Patent Publication Number: US-2009223922-A1

Title: Jaw seals for container closure assemblies

Description:
The present invention relates to improved seals for container closure assemblies. The invention is especially applicable to the sealing of containers in substantially gas-tight and liquid-tight fashion, such as the sealing of carbonated and non-carbonated beverage containers. 
     It is well known to provide beverage containers of glass, paper, card, metal or plastic having a screw top that can be resecured on the bottle neck. It is desirable to provide such containers with a screw top closure assembly that provides an airtight and liquid-tight seal to retain the a quality of the beverage both during initial transport and storage, and after partial consumption of the contents when the closure has been resecured onto the container neck. 
     Certain existing container and closure assemblies make use of an elastomeric liner in the base of the closure cap. This liner is pressed against the lip of the bottle neck when the cap is screwed firmly onto the bottle neck, and the compression between the soft, deformable liner and the lip of the container provides a tight seal. Unfortunately, the manufacture and insertion of the liner into the closure cap are relatively costly additional process steps. Furthermore, care must be taken not to over-tighten such closures onto the container neck, since the liner can become brittle or damaged if excessive, pressure is applied thereto. 
     It is also known to provide a cylindrical plug seal projecting downwardly from the base of the closure cap, such that the plug forms an interference fit with an inner surface of the bottle neck close to the lip of the bottle. Effective sealing by such plug seals requires the cap to be screwed down very tightly on the container neck in order to deform the base of the cap and thereby force the plug radially outwardly into a tight sealing engagement with the container neck. It is very often the case that such caps are under-tightened, especially by children and elderly users. Furthermore, a sufficient sealing force can only be achieved by the use of threads on the cap and the neck having a low pitch, such that the closure torque applied to the cap is leveraged into a very strong downward sealing force between the lip of the container and the closure base. 
     WO02/42171 describes a container closure assembly comprising: a container neck having side walls defining an opening at one end thereof and a lip extending around the opening, wherein an inner surface of the side walls proximate to the lip is inwardly tapered; a closure for the neck, the closure having a base portion and a skirt portion; a first screw thread on the neck; a second screw thread on an inner surface of the skirt of the closure; the first and second screw threads being configured to enable a user to secure, remove and resecure the closure into a sealing-position on the neck by rotation of the cap on the neck; a sealing plug extending from the base portion of the closure inside and substantially concentric with the skirt portion of the closure, wherein the sealing plug comprises a plurality of circumferential sealing ribs on an outer surface of the sealing plug for engagement with the inner surface of the container neck when the closure is secured on the container neck; at least one flexible sealing fin between the sealing plug and the closure skirt for engagement with the lip of the container when the closure is secured on the container neck; and at least one circumferential sealing rib on an inner surface of the closure skirt for engagement with an outer surface of the container neck proximate to the lip when the closure is secured on the container neck. 
     FR-A-2327930 describes container closure assemblies comprising: a container neck; a closure for the neck; mutually engageable screw threads on the closure and the neck; and a sealing plug extending from the base of the closure for insertion into the container neck. The sealing plug is provided with two circumferential sealing ribs on an outer surface thereof for engagement with the inner-surface of the container neck when the closure is secured on the container neck. The assembly further includes a flexible sealing fin projecting from the base of the closure between the sealing plug and the closure skirt for engagement with the lip of the container when the closure is secured on the container neck. 
     Further container and closure assemblies incorporating a ribbed sealing plug on the closure cap are described in DE-A-4207997, WO99/44896, U.S. Pat. No. 3,944,104, FR-A-2340865, WO2005/058720 and GB-A-2022063. 
     A need remains for a screw-top container and closure arrangement that can provide an effective seal without the need four a liner, and also without the need for a strong axial sealing force between the container neck and the closure. 
     The present invention provides a container closure assembly comprising: a container neck having side walls defining an opening at one end thereof and a lip extending around the opening; a closure for the neck, the closure having a base portion and a threaded skirt portion; a first screw thread on the neck; a Second screw thread on an inner surface of the threaded skirt of the closure; the first and second screw threads being configured to enable a user to secure, remove and resecure the closure into a sealing position on the neck by rotation of the cap on the neck; a sealing plug extending from the base portion of the closure inside and substantially concentric with the threaded skirt portion of the closure, wherein the sealing plug comprises two or more longitudinally spaced circumferential sealing ribs on an outer surface of the sealing plug for engagement with an inner surface of the container neck proximate to the lip when the closure is secured, on the container neck. The closure further comprises a sealing skirt extending from the base portion of the closure intermediate the sealing plug and the threaded skirt portion of the closure and substantially concentric with the sealing plug and the threaded skirt portion of the closure, wherein the sealing skirt comprises two or more longitudinally spaced circumferential sealing ribs on an inner surface of the sealing skirt for engagement with an outer surface of the container neck proximate to the lip when the closure is secured on the container neck; wherein in use two of the sealing ribs on the sealing plug are located at substantially the same longitudinal distances from the base portion of the closure as two of the circumferential sealing ribs on the sealing skirt, whereby the lip of the container neck is pinched between the sealing ribs on the closure plug and the sealing skirt at two or more longitudinally spaced locations when the closure is in the secured position on the container neck. 
