Screw cap with security ring

The invention relates to a screw cap for a container neck, comprising an internally threaded cap portion and a security ring joined by means of inclined bridge portions to the cap portion. The sealing ring is resiliently deformable and is designed to be forced over and past a collar around the neck of the container, when the cap is being screwed on for the first time. Recesses are provided in the lower part of the cap portion and/or the upper part of the sealing ring, in which recesses the bridge portions are secured. The bridge portions are so inclined that the upper edge of the security ring can engage the lower edge of the cap skirt when, during screwing on of the cap for the first time, the security ring engages the collar, without undue bending of the bridge portions, so that the cap portion can support the security ring while the latter is forced over the collar. However, when the cap is unscrewed, and the security ring is stopped by the collar, the bridge portions are first bent substantially, and thereby weakened and are tensioned, to rupture, during continued unscrewing of the cap portion.

FIELD OF THE INVENTION 
The invention relates to a screw cap comprising an internally threaded 
cap-portion and a security ring joined with the cap portion by means of 
breakable bridge portions. 
BACKGROUND OF THE INVENTION 
Screw caps of this type, in which the security ring is resiliently 
deformable, are already known. The security ring is designed to be forced 
over and past a collar arranged around the neck of a container to be 
sealed, when the cap is screwed onto the neck of the container for the 
first time. The security ring, collar and bridge portions are shaped and 
dimensioned so that when, after the cap has been fully screwed on for the 
first time, it is subsequently unscrewed, the security ring is retained by 
engagement with the collar and the bridge portions are broken as the cap 
portion is unscrewed. 
In previously known screw caps of this type, it has been extremely 
difficult to shape and dimension the bridge portions and to devise their 
attachment to the cap-portion and/or sealing ring so that the bridge 
portions do not break when the cap is screwed on for the first time, but 
break easily when the cap is subsequently unscrewed. 
U.S. Pat. No. 3,455,478 describes a screw cap of this type in which an 
attempt is made to solve the latter problem by inclining the bridges 
forwards and downwards, where the cap is considered as being turned 
forwards and downwards to screw the cap onto the respective container 
neck. The bridges are thus subjected to compression loading when the cap 
is being screwed on for the first time and to loading in tension when the 
cap is being screwed off for a first time. The aim is to utilize the 
feature of certain materials, particularly plastics, of withstanding 
compression loading better than loading in tension. A problem with the 
screw cap shown in this U.S. patent is that the bridges must be made 
extremely thin and narrow at their attachment points to the lower part or 
skirt of the cap portion, in order to permit the cap to be screwed off 
with reasonably little exertion of force and at the same time achieve 
rupture at the points of attachment of the bridge portions. However, such 
thin, narrow attachment points are subjected to considerable shearing 
forces when the cap is screwed on and sealed in the normal way. This 
necessitates the use of a complicated machine, which grips both cap 
portion and security ring. 
SUMMARY OF THE INVENTION 
One of the objects of the present invention is to provide a screw cap with 
a security ring, which is less sensitive to variations in the shape and 
attachment of the bridges than known caps and is therefore better fitted 
for mass production. 
According to one aspect of the invention, there is provided a screw cap for 
a screw threaded container neck, the cap comprising an internally threaded 
cap portion having a head and a skirt extending from said head to a skirt 
edge, and further comprising a security ring adjoining said skirt edge and 
having an edge opposing said skirt edge, the security ring effectively 
constituting a continuation of said skirt, away from said head, beyond 
said skirt edge, at least one of said opposing edges of the skirt and the 
security ring having a plurality of recesses open towards the other said 
edge, said recesses being distributed around the circumference of the cap, 
the cap further including a plurality of bridge portions connecting the 
cap with the security ring, each said bridge portion being disposed in a 
said recess and extending from a respective first point on the security 
ring to a respective second point on the cap skirt which is located in 
advance of the respective first point in the rotational sense in which, 
according to the internal threading of the cap, the cap must be turned to 
screw it onto a container neck, whereby when the cap is screwed onto a 
container neck having a collar for engagement with said security ring, 
after the security ring engages said collar, further screwing on of the 
cap will cause the skirt edge of the cap skirt to press against the 
opposing edge of the security ring after, at most, relatively slight 
bending of the bridge portions at said first and second points, to allow 
the cap portion to force the security ring past said collar, whilst after 
the cap has been fully screwed onto a container and neck and is 
subsequently unscrewed therefrom, after the security ring engages said 
collar to be retained thereby, the bridge portions will be subjected to 
relatively great bending at said first and second points whilst being 
tensioned and thereby fractured. 
