The micro-scale roughness on lotus surfaces is effective in increasing the static contact angle and the presence of the nano-scale hair-like structure is responsible for the additional increase of the value. This is the basic principle we have to achieve with our new nano coating.
The principal technology used for the synthesis of these materials was the sol-gel technology; a very used reaction thanks to the high variety of applications and the possibility of tailoring the final materials.
In order to improve both: the global process (saving economically and energetically speaking) and the behavior of the final coating, different points were faced, studying and analyzing a wide range of variables on each one. Since we started from lab scale and move forward to industrialization scale, is it very important the optimization of each individual point. Following are listed the main topics studied.
- Sample
As far as the microstructure of a surface is concerned, the hydrophobic property is well known to be enhanced by roughness. Thanks to the sandblasting equipment present in Pramar, it was possible the study of different values of roughness.
- Application process
During the several developed methodologies, there were studied parameters as position of the sample, distance between the airbrush and the enameled piece, amount of coating applied, kind of airbrush (pressure, opening of the nozzle…), analyzing the time involved in the preparation of the sample, time of application process and also the final homogeneity of the sample after application of the coating.
Once the methodology was stablished, other parameters were controlled, always taking into account the industrial applications and trying to save energy, time and money.
- Test procedure.
It was stablished a complete procedure for carrying out both, the preparation of the sample and applicaton of the coating, together with the tests which are essential for analyzing the behavior of the coated piece.
- Coating composition.
There exist a wide range of possible reagents and variables to modify during this kind of sol-gel reaction in order to achieve our goals; a hydrophobic, thermal-stable coating. The main research lines were based on one side, inorganic based coating and on the other side organic-inorganic based coating. Some of the studied variables during the synthesis of the coating were: time of hydrolysis and condensation during the sol-gel reaction, types of catalysts, solid percentage and amount of the coating deposited, additives addition, etc.
- Coating characterization.
During all the experimental process, several systems were used for:
- Verification of the hydrophobic properties: contact angle system.
- Thermal treatments: oven and muffle.
- Characterization of the coatings: FTIR, TGA, SEM, measurement of the color.
- Characterization of the behavior of the coatings once they are applied: scratch test, roughness measurement, determination of the colour. Together with the quality tests: Bunsen burner, acidic resistant, thermal shock, adhesion test, corrosion resistant, etc.
They have helped us to understand better the reaction and analyze the coating behavior over the sample in “real conditions” to check the industrial application. Part of this equipment is used during the lab scale coating development and other part correspond to the quality tests that Pramar normally use for assure the quality of its products to its costumers.
The best results have been obtained with a hybrid sol-gel precursor in combination with other additives; achieving a value of 150±2 at 450 oC and 136 as a maximum value at 450 oC. According the classification of contact angles, these values correspond to super-hydrophobic surfaces.
Due to the complexity of the project, taking into account the time needed for a product development starting from lab scale, the values obtained are excellent. Even this coating is not prepared yet for using at industrial level, since cohesion of the network formed by the coating should be improved, it has already passed some of the quality tests done in Pramar for the existing enamels. This means that we are in the right way; the developed product is a good pillar for modifying the formulation and improve the performance.
Thanks to REsiliENCE project, Pramar S.r.l that is an enameling company, has gone more deeply in the coatings field, stablishing a R&D Department involving all the technology transfer, increasing its visibility to other markets. It has developed a base formula for continueing with the research line.
