DE69027447T2 - FOOD PACKAGING FOR USE IN MICROWAVE OVENS - Google Patents

Description

TECHNICAL AREA

The invention relates to microwave food packages which are packages suitable for microwaveable articles, such as food pieces accommodated in the packages for cooking and/or frying and possible browning of the food pieces. This includes packages suitable for storage, transport and marketing with food pieces contained therein, as well as packages suitable for containing food pieces which are introduced where the heating and frying takes place: e.g. in the consumer's kitchen. This also includes microwave food packages which have features enabling consumption from the package: i.e. features enabling the consumer to open the package so that it becomes a serving container for the foodstuffs contained therein.

STATE OF THE ART

A microwavable food package and carton comprising microwave receptors (i.e., materials that are heated by internally generated heat when exposed to microwave energy) for browning and frying two sides of food pieces contained therein is disclosed in U.S. Patent 4,590,349, Microwave Cooking Carton for Browning and Frying Food on Two Sides, which patent issued to Brown et al. on May 20, 1986. It is particularly directed to browning and frying two sides of food pieces that are not of uniform dimensions; the carton has an internal height that exceeds the average length of the food pieces; and it is stated that the package is inverted during microwave heating so that the food pieces are in contact, by gravity, with a food support layer located in the upper region of the carton.

A microwaveable food carton comprising a unitary mid-height food carrier sheet having a plate of microwave interactive material disposed on one surface is disclosed in U.S. Patent 4,836,383, Microwave Food Carton With Divider Plate, which patent issued June 6, 1989 to Gordon et al. Essentially, the construction of the carton is such that the food contained in the carton is elevated above the carton bottom onto an intermediate shelf: i.e., onto the mid-height food carrier sheet. Thus, the microwave interactive material on the mid-height food carrier sheet causes the carrier sheet to have a hot plate which effects heating of the food placed thereon. The stated function of the microwave interactive plate is to brown or sear the contacted surface of the food product.

Other U.S. patents disclosing microwaveable food packages and browning of food contained therein are: No. 4,190,757, Microwaveable Package and Method, issued February 26, 1980 to Turpin et al.; No. 4,267,420, Packaged Food and Method for Achieving Microwave Browning, issued May 12, 1981 to Brastad; No. 4,594,492, Microwaveable Package Containing a Spring-biased Browning Layer, issued June 10, 1986 to Maroszek; and No. 4,777,053, Microwaveable Package, issued October 11, 1988 to Tobelmann et al.

Further disclosures of microwave cartons, packages and receptacles are contained in the following U.S. Patents: Nos. 4,641,005 and 4,825,025, both entitled Food Containers for Microwave Cooking, issued February 2, 1987 and April 25, 1989, respectively, to Oscar E. Seiferth; and No. 4,230,924, Method and Material for Prepackaged Foods to Achieve Microwave Browning, issued October 28, 1980; and No. 4,864,089, Localized Microwave Radiant Heating, issued September 5, 1989, to Tighe et al. Tighe et al. (4,864,089) discloses the design of microwave pickup layers on suitable substrates by applying or printing a plastic binder with conductive and semiconductive particles.

The microwave suspector technology is further discussed in "Microwave Suspector Use Continues To Be Hot Topic, Paper, Film & Foil Converter", January 1989, pages 62-64 inclusive. In addition, the frying technique, which is considered incidental to the present invention, is disclosed in U.S. Patent 4,590,080, Method for preparing parfried and frozen potato products, issued May 20, 1986.

US-A-4,943,439 discloses a package for heating food products, particularly frozen French fries. The package of US-A-4,943,439 provides a complex non-planar receiver having protrusions to create a receiver surface that is adjacent to each surface of the food product, i.e., the top, bottom and both sides.

DISCLOSURE OF THE INVENTION

A microwave food package is provided in one embodiment of the invention which comprises a container, such as a disposable carton, a number of layers of pieces, such as food pieces, and sufficient microwave receptor layers, with portions of the microwave receptor layers disposed on adjacent, opposing surfaces of the food pieces. The package preferably further comprises means for ventilating the container during microwave heating and means for opening the container after heating has been completed so that the container is converted into a serving container. The container is preferably sized and constructed with respect to the food pieces and layers so that the layers of food pieces can be accommodated such that the microwave receptor layers and the adjacent surfaces of the food pieces are in intimate contact; and the container further comprises means for maintaining such intimate contact while the package is being heated in a microwave oven. Preferably, the food pieces have a uniform thickness and have opposing flat surfaces so that close contact is facilitated and therefore enables the direct conductive heating of these surfaces by the microwave sensors while the package is subjected to microwave energy in a microwave oven for a sufficient time interval. The microwave scavengers are preferably sized to effect sufficient heating to give the food pieces a well-done appearance. A two-layer embodiment of the invention comprises an upper microwave scavenger layer, a lower microwave scavenger layer, and a mid-height microwave scavenger layer; and a three-layer embodiment comprises an additional mid-height microwave scavenger layer. Individual microwave scavenger layers may be used within a container, or alternatively, microwave scavenger material may be disposed on surfaces of integral portions of the container and preferably covered with a protective material such as a thermoplastic film. In addition, the two mid-height microwave scavenger layers of a three-layer embodiment may be combined into a unitary element to facilitate simultaneous removal. In another embodiment of the invention, two means for opening the container are provided, whereby the container can assume a cup-like shape or alternatively a tray-like shape.

