The present invention relates to improved container closure assemblies having a tamper- evident ring.

Current commercially mass-produced beverage containers use threads on the container neck and cap of the continuous, helical type. The threads comprise a single, substantially continuous thread portion on the container neck with a low thread pitch angle, typically less than 5°. The low pitch angle is needed in order to ensure that the cap does not unscrew spontaneously. The low pitch angle also provides the necessary leverage to achieve an air tight compressive seal between the cap and the container neck when the cap is tightened onto the container neck. The low pitch of the helical threads also generally means that existing caps typically need to be rotated through more than 360° to disengage it completely from the container neck. A further advantage of unscrewing through more than 360° is that it provides gradual venting of pressure from inside the container, for example a carbonated beverage container, while the cap is being unscrewed and thereby reduces the risk of uncontrolled gas venting or missiling of the cap. Drawbacks of these low pitch helical threads include the laborious rotation required to remove and resecure the cap on the neck and excessive use of moulding material to form the long helical threads. A further problem is unreliable separation of tamper-evident rings from the cap skirt due to the low pitch angle of the threads. It is possible for the cap to be removed without separation of the tamper-evident ring by carefully and slowly unscrewing the cap whilst working the tamper-evident ring over the retaining flange on the neck.

US-A-20060060555 describes container closure assemblies having an improved tamper- evident ring designed to improve separation of the ring from the cap when the cap is unscrewed from the neck. The improved tamper-evident ring is more difficult to mould and may still be susceptible to tampering. EP-A-1698564, US-A-20010027957 and US-A-4392055 describe container closure assemblies having a tamper-evident ring. A tubular sealing plug on the cap forms a seal with the inner surface of the container neck and is of sufficient length to maintain the seal until the cap is substantially unscrewed and the tamper-evident ring has separated from the cap. These assemblies use conventional, continuous low-pitch helical threads. As a result, separation of the tamper-evident ring is unreliable, and unscrewing can be difficult because of friction between the tamper evident ring and the neck flange before the ring separates. In addition, the length of the sealing plugs and of the threads increases the amount of moulding material needed for the assemblies.

The present applicant has described an improved and safer cap for both carbonated and non-carbonated beverage containers in International Patent application WO-A-9505322. This describes container closure assemblies having multiple-start threads defining a plurality of steeply pitched, substantially continuous helical thread paths for securing the cap on the container neck. The cap can be moved from a fully disengaged to a fully secured position on the container neck by rotation through 360° or less. In order to prevent the cap from spontaneous unscrewing ("backing off) from the fully secured position on the neck, and to maintain the cap in the optimum sealing position, the cap assemblies are also provided with complementary locking elements (hereinafter also referred to as "side catches") on the container neck and on the cap skirt that snap into engagement at the fully secured position of the cap on the neck, and that resist unscrewing of the cap until a predetermined minimum opening torque is applied. Suitable locking elements are described in WO-A-9505322, and in particular in WO-A- 2005058720. The locking elements may cooperate in the fully closed position of the assembly to urge the cap into the sealing position as discussed in more detail in the above-referenced patent applications.

In the assemblies of WO-A-9505322, the threads on the neck or the cap are also provided with mutually engageable elements to block or restrict rotation of the cap in an unscrewing direction beyond an intermediate position when the cap is under an axial pressure in a direction emerging from the container neck, the neck and cap being constructed and arranged to provide a vent for venting gas from the container neck at least when the cap is in the intermediate position. This pressure safety feature prevents the cap from blowing off uncontrollably once unscrewing of the cap from the container neck has started. It thus allows the use of shorter, more steeply pitched or multiple-start threads in the container and cap assembly, thereby rendering the assembly much more elderly- and child-friendly without sacrificing pressure safety.

The assemblies of WO-A-9505322 further comprise a tamper-evident ring attached by frangible bridges to the skirt of the cap, and retained on the neck by a flange on the neck.

WO-A-9721602, WO-A-9919228 and WO-A-2005058720 describe improved versions of the assemblies of WO-A-9505322. WO-A-2007057706 describes assemblies of this type having sealing jaws projecting from the cap instead of a simple sealing plug.

The beverage container closure assemblies exemplified in WO-A-9505322 have short projecting thread segments on the cap and longer projecting thread segments on the container neck. This arrangement is conventional, in part because of the requirements of high-speed injection moulding of the caps, according to which the caps must be "bumped" off a (preferably) one-piece mould mandrel with minimum distortion. WO-A- 03045806 describes similar assemblies in which a smoother neck finish has been achieved by using short thread segments on the neck and longer thread segments on the inside of the cap skirt, with interruptions being provided in the thread segments of the cap to make the caps easier to manufacture.

The above cap assemblies of the present applicant can still permit the cap to be unscrewed slightly without separation of the tamper-evident ring, thereby allowing pressure to be vented from inside the container (e.g. a carbonated beverage container) without separation of the tamper-evident ring. Once the pressure has been vented from the container, it is less difficult to work the tamper-evident ring off the neck without separating the tamper-evident ring from the cap. Thus, a need remains for a still more secure tamper-evident feature.

In a first aspect, the present invention provides a container closure assembly comprising: a container neck having a first screw thread and a radially projecting flange located below said first screw thread for retaining a tamper-evident ring; a cap for said neck, the cap having a base portion and a skirt portion having a second screw thread; said first and second screw threads being mutually engageable to enable a user to secure, remove or resecure the cap into a final sealing position on the neck by rotation of the cap on the neck through less than about 360°; a sealing plug extending from said base portion of the cap inside and substantially concentric with said threaded skirt portion of the cap, for forming a seal against an inside surface of the container neck when the cap is secured on the container neck; and a tamper-evident ring concentric with said cap skirt and frangibly attached to said cap skirt, wherein said tamper-evident ring comprises one or more inwardly projecting retaining elements for retaining the tamper-evident ring under said flange when the cap is unscrewed from the neck; characterized in that said assembly is configured to prevent release of said seal before separation of the tamper-evident ring from the cap skirt when the cap is unscrewed from the container neck for the first time.

