Note: Descriptions are shown in the official language in which they were submitted.
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~ackground of the Invention
Thls invention relates to a device for indicating whether or not
a product has ever exceeded a predetermined temperature, and, more particu-
larly, to such a device which is quite inexpensive in use and reliable, but
does not require special handling prior to its association with a product
which is to be monitored.
It is common practice in the food and medical industries, for ex-
ample, to store perishables by freezing them until such time as they are to
be used. For example, a significant part of any modern grocery store is
devoted to frozen vegetables, juices, dinners, etc. It is also common to
store blood plasmas in a fro~en condition, and many vaccines are stored at
reduced temperature.
It will be recognized that the unthawing or elevation of the tem-
perature of a product prior to the time it is to be used, can affect the
quality of such product. This is especially true of frozen unsterilized
products, which normally contain bacteria and certain enzymes which cause
deleterious changes ~o the product once it becomes unthawed. Unwanted thaw-
ing can occur during handling of a product. Such thawing and consequent pro-
duct deterioration is often not detectable by the ultimate user of the pro-
duct because of later refreezing. It will be recognized that use of a pro-
duct, such as a blood plasma, certain foods and vaccines, after such unde-
tected thawing or temperature elevation can have grevious results.
Because of the thawing-refreezing and temperature elevation prob-
lems, much effort has been devoted to providing a simple~ effective and re- ~;
liable means for indicating the thermal history of a product to a potential
user so that assurance can be had that the product has not at any time at-
tained such an elevated temperature that its quality is adversely affected.
The paper entitled "Defrost Indicators" appearing in Food Technology, Vol.
26, pp. ~6 - 50 ~1972) provides a comprehensive list of patents ancl refer-
ences setting forth the state of the art on this problem, with particular
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emphasis on frozen food thaw indicators. As pointed out in said paper,
many thaw indicators have been designed in the past, and some have even been
commercially produced and marketed. ~lowever, the ideal indicator does not
exist, and none of those designed to date have been commercially successful.
Presently available thermal history indicators generally either
require modification of the existing package,for the frozen product so that
the indicator can have access to the interior of the product while at the
same time enabling checking from the exterior of such package, or merely
measure the surface temperature of the product. Modification of the package
is generally too expensive and cumbe~some to be acceptable to the industry,
and measurement of the surface temperature of the product is often not re-
flective of the state of the product on a whole. Because of such, neither
approach is satisfactory. Another magor difficulty with most present indi-
cators emanates from the fact that they rely on the thawing of an indicating
substance of one sort or ano~her for their operation. Special handling has,
therefore, been necessary during fabrication and later storage of the majority
of such devices to assure that the indicating substance remains frozen, or `
such devices must be fabricated immediately prior to being applied to the
product. While some devices include a membrane for containing the indicating
substance, which membrane breaks to release the substance when the substance
is frozen, such devices have not been reliable. That is, freezing may not ;
always cause the membrane to break and release the diffusion agent. These
problems have contributed to the reluctance of industry to adopt such devices.
Summary of the Invention
The present invention provides a thermal history indicator `
for products which is not subject to the above difficulties and problems.
In its ~asic aspects, the indicator of the invention includes
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a housing having an indication area at a first location therein; a diffusion ;
agent; a reservoir for said difusion agent within said housing at a second
location spaced Erom sald first location; a wick for said diffusion agent
extending between said first and second locations within said housing, said
diffusion agent being capable of diffusion through said wick only when the
temperature of said agent is above said prescribed temperature; said housing
including a thermal conducting wall portion providing thermal communication
between said product and the interior of said housing, and a thermal insulat-
ing wall portion substantially isolating the interior of said housing from
the ambient temperature around said product, said thermal insulating wall
portion including both a heat reflective surface and a material of lower heat
conductivity than said reflective surface and said thermal conducting wall
portion; and an adhesive covering substantially the full external surface
area of said thermal conducting wall portion whereby substantially said full
surface area may be adhered to said product in good heat transfer contact
therewith.
Thus, although the device is designed for securance to the exterior
of a product, such device is adapted to reduce or entirely eliminate the
effects of the package environment on its operation.
Preferably both the thermal conducting wall and the heat reflective
surface are provided by a metal foil layer.
