GB2211380A

GB2211380A - Flexible package for microwave cooking

Info

Publication number: GB2211380A
Application number: GB8824287A
Authority: GB
Inventors: James W Mitchell; James R Quick; Dennis F Cooley
Original assignee: International Paper Co
Current assignee: International Paper Co
Priority date: 1987-10-21
Filing date: 1988-10-17
Publication date: 1989-06-28
Also published as: JPH01169240A; GB8824287D0; DE3835796A1

Description

2' 2 8 0 FLEXIBLE PACKAGE FOR MICROWAVE COOKING

BACKGROUND OF THE INVENTION

This invention relates to a package f or the microwave cooking of foodstuffs and particularly to a package whereby the foodstuff becomes browned or crispened over at least a portion of its area upon such cooking.

The prior art is aware of food packages which can be placed directly into a microwave oven for cooking of the foodstuff, without first removing the foodstuff from the package. The prior art is also aware of a microwave browning technique wherein a food product to be cooked in a microwave oven is placed in a package provided with a microwave interactive material. This microwave interactive material becomes hot during exposure to microwave energy in a conventional microwave oven, so that any food in direct thermal contact with this microwave interactive material becomes browned or crispened. An example of such browning or crisping food package is afforded bfy U.S. Patent 4,267,420, issued to Brastad.

SUMARY OF THE INVENTION

The present invention deals with a package for containing food during cooking or heating in a microwave oven and for providing thermal heating effects such as the heating of the surftice of the food to a temperature sufficiently high to cause. browning or crisping of the food surface. In contrast to the prior art, all forms of this invention provide package features that facilitate the placement and positioning of the package and food in a microwave oven. Also, all forms of this invention utilize materials more effectively than prior art packages that attempt to accomplish similar purposes.

Also, this invention provides package forms that are easier to 30 manufacture, requiring less steps and less production time than various prior art packages for microwave browning and crisping.

2 Most r,ant, the package forms that this invention makes possible provide better cooking results for many types of food than the packages heretofore available.

The package forms made possible by the present invention are highly suitable for foods with a doughy or crusty portion such as pizza, bread items, dessert pastries, -breaded fish portions and battered chicken pieces. These items do not normally cook in a suitable manner in a microwave oven. due primarily to the absence of the thermal heating effects that are present in conventional cooking environments such as a conventional oven.

This invention may take the form of a pouch, a bag or an envelope; or it may also take other forn to be described later in this document. All package forms covered by this invention will have a substantial portion of the package made from a flexiISIe composite that has material that includes a microwave interactive cornpQnent the essential characteristics of converting microwave': energy to thermal energy which may be transmitted to the food item via conduction, convection and/or radiation. In many embodiments of this invention all three modes of heat transfer are operative. The flexible composite material that provides this heating effect may be made of a variety of materials. - In the preferred embodiments a laminated flexible material comprised of paper and a lightly metallized polyester fiber, but this invention is not limited by the selection of any specific materials for the flexible microwaveinteractive composite material. The flexible composite material that thus functions to provide thermal heating effects may make up the total package, or it may be used with other flexible material, or in some cases with relatively stiff material such as paperboard. In any case, an important aspect of the design of packages of this invention is that the area covered by the microwave interactive component is greater than the bulk area of the food over the area of mutual contact between the food and the flexible portion of the package that carries the microwave interactive component. It is important to note that the microwave interactive component may not cover the full area of the flexible portion of the package, although the area covered by the microwave interactive component will-always extend beyond the area in contact with the food. Also, the microwave interactive component may be present in the form of a discontinuous pattern. such as stripes or dots. and in such a case, it is the overall area covered by such a pattern that will exceed the area contacted by the food.

Another important aspect of the design of packages covered by this 10 invention is that the volume of the space defined by the package for containment of the food in the microwave oven is greater than the bulk volume of the food at any time during the microwave cooking process.

