Inline color calibration with respect to plastic recyclate

Sensor Instruments: The Windows® Software SPECTRO3 MSM DOCAL Scope facilitates inline calibration of the color sensor system in different ways, which are explained below in further detail.

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• Inline color calibration with respect to plastic recyclate

Calibration with RAL plastic color cards

The nonprofit organization RAL gGmbH, Bonn offers a collection of 300 different colored plastic cards calibrated according to the d/8° method. The corresponding L*a*b*-values are noted on every sleeve that is enclosed with the plastic color card.

In addition, for the RAL plastic color cards, which can be obtained from Sensor Instruments GmbH, the respective L*a*b*-value, which is obtained from the 45°/0° measurement, is noted on both the RAL plastic color card as well as on the sleeve and in EN_PI_2023-11-03_SI_Inline color calibration with respect to plastic recyclate.docx 2/19 addition, assigned a 5-digit number. Sensor Instruments assigns and enters successive 5-digit numbers for new RAL plastic color cards to be calibrated, along with the L*a*b* color value that is calibrated on the RAL plastic color card, to a calibration file. Thus, during the calibration process, the sensor system only has to be presented the RAL plastic color cards to be calibrated and the matching 5-digit number input in the software. With this calibration mode, reference is made solely to the RAL plastic color cards, as a result of which a locationindependent comparison of the measurement results is made possible, for example, for companies with several locations, since in such a case, manual color measuring instruments, the so-called manual colorimeters, can be dispensed with.

Calibration using injection molded color platelets and recyclates

But very often, it is exactly this relation to the manual or laboratory colorimeters already present in the facility that is desired, since it then becomes possible to better compare the measurement values between production and laboratory. This referencing to colorimeters that are already available in the facility through the SPECTRO3 MSM DOCAL Scope software is described in some more detail below. To do this, apart from the inline color measurement systems, Sensor Instruments also supplies laboratory equipment that work according to exactly the same process and whose sensor systems are identical. The systems that are available are both those that measure through an inspection glass as well as those which directly view the recyclate itself, of which measurements are to be taken.

Inline colorimetry using the SPECTRO-3-0°/45°-MSM-INLINE-ANA and the matching laboratory equipment SPECTRO-3-0°/45°-MSM-CMU

In both cases, calibration can be done directly with reference to the recyclate, while the L*a*b* reference values are determined using injection molded platelets, made from the same batch of the recyclate that is available to the devices to be calibrated. The L*a*b* reference values are determined using the injection molded platelets by means of the manual or laboratory colorimeters available in the respective facility.

Inline colorimetry using a SPECTRO-3-FIO-MSM-ANA-DL in conjunction with a frontend KL-D-0°/45°-85-1200-D-S-A3.0-VIS and the matching SPECTRO-3-0°/45°-MST laboratory device

Here too, the injection molded platelets provide the L*a*b* reference values. The optical frontend is pointed directly at the recyclate at a distance of 85 mm. The recyclate that is available during the calibration is also used for making the injection molded platelets. Thus, the injection molded platelets and the recyclate originate from the same batch.

When calibrating using a SPECTRO-3-0°/45°-MST laboratory device, it is recommended that when recording the measurement value during the calibration process, the recyclate holding bowl should be moved in the x and y directions with the distance to the front end of the sensor being constant, so that the random position of the pellets can be compensated. Inline, this is done by transporting the pellets on a jolting conveyor. Here, the recyclate flow assumes a speed of typically 50mm/s to 100mm/s. During a calibration process with a duration of 30s, for example, the recyclate stream moves through 1.5m to 3m, i.e. an average is calculated across this measurement path during the calibration process. The measurement result is then correspondingly accurate and independent of the random position of the granulate grains. Even with vibrations that set the pellets in resonance and then cause them to "bounce", this can achieve significant compensation during the measurement process with a duration of a few seconds. What is decisive here is the large light spot size of approximately 20 mm diameter, as a result of which, even at standstill, optical averaging takes place across a large number of pellets.

The typical procedure during the calibration directly with reference to the recyclate and using injection molded platelets is explained below with an example.

Place the white reference RAL plastic color card at a distance of approximately 75 mm to the optical sensor front end. It must be ensured here that the rear side of the RAL plastic color card is facing up (in the direction of the light spot) (a sliding carriage that holds the RAL plastic color card and is placed at the sensor front end during the white calibration, is provided for the inline calibration). Next, the SPECTRO3 MSM DOCAL Scope software is started and the menu option CALIB is selected. The software-supported calibration process is started with a double-click on START CALIBRATION ASSISTANT on the user interface.

Continue to read the entire press release including pictures with the following link:

• Inline color calibration with respect to plastic recyclate