More specifically the present invention provides a container closure assembly comprising: a container neck having a first screw thread and a radially projecting flange located below said first screw thread for retaining a tamper-evident ring; a cap for said neck, the cap having a base portion and a skirt portion and a second screw thread on said skirt portion; said first and second screw threads being mutually engageable to enable a user to secure, remove or resecure the cap into a final sealing position on the neck by rotation of the cap on the neck through less than about 360°; a sealing plug extending from said base portion of the cap inside and substantially concentric with said threaded skirt portion of the cap, for forming a seal against an inside surface of the container neck when the cap is secured on the container neck and for maintaining said seal as the cap is unscrewed until a seal release position is reached; and a tamper-evident ring concentric with said cap skirt and frangibly attached to said cap skirt, wherein said tamper-evident ring comprises one or more inwardly projecting retaining elements for abutment against said flange when the cap is unscrewed from the neck to cause separation of the tamper-evident ring from the cap skirt when a tamper-evident-ring separation position is reached; wherein said assembly is configured such that: (i) said tamper-evident ring separation position is reached as or before said seal release position is reached when the cap is unscrewed from the neck, and (ii) said first and second threads are configured to prevent rotation of the cap without vertical movement of the cap relative to the neck when the cap is in the vicinity of the tamper-evident-ring separation position, and wherein said first and second threads define a substantially helical path for said cap skirt as it is unscrewed from the fully sealing position, said helical path having a first pitch in a first region including said fully sealing position and a second pitch steeper than said first pitch in a second region displaced in an unscrewing direction from said first region, where said seal release position is located in said second region of the thread path.

Here and elsewhere in this specification, the term "fully secured position of the cap on the neck" refers to the normal storage and shipping configuration of the assembly when secured on a filled container. The fully secured position is normally the position at which the cap is optimally tightened on the neck for sealing. It may be defined by the presence of one or more thread stops on the container neck and the cap that prevent overtightening of the cap beyond the fully secured position. It may alternatively or additionally be defined by locking elements on the container neck and the cap as described below that click into engagement to retain the cap at the fully secured position to prevent unscrewing from the fully secured position until a predetermined minimum unscrewing torque has been applied.

Here and elsewhere in this specification, references to the angle of rotation required to release the seal between the cap and the neck refer to the minimum angle of rotation from the fully sealed position required for escape of gas from a pressurized container at carbonated beverage gauge pressures of up to about 4.6 bar (69psi) to become detectable. Here and elsewhere in this specification, references to a helical path for the cap skirt refer to the path followed by a point on the cap skirt as the cap is screwed or unscrewed on the neck.

The neck is suitably formed by injection molding of plastic material, such as polyethylene terephthalate (PET). The neck is suitably formed integrally with a container body, such as a blow-molded carbonated beverage container. The neck comprises a tubular portion having an internal surface that is typically substantially cylindrical. The mean internal diameter of the neck may be typical for beverage containers, for example about 1.5 to about 3 cm. In other embodiments the neck has a larger diameter to assist drinking or pouring from the neck, for example a mean inside diameter of from about 3 to about 8 cm, suitably from about 4 to about 6 cm.

The container neck comprises an outside surface that is provided with threads for securing the cap on the neck by relative rotation of the cap and the neck, as described further below. The outside surface of the neck further comprises a circumferential retaining flange (retaining bead) located below the threads for retaining the tamper- evident ring on the neck. Suitably, the retaining flange has a profiled cross-section, whereby at least a radially outer portion of an upper surface of the retaining flange is sloped downwardly, whereas at least a radially outer portion of the lower surface of the retaining flange suitably extends substantially perpendicularly to the axis of the neck. This configuration of the retaining flange reduces stress on the tamper-evident ring during capping, but maximizes the retaining force on the ring during separation. It is to be understood that the term "flange" used herein includes any sort of continuous or interrupted projecting flange extending around the container neck.

The outside surface of the neck suitably also comprises a circumferential support flange located below the retaining flange. The support flange is used to support the container neck during automated filling and sealing operations on a production line. The support flange may also support the tamper-evident ring after the tamper-evident ring has separated from the cap, since the maximum diameter of the support flange is greater than the inside diameter of the tamper-evident band. Suitably, the top of the support flange is located at least about 1mm, for example at least about 2mm, below the bottom of the tamper-evident ring before separation of the ring, so that separation of the ring is clearly visually indicated when the ring drops down onto the support flange.

Here and elsewhere in the present specification, the terms "below" and "lower" refer to positions relatively axially more distant from the opening of the container neck, and thus also more remote from the base of the cap when the cap is secured on the neck. Conversely, the terms "above" and "upper" refer to positions relatively closer to the base of the cap (as measured along the longitudinal axis of the assembly) when the cap is secured on the neck. The cap (closure) is suitably formed integrally in one piece, for example by injection molding or compression molding of a plastic material such as polyethylene. The cap comprises a base and a skirt. The cap has an external surface, which suitably is provided with projections, such as longitudinal ribs on the outside of the skirt, to assist gripping and turning of the cap. The cap has an internal surface. The internal surface of the cap skirt is provided with one or more threads for securing the cap on the neck by relative rotation of the cap and the neck, as discussed further below.

Suitably, the cap is a low-profile cap having an axial height from the top of the base to the bottom of the skirt, but excluding the tamper-evident ring attached to the cap, of from about 10mm to about 15mm. It is an advantage of the present invention that it enables reliable separation of tamper-evident rings from low-profile caps, thereby reducing the total amount of moulding material required for the cap.

