CLOSURE

Abstract: A PT (Press-on/Twist-off) closure cap comprises a shell (2) including a skirt (4) and an end panel (3). A one-piece, preformed gasket (6) is secured in position within the shell, and performs a dual function, firstly to form a seal between the end panel (3) and an end sealing surface (12) on a container such as a glass jar, and secondly to provide a thread retention portion (8) between the skirt (4) and a thread finish (11) provided on the container. The thread retention portion (8) ensures that the closure may be initially applied by an axial movement and subsequently removed by a rotary movement. The preformed gasket is preferably formed of a polypropylene material or a Thermoplastic Elastomeric material having a flexural modulus of between 30 and 900 MPa.

Description: "CLOSURE " This invention relates to closure caps, to closure/neck finish combinations, and to a method of manufacturing closure caps. In particular the invention relates to PT (Press-On/Twist-off ) closures which are designed to be applied to a container by an axial movement and removed from the container by a rotary movement . In conventional PT caps a plastJsol compound is flowed into a cap to provide sealing and thread forming features. The compound is injected as a viscous fluid onto the inside of the wall portion of the metal cap, which is spun in order to distribute the compound evenly. The compound is then subjected to a moulding operation by means of a plug pressed into the closure to produce the desired distribution of compound. The cap is then passed through an oven, the heat from which causes the compound to expand and solidify. An example of this type of closure is described in US4562930. The present invention provides an alternative to this kind of closure. Accordingly there is provided a closure cap of the press-on/twist-off type comprising a shell including a skirt and an end panel, a first sealing portion adapted to form a seal between the end panel and at least the end sealing surface of a container, and a second liner portion adapted to be located between the skirt and a thread finish provided on the container, the liner portion being such that the closure may be applied to a container by an axial movement and removed from the container by a rotary movement, characterised in that the first sealing portion and the second liner portion are both provided by means of a single pre-formed gasket which is firstly moulded and subsequently secured in position within the closure. The closure skirt conveniently includes an inwardly facing projection, and the pre-formed gasket is secured in position by means of this inwardly facing projection. Preferably the skirt includes an inwardly facing curl at the extremity thereof, and the pre-formed gasket is crimped in position by means of the curl. This avoids the need for any adhesives, or any heat treatment of the gasket as is required with flowed-in p] astisoJ compounds. Conceivably, where the cap is provided with a tamper evident band, the tamper evident band is also secured into position by means of the inwardl facing projection or curl. The pre-formed gasket is conveniently formed of a polymeric material having a flexural modulus of between 30 and 900 MPa, typically between 36 and 500, and ideally around 100. The pre-formed gasket is preferably formed of polypropylene, although alternative materials such as polypropylene/nylon blends or even thermoplastic elastomers (TPEs) such as Santoprenes may be appropriate. The pre-formed gasket is preferably such that the thread finish on the container forms complementary threads on the gasket when the closure is applied to the container. The pre-formed gasket provides both the sealing function between the end panel and the end sealing surface of a neck finish, and also the thread retention function which allows the PT cap to be twisted off and also reapplied to the neck finish by the user. Whereas pre-formed gaskets have been proposed for vacuum closures, this has typically only been to carry out the sealing function in closures other than PT closures. The pre-formed gasket is preferably provided with a plurality of projections adapted to be deformed by the thread finish on a container, so as to retain the impression of the complementary threads on the gasket. The projections are conceivably ribs running transverse to the thread finish on the conainer, although other projections, such as pimples etc., could be envisaged. Alternatively the pre-formed gasket is provided with preformed thread formations, adapted to engage the thread finish on the container. One way or another, the preformed gasket has or rec e ives thread formations, to allow the closure to be ramped-off by the user and reapplied with a twist-on action. According to a further aspect of the invention, there is provided a closure and neck finish combination wherein the neck finish has a rim and at least one helically extending thread, and the closure has a shell including a skirt and an end panel, a first sealing portion forming a seal between the end panel and at least the rim of the container, and a second liner portion located between the skirt and the at least one helically- extending thread, the liner portion being such that the closure may be applied to a container by an axial movement and removed from the container by a rotary movement, characterised in that the first sealing portion and the second liner port. ion are