WO1996041751A1

WO1996041751A1 - Closure

Info

Publication number: WO1996041751A1
Application number: PCT/GB1996/001353
Authority: WO
Inventors: Cyril Saunders; Thomas Hayes
Original assignee: CarnaudMetalbox SA; CarnaudMetalbox PLC; Metal Box PLC; CarnaudMetalbox NV; CarnaudMetalbox Holdings USA Inc
Current assignee: Crown European Holdings SA; Crown Packaging UK Ltd; Eviosys Aerosols and Promotional Packaging Netherlands BV; CarnaudMetalbox Holdings USA Inc
Priority date: 1995-06-09
Filing date: 1996-06-07
Publication date: 1996-12-27
Anticipated expiration: 1997-12-09
Also published as: AU6009496A

Abstract

A composite closure for a hot filled product, which comprises a mouled plastics ring (20) with internal formations for engaging complementary formations on a container neck, and an all-plastics laminated disk (40) which is top loaded into the ring. When the closure is fitted onto the container, the disk (40) is pinched between a shoulder (24) on the ring and an outside radius (13) on the container rim. Further engagement between disk and the ring occurs where the free edge (44) of the disk engages the ring beneath its shoulder. The ring and disk therefore engage one another at two concentric and spaced locations, and these engagements together determine a predetermined desired position of the ring in relation to the disk and to the container, despite high flexibility of the disk at the elevated temperature to which it is subjected.

Description

'CLOSURE '

This invention relates to closures for packaging containers.

In particular, the invention relates to such closures having an open-ended generally tubular skirt or ring member arranged to be fitted in telescoped relation over the neck of a bottle or the like, and a substantially planar disk member which is held captive at one end of the ring and adapted to close and seal over and against the container rim. The ring is formed internally with one or more formations such as screw threading or a snap bead arranged for engagement with a complementary formation or formations on the container neck to attach the closure releasably to the container. If desired the free edge of the ring, defining the mouth of the closure, may be formed as a tamperevident band attached by a line of weakening and arranged to be broken away if an attempt is made to remove the closure. Closures of this general kind are often referred to as "composite" closures, a nomenclature which will be used hereafter for brevity.

Composite closures are known in which the ring is moulded from a plastics material such as polyethylene or polypropylene, and the disk is made from pressed metal sheet having suitable protective and/or decorative coatings and carrying on its undersurface a soft gasket compound by which to make an hermetic seal with the container neck. The disk may be fitted to the ring by movement either through the adjacent end of the ring ("top-loaded") or from the remote end of the ring, that is to say, past the tamper-evident band (if provided) and past the screw threading or snap bead; in the latter possibility it is normally referred to as being "bottom- loaded". A top-loaded closure is featured in US patent No. 4694970 (Agents ref. 4321), whereas a bottom-loaded closure is shown in GB patent no. 1477902 (Agents ref. 4333) .

Top-loading may have advantage over bottom-loading by avoiding the necessity of the disk to pass, and possibly damage, the screw-threading or snap bead and any tamperevident band on the ring as the closure is being assembled; in some circumstances top-loading may also facilitate moulding by allowing the ring to be ejected mouth-first from the mould core.

EP patent publication no. EP 0272431A (Agents ref. 4386) discloses a composite closure in which the disk is made from laminated plastics material. This confers some desirable properties to the disk, and, by use of a material capable of forming a seal with a container neck as the bottom layer of the laminate, does away with any need for a gasket-forming compound to be added as a post- operation after the disk has been stamped from a parent sheet.

In EP 0272431A the all-plastics disk has a substantial flexibility particularly at elevated temperatures, and it is bottom-loaded into the plastics ring; top-loading, with its attendant potential advantages discussed above, is impractical with the arrangement shown. The present invention seeks to provide a composite closure, whether twist-off (i.e. with screw-threading) or pry-off (i.e. with a snap bead), which can be top-loaded and yet which may have a high degree of integrity and seal security despite a substantial inherent flexibility of the disk. According to the present invention from a first aspect there is provided a composite closure for closing a container, which comprises an open-ended generally tubular plastics ring member and a substantially flexible plastics disk member, the ring member having one or more formations to attach the closure to the container by cooperation with a complementary formation on the container and having at one end a shoulder extending inwardly to a free edge which defines an orifice, the disk member having a generally transversely extending top portion to overlie the container rim, a generally tubular wall portion outside the top portion and attached thereto at a radius, and a marginal edge portion outside, and attached to, the wall portion and formed with the free edge of the disk member, characterised in that the disk member has been top-loaded through the orifice, and in the fitted condition of the closure the disk and ring members engage one another both at the said radius and at the free edge of the disk member, these locations of engagement being separated by free space radially of the closure but having the marginal edge portion of the disk member extending therebetween.

