SCREW CLOSURE WITH CONTROLLED SEAL

Abstract

The invention concerns a plastic closure for fitting on to the neck of a liquid container in positively locking and sealed relationship comprising a head plate (1) provided for covering a container opening and an outer seal (7) which is circumferential along the edge of the head plate (1) and is provided for engagement with the outside of a container neck (20) defining the container opening, and an inner seal (5) which is circumferential within the outer seal (7) and parallel thereto and which is provided for engagement with the inside of the container neck, wherein the outer and the inner seals (7, 5) respectively extend approximately perpendicularly or slightly inclined from an inside (11) of the head plate (1). To provide a closure and also a container having a closure which generally prevent the closure being blown off under a high positive pressure it is proposed according to the invention that the outer seal (7) has a weakened region (6, 6, 6) in at least one circumferential portion so that the outer seal (7) becomes unsealed at a lower internal positive pressure than when the outer seal is of a configuration without the weakened region.

Claims

1. A plastic closure for fitting on to the neck of a liquid container in positively locking and sealed relationship comprising a head plate (1) provided for covering a container opening and an outer seal (7) which is circumferential approximately parallel to the edge of the head plate (1) and is provided for engagement with the outside of a container neck (20) defining the container opening, and an inner seal (5) which is circumferential within the outer seal (7) and parallel thereto and which is provided for engagement with the inside of the container neck, wherein the outer and the inner seals (7, 5) respectively project from an inside (11) of the head plate (1) in the direction of the container neck to be covered by the head plate, characterised in that the outer seal (7) has a weakened region (6, 6, 6, 16) in at least one circumferential portion, wherein the configuration of the closure is such that the outer seal yields in the weakened region (6, 6, 6, 16) at a lower internal positive pressure than without the weakened region, in particular yields at a lower internal positive pressure than in the remaining regions of the outer seal.

2. A plastic closure according to claim 1 characterised in that it is in the form of a screw closure, wherein the screw closure (100) has a head plate (1) and a cylindrical cap skirt (2) with a female thread (3) which define an axis (50) of the closure, wherein the outer and inner seals are in the form of webs which extend circumferentially in an annular configuration at a spacing relative to the cap skirt and parallel thereto and the weakened portion is preferably restricted to an angle sector (a) measured with respect to the axis.

3. A screw closure according to claim 1 characterised in that it has a sealing region which is an axial region of the outer seal of constant inside diameter, which at least partially includes the central third of the axial length of the outer seal and corresponds at maximum to the axial length of the outer seal.

4. A screw closure according to claim 1 characterised in that the weakened region (6, 6, 6, 16) is formed by a groove (6) or rib (6) which extends on the inside surface of the outer seal and which extends on the inside of the outer seal over the axial extent of the sealing region of the outer seal.

5. A screw closure according to claim 2 characterised in that the groove (6) or the rib (6) extends substantially axially and is of a cross-section of less than 0.05 mm.sup.2, in particular less than 0.02 mm.sup.2 and for example is of a width and a depth of 0.1 mm each.

6. A screw closure according to claim 1 characterised in that the weakened region (6, 6, 6, 16) comprises a circumferential portion of the outer seal, that is axially shortened in the angle sector (a).

7. A screw closure according to claim 4 characterised in that the axial length of the shortened circumferential portion is less than of the axial length of the outer seal outside the weakened region (6, 6, 6, 16).

8. A screw closure according to claim 1 characterised in that the weakened region (6) comprises a circumferential portion of the outer seal (7) with a wall thickness which is reduced in relation to the rest of the outer seal (7), wherein the outer seal (7) in the weakened region (6) thereof is of the same internal radius as the outer seal (7) elsewhere but is of a smaller external radius.

9. A screw closure according to claim 5 characterised in that the reduced wall thickness of the outer seal in the weakened region (6) extends axially over at least a part of the central axial third of the length of the outer seal and is less than half of the wall thickness outside the weakened region, wherein the extent of the weakened region (6) in the circumferential direction is preferably restricted to preferably a circumferential angle of between 20 and 90.

