Seal stock laminate

Abstract

A method for producing a primary laminate including a tabstock by feeding a seal laminate comprising bottom food contact layers including a foil layer and a top polyester layer to a laminating station wherein either the foil layer of the underside of the polyester layer has been printed; simultaneously feeding a tabstock, which is narrower than the seal laminate, to the laminating station such that the bottom of the tabstock and the top polyester layer of the seal laminate come into contact to form a primary substrate, simultaneously feeding a plastic film stock; and continuously extruding a polymeric adhesive between the top face of the primary substrate and bottom surface of the plastic film stock.

Claims

1. A primary laminate configured to form a tabbed container sealing member having a tab defined wholly within a perimeter thereof, the primary laminate comprising: a seal laminate including at least a bottom layer for securing to a rim surrounding a container opening, a foil layer, and a top polyester film layer; a tab stock film layer with a top and bottom face wherein the bottom face of the tab stock film layer is above the top polyester film layer of the seal laminate to form a primary substrate; an upper surface of the primary substrate having a first and a second portion wherein the first portion is formed by the top polyester film layer and the second portion is formed by the top face of the tab stock film layer; a layer of plastic film adhered to both the top face of the tab stock film layer and the top polyester film layer by an extruded polymeric adhesive, the layer of plastic film selected from polyethylene terephthalate, polyamide, polypropylene or a composite thereof, and the extruded polymeric adhesive selected from polyethylene, polyethylene vinyl acetate, maleic anhydride/acrylate ester/polyethylene copolymer, and ethylene methyl acrylate; a bond between the layer of plastic film and the top polyester film layer formed by the layer of extruded polymeric adhesive of at least about 15 N/cm; and further comprising a secondary seal stock having an overall stiffness in the range from 200-1200 gcm and wherein the layer of plastic film of the primary laminate is bonded to the secondary seal stock by a second extruded polymeric adhesive having a melt flow index of 5 to 25 dg/min, wherein the secondary seal stock is configured to remain in a screw cap and separate from the primary laminate when the screw cap is removed from a container.

2. The primary laminate of claim 1, wherein the upper surface of the primary substrate is free of printing that interferes with the bond formed between the layer of plastic film and the top polyester film layer.

3. The primary laminate of claim 1, wherein one of the foil layer or an underside of the top polyester film layer facing the foil layer is printed so that the printing is not in direct contact with the extruded polymeric adhesive, and the layer of plastic film, the top polyester film layer, and the extruded polymeric adhesive are transparent so that the printing is visible through the top of the primary laminate.

4. The primary laminate of claim 1, wherein the extruded polymeric adhesive is ethylene methyl acrylate, the layer of plastic film is polyethylene terephthalate, and the top polyester film layer is polyethylene terephthalate.

5. The primary laminate according to claim 1, wherein a bond of the second extruded polymeric adhesive to the secondary seal stock is greater than a bond of the second extruded polymeric adhesive to the layer of plastic film.

6. The primary laminate according to claim 5, wherein a surface energy of a lower surface of the secondary seal stock is lower than a surface energy of the layer of plastic film.

7. The primary laminate according to claim 1, further comprising a plurality of tab stock film layers spaced across the primary laminate.

8. A primary laminate configured to form a tabbed sealing member having a tab defined wholly within a perimeter thereof, the primary laminate comprising: a seal laminate including at least a bottom layer for securing to a rim surrounding a container opening, a foil layer, and a top non-foam polymer layer; a tab stock with a top and bottom face wherein the bottom face of the tab stock is in non-adhesive contact with the top non-foam polymer layer of the seal laminate to form a primary substrate, the tab stock being narrower in width than the seal laminate; an upper surface of the primary substrate having a first and a second portion wherein the first portion is formed by the top non-foam polymer layer and the second portion is formed by the top face of the tab stock; a layer of plastic film adhered to both the top face of the tab stock and the top non-foam polymer layer by an extruded polymeric adhesive; a bond between the layer of plastic film and the top non-foam polymer layer formed by the layer of extruded polymeric adhesive of at least about 15 N/cm; and further including a secondary seal stock having an overall stiffness in the range from 200-1200 gcm and wherein the layer of plastic film of the primary laminate is bonded to the secondary seal stock by a second extruded polymeric adhesive having a melt flow index of 5 to 25 dg/min, wherein the secondary seal stock is configured to remain in a screw cap and separate from the primary laminate when the screw cap is removed from a container.

