WO2004087391A1

WO2004087391A1 - Method and device for plasticizing a plastic material

Info

Publication number: WO2004087391A1
Application number: PCT/AT2004/000054
Authority: WO
Inventors: Helmut Bacher; Helmuth Schulz; Georg Wendelin
Original assignee: Helmut Bacher; Helmuth Schulz; Georg Wendelin
Priority date: 2003-04-01
Filing date: 2004-02-20
Publication date: 2004-10-14
Also published as: AT503334A1; AT503334B1

Abstract

The invention relates to a method for plasticizing a plastic material by means of a plasticizing unit formed by a gear extruder or a gear pump. According to said method, the thermoplastic material is shaped in a container (1) by means of mobile tools (12) located in the same and is heated to a temperature below the softening point and thus softened. Only in this softened state is the material introduced into the plasticizing unit (19) and is only then plasticized therein. The invention also relates to a device for carrying out the inventive method, said device comprising a plasticizing unit (19) housing (31) provided with toothed wheels (20, 21, 41, 42, 44, 45) and the inlet of said housing being fluidically connected to the (18) discharge opening (17) of a container (1). Tools (12) displaced by at least one motor (14) are arranged in the container (1), said tools shaping the plastic material, heating said plastic material to a temperature below the softening point, and thus softening the same.

Description

Method and device for plasticizing plastic material

The invention relates to a method for plasticizing plastic material, the plastic material being plasticized in a gear extruder or in a gear pump. The invention further relates to an apparatus for performing the method.

It is known to use gear extruders for plasticizing and homogenizing rubber mixtures (DE 196 52 924 A1), but the gear extruders shown there are not readily suitable for the continuous plasticization of thermoplastic material, because the properties of the plastic material to be plasticized can be very different, in particular then when goods to be recycled are to be processed. Studies have shown that the direct supply of the plastic material to be processed into the gear extruder, as is proposed for rubber mixtures in DE 196 52 924, leads to difficulties, on the one hand due to the frequently inhomogeneity of the material to be processed, and on the other hand for the reason that the material to be processed, in particular the goods to be recycled, is often in the form of relatively large or bulky parts which resist direct feeding into the gear extruder. The invention is based on the knowledge gained through tests that a suitable pretreatment of the plastic material is required for the processing of plastic material by means of a gear extruder in order to be able to process this material in a targeted manner by the gear extruder. Proceeding from this, the method according to the invention avoids the difficulties mentioned at the outset in that the thermoplastic material in a container is processed by moving tools located in this container and heated to a temperature below the plasticizing temperature and is thereby softened and only in this softened state through a discharge opening of the Container is inserted into the gear extruder or the gear pump and is only plasticized there. This avoids that the use of the gear extruder results in a significant narrowing of the properties of the plastic material to be processed, since by suitable adaptation of the treatment of the plastic material in the container by means of the moving tools or by the resulting heating and softening of the material to be processed can be easily taken up by the gear extruder. The procedure is preferably such that the plastic material is largely homogeneously heated to a temperature close to the plasticizing temperature. Polyolefins are particularly suitable for this, because their preheating in the container by the moving tools to a level close to Melting point temperature is possible. The moving tools simultaneously cause mixing and, if necessary, drying and / or comminution of the processed material and thus homogenization of the temperature distribution in the material, so that the material introduced into the gear extruder or the gear pump has a very narrow temperature spectrum, which is close to the melting point of the respective processing material can be brought.

If a shredding of the material brought into the container is required, the tools can be easily used as shredding tools, e.g. Knife, train. Pre-shredded material (e.g. granules) usually only requires mixing and heating, possibly also drying. Tools that are driven to rotate around at least one vertical axis are suitable for this. The motor energy introduced for this circulation is converted into thermal energy of the processed material by friction of the material on the tools or on the container wall or the material particles. Rotating tools can also be used to:

Press plastic material directly into the gear extruder or gear pump through the discharge opening arranged in the side wall of the container. This ensures that the plasticizing element is filled continuously and as a rule evenly, so that the plasticized material processed by it can be processed continuously without any problems. The introduction of the plastic mass circulating in the container into the gear extruder or the gear pump can be supported by at least one deflector arranged in the container.

