in the form of a granule average particle diameter 0 3 micrometers moh 39 s hardness 8 to u03b1 alumina in the form of a granule average particle diameter 3 0 micrometers moh 39 s hardness 9 0 the average particle diameter of the abrasive material is a mean value obtained by measuring the size of 500 particles randomly sampled over a transmission type electron microscope picture the number of scratches generated on the surface of a floppy disk and an output from the floppy disk were measured using a burnishing polisher type fb 35 which is available from high tech seiko co ltd japan after a 3 5 34 floppy disk is burnished with abrasive tapes prepared by the embodiments 1 13 and comparative examples 1 4 the number of scratches represents a total number of scratches which were generated on 50 planes of a floppy disk measured by a microscope having a magnifying power of 20 u00d7 provided that the output of the comparative example 1 is assumed as 100 the output is a relative value with respect to the comparative example 1 by measuring an output level provided as an output from a certifier hfq 35 produced by high tech seiko co ltd japan evaluation results set forth above are listed in the following table table 1__________________________________________________________________________ surface smoothing treatmentabrasive material pressur surface temp burnishing performance average particle metal elastic ing force of elastic number of outputtypes diameter u03bcm roller.