The two critical aspects of design discussed above pertain to all 15 the varied forms of packages embraced by the present invention, i.e., all forms will have a microwave interactive component covering an area greater than the area of the food contacting that portion of the package and all forms will have an internal volume greater than the maximum bulk volume of the food. The combination of these design aspects with the use of a flexible material to convey the microwave interactive component is the basis for the advantages of the packages of this invention over packages possible via prior art concepts or methods. The end result is a package that provides a cooking environment for the food in a microwave oven that combines, controlled thermal heating effects on the surface of the food with the speed of microwave heating for the interior of the food item.

Substantial improvement over prior act packages are provided by the use of a flexible carrier material for the microwave interactive component in combination with the extended area of coverage of the microwave interactive component beyond the area contacted by the food. The combination of these two package features insures a 4 degree of proximity of the microwave interactive component to the edges of the food regardless of the exact shape of the food item. This provides thermal heating effects so that the texture of the edges of the food will be like the bottom or that area in direct contact with the microwave interactive component. Without this provision for the transmission of thermal energy to the edges of the food, many food items will have undesirable moistness or sogginess along the edges. This is because the edges would be relatively cool compared to that part of the food contacting the microwave interactive material and moisture would migrate to the cooler portion of the food. Of course., the full coverage of the package interior with microwave interactive component provides an even more encompassing thermal heating effect for the food; and full coverage is especially important in those embodiments of this invention that are intended to provide an equal cooking effect on both sides of the food via a complete inversion of the package midway through the microwave cooking cycle.

The relationship of the internal volume of - the package to the maximum bulk volume of the food is required to provide a hot air space around the food and thereby allow the food to cook in'-,an environment that simulates conventional (not microwave) coiking conditions. The package forms of this invention may be totally closed so that a moist hot air environment is produced due to the moisture driven off the food during the cooking process, or the packages may be partially open to allow the release of moisture and maintain a relatively dry hot air environment. A hot air space above the food is particularly important for some food items that have a top surface that would otherwise stick to the package interior. such as a French bread pizza or a frosted pastry item.

The package forms of this invention are totally dependent on the use of a flexible material to convey the microwave interactive component. The use of a flexible material in this function permits the various package forms of this invention to accommodate irregular shaped food items and maintain some conf ormity of the microwave interactive component with the surface of the food item. Also. the package forms of this invention generally utilize less material than other relatively stiff package forms and thereby cost less to manufacture and require lower storage volume prior to f illing with food. Also, a pouch envelope or bag made f rom a flexible stock is relatively easy to hold in an open position for filling with food. In some cases, the material to make the package forms of the present invention will conveniently be shipped in roll form for f abrication into a form such as a pouch at the site of food packaging.

A thorough consideration and analysis of the package forms and concepts provided by the prior art will reveal that none combine the essential elements of the packages of the present invention, and consequently, none will provide the important advantages f or microwave cooking of foods within the package that are afforded by the present invention. A number of prior art patents describe the use of microwave interactive materials to provide surf ace heating ef fects in microwave - food packages, and in many cages,' the microwave interactive material is a thin vacuum-deposited layer of a metal such as aluminum or a polyester film. In many cases in the prior art the vacuum-metallized film is secured to a rigid support material such as paperboard to form a totally self- supporting package, but one that cannot conform to the shape of the food.

Examples of such rigid, self-supporting, inflexible food packages are seen in U.S. 4,555,605 (Brown et al.), U.S. 4,592,914 (Kuchenbecker), and U.S. 4,594,492 (Maroszek) and U.S. 4,641,005 (Seiferth). The Maroszek patent is an attempt to overcome the limitations of a rigid paperboard package via the design of the package, specifically the formation of a paperboard spring to maintain contact of the food with either one or two interior surfaces of the package that carry the vacuum-metallized polyester film. Although apparently somewhat effective, the package concept of Maroszek does not overcome the fact that a rigid package form 6 can not conform the shape of the food. especially if the food item is of an irregular shape. In contrast to the rigid, self-supporting package forms just discussed, some prior art packages are made from relative flexible materials that provide surface heating effects for food during microwave cooking. Such flexible packages are disclosed in U.S. 4,267,420 (Brastad), U.S.

