System for recycling plastic materials and waste

Abstract

The present invention relates to a system for recycling plastic materials and waste with an injection device (1) which in turn comprises a plasticisation unit (2) and an injection unit (3), such that the plasticisation unit (2) comprises a plastifying spindle actuated by means of a rotary actuation configured to extrude a material from forced feed means at the inlet of the plasticisation unit (2). The plasticisation unit (2) and the injection unit (3) are connected via a connection element (4) configured to enable the passage of the plastified mass into the plasticisation unit (2) towards a feed inlet of the injection unit (3).

Description

[0001] PLASTIC MATERIALS AND WASTE RECYCLING SYSTEM

[0002] Technical field

[0003] The present invention relates to a system for recycling plastic materials and waste in film format, whether shredded or not, with very low densities and / or high humidity (up to 12% w / w). This is another object of the invention.

[0004] State of the art

[0005] US patent application No. US 2022 / 0009140 A1 describes an injection device for a molding machine that includes a molding compound reservoir and an injection unit. The molding compound reservoir is configured to provide a plasticized mass and to eject the plasticized mass through a discharge opening, and a connecting device is coupled to the discharge opening of the molding compound reservoir and a feed opening of the injection unit, and is configured to direct the plasticized mass from the molding compound reservoir to the injection unit. The connecting device includes a hinged element, and with the hinged element a relative movement between the molding compound reservoir and the injection unit can be realized.

[0006] This document essentially describes a plastic injection machine incorporating a plasticizing screw that literally melts the plastic material. The molten material then passes through a filtration system and then a degassing system. The filtration stage cleans the material, while the degassing stage removes the gas created by contamination of the recycled plastic material. This solution is ideal for essentially rigid plastics, but is not suitable for film-like plastics, which comprise the majority of post-consumer plastics and are also the most difficult to recycle. Therefore, a system and method are required to recycle this type of plastic.

[0007] Document WO 2006077207 A1 is considered the closest to the state of the art and discloses a plant and a method for processing heterogeneous plastic materials from waste recycling, to obtain a plastic article. The plant comprises: (I) a preprocessing unit that receives the waste at the input and subjects it to at least one crushing and screening process, where the preprocessing step is carried out; and (II) a mixing and plasticizing unit into which the mass of heterogeneous plastic materials, originating from the preprocessing unit, is introduced to carry out the plasticizing step. This plasticizing unit comprises a forced feed screw and a main extrusion unit, with which degassing devices are associated, to carry out a strong degassing of the plastic mixture, at least during extrusion.The degassed plastic mixture then passes through a conveying element (not shown) to an injection unit to form the desired article in the molds. The injection unit comprises a storage head, an injection plunger associated with the storage head, and injects the molten plastic under pressure through an adjacent injection chamber, which consists of a manifold that then divides into several branches that feed the injectors, each with a relatively wide cross-section, to better fill the molds. The injectors also allow for high compaction of the molded material, improving the mechanical characteristics of the article.Advantageously, both the injection pusher and the pressure unit are fed by a hydraulic plant, not shown, and consisting in a substantially known manner of a pump, a tank and other accessories such as filters, level controls, control valves, cylinders, connections and pipes.

[0008] However, the plant according to this document is a system for cleaning, grinding, and extruding materials, which are then connected to an injection molding machine. In the present invention, the materials are not ground, but the extruded material is transported to an injection molding machine. This document does not describe a compactor, forced feed, or a combination thereof. Both systems are specifically designed to feed material in film form.

[0009] Document WO 2006077218 A1 describes a device for processing heterogeneous plastic materials from the separate and / or unseparated collection of waste, to obtain a plastic mixture with specific technical and / or structural characteristics. The device comprises a mixing and plasticizing unit, in which an extrusion unit is arranged, into which the heterogeneous plastic materials are introduced, and in which they are transformed into the substantially molten heterogeneous plastic mixture. The device also comprises degassing elements, associated with the extrusion unit, which carry out a strong degassing action on the plastic mixture, at least before it exits the extrusion unit. The extrusion unit is formed by a forced feed screw and a main extruder. Optionally, a second extruder is provided, capable of operating in series or in parallel with the main extruder.Downstream of the device, an injection unit is provided with injection means that inject the molten plastic mixture into a mold to manufacture the article.

