Process for preparing microcapsules containing hydrophobic oil drops

In a complex coacervation process for preparing microcapsules containing a hydrophobic oily liquid wherein gelatin is employed as one of the hydrophilic colloids forming the microcapsule walls in combination with a hydrophilic colloid, ionizable in water and having an electrically opposite charge to that of gelatin, said process comprising:

• 1. emulsifying said hydrophobic oily liquid in an aqueous solution of at least one hydrophilic colloid, ionizable in water to form a sol;
• 2. optionally, mixing said sol with an aqueous solution of a hydrophilic colloid to form a second sol;
• 3. forming coacervates comprising hydrophilic colloids, so as to encapsulate individual drops of said hydrophobic oily liquid in said sol;
• 4. cooling the resulting coacervates to gel the hydrophilic colloid thereof at a temperature lower than the gelling point of said gelatin;
• 5. subjecting the system to a conventional prehardening treatment in which an aldehyde and an alkali material are added to adjust the pH of the system to the alkaline side;
• and
• 6. hardening the gelled hydrophilic colloid to form the microcapsule walls;
• the improvement which comprises:
• adding to the system gelatin having an isoelectric point lower than that of the gelatin employed as the hydrophilic colloid wall-forming material at a temperature lower than the gelling point of the gelatin employed as the hydrophilic colloid wall-forming material, but prior to the simultaneous presence in the system of said aldehyde and alkali material, in such an amount as sufficient to prevent an increase in viscosity due to the reaction of gelatin and aldehyde during said pre-hardening step.