WO2025093622A1 - Method for further treatment of paper labels detached from plastic containers - Google Patents

Abstract

The invention relates to a method for the further treatment of paper labels detached from plastic containers for the production of PCR (post-consumer recycled) pellets, comprising the following method steps: (a) detaching the paper labels using washing water in a washing step, (b) comminuting the containers to form flakes, preferably in a wet mill (13), (c) removing the washing water together with the detached paper labels, present in the form of paper fibres, as a paper fraction (18) from the flakes as a flake fraction (17), and (d) removing the paper slurry from the washing water. The paper fibres of the paper fraction (18) are loosened or mobilized by a fluid during removal from the water.

Description

Process for further treatment of detached paper labels from plastic containers

Field of the invention

The invention relates to a method for further processing of detached paper labels from plastic containers.

State of the art

A processing method for producing plastic recyclates is known from the prior art. This involves producing a plastic material from baled post-consumer containers that is used to manufacture new plastic containers. In particular, used PET bottles are used to produce rPET, which is used to produce post-consumer recycled (PCR) granules and the resulting new PET bottles.

Depending on the input material used, usually only 70% +/-10% of the PET bottle material can be recycled. Residual amounts in the bottle, labels and sleeves, adhesives, caps, and other contaminants must be separated. Polyolefin (PO)-based caps can be further recycled as a separated PO stream.

During each sorting and separation step, a small portion of good material, such as PET and polyolefins, is inevitably unintentionally separated as a loss.

Paper labels, in particular, pose major problems in the recycling of plastic containers, especially PET bottles. There is no sustainable use for them, and the only option is to dry them at great expense and sell them as fuel. Printing inks, coatings, and adhesives render the paper labels unusable for other high-quality applications in paper recycling, or the quantities are too small to warrant high-quality paper recycling.

When wet, paper can absorb a lot of water, which means that the paper sludge generated during PET recycling must be disposed of at considerable expense, sometimes by weight. Known and state-of-the-art measures are available to press out or dry this fraction to reduce the disposal weight. Today, the separation of the paper sludge is usually carried out after the bottles have been cut or Trays are processed into flakes in a wet mill using dewatering centrifuges. The PET flakes are dewatered and discharged into the main stream. The paper labels, which remain as paper fibers after the wet cutting mill, leave the centrifuges with the wash water. Remaining adhesive residues and stuck-on contaminants are removed in subsequent hot wash steps with washing chemicals at temperatures up to 95°C.

The water is usually separated through a 3mm hole, although holes between 2 and 4mm are also common, using a dewatering centrifuge. Hole extruder presses or other press types such as calender presses are rarely used.

The water coming from the granulator or centrifuge is contaminated by various contaminants and must be purified before being returned to the process. For this purpose, a dewatering screen with a pore size of 200 μm to 800 μm, usually 400 μm, is used. Paper sludge, small PET particles from the mill, residues of label adhesive, and ink remain trapped on the screen lining. The wash water is typically not heated during this process step, but the mechanical stress still causes impurities and parts of the label adhesive to detach from the PET flakes in the water.

In this mixture, this fraction is usually finally separated as "paper fiber sludge" and disposed of in a more or less dry state or offered as fuel. However, the PET residues in this sludge are significant and, depending on the type of mill, the condition of the blades, and the material fed in, can account for up to 4% of the main PET stream, which is missing from the yield and thus lost during the recycling process.

The residue also contains ink residues, although label and sleeve inks are only suitable if they do not color the wash water at the temperatures normally encountered in the washing process.

Object of the invention

The disadvantages of the described state of the art result in the task of creating an improved processing method in which the lost PET quantities present in the paper sludge are reduced and the effectiveness of the PET recycling plant is thereby significantly improved. Description

The stated problem is solved in a method for further processing detached paper labels from plastic containers for the production of PCR (Post Consumer Recycled) granules by the features stated in the characterizing portion of patent claim 1. Further developments and/or advantageous embodiments are the subject of the dependent patent claims.

The invention is preferably characterized in that the paper fibers of the paper fraction are loosened or mobilized by a fluid during separation from the water. As a result, the paper fibers do not form clumps when the paper sludge is separated from the wash water, and any clumps that have already formed are dissolved again. The mobilization and their flexible properties allow the elongated paper fibers to migrate through a sieve, even if the length of the paper fibers is longer than the mesh size of the sieve. Surprisingly, this process step allows the paper fibers to be separated from the flakes present in the paper fraction, since the flakes are mostly larger than the mesh size. The separated flakes can be fed into the flake stream (main stream) or used for other purposes. In any case, they are not lost in the paper sludge, as is the case in the prior art. The effectiveness of the recycling process and the yield of the target polymer are significantly improved by separating a large portion of the flakes present in the paper fraction.

