Sensor systems

Why should the color of recyclates also be measured?
A lot of effort is already put into separating the color of the objects to be recycled. The color separation of whole plastic objects is followed by a further color separation of the flakes or plastic fragments after shredding and the subsequent washing and drying process.
However, due to the changes in the EU Packaging and Packaging Waste Regulation (PPWR) regarding the proportion of recycled material in plastics (for example, from 2025, at least 25% of disposable PET beverage bottles must contain recycled plastic (recyclate) and from 2030 at least 30%), the quality require¬ments for the recyclate to be produced is increasing.
The plastics processing industry places the same quality demands on the recyclate as it does on virgin material, and the color of the recyclate is one of these quality demands. Although random recyclate color measurements are carried out in the laboratory at recycling companies, in most cases, the color of the recyclate is not monitored at the production facilities.
This is certainly also due to the fact that fewer recyclates have been used in new plastic products to date and also to the lack of suppliers of such inline recyclate color measurement systems, but measuring systems are now also available for this field of application. Sensor Instruments took care not only to develop an inline color measurement system, but also include the items required for on-site calibration in its product range. (...)

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Measurement of the lowest spray quantities in the Ex area
For applications with extremely low spray application, it is advisable to use a solution based on the reflected light principle. Many of these applications also take place in hazardous areas, which makes a fiber optic solution to the preferred choice. The respective spray jet is usually no longer visible to the naked eye. 
Using the ABL-V-ARRA-KL-M18-XL-A3.0 fiber optic frontend in conjunction with the SPECTRO-T-1-FIO-R/R control electronics, both the presence and the spray jet density can be reliably determined from a distance of typ. 60 mm between the front end and the spray jet.

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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.

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 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 location-independent 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.

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The increasing use of recyclates in the plastics industry means that efficient product control is assuming ever-greater importance. Whilst laboratory-based random quality control was sufficient in the past, the industry is increasingly considering the deployment of 100% control, especially in terms of the color gradient. Sensor Instruments has launched a number of inline systems to perform this function. Providing production staff with information about recyclate production at a very early stage, this covers not only the trend in the color of the recyclates, but the color of the recyclates in combination with their temperature, whilst monitoring the product flow level. The product flow level is important for exact determination of the recyclate color, whilst also providing timely information about a possible blockage of the sieve immediately after the vibrating feeder. The data is also made available for quality assurance via a digital-serial interface (Ethernet).

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While downcycling of plastic products still predominated in the past, the form of recycling in which the reused plastic is put to the same or a comparable use is now becoming increasingly important. This in turn means considerable additional technical effort in separating and sorting the items delivered to the recycling plant throughout the recycling process. After separation of as many non-plastics as possible, for example by means of metal separators and wind separation, sorting is currently primarily by color (color sorting systems) and type of plastic (NIR cameras). Despite pre-sorting, where mainly whole articles are checked, as well as post-sorting (after shredding the plastic articles and subsequent washing) of the plastic particles known as flakes, it is not possible to achieve 100% grade purity. Certain variations in color must also be expected. In order to allow unrestricted use of the recyclates produced in this way, they must be checked for purity before the next processing step, at the very latest immediately before extrusion. Typically, this could be done by a metering system equipped with appropriate sensors.

 
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Sometimes it makes sense to follow. For example, your conscience or good advice from friends. But following people or brands on Instagram or LinkedIn? That is not obligatory. And what about the mainstream? "All is well! Just not always, just not everywhere and not for everyone" (to “follow” Novalis). At Sensor Instruments, although we prefer to choose our own path, we do see the need to follow certain things; for instance the colors.
Especially in terms of the color of recyclates, our esteemed market companions have been quite busy lately. Today, almost every company in the plastics recycling sector uses a portable device to measure the color of recyclates. These do their job, with the expected ease of use, at an affordable price and with precision. But are they really precise?

 
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► Press release (Word/pdf)