Process for preparing an aqueous composite-particle dispersion

A process for preparing an aqueous dispersion of composite particles, comprising:

• a) providing a stable aqueous dispersion of at least one inorganic solid, said dispersion having the characteristic features that 1) at an initial solids concentration of ≧0.1% by weight it retains, in dispersed form, one hour after its preparation, more than 90% by weight of the originally dispersed solid and 2) its dispersed solid particles have a diameter ≦100 nm and 3) the amount of the inorganic solid is 1 to 1000 parts by weight per 100 parts by weight of ethylenically unsaturated monomers, and
• b) providing as ethylenically unsaturated monomers ≧0.01% and ≦10% by weight of at least one ethylenically unsaturated monomer A comprising a silicon functional group and ≧90% and ≦99.99% by weight of at least one further ethylenically unsaturated monomer B which is different from monomer A, the amounts of monomers A and B adding to 100% by weight,
• c) feeding at least a portion of the stable aqueous dispersion of at least one inorganic solid as an initial charge of an aqueous polymerization medium, and subsequently
• d) feeding at least portion of monomer A into the initial charge of the aqueous polymerization medium containing at least a portion of the stable aqueous dispersion of the at least one inorganic solid over a period of ≧5 and ≦240 minutes to provide an intermediate composition, and subsequently
• e) feeding any reminder of the stable aqueous dispersion of the at least one inorganic solid, any remainder of monomer A and the total amount of monomer B to said intermediate composition under polymerization conditions.