1. Technical Field
The present invention is directed to molded plastic bottles having a champagne style bottom structure closing the container lower end. The phrase champagne style is used in reference to a base having an outside surface rotationally symmetric about a longitudinal axis of the bottle including a convex heel having an upper margin integrally formed with the lower end portion of the bottle sidewall, and a central concavity separated from the convex heel by a continuous standing ring that supports the bottle on any underlying planar surface.
The present invention particularly relates to blow-molded containers of biaxially oriented thermoplastic materials such as polyethylene terephthalate that are designed to be filled with a hot liquid or semi-liquid product and hermetically sealed, generally referred to as thin-walled, hot-fill containers. The invention pertains to improvements in the design of such containers intended to achieve a container base that, despite the low weight of polymer used to form the container, resists the hydraulic and thermal shock of the entering hot product during a filing operation, yet when cooled, retains the desired container configuration despite the development of a partial vacuum within the container.
2. General Background
It is well recognized that the exposure of any plastic container to elevated temperatures tends to soften the plastic material and make the container less resistant to deformation. Thin-walled, hot-fill containers are typically used for packaging beverages and other food products that must be placed in the container while hot, the container being quickly capped to preserve the quality of the contents. During the filling process, the container is subjected to temperatures from the hot product on the order of about 85° C. The interior of the container base is also subjected to a hydraulic force from the fast flowing hot product as it enters the container. The combination of the thermal and hydraulic forces can easily cause deformation of the container base, which if insufficiently controlled can lead to failure during the immediately subsequent capping operation.
The desire for stability of base configuration is not limited to hot-filled containers. Plastic containers used for beverages and other food products that are subjected to a post-capping pasteurization process are also subjected to considerable internal pressures that can lead to base deformation. During a typical pasteurization process, the contents of the container are heated, to a temperature that is within the general range of about 62° to 67° C. As the temperature rises during the pasteurization process, the internal pressure also rises, sometimes to a level of about 2 to 2½ times higher than what occurs during the packaging of non pasteurized beverages. Under these circumstances, the base of the molded plastic container is vulnerable to outward deformation due to the internal pressures, which can affect the continued serviceability of the container.
- BRIEF SUMMARY
Dimensional stability in the base region of molded plastic containers is most important, and particularly in the portions of the base region that are designed to support the container with respect to any underlying surface. In the case of a champagne type base, the dimensional stability of the areas adjacent to the annular support ring is particularly important. Thus, there is a continuing need for an improved molded plastic container having a base that exhibits outstanding dimensional stability under conditions of relatively high pressure and/or temperature and, in particular, that is designed to be particularly resistant to deformation in areas of the base that are designed to support the container with respect to any underlying surface.
A molded polymeric container of the present invention satisfies such needs by providing a champagne type base having an annular contact ring for supporting the container with respect to an underlying surface. An annular step is situated immediately radially inward of the annular contact ring, the annular step having a substantially vertical outer wall and a substantially horizontal inner wall. A push-up area is provided at a central portion of the base that is immediately adjacent to and surrounds the longitudinal axis of the container. A transition region is interposed between the push-up area and the annular step that provides for outstanding base stabilization. The transition region includes an upwardly arching surface extending between the annular step and the push-up area with a plurality of integrally molded, spaced apart, radially extending and downwardly projecting hollow ribs. Each of the ribs has a lower curved surface extending substantially continuously from the push-up area to the inner margin of the annular step.
The upwardly arching surface of the container base of the present invention can have a radius of curvature RS that is greater than the radius of curvature of the rib lower surface RR. The radius of curvature RS can be between about 1.5 RR and 2.0 RR, and in a preferred embodiment the radius of curvature RS can be about 1.7 RR. The ratio of the height to base width of each rib can be less than 1.0 down to at least about 0.7. Each of the ribs can have two sides diverging from the lower curved surface to an adjacent portion of the upwardly arching surface. The angle of divergence of the two sides can be between about 25° and about 35°. The contact ring can be defined by a horizontal planar annulus that can be several times the width of the horizontal inner wall of the annular step. The push-up area of the base can include a horizontal planar ring with a central depending nib aligned with the longitudinal axis of the container.
BRIEF DESCRIPTION OF THE DRAWINGS
The champagne type base of the present invention exhibits exceptionally stable geometry from manufacture through typical hot-fill conditions and subsequent storage despite the use of a modest amount of polymer. This base can be combined with a variety of side wall structures to provide a remarkably satisfactory container for hot-fill operations. The scope of the containers that can be constructed with a champagne type base of the present invention will become more apparent from the following description and accompanying drawings detailing an illustrative example of the present invention.
FIG. 1 is a side elevation view of a molded polymeric container that can incorporate a champagne type base of the present invention.
FIG. 2 is a bottom plan view of the container shown in FIG. 1.
FIG. 3 is another bottom plan view of the same container.
FIG. 4 is a sectional view taken along line A-A of FIG. 2.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 5 is a sectional view taken along line B-B of FIG. 3.
