Defect Analysis of Whitening Phenomenon in Coating Construction Process

After the coating is cured, the coating film appears white mist, cloudy, and seriously loses gloss. Micropores and silk lines appear on the film , no expected gloss, and the mechanical properties of the coating are reduced, but sometimes they will return to their original appearance during the curing process . This is due to the condensation of water vapor in the air on the wet coating surface.

cause:

(1) Using the wrong paint;

(2) The air temperature in the roller coating room is too low and the humidity is too high (above 80%);

(3) The diluent evaporates too fast, exceeding the ratio of the solvent diluted by water, or the heat of the coating surface is taken away by the volatilization of the solvent during the curing process, so that the air temperature on the coating surface drops below " zero point ", at this time Moisture in the air condenses and infiltrates into the interior or the paint and thinner contain water. During the curing process, when the water evaporates at the end, the gaps are replaced by air to form a layer of porous and dull coating;

(4) Solvents, pigments, and fillers in the paint production process contain water, or accidentally enter water during the stirring before the paint is put on the machine;

(5) Excessive dilution, the paint film is too thin, and the resin cannot effectively bond pigments and fillers;

(6) The surface of the substrate is too cold or covered with water mist, resulting in poor film formation;

Method of exclusion:

(1) Choose the right paint;

(2) Follow the construction specifications and do not over-dilute;

(3) The construction humidity of the coating should be controlled above 80%. The ambient temperature of the roller coating room should be 3°C higher than the dew point temperature. cold;

(4) The diluent and compressed air used should be checked to see if they are pure, to confirm that they are cured without moisture, and to check the liquid supply system of the paint to ensure that the pneumatic tube does not leak;

(5) Make sure that the surface temperature of the substrate should be higher than the ambient temperature.