Most of the corrosion of metal materials occurs in the atmosphere, which contains corrosive components and corrosive factors such as oxygen, humidity, temperature changes, and pollutants. Salt spray corrosion is a common and most destructive atmospheric corrosion. The corrosion of metal materials by salt spray is mainly caused by the electrochemical reaction of the conductive salt solution infiltrating the metal to form a "low-potential metal-electrolyte solution-high-potential impurity" micro-battery system, electron transfer occurs, and the metal as the anode dissolves. The formation of new compounds, namely corrosives. Chloride ions play a major role in the process of salt spray corrosion damage. It has strong penetrating power and easily penetrates the metal oxide layer into the metal, destroying the passivation of the metal. At the same time, the chloride ion has a small hydration energy. It is easily adsorbed on the surface of the metal, replacing the oxygen in the oxide layer that protects the metal, and destroying the metal. So how can the salt spray resistance of the coating be improved?
1. Increase the crosslinking density of the system.
The cross-linking modification performance significantly improves the coating film performance. After the crosslinking density of the coating system is increased, the water and oxygen transmission rate can be greatly reduced, and the corrosion of the substrate can be effectively slowed down. At the same time, after the crosslinking density is increased, the glass transition temperature of the coating film is increased.
2.Increase the color
The pigment-to-base ratio is the ratio of the pigment to the resin in the coating. If the pigment-to-base ratio is high, the base polymer cannot fully cover the surface of the pigment and filler, which reduces the overall performance of the coating. A low pigment-to-base ratio will increase the cost of the coating. The compactness of the film affects the penetration of salt spray. As the ratio of pigment to base increases, the blistering of the coating gradually decreases, while the rust gradually increases, and the flexibility and impact resistance gradually decrease. This is because under normal circumstances, the amount of polymer resin base material in the coating is sufficient to cover the pigment and filler particles in the coating. At this time, the coating is a continuous dense film, and when the volume of the pigment and filler in the coating film is When it is increased to a certain value and the resin base material is not enough to cover these pigment and filler particles, the various properties of the coating film will have a sudden change. It is recommended to determine the critical volume pigment concentration according to the oil absorption of the pigment and filler.