Use of a mixture of water and essential oils for separating multilayer composites in order to sort the polymer films or metal films

Abstract

The present invention relates to the use of a mixture of water and an essential oil selected from phenolic, phenylpropanoid and furanocoumarin for separating multilayer composites in order to sort the polymer films or metal films.

Description

[0001] Multilayer composite materials used, for example, in food packaging, consist of at least two film layers bonded together in a facet manner. The film is, for example, a polymer film made of polyethylene, polypropylene, polyester, and polyamide. The polymer film can also be a co-extruded polyolefin film having an ethylene-vinyl alcohol inner layer.

[0002] Multilayer composites may optionally include an aluminum film or a polypropylene or polyester film deposited from aluminum or silica as a layer. Multilayer composites may also include a paper layer. Multilayer composites typically include a layer of printing ink that can be applied by front or back printing (https: / / roempp.thieme.de / roempp4.0 / do / data / RD-06-01930).

[0003] Typically, two-layer (double-layer composite) or three-layer (triple-layer composite) packaging is used for food packaging. However, multi-layer composites with more than three layers are also possible.

[0004] In many cases, the individual layers are bonded together facet-to-face using an adhesive polymer. For this purpose, a one-component or two-component polyurethane adhesive polymer is typically used, which is applied as a solvent-free, solvent-based, or water-based adhesive to at least one of the layers to be bonded before they are joined together. The weight of the adhesive polymer applied between the two layers to be bonded is 0.5 g / m². 2 Up to 5 g / m 2 This depends on the type of adhesive. This does not include solvents or water that may be present in the adhesive. For example, adhesion promoters based on polyurethane can also be used in a similar manner. This is typically the case with co-extruded polymers, such as the co-extruded polyolefin film with an ethylene-vinyl alcohol inner layer described above. The adhesive or adhesion promoter is not considered a layer.

[0005] The advantages of multilayer composite materials used for food packaging – compared to other types of packaging such as glass or metal packaging – include not only lower cost and weight, but also smaller space requirements for food packaging.

[0006] Multilayer composite materials used for food packaging must meet stringent requirements. For example, the barrier provided by the multilayer composite must be sufficiently high to prevent food from contacting oxygen. This barrier is also essential for protecting the flavor and vitamins in the food. Sometimes, protective gases (such as nitrogen) are introduced into the packaging. These protective gases must remain in the packaging throughout the entire shelf life of the food. The barrier function of the packaging is therefore necessary to ensure that the food has the longest possible minimum shelf life. The barrier properties of multilayer composite materials can be ensured through the selection of the film layers or combinations thereof.

[0007] In addition to the barrier properties of multilayer composites, reliable adhesion between the individual films must be ensured. This is especially important for multilayer composites exposed to steam sterilization processes after food packaging. Steam sterilization is carried out at a temperature of up to 134°C for a maximum of 60 minutes. During this period, the film layers must not separate from each other. To meet this requirement, the adhesive polymer used must have high resistance. This requirement can essentially only be achieved through cross-linked adhesive polymers.

[0008] However, multilayer composites do have a drawback: after the food has been consumed, they can only be separated back into individual layers with difficulty. However, separating them into individual layers helps the polymer or aluminum return to the material cycle as a single type of material.

[0009] German packaging law mandates a 63% recycling rate for plastic packaging starting in 2022. This is helpful when recycling yields the highest possible quality and, as far as possible, only a single type of plastic. To sort the individual film layers into single-type materials, these layers must be separated from each other. However, separating these layers is not straightforward because the cross-linked adhesive polymers have very low solubility.

[0010] Therefore, a way must be found to weaken the adhesive layer or adhesion promoter layer between the film layers so that these layers can be separated from each other.

[0011] Specialized separation methods have now been developed that can be used for various membrane assemblies or plastics.

[0012] For example, patent EP 0 543 302 B1 discloses a method for separating aluminum film and polyethylene film or polyester film under the action of fatty acids and in a closed container at 100°C to 122°C.

[0013] The drawback of this invention is that it can only separate selected membrane combinations. This method cannot be used to separate all multilayer composite materials used in food packaging.

[0014] WO 2015 / 000681 A1 describes a solvent-based plastic recycling method that can be used to recover polymers from plastic waste. This method is based on the use of a heat stabilizer in a mixture of alkanes. The polymer dissolved in the hydrocarbon mixture at elevated temperatures precipitates upon cooling. The polymer is mechanically separated, and the hydrocarbon mixture present in the polymer is removed by applying a vacuum, for example, in a vented extruder. The heat stabilizer prevents polymer degradation of the dissolved polymer. The resulting polymer contains 50-1000 ppm of the hydrocarbon mixture.

