Method of compensating for vacuum pressure within a container generated by cooling

<u>Background To Invention</u>

0001This invention relates to a method of compensating for vacuum pressure within a container generated by cooling of liquid contents, and is applicable to polyester containers, particularly semi-rigid collapsible containers capable of being filled with hot liquid. The method more particularly relates to application of an improved construction for initiating collapse in such containers.

0002'Hot-Fill' applications impose significant mechanical stress on a container structure. The thin side-wall construction of a conventional container deforms or collapses as the internal container pressure falls following capping because of the subsequent cooling of the liquid contents. Various methods have been devised to sustain such internal pressure change while maintaining a controlled configuration.

0003Generally, the polyester must be heat-treated to induce molecular changes resulting in a container that exhibits thermal stability. In addition, the structure of the container must be designed to allow sections, or panels, to 'flex' inwardly to vent the internal vacuum and so prevent excess force being applied to the container structure. The amount of 'flex' available in prior art, vertically disposed flex panels is limited, however, and as the limit is reached the force is transferred to the side-wall, and in particular the areas between the panels, of the container causing them to fail under any increased load.

0004Additionally, vacuum force is required in order to flex the panels inwardly to accomplish pressure stabilisation. Therefore, even if the panels are designed to be extremely flexible and efficient, force will still be exerted on the container structure to some degree. The more force that is exerted results in a demand for increased container wall-thickness, which in turn results in increased container cost.

0005The principal mode of failure in all prior art known to the applicant is non-recoverable buckling, due to weakness in the structural geometry of the container, when the weight of the container is lowered for commercial advantage. Many attempts to solve this problem have been directed to adding reinforcements to the container side-wall or to the panels themselves, and also to providing panel shapes that flex at lower thresholds of vacuum pressure.

0006To date, only containers utilising vertically oriented vacuum flex panels have been commercially presented and successful.

0007In our New Zealand Patent 240448 entitled "Collapsible Container", a semi-rigid collapsible container is described and claimed in which controlled collapsing is achieved by a plurality of arced panels which are able to resist expansion from internal pressure, but are able to expand transversely to enable collapsing of a folding portion under a longitudinal collapsing force. Much prior art in collapsible containers was disclosed, most of which provided for a bellows-like, or accordion-like vertical collapsing of the container.

0008Such accordion-like structures are inherently unsuitable for hot-fill applications, as they exhibit difficulty in maintaining container stability under compressive load. Such containers flex their sidewalls away from the central longitudinal axis of the container. Further, labels cannot be properly applied over such sections due to the vertical movement that takes place. This results in severe label distortion. For successful label application, the surface underneath must be structurally stable, as found in much prior art cold-fill container sidewalls whereby corrugations are provided for increased shape retention of the container under compressive load. Such compressive load could be supplied by either increased top-load or increased vacuum pressure generated within a hot-fill container for example.

0009<patcit id="pcit0001" dnum="US6105815A"><text>US-A-6105815</text></patcit> describes a contraction-controlled bellows container, which can retain half or fully contracted configurations of the bellows ridges. The upper walls and/or lower walls of the bellows ridges have circumferential indentations adjacent the outer or inner hinges. Pressure applied to the container causes the indentations to be depressed further into the bellows ridges prior to the corresponding portions of the other walls, reducing the pressure requirement.

Objects of the Invention

0010It is an object of the invention to provide a method of compensation for vacuum pressure which is able to more efficiently compensate for vacuum pressure in the container and to overcome or at least ameliorate problems with prior art proposals to date and/or to at least provide the public with a useful choice.

<u>Summary Of The Invention</u>

0011According to one aspect of this invention there is provided a method as set out in claim 1.

0012Preferably in the method the panel portion is adapted to fold inwardly under an externally applied mechanical force in order to completely remove vacuum pressure generated by the cooling of the liquid contents, and to prevent expansion from the collapsed state when the container is uncapped.

0013Preferably the panel portion is adapted to fold inwardly under a vacuum force below a predetermined level and to enable expansion from the collapsed state when the container is uncapped and vacuum released.

0014Further aspects of this invention, which should be considered in all its novel aspects, will become apparent from the following description.

