Method for recycling painted plastics

Abstract

The invention relates to a method for recycling painted plastic parts. In order to provide a method for recycling painted plastic materials, which makes it possible without the addition of chemicals to obtain a granulate material, the physical properties of which almost correspond with those of new material, the invention discloses a method in which · the plastic parts are comminuted in one or more steps to a particle size in the range from approximately 50 to 500 µm, · wherein the plastic particles are then fed to an extruder, which is used to extrude a plastic strand after a melting and kneading phase and a filtration process, and · the plastic strand is then granulated. In the context of the invention it has surprisingly been shown that, in this way - preferably without the addition of chemicals - a plastic granulate is obtained, with which painted plastic parts can also be produced, the physical properties of which almost correspond with those of new material.

Description

[0001] DESCRIPTION

[0002] Process for recycling painted plastics

[0003] The invention relates to a method for recycling painted plastic parts.

[0004] Plastic products are often used for automotive parts. For example, when recycling plastic bumpers with unpainted surfaces, improperly molded bumpers and bumpers removed from scrap vehicles are roughly crushed into cubes approximately 3 mm in size, then mixed with virgin or new material and reused to mold bumpers. This is possible because the physical properties of recycled plastic material are not significantly worse than those of virgin material.

[0005] However, for plastic parts with painted surfaces, plastic materials recovered in this way cannot be reused for identical new parts. If painted plastic parts are shredded, the paint degrades the physical properties of the plastic material, such as impact resistance, elongation, and surface quality, to such an extent that satisfactory quality for a new part can no longer be achieved.

[0006] Therefore, painted plastic parts that have been molded incorrectly or removed from scrap vehicles are dumped in landfills or incinerated, which is harmful to the environment.

[0007] Methods for removing paint by sandblasting are known from the prior art. Sandblasting materials are blown onto the paint of painted plastic parts using compressed air to mechanically remove the paint.

[0008] Processes for melting resin and separating the coating using a screening device are also known. A coated plastic part is coarsely crushed and fed into an extruder, where the plastic part is melted. Since the coating does not melt in the extruder due to its heat curing, it can be separated using a screening device attached to the extruder outlet.

[0009] There are also known methods for removing paint from plastic using chemicals.

[0010] EP 1 205 513 A2 describes a process for stripping paint from plastic bodies coated with paint layers, in which the pieces are first reduced to a pourable size. These plastic pieces are then mixed with a paint stripping agent that reduces the adhesion of the paint layers present thereon and circulated by a conveyor screw. The paint stripping agent is formed from an emulsion of at least one benzyl-substituted alkanol, an alkyl glycol acetate, or N-alkylpyrrolidone with an aqueous alkali, which are not completely miscible. The mixing ratio of the individual components of the paint stripping agent is selected such that it lies within the range of a miscibility gap. After the paint stripping agent has acted on the painted plastic parts, a liquid-absorbing solid is added to enable the further process to be carried out in a dry state.The plastic parts are then fed into a hammer mill, where the paint layers that have swollen due to the paint stripper are removed. This process is complex, costly, and environmentally harmful due to the chemicals used.

[0011] There are also processes in which the plastic parts are shredded and mixed with new plastic.

[0012] According to DE 197 15 945 A1, shredded plastic parts are placed in a hammer mill and agitated with plastic granules made of PA 66 GF 30. The heating and impact dissolve paint particles, resulting in largely paint-free plastic particles.

[0013] Finally, there are purely mechanical processes for recycling painted plastic parts.

[0014] EP 0 575 751 A1 and DE 42 17 005 A1 describe a process in which painted plastic parts are finely shredded into chips in several stages, but not pulverized. Due to density differences, the chips are separated into a sink and a float fraction in a sink-float system. The float fraction, which consists predominantly of plastics, is then ground, with the good fraction having an average fiber length of 1 to 3 mm. The good fraction is subjected to shearing, freeing it from adhering paint particles. The detached paint is sieved out and removed in a vibrating screen. The paint-free good fraction is transferred to a vacuum granulation extruder for further processing, whereupon a recyclate in the form of granules is obtained.Due to the significantly higher proportion of fillers and the better adhesion of the paint in the paint systems developed in the 1990s, as well as the higher filler content in the plastics, such a procedure is no longer possible with newer painted plastic products.

[0015] It is therefore the object of the invention to provide a process for recycling painted plastic materials which makes it possible - preferably without the addition of chemicals - to obtain granules whose physical properties are almost identical to those of new material.

