Method and material for prepackaging food to achieve microwave browning

• US 4,230,924 A
• Filed: 10/12/1978
• Issued: 10/28/1980
• Est. Priority Date: 10/12/1978
• Status: Expired due to Term

• Current Assignee: General Mills Incorporated
• Original Assignee: General Mills Incorporated
• Inventors: Beall, Nelson J., Brastad, William A.
• Primary Examiner(s): Grimley, Arthur T.
• Application Number:
  US05/950,759
• Time in Patent Office: 747 Days
• Field of Search: 219/10.55 E, 219/10.55 M, 219/10.55 F, 219/10.55 R, 426/107, 426/234, 229/3.5 MF, 229/87 F
• US Class Current: 219/730
• CPC Class Codes: B65D 2581/344 Geometry or shape factors influencing the microwave heating properties
• CPC Class Codes: B65D 2581/3466 Microwave reactive material applied by vacuum, sputter or vapor deposition
• CPC Class Codes: B65D 2581/3472 Aluminium or compounds thereof
• CPC Class Codes: B65D 2581/3479 Other metallic compounds, e.g. silver, gold, copper, nickel
• CPC Class Codes: B65D 2581/3494 Microwave susceptor B65D2581/3487 takes precedence
• CPC Class Codes: B65D 81/3446 specially adapted to be heated by microwaves

Abstract

The food package includes a flexible wrapping sheet of dielectric material, such as polyester or paperboard, capable of conforming to at least a portion of the article of food'"'"'s shape. The dielectric wrapping sheet has a flexible metallic coating thereon, such as aluminum, in the form of a relatively thin film or relatively thick foil, the coating being subdivided into a number of individual metallic islands or pads separated by criss-crossing non-metallic gaps provided by exposed dielectric strips on the wrapping sheet. When the food package is placed in a microwave oven, some of the microwave energy passes through the wrapping sheet so as to dielectrically heat the food item, but a lesser amount of the microwave energy is converted into thermal energy by the metallic coating so as to brown or crispen that portion of the food adjacent thereto. Various degrees of microwave transparency can be incorporated into the metallic coating so that a desired or preferred amount of browning is realized by the time that the particular item of packaged food is fully heated or cooked.

Claims

1. A package containing an article of food, at least a portion thereof being capable of having either its color changed or crispened, said food article to be heated in a microwave oven, comprising a flexible dielectric material having at least a section thereof conforming generally to the shape of said portion of the food article, and individual electrically resistive islands carried by said dielectric material for converting some of the microwave oven energy to heat, said electrically resistive islands also conforming generally to the shape of said portion of food and residing in a proximal relation therewith, whereby the microwave energy converted to heat by said dielectric material and islands modifies the color or crispness of the food portion adjacent thereto.

2. A package in accordance with claim 1 in which said islands are partially transparent to microwave energy so that some of the microwave oven energy passes therethrough and some through said dielectric strips.

3. A package in accordance with claim 1 in which said islands are metallic and opaque to microwave energy so that some of the microwave oven energy is converted into heat by said islands and the dielectric material forming said strips, and some of the microwave energy passes through said dielectric strips.

4. A package in accordance with claim 1 in which said islands are rectangular with criss-crossing strips of said dielectric material residing therebetween.

5. A package in accordance with claim 1 in which said islands are metallic and are on the surface of said dielectric material nearer the portion of food.

6. A package in accordance with claim 1 in which said dielectric material is a sheet of plastic.

7. A package in accordance with claim 1 in which said dielectric material is a sheet of paperboard.

8. A package in accordance with claim 1 in which said islands are metallic and range from about 0.1 micron to 0.00035 inch thick.

9. A package in accordance with claim 8 in which said islands range from about 1/32 inch on a side to about 0.75 inch on a side and the strips therebetween range from 0.0001 to 0.0625 inch in width.

10. A package in accordance with claim 9 in which said islands range from about 1/16 inch on a side to about 1/4 inch on a side.

17. Packaging material in accordance with claim 1 in which the thickness of said islands is from approximately 0.1 micron to 0.00035 inch.

18. Packaging material in accordance with claim 17 in which said islands are from about 1/32 inch on a side to about 3/4 inch on a side.

19. Packaging material in accordance with claim 18 in which said islands have dielectric strips extending therebetween, said strips having a width from 0.0001 to 0.0625 inch.

20. Packaging material in accordance with claim 19 in which said islands are from about 1/16 inch on a side to about 1/4 inch on a side.

11. A method of packaging an article of food to be heated in a microwave oven comprising the steps of conforming at least a section of a flexible sheet of dielectric material to the shape of at least a portion of the food article, said flexible sheet section having thereon electrically resistive islands for converting at least some of the microwave oven energy into heat for browning the surface of said food article which is adjacent thereto.

12. A method of heating an article of food in a microwave oven comprising the steps of confronting at least a surface portion of the food article to be heated with a section of flexible dielectric material, said section of material carrying thereon spaced metallic islands capable of converting some of the microwave oven energy into heat, retaining said section of flexible dielectric material and said metallic islands close to said surface portion of said food article, and subjecting said dielectric material, said metallic islands and said article of food to microwave energy for a period of time sufficient to modify the color of said surface portion.

13. Packaging material for regulating the amount of microwave cooking energy passing therethrough to an article of food when contained therein, said food to be heated in a microwave oven, said packaging material comprising a flexible dielectric substrate, and a plurality of electrically resistive islands on one side of said flexible substrate, said islands also being flexible so that at least a section of said substrate and the islands on said section can be flexed against food having a surface portion that is nonplanar.

14. Packaging material in accordance with claim 13 in which at least some of said islands are partially transparent to microwave energy, said islands having gaps of said dielectric substrate therebetween.

15. Packaging material in accordance with claim 14 in which said islands are generally rectangular.

16. Packaging material in accordance with claim 13 in which at least some of said islands are opaque to microwave energy, said opaque islands having strips of said dielectric substrate therebetween.

21. Packaging material in accordance with claim 13 in which said electrically resistive islands are metallic.