CAP FOR A CONTAINER CLOSURE

Abstract: A cap for a container closure is adapted to receive an insert (shown in Figure 3) by engagement of a projec­ tion on the insert in a recess (34) in the cap. The cap is recessed to receive the insert in a region (40) near the open mouth (36) of the cap. The cap is outwardly flared in this region so that no significant reduction in wall thickness of the cap occurs in this region (40), the outer form of the flaring comprising a smooth curve which, in the direction towards the mouth opening (36) of the cap comprises a portion which has an outwardly presented concave curve (42) swelling smoothly from the upper wall (43) of the cap and merging by a convex curve (44) into the lower, larger diameter wall (45) of the cap. The convex curve (44) can be sharper than the con­ cave curve (42).

Description: This invention relates to a cap for a container closure which is adapted to receive and interengage with an insert to form the container closure and is concerned to provide a cap which is convenient to mould and is reliably strong in use. The insert may, for example, incorporate a guarantee band, that is a band which will engage below a bead formed around a container neck, when the closure is applied to the container, and which is so formed that it cannot subsequently be removed from the container without breaking the band and/or breaking the connection of the band to the closure. Thus, the fact that the guarantee band, and therefore the closure to which it is attached, has been removed from the container becomes visible and such bands are sometimes known as tamper-indicating bands. It is convenient, in order to facilitate the removal of parts from a mould to mould the cap of the closure separately from a part (the insert) comprising an element constituting the guarantee band and an element to which the guarantee band is attached by breakable connections and which serves to attach this part to the cap by means of a projecting annular rib which engages in an annular recess provided in the wall of the cap. The present invention relates to the form of the cap of such a two-part container closure comprising a cap and an insert adapted to be received in the cap and retained therein by engagement of a projection on the insert in an annular recess or a plurality of annular recesses in an annular region of the cap. The form of such a cap is such that the recess or recesses for receiving and interengaging with the insert is/are provided in a region near the open mouth of the cap, the cap being outwardly flared in this region so that no significant reduction in wall thickness of the cap occurs in this region, the outer form of the flaring comprising a smooth curve which, in the direction towards the mouth opening of the cap comprises a portion which has an outwardly presented concave curve swelling smoothly from the upper wall of the cap and merging by a convex curve into the lower, larger diameter wall of the cap. A cap of this form is described in EP-A-0185288. According to the invention, in such a cap for a two-part container closure the or each recess in the cap for receiving the insert as described is defined by a lower edge (nearer the mouth opening of the cap) which is inclined at an angle no greater than 70° and no less than 60° to the axis of the cap. Preferably, the intersection of the said lower edge of the or each recess with the base of the recess is constituted by a sharp corner defined, substantially, by the intersection of two lines which are straight in cross-sectional configuration, and the outer lip of the said lower edge of the or each recess is defined by a convex curve which in cross-section is part of a circle having a radius in the range of 0.25 to 0.35 mm. The measures just mentioned provide a form of recess which shows good retention of an appropriately shaped projection on the insert but which facilitates moulding of the cap. The invention will be further described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a cross-section through a cap according to the invention, Figure 2 is a cross-section on an enlarged scape of part of the cap of Figure 1, and Figure 3 is a cross-section through an insert for attachment to the cap of Figure 1. The cap shown in the drawings which, together with the insert also shown may be made by injection moulding in synthetic plastics material, for example polyethylene or polypropylene, comprises an end wall 10 and a generally cylindrical side wall 11. The end wall 10 has internal annular lips 12 and 13 and a ring of retaining members 14 to retain in the cap a sealing gasket 15 formed by running gasket material in a liquid state into the cap and solidifying and curing it. The side wall 11 has an internal screw thread 16 for engagement with a corresponding screw thread on the neck of a container, and one or more axial slots 17 to relieve the pressure in a container to which the cap is applied immediately the sealing gasket 15 lifts away from the open end of the container at the start of the operation of removing the cap. The cap is adapted to receive and interengage with an insert to form a container closure in which the insert is attached to the cap. An insert 18 incorporating a guarantee band is shown in Figure 3 but such inserts may incorporate other elements for a closure in addition to or instead of a guarantee band. The insert 18 comprises two elements; a guarantee band 21, and an annulus 22 having a projecting lip 23 for engagement in an annular recess 34 provided internally of the cap wall. The guarantee band 21 has an internally projecting rib 24 for engagement under a bead of a container so that after application to a suitable container of a closure comprising a cap with an insert 18 attached to it, the closure cannot be removed from the container without breaking the guarantee band 21, and/or its connection to the annulus 22. In the present case, the guarantee band is connected to the annulus 22 by breakable bridges 25. A further bridge 26 may be stronger than the bridges 25 so that it does not break and the guarantee band remains attached to the annulus 22 and the cap after removal of the cap from a suitable container. The bridges 25 and 26 are extensions of internal axially extending ribs 27 formed on the annulus 22 for a purpose mentioned below. The projecting lip 23 has a downwardly and outwardly inclined surface 28, a short cylindrical surface 29 parallel to the axis 30 of the insert and an under-surface 31 which is substantially flat and extends at right angles to the axis of the insert. In the present example of an insert for a cap having a maximum external diameter of approximately 38mm, the height of the surface 29 may be 1.0mm whereas the total height of the projecting lip is 2.3mm and the vertical height of the inclined surface 28 is 1.3mm. The total height of the annulus 22 is 4.6mm and the depth of projecting lip 23 (i.e. the width of the surface 31) is 0.5mm. The surface 28 makes an angle of 25° with the axis 30 of the insert and serves to guide the insert into the cap when the insert is to be attached to the cap. The projecting lip 23 of the annulus 22 engages in the annular recess 34 formed internally of the side wall 11 of the cap. The recess 34 has a lower edge 35 nearer a mouth opening 36 of the cap which is inclined at an angle of 60° to the axis of the cap (that is at an angle of 30° to a radius of the cap). The inclination of this edge 35 assists in ejection of the cap from the mould but too great an inclination may allow the insert 18 to escape from the cap under some circumstances. Thus the inclination of the edge 35 to the axis of the cap should be no less than 60° and no more than 70° (30° and 20° respectively in relation to the radius direction of the cap). Retention of the lip 23 of the insert 18 in the recess 34 is assisted if, as in the present example, the intersection of the lower edge 35 with the base 37 of the recess 34 is constituted by a sharp corner 38 defined by the intersection of substantially straight lines constituting the edge 35 and base 37 in cross-sectional configuration. Ejection from the mould is facilitated if the outer lip 39 of the edge 35 is convexly curved, as in the present example. Here, the lip 39 is part-circular in cross-section with a radius of 0.3mm (advantageously 0.25 to 0.35mm). The depth of the recess 34, that is the width of the edge 35 (in the direction at right angles to the axis of the cap) is 0.5mm so that the radius of the lip 39 is 3/5 of the depth of the recess and the depth of the recess 34 is equal to the depth of the projecting lip 23. In order to retain the wall strength of the side wall 11 in a flared region 40 near the open mouth 36 of the cap, the wall thickness and thus the strength of the side wall 11 are maintained without significant reduction. The outer form of the flared region is such that it comprises a smooth curve which, in the direction towards the mouth opening of the cap comprises a portion 42 which is outwardly concave and swells smoothly from the upper wall 43 of the cap and merges through a sharper outwardly convex curve 44 into the lower, larger diameter wall 45 of the cap. An outer knurling 46 is retained on the external surface of the cap through the flared region 40 almost down to the open mouth 36 of the cap. The inner surface of the cap in the flared region 40 comprises a region 47 extending at right angles to the axis of the cap and a downwardly and outwardly inclined region 48 which together form the upper edge of the recess 34 and are located and dimensioned in relation to the outer surface of the side wall 11 in the flared region 40 that the wall thickness in the flared region 40 does not fall below the wall thickness of 0.75mm at a level 49 where the flaring commences and is usually above this, reaching a maximum of 1,2mm at a level where the change from an outwardly concave to an outwardly convex curvature takes place. When a closure comprising a cap with an insert 18 introduced into it is applied to a container, the ribs 27 on the annulus 22 will engage against the bead on the neck of the container and serve to urge the projecting lip 23 into the recess 34. It is preferred, in the present example, to make the cap of polypropylene because its resistance to high temperatures permits high temperature curing of gasket material introduced into it. The preferred material for the insert 18 is low density polyethylene because this allows the guarantee band to stretch more readily to pass over the retaining bead on a container neck when the closure is applied to a container and it also allows the insert 18 to be pushed into a cap more easily. When moulded from two different materials, a colour contrast can be provided between the cap and the insert which can make it easier to spot when a guarantee band has been broken.

