Electrically conductive foam and method of preparation and use

Claim 2

An electrically conductive foam adapted for use with electronic components sensitive to static charges, which foam consists essentially of: an open-cell polymeric foam uniformly impregnated with electrically conductive particulate material in an amount of from about 2% to 40% by weight of the impregnated foam and sufficient to provide for a surface resistance of the foam of less than about 30,000 ohms per square inch, the particulate material having a particle size of less than 40 millimicrons, and from about 1% to 60% by weight of the impregnated foam of a film-forming polymeric-binding material securing the conductive particulate material to the foam.

Claim 3

The foam of claim 1 wherein the foam density ranges from about 0.5 to 10 pounds per cubic foot.

Claim 4

The foam of claim 1, which foam is an open-cell urethane foam.

Claim 5

The foam of claim 1 wherein the conductive particulate material comprises from about 10% to 30% by weight of the foam.

Claim 6

The foam of claim 1 wherein the electrically conductive particulate material is carbon black.

Claim 7

The foam of claim 5 wherein the carbon black has a nitrogen surface area ranging from about 100 to 1200 m 2 /gram.

Claim 8

The foam of claim 1 wherein the film-forming polymeric binder comprises a styrene-butadiene polymer or a combination of a styrene-butadiene copolymer with a polystyrene polymer.

Claim 9

The foam of claim 7 wherein the particulate material is carbon black and the polymeric-binding material has over about 60% by weight of styrene.

Claim 10

The foam of claim 1 wherein the particulate material is carbon black, and which foam has a surface resistance of less than about 5000 ohms per square inch.

Claim 11

An electrically conductive foam adapted for use with electronic components sensitive to static charges, which foam consists essentially of: an open-cell, polymeric, urethane foam having a foam density ranging from about 0.5 to 10 pounds per cubic foot and uniformly impregnated with electrically conductive, carbon-black particulate material having a particle size of less than about 40 millimicrons and a nitrogen surface area ranging from about 100 to 1200 m 2 /gram, the carbon-black particulate material comprising from about 10% to 30% by weight of the foam and in an amount sufficient to provide for a surface resistance of the foam of less than about 10,000 ohms per square inch, and a film-forming polymeric-binding material comprising a styrene-containing polymer and a polystyrene polymer, present in an amount of from 25% to 60% by weight of the impregnated foam, securing the conductive particulate material to the foam.

Claim 12

An electrically conductive foam adapted for use with electronic components sensitive to static charges, which foam consists essentially of: an open-cell, polymeric, urethane foam having a foam density ranging from about 0.5 to 10 pounds per cubic foot and uniformly impregnated with electrically conductive, carbon-black particulate material having a particle size of less than about 40 millimicrons and a nitrogen surface area ranging from about 100 to 1200 m 2 /gram, the carbon-black particulate material comprising from about 10% to 30% by weight of the foam and in an amount sufficient to provide for a surface resistance of the foam of less than about 10,000 ohms per square inch, and a film-forming polymeric-binding material comprising a styrene-containing polymer and a polystyrene polymer, present in an amount of from 25% to 60% by weight of the impregnated foam, securing the conductive particulate material to the foam.

Claim 13

The process of claim 1 wherein the foam density ranges from about 0.5 to 10 pounds per cubic foot.

Claim 14

The process of claim 1 wherein the foam is an open-cell urethane foam.

Claim 15

The process of claim 1 wherein the conductive particulate material comprises from about 10% to 30% by weight of the foam.

Claim 16

The process of claim 1 wherein the electrically conductive particles are carbon black.

Claim 17

The process of claim 14 wherein the carbon black has a particle size of about 25 to 35 millimicrons and a nitrogen surface area ranging from about 100 to 1200 m 2 /gram.

Claim 18

The process of claim 1 wherein the film-forming polymeric binder comprises a styrene-butadiene polymer.

Claim 19

The process of claim 1 which includes drying the impregnated foam by drying the foam while the foam is secured to prevent shrinkage of the impregnated foam.

Claim 20

A process for preparing an electrically conductive foam adapted for use with electronic components sensitive to static charges, which process consists essentially of: (a) providing an aqueous dispersion which comprises (i) electrically conductive carbon black having a particle size of less than 40 millimicrons, (ii) a dispersing agent for the carbon black, and (iii) a styrene-butadiene copolymer and a polystyrene-polymer latex having over about 60% of styrene (b) immersing an open-cell, porous urethane foam into the aqueous dispersion to impregnate uniformly the foam with the carbon-black particles; and (c) drying the impregnated foam to remove water and to bind the carbon-black particles to the foam with the copolymer, to provide an impregnated foam having from about 25% to 60% by weight of the styrene-butadiene copolymer and about 10% to 30% by weight of carbon-black particles, the foam having a surface resistance of less than about 10,000 ohms per square inch.

