Preparation method for ethylene-vinyl alcohol copolymer

1 . A method for preparing ethylene-vinyl alcohol copolymer, comprising:

a first saponification reaction step wherein a first saponification reaction is performed while adding a first alkali catalyst solution dropwise to ethylene-vinyl acetate copolymer dispersed in an alcohol solvent, and a first saponification reaction mixture is obtained after the first saponification reaction step is completed; and

a second saponification reaction step wherein a second saponification reaction is performed while adding a second alkali catalyst solution dropwise to the first saponification reaction mixture,

wherein a total amount of the first alkali catalyst and second alkali catalyst used are 0.01 moles or more to less than 0.03 moles, based on 1 mole of vinyl acetate unit of the ethylene-vinyl acetate copolymer,

the first saponification reaction step is completed when the dropwise addition of the first alkali catalyst solution is completed, and

the second saponification reaction step is completed when the dropwise addition of the second alkali catalyst solution is completed.

2 . The method according to claim 1 , wherein the first alkali catalyst and second alkali catalyst are used respectively in an amount of 0.0025 moles to 0.02 moles, based on 1 mole of vinyl acetate unit of the ethylene-vinyl acetate copolymer.

3 . The method according to claim 1 , wherein the dropwise addition of the first alkali catalyst solution is conducted so that an introduction amount of the first alkali catalyst per minute is 1.0*10 −5 moles to 13*10 −5 moles, based on 1 mole of vinyl acetate unit of the ethylene-vinyl acetate copolymer.

4 . The method according to claim 1 , wherein the dropwise addition of the second alkali catalyst solution is conducted so that an introduction amount of the second alkali catalyst per minute is 2.0*10 −5 moles to 8.0*10 −5 moles, based on 1 mole of vinyl acetate unit of the ethylene-vinyl acetate copolymer.

5 . The method according to claim 1 , wherein the first saponification reaction step and the second saponification reaction step are continuously conducted.

6 . The method according to claim 1 , wherein the second saponification reaction step is conducted at a temperature equal to or higher than a temperature at which the first saponification reaction step is conducted.

7 . The method according to claim 1 , wherein the first saponification reaction step is conducted at a temperature of 40° C. to 120° C.

8 . The method according to claim 1 , wherein the second saponification reaction step is conducted at a temperature of 60° C. to 120° C.

9 . The method according to claim 1 , wherein ethylene content of the ethylene-vinyl acetate copolymer is 20 mol % or more, and 60 mol % or less.

10 . The method according to claim 1 , wherein the ethylene-vinyl acetate copolymer has a weight average molecular weight (Mw) of 180,000 g/mol or more, and 290,000 g/mol or less.

11 . The method according to claim 1 , wherein the first alkali catalyst and second alkali catalyst are identical to or different from each other, and each independently at least one selected from sodium hydroxide, potassium hydroxide, lithium hydroxide, sodium methoxide, sodium ethoxide, potassium t-butoxide, sodium carbonate, sodium hydrogen carbonate, potassium carbonate, potassium hydrogen carbonate, sodium acetate, potassium acetate, or sodium propionate.

12 . The method according to claim 1 , wherein the first alkali catalyst and second alkali catalyst are used at a mole ratio of 1:1 to 1:4.

13 . The method according to claim 1 , wherein the alcohol solvent is methanol, ethanol, propanol, isopropanol, or butanol.

14 . The method according to claim 1 , wherein the alcohol solvent is used in an amount of 100 parts by weight to 1000 parts by weight, based on 100 parts by weight of the ethylene-vinyl acetate copolymer.

15 . The method according to claim 1 , wherein the ethylene-vinyl alcohol copolymer has a saponification degree of 99% or more.