To monitor the achievement or compliance with the desired state of the processed plastic material, a direct temperature measurement in the container can take place within the scope of the invention and / or the energy absorbed by the drive motor of the tools can be used and / or the material supply into the container. In the latter two cases, the fact is used that the condition of the material and the amount thereof in the container affect the energy consumed by the motor. The inventive device for performing the inventive

The method is based on a construction with a plasticizing element which carries out the plasticization of the plastic material and has gear wheels, to which the plastic material to be plasticized is fed through an inlet opening of a housing which accommodates the gear wheels. The invention consists in that the inlet opening is in flow connection with the discharge opening of a container in which tools which are moved by at least one drive are arranged and which serve to soften the plastic material introduced into the container by heating it to a temperature below the plasticizing temperature. According to a preferred embodiment of the invention, at least one monitoring device is provided to achieve or maintain this temperature. This monitoring device can have at least one temperature sensor arranged in the container and / or a sensor for the energy absorbed by the drive of the tools and / or a sensor for the amount of plastic material introduced into the container.

As already mentioned, it is advisable to use rotating tools to heat the material to be processed. According to a development of the invention, some tools can be attached to a carrier disk which is driven by the drive for rotation about a vertical axis and whose tools are arranged at least approximately at the height of the discharge opening of the container. Due to the centrifugal force exerted by these tools on the processed material and, if necessary, by a spatula-like design of the tools, the aforementioned pressing of the processed material into the discharge opening and thus intensive feeding of the gear extruder can be achieved. To a certain extent, the carrier disc forms a subdivision of the container interior, so that it is substantially avoided that the material whirled up by the rotating tools and driven in the container to circulate in the form of a mixing drum gets under the carrier disc. However, additional tools can also be fastened on at least one further carrier disk driven for rotation about a vertical axis, which further carrier disk is arranged in the container at a distance above the carrier disk assigned to the discharge opening. This additional carrier disc can sit on the same drive shaft as the carrier disc assigned to the discharge opening, this shaft expediently penetrating the container bottom in a sealed manner and being driven from below. However, it is also possible to drive the shaft from above and constructions are also conceivable in which the two carrier disks are moved by different drives, which can be arranged both below and above the container.

The inlet opening of the plasticizing element is expediently connected directly, that is to say directly, to the discharge opening of the container in order to take full advantage of the filling effect mentioned. In special cases, however, it is conceivable to connect the discharge opening of the container to the inlet opening of the plasticizing member by means of a pipe; in this case, a screw conveyor can be arranged in this pipe.

As tests have shown, a single-stage gear pump forming the plasticizer can only achieve complete plasticization of the processed material to a limited extent, so that this simple arrangement is reserved for cases in which no homogeneous, melt-filtered mass is necessary, but the low melt temperature and the low energy consumption as well as the simple construction of Meaning. If there are higher demands with regard to the melt quality obtained from the plasticizing element, then according to a further development of the invention the plasticizing element has at least two gearwheel pairs arranged one behind the other in the direction of flow of the plastic material. The additional gear pairs form mixing elements. The melt viscosity determines the geometry of these mixing gears and vice versa. If a third gear pair is arranged, the discharge gear pair following the mixing gear pair enables a further improved plasticization and homogenization, but also the generation of higher pressures in the material leaving the plasticizer, so that the resistances exerted by downstream system components, such as melt filters, nozzles, etc., are overcome.

When using at least two pairs of gears, according to a development of the invention, the arrangement is such that, in at least two meshing gears, their teeth mesh without blocking with respect to the plastic material being conveyed. A strict combing of the gears would block the material to be conveyed. This freedom from blocking can be achieved in the context of the invention by designing the teeth of the gears of at least one gear as stub teeth. Further possibilities for achieving freedom from blocking are slots or channels in at least one of the meshing gears and / or a thread cut over the teeth. Finally, it is also possible to have the gears mesh with one another only via the tooth tips.

