The use of foils to seal the openings of plastic and glass containers to prevent products within the containers from being contaminated and pilfered is well-known.

Typically, a plastic or glass container is sealed by applying a suitable foil to the opening of the container by induction heating. In a first example, foil is laminated on one side with polyethylene or any other plastics material which is compatible with the material of the container. In another example, the uncoated surface of the aforementioned laminated foil is attached to a board (cardboard) backing by a wax adhesive.

In the first example, the laminated foil is placed in the cap of a container and the cap is applied to the container so that the foil is held between the cap and the opening of the container. The cap of the container is then passed under an induction sealing head and the electrical field created by the induction sealing head melts the polyethylene or plastic on the foil which, because of the pressure between the cap and container, is attached to the opening of the container. In this way the foil is sealed to the container. When the product is used, the cap is removed and the seal is broken.

In the second example, the seal is inserted into a cap with the board portion abutting the inside of the cap. The board is fixed within the cap by an adhesive or by clips within the cap. The cap is applied to the opening of a container so that the seal is held between the cap and the opening of the container. The cap is then passed under an induction sealing head. The electrical field created by the induction sealing head melts the polyethylene laminated foil and, because of the pressure between the cap and the container, the foil is attached to the rim of the container. At the same time, the wax adhesive in the seal melts, releasing the foil from the board. In use, the container is opened by removing the cap and breaking the seal.

The board is held within the cap by the adhesive or clips and serves to seal the container when the cap is once again attached to the container.

A problem which arises with containers sealed in the abovementioned manner is that either a vacuum or pressure is created within the container when the container moves from a higher to a lower altitude and from a lower to a higher altitude, respectively. Containers which have flexible walls tend to either collapse or bulge when moving from a higher altitude to a lower altitude, or from a lower altitude to a higher altitude, respectively.

It is an object of this invention to provide a new seal for a container which addresses the abovementioned problem.

SUMMARY OF THE INVENTION According to the invention there is provided a sealing member for a container, the sealing member including a selective membrane which is liquid-resistant and gas-permeable.

Typically, the sealing member includes a foil, preferably an aluminium foil with at least one aperture extending through the foil, with the selective membrane sealing the at least one aperture in the foil.

Conveniently, the foil is coated with a plastics film which is responsive to induction heating, such as polyethylene.

The sealing member may also include a board having at least one aperture which is in communication with the at least one aperture extending through the foil, with the selective membrane sealing the at least one aperture in the foil and the board.

The invention also covers a container including a sealing member as described above, and a method of sealing a container using the sealing member described above.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a cross-sectional side view of a sealing member for a container, according to a first embodiment of the invention; Figure 2 is a pictorial view of the sealing member of Figure 1; Figure 3 is a pictorial view of a sealing member for a container, according to a second embodiment of the invention; Figure 4 is a cross-sectional side view of the sealing member of Figure 1 attached to a container; and Figure 5 is a cross-sectional side view of a sealing member according to a third embodiment of the invention attached to a container.

DESCRIPTION OF EMBODIMENTS Referring to Figure 1, a sealing member according to a first embodiment of the invention is shown generally by the reference numeral 10 and includes a strip of foil 12 which is a metal foil, typically aluminium foil having a thickness of 0, 1mm. The operatively lower surface of the foil 12 is coated with a plastics film 14 which is responsive to induction heating. In this case the plastics film 14 is polyethylene. A number of apertures 16 extend through the foil 12 and the film 14. The apertures may be of any size but typically have a diameter of from 5 to 0, 1mm. A selective membrane 18 is bonded to the foil 12 with an adhesive material or by ultrasonic welding 20 at the periphery of the foil 12, so that the selective membrane 18 covers the apertures 16. The selective membrane 18 is liquid-resistant and gas- permeable and thus provides a liquid-resistant seal over the apertures 16.

A typical selective membrane is coated expanded polytetraflouroethylene membrane 18 which is available from WL Gore & Associates Inc.

Figure 2 shows the sealing member 10 of Figure 1, for use in sealing the closure of a container having a round opening. It can be seen that the selective membrane 18 is bonded to the foil 12 by an adhesive or ultrasonic welding 20 around the periphery of the foil 12 so that the apertures 16 are covered by the selective membrane 18. This ensures that there is a liquid- resistant seal between the foil 12 and membrane 18. Although the sealing member 10 shown in Figures 1 and 2 includes a plurality of apertures 16 extending through the foil 12, there may, of course, be only one large aperture extending through the foil 12.

Referring to Figure 3, the apertures 16 extending through the foil 12 may be grouped together on a portion of the foil 12 and the selective membrane 18 may be of smaller size than the foil 12, but still of sufficient size to seal the apertures 16.

Referring to Figure 4, in use, the seal member 10 shown in Figures 1,2 or 3 is attached to the opening 26 of a container 22 containing a product 24.

The product 24 may be a liquid product, or a solid product such as a powder. The seal member 10 may be attached to the opening 26 of the container 22 by any method known in the art, for example by the induction sealing method described in the background to the invention. In use, the seal member 10 allows gas 28 to pass into, or out of, the container 22.

However, liquid 30 is prevented from entering, or leaving, the container 22 by the selective membrane 18. Thus, when the container 22 is transported from a higher altitude to a lower altitude, or from a lower altitude to a higher altitude, gas (in this case air), is allowed to pass from the atmosphere into the container and from the container 22 into the atmosphere, respectively, so that the gas pressure within the container 22 is the same as the atmospheric pressure and there is no build-up of a vacuum or of pressure within the container 22. Thus, when the container 22 is transported from a lower altitude to a higher altitude or from a higher altitude to a lower altitude, the gas pressure within the container 22 is the same as the air pressure outside the container 22 and there is no collapsing or bulging of the container 22.

Referring to Figure 5, a seal member 32 according to a second embodiment of the invention is attached to the opening 34 of a container 36, below a screw-cap 38 which is attached to the container 36. The seal member 32 includes an aluminium foil 40 (having a thickness of 0,6mm), the lower surface of which is coated with a plastics film 42 (in this case polyethylene) which has already been inductively heated and which seals the foil 40 to the opening 34 to the container 36. The operatively upper surface of the foil 40 is attached to a board 44 by a wax adhesivf An Tl__ board 44 may have a thickness of from 0,5 to 1,2mm. Apertures 48 extend through the plastics film 42, foil 40, board 44 and wax adhesive 46. The apertures 48 are covered by a selectively permeable membrane 50. The selectively permeable membrane 50 is adhered to the periphery of the board 44, by adhesive 52 and provides a liquid resistant seal over the apertures 48 which extend through the board 44. Although the wax 46 may melt during the inducting heating process, the pressure of the screw-cap 38 on the seal 32, ensures that there is an effective liquid-resistant seal between the board 44 and foil 40. The seal 32 works in the same way as the seal 10 shown in Figures 1,2 and 3. Gas, in the form of air, is able to move through the seal 32 and out of the container 36 under the cap 38, or under the cap 38, through the seal 32 and into the container 36 when the container 36 is moved from a higher altitude to a lower altitude or from a lower altitude to a higher altitude, respectively, while liquid is not able to pass through the seal member 32.