CA2085903A1

CA2085903A1 - Package with microwave induced insulation chambers

Info

Publication number: CA2085903A1
Application number: CA002085903A
Authority: CA
Inventors: Lawrence C. Brandberg; Jeffrey T. Watkins
Original assignee: Individual
Current assignee: Golden Valley Microwave Foods Inc
Priority date: 1990-07-11
Filing date: 1991-06-27
Publication date: 1992-01-12
Also published as: JPH05507898A; ZA915210B; CN1058938A; US5081330A; MX9100159A; AU8093491A; IL98734A0; BR9106625A; EP0537213A1; WO1992000899A1

Abstract

The present invention provides an insulating microwave heating package (10) with at least one and preferably a multiplicity of latent, uninflated or potential insulation chambers (C) capable of inflating when exposed to microwave energy. The package includes at least two sheets of material (22, 24) bonded together (28) at selected points, patches or along seal lines (28a) separated by unsealed areas (28b) which define unfilled inflation chambers (C) between the lines, patches or points. Upon exposure to microwave energy, the package and its contents become heated. As a result of this heating process, the unfilled chambers also become heated, causing them to become filled with hot expanding air or moisture vapor. These chambers (C) serve as insulation for the package and enhance heating of the food (20) by reducing heat loss from the package.

Description

W~:) 9~01)899 PC~/US~1/0461~1 2~8~

PACKA(;E WITH MICROWAVE INDUCED INSULATION CHAMBERS
FIELD OF THE INVENTION

The present inYention relate!s to packaging and more particularly to packaging for heatiny foods in a microwave oven.

BACKGROUND OF THE INVENTION
While many packages for heating food in a microwave oven have been successful, heat loss often interferes with achieviny optimum results. For example, in popping corn, heat losses can reduce the volume of the popped corn and increase the number of "old maids", especially in low powered ovens. This can result in consumer dissatisfaction. Insulation for microwave packaging has in the past b~en bulky and requires assembly steps and materials which make the package more expensive. In addition, the insulation has been located only in the bottom portion of the package, i.e~ the portion re~ting on the floor of ~-he microwa~e oven, thereby reducing heat loss only in that area.~ One example is described in patent 4,219,573 which re~uires enough insulation to 2S prevent the loss of at least ~bout 18 cal. per gram of popcorn. It has now be~n discovered ~hat excellent results can be provided with a loss of only about 9 calories per gr~m of popcorn. In addition, the insula~ion materials ~- corX, wood, corrugated pad or ceramic paper -- proposed in pa~en~ 4,219,573 are not required in the present invention. This reduces the cost of the package substantially. Insulation previously used reduces the cooling rate of the food when the package is chill~d or frozen. It has now been discovered that the microwave ener~y itself can be used to i~duce the formation in ~itu of an insulation structure without adding material to ~he package. In developing the present invention, it has also been discovered that the most efficient formation of the WO 92/008g9 PC~/US91/04611) 2~5~

insulation structure can be achieved by augmenting the heat supplied by the microwave energy alone to the ~nformed potential insulation before the insulation structure actually comes into being.
In view of the deficiencies of the pxior art, it is a major object of the in~ention to reduce the loss of heat from microwave packaging without increasing the co~t of the package or adAing materials, to reduce heat loss in one or more selected ares or throughout the entire package, thereby pe.rmitting foods contained in the package to be cooked or heated more efficiently and to enable the package to be chilled or frozen as efficiently as a bag with no insulation. : :
These and other more detailed and specific objects of the invention will be be~ter understood by reference to the following detailed description and figures which -illustrate by way of example but a few of the various forms of the invention within the ~cope of the appended claims.
. SUMMARY OF THE INVENTION

The pr~sent invention pro~ides an improv~d microwave heating package with at least one and preferably a multiplicity of la~ent, uninflated or potential insula~ion chambers capable of becoming inflating when exposed to microwave encrgy. The packa~e includes a package-enclosing wall having inflatable means in the wall adapted to expand the ~hickness of the wall upon exposure to microwave energy. In a preferred embodiment, the wall include~ two sheet~ of material including at lleast one flexible shee~. The sheets are bonded togethe:r at selected points, patches or along seal lines with unsealed areas between them to defin~
unfillPd inflation chambers between the lines, patches or points. A microwaYe susceptor is preferably placed adjacent to the potential inflation chambers. Upon .. ~ . ~. . . .
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W092/00~99 ~Cr/US~1/0461n 2Q~9~3 exposure to microwave energy, the package and its contents become heated. As a re,sult of this heating process, the unfilled chambers between the patches, poin~s or seal lines also become heated, causing them to become filled with heated air or vapor.

