U.S. patent number 3,865,301 [Application Number 05/415,962] was granted by the patent office on 1975-02-11 for partially shielded food package for dielectric heating.
This patent grant is currently assigned to Trans World Services, Inc.. Invention is credited to Thomas E. Ford, Robert G. Pothier.
United States Patent |
3,865,301 |
Pothier , et al. |
February 11, 1975 |
PARTIALLY SHIELDED FOOD PACKAGE FOR DIELECTRIC HEATING
Abstract
A food package comprising a container of dielectric sheet
material and a conductive sheet thereon. The conductive sheet is of
smaller area than the dielectric sheet and is shaped and oriented
in relation to the package wall configuration to expose a plurality
of food articles therein differentially to microwave radiation.
Inventors: |
Pothier; Robert G. (Amherst,
NH), Ford; Thomas E. (Arlington, MA) |
Assignee: |
Trans World Services, Inc.
(Melrose, MA)
|
Family
ID: |
23647949 |
Appl.
No.: |
05/415,962 |
Filed: |
November 15, 1973 |
Current U.S.
Class: |
229/5.82;
426/107; 99/DIG.14; 229/903; 219/729 |
Current CPC
Class: |
B65D
5/6626 (20130101); B65D 81/3453 (20130101); B65D
2581/3416 (20130101); B65D 2581/3466 (20130101); Y10S
229/903 (20130101); Y10S 99/14 (20130101); B65D
2581/3406 (20130101); B65D 2581/3472 (20130101); B65D
2581/3489 (20130101); B65D 2581/3479 (20130101); B65D
2581/3464 (20130101) |
Current International
Class: |
B65D
5/66 (20060101); B65D 5/64 (20060101); B65D
81/34 (20060101); B65d 005/40 (); B65d 005/56 ();
B65d 025/14 () |
Field of
Search: |
;229/14R,14C,14H,14BW
;426/107,234 ;99/646,DIG.14 ;219/387,438-440,521 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Christian; Leonard D.
Attorney, Agent or Firm: Kenway & Jenney
Claims
We claim:
1. A food package comprising, in combination, a dielectric sheet
and a conductive sheet thereon, said dielectric sheet having a
plurality of panels and forming when set up a substantially closed
container having a first wall and second and third walls contiguous
with the first wall at fold lines intersecting at a corner point of
the package, said conductive sheet having portions covering a
region of each of said walls and having an edge substantially
spaced from said corner point.
2. A food package according to claim 1, in which said second and
third walls are mutually contiguous at a corner line of the package
when set up, said edge of the conductive sheet being substantially
spaced from said corner line throughout its length.
3. A food package according to claim 2, in which said edge is
smoothly rounded adjacent said corner point.
4. A food package according to claim 1, in which the dielectric
sheet has sufficient stiffness to form a self-supporting box.
5. A food package according to claim 1, in which the conductive
sheet is a metallic foil.
6. A food package according to claim 1 with a wall having an
unshielded region uncovered by the conductive sheet for exposure
toward a high frequency source, said package being adapted to
contain a plurality of food articles with one of said articles
being located more closely adjacent to said unshielded region.
7. A food package according to claim 6, in which the edges of the
conductive sheet adjacent to said unshielded region are folded to
form flaps substantially perpendicular to the direction of
radiation from said source.
8. A food package according to claim 7 adapted to overlie the
source, in which the dielectric sheet is adapted to space said
flaps from said source.
9. A food package according to claim 1, in which the conductive
sheet is continuous over a fold line between contiguous walls, and
has a smoothly rounded indentation adjacent said fold.
10. A food package according to claim 1, in which the portions of
the conductive sheet on said second and third walls are
substantially spaced from one another when the package is set
up.
11. A food package according to claim 6, in which the unshielded
region is elongate and bounded on its elongate sides by opposed
edges of the conductive sheet, said last-mentioned edges being
curved to widen the center of said unshielded region intermediate
its ends.
Description
BRIEF SUMMARY OF THE INVENTION
This invention relates generally to shielded containers for
selective and controlled heating or cooking of foods in microwave
ovens. More particularly, it relates to containers for a plurality
of food articles that are to be heated or cooked to a differing
extent.