10. A screw closure according to claim 8 characterised in that the weakened region of reduced wall thickness extends axially from a free axial end at least into the upper axial third, with respect to the axial extent of the outer seal outside the weakened region.

11. A screw closure according to claim 1 characterised in that a portion (14) in the form of an annular disk of the head plate (1) between the outer and inner seals defines an axial abutment surface (4) for the end face (24) of a container mouth opening and the maximum outside diameter of the inner seal (5) is provided at an axial spacing of between 0.4 and 1.0 mm from the abutment surface.

12. A screw closure according to claim 1 characterised in that a circumferential groove is provided in the internal surface (11) of the head plate at the transition from the portion (4) of the head plate (1), that is in the form of an annular disk, to the inner seal (5).

13. A screw closure according to claim 1 characterised in that the inner seal (5) is of an axial length of at least 2 mm with an end portion which conically tapers from its maximum diameter towards its axially free end.

14. A screw closure according to claim 1 characterised in that the maximum outside diameter of the inner seal is greater by at least 1.5 mm than its maximum inside diameter.

15. A screw closure according to claim 1 characterised in that the screw closure comprises polyethylene and the wall thickness of the head plate within the region embraced by the outer seal is at a maximum 1.2 mm.

16. A container for liquids having a container neck on which a plastic closure is fixedly and sealingly fitted, characterised in that it has a plastic closure according to claim 1.

17. A container according to claim 16 characterised in that the container neck has a male thread and the plastic closure is a screw closure.

18. A container according to claim 16 or claim 17 characterised in that the maximum external radius of the inner seal is greater by 0.3 to 0.7 mm than the nominal internal radius of the container neck at the respective position.

19. A container having a screw closure according to claim 1 characterised in that a constant internal radius of the outer seal, insofar as same comes into sealing contact with the outside (22) of the container neck (20), is 0.3 to 0.7 mm smaller than the nominal constant external radius of the container neck (20) in the region of the sealing contact with the outer seal.

Description

[0044] Further advantages, features and possible uses of the present invention will be apparent from the description hereinafter of preferred embodiments and the accompanying Figures in which:

[0045] FIG. 1A shows a section containing the axis of a closure through a screw closure fitted on to a bottle neck in accordance with a first embodiment of the invention, wherein the view is limited to the region of the seals and shows a normal portions of the outer seal,

[0046] FIG. 1B shows a section perpendicular to the axis of the closure in FIG. 1A corresponding to section line B-B,

[0047] FIG. 2 shows a section corresponding to FIG. 1A of a closure on a container under an increased pressure,

[0048] FIG. 3A shows a section through the portion diametrally opposite to the portion shown in FIG. 1A of the same closure as shown in FIG. 1A with an outer seal weakened in a segment,

[0049] FIG. 3B shows a section along line B3-B3 in FIG. 3A,

[0050] FIG. 4 shows a view corresponding to FIG. 3A with an additionally illustrated contour of the outer seal outside the weakened region,

[0051] FIG. 5A shows a plan view of a portion of the internal surface of an outer seal according to a further embodiment, having a recess in the sealing region,

[0052] FIG. 5B shows a horizontal section through a closure as shown in FIG. 5A, the section plane extending through the recess and the section showing only a portion of the closure on a bottle neck,

[0053] FIG. 6A shows a plan view of a portion of the internal surface of an outer seal according to a further embodiment, having a projection in the sealing region,

[0054] FIG. 6B shows a horizontal section through a closure as shown in FIG. 6A, the section plane extending through the projection and the section showing only a portion of the closure on a bottle neck,

[0055] FIG. 7A shows a section similar to FIG. 1A of a further embodiment,

[0056] FIG. 7B shows a horizontal section through a closure as shown in FIG. 6A, the section plane extending through the weakened region of the outer seal and the section showing only a portion of the closure on a bottle neck, and

[0057] FIG. 8 for providing a better overview shows a cross-section through the complete closure as shown in FIGS. 1 and 3.

