1 TAMPER PROOF CLOSURE AND A TAMPER PROOF CLOSURE AND CONTAINER ASSEMBLY The present invention relates to a tamper proof closure and a tamper proof closure and container assembly and particularly, but not exclusively, to a plastic 5 tamper proof screw closure of the type intended to indicate whether a container has previously been opened. Different closures for containers containing liquids or powdered solids are known. These closures are usually made from plastic or metal and generally comprise a cap or lid, often containing means for preventing egress of the 10 contents of the container, especially when the contents are a liquid. The cap normally has an internal thread suitable for engaging, to open or close the container, with a corresponding thread on the outside of the container. Tamper proof versions of closures are also known. Most commonly, tamper proof versions of closures include a "tamper band", which is an annular 15 ring located below a cap and joined to the cap by a perforated breaking line. The first time the container is opened, the cap is detached from the annular ring at the breaking line, thereby indicating to any subsequent user that the container has been previously opened. Prior art tamper proof closures are typically manufactured from plastic 20 materials. Moreover, the annular ring is typically created by manufacturing the closure and annular ring as one piece and subsequently creating a breaking line by cutting slits to form an annular ring below the breaking line. It is also known to create a tamper proof closure with a cap, annular ring and breaking line in a single operation, such as by injection moulding. Prior art 25 tamper proof closures of this type require significant strength and, therefore, large connections between the annular ring and the cap, as well as a greater amount of material is required in the annular ring and cap itself. Without this additional strength, these prior art closures cannot be applied to containers or stacked in preparation for application without significant deformation of the annular ring 30 and/or connections. According to a first aspect of the present invention there is provided a tamper proof closure including a cap for a container and an annular ring attached to the cap by a plurality of bridges, the bridges including a first portion and a 2 second portion, the first portion having a greater width than the second portion and the second portion having a predetermined width which enables the detachment of the annular ring from the cap at the second portion upon application of a predetermined force. 5 Preferably, the first bridge portion has a greater width in a circumferential direction, with respect to the closure, than the second bridge portion. For the purposes of this specification, the circumferential direction is a direction following the path of the circumference of the closure. Alternatively or additionally, the first bridge portion may have a greater 10 width in the radial direction than the second bridge portion. Preferably, the first bridge portion is attached to the cap and, the second bridge portion is attached to the annular ring. Preferably, a shoulder formed between the first and second portions is arranged at an abrupt angle. The second bridge portion preferably has an 15 inclined surface attached to the inclined surface of the annular ring. Preferably, the second portion of the bridge has a circumferential width between 20% and 70%, and most preferably between 50% and 70%, of the first portion. Most preferably, the circumferential width of the first portion is between 0.8mm and 3mm and the circumferential width of the second portion is between 0.4 mm and 20 1mm. Preferably, the length of the second portion between the first portion and the top of the annular ring is between 0.1mm and 0.5mm. Alternatively or further preferably, the second portion is shorter than the first portion in a direction perpendicular to the circumference of the closure, between the first portion and 25 the top of the annular ring. Preferably, the annular ring includes a collar portion and a lip extending beyond the outer diameter of the collar portion. Preferably, the annular ring further includes an annular chamfer at the end of the annular ring closest to the cap. Most preferably, the annular chamfer extends from the lip. 30 Preferably, the closure is made from polyethylene. According to a second aspect of the present invention there is provided a method of manufacturing a tamper proof closure comprising: 3 creating a tool or mould for an plastic moulding machine incorporating structural features for a closure as described according to the first aspect of the present invention; injecting the tool with plastic; and 5 removing the closure from the tool. Preferably, where the method includes a closure including a lip as described according to the first aspect of the present invention, the method further includes removing the closure from the tool by acting against the lip. According to a third aspect of the present invention there is provided a 10 tamper proof closure and container assembly including: a cap for a container and an annular ring attached to the cap by a plurality of bridges, the bridges including a first portion and a second portion, the first portion