Method and device for granulating plastic ground material

Abstract

The present invention relates to a method for granulating plastic ground material (1), which method comprises the following successive method steps: a) the plastic ground material (1) is first pressed into a plurality of hollow chambers (8) arranged or formed on a conveying device (7), wherein the plastic ground material (1) is pre-compacted with a defined pressure during this pressing process. The method according to the invention is characterized in that b) the pre-compacted plastic ground material is then transported by means of a conveying device (7) to a compacting station (10), in which it is further compacted within the hollow chambers (8) using an increased contact pressure with respect to a), wherein b) subsequently the pre-compacted plastic ground material (1) is transported by means of the conveying device (7) to an ultrasonic device having at least one sonotrode (13) which generates uniform ultrasonic vibrations which plasticize the plastic ground material (1) and fuse it together, without it being completely melted.

Description

20263498PUET - 1 - Method and apparatus for granulation of plastic regrind DESCRIPTION Technical field

[0001] The present invention relates to a method for granulating plastic regrind according to the preamble of claim 1. Furthermore, the present invention relates to a device for granulating plastic regrind according to the preamble of claim 2. The device according to the invention enables the production of plastic granules from recycled polymer materials without the need for complete melting of the plastic particles. This significantly reduces energy consumption compared to conventional extrusion processes, while simultaneously preserving the material properties of the recycled material.

[0002] The invention is used in plastics processing, in particular in the production of secondary raw materials for the plastics industry, including the reprocessing of post-consumer and post-industrial recyclates.

[0003] The process according to the invention is suitable for various types of plastics, including polyolefins (e.g. polyethylene and polypropylene), polyesters (e.g. PET) and engineering plastics (e.g. ABS, PA). State of the art

[0004] The production of recycled plastics currently takes place predominantly through mechanical and chemical recycling processes. In mechanical recycling, plastic waste is shredded, cleaned, and processed. - 2 -dries and then melts by extrusion and processes into granules. This process is established, but is associated with high energy consumption and material degradation due to thermal stress.

[0005] An alternative is chemical recycling, in which plastics are broken down into their basic chemical building blocks through pyrolysis, depolymerization, or solvolysis and then resynthesized. While this process allows for higher material quality, it is cost-intensive and not yet economically scalable for many types of plastic.

[0006] Known approaches to granulating recycled plastics rely on extrusion processes with strand or underwater pelletizing, in which the plastic mass is forced through dies and then shredded. These processes require high process temperatures and often lead to thermal damage to the plastic.

[0007] Conventional methods for granulating plastic regrind typically involve completely melting the material and processing it as a homogeneous molten mass. Such extrusion processes result in complete mixing and fusion of the material, leading to the loss of the original fragmented structure of the regrind. Complete melting is energy-intensive and can cause thermal degradation of the polymer chains. Furthermore, corresponding extrusion systems are structurally complex and often require additional cooling and post-treatment equipment.

[0008] Despite these technologies, there is a need for energy-efficient alternatives that minimize the thermal stress on recyclates and maintain material quality, especially for high-performance plastics or sensitive polymer blends. 20263498PUET - 3 - Description of the invention

[0009] The object of the invention is to eliminate the disadvantages of conventional granulation processes, in particular the high energy consumption and the thermal degradation of the plastic recyclates caused by complete melting in the extrusion process.

[0010] The present invention overcomes these disadvantages through a multi-stage process in which the plastic regrind is first mechanically pre-compacted and then compacted under further pressure before being subjected to ultrasonic vibrations. This process does not result in complete homogenization or fusion of the plastic regrind into a homogeneous melt mass, so that the original fragment structure within the produced plastic regranulate particles is retained.

[0011] According to the invention, ultrasonic welding is used for the granulation of regrind plastics. In this process, the plastic particles are selectively heated at their contact surfaces by high-frequency vibrations and bonded together without requiring a complete melting phase. This significantly reduces energy consumption and preserves the mechanical properties of the recycled material.

[0012] The essential aspect of the invention is that the energy introduced by the ultrasonic vibrations is dosed in such a way that only the outer zones of the individual plastic particles are plasticized and welded together, while the core of the particles remains below the melting temperature. This results in a mechanically stable, but only edge-welded, plastic regranulate whose internal structure consists essentially of unaltered plastic fragments. 20263498PUET - 4 -

[0013] The process enables gentler processing of plastic waste and improves the quality of the resulting granules, especially for sensitive polymers and recycled plastics. Furthermore, the targeted control of the ultrasonic parameters allows for a more precise granule size, which facilitates further processing.

