“Norsjö One, our outdoor paint, has been used for a long time. New and improved, it is now self-cleaning.” 3D image from Myresjöhus.

Keeping a painted facade free from algae, mold and other growth is a major problem in the Nordic climate – which can be characterized as having a combination of sun, wind, rain, snow and extreme temperature changes. Add to this dirt particles carried by rain and winds.

“You don’t have to be an expert to understand that a durable and protective product is required for long term and sustainable results on a painted wood facade in the Nordic region,” says Jenny Lundegård, Innovation Manager at Akzo Nobel Decorative Coatings. “Not needing to repaint is an obvious advantage both environmentally and financially.”

The secret of nanoparticles

“Norsjö One, an outdoor paint, has been used for years. Now, it has been improved with self-cleaning features and a shelf life of up to 16 years. A smooth, hard surface means it catches minimal dirt and prevents algae and mold from growing. Norsjö One Supertech is environmentally certified and Swan labeled. We believe it to be the best wood product we’ve ever developed,” says Lundegård.

The paint owes its self-cleaning properties to a special type of nanoparticle. These are made of silicic acid (collodial silica; amorphous silica, SiO2) and were developed by a business unit within Akzo Nobel. Classed as a low risk material, SiO2 nanoparticles have been used industrially since the 1950s and are active in more than one hundred different applications. Akzo Nobel is the world’s largest manufacturer of silicic acid and forecasts great growth in these environmental applications.

Silicic acid improves color properties by repelling dirt, hardening the surface and optimally distributing color pigments, which results in better coverage and minimal use of the titanium dioxide (TiO2) white pigment. In Sweden, the first houses were painted with this type of paint in 2008 and since then a number of improvements have been made.

Hydrophilic surface repels dirt

Dirt particles seek surfaces that are hydrophobic, i.e., that are water repellant. But surfaces that have the opposite quality, hydrophilic or ‘water-loving,’ are dirt enemy Number 1. Silicic acid has lots of hydrophilic hydroxyl silanol groups on its surfaces, which thus prevents dirt from sticking.

“North Sea One Supertech is a water-based acrylic paint which provides a surface that is resistant to abrasion and that does not scratch so easily. It is the silicic acid that provides these improved properties,” continues Lundegård. “These hard hydroxyl groups increase the number of chemical cross-links, which gives them a harder, denser surface.”

This article was published in June 2015