In a particularly preferred embodiment of the invention, the paper fibers loosened by a fluid are separated from the wash water using a screen, whereby the screen is agitated, or the separation takes place using a screen screw. The screen agitation leads to further mobilization of the paper fibers, which further improves their passage through the screen. This optimizes the separation efficiency between the flakes and the paper fibers, and the flake value stream contains as few paper fibers as possible. If a screen screw is used, the paper fibers are loosened by the screw. The wash water flows through a screen basket surrounding the screw, whereby the paper fibers are retained by the screen basket. The screw mobilizes the paper fibers and simultaneously conveys them along the screen basket.

The sieve is preferably agitated by vibration. This ensures reliable drive. The vibration can be generated, for example, by vibration and/or ultrasonic screening technology. It is advantageous to mobilize the paper fibers using water as a fluid at a temperature between 2°C and 92°C, and to use 0.1 to 25 kg of water per kg of paper fraction to mobilize the paper fibers in the paper sludge. This optimally mobilizes the paper fibers so that they can be separated as completely as possible from the flakes in the paper fraction.

In a further preferred embodiment, the water for mobilizing the paper fibers is introduced into the screen through fixed or movable nozzles, in particular a rotating spray bar. This leads to the most complete mobilization of the paper fibers possible through the portion accessible by the fluid.

In a particularly preferred embodiment of the invention, the screen comprises at least a first and a second screen plate, with the plastic flakes present in the paper fraction being separated on the first screen plate, and the paper fibers being separated as paper sludge from the wash water on the second screen plate. The first screen plate has a larger mesh size than the second screen plate. The two screen plates enable separation into three streams that are as pure as possible:

1.) Into a value stream that primarily contains the plastic flakes. This value stream consists primarily of the target polymer (e.g., PET), and the sum of the remaining impurities accounts for less than 6% by weight. This means that the material falls under green-listed waste (ELI3011) and can be used for further recycling within the EU without notification.

2.) The paper sludge, which contains, in addition to the paper fibers, impurities (e.g. pigments, fillers, hot melts and fragments of the color coatings, all of which are smaller than the mesh size of the first screen plate) and flakes with a size smaller than the mesh size of the first screen plate.

3.) The wash water, which must be purified before being returned to the wet mill because it contains dissolved adhesive and other very fine impurities.

In a further particularly preferred embodiment of the invention, the first sieve plate has a mesh size between 0.9 mm and 1.1 mm and the second sieve plate has a mesh size between 0.2 mm and 0.8 mm. Different tests with different amounts of water and pore size have shown that A mesh size of 1mm is ideal for separating valuable PET and polyolefins from paper fibers, pigments, fillers and adhesive residues.

It is advantageous if the first and second screen plates are arranged horizontally and the mobilized paper fibers and wash water flow vertically through them. This allows gravity to be used as a driving force to move the paper fibers through the first screen plate, in addition to agitating the filter and mobilizing the paper fibers.

The paper sludge is conveniently dewatered in a press. This allows the remaining water in the paper sludge to be fed to the wet mill.

It is advantageous if the separated water from the screen and press is returned to the wet mill. This minimizes water loss and makes the process environmentally friendly.

By separating the flake fraction from the paper fraction in a centrifuge, the main stream of the target polymer can be separated in a first step before the paper fraction is separated into further fractions.

Further advantages and features will become apparent from the following description of an embodiment of the invention with reference to a schematic flow diagram.

Figure 1 shows a flow diagram of a method according to the invention for further processing paper labels from plastic containers to produce PCR (Post-Consumer Recycled) granules. PET bottles from post-consumer collection points are processed as an example, but the method shown can also be applied to other plastic containers, for example, containers made of polyolefins or polyesters other than PET.

After a washing step, the containers are shredded into flakes in a wet mill 13, which also removes the paper labels and contaminants such as color coatings and fillers. The stream is fed into a centrifuge 15, where the flakes are separated as the flake fraction, or main stream 17, from the paper fraction, which forms a side stream 18. The side stream 18 is a heterogeneous mixture of materials. After the main stream 17 has passed through an air classifier 19, the flakes can be fed, for example, to a hot wash.

Analysis of the paper fraction revealed that the paper is typically present in the sludge as fibers measuring 1–4 mm in length and 0.001–0.2 mm in thickness. Depending on the region, the label adhesive is present as a water-soluble or hot melt adhesive, or as a mixture of both. The majority of the PET flakes or particles in the paper fraction that could not be separated in centrifuge 15 are typically larger than 1 mm. Pigments, fillers, and fragments of the color coatings are smaller than 1 mm. Water-soluble adhesives are present in dissolved form, and hot melt adhesives are present in the paper fraction with domains smaller than 1 mm.

This “grain size distribution” surprisingly makes it possible for the PET flakes in the paper fraction 18 to be separated from the remaining ingredients of the paper fraction 18 in a sieve 21.

