Note: Descriptions are shown in the official language in which they were submitted.
108~6S~
This invention relates to sealing containers with
gaskstted closures, in particular to the configuration (profile)
of gaskets for threaded closures.
Container closures are provided with ga~kets primarily
in order to prevent air from entering the container and/or los~ of
contents of the container to the outside. Such gaskets are
especially important in closures for containers which hold food or
drink since contamination of the food or drink within a container by
the entry of air before consumption can be a serious health hazard.
A major area of use of gasketted closures i~ for the closing of
bottles, especially glass bottles.
In order to enable a customer to re-close the container
after it has been opened it is desirable to provide a threaded
closure which can be removed by unscrewing. One general type of
threaded closure which has found widespread commercial acceptance
with clo~ing of glass bottles is the in situ-threaded type in which
threads are formed during or after the operation of closing the
closure onto the threaded container neck. Generally, a closure
which is initially unthreaded is closed by pressure onto the neck
of a threaded container. Lateral pressure is then applied to impart
threads to the skirt of the closure using the container neck as a
die so that the threads formed in the closure correspond to those
on the neck of the conta$ner. For example the threads may be
formed with the aid of a roller. Closure caps having threads
; formed in this way are termed "roll-on" caps and are usually used
on bottles.
Gaskets for closures of the above type have hitherto
been produced by the so-called spin-line process. In the spin-line
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10816~7
process a predetermined quantity of a plastisol of polyvinyl
chloride is metered into a closure, the closure is spun rapidly
about an axis through the centre of the flat top of the closure so
as to distribute the plastisol by the action of centrifugal force,
and the plastisol in the closure is then fluxed. The plastisol is
a viscous dispersion of polyvinyl chloride in a plasticiser and
is fluxed by heating it to a temperature at which the plasticiser
is absorbed by the polyvinyl chloride to form a homogeneous mass,
which upon cooling gives a rubbery solid.
The spin-line process, although commercially succes~ful,
has some limitations, and in our-R~ ~ l~cuL vrl
Ne_ 17~1l6,'7~, we have proposed moulding certain gaskets which may
~; therefore have a profile different from those produced by the
spin-line process. Before the closure is closed onto the container
these gasket~, in their undeformed configuration, comprise a
- substantially flat central panel and an adjoining peripheral portion,
the thickness of which is at all points greater than the thickness
of the central panel.
Looking at the closure (cap blank before thread formation)
in its inverted or up-turned position, meaning the oppo~ite way up
to which it is seen when closed onto a bottle, the peripheral portion
of the gasket extends radially outwards to a point on the skirt
of the closure which i~ overall upwards from the central panel of
the gasket, and, considered in the radially outward direction, the
height of the peripheral portion above the central panel starts by
increasing and thereafter either continues to increaQe or remains
the same.
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108i~S7
United States Patent No. 3,255,909 discloses a
linerless closure using an integrally moulded bead upstanding
on the inner face of the closure end wall and adapted to fold
radially outwardly to act as a top seal during closing of a bottle
neck using such a closure. However top seal èffect alone is
in~ufficient to ensure ade~uate ~helf life of ~assy liquid
beverages such as soda water and other pressurised drinks.
In German Offenlegungsschrift No. 2,417,173 we described
at Figures 11, 12 and 13, a moulded gasket profile in which the
gasket had a central panel surrounded by an annular bead which
stopped short of the closure skirt and was joined to the skirt by a
foot portion of a height comparable to that of the central panel.
Such a gasket, after closing of the container and rolling of a thread
on the container skirt using a "reform" operation gave a top seal
which with a carefully formulated gasket composition would hold a
venting pressure of as high as 100 p.s.i. In the "reform" operation,
during the closing of the cap force is exerted not only downwardly
but also laterally inwardly on the top of the skirt of the cap above
the thread-forming zone of the skirt, so as to pinch the top of the
skirt inward~. In other words, the diameter of the skirt is reduced
\ 80 that, in the caqe of a spin-lined ga~ket profile as disclosed in
B~itish Patent Specification No. 975,739, the gasket is compressed
between the top of the skirt of the cap and the side of the neck
of the ¢ontainer.
