Role of tape abrasivity on friction, wear, staining and signal degradation in audio tapes

Abstract

Audio tapes with varying amounts of head cleaning agent (HCA), pigment volume concentration (PVC) and lubricant concentration were run against a mu-metal audio head in a linear tape drive. Surfaces were characterized with atomic force microscope (AFM). Head wear was measured using a Knoop indentation technique in which the change in the length of the indent diagonal corresponds to the wear depth. Any formation of head stains was optically observed. An electrical sine wave signal was recorded at different frequencies. Degradation in this signal was measured by measuring the changes in its RMS value. Coefficients of friction for each tape were measured using an off-line friction tester. Tests were also conducted on uncalendered tapes with various HCA contents. Tapes with different HCA contents, PVC and lubricant levels have the same average roughness statistics, within a given roughness matrix. Consequently, they exhibit similar friction characteristics. Increasing HCA and/or roughness reduces propensity of head stains, resulting in better signal reproduction at the expense of higher head wear. However, there seems to be a limit to improving signal quality by increasing HCA or roughness. Increase in PVC results in a slight decrease of head wear and better signal reproduction. Signal reproduction remains largely unaffected by varying lubricant level. Head wear however slightly increases with decreasing lubricant content. Abrasive wear is the dominant wear mechanism for the head in each case as evidenced by extensive scratches on the head surface. Adhesive transfer debris is also formed by each tape. The tape wear occurs mainly by burnishing, i.e. high asperities on the tape surface are knocked off during the wear process. This study provides a data base which is expected to be useful to design engineers in predicting behavior of new tape formulations and plant engineers in understanding the implications of their process variability.