This invention relates to closure arrangements and, more particularly, to closure arrangements incorporating locking caps for pressurised containers. The invention is applicable to containers, particularly bottles, intended to contain carbonated drinks.

It will be appreciated that such drinks generate a pressure which can be considerably higher than atmospheric pressure, which is thus exerted on the locking cap, thereby causing difficulty in initial opening of the cap. To facilitate opening of screw-caps infirm people, children and others who do not have sufficient gripping strength, tend to use a gripping tool, such as a wrench, pliers, or the like. It has been found that use of such tools can result in distortion of the cap to such an extent that the mating screw threads of the cap and bottles are free from each other, whereby the pressure of the liquid causes the cap to fly-off the bottle. In some instances, users have sustained injury around the face, particularly the eyes, and this has become a cause for concern.

An object of the invention is to provide a closure arrangement which eliminates the possibility of the cap flying-off the bottle.

The invention provides a removable closure cap for a necked container of the kind comprising a cup-shaped cap member and a gasket adapted to seal between the neck opening and the end wall of said cap member, and in which

the skirt wall of the cap member has an internal thread or thread parts for co-operating with a mating external thread or thread parts on the container neck, characterised in that said end wall defines a first opening, in that the gasket is adapted when the closure cap is fitted to a container filled with fluid under pressure to be urged into a normally closed condition to seal said first opening, in that the gasket defines a second opening which communicates with said first opening to release fluid pressure only when said gasket is moved from its closed condition, and in that release means are provided externally of said closure cap, for applying pressure to said gasket for moving the latter away from its closed position to reduce the pressure in said container, whereby the closure cap can be safely removed from the container.

Preferably, a lip encircles said first opening and projects inwardly from the end wall of said cap member to facilitate sealing engagement by said gasket.

Advantageously, the closure member may be fitted to the cap member in a manner such that it is normally pre-biased into its closed condition.

Preferably, said opening is defined in the end wall of the cap member and the closure member comprises a diaphragm of resilient material which is elastically deformed to seal across the opening of the cap member.

Conveniently, the vent means comprises one or more apertures in the wall of the closure member, providing a

leakage path between the container and the opening only when the closure member is moved out of sealing engagement with said opening.

To avoid the possibility of unintentional opening, _c the cap member may conveniently be provided with protective cover which can be fitted over the cap opening.

According to a feature of the invention, an area i the cap wall is defined by a shaped opening, th arrangement being such that sealing pressure is release ₀ via the shaped opening by applying pressure to said area.

In order that the invention may be readil understood, two embodiments and two modifications o screw-caps for bottles intended to contain carbonate drinks, will now be described with reference to th

, _c accompanying drawings, in which:-

Figure 1 is a perspective view of the firs embodiment,

Figure 2 is a side view thereof,

Figure 3 is a half-sectional view thereof,

Figure 4 is a perspective view of the secon

20 embodiment,

Figure 5 is a half-sectional view of Figure 4, and

Figures 6 and 7 are half-sectional views of modifie forms of the second embodiment.

Referring to Figures 1 to 3 of the drawings, in thi

25 embodiment, the screw-cap 1 is of circular form an comprises an end wall 2 and a skirt wall 3. The inne face of the skirt wall is formed with a screw-thread

intended to fit onto a mating thread (not shown) around the neck of the bottle. The inner face of the end wall 2 supports a closure member 5, in the form of a circular plastics disc, against which the free edge of the bottle is sealed in use when the mating threads are tightened.

The closure member 5 is made resilient and is oversized with respect to the inner diameter of the skirt so that when fitted within the skirt wall 3, as shown in Figure 3, its outer perimeter is gripped by internal ribs 6 provided on the inner face of the skirt wall and is thereby deformed to be convex. The member 5 thereby acts as a diaphragm with its central portion elastically biased into sealing engagement with an inwardly projecting circular lip 8 defining the mouth of a central opening 9 through the end wall 2. A boss 10 is provided on the central portion of the closure member 5 and projects into the opening 9. It will also be noted from Figure 3 that the closure member 5 is provided with at least an aperture or series of apertures 11 which, when the cap is fitted onto a bottle, provides a vent for the pressure of the liquid contained therein to a space 12 defined in the end wall between the lip 8 and the skirt wall 3.

A protective cover 13 is preferably hinged to the end wall of the cap to close over the boss 10 and hence prevent unintentional operation.

It will be appreciated that the screw cap, when fitted to a bottle containing a carbonated drink, the carbonated pressure will act on the closure member 5 to

increase its sealing pressure. To open the bottle safely, the user must first press the boss 10 to release the seal between the lip 8 and the member 5, thereby releasing the pressure within the bottl-e via the vent aperture 11, space 12 and cap opening 9. This release of pressure reduces the frictional tension between the mating threads whereby the cap can be readily opened with a minimum gripping pressure and without any possibility of the cap flying-off the bottle neck.

Referring to Figures 4 and 5, in the second embodiment like parts have been given the same reference numerals. In this embodiment, it will be seen that the opening is in the form of a near circular slit 9A in the end wall 2 of the cap member 1, the portion 14 of the end wall between the ends of the slit being left to act as a hinge. In this embodiment, the plastics closure member 5 is dimensioned to fit snugly within the inner diameter of the skirt wall 3 and be retained in position against the inner face of the end wall behind a circular rib 6. Thus, the closure member 5 is not pre-biased into contact with the end wall; instead it relies upon the carbonation pressure, exerted upon it when fitted, to effect sealing of the opening 9A. In use, it will be appreciated that the bottle can be depressurised via the apertures 11 by applying pressure to the area 15 bounded by the slit opening 9A.

It will be appreciated that if the bottle is partly used and re-sealed by the cap member, a reduced

carbonation pressure would be retained within the bottle which should be sufficient to re-seal the closure member 5 although the reduced pressure may be such that the problem this invention seeks to overcome is not present. However, to ensure that the closure member 5 will remain effective, even after repeated opening and re-sealing, the closure member 5 could be pre-biased, e.g. by oversizing said closure member as for the first embodiment described above.

Referring to Figure 6, in a modification of the second embodiment, the inner face of the end wall 2 of the screw-cap 5 may be curved as shown, and the closure member 5 dimensioned to provide a corresponding curve when seated behind the rib 6.

Referring to Figure 7, in a further modification, the outer face of the end wall 2, instead of being provided with a protective cap, may be formed as a concave surface 16 to reduce the possibility of accidental pressure being applied to the area 15.

It will be appreciated that, instead of presenting a preformed slit opening 9A, the end wall 2 of the cap can be formed with a tear-off tab defined by lines of weakness so that the tab must first be removed to produce the opening.