SHORT DESCRIPTION OF THE DRAWING

While the specification concludes with claims particularly pointing out and distinctly claiming the subject matter regarded as the invention, it is believed that the invention will be better understood from the following description, taken in conjunction with the accompanying drawings, in which like aspects are indicated by like reference numerals throughout the several views, and different aspects of the several embodiments are indicated by reference numerals having like tens and units numerals, and in which:

Figure 1 is a perspective view of an embodiment of a package of the invention, which package comprises a carton having inside several layers of equally sized and shaped food pieces and having its lid arranged in its open position;

Fig. 2 is a perspective view of an empty carton according to the type shown in Fig. 1;

Fig. 3 is a plan view of a microwave pickup layer arranged at mid-height in the carton of Fig. 1;

Fig. 4 is a perspective end view of an embodiment of a package of the invention after it has been opened;

Fig. 5 is an end perspective view of the package of Fig. 4 after its side walls have been depressed inwardly and its front and rear walls have been bulged outwardly so as to facilitate consumption of the food items arranged in the package;

Fig. 6 is a rear perspective view of the package of Fig. 5 with an optional holder of the carton in its erected position;

Figure 7 is a perspective, partially broken away view of an alternative embodiment of a microwave food package of the invention;

Fig. 8 is a perspective view of the package of Fig. 7 with two ventilation flaps in their open positions, and with the package in its preferred orientation for placement in a microwave oven;

Fig. 9 is a fragmentary perspective view of the package of Fig. 8 after its fastening closure has been lifted and one of its two mid-height microwave pickup layers has been partially removed;

Fig. 10 is a perspective view of the package of Fig. 8 after it has been repositioned so that it lies on its bottom layer and its upper layer regions are opened to provide access to the contents of the package for layer-by-layer consumption;

Fig. 11 is a plan view of a carton blank which can be assembled to form the carton of the package shown in Figs. 7 to 10;

Fig. 12 is a plan view of an alternative embodiment of the mid-height microwave pickup layer;

Fig. 13 is a fragmentary cross-section of the alternative embodiment of the mid-height microwave pickup layer of Fig. 12;

Figure 14 is a plan view of a unitary, double, medium height microwave pickup layer for use in an embodiment of the package of the invention;

Figure 15 is a perspective view of an embodiment of the package of the invention having a double mid-height microwave pickup layer of the construction shown in Figure 14;

Fig. 16 is a plan view of a carton blank which can be assembled to form a carton having two integral microwave receptor layers of intermediate height;

Fig. 17 is a cross-section of a carton formed by assembling a carton blank of the construction shown in Fig. 16;

Fig. 18 is a perspective view of a carton formed by assembling a carton blank of the construction shown in Fig. 16, but before it has been filled and before its integral intermediate height layers have been folded into the interior;

Fig. 19 is a sectional view of the carton shown in Fig. 18;

Fig. 20 is a section through the carton of Fig. 19 after a layer of the food pieces has been filled;

Fig. 21 is a section through the carton of Fig. 20 after a second layer of the food pieces has been filled in and with an integral microwave pickup layer arranged at mid-height between the two layers;

Fig. 22 is a section through the carton of Fig. 21 after it has been fully filled with three layers of the food pieces and with its two integral microwave pick-up layers arranged at mid-height between the layers;

Fig. 23 is a section through the filled carton of Fig. 22 after the lid has been closed;

Fig. 24 is a plan view of an alternative embodiment of the carton blank that can be assembled to form a carton having two integral intermediate height microwave receptor layers;

Fig. 25 is a cross-section of the carton formed by assembling a concrete blank of the embodiment shown in Fig. 24;

Fig. 26 is a perspective view of an opened package comprising a carton blank of the embodiment shown in Fig. 24 with the top layer of food pieces removed and portions of the upper mid-height receiver layers folded back to provide top access to the middle layer of food pieces.