     The inventive arrangement of sealing plug, sealing skirt and sealing ribs is new, and provides surprisingly improved sealing at low sealing forces. 
     Suitably, the closure assembly according to the present invention is applied to a carbonated beverage container, such as a molded plastic or glass carbonated beverage bottle. 
     Suitably, the container lip is rounded to provide for easy and comfortable drinking directly from the container neck, and more suitably it is fully radiused (i.e. semi-circular) in cross-section. It is a further advantage of the present invention that the sealing arrangement is so effective that it can provide a pressure-tight seal on a fully radiused container lip. Suitably, at least one of the circumferential sealing pinches provided by the circumferential sealing ribs is applied across the rounded portion of the container lip. That is to say, respective sealing ribs on the sealing plug and the sealing skirt engage the rounded surface of the lip near the top of the neck. 
     It is an advantage of the present invention that it can provide an effective pressure-tight seal on a conventional container neck having internal walls substantially parallel to the longitudinal axis of the neck. However, in some embodiments the inner sealing surface of the container neck optionally be inwardly tapered. That is to say, the internal diameter of the neck may decrease with increasing distance from the lip. Suitably, in these embodiments the interior of the neck presents a substantially inverted, truncated conical surface. Suitably, the taper of the inner sealing surface of the container neck is from about 1° to about 10° from the longitudinal axis of the neck, more suitably from about 2° to about 6°. The taper can assist effective sealing of the plug against the inner wall of the neck. 
     The sealing plug is suitably in the form of a tube, preferably a cylinder, typically projecting perpendicularly downwardly from the base of the closure and preferably substantially concentric with the threaded skirt and coaxial with the longitudinal axis of the closure. The height of the sealing plug is suitably from about 1 mm to about 5 mm, for example about 1.5 mm to about 2.5 mm. The sealing plug is normally molded integrally with the base of the closure cap. The mean thickness of the tubular wall of the sealing plug is suitably from about 0.5 mm to about 2 mm, for example about 0.7 mm to about 1.2 mm. This gives the sealing plug the right degree of resilience and strength for the desired sealing function. 
     Suitably, the outer surface of the sealing plug may be tapered inwardly from the base of the closure, for example it may taper in a manner substantially complementary to the optional inward taper of the interior of the container neck. The mean angle of taper is suitably from 1° to 10° from the longitudinal axis of the neck, more suitably from 2° to 6°. 
     The container closure in the assembly according to the present invention further comprises a circumferential sealing skirt. The sealing skirt is separate and radially spaced from the threaded closure skirt that engages the thread on the outside of the container neck. Suitably, the sealing skirt is substantially tubular, preferably cylindrical, and projects downwardly from the base of the closure intermediate the closure skirt and the sealing plug. The sealing skirt is preferably substantially concentric with the threaded skirt and the sealing plug, and coaxial with the longitudinal axis of the closure. The height of the sealing plug is suitably from about 1 mm to about 5 mm, for example about 1.5 mm to about 2.5 mm. The height of the sealing plug in certain embodiments is substantially equal to the height of the sealing plug. The sealing skirt is normally molded integrally with the base of, the closure cap. The mean thickness of the tubular wall of the sealing skirt is suitably from about 0.5 mm to about 2 mm, for example about 0.7 mm to about 1.2 mm. This gives the sealing skirt the right degree of resilience and strength for the desired sealing function. 
     The assembly according to the present invention further comprises two or more circumferential sealing ribs on an outer surface of the closure plug for engagement with an inner surface of the container neck, and two or more circumferential sealing ribs on an inner surface of the closure skirt for engagement with an outer surface of the container neck. Two or more of the further circumferential sealing ribs on the sealing skirt are located at substantially the same heights above the base of the closure, respectively, as two or more of the circumferential sealing ribs on the sealing plug, whereby they cooperate to apply a symmetrical sealing pinch at two or more vertically spaced locations on the container neck when the closure is in the sealing position on the neck. That is to say, the ribs apply a symmetrical sealing pinch at two or more vertical heights below the top of the container lip. 
