The hole is formed by the substrate on the surface of the film to form a corrosion channel. The appearance of pinprick like pores on the surface of the coating, or larger pores like leather pores, is called pockmarks. It is due to the air and sea in the
hu'ao coating, but the air and fish cracks, and can not be pushed by leveling before rounding
The causes are as follows
(1) The humidity of the construction environment is too high, and there are water, oil or other impure substances left on the surface of the steel strip, which are not cleaned up. (2) the viscosity of the coating is too high, and the tightness and covering power of the coating itself are poor（ 3) When the coating is produced, it carries air and moisture, or the storage temperature is too low;
(4) The coating is stirred intensely for a long time, and air is mixed into the coating to generate numerous bubbles;
(5) The coating speed of roller coating machine is too fast, the coating is too thick, and the solvent is wrapped in the coating and difficult to volatilize;
(6) The curing temperature of the coating at the initial stage of solvent volatilization is too high. Because the solvent volatilizes too fast, the film itself has no time to make up for the holes, forming a series of small holes, namely pinholes.
(1) the paint should be stored at suitable temperature after entering the warehouse, so as to prevent the occurrence of defects such as precipitation, crusts and gels caused by low temperature.
(2) The viscosity should be adjusted properly, and the mixing time should be avoided too long;
(2) Ensure that the relative humidity of the roller coating chamber is not more than 85%, and ensure that the surface of the steel strip is clean and free from oil, water and contamination（ 3) The roller coating speed should be controlled according to the process requirements, the first coating should not be too thick, and the wet film thickness should not exceed 40 pm（ 4) The temperature of curing furnace should be set from low temperature to high temperature in the direction of population to outlet, so that the solvent can be fully volatilized.