Apparatus for processing recycled plastic material for granule forming, and associated method

Abstract

An apparatus (1) for processing recycled plastic material for granule forming, comprising: – means (2) for the extrusion of plastic material to be recycled in order to obtain a stream of melted plastic material that can move along an advancement direction (A), – means (3) for introducing a deodorization fluid in the stream of melted plastic material, and – an assembly (4) for degassing the stream of melted plastic material additized with the deodorization fluid; the introduction means (3) are arranged between the extrusion means (2) and the degassing assembly (4) along the advancement direction (A).

Description

[0001] APPARATUS FOR PROCESSING RECYCLED PLASTIC MATERIAL FOR GRANULE FORMING, AND ASSOCIATED METHOD

[0002] The present invention relates to an apparatus for processing recycled plastic material for granule forming and to an associated method.

[0003] There is an increasing need in the plastics processing field to use recycled materials in combination with or as a replacement of virgin raw material, due to both economic and ethical issues.

[0004] The process of forming granules of plastic material conventionally entails melting the material to be recycled inside an extruder, filtering and degassing the melted material, and then forming the granules.

[0005] The plastic material to be recycled retains odor-producing impurities (residues of labels, glues, substances contained in the original bottles, low- melting plastic components) which, if not evacuated appropriately, risk polluting the granules obtained, making them unsuitable for use as a replacement of virgin raw material.

[0006] One known method for deodorization of recycled plastic material consists in so-called stripping, which provides for the introduction of a liquid, for example water possibly mixed with scented substances, during the advancement of the mass of melted plastic material along the extruder. The liquid, as it mixes with the melted plastic material, tends to turn into steam, trapping the odor-producing substances, which are then removed in the subsequent degassing step.

[0007] This method is generally used in apparatuses provided with twin- screw extruders, in which it is possible to provide one or more longitudinal sections in which the melted plastic material is not under pressure and at which the stripping liquid is introduced in the mass of melted plastic material.

[0008] For single-screw extruders, instead, this method is difficult to be applied since it entails the need to considerably lengthen the extruder in order to provide a portion in which the melted plastic material is not under pressure and into which to introduce the stripping liquid. However, lengthening the extruder entails an increase in the holding time of the melted plastic material inside it, with the consequent risk of deterioration.

[0009] The aim of the present invention is to eliminate the above-mentioned drawbacks of the background art by devising an apparatus for processing recycled plastic material for granule forming and an associated method that allow to achieve optimal deodorization of the recycled plastic material regardless of the type of extruder in use, without risking compromising the mechanical and rheological characteristics of the material being processed.

[0010] Within this aim, an object of the present invention is to avoid entailing structural complications or increased space occupations with respect to the apparatuses conventionally used.

[0011] A further object of the present invention is to allow effective control of the processing parameters in order to achieve optimal quality of the granules of plastic material.

[0012] A further object of the present invention is to have a structure that is simple, relatively easy to provide in practice, safe in use, effective in operation, and relatively low in cost.

[0013] This aim and these and other objects that will become more apparent hereinafter are all achieved by the present apparatus for processing recycled plastic material for granule forming according to claim 1 that follows, and optionally provided with one or more of the characteristics given in dependent claims 2-15.

[0014] The above aim and objects are furthermore all achieved by the present method for processing recycled plastic material for granule forming according to the indications of claim 16 that follows, and optionally provided with one or more of the characteristics given in dependent claims 17-20.

[0015] Further characteristics and advantages of the present invention will become better apparent from the detailed description of a preferred but not exclusive embodiment of an apparatus for processing recycled plastic material for granule forming, illustrated by way of non-limiting example in the accompanying drawings, wherein:

[0016] Figure 1 is a perspective view of an apparatus for processing recycled plastic material for granule forming according to the invention;

[0017] Figure 2 is a front elevation view of the apparatus according to the invention, in which the associated management and control system has been shown schematically;

[0018] Figure 3 is a lateral elevation view of the apparatus according to the invention;

[0019] Figure 4 is a sectional view taken along the plane IV-IV of Figure 3;

[0020] Figures 5 and 6 are views of a portion B of Figure 4 at the injection port with the corresponding flow control element in the closed and open configuration, respectively;

[0021] Figures 7 and 8 are views similar to the preceding ones, in which a variation of the flow control element is shown in the closed and open configuration, respectively.

