EP1858773A1

EP1858773A1 - Container closure

Info

Publication number: EP1858773A1
Application number: EP06737953A
Authority: EP
Inventors: Joseph Smelko; Robert William Thorstensen-Woll
Original assignee: Illinois Tool Works Inc
Current assignee: Illinois Tool Works Inc
Priority date: 2005-03-14
Filing date: 2006-03-13
Publication date: 2007-11-28
Also published as: AU2006223228A1; WO2006099260A1; TW200706462A; US20050208242A1

Abstract

Method of manufacture of a vessel closing assembly (1) for adhesion into a screw cap (16) in which a liner laminate (2) comprising a substrate layer and a layer of stiff film on at least one side of the substrate layer , having an attachment surface (12) for attachment to the seal laminate (3) , is attached to a seal laminate comprising induction heat sealable layers for sealing at one side to a container and comprises at least one stiff film layer and an attachment surface (10) at the other side whereby the attachment surface of the seal laminate faces the side of the liner laminate formed by the stiff film, the joining involving the steps of : providing a release surface on one of the attachment surfaces; applying a pressure sensitive adhesive composition (11) , from a liquid composition to one of the attachment surfaces and drying the composition to leave an adhesive coating; and contacting the attachment surfaces to adhere the liner laminate to the seal laminate.

Description

CONTAINER CLOSURE

This application is a continuation in part of US application no. 10/359,287 filed on 6 February 2003.

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 US-A-4961986. 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 US-A-4961986 this is achieved by forming the substrate from multiple layers which are adhered together over only a part of their extent. US-A-5702015 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 US-A-4961986 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 be fitted 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. The present invention provides a method of manufacture of a vessel closing assembly for adhesion into a screw cap in which a liner laminate comprising a substrate layer and a layer of stiff film on at least one side of the substrate later, having an attachment surface for attachment to the seal laminate, is attached to a seal laminate comprising induction heat sealable layers for sealing at one side to a container and comprises at least one stiff film layer and an attachment surface at the other side whereby the attachment surface of the seal laminate faces the side of the liner laminate formed by the stiff film, the joining involving the steps of: providing a release surface on one of the attachment surfaces; applying a pressure sensitive adhesive composition, from a liquid composition, to one of the attachment surfaces and drying the composition to leave an adhesive coating; and contacting the attachment surfaces to adhere the liner laminate to the seal laminate.

Following the manufacture, the said vessel closing assemblies are cut from the pair of adhered laminates and adhered into screw caps in a procedure separate to the laminate adhesion. The vessel closing assembly is adhered into said screw cap by means of a hot melt adhesive. The screw cap is then screwed onto a container containing a liquid or a solid substrate which can optionally be potable or edible such that the induction heat sealable surface is in contact with the mouth of the container. The seal is then adhered to the mouth of the container by induction heating.

Preferably the stiff film is formed from polyethylene ester or a polypropylene, preferably polyethylene terephthalate (PET). Preferably the stiff film is white PET, in particular Melinex 891 (Trade Mark) supplied by Dupont.

Preferably the thickness of the stiff film is in the range 5 to 40μm. Where the thickness of the stiff film used is at the lower end of the preferable range, it is advantageous to include an additional layer of polypropylene laminated to the PET layer. This ensures an ease of handling and avoids the formation of wrinkles in the thin PET layer.

It has been found that Melinex 891 has a very marked effect on reducing bond values of coatings applied to the non-treated side of this material. A clear polyester is not appropriate to be in direct contact with the release coating as the bond formed to the coating would be too strong. It is believed that this difference lies in the fact that in comparison to clear polyester which has a very smooth surface, white polyester has a "microvoided" surface which is low gloss. A clear polyester can be used in the case where it is coated with a silicone release coating which will subsequently be partially transferred to the adhesive. A further advantage gained from the use of polyesters is that there are no related safety issues. The use of polyester is acceptable for all purposes including those involving contact with food. The release surface is provided by coating the relatively stiff film with release material. Where the stiff layer is white PET, preferably the release material is a cellulose acetate prophonate (CAP). CAP coatings are applied from an isopropanol solution. Appropriate CAP materials are supplied by Eastman Chemical supplies and in particular, CAP 504-0.2 (Trade Mark) is preferable.

