Note: Descriptions are shown in the official language in which they were submitted.
WO 95/06862 PCT/US94/09248
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THERMALLY RESPONSIVE INDICATOR
WITH ORGANIC RETAINING MEANS
BACKGROUND OF THE INVENTION
1. TECHNICAL FIELD
This invention relates to thermally responsive
indicating devices. More particularly, it relates to
devices that provide a signal upon the attainment of
specified temperatures.
2. DISCUSSION OF THE ART
Thermally responsive indicators are useful in a
variety of fields for providing a visual indication of the
attainment of a specified temperature. For example, U.S.
Patent No. 4,083,364 discloses a thermal indicator mounted
through the skull of an animal to detect the presence of an
elevated body temperature. German Patent No. 3,229,020
discloses a thermally responsive indicator that is designed
to be mounted on an electrical conductor. The device
provides a .visual indication of the attainment of an
elevated temperature in the conductor. U.S. Patent No.
4,818,119 discloses a railroad wheel bearing bolt with an
axially extending bore into which a heat sensor and
indicator are inserted. The indicator is exposed when a
specified temperature is attained. U.S. Patent No.
4, 289, 088 discloses a sterility indicating device for use in
a steam autoclave.
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Thermally responsive indicating devices are
especially useful in preparing food products, particularly
meat and fowl. Such devices can be used to indicate the
elevated temperature of the interior of the food product, ,
rather than the temperature of the exterior thereof. By
indicating the attainment of a specified internal
temperature of the food product, the device can signal when
the food product is organoleptically acceptable. These
devices must be sufficiently accurate to prevent
l0 undercooking or overcooking, which not only may
significantly diminish the palatability of the food, but may
also even render the food dangerous to eat, as in the case
of undercooked pork.
Several such devices for use in cooking food are
known. Examples of early indicating devices are described
in U.S. Patent Nos. 945,978 and 1,509,110, each of which
allows a plunger biased by a spring to be released into an
extended position upon attaining a specified temperature.
Retaining means, which is typically a fusible material,
holds the plunger in a retracted position until the fusible
material yields, at which time a spring urges the plunger
into an extended position. When in the extended position,
the plunger provides a visual indication to the user that
the food is °'done." To further enhance the visibility of
the plunger when it is in the extended position, a cap may
be attached to the end thereof.
The material of the retaining means has typically
comprised metal alloys, as in U.S. Patent Nos. 3,140,611,
3,682,130, 3,693,579 and 3,713,416. Indicators that use
such alloys include the ''Vue-Temp" brand and "Pop-Rite"
brand pop-up timers, manufactured by the Volk Development '
Company of Turlock, California 95381. While devices
employing such retaining materials have proven useful, they
have certain drawbacks. For example, such alloys are
typically prepared from toxic metallic substances such as
bismuth, lead, cadmium, tin, and other materials.
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Furthermore, metal alloys have high density. Thus, a given
volume of retaining material requires a significant amount
of alloy, thereby adding to the expense of the device.
Organic compounds, such as waxes, have been
suggested as replacements for metal alloys. However, waxes
typically yield over a relatively wide temperature range,
and, if composed of a mixture of different materials, can
have multiple melting temperatures, thereby resulting in a
premature or a delayed signal. This, as mentioned above, is
undesirable because the food item could either be
undercooked or overcooked, respectively.
A device that attempts to overcome the problems
exhibited by alloy and wax retaining materials is described
in U.S. Patent No. 4,170,956. This patent discloses a
nitrogen-containing organic retaining material. Devices
using these nitrogen-containing materials have been sold in
the United States under the name "Dun-Rite°~ brand pop-up
timers by Minnesota Mining and Manufacturing Company of St.
Paul, MN. The nitrogen-based materials used in these
devices do not exhibit the toxicity problems of their alloy
predecessors and exhibit better release characteristics than
waxes. However, the nitrogen-based materials disclosed in
this patent also have certain drawbacks.
For example, the nitrogen-based materials of this
patent are very pure when they are prepared. Melting
temperature (and therefore yield temperature) tends to
increase with increased purity, and the materials of this
patent melt at approximately 84.9°C when they are tested in
their purest state. A turkey is considered '~done" when the
interior temperature thereof reaches approximately 82.2°C.
Consequently, the nitrogen-based retaining material must be
mixed with a foreign substance to reduce its purity. The
use of foreign substances adds unnecessary expense. Salts,
which are added to the nitrogen-based material to clean it,
tend to solidify to form gel globules in the material,
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thereby requiring that the material be strained. The
straining process often must be conducted repeatedly,
thereby increasing the time and cost of production. The
yield is reduced, and, consequently, a greater amount of
material must be manufactured and processed to obtain a
given amount of retaining material.
