Process for hardening microcapsules containing hydrophobic oil droplets

In a process for hardening microcapsules produced by microencapsulating hydrophobic oil droplets using a complex coacervation process with gelatin as one of the hydrophilic colloids wherein the process includes the steps of

• 1. emulsifying a water-immiscible oil in an aqueous solution of at least one first hydrophilic colloid ionizable in water and admixing an aqueous solution of at least one second hydrophilic colloid having an electric charge opposite to that of said first colloid,
• 2. causing coacervation of said colloids to occur by adding water thereto or adjusting the pH thereof to form coacervates,
• 3. cooling said coacervates to cause gelling thereof,
• 4. adjusting the pH to alkalinity and adding a hardening agent sequentially or simultaneously,
• 5. increasing the temperature so as to cause hardening, the improvement wherein glyoxal or glutaraldehyde together with formaldehyde is present during step (4), the amounts employed being (a) with glyoxal, as the amount of glyoxal increases the minimum amount of formaldehyde decreases, such that when the amount of glyoxal per 100 parts of gelatin is 0.6 parts the minimum amount of formaldehyde per 100 parts of gelatin is 0.6 parts, the minimum amount of formaldehyde per 100 parts of gelatin being at least 0.05 parts, and (b) with glutaraldehyde, when the amount of glutaraldehyde per 100 parts of gelatin is less than 5 parts the minimum amount of formaldehyde is at least 0.7 parts, and when 5 or more parts of glutaraldehyde are employed the amount of formaldehyde is not less than 0.05 parts, said parts being by weight.