Checking colour quality at speed

ICI Imagedata asked AstraNet Systems Ltd to design and install an on-line monitoring system to check production of dye sublimation printing ribbons. Three Astra UV/VIS Spectrometers now provide high speed measurement of the total optical density (TOD) of each coloured dye panel applied to a moving web.

ICI Imagedata is one of only a few manufacturers of thermal dye sublimation printing ribbons, which carry a repeating sequence of yellow, magenta and cyan dye panels. AstraNet designed a quality control solution using three fibre optic Astra UV/VIS Spectrometers. Fibres deliver light from a tungsten lamp to one side of the moving web, and collection fibres carry transmitted light from the other side to the three computer-controlled spectrometers. A stepper motor provides transverse movement of the monitoring system so that the whole ribbon is checked over a 10-minute cycle. Product parameters, such as the sequence of colours, panel length and absorbance specifications, are input to the software program and if averaged absorbance values fall outside specified limits, an alarm is triggered.

The latest version of the Astra UV/VIS Spectrometer is the first to include USB2 and to enable more than one instrument to interface with a single PC. Also included is the facility to switch the lamp on and off and control a stepper motor directly from the spectrometer. According to Mike Mills, AstraNet MD, ‘This is an ideal application for our spectrometers. Even though we have only milliseconds in which to measure each dye panel on the fast-moving web, that is enough time to complete several full wavelength scans. Using USB2 enables fast data transfer between the spectrometers and the PC, another key requirement for this set-up.’

Previously ICI Imagedata relied on visual inspection of the moving ribbon, combined with spot measurements on random samples on completion of each three-kilometre roll. Now, using the AstraNet spectrometers, quality is continually monitored at the end of the production line across the whole width of the web. Mike Mills explains why this was a particularly complex project, ‘This was the first time we had designed a solution using multiple spectrometers linked to a single PC. The PC also had to be networked to enable managers to monitor and analyse quality information remotely, without having to enter the controlled environment of the manufacturing area. ICI Imagedata now has a powerful, versatile monitoring system which delivers greatly enhanced quality control for its dye sublimation printing ribbons.’