4,55.33,010 (Bohrer et al), and U.S. 4,641,005 (Seiferth); but none of these prior art flexible packages provide the essential features of the packages of the present invention. Brastad discloses only packages that are in the form of wrappers that are in direct contact with the food at all points. The wrappers of Brastad do not provide a hot air space around the food. With the wrapper-form package of Brastad there is no heating of the food item(s) by convection or radiation and this limits the capability of the packages to provide microwave cooking results that simulate the results obtained by conventional cooking means. The packages of Bohrer are designed specifically as microwave popcorn packages and as such have only a limited area at the bottom of the package covered with a "microwave converting" material that will gener,.te a surface heating effect for a layer of popcorn kernels tb,3t cover the full area of that material. The packages of Bohrer have no provision for extension of the area covered by the microwave converting material beyond the area contacted by the food, i.e., the popcorn kernels. Also the microwave converting material in the packages of Bohrer is in all cases attached to a flat horizontal wall of the package and is not in a configuration that will permit confirmation with the surface of the food and insure a degree of proximity of the microwave converting material to the edges of a food item. Clearly these considerations, that were essential in the case of the present invention have not been involved in the design of the microwave popcorn packages of Bohrer. Seiferth discloses a wrapping material, very similar in character and function to the wrapping material of Brastad. Like the wrapper-form packages of Brastad, this package form as shown by Seiferth lacks the important feature of a hot air space around the food that is afforded by the package forms of the present invention.

The package forms of this invention are useful for frozen foods, refrigerated foods and foods stored at room temperature. Further, these package forms may be used in fast food service, cafeteria service and similar food dispensing situations where the food may be cooked, placed in the pouch, held for a period of time before servin,-- and then reheated in a microwave oven at the time of serving. This reheating step may serve to bring the food back to the desired temperature for consumption and provide the desired surface texture and color for maximum consumer appeal. Alternatively, the reheating step may serve to finish the cooking process for food items that are only partially cooked before the time of serving. In any case, the package forms of this invention are ideal for microwave reheating of foods because the cooking environment in the package provides thermal heating effects for the surface of the food in conjunction with the rapid internal heating of the food by the microwave energy. The pouch, ba- and envelope forms of the present invention are especially suited for food restaurants, convenience stores and the like becaus6 of the relative low cost of the package, the overall suitability of the package form for handling the food product and the Cxcellent combination of thermal and microwave cooking effects. Other available packages do not offer all these advantages within a single package.

DETAILED DESCRIPTION OF THE DRAWINGS

Figure 1 is a plan view of a blank from which a pouch is fashioned.

Figure 2 is a view illustrating an intermediate stage of formation of the pouch of this invention from the blank of Figure 1.

Figure 3 is a view similar to Figure 1, and illustrates the pouch in its fully closed configuration.

Figure 4 is a cross-section taken along section 4-4 of Figur e 1. and illustrates the laminar composition of the blank form which the pouch is formed.

Figure 5 is a cross-sectional view.illustratingg the package of this invention while it is in a conventional microwave oven and being subjected to microwave energy.

Cn Figure 6 is an illustration of a fully sealed pouch form of the package of this invention.

Figure 7 is an illustration of a pouch form with one open end.

Figure 8 is an illustration of a pouch form with two open ends.

Figure 9 is an illustration of a pouch form with vent holes.

is Figure 10 is an illustration of a pouch form with a self - opening seal at one end.

Figure 11 is an illustration of a pouch form with a vent holes covered with a self-opening flap.

Figure 12 is an illustration of a pouch form with extended portions at both ends which serve as handles.

Figure 13 is a cross-section view of a two compartment pouch form of the package of this invention. i Figure 14 is a cross-sectional view of a two compdrtment pouch with one compartment serving to expand and provide eldvation of the foodstuff above the resting surface in a microwave oven.

Figure 15 is an illustration of a pouch with a feature which allows the pouch containing the foodstuff to be hung on a fixture in a microwave oven.

Figure 16 is a cross-sectional view of a two compartment panel designed to starid in a semivertical position in a microwave oven.

Figure 17 is a crosssectional view of a pouch secured to a piece of stiff supporting material.

