Patent Application
20070186577
In the pharmaceutical, transplant and food industries, maintaining the temperature of shipped materials at refrigeration levels is necessary for proper preservation of the product. The temperature inside a shipping container can be actively maintained, for example, with a refrigeration unit, but passive regulation is preferred, due to decreased cost and the elimination of the need for a continuous power source during shipment. Any temperature regulation mechanism, however, should be suitable for use in a variety of weather and external temperature conditions, so that the customers do not have to purchase and then use several different passive regulation systems, which compensate for ambient temperature differences in shipment. With such systems, the customers would also be required to predict weather and shipping conditions.
Passive regulation with conventional means, e.g., ice or ice “gel packs,” which keep the temperature near 0° C. cannot maintain a consistent internal refrigeration-like temperature (about 5° C.) in a shipping container. Attempts have been made to enhance temperature regulation at refrigeration levels using a phase change material—with a phase change at or near the desired internal temperature. See, e.g., U.S. Patent Application Publication Ser. No. 2005/0031809, incorporated by reference. The principle is that whether the external temperature rises above or falls below the phase change temperature, the internal temperature is maintained at a relatively consistent level, as the phase change material absorbs internal heat as it liquefies, and releases heat as it freezes. One drawback is that such phase change materials (such as alcohols as disclosed in U.S. Patent Application Publication Ser. No. 2005/0031809) can be relatively expensive. Thus, minimizing their use is desirable to achieve a competitively priced shipping container.
Given the formula for determining q, the power lost through an insulator:
where, ΔT represents the temperature difference across an insulator, and R is the thermal resistance of an insulator (R=L/kA, where L is the wall thickness, k is coefficient of thermal conductivity, and A is the surface area of the insulator), it can be seen that if the insulator is being used to maintain refrigeration temperatures using an internal phase change material with a phase change at about 5° C. the reduction in q for that material, between the case where the ambient temperature is 35 to 45° C. (as can occur in hot summer conditions in the unregulated interior of a railroad car or truck trailer), and where the temperature across the insulator is 0° C. (i.e., ice is on the other side of the insulator), would be between 1/7 and 1/9. Thus, ice could be used in an appropriately constructed container/insulator system to reduce quantities of phase change material needed. Minimizing use of phase change material is desirable to achieve a competitively priced shipping container.
Disclosed is a shipping container suitable for use for biological materials, blood or tissues, or food products, having a double-walled multiple-chamber structure, wherein a first phase change material, with a phase change temperature between 2° to 8° C. (and in a preferred embodiment, 5° C.) is placed in a payload chamber, and wherein the container includes one or more first chambers surrounding and sharing a wall with the payload chamber, and housing ice (or ice gel packs). In a preferred embodiment, the first chamber(s) outer wall is the container exterior wall. A lid fits over (or is hinged to) the upper edges of the walls to seal the container and the payload.
The container is preferably made of an insulating material ,e.g., expanded polystyrene (EPS) or urethane, and/or can include a vacuum panel or an air baffle—additional insulating material for the container is optional.
The advantages of the container include those resulting from the first change material undergoing a phase change near the middle of the 2° to 8° C. range. This temperature range is the standard for shipping pharmaceutical, biological materials and food products. It is insulated (by a wall) from the ice in the first chamber and double-insulated (two walls) from the exterior, thereby minimizing the effects on the first phase change material of exterior temperature, and reducing the required amount of the first phase change material. Suitable first phase change materials include 1-decanol (melting at 5° C.); sometimes a higher phase change material such as 1-dodecanol (melting at 22° C.) may be used for particular purposes. Use of less costly ice or gel packs in the first chambers permits use of these more costly alcohols to be reduced. Moreover, external temperatures encountered in shipment (including whether its shipped in summer or winter) are of lessened concern.
The container is designed such that the payload, the ice/gel packs and the first phase change material can all be “dropped in” to their respective chambers, from the top, increasing the ease of loading for the user. Other advantages are described below and are apparent from the description and drawings.
The walls 24 of the container are depicted as one molded unit, e.g., EPS, but they could also be formed from multiple sections, or can have additional insulation added following construction. Additional padding or protective materials for the payload can also be added. The lid 26 (shown in
Suitable payloads include biological materials, e.g., cells, pharmaceuticals, blood or tissues or food products, or other materials which need temperature-regulated refrigeration during shipment.
It should be understood that the terms, expressions and features in the drawings shown herein are exemplary only and not limiting, and that the invention scope is defined only in the claims which follow, and includes all equivalents of the subject matter of the claims.
