Method for processing coated plastic material

Abstract

The invention relates to a method for processing coated plastic material, wherein a coated plastic material is provided, subjected to a grinding process at low temperatures and the ground coated plastic material is subjected to a separation process, wherein the grinding process is carried out in the presence of at least one auxiliary substance. The method is particularly suitable for recycling printed plastic foils.

Description

TECHNICAL FIELD

[0001] The present invention relates to a method for processing coated plastic material, by means of which method inter alia printed plastic material can be recovered. BACKGROUND

[0002] Coated plastic materials (Beschichtete Kunststoffmaterialien) are found in many commercial and industrial fields, for example in the form of coated plastic packaging. It is desirable that these materials, after their prescribed use, are supplied to the recycling sector in order to recover their components as far as possible in a sorted manner.

[0003] Different types of plastic material of different thicknesses can be printed by means of printing machines. As a result, printed plastic material is obtained, which printed plastic material can be used for example in the form of printed plastic packaging as a box, can, bottle, etc. for foodstuffs or other goods. Large amounts of printed plastic material are produced worldwide every year, which printed plastic material enters the commercial sector in the form of printed plastic packaging. It is desirable that these printed plastic materials, after their use, are recovered and supplied to the re-use sector as far as possible in a sorted manner.

[0004] Methods are known in principle from the prior art in which articles composed of a plurality of components, such as for example automobile tyres or cables, are subjected to cryogenic grinding and subsequently to material separation. These methods are based inter alia on the phenomenon that certain materials become brittle at low temperatures. SUMMARY

[0005] It has surprisingly been found that printed plastic material can be separated very effectively into a plastic part and a coating part by cryogenic grinding in the presence of an auxiliary substance, which auxiliary substance promotes the separation of the printed coating from the plastic material under these low-temperature conditions.

[0006] It has been established that such substances are particularly suitable for the method according to the invention: these substances are absorbed in liquid form by the coating of the coated plastic material and change into a solid state on temperature reduction and additionally undergo a volume expansion there. In the simplest case, this auxiliary substance is water, wherein the density anomaly of water is utilised after the expansion of water below approximately 4°C.

[0007] According to the application, the at least one auxiliary substance is added to the coated plastic material prior to the grinding process at low temperature, so that the at least one auxiliary substance can penetrate into and be absorbed by the coating of the plastic material. Under the conditions of the subsequent low-temperature grinding process, the at least one auxiliary substance in the coating becomes solid, expands and thus contributes to the coating of the plastic material being able to be detached significantly better and to the treatment of the coated plastic material being significantly improved. The at least one auxiliary substance causes the coating of the plastic material to be abgesprengt at low temperature in the grinding process to some extent.

[0008] Accordingly, the application relates to a method for treating a coated plastic material, wherein a coated plastic material is provided, subjected to a grinding process at low temperature and the ground coated plastic material is subjected to a separation process, wherein the grinding process is carried out in the presence of at least one auxiliary substance, wherein the at least one auxiliary substance is in liquid or gaseous form at a temperature above the temperature of the grinding process and is in solid form at the temperature of the grinding process, wherein the at least one auxiliary substance has a volume at a temperature above the temperature of the grinding process which is smaller than the volume at the temperature of the grinding process, and wherein the at least one auxiliary substance is added to the coated plastic material prior to the grinding process.

[0009] The provided coated plastic material consists of a base plastic material, for example in the form of a foil, and a coating.

[0010] In a preferred embodiment, the provided coated plastic material has a coating which is produced by at least one printing method, wherein the printing method is preferably selected from the group consisting of inkjet printing, offset printing, flexographic printing, screen printing, intaglio printing, transfer printing methods (for hot or cold foil transfer) and combinations thereof.

[0011] In another preferred embodiment, the provided coated plastic material has a coating which has at least one printing medium selected from the group consisting of inkjet inks, offset pigments, flexographic printing pigments, screen printing pigments, intaglio printing pigments and metal transfer layers.

