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 recovered monomers; a preparation method thereof; and a polyester film prepared therefrom, in which the polyester resin mixture has excellent extrudability (processability), and thus can provide a polyester film having excellent physical properties and / or quality.

Description

Technical Field

[0001] The present invention relates to a polyester resin mixture comprising a polyester copolymer prepared using recycled monomers, a preparation method thereof, and a polyester film prepared therefrom. Background Art

[0002] Polyester among polymers has excellent mechanical strength, heat resistance, transparency and gas barrier properties, so it is used as a material in various fields. In particular, polyester films or sheets have good transparency and excellent mechanical strength, so they are widely used in boxes, boxes, partitions, shelves, panels, packaging materials, building materials, interior and exterior materials.

[0003] As a result, the amount of plastic waste such as polyester generated worldwide each year has reached an uncontrollable level. Recently, countries around the world have formulated regulations and plans for the recycling of waste plastic resources, including waste polyester.

[0004] Methods for recycling waste polyester include a physical method for recycling waste polyester through processes such as pulverization and melting and a chemical method for recycling waste polyester through a depolymerization process for breaking 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 obtaining polyester with good physical properties due to foreign matter in the waste polyester. In particular, polyester prepared using recycled monomers obtained by depolymerization of waste polyester has poor extrudability (processability) and transparency due to side reactants (e.g., DEG esters) formed during the depolymerization process; therefore, its use is limited.

[0006] [Prior art literature]

[0007] [Patent Literature]

[0008] (Patent Document 1) Korean Patent Publication No. 2013-0041205. Summary of the invention

[0009] Technical issues

[0010] In order to solve the above conventional problems, the present inventors have conducted various studies. As a result, it was found that when a polyester copolymer is prepared using recycled monomers, the types and amounts of recycled monomers and raw monomers are optimized to obtain a polyester copolymer, which is mixed with polyethylene terephthalate to obtain a polyester resin mixture having significantly enhanced extrudability (processability).

[0011] Therefore, an object of the present invention is to provide a polyester resin mixture comprising a polyester copolymer prepared using recycled monomers and polyethylene terephthalate, the extrudability of which is controlled, and a method for preparing the same.

[0012] In addition, another object of the present invention is to provide a polyester film prepared from the polyester resin mixture and a preparation method thereof.

[0013] Solution to the problem

[0014] In order to solve the above problems, the present invention provides a polyester resin mixture, which comprises a polyester copolymer and polyethylene terephthalate, wherein the polyester copolymer 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; wherein, when the mixture is extruded to a thickness of 1 mm, the extrusion coefficient according to the following equation 1 is 6 or less.

[0015] [Equation 1]

[0016] Extrusion coefficient = A / 10 7

[0017] In Equation 1, A is a quantitative analysis value (area / g) of oligomers confirmed by gas chromatography (GC) analysis of the polyester copolymer.

[0018] In addition, 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 into a reactor, and 2 Up to 10.0kgf / cm 2 The method comprises the steps of: performing an esterification reaction at a pressure of 150° C. to 300° C. and a temperature of 150° C. to obtain a reactant; performing a polycondensation reaction on the reactant to obtain a polyester copolymer; and mixing the polyester copolymer with polyethylene terephthalate.

[0019] Furthermore, the present invention provides a polyester film prepared from the polyester resin mixture.

[0020] In addition, the present invention also provides a method for preparing a polyester film, which comprises: preparing an unstretched sheet from a polyester resin mixture; and stretching the unstretched sheet.

[0021] Advantageous Effects of the Invention

[0022] Since the extrusion coefficient of the polyester resin mixture of the present invention is controlled within a specific range, it can prevent contamination of process equipment when it is used to manufacture various products, while imparting excellent extrudability (processability), transparency, heat shrinkage (stretchability), etc. Therefore, even when a polyester copolymer prepared from recycled monomers is used, the present invention can provide a product (e.g., a polyester film) having excellent physical properties and / or quality. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1is a cross-sectional view of a polyester film according to one embodiment of the present invention. DETAILED DESCRIPTION

[0024] Best Mode for Carrying Out the Invention

[0025] The present invention will be described in detail below. The present invention is not limited to the disclosure given below, and can be modified into various forms as long as the gist of the present invention is not changed.

[0026] In this specification, the term "comprising" is intended to specify specific features, regions, steps, methods, elements and / or components. Unless otherwise expressly stated, the existence or addition of any other features, regions, steps, methods, elements and / or components is not excluded.

[0027] Unless otherwise indicated, all numbers and expressions relating to quantities of ingredients, reaction conditions, and so forth used herein are to be understood as modified by the term "about."

[0028] Polyester resin mixture

[0029] The present invention provides a polyester resin mixture whose extrudability is controlled so that a polyester article having excellent physical properties can be produced even when the content of recycled components is high. Specifically, the polyester resin mixture comprises a polyester copolymer and polyethylene terephthalate, the polyester copolymer comprising 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 the polyethylene terephthalate is described below.

[0030] Here, the term "derived" may mean that a specific part or unit derived from a specific compound is included in a product obtained by a chemical reaction of the specific compound.

[0031] In addition, the term "recovery component" may refer to a monomer obtained by decomposing, depolymerizing, reprocessing or repolymerizing waste plastics by a physical or chemical method, or a component derived from a polymer. Specifically, the recovery component may refer to at least one selected from the group consisting of recovered terephthalate (recovery-BHET), recovered ethylene glycol (recovery-EG), recovered cyclohexanedimethanol (recovery-CHDM), recovered terephthalic acid (recovery-TPA), recovered isophthalic acid (recovery-IPA), recovered dimethyl terephthalate (recovery-DMT), recovered dimethyl isophthalate (recovery-DMI), mechanically recovered polyethylene terephthalate (mechanically recovered-PET) and chemically recovered polyethylene terephthalate (chemically recovered-PET).

[0032] Polyester copolymer

[0033] The polyester copolymer according to the present invention comprises repeating units (a) derived from recycled monomers, repeating units (b) derived from dicarboxylic acid compounds, and repeating units (c) derived from diol compounds. That is, the polyester copolymer according to the present invention is obtained by esterification and / or polycondensation of recycled monomers, dicarboxylic acid compounds, and diol compounds.

[0034] 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, it can be recycled ethylene terephthalate (recycled-BHET, r-BHET). More specifically, r-BHET can be obtained by depolymerizing waste polyester (e.g., waste PET, waste PETG) by chemical methods such as glycolysis, hydrolysis, methanolysis, and aminolysis. Since the r-BHET obtained by the depolymerization method has a high purity, the polyester resin mixture containing the polyester copolymer prepared using it can have excellent extrudability (processability), transparency, stretchability, etc.

[0035] The content of the repeating unit (a) may be 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 wt % to 95 wt %, 3 wt % to 80 wt %, 5 wt % to 75 wt %, or 7 wt % to 70 wt %) based on the total weight of the polyester copolymer. Specifically, the polyester copolymer may contain 7 wt % or more, 10 wt % or more, 30 wt % or more, or 50 wt % or more (e.g., 1 wt % to 95 wt %, 3 wt % to 80 wt %, 5 wt % to 75 wt %, 7 wt % to 70 wt %) of the repeating unit (a) derived from r-BHET based on the total weight of the polyester copolymer. r-BHET When the content of the repeating unit (a) is within the above content range, a polyester resin mixture having excellent extrudability (processability), stretchability, etc. can be obtained even when a recycled monomer is used.