A container 10 of the present invention is shown in FIG. 1 to be generally symmetric about a vertical axis Y, and has an open mouth 12 surrounded by a lip 14 intended to cooperate with a cap, not shown, to seal the container and contents. A cap-engaging finish 16 is located below the lip 14, which is illustrated to have the form of a spiral thread 18. The particular form of the finish 16 can be varied to include a range of thread styles or even be replaced with any number of non-threaded finishes designed to accept a crown type or other cap. A pilfer ring 20 can be located immediately below the finish 16 to engage a pilfer-indicating band of a cap. A support ring 22 can be provided below the pilfer ring 20 that facilitates handling of the container 10 as well as the handling of the parison or preform from which the container 10 is formed. A neck portion 24 is located immediately below the support ring.
A shoulder portion 26 extends outward and downward from a lower margin of the neck portion 24. The shoulder portion 26 can include an indented hoop ring 28 to provide added strength to the container 10. A bumper ring 30 can be provided at a lower margin of the shoulder portion 26 that can define the maximum radius R of the container sidewall 32 measured from the axis Y. A lower margin of the bumper ring 30 can also define the upper margin 34 of a label receiving portion 36 that is intended to receive a separate label, not shown. The label can be a sheet of plastic, paper, or other similar material of suitable dimension that can surround the entire sidewall 32 of the container 10. The label typically covers the container 10 from the upper margin 34 down to the lower margin 38 of the label receiving portion 36. The label receiving portion 36 can also include one or more reinforcing hoop rings 40. A plurality of vacuum compensation panels 42 can also be provided within the label receiving portion 36 of the sidewall 32. A convex heel portion 44 extends downward from the container sidewall 32 to an annular contact ring 46 that supports the container 10 with respect to any underlying surface.
The convex heel portion 44 and annular contact ring 46 form the outer margin of the base 48 of container 10 shown in FIGS. 2 to 5. When viewed in a vertical section as shown in FIG. 4, the convex heel portion 44 is arcuate, generally having a vertical radius of curvature RH that is less than R. The vertical radius of curvature RH of the convex heel portion 44 can be about 0.5 R. The annular contact ring 46 can have a generally planar bottom surface 50 that extends from a point of merger 52 with the convex heel portion 44 inward to a small annular step 54. The distance between the point of merger 52 and the annular step 54 can be about 0.15 R. The annular step 54 is formed by a substantially vertical, inwardly facing, outer wall 56 that extends upward to a substantially horizontal band 58. The band 58 extends inwardly from the vertical outer wall 56 to an inner margin 60 of the annular step 54.
A transition region 62 extends radially inward from the inner margin 60 of the annular step 54. The transition region 62 includes a plurality of upwardly arching segments 64 that are spaced from each other by a plurality of ribs 66. When viewed in a vertical section as shown in FIG. 4, the upwardly arching segments 64 can be defined by a single radius of curvature RS extending substantially continuously from the annular step inner margin 60 to a margin 72 that defines the outer perimeter of a central push-up area 74. The radius of curvature RS of the upwardly arching segments 64 can be about 0.5 R. Each of the ribs 66 has two sides 68 diverging from adjacent portions of the upwardly arching segments 64 to merge with a lower curved surface 70 of the rib 66. The sides 68 of the ribs 66 diverge from each other at an angle θ that can be between about 25° and 35° as shown in FIG. 5. Due to the differences in curvature of the surfaces 64 and 70 the ribs achieve a maximum height H about half way between the annular step inner margin 60 and the central push-up area margin 72 as shown in FIG. 4. As seen in FIG. 5, each rib 66 has a base width W at the point of maximum height H, ratio of H/W being less than 1 and can be about 0.7. When viewed in a vertical section, as shown in FIG. 4, the lower curved surface 70 of the ribs 66 is defined by a radius of curvature RR extending over a major portion of the rib lower surface 70. The radius of curvature RS of the upwardly arching segments 64 is generally greater than the radius of curvature RR of the rib lower surfaces 70. The radius of curvature RS can be between about 1.5 and 2.0 times the radius of curvature RR. The radius of curvature RS is preferably about 1.7 times the radius of curvature RR.
Both the upwardly arching segments 64 and ribs 66 converge to an inner margin 72 that defines the outer perimeter of a central push-up area 74 immediately surrounding the longitudinal axis Y of the container 10. The central push-up area 74 is generally horizontally planar, but can contain a spru artifact 76. The central push-up area is maintained in position relative to the annular contact ring 46 by virtue of the stress created in the sides 68 of the ribs 66 in the event of any downward displacement of the central push-up area 74. As a result, the champagne type base 48 exhibits exceptionally stable geometry from manufacture through typical hot-fill conditions.
During the blow-molding of a container to have a base of the present invention, the plastic forming the base 48 more intimately contacts the mold interior and is thus subjected to better heat transfer from the plastic forming the base to the cooled mold. This more intimate contact is established because of the previously described special geometric relationships in the base 48 which reduce or eliminate any extreme angles and tapers that commonly are present in similar contemporary base designs. As a result, the plastic forming the base 48 of the present invention cools more completely during a molding cycle of a given length of time. The more thorough cooling results in less post molding creep of the base structure. The more thorough cooling may be used to increase the bottle production rate. The base 48 can be combined with a variety of side walls 32 to provide a remarkably satisfactory container for hot-fill operations.
The foregoing detailed description of the embodiment shown in the Figures should be regarded as merely illustrative rather than limiting, and the following claims, including all equivalents, are intended to define the spirit and scope of this invention.