[0022] With reference to the figures, an apparatus for processing recycled plastic material for granule forming is generally designated by the reference numeral 1.

[0023] The apparatus 1 comprises extrusion means 2 for the extrusion of the plastic material to be recycled in order to obtain a stream of melted plastic material moving along an advancement direction, designated by the arrows A in the figures.

[0024] The extrusion means 2 can be of the type of a conventional singlescrew or twin-screw extruder, and therefore they are not shown in detail in the figures. Preferably, the extrusion means also provide for a filtration stage for the melted plastic material, which is also not shown in detail since it is of a known type. Said extrusion means 2 may therefore comprise one or two parallel screws supported in rotation within a box-like shell; by means of the adjustment of the rotation rate of the screw(s) it is possible to change the speed at which the melted plastic material passes through, along the advancement direction A, and therefore the flow rate and the holding time of the material.

[0025] The extrusion means 2 are provided with an outlet 9 for the discharge of the stream of melted plastic material.

[0026] Moreover, the apparatus 1 comprises introduction means 3 for introducing a deodorization fluid into the stream of melted plastic material and an assembly 4 for degassing the stream of melted plastic material added with the deodorization fluid for the removal of the gaseous component that is present in the mass of melted plastic material together with the odorgenerating impurities.

[0027] The deodorization fluid can be in the liquid state or in the gaseous state.

[0028] For example, a deodorization fluid of the type of water, water mixed with scented substances (fragrances) or another liquid with an evaporation temperature above 75°C, preferably comprised between 100°C and 150°C, may be used.

[0029] Alternatively, a deodorization gas of the type of carbon dioxide, nitrogen or other inert gas can be used.

[0030] Preferably, the degassing assembly 4 consists of an intake manifold 5 for the melted plastic material associated in communication with a chamber 6 to which a partial vacuum is applied by means of a conventional vacuum pump, not shown. Between the manifold 5 and the chamber 6 there is generally a forming die 7 for the melted plastic material, which is introduced into the chamber 6 in the form of portions having a constant cross-section, of the type of spaghetti or the like, to maximize the surface exposed to the partial vacuum inside said chamber and thus the removal of the gaseous component.

[0031] Preferably, the die 7 is supported by a deck 8 which can be removed to facilitate its cleaning and replacement operations.

[0032] The degassing assembly 4 is provided with an inlet 10 for the stream of melted plastic material.

[0033] Second extrusion means, or another system for recycled plastic granule forming, not shown since they are of a known type, are conventionally provided downstream of the degassing assembly 4, along the advancement direction A.

[0034] The introduction means 3 are arranged downstream of the extrusion means 2 and upstream of the degassing assembly 4 along the advancement direction A.

[0035] The introduction means 3 are therefore arranged externally to the extrusion means 2 so as not to entail structural and / or dimensional changes of said extrusion means.

[0036] The introduction means 3 comprise a channel 11 for the passage of the stream of melted plastic material, which is arranged between the outlet 9 and the inlet 10 and means 12 for feeding the deodorization fluid along said channel.

[0037] In greater detail, the channel 11 is associated hermetically, by means of the interposition of gaskets or the like, with the outlet 9 and the inlet 10; therefore, a positive working pressure, i.e., a pressure higher than the ambient pressure, is present inside the channel 11.

[0038] The working pressure present inside the channel 11 is directly correlated to the geometry of said channel and of the die 7 and to the pumping capacity of the extrusion means 2.

[0039] The feeding means 12 comprise at least one deodorization fluid supply duct 13, provided with an injection port 14 associated in fluid communication with the channel 11. Preferably, the duct 13 is associated with the discharge of a variable flow rate pump 15 for delivering deodorization fluid under pressure.