According to the invention from a second aspect there is provided a composite closure in combination with a container the mouth-defining rim of which has a generally transversely extending top portion, a side wall portion, and a radius joining the two said portions, the closure comprising a substantially flexible plastics disk member and an open-ended generally tubular plastics ring member having at its end adjacent the container rim a shoulder which defines an orifice, the ring member and the container having complementary formations engaged together to attach the closure releasably to the container, and the disk member having a generally transversely extending top portion overlying the said top portion of the container rim, a radius engaging the rim radius, a generally tubular wall portion adjacent the rim side wall portion and attached by the said radius of the disk member to its top portion, and a marginal edge portion attached to the wall portion of the disk member and from there extending outwardly of the closure to the disk member free edge, characterised in that the disk member has been assembled with the ring member by top- loading through the said orifice, and the radius of the disk member is locally pinched against the rim radius by the shoulder of the ring member. Preferred embodiments of the invention will now be described, by way of example only, with reference to the drawings, in which:

Fig.l is a partial side section of a first embodiment of closure with pry-off features, immediately after its application to the neck of a container of a product which is hot-filled;

Fig.2 is a simplified plan view of the disk of the closure shown in Fig.l;

Fig.3 is a partial side elevation of the disk of figure 2;

Fig.4 is a reproduction of Fig.5 of patent publication No. EP 0272431A;

Fig.5 is a perspective view of a modified disk; Fig.6 shows a further modification of the disk; Fig.7 is a view similar to Fig.l and showing a second embodiment of closure with internal screw thread formations; Fig.8 illustrates an apparatus and method for forming an alternative disk; and

Fig.9 shows the disk formed by the apparatus and method of Fig.8. In Figure 1 there is shown the neck 5 of a glass container which is closed by a composite pry-off closure 1 comprising a generally tubular ring 20 and diaphragm disk member 40 both of thermoplastics material. The neck 5 has a continuous external bead 6 the crest 7 of which lies, axially of the closure, between a downwardly and outwardly inclined camming surface 8 above the crest, and a downwardly and inwardly inclined snap-engaging surface 9 below the crest.

The ring 20 has a circumferentially short exterior lug 22 for thumb engagement by the user to pry off the closure, and a peripherally continuous, rounded inner shoulder 24. An open-ended generally tubular skirt 26, which terminates in a snap bead 28 and a continuous tamper-evident band 30 integrally attached by spaced bridges 31, extends downwardly from the enlarged top end of the ring which includes the lug and shoulder as shown. The snap bead has a downwardly and inwardly inclined upper flank which is ^"denoted 21 in Fig.l. The ring is injection-moulded from a suitable thermoplastics polymer material such as polypropylene.

The shoulder 24 has an upper, inwardly and downwardly inclined, frustoconical face 25, a lower, outwardly and downwardly inclined, frustoconical face 16, and a part-circular (in section) inner edge 17 which connects the faces 25 and 16 and which itself defines a circular orifice for the ring 20. At its bottom end the lower face 16 of the shoulder is connected at a radius 18 to a cylindrical inner face 19 of the skirt 26 above the snap bead 28. The upper face is inclined to the horizontal, i.e. to a transverse plane of the closure, by about 45°; the lower face is inclined by the smaller angle of about 30° to the horizontal. The included angle subtended by the edge 17 is accordingly about 75°.

The disk 40 is generally plane and directed transversely of the closure, and is formed by thermoforming and severance from a multilayer plastics sheet. The disk particularly illustrated in Fig.l by way of example (but not to scale) has a 400μ (micrometer) structural upper layer 51 of a normal grade of polypropylene, a lOOμ sealing lower layer 52 of a soft polypropylene, and a 20μ barrier layer 53 of EVOH which separates the upper and lower layers and is bonded to them by thin tie layers (not shown) on either side.

