Method for recycling mixed-colour polyolefin containers

Abstract

A method for recycling mixed-colour polyolefin containers for producing PCR (Post Consumer Recycled) granules. The method comprises the following method steps: (a) colour-sorting the containers, (b) shredding the containers into flakes, (c) a first washing step for removing labels from the flakes with water at a temperature T1, (d) drying the flakes and labels, (e) separating the dried flakes from the dried labels, (f) a second washing step for hot-washing the flakes with an alkaline liquid at a temperature T2 > 80°C for removing printing ink from the flakes, (g) drying the flakes, (h) sorting the flakes to remove ink contamination and foreign polymers, (i) optional preheating of the flakes in a cutting compressor, (j) degassing and granulating the flakes in an extruder, (k) decontaminating the granules and (l) providing the granules for further use. The first washing step (c) is performed without cleaning additives at a temperature T1 between 60°C and 80°C while thermal energy is supplied.

Description

[0001] Process for recycling color-mixed polyolefin containers

[0002] Field of the invention

[0003] The invention relates to a process for recycling color-mixed polyolefin containers for producing PCR (Post Consumer Recycled) granules according to the preamble of claim 1.

[0004] State of the art

[0005] A processing method for producing polyolefin recyclates is known from the prior art. Color-mixed polyolefin-containing residues are crushed into flakes. The flakes are subjected to a first wash at low temperature, a second wash at elevated temperature in an alkaline medium, sorting, and granulation and degassing in an extruder. The resulting granules can be used to manufacture new consumer product packaging.

[0006] The first wash is performed with water, without applying thermal energy, to prevent the inks from bleeding from the label residue on the flakes. However, the label residue is only inadequately removed in the first wash.

[0007] Object of the invention

[0008] The disadvantages of the described prior art give rise to the task of creating an improved processing method in which the label residues are reliably removed from the flakes.

[0009] Description

[0010] The stated object is achieved in a process for recycling color-mixed polyolefin containers for the production of PCR (Post Consumer Recycled) granulate by the features recited 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 first washing step (c) takes place without cleaning additives at a temperature Ti between 60°C and 80°C with the addition of thermal energy. According to the prior art, the washing step (c) is carried out as a cold wash without the addition of thermal energy. The wash water therefore has a temperature T 1 of usually less than 40°C. The temperature T 1 is slightly above the ambient temperature due to the considerable mechanical energy input by the shredders and washing units.This temperature ensures that the label ink is not dissolved in the wash water (bleeding) and therefore the flakes are not contaminated with the ink. Therefore, at wash water temperatures of 60°C <Ti<80°C ein Ausbluten der Etikettendruckfarbe zu erwarten gewesen. In überraschender Weise wird die Druckfarbe der Etiketten in diesem Temperaturbereich nicht ausgewaschen. In diesem Temperaturbereich können die Etiketten und deren Klebereste nahezu vollständig von den Flakes entfernt werden, was zu einer wesentlichen Qualitätsverbesserung im Vergleich zum am Markt erhältlichen Rezyklaten führt, die zur Herstellung von neuen Consumer-Produktverpackungen verwendet werden können.

[0011] In a preferred embodiment of the invention, the color purity during the color sorting of step (a) is greater than 90 wt%, and preferably greater than 93 wt%, by connecting several color sorters in series. Preferably, white and transparent containers are separated from colored containers in a first step. This allows different color fractions with high color purity to be obtained, and the respective main color of the individual color fraction is only insignificantly affected by faulty color sorting.

[0012] Conveniently, the color-sorted containers according to step (a) are compressed into bales in a pressing step (a1), and the bales are transported to the location for further processing according to steps (b) to (i) in a transport step (a2). Compression into bales enables efficient intermediate storage of the sorted bottles and potentially saves transport costs.

[0013] Further advantages and features emerge from the following description of an exemplary embodiment of the invention with reference to a schematic flow diagram. Figure 1 shows a flow diagram of a process according to the invention for recycling color-mixed polyolefin containers. The flow diagram of the process for recycling color-mixed polyolefin containers to produce PCR (Post Consumer Recycled) granulate shows process steps (a) to (i) in a predetermined order. In a first process step (a), the discarded and collected polyolefin containers, which are still unwashed, are color-sorted. Color sorting is carried out with a color purity of over 90%, preferably more than 93% by weight. This means that at least 93% by weight of the color-sorted containers have a specific color. This high degree of color separation is achieved by connecting several color sorters in series.This allows several color-pure polyolefin fractions to be obtained.

