Method for preparing a copolyester
The present disclosure relates to a method for preparing a copolyester. More specifically, the present disclosure relates to a method for preparing a copolyester that reduces the use of a cobalt-based coloring agent but minimizes yellowing, by using a specific thermal stabilizer.
1 . A method for preparing a copolyester comprising steps of:
conducting an esterification reaction of terephthalic acid, ethyleneglycol, and 1,4-cyclohexanedimethanol (CHDM), in the presence of a titanium-based catalyst; and
conducting condensation polymerization of the reaction product of the esterification reaction, in the presence of a phosphorus-based thermal stabilizer,
wherein the phosphorus-based thermal stabilizer is calcium bis[monoethyl(3,5-di-tert-butyl-4-hydroxylbenzyl)phosphonate] or triethyl phosphonoacetate,
wherein, when using calcium bis[monoethyl(3,5-di-tert-butyl-4-hydroxylbenzyl)phosphonate] as the phosphorous-based thermal stabilizer, the phosphorous-based thermal stabilizer is added in an amount such that a content of phosphorous element is 300 ppm or more and 1,000 ppm or less, based on a weight of a finally produced copolyester, and
wherein, when using triethyl phosphonoacetate as the phosphorous-based thermal stabilizer, the phosphorous-based thermal stabilizer is added in an amount such that a content of phosphorous element is 5 ppm or more and 20 ppm or less, based on the weight of the finally produced polyester.
2 . The method for preparing a copolyester according to claim 1 , wherein the titanium-based catalyst comprises one or more selected from the group consisting of tetraethyltitanate, acetyltripropyltitanate, tetrapropyltitanate, tetrabutyltitanate, polybutyltitanate, 2-ethylhexyl titanate, octylene glycol titanate, lactate titanate, triethanolamine titanate, acetylacetonate titanate, ethylacetoacetic ester titanate, isostearyl titanate, and titanium dioxide.
3 . The method for preparing a copolyester according to claim 1 , wherein the titanium-based catalyst is added in an amount such that the content of titanium element is 5 ppm or more and 200 ppm or less, based on the weight of the finally produced copolyester.
4 . The method for preparing a copolyester according to claim 1 , wherein the step of reacting terephthalic acid, ethyleneglycol, and 1,4-cyclohexanedimethanol is conducted at a temperature of 200 to 270° C. for 1 to 10 hours.
5 . The method for preparing a copolyester according to claim 1 , further comprising a cobalt-based coloring agent, in the condensation polymerization step.
6 . The method for preparing a copolyester according to claim 5 , wherein the cobalt-based coloring agent comprises one or more selected from the group consisting of cobalt acetate, cobalt acetylacetonate, cobalt benzoylacetonate, cobalt hydroxide, cobalt bromide, cobalt chloride, cobalt iodide, cobalt fluoride, cobalt cyanide, cobalt nitrate, cobalt sulfate, cobalt selenide, cobalt phosphate, cobalt oxide, cobalt thiocyanate and cobalt propionate.
7 . The method for preparing a copolyester according to claim 5 , wherein the cobalt-based coloring agent is used in an amount such that the content of cobalt element included in the cobalt-based coloring agent is 3 ppm or more and 100 ppm or less, based on the weight of the finally produced copolyester.
8 . The method for preparing a copolyester according to claim 1 , wherein the step of condensation polymerization of the reaction product of the esterification reaction is conducted at a temperature of 250 to 300° C. and a reduced pressure of 760 to 0.01 mmHg for 30 minutes to 6 hours.
9 . The method for preparing a copolyester according to claim 1 , wherein, the copolyester has an intrinsic viscosity (IV) of 0.65 to 0.74 dl/g and a color b value of −3.5 or more and 0 or less.
10 . The method for preparing a copolyester according to claim 1 , wherein the copolyester has an intrinsic viscosity (IV) of 0.75 to 0.80 dl/g and a color b value of −8.0 or more and 5 or less.
11 . A copolyester prepared by the method according to claim 1 .
12 . The copolyester according to claim 11 , wherein the copolyester is suitable for cosmetics, beverage, food-related containers, shrink films, or sheets.