Method for recycling plastic materials

Abstract

The invention relates to a method and to an assembly for recycling plastic materials, comprising the following processing steps: a) reprocessing the raw material, wherein the material, if necessary, is comminuted and brought into a fluid-like form and heated and permanently mixed, while preserving the lumpiness and pourability thereof, and optionally the viscosity thereof is increased and/or it is degassed, softened, dried and/or crystallized; b) melting the reprocessed material, at least so much that filtration is possible; c) filtering the melt in order to remove impurities; d) homogenizing the filtered melt; e) degassing the homogenized melt; and f) discharging and/or subsequently processing the melt, such as by granulation, blown film processing, with said processing steps being carried out consecutively in the order listed.

Claims

1. A system for recycling a material, comprising: (a) at least one reprocessing unit, configured to form a reprocessed material by heating and mixing the material while retaining a particulate and flowable form of the material; (b) at least one melting unit configured to form a melt by melting the reprocessed material at least to a point where filtration of the melt is possible; (c) at least one filtration unit configured to filter the melt to form a filtered melt; (d) at least one homogenization unit configured to homogenize the filtered melt, wherein the homogenization unit comprises first and second homogenizers, wherein the first homogenizer comprises a Maddock shearing element, wherein the second homogenizer comprises a cylindrical rotatable body having an outer surface with a plurality of projections, wherein the first homogenizer receives the filtered melt and generates a first homogenized melt, and wherein the second homogenizer receives the first homogenized melt and generates a second homogenized melt; (e) at least one degassing unit configured to degas the second homogenized melt to form a degassed melt; and (f) at least one member of the group consisting of: at least one discharge unit configured to discharge the degassed melt from the system to form a discharged melt; and at least one subsequent processing unit configured to process the degassed melt to form a processed melt, wherein the reprocessing, melting, filtration, homogenization, degassing, and discharge or subsequent processing units are serially connected in the above order, wherein the temperatures of each of the first and second homogenized melts are equal to or greater than the highest temperature of the temperatures of the reprocessed material, the melt, the filtered melt, the degassed melt, and the discharged or processed melt.

2. The system of claim 1, wherein the reprocessing, melting, filtration, homogenization, degassing, and discharge or subsequent processing units are connected in series consecutively and directly in spatial order without intermediate units.

3. The system of claim 1, wherein the temperatures of each of the first and second homogenized melts are greater than the temperature of the discharged or processed melt.

4. The system of claim 1, wherein the homogenization unit is configured such that the filtered melt is sheared and mixed therein or is subjected to an intensive shear stress and tensile stress and is greatly accelerated.

5. The system of claim 1, wherein the melting, filtration, homogenization, and degassing units lie on a common longitudinal axis.

6. The system of claim 1, further comprising a unit configured to add nucleating media into the material, wherein the unit configured to add the nucleating media into the material is disposed downstream of the filtration unit and upstream of the degassing unit.

7. The system of claim 1, further comprising a cooling mechanism disposed downstream of the degassing unit, wherein the cooling mechanism is configured to cool the degassed melt.

8. The system of claim 7, wherein the cooling mechanism is configured to cool the degassed melt by less than or equal to 20%.

9. The system of claim 7, wherein the cooling mechanism is configured to cool the degassed melt by 5% to 10%.

Description

(1) Below, the inventive process and the inventive arrangement are described by means of examples and with reference to the figures, where

(2) FIG. 1 shows a sketched schematic view of an inventive arrangement;

(3) FIG. 2 shows a concrete embodiment of an inventive arrangement;

(4) FIGS. 3a and 3b show the results of comparative experiments with printed foils;

(5) FIGS. 4 and 5 show the results of comparative experiments with foils to which adhesive labels are attached.

