The present invention relates to containers where a closure system providing a high barrier to ingress of moisture is required.

The present invention relates more specifically but not exclusively to a closure system for containers made from metal , where a high moisture barrier is required.

Certain dry products are highly sensitive to degradation due to absorption of moisture . For example , milk powders and infant formulations contain labile vitamins which may degrade rapidly if excessive moisture levels are reached. As a further and more extreme example, certain types of nutritional/flavoured milk additives have been found by the applicant to be extremely moisture sensitive, requiring less than 2% increase in weight due to moisture pickup to become unusable .

For these reasons , products of this type have traditionally been and still are packed in hermetically sealed metal cans .

For ease of access , with high performance re- sealing, and tamper evidence, the metal cans typically comprise a closure system that is referred to in the art as a "tagger ring and foil" ("TRF") system.

A traditional TRF system comprises a first component in the form of a "ring" . The ring is adapted to seal to a can body by a process of double seaming as understood in the art of can manufacture , and comprises the use of a flowed-in seaming sealant also according to the known art. The sealant is typically a rubber composition providing desirable sealing properties under compression . The ring defines a central opening of controlled internal diameter, having a substantially vertical wall with a cut edge inwards to the container , against which a second component can provide an interference seal .

The traditional TRF system further comprises a second component in the form of a "lever plug". The lever plug comprises a flat panel, adjoining a substantially cylindrical vertical wall of an external diameter appropriate to provide an interference fit with the opening of the ring, and a flange extending from this vertical wall, which prevents the plug being pushed inside the can, and allows the plug to be levered out of the can with an appropriate implement such as a spoon .

For the purposes of this specification an interference seal is understood to be a seal provided by forcing one component of controlled diameter, in this case the plug, into an opening of controlled diameter in another component, in this case the ring, where the diameter of the plug is greater than or equal to the diameter of the opening in the ring.

The traditional TRF system further comprises a third component in the form of a foil seal . The foil seal is located inside the can, and extends from the seaming flange on the ring across the entire end. The foil is restrained in the seaming flange, and is encapsulated in the double seam at sealing. The method of restraining the foil may be application of the seaming sealing material over the foil cut edge.

In use, the foil provides an initial hermetic seal . On opening , the interference seal between the ring and the plug provides sufficient moisture barrier to maintain product quality during step-wise use of the product over a typical consumption period, which can be some weeks or months in some homes .

In an alternate closure system, the foil encapsulated in the seam is replaced by a foil that is heat sealed to a flat section on the ring. This reduces the amount of foil used and therefore direct foil costs . However, costs increase as a consequence of the use of heat sealable systems .

For reasons of strength and formability, typically the foil is made from aluminium. Aluminium foil is expensive. Further, consumers find the need to puncture and remove the foil after removal of the plug to be inconvenient. Further still, the cut edge of a punctured foil presents an injury risk for consumers . This is especially the case where attempts to reduce cost by reducing the thickness of the foil have been made . Further, in times of increasing environmental consciousness, the use of aluminium foil as a seal in a steel can is undesirable as aluminium is a contaminant which must be removed as slag in the re-cycling of steel packaging .

For the above reasons , a TRF system that does not include the use of an aluminium foil is desirable .

The applicant determined some time ago that the moisture barrier performance of a steel-on-steel plug and ring assembly is not sufficiently consistent to provide long term storage of sensitive products in humid environments . This led to the applicant continuing to use traditional TRF closure systems for such products .

The above discussion should not be taken as an admission of the common general knowledge in Australia or elsewhere . The applicant has now discovered that the use of a thin coating of a malleable sealing substance between a plug and a ring of a TRF system makes it possible to increase the moisture barrier of the system to a point where extensive shelf life can be achieved without the use of a separate sealing foil .

Accordingly, the present invention provides a closure system for a container where a high moisture barrier is required that comprises a ring that defines an opening, a plug for closing the opening, and a malleable sealing material for contacting the plug and the ring and forming a seal between the plug and the ring when the system is in a closed position.

A foil seal of the type used with known TRF systems is not required.

The ring may be made from metal .

The metal may be steel .

The plug may be made from metal .

The metal may be steel .

The ring and/or the plug may be made from a polymeric material where the moisture barrier properties of the polymeric material are sufficient to provide moisture barrier suited to the contained product.

The malleable sealing material may be in a form of a sealing compound, such as a flowed-on sealing compound, applied between the plug and the ring. The sealing compound may be any suitable composition, such as a rubber solution, rubber emulsion, natural latex composition, synthetic latex, synthetic polymer, molten wax, natural oil, synthetic oil or other composition providing suitable moisture barrier properties and suitable to be applied to a joint and provide a seal.

The malleable sealing material may be applied in any form or in any phase of the material .

The form or the phase of the malleable sealing material may include liquid at ambient temperatures , solutions , suspensions , organosols (defined as polymeric particles in suspension in a carrier, that on heating invert to become a plasticizer in a polymer matrix) , and solid or semi-solid.

