AN ANTI-MICROBIAL SILICONE RUBBER COMPOSITION AND METHOD MAKING SAID COMPOSITION

Abstract: The present invention relates to a curable, antimicrobial silicone rubber composition. The composition comprises an organic matrix containing homogeneously dispersed particles of metallic silver having a particle size in the range of 1 to 50 nm (silver nano particles) in an amount providing on the surface of said composition an anti-microbially effective but less than cytotoxic silver concentration.

Description: An Anti-Microbial Silocone Rubber Composition and Method Making Said Composition FIELD OF THE INVENTION The present invention relates to a curable, antimicrobial silicone rubber composition. BACKGROUND Silicone rubber compositions have been widely used in industry for a wide variety of different applications. These applications include for example pan grips, camera eye caps, handles of bicycles, slipping preventors for spectacles, various rubber sheets and rubber coated cloth such as sheets and curtains that are used for example in hospitals. Silicone rubber compositions are further used as tubes and backings for food containers or various kinds of hygienic appliances. In many of these applications, there is a demand for antimicrobial and antifungal efficacy of the silicone rubber compositions. This demand stands from the fact that many of the usage environments are prone to microbial or fungal contamination. For example, such usage environments include the presence of contaminated surfaces such as to and/or the presence of ambient wetness in combination with room or even higher temperatures. In Japanese patent application 7 - 65149,filed on February 28, 1995, it has been suggested to incorporate into a silicone rubber composition and inorganic antimicrobial agent, the agent comprising silver loaded on an inorganic material such as a zeolite, a zirconium phosphate, or a calcium phosphate. Such silicone rubber compositions, however, are only capable of releasing the silver atoms in ionic form and hence are cytotoxic. It is therefore an object of the present invention to provide a silicone rubber composition, which overcomes the disadvantages of the prior art silicone rubber compositions. It is a further object of the present invention to provide a silicone rubber composition, which is antimicrobial by releasing silver atoms. It is a further object of the present invention to provide a silicone rubber composition, which is antimicrobially effective whilst not being cytotoxic. SUMMARY OF THE INVENTION The present invention provides an anti-microbial, curable silicone rubber composition comprising in at least a portion of the exposed surface of said composition an organic matrix containing homogeneously dispersed particles of metallic silver having a particle size in the range of 1 to 50 nm (silver nano particles) in an amount providing on the surface of said composition an antimicrobially effective but less than cytotoxic silver concentration. The present invention further provides a silicone rubber composition according to claim 1 , characterized by comprising said silver nano particles in an amount providing a silver concentration of from more than 1 nmol/l to less than 1 μmol/l on at least a portion of the surface of said composition. The present invention further provides a silicone rubber composition according to claims 1 and 2, characterized in that said organic matrix comprises said silver nano particles in an amount of 1 to 2000 ppm, preferably 5 to 1000 ppm and more preferably 10 to 250 ppm. The present invention further provides a silicone rubber composition characterized by comprising silver nano particles having a particle size of 2 to 20 nm preferably 5 to 10 nm. The present invention further provides a silicone rubber composition characterized in that said fluid organic matrix comprises an organic fluid wherein said silver nano particles are dispersed. The present invention further provides a silicone rubber composition characterized in that said viscous organic fluid comprises an aliphatic or aromatic hydrocarbon, a mineral oil, petrolatum, glycerol, a fatty alcohol, polypropylene glycol, an animal and/or vegetable oil or fat, or a silicone oil. The present invention further provides a method for manufacturing a curable, antimicrobial silicone rubber composition comprising the steps of: - providing a curable silicone rubber composition in a configuration ready for mixing - providing a liquid organic matrix comprising metallic silver having a particle size in the range of 1 to 50 nm - mixing said liquid organic matrix into said silicone rubber composition - optionally curing the mixture of said composition with said organic matrix DETAILED DESCRIPTION OF THE INVENTION It has been surprisingly found that the antimicrobial silicone rubber composition of the present invention shows an excellent antimicrobial and fungicidal activity by not providing any cytotoxicity and is active against a broad range of microbes without any indication of resistance because of the very small quantities of silver released from the surface of said silicone rubber composition over a long period. Based on this the body care product of the present invention is ideally suited for applications, wherein said composition is used under conditions which allow for proliferation of microbes and fungi. For the purpose of the present invention, anti-microbial efficacy, i.e. activity against a broad range of microbes, may be quantified for example by methods such as described in "Der Erlanger Silberkatheter: In-vitro Ergebnisse zur antimikrobiellen Wirksamkeit" in Infection 26 (1998) Suppl. 1 , German edition, pages 25 through 31. For the purpose of the present invention, cytotoxicity may be quantified for example by methods such as described in "Untersuchung der akuten Zytotoxizitat des Erlanger Silberkatheters zur Bestimmung der Biokompatibilitat" in Infection 26 (1998) Suppl. 1 , German edition, pages 36 through 39. According to a preferred embodiment of the present invention, said silver nano particles are dispersed in said silicone rubber matrix in such an amount that a silver concentration of from more than 1 nmol/l to less than 1 μmol/l is provided, specifically when in contact with aqueous fluids present on the surface the composition of the present invention. Preferably at least the exposed surfaces of the silicone rubber composition of the present invention comprises said silver nano particles in an amount from 1 to 2000 ppm, preferably from 5 to 1000 ppm and more preferably from 10 to 250 ppm. The silver nano particles homogeneously dispersed in said silicone rubber matrix preferably have a particle size of at least 2 nm, more preferably of at least 5 nm. In addition, the dispersed silver nano particles preferably have a particle size of not more than 20 nm, more preferably not more than 10 nm, most preferably not more than 8 nm. The silicone rubber matrix into which said silver nano particles then are homogeneously dispersed can be solid or fluid. The term fluid includes liquid and semisolid and covers a viscosity range of from 5 to 5000 mPa-s, preferably 5 to 500 mPa-s measured at 60°C using a rotational viscosimeter (such as a Brookfield viscosimeter) at 60 rpm using a number 2 spindle. According to one embodiment of the present invention, at least the exposed surfaces of the silicone rubber composition of the present invention comprise a fluid organic matrix wherein said silver nano particles are homogeneously dispersed. Said fluid organic matrix preferably is a viscous organic fluid having a viscosity as referred to above and comprises preferably aliphatic or aromatic hydrocarbon, a mineral oil, petrolatum, glycerol, a fatty alcohol, propylene glycol, polypropylene glycol, an animal and/or vegetable oil or fat or a silicone oil. Specifically preferred are silicone oils, i.e. polysiloxanes such as phenyl- functional-polymethylsiloxane compounds having a viscosity at 37°C ranging from 5 to 5000 mPa-s, more preferably 5 to 2000 mPa-s, as measured with the viscosimeter preferred to above at a temperature of 37°C. A suitable silicone oil is available from Dow Corning Corporation, Michigan, USA, under the designation DC556 poly dimethyl silicone cosmetic grade (Dimethicone). The incorporation of the silver nano particles can be done with an apparatus such as disclosed in German patent 44 40 521 using a method involving the vacuum evaporation of metallic silver on a liquid in a vacuum chamber in which the organic fluid flows along the outside of a cylinder. This allows for the preparation of a liquid organic matrix comprising a homogenous extremely fine dispersion of silver nano particles having a particle size of about 5 nm. This silver-containing liquid organic matrix can be used to either coat the part of the body care product of the present invention contacting the skin and/or to impregnate or to incorporate by kneading into the material providing said surface, made of for example polyvinyl benzol, polyethylene, polypropylene or creamy oligomers, such as white petrolatum. A suitable liquid rubber composition comprises 100 weight parts of organopolysiloxane rubber where of the average unit is represented by R a SiO( 4 -a)/2 (wherein R is a substituted or non-substituted monovalent hydrocarbon radical and eight is between 1.95 and 2.05), 10 - 100 weight parts wet silica with a specific surface area of 50 square meters per gram or more, and a sufficient quantity of a hardening agent. In principle, all silicone rubber compositions known in the art can be rendered antimicrobial and antifungal by the means described herein. Example A suspension containing silver nano particles with an individual size range of 5 to 50 nm was produced through thermal evaporation of silver into a liquid silicone oil base. The silicone oil containing the silver nano particles was then incorporated into a silicone rubber rubber obtained by addition condensation and crosslinking providing a children comfort. The children comfort or silencer demonstrated anti-fungal and antibacterial efficacy when containing 50 ppm silver nano particles when directly added into one component before crosslinking. The samples were placed on (non-nutrient) mineral salt agar and inoculated with a mixed fungal spore suspension of Aspergillus niger and Penicillium pinophilium, Chaetomium globosum, Aureobasidium pullulans and Gliocladium virens. After an incubation of 28 days at 28°C no growth of any of the microorganism was observed.

