It has been known to use cold packs which contain water in liquid form or in the form of ice. Water is a particularly good substance for use in cold packs since, due to its exceptionally high specific heat and high heat of liquefaction when in the form ice, it can absorb more heat than any other common substance within cooling ranges normally desired. The specific heat of water is about one calorie per gram per degree Celsius and. the heat of liquefaction (heat of fusion when water is turned to ice) is about 80 calories per gram. Ice in flexible or rigid containers has thus been the substance of choice for use in cold packs. Cold packs containing ice or even unpacked raw ice itself have thus been used for numerus medical and storage purposes. Such purposes for example include application to sprains, breaks, and bruises, application to the head for relief of migraine type headaches, temporary storage of transplantable organs or tissue, and storage of food products such as meats, dairy products, fruits and vegetables.

Unfortunately, water has some disadvantages. In particular, when ice is used to maximize cooling time by taking avantage of the absorbe heat of liquefaction, the temperature is zero degrees Celsius which is too cold to be ideal when living tissue is being cooled. At such a low temperature, damage to issue can result and the discomfort level is so high

that an individual repeatedly removes the cold pack from an area of swelling for relief from numbness and pain. Furthermore zero degrees Celsius is too cold for ideal storage of some food products since tissue damage can cause wilting and discoloration. Other materials which require cooling may also ideally be cooled by a cold pack having a temperature above freezing (0°C, 32°F), but below normal ambient temperature, e. g. 60 to 100°F (15 to 38°C).

Water may of course be used in liquid form at temperatures above zero degrees Celsius, but the temperature rapidly rises as compare with the use of ice since the heat of liquefaction is not available for cooling.

Other materials can be used in cold packs which have higher melting temperatures and thus have a higher comfort level but such materials almost universally have lower specific heats and lower heats of liquefaction which results in cold packs which do not last nearly as long as cold packs containing ice.

Recently, in an unrelated art area, new physical combinations of water and other substances have been discovered which have been found to be clathrates. Clathrates are complex compositions compose of two or more components. They differ from other complex compound in that molecules of their components are associated without ordinary chemical bonding. It is believed that in each case there is complete enclosure of the molecules of one of the components in a structure which has been formed by the other component. Clathrates have unique and often unpredictable properties. Aqueous clathrates have been discovered in the sea formed from water and methane and are in solid form at temperatures above the normal freezing temperature of water. Aqueous clathrates are also being examine for use in thermal storage systems, e. g., as described in U. S.

Patents 4,540,501 and 4,821,794.

Brief Description of the Invention In accordance with the present invention, a novel cold pack is provided which comprises a composition containing a combination of water and at least one other compound where the combination has a melting (and freezing) temperature above zero degrees Celsius and preferably between 1 and 15 degrees Celsius.

The novel cold pack nevertheless maintins almost all of the heat capacity of a similar cold pack using water.

Typically the combination is an aqueous clathrate high melting eutecfic containing over 90 weight percent and usually over 95 weight percent water.

The invention further inclues the method of using the cold pack for cooling of a material by freezing the contents of the cold pack and placing it in proximity to the material to be cooled.

Detailed Description of the Invention "Cold pack", as used herein, means a container containing a frozen or freezable fluid which, when the fluid is frozen, acts as a heat sink to cool materials in proximity with the container. The container may be of flexible or rigid construction and is commonly made of a flexible plastic water tight film such as polyester, nylon, polyethylene, polypropylene, polyvinylchloride, butyl rubber, polytetrafluoroethylene or neoprene. The material of the film is selected so that it is insoluble in any of the components of the fluid, e. g. when one of the components of the film will dissolve polyalkylene polymers, nylon, polyvinylchloride, polyester, polytetrafluoroethylene, or neoprene might be selected. Alternatively, laminates may be used to obtain the properties desired. A suitable container is, for example, a heat sealable polyester bag having a

polyethylene lining. The thickness of plastic films, when used, may vary widely, e. g. from 1 to 6 mils.

The pack may have a single compartment or multiple compartments and may be of any size suitable for cooling the desired material. Such packs are, however, usually of a small enough size to render them easily portable and preferably weigh less than five pounds.

The composition in the cold pack is a mixture of water and at least one other compound which together result in a freezing and melting point of between 1 and 15 degrees Celsius. Such a combination is usually a clathrate high melting eutectic composition.

"Eutectic", as used herein, means a combination of components which has a solidification (freezing) point which is different than either component alone."High melting eutectic"means a eutectic which has a melting or freezing temperature which is higher than the melting or freezing temperature of either component alone.