[0015] The disadvantage of this method is that the recovered polymer still contains residual amounts of hydrocarbons used in the separation.

[0016] EP 2 668 226 B1 discloses a separation medium for multilayer systems, comprising a nanoscale dispersion containing organic components, aqueous components, and surfactants. This method is intended for the recovery of photovoltaic modules.

[0017] US 2017 / 0080603 A1 describes a method for separating packaging materials, wherein the separating liquid contains a carboxylic acid and a swelling agent, wherein the swelling agent is a hydrocarbon solvent such as toluene, xylene, ethylbenzene, cyclohexane or decahydronaphthalene, or an olefin, terpene, ketone, ether or ester.

[0018] Therefore, methods are needed to separate multilayer composite materials, especially those used for food packaging. These methods should weaken the adhesive layers or adhesion promoter layers between the film layers of the multilayer composite material so that the multilayer composite material can be separated into individual layers.

[0019] This method should be implemented, as far as possible, without the use of hazardous or highly flammable materials.

[0020] This objective is achieved by using a separation medium consisting of an aqueous mixture (emulsion) of at least one essential oil selected from phenols, phenylpropanoids, and furanocoumarins.

[0021] The subject of this invention is the use of a separation medium comprising at least one essential oil selected from phenols, phenylpropanoids and furanocoumarins, or at least one essential oil selected from phenols, phenylpropanoids and furanocoumarins, for separating at least two layers of a multilayer composite material bonded together in a surface manner by at least one adhesion promoter and / or at least one adhesive polymer, preferably at least one polyurethane-based adhesion promoter and / or at least one polyurethane-based adhesive polymer.

[0022] Another subject of the invention is a method for separating at least two layers of a multilayer composite material bonded together in a surface form by at least one adhesion promoter and / or at least one adhesive polymer, preferably at least one polyurethane-based adhesion promoter and / or at least one polyurethane-based adhesive polymer, characterized in that the multilayer composite material is treated with a separation medium comprising at least one essential oil selected from phenols, phenylpropanoids and furanocoumarins or at least one essential oil selected from phenols, phenylpropanoids and furanocoumarins.

[0023] Adhesives are non-metallic substances capable of bonding materials through surface adhesion (adhesion) and internal strength (cohesion). They are therefore process materials that acquire their mechanical strength only through a (physical or chemical) curing reaction during the manufacturing process and are used in adhesive (EN923:2015) joining processes to bond different parts to be joined. Here, the parts to be joined are understood to refer to two or more workpieces (of geometrically specific shape or shapeless material) that are permanently bonded together, such as the individual layers in a multilayer composite material. The joining process is therefore a process used to permanently bond workpieces together.

[0024] In this invention, adhesion promoters are understood to refer to polymers introduced into the interlayer of a multilayer composite material during a co-extrusion process—for example, to improve adhesion. Typical types of polymers used as adhesion promoters are: poly(ethyl-vinyl alcohol) polymers, modified polyolefins, polyesters, and polyurethanes. Polyesters and polyurethanes are particularly preferred, polyurethanes are especially preferred, and polyester-polyurethanes are very particularly preferred.

[0025] In this invention, polyurethane-based adhesion promoters and / or polyurethane-based adhesive polymers are understood to refer to polymers that, upon curing, have at least one structural element in their polymer chains formed by the reaction of isocyanate groups with isocyanate reactive compounds. Examples of structural elements formed by the reaction of isocyanate groups with isocyanate reactive compounds are urethanes, urethanes, biuret, and urea groups.

[0026] In the remainder of the specification, adhesion promoters relate to the state before and after curing (the process by which an adhesive acquires its cohesive strength and the adhesive forms its physical and chemical properties).

[0027] The separation medium used can be the essential oil or essential oil mixture itself, a single-phase mixture of the essential oil or essential oil mixture with other substances, or a multiphase composition containing essential oil, such as an aqueous emulsion of the essential oil or essential oil mixture.

[0028] The separation medium is preferably composed of an aqueous emulsion of the at least one essential oil.

[0029] In another preferred embodiment, the separating medium comprises an aqueous emulsion of the at least one essential oil. In this embodiment, the separating medium is preferably free of carboxylic acids.

