Polyester composition for improved stress crack resistance in polyester articles
View Patent ↗Polyester compositions for use in injection stretch blow molded articles having intrinsic viscosities in the range from about 0.65 to about 0.78 dl/g, and carboxyl end group concentrations of about 47 mmole/kg or more are provided. Stretch blow molded articles formed from these polyester compositions and methods to produce these articles are also described.
1. A polyester composition for use in an injection stretch blow molded article comprising: i) an intrinsic viscosity in the range from about 0.65 to about 0.78 dl/g, and ii) a carboxyl end group concentration of at least about 47 mmole/kg; wherein the intrinsic viscosity and the carboxyl end group concentration of the polyester composition are measured after the article has been injection stretch blow molded; wherein the composition is adapted to provide the injection stretch blow molded article with a CSC time to failure of 180 minutes or more; and wherein the composition comprises no cyclic anhydrides.
2. The composition of claim 1 wherein said intrinsic viscosity is in the range of about 0.65 to about 0.75 dl/g.
3. The composition of claim 1 wherein said intrinsic viscosity is in the range of about 0.65 to about 0.70 dl/g.
4. The composition of claim 1 wherein said intrinsic viscosity is in the range of about 0.70 to about 0.78 dl/g.
5. The composition of claim 1 wherein said intrinsic viscosity is in the range of about 0.70 to about 0.75 dl/g.
6. The composition of claim 1 wherein said carboxyl end group concentration is at least about 50 mmole/kg.
7. The composition of claim 1 wherein said carboxyl end group concentration is at least about 55 mmole/kg.
8. The composition of claim 1 wherein said polyester is selected from the group consisting of polyethylene terephthalate, polyethylene naphthalate, polyethylene terephthalate-co-isophthalate, polyethylene naphthalate-co-isophthalate, polyethylene-co-cyclohexane dimethylene terephthalate and mixtures thereof.
9. The composition of claim 1 wherein said polyester is a copolymer of polyethylene terephthalate having a comonomer content of less than 10 mole % of the polyester.
10. An injection stretch blow molded article comprising the composition of claim 1 .
11. The article of claim 10 wherein said article comprises a container.
12. The article of claim 10 wherein said article comprises a bottle for carbonated beverages having a pentaloid base.
13. The article of claim 12 , wherein the beverage bottle has an interior volume of about 0.6 liters and a burst pressure of greater than about 1200 kPa.
14. The article of claim 12 , wherein the beverage bottle has an interior volume of about 2 liters and a burst pressure of greater than about 1000 kPa.
15. The article of claim 12 , wherein the beverage bottle has a CSC time to failure of 180 minutes or more.
16. A method for improving resistance to caustic stress cracking in an injection stretch blown article comprising: i) preparing a polyester resin; ii) melting the resin; and iii) injection stretch blow molding the resin into the article, wherein the polyester resin in the article has an intrinsic viscosity in the range of 0.65 to 0.78 dl/g and a carboxyl end group concentration of greater than about 47 mmole/kg; and wherein the polyester resin in the article comprises no cyclic anhydrides.
17. The method of claim 16 wherein the article is a container.
18. The method of claim 16 wherein the article is a bottle for carbonated beverages having a pentaloid base,
19. The composition of claim 1 , wherein the minimum CEG required at a given IV to meet the minimum CSC time of failure of 180 minutes is defined by the following table:
Iv
CEG
0.650
47.4
0.675
47.2
0.700
46.9.