CA2179840A1

CA2179840A1 - Composite strip of lids for peel-open thermoplastic receptacles

Info

Publication number: CA2179840A1
Application number: CA002179840A
Authority: CA
Inventors: Marianne Boehrer; Laurent Kretz
Original assignee: Alsacienne DAluminium
Current assignee: Amcor Flexibles Selestat SAS
Priority date: 1996-06-25
Filing date: 1996-06-25
Publication date: 1997-12-26

Abstract

The present invention relates to a composite strip for manufacturing lids for peel-open flat-rimmed thermoplastic receptacles of the type comprising an outer film of aluminum or equivalent material, an inner film of thermoplastic material suitable for adhering to the rim of the receptacle by heat-sealing, and an intermediate bonding layer disposed between the outer film and the inner film. The inner film has a score line in the location of each lid so as to form an opening when the outer layer is peeled off. The intermediate layer is non-uniform, including first zones constituted by a first substance that is sensitive to heat and that has high of affinity for the thermoplastic film under the effect of hot calendaring. The major portion of the intermediate layer is constituted by a substance that resists heat and that has medium affinity for the thermoplastic film, thereby making peeling possible.

Description

~:1798~0 The present invention relates to a composite strip for making lids for peel-open flat-rimmed thermoplastic receptacles, said strip being of the type comprising an outer film of aluminum or equivalent material, an inner film made of a thermoplastic material suitable for adhering to the rims of the receptacles on heat-sealing, and an intermediate bonding layer disposed between the outer film and the inner film;
the inner film being suitable, on heat-sealing, for adhering more strongly to the rims of thermoplastic receptacles than to the intermediate layer so as to make it possible subsequently, after the lid has been cut out and heat-sealed on a receptacle, to peel off the outer film of the lid by exerting traction on a grasping zone of the lid, and the inner film also including, in the location of each subsequently cut-out lid, a score line in the form of a closed curve suitable, during subsequent peeling-off of the outer film of the lid sealed on a receptacle, for making an opening defined by the score line in the thermoplastic film of said lid.

Such a strip is known, in particular from FR-A-2 503 036. It makes it possible to provide lids for receptacles that are heat formed, in particular on the site where they are filled, which strip enables an opening to be made through the thermoplastic film of the lid sealed on the receptacle by peeling away the outer film of the lid that is sealed to the rim of the receptacle. That disposition makes it possible to avoid scrap during manufacture of the lids.
In that document, provision is made for the intermediate layer to be constituted by a very thin f ilm of hot-melt wax or of lacquer applied over the entire surface of the inside face of the outer film. The thermoplastic film and the intermediate layer are caused to adhere by hot calendaring while the score lines are being made by melting.
The heat used for heat-sealing the lid to the rim of the receptacle also gives rise to adhesion that is difficult to control between the thermoplastic film and the intermediate layer in the zone of the heat-sealing fillet.
In addition, the temperatures used in lines for thermoforming and for filling receptacles are relatively high. The heat given off downstream from the heat-sealing station and the heat given off in the stations for sterilizing lids can activate the intermediate layer in zones other than the score lines and the heat-sealing fillets, and that can increase adhesion between the thermoplastic film and the intermediate layer in a manner that is difficult to control and that makes it more difficult subsequently to peel off the aluminum film of the lid.
In FR-A-2 585 986, the intermediate layer includes a material that adheres strongly inside the zone defined by the score lines, and the score lines are made leakproof by means of an additional thermoplastic film which adheres strongly over the entire bottom face of the inner film. That structure therefore requires a fourth layer.
The object of the present invention is to mitigate these drawbacks and to propose a composite strip of the above-mentioned type that enables peel-off lids to be made regardless of the temperature conditions implemented in packaging lines.
The invention achieves this object by the intermediate layer being non-uniform and including first zones constituted by a first substance that is heat-sensitive and that has a high degree of affinity for the thermoplastic film under the effect of hot calendaring, said first zones covering the subsequent openings in the thermoplastic film and projecting out therefrom a little 21798~

