The typical offline color measurement on injection molded or pressed specimens is a very expensive and time-consuming process. In order to optimize productivity and quality, it is desirable to measure the color already during production. Therefore, several systems have been developed to monitor the color e.g. on melts, strands, pellets, the extrudate, or injection molded part already during the process. Different kinds of inline, online, and at-line methods with their respective advantages and disadvantages will be compared. The criteria are e.g. the testing time, which ranges from real-time to some minutes, the required calibration procedure, the spectral resolution, and the final measuring precision. The latter ranges from 0.05 to 0.5 in the CIE L*a*b* system depending on the particular measurement system. Due to the high temperatures in typical plastics processes, thermochromism of polymers and dyes has to be taken into account. This effect can influence the color value in the magnitude of some 10 % and is barely understood so far. Different suitable methods to compensate for thermochromic effects during compounding or injection molding by using calibration curves or artificial neural networks are presented. Furthermore, it is even possible to control the color during extrusion and compounding almost in real-time. The goal is a specifically developed software for adjusting the color recipe automatically with the final objective of closed-loop control.
Color monitoring, process measurement, thermochromism, injection molding, extrusion
One of the most important quality parameters in the plastics processing industry is the color [1,2]. Particularly in the automotive industry, it is difficult to combine differently dyed materials such as leather, plastic, and wood. Color is an interpretation by the human brain obtained from the eye´s perception of visible electromagnetic waves. To define a specification, however, the measurement of physical values is more precise and reproducible than the human visual inspection.
It is important to characterize the color by numerical data and not only by the visual impression. For this reason, the CIE (Commission de l´éclairage, International Commission on Illumination) introduced the commonly used CIE L*a*b* system in 1931 to describe the color quantitatively . There are two main options for color matching, namely the visual inspection and the instrumental color matching.
All color measuring systems for plastics processing are well suited for their specific range of applications. In many cases even 100 % control and monitoring are possible. It is essential to scrutinize and evaluate the respective supplier information and application for each individual case. For some applications, the easiest way is to improve current measurement techniques. Easy handling and calibration should be carefully considered in the development of new devices. Thermochromism of colored plastic compounds still is an open field for research, which could be the base for future and easy calibration procedures.
The Kavian Scientific Research Association (KSRA) is a non-profit research organization to provide research / educational services in December 2013. The members of the community had formed a virtual group on the Viber social network. The core of the Kavian Scientific Association was formed with these members as founders. These individuals, led by Professor Siavosh Kaviani, decided to launch a scientific / research association with an emphasis on education.
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FULL Paper PDF file:Color measurement of plastics - From compounding via pelletizing, up to injection molding and extrusion
Published Online: 17 February 2015
Color Measurement of Plastics – from Compounding via Pelletizing, up to Injection Molding and Extrusion
AIP Conference Proceedings, Volume 1593, Issue 1, 10.1063/1.4873725
PDF reference and original file: Click here
Professor Siavosh Kaviani was born in 1961 in Tehran. He had a professorship. He holds a Ph.D. in Software Engineering from the QL University of Software Development Methodology and an honorary Ph.D. from the University of Chelsea.