Composite film

Abstract

Composite film (1) for closing a container (10) by sealing the composite film (1) against a circumferential sealing surface (11) of the container (10) or of a cap ring (12) to be connected to the container (10). The composite film (1) comprises an outer support layer (30) made of a metal film and an inner multilayer membrane (20) laminated to the outer support layer (30) using a bonding layer (28). The membrane (20) has a consecutive layer structure from the outside to the inside consisting of a backbone layer (21) made of polypropylene, an intermediate layer (23) made of a partially crystalline polyamide and a cohesively breakable peeling layer (25) made of polypropylene, polyethylene and talc, wherein between the intermediate layer (23) and the backbone layer (21) as well as between the intermediate layer (23) and the peeling layer (25) there is arranged a tie layer (22, 24) made of a maleic acid anhydride grafted polypropylene. The membrane has further an innermost sealing layer (26) made of a random copolymer comprising monomers of propylene, ethylene and butylene, wherein the random copolymer is grafted with maleic acid anhydride. The softening point of the sealing layer (26) lies at least between 15 and 25° C. lower than that of the tie layers (22, 24). A use and a method of producing said composite film (1) are also disclosed.

Claims

1. A composite film for closing a container by sealing the composite film against a sealing surface of the container or of a cap ring to be connected to the container, the composite film comprising: an outer support layer comprising a metal film, an inner multilayer membrane, and an intermediate tie layer bonding the outer support layer to the inner multilayer membrane, wherein the inner multilayer membrane comprises an intermediate layer comprising a hygroscopic polyamide encapsulated by two tie layers each comprising a maleic anhydride grafted polypropylene, and wherein the inner multilayer membrane further comprises a backbone layer comprising polypropylene, and wherein the inner multilayer membrane further comprises a cohesively breakable peeling layer comprising polypropylene, polyethylene and talc and an innermost sealing layer comprising a random copolymer grafted with maleic anhydride, the tie layer is located between the backbone layer and the intermediate layer, and the tie layer is located between the intermediate layer and the cohesively breakable peeling layer.

2. The composite film according to claim 1, wherein the random copolymer grafted with maleic anhydride of the innermost sealing layer comprises monomers of propylene, ethylene and butylene, and wherein the ethylene and butylene content together is less than 10 percent weight of the copolymer.

3. The composite film according to claim 1, wherein the content of talc in the cohesively breakable peeling layer is between 5 and 49 weight percent.

4. The composite film according to claim 1, wherein the hygroscopic polyamide is a partially crystalline polyamide.

5. The composite film according to claim 4, wherein the partially crystalline polyamide is a polyamide 6.6 or polyamide 66,6.

6. The composite film accordingly to claim 1, wherein the maleic anhydride grafted polypropylene of each of the tie layers is a homopolymeric polypropylene.

7. The composite film according to claim 1, wherein the intermediate tie layer comprises a maleic anhydride grafted polypropylene.

8. The composite film according to claim 1, wherein the intermediate tie layer comprises an adhesive.

9. The composite film according to claim 1, wherein the metal film of the outer support layer is an aluminum film having a thickness of 20 to 160 micron.

10. The composite film according to claim 1, wherein the thickness of the backbone layer is from 8 to 12 micron.

11. The composite film according to claim 1, wherein the thickness of the intermediate layer is from 8 to 12 micron.

12. The composite film according to claim 1, wherein the thickness of each tie layer is from 3.5 to 4.5 micron.

13. A composite film for closing a container by sealing the composite film against a sealing surface of the container or of a cap ring to be connected to the container, the composite film comprising: an outer support layer comprising a metal film, an inner multilayer membrane, and an intermediate tie layer bonding the outer support layer to the inner multilayer membrane, characterized in that the inner multilayer membrane comprises: a backbone layer comprising polypropylene, an intermediate layer comprising partially crystalline polyamide, a cohesively breakable peeling layer comprising polypropylene, polyethylene and talc, an innermost sealing layer comprising a random copolymer grafted with maleic anhydride, a tie layer comprising a maleic anhydride grafted polypropylene, the tie layer located between the backbone layer and the intermediate layer, and a tie layer comprising a maleic anhydride grafted polypropylene, the tie layer located between the intermediate layer and the cohesively breakable peeling layer.

14. The composite film according to claim 13, wherein the partially crystalline polyamide is polyamide 6,6 or polyamide 66,6.

15. The composite film according to claim 1, wherein the maleic anhydride grafted polypropylene of each of the tie layers is a homopolymeric polypropylene.

