Roughness and deformation aspects in calendering of particulate magnetic tape

Calendering of magnetic tape is applied to achieve a smooth magnetic coating. The purpose of this study is to gain a better understanding of the calendering process. The investigation is focussed on the roughness and elastoplastic deformation of the uncalendered coating, the substrate and the compliant roll material. It is found that these properties do determine the calendering efficiency to a great extent. Model calculations that are performed using the actual elasto-plastic deformation properties of coating and substrate, confirm the experimental results. A small-scale calender is developed with which coatings are calendered by means of a rolling ball. In this way small samples can be used and a large flexibility is obtained. Surface roughness and modulation noise are measured in order to characterize the calendering efficiency. The elasto plastic deformation properties are determined by means of ultra-microindentation measurements. Implementation of the results of this study resulted in an average surface roughness of 4 nm on lab-scale and of 6 nm on semi-production scale.