Stoves and furnaces – Heaters – Chemical
Reexamination Certificate
2000-04-12
2001-11-20
Lazarus, Ira S. (Department: 3743)
Stoves and furnaces
Heaters
Chemical
C252S070000
Reexamination Certificate
active
06318359
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to disposable heat packs for therapeutic use and more particularly to heat packs employing super-cooled aqueous salt solutions.
FIELD OF THE INVENTION
The use of disposable heat packs has grown considerably over the last several years. These heat packs offer an economical, safe and reliable way of applying heat for therapeutic use in both home and institutional settings. Disposable heat packs are often used at home for a number of ailments including to relieve pain caused from muscle strain or injury, or to relieve soreness. Certain specialized uses have also developed including relieving discomfort in the breast area in nursing mothers. Hospitals use disposable heat packs in a number of ways including to warm a newborn's heel prior to drawing blood, as is customary or required in many jurisdictions.
Heat packs can be both disposable and reusable and many types of both kinds are known. In institutional settings such as hospitals, disposable packs are preferred for ease of use and sanitary reasons. Typically such packs are used for only a few minutes and then discarded. An ideal disposable heat pack is both easy and quick to use, is completely safe and reliable, and is economical.
Disposable heat packs utilizing super-cooled aqueous salt solutions are well-known. These packs typically employ a flexible plastic container which houses the salt solution. The solution is “super-cooled” which means it is prepared in a very pure state and then heated to a high temperature. It is then cooled gradually to a temperature below its normal crystallization temperature. Normally the salt solution is prepared so that the super-cooled solution remains stable at ambient temperatures found in homes, hospitals and their related storage areas.
When the pack is to be used, crystallization in the solution is initiated. The latent heat of crystallization warms the pack as the solution turns from liquid to solid phase. If the correct formulation of salt solution is chosen, the phase change occurs at a constant temperature in a narrow range which is appropriate to warm human skin, The reaction is predictable and stable and lasts several minutes—enough for the pack to perform its task.
Much prior art exists teaching different container structures for the heat packs, and employing different salt solutions and different methods of initiating crystallization. In particular, much attention has been focused on various means or “triggers” to initiate crystallization of the solution.
U.S. Pat. No. 4,077,390 describes a flexible container filled with a super-cooled aqueous salt solution and also containing a flexible ferrous metal strip characterized by one or more fissures or slits which are said to initialize crystallization when the strip is flexed. The length, shape and location of the fissures and slits is carefully set out. The flexing is said to produce minute particles of metal around which crystallization occurs. Problems with this device can include breakage of the strip along a fissure which can render the device incapable of being triggered, or which can leave a sharp metal fragment in the container leading to rupture.
To overcome these problems, U.S. Pat. No. 4,460,546 (issued to the same patentee) teaches the use of pinhole openings in the metal strip in place of the fissures or slits. The material of the strip is amended from ferrous metal (or sometimes stainless steel) to a more exotic beryllium-copper alloy or phosphor-bronze. The problems with this trigger means include accidental triggering caused by routine handling and also the inability to trigger even after repeated attempts.
A third effort along these lines was made in U.S. Pat. No. 4,572,158. In this patent further refinement of the location, shape etc. of the slits is taught. This refinement is said to encourage minute “tearing” of the metal upon flexing, which exposes new metal to the solution and hence initiates crystallization. Again, repeated flexing can still fail to trigger this device in a significant number of units.
U.S. Pat. No. 4,872,442 (issued to a different patentee) is stated to solve these problems by providing a similar metal strip, additionally having eroded and roughened surfaces. The surface texture is said to enhance the separation of minute particles of metal upon flexing, which particles can then act as a nesting site for crystallization. Incidence of non-triggering units is said to be reduced. Manufacturing costs for these types of sophisticated triggering devices is high.
As early as 1933, in U.S. Pat. No. 1,915,523, it was taught that crystallization of a super-cooled aqueous solution of sodium acetate could be triggered by injecting the solution with air. A flexible container is provided with a semi-automatic valve that can be operated to allow air into the container thereby inducing crystal formation.
Recently, in U.S. Pat. No. 5,305,733, further attempts were made to trigger crystallization by introducing air into a container filled with super-cooled solution by building onto the container a metallic puncturing device. The puncturing device is attached to the outside of the container and is provided with prongs which are pushed through the container walls to allow air to enter and initiate crystallization. A sealing means has to be provided to prevent the solution from escaping the container once puncturing occurs. This device is stated to be an improvement over much earlier valve operated devices as triggering can be initiated with only one hand. Leakage after triggering is a problem that occurs with these devices. They must also be manufactured and handled carefully to avoid accidental triggering.
Attempts have also been made to employ chemical as opposed to mechanical triggering devices. Typically these devices are chemical-specific and not always adaptable for solutions with optimum properties.
U.S. Pat. No. 3,951,127 teaches triggering of a super-cooled salt solution, such as a sodium thiosulfate pentahydrate or a sodium acetate trihydrate solution, by introduction of a second chemical, being either sodium borate pentahydrate or sodium sulfite. The second chemical can be in crystal or solution form. The second chemical in solution form can be introduced to the first chemical through a valve arrangement. Alternatively, the second chemical, provided in crystal form, can be located in an outer container disposed around an inner container holding the first chemical in solution, and into which the first container is ruptured, thereby mixing the two chemicals. Problems with this arrangement include the properties of chemicals themselves, being both toxic to humans and also reacting at a higher than ideal temperature. To offset this the patent further teaches use of insulation to prevent excessive heat transfer to the person. Excessive heat can cause burning and in many jurisdictions non food-grade (toxic) chemicals are prohibited in institutional use.
It is an object of this invention to provide a disposable heat pack that is both easy and quick to use, is completely safe and reliable, and is economical. It is a further object of this invention to provide a heat pack devoid of ancillary mechanical or chemical triggering means, thus reducing the cost and complexity of manufacture.
SUMMARY OF THIS INVENTION
Thus there is provided a disposable heat pack using a food grade (non-toxic) aqueous salt solution hermetically sealed in a flexible container, with which air can be mixed by applying simple mechanical pressure with one hand to the exterior of the heat pack. Triggering requires no second chemicals, no metal or plastic disk or strip triggering means, and does not require puncturing of the pack in such a way as to ever allow the solution to escape outside the pack.
One embodiment of the pack uses a container with an interior baffle, or flangible seal, to create two separate compartments. One compartment houses the super-cooled solution and the other compartment houses just air. Upon applying firm but modest pressure the baffle, or seal, can be ruptured
Schmidt George
Whitely Jeffrey Thomas
Clarke Sara
Dowell & Dowell , P.C.
Lazarus Ira S.
LandOfFree
Heat pack using super-cooled aqueous salt solutions does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Heat pack using super-cooled aqueous salt solutions, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Heat pack using super-cooled aqueous salt solutions will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2599735