AU635667B2

AU635667B2 - A container

Info

Publication number: AU635667B2
Application number: AU86700/91A
Authority: AU
Inventors: Maurice Courteney Groves; Geoffrey Ronald Hamblin
Original assignee: Amcor Limited
Priority date: 1991-01-29
Filing date: 1991-10-24
Publication date: 1993-03-25
Anticipated expiration: 2011-10-24
Also published as: AU8670091A

Description

I

635667

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT 0es go* :0.o too.

we *0 0 0 Name of Applicant: Actual Inventors: Address for Service: Invention Title: AMCOR LIMITED MAURICE COURTENEY GROVES GEOFFREY RONALD HAMBLIN CULLEN CO., Patent Trade Mark Attorneys, 240 Queen Street, Brisbane, Qld. 4000, Australia.

A CONTAINER 00 0 0 00 0 0 Details of Associated Provisional Applications: Nos. PK4354 The following statement is a full description of this invention, including the best method of performing it known to us: 2 THIS INVENTION concerns a container for storing food products and for use in heating the food product in a microwave oven.

Pastry based convenience foods are available and have traditionally been heated and kept hot for sale in a conventional oven. Such ovens tend to achieve a crispy brown crust on the food product and this is desirable. However the vendor must ensure that an adequate quantity of product is always kept at a ready temperature and condition and it is difficult to precisely determine what quantity is necessary.

Dee* This leads either to an undersupply in which case custom is lost or an oversupply in which case wastage may result as the See product cannot or should not be re-heated many times. Where a variety of different food products, say with different fillings, is to be provided, these difficulties are compounded.

The advent of microwave ovens has to a large extent eliminated the need to keep quantities of food products warm in an oven. With a microwave oven it is possible to heat food eo products quickly on demand from a frozen or thawed state.

S

Thus large quantities of food need not be kept warm ready for S. sale.

Microwave heating of pastry products does not result in a crisp brown texture but rather the product tends to have a soggy texture and does not brown. This is undesirable.

It has been proposed to employ microwave interactive layers or materials in food containers which were intended to overcome this problem. Ceramic dishes which become hot when 3 heated in a microwave oven have been proposed to overcome this difficulty. Such dishes are heavy, fragile and expensive and unsuitable for fast food or convenience food products were it desirable to sell the product in a disposable container with a minimum of handling.

Plastic film having a thin metal coating or including a microwave interactive material has also been proposed. Such film is generally placed into direct contact with the food product. Experiments have shown that a better result is possible where the material is in fact spaced from a the food product rather than in contact with it. Better crisping or browning results.

United States patent specification 4,626,641 discloses a container made of paperboard for uniformly heating and crisping the top crust of a food product. The container has a top panel having a flat layer of microwave interactive material on its undersurface and spaced from the product by a distance less than 2.7 cm which converts microwave energy into radiant heat for browning and crisping the top surface of the product. The food product in this instance does not have a lower crust and in any event this container is unsuited for crisping anything but the top surface.

This specification recognises the need for spacing between the food product and the microwave interactive layer and states that crisping is achieved by spacing this layer from the product with effectiveness being lost once a predetermined maximum spacing is exceeded.

United States patent specification 4,590,349 discloses a container having twb microwave interactive layers and at least one of these layers was in contact with the food product. This rendered the container less effective.

United States patent specification 4,703,148 disclosed a container similar to that of specification 4,590,349 except that vent openings were present. Microwave heating or susceptor panels were in direct contact with the food.

United States patent specification 4,777,053 discloses a further container for food. The container in one 9 embodiment had a heating layer which was corrugated and either the upper or lower layer or both were made of such a material and was said to be in contact with the food product.

Most of these earlier proposals did not appreciate that spacing between the food product and the microwave interactive layer was necessary or if they did made no real attempt at crisping or brown 'more than the top and/or bottom of the food product.

It is an object of the present invention to provide a container which at least minimises the disadvantages

S

referred to above.

According to one aspect of the invention there is 9 provided a container for a food product for use in storing and heating the product in a microwave oven, the container including a top panel and a bottom panel, a microwave interactive layer adhered to each said panel by an adhesive which is able to melt when the container is employed to heat the product and at least 'one of the layers can thereby be released from the panel, each said layer having a corrugated layer of metallized film bonded to a substrate.

