Rapid routine analysis in the production of plastic granulate is important in order to detect whether the colour of the product is correct at an early stage in the process. Particularly in the case of translucent granules, close attention is paid to the degree of yellowness (Yellowness Index YI). This allows you to intervene in the process in good time to ensure the correct colour of the end product. Due to the non-uniform surface of the pellets, it is important to measure as large a surface as possible. Of course, the measuring process should be as simple as possible and not hold up the production process.
The task
Since pellets have a non-uniform surface, the largest possible surface area must be examined during colour measurement. With the usual measurement via the bottom of a glass cuvette, this area is usually not large enough to obtain repeatable measured values. For this reason, several individual measurements must be averaged for smaller measurement areas. It is therefore desirable to measure as large a surface area as possible without complications. In addition to the colour values L*, a* and b*, the industry-standard Yellowness Index should also be determined directly.
The solution
HunterLab specifically recommends non-contact colour measurement with the Aeros spectrophotometer for the colour measurement of plastic pellets. The sensor of the Aeros sits eccentrically above the edge of a bowl with which a larger quantity of pellets, for example, can be easily scooped. During the measurement, the device automatically sets the correct height above the sample and the pan rotates once under the sensor. In the process, 35 measurement flashes are triggered in five seconds and averaged to produce the result. This means that a measuring area of approx. 177 cm2 is evaluated in a single process, which means that this measurement corresponds to approx. 20 conventional individual measurements in a cuvette and is therefore very representative. The device then outputs the colour values and the desired indices, such as the Yellowness Index, directly on the integrated touchscreen.
The measurement – very simple
- Pour the pellets into the bowl
- Place the bowl on the turntable
- Trigger measurement at the touch of a button
- Read the values on the screen after 5 seconds
