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Protecting Color
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Visible light and wavelengths of light below 400nm have sufficiently high energy to alter the chemical structures of many pigments and dyes, leading to color fade. During outdoor exposure (weathering), the part encounters moisture in combination with light, and this may further hasten fading. The pigments and dyes used in matching the desired color therefore have to be selected carefully to ensure performance in the application’s environment.
Ultraviolet (UV) light can alter both the colorants and the plastic. Even if light-stable/weatherable pigments are used, color shifts can occur if the plastic is altered by exposure. Microscopic cracks can form that leave a haze on the surface, making the color appear lighter (washes out the color). Weathering also causes oxidation that can impart a yellow cast in some plastics, causing a blue to shift toward green and a red to shift toward orange.
Where appropriate, CCC adds non-colored chemicals to protect the plastic against the damaging effects of UV light. UV stabilizers work through several mechanisms. Some absorb the UV light and convert it to heat before it can damage the plastic. Others short circuit the reactions that result in the damage. AOs (anti-oxidants) scavenge many of the free radicals formed when plastics are exposed to UV rays, thereby assisting the UV stabilizers in preventing damage. CCC has developed cost-effective packages for many applications for one-year, three-year, five-year and ten-year protection.
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