Preparation Of Environmentally Friendly Water-based Coatings

Waterborne coating refers to an environmentally friendly coating that primarily use water as the solvent to disperse the resin. This kind of coating has much more advantages than solvent borne coating, such as reducing VOC emissions during application, improving worker safety and comfort, reducing risk of fire, and are easier to clean up (creating less hazardous residues). Especially in recent years, the price of oil coatings has been forced to raise sharply because the price of crude oil has greatly jumped up. This, to a certain extent, will drive up the development of waterborn coatings. The content of this paper were disparted into two segments. The first part was two-component waterborne polyurethane coatings and the second part was waterbased over-rust anti-rusting coating, conducting studies as follows:(1) Several environmental friendly catalysts have been used in the preparation of2K waterborne polyurethane. It was found that organic bismuth/zinc composite catalyst had the best performance from the result of fourier transform infrared (FTIR), electrochemical polarization curves and the change of the properties of polyurethane coatings. The reaction dynamics of2K waterborne polyurethane has been studied by NCO titration method with organic bismuth/zinc composite as catalyst. The results further revealed that the existence of organic bismuth/zinc composite catalyst can efficiently reduce the activation energy of the reaction between NCO and OH, accelerate the formation of cross-linking structure and improve corrosion resistance property, a reasonable coating pot-life and tack-free time can be achieved in the presence of0.25%organic bismuth/zinc composite catalyst.(2) A polyester intermediate was synthesized using5-sulfoisophthalic acid monosodium salt (5-SSIPA) and neopentyl glycol (NPG) as materials, and then used to prepare polyester polyol dispersion with polycarboxylic acids, polyols and CARDURA E10. The structure and the stability of the product were characterized by FTIR and laser particle size analyzer. The effect of5-SSIPA/NPG on the properties of the polyester intermediate and the influences of sythetic process, catalytic agent, amount of polyester intermediate and CARDURA E10on the reaction system were investigated. The experiment results show that the reaction time could be shortened remarkably by the choice of suitable synthetic process or the addition of catalyst; The dispersion showed a better stability when12wt%intermediate was used; In addtion, the viscosity of polymer would be reduced, the particle size of dispersion would be minished and the acid, alkali and water resistance of the film would be improved by introducing CARDURA E10.(3) A waterborn rust converter was synthesized by heating gallic acid (GA) with maleic anhydride (MA) and investigated by electrochemical tests, gel permeation chromatography (GPC), FTIR, scanning electron microscopy (SEM) equiped with energy dispersive X-ray (EDX) and X-ray photoelectron spectroscopy (XPS), respectively. The results demonstrated that the best ratio of GA and MA should be1.6mol:1mol. MA characteristic-HC=CH-bonds and multi-phenolic-hydroxyl groups were exists on the macromolecular chain of the rust converter. The multi-phenolic-hydroxyl groups of the rust converter could chelate with iron oxides by forming Fe-O-C bonds and generated a homogeneous layer on the steel surface.(4) An acrylic modified alkyd resin dispersion was prepared at first. Then added the rust converter synthesized by ourselves which was contained active groups into the dispersion via two approaches to obtain a waterborne rust conversion emulsion. The optimal route and the most proper amount of rust converter had been established by adherence tests and electrochemical tests. The results demonstrated that the corrosion resistance and the adhesion of coatings would be better when used the second method to prepare the rust conversion emulsion; The stability of the emulsion and the effectiveness of converting rust would be better when the amount of rust converter was2.6%-3.5%.