WO2005110707A1

WO2005110707A1 - Injection moulding plastic container caps

Info

Publication number: WO2005110707A1
Application number: PCT/GB2005/001859
Authority: WO
Inventors: Matthew Eric Smith; Karl Mondszein
Original assignee: Carbonite Corporation
Priority date: 2004-05-13
Filing date: 2005-05-12
Publication date: 2005-11-24
Also published as: GB0410731D0

Abstract

A method of injection moulding a rotationally symmetrical container cap includes injecting molten plastic material into a mould cavity (50) defined by at least two mould members (52, 56, 58, 60, 62). The mould cavity is shaped to form a container cap comprising a closure plate (30, 32), which extends, in use, over the mouth and rim of a container, an integral depending skirt (18), which, in use, extends down around the outer surface of the rim (8) of the container and a fastening flange (20), which is integral with the inner surface of the skirt and extends generally away from the closure plate and inwardly towards the axis of the cap. The plastic material is permitted to solidify within the cavity. A first mould member (58), which defines the inner surface of the fastening flange, and a second mould member (52), which defines the upper surface of the cap, are moved relatively apart so as to move the solidified cap out of contact with the second mould member (52). The first mould member (58) is moved relative to the solidified cap until its free end closest to the second mould member (52) has moved beyond the free end of the fastening flange. The first and second mould members (52, 58) are then moved towards one another so that the said free end of the first mould member (58) engages the fastening flange and rotates it about its connection (22) with the skirt (18) to a position in which it extends generally towards the closure plate and inwardly towards the axis of the cap.

Description

INJECTION MOULDING PLASTIC CONTAINER CAPS

The present invention relates to a method of moulding plastic lids or caps for bottles or other containers, particularly beverage containers with a wide mouth with a diameter in excess of 25 mm, of the type disclosed in International Patent Application No. PCT/GB2005/000986. More specifically, the invention is concerned with moulding plastic caps of the type comprising a closure plate, integral with the peripheral edge of which is a depending skirt, the inner surface of which carries a fastening flange, the free end of which, when the lid is applied to a container, engages the underside of a peripheral annular flange on the outer surface of the neck of the container and retains it in position on the container.

Such a container lid will now be described in more detail with reference to Figures 1, 2 and 3 of the accompanying drawings which are an axial section view of the lid after being moulded, a similar view of the lid whilst being applied to the neck of a beverage container and a further similar view of the lid after application to the neck of a beverage container, respectively.

The lid comprises a one-piece component, integrally moulded from resilient plastic material, such as polypropylene. It comprises a shaped closure plate, integral with which is a web 16 which extends, when the lid is connected to the bottle, over the rim of the bottle. Integral with the web 16 is a depending skirt 18, which extends, in use, downwardly around the exterior of the upper portion of the bottle. Integrally connected to the lower edge of the skirt 18 or to the inner surface of the skirt at a position adjacent its lower edge is an annular retaining flange 20. The flange 20 is connected to the skirt 18 by a resilient connecting web 22, which is of reduced thickness and thus constitutes an annular line of weakness or predetermined breaking point. Connected to the lid at one circumferential position is a rupturing tab 24 which extends downwardly below the lower edge of the skirt 18. This tab is connected to the skirt 18 at its side by two lines of weakness, i.e. regions of reduced thickness.

The closure plate of the lid is concave and thus extends into the neck of the bottle, when it is connected to the bottle. The closure plate comprises a wall portion 30 which extends generally downwardly and inwardly and merges at its lower edge with a base portion 32, which is downwardly arcuate, that is to say is of downwardly curved convex shape.

The lid is shown in Figure 1 in the configuration in which it is moulded. In this configuration, the flange 20 extends downwardly and inwardly and the diameter of its lower edge is less than that of the upper edge of the rim of the bottle, to which it is to be applied, whilst the diameter of its upper edge is greater than that of the upper edge of the rim of the bottle.