The disk 40 has an initially plane central panel 42 forming its major part; in sequence in the radially outward direction it further comprises a generally tubular, upwardly and outwardly inclined, inner wall 43, a substantially plane annulus 44, a generally tubular, downwardly and outwardly inclined, outer wall 45, and a shallow, upwardly facing, arcuate outer channel 46 which is formed with the free edge 49 of the disk. The channel 46 merges smoothly into the outer wall 45, and the central panel 42, inner wall 43, annulus 44, and outer wall 45 are joi-ned smoothly together by respective radii 70, 71 and 72 to form a downwardly facing inner channel 89 lying concentrically within the outer channel 46. The channels 89,46 together form the peripheral margin of the disk, in surrounding relation to the central panel 42. As can clearly be seen, this margin is generally S-shaped in cross-section.

The outer channel 46 of the disc 40 has a "U" shaped configuration and is reinforced by hollow webs 50 each of which extends from the outer side wall 47 of the channel to its inner side wall 48, so as to bridge the free space which exists between the walls 47,48. As shown in Fig.2, the webs 50 are spaced regularly around the outer channel 46. They are also visible in the side view of Fig.3. The closure of Fig.l is "top-loaded", that is to say, for its assembly the disk 40 is force-fitted downwardly (as shown) through the orifice formed by the ring shoulder 24. The rounded undersurface of the disk outer channel 46 and the frustoconical upper surface 25 of the ring shoulder assist in this insertion. The opposed faces 16,21 of the formations 24 and 28, together with the radius 18 and cylindrical face 19 lying between them, form the ring with an inwardly facing annular channel which is denoted by the reference 32 and within which the disk is then held captive.

The free edge 49 of the disk 40 lies on a radius of the disk which is somewhat greater than the radius of the band 20 at its face 19. Even though after assembly into the ring the disk may adopt a random and possibly tilted position within the groove 32, it has the capability, when the disk is transversely orientated within the ring, of making a tight interference fit with the ring around its whole circumference.

The closure is fitted onto the container neck at a time when the product within the container is still substantially at its filling temperature, typically 85°C. The headspace above the product and the container itself are therefore also at an elevated temperature.

Heat from the container headspace and from the container neck is transmitted to the disk 40 and causes it to soften with a tendancy to shrink. In addition, the disk material may become thinned, and therefore extended laterally, where it is subject to compressive stress. Accordingly, the disk is subject to substantial dimensional variability, and its flexibility, which is already much greater than that of its equivalent metal counterpart, is further increased by the elevated temperature to which it is subjected.

This substantial flexibility and dimensional variability of the disk and the requirement for it to be top-loaded into the ring militate against accurate location of the ring on the container neck during capping and thereafter, and particularly if the surfaces of the container neck are wet there is a substantial danger that the ring will be moved too far down and/or tilted on the container neck by the capping operation. Even if it does not impair sealing or tamperevidence, misplacement of this kind is likely to result in user rejection and for that reason alone is undesirable.

For fitting it to the container the closure is moved vertically downwardly over the neck 5 by downward pressure applied to the ring 20 by a capping machine, thereby initially engaging the tamperevident band 30 and, subsequently, the snap bead 28 with the inclined camming surface 8 of the neck. The band 30 and bead 28 are therefore expanded radially until they pass the crest 7, after which they respectively become snap-engaged with the shoulder 10 and the snap-engaging surface 9 as shown. The overlap shown in Fig.l between the beads 6, 28 represents the degree of interference which then exists between those formations and which is accommodated by residual enlargement of the ring bead.

The disk 40 is randomly located (and possibly tilted) within the channel 32 when the closure is first applied to the container neck. The downward movment of the ring brings the disk into engagement with the container rim so that in relative terms it moves upwardly within the ring until its free edge 49 engages the radius 18 around its whole circumference. At the same time the disk is centred as necessary in relation to the ring, and any inclination of it from a desired horizontal orientation is removed. Further downward movement of the ring then enters the container rim fully within the disk channel 89, and the movement terminates when the radius 72 of the disk becomes pinched between the radius 13 of the rim and the rounded free edge 17 of the ring shoulder 24 as illustrated.