[0010] Document WO 2020115335 A1 relates to a process for the recovery of plastics, in particular polypropylene plastic material, comprising in sequence at least the steps of: crushing and reducing the material to be recovered into flakes of predetermined dimensions, conveying the flakes in the form of flakes mixed with air, mixing the flakes mixed with air, conveying and weighing the flakes mixed with air, compacting and dosing the flakes, separating them from the air, performing a forced feeding of materials comprising compacted flakes free of air, process materials and additives, extruding both the materials exiting the forced feeding stage and the mineral fillers provided to complete the recovery process of the plastic material. The invention also relates to a plant for carrying out the process.

[0011] Explanation of the invention

[0012] The object of the present invention is a system and method for recycling plastic materials and waste, in accordance with the claims accompanying this specification.More specifically, the recycling system for plastic materials and waste of the invention comprises one or more injection devices, each of said injection devices comprising a plasticizing unit and an injection unit, the plasticizing unit comprising a plasticizing screw, which is driven by a rotary drive; and the plasticized mass reaches the feed inlet of the injection unit through a connection element; and the injection unit comprises a rotating extrusion screw, configured to perform a second additional plasticization of the plasticized mass fed from the plasticizing unit and inject it into a molding unit through an outlet nozzle of the injection unit.In order to use plastic materials in film format, plastics with very low specific density, high humidity, and / or contamination, the present invention recommends the use of forced feeding means at the inlet of the plasticizing unit, selected from: (a) a compactor; (b) forced feeding by means of a screw; or (c) a combination of the foregoing. It also comprises a contaminant filter and a degasser, where the filter will be located immediately after the degasser between the plasticizing unit and the injection unit.

[0013] In a particular embodiment, the forced feeding means by means of a compactor comprise a conveyor belt connected to a compactor that has rotating blades in its lower part.

[0014] In another particular embodiment, the semi-molten material is extracted from the compactor according to one of the following options: (a) through the bottom of the compactor by gravity toward the plasticizing unit; and / or (b) through a lower transport screw.

[0015] In another particular embodiment, the screw-type forced feed consists of a suction system that carries the plastic film to a tank comprising lower blades; and where the lower part of the tank contains the outlet for the material that falls by gravity onto a horizontal screw that carries it to a vertical screw with variable geometry, which is responsible for feeding: (a) the compactor of the agglomeration system; or (b) the plasticizing unit directly.

[0016] In another particular embodiment, the injection unit comprises an injection screw selected from: (a) a conventional screw; (b) a pusher compactor; or (c) a double screw configured for compounding or additivation processes.

[0017] In another embodiment of the invention, a tandem extrusion system is described, where the first extruder is a single-screw extruder and the second extruder is a twin-screw extruder. Before the first extruder, the system has a compactor, so that it is possible to work with plastic films. The current state of the art uses a single filter between the first extruder and the second extruder such that, once the material is filtered, the molten material is passed to the second twin-screw extruder to provide a higher quality product. This embodiment—advantageously—includes at least one additional filter, preferably continuous, at the end of the twin-screw extruder to obtain higher quality extruded material. Furthermore, another filter is advantageously added after the first filter and the melt pump, just before entering the second extruder.Thanks to this additional filter, the material is less contaminated before entering the second extruder, which could optionally have a filter at the end of the extruder. Finally, in one particular embodiment, a degassing system is added between the first and second extruders.

[0018] Throughout the description and claims, the word "comprises" and its variants are not intended to exclude other technical features, additives, components, or steps. For those skilled in the art, other objects, advantages, and features of the invention will be apparent in part from the description and in part from the practice of the invention. The following examples and drawings are provided by way of illustration and are not intended to restrict the present invention. Furthermore, the present invention covers all possible combinations of particular and preferred embodiments indicated herein.

[0019] Brief description of the drawings

[0020] Below, a very brief description is given of a series of drawings that help to better understand the invention and that are expressly related to an embodiment of said invention that is presented as a non-limiting example thereof.

[0021] Figure 1 - Shows the invention in its embodiment with a filter.

[0022] Figure 2 - Shows the invention in a degasser and filter.

[0023] Figure 3 - Shows the invention in two other alternative embodiments

[0024] Figure 4 - Shows the invention in another embodiment with forced feeding Figure 5 - Shows the invention with tandem extrusion.

[0025] Detailed explanation of an embodiment of the invention

[0026] The attached figures illustrate different embodiments of an injection device.

