GB1584177A - Temperature responsive indicaing device - Google Patents

Description

(54) TEMPERATURE RESPONSIVE INDICATING DEVICE (71) We, MINNESOTA MINING AND MANUFACTURING COMPANY, a corporation organised and existing under the laws of the State of Delaware, United States of America, of 3M Center, Saint Paul, Minnesota 55101, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to temperature-responsive indicating devices. More particularly, it relates to devices which indicate the attainment of predetermined temperatures.

Temperature-responsive indicating devices are especially useful in preparing foods, particularly meats and fowl. By providing means by which the device indicates the attainment of predetermined temperatures, such devices can signal the degree of doneness of the food.

Such devices are, of course, known as exemplified by the number of patents issued for such devices. Thus, see, for example, U.S. Patent Nos. 3,140,611; 3,280,629; 3,479,876; 3,548,780; 3,559,615; 3,626.897; 3,656,452; 3,682,130; 3,693,579 and 3,965,849. The devices described in these patents employ fusible latching means for normally securing the indicating means in a non-indicating position relative to the housing of the device. Typically, the latching means employed in these devices coinprise metal alloys or waxes.

While devices employing such latching means have proven useful, they have certain drawbacks. For example, the metal alloys are high density materials. Thus, in addition to being expensive in themselves, relatively large quantities of alloy must be utilized in order to provide a given size latching means thereby adding to the expense of such means. Moreover, such alloys are typically prepared from toxid substances such as bismuth, lead, cadmium, tin, etc.

Waxes have been suggested as replacements for metal alloys. However, they have not proven entirely satisfactory. Typically, waxes fuse over a temperature range of at least 5"C.

Thus. they do not provide a quick response when a predetermined temperature has been attained. Moreover. many of such waxes can escape from the indicating device during preparation of the food. As a result. the device is likely to prematurely indicate attainment of the predetermined temperature.

In accordance with the present invention. there is provided a temperature-responsive indicating device comprising a housing which defines a cavity closed at one end and open at the other end. an indicating means within said cavity for movement relative to said housing, a biasing means within said cavity for urging the movement of said indicating means relative to said housing. and a fusible locking means within said cavity. wherein said locking means is adapted to fuse at a predetermined temperature and wherein said locking means has the formula

where R is selected from lower alkyl groups of from l to 4 carbon atoms; m isO or l; and n is from 4 to 20.

The locking means used in devices of the invention is substantially less dense and less expensive than the metal alloys. Thus. devices of the invention require significantly less of the locking means per unit and thereby afford substantial cost savings. Moreover. the toxic alloys are replaced with materials which arc considered non-toxic and, in the most preferred case.

exhibit essentially no acute oral toxicity. Furthermore, typical organic locking means employed in the present invention fuse over a temperature range of 3 "C or less and are resistant to extraction from the device by water and cooking fats and oils. Thus, devices of the present invention provide a quick and acurate response upon attainment of a predetermined temperaturc.

The devices of the invention employ a class of anilide compounds of formula I above as the locking means. In said formula, when m is 1, R is preferably a methyl group which is ortho or para to the amino group. In any event, n is preferably from 7 to 17 and most preferably 11 or 13.

The anilide preferably has a relatively sharp trigger temperature (defined hereinafter).

Thus, while the anilide may trigger over a range of temperatures that range is not normally grcatcr than 3"C.

Additionally, the analide is stable under severe storage conditions (e.g., 100 percent relative humidity and 50"C). Thus, when exposed to such conditions for a period of 30 days, the anilide does not exhibit any substantial change in trigger temperature.

Moreover, the preferred anilides exhibit essentially no acute oral toxicity. Consequently, there is virtually no danger from their accidental oral ingestion by humans.

The preferred anilides are also virtually impossible to extract from the signaling device when exposed to conditions which simulate the cooking environment. Thus, the danger of accidental oral ingestion by humans is very remote.

