Application of Electrostatic Dry Powder Coating Technology on Hard Capsules

This project applied electrostatic dry powder coating technology on hard gelatin and HPMC capsules using Eudragit® RS/RL and Eudragit® L 100-55 to achieve sustained release and enteric release respectively. Dry powder coating eliminated the difficulties associated with conventional liquid coating processes such as poor adhesion and stickiness for capsules. Additionally, through optimizing sprayed plasticizer volume, the coating powders deposited on the capsules could be efficiently maximized. The weight gain of coating and the formulation of coating materials were important parameters which controlled the release profiles of coated capsules. The release mechanism of coated capsules was quite different from tablets owing to the existence of capsule shells. Enteric release aspirin capsules were developed and compared with aspirin tablets. The investigation showed that enteric release capsules could be an alternative form to deliver aspirin. The capsules eliminated the migration of the drug from cores to the coating films, a problem observed with aspirin tablets. It was also found that enteric coating film would not protect aspirin from hydrolysis for both tablets and capsules. And an important factor that caused hydrolysis of aspirin could be the moisture in the environment that penetrated the film. Finally, the dry powder coating process was scaled up and optimized successfully with tablets. Compared to the conventional aqueous coating process, the dry powder coating process had shorter processing time, lower energy consumption and comparable coating efficiency. And the coated aspirin tablets had similar release profiles as aqueous coated. Additionally, due to the absence of water, less hydrolysis occurred for aspirin coated by the dry powder coating process