Suitably, the container and cap further comprise complementary locking elements on the container neck and the cap that block or resist unscrewing of the cap from the fully secured position on the container neck until a predetermined minimum opening torque is applied. These elements help to prevent backing off of the cap from the sealing position, especially when the closure assembly is used for storage of pressurised materials such as carbonated beverages, and thereby reduce leakage from the sealed assembly. Furthermore, the elements normally provide a positive "click" sound and feel when the sealing position is reached, which helps the user to avoid under-tightening of the cap.

In certain embodiments, the locking elements comprise a longitudinal locking rib on one of the container neck or on the skirt portion of the cap, and a complementary locking ramp on the other of the container neck or the skirt portion of the cap, wherein the locking rib abuts against a retaining edge of the locking ramp when the cap is fully engaged on the container neck. Locking elements of this type are described in detail in WO-A-9118799 and WO-A-9505322. Suitably, the locking projections comprise a first locking projection on the container neck separate from the first thread segments and a second locking projection on the inner surface of the skirt of the closure separate from the second thread segments. Suitably, the said first and second locking projections longitudinally overlap the first or the second thread segments when the closure is in the fully engaged position on the container neck, for example as described in detail in WO- A-2005058720. This overlap between the locking projections and the threads also assists in reducing the total height of the cap for production of low-profile caps having reduced amounts of moulding material. The assemblies according to the present invention further comprise a tamper-evident ring (band) comprising a collar attached to the bottom of the cap skirt by one or more severable connections. The tamper-evident ring and severable connections are generally formed integrally with the cap, for example by injection moulding or compression moulding. The severable connections are suitably in the form of narrow bridges of the moulding material joining the collar to the skirt. The connections may be moulded in one step, or they may be formed in two steps, for example compression moulding to form a continuous junction between the skirt and the collar, followed by cutting (slitting) regions of the junction to leave bridging regions spaced circumferentially around the collar.

The tamper-evident band comprises one or more projections extending radially inwardly from the inside of the collar that are configured to allow the collar to pass over the retaining flange on the container neck without separation from the skirt when the cap is screwed onto the neck for the first time, but that abut against an underside of the flange to resist removal of the collar and cause separation of the collar form the skirt at the severable connections when the cap is unscrewed from the neck for the first time. The projections are suitably moulded integrally with the cap as described above.

In certain embodiments, the radially-inwardly facing projections are generally ramp- shaped projections that comprise a lower surface extending from an inside surface of the collar at a first angle relative to the axis of the band, and an upper surface extending from the inside surface of the collar at a second angle to the axis of the band that is greater than the first angle. In these embodiments, the first angle is typically less than about 45°, for example about 15° to 30°. The second angle is suitably greater than about 60°, for example about 90°. The radially-inwardly facing projections may be solid projections, or they may be flexible fin-like projections anchored to the collar at the bottom of the projections wherein the top of the projections can flex outwardly when the tamper evident ring is fitted over the flange, but abut against the underside of the flange on the neck to block removal of the tamper evident ring from the neck.

Suitably, there is minimal clearance between the top of the radially-inwardly facing projections on the tamper-evident ring and the underside of the retaining flange on the neck when the cap is in the fully secured position on the neck. This minimizes the unscrewing rotation of the cap on the neck that is needed to cause separation of the tamper-evident ring. Suitably, this clearance is from 0 to about 1mm, for example from 0.1 to about 0.5mm, typically from about 0.1 to about 0.3mm. A finite clearance (greater than 0.05mm) may be desirable to avoid premature separation of the ring due to deformation of the cap under pressure from inside the container in use.

The assemblies according to the present invention further comprise a cylindrical sealing plug projecting downwardly from the base of the cap for sealing with an internal surface of the neck. Suitably, the height of the cylindrical sealing plug (that is to say, the maximum distance that the sealing plug extends below the adjacent internal surface of the base of the cap) is from about 1mm to about 5mm, for example from about 2mm to about 4mm, typically about 3mm. The use of such a small sealing plug reduces the amount of moulding material needed to make the cap, and also makes it easier to secure the cap on the neck because friction between the plug and the container neck is only experienced during a short angle of rotation just before the fully secured position is reached. This contrasts with some existing low-pitched closure assemblies that use a larger sealing plug to maintain sealing for a larger angle of rotation. However, the use of a smaller sealing plug presents a challenge in achieving reliable separation of the tamper-evident ring before release of the pressure seal when unscrewing the cap.

Suitably, the sealing plug is an olive sealing plug. That is to say, the plug has a circumferentially projecting radially outer surface having a bulbous shape (when viewed in longitudinal cross-section). The bulbous projection has a substantially smooth, continuous surface and a height suitably from about 10% to about 50% of the radial thickness of the plug. The minimum radius of curvature of the bulbous projection is suitably no less than about the mean radial thickness of the plug. Suitably, the minimum radius of curvature of the bulbous projection is from about 0.5mm to about 1mm. Such olive sealing plugs are relatively tolerant of small axial displacements of the plug, for example caused by doming of the cap base under pressure from inside the container, without loss of sealing effectiveness. The use of an olive sealing plug thereby also allows the seal to be maintained until the tamper-evident ring has separated from the closure skirt during unscrewing of the cap.

Further sealing elements may be present, including but not limited to: (a) a cylindrical sealing skirt depending from the base of the cap intermediate the sealing plug and the threaded skirt, for abutment against the outside of the container neck adjacent to the lip; (b) sealing ribs on the sealing skirt or the threaded skirt (where no sealing skirt is present) for concentrating a sealing force on regions of the neck; and (c) sealing fins for abutment against the top of the container neck. Suitable further sealing elements are described, for example, in WO-A-0242171 and WO-A-2007057706.

