Container and closure and method for applying a closure to a container

In a combination of a screw-threaded metal closure cap with a container having an externally screw-threaded neck, of the type in which the closure thread is formed by a thread rolling operation in a blank in situ on the container, one or more interruptions are made in the closure thread to provide a pressure leakage path, through which gas can blow off in the interval between unsealing the container and the release of the closure from the container thread. Complementary notches may be formed in the container thread. The interruptions in the closure thread are conveniently provided by forming the thread by means of a thread roller having one or more notches in its periphery.

The present invention relates to screw closures for containers having 
externally screw-threaded necks and in particular to screw closures of the 
type in which the thread is rolled in situ by inwardly deforming the skirt 
of a cup-shaped metal blank between adjacent turns of the screw thread on 
the container neck. The invention is also concerned with apparatus for 
applying the closure blanks to such containers. 
A screw-capped bottle containing a carbonated beverage is susceptible to 
release a large quantity of carbon dioxide from solution as a result of 
shaking. As discussed in British Patent Specification No. 2,029,808, this 
may involve somewhat violent release of the cap when fully unscrewed. In 
that Specification it was proposed that one or more transverse notches be 
formed in the container thread and/or in the closure cap thread to allow 
the pressurised gas to blow off after release of the seal between the cap 
gasket and the container and before complete removal of the cap from the 
container. In other words at least part of the gas pressure is released 
across the threads, via the notches, whilst the closure cap thread is 
still engaged with the container thread. This release of pressure reduces 
or avoids the danger of the closure cap flying off on becoming fully 
unscrewed from the container. 
In the prior proposal the notches both in the container thread and in the 
cap thread were preformed. We have now realised that the principle of the 
prior proposal can be adapted to rolled-on closures, in which the notches 
cannot be preformed. 
According to one aspect of the invention there is provided a combination of 
a container and closure of the type in which the thread is formed by 
inwardly deforming the skirt of a cup-shaped metal blank wherein the 
inwardly-directed closure thread is interrupted at at least one position 
along its length to provide at least one notch for release of pressurised 
gas during unscrewing the cap. 
In the container-closure combination of the present invention the neck of 
the bottle or other container is preferably provided with at least one 
vertical groove, forming a notch through each turn of the container thread 
to form a gas escape passage, which becomes particularly effective when it 
is brought into register with like notches in the cap thread. 
It is preferred to provide more than one such vertical groove in the 
container thread and/or to provide notches in the cap thread at angular 
intervals of substantially less than 360.degree.. In the normal course of 
applying closure blanks to containers by the roll-on method the containers 
are presented in random orientation to the capping machinery and it is 
impracticable to relate a notch or notches in the cap thread formed by 
rotating thread rollers with the start or starts of the container thread. 
By adopting this preferred arrangement registration of a container thread 
groove with a cap thread notch is ensured before the cap has been turned 
360.degree.. 
In conventional rolled-on closures, the closure thread is normally formed 
by pressing at least one free-turning roller against the closure skirt, 
the rollers being narrow and deforming the metal, generally aluminium, 
into the valleys between the neck threads and being arranged to follow 
such threads. As the roller is rolled around the closure, it follows the 
neck thread down and runs out at the bottom of the neck thread, leaving 
the closure firmly engaged with the neck thread. 
Conventional metal closure blanks are somewhat oversize in relation to the 
container thread and the skirt becomes somewhat reduced in diameter over 
the apices of the container thread as a result of the action of the thread 
rollers. Where an interruption is provided in the rolled closure thread, 
there tends to be greater clearance between the closure and the adjoining 
container thread apices at such position, to provide an improved gas 
leakage path. In consequence notches in the container thread are not 
essential for the improved container/closure combination, in which 
notch-forming interruptions are provided in the thread rolled into the 
closure skirt. 
According to another aspect of the invention a method of securing a 
cup-shaped metal closure blank to a container having an externally 
screw-threaded neck, comprising placing the blank over the container mouth 
and pressing it down against the container mouth to close and seal the 
mouth and deforming the skirt of the blank inwardly between adjacent 
outwardly-projecting thread formations on the container neck to produce 
inwardly-projecting thread formations in said thread is characterised by 
interrupting said inward deformation at one or more positions to define a 
notch or notches in such inwardly-projecting thread formations. 
According to another aspect of the invention, a head set, for applying a 
closure blank to an externally screw-threaded container comprises a 
pressure block for applying vertical pressure to press the blank into 
sealing relationship with the mouth of a container and at least one 
thread-forming roller movable radially inwardly to deform the wall of the 
skirt of the closure blank between adjacent turns of the container thread 
and arranged to follow the trough between adjacent container thread turns 
to form a thread in said closure skirt is characterised in that said 
thread roller is provided with at least one cut-out in its periphery so 
that there is a corresponding interruption in the closure thread formed 
thereby. The cut-out or cut-outs in the roller or rollers may be of 
various shapes, for example semi-circular, vee or rectangular. The corners 
of the cut-outs may be sharp corners or radiused. 
Conventionally in a headset employed for applying closure blanks of the 
present type a plurality of thread-forming rollers are used, with the 
rollers arranged around the axis of rotation of the headset in such manner 
that the radial forces with which they are urged against the closure are 
balanced. If a plurality of notched thread-forming rollers are used they 
may be geared, or otherwise ganged to turn in synchronism with each other 
about their respective axes, to ensure that the notch or notches left by 
one roller are not rolled out by the next roller, but rather that a 
cut-out in the next roller registers with the previously-left 
interruptions in the thread. Alternatively, where the closure is of the 
pilferproof type, in which the free end of the skirt is tucked under an 
abutment shoulder on the container neck, a single notched-thread forming 
roller may be employed together with one or more tuck-under rollers so 
positioned to balance the roller forces. A further alternative is to 
oppose a single thread-forming roller by one or more plain rollers which 
bear against the closure skirt over the apices of adjacent projecting 
container thread formations and thus do not deform the closure skirt 
inwardly between said formations. A further alternative is to rely upon 
the pressure block, which is strongly urged onto the top of the closure, 
to resist the thread-roller force.