9. The primary laminate of claim 8, wherein the layer of plastic film, the top non-foam polymer layer, and the extruded polymeric adhesive are transparent.

10. The primary laminate of claim 8, wherein the layer of plastic film is polyethylene terephthalate, polyamide, polypropylene or a composite thereof.

11. The primary laminate of claim 8, wherein the layer of plastic film is a coextruded multi-layer film.

12. The primary laminate of claim 8, wherein the extruded polymeric adhesive is selected from the group consisting of polyethylene, polyethylene vinyl acetate, maleic anhydride/acrylate ester/polyethylene copolymer, and ethylene methyl acrylate.

13. The primary laminate of claim 8, wherein the top non-foam polymer layer is polyethylene terephthalate.

14. The primary laminate according to claim 8, wherein a bond of the second extruded polymeric adhesive to the secondary seal stock is greater than a bond of the second extruded polymeric adhesive to the layer of plastic film.

15. The primary laminate according to claim 14, wherein a surface energy of a lower surface of the secondary seal stock is lower than a surface energy of the layer of plastic film.

16. The primary laminate according to claim a wherein the secondary seal stock is a laminate having a core layer with facing layers on opposite sides thereof.

17. The primary laminate according to claim 8, wherein the secondary seal stock is configured to separate from the primary laminate with an audible cracking indication upon unscrewing of a cap including a sealing member formed from the primary laminate to provide audible evidence that the container has not been tampered with.

18. The primary laminate according to claim 8, wherein the tab stock is a laminate of polymer layers with an adhesive tie layer therebetween.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) An embodiment of the present invention will now be described with reference to the following figures, in which:

(2) FIG. 1 is a cross section through an example of a primary laminate including a tabstock as formed according to the method of the present invention with a vertical dimension greatly exaggerated.

(3) FIG. 2 is a schematic diagram of the laminating apparatus used in the method of the present invention.

(4) FIG. 3 is a cross section through an example of the seal stock laminate with a vertical dimension greatly exaggerated.

(5) FIG. 4 is a cross-section through a screw cap showing the vessel closing assembly in place.

(6) FIG. 5 is a perspective view showing the seal in place on the neck of a container.

(7) FIG. 6 is a cross section through a second embodiment of a primary laminate including a tabstock as formed according to the method of the present invention with a vertical dimension greatly exaggerated.

DETAILED DESCRIPTION

Example 1

(8) A seal laminate (1) was obtained commercially from Gerosa, Spain. The seal laminate comprised heat sealable layers (2,3) for adhesion to a container to be sealed and a foil layer (4). The top layer of the seal laminate (5) is PET which has been printed on the reverse side. As an alternative to purchasing this part of the structure (2, 3, 4) as in this example, it may be laminated to the foil layer in a separate step to form the heat sealable laminate. This seal laminate is rolled onto a first feed roll (9) in the laminating apparatus.

(9) The second feed roll (10) in the laminating apparatus is the source of the tabstock (6). The tabstock used is formed of PET which has a thickness in the range from 12-25 m. The width of the (6) is in the range from 20-60 mm.

(10) A third feed roll (11) is loaded with a PET stock (8) which can be obtained commercially from Toray, Europe. The thickness of the PET stock (8) is in the range from 12-36 m. The PET stock (8) used is a co-extruded PET heat seal layer in order to ensure optimal adhesion.

(11) The seal laminate (1), tabstock (6) and PET stock (8) are simultaneously fed to the laminating station (12) where an extruder (13) is positioned vertically above the point of contact between the feeds. Prior to reaching the laminating station (12), the seal laminate (1) and tabstock (6) are brought into contact to form a primary substrate (1a).

(12) Ethylene methyl acrylate copolymer (7) is then extruded continuously as a curtain from the extruder (13) between the top face of the primary laminate (1a) and the bottom face of the PET stock (8). The extrusion conditions were such that a temperature of 100 C. to 200 C. was attained at the nip. The rollers (14) and (21) are moving at a speed of 70 m/min relative to the speed of application of the adhesive. the bottom face of the PET. Stock (8) and the resulting primary laminate including a tabstock is passed via a chill roller (14) to be rolled on to a final product roll (15). This process is illustrated schematically in FIG. 2.

