Stabilisierte Suspensionen von SiO2-Partikeln

DE 102007003622 A1 UPAB: 20081023 NOVELTY - A novel suspension (I) of silicon dioxide particles (SDOP's) comprises (a) an external phase comprising (a1) polymerizable monomers, oligomers and/or prepolymers and (a2) copolymerizable or other organic acid(s) and (b) a dispersed phase consisting of optionally surface modified SDOP's. The acid (a2) stabilizes the SDOP's against agglomeration in presence of hexamethylene diisocyanate biuret. DETAILED DESCRIPTION - A novel suspension (I) of silicon dioxide particles (SDOP's) comprises: (a) an external phase comprising (a1) polymerizable monomers, oligomers and/or prepolymers and (a2) copolymerizable or other organic acid(s); and (b) a dispersed phase consisting of optionally surface modified SDOP's, prepared by a sol-gel process and having average particle size at most 100 nm. The amount and nature of the acid(s) (a2) are such that the SDOP's are stabilized against agglomeration to particles of average size at least 1000 nm after mixing equal weights of hexamethylene diisocyanate biuret and (I). INDEPENDENT CLAIMS are included for: (1) the preparation of (I), by forming a pre-suspension containing an external phase and (b), then mixing with the organic acid(s) (a2) (optionally in anhydride form); (2) the use of the organic acid(s) (a2) for stabilizing suspended, optionally surface modified SDOP's against agglomeration; and (3) a partially or completely hardened dispersion, obtained by polymerization of components (a1) in (I). USE - (I) is specifically a clear or pigmented lacquer system (claimed), especially for use in the automobile sector. The SDOP's are included in (I) to increase the fracture resistance, impact strength, modulus, scratch resistance and abrasion resistance and reduce the shrinkage on hardening and thermal expansion, and in comparison with conventional reinforcing fillers cause a lesser increase in viscosity and can be incorporated in larger amounts. ADVANTAGE - Inclusion of the organic acid component (a2) greatly reduces agglomeration, aggregation and flocculation of the SDOP's in (I), even when (I) is treated with other binders, solvents, additives and/or reactants (specifically isocyanates)