Abstract:
The invention relates to a self-opening closure with a pouring spout ( 12 ), a self-opening sleeve ( 20 ) which is guided in the connector in a helical manner, and a cover ( 30 ) which covers the pouring spout ( 12 ). A driver cam ( 24 ) is formed on the self-opening sleeve, said driver cam defining a guide surface ( 241 ). The cover has a driver ( 34 ) which defines a front edge ( 341 ). The front edge interacts with the guide surface of the driver cam. The front edge and the guide surface are inclined by the same angle of inclination relative to the longitudinal axis in order to allow an optimal force transmission between the cover and the self-opening sleeve. Additionally, the guide surface can be designed in a concave manner, and the front edge of the driver can be rounded in a corresponding manner in order to prevent a radial deflection of the driver towards the inside.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a National Stage of International Application No. PCT/EP2014/069988, filed Sep. 19, 2014, claiming priority based on Swiss Patent Application No. 01803/13, filed Oct. 25, 2013, the contents of all of which are incorporated herein by reference in their entirety. 
     TECHNICAL FIELD 
     Prior Art 
     Pourable food products, such as drinks, are frequently packed in composite packagings. In such packagings, a cardboard support is usually coated on both sides with plastic, usually polyethylene (PE). In order to create an oxygen barrier, a barrier layer of aluminum or of an oxygen-impermeable plastic, such as EVOH, and auxiliary layers for lamination of the barrier layer are frequently additionally present. It is known to weaken the packaging wall in the region to be opened, in order to facilitate opening, for example by a weakening line being punched into the cardboard support, or by a complete hole being punched out of the cardboard support prior to the lamination of the films. 
     In order to open packagings of this type, various self-opening closures, in which a self-opening sleeve, which usually has a plurality of teeth, is threadedly guided in a pouring spout, have become known from the prior art. When it is unscrewed for the first time, a screw cap cooperates with the self-opening sleeve such that the latter moves helically downward and hereupon, with its teeth, pierces or cuts open the underlying packaging wall. In order to transport the self-opening sleeve, one or more drivers are configured on the screw cap, which drivers cooperate with corresponding driving cams on the inner peripheral wall of the self-opening sleeve. Generally the drivers have a front edge which runs parallel to the longitudinal axis of the pouring spout and points in the circumferential direction and which cooperates with a face, likewise pointing in the circumferential direction, of the corresponding driving cam. This is the case, for example, in EP 1 088 764 A1, in WO 03/002419 A1 or WO 2008/092289 A2. 
     Self-opening closures frequently require a relatively large force application in order to generate on the cap the torque which is necessary for the first-time opening. Specifically for elderly persons or persons restricted by illness, the necessary forces can be applied only with difficulty. It is therefore desirable to minimize as far as possible the torque which is necessary for the first-time opening. 
     WO 2004/000667 A1 and WO 2006/050624 A1 disclose self-opening closures in which the self-opening sleeve does not execute a screw-like movement, but rather, when the closure is opened for the first time, is firstly pushed axially downward without rotation and subsequently executes a pure rotation. In order to enforce this form of movement, on the inner side of the pouring spout and the outer side of the self-opening sleeve corresponding vertically and horizontally running ribs are provided. The cap has drivers in the form of cylinder wall segments, the respective front edge of which runs firstly at an acute angle obliquely to the cap face and subsequently perpendicular to the cap face, i.e. axially. That region of the front edge of the drivers which runs obliquely to the cap face cooperates with driving cams on the self-opening sleeve in order to push these firstly perpendicularly downward when the cap is unscrewed, while the axially running region of the front edge serves to transport the driving cams subsequently in the peripheral direction and to thereby set the self-opening sleeve in a pure rotation. Since, in closures of this kind, the distance which the self-opening sleeve covers in its initial axial movement against the resistance of the packaging wall is very short, even greater opening forces than in closures having thread-guided self-opening sleeves have to be surmounted in such closures. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to define a self-opening closure by which a packaging can be opened with reduced force expenditure. At the same time, it should be possible to produce such a closure easily and with low material costs. 
