PET Preform Injection Molding

• Dry and dehumidify PET material -- autoloader, hopper dryer & dehumidifier;
• Melting  PET material into preform mold -- PET injection molding  machine;
• PET preform cooled down and formed in the preform mold -- preform mold, hot runner temperature controller, water chiller, cooling water tower.

The common drying methods:

• By oven:
  A kind of outdated and laborious drying method. Oven is apart from injection machine, dried PET is moved into the hopper of injection machine manually, and un-dried PET is moved into oven manually too.
  As LVPET may get damp and caking while drying, only oven drying method can be used for LVPET so that it can be turned over for 2 to 3 times during drying. The thickness of PET in the trays can be about 50mm. If dried material is not used up, set oven's working temperature to 110⁰C to keep it warm. PET should not be stayed in oven for more than 8 hours, or it will deteriorate. Cooled material should be dried again.
  For LVPET, luster will appear when it is being dried. And the luster will disappear when drying finished.
   
• By Hopper Dryer
  Most common and economical method to dry PET. If works together with autoloader, PET will be loaded into hopper dryer and dried continuously and automatically.
   
• By Dehumidifier
  Efficient but costly drying method, works together with hopper dryer and autoloader. It dries PET in a closed loop system to reach dew-point of at least -32⁰C, thus to exhibit the optimum physical performance and surface finish of PET products.

Drying target is to get moisture level <=0.005% (at the same time, AA level should be strictly controlledto avoid peculiar smell in the drink)

The best drying temperature and time are decided by IV value of PET resin. But generally speaking, it should be 150~ 170⁰C for about 4 hours.

If dried PET contact air with relative humidity 35~40% for 12 minutes, it's moisture content will reach 0.005%. Long-time drying will reduce its IV value. So it is better to shorten drying time. Drying time should not exceed 7~8 hours.

These temperature vary a little bit with IMM, preform's design and weight, mold's structure and cooling, etc.