Claims: WHAT IS CLAIMED IS: 1. An anti-microbial, curable silicone rubber composition comprising in at least a portion of the exposed surface of said composition an organic matrix containing homogeneously dispersed particles of metallic silver having a particle size in the range of 1 to 50 nm (silver nano particles) in an amount providing on the surface of said composition an anti-microbially effective but less than cytotoxic silver concentration. 2. The silicone rubber composition according to claim 1 , characterized by comprising said silver nano particles in an amount providing a silver concentration of from more than 1 nmol/l to less than 1 μmol/l on at least a portion of the surface of said composition. 3. The silicone rubber composition according to claims 1 and 2, characterized in that said organic matrix comprises said silver nano particles in an amount of 1 to 2000 ppm, preferably 5 to 1000 ppm and more preferably 10 to 250 ppm. 4. The silicone rubber composition according to any one of claims 1 to 3, characterized by comprising silver nano particles having a particle size of 2 to 20 nm preferably 5 to 10 nm. 5. The silicone rubber composition according to any of the preceding claims, characterized in that said fluid organic matrix comprises an organic fluid wherein said silver nano particles are dispersed. 6. The silicone rubber composition according to claim 5, characterized in that said viscous organic fluid comprises an aliphatic or aromatic hydrocarbon, a mineral oil, petrolatum, glycerol, a fatty alcohol, polypropylene glycol, an animal and/or vegetable oil or fat, or a silicone oil. A method for manufacturing a curable, antimicrobial silicone rubber composition comprising the steps of: - providing a curable silicone rubber composition in a configuration ready for mixing - providing a liquid organic matrix comprising metallic silver having a particle size in the range of 1 to 50 nm - mixing said liquid organic matrix into said silicone rubber composition - optionally curing the mixture of said composition with said organic matrix

Inventors: BAST TIM, HANKE BERNHARD, BAST, TIM, HANKE, BERNHARD
Applicants: BAST TIM, HANKE BERNHARD, PROCTER & GAMBLE, BAST, TIM, HANKE, BERNHARD, THE PROCTER & GAMBLE COMPANY
Application year: 2000
Main classification: A61K7
IPC codes: A01N59, A61K8, A61K33, A61L15, A61Q11, A61Q15, A61Q17, A61Q19