Package having aluminum laminate side wall shield

A package for heating food has a cover for covering a tray and provides an aluminum laminate for covering the tray side wall. The cover is configured to extend over the top opening or over the base of the tray and cover the tray side wall. In one embodiment, only side edge portions of the cover are formed of an aluminum laminate. In another embodiment, the entirety of the cover is formed of an aluminum laminate, in which case, the cover has lines of weakening positioned therein for tearing and removing a central portion of the cover.

BACKGROUND OF THE INVENTION 
This invention relates to a food package for controlled heating or cooking 
of food in hot air, convection, household and microwave ovens. 
The rapid increase of microwave oven sales to private households and the 
development of catering have changed the conditions for the prepared food 
manufacturers, implying great advantages as well as problems. The 
advantages are evident and connected with the rapid heating in microwaves 
which makes frozen prepared food even more convenient. There are two main 
problems: 
The traditional metallic tray is opaque to microwave radiation and is not 
suitable in microwave ovens, as arcing may occur inside the oven cavity 
resulting in a very bad perception of this package by the consumer. Since 
metals are not transparent to microwaves and heating is obtained only from 
the top, when compared to heating in a plastic container, cooking is not 
only longer but also uneven, especially with frozen products in which the 
bottom layer is still frozen while the top layer is overcooked and 
unacceptable (dry or burnt). 
Plastic trays are transparent to microwave radiation but owing to the 
limited penetration of microwaves and to the different absorptions of 
microwaves by the components of the products, e.g., water and ice, the 
cooking of frozen products is uneven. Hot spots appear in the corners and 
along the walls of the tray while the center is still frozen. 
Development work in the package industry in relation to microwave cooking 
has dealt with the problem of selective cooking of multi-component meals 
in which the individual food components generally require different 
quantities of microwave energy exposure. 
For example, U.S. Pat. No. 3,865,301 describes a shielded container for a 
plurality of ingredients of a sandwich-type food product that are to be 
heated or cooked to a different extent and which is opaque to microwave 
radiation except for radiation-transparent windows. 
U.S. Pat. No. 4,081,646 illustrates a tray of a material transparent to 
microwave energy with a plurality of compartments, a cover formed of a 
material that is transparent to microwave radiation and adapted to the 
tray and a shielding box having walls opaque to microwave energy and 
bearing apertures at predetermined locations for inserting the tray with 
the cover therein, in order to control the amount of radiation received by 
each of the individual components of a meal. 
In the prior developments, very little attention has been paid to uneven 
cooking of a prepared dish within a single compartment or tray in a 
microwave oven. In U.S. Pat. No. 4,351,997, there is described a new 
design for a dual ovenable tray to avoid this uneven cooking in microwave 
ovens. This design is related to a tray including a bottom wall and a 
peripheral wall ending with a horizontally extending rim. The rim is 
coated partly or totally with a material reflecting or opaque to microwave 
radiation, such as an aluminum foil. This provides a package in a tray 
form which gives an excellent temperature distribution in microwave ovens, 
and it is possible to use the package in hot air, convection and household 
ovens at temperatures up to 250.degree. C. 
The present invention relates to technical and economical new solutions to 
achieve such a package. 
SUMMARY OF THE INVENTION 
The present invention provides a food package formed from high temperature 
resistant materials wherein the side wall is shielded with an aluminum 
laminate which reflects microwave radiation. 
DESCRIPTION OF PREFERRED EMBODIMENTS 
The high temperature resistant package of the present invention includes a 
tray and is conveniently made of a cardboard or paperboard or of a plastic 
material with good thermal resistance, e.g., crystalline polyethylene 
terephthalate (CPET), polyether sulfone, polyether imide, 
polymethylpentene, or suitable combinations of such materials. The package 
may be polygonal and may have, for example, from 3 to 10 sides. 
Preferably, the corners have angles rather than curves. The package may be 
locked by a conventional plastics cap or a cardboard cap. 
The aluminum laminate shield may be a simple laminate with a layer of 
aluminum foil coated onto the inside or the outside of a layer of plastics 
or cardboard material, i.e., an aluminum-plastics laminate or an 
aluminum-cardboard laminate, or it may be a complex laminate having at 
least one layer of aluminum foil and plastics, cardboard or paperboard. 
The shield may act as an insulating label so that consumers can handle the 
tray after heating without burning their fingers. 
The aluminum foil may have a thickness of from 4 to 80 .mu.m and preferably 
from 5 to 15 .mu.m. 
In a first embodiment of the invention, there is provided a microwave 
transparent high temperature resistant tray suitable for holding a food 
product and an aluminum laminate shield providing a tray-top cover having 
a depending side edge adapted to be secured to the side wall of the tray 
and provided with lines of weakening capable of being torn by hand to 
enable removal of the top portion of the cover by the consumer just before 
heating. 
In one alternative of the first embodiment, the tray is advantageously made 
of a conventional plastics material, such as CPET, and the depending side 
edge of the cover may advantageously be secured to the side wall of the 
tray by an adhesive, or by suitable seals. The tray is preferably provided 
with a peelable CPET film lid or any other system for easy opening. The 
lid could also be a simple heat-sealable film. In both cases, it is 
preferably pilfer-proof. 
A second embodiment of the present invention is to achieve the shielding 
with a cardboard or plastics cover with depending side edge portions 
formed from a partially laminated blank wherein the blank is laminated 
with an aluminum foil along a major or total part of side edge portions of 
the blank which provide for, as defined by fold lines, the depending side 
edge portions about a central portion which is not laminated with an 
aluminum foil. A suitable design permits a complete shield of the side 
wall of the tray after folding the blank side edge portions along the fold 
lines. The advantages of this alternative is that the consumer does not 
have to remove the top portion of the cover since it is not shielded with 
aluminum. 
In a third embodiment of the present invention, a cover as described in the 
first or second embodiments above is employed which preferably covers only 
the base and side wall of a tray. The tray is advantageously provided with 
a peelable plastics film lid, or a plastic or cardboard lid, and a plastic 
over-cover. The tray is advantageously made of a conventional plastics 
material such as CPET. Preferably, the cover is secured to the side wall 
of the tray by means of an adhesive or suitable seals by using glue, or by 
sealing or by mechanical locking, the latter of which enables easy removal 
of the shield should it be desired to recycle the tray. In the embodiment 
wherein the shield cover is provided with lines of weakening capable of 
being torn by hand, removal of the shield portion adjacent the tray base 
by the consumer just before heating is enabled. 
This alternative is advantageous because it enables: 
a) the use of a standard cardboard/aluminum laminate, and 
b) the use of existing machinery to deposit the shield onto the tray. Such 
machinery is currently used to produce packages for margarine and butter. 
In a fourth embodiment of the invention, there is provided a high 
temperature resistant cardboard or paperboard tray formed from a blank 
having a major portion of side edge portions laminated with an aluminum 
foil for forming a tray having an aluminum laminated sidewall. 
The tray may be made of a conventional high temperature resistant cardboard 
or paperboard and is usually laminated with a plastics material such as 
polyester or other temperature resistant polymers. The plastics material 
may also be applied by extrusion coating. 
The aluminum foil may be positioned on the outside of the tray, but it is 
preferably positioned on the inside. The tray may be formed from a blank 
having corner flaps which are folded to form the walls and glued. 
The food packages of the present invention are very cheap and convenient 
because they may be formed by a simple adaptation of conventional 
containers commercially available at the present time. The different 
designs allow a shield very close to the product and this is very 
important. 
The present invention is illustrated further by way of example with 
reference to the accompanying drawings.