The forms and the phases listed above are intended as examples and not to limit or define the scope of the present invention .

The malleable sealing material may be in a form of a polymer coating on a surface of the plug and/or the ring that forms the seal in use of the closure system, with the polymer coating being malleable to flex and seal microscopic gaps between the ring and the plug. The polymer coating may be formed on the surface of the plug and or on the ring during the manufacture of a polymer coated steel used as a feed material to make the plug or the ring. The polymer coating on the surface of the plug or the ring may be applied on the feed steel and or other material during the manufacture of the closure system.

The polymeric coating may be made from any polymer which has sufficient moisture barrier properties and is sufficiently malleable to take up inaccuracies in the underlying metal ring and/or plug. The polymeric coating is desirably selected from a range comprising low density polyethylene, polypropylene, ethylene and/or propylene copolymers with other olefin monomers , ionomers , polyesters , polyamides , or other suitable polymers .

The polymer coating may be a thin coating.

The polymer coating may be no more than 100 microns thick .

The polymer coating may be no more than 75 microns thick .

The polymer coating may be no more than 50 microns thick .

The present invention also provides a container that comprises the above-described closure system.

A foil seal of the type used with known TRF systems is not required with the container.

The container may be a metal container.

The container may be a steel container.

The container may be a container of a composite of different materials of any description where the moisture barrier properties of the container are sufficient to provide a required performance in moisture barrier in conjunction with a TRF system of the known art.

The container may be made from a polymeric material where the moisture barrier properties of the container are sufficient to provide the required performance in moisture barrier in conjunction with a TRF system of the known art. The container may be a can .

The closure system may be manufactured by an appropriate method.

Rings or plugs of metal or polymer coated metal may be manufactured by metal pressing.

Rings or plugs of polymeric material may be made by any means of polymeric material moulding process . Injection moulding is a method that may be particularly suited to the manufacture of such polymeric components .

Where the malleable sealing material is in a form of a polymer coating on the ring and/or the plug, there is no requirement for a separate sealing material application step.

Where the malleable sealing material is in a liquid phase when applied to the closure system in the closed position, any suitable method of application of the liquid phase material may be used.

For example, one method for applying the malleable sealing material is a method used to apply a seaming sealant material to a seaming panel of closure rings. In one example of the method in the known art, a TRF closure is placed on a mandrel and rotated around its centre at speed. A liquid seaming sealant material is dispensed as a fine stream on to the closure for a time period that is in excess of the time period for two rotations of the closure to provide a coating of the seaming sealant material on the closure that can form a compressible seal when the outer ring of the TRF system is seamed to a side wall of a container. A method of manufacturing a closure system of the present invention may comprise applying the malleable sealing material where required on the plug and the ring of the above-described closure system prior to assembling the plug and the ring together or when the plug and the ring are in the closed position .

The method may comprise using a seaming sealant material lining machine of the existing art that has a dispensing head for dispensing the seaming sealant material and has been modified to have a second dispensing head that is positioned to apply the malleable sealing material where required on the plug and the ring prior to assembling the plug and the ring together or when the plug and the ring are in the closed position

By using such a system, both the current art seaming sealant material and the malleable sealing material of the present invention can be conveniently applied to the closure system.

More particularly, a method of manufacturing the closure system may comprise :

(a) assembling together a ring and a plug by pressing the two components together to form an interference seal and forming an assembly of the ring and the plug;

(b) placing the assembly on a mandrel,

(c) rotating the mandrel and the assembly at a controlled speed;

(d) applying a seaming material to the assembly, for example by means of a compound lining machine of the known art, and (e) dispensing a flow of a liquid form of a malleable sealing material as described herein to a part of an edge of the ring of the assembly where the edge contacts the plug and thereby forming a seal between the plug and the ring.

The same sealing material may be used to join the ring of the closure system to a wall of the container and to form the seal between the plug and the ring.

A different sealing material may be used to join the ring of the closure system to the wall of the container and to form the seal between the plug and the ring.

The present invention is described further by way of example with reference to the attached drawings , of which :

Fig 1 is a transverse section of a known TRF system;

Fig 2 is a detailed section of the area circled as A in Fig 1 ;

Figs 3A, 3B, 3C show in diagrammatic form the presence of three different seal defects in a seal region between the ring and the plug of the known TRF system shown Fig 1 and in Fig 2 ;

Fig 4 shows in cross-section a plug having a coating of a malleable sealing material that forms a part of one embodiment of a closure system in accordance with the present invention; Fig 5 shows how the malleable sealing material of the coating shown in Fig 4 fills seal defects in the seal region shown in Fig 4 ;

Fig 6 shows the placement of a flowable seal material across the seal area of the closure system shown in Figs 4 and 5 ;

Fig 7 shows another embodiment of a closure system in accordance with the present invention in which a liquid sealant such as an oil is used as a malleable sealing material in the seal region to fill seal defects such as the defects shown in Figs 3A, 3B, 3C.