having a greater width than the second portion and the second portion having a predetermined width which enables the detachment of the annular ring 15 from the cap at the second portion upon application of a predetermined force, the annular ring, further including an annular lip on the inner face of the annular ring a container having an opening corresponding to the cap and further including a retaining lip capable of allowing the annular lip of the annular ring to pass over the retaining lip in a first direction but engaging with the annular lip and 20 retaining the annular ring in a second direction, the retaining lip further including at least one bridge cutting projection, the projection extending radially from the retaining lip and arranged and positioned such that the annular ring and bridges can pass over the at least one projection in a first rotational direction and the projection prevents movement of the bridges in 25 the opposite radial direction. Aspects and advantages of the present invention will become apparent upon reading the following detailed description and upon reference to the following drawings in which: Figure 1 shows a perspective view of a tamper proof closure according to 30 the present invention; Figure 2 shows a front sectional view across the middle of the tamper proof closure according Figure 1; 4 Figure 3 shows a front view of the tamper proof closure according Figure 1; Figure 4 shows a close up of bridges attaching an annular ring to a cap and a lip of the annular ring; 5 Figure 5 shows a close up of a bridge attaching a cap and annular ring; and Figure 6 shows a close up of the cap and annular ring of Fig. 4 after the bridges have been broken. Referring to Fig. 1, a linerless closure 2 for a container is shown having a 10 cap 4 and an annular ring 6. The closure 2 can be used with a great variety of containers and can be made of various materials, especially plastic and metal. Plastic closures are particularly advantageous due to their low manufacture cost and flexibility of shape and design. Fig. 2 shows a sectional view across the middle of the closure 2. The 15 inside of the cap 4 has a screw thread 8 and container receiving areas 10. The screw thread 8 and container receiving areas 10 allow the cap 4 to be securely fastened to a container (not shown) such that any contents contained with the container are substantially prevented from egress when the cap 4 has been fastened. In particular, the closure 2 is capable of creating a seal, through contact 20 with the container in the container receiving areas 10, without the need for a liner insert. Preferably, the closure is made from polyethylene, which has particularly appropriate properties for creating a seal of this type. The container receiving areas 10 are sized such that the neck of a container fits securely into them, forming a seal. Liner inserts are often used in closures where either the material 25 or design does not create a sufficient seal on a container. Closures with liner inserts require an extra processing step during manufacture and are, therefore, less desirable. To prevent tampering of containers after a particular provider has filled a container, it is common for a cap for the container to have a tamper band, which 30 is generally in the form of an annular ring which detaches from the cap at a breaking line when the cap is first removed from the container. The annular ring 6 shown in Figures 1 and 2 also provides this function. When the closure 2 is first secured to a container by a genuine producer the 5 annular ring 6 is forced over a retaining lip on the container when the cap 4 is screwed on. The annular ring 6 is then held in place by a corresponding annular lip 12 on the inner surface of the annular ring 6. Fig. 3 shows a front view of the closure 2. Area 14 shows the region of the 5 closure 2 which is shown in more detail in Fig. 4 and area 16 shows the region of the closure 2 which is shown in more detail in Fig. 5. Referring to Fig. 4 and Fig. 5, a plurality of bridges 18 are shown attaching the annular ring 6 to the cap 4. In addition, a lip 20 is located on the outer diameter of the annular ring 6. A chamfer 22 extends from the lip 20 to the inner 10 surface of the annular ring 6. The bridges 18 are connected to the top edge of the annular ring, which is also the top edge of the chamfer 22. Each bridge has a first bridge portion 24 attached, in this example, to the cap 4 and a second bridge portion 26 connected to the annular ring 6 at the chamfer 22, whereby the bottom edge of the second portion 26, where it is connected to the chamfer 22, is at an 15 inclined angle the same as the chamfer 22. The first portion 24 has a width W in a circumferential direction, that is following the path of the circumference of the closure 2, greater than a width w in the circumferential direction of the second portion 26. Thus, the first portion 24 extends beyond the second portion 26 in, at least, both of the circumferential directions of the closure. It is also evident from 20 Figure 4, at least, that the first portion 24 has a width in the radial direction that is greater than the width of the second portion 26 in the radial direction. Thus, the first portion 24 extends radially, with respect to the closure 2, beyond