COMPOUNDED CLOSURE

Abstract: A thermoplastic closure consisting of a circular top wall (1) and an internally threaded skirt (2, 3) with an annular inwardly directed protrusion (15) extending from the inner wall of the skirt (2) below the intersection (7) of the skirt (2) with the closure top wall (1). The protrusion (15) is adapted to receive a flowed in gasket (8) and as the closure is screwed into place on a container (4) to urge the gasket (8) against the outside of the container neck (16) to thereby effect a side seal in this area (16). A method of flowing a gasket into a closure shell by injecting a metered amount of EVA through a nozzle into the shell while spinning the shell is also disclosed.

Description: COMPOUNDED CLOSURE FIELD OF THE INVENTION The present invention relates to the field of closures and in particular to thermoplastic closures having an internally threaded skirt and adapted to seal containers with contents at superatmos- pheric pressure such as,for example, carbonated beverages. BACKGROUND OF THE INVENTION As such closures are commonly manufactured of relatively inflexible plastics in order to achieve the desired resistence to deformation under pressure they commonly additionally incorporate resiliently deformable gaskets flowed onto that area of the closure intended to abut against the neck of a container thus effecting a seal. A compounded closure as las.mentioned has the advantage that the gasket may deform so as to take up manufacturing variations commonly encountered with containers whilst the structural integrity of the closure as a whole is ensured by the relatively rigid nature of the thermoplastic shell. A number of difficulties occur in the design and manufacture of such compounded closures and in particular it has been found that (unless they are excessively thick walled with attendant additional material costs) they suffer from outward doming of the top wall of the closure when the contents of a container are at superatmospheric pressure. This doming effect serves to destroy any seal which relies upon contact between the inside top wall of the closure (or a gasket adhered or affixed thereto) and the top of the container neck. Furthermore it has been found that known flow in compounds commonly used to form gaskets do not readily adhere to the thermoplastic shell of the closure, typically of polypropylene. This lack of adhesion makes it difficult to ensure that such a gasket does not move out of the desired relationship with the closure shell during relative rotation between closure and container when sealing a container, the subsequent removal of the closure or indeed a subsequent resealing operation. The gaskets for example have a tendency to rotate with respect to the closure shell during a sealing or removal operation and furthermore they may stick to the container and come away from the closure shell during a removal operation. Various closures have been proposed to alleviate the abovementioned difficulties including gasket retaining means and sealing surfaces not affected by doming but many are relatively complex and hence expensive whereas others are ineffective. OBJECTS Accordingly it is- the object of the present invention to provide the consumer with a relatively inexpensive closure which avoids one or more of the aforementioned disadvantages with existing compounded closures or at least to provide the consumer with a useful choice. SUMMARY OF THE INVENTION According to the present invention there is provided a thermo¬ plastic shell for a compounded closure having a circular top wall and an annular internally threaded skirt,an annular inwardly directed protrusion from the inner wall of the skirt below the intersection of said skirt with the closure top wall adapted to receive a flowed in gasket and, as the closure is screwed into place upon a container, to urge such gasket against the outside wall of the neck of such container thereby effecting a side seal. The present invention also discloses a method of distributing EVA solution in a closure in accordance with the present invention in order that such compounded closure may conrounicate with a container and effect a side seal thereon. A preferred embodiment of the present invention will now be described by way of example only with reference to the accompanying- drawing. DESCRIPTION OF THE DRAWINGS Figure(i)is a part radial sectional view of a closure in accord¬ ance with the present invention in sealing relationship with the neck of a container. DESCRIPTION OF THE EIBODIMENT Figure 1 depicts a closure having a circular top wall (1) and an annular skirt (2) depending therefrom and provided with internal threads (3) adapted to comrnunicate with a threaded bottle neck (4). The circular top wall of the closure (1) is relieved at (5) so as to be relatively thin walled~-adjacenfe~__gea.- 6.)...Thi_ -th___-^ .bein concentric with and inboard of the peripheryof top wall (1) acts as a hinge allowing the central portion of tne top wall of the closure to dome with minimum effect upon the top seal between the flowed in gasket (8) and the container neck at (9). If the top wall of the closure were not relieved adjacent (5) then hinging may occur at the intersection (7) of the top wall and skirt with attendant deterioration in the top seal at area (9). The closure in figure (1) additionally depicts a radially in¬ wardly directed annular bead (10) with an undercut at (11) adjacent the intersection of the inner surfaces of the top wall and the annular skirt. This undercut,in conjunction with opposing undercut (12) in the annular lip (13) depending from the inside surface of top wall (1), mechanically restrains gasket (8) from downward axial MPI and lateral movement with respect to the closure whilst a plurality of radial ribs (14) depending from the inner surface of top wall (1) assist in preventing rotational movement of the gasket (8) witn respect to the main body of the closure. An annular inwardly directed protrusion from the inner wall of the sKirt is depicted at (15) ana it will be observed ttiat this is located sufficiently below tne intersection of the top wall and tne skirt in order that during application of the closure it may urge gasket material in area (17) against tne outside wall of the con¬ tainer neck adjacent area (16) in order to provide a side seal. In closures adapted for use with bottle necks of internal diameter 18mm a clearance of .5mm between the radially inner extremity of protrusio (15) and the container neck at (16) has been found to be satisfactory to accomodate manufacturing variations in neck diameters and hence avoid direct protrusion/neck contact yet still ensure adequate com¬ pression of gasket material at (17). It will be appreciated that the preferred embodiment of the present invention therefore provides botn a top seal adjacent area (9) and a side seal adjacent area (lb). In the event tnat doming of tne top wall of the closure occurs lessening the effectiveness of the seal at area (9) then the seal adjacent area (16) should not be effected and indeed to the extent tnat doming tends to pull the skirt radially inwards then a side seal may actually be enhanced by doming. The gasket (8) is formed- from a metred quantity (about 280 mg for a cap to suit a glass closure of 18mm bore diameter) of EVA flowed onto the cap in the area adjacent undercut (12) whilst the cap is being spun preferably between 1,300 and 1,500RPM. Centrifugal force ensures migration of EVA solution radially outward from undercut (12) over ribs (14) undercut (8) flange (10) and up to a point adjacent the radially innermost extremity of protrusion (15). It has been found that ethylene vinyl acetate applied as las.mentioned and in accord¬ ance with known hot melt curing techniques facilitates a desirable distribution of the gasket material such that in radial section the exposed surface of the material exhibits a concavity extending from lip (13) to an area adjacent protrusion (15) witn the majority of the EVA deposited against the skirt above protrusion (15) and a relatively thin film against the inner surface of top wall (1). Polyvinyl chloride,commonly utilised to form gaskets in such closures in not as satisfactory as EVA because it tends to rεflow thus losing the desired gasket profile depicted in figure 2. When a compounded closure with an EVA gasket distributed as lastmentioned is applied to a container then axial compression of the gasket results in the gasket material being urged towards (but not significantly below) the gap between the radially innermost extremity of protrusion (15) and the container side adjacent (16) thus ensuring full charging of the area between the container neck and skirt (2) above the radially inner extremity of protrusion (15). In order that an effective side seal is obtained it is important that protrusion (15) may not flex and for this purpose fillets (18) are provided extending between the internal surface of the skirt (19) and protrusion (15).

