PURPOSE:To obtain the base featuring the reduced amount of dropout and suited to the video tape and the like by lowering the particle ratio of the calcium carbonate to 25% or less among the inactive external particles which formed the projection in the size within the specified range onto the surface of the magnetic tape base. CONSTITUTION:In case the polyester is used for the magnetic tape base, the calcium acetate is used for the ester conversion catalyst. And the calcium compound composed of terephtalic acid calcium and calcium salt of the polyester oligomer is deposited as the inactive external particle, thus forming the projection on the base surface. The projection featuring the height of 0.54-0.8mu exists in a certain number of units or more per 1mm2 of the film. Among these projections, those of the additive calcium carbonate are reduced to 25% or less. In such way, the base for the magnetic tape can be obtained for the audio, video and other purposes with the reduced amount of dropout.
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