     Proposed is a self-opening closure which comprises:
         a tubular pouring spout, which defines a longitudinal axis and is provided on its inner side with an internal thread,   a cap, which upwardly covers the pouring spout and which, for the purpose of opening the closure, is rotatable relative to the pouring spout in an opening direction and, for the purpose of reclosing the closure, is rotatable in a closing direction opposite to the opening direction, wherein the cap has at least one driver, which defines a front edge; and   a self-opening sleeve, which is provided with an external thread that engages in the internal thread of the pouring spout, and which on its inner side has at least one driving cam, wherein the driving cam defines a guide face which, when the closure is opened, cooperates with the front edge of the driver in order to move the self-opening sleeve in a screw-like manner downward out of its starting position in the pouring spout,   wherein the front edge runs inclined downward by a first angle of inclination relative to the longitudinal axis, and wherein the guide face runs inclined by the same angle of inclination as the front edge.       

     This design is based on the recognition that, in self-opening closures of the prior art in which the front edge of the driver runs parallel to the rotational axis, the force transmission between the cap and the self-opening sleeve is not optimally achieved if the self-opening sleeve executes a screw-like movement. In the case of a driver edge running parallel to the rotational axis, the opening torque applied to the cap by the user is transmitted precisely in the peripheral direction, i.e. the opening torque is converted into a pure torque at the self-opening sleeve. In actual fact, however, by executing a screw-like movement, the self-opening sleeve not only moves in the peripheral direction, but also has a motional component downward in the axial direction. It is therefore better if the opening torque is converted both into a torque bearing against the self-opening sleeve and into an axial force acting downward onto the self-opening sleeve. The present invention ensures an optimal force transmission, since the front edge (situated at the front with respect to the opening direction) of the driver is inclined downward and cooperates with a correspondingly inclined guide face on the driving cam. As a result, the opening torque is partially converted into a torque bearing against the self-opening sleeve and partially into an axial force. At the same time, the forces between driver and driving cam which are at play during the opening process are in this way distributed particularly evenly onto the guide face of the driving cam. As a result, the frictional forces which act between driver and driving cam are minimized. In total, the torque which is necessary to open the closure for the first time is thus reduced. 
     The angle of inclination of the front edge of the driver is preferably greater than or equal to the pitch angle of the internal thread, but in any case amounts to at least 50% of the pitch angle of the internal thread in the pouring spout, in order to generate a sufficiently large force component in the downward direction. In practice, an angle of inclination of the front edge of about 10°-30° has proved successful. 
     The cap usually has a cover wall and a circumferential side wall. On the inner side of the side wall are usually configured one or more guide structures, which effect a guidance of the cap on the pouring spout. Preferably, these guide structures are constituted by a single or multiple internal thread, but e.g. a bayonet guide, in which the cap, when opened, firstly performs a pure rotation and can subsequently be pulled off axially, can also be provided. On the pouring spout are usually likewise configured one or more guide structures, which are complementary to the guide structures on the cap. If, for example, an internal thread is provided on the cap, the guide structure on the pouring spout is constituted by a thereto complementary external thread. The driver is preferably attached to the cover wall of the cap and, starting from the cover wall, preferably extends downward. It preferably has the basic shape of a cylinder wall segment, wherein the front edge of the cylinder wall segment forms the aforementioned front edge of the driver and is accordingly inclined relative to the longitudinal axis. Preferably, precisely one driver is present. 
     In order to prevent the driver from evading the opening forces in the radially inward direction when the closure is opened for the first time, the guide face is preferably not flatly, but concavely configured with respect to the radial direction, so that it at least partially embraces the front edge of the driver when the closure is opened. Accordingly, the front edge of the driver is preferably curved correspondingly convexly. 