way beyond the score lines in order to ensure that the thermoplastic film is leakproof.
The remainder of the intermediate layer, outside the zones for grasping the subsequently cut-out lids, is constituted by a heat-resistant substance that has medium affinity for the thermoplastic film.
The zones of the intermediate layer facing the lid-grasping zones can be constituted by a substance that is anti-adhesive and heat-resistant or by the first substance. In which case, additional score lines are provided in the thermoplastic film in the vicinity of said grasping zones.
Adhesion between the first substance and the thermoplastic film is preferably greater than 5 N/15 mm.
Adhesion between the heat-resistant substance and the thermoplastic film is about 1 N/15 mm.
By means of this disposition, the thermoplastic film adheres strongly to the intermediate layer over the entire area of the orifices. On peeling, this keeps the torn-off thermoplastic pellet on the outer film of the lid.
In contrast, the adhesion between the intermediate layer and the thermoplastic film is uniform over the entire peel area and does not vary as a function of temperature conditions on packaging lines because the substance used facing the peel surface is a heat-resistant substance.
The invention also provides a method of manufacturing the proposed composite strip.
To manufacture such a strip, starting from a film of aluminum or of similar material, the non-uniform layer is continuously applied to the inside face thereof in a printing machine and the thermoplastic film is applied to the intermediate layer by lamination.
While the film of aluminium or equivalent material is passing through the printing machine, longitudinally spaced apart reference marks are advantageously printed 21798~0 as a function of the way the lids will subsequently be cut out, optionally together with decorative patterns on the outside face of said film of aluminum or equivalent material.

Other advantages and characteristics of the invention appear on reading the following description given by way of example and made with reference to the accompanying drawings, in which:
Figure 1 is a perspective view of a thermoplastic receptacle closed by a lid heat-sealed to the rim of the receptacle, said lid being taken from a composite strip of the invention;
Figure 2 is a perspective view of the Figure 1 receptacle while the lid is being peeled off;
Figures 3 and 4 are cross-section views through the lid sealed to the rim of the receptacle, before and during peeling, the sections being on line III-III of Figure l and on line IV-IV of Figure 2;
Figure 5 is a diagrammatic view of a line for manufacturing a composite strip of the invention; and Figure 6 shows how the substances making up the intermediate layer are disposed on leaving the printer, prior to being covered by the thermoplastic film, the lines along which the lids are subsequently cut out being shown dashed.

The drawings show a hollow receptacle 1 having a flat rim 2 generally obtained by thermoforming a strip of thermoplastic material, which receptacle is closed by heat-sealing a lid 4 along a heat-sealing fillet 3, the lid being taken from a composite strip.
The lid 4 has an outer film 5 of aluminum or equivalent material such as paper or plastics material, an inner film 6 made of a thermoplastic material suitable for adhering to the rim 2 of the receptacle 1 by heat-sealing, and an intermediate bonding layer disposed ~1798~0 between the outer film 5 and the inner film 6. Adhesion between the inner film 6 and the intermediate layer 7 is less strong than adhesion between the material constituting the rim 2 of the receptacle 1 and the inner film 6, thereby enabling the outer film 5 to be peeled off by exerting traction on a grasping zone 8 of the lid, e.g. a tab, situated outside the heat-sealing fillet 3.
In the opening of the receptacle 1, the inner film 6 has a score line 9 so that when the outer film 5 is peeled off, an opening 10 is made through the inner film 6, with the pellet 11 corresponding to the opening 10 remaining attached to the outer film 5, as can clearly be seen in Figure 2.
In the present invention, the intermediate layer 7 is non-uniform. It comprises at least three zones:
a first zone 20 situated facing the pellet 11;
a second zone 21 situated in the region of the tab 8; and a third zone 22 covering the remainder of the surface of the outer film 5.
The first zone 20 is constituted by a first substance that is sensitive to heat and that has a high degree of affinity for the thermoplastic film 6 under the effect of hot calendaring. The first zone 20 extends outwardly slightly beyond the score line 9 so as to ensure that the lid 4 is leakproof when sealed by heat-sealing to the rim 2 of the receptacle 1. Adhesion between the first substance and the thermoplastic film 6 is greater than 5 N/15 mm.
The second zone 21 is constituted by a substance that is anti-adhesive and heat-resistant so that in said second zone 21 the outer film 5 is not bonded to the thermoplastic film 6. This second zone 21 lies outside the heat-sealing fillet. This second zone 21 may also be constituted by a substance that provides adhesion between the outer film 5 and the inner film 6. Under such circumstances, an additional score line 25 is formed '~179~4~1 outside the heat-sealing fillet 3 in order to form the tab 8.
The third zone 22 is constituted by a substance of the varnish type having medium peel-ability and that resists heat, in order to obtain peel-ability of about 1 N/15 mm.
The substances constituting the zones 20, 21, and 22 are coated onto the bottom face of the outer film 5.
The lid 4 is made by cutting up a composite strip 30.
To make the composite strip 30, the starting material is a roll 31 of a film 5 of aluminum or equivalent material that is passed continuously through a printer 32 for the purpose of coating the various zones of the bottom face 33 of the film 5 with the different substances making up the intermediate layer 7.
In one of the stations of the printer 32, marks 34 are printed which are distributed uniformly along the entire length of the film 5 as a function of where the lids 4 will subsequently be cut out.
The zones 20, 21, and 22 of the intermediate layer 7 are applied accurately relative to the marks 34.
Decorative patterns may advantageously be printed on the top face of the film 5 as it passes through the printer 32.
The thermoplastic film 6 is applied by being laminated onto the intermediate layer 7 at the outlet from the printer 32. The temperature of the material constituting the thermoplastic film 6 during lamination ensures adhesion between the thermoplastic film 6 and the first substance constituting the first zones 20.
The score lines 9 are made by melting the thermoplastic film. The composite strip 30 passes between cylinders 40 and 41. The upper cylinder 40 is smooth and in contact with the outer film 5 and serves as backing for the composite strip 30. The lower cylinder 41 bears against the bottom face of the thermoplastic film 6 and it has projecting ribs 42 on its periphery for making the score lines 9.
The material constituting the thermoplastic film 6 comes from an extruder 44. This material depends on the structure of the thermoplastic receptacle 1.
For receptacles 1 made of low density polyethylene, the film 6 is a polyethylene polyolefin, and the substance covering the first zones 20 is either a heat-sealing varnish or Suryln 1652 from Dupont de Nemours.
For polystyrene receptacles, the film 6 is a polyolefin, e.g. polyethylene, and the adhesion promoter applied to the first zones 20 may be a grafted copolymer of ethylene and vinyl acetate (EVA), a grafted copolymer of ethylene and butyl acrylate (EBA), or a grafted copolymer of ethylene and methyl acrylate (EMA), with the grafting substance being an unsaturated monomer including at least one carboxylic acid group.
For polypropylene receptacles, the film 6 is also made of polypropylene and the adhesion promoter covering the first zones 20 may be constituted by a grafted polypropylene.
For receptacles made of polyethylene terephthalate (PET), the film 6 is also made of PET, and the adhesion promoter is a PET-based primary.