DETAILED DESCRIPTION OF THE DRAWINGS 
Referring to FIGS. 1 to 4 of the drawings, which illustrate a first 
embodiment of the present invention, the package comprises a high 
temperature resistant CPET tray 10 having a peelable film lid 11, the tray 
being defined by a base, and a sidewall which extends from the base to a 
top edge which defines a tray opening. The package is provided with an 
aluminum laminate tray-top cover 12 with depending side edge portions 13 
and with precut lines of weakening 14, 15 to enable the top central 
portion of the cover to be removed by tearing off. The cover is formed 
from a blank, as illustrated in FIG. 3, in which fold lines 17 are 
provided to conform the blank after folding to the shape of the tray. The 
depending cover side edge portions 13 are glued or sealed to the tray side 
wall 16. 
The top of the laminate cover 12 may be sealed together with the lid 11 and 
tray side wall top edge flange 18 (FIG. 4) of the package. 
FIG. 5 illustrates a blank for an alternative cover having two side edge 
portions 19 of aluminum laminate containing fold lines 20 and 21 and 
having two side edge portions 22 without aluminum foil containing fold 
lines 23 to conform the blank after folding to the shape of a tray. The 
central portion 24 of the blank adjacent fold lines 20 and 23 is a 
cardboard laminate without aluminum foil. After folding, edge portions 19 
and 22 will be glued or sealed to a tray side wall, such as tray side wall 
16 of FIG. 4. 
FIG. 6 shows a package comprising a high temperature resistant CPET tray 25 
having side wall 26, a peelable lid 27 and a plastic over-cover 28. A 
cardboard cover blank 29, having side edge portions 30 laminated by a 
coating of aluminum foil, is provided for being wrapped around the base 
and side wall of the tray so that the aluminum laminate side edge portions 
30 form a shield around the total part of the tray side wall. 
FIG. 7 illustrates a further partially laminated cardboard shield blank 
design which has two side edge portions 29 without aluminum foil and two 
side edge portions 30 of aluminum laminate. Fold lines 31, 32, 33 and 34 
provide for folding the blank. The central cover portion 35 is a cardboard 
laminate without aluminum foil. 
FIG. 8 shows a blank 36 made of ovenable cardboard material scored with 
fold lines so that when folded, a base is formed from blank central 
portion 37 and a side wall is formed from blank side edge portions 38, 39, 
40, 41, which are provided with rims 42, 43, 44, 45, respectively, to seal 
a cardboard cover (not shown). Corner flaps 46, 47, 48, 49 are provided 
with fold lines to ensure that when the blank has been folded, the side 
walls are held together. 
The blank side edge portions 40, 41 and the corner flaps 46, 47, 48 and 49 
are coated with aluminum foil as shown by the shading. The advantage of 
this embodiment is that the product may be packed in the carton directly 
without the necessity of any overpackage. 
FIG. 9 illustrates the design of a cardboard shield blank completely 
laminated with aluminum. The shield has four edge portions 50 and 51 of 
cardboard/aluminum aluminum laminate. Fold lines 52 and 53 provide for 
folding the blank. The central portion 54 is a card-board/aluminum 
laminate provided with precut lines 55 and a tab 56 in order to facilitate 
the removal of the central portion.