(6) FIG. 1 shows an arrangement or configuration for recycling plastics. The configuration includes from left to right a reprocessing unit 1, which as a rule is a conventional cutter compactor or reprocessing bin containing rotating mixing and comminuting tools process and if need be comminute the presented plastic material. The material is permanently in freely flowing form and is always kept particulate and flowable by the mixing and comminuting tools in spite of the increased temperature. In reprocessing unit 1, the material is not yet molten, bust at best heated to a temperature just below the melting point, in particular to a temperature in the range of the material's Vicat softening point. Depending on the type of polymer to be processed, the polymer is already degassed in this early processing step, softened, dried, crystallized and/or increased in viscosity. If practicable, a vacuum can be applied in reprocessing bin 1. Various designs of such reprocessing units 1 have been well known in prior art. Only as an example, reference is made to EP 123 771 B, EP 390 873 B, AT 396 900AT 407 235, At 407 970, etc.

(7) In the lower part of reprocessing unit 1 a melting unit 2 is connected, in particular compacting extruder. The melting unit 2 melts the reprocessed material at least to a point where filtration of the material is possible. In the arrangement according to FIG. 1, the melting unit 2 is immediately and directly connected to reprocessing unit 1, for which various conventional connecting means, radial or tangential, are known. This has the advantage that the mixing and agitating tools in reprocessing unit 1 stuff or bring the softened plastic material into the input region of melting unit 2.

(8) Alternatively, the material can also be conveyed to the melting unit 2 via an intermediate unit, for example a non-compressing transfer device such as a stuffing auger, in particular an auger with constant thread depth which connects the reprocessing unit 1 directly or indirectly with the melting unit 2, but does not allow a continuous material stream into melting unit 2.

(9) Downstream from melting unit 2 is a filtration unit 2 for filtering the melt. Various designs of such melt filters are also known in prior art. For example, solid foreign bodies, unwanted polymers and/or non-molten polymer residues are removed in that manner.

(10) Subsequently the melt passes into a homogenization unit 4. This usually consists of a rotating body such as an auger, which is designed to have a certain sequence of shearing regions and mixing regions. The intensive mixing of the polymer for homogenization is accomplished by complex flow conditions in the interior of the rotating body or auger or in the various auger sections. Apart from axial flows in conveying direction there are also radial flows and axial flows against the conveying direction, so-called leakage flows. In the shearing regions, the temperature of the melt is increased, while in the mixing regions the sheared particles are mixed together with the less sheared particles, resulting in a certain temperature exchange. In that manner, unwanted particles are comminuted and distributed, and the melt is effectively homogenized and prepared for degassing.

(11) Directly downstream, a degassing unit 5 is provided to remove any gas bubbles and gas enclosures from the homogenized melt. Various arrangements are also know in prior art that can effectively remove gas from the melt. Thus, for example, the auger can be very long, a pressureless zone can be provided, or the plastic material can be degassed via a thin film or tube.

(12) On the very right in the schematic view according to FIG. 1 is a discharge unit 6 and a subsequent processing unit 7. The discharge unit 6 serves to transfer the degassed melt to subsequent processing unit 7. The latter can be, for example, a granulating unit, a blow film unit or an injection moulding unit which turns the melt back into a solid form again, for example into a granulate or a foil.

(13) In the embodiment shown in FIG. 1, units 1 to 7 are series connected, and the plastic material passes through units 1 to 7 in the prescribed order continuously from left to right. Furthermore in the configuration according to FIG. 1, the individual units are immediately and directly coupled together, and the material passes from each unit consecutively and directly without intermediate steps to the next unit. Further units, in particular intermediate storage, transfer augers, etc. are possible, but not shown in FIG. 1. That is why the arrangement according to FIG. 1 is relatively short and compact.

(14) Units 2 to 7. i.e. melting unit 2 to subsequent processing unit 7, are on a common longitudinal axis, i.e. are arranged behind each other. This makes the entire arrangement very narrow and space-saving.

(15) Furthermore, a control means is provided which can regulate the temperatures in each individual unit. In that manner, the temperature can be set as required anywhere in the processing chain.