Here and elsewhere in this specification, the term "threads" or "thread assembly" refers collectively to the projections extending circumferentially around the container neck and the cap skirt that provide for securing the cap on the neck by rotation. The threads on the neck and the skirt are each made up of one or more "thread segments" spaced circumferentially around the neck and the cap, wherein there is generally one thread segment for each thread start of the assembly. Generally, each of the cap and the skirt has one thread segment per thread start of the assembly, and generally each of the thread segments on the cap is substantially identical and each of the thread segments on the neck is substantially identical. Generally, the thread segments on each of the cap and the neck are uniformly circumferentially spaced around the cap and the neck, respectively. Each of the thread segments may itself be made up of one or more projecting "thread portions" projecting from the neck or the cap and circumferentially and/or longitudinally spaced from the other thread portions making up the thread segment. Suitably, the first and second threads are multi-start threads having four or more thread starts. Suitably, the number of thread segments on each of the neck and the cap is equal to the number of thread starts, and suitably each of the thread segments on the neck is substantially identical and equally circumferentially spaced around the neck, and suitably each of the thread segments on the cap is substantially identical and equally circumferentially spaced around the cap. Suitably there are four to eight thread starts depending on the size of the container neck. In these embodiments, there are four to eight substantially identical first thread segments and four to eight substantially identical second thread segments, respectively, the segments being equally spaced around the neck and skirt, respectively. More suitably, for a standard container neck of 20-30mm internal diameter, there are four thread starts.

The threads allow the cap to be moved from a fully unsecured to a fully secured position on the container neck by a single smooth rotation through about 360° or less, suitably about 180° or less, and more suitably about 90° or less. The amount of rotation needed will depend on the number of thread starts. Most suitably, the cap can be moved from a fully unsecured to a fully secured position on the container neck by a single smooth rotation through about 45° to about 120°. The term "continuous smooth rotation" signifies that the threads follow a continous helical thread path with a pitch less than 90° (i.e. not a stepped path) during said operation of moving the cap from a fully unsecured to a fully secured position on the container neck. The gradient of the helical path may change abruptly, but the gradient remains less than 90°, and in practice less than about 35° throughout the path. Suitably, the threads are steeply pitched screw threads. The use of such steeply pitched threads further assists reliable separation of the tamper-evident band in use. For example, the first and second threads suitably have a mean thread pitch of from about 5° to about 35°, more suitably from about 8° to about 20°, for example about 10° to about 15°. The mean thread pitch (p) is defined as follows: p = arctan (360η/πάα) Where h is the vertical height travelled by the cap relative to the neck when screwing the cap onto the neck from the last fully disengaged position of the threads (i.e. the last position at which the cap can be lifted vertically off the neck) to the fully sealing position, d is the diameter of the radial mid-point of the threads, and a is the angle of rotation in degrees required to screw the cap from the last disengaged position to the fully sealing position.

Suitably, the threads are free-running, which is to say that there is substantially no frictional torque between the thread segments until the fully engaged position is neared, i.e. until the sealing plug comes into frictional engagement with the inside of the neck. One consequence of this is that, for at least part of the thread path, there is normally some "play" between the cap and the neck. That is to say, some rotation of the cap on the neck is possible without vertical displacement of the cap on the neck. This arises because the thread path defined by the second thread segments is wider than the first thread segments in these regions. The present invention seeks to eliminate this "play" of the cap on the neck in the region of separation of the tamper-evident ring from the cap.

The above features of the threads make the assembly especially easy to close by the elderly and infirm, or by children. Conventional, low-pitch threads require multiple turns to secure the cap on the neck. Conventional threads are also not free-running, which means that there is frictional resistance between the threads when screwing and unscrewing the cap that requires applied torque to overcome. Threads that are not continuous helical threads, such as bayonet-type threads, require a relatively complex, stepped manipulation to secure the cap onto the container neck, with the result that the closure is often inadequately secured on the container neck.

Suitably, the first thread comprises a plurality of shorter thread segments circumferentially spaced around the neck, and the second thread comprises a plurality of longer thread segments circumferentially spaced and overlapping around the cap, whereby gaps between adjoining longer thread segments define the thread path along which the short thread segments travel when the cap is secured onto, or removed from, the neck. It will be appreciated that in the assemblies of the present invention, the relative positions of the short and long thread segments on the neck and the cap can be reversed, so that the longer thread segments are on the neck. However, for convenience, in the description that follows only the configuration with the shorter thread segments on the neck will be described. Suitably, the first thread on the container neck comprises four or more short thread segments each extending less than about 45°, for example less than about 30°, around the circumference of the neck, and said second thread comprises four or more longer thread segments each extending more than about 60°, for example more than about 90° around the circumference of the cap.

Suitably, the maximum radial height of the first and/or the second thread segments is from about 0.5 mm to about 3 mm, for example from about 1mm to about 2mm. Such high-profile threads provide additional security by preventing the threads on the neck and the cap from riding over each other, thereby preventing the cap from being worked off the neck by rocking the cap on the neck or by cross-thread unscrewing. Suitably, the assemblies according to the present invention further comprise one or more thread stops on the cap or the neck to block rotation of the cap on the neck in a sealing direction beyond the sealing position. This prevents over-tightening of the cap on the container neck that could damage the thread finish. Suitable thread stops are described for example in WO93/01098 and WO95/05322.

The first and second threads comprise thread elements on the neck and the cap that engage to vertically displace the cap from the neck through a distance sufficient to cause separation of the tamper-evident ring from the cap skirt when the cap is unscrewed from the final sealing position, wherein the angle of rotation in an unscrewing direction required to cause said vertical displacement is less than or equal to the angle of rotation required to release said seal.

