Patent Publication Number: US-2011076152-A1

Title: Ventilator wheel or fan wheel with antibacterial coating

Description:
The present invention relates to ventilator wheel or fan wheel consisting of a hub and blades fastened thereto, and to a ventilator or a fan using such a ventilator wheel or fan wheel. 
     Filter material and cable surfaces of air conditioning equipment and cooling or ventilation equipment become contaminated over time by layers of grime and grease settling on them. These layers contain bacteria and fungi which can be spread further via the stream of air. This may lead to allergies and infections in people who spend time in the particular air-conditioned or ventilated room. 
     In order to avoid this or to reduce this risk, it is known to provide the respective surfaces of the air-conveying parts of the equipment with an antibacterial or antimicrobial coating. Suitable active ingredients for this purpose are nanoscale molecules of metal complexes of precious metal such as e.g. silver, copper, molybdenum or the like. It is also known to use for this purpose ceramic carriers in powder form provided with silver ions, as a result of which metal ions are reversibly bonded to the metal surface. 
     It was found that purely metallic colloidal metal particles, like so-called “nanosilver particles”, only have a highly restricted, in particular not long-lasting efficiency, while metal ions have a stronger and more sustained effect. For various reasons, such as the toxicity or corrosive effect of some substances with ionic bonding, these substances cannot always be used, however. 
     With regard to silver oxide, for example, it should be noted that it is not optimally suitable for the indicated application because when exposed to air it transforms into silver carbonate, which can in turn have skin irritating effects, so that protective gloves have to be worn when handling this substance. Also known is the strong irritating effect of silver nitrate, which is, for example, used because of its caustic effect in the medical field as “Höllensteinstift™”, for removing warts, is likewise known. 
     Compared to other appliances, like, for example, medical devices, refrigerators, refrigerated counters, dashboards in vehicles, mouse pads, etc., the difference in fan wheels or blower wheels is that, in the operating state, the antibacterial substances are not normally in contact with the human body, like hands, or with food, but only with the air streaming through the fan or blower which requires increased oligodynamic efficiency to guarantee antibacterial or antimicrobial protection. There is such direct physical contact, however, during production and assembly, so that physiologically questionable substances cannot be used. 
    
