WO1999026855A1

WO1999026855A1 - Closures for pressurised products

Info

Publication number: WO1999026855A1
Application number: PCT/GB1998/003013
Authority: WO
Inventors: Malcolm George Collins; Andrew Robert Lockley
Original assignee: Crown Cork & Seal Technologies Corporation; Carnaudmetalbox Plc
Priority date: 1997-11-21
Filing date: 1998-10-09
Publication date: 1999-06-03
Also published as: GB9724635D0; AU9358498A

Abstract

A closure for a pressurised product is formed of a screw-threaded plastics ring (16), and a metal lid (14) held loosely captive in the ring and having a peripheral channel (22) containing sealing compound (42) for sealing with a container neck (12). The ring has a multi-start screw thread, with vent slots (58') formed between or in the thread segments. For pressure relief the lid can distort in a controlled manner so that spreading of the peripheral channel allows gas to escape.

Description

"CLOSURES FOR PRESSURISED PRODUCTS"

This invention relates to screw closures for packaging containers of products which are, or may be, subject to an above-ambient pressure at the time when the closures are unscrewed for product dispensing or otherwise. For brevity such closures are hereinafter referred to as "closures for pressurised products" .

A well known problem for closures of pressurised products such as beers and other carbonated beverages is that of " issiling", that is to say, uncontrolled and potentially dangerous pressure-driven movement of the closure when the closure is first disengaged from the container. For PET (polyethylene terephthalate) bottles having reduced-diameter necks of considerable axial depth the danger of missiling has largely been prevented by the use of multiturn (but single start) screw engagement of the closures with the bottle necks, and vent slots which are formed down the bottle and/or closure threads so that the pressure within the bottle can be reduced to substantially ambient pressure during the extended unscrewing movement which is required for a user to remove the closure for product consumption.

However, for larger container necks, for example having a 60mm external diameter, an axially extensive screw thread engagement of this kind may be prohibitively expensive in material cost and may be tiring and inconvenient for the consumer. The use of axially shorter thread engagement, however, brings an increased risk of missiling which is exacerbated by the large forces exerted on the closure by virtue of its substantial area.

The present invention has as one of its aims to provide a closure for a pressurised container, especially (but not necessarily) one having a large diameter neck, which may have an efficient anti -missiling performance despite making a relatively short length of screw thread engagement with the container. A further aim of the invention is to provide such a closure which is capable of releasing gas by way of pressure relief when the internal gas pressure of an associated container exceeds a predetermined value.

In accordance with one aspect thereof the invention provides a closure for a pressurised product, the closure comprising a metal closure lid having substantial rigidity, a tubular ring of plastics material m which the closure lid is held captive, a multistart thread formed on the interior of the ring adjacent an inner side of the lid, a radially inwardly projecting formation formed on the interior of the ring adjacent an outer side of the lid and engaged or engageable with the lid outer margin to retain the same against product pressure, the closure having sealing material arranged to form a seal between the inner side of the lid and an associated container, and one or more venting orifices provided at the interface of the lid with the ring to allow gas escape past the periphery of the lid when m engagement with the formation.

Preferably the lid is circular, and a plurality of grooves are formed around the interior of the ring and through the formation to provide said venting orifices. The lid is preferably rotatable in the ring to reduce opening torque .

From a second aspect thereof the invention provides a closure for a pressurised product, the closure comprising a metal closure lid having substantial rigidity, a tubular ring of plastics material in which the closure lid is held captive, a multistart thread formed on the interior of the ring adjacent an inner side of the lid, a radially inwardly projecting formation formed on the interior of the ring adjacent an outer side of the lid and engaged or engageable with the lid outer margin to retain the same against product pressure, the closure having sealing material arranged to form a seal between the inner side of the lid and an associated container, and the multistart thread comprising a plurality of thread segments which are disposed around the ring in non-overlapping manner, the segments being separated peripherally of the ring by gaps therebetween. The multistart thread preferably has three segments, although other numbers of segments (e.g. 2,4,5,6) may be used. The gaps between them may serve to allow axial movement of parts of a mould core during removal of the closure from the mould. They may additionally or alternatively act as anti-missiling slots for closure operation.

