| 摘要 |
Provided is a valved extended time-temperature indicator. This indicator comprises a base substrate and two transparent polymeric layers on top of the base substrate in adhesive contact with each other. The indicator further comprises a valve member which is restrictive of the flow of dye therethrough, which valve is interposed between the two polymer layers such that there is no adhesive contact between the two polymer layers in the area of the valve. A deposit of colored dye is either on the lower polymeric layer, in which case the valve may be in physical contact with the dye, or on the base substrate. In either case the dye is visible through the polymeric layers, with the dye being positioned directly below the valve member, however, so that the valve member at least partially obstructs visibility of the dye deposit.
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