Preferably the coating weight of the CAP layer is in the range 1 to 3g/m².

CAP has been chosen because it is a product which has not been modified with other materials and therefore a smaller variation in bond behaviour is expected. CAP also has a relatively high melting point meaning that it is unlikely to be affected by the heat during the induction sealing process. Upon application of a torque, separation occurs between the attachment surface of the stiff layer and the release layer.

Preferably the peel strength of the attachment surface at the release layer is within the range 20 to 90 grams at a rate of 1500mm/min on a sample strip 25mm wide. A more preferred range of peel strength is 30 to 60g/25mm under these conditions. The measurement of peel strength is carried out in a direction perpendicular to the strip. The bond between the release surface and the adhesive must be greater in strength than the bond between the attachment surface and the release surface. This is important as it ensures that the adhesive remains on the seal portion adhered to the cap. It would be undesirable to have the adhesive in the cap as it would cause problems when resealing the bottle.

It has also been found that a nitrocellulose-based lacquer works in the place of CAP. In particular the product TLKGS0035562 (Trade Mark) supplied by Sun Chemical was found to have the appropriate properties.

Alternatively, in the case where the stiff layer is PET, the coating used is silicone. Silicone release coated polyester film is available from Vitex Packaging Inc. The silicone only bonds very weakly to the adhesive and upon application of a torque the bond is broken. A portion, but not all, of the silicone is transferred to the adhesive to render it no longer tacky.

Preferably the pressure sensitive adhesive is formulated with a natural or synthetic latex with rubbery properties. This introduces the characteristic that the adhesive is relatively soft and extensible thus mechanical stability of the laminate is achieved. The term "soft" is used in the present invention to indicate that the adhesive has high elongation properties.

Preferably there is no organic solvent present in either the dispersed or continuous phase of the adhesive. After coating one of the attachment surfaces the adhesive is subsequently dried to give a stable structure which can be easily manipulated.

Preferably the coating weight of the pressure sensitive adhesive composition is in the range 3 to 6 g/m² Where the release layer is formed from CAP or a nitrocellulose based lacquer, it is preferable that the pressure adhesive composition has a degree of tackiness. This tackiness is not evident to the person opening the cap as a continuous layer of CAP or nitrocellulose will cover the adhesive layer once the cap has been removed. The degree of tackiness varies depending on the particular composition used. Use of a tacky adhesive contributes to an ease of laminating materials together and the heat and pressure during the laminating step can be adjusted to allow for the variation in tackiness.

It is also possible to use the above described pressure sensitive adhesive composition with a silicone coated polyester film but only in the case where there is a partial transfer of the silicone material to the adhesive layer.

Preferably the pressure sensitive adhesive composition is either 9126 (Trade Mark) or XS120 (Trade Mark) supplied by Dyna-Tech. In the case where the stiff film is a silicone coated polyester, it is preferable to use a cohesive adhesive. Cohesive adhesives are used industrially in packaging processes and are not tacky. Such adhesives are specifically designed to bond to themselves upon application of pressure only. No heat is required. In the present invention, these adhesives are not used in this manner. Instead, their very low tack nature is being exploited such that the presence of these adhesives on the top of a liner does not cause any consumer concern. Cohesive adhesives provide an effective means of laminating the structures together, providing stable laminates even where the area of bonding is reduced to as little as 25%. Use of these adhesives simplifies the structure and thus results in a reduction in associated costs. A cohesive adhesive is applied from an aqueous solution or appropriate solvent to the upper surface of the seal laminate and the layer to which it is applied is corona treated prior to this application to ensure that a strong bond results between the seal laminate and the adhesive.

The cohesive adhesives used in the present invention were supplied by Sovereign Packaging Group Inc. Particularly suitable materials are Primaseal 22-184 (Trade Mark) and Primaseal 22-185 (Trade Mark). Preferably the thickness of the liner is in the range 0.4-1 .2mm. Preferably the liner is formed from polypropylene faced polyethylene foam. It is preferable that the density of the liner is in the range 250 to 500g/l.

