Assessment of pigment distribution in molded samples using an image processing technique

Computerized image processing was used to characterize the mixing quality of injection molded samples of linear low-density polyethylene blended with 1% pigment colorant. The effect of process conditions, including back pressure and screw speed, on the pigment distribution in the molded samples was investigated. Micrographs of moldings produced at various operating conditions were scanned optically and the resulting grey level distribution of these micrographs was measured and related to the state of pigment distribution in the molded samples. It was found that an improvement in the mixture quality can be achieved by increasing the back pressure and screw speed during the injection molding cycle. The technique used in this study has proved to be an efficient means of assessing pigment distribution in small or large translucent molded products. (C) 1996 John Wiley & Sons, Inc.