In an arrangement which is alternative to the arrangement of the penultimate paragraph, the thread segments are in mutually overlapping relation at their leading and trailing ends, and each thread segment is formed with an axially directed slot or interruption preferably having its leading edge further axially aligned with the trailing end of a further thread segment with which it overlaps. As in the previous paragraph, the slot may serve to allow axial movement of core parts during moulding and/or it may act as an anti-missiling slot for closure operation.

In accordance with a third aspect thereof the invention provides a closure for a pressurised product, the closure comprising a metal closure lid having substantial rigidity, a tubular ring of plastics material in which the closure lid is held captive, a thread formed on the interior of the ring adjacent an inner side of the lid, a radially inwardly projecting formation formed on the interior of the ring adjacent an outer side of the lid and engaged or engageable with the lid outer margin to retain the same against product pressure, the lid having a downwardly open peripheral channel m which is located sealing material arranged to form a seal between the inner side of the lid and an associated container, and the lid further comprising a central panel which is peripherally attached to the inner periphery of the channel, in response to an overpressure of gas of a predetermined magnitude exerted on its underside the lid suffering distortion by which pressure-relieving gas is able to leave the container past the sealing material in the channel .

In each of the three aspects of the invention recited above, the sealing material may be a flowed- in compound, a preformed ring, or a coating or layer of a polymer which forms the inner surface of the lid.

In order that the invention may be more fully understood, closures embodying the invention will now be described by way of example only and with reference to the accompanying drawings, in which: -

Fig.l shows the plastics ring of a first closure as seen in upper plan view;

Fig.2 is an enlarged sectional view of the ring as seen on line II-II in Fig.l;

Fig.3 is a similar view of the ring as seen on line III-III in Fig.1;

Fig.4 shows the closure lid on a radial section;

Figs .5A and 5B show the first closure when assembled and fitted on the neck of a wide-mouthed PET bottle containing beer or other carbonated beverage, at different points on the closure circumference;

Fig.6 is a developed view of part of the inside of the plastics ring of a second closure embodying the invention;

Figs. 6A and 6B are enlarged views respectively taken in section on the lines VIA-VIA and VIB-VIB of Fig .6 ;

Fig.7 is an enlarged scrap view of the second closure as seen in section on the line VII-VII of Fig.7B, illustrating the pressure venting which occurs at a predetermined elevated value of container headspace pressure;

Figs .7A and 7B show the second closure as seen from above, respectively before and after pressure venting; Fιgs.8A to 8E show various modifications of the closure lid to control its pressure venting performance; and

Fig.9 shows a third closure embodying the invention m a view which is basically similar to that of Fig.7. Referring firstly to Figs .1 to 5 the drawings, a closure 10 (Fig.5) is provided for closing the neck 12 of a wide-mouthed container which is moulded from PET (polyethylene terephthalate) . The container holds a carbonated product (not shown) , and is therefore subject to an internal pressure which is above ambient pressure. Typically the product is a 2.7 value beer, and the superatmospheric pressure is about 2.5 bar at 20°C.

The closure 10 is composite and formed essentially of two parts, namely a closure lid in the form of a substantially plane disc 14, and an open ended ring 16 m which the lid is held captive. The lid is shown m part in Fig.4, and should be understood to be circular and stamped from tmplate or other metal having protective varnish or decoration on its upper and lower faces 18, 20 as required. When the closure is m use the lower face is directed towards the container interior and the upper face faces outwardly.

From Fig.4 the lid 14 will be seen to have a downwardly (i.e. inwardly) facing annular channel 22 which is defined by shorter and longer, generally parallel and axially directed, sides 24, 26, and an annular base 28 which joins the sides together via radii 30, 32. Radially inside the channel, and surrounded by it, the lid has an upwardly domed central panel 34 which rises to approximately the same level as the base 28 at the centre of the closure. The domed central panel merges with the short inner side 24 of the channel at a radius 36. Outside the channel the lid is formed with an upwardly directed curl 38 of approximately semi -toroidal cross-section which presents the free edge 40 of the lid in a generally upward axial direction as shown. As shown, the curl is carried by the bottom end of the long outer side 26 of the channel.

