Container closure

When packaging a wide variety of materials ranging from pharmaceutical tablets to instant coffee in containers such as bottles and jars it is nowadays commonplace to provide a closure in the form of a seal connected to the neck of the container and a screw cap covering and protecting the seal and providing a reclosable cap after the seal has been removed to gain access to the contents of the container. A convenient way of providing such a closure is to provide the undersurface of the seal with a heat sensitive adhesive coating or a meltable plastics layer covered by a metal foil. The metal foil can provide the substrate of the seal or the seal may include a separate substrate made from paper or plastics material. Such a seal is then placed against the top of the neck of a container and sandwiched against it by the applied screw cap, whilst the closure is subjected to an induction heating step which heats the metal foil and in turn activates the heat sensitive adhesive layer or melts the plastics layer so that, on cooling, the seal bonds to the top of the neck of the container.

It is difficult for the eventual consumer to remove such seals and so attempts have been made to provide a tab extending sideways from the neck of the container so that the consumer can grip this to facilitate the removal of the seal. One difficulty with this is that the eddy currents induced in the foil during inductance heating are induced mainly in the periphery of the seal. When the seal includes a tab they are therefore induced around the edge of the tab which is remote from the neck of the container so that the seal is often not completely fixed to the top of the neck of the container adjacent the tab.

One way of overcoming this, which is proving popular at present, is the so-called "Top Tab" (Registered trademark) system, which is described fully in <patcit id="pcit0001" dnum="US4961986A"><text>US-A-4961986</text></patcit>. This system includes a multilayer substrate which is partly de-laminated to provide a lifting tab lying wholly within the circumference of the container neck. Typically, the lifting tab occupies about 50% of the seal area for seals of a diameter up to 36 mm and then the tab remains this size for seals of larger diameter. In <patcit id="pcit0002" dnum="US4961986A"><text>USA-4961986</text></patcit> this is achieved by forming the substrate from multiple layers which are adhered together over only a part of their extent. <patcit id="pcit0003" dnum="US5702015A"><text>US-A-5702015</text></patcit> also discloses such a seal but, in this case, the sealed substrate is formed by an extrusion process in which a first layer of plastics material is extruded, followed by extrusion lamination of a second layer of release material using a third layer of extrusion material which is of the same composition to that of the first layer which integrates with the first layer where the second layer is not present. In this way the tab, which is formed by the third layer, is formed integrally with the first layer without the need for adhesive between the layers.

As shown in <patcit id="pcit0004" dnum="US4961986A"><text>US-A-4961986</text></patcit> the screw-cap may include some form of liner in addition to the seal material. At present, one of the difficulties of the "Top Tab" (RTM) system is that it is, essentially, a two-component system with the seal material and the liner provided separately and having to befitted inside a screw-cap in two separate operations. This naturally adds to the expense and difficulty of using the system. Accordingly, in commercial use, at present, the "Top Tab (RTM) System is normally used without a separate liner.

<patcit id="pcit0005" dnum="DE9108868"><text>DE9108868</text></patcit> describes an one component seal and liner system for a screwcap which includes a seal having lower layers forming an induction heating sealable system for attaching the seal to the neck of a container. The lower portion is formed from cardboard material and adhered to the seal portion by means of a wax layer.

The present invention relates to an one-component seal and liner comprising the features of claim 1. Further, preferred embodiments are disclosed in the dependent claims.

According to this invention an one-component seal and liner system for a screw-cap includes a seal having lower layers forming an induction heating sealable system for attaching the seal to the neck of a container, a seal substrate attached to the uppermost layer of the induction heating sealable system wherein the seal substrate includes a free tab lying wholly within the circumference of the seal, a layer of liner, and attachment means including a release layer for attaching the seal substrate including the tab to the liner.

The peel strength of the attachment means at the release layer is within a range from 20 to 90 grams at a rate of 1500 mm/min on a sample strip 25 mm wide. A more preferred range of peel strength is 50 to 60 g/ 25mm under these conditions. The measurement of peel strength is carried out in a direction perpendicular to the strip.

