Metallized microwave diffuser films

• US 5,300,746 A
• Filed: 09/06/1991
• Issued: 04/05/1994
• Est. Priority Date: 11/08/1990
• Status: Expired due to Fees

• Current Assignee: Advanced Deposition Technologies, Inc.
• Original Assignee: Advanced Deposition Technologies, Inc.
• Inventors: McCormick, John A., Walters, Glenn J.
• Primary Examiner(s): Reynolds, Bruce A.
• Assistant Examiner(s): HOANG, TU BA
• Application Number:
  US07/756,165
• Time in Patent Office: 942 Days
• Field of Search: 219/10.55 E, 219/10.55 F, 219/10.55 R, 219/10.43, 99/DIG. 14, 428/323, 428/332, 156/651, 156/272, 156/233, 156/234, 426/107, 426/234, 426/243, 426/211, 426/213
• US Class Current: 219/745
• CPC Class Codes: B65D 2581/3406 Pizza or bread
• 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 2581/3474 Titanium or compounds thereof
• CPC Class Codes: B65D 2581/3477 Iron or compounds thereof
• CPC Class Codes: B65D 2581/3479 Other metallic compounds, e.g. silver, gold, copper, nickel
• CPC Class Codes: B65D 2581/3489 Microwave reflector, i.e. microwave shield B65D2581/3487 takes precedence
• CPC Class Codes: B65D 81/3453 Rigid containers, e.g. trays, bottles, boxes, cups
• CPC Class Codes: H05B 6/64 Heating using microwaves containers, packaging elements or packages specially adapted to be heated by microwaves B65D81/3446

Abstract

Microwave diffuser films are describe that provide a modified microwave energy field on one side of the diffuser film and on the other side. The films include an insulative substrate having a first side upon which is deposited a metallic coating capable of selectively reflecting a portion of incoming microwave energy. A coating is formed in a plurality of discrete areas having a predetermined reflectivity. The shape and spacing of the areas may be varied so that energy emission from noncoated surfaces of the substrate is spatially distributed in one or more ways; i.e. the energy emission more uniform than the energy impinging on the coated surface, the energy emission is focused on one or more particular location and/or the energy emission is shielded. A food packaging system for microwave cooking, which includes the microwave diffuser film of this invention, is also described.

Claims

1. A microwave diffuser film for use during microwave heating of objects, comprising:

(a) a first substrate that is substantially transparent to microwave energy, the substrate having a first surface for receiving a microwave energy field and at least one second surface across which microwave energy is transferred; and

(b) microwave-interactive elements deposited on the first surface for interacting with microwave energy received thereon to produce a modified microwave energy field and to transfer said microwave energy field across said at least one second surface, said microwave-interactive elements comprising a plurality of discrete metallic elements having a sheet resistance in the range of 2.0 to 0.05 ohms per square arranged in a pattern so that the transferred microwave energy field is substantially uniform, the metallic elements separated by nonmetallic areas, said metallic elements substantially incapable of converting microwave energy to heat.

2. The microwave diffuser film of claim 1, wherein the metallic elements are vapor-deposited.

3. The microwave diffuser film of claim 2, wherein the metallic elements include metallic material selected from the group consisting of a single metal, a metal alloy, a metal oxide, a mixture of metal oxides, a dispersion of metals, and combinations of the foregoing metallic material.

4. The microwave diffuser film of claim 3, wherein the metallic material is selected from the group consisting of aluminum, iron, tin, tungsten, nickel, stainless steel, titanium, magnesium, copper, and chromium.

5. The microwave diffuser film of claim 1, wherein the first substrate is an electrical insulator comprising a polymeric material selected from the group consisting of polyolefins, polyesters, polyamides, polyimides, polysulfones, polyethers, ketones, cellophanes and combinations of the foregoing polymeric materials.

6. The microwave diffuser film of claim 1, further comprising a second substrate in contact with the microwave-interactive elements, the second substrate substantially transparent to microwave energy.