Figure 18 is a cross-sectional view of a package form of this invention made partially of a stiff supporting material.

Figure 19 is an illustration of a pouch carried within a paperboard sleeve.

Figure 20 is an illustration of a pouch with aluminum foil shielding strips secured on the inside surface of the pouch.

Figure 21 is a cross-sectional view of a package with the microwave interactive component supplied as an insert placed within a pouch made from microwave transparent material.

Figure 22 is an illustration of a roll stock f orm of material for making packages of this invention and the steps of connecting the roll stock to a finished package containing foodstuff.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to Figures 1 - 4 of the drawings particularly, the numeral 10 denotes a unitary blank from which the pouch of this invention is formed. As illustrated in Figure 4, the blank is generally planar and is formed of layers, from one of its surfaces to the other, of polyethylene terephthalate (PET), denoted by the numeral 40, a microwave interactive material, denoted, by the numeral 42, and having the property that when subjected to microwave radiation from a conventional microwave oven, its temperature will increase, as adhesive layer 44, and a paper layer 46. The adhesive layer 44 functions to secure the paper 46 to the microwave interactive material.

A specific set of materials suitable for the manufacture of a 25 laminated construction as shown at Figure 4 consists of the following:

-- A lightly-metallized polyester film such as that described by Seiferth (U.S. 4,641,005) with a sufficiently thin coating of a metal such as aluminum to provide the desired interaction with microwave energy to cause a surface heating effect for the food. A suitable polyester film is the type sold commercially as Mylar or Melinex, more specifically a biaxiallyoriented polyester film. For use in the practice of the present invention the polyester films may be prepared with a vacuumdeposited layer of aluminum. such that the optical density of the aluminum-coated film is in the general range of 0.15 to 0.30, and the polyester film thickness may be in the general range of 0.5 to 2. 0 mils. The lightly-metallized polyester film as has been described provides the combination of layers 40 and 42 shown in Figure 4.

-- An uncoated bleached white paper, for example of the type known as uncoated offset paper, with a basis weight in the range of about 20 to 80 pounds per 3000 sq. feet. Paper stocks up to about 8-10 mils in thickness have sufficieAt flexibility to serve the function of the carrier or support material for the microwave interactive material in the present invention.

---An adhesive that will provide a heat-resistant bond between the metallized polyester film and the paper such as the following water-based adhesive formulation:

LAMINATING ADHESIVE FORMULA RHOPLEX (TM) N-1031 acrylic latex from Rohm & Haas Co. 375 lbs.

Cymel (TM) 325 melamine-formaldehyde cross-linking agent 11.5 lbs.

Isopropyl alcohol 11.5 lbs.

Water 23 lbs.

(3 components listed immediately above were premixed before combination with the acrylic latex) Foamaster NXZ defoamer from Diamond Shamrock Chemicals Co. 3 oz.

(Predispersed in an equal volume of water) The combination of materials as described above may be converted to a suitable laminated construction for use in the package forms of the present invention using a conventional wet bond laminator. on such a laminating machine the adhesive may be applied to either the paper substrate or the metallized surface of the film, or both, and then the paper and film are joined in a pressure nip with the machine running at about 200-800 feet per minute. A suitable adhesive application level will usually be in the range of 2-5 pounds per 1000 sq. feet, and a typical level of about 3 bounds per 1000 sq. feet can be applied with a 110 line gravure applicator roll. Following the pressure nipping of the paper and the film with the adhesive layer sandwiched therein, the laminated stock may be run through a hot air curing oven to af fect the setting of the adhesive bond. A suitable oven temperature for stock running speeds of 300-600 feet per minute will be about 300 to 500 degrees F. Finally, the laminated stock will generally be rewound, possibly after passing over a chill roll after exiting the curing oven.

It is to be understood that the specific materials and wethods described above for the manufacture of a microwave interactive stock should not be taken to limit the scope of this invention. other materials may be used and the method of manufacture need not be lamination in all cases. The description that has been given is intended to only provide the reader with an understanding of the manufacture of one type of flexible microwave interactive stock suitable for use in the package form of this invention.

