Patent ID: 6077904
Filing Date: 2000-06-20
Classification: B29C,B29K,B65D,C08G,C08L

Abstract:
A drawing thermoforming process for producing a dimensionally-stable, impact modified polyester with improved low temperature impact strength and improved gas barrier properties comprising the steps:(a) heating a composition comprising a crystallizable polyester and an impact modifier to a temperature above the melting point temperature of the polyester for a time sufficient to bring said polyester to a substantially amorphous molten state;(b) maintaining the composition heated in step (a) at a temperature above said melting point temperature for a time sufficient to substantially eliminate previous molecular stress imprinting and until an effective amount of said impact modifier is dissolved in said polyester;(c) controlling cooling of the composition in step (b) at a rate of from about 1.degree. C. to about 89.degree. C. per minute until there is crystallization of the polyester and impact modifier forming a mixture of precipitated particles of impact modifier embedded in a matrix of the polyester, said precipitate of the impact modifier having a particle size of from about 0.1 to about 10 microns in diameter; and(d) continuing controlled cooling of the composition by contacting the composition to a surface capable of imparting shape for from about 1 second to about 5 minutes, said contact surface being at a temperature of at least the lower boundary crystallization from melt temperature of said polyesterto provide an impact modified polyester, wherein said impact modified polyester has an oxygen permeability of from about 0.2 to about 4.0 cc-mil/100 in.sup.2 -24 hr-atm at 23.degree. C. and 60% relative humidity outside/100% relative humidity inside and a heat of recrystallization of from about 0 to about -4.0 calories per gram as measured by differential scanning calorimetry at a heating rate of about 25.degree. C./minute.