(l) phenomenon
The gloss relief coating does not achieve the proper gloss after drying, or the coating has a decrease in gloss relief and a hazy phenomenon shortly after coating, as shown in Figure 9-21.
(2) Reason analysis
① Improper choice of diluent, such as using a different season diluent in winter, which has poor miscibility with resin.
②The surface to be coated is rough, and the absorption of paint is large and uneven.
③The surface treatment is not clean before spraying.
④ Due to excessive spraying air pressure or low viscosity, the atomization is excessive and the leveling of the coating film is poor. (Related instrument: leveling meter)
⑤ Poor exhaust or improper air flow in the spray booth, causing the paint to fall back on the sprayed surface and cause loss of gloss.
⑥ The ventilation in the drying room is insufficient, and the air in the low-temperature drying room is polluted. (Related instrument: oven)
⑦ Polish the coating that can be polished before it is completely dry.
⑧The coating should be dried under low temperature, high humidity and lack of ventilation.
(3) Preventive measures
①Correctly use high-quality diluent to make the volatilization speed of the diluent appropriate.
②Smoothing and cleaning the surface before painting is the basis for ensuring gloss. (Related instrument: gloss meter)
③ Correctly master the spraying technology, adjust the spraying pressure and the construction viscosity of the paint. (Related instrument: viscometer)
④ Make sure that the exhaust of the spray booth is proper, warm and dry.
⑤Apply the corresponding back cover paint to eliminate the absorption or uneven absorption of the topcoat on the painted surface.
⑥Pay attention to the spraying sequence to ensure that the sprayed film thickness is uniform and reduce the fall and adhesion of the sprayed paint mist.
⑦ The drying room should be properly ventilated to avoid the accumulation of dirty air in the drying room. If the drying room is directly heated by fuel, the correct fuel should be used.
⑧ Polishing should be carried out after the coating film is completely dry.
(4) Remedy
① After the coating film is completely cured, use polishing to reappear the gloss.
②If it is caused by the paint mist falling back on the surface, let the coating film dry, then polish it with very fine sandpaper, and polish and wax it.
③If the bottom layer is caused by the pollution or roughness of the painted surface, the paint film should be removed, the affected surface should be cleaned and leveled and re-sprayed. Note: The glossiness of the coating film surface is related to the pre-coating treatment and spraying technology, and it is also the real performance of the coating film, which lasts for a long time. The use of car wax to improve gloss is a "false gloss" with a short duration.
