Analysis and processing issues of plastic color mismatch
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Color is a visual characteristic which imparts the ability to categorize different objects. When light strikes an object, there are three possibilities as to what can happen. The light may be reflected, refracted or scattered. Human perception of color is due to a combination of these. Plastics are polymeric materials. Polymers are generally colorless and need colorants in order to have some color. One or more pigments in certain ratios can be used to give a specific color to plastics. Slight variations in the proportions of either of the used pigments, or their dispersion, may result in a color that is different from the desired one. There can also be many other reasons for color mismatch such as processing or degradation effects. This study utilized the historical data records of SABIC IP to look at effects of changing Grade on color (i.e. when the same color is produced from resin blends which may have different amounts of resins, pigments or additives). These records were also used to study effects of change in screw diameter and configuration on color (i.e. when the same grade of a color is produced on two different production lines, different screw diameters and configurations). The effects of the processing parameters on the colors were also investigated by carrying out experiments using a twin screw extruder at SABIC IP’s plant in Cobourg. Resins, pigments and additives were dry blended and extruded while being subjected to different processing conditions. Three processing parameters, namely temperature, rpm and feed-rate, were chosen for the study. A three level factorial design of experiments was used. An analysis of variance (ANOVA) has been utilized to find the effects of individual parameters on color and the interaction between two parameters and their cumulative effect on color.