Several major reasons for paint filtration (一)

1.Bubble: the phenomenon that bubbles form on the surface of sintered parts due to the violent discharge of gas. Also called blister, it is a coating defect. Due to the poor permeability and water resistance of the coating film of solvent-based paint, during the outdoor aging process, due to the influence of rain or wet environment, there is water seeping under the coating film, and after vaporization, the impermeable and water-softened coating film swells, forming bubbles. The surface moisture content is high, the ambient humidity is high, the temperature is too high, the putty is poorly sealed, and the interval between layers is not enough.

2.Pinhole: After the coating film is dried, the surface of the paint filter will form pinhole, which is like leather pores. This defect is called pinhole. During the spraying construction, the solvent and air will vaporize quickly and escape from the wet coating film, which will form a small hole. At this time, the wet film has not enough fluidity, which can not level the small hole, leaving a needle-shaped hole. When there is a trace of water in the paint or solvent, pinholes are more likely to occur. The diluent shall be strictly selected to prevent water and other sundries from mixing, and the construction viscosity shall be controlled at the same time to reduce or avoid the appearance of pinholes. But if it is the pinhole problem of water-based paint, it will be the formula problem.
The diluent is added too little, the viscosity of the paint filter is too large, the coating is too thick, the interval between layers is not enough, the static time after the paint is diluted is not enough, and the diluent volatilizes too slowly.

3.Pelleting: the construction environment of spraying filter screen is not clean, the workpiece contains oil, water and dust, the impurities mixed in the coating are not filtered, the painting tools and containers are not clean, the paint is not fully mixed, and the filtering time and standing time are not enough.

4.Shrinkage hole: spray filter screen is also called pit. It refers to the defect of small round pits on the coating film. After the coating is applied, the wet film shrinks during the leveling process, leaving a number of shrinkage holes with different sizes and distribution after drying. This is due to the difference in surface tension between the upper and lower parts of the wet film and poor leveling. It can be solved by adding suitable leveling aids or low surface tension solvents.
The bottom layer is dirty, the workpiece contains oil, water and dust, etc. The bottom layer is too smooth, the grinding is not enough, the construction temperature is too low or the humidity is too high.

5.Underbite: When spraying the filter screen with the second coat of paint, the newly applied paint bites the previously dried film from the substrate. When this happens, the coating will expand, shift, shrink, wrinkle, bulge, or even lose adhesion and fall off. The primer and finish coat are not matched; The solvent solubility of finish paint is too strong; If the primer is not completely dry, it will cause “undercut”.
The primer and finish paint are not matched, the interval between layers is not enough, the bottom layer is not dry, the diluent is too strong, and the coating is too thick at one time.

Post time: Jan-11-2023