    
     The object of the present invention is to make the transmission route of bacteria, fungi, viruses, i.e. germs in ventilation technology even safer against the transmission of these germs. 
     According to the invention, this is achieved by, for ventilator wheels or fan wheels present in ventilation equipment, providing the hub and/or the blades on their surface at least partially with an antibacterially effective active ingredient. 
     Furthermore, according to the invention, it is advantageous if the ventilators or fans which are used, which consist of a housing, preferably with a safety grid, and a ventilator wheel or fan wheel stored in the housing, and of an electric motor driving this, and of a motor mounting, have an antibacterially effective active ingredient on the surface at least of their air-conveying housing sections. 
     As substances with antibacterial effects, mainly nanoscale aggregated molecules of metal complexes, in particular of noble metals like silver, copper, molybdenum or the like, can be used. These molecules have biocidal, oligodynamic and antimicrobial effects. By using coatings containing nanoscale molecules of this type, the correspondingly coated surface is prevented from being infested by bacterial and viral microorganisms like fungi. The nanoscale molecules prevent the formation of a biofilm and cause the destruction of microorganisms on the coated surface. 
     According to the present invention, in a preferred embodiment monovalent and preferably divalent silver or copper, which respectively forms the central atom of the complex, can in particular be used as metal complexes. They can be formed with hydroxycarboxylic acids like, for example, 2-hydroxypropanoic acid (lactic acid), 2-hydroxypropane-1,2,3-tricarboxylic acid (citric acid) or 2,3-dihydroxybutanedioic acid (tartaric acid), as substances forming ligands in the complex ions. 
     Also ammine complexes of the chemical formula [Ag(RNH 2 ) 2 ] + , where R is hydrogen, a methyl or an ethyl group, for example, can preferably be used. These complexes are characterized, in particular, by increased stability in comparison to other complexes. 
     It is particularly advantageous to use mixed copper- and silver-containing compounds because it has been found that, when interacting, copper and silver ions have a synergy with regard to the oligodynamic efficiency, which can be explained by the occurrence of different and reciprocally interacting mechanisms of action. In particular, catalytic oxidation, which inhibits the supply of oxygen required for the survival of the microorganisms, a reaction with the cell membranes and their proteins, which inhibits the ingestion, and a binding to enzymes and nucleic acids of the microorganisms, which prevents their reproduction, are considered to be such mechanisms of action. Each mechanism of action can be selectively influenced to different degrees by the copper and silver, which, in the interaction of the different ions, results in that the oligodynamic efficacy progressively increases with concentration, but is disproportionately higher compared to the same concentrations in which only silver or only copper is present. 
     Copper (I) and silver (I) diammine complexes and/or copper (II) and silver (II) tetra-ammine complexes, or also possibly mixed aqua-ammine complexes can thus, for example, be used advantageously not only respectively alone, but also preferably as a mixture. A higher efficacy should be attributed to the ions of divalent metals because of their higher redox potential. 
     The respective ligands of the substances constituting the complex ions need not necessarily be organic compounds, as described above. The complex can, for example, also be inorganic compounds, like a thiosulfato compound, which, for example, contains the bis(thiosulfato)argentate ion [Ag(S 2 O 3 ) 2 ] 3− . 
     As is also apparent from both preceding exemplary chemical formulas, the complex ions can be cations as well as anions. The respectively complementary anions or cations in the complex compounds can be those resulting in salts that are easily soluble, hardly soluble or insoluble in water, the formation of soluble substances being favorably associated with the advantage of higher ion mobility, and the formation of insoluble or hardly soluble salts with the advantage of an easier extraction of nanoparticles by means of colloidal precipitation. 
     While the chemical binding of the corresponding metals in the complex ions can attack the microorganisms with a marginally reduced intensity as compared to the free metal ions in short-term usage, but a potentially harmful effect on the human body is advantageously eliminated, on the one hand, and on the other, a prolonged effect is ensured compared to free metal ions. 
     It has surprisingly been found that silver-containing sulfonamides, like silver sulfadiazine (empirical formula: C 10 H 9 AgN 4 O 2 S) in particular, which, as is known, is used as an antibacterial active ingredient for treating second and third grade burns as well as extensive lacerations, has an oligodynamic effect on the surface of hubs and/or blades of fans and/or blower wheels which are in contact with the air streaming through them. This results in a synergistic effect of the acid residue of the amide-containing sulfonic acid and silver ions. 
     Although high ion mobility is desirable in line with the present invention, it is evident that from the possibility of using silver sulfadiazine that the antibacterial active ingredient, such as silver chromate Ag 2 CrO 4 , need not necessarily be water soluble, but may also be water insoluble, such as silver dichromate AgCr 2 O 7 . 
     The active ingredient can also be a ceramic carrier with e.g. silver or oligodynamic ions bound therein, aluminum silicate being particularly used as a ceramic carrier. By means of an active ingredient of this kind, in which the active ingredients are preferably kept in a zeolitic cage matrix, and which can be introduced into the coating in powder form, it is possible to sustain a long term dosed release of the active ingredient. 
     The presence of hydroxyl groups in the active ingredient, like those contained in the above mentioned hydroxycarboxylic acids, has a particularly advantageous effect because by interacting with them the metals on the surface of the hub and/or blade can have a higher, still physiologically harmless, concentration than is permissible for free copper or silver ions, for example. The hydroxyl groups can be bound in different ways, preferably chemically, in the ceramic matrix. 
     According to the invention, the antibacterially effective active ingredients can be incorporated into paints, powder coatings or plastics mixtures, meaning that they can be applied either as a coating to the surface or in the form of a paint coat or a surface film by adding them to these particular materials in a different concentration depending on the requirements. In particular, alkyd, acrylic, epoxy or polyurethane resins are possible options as basic formulations for the lacquers. Polyolefins, in particular polyethylene and polypropylene as well as polyvinyl chloride, are suitable as base materials for the surface films. It is likewise possible to mix the antibacterially effective active ingredients into the manufacturing material of the ventilator wheel or fan wheel or parts of the ventilator housing or fan housing. 
     Ventilators or fans usually consist of a housing in which the ventilator wheel or fan wheel is rotatably stored, where the ventilator wheel with the electric motor integrated therein is fastened to a motor mounting. Moreover, the housing can be provided with a safety grid. It is within the scope of the invention if the parts of the ventilator, in particular those which are air-conveying and/or are located in the stream of air to be conveyed, are provided on their surface in an antibacterial manner with an active ingredient according to the invention. Here, the concentration of the active ingredient coating on the individual parts can be the same or different depending on where the highest bacterial loading is expected. It has been found that the total concentration of the oligodynamic metals, preferably present in ionic form, on the surface of the hub and/or blades should optimally be in the range of 0.05 to 15% by mass, preferably in the range of 0.2 to 2.8% by mass. 
     The design of the particular ventilator is not essential to the implementation of the invention, meaning that it can be used for any type of ventilator; in particular, axial and radial ventilators are customary. 
     The present invention is not restricted to the illustrated and described exemplary embodiments, but also comprises all identically functioning means within the meaning of the invention. Apart from silver, copper and molybdenum, which are mentioned above as biocidal metals, cadmium and/or vanadium can, for example, also be used within the scope of the present invention. Mixtures of the above substances, mentioned above as single compounds or compound groups, can also be used. 
     Furthermore, the present invention is not restricted to the combination of characteristics defined in claims  1  and  23 , but can also be defined by any other combination of certain characteristics of all disclosed individual characteristics. This means that basically each individual characteristic of the independent claims can be omitted and/or replaced by at least one individual characteristic disclosed at another point of the application. To that extent, the claims are to be merely understood as a first attempt at formulating the invention. 
     In connection with the use of photosensitive silver compounds, like silver chromate, it should be noted that it is also within the realm of the present invention that the efficacy of the antibacterial active ingredient on the surface of the hub and/or blades only gradually develops or increases as a result of environmental effects, and also as a result of the action of light, acids, etc. 
     For the purpose of the present invention, nanoscale particles are understood to be particles from monomolecular size up to an average particle diameter of 1000 nm. The average particle diameter should preferably be in the range of 1 nm to 40 nm, especially preferably in the range of 15 nm to 30 nm. With a disproportional increase of the specific particle surface when the particle size decreases, the oligodynamic efficacy also increases accordingly because a larger reaction surface is available for chemical and physical reactions like the already mentioned catalytic reaction or, among others, for the adsorption and absorption reactions, and in addition, the smaller particles also have a higher mobility. 
     Antibacterial within the context of the invention means both effective against bacteria and also against viruses and fungi.