Next-generation nanotechnology processes for the pre-treatment of metal surfaces prior to painting.

Background: What is phosphating?

One of the earliest technologies developed and still most widely used for the treatment of metal surfaces prior to painting is phosphating. Phosphating is an industrial process widely used as a chemical pretreatment to protect metal surfaces. It consists of the formation of a surface conversion layer of metal phosphate, generally based on iron (amorphous phosphating) and/or zinc. The layers formed have a dual function: passivation through an oxygen barrier effect, which limits metal corrosion, and promotion of adhesion for subsequent coatings such as paints. Amorphous (iron) phosphating offers ease of application, simple process control, and performance suitable for materials exposed to low-to-medium corrosive environments. Zinc phosphating, on the other hand, is a more complex treatment process designed to achieve the highest performance levels, even in highly corrosive environments. This technology is widely used in numerous industries, including automotive, automotive supply chain, coil coating, and household appliances. However, it involves a greater number of process stages, strict control requirements, the formation of sludge containing heavy metals, scale build-up in equipment, frequent maintenance operations, high water consumption, and significant energy use for heating the treatment baths.

Alternative technologies to amorphous phosphating: first-generation nanotechnology processes

At PROQUIMIA, for more than 20 years, there has been a strong commitment to the research and development of conversion technologies that are alternatives to phosphating, are more environmentally friendly, technically and economically viable, and capable of delivering corrosion resistance and paint adhesion performance comparable to phosphate coatings. With the implementation of the first generation of nanotechnology conversion coatings developed  the CONVERCOAT range mainly based on zirconium ceramic oxide deposition technology, significant process savings have been achieved in terms of energy and water consumption, together with reduced maintenance requirements and lower environmental impact, while maintaining anticorrosion performance equal to or higher than that of amorphous phosphating. However, when anticorrosion performance is compared with that obtained using traditional zinc phosphating technology, the same performance level is not yet achieved.

Can nanotechnology processes match the anticorrosion performance of zinc phosphating?

The challenge has been set: to match the performance level of zinc phosphating by developing a second generation of nanotechnology products while retaining the benefits of this technology. As a result of this need and the continuous improvement philosophy of PROQUIMIA, the R&D&I project called NACAR (High-Performance NanoCoatings) has been carried out over the past two years. The project was co-funded by the CDTI and the FEDER under file number IDI-20220983. It enabled the development of a new-generation nanotechnology process, named CONVERCOAT NT, designed for multi-metal treatments in 3- and 5-stage spray lines as well as immersion lines. The CONVERCOAT NT process incorporates cathodic nucleation agents as well as organic and inorganic accelerators, enabling the formation of a conversion layer that is more compact and thicker than those obtained with first-generation nanotechnology processes, thereby delivering excellent anticorrosion performance and paint adhesion.

Confocal and interferometric microscopy performed on a steel panel treated with CONVERCOAT NT

Specifically, in 5-stage multi-metal lines, implementation of the CONVERCOAT NT process has significantly increased the corrosion resistance of the substrate–treatment–paint system, achieving an improvement of one corrosivity category according to ISO 12944.

	CONVERCOAT 1st generation + single-coat polyester paint	5 stage process with CONVERCOAT NT + single-coat polyester paint
Steel	Achieved category: C3H	Achieved category: C4H
Aluminium	Achieved category: C3H	Achieved category: C5H
HDG	Achieved category: C4H	Achieved category: C5H

Classification of corrosivity categories according to ISO 12944-2 Therefore, the newly developed CONVERCOAT NT process makes it possible to match the anticorrosion performance levels achieved with zinc phosphating, while operating at low temperatures (35–45 °C) and significantly reducing sludge formation and scale build-up in equipment. With more than 50 years of experience in the field of metal surface treatment, PROQUIMIA provides a comprehensive service covering the study, design, and implementation of metal surface treatment processes tailored to the specific needs of each project.