The lid may be fastened and sealed to the bottle by a simple snap- fit procedure. This is effected simply by lowering the lid into the rim of the bottle and then applying pressure. As the lid is lowered, the lower edge of the flange 20 comes into contact with the rim. This causes the flange to rotate inwardly about the web 22. As downward movement of the lid continues, the flange 20 moves downwardly in contact with the downwardly and outwardly inclined surface 12, on the outer surface of the rim of the bottle, as shown in Figure 2, and the increasing diameter of this surface in the downward direction results in the rotation of the flange continuing, thus moving it ever closer to the inner surface of the skirt 18. The underside of the web 16 then contacts the upper surface of the rim of the bottle. However, the pressure on the cap is maintained and this results in slight deformation of the web 16. The cap and bottle are so dimensioned that the slight further downward movement of the cap caused by the deformation of the web 16, is sufficient to permit the free end of the flange 20 to move past the shoulder 14. It is then rotated in the opposition direction, i.e. inwardly, by the resilience of the web 22 and thus becomes locked behind the shoulder, as shown in Figure 3. The lid is now retained in position on the bottle and cannot be removed without damaging or deforming it. The tension maintains the underside of the web 16 in engagement with the upper surface of the rim with a contact pressure sufficient to ensure that a first gas seal is formed along the annular line of contact. The tension in the skirt 18 also maintains the free end of the flange 20 in engagement with the surface of the shoulder 14 with a contact pressure sufficient to ensure that a second gas seal is formed along the annular line of contact. Furthermore, the resilience of the connecting web 22 forces the side surface of the free end of the flange 20 into contact with the side surface of the bottle and the contact pressure is preferably sufficient to form a third gas seal. The integrity of the first gas seal may be further enhanced, if required, by the provision of an annular bead or flange 17, which is shown in phantom lines in Figure 1 and which will engage the upper or side surface of the rim of the bottle and constitute an additional lip seal. If the pressure in the bottle should rise to a high value sufficient to deform the cap away from the rim of the bottle, thereby breaking the first gas seal, pressurised gas will flow into the space defined by the outer surface of the rim, the skirt 18 and the flange 20. This pressure will act on the flange 20 to press it yet more firmly against the side surface of the rim, thereby increasing the integrity of the third gas seal.

Yet a further gas seal may be provided between the surface 10 of the rim and the outer surface 34 of the wall portion 30. Thus these two surfaces are formed as complementary sealing surfaces in sealing engagement with one another. If the pressure in the bottle should become super-atmospheric, either as a result of the liberation of carbon dioxide from a carbonated beverage or as a result of the expansion of gas in the head space of the bottle due to an increase in temperature, the centre of the concave base portion 32 will be deformed upwardly and this will inherently result in the outer edge of the base portion 32 and thus the lower edge of the wall portion 30 moving slightly outwards. This will result in an increase in the contact pressure between the sealing surfaces 12 and 34 and thus in an enhancement to the integrity of this further gas seal.

When it is desired to open the bottle, the user merely grasps the lower edge of the rupture tab 24 and pulls it outwardly. The lines of weakness immediately rupture or stretch and the upper edge of the tab 24, which is connected to the web 16, rotates, thereby breaking the second and third gas seals. This rotation is transmitted to the web 16, which thus moves away from the rim of the bottle, thus breaking the first gas seal. This movement of the web 16 also causes the sealing surfaces 12 and 34 locally to move apart, thereby also breaking the further gas seal. The container is thus depressurised. The outward movement of the tab 24 initiates tearing of the thin connecting web 22, and once tearing has started it is a simple matter to keep it going by exerting upward and outward pressure on the tab 24 until the lid is completely disconnected from the flange 20, which remains in position around the neck of the bottle. The lid may now be discarded and the contents of the bottle dispensed or drunk. Thus when the lid is fitted to a bottle, the flange 20 is caused to rotate by engagement with the rim of the bottle from the position shown in Figure 1 to that shown in Figure 3. This necessarily happens whilst the plastic material is cold. However, polypropylene, which is one of the most commonly used thermoplastic materials for bottle lids, is semi-crystalline and rotation of the web or integral hinge 22 through a substantial angle, which is likely to be in excess of 90°, introduces significant stresses which can result in cracks forming in the web 22 or even in complete failure of the web 22. This can result in failure of the gas seal and even in the lid coming free from the container, both of which are unacceptable.