A principal object of this invention is to provide a container in
which all of the principal ingredients of a sandwich-type food
product may be included, and which may be placed in a microwave
heating oven so as to expose the ingredients to the high frequency
field, in such manner that each ingredient is properly heated or
cooked. For example, a hamburger may be thoroughly heated to a
cooked, sizzling state, whereas the bun will be only warmed. Many
other examples of use for such containers will occur to those
engaged in the food service and vending industries.
Another object of the invention is to accomplish the necessary
heating or cooking without arcing or charring of the foods or the
container. Arcing is a plasma arc discharge that produces a flash
of light, a noise, and sometimes ignition of the container, where
the same is constructed of paper, plastic or other flammable
material. A major cause of arcing is the conductive shield which in
some instances is placed adjacent the food articles to protect the
same from excessive heating in the dielectric field. Any deviation
of a conductive shield edge from a straight line produces an
intensification of the electric field emanating from that edge. For
any irregularity having a dimension significantly less than one
quarter wavelength, the longer and the more pointed it is, the
stronger the field strength associated with it. At locations where
the field strength is sufficiently large, an arc discharge will
occur, and the heat developed in the arc may be sufficient to cause
browning or burning of adjacent portions of the food articles or
the container. If the container is thermoplastic, it may deform or
melt. In severe cases a paperboard container may char badly, and a
hole may be produced.
Closely related to arcing is charring, which is less severe, but
which may result in browning of container materials or charring
thereof.
Charring and arcing may be influenced by other factors such as
resonant shield geometries, standing wave patterns in the microwave
oven, the oven power level, and the quantity of food exposed to the
microwave radiation.
The objects of this invention include the provision of food
packages so constructed as to minimize the effects of arcing and
charring, while providing for uniform, controlled heating and
cooking of each of the food items contained within the package.
Other objects of the invention will be appreciated from the
following detailed description.
With the foregoing objects in view, the features of the invention
reside in the provision of a food package comprising a container of
dielectric sheet material and a conductive sheet thereon. The
conductive sheet is of smaller area than the dielectric sheet and
is shaped and oriented in relation to the package wall
configuration so as to minimize arcing and charring while properly
exposing food articles in the package differentially to microwave
radiation. The manner of shaping and orienting the conductive sheet
is a function of the package configuration and of the food articles
therein, as will become evident from the following description.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a plan view of a box blank embodying a first form of the
invention suitable for use with hamburgers to be heated or cooked
in a microwave oven.
FIG. 2 is a view in perspective showing the blank of FIG. 1 in set
up form.
FIG. 3 is an elevation in section of the box of FIGS. 1 and 2
containing the ingredients of a hamburger, as oriented on the shelf
of a microwave oven.
FIG. 4 is a view in perspective of a box containing a frankfurter,
representing a second embodiment of the invention.
FIGS. 5A to 5F are schematic illustrations of a plurality of
embodiments representing different food package configurations.
FIG. 6 is a view illustrating the application of the invention to
the cooking or heating of liquid or semi-liquid food
ingredients.
DETAILED DESCRIPTION
FIG. 1 illustrates a first embodiment of the invention suitable for
heating or cooking hamburgers. The package comprises a blank 12
formed of a sheet 14 of dielectric material, preferably but not
necessarily of paper sufficiently stiff to form a box 16 as shown
in FIGS. 2 and 3, and a one-piece conductive sheet or shield 18
laminated to the sheet 14 to cover portions thereof. Preferably,
the conductive sheet 18 is a metallic foil such as aluminum or tin.
The conductive sheet is preferably but not necessarily attached to
the side of the dielectric sheet 14 that forms the inside of the
box 16. It will be understood, however, that while the sheet 18 is
preferably laminated on the sheet 14, this invention also
contemplates other means of putting the conductive sheet on the
dielectric sheet such as chemical deposition, silver painting,
vacuum metallic deposition and any other known equivalent
techniques.
For use in a vending machine, the box 16 is filled with a pair of
roll halves 20 and 22, over which a meat patty 24 is placed in a
position adjacent to a cover or closure 26 formed by a panel 28 of
the blank 12. With the cover 26 closed, the box 16 is placed on a
shelf 29 in a microwave oven with the cover in contact with the
shelf. As further explained below, in this position the meat patty
is located in a relatively unshielded region of the box and is
exposed to microwave energy from the direction of the shelf 29. On
the other hand, the roll halves 20 and 22 are more remote from the
shelf and are relatively protected by portions of the conductive
sheet 18 on the sides other than that adjacent to the meat patty.