[0036] The dicarboxylic acid compound forming repeating unit (b) is not particularly limited. Specifically, the dicarboxylic acid compound can be selected from at least one compound in the group consisting of terephthalic acid, isophthalic acid, dimethyl isophthalate, phthalic acid, dimethyl terephthalate, dimethyl phthalate, phthalic anhydride, 2,6-naphthalene dicarboxylic acid, 2,6-naphthalene dicarboxylic acid dimethyl ester, biphenyl dicarboxylic acid, 1,4-cyclohexane dicarboxylic acid, 1,3-cyclohexane dicarboxylic acid, 1,4-cyclohexane dicarboxylic acid dimethyl ester, 1,3-cyclohexane dicarboxylic acid dimethyl ester, sebacic acid, succinic acid, isodecyl succinic acid, maleic acid, maleic anhydride, fumaric acid, adipic acid, glutaric acid and azelaic acid. More specifically, the dicarboxylic acid compound can be selected from at least one compound in the group consisting of terephthalic acid, isophthalic acid, dimethyl isophthalate and dimethyl terephthalate.

[0037] In addition, the dicarboxylic acid compound may include a recycled monomer derived from waste plastics. Specifically, the dicarboxylic acid compound may include at least one compound 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).

[0038] The content of repeating unit (b) can be 0 wt % to 50 wt %, greater than 0 wt % to 25 wt %, 1 wt % to 15 wt %, 1 wt % to 10 wt %, or 1 wt % to 5 wt %, based on the total weight of the polyester copolymer.

[0039] The diol compound forming the repeating unit (c) is not particularly limited. Specifically, it can be selected from isosorbide, ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 2-methyl-1,3-propylene glycol, 2-methylene-1,3-propylene glycol, 2-ethyl-1,3-propylene glycol, 2-isopropyl-1,3-propylene glycol, 2,2-dimethyl-1,3-propylene glycol, 1,4-butylene glycol, 2,3-butylene glycol, 3-methyl-1,5-pentanediol, 3-methyl-2,4-pentanediol, 1 At least one compound selected from the group consisting of ethylene glycol, diethylene glycol, 1,4-cyclohexanediol, cyclohexanedimethanol (e.g., 1,2-cyclohexanedimethanol, 1,3-cyclohexanedimethanol, 1,4-cyclohexanedimethanol, etc.) and cyclohexanedimethanol derivatives (e.g., 4-(hydroxymethyl)cyclohexylmethyl-4-(hydroxymethyl)cyclohexanecarboxylate, 4-(4-(hydroxymethyl)cyclohexylmethoxymethyl)cyclohexylmethanol, etc.). 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)cyclohexanecarboxylate, and 4-(4-(hydroxymethyl)cyclohexylmethoxymethyl)cyclohexylmethanol.

[0040] In addition, the diol compound may include recycled monomers derived from waste plastics. Specifically, the diol compound may include at least one compound selected from the group consisting of recycled ethylene glycol (recycled-EG) and recycled cyclohexanedimethanol (recycled-CHDM).

[0041] The repeating unit (c) may be included 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.

[0042] Here, in consideration of the extrudability of the polyester resin mixture, the repeating unit (c) may include a 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 moles of the repeating unit (c). In addition, the repeating unit (c) may include a 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 moles of the repeating unit (c). In addition, based on the total moles of the repeating units (c), the repeating units (c) may include 0 to 25 mol%, greater than 0 to 20 mol%, 0.5 to 20 mol%, 1 to 10 mol%, or 3 to 5 mol% of the repeating units (c3) derived from the cyclohexanedimethanol derivative. In addition, based on the total moles of the repeating units (c), the repeating units (c) may include 0 to 45 mol%, greater than 0 to 30 mol%, 1 to 25 mol%, or 5 to 20 mol% of the repeating units (c4) derived from neopentyl glycol.

[0043] When the polyester copolymer according to the present invention is dissolved in o-chlorophenol at a concentration of 1.2 g / dl at 150° C. for 15 minutes and then measured at 35° C., the polyester copolymer may have an intrinsic viscosity of about 0.45 dl / g to 1.2 dl / g, about 0.55 dl / g to 1.0 dl / g, about 0.60 dl / g to 1.0 dl / g, or about 0.60 dl / g to 0.9 dl / g. When the intrinsic viscosity is within the above range, the polyester copolymer has a desired (appropriate) molecular weight to have excellent mechanical properties, and it can be uniformly mixed with polyethylene terephthalate under mild pressure and temperature conditions to facilitate molding of the polyester resin mixture.

[0044] Polyethylene terephthalate

[0045] The polyethylene terephthalate according to the present invention can be obtained by esterification and / or polycondensation of well-known glycol compounds and dicarboxylic acid compounds. Both glycol compounds and dicarboxylic acid compounds can be original monomers or recycled monomers. In addition, the polyethylene terephthalate can be obtained by crushing and melting the waste polyethylene terephthalate collected after use.

[0046] 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).

[0047] In addition, 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 (eg, 130°C to 170°C).

[0048] Considering extrudability, stretchability, etc., the polyester resin mixture according to the present invention may have a weight ratio of the polyester copolymer to the 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 20:80.

[0049] When the polyester resin mixture is extruded to a thickness of 1 mm, the extrusion coefficient according to the following Equation 1 may be 6 or less.

[0050] [Equation 1]

[0051] Extrusion coefficient = A / 10 7

[0052] In Equation 1, A is a quantitative analysis value (area / g) of oligomers confirmed by gas chromatography (GC) analysis of the polyester copolymer.

[0053] 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 g / mol to 1,000 g / mol).

[0054] When the extrusion coefficient according to Equation 1 is controlled to be 6 or less in the polyester resin mixture according to the present invention, the fouling phenomenon of the roller and the generation of degassing during the extrusion process can be minimized. Therefore, when a polyester product is manufactured using the polyester resin mixture according to the present invention, a polyester product (e.g., a polyester film) having excellent physical properties (e.g., heat shrinkage) can be obtained while preventing contamination of processing equipment.

[0055] Specifically, the lower the extrusion coefficient, the better the extrudability (processability). The polyester resin mixture according to the present invention can have an extrusion 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 can have an extrusion 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.

[0056] Based on the gross weight of the polyester resin mixture, the polyester resin mixture according to the present invention may include 30% by weight or more of the recovered components. Specifically, the polyester resin mixture may include 30% by weight to 90% by weight, 30% by weight to 88% by weight, 33% by weight to 85% by weight or 35% by weight to 80% by weight of the recovered components as defined above. Although the polyester resin mixture according to the present invention includes a relatively high content of recovered components, it includes a polyester copolymer prepared by optimizing the type and amount of recovered monomers and raw material monomers. Therefore, it ensures the desired level of extrudability, stretchability, etc., and it can be used to manufacture polyester products with excellent physical properties and / or quality.

