Volume 42, Issue 10 - October 2007

the Aluminum Citings

Color Variation

Itís Not Just a Result of Anodizing Anymore 
by John B. McClatchey Jr.

Anodized aluminum, as you should know by now, is always subject to color variation. There are many factors that affect the appearance of anodized aluminum such as alloy, constituents within the same alloy, the amount of time in the anodizing tank and even the direction at which the material is viewed. As a result, there has been an increased demand for Kynarģ painted aluminum.

Liquid Kynar painted aluminum is a different bird than powder coated aluminum. Most liquid Kynar applicators blend their own paints in house as well as purchase from suppliers such as Valspar, PPG or Akzo Nobel. Powders are not blended by the applicator. The manufacturer supplies the powder they have blended to the applicator. The result is better color consistency. The disadvantage can be lead time, minimum order size and, accordingly, price. All parties involved need to be aware of the possibility of color variation on liquid Kynar painted materials so they can work to minimize the frequency.

All Kynar paints are susceptible to color variation that falls within spec. When the shift began to swing from anodizing to painting, the specifiers still wanted the brilliant appearance that anodizing provided. This is one big reason why so many painted aluminum jobs now call for metallic and mica paints. These are more expensive finishes than anodizing but may not necessarily provide a more consistent finish depending on the circumstances. 

Possibilities for Variation 
Metallic and mica paints have more variation for several reasons. First, there is normal variation due to the batch spraying technique. Because a typical hand spray gun covers a maximum area of about 18 inches, any part larger than 18 inches may show variation under certain light and angles of viewing. Second, different paint applicators will often produce varying colors, even when using the exact same paint. Spray guns may be different. Techniques may be different. The environment may be different. To minimize variation, paint as much material as you can at once at the same facility. The third reason is that material needs to be painted at the same time and preferably from the same batch of liquid paint. 

When mixing paints, the slightest change in formula may change the appearance of the paint. The AAMA 2605 specification allows for a color variation of 5deltaE from the target. It is important to note, and to let all parties involved understand, that anything over 1deltaE is visible by the human eye. There may be variation, although the color still falls under the appropriate specification. Bottom line: use one release and one batch of paint to minimize variation. 

Lastly, the appearance of the metallic or mica paints will change based on the angle of viewing. Because these paints contain actual mica and metallic, the angle of how these flakes lay in the paint can make consistency unattainable. Light reflects off these flakes differently at varying angles, which will affect the appearance. This variation can be limited by having the same applicator paint as much material at the same time as possible, but it could appear different and still fall within spec.

Work with your applicator to minimize the potential for variation. Temper your customerís expectations. They need to realize that while there may be no variation issues at all, the potential is there. If you are educated as to what causes the variation, you will be able to explain it better and thus have a better chance of selling the characteristic that is inherent to Kynar painted aluminum. 

John B. McClatchey Jr. is an account manager and third generation owner of Southern Aluminum Finishing Co. and SAF Metal Fabrication in Atlanta. Mr. McClatchey's opinions are solely his own and not necessarily those of this magazine. 

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