The blank 10 is flexible and includes panels 12, 14, 16, 18, 30 and 34. The numerals 22, 24 and 26 denote fold lines which extencl vertically, as shown in Figure 1, while the numerals 28 and 32 denote horizontally extending fold lines. As indicated by the stippling, panel portion 18 is provided with an adhesive, the adhesive facing the reader. The PET film 40 faces the viewer irL 12 Figure 1 and is adapted to become the inside of the pouch. Panel 12 mav include a transparent plastic strip 36 for viewing the foodstuff.

Referring now to Figure 2. an intermediate stage of manufacture or formation of the pouch is illustrated, and the reader will note that the flaps 30 and 34 have been bent upwardly 90 degrees, while side panels 34 have been bent upwardly 90 degrees, while side panels 14 and 16 are being folded over towards the the center. Later in the assembly, indicated at Figure 2, the adhesive on panel 18 is secured to a complimentary portion of the right-hand free edge of panel (16 (vertically extending and shown at Figure 1) to thereby form a seam. The adhesive on panel 18 is glued to the PET portion along the right-hand or free edge of panel 16, and then, as indicated at Figure 3, folding takes place about fold line 22.

A suitable adhesive for forming the seam of the subject pouch must exhibit good bonding to both the paper surface and..the opposing polyester film surface. Also, the adhesive must exhibit sufficient heat resistance to hold the seam secure even as the 'materials of the package become heated to temperatures as high as 400 degrees F.

due to the conversion of microwave energy to heat by the thin vacuumdeposited aluminvim coating on the polyester film. Of course, the adhesive must be suitable for a food packaging application and must be easy to apply with conventional equipment used for making pouches, bags, envelopes and similar package forms.

A suitable adhesive for this application, based on all of the considerations just discussed, is AIRFLEX 421, a self cross-linking, water-based vinyl acetate-ethylene copolymer adhesive supplied by Air Products and Chemicals, Inc. This adhesive is also likely suitable for scaling the end-flaps (30) and (34) of the subject pouch.

Figure 3 indicates the completed pouch. As will be apparent from the description now to be given, a foodstuff is placed into the pouch prior to its final and complete peripheral closure.

Referring now to Figure 5 of the drawings, the numeral 10 again denotes the pouch of this invention, the pouch being shown in a microwave cavity of a conventional microwave oven, the cavity being denoted by the numeral 50. The numeral 52 denotes a f oodstuf f typically a frozen foodstuff, such as a frozen pizza, having a crust on the bottom and having cheese on top. The numeral 54 denotes a space above the food product. It will be observed that the crust or bottom of the food product 52 is in direct thermal contact with the microwave interactive material.

During the heating process by the microwave energy in cavity 50, the microwave strike the pouch, with a portion of their energy passing through the microwave interactive material (the remaining three elements of the laminate being transparent to microwave energy of this frequency). This passthrough energy impinges upon the foodstuff and acts upon the foodstuff in the usuai manner of microwave heating. Another portion of the microwave energy generated by the klystron or other generator of the oven is absorbed by the microwave interactive material, causing the latter to increase in temperature. Because the volume of the envelope 10 is greater than the volume of the foodstuf 52, a space 54 is formed by hot vapors, mostly water vapor. This heated water vapor contributes to the uniform heating of the foodstuff, because it is - able to come into surface contact with any irregularly spaced 25 surfaces of the foodstuff. The bottom of the foodstuff 54, being in direct thermal contact with the microwave interactive material, is browned or crispened, due to the elevation of the temperature of the microwave interactive layer 42.

The pouch 10 has thus far been described as having a layer of 30 microwave material 4-9 over its entire surface. It is to be noted that it is not necessary.5 in some applications, that both the main panel 12 and the secondary panels 14, 16 (which form, effectively, 14 one other panel), be both provided with the interactive material. For example, only the panel 12 may be provided with the interactive material in forming the laminate. It will be further apparent that the interactive material need not be a continuous layer, but may be 5 applied in strips or in disparate islands or the like.

