Infrared Welding of Thermoplastics. Colored Pigments and Carbon Black Levels on Transmission of Infrared Radiation

Abstract

Infrared welding has been characterized as unpredictable because different polymers or formulations have been observed to heat at widely different rates under similar conditions. Pigments, fillers, coatings, and other components of polymer formulations affect what happens to incident infrared radiation. They will strongly affect the ability of polymers to absorb the IR radiation, and can lead to various amounts of reflection and absorption (and transmission). This chapter studies the absorption characteristics of IR energy by different polymers, by variously colored ABS materials, and by polymers with different levels of carbon black. This information should provide practical guidelines and process understanding when infrared welding is being used. The heating characteristics of infrared energy are evaluated from a quartz-halogen lamp on some colored polymers. One polymer was acrylonitrile-butadiene-styrene, ABS, pigmented with different colors: blue, green, orange, yellow, and red. Making mixtures of polyethylene with different levels of carbon black makes studies of the effect of carbon black on infrared absorption. Polymers pigmented with carbon black showed the least transmission (most absorption) and only very low levels of carbon black were needed to make them opaque. Examination of colored films of ABS showed increased transmission as the colors progressed through the spectrum from red to blue. That is, red absorbed more energy relative to the other colors even though the spectral output was weighted more heavily in the red part of the spectrum.