16. The composite film according to claim 1, wherein the metal film is an aluminum film having a thickness of 20 to 160 micron.

Description

(1) The encapsulated intermediate layer is improving the corrosion resistance of the other layers of the composite film, especially against migration of components from acidic and greasy products packaged in the container.

(2) FIG. 1: shows schematically a structure of a composite film according to the present invention;

(3) FIG. 2 shows schematically a section through a cap ring and an opening area of a container with a composite film sealed onto the cap ring;

(4) FIG. 3 shows schematically a section through the opening area of a container having an inside bent flange and a composite film sealed onto the outside of said flange.

(5) The composite film 1 shown in FIG. 1 has the following structure: 30 Outer support layer made of a metal film 28 Intermediate tie layer 21 Inner multilayer membrane, comprising the following layers: 21 Backbone layer made of polypropylene 22 Tie layer made of MAH-PP 23 Intermediate layer made of partially crystalline PA 24 Tie layer made of MAH-PP 25 Cohesively breakable peeling layer made of PP, PE and talc 26 Innermost sealing layer made of a random copolymer grafted with MAH

(6) The sealable and peelable composite film 1 mainly consists of a support layer 30 made of a metal film (top layer shown in FIG. 1) and a multilayer membrane 20 laminated to the metal film using a bonding layer 28. The inner multilayer membrane 20 has a structure of sequently arranged and coextruded layers 21, 22, 23, 24, 25, 26, wherein the innermost layer, i.e. sealing layer 26 (bottom layer shown in FIG. 1), is directed to a rim having a sealing surface 11 of a container 10 or to a cap ring 12 to be connected to a container 10 when the composite film 1 is used as closure of a container. The backbone layer 21 is directed to the outer support layer 30 of the composite film 1.

(7) The inner multilayer membrane 20 may be extrusion laminated on the outer support layer 30, wherein the bonding layer is continuously provided between the outer backbone layer 21 and the extruded multilayer membrane film 20. On the other side, the multilayer membrane 20 may be laminated to the support layer 30 in a separate process step using e.g. an adhesive.

(8) The intermediate layer 23 of the inner multilayer membrane 20 is encapsulated by the two tie layers 22, 24 on each side—the top and the bottom of said intermediate layer 23. This encapsulation protects the intermediate layer 23 made of hygroscopic polyamide against moisture from the inside of the container 10 when the composite film is used as container closure as well as from the outside. The amount of moisture coming from the inside of the container 10 depends on the container content, especially on the kind of food packed within the container 10.

(9) The top side of the cohesively breakable peeling layer 25 is next to the bottom side of the encapsulated intermediate layer 23 joined by the tie and moisture barrier layer 24. Next to the bottom of the cohesively breakable peeling layer 25 the multilayer membrane 20 exhibits the innermost sealing layer 26.

(10) In FIG. 2 a cap ring 12 with a beaded edge 13 for beading onto the opening edge of the container 10 is shown. The cap ring 12 has a ring-shaped, circumferential sealing surface 11, protruding horizontally inwards from the beaded edge 13. In case the sealing surface is made of a metal, it is preferably a polished surface.

(11) The composite film 1, provided with a pull tab 14, is sealed onto the sealing surface 11. When peeling the composite film 1, the peeling layer 25 breaks cohesively and a part of the peeling layer 25 may stick on the container rim or the cap ring and serves as a “footprint” on the sealing surface 11.

(12) In FIG. 3, the sealing surface 11 is an integral part of the container 10. The sealing flange providing the sealing surface 11 is formed as an inwardly bent rim of a container sleeve, i.e. the sealing flange having the sealing surface 11 is designed as a horizontally inwards running ring flange. In case the sealing surface is made of a metal, the sealing surface 11 is preferably a polished metal surface. As described above for the cap ring 12, after peeling the composite film 1 from the container 10 the peeling layer 25 or at least a part thereof may stick on the container rim and serve as a “footprint” on the sealing surface 11.

(13) Test Results:

(14) An inventive composite film has been used to close a container made of tinplate wherein the packaged good was acid having a pH of 2. The resulting shelf life, i.e. the storing time without showing any disturbance of the lid made of the composite film was more than one year.

(15) An inventive composite film has been used to close a container made of tinplate wherein the packaged good was acid having a pH of 3. The resulting shelf life, i.e. the storing time without showing any disturbance of the lid made of the composite film was more than two years.

(16) Furthermore, compared to the composite film described in EP 2 678 154 B1 the waste quote has been improved by 95%.