Many small needles appear after film drying, what is the reason and how to prevent it?

The pinhole of the paint film refers to the appearance of small circular circles in the paint film, which are shaped like small holes pierced by needles, and the larger ones are like pits. It is usually based on varnish or enamel with a relatively low pigment content. It is easy to appear when applying by dipping, spraying or rolling. The main reason is that there are air bubbles, the wettability of the paint is not good, the moisture content of the wood is high, the putty and primer are not dry, or the paint film is too thin; in addition, the solvent is not properly selected, and the low boiling point solvent is used excessively, such as asphalt paint If it is diluted with gasoline, some resin will precipitate out, and if it is baked, serious pinholes will appear. If the paint is not stirred evenly, the paint film is too thick, the bottom layer is polluted, the temperature of the painting environment is too high, it enters the oven too early, or the distance between the nozzle and the object surface is too far, and the pressure of the compressed air is too high, all of which are prone to pinholes.

Pinhole prevention methods are as follows:

For pinholes in asphalt paint, you can use a blowtorch to warm the surface of the paint film; for cellulose paint, you can add some methylcyclohexanol stearic acid or chlorinated paraffin, and for perchlorethylene paint, you can adjust the volatilization speed of the solvent to prevent pinholes; Adding 100% ethyl cellulose to the ester varnish can prevent pinholes and improve dryness and hardness.