GB2264701A - A one piece plastics closure having parallel wad support ribs, and moulding apparatus - Google Patents

Abstract

A one piece plastics closure 10 comprises top portion 24 having on its internal face a plurality of upstanding, substantially parallel wad, eg seal, support ribs 28 which extend from an internal peripheral wall 26 of radially recessed parts 20 and 22 of the top portion 24 inwardly beyond a skirt portion 12. The closure top 24 projects outwards and has a depending skirt portion 12. The internal face of the closure top portion 24 also has diametrically opposed parts 20 and 22 which are recessed radially outwardly relative to the internal wall 14 of the skirt 12. Preferably the closure is a one piece moulding having either screw threads for engaging the container or formations for a snap-on fit. The wad may preferably be laminated with a seal on one side and a low friction film on the other. Moulding apparatus comprises a central piece (43, fig 8) having two flanking pieces (50, 52, fig 6) arranged so that inner surfaces (70, 72, fig 6) cooperate with surfaces (74, 76, fig 8). This cooperation allow the central piece to be withdrawn, collapsing the mould so that the closure 10 may be removed. Moulding pieces (42, fig 8 and 50, 52, fig 6) are assembled into a mould cavity and liquid plastics, eg Homo Polymer Polypropylene, is introduced through feed lines and outlet nozzles (68, fig 6). During packaging a container is filled and flushed with nitrogen or oxygen. Adhesive is then applied to the containers rim and the closure with the wad in place is applied to the container pressing the wad onto the rim. On removal a foil or glassine layer is sheared from a pulpboard layer which remains on the rim. <IMAGE>

Description

CLOSURE The present invention relates to moulded plastics closures for containers and more particularly, but not exclusively, to moulded plastics closures for foil or glassine or card-sealed containers.

Instant beverages are usually sold in granulated or powdered form. Such products are commonly packaged in jars with plastics closures. In order to limit surface oxidation and thus maintain the quality of the granules or powder, the containers undergo a nitrogen or oxygen flushing process after filling. A foil or glassine hermetic seal is then applied to the mouth of the container during the capping process.

Marketing such beverage products is highly competitive and a great deal of effort is expended in designing attractive packaging. Closure shape and configuration in particular are the focus of considerable design effort. For certain beverages, particularly coffee, there is a demand for closures having a top portion which projects radially outwardly of the main lower skirt portion.

Usually such closures are made by plastics moulding methods and thus, to some degree, the shapes of the closures are limited by technical considerations of the moulding process. For example, caps having outwardly projecting top portions are technically difficult to produce as mouldings with thick upper sections because of the disparity in cooling time between the relatively thin skirt sections and the thicker upper sections in the mould. In order to avoid such problems, the thick sections can be undercut.

Further technical problems can arise in moulding the internal contours of the closure which fix the closure onto the container and which support a wad. A wad is a laminate structure which fits within the closure and is the means by which the foil or glassine hermetic seal is applied to the mouth of the container. The laminate commonly comprises a pulp-board backing to which a foil or glassine layer is releasably bonded. The wad is inserted into the closure such that the foil or glassine layer is adjacent the mouth of the container. During the capping process the wad is pressed onto the mouth rim, to which adhesive has been pre-applied, and thus seals the container. When the closure is removed, the torsional force applied causes the foil or glassine to rend from the pulp-board backing thereby leaving it covering the container mouth.

It is usual to have a flat, smooth and mainly continuous surface behind the wad so that during adhesion of the wad face to the mouth rim, the closure rotates freely over an essentially stationary wad. If such a surface is not provided, friction occurs between the wad and closure which can cause rotation of the wad. This can result in premature separation or tearing of the foil or glassine layer and impaired wad performance in providing a hermetic seal. Similarly, when removing the closure, if the closure does not rotate freely over the wad backing during the unscrewing action the torsional force may cause premature separation or tearing of the layer.

Although tearing at this stage would not adversely affect the product, it is highly undesirable since the consumer must be assured of the integrity of the product prior to first use.

