AU680415B2 - Microwave oven heatable food package - Google Patents

Description

OPI DATE 29/11/93 AOJP DATE 10/02/94 APPLN. ID 42545/93 i j PCT NUMBER PCT/AU93/00182 III l111 111111111 lillllll llI1llll l III AU9342545 INTERNATIONAL APPLICATION PUBLISHED UNDER THE PATENT COOPERATION TREATY (PCT) (51) International Patent Classification 5 (11) International Publication Number: WO 93/22219 81/34, 25/36 Al (43) International Publication Date: II November 1993 (11.11.93) (21) International Application Number: PCT/AU93/00182 Published Willh international search report.

(22) International Filing Date: 27 April 1993 (27.04.93) Priority data: PL 2022 24 April 1992 (24.04.92) AU 64 (71) Applicant (for all designated States except US): J. GADS- DEN PROPRIETARY LTD. [AU/AU]; 42-46 Dudley Street, West Melbourne, VIC 3003 (AU).

(72) Inventor; and Inventor/Applicant (for US only) WALLIS, David, Edwin, Spencer [AU/AU]; 74 Castle Street, Eaglemont, VIC 3084 (AU).

(81) Designated States: AU, CA, JP, NZ, US, European patent (AT, BE, CH, DE, DK, ES, FR, GB, GR, IE, IT, LU, MC, NL, PT, SE).

(54)Title: MICROWAVE OVEN HEATABLE FOOD PACKAGE 34 S32 3638 26- 28 (57) Abstract A package (10) suitable for food including a hermetically sealable metal can (12) combined with an encapsulation to avoid arcing when microwave oven heating of the contents, the encapsulation comprising a heat and electrical insulating capsule (26) and a removable vented overcap (32) of microwave transparent flexible plastics material. The metal can (12) has a specified ratio of notional diameter to effective height of at least 2. The top end (16) of the can (12) is to be removed before heating, which may be more conveniently enabled by provision of a tear-out easy-open end panel (18) in the top end.

WO 93/22219 PCr/AU93/00182 -1- MICROWAVE OVEN HEATABLE FOOD PACKAGE

BACKGROUND

This invention relates to a package suitable for containing food that includes essentially a hermetically sealable metal can of specific shape (providing long shelf-life storage of food contents without requiring refrigeration) combined with a non-metallic encapsulation, the package as a whole enabling the contents to be heated effectively, in a microwave oven, In the opened package, to a temperature suitable for eating.

A commonplace metal can cannot be used safely or effectively for microwave oven heating of food contents, there being potential problems as follows: the metal of the can is opaque to the microwave field such that there may be inadequate heating at the interface between the metal can walls and the contents; (ii) arcing, i.e, corona discharge, that results when an electrical potential builds up between the metal wall of the can and the metal wall of the inside of the microwave oven; and (iii) the most commonplace food can geometrical shapes are not conducive to satisfactorily uniform heating of food contents even if the potential problems (i) and (ii) are overcome.

The electrically conductive metal of the can walls suppresses the microwave field in its immediate vicinity so that the only heating of the food that occurs is: when the top of the can Is opened; and, given that condition, by (ii) conductive or convective heat transfer in a direction from the dielectrically heated body of food contents situated further away from the interface between the metal walls towards the food contents situated closer to that or those interfaces.

The present invention addresses the above-mentioned problems by incorporating the hermetically sealable can as a component of a composite package in which the can component is enclosed in an outer electrically non-conductive capsule. The capsule 02/06 '97 MON 15:40 FAX 61 2 9684 4270 SOUTHCORP IPIS -2includes a repeatedly removable and replaceable vented flexible plastics overcap that may enclose the top end of the package during storage and heating, it being removable to enable the consumer to: remove an easy-open top; and (ii) heat the package and contents in the microwave oven with minimal spatter after re-fitting the overcap.

Further, the geometrical shape parameters of the can are specified, to enable attainment of sufficiently rapid and adequately uniform temperature rise throughout the contents.

SUMMARY OF THE INVENTION The invention consists of a package for a food product comprising a hermetically sealable metal can, the can comprising: S a side wall; S a bottom end wall extending radially inwardly from a bottom end of the side wall; and .a top end wall extending radially inwardly from a top end of the side wall, at least said top wall being attachable by a seam to the side wall after the can has been filled with the food product; the package further comprising an insulating capsule comprising a sleeve formed from a heat shrinkable non-metallic material having properties of high electrical insulation and low heat conductivity and adapted to encapsulate the side wall and at .e least an outer peripheral portion of the bottom end wall of the can; and wherein the metal can is of being squat shape having a notional diameter D at least twice the effective length H and wherein the can has a shape consisting of the group selected from: cylindrical; circular tapered, that is, frusto-conical; square, cubical or rectangular cubical including such shapes having large corner radii including examples with a tapered sidewall; and elliptical or oval, in plan view, including examples with a tapered sidewall; and the package further comprises a microwave transparent vented plastics overcap fd. pted to overlie the top seam region and at least a portion of the top end 02/06 '97 MON 15:40 FAX 61 2 9684 4270 SOUTHCORP IPIS i010 -3wall and which is adapted to be both manually removable from the package to enable the top end wall to be opened and replaceable preparatory to heating the package in a microwave oven.