Suitably, the angle of rotation required to cause said vertical displacement to separate said tamper-evident ring is from about 10° to about 25°, and/or said angle of rotation required to release said seal is from about 15° to about 35°, provided of course that the latter angle is greater than the former angle, suitably greater by at least about 5°. Furthermore, the vertical displacement of the cap from the fully secured position on the neck required to separate the tamper-evident ring is suitably from about 0 to about 1mm, for example about 0.5mm to about 1mm.

The first and second threads define a substantially helical path for the cap skirt as it is unscrewed from the fully sealing position, said helical path having a first pitch at said fully sealing position and a second pitch at a second position at which the seal is released when unscrewing the cap, wherein said second pitch is steeper than said first pitch. The cap skirt is constrained by the threads to follow the steeper-pitched path when it is rotated through said second position. Suitably, the first pitch is from about 0° to about 10° and the second pitch is from about 15° to about 30°.

Suitably, the first thread comprises one or more first thread segments each having an upper surface and a lower surface, and the second thread comprises one or more second thread segments, wherein adjoining second thread segments abut against the upper surface and the lower surface of the first thread segments to prevent rotation of the cap without vertical movement of the cap when the cap has been unscrewed sufficiently to bring the tamper-evident ring into abutment with an underside of the retaining flange, that is to say at or in the vicinity of the tamper-evident-ring separation position. In certain embodiments, the seal release position is also located in said second region of the thread path. As already noted, the tamper-evident-ring separation position is also located in said second region of the thread path. This has the advantage that internal pressure from inside the container tends to force the cup upwards more strongly in the steeply pitched region of the thread path, thereby driving separation of the tamper- evident ring.

Suitably, the longer thread segments (i.e. the second thread segments on the cap in the embodiments described here) are made up of a lower, first portion and an upper, second portion, said portions being separated by a gas venting groove. The upper surface of the first portion abuts against the underside of the short, first thread segments at the sealing and seal release positions. The second portion typically does not abut against the first thread segments at the sealing position, but is configured to come into abutment with the upper side of the first thread segments at or in the vicinity of the tamper evident seal release position and/or the sealing release position, to block play of the cap on the neck at these positions.

In certain embodiments, the short thread segments abut against a first region of an upper surface of said longer thread segments at the fully sealing position, said first region of said upper surface having a first, low pitch; said longer thread segments have a second region adjacent to said first region, wherein the pitch of the upper surface of said thread segments in said second region is higher than said pitch in said first region; wherein said seal not released until said shorter thread segments have been rotated into abutment with said second region of the longer thread segments, and wherein an uppermost region of an adjoining longer thread segment abuts against an upper surface of said shorter thread segment to force a lower surface of said shorter thread segment into abutment with said upper surface of said second region of the first longer thread segment at said position where said seal is released. In other words, the second portion of the second thread is configured to force the first thread segment to follow the relatively steep helical thread path defined by the said second region of the upper surface of the adjacent second thread segment at or in the vicinity of the tamper evident ring release position. There is no play of the cap on the neck possible at this position. Otherwise put, the thread path defined between adjacent second thread segments is narrowed at the tamper evident ring separation position so as to reduce or eliminate play between the first thread segments and the second thread segments at this position. In the narrowed region, the second thread segments abut both the upper side and the lower side of each first thread segment to substantially eliminate play in the cap and to force the first thread segments along the steeply pitched part of the helical path.

Suitably, the container closure assembly according to the present invention further comprises mutually engageable elements on the neck and the cap to block or restrict rotation of the cap in an unscrewing direction beyond an intermediate position when the cap is under axial pressure in a direction emerging from the container neck.

In these embodiments, suitably the first and second screw threads are constructed and arranged to permit axial displacement of the cap relative to the neck at least when the cap is at the intermediate position, and the engageable elements are adapted to engage each other when the cap is axially displaced in a direction emerging from the neck, for example by axial pressure from inside the pressurized container. Suitably, the mutually engageable elements are constructed and arranged not to mutually engage each other when the cap is axially displaced in a direction inwardly towards the neck at the intermediate position, for example when the cap is being screwed down onto the container neck.

Suitably, the mutually engageable elements comprise a step or recess formed in the lower surface of one of the second screw thread segments to provide a first abutment surface against which a second abutment surface on one of the first screw thread segments abuts to block or restrict rotation of the cap in an unscrewing direction at the said intermediate position when the cap is under axial pressure in a direction emerging from the container neck, but which allows easy removal of the cap when the container is not unduly pressurized.

In certain embodiments of this type, the second thread segment comprises a first thread portion having a first longitudinal cross section and a second thread portion having a second longitudinal cross section narrower than the first cross section, whereby the first thread segment abuts against the second thread portion. The relatively broad first cross section is preferably adjacent to the circumferentially overlapping region of the second thread segments, resulting in a relatively narrow thread gap in that region.

In a second aspect, the present invention provides a beverage container sealed with a container closure assembly according to the present invention. Suitably, the container according to this aspect of the invention contains a carbonated beverage. The present invention is applicable to a wide variety of containers, including containers for both carbonated and non-carbonated beverages. The present invention is applicable to molded thermoplastics containers, and also to glass or metal containers

An embodiment of the present invention will now be described further, by way of example, with reference to the accompanying drawings, in which: Fig. 1 shows a partial longitudinal cross-section through an assembly according to the present invention with the cap part-way secured onto the neck;

Fig. 2 shows the assembly of Fig. 1 with the cap fully secured on the container neck. In this figure, the neck is shown in elevation and the cap is shown in longitudinal cross- section.