According to another aspect of the invention, there is provided a container 
having a neck terminating in an opening, an external screw thread around 
said neck and an external collar around said neck, further from said 
opening than said external screw thread, and a screw cap for said neck, 
the cap comprising an internally screw threaded cap portion for screwing 
onto said neck, the cap portion having a head and a skirt extending from 
said head to a skirt edge, and further comprising a security ring for 
cooperation with said collar, the security ring adjoining said skirt edge 
and having an edge opposing said skirt edge, the security ring effectively 
constituting a continuation of said skirt, away from said head, beyond 
said skirt edge, at least one of said opposing edges of the skirt and the 
security ring having a plurality of recesses open towards the other said 
edge, said recesses being distributed around the circumference of the cap, 
the cap further including a plurality of bridge portions connecting the 
cap with the security ring, each said bridge portion being disposed in a 
said recess and extending from a respective first point on the security 
ring to a respective second point on the cap skirt which is located in 
advance of the respective first point in the rotational sense in which, 
according to the screw threading on the cap and container neck, the cap 
must be turned to screw it onto the container neck, the security ring 
being dimensioned to clear the screw thread on the container neck during 
such screwing on of the cap, but to engage said collar, the collar and 
security ring being configured to promote resilient deformation of the 
security ring to allow the same to pass over the collar during screwing on 
of the cap for the first time, but to prevent subsequent withdrawal of the 
security ring over the collar, whereby, when the cap is screwed onto the 
container neck for the first time, after the security ring engages said 
collar, further screwing on of the cap will cause the skirt edges to press 
against the opposing edge of the security ring after, at most, relatively 
slight bending of the bridge portions, at said first and second points to 
allow the cap portion to force the security ring past said collar, whilst 
after the cap has been fully screwed onto the container neck and is 
subsequently unscrewed, after the security ring engages the collar to be 
prevented thereby from being withdrawn further, the bridge portions will 
be subjected to relatively great bending at said first and second points 
whilst being tensioned as the cap portion is unscrewed and will thereby be 
fractured allowing removal of the cap portion. 
An embodiment of the invention is described below with reference to the 
accompanying drawings.

DESCRIPTION OF PREFERRED EMBODIMENTS 
Referring to FIGS. 1 and 2, a screw cap for a container neck includes a cap 
portion 1 having a flat head and a skirt provided with internal screw 
threads 2 fitting complementary threads in the neck of the container, and 
external corrugations 3 in the form of axially directed ridges to provide 
grip for screwing and unscrewing the cap. A sealing, annular washer 4 is 
clamped between the head of the cap portion 1 and the free end of the 
container neck. The container neck, below the external screw thread 
thereon, is provided externally with a circumferential annular collar 5, 
which is of saw-tooth form in cross-section providing a ramp face 
gradually increasing in outer diameter downwardly to meet, in a relatively 
sharp edge, with a downwardly facing abutment face substantially 
perpendicular to the axis of the container neck. A security ring 6 is 
attached to the lower edge of the skirt of the cap portion by means of 
four bridge portions 7, two of which are shown in the figures. The bridge 
portions are arranged at regular intervals around the circumference of the 
cap. The security ring adjoins the free edge of the cap skirt and 
effectively constitutes a continuation of said skirt, away from the head 
of the cap. The bridge portions 7 are each elongate in form, and each is 
attached at one end, at a respective first point, to the security ring and 
at its other end, at a respective second point, to the cap skirt. 