Preferably the package further comprises a manually removable tear-out panel in said top wall.

Where the can component is cylindrical in shape the notional diameter for the purpose of characterising the squat shape of the can is defined as the actual inside diameter of the sidewall.

The effective length for the purpose of characterising the squat shape of the can component is defined as the shortest linear distance measurable from the meeting point of the botlom end wall and the sidewall and the plane of the top end wall.

S This definition of effective length is not altered in instances where the bottom end may appreciably depart from a planar shape by being curved inwardly at its centre.

If so curved, the effective length for the purpose of characterising the squat shape of the can component is defined as the shortest linear distance measurable from the meeting point of the bottom end wall and the sidewall and the plane of the top end wall, 8 In an instance in which the can component is tapered circular (ie. frusto-conical) S in shape, the smallest diameter being situated adjacent the junction of the bottom end wall and the sidewall, that notional diameter is defined in such a case as the smallest diameter.

In any instance in which the can component is generally of square cross-section in plan view including square with radiused corners, the notional diameter is defined as the distance between opposite parallel sides of the square. if the square shape includes a taper (again, as with the frusto-conical shape, the smallest cross sectional area being adjacent the bottom end) the notional diameter is defined as the shortest distance between the opposite parallel faces of the sidewall.

/A^j instance in which the can component is generally of rectangular cross-section S /An view the notional diameter is defined as the shorter distance between either WO 93/22219 PCT/AU93/00182 -4of the opposite pairs of parallel sides of the rectangular faces of the sidewall, that being the shortest distance so measurable if the can is tapered.

The meaning of tapered sidewall In this specification and the claims means having a uniform not step-wise) variation in cross-sectional area from one end to the other, as illustrated in the accompanying Figures 4, 5 and 6; or embodying shapes of can body formed by; a straight line divergence of the side wall increasing from the bottom seal to the top seam; a curved line divergence of the side wall increasing from the bottom seal to the top seam; either of the foregoing divergences but where a minor portion of the side wall adjacent either bottom and/or top seam is not divergent BRIEF DESCRIPTION OF THE DRAWINGS.

The invention is further described by way of an example and variations thereof with respect to the accompanying illustrations in which: Fig 1 is a broken cross-sectional elevation of a package according to the invention; Fig 2 and 3 are perspective views of alternative shapes of package according to the invention; and Fig 4 to 10 inclusive are schematic representations, in plan and elevation view, of various forms of metal can components of packages according to the invention, to illustrate geometrical shape characteristics within the scope of the invention.

DETAILED DESCRIPTION.

With reference to Fig 1, the package 10 comprises a metal can 12, that may have tapered shaped sidewalls 13 as illustrated or may have parallel sidewalls (as illustrated for example In Fig A bottom end wall 14 connects to the lower (as illustrated) edge of the sidewall by being hermetically seamed together at a bottom seam 28 In the 3-piece can construction illustrated. Alternatively the sidewall and bottom end wall connection may be seamless as in 2-piece can constructions, see, WO 93/22219 PCVAU93/00182 e.g. Fig 10. A top end wall 16 is provided that in the normal manner is joined by top seam 22 to the can sidewall after the can is filled with food contents.

In the case of a 3-piece can construction it may be the top end wall 16 that is seamed to the sidewall by the can maker and supplied to the can filler who would in that case fill the can inverted with respect to the Fig 1 orientation, that Is through the bottom end and hermetically seal the can by joining, at seam 28, the bottom end wall 14 to the sidewall 13.

The top end 16 may be of the type provided with an easily openable panel 18 whereby the user requires no mechanical can opener to gain access to the contents; rather, by use of a ring-pull 20 or the like, the panel 18 of the top end amounting to approximately 80% of its area, can be readily opened from the top end and detached, forming an opening bounded by edge 24.

The package further comprises an insulating capsule 26 that encapsulates substantially all the peripheral outer side wall 13. Preferably the capsule 26 wraps further around the bottom seam 28 or, otherwise, the bottom corner as in the case of a 2-piece can. The capsule need not enclose the entire bottom end 14 and adequately serves its principal function if terminated as illustrated at an edge It may be conveniently applied to the can by heat shrinking and the wrap around of the edge 30 may be facilitated by heat shrinking. It may also wrap around the top seam, 22 (not shown).

