Measurement of Creep Properties in Compression and Their Influence on the Friction of Magnetic Tapes

Abstract

A n experimental technique to measure creep properties in compression of thin polymeric film is developed. An analysis is derived to calculate creep compliance and elastic and creep strains in compression of the thin films. Measurements were made on five typical magnetic inks and the poly (ethylene terephthalate) substrate wed in magnetic tapes. Modulw of inks as measured by the devekped technique is a n order of magnitude lower than the bulk modukls measured by other techniques. This indicates that the inkfilm suface is mechanically dijjferent from that of the bulk of the film. No significant changes in mechanical properties between film suface and bulk were seen in the case of PET film. Calendered magnetic inks showed slightly lower creep compliance than uncalendered film. Recovery experiments showed that the ink surface goes through some permanent deformation which would affect tape friction.Magnetic tapes under compression against a smooth suface, such as found at the hub of conventional tape reels, exhibit changes in friction due to creep. This phenomenon can be accelerated by temperature and humidity. Friction measurements were made on unbackcoated magnetic tapes at end of tape (EOT), wound on a spool, as received and after accelerated aging. Tapes having high creep compliance exhibited high friction after aging. Thus, measztrements of creep compliance can predict friction at EOT after agzng.