Inside the Colorful Side of Composites

If you tend to regard the color of a product as a non-influential part of the manufacturing process, you’d be mistaken, says Kip Howard, technical service representative for Plasticolors, Inc. He explained in a Thursday morning session titled Color Science and Pigment Dispersions for Thermoset Composites that it’s a factor manufacturers must consider when working with this seemingly-simple element.

The presentation began with the definition of color itself: a combination of light, object, and observer. To demonstrate this (particularly the latter characteristic), Howard pointed two lasers at the wall, one red and one blue. The blue one appeared to be further away, and Howard used this example to show how the mind plays a role in color. “Choosing the right color is part of the design of any composite part,” he said.

But light also plays a big part in the process. “The light source is the number one source of color variance,” says Howard. For example, daylight results in even levels of color, tungsten lamps feature decreased levels of blue, and fluorescent bulbs result in random spikes across the spectrum. How composites interact with the light depends on the geometric attributes of the product itself, which include surface smoothness. Because of this, Howard notes that composite products will not be able to look like another material. “Only metals look like metals,” he says.

Color matching is another important factor. “There are only a finite amount of available pigments, so they’re blended to reach the desired color and keep it under control,” says Howard. He went on to discuss some specific pigments and how they act as chemicals in color composition. Phthalocyanines and azos tend to accelerate the rate of cure in composites. Carbon blacks feature 100s of grades, and thus can accelerate or inhibit the cure depending on the grade. Ultramarines feature metal complexes, whose ions may react with composite components. Inorganic whites such as titanium dioxide and zinc sulfide are commonly used in composites, but not in outdoor applications because their intensity fades under those conditions.

Howard also detailed some appearance issues that pop up. A lack of pigment opacity can be resolved by using higher pigment dispersion concentrations. UV stability can be addressed by optimizing the full composite system to meet stability requirements, and also using additives to improve outdoor weathering performance. Glass fibers near the molded surface can result in color variation and degradation, and can be compensated for by using additional pigment dispersion. Regions of dry glass impact the structural properties of the composite. “Whatever appearance issue you have, realize it’s application-specific and must be addressed independently,” says Howard.

This entry was posted on Thursday, February 11th, 2010 at 11:00 am and is filed under General Interest, Manufacturing and Processes, Materials. You can follow any responses to this entry through the RSS 2.0 feed.