Although the said British Patent Specification No.975,739
did not ernphasise the degree of reform required, the reform operation
widely employed commercially as a result of the invention claimed in
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iOB~657
British Specification No. 975,739 has now been found to be capable
of improvement by u~ing a more severe reform operation which will
be referred to throughout thi~ Specification as "tight" reform.
The axial depth of the root of the closure skirt which is affected
by the refonm is increased and the diametral contraction i^~ also
increased so as to reduce still further the volume of the space
remaining between the corner of the glass finish of the bottle neck
and the corner of the closure.
One aspect of the pre~ent invention provide~ a method of
closing a container with a "roll-on" type of screw threaded closure,
such method comprising: taking a closure blank with a moulded
re~ilient gasket on the inner face of the end wall of the closure,
which gasket i8 profiled 80 as to have a central circular panel and
an adjoining annular bead which, when viewed in an axial cross-section
through the closure, consists of a hump.projecting above the level
of the central panel of the ga~ket and terminating just short of
the skirt of the closure, with the centre of area o~ the hump
disposed closer to the skirt of the closure than is the centre of
the base line of the hump7 pressing the closure and container neck
axially together to close the bottle-neck and to compress the
hump-shaped bead of the closure axially and to defonm the hump-shaped
bead radially outwardly towards the skirt of the closure, reformlng
the closure by diametral contraction of the root of the closure skirt
above.the threads on the container neck under "tight" reform
conditions 80 that the said bead of the gasket acts as at least a
partial side seal again~t the upper part of the neck of the container,
and deforming the closure skirt radially inwardly against the threads
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1081~
of the bottle neck to form thread~ in the clo~ure ~kirt
corresponding to the thread~ on the container neck.
By using tight reform condition~ with an annular-beaded
ga~ket moulded to h preci~e profile, it i~ possible to reduce
drastically the volume of ga~ketting material necessary to achieve
both a top seal and a ~ide ~eal effect. Whereas the spin-lined
form of closure proposed in Patent Specification No. 975,739
traditionally employs film volume~ of 400 mm3 or thereabouts in the
ga~ket, judiciou~ selection of the gasket profile for use with the
present invention enables a quite satisfactory sealing effect to be
obtained with a gasket having a film volume of the order of 200 mm3.
In a preferred form of the first a~pect of the present
invention the hump-shape o the cro~s-section through the gasket
~ead is in the form of a truncated triangle having its base parallel
to the end wall of the closure, a ~ub~tantially straight radially
inner side of the triangle being digposed at an angle of from 15
to 70 with respect to the plane of the closure end wall, and a
substantially straight radially outwardly facing side being disposed
at an angle of from 70 to 86 with respect to the plane of the end
wall.
In one particularly convenient form of the pre~ent
invention the radially inwardly facing side of the triangular hump
i8 inclined at an angle of 54~ to the plane of the closure end wall,
the radially outwardly facing side is inclined at an angle of 74
to the end wall, and the height of the hump above the general level
of the central panel of the gasket i~ 1.07 mm with a flat truncated
top to the triangle.
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lOB16S7
The invention also relates to bottles which have been
closed by the method of the first aspect of the present invention.
Another aspect of the present invention provides a
gasketted closure compri~ing a closure end wall having a generally
cylindrical skirt depending from its periphery; and a gasket moulded
on the inner face of the end wall of the closure with a gasket profile
comprising a circular central panel bounded by an upstanding annular
bead which bead is spaced from the skirt of the closure by a foot
portion of the gasket having a height substantially the same as that
of the central panel of the gasket, the profile of the bead being
such that, in an axial cross-sectional view, the bead consists of a
substantially triangular hump haviny its centre of area disposed
closer to the skirt of the closure than is the centre of the
base-line of the hump, with the radially inwardly facing substantially
straight side of the triangular hump inclined at an angle of from
15 to 70 with respect to the end wall of the closure, the radially
outwardly facing side of the triangular hump being substantially
straight and inclined at an angle of from 70 to 86~ with respect
to the said end wall of the closure, and the triangular hump having
a truncated top. The truncated top is in the form of a radiused
apex or a flat top face to the hump.
