Application of spot colour measurement for the optimisation of colour coating

The colour coating of pellets was carried out in a bottom spray Wurster fluidised bed equipment. Coating quality could be affected by a number of operating variables. In this study, the relationship between process parameters and colour coat development was investigated by measuring a small area of colour coating on individual pellets using a tristimulus colorimeter. Colour coating,was determined in terms of CIE (Commission internationale de l'eclairage) L*a*b* units, and colour difference (Delta E) values with respect to base-coated pellets were calculated. Standard deviations of colour difference (SDDelta E) values represented colour variations in pellet coatings sampled at different coating times. Higher SDDelta E values indicated a wider spread of Delta E values from the mean and hence, less uniformly distributed colour coating.