It is important that the stiffness of the secondary liner is appropriate. The secondary liner is formed from both the stiff film layer and the liner and it is the overall stiffness of the composite rather than the individual stiffness of the components which is of importance. If the film is not sufficiently stiff then upon opening the cap, unacceptable torquing of the liner will occur leading to unacceptable distortion of the liner. This is detrimental to the secondary seal and makes it more difficult to separate the seal and liner portions as the required shear forces cannot be generated. For the purposes of the present invention, stiffness is defined as a resistance to distortion of the secondary liner when the cap is removed form the body.

Appropriate composites were determined by comparative testing. It has been found that use of a foam with a higher foam density, use of a foam made from a higher density resin and use of a foam surfaced with a material having a higher tensile modulus results in a secondary liner less prone to distortion upon application of a shear force. Polypropylene has a higher tensile modulus than polyethylene foam and therefore by coating the surface of the polyethylene foam with polypropylene to give a polypropylene faced polyethylene foam, a stiffer foam is obtained. Preferably the thickness of the polypropylene layer is in the range 20-50μm. In particular, the product Sureseal 626 (Trade Mark) supplied by J S Plastics was found to have the appropriate properties.

The Applicant has further surprisingly found that where a particular release surface, adhesive composition and attachment surface are used in combination, it is possible to produce a laminate where there is no need to include a separate release layer. This simplifies the process of production and reduce the costs of the vessel closing assembly. Such a laminate can be adhered within a conventional screw cap.

In this respect, the present invention further provides a vessel closing assembly for adhesion into a screw cap including a seal laminate having lower layers which form an induction heating sealable system for attaching the seal to the neck of a container to be sealed and a top polyester layer which has been corona treated; a liner laminate comprising a substrate layer and a bottom stiff polyester film layer which has a bottom surface with release properties; and a non-continuous layer of cold seal adhesive bonded between the top polyester layer of the seal laminate and the bottom surface of the stiff polyester film layer of the liner laminate; wherein the bonding force between the adhesive and the top polyester layer of the seal laminate is sufficiently strong that the adhesive remains bonded to the top polyester layer upon removal of the liner laminate from the seal laminate by a shear force and the bonding force between the adhesive and the bottom surface of the stiff polyester film layer of the liner laminate is sufficiently weak that the two layers separate from one another upon removal of the liner laminate from the seal laminate.

The crucial aspect of this part of the present invention lies in the selection of the materials which make up the top polyester layer of this seal laminate, the adhesive and the bottom stiff polyester film layer of the liner laminate which removes the need for a release layer. The selections are made in order to ensure that the correct balance of bonding strength is achieved. In this aspect of the present invention, the top layer of the seal is a polyester layer. Preferably the top polyester layer is polyethylene terephthalate. Prior to application of the adhesive layer, this top polyester layer is corona treated. This involves applying a high frequency, high voltage charge that causes the surrounding air to be ionized. This surrounding air after ionization is referred to as the corona discharge. The ionized particles in the corona discharge then contact the surface of the layer being treated and cause surface oxidation which leads to an increase in the surface energy of the surface being treated. It is necessary to corona treat the top polyester layer in order to ensure that the bond between the adhesive layer and the top layer is sufficiently strong that it does not fail upon the application of the turning force required to remove a screw cap into which the vessel closing assembly is fitted from the neck of a container. This means that the adhesive layer remains bonded to the top polyester layer. In order to meet this requirement , the shear strength at the interface between the top polyester layer of the seal and the adhesive layer is preferably in the range from 100 to 300gcm^"2. Shear strength was measured using the overlap shear test. In the overlap shear test, a sample is first prepared by removing 1.3cm (0.5 inches) of the seal laminate at one side of a 13mm x 30mm wide sample and removing 1.3cm (0.5 inches) of the liner laminate from the other side of the sample. The exposed seal laminate at one side and liner laminate at the other side are placed in clamps respectively. The two clamps are then pulled in opposite directions at 180EC in lab shear mode at a pull speed of 0.3m/min. The shear force required to pull the components apart is then measured as required.

