Among various metal pretreatment methods, phosphating treatment is the most widely used method. In industries such as household appliances, bicycles, motorcycles, and automobiles, phosphating treatment is used as a pre-treatment for coating to ensure excellent durability and corrosion resistance. However, phosphating treatment is facing an increasingly severe environmental situation due to the presence of harmful heavy metals such as zinc, nickel, manganese, as well as substances such as phosphorus, nitrogen, and sodium nitrite that limit emissions. The treatment temperature is high, and the treatment of wastewater and waste residue is complex.
Silanization treatment is currently a mature pre-treatment technology that can replace phosphating. Compared with traditional phosphating, silane treatment has several advantages: no harmful heavy metal ions such as nickel, zinc, manganese, etc., no phosphorus, and no need for heating. The silane treatment process is slag free, with short processing time and easy control. The processing steps are few, which can eliminate the need for surface adjustment and passivation processes. The service life of the tank solution is long, and maintenance is simple. Effectively improving the adhesion of paint to substrates, it can process various substrates such as steel plates, galvanized plates, aluminum plates, etc. in parallel. The successful application of silane technology has brought revolutionary changes to phosphating technology. Before the discovery of its excellent anti-corrosion performance, silane was widely used as an adhesive in glass or ceramic reinforced high polymer composite materials. The systematic and comprehensive research on the rust prevention performance of silane began in the early 1990s. Through research, it has been found that silane can be effectively used for corrosion prevention of metals or alloys.
Silane usually exists in the form of hydrolysis in aqueous solution. After hydrolysis, silane is rapidly adsorbed on the metal surface through its SiOH group and MeOH group (Me=metal) on the metal surface through shrinkage reaction. On the one hand, silane forms Si-O-Me covalent bonds at the metal interface. Generally speaking, the interaction force between covalent bonds can reach 700 kj/mol, and the bond between silane and metal is very strong. On the other hand, the remaining silane molecules form a silane film with a Si-O-Si three-dimensional network structure on the metal surface through the condensation reaction between SiOH groups. The silane film is bonded to the subsequent electrophoretic paint or powder coating through cross-linking reaction during the drying process, forming a strong chemical bond. In this way, a stable film structure can be formed between the substrate, silane, and paint through chemical bonds.
The use of silane treatment instead of iron based and zinc based phosphating treatment has begun to be widely applied in ordinary industry. The old production line only needs to clean the phosphating tank and directly put it into silane material for production. Currently, Kemeteer has cooperated with most European and American automotive companies to start testing and application on the automotive production line. Silane pretreatment has replaced traditional surface adjustment, phosphating, and passivation processes, making the process much simpler. After silane treatment, cathodic electrophoresis can be performed directly without drying, and the curing process of silane is completed simultaneously with the baking of electrophoretic paint. Silane coatings produce different visual appearances depending on the substrate being processed. For example, on iron plates, silane coatings are light yellow in color; On galvanized sheet, the silane coating is slightly blue; On aluminum plates, the silane coating is reflective gray.
Silane technology is an excellent technology that is energy-saving, environmentally friendly, and cost-effective. Coating pretreatment technology has undergone a revolutionary change and will quickly replace phosphating technology in the metal surface treatment industry.