     Preferably, the guide face has no sharp bends. In this way, a situation in which the driver and the driving cam hook together in such a way that the opening operation is impeded can be avoided. Preferably, the front edge of the driver has a shape which is at least in one area complementary to the shape of the guide face of the driving cam. As a result, at least a region of the guide face bears squarely and not just at certain points against the front edge of the driver when the closure is opened. The guide face preferably bears along the whole of its length against the front edge of the driver, wherein “length” is here denoted as the extent parallel to the front edge of the driver. As a result, the forces at play during the opening process are transmitted over a greater region, i.e. the pressure (force per unit of area) is thus diminished. An optimal slideway between driver and driving cam is hereby ensured. Preferably, the length of the guide face is at least 2 mm. 
     Preferably, the closure is configured such that the self-opening sleeve, after the closure has been opened for the first time, remains in its lower end position, i.e. is not transported back upward in the direction of its starting position by the driver when the closure is reclosed. In order to enable this, the driving cam is preferably of ramp-shaped configuration in a region situated, with respect to the opening direction, before the guide face, with a slide face directed inward obliquely to the opening direction, which slide face merges smoothly (without steps) into an inner cylindrical lateral surface of the self-opening sleeve. When the closure is reclosed, the driver then slides with its rear edge over the ramp-like slide face of the driving cam, so that the driver, upon reclosure by the driving cam, deflects radially inward and slides past the driving cam. 
     In order to facilitate the sliding of the driver over the slide face, the rear edge of the driver preferably runs inclined by a second angle of inclination in relation to the longitudinal axis, wherein the second angle of inclination is greater in magnitude than the first angle of inclination. In particular, it is preferred that the second angle of inclination is at least 50% greater, more preferably at least twice as large as the first angle of inclination. In practice, an angle of inclination of the rear edge within the range of about 30°-45° has proved successful. Should the rear edge be continuously curved in relation to the longitudinal axis, these data relate to the angle of inclination in the middle of the rear edge. 
     The resulting driver has in its upper region, close to the cover wall of the cap, its greatest extent along the circumferential direction, while this extent increasingly diminishes in the downward direction (toward its free end). As a result, the driver is most stable where the greatest forces are at play during first-time opening, namely in the upper region which is active at the start of the opening movement, when the self-opening sleeve begins to split the packaging wall. Moreover, by virtue of this design, the reaction forces which act on the driver during opening and closing are transmitted particularly well to the cover wall of the cap and thus to the whole of the cap structure, and a situation in which there are places in which excess stresses arise in the material, which stresses could lead to deformations or even to breaking off of the driver, is avoided. Due to this optimized force transmission, the driver can be produced particularly thin in the radial direction. This not only has advantages for the production (lower material consumption), but also minimizes the forces involved in the reclosure, since a thinner driver can more easily be deflected inward. 
     In order to prevent the self-opening sleeve from falling downward out of the pouring spout, on the lower end of the pouring spout can be configured a radially inwardly extending holding cam. In addition, measures are conceivable to prevent the self-opening sleeve from moving back in the direction of the starting position, for example measures which provide that the axial distance between two threaded segments of the internal thread is tapered at the lower end of the pouring spout in order to produce a clamping effect on a therewith cooperating turn of the external thread of the self-opening thread. 
     The self-opening sleeve preferably has a supporting ring, on which the external thread is configured, as well as a first tooth, which extends downward protruding from the supporting ring, and which defines a front cutting edge. The front cutting edge is preferably inclined by a third angle of inclination relative to the longitudinal axis. This angle preferably corresponds to at least the pitch angle of the internal thread of the pouring spout, preferably to at least double this pitch angle. As a result, the cutting edge acts on the packaging wall partly along the motional direction of the self-opening sleeve, and partly downward, during cutting. 