7. The microwave diffuser film of claim 6, wherein the second substrate is an electrical insulator comprising a polymeric material selected from the group consisting of polyolefins, polyesters, polyamides, polyimides, polysulfones, polyethers, ketones, cellophanes and combinations of the foregoing polymeric materials.

8. The microwave diffuser film of claim 1, wherein said metallic elements have an area ranging from about 1 mm² to about 625 mm².

9. A microwave diffuser film for use during microwave heating of objects, comprising:

(a) a first substrate that is substantially transparent to microwave energy, the substrate having a first surface for receiving a microwave energy field and at least one second surface across which microwave energy is transferred; and

(b) microwave-interactive elements deposited on the first surface for interacting with microwave energy received thereon to produce a modified microwave energy field and to transfer said microwave energy field across said at least one second surface, said microwave-interactive elements comprising a plurality of discrete metallic elements having a sheet resistance in the range of 2.0 to 0.05 ohms per square arranged in a pattern so that the transferred microwave energy field is substantially uniform, the metallic elements separated by nonmetallic areas, said metallic elements substantially incapable of converting microwave energy to heat, wherein the metallic elements are arranged in a pinwheel pattern.

10. A microwave diffuser film for use in food packaging, comprising:

(a) a flexible substrate having opposed first and second surfaces, said substrate being substantially transparent to microwave energy from a microwave energy source;

(b) a plurality of first microwave-interactive elements deposited on the first surface of the substrate for spatially distributing microwave energy produced by the microwave energy source and received upon said first microwave-interactive elements, the first microwave-interactive elements arranged in a discontinuous pattern, said elements separated by first continuous, nonmicrowave-interactive areas;

(c) a plurality of second microwave-interactive elements deposited on the second surface of the substrate for spatially distributing microwave energy received upon said elements, the second microwave-interactive elements arranged in a discontinuous pattern, said second microwave-interactive elements separated by second continuous, nonmicrowave-interactive areas, the first and second microwave-interactive elements of both surfaces substantially incapable of converting microwave energy into heat.

11. The microwave diffuser film of claim 10, wherein the first and second microwave-interactive elements include metal-containing material selected from the group consisting of a single metal, a metal alloy, a metal oxide, a mixture of metal oxides, a dispersion of metals, and combinations of the foregoing metal-containing material.

12. The microwave diffuser film of claim 11, wherein the microwave-interactive elements are vapor-deposited.

13. The microwave diffuser of claim 12, wherein the first microwave-interactive elements comprises a plurality of quadrilateral microwave reflective elements in a pattern, said pattern covering at least about 85% to about 95% of the surface area of the first surface of the substrate.

14. The microwave diffuser of claim 11, wherein the first and second microwave-interactive elements have a resistivity between about 0.05 and about 2.0 ohms per square.

15. The microwave diffuser of claim 10, wherein the plurality of second microwave-interactive elements deposited on the second surface of the substrate are in phased array relative to the first microwave-interactive elements deposited on the first surface of the substrate.

16. The microwave diffuser of claim 10, wherein the substrate is an electrical insulator comprising a polymer material selected from the group consisting of polyolefins, polyesters, polyamides, polyimides, polysulfones, polyethers, ketones, cellophanes, and combinations of the foregoing polymeric material.

17. The microwave diffuser film of claim 10, wherein said first and second microwave-interactive elements have an area ranging from about 1 mm² to about 625 mm² and said first and second nonmicrowave-interactive areas range from about 0.2 mm to about 2.0 mm.

