CLOSURE CAP WITH BRAKING STRUCTURE

Abstract: A closure (26) for a container having a threaded finish portion, with a braking structure to resist unscrewing of the closure and thereby provide sufficient time for any gases within the container to vent. The braking structure comprises a restrictor means (44) located adjacent to the leading edge (43) of the closure thread (42) and arranged such that the container thread is squeezed between the restrictor means and the axially adjacent portion of the closure thread. The restrictor means provides braking with a minimum of radial force being exerted on the closure.

Description: CLOSURE CAP WITH BRAKING STRUCTURE The present invention relates generally to closures for containers, such as carbonated beverage containers, and to the finish portions of such containers. In particular, the invention relates to an improved closure or container finish portion which acts to provide a braking effect when the closure is unscrewed from the container and does so with minimum effect on the stripping torque between the closure and the finish portion of the container. Conventional mating closures and bottle finish structures for carbonated beverage containers typically utilise a screw type or threaded arrangement between the closure and the finish portion. These types of screw caps are mass produced by injection or compression moulding and have achieved commercial success mainly in the soft drink industry, where tliey are applied robotically to the finish portions of filled soft drink bottles on rapidly moving filling lines. One constraint that exists in the design of conventional screw caps is that the screw connection between the cap and the thread of the finish portion must be able to withstand a defined amount of unscrewing torque, which is in excess of the amount of torque that must be applied to ensure a sealed fit when the cap is installed on the container after filling. This is known as the "stripping torque". The stripping torque is affected by a number of factors including the rigidity of the cap threads and the supporting outer wall of the cap. The thicker the outer wall, the greater the stripping torque will tend to be. Of course, material costs for the manufacturer will increase significantly as the thickness of the outer wall is increased. Another important factor in the design of screw-type closure caps for carbonated beverage bottles is that of ensuring that the connection between the cap and the finish portion of the container is properly vented, so as to permit compressed gases from within the container to be released gradually as the cap is unscrewed by the consumer. To achieve the necessary venting, it is common for the threads of the finish portions of conventional soft drinks containers to be intermittent as opposed to a continuous helix. It is also common for the internal threads of the closure caps to have periodic gas venting gaps . To ensure that the pressurised gases are relieved before the closure is removed from the container by a consumer, techniques have also been developed to retard or brake the unscrewing of the closure cap. The most common way of achieving a braking effect is the use of a "speed bump", which is a portion of the outer wall of the closure that is raised slightly so as to extend radially inwardly towards the threads of the finish portion of the container. During unscrewing of the closure, the speed bump frictionally engages the crest of the thread on the finish portion, thus imparting some resistance to the unscrewing of the closure cap. This ensures that it takes several turns of the consumer's wrist to completely separate the closure from the container, providing sufficient time for the pressurised gases within the container to vent. Although speed bumps are effective to some extent, the radial force that is imparted by the engagement of the speed bump with the thread of the container finish portion tends to deform the outer wall of the closure radially outwards, away from the container finish. This effect substantially reduces the stripping torque value of the closure cap on a particular container finish. Existing speed bump designs have reached their design limit in that any increase in the radial dimensions of the speed bump, to increase the braking effect of the structure, tends to lead to an unacceptable reduction in the stripping torque value. This problem can be mitigated somewhat by increasing the thickness and thus the rigidity of the outer wall of the closure, but at the expense of greater material costs for the manufacturer. Hence, an aim of the present invention is to provide an improved closure cap and/or container finish having a braking structure that will have a less profound effect on the stripping torque value of the closure than the closure caps with conventional braking structures. Accordingly, the present invention provides a closure for a container having a threaded finish portion, comprising a top portion, a side wall portion with at least one raised thread defined thereon and a braking structure to frictionally resist unscrewing of the closure from the container characterised in that the braking structure comprises a restrictor means positioned adjacent to the leading edge of the closure thread and axially spaced from an adjacent portion of the closure thread by a distance that is sufficient to squeeze the container thread between the restrictor