As used herein, trigger temperature refers to that temperature, or range of temperatures, at which five devices fire (i.e.. the locking means fuses). It may be easily determined by suspending the devices in an appropriate liquid bath so that the tip and most of the body of the device, but not the top, is submerged. The temperature of the bath is controlled so that it cycles within a 0.55"C temperature band. The bath is held in each band for two minutes after which the temperature is raised in 0.55"C increments to the next band. The number of devices that fire in each band is recorded.

Extraction tests are performed in separate water and heptane baths. Devices containing a 50 percent by weight cxcess of the anilide and having a polypropylene body are used. The water bath simulates the cffect of water of the device during cooking. The heptane bath simulates the effcct of fats and oils on the device during cooking. Water extraction tests are performed at I I 80C under sufficient pressure to prevent the water from boiling off. Heptane extraction tests are performed at a temperature of 3"C above the melting point of the anilide being tested. The tests are run by submerging the tip and lower portion of the device in the appropriate bath at said temperature for two hours.The water or heptane is then evaporated to determine the amount of anilide extracted thereby.

The anilide is preferably prepared by the reaction of

wherein R and m are as defined above. with

wherein n is as defined above. Alternatively. the halide derivative of formula III may be employed in place of the compound of formula III. Such derivative may be represented by the formula

wherein n is as defined above and X is preferably chlorine.

A number of methods for preparing the anilide are known. For example. the reactants may be combined in a suitable vessel in the presence of a solvent (e.g.. xylene) and heated (c.g.. to from I 70C-2 IO"C) at atmospheric pressure in an inert atmosphere until substantially all of the liberated water has been azeotropically removed. The reaction mixture may then be cooled and simultaneously diluted with alcohol to precipitate the anilide. The precipitate may then be filtered from the mixture washed with alcohol and air dried.

A specific example of the preparation of a particularly preferred anilide is now set forth.

Preparation of myristanilide.

A three liter flask equipped with a stirrer, thermometer. nitrogen inlet. Barrett trap and condenser was used. Myristic acid (commercially available from Emery Chemicals, 97 percent purity. 685 grams, 3.0 moles). aniline (300 ml.. 3.2 moles) and 120 ml. xylene were charged to the flask. The mixture was stirred and heated for approximately 6 1/2 hours at a temperature of from about 170"C-220"C. The reaction was conducted in a nitrogen atmosphere. The reaction mixture was then cooled to 140"C and poured into a 4 liter beaker.

About 1.8 liters of denatured alcohol were slowly added to the reaction solution. After standing overnight. the semi-solid myristanilide was collected by filtration. The filter cake was washed thoroughly with two portions of denatured alcohol and then air dried at about 27"C. The resultant white crystalline solid weighed 706 grams and had a melting point of 83."C-84.5"C.

Thermally-responsive signaling devices employing this myristanilide as the locking means were prepared and tested for trigger temperature. stability and extractability. It was found that the device had a trigger temperature of 83"C-84.5"C immediately after preparation.

After being subjected to aging at 50"C and 100 percent relative humidity for 30 days the trigger temperature remained substantially the same. Moreover. the myristanilide was not extracted from a signaling device when subjected to the hot heptane and hot water extraction tests.

Other anilides of the formula I above were also prepared. These anilides. their melting points and their trigger temperatures are set forth in Table I below.

TABLE I ANALIDE FORMULA MELTING POINT ( C) TRIGGER TEMPERATURE ( C)

3 9C4C11-N 60-62 53-56 =r H15C7C1-N 50-51 47.5-49 OH c; H19C9C-ll 63-65.5 64-65 C. 1135C C-N 93.5-95 92.5-94 1711 1 N IC t)=0 U On e O < J Z < > U U V7 (Melting points were determined by the Fisher-Johns method.) Two embodiments of the invention are described in more detail hereinafter with reference to the accompanying drawings wherein like reference characters refer to the same parts throughout the several views and in which:: Figure 1 is a cross-sectional view of a preferred embodiment of the invention having an indicator rod in a lowered position relative to the body of the device; Figure 2 is a cross-sectional view of the embodiment of Figure 1 having the indicator rod in a raised position relative to the body of the device; and Figure 3 is a cross-sectional view of the upper portion of an alternative embodiment of the invention.