~s another feature of the invention, it enables fabrication and
storage for extended pariods of time without the necessity of the diffusion
agent being frozen. To this end, the reservoir is most desirably a closed
membrane which completely contains the diffusion agent but which is ruptur-
able from exteriorly of the housing to release the diffusion agent therefrom
for contact with
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the wick. Thus, the device can be fabricated and stored for extended lengths ;~
of time prior to the time it is desired to utilize the same. More important-
ly, because breaking of such membrane is performed as an intentional act
from the exterior of the housing, such breaking is assured.
As another salient feature, the prefeTred embodiment of the inven-
tion includes, in addition to a rupturable reservoir" means for controlling
the passage of the indicating fluid from the reservoir to the indication area
~J between such time that the reservoir is broken and the indicating substance
is frozen with the packagé. More particularly, a dam is provided across the
wick at a location betwe~n the reservoir and the indication area for control-
ling diffusion of such agent. Such dam is most simply made providing a por-
tion of such wick of increased density to reduce the time rate of diffusion
of such agent through the portion. It should be noted that such dam is also
useful for providing a control on the length of time that the difusion agent
must be thawed prior to the device providing an indication that the product
may have deteriorated more than an acceptable amount.
The invention includes other features and advantages which will
become apparent from the following, more detailed description of a preferred
embodiment.
Brief Description of the Drawing
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With reference to the accompanying single sheet of drawing: -
Figure 1 is a perspective view showing a preferred embodiment o a
davice of the invention secured to a package of a frozen product, e.g., a ~;
food;
Figure 2 is an enlarged sectional view of the device of the inven-
tion illustrated in Figure 1, taken on a plane indicated by the lines 2 - 2
in Figure 1, and illustrating its make-up;
~igure 3 illustrates a section of a continuous tape of devices of
the invention, passing between rollers for breaking the diffusion fluid re
servoir of`each device from the exterior of such device;
Figure 4 is an enlarged, plan view of another preferred embodiment
of the invention; and
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Figure 5 is an elevation view of a package of frozen vaccine, for
example, illustrating the embodiment of ~lgure ~ secured thereto.
Detailed Description of Preferred Embodiments
~Yith reference first to Figures 1 and 2 of the accompanying draw-
ings, a device of the invention is generally indicated by the reference nu-
meral 11 secured to the exterior surface of a package 12 of, for example, a
frozen food. The device 11 includes an enclosure or housing 13 defined by
upper 14 and lower 16 sheets of material which are peripherally secured to-
gether as illustrated at 17. ;
Means are associated with the housing 13 for insulating the interior
of the same from the ambient temperature around the product to which it is
secured. That is, the wall 14 is defined by a lamination of a layer 18 of a
transparent plastic mateiial and a layer 19 providing heat reflection. The ~ ;
layer 18 is most desirably of a plastic material having good heat insulating
qualities, such as a cellulosic, polyamide, polycarbonate, polyester, poly-
olefin, polyvinylchloride, polystyrene, or copolymers thereof. Such layer 18
will thus isolate the interior of the package and the layer 19 from direct
thermal contact with the package environment. In this connection, it is de-
sirable that the layer 18 be relatively thick, e.g., 20 mils.
The layer 19 is, for example, an aluminum foil or other metal foil
providing a heat reflective surface at the interior side of the transparent
layer 18. Such layer will thus prevent radiation through the plastic layer ;
18 from heating the interior of the housing. However~ the layer 19 has re-
moved sections providing light transmitting windows 21 through the housing at
specific locations as illustrated. The purpose of such windows will be des-
cribed in detail hereinafter. ~
The bottom wall 16 of the housing has a generally flat configura- ~ -
tion which conforms to the surface of the package. In addition, such wall
includes a layer 22 of a metal foil or the like providing good thermal conduc-
tion between the interior of indicator housing and the food package, and as
coating or layer 23 of a suitable adhesive is provided on the underneath side
of layer 22. Such adhesive will provide securance of the housing 13 to the
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package over the ull surface area of such metal foil layer 22 for good
thermal conduction therebetween. In this connection, the foil providing the
layer 22 can be of the same material providing the layer 19 of the wall 14.