the second portion 26 as well as circumferentially. Where the first portion 24 does extend beyond the second portion 26, the resulting shoulder should preferably be a 25 sharp delineated edge, that is the surfaces of the first and second portions 24, 26 meet at an abrupt angle. The example shown in Figures 4 and 5 clearly show an angle of 90 degrees, which is the preferable shoulder angle, but other shoulder angles which perform the same function are also envisaged. Referring to Fig. 5, the first portion 24 is of generally semi-circular cross 30 section and is wider in the circumferential direction of the closure than the second portion 26, which is also of generally semi-circular cross-section, giving greater strength to the first portion 24 than the second portion 26. The radially inner edges, with respect to the closure 2, of the first and second portions 24, 26 are, in 6 this example, flush with the radially inner surfaces of the annular ring 6 and the cap 4. The semi-circular sides of the first and second portions 24, 26 face radially away from the centre of the closure. Although generally semi-circular cross sections are used for both the first and second portion 24, 26, they are not limited 5 to these cross-sectional shapes. The first portion 24, preferably, extends between 20% and 70%, and more preferably between 50% and 70%, greater circumferentially in both directions than the second portion 26. For a typical closure as shown in Figures 1 to 6, the diameter, or circumferentially extending width W, of the first portion 24 would be 10 between 0.8mm and 3mm and the diameter, or circumferentially extending width w, of the second portion would be between 0.4mm and 1 mm (the dimensions given for the second portion are not necessarily the limits of the first portion and vice versa). When the cap 4 is screwed off for the first time, the annular ring 6 is held 15 against the retaining lip of the container by the annular lip 12. As a result, the cap 4 is separated from the annular ring 6 due to the bridges 18 breaking, at the second bridge portion 26, from the annular ring 6, as shown in Fig. 6. When the cap 4 is removed, the second portion 26 breaks and the shoulder formed between the first portion 24 and second portion 26 encourages a clean break. 20 It is envisaged that a closure as described herein is particularly suitable for the soft drinks market, although any containers requiring tamper proof closures are of course applicable. In particular, closures of "standard" drinks cartons would be possible from closures according to the invention, such as 25mm, 28mm, 30mm, 32mm, 38mm, 42mm and 48mm, although non-standard closures are also 25 envisaged. As the first portion 24 is of greater circumferential and/or radial width than the second portion 26 and a shoulder with a sharp angle is formed between the first and second portions 24, 26, a break occurs on the second portion 26. By minimising the length of the second portion 26 between the first portion 24 and 30 the annular ring 6, the break is made more quickly and cleanly. This is particularly the case when the closure is made from plastic, as additional length (perpendicular to the circumference of the closure) would cause the polymers of the plastic to align and stretch further away before breaking. By providing the first 7 portion 24 with a greater circumferential width than the second portion 26 and extending down from the cap 4 towards the annular ring 6, the length of the second portion 26 is minimised. It should also be noted that creating a second portion of too short length can cause issues during manufacture, particularly 5 "flashing", where thin sections of injected plastic span elements of the closure in unintended areas. By providing the first portion 24 of greater width and extending down towards the annular ring 6, the second portion 26 can be manufactured with a particularly short length without inducing flashing to the same extent. Causing the second portion 26 to break as early as possible when the cap 10 4 is initially screwed off the container is also important in terms of maintaining seal integrity until after the annular ring 6 has been separated from the cap 4. That is, seal integrity should be maintained on a container unless the annular ring 6 has been fully separated from the cap 4. A greater length (perpendicular to the circumference of the closure) of the second portion 26 would stretch further 15 before breaking resulting in breaking the seal before the annular ring 6 is separated. The bridges 18 as described herein break quickly such that the closure 2 does not require a seal liner insert. Furthermore, the length of the bridge 18 has a bearing on the rigidity of the closure 2. In the example embodiment of Fig. 5, the total gap between the cap 4 20 and annular ring 6 is represented by dimension 28 and the first portion 24 extends from the cap 4 towards the annular ring and is represented by dimension 30. The second portion 26 also extends down the face of the chamfer 22 and, therefore, actually has a length, at least on the side facing away from the centre of the annular ring 6, greater than dimension 30, but not all of the length is 25 between the cap 4 and annular ring 6. Typical values for dimension 28 would be between 0.3mm and 1mm and for dimension 30 would be between 0.2mm and 0.5mm. The length of the second portion 26 between the first portion 24 and the top 31 of the annular ring 6, shown as dimension 32, is, therefore, between 0.1mm and 0.5mm. Preferably, the second portion 26 is shorter than the first 30 portion 24, between the first portion 24 and the top 31 of the annular ring 6, with the first portion 24 spanning the majority of any gap between the cap 4 and annular ring 6.