18. A food package for microwave cooking of food contained therein, having

a susceptor for converting microwave energy into heat;

a diffuser for achieving uniformity of heating;

wherein said susceptor and said diffuser are copackaged so that microwave energy passes through both and that the heat produced by the susceptor is capable of reaching the food;

wherein the diffuser includes a substrate having a first surface for receiving microwave energy from a microwave source and a second surface across which microwave energy is transferred, the substrate having deposited on the first surface a plurality of microwave-interactive elements for spatially distributing microwave energy received thereon, said microwave-interactive elements substantially incapable of converting microwave energy into heat, said microwave-interactive elements having a sheet resistance in the range of 2.0 to 0.05 ohms per square arranged in a discontinuous pattern so that the transferred microwave energy field is substantially uniform, the microwave-interactive elements separated from each other by a continuous gap lacking said microwave-interactive elements.

19. The food package of claim 18, wherein the substrate of the diffuser is an electrical insulator comprising a polymeric material selected from the group consisting of polyolefins, polyesters, polyamides, polyimides, polysulfones, polyethers, ketones, cellophanes, and combinations of the foregoing polymeric material.

20. The food package of claim 18, wherein the microwave-interactive elements include metal-containing material selected from the group consisting of a single metal, a metal alloy, a metal oxide, a mixture of metal oxides, a dispersion of metals, and combinations of the foregoing metal-containing material.

21. The food package of claim 19, wherein the discontinuous pattern of microwave-interactive elements comprises a plurality of quadrilateral microwave-reflective elements covering at least about 85% to about 90% of the surface area of the first surface of the substrate.

22. The food package of claim 21, wherein the reflecting elements are vapor-deposited.

23. The food package of claim 18, wherein the continuous gap lacking said microwave-interactive elements includes at least one substantially rectangular-shaped gap.

24. The food package of claim 18, further comprising a second plurality of microwave-interactive elements for spatially distributing microwave energy, said second plurality of microwave-interactive elements deposited on the second surface of the substrate in a discontinuous pattern, the second plurality of microwave-interactive elements separated from each other by a continuous gap lacking said microwave-interactive elements, said second plurality of microwave-interactive elements substantially incapable of converting microwave energy into heat.

25. The food package of claim 24, wherein the plurality of elements deposited on said first and second substrate surfaces are in phased array relative to each other.

26. A microwave diffuser film for use in food packaging, comprising:

(a) a flexible substrate having opposed first and second surfaces, said substrate being substantially transparent to microwave energy from a microwave energy source;

(b) a plurality of first microwave-interactive elements deposited on the first surface of the substrate for spatially distributing microwave energy produced by the microwave energy source and received upon said first microwave-interactive elements, the first microwave-interactive elements arranged in a discontinuous pattern, said elements separated by first continuous, nonmicrowave-interactive areas;

(c) a plurality of second microwave-interactive elements deposited on the second surface of the substrate for spatially distributing microwave energy received upon said elements, the second microwave-interactive elements arranged in a discontinuous pattern, said second microwave-interactive elements separated by second continuous, nonmicrowave-interactive areas, the first and second microwave-interactive elements of both surfaces substantially incapable of converting microwave energy into heat, wherein the first and second plurality of microwave-interactive elements are in a pinwheel configuration on a surface of the substrate, the surface selected from the group consisting of the first surface, the second surface and both first and second surfaces.

27. A food package for microwave cooking of food contained therein, having

a susceptor for converting microwave energy into heat;

a diffuser for achieving uniformity of heating;

wherein said susceptor and said diffuser are copackaged so that microwave energy passes through both and that the heat produced by the susceptor is capable of reaching the food;

the diffuser including a substrate having a first surface for receiving microwave energy from a microwave source and a second surface across which microwave energy is transferred, the substrate having deposited on the first surface a plurality of microwave-interactive elements for spatially distributing microwave energy received thereon, said microwave-interactive elements substantially incapable of converting microwave energy into heat, said microwave-interactive elements having a sheet resistance in the range of 2.0 to 0.05 ohms per square arranged in a discontinuous pattern so that the transferred microwave energy field is substantially uniform, the elements separated from each other by a continuous gap lacking said microwave-interactive elements, wherein the plurality of microwave-interactive elements are arranged in a pinwheel pattern.