Note: Descriptions are shown in the official language in which they were submitted.
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SNAP-ACTION CLOSURE WITH AN ELASTIC SEAL
Field of the Invention
This invention relates to improvements to snap action closures.
Background to the Invention
Snap-action closures are used extensively on containers for liquids and
creams, such as
cosmetics and household cleaning products. While not necessarily more
effective than
other closures, such as screw closures for example, they are well liked by
consumers and
consequently have had considerable commercial success.
Figures 1 a-1 c show an example of a snap-action closure which is described in
more detail
in UK patent application GB 2 269 811. Part of the wall at the dispensing end
of the
container is flexible and is defined by a thin section which acts as a hinge.
The hinge also
defines an aperture through which a flexible panel must pass. The area of the
aperture is
slightly smaller than the area of the flexible panel. The flexible panel can
either be in a
convex, open position (not shown) or a concave, closed position (shown). By
pressing on
the flexible panel when it is in the convex and open position, it is deformed
to pass
through the smaller aperture, so as to reverse its curvature and snap into a
concave
opening in the container thus closing it.
In practice, however, snap closures of this type usually fail to seal solely
by the action
described above. A flexible panel made from plastics may fail to seal at the
corners of the
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aperture (see Figures la and 1b), since the force distribution over the
flexible panel is not
normal to the closure surfaces except at the centre of the panel. Furthermore,
although the
aperture should be moulded to conform to the natural shape of the flexible
panel, the seal
will not be consistent due to the variations in the material properties of the
closure, such
as stiffness at different temperatures, or hysteresis and creep in the
materials used in its
construction.
Thus, insufficient force is provided by the flexible panel in the closed
position to
maintain a seal. Whilst this may be adequate for powdered or granulated
products, this is
not true of liquids. In particular, when such containers are subjected to
increased internal
pressure, through a temperature rise for example, leaks may occur. Clearly, a
closure
which does not seal properly in these circumstances is of limited use
particularly when it
is required for longer term storage.
I 5 Summary of the Invention
According to a first aspect of the present invention, a resealable closure
comprises a
curved flexible panel forming part of the wall of a container or cap
therefore, the area of
the curved flexible panel being greater than the area of the wall of the
container or cap
defined by a hinge line of action, so that the curved flexible panel may be
forced to pass
from a convex form to a concave form and vice versa with an over centre snap
action as
the curved flexible panel is caused to pass through area of the wall of the
container or cap
defined by the hinge, and the curved flexible panel being inwardly concave to
at least
partially close an opening in the container or cap when in a first position,
and being
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outwardly convex to form a dispensing opening in the second position, wherein
the
container or cap has a seal comprising an elastic seal attached thereto which
seals the
opening when the curved flexible panel is in the first position.
In the present invention, the problem of leakage in the conventional snap-
action closures
described above is overcome by providing a resilient seal between the opening
and the
flexible panel which deforms when the flexible panel is closed to create a
liquid-tight
seal. In particular, the gap in the region of the closure hinge is closed by
the elastic flow
of sealant material where very little, if any, closing force is otherwise
exerted.
The seal may be co-injection moulded onto a portion of the perimeter of the
opening or
instead, or in addition, onto a perimeter portion of the flexible panel.
Alternatively, the
seal may be an initially separate component which is then assembled to the
closure during
manufacturing.
Preferably, the material of the elastic seal has an elongation of at least
100%, preferably
at least 200%, most preferably at (east 1000%, a compression set at
70°C of less than
30%, preferably less than 20%, most preferably less than 10%, a cone
penetration
(ASTM D217 for greases) of from 10 to 40 mm, an initial softening point of
greater than
100°C and a stress relaxation of greater than 500 seconds.
Whilst the elastic seal can be a closed cell foam, silicone or polyurethane
rubber,
preferably it is an elastic gel composition.
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It is advantageous if the elastic gel composition exhibits a low compression
set since this
enables the seal to return rapidly to essentially the same form when the
compressive force
of the flexible panel is removed. It is desirable that the elastic gel
composition is tacky,
so that it conforms and lightly adheres to the mating surface. This enables
the closure to
survive transient pressure increases. Preferably, the seal is capable of
adhesive release
from the mating surface without rupture, and further should be sufficiently
soft to
accommodate some foreign material contaminating the seal surface without loss
of
sealing.