Forming a further part of the package is a removable vented overcap 32 made of a non-metallic material, polyethylene or polypropylene being suitable. The overcap has a generally planar top surface 34 and a peripheral rim 36 extending downwardly from surface 34. The rim 36 may terminate at its lower end with radially inwardly directed lip 38 to snap over and be retained by the top seam 22. In the planar surface one or more vent holes 40 are provided to enable gases and vapours to escape from the package while it is being heated.

The insulating capsule 26 is preferably supplied to a food canner separately from the can, enabling more convenient filling, seaming, heat processing and, if necessary, drying the can. The insulating capsule 26 may then be applied to the can by any suitable means, preferably including heat shrinking if required. The WO 93/22219 PC/AU93/0182 -6insulating capsule may be pre-printed in the form of a label, supplied either in flat form or, otherwise, in cylindrical or other formed shape. A suitable material comprises polystyrene foam either alone, in the form of a flexible sheet 1 to 3 millimetres in thickness, or in combination with one or more other plastics material layers. For example, a smooth non-foamed outer skin layer may be provided to facilitate improved print quality. The heat insulating quality of the capsule is in part provided by its foamed structure and enables the can when heated to be handled directly from the microwave oven. The overcap 32 would normally be applied over the top of the top seam and left in place there until the intended consumer of the contents of the package desires to heat it to a suitable temperature for consumption. Prior to the commencement of heating, the overcap would be manually detached, the easily openable panel 18 would be torn out using the ring-pull 20 and the panel would be discarded. Preferably the overcap would then be replaced and the package place- ;n a microwave oven to be heated. The overcap provides reduced spattering of food during heating and its outer peripheral edge Irotects the top seam against possible arcing across to the metallic interior walls of the microwave oven.

Because the heat producing interaction of microwaves and the contents of the package relies on the opening formed by removal of panel 18, the top should not be obscured from the microwave field such as by placing one package directly on top of another during heating. Foods of a very thick consistency in which the heat transfer mechanism is only by way of dielectric loss to generate the heat initially combined with conductive heat transfer from the more rapidly heating material adjacent the opening to the remainder of the contents should be subjected preferably to an interrupted heating cycle that allows for a time lag between the more rapid microwave induced heating and the relatively slower dissipation of this heat by conduction towards the cooler portions of the contents at, for example, the lower corners of the package most remote from the opening formed when panel 18 is removed.

Fig 2 shows a form of the invention in upright perspective with a portion of the insulating capsule 26 cut away to show the can 12 including its cylindrical sidewall 13 and lower circumferential seam 28. The obscured remainder of the seam and sidewall are shown schematically as dotted lines. The overcap 34 is shown fitted to the package as preferably for transport, storage and during heating.

WO 93/22219 PCrAU93/00182 -7- Fig 3 shows a further form of package according to the Invention, in uprighL perspective schematic view, namely a rectangular in cross-section shaped package.

The insulating capsule 26 Is Indicated schematically in chain outline. Other Items illustrated correspond to the reference numbers used in Fig 1, namely: the package the removable panel 18; ring pull top seam 22; vented overcap 32; and vent holes Figures 4 to 10 schematically illustrate geometrical variations in the metal can component 12 of a variety of package shapes within the scope of the invention.

In all cases the metal thickness of any can comprising a package according to the inven ition is to be understood as being the same as is usually provided for food containing applications, having in mind the size of the can and its process and intended product-related requirements. For example, the metal thickness of the can component, the seam specifications and internal lacquer specifications are the same as would be normally used in the food canning industry.

In each Figure, the diameter (or, in the case of non-circular cross-sectional shapes, the notional diameter) as defined D is shown in the upper plan view and where possible in the lower elevation view as well. In each elevation view,the effective length H as defined, is shown.

Claims (2)

1. A package for a food product comprising a hermetically sealable metal can, the can comprising: a side wall; a bottom end wall extending radially inwardly from a bottom end of the side wall; and a top end wall extending radially inwardly from a top end of the side wall, at least said top wall being attachable by a seam to the side wall after the can has been filled with the food product; the package further comprising an insulating capsule comprising a sleeve formed from a heat shrinkable non-metallic material having properties of high a" electrical insulation and low heat conductivity and adapted to encapsulate the side wall and at least an outer peripheral portion of the bottom end wall of the can; and is wherein the metal can/of squat shape having a notional diameter D at least twice the effective length H and wherein the can has a shape consisting of the group selected from: cylindrical; circular tapered, that is, frusto-conical; square, cubical or rectangular cubical including such shapes having large corner radii including examples with a tapered sidewall; and elliptical or oval, in S. plan view, including examples with a tapered sidewall; and the package further comprising a microwave transparent vented plastics overcap adapted to overlie the top seam region and at least a portion of the top end wall and which is adapted to be both manually removable from the package to enable the top end wall to be opened and replaceable preparatory to heating the package in a microwave oven.

2. A package as claimed in claim 1 further comprising a manually removable tear- out panel in said top end wall