DETAILED DESCRIPTION OF THE INVENTION

A microwave food package 30 embodying the present invention is shown in Fig. 1 prior to sealing and comprises a carton 31, a microwave receiving layer 32 of intermediate height having an upturned and recurved corner, and a number of elongated food pieces 33 arranged side by side, laterally spaced, substantially parallel to one another in several layers. The carton 31 further comprises, as shown in Fig. 1, a lid 34 having an upper wall 35 provided with a microwave receiving layer 36 attached thereto: for example with adhesive. In a preferred embodiment of the package there are provided three layers of food pieces 33, although only two layers are visible in Fig. 1, and two microwave receiving layers 32 of intermediate height, only one of which is visible in Fig. 1. A microwave receiving layer 32 is arranged at intermediate height between the lower layer and the middle layer of food pieces 33; and the second microwave receiving layer 32, seen in Fig. 1, is disposed midway between the middle layer and the upper layer of food pieces 33. The package 30 preferably also includes a lower microwave receiving layer (not shown in Fig. 1) disposed beneath the lower layer of food pieces 33. Preferably, the lower microwave receiving layer is attached to the bottom wall of the carton 31 or is an integral portion thereof. The terms upper, lower, sideways, upward, downward and the like are relative terms and are not intended to imply any particular spatial orientation. Incidentally, although the food pieces 33 shown in Fig. 1 are laterally spaced from one another, it is not intended to limit the present invention to embodiments in which the articles are laterally spaced from one another.

Briefly, the invention provides a microwave food package in which, for example, multiple layers of food pieces having opposed planar surfaces are arranged relative to the microwave receiving elements of the package such that two opposed planar surfaces of each food piece are in closely fitted contact with the microwave receiving elements. This enables direct conductive heating by the microwave receiving elements, for example to effect the cooking and possible browning of the outer regions of the food pieces. when the package is heated in a microwave oven. The food pieces may, for example, be evenly shaped potato strips which have preferably been thoroughly fried before packaging. Such potato strips, whether thoroughly fried or not, are generally and hereinafter referred to as French fries, although they are not fried to a cooked state.

The lid 34 of the carton 31 comprises, as shown in Fig. 2, a top wall 35, an upper microwave receiving layer 36, a front flap 38 and side flaps 39, 40; a bottom wall 43, a rear wall 44, a front wall 45, and side walls 46 and 47. In addition, the rear wall 44 has strips 51 and 52, and the front wall 45 has strips 53 and 54. Preferably, the strips 51 to 54 are glued to the side walls of the carton so that an open, box-like bottom 55 of the carton 31 is formed, as shown. The carton 31 further comprises a lower microwave receiving layer 56 which can be attached to the bottom wall 43, for example by gluing. However, it is not intended to limit the present invention to such carton constructions having individual microwave receptor layers, whether attached or not. That is, the microwave receptor material may be applied directly to integral layers of the carton blank; or individual microwave receptors may be incorporated into the carton 31. After the carton 31 has been filled, the lid 34 is closed and the flaps 38-40 are attached to the walls 45-47.

Referring to Figure 2, the carton 31 is provided with opening means comprising a pre-weakened line in the lid 34. Such a pre-weakened line may, for example, be a perforated line or interrupted cut line in the lid 34 which enables the package/carton to be opened by tearing the pre-weakened line. Alternatively, a tear strip or other modern carton opening means may be provided. A tear strip or tear tape may be constructed to provide a hinged opening means similar to the hinged construction of Figure 4; or alternatively, a tear strip or tear tape may be constructed to enable the separation of a removable portion of the carton from a remainder: i.e. a serving container area.

The carton 31 further comprises, as shown in Fig. 2, means for venting so that escape of volatile components and the like is enabled when a package comprising a closed carton 31 is heated in a microwave oven. In the carton 31, as shown in Fig. 2, the means for venting is a number of vent holes 58 in the rear wall 44. Means for closing the vent holes 58 before heating the package may comprise a strip of peelable tape (not shown). Alternatively, of course, a tear tape may be integrated into the rear wall 44 or another area of the carton 31 so that the vent means are provided. Another, further, possibility is to wrap the package. Of course, in the case of wrapped packages, the wrapping must be removed before placing in a microwave oven. It is assumed that such wrapped packages do not require additional devices to close the ventilation holes.