As a result, the meat patty develops a substantial amount of heat
and may be heated to a sizzling, cooked condition while the roll
halves are only warmed. After a few seconds the package 16 may be
removed from the oven, the cover 26 opened and the contents
rearranged so that the roll half 20 may be placed over the meat
patty to complete the sandwich in edible form.
The blank 12 may be formed in any of several configurations well
known in the box making art, the preferred form being illustrated
in FIG. 1. The sheet 14 comprises a number of panels defined by
edges, score lines and fold lines so as to form the six-sided box
16. The foil sheet 18 comprises portions 30, 32, 34, 36 and 38, the
four last-mentioned portions having right angle folded flaps 40.
The edges of the sheet 18 are substantially spaced from
three-dimensional corner points 42 of the box, and they are also
substantially spaced from the corner lines 44 when the box is in
the set up position as illustrated in FIG. 2. The edge of the sheet
18 is also smoothly rounded adjacent the corner points 42 as most
clearly shown by fillet-like curves at 46 in FIG. 1.
It will be further observed in FIG. 2 that when the box is set up,
the most closely adjacent peripheral edges 48 of the flaps 40 are
substantially spaced from one another, as well as being smoothly
rounded. Moreover, as shown in FIG. 1, at the fold lines such as 50
adjacent to the flaps 40, the edges of the sheet 18 have smoothly
rounded indentations such as 52.
As shown in FIG. 3, when placed on the shelf 29 of the oven, the
substantially unshielded cover 26 spaces the flaps 40, which are
parallel to the shelf, from the shelf. This spacing may be simply
the thickness of the dielectric sheet, or it may be made
substantially greater than such thickness by suitable configuration
of the cover 26.
The object of these structural features is to minimize charring and
arcing, while permitting differential exposure of the package
contents to microwave energy. This is explained in further detail
as follows.
It has been found desirable to reduce the number and sharpness of
points in the conductive sheet 18, which tend to increase the
strength of the electrical field in a microwave oven. To a maximum
extent, all corners are rounded, as illustrated for example by the
inside corners 46 and the outside corners 48. Rounding of the
corners of the conductive sheet 18 is carried out with respect to
two-dimensional corners as well as three-dimensional corners, as
illustrated. Such rounding is carried out by suitable shaping of
the edge contours of the sheet 18, whether or not the dielectric
sheet 14 is provided with relatively sharp corner points and corner
lines, since the latter are non-conductive and of relatively less
importance to the phenomena of charring and arcing.
The portions of the conductive sheet 18 adjacent the shelf 29,
because of this proximity, are possible sites of arcing or
charring. It has been found that, in general, a conductive edge
perpendicular to the shelf in a microwave oven is likely to produce
these phenomena. It has been discovered that these phenomena may be
inhibited or reduced by the features illustrated in the embodiment
of FIG. 1. Thus, the folding over of portions of the conductive
sheet to form the flaps 40 parallel to the shelf results in reduced
charring and arcing, as compared with an embodiment having no flap
40. Secondly, the spacing of the foil edges and flaps away from the
shelf reduces charring and arcing, and in the illustrated
embodiment this spacing is provided by the thickness of the closure
or cover 26.
As previously noted, the illustrated embodiment of FIG. 1 provides
an additional feature at points where the edge of the conductive
sheet 18 is folded, as at fold lines such as 50. Indentations such
as 52 provide curvatures at points of folding which reduce arcing
and charring.
Moreover, providing sufficient distances between proximate
extremities of the conductive sheet, such as the corners 48,
further serves to reduce charring and arcing.
It will be noted that the entire conductive sheet 18 of the
embodiment in FIG. 1 is a single integral metallic foil piece, with
no overlapped joints. As compared with a structure in which the
conductive sheet comprises plural pieces having a joint or seam, or
one piece with an overlapped joint, the present embodiment is more
char and arc resistant.
It is noted that the above-described features of the conductive
sheet 18 result in unshielded regions or holes in the container
through which microwave energy may leak. However, such leakage is
not necessarily detrimental to the proper heating of the food,
since the size and shape of the holes may be controlled to alter
the standing wave pattern inside the shielded container, thereby
producing heating nulls and peaks at desired locations therein. In
general, by controlling the size, shape, number and location of the
holes or unshielded regions, such desired results are
obtainable.
