Patent Application
20110226787
1. Field of the Invention
This invention relates generally to the field of packaging, and more specifically to the field of plastic containers that have size, shape and functionality that permits them to serve as a replacement for conventional metal cans.
2. Description of the Related Technology
The use of metal cans to package products such as foodstuffs is well over a century old. Conventional metal cans are either of a two-piece configuration, in which a lid is secured to a can body having an integral bottom portion using a double seaming process, or of a three-piece configuration in which a lid and a bottom member are respectively secured to opposite open ends of a substantially cylindrical can body.
Plastic cans have been proposed as a substitute for conventional metal cans, but to date they have not achieved any significant commercial success. The use of plastic to fabricate a can body offers a number of potential advantages, such as lower energy costs during both the manufacturing and recycling stages, better formability and less susceptibility to denting during handling. Dented metal cans present potential health risks, such as increased susceptibility to contamination that can lead to conditions such as botulism.
In addition, a can that is fabricated out of food grade plastic would not require potentially harmful coatings of such materials as Bisphenol A (BPA). However, plastic lacks the inherent strength of metals such as steel and aluminum. It also tends to soften at much lower temperatures than steel and aluminum.
Conventional plastic cans accordingly may lack the column strength that is necessary to avoid deformation of the sidewall of the can when a number of cans or containers or palettes of cans are stacked during transportation or in packaging or retail facilities. While it is possible to increase the strength of a plastic container by increasing the thickness of the sidewall, doing so also increases manufacturing costs by increasing the amount of plastic material that is required. Lightweighting is an important consideration in the design of plastic containers because plastic material tends to be relatively expensive.
Plastic cans also typically lack the requisite circumferential or hoop strength that is required to avoid excessive deformation when the contents of the can become pressurized. Certain products, particularly food, require sterilization during the packaging process in order to inhibit the growth of bacteria.
The most common commercial procedure for heat sterilizing canned foods is a retort process in which filled but unsterilized sealed cans are placed in a retort chamber that is injected with steam and held at a predetermined elevated temperature (typically between about 210° F. to about 260° F.) for a predetermined period of time. Conventional plastic cans have been considered unsuitable for packaging applications in which heat sterilization is required, because the heat and pressurization that is inherent to such processes has the tendency to cause irreversible damage and deformation to the sidewall of the plastic can.
Metal cans are also commonly used to package pressurized beverages such as beer and soft drinks. In addition, other beverages that are not carbonated may develop a positive pressure with respect to ambient atmospheric conditions when the container is heated or transported to higher altitudes. Conventional extrusion blow molded plastic cans have been considered unsuitable for use in the packaging of such beverages.
A need exists for a plastic can body that has sufficient column strength and hoop strength to replace a conventional metal can, and that has sufficient rigidity and stability under elevated pressures and temperatures to permit heat sterilization without experiencing excessive deformation. A need further exists for a plastic can body that has sufficient strength to resist internal pressurization, so that it could be used to package carbonated beverages and the like. In addition, a need exists for a method of producing a heat sterilized packaged product that utilizes a plastic can body.
Accordingly, it is an object of the invention to provide a plastic can body that has sufficient column strength and hoop strength to replace a conventional metal can, and that has sufficient rigidity and stability under elevated pressures and temperatures to permit heat sterilization without experiencing excessive deformation.
It is further an object of the invention to provide a plastic can body that has sufficient strength to resist internal pressurization, so that it can be used to package carbonated beverages and the like.
It is yet further an object of the invention to provide a method for producing a heat sterilized packaged product that utilizes a plastic can body.
In order to achieve the above and other objects of the invention, a plastic can body, according to a first aspect of the invention includes a bottom portion and a main body portion having a plastic sidewall that is connected to the bottom portion. The main body portion is shaped to define an upper rim that is adapted to be secured to a lid. The sidewall includes a plurality of first sidewall portions that have a substantially flat circumferentially extending outer surface and a plurality of second sidewall portions. Each of the second sidewall portions are interposed between two adjacent first sidewall portions. Each of the second sidewall portions are shaped to define a plurality of circumferentially spaced indentations.
