Preparation And Scratch Resistant Properties Of Waterborne Nanocomposite Coating

Epoxy coatings is one of the most widely used protective coatings because of its excellent chemical resistance,high strength and strong adhesion to various kinds of substrates.However,it is hard to resist scratch and mar for epoxy because of its brittleness.As the economy develops and living standard rises,the protecting and decorating function of coatings is considered to be more and more important by coatings manufactures and customers in some fields.During the daily use of cars, floors or furniture,their surface could be easily scratched by sands,washing,or accidental scratch,which causes nicks and loss of gloss,and badly affect their appearance,so that development of scratch resistant coatings with high transparency and gloss is of great importance.Embedding with nano-sized inorganic particles has been proved as an efficient way to enhance the scractch resistance.Among all the alternatives,nano-silica particles are most frequently used for fabrication of transparent scratch and mar resistant coatings,due to its high hardness and relatively low refractive index. However,almost all the systems are involving the introduction of nano-silica into solvent-based epoxy coatings.With increasing environmental restriction,waterborne epoxy coatings are being developed quickly in recent years,therefore,how to improve the scratch and mar resistances of waterborne epoxy coatings is an urgent theme.In this study,inorganic nanoparticles were used to blend with waterborne epoxy clearcoat to prepare scratch resistant coating with high transparency and gloss.First, different kinds of nanoparticles(SiO₂,Al2O₃) were picked out to prepare nanocomposite coatings by direct blending,and multi-finger scratch tester,automatic scratch tester,gloss tester,and UV-Vis were used to characterize the concerned properties of the coatings.It was found that ST-C SiO₂ could improve the scratch resistance in some extent,and keep higher gloss and transparency than the other kinds of nanoparticles did.So that it was considered as the most promising alternative and would be further studied.In the further study,the surface of ST-C SiO₂ nanoparticles were treated by 3-glycidoxypropyl-trimethoxysilane(GPTMS) in the medium of water/ethanol mixture.TEM,FT-IR and TGA analysis showed that GPTMS was effectively grafted onto the nanoparticle surface and SiO₂ particles could be well dispersed in the water phase.It was found that the surface treated SiO₂ nanoparticles performed more significant improvement on the scratch resistant property and less negative effect on the transparency and gloss.The effects of SiO₂ content and the amount of GPTMS used on the scratch and mar resistance,transparency and gloss of the waterborne epoxy coating were also investigated.And the nanocomposite coatings with 2 wt%of SiO₂ and 30 wt%of GPTMS(based on the total weight of SiO₂).Moreover, nano-scratch test was performed to characterize the mechanical property of the nanocomposite coating on the micro-scale.It proved that the scratch resistance was improved not only on the macro-scale,but also on the micro-scale.