried out until the intrinsic viscosity (IV) of the mixture (melt) in the reactor reached 0.60 dL / g. When the intrinsic viscosity of the mixture in the reactor reached the desired level, the mixture was discharged from the reactor to form strands. The strands were solidified using a cooling liquid and then granulated to prepare polyester copolymers with an average weight of approximately 12-14 mg.

[0095] [Comparative Polymerization Example 2] A 10-liter reactor equipped with a water-cooled column and condenser was charged with terephthalic acid (TPA, 3,067.0 g), neopentyl glycol (NPG, 210.6 g), and diethylene glycol (DEG, 211.1 g), followed by the addition of germanium dioxide (GeO, 1.0 g) as a catalyst and phosphoric acid (1.5 g) as a stabilizer.

[0096] Next, nitrogen was injected into the reactor to apply pressure to the reactor, and the pressure was increased by 2.0 kgf / cm from atmospheric pressure. 2 The temperature was increased (absolute pressure: 2,231.1 mmHg). The temperature of the reactor was then increased to 220°C over 90 minutes, maintained at 220°C for 2 hours, and then the temperature was increased again to 265°C over 2 hours. Thereafter, the esterification reaction was carried out at a temperature of 265°C while visually observing the mixture in the reactor until it became transparent. During this procedure, by-products were discharged through a column and a condenser. Upon completion of the esterification reaction, the nitrogen in the pressurized reactor was released to the outside, and the pressure in the reactor was reduced to atmospheric pressure. The mixture in the reactor was then transferred to a 7-liter reactor capable of reaction under reduced pressure.

[0097] The reactor pressure was then reduced from atmospheric pressure to 5 torr (5 mmHg absolute) over 30 minutes. Simultaneously, the reactor temperature was increased to 280°C over 1 hour, and the polycondensation reaction was carried out while maintaining the reactor pressure at 1 torr (1 mmHg absolute) or less. A high stirring speed may be set at the start of the polycondensation reaction. As the polycondensation reaction progresses, if the stirring force weakens due to an increase in the viscosity of the reactants, or if the temperature of the reactants rises above the set temperature, the stirring speed may be adjusted accordingly. The polycondensation reaction was carried out until the intrinsic viscosity (IV) of the mixture (melt) in the reactor reached 0.70 dL / g. When the intrinsic viscosity of the mixture in the reactor reached the desired level, the mixture was discharged from the reactor to form strands. The strands were solidified using a cooling liquid and then granulated to prepare polyester copolymers with an average weight of approximately 12-14 mg.

[0098] [Comparative Polymerization Example 3] A 10-liter reactor equipped with a water-cooled column and a condenser was charged with terephthalic acid (TPA, 3,005.3 g), ethylene glycol (EG, 1,088.8 g), 1,4-cyclohexanedimethanol (CHDM, 834.3 g), and diethylene glycol (DEG, 211.1 g), followed by the addition of titanium dioxide (TiO, 1.0 g) as a catalyst and phosphoric acid (1.5 g) as a stabilizer.

[0099] Next, nitrogen was injected into the reactor to apply pressure to the reactor, and the pressure was increased by 2.0 kgf / cm from atmospheric pressure. 2 The temperature was increased (absolute pressure: 2,231.1 mmHg). The temperature of the reactor was then increased to 220°C over 90 minutes and maintained at 220°C for 2 hours, and then the temperature was increased again to 255°C over 2 hours. Thereafter, the esterification reaction was carried out at a temperature of 255°C while visually observing the mixture in the reactor until it became transparent. During this procedure, by-products were discharged through a column and a condenser. Upon completion of the esterification reaction, the nitrogen in the pressurized reactor was released to the outside, and the pressure in the reactor was reduced to atmospheric pressure. The mixture in the reactor was then transferred to a 7-liter reactor capable of reaction under reduced pressure.

[0100] The reactor pressure was then reduced from atmospheric pressure to 5 torr (5 mmHg absolute) over 30 minutes. Simultaneously, the reactor temperature was increased to 285°C over 1 hour, and the polycondensation reaction was carried out while maintaining the reactor pressure at 1 torr (1 mmHg absolute) or less. A high stirring speed may be set at the start of the polycondensation reaction. As the polycondensation reaction progresses, if the stirring force weakens due to an increase in the viscosity of the reactants, or if the temperature of the reactants rises above the set temperature, the stirring speed may be adjusted accordingly. The polycondensation reaction was carried out until the intrinsic viscosity (IV) of the mixture (melt) in the reactor reached 0.70 dL / g. When the intrinsic viscosity of the mixture in the reactor reached the desired level, the mixture was discharged from the reactor to form strands. The strands were solidified using a cooling liquid and then granulated to prepare polyester copolymers with an average weight of approximately 12-14 mg.