[0057] Preparation method of polyester resin mixture

[0058] The present invention provides a method for preparing the polyester resin mixture. Specifically, the method for preparing the polyester resin mixture of the present invention comprises feeding the recycled monomer, the dicarboxylic acid compound and the diol compound into a reactor, and 2 Up to 10.0kgf / cm 2 and 150° C. to 300° C. to obtain a reactant; and subjecting the reactant to a polycondensation reaction to obtain a polyester copolymer; and mixing the polyester copolymer with polyethylene terephthalate.

[0059] The step of obtaining the reactant can be carried out by feeding each monomer into a reactor and conducting an esterification reaction (ester exchange reaction) under specific reaction conditions. Details about the recycled monomers, dicarboxylic acid compounds and diol compounds fed into the reactor are the same as those of the polyester resin mixture.

[0060] Based on the total weight of the composition (slurry) for preparing the polyester copolymer, the amount of the recycled monomer fed to the reactor may be 1 wt% to 95 wt%, 3 wt% to 80 wt%, 5 wt% to 75 wt%, or 7 to 70 wt%. In addition, based on the total weight of the composition (slurry) for preparing the polyester copolymer, the amount of the dicarboxylic acid compound fed to the reactor may be 0 wt% to 50 wt%, greater than 0 wt% to 25 wt%, 0 wt% to 15 wt%, 1 wt% to 10 wt%, or 1 wt% to 5 wt%. In addition, based on the total weight of the composition (slurry) for preparing the polyester copolymer, the amount of the diol compound fed to the reactor may be 0 wt% to 50 wt%, 1 wt% to 35 wt%, 3 wt% to 25 wt%, 4 wt% to 20 wt%, or 4 to 15 wt%.

[0061] Meanwhile, additives such as catalysts, stabilizers, colorants, crystallizing agents, antioxidants, branching agents, etc. may be further added to the reactor to promote the esterification reaction and / or polycondensation reaction and enhance the physical properties of the resulting polyester copolymer.

[0062] The catalyst may be methides of sodium and magnesium; 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.

[0063] As the stabilizer, phosphorus-based compounds such as phosphoric acid, trimethyl phosphate, and triethyl phosphate can be used.

[0064] As the colorant, organic compounds such as cobalt-based compounds, anthraquinone-based compounds, cyclic ketone-based compounds, azo-based compounds, and methine compounds (eg, cobalt acetate, cobalt propionate, Polysynthren Blue RLS toner from Clarient, and Solvaperm Red BB toner from Clariant) can be used.

[0065] As the crystallization agent, a crystal nucleus agent, an ultraviolet absorber, a polyolefin resin, a polyamide resin, and the like can be used.

[0066] As the antioxidant, hindered phenol compounds, phosphite compounds, thioether compounds and the like can be used.

[0067] As the branching agent, trimellitic anhydride, trimethylolpropane, trimellitic acid, and the like can be used.

[0068] The esterification reaction may be carried out at a temperature of about 200° C. to 300° C., about 230° C. to 280° C., about 230° C. to 265° C., or about 245° C. to 255° C., and at 0 kgf / cm 2 Up to 10.0kgf / cm 2(0mmHg to 7,355.6mmHg), greater than 0kgf / cm 2 Up to 5.0kgf / cm 2 (greater than 0mmHg to 3,677.8mmHg), 0.1kgf / cm 2 Up to 3.0kgf / cm 2 (73.6mmHg to 2,206.7mmHg) or 1.0kgf / cm 2 Up to 3.0kgf / cm 2 The transesterification reaction may be carried out at a pressure of 150 to 270°C or 180 to 260°C and at 0 kgf / cm 2 Up to 5kgf / cm 2 (0mmHg to 3,677.8mmHg), greater than 0kgf / cm 2 Up to 5.0kgf / cm 2 (greater than 0mmHg to 3,677.8mmHg) or 0.1kgf / cm 2 Up to 3.0kgf / cm 2 (73.6mmHg to 2,206.7mmHg). In kgf / cm 2 The pressure in mmHg is the gauge pressure, and the pressure in mmHg is the absolute pressure.

[0069] The esterification reaction (transesterification reaction) can be carried out in a batch or continuous manner. The recovered monomer, the dicarboxylic acid compound and the diol compound can be added to the reactor individually, or can be added in the form of a mixed slurry.

[0070] The step of obtaining the polyester copolymer may be performed by polycondensing the reactants obtained by the esterification reaction. Specifically, the polycondensation may be performed at a temperature of 150° C. to 300° C. and a reduced pressure of 600 mmHg to 0.01 mmHg for 1 to 24 hours.

[0071] The mixing step can be performed by mixing the polyester copolymer obtained by the polycondensation reaction with the polyethylene terephthalate prepared in advance. The mixing can be performed by a conventionally known method.

[0072] Polyester film

[0073] The present invention provides a polyester film prepared from the polyester resin mixture. Specifically, the polyester film according to the present invention comprises a polyester copolymer and polyethylene terephthalate, wherein the polyester copolymer 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; wherein, when the mixture is extruded to a thickness of 1 mm, the extrusion coefficient according to the above equation 1 is 6 or less. Since the polyester film according to the present invention is prepared from the above polyester resin mixture, it can exhibit high transparency and a desired heat shrinkage (target heat shrinkage) even if the content of the recycled component is high.

[0074] Specifically, the polyester film according to the present invention may have 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.

[0075] In addition, the polyester film according to the present invention has a low shrinkage initiation temperature of 65° C. or less; therefore, when used to produce a heat shrink label for a PET container, it can be molded with excellent quality without causing turbidity or deformation of the PET container. Specifically, the polyester film according to the present invention has a maximum shrinkage rate 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%) at 95° C.; therefore, it can be effectively used as a heat shrink film.

[0076] The polyester film according to the present invention may have a single-layer structure or a multi-layer structure. Figure 1 a), 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 polyester resin mixture. Figure 1 b) The polyester film (10) according to the present invention may have a multilayer 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 stacked on the base layer (11) is not limited to Figure 1 b), and at least one resin layer can be laminated on the upper and lower parts of the base layer (11) in various structures.

[0077] When the polyester film according to the present invention has a multi-layer structure, each layer is prepared from the above polyester resin mixture. Here, the content ratio of the polyester copolymer and the polyethylene terephthalate contained in each layer may be adjusted.

[0078] Specifically, when the base layer (11) is formed from the polyester resin mixture containing polyethylene terephthalate and a polyester copolymer, it may contain a polyester resin mixture containing polyethylene terephthalate and a polyester copolymer in a weight ratio of 1:99 to 50:50. Therefore, the base layer (11) may contain polyethylene terephthalate and a 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.

[0079] In addition, when at least one resin layer (12, 13) is formed from the polyester resin mixture containing polyethylene terephthalate and a polyester copolymer, it may contain a polyester resin mixture containing polyethylene terephthalate and a polyester copolymer in a weight ratio of 10:90 to 99:1. Therefore, 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.

[0080] Since the base layer (11) and at least one resin layer (12, 13) each contain polyethylene terephthalate and a polyester copolymer in the above weight ratio, a polyester film having excellent physical properties such as transparency and heat shrinkage can be obtained even if the content of recycled components is high.

