Surface stress problems and solutions in coating construction

"China Paint Online News Information" paint construction, some leveling is very good, and some will occur a variety of ills, most of these phenomena and surface stress related.
(1) leveling the
the flow leveling force comes from the surface pressure, the leveling can reduce the surface area of the liquid; At the thin part of the coating, the gas evaporates relatively quickly, the surface pressure rises rapidly, and the coating at the surrounding height tends to spread to it. The coating should have sufficient flow time before curing to ensure leveling.
thick edge phenomenon: the edge surface of the coating is larger, volatile faster, so the temperature drops, the surface pressure increases, the nearby coating automatically spread to it, thus forming the phenomenon of thickening the edge.
(2) Shrinking phenomenon
If a drop of low surface pressure liquid is dropped on the wet coating, such as solvents or dirt (e.g. oil) dropped after condensation in the oven, the surface pressure of the adjacent coating can be reduced and spread to the surrounding surface with higher pressure, thus forming a crater phenomenon, which is called a shrink hole.
(3) orange peel phenomenon
the phenomenon of orange peel refers to the coating surface slightly uneven, shaped like orange peel situation. There are many reasons for the formation of orange peel, for example, when spraying, the distance control of the spray gun is not good or the coating and solvent cooperation is not good, atomization is not good, etc. can cause orange peel. Spraying, atomized droplets after a long distance, solvent volatilization a lot, fell on the wet film, because of this drop concentration is high, the surface strength is large, the surrounding paint will automatically spread to this droplet, so the formation of a protrusion. The orange peel phenomenon is also related to the so-called Bernal vortex.
(4) Bernal vortex
coating in the drying process, with the evaporation of solvents, surface concentration increased, temperature decreased, surface tension increased. Because the surface and the bottom surface are different in surface pressure, a great push is generated, causing the coating to move from the bottom layer to the upper layer, which causes a local vortex to form the so-called Benardcell vortex. The origin of the vortex is like a crater, which emits a lower coating outwards, and these surface-low-profile coatings spread to the surface with high pressure on the surrounding surface, forming a bulge section. And the wet film forms a rule hexagonal shape, the center and edge pigment concentration will be different. If the paint leveling is not good, leave a bumpy orange peel after the paint film is dry.
(5) flowering and floating phenomenon
hair flower refers to the uneven distribution of pigments in the paint film after construction, so that the appearance of a flower spot (cellular stripes). Floating color refers to the paint film surface color is different from the bottom layer, after construction, the paint film color is uniform change, which is caused by different pigments in the paint film layer uneven distribution. The causes of flowering and floating color are complex, but the causes of uneven pigment distribution (separation) are related to the benar vortex nest formed by solvent evaporation: when the paint movement also drives the suspension of pigment particles movement, if the pigment size, specific gravity is different, this can cause pigment redebution, the result is a pigment on the surface or some parts of the surface of a higher concentration.
(6) leveling agent
In order to overcome the shortcomings of the paint film in the construction process, the paint is often added leveling agent to help the paint film before drying to complete the leveling process. The function of LB-203, a leveling agent of Jinan good decorator chemical industry, is mainly to reduce the surface pressure of coatings to eliminate all kinds of ills; adjust the speed of solvent volatility, improve mobility and extend the leveling time; The formation of a single molecular layer on the surface of the lacquer film to provide uniform low surface tension can alleviate similar problems of latex paint.