Further characteristics and advantages of the invention result from the description of exemplary embodiments of a device according to the invention, which are shown schematically in the drawings. Fig. 1 shows a vertical section through a simple embodiment in which only one pair of gears is provided. FIG. 2 is a section along the line II-II of FIG. 1. FIG. 3 shows an embodiment in which two tool carrier disks arranged one above the other are provided in the container. Fig. 4 shows an embodiment with two tool carrier disks in the container and two gear pairs in the gear extruder. FIG. 5 shows an embodiment variant with three gear pairs in the gear extruder. 6 shows gearwheels designed with overflow channels in a perspective view. Fig. 7 shows the formation of mixed grooves in the gear pairs and Fig. 8 shows mixed grooves in the form of threads.

The embodiment according to FIGS. 1 and 2 has a container 1 for the pre-processing of the thermoplastic material, for example polyolefins, polypropylene, polyethylene, etc. This container 1 is filled from above through a filling opening 2 in the direction of arrow 3. If the processing of the plastic material is to take place under vacuum, the container 1 is connected via a line 4 to an evacuation device 5. In this case, one is at the filling opening 2 Lock 6 connected, the lock chamber 7 can be locked by two hydraulically or pneumatically operated slide 8 and is connected via a line 9 to the evacuation device 5. The slide 8 are shown in Fig. 1 in the half-open position. In the container 1 near the bottom 10, a disc 11 is arranged, which as

Carrier for rotating tools 12 is used. These tools can be pure mixing tools and / or, if the material introduced into the container 1 is to be crushed, as a knife. The disc 11 is fastened on a shaft 13 arranged vertically in the axis of the cylindrical container 1, which passes through the container base 10 in a sealed manner and is driven to rotate by a motor 14. The rotation of the tools causes the plastic material in the container 1 to be processed to be whirled up and to rise in the form of a mixing drum 15 along the side wall 16 of the container and, after reaching the maximum height, to fall back inwards towards the center of the container. In its lower region, the container 1 has one in the side wall 16

Discharge opening 17, which in the construction shown in FIG. 1 coincides with the inlet opening 18 of the housing 31 of a plasticizing member 19, which has a gear pair 20, 21 directly adjoining the inlet opening 18. The two toothed wheels 20, 21 mesh with one another and rotate in the direction shown by arrows 22, that is to say in the direction away from the center of the inlet opening 18. This forms at the edge of the inlet opening 18 two feed gaps 23 into which the material to be plasticized is drawn from the discharge opening 17 in the direction of the arrows 24 into the plasticizing member 19. The meshing gears 20, 21 effect kneading and thus plasticizing of the processed plastic material, which is expressed by the pair of gears 20, 21 through a discharge channel 25 in the direction of arrow 39 from the housing 31. In the embodiment shown, the plasticizing element 19 forms a gear pump. However, there can be a nozzle or the like on the discharge channel 25. be connected so that the plasticizing member 19 acts as a gear extruder. The aforementioned mixing or comminution of the goods in the container 1 by means of the tools 12 causes the processed goods to be heated and possibly dried by means of the energy introduced by the motor. This heating is designed in such a way that the material in the container 1 is brought to a temperature just below its plasticizing temperature, that is to say it reaches a softened state, and is only finally plasticized in the plasticizing element 19. This procedure can be carried out in batches or continuously if a suitable ongoing loading of the container 1 is ensured. If the type of plastic material to be processed is uniform and its temperature behavior is known, then it is sufficient Experience to operate the device in a targeted manner. However, if the aforementioned requirements do not apply, or do not meet with certainty, it is advisable to monitor the temperature of the material processed in container 1. For this purpose, at least one temperature sensor 26 can be provided in the container 1, which is connected via a line 27 to a control device 28, the output signal of which is connected to the motor 14 via a line 29 and controls it in such a way that the temperature of the material processed in the container 1 is kept at least approximately at the desired value. This ensures that the material entering the plasticizing member 19 through the discharge opening 17 is sufficiently softened to be gripped and plasticized by the gear wheels 20, 21 of the plasticizing member 19 without any problems.

