Note: Descriptions are shown in the official language in which they were submitted.
i7~
The present invention relates to container end
closures, preferably manufactured completely or partially from a
material that is sensitive to a pressure difference between the
interior region and the exterior region of the container. Such a
container may, for instance, comprise a casing of a supporting
layer of plastic having a suitable foil or laminate thereon and a
pair of end closures to be applied onto the ends of the casing.
The idea behind the invention is to master, in a
lo controlled manner, the "panelling" problems that arise in such
packaging containers havlng a deformation tendency. By the term
llpanellingl' is meant the deformation inwardly of the wall o~ a
packaging container that occurs when an under-pressure is
obtained ln the sealed container. Such an under-pressure may for
instance arise from the fact that the container has beerl hot
filled or due -to consumption of oxygen by the product packed in
the container.
It has previously been suggested to arrange specific
pressure sensitive closure panels, of the membrane type,
operating between two "stable" end positions.
AS su~h, the conventional arrangements for controlled
pressure difference elimination form a solution to the problem
according to the present inventlon. However, the solution
implies that an extremely unreliable and instable state is
created as soon as the arrangement departs from either of the two
natural "stable" end positions until the stable second end
posltion is assumed. The conventional solution operates with a
too large "stroke". In practice this may resul-t in a state where
the pressure difference is not compensated in the manner that was
intended. There may, for instance, arise an "equilibrium~' state
where an under-pressure exists in the container, implying a
forced suction in of contamination and bacteria to the product,
if the relatively weak seal breaks up due to the pr~ssure
difference.
-- 1 --
It is of a great impor ance to provide an arrangement
that g.ives a quick acting ~panelling~ and an exact pressure
compensation.
In the broadesk sense thereof, the present invention
provides an end closure for a packaging container, comprising a
panel arranged to generally cover an openlng ln a container end,
and a marginal portlon merging into the panel in which radially
ad~acent portions of the panel have a mutually different wall
o thickness for forming pressure sensitive deformation zones.
The radially, close to each other, deformation zones
are formed over substantially the whole area of the end closure.
In one embodiment the radially ad;acent portions are
formed by a spiral shaped groove in the panel giving a first ~all
thickness and leaving a splral shaped ridge in the p~nel of a
second wall thickness.
Preferably, the spiral shaped groove is formed in that
side of the end closure which is to be turned towards the
interior of the container.
The arrangement is such that the first wall thickness
is considerably less than the second wall thickness.
In a specific embodiment that is obtainable by
in~ection mouldable plastics, the groove starts in the region of
the centre portion of the end closure and extends generally out
to the marginal portion.
In an alternative embodiment the radially ad~acent
portions are obtained by concentric grooves in the panel leaving
a first wall thickness in the panel and concentric ridges of a
second wall thickness.
-- 2 --
The grooves are preferably arranged oYer substantially
the entire area of the end closure.
Preferably, the grooves are formed in that slde of the
end closure -that is to be turned towards the interior of the
container.
- 2a -
Pre~erably, the wall thickness is such that the first
wall thickness is considerably less than the second wall
thickness.
In order to Eacilltate axial movement the groove width
preferably is relatively large, within the interval oE some
millimetres.
In either embodiment the end closure preferably is
formed as a domed panel.
For instance, the end closure is manuEactured from an
injection mouldable/thermoformable material, preEerably a
thermoplastic material.
The invention will now be exemplified by reference to
the accompanying drawings, where
Figure 1 seen from the thought inside of a packaging con-
tainer shows an end closure according to a first
embodiment,
Figure 2 is a section along line II-II in Figure 1,
Figure 3 shows a second embodiment of an end closure, and
Figure 4 is a section along line IV-IV in Figure 3.
The end closure 10 in Figure 1 basically comprises a
closure panel 11 and a marginal portion 12. Said parts are
formed integrally, or instance by injection moulding or
thermoforming, from an injection mouldable and thermoEorm-
able, respectively, mate7ia~,~ Eor instance a thermoplastic
material, preferably a ~r~r~sn, for instance polypropy-
lene.
In the side 13 oE the panel 11 - the thought inside oE
the closure - there is formed a spiral shaped groove 14
having one end in the area oE the central por-tion 15 of the
closure and a seconcl end adjacent^~o the~ ~g~ 12. I'he
groove leaves a wall thickness 16 ~ considerably less
than -the wall thickness 17 oE the spiral shaped ridge 18
tha-t is Eormed on -the closure 10.
As appears from Fig1lre , the ck)sllre has a domed shape.
The spirals 18, 14 having radia]ly adjacent portions of
rnutually different wall ~ ickness along the entire area o~
the clo~sure 10 give evenly clistributed de~ormatlon zones
alon-~ ~he e-ntire area of -the closure. This dlstributiol- of a
larger n-llnber of zones imply a quick reaction -to a pressure
difference in the con-tainer (not shown) which is to be
closed by the closure 10 at one or both ends thereof. The
quick reaction implies a momen-taneous pressure compensa-tion
and this is extremely advantageous Eor minimizing stress in
the weld/sealing areas.
The embodiment according -to Figures 3 and 4 comprises
concentric grooves/ridges 14, 18. The groove width is pre-
ferably selected somewhat wider than in the first embodiment
in order to obtain a quicker reaction. For the same reason
it may be feasible to place in an angle, for instance as a
parallelogram or as a cone, the sides of the groove, as has
been shown by the re~erence numeral l9.
The marginal portion of the closure has been shown as a
single rim, but it is o:~ course possible to have a double
rim and this has been indicated by the broken lines 20 in
Figures 2 and 4.
It is further to be understood that the closure, speci-
~ically if it is manu~actured ~rom plastics, may be provided
with a foil that is gas and vapour tight, for instance a
metal ~oil 21.