[0101] [Comparative Polymerization Example 4] A 10-liter reactor equipped with a water-coolable column and condenser was charged with terephthalic acid (TPA, 2,791.0 g), isophthalic acid (IPA, 310.1 g), ethylene glycol (EG, 1,127.0 g), 1,4-cyclohexanedimethanol (CHDM, 852.8 g), and diethylene glycol (DEG, 300.0 g), followed by the addition of germanium dioxide (GeO, 1.0 g) as a catalyst, phosphoric acid (1.5 g) as a stabilizer, and blue toner (0.012 g) and red toner (0.004 g) as colorants.

[0102] Next, nitrogen was injected into the reactor to apply pressure to the reactor, and the pressure was increased by 2.0 kgf / cm from atmospheric pressure. 2 The temperature was increased (absolute pressure: 2,231.1 mmHg). The temperature of the reactor was then increased to 220°C over 90 minutes, maintained at 220°C for 2 hours, and then the temperature was increased again to 260°C over 2 hours. Thereafter, the esterification reaction was carried out at a temperature of 260°C while visually observing the mixture in the reactor until it became transparent. During this procedure, by-products were discharged through a column and a condenser. Upon completion of the esterification reaction, the nitrogen in the pressurized reactor was released to the outside, and the pressure in the reactor was reduced to atmospheric pressure. The mixture in the reactor was then transferred to a 7-liter reactor capable of reaction under reduced pressure.

[0103] The reactor pressure was then reduced from atmospheric pressure to 5 torr (5 mmHg absolute) over 30 minutes. Simultaneously, the reactor temperature was increased to 265°C over 1 hour, and the polycondensation reaction was carried out while maintaining the reactor pressure at 1 torr (1 mmHg absolute) or less. A high stirring speed may be set at the start of the polycondensation reaction. As the polycondensation reaction progresses, if the stirring force weakens due to an increase in the viscosity of the reactants, or if the temperature of the reactants rises above the set temperature, the stirring speed may be adjusted accordingly. The polycondensation reaction was carried out until the intrinsic viscosity (IV) of the mixture (melt) in the reactor reached 0.78 dL / g. When the intrinsic viscosity of the mixture in the reactor reached the desired level, the mixture was discharged from the reactor to form strands. The strands were solidified using a cooling liquid and then granulated to prepare polyester copolymers with an average weight of approximately 12-14 mg.

[0104] <Preparation of Polyester Resin Mixture> [Example 1] The polyester copolymer obtained in Polymerization Example 1 and recycled PET were mixed in a weight ratio of 90:10 to prepare a polyester resin mixture. Specifically, the recycled PET resin was prepared by crushing and washing waste plastic to obtain flakes, and melt-extruding the flakes for re-pelletization. The recycled PET resin was dry-mixed at room temperature with the separately pelletized polyester copolymer of Polymerization Example 1, and then dried at 50 to 150°C to prepare a polyester resin mixture.

[0105] [Examples 2 to 7] Each polyester resin mixture was prepared in the same manner as in Example 1, except that the composition was changed as shown in Table 1 below.

[0106] [Comparative Examples 1 to 4] Each polyester resin mixture was prepared in the same manner as in Example 1, except that the composition was changed as shown in Table 1 below.

[0107] [Table 1]

[0108] <Preparation of Single-Layer Polyester Film> [Preparation Examples 1 to 7 and Comparative Preparation Examples 1 to 4] The polyester resin mixtures obtained in the Preparation Examples and Comparative Preparation Examples were each extruded through a die at a temperature of 260 to 290°C, and then cooled to 20 to 50°C to prepare an unstretched sheet. The unstretched sheet was then reheated to 75 to 90°C and stretched 5 times in the transverse direction to prepare a polyester film having a thickness of 40 μm.

[0109] <Preparation of Multilayer Polyester Film> [Preparation Examples 8 to 12 and Comparative Preparation Examples 5 to 7] (1) Preparation of polyester resin mixture Each polyester resin mixture was prepared in the same manner as in Example 1, except that the composition was changed as shown in Table 2 below.

[0110] (2) Preparation of multilayer polyester film A polyester resin mixture for forming the base layer and a polyester resin mixture for forming the first and second resin layers, each having the composition shown in Table 2 below, were coextruded through a die at a temperature of 260 to 290°C and then cooled at 20 to 50°C to prepare an unstretched sheet having a three-layer structure in which the first and second resin layers were laminated on both sides of the base layer.The unstretched sheet was then reheated to 75 to 90°C and stretched five times in the transverse direction to prepare a polyester film having a thickness of 50 μm (first resin layer 5 μm, base layer 40 μm, and second resin layer 5 μm).