In addition to the embodiment of the present invention, the top layer of the seal is a polyester layer, the seal laminate may also include a seal substrate attached to the upper surface of the heat sealable layers. This substrate may be included in order to impart stability to the seal portion of the final one component vessel closing assembly. The seal substrate may include a paper laminate but preferably includes a foamed polymer. In one embodiment of the present invention, the seal substrate includes foamed polyethylene bonded to the foil layer and the top polyester layer. Preferably the foamed polyethylene is high density polyethylene (HDPE). The thickness of the foam layer is generally in the range from 76 to 380μm (0.003 to 0.0015 inches), more preferably the thickness of the foam layer is approximately 125μm (0.005 inches).

In one embodiment the seal substrate includes a tab lying wholly within the circumference of the seal. Such a tab is produced by the seal substrate including an upper layer and a lower layer which are adhered in a first region but not a second region. In the second region where there is no bonding, an intermediate layer is interposed between the upper and lower layers and adhered to the upper layer but not the lower layer. This results in a partly delaminated structure and consequently the inclusion of a tab. The upper layer may, in one embodiment, be the top polyester layer of the seal. Alternatively, the seal substrate may include an upper layer of foamed plastics. The lower layer of the seal substrate is preferably a polyolefin foam, for example HDPE. In this embodiment, the intermediate layer may be formed from polyethylene terephthalate, nylon or polypropylene. Preferably the intermediate layer is polyethylene terephthalate. The thickness of this polyethylene terephthalate is preferably in the range from 0.1 to 0.3mm, more preferably approximately 0.13mm. substrate attached to the upper surface of the heat sealable layers.

The liner laminate is the part of the vessel closing assembly which, in use, will remain within a screw cap after opening the container. The bottom layer of the liner laminate is a stiff polyester film layer which has a bottom surface with release properties. This means that the bond formed between the bottom surface of the stiff polyester film layer and the adhesive is sufficiently weak that upon application of a shear force upon opening, separation occurs at the interface between the two layers. However, this bond must be sufficiently strong that it remains intact during the handling and production of the vessel closing assembly.

As noted above, it has been found that certain polyesters have a marked effect on reducing the adhesion to the adhesive layer. In this embodiment of the present invention, preferably a white polyester is used. A particularly preferred example of a suitable white polyester includes Melinex 891 commercially available from Dupont. This film is a microvoided 60 gauge white polyester film that has a static coefficient of friction of 0.3. This layer must be sufficiently stiff in order to prevent distortion on opening. In this respect, the liner laminate also includes a substrate layer. Preferably the combined thickness of the polyester layer and substrate layer is in the range from 0.4 to 1.5mm (0.015 to 0.060 inches). This further layer may be of food grade cardboard or a layer of foamed plastics material such as polyethylene. This layer forms the uppermost layer of the liner and preferably has a thickness in the range from 0.37 to 1 .5mm (0.014 to 0.06 inches).

The liner laminate and the seal laminate are adhered to one another by a non-continuous adhesive layer. Previously in order to ensure that the correct balance of bond strength was achieved, in particular in relation to the bond between the top polyester layer of the seal laminate and the adhesive, it was always necessary to include a continuous layer of adhesive. However, by virtue of the selection of the present invention, this is no longer necessary.

The adhesive is applied to the top polyester layer of the seal after it has been corona treated as described above. Preferably the adhesive layer comprises an array of regularly spaced dots of adhesive. Preferably the bonding area represents between 10 and 15% of the total surface area. The distance between adjacent dots is preferably in the range from 1 to 1.5mm. In a preferred embodiment of the present invention, the adhesive layer comprises an array of dots with a diameter of 2.5mm regularly spaced by a. distance of 7mm wherein the total bonding area represents between 10 to 15% of the total surface area.