Figs. 3a-3f show a plane development of the threads on the neck and the cap with the cap at the fully secured position in Fig. 3a and progressively more unscrewed positions in Figs 3b to 3f. Referring to Figs. 1 and 2, this embodiment is a container closure assembly especially adapted for a carbonated beverage container. The main features of this assembly resemble those of the assembly described and claimed in our International Patent Application WO-A-2005058720 and our earlier applications referenced therein. The assembly according to this embodiment includes a container neck 10 of a container for carbonated beverages, and a cap 11. The internal diameter of the neck is about 24mm. Both the container neck and the cap are formed from plastics material, but the container neck could also be made from glass. The container is preferably formed by injection moulding and blow moulding of polyethylene terephthalate in the manner conventionally known for carbonated beverage containers. The cap is preferably formed by injection moulding of polyethylene.

The container neck has a rounded lip 12 to enhance the user-friendliness of the neck. A circumferential retaining flange 13 is provided on the container neck 10 for retaining the tamper-evident ring. The retaining flange has a tapered upper surface 14 and a lower surface 15 that extends substantially perpendicularly to the longitudinal axis of the assembly. A larger flange 16 extends from the container neck below the retaining flange 13 and is used for handling and filling of the container. The cap comprises a base 18 and threaded outer skirt 20. The height of the cap (excluding the tamper-evident ring) is about 12mm, hence it can be seen that this is a very low-profile cap. A cylindrical olive sealing plug 22 projects downwardly a distance of about 3mm from the base. The cap 11 further comprises a cylindrical sealing skirt 24 that is substantially concentric with the sealing plug. The sealing plug 22 and the sealing skirt 24 are concentric with the threaded skirt 20 and located inside the threaded skirt 20 for sealing abutment against opposite sides of the container neck proximate to the container lip 12.

The sealing plug 22 is an olive sealing plug having a bulbous projection 23 on the radially outer surface thereof that forms a seal against the inside surface of the container neck in use, as shown in Fig.2. The sealing skirt 24 has a concave region 25 on its radially inner surface. Two small circumferential sealing ribs 26 of substantially triangular cross-section project inwardly from the concave region. The circumferential sealing ribs on the sealing skirt have a substantially equilateral triangular cross-section, and are approximately 150 micrometers high, in the unstressed state. However, they deform when pressed against the harder material (glass or PET) of the container neck to form the pressure-tight seal. The small dimensions of the sealing ribs 26 enable a pressure-tight seal to be achieved without substantial force having to be applied to the sealing skirt to form the seal.

The container closure assembly according to this embodiment also comprises a tamper- evident ring that is initially formed integrally with the threaded outer skirt 20 of the cap 11 and joined thereto by frangible bridges 28. The tamper-evident ring comprises a collar 30 joined to the frangible bridges 28 and a plurality of integrally formed, flexible, radially inwardly pointing retaining tabs 32 situated in windows 33 formed in the collar 30. An upper surface 33 of the retaining tabs 32 abuts against the lower surface 15 of the retaining flange to retain the tamper-evident ring on the neck when the cap is unscrewed for the first time. The structure and operation of the tamper-evident ring feature are as described and claimed in our International Patent Application W0-A- 9411267. In the fully closed and sealing position shown in Fig. 2 there is a very small clearance of only about 0.2mm between the top 15 of the flexible tabs 32 and the lower surface 15 of the retaining flange, whereby only minimal vertical movement of the cap is needed to cause separation of the tamper-evident ring. On the container neck 10 there is provided a four-start first screw thread made up of four first thread segments 36, as shown in Figure 2 and in hatched lines in the thread developments of Figs. 3(a)-3(f). The first thread segments 36 are short thread segments each consist of a single thread element extending about 33° around the neck and having a lower surface 37 with relatively low pitch of about 6° and an upper surface 38 with intermediate pitch of about 13.5°. The first thread segments present a substantially trapezoidal cross-section along the axis of the neck. The use of short thread segments on the container neck results in a more user-friendly neck finish that makes drinking directly from the neck more comfortable for a consumer. It also reduces the amount of moulding material needed to make the neck. However, it will be appreciated that the configuration of the threads could be reversed to locate the short thread segments on the cap skirt, if so desired. The average pitch of the threads is about 10.5°. The cap can be rotated from a fully engaged to a fully disengaged position on the neck by rotation through about 106°.

The cap skirt 20 is provided with a second screw thread formed from four elongate second thread segments. Each of the second thread segments is made up of first and second radially spaced elements 40,41 separated by a gas venting gap 42. Further gas venting gaps could be provided by interrupting the longer thread elements 40. Each of the elements 40,41 has a lower thread surface and an upper thread surface as described further below. (The term "upper" in this context means closer to the base of the cap, i.e. further from the open end of the cap). The upper and lower surfaces are profiled in longitudinal cross-section to give the thread elements 40,41 substantially trapezoidal side edges that are complementary to the side edges of the first thread segments 36. A substantially continuous, approximately helical thread path for the first thread segments is defined between adjacent second thread segments, as will be described further below.

A feature of this assembly is the variable pitch of the upper surfaces of the principal portions 40 of the second thread segments. The upper thread surfaces in a first, upper region 44 have a substantially constant pitch of only about 6°. The upper region 44 adjoins an intermediate region 46 having a substantially constant, much higher pitch of about 25°. The intermediate region 46 adjoins a lower region 50 having a substantially constant pitch of about 6°. The mean pitch of the helical thread path defined by the second thread segments is about 14°. The variable pitch, in conjunction with the other features of the present assembly, provides improved separation of the tamper-evident ring as described further below. The variable pitch also provides improved sealing and pressure safety as described below, and in more detail in our International patent application WO-A-9721602.

