Note: Descriptions are shown in the official language in which they were submitted.
CA 02750878 2011-07-27
WO 2010/086609 PCT/GB2010/000140
1
CONTAINER CLOSURE ASSEMBLY WITH PRESSURE SEAL
The present invention relates- to improved seals for container closure
assemblies.
The invention is especially applicable to. the sealing of containers in
substantially
gas-tight and liquid-tight fashion, such as the sealing of carbonated and non-
carbonated beverage containers.
It is well known to provide beverage containers of glass, paper, card, metal
or
plastic having a screw top that can be resecured on the bottle neck. It is
desirable
to provide such containers with a screw top cap assembly that provides an
airtight
and liquid-tight seal to retain the quality of the beverage both- during
initial
.transport and storage, and after partial consumption of the contents when the
cap
has been resecured onto the container neck.
Certain existing container and cap assemblies make use of an elastomeric liner
in
the base of the cap. This liner is pressed against the lip of the bottle neck
when
the cap is screwed firmly onto the bottle neck, and the compression between
the
soft, deformable liner and the lip of the container provides a tight seal.
Unfortunately, the manufacture and insertion of the liner into the cap are
relatively
costly additional process steps. Furthermore, care must be taken not to over-
tighten such caps onto the container neck, since the liner can become brittle
or
damaged if excessive pressure is applied thereto.
It is also known to provide a cylindrical plug seal projecting downwardly from
the
base of the cap cap, such that the plug forms an interference fit with an
inner
surface of the bottle neck close to the lip of the bottle. Effective sealing
by such
plug seals requires the cap to be screwed down very tightly on the container
neck
in order to deform the base of the cap and thereby force the plug radially
outwardly
into a tight sealing engagement with the container neck. It is very often the
case
that such caps are under-tightened, especially by children and elderly users.
Furthermore, a sufficient sealing force can only be achieved by the use of
threads
on the cap and the neck having a low pitch, such that the cap torque applied
to the
CA 02750878 2011-07-27
WO 2010/086609 PCT/GB2010/000140
2
cap is leveraged into a very strong downward sealing force between the lip of
the
container and the cap base.
W002/42171 describes a container closure assembly comprising: a sealing plug
extending from the base portion of the cap inside and substantially concentric
with
the skirt portion of the cap, wherein the sealing plug comprises a plurality
of
circumferential sealing ribs on an outer surface of the sealing plug for
engagement
with the inner surface of the container neck when the cap is secured on the
container neck; at least one flexible sealing fin between the sealing plug and
the
cap skirt for engagement with the lip of the container when the cap is secured
on
the container neck; and at least one circumferential sealing rib on an inner
surface
of the cap skirt for engagement with an outer surface of the container neck
proximate to the lip when the cap is secured on the container neck. In use,
the lip
of the container neck is pinched between the ribs on the outer surface of the
sealing plug and the sealing rib on the inner surface of the cap skirt to form
a
pressure-tight seal.
W02007/057706 describes a container closure assembly comprising: a sealing
plug extending from the base portion of the cap inside and substantially
concentric
with the threaded skirt portion of the cap, wherein the sealing plug comprises
two
or more longitudinally spaced circumferential sealing ribs on 'an outer
surface of
the sealing plug for engagement with an inner surface of the container neck
proximate to the lip when the cap is secured on the container neck. The cap
further comprises a sealing skirt extending from the base portion of the cap
intermediate the sealing plug and the threaded skirt portion of the cap and
substantially concentric with the sealing plug and the threaded skirt portion
of the
cap, wherein the sealing skirt comprises two or more longitudinally spaced
circumferential sealing ribs on an inner surface of the sealing skirt for
engagement
with an outer surface of the container neck proximate to the lip when the cap
is
secured on the container neck. In use two of the sealing ribs on the sealing
plug
are located at substantially the same longitudinal distances from the base
portion
of the cap as a two of the circumferential sealing ribs on the sealing skirt,
whereby
the lip of the container neck is pinched between the sealing ribs on the cap
plug
CA 02750878 2011-07-27
WO 2010/086609 PCT/GB2010/000140
3
and the sealing skirt at two or more longitudinally spaced locations when the
cap is
in the secured position on the container neck.
Sealing arrangements for plastic container closures are also known that make
use
of a sealing olive extending from the base of the cap that forms an
interference fit
inside the container neck for sealing against an inside surface of the
container
neck proximate to the lip of the container neck. The sealing olive is a
sealing plug
that is characterized by having a smooth, bulbous circumferential projection
(when
viewed in longitudinal cross-section) on its radially outer surface. The olive
seal is
robust, easy to mould, and can maintain a good seal even when the base of the
cap is distorted (domed) by pressure from inside the container. However, the
olive
seal on its own is not sufficient to provide a good, pressure-tight seal on
carbonated beverage containers.
US-A-5871111 and WO-A-9944896, US-A-20040060893, USA-20020158037,
GB-A-2131774, EP-A-0076778, WO-A-2007132254, US-A-20010027957 and
W02008012426 show arrangements in which a sealing olive or sealing plug is
used together with one or more circumferential sealing ribs on the base of the
cap
that abut against the top of the container neck in the sealing position.
In a further development of closures of this type, W098/35881 describes
container
closures in which a sealing olive is used together with a highly flexible
sealing skirt
that deforms to cover the lip of the container neck when the cap is secured on
the
neck. The contact area between the sealing skirt and the neck is quite large
in the
sealing position, which reduces problems caused by defects or dirt on the lip.
Caps of this type, manufactured by Bericap GmbH, probably represent the most,
effective sealing caps on the market. However, the large contact area between
the sealing skirt and the container neck in the sealing position results in an
undesirably high sealing and opening torque. Furthermore, over-tightening of
the
cap can result in damage to the sealing skirt. W02008/012426 describes a
similar
cap with an olive seal and a relatively short sealing skirt. However it
appears that
this cap further requires an elastomeric liner in the base of the cap and a
further
sealing rib near the bottom of the cap in order to produce a satisfactory
seal.
CA 02750878 2011-07-27
WO 2010/086609 PCT/GB2010/000140
4
The present inventors have found that the above sealing arrangements in which
a
portion of the cap abuts directly against the top of the container lip present
a
problem, which is that the application of an axial force on the cap to
displace it
further towards the neck from the fully closed and sealing position results in
permanent deformation and damage to the cap and impaired subsequent sealing.
This excess axial displacement of the cap towards the neck can occur not only
as
a result of over-tightening of the cap on the neck (which can generally be
prevented by means of suitable thread stops) but also as a result of the
weight of
superimposed containers when the containers are stacked, as is commonplace in
the storage and transport of, for example, beverage containers.