It can be envisaged that various different arrangements of adhesive dots may be employed provided there is sufficient surface coverage for a bond of the appropriate strength to be present. As is clear from the discussion above, the choice of adhesive is crucial to ensuring that the appropriate strengths of bonds result with the top polyester layer of the seal laminate and the bottom surface of the polyester film layer of the liner laminate respectively. The bond formed to the top layer of the seal must be stronger than the bond formed to the bottom polyester layer of the liner.

The adhesive used is a cold seal adhesive. As noted previously and is known in the field, cold seal adhesives have a low tackiness and are specifically designed to bond to themselves upon application of pressure only. A major advantage of the low tackiness is that upon separation of the bottom polyester layer of the liner from the adhesive layer, the top surface of the seal which will be the adhesive layer, will not be tacky to the touch and thus will cause no consumer concern. While the tackiness is low, it is sufficient to hold the structure together during production and stable laminates can be produced where the area of bonding is as low as 25%. Examples of suitable adhesives include Primaseal 22_:184 available from Sovereign Speciality Chemicals which is vinyl acetate-ethylene based water based emulsion cold seal adhesive and Primaseal 22-185 also available from Sovereign Speciality Chemicals, which is a an acrylic based cold seal adhesive. Preferred cold seal adhesives are latex containing synthetic cold seal adhesives.

A preferred example of such a cold seal adhesive is HB Fuller NP- 4134 M available from HB Fuller Canada Inc. This particular example is a synthetic resin containing 60% solids by weight and has a viscosity of 250cps. The adhesive is applied to form a non-continuous layer with a coat- weight in the range from 0.3 to 0.60gcrτf². In one embodiment of the present invention the bottom surface of the stiff polyester layer is adhered to the top polyester layer by coated the top polyester layer with cold seal adhesive at a speed of approximately 3m/minute and then applying a pressure in the range from 380 to 415kPa at a temperature in the range from 80 to 100EC.

Having formed the vessel closing assembly, the next step is to cut it into a shape appropriate for inclusion in a screw cap. This can be done, for example, by punching or die cutting. The shaped vessel assembly is then adhered within a conventional screw cap. While it is not an essential requirement, the screw cap may in one embodiment include a circumferentially extending rib or series of fingers. The screw cap is then attached to the neck of a container. The container may be made of glass or plastics material, such as polyethylene, polyester, polyvinyl chloride, polypropylene or acrylonitrite butadiene styrene.

Three embodiments of a vessel closing assembly in accordance with this invention will now be described with reference to the accompanying drawings, in which:-

Figure 1 is a cross-section through a first embodiment with a vertical dimension greatly exaggerated;

Figure 2 is a cross-section through a second embodiment, again with a vertical dimension greatly exaggerated;

Figure 3 is a cross-section through a third embodiment with a vertical dimension greatly exaggerated. Figure 4 is a cross-section through a screw cap showing the liner and seal in place; and,

Figure 5 is a perspective view showing the seal in place on the neck of a container.

The vessel closing assembly 1 comprises a liner laminate 2 and a seal laminate 3 attached together as shown in Figure 1 . The vessel closing assembly 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. The liner laminate 2 is formed by application of a layer of CAP coating 12 from an isopropanol solution to the white polyester film surface 13 of a laminated structure formed from a layer of white PET film with a thickness in the range 8 to 40μm laminated to a layer of polypropylene film with a thickness in the range 30 to 50μm. A pressure sensitive coating 11 is then applied from an aqueous solution to the CAP layer 12 wherein the coating weight of the adhesive layer is in the range 3 to 6g/m². The layer 11 is then dried to leave a tacky stable adhesive layer to which the attachment surface formed of white PET 24 coated with CAP to form a release layer 12, is subsequently adhered by a heat and pressure lamination step. The binding of layers 11 and 12 is sufficiently strong so as to give a stable system but weak enough that only weak shear forces are required to separate the two layers. A layer of polypropylene faced polyethylene foam 15 is then adhesively laminated to the upper surface of the polypropylene film 14 to give the completed vessel closing assembly wherein the foam layer has a thickness in the range 0.4 to 1.1 mm and a density in the range 250 to 500g/l.