Fig. 3 is a plan view of a preferred embodiment of an exemplary single mid-height microwave pick-up sheet 32. Pick-up sheet 32 is a laminate comprising a paper substrate 60 and an attached thermoplastic film 61 having a layer 62 of microwave interactive material such as metal, which layer is sufficiently thin that it can be heated to a sufficiently high temperature when exposed to microwave energy and the heating of the food will effect searing and browning. Pick-up sheet 32 is preferably constructed to conform to the internal dimensions of carton 31 and includes a pull tab 63. Preferably, the coated surface of the thermoplastic film is attached to the paper substrate but does not overlie pull tab 62 so that pull tab 62 is not directly heated by microwave energy. Referring to Fig. 3, the upper edge of film 61 is designated 64. Such application and coating may be carried out in accordance with U.S. Patent 4,825,025, which is hereby incorporated by reference. In addition, layers of this type used in the embodiments of the present invention were obtained from the metal fabrication department of Leigh-Mardon PTY, LTD, 9 Melissa St., Auburn, New South Wales 2144, and identified by them as VF.2172.75.A. This layer comprises a base of Microlamtm 44 which is a vapor deposited overlay of metal, which may be aluminum; and the layer has a basis weight of about sixty-two (62) grams per square meter and a nominal thickness of about seven hundredths of a millimeter (0.07 mm).

The package 30 is formed as shown in Figure 1 by placing a first layer of food pieces in the carton 31 and then positioning a first microwave pick-up layer at mid-height to cover the first layer; then placing a second layer of food pieces on top of the first microwave pick-up layer at mid-height; then placing a second microwave pick-up layer at mid-height to cover the second layer; then placing a third layer of food pieces 33 on top of the second microwave pick-up layer at mid-height; and then closing the lid and securing the flaps 38-40 to the walls 45-47. The package may further include an overwrap (not shown) to secure the closure and/or provide surface areas for instructions, product information and other desired packaging indicia.

The package 30 is preferably unopened and oriented in the position shown in Figure 4 when placed in a microwave oven and has the vent holes 58 open. This orientation is preferred during heating because the vent holes 58 are positioned facing upward. Of course, for packages that have outer packages, the outer packages are removed prior to placement in a microwave oven.

The package 30 is opened as shown in Fig. 4 and arranged in its preferred orientation for consumption: that is, with its rear wall 44 extending upwards and its upper wall 35 directed forwards. As shown, the upper wall 35 is divided into two regions 35t and 35b having edges 57t and 57b respectively. Such opening of the package 30 is achieved by tearing off the upper wall 35 of the carton 31 as shown in Fig. 2 and the upper take-up layer 36 along the above-mentioned pre-weakened line 57 and lifting the rear wall 44 and the upper wall region 35t to the position shown in Fig. 4. The region the upper microwave receiving layer 36 of Fig. 2, which is attached to the upper wall portion 35t, is designated as layer portion 36t in Fig. 4. It is of course preferable that the heating is completed before the package is opened, otherwise the intimate contact between the microwave receiving layers and the food pieces will be impaired.

Referring to Fig. 4, the opened package 30 has three layers of food pieces 33, which layers are separated from each other by the mid-height microwave pickup layers, with only the pull tabs 63 visible. Also shown in the wall area 35t are score lines 67 and 68. The score lines 67 and 68, as well as the score lines in the opposite wall surface of the carton, enable the carton 31 to be converted into a cup-shaped serving container by compressing the sides of the package toward each other. The cup-shaped carton achieved by such compression is shown in Fig. 5.

Fig. 5 is an end perspective view of the opened package 30 of Fig. 4 after it has been compressed in the manner described above to effect the shape shown in Fig. 5. Also, the mid-level pickup layers have been removed as evident by the absence of pull tabs 63 in Fig. 5, while pull tabs 63 are shown in Fig. 4.

6 is a rear perspective view of the opened package 30 of FIG. 5. In addition to the features of the carton 31 described above, this view shows score lines 71 and 72. The score lines 71 and 72 extend from the lower corners of the bottom wall 43 of the package 30 to the center of the score lines 73 which demarcate wall 43 from wall 44. The score lines 71 and 72, in conjunction with the score lines 67 and 68 of FIG. 5, effect the compression conversion of the carton 31 from the cuboid shape of FIG. 4 to the cup shape of FIG. 5 described above. Also shown in FIG. 6 is an optional handle 75 attached to the wall 43. The handle 75 has a central layer 76 attached to the wall 43; two folded layers 77 and 78; and a closure strip 79 which is a portion of the folded layer 78 and has a distal portion extending through an opening 80 of the folded sheet 77 so that the folded sheets 77 and 78 are connected together. Such a handle is preferably arranged in a flat condition until the package 30 is prepared for placement in a microwave oven. At this time, the handle is constructed in the configuration shown in Fig. 5. Preferably, the handle 75 does not comprise any materials that substantially react with the microwave energy so that it remains cool while the food pieces within the package 30 are heated.