[0081] 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% by weight 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% by weight to 35% by weight), based on the total weight of the polyester film.

[0082] Meanwhile, the polyester film according to the present invention may be a uniaxial or biaxially stretched film. As a result, it may have excellent transparency, heat shrinkage, thickness uniformity, and the like. 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 longitudinal 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 biaxially stretched 1.1 to 5 times, 1.2 to 4.9 times, or 1.5 to 4.5 times in the longitudinal direction (MD).

[0083] Method for preparing polyester film

[0084] The present invention provides a method for preparing the above-mentioned polyester film. Specifically, the method for preparing a polyester film according to the present invention comprises preparing an unstretched sheet from a polyester resin mixture, and stretching the unstretched sheet; the polyester resin mixture comprises a polyester copolymer and polyethylene terephthalate, the polyester copolymer 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; wherein, when the mixture is extruded to a thickness of 1 mm, the extrusion coefficient according to the above equation 1 is 6 or less.

[0085] The step of preparing the unstretched sheet can be performed by extruding the above-mentioned polyester resin mixture. Here, when the polyester film has a multilayer structure, a polyester resin mixture for forming each layer is prepared and coextruded to prepare the unstretched sheet. The extrusion of the polyester resin mixture can be performed at a temperature range of about 230° C. to 310° C., about 240° C. to 300° C., or about 250° C. to 290° C.

[0086] The step of stretching the unstretched sheet can be performed by uniaxial stretching or biaxial stretching. Uniaxial stretching refers to stretching the unstretched sheet in the longitudinal direction (MD) or transverse direction (TD) of the unstretched sheet. Biaxial stretching can be performed by stretching the unstretched sheet in the longitudinal direction (MD) and transverse direction (TD) simultaneously or sequentially.

[0087] The stretching ratio of the unstretched sheet in the machine direction (MD) may be 1.1 to 5 times, 1.2 to 4.9 times, or 1.5 to 4.5 times. In addition, the stretching ratio of the unstretched sheet in the machine direction (TD) may be 1.5 to 6 times, 1.6 to 5.8 times, or 1.8 to 5.5 times. When the stretching ratios in the machine direction (MD) and the transverse direction (TD) are each within the above range, a polyester film having a uniform thickness and a desired shrinkage rate can be obtained.

[0088] If necessary, the film obtained by stretching may be further subjected to well-known steps of heat fixing, relaxation and cooling.

[0089] Invention Mode

[0090] The present invention will be described in more detail below with reference to embodiments. However, these embodiments are provided for illustrative purposes only, and the present invention is not limited thereto.

[0091] <Preparation of polyester copolymer>

[0092] [Polymerization Example 1]

[0093] A 10-liter reactor equipped with a column and a condenser that can be cooled with water was charged with recovered ethylene 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 (TiO2, 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.

[0094] Then, nitrogen was injected into the reactor to pressurize the reactor to 2.0 kgf / cm above the normal pressure. 2 (Absolute pressure: 2,231.1 mmHg). Then, the temperature of the reactor was raised to 220° C. within 90 minutes, and maintained at 220° C. for 2 hours, and was again raised to 260° C. within 2 hours. Then, the esterification reaction was carried out at a temperature of 260° C. while visually observing the mixture in the reactor until the mixture became transparent. During this process, by-products were discharged through the column and the condenser. After the esterification reaction was completed, the nitrogen in the pressurized reactor was released to the outside, the pressure in the reactor was reduced to normal pressure, and then the mixture in the reactor was transferred to a 7-liter reactor capable of reacting under vacuum.

[0095] Then, the pressure of the reactor is reduced from normal pressure to 5 Torr (absolute pressure: 5 mmHg) within 30 minutes. At the same time, the temperature of the reactor is raised to 265°C within 1 hour, and the polycondensation reaction is carried out while the pressure of the reactor is maintained at 1 Torr (absolute pressure: 1 mmHg) or lower. At the beginning of the polycondensation reaction, the stirring speed can be set higher. As the polycondensation reaction proceeds, when the stirring power weakens due to the increase in the viscosity of the reactants or the temperature of the reactants rises to above the set temperature, the stirring speed can be appropriately adjusted accordingly. The polycondensation reaction is carried out until the intrinsic viscosity (IV) of the mixture (melt) in the reactor reaches 0.70 dl / g. When the intrinsic viscosity of the mixture in the reactor reaches the desired level, the mixture is then discharged to the outside of the reactor to form a strand, solidified with a coolant, and then granulated to an average weight of about 12 to 14 mg to prepare a polyester copolymer.

[0096] [Polymerization Example 2]

[0097] A 10-liter reactor equipped with a column and a condenser that can be cooled with water was charged with recovered ethylene 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 (TiO2, 1.0 g) as a catalyst, phosphoric acid (1.5 g) as a stabilizer and cobalt acetate (0.7 g) as a colorant.

[0098] Then, nitrogen was injected into the reactor to pressurize the reactor to 1.0 kgf / cm above the normal pressure. 2 (Absolute pressure: 1,495.6 mmHg). Then, the temperature of the reactor was raised to 220° C. within 90 minutes, and maintained at 220° C. for 2 hours, and was again raised to 255° C. within 2 hours. Then, the esterification reaction was carried out at a temperature of 255° C. while visually observing the mixture in the reactor until the mixture became transparent. During this process, by-products were discharged through the column and the condenser. After the esterification reaction was completed, the nitrogen in the pressurized reactor was released to the outside, the pressure in the reactor was reduced to normal pressure, and then the mixture in the reactor was transferred to a 7-liter reactor capable of reacting under vacuum.

[0099] Then, the pressure of the reactor is reduced from normal pressure to 5 Torr (absolute pressure: 5 mmHg) within 30 minutes. At the same time, the temperature of the reactor is raised to 285°C within 1 hour, and the polycondensation reaction is carried out while the pressure of the reactor is maintained at 1 Torr (absolute pressure: 1 mmHg) or lower. At the beginning of the polycondensation reaction, the stirring speed can be set higher. As the polycondensation reaction proceeds, when the stirring power weakens due to the increase in the viscosity of the reactants or the temperature of the reactants rises to above the set temperature, the stirring speed can be appropriately adjusted accordingly. The polycondensation reaction is carried out until the intrinsic viscosity (IV) of the mixture (melt) in the reactor reaches 0.75 dl / g. When the intrinsic viscosity of the mixture in the reactor reaches the desired level, the mixture is then discharged to the outside of the reactor to form a strand, solidified with a coolant, and then granulated to an average weight of about 12 to 14 mg to prepare a polyester copolymer.

[0100] [Polymerization Example 3]

[0101] A 10-liter reactor equipped with a column and a condenser that can be cooled with water was charged with recovered ethylene 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 (TiO2, 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.

