New thin film coatings improve corrosion resistance

Louise Smyth

Henkel can now offer a number of new generation solutions to metal pre-treatment processes. Bonderite M-NT thin film conversion coatings are designed to enhance multi-metal parts (steel, iron, aluminium, zinc) and overcome the issues associated with traditional phosphating, such as high energy costs, excessive sludge and scale generation, environmental and health and safety concerns. In contrast, Bonderite M-NT coatings, which are much thinner than traditional zinc or iron phosphates, offer a 10-30% process cost saving, while further advantages include the absence of phosphate or nickel salts, and no polymers in the conversion bath. 

To illustrate the potential benefits available, a traditional zinc phosphating process comprises seven steps: cleaning, rinse, conditioner/activator, phosphating at 55°C, rinse, post-rinse and DI (deionised water) rinse. Using Bonderite M-NT 1200, however, this can be reduced to just five steps, or possibly six depending on the cleaning. In addition, conversion coating takes place at ambient temperature, so there is no need to use energy heating the bath.

In a customer case study, a UK painting subcontractor switched from zinc phosphating to thin film B Bonderite M-NT 1200, achieving a safe and reliable process as a result of easy bath controls and fewer steps to monitor. Not only did the company reduce its energy costs, but maintenance was also reduced considerably as very little sludge or scale is produced. Furthermore, the high-performance product passed the 1000-hour neutral salt spray test.

Similar success has been witnessed at a French manufacturer of agricultural plant that is now using zirconium-based Bonderite M-NT 20120 in place of a five-step phosphating process. Along with reduced energy consumption, the plant is experiencing excellent paint adhesion and no flash-rusting. The latter creates a powdery layer that lowers paint adhesion and was previously causing a problem for the plant.

Also in France, outdoor furniture manufacturer, Fermob, is exploiting the benefits of Bonderite M-NT 20120 to protect its products against corrosion while at the same time minimising environmental impact.

Fermob processes some 3200 tonnes of steel and aluminium every year at its Thoissey plant. With a thickness of only 20 to 30nm, the nano-ceramic Bonderite M-NT 20120 coating is much thinner than the layer achievable with conventional iron phosphating, which is typically 500 to 1000nm. What’s more, paint adhesion and corrosion protection are substantially better – salt spray tests show that switching to Bonderite M-NT 20120 improves anti-corrosion performance by about 30%. 

A further product of interest is Bonderite M-NT 2011, an advanced pre-treatment system that provides a nano-ceramic coating to metal substrates, and is especially formulated for use on steel surfaces, aluminium and zinc. Totally free of phosphorus, COD, BOD and heavy metals, the product operates at room temperature and offers a high level of pre-treatment performance. It needs fewer chemical steps and reduces power consumption, water and space requirements in plants.