A need remains for a screw-top container and cap arrangement that can provide
an effective seal without the need for a liner, and also without the need for
a strong
axial sealing force between the container neck and the cap, and which
furthermore
is tolerant of high axial forces applied to the cap when it is in the closed
and
sealing position on the neck, for example the weight of superimposed
containers
when the containers are stacked.
The present invention provides a container closure assembly. comprising: a
container neck having side walls defining an opening at one end thereof and a
lip
extending around the opening; and a cap for said neck, the cap having a base
portion and a threaded skirt portion; a first screw thread on the neck; a
second
screw thread on an inner surface of the threaded skirt of the cap; said first
and
second screw threads being configured to enable a user to secure, remove and
resecure the cap into a sealing position on the neck by rotation of the cap on
the
neck; a sealing plug extending from said base portion of the cap inside and
substantially concentric with said threaded skirt portion of the cap, wherein
the
sealing plug is an olive sealing plug for forming a seal against an inside
surface of
the container neck when the cap is secured on the container neck; and a
sealing
skirt extending from said base portion of the cap intermediate said sealing
plug
and said threaded skirt portion of the cap and substantially concentric with
said
sealing plug and said threaded skirt portion of the cap, wherein said cap can
be
CA 02750878 2011-07-27
WO 2010/086609 PCT/GB2010/000140
displaced towards said neck from said sealing position by application of an
axial
force without rotation of the cap on the neck and substantially without
plastic
deformation of the cap.
5 Generally, the seal between the cap and the neck is maintained during said
displacement. The ability to displace the cap by axial force provides improved
performance of the closure assembly when containers equipped with the assembly
are stacked so that the assemblies at the bottom of the stack are subjected to
axial force due to the superimposed containers. Suitably, the displacement is
a
resilient displacement, whereby the closure tends to spring back to
substantially
the original sealing position when the axial force is removed even in the
absence
of any external restoring force such as pressure inside the container. This
resilience can be primarily due to the elastic flexure of the sealing skirt.
It goes
without saying that the prior art closure assemblies. currently in use, as
described
above, do not have this property, as they all require direct abutment between
the
top of the container lip and the cap at the sealing position that blocks
further axial
movement of the cap towards the neck under axial force and/or results in
permanent, plastic deformation of the cap under the axial force that
impairs.the
sealing properties of the assembly both during and after the axial force is
applied.
Suitably, the axial displacement of the cap in the assemblies of the present
invention takes place substantially or completely without plastic (permanent)
deformation of the cap. Suitably, the resilient axial deformation may be at
least
0.1 mm, more suitably from about 0.2mm to about 2mm, typically from about
0.5mm to about 1 mm. Suitably, the axial force may be from about 1N to about
1000N, for example from about 10N to about 100N.
In order to allow for the above axial displacement, the assemblies according
to the
invention suitably have a clearance (gap) between the top of the container lip
and
the axially adjacent point on the cap at the sealing position. Suitably, the
clearance between the topmost point of the lip and the axially adjacent point
on
the base of the closure at the sealing position (in the absence of external
applied
axial force) should be at least about 0.1 mm, suitably about 0.2mm to about
2mm,
for example about 0.5mm to about 1 mm. Suitably no part of the cap should
CA 02750878 2011-07-27
WO 2010/086609 PCT/GB2010/000140
6
contact the. top surface of the container lip at the sealing position. The
term "top
-surface" in this context refers to any portion of the lip that is inclined
(in longitudinal
cross-section) at an angle of more than about 45 degrees to the main axis of
the
assembly, preferably about 30 degrees to the main axis of the assembly.
5-
Suitably, a region of the radially inner surface of the sealing skirt is
concave for
engagement with an outer surface of the container neck proximate to said lip
when
the cap is secured on the container neck. Such a concave sealing skirt is well
adapted to slide around the side of the lip to maintain effective sealing
during the
axial displacement.
The combination of olive sealing plug and concave sealing skirt is new, and
provides surprisingly improved sealing at low sealing forces, in addition to
the
improved performance when subjected to axial force at the sealing position.
Suitably, the neck is moulded in one piece from thermoplastic material, such
as
polyethylene terephthalate. The neck may form part of a beverage container,
such
as a molded plastic or glass carbonated beverage bottle.
Suitably, the container lip is substantially fully radiused in longitudinal
cross-
section. That is to say, the longitudinal cross-section of the lip surface
presents a
substantially continuous curve extending from the inside surface of the neck
to the
outside surface of the neck, so that the top of the lip is rounded, not flat.
More
suitably, the surface of the lip is shaped substantially as a segment of a
circle in
cross-section, for example it may be substantially semi-circular. The rounded
lip
provides for easy and comfortable drinking directly from the container neck.
It is a
further advantage of the present invention that the sealing arrangement is
effective
to provide a pressure-tight seal on a rounded container lip by engagement of
the
concave inner surface of the sealing skirt on the rounded surface of the lip.
Suitably, the inner and/or the outer surfaces of the container neck adjoining
the lip
are slightly tapered. That is to say, the internal diameter of the neck
adjacent to
the bottom of the lip may be slightly tapered inwardly providing a
substantially
CA 02750878 2011-07-27
WO 2010/086609 PCT/GB2010/000140
7
conical surface wherein the internal diameter decreases slightly with
increasing
distance from the junction with the (radiused part of) the lip. Suitably, this
region
of taper extends for an axial distance from about 1 mm to about 10mm, for
example about 2mm to about 5mm. so that the olive seal abuts against the
tapered inside surface as the sealing position is approached when screwing the
cap onto the neck. Similarly, the outer diameter of the neck adjacent-to the
bottom
of the lip may be slightly tapered outwardly so that the outer diameter
increases
slightly with increasing distance from the the junction with the (radiused
part of) the
lip. Suitably, this region of taper extends for an axial distance from about 1
mm to
about 10mm, for example about 2mm to about 5mm, so that the sealing skirt
abuts
against the tapered inside surface as the the sealing position of the cap on
the
neck is approached.. The angle of each taper, measured in longitudinal cross-
section, is suitably independently from about 1 degree to about 30 degrees,
more
suitably from about 5 degrees to about 20 degrees from the longitudinal axis
of the
assembly. The slight taper of the neck below the lip results in a more
constant
torque being required to secure the cap on the neck close to the sealing
position.
In other words, there is a less abrupt increase in screwing torque as the
sealing
plug and sealing skirt first engage the neck.
The assembly according to the invention further comprises a cap having a base
portion and a threaded skirt portion. The cap is suitably moulded in one piece
from thermoplastic material, for example by injection moulding or by
compression
moulding. The cap includes a sealing plug and a sealing skirt-depending from
the
base of the cap, as defined above.
The sealing plug is suitably in the form of a tube, typically projecting
perpendicularly downwardly from the base of the cap and preferably
substantially
concentric with the threaded skirt and coaxial with the longitudinal axis of
the cap.