From Fig.l the engagement of the disk 40 and the ring 20 and their cooperation with the container neck 5 will be apparent. It will be seen that the disk engages the ring at two spaced locations. The first of these locations is radially the outermost one and occurs where the free edge 49 of the disk engages the ring radius 18. The second, innermost, location occurs at the engagement of the ring free edge 17 with the disk radius 72 as mentioned in the previous paragraph. During capping, when the ring is moving downwardly in relation to the disk, the engagement at the outermost location occurs slightly before the engagement at the innermost location. Together with the tight interference fit of the free edge 49 with the ring this ensures that the channel 46 is compressed downwardly and inwardly by the free edge 49 in such a way as to establish close engagement of the disk and the container at their respective radii 72,13 in advance of the engagement of the ring radius 17 with the disk at the innermost location of engagement. The webs 50 reinforce the channel 46 against the compressive forces, so as to allow it to undergo a small degree of controlled but resilient deformation.

The engagement which occurs between the ring 20 and the disk 40 at the innermost location after capping is of particular importance to the present invention. It will be seen from Fig.l that it is localised in extent and so located that the resultant force R between the two members is substantially normal to the external radius 13 of the container rim 11 and passes through that radius. With an inclination of about 18° to the vertical for the camming surface 8, Applicants have found that the resultant R should preferably lie within the range 30° to 70°, especially 40° to 55°, to a transverse plane (i.e. to the horizontal as shown) . Furthermore, the lead-in surface 25 of the ring should be substantially parallel to the resultant force R or it should lie at a small

(e.g. 5°) angle in the vertical direction in relation to it, and the minimum spacing of the surface 25 from the resultant force should be approximately 2mm.

From the foregoing it will be understood that at the innermost location of engagement between the ring 20 and the disk 40, the disk is pinched against the glass finish of the container at an angle which is inclined substantially to the horizontal. This engagement accordingly determines the vertical position of the ring on the container neck, allowance being made for any thinning of the disk material in response to the compressive forces involved. Additional resistance against downward movement of the ring on the disk and the container may be provided by the outer channel 46 of the disk, reinforced by the ribs 50. Some camming movement of the disk free edge 49 upwardly and inwardly along the lower surface 16 of the shoulder 24 may occur during this time, thereby further enhancing the engagement of the disk with the container at their respective radii 72,13.

Applicants have found that if the angle of the resultant force R to the horizontal is more than 70°, difficulty may be experienced in top loading the disk into the ring in the assembly of the closure. On the other hand, angles of the resultant force of less than 30° to the horizontal may be insufficient to ensure that the ring cannot drop locally or overall beyond its required position.

In addition to determining the vertical position of the ring 20 on the container neck 5 as described above, the pinched engagement of the ring at the innermost location (that is, against the external radius 13 of the container rim) is the primary site at which a desired hermetic seal is created between the ring and the container. The seal can best be regarded as being centred at the resultant R of the engagement forces in that locality, although it should be appreciated that the location of sealing may shift somewhat in relation to the container rim. Furthermore, and as is illustrated at 40A in Fig.l, when the product cools after filling and a partial vacuum is created in the container headspace, additional sealing may occur where downward doming of the central panel 42 of the disk brings it into contact with the inside radius 14 of the container neck.

The disk 40 should be strong enough to withstand the internal and external forces encountered during capping and afterwards, and yet be sufficiently flexible to conform to any non-planar and surface irregularities presented by the container. Flexibility can be defined in terms of the reciprocal of the product of the elastic modulus and the cubed thickness of the material. For example, steel having a thickness of 0.17mm (0.007 inches) and an elastic modulus of 205 GPa has a resultant flexibility of 0.993 GPa^" mm The elastic modulus and flexibility of a variety of materials are shown in the table which follows. The modulus is given for a nominal temperature of 90°C. It is dependant upon the particular formulation of the polymer, and figures are given for different grades of polypropylene (PP) , polyvinylchloride (PVC) , and polyethylene terephthalate (PET) .

Material Elastic Modulus Flexibility (GPa) (GPa^-1 mm^"3)

Steel (.17mm) 205 0.993

PP .4mm 0.2 78.1

PP .4mm 0.5 31.3

PVC .4mm 0.2 78.1

PVC .4mm 0.3 52.1

PET .4mm 0.4 39.2

PET .4mm 0.8 19.5 1 The overall flexibility of the disk should be no less than 5 GPa^"1 mm^"3. Furthermore, for adequate strength and resistance to rupturing the disk material should be at least .25mm (0.01 inches) thick.

Preferably, the flexibility of the disk will be from 15 to 90 GPa^"1 mm^"1, and its thickness will be at least about 0.3mm (0.012 inches) .