Referring to Figure 1, there is shown a temperature-responsive signaling device 10 comprising a housing 12 defining a cavity 14, an indicating means 16 within said cavity, a biasing means 18 within said cavity and a locking means 20 within said cavity.

Housing 12 has a closed end 22 and an open end 24. Closed end 22 is preferably pointed. as shown. although it is not necessary that it be so. Additionally, said end is preferably provided with a flange 26 which may either circumscribe housing 12 or project from only a portion thereof. In this latter case, flange 26 may also be referred to as a barb. In either event, flange 26 permits penetration of device 10 into the food to be prepared while preventing the tendency of the food to urge the device outwardly during preparation.

Open end 24 is provided with a reverse curl lip 28 which is adapted to slideably receive indicating means 16 and form a mating seal with shoulder 30 of said indicating means. (See Figure 2).

Alternatively open end 24 may be provided with a cap 32 (See Figure 3) rather than the reverse curl lip. In this embodiment, cap 32 is received within open end 22 of the housing 12.

Cap 32 has a passage 34 therethrough which is in registry with the indicating means (not shown) and adapted to slideably receive said indicating means. Additionally, it is preferred that cap 32 have tapered shoulder 36 to form a mating seal with the shoulder of the indicating means.

The material of construction of housing 12 must be capable of (i) withstanding the rigors of the environment to which it is subjected and (ii) conducting the internal temperature of the article being cooked to the locking means relatively quickly. Moreover, it is preferred that the material be chemically inert. Representative of useful materials are metals (e.g., aluminum), glass, polymers (e.g.. nylon, polypropylene, etc.).

The shape of housing 12 may vary. Circular cross-sections are preferred, but any shape.

symmetrical or asymmetrical. may also be used.

Indicating means 16 is preferably axially disposed within cavity 14. In the embodiment shown. it is adapted so as to be substantially within said cavity when prior to the attainment of the predetermined temperature and substantially outside of said cavity after the attainment of said predetermined temperature. However, it may also be adapted to operate in the opposite manner (e.g.. raised prior to attainment of a predetermined temperature and lowered at attainment of a predetermined temperature). Moreover, said indicating means may be disposed so as to rotate to an indicating position without changing its height relative to the housing. In any event, the exact type of movement of the indicating means relative to the housing is not critical to the invention.

Indicating means 16 may be constructed from the same materials used for housing 12.

Additionally, it may have a variety of cross-sectional areas. although circular cross-sections are preferred.

The movement of indicating means 16 relative to housing 12 so as to indicate the attainment of a predetermined temperature is brought about by biasing means 18. In the embodiment shown, such movement is between lowered and raised positions, although, as pointed out above, other movements are also possible. Typically. said biasing means comprises a spring. Said spring is generally held in compression until such time as locking means 20 fuses. although it may be held in any configuration such that it can urge the indicating means to an indicating position.

Locking means 20 may either secure indicating means 16 directly to housing 12, or alternatively. it may directly restrain biasing means 18 (e.g.. by joining said means to itself or encasing said means within the locking means). Moreover. a quantity of the locking means may be provided around the lower end of the indicating means so as to hold the biasing means in compression (or other configuration) between such point and the shoulder of the indicating means. Still other arrangements are also possible as will be understood by those skilled in the art and are included within the scope of the invention.

Temperature-responsive signaling devices of the invention may be easily assembled. For example. the embodiment shown in the figures may be assembled by forming a pellet of predetermined size of the material of the locking means; inserting it into the closed end of the housing; inserting the biasing means and indicating means into the housing; forming the reverse curldown lip at (or inserting the cap in) the open end; and heating the material of the locking means until it fuses. Methods of forming the reverse curldown lip are described in U.S. Patent No. 3,965,849. The indicating means may then be urged toward the closed end of the device (thereby compressing the biasing means) and held in that position until the fused locking means material solidifies.

