Waterborne coatings for corrosion protection

09/27/2011

Looking for best product-process combinations

Frédéric Gheno, Marketing Manager at NOF METAL COATINGS EUROPE, interviewed by European Coatings Journal - April 2011

-         Can waterbased coatings for corrosion protection keep pace with solvent based products?

Coatings for corrosion protection of steel or iron components are usually of 2 types: zinc coatings, providing a cathodic protection, or paints, providing a barrier protection. Under this classification, zinc flakes coatings belong to both families, as they combine sacrificial and barrier protection. This duality offers better performance at low thickness. Among existing zinc flakes materials, you can find solvent-based and water-based dispersions, whereas all products are proprietary and do have different dry compositions. Such products have found a large acceptance in technical applications, especially for small size fasteners coated in bulk, but also for a variety of other metal parts, some of large size coated on racks by dipping or spraying.

Of course it is more desirable for the environment to use water-based coatings than solvant-based ones, but is it possible ? The answer is certainly positive : the salt spray test resistance of the water-based GEOMET^® chrome-free coating applied industrially on bulk parts is usually of 1,000 hours for 8 µm thickness.

All chemical companies involved are seeking for water-based products. Beside environmental considerations, one technical feature is important in the day-to-day operation of these coatings chemicals : the risk of destruction of solvent-based  chemicals due to water addition; obviously this risk does not exist with water-base materials, their adjustment being realized with water. The origin of the water can be the water vapour in the air, the relative humidity can be very high in some regions, the other possible origin are the components to be coated, the drying phase after surface cleaning being the key process parameter. 

-          What are the current challenges in manufacturing waterbased anti-corrosion coatings?

Water-based anti-corrosion coatings have good performances, but one could ask himself about the reliability of such coatings. Compared to water-based paints, that are very commonly in use, difficulties might arise due to the presence of zinc and aluminium particles in water dispersion. The stability is the first challenge to overcome, but if you take the example of GEOMET^®, there is an expertise that have been gained over 4 decades, starting with the DACROMET^® coating.

The coating application is another challenge , especially in order to obtain a good thickness distribution for parts in bulk. In this field, it is important to have a good chemistry, independantly of the nature of the solvent, water or organic. Of course, water-based dispersions do contain some organic chemicals in small amount that will help obtaining a good coating.

NOF Metal Coatings is continuously seeking for the best product-process combinations, the challenge being in specifying well adapted processing conditions for a given coating material. These conditions shall remain simple and effective in order to keep the application cost at a low level. The coating material shall have versatile features, accomodating multiple component geometries and multiple coating application technologies.

-         What new developments are you working on?

Since 2004, we are working on technologies focused on further environmental and health benefits. This long-term research activity has been awarded by the 2009 Pierre Potier price for “chemical innovation favoring sustainable development” and the 2010 European Responsible Care^® price. It consists of developing innovative production processes for our water-based chemicals, that allow to reduce considerably the VOC amount in the chemicals.These innovative technologies can then be applied for each of our products, with different practical results. One example is the production of a ready-to-use chemical instead of a 2-K package, reducing the VOC amount under 5% and keeping a long shelf-life at 20°C.

For more information about this interview, please contact; infofr@nofmetalcoatings.com