Process for producing microcapsules

Claim 1

A process for preparing mononucleic capsules having chemically hardened walls of hydrophilic polymeric material and an average diameter of less than about five microns consisting essentially of the steps of: (a) establishing, at a pH less than 7.0, an agitating aqueous system of mononucleic capsules having an average diameter of less than about five microns and capsule walls comprising a gelled complex coacervate combination of gelatin and a negatively-electrically charged hydrophilic polymeric material; (b) adding to the system, once established, from 5 to 10 percent, by weight, of the amount of the gelatin present in the system, of a relatively slow acting chemical hardening agent for the capsule walls selected from the group consisting of formaldehyde, glyoxal, and 2,3-dihydroxy-1,4-dioxane; (c) after completion of the addition of step (b), adding to the system from 80 to 200 percent, by weight, of the amount of gelatin present in the system, of a negatively-electrically charged hydrophilic polymeric material selected from the group consisting of gum arabic, poly(vinylmethylether-co-maleic anhydride), poly(styrene-co-maleic anhydride), poly(acrylic acid-co-maleic anhydride), poly(vinylacetate-co-maleic anhydride), poly(ethylene-co-maleic anhydride), carboxymethyl cellulose, sodium alginate and carrageenan; (d) after completion of the addition of step (c), adding to the system from b 5 to 10 percent, by weight, of the amount of gelatin present in the system, of a relatively rapid acting chemical hardening agent for the capsule walls selected from the group consisting of glutaraldehyde, acrolein and 2-methylglutaraldehyde; and (e) after completion of the addition of step (d), raising the pH of the system to greater than 8.0.