The microwave interactive layer, as mentioned, includes a corrugated metallized film. Preferably the film is metallized polyester. The film may have an optical density of about 0.24 10%. The corrugations preferably have a height of between 2.4 to 3.4 mm. A particular preferred height is about 3 mm or B flute. The layer includes film and a substrate. The substrate may consist of a corrugated paper medium, preferably bleached kraft paper. The film and medium may be bonded to a planar liner preferably of kraft. paper.

0S00 The planar liner is secured to the panel such that the food product may contact the film.

0**o The corrugations may either extend lengthwise or transversely of the panel.

The container may include opposed pairs of end and side walls hinged to the top and bottom panels. The walls may either extend at right angles to the panels to result in a 0* right prismatic container or at some other angle in which case the container may comprise two shells of frusto pyramidal shape. The shells may be present as separate parts and in *g.0 which case the container is a two part container.

Alternatively the shells may be integrally formed by having an end wall of one shell hinged to an end wall of the other shell. The other end wall of each shell may be provided with complementary locking means. In one embodiment the locking means comprise locking extensions on respective end walls.

Either the end or side walls may have opposed joinder flaps hinged thereto. Preferably these flaps are hinged to end walls of the container and secured to an adjacent side wall. The flaps may be secured by an adhesive.

Preferably a high temperature acceptance adhesive is employed.

PV is suitable.

The side walls may have peripheral cut outs which provide for venting during heating of the food product.

A particular preferred embodiment of the invention will now be described with reference to the drawings in which: Figure 1 is a view of a blank from which a nontainer according to an embodiment of the invention may be made; *see Figure 2 shows a perspective view of a container made from the blank of Figure 1; 6 Figure 3 shows a perspective view of the container of Figure 2 in its closed position; and Figure 4 shows another view of the blank of Figure 1 with one of the microwave interactive layers removed.

The container blank 10 of Figure 1 is made from any suitable paperboard, cardboard or corrugated material or other *060 microwave transparent material. In this instance double faced corrugated board is employed. Typically, the corrugations are E flute (average height of 2.46 mm) although other flute sizes may be used.

The blank 10 has an upper panel 11, with two opposed side walls 12, 13 and two opposed end walls 14, 15. These walls and the panel 11 form, in a container made from the blank, an upper shell. Walls 14 and 15 are formed with hinged joinder flaps 16 and 17 respectively joined to the wall by fold lines 18. These fold lines may be perforated to give a crisper fold. A cut 19 separates flaps 16, 17 from walls 12, 13.

The panel 11 is covered with a corrugated microwave interactive layer or sheet 20, the corrugations of which are more readily seen in Figure 2. The layer or sheet 20 consists of an outer corrugated metallized polyester film, typically reflective to a desired extent and having an optical density of about 0.24 10%. The film absorbs microwave energy and radiates heat for browning and crisping a food product placed 0 within the container. The film 20 is carried by a similarly corrugated bleached kraft paper medium and a planar sheet of kraft paper is bonded to the medium to act as a liner. This composite is secured to the panel 11.

Experiments have shown that the corrugations may have a height of about 3 mm (that is, B flute) to achieve the best browning and crisping result. A range between 2.4 to 3.4 a *es, mm is acceptable. These corrugations not only ensure that the food product is kept an optimum distance from the microwave interactive layer but allows moisture or oil released from the food product to escape. The corrugations may extend lengthwise or transversely of the blank. The walls 12, 13 may be likewise covered with a similar microwave interactive layer.

The blank has a lower panel 30, opposed side walls 31, 32 and opposed end walls 33, 34. These walls and panel form a lower shell of a container when the blank is made up.

Walls 33, 34 have joinder flaps 35, 36 respectively hinged thereto by fold lines 37. These fold lines may be perforated to provide a crisper fold. Flaps 36, 37 are separated from adjacent panels by a cut 38.

Walls 34 and 14 are hinged about fold lines 39 to provide a unitary blank. Panel 30 is provided with a microwave interactive layer 40 identical to layer Walls 15 and 33 have opposed locking extensions 41, 42 undercut at 43, 44 respectively. Walls 12, 13, 31, 32 have recessed portions 45 alonq their free edges which when the container is closed prove vent openings 46 (see Figure 3).

ooo ,The inner surface of the blank is coated with a grease and moisture resistant coating typically a water based polymeric emulsion which can be applied at the size press employed to make the material from which the blank 10 is cut.

Figure 2 shows a container 50 made from the blank of Figure 1. The container of Figure 2 results when flaps 17 and 36 are glued to adjacent walls 12, 13 and 321, 32. A PVA adhesive or other suitable high temperature acceptance ,ee. adhesive is used for this purpose.