[0030] In this method, it is preferred to use an aqueous emulsion of the at least one essential oil containing > 0.1% by volume, particularly preferably ≥ 0.5% by volume, very particularly preferably ≥ 1% by volume, and even more preferably ≥ 10% by volume, based on the water volume meter used.

[0031] Examples of essential oils selected from phenols, phenylpropanoids, and furanocoumarins include carvacrol, carvacrol, thymol, celery oleoresin, methyl trans-cinnamate, cis and trans-anetinoside, dill oil oleoresin, artemisia oleoresin, eugenol, and coriander isocoumarin.

[0032] Essential oils can be of natural origin, meaning they are obtained from plants or plant parts, or they can be produced synthetically.

[0033] Essential oils can also be chemically modified through oxidation, esterification, or alkylation.

[0034] Of the substances mentioned above, phenylpropanoids are particularly suitable for the method of the present invention.

[0035] A particularly suitable compound is eugenol.

[0036] Essential oils or mixtures thereof selected from phenols, phenylpropanoids, and furanocoumarins, as mentioned above, may also be mixed with essential oils selected from acyclic and cyclic monoterpenes and sesquiterpenes for use in the methods of the present invention. Examples of acyclic and cyclic monoterpenes and sesquiterpenes are ocimene, myrcene, limonene, α-terpinene, phellandrene, α-pinene, camphene, linalool, geraniol, menthol, sapinol, borneol, neraldehyde, citronellol, carvone, menthone, camphor, anisone, mentha furan, eucalyptol, anetofuran, geraniol acetate, linalool acetate, borneol acetate, isoborneol acetate, farnesol, farnesene, α-bimethanol, α-caryophyllene, matricaria, and β-caryophyllene. However, it is preferred to use essential oils and mixtures thereof selected only from phenols, phenylpropanoids, and furanocoumarins.

[0037] In a preferred embodiment, the aqueous emulsion contains an essential oil mixture of ≥ 0.5% by volume, preferably ≥ 0.9% by volume, based on the volume of water used, wherein eugenol accounts for at least (≥) 1 / 3 by volume in the essential oil mixture.

[0038] The effectiveness of this method can be improved by adding surfactants, emulsifiers, or other surfactants to water and a mixture of one or more essential oils.

[0039] For the purposes of this invention, a multilayer composite material consists of at least two layers bonded together in a surface manner, the layers being composed of the same or different materials.

[0040] These layers are polymer layers, preferably made of polyethylene, polypropylene, polyester, or polyamide. These can be co-extruded polymer layers, such as polyolefin films with an ethylene-vinyl alcohol inner layer. The surface of the polymer layers can be treated, i.e., deposited with, for example, aluminum or SiOx, or printed with printing ink. In this case, the polymer layers (including layers made through surface treatment) are considered as a single layer of a multilayer composite material.

[0041] Conversely, aluminum films bonded to the composite material layers in a surface manner using adhesion promoters or adhesive polymers are considered as independent layers. This also applies to aluminum layers that are first vapor-deposited onto a carrier and then bonded to the composite material layers in a surface manner using adhesion promoters or adhesive polymers via transfer coating. The composite material layers can also be paper or cardboard layers, or layers containing plant fibers.

[0042] Polyurethane-based adhesion promoters or adhesive polymers that can be used to bond layers in a surface manner are described in detail in the prior art, for example in Manufacturing Flexible Packaging, Thomas Dunn, ISBN 978-0-323-264-36-5, Ulrich Meier Westhues; Polyurethane, Lacke, Kleb- und Dichtstoffe, ISBN 978-3-86630-896-1. This list should not be interpreted as limiting. Of course, the methods of the present invention can also be used to separate multilayer composite materials in which layers are bonded with adhesion promoters or adhesive polymers not described in the aforementioned documents.

[0043] Method description:

[0044] Optionally, the multilayer composite material is pulverized and refluxed using a separation medium containing at least one essential oil selected from phenols, phenylpropanoids, and furanocoumarins. This treatment can also be carried out at pressures >1013 mPas, for example in an autoclave, and thus at higher boiling temperatures. The dependence of a substance's boiling point on ambient pressure is well known to those skilled in the art. Therefore, the temperature set depending on the pressure during the treatment is determined by those skilled in the art based on their expertise.

[0045] During the processing, the adhesive layer or adhesion promoter layer is weakened so that the multilayer composite material can be separated into individual layers by slight mechanical stress (such as shear stress).

