Anti-microbial porcelain enamel coating

Details Anti-microbial porcelain enamel coating Anti-microbial porcelain enamel coating

1999-11-08

2001-10-16

Parker, Fred J. (Department: 1762)

Coating processes

Solid particles or fibers applied

Uniting particles to form continuous coating with...

C427S201000, C427S204000, C427S205000, C427S376200

Reexamination Certificate

active

06303183

ABSTRACT:

FIELD OF INVENTION
This invention relates to porcelain enamel coatings suitable for applications such as domestic appliances and sanitary ware.
BACKGROUND
Porcelain enamel water contact surfaces are susceptible to the growth of microorganisms, especially when used infrequently. This microorganism growth can lead to problems ranging from offensive appearance and odor to health concerns. On sanitary ware surfaces, for example, bathtubs and sinks, and on stove top ranges, chemicals such as detergent and the like are customarily employed to control bacteria after it has grown. Infrequently utilized water heaters, as in summer houses, contain stagnant water in which microbes may proliferate. Once the bacteria forms, a foul odor may be created. In the case of a water heater containing stagnant water, the foul odor tends to linger until enough water has been used over time to replace the stagnant water with fresh water.
It would be desirable to prevent or mitigate the growth of bacteria on surfaces such as sanitary ware and water heaters while maintaining the protective corrosion resistant properties of the porcelain enamel coating.
SUMMARY OF THE INVENTION
The aim of the invention is to produce a functional anti-microbial, anti-mold, or anti-fungal porcelain enamel coating for use as a groundcoat or covercoat in the manufacture of those home appliances and sanitary ware that may benefit from such a coating.
Materials such as copper and silver exhibit anti-microbial properties. Several patents have been issued that, among other things, describe the anti-microbial effects of silver, copper, and zinc (see, for example U.S. Pat. No. 5,147,686 to Ichimura and U.S. Pat. No. 4,906,466 to Edwards).
Silver compounds have been described for use as glaze additive. For example, Japanese Publication 08333135 describes a sintered and crushed mixture of silver phosphate and kaolinite silicate which is said to impart antibacterial properties to the glaze. Also, silver compounds have been applied to the surface of baked enamel. For example, Japanese Publication 8100274 mentions a glaze containing borosilicate glass and a silver salt or a chromium salt which is coated and baked on the surface of baked enamel.
In attempting to produce an anti microbial porcelain enamel coating, one must not lose sight of the primary function of a porcelain enamel coating, which is to protect the substrate to which it is applied. Hence, modifying the porcelain enamel to obtain additional beneficial properties such as anti-microbial properties, requires a balance to ensure the corrosion resistant properties, adhesion properties or other desirable coating properties are not adversely affected in order to achieve anti-microbial properties.
Also, many types of additives would be destroyed in the milling and firing conditions employed in the manufacture of porcelain enamel. For instance, applying raw metal in a porcelain enamel tends to give a reducing effect and tends to cause problems with color stability. In addition, raw metal tends to float to the surface giving the enamel an undesirable sheen.
It has been found that anti-microbial porcelain enamel coatings may be successfully prepared according to the invention.
The invention provides a process for the preparation of an anti-microbial porcelain enamel coating. Generally, this process comprises incorporating an anti-microbial agent into a porcelain enamel composition, wherein the anti-microbial agent includes an anti-microbial metal disposed on a particulate support. The anti-microbial metal is silver, zinc, copper or mixtures thereof. The invention also provides an anti-microbial porcelain enamel coating prepared by the above process.
A more specific process for the preparation of the anti-microbial porcelain enamel coating comprises adding an anti-microbial agent to a glass frit or to a slip to form a mixture; applying the mixture to a substrate; and curing the mixture. The anti-microbial agent includes an anti-microbial metal selected from the group consisting of silver, zinc, copper and mixtures thereof disposed on a particulate support. The anti-microbial agent is added in an amount sufficient to provide anti-microbial properties to the coating; preferably, at least about 1 weight percent based on the total weight of the mixture. The anti-microbial agent is preferably selected from the group consisting of silver coated zinc oxide; copper coated zinc oxide; silver and zinc silicate coated titanium dioxide; silver, copper oxide, and zinc silicate coated titanium dioxide; and silver coated titanium dioxide. The mixture is preferably applied to a metal substrate; and the coated substrate is then fired at a temperature from about 1400° F. to about 1700° F. Thus, the anti-microbial agent is preferably incorporated into the porcelain enamel composition prior to curing the porcelain enamel composition.
The invention also provides an anti-microbial porcelain enamel coating comprising a porcelain enamel composition, and an anti-microbial agent dispersed throughout the porcelain enamel composition and present in an amount effective to provide anti-microbial properties. The anti-microbial agent comprises silver, zinc, copper or mixtures thereof disposed on a particulate support.
Anti-microbial porcelain enamel coatings of the invention may offer increased protection from bacteria (such as escherichia coli, pseudomonas aeruginosa, klebsiella pneumonia, staphylococcus aureus) and fungus (such as mold-aspergillis niger, yeast-candida albicans).
The resulting porcelain enamel coating may be useful in applications such as food contact surfaces, water contact surfaces, water heaters, water storage tanks, range tops, barbecues, and sanitary ware such as bathtubs and sinks.
Other features and advantages of the invention will become apparent to those skilled in the art upon review of the following Detailed Description and claims.
Before embodiments in the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of the composition or concentration of components, or to the steps or acts set forth in the following description. The invention is capable of other embodiments and of being practiced or being carried out in various ways. Also, it is understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting.
DETAILED DESCRIPTION OF THE INVENTION
The present invention is an anti-microbial porcelain enamel coating which inhibits the growth of microorganisms and a process for making same.
The anti-microbial porcelain enamel coating generally comprises a porcelain enamel composition and an anti-microbial agent having an anti-microbial metal disposed on a particulate support. Preferably, the anti-microbial agent is dispersed throughout the porcelain enamel composition. The anti-microbial agent should be present in an amount sufficient to provide the desired anti-microbial properties to the porcelain enamel coating. This may be achieved, for example, by adding the anti-microbial agent to the porcelain enamel coating in an amount of at least about 1 weight percent, based on the total weight of the porcelain enamel composition and the anti-microbial agent; more preferably, at least about 4 weight percent. The level of anti-microbial compounds may be varied depending on the degree of anti-microbial and anti-fungal resistance that is needed. For example, for top coat applications, it may be desirable to add the anti-microbial agent in an amount of at least about 15 weight percent.
The anti-microbial agent should be added in an amount less than that at which the anti-microbial agent substantially inhibits the corrosion resistant or other desirable properties of the porcelain enamel coating. Preferably, the anti-microbial agent constitutes at most about 25 weight percent; more preferably, at most about 10 weight percent; most preferably at most about 4 weight percent based on the total weight of the porcelain enamel composition and the anti-microbial agent. For to

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