[0058] FIG. 1 shows an axial section through the edge of a container neck with a closure 100 fitted thereon. The container neck is described hereinafter as a bottle neck and shows the contour of a bottle neck edge of a PET bottle with a 30 or 43 mm thread.

[0059] The inner seal 5 is shown here overlapping with the internal surface of the bottle neck 20, which however is only intended to indicate that the external surface of the inner seal, in particular the bead 5 provided on the outer surface, bears with elastic prestressing against the internal surface of the bottle neck 20, as is also shown in FIG. 2, FIG. 2 additionally showing a head plate 1 which is bulged up by an increased internal pressure. The increased pressure also provides that the conical outside surface between the maximum diameter of the bead 5 and the lower free end of the inner seal 5 is acted upon by the increased internal pressure so that, as from a certain internal pressure, the inner seal 5 or its outwardly projecting bead lifts off the internal surface of the bottle neck 20 and thus allows the pressure to escape into the region between the outer seal 7 and the inner seal 5.

[0060] The state shown in FIG. 2 corresponds to a situation in which the inner seal 5 is lifted off and tilted to such an extent that it is lifted off the internal surface 22 of the bottle neck and is now non-sealing. The rounded configuration provided in accordance with usual standards at the inner upper edge of the bottle neck in turn contributes to the inner seal at least locally losing sealing contact with the bottle neck as from a certain pressure.

[0061] FIG. 1A shows a part of the closure 100 having a head plate 1, a cap skirt 2 with a screw thread 3 and an inner seal 5 and an outer seal 7. When the closure 100 is screwed on to a bottle neck 20 the mouth of the bottle neck 20 is moved between the outer seal 7 and the inner seal 5, more specifically generally until the end face 24 of the bottle neck mouth bears against an abutment surface 4 of the annular portion 14 at the underside of the head plate 1, that is between the two seals 5 and 7.

[0062] The conically inwardly tapering lower portion of the inner seal 5 and the lower portion of the outer seal 7, which portion expands conically or in a rounded configuration, like the rounded configurations at the upper edge of the bottle neck mouth, contribute to the bottle neck 20, when the closure 100 is being fitted in place, being displaced between the inner seal 5 and the outer seal 7 and not compressing a seal which bears against the end face 24 of the bottle neck.

[0063] FIG. 2 shows (once again only as a portion) a head plate 1 which is bulged up under an increased internal pressure so that the internal pressure triggers a lack of sealing integrity of the inner seal 5, wherein the internal spacing between the bead 5 of the inner seal 5 and the inside 22 of the bottle neck 20 is shown on a somewhat exaggerated scale to illustrate the effects which occur. By virtue of the bulging action in respect of the head plate 1 which is also promoted by a smaller wall thickness d of the head plate 1 in the region of the annular portion 14 of the head plate 1 (see FIG. 4) the inner seal 5 has a tendency to tip inwardly, as initially already occurs due to the radially inward displacement of the bead 5 upon engagement with the inner sealing surface of the bottle neck 20. In the region radially within the inner seal 5 the head plate 1 is of a somewhat greater wall thickness D, wherein the different wall thicknesses d, D are not a necessary feature but can simplify or promote the desired overpressure limitation in respect of the closure.

[0064] As an alternative to a reduced wall thickness for the annular portion 14 or in addition a groove can be provided at the transition from the abutment surface 4 and the inner seal 5 on the inside of the head plate 1, which makes the inner part of the head plate 1 with the inner seal 5 even more moveable with respect to the radially outer portion 14, and this makes it even easier for the head plate 1 to assume its bulged configuration and for the inner seal 5 to tilt and axially lift off until it loses its sealing integrity. With a sufficiently high internal pressure also acting on the outside of the inner seal 5, insofar as it does not have an opposite surface acted upon with pressure in the axial direction the bead 5 lifts off at least at some locations from the internal surface 22 of the bottle neck 20 so that the pressure can escape until the bulge in the head plate 1 has correspondingly reversed and the elastic return forces of the inner seal move the bead 5 of the inner seal 5 into sealing engagement with the bottle neck again.