<u>Brief Description Of Drawings</u>

0015<dl id="dl0001"><dt><b><u>Figure 1:</u></b></dt><dd>shows diagrammatically a semi-rigid collapsible container which is used in one possible embodiment of the invention, in its pre-collapsed condition:</dd><dt><b><u>Figure 2:</u></b></dt><dd>shows the container of <figref idref="f0001">Figure 1</figref> in its collapsed condition;</dd><dt><b><u>Figure 3:</u></b></dt><dd>very diagrammatically shows a cross-sectional view of the container of <figref idref="f0001">Figure 2</figref> along the arrows A-A;</dd><dt><b><u>Figure 4:</u></b></dt><dd>shows the container of <figref idref="f0001">Figure 1</figref> along arrows A-A;</dd><dt><u>Figure 5:</u></dt><dd>shows a container which is used in a further possible embodiment of the invention;</dd><dt><b><u>Figure 6:</u></b></dt><dd>shows the container of <figref idref="f0002">Figure 5</figref> after collapse;</dd><dt><b><u>Figure 7:</u></b></dt><dd>shows a cross-sectional view of the container of <figref idref="f0002">Figure 6</figref> along arrows B-B; and</dd><dt><b><u>Figure 8:</u></b></dt><dd>shows a cross-sectional view of the container of <figref idref="f0002">Figure 5</figref> along arrows B-B.</dd></dl>

<u>Description Of Preferred Embodiments</u>

0016The present invention relates to a method using collapsible semi-rigid containers having a side-wall with at least one substantially vertically folding vacuum panel section which compensates for vacuum pressure within the container.

0017Preferably in one embodiment the flexing may be inwardly, from an applied mechanical force. By calculating the amount of volume reduction that is required to negate the effects of vacuum pressure that would normally occur when the hot liquid cools inside the container, a vertically folding portion can be configured to allow completely for this volume reduction within itself. By mechanically folding the portion down after hot filling, there is complete removal of any vacuum force generated inside the container during liquid cooling. As there is no resulting vacuum pressure remaining inside the cooled container, there is little or no force generated against the sidewall, causing less stress to be applied to the container sidewalls than in prior art.

0018Further, by configuring the control portion to have a steep angle, expansion from the collapsed state when the container is uncapped is also prevented. A large amount of force, equivalent to that mechanically applied initially, would be required to revert the control portion to its previous position. This ready evacuation of volume with negation of internal vacuum force is quite unlike prior art vacuum panel container performance.

0019The present invention may employ a container of any required shape or size and made from any suitably material and by any suitable technique. However, a plastics container blow moulded from polyethylene tetraphalate (PET) may be particularly preferred.

0020One possible design of semi-rigid container is shown in <figref idref="f0001">Figures 1 to 4</figref> of the accompanying drawings. The container referenced generally by arrow C is shown with an open neck portion 4 leading to a bulbous upper portion 5, a central portion 6, a lower portion 7 and a base 8.

0021The central portion 6 provides a vacuum panel portion that will fold substantially vertically to compensate for vacuum pressure in the container 10 following cooling of the hot liquid.

0022The vacuum panel portion has an initiator portion 1 capable of flexing inwardly under low vacuum force and causes a more vertically steeply inclined (a more acute angle relative to the longitudinal axis of the container 10), control portion 2 to invert and flex further inwardly into the container 10.

0023The provision of an initiator portion 1 allows for a steep, relative to the longitudinal, angle to be utilised in the control portion 2. Without an initiator portion 1, the level of force needed to invert the control portion 2 may be undesirably raised. This enables strong resistance to expansion from the collapsed state of the bottle 1. Further, without an initiator portion to initiate inversion of the control portion, the control portion may be subject to undesirable buckling under compressive vertical load. Such buckling could result in failure of the control portion to fold into itself satisfactorily. Far greater evacuation of volume is therefore generated from a single panel section than from prior art vacuum flex panels. Vacuum pressure is subsequently reduced to a greater degree than prior art proposals causing less stress to be applied to the container side walls.

0024Moreover, when the vacuum pressure is adjusted following application of a cap to the neck portion 4 of the container 10 and subsequent cooling of the container contents, it is possible for the collapsing section to cause ambient or even raised pressure conditions inside the container 10.

0025This increased venting of vacuum pressure provides advantageously for less force to be transmitted to the side walls of the container 10. This allows for less material to be necessarily utilised in the construction of the container 10 making production cheaper. This also allows for less failure under load of the container 10, and there is much less requirement for panel area to be necessarily deployed in a design of a hot fill container, such as container 10. Consequently, this allows for the provision of other more aesthetically pleasing designs to be employed in container design for hot fill applications. For example, shapes could be employed that would otherwise suffer detrimentally from the effects of vacuum pressure. Additionally, it would be possible to fully support the label application area, instead of having a 'crinkle' area underneath which is present with the voids provided by prior art containers utilising vertically oriented vacuum flex panels.

