1. Field of the Invention

The invention is directed to improved antimicrobial surface treatments for plastic materials .

2. Description of Related Art

Antimicrobial coatings have many uses in textiles and other materials that are exposed to microbial contamination. One such use is with toothbrushes. Modern toothbrushes are made out of thermoplastic materials and typically have bristles made from an appropriate thermoplastic material such as nylon.

One drawback of toothbrushes is that they can, under the proper conditions of heat and humidity, develop into sources of the very microbial agents that they are used to combat. Others have attempted to control this tendency to contamination by coating the nylon bristles with antibacterial or antimicrobial agents. Coating of the bristles, however, has not generally proven effective for continued antimicrobial activity. The bristles of a toothbrush are exposed to high abrasion levels, and any coating generally wears off after only a few uses of the toothbrush. After the coating is sufficiently worn to expose

part of the underlying fiber, the toothbrush is susceptible to contamination.

The art still has not come up with an adequate antimicrobial coated toothbrush, or indeed any antimicrobial shaped article, suitable for everyday use that can be incorporated into an abrasive article such as a toothbrush designed for human use.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a material that has antimicrobial activity and that can withstand abrasion found in a environment that a toothbrush encounters in ordinary use.

To achieve the object of the invention as broadly described herein, the invention comprises a coating material comprising a nylon multipolymer resin, an acid and a silane quaternary ammonium solution.

In addition, the invention comprises a method of providing antimicrobial protection for a coated article, comprising the^ steps of acid etching the article to be coated and applying to the etched article a coating material comprising a nylon multipolymer resin, an acid and a silane quaternary ammonium solution.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The presently preferred embodiments of the invention will now be set forth.

The invention comprises a coating material comprising a nylon multipolymer resin, an acid and a silane quaternary ammonium solution. These ingredients may be combined in a solvent to form a suspension or solution, and the article to be coated may be dipped or otherwise painted with the coating solution. The coating is then preferably dried before use.

The nylon multipolymer resin preferably comprises Elvamide 8061, a nylon multipolymer resin manufactured by DuPont Polymers, Wilmington, Delaware. Elvamide is a nylon multipolymer resin comprising polyamides. It is soluble in alcohol.

The acid is preferably a mineral acid such as hydrochloric acid or an organic acid such as acetic acid.

The silane quaternary ammonium compound is preferably 3 (trimethoxysilyl) propyloctadecyl dimethyl ammonium chloride: Preferably, this compound is Dow Corning 5700 Antimicrobial Agent, manufactured by Dow Corning Corporation, Midland, Michigan.

The three components may be dissolved or suspended in a

suitable solvent such as methanol or another alcohol, and articles to be coated may be painted with or dipped in the solution.

Preferably, articles to be coated comprise thermoplastic materials, and more preferably comprise materials that have an affinity for the coating solution. Most preferred are nylon and cellulose acetate propionate.

The materials to be coated are preferably acid etched before exposure to the coating solution. Hydrochloric acid and methanol are a preferred combination for the etching agent, but other suitable agents are known in the art for etching thermoplastic materials.

After coating, the coated articles may be dried at room temperature or at elevated temperature.

Various examples of the invention will now be set forth.

Example 1

183.5 g methanol, 25.0 g Elvamide 8061 pellets, 21.5 g hydrochloric acid and 20 g C ₁₄ or C ₁₈ quaternary ammonium compound were charged to a 500 ml beaker on a magnetically driven stirring hot plate in the following manner. A magnetic stir bar was used to suspend all the materials. The methanol was heated

to 50 degrees C. 25.0 g Elvamide 8061 pellets were stirred into the heated methanol and dissolved. The other materials were then added in order to the solution. The mixture was allowed to hydrolyze for thirty minutes.

Nylon 6-12 plaques were suspended in the 50 degrees C quat solution for a total of one hour and cured in a 150 degrees F oven for two hours.

A portion of the cured plaques were scrubbed using a brush with a cleaning solution. Both scrubbed and unscrubbed plaques were tested for antimicrobial activity and gave a greater than one log kill when compared to a control.

Example 2

Nylon 6-12 plaques were acid etched for 60 seconds in a 10 volume percent hydrochloric acid (37%) and methanol solution.

200.25 g methanol, 5.0 grams Elvamide 8061 pellets, 22.25 g distilled water, 2.5 g acetic acid, and 20 g C ₁₄ or C ₁₈ quaternary ammonium compound were charged to a 500 ml flask on a magnetic driven stirring hot plate in the following manner. A magnetic stir bar was used to suspend all materials. The methanol was heated to 50 degrees C. The Elvamide was stirred into the heated methanol and dissolved. The other materials were

added in order to the solution. The mixture was allowed to hydrolyze for thirty minutes. The acid etched plaques were then treated in the solution for one second and cured in a 50 degrees C oven for thirty minutes.

A portion of the cured plaques was scrubbed using a brush with a cleaning solution. Both scrubbed and unscrubbed plaques were tested for antimicrobial efficacy and gave a greater than one log kill when compared to a control.

Example 3

The following materials were charged to a 500 ml beaker on a magnetic driven stirring hot plate in the following manner. A magnetic stir bar was used to suspend all materials. 196.8 g methanol was heated to 50 degrees C. 25.0 g Elvamide 8061 pellets were stirred into the- heated methanol and dissolved. 21.7 g distilled water, 2.5 g glacial acetic acid, and 20 g C ₁₄ or C _lg quaternary ammonium compound were added sequentially to the solution. The mixture was allowed to hydrolyze for thirty minutes.

Cellulose Acetate Propionate (CAP) plaques were suspended in the above solution at room temperature for 60 minutes. The plaques were air dried for thirty minutes and cured in a 120 degrees F oven for two hours.

A portion of the cured plaques was scrubbed using a brush with a cleaning solution. Both scrubbed and unscrubbed plaques were tested for antimicrobial efficacy and gave a greater that one log kill when compared to a control.

Example 4 (Comparative)

196.8 g methanol, 21.7 g distilled water, 2.5 g glacial acetic acid, and 20 g C ₁₄ or C ₁₈ quaternary ammonium compound were mixed and heated to 95 degrees C. Nylon plaques were suspended in the solution for one hour, air dried for fifteen minutes and cured in a 55 degree C oven for one hour.

A portion of the cured plaques was scrubbed using a brush with a cleaning solution. Both the scrubbed and unscrubbed plaques were tested for antimicrobial efficacy. The unscrubbed plaques gave a greater than three log kill when compared to a control. The scrubbed plaques showed no efficacy compared to the control.

It will be apparent to those skilled in the art that various modifications may be made to the above examples without departing from the scope and spirit of the invention.