Microwavable package

• US 6,251,451 B1
• Filed: 05/26/1999
• Issued: 06/26/2001
• Est. Priority Date: 08/26/1996
• Status: Expired due to Term

• Current Assignee: Graphic Packaging International Incorporated
• Original Assignee: Graphic Packaging Corporation
• Inventors: Zeng, Neilson
• Primary Examiner(s): Brouillette, Gabrielle
• Assistant Examiner(s): Dauerman, Sherry A.
• Application Number:
  US09/242,930
• Time in Patent Office: 762 Days
• Field of Search: 426/107, 426/234, 426/243, 219/728-730, 219/759
• US Class Current: 426/107
• CPC Class Codes: B65D 2581/344 Geometry or shape factors influencing the microwave heating properties
• CPC Class Codes: B65D 2581/3441 3-D geometry or shape factors, e.g. depth-wise
• CPC Class Codes: B65D 2581/3452 Packages having a plurality of microwave reactive layers, i.e. multiple or overlapping microwave reactive layers
• CPC Class Codes: B65D 2581/3464 Microwave reactive material applied by ink printing
• CPC Class Codes: B65D 2581/3466 Microwave reactive material applied by vacuum, sputter or vapor deposition
• CPC Class Codes: B65D 2581/3489 Microwave reflector, i.e. microwave shield B65D2581/3487 takes precedence
• CPC Class Codes: B65D 2581/3494 Microwave susceptor B65D2581/3487 takes precedence
• CPC Class Codes: B65D 81/3453 Rigid containers, e.g. trays, bottles, boxes, cups
• CPC Class Codes: Y10S 99/14 Induction heating

Abstract

The disclosed invention provides a microwavable package for a food product. The package comprises a base with an active microwave energy heating element to support the food product. The active microwave heating element comprises energy collecting resonant loops, tuned structures, and transmission lines to collect incident microwave energy and redirect it to other parts of the food product. The microwave package also includes a cover comprising a microwave energy interactive layer including one or more apertures within the cover. The apertures promote localized fields to promote browning of the food product in the local areas around the apertures. The cover may also comprise a susceptor layer that is heated in localized areas around the apertures due to the fields promoted by the apertures and impingement by incident microwaves energy through the apertures, thereby providing localized browning of the food product.

Claims

1. A microwavable package comprising:

a base to support a food product;

an active microwave energy heating element on said base to effect heating of a food product upon impingement by microwave energy; and

a cover spaced apart from said active microwave energy heating element to overlie said food product, said cover including a microwave energy interactive material layer extending substantially over said food product, said microwave energy interactive material including a plurality of apertures spaced about said cover, said apertures being sized to promote localized fields to promote browning of said food product.

2. A microwavable package as defined in claim 1 wherein said apertures are in the form of elongate slots.

3. A microwavable package as defined in claim 2 wherein said elongate slots are arranged in concentric rings.

4. A microwavable package as defined in claim 3 wherein said rings are circular.

5. A microwavable package as defined in claim 4 wherein the slots in said concentric rings are staggered.

6. A microwavable package as defined in claim 5 further including at least one layer of suscepting material on said cover and overlying said microwave energy interactive material.

7. A microwavable package as defined in claim 2 wherein microwave energy interactive material islands are located within said elongate slots.

8. A microwavable package as defined in claim 7 wherein said elongate slots are arranged in concentric rings.

9. A microwavable package as defined in claim 8 wherein said rings are circular.

10. A microwavable package as defined in claim 9 wherein the slots in said concentric rings are staggered.

11. A microwavable package as defined in claim 7 wherein each of said microwave energy interactive material islands has an aperture formed therein.

12. A microwavable package as defined in claim 11 wherein said apertures are substantially decussate.

13. A microwavable package as defined in claim 1 wherein said active microwave energy heating element includes a plurality of energy collecting structures, each of said energy collecting structures including resonant loops having a perimeter sufficient to limit currents induced therein to below a predetermined level upon impingement by incident microwave energy, said energy collecting structures distributing energy towards a central region of said food product to uniformly heat said food product and to inhibit charring of said base.