THE F IGURES

Figure 1 is a perspective vi~sw of a package embodying one fo~n of the invention;
Flgure 2 is a transverse sectional view taken on line 2-2 of Figure 1;
Figure 3 is a side view of the package of Figure l as it appears after being heated in a microwave oven;
lS Figùre 4 is a perspecti~e view partly broken away of another fo~n of the invention;
Figure 5 is a partial transverse seotional view taken on line 5-5 of Figure 4 with the outer wall of the package partially drawn back;
Fi~ure 6 is an enlarged cross~sectional view of a portion of a package in accordance with the invention showing inflation chamber.s in unexpanded and expanded condition (dotted lines);
Figure 7 is a bar chart comparing the popped volume of popcorn popped in a package wi~h and without the present invention;
Figure 8 is a similar to Figure 7 but compares the percent Qf kernels that are popped;
Figures 9 and 10 are similar to Figures 7 and 8 but show results achieved with a different microwave oven.

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Figures l, 2 and 3 illustrate a package, in ~his case a collapsible bag 10 embodying the invention. The bag 10 is formed from paper and includes a lower facP
12, an upper face 14, gussets 16 and l8, and a bottom . .

W09~/00899 2 ~ 3 PCTtVSYI/04610 seal 17. Before the bag 10 is filled with food, it is open at one end which serves as a mouth 15. The bag 10 c~n be f illed through the mouth 15 with any suitable ~ood 20 such as a charge of unpopped popcorn and shortening which is to be poppecL within the bag 10 by microwave energy supplied by a microwave oven. The mouth 15 of the package is then sealed shut. The bottom wall or lower face 12 of the bag i8 shown in Figure l.
During the ~opping operation the bag 10 is oriented so that the bottom wall 12 faces downwardly with the food 20 in contact with it as shown in figures 2 and 3.
As can be seen in ~igure 2, the bag 10 is made up of flexible outex and inner layers of paper 22 and 24 which are glued, i.e. laminated, together by means of an adhesive 28. However, at least on the lower face 12 of the bag 10, the pattern of adhesive 28 is provided such that there e~ists a series of strips, dots or patches of adhesive 28a separated by areas with no adhesive 28b.
This provides several latent or potential inflation chambers C. The sheet 22 and 24 can, for example, comprise 30 lb. bleached kraf~ pap~r and 30 lb.
greaseproof kraft paper, respectively. The adhesive 28 can comprise a suitable heat-resistant adhesive such as a vinyl chloride emulsion adhesive~ an ethylene vinyl chloride emulsion adhesive or a polyvinylacetate polymer emulsion adhesi~e such as Duracet~ adhesive manufactured by Franklin International, Inc. of ~Columbus, Ohio. Other adhesives will be apparent to those skilled in the art. The other adhesive 28a can bP
applied in any suitable manner, for example by a p~tterned adhesive applica~or roll (not shown). No effort has to be made to provide a space or air chamber of any kind between the sheets 22 and 24 in the unsealed areas 28a. It is believed, however, that a small space exists and that a small amount of air will be presen~
between the two sheets. The important requirement is simply that the sheets be unbonded in the areas 28b.