[0014] The requirement for this granulation arises from the need for reliable feeding and melting behavior in the subsequent extrusion and injection molding processes. For this reason, regrind (undefined flakes) is currently melted and reprocessed into granules (with a defined particle size).

[0015] This edge-to-edge welding of the plastic fragments creates regranulate that, during subsequent thermal melting in an extrusion or injection molding process, deliberately breaks apart again. The welds created at the edges dissolve even at relatively low temperatures, causing the regranulate to disintegrate into smaller plastic fragments. This results in reduced individual volumes and increased effective surface areas, enabling particularly rapid and homogeneous melting of the material. Brief description of the drawing

[0016] Further objectives, features, advantages and application possibilities of the method according to the invention and a device provided for it will become apparent from the following description of an exemplary embodiment with reference to the drawing. 20263498PUET - 5 -

[0017] The drawing shows

[0018] Fig. 1 shows the device according to the invention in an advantageous embodiment in a schematic side view. Execution of the procedure

[0019] In a first step a), the plastic regrind 1 is introduced into several hollow chambers 8 arranged or formed on a conveying device 7. During this pressing process, the plastic regrind 1 is pre-compacted with an initial contact pressure. The conveying device 7 can be designed as a circulating conveyor belt or as a functionally equivalent transport device.

[0020] In a further step b) according to the invention, the pre-compacted plastic regrind 1 is transported to a compaction station 10. In the compaction station 10, the plastic regrind 1 is further compacted within the hollow chambers 8 with a second contact pressure that is higher than the first contact pressure. The compaction station 10 can comprise suitable pressure elements for this purpose, in particular rotating rollers 11 with projecting plungers, by means of which the plastic regrind 1 is selectively pressed into the hollow chambers 8.

[0021] In a further step c) according to the invention, the compacted plastic regrind 1 is fed to an ultrasonic device with at least one sonotrode 13.

[0022] In the subsequent step d) according to the invention, the compacted plastic regrind 1 is subjected to ultrasonic vibrations by means of the at least one sonotrode 13. During the subjection of the plastic regrind 1 to ultrasonic vibrations, a mechanical contact pressure is applied to the plastic regrind 1. The contact pressure is generated by the sonotrode 13 itself and / or by a [missing information - likely a specific component or element]. - 6 - the sonotrode 13 generates a functionally connected or non-functionally connected pressure element 15.

[0023] This combination of multi-stage mechanical compaction and subsequent application of ultrasonic vibrations under simultaneous mechanical pressure enables targeted welding of the plastic fragments without requiring complete melting of the entire material.

[0024] In an advantageous embodiment, the plastic material 1 is positively supported against the hollow chambers 8 during the application of ultrasonic vibrations. This ensures a defined energy input and a stable positioning of the material within the hollow chambers 8.

[0025] In a further embodiment, the ultrasonic vibrations are introduced under mechanical pressure in such a way that the heat generated by friction and / or vibration damping is generated at least predominantly at contact surfaces between adjacent plastic fragments of the plastic regrind 1, so that plasticization is essentially limited to edge zones of the plastic fragments of the plastic regrind 1.

[0026] In an additional embodiment, the plasticization of the edge zones is achieved by a local dissipation of the ultrasonic energy limited to contact surfaces between adjacent plastic fragments of the regrind 1. This spatially concentrates the energy input.

[0027] In a further advantageous embodiment, a complete 20263498PUET is achieved through dissipation of the ultrasonic energy occurring predominantly at contact surfaces between adjacent plastic fragments of the plastic regrind 1 and a time-limited energy effect. - 7 - Heating of the plastic fragments is prevented, so that core areas of the plastic fragments of the plastic ground material 1 remain below the melting temperature.

[0028] In a preferred embodiment, the plastic regrind 1 is formed in prismatically shaped hollow chambers 8. Due to the geometry of the hollow chambers 8, the plastic regranulate grains have a prismatic shape.

[0029] Of course, other granule shapes are also possible (for example, spherical, cylindrical).

[0030] In a further embodiment, the plastic regranulate grains, which are only welded at the edges, break down into smaller plastic fragments during the subsequent thermal melting process, thereby achieving accelerated and more homogeneous melting.