Since the seal includes a free tab, its uppermost layer or layers are not completely attached to the remainder of the seal. It was expected that this partly de-laminated structure would lead to considerable difficulties when attempts were made to form a one-component wadding and seal system. However, we have discovered that this is not the case and, by incorporating a release layer in the attachment between the seal and the wadding the initial unscrewing of the screw-cap by the eventual consumer allows the two halves of the single component system to separate at the release layer without, in any way, damaging the liftable tab or seal.

The attachment means is formed by a layer of polyethylene terephthalate which forms the uppermost layer of the seal substrate, and which is coated with a release layer formed by nitrocellulose or a silicone compound, and a layer of low density polyethylene to act as an adhesive between the release layer and the undersurface of the liner. The nitrocellulose or silicone compound coated onto the polyethylene terephthalate bonds tightly onto this layer. The layer of low density polyethylene bonds tightly onto the wadding but frangibly onto the nitrocellulose or silicone layer. When subject to a parting force in a direction generally perpendicular to the seal and liner, the bond strength between the nitrocellulose or silicon compound and the polyethylene is easily exceeded so that the seal and liner components separate from one another.

The liner may be formed by a layer of food grade cardboard or a layer of foamed plastic material such as foamed polyethylene. In this later case a layer of polypropylene may be included between the foamed layer and the layer of low density polyethylene of the attachment means.

The seal preferably includes an induction heating sealable system comprising a layer of aluminium foil coated on its lowermost face with a hot melt adhesive. A layer of polyethylene teraphthalate may be interposed between the hot melt adhesive and the aluminium foil layer to isolate the foil from the contents of the container and so prevent corrosion of the foil layer. The seal also includes a substrate which may include a paper laminate as described in <patcit id="pcit0006" dnum="US4961986A"><text>US-A-4961986</text></patcit> but preferably includes a layer of foamed polymer such as a foamed polyolefin, for example, polyethylene, bonded to the foil layer and a layer of polyethylene teraphthalate bonded to the foamed layer. A further layer of polyethylene teraphthalate, nylon or polypropylene may be interposed between the layer of polyethylene teraphthalate and the foam in the region where they are not bonded together. The seal substrate may include an upper layer of foamed plastics such as ethylvinyl acetate foam interposed between the layer of polyethylene foam and the layer of polyethylene teraphthalate. In this way the liftable tab then also includes a foam layer.

The screw-cap is generally conventional and may include a multi-turn screwthread or a multi-start part turn screw thread. Preferably it includes a circumferentially extending rib or series of fingers which hold the combined one-component liner and seal in place during initial application of the cap to the container and continue to hold the liner portion in place during subsequent opening and closing of the cap. Preferably the cap is arranged so that there is sufficient clearance between the top of the cap and the rib or fingers that the entire one-component liner and seal can rotate with respect to the cap. This allows the liner to be separated from the seal under a peel force perpendicular to the liner and seal. The container may be made of glass or plastics material such as polyethylene, polyester, polyvinyl chloride, polypropylene, polystyrene or acrylonitrile butadiene styrene.

Two embodiments of a one component liner and seal system in accordance with this invention will now be described with reference to the accompanying drawings, in which:- <ul id="ul0001" list-style="none" compact="compact"><li><figref idref="f0001">Figure 1</figref> is a cross-section through a first example with a vertical dimension greatly exaggerated;</li><li><figref idref="f0001">Figure 2</figref> is a cross-section through a second embodiment, again with a vertical dimension greatly exaggerated;</li><li><figref idref="f0002">Figure 3</figref> is a cross-section through a screw cap showing the liner and seal in place; and,</li><li><figref idref="f0002">Figure 4</figref> is a perspective view showing the seal in place on the neck of a container.</li></ul>

The one-component liner and seal 1 comprises a wadding portion 2 and a seal portion 3 attached together. The one-component wadding and seal 1 is formed by a laminate of a number of layers which, starting from the bottom comprise a coating of hot melt adhesive 4 deposited typically at a rate of in the range 25 to 38 g/m² and may include polyester coatings, ethylene vinyl acetate, polypropylene, ethylene-acrylic acid co-polymers, or Surlyn (rtm) ; a layer of aluminium foil 5 for instance 20 or 25 microns thick; a layer of polymeric adhesive 6 applied, for instance at a rate in the range of 3g/m² to 20; a layer of polyethylene foam 7 125-250 microns thick; a layer of polyethylene terephthalate 8 extending only part way across the layer of foam 7 and not adhered to the layer of foam 7; a layer of polymeric adhesive 9 applied, for instance at a rate of 50g/m²; a layer of polyethylene terephthalate layer 10 23 microns thick which is adhered both to the foam 7 and the polyethylene terephthalate layer 8; a layer 11 of nitrocellulose applied at a rate of 1-2 g/m², which acts as a release layer, a layer 12 of low density polyethylene deposited at a rate of 20 g/m^2; and, a layer 13 of food grade cardboard typically 700 to 900 microns thick.

