BASE MATERIAL FOR MAGNETIC RECORDING CARD

PROBLEM TO BE SOLVED: To effectively prevent forgery or falsification by disposing a sheet containing magnetosensitive fiber between two layers of polyester resin films, and satisfying a surface smoothness index of the obtained composite sheet for a range of a specified formula. SOLUTION: A composite sheet for forming the base material for a magnetic recording card is obtained by laminating a sheet made of magnetosensitive fiber partly or entirely of its constitution between film layers containing polyester resin of two layers of the same type or different type as main component via polymer adhesive or as required crosslinker. At least one of the film layer containing the polyester resin as a main component is constituted by microcavity-containing thermoplastic polyester resin easily adhered to one surface. Surface smoothness index S1 of the composite sheet is set to a range of a formula (s1 =P/λ, λ: mean interval μm between ridges of a surface P mode curve and P: mean height μm of the ridges of the surface P mode curve). When it is large, a disposing position of the fiber is easily sensed from the base material sheet surface layer.