[0014] To increase the overall availability of the plant technology, it is advisable to decouple the pre-sorting and washing processes by creating an intermediate storage facility. For efficient storage, and if the subsequent process steps (b) to (I) are located at a different location, it is advisable to press the polyolefin containers into bales (step (a1)) and transport the bales to the site for further processing (step (a2)). This can significantly reduce the transport and storage volume of the recycled material.

[0015] In step (b), the containers are shredded into flakes. Shredding can be performed, for example, in a cutting mill or shredder. Shredding can be performed either wet (i.e., with the addition of water or moisture) or dry. Wet grinding effectively prevents dust formation and limits costly wear on the cutting tools.

[0016] Typically, the first washing step (c) is carried out with wash water without heating the wash water. Therefore, according to the state of the art, the temperature T1 of the wash water is always colder than 60°C and its temperature is often 40°C or less. In the first washing step, the labels still adhering to the flakes, as well as food residues or salts, are removed. The cold wash ensures that the labels do not "bleed", i.e. that printing ink does not detach from the labels and contaminate the color-sorted flakes. In contrast, in the process according to the invention, the first washing step (c) is carried out with wash water that is heated to a temperature of < 80°C, preferably to a temperature between 60°C and 80°C by heating (external heat supply, e.g. via a heat exchanger). One would actually assume that the label ink bleeds at a temperature Ti above 60°C.Surprisingly, however, it has been shown that the first wash step without cleaning additives at a temperature between 60°C and 80°C with the addition of thermal energy does not result in any washout of the label ink. However, label removal is significantly improved in this temperature range.

[0017] After the flakes and labels have dried together (step (d)), the flakes are separated from the labels in step (e).

[0018] In a second washing step (f), the flakes are washed in a hot wash with an alkaline liquid at a temperature T2 greater than 80 °C. The washing liquid is heated by applying thermal energy. At this high temperature in the additionally alkaline environment, the few remaining label residues and printing inks from the direct printing process are removed from the flakes.

[0019] After the second washing step (f), the flakes are dried in step (g) and can be prepared for further processing, for example in a first bunker.

[0020] In step (h), the flakes are sorted to remove color impurities and foreign polymers, which significantly improves the purity of the recyclate.

[0021] In an optional preheating step (i), the flakes are fed into a cutter / compactor. In process step (j), the flakes are melted in an extruder, and the melt is degassed, filtered, and granulated. Degassing of the material is achieved by applying a vacuum, which removes volatile components from the polyolefin melt and significantly reduces the odor emanating from the granules.

[0022] In step (k), the granules are decontaminated by exposing them to a temperature in the range of 50 to 155 °C, preferably for a period of at least 60 minutes. This treatment removes as much of the pollutants, migration products, or contaminants still present in the granules that have diffused into the outermost layer of the container as possible. This removes any odorous substances still present in the granules.

[0023] Finally, the high-quality granulate is stored for further use, for example in a bunker or it is filled into big packs (step (!)) • Key: a Color sorting of the containers a1 Pressing of the containers a2 Transport of the bales b Crushing of the containers c First washing step of the flakes d Drying of the flakes e Separation of the flakes from the labels f Second washing step of the flakes g Drying of the flakes h Sorting of the flakes i Preheating of the flakes j Degassing and granulation of the flakes k Decontamination of the granulate I Preparation of the granulate

Claims

1. Process for recycling colour-mixed polyolefin containers for the production of PCR (Post Consumer Recycled) granules comprising the following process steps (a) Color sorting of containers, (b) crushing the containers into flakes, (c) first washing step to remove labels from the flakes with water at a temperature Ti, (d) drying of the flakes and labels, (e) separating the dried flakes from the dried labels, (f) second washing step for hot washing the flakes with an alkaline liquid at a temperature T2> 80 °C to remove printing ink from the flakes, (g) drying the flakes, (h) Sorting the flakes to remove color impurities and foreign polymers, (i) Optional preheating of the flakes in a cutter-compactor, (j) degassing and granulating the flakes in an extruder, (k) decontaminating the granules and (l) Providing the granules for further use, characterized in that the first washing step (c) is carried out without cleaning additives at a temperature Ti between 60°C and 80°C with the supply of thermal energy.

2. Process according to claim 1, characterized in that the color purity in the color sorting of step (a) is greater than 90% by weight and preferably greater than 93% by weight, by connecting several color sorters in series.

3. Method according to claim 1 or 2, characterized in that the color-sorted containers according to step (a) are pressed into bales in a pressing step (a1) and the bales are transported to the location of further processing according to steps (b) to (I) in a transport step (a2).

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