14. A microwave package as defined in claim 13 wherein said energy collecting structures include a pair of resonant loops interconnected by transmission lines, said transmission lines configured to provide a progressive power loss between said resonant loops.

15. A microwavable package as defined in claim 14 wherein the perimeter of said resonant loops and the length of each of said transmission lines are substantially equal to an integer multiple of the effective wavelength of said incident microwave energy projected onto said microwave energy heating element.

16. A microwavable package as defined in claim 15 wherein said resonant loops are circular.

17. A microwavable package as defined in claim 16 wherein said energy collecting structures are circumferentially spaced and arranged in a ring about the center of said active element.

18. A microwavable package as defined in claim 17 wherein said active microwave energy heating element further includes a plurality of tuned structures at spaced locations and positioned between adjacent resonant loops.

19. A microwavable package as defined in claim 18 wherein said tuned structures include nested loops.

20. A microwavable package as defined in claim 19 wherein said nested loops are joined by bridges.

21. A microwavable package as defined in claim 1 further including a plurality of spaced apertures provided through said base and active microwave energy heating element to allow moisture released from said food product to pass.

22. A microwavable package as defined in claim 21 wherein said apertures are arranged in concentric rings.

36. A microwavable package as defined in claim 1 further comprising:

a tray comprising said base and including a plurality of spaced apertures in said tray to permit moisture released from a food product to pass through said tray.

37. A microwavable package as defined in claim 36 wherein said apertures are arranged in concentric rings.

38. A microwavable package as defined in claim 1 wherein the apertures are spaced about a peripheral margin of said cover.

23. A microwavable package comprising:

a base to support a food product;

an active microwave energy heating element interposed between said food product and said base to effect heating of said food product upon impingement by microwave energy;

a cover spaced apart from said active microwave energy heating element to overlie said food product, said cover comprising;

microwave energy interactive material covering at least a portion of said food product, said microwave energy interactive material containing a plurality of apertures spaced about said cover;

a substrate supporting and extending beyond the peripheral edge of said microwave energy interactive material to isolate electrically said base and said cover; and

at least one layer of suscepting material interposed between said food product and said microwave energy interactive material;

wherein said apertures are sized to promote a localized fields to locally enhance said at least one layer of suscepting material and promote browning of said food product.

24. A microwavable package as defined in claim 23 wherein said microwave energy interactive material extends substantially over said food product.

25. A microwavable package as defined in claim 24 wherein said apertures are in the form of elongate slots.

26. A microwavable package as defined in claim 25 wherein said elongate slots are arranged in concentric circular rings, the slots in adjacent concentric rings being staggered.

27. A microwavable package as defined in claim 26 wherein microwave energy interactive material islands are located within said elongate slots.

28. A microwavable package as defined in claim 27 wherein said elongate slots are arranged in concentric circular rings, the slots in adjacent concentric rings being staggered.

29. A microwavable package as defined in claim 28 wherein each of said microwave energy interactive material islands has an aperture formed therein.

30. A microwavable package as defined in claim 29 wherein said apertures are generally decussate.

31. A microwavable package as defined in claim 23 wherein said base and active microwave energy heating element further include a plurality of spaced venting apertures to allow moisture released from said food product to pass.

32. A microwavable package as defined in claim 31 wherein said venting apertures are arranged in concentric rings.

33. A microwavable package as defined in claim 23 wherein said cover is flexible to overlie and conform to said food product, and further comprising a flexible wrap to constrain said base and cover and inhibit relative movement there between.

34. A microwavable package as defined in claim 33 wherein said base and cover are generally circular.

35. A microwavable package as defined in claim 33 wherein said food product is in the form of a pizza.

39. A microwavable package as defined in claim 23 wherein the apertures are spaced about a peripheral margin of said cover.