New ceramic applications with antimicrobial functions

The Colorobbia solution for indoor sanitisation

Newly developed ceramic products with antimicrobial functions are produced by means of either direct coating or addition to ceramic body compositions. The active ingredient consists of metallic silver and other biocidal elements that are specially prepared to make them compatible with ceramic compositions and technologies.

Since the 1990s, Colorobbia’s Ce.Ri.Col. Research Laboratory has been developing suspended nanomaterials capable of giving surfaces special functions, in particular that of sanitisation.

Among the numerous technological solutions that Colorobbia has identified in recent years and which are covered by more than 200 international patents, one of the most important for today’s world is the production of antibacterial ceramic tiles using glazes with compositions containing biocides, particularly metallic silver.

This technology provides disinfection/sanitisation treatments directly integrated into the floor and wall coverings. Specifically, metallic Ag nanoparticles are used to eliminate a wide range of bacteria and moulds belonging to the following groups: Escherichia (particularly E. coli), Arcobacter, Enterobacteriaceae, Enterobacter, Salmonella, Legionella, Staphylococcaceae (particularly Staphylococcus aureus), and their combinations. The system also reduces fungal load and has an effect on fungi in general.  

The technology was developed at the laboratories of Colorobbia Italia in Fiorano and Colorobbia España in Villafames to meet the needs of the ceramic sector and was designed to be compatible with glazes and the various firing temperatures and application techniques.

This technology now uses two products, identified by the acronyms IG and IGEA, both of which are able to make metallic silver compatible with ceramic materials and are applied in the form of a coating or introduced directly during the glaze milling phase. The products are applied prior to firing and have no impact on the expected aesthetic results in terms of colour or finish or on physical characteristics such as abrasion, acid or alkali resistance.

IG and IGEA differ from other products available on the market in terms of their high concentration of metallic silver nanoparticles, up to 4% in suspension and 8% in the form of admixed powder. They easily outperform similar products described in the scientific and patent literature in terms of active ingredient concentration and stability. The high concentration of the suspensions allows for wide flexibility of application; moreover, the metallic form offers advantages compared to the entire category of products based on soluble salts or other chemotoxic substances in ionic form. The action of the active ingredient is delivered on demand, avoiding undesirable release into the environment.

The metallic Ag nanoparticle suspension Parnasos IG

The Parnasos IG series consists of stable water and/or water/glycol based suspensions (stability of 12 months) of brown coloured metallic silver with a metallic silver content of up to 4%. Through controlled dilution of this master formulation it is possible to obtain a class of products with a concentration varying from 0.5% to 4%.

This suspension is suitable for airless and/or rotary screen printing applications following optimisation of rheological conditions. The quantities to be applied may vary according to the conditions of the available machine and the initial dilution. Colorobbia recommends depositing a quantity of metallic silver of between 100 and 500 mg/m² on the surface.

In the airless application technique, glaze is deposited uniformly on the surface by means of high pressure nebulisation. Application is performed without any contact between the machine and the ceramic substrate. The deposited quantity is determined by the diameter of the liquid outlet orifice, the spray pressure and the speed of the glazing line or the application time and may vary according to the initial dilution. The standard application involves depositing 25 g/m² of IG 405 with 1% SILVER on a matt surface. After application, the surface has a uniform brown colour. The tile then undergoes a firing cycle at 1200°C for 45 minutes, after which there is no change in the aesthetic or physical characteristics of the surface matt glaze.

Screen printing application is carried out using a rotating or pad printing screen technique in which the material passes through the holes in the screen due to the application of pressure with a mobile spatula. This process guarantees uniform application of a layer in a quantity that may vary according to the conditions of the available machine and the initial dilution. The standard application for a matt surface involves depositing 30 g/m² of IG08 with a silver concentration of 1% and density and viscosity adapted to screen printing use. A uniform full field colour must be achieved to guarantee good results. The tile then undergoes a firing cycle at 1200°C for 45 minutes. Here too, at the end of the cycle, there is no change in the aesthetic or physical characteristics of the matt surface glaze.

Aluminosilicate additive functionalised with IGEA series metallic Ag

IGEA series products come in the form of a micrometric powder in the brown colour typical of the presence of metallic silver, which is found in nanoparticular form in a quantity of 8% ± 0.5% with respect to the weight of the powder.

The product is obtained by treating an aluminosilicate of mineral origin with a silver-based precursor in a process capable of generating the nanoparticle of metallic silver in situ. Subsequent calcination guarantees its adhesion and stability over time.

The IGEA powder is suitable for applications with the “salting” technique (performed at the end of the line using airless technology), in-body through direct addition to the glaze during milling. Subsequent brushing can be performed without altering the functionality of the metallic silver. The composition of the post-fire salting application, consisting of frits, raw materials and additives, gives the ceramic tile a series of chemical and physical properties that depend on the nature of the elements introduced.

The quantities to be applied may vary according to the refractoriness of the glazes, with more fusible glazes requiring a larger quantity. Colorobbia recommends using an application weight sufficient to supply a quantity of metallic silver of between 100 and 500 mg/m².

Analysis of antibacterial efficacy

In today’s world where people are constantly exposed to the risk of infections and viral pandemics, the possibility of having floors, walls and other elements normally present in residential, healthcare and public spaces that are capable of destroying fungi and bacteria could make an important contribution to maintaining hygiene and safer conditions in general.

Tiles produced using Parnasos IG series and IGEA series products have been tested at the Biochemie Lab certified laboratory in Florence against Escherichia coli, a Gram-negative pathogenic bacterium. The results for antibacterial efficacy (in accordance with ISO 22196 for non-porous surfaces, compared to white) are shown in the table.

This analysis was conducted in collaboration with the N&G patent office by analysing an initial group of 14,000 patents on the topic of “silver vs. microorganisms” and verified that there is no application on the market equivalent to the one proposed and described in the Colorobbia patent WO2010100107 2010-03-01.