Although solvent borne systems are still dominant in many areas of coating technology, water-based binders for direct-to-metal (DTM) coatings are increasing in popularity – and for good reason. DTM coatings combine the physical characteristics of a top-coat system and a primer in one layer, saving time and money on the application process, while waterborne technology offers a lower VOC profile.
The two together are a match made in heaven, but in the past formulators have struggled to achieve the same level of performance with waterborne DTM coatings. To make that winning combination work, BASF developed ACRONAL® PRO 770, a new acrylic high-performance binder with improved corrosion protection compared to other one-component water-based binders at the same dry film thickness.
The balanced hydrophobicity and chemical functionality of the resin allows for excellent resistance while still enabling ease of formulation and superior adhesion on a variety of substrates, including plastic.
The corrosion challenge
At the surface level, corrosion eats away at the gloss and color of an industrial paint. Corrosion isn’t especially easy on the eyes, but more importantly, it impairs the resistance and structural integrity of metals, potentially acting as a point of failure in some cases.
A DTM coating’s ability to resist corrosion is only as good as its formulation ingredients, according to Tony Neely, Technical Specialist at BASF.
“Rusting is an electrochemical process, so that needs to be taken into account,” says Neely. “I could have the best resin in the world, but if I include a lot of ionic species, I'm adding things with a bigger potential to rust and take away the protective properties with that resin.”
Acronal PRO 770 is designed to have a cleaner water phase with fewer ionic species.
Traditional metal coatings require a primer layer for adhesion and corrosion protection, followed by a topcoat for gloss and UV protection. The beauty of DTMs is that they bring the capabilities of a primer and a topcoat together in a single coat.
“DTMs provide the physical characteristics of both layers,” Neely explains. “It needs good adhesion and corrosion protection, but also it also needs high gloss and enough durable exterior factors like UV-resistance and hardness to withstand day-to-day life.”
Different formulations are available to meet specific needs. In cases where the user requires a more specifically formulated topcoat to be applied, ACRONAL PRO 770 can also be used as a primer. And while ACRONAL PRO 770 is designed to perform as a monocoat, multiple coats can be applied for added protection.
“It's compatible with anti-corrosive pigments. If you'd like to have a highly filled system, you can topcoat it later or use it as a pure DTM,” says Neely.
The application of only one coating requires less product, which reduces labor and saves time and money. You also don’t have to wait for the coat to fully dry before applying the next coat, so there’s a quicker return to service.
“With ACRONAL PRO 770, we're providing that same level of protection at an equal or lower film build to have our customers save on material cost. You're also saving on labor cost, because you only have to pay for the application of one coating,” Neely explains.
Lower environmental impact
VOCs, or volatile organic compounds, are common in many paints and cleaning products, and they have been scrutinized for causing short- and long-term health effects. Waterborne solutions already have lower VOCs compared to traditional solvent borne systems, but ACRONAL PRO 770 contains even lower VOCs than its competitors.
“We can make formulations down to 50 grams per liter,” says Neely.
ACRONAL PRO 770 is also APEO-free. APEOs (alkylphenol ethoxylates) are often found in paints and textiles and are slow to biodegrade. They’ve also been found to damage aquatic organisms and their ecosystems, which may eventually impact humans. ACRONAL PRO 770 is zinc-free as well, reducing the risk of zinc runoff, another environmental concern.
A DTM coating is only effective if it sticks to the surface in a variety of different conditions. ACRONAL PRO 770 performed well in both wet and dry conditions in a variety of ASTM-standard tests.
“We’re ahead of the competition on adhesion to the substrate, both in wet and dry adhesion and then also chemical resistance,” says Neely.
For the dry test, strips of tape are ripped off a scored surface, and adhesion is rated based off the amount of paint taken off. For the wet adhesion test, the scored coating is kept wet via saturated filter paper for one hour and then tested.
Compared to others, ACRONAL PRO 770 had the best overall adhesion and chemical resistance with great UV resistance, in addition to testing very well in corrosion and humidity resistance.
The gloss factor
While not essential for protection, a good gloss will make the finished coating look more visually appealing. ACRONAL PRO 770 can achieve different grades of gloss, so formulators can create the visual effect they need when they need it.
“The ability to have one resin that can reach levels of gloss from matte to high gloss is beneficial for the formulator, because it simplifies the amount of resins they need to use and purchase," says Neely.
Gloss is tested after thousands of hours exposed to UV rays, which can slowly eat away and damage coatings. In testing, ACRONAL PRO 770 was one of the top performers in gloss retention after 1000 hours of QUV exposure.
There may be some technical benefit to gloss.
“The reason the coating is glossy is because it’s physically smoother. Because of this, you can achieve increased resistance to abrasion and staining,” says Neely. “There are fewer bumps on the surface to catch when something slides across and fewer ‘valleys’ for dirt to sit in. Therefore, many people consider glossy coatings to be more durable.”
A true one-coat solution
The gap in the market for waterborne solutions is in part due to a mostly perceived gap in performance versus solvent borne solutions. With new advancements and formulations, BASF is starting to close this gap and offer solutions that can perform more efficiently while minimizing environmental impact.
ACRONAL PRO 770 is manufactured in America and is available now. Learn more and request a sample here.