If desired, with the method or the closure of the present
invention, the said central panel of the gasket may include a series
of concentric annular ribs.
The hump constitutes the main part of the peripheral
portion. It will usually have a height of 0.7 to 2.5 mm. above the
central panel and the area of it will usually be in the range 0.9 to
lOR16~7
3 . 7 9q . mm. Its radial length is much greater than that of the
foot part.
The foot part typically ha~ a radial length of from 0.25
to 0.16 mm. and its thicknes~ is typically from 0.1 to 0.35 mm.
(mea~ured perpendicularly to the corner of the cap).
The marginal part correspond~ to the tolerance between
a moulding member used to mould the gasket in the cap blank and the
minimum diameter of the cap blank itself. It will generally have a
radial length of about 0.02 to 0.15 mm~
The invention will be explained, and particular embodiments
described, with reference to the accompanying drawings, in which:-
Figures 1 to 3 are vertical ~ections, through part of a
radius, of the corner of a gasXetted cap blank of the invention,
showing the configuration of the peripheral portion of the gasket:
Figure 4 is a partial vertical section of a moulding
member used to make the gasket of Figure 1
Figure S ~hows a side elevation of the glass bottle neck
onto which the gasketted cap blanks of the invention can be closed,
Figure 6 i~ a sectional view showing the profile of
Figure 3 just prior to closing of a glass bottle neck, and
Figure 7 i8 a sectional view showing the closurs corner
and a gasket bead of a further embodiment of gasket.
Reference is directed first to Figure 1 to explain the
invention generally. The cap blank 1 of internal diameter in the
range from 25 to 32 mm., i8 preferably made of thin aluminium,
typically of a thickness in the range from 0.20 to 0.30 mm., and
will normally be lacquered on the inside and outside. The cap blank is
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10816S7
~hown in it~ up-turned position relative to that which it occupies
on the container and compri~es a s~irt 2 upstanding from a ba~e 3.
The ga~ket, which i~ made of a re~ilient plastic~ material, has a
flat central panel 4 and an adjoining peripneral portion designated
generally at 5.
The peripheral portion of the ga~ket i~ bounded by the
~olid lines M, N, 0, P, Q, R. Taking it radially outwards from
the edge M of the central panel 4, the hump portion 6 is bounded
by M, N, 0 and P, the adjoining foot portion 7 lie~ beneath PQ
and the marginal portion 8 beneath QR.
To facilitate explanation of the dimension~ of the
peripheral portion, Figure 1 include~ broken lines which are line~
of geometric construction as follows:-
The hump portion 6 shown consi~ts of a slope of constantgradient extending upwardly from the edge M of the central panel
and making an angle therewith. me top of the slope is denoted by
N. In~tead of a 810pe of constant gradient, a convex or concave
slope could be given to this part of the hump. The summit of the
hump N0 may be flat as in Figure 1 or rounded as in Figure 3. At
the point 0, a steep downward 810pe OP, conveniently but not
necessarily, of constant gradient begins. In principle this downward
slope could be vertical, but practical considerations of moulding
dictate that the angle made by this slope with the plane of the
central panel be normally in the range 75-86.