[0046] To improve the effectiveness of this method, multilayer composite materials are pulverized, for example, using a cutting mill or shredder. The multilayer composite material has two surfaces (so-called cover surfaces) formed by a top and bottom layer and facing away from the other layers of the multilayer composite material, and multiple side surfaces, each corresponding to a cross-section of the layer from the top cover surface to the bottom cover surface. Pulverizing the multilayer composite material increases the total area formed by the side surfaces, thus increasing the contact area between the separation medium and the adhesive polymer or adhesion promoter. This improves the penetration of the separation medium into the adhesive layer or adhesion promoter layer and allows for faster weakening of the adhesive layer or adhesion promoter layer.

[0047] The term "multilayer particle" is understood in this invention to refer to all parts made of multilayer composite material by mechanical crushing, such as by cutting, shredding, tearing, etc.

[0048] The multilayer composite material is pulverized such that the dimensions of the multilayer particles along the axis parallel to the covering surface of the multilayer particles are preferably ≤ 400 mm. 2 More preferably ≤ 100 mm 2 For the average value of all multilayer particles.

[0049] In this invention, the term "covering surface of multi-layer particles" is understood to refer to the two surfaces of the top and bottom layers of multi-layer particles that are opposite to the other layers of multi-layer particles.

[0050] The longer the reflow process continues, the greater the weakening of the adhesive layer or adhesion promoter layer.

[0051] Based on the concentration of the one or more essential oils in the aqueous emulsion and the multi-layered particle size as shown above, the duration of the reflux treatment should therefore preferably, or particularly preferably, continue as follows:

[0052] ≥ 0.5% by volume (based on the water volume meter used): Preferably greater than 2 hours, particularly preferably at least 3 hours, and very particularly preferably at least 4 hours.

[0053] ≥ 1% by volume (based on the water volume meter used): Preferably at least 1.5 hours, particularly preferably at least 2 hours, very particularly preferably at least 3 hours.

[0054] ≥ 10% by volume (based on the water volume meter used): preferably at least 0.5 hours, particularly preferably at least 1 hour, very particularly preferably at least 2 hours.

[0055] Before or after pulverization – and before introducing the multilayer particles into the separation medium – multilayer composites or multilayer particles can be desorbed (removed) from adhering food, etc., through a washing process. For this purpose, surfactants, surface-active substances, aqueous solutions of acids or alkalis can be used, for example.

[0056] Before or after introducing multilayer particles into the separation medium, the separation medium can be heated to its boiling point. The separation of multilayer particles into individual layers can be accelerated by generating laminar or turbulent motion / flow within the separation medium.

[0057] This operation method can be implemented in either batch or continuous methods.

[0058] After treatment with the separation medium, the particles in each layer are separated from the separation medium by sieving, filtration, or centrifugation. Layers that are still adhered to each other, i.e., layers that have not been completely separated after treatment with the separation medium, can be separated from each other by mechanical means, such as by a pair of shearing rollers.

[0059] The particles are separated into single types of polymers and aluminum particles, which can be achieved by known separation methods such as flotation, suspension or sedimentation, or by eddy current separation (for aluminum).

[0060] The printing ink can then be removed from the polymer or aluminum particles using a suitable washing process. For example, reference should be made to patent EP 2 832 459 A1.

[0061] Adhered essential oils can be washed off polymer or aluminum particles by a washing process using a suitable surfactant, or removed from polymer or aluminum particles by steam distillation.

[0062] After the polymer or aluminum particles that have been separated, cleaned, and optionally de-inked can be dried, they can be returned to the material recycling process.

[0063] In batch or continuous processing of multilayer composite materials, the volume proportion of essential oil in the separation medium can be determined. If necessary, the volume proportion in the separation medium can be maintained constant or increased by adding essential oil.

[0064] During the processing of multilayer composite materials using a separation medium, polyurethane polymers migrate into the separation medium. These polymers may migrate into the separation medium undissolved, such as in the form of swollen polymer particles, or in a dissolved form. The polyurethane particles can be separated from the separation medium by suitable methods, such as filtration or centrifugation.

[0065] Example

[0066] Multilayer composite materials:

[0067] Multilayer composite material 1: Polyester / Printing ink / / Aluminum / / Polyethylene

[0068] Eduscho Espresso packaging (label: 29.06.2020 L9031 H57 / 2 08:56)

[0069] Multilayer composite material 2: Polyester / Printing ink / Polyethylene

[0070] Josera's "Minivita" dry dog ​​food

[0071] Polyester and printing ink are considered as one layer together.