Claim 21

A process for preparing an electrically conductive foam adapted for use with electronic components sensitive to static charges, which process consists essentially of: (a) providing an aqueous dispersion which comprises (i) electrically conductive carbon black having a particle size of less than 40 millimicrons, (ii) a dispersing agent for the carbon black, and (iii) a styrene-butadiene copolymer and a polystyrene-polymer latex having over about 60% of styrene (b) immersing an open-cell, porous urethane foam into the aqueous dispersion to impregnate uniformly the foam with the carbon-black particles; and (c) drying the impregnated foam to remove water and to bind the carbon-black particles to the foam with the copolymer, to provide an impregnated foam having from about 25% to 60% by weight of the styrene-butadiene copolymer and about 10% to 30% by weight of carbon-black particles, the foam having a surface resistance of less than about 10,000 ohms per square inch.

Claim 22

The process of claim 18 which includes drying the impregnated foam in a stretched condition between fixtures at an oven temperature of 100° F. to 300° F.

Claim 23

An article which comprises in combination: (a) the foam of claim 1 wherein the foam is a rigid foam; and (b) an electronic device subject to damage by static charges and having one or more electrical leads, the leads inserted and retained in the rigid foam and in an electrically conductive relationship therewith, to prevent the accumulation of damaging static charge on the electronic device.

Claim 24

An article which comprises in combination: (a) the foam of claim 1; and (b) an electronic device subject to damage by static charge, the device being in electrical contact with the foam of claim 1.

Claim 25

The article of claim 21 wherein the electrical device comprises a metal-oxide semiconductor device, a microprocessor chip or an integrated circuit.

Claim 26

The article of claim 21 wherein the foam is a flexible foam and wherein the electronic device is packaged in and is surrounded by the foam, to provide for a cushioning of the electronic device, as well as preventing the accumulation of static charge therein.

Claim 27

A process for preparing electrically conductive foam adapted for use with electronic components sensitive to static charges, which process consists essentially of: (a) impregnating a substantially open-cell, porous foam with an aqueous dispersion consisting essentially of from about 2% to 40% by weight of electrically conductive particulate material in an amount sufficient to provide for the surface resistance of the dried foam of less than about 30,000 ohms per square inch, the particulate material having a particle size of less than 40 millimicrons, the dispersion containing from about 1% to 60% by weight of the impregnated foam of a film-forming polymeric-binding material to secure the conductive particulate material to the foam, and a dispersant agent for the dispersion of said particulate material in the aqueous dispersion; (b) removing excess water from the foam; and, thereafter, (c) heating the uniformly impregnated foam at a temperature sufficient to dry the foam and to bind the particulate material in the foam by the film-forming polymer, and to provide a surface resistance of the impregnated, bound, dried foam of less than about 30,000 ohms per square inch.

Claim 28

A process for preparing electrically conductive foam adapted for use with electronic components sensitive to static charges, which process consists essentially of: (a) impregnating a substantially open-cell, porous foam with an aqueous dispersion consisting essentially of from about 2% to 40% by weight of electrically conductive particulate material in an amount sufficient to provide for the surface resistance of the dried foam of less than about 30,000 ohms per square inch, the particulate material having a particle size of less than 40 millimicrons, the dispersion containing from about 1% to 60% by weight of the impregnated foam of a film-forming polymeric-binding material to secure the conductive particulate material to the foam, and a dispersant agent for the dispersion of said particulate material in the aqueous dispersion; (b) removing excess water from the foam; and, thereafter, (c) heating the uniformly impregnated foam at a temperature sufficient to dry the foam and to bind the particulate material in the foam by the film-forming polymer, and to provide a surface resistance of the impregnated, bound, dried foam of less than about 30,000 ohms per square inch.

Claim 29

The process of claim 24 wherein the dispersing agent comprises an anionic surfactant.

Claim 30

The process of claim 25 wherein the surfactant has a pH in an aqueous composition of from 8.5 to 11.5.

Claim 31

The process of claim 24 which includes, firstly applying an aqueous dispersion of the carbon-black particles with an anionic-surfactant dispersing agent in an aqueous composition to the foam to penetrate the foam and, thereafter, impregnating the foam with an aqueous composition of a film-forming polymer-binding material.