[0102] Then, nitrogen was injected into the reactor to pressurize the reactor to 2.0 kgf / cm above the normal pressure. 2 (Absolute pressure: 2,231.1 mmHg). Then, the temperature of the reactor was raised to 220° C. within 90 minutes, and maintained at 220° C. for 2 hours, and was again raised to 255° C. within 2 hours. Then, the esterification reaction was carried out at a temperature of 255° C. while visually observing the mixture in the reactor until the mixture became transparent. During this process, by-products were discharged through the column and the condenser. After the esterification reaction was completed, the nitrogen in the pressurized reactor was released to the outside, the pressure in the reactor was reduced to normal pressure, and then the mixture in the reactor was transferred to a 7-liter reactor capable of reacting under vacuum.

[0103] Then, the pressure of the reactor is reduced from normal pressure to 5 Torr (absolute pressure: 5 mmHg) within 30 minutes. At the same time, the temperature of the reactor is raised to 285°C within 1 hour, and the polycondensation reaction is carried out while the pressure of the reactor is maintained at 1 Torr (absolute pressure: 1 mmHg) or lower. At the beginning of the polycondensation reaction, the stirring speed can be set higher. As the polycondensation reaction proceeds, when the stirring power weakens due to the increase in the viscosity of the reactants or the temperature of the reactants rises to above the set temperature, the stirring speed can be appropriately adjusted accordingly. The polycondensation reaction is carried out until the intrinsic viscosity (IV) of the mixture (melt) in the reactor reaches 0.70 dl / g. When the intrinsic viscosity of the mixture in the reactor reaches the desired level, the mixture is then discharged to the outside of the reactor to form a strand, solidified with a coolant, and then granulated to an average weight of about 12 to 14 mg to prepare a polyester copolymer.

[0104] [Polymerization Example 4]

[0105] A 10-liter reactor equipped with a column and a condenser that can be cooled with water was charged with recovered ethylene 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 (containing 4-(hydroxymethyl)cyclohexylmethyl-4-(hydroxymethyl)cyclohexanecarboxylate and 4-(4-(hydroxymethyl)cyclohexylmethoxymethyl)cyclohexylmethanol in a molar ratio of 1:3, 345.5 g), followed by the addition of germanium dioxide (GeO2, 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.

[0106] Then, nitrogen was injected into the reactor to pressurize the reactor to 0.5 kgf / cm above the normal pressure. 2 (Absolute pressure: 1,127.8 mmHg). Then, the temperature of the reactor was raised to 220° C. within 90 minutes, and maintained at 220° C. for 2 hours, and was again raised to 260° C. within 2 hours. Then, the esterification reaction was carried out at a temperature of 260° C. while visually observing the mixture in the reactor until the mixture became transparent. During this process, by-products were discharged through the column and the condenser. After the esterification reaction was completed, the nitrogen in the pressurized reactor was released to the outside, the pressure in the reactor was reduced to normal pressure, and then the mixture in the reactor was transferred to a 7-liter reactor capable of reacting under vacuum.

[0107] Then, the pressure of the reactor is reduced from normal pressure to 5 Torr (absolute pressure: 5 mmHg) within 30 minutes. At the same time, the temperature of the reactor is raised to 275°C within 1 hour, and the polycondensation reaction is carried out while the pressure of the reactor is maintained at 1 Torr (absolute pressure: 1 mmHg) or lower. At the beginning of the polycondensation reaction, the stirring speed can be set higher. As the polycondensation reaction proceeds, when the stirring power weakens due to the increase in the viscosity of the reactants or the temperature of the reactants rises to above the set temperature, the stirring speed can be appropriately adjusted accordingly. The polycondensation reaction is carried out until the intrinsic viscosity (IV) of the mixture (melt) in the reactor reaches 0.83 dl / g. When the intrinsic viscosity of the mixture in the reactor reaches the desired level, the mixture is then discharged to the outside of the reactor to form a strand, solidified with a coolant, and then granulated to an average weight of about 12 to 14 mg to prepare a polyester copolymer.

[0108] [Polymerization Example 5]

[0109] A 10-liter reactor equipped with a column and a condenser that can be cooled with water was charged with recovered ethylene terephthalate (r-BHET, 3,222.7 g), terephthalic acid (TPA, 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 manganese (II) acetate tetrahydrate (1.5 g) and antimony trioxide (Sb2O3, 1.8 g) as a catalyst, phosphoric acid (1.5 g) as a stabilizer and cobalt acetate (0.7 g) as a colorant.

[0110] Then, nitrogen was injected into the reactor to pressurize the reactor to 0.1 kgf / cm above the normal pressure. 2 (Absolute pressure: 833.6 mmHg). Then, the temperature of the reactor was raised to 220° C. within 90 minutes, and maintained at 220° C. for 2 hours, and was again raised to 240° C. within 2 hours. Then, the esterification reaction was carried out at a temperature of 240° C. while visually observing the mixture in the reactor until the mixture became transparent. In the process, by-products were discharged through the column and the condenser. After the esterification reaction was completed, the nitrogen in the pressurized reactor was released to the outside, the pressure in the reactor was reduced to normal pressure, and then the mixture in the reactor was transferred to a 7-liter reactor capable of reacting under vacuum.

[0111] Then, the pressure of the reactor is reduced from normal pressure to 5 Torr (absolute pressure: 5 mmHg) within 30 minutes. At the same time, the temperature of the reactor is raised to 265°C within 1 hour, and the polycondensation reaction is carried out while the pressure of the reactor is maintained at 1 Torr (absolute pressure: 1 mmHg) or lower. At the beginning of the polycondensation reaction, the stirring speed can be set higher. As the polycondensation reaction proceeds, when the stirring power weakens due to the increase in the viscosity of the reactants or the temperature of the reactants rises to above the set temperature, the stirring speed can be appropriately adjusted accordingly. The polycondensation reaction is carried out until the intrinsic viscosity (IV) of the mixture (melt) in the reactor reaches 0.75 dl / g. When the intrinsic viscosity of the mixture in the reactor reaches the desired level, the mixture is then discharged to the outside of the reactor to form a strand, solidified with a coolant, and then granulated to an average weight of about 12 to 14 mg to prepare a polyester copolymer.

[0112] [Polymerization Example 6]

[0113] A 10-liter reactor equipped with a column and a condenser that can be cooled with water was charged with recovered ethylene 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 (containing 4-(hydroxymethyl)cyclohexylmethyl-4-(hydroxymethyl)cyclohexanecarboxylate and 4-(4-(hydroxymethyl)cyclohexylmethoxymethyl)cyclohexylmethanol in a molar ratio of 1:3, 350.5 g), and then germanium dioxide (GeO2, 1.0 g) as a catalyst, phosphoric acid (1.5 g) as a stabilizer, and a blue toner (0.012 g) and a red toner (0.004 g) as colorants were added thereto.

[0114] Then, nitrogen was injected into the reactor to pressurize the reactor 1.0 kgf / cm above normal pressure. 2 (Absolute pressure: 1,495.6 mmHg). Then, the temperature of the reactor was raised to 220° C. within 90 minutes, and maintained at 220° C. for 2 hours, and was again raised to 255° C. within 2 hours. Then, the esterification reaction was carried out at a temperature of 255° C. while visually observing the mixture in the reactor until the mixture became transparent. During this process, by-products were discharged through the column and the condenser. After the esterification reaction was completed, the nitrogen in the pressurized reactor was released to the outside, the pressure in the reactor was reduced to normal pressure, and then the mixture in the reactor was transferred to a 7-liter reactor capable of reacting under vacuum.