[0040] Preferably, the duct 13 has a decreasing transverse cross-section proximate to the port 14 so as to act as a nozzle.

[0041] In the embodiment shown, the duct 13 has an S-shaped longitudinal extension, being constituted by two horizontal portions joined by a vertical central portion; however, the geometry of the duct 13 may vary as a function of the requirements of the specific application and of the available space. The shape of the duct 13 is such as to not significantly affect the overall space occupation of the apparatus 1.

[0042] Advantageously, the feeding means 12 comprise a flow control element 16 for the port 14, which is accommodated within the duct 13 and can move between an open configuration and a closed configuration of the port.

[0043] The duct 13, at the port 14, is contoured internally so as to form a sealing seat 25 against which the flow control element 16 abuts in the closed configuration.

[0044] Preferably, the flow control element 16 is shaped like a stem which is accommodated along the duct 13 and has a transverse cross-section that is smaller than that of the duct, so as to form an interspace for the passage of the deodorization fluid. The flow control element is longitudinally movable with respect to the duct 13.

[0045] In a first embodiment, the flow control element 16 is contained within the duct 13 (Figures 5 and 6).

[0046] The flow control element 16 is normally in the configuration for opening the port 14 (Figure 6) and can be moved to assume the configuration for closing said port (Figure 5).

[0047] The feeding means 12 may, therefore, comprise means 17 for moving the flow control element 16 between the open and closed configurations.

[0048] Such movement means 17 can be of the manual or, preferably, automatic type.

[0049] In the embodiment shown, the movement elements 17 comprise a threaded 18 element mated with a female thread associated with the duct 13 and supported in rotation inside it with a portion that protrudes externally with respect to said duct and is associated with a control knob 19 or rotational actuator, not shown. The threaded element 18 is integrally connected to the flow control element 16 so as to move it axially between the open and closed configurations when it is screwed / unscrewed with respect to the corresponding female thread.

[0050] In a variation, shown in Figures 7 and 8, the flow control element 16 has an end which protrudes into the channel 11 through the port 14. Said end is associated with a first working surface 26 which is exposed to the pressure inside the channel 11. For example, the end of the flow control element may be associated with a plate 27 which forms the first working surface 26.

[0051] Moreover, the flow control element 16 is associated with a second working surface 28, which is exposed to the pressure of the deodorization fluid along the channel 11. For example, the flow control element 16 may be provided with an annular raised portion 29 which forms the second working surface 28.

[0052] Preferably, the extensions of the first and second working surfaces are substantially the same. The term "substantially" is understood as meaning except for the usual machining and assembly tolerances of the component parts.

[0053] In this case, no means for moving the flow control element 16 are required, since it is the difference between the pressures acting on the working surfaces 26 and 28 that determines its positioning in the open configuration (Figure 7) or closed configuration (Figure 8).

[0054] When the pressure of the deodorization fluid acting on the second working surface 28 is higher than the pressure inside the channel 11 acting on the first working surface 26, the flow control element maintains the open configuration (Figure 7).

[0055] Vice versa, when the pressure inside channel 11 acting on the first working surface 26 is higher than the pressure of the deodorization fluid acting on the second working surface 28, the flow control element moves to the closed configuration (Figure 8).

[0056] However, alternative embodiments of the flow control element 16 are not excluded.

[0057] Moreover, the feeding means 12 might provide for two or more ducts 13 communicating with the channel 11 through respective ports 14 cooperating with corresponding flow control elements 16 of the type described above.

[0058] Usefully, the introduction means 3 comprise means 24 for mixing the stream of melted plastic material and the deodorization fluid that flow along the channel 11.

[0059] Such mixing means 24 are accommodated within the channel 11 downstream of the feeding means 12.

[0060] For example, said mixing means 24 may provide for a conventional static mixer accommodated along a portion of the channel 11 downstream of the port 14.

