Method for further processing paper labels detached from plastic containers

Abstract

This invention relates to a method for further processing paper labels removed from plastic containers for the production of PCR (post-consumer recycled) pellets, the method comprising the following steps: (a) removing the paper labels using wash water in a washing step; (b) preferably pulverizing the container in a wet mill (13) to form a sheet; (c) removing the wash water along with the removed paper labels, which are present as paper fibers, as a paper portion (18) from the sheet, which is a sheet portion (17); and (d) removing the pulp from the wash water. The paper fibers of the paper portion (18) are loosened or moved by the fluid during removal from the water.

Description

Technical Field

[0001] This invention relates to a method for further processing paper labels removed from plastic containers. Existing technology

[0002] A processing method for producing recyclable plastics is known from the prior art, wherein plastic material is produced from compressed post-consumer containers into bundles and used to produce new plastic containers. Specifically, used PET bottles are used to produce rPET, which is then used to produce post-consumer recycled (PCR) pellets and new PET bottles produced therefrom.

[0003] Depending on the input materials used, typically only 70% + / - 10% can be recycled into new PET bottle material. Residues from bottles, labels and sleeves, adhesives, caps, and other impurities must be removed. Polyolefin (PO) based caps can be fed as a separate PO stream for further recycling.

[0004] During each sorting and removal step, a small portion of good materials (such as PET and polyolefins) are inevitably and unintentionally separated as loss.

[0005] Paper labels pose a particularly significant problem in the recycling of plastic containers, especially PET bottles. Paper labels are not sustainable and, at best, can be laboriously dried and sold as fuel. The printing inks, coatings, and adhesives render paper labels unsuitable for other high-quality applications in paper recycling, or the quantities are too small to justify any interest in high-quality paper recycling.

[0006] In a wet state, paper can absorb a large amount of water, meaning that the pulp produced in PET recycling can sometimes be very expensive to process, depending on its weight. Known and existing techniques involve pressing or drying this portion to reduce its processing weight. Currently, pulp removal is typically performed after bottles or trays are cut into sheets in a wet mill using a dewatering centrifuge. The PET sheets are dewatered and discharged in the main feed stream. Paper labels (which exist as paper fibers after the wet cutting and milling process) leave the centrifuge along with the wash water. Residual adhesive residues and bonded impurities can only be removed in a subsequent hot washing step using washing chemicals at temperatures up to 95°C.

[0007] Water is typically separated by a dewatering centrifuge through 3mm orifices, although orifices between 2mm and 4mm are also common. Extruders or other types of presses, such as calenders, are rarely used.

[0008] Water flowing from the cutting and grinding mill or centrifuge is contaminated with a variety of pollutants and must be purified before being returned to the process. For this purpose, a dewatering screen with an aperture of 200 μm to 800 μm (typically 400 μm) is used, in which pulp, small PET particles from the mill, label adhesive residue, and ink residue are retained on the screen coating. In this process step, the wash water is typically not heated; however, due to mechanical stress, impurities and some label adhesive are still detached from the PET sheet in the water.

[0009] In this mixture, this portion is typically separated as "paper pulp" and is either dried to some extent or used as fuel. However, the PET residue in this pulp is significant and, depending on the type of mill, the condition of the blades, and the materials introduced, can account for up to 4% of the main PET stream, which is lost from the yield and thus lost during recycling.

[0010] The residues also include color residues, where label and sleeve inks are only applicable if they do not stain the wash water at the typical temperature of the washing method. Summary of the Invention

[0011] The shortcomings of the prior art described led to the creation of improved processing methods that reduce the amount of PET lost in the pulp and thereby significantly improve the efficiency of PET recycling plants. Detailed Implementation

[0012] A solution to the stated objective is found in a method for further processing paper labels removed from plastic containers to produce PCR (post-consumer recycled) pellets, based on the features indicated in the characterizing portion of claim 1. The dependent claims relate to the development and / or advantageous alternative embodiments.

[0013] Preferably, the invention is characterized in that the paper fibers in the paper portion are loosened or moved by the fluid during removal from the water. Therefore, during the separation of the pulp from the wash water, the paper fibers do not form clumps, or any clumps that have formed are broken up. Even if the length of the paper fibers is longer than the width of the sieve openings, the elongated paper fibers can travel through the sieve due to their movement and flexibility. Surprisingly, this method step allows the paper fibers to be separated from the flakes present in the paper portion, as the flakes are typically larger than the sieve opening width. The separated flakes can be fed into the flake stream (main stream) or otherwise used. In any case, they are not lost in the pulp as is the case in the prior art. By removing most of the flakes present in the paper portion, the efficiency of the recycling method or the yield of the target polymer is significantly improved.