The upper layer 51 of the insert disk 40 can be formed of a variety of thermoplastic materials. These will generally be inherently stiffer than the material of the lower layer 42 and can be used with a greater thickness, preferred ranges of their elastic modulus and thickness being:- elastic modulus 800 -3000 Mpa (N/mm²) ) thickness .01-.04" (0.25 - 1mm)

Suitable materials for the upper layer include polyesters such as polyethylene terephthalate (PET) , acrylates, polyamides, polypropylenes, high-density polyethylene, and polyvinyl chloride. The material used should have softening and melting temperatures higher than those of the lower layer.

The material of the lower layer 52 is preferably one which will soften, if appropriate, at or below its elevated temperature during capping, for example 85 - 90°C. Preferred ranges for its elastic modulus and thickness are:- elastic modulus 20-100 Mpa (N/mm^2') thickness .001-.012" (.025-.3mm) Linear low density polyethylene, thermoplastic elastomers and soft grades of polypropylene are particularly suitable for the lower layer. Typical materials for the barrier layer 53 include ethylene vinyl alcohol (as described) , and polyvinylidene chloride. Metal foil or a deposited metal film may also be used for some applications. Furthermore, the barrier layer (if provided) may be located on the exterior of the disk instead of being used as an intermediate layer as shown.

To remove the closure the consumer presses up on the tab 22 in relation to the container. In known manner for composite closures the ring 20 first moves upwardly alone in relation to the container and the disk, so disengaging the snap bead 28 from the container and severing the tamper-evident band 30 at the bridges 31. The bead 28 subsequently comes into engagement with the underside of the outer channel 46 of the disk, so forcing the disk off the container rim and allowing the ring and disk to be removed together. This two-stage removal operation reduces the maximum force which the user must exert, and may be particularly desirable if a substantial vacuum exists in the container headspace.

Reference is now made to Fig.4 which is a reproduction of Fig.5 of EP 0272431A discussed in the introduction to this specification, when suitably renumbered. In a similar arrangement to that of the disk 40 of Figs. 1 to 3, the all-plastics insert disk of Fig.4 has a downwardly facing annular channel (89) in which the rim (11) of the container is received in sealing relationship when the closure has been fitted. Moreover, the outer wall (45) of the disk channel (89) is then urged by the closure ring (20) against the outside surface of the container rim. The insert disks 40 of EP 0272431A and the present application differ especially in their arrangements and in the manner in which they are engaged by the closure rings 20. In Fig.4 of EP 0272431 the free edge 49 is formed on a short outturned end portion 100 of the disk, and the ring engages the disk over the whole of its outer wall 45 plus the portion 100 (including the free edge 49) in addition. The inside wall 43 of the disk is similarly engaged by the ring over its whole length, and because of the substantial areas of contact between the ring, disk and container it can be expected that the forces which the user must generate to remove the closure will be at an undesirably high level. This is despite arrangement of the closure to provide a two-stage removal operation as mentioned in the penultimate paragraph. In contrast, in Fig.l of the present application the engagement of the ring with the disk occurs at two localised areas which are separated from one another by the free-standing and resilient marginal channel 46. Accordingly, the forces required by the user for closure removal are substantially reduced.

Fig.5 shows a modified disk 40 which is most suitable for large containers sealed under vacuum, or small containers which have an elevated internal pressure such as might be generated by a carbonated product. In this modification the central panel 42 is reinforced against vertical distortion by radially extending, hollow reinforcing ribs 60 arranged in the form of a cross. As shown, the upper surfaces 61 of the ribs are coplanar with the upper surface of the annulus 44. If desired, ribs such as the ribs 60 may be used in conjunction with webs 50 which reinforce the outer channel 45 as described above.

Fig.6 illustrates a further modification of the insert disk 40, in which the central panel 42 of the disk incorporates an oxygen indicator 61 to indicate the presence of undesirable oxygen in the container headspace. Preferably the indicator is inert until the closure has been fitted to the container, and is then activated (and so made capable of indicating the presence of oxygen) by controlled exposure to an intense source of appropriate radiation, for example ultraviolet light. For that purpose, and depending upon the position of the indicator on or within the disk material, one or more of the layers of the disk may be transparent to the radiation used.