In order to form a sati~factory ~eal between the neck
of the container and the cap, it is necessary to ensure that an
adequate supply of gasket material i9 positioned in the corner part
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1~816S7
of the cap blank. The present invention enables this supply to be
provided without leaving flashing up the skirt to an undesirable
extent in that the supply in the corner is provided by deformation
of the hump 6 and foot portion 7 together with the deformation of
the bottom of the skirt 2 under tight reform conditions. Thus the
gasket moulding member (refer to Figure 4) has a hollowed-out
portion 6a which provides the hump 6 of the gasket and an annular
flange 7a which forms a leg when viewed in an axial cro~s-section,
-
extends down to about the level of, or slightly above, the central
panel and thereby limits the extent to which gasket material can
creep up the skirt during the moulding of the cap blank. '~he leg
7a of the mould cross-section corresponds to the foot part 7 of the
gasket. The leg 7a may be cut away slightly upwardly and radially
outwardly at its lower end, as in Figure 4, e.g. at an angle of
25 with the horizontal, so as to enable it to conform better to
the curved corner of the cap blank. Thus the radially outward end
Q of the foot part 7 of the gasket may be above the point P at
which the foot part joins the downward slope of the hump. The foot
part 7 may include a flat portion PS, as illu~trated in Figure 2,
or be wholly flat, a~ illustrated in Figure 3.
The leg 7a of the moulding member must be given a certain
minimum radial thickne~ in order to give it enough mechanical
strength to withstand repeated use in high-speed moulding operations.
Of course this minimum radial thickness will depend on the toughnes~
of the particular metal used for the moulding member, but in general
it will not be les~ than ~.25 mm. On the other hand, the leg 7a
must not be made too thick in the radial direction, since otherwise
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~0816S7
the hump will be located too far radially inwards, with the result
that the supply of gasket material in the corner of the cap blank
may be in~ufficient to form the corner ~eal even under tight reform
condition~.
It will now be evident why tbe slop~ OP is steep:
it is important to provide as much gasket material a3 possible in
the radially outward region of th~ hump, but it i~ also important
to allow for a reasonable thicknes~ for the leg 7a o~ the moulding
member, particularly at the root of the leg 7a. A ~teep slope
enablea both requirements to be met, and al50 ensures that the
radially inner face of the flange forming the leg can be withdrawn
from the radially outwardly facing part o~ the an~ular profile hump
during removal or "stripping" of the mould from the closure.
The volume of the hump, or the area o~ the hump in vertical
section in Figure l, should be kept as small as po~sible in order to
achieve maximum economy of gasket material consistent with obtaining
a reasonable seal. The sectional area will typically be rom 0.5
to 3.7 sq.mm, but it may be possible to u9e even less ga~et material,
and of course there i8 no upper limit other than that dictated by
common Yense and economies. A rough guide to the area under the
hump may be obtained from the constructed triangle KLM, in which K
i8 a conqtructed point representing the intersection of a line
vertically through point 0 with an extrapolation o~ the upward
slope MN and L is a point coplanar with the central panel and
vertically beneath 0. The area of triang~e KLM is equal to B2cot
where B i~ the distance KL. Usually the angle a will be between
15 and 70~.
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10~16S7
Construction lines have been drawn in Figure 1 to show
the centre of area G of the triangle KhM, i.e. the point at which
the medians of the triangle meet. Referring now to Figure 5, it
is desirable that the point marked T on the glas~ neck, i.e. the
point at which the flat top 10 ends and curvature 11 leading to
the side-wall 12 begins, should impinge upon the gasket at a point
vertically above the centre of area G or not greatly distant
radially from G. The cap blank, gasket dimensionq and glass neck
configuration should be arranged accordingly. When the closure
ga~ket i9 pressed hard axially onto the glass finish of the bottle
neck during the closing operation, and the root of the clo~ure skirt
deformed radially inwardly upon tight reform of the closure, the
gasket material is pushed around the corner of the glass finish so
that a substantial proportion eventually lies between the skirt 2
of the cap blank and the curvature 11 and side-wall 12 of the finish.
It is considered most advantageous for the displaced gasket material
to come into contact with the clo~ure skirt as a result of the reform
operation.
It will be appreciated that there may be curvature in the
region of points M, N, 0, P and Q to facilitate obtaining a good
definition by moulding.
