CONDITIONNEMENT A REGION D'AERATION

PACKAGING WITH A VENT REGION

Abrégé français

La présente invention concerne un conditionnement qui comprend un film polymère (1), des parties du film (1) étant scellées les unes aux autres pour former une enceinte pour aliments, lesdites parties scellées étant scellées par un scellage de film à film sauf dans une région d'aération (5) où une couche de vernis (6) est collée sur chaque partie de film avant que lesdites parties ne soient scellées les unes aux autres avec les couches de vernis adhérentes, la résistance au scellage de l'interface de vernis à vernis (6) étant similaire à celle de l'interface de film à film dans des conditions de stockage prédéterminées et la résistance au scellage de l'interface de vernis à vernis (6) étant réduite par rapport à celle de l'interface de film à film à des températures au-dessus de celles prévues dans lesdites conditions de stockage prédéterminées de sorte que l'enceinte soit aérée en contact avec l'atmosphère par une action de décollage cohésive dans la région d'aération (5) entre lesdites couches de vernis (6).

Abrégé anglais

Packaging comprises polymer film (1) with portions of the film (1) sealed
together to form an enclosure for the food stuff, said sealed portions being
sealed by a film-to-film seal except in a vent region (5) where a lacquer
layer (6) is bonded to each portion of film before said portions are sealed
together with the lacquer layers cohering, the seal strength of the lacquer-to-
lacquer interface (6) being similar to that of the film-to-film interface
under predetermined storage conditions, and the seal strength of said lacquer-
to-lacquer interface (6) being reduced compared with that of the film-to-film
interface at temperatures above those expected under said predetermined
storage conditions so that the enclosure is vented to atmosphere by a cohesive
peel action in the vent region (5) between said lacquer layers (6).

Revendications

CLAIMS
What is claimed is:
1. Packaging for food stuff intended to be heated comprising polymer film with
portions of
the film sealed together to form an enclosure for the food stuff,
characterized in that said
sealed portions are sealed by a film-to-film seal along a film-to-film
interface except in at
least one vent region where a lacquer layer is bonded to each portion of film
before said
portions are sealed together with the lacquer layers cohering at a lacquer-to-
lacquer
interface, the seal strength of the lacquer-to-lacquer interface being similar
to that of the
film-to-film interface under predetermined storage conditions, and the seal
strength of said
lacquer-to-lacquer interface being reduced compared with that of the film-to-
film interface
at temperatures above those expected under said predetermined storage
conditions so that
the enclosure is vented to atmosphere by a cohesive peel action in one or more
of the at least
one vent region between said lacquer layers.
2. Packaging as claimed in claim 1 in which said enclosure is formed by
sealing portions of
the film together along multiple seams with the at least one vent region
formed in one or
more seams.
3. Packaging as claimed in claim 2 in which said enclosure is formed by
sealing portions of
the film together along multiple seams with the at least one vent region
formed along the
whole of one seam, but not along the whole of the length of all seams.
4. Packaging as claimed in any one of claims 1 to 3 in which the lacquer
layers are applied
to the film by a gravure or flexo printing process.
5. Packaging as claimed in any one of claims 1 to 4 in which the film
comprises
polypropylene, polyethylene, polyester, polyamide, regenerated cellulose,
polylactic acid, or
combination of any of the preceding. 5

6. Packaging as claimed in claim 5 in which the lacquer layers comprise an EVA
based
resin.
7. Packaging as claimed in claim 6 in which the lacquer layers comprise a
combination of
solvents comprising alcohols, esters and hydrocarbons.
8. Packaging as claimed in any one of claims 1 to 5 in which the lacquer
layers comprise a
water-based EVA lacquer or an epoxy/acrylic solvent based lacquer.
9. Packaging as claimed in any one of claims 1 to 8 in which the film is
formed with
microperforations to support a modified atmosphere within the packaging when
it contains
respiring food stuff.
10. Film for the production of packaging of any one of claims 1 to 9 in which
at least one
region of the film adapted to be incorporated in a packaging seal between two
portions of
the film is coated with the lacquer layer.
6

Description

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PACKAGING WITH A VENT REGION
Technical Field
This invention relates to packaging of the type suitable for use with food
stuff to allow the
food stuff to be cooked, say in a microwave oven, with the packaging still in
place.
Packaging of this type must form a sealed enclosure to contain the food stuff
and prevent it
from becoming contaminated during storage. Also, for convenience, it must be
adapted to
allow venting of steam from the sealed enclosure as the food stuff is cooked,
without
having to first pierce the packaging. Various venting arrangements have been
provided for
microwave packaging including wax plugs, weakened seals and leak paths which
all vent at
increased tenlperatures and/or pressures.
An object of the present invention is to provide an improved packaging of the
aforesaid
type which is especially suitable for fresh foods.
Disclosure of the Invention
According to the invention, packaging comprises polymer film with portions of
the film
sealed together to form an enclosure for the food stuff, said sealed portions
being sealed by
a film-to-film seal except in a vent region where a lacquer layer is bonded to
each portion
of film before said portions are sealed together with the lacquer layers
cohering, the seal
strength of the lacquer-to-lacquer interface being similar to that of the film-
to-film interface
under predetermined storage conditions, and the seal strength of said lacquer-
to-lacquer
interface being reduced compared with that of the film-to-film interface at
temperatures
above those expected under said predetermined storage conditions so that the
enclosure is
vented to atmosphere by a cohesive peel action in the vent region between said
lacquer
layers.
Description of the Drawinjzs
The invention will be described by way of example with reference to the
accompanying
drawings in which:

