Drug – bio-affecting and body treating compositions – Preparations characterized by special physical form – Matrices
Reexamination Certificate
2001-12-12
2003-11-04
Page, Thurman K. (Department: 1615)
Drug, bio-affecting and body treating compositions
Preparations characterized by special physical form
Matrices
C424S484000, C424S485000, C424S422000
Reexamination Certificate
active
06641842
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to improvements in increasing the amount of surface-available silver in thermoplastic articles comprising certain silver-containing antimicrobial agents. Such an invention requires the incorporation of a sufficient amount of a carboxylic acid salt within the thermoplastic article simultaneously with the necessary silver-containing antimicrobial agent. Certain carboxylic acid salts are standard acid scavengers and lubricants for certain thermoplastic applications; however, the amounts required within this inventive thermoplastic article are in excess of that commonly added within such articles, and the types of acid scavengers possibly added within such target thermoplastic articles are preferably neutralized hydrotalcite compounds, thereby permitting the carboxylic acid salt to function in the inventive manner. Surprisingly, such a high amount of such standard salts, as well as potentially other non-standard salts, present within the target thermoplastic cause the release of greater amounts of silver to the target article's surface, thereby permitting a greater degree of antimicrobial activity, among other potential benefits for such an increase in surface-available silver. Methods of producing such inventive thermoplastics are also encompassed within this invention.
DISCUSSION OF THE PRIOR ART
There has been a great deal of attention in recent years given to the hazards of bacterial contamination from potential everyday exposure. Noteworthy examples of such concern include the fatal consequences of food poisoning due to certain strains of
Eschericia coli
being found within undercooked beef in fast food restaurants; Salmonella contamination causing sicknesses from undercooked and unwashed poultry food products; and illnesses and skin infections attributed to
Staphylococcus aureus
, yeast, and other unicellular organisms. With such an increased consumer interest in this area, manufacturers have begun introducing antimicrobial agents within various household products and articles.
Silver-containing inorganic microbiocides have recently been developed and utilized as antimicrobial agents on and within a plethora of different substrates and surfaces. In particular, such microbiocides have been adapted for incorporation within plastic compositions and fibers in order to provide household and consumer products which inherently exhibit antimicrobial characteristics. Although such silver-based agents provide suitable antimicrobial properties within thermoplastic articles, and other types of articles, there are certain limitations as to the potential antimicrobial efficacy of such thermoplastic articles. Such limitations are apparently due to relatively low amounts of surface-available silver within and/or on such thermoplastic articles. Without intending to be bound to any specific scientific theory, it is believed that such low surface-available amounts of silver are the result of the inability of a sufficient amount of the integrated silver compounds to migrate to the thermoplastic surface. Such a result is observed for standard thermoplastics comprising silver-containing antimicrobials. Thus, there exists a need to provide efficacious amounts of silver-containing antimicrobial agents within thermoplastic compositions that exhibit such heretofore unattainable high levels of surface-available silver compounds, thereby providing more effective antimicrobial activity, among other potential desirable characteristics as a result thereof.
Past plastic compositions and articles comprising silver-containing antimicrobial agents include U.S. Pat. No. 5,405,644 to Ohsumi et al., which includes the addition of certain triazoles, U.S. Pat. No. 4,938,955 to Niira, deceased et al. (also including benzotriazole stabilizers), U.S. Pat. No. 5,750,609 to Nosu et al., which discloses an ultraviolet protective agent for incorporation within a variety of compositions, such as films, fibers, cosmetics, and the like, comprising a zinc-based hydrotalcite which acts solely as an ultraviolet absorber. However, these particular methods and plastics have proven to be costly (with the high expense of benzotriazoles initially), particularly since relatively high concentrations of the expensive stabilizing compounds are required, and do not provide any appreciable increase of available silver on the surface of such articles. Also, as these stabilizers are not thermally stable, they introduce additional processing complications. As such, there is no teaching or fair suggestion within the prior art which pertains to the needed improvement in increasing the amounts of surface-available silver compounds on target thermoplastics.
DESCRIPTION OF THE INVENTION
It is thus an object of the invention to provide an increase in the amount of surface-available silver to actual thermoplastic articles (containers, plaques, films, fibers, and the like). A further object of the invention is to provide such an increase through the utilization of acceptable, commercially available, components for thermoplastic formulations. Another object of the invention is to provide a highly efficacious antimicrobial thermoplastic article. Yet another object of this invention is to provide a cost-effective method of increasing the amount of surface-available silver on such target inventive thermoplastic articles and thereby reducing the amount of active silver remaining within the target resin itself.
Accordingly, this invention encompasses a thermoplastic article comprising at least one silver-containing antimicrobial agent, optionally at least one acid scavenger compound, and from 0.1% to 1.25% by weight, preferably from about 0.2 to about 1.0%, more preferably from about 0.2 to about 0.5%, and most preferably about 0.3% by weight of at least one carboxylic acid salt component other than or in excess of said optional at least one acid scavenger compound. Furthermore, this invention also encompasses a method of forming a thermoplastic article comprising the steps of providing a thermoplastic polymer, introducing at least one silver-containing antimicrobial agent, optionally at least one acid scavenger compound, and from at least 0.1% to 1.25% by weight, preferably from about 0.2 to about 1.0%, more preferably from about 0.2 to about 0.5%, and most preferably about 0.3% by weight of at least one carboxylic acid salt component other than or in excess of said optional at least one acid scavenger compound, melting said resultant mixture of polymer, silver-containing antimicrobial agent, and at least one carboxylic acid salt, and cooling said molten mixture in a desired shaped thermoplastic article. Also, this invention encompasses a polyolefin article comprising at least one silver-containing antimicrobial agent and exhibiting a surface-available amount of silver of at least 0.25 micrograms of silver/square decimeter (or a styrenic thermoplastic article exhibiting an amount of at least 0.80 micrograms of silver/square decimeter in terms of surface-available silver) of said surface, as measured by a salt-extraction test for 24 hours at room temperature. Nowhere within the prior art has such a specific plastic article or method of making thereof been disclosed, utilized, or fairly suggested to produce a thermoplastic article with such desirable increased surface-available silver characteristics.
The term “surface-available silver” is intended to encompass the phenomenon of the detectable presence of available silver, either as metals or ions, on the target article's surface or, possibly from a distance very close to such surface but imbedded therein until extracted out with relative ease. Detection in this instance is accomplished through a particular method, as eluded to above, wherein the sample article is immersed within an extracting solution, such as, as one example, a mixed salt solution (in this instance a sodium-potassium-phosphate buffer solution) for at least twenty-four hours at room temperature. After such time, the extract solution is then analyzed through, for example, and with
Dankel Robert
Haas Geoffrey
Laridon Erik
Bennett Rachel M.
Milliken & Company
Moyer Terry T.
Page Thurman K.
Parks William S.
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