For ease of reference Figure 1 also shows lines of
geometrical construction dependent perpendicularly from M, G, 0, P,
Q and R onto the closure end wall at points U, V, W, X, Y and Z
respectively.
Figure 6 shows in more detail the cross-~ection of the
gas~et of Figure 3 and illustrates the relative positioning of the
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10816S7
gasket and the radially outwardly rounded end of the glas~ neck
of a bottle on which the closure i~ to be fastened by a "tight"
reform thread rolling operation.
Figure 7 ~hows an alternative form of the gasket with
certain differences from the form shown in Figure 6, for example
Figure 7 shows a flat top face to the truncated triangular section
of the hump, making it in effect of trapezoidal section.
The following Table gives dimensions of the ga~ketted cap
blanks of Figures 6 and 7. These gasket~ are in accordance with
the invention and give a satisfactory ~ealing performance when
closed as roll-on bottle cap~ onto a bottle nec~ by a tight refonm
operation.
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108~6S7
TABLE
Fig. 6 Fig. 7
. .
Internal diameter of cap blank 27.35 27.35
Radial tolerance of moulding
member (ZY) O.025 O.025
.A
Radial distance tYX) 0~32 O.32
.
Height (KL) 1.128 1.265
. .
Vertical truncation distance(R0) .516 .198
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: ~adial distance (YW) ,460 .622
.,
Height of P abovo çentral panel 0.127 0.127
.
Angle a 3054~o
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Area of triangle KLM (=~ cota) 1.102 .571
8q~. 111111. 9q. ~ .
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~08~6~7
Con~iderable variation is po~Rible from the dimen~ions
given in the Table, but in general the overall volume of gasket
material ("film volume") will be much les~ than the 400 cu. mm.
frequently needed for spin-lined gasket~ in thi~ type of cap. A
film volume as low a~ about 200 cu. mm. can ea~ily be attained by
the pre~ent invention.
These gasket configuration~ have been found to be effective,
when formed of ~la~tici~ed PvC or other suitable plastic material,
under both tight and loose reform conditions, allowing in each case a
reduction in the quantity of plastics composition used in the gasket.
The preferred method of closing the cap blank onto a
container comprise~ placing the gasketted metal cap blank (which
by definition i8 of course made of thin metal) over the threaded
neck of the container, pressing the cap blank down axially against
the neck of the container, and whilst holding it 80 pressed, reducing
the diameter of the skirt of the cap blank at a position above the
threads on the neck of the container, in this case near the root
of the closurQ skirt, 80 as to compress the ga~ket material between
; the top of the skirt of the cap blank and the side of the neck of the
container, and forming thread~ in the skirt of the closure by deforming
it at a position and in a configuration corresponding to the threads
on the neck of the container. The reform operation, which will
normally just precede the operation of forming the threads, may be
effected by use of a clo~ure head of suitable shape, as described
in British Patent Specification No. 975,739.
However, although there was no particular significance
attached in British Patent Specification No. 975,739 to the extent
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~0816S7
of reform, the method of the pre~ent invention involves what i8
termed "tight" or "~evere" reform in which the severity of the
reform operation is increased over that used in both Briti~h
Patent Specification No. 975,739 and our said German
Offenlegungsschrift No. 2,417,173. This reduce~ the amount of
gasket material necessary compared with the volume neces~ary in
the spin-line proces~.
In a "tight" or "severe" reforming operation, a 28 mm.
(external diameter) cap blank may have its external diameter reduced
to about 26.3 mm., instead of the 26.5 mm. u~ual in reforming and
the depth over which the cap blank is reformed i8 1.7 to 1.9 mm.
instead of the 1.6 to 1.7 mm., u~ual in loose reforming. In practice
a typical 1003e reform die for u~e with a 28 mm. diameter cap blank
ha~ a reforming reces~ 26.3 mm. in diameter and 1.9 mm. deep to give
the above loose reform re~ults and a typical tight reform die ha~
its rece~s 2.4 mm. deep and 26.0 mm. in diameter. The mouth of the
reforming reces~ in the die i~ of course tapered as shown in Figures
4 and 5 of Patent Specification No. 975,739. Thus under tight reform
conditions on a 28 mm. cap blank the diametral reduction i5 6.07%
instead of 5.35% usual with loose reform.