It has been found that some food condiments, when smeared over
shield extremities, will produce arcing. The high field strength
associated with conductive extremities, if contiguous with
semi-conductive condiments, promotes arcs. This may be avoided by
locating shield extremities so that they are less likely to be
smeared inadvertently by condiments for the food components in
use.
It will be recognized that certain variations in the contents of
the package of FIG. 1 may be readily accomplished. For example, to
make a cheeseburger a slice of cheese is placed between the bun
half 22 and the hamburger patty 24. In the event that other items
are to be kept cool, such as lettuce, pickle chips or tomato
slices, these are conveniently placed between the bun halves 20 and
22.
FIG. 4 illustrates a second embodiment of the invention, comprising
a box 56 for a frankfurter 58 and sliced bun 60. This box is
constructed in accordance with many of the principles described
above in detail with reference to FIG. 1. The blank is formed of a
dielectric sheet 62 to form the panels of the box in accordance
with existing box making techniques, and a conductive sheet 64 is
laminated thereto, having portions covering a region of each of the
walls of the box, except for the portions thereof adjacent to its
corner points and corner lines, all as illustrated in FIGS. 1 and
2. A region of the box adjacent to a corner line 66 is unshielded
and bounded by edges 68 that are smoothly curved to widen the
center of the unshielded region intermediate its ends. Preferably,
the frankfurter 58 is placed in the box adjacent to the unshielded
region in the manner illustrated in FIG. 5D.
The edges 68 of the conductive sheet or foil are shaped in the
foregoing manner to provide for evenly heating the frankfurter 58
throughout its length. A meat frankfurter is a semi-conductor of
electricity and therefore acts as a dipole antenna when heated in a
microwave oven. For a standard length frankfurter that is not
differentially shielded from end to end, the ends often overheat
and the middle underheats. The resonant, standing waves produce
heating peaks at the ends. The foil shield or conductive sheet 64,
at the edges 68, illustrated in FIG. 4 compensates for this effect
and produces an evenly heated frankfurter.
FIG. 6 illustrates a variant of the frankfurter sandwich in the
form of what is sometimes called a submarine sandwich. This
comprises an elongate bread roll or bun 70 and a plurality of meat
balls or other particulate foods 72 with a soft or other
semi-liquid filling (not shown) covering the meat balls. This
filling is of such consistency that, when placed directly upon the
bread roll 70, it would soak into the bread roll and produce an
undesirable effect thereon. To obviate this effect, the meat balls
72 and sauce are placed within a tube 74 of plastic film. The tube
is removed after heating in the oven. One end 76 of the tube is
folded over to close it, while the other end is closed by a
slotted, circular plastic squeegee 78. The tube 74 may be placed
within a container such as that illustrated in FIG. 4 in
substantially the same manner as the frankfurter 58.
FIGS. 5A to 5C, 5E and 5F illustrate alternative configurations of
the conductive foil or sheet in relation to the contents, for
example a frankfurter or other filling 80 and a bun or other bread
product 82. In these drawings, outlines 84, 86, 88, 90 and 92
represent the appropriate configurations of the conductive foil or
sheet, and it is assumed that the same is laminated to a dielectric
sheet of larger area which is suitably constructed in accordance
with known box making techniques to provide a closed or
substantially closed container or box. In each of these embodiments
a suitable unshielded region is provided, adjacent to which is
located the particular food item to be most thoroughly heated or
cooked.
With respect to all of the container embodiments described
hereinabove, the formation of the container blank may be followed
by additional steps of fabrication, such as the application of glue
lines or spots and the adhesion thereto of certain flaps and panels
as preliminary steps. For example, in FIG. 1 shaped glue spots 94
may be placed upon a pair of flaps and adhered to adjacent panels
of the box after folding upon a line 96. Other glue spots may also
be applied, if desired. After the glue is set, the box may be
folded flat for storage and shipment along creased lines 98. This
facilitates setting up the collapsed box for the loading of
sandwich ingredients without the further use of glue. Other
techniques of the box making art may also be employed without
departing from the spirit or scope of this invention.
* * * * *