[0027] 1 for a recycling system according to the invention. The injection device comprises a plasticizing unit 2 and an injection unit 3. The plasticizing unit 2 comprises a plasticizing screw, which is driven by a rotary drive. The plasticizing screw extrudes a material that is fed through various embodiments for the feed system, as will be described below. Via a connection element 4, the plasticized mass reaches the feed inlet of the injection unit 3. In this embodiment, the injection unit 3 is shown by the rotating extrusion screw, which further plasticizes the plasticized mass fed from the plasticizing unit 2 and injects it into a molding unit 7 through an outlet nozzle of the injection unit 3.

[0028] This structure is typical of the systems known and described in the prior art. However, although this solution is ideal for rigid plastics, it is not useful for plastics in film form, which constitute the majority of post-consumer plastics and, furthermore, those that are most difficult to recycle.

[0029] To be able to use plastics in film or film format, as well as unshredded films with moisture levels of up to 12% w / w, the described structure must be modified. To this end, the present invention proposes two solutions:

[0030] Establish a feeding system with a compactor (Figures 1-3). Establish a forced feeding system (Figure 4).

[0031] Feeding with compactor

[0032] If the material is not crushed and / or contains a moisture content greater than 2% w / w, a compactor must be installed. This compactor operates as follows. The material rises on a conveyor belt 11 and enters a compactor 12, which has rotating blades at its bottom. The rotating blades reduce the size of the input material. Furthermore, applying heat to the compactor 12 helps reduce the moisture content of the raw material.

[0033] An outlet for the semi-molten material is located at the bottom of the side of the compactor 12, and the material is transferred to the plasticizing unit 2. Alternatively, the semi-molten material can also be expelled from the compactor 12 via a conveying screw, which is optional. Ultimately, once the semi-molten material is removed from the agglomerator, it is transported to the plasticizing unit 2 and subsequently to the injection unit 3.

[0034] In a practical embodiment shown in FIG. 1(A) the outlet of a filter 5 is coupled directly to the injection unit 3 through connection 4. In another practical embodiment (FIG. l(B)) the outlet of the filter 5 is coupled to a simple extruder (3a) and from there to the injection unit 3. In yet another practical embodiment (FIG. l(C)) it can be seen how the outlet of the filter is coupled to a twin-screw extruder (3b) and from there to the injection unit 3.

[0035] In the practical embodiment of FIG.2 it is shown how a degasser 6 is incorporated at the outlet of the filter 5 and, in any case, before the injection unit 3. However, the combined use of the degasser 6 and the filter 5 is better shown in FIG.3.

[0036] In FIG. 3(A) it can be seen how a degasser 6 is incorporated in the plasticizing unit 2, combined with a filter 5 and a degasser 6 coupled to the outlet of this first filter 5 of the plasticizing unit. In this same embodiment, a second degasser 6 is included in a twin-screw extruder (3b), before a second filter 5, whose outlet is coupled to the injection unit 3. FIG. 3(B) is the same embodiment, but the injection unit 3 is formed by a piston instead of a screw as in FIG. 3(A).

[0037] Force-feeding

[0038] This forced feeding system can be complementary to the feeding of the agglomerator (as shown in figure 2) or its output can be directly coupled to the inlet of the plasticizing unit 2.

[0039] Screw forced feeding consists of a suction system that carries the plastic film to a tank 200. This tank 200 comprises lower blades 201 that rotate, but do not cut (they are not knives, unlike the compactor 12 in the agglomerator). At the bottom of the tank 200 is the outlet for the material that falls by gravity onto a horizontal screw 202 that carries it to a vertical screw 203 of variable geometry, which is responsible for feeding: (a) the compactor 12 of the agglomeration system; or (b) the plasticizing unit 2 directly from the injection device 1.

[0040] For both embodiments, the injection unit 3 comprises an injection screw 31, which may be: (a) a conventional screw; (b) a push-type compactor; or (c) a twin screw, which is the preferred embodiment. The use of a twin screw in the injection unit 3 allows for the introduction of compounding material.

[0041] Additivation or "compounding" involves preparing plastic formulations by mixing and / or blending polymers and additives in the molten state to achieve desired characteristics. These blends are automatically dosed at fixed set points, usually via feeders / hoppers. It is primarily a mixture of copolymers with additives such as antioxidants, UV stabilizers, and other value-added agents, and sometimes a strengthening component such as glass fiber is added. There are several critical criteria for achieving a homogeneous blend of the different raw materials. Dispersive and distributive mixing, as well as heat, are important factors. Therefore, the ability to use these types of materials is an additional advantage for the present invention.

