GB2166868A - Temperature change indicating device - Google Patents

Abstract

A device for indicating a rise in temperature above a predetermined value comprising a quantity of a material (5) which changes from a solid state to a liquid state at the predetermined temperature, and an enclosure (1) for the material which is adapted to be fractured by the application of pressure thereto from outside the enclosure (1) whilst the temperature of the device is below the predetermined value. Once the enclosure (1) has been fractured (which is done when the device is put into use) the material (5), on melting, produces a detectable change which cannot be reversed by subsequent reduction of the temperature of the device below the predetermined temperature, e.g. by escaping from the fractured enclosure. Before fracturing the device may be cycled above and below the predetermined temperature without causing the detectable change. The device does not therefore need to be stored before use (i.e. before fracturing of the enclosure) at a temperature below the predetermined value. <IMAGE>

Description

SPECIFICATION Temperature change indicating devices and methods This invention relates to temperature change indicating devices and methods.

More particularly the invention relates to devices and methods for indicating whether a rise in temperature above a predetermined value has taken place.

Such devices find application, for example, in the storage of materials such as drugs, foods and chemicals.

In such an application the indicating device is typically attached to the stored material and is required to indicate whether the temperature of the material has risen above a predetermined storage temperature at any time since the device was attached to the material.

Such devices are suitably constructed so that they undergo an easily detectable change, e.g. a change in visual appearance, when their temperature rises above the predetermined value, and do not regain their original condition when their temperature is subsequently reduced below the predetermined value. One convenient way to achieve this is by utilizing the ability of certain materials to change abruptly from the solid to the liquid state at a predetermined temperature.

Thus property can, for example, be exploited to obtain a change of visual appearance by enclosing a liquid in an elastic container and deforming the container during fabrication i.e. during freezing. When the liquid melts the container will then adopt the shape of minimum surface area.

Alternatively objects may be positioned with a frozen block of material so that the objects change their position when the material melts. A further possibility is to provide passages or compartments which a material can only enter when the material becomes liquid, e.g. by capillary action.

Known forms of such devices, however, suffer from the shortcoming that, since they respond irreversably to a rise in temperature above a predetermined value, once they have been fabricated they must be maintained at a temperature below the predetermined value until put into use.

It is an object of the present invention to provide a device and method for indicating a rise in temperature above a predetermined value which avoids this difficulty.

According to one aspect of the present invention a device for indicating a rise in temperature above a perdetermined value comprises: a quantity of a material which changes from a solid state to a liquid state at said predetermined temperature value; and an enclosure for said material which is adapted to be fractured by the application of pressure thereto from outside the enclosure while the temperature of the device is below said predetermined value; said material being arranged to cause on becoming liquid after said enclosure has been fractured as aforesaid, a detectable change is said device which is not reversed by subsequent reduction of the temperature of the device below said predetermined value.

Said change is suitably a change in the visual appearance of the device.

According to a second aspect of the invention, a method of indicating a rise in temperature of an article above a predetermined value comprises attaching a device according to the first aspect of the invention to said article, and fracturing said enclosure by the application thereto of pressure from outside the enclosure after the device has reached a temperature below said predetermined value.

Several devices and methods in accordance with the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a sectional view of a first device; Figure 2 is a sectional view of the device of Fig. 1 after it has been raised above its indicating temperature; Figure 3 is a sectional view of a second device; and Figure 4 is a sectional view of the device of Fig. 2 after it has been raised above its indicating temperature.

Referring to Fig. 1, the first device to be described comprises a flat sachet of plastics material 1 adapted to be secured to a package 3 of a material whose temperature is required to be kept below a predetermined value -T"C during storage.

The sachet 1 contains a material 5 which melts at -T"C and the plastics material of the sachet 1 is chosen so as to be capable of being broken by the application of pressure from outside the sachet, e.g. by passing the sachet between a pair of corrugated spring-loaded rollers.

The sachet 1 is fabricated at normal room temperatures and may be stored at such temperatures until required for use. When required for use the sachet 1 is first reduced to a temperature below -T"C and then passed between the above-mentioned rollers to puncture its envelope, the material 5 not then escaping from the sachet 1 because it is frozen solid.

The sachet 1 is then attached to the package 3 whose temperature is required to be kept below -T"C during storage.

If the package 3 and hence the sachet 1 rises above -T"C the material 5 in the sachet 1 melts and escapes from the sachet 1, as illustrated in Fig. 2. It is thus readily apparent from visual inspection of the sachet 1 whether at any time during storage the temperature of the material 5 has risen above -T"C.

Referring now to Fig. 3, the second device to be described comprises a flat sachet of plastics material 7 which has two compartments separated by a membrane 9 which is appreciably thinner than the external wall of the sachet 7.

One of the compartments contains a quantity of a material 11 which melts at --T"C and the other compartment contains a quantity of another material 13 which forms a eutectic system with the material 11 when the material 11 is liquid, the eutectic system having a melting point below -T"C and preferably below the minimum temperature at which it is possible to maintain the enclosure (not shown) in which a package 3 whose temperature is being monitored is stored.

