New environmental protection technology of metal surface treatment -- silanization treatment


[Abstract] silanization is a process of surface treatment of metal or nonmetal materials with organosilane aqueous solution as the main component. In the coating industry, phosphating is the main surface treatment before coating. Compared with traditional phosphating, silane treatment has the advantages of energy saving, environmental protection and cost reduction. In this paper, the characteristics, basic principle and construction technology of silylation treatment are described.


[Key words] silane; surface treatment; phosphating
Silane treatment is a process of surface treatment of metal or non-metal materials with organosilane as the main raw material. Compared with traditional phosphating, silane treatment has the following advantages: no harmful heavy metal ions, no phosphorus, no heating. There is no sediment in the silane treatment process, the treatment time is short and the control is simple. The treatment steps are few, the surface adjustment process can be omitted, and the tank liquid can be reused. Effectively improve the adhesion of paint to substrate. It can be used for CO processing of iron plate, galvanized plate, aluminum plate and other base materials
0 Fundamentals
Silane contains two different chemical functional groups. One end can react with the hydroxyl group on the surface of inorganic materials (such as glass fiber, silicate, metal and oxide) to form covalent bond; the other end can form covalent bond with resin, so that the two materials with different properties can be combined to improve the performance of composite materials. Silylation can be described as a four step reaction model: (1) three Si or groups connected with silicon are hydrolyzed to Si Oh; (2) Si Oh is dehydrated to form siloxane containing Si Oh; (3) Si Oh in the oligomer forms hydrogen bond with Oh on the surface of the substrate; (4) in the process of heating and curing, a covalent bond is formed with the substrate along with dehydration reaction, but on the interface, silicon hydroxyl and base of silane There is only one bond on the surface of the material, and the remaining two Si Oh are condensed or free with Si Oh in other silanes.
In order to shorten the curing time required for the field use of the treatment agent, the first step before the use of the silane treatment agent is to carry out a certain concentration of pre hydrolysis.
① hydrolysis reaction:
In the process of hydrolysis, condensation reaction can not be avoided between silanes to form oligosiloxanes. Too little oligosiloxane will prolong the curing time of silane treatment agent on site, which will affect the production efficiency; too much oligosiloxane will make the treatment agent turbid or even precipitated, reduce the stability of the treatment agent and affect the treatment quality.


② condensation reaction:


The film-forming reaction is the key step to affect the quality of silylation. The quality of the film-forming reaction directly affects the corrosion resistance of the film and the adhesion of the film. Therefore, it is particularly important to control the pH value and other parameters of the treatment agent. Moreover, higher requirements are put forward for the surface state of the workpiece before silylation: 1. Complete oil removal; 2. The workpiece entering the silane tank shall not contain metal chips or other impurities; 3. Deionized water is the best way for the pre-treatment of silylation.


③ film forming reaction:


Where R is alkyl substituent and me is metal substrate


The metal silanized film after film formation is mainly composed of two parts: one is on the metal surface, the silane treatment agent forms reaction ③ products through film formation reaction, the other is to form a large number of reaction ② products through condensation reaction, thus forming a complete silane film. The micro model of film formation state on the metal surface can be described as the structure shown in Figure 1.