means and the adjacent portion of the closure thread as the closure is unscrewed from the container, whereby braking is achieved with a minimum of radial force being exerted on the closure. In the closure according to the invention, the restrictor means acts on the side surface of the container thread, to squeeze it between the upper surface of the restrictor means and the lower surface of the adjacent closure thread. This squeezing effect provides frictional resistance to unscrewing of the closure but does not produce the radial forces on the closure that are inherent with the use of speed bumps. Thus, the restrictor means according to the invention can provide an equivalent braking resistance to a conventional speed bump but with a higher value stripping torque for the closure and container finish combination. The restrictor means is placed adjacent to the leading edge of the closure thread (the portion of the closure thread which is the first to engage with the container thread) . In this position, the restrictor means will act on the container thread during the whole time that the closure is being unscrewed, providing the braking resistance during the unscrewing process. A second aspect of the invention provides a container for co-operation with a threaded closure, comprising a body portion, a finish portion with at least one raised thread defined thereon and a braking structure to frictionally resist unscrewing of a closure from the container characterised in that the braking structure comprises a restrictor means positioned adjacent to the leading edge of the container thread and axially spaced from an adjacent portion of the container thread by a distance that is sufficient to squeeze the closure thread between the restrictor means and the adjacent portion of the container thread as the closure is unscrewed from the container, whereby braking is achieved with a minimum of radial force being exerted on the closure. A conventional closure may be used on the container described in the paragraph above. The restrictor means should again be placed adjacent to the leading edge of the container thread so that it acts on the closure thread during the whole of the unscrewing process. In this configuration, the closure thread will be squeezed between the restrictor means on the container and the lower surface of the adjacent container thread. The restrictor means is preferably provided by a projection moulded on either the closure or the container finish portion. The projection may either be provided as an integral part of the leading edge of the closure or container thread, or it may be provided as a separate structure in front of and spaced from the leading edge of the thread. Furthermore, the braking effect of an existing closure/container finish portion combination having one or more speed bumps, may be enhanced by providing a restrictor according to the invention in combination with the existing speed bump arrangement. Preferably, the restrictor means is integral with one or more of the speed bumps. This has the advantage that an existing mould for a closure or container finish portion may be modified to provide the additional restrictor means and thereby improve the braking effect of the closure/container finish portion combination. In order to ensure that the speed bump acts on the crest of the container thread and the projection acts against the side of the container thread, the restrictor means should be arranged so that the speed bump extends radially inwardly, towards the container finish portion by a distance which is less than the distance that the projection extends radially inwardly. Preferred embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows a developed view of the inside surface of the cylindrical wall portion of a prior art closure having a speed bump. Figure 2 shows a cross sectional view taken through a closure cap according to a preferred embodiment of the invention. Figure 3 shows a developed view of the inside surface of the cylindrical wall portion of the closure cap shown in figure 2 vii th a portion of the thread on the container finish portion included to better illustrate the invention. Figure 4 shows an enlarged fragment of a small area of figure 3 around the braking structure according to the invention. Figure 5 shows a partial cross sectional view taken along line X-X in Figure 4. Figure 6 shows a developed view of the inside surface of the cylindrical wall portion of a closure cap according to a second embodiment of the invention. Figure 7 shows an enlarged fragment of a small area of figure 6 around the braking structure according to the second embodiment of the invention. Techniques have already been developed to retard or brake the unscrewing of a closure cap using a so called speed bump. Referring to figure 1 , a closure 10, in commercial use, includes an outer wall 12 that is shown projected as if it were flat, instead of being shaped substantially as an inside curved surface of a cylinder, as it is in use. As is common, closure 10 also includes a tamper-evident (TE) strip 14 having a number of ratchet teeth 16 about its lower periphery that are orientated so as to slip over a flange on the container finish portion (not shown) during fastening of the closure, but to resist removal with sufficient force that, upon attempts at removal, a frangible score 18 between the TE strip 14 and the rest of