| 摘要 |
1,153,959. Temperature indicators; gas analysis; voltage testing. WESTINGHOUSE ELECTRIC CORP. May 30, 1967 [June 13, 1966], No.24855/67. Headings G1B, G1D and G1U. A temperature indicator comprises a film 11 of polyethylene terephthalate backed by a pigmented layer 12 and on which is deposited a cholestenic liquid crystalline composition 13 which reversibly changes colour at a predetermined temperature. The pigmentation in the layer 12 is arranged to be of the complementary colour to that of the light used to illuminate the indicator i.e. carbon black may be used as a pigment with white light. The composition 13 has a characteristic colour when in the cholestenic crystalline phase and when heated it changes at a predetermined temperature to the liquid phase and becomes colourless. The change back to the coloured state is accompanied by a time lag of at least three minutes so that the composition provides a semipermanent record of the temperature change. As described the composition comprises 15 to 40% by weight of at least one of the cholesteryl or cholestanyl halides and at least 30% of at least one of the cholesteryl erucyl carbonates, oleyl carbonates, erucates or oleates. The indicated temperature may be varied by varying the proportions of the constitutents of the composition. However, the indicated temperature may be raised appreciably by the addition of up to 35% by weight of one of the cholesteryl nonanoates or decanoates, and it may be depressed appreciably by the addition of up to 10% by weight of one of the fatty acids, fatty esters or fatty alcohols particularly the triglyceryl ester of a fatty acid. Specific examples are given in the Specification. The colour change of the composition 13 will also occur if it is exposed to air containing 70 to 100 p.p.m. chloroform or trichloroethylene. The composition will remain colourless for about ten minutes after removal from the atmosphere. Electric fields e.g. of 200 volts/cm also cause the change of the composition to colourless and in this case the composition does not revert to its original colour until after about three weeks. |