The various package forms that are within the scope of the present invention may be sealed to provide a closed environment for the food during the microwave cooking process, thereby maximizing the convective heating effect provided by the microwave interactive component and also retaining the moisture vapor from the food within the package. A totally sealed pouch is-shown at Figure 6.

Alternatively, and more desirable for some food products, the package may be open to some predetermined degree during the microwave cooking process, thereby permitting the escape of the moisture evolved by the food. For example, a pouch may be open at one end. , as shown at Figure 7, or at both ends, as shoi^ at Figure 8, during the cooking process; or a pouch may be provided with vent holes (60) above the food or along the sides of the pouch as shown at Figure 9. Another alternative within the scope of the present invention is to manufacture a pouch with at least a portion of the seal area made with an adhesive that will soften when heated particularly due to the heat generated by the microwave interactive. material. and allow the pouch to open spontaneously during the cooking process. A hot melt adhesive, such as an ethylene-vinyl acetate hot melt adhesive with a softening point of about 200 degrees F., can be used to affect this type of a self-opening seal. Figure 10 shows a pouch with a seal (70) made in the manner just described. Figure 11 shows another type of self-venting package form that is within the scope of the present invention. In this case, vent hole (80) is covered by a flap (82) that is sealed in place with a lowsoftening adhesive such as has been discussed above.

- One of the advantages of the package f orms of this invention over prior art packages is the ease of handling for placement in the microwave oven, removal from the oven after cooking, and especially for repositioning or reorienting the food in the oven at some intermediate point in the cooking process. In general the package forms of this invention have extended areas, such as the end seals of a pouch that provide a convenient means of lifting or turning the package. - When desired, supplemental tabs or handles can readily be incorporated into the design of a pouch, envelope or bag that embraces the essential elements of this invention. Further, that portion of the package that is intended to serve as a means for lifting or turning the package can be made devoid of the microwave interactive component, so that said portion of the package is not uncomfortably hot after the package has been in the microwave oven. Figure 12 shows a pouch with supplemental handles (90) and (92) of the type just described.

Food products that have two sides that are essentiallye the same, 1 A such as waffles or breaded fish portions, will gener&lly-s benefit from beingturned completely over, side-for-side, mi.y through the microwave cooking process. The pouch or envelope 'form of package, with the microwave interactive component covering both faces of the package, is ideal for such food products.- For example, the pouch form, with the full internal surface covered with the microwave interactive component, will allow breaded fish portions to be cooked uniformly on both sides, because of the ease of turning the pouch completely over at a mid-point in the microwave cooking process. This procedure brings each surface of the food into contact with the hot surface provided by the microwave interactive component during a part of the cooking process; and each surface of the food is also exposed for a period of time to a hot-air environment within the pouch. This provides an overall cooking effect that is not possible with prior art microwave food packages, including those that are intended specifically to provide a browning or crisping effect for the food.

- 16 The present invention encompasses package fornts that have more than one compartment or enclosed space for the containment of food. For example, a multi-corrpartment pouch way have either individual portions of the same food produce in each compartment, or a aulti-ccapartmnt pouch may have either individual portions of the same food product in each compartment, or a multi-compartment pouch way be designed to accomodate different food items in each compartment. In the latter case, the separate compartments may not all utilize the same microwave interactive component or have the same degree of coverage of the microwave interactive component. Figure 13 shows a two-compartment pouch with both compartments (100) and (102) of the same size.

A multi-conpartment pouch or bag or envelope can also be used to provide elevation of the food product above the resting surface in the microwave oven. For example, a two compartmental pouch, as shown at Figure 14, can be designed with a first compartment (110) that will contain a second sealed compartment (112) that will inflate, due to the heating of the air or moisture contained therein during the microwave cooking process. Such a self- elevating, two-compartrent pouch is placed in the microwave oven with the first compartment, containing the food, positioned above the inflating compartment. A controlled amount of water may be placed in the inflating compartment to insure adequate expansion of that compartment, and thereby adequate elevation of the food- containing ccopartment during the microwave cooking process. As embraced by the present invention, such a self-elevating, twoartment pouch will utilize a microwave interactive component in at least the food-containing compartment.

