Fabrication of Nano-Silver–Silver Ion Composite Antibacterial Agents for Green Powder Coatings

Nano-silver is characterized by broad-spectral, strong and stable antibacterial properties, which make it a promising material in coating applications. However, the efficiency of nano-silver is generally low in the coating of films. Here, we developed a series of highly active and durable silver ions–nano-silver antimicrobial agents for powder coatings. To optimize antimicrobial activity and durability, two different nano-silver generation methods, i.e., in situ and ex situ methods combined with different carrier materials, i.e., zeolite with high ion-exchange ability and montmorillonite of layered structure were adopted and investigated. All four antibacterial additives show high activity with a reduction rate of over 99.99% and R value of over 5. The ex situ generated nano-silver antibacterial agents with both carriers exhibit higher activity in the initial antibacterial property and antibacterial durability that the coating films are able to maintain over 99% antimicrobial reduction after 20 cycles (1200 times) of soap solution wiping. They also show a lower yellowish color difference of less than three compared to the films with in situ generation method. The one with montmorillonite as carrier shows the stronger antibacterial property with an R value of 5.88 and slightly better film appearance of lower color difference, smaller reduction in gloss and increase in haze as compared to zeolite carrier due to the layered structure.