Color control of polyester-cobalt compounds and polyester-cobalt compositions
The present invention is to a composition made from a polyester produced by the acid or ester polyester process, a cobalt salt and a base, preferably an alkaline metal base. The composition can be made by blending a cobalt salt with a polyester which has been polymerized in the presence a alkaline metal ion derived from a basic alkaline metal compound, e.g. alkaline metal base or basic alkaline metal salt. The composition may optionally comprise an ionic compatibilizer, which may further be blended with a partially aromatic polyamide. This blend can be processed into a container having both active and passive oxygen barrier with an improved color and clarity than that achieved by cobalt alone. The use of the cobalt salt in combination with the base can also be used to improve the color of recycled polyester during processing.
1. A process for improving the color by lowering the b* of a polyester resin composition comprising a partially aromatic polyamide and a cobalt compound having free cobalt ions wherein the polyester resin is obtained from polyester preforms or polyester bottles, said process including the steps of:
A. Extruding the polyester resin composition comprising the partially aromatic polyamide and the cobalt compound, wherein the amount of free cobalt ions present in the polyester resin composition is in the range of 20 to 500 ppm based upon the weight of the polyester resin composition;
B. Melt mixing an amount of a base into the polyester resin comprising the partially aromatic polyamide and the cobalt compound during the extruding step A, and
C. Pelletizing the extruded polyester resin comprising the partially aromatic polyamide and the cobalt compound;
wherein the base is an alkali metal base having alkaline metal ions wherein the mole ratio of alkaline metal ions to free cobalt ions is in the range of 1:10 to 3:1, and the alkaline metal ions are not associated with or derived from a sulfonate group.
2. The process according to claim 1 , wherein the cobalt compound is a cobalt salt.
3. The process according to claim 1 , wherein the alkali metal base having alkaline metal ions is selected from the group consisting of lithium acetate, sodium acetate, lithium hydroxide and sodium hydroxide.
4. A process for improving the color by lowering the b* of a polyester resin composition comprising a partially aromatic polyamide wherein the polyester resin comprising the partially aromatic polyamide is obtained from polyester preforms or polyester bottles, said process including the steps of:
A. Extruding the polyester resin comprising the partially aromatic polyamide,
B. Melt mixing an amount of a base and an amount of a cobalt compound into the polyester resin comprising the partially aromatic polyamide during the extruding step A, wherein the amount of cobalt is sufficient to have free cobalt ions present in the polyester resin with the amount of free cobalt ions in the range of 20 to 500 ppm based upon the weight of the polyester resin composition and
C. Pelletizing the extruded polyester resin comprising the partially aromatic polyamide;
wherein the base is an alkali metal base having alkaline metal ions wherein the mole ratio of alkaline metal ions to free cobalt ions is in the range of 1:10 to 3:1, and the alkaline metal ions are not associated with or derived from a sulfonate group.
5. The process according to claim 4 , wherein the cobalt compound is a cobalt salt.
6. The process according to claim 4 , wherein the alkali metal base having alkaline metal ions is selected from the group consisting of lithium acetate, sodium acetate, lithium hydroxide and sodium hydroxide.