Defects and solutions of nitro topcoat

Defects caused by nitro topcoat mainly include coarse grain, bottom bite, whitening, pinhole, air bubble, backlight and so on. For the causes and solutions of whitening, pinholes, air bubbles and backlighting, please refer to perchlorethylene topcoat. Here we mainly introduce the causes and solutions of the two defects of coarse grain and bottom bite.

1. Coarse grain

Coarse grains are also called grain protrusions. It means that after the topcoat is sprayed, there are obvious coarse particles (paint mist particles instead of impurities) on the surface of the paint film, which seriously affects the appearance quality. There are two main reasons: one is that the paint is too thick and the spraying air pressure is too small, and the atomization of the sprayed paint mist is not good, resulting in coarse particles; If the angle is not correct (not parallel), such as oblique spraying or spraying distance from top to bottom, or top to bottom, etc., it is easy to cause coarse grains. To solve the problem of coarse particles, one is to pay attention to controlling the spraying viscosity (testing instrument: viscometer) and air pressure; the other is to keep the nozzle of the Spray Gun parallel to the surface of the sprayed object when spraying. In addition, sometimes if the spraying air pressure is too small or the spraying distance is too far, coarse particles will also be produced, so attention should be paid to the construction method.

2. Bite the bottom

The bottoming of the nitro topcoat is mainly caused by poor matching of primers, such as alkyd, epoxy or phenolic primers. If the nitro topcoat is not fully dry, the solvent in the nitro paint It has a strong solvency, and the primer will swell after spraying and cause wrinkles at the bottom. Therefore, when spraying nitro topcoat on the surface of alkyd, epoxy, phenolic and other primers, one should wait for the primer to dry effectively before spraying; The third is to conduct a partial spraying test first, and then fully spray after the test has no bottoming phenomenon. In addition to the above-mentioned defects, the nitro topcoat sometimes has excessive spraying air pressure, too close spraying distance or too slow moving speed of the Spray Gun, which may also cause flow and sag. Therefore, attention should be paid to construction techniques.