Composite film

Abstract

A composite film for closing a container by sealing the composite film against a circumferential sealing surface of the container or of a cap ring to be connected to the container has a support layer made of a metal film and a sealing layer connected to the metal film. The sealing layer comprises a coextruded layer with a cohesively breaking intermediate layer and adhesion promoter layers arranged on both sides of the intermediate layer. The composite film is suitable for tight sealing against sealing surfaces made of polished tinplate.

Claims

1. A method for closing a container, comprising sealing a composite film against a circumferential sealing surface of the container or of a cap ring to be connected to the container, wherein the sealing surface consists of polished tinplate, polished aluminum, or a heat-sealable, modified, metal surface, wherein the composite film has a support layer made of a metal film and a sealing layer, wherein the sealing layer comprises a coextruded layer with a cohesively breaking intermediate layer and adhesion promoter layers arranged on both sides of the intermediate layer, and wherein the adhesion promoter layers are made of a polypropylene modified with maleic acid anhydride (PP-MAH) and a thermoplastic plastic containing more than 50 wt. % polypropylene (PP) is used as the intermediate layer.

2. The method of claim 1, wherein a closing membrane made of the composite film, peelable from the sealing surface, is sealed onto the sealing surface.

3. The method of claim 1, wherein the metal film has a thickness of 20 μm to 160 μm, at least one of the adhesion promoter layers has a thickness of 1 μm to 10 μm, and the cohesively breaking intermediate layer has a thickness of 5 μm to 60 μm.

4. The method of claim 1, wherein the cohesively breaking intermediate layer contains talc as an additive.

5. The method of claim 4, wherein the talc content is 5 wt. % to 49 wt. % of the cohesively breaking intermediate layer.

6. The method of claim 1, wherein the cohesively breaking intermediate layer contains 5 wt. % to 35 wt. % of polyethylene (PE).

7. The method of claim 1, wherein the sealing surface consists of polished tinplate which is provided with a chromium application of 1 mg/m.sup.2 to 3 mg/m.sup.2 by a dip passivation, with a chromium application of 3.5 mg/m.sup.2to 9 mg/m.sup.2 by a cathodic passivation or with a chromium application of 5 mg/m.sup.2 to 9 mg/m.sup.2 by an electrochemical passivation.

8. The method of claim 1, wherein the metal film is an aluminum film.

9. The method of claim 1, wherein the metal film has a thickness of 50 μm to 100 μm.

10. The method of claim 4, wherein the talc content is 10 wt. % to 30 wt. % of the cohesively breaking intermediate layer.

11. The method of claim 1, wherein the cohesively breaking intermediate layer is comprised of polypropylene, talc and low density polyethylene.

12. The method of claim 1, wherein the sealing surface consists of polished tinplate.

13. The method of claim 1, wherein the sealing surface consists of polished aluminum.

14. The method of claim 1, wherein the sealing surface consists of a heat-sealable, modified, metal surface.

Description

(1) Further advantages, features and details of the present invention arise from the description below of preferred exemplary embodiments as well as on the basis of the drawing, in which

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

(3) FIG. 2 schematically shows a section through the cap ring with closing membrane;

(4) FIG. 3 schematically shows a section through the opening area of a container with a closing membrane sealed on the outside of the container;

(5) FIG. 4 schematically shows a section through the opening area of a container with a closing membrane sealed on the inside of the container.

(6) A composite film 10 shown in FIG. 1 has the following structure:

(7) TABLE-US-00001 12 Protective coating 14 Aluminum film 16 Adhesion promoter made of PP-MAH 18 Intermediate layer made of PP/PE with 5 wt. % to 49 wt. % talc 20 Adhesion promoter made of PP-MAH

(8) On a container closed with composite film 10, the protective coating 12 is directed at the container outside, and intermediate layer 18 with the adhesion promoter 20 is directed at the container inside.

(9) A cap ring 30 made of tinplate with a beaded edge 32 for beading onto the opening edge of a container 40 shown in FIG. 2 has a ring-shaped, circumferential sealing surface 34, protruding horizontally inwards from the beaded edge 32. The sealing surface 34 is uncoated, i.e., the sealing surface 34 has a polished surface, like the remaining cap ring.

