PET is kind of hygroscopic resin and absorbs moisture in the air. If the moisture is not removed before processing, the resin will hydrolyze and cause rejects. The simplest drying way is to use hopper dryer, however the drying effect is dependent on the air humidity and the drying is unstable and in any case could not reach the 50ppm requirement. While dehumidifying dryer recycles the air for reuse and attains the drying requirement of PET resin.
Plasticizing the PET
The dried PET resin are compressed and melt by a rotary screw.
Injection molding the PET preform
Molten PET is injected into the injection cavity and cooled rapidly to form a preform.
Heating the PET preform
The PET preform is heated up to a certain temperature for blowing.
Stretch blow molding the PET preform
The heated preform is simultaneously stretched and blown in a shaped blow mold to form a tough, lightweight container.
When PET is heated to a temperature, its chain-like molecules are sufficiently mobile to uncoil instead of breaking when extended so that stretching can orient it. In stretch blow molding, stretching from two directions at right angles gives biaxial orientation. Oriented PET contains closely packed chains aligned in the directions of stretch. The material becomes stronger because the molecules act together instead of individually. The tensile strength of oriented PET is several times that of the material without stretching, as well as the impact strength, barrier and chemical resistance are also significantly improved, so bottles can be lighter without sacrificing performance.
Ejecting PET container
The finished container is ejected from the molds.
During the heat processing, as PET melted temperature is too high, PET degrades to AcetAldehyde (abbreviated to AA).