Influence of tableting forces and lubricant concentration on the adhesion strength in complex layer tablets.

The strength of adhesion in complex two-layer tablets is assessed using statistical methods with respect to the applied tableting forces for the first layer and for applying the second layer on the first, as well as regarding the fraction of the lubricant. These results, obtained on a single-punch tablet press, are compared with the results for three-layer tablets produced on a rotary press at production scale. The strongest negative influence on adhesion strength was exerted by the amount of lubricant in the central layer. As expected, compression forces for central-layer tableting also had a negative effect, whereas the compression forces for complex layer tableting exerted a positive effect on layer adhesion. The validity of the derived model equation was proved by experiments: It was shown that the adhesion strength in complex layer tablets produced in production scale can be predicted from laboratory-scale experiments. This makes optimization of the formulation and parameter settings at an early stage of development possible.