SUMMARY OF THE INVENTION
This invention provides a thermal indicator
capable of indicating that an article of food is heated to
a specified temperature. The indicator comprises a barrel
having an opening communicating with a chamber within the
barrel, a plunger disposed in the chamber and adapted for
sliding travel therein between a retracted position and an
extended position, means for resiliently biasing the plunger
away from the retracted position and toward the extended
position, and retaining means for releasably retaining the
plunger in the retracted position. The barrel is adapted
for insertion into the article of food to be heated.
The retaining means comprises a material formed
from a mixture comprising at least two organic compounds
selected from the group consisting of fatty acids, fatty
ketones, fatty amides, and fatty anilides, provided that at
least one of said two organic compounds is selected from the
group consisting of fatty ketones and fatty acids and at
least one other of said two organic compounds is selected
from the group consisting of fatty amides and fatty
anilides. The melting point of the mixture is preferably
lower then the melting point of any individual component.
The organic compounds must be at least 80% pure,
more preferably at least 95~ pure. These organic compounds
preferably have a single melting point. It is also
preferred that the melting temperature of the mixture range
from about 56°C to about 95°C and melt within 15°C of the
melting point. The aforementioned organic compounds are
inexpensive and result in a substantial cost savings per
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unit. More importantly, the organic compound retaining
materials are not toxic and are therefore safer for use in
food than retaining materials comprising metal alloys.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an inclined side elevation view of the
indicator of the present invention.
FIG. 2 is a central longitudinal sectional view of
the indicator of FIG. 1 in a retracted position, viewed in
the plane 2-2 of FIG. 1.
FIG. 3 is a central longitudinal sectional view of
the indicator of FIG. 1 in an extended position.
FIG. 4 is a top view of the indicator of FIG. 1.
FIG. 5 is a side elevation view of an alternate
embodiment of the indicator of the present invention.
FIG. 6 is a graph showing the effect of relative
concentration of each organic compound of the mixture on the
melting point of the mixture.
DETAILED DESCRIPTION OF THE INVENTION
Referring specifically to Figures 1 and 2,
indicator 10 is shown including barrel 12. Barrel 12 is a
monolithic molded body made of a material capable of
withstanding the elevated temperatures encountered in a
cooking environment. Nylon is the preferred material,
although other materials could be adapted for use in the
cooking environment as well. Barrel 12 includes lower
barrel end 14 adapted for insertion into a food item and may
be provided with one or more barbs 20 radially disposed near
lower barrel end 14 for retaining the indicator in the food
once inserted. Barrel 12 also includes annular flange 16
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located adjacent upper barrel end 18. Flange 16 may be of
varying radial dimensions so as to contact the surface of
the food item when indicator 10 is inserted therein to
prevent further insertion.
Barrel 12 communicates through orifice 22 with
cavity 24. Cavity 24 is adapted to contain at least part of
plunger 26 that is disposed through orifice 22 of barrel 12
and is maintained in slidable relation thereto within cavity
24. Plunger 26 is adapted to travel between a retracted
position and an extended position. Figures 1 and 2
illustrate plunger 26 in a retracted position, but the term
"retracted position" is not limited to one in which cap 28
is in intimate contact with flange 16. Additionally, the
indicator of the present invention, when constructed without
the cap of the preferred embodiment, may be in a retracted
position with upper plunger end 30 either within cavity 24
or partially protruding therefrom. Figure 3 illustrates
plunger 26 in an extended position. Plunger 26 provides a
visual indication of the attainment of a predetermined
temperature when plunger 26 is in an extended position.
Means are provided to resiliently bias plunger 26
toward the extended position. In the illustrated
embodiment, the biasing means comprises a spring 34. In
Figure 2, spring 34 is circumferentially disposed about
plunger 26 and exerts a force in direction 50 against
annular plunger flange 36 located on plunger 26. The
opposite end of spring 34 contacts and exerts a force
against annular seat 38, formed in cavity 24.
Retaining means are provided to maintain plunger
26 in a retracted position prior to use against the force of '
spring 34. The retaining means includes a retaining
material 40 positioned within cavity 24 to mechanically '
interfere with plunger 26. In the illustrated embodiment,
retaining material 40 is positioned with annular retainer
cavity 42, which is aligned with annular plunger depression
WO 95/06862 ' PCT/US94/09248
44. Both retainer cavity 42 and plunger depression 44 are
illustrated as annular semi-hemispherical depressions, but
any configuration which will permit mechanical interference
between retaining material 40 and retainer cavity 42, and/or
between retaining material 40 and plunger depression 44 is
contemplated. Furthermore, retaining material 40, plunger
depression 44 and retainer cavity 42 could be located at any
point along plunger 26 so as to retain plunger 26, but are
preferably located adjacent lower barrel end 14.
