Study On UV-curable Epoxy Acrylate/SiO₂(TiO₂) Nanocomposite Coatings

UV curing technology is one technology with advantages such as environmental-friend, efficiency, economy and energy saving. Due to even strict environmental protection policy, this new technology has gained a very rapidly development in the past few years and therefore being widely used in electronic packaging, surface protection of plastic device, flooring and small pitch car refinish. On the other hand, in recent years, nanocomposites become the hot topic for research and development in order to improve the property and comprehensive performance of traditional organic coating. The UV curable nanocomposite coatings combine the advantages of nanomaterials and UV curing technology together and propel the development and application of UV curable coatings greatly. Up to now, some UV curable nanocomposite coatings were reported. However, the types of the coatings are still limited and only a few reports about its preparation and photopolymerization kinetics were available. In this study, three series of nancomposite coatings with SiO₂ and TiO₂ as inorganic phase were prepared. Their UV curing behavior, surface property, thermal property and optical property were investigated as well. All these results are expected to provide some concrete evidence for the development and application of UV curable nanocomposites. The detailed research contents and results are summarized as follows:UV-curable SiO₂ particle nanocomposite coatingsNanosilica sols with various particle size were firstly synthesized by Stober method, and then modified by 3-trimethoxysilylpropyl methacrylate (MPS). After that, the ethanol was evaporated and resulted in condensed nanoslica sol with residual free MPS as the dispersing media. The particle size, viscosity and surface modification situation for the condensed nanosilica sol were characterized as well. The obtained paste-like slurries were then cured under UV irradiation directly after adding the photoinitiator, Irgacure 651. With increasing nanosilica particle size, the photopolymerization rate, final double bond conversion, and tack-free time of nanocomposites increased, while the surface roughness, glass-transition temperature, and UV absorbance of nanocomposites decreased.UV-curable epoxy acrylate/SiO₂ nanocomposite coatingsThe condensed nanosilica (40nm) was also incorporated into epoxy acrylate prepolymer and trimethylolpropane triacrylate (TMPTA) reactive dilute to prepareUV-curable epoxy acrylate/SiO₂ nanocomposite coatings. Effect of the silica content on the UV-cured coatings was investigated. The influence of photoinitiator types, photoinitiator content, UV irradiation intensity, coating thickness, curing with or without oxygen and the impurities such as ethanl, MPS, water, etc. on the UV-curing behavior were also investigated. Finally, the influence of preparing method, namely blending method described above and in situ method in which tetraethyl orthosilicate (TEOS) was directly hydrolyzed and condensed in EA, on the structure and property of nanocomoposites were compared.Improved inorganic particles dispersion state, thermal and optical properties were observed as well. It was also found that embedment of condensed functional nanosilica prepared by sol-gel method can surprisingly accelerate the UV curing process of epoxy acrylate matrix. It's found that the existence of MPS and ethanol can accelerate the curing speed while the presence of water decelerate the curing speed. Finally, the UV curable nanocomposites are more sensitive to the oxygen compared with the pure organic system. During the blending method, TEOS completely hydrolyzed to form nanosilica particles, which were evenly dispersed in the polymer matrix. However, for the in situ method, TEOS only partially hydrolyzed to form inorganic phases intertwisted with organic molecules. The nanocomposites prepared by the in situ method had much higher curing rates than those from the blending method, but the latter had greater glass transition temperatures and UV shielding property than the former because the blending method caused uniformly dispersed nanosilica particles whereas the in situ method did not.UV-curable epoxy acrylate/TiO₂ nanocomposite coatingsNano-TiO₂ slurries with TMPTA or n-butyl acetate as dispersing media were prepared by ball milling methods. Then, these slurries were incorporated into epoxy acrylate matrix to prepare two series of the nanocomposite formulations. In order to further improve the dispersion of titanium dioxide in the formulation, the ultrasonication was used to treat the formulation.The influence of nano-TiO₂ content and volatile organic compound on UV-curing behaviour, surface property, thermal property, optical property and titanium dioxide dispersing state of nanocomposites were investigated.TEM pictures show that the titanium dioxide has a good dispersion both in trimethylolpropane triacrylate and n-butyl acetate after the ball milling. The viscositymeasurement showed that the type of the slurry has a great effect on the viscosity of nanocomposite formulation. In brief, titanium dioxide with TMPTA as dispersion media enhanced the viscosity of formulation, while the titanium dioxide with n-butyl acetate as dispersion media decreased the viscosity.It was found that nano-TiO₂ slurry with different medium had various impacts on the photopolymerization kinetics, tack free time, thermal and optical properties of nanocomposites. The nano-TiO₂ slurry in TMPTA decreased the UV cured rate of the nanocomposites, while the nano-TiO₂ slurry in butyl acetate increased the UV cured rate of the nanocomposites. With the increasing nano-TiO₂ content, this tendency is more obvious. However, the former could more efficiently improve tack free time, thermal stability and UV shielding properties of their nanocomposite coats than the latter.