W092/00~99 . 2 0 8 ~ ~ ~ 3 PCr/US~I,046l0 Between the inflation chambers C and the inner wall 24 of the bag 10 is a susceptor ~6 of any suikable known construction, for example a flexible sheet of plastic film having a microwave interactive coating on one or both surfaces. It is preferred that the sllsceptor 26 be located adjacent to the food 20 and that the expandable chambers C be on the opposite si.de of the susceptor 26 from the food 20 to maximize heat transmission to the food and minimize loss to the oven floor F. Microwave interactive susceptors of various compositions are well known to the art for heating food. Examples are described in patents 4J735,513; 4 r 878,765; 4,190,757 and 4,267,420. It will be seen in Figure 2 that the sheets 22 and 24 are laminated together in flat condition.
That is to say, with the adjacent surfaces at ~he location of the unbonded areas 28b which define the latent chambers C either in contact or ne~rly in contact.
It has now been discovered that when a package having latent chambers C as descxibed is heated in a microwave oven, the un~ealed sections 28b will expand as the result of the expansion of air or moisture vapor or, most probably, both to produce inflated chambers C and create a microwave-induced layer of insulation between the food 20 and the floor of the oven F. The chambers C
are often about 1/4" in height. While the preci5e mechanism of expansion of these of chambers during microwave heating is not known with certainty, it is believed that it cannot be explained fully as a result of air expansion because no effort is necPssary to assure that ai.r is present in the unexpanded chambers.
Consequently, it is believed that moistu.re vap4r may be partially responsible for the expansion of the chambers.
The susceptor 26 typically reaches a temperature of about 325F to 400F, and at this tempexature, air and moisture vapor present in the unexpanded chambers can expand to ten times their original volume.

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WO9~/0089~ PCr/US91/046~0 2~85~3 It will be noted that no adclitional matexial is required to provide the insulation chambers C.
Noreover, the insulation layar provided by the chambers C does not rigidify the package as a layer of corrugated S cardboard will do as described i.n patent 4,219,573. In addition, the food can be chilled or frozen as efficiently as in an uninsulatecl package.
By arranging the adhesive strips 28a in a star pattern which intersects at a center point 29 near the center of the bag 10, it has been discovered that the bag tends to develop a conical bottom surface that has an apex at the intersection point 29 of the adhesive bands 28a. This is desirable since it tends to clump the unpopped popcorn near the center of the bag during the popping operation, thereby keeping it at a location where heat can be transferred to it most effectively so as to enhance the popping effect. Thus, in this confi~uration, the chambers C tend to shape the package 10 and act as a conical truss or form for concentrating the charge of popcorn and shortening 20 at a center point. In an alternative form of the inv~ntion~ if a series of elongated parallel chambers C are employed, they will help to unfold the bag 10 which is shipped in a folded condition as they inflate during the microwave heating process.
The susceptor 26, instead of compxising a separate sheet of material, can be a coating applied as a liquid to the outer surface of the inner sheet 24 and dried in the manner of a printing ink. In thi~ case, the susceptor coatins will contain a microwave interactive heating substance in particulate form which is bonded to the sheet ~4 as a par~ of the coaking which makes up the susceptor 26.
It can also be seen that an insula~ion effect is achieved withou~ insulation material being added to the package. In this sense the bag i5 self-insulating, the height o~ the ch~nbers C providing insulation. Since .. . .
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W092/00899 PCT/~Sg1/04610 nothing is addedr the bag 10 remains supple, flexible, pliable and foldable. This ic important since the ends of the bag 10 are folded over a center portion containing the popcorn 20. It will also be noted that the insulation is formed dynamically during the microwave heating.
Many variations can be made. For example, a moisture or vapor releasing substance can be provided in the susceptor 26 or at least in co~nunication with the chambers C to release gas, vapor or fumes during the heating process. One example is a vapor-releasing mineral hydrate as described in U.S. patent application SN 07/456,159 entitled MICROWAVE SUSCEPTOR WITH
ATTENVATOR FOR HEAT CONTROL.
Because ~he invention provides a substantial improvement in heating of food, the size or amount of the susc~ptor 26 can be reduced in so~e cases, ~hich is an advantage under certain conditions, for example when the su~ceptor 26 tends to burn or ~corch the package.
Another form of the invention is shown in Figures 4, 5 and 6 wherein the same numerals refer to corxesponding parts in the embodiment illustrated above. In this embodiment, the primary difference from Figures 1~3 i5 that the inflation chambers C have a different pattern.
In Figure 4-6, the inflation chambers C comprise a plurality of relatively small blisters arranged in rows.
As seen in Figures 4-6, the bag indicated generally at ll includes a lower face 12, an upper face 14, gussets 16 and 18, and susceptor 26 as described above.
Adhesive 28 is employed for bonding the sheets 22 and 24 toge~her. In ~he area where the chambers C form during heating, the a~hesive 28 is arranged as a plurality of circles of adhe~ive 28a ha~ing adhesive~free areas 28b between them. Before heating, the condition of the latent inflation chambers C is shown as narrow spaces between the circles of adhesive 28a. ~hen the package is placed in a microwave oven and exposed to microwave ..~ ., WO 92/008g9 PCI`/USg1/04610 20~5~a~ -energy, the heat produced by the microw~ve energy, and particularly that produced by the susceptor 26, will cause the latent or potential inflation chambers C
corresponding to the adhesive-free areas 28b to expand as shown by dotted lines in Figure 6 and solid lines in Figure 4 to produce the inflation chambers C which provide an insula~ing effect for reducing heat loss from the food and the susceptor 26.
The in~ention can be used in connection wi~h a variety of foods, such as popcorn, pizza, french fri~s, griddle food (e.g. french toast, pancakes, waf~les), rolls, doughnuts and the like. Since the sheets of paper 22 and 24 are flexible, they are better able to conform to the surface of an irregularly shaped food product, such as the lower surface of a pizza crust, than a flat stiff object such as a sheet of corrugated cardboard. This promotes heat transmission into the food.
Refer now to Figures 7-8 which show the effectiveness of the invention in popping popcorn in a microwave oven, in this case a GE 479-watt oven.
Fif~y-six grams of unpopped popcorn and 23.5 grams oi shortening were placed in a bag having a height of 11 inches and width of 4 1/2 inches, and popped. It can be seen that by providing a susceptor and a full lamination, i.e. fully bonded between the sheets, a volume increase of from 1200 ml to 1600 ml is achieved.
However, by using the invention, an additional increase from 1600 ml to about 1800 ml is achieved, a mean ~olume increase of about 19%. A similar increase is achieved in the percent of the kernels that are popped, as shown in Figure 8.
Refer now l:o Figures 9 and 10 which illustrate popping of popcorn in a Litton 975-watt oven.
As shown in Figure 9 at the right as a mean of th0 samples tested with no susceptor, the ~olume of popped corn is about 1600 ml. When a susceptor is used with , ~ . . .. .. . .. .. .

