Method for forming laminate for microwave oven package

• US 5,221,419 A
• Filed: 04/21/1992
• Issued: 06/22/1993
• Est. Priority Date: 02/19/1991
• Status: Expired due to Term

• Current Assignee: Graphic Packaging International Incorporated
• Original Assignee: Beckett Industries, Inc.
• Inventors: Beckett, D. Gregory
• Primary Examiner(s): Powell, William A.
• Application Number:
  US07/871,671
• Time in Patent Office: 427 Days
• Field of Search: 156/630, 156/634, 156/656, 156/659.1, 156/665, 219/10.55 E, 219/110.55 F
• US Class Current: 216/33
• CPC Class Codes: B32B 15/043 of metal B32B15/01 takes precedence
• CPC Class Codes: B32B 15/08 of synthetic resin
• CPC Class Codes: B32B 15/12 of paper or cardboard
• CPC Class Codes: B32B 15/20 comprising aluminium or copper B32B15/016 and B32B15/017 take precedence
• CPC Class Codes: B32B 2311/24 Aluminium
• CPC Class Codes: B32B 2439/70 Food packaging
• CPC Class Codes: B32B 3/266 characterised by an apertured layer, the apertures going through the whole thickness of the layer, e.g. expanded metal, perforated layer, slit layer regular cells B32B3/12
• CPC Class Codes: B32B 7/12 using interposed adhesives or interposed materials with bonding properties
• 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 2581/3452 Packages having a plurality of microwave reactive layers, i.e. multiple or overlapping microwave reactive layers
• CPC Class Codes: B65D 2581/3454 Microwave reactive layer having a specified optical density
• CPC Class Codes: B65D 2581/3466 Microwave reactive material applied by vacuum, sputter or vapor deposition
• CPC Class Codes: B65D 2581/3467 Microwave reactive layer shaped by delamination, demetallizing or embossing
• CPC Class Codes: B65D 2581/3472 Aluminium or compounds thereof
• CPC Class Codes: B65D 2581/3478 Stainless steel
• 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 81/3446 specially adapted to be heated by microwaves

Abstract

A laminate structure useful for incorporating into a package structure for the microwave cooking of foodstuffs for consumption comprises an outer layer polymeric material, an outer layer of microwave transparent material, a grid layer having an electroconductive surface surrounding transmissive apertures located between the outer layers, and a thin layer of electroconductive material of sufficient thickness so that a portion of incident microwave energy is converted to thermal energy also located between the outer layers. The structure is useful in providing controlled surface heating and microwave transmittance to achieve a more uniformly heated product employing less structural material than the prior art.

Claims

1. A method of forming a laminate structure useful for forming a food package for a microwave oven, which comprises:

forming a first laminate comprising a layer of material defining a grid having an electroconductive surface surrounding transmissive apertures adhered to a polymeric film layer,

directly depositing a thin layer of electroconductive material over said grid layer to adhere to said electroconductive surface and to said polymeric film layer in said apertures, said thin electroconductive material layer having a thickness sufficient to convert a portion of incident microwave energy to thermal energy, and

adhering said thin electroconductive material layer to a substrate layer of microwave transparent material.

2. The method of claim 1 wherein said first laminate is formed by:

laminating a layer of electroconductive material to said polymeric film layer, and

effecting selective demetallization of said electroconductive material layer to form said grid.

3. The method of claim 2 wherein said selective demetallization is effected by:

applying a pattern of etchant-resistant material to said electroconductive material layer in the pattern of said electroconductive surface in said grid, and

applying an etchant for said electroconductive material to said electroconductive material layer to remove said electroconductive material from locations not bearing said etchant-resistant material, thereby forming said transmissive aperture.

4. The method of claim 3 wherein said thin layer of electroconductive material is applied by vapor deposition.

8. The method of claim 1 including applying a layer of etchant-resistant material to said thin layer of electroconductive material prior to laminating said layer of electroconductive material thereto.

5. A method of forming a laminate structure useful for forming a food package for a microwave oven, which comprises:

forming a first laminate comprising a layer of material defining a grid having an electroconductive surface surrounding transmissive apertures adhered to a thin layer of electroconductive material supported on a polymeric film layer, said thin electroconductive material layer having a thickness sufficient to convert a portion of incident microwave energy to thermal energy, and

adhering said grid layer to a substrate layer of microwave transparent material.

6. The method of claim 5 wherein said first laminate is formed by:

laminating a layer of electroconductive material to said thin layer of electroconductive material, and

effecting selective demetallization of said electroconductive material layer to form said grid.

7. The method of claim 6 wherein said selective demetallization is effected by:

applying a pattern of etchant-resistant material to said electroconductive material layer in the pattern of said electroconductive surface in said grid, and

applying an etchant for said electroconductive material to said electroconductive material layer to remove said electroconductive material from locations not bearing said etchant-resistant material, thereby forming said transmissive apertures.