8 The two step shoulder configuration of the bridges 18, due to the differing dimensions of the first portion 24 and the second portion 26, at least in the circumferential direction of the closure 2, the sharp corner angle between the first and second portions 24, 26 and because the second portion 26 is only required to 5 be relatively short, results in a clean break of the bridge 18 at the second portion 26 when the cap 4 is screwed off a container for the first time. As mentioned above, prior art tamper bands cause an elongation of the connecting portions when the cap is removed from the container by the end user. Accordingly, the closure of the present invention results in a cap which quickly separates from the 10 tamper band and provides a more aesthetically pleasing tamper band, or annular ring, after the cap has been removed. The bridges 18 also give improved strength, in comparison with prior art tamper band connections. Prior art tamper band connections require a larger amount of plastic to ensure that the cap and tamper band can be fitted onto a 15 container without breaking or distorting the connections, because all the compression forces must be transmitted on the connections between the cap and tamper band, which are relatively long. The two step configuration of the bridges 18 give additional strength, as there is only a relatively short length (perpendicular to the circumference of the closure 2) of the intended breaking portion on each 20 bridge, providing a lightweight closure with the strength of a heavier closure. As a result, the closures may be up to 30% cheaper to manufacture than closures which rely on creating the tamper band by slitting after plastics manufacture or which require a separate seal. Furthermore, the closures are faster to manufacture as a closure with less material comes off a plastics moulding tool 25 faster and only require one process step. That is, no additional slitting is required to create the tamper band and no insertion of additional seals is required. During manufacture of the closure 2, the bridges 18 are formed integrally in an plastics moulding tool, which is preferably a plastic injection moulding tool but could also be a compression moulding tool. Accordingly, there are no further 30 process steps required to manufacture the closure which further reduces manufacture cost. The lip 20 and chamfer 22 also performs a function during manufacture. After plastic has been injected into the injection mould tool, the closure 2 is then removed from the tool and, in particular, from a core within the 9 tool. The lip 20 allows the closure to be more easily removed from the tool as the lip 20 can be acted against to remove it from the core. The chamfer 22 allows the closure 2 to be ejected from the tool more easily, as the angled surface allows the closure 2 to gently deform. 5 Referring now to Fig. 7, an opening 72 of a container 70 is shown. The remainder of the container 70 could be any size or shape but the opening 72 is designed to correspond to the cap 2 described above. The opening 72, in this case, includes a screw thread 74, which allows the cap 2 to be screwed on and off the opening. When the cap 2 is first placed over the opening 72, the annular 10 ring 6, being the tamper band, is attached by the bridges 18. The opening 72 includes a retaining lip 76 which is shaped to have a rounded upper surface with a flat lower surface. In this manner, the lip 76 allows the annular ring 6 to pass over the lip 76 when first placed on to the opening 72 but engages with annular lip 12 of the cap to prevent the annular ring 6 from being screwed off when the cap 2 15 is screwed off. That is, the annular ring 6 detaches at the bridges, thereby providing a tamper proof closure. The retaining lip 76 further includes bridge cutting projections 78, projecting our from the retaining lip 76 or just above the retaining lip 76 so that, when the annular ring 6 has it's annular lip 12 engaged with the retaining lip 76, the bridge cutting projections 78 are in line with the 20 bridges 18. The bridge cutting projections 78 are shaped and arranged such that when the cap 2 and annular ring 6 are first placed over the opening 72, the projections 78 do not break the bridges 18. For example, as shown in Fig. 7, the projections 78 are shaped to have a slope which when the cap is screwed on in a clockwise direction the bridges 18 and annular ring 6 will pass over the 25 projections 78 without resistance. However, when the cap 2 is turned in an anti clockwise direction, the bridges 18 catch on the projections, preventing further turning of the annular ring 6 and causing the bridges 18 to be sheared, separating the annular ring 6 and cap 2. Further modifications and improvements may be made without departing 30 from the scope of the present invention.