Common problems in thermosetting powder coating construction (3)

Coating shrinkage

1. The quality of the raw material itself: If the relative molecular mass distribution of the same polyester is very wide, the curing speed is significantly different, and the curing speed cannot be fully flowed, and the curing speed is slow, it is difficult to level the cured part, resulting in a fast curing speed. The part becomes shrinkage cavity. The resin has a high content of low molecular weight, and when the coating is slightly thicker, it is easy to produce larger pores. Low-cost raw materials are used in the synthesis of polyester resin, which has poor anti-interference ability.

2. The material has poor miscibility and mismatch: the leveling agent can sometimes have a good leveling effect on a certain polyester, but it is difficult to have a leveling effect on another kind of polyester; the moisturizing brightener can sometimes promote leveling and eliminate Shrinkage sometimes has a counterproductive effect, so it is very important to conduct material matching tests in advance during formulation design.

3. Active fillers: Some fillers are treated with surfactants, and some surfactants are more likely to cause reverse ionization during electrostatic spraying, which may cause the deposited powder coating to break down, causing pits and shrinkage holes. In view of this phenomenon, lower voltage spraying should be used to eliminate the influence caused by reverse ionization.

4. The impact of production equipment: oil leakage in the feeder, local water seepage in the extruder, and the lubricant of the ACM grinding core bearing due to high temperature, and once the material seeps with oil, it is the root cause of the coating defects.