The above de~cribed "tight" or "severe" reforming increases
the tendency of the material in the corner of the gasket to suffer
108a of adhesion, and the ga~ket~ therefore have a configuration
which act~ counter to thi~ tendency, in that the centre of area of
the profile hump 6 is disposed radially outwardly beyond the centre
of the ba~e of the hump (when viewed in axial cross-section) 80 as
to enhance the tendency of the reform operation to cause the ga~ket
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~0816g7
material in the radially outward region of the hump 6 to be
squeezed towards the periphery of the cap. Thu~, wherea~ in
previou~ly propo~ed moulded gasket~ there i~ a large amount of
corner material present in the gasket of the cap blank, as for
example in our said Offenlegungsschrift No. 2,417,173, in the
present invention the amount of gasket material initially in the
corner i~ reduced, but thi~ is compensated for by movement of
material into the corner during the reform operation. Since
relatively little material is present in the corner initially, the
moment of the force which decreases adhe~ion iY relatively small.
The axial force exerted by the clo~ing head downwardly on
the cap blank may vary widely, e.g. from 120 kg. upwards, normally
from 180 to 22~ kg.
The gasketted cap blanks of the invention may be closed
onto a variety of containers, but it is envisaged that the invention
will be of use mainly for cap3 clo~able onto glass bottles. The
glas~ bottle~ may have gla~ finishes ~necks) of various types. One
well known type ~hown in Figure 5 i~ the so-called "MCA 1 finish",
widely used in Germany, Belgium, Netherlands and Luxembourg. The
locking band 13 located below threads 14 iq wider than on ~ome other
fini~he~ 80 that the MCA 1 may, if desired, be used with a pilfer
proof type of roll-on cap, i.e. a cap with a long ~kirt which become~
closed over the locking band 13 and into the area 15 of narrower
diameter below it. The bottom or rim of the cap skirt i~ then preqsed
into the container neck in the area 15. A narrow band which i9
easily frangible is provided in the skirt of the cap in the region
corre~ponding to the locking band 13. It is then impo~ible to unscrew
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10816~7
the cap from the neck without causing fracture at the said narrow
band~ The diameter t of the threads in Figure 5 is typically
27.65 mm., the diameter e of the rim corre~pondingly 25.25 mm.,
and the height h from the rim of the nec~ to the top of the locking
band about 9.65 mm.
I A series of comparative tests was carried out using
profiles similar to that illustrated in Figure 6 but with variation9
in the angle a between the end wall of the closure blank and the
radially inwardly facing side 21 of the triangular hump 22 of the
gasket profile. The height A of the rounded apex 24 of the profile
hump above the general plane of the top face 23 of the central panel
4 of the gasket was varied but the angle of the radially outwardly
facing side 25 of the triangular profile hump with respect to the
end wall of the gasket was maintained at 74. The height of the foot
portion 26 above the general plane of the central panel 23 was
maintained at 0.127 mm. throughout. The results showed that optimum
venting pressure values in the sealed bottle could be obtained using
a value for the angle a ~ 54~ and A ~ 0.042" ~1.07 mm.). In thi8
case the venting pressure was in excess of 120 lbs. per sq. inch
as determined on a te~t rig using a glass bottle which had the bottom
connected to a source of gas under pressure and wa8 placed under water
while the different internal pressure9 were applied up to a test rig
maximum ~for safety purpose9) of 120 p.s.i. to observe at what
pressure value gas bubbles could be seen to be escaping from the
bottle to indicate the onset of venting.