Some closures support the wad on the closure base and retain it in position with a flange. However, bigger closures often have a wad support flange spaced from the top of the closure and a wad retaining flange, between which flanges the wad is sandwiched.

Obviously the more external and internal detail required on a closure, the more complicated it is to manufacture and closures having both an undercut and a wad support arrangement are difficult and expensive to produce.

It has been previously proposed to produce with an iris-type mould, closures having outwardly projecting top portions which are radially undercut to avoid thick walled upper sections.

Such a mould is a collapsing mould with a plurality of cooperating segments. However, it is a complicated mould and the individual segments are vulnerable and prone to damage.

Using such a mould it is possible to produce an undercut around the entire inner circumference of the outwardly projecting top portion of the closure, but all the reduction in diameter provided when the mould is in the collapsed disposition is needed to clear the undercut when withdrawing the mould from the moulded product. Using such apparatus it is not possible to provide a wad supporting flange as well as the undercut since the mould cannot collapse far enough to clear both when it is withdrawn.

Collapsing core moulds comprising a pair of segment shaped moulding pieces movable towards and away from one another, are also used in closure manufacture. This type of mould can be used to produce radially extensive, diametrically opposed arcuate wad supporting flanges spaced from the top of the closure since they can reduce significantly in diameter when in collapse. However, the degree of collapse is not sufficient to produce a closure having a radially outward undercut in addition to a radially extensive wad support flange.

Furthermore collapse can only occur in one direction thus each closure must have a region where there is no overhanging internal detail, so that a radial undercut around the entire periphery of the closure cannot be produced by such a mould.

In order to produce a plastics closure having both an undercut section and a wad supporting arrangement it has been previously necessary to manufacture the closure in two parts, namely an outer shell having a 3600 undercut and an inner shell having no undercut but a wad supporting flange. The two halves must be produced using separate moulds and must be fixed together in an assembly process. The resultant product is correspondingly expensive.

It is an object of the present invention to produce one piece plastics closures having both undercut outwardly projecting top sections and means for supporting wads spaced from the tops of the closures.

According to a first aspect of the present invention, there is provided a plastics closure for a container comprising a skirt portion having on its internal wall, formations for complementary engagement with corresponding formations on the container; and a radially outwardly projecting closure top portion from which said skirt portion depends, wherein a pair of diametrically opposed parts of the internal face of said top portion are recessed radially outwardly relative to the internal wall of the skirt and wherein said top portion has arranged on its internal face a plurality of upstanding, substantially parallel wad support ribs which extend from the internal peripheral wall of said radially recessed parts of the top portion inwardly beyond the skirt portion.

In a preferred embodiment, the closure is a one piece moulding.

Preferably the complementary engaging formations are screw threads.

In an alternative embodiment the complementary engaging formations may be snap-on closures.

Preferably the skirt includes a pair of diametrically opposed arcuate wad retaining flanges at positions corresponding to said radially recessed parts of said top portion, respectively to cooperate with said wad support ribs.

There is also provided a closure according to the invention having a wad laminated on one side with a container-seal and on the other side with a low friction film, eg of a polymer material, such as a polyester Melinex (Trade Mark).

The number , thickness and end shape of the ribs must be balanced against the wad top coefficient of friction, wad thickness and adhesive type used at the application stage to provide significantly continuous holding pressure to provide an uninterrupted glue seal and not disrupt the wad during application or removal.

According to a second aspect of the invention there is provided moulding apparatus specially adapted for producing plastics closures according to the invention, comprising a mould cavity component and a mould forming component, said mould cavity component having an outwardly projecting annular recess, said mould forming component having a central piece and two diametrically opposed flanking pieces, each flanking piece having an outwardly projecting arcuate flange engageable within a respective diametrically opposed portion of said annular recess so as to form regions of reduced wall thickness; and having, at the free end thereof, at least one slot for producing at least one rib in the moulded product, said slots extending in the direction of movement of the mould forming components, and each flanking piece also having an inner surface capable of cooperating with a corresponding surface of the central piece so as to facilitate withdrawal of the central piece and subsequent inward collapse of the mould flanking pieces during disengagement of the mould forming component.