A plastic can body according to a second aspect of the invention includes a bottom portion and a main body portion having a plastic sidewall that is connected to the bottom portion. The main body portion is shaped to define an upper rim that is adapted to be secured to a lid. The sidewall includes a plurality of horizontally circumferentially extending first sidewall portions and a plurality of horizontally circumferentially extending second sidewall portions.
Each of the second sidewall portions are interposed between two adjacent first sidewall portions. In addition, each of the second sidewall portions includes a plurality of circumferentially spaced vertical columns. Adjacent second sidewall portions are rotationally staggered with respect to each other so that the vertical columns on one second sidewall portion are not aligned with the vertical columns of an adjacent second sidewall portion.
A heat sterilized plastic container according to a third aspect of the invention includes a container having a plastic sidewall that has a thickness that is substantially within a range of about 0.040 inch to about 0.065 inch. The sidewall includes a plurality of first sidewall portions and a plurality of second sidewall portions that are respectively interposed between the first sidewall portions. Each of the second sidewall portions is shaped to define a plurality of circumferentially spaced structures that are selected from the group consisting of indentations and projections.
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
Alternatively, plastic can body 10 may be fabricated from a material such as polyethylene terephthalate (PET) using a conventional reheat stretch blow molding process.
As is best shown in
The lid member 30 is preferably fabricated from a metallic material such as steel, but it alternatively could be fabricated from a plastic material or any other suitable material. The lid member 30 is preferably secured to the upper rim 16 using a standard double seaming process of the type that is used to seal metal cans. Alternatively, the lid member 30 could be welded or otherwise secured to the upper rim 16.
In the preferred embodiment, the bottom portion 12 is integral with the plastic sidewall 16 and is also fabricated from a plastic material. Alternatively, the plastic can body 10 could be made for a three-piece can construction, in which the can body 10 is constructed as an open tube having a bottom rim that is similar to the upper rim 16, and a bottom lid could be secured in the manner described above with reference to the lid member 30.
As is best shown in
The substantially flat circumferentially extending outer surfaces 24 are preferably oriented so that they are substantially vertical as viewed in side elevation, as shown in
Alternatively, the outer circumferential surface of the first sidewall portions 20 could be convexly or concavely curved, or it could have a more complex shape.
In addition, each of the substantially flat circumferentially extending outer surfaces 24 preferably intersect a horizontal plane 32 that is perpendicular to the longitudinal axis 28 of the main body portion 14, as is shown diagrammatically in
The main body portion 14 is preferably substantially cylindrical in shape, but it could alternatively be constructed of anyone of a plurality of possible alternative shapes, including a tapered shape or a complex shape according to the preferences of a packaging customer. The use of the plastic material in the sidewall 18 facilitates the fabrication of complex shapes that are difficult or impossible to achieve using a metal can body. Preferably, but not necessarily, the main body portion is shaped so that it is substantially symmetrical about the longitudinal axis 28.
Each of the second sidewall portions 22 is preferably shaped to define a plurality of circumferentially spaced indentations 26. Each of the second sidewall portions 22 preferably extend about an entire circumference of the main body portion 14. The circumferentially spaced indentations 26 are preferably spaced substantially evenly about the entire circumference of the main body portion 14. Preferably, although not necessarily, there are an even number of the circumferentially spaced indentations 26 within each of the second sidewall portions 22.
In the illustrated embodiment, there are twelve of the indentations 26 defined within each of the second sidewall portions 22. Preferably, the number of indentations within each of the second sidewall portions 22 is within a range of about four to about fifty, and more preferably within a range of about eight to about twenty-four.
Referring again to
Each of the substantially vertical columns 34 preferably has an outer surface that is convexly curved as viewed in transverse cross-section, as is shown diagrammatically in
In the preferred embodiment, the convex curvature of the outer surface of the substantially vertical columns 34 is a substantially constant radius, but alternatively a nonconstant radius could be used. Preferably, a ratio of the average radius R1 of the outer surface of the substantially vertical columns 34 to the maximum diameter DMAX is substantially within a range of about 0.0195 to about 0.15, and more preferably substantially within a range about 0.03 to about 0.075.
As is diagrammatically shown in
The staggering of the vertical columns 34 maintains the high column strength that is imparted by the columns 34, while increasing the overall hoop and shear strengths of the main body portion 14.
