GB1506401A - Time temperature integrating indicator - Google Patents

Abstract

1506401 Temperature responsive indicators BIO-MEDICAL SCIENCES Inc 13 May 1975 [14 May 1974 16 Oct 1974] 20089/75 Heading G 1D The thermal history of a substance may be indicated by a device comprising a sealed envelope having an upper wall 12 and a lower wall 14, both of gas impermeable material, sealed together about their periphery, one section 28 containing a gas generating material, a second section 26 containing a wick 18 one end 19 of which being in communication with section 28, there being a rate-controlling gas permeable film 24 interposed between the gas generating material and the indicator section. The wick 18 has an indicator composition deposited thereon which produces a colour change in the presence of the gas generated by the gas generating material, and the wick 18 is substantially the only means of gas communication between sections 28, 26. This latter requirement may be provided either by a longitudinal barrier 40 on both sides of the wick, as shown, or by transverse barriers which extend from or adjacent the wick end 19. The gas generating material may be encapsulated, or enclosed in a glass ampule 22, as shown. If a glass ampule 22 is employed, a braided fibreglass resilient sleeve (60), Fig. 5 (not shown), may enclose it to avoid rupture of the device. The walls 12, 14 may be completely or partly transparent and may include a metal foil layer. The indicator may be (i) a pH sensitive dye e.g. phenolphthalein, xylenol blue, nile blue A, mcresol purple, bromocresol green, o-cresol red, cyanidine chloride, bromocresol purple, alizarin, thymol blue, brilliant yellow, bromophenol red, methyl red, acid fuchsin, logwood extract, bromothymol blue, phenol red, or phenolphthalexon, (2) a compound, e.g. a copper or cobalt halide which can form complexes of a different colour (3) incorporate a redox system, the generated gas being one which is susceptible to oxidation e.g. thymol; (4) incorporate a composition which converts the gas or vapour into a material which can be detected by a dye. The gas generating material may be (1) one which sublimes or vaporizes, e.g. water (or ice), iodine, aliphatic and aromatic alcohols e.g. thymol, hydrogen peroxide, lower alkanoic and aromatic acids such as acetic acid, Ketones and aldehydes (2) a salt which decomposes with the generation of a gas e.g ammonium carbonate, acetate, oxalate or formate, and sodium bicarbonate. The film 24 may be of polyethylene, polypropylene, nylon or cellulose. The wick may be of paper, polypropylene, glass fibre paper, alumina, silica gell or a polyester or polyamide.