[0031] The ultrasonic vibrations are preferably introduced at a frequency in the range of 15 kHz to 40 kHz and under simultaneous mechanical pressure of the sonotrode on the plastic material being ground. The combination of mechanical pre-compaction and ultrasonic action under load ensures that plasticization remains localized to the contact surfaces of the plastic fragments.

[0032] In a further embodiment according to the invention, no complete homogenization of the plastic ground material 1 takes place during granulation and the original fragment structure inside the granule grains is retained.

[0033] Alternatively or additionally, during granulation, the plastic regrind 1 is not completely mixed or melted into a homogeneous melt mass, so that inside the plastic-20263498PUET - 8 -stoffregranulatkorne a structure composed of several plastic fragments is retained.

[0034] In a further embodiment, the introduction, transport and feeding of the plastic regrind 1 between process steps a) to c) is carried out by means of a timed conveying device 7. Design of the device

[0035] The invention overcomes the described disadvantages of conventional granulation processes through the use of a special device. This device first compacts the regrind and then welds it into granules using ultrasound, without requiring energy-intensive melting. The process is based on a multi-stage procedure that enables efficient and gentle granulation.

[0036] The feeding and timing of the plastic regrind between the individual process stations is achieved by means of a timed conveying device 7. This conveying device 7 can preferably be designed as a circulating conveyor belt with integrated hollow chambers. Alternatively, the conveying device 7 can be designed as a rotary indexing machine, in particular as a rotary table or carousel system, in which the hollow chambers 8 are arranged along a circumference and fed successively to the compaction and ultrasonic stations.

[0037] The device has a conveying unit 7 in which hollow chambers 8 for receiving the plastic regrind 1 are arranged or formed. Furthermore, at least one device is provided by means of which the plastic regrind 1 is pressed into the hollow chambers 8. - 9 -

[0038] A compaction station 10 is preferably arranged downstream of the conveying device 7. The pre-compacted plastic regrind 1 can be transported to the compaction station 10 by means of the conveying device 7. The compaction station 10 is advantageously designed such that the plastic regrind 1 is further compacted within the hollow chambers 8 with a contact pressure increased compared to the previous pressing stage.

[0039] In the compaction station 10, the plastic regrind 1 can, for example, be pressed into the hollow chambers 8 by rotating rollers with the protruding rams, thereby further compacting it with increased contact pressure and pressing it into the desired shape. The highly compressed material can then be transported via the conveyor 7 to the ultrasonic welding station 12.

[0040] Furthermore, an ultrasonic device with at least one sonotrode 13 is provided, to which the compacted plastic regrind 1 can be transported by means of the conveying device 7. A pressure element 15, either functionally connected to the sonotrode 13 or not, is associated with the ultrasonic device, whereby alternatively the sonotrode 13 itself can be designed as the pressure element 15. The pressure element 15 or the sonotrode 13 is designed such that a mechanical pressure is applied to the plastic regrind 1 during the application of ultrasonic vibrations.

[0041] In a particularly advantageous embodiment of the device, the plastic regrind 1 is first conveyed by means of a material suction device 2 into a hopper 3, at the lower end of which an intermediate chamber 4 with a rotating impeller 5 is located. This impeller 5 ensures a uniform distribution of the plastic regrind 1 by passing the material through a die 6 and pressing it with slight pressure into a conveying device 7 below (here in the form of a conveyor belt) with granule-shaped hollow chambers 8. The slightly pre-compacted material can 20263498PUET - 10 - are transported to the next station via a conveyor belt 9 at regular intervals.

[0042] In a further embodiment, the compaction station 10 is equipped with rotating rollers on which projecting plungers are arranged. By means of these plungers, the plastic regrind 1 is pressed in a controlled manner into the hollow chambers 8.

[0043] In an additional embodiment, the ultrasonic device is associated with a height and pressure adjustment 14. This height and pressure adjustment 14 allows the sonotrode 13 and / or the pressure element 15 to penetrate the filled hollow chambers 8 to a defined depth and / or to varying depths, thereby enabling targeted control of the welding process.

[0044] The hollow chambers 8 are preferably geometrically designed such that the resulting plastic regranulate grains have a substantially prismatic shape. This prismatic geometry deliberately differs from conventional spherical or cylindrical granules and leads to a comparatively larger specific surface area of ​​the granule grains.

[0045] The prismatic shape of the plastic regranulate granules means that they absorb energy faster than conventional granules when remelted during extrusion or injection molding. In particular, the edges and surfaces of the prisms experience accelerated heat input, which reduces the melting time and results in more uniform plasticization of the material.