both provided by means of a single pre-formed gasket which is firstly moulded and subsequently secured in position within the closure. According to a further aspect of the invention there is provided a method of manufacturing a press-on/twist- off type closure comprising the steps of:- i) stamping a shell including a skirt and an end panel, ii) moulding a gasket of polymeric material, comprising a first sealing portion and a second liner portion, and iii) attaching the gasket to the shell such that the first sealing portion is adjacent the end panel to form a seal between the end panel and at least the end sealing surface of the container, and the second liner portion is adjacent the skirt such that it is adapted to be located between the skirt and the thread finish provided on the container, the liner portion being such that the closure may be applied to a container by an axial movement and removed from the container by a rotary movement. The invention further resides in a method of manufacturing a press-on/twi st-off type closure comprising the steps of :- i) stamping a shell including a skirt and an end panel, ii) moulding a gasket of polymeric material comprising a first sealing portion and a second liner portion, iii) presenting the gasket to the shell such that the first sealing portion is adjacent the end panel, and a second liner portion is adjacent the skirt, and iv) forming the edge of the shell into a curl such that the polymeric gasket is crimped in position such that the first sealing portion is adapted to form a seal between the end panel and at least the end sealing surface of a container, and the second liner portion is adapted to be located between the skirt and the thread finish provided on the container, t " liner portion being such that the closure may be applied t o the container by an axial movement and removed from the container by a rotary movement. The invention will now be further described, by way of example only, with reference to the accompanying drawings, in which: - Fig.l is a schematic cross sectional view of a vacuum closure in accordance with the present inventon, Fig.2 is a schematic cross sectional vie'-/ of the vacuum closure of Fig.l shown applied to the neck finish of a container, Fig.3 is a sectional- perspective view of an alternative embodiment of vacuum closure according to the present invention, Fig.4 is a schematic sectional He of a further alternative embodiment of vacuum closure according to the present invention, and Fig.5 is a schematic sectional π of an alternative embodiment of the vacuum closure of Fig.3 incorporating a tamper-evident band. Referring to Fig.l, the vacuum closure is shown generally at 1, and comprises a metal shell 2, including an end panel 3 and a downwardly dependant skirt 4. A polypropylene gasket 6 is received within the shell 2, and comprises a sealing portion 7, a thread retention portion 8, and a securing rim 9. The gasket is typically formed by injection moulding. The gasket 6 is applied to the shell 2, and the skirt 4 is curled over to form an inwardly facing curl 5. The curl 5 traps the rim 9 and secures the gasket 6 within the shell. Fig.2 shows the vacuum closure applied to the neck finish 10 of a container such as a glass jar. The neck finish includes thread formations 11 and an end sealing surface 12. When the vacuum closure is applied to the neck finish in a conventonal manner, the sealing portion 7 of the gasket 6 forms a hermetic seal between the end panel 3 and the end sealing surface 12 of the container at Area 'A'. Typically a side seal is also formed between a portion of the gasket and the neck finish at Area '--.'. Similarly, a lower portion of the gasket 6 cooperates with the sidewall of the neck finish at Area 'C, in order to provide a barrier to the ingress of foreign bodies such as dust, dirt and insects etc. The thread retention portion 8 of the gasket is deformed by the thread format ions 11 on the neck finish so that the vacuum closure 1 can be removed from the container by the user in a "twist-off" manner. The thread retaining portion 8 of the gasket 6 remains at least partially deformed by the thread formations 11, so that the closure can be reapplied to the glass jar by twisting it back on to the neck finish. Suitable materials for the gasket 6 are shown in Table 1. Fig.3 shows a variant to the vacuum closure of Figs. 1 and 2, in which the gasket 6 is provided with pre-formed longitudinally extending ribs 13. The ribs are typically 0.35 mm in radial depth as compared to an overall gasket radial thickness of 0.6 mm. The thread formations 11 make indentations in the ribs 13 which allow the closure to be easily reapplied to the container, whilst ensuring that the initial opening torque necessary to remove the closu-e from the container is not excessive and typically in the range 10 - 30 Kgf-cm. The ribs 13 also act as a cushion, so as to improve the abuse resistance of the closure. Other forms of projections, such as pimples etc. (not shown) could also be employed to retain the impression of the thread formations 11 and so as to ensure that the closure 'ramps off when twisted. Fig. shows an alernative design of closure in which the gasket 6 has thread features 14 pre-formed therein, as opposed to relying on the impressions formed from the thread formation 11. Fig.5 shows an embodiment in which a tamper-evident plastics band 15 is crimped under the curl 5 together with the securing ring 9 of the gasket 6. The tamper- evident band 15 has weak sections (not- shown) which cause the band to break as the closure 1 is first removed from the container neck finish 10, as described in our European Patent No. 0450959B. TABLE 1