     Suitably, there are two of the sealing ribs on the sealing plug and/or on the sealing skirt, but in some embodiments there are suitably from 3 to 10 of the ribs, and for example 4 to 6 ribs. 
     Suitably, at least one of the sealing ribs has a substantially triangular cross-section when the closure cap is viewed in longitudinal cross-section, for example substantially equilateral triangular. This enables the sealing force to be concentrated in the tip of the sealing rib to maximise sealing effectiveness. Suitably, at least one of the sealing ribs has a height in the range of 10 to 500 micrometers, more suitably 50 to 250 micrometers. The height is defined as the maximum distance that the sealing rib projects above the adjacent surface of the sealing plug or sealing skirt, when the cap is viewed in longitudinal cross-section. Such micro sealing ribs are especially effective to concentrate the sealing force and achieve an effective seal with a substantially smooth sealing surface on the container neck. Furthermore, such micro ribs are especially easy to mold in high-speed cap molding equipment, and to bump off the mold mandrel of the equipment after molding. 
     A further advantage of using multiple sealing ribs on the sealing plug and the sealing skirt is that the plurality of sealing ribs may have more than one dimension in order to optimise sealing. For example, the size of the sealing rib closest to the base of the closure may be greater than the size of the sealing rib remote from the base of the closure. This allows the sealing rib closest to the base of the closure (i.e. closest to the lip of the container) to deform more that the sealing rib furthest from the base of the closure. 
     Suitably, the sealing plug and the sealing skirt are profiled so as to define a symmetrical jaw for gripping the container neck. The circumferential sealing ribs appear as “teeth” of the jaw in longitudinal cross-section. Suitably, respective lower ends of the sealing skirt and the sealing plug distal from the base of the closure are profiled to provide further circumferential sealing ribs on each of the sealing skirt and the sealing plug for gripping the neck of the closure. 
     The use of multiple symmetrically disposed circumferential sealing ribs on a sealing plug and a sealing skirt, each of which has a degree of radial flexibility, allows a pressure-tight seal to be formed between the container neck and the closure without application of excessive force to the closure, and without any need for a sealing liner in the base of the closure. 
     The container closure assembly according to the present invention is especially suitable for use in conjunction with thread arrangements that are quick and easy to secure and resecure, wherein the closure can be secured and resecured on the container neck by a single, smooth rotation through 360° or less, more suitably 180° or less, and most suitably about 90°. 
     Suitably, the first and second threads are multiple start threads such as two-start threads or three-start threads, and more suitably they are four-start threads. This further assists securing of the closure on the neck, since the user needs to rotate the cap less in order to find a thread start. Suitably, the threads are substantially free-running or parallel threads. That is to say, the threads on the closure and cap slide past each other freely without forming an interference fit between the thread segments on the closure and cap. 
     Suitably, the first and second threads are continuous helical threads. That is to say, they are not bayonet-type threads that require a stepped motion of the closure to secure the closure on the neck, but rather they define a substantially continuous helical thread path having a thread gradient less than 90 degrees substantially throughout. Suitably the threads have a mean thread pitch of from 5° to 25°, more suitably from 10° to 20°. Typically, the minimum vertical displacement of the cap between the fully secured position on the container neck and a fully disengaged position of the cap on the neck of from about 2 mm to about 10 mm, for example from about 4 mm to about 8 mm. 
     Steeply pitched threads provide advantages in terms of ease of use and more reliable separation of tamper-evident rings from the closure skirt. However, it will be appreciated that such steeply pitched threads result in a relatively small leverage of rotational force applied to the closure into downward force on the closure, and it is a feature of the sealing arrangement according to the invention that it can provide a reliable pressure-tight seal without strong downward force being applied to the closure as in previous sealing arrangements. 
     It is an advantage of the assemblies according to the present invention that they can provide a pressure tight seal without the need for additional circumferential flexible sealing fins between the sealing plug and the sealing skirt of the kind described in WO02/42171. Nevertheless, in certain embodiments, the closure in the assemblies according to the present invention may further comprise one or more circumferential flexible sealing fins between the sealing plug and the sealing skirt for engagement with the lip of the container when the closure is secured on the container neck. The sealing fins may have their base in the base of the closure between the sealing skirt and the sealing plug, or they may extend inwardly or outwardly and downwardly from the base of the sealing skirt or the sealing plug. 
     Suitably, the closure comprises two sealing fins extending around the closure in concentric fashion. Suitably, two sealing fins are disposed substantially symmetrically on either side of the container lip to provide a balanced sealing pinch on the lip. In these embodiments, the container closure assembly comprises a second sealing fin extending downwardly and inwardly from the base of the closure between the sealing plug and the sealing skirt. The first and second sealing fins then seal against opposite sides of the container lip, suitably in substantially symmetrical and balanced fashion. The first and second sealing fins flex in opposite directions as the closure is secured onto the container neck. This dual action ensures that at least one, and usually both, of the sealing fins makes a pressure-tight seal against the lip. 