The height of the sealing plug (measured from the inside surface of the base
of the
cap) is suitably from about 1 mm to about 5mm, for example about 1.5mm to
about
2.5mm. The sealing plug is normally molded integrally with the base of the
cap.
The mean thickness of the tubular wall of the sealing plug is suitably from
about
0.5mm to about 2mm, for example about 0.7mm to about 1.2mm. This gives the
CA 02750878 2011-07-27
WO 2010/086609 PCT/GB2010/000140
8
sealing plug the right degree of resilience and strength for the desired
sealing
function.
The sealing plug is in the form of an olive seal. That is to say, the plug has
a
circumferentially projecting radially outer surface having 'a bulbous shape
(when
viewed in longitudinal cross-section). The bulbous projection has a
substantially
smooth, continuous surface and a height suitably from about 10% to about 50%
of
the radial thickness of the plug. The minimum radius of curvature of the
bulbous
projection is suitably no less than about the mean radial thickness of the
plug.
Suitably, the minimum radius of curvature of the bulbous projection is from
about
0.5mm to about 1 mm. Such olive sealing plugs are relatively tolerant of small
axial displacements of the plug, for example caused by doming of the cap base
under pressure from inside the container, without loss of sealing
effectiveness.
The container closure in the assembly according to the present invention
further
comprises a circumferential sealing skirt. The sealing skirt is separate and
radially
spaced from the threaded cap skirt that engages the thread on the outside of
the
container neck. Suitably, the sealing skirt is substantially tubular, and
projects
downwardly from the base of the cap intermediate the cap skirt and the sealing
plug. The sealing skirt is preferably substantially concentric with the
threaded
skirt and the sealing plug, and coaxial with the longitudinal axis of the cap.
The
height of the sealing skirt is suitably from about 1 mm to about 5mm, for
example
about 1.5mm to about 2.5mm. The height of the sealing skirt in certain
embodiments (measured from the inside surface of the cap adjacent to the
inside
surface of the sealing skirt) is at least about 50%, for example at least
about 75%
of the height of the sealing plug. The sealing skirt is normally molded
integrally
with the base of the cap. The mean thickness of the tubular wall of the
sealing
skirt is suitably from about 0.5mm to about 2mm, for example about 0.7mm to
about 1.2mm. This gives the sealing skirt the right degree of resilience and
strength for the desired sealing function.
The sealing skirt in the arrangement of the present invention is suitably
relatively
thick relative to its height, and undergoes relatively little deformation upon
sealing
CA 02750878 2011-07-27
WO 2010/086609 PCT/GB2010/000140
9
when compared to the sealing skirt of, for example, W098/35881. Suitably, the
sealing force applied by the skirt is provided by the resilience of the skirt
itself, not
by abutment of the outside of the sealing skirt against the inside of the
threaded
skirt or the cap base'as taught in W098/35881. The relatively thick and
resilient
sealing skirt is less likely to be damaged by repeated use, in particular by
over-
tightening. Suitably, the sealing skirt has a radial thickness at half-height
(said
height of the sealing skirt being measured from the base of the radially inner
surface of the sealing skirt) equal to from about 40% to about 80% of the
radial
thickness of the sealing plug measured at the same height. Suitably, the
sealing
skirt has a radial thickness at half-height (said height of the sealing skirt
being
measured from the base of the radially inner surface of the sealing skirt)
equal to
from about 20% to about 50% of the height of the sealing skirt, for example
from
about 25% to about 40% of said height.
Suitably, the inside diameter of the sealing skirt at half-height is from
about
0.05mm to about 0.5mm less than the outside diameter of the container neck.
For
example, it may be from about 0.1 mm to about 0.25mm less than the outside,
diameter of the container neck. In other words, the inside diameter of the
sealing
skirt is only slightly less than the outside diameter of the container neck
proximate
to the rounded lip, whereby the skirt is only slightly deformed in the sealing
position. However, the resilience of the sealing skirt is sufficient for a
slight
deformation to produce a strong sealing force against the lip. Moreover, the
resilience of the sealing skirt allows the skirt to flex outwardly without
plastic
deformation and without loss of sealing effectiveness when the cap is forced
axially downwardly beyond the normal sealing position by an external force,
for
example the weight of another container stacked on top of the assembly. The
same resilience of the sealing skirt restores the original sealing position of
the cap
when the external axial force is removed.
The sealing effectiveness of the sealing skirt may be further enhanced by
providing at least one circumferential sealing rib in said concave region of
said
sealing skirt. Suitably, there are two of the sealing ribs on the sealing
skirt, but in
CA 02750878 2011-07-27
WO 2010/086609 PCT/GB2010/000140
some embodiments there could be from 3 to 10 of the ribs, and for example 4 to
6
ribs.
Suitably, at least one of the sealing ribs has a substantially triangular
cross-section
5 when the cap is viewed in longitudinal cross-section, for example
substantially
equilateral triangular. Suitably, the contact angle between the sides of the
sealing
ribs and the radially inside surface of the sealing skirt is from about 30
degrees to
about 75 degrees, for example from about 45 degrees to about 60 degrees. This
.enables the sealing force to be concentrated in the tip of the sealing rib to
10 maximise sealing effectiveness. Suitably, at least one of the sealing ribs
has a
height in the range of 10 to 250 micrometers, more suitably 20 to 150
micrometers, for example 50 to 150 micrometers. The height is defined as the
maximum distance that the sealing rib projects above the adjacent surface of
the
sealing skirt, when the cap is viewed in longitudinal cross-section. Such
micro
sealing ribs are especially effective to concentrate the sealing force and
achieve
an effective seal with a substantially smooth sealing surface on the container
neck.
Furthermore, such micro ribs are especially easy to mold in high-speed cap
molding equipment, and to bump off the mold mandrel of the equipment after
molding.
An advantage of using multiple sealing ribs on the sealing skirt is that the
plurality
of sealing ribs may have more than one dimension in order to optimise sealing.
For example, the size of the sealing rib closest to the base of the cap may be
greater than the size of the sealing rib remote from the base of the cap. This
allows the sealing rib closest to the base of the cap (i.e. closest to the lip
of the
container) to deform more that the sealing rib furthest from the base of the
cap.
The use of multiple circumferential sealing ribs on the sealing skirt, which
has a
degree of radial flexibility, allows a pressure-tight seal to be formed
between the
container neck and the cap without application of excessive force to the cap,
and
without any need for a sealing liner in the base of the cap. Accordingly, the
caps
in the assemblies according to the present invention suitably do. not include
a liner,
i.e. they are linerless caps. Furthermore, the cap assemblies do not require,
and
CA 02750878 2011-07-27
WO 2010/086609 PCT/GB2010/000140
11
preferably do not include, any sealing elements on the cap other than the
olive
seal plug and the sealing skirt; In particular, as previously explained, and
in
contrast to almost all prior art closure assemblies for carbonated beverages,
the
assemblies according to the present invention do not require, and normally do
not
have, any sealing elements abutting against the top of the lip.