Claims: CLAIMS 1. A closure cap of the press-on/f ist-off type comprising a shell including a skirt and an end panel, a first sealing portion adapted to form a seal between the end panel and at least the end sealing surface of a container, and a second liner portion adapted to be located between the skirt and a thread finish provided on the container, the liner portion being such that the closure may be applied to a container by an axial movement and removed from the container by a rotary movement, characterised in that the first sealing portion and the second liner portion are both provided by means of a single pre-formed gasket which is firstly moulded and subsequently secured in position within the closure. 2. A closure cap according to claim 1, in that the skirt includes an inwardl facing pr jection, and the pre-formed gasket is secured in position by means of the inwardly facing projection. 3. A closure cap according to claim 2, characterised in that the skirt includes an inwardly facing curl at the extremity thereof, and the pre-formed gasket is crimped in position by means of the curl. 4. A closure cap according to claim 2 or claim 3, characterised in that the cap is provided with a tamper- evident band which is also secured in position by means of the inwardly facing projection. 5. A closure cap according to any of claims 1 to 4, characterised in that the pre-formed gasket is formed of a polymeric material having a flexural modulus of between 30 and 900 MPa . 6. A closure cap according to any of claims 1 to 5, in that the pre-formed gasket is formed of polypropylene, or polypropylene based polymeric material. 7. A closure cap according to any preceding claim characterised in that the pre-formed gasket is such that the thread finish on the container forms complementary threads on the gasket when the closure is applied to the container . 8. A closure cap according to claim 7, characterised in that the pre-formed gasket is provided with a plurality of projections adapted to be deformed by the thread finish on the container, so as to retain the impression of the complementary threads on the gasket. 9. A closure cap according to claim 8, characterised in that the plurality of proj eel ions are ribs running transverse to the thread finish on the container. 10. A closure cap according to any of claims 1 to 6, characterised in that the pre-formed gasket is provided with pre-formed thread formations, adequate to engage the thread finish on the container. 11. A closure and neck finish combination wherein the neck finish has a rim and at least one helically extending thread, and the closure has a shell including a skirt and an end panel, a first sealing portion forming a seal between the end panel and at least the rim of the container, and a second liner portion located between the skirt and the at least one helically extending thread, the liner portion being such that the closure may be applied to a container by an axial movement and removed from the container by a rotary movement, characterised in that the first sealing portion and Lh Q second liner portion are both provided by means o f a single pre-formed gasket which is firstly moul ed and subsequently secured in position within the closure. 12. A method of manufacturing a press-on/ twist-off type closure comprising the steps of :- i) stamping a shell including skirt and an end panel, ii) moulding a gasket of polymeric material, comprising a first sealing portion and a second liner portion, and iii) attaching the gasket to the shell such that the first sealing portion is adjacent the end panel to form a seal between the end panel and at least the end sealing surface of a container, and the second liner portion is adjacent the skirt such that it is adapted to be located between the skirt and a thread finish provided on the container, the liner portion being such that the closure may be applied to a container by an axial movement and removed from the container by a rotar" movement. 13. A method of manufacturing a press-on/twist-off type closure comprising the steps of :- i) stamping a shell including a skirt and an end panel, ii) moulding a gasket of polymeric material, comprising a first sealing portion and a second liner portion, iii) presenting the gasket to the shell such that the first sealing portion is adjacent the end panel, and the second liner portion is adjacent the skirt, iv) forming the edge of the shel 1 into a curl such that the polymeric gasket is crimped in position such that the first sealing portion is adapted to form a seal between the end panel and at least the end sealing surface of a container, and the second liner portion is adapted to be located between the skirt and a thread finish provided on the container, the liner portion being such that the closure mav be applied to the container by an axial movement and removed from the container by a rotary movement .

Inventors: COLLINS MALCOLM GEORGE, COLLINS, MALCOLM, GEORGE
Applicants: COLLINS MALCOLM GEORGE, CROWN CORK & SEAL TECH CORP, METAL BOX PLC, CARNAUDMETALBOX PLC, COLLINS, MALCOLM, GEORGE, CROWN CORK & SEAL TECHNOLOGIES CORPORATION
Application year: 1998
Main classification: B65D41
IPC codes: B65D41