[0014] In a particularly preferred embodiment of the invention, the removal of loose paper fibers from the wash water by the fluid is carried out using a screen, wherein the screen is agitated, or the removal is carried out by a spiral screen. Screen agitation results in further movement of the paper fibers, which further improves the permeability through the screen. This optimizes the “selectivity” between the sheet and the paper fibers, and the valuable flow of the sheet contains as few paper fibers as possible. When a spiral screen is used, the paper fibers are loosened by a screw. Wash water flows through a screen basket surrounding the screw, where the paper fibers are retained. The screw agitates the paper fibers and simultaneously conveys them along the screen basket.

[0015] The sieve is suitably agitated by vibration. This makes the sieve drive reliable. Vibration can be generated, for example, by vibration and / or ultrasonic sieving.

[0016] Advantageously, the paper fibers move with water as a fluid at temperatures between 2°C and 92°C, and the amount of water (0.1 kg to 25 kg per kilogram of paper portion) activates the paper fibers in the pulp. This ensures optimal movement of the paper fibers, allowing them to separate from the sheets in the paper portion as completely as possible.

[0017] In another preferred embodiment, water for agitating the paper fibers is introduced into the screen through a fixed or movable nozzle (particularly a rotating spray bar). This allows the paper fibers to move as fully as possible within the portions reached by the fluid.

[0018] In a particularly preferred embodiment of the invention, the sieve has at least one first sieve plate and a second sieve plate, wherein plastic flakes present in the paper portion are separated on the first sieve plate, and paper fibers are separated from the wash water as pulp on the second sieve plate, and the first sieve plate has a larger sieve aperture width than the second sieve plate. The two sieve plates allow for removal into three streams that are as pure as possible: 1.) Entering a valuable stream that primarily consists of plastic sheets. This valuable stream is primarily composed of the target polymer (e.g., PET), and the total amount of remaining impurities is less than 6% by weight. This means that the material falls under the category of Green List Waste (EU 3011) and can be further recycled within the EU without notification.

[0019] 2.) Pulp, which, in addition to paper fibers, contains impurities (e.g., pigments, fillers, hot melts and ink coating fragments, all of which are smaller than the sieve aperture width of the first sieve plate) and flakes smaller than the sieve aperture width of the first sieve plate.

[0020] 3.) Wash water, which must be purified before being returned to the wet mill because it contains dissolved binders and other very fine impurities.

[0021] In another particularly preferred embodiment of the invention, the sieve aperture width of the first sieve plate is between 0.9 mm and 1.1 mm, and the sieve aperture width of the second sieve plate is between 0.2 mm and 0.8 mm. Different tests conducted with varying water volumes and aperture sizes have shown that a sieve aperture width of 1 mm is ideal for removing valuable PET and polyolefins from paper fibers, pigments, fillers, and adhesive residues.

[0022] Advantageously, the first and second screen plates are arranged horizontally, and the moving paper fibers or washing 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 moving the paper fibers.

[0023] It is recommended to dewater the pulp in the press. This also allows any remaining water in the pulp to be fed into the wet refiner.

[0024] It has been proven advantageous to return the water separated from the screen and press to the wet mill. This minimizes water loss, and the method is thus correspondingly environmentally friendly.

[0025] By removing the sheet portion from the paper portion in a centrifuge, the main stream of the target polymer can be separated in a first step before the paper portion is separated into other portions.

[0026] Further advantages and features will become apparent from the following description of embodiments of the invention, illustrated by reference to schematic flowcharts.

[0027] Figure 1 A flowchart of a method according to the invention for further processing paper labels from plastic containers to produce PCR (post-consumer recycled) pellets is shown. As an example, PET bottles from post-consumer collection points are processed, but the method shown can also be used for other plastic containers, such as those made of polyolefins or polyesters other than PET.

[0028] The containers from the washing step are pulverized in a wet mill 13 to form flakes, in which paper labels and impurities (such as ink, paint, and fillers) are also pulverized. This stream is directed to a centrifuge 15, where the flakes are separated as a flake portion or as the main stream 17 from the paper portion as a side stream 18. The side stream 18 exists as a heterogeneous mixture of substances. After the main stream 17 passes through an air separator 19, the flakes can be fed, for example, into a hot wash.

[0029] Analysis of the paper portion has revealed that paper typically exists in the pulp as fibers ranging from 1 mm to 4 mm in length and 0.001 mm to 0.2 mm in thickness. Depending on the region, the label adhesive exists in water-soluble or hot-melt form, or as a mixture of both. Most particles in the PET sheet or paper portion that cannot be separated in centrifuge 15 are generally larger than 1 mm. Pigment, filler, and ink coating fragments are smaller than 1 mm. Water-soluble adhesives exist in dissolved form, and / or hot-melt forms exist in the paper portion in domains smaller than 1 mm.

[0030] This “particle size distribution” surprisingly enables the separation of the PET flakes in the paper portion 18 from the remaining components of the paper portion 18 in the sieve 21.