[0016] This object is achieved according to the invention by a method in which

[0017] • the plastic parts are crushed in one or more steps to a particle size in the range of approximately 50 to 500 pm,

[0018] • the plastic particles are then fed to an extruder, which, after a melting and kneading phase and a filtration, extrudes a plastic strand and • the plastic strand is then granulated.

[0019] The particle size is the average particle size.

[0020] It has surprisingly been found within the scope of the invention that, in this way, plastic granules can be obtained from single-variety plastic parts, which can also be used to produce painted plastic parts whose physical properties almost correspond to those of new material. The process according to the invention can be carried out without the addition of chemicals. Contrary to the procedure in EP 0 575 751 A1 or DE 42 17 005 A1, the plastic is not freed of the paint before extrusion (which would no longer be possible with today's painted plastics using the process described therein), but rather it is subjected to extrusion with the paint still attached.

[0021] In a preferred embodiment of the invention, it is provided that the plastic parts are comminuted in one or more steps to a particle size of approximately 100 to 400 pm and particularly preferably approximately 200 to 300 pm.

[0022] It is possible to reuse only the recycled plastic granulate as a raw material for the production of new plastic parts of the original or a new use.

[0023] However, it is preferred that the resulting recycled plastic granulate and / or recycled plastic granulate from unpainted raw material is mixed with virgin plastic to produce new plastic parts of the original or a new use.

[0024] Pure plastic granules recycled from painted starting material according to the present invention can be mixed with virgin plastic, or recycled plastic granules from painted starting material according to the present invention can be mixed with recycled plastic granules from unpainted starting material, and this mixture can then be mixed with virgin plastic. The specific type and composition of the mixture depends on the specific product requirements.

[0025] The mixture contains, for example, between 10 and 90 wt.% recycled plastic granulate and / or recycled plastic granulate from unpainted plastic parts, preferably between 20 and 80 wt.% and particularly preferably between 30 and 50 wt.%.

[0026] An advantageous embodiment of the invention is that the comminution of the plastic parts takes place in several steps, whereby first a pre-comminution takes place, for example by means of a shredder, then optionally an intermediate comminution, for example in a cutting mill, and finally a grinding of the plastic parts, for example in a disk mill or a vibrating mill.

[0027] It is preferred within the scope of the invention that after the comminution of the plastic parts, an electrostatic separation takes place, in which the paint particles that have become detached from the plastic parts during comminution are removed.

[0028] This electrostatic separation is preferably carried out after the plastic parts have been shredded and before grinding.

[0029] After pre-shredding, plastic parts are preferably approximately 20 to 80 mm in size, and after intermediate shredding, they are approximately 4 to 20 mm in size. Depending on the starting product and the selected shredding process, other dimensions of the plastic parts may also be obtained after the individual process steps. It is also possible to skip the intermediate shredding step and proceed directly from pre-shredding to grinding. Furthermore, it is preferred that the material to be ground be cooled during the grinding of the plastic parts. Cooling the material to be ground results in a better grinding result.

[0030] Plastic particles with a particle size of approximately 50 to 500 pm are now present (hereinafter referred to as “ground material”), which are then subjected to extrusion.

[0031] According to the invention, the extruder can be a single-screw extruder or a twin-screw extruder, with the latter being preferred. In twin-screw extruders, the plastic is exposed to higher shear forces, which is advantageous for the present application. Filtration is preferably carried out using a melt filter.

[0032] Preferably, an additive containing a stabilizer and an impact modifier is added to the millbase before or during extrusion. Between 0.5 and 3% by weight of additive, based on the amount of millbase, is added. This further enhances the quality of the final product.

[0033] If necessary, the additive may also contain odor absorbers. This is particularly useful if the final product is used indoors.

[0034] Preferred embodiments of the invention consist in that the plastic strand is granulated by means of strand granulation or underwater granulation, the former being preferred.

[0035] However, other granulation processes can also be used.

[0036] It is within the scope of the invention that the plastic parts are painted plastic parts from motor vehicles. These can be, for example, painted bumpers. Of course, other painted plastic parts, both from motor vehicles and from other sectors, can also be recycled using the process according to the invention.

[0037] The process according to the invention is basically suitable for all coated plastics, in particular PA, PE, PP, PC, PET, whereby non-fiber-reinforced plastics are preferably used.