(10) A closing membrane 36 punched out of the composite film 10, provided with a pull tab 38, is sealed onto the sealing surface 34. When peeling the closing membrane 36, the intermediate layer 18 breaks cohesively and a part of the intermediate layer 18 remains behind as a “footprint” on the sealing surface 34.

(11) In FIG. 3, the sealing surface 34 is an integral part of the container 40 made of tinplate. The sealing surface 34 is formed here directly from the container 40 and is designed as a horizontally inwards directed ring flange. The outside of the container 40 and thus also the sealing surface 34 is uncoated, i.e., the sealing surface 34 has a polished tinplate surface. As described above for the cap ring 30, the intermediate layer 18 also remains behind here on the sealing surface 34 when opening by means of peeling as a consequence of the cohesive break as a “footprint” on the sealing surface 34.

(12) In FIG. 4, the sealing surface 34 is an integral part of the container 40 made of tinplate. The sealing surface 34 is formed here directly from the container 40 and is designed as a horizontally inwards directed ring flange. The inside of the container 40 and thus also the sealing surface 34 is uncoated, i.e., the sealing surface 34 has a polished tinplate surface. As described above for the cap ring 30, the intermediate layer 18 also remains behind here on the sealing surface 34 when opening by means of peeling as a consequence of the cohesive break as a “footprint” on the sealing surface 34.

(13) When detaching the closing membrane 36 sealed against the sealing surface 34 by pulling on the pull tab 38, the material separation takes place in the interior of the intermediate layer 18. After the complete removal of the closing membrane 36 for the first-time opening of the container 40, a part of the intermediate layer 18 remains behind as a uniform coating on the sealing surface 34. This coating or footprint is used as proof that can be recognized simply and without further aid of an original packaging with tamper-proof seal.

TEST EXAMPLES

(14) Tests on adhesive strength on tinplate with polished and coated surface and on peelability were carried out on composite films with the following layer structures. A. 1.5 μm protective coating 60 μm aluminum film EN AW-8021/AlFe1.5 soft-annealed 4.5 μm PP-MAH 11 μm PP with 40% talc+LDPE 1.5 μm PP-MAH B. 1.5 μm protective coating 90 μm aluminum film EN AW-8021/AlFeSi (A) soft-annealed 4.5 μm PP-MAH 11 μm PP with 40% talc+LDPE 1.5 μm PP-MAH C. 1.5 μm protective coating 60 μm aluminum film EN AW-8021/AlFe1.5 soft-annealed 1.5 μm PP-MAH 11 μm PP with 40% talc+LDPE 4.5 μm PP-MAH D. 1.5 μm protective coating 90 μm aluminum film EN AW-8011 (A)/AlFeSi (A) 1.5 μm PP-MAH 11 μm PP with 40% talc+LDPE 4.5 μm PP-MAH E. 1.5 μm protective coating 60 μm aluminum film EN AW-8021/AlFe1.5 soft-annealed 4.0 μm PP-MAH 11 μm PP with 40% talc+LDPE 2.0 μm PP-MAH F. 1.5 μm protective coating 60 μm aluminum film EN AW-8021/AlFe1.5 soft-annealed 8.0 μm PP-MAH 11 μm PP with 40% talc+LDPE 4.0 μm PP-MAH

(15) The composite films were subjected to a peel test for determining the sealing seam strength. The composite films were sealed under comparable sealing conditions in the form of 15-mm-wide strips against a tinplate surface.

(16) The force needed to detach the strips from the plate support was determined as indicator of the sealing seam strength. The pull-off angle of the strips against the tinplate surface displaceable on a carriage was always 90°.

(17) All composite films with the structure according to the present invention showed comparable peel forces and sealing seam strengths in the peel tests with polished tinplate. The coating remaining behind as a footprint on the tinplate was white in all cases tested. Comparison tests with polished tinplate as a reference showed that comparable sealing seam strengths are obtained with polished tinplate.

(18) Peel tests with tinplates with different passivations showed no differences in sealing seam strength in the usual passivations according to the codes 300, 311 and 314. Also, the aging occurring during the passivations had no effect on the sealing seam strength, i.e., the composite film reacts neutrally to the aging of the tinplate.