Following the formation of the laminate, it is die cut to form discs of the vessel closing assembly 1 . The vessel closing assembly 1 is fixed inside the top of a screw cap 16 by means of hot melt adhesive 30. A screw cap equipped with a vessel closing assembly in accordance with the present invention is screwed onto the open neck of a bottle thus sandwiching the vessel closing assembly 1 between the open neck of the bottle and the top of the cap. The cap 16 and the bottle 17 are then subjected to an induction heating step in which the aluminium foil is heated around its periphery by the generation of eddy currents within it which, in turn, melts the coating 4 of the hot melt adhesive to bond the seal portion onto the open neck of the bottle. The sealed container is then distributed.

When the screw cap is removed from the bottle by the eventual user, the seal laminate 3 remains adhered to the open neck of the bottle 17 whilst the liner remains fixed in the cap 16. The seal and liner portions separate between the release and attachment layers, specifically layers 12 and 13. The CAP coating of the attachment surface 12 is transferred to the adhesive layer 11 so the top of the seal portion is no longer left tacky.

In this embodiment, the seal portion includes a tab 18 so the eventual user can easily remove the seal portion 3 from the neck of the bottle 17 by gripping the tab portion 8 and the manual force applied to the tab overcomes the adhesion provided between the hot melt coating 4 and the neck of the bottle to enable the entire seal portion 3 to be removed to allow the user to gain access to the contents of the bottle. The liner portion 2 has remained glued into the cap 16 meaning that the bottle is resealable following the removal of the seal.

As shown in Figure 2, in the second embodiment, the seal laminate (3) does not include a tab. The bottom layer of the seal is a layer of hot melt adhesive (19) chosen partly based on the nature of the characteristics of the container wherein suitable adhesives include polyester coatings, ethylene vinyl acetate, polypropylene, ethylene acrylic acid copolymers, Surlyn (RTM) and other materials known in the industry. A layer of polyethylene terephthalate (20) is laminated to the hot melt adhesive (19). The thickness of this layer is 13μm (O.δmil, 48 gauge). A layer of aluminium foil (21 ) with a thickness of 25μm is on top of the layer of polyethylene terephalate and above the aluminium foil layer is a layer of polyester foam (22) with a thickness of 125 to 250μm. The top face of the polyester foam is adhered to a layer of polyethylene terephthalate (23). The top layer of polyethylene terephthalate is then corona treated by application of high frequency, high voltage charge.

A non-continuous layer of cold seal adhesive (24) is then applied to the corona treated polyethylene terephthalate (23). The adhesive is applied by printing using a pattered rubber roll and is then oven dried to form a regular array of dots of adhesive which cover approximately 10 to 15% of the surface area of the top polyethylene terephthalate layer (23). The cold seal adhesive used was HB Fuller NP-4134M available HB Fuller Canada Inc. and the coat weight was 0.55+gcιτf². The liner (2) is formed by laminating a layer of white PET film (25) with a thickness of 75μm to a layer of polyethylene foam (26) to give a liner with a final thickness in the range from 0.4 to 1.5m (0.015 to 0.060 inches). The bottom surface of the white PET film (25) is then brought into contact with the adhesive layer (24) and a pressure is applied in the range from 380 to 415kPa (55 to 60psi). The result is the completed vessel closing assembly laminate (1 ).

Following formation of the laminate it is die cut to form discs of the vessel closing assembly (1 ). The vessel closing assembly (1 ) is adhered into a screw cap (16) by means of a hot melt adhesive (30). A screw cap equipped with a vessel closing assembly in accordance with the present invention is screwed onto the open neck of a bottle thus sandwiching the vessel closing assembly (1 ) between the open neck of the bottle and the cap. The cap (16) and the bottle (17) are then subjected to an induction heating step in which the aluminium foil is heated around its periphery by the generation of eddy currents within it which, in turn, melts the coating (19) of the hot melt adhesive to bond the seal portion onto the open neck of the bottle. The sealed container is then distributed. When the screw cap is removed from the bottle by the eventual user, the seal (3) remains adhered to the open neck of the bottle (17) and the liner remains fixed in the cap (16). The seal and liner portions separate at the interface between the adhesive layer (24) and the bottom polyester with release properties of the liner (25). In a third embodiment of the present invention as illustrated in Figure

