For centuries, silver metal has been known to be an agent capable of killing many different microbial species. It was commonly used to purify drinking solutions or administered to sick individuals before the existence of modern antibiotics. Even after the discovery of penicillin and its descendents, colloidal silver solutions were often used in cases in which troublesome bacteria had become resistant to antibiotics.
Colloidal silver solutions are commercially available today. They are often unstable, however, and have a short shelf life. This is due to the tendency of the silver particles to aggregate and form clusters so large that they are no longer suspended in solution. For this reason, undesirable gelling agents are added to solutions to keep the silver particles suspended by preventing particle aggregation. Another problem of the commercially available solutions is that the majority of the silver content is usually found to be silver ions. This poses a large problem in medical applications where silver ions rapidly combine with ubiquitous chloride to form an insoluble white precipitate.
Nanoparticles have been known to be used as fillers as disclosed in U.S. Pat. No. 6,492,453, as coatings as disclosed in U.S. Ser. No. 2003/0185964 and as foam components as disclosed in U.S. Pat. No. 6,518,324.
Nanoparticle systems are disclosed in U.S. Ser. No. 2002/0150678 as being used in a composition and a method to impart surface modifying benefits to soft and hard surfaces. In particular, this application discloses a soft surface coating for articles such as fabrics and garments.
Inorganic particulates, such as, clays, silicates, and alumina have been widely used in combination with adjunct detergent and laundry compounds to impart some form of antistatic control and/or fabric softening benefit.
The present invention relates to composite materials comprising metal loaded onto exfoliated nanoparticles. Such functionalized nanoparticles may be incorporated into soft surface coatings to enhance or modify their bulk physical and performance characteristics. Such soft surface coatings may in turn be used in the preparation of absorbent articles with improved properties. Addition of the coatings to for example the absorbent core of a disposable, absorbent article may help control malodor formation and increase absorbency.
In one embodiment, the metal is silver and the nanoparticle comprises a nanoclay. Silver ion is reduced to its neutral metal state (Ag0) and loaded onto the nanoclay. Silver-coated nanoclays in particular have excellent antimicrobial properties, and represent a less expensive alternative to the use of colloidal silver solutions. Such nanoparticles made according to the invention are stable and use less silver metal to generate the same surface area as solid silver particles, making them more cost efficient.