[0012] In another preferred embodiment, the provided coated plastic material has a coating having a thickness in the range from 0.5 to 100 micrometers, preferably in the range from 1 to 50 micrometers and particularly preferably in the range from 1 to 20 micrometers, based on the total thickness of the coating of the coated plastic material.

[0013] In a preferred embodiment, the coating of the coated plastic material has a high absorption for the at least one auxiliary substance. High absorption in this context means an absorption capacity of at least 1 ml of auxiliary substance per kg of coated plastic material, preferably an absorption capacity of at least 10 ml of auxiliary substance per kg of coated plastic material.

[0014] The basic plastic material preferably relates to a plastic material which can be processed and printed in a printing machine. Examples of such plastic materials are selected from the group consisting of polyethylene (PE), polypropylene (PP), polyethylene terephthalate (PET), polyvinyl chloride (PVC), polystyrene (PS), polyamide (PA) and polycarbonate (PC). The plastic material can also be a mixture (blend) of various plastics.

[0015] In a preferred embodiment, the basic plastic material is provided in the form of a plastic film / plastic foil, particularly preferably in the form of a plastic foil which can be processed in a printing machine.

[0016] According to the application, the at least one auxiliary substance is added to the coated plastic material prior to the grinding process. In a preferred embodiment, the at least one auxiliary substance is added in liquid form. This addition can be carried out from a reservoir container, for example by means of injection by means of a nozzle, according to methods known in principle from the prior art.

[0017] As a device for carrying out the grinding process, a grinder known in principle from the prior art can be used, for example a rotor grinder or a fine impact grinder (pin mill).

[0018] In a preferred embodiment, the grinding process is carried out at a temperature of less than 0°C, preferably less than -70°C and particularly preferably less than -190°C.

[0019] Grinding methods at low temperatures (cryogenic grinding methods) are known in principle from the prior art. For example, carbon dioxide (dry ice) or liquid nitrogen are used as coolants in such methods in order to achieve the required low temperatures.

[0020] According to the application, the at least one auxiliary substance has a volume at a temperature above the temperature of the grinding process which is smaller than the volume at the temperature of the grinding process. Auxiliary substances with anomalous densities are used in this embodiment (for example water and ammonia).

[0021] In a preferred embodiment, the at least one auxiliary substance is selected from the group consisting of water and ammonia. In a very particularly preferred embodiment, the at least one auxiliary substance is selected from the group consisting of water. As long as the at least one auxiliary substance involves water, both pure substances of water (such as distilled water) and salt-containing water (such as tap water or rainwater) are included.

[0022] In another preferred embodiment, the coating of the provided coated plastic material comprises at least one swellable component. In principle, all materials that absorb the at least one auxiliary substance in liquid form and in which it increases in volume (i.e. swells) are suitable as swellable components. Preferably, the at least one swellable component is selected from the group consisting of hydrogels, zeolites, gelatin and cellulose.

[0023] In another preferred embodiment, the coated plastic material involves a plastic foil that is printed in a printing machine. In principle, all plastic types that can be provided in the form of a film / foil and are processed in a printing machine (preferably the plastic materials previously mentioned as preferred) are suitable as material for the underlying plastic foil. In this preferred embodiment, the plastic foil is preferably printed with at least one printing medium, wherein the plastic foil and the printed-on printing medium together constitute the coated plastic material. In this embodiment, as printing medium for the production of the printed plastic foil, preferably are: inkjet inks, offset pigments, flexographic printing pigments, screen printing pigments, gravure printing pigments and mixtures thereof. The printing medium can also include one or more printing varnishes.

[0024] According to the application, before the cryogenic grinding process is carried out, a step for preparing the coated plastic material can be provided. For example, the coated plastic material can be subjected to a cleaning process at the beginning. Furthermore, the coated plastic material can be subjected to a coarse comminution (chopping) before the cryogenic grinding process is carried out. Furthermore, the coated plastic material can be subjected to a precooling (for example by means of a vortex screw cooler) before the cryogenic grinding process is carried out.

