Patent ID: 6745492
Filing Date: 2004-06-08
Classification: B29B,B29C,B29K

Abstract:
A process for manufacturing a preform from pellets, of at least one thermoplastic resin, substantially in a crystalline state wherein the thermoplastic resin is a PET homopolymer or copolymer resin, comprising the steps of:drying the pellets in drying means the output of which is connected to an extruder; melting the dried pellets of resin in the extruder; and injecting the melted resin into a mould and removing the preform from the mould; wherein the drying operation is carried out in at least two successive separate steps, thereby raising the temperature of the pellets prior to extrusion: a first step, wherein the pellets of resin substantially in a crystalline state are dried for a predetermined duration at a predetermined drying temperature, wherein the duration of the first driving step is between 6 hours and 7 hours, and the driving temperature of the first driving step is fixed at a value such that the temperature of the pellets at the output from the first drying step is between 140Â° C. and 150Â° C.; and a second step, wherein the drying of the pellets from the first step is continued at a drying temperature that is strictly higher than the drying temperature of the first stage, and for a duration that is strictly shorter than the period of the first step, wherein the duration of the second driving step is between 1 hour and 3 hours, and the driving temperature of the second drying step is determined in such a way as to obtain, at the beginning of the following melting step, a pellet temperature of between 155Â° C. and 165Â° C.