     Suitably, the height of the sealing fins is greater than their width at their base. Suitably, the cross-section of the sealing fins is substantially in the shape of an isosceles triangle. Suitably, at least one sealing fin has a height of from 1 to 4 mm. 
     Suitably, at least one sealing fin abuts against a stop surface when the closure is secured on the container neck. Suitably, two flexible fins are provided for sealing on either side of the container lip, as described above, and the two stop surfaces are provided by the bases of the sealing plug and the sealing skirt for abutment against each of the sealing fins at the fully secured and pressure-tight position. 
     Suitably, the container and closure further comprise complementary locking elements on the container neck and the closure that block or resist unscrewing of the closure from the fully secured position on the container neck until a predetermined minimum opening torque is applied. For example, the locking elements may comprise a longitudinal locking rib on one of the container neck or the skirt portion of the closure, and a complementary locking ramp on the other of the container neck and the skirt portion of the closure, the locking rib abutting against the retaining edge of the locking ramp when the closure is fully secured on the container neck. 
     In certain embodiments, the first and second locking projections (side catches) longitudinally overlap the first and/or the second thread segments when the closure is in said fully engaged position on the container neck. In other words, the first and second locking projections are not located entirely above or below the threads (the terms above and below refer to relative positions along the longitudinal axis of the assembly), but are located, at least in part, radially in-between the threads. The side catches are preferably located adjacent to an end of the threads. This enables the entire thread assembly to be made more compact in the longitudinal (vertical) direction, thereby reducing the total amount of moulding material needed to make the assembly, and the space taken up by the assembly. In certain embodiments, it also enables the neck thread to be made more suitable for consumption directly from the neck. 
     Typically, the first and second locking elements are situated near the lower end of the threads when the closure is fully secured on the container. Preferably, the first and/or second locking projections do not extend below the lower edge of the first or second thread segments when the closure is in said fully engaged position on the container neck. The term “lower” refers to the part of the neck thread furthest from the opening of the container neck. In such assemblies, the locking projections are preferably located substantially completely radially between the threads and not above or below the threads. Preferably, the locking projections on the neck are not joined at the lower edge to a circumferential flange or shoulder (e.g. the shoulder used to retain a tamper-evident band), thereby enhancing the flexibility of the locking projections and enhancing the “click-to-close” noise. 
     Further to the aforesaid, at least one, and preferably both of the complementary locking projections on the neck and/or the closure is substantially separate from the thread segments and can flex substantially independently of the thread segments in order to provide the snap-fitting and clearly audible click as the fully secured position of the closure on the neck is reached. In general, a radially innermost vertex of the second locking element on the closure skirt rides over a radially outermost vertex of the first locking element on the container neck as the fully secured position is approached. The second locking element then rides back over the outermost vertex of the first locking element when the closure is removed from the secured position, for example when opening the assembly. 
     At least one, and preferably both of the complementary locking projections on the neck and/or the closure has a length in the longitudinal direction (i.e. along the rotational axis of the closure assembly) of from about 1 mm to about 6 mm, for example from about 2 mm to about 4 mm. At least one, and preferably both of the complementary locking projections on the neck and/or the closure has a height of from about 0.25 mm to about 2 mm, for example from about 0.5 mm to about 1.5 mm. In any case the height of the locking projections is normally less than the average height of the respective thread segments. At least one, and preferably both of the complementary locking projections on the neck and/or the closure has a maximum width (i.e. around the circumference of the neck or closure skirt) of from about 0.5 mm to about 3 mm, for example from about 1 mm to about 2 mm. At least one, and preferably both of the complementary locking projections on the neck and/or the closure has a ratio of the maximum height to the maximum width of at least about 0.5, more preferably at least 1, for example from about 1 to about 5. 
     In suitable embodiments, the first locking projection is located longitudinally overlapping with and radially spaced from an upper end of a first thread segment. In other embodiments, the second locking projection is located longitudinally overlapping with and radially spaced from a lower end of a second thread segment. These latter embodiments are preferred, since the first locking projections are then located further from the opening of the container neck. The circumferential spacing between the projections and the respective thread segments in these embodiments is typically from about 1 mm to about 10 mm, for example from about 1 mm to about 4 mm. In these embodiments, the radially spaced locking projections may abut against the thread segments of the other assembly component as the assembly is screwed together. That is to say, the radially spaced projections may define a part of the thread path on the enclosure or neck. For example, in the case where there are relatively long thread segments on the closure skirt defining a thread path for relatively short thread segments on the container neck, the locking projections on the closure skirt may be radially spaced from the lower end of the relatively long thread segments on the closure skirt and may thereby define an extension at the start of the thread path followed by the thread segments on the neck when the closure is applied to the neck. This method of using the locking projections to form an extension of the thread path on one of the neck or the closure solves the problem of providing larger locking projections that overlap with the threads, but do not interfere with the running of the threads. The locking projections are generally in the line of and, as it were, are extensions of the thread path on one of the neck or the closure. 