The indicator 61 is preferably printed on the upper surface of the lower layer 52 of the disk, so as to be located within the disk materia. It may be a partial or an overall coating, or it may convey information as shown. Amongst the suitable materials for the indicator are ferrous sulphate, ferrous hydroxide and methylene blue microencapsulated in a UV-sensitive polymer.

Fig.7 shows a screw closure forming the second embodiment of the invention. Again the closure comprises a plastics ring and a multilayer plastics disk which is top-loaded into the ring. For ease of comparison the same reference numerals as before are used, wherever appropriate, to indicate corresponding or analogous parts. The closure 1' and its associated container neck 5' differ from the corresponding items of Fig.l in the following respects:- a) the ring 20' has a screw thread 28' for engagement with a complementary screw thread 6' of a container which is of polyethylene terephthalate (PET) ; b) the outer surface of the container neck 5' above its screw thread 6' is cylindrical rather than downwardly and outwardly inclined; c) The lower face of the inwardly facing channel 32' in which the disk 40' is held captive is provided by a specially provided continuous bead 80 with concave upper surface 81; d) The container neck has a specially provided bead 82 for engagement by the tamperevident band 30', which in this embodiment is formed of peripherally spaced independent tabs 83; and e) The outer channel 46' of the disk has no reinforcing webs but instead has its outer and inner side walls vertical and spaced more closely apart. Except that it is rotated rather than moved axially for removal, the performance of the closure of Fig.7 for assembly and capping is essentially the same as that of Fig.l. In particular, the disk 40' is top-loaded into the ring 20' for assembly, and after capping the disk is engaged by the ring at two spaced locations, one at its free edge 49' and the other adjacent the outside radius 13' of the container neck 5'.

If desired, reinforcing structures such as the webs 50 and ribs 60 of Figs.l and 5 can be provided for the closure of Fig.7. Likewise in Fig.l the rigidity of the outer channel 46 can be further increased by making it radially tighter in the manner of the channel 46'. hilst it is preferred for the disks 40, 40' of the described embodiments to be formed by a thermoforming and cutting operation performed on a multilayer sheet, other methods of forming the disks are possible. Fig.8 shows a method of forming a disk 130 by injection-moulding two different polymers sequentially in a mould, Fig.9 showing the disk formed by this method.

In Fig.8 a two-piece mold 140 includes a lower mold section 141 and an upper mold section 142. The lower mold section 141 includes an annular cavity 144. With the two-piece mold 140 in its fully closed position, the lower surface 145 of upper mold section 142 forms the upper surface of annular cavity 144 and no cavity 146 or clearance 143 exists. The annular cavity 144 is then injected with a soft material capable of forming a seal with a container neck, for example a soft grade of polypropylene. This material is allowed to cool and set to form an annular sealing ring 132.

After the material in cavity 144 solidifies, the lower mold section 141 is retracted through the distance 143 to create a second mold cavity 146 as shown. This cavity is then injected with a second themoplastic material to form the main body 131 of the disk. On cooling this material bonds to the material of the sealing ring 132 to form the complete disk 130.

The invention has been particularly described in relation to closures which are wholly of thermoplastics material. Nevertheless, and as previously indicated, the invention also extends to closures of which, in addition to thermoplastics material, the disks have one or more metal layers not contributing significantly to the rigidity of the disk. Also, the invention may be applied to the closing of containers onto products which are cold-filled and/or of which the headspace is substantially at atmospheric pressure.

Claims

CLAIMS :

1. A composite closure for closing a container, which comprises an open-ended generally tubular plastics ring member (20,20') and a substantially flexible plastics disk member (40,40'), the ring member having one or more formations (28,28') to attach the closure to the container by cooperation with a complementary formation (6,6') on the container and having at one end a shoulder (24,24') extending inwardly to a free edge (25,25') which defines an orifice, the disk member having a generally transversely extending top portion (44) to overlie the container rim, a generally tubular wall portion (48) outside the top portion and attached thereto at a radius (72), and a marginal edge portion (46,46') outside, and attached to, the wall portion and formed with the free edge (49,49') of the disk member, characterised in that the disk member (40,40') has been top-loaded through the orifice, and in the fitted condition of the closure the disk (40,40') and ring (20,20') members engage one another both at the said radius (72) and at the free edge (49,49') of the disk member, these locations of engagement being separated by free space radially of the closure but having the marginal edge portion (46,46') of the disk member extending therebetween.

