PET bottle is light, easy to form and solid. The strength and ductility are significantly higher than other raw materials. PET bottles, which are suitable for thin wall, light weight and high strength medical plastic bottles, have been used in China for 40 years and have a rapid development potential. PET plastic bottles are light, clear, impact resistant, not easy to crack, and easy to transport. They are mostly used without final bactericidal slurry, oil system agent, and oral solid Chinese medicine preparation. In the recent 20 years, it has become the most critical liquid and solid packaging materials all over the country. Now let's take you to know why the bubbles and vacuum pump bubbles occur in the production of PET plastic bottles.
1. Material factor
The raw materials contain water.
2. Mold factor
If the mold is trapped, maintain the mold or add an exhaust slot.
3. Process factors
(1) If the speed is too fast, the molten plastic will be decomposed under the action of large shear and generate gas.
(2) The local cooling of the product is too fast, and the shrinkage is uneven. Especially when the wall thickness of the product is large, the surface cooling speed is faster than that of the central part. During the cooling process, the plastic in the central part shrinks while expanding to the outside, making the central part insufficiently filled, forming a vacuum bubble.
(3) Insufficient pressure and pressure holding make the molten material not close to the surface of the cavity, which is not conducive to the discharge of air.
(4) The back pressure is insufficient. The back pressure controls the speed of the screw retreating. When the back pressure is small, the speed of the screw retreating will be fast, which is easy to cause insufficient feeding. The air brought in by the material is too much to be discharged from the feeding port in time, resulting in a large number of bubbles.