EXAMPLE 1

A package having the construction shown above and described in connection with the discussed Figs. 1 through 6 was prepared as follows. The carton 31 was about three and one-half (3 1/2) inches (about 8.9 cm) from the front to the back, about four (4) inches (about 10.2 cm) wide and about seven eighths (7/8) inches (about 2.2 cm) high. The carton 31 was made from twenty-four (24) paperboard. The vent assembly includes five (5) one-quarter (1/4) inch (about 6.4 mm) diameter circular openings 58 in the wall 44. The microwave pickup layers 32, 36 and 56 were of the laminated type described above comprising a paper substrate and a thin thermoplastic film layer having a deposit of a evaporated metal (assumed to be aluminum) on its surface covering the paper substrate.

Carton 31 was filled with approximately eighty-five (85) grams of potato strips arranged side by side in abutting relationship in three (3) layers. The potato strips were approximately one-quarter (1/4) inch (about 6.4 mm) in cross-section and up to approximately three seven-sixteenths (3 7/16) inches (about 8.7 cm) long. The potato strips were selectively repackaged from conventional packages identified as Simplot Bake-A-Fry, Shoestring Frozen Potatoes; a product of the J.R. Simplot Company, Boise, Idaho. The potato strips are believed to have been cooked through; possibly as disclosed in U.S. Patent 4,590,080, issued May 20, 1986 to Richard K. Pinegar and assigned to Simplot. However, it is not intended to limit the scope of the present invention to potato strips in general or to well-done potato strips in particular.

In addition to the three layers of potato strips, two receiver layers 32 were placed between the layers in the carton 31. The carton was then closed and sealed with adhesive. This completed the preparation of the package 30. In particular, the sizes of the carton, the receiver layers and the potato strips were related to each other to create a close fit so that each potato strip had two opposing surfaces in close contact with surface areas of the receiver layers.

The package 30 was then placed, ventilated but unopened, in the orientation shown in Fig. 4 (with its rear wall 44 facing upward) in a Dual Wave II microwave oven manufactured by the General Electric Company and rated at about 625 watts. The oven was set to its high power setting and turned on for one hundred twenty-five (125) seconds. The package was then immediately removed from the oven and opened to the configuration shown in Fig. 4; the mid-level microwave pickups 32 were removed; and the sides of the carton were compressed so as to effect the configuration of Fig. 5.

In fact, the weight of the potato strips was reduced from about eighty-five (85) to about seventy-one and eight-tenths (71.8) grams: presumably due primarily to moisture loss. The potato strips were substantially evenly cooked and browned on their outer surfaces; and their masses were moist and meaty, like deep-fried French fries. In comparison, similar packages that did not have pick-up layers produced mushy, unbrowned potato strips when microwaved for the same time; produced uniformly chewy potato strips when microwaved for one hundred eighty (180) seconds in an extended cooked-through attempt in the absence of the microwave pick-up layers; and when microwaved for two hundred forty (240) seconds, produced French fries that were overcooked and tough throughout. In the absence of the pick-up layers, no time interval was discovered which produced the combination of a well-cooked outer surface with a meaty inner mass as envisaged by the present invention. In addition, a similar package, having the pick-up layers 36 and 56, but not having the mid-level microwave pick-up layers 32, for one hundred twenty-five (125) seconds at the same power and in the same oven specified above. The total weight of the potato strips was reduced from about eighty-five (85) to about seventy-two and two-tenths (72.2) grams. Examination of the potato strips revealed that the layers were not evenly cooked; and that the strips were not evenly cooked and brown on their outsides or meaty on the inside.

ALTERNATIVE DESIGNS

The package 130, as shown in Figure 7, which is a perspective view of an alternative embodiment of the present invention, comprises a carton 131 and three (3) layers of food pieces 33, such as potato strips. A portion of an upper microwave receiving layer 136 is visible through a hole torn in the top wall 135 of the carton 131, which hole is indicated by edge 137a; and some food pieces 33 are visible through a hole torn in the upper microwave receiving layer 136, which hole is indicated by edge 137b. Also visible through a hole torn in the side wall 146, which hole is defined by edge 148, are two mid-height microwave receiving layers 132 disposed between the layers of food pieces 33; and a lower microwave pickup layer 156 is disposed between the lower layer of food pieces 33 and the upwardly facing surface of the carton's lower wall 143. The front flap 138 and the front wall 145 are also seen in Fig. 7.

The top wall 135 is divided as shown in Fig. 7 by pre-weakened lines 141a-141c and score lines 142a and 142b to provide hinged layers 135a and 135b when the carton 131 is opened, as described below. In addition, the side wall 146 of the carton 131 is divided as shown in Fig. 7 by pre-weakened lines 149a to 149d to provide support layers 146a and 146e, vent layers 146b and 146, and a strip layer 146c, the functions of which are described below.

