Bottles and jars – Sidewall structure – Pressure-responsive structure
Reexamination Certificate
2002-07-17
2004-08-24
Weaver, Sue A. (Department: 3727)
Bottles and jars
Sidewall structure
Pressure-responsive structure
C215S382000, C215S383000, C220S675000
Reexamination Certificate
active
06779673
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to a pressure-adjustable container, and more particularly to such containers that are typically made of polyester and are capable of being filled with hot liquid. It also relates to an improved sidewall construction for such containers.
2. Statement of the Prior Art
“Hot-fill” applications impose significant and complex mechanical stress on the structure of a plastic container due to thermal stress, hydraulic pressure upon filling and immediately after capping the container, and vacuum pressure as the fluid cools.
Thermal stress is applied to the walls of the container upon introduction of hot fluid. The hot fluid causes the container walls to first soften and then shrink unevenly, causing distortion of the container. The plastic material (e.g., polyester) must, therefore, be heat-treated to induce molecular changes resulting in a container that exhibits thermal stability.
Pressure and stress also act upon the sidewalls of a heat resistant container during the filling process, and for a significant period of time thereafter. When the container is filled with hot fluid and sealed, there is an initial hydraulic pressure and an increased internal pressure is placed upon the container. As the liquid and the air headspace under the cap subsequently cools, thermal contraction results in partial evacuation of the container. The vacuum created by this cooling tends to mechanically deform the container walls.
Generally speaking, plastic containers incorporating a plurality of longitudinal fiat surfaces accommodate vacuum force more readily. For example, U.S. Pat. No. 4,497,855 (Agrawal et al.) discloses a container with a plurality of recessed collapse panels, separated by land areas, which allows uniformly inward deformation under vacuum force. The vacuum effects are controlled without adversely affecting the appearance of the container. The panels are drawn inwardly to vent the internal vacuum and so prevent excess force being applied to the container structure. Otherwise, such forces would deform the inflexible post or land area structures. The amount of “flex” available in each panel is limited, however. As that limit is approached, there is an increased amount of force that is transferred to the sidewalls.
To minimize the effect of force being transferred to the sidewalls, much prior art has focused on providing stiffened regions to the container, including the panels, to prevent the structure yielding to the vacuum force. For example, the provision of either horizontal or vertical annular sections, or “ribs”, throughout a container has become common practice in container construction. The use of such ribs is not only restricted to hot-fill containers. Such annular sections strengthen the part upon which they are deployed.
Examples of the prior art teaching the use of such ribs are U.S. Pat. No. 4,372,455 (“Cochran”), U.S. Pat. No. 4,805,788 (“Ota I”), U.S. Pat. No. 5,178,290 (“Ota II”), and U.S. Pat. No. 5,238,129 (“Ota III”). Cochran discloses annular rib strengthening in a longitudinal direction, placed in the areas between the flat surfaces that are subjected to inwardly deforming hydrostatic forces under vacuum force. Ota I discloses longitudinally extending ribs alongside the panels to add stiffening to the container, and the strengthening effect of providing a larger step in the sides of the land areas. This provides greater dimension and strength to the rib areas between the panels. Ota II discloses indentations to strengthen the panel areas themselves. Ota III discloses further annular rib strengthening, this time horizontally directed in strips above and below, and outside, the hot-fill panel section of the bottle.
In addition to the need for strengthening a container against both thermal and vacuum stress, there is a need to allow for an initial hydraulic pressure and increased internal pressure that is placed upon a container when hot liquid is first introduced and then followed by capping. This causes stress to be placed on the container sidewall. There is a forced outward movement of the heat panels, which can result in a barreling of the container.
Thus, U.S. Pat. No. 4,877,141 (“Hayashi et al.”) discloses a panel configuration that accommodates an initial, and natural, outward flexing caused by internal hydraulic pressure and temperature, followed by inward flexing caused by the vacuum formation during cooling. Importantly, the panel is kept relatively flat in profile, but with a central portion displaced slightly to add strength to the panel but without preventing its radial movement in and out. With the panel being generally flat, however, the amount of movement is limited in both directions. By necessity, panel ribs are not included for extra resilience, as this would prohibit outward and inward return movement of the panel as a whole.
U.S. Pat. No. 5,908,128 (“Krishnakumar I”) discloses another flexible panel that is intended to be reactive to hydraulic pressure and temperature forces that occur after filling. Relatively standard hot-fill style container geometry is disclosed for a “pasteurizable” container. It is claimed that the pasteurization process does not require the container to be heat-set prior to filling, because the liquid is introduced cold and is heated after capping. Concave panels are used to compensate for the pressure differentials. To provide for flexibility in both radial outward movement followed by radial inward movement however, the panels are kept to a shallow inward-bow to accommodate a response to the changing internal pressure and temperatures of the pasteurization process. The increase in temperature after capping, which is sustained for some time, softens the plastic material and therefore allows the inwardly curved panels to flex more easily under the induced force. It is disclosed that too much curvature would prevent this, however. Permanent deformation of the panels when forced into an opposite bow is avoided by the shallow setting of the bow, and also by the softening of the material under heat. The amount of force transmitted to the walls of the container is therefore once again determined by the amount of flex available in the panels, just as it is in a standard hot-fill bottle. The amount of flex is limited, however, due to the need to keep a shallow curvature on the radial profile of the panels. Accordingly, the bottle is strengthened in many standard ways.
U.S. Pat. No. 5,303,834 (“Krishnakumar II”) discloses still further “flexible” panels that can be moved from a convex position to a concave position, in providing for a “squeezable” container. Vacuum pressure alone cannot invert the panels, but they can be manually forced into inversion. The panels automatically “bounce” back to their original shape upon release of squeeze pressure, as a significant amount of force is required to keep them in an inverted position, and this must be maintained manually. Permanent deformation of the panel, caused by the initial convex presentation, is avoided through the use of multiple longitudinal flex points.
U.S. Pat. No. 5,971,184 (“Krishnakumar III”) discloses still further “flexible” panels that claim to be movable from a convex first position to a concave second position in providing for a grip-bottle comprising two large, flattened sides. Each panel incorporates an indented “invertible” central portion. Containers such as this, whereby there are two large and flat opposing sides, differ in vacuum pressure stability from hot-fill containers that are intended to maintain a generally cylindrical shape under vacuum draw. The enlarged panel sidewalls are subject to increased suction and are drawn into concavity more so than if each panel were smaller in size, as occurs in a “standard” configuration comprising six panels on a substantially cylindrical container. Thus, such a container structure increases the amount of force supplied to each of the two panels, thereby increasing the amount of flex force available.
Even so, the convex portion of
Bysick Scott E.
Harrell George T.
Melrose David Murray
Ogg Richard K.
Pritchett, Jr. Raymond A.
Burdett James R.
Graham Packaging Company L.P.
Weaver Sue A.
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