| PATENT NUMBER | This data is not available for free |
| PATENT GRANT DATE | August 13, 2002 |
| PATENT TITLE |
Anti-microbial power coating |
| PATENT ABSTRACT |
Improved powder coatings exhibit enhanced resistance to bacterial and fungal attack, while possessing excellent toughness, appearance, corrosion resistance, durability, processability, and ease of application. The coating is comprised of anti-microbial agents melt-processed into the matrices of coating powders or bonded to coating powders. An article may be coated with a thermoset or thermoplastic powder that may be applied by electrostatic spray or fluidized bed or by thermal or flame spray. |
| PATENT INVENTORS | This data is not available for free |
| PATENT ASSIGNEE | This data is not available for free |
| PATENT FILE DATE | November 16, 2000 |
| PATENT REFERENCES CITED | Healthshield.TM. Antimicrobial, AgION Technologies LLC, printed from http://healthshield.com, 2000. |
| PATENT PARENT CASE TEXT | This data is not available for free |
| PATENT CLAIMS |
What is claimed is: 1. An anti-microbial powder coating composition comprising one or more anti-microbial metals or metal ions homogeneously dispersed within particles of a resin-based powder. 2. The composition of claim 1 wherein the anti-microbial metal or metal ion is silver. 3. The composition of claim 2 wherein the silver is in the form of a silver ion carried by a zeolite. 4. The composition of claim 2 wherein the silver is supplied by a silver salt. 5. The composition of claim 2 wherein the silver is supplied by an organic compound containing silver. 6. The composition of claim 2 wherein the powder coating composition comprises a thermosetting composition based on a cured polyester resin composition. 7. The composition of claim 6 wherein the silver is carried by a zeolite. 8. The composition of claim 7 wherein the polyester resin composition is cured with a urethane curing agent. 9. The composition of claim 8 wherein the urethane curing agent is a caprolactam-blocked isocyanate. 10. The composition of claim 8 wherein the urethane curing agent is a uretidione-blocked isocyanate. 11. The composition of claim 8 wherein the silver containing zeolite is about 1 to 3 percent of the sum of the components comprising the powder coating composition. 12. The composition of claim 7 wherein the polyester resin composition is cured with a triglycidylisocyanurate. 13. The composition of claim 12 wherein the silver containing zeolite is about 10 percent of the sum of the components comprising the powder coating composition. 14. A method for preparing an anti-microbial powder coating composition comprising homogeneously mixing an anti-microbial metal or metal salt into a powder coating pre-mix. 15. The method of claim 14, further comprising blending the components of the powder coating composition using a premixer, feeding the mixture into an extruder, and heating the mixture to a temperature high enough to melt it, cooling the melt, and processing the solid extrudate into a coating powder. 16. The method of claim 15 further comprising treating the powder coating particles by impacting the powder coating particles with particles containing an anti-microbial metal or metal salt to adhere the anti-microbial metal or metal salt to the coating powder particles. |
| PATENT DESCRIPTION |
BACKGROUND This invention relates generally to powder coatings and particularly to anti-microbial powder coatings. Public concern about the health hazards arising from microorganisms such as bacteria, fungi, viruses and the like is high. Many people are concerned that contact with objects in public facilities may result in illness. Also, it is desirable to prevent biological defacement of object surfaces due to the growth of microorganisms. Thus, a number of efforts have been undertaken to produce objects with the ability to kill or inhibit the growth or reproduction of microorganisms, which is termed "anti-microbial activity" herein. For example, plastic materials with anti-microbial activity are known. The resulting plastic products then exhibit some degree of anti-microbial activity. For example, some toys for young children include anti-microbial agents (i.e., agents with anti-microbial activity) within a plastic matrix. These anti-microbial agents, which are believed to be safe, are believed to inhibit the growth of various microorganisms. Anti-microbial agents in the final coatings including paint and powder coatings are known. However, none of the existing techniques in powder coatings have gained substantial acceptance. Therefore, there is a continuing need for improved coatings and particularly for improved powder coatings that exhibit anti-microbial activity when applied to substrates. SUMMARY An anti-microbial powder coating composition includes an anti-microbial agent homogeneously dispersed within particles of a resin-based powder. BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a diagrammatic depiction of a process for making a powder coating. DETAILED DESCRIPTION A stable anti-microbial powder coating composition may coat a product that may be exposed to bacteria and fungal spores. The powder coating may be made by a process that produces a homogeneous distribution of anti-microbial agents that may promote consistent and efficient anti-microbial