Suitably, the cap is a low-profile cap having an axial height from the top of
the
base to the bottom of the threaded skirt (i.e. excluding any tamper-evident
ring,
attached to the bottom of the threaded skirt), of from about 10mm to about
15mm,
for example about 12mm to about 14mm. The sealing arrangement of the present
invention is especially suitable for use with low-profile caps, because the
minimal
distortion of the sealing skirt during sealing makes it possible to arrange
the
sealing skirt and plug so that they axially overlap the top of the threads on
the cap
skirt without interfering with the running of those threads.
It has been found that the assemblies according to the invention provide
excellent
sealing of carbonated beverage containers even under high pressure/high
temperature conditions such as storage at 38 C. This is because the distortion
(doming) of the base of the cap cap leverages increased sealing force onto the
sealing skirt, while the olive seal on the inside of the container neck is
more
tolerant of deformation of the cap base compared to the sealing plugs
described in
W002/42171 and W02007/057706. However, the arrangements according to the
present invention maintain the advantages of robustness, resistance to over-
tightening, ease of moulding, and low sealing/opening torque of those prior
art
assemblies.
The container closure assembly according to the present invention is
especially
suitable for use in conjunction with thread arrangements that are quick and
easy to
secure. and resecure, wherein the cap can be secured and resecured on the
container neck by a single smooth rotation through 360 or less, more suitably
180 or less, and most suitably about 90 .
CA 02750878 2011-07-27
WO 2010/086609 PCT/GB2010/000140
12
Suitably, the first and second threads may be multiple start threads such as
two-
start threads or three-start threads, and more suitably they are four-start
threads.
This further assists securing of the cap on the neck, since the user needs to
rotate
the cap less in order to find a thread start. Suitably, the threads are
substantially
free-running or parallel threads. That is to say, the threads on the cap and
the
neck slide past each other freely without forming an interference fit between
the
thread segments on the cap and the neck. However, the present invention is
also
applicable to embodiments in which the first and second threads may be more
conventional, single-start, low-pitch continuous threads.
Suitably, the first and second threads are continuous helical threads. That is
to
say, they are not bayonet-type threads that require a stepped motion of the
cap to
secure the cap on the neck, but rather they define a substantially continuous
helical thread path having a thread gradient (pitch) less than 90 degrees
substantially throughout. Suitably the threads have a mean thread pitch of
from
5 to 25 , more suitably from 10 to 20 . Typically, the minimum vertical
displacement of the cap between the fully secured position on the container
neck
and a fully disengaged position of the cap on the neck of from about 2mm to
about
10mm, for example from about 4mm to about 8mm.
Steeply pitched threads provide advantages in terms of ease of use and more
reliable separation of tamper-evident. rings from the cap skirt. However, it
will be
appreciated that such steeply pitched threads result in a relatively small
leverage
of rotational force applied to the cap into downward force on the cap, and it
is a
25. feature of the sealing arrangement according to the invention that it can
provide a
reliable pressure-tight seal without strong downward force being applied to
the cap
as in previous sealing arrangements.
Suitably, the torque required to secure the cap in a sealing position on the
container neck is less than 1.2 Nm, more suitably less than 1 Nm and most
suitably from about 0.7 to about 0.9 Nm. This is the torque required to engage
the
complementary locking arrangement (where present) at the sealing position,
CA 02750878 2011-07-27
WO 2010/086609 PCT/GB2010/000140
13
and/or otherwise the force required to substantially eliminate gas leakage at
normal carbonated beverage pressure differentials.
It is an advantage of the assemblies according to the present invention that
they
can provide a pressure tight seal without the need for additional
circumferential
flexible sealing fins between the sealing plug and the sealing skirt of the
kind
described in W002/42171.
In certain embodiments, the container closure assembly according to the
invention, the container further comprises mutually engageable elements on the
neck and the closure to block or restrict rotation of the closure in an
unscrewing
direction beyond an intermediate position when the closure is under axial
pressure
in a direction emerging from the container neck. This is the so-called
pressure
safety feature that is intended to prevent the closure unscrewing
uncontrollably or
missiling as it is removed from a container neck under pressure. Preferably,
the
pressure safety feature is as described in W095/05322, W097/21602 and
W099/19228.
In these embodiments, the first and second screw threads are constructed and
arranged to permit axial displacement of the closure relative to the neck at
least
when the closure is at the said intermediate position, and preferably the
engageable elements are adapted to engage each other when the closure is
axially displaced in a direction emerging from the neck, for example by axial
pressure from inside the pressurized container. More preferably, the mutually
engageable elements are constructed and arranged not to mutually engage each
other when the closure is axially displaced in a direction inwardly towards
the neck
at the intermediate position, for example when the closure is being screwed
down
onto the container neck.
Preferably, the mutually engageable elements comprise a step or recess formed
in
the lower surface of one of the second screw thread segments to provide a
first
abutment surface against which a second abutment surface on one of the first
screw thread segments abuts to block or restrict rotation of the closure in an
CA 02750878 2011-07-27
WO 2010/086609 PCT/GB2010/000140
14
unscrewing direction at the said intermediate position when the closure is
under
axial pressure in a direction emerging from the container neck, but which
allows
easy removal of the closure when the container is not unduly pressurized.
More preferably, the second thread segment comprises a first thread portion
having a first longitudinal cross section and a second thread portion having a
second longitudinal cross section narrower than the first cross section,
whereby
the first thread segment abuts against the second thread portion. The
relatively
broad first cross section is preferably adjacent to the circumferentially
overlapping
region of the second thread segments, resulting in a relatively narrow thread
gap
in that region.
Preferably, the first and second threads on the container neck and closure are
variable pitch threads, preferably as described in W097/21602. Preferably, the
pitch of an unscrewing thread path defined by the first and the second thread
segments is relatively lower in a first region and relatively higher in a
second
region displaced from the first region in an unscrewing direction. The pitch
of the
thread path in the first region is preferably substantially constant. The
first region
normally includes the position at which the closure is sealed on the container
neck.
Preferably, the first region extends for 20 -40 about the circumference of
the
container neck or the closure skirt. Preferably, the pitch of the lower thread
surface in the first region is in the range of 1 to 12 , more preferably 2
to 8 .
Preferably, the second region is adjacent to the first region of the thread
path.
Preferably, the pitch of the helical thread path in the second region is
substantially
constant, and the second region preferably extends for 15 to 350 about the
circumference of the container neck or the closure skirt. Preferably, the
pitch of
the thread path in the second region is in the range of 15 to 35 .
