TAGTEC – in search of the hidden

Marker-based sorting with TAGTEC (Taggant Technology)

Sensor Instruments: There are already a number of systems for separating and sorting plastic waste according to color and plastic type. In addition, image processing systems, paired with artificial intelligence (AI), provide good services in the recognition of shapes or in the search for applied barcodes or QR codes and so-called digital watermarks when separating plastic packaging. But what happens in the further course of the recycling process after washing and shredding the pre-sorted material? Especially if they are fragments or flakes of the same color and the same type of plastic? A printed code or digital watermark can then no longer be used, which means that it is no longer possible to differentiate between food and non-food, for example. After regranulation, the recyclate can no longer be used to determine the area in which the source material was used.

In order to be able to check the section in the recycling process immediately before and after the recyclate is extruded, a permanent, processing-resistant and temperature-resistant marking or coding must be applied to the plastic matrix. This makes it possible to close the gap in material monitoring, particularly with regard to identity, origin and quality. The marking typically consists of phosphorescent, inorganic microparticles. Due to their inert properties and size, they can be incorporated into almost all plastic products. Marker-based masterbatches from Gabriel-Chemie are now available under the brand name TAGTEC (Taggant Technology).

To ensure that even the smallest amounts of marker in the plastic end product can still be detected, Sensor Instruments had to develop a series of TAGTEC measuring systems. With the sensor traverses of the LUMI-TAU-SCAN series a pre-sorting can already be carried out. For this purpose, the sensor traverse suitable for the respective conveyor belt width is mounted on a system from a partner company. The objects are then separated using the familiar pneumatic process.

But even after washing and shredding the plastic materials, there is the option of further sorting. During flake sorting, which is also carried out in cooperation with a partner company, a line scanner from the LUMI-TAU-FLAKESCAN series is used. The detection grid is so finely meshed that even small, marked objects can be reliably detected. The separation is also carried out pneumatically.

The first option for monitoring the recyclate is after extrusion and sub¬sequent pelletizing on the vibrating feeder. With the help of an inline sensor from the TAUTEM-150 series, the recyclate can be monitored from a distance of typically 150mm. In addition to the TAU sensor technology for marker detection, the sensor head also has an integrated sensor that monitors the temperature of the recyclate and a laser distance sensor that provides information on the height of the recyclate flow. The DOCAL Window® software pro¬vides good service displaying measurement data for on-site calibration. The operator is informed graphically and numeri¬cally about the marker concentration in the recyclate by means of a panel PC (SI-PPC-500-15“).

However, the recycled material can also be monitored at the plastics processing plant after delivery and storage in the silo by means of an attached sight glass with regard to the marker and its concentration in the recycled material using the LUMI-TAU-INLINE sensor system and DOCAL software. If, on the other hand, the recyclate is delivered to the plastics processing plant packed in bags, the incoming material can be measured at the material feed unit. A LUMI-TAU-INLINE sensor can also be used at this position. The SI-PPC-500-15” panel PC unit, in conjunction with the DOCAL software, provides an insight into the marker concentration in the recyclate. Furthermore, the trend of the marker concentration and the TAU value are displayed on the screen. The measured values are made available to the quality assurance department (QA) via the Ethernet interface. The QA can already view the ongoing production, virtually in real time.

Immediately upstream of the extruder or injection molding machine, it is possible to measure the concentration of the TAGTEC marker in the recyclate by means of a sight glass attached to the hopper and a TAGTEC sensor from the LUMI-TAU-INLINE series. The Profinet® field bus interface can also be used to inform the control unit of the dosing system about the marker concentration. It is possible to add TAGTEC masterbatch as required to ensure a constant marker concentration in the plastic product being produced. TAGTEC sensors are also available to check the quality of the plastic products in terms of marker concentration inline, at the injection molding machine or at the outlet of the extruder.

However, hand-held devices are also available for mobile, random product checks, which provide information on the correct marker concentration via an integrated LED display. Furthermore, the mobile and stand-alone unit can also be connected to a suitable tablet, for example. The measurement data is displayed graphically and numerically.