According to a third aspect of the invention, there is provided a method of producing a plastics closure according to the first aspect of the invention, using moulding apparatus according to the second aspect of the invention.

For a better understanding of the present invention and to show more clearly how it may be put into effect reference will now be made to the accompanying drawings in which: Figure 1 is a top plan view of one embodiment of a plastics closure embodying the invention; Figure 2 is a bottom plan view of the closure shown in Figure 1; Figure 3 is a partially sectional side view of the closure; Figure 4 is a transverse sectional detail, on an enlarged scale of a section of the wall of an upper part of the closure; Figure 5 is a vertical sectional view through part of the closure showing the complementary engaging formations and a wad support rib; Figure 6 is a side elevation of the flanking pieces of a mould forming component in accordance with the invention; Figure 7 is a plan view of the flanking pieces of the mould forming component of Figure 5;; Figure 8 is a side view of a central piece of the mould forming component; Figure 9 is a plan view of the central piece of the mould forming component.

Referring to Figures 1, 2 and 3 of the drawings, a plastics closure 10 has a skirt portion 12 with an internal wall 14 bearing screw thread formations 16 for complementary engagement with corresponding threading on a container (not shown) and a wad retaining flange 17. The top portion 24 of the closure 10, is formed with an outwardly extending peripheral rim 18 from which the skirt 12 depends. In the illustrated embodiment the peripheral rim 18 has an outer surface with fifteen flats 18a to provide both grip and surface ornament and a smooth inner surface. Two diametrically opposed parts 20 and 22 of the internal face of the rim 18 are recessed radially outwardly relative to the internal wall 14 of the skirt 12. The top portion 24 has arranged on its internal face 26 a plurality of substantially parallel ribs 28 which extend inwardly from the recess beyond the skirt 12.In the illustrated embodiment the top portion also has two additional ribs 30 which extend inwardly from the non-recessed regions 32 of the rim 18 between the opposed parts 20 and 22, in a direction perpendicular to the ribs 28. Figure 4 shows more clearly the generally parallel arrangement of the ribs 28 and the perpendicular arrangement of the rib 30. The ribs 28, 30, in use, support a laminated wad adjacent the upper end of the skirt 12, so that the wad is sandwiched between those ribs and the wad retaining flange 17.

Figures 6, 7, 8 and 9 show a mould forming component for forming the closure 10. This component comprises a central piece 42 which has a generally wedge shaped upper portion having a relatively narrow distal end 44 and a relatively wide proximal end 46. On the outer surface of the distal end 43 are two slots 78 (Fig. 9) which will produce the ribs 30 in the moulded end product.

Arranged on either side of the central piece 42 are two diametrically opposed flanking pieces 50 and 52 (shown in Figs 10 & 11). Each flanking piece has a distal end 54 and a proximal end 56. Located at each distal end 54 is an outwardly projecting arcuate flange 58. Each flange 58 is engageable within a respective diametrically opposed portion of the outwardly projecting annular recess of the mould cavity (not shown). The engagement of the flanges 58 in the annular recess results in a moulded product having two opposed regions of reduced wall thicknesses 20, 22 separated by two smaller regions of unreduced wall thickness 32 as shown in Fig. 2. The distal ends of the flanking pieces are formed with a plurality of slots 62 extending inwards from the periphery 64 in a generally parallel arrangement. The slots 62 produce the ribs 28 in the moulded product.Within the flanking pieces 50 and 52 are feed lines 66 through which liquid plastics material flows to outlet nozzles 68 and then out into the mould cavity.

The tapered inner surface 70 and 72 of the flanking pieces 50 and 52 cooperate with the corresponding tapered outer surfaces 74 and 76 of the central pieces. This cooperation allows for relative movement between the central piece and the flanking pieces so that the central piece may be withdrawn to facilitate inward movement of the flanking pieces and subsequent collapse of the mould for withdrawal from the finished component. The slots 62 extend in the direction of movement of the flanking pieces to allow collapse of the mould and withdrawal from the finished component.