The use of a variable pitch thread renders it easier to combine fast-turn
threads
having a steep average pitch that are elderly-and child-friendly with pressure
safety. A problem that could arise with fast-turn threads is that they are
steeply
pitched, which results in a tendency to back off from the fully secured
position on
CA 02750878 2011-07-27
WO 2010/086609 PCT/GB2010/000140
the container neck when the container is pressurized. This problem can be
overcome by using bayonet-type threads, but the use of bayonet-type threads
results in a number of different problems, as described above. In contrast,
the
variable pitch threads solve the problem of backing off of the closure under
5 pressure, whilst retaining all of the advantages of continuous, fast-turn
threads.
Preferably, the helical unscrewing thread path further comprises a third
region
adjacent to the second region, wherein the third region has a relatively low
pitch.
Preferably, the third region has a relatively constant pitch, preferably in
the range 1
10 to 12 , more preferably 2 to 8 . The third region preferably includes the
position of
the closure on the container neck when the closure is blocked at the
intermediate
gas venting position. The relatively low pitch of the third region reduces the
tendency of the closure to override the blocking means at high gas venting
pressures.
Suitably, the container and cap assmblies according to the present invention
comprise complementary locking elements on the container neck and the cap that
block or resist unscrewing of the cap from the sealing position on the
container
neck until a predetermined minimum opening torque is applied. For example, the
locking elements may comprise a longitudinal locking rib on one of the
container
neck or the skirt portion of the cap, and a complementary locking ramp on the
other of the container neck and the skirt portion of the cap, the locking rib
abutting
against the retaining edge of the locking ramp when the cap is fully secured
on the
container neck.
In certain embodiments, the first and second locking projections (side
catches)
longitudinally overlap the first and/or the second thread segments when the
cap is
in said fully engaged position on the container neck. In other words, the
first and
second locking projections are not located entirely above or below the threads
(the
terms above and below refer to relative positions along the longitudinal axis
of the
assembly), but are located, at least in part, circumferentially in-between the
threads. The side catches are preferably located adjacent to an end of the
threads. This enables the entire thread assembly to be made more compact in
the
CA 02750878 2011-07-27
WO 2010/086609 PCT/GB2010/000140
16
longitudinal (vertical) direction, thereby reducing the total amount of
moulding
material needed to make the assembly, and the space taken up by the assembly.
In certain embodiments, it also enables the neck thread to be made more
suitable
for consumption directly from the neck.
Typically, the first and second locking elements are situated near the lower
end of
the threads when the cap is fully secured on the container. Preferably, the
first
and/or second locking projections do not extend below the lower edge of the
first
or second thread segments when the cap is in said fully engaged position on
the
container neck. The term "lower" refers to the part of the neck thread
furthest from
the opening of the container neck. In such assemblies, the locking projections
are
preferably located substantially completely circumferentially between the
threads
and not above or below the threads. Preferably, the locking projections on the
neck are not joined at the lower edge to a circumferential flange or shoulder
(e.g.
the shoulder used to retain a tamper-evident band), thereby enhancing the
flexibility of the locking projections and enhancing the "click-to-close"
noise..
Further to the aforesaid, at least one, and preferably both of the
complementary
locking projections on the neck and/or the cap is substantially separate from
the
thread segments and can flex substantially independently of the thread
segments
in order to provide the snap-fitting and clearly audible click as the fully
secured
position of the cap on the neck is reached. In general, a radially innermost
vertex
of the second locking element on the cap skirt rides over a radially outermost
vertex of the first locking element on the container neck as the fully secured
position is approached. The second locking element then rides back over the
outermost vertex of the first locking element when the cap is removed from the
secured position, for example when opening the assembly.
At least one, and preferably both of the complementary locking projections on
the
neck and/or the cap has a length in the longitudinal direction (i.e. along the
rotational axis of the cap assembly) of from about. 1 mm to about 6mm, for
example from about 2mm to about 4mm. At least one, and preferably both of the
complementary locking projections on the neck and/or the cap has a height of
from
CA 02750878 2011-07-27
WO 2010/086609 PCT/GB2010/000140
17
about 0.25mm to about 2mm, for example from about 0.5mm to about 1.5mm. In
any case the height of the locking projections is normally less than the
average
height of the respective thread segments. At least one, and preferably both of
the
complementary locking projections on the neck and/or the cap has a maximum
width (i.e. around the circumference of the neck or cap skirt) of from about
0.5mm
to about 3mm, for example from about 1 mm to about 2mm. At least one, and
preferably both of the complementary locking projections on the neck and/or
the
cap has a ratio of the maximum height to the maximum width of at least about
0.5,
more preferably at least 1, for example from about 1 to about 5.
In suitable embodiments, the first locking projection is located
longitudinally
overlapping with and circumferentially spaced from an upper end of a first
thread
segment. In other embodiments, the second locking projection is located
longitudinally overlapping with and circumferentially spaced from a lower end
of a
second thread segment. These latter embodiments are preferred, since the first
locking projections are then located further from the opening of the container
neck.
The circumferential spacing between the projections and the respective thread
segments in these embodiments is typically from about 1 mm to about 10mm, for
example from about 1 mm to about 4mm. In these embodiments, the
circumferentially spaced locking projections may abut against the thread
segments
of the other assembly component as the assembly is screwed together. That is
to
say, the circumferentially spaced projections may define a part of the thread
path
on the cap or neck. For example, in the case where there are relatively long
thread segments on the cap skirt defining a thread path for relatively short
thread
segments on the container neck, the locking projections on the cap skirt may
be
circumferentially spaced from the lower end of the relatively long thread
segments.
on the cap skirt and may thereby define an extension at the start of the
thread path
followed by the thread segments on the neck when the cap is applied to the
neck.
This method of using the locking projections to form an extension of the
thread
path on one of the neck or the cap solves the problem of providing larger
locking
projections that overlap with the threads, but do not interfere with the
running of
the threads. The locking projections are generally in the line of and, as it
were, are
CA 02750878 2011-07-27
WO 2010/086609 PCT/GB2010/000140
18
extensions of the thread path on one of the neck or the cap. Suitably, the
locking
projections are as described in WO-A-2005058720.
The assemblies according to the present invention may comprise more than one
pair of complementary locking projections on the container neck and the cap.
Preferably there are at least two such complementary pairs radially spaced
around
the neck and cap skirt. There will normally be at least one pair for each
thread
start, for example there may be four pairs radially spaced around the neck and
cap
skirt.
The said sealing position of the cap on the neck is thus normally the first
rotational
position in the screwing direction at which the locking projections are in
locking
engagement, i.e. normally in abutment.