(16) Advantageously the temperature is regulated such that the temperature T4 in homogenization unit 4 or the temperature T4 of the material or the melt during homogenization, but at least at the end of homogenization, but in any case before the degassing begins in degassing unit 5, is as high or higher than in each of the other processing steps or in any other unit of the arrangement. Thus for example, the temperature T2 in melting unit 2, the temperature T3 in filtration unit 3, the temperature T5 in degassing unit 5, the temperature 6 in discharge unit 6, and the temperature T7 in subsequent processing unit 7 are lower than or at a maximum as high as the temperature 4 in homogenization unit 4.

(17) Furthermore, a unit 8 is provided for the addition of nucleating media, via which carbon dioxide, nitrogen or water, etc, can be added to the melt. Such nucleating media are added in particular in homogenization unit 4 just before or after homogenization, but in any case after filtration or also before degassing.

(18) In discharge unit 6, a melt cooling device 9 is provided for cooling the melt as it is discharged from the degassing unit 5. This device may consist, for example, of a cylinder or an auger. The temperature of the melt is cooled by as much as 20%, preferably by 5 to 10%.

(19) FIG. 2 expands upon and is based on FIG. 1 and shows in detail a concrete embodiment of an advantageous arrangement to implement the process according to the invention.

(20) This arrangement comprises of a reprocessing unit 1 in form of a pot-shaped bin or cutter compactor 1 into which the plastic material to be processed is filled at the top. In the area of the bottom 33 of bin 1, a tool 34 is pivoted in conventional manner about a vertical axis in the middle of bin 1 and rotated via a shaft 35 that passes through bottom 33 and is driven by a motor 36. The tool 34 has at least two radial arms 37 provided with working edges 38 that are designed as cutting edges for the plastic material. These working edges 38 mix the plastic material and may also comminute it if required.

(21) The plastic material thus processed is moved into a melting unit 2, namely in a housing 10 of a first auger section 11. This auger section 11 extends into an opening 12 formed by housing 10. When the tools 34 rotate about the axis of shaft 35, the plastic material rotation in bin 1 rises up in the form of a mixing spout along the bin walls, which is indicated by arrows 13. The centrifugal force exerted upon the rotating plastic material supports the intake of the plastic material through opening 12 into housing 10 of auger 11, which is tangentially connected to bin 1. Alternatively, auger housing 10 can also be almost radially connected to bin 1. The core diameter of the first auger section 11 enlarges in the direction away from opening 12, which compresses and plasticizes the plastic material pulled in by auger section 11.

(22) The plasticized material is discharged from housing 10 of the first auger section 11 through openings 14 into filtration unit 3 and flows via connecting channels 15 to at least one filter 16 which filters out the coarse contaminants contained in the plastic melt.

(23) After passing filtration unit 3, the plasticized material passes through connecting channels 15 and via intake openings 17 into a homogenization unit 4 located in the interior of another housing 18. Arranged in homogenization unit 4 is a homogenizer 40 which is coaxially aligned with auger 11 and has the form of a cylindrical rotating body, whereby homogenizer 40 rotates inside housing 18 and thus exerts a shearing and mixing force upon the polymer film or tube that flows around it. To increase the mixing affect and also the shearing effect, a large number of projections 41 is arranged on the outer surface of homogenizer 40. Any gases that form can already escape in this section.

(24) Also in housing 18, a second auger section 19 is pivoted which connects coaxially to homogenizer 40. This second auger section 19 conveys the plasticized plastic material into a degassing section or degassing unit 5, past degassing openings 20 through which the gases escaping from the plastic material are discharged, collected and if need be passed on to be further used.

(25) After passing these degassing openings 20, the plastic material is conveyed via a discharge unit 6 in the form of a discharge auger with a slight shear effect to an outlet 21, to which tools or subsequent processing units 7, such as granulating devices, can be connected.