0026In a particular embodiment of the present invention, support structures 3, such as raised radial ribs as shown, may be provided around the central portion 6 so that, as seen particularly in <figref idref="f0001">Figures 2 and 3</figref>, with the initiator portion 1 and the control portion 2 collapsed, they may ultimately rest in close association and substantial contact with the support structures 3 in order to maintain or contribute to top-load capabilities, as shown at 1 band 2b and 3b in <figref idref="f0001">Figure 3</figref>.

0027In a further embodiment a telescopic vacuum panel is capable of flexing inwardly under low vacuum force, and enables expansion from the collapsed state when the container is uncapped and the vacuum released.

0028Preferably in one embodiment the initiator portion is configured to provide for inward flexing under low vacuum force. The control portion is configured to allow for vacuum compensation appropriate to the container size, such that vacuum force is maintained, but kept relatively low, and only sufficient to draw the vertically folding vacuum panel section down until further vacuum compensation is not required. This will enable expansion from the collapsed state when the container is uncapped and vacuum released. Without the low vacuum force pulling the vertically folding vacuum panel section down, it will reverse in direction immediately due to the forces generated by the memory in the plastic material. This provides for a 'tamper-evident' feature for the consumer, allowing as it does for visual confirmation that the product has not been opened previously.

0029Additionally, the vertically folding vacuum panel section may employ two opposing initiator portions and two opposing control portions. Reducing the degree of flex required from each control portion subsequently reduces vacuum pressure to a greater degree. This is achieved through employing two control portions, each required to vent only half the amount of vacuum force normally required of a single portion. Vacuum pressure is subsequently reduced more than from prior art vacuum flex panels, which are not easily configured to provide such a volume of ready inward movement. Again, less stress is applied to the container side-walls.

0030Moreover, when the vacuum pressure is adjusted following application of the cap to the container, and subsequent cooling of the contents, top load capacity for the container is maintained through side-wall contact occurring through complete vertical collapse of the vacuum panel section.

0031Still, further, the telescopic panel provides good annular strengthening to the package when opened.

0032Referring now to <figref idref="f0002">Figures 5 to 8</figref> of the drawings, preferably in this container there are two opposing initiator portions, upper initiator portion 103 and lower initiator portion 105, and two opposing control portions provided, upper control portion 104 and lower control portion 106. When the vacuum pressure is adjusted following application of a cap (not shown) to the container 100, and subsequent cooling of the contents, top load capacity for the container 100 is maintained through upper side-wall 200 and lower side-wall 300 contact occurring through complete or substantially complete vertical collapse of the vacuum panel section, see <figref idref="f0002">Figures 6 and 7</figref>.

0033This increased venting of vacuum pressure provides advantageously for less force to be transmitted to the side-walls 100 and 300 of the container 100. This allows for less material to be necessarily utilised in the container construction, making production cheaper.

0034This allows for less failure under load of the container 100 and there is no longer any requirement for a vertically oriented panel area to be necessarily deployed in the design of hot-fill containers. Consequently, this allows for the provision of other more aesthetically pleasing designs to be employed in container design for hot-fill applications. Further, this allows for a label to be fully supported by total contact with a side-wall which allows for more rapid and accurate label applications.

0035Additionally, when the cap is released from a vacuum filled container that employs two opposing collapsing sections, each control portion 104, 106 as seen in <figref idref="f0002">Figure 7</figref>, is held in a flexed position and will immediately telescope back to its original position, as seen in <figref idref="f0002">Figure 8</figref>. There is immediately a larger headspace in the container which not only aids in pouring of the contents, but prevents 'blow-back' of the contents, or spillage upon first opening.

0036Further embodiments of the present invention may allow for a telescopic vacuum panel to be depressed prior to, or during, the filling process for certain contents that will subsequently develop internal pressure before cooling and requiring vacuum compensation. In this embodiment the panel is compressed vertically, thereby providing for vertical telescopic enlargement during the internal pressure phase to prevent forces being transferred to the side-walls, and then the panel is able to collapse again telescopically to allow for subsequent vacuum compensation.

0037Although two panel portions 101 and 102 are shown in the drawings it is envisaged that less than two may be utilised.