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Small particles that breathe new life into paint

Time to repaint the house this summer, yet again? Soon, you will be able to take a summer holiday instead. By adding silica particles to commercial paints, life expectancy can be increased and dirt build-up and biodegradation reduced. Comprehensive exterior testing shows that paints remain fresh and maintain their colour for longer.

An idea occurred to Anders Larsson, a senior researcher at RISE. Adding silica particles to paint to increase surface hardness should make the paint more resistant to dirt and the growth of microorganisms.

The first challenge was to identify the correct formulation to ensure that the silica particles attach to the paint and perform the desired function.

“This is a matter of correctly mixing the paint. It follows the same principle as a food recipe; add the right amount of each ingredient in the correct order so that the dish has the desired consistency and taste,” says Anders Larsson by way of comparison.

Tested for scratches, weather and wind

The particles, known as colloidal silica particles, are provided by Akzo Nobel Pulp and Performance Chemicals (Akzo Nobel PPC). These types of particles do not cause gelation, a common problem when normal silica particles are added to paints that may be stored for long periods.

The first phase of the project began in 2008 as a degree project. Scratch resistance was tested in a instrument that abrades two surfaces against one another, with Scotch Brite Pad used as an abrasive. The results demonstrated that Anders Larsson’s thesis was sufficiently robust for further development.

In order to really put the particles to the test, it was then decided to add them to commercial paint containing acrylate and/or alkyd, the most common components of paints in the Nordics. Wooden planks, supplied by RISE, were painted in four white original paints, and each paint with two different surface modifications of silica particles. Nine planks of each paint sample, 108 planks in total, were installed at a 45° angle on various parts of RISE’s Bogesund field station for maximum exposure to weather and wind.

Paint with self-cleaning properties

Testing concluded in 2010 after nine months. The final step was to measure the lightness of the paint against a grey scale. This allowed a comparison of how much darker each paint sample had become as a result of exposure to the elements during the test period. 

The results showed that Anders Larsson’s thesis was indeed correct; the paint samples with added silica particles maintained their shade better than the original paints. This was also heartening news for Akzo Nobel PPC.

“The self-cleaning properties of the paint and the fact that it maintained its whiteness so well are very interesting to us and our customers,” says Hans Lagnemo, business development manager at Akzo Nobel PPC.

The project has proved to be a commercial success. Akzo Nobel PPC sells silica particles to the paint industry worldwide to reduce dirt adhesion and, together with RISE, is now examining entirely different applications for colloidal silica.

Current laboratory methods for monitoring the resistance of paint to dirt often rank experimental paints in the wrong order. This not only delays research and development, it also makes it more expensive. RISE is using paint both with and without silica particles in order to develop a quick method that provides the correct rankings.