[0046] The ultrasonic device moves the sonotrode 13 up and down in a pulsed manner; the sonotrode is also equipped with protruding pressure elements 15. Precise height and pressure adjustment 14 allows the pressure elements 15 to be inserted to varying depths into the filled hollow cavity. - 11 -chambers 8 penetrate, thereby specifically optimizing the welding process. At the same time, the sonotrode 13 generates uniform ultrasonic vibrations that plasticize the regrind 1 and reliably weld it together without completely melting it.

[0047] After ultrasonic welding, the recovered plastic regranulate 18 is preferably guided through a (passive) cooling section 16 before reaching a receiving area 19, which is advantageously funnel-shaped. The receiving area 19 is preferably connected to a further material extractor 2a, for example via an extraction box 20, through which the plastic regranulate 18 can be extracted by vacuum from the hollow chambers 8 into a container 21 such as a silo, an octabin, or a bag by means of the further material extractor 2a, and can thus be used for further processing.

[0048] This innovative process significantly reduces the energy required for granulation, as the regrind does not need to be completely melted. This minimizes thermal degradation and preserves the mechanical and chemical properties of the regranulate. At the same time, the granulation process becomes more efficient and gentler on the material, thus improving the quality of the plastic regranulate.

[0049] The plastic regranulate produced according to the invention differs structurally from extruded granules in that it does not have a completely homogenized melt structure. Rather, the original fragment structure of the plastic regrind remains in the interior of the granule, which reduces the thermal stress on the material and minimizes the degradation of polymer chains.

[0050] In contrast to conventional methods in which the plastic regrind is first melted and then cooled again, the method according to the invention enables direct compaction-20263498PUET - 12 - ing and welding of the plastic regrind. This avoids unnecessary temperature cycles, which reduces material wear and increases the reusability of the recyclates.

[0051] In addition, the need for cooling capacity for subsequent water or air cooling of the pellets is eliminated, further reducing the overall energy consumption of the granulation process. At the same time, the material properties of the recycled plastics are preserved in the long term.

[0052] Thanks to its compact design, the device can be seamlessly integrated into existing production lines, enabling the inline granulation of production rejects without requiring additional space. Companies benefit from increased resource efficiency, as reject material can be recycled directly on-site – without external service providers or large-scale facilities. This not only leads to lower disposal and transport costs but also promotes a sustainable circular economy by processing plastic waste directly within the company and reintroducing it into production.

[0053] The inventive combination of multi-stage compaction, application of ultrasonic vibrations under mechanical pressure, and targeted local energy input enables the granulation of the plastic regrind 1 into a homogeneous melt mass without complete homogenization. This reduces the energy requirement compared to extrusion-based processes. At the same time, the internal structure of the plastic regranulate particles, composed of several plastic fragments, is retained.

[0054] The device with conveying unit 7, compaction station 10, sonotrode 13, optional height and pressure adjustment 14, cooling section 16, roller scraper 17, intake 19 and preferably extraction box 20 enables a compact, modular system, which is best-20263498PUET - 13 - can be integrated into production lines. This makes the invention particularly suitable for energy-efficient inline granulation of production residues and recycled materials.

Claims

20263498PUET - 14- PATENT CLAIMS 1. Method for granulating plastic ground materials (1) comprising the following process steps: a) Introducing the plastic regrind (1) into several hollow chambers (8) arranged or formed on a conveying device (7), wherein the plastic regrind (1) is pre-compacted with a first contact pressure during this pressing process; b) Transport of the pre-compacted plastic regrind (1) to a compaction station (10) where it is further compacted within the hollow chambers (8) with a second contact pressure that is higher than the first contact pressure; c) Feeding the compacted plastic regrind (1) to an ultrasonic device with at least one sonotrode (13), d) subjecting the compacted plastic regrind (1) to ultrasonic vibrations by means of the at least one sonotrode (13), wherein During the application of ultrasonic vibrations to the plastic material (1), a mechanical pressure is applied to the plastic material (1), the pressure being generated by the sonotrode (13) itself and / or by a pressure element (15) that is operatively connected or not operatively connected to the sonotrode (13).

2. Method according to claim 1, characterized by the fact that The plastic material being ground (1) is force-fitted against the hollow chambers (8) during the application of the ultrasonic vibrations. 20263498PUET - 15 - 3. Method according to claim 1 or 2, characterized by the fact that the ultrasonic vibrations are introduced under the mechanical contact pressure in such a way that the heat generated by friction and / or vibration damping is generated at least predominantly at contact surfaces between adjacent plastic fragments of the plastic regrind (1), so that plasticization is essentially limited to edge zones of the plastic fragments of the plastic regrind (1).