As will later become apparent, in use of the closure the mouth-deflning rim of the neck 12 of the associated container is received within the channel 22 m sealing relationship. For that purpose a plastisol sealing compound 42 is flowed into the channel and subsequently cured, m well known manner.

The plastics ring 16 of the closure 10 is shown in detail m Figs. 1 to 3. It is essentially cylindrical, and has a relatively thick tubular wall 50. In use the ring has to hold the lid 14 securely against substantial pressure which may exist m the associated container; the ring is therefore moulded from a relatively hard, creep-resistant polymeric material, polypropylene filled with 20% talc being preferred.

As is particularly evident from Figs. 2 and 3, the ring has a generally cylindrical exterior surface 52 which may be knurled or otherwise roughened as desired to assist gripping by the consumer. The interior surface 54 of the ring is generally cylindrical, but an interrupted multi-start thread formed of three identical and circumferentially spaced segments 56 projects inwardly from it. The segments have a thread pitch of typically 8 mm in a closure of 65mm diameter. The gaps 58 between them are then typically 5mm in circumferential extent. The thread segments 56 are located adjacent the bottom end of the ring 16 as it is shown in Figs. 2 and 3. This end is to form the leading end of the closure as it is being fitted to the container - see Figs. 5A and 5B . Around its upper, trailing end the ring is formed with an inwardly projecting shallow bead 60 having a cylindrical inner face 62 and a chamfer 64 at which it intersects the annular top face 66 of the ring. Along its underside the bead has a shallow but steeply angled shoulder 68 forming an undercut at which the bead joins the cylindrical interior 54 of the ring. The shoulder, and therefore the bead as a whole, is spaced from the thread segments 56 by a substantial axial spacing 69.

Nine axially extending grooves 70 are formed in the interior surface 54 at regular intervals around the ring

16. In use of the closure they serve to vent gas from the container headspace as will be described. As can particularly be seen on the right hand side of Fig.4, they therefore have a substantial depth so as to penetrate completely through the bead 60 and they communicate the interior of the ring at its spacing 69 with the top face 66 of the ring.

Figs. 5A and 5B show the closure 10 as assembled and as subsequently fitted to a container neck 12 which has three thread segments 82 complementary to the thread segments 56 of the closure. The ring 16 is formed by injection-moulding using a collapsible mould core so that, in particular, the shoulder 68 of its bead 60 and the upper flanks 72 of its thread segments 56 can be closely toleranced and steeply angled as required. The gaps 58 between the thread segments facilitate removal of the collapsible core from the closure.

For assembly the lid is top-loaded into the ring, that is to say, it is forced into the ring through its top end as shown in Figs. 2,3 and 5. The chamfer 64 of the ring and the rounded undersurface of the lid curl 38 assist initial entry, and the lid is able to resiliently deform at its channel 22 in particular to allow the lid to move downwardly until the curl is located in the gap 69 beneath the thread formations 56 and the bead 60. The lid then resiles so that, as depicted in Figs. 5A and 5B, the lid is held firmly captive by the ring. In this condition the closure is ready for application to a container neck 12. The closure is fitted to the container in a conventional way by downward pressure and rotational torque (in the screwing-up direction) which are applied to the ring 16 after the closure has been presented to the container neck. Figs. 5A and 5B show the closure and container when the screw thread segments 56, 82 of the ring and container neck have been fully engaged. The container neck rim then indents the sealing compound 42 in the lid channel 22, the shoulder 68 of the ring bead 60 bearing resiliently down upon the free edge 40 of the lid to maintain a secure gas and liquid-tight seal by the sealing compound despite the lifting action of product pressure on the underside of the lid.

The closed package is intended for a pop concert or other such occasion at which beer (or other carbonated product) must be dispensed from the packages to individual consumers in a quick and safe manner. Opening is simply achieved by a server who twists the ring 16 in the normal anti-clockwise direction, manually or otherwise. The ring is accordingly allowed to rise on the container neck, driven by product pressure the effect of which is transmitted to the ring by the engagement of its bead 60 with the free edge 40 of the lid.

