Encapsulated salts of sparing solubility in water, their preparation and their use

Claim 1

In the process for the production of microcapsules of a solid substance being insoluble in water whereby a mixture of the substance to be microencapsulated and a polyurethane prepolymer containing free isocyanate groups is emulsified in water in the presence of a protective colloid and then reacting the polyurethane prepolymer of the mixture with a diamine or a polyamine with vigorous mixing, whereby from the polyurethane prepolymer and the diamine or polyamine a high molecular weight polyurethane is formed which encapsulates the substance to be encapsulated and the microcapsules formed are separated off, the improvement comprises that the substance to be encapsulated is a salt of sparing solubility in water and the mixture contains the salt of sparing solubility in water and the polyurethane prepolymer in a weight relation of from 83:17 to 28:72 and that the polyurethane prepolymer contains 20 to 70 mole % of free isocyanate groups and that the polyurethane prepolymer is reacted with 10 to 100% of the equivalent amount of a diamine or a polyamine at temperatures of 0° to 80° C. and that the aqueous phase contains an electrolyte having a monovalent to trivalent cation selected from the first three groups of the periodic table, and from a monovalent to trivalent acid, in a concentration of 0.25% up to the saturation concentration, but not more than 50%.