Reflective sense marker for magnetic recording tape

Claim 1

Magnetic recording tape having firmly adhered to its back side a reflective sense marker which has a thickness not greater than 2.5 micrometers and acts as if it has zero thickness in that when the tape is wound upon itself in roll form, the sense marker produces essentially no permanent plastic deformation in overlying convolutions of the tape, said sense marker comprising (a) a thin-film metal coating having at least 90% reflectivity at an incident angle of 45° and a maximum thickness of 1000 A, (b) a layer of heat-activated adhesive which has a thickness of 0.2-1.5 micrometers, will not soften at 55° C., and bonds the thin-film coating to the back side of the tape, and (c) a tough, abrasion-resistant, transparent polymeric protective layer which covers the thin-film coating, has a thickness of 0.2-1.5 micrometers and will not transfer to the overlying convolution of the tape when the tape is stored in roll form at 52° C. and 85% relative humidity for 18 hours followed by 38° C. and 0-10% relative humidity for 4 hours.