| 摘要 |
<p>Device which visually indicates exposure to a temperature within a predetermined range for a predetermined length of time. The device may be used in the fast food industry to make certain that all food sold has been recently prepared. An opaque microporous sheet has a colored stratum on the back and a transparent fusible coating on the face. The coating is a solid solution of amorphous rubbery polymer in crystallizable solvent which, upon melting, gradually penetrates and transparentizes the microporous layer, rendering the colored stratum visible.</p> |
