COLOUR MEASUREMENT | INLINE SYSTEMS
Result 1
Result 2
ce measurement of granules, recycled pellets and flakes. “We have also just modified our pellet measuring equipment, so that the system is more mobile,“ Pryor says. “The system uses a vacuum to extract samples from the production process into a measuring chamber. These are measured using a specially adapted probe, which can operate over an 80mm wide area. After measurement, the sample falls back into production. The system has been tested in cooperation with the German SKZ Plastics Institute.” The MA80-P probe head’s wide range of
Figure 1: dL* and db* colour value data taken over a one hour period for a masterbatch coloured compound produced in a single screw extruder. Result 1 shows original masterbatch; result 2 the same masterbatch after a second compounding cycle Source: ColVisTec
the strand is accurately positioned beneath the probe (the technology can also be used for colour measurement of semi-finished products such as cables, pipes, profiles or films). The systems incorporate a modular design allowing them to be configured for reflection and transmission measu- rement while different probe head variants support contact and non-contact measurement. In the ColorLite SPH9i system, the external
probe head is connected to a PC via an optical fibre, which can be several metres long. In its simplest set-up, the 9i would be connected via an industrial BUS to a process control system allowing it to display and store measured values. The SPH IPM system is equipped with a 7-inch colour touch screen display and does not require connection to a PC module. Measured values, as well as status and alarm information, can be displayed and data trasferred via a number of different interface variants. ColorLite systems can also be used for reflectan-
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measurement makes it well suited for applications such as PET recycling, where material colour deviations can be determined directly in the production process and communicated to the colour dosing system via a control loop for auto- matic adjustment.
Compound benefits Germany-based ColVisTec also has a long history in manufacture of inline spectroscopic process control solutions. It highlights several examples where its colour measuring equipment can provide benefits for compounders. The first example is to monitor the distribution and dispersion characteris- tics of a masterbatch without sampling, which can be significantly affected by processing conditions. The company set-up an experiment using a single-screw extruder to mix a colour masterbatch into a base polymer. It used its InSpectro X spectro- photometer combined with a fibre optic probe in contact with the molten compounded polymer to continuously measure optical properties. High levels of noise were detected for the colour values dL* (lightness) and db* (blue-yellow colour axis). However, the company says it was not known what was causing these large variations — the meas- urement system, extruder, feeding system or lack of consistency in the raw materials. One parameter was changed at a time to establish the cause. When
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