     The self-opening sleeve can have a second tooth, which, with respect to the opening direction, follows the first tooth. If precisely two teeth are present, i.e. if the self-opening sleeve otherwise has no further teeth, it is preferred if the second tooth follows the first tooth at an angular distance of about 90°-180°, preferably of about 110°-150°, particularly preferably of about 130°, with respect to the peripheral direction or opening direction, measured from tip to tip. It is also conceivable, however, for the self-opening sleeve to have three or more teeth, in which the case the distance between the teeth should be chosen correspondingly smaller. 
     A self-opening sleeve having precisely two teeth at said distance apart has proved successful, above all, in composite packagings in which a hole has been punched out in the cardboard support already prior to the lamination of the plastics and, if need be, metal layers. In prepunched packagings of this kind, this hole is spanned by a film composite, which can be fairly tough and in some circumstances very extensible and which thereby resists being torn open. Since precisely two teeth act on the film composite, during opening the film composite is clamped, so to speak, between two tooth tips. As a result, the film composite rips more easily. It has also been confirmed in trials that for prepunched packagings two teeth are optimal. Closures having just one tooth or having precisely three teeth can also however be used. 
     Preferably, the second tooth extends downward with respect to the longitudinal axis substantially equally as far as the first tooth. As a result, two regions of the film composite are reached simultaneously by the tooth tips, so that the clamping effect sets in early and a high tearing effect is obtained. 
     Preferably, the second tooth has a front cutting edge, which runs substantially at the same angle of inclination relative to the longitudinal axis as the front cutting edge of the first tooth. As a result, both teeth have the same cutting effect. This has a positive impact on the further opening operation once the film composite has been torn. 
     Between the first tooth and the second tooth can be continuously configured a ring segment (a material region in the shape of a cylinder wall segment), which extends downward from the supporting ring, wherein this ring segment, after the closure has been opened for the first time, projects jointly with the first and second tooth downward from the pouring spout, to be precise in particular by at least 1 mm. This material region, on the one hand, reinforces the self-opening sleeve and thus contributes to the stability thereof. On the other hand, such a material region can also serve to keep the cut-out packaging segment (“flap”) away from the pouring opening after the cutting operation. 
     In order to nevertheless ensure good residue emptying, the self-opening sleeve preferably has a segment along its periphery, which, after the closure has been opened for the first time, remains substantially fully within the pouring spout. In other words, there is a peripheral region in which the self-opening sleeve, after the closure has been opened for the first time, does not protrude downward from the pouring spout, or protrudes from the pouring spout at most by the thickness of the packaging wall, in concrete terms at most by about 1 mm, preferably no more than 0.5 mm. In this region (hereinafter referred to as the “residue emptying gap”), the content of the container can make its way unhindered into the pouring spout without a part of the self-opening sleeve getting in the way. 
     In order to prevent unintentional movement of the self-opening sleeve following fitting of the closure, for example as a result of vibrations during the application or during the later transport, the self-opening sleeve can have on its inner side, at a certain distance from the driving cam, a fixing cam. After the closure has been assembled and before the closure has been opened for the first time, the driver is located between the driving cam and the fixing cam. As a result, the mobility of the self-opening sleeve in relation to the driver (and thus in relation to the screw cap) is limited. Ideally, such a movement (play) of the self-opening sleeve is fully prevented. At the very least, however, the play is limited to a small angular range, for example of max. 20°. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Preferred embodiments of the invention are described below on the basis of the drawings, which serve merely for illustration and should not be interpreted restrictively. In the drawings: 
         FIG. 1  shows a perspective view of a closure according to a first embodiment in its opening position; 
         FIG. 2  shows a further perspective view of the closure of  FIG. 1 ; 
         FIG. 3  shows a central longitudinal section through the closure of  FIG. 1  in its starting position; 
         FIG. 4  shows a perspective view of the base of the closure of  FIG. 1 ; 
         FIG. 5  shows a perspective view of the self-opening sleeve of the closure of  FIG. 1 ; 
         FIG. 6  shows a perspective view of the cap of the closure of  FIG. 1 ; 
         FIG. 7  shows a perspective view of the closure of  FIG. 1  in its starting position; 
         FIG. 8  shows a perspective view of a self-opening sleeve of a closure according to a second embodiment, having only one tooth; and 
         FIG. 9  shows a perspective view of a self-opening sleeve of a closure according to a third embodiment, having three teeth. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     In  FIGS. 1 to 7 , a first embodiment of a closure according to the invention is illustrated in different views. This variant of the closure is particularly well suited to composite packagings having a cardboard layer with prepunched opening which is overlaminated with plastics films and, if need be, a metal foil. The closure consists of a base  10 , which in  FIG. 4  is represented in isolation, of a self-opening sleeve  20 , which in  FIG. 5  is represented in isolation, and of a cap  30 , which in  FIG. 6  is represented in isolation. 