In the preferred embodiment, a fillet 46 is defined between each of outer surfaces 24 of the adjacent first sidewall portions 20 and the floor 48 of each of the indentations 26. As
The second ends 52 of the vertical columns 34 on each side of the indentation 26 together with the first end 50 of the vertical column 34 that is centered with respect to the indentation 26 within the adjacent underlying second sidewall portion 22 together define a triangular shape that, in aggregate with the other triangular shapes that are likewise defined on the sidewall 18 creates an intermeshed complex force transmission structure that optimizes the column strength, the hoop strength and shear strength of the sidewall 18 and the main body portion 14.
Moreover, the complex curvature that is created by the fillets 46, the vertical columns 34 and the outer surfaces 24 of the adjacent first sidewall portions 20 provide structural reinforcement longitudinally, circumferentially and diagonally throughout the extent of the sidewall 18.
Each of the fillets 46 is preferably angled with respect to the longitudinal axis 28 at an angle A1 that is preferably substantially within a range of about 114° to about 134°, and more preferably substantially within a range of about 119° to about 129°.
At least one of the first sidewall portions 20 has a first vertical height H3, and at least one of the second sidewall portions 22 has a second vertical height H4. In the preferred embodiment, all of the first sidewall portions 20 are of the same vertical height H3, and all of the second sidewall portions 22 are of the same vertical height H4. A ratio H3/H4 of the first vertical height to the second vertical height is preferably substantially within a range of about 0.20 to about 5.0, and more preferably substantially within a range of about 0.50 to about 2.0.
In an alternative embodiment, the structure of the sidewall 18 that is described above could be inverted so that the indentations 26 are protrusions and the vertical columns 34 are concave and extend inwardly rather than being convex.
In another alternative embodiment, the first and second sidewall portions 20, 22 could have a helical construction that would extend through the entire length of the sidewall 18 so that the sidewall 18. For purposes of this document, such an embodiment would be considered to have a plurality of first sidewall portions and a plurality of second sidewall portions, since parts of both of the first and second sidewall portions would be longitudinally displaced from each other.
Preferably, the sidewall 18 is fabricated from an extruded multilayer material, shown diagrammatically in
In the most preferred embodiment, the outer surface 60 of the sidewall 18 is defined by a first layer 64 of plastic material, which is fabricated from a food grade polypropylene. A second adhesive layer 66 attaches the first layer 64 to a third layer 68, which is preferably fabricated from ethylene vinyl acetate (EVOH). A fourth layer 70 of adhesive secures the third layer 68 to a fifth layer 72 of regrind polypropylene material. A sixth, inner layer 70 of a virgin polypropylene material is blended with the fifth layer 72.
The sidewall 18 is preferably shaped to have a substantially constant thickness TS, as is shown diagrammatically in
A method of providing a heat sterilized package product according to a preferred embodiment of the invention is depicted in
The lid 30 could be fabricated from a metallic material such as steel or aluminum, from a plastic material, or be of a composite design that includes both metallic material and plastic material. For example, the lid 30 could be fabricated from a plastic material that has a metallic insert with a tamper evident button that is designed to pop outwardly when the lid 30 is first removed from the container.
The closed container would then be subjected to a heat sterilization process such as a retort process in which the closed container is exposed to heated steam at temperatures of about 210° F. to about 260° F. for a predetermined period of time that is sufficient to kill any bacteria that may be within the closed container. The unique construction of the plastic can body 10 ensures that it will be able to survive such a heat sterilization process with a minimum of deformation and without being breached. The closed container is then commercially distributed to consumers.
A method of packaging materials that are expected to undergo internal pressurization, such as carbonated beverages, according to another embodiment of the invention is depicted in
In this and other embodiments, the lid 30 could be an easy open lid that may be opened by a consumer without needing an additional tool such as a can opener. After filling and sealing, the product would be commercially distributed to consumers. The unique construction of the plastic can body 10 will ensure that any deformation as a result of internal pressurization will not be excessive.
The use of plastic material to fabricate the can body offers a number of potential advantages, such as lower energy costs during both the manufacturing and recycling stages, better formability and less susceptibility to denting during handling in comparison to metal cans. It also reduces the potential for contamination that can lead to conditions such as botulism.
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.