Although it makes firm engagement with the bead 60 substantially at all times, the lid is able to rotate relatively freely in relation to the ring. This freedom of the ring to rotate independantly of the lid substantially reduces the torque which must be applied at the beginning of the unscrewing operation, when substantial stiction (static friction) still exists between the lid and the container at the sealing compound 42.

As unscrewing proceeds the gas-tight seal between the lid and the container neck is broken, and gas is able to escape between the lid and the neck in a radially outward direction into the annular chamber 80 (Figs. 5A, 5B) which is formed between the opposed cylindrical surfaces of the ring and neck.

From the chamber 80 the escaping gas can pass to atmosphere upwardly through the vent orifices which are formed around the lid free edge 40 by the grooves 70. It can also escape downwardly through the gaps 58 between the thread segments 56. The total cross-sectional area provided for gas flow is such that by the time the threads 56 and 82 of the closure and container have lost engagement with one another during the unscrewing of the closure, the superatmospheric pressure in the container has reduced to a value at which there is little or no danger that the closure will missile and possibly cause injury or damage. Thus the closure can be removed quickly but with safety. The chamber 80 acts as a gallery by which the escaping gas is distributed evenly to the grooves 70.

In the closure before application to the container the lid 14 is not only able to rotate in the ring 16, but it can move axially within the ring between the thread segments 56 and the bead 60. In a first modification of the first closure (not illustrated) small, circumferentially spaced but axially directed ribs are moulded on the inside surface 54 of the ring for indenting engagement by the free edge 40 of the lid. The ribs help frictionally to locate the lid in its desired position against the bead 60 for cap application, but they preferably allow relative rotation of the lid in the ring as described above . In a further possible modification of the first embodiment the spacing 69 between the closure bead 60 and thread segments 56 is dimensioned to receive the curl 38 of the lid 14 with only a small clearance remaining. With such an arrangement the ribs described in the previous paragraph are omitted. If desired, the grooves 70 of the closure described above may be omitted, in which case the gaps 58 are dimensioned to provide for all the necessary gas release by which to prevent the danger of missiling when the closure is unscrewed.

The modified ring of a second closure embodying the invention is illustrated in Figs.6, 6A and 6B which show details of the ring, now denoted 16'. As before the ring has three thread segments, but whereas in the first embodiment the segments are non-overlapping and spaced apart circumferentially of the closure by gaps 58, in this modification the segments partially overlap one another; they are accordingly denoted by the reference numeral 56 ' . It will be seen from Fig.6 that the leading end 74 of each thread segment 56' underlies the trailing end of the thread segment above. Furthermore, each thread segment is interrupted at a slot 58 ' which serves the same functions as a gap 58 of the previous embodiment. The slot 58' is axially directed and flanked by the trailing face 90 of the thread segment above, and accordingly is likewise capable of providing a vent path and of facilitating moulding by providing access to the face 90 for axially moving mould parts. As can be seen from Figs .6A and 6B, the slot extends with a generally uniform depth up the inside face of the ring, as far as the lid-engaging shoulder 68. In one possible variation, however, the slot does not penetrate the inside face of the ring. Reference is now made again to the lid 14, of which the shape and arrangement is similar for all the embodiments described above. As previously mentioned m relation to Fig.4, the lid has a downwardly facing annular channel 22 m which sealing compound 42 is received, and an upwardly domed central panel 34 which is attached by a radius 36 to the inner side 24 of the channel .

As is discussed in detail below, the lid is arranged to provide pressure relief for a container closed by the closure, at a predetermined value of the pressure m the container headspace . This facility is particularly useful for carbonated beverages where excessive agitation or heat may cause the headspace pressure to rise to dangerous levels at which the container may burst or the closure blow off.

As can be understood from Figs .7 , 7A and 7B m combination, this pressure relief function of the closure is provided by the central panel 34 of the lid acting in conjunction with the radius 36 and the adjacent part of the channel 22. The radius forms an outwardly concave but tight transition between the central portion 34 and the channel, a typical magnitude of the radius being 1.0mm. At the predetermined value of the headspace pressure the central panel buckles upwardly and suddenly by folding along a substantially diametral line. This fold line is illustrated m Fιg.7B and denoted by the chain-dotted double line 94, to indicate that its angular position on the closure may be random and not necessarily diametral; however, as depicted, it will usually be substantially diametral and transverse to the grain or rolling direction of the tinplate of the disc, which is indicated by the arrow G.