     The base  10  has a base plate  11  for connecting the closure to a packaging wall (not represented). The base plate  11  has a circular opening, which is surrounded by a tubular, cylindrical pouring spout  12 . The pouring spout  12  extends upward from the base plate  11  up to a circumferential, circular upper rim  13 . The pouring spout  12  defines, due to its cylindrical basic shape, a central longitudinal axis L (see  FIG. 3 ), as well as an opening direction U along its periphery (see  FIG. 4 ). A radial direction is accordingly a direction which extends from the central longitudinal axis L outward in the direction of the peripheral wall of the pouring spout  12 . 
     On the inner side of the pouring spout  12  is configured an internal thread  14 , which has a pitch angle α relative to a plane running perpendicular to the longitudinal axis  11 . In the present example, this is constituted by a double thread having a pitch angle α of about 6.5° and about 1.5 windings. On the lower end of the thread  14  is configured a holding cam  19 . On the outer side of the pouring spout  12  is configured an external thread  15 , which has a significantly smaller pitch angle than the pitch angle α of the internal thread. Beneath the external thread are disposed on the base  10  a plurality of retaining webs  16 , which cooperate with a guarantee band described in further detail below. Ramps  17  on the base plate  11  aid the transport of the closure in an application device. Reinforcing ribs  18  strengthen the base plate  11  on its bottom side. 
     The self-opening sleeve  20  has a supporting ring  21 , on which two teeth  22 ,  23  are configured. The supporting ring  21  is provided on its outer side with an external thread  25 , which is complementary to the internal thread  14  of the pouring spout  12 . In the present example, the (likewise double) external thread  25  extends over somewhat more than half a winding. 
     On the inner side of the supporting ring  21  is configured a hook-shaped driving cam  24 . This defines a guide face  241 , which is inclined to the longitudinal axis L and is not configured flat, but concavely curved, with respect to the radial direction. The guide face  241  has no sharp bends whatever. The guide face is about 4 mm long. Before the guide face  241 , viewed in the opening direction, the driving cam  14  is of wedge-shaped or ramp-shaped configuration and forms a ramp-like slide face  242  which is inclined inward in the opening direction. This slide face  242  has no steps or bends and merges steplessly into the cylindrical inner peripheral face of the supporting ring  21 . 
     At some distance from the driving cam, situated behind the driving cam in the opening direction, is found a fixing cam  243 , which is discernible in  FIG. 7 . 
