Preparation And Characterization Of Lithium Silicate Base Organic-Inorganic Composite Coating

Using inorganic material such as silicate, silica sol, etc as film forming matters, water-borne inorganic coatings, which posses the advantage of excellent solvent resistance, weather resistance and relatively high hardness. In addition, water is used as the solvent of the coating, which makes it cleaner and safer during transporting and coating. Therefore, water-borne inorganic coatings have been widely used in architectural coatings and anticorrosion coatings. However, it also has the natural disadvantages of inorganic material, including poor properties of film forming, brittleness and easiness to shrinking and cracking, which greatly limits the popularization and use of water-borne inorganic coatings. In this paper, the organic-inorganic composite coatings are prepared by using lithium silicate as mainly film forming matter, and the problem of discontinuous film forming, cracking and powder falling of the lithium silicate coating are successfully solved.(1) Li2SiO3-KH560-PDMS organic-inorganic composite sols are prepared by sol-gel method, with lithium silicate as inorganic component, KH560 as coupling agent, polydimethylsiloxane as organic precursor. The sols are then coated on the surface of sandblasting steel sheet to prepare organic-inorganic composite coating.(2) The effects of the amount of water added on the hydrolysis process of lithium silicate and the content of KH560 on the the stability of sol, and the content of PDMS on the hydrophobicity of the coating, are all studied. The result of test and analysis show that the KH560 hydrolyze in lithium silicate aqueous solution, generating hydroxyl and glycidyl, and then polymerized with PDMS, which increases the amount of hydroxyl and hydrophilicity of PDMS. When the content of KH560 reaches a certain value, the system form a stable composite sol. PDMS is combined to lithium silicate through the coupling role of KH560. In the meanwhile the hydrophobic functional group Si-CH3 are introduced into the coating structure, increasing the hydrophobic properties of the composite coating. With the increasing content of PDMS, the contact angle of the coating increases. The maximum contact angle of the coating reaches 109°, higher 24.5° than that contains no PDMS.(3) Inorganic-organic composite emulsions are prepared by adding styrene acrylic emulsion into the lithium silicate in the method of mechanical blending. The research shows that, appropriate amount of organic polymer emulsion added can greatly improve the film forming property and anti-corrosion property of lithium silicate. The results of infrared analysis showed that the chemical binding was formed between lithium silicate and styrene acrylic. The glossiness and flexibility of the coating improves while the the hardness and thermal stability decreases with the increasing content of styrene acrylate emulsion. Salt spray corrosion test results show that there is no obviously positive correlation between anti-corrosion properties of the coating and adding amount of styrene acrylic emulsion due to the organic film is less dense than inorganic film. The zinc rich coatings are prepared by mixing the composite emulsion of good comprehensive properties with zinc powder by proportion. The test results show that the zinc rich coatings posses the excellent mechanical properties and anti-corrosion performance, which can be used as heavy-duty anti-corrosive coating.