     The assemblies according to the present invention may comprise more than one pair of complementary locking projections on the container neck and the closure. Preferably there are at least two such complementary pairs radially spaced around the neck and closure skirt. There will normally be at least one pair for each thread start, for example there may be four pairs radially spaced around the neck and closure skirt. 
     Preferably, the locking projections on the neck and the closure, skirt are radially positioned such that they are in abutment when the closure is at the fully closed and sealing position on the container neck. That is to say, the projection on the closure has ridden over one side of, and is resting in abutment with the opposite side of, the corresponding projection on the container neck at said fully closed and sealing position. This ensures that there is no play in the cap at said closed and sealing position that could allow leakage from the seal. Preferably, when the projections are in abutment at the closed and sealing position, the closure skirt and/or the projections are still slightly distorted such that a resilient force is exerted between the projections in abutment. This resilient force is leveraged by the abutment into a closing torque between the closure and the neck that urges the closure into the fully closed and sealing position. This can ensure that the respective sealing surfaces of the container neck and the closure are automatically seated against each other, even though the closure may not be screwed down especially tightly. Furthermore, the locking projections allow for considerably lower manufacturing tolerances in the moulding of the assembly, since effective sealing is achieved over a broader range of radial sealing positions due to the interaction between the locking projections and the radial deformation of the closure skirt. 
     The advantages of locking projections that urge the closure into the sealing position are discussed in detail in WO93/01098, the entire content of which is incorporated herein by reference. 
     The complementary locking elements according to the present invention provide a number of other important advantages, besides urging the closure into the fully secured and sealing position as described above. Firstly, they prevent accidental backing off of the closure from the fully engaged and sealing position on the container neck due to pressure from inside the container. These elements enable more steeply pitched threads and free running (parallel) threads to be used without risk of the closure unscrewing spontaneously. The use of more steeply pitched threads in turn makes it easier to remove and resecure the closure. 
     In some embodiments, the locking elements according to the present invention may also provide a positive “click” when the fully engaged and sealing position of the closure on the container neck is reached, thereby giving the user a positive indication that the closure is in the closed (sealed) position. This system also ensures that exactly the right degree of compression is applied between the container and closure to achieve an effective airtight seal. 
     Suitably, the container closure assembly according to the present invention further comprises a projecting stop surface on one of the container neck and the closure skirt for abutment against a second stop or a thread on the other of the container neck or the closure to block over-tightening of the closure beyond a predetermined angular sealing position of the closure on the container neck. The stop elements act in conjunction with the locking arrangement to ensure that exactly the right degree of screwing of the closure is achieved in order to provide a pressure-tight seal with the sealing arrangement of the present invention. 
     Suitable locking and stop arrangements are described in detail in WO 91/18799, WO 95/05322 and WO2005/058720, the entire contents of which are expressly incorporated herein by reference. 
     The container closure assembly also suitably comprises a tamper-evident safety feature. The safety feature preferably includes a tamper-evident ring that is initially formed integrally with the skirt of the container closure and joined to the lower edge thereof by one or more frangible bridges. The tamper-evident ring is retained on the container neck when the closure is removed from the neck for the first time, suitably by abutment with the underside of a circumferential retaining lip provided on the container neck below the threads. 
     In certain embodiments, the tamper-evident ring comprises a plurality of integrally formed, flexible, radially inwardly pointing retaining tabs to retain the ring under the retaining lip. In these embodiments, ratchet projections may also be provided on the container neck below the circumferential retaining lip and radially spaced around the container neck to block rotation of the tamper-evident ring on the container neck in an unscrewing direction and thereby assist separation of the tamper-evident ring from the neck. The structure and operation of the tamper-evident ring feature according to these embodiments may be as described and claimed in our International Patent Publication WO94/11267, the entire contents of which are expressly incorporated herein by reference. 
     Suitably, the torque required to secure the closure in a sealing position on the container neck is less than 1.2 Nm, more suitably less than 1 Nm and most suitably from about 0.7 to about 0.9 Nm. This is the torque required to engage the complementary locking arrangement (where present) at the sealing position, and/or otherwise the force required to substantially eliminate gas leakage at normal carbonated beverage pressure differentials. 