[0072] / / Refers to an adhesive layer based on polyurethane adhesive.

[0073] Essential oils:

[0074] The following are the suppliers of all oils mentioned: Sigma-Aldrich, Munich

[0075] Eugenol (CAS# 97-53-0) - Phenylpropanol

[0076] Trans-anetine (CAS# 104-46-1) (Phenylpropanol)

[0077] Methyl trans-cinnamate (CAS#: 1754-62-7) (phenylpropanoid derivative)

[0078] Linalool (CAS# 78-70-6) - Monoterpene

[0079] Citronellol (CAS# 106-23-0) - Monoterpene

[0080] Determination of composite strength:

[0081] The composite adhesion of the film layers was determined using a Zwick 5kN Allround benchtop testing machine in a 180° peel test according to DIN 55533-5. The values ​​shown are the average of five individual measurements.

[0082] Experiment 1: Visual inspection of separation (Table 1)

[0083] Multi-layer composite materials are cut into pieces approximately 1 cm in size using scissors. 2 A square. Place 10 pieces, each approximately 1 cm in size. 2 The multi-layered composite material was placed in a 250 ml multi-necked flask with a stirrer, thermometer, and reflux condenser heated by an oil bath.

[0084] Fill the stirring apparatus with 100 ml of water, or 100 ml of water containing 0.1 ml, 0.5 ml, 1 ml, or 10 ml of essential oil, and heat to boiling temperature. Boil the contents of the flask under reflux at approximately 100°C for up to 20 hours. Visually inspect the separation of the multilayer composite material at 1-hour intervals.

[0085] Multilayer composite material 1

[0086]

[0087] - No change in composite adhesion / no visible separation effect

[0088] -+: Layers separate at the cut edge

[0089] +: Layers that are already visible in surface form

[0090] ++: Complete delamination

[0091] 0: Not tested

[0092] % = Volume%

[0093] Both terpenes and phenylpropanoids produced separation effects, with phenylpropanoids showing a greater effect than terpenes. The addition of 1% eugenol resulted in complete separation of the composite material after 3 hours. In pure water, the composite material did not separate even after 20 hours.

[0094] Experiment 2: Measurement of the decrease in composite strength of the film layers (Table 2)

[0095] Cut strips of the multilayer composite material, 15 mm wide and 20 cm long, from the packaging. In a 250 mL multi-necked flask with a reflux condenser and stirring apparatus, boil the strips in 100 mL of water or 100 mL of water mixed with 1 mL of eugenol or trans-anestin under reflux (p ~ 1 bar) for 3 hours. After boiling, remove the strips from the apparatus and measure the composite adhesion within 30 minutes. Determine the composite adhesion of the film layers in a 180° peel test using a Zwick 5kN Allround benchtop testing machine according to DIN 55533-5. Clamp the separated end of the 15 mm wide strip of the film composite material in the clamping grip of the Zwick testing machine. During the measurement, pull the test clamp open at a speed of 100 mm / min. The values ​​shown are the average of five individual measurements.

[0096]

[0097] % = Volume%

[0098] *: The membrane composite material cannot be separated. This directly led to membrane tearing in the experiment.

[0099] The weakening effect of styrene-based compounds on the adhesive layer is obvious. After treatment with an aqueous mixture, the composite strength of the multilayer composite is significantly lower than that of the multilayer composite treated with water alone.

Claims

1. The use of a separation medium comprising at least one essential oil selected from phenols, phenylpropanoids and furanocoumarins, or composed of at least one essential oil selected from phenols, phenylpropanoids and furanocoumarins, for separating at least two layers of a multilayer composite material bonded together in a surface form by at least one polyurethane-based adhesion promoter and / or at least one polyurethane-based adhesive polymer.

2. The use as described in claim 1, characterized in that... The separation medium contains at least one essential oil selected from phenols, phenylpropanoids, and furanocoumarins. a) It exists as a single-phase mixture of the at least one essential oil and at least one other substance. or b) It exists in the form of a multiphase composition of the at least one essential oil and at least one other substance.

3. The use as described in claim 2, characterized in that... The separation medium contains at least one essential oil selected from phenols, phenylpropanoids, and furanocoumarins, and exists in the form of an aqueous emulsion of the at least one essential oil.

4. The use as described in claim 3, characterized in that The aqueous emulsion contains at least one essential oil at a volume percentage of >0.1% based on the volume of water used.