As shown in Fig.7, at each end the fold line 94 extends to the radius 36 which forms a structurally rigid connection between the central panel 34 and the channel 22 with its sealing compound 42. The forces transmitted by the radius to the channel at the ends of the fold line are therefore substantial and highly localised, with the result that in those localities the channel becomes distorted by generally inward and upward spreading movement of its inner side 24 and base 28 in relation to its outer side 26.

This distortion, which is represented by broken lines in Fig.7, creates a sudden disruption of the gas- tight seal which had formerly been made between the sealing compound 42 and the container rim 92, and the resulting leakage path allows gas to escape from the container headspace as is illustrated by the arrow A Accordingly, the desired pressure relief is provided, and the headspace pressure is reduced to at least a safe level. After pressure relief has occurred, the lid retains its deformed condition so as subsequently to indicate that the package has "blown". Nevertheless, a seal with the container is usually reestablished to retain a lower level of pressurisation.

The headspace pressure at which pressure relief occurs and the nature and position of the lid deformation which causes it can be controlled by choice of various factors, two of which are the material of the disc and lts thickness. For example, the lid 14 may be formed of single reduced tmplate of predetermined thickness for pressure relief at a first, relatively low level, and it may be formed of double reduced tmplate of the same thickness if higher values of pressure relief are required. Correspondingly, increased pressure relief can be achieved by the use of greater thicknesses of the lid material .

Additional or alternatively, control of pressure relief may be provided by shaping the central panel 34 so as to modify its rigidity in localised areas. Figs .8A to 8E show various possibilities for achieving this.

In Fιg.8A a continuous bead 94 is formed as an upstanding projection around the central panel 34 just inside the radius 36. By reinforcing the panel against buckling the bead increases the value at which pressure relief occurs.

The bead 94 of Fιg.8A may be segmented so that gaps between the segments positively define the ends, and therefore the angular position, of the fold line. Fιg.8B shows the bead (94') when provided with two diametrically opposed gaps 95 for this purpose, but it will be understood that other numbers of gaps, preferably arranged in diametrically opposed pairs, may be used. Fig.δC shows a modification of Fιg.8B with additional beads 97 disposed inside the segmented bead 95 in alignment with the gaps; Fig.δD shows parallel beads 97 alone, i.e. with no surrounding bead; and Fιg.8D shows rigidifymg beads 98 which are radially directed. Yet a further parameter of the lid which can be used in the control of pressure relief is the curvature (if any) of the central panel 34. The central panel may be domed outwardly (as shown) or inwardly, and the doming may be used in combination with the bead structures shown in Figs .8A to 8E, or otherwise.

A further closure embodying the invention is illustrated in Fig.9. In this embodiment the lid 14 is bottom-loaded into the ring rather than being top-loaded as in the other embodiments. Accordingly the ring, now denoted 16", has an inwardly projecting flange 98 of substantial radial depth, which overlies the channel 22 of the lid to retain the lid against carbonation pressures. In this embodiment the free edge 40 of the lid is formed on a cylindrical part 99 of the lid so as to be free of contact with the ring 16. This avoids any tendancy for the free edge to dig into the plastics material of the ring and so prevent or hinder relative rotation between them when the closure is unscrewed by the user. The torque required for opening is accordingly reduced.

The pressure venting provisions which are described with reference to Figs .7 and 8 in relation to the second embodiment may be used for the other embodiments (Figs.l to 5 and Fig.9) in an analogous manner. Also, lid distortion to achieve pressure venting may be other than by upward buckling along a generally diametral fold line as has been particularly described.

Claims

CLAIMS :

1. A closure for a pressurised product, the closure comprising a metal closure lid (14) having substantial rigidity, a tubular ring (16, 16', 16") of plastics material in which the closure lid is held captive, a thread (56,56') formed on the interior of the ring adjacent an inner side of the lid, a radially inwardly projecting formation (60,98) formed on the interior of the ring adjacent an outer side of the lid and engaged or engageable with the lid outer margin to retain the same against product pressure, the lid having a downwardly open peripheral channel (22) in which is located sealing material (42) arranged to form a seal between the inner side of the lid and an associated container, and the lid further comprising a central panel (34) which is peripherally attached to the inner periphery of the channel, in response to an overpressure of gas of a predetermined magnitude exerted on its underside the lid suffering distortion by which pressure-relieving gas is able to leave the container past the sealing material in the channel .