Package forms within the scope of the present invention way have design features that facilitate placement of the package, with the food contained therein, in the microwave oven in a predetermined position to either elevate the food above the resting surface in the oven or provide other advantages of orienting the package and food in a particular position within the oven. For examle, a A pouch as shown at Figur e 15 may be provided with a feature (120) that allows the package, containing the food, to be hung in a vertical position from a fixture in the microwave oven. Another package form with a special positioning feature is provided by a two-compartment pouch with a flexible section (130) joining the two compartments. Such a package form can beset up as an inverted "V" in the microwave oven. as shown at Figure 16. with the flexible section at the apex of the W" and the two compartments in an inclined vertical position.

As mentioned earlier, not all embodiments of this invention are totally flexible packages. Packages with a section of the package made from a stiff material may still use a flexible material for that portion of the package that conveys the microwave interactive component and utilizes the two critical design aspects of this invention described earlier. An example of such a package is shown at Figure 17, where a pouch (140) of the type that has been described in detail is secured to a piece of paperboard (142). A heat-resistant adhesive such as the adhesive used on the seams of the pouch is used to secure the pouch to the paperboard support. A package of this type, with a portion thereof made of a relatively stiff material such as paperboard, has certain specific advantages. Such a package will be preferred for some fragile food items, such as frozen pastries, that require more protection than that provided by a totally flexible package. This type of package, being relatively self-supporting, will also be preferred when no supplemental outer package of any sort is used to transport the product to market. A variation of the package form just discussed is s6own at Figure 18. In this variation, about half of the package is made from a flexible composite material (150) that contains a microwave interactive component, and about half is made from a relatively stiff material such as paperboard (152), with the flexible material formed into a contoured shape and joined to the stiff material to form an enclosed space for the food. As with all other package forms of this invention, the area covered by the microwave interactive component will exceed the bulk area of the food over the area of mutual contact between the food on the flexible portion of the package and the volume that the package provides for containment of the food during microwave cooking will be greater than the greatest bulk volume of the food at any point in the cooking process.

It will be understood that the envelope or pouch of this invention may be provided with an external paperboard sleeve of generally rectangular parallelepiped form for additional packaging. Figure 19 shows a pouch, such as has already been described, carried within a paperboard sleeve (160).

In some cases, a food item requires a package that provides some shielding of a part of the food from microwave energy along with the thermal heating effects that are provided by the microwave interactive component(s) of the packages of the present invention. When required, such sheilding can be included in the package form of the present invention by the placement of pieces of aluminum. foil either within the package, on the external surface or between the layers of the stock used to form the package.

Figure 20 shows a pouch with aluminum foil shielding strips (170) and (172) secured m the inside of the pouch. An adhesive of the type used to seal the seams of the pouch, e.g., AIRFLEX 421, can be used to secure the foil- strips to the pouch's interior surface.

It is not necessary in the practice of this invention to include 25 the microwave interactive component in the material that provides the overall shape of the package. For example, a pouch may be made as shown at Figure 21, with the primary structure of the pouch made from materials that are not microwave interactive (180), and an insert (182) of the general composition as shown at Figure 4 may be placed in the pouch to provide the required thermal heating effects.

19 - The package forms of this invention are adaptable to several methods of introducing the package into a food packaging operation. First. fully formed packages, such as pouches, may be supplied to the food packaging operation with only one end open for insertion of the food item. In such a case, the open end may be sealed after insertion of the food, or the package may be simply left in this open form and possibly placed in an outer carton for distribution. A second approach, uses blanks., such as the unitary blank that has been described in detail herein. with such blanks supplied to the food packaging operation. In the practice of this second approach, the formation of the blank into the final package form and the placement of food therein may be carried out in a variety of different manners, including, for example, placement of the food upon the blank before making any of the seals to establish the package form. In a third approach, a roll stock, such as a laminate of lightly-metallized film and paper as has been described, may be supplied to the food packaging operation. Such a roll stock may be run on a food packaging line that cuts, forms and seals the stock to make the packages and places the food therein, as a simple operation.