[0061] Preferably, the apparatus 1 comprises first means 20 for measuring the pressure of the deodorization fluid along the supply duct 13. The first measurement means 20 are adapted to detect a first pressure value.

[0062] Moreover, the apparatus 1 preferably comprises second means 21 for measuring the pressure within the passage channel 11. The second measurement means 21 are adapted to detect a second pressure value.

[0063] The second measurement means 21 are associated with the channel 11 downstream of the introduction means 3.

[0064] The apparatus may, therefore, be provided with an electronic management and control unit 22 functionally associated in input with the first and second measurement means 20 and 21 to compare the first and second pressure values and activate an intervention when the second pressure value is higher than the first pressure value. The electronic unit 22 can be of the type of a conventional programmed or programmable electronic board.

[0065] If the pressure along the channel 11 is higher than the pressure with which the deodorization fluid is supplied, there is the risk that the melted plastic material advancing along said channel might re-enter along the duct 13 through the port 14, causing malfunctions or failures.

[0066] In this case, the electronic unit 22 can activate a warning alarm for the assigned operators and / or act on the adjustment of the apparatus 1 to restore an appropriate difference between the supply pressure of the deodorization fluid and the pressure inside the channel 11 in which the melted plastic material flows.

[0067] If the apparatus 1 provides for automatic means 17 for the movement of the flow control element 16, the electronic unit 22 can be functionally associated in output with said movement means 17 to actuate the movement of the flow control element 16 to the closed configuration when the second pressure value is higher than the first pressure value, such as to prevent the melted plastic material from flowing back along the duct 13.

[0068] Prior to performing this intervention, the electronic unit 22 can activate an increase in the supply pressure of the deodorization fluid by acting on the pump 15 and / or reduce the flow rate of melted plastic material exiting the extrusion means 2, for example by actuating a reduction in the rotation rate of the corresponding screw(s). If a first pressure value higher than the second pressure value cannot be restored, the electronic unit 22 can activate the closing of the port 14 by means of the movement of the flow control element 16.

[0069] If the apparatus 1 is provided with a flow control element 16 of the type shown in Figures 7 and 8, the electronic unit 22 still allows to monitor its operation, activating appropriate corrective actions so as to restore a pressure inside the channel 11 that is lower than the supply pressure of the deodorization fluid, so that flow control element 16 autonomously returns to the open configuration.

[0070] Moreover, the apparatus 1 may comprise third means 23 for measuring the pressure from the inside of the degassing assembly 4. Such third measurement means 23 are adapted to detect a third pressure value.

[0071] In this case, the electronic unit 22 can be functionally associated in input to the third measurement means 23 in order to compare the third pressure value with a reference value and activate an intervention when the third value is higher than the reference value.

[0072] The reference value can be stored or set by the user in the electronic unit 22 as a function of the degree of vacuum that one wishes to apply in the degassing assembly 4.

[0073] If the third pressure value, corresponding to the pressure inside the degassing assembly, is higher than the reference value, the treatment does not allow optimal purification of the melted plastic material, and therefore the electronic unit 22 can activate a warning alarm for the assigned operators and / or act on the adjustment of the apparatus 1 to restore the optimal operating conditions.

[0074] For example, the electronic unit 22 can be functionally associated in output to the pump 15 in order to reduce the flow rate of deodorization fluid introduced in the melted plastic material when the third pressure value is higher than the reference value.

[0075] Before performing this intervention, or alternatively, the electronic unit 22 can intervene by increasing the rotation rate of the vacuum pump of the degassing assembly 4 and, if the desired degree of vacuum is not achieved, reduce the flow rate of deodorization fluid introduced into the melted plastic material to allow proper removal of the gaseous component as a function of the partial vacuum obtained within the degassing assembly 4.

[0076] The operation of the apparatus 1 is therefore as follows.

[0077] The plastic material to be recycled is introduced in the extrusion means 2 in which, by means of a known technology, a stream of melted plastic material flowing along the advancement direction A is obtained.

