Spectrophotometry minimises rejection rate in the plastics production

For the continuous colour control in the production line a colour measurement system has been developed by Micro-Epsilon. The new system does not only recognise the saved colours according to the yes-no-principle but also determines the exact colour of the components spectrophotometrically. With a precision that exceeds the human eye, and a measuring rate of 2000 Hz the system is variously used in the plastics industry.

Colour recognition is necessary in the production line in order to identify quality defects early, avoid rejection and to increase the productivity of the production process. The typical colour sensors measure with a precision of ΔE > 0.5. The increasing industrial requirements, however, need inspection systems with ΔE < 0.1.  Currently, this is only possible with spectrophotometry. The inline colour measuring system colorCONTROL ACS 7000 by Micro-Epsilon meets these requirements with a colour resolution of ΔE < 0.08. The measuring system has three operation modes. In the first mode – the colour recognition – up to 15 colours can be saved and verified. In the second mode – the colour measurement -  the colour values are measured and the tendency is analysed. This mode is best suited for the plastic production because of the non-contact measurement method and the high measuring frequency of 2000 Hz. In the spectral comparison mode the reflection spectrum of the measurement object is displayed and evaluated. A wide range of colour spaces (XYZ, L*a*b*, L*u*v*, L*a*b*99, L*c*h, L*c*h99), distance models (ΔE(CMC), ΔE99, ΔE94, ΔEDE2000) and standard illuminants (A, C, D65, D50, D75, E, F4, F7, F11) is available to calculate the colour values.

The non-contact sensor has a measurement geometry of 30°/0°. Therefore, the self-reflection of wet or shiny surfaces has no direct influence on the measuring result. The sensor realises a measuring distance of 50 mm and a measuring spot of 9 mm.

The colour measurement system colorCONTROL ACS 7000 is already used for the continuous inline colour control in several areas such as the production of plastic plates and plastic bands, the examination of window frames, and film extrusion.