Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Including a second component containing structurally defined...
Reexamination Certificate
2000-03-24
2003-11-11
Nakarani, D. S. (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Including a second component containing structurally defined...
C427S212000, C427S218000, C428S323000, C428S423100, C524S439000, C252S512000, C252S513000, C252S514000
Reexamination Certificate
active
06645613
ABSTRACT:
FIELD OF THE INVENTION
The present invention is directed to a coating composition comprising a pigment, a water-dispersible urethane resin, and a solvent effective amount of a water-soluble solvent. The water-dispersible urethane resin exists as a colloidal dispersion in water but when mixed with a water-soluble solvent swells to provide a dispersion having a viscosity sufficiently high in the solvent so as to maintain the pigment in suspension in the solvent for a time sufficient to apply the coating composition. The present invention is also directed to a method for coating a substrate with the novel coating composition and to a coated substrate prepared by the novel method.
DESCRIPTION OF THE BACKGROUND
Certain electronic appliances, such as cellular phones and computers, require a thin coating of a conductive metal around their internal components, such as inside the housing, to shield the internal components. These conductive coatings may be applied to the inside of the housing by spraying, brushing, dipping, rolling, or screen printing a coating composition of finely divided, conductive metal particles suspended in a liquid vehicle. Spraying is a preferred method of applying the conductive coating because it is fast and can lay down uniform, thin layers on intricately shaped parts. Subsequently, the coating composition is dried at ambient or an elevated temperature.
The conductive coating composition is generally a mixture of an adhesive resin and a conductive metal such as silver, nickel, or copper, in an aqueous or organic medium. Traditionally, the solvent medium for the coating composition has been an organic compound in the aromatic or ketone family. Some organic compound-based vehicles, however, have many draw-backs such as toxicity, flammability, and are subject to environmental regulatory standards. the expense to purchase and to discard the organic solvent. In addition, some organic solvents, such as methyl ethyl ketone, methyl i-butyl ketone, and toluene) tend to attack solvent sensitive substrates such as substrates made of plastic polycarbonate and polycarbonate blends including those used in the housing of cellular phones and computers. Aqueous-based mediums, on the other hand, tend to be slow to dry and are impractical for large scale production.
U.S. Pat. No. 4,622,269 (Leung et al.) discloses a process for manufacturing contacts formed of an electrically conductive metal and a minor amount of graphite or cadmium oxide. The process comprises forming a mixture of finely divided electrically conductive metal and graphite or cadmium oxide, and compressing the mixture into a body having a working surface and an obverse side. The working surface is adapted to contact another electrically conductive surface and the obverse side is adapted to be secured to an electrically conductive support. The obverse side of the body is coated with a thin layer of the finely divided electrically conductive metal and the coated contact is sintered at a temperature less then the melting point of the electrically conductive metal to secure the electrically conductive metal to the working surface. Leung et al. describes an example employing the use of a slurry of silver powder in an aqueous alcoholic solution of Carbowax.
U.S. Pat. No. 5,089,173 (Frentzel et al. '173) discloses a thermally curable conductive polymeric thick film composition. The composition comprises by weight (a) about 3-15 parts of a thermoplastic vinyl acetate/vinyl chloride/dicarboxylic acid multipolymer resin; (b) a second thermoplastic resin selected from the group consisting of (i) about 1-6 parts of a thermoplastic polyurethane resin; (ii) about 2-10 parts of a thermoplastic polyester resin; and (iii) about 1-10 parts of a mixture of a thermoplastic polyurethane and a thermoplastic polyester resin; (c) about 0.05-1 parts of a tertiary amine; (d) an effective dissolving amount of an organic solvent; and (e) about 50-80 parts of silver flake. Frentzel et al. '173 states that the organic solvents employed may be nonhydrocarbon polar solvents such as acetone and methyl ethyl ketone.
U.S. Pat. No. 5,141,777 (Frentzel et al. '777) discloses a method of curing a polymer thick film on a substrate. The method comprises the steps of providing a polymer thick film composition comprising, by weight (a) about 3-15 parts of at least one thermoplastic vinyl acetate/vinyl chloride/dicarboxylic acid multipolymer resin; (b) a second thermoplastic resin selected from the group consisting of (i) about 1-6 parts of at least one thermoplastic polyurethane resin; (ii) about 3-10 parts of at least one thermoplastic polyester resin; or (iii) about 1-10 parts of a mixture of at least one thermoplastic polyurethane and at least one polyester resin; (c) about 0.05-1 parts of a tertiary amine; (d) at least one organic solvent capable of substantially dissolving (a), (b), and (c) ingredients; and (e) about 50-80 parts silver flake. The polymer thick film composition is then applied to a substrate and cured onto the substrate by exposing the coated substrate to an elevated temperature. Frentzel et al. '777 states that the organic solvents employed may be nonhydrocarbon polar solvents such as acetone and methyl ethyl ketone.
U.S. Pat. No. 5,286,415 (Buckley et al.) discloses an aqueous conductive polymeric thick film-forming and printable composition. The composition comprises (a) about 0.25% to about 20% by weight of a water-soluble thermoplastic polymer selected from the group consisting of polyethyloxyazoline, polyvinyl pyrrolidone, polyvinyl alcohol, polyacrylamide, polyglycol, and polyacrylic acid; (b) about 10 to 70% by weight of a water-insoluble polymer dispersion in water selected from the group consisting of polyurethane resin polymer, acrylic resin polymer, polyester resin polymer, and vinyl resin polymer; (c) about 2% to about 20% by weight of a glycol compound drying retarder agent; (d) an effective amount conductive particles selected from the group consisting of conductive metal particles, carbon black particles, and graphite particles; and (e) an effective solvating amount of water to dissolve the water-soluble thermoplastic polymer. Buckley et al. states that the polyurethane resin polymer employed is a water-insoluble polymer.
U.S. Pat. No. 5,399,547 (Negm et al.) discloses a method for increasing the critical current density carried by a high transition temperature superconductive material. The method comprises providing an elongated article of high transition temperature superconductive material; providing a noble metal in fragmented form selected from the group consisting of silver, gold, and platinum; applying the noble metal fragments as a superficial coating over the external surface of the elongated article of high transition temperature superconductive material; heating the superficial coating of noble metal fragments upon the external surface of the elongated article of high transition temperature superconductive material to a temperature greater than the softening-point temperature and less than the melting-point temperature of the noble metal such that the heated noble metal fragments of the superficial coating soften, migrate over, and superficially cover the external surface of the elongated article and become superficially embedded within the high transition temperature superconductive material; and allowing the heated noble metal superficial covering on the external surface of the elongated article of high transition temperature superconductive material to cool and solidify.
U.S. Pat. No. 5,425,969 (Wakabayashi et al.) discloses a method for coating an article made of polypropylene with an electrically conductive primer and thereafter electrostatically applying an organic solvent overcoat composition to the resulting coating. The conductive primer comprises (A) a urethane-modified chlorinated polypropylene which is a mixture or addition reaction product of a chlorinated polypropylene and a polyurethane resin, (B) a melamine resin, (C) a polyester resin, and (D) an electrically conduct
Muccino Richard R.
Nakarani D. S.
Spraylat Corporation
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