Pressure container with differential vacuum panels

Abstract

A plastic container (1) has a first set of flex panels (2) and a second set of flex panels (3) at least one set being adapted to react to pressure changes within the container to a different degree which can be achieved by different curvature and / or size and / or different distance from a central longitudinal axis of the container. At least one of the panels has at least two different extents of curvature. In some embodiments one or more of the panels may be flat.

Description

FIELD OF THE INVENTION[0001]The present invention relates to hot-fillable containers. More particularly, the present invention relates to hot-fillable containers having collapse panels.BACKGROUND OF THE INVENTION[0002]‘Hot-Fill’ applications impose significant and complex mechanical stress on a container structure due to thermal stress, hydraulic pressure upon filling and immediately after capping, and vacuum pressure as the fluid cools.[0003]Thermal stress is applied to the walls of the container upon introduction of hot fluid. The hot fluid will cause the container walls to soften and then shrink unevenly, causing distortion of the container. The polyester must therefore be heat-treated to induce molecular changes resulting in a container that exhibits thermal stability.[0004]Pressure and stress act upon the side walls of a heat resistant container during the filling process, and for a significant period of time thereafter. When the container is filled with hot liquid and sealed, ...

AI Technical Summary

Benefits of technology

[0017]The present invention provides according to one aspect a plastic container, having a body portion including a sidewall, wherein said body portion includes; a first controlled deflection flex panel on one sidewall portion and a second controlled deflection flex panel on a second sidewall portion, at least one of said controlled deflection flex panels having at least two different extents of outward curvature, said first and second flex panels being adapted to react to pressure changes within the container to a different degree. By way of example, a container having four controlled deflection flex panels may be disposed in two pairs on symmetrically opposing sidewalls, whereby one pair of controlled deflection flex panels responds to vacuum force at a different rate to an alternately positioned pair. The pairs of controlled deflection flex panels may be positioned an equidistance from the central longitudinal axis of the container, or may be positioned at differing distances from the centerline of the container. In addition the design allows for a more controlled overall response to vacuum pressure and improved dent resistance and resistance to torsion displacement of post or land areas between the panels. Further, improved reduction in container weight is achieved, along with potential for development of squeezable container designs.

[0020]The vacuum panels should be selected so that they are highly efficient. See, for example, PCT application NO. PCT / NZ00 / 00019 (David Melrose) where panels with vacuum panel geometry are shown. ‘Prior art’ vacuum panels are generally flat or concave. The controlled deflection flex panel of Melrose of PCT / NZ00 / 00019 and the present invention is outwardly curved and can extract greater amounts of pressure. Each flex panel has at least 2 regions of differing outward curvature. The region that is less outwardly curved, the initiator region, reacts to changing pressure at a lower threshold than the region that is more outwardly curved. By providing an initiator portion, the control portion (the region that is more outwardly curved) reacts to pressure more readily than would normally happen. Vacuum pressure is thus reduced to a greater degree than prior art causing less stress to be applied to the container sidewalls. This increased venting of vacuum pressure allows for many design options: different panel shapes, especially outward curves; lighter weight containers; less failure under load; less panel area needed; different shape container bodies.

[0022]All sidewalls containing the controlled deflection flex panels may have one or more ribs located within them. The ribs can have either an outer or inner edge relative to the inside of the container. These ribs may occur as a series of parallel ribs. These ribs are parallel to each other and the base. The number of ribs within the series can be either an odd or even. The number, size and shape of ribs are symmetric to those in the opposing sidewall. Such symmetry enhances stability of the container.

[0024]The advanced highly efficient design of the controlled deflection panels of the first pair of panels more than compensates for the fact that they offer less surface area than the larger front and back panels. By providing for the first pair of panels to respond to lower thresholds of pressure, these panels may begin the function of vacuum compensation before the second larger panel set, despite being positioned further from the centerline. The second larger panel set may be constructed to move only minimally, and relatively evenly in response to vacuum pressure, as even a small movement of these panels provides adequate vacuum compensation due to the increased surface area. The first set of controlled deflection flex panels may be constructed to invert and provide much of the vacuum compensation required by the package in order to prevent the larger set of panels from entering an inverted position. Employment of a thin walled super light weight preform ensures that a high level of orientation and crystallinity are imparted to the entire package. This increased level of strength together with the rib structure and highly efficient vacuum panels provide the container with the ability to maintain function and shape on cool down, while at the same time utilizing minimum gram weight.

[0025]The arrangement of ribs and vacuum panels on adjacent sides within the area defined by upper and lower container bumpers allows the package to be further light weighted without loss of structural strength. The ribs are placed on the larger, non-inverting panels and the smaller inverting panels may be generally free of rib indentations and so are more suitable for embossing or debossing of Brand logos or name. This configuration optimizes geometric orientation of squeeze bottle arrangements, whereby the sides of the container are partially drawn inwardly' as the main larger panels contract toward each other. Generally speaking, in prior art as the front and back panels are drawn inwardly under vacuum the sides are forced outwardly. In the present invention the side panels invert toward the centre and maintain this position without being forced outwardly beyond the post structures between the panels. Further, this configuration of ribs and vacuum panel represents a departure from tradition.

Problems solved by technology

‘Hot-Fill’ applications impose significant and complex mechanical stress on a container structure due to thermal stress, hydraulic pressure upon filling and immediately after capping, and vacuum pressure as the fluid cools.

The hot fluid will cause the container walls to soften and then shrink unevenly, causing distortion of the container.

As the liquid, and the air headspace under the cap, subsequently cool, thermal contraction results in partial evacuation of the container.

The vacuum created by this cooling tends to mechanically deform the container walls.

The amount of ‘flex’ available in each panel is limited, however, and as the limit is approached there is an increased amount of force that is transferred to the side walls.

This causes stress to be placed on the container side wall.

There is a forced outward movement of the heat panels, which can result in a barrelling of the container.

With the panel being generally flat, however, the amount of movement is limited in both directions.

However, a container that is used for hot-fill applications is subject to additional mechanical stresses on the container that result in the container being more likely to fail during storage or handling.

For example, it has been found that the thin sidewalls of the container deform or collapse as the container is being filled with hot fluids.

However, the inward flexing of the panels caused by the hot-fill vacuum creates high stress points at the top and bottom edges of the vacuum panels, especially at the upper and lower corners of the panels.

These stress points weaken the portions of the sidewall near the edges of the panels, allowing the sidewall to collapse inwardly during handling of the container or when containers are stacked together.

In the case of non-round containers, this is more challenging due to the fact that the level of orientation and, therefore, crystallinity is inherently lower in the front and back than on the narrower sides.

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