CLOSURE SYSTEM

Abstract

A foil of a tagger ring foil (TRF) closure system for a container, such as a can, is provided. The foil comprises a composite of two or more layers made from different materials instead of aluminum only.

Claims

1. A foil of a tagger ring foil (TRF) closure system for a container comprising a composite of two or more layers made from different materials, wherein at least one layer comprises aluminium, and having a board burst strength, when measured with Australian Standard (AS) 1301.438s, of less than 400 KPa and a cross direction ring crush resistance pressure, defined as the ring crush measured using AS 1301.407s, divided by 0.152 and multiplied by the foil thickness measured using AS 1301.426s, of less than 10 MPa so that, in use, when the foil is part of a TRF closure system on a container and the foil is ruptured to gain access to the contents of the container, the ruptured foil does not form a sharp edge.

2. The foil defined in claim 1 wherein the materials that form the layers of the composite foil and the combination of the layers are selected so that the foil can be processed in a conventional container manufacturing process that includes forming the container with a TRF closure system.

3. The foil defined in claim 1 comprising a composite of the following layers: paper, a first polymer, an aluminium layer comprising one of an aluminium and an aluminium alloy, and a second polymer.

4. The foil defined in claim 3 wherein the paper ranges in thickness between 25 and 100 gsm.

5. The foil defined in claim 3 wherein the first polymer layer ranges in thickness of between 10 and 30 m.

6. The foil defined in claim 3 wherein the polymer of the first polymer layer comprises a low density polyethylene co-extruded with an acrylic acid.

7. The foil defined in claim 3 wherein the aluminium layer has a thickness of between 7 and 60 m.

8. The foil defined in claim 1 further comprising a filler for reducing the board burst strength or the ring crush resistance pressure to a required level.

9. A tagger ring foil (TRF) closure system for a container that comprises the composite foil defined in claim 1.

10. A container that comprises the tagger ring foil (TRF) closure system defined in claim 9.

11. The container defined in claim 10 wherein the composite foil of the closure system comprises a paper side and is applied to the container so that the paper side of the foil is an outward facing side of the foil.

12. The container defined in claim 10 wherein the container is a metal container.

Description

DESCRIPTION OF THE DRAWINGS

[0055] The present invention is described further by way of example with reference to the accompanying drawings, of which:

[0056] FIG. 1 is a transverse section of a traditional TRF closure system;

[0057] FIG. 2 is a detailed section of the area circled as A in FIG. 1, and

[0058] FIG. 3 is a section of one embodiment of a TRF closure system in accordance with the present invention which shows the multiple layers of material that make up the system.

DETAILED DESCRIPTION OF THE INVENTION

[0059] FIG. 1 shows a traditional TRF closure system of the known art.

[0060] The traditional TRF system comprises a ring 1, a plug 5, and a foil 9.

[0061] The ring 1 of the traditional TRF system comprises a seaming curl 2, a vertical sealing surface 3 that defines an orifice to allow access to a container, and an inwardly facing cut edge 4 of a foil.

[0062] The plug 5 of the traditional TRF system comprises a panel 6, a substantially vertical sealing surface 7, and an outwardly extending flange 8 allowing the plug to be levered from the orifice in the ring.

[0063] The foil 9 of the traditional TRF system extends across the inside of the TRF system to the sealing material 10 around the periphery in the seaming curl 2. Alternately, the foil 9 can be heat sealed to a flat section of the ring, not shown. The foil 9 provides the primary seal for extended shelf life prior to opening.

[0064] The traditional TRF closure system has 3 critical dimensions, namely a nominal diameter D measured as shown, a ring diameter d.sub.R, and a plug diameter d.sub.p. The interference seal between the ring 1 and the plug 5 is provided by selecting d.sub.p to be sufficiently larger than d.sub.R so that a seal and grip is achieved, but not so large that insertion of the plug is excessively difficult. The range of acceptable interference is known to those skilled in the art and is embodied in manufacturing specifications for such parts.

[0065] FIG. 2 shows in greater detail the critical seal areas of the traditional TRF system.

[0066] FIG. 3 shows one embodiment of the composite foil 17 of the present invention. The composite foil comprises successive layers of paper layer 1, a polymer layer 2, an aluminium foil layer 3, and another polymer layer 4.

[0067] The paper may be any suitable paper. Suitable paper includes a 35 gsm or 50 grams per square metre (gsm) bleached kraft sheet made by Australia Paper. Alternative options include grammages ranging from 25 to 100 gsm. The functions of the paper layer 1 are: (a) bulk at low cost, (b) high tensile strength to permit seaming without fracture, (c) easy tearing for consumer access, and (d) minimise risk of a consumer being cut by exposed edges of a ruptured composite foil.

[0068] The polymer layer 2 comprises a co-extruded copolymer of (a) a low density polyethylene (LDPE) in the section of the layer 2 that joins the paper layer 1 and (b) an ethylene acrylate acid resin adjacent the aluminium foil. The LDPE layer is about of the total of thickness of the layer 2. The thickness of the layer 2 ranges from 8 to 30 um, and is preferably 12 um. The polymer layer 2 is provided to adhere together the paper layer 1 and the aluminium foil layer 3. The LDPE is selected on the basis of its capacity to adhere to paper and the ethylene acrylate acid resin is selected on the basis of its capacity to adhere to aluminium.

[0069] The aluminium foil layer 3 in the composite foil is 30 um in thickness, but could conceivably range from 15 to 60 um in thickness. The function of the aluminium foil is to provide high oxygen and moisture barrier properties, both of which are important for long term shelf stability of an unopened container. The aluminium foil layer 3 also contributes to the mechanical properties of the composite foil.

[0070] The bottom layer 4 is a co-extruded co-polymer. The bottom layer comprises (a) a LDPE filled with 30% talc to weaken the overall structure, with this material forming an exposed surface of the composite foil and (b) a terpolymer of ethylene methyl or butyl acrylate grafted with a maleic anhydride to adhere the layer 4 to the aluminium foil layer 3. Preferably the thickness of this layer is 20 um, but can conceivably range from 15 to 50 urn. An important function of the bottom layer 4 is to protect the aluminium of the foil layer 3 from oxidation and other undesirable chemical reactions and to provide a layer of a material that is approved for direct food contact.

[0071] Many modifications may be made to this invention shown without departing from the spirit and scope of the invention.