(26) Practicably the two auger sections 11, 19 are located in drilled holes 40 or 41 of the two housings 10, 18, whereby the drilled holes are in coaxial alignment to each other and both have the same diameter. The coaxial alignment of the two auger sections 11, 19 and the homogenizer 40 allows that in a simple manner, these two auger sections 11, 19 are united in a single component with a common core, and that these two auger sections 11, 19 can be driven together from one side, i.e. from the left side in FIG. 2, The rotating direction of the two auger sections 11, 19 is indicated by an arrow 23.

(27) To promote degassing of the processed plastic material in housing 18, the degassing unit 5 has a pressureless zone 27 that is located in the area of intake opening 17 and degassing opening 20 and is formed by a part of auger section 19 with a reduced core diameter. After degassing opening 20, this reduced core diameter again increases to a full core diameter of discharge unit 6 to ensure that the plastic material is again under pressure and thus sufficiently plasticized.

(28) In the embodiment shown in FIG. 2, units 1 to 7 are also series connected, and the plastic material or the melt runs through units 1 to 7 continuously in the prescribed order. In addition, the individual units are spatially immediately and directly coupled with each other, and the material passes, from each individual unit consecutively and directly and without intermediate steps to the next unit downstream. Units 2 to 6, i.e. melting unit 2 to discharge unit 6 also lie on a common longitudinal axis, and their augers are axially arranged behind each other, which makes the entire arrangement very small and space-saving.

(29) Without deviating from the core of the invention, various embodiments of the arrangement are possible. Thus, in each unit, for example, single augers, double augers or even multiple augers are possible. Furthermore, the individual processing steps can be operated under atmospheric conditions or with the support of a vacuum.

(30) Numerous design embodiments are possible for each individual unit, which persons skilled in the art can take from prior art. The temperatures, dwell times and other parameters depend for the most part on the material to be processed or recycled and persons skilled in the art can adapt these. However, the inventive advantages can only be achieved if persons skilled in the art use the process and/or the arrangement of the present invention.

(31) The examples below demonstrate the advantageous technical effects of the inventive process and the inventive arrangement:

(32) Contaminated plastic materials such as foils that were printed or had adhesive labels were processed in comparative experiments, namely once with an arrangement known from prior art without homogenization according to the conventional method, and parallel to it with the inventive arrangement according to the inventive process with homogenization, whereby the directly comparable operating parameters, such as temperatures, throughputs, dwell times, pressure, etc. were kept as comparable as possible in the cutter compactor or during subsequent processing.

EXAMPLE 1

Processing of Printed Plastic Foils

(33) FIGS. 3a and 3b show a comparison of the original material and the resulting final products. The left portion in FIG. 3a and FIG. 3b shows the initial foil to be treated in the form of a plastic foil with coloured printing. The right portion shows a foil produced 100% from the regenerate after processing.

(34) It can be seen that in the process according to prior art or with the arrangement according to prior art, the material is not completely degassed, but that small gas bubbles, caused by the decomposed printer inks, remain in the final product. With the inventive process, in particular through homogenization prior to degassing, the degassing result is further improved, and that hardly any gas bubbles can be seen.

EXAMPLES 2 AND 3

Processing of LD-PE Film with Paper Labels

(35) FIGS. 4 and 5 also show a comparison: on the left side is the result after to the previous process, and on the right side is the result after the process according to the invention. In both cases, the original material consisted of packaging foils of LD-PE, contaminated by paper labels. The contamination rate was about 1% of total weight. FIGS. 4 and 5 show microscopic views of film made 100% of the recycled material after processing. Filtration fineness in FIG. 4 is 110 μm, in FIG. 5 it is 125 μm.

(36) It is recognizable that on the right side (process according to the invention), the contaminants, especially paper articles, adhesive residues, but also gas bubbles, are fewer, smaller and more finely distributed than on the left side (prior art). Therefore the mechanical and optical properties of the foils on the right side are better.

(37) In all cases, the proportion of contaminants in the final product is clearly reduced, and the quality therefore increased.