It is because transfer of heat from the package to the housing will be pri-
marily via conduction, whereas transfer of heat from the surrounding environ-
ment to the package will be by radiation, that an aluminum foil is capable of
unctioning both as insulation for the wall 14 and a thermal conductor for
wall 16.
A reservoir 24 for a diffusion agent is provided within the housing
13 at a location spaced from the windows 21. Such reservoir is formed by a
closed, thin walled membrane of a flexible but inelastic material which can
be ruptured from exteriorly of the housing to release a liquid diffusion
agent contained therein. As shown, such membrane is centrally located within
the housing, whereas the windows 21 are positioned adjacent the side edges of
such housing. A wick for transferring the diffusion agent when it is not
frozen, from the réservoir to the vicinity of the windows is also included.
More specifically, the remainder of the interior of the housing is filled
with a generally porous material. The exact nature of such material will de-
pend upon its relationship with the chosen diffusion agent, i.e., for wicking
action, the diffusion agent must wet such material. A cellulosic absorbent,
such as that from which Whatman filter papers are made, is wetable by most
liquids used as diffusion agents in devices of this nature and is otherwise
suitable for use with the present invention.
From the above, it will be recognized that once reservoir 24 is
broken to release the diffusion agent, such diffusion agent, when it is in li-
quid form, will be transmitted by the wick material 26 to locations underneath
the windows 21. The time required for the diffusion agent to pass from the
reservoir to the indication areas beneath the windows will depend upon the
natures of the diffusion agent and the cellulosic materiai. Thus, by ap-
propriately choosing the diffusion agent and the material for the wick, the
thermal condition to which the product must be subjected before an indication
of such will be given at the windows 21 can be selected.
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As discussed previously, one pro~lem which has precluded many prior
indicators from being adopted is that they must be fabricated and stored at
temperatures below the freezing point of the diffusion agent so that false
indications are not given. As a particularly salient feature of the present
invention, it includes means which overcomes this problem. More particularly,
not only is the diffusion agent maintained out of contact with the wick ma-
terial by the unruptured membrane until such time as the device is to be used,
but the device also includes means which assures that even after rupture of
the membrane, diffusion of the agent through the wick'is prevented for a
selected period'of time sufficiént to enable the device to be applied to a
package and then frozen. To this end, dams 27 are provided in the wick sepa- ~
rating the reservoir and the windows 21 on each side of the device. As best ' -
illustrated in Figure 2, each dam 27 is simply a portion of the wick material ~ '
of increased density to reduce the time rate of diffusion of the agent through
such portion. When the wick material is of a relatively inelastic cellulosic '
absorbent, for example, the dam can be provided merely by compressing the ma- ;~
terial as indicated for such increased density. The degree of compression or "~
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increased density will depend upon the nature of the wick material and the '~
time delay desired. The diffusion agent can be any of the liquid materials
normally used for such purpose, and flowable through the selected wick materi- ' ~
al at the desired temperature. A preferred material for use as a diffusion ~ '
agent when it is desired to know whether or not a product, such as a vaccine
or a pl~sma, has been subjected to a temperature greater than -20 for a pre-
determined period of time is corn oil. If the product is a frozen food, for
example, ~hich will deteriorate if subjected to a temperature greater than 0C '
for a predetermined period of timeJ a preferred indicating material is pal-
mitoleic-acid.' Jojoba Wax is a suitable diffusion agent for us0 when it is
desired to know when a product has been subjected to a temperature greater
than 10C for more than a predetermined period of time. Of course, a color
3~ additive is desirably added to the chosen diffusion agent to provide a suit-
abIe visually detectable contràst at the windows 21 when the diffusion agent
has reached the same. Visual indication can also be obtained at the windows 21
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by providing a color or indicia signifying thawing on the interior side sur-
fare of the wall 16 directly below the windows 21 but covered by the wick
material. If the wick is relatively thin, e.g. J 10 mils, at such location
and is of a good grade of a cellulosic absorbent such as that from which
Whatman filter papers Nos. 1 and 3 are made, the above and other diffusion
agents will cause the same to become -translucent at the windows 21. Such
translucency will then expose the indicating color or indicia on the interior
side surface of the wall 16 to provide the desired visible indication of the
*hermal history of the product.
