Temperature sensitive material

Details Temperature sensitive material Temperature sensitive material

1997-03-25

1999-05-11

Cain, Edward J.

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Processes of preparing a desired or intentional composition...

C08J3/00

Patent

active

059028424

DESCRIPTION:

BRIEF SUMMARY
This invention relates to a method of preparing a temperature sensitive material and to a temperature sensitive material prepared by the method.
In U.S. Pat. No. 2,971,852 there is disclosed a temperature telltale including a temperature sensitive material which may comprise an oil-in-water emulsion the freezing point of which, it is stated, may be easily adjusted by the addition of freezing point depressants, such as salt, sugar and glycerol. It is assumed that there is a single freezing temperature for the emulsion; that the freezing temperature and thawing temperature are the same; and that the freezing/thawing temperature can be controlled by addition of additives to the emulsion.
We have discovered that with oil-in-water emulsions there is no single "freezing" and "thawing" temperature but that there is an "activation temperature" below which the material must be cooled if it is to undergo a substantial visual change on subsequent heating and that there is a "reveal temperature" at which the material undergoes an irreversible optical change on reheating after having been cooled below the activation temperature. We have also discovered that the activation temperature and the reveal temperature for an oil-in-water emulsion can be different one from another and can be controlled independently one from another. We have further discovered how to control both the activation and reveal temperatures by using a range of additives both to the oil and water phase of the emulsion and using other compositional, preparation and material parameters.
In this manner, independently controlling both the activation temperature and reveal temperature provides for manufacture of a temperature sensitive material which is suitable for use in temperature indicators for use in a wider range of applications than hitherto.
According to the present invention there is provided a method of preparing a temperature sensitive material comprising an oil-in-water emulsion the method including controlling emulsifier type and content; the freezing point of the oil phase; the freezing point of the water phase; the oil-to-water ratio; and the particle size of the oil phase of the material so as to determine, in use, activation and reveal temperatures of the material.
Also according to the present invention, there is provided a temperature sensitive material prepared in accordance with the method.
The invention thus provides for independently controlling both the activation and the reveal temperatures so that a temperature indicator embodying the material can be rendered suitable for a wide range of applications.
Following is a series of Tables indicating a range of factors that control activation and reveal temperatures of a material in accordance with the present invention.
Referring now to Table 1 below there is shown the relationship between the concentration of emulsifier in the material and the activation temperature. In this example the emulsifier is in the form of sodium alkyl ether sulphate and the oil is paraffin oil. The oil-to-water ratio is 4:1.


TABLE 1 ______________________________________ Effect of emulsifier content on activation temperature. Concentration of Emulsifier (pph/Parts per hundred of Activation Temperature the total emulsion) (.degree. C.) ______________________________________ 4.0 -20.0 1.0 -13.5 0.5 -11.0 ______________________________________
The Table indicates that change of the activation temperature is inversely proportional to concentration of the emulsifier. The concentration of emulsifier does not affect the reveal temperature to any significant extent.
The reveal temperature is considerably affected by the freezing point of the water phase of the emulsion and can thus be controlled by the addition of freezing point depressants to the water phase.
Referring now to Table 2 below there is shown the relationship between concentration of salt added to the water phase of the emulsion and the reveal temperature. In this example the emulsifier content is 0.15 pph of the total emulsion.


TABLE 2

REFERENCES:
patent: 2971852 (1961-02-01), Schulein
JP,A,59 017121 (KAO Sekken KK), Jan. 28, 1984.
Patent Abstracts of Japan, vol. 006, No. 104 (P-122), Jun. 15, 1982 & JP,A,57 037227 (Green Cross Corp:The), Mar. 1, 1982. JP,A,57 037228 (Green Cross Corp:The), Mar. 1, 1982.
Database WPI, Week 7820, Derwent Publications Ltd., London, GB; AN 78-35699 & JP,A,53 037 479 (Dainippon Printing KK), Apr. 6, 1978.

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