The assembled signaling devices are then preferably quality assurance-tested by heating them at about 75"C for 2 hours. This test causes those devices which have received an insufficient amount of the material of the locking means to fire prematurely. Those devices which have received a sufficient amount of the material of the locking means do not fire prematurely in this test.

The trigger temperature of the devices of the invention may be lowered slightly if desired by incorporating a minor amount of an impurity in the material of the locking means. The impurity should be a lower melting material and should be dispersed uniformly throughout the locking means. Thus, for example the trigger temperature of a myristanilide locking means may be lowered by the incorporation of myristic acid therein.

WHAT WE CLAIM IS: 1. A temperature-responsive indicating device comprising a housing which defines a cavity closed at one end and open at the other end, an indicating means within said cavity for movement relative to said housing, a biasing means within said cavity for urging the movement of said indicating means relative to said housing, and a fusible locking means within said cavity, wherein said locking means is adapted to fuse at a predetermined temperature and wherein said locking means has the formula

wherein R is selected from lower alkyl groups of from 1 to 4 carbon atoms; mis 0 or 1; and n is from 4 to 20.

2. A temperature-responsive indicating device according to claim 1 wherein m is 0.

3. A temperature-responsive indicating device according to claim 2 wherein n is from about 7 to 17.

4. A temperature-responsive indicating device according to claim 3 wherein n is 13.

5. A temperature-responsive indicating device according to claim 1 wherein m is 1.

6. A temperature-responsive indicating device according to claim 5 wherein R is a methyl group.

7. A temperature-responsive indicating device according to claim 6 wherein said methyl group is ortho or para to the amino group.

8. A temperature-responsive indicating device according to claim 7 wherein n is from about 7 to 17.

9. A temperature-responsive indicating device according to claim 8 wherein n is 11.

10. A temperature-responsive indicating device substantially as herein described with reference to Figures 1 or 2, or Figure 3 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (10)

**WARNING** start of CLMS field may overlap end of DESC **. locking means until it fuses. Methods of forming the reverse curldown lip are described in U.S. Patent No. 3,965,849. The indicating means may then be urged toward the closed end of the device (thereby compressing the biasing means) and held in that position until the fused locking means material solidifies. The assembled signaling devices are then preferably quality assurance-tested by heating them at about 75"C for 2 hours. This test causes those devices which have received an insufficient amount of the material of the locking means to fire prematurely. Those devices which have received a sufficient amount of the material of the locking means do not fire prematurely in this test. The trigger temperature of the devices of the invention may be lowered slightly if desired by incorporating a minor amount of an impurity in the material of the locking means. The impurity should be a lower melting material and should be dispersed uniformly throughout the locking means. Thus, for example the trigger temperature of a myristanilide locking means may be lowered by the incorporation of myristic acid therein. WHAT WE CLAIM IS:

1. A temperature-responsive indicating device comprising a housing which defines a cavity closed at one end and open at the other end, an indicating means within said cavity for movement relative to said housing, a biasing means within said cavity for urging the movement of said indicating means relative to said housing, and a fusible locking means within said cavity, wherein said locking means is adapted to fuse at a predetermined temperature and wherein said locking means has the formula

wherein R is selected from lower alkyl groups of from 1 to 4 carbon atoms; mis 0 or 1; and n is from 4 to 20.

2. A temperature-responsive indicating device according to claim 1 wherein m is 0.

3. A temperature-responsive indicating device according to claim 2 wherein n is from about 7 to 17.

4. A temperature-responsive indicating device according to claim 3 wherein n is 13.

5. A temperature-responsive indicating device according to claim 1 wherein m is 1.

6. A temperature-responsive indicating device according to claim 5 wherein R is a methyl group.

7. A temperature-responsive indicating device according to claim 6 wherein said methyl group is ortho or para to the amino group.

8. A temperature-responsive indicating device according to claim 7 wherein n is from about 7 to 17.

9. A temperature-responsive indicating device according to claim 8 wherein n is 11.

10. A temperature-responsive indicating device substantially as herein described with reference to Figures 1 or 2, or Figure 3 of the accompanying drawings.