[0115] Then, the pressure of the reactor is reduced from normal pressure to 5 Torr (absolute pressure: 5 mmHg) within 30 minutes. At the same time, the temperature of the reactor is raised to 285°C within 1 hour, and the polycondensation reaction is carried out while the pressure of the reactor is maintained at 1 Torr (absolute pressure: 1 mmHg) or lower. At the beginning of the polycondensation reaction, the stirring speed can be set higher. As the polycondensation reaction proceeds, when the stirring power weakens due to the increase in the viscosity of the reactants or the temperature of the reactants rises to above the set temperature, the stirring speed can be appropriately adjusted accordingly. The polycondensation reaction is carried out until the intrinsic viscosity (IV) of the mixture (melt) in the reactor reaches 0.70 dl / g. When the intrinsic viscosity of the mixture in the reactor reaches the desired level, the mixture is then discharged to the outside of the reactor to form a strand, solidified with a coolant, and then granulated to an average weight of about 12 to 14 mg to prepare a polyester copolymer.

[0116] [Polymerization Example 7]

[0117] A 10-liter reactor equipped with a column and a condenser that can be cooled with water was charged with recovered ethylene 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 (GeO2, 1.0 g) and titanium dioxide (TiO2, 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.

[0118] Then, nitrogen was injected into the reactor to pressurize the reactor to 0.5 kgf / cm above the normal pressure. 2 (Absolute pressure: 1,127.8 mmHg). Then, the temperature of the reactor was raised to 220° C. within 90 minutes, and maintained at 220° C. for 2 hours, and was again raised to 260° C. within 2 hours. Then, the esterification reaction was carried out at a temperature of 260° C. while visually observing the mixture in the reactor until the mixture became transparent. During this process, by-products were discharged through the column and the condenser. After the esterification reaction was completed, the nitrogen in the pressurized reactor was released to the outside, the pressure in the reactor was reduced to normal pressure, and then the mixture in the reactor was transferred to a 7-liter reactor capable of reacting under vacuum.

[0119] Then, the pressure of the reactor is reduced from normal pressure to 5 Torr (absolute pressure: 5 mmHg) within 30 minutes. At the same time, the temperature of the reactor is raised to 275°C within 1 hour, and the polycondensation reaction is carried out while the pressure of the reactor is maintained at 1 Torr (absolute pressure: 1 mmHg) or less. At the beginning of the polycondensation reaction, the stirring speed can be set higher. As the polycondensation reaction proceeds, when the stirring power weakens due to the increase in the viscosity of the reactants or the temperature of the reactants rises to above the set temperature, the stirring speed can be appropriately adjusted accordingly. The polycondensation reaction is carried out until the intrinsic viscosity (IV) of the mixture (melt) in the reactor reaches 0.79 dl / g. When the intrinsic viscosity of the mixture in the reactor reaches the desired level, the mixture is then discharged to the outside of the reactor to form a strand, solidified with a coolant, and then granulated to an average weight of about 12 to 14 mg to prepare a polyester copolymer.

[0120] [Comparative Polymerization Example 1]

[0121] A 10-liter reactor equipped with a column and a condenser that can be cooled with water 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 (GeO2, 1.0) as a catalyst and phosphoric acid (1.5 g) as a stabilizer.

[0122] Then, nitrogen was injected into the reactor to pressurize the reactor 1.0 kgf / cm above normal pressure. 2 (Absolute pressure: 1,495.6 mmHg). Then, the temperature of the reactor was raised to 220°C within 90 minutes, and maintained at 220°C for 2 hours, and was again raised to 265°C within 2 hours. Then, the esterification reaction was carried out at a temperature of 265°C while visually observing the mixture in the reactor until the mixture became transparent. During this process, by-products were discharged through the column and the condenser. After the esterification reaction was completed, the nitrogen in the pressurized reactor was released to the outside, the pressure in the reactor was reduced to normal pressure, and then the mixture in the reactor was transferred to a 7-liter reactor capable of reacting under vacuum.

[0123] Then, the pressure of the reactor is reduced from normal pressure to 5 Torr (absolute pressure: 5 mmHg) within 30 minutes. At the same time, the temperature of the reactor is raised to 275°C within 1 hour, and the polycondensation reaction is carried out while the pressure of the reactor is maintained at 1 Torr (absolute pressure: 1 mmHg) or less. At the beginning of the polycondensation reaction, the stirring speed can be set higher. As the polycondensation reaction proceeds, when the stirring power weakens due to the increase in the viscosity of the reactants or the temperature of the reactants rises to above the set temperature, the stirring speed can be appropriately adjusted accordingly. The polycondensation reaction is carried out until the intrinsic viscosity (IV) of the mixture (melt) in the reactor reaches 0.60 dl / g. When the intrinsic viscosity of the mixture in the reactor reaches the desired level, the mixture is then discharged to the outside of the reactor to form a strand, solidified with a coolant, and then granulated to an average weight of about 12 to 14 mg to prepare a polyester copolymer.

[0124] [Comparative Polymerization Example 2]

[0125] A 10-liter reactor equipped with a column and a condenser that can be cooled with water 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 (GeO2, 1.0) as a catalyst and phosphoric acid (1.5 g) as a stabilizer.

[0126] Then, nitrogen was injected into the reactor to pressurize the reactor 2.0 kgf / cm above normal pressure. 2 (Absolute pressure: 2,231.1 mmHg). Then, the temperature of the reactor was raised to 220°C within 90 minutes, and maintained at 220°C for 2 hours, and was again raised to 265°C within 2 hours. Then, the esterification reaction was carried out at a temperature of 265°C while visually observing the mixture in the reactor until the mixture became transparent. During this process, by-products were discharged through the column and the condenser. After the esterification reaction was completed, the nitrogen in the pressurized reactor was released to the outside, the pressure in the reactor was reduced to normal pressure, and then the mixture in the reactor was transferred to a 7-liter reactor capable of reacting under vacuum.

[0127] Then, the pressure of the reactor is reduced from normal pressure to 5 Torr (absolute pressure: 5 mmHg) within 30 minutes. At the same time, the temperature of the reactor is raised to 280° C. within 1 hour, and the polycondensation reaction is carried out while the pressure of the reactor is maintained at 1 Torr (absolute pressure: 1 mmHg) or less. At the beginning of the polycondensation reaction, the stirring speed can be set higher. As the polycondensation reaction proceeds, when the stirring power weakens due to the increase in the viscosity of the reactants or the temperature of the reactants rises to above the set temperature, the stirring speed can be appropriately adjusted accordingly. The polycondensation reaction is carried out until the intrinsic viscosity (IV) of the mixture (melt) in the reactor reaches 0.70 dl / g. When the intrinsic viscosity of the mixture in the reactor reaches the desired level, the mixture is then discharged to the outside of the reactor to form a strand, solidified with a coolant, and then granulated to an average weight of about 12 to 14 mg to prepare a polyester copolymer.

[0128] [Comparative Polymerization Example 3]

[0129] A 10-liter reactor equipped with a column and a condenser that can be cooled with water 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 (TiO2, 1.0 g) as a catalyst and phosphoric acid (1.5 g) as a stabilizer.

