Heat exchange – With coated – roughened or polished surface
Reexamination Certificate
1998-12-30
2001-01-09
Dudash, Diana (Department: 1619)
Heat exchange
With coated, roughened or polished surface
C106S015050, C165S134100, C165SDIG005, C165SDIG005, C424S407000, C424S411000
Reexamination Certificate
active
06170564
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates in general to antimicrobial coatings and, more particularly, to room temperature cure, antimicrobial coatings that demonstrate a balance of properties including low dissolution and good cohesion and adhesion.
BACKGROUND OF THE INVENTION
Antimicrobial coatings can be used in a variety of space life support and commercial applications where control of microbial growth is of particular concern.
High temperature cure, hydrophilic (optionally antimicrobial) coatings that rely upon an inorganic compound, such as silica, to provide hydrophilic characteristics to the coating, are known.
U.S. Pat. No. 5,562,949 to Steele et al. discloses an optionally antimicrobial, hydrophilic, high temperature cure coating composition that contains from about 10% to about 20 wt. % of an inorganic compound (e.g., silica, calc ium silicate or mixtures thereof). This reference teaches that complete curing of the coating occurs at temperatures up to and including 260° C.
U.S. Pat. No. 5,305,827 to Steele et al. discloses an antimicrobial, hydrophilic coating that comprises an adhesive agent (e.g., potassium silicate); an insolubilizer (e.g., zinc oxide); an inorganic compound (e.g., silica, calcium silicate, and mixtures thereof); and from about 0.1 wt. % to about 1.0 wt. % of silver oxide. The coating of U.S. Pat. No. '827 is cured at a temperature of 5000° F. (260° C.) either sequentially or very slowly over a period of from 1 to 6 hours (see Col. 5, lines 62-65 of U.S. Pat. No. '827).
U.S. Pat. No. 5,264,250 to Steele et al. discloses a method for coating heat transfer surfaces of a condensing heat exchanger with the above-referenced antimicrobial, hydrophilic coating. Again, this reference teaches a cure temperature of 500° F. (260° C.).
As will be readily evident to those skilled in the art, such high temperature cure coatings are not applicable to, nor can such coatings be applied in close proximity to, heat sensitive materials. Further, the need to cure coatings at high temperatures complicates the coating process by increasing the processing time and the complexity of the equipment associated therewith.
It is therefore an object of the present invention to provide a room temperature cure, antimicrobial coating.
It is a more particular object to provide a room temperature cure, antimicrobial coating that demonstrates a balance of properties including low dissolution and good cohesion and adhesion.
It is yet a more particular object to provide a room temperature cure, antimicrobial coating that demonstrates a greater zone of microbial inhibition, greater cohesion and a greater degree of adhesion to target surfaces when compared to high temperature cure, antimicrobial, hydrophilic coatings.
It is a further object to provide an air handling or water processing system or subsystem having chronically moist or wet surfaces that have been coated with such a room temperature cure, antimicrobial coating.
SUMMARY OF THE INVENTION
The present invention therefore provides a room temperature cure, antimicrobial coating. The coating, in the form of a slurry, comprises:
a. from about 1.0% to about 3.6% by weight of an antimicrobial agent;
b. from about 22.6% to about 33.8% by weight of an adhesive agent;
c. from about 12.8% to about 18.7% by weight of an insolubilizer for insolubilizing the adhesive agent; and
d. from about 47.4% to about 60.3% by weight of water or a water-based solvent,
where the sum of the components is 100% by weight, based upon the total weight of the slurry.
The present invention also provides an air handling or water processing system or subsystem having chronically moist or wet surfaces that have been coated with the room temperature cure, antimicrobial coating described hereinabove.
The foregoing and other features and advantages of the present invention will become more apparent from the following description.
DETAILED DESCRIPTION OF THE INVENTION
Although the present inventive room temperature cure, antimicrobial coating will be described herein in reference to air handling or water processing systems or subsystems (e.g., air conditioner cooling coils) it is not so limited. This coating can be utilized on any surface where control of microbial growth is of particular concern. In particular, any chronically moist or wet substrate, the functionality of which can be disrupted by biogrowth, represents a potential application area for the present inventive coating. In addition, any chronically moist or wet system or subsystem that can shed microbes into an effluent air or water stream and potentially adversely effect occupant health represents another potential application area for this coating.
The antimicrobial agent of the present invention provides biocidal characteristics to the coating. In order to prevent microbial proliferation, the antimicrobial agent is preferably a substance which slowly dissolves into a condensate and inhibits microbial growth. For example, if silver oxide is utilized as the antimicrobial agent, it slowly dissolves into the condensate in the form of silver ions. The silver ions diffuse through the cell walls of the microbe, and complex with the cellular DNA therein. This complex formation interrupts the normal role of DNA and thus prevents reproduction of the microbe. Conventional biocides which have an equilibrium dissolution rate similar to that of the adhesive agent and the insolubilizer described below can be employed. If the antimicrobial agent dissolves into the condensate at a faster rate than the adhesive agent and/or insolubilizer, the effectiveness of the antimicrobial agent can be reduced.
Possible antimicrobial agents include salts such as arsenic salts, iodine salts, iron salts, mercury salts, silver salts, tin salts, and mixtures therein)f, with mercury salts and silver salts preferred. Silver salts are especially preferred. A silver salt which has proven particularly useful as an antimicrobial agent having an appropriate equilibrium dissolution rate is silver oxide, which can be purchased from Mallinckrodt Co., Paris, Ky., in a purified powder form.
The preferred concentration of the antimicrobial agent, based upon the total weight of the slurry of the present invention, is from about 1.0% to about 3.6% by weight, with the more preferred concentration being from about 3.0% to about 3.6% by weight.
It is noted herein that an absence of any detrimental effect on the desirable properties of the coating (e.g., adhesion, cohesion) when using such increased quantities of an antimicrobial agent is both unexpected and surprising. Prior studies have indicated that an increase in the concentration of silver oxide to the levels indicated above will result in a corresponding drop off in the adhesion and cohesion properties of the resulting coating.
The antimicrobial agent preferably has an average particle size of from about 6 to about 14 microns, with about 8 to about 10 microns especially preferred. Particle sizes in this range contribute to desirable dissolution properties, increase the slurry life, components do not separate out as quickly, and the slurry is easier to mix.
The adhesive agent and insolubilizer used in the present inventive coating collectively provide structural integrity to the coating by binding it together and by preventing flaking and cracking. The adhesive agent and insolubilizer also serve to effect good adherence to and uniformity of coverage of the coating on target surfaces.
The increased cohesion/adhesion demonstrated by the present inventive coating, that is cured at room temperature, is surprising and unexpected. As is well known to those skilled in the art, curing is a process by which a network of cross-links is introduced into a material. As curing temperatures are increased, the expectation is that the level of cross-linking, not only within the material but also between the material and the surface it coats, will increase as well, thereby producing a stronger, tougher and more adherent material. As curing temperatures are decreased, the expectation is that th
Bonzagni, Esq. Mary R.
Dudash Diana
Holland & Bonzagni, P.C.
Sharareh Shahnam
Unted Technologies Corporation
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