Suitably, the locking projections on the neck and the cap skirt are
circumferentially
positioned such that they are in abutment when the cap is at the said sealing
position on the container neck. That is to say, the projection on the cap has
ridden
over one side of, and is resting in abutment with the opposite side of, the
corresponding projection on the container neck at said fully closed and
sealing
position. This ensures that there is no play in the cap at said closed and
sealing
position that could allow leakage from the seal. Preferably, when the
projections
are in abutment at the closed and sealing position, the cap skirt and/or the
projections are still slightly distorted such that a resilient force is
exerted between
the projections in abutment. This resilient force is leveraged by the abutment
into
a closing torque between the cap and the neck that urges the cap into the
fully
closed and sealing position. This can ensure that the respective sealing
surfaces
of the container neck and the cap are automatically seated against each other,
even though the cap may not be screwed down especially tightly. Furthermore,
the locking projections allow for considerably lower manufacturing tolerances
in
the moulding of the assembly, since effective sealing is achieved over a
broader
range of rotational sealing positions due to the interaction between the
locking
projections and the radial deformation of the cap skirt.
CA 02750878 2011-07-27
WO 2010/086609 PCT/GB2010/000140
19
The advantages of locking projections that urge the cap into the sealing
position
are discussed in detail in W093/01098.
The complementary locking elements according to the present invention provide
a
number of other important advantages, besides urging the cap into the fully
secured and sealing position as described above. Firstly, they prevent
accidental
backing off of the cap from the fully engaged and sealing position on the
container
neck due to pressure from inside the container. These elements enable more
steeply pitched threads and free running (parallel) threads to be used without
risk
of the cap unscrewing spontaneously. The use of more steeply pitched threads
in
turn makes it easier to remove and resecure the cap.
In some embodiments, the locking elements according to the present invention
may also provide.a positive "click" when the fully engaged and sealing
position of
the cap on the container neck is reached, thereby giving the user a positive
indication that the cap is in the closed (sealed) position. This system also
ensures
that exactly the right degree of compression is applied between the container
and
cap to achieve an effective airtight seal.
Suitably, the container closure assembly according to the present invention
further
comprises a projecting stop surface on one of the container neck and the cap
skirt
for abutment against a second stop or a thread on the other of the container
neck
or the cap to block over-tightening of the cap beyond a predetermined angular
sealing position of the cap on the container neck. The stop elements act in
conjunction with the locking arrangement to. ensure that exactly the right
degree of
screwing of the cap is achieved in order to provide a pressure-tight seal with
the
sealing arrangement of the present invention. The stop surfaces may be in
abutment at said sealing position of the cap on the neck, or they may be very
close to abutment, for example within less than about 2mm, suitably less than
about 1 mm of abutment at said sealing position, to allow for manufacturing
tolerances.
CA 02750878 2011-07-27
WO 2010/086609 PCT/GB2010/000140
Suitable locking and stop arrangements are described in detail in WO 91/18799,
WO 95/05322 and W02005/058720.
The container closure assembly also suitably comprises a tamper-evident safety
5 feature. The safety feature preferably includes a tamper-evident ring that
is initially
formed integrally with the skirt of the container closure and joined to the
lower
edge thereof by one or more frangible bridges. The tamper-evident ring is
retained
on the container neck when the cap is removed from the neck for the first
time,
suitably by abutment with the underside of a circumferential retaining lip
provided
10 on the container neck below the threads.
In certain embodiments, the tamper-evident ring comprises a plurality of
integrally
formed, flexible, radially inwardly pointing retaining tabs to retain the ring
under the
retaining lip. In these embodiments, ratchet projections may also be provided
on
15 the container neck below the circumferential retaining lip and radially
spaced
around the container neck to block rotation of the tamper-evident ring on the
container neck in an unscrewing direction and thereby assist separation of the
tamper-evident ring from the neck. The structure and operation of the tamper-
evident ring feature according to these embodiments may be as described and
20 claimed in our International Patent Publication W094/11267.
Embodiments of the present invention will now be described further by way of
example with reference to the accompanying drawings, in which:-
Figure 1 shows a partial longitudinal cross-section through a container
closure
assembly according to the invention with the cap shown immediately prior to
application to the neck;
Figure 2 shows a view partially in longitudinal cross-section and partially in
elevation of the container closure assembly of Figure 1, with the cap in the
fully
secured and sealing position on the container neck; and
Figure 3 shows a partial longitudinal cross-section through the top region of
the
neck of a container closure assembly according to the invention
CA 02750878 2011-07-27
WO 2010/086609 PCT/GB2010/000140
21
Referring to Figs. 1 and 2, this embodiment is a container closure assembly
especially adapted for a carbonated beverage container. Many features of this
assembly resemble those of the assembly described and claimed in our
International Patent Applications W095/05322 and W097/21602 and
W099/19228. However, it is important to note that the threads on the closure
and
the neck are reversed in the present invention relative to the closure
assemblies
described in those applications. That is to say, the earlier patent
specifications
describe in detail assemblies having short thread segments in the closure
skirt and
longer thread segments on the neck, whereas the present invention provides
only
short thread segments on the neck and longer thread segments on the closure
skirt.
The assembly according to this embodiment includes a container neck 10 of a
container for carbonated beverages, and a closure 12. Both the container neck
and the closure are formed from plastics material, but the container neck
could
also be made from glass. The container is preferably formed by injection
moulding
and blow moulding of polyethylene terephthalate in the manner conventionally
known for carbonated beverage containers. The closure is preferably formed by
injection moulding or compression moulding of polyethylene. The container neck
has a cylindrical inner surface 13 terminating in rounded lip. 14.
Referring to Fig. 3, an embodiment of the lip region of the container neck is
shown
in more detail. The neck has an internal surface 80, an outside surface 82,
and a
radiused lip 84. A region 86 of the internal surface adjacent to the radiused
lip 84
is tapered at an angle a of approximately 16 degrees. A region 88 of the
outside
surface adjacent to the radiused lip 84 is tapered at an angle R of
approximately 9
degrees. These regions of taper provide that there isa less ,abrupt increase
in
screwing torque when the sealing plug and sealing skirt of the cap come into
engagement with the neck as the sealing position of the. cap on the neck is
approached.
On the container neck 10 there is provided a four-start first screw thread
made up
of four first thread segments 16, as shown in Figure 2. The first thread
segments
CA 02750878 2011-07-27
WO 2010/086609 PCT/GB2010/000140
22
16 are short thread segments extending about 33 around the neck and having a
lower surface 18 with relatively low pitch of about 6 and an upper surface 20
with
intermediate pitch of about 13.5 . The first thread segments present a
substantially trapezoidal cross-section along the axis of the neck.