Referring to Figure 8, the package 130 is oriented with its top wall 135 forward and its side flap 146 upward in the figure. The configuration and orientation shown in Figure 8 is the preferred configuration and orientation for placing the package 130 in a microwave oven for heating/cooking the food items. The vent layers 146b and 146d are opened and extend upwardly, allowing the escape of volatiles during microwave heating. A fastening layer 146c is in its closed position so that the edge regions of the top wall 135 and bottom wall of the carton are secured together. Therefore, the attachment layer 146c provides for maintaining intimate contact between the microwave receiving elements of the carton and the adjacent surfaces of the food pieces 33 during microwave heating/cooking. As stated above, the intimate contact between the microwave receiving layers and the adjacent surfaces of the food pieces is provided so as to effect or ensure cooking and possible browning of the outer regions of the food pieces.

The package 130 includes, as shown in Fig. 7, dual or double opening means to provide access for removing the food pieces. Such access is referred to as an eating access. One form of eating access is provided as shown in Fig. 9. Fig. 9 is a fragmentary perspective view of the upper portion of the package 130 after the fastening layer 146c has been opened to provide end access to the food pieces 33 disposed within the package. Furthermore, a mid-level microwave pickup layer 132 is partially removed from the package 130 to further facilitate end access for eating. Preferably, both of the receiving layers 132 are removed at mid-height so that eating access to the food pieces from the end is facilitated through the opening created by the opened layers 146b-146d of the carton 131.

A second form of edible access to the contents of the package 133 is provided by the carton 131, which is shown in perspective in Fig. 10, and is referred to as layer-by-layer edible access. In Fig. 10, the Layers 135a and 135b are opened, opening being made possible by tearing the pre-weakened lines 141a-141c of Figure 7 as described above. Some of the food pieces 33 comprising the upper layer have been removed as is evident by a visible portion of the microwave pickup layer 132 at mid-height. The layer 132 is of course removed as the upper layer of food is pulled away so as to provide access to the second layer, etc.

Fig. 11 is a plan view of a carton blank 131b that can be assembled to form the carton 131 shown in Figs. 7-10. The upper microwave receiver layer 136 and lower microwave receiver layer 156 of Fig. 7 are not included in Fig. 11 as they are not parts of the blank per se. However, this is not intended to preclude applying microwave receiver material to the blank (e.g., cardboard) as mentioned above as an alternative to attaching individual microwave receiver layers to the top and bottom walls of the carton blank.

An alternative embodiment of the mid-level microwave pickup sheet 232 is shown in the plan view of Fig. 12 and the fragmentary sectional view of Fig. 13 taken along section line 13-13 of Fig. 12. The sheet 232 has a double-sided corrugated construction which provides means for effecting uniform lateral spacing between elongated pieces placed in microwave food packages as described above. Such spacing may be provided to allow more volatiles of the pieces to escape during microwave heating. The layer 232 has, as shown in Figure 12, a pull tab 263 which remains cool during microwave heating due to the advantage of not being coated or covered with microwave sensing material, the edge 264 being the edge of the microwave sensing region of the layer 232.

An alternative microwave pickup layer 232 at mid-height is shown in Fig. 13 and comprises a flat sheet 281 and two corrugated sheets 282 and 283. Microwave pickup materials not shown may be included in one or more of the sheets: for example, by coating a vapor-deposited aluminum-coated thermoplastic film onto a paper substrate to form a sheet before the various sheets are bonded together in a corrugator.

Fig. 14 is a plan view of a mid-height double microwave layer 332 which may be used, for example, in place of the two single microwave receptor layers 132 of package 130 of Fig. 7. Double layer 332 comprises layers 332a, 332b and 363 separated from each other by edges 364a and 364b: the edges of the microwave receptor layers of layers 332a and 332b. Layer 363 is as wide as the thickness of the middle layer of pieces 33 of Fig. 7; it is not coated with microwave receptor material; and is constructed to provide a cool pull tab as described above.

Fig. 15 is a perspective view, similar to Fig. 9, of an alternative embodiment of microwave food package 230 having a mid-level double microwave receiver layer 232 as shown in Fig. 14. In Fig. 15, package 230 is opened from the end to provide eating access; side layer regions 146b-d extend upward; and double layer 332 is partially removed.

In addition to the embodiments of the invention described above, two further alternative embodiments and features are shown in Figs. 16-26 and are described below. These alternative embodiments include cartons characterized by layer divider sheets that are integral portions of their respective carton blanks: one of these alternatives is disclosed in Figs. 16-23 inclusive; the second in Figs. 24-26 inclusive. These alternative embodiments are also characterized by dual opening means as described above: end access for eating or top access by manipulating the sheets of the carton as described above in connection with the described package 130. Incidentally, in most of the views, the microwave receiving elements, sheets and surfaces are not shown so that the other elements of the cartons and packages can be better seen. It should be noted that these cartons and packages include microwave receiving materials on their top, bottom and layer divider walls and sheets so that each piece 33 placed therein is arranged closely between two microwave pick-up support walls and/or layers so that the cooking and browning of each of the pieces 33 is achieved as described above.