Satisfactory results were obtained with an angle a = 30
and dimension A= 0.035" (0.889 mm.) where the film volume was then
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10816S7
substantially 200 mm3. Thi~ represents a most economical form of
closure gasket, particularly compared with the traditional film
volumes of 400 mm3 or more when using spin-lined closure~.
With the tight reform conditions to which the metallic
closure blank is subjected during the bottle closing operation,
and a judicious choice of gasket composition and gasket profile,
it is possible with the method of the present invention to clo~e a
bottle using film volumes of the order of 150 to 200 mm3 to withstand
a venting pressure of 120 p. 8 .i. or more and causing the triangular
hump of the gasket bead to migrate radially outwardly to occupy
the space between the radiused or toroidal surface portion 27 of
the end of the bottle neck 28 and the corner of the closure
cros~-~ection between the end wall 3 and the skirt 2. This achieves
the highly desirable results of combined top seal and side seal
effects using film volumes which are of the order of one half those
previously considered nece~ary in order to achieve combined top
and side seal effects.
Naturally, when selecting the values of the various
parameters of the configuration of the gasket, the flatter form
of gasket (i.e. when the dimension A is ~mall) will be more
economical in film volume. However there is of cour~e a minimum
depth of gasket bead for achieving the degired venting pre3sure values.
In the present invention the minimum value of film volume of gasket
attainable has been lowered by combining a moulded gasket profile
with combined top ~eal and side seal effects using a gasket bead
which readily migrates outwardly during axial compression and "tight"
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10816S7
(and in many ca~es also "loo~e") reform. Thus, after clo~ing, the
bead advantageously ends up in contact with the previously exposed
part of the root of the clo~ure skirt.
The gaskets may be formed within the caps by moulding
them, u~ing a punch (moulding member). A quantity of gasketting
material i~ deposited within the up-turned cap which, when
appropriate, may be pre-heated. It will normally be neces~ary to
heat the gasketting material to Yoften it and help it to adhere to
the surface of the cap. It i~ then moulded with the punch, which
may optionally itself be heated. The methods of moulding well known
to those skilled in the art of gasketting "crown" bottle cap~ have
general applicability.
It is for example possible to mould the gasket~ by the
CGn~ian
two stage punching process de~cribed and claimed in our ~i~i~h
~ote~ J 0~3,060
~atont ~pli6a~ion ~7O, '~00l~5f~3 uQing a hot preheating punch to
partially form the pla~tics material and a relatively cooler final
moulding punch.
In principle, any gasketting material may be employed
in the pre~ent invention. Suitable materials include e.g.
polyethylene, a mixture 80% or more polyethylene with up to 20% of a
compatible polymeric material, a mixture compri~ing polyethylene,
butyl rubber, and optionally an ethylene/vinyl acetate copolymer,
especially polyethylene h utyl rubber mixtureq containing e.g. 40-70%
by weight of polyethylene and 60-30% by weight of butyl rubber.
Gaskets are preferably formed from thege mixture~ by cold-moulding
as described e.g. in our Briti~h Patent Specification No. 1,112,023,
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~`t
.~ . ~ - , - ' , .
,
108~6S7
Australian Patent Specification No. 420,653 and German
Auslegeschrift 1,544,989. Other u~able gasketting material~
include plasticised polyvinyl chloride and other vinyl chloride
polymers known in the gasket-making art, other materials described
in our Briti~h Patent Specification~ Nos. 1,112,024 and 1,112,025
and thermoplastic block or part-block/part-random copolymers of
butadiene with styrene, optionally in admixture with other materials
~uch a~ polyethylene. This cla~s of material~ is dascribed in our
British Patent Specifications Nos. 1,196,125 and 1,196,127.
The gasketting materials may of cour~e contain any of the
usual additive~ such a~ a stabiliser, plasticiser, pisment, dye,
filler, 91ip agent or lubricant.
The invention includes containers, especially bottle~
filled with beverage~ for human con~umption, closed by the proces~
of the invention.
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