Plunger 26 is maintained in a retracted position
by the retaining material 40 until, after exposure to an
elevated temperature at or near the preselected temperature,
retaining material 40 yields, allowing spring 34 to move
plunger 26 in direction 50. The "melting temperature," as
used herein, means the onset temperature or the temperature
at which the retaining material begins'to melt. The
temperature at which all the material has melted is
immaterial to the present invention, because yielding will
occur before all the material has melted. "Yield," as used
herein, means fuse, melt, plasticize, or become ductile,
malleable, or deformable to the point where the retaining
material is of insufficient shear strength to maintain the
plunger in a retracted position against the pressure of
spring 34. "Yield temperature," as used herein, means the
temperature at which yielding occurs, and is typically near
the melting temperature, although the exact yield
temperature differs depending on the particular retaining
material selected.
Yielding may occur by one of several mechanisms.
Once the ambient temperature reaches the melting temperature
of retaining material 40, part of the material may liquefy,
and thereafter function as a lubricant. Alternatively,
retaining material 40 may liquefy quickly and be of
insufficient shear strength to maintain shaft 36 in the
retracted position. Retaining material 40 may also soften
until spring 34 causes part of the material to be sheared
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away by retainer cavity 42. Once the shear strength of
retaining material 40 has diminished, spring 34 urges shaft
36 into an extended position, which provides a visual
indication of the attainment of the specified temperature. ,
Referring to Figure 3, plunger 26 is shown in the extended
position, which position corresponds to the ambient
a
temperature being above the yield temperature of retaining
material 40.
Referring to Figures 1 and 4, the preferred
embodiment of the present invention is shown. Cap 28 is
affixed atop plunger 26 and is adapted to maintain intimate
contact with flange 16. When plunger 26 is in a retracted
position, cap 28 prevents contaminants from entering cavity
24, and prevents retaining material from leaking out of
indicator 10. Cap 28 also provides increased visibility
when plunger 26 is in the extended position. Upper plunger
end 30 can be adapted to maintain sliding sealing contact
with cavity wall 32 to further aid in preventing
contaminants from entering, or retaining material from
leaving cavity 24.
Referring to Figure 5, an alternate embodiment 10'
of the present invention is shown. Cap 28 has been omitted,
thereby presenting plunger 26' for visual identification
upon the attainment of the specified temperature.
The present invention is primarily directed to
improvements. in retaining material 40. The composition
suitable for preparing the retaining material of this
invention comprises at least two organic compounds selected
from the group consisting of (1) fatty acids, (2) fatty
ketones, (3) fatty amides, and (4) fatty anilides, provided
that at least one of said two organic compounds is selected
from the group consisting of fatty ketones and fatty acids
and at least one other of said two organic compounds is
selected from the group consisting of fatty amides and fatty
anilides. For the purposes of this invention, °'fatty acids"
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include myristic acid, stearic acid, and lignoceric acid,
"fatty ketones" include stearone (i.e., 18-
pentatriacontanone), myristone (14-heptacosanone), and
palmitone (16-hentriacontanone), "fatty amides°' include
stearyl stearamide, stearamide, and lauryl palmitamide,
"fatty anilides" include myristanilide and stearanilide.
Fatty acids suitable for this invention can be represented
by the general formula:
CH3 ( CHZ) aCOOH
wherein n >_ 5, preferably 12 < n < 28
Fatty ketones suitable for this invention can be represented
by the general formula:
CpHZP+I COC",HZm+t
wherein p >_ 5 and m >_ 5, preferably
8 <_ p < 30 and 8 < m < 30
Fatty amides suitable for this invention can be represented
by the general formula:
CqH2q+iCONHR
wherein R represents H or C,Hz~+~
and q >_ 5 and r >_ 5, preferably
15 <_ q < 30 and 15 < r < 30
Fatty anilides suitable for this invention can be
represented by the general formula:
CH3 ( CHZ ) aCONHC6H5
wherein s >_ 5, preferably 13 < s <_ 28
The organic compounds can be straight-chain or cyclic.
However, up to 20~, preferably no more than 5~ of the
organic compound can be branched. The compounds should have
a sufficient number of carbon atoms in the straight chain or
cyclic ring such that they will be solids at temperatures
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equal to or less that 55°C. The atoms in the straight chain
or ring consist only of carbon atoms. However, the straight
chain can be terminated by atoms that are not carbon atoms.
If straight-chain compounds are used, the functional groups
(e.g., -COOH, -OCH3, -OH) are preferably located at the end
of the straight chain. However, they can also be attached
i
to carbon atoms in the straight chain.
