Patent Application
20110303682
1. Field of the Invention
This invention relates generally to the field of plastic containers that are adapted to be heat sterilized. More specifically, the invention relates to an improved retortable container that is more dimensionally stable during the sterilization process than conventional predecessor containers.
2. Description of the Related Technology
Certain products require sterilization during the packaging process in order to inhibit the growth of bacteria. Products requiring sterilization include foods such as milk, yogurt and various sauces, as well as certain pharmaceutical products.
Traditionally, products that require heat sterilization have been packaged in glass containers, which are relatively stable at elevated temperatures and pressures. However, in recent years plastic retortable containers have come into use. Plastic containers tend to be less expensive than glass containers and safer in many respects because they will not shatter when dropped.
In the retort process, the container is filled with product that is relatively cool and then subsequently exposed to temperatures that are elevated enough to sterilize the product and the internal surfaces of the container. This may be done by injecting steam into the container just prior to the container being sealed. The temperatures of the retort process are elevated enough to substantially temporarily increase the internal pressurization of the container. Plastic retortable containers accordingly have been designed to permit limited and reversible controlled flexure of one or more surfaces in order to accommodate the internal volumetric changes that are inherent to the retort sterilization process. U.S. Pat. No. 5,217,737 to Gygax et al. discloses a retortable plastic container that has a flexible bottom portion to accommodate internal volumetric changes. Other retortable containers that have been in commercial use have a champagne style bottom portion that is designed to permit a certain amount of flexure.
In designing such containers, the sidewall must be formed of a sufficient thickness to provide the requisite strength and stability. However, because of the significant expense of plastic resin when such containers are being produced on a commercial scale, keeping the containers as lightweighted as possible is also an important consideration. These two design factors are obviously in tension with each other. Any improvements to retortable container designs that would tend to enhance strength and stability without significantly adding to material costs would be appreciated by those skilled in this area of technology as an important advance.
Unfortunately, a certain fraction of conventional retortable containers experience irreversible deformation during the retort process that result in the product becoming unsalable. For example, the bottom portion of a conventional retortable container will often buckle or completely invert in an irreversible manner.
A need accordingly exists for an improved retortable container that exhibits improved dimensional stability and strength during the retort process without significantly adding to material costs.
It is therefore an object of the invention to provide an improved retortable container that exhibits improved dimensional stability and strength during the retort process without significantly adding to material costs.
In order to achieve the above and other objects of the invention, a retortable container according to a first aspect of the invention includes a neck portion defining an opening, a main body portion and a bottom portion. The bottom portion includes four support feet, each of which has an inwardly extending convex surface, giving the bottom portion a cross like configuration as viewed in bottom plan. Each of the support feet further includes an outwardly extending concave surface.
A retortable container according to a second aspect of the invention includes a neck portion defining an opening, a main body portion and a bottom portion. The bottom portion includes a plurality of support feet, each of which has an inwardly extending convex surface and an outwardly extending concave surface. The outwardly extending concave surface of at least one of the support feet extends upwardly into the main body portion as a substantially longitudinally oriented groove.
These and various other advantages and features of novelty that characterize the invention are pointed out with particularity in the claims annexed hereto and forming a part hereof. However, for a better understanding of the invention, its advantages, and the objects obtained by its use, reference should be made to the drawings which form a further part hereof, and to the accompanying descriptive matter, in which there is illustrated and described a preferred embodiment of the invention.
Referring now to the drawings, wherein like reference numerals designate corresponding structure throughout the views, and referring in particular to
Container 10 is constructed and arranged to exhibit improved dimensional stability and strength when undergoing heat sterilization, such as the retort or pasteurization process, without significantly adding to material costs. Specifically, the bottom portion 18 is constructed and arranged to preclude irreversible deformation during the heat sterilization process.
The bottom portion 18 includes a plurality of support feet 20. In the preferred embodiment, there are four support feet 20. Each of the support feet 20 is preferably constructed to have an inwardly extending convex surface 22, as is best shown in
The support feet 20 are also preferably substantially evenly spaced about the circumference of the bottom portion 18. The support feet 20 and the rest of the bottom portion 18 are preferably shaped and sized so that the bottom portion has a cross-like configuration 24 defined by the floor 50 as viewed in bottom plan, as is shown in
Each of the support feet 20 also preferably has an outwardly extending concave surface 26 which in the preferred embodiment is substantially evenly spaced from the inwardly extending convex surface 22 so as to give the bottom surface 48 of each of the support feet 20 an arc-like appearance as viewed in bottom plan, as is shown in
The bottom portion 18 also preferably includes a recessed central portion 28 that is preferably centered with respect to the cross like configuration 24 and the support feet 20.
The outwardly extending concave surface 26 of each of the respective support feet 20 also preferably extends upwardly into the main body portion 16 as a substantially longitudinally oriented groove 30, as is best shown in
The main body portion 16 preferably includes reinforcement structure 31 for increasing the circumferential or hoop strength of the retortable container 10, which minimizes deformation of the main body portion 16 as a result of the heat sterilization process. Preferably, the reinforcement structure 31 includes at least one circumferentially extending groove that is defined in the main body portion 16. In the illustrated preferred embodiment, reinforcement structure 31 includes a plurality of circumferentially extending grooves, specifically grooves 32, 34, 38, that are longitudinally spaced with respect to each other within a sidewall 40 of the main body portion 16.
Alternatively, the reinforcement structure 31 could be constructed as one or more circumferentially oriented ribs or projections, instead of grooves, or a more complex surface structure that includes circumferentially extending structure together with non-circumferentially extending structure.
The sidewall 40 of the main body portion 16 has an inner surface 42 that defines the interior space 46 and an outer surface 44, as is best shown in
The main body portion 16 is preferably shaped so as to be substantially symmetrical about a longitudinal axis 36. In addition, the bottom portion 18 is also preferably shaped so as to be substantially symmetrical about the longitudinal axis 36.
The retortable container 10 is preferably fabricated using a conventional extrusion blow molding process from a plastic material that is selected from the group consisting of polyethylene, polypropylene and polyolefins. A multi-layer material having an internal barrier layer could also be used. Most preferably, the sidewall 40 of the main body portion 16 is fabricated using a multilayer plastic material having inner and outer layers that are fabricated from polypropylene and an interior layer of EVOH.
A method of making the retortable container 10 would include extruding a continuous hollow parison from extrusion nozzle and periodically capturing portions of the parison in a moving blow mold, which could be of a shuttle design or a wheel design. The portion of the parison that is capture within the mold is inflated, causing the plastic material to conform to the inner dimensions of the mold, which are substantially complementary to the dimensions of the retortable container 10 that is shown in the drawings and has been described above. The retortable container 10 is then removed from the mold and trimmed to remove excess flash.
The container 10 is then filled with product, which could be a food material such as milk or yogurt, and then sealed. The sealed filled container is then subjected to a heat sterilization process such as the retort or pasteurization process, in which a limited amount of deformation will be permitted in the bottom portion 18, but no irreversible deformation will occur.
It is to be understood, however, that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.