The adhesive layers 6 and 9 are typically ethylene vinyl acetate copolymer, polyethylene or polyurethane. The layer of low density polyethylene 12 is typically applied in a molten state and, on cooling, bonds tightly to the cardboard 13 and adequately to the nitrocellulose layer 11.

As a result of the presence of the polyethylene teraphthalate layer 10, the nitrocellulose layer 11 and the low density polyethylene layer 12 a bond is formed between the seal portion 3 and the liner portion 2. However, this attachment includes a weakened zone formed by the weak bond formed between the release layer 11 and the low density polyethylene layer 12. This bond is adequate to hold the two portions 2 and 3 together during subsequent processing and handling but weak enough so that when subjected to an appropriate parting force in the upright direction as shown in the Figures, the liner portion 2 separates from the seal portion 3. The presence of the polyethylene terephthalate partial layer 8 and the fact that it is not bonded to the foam layer 7 provides a separate tab portion formed by the layer 8 and 10 which is not adhered to the layer 7 and so forms a liftable tab 50 (shown in <figref idref="f0002">Figure 4</figref>) which will be described subsequently.

The second embodiment which is shown in <figref idref="f0001">Figure 2</figref> is identical to the first from the layer 4 to the layer 12 but, in this example the layer 12 is attached to a layer 14 of polypropylene film 20 microns thick. A layer of polypropylene polyethylene polymeric adhesive 15 applied at a rate of 20 g/m² adheres the polypropylene layer 14 to a layer of expanded polyethylene foam 16 of typical thickness 1.0 or 1.6 mm. A layer of polypropylene polyethylene polymeric adhesive 17 applied at a rate of 20 g/m² adheres the expanded polyethylene foam 16 to a layer 18 of polypropylene film of 20 microns thick. In this second embodiment the liner portion 2 is essentially formed by an expanded polyethylene foam 16 covered by polypropylene layers 14 and 18 which replaces the food grade cardboard used in the first example.

After formation of the laminate it is die cut to form individual discs of one-component liner and seal 1. The one-component liner 1 is press-fitted inside the top of a screw cap 20 and held in place by a circumferential rib 21. The one-component liner and seal 1 is sized so as to be able to rotate freely in the top of the cap 20 whilst, at the same time, being held securely in place by the rib 21. In use, a screwcap equipped with an one-component liner and seal 1 in accordance with the present invention is screwed onto the open neck of a bottle 30 so sandwiching the one-component liner and seal 1 between the open neck of the bottle 30 and the top of the cap 20. The cap 20 and bottle 30 are then subjected to an induction heating step in which the aluminium foil 5 is heated around its periphery by the generation of eddy currents within it which, in turn, melts the coating 4 of hot melt adhesive to bond the seal portion 3 onto the open neck of the bottle 30. The sealed container is then distributed.

When the screw cap 20 is removed from the bottle 30 by the eventual user the seal portion 3 remains adhered to the open neck of the bottle 30 whilst the liner portion 1 is retained by the rib 21 in the top of the cap 20. The seal portion 3 and liner portion 2 part at the nitrocellulose release layer 11 during this initial removal of the cap 20 from the neck of the bottle 30. The eventual consumer can then easily remove the seal portion 3 from the neck of the bottle 30 merely by gripping the tab portion 50 formed by the layers 8 and 10 with the manual force applied to the tab 50 overcoming the adhesion provided between the hot melt coating 4 and the neck of the bottle 30 to enable the entire seal portion 3 to be removed to allow the eventual user to gain access to the contents of the bottle 30. The liner portion 2 remains adhered within the cap to form a secondary seal when reclosed.