activity. Once coated with the anti-microbial powder coating, a substrate may be protected from physical abuse by the film's physical properties and durability and from degradation due to attack by microorganisms and also potentially protecting the user from various microorganisms. The powder coating formulation may be applied to the substrate so that bacterial or fungal contact with the coating either kills them or at least inhibits their growth. For example, in some embodiments, anti-microbial activity with respect to Staphylococcus aureus, Escherichia coli, Bacillus subtillus, Streptococcus faecalis, Salmonella typhinurium, Pseudomonas aeruginosa, and other Gram positive and Gram negative bacteria may be achieved. Powder coating formulations, in some embodiments, may also inhibit the growth of certain higher organisms like algae, fungi, filamentous fungi (Aspergillus, Aureobasidium, Botrytis, Ceratostomella, Cuvularia, Fusarium and Penicillium species), yeast and also, some viruses. Potential applications for these improved powder coatings may include, for example, food preparation areas, restrooms, hospitals, garbage disposals, stockyard areas, animal feed troughs, schools, kitchens, swimming pool areas, dishwashers, automobile fixtures, public access fixtures, public seating, public transportation fixtures, toys, and other industrial, agricultural, commercial or consumer products. The resin may be one or more of the thermosetting and/or thermoplastic resins including those based on epoxy, polyester, acrylate, acrylic, polysiloxane and/or polyurethane resins. The coating may also include from about 0.1 percent to about 10 percent by weight of the total composition of one or more liquid or solid anti-microbial agents. Examples of thermoplastic or thermosetting coatings that may be used, include: but are not limited to epoxies, saturated and unsaturated polyesters, carboxylic acid-functional polyesters, hydroxyl-functional polyesters, epoxy/polyester hybrids, acrylics, epoxy/acrylic hybrids, glycidyl-functional acrylics, polyester-urethanes, acrylic urethanes and siloxanes. Thermoplastic powder coatings that may be useful include, but are not limited to nylon, polyvinyl chloride (PVC), polyethylene, polyethylene terephthalate (PET), polybutylene terephthalate (PBT), and polypropylene as examples. These powder coatings may be cured or fused by thermal or photochemical methods. The anti-microbial agents include but are not limited to phthalimides, acetamides, phthalonitriles, hydroxy benzoates, isothiazolinones, nitropropane diols, carbamates, methyl ureas, benzimidazoles, salicylanilides, mercury acetates, organozinc compounds, metals such as silver, copper and zinc, and ions of such metals. Among the liquid anti-microbial agents which are suitable in certain applications, a preferred anti-microbial agent is dibromocyanoacetamide (for example, Amerstat.RTM. 300 made by Drew Industrial Division of Ashland Chemicals, Boonton, N.J. 07005). In addition, solid anti-microbial agents that are preferred include 2-bromo-2-nitropropane-1,3-diol (for example, Canguard.RTM. 409 made by Angus Chemical Co., Buffalo Grove, Ill. 60089) and 3,5-dimethyltetrahydro-1,3,5-2H-thiazine-2-thione (for example, Nuosept.RTM. S made by Creanova, Inc., Piscataway, N.J. 08855 or Troysan.RTM. 142 made by Troy Chemical Corp., West Hanover, N.J. 07936). Other solid anti-microbial agents include N- (trichloromethyl)-thiophthalimide (for example, Fungitrol.RTM. 11 made by Creanova, Inc.), butyl-p-hydroxy-benzoate (for example, Butyl Parabens.RTM. made by International Sourcing Inc., Upper Saddle River, N.J. 07458), diiodomethyl-p-tolysulfone (for example, Amical.RTM. WP made by Angus Chemical Co.), and tetrachloroisophthalonitrile (for example, Nuocide.RTM. 960 made by Creanova, Inc.). Metals such as silver, copper and zinc and ions of such metals also have anti-microbial properties. Silver ions have widespread effect as an anti-microbial agent. For example, silver ions may be effective against bacteria such as Escherichia coli and Salmonella typhimurium, and mold such as Asperigillus niger. Sources of silver for anti-microbial use include metallic silver, silver salts and organic compounds that contain silver. Silver salts may include for example: silver carbonate, silver sulfate, silver nitrate, silver acetate, silver benzoate, silver chloride, silver fluoride, silver iodate, silver iodide, silver lactate, silver nitrate, silver oxide and silver phosphates. Organic compounds containing silver may include for example, silver acetylacetonate, silver neodecanoate and silver ethylenediaminetetraacetate in all its various salts. Silver containing zeolites (for example, AJ10D containing 2.5% silver as Ag(I), made by AgION.TM. Tech. L.L.C., Wakefield, Mass. 01880) are of particular use. Zeolites are useful because when carried in a polymer matrix they may provide silver ions at a rate and concentration that is effective at killing and inhibiting microorganisms without harming higher organisms. The powder coating may be sprayed electrostatically onto a metal or nonmetal substrate. Charged particles of the powder coating are sprayed onto the substrate until a desired thickness is achieved. Other methods, such as fluidized bed coating methods, thermal spraying and flame spraying may also