It will be recognized that not only should the wall 13 of the de-
vice isolate the diffusion agent from the temperature of the surrounding en-
vironment, bu~ it is also important that the effect on the surface of the
product of such environment not de~rimentally affect operation of the device.
In this connection, it is not unusual for the surface of a package to be at
a much higher temperature than the procluct conta1ned therein. The device of
the invention is designed to assure that the surface temperature of the pack-
age does not cause erroneous operation of the device. That is, the housing
of the device will insulate from the temperature of the environment that por- ;~
tion of the package surface which it covers, and there is a substantial dis-
tance between the location at whlch the diffusion agent is normally located
within the housing, i.e., between the dams 27, and the edges of such housing`.
Because of such, the device not only directly insulates the diffusion agent
from the environment, but also reduces to an insignificant amount, transfer
of thermal energy from the surface of the package not covered by the device,
to the location at ~hich the diffusion agent is in close thermal contact with
the package.
The thermal indicator of the invention readily lends itself to
fabrication, storage and application to a product. More particularly, the
device can be made by laminating together the various materials without re-
quiring extensive modificàtion of machinery presently available. Moreover,
a plurality of such devices can be made simultaneously in a sheet or web
material. In this connection, Figure 3 illustrates a plurality of indicators
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of the invention providecl on a continuous backing strip 31. Such strip is,
for example, a silicone treated easily peelable strip upon which the devices
are adhered by laminating at the time of manufacture. It will be recognized
that not only does the utilization of such strip protect the adhesive layer
23 on the underneath side of each of the devices, but it also enables a
plurality of such devices to be provided in a convulute roll form or the like. ~ -
As mentioned previously, a major advantage of the instant invention
is that it is quite reliable, although it may be fabricated and storecl at -
normal temperatures. That is, with proper processing one is ass~lred that the
device is activated, i.e., that the diffusion agent is released, at the time
it is applied to a product to be frozen. Figure 3 further illustrates an
arrangement for simply and effectively activating the devices. More particu-
larly, a pair of pressure nip rollers 32 are provided, between which the
strip of material 31 is passed immediately prior to the time it is desired to
apply indicators of the invention to packages of a product.
As schematically illustrated, such nip rollers apply sufficient
pressure to the strip to rupture the membrane of the reservoir, thereby as-
suring release of the diffusion agent. The dams 27, however, prevent such :~
diffusion agent from immediately being transmitted to the indication area, ~ ~:
i.e., the wickable material underneath the windows 21. Thus, time is provided
for application of the indicators to the desired packages and later freezing
of the same. It will be recognized, that once the diffusion agent is frozen,
wicking action thereof will be prevented.
Although the features of the invention are illustrated embodied in
a rectangular indicatorJ it will be recognized that the invention is applic-
able to varlous other configurations as well.~ In this connection, Figure 4
illustrates a plan view of a circular indicator embodiment of the invention.
With reference to such figure, the reservoir of such device 41 is located
centrally therwithin as indicated at 42. Rather than the dams being provided
by two linear compressions on opposite sides of the reservoir as in the pre-
viously described embodiment, only one, circular dam as indicated at 43 is
provided. Such dam 43 circumscribes the reservoir 42 to isolate it from the
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windows 44 positioned in a circle on the side of such dam opposite of the
reservoir. I~ will be recogni~ed that this embodiment of the invention also
includes a wickable material, the outer peripheral edge of which is indicated
by the dotted line 46.
The embodiment of the invention shown in Figure 4 is in all other
respects basically the same as the embodiment shown in Figures 1 through 3.
In this connection, indicator 41 can be also combined with a backing sheet if
desired. Figure 5 illustrates an indicator 41 applied to a bottle 47 for a
frozen product, e.g., a vaccine or plasma.
Although the invention has been described in connection with prefer-
red embodiments thereof, it will be appreciated by those skilled in the art ~`
that various changes and modifications can be made without departing from its
spirit. For example, in certain instances it may be desirable to secure a
plurality of indicators of the invention to one package, which insulators are
designed to be responsive at different temperatures and times so that the
thermal history of the product can be more accurately determined. Because
of this and other changes, additions or modifications which can be made, it
is intended that the coverage afforded applicant be limited only by the
language of the claims and its equivalent.