[0078] The melted plastic material in output from the outlet 9 flows through the channel 11, along which the deodorization fluid is first added at the introduction means 3 and mixing of said fluid into the stream of melted plastic material is then performed by virtue of the mixing means 24.

[0079] If the deodorization fluid is in the liquid state in contact with the hot melted plastic material, it tends to evaporate, obtaining a gaseous component mixed with the melted plastic material.

[0080] The stream of melted plastic material mixed with the deodorization fluid in the gaseous state then enters the degassing assembly 4 by passing through the inlet 10. In the degassing assembly 4, by means of a known technology, the gaseous component mixed with the melted plastic material is evacuated.

[0081] Downstream of the apparatus 1 it is possible to provide additional extrusion means or a different system of a known type for obtaining granules of recycled plastic material.

[0082] During operation, the electronic unit 22 with the measurement means 20, 21, 22, if provided, allows to monitor and manage the operation of the apparatus 1 as described above.

[0083] The method according to the invention for processing recycled plastic material for granule forming comprises the following sequence of steps, performed in succession one after the other:

[0084] - a step of extruding plastic material to be recycled, so as to obtain a stream of melted plastic material that can move along an advancement direction,

[0085] - a step of introducing a deodorization fluid within the stream of melted plastic material, and

[0086] - a step of degassing the stream of melted plastic material added with the deodorization fluid. The introduction step is therefore performed after the extrusion step and before the degassing step. The introduction step is performed separately from the extrusion step and the degassing step.

[0087] In greater detail, the introduction step consists in mixing with the stream of melted plastic material a deodorization fluid fed with a pressure that is higher than the pressure of said stream. Preferably, the deodorization fluid is fed with a pressure that is at least 20% higher than that of the stream of melted plastic material.

[0088] Moreover, the introduction step consists in mixing with the stream of melted plastic material a deodorization fluid fed with a flow rate comprised between 1% and 15% of that of the stream of melted plastic material. Preferably, the flow rate of the deodorization fluid is 2-10% higher than that of the stream of melted plastic material.

[0089] In practice it has been found that the described invention achieves the proposed aim and objects and in particular the fact is stressed that the apparatus and method according to the invention allow to achieve effective deodorization of the melted plastic material, regardless of the extrusion means used and without entailing structural and / or dimensional changes of said means.

[0090] Moreover, the invention allows to perform constant monitoring of the process in progress, so as to optimize the effectiveness of the treatment performed.

[0091] The invention thus conceived is susceptible of numerous modifications and variations, all of which are within the scope of the appended claims.

[0092] All the details may furthermore be replaced with other technically equivalent elements.

[0093] In practice, the materials used, as well as the contingent shapes and dimensions, may be any according to the requirements without thereby abandoning the protective scope of the claims that follow. The disclosures in Italian Patent Application No. 102022000024528 from which this application claims priority are incorporated herein by reference.

[0094] Where technical features mentioned in any claim are followed by reference signs, those reference signs have been included for the sole purpose of increasing the intelligibility of the claims and accordingly such reference signs do not have any limiting effect on the interpretation of each element identified by way of example by such reference signs.

Claims

CLAIMS1. An apparatus (1) for processing recycled plastic material for granule forming, comprising means (2) for the extrusion of plastic material to be recycled in order to obtain a stream of melted plastic material that can move along an advancement direction (A), introduction means (3) for introducing a deodorization fluid in the stream of melted plastic material, and an assembly (4) for degassing the stream of melted plastic material additized with the deodorization fluid, characterized in that said introduction means (3) are arranged between said extrusion means (2) and said degassing assembly (4) along the advancement direction (A).

2. The apparatus (1) according to claim 1, characterized in that said introduction means (3) comprise a channel (11) for the passage of the stream of melted plastic material arranged between an outlet (9) associated with said extrusion means (2) and an inlet (10) associated with said degassing assembly (4) and means (12) for feeding the deodorization fluid along said passage channel (11).

