Refrigeration – Processes – Packaging
Reexamination Certificate
2001-09-25
2003-02-18
Doerrler, William C. (Department: 3744)
Refrigeration
Processes
Packaging
C062S371000, C062S529000, C062S530000, C062S430000, C062S457100, C252S071000, C435S374000
Reexamination Certificate
active
06519953
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to unfrozen cold storage of perishable materials. More particularly, the present invention relates to packs, which incorporate thermal control material, capable of maintaining perishable biological materials that are in contact with or are enclosed by the packs at selectable temperatures, including sub-zero degree centigrade (“C.”) temperatures, for protracted periods of time.
2. Description of the Related Technology
It is known that perishable materials especially biological materials, e.g., food, flowers, pharmaceuticals, etc., can be stored at temperatures reduced from those at ambient to decrease rates of deterioration for extended periods of time. Reduced temperatures inhibit, for example, the activity of degradation enzymes indigenous to many biological materials as well as inhibit the growth of microorganisms. Currently practiced methodologies of reduced temperature storage can be divided into two categories: 1) storage of materials in an unfrozen state; and 2) storage of materials in a frozen state. When stored unfrozen, materials now generally are refrigerated or maintained at temperatures between 0° C. and 10° C. Alternatively, materials, when stored in a frozen state, customarily are stored at temperatures of −15° C. or less. These practiced methodologies do not normally utilize the temperature range between about 0° C. and −15° C.
Existing cold storage methods and technologies suffer from serious defects. For example, with unfrozen storage, the temperature reductions into the 10° C. to 0° C. range slows enzymatic degradation and microbial growth in biological materials, but does not stop these processes completely. Thus, maintaining biological materials at temperatures between 0° C. and 10° C. will extend storage times, but such extensions are actually limited in duration from what is now known to be feasible, as is discussed below. Some biological materials stored at temperatures from 0° C. and above, such as RNA and mixed pharmaceutical test reagents, begin to undergo a noticeable amount of deterioration in as short a period as one or two days, and can become completely unusable after two or more days. As is generally appreciated, short storage times place major constraints on the availability of fresh, non-frozen materials such as foodstuffs and/or other biological materials, such as vaccines and other biomedical materials. In essence, these materials must be obtained or produced in close proximity to where they will be sold or used in order to provide commercially practical storage times after shipping.
Freezing biological materials overcomes some of the deleterious consequences inherent in shipping fresh materials at unfrozen temperatures. For example, once frozen, biological materials may be stored for protracted periods during which they can be shipped over long distances, because freezing essentially stops enzymatic and microbial degradation processes. However, ice crystals unavoidably form within the biological materials during freezing, these crystals can damage the materials. Specifically, the formation of ice crystals can destroy the cellular integrity of the materials or cause “freezer burn.” As is generally appreciated, the consequential damage to biological materials resulting from freezing reduces the quality of the thawed materials. In particular, with many foodstuffs, for example, the reduction in the quality caused by freezing results in reduced palatability and a corresponding reduction in the commercial value of the food relative to that same food in a fresh, unfrozen state.
In U.S. Pat. No. 5,804,444 (the “'444 patent”) to Kukal and Allen (the same inventors as here), which is hereby incorporated by reference in its entirety, the present inventors disclose novel technology for storing any biological material in an unfrozen state by determining the optimum storage temperatures for biological materials so as to overcome many of the limitations of prior storage methodologies. This novel technology is based on an appreciation of the fact that most biological materials have distinct sub-zero ° C. melting point depressions. By determining the melting point depression for a given biological material and then storing that material at its optimum storage temperature, which is slightly greater than but as close to the melting temperature as feasible, very substantial improvements in the duration and quality of the stored non-frozen biological material is achieved.
The discovery that biological materials have determinable lowest optimum storage temperatures at which they can be stored for extended periods of time has produced a need for refrigeration and packaging adapted to maintain biological materials at very stable temperatures just above the determined melting temperatures. These temperatures are predominantly below 0° C.
Currently known and available cold storage packaging materials, such as those called “cold packs” or “gel packs,” are not capable of meeting these needs because they are not capable of being adjusted to maintain different specific temperatures required to achieve the improvements in storage of non-frozen biological materials described above. These known devices, i.e., “cold packs” or “gel packs”, for storing biological materials at reduced temperatures generally fall into two categories: 1) those that function by absorbing sensible heat to preserve storage temperatures reduced from ambient; and 2) those that function utilizing a latent heat capacitance incorporated in the container to preserve a desired storage temperature. As used here, “sensible heat” is heat energy absorbed by a thermal control or temperature maintenance material that results in a corresponding increase in the temperature of the temperature maintenance material. Consequently, it is not feasible to maintain a desired temperature using a pack that functions by absorbing sensible heat, because as heat is absorbed the maintained temperature concomitantly increases. In contrast, “latent heat” is a determinable quantity of heat energy for a specified mass of a temperature maintenance material required to affect a phase transition in the material, e.g., from frozen to liquid states. During the phase transition the material maintains a substantially constant melting temperature. Latent heat equates to the amount of heat energy required to cause a given mass of solid material that is maintained at its melting temperature to become a liquid at that same temperature. Thus, the solid material continues to maintain a substantially constant temperature—its melting temperature—while external input heat energy is absorbed by the solid material to provide latent heat for affecting the process of melting.
An advantage in using latent heat when absorbing heat energy, as opposed to utilizing a sensible heat absorption process during corresponding warming, lies in the typically tremendous thermal capacitance associated with a material undergoing a phase change. In the case of water, one kilocalorie (1 Kcal) of heat absorbed as sensible heat is required to raise the temperature of one kilogram (1 kg) of the water by 1° C. Whereas, the same 1 kg of water in a solid ice state at 0° C. requires absorption of 144 Kcal of heat to affect the phase change to the liquid state for the water that remains at 0° C. throughout the phase change. Hence, 144 Kcal of heat can be absorbed by the 1 kg of ice which maintains a constant temperature of 0° C. In sum, utilization of latent heat permits absorption of increased amounts of heat energy while a melting temperature is maintained; whereas, absorption of sensible heat occurs over an unavoidable ever increasing dynamic range of temperatures.
Despite the advantages of using latent heat processes, there still are many drawbacks encountered when using currently available containers or packs employing latent heat to maintain constant temperatures. For example, these devices are not capable of providing selectable melting temperatures, and, thus, are not
Allen Thomas
Kukal Olga
Doerrler William C.
Fulbright & Jaworski LLP
Zec Filip
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