Coatings that are up to scratch

Even a tiny scratch can spoil the look of a good paint finish, so BASF Coatings has studied how nature resists at the nanoscale and come up with a new option

In addition to its original protective function, the marketing significance of a vehicle’s finish has increased exponentially in the past few years. Pearlescent and metallic effects, ever-new colours and special-effect finishes are designed to whet the consumers’ appetite for a particular model. The finish transports an image, which may be classy and exclusive, sporty or classic. That increases the expectations of both carmakers and consumers for a long-lasting brilliant appearance of the finish. In this context, scratch resistance is a trend that is attracting a lot of attention.

BASF Coatings is currently working on new solutions that can be integrated into OEM production starting in 2011 at the latest. But there is a precondition: new coatings with improved properties may not negatively impact on the overall process, either from an economic or an ecological point of view. Clearcoats are at the centre of the discussion. “Our objective is to see the requirement and the road to higher scratch resistance from a holistic point of view” , says Dr Winfried Kreis, head of Coatings Innovations at BASF Coatings. “[This applies to] the process, durability of the new coating property, as well as reproducibility, for instance at the body shop. And from a business point of view, the new coatings will have to measure up to the materials that are already available.”

The motto is “lock and load”: developing a new coating with an enhanced property profile that can be transferred to the carmakers' existing processes without necessitating a changeover. “Scratch resistance, meaning the improvement of permanent appearance and effective protection against microscratches, like those that occur at the car wash, is feasible,” says Dr Kreis. “Not only that, it is feasible with significant results.”

Nature's way
BASF researchers see three analogies in nature for especially scratch-resistant materials: first, the diamond, with its extreme hardness; second, any kind of liquid that separates under pressure and then flows together again, and finally, elastic materials like rubber, that also return to their original form after impact. When transferred to the polymer coating of a vehicle, these images have led to two objectives: achieving the highest possible regularities in network formation and simultaneously creating an extremely stable network through very solid compounds.

This poses demands that so far had seemed to be nearly impossible to meet with a polymer. “It’s a matter of designing a formation process of the 'plastic film' that is characterised by high regularity and prevents freely moving polymer chain ends from occurring and keeps polymer chains from becoming entangled. At the same time, this sophisticated network needs to continue forming in the same way under a wide variety of conditions,” Dr Kreis explains. He sees this as an ideal example of a “smart” chemical approach. “We achieved the property of scratch resistance very quickly during our research activities. The real challenge, however, was maintaining this property profile of the film over a very long lifespan and guaranteeing the reproducibility described earlier. We had to wait until long-term stability was absolutely guaranteed before we could contact our customers.”

Refinish with rebound
The BASF solution is based on a new network design in which silica nanoclusters form that are similar to glass. These “silicate” domains are generated as “hubs” in situ. Other segments of this network serve to optimise the “elastic rebound”. This means that the use of nanoparticles can be completely avoided. The outstanding level of scratch resistance has no negative impacts on the other properties of the coating. Highly significant in this context are viscosity and the avoidance of brittleness. The technology, which is now already in use for pilot applications, is the basis for all areas of application, including automotive refinishing. It can also be applied to various materials, including steel, aluminium and plastic. “We are now at the point where the automotive industry is testing our approach by carrying out pilot applications, a wide variety of weathering tests, and sweeping risk evaluations,” Dr Kreis adds. “The current pilot applications are still running on the basis of the two-component paint systems, which are already top quality today, and the results have been outstanding,” says Dr Kreis. “The probability is very high that the first vehicles with this type of coating technology will be available on the market in 2011.”

One-component market
However, BASF Coatings does not aim to focus solely on the premium segment. It wants to outfit one-component applications with the new scratch-resistant durability as well, so that this property can also be offered in large-scale production. And there’s good reason for this. Seventy per cent of the global market is covered by one-component coatings. And while the requirements for an intelligent chemical solution may even higher for these products, the market is likely to clamor for this next level more or less automatically. There are plenty of examples of innovations that were transferred to the lower vehicle classes from the premium segment in a matter of a few years, including ABS, ESP, and all kinds of luxury features.

Tipping the nanoscales
However, the end of the development of “scratch-resistant systems” isn’t in sight by any means. “The next level will consist of achieving a property profile for finishes that corresponds to that of glass surfaces, meaning that it has extraordinary abrasion resistance.”

It’s a topic that will be of great benefit for transparent applications such as headlights and taillights. The design of the old diffusion light reflectors has given way to lights with a three-dimensional shape, marking a leap in development. These types of parts can no longer be manufactured from glass. However, the plastic substrates need to have the same abrasion resistance as glass.

“Our focus is on mastering sophisticated chemical network formation, which by nature occurs on the nanoscale,” says Dr Kreis. This technology involves mastering highly uniform network structures in the 5-nanometer area, which he describes as 'nano-architecture'. “We aim to do controlled construction in the tiniest dimensions. When it comes down to it, that’s the way chemistry, especially polymer chemistry, has always worked.”