| 摘要 |
<p>Optical control indicator "deep-frozen" prods. e.g. foodstuffs, pharmaceutical or photographic materials, that signals irreversibly with time delay any critical temp. being exceeded, comprises two porous carrier layers sepd. by an intermediate layer, one of which is impregnated by condensation water when defrosting occurs, whilst the other layer is provided with a water-soluble colouring that dissolves in the condensation water after overcoming the obstacle presented by the intermediate layer, thereby spreading colouration through >=1 carrier layer. The intermediate layer comprises water-permeable and water-impermeable zones, the proportions of these being adjusted to the desired, permissible, thawing time of the deep-frozen prods. The intermediate layer is a polyethylene film, 5-250 mu thick.</p> |