One particularly suitable material for use as a sealant is a liquid-extended
polymer
composition. Preferably, the polymer of the liquid-extended polymer
composition is a
block co-polymer. More preferably, the polymer of the liquid-extended polymer
composition is a block copolymer having hard blocks and soft blocks. More
preferably,
IS the polymer of the liquid-extended polymer composition is a styrene-diene
block
copolymer. Most preferably, the polymer of the liquid-extended polymer
composition is
a polystyrene-butadiene-styrene) block copolymer (SBS), a polystyrene-isoprene-
styrene) block copolymer (SIS), a poly(styrene-ethylene-butylene-styrene)
block
copolymer (SEBS), a poly(styrene-ethylene-propylene-styrene) block copolymer
(SEPS)
or a poly(styrene-ethylene-propylene) block copolymer (SEP).
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Other suitable elastic gels include bio-gels, ie gels derived from plants and
animals.
Examples of these include polysaccarides, for example hydroxypropyl cellulose,
derived
from cellulose; or protein gels such as gelatin, derived from collagen; and,
latex rubber.
5 According to a second aspect of the present invention, there is provided the
combination
of a container and a resealable closure according to the first aspect of the
present
mvent~on.
A package comprising the combination of the container and a resealable closure
according to the present invention is capable of containing a liquid under
pressure, and in
particular a liquid which contains a dissolved gas. Accordingly, the invention
may be
used to store and dispense carbonated beverages.
In one preferred example, the container comprises a flexible tube which may
contain a
I 5 paste or cream.
In another example, the container has a tab fitted to or integral with the
flexible panel, to
assist operation of the resealable closure.
Brief Description of the Drawings
Examples of the present invention will now be described in detail with
reference to the
accompanying drawings, in which:
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Figure la shows an example of a known snap-action in the closed position and
Figures 1b
and I c are scrap cross-sections through that closure and its film hinge
showing the poor
seal resulting from a gap in the corners;
Figure 2a shows the same closure as in Figures la-Ic having a seal according
to the
present invention and Figure 2b shows the same closure in the open position;
Figures 3 and 4 show the flexible panel closure as an integral part of a
container, each in
the closed and open positions;
Figure 5 shows an alternative integral design based on a flexible tube type of
container;
Figures 6a, 6b and 7 show examples of tamper-evident closures;
Figures 8a-8f show a flexible panel-type closure in which the flexible panel
section is an
initially separate part;
Figures 9a-9d show a closure with integral seal for sealing between a
container and the
closure body;
Figures 1 Oa and l Ob show a cap attached to a container by a co-operating
snap fit;
Figure 1 1 shows a flexible panel closure welded to a container; and,
Figures 12a-15c show a tab attached to the flexible panel to assist operation
of the
resealable closure.
Detailed Description
Figure la is a cylindrical closure for attachment to a container, comprising a
body 1, with
a flexible panel 2 attached to the cylindrical wall, and an end wall 4 against
which the
flexible panel 2 closes - that is, the curved flexible panel 2 co-operates
with a
substantially matching cut-out 5 in the end wall 4. One or more ribs 3
attached to or
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integral with flexible panel 2 stiffens the flexible panel 2 in the
longitudinal direction,
whilst maintaining flexibility in the radial plane; this results in a crisp
and repeatable
action of the closure.
Figure 1 b is a scrap cross-section through the end wall 4 of closure shown in
Figure 1 a,
showing how the flexible panel 2 closes against the cut-out 5 in the end wall
4.
Unfortunately, in some circumstances the closure does not offer an adequate
seal,
particularly at the corners.
The reason that this simple closure does not always provide a good seal may be
seen from
Figure lc. When the flexible panel 2 is closed, as shown in Figure lc, the
film hinge 7 is
too stiff to permit a complete matching of the flexible panel 2 and cut-out 5,
with the
result that an aperture 8 remains. Another cause of this problem is that all
of the force on
the flexible panel 2 in the area of the film hinge 7 will be in the direction
of arrow F, and
the maximum closing force will be at the centre of the flexible panel 2 in the
direction of
arrow G. Thus there is almost no force available to close the aperture 8
against the
resistance of the film hinge 7.
An example of the present invention is shown in Figures 2a and 2b. In the
present
invention, the aperture 8 is sealed by the application of a seal 9 to the cut-
out 5. It may
not be desirable or possible for the seal 9 to join with the film hinge 7,
particularly if the
seal 9 is to be co-injection moulded onto the cut-out 5, where for certain
sealant
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materials, the moulding temperature would melt the film hinge 7. In this case,
a small gap
may remain between the seal 9 and film hinge 7; this is not detrimental
because the
sealant material will flow to seal the small gap 10. If the application so
requires the
sealant material may be moulded onto the flexible panel 2.
5
When the flexible panel 2 is closed against the cut-out 5, as shown in Figure
2a, the seal 9
is sufficiently soft to elastically flow into the apertures 8 and 10, thus to
form a seal
between the adjacent surfaces of the cut-out 5, flexible panel 2, and film
hinge 7. Even
though the closing force of the flexible panel 2 is virtually zero at the film
hinge 7 area,
10 the sealant material elastically flows into the apertures 8 and 10, and
will in fact exert a
small pressure against the adjacent surfaces, and compensate for the lack of
closing force
in this area.