[0065] FIG. 3A shows the same closure as FIG. 1A with the section plane however extending through a weakened region 6 of the outer seal 7.

[0066] In this case the weakened region 6 comprises an optionally axially shortened portion 6 of the outer seal 7, which portion is of a reduced wall thickness and which admittedly is of the same inside diameter as the outer seal 7 in the rest of the region, but is of a markedly smaller outside diameter. FIG. 3B shows a section through the line B3-B3 in FIG. 3A. The inner seal 5 bears against the internal surface 21 of the bottle neck 20 (the overlap of the inner seal 5 with the bottle neck 20 in FIG. 3A is only intended to represent the stress-free state before the inner seal 5 or the bead 5 thereof is pressed inwardly by the bottle neck).

[0067] The upper third of the outer seal 7, adjoining the head plate, is disposed in the region of a radius of curvature at the upper edge of the neck mouth and thus does not come into contact with the bottle neck and the lower third is already radially enlarged in order in that way, when fitting the closure on to a bottle neck, to make it easier for the mouth of the bottle neck 20 to slide into the intermediate space between the two seals 5 and 7. If now the seal 7 is shortened over a certain angle sector which for example can be 30 to half or the entire axial length of the outer seal 7 then in that region there is still only an axially relative short portion of the outer seal 7 in contact with the outside 21 of the bottle neck 20, in which case a relatively slight increased pressure within the outer seal 7 is sufficient to lift that relatively short portion which is still in sealing contact off the outside 21 of the bottle neck 20 and thus cause pressure relief.

[0068] The outer seal 7 of which two end portions are shown in the angle portion illustrated in FIG. 3B is not only axially shortened in the weakened segment within the angle sector but is also replaced by a weakened region 6 which is of reduced wall thickness but which is of the same inside diameter as the inner seal 7 elsewhere. Under normal conditions, that is to say when no or only a slight increased pressure of for example 2 bars prevails in the region between the inner seal 5 and the outer seal 7 the weakened region 6 of the outer seal therefore also bears sealingly against the outside 22 of the bottle neck 20 and provides protection from the ingress of germs prior to first being put to use, that is to say on the way from the filler to the consumer.

[0069] The dimensional relationships between the weakened region 6 of the outer seal 7 are moreover shown once again in FIG. 4 where, in addition to the weakened region 6 shown in section, the contour of the outer seal 7 has also been shown again, as is to be found in the regions of the outer seal 7 outside the weakened region 6. It can also be seen from FIG. 4 that the wall thickness d of the head plate in the region between the inner seal 5 and the outer seal 7 is somewhat smaller than the wall thickness D radially within the inner seal 5.

[0070] FIG. 8 shows the complete closure in the sectional plane in FIGS. 1A and 3A. In this case FIG. 1A corresponds to the region I enclosed in the broken line in FIG. 8 and FIG. 3A corresponds to the region III enclosed in the broken line in FIG. 8.

[0071] In the weakened region 6 on the right-hand side in FIG. 8 the outer seal 7 is axially shortened and reduced in its wall thickness whereby the outer seal 7 is more easily stretchable in the weakened region 6 and yields at a lower internal pressure than would be the case with a uniform configuration of the outer seal 7 with full wall thickness and axial length as in the region I and in the other region.

[0072] FIG. 5A shows a small portion of the head plate 1 with the seal 7 extending downwardly from the head plate 1, FIG. 5A being a plan view on to the internal surface of the outer seal 7, which is normally in sealing contact with the external surface 22 of the bottle neck.