C

Figure 3 shows the container 50 in its closed

C

position with locking extensions 41, 42 (see Figures 1 and 2) engaged. The container 50 may be opened by moving the shells

C

relative to one another in the directions of arrows A and B.

Figure 4 shows one way in which layers 20 and 40 may be secured to panels 11 and 30. A hot melt adhesive is employed and this adhesive may be applied at one or more locations 51. The adhesive is chosen such that the heat generated by the layers 20, 40 and of course the food product 9 is sufficiently high to melt the adhesive and release the layers 20, 40 from respective panels 11, 30. Once this occurs there is a tendency for the layers then to be able to curl around ends of the food product. The layers 20 (not shown) and since they have a planar sheet of kraft paper on one side and are corrugated on the other have a natural tendency to curl away from the panel to which they are glued. In this way the layers curl around ends of the food product and those ends are :l.so browned and crisped without the need for any additional microwave interactive layer.

*a A preferred hot melt adhesive for the purpose a described above has the following preferred characteristics: Raw Material Base :Synthetic Resin Colour Ivory/Opaque Viscosity 400 cps Ring Ball Softening Point 79C Application Tfmperature Range 140-180°C Speed of set Fast 8 i The PVA adhesive employed to glue the joinder flaps to the adjacent side walls may have the following preferred a characteristics: Raw Material Base :Synthetic Resin

C

Type :Emulsion Solids (oven dry) :54-55% pH :4-6 Viscosity (Brookfield) 1400-1600 cps 25 0

C

Specific Gravity 1.08 Colours Clear and Red The container is of such a construction that the food product has sufficient space between it and the upper interactive laj3r to allow for any expansion of the product.

The corrugations in the liyers ensure that at least some of the product is not in direct contact with the interactive layer and thus effective browning and crisping is assured.

6 f* 4 *4

Claims

1. A container for a food product for use in storing and heating the product in a microwave c the container including a top panel and a bottom panel, a microwave interactive layer adhered to each said panel by an adhesive which is able to melt when the container is employed to heat the product and at least one of the layers can thereby be released from the panel, each said layer having a corrugated layer of metallized film bonded to a substrate.

2. The container of Claim 1 wherein both said microwave 0 interactive layers release from the panels upon heating in a microwave oven.

3. The container of Claim 1 or 2 wherein the panels form part of an upper shell and a lower shell consisting of side walls hinged to edges of the panels.

4. The container of Claim 3 wherein the shells are &ieA hinged relative to each other and formed from a unitary blank a L of foldable material.

5. The container of Claim 3 or 4 including vent openings in opposed sides of each of the shells.

6. The container of any one of Claims 3 to 5 including complementary locking means provided on the shells. 4 0

7. The container of any one of Claims 1 to 6 made from a blank of foldable material selected from paperboard, cardboard and corrugated paperboard or cardboard.

8. The container of Claim 7 made from double faced corrugated board material. The container of any one of Claims 1 to 8 wherein 12 the metallized film has an optical density of about 0.24. The container of any one of Claims 1 to 9 wherein the corrugations of the film have a height between 2.4 to 3.4 mm.

11. The container of Claim 10 wherein the corrugations of the film have a height of about 3 mm.

12. The container of any one of Claims 1 to 11 wherein the microwave interactive layer consists of said metallized film and a corrugated paper medium as the substrate.

13. The container of Claim 12 wherein the corrugated paper medium is bonded to a planar liner.

14. The container of any one of Claims 1 to 13 wherein the microwave interactive layers are adhered to the panels by a hot melt adhesive. U.

15. The container of Claim 14 wherein the hot melt adhesive has a synthetic resin base, a viscosity of about 400 c ps, a ring and ball softening point of ab 79 0 C and an 0 0**O application temperature range of between 140-180 0 C.

16. A container substantially as herein described with 0q. reference to the drawings. 9 DATED this 24 day of October, 1991 AMCOR LIMITED By their Patent Attorneys CULLEN CO. ABSTRACT A container (50) is disclosed having, a lower panel with opposed side walls (31, 32) and opposed end walls (33, 34) defining a lower shell. An upper shell is hinged to the lower shell and is defined by end walls (14, 15), side walls (12, 13) and an upper panel Corrugated microwave interactive sheets (20, 40) are secured to the upper and lower panels respectively with an adhesive which enables the sheets to release from the panels when the container is heated in a a microwave oven. 4 4 0 a. C i S S S