ALTANA

A New Challenge for Color Measurement

Since they made their first appearance 30 years ago, effect coatings became increasingly popular - not only in the car industry.

A paint coating shall not only protect the surface underneath, it is also an important quality criterion, especially for exterior automotive finishes. Often there are discrepancies between body panels and adjacent add-on components. Unsatisfactory color matching after a repair job results in customer complaints. And many people wish to distinguish themselves by driving cars with a brilliant coating.

The first effect coatings on the market were metallic coatings. In contrast to conventional solid coatings, they contain aluminum-flake pigments, which are responsible for the fact that the color varies depending on the illumination or the position you look at it. This effect is called darklight flop and it is caused by the mainly flat orientation of the flakes in the paint. The flop effect accentuates curved contours and thus increases the attractiveness of the product, especially that of cars.

In the 1980s, pearlescent pigments were introduced. The lustre of pearlescent paints is milder than that of metallic paints, which is caused by a different sort of flakes.

As the demand in effect paints is constantly increasing, the industry keeps developing new kinds of effect pigments. Not long ago a new generation of effect coatings was introduced to the market that show large color shifts under changing viewing conditions. For example, the color may travel from red to green. Such color shifts are based on different physical phenomena: how the light is scattered, absorbed or reflected.

The visual perception of effect paints is influenced by color as well as "sparkle" and "graininess". Sparkles are the many tiny light-spots which are strikingly brighter than their surrounding or which have a different color. The sparkling impression is only visible under intense unidirectional illumination. The graininess is the contrast you see in the irregular light/dark patterns exhibited by effect coatings under diffuse lighting conditions. In other words, you will see the sparkling impression under direct sunlight and graininess when the sky is overcast.

Conventional multi-angle spectrophotometers can no longer adequately characterize the new effect coatings. Up to now metallic finishes were measured using a fixed illumination and detection at several viewing angles. This type of measurement does not really reflect what we actually see. Our visual perception is influenced by the color change caused by the viewing angles as well as the changing effects which result in more or less sparkling or a finer/coarser look.

Already some time ago BYK-Gardner has started a close cooperation with key automotive OEM and refinish paint companies as well as leading car producers to find a way to objectively characterize the total impression of effect coatings. This "research" turned out to be successful and the result is a new instrument, the BYK-Gardner BYK-mac.

BYK-mac

With the new BYK-mac it is possible to describe the total impression of effect coatings as we really see them. Additionally to the traditional color measurement at 5 angles: 15°/25°/45°/75°/110°, the BYK-mac measures color "behind the gloss" at -15°. This is necessary to measure the color travel of interference pigments. The instrument also does sparkle and graininess measurements for the characterization of flakes.

We introduce our new BYK-mac on the European Coatings Show (08th to 10th May 2007) in Nuremberg, Germany. If you attend the show, come to our booth and see for yourself!