Claims: AMENDED CLAIMS [received by the International Bureau on 19 November 1984 (19.11.84); original claim 3 replaced by amended claim 3] 1. A thermoplastic shell for a compounded closure having a cir¬ cular top wall and an annular internally threaded skirt, an annular inwardly directed protrusion from the inner wall of the skirt below the intersection of said skirt with the top wall adapted to receive a flowed in gasket and, as the closure is screwed into place upon a container to urge such gasket against the outside wall of the neck of such containerthereby effecting a side seal. 2. A shell as claimed in claim 1 having an annular lip depending from the inside surface of the top wall adapted to lie radially inward of a container neck and with a radially outwardly directed undercut for retaining gasket material. 3. A shell as claimed in claim 2 wherein the channel defined by the radially outer extremity of the annular lip and the radially inner extremity of the protrusion is between 2.5 and 3.8 millimetres in width. 4. A shell as claimed in any one of claims 1 to 3 wherein the inner¬ most extremity of the protrusion is adapted to sit adjacent but spaced from a substantially vertical portion of the outside wall of a container neck below the radiused shoulder thereof when the shell is in a sealing relationship with such container. 5. A shell as claimed in any one of claims 1 to 4 having an annular relieved and weakened area in the top wall inboard of its periphery, such relieved and weakened area adapted to act as a hinge to permit doming of that area of the top wall radially inward thereof. 6. A shell as claimed in any one of claims 1 to 5 with a radially inwardly directed bead with an undercut adjacent the intersection of the inner surfaces of the top wall and annular skirt. 7. A shell in accordance with any one of claims ' 1 to 6 having radially $ directed ribs depending from the top wall inner surface to prevent rotational movement of a flowed in gasket. 8. A shell in accordance with any one of claims 1 to 7 including radially spaced fillets extending between the internal surface of the skirt and the underside of the protrusion to minimise flexing of the protrusion. 9. A shell in accordance with any one of claims 1 to 8 wherein the shell is of polypropylene. 10. ' A method of flowing a gasket into the shell of claim 2 or 3 in accordance with known hot melt curing techniques comprised of the steps of: (a) selecting ethylene vinyl acetate as the gasket material; (b) spinning the shell at between 1,000 and 1,800 RPM; (c) injecting a metred amount of EVA through a nozzle directed to an area of the top wall inner surface just radially out¬ board of the annular lip; (d) spinning the shell until the so introduced EVA is distributed over the top wall outboard of the lip, the top wall skirt inter¬ section, and the skirt down to a point adjacent the radially innermost extremity of the protrusion with most of the EVA being distributed adjacent the skirt as opposed to the top wall and the exposed surface of the EVA gasket material in radial section displaying a concavity extending between the lip and a point adjacent the protrusions radially innermost extremity. 11. A thermoplastic shell for a compounded closure as hereinbefore described with reference to the accompanying drawings. 12. A method of flowing an EVA gasket into a thermoplastic shell as hereinbefore described with reference to the accompanying drawings. - ° j - [F -L

Inventors: DRUITT RODNEY MALCOLM, DRUITT, RODNEY, MALCOLM
Applicants: BEV CAP PLASTICS PTY LTD, BEV-CAP PLASTICS PTY. LTD.
Application year: 1984
Main classification: B65D41
IPC codes: B05D1, B29C41, B29C70, B65D41