Stabilisation of nano - SiO2 particles in 2 K Polyurethane containing clearcoats by use of carboxylic acids

A new method for the stabilisation of SiO2-nanoparticles, which are produced in an UV-curable resin by a Sol-Gel-process, was developed. These particles have, due to the production process, hydroxyl-groups on their surface. These groups can lead to a flocculation of the particles during addition of free isocyanates to the dual-cure-clearcoat. A method for the stabilisation of nano-particles in the matrix was applied, which permits concentrations up to 40% SiO2 without flocculation. As stabilising-agent organic acids have been used, whose intermolecular hydrogen bonding is responsible for the prevention of flocculation. The stabilising-agent carries also a double bond, which participates in the UV-initiated radical-polymerisation, so that a network between the anorganic nanoparticles and the organic matrix generates. The resulted clearcoat shows good properties in abrasion- and scratch resistance. Transparency, gloss and levelling of the nanoparticie containing coatings were very good. The optimal size and concentration of nanoparticles for different applications have been investigated. Entnommen aus <a_href="http://www.fiz-technik.de/db/b_tema.htm" target="_blank">TEMA</a>