Color in Thermoplastic Injection Molded Parts Specifying a color for a plastic molded part can be very important. The molded part may need to match other colored parts in an assembly or it may need to stand out to give a more dramatic appearance. Yet, before discussing the importance of color in plastic parts, let’s first gain an understanding of what factors affect color. Introduction To help understand color, imagine a light source, an object, and an observer. We must have all three for color to exist. Consider an object in a completely darkened room. There is an observer and an object, but because there is no light, there is no color. Or look at the night sky, don’t look at a star, planet or other satellite. While there is an observer and a light source, there is no object, thus no color. Finally, if there is no one to view an object under a light source there is no color; color requires an observer. Now that we know the components of color, let’s examine how these components work together to give us our perception color. Light Source Let’s start with light. Light is electromagnetic radiation with wavelength to which our eyes are sensitive. The range of visible light, with some individual variation, is 390 to 770 nm. Light sources, or illuminants, are characterized by their power of light at each wavelength in the visible spectrum (the energy distribution). The energy distributions of light vary widely depending on the source. How the energy distribution and the object interact is the important factor in determining how color is observed. Object When an illuminant is directed at an object, some light is reflected at the surface and some is absorbed into the object. Thus, color is the result of how the object reflects and absorbs energy from the illuminant. If one uses two differing illuminants, each having differing energy levels in the visible wavelength, the color will be different. At the same time, two differing objects colored with the same pigment will have a different color since they absorb and reflect light differently. Observer The observer is the final piece to the color puzzle. If a human is the observer, the eye and the brain are involved. Since there are variations from person to person to their degree of light sensitivity, colors seen by different humans are not identical. To decrease human variation, a “standard human observer” model was established and is known by its French name as CIE (Commission Internationale de l'Eclairage). This standard uses terms of L* a* b* to characterize all color. L* represents lightness, a* represents redness-greenness, and b* represents yellowness-blueness. The CIE standard allows for repeatable measurement of color in order to standardize the observer component. Conclusion Color depends on the interaction of three factors: light source, object, and observer. If any of the factors change, the color also changes. These components have individual and interactive properties that affect overall color of an object. Now that we have a background understanding of what color is and what affects it, next month’s article will discuss the steps to take when attempting a color match. References: F. W. Billmeyer, Jr. and M. Saltzman, Principles of Color Technology, 2nd ed., Wiley, New York, 1981. Zeno W. Wicks, Jr., Frank N. Jones, S. Peter Pappas, Organic Coatings: Science and Technology, 2nd ed., Wiley, New York, 1999. |
