Microwave heatable composites

• US 5,446,270 A
• Filed: 01/12/1994
• Issued: 08/29/1995
• Est. Priority Date: 04/07/1989
• Status: Expired due to Term

• Current Assignee: 3M Company
• Original Assignee: 3M Company
• Inventors: Minick, Chris A., Vesley, George F., LePere, Pierre H., Chamberlain, Craig S., Zimmerman, Patrick G., Connell, Glen, Palmgren, Charlotte M., Tait, William C.
• Primary Examiner(s): HOANG, TU BA
• Application Number:
  US08/180,448
• Time in Patent Office: 594 Days
• Field of Search: 219/730, 219/731, 219/729, 219/759, 99/DIG. 14, 426/103, 426/113, 426/234, 426/243, 428/49, 428/209, 428/403, 428/408, 428/407, 427/221, 427/218, 427/125, 427/217, 427/229, 427/279, 427/457, 427/516, 427/215, 427/219
• US Class Current: 219/730
• 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, said susceptors comprising a particulate substrate substantially non-reflective of microwave energy and a coating capable of absorbing microwave energy, and (b) a matrix substantially non-reflective of microwave energy. Susceptors are typically particles having a thin-film coating thereon. 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. An article comprising a flowable meltable particle being spheroidal, rod-like or acicular in shape and having a surface, said surface bearing a coating having an electrical resistivity from 1×

10^-6 Ohm-cm to 1×

10⁷ Ohm-cm which absorbs sufficient microwave energy to cause said particle to melt and flow.

2. The article of claim 1, wherein said particle is a hot melt adhesive.

3. The article of claim 1, wherein said particle is substantially non-reflective of microwave energy.

4. The article of claim 1, wherein said coating is electrically conductive.

5. The article of claim 1, wherein said coating is semi-conductive.

6. The article of claim 1, wherein said coating is inorganic.

7. The article of claim 1, wherein said particle has a regular geometric shape.

8. Method of preparing a hot melt adhesive capable of being heated by microwave energy comprising the steps of:

(a) preparing susceptors comprising a particle substantially non-reflective of microwave energy, said particle bearing a thin, electrically conductive coating, said coating having a electrical resistivity from 1×

10^-6 Ohm-cm to 1×

10⁷ Ohm-cm which absorbs microwave energy, and

(b) incorporating the susceptors into a hot-melt adhesive matrix.

9. Method of preparing a susceptor having a capability of absorbing microwave energy, said susceptor comprising a particle substantially non-reflective of microwave energy and a coating capable of absorbing microwave energy comprising the steps of:

(a) providing a particle substantially non-reflective of microwave energy,

(b) applying a coating having an electrical resistivity from 1×

10^-6 Ohm-cm to 1×

10⁷ Ohm-cm which absorbs microwave energy over said particle, said coating having an outer portion, and

(c) causing the outer portion of said coating to oxidize sufficiently to change the electrical conductivity of said outer portion of said coating.