     Suitably, the assembly achieves a sealing pressure around at least one circumferential surface between the container neck and the closure at the fully closed position of at least about 7 MPa (1000 psi), suitably at least about 10.5 Mpa (1500 psi), suitably over a temperature range of from about 0° C. to about 40° C., and suitably over an pressure range within the container of from about zero to about 1.2 MPa gauge (175 psig), i.e. covering the maximum ranges of temperature and pressure required for carbonated beverages. Suitably, the assembly provides at least two such circumferential seals, suitably over the whole of the above temperature and pressure ranges. 
    
    
     
       Embodiments 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 comparative view of a container neck (in elevation) and a closure (in cross section) secured to the neck in a sealing position, wherein the left side of the closure is shown with a prior art sealing liner and the right side of the closure is shown with a sealing arrangement in accordance with the present invention; 
         FIG. 2  shows a detailed longitudinal view partially in cross-section of the operative region of a container closure assembly according to the present invention from  FIG. 1 , with the closure unscrewed from the container neck; 
         FIG. 3  shows a detailed longitudinal view partially in cross section of the operative region of a container closure assembly according to the present invention from  FIG. 1 , with the closure shown in the closed and sealing position the container neck; 
         FIG. 4  shows an enlarged partial longitudinal sectional view through the sealing region of the container closure according to the embodiment of  FIGS. 2 and 3 ; 
         FIG. 5  shows a partial longitudinal sectional view similar to that of  FIG. 4  through the sealing region of a closure according to a further embodiment of the invention; 
         FIG. 6  shows a partial longitudinal sectional view similar to that of  FIG. 4  through the sealing region of a closure according to a further embodiment of the invention; 
         FIG. 7  shows a partial longitudinal sectional view through the sealing region of the closure according to a further embodiment with the closure disengaged from the container neck; 
         FIG. 8  shows a partial longitudinal sectional view through the embodiment of  FIG. 7  with the closure fully secured on a container neck (shown in phantom); and 
         FIG. 9  shows a view of a further assembly according to the present invention with a container neck (in elevation and partially in cross-section) and a closure (in cross section) secured to the neck in a sealing position. 
     
    
    
     Referring to  FIG. 1 , the assembly comprises a container neck  1  and a closure  2 . The closure  2  comprises a base  3  and an outer, threaded skirt  4 . The container neck  1  terminates in a rounded, smooth-surfaced lip  5 . In prior art closure assemblies, this lip forms a pressure-tight seal with an elastomeric liner  6  shown hatched in the “prior art” portion of  FIG. 1 . 
     The container neck  1  is formed from polyethylene terephthalate (PET) by injection molding. The closure  2  is likewise molded in one piece by injection molding from polyethylene. The neck  1  and closure  2  are provided with integrally molded, fast-turn, steeply-pitched threads incorporating a pressure safety feature, as described in detail in our International patent application EP-A-1446332, the entire content of which is expressly incorporated herein by reference. 
     Briefly, on the inside of the skirt portion  16  there is provided a four-start first screw thread made up of four first thread segments each made up of two portions  10 , 11 , as shown in phantom on  FIG. 1 . The thread segments extend a total of about 170 degrees around the skirt, whereby adjacent thread segments overlap around the circumference of the skirt. A substantially continuous, approximately helical thread gap is defined between overlapping regions of the first thread segments on the skirt  4 . 
     The container neck  10  is provided with a second screw thread formed from four short second thread segments  8 , each of which is a substantially continuous helical thread extending about 20 degrees around the container neck. 
     An important feature of this assembly is the profiling of the upper surface of the thread segments on the closure skirt, which is described in more detail in EP-A-1446332. 
     The thread segments on the closure skirt also include a pressure safety feature similar to that described and claimed in our International Patent Publication WO95/05322. Briefly, a step  9  is provided in the upper surface of the thread portion  11  to abut against an end of the neck thread segments  8  and block unscrewing of the closure  2  from the neck  1  when the neck thread segments  8  are in abutment with the upper surface of the skirt threads, i.e. when there is a net force on the closure in an axial direction out of the container neck. This abutment acts to block further unscrewing of the closure until venting of gas pressure from inside the container is substantially complete, so that the closure can drop down to bring the thread  8  out of abutment with the step  9 . A region of the upper surface of the skirt thread segments  11  situated adjacent to the step  9  has a low pitch of about 6 degrees to reduce the risk of the pressure safety feature being over-ridden by high pressure inside the container. 