the closure 10 will rupture first. Closure 10 also has a thread 20 defined in the outer wall 12 . The thread 20 has periodic venting recesses 22 defined therein. In the closure 10, the braking effect is achieved by means of a speed bump 24, which is a portion of the outer wall 12 that is slightly raised so as to extend radially inwardly towards the threads on the finish portion of a container. It will be noted that the speed bump 24 is centered in relation to the helical turns of the closure thread 20 so as to lie centrally between the lines of the thread. During removal of the closure by unscrewing, the speed bump frictionally engages the crest of the thread on the finish portion of the container, thus imparting some resistance to the unscrewing of the closure 10. However, the radial force imparted by the engagement of the speed bump 24 on the crest of the container thread tends to deform the outer wall 12 of the closure 10 radially outwardly, away from the container finish. This effect substantially reduces the value of the stripping torque . In figures 2 to 5, like components have been given the same reference numerals . Referring to figures 2 and 3, a closure cap 26 includes an outer wall 28 that defines a top wall portion 30, a side wall portion 32 having a substantially cylindrical inner surface 34 and at least one internal raised helically orientated thread 42. The thread 42 has a predetermined pitch and a leading edge 43. The leading edge 43 of the thread 42 is the first part of the closure thread to engage with the threads on the container finish portion (not shown) . Closure cap 26 also includes a tamper-evident (TE) strip 36 having a number of ratchet teeth 38 about its lower periphery that are orientated to slip over a flange on the container finish portion, as is well known from the prior art. A frangible score 40 is provided between the TE strip 36 and the rest of the closure cap 26. Referring to figures 3 to 5, a particularly advantageous aspect of the invention involves the provision of a resistor structure 44 for frictionally resisting unscrewing of the closure cap 26 from a container finish portion (not shown) . The restrictor structure 44 is positioned before the leading edge 43 of the closure thread 42 and is therefore the first structure on the closure to engage with the thread 60 on the container finish portion. The restrictor structure 44 takes the form of a projection 46 that extends radially inwardly from the side wall portion 32. The projection 46 is positioned so as to be axially spaced from an adjacent portion of the closure thread 42 by a distance that is sufficient to squeeze the container thread 60 between the restrictor structure 44 and the adjacent portion of the closure thread 42. Hence, the upper side 52 of the projection 46 bears against the lower side 58 of one of the container threads 60 and squeezes the upper surface of the container thread 60 against the lower side of the adjacent closure thread 42. During unscrewing of the closure 26, the braking effect of the restrictor structure 44 is achieved with a minimum of radial force being exerted on the closure as the restrictor structure 44 acts on the side surface 58 of the container thread 60 rather than on its crest. As shown in figure 5, projection 46 extends radially inwardly from the side wall portion 32 by a distance Rp that is preferably within the range 0.025 inches to about 0.045 inches, in particular about 0.035 inches. Projection 46 also has a length Lp (as shown in figure 4) that is within the range of 0.20 to about 0.50 inches, in particular about 0.34 inches. Referring to figure 4, the closure cap 26 may also have a speed bump 48 that is positioned to extend radially inwardly from the side wall portion 32 by a distance Rs (dimension not shown) . Speed bump 48 is distinguished from the projection 46 in that the distance Rs by which it extends radially inwardly from the side wall portion 32 is substantially less than the distance Rp which the projection 46 extends radially inwardly from the side wall portion 32. Distance Rs is preferably within the range of about 0.011 inches to about 0.023 inches, in particular about 0.017 inches. Projection 46 is also distinguished from speed bump 48 in that it is positioned to achieve braking by frictional engagement that has a substantial axial force component, as opposed to the speed bump 48 which achieves braking by frictional engagement that has a significant radial force component. In other words, referring to figure 5, the speed bump 48 is positioned to engage the outer surface or crest 56 of the external thread 60 on the container finish portion, whereas the projection 46 is positioned to engage the side surface 58 of the container thread 60. In a preferred embodiment of the invention, the projection 46 is provided integral with speed bump 48 as this simplifies the mould configuration. In operation, closure 26 is first placed on a container finish portion by screwing to a predetermined torque. As torque is applied, the internal threads of the closure are not as radially displaced by the presence of the projection 46 and the bump 48 as they would be by a speed bump having similar braking efficacy. Accordingly, a high strip torque value can be maintained without reinforcing the closure. After it has been received by the customer, the container is opened by first twisting the closure with respect to the