(l) phenomenon
Due to the poor adhesion of the coating, the phenomenon that the coating film falls off due to external force is called coating film peeling. The degree of peeling can be divided into small pieces with a diameter of about 5mm or less called scale peeling; those that fall off in large pieces are called skin peeling; those that can be torn off in pieces are called peeling; the separation between the coating film and the coating film is called layer stripping. In the case of repair coating, it is usually easy to tear off the coating film when removing the masking tape, which is called poor adhesion, as shown in Figure 9-11. Peeling is one of the common defects in the coating of plastic parts.
(2) Reason analysis
①The surface is polluted before painting, such as wax, silicone, resin, oil stain, rust, soap, hard western acid powder, grinding dirt, engine discharge, that is, the surface pretreatment before painting is not effective.
②The surface to be coated is too smooth and the bonding area is small.
③The selected primer does not match the substrate or the old paint surface, and the primer layer is not completely dry.
④ The quality of the diluent is unacceptable (poor solvency).
⑤ Inappropriate paint matching.
⑥During the two-tone spraying process, the sub-sticker covers the first color finish before it is moderately cured. (Related instrument: hiding power paper)
⑦Letting the topcoat dry too long before removing the masking tape.
⑧The weather is humid when spraying the intermediate coating, the diluent volatilizes too quickly or the primer is prepared overnight in a humid environment, forming an invisible water film on the surface of the intermediate coating, and poor adhesion, Peeling defects.
⑨The metal base paint is left for too long after spraying (exceeding the time allowed by the paint manufacturer), spraying varnish, and the adhesion between the finishing layer and the base paint layer becomes poor.
(3) Preventive measures
① Properly polish the surface to be coated (especially the old paint layer should be polished to improve the adhesion of the coating).
②Make sure the surface to be painted is effectively cleaned before painting
③ Select a good matching paint (primer and topcoat).
④Use qualified and good diluent to spray with correct viscosity.
⑤The primer layer should be completely dry before spraying the topcoat or spray the next primer (or topcoat) within the period suggested by the paint factory.
⑥ Cover and remove the cover at the right time and with the correct operation method.
⑦ After drying the moisture on the primer surface, spray the topcoat. (Related instrument: oven)
(4) Remedies
① In severe cases (a large area of the coating film is peeled off from the substrate due to improper surface treatment, and there is a tendency to spread further), remove the coating film to the substrate, and perform surface treatment and spraying again.
②If a small area of the French membrane is separated due to an operation error (improper removal of the cover), re-level the missing step, and polish the edge of the hospital, and then call the law again.