[0031] The sieve 21 has a first sieve plate 23 and a second sieve plate 25. The first sieve plate preferably has a sieve aperture width of 1 mm, and the second sieve plate preferably has a sieve aperture width between 0.2 mm and 0.8 mm.

[0032] The paper portion 18 moves or agitates on the first screen plate 23. This allows the paper fibers to move through the first screen plate 23 due to their flexibility, even if some fibers are longer than 1 mm in the screen aperture width. This allows the PET sheet to separate from the rest of the paper portion, and a large portion of the valuable sheet can be retained on the first screen plate 23. The sheet can then be removed from the first screen plate 23 as the valuable material stream 27.

[0033] For the paper fibers to pass through the first screen plate 23, the paper fibers need to be mobile. This can be achieved by agitating or shaking the screen 21 or screen plates 23, 25. Alternatively, an agitator can be used to stir the paper portion 18. Furthermore, the movement of the paper fibers can be achieved by water 29, which is sprayed onto the paper portion via a rotating spray bar 31. Fixed or movable nozzles can also be used to apply water 29. By making the paper fibers mobile, the situation where the paper fibers clump together and cannot pass through the first screen plate 23 is prevented.

[0034] The pulp 33 is produced on the second screen plate 25 by removing it from the wash water 35. Advantageously, the screen plates 23 and 25 are aligned horizontally so that gravity, in addition to agitation, also helps the pulp pass through the screen plates. The pulp 33 is dewatered in the press 37 before being discarded.

[0035] The wash water 35 separated in sieve 21 and press is decanted in decanter 39 to remove fine suspended solids and is collected in tank 41. From this tank, the treated wash water 35 can be returned to centrifuge 15 via pump 43.

[0036] PET residue in pulp is significant and can account for up to 4% by weight of the total PET stream, depending on the type of mill, blade conditions, and introduced materials. The method of this invention ensures that the valuable stream 27 is not lost because it can be separated from the pulp 33. This method significantly improves the yield of the target polymer without losing the valuable stream 27 during the recycling process.

[0037] List of reference numerals : 13 Wet grinding mill 15 Centrifuges 17 Main material flow, thin sheet portion 18. Side flow, paper portion 19. Wind-powered screen 21 sieves 23 First sieve plate 25 Second sieve plate 27 Valuable Material Flow 29 Water 31 Rotating spray bar 33 Pulp 35 Washing water 37 Press 39 Decanter 41 cans 43 pumps

Claims

1. A method for further processing paper labels removed from plastic containers for use in the production of PCR (post-consumer recycled) pellets, the method comprising the following steps: (a) The paper label is removed using washing water during the washing step. (b) Preferably, the container is pulverized in a wet mill (13) to form flakes. (c) The washing water, together with the detached paper label which is present as paper fiber, is removed as paper part (18) from the sheet which is sheet part (17), and (d) Remove the pulp from the washing water. Its features are, The paper fibers of the paper portion (18) are loosened or activated by the fluid during removal from the water.

2. The method according to claim 1, characterized in that, The removal of the paper fibers from the wash water by means of fluid loosening is carried out using a sieve (21) which is agitated, or the removal is carried out using a spiral sieve.

3. The method according to claim 2, characterized in that, The sieve (21) is agitated by vibration.

4. The method according to any one of the preceding claims, characterized in that, The paper fibers move at a temperature between 2°C and 92°C using water as the fluid, and the paper fibers move with 0.1 kg to 25 kg of water per kilogram of paper portion (18).

5. The method according to any one of claims 2 to 4, characterized in that, Water for agitating the paper fibers is introduced into the sieve (21) through a fixed or movable nozzle, particularly a rotating spray bar (31).

6. The method according to any one of claims 2 to 5, characterized in that, The sieve (21) has at least one first sieve plate and a second sieve plate (23, 25), wherein the plastic sheet present in the paper portion (18) is separated on the first sieve plate (23), and the paper fibers are separated from the washing water as pulp on the second sieve plate (25), and the first sieve plate (23) has a larger sieve aperture width than the second sieve plate (25).

7. The method according to claim 6, characterized in that, The sieve hole width of the first sieve plate (23) is between 0.9 mm and 1.1 mm, and the sieve hole width of the second sieve plate (25) is between 0.2 mm and 0.8 mm.

8. The method according to claim 6 or 7, characterized in that, The first sieve plate and the second sieve plate (23, 25) are arranged horizontally, and the moving paper fibers or the washing water (35) flows vertically through them.

9. The method according to any one of the preceding claims, characterized in that, The pulp is dewatered in a press (37).

10. The method according to claim 9, characterized in that, The water separated from the screen (21) and the press (37) is returned to the wet mill (13).

11. The method according to any one of the preceding claims, characterized in that, The sheet portion (17) is separated from the paper portion (18) in a centrifuge (15).

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