     The container and closure assembly is also provided with complementary locking elements on the container neck and the closure to block unscrewing of the closure from the fully engaged position on the container neck unless a minimum unscrewing torque is applied. These locking elements comprise four equally radially spaced locking ribs  13  on the inside of the closure skirt  16 , and four equally radially spaced retaining ramps on the container neck. The ramps have a radially sloped outer face  12  and a radially projecting retaining edge  14  against which the rib  13  on the closure abuts when the closure is fully engaged on the container neck. The complementary locking elements may be as described in our International Patent Publication WO91/18799, the entire content of which is hereby expressly incorporated by reference. The complementary locking elements signal to the user by means of an audible “click” when the sealing position has been reached. The complementary locking elements resist “backing-off” of the closure, which is especially advantageous for the steeply pitched threads when the contents of the container are pressurized. 
     The skirt thread portions  10  are provided at one end with an upwardly projecting a stop shoulder  18  forming a first stop against which an end of the neck thread segments  8  may abut, thereby to block over-tightening of the closure on the neck. 
     The container closure assembly also comprises a tamper-evident safety feature. The safety feature includes a tamper-evident ring  15  that is initially formed integrally with the skirt  4  of the container closure  2  and joined thereto by frangible bridges. The tamper-evident ring  15  comprises a plurality of integrally formed, flexible, radially inwardly pointing retaining tabs  16 . A circumferential retaining lip  17  is provided on the container neck  1 . 
     Referring to  FIGS. 2 and 3 , the closure comprises a cylindrical sealing plug  24 . The closure further comprises a cylindrical sealing skirt  20  that is substantially concentric with and equal in height (measured from the base of closure) to the sealing plug. The sealing plug  24  and the sealing skirt  20  are concentric with the threaded skirt  4  and located inside the threaded skirt  4  for sealing abutment against opposite sides  25 , 29  of the container neck proximate to the container lip  5 . 
     The sealing skirt  20  has two small circumferential sealing ribs  21 , 22  of substantially triangular cross-section on a radially inner side thereof. The cylindrical sealing plug has two circumferential sealing ribs  26 , 27  provided on a radially outer surface of the sealing plug  24 , the dimensions of the circumferential sealing ribs  26 , 27  being the same or similar to those of sealing ribs  21 , 22  on the sealing skirt. The circumferential sealing ribs  26 , 27  are located at substantially the same heights respectively above the base of the closure  2  as the respective circumferential sealing ribs  21 , 22  on the sealing skirt  20 . 
     The circumferential sealing ribs on the sealing plug and 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 enable a pressure tight seal to be achieved without substantial force having to be applied to the sealing plug to form the seal. 
     In use, the closure is secured on the container neck as shown in  FIG. 3 , Both the sealing skirt  20  and the sealing plug  24  are radially slightly flexible to engage the sealing lip. The circumferential sealing ribs on the sealing skirt and the plug engage opposite sides  25 , 29  of the sealing lip  5 , and pinch the lip between them at two vertically spaced locations to form a highly effective seal by concentrating pressure at the sealing ribs. The upper sealing ribs  22 , 27  provide a pinch across the rounded lip  5  of the container neck, thereby substituting for the flexible sealing fins that are described in WO02/42171. 
     Referring to  FIG. 4 , the sealing region of the closure is shown in more detail. It can be seen that the sealing skirt  20  is provided with two circumferential sealing ribs  21 , 22  on a radially inner surface thereof that are substantially triangular in cross-section. In addition, the bottom  30  of the sealing skirt  20  is profiled to form a further circumferential sealing rib  31  for applying concentrated force to a the outside surface  25  of the container neck proximate to the lip  5  to effect a seal. The bottom of the sealing plug  24  is provided with an exactly corresponding further circumferential sealing rib  32  spaced at the same longitudinal distance above the base of the closure as the corresponding feature on the sealing skirt, for applying a further pinch across the container neck. The overall effect is to provide a substantially symmetrical sealing jaw for gripping the top of the container neck. 
     Referring to the embodiment of  FIG. 5 , the sealing skirt and the sealing plug are profiled in similar fashion to the embodiment of  FIG. 4  to form a jaw for sealing against the upper part of the container neck proximate to the container lip. However, the jaw profile is slightly different, such that the angle of the further circumferential sealing ribs  37 , 39 , at the bottom of the sealing skirt and the sealing rib respectively, is more obtuse. This profile of the further circumferential sealing ribs  37 , 38  may be preferable for certain container neck profiles, and may also offer certain advantages for ease of molding of the closure. 
     Referring to  FIG. 6 , the sealing skirt and the sealing plug are profiled in similar fashion to the embodiment of  FIG. 4  to form a jaw for sealing against side walls of the container neck proximate to the container lip. However, the jaw profile is slightly different, such that the angle of the further circumferential sealing ribs  42 , 44 , at the bottom of the sealing skirt and the sealing rib respectively, is more acute. This profile of the further circumferential sealing ribs  42 , 44  may be useful to apply a high, localised sealing pressure at the points where the further sealing ribs contact opposite sides of the container neck. 