2. A closure as claimed in claim 1, characterised in that the central panel (34) is adapted to buckle upwardly by folding along a generally diametral fold line (94) .

3. A closure as claimed in claim 1 or claim 2, characterised in that the central panel (34) is joined to the channel by a generally arcuate and outwardly concave transition portion (36) having substantial rigidity.

4. A closure as claimed in any preceding claim, characterised in that the central panel (34) is domed upwardly .

5. A closure as claimed in any claim of claims 1 to 3 , characterised in that the central panel (34) is domed downwardly.

6. A closure as claimed in any preceding claim characterised by a bead (94,94') formed around the central panel (34) .

7. A closure as claimed in claim 6, characterised in that the bead (94') is formed with at least one pair of diametrically opposed interruptions (95) .

8. A closure as claimed in claim 6 or claim 7, characterised by a plurality of parallel beads (96) formed across the central panel (34) .

9. A closure as claimed in any claim of claims 1 to 5 , characterised by a plurality of radially extending beads (97) formed across the central panel (34) .

10. A closure as claimed in claim 7, characterised in that the interruptions (95) lie on a diameter which is perpendicular to the grain direction of the metal of the lid (14) .

11. A closure as claimed in claim 8, characterised in that the beads (96) are perpendicular to the grain direction of the metal of the lid (14) .

12. A closure for a pressurised product, the closure comprising a metal closure lid (14) having substantial rigidity, a tubular ring (16) of plastics material in which the closure lid is held captive, a multistart thread formed on the interior of the ring adjacent an inner side of the lid, a radially inwardly projecting formation (60) formed on the interior of the ring adjacent an outer side of the lid and engaged or engageable with the lid outer margin to retain the same against product pressure, the closure having sealing material (42) arranged to form a seal between the inner side of the lid and an associated container, and one or more venting orifices (70) provided at the interface of the lid with the ring to allow gas escape past the periphery of the lid when in engagement with the formation.

13. A closure as claimed in claim 12, characterised in that a plurality of grooves (70) are formed around the interior of the ring (16) and through the formation (60) to provide said venting orifices.

14. A closure for a pressurised product, the closure comprising a metal closure lid (14) having substantial rigidity, a tubular ring (16) of plastics material in which the closure lid is held captive, a multistart thread formed on the interior of the ring adjacent an inner side of the lid, a radially inwardly projecting formation (60) formed on the interior of the ring adjacent an outer side of the lid and engaged or engageable with the lid outer margin to retain the same against product pressure, the closure having sealing material (42) arranged to form a seal between the inner side of the lid and an associated container, and the multistart thread comprising a plurality of thread segments (56) which are disposed around the ring in non- overlapping manner, the segments being separated peripherally of the ring by gaps (58) therebetween.

15. A closure for a pressurised product, the closure comprising a metal closure lid (14) having substantial rigidity, a tubular ring (16') of plastics material in which the closure lid is held captive, a multistart thread formed on the interior of the ring adjacent an inner side of the lid, a radially inwardly projecting formation (60) formed on the interior of the ring adjacent an outer side of the lid and engaged or engageable with the lid outer margin to retain the same against product pressure, the closure having sealing material (42) arranged to form a seal between the inner side of the lid and an associated container, and the multistart thread comprising a plurality of thread segments (56') which are disposed around the ring, the thread segments being in mutually overlapping relation at their leading and trailing ends and being each formed with an axially directed slot (58 ' ) having its leading edge aligned with the trailing end (90) of a further thread segment (56 ') with which it overlaps.

16. A closure as claimed in claim 14 or claim 15, characterised in that it has three thread segments (56,56') .

17. A closure as claimed in any preceding claim, characterised in that the lid (14) is rotatable in the ring (16,16' ,16") .

18. A closure as claimed in any preceding claim, characterised in that, the lid (14) may move axially within the ring (16,16'16").