Tamper indicator tape

Claim 1

In a hermetically sealed container which encloses pourable material within a rigid wall having a preformed aperture therein, said aperture being covered and said container being hermetically sealed by a closure comprising a sheet material removably adhered directly to the portion of said wall which surrounds said aperture, said closure having a free end not attached to said wall, said closure being capable of being grasped by said free end and pulled back on itself without rupture to expose the underlying aperture and permit removal of the pourable material, the improvement which comprises: on the outer surface of said closure an indicator layer comprising a strong, flexible binder matrix having a Young''s modulus at 2% elongation of at least about 125,000 pounds per square inch containing, dispersed throughout, a solid colorforming substance and capsules containing a liquid dye precursor reactable with said color-forming substance, at least a portion of said indicator layer being intermediate said free end and the nearer edge of said aperture, whereby, when said closure is flexed by force applied to said free end, said capsules rupture and the color-forming substance and dye precursor react to form a colored dye indicating that said can closure has been at least partially removed.