Microwave heatable composites

• US 5,294,763 A
• Filed: 09/26/1990
• Issued: 03/15/1994
• Est. Priority Date: 04/07/1989
• Status: Expired due to Term

• Current Assignee: Minnesota Mining and Manufacturing Co (3M Company)
• Original Assignee: Minnesota Mining and Manufacturing Co (3M Company)
• Inventors: Connell, Glen, Chamberlain, Craig S., Zimmerman, Patrick G., Minick, Chris A., Vesley, George F., LePere, Pierre H., Palmgren, Charlotte M., Tait, William C.
• Primary Examiner(s): Reynolds, Bruce A.
• Assistant Examiner(s): HOANG, TU BA
• Application Number:
  US07/588,591
• Time in Patent Office: 1,266 Days
• Field of Search: 219/10.55 E, 219/10.55 M, 219/10.55 F, 426/107, 426/113, 426/124, 426/234, 426/243, 428/207, 428/208.2, 428/208.4, 428/208.8, 428/215, 428/217, 428/221, 428/328, 428/403, 428/408, 99/DIG. 14
• US Class Current: 219/729
• CPC Class Codes: B29C 65/1425 Microwave radiation
• CPC Class Codes: B29C 65/4815 Hot melt adhesives, e.g. thermoplastic adhesives
• CPC Class Codes: B29C 65/486 characterised by their physical form being non-liquid, e.g. in the form of granules or powders B29C65/50 takes precedence
• CPC Class Codes: B29C 65/524 by applying the adhesive from an outlet device in contact with, or almost in contact with, the surface of the part to be joined
• CPC Class Codes: B65D 2581/3443 Shape or size of microwave reactive particles in a coating or ink
• CPC Class Codes: B65D 2581/3445 Microwave reactive adhesives, e.g. also used in valves or lids
• CPC Class Codes: B65D 2581/3448 Binders for microwave reactive materials, e.g. for inks or coatings
• CPC Class Codes: B65D 2581/3464 Microwave reactive material applied by ink printing
• CPC Class Codes: B65D 2581/3472 Aluminium or compounds thereof
• CPC Class Codes: B65D 2581/3475 Titanium nitride
• 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
• CPC Class Codes: Y10S 99/14 Induction heating
• CPC Class Codes: Y10T 428/24901 including coloring matter
• CPC Class Codes: Y10T 428/2991 Coated

Abstract

Composition comprising (a) susceptors having the capability of absorbing microwave energy, and (b) a matrix substantially non-reflective of microwave energy. The susceptors comprise a particulate substrate having a thin-film coating thereon. The particulate substrate is substantially non-reflective of microwave energy and the coating is capable of absorbing microwave energy. The matrix typically comprises polymeric or ceramic materials that are stable at temperatures conventionally used in microwave cooking. The composition allows reuse of the susceptors, eliminates decline in heating rate, eliminates arcing, allows the heating rate to be controlled, allows overheating to be controlled, and allows formation of microwave heatable composite materials having very low metal content.

Claims

1. Composition comprising:

(a) a plurality of susceptors, each of said susceptors comprising a particle substantially non-reflective of microwave energy, said particle bearing a coating capable of absorbing microwave energy and converting said energy to heat, said susceptors being dispersed in

(b) a matrix substantially non-reflective of microwave energy.

2. The composition of claim 1, wherein at least one of said susceptors has a regular geometric shape.

3. The composition of claim 2, wherein said shape is spheroidal.

4. The composition of claim 2, wherein said shape is acicular.

5. The composition of claim 2, wherein said shape is rod-like.

6. The composition of claim 1, wherein at least one of said susceptors has an irregular shape.

7. The composition of claim 1, wherein said coating is electrically conductive.

8. The composition of claim 1, wherein said coating is semi-conductive.

9. The composition of claim 1, wherein said coating has a thickness of from about 1 to about 10,000 Angstroms.

10. The composition of claim 7, wherein said coating is inorganic.

11. The composition of claim 10, wherein said coating is made of metal.

12. The composition of claim 11, wherein said coating has a thickness of from about 1 to about 1,000 Angstroms.

13. The composition of claim 11, wherein said coating has a thickness of from about 1 to about 100 Angstroms.

14. The composition of claim 7, wherein an electrically insulating coating is subsequently deposited over the conductive coating.

15. The composition of claim 1, wherein said particle is non-conductive.

16. The composition of claim 1, wherein said particle is selected from the group consisting of glass, ceramic, and polymeric material.

17. The composition of claim 16 wherein said ceramic is selected from the group consisting of quartz, plaster of Paris, mica, and inorganic salt.

18. The composition of claim 1, wherein said composition is capable of being heated by microwave energy.

19. The composition of claim 1 wherein said matrix is flowable.

20. The composition of claim 1 wherein said matrix is non-flowable.

21. The composition of claim 1, wherein said susceptor is flat.

22. The composition of claim 21, wherein said flat susceptor is a flake.

23. The composition of claim 22, wherein said flake is made of mica.

24. Method of heating a composition comprising the steps of:

(a) providing a composition comprising;

(1) a plurality of susceptors, each of said susceptors comprising a particle substantially non-reflective of microwave energy, said particle bearing a coating capable of absorbing microwave energy and converting said energy to heat, said susceptors being dispersed in

(2) a matrix substantially non-reflective of microwave energy, and

(b) subjecting said composition to microwave radiation.

25. The method of claim 24, wherein said coating absorbs less microwave energy as the temperature of said composition increases.

26. The method of claim 25, wherein said coating is electrically conductive, and the conductivity of said electrically conductive coating changes as the temperature of said composition changes.

27. The method of claim 26, wherein said coating partially oxidizes.

28. The method of claim 24, wherein said coating absorbs more microwave energy as the temperature of said composition increases.

29. The method of claim 24 wherein said matrix is a heatable resin.

30. An article capable of browning an article of food comprising:

(a) a plurality of susceptors, each of said susceptors comprising a particle substantially non-reflective of microwave energy, said particle bearing a coating capable of absorbing microwave energy and converting said energy to heat, and

(b) a matrix substantially non-reflective of microwave energy, said susceptors being embedded in said matrix.

31. The article of claim 30, wherein said matrix is selected from the group consisting of silicones, polyesters, and ceramics.