[0111] [Table 2]

[0112] [Test Example 1] Extrudability (roll plate out) The extrudability of polyester resin blends and polyester films was evaluated using Breyer equipment having the following specifications: Supplier: Breyer GmbH (Germany, December 2000) Main extruder: Single screw extruder with or without vent Diameter: 45mm L / D:33:1 Evaluation method: A sheet sample having a thickness of 1 mm was formed by extrusion at 260° C. One hour after the start of sheet extrusion, the plate-out phenomenon of the roll during extrusion was subjected to a sensory evaluation according to the following evaluation criteria. Evaluation criteria: No roll contamination after sheet extrusion "× (cross)"; slight roll contamination after sheet extrusion "△ (triangle)"; roll contamination after sheet extrusion "○ (circle)"

[0113] [Test Example 2] Extrusion coefficient The extrudability coefficient of the polyester resin mixture was calculated by gas chromatography (GC) and the following equation 1. Specifically, for the quantitative analysis of oligomers and short molecules by thermal decomposition of the polyester resin mixture (polyester copolymer contained in the polyester resin mixture), gas chromatography analysis was carried out under the following conditions: The gaseous substances generated under the pretreatment conditions were collected and converted into the total area / g in the graph.

[0114] In the pretreatment, polyester resin mixture (polyester copolymer contained in the polyester resin mixture) pellets were heated in an air atmosphere at 260°C for 1 hour, and the substances produced were collected in the GC headspace. The total area of the collected substances was quantified (unit area / g). A higher total area / g value means that there are more unreacted substances and oligomers in the polyester resin mixture (or polyester copolymer), indicating an increased amount of short molecules produced by thermal decomposition. On the other hand, oligomers (area / g) detected by gas chromatography (GC) analysis generally refer to substances (polymers) with a molecular weight of 1,000 g / mol or less. *Measurement conditions for gas chromatography (GC) Model: Triplus 500 (Thermo) Incubation temperature: 260℃ Incubation time: 60 minutes Loop temperature: 260℃ Loop volume: 1 mL Infusion time: 0.5 minutes Injection mode: Standard [Equation 1] Extrusion coefficient = A / 10 7 A is the quantitative analysis value (area / g) of oligomers confirmed by gas chromatography (GC) analysis of the polyester copolymer.

[0115] [Test Example 3] Outgassing The equipment used to evaluate extrudability was used to evaluate outgassing from the polyester resin mixture and polyester film. Specifically, the outgassing generated when the mixture was compressed on a roll during the sheet extrusion process was subjected to sensory evaluation (six times at 10-minute intervals) according to the following evaluation criteria: Evaluation criteria: no outgassing "◎ (double circle)"; almost no outgassing "○ (circle)"; slight outgassing "△ (triangle)"; continuous outgassing "× (cross)"

[0116] [Test Example 4] Stretchability (fisheye) Immediately after sheet extrusion, the sheet was stretched 5 times in the transverse direction (TD) at Tg+10°C of the polyester resin mixture, and the presence of fisheyes in the stretched film was visually and organoleptically evaluated according to the following evaluation criteria. Evaluation criteria: Many fisheyes present "○ (circle)"; slight fisheyes present "△ (triangle)"; almost no fisheyes present "× (cross)" The results of Test Examples 1 to 4 are shown in Tables 3 and 4 below.

[0117] [Table 3]

[0118] [Table 4]

[0119] Referring to Table 3 above, the polyester resin mixtures according to the present invention have an extrudability coefficient of 6 or less, which indicates excellent stretchability during film stretching, as well as little contamination of process equipment and little outgassing. In particular, compared with the polyester resin mixture in Comparative Example 4 containing the virgin polyester copolymer of Comparative Polymerization Example 4 in which no recycled monomers were used during polymerization, the polyester resin mixtures according to the present invention in Examples 1 to 7 had lower extrudability coefficients and equal or better outgassing and stretchability (see Preparation Examples 1 to 7 and Comparative Preparation Example 4). The above results support that the present invention can provide polyester articles with excellent physical properties and / or quality, even when recycled monomers are used.

[0120] On the other hand, referring to Table 4 above, when the polyester resin mixture according to the present invention was used to prepare a multi-layer polyester film, the multi-layer polyester film had excellent extrudability, processability, stretchability, etc.

[0121] [Explanation of symbols] 10: Polyester film 11: Base layer 12: First resin layer 13: Second resin layer

Claims

1. A polyester resin mixture containing a polyester copolymer including a repeating unit (a) derived from a recycled monomer, a repeating unit (b) derived from a dicarboxylic acid compound, and a repeating unit (c) derived from a diol compound, and polyethylene terephthalate, when extruded to a thickness of 1 mm, satisfies the following equation 1: [Equation 1] Extrudability coefficient = A / 10 ７ [In Equation 1, A is the quantitative analysis value (area / g) of oligomers as determined by gas chromatography (GC) analysis of the polyester copolymer] 1. A polyester resin mixture having an extrudability coefficient according to the method of claim 1, wherein the extrudability coefficient is 6 or less.