4. Method according to a preceding claim, characterized in that The plasticization of the edge zones is carried out by a local dissipation of the ultrasonic energy limited to contact surfaces between adjacent plastic fragments of the plastic regrind (1).

5. Method according to a preceding claim, characterized in that by dissipation of the ultrasonic energy occurring predominantly at contact surfaces between adjacent plastic fragments of the plastic regrind (1) and by a time-limited energy effect, a complete heating of the plastic fragments is prevented, so that core areas of the plastic fragments of the plastic regrind (1) remain below the melting temperature.

6. Method according to a preceding claim, characterized in that The plastic regrind (1) is formed in prism-shaped hollow chambers (8). 20263498PUET - 16- 7. Method according to a preceding claim, characterized in that The plastic regranulate grains have a prismatic shape due to the geometry of the hollow chambers (8).

8. Method according to a preceding claim, characterized in that The plastic regranulate grains, which are only welded at the edges, are selectively broken down into smaller plastic fragments during the subsequent thermal melting process, resulting in accelerated and more homogeneous melting.

9. Method according to a preceding claim, characterized in that The ultrasonic vibrations are generated with a frequency in the range of 15 kHz to 40 kHz.

10. Method according to a preceding claim, characterized in that During granulation, the plastic ground material is not completely homogenized and the original fragment structure inside the granules is retained.

11. Method according to a preceding claim, characterized in that During granulation, the plastic regrind (1) does not fully mix or melt into a homogeneous mass, so that the interior of the plastic regranulate grains retains a structure composed of several plastic fragments. 20263498PUET - 17 - 12. Method according to a preceding claim, characterized in that the introduction, transport and feeding of the plastic regrind (1) between process steps a) to c) is carried out by means of a timed conveying device (7).

13. Device for granulating plastic ground materials (1), a) with a conveying device (7) and hollow chambers (8) arranged or formed on this conveying device (7) for receiving the plastic regrind ( 1 ), wherein b) the device comprises at least one device by means of which the plastic regrind (1) is pressed into the hollow chambers (8), characterized in that c) the device comprises a compaction station (10) to which the pre-compacted plastic regrind can be transported by means of the conveying device (7), wherein d) the compaction station (10) is designed to further compact the plastic regrind (1) within the hollow chambers (8) with a contact pressure increased compared to b), wherein e) the device comprises an ultrasonic device with at least one sonotrode (13) to which the compacted plastic regrind can be transported by means of the conveying device (7), wherein f) the sonotrode (13) and / or a pressure element (15) operatively connected or not operatively connected to the sonotrode (13) is designed to apply a mechanical contact pressure to the plastic regrind (1) during the application of ultrasonic vibrations to the plastic regrind (1). - 18 - 14. Device according to claim 13, characterized by the fact that it comprises a material suction device (2) and a hopper (3) into which the plastic regrind (1) is conveyed by means of the material suction device (2), wherein an intermediate chamber (4) with a rotating impeller (5) is arranged at the lower end of the hopper (3), which is designed to achieve a uniform distribution of the plastic regrind (1) by striating the plastic regrind (1) through the die (6) and pressing it into the hollow chambers (8) with defined pressure.

15. Device according to claim 13 and / or 14, characterized by the fact that The compaction station (10) comprises rotating rollers with protruding punches by means of which the plastic regrind (1) is pressed into the hollow chambers (8).

16. Device according to one of claims 13 to 15, characterized by the fact that The ultrasonic device includes a height and pressure adjustment (14) by means of which the sonotrode 13 and / or the pressure element 15 can penetrate into the filled hollow chambers (8) to a defined depth and / or to different depths, thereby optimizing the welding process.

17. Device according to one of claims 13 to 16, characterized by the fact that it includes a cooling section (16) through which the recovered plastic regranulate (18) is passed after ultrasonic welding. 20263498PUET - 19 - 18. Device according to one of claims 13 to 17, characterized by the fact that it includes a recording (1 ) in which the plastic regranulate (18) removed from the hollow chambers (8) falls.

19. Device according to claim 18, characterized by the fact that it includes a further material suction device (2a) by means of which the plastic regranulate (18) is extracted by vacuum from the hollow chambers (8) into a container (21).

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