     Each of the two teeth  22 ,  23  has a front cutting edge  221  and  231  respectively, as well as a blunt rear edge  222 ,  232 . The front cutting edge  221  or  231  is inclined downward by an angle δ relative to the longitudinal axis. In the present example, the angle of inclination is about 18°. The rear edge  222  or  232  runs at an angle to the longitudinal axis L which is greater than the angle δ. In the present example, this angle is about 65°. The two teeth have a distance apart of about 120° along the peripheral direction. Between the first and the second tooth is configured a ring segment  26  (i.e. a material region in the shape of a cylinder wall segment), which extends downward from the supporting ring  21 . Before the first tooth  22  and behind the second tooth  23 , viewed in the opening direction, are configured further ring segments  27 , which extend downward from the supporting ring  21 , however, only by a comparatively small section. Between these two ring segments  27  there is a gap, which defines a residue emptying region  28  and the function of which is explained in greater detail below. The teeth  22 ,  23  and lateral wall regions  26 ,  27  are offset slightly radially inward in relation to the supporting ring  21 . Between them is configured, on the inner side of the self-opening sleeve  20 , a circumferential edge  29 , which, in the residue emptying region  28 , at the same time forms the bottom edge of the self-opening sleeve  20 . 
     The cap  30  has a cover wall  31  and a circumferential, substantially cylindrical side wall  32 . On the inner side of the side wall  32  is configured an internal thread  33 , which cooperates with the external thread  15  on the pouring spout  12 . From the cover wall  31 , a single driver  34  extends axially downward. The driver  34  forms a front edge  341  and a rear edge  342 . The front edge  341  is inclined relative to the longitudinal axis L by an angle β. The angle β amounts in the present example to about 20°. It is thus significantly greater than the pitch angle α of the internal thread  14  in the pouring spout  12 . The rear edge  342  is inclined relative to the longitudinal axis L by an angle γ. The angle γ is in the present case about twice as large in magnitude as the angle β and has the opposite sign hereto. The driver has the basic shape of a cylinder wall segment, wherein the helical front edge of the cylinder wall segment forms the aforementioned front edge  341  of the driver and the helical rear edge of the cylinder wall segment forms the aforementioned rear edge  342  of the driver. The bottom edge of the driver runs perpendicular to the longitudinal axis. The front edge  341  of the driver  34  is configured, in a region extending over the entire length of the front edge  341 , complementary to the guide face  241  of the driving cam  24 . As a result, this region of the front edge  341  bears squarely against the guide face  241 . 
     On the lower end of the side wall  32  of the cap  30  is configured a guarantee band  35  having inwardly directed retaining cams  36 . Between side wall  32  and guarantee band  35 , a cut is executed prior to fitting (“slitting”), so that the guarantee band remains connected to the rest of the cap only by thin material regions. The retaining cams  36  cooperate with the retaining webs  16  on the base  10  in order to prevent the co-rotation of the guarantee band  35  when the closure is opened for the first time. As a result, upon first-time opening, the guarantee band  35  is separated from the rest of the cap, falls downward onto the base plate  11  and thus indicates the first opening. Possible other configurations of the guarantee band are known from the prior art. 
     The closure is preferably produced in two pieces, wherein the base  10  and the self-opening sleeve  20  are produced in one piece in a single injection mold, for example from HDPE. To this end, the self-opening sleeve  20 , following production, is initially connected on its top edge by narrow material bridges  201  ( FIG. 5 ) to the bottom side of the base  10 ; these material bridges are broken upon fitting of the closure. The cap  30  is produced in a separate injection mold and can consist of the same material as the base  10  and the self-opening sleeve  20 . Such a two-piece production of the closure is in principle known from the prior art. 
     The closure is fitted by pressing the self-opening closure  20  axially into the pouring spout  12  and pressing the cap  30  axially onto the pouring spout  12 . The closure is then in its starting position, which is illustrated in  FIGS. 3 and 7 . The self-opening sleeve  20  is here fully within the pouring spout  12 . As can be seen in  FIG. 7 , in this position the driver  34  is disposed between the driving cam  24  and the fixing cam  243 . As a result, unintended rotation of the self-opening  20  in the fitted closure is prevented. In this form, the closure is positioned above an overlaminated opening of the packaging wall and fastened (for example welded or glued) onto the packaging wall. 