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full Lamination, i.e. adhesive applied over all of the mating surfaces, the volume increases to about 1900 ml.
However, with the present in~ention there is a further volume increase to about 2300 ml, a mean volume increase of about 21%. Similar improvements are achieved in the percentage of the kernels popped as shown in Figure 8.
Many variations of the present invention within the scope of the appended claims will be apparent to those skilled in the art once the principles described herein are understood~

Claims

WHAT IS CLAIMED IS.

1. A microwave cooking construction comprising:

(a) a package comprising first and second opposite sidewalls defining an internal food chamber therebetween;
(b) said first sidewall comprising inner and outer sheets of flexible packaging materials;
(c) means sealing said inner and outer sheets of flexible packaging material to one another in selected areas to define at least one inflatable chamber between said inner and outer sheets of flexible packaging material; said at least one inflatable chamber being spaced from said internal food chamber by a portion of said first sidewall; and, (d) inflation means for selectively inflating and expanding said at least one said inflatable chamber when said package, with a microwavable food substance included within said internal food chamber, is exposed to microwave energy in a microwave oven; said inflation means including a microwave interactive susceptor operably positioned:

(i) in heat transfer relationship with a region of said internal food chamber whereat food is operably positioned during cooking; and, (ii) in heat transfer relationship with said at least one inflatable chamber;
(e) said inflatable chamber being positioned between said susceptor and an exterior surface of said outer sheet, to insulate said susceptor from a portion of the microwave oven engaged by said outer sheet, during use.

2. A construction according to claim 4 including a plurality of said inflatable chambers in said first sidewall.

3. A construction according to claim 2 wherein said means sealing said inner and outer sheets of flexible packing material to one another includes a plurality of strips of adhesive adhering said inner and outer sheets to one another and intersecting at a central point, in a central region of said package.

4. A construction according to claim 3 wherein said means sealing said inner and outer sheets of flexible packing material defines said plurality of inflatable chambers in a radial pattern about said central point; each of said inflatable chambers diverging from said central point whereby, upon inflation and expansion, said inflatable chambers will define a conical truss configuration with an apex thereof corresponding to said central point.

5. A construction according to claim 2 wherein said means sealing said inner and outer sheets of flexible packing material to one another defines a plurality of circular inflatable chambers.

6. A construction according to claim 5 wherein the circular inflatable chambers comprise a series of closed cells positioned adjacent to one another and spaced laterally by adhesive sealing said inner and outer sheets to one another.