2. 2. The polyester resin blend of claim 1, wherein the recycled monomer is recycled bis-2-hydroxyethyl terephthalate (recycled BHET).

3. 2. The polyester resin mixture according to claim 1, wherein the diol compound comprises at least one selected from the group consisting of isosorbide, ethylene 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, cyclohexanedimethanol, and cyclohexanedimethanol derivatives.

4. 2. The polyester resin mixture according to claim 1, wherein the dicarboxylic acid compound comprises at least one selected from the group consisting of terephthalic acid, isophthalic acid, dimethyl isophthalate, phthalic acid, dimethyl terephthalate, dimethyl phthalate, phthalic anhydride, 2,6-naphthalenedicarboxylic acid, dimethyl 2,6-naphthalenedicarboxylate, diphenyldicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, 1,3-cyclohexanedicarboxylic acid, dimethyl 1,4-cyclohexanedicarboxylate, dimethyl 1,3-cyclohexanedicarboxylate, sebacic acid, succinic acid, isodecylsuccinic acid, maleic acid, maleic anhydride, fumaric acid, adipic acid, glutaric acid, and azelaic acid.

5. The polyester copolymer contains 0 to 30 mole % of repeating units (c) derived from diethylene glycol, based on the total number of moles of repeating units (c) derived from the diol compound. １ ), 0 to 45 mol % of repeating units derived from cyclohexanedimethanol (c ２ ), 0 to 25 mol % of repeating units derived from cyclohexanedimethanol derivatives (c ３ ), and 0 to 45 mol % of repeating units derived from neopentyl glycol (c ４ 2. The polyester resin blend of claim 1, comprising:

6. 2. The polyester resin blend of claim 1, wherein the polyethylene terephthalate is one or more selected from the group consisting of mechanically recycled polyethylene terephthalate (mechanically recycled PET), chemically recycled polyethylene terephthalate (chemically recycled PET), and virgin polyethylene terephthalate (virgin PET).

7. 10. The polyester resin mixture of claim 1, wherein the recycled content is 30% by weight or more, based on the total weight of the polyester resin mixture.

8. 1. A method for preparing a polyester resin mixture, comprising: The recycled monomer, the dicarboxylic acid compound, and the diol compound are fed to the reactor, and the pressure is 0 to 10.0 kgf / cm ２ and a temperature of 150 to 300°C to obtain a reaction product; subjecting the reactants to a polycondensation reaction to obtain a polyester copolymer; blending the polyester copolymer with polyethylene terephthalate; A method comprising:

9. A polyester film prepared from a polyester resin mixture containing a polyester copolymer including a repeating unit (a) derived from a recycled monomer, a repeating unit (b) derived from a dicarboxylic acid compound, and a repeating unit (c) derived from a diol compound, and polyethylene terephthalate, wherein when the mixture is extruded to a thickness of 1 mm, the polyester film satisfies the above-mentioned equation 1. [Equation 1] Extrudability coefficient = A / 10 ７ [In Equation 1, A is the quantitative analysis value (area / g) of oligomers as determined by gas chromatography (GC) analysis of the polyester copolymer] A polyester film having an extrudability coefficient according to the method of claim 1 of 6 or less.

10. The polyester film according to claim 9, which has a single-layer structure or a multi-layer structure.

11. the multilayer structure includes a base layer and at least one resin layer; the base layer comprises the polyethylene terephthalate and the polyester copolymer in a weight ratio of 1:99 to 50:50; the resin layer contains the polyethylene terephthalate and the polyester copolymer in a weight ratio of 10:90 to 99:1; The polyester film according to claim 10.

12. The polyester film according to claim 9, which is uniaxially stretched 1.5 to 6 times in the transverse direction (TD) or 1.1 to 5 times in the machine direction (MD).

13. The polyester film according to claim 9, which is biaxially stretched 1.5 to 6 times in the transverse direction (TD) and 1.1 to 5 times in the machine direction (MD).

14. 1. A method for preparing a polyester film, comprising: A step of preparing an unstretched sheet from a polyester resin mixture containing a polyester copolymer including a repeating unit (a) derived from a recycled monomer, a repeating unit (b) derived from a dicarboxylic acid compound, and a repeating unit (c) derived from a diol compound, and polyethylene terephthalate, wherein when the mixture is extruded to a thickness of 1 mm, the unstretched sheet satisfies the above-mentioned equation 1. [Equation 1] Extrudability coefficient = A / 10 ７ [In Equation 1, A is the quantitative analysis value (area / g) of oligomers as determined by gas chromatography (GC) analysis of the polyester copolymer] and stretching the unstretched sheet. A method comprising:

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