Referring to Figure 16, an alternative embodiment of a carton blank 431b is shown in plan view and includes a top wall 435, a bottom wall 443, a rear wall 444, a front wall 445, side walls 446 and 447, spacer plies 490 and 491, and integral ply divider plies 432a and 432b. Top wall 4323 is divided by pre-weakened lines 441a-441c and score lines 442a and 442b to provide hinged plies 435a and 435b. Side walls 446 and 447 are divided by pre-weakened lines to provide vent plies 446b and 446d and 447b and 447d, respectively; and fastening layers 446c and 447c, respectively, for the purposes described with respect to the corresponding elements of the carton 131. The spacer layer 490 has a height equal to the combined heights of the two layers of the pieces that will be packaged in the carton made from the blank 431b; and the spacer layer 491 has a height equal to the height of a layer of the pieces.

Fig. 17 is a cross-sectional view of a carton 431 formed by assembling a carton blank 431b according to Fig. 16, taken along a cutting line corresponding to cutting line 17-17 shown in Fig. 16. This view shows the relative positions of the one-piece layer divider sheets 432a and 432b as they would be arranged if there were three layers of pieces, such as the pieces 33 described above.

Fig. 18 is a perspective view of a carton 431 according to Fig. 17, before it has been filled and sealed. Figs. 19 to 23 show the steps of filling the three layers of pieces 33 into the carton 431, and folding the interconnected rows of layers 490, 432a, 491 and 432b so that the layers are arranged as indicated in Fig. 17. In Fig. 23, the filled carton 431 is identified as package 430; an alternative embodiment of the invention.

Briefly, carton blank 531b of Fig. 24 is a second alternative carton blank having integral layer divider sheets as described above. Carton blank 531 is preferably provided on its top and bottom walls with microwave receiver materials (not shown) as discussed above in connection with carton 130 and its integral layer divider sheets in the same manner before it is assembled and has the cross-sectional configuration shown in Fig. 25; and can be filled and substantially opened as indicated in Fig. 26.

Referring back to Figure 24, carton blank 531b includes a top wall 535, a bottom layer 543, a back wall 544, a front wall 545, side walls 546 and 547, and an interconnected series of layers including spacer layer 490, a first integral layer divider layer 532a, a spacer layer 591, a second integral layer divider layer 532b, and a closure layer 592. Part for part and feature for feature, the parts and features of carton blank 531b that correspond to those of carton blank 431b are identically numbered, but the reference numerals for blank 431b are in the 400 series and the reference numerals for blank 531 are in the 500 series. Accordingly, carton blank 531b is assembled, ventilated and opened in the same manner as described above with respect to carton blank 431b. However, the integral layer divider sheets 532a and 532b of carton blank 531b are divided by pre-weakened lines and score lines as shown so that they can be folded open to provide layer-by-layer eating access to the lower layers of the items packaged therein. The first integral layer divider sheet 532a is more specifically divided into sheets 532aa and 532ab by pre-weakened lines 594a-594c and foldable score lines 595a and 595b; and the second integral layer divider layer is divided into layers 532ba and 532bb by pre-weakened lines 596a-596c and hinged score lines 597a and 597b. Of course, such layer-by-layer eating access may also be included in carton blank 431b, although not so shown in the figure.

Fig. 25 is a cross-section through the carton 531 along the parting line corresponding to the parting line 25-25 of Fig. 24. The carton 531 is Assembling the carton blank 531b is formed as shown in Fig. 24 so that the layers and walls are arranged as shown in Fig. 25. Surface areas of the layers 590, 591 and 592 which cover areas of the walls 544 and 545 may be bonded together by adhesive, although this is not intended to limit the scope of the present invention. The carton 531 is filled with three layers of the pieces and closed so that the package 530 in Fig. 26 is formed.

The package 530 of Figure 26 is shown after being opened by folding back the upper sheets 535a and 535b; and after the upper layer of pieces has been removed and access to the second layer of pieces 33 is provided by folding back the sheet portions 532ba and 532bb of the upper integral layer divider sheet, as shown. Additionally, the wall portions 546b and 546d are shown in their open positions: the positions they would assume to allow ventilation of the package during microwave heating, as described above in connection with the other embodiments of the invention.