Claims: A cap for a container closure comprising a cap and an insert (18) adapted to be received in the cap and retained therein by engagement of a projection (23) on the insert (18) in an annular recess (34) in the cap, or a plurality of recesses in an annular region (40) of the cap, near the open mouth (36) of the cap, the cap being outwardly flared in this region so that no significant reduction in wall thickness of the cap occurs in this region (40), the outer form of the flaring comprising a smooth curve which, in the direction towards the mouth opening (36) of the cap comprises a portion which has an outwardly presented concave curve (42) swelling smoothly from the upper wall (43) of the cap and merging by a convex curve (44) into the lower, larger diameter wall (45) of the cap, characterised in that the or each recess (34) has a lower edge (35) inclined at an angle no greater than 70° and no less than 60° to the axis of the cap. A cap as claimed in claim 1, characterised in that the intersection of said lower edge (35) of the or each recess (34) with the base (37) of the recess is constituted by a sharp corner (38) defined, substantially, by the intersection of two lines which are straight in cross-sectional configuration and the outer lip (39) of the said lower edge (35) of the or each recess (34) is defined by a convex curve which in cross-section is part of a circle having a radius in the range of 0.25 to 0.35 mm. A cap as claimed in claim 2, characterised in that the radius of the circle of which the convex curve of the outer lip (39) is a part is some 60% (3/5ths) of the depth of the or each recess (34) (measured in the radial direction of the cap). A cap as claimed in any preceding claim, characterised in that of the curves defining the outer form of the flaring of the cap in the region (40) near the open mouth (36) of the cap, the convex curve (44) is sharper than the concave curve (42).

Inventors: BAXTER, ALAN ANDREW
Applicants: NATIONAL PLASTICS LIMITED
Application year: 1987
Main classification: B65D55
IPC codes: B65D41