The thread assembly also includes a pressure safety feature similar to that described and claimed in our International Patent Application W0-A-9505322. Briefly, an upwardly projecting step 48 is provided proximate to the lower region 50 of the upper surface of each second thread element 40. This step 40 abuts against a first end 43 of the first thread segments 36 and blocks unscrewing of the cap 11 from the neck 10 at this intermediate position when the said first thread segments 36 are in abutment with the second thread elements 40, i.e. when there is a net force on the cap in an axial direction out of the container neck due to pressure inside the container. As noted above, the lower region 50 of the upper surfaces of the second thread segments situated adjacent to the step 48 has a low pitch of about 6°, the effect of which is to reduce the unscrewing force exerted by pressure inside the container when the first thread segments 36 are in abutment with the step 48. Once the pressure has vented from inside the container at this intermediate, partially unscrewed position, then the cap can drop down so that the first thread segments 36 are in abutment with the lower side 52 of the second thread elements 40, from which position smooth unscrewing of the cap can be continued.

The container and closure assembly is also provided with complementary locking elements on the container neck and the cap to block unscrewing of the cap from the fully engaged position on the container neck unless a minimum unscrewing torque is applied. These locking elements comprise four equally radially spaced first locking projections 54 on the container neck, and four equally radially spaced second locking projections 56 on the inside of the cap skirt 20. The projections 54 on the container neck are located well below the thread segments 36, where they are least noticeable to a person drinking directly from the container neck. The locking projections 56 on the cap skirt are located level with, and radially spaced by about 2mm from, the bottom of the thread elements 40 on the skirt. The locking projections on the cap skirt 20 are formed as a continuation of the lower elements 40 of the cap thread segments, whereby the thread segments 36 on the neck 10 can pass smoothly past the locking projections on the neck as the cap is secured on the neck.

Each of the locking projections 54,56 is substantially in the form of a triangular prism having its long axis aligned with the axis of the cap assembly. The height of each locking projection is about 1.5mm, and the base width is about 1.5mm. This ensures that the projections have sufficient strength to snap over each other without permanent deformation. Each of the second thread segments includes a longitudinally upwardly projecting portion 58 located at an upper end of the principal element 40 that defines a longitudinal stop surface 60 against which a second end 62 of one of the first thread segments 36 may abut when the cap is fully secured on the neck to block overtightening of the cap on the neck.

The short, upper elements 41 of the second thread segments are especially designed to ensure that, when unscrewing the cap for the first time, separation of the tamper-evident ring must take place before gas venting. The upper elements 41 each have a lower surface 64 that is positioned to abut against the upper surface 38 of the first thread segments almost immediately after unscrewing of the cap from the fully sealing position has commenced, i.e. after an unscrewing of the cap through only about 15° from the fully sealing position. The second elements 41 are therefore positioned at an angular distance of only about 15° from the lower end 43 of the first thread segments 36 at the sealing position. Moreover, the lower surface 66 of the elements 41 is actually positioned slightly lower than would be expected from simple extrapolation of the lower surface 52 of the principal thread elements 40 of the cap thread. Finally, the elements 41 are located directly above the relatively steeply pitched region 46 of the neighbouring second thread segment. This ensures that the cap cannot be unscrewed by more than about 15° without the elements 41 forcing the thread segments 36 downwardly into abutment with the steeply pitched region 46, which results in steep unscrewing of the cap and separation of the tamper-evident ring before an angular position is reached (typically at 15°-35° unscrewing) at which the seal is released and gas venting from the container neck can take place. In use, the cap 1 1 with the tamper-evident ring attached is secured onto the container neck 10 by screwing down in conventional fashion, as shown in Fig. 1. There are four thread starts, and the cap 11 can be moved from a fully disengaged position to a fully engaged position on the container neck 10 by rotation through about 90°. It can be seen that the thread segments 36 on the neck initially ride past the upper end of the locking projections 56 on the cap skirt, and are thereby guided into a helical thread path. In other words, the locking projections 56 on the skirt 20 define an initial extension of the helical thread path followed by the thread segments 36 on the neck. In this way, the locking projections on the skirt do not interfere or block the free running of the threads.

When the cap is being screwed down, there is normally a net axial force applied by the user on the cap into the container neck, and accordingly the first thread segments 36 on the neck abut against and ride along the lower surfaces 40 of the second thread segment elements 40 on the cap. It can thus be seen that the first thread segments 36 follow a substantially continuous path along a variable pitch helix. The first and second threads are free-running, which is to say that there is substantially no factional torque between the thread segments until the fully engaged position is neared. These features of multiple thread starts, a 106° cap rotation, substantially continuous thread path, and free- running threads, all make the cap extremely easy to secure on the container neck, especially for elderly or arthritic persons, or children.

As the cap nears the fully engaged position on the container neck 10, the tamper-evident ring starts to ride over the retaining flange 13 on the container neck. The flexible tabs 33 on the tamper-evident ring flex radially outwardly to enable the tamper-evident ring to pass over the retaining flange 13 without excessive radial stress on the frangible bridges 68. The tapered profile of the upper surface 14 of the retaining flange 13 also assists passage of the tamper-evident ring. At the same time, the initial abutment between the sealing plug 22 and the lip 12 of the container neck results in a net axial force on the cap in a direction out of the container neck. This pushes the thread segments 36 out of abutment with the lower surfaces 40 of the second thread elements 40 and into abutment with the upper surface of the adjacent second thread element 40. Continued screwing-down of the cap causes the first thread segments 36 to travel along the upper surface of the second thread elements 40 until the final, fully engaged position shown in Figs. 2 and 3a is reached. The low pitch of the upper surface regions 44 means that this further rotation applies powerful leverage (camming) to compress the sealing plug 22 and sealing skirt 24 against the container lip 12 in order to achieve an effective gas-tight seal.