The applicant has found that a sealant material comprising a liquid-extended
polymer
composition is particularly effective in this application as it acts almost as
a hydraulic
fluid, so that the pressure exerted in the centre of the flexible panel 2 is
transmitted
laterally until the pressure throughout the seal 9 is nearly uniform.
Figures 3 and 4 show containers having a flexible panel closure, in the closed
and open
positions. In Figure 3, the flexible panel 2 is attached to the top wall 11
with a film hinge
7 and closes against the cut-out 5 in the side wall 12. This arrangement is
preferred for
pourable liquids such as fruit juice or milk, because the air can enter the
container via the
open part marked Z, whilst the liquid pours from the lower part K, and this
prevents
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"glugging" caused by air passing through the liquid and into the container. A
lip 13
extending from cut-out 5 helps the liquid to pour in a controlled fashion, and
may also
serve to provide a convenient opening from which to drink. Furthermore, the
lip may be
the remainder of the tamper-evident device after removing the tear-off strips
described
below with reference to Figures 6a and 6b. In Figure 4 the flexible panel 2 is
attached to
the side wall 12 of a container by film hinge 7, and closes against a cut-out
5 in the end
wall 4 of the container. This arrangement is suitable for more viscous
liquids, powders
and granules.
Figure 5 shows a flexible tube type of container frequently used for creams
and pastes.
Flexible tube 14 has a flexible panel closure 2 attached to end wall 4 with a
film hinge 7,
and which closes against the cut-out 15 in side wall 16. A seal 9 as
previously described
is attached to the flexible panel 2 or the cut-out 15. Preferably, the side
wall 16, cut-out
15, film hinge 7 and flexible panel 2 are moulded integrally with the flexible
tube 14. The
flexible panel 2 may be thermo-sealed or otherwise bonded to the cut-out 1 S
to provide
tamper evidence, as described below. The advantage of this design is that the
flexible
tube type of container may be filled from the open end, and heat sealed,
crimped, or
otherwise sealed to retain the contents, to provide a cost-effective pack.
Another
advantage of this embodiment is that the tube may be safely stood upright on
the closure
end without the contents leaking.
A common requirement for closures is that they should be tamper-evident -
I.e., there
should be unambiguous evidence that the closure has been opened. Figures 6a
and 6b are
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a scrap cross-section on the longitudinal axis through a flexible panel type
of closure, and
illustrate a principle applicable to all of the examples described herein.
Body I has an
end wall 4, and flexible panel 2, shown in the open position. During
manufacture, the
seal 9 is moulded onto either the sealing face of cut-out 5, or preferably
onto the flexible
5 panel 2, when the flexible panel 2 is in the open position. The flexible
panel 2 has a strip
17 attached by a thin web 18, and the cut-out 5 has a flange 19, also with a
rib 17
attached by a thin web 18. The flexible panel 2 is then closed as shown in
Figure 6b, and
the strips 17 are heat sealed together or otherwise sealingly bonded. The thin
webs
should be adjacent to one another. Seal 9 is compressed to seal the aperture,
and a further
10 seal is provided by the bonded strips 17. When it is required to open the
closure for the
first time, the bonded strips 17 are torn off along the line of the thin web,
which permits
the flexible panel 2 to be opened. The seal 9 then performs as previously
described.
Figure 7 shows an enhancement which may be adapted to all of the foregoing
flexible
panel types of closure. Cap 20 has a flexible panel 2, and attached to it by
frangible
means at approximately right angles is a tear-off strip 21, having a finger
grip 22. This
construction prevents the flexible panel 2 from flexing until the tear-off
strip 21 is
removed.
An alternative method of making a flexible panel closure is shown in Figures
8a-8f,
where the flexible panel is an initially separate component. Referring to
Figure 8a, body
1 has an end wall 4, and a panel 22 between the end wall 4 and body t . The
panel 22 is
perforated by an aperture 23, and the wall 24 of the body 1 is cut away to
form a groove
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25 around the panel 22. The groove 25 extends to form a pocket 26 between the
wall 24
and panel 12. A hole 27 is formed through the wall 24 into the pocket 26.
Flexible panel
2 has a retaining clip 28 having a hole 29 through, and is attached to the
flexible panel 2
by at least one frangible connection 30. The hole 29 is of a size to engage
with the
frangible undercut projection 31 on the top surface of the end wall 4. A
detent 32 is sized
to fit into the hole 27 in wall 24 of the body 1. A seal 9 is attached to the
perimeter of the
flexible panel 2. A view of the other side of the flexible panel 2 shows the
seal 9. To
build the closure, the flexible panel 2 is inserted into the groove 25 until
the detent 32
engages in the hole 27. The undercut on detent 32 ensures that the panel 2
cannot be
removed once assembled. The hole 29 is then pushed over the frangible
projection 31,
and again, the undercut on the frangible projection prevents removal without
breaking the
projection.