Claims

1/ A composite strip for making lids for peel-open flat-rimmed thermoplastic receptacles, said strip being of the type comprising:
an outer film of aluminum or equivalent material;
an inner film made of a thermoplastic material suitable for adhering to the rims of the receptacles on heat-sealing; and an intermediate bonding layer disposed between the outer film and the inner film;
the inner film being suitable, on heat-sealing, for adhering more strongly to the rims of thermoplastic receptacles than to the intermediate layer so as to make it possible subsequently, after the lid has been cut out and heat-sealed on a receptacle, to peel off the outer film of the lid by exerting traction on a grasping zone of the lid, and the inner film also including, in the location of each subsequently cut-out lid, a score line in the form of a closed curve suitable, during subsequent peeling-off of the outer film of the lid sealed on a receptacle, for making an opening defined by the score line in the thermoplastic film of said lid;
wherein the intermediate layer is non-uniform and includes first zones constituted by a first substance that is heat-sensitive and that has a high degree of affinity for the thermoplastic film under the effect of hot calendaring, said first zones covering the subsequent openings in the thermoplastic film and projecting out therefrom a little way beyond the score lines in order to ensure that the thermoplastic film is leakproof.

2/ A strip according to claim 1, wherein adhesion between the first substance and the thermoplastic film is greater than 5 N/15 mm.

3/ A strip according to claim 1, wherein the intermediate layer includes second zones constituted by a second substance that is anti-adhesive and heat-resistant, said second zones being provided in the grasping zones of the subsequently cut-out lids.

4/ A strip according to claim 3, wherein the intermediate layer, outside the first and second zones, is constituted by a third substance that is heat-resistant and that has medium affinity for the thermoplastic film, in order to make peeling possible.

5/ A strip according to claim 1, wherein the intermediate layer, outside the first zones and the grasping zones of the subsequently cut-out lids, is constituted by a third substance that is heat-resistant and that has medium affinity for the thermoplastic film, in order to make peeling possible.

6/ A strip according to claim 5, wherein the intermediate layer facing the grasping zones of the subsequently cut-out lids includes second zones constituted by said first substance, score lines being formed in the thermoplastic film in the vicinity of said second zones.

7/ A strip according to claim 4, wherein adhesion between the third substance and the thermoplastic film is about 1 N/15 mm.

8/ A strip according to claim 1, wherein the outer film includes, on at least one of its faces, marks that are longitudinally spaced apart as a function of where the lids are subsequently cut out.

9/ A method of manufacturing a composite strip according to claim 1, wherein the non-uniform intermediate layer is applied continuously on the inside face of the film of aluminum or equivalent material by means of a printing machine, and wherein the thermoplastic film is applied to the intermediate layer by lamination.

10/ A method according to claim 9, wherein marks are printed on at least one of the faces of the film of aluminum or equivalent material, which marks are longitudinally distributed as a function of where the lids are subsequently cut out.

11/ A method according to claim 9, wherein decorative patterns are printed on the outer face of the film of aluminum or equivalent material.