[0038] An embodiment of the invention is explained in more detail below with reference to a drawing.

[0039] It shows

[0040] Fig. 1 shows the schematic sequence of a method according to the invention for recycling painted plastic parts.

[0041] First, the plastic parts are pre-treated manually or mechanically if necessary, so that pure plastic parts are available.

[0042] In a first step, the plastic parts are pre-shredded in a shredder to a size of approximately 20 to 80 mm. Before or after this step, they are sorted and / or metal parts are removed.

[0043] The pre-shredded plastic parts are fed to a cutting mill (1 ) by means of a conveyor belt, where they are shredded to a size of approximately 4 to 20 mm.

[0044] Any paint particles that have come loose are then removed using an electrostatic separation system (not shown).

[0045] The plastic parts are then transported to a disc mill (2) via a conveyor belt or a screw conveyor system. In the disc mill (2), the plastic parts are then ground to a particle size of approximately 300 pm and then fed into a screening system (3), which ensures the desired particle size.

[0046] Plastic particles with a particle size of approximately 50 to 500 pm are now present (hereinafter referred to as “ground material”), which are then subjected to extrusion.

[0047] Before or during extrusion, 1 wt.%, based on the amount of plastic particles, of an additive containing a stabilizer and an impact modifier and, if appropriate, an odor absorber is added.

[0048] The screened plastic particles are fed via a dosing unit to an extruder (4). Depending on the material, this can be a single-screw or a twin-screw extruder, with the latter being preferred. The extrusion process involves a melting and kneading phase.

[0049] Following extrusion, the plastic is granulated, preferably by strand granulation (6) in a water bath (5), although alternative granulation processes can also be used.

[0050] The granulate, which has a size of approximately 3 to 8 mm, is sieved using a glazing sieve and fed to a packaging unit (7).

[0051] If necessary, homogenization of both the intermediate products of the process and the granulate can also be carried out.

Claims

CLAIMS 1 . Process for recycling painted plastic parts, characterized by the following process steps: • Crushing of the plastic parts in one or more steps into plastic particles with a particle size in the range of 50 to 500 pm, • Feeding the plastic particles into an extruder, which, after a melting and kneading phase and filtration, extrudes a plastic strand, and • the plastic strand is then granulated.

2. Process according to claim 1, characterized in that the plastic parts are comminuted to a particle size of approximately 100 to 400 pm and particularly preferably approximately 200 to 300 pm.

3. A method according to claim 1 or claim 2, characterized in that only the recycled plastic granulate is reused as raw material for the production of new plastic parts of the original or a new use.

4. A process according to claim 1 or claim 2, characterized in that the resulting recycled plastic granulate from painted starting material and / or recycled plastic granulate from unpainted starting material is mixed with virgin plastic to produce new plastic parts in the original or a new use, the mixture containing between 10 and 90 wt.% recycled plastic granulate and / or recycled plastic granulate from unpainted plastic parts, preferably between 20 and 80 wt.% and particularly preferably between 30 and 50 wt.%.

5. A method according to any one of claims 1 to 4, characterized in that the comminution of the plastic parts takes place in several steps, wherein first a pre-comminution takes place, then optionally an intermediate comminution, and finally a grinding of the plastic parts, for example in a disk mill or a vibrating mill.

6. Process according to claim 5, characterized in that after the pre-shredding, plastic parts with a size of approximately 20 to 80 mm are present and after the intermediate shredding, with a size of approximately 4 to 20 mm.

7. A method according to any one of claims 1 to 6, characterized in that after the comminution of the plastic parts, an electrostatic separation takes place, in which the paint particles which have become detached from the plastic particles during the grinding process are removed.

8. Method according to one of claims 1 to 7, characterized in that the material to be ground is cooled during the grinding of the plastic parts.

9. Process according to one of claims 1 to 8, characterized in that a single-screw extruder or a twin-screw extruder is used as the extruder, a twin-screw extruder being preferred.

10. Process according to one of claims 1 to 9, characterized in that an additive containing a stabilizer and an impact modifier is added to the plastic particles before extrusion in an amount of between 0.5 and 3% by weight, based on the amount of plastic particles.

11. A process according to claim 10, characterized in that the additive contains odor absorbers.

12. A method according to any one of claims 1 to 11, characterized in that the plastic strand is granulated by means of strand granulation or underwater granulation.

13. A method according to any one of claims 1 to 12, characterized in that the plastic parts are painted parts of motor vehicles.

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