INSTRUMENTATION | COLOUR MEASUREMENT
Right: ColorLite has developed a continuous colour
monitoring system to reduce reject rates and downtime
company says. The probe head adapter is fitted with an array of high-powered LEDs to illuminate the samples, with a white barium sulphate coating used to diffuse the light. Like other equipment suppliers, ColorLite emphasises the importance of the effect of temperature on the colour of plastics. “Neglecting this fact leads to false measurements,” it warns. To counter this risk, its system can be equipped with an optional integrated infrared thermometer. This allows colour deviations caused by thermochro- matic effects to be measured and compensated for in the measurement software. ColorLite offers inline solutions for various plastics compounding and processing operations. Its portfolio also includes portable spectrophotom- eters and benchtop instruments.
The company has recently added a special version to its range of Nano devices that detects an invisible ink that can be mixed into plastics to provide counterfeit protection. The system was developed in collaboration with Israel-headquar- tered company Dotz, which has developed propri- etary technology for tagging polymer products. Its ValiDotz taggants, supplied in masterbatch form or in finished compounds, show up in UV light.
Right:
Equitech’s EquiSpec system uses fibre optic probes to measure
colour in the extrusion die
22
Continuous control Meanwhile, ColorLite has developed a continuous monitoring process to reduce production costs, reject rates and downtime. It says its compact high-performance “sph ipm” spectrophotometer provides 100% colour control. “Due to the high precision and repeatability, time-consuming laboratory analyses can be reduced,” it claims. As soon as the system detects a colour deviation outside a specified tolerance it forwards the information to the process control system so production can be stopped. A “traffic light” system then shows the error. The sph ipm, which has an IP65 rating for protection against dust and water, can be connected to the process control system via various interfaces. Fitted with a 7” colour touch screen, it can display CIE L*a*b* colour values and other colour scales, including customised units. For colour measurement of granules, ColorLite
offers the MA80 probe head. This has a measuring surface 80mm across and can be mounted directly on a material feed or a separate measuring chamber. “To measure granules or other inhomogeneous samples it is necessary to measure over a relatively large area,” the
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Measuring in the die In line colour measurement systems are also available from US-based Equitech, which offers the EquiSpec fibre-optic spectrophotometer for measurement of chemical concentration and colour in the UV-Vis region of the light spectrum (200 to 800 nm) directly in manufacturing process- es under a variety of environmental conditions. The company’s systems use fibre optic probes to
transfer the signal from the sample to the spectro- photometer so absorption, transmission or L*, a* and b* values can be obtained. The company says it developed its Reflection and Transmission Polymer Melt Probes (RPMP and TPMP) for plastics compounding, making it possible to directly measure chemical concentration and colour in the polymer melt at up to 400°C and almost 35 MPa. The RPMP consists of six illumination fibres angled
at 28° from the surface normal and evenly spaced around the probe circumference. Reflected light is picked up by a single fibre at 0° from the normal. “The EquiSpec and probes system helps maintain colour matching in polymer masterbatch production while minimising time, sampling and scrap required to achieve colour tolerance or make colour changes online,” says Equitech President and CEO, Jaime Gómez. The system allows alarms to be set when colour and/or additives go off-specification, provid- ing continuous real-time quality assurance.
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IMAGE: COLORLITE
IMAGE: EQUITECH
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