BASE MATERIAL FOR MAGNETIC RECORDING CARD

PROBLEM TO BE SOLVED: To eliminate a trouble due to the warp of a card, to eliminate irregularities on the surface of the card by means of a magneto sensitive fiber arranged in a state where it cannot be reproduced inside, to securely read peculiar information by a magnetic head and to disable the providing position and the providing pattern of magnetosensitive fiber from outside as the authenticity discrimination means of the magnetic recording card. SOLUTION: The base material is a composite sheet formed by stacking a sheet body constituted of magnetosensitive fiber between inter-film layers which are mainly composed of the polyester resin of the two layers of the same type or different types by polymer adhesive or cross linking agent. The warps in a long side direction and a short side direction when a card size is set to be that decided to JISX 6311 are made to be not more than 0.5 mm. The average of the length direction and the difference of thermal shrinkage rates in both width ends at the time of processing both film layers which are mainly constituted of polyester resin at 150 deg.C for thirty minutes are made to be not more than 0.5%.