The bridge portions are inclined forwardly and upwardly in the direction of 
screwing on of the cap, so that each said second point is located in 
advance of the respective first point in the rotational sense in which the 
cap is screwed on. The inclination of each bridge portion, i.e. the 
inclination of an imaginary straight line passing through the respective 
first and second points, relative to a plane perpendicular to the 
rotational axis of the cap, is 45.degree. in the arrangement shown, and is 
preferably between 45.degree. and 75.degree. . Each bridge portion is 
disposed in a respective space defined by a respective recess 8 in the cap 
skirt and a respective, registering recess in the edge of the security 
ring, each bridge portion extending from the bottom of the respective 
recess 8 to the bottom of the respective recess 9. As a result of this 
construction and mode of attachment, when the cap portion is twisted very 
slightly relative to the security ring in the direction appropriate to 
screwing on, during screwing of the cap onto the container neck for the 
first time, after the security ring has engaged the ramp face of the 
collar 5, the security ring is moved into engagement with the cap skirt, 
the skirt edge engaging the opposing edge of the security ring, i.e. the 
narrow gap 10 between the cap portion and the sealing ring is temporarily 
closed. Due to the friction thus achieved between cap portion and security 
ring, the bridge portions will only be subjected to very limited tensile 
strength during the further part of the screwing on phase in which the 
security ring is forced downwardly, and thus resiliently outwardly, over 
the collar 5. The bridge portions can thus be made relatively weak and 
will therefore be relatively easy to break in the screwing off phase 
discussed below. 
In an alternative embodiment of the screw cap illustrated in FIG. 3, the 
opposing edges of the cap skirt and the security ring are provided with 
cooperating engagement means 11 to ensure that the security ring is 
entrained rotationally with the cap when the cap is screwed on. The means 
11 in the embodiment shown in FIG. 3, consists of one or more teeth 12 on 
the skirt edge and one or more corresponding notches 13 on the opposing 
edge of the security ring, the teeth 12 and notches 13 being of sawtooth 
or ratchet tooth form in the arrangement shown. When the cap is screwed 
on, said teeth and notches cooperate with one another and thereby ensure 
that the sealing ring is entrained rotationally with the cap portion. When 
the cap is unscrewed, the axial separation which occurs when the security 
ring abuts the collar 5 (see below) is sufficient to ensure that said 
teeth 12 are completely clear of the notches 13. 
When the cap portion is screwed off for the first time, the security ring 
will initially follow the rotary and axial movement of the cap portion but 
cannot be drawn back past the abutment face of the collar 5. The bridge 
portions are thus bent towards, and subsequently past, parallelism with 
the cap axis whilst being placed in tension during continued unscrewing of 
the cap portion. Due to the initially inclined positions of the bridge 
portions the bridge portions are locally weakened at their attachment 
points with the cap skirt and the security ring and if unscrewing is 
continued, the bridge portions will be broken at these attachment points. 
The bending of the bridge portions at their points of attachment with the 
skirt and security ring weakens the bridge portions at these points and 
facilites their subsequent fracture under tension. The security ring will 
thus remain below the collar, indicating that the container has been 
opened. By introducing a weakening at one or other end of the bridges 
during manufacture of the screw cap, the bridges can be caused to break at 
the desired ends, preferably at their ends connected with the cap skirt, 
so that the bridge portions remain as a fringe around the sealing ring. 
As can be seen in the drawings, the bridge portions are preferably thinner 
in the radial direction than the cap skirt. In other embodiments the 
number of bridge portions may be from 3 to 12, preferably from 4 to 8, the 
bridge portions in each case preferably being arranged at regular 
intervals around the cap, so that the circumferential distance between 
adjacent bridge portions is constant. 
Each of the screw caps described with reference to the drawings is 
manufactured most advantageously in a single, i.e. monolithic homogenous 
piece, for instance from a suitable plastics material such as polyethylene 
or, preferably, polypropene. The material used is, in any case, preferably 
a resiliently deformable material or an elastomeric material. Manufacture 
is effected preferably by injection moulding in known manner and with 
straight or screw ejection from the moulding tool. 
Whilst, in the embodiments shown, each bridge portion is diposed in a space 
defined by two registering recesses, one in the cap skirt and one in the 
security ring, if desired only the cap skirt, or only the security ring 
may be provided with recesses, each bridge portion in this case extending 
from the bottom of a respective recess to the unrecessed opposed edge of 
the security ring or cap skirt.