[0130] Then, nitrogen was injected into the reactor to pressurize the reactor 2.0 kgf / cm above normal pressure. 2 (Absolute pressure: 2,231.1 mmHg). Then, the temperature of the reactor was raised to 220°C within 90 minutes, and maintained at 220°C for 2 hours, and was again raised to 255°C within 2 hours. Then, the esterification reaction was carried out at a temperature of 255°C while visually observing the mixture in the reactor until the mixture became transparent. During this process, by-products were discharged through the column and the condenser. After the esterification reaction was completed, the nitrogen in the pressurized reactor was released to the outside, the pressure in the reactor was reduced to normal pressure, and then the mixture in the reactor was transferred to a 7-liter reactor capable of reacting under vacuum.

[0131] Then, the pressure of the reactor is reduced from normal pressure to 5 Torr (absolute pressure: 5 mmHg) within 30 minutes. At the same time, the temperature of the reactor is raised to 285°C within 1 hour, and the polycondensation reaction is carried out while the pressure of the reactor is maintained at 1 Torr (absolute pressure: 1 mmHg) or lower. At the beginning of the polycondensation reaction, the stirring speed can be set higher. As the polycondensation reaction proceeds, when the stirring power weakens due to the increase in the viscosity of the reactants or the temperature of the reactants rises to above the set temperature, the stirring speed can be appropriately adjusted accordingly. The polycondensation reaction is carried out until the intrinsic viscosity (IV) of the mixture (melt) in the reactor reaches 0.70 dl / g. When the intrinsic viscosity of the mixture in the reactor reaches the desired level, the mixture is then discharged to the outside of the reactor to form a strand, solidified with a coolant, and then granulated to an average weight of about 12 to 14 mg to prepare a polyester copolymer.

[0132] [Comparative Polymerization Example 4]

[0133] A 10-liter reactor equipped with a column and a condenser that can be cooled with water 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 (GeO2, 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.

[0134] Then, nitrogen was injected into the reactor to pressurize the reactor 2.0 kgf / cm above normal pressure. 2 (Absolute pressure: 2,231.1 mmHg). Then, the temperature of the reactor was raised to 220°C within 90 minutes, and maintained at 220°C for 2 hours, and was again raised to 260°C within 2 hours. Then, the esterification reaction was carried out at a temperature of 260°C while visually observing the mixture in the reactor until the mixture became transparent. During this process, by-products were discharged through the column and the condenser. After the esterification reaction was completed, the nitrogen in the pressurized reactor was released to the outside, the pressure in the reactor was reduced to normal pressure, and then the mixture in the reactor was transferred to a 7-liter reactor capable of reacting under vacuum.

[0135] Then, the pressure of the reactor is reduced from normal pressure to 5 Torr (absolute pressure: 5 mmHg) within 30 minutes. At the same time, the temperature of the reactor is raised to 265° C. within 1 hour, and the polycondensation reaction is carried out while the pressure of the reactor is maintained at 1 Torr (absolute pressure: 1 mmHg) or lower. At the beginning of the polycondensation reaction, the stirring speed can be set higher. As the polycondensation reaction proceeds, when the stirring power weakens due to the increase in the viscosity of the reactants or the temperature of the reactants rises to above the set temperature, the stirring speed can be appropriately adjusted accordingly. The polycondensation reaction is carried out until the intrinsic viscosity (IV) of the mixture (melt) in the reactor reaches 0.78 dl / g. When the intrinsic viscosity of the mixture in the reactor reaches the desired level, the mixture is then discharged to the outside of the reactor to form a strand, solidified with a coolant, and then granulated to an average weight of about 12 to 14 mg to prepare a polyester copolymer.

[0136] <Preparation of polyester resin mixture>

[0137] [Example 1]

[0138] The polyester copolymer obtained in Polymerization Example 1 and recycled PET were mixed at a weight ratio of 90:10 to prepare a polyester resin mixture. Specifically, a recycled PET resin prepared by pulverizing and washing waste plastics to obtain chips and melting and extruding them for re-granulation was dry-blended with the separately granulated polyester copolymer of Polymerization Example 1 at room temperature, and then dried at 50° C. to 150° C. to prepare a polyester resin mixture.

[0139] [Examples 2 to 7]

[0140] A 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.

[0141] [Comparative Examples 1 to 4]

[0142] A 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.

[0143] [Table 1]

[0144]

[0145] <Preparation of single-layer polyester film>

[0146] [Preparation Examples 1 to 7 and Comparative Preparation Examples 1 to 4]

[0147] The polyester resin mixtures obtained in the preparation examples and the comparative preparation examples were each extruded through a die at a temperature of 260° C. to 290° C., and then cooled to 20° C. to 50° C. to prepare an unstretched sheet. Then, the unstretched sheet was reheated to 75° C. to 90° C. and stretched 5 times in the transverse direction to prepare a polyester film having a thickness of 40 μm.

[0148] <Preparation of Multilayer Polyester Film>

[0149] [Preparation Examples 8 to 12 and Comparative Preparation Examples 5 to 7]

[0150] (1) Preparation of polyester resin mixture

[0151] A 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.

[0152] (2) Preparation of multilayer polyester film

[0153] A polyester resin mixture for forming a base layer and a polyester resin mixture for forming a first resin layer and a second resin layer, each having a composition shown in Table 2 below, were coextruded through a die at a temperature of 260° C. to 290° C. and then cooled at 20° C. to 50° C. to prepare an unstretched sheet having a three-layer structure in which the first resin layer and the second resin layer were laminated on both sides of the base layer. Then, the unstretched sheet was reheated to 75° C. to 90° C. and stretched 5 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).

[0154] [Table 2]

[0155]

[0156] [Test Example 1] Extrudability (roller plate removal)

[0157] The extrudability of the polyester resin mixture and the polyester film was evaluated using a Breyer apparatus having the following specifications.

[0158] -Supplier: Breyer GmbH (Germany, December 2000)

[0159] -Main extruder: Single screw extruder with or without venting section

[0160] -Diameter: 45mm

[0161] -L / D:33:1

[0162] - 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 fouling phenomenon of the roll during the extrusion process was sensory evaluated according to the following evaluation criteria.

[0163] -Evaluation criteria: No roller contamination after sheet extrusion "×"; Slight roller contamination after sheet extrusion "Δ"; Roller contamination after sheet extrusion "○"

[0164] [Test Example 2] Extrusion Coefficient

[0165] The extrudability coefficient of the polyester resin mixture was calculated by gas chromatography (GC) and the following equation 1. Specifically, in order to quantitatively analyze oligomers and short molecules caused by thermal decomposition of the polyester resin mixture (polyester copolymer contained in the polyester resin mixture), gas chromatography analysis was performed under the following conditions. Gaseous substances generated under the pretreatment conditions were collected and converted into total area / g in the graph.

[0166] In the pretreatment, the substances generated when the polyester resin mixture (polyester copolymer contained in the polyester resin mixture) pellets are heated at 260°C in an air atmosphere for 1 hour are collected in the GC head space. The total area of ​​the collected substances is quantified (unit area / g). The higher the total area / g value, the more unreacted substances and oligomers there are in the polyester resin mixture (or in the polyester copolymer), which indicates that the short molecular weight generated by thermal decomposition increases. At the same time, the 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.

