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Time duration indicator systems, and also products containing such indicator systems having a limited duration of use or life

  • US 4,921,636 A
  • Filed: 12/03/1986
  • Issued: 05/01/1990
  • Est. Priority Date: 12/16/1985
  • Status: Expired due to Fees
First Claim
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1. A time duration indicator, which comprisesa layer of a porous inert carrier material having two major surfaces, that is substantially opague when dry,a colorless, volatile liquid impregnated in the carrier material and selected such that the carrier material becomes transparent or translucent when impregnated with the liquid, the liquid being capable of evaporating from the carrier material, andan inert layer attached to one major surface of the carrier material, the inert layer having a color different from that of the carrier material, wherein the inert layer can be seen through the carrier material when the carrier material is impregnated with the liquid, and the inert layer cannot be seen through the carrier material when substantially all of the liquid has evaporated from the carrier material, the amount and volatility of the liquid being chosen such that, on expiration of a specified amount of time, the carrier material conceals the inert layer.

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