5. The use as described in claim 4, characterized in that... In implementation b), the aqueous emulsion comprises at least one essential oil at a volume percentage of ≥ 0.5% based on the volume of water used.

6. The use as described in any one of claims 1 to 5, characterized in that... A surface-active substance is added to the separation medium.

7. The use as described in any one of claims 1 to 5, characterized in that... The at least two layers of a multilayer composite material bonded together in a surface manner comprise at least one material selected from polyethylene, polypropylene, polyester or polyamide, aluminum, paper, paperboard and mixtures thereof.

8. The use as described in any one of claims 1 to 5, characterized in that... The at least two layers of the multilayer composite material bonded together in a surface manner are composed of at least one material selected from polyethylene, polypropylene, polyester or polyamide, aluminum, paper, paperboard and mixtures thereof.

9. A method for separating at least two layers of a multilayer composite material bonded together in a surface manner by at least one polyurethane-based adhesion promoter and / or at least one polyurethane-based adhesive polymer, characterized in that... The multilayer composite material is treated with a separation medium comprising at least one essential oil selected from phenols, phenylpropanoids, and furanocoumarins, or at least one essential oil selected from phenols, phenylpropanoids, and furanocoumarins.

10. The method as described in claim 9, characterized in that... The separation medium contains at least one essential oil selected from phenols, phenylpropanoids, and furanocoumarins. a) It exists as a single-phase mixture of the at least one essential oil and at least one other substance. or b) It exists in the form of a multiphase composition of the at least one essential oil and at least one other substance.

11. The method as described in claim 10, characterized in that The separation medium contains at least one essential oil selected from phenols, phenylpropanoids, and furanocoumarins, and exists in the form of an aqueous emulsion of the at least one essential oil.

12. The method as described in claim 11, characterized in that... The aqueous emulsion contains at least one essential oil at a volume percentage of >0.1% based on the volume of water used.

13. The method as described in claim 12, characterized in that In implementation b), the aqueous emulsion comprises at least one essential oil at a volume percentage of ≥ 0.5% based on the volume of water used.

14. The method according to any one of claims 9 to 13, characterized in that A surface-active substance is added to the separation medium.

15. The method according to any one of claims 9 to 13, characterized in that The at least two layers of a multilayer composite material bonded together in a surface manner comprise at least one material selected from polyethylene, polypropylene, polyester or polyamide, aluminum, paper, paperboard and mixtures thereof.

16. The method according to any one of claims 9 to 13, characterized in that The at least two layers of the multilayer composite material bonded together in a surface manner are composed of at least one material selected from polyethylene, polypropylene, polyester or polyamide, aluminum, paper, paperboard and mixtures thereof.

17. The method according to any one of claims 9 to 13, characterized in that The multilayer composite material is introduced into the separation medium, which is heated to boiling temperature before or after the introduction of the multilayer composite material, and then treated by reflux of the separation medium at standard pressure (10¹³ mPas) or at pressure > 10¹³ mPas.

18. The method according to any one of claims 9 to 13, characterized in that The method can be performed in continuous or discontinuous operation.

19. The method according to any one of claims 9 to 13, characterized in that Before being introduced into the separation medium, the multilayer composite material is mechanically crushed into multilayer particles.

20. The method as described in claim 19, characterized in that... For the average value of all multilayer particles, the dimension of the multilayer particles along the axis parallel to the coverage surface of the multilayer particles is ≤ 400 mm. 2 The phrase "covering surface of multi-layer particles" is understood to refer to the two surfaces of the top and bottom layers of multi-layer particles that are opposite to the other layers of multi-layer particles.

21. The method as described in claim 20, characterized in that For the average value of all multilayer particles, the dimension of the multilayer particles along the axis parallel to the coverage surface of the multilayer particles is ≤ 100 mm. 2 .

22. The method as described in claim 18, characterized in that, After treatment with a separation medium, the layers of multi-layered particles that are still adhered to each other are separated by mechanical means.

23. The method as described in claim 18, characterized in that, After treatment with a separation medium, the separation medium is separated from the separated layers of multilayer particles.

24. The method as described in claim 22, characterized in that, After treating and mechanically separating the layers of multilayered particles that are still adhered to each other with a separation medium, the separation medium is separated from the separated layers of multilayered particles.

25. The method as described in claim 23, characterized in that... The mixture of granular layers obtained after separating the separation medium is further separated according to the granular material.

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