Process for the preparation of hydrophilic hydrogels of high swelling capacity

A process for the preparation of granules, which are surface-modified with water-swellable, hydrophilic polymer in a fluidized bed zone having nozzles immersed therein and containing the granules, and at least one polymerizable hydrophilic polymer-forming monomer, said process comprising:

• introducing granules into the fluidized bed zone and generating a fluidized bed comprising granules by passing upwardly into the fluidized bed zone a gas flow, which is heated while in said fluidized bed zone, the gas of said gas flow being inert toward the granules and the hydrophilic polymer-forming monomer at the temperature of the fluidized bed,
• spraying through said nozzles upwardly onto the granules, in the fluidized bed, an aqueous medium and a said hydrophilic polymer-forming monomer and forming on granules thus sprayed a layer containing the aqueous medium and the hydrophilic polymer-forming monomer,
• heating the granules in the fluidized bed with the heated gas flow, and with polymerization taking place on the surface of the granules, said heating being sufficient to dry the granules sprayed with the aqueous medium, and
• recovering from said fluidized bed zone granules which have applied thereto a shell comprising water-swellable, hydrophilic polymer.