(692b) The Properties of Various Coating Polymers and Their Effects On Surface Frictional Behavior As Coatings On Pharmaceutical Tablets

Holbrook, D., The Dow Chemical Company
Blake, M., The Dow Chemical Company

Pharmaceutical tablets are typically coated for cosmetic and functional purposes, and the properties of coatings are important to ensure good performance and marketability. For immediate release applications, coatings provide a good barrier for taste masking, ease of swallowing tablets, and aesthetics.  Smooth coatings are usually desirable for appearance and ‘feel’, hence the type of polymer and processing method used can influence the texture of the coating surface.  Friction between tablets can also affect their performance in downstream manufacturing steps, such as during conveying, gravity filling, and packaging.  Tablets with low values of frictional resistance may have improved throughput and minimal defect formation during conveying operations, especially when extremely large batch sizes (hundreds of kilograms) are processed.   Assessment of in-process roughness and tackiness can also help during a coating operation, to prevent tablets from sticking and inducing further defects on the surface.

This study investigates the inter-relationship between physical properties of various coating materials and formulations, such as puncture and adhesion forces, surface roughness, and tablet-tablet sliding friction.  A Schulze ring shear tester and Aero-Flow avalanche tester, both typically used for measurement of powders, were utilized for testing the frictional behavior of tablets.   It was found that coatings with higher adhesion and low puncture forces (more hard and elastic materials) had lower values of friction than softer and plastically deforming materials.  The coating surface roughness parameters did not show correlations with tablet sliding frictional behavior; however had a strong relationship with its pull-off (adhesion) force to the tablet surface.  Based on this experimental study, it can be concluded that parameters relating to the elasticity and strength of the coatings influence their frictional behavior, agreeing with previous studies conducted on other material surfaces (Bellemare, et al., 2008 and Hancock, et al., 2010).  Future work would include measuring the values of Young’s modulus, yield strength, and strain hardening exponent of the films as well as understanding the effects of coating process parameters on the morphology and frictional characteristics of the tablet surfaces.