be used. After the deposition is complete, the coated substrate is heated. For example, an electrical or gas fired oven may be used to cure or fuse the coating at temperatures in the range of 80.degree. C. to 270.degree. C. The curing time may be about five to twenty minutes for most substrates, but may vary from less than a minute to greater than one hour depending on the type of coating, the substrate, and the curing system. In addition to thermal methods, curing may also be achieved by electron beam or photochemical methods such as ultraviolet, infrared and the like. Curing of the coating can be effected by heat conduction, convection, radiation, or any combination of the three. Advantageously, visible bubbling in the coating film after the curing process should be avoided. The presence of bubbles may indicate that some of the biocide may have been volatilized during the curing process. Advantageous anti-microbial agents should not produce visible bubbles indicative of volatilizing of the active element. The powder coatings may be made by a melt extrusion method, as illustrated in FIG. 1. For example, a powder formulation includes more than one ingredient as represented by items 1-4. Fillers, extenders, flow additives, catalysts, hardeners, catalysts, pigments and other additives may be blended together with the resin and the anti-microbial agent in a premixer 5. The mixture may then be fed into an extruder 6 and heated to a temperature high enough to melt and mix the constituents. A temperature in the range of 50.degree. C. to 150.degree. C. may be sufficient. The molten extrudate may be immediately cooled by chill rolls 7 to form solid sheets. The solid sheets may be further broken down to suitably sized chips. These chips are then fed into a grinder 8 which reduces the chips to fine particles. For example, particles having a mean particle size of about 10 microns to 180 microns are satisfactory. The resulting powder advantageously has a glass transition temperature that is greater than the storage temperature. A dust filter 9, a sieve screen 10, and powder inspection station 11 and 12 may also be provided. The anti-microbial agents are uniformly dispersed in the resin formulation (including the curing agent) during the premix stage. This is advantageous because there is no requirement that the anti-microbial agents have a specific particle size or particle size distribution. The anti-microbial agents are chosen to survive the extrusion process and the subsequent curing process in sufficient concentration to exhibit an anti-microbial effect in the final coating. In addition, it is preferable that the anti-microbial agent does not adversely change any important property of the final coating such as color. Solid anti-microbial agents including those, which are metallic or metal containing, may be premixed directly with the formulation components. Alternatively, the particles of anti-microbial agent may be bonded with pre-formed powder coating particles using impact fusion. This process is also known in the art as "fusion bonding." With either method, mixing the anti-microbial particles with coating particles of the same particle size distribution is not necessary. Liquid anti-microbial agents can be mixed readily with other components in the premix prior to extrusion. Liquid anti-microbial agents often are difficult to dry blend into a powder to a concentration that consistently, effectively protects against bacteria or fungi. Alternatively, liquid anti-microbial agents may be mixed initially with particles of a solid support material such as a silica, clay or other resins in a masterbatch. The dry mixture containing the liquid anti-microbial agent may then be mixed into a formulation of resin. For example, the liquid anti-microbial agent may be mixed at room temperature using high shear into fumed silica yielding high concentrations of active ingredients. The resulting granular solid may then be treated as a solid anti-microbial agent. For example, concentrations of approximately 66 percent of active ingredients in fumed silica may be utilized. Liquid and solid anti-microbial agents also may be incorporated within the powder coating particle by dissolving or mixing them and the other powder coating formulation components in a suitable solvent, e.g., organic liquids or supercritical fluids, and then removing the liquid in such a manner as to yield a powder or a solid product which can be processed into a powder. A suitable powder coating material, which is utilized in examples one through four is Gold Bond III, a catalyzed epoxy powder coating sold by DuPont Powder Coatings, Inc., of Houston, Tex. Fillers and extenders, melt flow additives, dry flow additives, pigments and other additives may also be used to enhance specific physical properties, aesthetics, durability or other attributes. Other powder coating materials, utilized in example 5, include urethane-cured polyesters compositions and triglycidylisocyanurate (TGIC) epoxy-cured polyesters compositions. Fillers, flow aids, degassing aids and pigments may also be used to enhance certain properties of the powder coating such at aesthetics and durability. |
| PATENT EXAMPLES | available on request |
| PATENT PHOTOCOPY | available on request |
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