Metal Coatings

Dow direct-to-metal solutions in demand

Coatings formulated with Maincote acrylic resins based on Avanse technology offer enhanced corrosion

The demand for direct-to-metal coating solutions – especially water-borne ones – to protect against corrosion is growing, according to Dow Coating Materials, which points out that the market now requires products that offer faster curing time and boost productivity.

For industrial applied-in-factory coatings in particular, the EU for instance has defined a cap on VOC (volatile organic compound) factory emissions, forcing applicators to look for lower VOC solutions in order to further grow their business.

“Therefore, for many applicators of corrosion-resistant coatings, direct-to-metal is the preferred solution to replace solvent-borne coating systems still used to date,” says a spokesman for Dow.

He says water-borne direct-to-metal solutions not only provide lower VOC, but also improve productivity by replacing the traditional system of a separate primer and topcoat.

The latest film-build technology developed by Dow offers formulators the ability to formulate direct-to-metal coatings with good adhesion for various substrates, and fast early hardness to enable high application line speeds with good corrosion resistance. 

Where higher film build is possible, for example, around 100-micrometre dry film thickness (DFT), the latest formulations without anti-corrosive pigments provide good anti-corrosive properties while simplifying the formulation space and increasing the gloss potential. 

However, one area for further improvement is still chemical resistance. “Albeit self-cross-linking technology has improved the chemical resistance performance of one-component water-borne direct-to-metal resins, a further boost was required to bridge the gap to two-component topcoat performance,” he says.

As the metal coating industry has been very much focused on increasing productivity in the last five years and significant cost savings can be made by applying coatings in-factory instead of on-site, the demand for pre-coated metal parts, whether for new construction projects like buildings and bridges, earthmoving vehicles or temporary pipe coatings for the oil and gas industry, has been increasing steadily, the spokesman points out.

“Paint formulators and raw material suppliers are working ever more together to develop products for these crucial applications. The particular focus for these coating systems is on improving application properties while maintaining corrosion resistance performance,” he says.

“This requires faster coating curing speed with systems that provide at the same time a longer pot life. It has created interest in alternative two-component technologies that avoid using traditional curing technologies like isocyanate for polyurethane or amine for epoxy that can offer improved application properties. There are various potential technical solutions, so much more is possible,” he remarks.

BASF offers a solution with Maincote acrylic resins based on Avanse technology that feature ambient self-crosslinking to help improve dirt pick-up resistance, chemical/solvent resistance and overall durability. In addition, novel polymer-pigment interaction in the wet phase produces a dried film structure that offers more uniform pigment distribution, improved barrier properties, and greater gloss potential.

General industrial metal applications can be found in consumer goods, agricultural vehicles (ACE), or general machinery where the coating is factory applied. Total factory VOC emission level restrictions as well as environmental awareness are the main drivers for coating applicators to look for water-borne solutions to replace traditional solvent-borne systems.

“Corrosion resistance, adhesion to a wide range of treated and untreated surfaces as well as chemical resistance are important coating performance requirements. Typical dry film thicknesses are between 40 and 100 micrometres. Early block will allow for fast stacking ability after coating application, therefore, improving productivity on high-speed production lines.

“Low-VOC metal protection next-generation Maincote resins for water-borne metal coatings offer good corrosion resistance and gloss whilst meeting lower VOC targets compared to solvent-borne coatings.

These features are helping to raise the performance level of water-borne industrial coatings and expand their utility beyond traditional light-duty environments,” the spokesman says.

Commenting on what Maincote water-borne binder based on Avanse technology can deliver, the spokesman says these offer low-VOC levels (lower than 100 gm per litre typically), and are APEO (Alkylphenol ethoxylates)-free, offering a better working environment

Other features include excellent adhesion to various substrates, either treated or untreated; fast hardness development for direct-to-metal applications; good chemical resistance for topcoat applications; high gloss and gloss retention; advanced UV protection; corrosion and water resistance; chemical and solvent resistance; blister resistance; and one component convenience.

“The gloss white coating formulated with Avanse technology demonstrates enhanced gloss retention when compared to a commercial solvent-borne polyurethane and a conventional acrylic in a two-year south 45-degree exposure study in eastern Pennsylvania. 

“Furthermore, coatings formulated with Maincote acrylic resins based on Avanse technology offer enhanced corrosion resistance, as demonstrated above on blasted, hot-rolled steel panels protected by one coat of a direct-to-metal, high-gloss yellow coating at 75-micrometre DFT – Salt Spray test method,” he concludes.