     Referring to  FIG. 7 , the principal features of the container neck and closure are as described above in relation to the embodiment of  FIGS. 2 and 3 . In particular, the closure  50  has an outer, threaded closure skirt  51  for engagement with complementary threads on the container neck  60 . The closure of  FIG. 7  further comprises a cylindrical sealing skirt  52  concentric with the threaded skirt  51  and located slightly inside the threaded skirt  51  for sealing abutment against outer surface of the container neck proximate to the container lip. The sealing skirt  52  has two small circumferential sealing ribs  54 , 55  of substantially triangular cross-section and height approximately 100 micrometers on a radially inner side thereof. 
     The container closure  50  in the embodiment of  FIG. 7  further comprises a cylindrical sealing plug  53  that is substantially concentric with and equal in height (measured from the base of closure) to the sealing skirt  52 . Two circumferential sealing ribs  56 , 57  are provided on a radially outer surface of the sealing plug, the dimensions of the circumferential sealing ribs  56 , 57  being the same or, similar to those of sealing ribs on the sealing skirt. The circumferential sealing ribs on the sealing skirt and the sealing plug are located at substantially the same heights above the base of the closure, respectively. 
     In addition, the closure in the assembly of  FIGS. 7 and 8  comprises two sealing fins  58 , 59  in the form of relatively thin-walled cylindrical projections extending from the base of the closure  50  concentric and intermediate the sealing skirt  52  and the sealing plug  53 . The height of the sealing fins  58 , 59  above the base of the closure is approximately half the height of the sealing skirt and the sealing plug. 
     In use, the closure is secured on the container neck as shown in  FIG. 8 . Both the sealing skirt  52  and the sealing plug  53  are radially slightly flexible to engage the lip of the container neck  60 . The circumferential sealing ribs on the sealing skirt and the plug engage opposite sides of the neck proximate to the lip of the neck, and pinch the lip between them at two vertically spaced positions to form a highly effective seal by concentrating pressure at the sealing ribs. In addition, the sealing fins  58 , 59  abut against the container lip intermediate the sealing skirt and the sealing plug to form a further seal. 
     Referring to  FIG. 9 , the principal features of the container neck and closure are as described above in relation to the embodiment of  FIGS. 2 and 3 , and will not be described again. The assembly of  FIG. 9  differs principally in the construction of the locking elements to resist unscrewing (backing off) of the closure when it is in the closed and sealing position. 
     Briefly, the locking elements comprise four equally radially spaced first locking projections  62  on the container neck  63 , and four equally radially spaced second locking projections  64  on the inside of the closure skirt  65 . The projections  62  on the container neck are located below the short neck thread segments  66 , where they are least noticeable to a person drinking directly from the container neck. The locking projections  64  on the closure skirt  65  are located level with, and radially spaced by about 2 mm from, the bottom of the threads  68  on the skirt. The locking projections  64  on the closure skirt form a continuation of the helical thread path defined by closure threads  68 , whereby the short thread segments  66  on the neck can pass smoothly past the locking projections  64  on the closure as the cap is secured on the neck. 
     Each of the locking projections  62 , 64  is substantially in the form of a triangular prism having its long axis aligned with the axis of the closure assembly. The height of each locking projection is about 1.5 mm, and the base width is about 1.5 mm. This ensures that the projections have sufficient strength to snap over each other without permanent deformation. 
     Each of the thread segments  68  on the closure skirt includes a longitudinally upwardly projecting portion  70  that defines a longitudinal stop surface against which a second end of one of the short thread segments  66  on the neck may abut when the closure is fully secured on the neck to block over-tightening of the closure on the neck. 
     The sealing arrangement in the assemblies according to the present invention enables the closure to be secured and resecured on the container neck without the need for high torque or low pitched threads to force a seal. It can be seen that the assembly according to the invention provides at least two circumferential seals having a high sealing pressure over the whole range of temperature and pressure normally encountered in carbonated beverage containers. It can further be seen that the closure is suitable for application to container necks having rounded top lips, such as glass container necks and plastic container necks having a rounded lip to assist drinking directly from the neck. The drawbacks associated with the use of soft sealing liners in the closure cap are eliminated, in particular the closures according to the present invention can be resecured on the container neck-repeatedly, without damage or loss of effectiveness. 
     The above embodiments have been described by way of example only. Many other embodiments falling within the scope of the accompanying claims will be apparent to the skilled reader.