QMT Features: November 2008
Matching sparkle in colour
A new colour measurement system will save automakers and automotive suppliers considerable time and money in applying metallic flake and other effect paints

How to accurately measure the colour and appearance of coatings with "sparkle" that confound optical instruments has been a a daunting problem for automotive suppliers and automakers ever since metallic flake, pearlescent and other effect paints were introduced in the 1970s. Now colour measurement specialist, X-Rite, has launched its xDNA system which, together with the MA98 handheld spectrophotometer, solves the problem.

Manufacturers often waste a significant amount of time and money trying to match body panels, bumper facias and other parts coated with effect paints because they do not have instruments that measure why the paints look different under various illuminations and observation angles. Quality control personnel on a production line may observe that body panel and bumper facia don't match properly, but prior instruments could not give consistent and accurate measurements to help explain why the mismatch was occurring. Consequently, companies spend an inordinate amount of time and resources trying to determine the root cause of painting problems through trial and error methods.

"With xDNA, X-Rite is giving automakers and their suppliers the appropriate tool to distinguish characteristics of effect paints that can't be detected - much less analyzed - by other systems," said Brian Teunis, market manager of X-Rite's industrial colour and appearance division. "We coined the term ‘xDNA' to emphasize the fact that each effect paint has a unique, three-dimensional mathematical model, similar to the way that each person has a unique DNA structure. The exact name for X-Rite's package is Dynamic Numerical Analysis, but we figured xDNA was a little easier to say."

The xDNA system promises to speed the introduction of new effect paints by designers and paint manufacturers, improve the first-time quality of products being coated with the paints, and reduce the time and effort of troubleshooting manufacturing problems that occur on the factory floor.

Key to xDNA
The key to xDNA is a new instrument called MA98 that uses twice the number of illumination angles and sensors of prior instruments, and a software package called X-ColorQC that manipulates the data with proprietary xDNA algorithms to generate easy-to-understand graphs that show unique characteristics of an effect paint.
The new xDNA package offers manufacturers reliable and consistent data that can help:

  • Troubleshoot whether a problem on the shop floor is due to the manufacturing process or the paint formulation
  • Assess whether existing equipment can be adjusted enough to accommodate a new process
  • Develop more exact quality standards on the painting lines that indicate quickly when a process is going out of control
  • Predict whether a person will be able to perceive a difference in colour and appearance when the formula of an effect paint, or the process used to apply the paint, are changed

From a hardware viewpoint, MA98 is a precision 31-point spectrophotometer that is designed for ease-of-use on the factory floor. Weighing approximately 1 kilogram (2 pounds) and covered with a soft over-mold case for two-handed use, the instrument is designed for frequent and comfortable measurement by shop floor personnel. Battery powered, it has a quick measurement time of about 1 second, with calculation and display in a total of 2 seconds.

Automotive case study
One of the world's largest automakers was able to resolve a problem matching the effect paints of bumper facia and body panels in three days using the xDNA package - after spending more than two months trying to resolve the issue through the use of other measurement systems.

Process engineers at the automaker applied traditional root cause analysis to the problem, first to try and identify whether the matching problem was an internal process, or due to changes in formulations by the paint supplier or whether parts were out-of-specification from bumper suppliers. Individuals working on the line told the engineers of a sudden difference in how the parts matched. Their floor inspectors, using an X-Rite MA68II instrument, said the instrument indicated there was a difference in reflectance values. With the available data , the engineers reasoned that the root cause of the problem was due to paint formulation and they asked for assistance form the paint supplier.

The paint manufacturer spent nearly two months unsuccessfully trying to match the colour and appearance of the bumper fascia s that appeared too light in comparison with the car body - even going as far as changing the formulation on the paint.
Using the new MA98 instrument, X-Rite personnel offered to analysis the paint problem. Since the MA98 takes measurements at 10 angles instead of 5 angles, the instrument can record relative comparisons of the critical aspects of special effect paints, such as flake size and particle distribution. The data indicated major variations at the +/-250 out-of-plane angles, which can be caused by differences in flake orientation. Further, the xDNA software interpreted the measurements of both the bumper fascia and the body panel by developing three dimensional plots that were uniquely representative of their particular special effect paints. The plots showed similar shapes but different positions in 3-D space that indicated a change in process rather than formulation.

X-Rite further analysed the data by translating, aligning and scaling 3-D plots, which confirmed that the best course of investigation was to check the process of how the paint was applied. The xDNA provided another important clue - the difference in reflectance curves at the 250 angle out-of-plane measurements indicated a difference in the way the flakes were oriented. It all pointed to a mis-match, or harmony problem, due to processing differences between the bumper and the car body.

The automaker then realised that it had altered a critical process parameter in prior months when it changed from a bell/air method of applying the base coat and the final coat to the body panels to an entirely bell/bell method.
When the automaker implemented the bell/bell method, the process delivered the flakes so they were oriented on their edges uniformly, cutting their reflective quality to give the paint a darker appearance. This phenomenon is understood by paint engineers, but the information wasn't considered during the process change and subsequent root cause analysis until the MA98 and xDNA brought the differences to light.

With the data measured by the MA98 and interpreted by xDNA in only two days by X-rite personnel, the automaker made adjustments to the paint supply in the bell/bell system and coordinated with the bumper supplier to achieve harmonious colour matching in body panels and bumper fascias.

"X-Rite will first market the xDNA system with MA98 to the automakers and automotive suppliers in the United States and Europe, but the package has potential applications in other industries, including appliance manufacturing and cosmetics formulation," says Teunis.



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