In the process of producing PET cosmetic plastic bottles, there are often bubbles in the bottle body. These bubbles will directly lead to the unqualified quality control. So what causes the bubbles? Let us analyze it from several aspects.
First, process factors:
1. The speed is too fast, so that the molten plastic will be decomposed by large shearing, and gas will be generated.
2. Part of the product is cooled too fast and shrinks unevenly, especially when the wall thickness of the product is large, the surface cooling rate is faster than the center part. During the cooling process, the plastic in the center part shrinks while expanding outward, so that the center part is filled. Insufficient, a vacuum bubble is formed.
3. Insufficient pressure and holding pressure make the melt and the cavity surface not adhere closely, which is not conducive to the discharge of air.
4. Insufficient back pressure, the back pressure controls the retreating speed of the screw. When the back pressure is small, the retreating speed of the screw will be fast, which is easy to cause insufficient feeding. There is more air in the material and it is too late to discharge from the feeding port. A lot of bubbles are produced.
Second, material factors
1. The raw material has moisture.
2. Mould factors
3. The mold is trapped in air, and the mold should be maintained or an exhaust groove should be added.
Therefore, we must pay attention to these aspects in the production process to make a perfect bottle.