Current status and technology of environmentally friendly silane metal surface treatment agent

I. Purpose and significance

With the development of industries such as automobiles, airplanes, ships, and home appliances, the requirements for corrosion resistance, high temperature resistance, wear, oxidation resistance, fatigue resistance, radiation resistance, electrical conductivity, magnetic permeability, insulation, decoration, etc. of metal parts are more extensive. Promote the rapid development of metal surface treatment technology.

The main method used for metal surface treatment in China is the phosphating method. Due to the high energy consumption, high pollution and high cost of phosphating, it is gradually replaced by silane surface treatment technology. The silane treatment technology is constantly being researched, matured and applied. Compared with the traditional phosphating method, the silane treatment has the following advantages: no harmful heavy metal ions, no phosphorus, no need for heating and no sedimentation during the silane treatment process, short processing time and simple control; the surface adjustment process can be omitted, and the bath can be omitted. Reuse; effectively improve the adhesion of the coating to the substrate; collinear treatment of iron, galvanized, aluminum and other substrates. Therefore, the new environmentally friendly, energy-saving, low-emission, low-cost silane metal surface treatment technology has become the focus of research at home and abroad.

The silane coupling agent is a class of silicon-containing compounds having an organic functional group. Its molecular formula can be represented by the general formula Y(CH2)nSiX3, where n=0-3; X is usually a chloro group, a methoxy group, an ethoxy group, a methoxyethoxy group, an acetoxy group, etc., and these groups are hydrolyzed. That is, a silanol group is formed and combined with an inorganic substance to form a siloxane. Y is a vinyl group, an amino group, an epoxy group, a methacryloxy group, a thiol group or a ureido group, and these organic functional groups can be reacted with an organic substance. When the silicon functional group is hydrolyzed, then Si-X is converted to Si-OH and HX is by-produced. Si-OH can be condensed and dehydrated with Si-OH in other molecules or Si-OH on the surface of the substrate to be treated to form Si-O-Si bond, and even with certain oxides (such as alumina, oxidation). Iron, tin oxide, zirconium oxide, titanium oxide, nickel oxide, etc. react to form a stable Si-O bond, thereby allowing the silane to be bonded to the inorganic or metal. By utilizing this property of silane, it can be applied to metal rust and oxidation prevention, and the metal such as Mg, Al, Cr, Fe, Zn can be greatly improved in corrosion resistance after being treated with silane.

The silane treatment technology utilizes the special properties of silane coupling agents. The film formation process on the metal surface is: (1) the silane coupling agent is hydrolyzed to form a silanol having a hydrophobic and hydrophilic structure; (2) the ordered oligomer is formed by intermolecular dehydration condensation; (3) The oligomer forms a hydrogen bond with a hydroxyl group on the surface of the metal; (4) due to intramolecular dehydration, a part of the covalent bond is formed, and is closely arranged on the metal surface to form a dense silane film.

Second, the status quo at home and abroad

Silane treatment technology can be effectively used for the protection of iron, aluminum, copper, zinc, magnesium and alloys.

Zhu Danqing et al. studied the metal surface silane treatment technology and the functional properties after treatment. Neutral salt spray, copper accelerated acetate spray, galvanic corrosion, atmospheric exposure and seawater immersion tests were carried out. The results show that the metal surface silane treatment technology can replace the phosphating and chromizing treatment before painting, and the technology has the characteristics of normal temperature treatment, non-toxicity and non-polluting, and can be widely used in the field of pre-coating treatment and anti-corrosion.

Zhang Wei et al. used the KH-550 silane solution to silanize the AZ31 magnesium alloy test piece, and evaluated by immersion and electrochemical testing techniques, 8% silane solution was dip coated for 50 s and dried at 100 ° C for 0.5 h. The interface between the silane film layer and the magnesium alloy substrate is better, and the corrosion of the magnesium alloy is well suppressed, and the corrosion resistance is improved.

Harbin Institute of Chemical Technology has selected a new type of metal surface protection silanization reagent, vinyl trichlorosilane, which is hydrolyzed in a mixed solvent of water and alcohol. The hydrolysis process is stable and the content of silanol can be ensured. . Through water resistance test, salt water immersion test, acid and alkali resistance test, 3% CuSO4 solution pitting test results show that the new metal surface protection silanization treatment reagent water resistance, salt water resistance, acid and alkali resistance, CuSO4 resistant solution The pitting performance is good, and it has the advantages of environmental protection and low cost. The corrosion resistance of the silane-treated metal surface is superior to the traditional phosphating technology.

VanOoij et al. conducted a series of studies on the surface of galvanized steel on hot-dip galvanized steel and aluminum alloy. The effects of single silane on the protective properties of aluminum alloy and hot-dip galvanized steel were studied. Then, nano-additives and rare earth modification technology were used to study silane. The influence of the film layer on its mechanical properties and corrosion resistance finally led to a more applicable mixed silane treatment.

MLZheludkevich used electrochemical impedance test (EIS) to study the corrosion resistance and self-healing properties of aluminum alloy films. It was found that the film layer has self-healing properties. The results of scanning oscillating electrode technology (SVET) test further confirmed the self-reduction of the film layer. The more it is.

F.Zucchi et al. studied the protective properties of the siloxane film on the copper surface, and found that the silane containing thiol bond has good adhesion to the copper surface, and can significantly inhibit the surface anode reaction, thereby effectively improving the corrosion resistance of copper.