It is noted that the known TRF system shown in Figs 1 to 3 and the embodiments of the closure system of the present invention shown in Figures 4 to 7 are intended to be used with cans or other types of containers and the TRF systems are connected to the upper rims of the cans . Typically, the TRF systems and the cans are made from steel and the TRF systems are seamed onto the upper rims of the cans . The present invention is not limited to use with steel cans . The present invention is also not limited to closure systems that are seamed to cans .

The known TRF system shown in Fig 1 comprises a ring 1 defining an opening generally identified by the numeral 3 for allowing access to the contents of a can on which the TRF is located. The ring comprises an outer seaming curl 2 retaining a flowed-in sealant 10, an inner vertical sealing surface 3 , and an inwards facing cut edge 4.

The known TRF system further comprises a plug 5 that closes the opening 3 with an interference seal , the plug comprising a panel 6, a cylindrical, substantially vertical sealing surface 7 , and a flange 8 allowing the plug to be levered from the opening in the ring.

The known TRF system further comprises a foil 9 extending across the inside of the can and meeting the sealing material 10 around the periphery in the seaming curl 2. Alternately , the foil can be heat sealed to a flat section of the ring, (not shown) .

The foil 9 acts as a primary seal for extended shelf life of a food product packaged in the can prior to opening the can.

The known TRF system shown in Fig 1 is characterized by 3 critical dimensions, namely, the nominal diameter D measured as shown, the ring diameter d _R , and the plug diameter dp. An interference seal is provided by dp being greater than d _R sufficiently that a seal and grip is achieved, but not so much greater 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 .

Fig 2 shows in greater detail the critical seal areas of the known TRF system. The seal area that is the focus of the present invention is shown as 11.

Fig 3 shows three potential defects in the interference seal between the ring 1 and the plug 5 in the seal area 11 of the known TRF system in Fig 1 and Fig 2.

In Fig 3A a defect in the form of a dent in the ring seal surface is shown as 12. Fig 3B illustrates ovality of the plug 5 causing a defect 13. Fig 3C shows damage to the plug causing a defect 14. Many other causes of slight miss-match between the parts may be envisaged, and can be detected by detailed metrology, but are not practical to avoid in a manufacturing environment .

Fig 4 shows in cross-section a plug 5 that forms part of an embodiment of a closure system of the present invention that includes a malleable sealing material. The embodiment of the closure system comprises a ring 1 and a plug 5 as described in relation to Figs 1 to 3. The plug 5 comprises a steel wall 15. In this embodiment, a layer 16 of the malleable sealing material in the form of a polymer material is applied to an outwardly facing surface of the steel wall 15 prior to inserting the ring 1 into the plug 5. The steel wall 15 provides structural strength, while the polymer layer 16 (shown at exaggerated thickness for illustration) provides a flexible seal between the ring 1 (which may be of the type shown in Fig.l or any other suitable configuration) and the plug 5 when the plug 5 is inserted into the ring 1 in a closed position of the closure system.

When the plug 5 shown in Fig 4 is inserted into the ring 1 with an interference fit to form an interference seal, the malleable sealing material fills the defects mentioned above and shown by way of example in Fig 3 and forms an effective seal .

Fig 5 shows in exaggerated form the defects shown in Figs 3A, 3B, 3C filled by the malleable sealing material of the layer 16 as 12' , 13' and 14'

Fig 6 shows in section an embodiment of a closure system in accordance with the present invention that uses a malleable sealing material in the form of a flowable sealant 17 over the cut edge of the ring 1 to provide a frangible seal across the seal area 11 after the ring 1 has been inserted into the plug 5. Fig 7 shows in schematic from an embodiment of a closure system in accordance with the present invention that uses a malleable sealing material in the form of an oil or molten wax to provide a semi-liquid seal across the seal area 11 after the ring 1 has been inserted into the plug 5.

The present invention is described further with reference to experimental work carried out by the applicant to investigate the effectiveness of malleable sealing materials in the closure system of the present invention .

Numerical data was derived using ASTM E96, which is incorporated herein by reference .

The tests carried out in the experimental work were carried out at 3O ⁰ C and 75% relative humidity ("RH") . These conditions were selected as being representative of humid environments where a proportion of products may be consumed. The tests evaluated the water vapour transmission rates of a range of closure systems where the seal area had been hermetically sealed by the use of a malleable sealing material as per the present invention

Results of water vapour transmission rates ("WVTR") were obtained for traditional TRF systems of different nominal sizes. The nominal size is related to the terms known in the art of can-making. A 99 mm TRF, for example , is the closure system for a steel can of approximately 99 mm body diameter. The results are presented in the following Table .

* Detection limit of the analysis was 0.0015g/package .day

From the above Table, it is clear that the provision of a malleable sealing material on a closure system in accordance with the present invention can reduce the measurable rate of moisture ingress by at least an order of magnitude.

The above data indicates that this level of improvement provides a commercially viable alternative to the current technology.

Many modifications may be made to the embodiments of the TRF system in accordance with the present invention shown in the drawings without departing from the spirit and scope of the invention.