As the fully closed position is reached, the locking projections 56 on the cap skirt flex and ride over the complementary locking projections 54 on the container neck. At the fully closed position, the complementary locking projections remain in abutment, such that the cap skirt is still slightly deformed. The resilient restoring force exerted by the cap skirt is leveraged by the projections 54,56 into a closing torque on the assembly, which helps to ensure that sufficiently strong sealing force is applied to the various sealing surfaces of the assembly. It will be appreciated that this effect, coupled with the relatively large size of the projections 54,56, enables effective sealing to be achieved even if the locking projections 54,56 are not moulded to a very high tolerance.

Finally, as the fully engaged position of the cap 11 on the container neck 10 is reached or passed, the second ends 62 of the first thread segments 36 may come into abutment with the stop shoulders 60 projecting from the second thread elements 40, thereby blocking further tightening of the cap that could damage the threads and/or distort the plug or sealing skirt.

When the cap 11 is in the fully engaged position on the container neck 10 as shown in Figs 2 and 3 a, the lower surfaces 37 of the first thread segments 36 abut against the upper regions 44 of the upper surfaces of second thread elements 40. The lower surface 37 of the first thread segments 36 has a low pitch to match that of the upper regions 44, so as to maximise the contact area between the thread elements, and thereby distribute the axial force exerted by the cap as evenly as possible around the container neck. Because of the low pitch in the regions 44, relatively little of the axial force emerging from the container neck due to pressure inside the container is converted into unscrewing rotational force by the abutment between the thread surfaces in this position. This greatly reduces the tendency of the cap to unscrew spontaneously under pressure. Spontaneous unscrewing is also prevented by the abutment between the first and second locking projections 54, 56. An advantage of the assembly is that the reduced tendency to unscrew spontaneously due to the low pitch of the thread in the lower regions 44 means that the minimum opening torque of the locking projections 54, 56 can be reduced without risk of the cap blowing off spontaneously. This makes the cap easier to remove by elderly or arthritic people, or by children, without reducing the pressure safety of the cap.

In use, the cap is removed from the container neck by simple unscrewing. An initial, minimum unscrewing torque is required to overcome the resistance of the locking projections 54, 56. Once this resistance has been overcome, essentially no torque needs to be applied by the user to unscrew the cap.

Referring in particular to Figs. 3a -3f, the unscrewing proceeds as follows. The internal pressure inside the container exerts an axial force on the cap in a direction emerging from the mouth of the container, as a result of which the first thread segments 36 initially ride along the upper surfaces regions 44 of the second thread elements 40 as the cap is unscrewed. After only about 10°- 15° of rotation, the first thread segments 36 come into abutment with second thread elements 41, which force the first thread segments to travel down the steeply pitched surface 46 as unscrewing is continued, as shown in Figs 3b and 3c. The resulting steep upward movement of the cap relative to the neck causes prompt separation of the tamper-evident ring. Note that there is no play in the cap at these positions shown in Figs 3b and 3c. That is to say, the cap cannot be rotated without causing relative vertical movement of the cap relative to the neck. This is because the first thread segments are abutted both above and below by the second thread elements 41 and 40, respectively, in this region.

The relative position of the cap and closure shown in Fig. 3b is substantially the position at which the tops 33 of the inwardly projection elements of the tamper-evident ring are in abutment with the underside 1 of the retaining flange 13 to cause separation of the tamper-evident ring. In prior art assemblies there is typically some play in the cap at this stage, that is to say the cap can be rotated back and forth through at least a small angle without vertical displacement of the cap, by application of suitable force to the cap to overcome the pressure from inside the container. This play of the cap can allow a user to work the tamper-evident ring over the retaining flange 13 without separation of the tamper-evident ring from the skirt. However, in the present invention the cap is constrained to move vertically along a steeply pitched path if it is rotated from the position of 3b, thereby ensuring separation of the tamper-evident ring.

This pressure seal between the cap and the container neck is suitably initially released after rotation of the cap through about 15°-35° from the fully secured position, suitably about 20°-25°, for example at approximately the position shown in Fig. 3c. This can be achieved, for example, by the use of the olive seal as described, since olive seals are relatively tolerant of small vertical displacements. Release of the pressure seal takes therefore takes place at a relative angular position of the cap on the neck at which the cap is constrained to follow a steeply pitched helical path, and at or beyond the rotational position at which separation of the tamper evident ring from the cap is inevitable. Gas from inside the container is vented through the threads and through gas venting channel 42.

Following release of the pressure seal and separation of the tamper-evident ring, further unscrewing causes first thread segments 36 ride along the steeply pitched regions 46, as shown in Fig. 3c. The first thread segments 36 then ride onto the low-pitched lower regions 50 of the upper surface of the second thread elements 40. The first thread segments 36 then come into abutment with lower projecting step 48 of the second thread elements 40, as shown in Fig. 3d. In this position, further unscrewing of the cap is blocked while gas venting takes place along the thread paths. It should also be noted that, in this intermediate gas venting position, the first thread segments 16 abut primarily against the region 50 of the upper surface of the second thread elements 40. The low pitch of this region 50 results in relatively little of the axial force on the cap being converted into unscrewing rotational torque, thereby reducing the tendency of the cap to override the pressure safety feature and blow off.

Once gas venting from inside the container neck is complete so that there is no longer axial upward force on the cap, the cap can drop down so as to bring the thread segments 36 into abutment with the lower surfaces 40 of the adjoining second thread element 40, as shown in Fig. 3e. In this position, unscrewing can be continued as shown in Fig. 3f to disengage the cap completely from the container neck.

The above embodiment has been described by way of example only. Many other embodiments of the present invention falling within the scope of the accompanying claims will be apparent to the skilled reader. In particular, the present invention is not limited to carbonated beverage containers, or to containers formed from moulded thermoplastics.

All patent specifications referred to above are incorporated herein in their entirety.