UV curable acrylate nanocomposites: Properties and applications

Transparent nanocomposites were prepared from nano-sized silica and radiation curable acrylates. To improve the embedding of silica nanoparticles within the acrylate matrix the filler surface was modified by trialkoxysilanes. Instead of an expected monomeric silane grafting polysiloxane structures were anchored on the nanoparticle surface due to acid catalyzed pre-hydrolysis/condensation of trialkoxysilanes. The polysiloxanes structures covering the silica surface were characterized by temperature-programmed oxidation, infrared and multinuclear MAS NMR spectroscopy. MALDI-TOF mass spectroscopy revealed the formation of polysiloxane oligomers with more than 20 monomeric silane units. Ladder-like polysiloxane chains have been proposed and atomic force microscopy were used to visualize the structure of surface-anchored organosilanes. These ladder-like structures are assumed to build up a short range interpenetrating network with polyacrylate chains during UV or EB curing. Due to the organophilic modification of silica nanoparticles reinforced acrylate formulations can contain up to 50 wt.-% nanofiller maintaining satisfactory rheological properties. These formulations can be used as coatings on substrates such as polymer films, paper, metal, wood, engineered wood, etc. After UV/EB curing nanoparticle reinforced polyacrylate coatings are obtained which show markedly improved properties as compared to neat polymers, e.g., increased microhardness and modulus, improved scratch and abrasion resistance, higher gas barriers and temperature resistance. Due to the nano-sized silica filler the cured coatings remain transparent, hazeless and glossy. On a pilot scale unit acrylate nanocomposite coatings are manufactured for roll coating, curtain coating and spray applications. Basic properties of acrylate nanocomposite coatings are described.