By keeping all the above at minimum values and having a good plasticized resin, it is possible to achieve low IV drop and low acetaldehyde generation in the produced preform. Especially for acetaldehyde, its formation rate depends on the melt temperature and the length of the time when PET stays molten. Therefore, the whole process must be set to run as fast as possible without forgetting to minimize the screw “dead time” , which has to be always less than 2 sec, and by injecting the molten PET into the mold at a slower rate to help reduce shear heating.
The limiting factor on cycle time for most injection molding processes is the cooling time in the mold. The target must be to always keep the mold at low temperature by minimizing the mineral deposits that usually occur in the cooling channels if the chilled water is not treated properly. Ambient moisture should not be allowed to accumulate on the mold because it can cause preform defects, which will not become apparent until the blowing process takes place. However, this can be avoided by employing dehumidified air in an enclosed mold.