Process for direct production of low acetaldehyde packaging material

Claim 1

Process for the reduction of the free aldehyde content in a polyester melt during production of shaped polyester food packaging material which does not affect taste of the food, the steps of which are carried out as polyester in the melt phase flows directly from a poly-condensation reactor to a shaping apparatus, said polyester having at least 70 wt % ethylene glycol units based on the total diol units, said process comprising (a) providing a polyester melt which contains, in addition to conventional reaction catalysts, an added 5-120 ppm of a) cobalt or b) cobalt and manganese in a molar ratio of 1:1 to 3:1 and c) phosphorus in a molar amount equal to or twice the molar amount of cobalt, each in the form of their polyester-soluble compounds, (b) introducing an inert gas through a gas inlet and uniformly distributing said inert gas into said polyester melt immediately after leaving said polycondensation reactor in an amount, by weight, not in excess of the amount of polyester by weight to reduce the free aldehyde content of said polyester melt, (c) adding from 0.05 to 1.0 wt % of a low-volatility acetaldehyde-reducing amide, said amide being added to the polyester melt through an inlet next to said inert gas inlet, (d) vacuum degassing said polyester melt immediately before entering said shaping apparatus, (e) sending said degassed polyester melt to said shaping apparatus for processing into said shaped polyester food packaging, and (f) maintaining the temperature of said polyester melt at not more than 35° C. above the crystallite melting point for a maximum dwell time of 30 minutes between steps (b) to (e).