Bacteriostatic and fungistatic additive in masterbatch for application in plastics, and method for producing same

Abstract

Disclosed is an additive of ZnO/Ag° with a bacteriostatic and fungistatic action in the production of plastic items based on resins such as polypropylene, polyethylene, polystyrene, high-impact polystyrene, polyurethanes, etc., especially for producing automotive products, electrical appliances, products for washing, for storing and conducting water, for packaging, etc. The additive is prepared by mixing nanometric silver concentrates and pre-treated zinc oxide with a polymer resin compatible with the target application as a vehicle, obtaining pellets of the additive in a ratio of between 10:90 and 90:10 in weight of ZnO/Ag° : vehicle. The additive is biologically effective at a ratio in the final product of between 0.01 and 0.5 wt. % of polymer mixture and does not have any negative effects on other properties of the polymer, such as the whiteness thereof.

1 . An additive in the form of masterbatch in pellet form, with bacteriostatic and fungistatic activity to be employed in the manufacture of plastic articles, obtained by mixing concentrates of Ag° and ZnO in paste form with a polymeric carrier, characterized in that:
 a) the metallic silver in the paste used for preparation of the concentrate is in the form of nanoparticles with the following specifications: 
 
       
         
           
                 
                 
                 
               
                     
                     
                 
                     
                   Characteristic 
                   Specification 
                 
                     
                     
                 
                     
                   Purity (%) 
                   99-99.3 
                 
                     
                   Size of the particles 
                 
                     
                   D 10  nm 
                   41.5 
                 
                     
                   D 50  nm 
                   47.0 
                 
                     
                   D 90  nm 
                   56.0 
                 
                     
                   Solid contents (weight %) 
                   80-85     
                 
                     
                     
                 
             
                
                
                
               
               
                
                
                
                
                
                
                
               
            
           
         
         b) the zinc oxide in the paste used for the preparation of the concentrate is in the form of nanoparticles with the following specifications: 
       
       
         
           
                 
                 
                 
               
                     
                     
                 
                     
                   Characteristic 
                   Specification 
                 
                     
                     
                 
                     
                   Purity (%) 
                   100 
                 
                     
                   Size of the particles 
                 
                     
                   D 10  nm (micron) 
                   0.04-0.09 
                 
                     
                   D 50  nm (micron) 
                   0.050-0.087 
                 
                     
                   D 90  nm (micron) 
                    0.1-0.13 
                 
                     
                   Solid contents (weight %) 
                   45-50 
                 
                     
                     
                 
             
                
                
                
               
               
                
                
                
                
                
                
                
               
            
           
         
         c) the polymeric carrier is selected to be compatible with the final application in which the additive will be used, and 
         d) the percentage by mass of ZnO and Ag° in relation to the vehicle in the additive is in the range of from 10:90 to 90:10. 
       
     
     
         2 . An additive in the form of masterbatch in pellet form, with fungistatic and bacteriostatic activity, for use in the manufacture of plastic articles according to  claim 1 , characterized in that, being present in a proportion of from 0.01% to 0.5% by weight in a mixture for a particular application for manufacturing plastic items, it produces a microbial reduction of bacteria and fungi higher than 97% before aging and greater higher 93% after 120 hours of aging in UV chamber. 
     
     
         3 . Method for the production of the additive paste according to  claim 1 , characterized in that it comprises the following steps:
 a) Preparation of the zinc oxide concentrate starting from a paste of nanometric zinc oxide which has been previously subjected to a surface treatment based on silane additives,   b) Preparation of the silver concentrate starting from a silver paste of nanometric metallic silver, and   c) Preparation of the additive by mixing the zinc oxide concentrate of step (a), the metallic silver concentrate resulting from step (b), and a polymeric carrier compatible with the resin for the end use in a proportion from 10:90 to 90:10, to obtain the concentrate additive of ZnO/Ag° in masterbatch in pellet form.   
     
     
         4 . Method for the production of the additive paste according to  claim 3 , characterized in that for the preparation of the zinc oxide concentrate, the following steps are followed:
 a) Subjecting a paste of nanometric zinc oxide at 45-50 wt % solids, to a surface treatment based on silane additives,   b) Feeding the treated zinc paste to a high intensity mixer where it is mixed with the polymer or mix of polymers compatible with the final application in which the additive is to be used,   c) concentrating the mixture of zinc oxide and polymer up to 20% by weight of zinc oxide, and   d) Homogenizing the material by means of a twin screw extruder, mixing the concentrate from the previous step with a polymer compatible with the final application, to a concentration by weight of zinc oxide of between 1 and 10%.   
     
     
         5 . Method for the production of the additive paste according to  claim 3 , characterized in that for the preparation of the nanometric metallic silver concentrate, the following steps are followed:
 a) mixing a paste of nanometric metallic silver with 80-85 wt % of solids, with a thermoplastic polymer that is compatible with the final application to which the additive will be destined, in a high intensity mixer, concentrating the resulting mixture to 10% by weight of silver,   b) Homogenizing the material by means of a twin screw extruder, mixing with a resin compatible with that of the final application, up to a concentration between 0.1 and 1% by weight of silver.   
     
     
         6 . Method for the production of the additive paste according to  claim 3 , characterized in that for the preparation of the additive:
 a) the silver and zinc oxide concentrates are mixed with a resin compatible with that to which the additive will be destined, up to obtaining a concentration of silver and ZnO of between 10 and 90% by weight of the mixture,   b) the mixture is extruded to form pellets of the additive.