Preparation Of Nanosilica Hybrid Materials And Their Properties In UV Curable Coatings

It is well known that UV curable technology has been applied in coatings because of its characteristics of economy, efficiency, ecology, energy and enabling. The cured film of pure organic coating has poor mechanical properties, such as thermal stability, hardness, resistance to scratching and abrasion, therefore, preparation of hybrid UV curable coating by adding inorganic compounds into the coatings has drawn considerable attention in recent years.Nanosilca, easy to make and low cost, play an important role in UV coatings. However, nanosilica have high specific surface area and hydrophilic property so that they can not disperse evenly in organic material, leading to their serious aggregation in coatings. Therefore, the mechanical properties can not be improved greatly, otherwish, the viscosity of coatings increases and photopolymerization rate of coatings decreases. To dissolve these problems, nanosilica must be modified before it is used in UV curable coating.In this study,nanosilica hybrid materials were prepared by chemical modification and/or sol-gel method. The main modification results were as follows:1. Nanosilica hybrid materials were prepared by esterifying the nanosilica with hydoxyethyl acrylate in the presence of p-toluenesulfionic acid. The grafting percentage based on nanosilica was 15.6%.2. Silica hybrid nanoparticles with tertiary amine structure were prepared by reaction of nanosilica with isophorone diisocyanate, then the nanosilica bearing isocyanate group reacted with N,N-di(3-propionic acid,1,4,7-trimethyl-3,6- dioxaoctane-8-yl acrylate, ester)ethanolamine synthesized from tripropylene glycol diacrylate and ethanolamine. The grafting percentage based on nanosilica was 105%.3. Nanosilica hybrid materials with nanosilica as node, isophorone diisocyanate and polypropylene glycol as link and acrylate as terminal group were prepared by reaction the nanosilica with isophorone disocyanate, then extending chain with polypropylene glycol in proportion to the mole of NCO on the surface of silica, further terminating the left NCO groups with hydoxyethyl acrylate. The grafting percentage based on silica could be up to 92.2%.4. Nanosilica/polyurethane acrylate prepolymer was prepared by in-suit reaction of nanosilica with isophorone disocyanate, polypropylene glycol and hydoxyethyl acrylate.5. Nanosilica was modified with 3-aminopropyltriethoxysilane, then reacted with trimethylpropane triacrylate to prepare silica hybrid nanoparticles with tertiary amine moiety. The percentage of grafting for silica was up to 22.6%.6. Nanosilica/acrylate hybrid prepolymer with amine structure was prepared by sol-gel of Michael addition product synthesized from 3-aminopropyl triethoxysilane and tripropylene glycol diacrylate.7. By sol-gel methold, nanosilica hybrid materials containing phosphorus were prepared by tetraethyl orthosilicate and acrylic acid,3-(triethoxysilyl) propyl ester containing phosphorus prepared from 3-aminopropyltriethoxysilane and acrylate containing phosphorus.The preparations were characterized by Fourier transform infrared spectrometry (FT-IR), 1H nuclear magnetic resonance (1H NMR), thermo gravimetric analysis (TGA) and so on. Applied in UV curable coatings, the effects of nanosilica hybrid materials on the photopolymerization rate and viscosity of coatings were studied. The effects of nanosilica hybrid materials on mechanical properties of cured films were also discussed by determining adhesion, pencil hardness, abrasion resistance and so on.It is found that coatings with silica hybrid materials had lower viscosities and faster curing kinetics of coatings than the coatings with unmodified nanosilica, meanwhile, the cured films with nanosilica hybrid materials had better properties than organic UV curable coatings or the coatings with unmodified silica. Nanosilica hybrid materials with amine structure increased the curing rate of coatings and nanosilica hybrid materials containing phosphorus improved the adhesion properties of coatings; All the silica hybrid materials possessed uniquue properties in UV coatings because the presence of reactive groups facilitated chemical attachment of the nanomaterials to crosslink with organic matrix, resulting in an inorganic phase interconnection with the polymer matrix after UV curing. Thereby, the mechanical properties of films were improved, such as thermal stability, hardness and resistance to scratching and abrasion.