(13) The peel strength of a primary laminate formed using a PET stock (8) thickness of 36 m and a tabstock thickness of 12 m wherein the coat weight of the extruded ethylene methyl acrylate copolymer (7) was 40 gm.sup.3.

(14) The coat weight was determined as follows: a 0.5 m to 1 m length of paper backed polyester which has a width of 1 m was passed to the laminating station in place of the primary laminate. A curtain of EVA was then extruded continuously between the top polyester face of the paper backed polyester and the bottom face of the PET stock (8). 1010 cm samples were then cut across the width of the web and their weight in g was recorded. The weight of the paper backed polyester and PET stock (8) were subtracted from this figure and the result was multiplied by 100 to give a coat weight in gm.sup.2.

(15) As detailed previously, the top face of the primary substrate and the bottom surface of the plastic film stock must be adhered together with a bond strength greater than 15 N/cm. In a separate experiment the bond strength was determined by using the method detailed as follows. The apparatus used was a Tensile Tester attached to a desktop PC, two jaws, a 8012.5 mm measuring template and a sharp knife. A sample with dimensions of 12.5 mm long and 10 mm wide perpendicular to the machine direction was cut across a section of the primary laminate. Steps are taken to ensure that a section of the PET stock (8) and the primary laminate including a tabstock is separated. The height of the jaws is adjusted such that the tab is inserted into one and the base into the other. The sample is positioned so as to be pointing towards the machine. The tab and base are then pulled apart and the force required to do so is recorded from the apparatus.

Example 2

(16) The primary laminate including a tabstock (1b) as formed in Example 1 was then adhered to a secondary seal stock to form a one component seal and liner system. The secondary seal stock (17) was manufactured on site at Unipac and comprises a foam layer with a thickness of 1.25 mm which is polyethylene foam (18) faced with layers on either side of polypropylene film (19). The stiffness was 320 gcm.

(17) The same apparatus as was used to form the primary laminate including a tabstock (1b) detailed in Example 1 was used. The primary laminate including a tabstock was loaded onto feed roll (11) and the secondary seal stock (17) was loaded onto the third feed roll (9). In this case, the second feed roll (10) was redundant and thus not used. The primary laminate including a tabstock and secondary seal stock (17) were fed simultaneously to the laminating station (12). A curtain of low density polyethylene (16) with a melt flow index of 7.5 dg/min and polypropylene (16a) with an MFI of 11 dg/min was extruded continuously from the extruder between the top polyester face (8) of the primary laminate including a tabstock and the lower face of the secondary seal stock (19a) adhering the two to form a seal stock laminate (20) wherein the polypropylene (16a) adheres to the lower face of the secondary seal stock (19a) and the polyethylene (16) adheres to the top polyester face (8).

(18) The seal stock laminate was then cut into narrow strips. From these strips, circular discs were punched to form discs of the seal stock laminate. The seal stock laminate (20) is fixed inside the top of a screw cap (22) by means of a retention feature (23). A screw cap equipped with the seal stock laminate in accordance with the present invention is then screwed onto the open neck of the cap. The cap (22) and bottle (24) are then subjected to an induction heating step in which the foil is heated around its periphery by the generation of eddy currents within it, which, in turn, melts the heat sealable layer (2) to bond the primary laminate including a tabstock to the open neck of the bottle.

Example 3

(19) A seal laminate (29) comprising bottom food contact layers (25, 26) for adhesion to a container to be sealed and a foil layer (27) which has been printed are purchased from Gerosa, Spain. The lowermost layer (25) of the seal laminate consists of glassine paper with a coat weight of at least 30 gm.sup.2. Layer (26) is a layer of water-based adhesive with a coat weight of at least 3 gm.sup.2 (dry weight). The layer of aluminium foil (27) has a thickness of 8 m. The top layer of the seal laminate (28) is PET. This is purchased as a part of the structure (25, 26, 27) or laminated to the foil layer in a separate step to form the seal laminate.

(20) The primary laminate was formed using this seal laminate (29) in place of the seal laminate (1) having heat induction sealable layers of example 1 to produce a primary laminate. The resulting primary laminate is illustrated in FIG. 6.