Basic knowledge of plastic parts spraying

1、 Spray characteristics

A widely used finishing process in painting construction. Air spraying is to use the airflow of compressed air to flow through the nozzle hole of the spray gun to form a negative pressure. The negative pressure causes the paint to be sucked in from the straw and sprayed out through the nozzle to form a paint mist. The paint mist is sprayed onto the surface of the painted parts to form a uniform paint film. Air spraying can produce uniform paint with fine and smooth coating; Concealed parts of components (such as gaps and bumps) can also be painted evenly. The coating utilization rate of this method is about 50%~60%.  

After plastic parts are sprayed, the following effects can be obtained:

1. It can cover the surface defects of formed parts;   

2. Because it is difficult to color the plastic itself, multiple colors can be obtained by spraying;  

3. Improve the electrostatic performance of plastics and reduce dust absorption;  

4. The hardness and scratch resistance of plastics are enhanced;  

5. The weatherability of plastics is improved;  

6. Adjust the gloss of the plastic part surface at will;   

7. Sand grain paint, fluff paint and other special paints can obtain good appearance and feel.   

In addition, the surface state of plastic after molding has a great impact on the appearance quality. It is required that the formed surface shall be flat and smooth, even and consistent, free of scratches, flash, burrs, pits, spots, bubbles and obvious weld lines.  

2、 Plastic spraying process: annealing, degreasing, eliminating static electricity, dedusting, spraying and drying

1. Annealing: the plastic is easy to form internal stress during molding, and the stress concentration is easy to crack after coating. Annealing treatment or full face treatment can be used to eliminate stress. The spray annealing treatment of Hanyang plastic parts is to heat the ABS plastic molding parts below the thermal deformation temperature, that is, 60 ℃, and keep the heat for 2h. Since the adoption of this process requires a large amount of equipment investment, the whole surface treatment technology can be used. Hanyang plastic parts can be sprayed with a solution that can eliminate the internal stress of the plastic parts, and the surface of the plastic parts can be treated for 15-20 minutes at room temperature.  

2. Degreasing: The surface of plastic parts is often stained with oil stain, sweat and release agent, which will make the adhesion of paint worse, and the coating will crack, blister and fall off. Oil removal treatment shall be carried out before painting. The plastic parts are usually cleaned with gasoline or alcohol, and then chemical degreasing. After chemical degreasing, the residual lye on the surface of the workpiece should be thoroughly cleaned, and finally cleaned with pure water, dried or dried.   

3. De electrification and dedusting: plastic products are insulators, and the surface resistance is generally about 1013 Ω, which is easy to generate static electricity. After electrification, it is easy to absorb fine dust in the air and attach to the surface. Because it is very difficult to remove the electrostatic adsorbed dust by general air blowing method, the effect of simultaneous removal of electrostatic precipitator by high-pressure ionized air flow is better.   

4. Spraying: the thickness of plastic coating is 15-20 μ m, which usually requires 2-3 layers of spraying. The second spraying shall be carried out after the first spraying is dried for 15min. Clear paint must also be sprayed on the surface that needs to be bright. The coated parts have little effect on the flame retardancy.

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