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End of use and time duration indicator system and method based on volatile dye

  • US 6,790,670 B2
  • Filed: 10/09/2001
  • Issued: 09/14/2004
  • Est. Priority Date: 10/09/2001
  • Status: Expired due to Fees
First Claim
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1. A time duration indicating system for a product, the system comprising:

  • a substrate having a volatile air treating component, and a volatile dye, wherein the volatile dye is guaiazulene, the volatile dye being coated onto the substrate thereby coloring the substrate, the volatile dye evaporating over time resulting in a color change for the substrate.

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