Surfaces treatment

Nanotechnology

27/03/2019

By nanotechnology we mean those applications in which technologies, products or raw materials that are a few nanometers in size are used. In the metal pretreatment sector, nanotechnology helps to make the surface more regular and constant, as well as increasing adhesion with the paint.

How does it work

Nanotechnology is usually used as the final treatment of a process, for example after degreasing or phosphating. The best results are obtained if the surface on which this technology is applied appears to be well cleaned and degreased. But what is this nanotechnology made of? Usually we are talking about molecules called silanes (and modified or hybrid silanes), or particular inorganic acids able to react with the substrate thus forming a film called "ceramic". Often these raw materials are used simultaneously, in the same product. In this way, the adhesion strength of the silanes (between metal and paint) and the corrosion resistance due to ceramic passivation, usually zirconic, are combined. Nanotechnologies are the last frontier of pretreatment and tend over time to replace the much more complex tricationic phosphating. The economic advantages of a leaner system and fewer controls by the operator or laboratory are certainly an advantage over the latter. Furthermore, with an optimized nanotechnology process management, in some cases it is possible to achieve the same performance as a tricanionics, we are talking about more than 1000 hours of resistance to salt spray test. The negative aspect is the delicacy of the silanes which, if used incorrectly, can react with themselves or with everything they come into contact, even the same water if it is not used demineralized.

Examples of formulation

Formulating silane-based preparations is never easy, precisely because of their high reactivity. There are many types of silanes on the market although we can say that those selected for the pretreatment of metals are for the most part amino-silanes, amino-alkyl-silanes or epoxysilanes. Another world is that of finishing for surfaces where silanes modified for example with silica are used to give a remarkable resistance to scratches and wear. However, these are final treatments on which we will not dwell at least in this context.

In synergy with the silanes, as already mentioned, special acids such as hexafluorozirconic acid and hexafluotitanic can be added, the dosages must be careful not to damage the silane (often alkaline) and the surface on which it is applied. It is preferable to formulate a concentrate already containing the acid part as this preserves the silane over time, otherwise the perishable nature of the latter, diluted in water alone, is compromised and can last even a few days before creating an alcoholic reaction.

Beyond this starting point of the formulation, it is appropriate to include bathers in the formula, being very careful that they do not remain on the surface before painting, as a principle we can say that the simpler the formula, the better we expect the final result. The final rinse, as just mentioned, is therefore important for removing the wetting additives and for interrupting the acid reaction on the metal, however some formulations can be used without this rinse. In plants, the nanotechnology solution is often sprayed as a final stage, in this case the possibility of contamination of the bathroom is avoided.

To complete the formulation, rare metals such as vanadium or other salts can be used, with the aim of refining the crystal and increasing resistance to corrosion.

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