Affected by the presence of foreign matter (such as oil, water, silicone, etc.) on the surface of the object to be coated or mixed into the paint, the paint cannot be evenly attached, shrinkage occurs and the surface to be coated is exposed, or the phenomenon that the coating film is uneven is called Shrinkage cavity series coating disadvantages. The reasons and phenomena are quite different. They are one of the common paint film ills.
1. Shrink
The large and irregular exposed area is called shrinkage.
2. Shrinkage cavity
The ones that are circular (mostly 0.1~2mm in diameter) are called shrinkage cavities; the coating film is produced by water backlash
Dimples are called water shrinkage cavities.
3. Oil shrinkage cavity
The depressions in the coating film produced by the backwash of oil are called oil shrinkage craters.
4. Fisheye
The depressions caused by the washback substances in the paint or from the outside, and those with particles in the round holes are called "fish eyes".
5. Electrophoretic shrinkage
During electrophoresis or after electrophoresis, holes with a diameter of 1 to 5mm produced by shrinkage substances (oil, silicone oil, etc.) are called electrophoretic shrinkage cavities.
6. Pit, depression or four pits, pockmarks
On the surface of the coating film, there are pits like craters, which do not expose the coated surface, with a diameter of 0.5~3mm. Such defects are called pits, depressions or pits, and pits.
Etiology
1) The surface to be coated is contaminated by water, wax, polish, dust, silicone, oil or lubricating oil, etc. exposed to soap, detergent, or
Residual stain pollution of material surface treatment agent.
2) Poor cleanliness of paint mixing and spraying tools and equipment and unclean air pipes allow harmful foreign matter to be mixed into the paint.
3) After the surface preparation is completed, the painted surface or wet paint film is polluted by the following when spraying.
a. Falling on the paint mist of other different paints, especially the dry spray or paint mist of the paint containing anti-shrinkage agent (silicone oil type).
b. Oil contamination in compressed air.
c. Dried polishing residue.
d. Spray can release vehicle.
4) The air in the painting environment is not clean: no dust, paint mist, silicon cave, grinding dust, wax mist dust, etc., or dust from neighboring factories
Air contamination of prepared painted or wet painted surfaces.
5) Painting tools, overalls, gloves, etc. are not clean.
6) The surface tension of the coating used is high, the leveling and air bubble release are poor, and the coating itself has poor shrinkage resistance or mixed with
foreign body.
prevention
1) Before carrying out any work, it should be determined that the surface has been effectively cleaned.
2) Any work involving silicone resin products should be carried out in a building separate from the painting workshop.
3) Make sure the compressed air is clean, free of oil and water.
4) Ensure that the painting environment is clean, and there should be no dust, oil mist and paint mist floating in the air.
5) Equipment, tools, hoses and auxiliary materials for production in the painting workshop must not contain shrinkage cavities in the paint.
harmful substances, especially organosilicon compounds.
6) It is strictly forbidden to touch the painted surface with bare hands, dirty gloves and dirty rags.
7) Choose a paint with low sensitivity to shrinkage cavities. When spraying on the old paint layer, it should be fully sanded with sandpaper and wiped clean.
(In the case of slight shrinkage, it will be improved by using multiple thin sprays.
remedy
Remove affected paint film and respray.
1) Choose an air hose suitable for painting. Contamination with organosilicon compounds may come from non-specially manufactured tubing. New paint or gas lines should be effectively cleaned before use.
2) Do not use silicone-containing additives to prevent shrinkage and shrinkage. Such additives will pollute the painting workshop and similar work, and may also cause poor adhesion in the future.