[0073] In this case the internal surface of the outer seal has a small groove-like recess 6 which in the axial direction bridges over the region in which the seal bears in other respects sealingly against the outside 22 of the bottle neck 20. This is diagrammatically shown once again in FIG. 5B in a section passing through the recess 6. For practical purposes it is sufficient if the cross-section of the groove-like recess 6, as can be seen in FIG. 5B, is less than 0.5 mm.sup.2, in particular less than 0.2 mm.sup.2. The approximately semicircular recess 6 in the section in FIG. 5B could for example be of a radius of 0.1 to 0.2 mm.

[0074] FIGS. 6A and 6B represent a further embodiment in which, instead of a recess 6, there is a radially inwardly projecting web or a rib or a projection 6. Even if the wall thickness of the outer seal 7 is constant in the circumferential direction of the outer seal and on both sides of the projection or the rib 6 nonetheless short portions of the inner seal 7 on both sides of the rib 6 are lifted off the external surface 22 of the bottle neck 20, which effectively means that two small recesses 6 of wedge-shaped cross-section are in turn formed on both sides of the rib 6. Here too the rib 6 is of such a size that the cross-section of the recesses 6 formed in that way in total is not more than 0.5 mm.sup.2, preferably less than 0.2 mm.sup.2. It will be appreciated that here too the rib 6 extends in a straight line or curved in the axial direction over the sealing region of the outer seal 7 so that the recess 6 makes a connection of the space between the outer and inner seals with the outside of the bottle neck 20.

[0075] FIG. 7 finally shows yet a further embodiment in which the outer seal 7 has been axially shortened in an angle region so that in the angle sector of the weakened region 16 there is only a very small contact axially between the outer seal 7 or the weakened region 16 and the bottle neck 20 or its external surface 22. It is of such a dimension that, when the head plate assumes the bulging configuration, the outer seal in spite of its proximity to a notional pivot point of the bulged part of the head plate 1 is still displaced sufficiently axially upwardly to open a gas passage.

[0076] The invention is based in substance on two effects, namely on the one hand making use of the upward bulging of the head plate, that occurs at the internal pressure, in order firstly to open the inner seal to such an extent that unwantedly high internal pressure of for example more than 3 bars is passed to the outer seal. Secondly that outer seal is also weakened in an angle sector in such a way that, when acted upon with the pressure exceeding for example 3 bars, it also yields and the pressure can be relieved from the container by gas discharge.

[0077] Those effects are also achieved inter alia by using the material polyethylene, in particular HDPE, for the closure, in conjunction with a wall thickness for the head plate of less than 2 mm, preferably less than 1.0 mm, as well as an inner seal, the bead of which is relatively close to the head plate and provides a sealing effect there and thus upon the movement of the region in question of the head plate at an increased internal pressure is axially displaced sufficiently far.

[0078] The invention also concerns in particular a combination of a container neck or a container with a plastic closure, wherein the maximum outside diameter of the outer seal is between 0.2 and 0.4 mm larger than the corresponding inside diameter of the container neck opening, while the inside diameter of the outer seal is also about 0.2 to 0.4 mm smaller than the corresponding outside diameter of the container neck in the respective angular position. The closure according to the invention is particularly well suitable for containers with cylindrical container necks which are of an inside diameter of 40 or 30 mm but can also be used for smaller closure diameters of for example 28 mm. The above-described embodiments are accordingly adapted in respect of their dimensions to corresponding standardised container necks or bottle necks.

LIST OF REFERENCES

[0079] 1 head plate [0080] 2 cap skirt [0081] 3 screw thread on the closure [0082] 4 abutment surface (internal surface of the head plate between the seals 5, 7) [0083] 5 inner seal [0084] 5 radially projecting region, bead [0085] 6 weakened region [0086] 6 weakened region [0087] 6 weakened region [0088] 7 outer seal [0089] angle sector [0090] 11 internal surface of the head plate [0091] 14 annular portion of the head plate 1 with the abutment surface 4 [0092] 16 weakened region [0093] 20 bottle neck [0094] 21 external surface/outside of the bottle neck [0095] 22 internal surface of the bottle neck [0096] 100 closure