Suitable high melting eutectics for use as compositions within the cold packs of the present invention usually contain from 90 to 99.5 weight percent water and from 10 to 0.5 weight percent of one or more other compound. Examples of such other compound and their aqueous eutectic melting (freezing) temperatures are l, l-dichloro, l-fluoroethane, 47°F (8.3°C); dichloromethane, 35°F (1.7°C); dichlorofluoromethane, 47.5°F (8.6°C); trichlorofluoromethane, 47°F (8.4°C); dibromo- fluoromethane, 41°F (4.9°C); dichlorodifluoromethane, 54°F (12. 1°C) ; bromotrifluoromethane, 50-54°F (10-12°C); chloro-difluoromethane, 61°F (16.3'C" ; 1,1,1.2-tetrafluoroethane, 50°F (9.9°C); trichloromethane, 35°F (about 2°C); 1,1,2,2,3,-pentafluoropropane, 47°F (8.3°C); 1,1,1,2,2- pentafluoropropane, 43°F (6.1°C); methyl iodide, 41°F (16°C) ; ethyl

chloride, 41°F (16°C); propane, 43°F (6°C) and bromine, 43°F (6°C). In each of ihese cases the combination has a water concentration greater than 95 weight percent, e. g. the water-l, l-dichloro, l-fluoroethane combination contains from 98 to 99 percent water. The above described combinations are believed to be clathrate compositions. While many of the fluorinated compound have very good properties for the purposes of the invention, some of them may not be desirable for environmental reasons.

In order to form the desired combination of water with the other compound which is usually very sparingly soluble or even considered insoluble in water, incorporation of a small amount of surfactant may be desirable, e. g. 0.01 to 0.5 percent by weight of the combination. A range of 0.05 to 0.2 weight percent is the usual and preferred range of surfactant when it is present. In using the term"consisfing essentially of'in the specification and claims, it is to be understood that any additional component may be included provided that it does not adversely affect the high temperature eutectic nature of the combination, thus surfactant needed to optimize or enhance the combination may be included.

The choice of suitable surfactant depends at least in part upon the compound being incorporated into the water. Both ionic and non-ionic surfactants may be used. Examples of suitable surfactants are: sorbitan derivatives such as sorbitan trioleate and polyoxyethylenated sorbitans; glycerol derivatives such as glycerol monostearate; cetyl alcohol derivatives such as sodium cetyl stearyl sulfate and cetyl ethyl morpholinium ethosulfate; polyoxyalkylenes such as polyoxyethylene alkyl amines; and sulfates and sulfonates such as sodium dodecyl sulfate and alkyl aryl sulfonates.

Fluorinated surfactants may also be desirable, especially when the compound being incorporated into water is itself fluorinated. Fluorinated

surfactants may be ionic or non-ionic and are often very similar to surfactants containing hydrocarbon structures except that at least some of the hydrogens have been substituted by fluorine. Examples of fluorinated surfactants are perfluorocarboxylic acids, perfluoroalkyl polyoxyethylenated alcools, and ammonium fluoroalkyl phosphates.

To make a cold pack in accordance with the invention, a high melting aqueous eutectic as previously described is simply placed in a suitable pacage. For purposes of obtaining optimum heat transfer, the package wall desirably has a high heat transfer rate due to a high heat transfer coefficient of the material of the wall or due to a thin wall structure or both.

To use the cold pack of the present invention, the pack is refrigerated, preferably to the point where the contained composition freezes. The refrigerated pack is then placed in proximity to the material to be cooled."Proximity"in this context means that the cold pack and material to be cooled are close enough that heat from the material can be transferred to and absorbe by the pack.

As previously discussed, the cold pack of the invention can be used to cool almost any material where cooling between normal aqueous freezing and normal ambient temperature is desired. Such materials include swollen tissue and other living substances such as fresh fruits, fresh vegetables, and transplantable tissue. The cold packs may also be used to cool non-living materials which one does not wish to freeze, such as meats and dairy products and certain chemical compound which are unstable or spoil at elevated temperatures, e. g. peroxides, organic nitrates, proteins, peptides and nucleic acid sequences.

Example 1 A 2 mil thick polyester bag with a polyethylene lining having a heat seal type closure was filled with a mixture of water and l, l-dichloro, 1- fluoroethane. The mixture was obtained by mixing about one percent of 1,1-dichloro, 1-fluoroethane into water by weight of the finished water- 1, 1-dichloro, 1-fluoroethane combination. The bag was then sealed and placed in freezer until the contents were frozen. The bag was removed and thawed at room temperature. The surface temperature of the bag was about 47 degrees Fahrenheit dring the thawing process which lasts for about the same period of time as the thawing of an equivalent weight of ice in a control bag. The surface of the bag (cold pack) of the invention was cool but comfortable to the touch; whereas, a control bag containing ice is uncomfortable to the touch and so cold that continuous contact cannot be maintained during the thawing process.

Example 2 Example 1 was repeated except that 1,1,2,2,3-pentafluoropropane at a concentration of two weight percent was substituted for the 1,1 dichloro, 1-fluoroethane. 0.1 percent of sodium dodecyl sulfate surfactant was incorporated into the combination. The surface of the bag was 43°F (6°C).

Example 3.

Example 2 was repeated except that 1,1,1,2,2-pentafluoropropane was used. The surface temperature of the bag was 41°F (5°C).