3, the seal includes a tab lying wholly within the circumference of the seal. Layers (19) to (22) of the seal are manufactured in the same manner as described above. In this embodiment, in addition to the lower layer of polyester foam (22), the seal laminate also includes an upper foam layer of ethylene vinyl acetate (EVA) (28). The layer of polyester foam (22) and layer of EVA (28) are adhered to each other in a first region but not in a second region. In the second region, a layer of polyethylene terephthalate (27) is interposed between layers (22) and (28) to form a tab. The vessel closing assembly is manufactured and adhered within a cap and then subsequently onto the neck of a container in the same way as in the first embodiment.

In this embodiment, however, the seal (3) includes a tab (18) so the eventual user can easily remove the seal (3) from the neck of a container (17) by gripping the tab portion (18) and applying a manual force to overcome the adhesion provided between the hot melt coating (19) and the neck of the bottle to enable the entire seal to be removed to allow the user to gain access to the container. As the liner (2) remains glued in the cap (16), it provides a means of resealing the container following removal of the seal.

These examples are merely illustrative and are in no way intended to limit the scope of the invention.

Claims

1.Method of manufacture of a vessel closing assembly for adhesion into a screw cap in which a liner laminate comprising a substrate layer and a layer of stiff film on at least one side of the substrate layer , having an attachment surface for attachment to the seal laminate, is attached to a seal laminate comprising induction heat sealable layers for sealing at one side to a container and comprises at least one stiff film layer and an attachment surface at the other side whereby the attachment surface of the seal laminate faces the side of the liner laminate formed by the stiff film, the joining involving the steps of: providing a release surface on one of the attachment surfaces; applying a pressure sensitive adhesive composition, from a liquid composition to one of the attachment surfaces and drying the composition to leave an adhesive coating; and contacting the attachment surfaces to adhere the liner laminate to the seal laminate.

2.A method according to claim 1 wherein the vessel closing assemblies are cut from the pair of adhered laminates and adhered into screw cap in a procedure separate to the laminate adhesion procedure. 3. The method according to claim 2 in which the assemblies are adhered into the caps by a hot melt adhesive.

4. The method according to claim 1 in which the release surface is provided by coating the relatively stiff film with release material.

5. The method according to claim 3 in which the release layer is a cellulose acetate proprionate coating.

6. The method according to claim 5 in which the coating weight of the CAP layer is in the range 1 to 3g/m².

7. The method according to claim 1 in which the release layer is a silicone coating. 8. The method according to claim 1 in which the liner is formed from foamed thermoplastics material.

9. The method according to claim 8 in which the foamed thermoplastics material is polypropylene faced polyethylene foam.

10. The method according to claim 8 in which the thickness of the foamed thermoplastics material is in the range 0.4 to 1.1 mm.

1 1. The method according to claim 8 in which the density of the foamed thermoplastics material is in the range 250 to 500g/l. 12. The method according to claim 1 in which the stiff layer is formed from a polyester or polypropylene.

13. The method according to claim 12 in which the stiff layer is polyethylene terephthalate. 14. The method according to any preceding claim in which the thickness of the stiff film is in the range 8.0 to 40μm. 15. The method according to claim 1 in which the stiff layer is white polyethylene terephthalate.

16. The method according to claim 1 in which the pressure sensitive adhesive composition is formulated with a natural or synthetic latex with high elongation properties.

17. The method according to claim 1 in which the release surface is on the stiff film layer and the pressure sensitive adhesive composition is applied to the surface of the release layer.

18. The method according to claim 1 in which the release surface is on the stiff film surface and the pressure sensitive adhesive composition is applied to the top surface of the seal laminate.

