Note: Descriptions are shown in the official language in which they were submitted.
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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
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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
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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
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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
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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
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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
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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.