Referring to Figures 1 and 2, the closure 12 comprises a base portion 22 and a
skirt portion 24. The closure skirt 24 is provided with a second screw thread
formed from four elongate second thread segments 26, each having a lower
thread surface 30 and an upper thread surface 32. (The term "upper" in this
context means closer to the base of the closure, i.e. further from the open
end of
the closure). The upper and lower second thread surfaces 30, 32 give the
thread
segments substantially trapezoidal side edges that are complementary to the
shape of the first thread segments. A substantially continuous, approximately
helical thread path for the first thread segments is defined between adjacent
second thread segments 26.
A feature of this assembly is the profiling of the upper surfaces 32 of the
second
thread segments 26, which is described in more detail in our International
patent
application W097/21602. The upper thread surfaces 32 in a first, upper region
have a substantially constant pitch of only about 6 . The upper region adjoins
an
intermediate region having a substantially constant, much higher pitch of
about
. The average pitch of the helical thread path defined by the second thread
segments 26 is 13.5 .
25 The second thread segments 26 also include a pressure safety feature
similar to
that described and claimed in our International Patent Application W095/05322.
Briefly, the lowermost portion of the second thread segment 26 defines a step
38
to abut against a first end 40 of the first thread segments 16 and block
unscrewing
of the closure 12 from the neck 10 when the said first thread segments 16 are
in
abutment with the upper surface 32, i.e. when there is a net force on the
closure in
an axial direction out of the container neck. A third region of the upper
surfaces
32 of the second thread segments situated adjacent to the step 38 also has a
low
pitch of about 6 .
CA 02750878 2011-07-27
WO 2010/086609 PCT/GB2010/000140
23
The container and closure assembly is also provided with complementary locking
elements on the container neck and the closure to block unscrewing of the
closure
from the fully engaged position on the container neck unless a minimum
unscrewing torque is applied. These locking elements comprise four equally
radially spaced first locking projections 44 on the container neck, and four
equally
radially spaced second locking projections 46 on the inside of the closure
skirt 24.
The projections on the container neck are located at the bottom of the thread,
where they are least noticeable to a person drinking directly from the
container
neck. The locking projections 46 on the closure skirt are located level with,
and
radially spaced by about 2mm from, the bottom of the threads 26 on the skirt.
The
locking projections on the closure skirt 24 are formed as a continuation of
the
closure thread segments 26, whereby the thread segments 16 on the neck 10 can
pass smoothly past the locking projections on the neck as the cap is secured
on
the neck.
Each of the locking projections 44,46 is substantially in the form of a
triangular
prism having its long axis aligned with the axis of the closure assembly. The
height of each locking projection is about 1.5mm, and the base width is about
1.5mm. This ensures that the projections have sufficient strength to snap over
each other without permanent deformation.
Each of the . second thread segments 26 includes a longitudinally upwardly
projecting portion 48 that defines a longitudinal stop surface against which a
second end 50 of one of the first thread segments 16 may abut when the closure
is fully secured on the neck to block overtightening of the closure on the
neck.
The cap comprises a cylindrical sealing plug 52. The cap further comprises a
cylindrical sealing skirt 54 that is substantially concentric with the sealing
plug.
The sealing plug 52 and the sealing skirt 54 are concentric with the threaded
skirt
24 and located inside the threaded skirt 24 for sealing abutment against
opposite
sides of the container neck proximate to the container lip 14.
CA 02750878 2011-07-27
WO 2010/086609 PCT/GB2010/000140
24
The sealing plug 52 is an olive sealing plug having a bulbous projection 56 on
the
radially outer surface thereof that forms a seal against the inside surface of
the
container neck in use.
The sealing skirt 54 has a concave region 58 on its radially inner surface.
Two
small circumferential sealing ribs 60 of substantially triangular cross-
section
project inwardly from the concave region. The circumferential sealing ribs on
the
sealing skirt have a substantially equilateral triangular cross-section, and
are
approximately 150 micrometers high, in the unstressed state. However, they
deform when pressed against the harder material (glass or PET) of the
container
neck to form the pressure-tight seal. The small dimensions of the sealing ribs
60
enable a pressure tight seal to be achieved without substantial force having
to be
applied to the sealing skirt to form the seal.
The container closure assembly according to this embodiment also comprises a
tamper-evident safety feature. This comprises a tamper-evident ring 66 that is
initially formed integrally with the skirt 24 of the container closure 12 and
joined
thereto by frangible bridges 64. The tamper-evident ring 66 comprises a
plurality
of integrally formed, flexible, radially inwardly pointing retaining tabs 70.
A
circumferential retaining bead 72 is provided on the container neck 10.
Ratchet
projections (not present in this embodiment) may also be provided on the
container neck below the circumferential retaining bead 72 and radially spaced
around the container neck to block rotation of the tamper-evident ring 66 on
the
container neck 10 in an unscrewing direction. However, it may be preferred to
smooth or omit the ratchet projections in order to improve user-friendliness
of the
neck finish. The structure and operation of the tamper-evident ring feature
are as
described and claimed in our International Patent Application W094/11267.
In use, the closure 12 is secured onto the container neck 10 by screwing down
in
conventional fashion. There are four thread starts, and the closure 12 can be
moved from a fully disengaged position to a fully engaged position on the
container neck 10 by rotation through about 90 . It can be seen that the
thread
segments 16 on the neck initially ride past the upper end of the locking
projections
CA 02750878 2011-07-27
WO 2010/086609 PCT/GB2010/000140
46 on the closure skirt, and are thereby guided into a helical thread path. In
other
words, the locking projections 46 on the skirt 24 define an initial extension
of the
helical thread path followed by the thread segments 16 on the neck. In this
way,
the locking projections on the skirt do not interfere or block the free
running of the
5 threads.
When the closure is being screwed down, there is normally a net axial force
applied by the user on the closure into the container neck, and accordingly
the first
thread segments 16 on the neck abut against and ride along the lower surfaces
30
10 of the second thread segments 26 on the closure. It can thus be seen that
the first
thread segments 16 follow a substantially continuous path along a variable
pitch
helix. The first and second threads are free-running, which is to say that
there is
substantially no frictional torque between the thread segments until the fully
engaged position is neared. These features of multiple thread starts, a 900
closure
15 rotation, substantially continuous thread path, and free-running threads,
all make
the closure extremely easy to secure on the container neck, especially for
elderly
or arthritic persons, or children.
As the closure nears the fully engaged position on the container neck 10,
several
20 things happen. Firstly, the tamper-evident ring 66 starts to ride over the
retaining
bead 72 on the container neck. The retaining tabs 70 on the tamper-evident
ring
66 flex radially outwardly to enable the tamper-evident ring to pass over the
retaining bead 72 without excessive radial stress on the frangible bridges 64.