[0042] In conclusion, thanks to the present invention, it is possible to feed the injection device 1 with films or materials of very low specific density. Furthermore, with the addition of the degasser 6 and filter 5 assembly, it is possible to work with highly contaminated materials.

[0043] Finally, it should be noted that plasticizing unit 2 can be expanded with an additional unit, which can be single- or double-screw (i.e., at least one screw). This additional plasticizing unit 2 would then be connected to injection unit 3. Similarly, it should be noted that injection unit 3 can have either a single screw or a piston, when larger volumes are required.

[0044] Tandem extrusion

[0045] As shown in Figure 5, the system of the invention comprises a feed belt 51 that feeds a compactor 52 to feed a first single-screw extruder 53 (that is, the plasticizing unit 2 in the previous embodiments), with the particularity that, before the molten material pump 54, there is a filter A, preferably a continuous filter.

[0046] In a particular embodiment, a filter B is additionally provided, after the molten material pump 54 and before the second twin-screw extruder 55 (that is, the injection unit 3 in the embodiments of Figures 1 to 4).

[0047] Finally, a filter C is advantageously incorporated at the outlet of the second extruder 55 to improve the quality of the product obtained. Optionally, a degassing system may be located between the first extruder 53 and the second extruder 55. However, in another particular embodiment of the invention, it is possible to place one or more degassing systems in the first extruder 53 and / or in the second extruder 55.

Claims

Claims 1.- A recycling system for plastic materials and waste with an injection device (1) comprising, in turn, a plasticizing unit (2) and an injection unit (3), such that the plasticizing unit (2) comprises a plasticizing screw driven through a rotary drive configured to extrude a material from forced feeding means at the inlet of the plasticizing unit (2), and where the plasticizing unit (2) and the injection unit (3) are connected through a connection element (4) configured to enable the passage of the plasticized mass in the plasticizing unit (2) towards a feed inlet of the injection unit (3).which is characterized in that the forced feeding means at the entrance of the plasticizing unit (2) are selected from: a conveyor belt (11) connected to a compactor (12) that has rotating blades in its lower part; or a forced feed (13) with a screw consisting of a suction system that carries the plastic film to a tank (200) comprising lower blades (201); and where in the lower part of the tank (200) is the exit of the material towards a horizontal screw (202) that carries it to a vertical screw (203) of variable geometry, which is the one in charge of feeding: (a) a hopper of a first extruder; or (b) the plasticizing unit (2) directly; or a combination of the above. 2.- The system according to claim 1 comprising a degasser (6) coupled to the outlet of a filter (5) and to the inlet of the connection element (4) of the injection unit (3).

3. The system according to any one of the preceding claims, comprising a degasser (6) at least in the plasticizing unit (2); and / or in an extruder (3a, 3b) located between the plasticizing unit (2) and the injection unit (3). 4.- The system according to claim 1 wherein the semi-molten material is extracted from the compactor (12) according to one of the following options: (a) by the lower part of the compactor (12) by driving the rotating blades towards the plasticizing unit (2); and / or (b) through a lower transport screw.

5. The system according to any one of the preceding claims, wherein the injection unit (3) comprises an injection screw (31) which may be: (a) a conventional screw; (b) a pusher compactor; or (c) a double screw configured for compounding or additivation processes.

6. The system according to any one of the preceding claims, wherein the plasticizing unit (2) further comprises an additional plasticizing unit with at least one screw, such that this additional plasticizing unit is connectable to the injection unit (3); and wherein the injection unit (3) can use either a screw or a piston when it is desired to produce larger volume parts.

7. The recycling system for plastic materials and waste according to claim 1, comprising a compactor (52) for feeding the plasticizing unit (2) consisting of a first single-screw extruder (53), and an injection unit (3) consisting of a second twin-screw extruder (5) connected to the outlet of the first extruder (53) by means of a melt pump (54), and at least one first filter (A) at the outlet of the first extruder (53) before the melt pump (54) and at least one second filter (C) at the outlet of the second extruder (55). 8.- The system according to claim 7 comprising a third filter (B) at the outlet of the molten material pump (54) before the inlet of the second twin-screw extruder (55). 9.- The system according to claim 7 or 8 comprising a degassing system between the first extruder (53) and the second extruder (55). 10.- The system according to one of claims 7 to 9 comprising one or more degassing systems in the first extruder (53), in the second extruder (55), or in the first and second extruders (53,55).

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