Figures 8b and 8c are cross-sections to show the flexible panel in the open
and closed
positions, respectively, and how the seal 9 seals against the panel 22. Figure
8d shows a
rear view of the flexible panel 2.
Figure 8e shows the assembled closure, and Figure 8f shows the appearance
after
removing the retaining clip 28 from the flexible panel 2. This breaks the
frangible
projection to leave a small pip 31a, thus providing evidence that the closure
has been
opened. The shape of the seal 9 should follow the shape of the aperture 13, so
that
product does not accumulate in the pocket 26. Again, it is quite possible to
mould or
otherwise attach the seal 9 to the face of panel 12, surrounding the aperture
13.
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Figures 9a-9d and Figures 10a and lOb show a closure of the flexible panel
type, where
the sealing element for the moveable panel is continuous with a seal for
sealing between
the closure body and its associated container.
Figure 9a shows a cap 20 comprising a side wall 1 and end wall 4, and the
flexible panel
2 attached by the film hinge 7 to the end wall 4. The flexible panel 2 is
shown in the open
position for clarity. Figure 9b is a view of the inside of the cap 20. A seal
9 is moulded
into or otherwise attached into a groove 33 on the inside face of the end wall
4, and
continues over the inside face of the flexible panel 2. Thus, the seal 9 may
be likened to
an 'O' ring (or similar section seal), fixed to the end wall 4 of the cap 20,
and free to
move with the flexible panel 2. There is a cut-out 34 in the side wall 1,
which is clear of
the flexible panel 2 and seal 9 when the panel 2 is closed. Referring to
Figure 9c, 35 is a
container or the body of a cap (for example a screw cap) having a rim 36 and
cut-out 37,
the shape of which conforms to seal against the seal 9 attached to the
flexible panel 2
when in the closed position. When the cap 20 is assembled to the container 35,
as shown
in Figure 9d, the panel 2 presses the seal 9 into the cut-out 37 in container
35.
In Figure 10a, the cap 20 and container 35 have a co-operating snap fit 38.
The cap 20 is
pushed on to the container 35 so that the rim 36 of container 35 presses
sealingly into the
seal 9 in the groove 33, and is maintained in that position by the snap fit
38. The seal 9,
which continues over the flexible panel 2 thus co-operates with and seals
against the cut-
out 37 in the wall of the container 35 when the flexible panel 2 is in the
closed position.
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Figure 1 1 shows a similar type of closure, with the seal 9 attached to the
container instead
of the flexible panel 2. In this arrangement, the connection between the cap
20 and
container 35 is effected by ultrasonic welding at 39, or by adhesive or
sealant.
Alternatively, a metal-loaded plastic sealing ring may be incorporated, which
is melted
by the application of radio frequency energy to join and seal the two parts.
For some applications, such as closures to be used for dispensing drinks, or
those for
dispensing irritating or harmful chemicals, it is preferable that the user's
hand does not
come into contact with the product to be dispensed. Figures 12a, 12b and 12c
show a
closure having a tab 40 attached by the hinge 41 to the flexible panel 2. As
shown in
Figures 12a and 12b, when the panel 2 is in the closed position, tab 40
provides
additional security to prevent inadvertent opening by co-operating with the
lip 42 of the
closure body 1. With the tab 40 is unclipped from the lip 42, it serves as a
grip which the
user grasps to pull open the flexible panel 2, as shown in Figure 12c.
Figures 13a and 13b show a flexible panel 2 with a fixed tab 43 with which the
user can
push or pull the flexible panel to close or open it.
A simpler way of keeping the user's hand clear of the product being dispensed
is to
extend the front of the flexible panel 2 to form a tab 44 by which the panel
may be
operated, as shown in Figure 14.
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Figures 15a, 15b and 15c show how the flexible panel may be operated more
remotely by
attaching a paddle 45 to a rib 46, which in turn is attached to the flexible
panel 2. The
paddle 45 operates a fulcrum 47, so that when the user presses on the paddle
45 in the
direction of the arrow S, a force is exerted on the panel 2 in the opposite
direction to the
arrow S causing the panel to open. To close the panel 2, the user pushes on
the rib 46.
In all of the embodiments shown in Figures 12-15, it is beneficial to have one
or more
ribs running longitudinally along the flexible panel to ensure sufficient
stiffness to
transmit the opening or closing force without buckling.
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