[0025] In the method according to the application, the ground coated plastic material is subjected to a separation process. Here, the coated plastic material is separated into a plastic fraction and a coating fraction. In principle, all separation methods known from the prior art for solid mixtures are suitable as separation method for the ground coated plastic material, such as mechanical or electrostatic methods, such as sieving, air classification, fluidized bed classification, flotation separation, flow classification processes, etc.

[0026] By means of the method according to the application it is possible in a relatively simple manner to separate the printed plastic material, in particular according to type, into a plastic portion and a printing pigment portion, and to recycle the two constituents. A new plastic foil can be produced from the plastic portion, for example by methods known in principle. The printing pigment portion, which is significantly smaller in volume compared to the plastic portion, can be supplied to waste utilization. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 A preferred embodiment of the method according to the application is schematically described in which an auxiliary substance is added before the grinding at low temperature; and

[0028] Figure 2 Another preferred embodiment of the method according to the application is schematically shown in which a printed plastic foil is employed as the coated plastic material and the auxiliary substance is added before the grinding at low temperature. DETAILED DESCRIPTION

[0029] Figure 1 A preferred embodiment of the method according to the application is schematically described in which an auxiliary substance is added before the grinding at low temperature.

[0030] As Figure 1 shown, the method according to the application comprises at least the steps: providing a plastic material; achieving a coated plastic material; adding an auxiliary substance; grinding at low temperature; separating the plastic material from the coating into a plastic material and a coating.

[0031] Figure 2 Another preferred embodiment of the method according to the application is schematically shown in which a printed plastic foil is employed as the coated plastic material and the auxiliary substance is added before the grinding at low temperature.

[0032] As Figure 2 shown, the method according to the application comprises at least the steps: providing a printed plastic foil; adding a liquid auxiliary substance; grinding at low temperature; separating the plastic material from the printing medium into a plastic material and a printing medium.

Claims

1. A method for processing coated plastic materials to recycle printed plastic materials, in, A coated plastic material is provided, wherein the provided coated plastic material has a coating, said coating being formed by at least one printing method. The coated plastic material is subjected to a grinding process at a temperature below 0°C, and The coated plastic material being ground undergoes a separation process. Its features are, The grinding process is carried out in the presence of at least one auxiliary substance. The at least one auxiliary substance is in liquid or gaseous form at temperatures above the grinding process temperature, and solid form at the grinding process temperature. Wherein, the volume of the at least one auxiliary substance at a temperature higher than that of the grinding process is smaller than the volume at the temperature of the grinding process, and In this process, at least one auxiliary substance is added to the coated plastic material before the grinding process, so that the at least one auxiliary substance can penetrate into the coating of the plastic material and be absorbed by it.

2. The method according to claim 1, in, The printing method is selected from: inkjet printing, offset printing, flexographic printing, screen printing, gravure printing, transfer printing, and combinations thereof.

3. The method according to claim 2, in, The transfer printing method is either a hot foil transfer method or a cold foil transfer method.

4. The method according to any one of claims 1 to 3, in, The provided coated plastic material has a coating having at least one printing medium selected from: inkjet ink, offset pigment, flexographic printing pigment, screen printing pigment, gravure printing pigment, and metal transfer layer.

5. The method according to any one of claims 1 to 3, in, Referring to the overall thickness of the coating on the coated plastic material, the provided coated plastic material has a coating thickness ranging from 0.5 micrometers to 100 micrometers.

6. The method according to any one of claims 1 to 3, in, The coating of the coated plastic material has high absorption of the at least one auxiliary substance.

7. The method according to any one of claims 1 to 3, in, The at least one auxiliary substance is selected from water and ammonia.

8. The method according to claim 7, in, The at least one auxiliary substance is water.

9. The method according to any one of claims 1 to 3, in, The coating of the provided coated plastic material includes at least one swellable component.

10. The method according to claim 9, in, The at least one swellable component is selected from: hydrogel, zeolite, gelatin and cellulose.

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