A particularly useful form of roll stock for use on a food packaging line as described above is shown at Figure 22. This roll stock (190) has a suitable heat-seal adhesive (192) printed on the inside surface of the stock in a pattern corresponding to the seal areas in the completed package. By applying the adhesive to the stock in such a pattern, it is feasible to avoid the presence of the adhesive in those areas of the package that will be in contact with the food. The adhesive pattern may be printed on the stock by conventional means, such as gravure or flexoprinting. A suitable printable heat-seal adhesive for use on a roll stock of this type is available from Roymal, Inc., as product #42151, a water-based, heat-seal coating.

Figure 22 shows further how a single blank (194), cut from the roll stock, is folded along center line (196) with the food in place on one half of the blank (52), and finally the pouch is heat-sealed along the edges (200), (202), and (204) to provide a finished package containing the food. Roll stock (190) is a laminate of paper and lightly metallized polyester film as has been described earlier.

Q

Claims

1. A unitary blank for forming a microwave food package, said blank defined by a flexible generally planar laminate having layers of, from one of its surfaces to the other, (1) PET, (2) a microwave interactive material, (3) an adhesive, and (4) paper, said blank having adhesive areas, said blank provided with a plurality of fold lines to permit it to be folded to thereby cause said adhesive areas to adhere together and thus form a pouch adapted to contain a foodstuff therein, said pouch adapted to be subjected to microwave oven radiation to thereby cook a foodstuff therein.

2. The blank of claim 1, characterized by the fact that said adhesive areas are on that surface of said PET layer which is not in contact with said microwave interactive layer.

3. The blank of claim 2, characterized by the fact that said blank is generally rectangular and wherein said adhesive areas are located at peripheral portions of said blank.

4. The blank of claim 3, characterized by the fact that one portion of said blank is provided with a window forming strip of transparent and flexible plastic material.

5. A pouch for microwave oven cooking of foodstuffs, said pouch formed from a laminate, the laminate defining a unitary blank according to claim 1, said blank having layers of, from one surface to the other, (1) PET, (2) a microwave interactive material, (3) an adhesive, and (4) paper, said blank having folded fold lines and having peripheral portions thereof adhered together to form a generally flat envelope, said pouch having an entrance peripheral portion not adhered together to thereby form an opening into which a foodstuff is adapted to be inserted, said entrance peripheral portion adapted to be closed subsequent to the insertion of a foodstuff into the pouch.

6. The pouch of claim 5, characterized by the fact that said pouch is generally rectangular.

7. The pouch of claim 6, characterized by the fact that one portionof said pouch is provided with a strip of transparent and flexible plastic material.

8. A food package for a foodstuff including a pouch and a foodstuff therein, said pouch formed from a flexible, unitary laminate blank according to claim 1, having layers of, from one of its surfaces to the other, (1) PET, (2) a microwave interactive material, (3) an adhesive, and (4) paper, the volume of said foodstuff being less than said internal volume of said pouch.

9. The food package of claim 8, characterized by the-fact that it includes at least one strip of a microwave opaque material overlying a portion of said foodstuff.

10. The food package of claim 8, characterized by the fact that it includes a paperboard stiffening member secured to an outer surface of said package.

11. The blank of claim 1, characterized by the fact that the surface area of said microwave interactive material is less than the surface area of the other components of said laminate.

r 'J

12. A unitary blank for forming a microwave food package, substantially as described herein with reference to and as illustrated in the accompanying drawinas.

13. A pouch for microwave cooking of a foodstuff, substantially as described herein with reference to and as illustrated in the accompanying drawings.

14. A food package including a pouch and a foodstuff therein, substantially as described herein with reference to and as illustrated in the accompanying drawings.

Published 1989 at The Patent OfEce, State House, 68171 High Holborn, London WC1R4TP. Purther copies maybe obtained from The Patent Sales Branch, St Mary Cray, Orpington, Kent BR5 3BD. Printed by Multiplex techniques ltd, St Mary, Kent, Con. 1187