     For the first-time opening of the packaging, the user turns the cap  30  counterclockwise (i.e. in the opening direction U). By means of the driver  34  and the driving cam  24 , the cap  30  here transports the self-opening sleeve  20  and sets this likewise in rotation. The front edge  341  of the driver  34  bears on the guide face  241  of the driving cam  24  over the entire length of the driving cam  24  and slides on said guide face. Due to the threaded joint between the self-opening sleeve  20  and the pouring spout  12 , the self-opening sleeve  20  moves helically downward. The teeth  22 ,  23  here pierce the laminated films, and, if need be, the metal layer, on the opening of the packaging wall, and afterward further cut these open. The cap  30  transports the self-opening sleeve  20  until such time as this has reached its lower opening position, as is illustrated in  FIG. 1 . At this point, the external thread  15  on the pouring spout  12  and the internal thread  33  on the cap  30  cease to engage in each other, and the cap  30  can be pulled off the pouring spout  12 . The self-opening sleeve is prevented by the holding cam  19  from being further rotated downward, so that it cannot fall downward out of the pouring spout  12 . The teeth  22 ,  23  and the ring segments  26 ,  27  now project downward from the pouring spout  12 . In the residue emptying region  28 , the self-opening sleeve  20 , by contrast, does not project downward from the pouring spout  12 , or at least does not project downward beyond the packaging wall. The residue emptying of the container is thereby facilitated. 
     When the closure is opened for the first time, the driver  34  exerts on the driving cam  24  a force which is directed obliquely downward. As a result of this force transmission between driver  34  and driving cam  24 , the downward movement of the self-opening sleeve  20  is aided. The here acting reaction forces are transmitted over the entire length of the base of the driver  34  to the cover face  31  of the cap  30 , without generation of excessive stresses. All in all, an almost optimal force transmission is in this way ensured. As a result of the hook-like configuration of the driving cam  24 , a radial swerving of the driver  34  in the inward direction is here prevented. 
     For re-closure, the user places the cap  30  back onto the pouring spout  12  and screws the cap  30  back onto the pouring spout  12 . The driver  34  here slides with its rear edge  342  over the slide face  242  of the driving cam  24  and is here deflected radially inward, so that the self-opening sleeve  20  remains in its lower opening position. 
     In  FIG. 8 , a self-opening sleeve (cutting ring) according to a second illustrative embodiment is illustrated by way of example. Mutually corresponding parts are provided with the same reference symbols as in the embodiment of  FIGS. 1 to 7 . This embodiment is in particular suited to packagings which have no prepunched and overlaminated opening. In particular, the packaging can be made of a single-layered plastics wall. In this case, it is advantageous to provide just a single tooth  22 . In this way, the opening forces are optimally concentrated on a single point. Apart from this, the closure of  FIG. 8  is configured substantially the same as that of  FIGS. 1 to 6 . 
     A self-opening sleeve (cutting ring) according to a third illustrative embodiment is represented by way of example in  FIG. 9 . Here three teeth  22 ,  23 ,  23 ′ are present, the tips of which are spaced apart by respectively about 70°. Otherwise, mutually corresponding parts are in turn provided with the same reference symbols as in the embodiment of  FIGS. 1 to 7 . 
     Of course, a large number of modifications are possible without departing from the scope of the invention. It is in particular conceivable not to connect the cap by a threaded joint to the pouring spout, but, for example, to provide a bayonet-type connection in which the cap firstly, upon opening, performs a pure rotation and is subsequently pulled off axially. It is clear that such a variant has only a small influence on the cooperation of the driver with the driving cam. The shape of the tooth or teeth can also, of course, be chosen differently than in the present example. In addition, a (blunt) tooth-like hold-down device can be provided in order to bend back the cut-out segment of the packaging wall (“flap”) downward, into the inside of the packaging, so that this cutout does not impede the pouring out of the content of the packaging. Designs of this type are in principle known from the prior art. The pouring spout can be configured, instead of on a separate base element, essentially also in one piece with the packaging wall, or can form the upper end of a bottle neck. A large number of further modifications is possible.