In use of the moulding apparatus, the three mould forming pieces 42, 50 and 52 are assembled into the mould forming component 40. The component 40 is inserted into the mould cavity of an injection moulding machine and liquid plastics material, eg Homo Polymer Polypropylene, is introduced through the feed lines. The material, which is delivered to the machine in granular form with colour additives included, is injected or rammed into the mould cavity in a molten condition, under suitably controlled conditions of heat, pressure and speed which will be well understood by persons skilled in the art.

Once the moulding has been completed, the central piece 42 is withdrawn and the outer flanking pieces 50 and 52 are pulled together to constitute a collapse of the mould. The collapse is sufficient to allow the flanking pieces to be withdrawn from the cavity without impediment from the inner moulding detail.

In use of the moulded product, a wad element (not shown) is inserted into the closure and is supported on the ribs 28. The wad may be held in position by a wad retaining flange 17 which is situated on the internal wall 14 of the skirt 12. During the packaging process the container is filled with the granulated or powdered product and flushed with nitrogen or oxygen. Adhesive is then applied to the rim of the mouth of the container and the closure is placed thereon. As the closure is applied, the wad is pressed onto the rim and seals the container. When the closure is removed the torsional force applied shears the foil or glassine layer from the pulpboard backing of the wad and that layer then remains adhered to the closure mouth rim.

In this construction, the wad comprises a pulpboard backing with a low friction polyester layer (eg Melinex - Trade Mark) laminated thereto. The low friction layer thus forms a contact surface for the wad support structure and facilitates rotation of the closure over the stationary wad after sealing. Melinex (Trade Mark) is a preferred material since it has a low coefficient of friction, is strong, low cost and most importantly has been approved for food use. Alternative materials such as aluminium foil and certain types of paper may be suitable but it is envisaged that a plastics material is most likely. The essential requirements of any such material are a low coefficient of friction and resistance to tear.

Claims (10)

1. A plastics closure for a container comprising a skirt portion having on its internal wall, formations for complementary engagement with corresponding formations on the container, and a radially outwardly projecting closure top portion from which said skirt portion depends, wherein a pair of diametrically opposed parts of the internal face of said top portion are recessed radially outwardly relative to the internal wall of the skirt and wherein said top portion has arranged on its internal face a plurality of upstanding, substantially parallel wad support ribs which extend from the internal peripheral wall of said radially recessed parts of the top portion inwardly beyond the skirt portion.

2. A plastics closure as claimed in Claim 1 wherein the closure is a one piece moulding.

3. A plastics closure as claimed in Claim 1 or Claim 2 wherein the complementary engaging formations are screw threads.

4. A plastics closure as claimed in Claim 1 or Claim 2 wherein the complementary engaging formations are snap-on closures.

5. A plastics closure as claimed in any one of the preceding claims wherein the skirt includes a pair of diametrically opposed arcuate wad retaining flanges at positions corresponding to said radially recessed parts of said top portion, respectively to co-operate with said wad support ribs.

6. A plastics closure as claimed in any one of the preceding claims wherein said plastics closure has a wad laminated on one side with a container seal and on the other side with a low friction film.

7. Moulding apparatus specially designed for the manufacture of plastics closures according to the invention comprising a mould cavity component and a mould forming component, said mould cavity component having an outwardly projecting annular recess, said mould forming component having a central piece and two diametrically opposed flanking pieces, each flanking piece having an outwardly projecting arcuate flange engageable within a respective diametrically opposed portion of said annular recess so as to form regions of reduced wall thickness; and having, at the distal end thereof, at least one slot for producing at least one rib in the moulded product, said slots extending in the direction of movement of the mould forming components, and each flanking piece also having an inner surface capable of co-operating with a corresponding surface of the central piece so as to facilitate withdrawal of the central piece and subsequent inward collapse of the mould flanking pieces during disengagement of the mould forming component.

8. A method specially adapted for producing a plastics closure according to Claims 1 to 5 using moulding apparatus according to Claim 7.

9. A plastics closure substantially as described herein with reference to the accompanying drawings.

10. Moulding apparatus substantially as described herein with reference to the accompanying drawings.