[0167] *Gas chromatography (GC) measurement conditions

[0168] -Model: Triplus 500 (Thermo)

[0169] -Incubation temperature: 260℃

[0170] - Incubation time: 60min

[0171] -Cycling temperature: 260℃

[0172] -Circulation volume: 1mL

[0173] -Injection time: 0.5min

[0174] -Injection method: Standard

[0175] [Equation 1]

[0176] Extrusion coefficient = A / 10 7

[0177] A is a quantitative analysis value (area / g) of oligomers confirmed by gas chromatography (GC) analysis of the polyester copolymer.

[0178] [Test Example 3] Degassing

[0179] The polyester resin mixture and the polyester film were evaluated for degassing generation using an apparatus for evaluating extrudability. Specifically, degassing generated when the mixture was compressed on a roll during sheet extrusion was sensory evaluated according to the following evaluation criteria (checked 6 times at intervals of 10 minutes).

[0180] —Evaluation criteria: no degassing “◎”; almost no degassing “○”; slight degassing “Δ”; continuous degassing “×”

[0181] [Test Example 4] Stretchability (Fisheye)

[0182] After the sheet was extruded, it was stretched 5 times in the transverse direction (TD) at Tg+10° C. of the polyester resin mixture, and the presence of fish eyes in the stretched film was visually and sensory evaluated according to the following evaluation criteria.

[0183] -Evaluation criteria: A lot of fish eyes "○"; Slightly produced fish eyes "Δ"; Almost no fish eyes "×"

[0184] The results of Test Examples 1 to 4 are shown in Tables 3 and 4 below.

[0185] [Table 3]

[0186]

[0187] [Table 4]

[0188]

[0189] Referring to Table 3 above, the extrusion coefficient of the polyester resin mixture according to the present invention is 6 or less, which indicates that there is little pollution and degassing of processing equipment, and excellent stretchability during film stretching. Specifically, compared with the polyester resin mixture in Comparative Example 4 containing the original polyester copolymer of Comparative Polymerization Example 4 in which no recycled monomer is used during polymerization, the polyester resin mixture according to the present invention in Examples 1 to 7 has a lower extrusion coefficient and the same or better degassing and stretchability (see Preparation Examples 1 to 7 and Comparative Preparation Example 4). The above results support that the present invention can provide a polyester product having excellent physical properties and / or quality even when recycled monomers are used.

[0190] Meanwhile, referring to the above Table 4, when a multi-layer polyester film using the polyester resin mixture according to the present invention is prepared, it is excellent in extrudability, processability, stretchability, and the like.

[0191] [Explanation of Reference Numerals]

[0192] 10: Polyester film

[0193] 11: Grassroots

[0194] 12: First resin layer

[0195] 13: Second resin layer.

Claims

1. A polyester resin mixture comprising a polyester copolymer and polyethylene terephthalate, wherein the polyester copolymer 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; wherein: When the mixture is extruded to a thickness of 1 mm, the extrusion coefficient according to the following equation 1 is 6 or less: [Equation 1] Extrusion coefficient = A / 10 7 In Equation 1, A is a quantitative analysis value (area / g) of oligomers confirmed by gas chromatography (GC) analysis of the polyester copolymer.

2. The polyester resin mixture according to claim 1, wherein the recycled monomer is recycled ethylene terephthalate (recycled-BHET).

3. The polyester resin mixture according to claim 1, wherein the diol compound comprises at least one compound selected from the group consisting of isosorbide, ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 2-methyl-1,3-propylene glycol, 2-methylene-1,3-propylene glycol, 2-ethyl-1,3-propylene glycol, 2-isopropyl-1,3-propylene glycol, 2,2-dimethyl-1,3-propylene glycol, 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. The polyester resin mixture according to claim 1, wherein the dicarboxylic acid compound comprises at least one compound selected from the group consisting of terephthalic acid, isophthalic acid, dimethyl isophthalate, phthalic acid, dimethyl terephthalate, dimethyl phthalate, phthalic anhydride, 2,6-naphthalene dicarboxylic acid, dimethyl 2,6-naphthalene dicarboxylate, biphenyl dicarboxylic acid, 1,4-cyclohexane dicarboxylic acid, 1,3-cyclohexane dicarboxylic acid, dimethyl 1,4-cyclohexane dicarboxylate, dimethyl 1,3-cyclohexane dicarboxylate, sebacic acid, succinic acid, isodecyl succinic acid, maleic acid, maleic anhydride, fumaric acid, adipic acid, glutaric acid and azelaic acid.

5. The polyester resin mixture according to claim 1, wherein the polyester copolymer comprises 0 to 30 mol% of repeating units (c1) derived from diethylene glycol, 0 to 45 mol% of repeating units (c2) derived from cyclohexanedimethanol, 0 to 25 mol% of repeating units (c3) derived from cyclohexanedimethanol derivatives, and 0 to 45 mol% of repeating units (c4) derived from neopentyl glycol, based on the total moles of repeating units (c) derived from diol compounds.

6. The polyester resin mixture according to 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. The polyester resin mixture according to claim 1, wherein The content of the recycled components is 30 wt% or more based on the total weight of the polyester resin mixture.

8. A method for preparing a polyester resin mixture, comprising: The recovered monomer, dicarboxylic acid compound and diol compound are introduced into the reactor and heated to 0 kgf / cm 2 Up to 10.0kgf / cm 2 esterification reaction is carried out at a pressure of 150° C. to 300° C. to obtain a reactant; subjecting the reactants to a polycondensation reaction to obtain a polyester copolymer; The polyester copolymer is mixed with polyethylene terephthalate.

9. A polyester film prepared from a polyester resin mixture, the polyester resin mixture comprising a polyester copolymer and polyethylene terephthalate, the polyester copolymer comprising 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; wherein, When the mixture is extruded to a thickness of 1 mm, the extrusion coefficient according to the above equation 1 is 6 or less: [Equation 1] Extrusion coefficient = A / 10 7 In Equation 1, A is a quantitative analysis value (area / g) of oligomers confirmed by gas chromatography (GC) analysis of the polyester copolymer. 10 . The polyester film according to claim 9 , which has a single-layer structure or a multi-layer structure.

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

1. 12 . The polyester film according to claim 9 , which is a film 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 a film uniaxially stretched 1.5 to 6 times in the transverse direction (TD) and uniaxially stretched 1.1 to 5 times in the machine direction (MD).

14. A method for preparing a polyester film, comprising: preparing an unstretched sheet from the polyester resin mixture, and stretching the unstretched sheet; The polyester resin mixture comprises a polyester copolymer and polyethylene terephthalate, wherein the polyester copolymer 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; wherein, when the mixture is extruded to a thickness of 1 mm, the extrusion coefficient according to the above equation 1 is 6 or less: [Equation 1] Extrusion coefficient = A / 10 7 In Equation 1, A is a quantitative analysis value (area / g) of oligomers confirmed by gas chromatography (GC) analysis of the polyester copolymer.

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