| UV curing depends on photoinitiator to absorb UV radiation and is rarely used incomplicated substrates, filled systems and thick coatings because there are shadows in thesesituations that lead to incompletely curing. To overcome the intrinsic defect of UV curing,dual curing systems are being exploited. Epoxy acrylate with siloxane can be cross-linkedeither by UV radiation or moisture. The UV-moisture dual curing ensures the cross-linking ofthe oligomers in the shadows and the coatings can exhibit excellent properties after dualcuring.In this article the effects of fillers on the penetration of UV radiation in filled epoxyacrylate have been investigated with UV-vis spectrometer. The UV curing behaviors wereanalyzed with FT-IR spectrometer and gel content. The features of the fillers to UV curingwere revealed. UV-moisture dually curable epoxy acrylates have been synthesized byattaching siloxane groups to epoxy acrylate through the reaction of hydroxyls in epoxyacrylate with TEOS. The structures of the siloxane modified epoxy acrylate were characterizedwith FT-IR；the UV and UV-moisturre dual curing behaviors of the modified epoxy acrylateshave been investigated. The properties of the modified epoxy acrylates were compared afterUV and UV-moisture dual curing. Fillers were added to the UV-moisture dually curable resins,the gel content and properties of the UV and UV-moisture dually cured coatings wereexamined. The effects of moisture curing on the properties of filled resins have been studied.Silicon dioxide, pulvistalci, calcium carbonate and titanium dioxide have significantimpact on the UV curing of epoxy acrylate. The extents of the negative impact are related tothe transmission and refractive index of the fillers. The order of the fillers in terms of curingimpact to epoxy acrylate is titanium dioxide> calcium carbonate> pulvistalci> silicondioxide. The filler size has impact on UV curing also. Of calcium carbonate and silicondioxide fillers with diameters of1.0,5.0and10μm, respectivelly, the fillers with diameter of5.0μm exhibited least impact on UV curing. The impact increases with increasing fillercontent. But for silicon dioxide, the gel content of the UV cured epoxy acrylate with5phr and 30phr silicon dioxide could be96%and92%, respectively, decreasing2%and6%only,compared to pure epoxy acrylate.With tetraethyl ammonium bromide as catalyst, epoxy acrylate with excellent transparentand storage stability can be synthesized from epoxy resin and acrylic acid. TEOS is easy toreact with the hydroxyls of epoxy acrylate. After the hydroxyls were capped with siloxane, theviscosity of the epoxy acrylate decreased. More siloxanes attached, lower the viscosity. As allthe hydroxyls of epoxy acrylate were capped the viscosity decreased about80%. Thesiloxane modified epoxy acrylates all exhibited the activity of UV and moisture curing. Themax UV-curing rate of the modified epoxy acrylate decreased slightly with increasingsiloxane content whereas the final conversion of C=C increased. Upon moisture curing for7days the pendulum hardness of UV cured epoxy acrylate with siloxane increased from0.601to0.756.After moisture curing the wear resistance, thermal stability, water contact angle andadhesion of the UV cured siloxane modified epoxy acrylate increased. As the mole ratio ofTEOS/OH was in1:0.5~0.8, the Tg of dually cured siloxane modified epoxy acrylateincreased about5℃, the pendulum hardness increased from0.766to0.778, compared to UVcured pure epoxy acrylate.Calcium carbonate and titanium dioxide have striking impact on UV curing and reducedthe gel content. However, moisture curing could enhance the gel content. For the UV curedsiloxane modified epoxy acrylate with20phr calcium carbonate or titanium dioxide, the gelcontent increased9%and28%, respectively, after moisture cured at room temperature forone week. The pendulum hardness, adhesion and corrosion resistance of the filled resins wereall improved after moisture curing. |
PDF Full Text Request