The sieve 21 has a first sieve bottom 23 and a second sieve bottom 25. The first sieve bottom preferably has a mesh size of 1 mm and the second sieve bottom preferably has a mesh size between 0.2 mm and 0.8 mm.

The paper fraction 18 is mobilized or agitated on the first screen plate 23. This allows the paper fibers to move through the first screen plate 23 due to their flexible nature, even though some of the fibers are longer than the 1 mm mesh size. This allows the PET flakes to be separated from the rest of the paper fraction, and a large portion of the valuable flakes can be retained on the first screen plate 23. The flakes can be withdrawn from the first screen plate 23 as value stream 27.

In order for the paper fibers to pass through the first screen plate 23, they must be mobilized. For this purpose, the screen 21 or the screen plates 23, 25 can be agitated or shaken. Agitation is also conceivable by an agitator that stirs the paper fraction 18. Additionally, the mobilization of the paper fibers can be achieved by water 29, which is sprayed onto the paper fraction by a rotating spray bar 31. Fixed or movable nozzles through which the water 29 is applied are also conceivable. Mobilizing the paper fibers prevents the paper fibers from clumping and preventing them from penetrating the first screen plate 23. Paper sludge 33 is created on the second screen plate 25 by separating it from the wash water 35. The screen plates 23, 25 are conveniently aligned horizontally so that, in addition to agitation, gravity assists the passage through the screen plates. The paper sludge 33 is dewatered in a press 37 before being disposed of.

The wash water 35 separated in the screen 21 and in the press is freed of fine suspended matter in a decanter 39 and collected in a tank 41. From there, the treated wash water 35 can be returned to the centrifuge 15 via a pump 43. The PET residues in the paper sludge are significant and, depending on the type of mill, the condition of the blades, and the material introduced, can account for up to 4% by weight of the total PET stream. Thanks to the inventive method, value stream 27 is not lost because it can be separated from the paper sludge 33. The yield of the target polymer is significantly improved by the method, and value stream 27 is not lost in this recycling process.

Legend:

13 wet mill

15 Centrifuge

17 Main stream, flake fraction

18 page stream, paper fraction

19 wind sifters

21 Sieve

23 First sieve tray

25 Second sieve tray

27 Value stream

29 Water

31 rotating spray booms

33 Paper sludge

35 Washing water

37 Press

39 decanters

41 tanks

43 Pump

Claims

1. Process for the further treatment of detached paper labels from plastic containers for the production of PCR (Post Consumer Recycled) granules comprising the following process steps (a) Removal of the paper labels with washing water in one washing step, (b) crushing the containers into flakes, preferably in a wet mill (13), (c) Separation of the washing water together with the detached paper labels present as paper fibres as paper fraction (18) from the flakes as flake fraction (17) and (d) Separation of the paper sludge from the washing water, characterized in that the paper fibers of the paper fraction (18) are loosened or mobilized by a fluid during separation from the water. 2. Method according to claim 1, characterized in that the separation of the paper fibers loosened by a fluid from the washing water is carried out with a sieve (21), the sieve (21) being agitated, or by a sieve screw. 3. Method according to claim 2, characterized in that the sieve (21) is agitated by vibration. 4. A method according to any one of the preceding claims, characterized in that the paper fibers are mobilized by water as a fluid having a temperature between 2°C and 92°C and 0.1 to 25 kg of water per kg of paper fraction (18) mobilize the paper fibers. 5. Method according to one of claims 2 to 4, characterized in that water for mobilizing the paper fibers is introduced into the screen (21) through fixed or movable nozzles, in particular a rotating spray bar (31). 6. Method according to one of claims 2 to 5, characterized in that the sieve (21) has at least a first and second sieve bottom (23, 25), wherein the plastic flakes present in the paper fraction (18) are separated on the first sieve bottom (23) and the paper fibers are separated as paper sludge from the wash water on the second sieve bottom (25), and the first sieve bottom (23) has a larger mesh size than the second sieve bottom (25). 7. Method according to claim 6, characterized in that the first sieve plate (23) has a mesh size between 0.9 mm and 1.1 mm and the second sieve plate (25) has a mesh size between 0.2 mm and 0.8 mm. 8. Method according to claim 6 or 7, characterized in that the first and the second sieve bottom (23, 25) are arranged horizontally and are vertically flowed through by the mobilized paper fibers or the washing water (35). 9. Method according to one of the preceding claims, characterized in that the paper sludge is dewatered in a press (37). 10. The method according to claim 9, characterized in that the separated water from the sieve (21) and the press (37) is returned to the wet mill (13). 11. Method according to one of the preceding claims, characterized in that the flake fraction (17) is separated from the paper fraction (18) in a centrifuge (15).