Refrigeration – Chemical reaction or solids dissolving
Reexamination Certificate
2001-01-24
2002-05-28
Doerrler, William C. (Department: 3744)
Refrigeration
Chemical reaction or solids dissolving
C252S070000, C126S263080
Reexamination Certificate
active
06393843
ABSTRACT:
FIELD OF THE INVENTION
The invention disclosed herein relates to the field of thermal packs. In particular, the invention relates to thermal packs wherein reduced or elevated temperatures can be generated for extended periods of time.
BACKGROUND OF THE INVENTION
The use of thermally reactive chemical systems in thermal packs is known. Typical uses of hot and cold packs include thermal therapy for treatment of muscle soreness, injuries such as sprains, maintenance of food and beverage temperature, and the like. The treatment of injuries or sore muscles using a hot pack is generally referred to as “warm therapy” or “heat therapy”, and the treatment using a cold pack is generally referred to as “cold therapy”. In the case of cold therapy, because the swelling associated with the injury or sore muscle begins almost immediately with the onset of injury, or the stress inducing the soreness, treatment should begin promptly. Conditions which benefit from heat therapy include hypothermia and thermal shock. Accordingly, it is desirable that whatever the source of thermal therapy used for such treatment, the thermal therapy source should be readily available, easy to use, and capable of providing thermal therapy for a duration that is effective in treating the injury, sore muscle or condition.
Several general types of thermal packs are known in the art. There are cold packs that contain an insulating material which, upon cooling in a refrigerator or freezer, gradually warm back to ambient temperature. Likewise, there are hot packs which contain an insulating material and are heated to a temperature which gradually cool to ambient temperature. There are hot and cold packs that operate via phase change of the thermal pack components. Also, there are thermal packs that employ chemical components that dissolve endothermically or exothermically in a solvent.
Examples of cold packs that employ an insulating material include cold packs that contain gelling agents, such as the thermal packs described in Williams U.S. Pat. No. 3,804,077 and Dunshee et al. U.S. Pat. No. 4,462,224. For example, these cold packs are cooled in a refrigerator or freezer. Once cooled, the cold pack is placed on the injured or sore area and thus provides cold therapy. Typical gels used in this type of cold pack are based on the gelation of xanthan gum, locust bean gum, gum tragacanth, guar gum, hydroxypropyl methylcellulose, absorbent poylmers, and the like. Gels may also be based on a high molecular weight polyacrylic acid cross-linked with a polyalkenyl ether, also referred to as cis-carbomers.
Other examples of cold packs that employ an insulating material exist in the art. For example, cold packs may employ an outer insulative layer. Alternatively, clays or silicates can be used in conjunction with cold therapy providing chemicals to form aqueous colloidal dispersions sometimes referred to as gels. These colloidal dispersions perform a similar life-extending function due to steric hindrance provision during dissolution.
Phase change materials can be converted between solid and liquid phases and utilize their latent heat of fusion to cool or heat during such phase conversion. The latent heats of fusion are greater than the sensible heat capacities of the materials. Accordingly, the amount of energy absorbed upon melting or released upon freezing is greater than the amount of energy absorbed or released upon increasing or decreasing the temperature of the material by 10° C. within a phase. Water or the silica based materials described in Salyer U.S. Pat. No. 5,211,949 are examples of phase change materials.
Certain chemical compounds, once dissolved into a solution, result in a lowering of the temperature of the solution below ambient temperature. On dissolution, these compounds take up heat from the surrounding environment. For example, inorganic salts or soluble organic compounds known to have a positive (greater than zero) enthalpy (&Dgr;
sol
H°) of aqueous solution are used to make the reduced temperature solutions useful in cold packs. However, solvents other than water can be used so long as &Dgr;
sol
H° of the solute is greater than zero. Similarly, there are also chemical compounds which upon dissolving in solution result in elevated temperatures above ambient temperature including inorganic salts or soluble organic compounds known to have a negative (less than zero) enthalpy (&Dgr;
sol
H°) of aqueous solution. These compounds are used to make elevated temperature solutions useful in hot packs. Other ingredients can be added to these compounds as well. For example, alternative solvents can be used in hot packs.
Any of these types of thermal packs can be used in combination with one another. For example, cold packs which employ a gel can also contain endotherm-producing compounds. Phase change materials can also be used in combination with endotherm-producing compounds or exotherm-producing compounds.
One problem associated with conventional thermal packs is the short duration of the temperature effect. To be useful in thermal therapy, the thermal pack must provide the desired temperature effect for a period of time needed for the particular therapy or use.
Thermal packs of the type that employ thermally reactive chemicals have employed various methods to extend the cold duration or the “life” of the thermal pack. Methods of extending the life of thermal packs can be summarized into three categories: 1) physical means to slow dissolution of the endotherm-producing or exotherm-producing chemical; 2) temperature means to provide a large temperature differential with respect to an ambient temperature; and 3) insulation means to control the rate of heat absorption or retention in an attempt to increase the time the thermal pack is at a desired temperature.
Physical means to slow dissolution of the endotherm-producing and exotherm-producing chemicals can use coated solutes whereby the coating slows dissolution. Thermal packs of this type have also used endotherm-producing or exotherm-producing chemicals pressed into pellets. For example, coated particles which control the reaction rate in cool packs are described in Lahey et al. U.S. Pat. No. 4,780,117. The pellet-form slows the dissolution of the endotherm-producing chemical and thus prolongs the life of the cold pack.
The second category wherein temperature means is used to provide a large temperature differential with respect to an ambient temperature operates by increasing temperature differential and thereby increasing the time required for the cold pack to return to ambient temperature. For example, the large temperature differential can be accomplished by using one or two endotherm-producing chemicals whereby one of the chemicals reduces temperature to an extremely low value and the other reduces the temperature to one which is useful for cold therapy. Similarly, two exotherm-producing chemicals, or a combination of one exothermic and one endothermic chemical, have been used to maintain usable temperature ranges.
Thermal packs which employ gelling agents are included in the third category of methods for extending the life of cold and hot packs. The gelling agents can be included in the same container as the endotherm-producing or exotherm-producing chemical. One example of a typical gelling agent is hydroxypropylmethylcellulose. When initiated, the endotherm-producing chemical reduces the temperature of the cold pack and the gelling agent gels. The formed gel provides some level of dissolution hindrance so the rate of dissolution is decreased.
Thermal device structures have also been explored as a means to extend the life of thermal packs. One such device is described in Brown et al., U.S. Pat. No. 5,603,729, wherein a prolonged reaction thermal device having three compartments and thermally reactive ingredients is described. A solvent is separated from two water-dissolving containers each containing ammonium nitrate and having varying thickness to control the rate of dissolution. The extended life, however, is the result of the rate of dissolving of the
Allegiance Corporation
Doerrler William C.
Rozycki Andrew G.
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