It is therefore the object of the invention to provide a method of moulding a container lid of the type specified which results in lids which are not subject to the problem referred to above.

According to the present invention there is provided a method of injection moulding a rotationally symmetrical container cap including injecting molten plastic material into a mould cavity defined by at least two mould members, the mould cavity being shaped to form a container cap comprising a closure plate, which extends, in use, over the mouth and rim of a container, an integral depending skirt, which, in use, extends down around the outer surface of the rim of the container, and a fastening flange, which is integral with the inner surface of the skirt and extends generally away from the closure plate and inwardly towards the axis of the cap, permitting the plastic material to solidify within the cavity, moving a first mould member, which defines the inner surface of the fastening flange, and a second mould member, which defines the upper surface of the cap, relatively apart so as to move the solidified cap out of contact with the second mould member, moving the first mould member relative to the solidified cap until its free end closest to the second mould member has moved beyond the free end of the fastening flange and moving the first and second mould members towards one another so that the said free end of the first mould member engages the fastening flange and rotates it about its connection with the skirt to a position in which it extends generally towards the closure plate and inwardly towards the axis of the cap.

Thus in the method in accordance with the invention the cap is injection moulded into the general configuration shown in Figure 1 in which the fastening flange extends generally away from the closure cap and inwardly towards the axis of the cap. However, whilst the plastic material is still hot, the mould members are moved sequentially so that the fastening flange is rotated through a significant angle, e.g. in excess of 60° and preferably about 90° or even more so that it extends generally towards the closure plate and axially inwardly. As a result of the fact that this rotation occurs whilst the plastic material is hot and has therefore not yet become crystalline, no stress cracking occurs. When the cap is subsequently applied to a container, only a small amount of further rotation is necessary, caused by engagement of the flange with the exterior of the container, before the flange is able to move under its own resilience into engagement with the shoulder on the exterior of the container. This small amount of further rotation, which necessarily happens after the plastic material has cooled, is insufficient to cause stress cracking or failure of the web connecting the flange to the depending skirt.

The mould may have many configurations and the manner and sequence in which the mould members are moved in order to rotate the hot flange into the desired position will depend on the configuration which is selected. However, in one embodiment, the mould cavity is partially defined by a third mould member which is in engagement with the free edge of the depending skirt of the moulded cap and the method includes moving the first and third mould members away from the second mould member, then moving the first mould member relative to the third mould member away from the second member thereby deflecting the fastening flange of the moulded cap outwardly until the free end of the first mould member has moved beyond the free end of the fastening flange, which then moves back inwardly under its resilience.

Further features and details of the invention will be apparent from the following description of one specific method in accordance with the invention, which is given by way of example with reference to Figures 4 to 7 of the accompanying drawings, in which:

Figure 4 is a diagrammatic sectional view of an injection mould for use in the method, when closed;

Figure 5 is a similar view showing the mould being opened after completion of the injection process;

Figure 6 is a further similar view showing the advance of the stripper core to rotate the fastening flange; and