The sachet 7 is fabricated and stored at normal room temperature. When required to be put into use, the sachet is first reduced to a temperature below --T"C and the membrane 9 is then fractured by application of pressure to the sachet 7 from outside the sachet. In this connection it may be convenient for the material 13 to be a liquid at temperatures below -T"C to facilitate fracturing of the membrane 9 by the application of pressure from the side of the membrane 9 on which the compartment containing the material 13 lies.

After being put into use with the membrane 9 fractured, if at any time the passage 3 and its attached sachet 7 have been allowed to rise to a temperature above -T"C, e.g. due to temporary removal from the storage enclosure or temporary failure of the enclosure refrigeration system, the contents of the sachet 7 will become and remain a liquid 15, as ilustrated in Fig. 4.

Thus, such a rise in temperature may be detected visually or by touching the sachet 7.

It will be appreciated that in other devices in accordance withe the invention other mechanisms for indicating an undesired rise in temperature may be utilised.

For example, in a modified form of the first device described above by way of example, instead of escaping from the sachet 1, the material 5 may be arranged on melting in use of the device to enter a previously empty compartment of the same or another sachet. This compartment is separated off from the interior of the sachet 7 or part of the sachet 7 originally contained the material 5 by a membrane which is fractured only after the device has been reduced to a temperature below --T"C, immediately before being put into use.

In a modified form of the second device described above by way of example, a colour change occuring when the two materials 11 and 13 form a eutectic system may be utilised as the temperature change indicating mechanism. Alternatively, the material 13 may be arranged always to remain solid until contacted by the melted other material 11, and have an object or particles distributed in it in a particular position or with a particular distribution which is only lost when the material 13 is contacted by the material 11 and liquified. Movement of such objects or particles when the materials 11 and 13 liquify may be arranged to reveal lettering or a symbol previously hidden by the object or particles.

It will be understood that the choice of the material which melts at a predetermined temperature, and if present the second material which forms an eutectic system with the material which melts, will depend not only on the required indicating mechanism and temperature of indication, but also on the kind of materials whose temperature is to be monitored. For example, for food storage purposes, the material or materials should be non-toxic and not noxious in any way.

Some suitable materials for such an application are salts and their aqueous solution, e.g.

common salt, calcium chloride and potassium carbonate. Other possibilities are certain sugars, which melt near --20"C and organic components such as

C2HsOO - C -(CH2)7 - COO- C2H5 CgH1g- COO- CH3 HO- (Cli2)5- OH Methods of fabrication of a device in accordance with the invention other than those described by way of example will also readily occur to those skilled in the art. For example, an indicating device in accordance with the invention may suitably be fabricated in label-like form by applying the chosen material or materials to a carrier using techniques well known in the printing industry.

In such devices the chosen material or material may be encapsulated using known microencapsu lating techniques, i.e. encapsulated as a large number of minute pellets or droplets of material each in a separate enclosure consisting of gelatine or other microencapsulant material. The pellets or droplets are then conveniently applied to a suitable carrier using an ink-jet printing technique.

Claims (12)

1. A device for indicating a rise in temperature above a predetermined value comprising: a quantity of a material which changes from a solid state to a liquid state at said predetermined temperature value; and an enclosure for said material which is adapted to be fractured by the application of pressure thereto from outside the enclosure while the temperature of the device is below said predetermined value; said material being arranged to cause on becoming liquid after said enclosure has been fractured as aforesaid, a detectable change in said device which is not reversed by subsequent reduction of the temperature of the device below said predetermined value.

2. A device according to Claim 1 wherein said change is a change in the visual appearance of the device.

3. A device according to Claim 1 or Claim 2 wherein said change is due to said material escaping from said device on becoming liquid.

4. A device according to Claim 1 or Claim 2 wherein said device includes a compartment which said material enters on becoming liquid when said enclosure is fractured, thereby to produce said change.

5. A device according to Claim 1 or Claim 2 wherein said device includes a compartment containing a second material which, when said enclosure is fractured and said first mentioned material becomes liquid mixes with said first mentioned material to produce said change.

6. A device according to Claim 5 wherein said second and first-mentioned materials when mixed form a eutectic system having a melting point below said predetermined value.

7. A device according to Claim 6 when dependent on Claim 2 wherein said change in visual appearance is a colour change.

8. A device according to Claim 6 when dependent on Claim 2 wherein said second material is solid until mixed wit said first-mentioned material and said change in visual appearance is due to movement of an object or particles in said second material.

9. A device according to any preceding claim wherein said first-mentioned material and where present said second material are in the form of a large number of pellets or droplets encapsulated by a microencapsulation process.

10. A method of fabricating a device according to Claim 9 wherein said pellets or droplets are applied to a carrier using an ink-jet printing technique.

11. A method of indicating a rise in temperature of an article above a predetermined value comprising the steps of attaching a device according to any one of Claims 1 to 9 to said article, and fracturing the or each enclosure by the application thereto of pressure from outside the enclosure after the device has reached a temperature below said predetermined value.

12. A device for indicating a rise in temperature above a predetermined value substantially as hereinbefore described with reference to Figs. 1 and 2 or Figs. 3 and 4 of the accompanying drawings.