The cap of FIG. 1 has a skirt 2 in which is rolled a thread 3 having 
notches 4, which may be aligned as shown or displaced from each other. 
Preferably there are notches 4 at two or more positions in each turn of 
the inwardly directed thread. As is conventional the cap has a rolled bead 
5 and a knurled grip 6. The cap is provided with a layer 8 of gasket 
material which covers the top 7 and extends onto the upper portion of the 
skirt 2 to form a sealing gasket. At this region the cap is deformed at 9 
during application of the blank to the container 10, which may be of 
plastics material or of glass, by a pressure block 11, see FIG. 5, to seal 
on the outer cylindrical surface 12 (FIG. 2) of the container adjacent the 
mouth 13. Also shown in FIG. 2 is the thread form of both the neck thread 
14 and the rolled cap thread 3. On initial application the thread 3 is 
held in close contact with the underside of the neck thread 14 by the 
upward thrust due to the gas pressure exerted by the contents of the 
bottle. 
When the cap 1 is unscrewed, the seal between the gasket material and the 
cylindrical surface 12 remains effective until the cap has been turned 
through approximately 1/4 of a revolution. In a conventional closure, in 
which there are no thread notches 4, rapid escape of gas is still 
prevented by the engagement of the thread 3 on the underside of the 
container thread 14. 
FIG. 3 shows a section of a skirt thread notch 4 with the cap partially 
unscrewed, with a notch 4 bridging container threads 14. A limited escape 
of gas pressure can now take place over the apices 17 of the individual 
neck threads 14 and through the notch 4 in the still engaged skirt thread. 
In FIG. 4 a thread notch 4 is in register with vertically aligned notches 
18 in the individual neck threads 14. When this alignment occurs a very 
rapid blow-off of gas can take place. 
FIG. 5 shows the blank 21 of a pilfer-proof cap at the start of application 
to the neck of a blow-moulded plastic bottle 30 by a sealing machine which 
includes a support 22 on which an integral bottle collar 31 rests, because 
the bottle body cannot withstand heavy axial pressure exerted by a 
conventional two-part pressure block 11. The block 11 is urged downwards 
in the direction of arrow 23 to press the closure blank against the bottle 
mouth and to deform the closure at 9 to establish a seal with the 
cylindrical surface on the bottle neck. A thread roller 24 is mounted in 
conventional manner to turn about the axis of the headset of which the 
pressure block 11 also forms part. The roller 24 and an opposed tuck-under 
roller 25 for the security band 26 of the closure are mounted on lever 
arms (not shown) for movement towards and away from the bottle neck to 
balance the forces with which the rollers are urged in the direction of 
arrows 27. In the construction of FIG. 5 there are preferably at least two 
tuck-under rollers arranged at 120.degree. intervals to balance the force 
exerted by a single thread roller 24. The rollers 24, 25 are mounted in 
the conventional way on pivoted arms and are moved inwards in the 
direction of the arrows 27 by conventional spring, hydraulic or pneumatic 
means to press against the skirt of the closure blank. 
As the rollers are rotated around the axis of pressure block 11 in the 
well-known manner, the thread-forming roller 24 runs down the closure 
skirt in the trough between adjacent turns of the bottle thread 14 to 
deform the skirt into engagement with the thread 14 and to form the cap 
thread 3. 
Where the bottle to be capped is of robust construction and the body of the 
bottle is capable of withstanding the crushing load applied by the 
headset, then the support 22 would be eliminated and the bottle supported 
on a table or the like in the conventional manner. 
Where the headset is employed to apply conventional plain closure blanks, 
having an outwardly curled bead at the bottom margin of the skirt, the 
tuck-under rollers are preferably replaced by plain rollers having a 
cylindrical profile to counteract the thread roller 24. 
As shown in FIG. 6 the thread roller 24 has a number of notch-forming 
cut-outs 28. 
The diameter of the thread roller need have no particular relationship to 
the diameter of the closure or bottle neck and indeed will be employed in 
practice (with suitable change of pressure block and other items) to apply 
closures to bottle necks of different diameter. It is however necessary 
that the peripheral distance between adjacent cut-outs is no more than the 
circumference of the neck to which a closure is applied to ensure that 
there is at least one notch in each turn of the neck thread. 
The closure/container combination illustrated in the accompanying drawings 
may be varied in a number of details. As already indicated it is not 
essential to provide any notch in the container thread. However where 
notches are provided in such container thread, they may be aligned in the 
vertical direction as shown in FIG. 4 or may be arranged at intervals 
along the length of the helical container thread so as not to be in 
vertical alignment. 
Similarly the notches in the closure thread may be vertically aligned as 
shown in FIG. 1. However, where such notches are formed by the thread 
roller of FIG. 6, the spacing between the notches is dependent upon the 
relationship between the container neck circumference and the peripheral 
distance between adjacent notches 28 in the roller periphery. In many 
instances the closure thread notches will be at staggered intervals around 
the container neck. 
The roller 24, shown in FIG. 5, may be mounted on arms which pivot about a 
vertical axis, parallel to the axis of the pressure block 11. The same 
modification may be made with respect to the mounting of the tuck-under 
rollers 25 or plain rollers which may replace the rollers 25.