Figure 7 is yet a further similar view showing ejection of the moulded container lid. The mould shown in Figures 4 to 7 defines, when closed, as shown in Figure 4, a mould cavity 50, whose shape corresponds to that of the lid shown in Figure 1. The mould comprises a stationary cavity member 52, which may in fact comprise two or more relatively fixed members, and accommodates an injection nozzle 54. The cavity member 52 cooperates with four further mould members, all of which are movable relative to the cavity member. The first movable member is a central ram member 56, which defines one side of that portion of the mould cavity which defines the central portion of the closure plate of the lid. Extending around the ram member is an annular core member 58, which defines one side of that portion of the mould cavity which defines the outer portion of the closure plate, most of the depending skirt and the fastening flange. Extending around the core member 58 is an annular stripper core 60, which defines the other side of that portion of the mould cavity which defines the fastening flange and one side of that portion of the mould cavity which defines the remainder, that is to say the free end portion, of the depending skirt of the lid. Finally, extending around the stripper core is an annular stripper ring 62 which defines that portion of the mould cavity which defines the free end surface of the fastening flange on the lid.

When the mould is in the closed configuration shown in Figure 4, hot molten thermoplastic material, e.g. polypropylene, is injected into the mould cavity 50 through the injector nozzle 54. When the plastic material has solidified but before it has cooled, the movable mould members 56, 58, 60 and 62 are moved away from the stationary cavity member 52, taking the solidified plastic moulding 64 with them, as shown in Figure 5. The annular stripper ring 62 then stops and the other members continue to move. The free edge of the depending skirt of the moulding engages the stripper ring 62 which thus prevents it from moving any further. The continued movement of the other movable mould members thus results in their separating from the moulding. As the core member 58 moves away from the moulding, it deflects or rotates the fastening flange outwardly, whereafter it returns to its original position under its own resilience. The central ram member 56 and the stripper ring 62 are then moved relative to the other two movable mould members back to their original position, thus moving the moulding back into contact with the fixed cavity member 50. The fastening flange is now in line with the free end of the annular core member 58, as seen in Figure 5. As the annular core member is advanced towards the fixed cavity member, it rotates the fastening flange inwardly until it is pointing generally towards the closure plate, as shown in Figure 6. This occurs whilst the plastic material is still hot and has therefore not as yet become crystalline. The rotation is therefore not accompanied by stress cracking or the like. The movable mould members are then all moved away from the fixed cavity member, as shown in Figure 7. Compressed air is then blown through the nozzle 54 to eject the moulding.

The moulding process is now complete and the moulded cap may now be applied to a container. The application process will, however, necessitate the fastening flange rotating through a very small angle as it is rotated by contact with the exterior of the container before it can snap under its own resilience into a position in which its free end is in engagement with a downwardly directed shoulder on the exterior of the container. This is in contrast to a manufacturing method in which the finished moulding has the configuration shown in Figure 1 and the fastening flange must thus be rotated through more than 90° when it is applied to a container.

Claims

1. A method of injection moulding a rotationally symmetrical container cap including injecting molten plastic material into a mould cavity defined by at least two mould members, the mould cavity being shaped to form a container cap comprising a closure plate, which extends, in use, over the mouth and rim of a container, an integral depending skirt, which, in use, extends down around the outer surface of the rim of the container and a fastening flange, which is integral with the inner surface of the skirt and extends generally away from the closure plate and inwardly towards the axis of the cap, permitting the plastic material to solidify within the cavity, moving a first mould member, which defines the inner surface of the fastening flange, and a second mould member, which defines the upper surface of the cap, relatively apart so as to move the solidified cap out of contact with the second mould member, moving the first mould member relative to the solidified cap until its free end closest to the second mould member has moved beyond the free end of the fastening flange and moving the first and second mould members towards one another so that the said free end of the first mould member engages the fastening flange and rotates it about its connection with the skirt to a position in which it extends generally towards the closure plate and inwardly towards the axis of the cap.

2. A method as claimed in Claim 1 in which the mould cavity is partially defined by a third mould member which is in engagement with the free edge of the depending skirt of the moulded cap and the method includes moving the first and third mould members away from the second mould member, then moving the first mould member relative to the third mould member away from the second member thereby deflecting the fastening flange of the moulded cap outwardly until the free end of the first mould member has moved beyond the free end of the fastening flange, which then moves back inwardly under its resilience.