It is preferred that any organic compound used to
prepare the retaining material be at least 80~ pure, more
preferably at least 95~ pure. It is also preferred that any
organic compound used to prepare the retaining material have
a single melting point, preferably between 56°C and 95°C.
The compound should be adapted to melt within a range of
15°C of the melting point. As used herein, the expression
"melting point'° means the temperature at which onset of
melting begins; the expression "melting range" means the
temperature interval over which all the retaining material
melts. Melting temperatures of the compounds disclosed
herein were determined by using a differential scanning
calorimeter (DSC) which was programmed to increase the
ambient temperature at the rate of 10 ° C per minute. The DSC
used was the DuPont 912 Differential Scanning Calorimeter,
manufactured by the E.I. DuPont de Nemours & Company, Inc.,
Wilmington, Delaware 19898.
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The following table shows mixtures that are suitable
for preparing the retaining means of the present invention:
Formulation Ingredient Melting pointAmount (% Melting point
of ingredientby weight) of mixture
(onset)(C) (C)
I stearone 84.3 60-95 79-84
stearyl 90.2 40-5
stearamide
II stearone 84.3 70-95 84-85
stearamide 103 30-5
III stearone 84.3 70-90 72-75
lauryl 76.9 30-10
palmita.mide
IV stearone 84.3 10-40 73-74
palmityl 76.5 90-60
lauramide
Y' , . c
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V stearone 84.3 15-50 77-78
myristanilide84.9 85-50
VI stearone 84.3 50-90 81-82
stearanilide94 50-10
VII stearone 84.3 15-59 69-72
stearyl 90.2 23-48
stearamide
myristanilide84.9 17-50
VIII stearone 84.3 47-80 78-83
stearanilide94 18-50
stearic acid67.2 0.1-6.0
IX myristanilide84.9 95.0-99.5 80-84
myristic 54 5.0-0.1
acid
It is preferred that the carbon atoms in the straight-chain,
in the ring, in the ester groups, and in the acid groups not
have substituents other than hydrogen atoms. However, these
carbon atoms can have substituents other than hydrogen
atoms, provided that these substituents are chemically and
physically inert upon being subjected to the heat which is
applied during use of the indicator in a cooking
environment.
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The organic compounds required to produce the
retaining material of the present invention can be ordered
in the desired purity from the following companies:
Tokyo Kasei Kogyo Co., Ltd.
Tokyo Chemical Industry Co., Ltd.
3-9-4 Nihonbashi-Honcho, Chuo-Ku
Tokyo 103
Japan
Pfaltz & Bauer, Inc.
Division of Aceto Corporation
172 E. Aurora Street
Waterbury, CT 06708
The indicator of the present invention is prepared
and assembled in the following manner. The organic
compounds are heated and melted in a glass or stainless
steel container to a temperature not to exceed 250°C. The
resultant molten material is poured through a screen into
another heated vessel (also less than 250°C) to strain out
any foreign matter. In contrast to the nitrogen-containing
material of U.S. Patent No. 4,170,956, the retaining
material of the present invention does not gel, and must be
screened only to remove any foreign particles that have
infiltrated the mixture. A metered amount of the material
is pumped into barrel 12. In the preferred embodiment,
spring 34 is guided into the barrel, and plunger 26 is then
guided through the spring and into the barrel.
The entire barrel is heated to between 130°C and
260°C while the plunger is slowly depressed into a retracted
position. The temperature to which the barrel must be
heated to melt the material within depends on several
factors, including the type of material used to construct
the barrel, the wall thickness, and the type of retaining
material used. Once the plunger has been pressed into a
retracted position and the organic material melted, the
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plunger is held in place by means known in the art, and
therefore not shown, while indicator 10 is cooled by a water
source, thereby solidifying retaining material 40.
The retaining materials of the present invention
are non-toxic, readily available from commercial resources,
and less expensive than alloys and the nitrogen-containing
materials of U.S. Patent No. 4,170,956. In addition, the
assembly process of the present invention is significantly
faster and more efficient than that required for the
nitrogen-containing materials of U.S. Patent No. 4,170,956,
because the retaining materials of the present invention do
not gel, and therefore require straining only to remove
foreign particulate matter.
The present invention has now been described with
reference to several embodiments thereof. It will be
apparent to those skilled in the art that many changes can
be made from the embodiments described without departing
from the scope of the present invention. For example, the
present invention has been described with reference to
heating food in a conventional oven, but the present
invention could be used in a microwave oven with suitable
modifications. Thus, the scope of the present invention
should not be limited to the structures described in this
application, but only by structures described by the
language of the claims, and the equivalents of those
structures.