container so that the internal raised threads on the closure begin to slide with respect to the external raised threads on the container finish portion. During this process, unscrewing of the closure from the container is frictionally resisted by the projection 46 squeezing the external raised thread of the container finish portion between the projection 46 and the adjacent internal raised thread of the closure from which the projection is axially displaced. As a result of this braking effect, the consumer will likely have to perform more than one twist of the wrist to remove the closure from the container, giving pressurised gases within the container plenty of time to vent. The projection 46 is placed adjacent to the leading edge of the closure screw thread 42 as this ensures that the whole length of the container screw thread 60 has to pass through the restriction between the projection 46 and the adjacent, axially displaced closure thread. Thus, the projection applies its braking effect throughout the unscrewing of the closure. Referring to figures 6 and 7, in an alternative embodiment of the invention, the restrictor means 44 is provided integral with the leading edge 43 of the closure thread 42. The restrictor means 44 is positioned so as to enlarge the leading edge 43 of the closure thread 42 to reduce the axial spacing between the leading edge 43 of the closure thread 42 and the adjacent portion of the closure thread. Thus, the upper surface of the restrictor means 44 is spaced from the adjacent portion of the closure thread 42 by a distance that is sufficient to squeeze the container thread 60 between the restrictor means 44 and the adjacent portion of the closure thread 42. Hence, the upper side 52 of the restrictor means 44 bears against the lower side 58 of one of the container threads 60 and squeezes the upper surface of the container thread 60 against the lower side of the adjacent closure thread 42. It will be appreciated that instead of enlarging the leading edge 43 of the closure thread 42 to provide the restrictor means 44, the leading edge 43 of the closure thread 42 could merely be locally axially displaced to provide the required squeezing of the container thread 60. Although the detailed description of the invention has been made using a closure cap as an example, it will be appreciated that a restrictor means, having all the characteristics of that described in relation to the closure cap, could equally have been provided adjacent to the leading edge of the thread on the finish portion of a container. In this case, the restrictor means would obviously be axially spaced from an adjacent portion of the container thread and the closure thread would be squeezed between the restrictor means and the adjacent portion of the container thread to provide the required braking effect.

Claims: CLAIMS 1. A closure for a container having a threaded finish portion, comprising a top portion, a side wall portion with at least one raised thread defined thereon and a braking structure to frictionally resist unscrewing of the closure from the container characterised in that the braking structure comprises a restrictor means positioned adjacent to the leading edge of the closure thread and axially spaced from an adjacent portion of the closure thread by a distance that is sufficient to squeeze the container thread between the restrictor means and the adjacent portion of the closure thread as the closure is unscrewed from the container, whereby braking is achieved with a minimum of radial force being exerted on the closure. 2. A closure according to claim 1, wherein the restrictor means comprises a projection which extends radially inwardly from the side wall portion. 3. A closure according to claim 2, wherein the projection is positioned before and spaced from the leading edge of the closure thread. 4. A closure according to claim 2, wherein the projection is integral with the leading edge of the closure thread. 5. A closure according to any one of claims 2 to 4, further comprising a speed bump positioned so as to extend radially inwardly from the side wall portion. 6. A closure according to claim 5 wherein the speed bump extends radially inwardly from the side wall portion by a distance that is less than the distance by which the projection extends. 7. A closure according to any one of claims 5 to 6, wherein the restrictor means is integral with the speed bump. 8. A container for co-operation with a threaded closure, comprising a body portion, a finish portion with at least one raised thread defined thereon and a braking structure to frictionally resist unscrewing of a closure from the container characterised in that the braking structure comprises a restrictor means positioned adjacent to the leading edge of the container thread and axially spaced from an adjacent portion of the container thread by a distance that is sufficient to squeeze the closure thread between the restrictor means and the adjacent portion of the container thread as the closure is unscrewed from the container, whereby braking is achieved with a minimum of radial force being exerted on the closure.

Inventors: SEIDITA THOMAS M, SEIDITA, THOMAS, M.
Applicants: CROWN CORK & SEAL TECH CORP, METAL BOX PLC, SEIDITA THOMAS M, CARNAUDMETALBOX PLC, CROWN CORK & SEAL TECHNOLOGIES CORPORATION, SEIDITA, THOMAS, M.
Application year: 1998
Main classification: B65D41
IPC codes: B65D41