3. The apparatus (1) according to claim 2, characterized in that said channel (11) is associated hermetically with said outlet (9) and said inlet(10), a positive working pressure being present within the passage channel(11).

4. The apparatus (1) according to claim 2, characterized in that said feeding means (12) comprise at least one supply duct (13) for supplying deodorization fluid having an injection port (14) associated in fluid communication with said passage channel (11).

5. The apparatus (1) according to claim 4, characterized in that said feeding means (12) comprise a flow control element (16) of said injection port (14) which is accommodated within said supply duct (13) and can movebetween an open configuration and a closed configuration of said port.

6. The apparatus (1) according to claim 5, characterized in that said flow control element (16) is associated with a first working surface (26) exposed to the pressure inside the channel (11) and with a second working surface (28) exposed to the pressure inside the duct (13).

7. The apparatus (1) according to one or more of the preceding claims, characterized in that said introduction means (3) comprise means (24) for mixing the stream of melted plastic material and deodorization fluid in transit along said passage channel (11).

8. The apparatus (1) according to one or more of the preceding claims, characterized in that said mixing means (24) are accommodated along said passage channel (11) downstream of said feeding means (12) along the advancement direction (A).

9. The apparatus (1) according to one or more of the preceding claims, characterized in that it comprises first means (20) for measuring the pressure of the deodorization fluid along said supply duct (13) which are adapted to detect a first pressure value.

10. The apparatus (1) according to one or more of the preceding claims, characterized in that it comprises second means (21) for measuring the pressure within said passage channel (11) which are adapted to detect a second pressure value.

11. The apparatus (1) according to one or more of the preceding claims, characterized in that it comprises an electronic management and control unit (22) functionally associated in input with said first and second measurement means (20, 21) in order to compare the first and second pressure values and activate an intervention when the second pressure value is greater than the first pressure value.

12. The apparatus (1) according to claims 5 and 11, characterized in that said feeding means (12) comprise automatic means (17) for the movement of said flow control element (16) between the open and closedconfigurations, and in that said electronic unit (22) is functionally associated in output with said movement means (17) to actuate the movement of said flow control element (16) from the open configuration to the closed configuration when the second pressure value is greater than the first pressure value.

13. The apparatus (1) according to one or more of the preceding claims, characterized in that it comprises third means (23) for measuring the pressure within said degassing assembly (4) which are adapted to detect a third pressure value.

14. The apparatus (1) according to claims 11 and 13, characterized in that said electronic unit (22) is functionally associated in input with said third measurement means (23) in order to compare the third pressure value with a reference value and activate an intervention when the third value is greater than the reference value.

15. The apparatus (1) according to claims 4 and 14, characterized in that said feeding means (12) comprise a variable flow rate pump (15) for the delivery of the deodorization fluid along said supply duct (13) and in that said electronic unit (22) is functionally associated in output with said pump (15) in order to reduce the flow rate of deodorization fluid when the third pressure value is greater than the reference value.

16. A method for processing recycled plastic material for granule forming, comprising a step of extruding plastic material to be recycled so as to obtain a stream of melted plastic material which can move along an advancement direction, a step of introducing a deodorization fluid within the stream of melted plastic material, and a step of degassing the stream of melted plastic material added with the deodorization fluid, characterized in that said introduction step is performed after saidextrusion step and before said degassing step.

17. The method according to claim 15, characterized in that said introduction step consists in mixing the stream of melted plastic material with the deodorization fluid fed with a pressure greater than the pressure of the stream itself.

18. The method according to claim 16, characterized in that the pressure of the deodorization fluid is greater than the pressure of the stream of melted plastic material by at least 1%.

19. The method according to claim 15, characterized in that said introduction step consists in mixing the stream of melted plastic material with the deodorization fluid fed with a flow rate comprised between 1% and 15% of the flow rate of the stream.

20. The method according to one or more of claims 16-19, characterized in that said deodorization fluid is selected from the group comprising water, water added with scented substances, carbon dioxide, inert gases.