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Figure 1 illustrates packaging according to the invention;
Figure 2 shows a section tlirough a vent seal of the packaging in Figure 1.
Mode of canying out the Invention
The illustrated microwave packaging coinprises a sheet 1 of Orientated
Polypropylene
(OPP) film which is folded on itself to bring together opposite edges which
are heat sealed
together along a back seal 2 to form a tube. The lower open end of the tubular
sheet is
closed by bringing together opposite portions of the lower edge and heat
sealing them
together to form a lower seal 3. The packaging is then filled with food stuff
and the open
upper end closed by bringing togetlier opposite portions of the upper edge and
heat sealing
them together to form an upper seal 4.
However, a portion 5 of the upper seal 4 incorporates a lacquer-to-lacquer
interface
between the two portions of the sheet 1 so as to form a peelable seal which
extends across
the full width W of the seal 4. The lacquer is a coating 6 adhering to the
inner face of each
of the opposite portions of the sheet 1, which may be applied by a gravure or
flexo printing
process in advance of the sheet being formed into the final enclosure
illustrated.
The lacquer coating 6 comprises a colourless, coloured or opaque coating made
up of resins
or cellulose derivatives and a plasticizer in a solvent. The resin comprises a
synthetic
polymeric compound physically resembling natural resin, such as polyvinyl,
polystyrene or
epoxy. A preferred example comprises a composition of EVA based resins and a
mixture
of solvents comprising ethyl acetate, isopropyl acetate and hydrocarbon such
as
non-aromatic naptha. Such a lacquer is available as "Sovereign Proxseal
J9683A"
comprising an EVA copolymer dispersed in a solvent mix of ethyl acetate and
aliphatic
hydrocarbon.
The properties of the seals, both those portions comprising OPP sheet sealed
face-to-face,
and those portions which incorporate the layer-to-lacquer interface, are
similar in strength
at ambient, chill and freezer temperatures such as apply when the packaging is
in use to
store food stuff. Also, high humidity conditions caused by the food stuff
within the
packaging does not adversely affect the strength of the seal under ambient,
chill and freezer

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conditions. High humidity conditions might comprise those up to 100% at 5-8 C,
but
typical humidity conditions comprise 85% or 95% at 5-8 C.
However, when the packaging is heated in a microwave oven to cook the food
stuff, the
strength of that portion of the seal 5 incorporating the lacquer coatings 6 is
significantly
reduced at the elevated temperatures that are generated up to 100 C or above,
the strength
being only - 30g/25mm. This reduced strength of the lacquer-to-lacquer seal is
such as to
allow cohesive peeling, and provides an open vent path between the two
portions of the
OPP sheet to allow pressurised steam and gases to escape from within the
packaging. In
contrast, the strength of the seal where the OPP sheet is sealed face-to-face
without the
intermediate lacquer coatings, remains strong enough to hold the seal closed.
Thus, venting
of the packaging is controlled to occur only in the lacquer coated region 5 of
the upper seal
4. Typically, the seal strength of the lacquer-to-lacquer is reduced
significantly at
temperatures of 60 C and above.
The size of the lacquered vent region 5 is selected to give an appropriated
vent
cross-section. If required the vent region 5 could extend the full length of
the seal 4.
Alternatively, the position of the lacquered region 5 can be varied to suit
the particular
application and it may be located in one or more of the other seals 2 and 3.
Alternatively,
multiple vent regions 5 may be provided in one or more of the seams 2, 3, 4.
In alternative embodiments of the invention, the film may comprise any one of
the
following: polypropylene, polyethylene, polyester, polyamide, regenerated
cellulose,
polylactic acid, or combination of any of the preceding. The film may also
comprise films
with a heat seal coating.
The film may be adapted for modified atmosphere packaging by forming
microperforations
in it which are small enough to control the oxygen/ carbon dioxide gas
atmosphere within
the bag. The food stuff will have a respiration rate which is matched to the
natural
permeability of the film and the additional permeability of the
microperforations so as to
produce the required modified atmosphere within the packaging. However, the
total area

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of the microperforations would be too small to have any significant effect on
the water
vapour permeability of the film or the need to provide a separate vent.
Also, in alternative embodiments of the invention, the lacquer may comprise a
water-based
EVA lacquer or an epoxy/ acrylic solvent based lacquer.

Dessin représentatif