Method for preparing polycondensation resin

1. A method for preparing a polycondensation resin, comprising:

preparing a low degree condensate; and

solid phase polymerizing the low degree condensate,

wherein a granular molded article is provided upon solid phase polymerization and wherein the granular molded article has a particle diameter of 3 mm to about 30 mm.

2. The method according to claim 1 , wherein the granular molded article is a granular compression-molded article of the low degree condensate.

3. The method according to claim 2 , wherein the granular molded article of the low degree condensate is prepared by compression molding of the low degree condensate at about 10 MPa to about 800 MPa.

4. The method according to claim 2 , wherein the solid phase polymerization is performed in a longitudinal tower type apparatus or a longitudinal tower type machine.

5. The method according to claim 1 , wherein the granular molded article is a granular molded article of a thermoplastic resin.

6. The method according to claim 5 , wherein the low degree condensate is prepared in the form of crystalline powder, and the crystalline powder of the low degree condensate and the granular molded article of the thermoplastic resin are mixed to carry out solid phase polymerization.

7. The method according to claim 5 , wherein the thermoplastic resin is end-capped with an end capping agent.

8. The method according to claim 6 , wherein the granular molded article of the thermoplastic resin is mixed in an amount of about 0.1 wt % to 10 wt % with respect to the crystalline powder of the low degree condensate.

9. The method according to claim 5 , wherein the granular molded article of the thermoplastic resin is the same kind as the low degree condensate.

10. The method according to claim 5 , wherein the granular molded article of the thermoplastic resin has an inherent viscosity of about 0.3 dl/g to about 5 dl/g as measured at a concentration of 0.5 g/dl.

11. The method according to claim 1 , wherein the polycondensation resin comprises a polyamide, polycarbonate or polyester resin.

12. The method according to claim 1 , wherein the solid phase polymerization has a maximum reaction temperature of about 170° C. to about 350° C.

13. The method according to claim 1 , wherein the low degree condensate is prepared by polycondensation of a dicarboxylic acid and a diamine, and the moisture content in a reaction system is about 15 wt % to about 35 wt % at the end of polycondensation.

14. The method according to claim 13 , wherein the preparing the low degree condensate is performed at a reaction temperature of about 230° C. to about 250° C.

15. The method according to claim 13 , wherein the preparing the low degree condensate is performed at a pressure ranging from about 1.5 MPa to about 3.5 MPa for a reaction time ranging from about 0.5 hours to about 4.0 hours.

16. The method according to claim 13 , wherein the low degree condensate is provided to solid phase polymerization after being discharged and cooled under an inert gas atmosphere and atmospheric pressure or less.

17. The method according to claim 16 , wherein the cooled low degree condensate has an inherent viscosity of about 0.07 dl/g to about 0.20 dl/g as measured at 25° C. and at a concentration of 0.5 g/dl in concentrated sulfuric acid, and 5 wt % reduction temperature of about 300° C. or more as measured by thermogravimetry under nitrogen atmosphere.

18. The method according to claim 16 , wherein the inert gas has an oxygen concentration of about 1% by volume or less, and, in the cooling, the low degree condensate is cooled to about 100° C. or less.

19. The method according to claim 13 , wherein the dicarboxylic acid comprises about 30 mol % to about 100 mol % of terephthalic acid and about 0 to about 70 mol % of dicarboxylic acid except for terephthalic acid, the diamine comprising about 50 mol % to about 100 mol % of a C 4 to C 25 aliphatic alkylene diamine and about 0 to about 50 mol % of a C 3 to C 25 cycloaliphatic diamine.