25 Secondly, the initial abutment between the sealing plug 52 and sealing
skirt 54 in
the container closure base and the sealing lip 14 on the container neck
results in a
net axial force on the closure in a direction out of the container neck. This
pushes
the thread segments 16 out of abutment with the lower surfaces 30 of the
projecting portions of the second thread segments 26 and into abutment with
the
upper surfaces 32 of the projecting portions of the second thread segments 20.
More specifically, it brings the first thread segments 16 into abutment with
the
upper regions 34 of upper thread surfaces 32. Continued rotation of the
closure in
a screwing-down direction causes the first thread segments 16 to travel along
the
CA 02750878 2011-07-27
WO 2010/086609 PCT/GB2010/000140
26
upper regions 34 until the final, fully engaged position shown in Figs. 1 and
4 is
reached. The low pitch of the upper surfaces 34 means that this further
rotation
applies powerful leverage (camming) to compress the sealing plug 52 and
sealing
skirt 54 against the container lip 14 in order to achieve an effective gas-
tight seal.
The concave inner surface 58 of the sealing skirt 54 conforms to the curved
container lip 14 to form an effective seal without substantial deformation of
the
sealing skirt 54.
Thirdly, as the fully closed position is reached, the locking projections 46
on the
closure skirt flex and ride over the complementary locking projections 44 on
the
container neck. At the fully closed position, the complementary locking
projections
remain in abutment, such that the closure skirt is still slightly deformed.
The
resilient restoring force exerted by the closure skirt is leveraged by the
projections
44,46 into a closing torque on the assembly, which helps to ensure that
sufficiently
strong sealing force is applied to the various sealing surfaces of the
assembly. It
will be appreciated that this effect, coupled with the relatively large size
of the
projections 44,46, enables effective sealing to be achieved even if the
locking
projections 44,46 are not moulded to a very high tolerance.
Finally, as the fully engaged position of the closure 12 on the container neck
10 is
reached or passed, the second ends 76 of the first thread segments 16 may come
into abutment with the stop shoulders 50 projecting from the second thread
segments 26, thereby blocking. further tightening of the closure that could
damage
the threads.and/or distort the sealing fins and ribs on the closure.
When the closure 12 is in the fully engaged position on the container neck 10,
the
lower surfaces 18 of the first thread segments 16 abut against the upper
regions
34 of the upper thread surfaces 32 of the projecting portions of the second
thread
segments 26, as shown in Fig. 2. The lower surface 18 of the first thread
segments 16 has a low pitch to match that of the upper regions 34, so as to
maximise the contact area between the projecting portions in the regions 34,
and
thereby distribute the axial force exerted by the closure as evenly as
possible
around the container neck. Because of the low pitch in the regions 34,
relatively
CA 02750878 2011-07-27
WO 2010/086609 PCT/GB2010/000140
27
little of the axial force emerging from the container neck due to pressure
inside the
container is converted into unscrewing rotational force by the abutment
between
the thread surfaces in this position. This greatly reduces the tendency of the
closure to unscrew spontaneously under pressure. Spontaneous unscrewing is
also prevented by the abutment between the first and second locking
projections
44, 46. An advantage of the assembly is that the reduced tendency to unscrew
spontaneously due to the low pitch of the thread in the lower regions 34 means
that the minimum opening torque of the locking projections 44, 46 can be
reduced
without risk of the closure blowing off spontaneously. This makes the closure
easier to remove by elderly or arthritic people, or by children, without
reducing the
pressure safety of the closure.
In the fully engaged and sealing position, the cap is secured on the container
neck
as shown in Figure 2. Both the sealing skirt 20 and the sealing plug 24 are
radially
slightly flexible to engage the sealing lip. The bulbous projection on the
sealing
plug and the circumferential sealing ribs on the sealing skirt engage opposite
sides
of the sealing lip 5, and pinch the lip between them to form a highly
effective seal.
The overall effect is to provide a sealing jaw for gripping the top of the
container
neck.
In use, the closure is removed from the container neck by simple unscrewing.
An
initial, minimum unscrewing torque is required to overcome the resistance of
the
locking projections 44, 46. Once this resistance has been overcome,
essentially
no torque needs to be applied by the user to unscrew the closure. The internal
pressure inside the container exerts an axial force on the closure in a
direction
emerging from the mouth of the container, as a result of which the first
thread
segments 16 ride along the upper surfaces 32 of the second thread segments 26
as the closure is unscrewed. The first thread segments 16 initially ride along
the
upper regions 34, and then along the steeply pitched intermediate regions 36
of
the upper surface of the second thread segments 20. The first thread segments
16 then come into abutment with lower projecting portion 38 of the second
thread
segments 26. In this position, further unscrewing of the closure is blocked
while
gas venting takes place along the thread paths. It should also be noted that,
in
CA 02750878 2011-07-27
WO 2010/086609 PCT/GB2010/000140
28
this intermediate gas venting position, the first thread segments 16 abut
primarily
against the region 42 of the upper surface of the second thread segments 26.
The
low pitch of this region 42 results in relatively little of the axial force on
the closure
being converted into unscrewing rotational torque, thereby reducing the
tendency
of the closure to override the pressure safety feature and blow off..
Once gas venting from inside the container neck is complete so that there is
no
longer axial upward force on the closure, the closure can drop down so as to
bring.
the thread segments 16 into abutment with the lower surfaces 30 of the second
thread segments 26. In this position, unscrewing can be continued to disengage
the closure completely from the container neck.
The sealing arrangement in the assemblies according to the present invention
enables the cap to be secured and resecured on the container neck without the
need for high torque or low pitched threads to force a seal. It can be seen
that the
assembly according to the invention provides at least two circumferential
seals
having a high sealing pressure over the whole range of temperature and
pressure.
normally encountered in carbonated beverage containers. It can further be seen
that the cap is suitable for application to container necks having rounded top
lips,
such as glass container necks and plastic container necks having a rounded lip
to
assist drinking directly from the neck. The drawbacks associated with the use
of
..soft sealing liners in the cap are eliminated, in particular the caps
according to the
present invention can be resecured on the container neck repeatedly, without
damage or loss of effectiveness.
The performance of the container closure assembly according to this embodiment
applied to a PET carbonated beverage container was studied under extended
storage at 38 C (high temperature/pressure test). The assembly met the most
rigorous industry standard, set by the current Bericap closure according to
W098/35881, but with lower and more controllable opening and closing torque
than the Bericap closure. Furthermore, the assembly according to the present
invention significantly outperformed the closure of W02007/057706 in this
test.
CA 02750878 2011-07-27
WO 2010/086609 PCT/GB2010/000140
29
The above embodiments have been described by way of example only. Many
other embodiments falling within the scope of the accompanying claims will be
apparent to the skilled reader.
All patent publications referred to in the foregoing specification are thereby
incorporated by reference in their entirety.