19. The method according to claim 1 in which the peel strength of the attachment surface at the release layer is in the range 20 to 90g/25mm. 2O.The method according to claim 1 in which the peel strength of the attachment surface at the release surface is in the range 30 to 60g/25mm. 21. The method according to claim 1 in which the pressure sensitive adhesive composition is a cohesive adhesive.

22. The method according to claim 1 , wherein prior to applying the pressure sensitive adhesive composition, the attachment surface of the seal laminate is corona treated.

23. A vessel closing assembly for adhesion into a screw cap including a seal laminate having lower layers which form an induction heating sealable system for attaching the seal to the neck of a container to be sealed and a top layer of polyester which has been corona treated; a liner laminate comprising a substrate layer and a bottom layer of stiff polyester film which has a bottom surface with release properties; and a non-continuous layer of cold seal adhesive bonded between the top polyester layer of the seal laminate and the bottom surface of the stiff polyester film layer of the liner laminate; wherein the bonding force between the adhesive and the top polyester layer of the seal laminate is sufficiently strong that the adhesive remains bonded to the top polyester layer upon removal of the liner laminate from the seal laminate by a shear force and the bonding force between the adhesive and the bottom surface of the stiff polyester film layer of the liner laminate is sufficiently upon removal of the liner laminate from the seal laminate. 24. The vessel closing assembly according to claim 23, wherein the top polyester layer of the seal laminate is polyethylene terephthalate. 25.The vessel closing assembly according to claim 23, wherein the bottom polyester layer of the liner is polyethylene terephthalate.

26. The vessel closing assembly of claim 25, wherein the polyethylene terephthalate is Melinex 891.

27. The vessel closing assembly of claim 23, wherein the adhesive is selected from the group consisting of latex containing synthetic cold seal adhesives.

28. The vessel closing assembly of claim 23, wherein the adhesive is H B Fuller NP-4134M.

29. The vessel closing assembly of claim 23, wherein the non-continuous adhesive layer is a pattern of regularly spaced dots of adhesive.

30. The vessel closing assembly of claim 23, wherein the shear strength at the interface between the top polyester layer of the seal and the adhesive layer is in the range from 100 to 300gcm^"2.

31. The vessel closing assembly of claim 23, wherein the seal laminate includes an upper layer and a lower layer which are adhered in a first region but not in a second region and an intermediate layer interposed between the upper and lower layers and adhered to the upper layer but not the lower layer, so as to form a tab lying wholly within the circumference of the seal.

32. The vessel closing assembly of claim 31 , wherein the upper layer is ethylene vinyl acetate (EVA).

33. The vessel closing assembly of claim 31 , wherein the lower layer is a polymeric foam.

34. The vessel closing assembly of claim 33, wherein the polymeric foam is high density polyethylene foam. 35.. The vessel closing assembly of claim 31 , wherein the intermediate layer is polyethylene terephthalate.

36. The vessel closing assembly of claim 31 , wherein the liner laminate includes a top layer of polyethylene foam.

37. The vessel closing assembly of claim 23 which is cut and shaped so as to fit inside a screw cap.

38. A screw cap which has adhered within it the vessel closing assembly according to claim 31.

39. A container which is fitted with the screw cap according to claim 38. 40. A method of forming a vessel closing assembly comprising the steps of: providing a seal laminate comprising lower layers which form an induction heat sealable system and a top polyester layer; corona treating the top polyester layer of the seal; applying a cold seal adhesive onto the top polyester layer of the seal which has been corona treated, such that the resulting adhesive layer is not continuous and covers only a portion of the surface area of the top polyester layer; providing a liner which has a bottom stiff polyester film layer which has a bottom surface with release properties; and adhering the bottom stiff polyester film layer of the liner to the adhesive layer to form a laminate.

41. The method of claim 40, wherein the laminate is cut to form a shaped vessel closing assembly.

42. The method of claim 40, wherein the seal substrate includes an upper layer and a lower layer which are adhered in a first region but not in a second region and an intermediate layer interposed between the upper and lower layers and adhered to the upper layer but not the lower layer so as to form a tab lying wholly within the circumference of the seal.