Composite material containing microwave susceptor materials

Claim 2

A composite material for controlled generation of heat by absorption of microwave energy comprising (a) a dielectric substrate substantially transparent to microwave radiation, and (b) a coating on at least one surface of the substrate comprising (i) about 5 to 80% by weight of metal or metal alloy susceptor in flake form, and (ii) about 95 to 20% by weight of a thermoplastic dielectric matrix, wherein the surface weight of said coating on the substrate is in the range of about 2.5 to 100 g/m 2 .

Claim 3

A composite of Claim 1 where the coating contains about 25 to 80% by weight of metal or metal alloy susceptor and about 75 to 20% by weight of a thermoplastic dielectric matrix, and wherein the D.C. surface resistance of the resulting composite material is at least 1 x 10 6 ohms per square.

Claim 4

A composite of Claim 1 or 2 where the thermoplastic matrix is selected from the group consisting of copolymers of ethylene glycol, terephthalic acid and azelaic acid, copolymers of ethylene glycol, terephthalic acid and isophthalic acid, or mixtures of said copolymers.

Claim 5

A composite of Claim 1, 2 or 3 where the susceptor is aluminum.

Claim 6

A composite of any one of Claims 1 to 4 where the dielectric substrate is polyethylene terephthalate film, and the coating on at least one surface thereof comprises 30 to 60% by weight aluminum flake and 70 to 40% by weight of a copolymer of ethylene glycol with terephthalic acid and either isophthalic acid or azealic acid or mixture of such copolymers.

Claim 7

A packaging material comprising a composite of any one of Claims 1 to 5 laminated to a second dielectric substrate substantially transparent to microwave radiation.

Claim 8

A packaging material of Claim 6 where the second dielectric substrate is a polyester film or paper.

Claim 9

A composite of any one of Claims 1 to 7 capable of heating to a temperature of about 150°C or higher when subjected to microwave energy of 550 watts at 2450 megahertz for a period of 120 seconds.

Claim 10

A composite of any one of Claims 1 to 7 capable of heating to a temperature of about 190°C or higher when subjected to microwave energy of 550 watts at 2450 megahertz for a period of 120 seconds.

Claim 11

A composite of any one of Claims 1 to 9 where the susceptor comprises a circular flake having an ellipticity in the range of about 1:1 to 1:2.

Claim 12

A composite of Claim 10 where the susceptor comprises an aluminum flake.

Claim 13

A composite of Claim 11 where the susceptor comprises about 40 to 70 % by weight of the coating.

Claim 14

A composite of any one of Claims 1 to 9 where the susceptor comprises an oblong flake having an ellipticity greater than 1:2.

Claim 15

A composite of Claim 13 where the susceptor comprises an aluminum flake.

Claim 16

A composite of Claim 14 where the susceptor comprises about 20 to 60 % by weight of the coating.

Claim 17

A composite of any one of Claims 1 to 15 where the coating comprises at least two layers and the direction of alignment of susceptor flakes in at least one of said layers is oriented at about ninety degrees to the direction of alignment of susceptor flakes in at least one other of said layers.

Claim 18

A composite of Claim 16 where the susceptor is an oblong flake having an ellipticity greater than 1:2.

Claim 19

A composite of any one of Claims 1 to 17, samples of which then exposed to a microwave electric field of 243 V/cm for four minutes, said electric field parallel to the longitudinal direction of the composite in half of said samples and said electric field parallel to the cross direction of the composite in half of said samples, meet the following requirements: (1) M D and TD are each within Temp ±5%; (2) Each MD Temperature is within MD ±10%, and (3) Each TD Temperature is within TD ±10%, where MD Temperature is the temperature for any sample exposed with said electric field direction parallel to the longitudinal direction of the composite and MD is the mean temperature of all of such samples; TD Temperature is the temperature for any sample exposed with said electric field direction parallel to the cross direction of the composite and TD is the mean temperature of all of such samples; and Temp is the mean of all MD Temperatures and TD Temperatures, all temperatures being in Centigrade and measured after four minutes exposure to the microwave electric field.

Claim 20

A method for making a composite of Claim 1 comprising applying a plurality of thin, dilute coats of a dispersion of susceptor and thermoplastic matrix in a suitable solvent to the dielectric substrate.

Claim 21

The method of Claim 19 in which said thin, dilute coats are applied in a manner so that the direction of alignment of susceptor flakes in at least one said coat is oriented at about ninety degrees to the direction of alignment of susceptor flakes in at least one other of said coats.

Claim 22

A composite made by the method of Claim 19 or Claim 20.

Claim 23

A composite of any one of Claims 1 to 18 or 21 capable of heating to a temperature of about 150 degrees C or higher when subjected to microwave energy of 550 watts at 2450 Mhz for a period of 120 seconds.

Claim 24

A composite of any one of Claims 1 to 18 or 21 capable of heating to a temperature of about 190 degrees C or higher when subjected to microwave energy of 550 watts at 2450 Mhz for a period of 120 seconds.