Reference numeral 536b of Fig. 26 designates a portion of a microwave receiving layer corresponding to layer 136a of carton 131 of Fig. 10. The other microwave receiving elements of carton 531, already mentioned above, are not shown in Fig. 26. Suffice it to say that carton 531 has microwave receiving materials on its walls and layers so that each piece 33 contained therein is tightly wedged between two microwave receiving retaining walls and/or layers to provide for the cooking and browning of each piece 33 as described above. The same applies to carton 431 of Figs. 17-23, wherein the microwave elements or surfaces have not been shown so that the other elements of the carton can be better seen.

While particular embodiments of the present invention have been shown and described, it will be apparent to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended by the appended claims to cover all changes and modifications that come within the scope of this invention.

Claims (17)

1. A package (30) for use in microwave heating opposing surfaces of a number of food pieces, which food pieces are arranged in at least two layers within the package, which package comprises: (a) container means for receiving at least two layers of food pieces, which food pieces have two opposing surfaces and at least two further surfaces; (b) a substantially planar upper microwave pickup (36); (c) a substantially planar microwave receiver (32) at an intermediate height between two adjacent layers of the food pieces; and (d) a substantially planar lower microwave receiver (56), which receivers are arranged in contact with the adjacent, opposing surfaces of the food pieces located in the adjacent layers, which substantially planar receivers are adapted to fry the opposing surfaces and the other surfaces of the food pieces in a substantially uniform manner, which receivers are the only microwave active elements in the package. 2. A package according to claim 1, wherein the food pieces are of uniform thickness and have substantially flat, opposing surfaces, and wherein the container and the receivers are sized and shaped with respect to the food pieces such that the food pieces are precisely fitted between the receivers and the flat surfaces are in contact with the surface areas of the receivers. 3. Packaging according to claim 2, in which the food pieces are elongated and arranged substantially parallel to one another. 4. A package according to claim 3, comprising means for forming a lateral spacing between adjacent food pieces in each layer of food pieces. 5. A package according to claim 1, 2, 3 or 4, wherein the food pieces are potato strips. 6. Packaging according to claim 5, in which the potato strips are baked before packaging. 7. A package according to claim 1, 2, 3 or 4, wherein the food pieces are reconstituted potato strips. 8. Packaging according to claim 1, with a device for ventilating/de-ventilating the container during the treatment of the packaging with microwave energy. 9. Packaging according to claim 1, comprising means for opening the container to convert the container into a serving container. 10.Packaging according to claim 1, comprising a double opening device, through which a consumer can selectively open the packaging to provide access to the food pieces from the end or access to the food pieces layer by layer. 11. A package according to claim 1, wherein the container is a integral construction and each of the inserted microwave receiver plates comprises an integral portion of the container on which microwave receiver material is disposed. 12.Packaging according to claim 1 for use in microwave heating of two opposing surfaces of a number of articles arranged in at least two layers within the packaging, which packaging comprises: (a) a container means having a top layer and a bottom layer, which container means is dimensioned with respect to the thickness of the articles so that contact occurs between opposing surfaces of microwave receptors and adjacent articles, which container can accommodate at least two layers of the articles, which articles have an upwardly facing surface, a downwardly facing surface and at least two further surface areas; (b) a substantially planar upper microwave pickup (36) disposed in contact with the upwardly facing surface of the articles disposed in the layer of articles disposed immediately below the upper layer; (c) a substantially planar mid-height microwave pickup (32) disposed between two of the layers adjacent upwardly and downwardly, the mid-height microwave pickup being in contact with the upwardly facing surface of the objects disposed in a layer of objects immediately below the mid-height pickup and in contact with the downwardly facing surfaces of the objects disposed in a layer of objects immediately above the mid-height pickup; (d) a substantially planar bottom microwave pickup (56) in contact with the downwardly facing surfaces of the articles arranged in a layer of articles immediately above the bottom layer, the substantially planar pickups being adapted to cook the upwardly facing surfaces and the downwardly facing surfaces of the articles in a substantially uniform manner, the pickups being the only microwave active elements in the package; (e) means for venting the container to allow the emergence of volatile components given off by the articles when the packaging is heated in a microwave oven; and (f) means for opening the container to enable the articles to be removed upon completion of their heating in the microwave oven, the container becoming a serving container. 13. Packaged food products according to claim 12, wherein one or more of the receptors comprise integral portions of the container upon which microwave receptor material is deposited. 14. Packaged food product according to claim 1, 12, wherein two layers are provided. 15. A packaged food product according to claim 1, 12, wherein three layers are provided and wherein two intermediate height receivers are provided. 16. A packaged food product according to claim 15, comprising means for simultaneously removing the intermediate height sensors when opening the container. 17. A packaged food product according to claim 16, wherein two intermediate height receivers are combined into a unitary part.