Patent GB-1212859-A (GB)
Title: Method and apparatus for indicating the condition of deep-freeze products, particularly foods
Inventor: MICHEL JOHANN
IPC: G01K11/06
Filed: 1967-12-07
Abstract: 1,212,859. Temperature indicators. J. MICHEL. Dec.7, 1967 [Dec. 19, 1966], No. 55670/67. Heading G1D. An indicator for indicating the condition of deep freeze goods comprises a signalling medium 6 e.g. an aqueous solution of a dye in a container 5 which normally remains frozen and the container 5 being ruptured during or subsequent to the freezing process, a signal body 4 which may be a sheet of blotting paper visible through a transparent casing 1, an inhibitor in the form of a layer 10 of a water soluble substance being interposed between the signalling medium 6 and the signal body 4 to extend the time interval between melting of the medium 6 and its visible effect on the signal body 4. The layer 10 is preferably of sugar of a glassy consistency, egg white, glue, gelatine or albumen and when the medium 6 melts it will dissolve away this layer before being visibly absorbed on the blotting paper. Thus it will be the cumulative effect of a number of undesirable temperature rises or a single temperature rise of sufficient duration that will cause an indication to be given. The rupturing of the container 5 for the medium 6 may be achieved by eddy current heating from a coil 24 of a metal ring 25 or disc attached to the container 5, this heating being sufficient to melt the container walls which are of a plastics sheet material. This will release a small quantity of the medium 6 to colour a small area 16 of the signal body 4 to indicate that the indicator is ready for use. On melting of the medium 6 it passes through apertures 18 and then dissolves the layer 10 as stated before. The casing 1 for the indicator is sealed to prevent ingress of water or other substances which would affect the action of the indicator. The indicator may be cylindrical in shape as opposed to the shape shown in the drawings, with the medium 6 and the signal body 4 in the form of absorbent material such as diatomaceous earth or chalk, disposed at either end of the body and separated by the layer 10. The container 5 may be ruptured prior to use by means other than dielectric heating e.g. a metal spike within the indicator which pierces the container 5 either by use of manual pressure or by the expansion of the container 5 on freezing or by differential expansion between the casing 1 and the spike. Otherwise a beam of intense radiation may be used, or a bimetallic strip which bends with temperature changes to rupture the container 5. The signalling medium 6 may be other than a dye solution, e.g. a reagent solution which reacts with reagents present in the signal body 4 to give a colour effect. These effects may be made to make characters appear or disappear on the signal body. The medium 6 may be of pasty dry or pulverulent consistency and may contain additives for lowering the freezing point if desired. The medium 6 may be held in a container away from contact with the layer 10 against the action of a spring and may be released to engage the layer 10 on temperature rise by means of a bimetallic latch or by melting of a gel solution holding the medium clear of the layer 10. The signal body 4 may have a spiral configuration so that the length thereof which has become stained indicates the time for which the indicator has been subject to undesirable temperature rises. Also a spiral capillary tube may be used as the signal body 4. In another embodiment iron particles may be held in the form of wording whilst the layer 10 is applied to keep the particles in place. On dissolution of the layer 10 the wording will be rendered obscure. Also the medium 6 and the signal body may be arranged to produce a gas which inflate the container 1 and this will give an indication discernable to blind persons.