To provide output and running durability to a tape for digital recording and to decrease oligomer deposited on the surface by providing projections with specified height and density at least one face of a laminated polyester film with at least three layers and specifying the angle of contact to the water on the surface and the wholly reflecting Raman crystallization index.
For a biaxially oriented laminated polyester film with at least three layers, there exist at least 200 million/mm2 projections with a height of 10-50nm at least on one surface and the angle of contact to the water on the surface is 40-55° and the wholly reflecting Raman crystallization index is at most 20cm-1. For forming the fine projections, 0.05-1.5wt.% inactive particles such as a colloidal silica to the whole wt. or the surface layer are incorporated in the surface layer. To make the angle of contact in a specified range, a metal sulfonate of the general formula CnH2n+1-C6H4-SO3M (wherein n=6-30 and M = an alkali metal or an alkali earth metal) is incorporated in the inner layer of a film and coextrusion is performed for the wholly reflecting Raman crystallization index.
MIYAKE TORU
NAKAMORI YUKARI
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