Base for plastic container

Details Base for plastic container Base for plastic container

2001-09-17

2003-10-21

Weaver, Sue A. (Department: 3727)

Bottles and jars

End wall structure

One-piece side and end wall

C215S371000, C220S606000, C220S608000

Reexamination Certificate

active

06634517

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates broadly to the field of container making, and more specifically to blow molded plastic bottles, such as the PET bottles that are in common use today for packaging beverages. More specifically, the invention relates to an improved container and base therefor that exhibits outstanding dimensional stability even under conditions of high pressurization.
2. Description of the Related Technology
During the last twenty-five years or so, there has been a dramatic shift in the packaging of carbonated beverages, particularly, soft drinks, away from glass containers and toward plastic containers. The plastic containers initially took the form of a two-piece construction, wherein a plastic bottle having a generally hemispherical bottom was applied a separate base cup, which would permit the bottle to be stood upright. The hemispherical bottom was seen as the most desirable shape for retaining the pressure generated by the carbonation within the container. Pressures in such containers can rise to 100 p.s.i. or more when the bottled beverage is exposed to the sun, stored in a warm room, car trunk, or the like. Such plastic containers represented a significant safety advantage over glass containers when exposed to the same internal pressures. However, the two-piece construction was not economical because it required a post molding assembly step, and, also a separation step prior to reclaiming or recycling the resins forming the bottle and base cup.
During this period of development, various attempts were made to construct a one-piece, self-supporting container that would be able to retain the carbonated beverages at the pressures involved. Such a one-piece container requires the design of a base structure which will support the bottle in an upright position and will not bulge outwardly at the bottom. A variety of designs were first attempted, with most following one of two principal lines of thought. One line of designs involved a so-called champagne base having a complete annular peripheral ring. Another variety of designs is that which included a plurality of feet protruding downward from a curved bottom.
One issue that must receive the continuous attention of designers of such containers is the fact that some deformation of the container is likely to occur when high internal pressures exist within the container. All carbonated beverages create the risk of overpressurization within the container. In addition, certain carbonated beverages such as beer are also subjected to a pasteurization process in which the contents of the container are heated, typically to a temperature that is within the general range of 62-67 degrees Celsius. As the temperature rises during the pasteurization process, internal pressure also rises, typically to 2 to 2½ times higher than what occurs during the packaging of non pasteurized carbonated beverages. Further complicating the situation is the fact that the rising temperatures also tend to soften the plastic material and make it less resistant to deformation. Under these circumstances, molded plastic containers are at their most vulnerable to deformation.
Dimensional stability in molded plastic containers is most important in the base region, and particularly in the portions of the base region that are designed to support the container with respect to an underlying surface. In the case of a champagne type base, dimensional stability of the area about the annular support ring is an important concern. In the case of a footed base, it is important that the lower surface of each foot remain properly positioned and angled.
A continuing need exists for an improved molded plastic container and a base therefor that exhibits outstanding dimensional stability under conditions of relatively high pressure and 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 an underlying surface.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the invention to provide an improved molded plastic container and a base therefor that exhibits outstanding dimensional stability under conditions of relatively high pressure and 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 an underlying surface.
In order to achieve the above and other objects of the invention, a molded polymeric container that is constructed according to a first aspect of the invention includes a body portion having a sidewall and an integral champagne type base. The base includes a lower end that defines an annular contact ring for supporting the container with respect to an underlying surface. An annular step ring is defined immediately radially inwardly of the annular contact ring and has a radial length L
S
. The base further has a central push-up area and a generally concave transition region interposed between the central push-up area and the annular contact ring. The transition region further includes a plurality of integrally molded radially extending ribs, each of the ribs having a length L
R
. According to one advantageous aspect of the invention, the ratio L
R/L
S
is within a range of about 1.0 to about 4.0.


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