2. A composite closure according to claim 1, characterised in that the free edge (49,49") of the disk member (40,40') is received in an inwardly facing annular groove (32,32') formed in the ring member (20,20') .

3. A composite closure according to claim 2, characterised in that the top end of the groove (32,32') is defined by the said shoulder (24,24') of the ring member (20,20' ) .

4. A composite closure according to any preceding claim, characterised in that the disk member (40,40') is an interference fit in the ring member (20,20') .

5. A composite closure according to any preceding claim, characterised in that by virtue of the engagement of the ring member (20,20') and the disk member (40,40') at the two locations of engagement, in the fitted condition of the closure the free edge (49,49') of the disk member is urged downwardly and inwardly.

6. A composite closure according to any preceding claim, characterised in that the marginal edge portion (46,46') of the disk member (40,40') is generally U- shaped and in the form of an upwardly facing channel on the outer wall of which is formed its free edge (49,49') .

7. A composite closure according to claim 6, wherein the marginal edge portion (46,46') of the disk member (40,40') is reinforced by a plurality of bridging webs (50) formed between its inner and outer walls.

8. A composite closure according to claim 6 or claim 7, characterised in that the inner and outer walls of the marginal edge portion (46,46') are generally parallel and spaced closely together.

9. A composite closure according to any preceding claim, characterised in that the disk member (40,40') has a downwardly offset central panel (42) disposed within the top portion (44) and attached thereto by a further generally tubular wall portion (43) .

10. A composite closure according to claim 9, characterised in that the central panel (42) is reinforced by hollow upstanding ribs (60) .

11. A composite closure according to any preceding claim, characterised in that the disk member (40,40') comprises an outer structural layer (51) of a first polymer, and an inner layer (52) of a highly compliant polymer capable of making an hermetic seal with the container.

12. A composite closure according to claim 11, characterised in that the highly compliant polymer is a soft grade of polypropylene.

13. A composite closure according to claim 11 or claim 12, characterised in that the disk member (40,40') includes an intermediate layer (53) of a barrier material between the outer and inner layers.

14. A composite closure according to any claim of claims 11 to 13, characterised in that between two said layers thereof the disk member incorporates an oxygen-sensitive substance (61) for indicating the presence of oxygen in the headspace of a container to which the closure is fitted.

15. A composite closure in combination with a container the mouth-defining rim of which has a generally transversely extending top portion, a side wall portion, and a radius joining the two said portions, the closure comprising a substantially flexible plastics disk member (40,40') and an open-ended generally tubular plastics ring member (20,20') having at its end adjacent the container rim a shoulder (24,24') which defines an orifice, the ring member and the container having complementary formations (28,28' and 6,6') engaged together to attach the closure releasably to the container, and the disk member having a generally transversely extending top portion (44) overlying the said top portion of the container rim, a radius (72) engaging the rim radius, a generally tubular wall portion (48) adjacent the rim side wall portion and attached by the said radius of the disk member to its top portion, and a marginal edge portion (46,46') attached to the wall portion of the disk member and from there extending outwardly of the closure to the disk member free edge (49,49'), characterised in that the disk member has been assembled with the ring member by top-loading through the said orifice, and the radius (72) of the disk member is locally pinched against the rim radius by the shoulder (24,24') of the ring member.

16. A combination according to claim 15, wherein the resultant force at the pinched engagement of the disk member with the rim radius is inclined by between 30° and 70° to a transverse plane of the closure.

17. A combination according to claim 15 or 16, characterised in that the wall portion (48) of the disk member (40,40') is free of engagement by the ring member

(20,20') .

18. A combination according to any claim of claims 15 to 17, characterised in that the ring member (20,20') has a substantially frustoconical lead-in surface (25,25') which is substantially parallel or inclined by a small angle to the resultant force at the said engagement of the disk member (40,40') with the rim radius.

19. A combination according to claim 18, characterised in that the maximum spacing of the lead-in surface (25,25') and the resultant force is approximately 2mm.

20. A combination according to any claim of claims 15 to 19, characterised in that in addition to their engagement at the radius (72) of the disk member (40,40'), the ring and disk members further engage one another at the free edge (49,49') of the disk member, the two locations of engagement being separated by free space radially of the closure, but having the marginal edge portion (46,46') of the disk member extending therebetween, by virtue of its engagement with the ring member the free edge of the disk member being urged downwardly and inwardly.