As an alternative to this, however, the control device 28 can also be designed such that it monitors the energy absorbed by the motor 14, which is dependent on the condition of the material processed in the container 1. If its temperature behavior is sufficiently known, the aforementioned control of the motor 14 can suffice. Another alternative for monitoring the achievement or maintenance of the heated state of the plastic material in the container 1 is to control the material supply into the container 1. The energy absorbed by the motor 14 and thus the average temperature of the processed material in the container 1 also depends on the degree of filling of the container 1.

Another way of influencing the temperature of the processed material is to provide additional heating or cooling of the container 1 and / or the plasticizing element 19. For this purpose, at least one heating and / or cooling winding 30 can be provided on the side wall 16 of the container 1. In the same way, 19 heating and / or cooling channels 32 can be embedded in the housing 31 of the plasticizing element 19. Furthermore, it is expedient to monitor the pressure and temperature of the material mass processed by the plasticizing element 19 and flowing in the discharge channel 25. Suitable sensors 33 can be embedded in the housing 31 for this purpose.

As shown in FIG. 2, one of the gears 20, 21 is keyed onto a shaft 34 which is mounted in the housing 31 and is driven by a motor 35.

It can also be seen from FIG. 2 that the tools 12 fastened on the disk 11 are bent or curved against the direction of rotation (arrow 36) of the disk. This results in a spatula-like impression of the material circulating in the container 1 into the discharge opening 17 of the container 1. While FIG. 1 shows an embodiment with only one tool carrier disk 11, the tools 12 of which at least approximately at the level of the lower feed gap 23 of the gear pair 20, 21 3 shows an embodiment with two tool carrier disks 11 which are arranged one above the other at a distance from one another and which are arranged on one another sit on a common shaft 13 and are driven together by the motor 14 arranged under the tank bottom 10 for rotation. The lower tool carrier disk 11 is arranged analogously to the construction according to FIG. 1, its tools 12 are at least approximately at the height of the lower feed gap 23 and convey the material moved by them into the feed gap 23 due to the effect of centrifugal force and possibly also a spatula. The upper tool carrier disk 11 is arranged somewhat higher than the upper feed gap 23, their tools 12 move the processed plastic material in the form of the mixing drum 15. In the space 38 lying between the two tool carrier disks 11, such a mixing drum 15 can only be formed to a limited extent, since a rise in the circulating material essentially occurs the upper tool carrier disk 11 is limited, the circumference of which can be close to the container side wall 16. Therefore, the material introduced into the container 1 through the filling opening 2 is first grasped by the tools 12 of the upper disk 11 and mixed or, if appropriate, also comminuted in the form of the mixing drum 15. This material can only gradually pass through the annular gap 37 between the container wall 16 and the circumference of the upper disk 11 into the space 38, where it is again picked up and mixed or, if necessary, comminuted again by the tools 12 of the lower disk 11. Only now is the material thus pre-processed and heated to the suitable temperature below the plasticizing temperature and thereby softened, introduced into the gear pump formed by the gear wheels 20, 21, plasticized there and finally discharged through the discharge channel 25 in the direction of arrow 39. This results in a sufficient dwell time of the processed plastic material in the container 1 and thus the desired homogeneous temperature of the plastic compound introduced into the plasticizing member 19. If necessary, more than two tool carrier disks with tools 12 carried by them can be arranged one above the other in the container, as a result of which a further increase in the dwell time of the processed plastic material in the container 1 can be achieved.

In order to avoid that plastic material can climb back through the annular gap 37 from the space 38 back into the container space above the upper disc 11, and to promote the introduction of the plastic material circulating in the space 38 into the upper feed gap 23 of the plasticizing element 19 In the area of this annular gap 37 or in the area of this pull-in gap 23, a deflector 50 may be provided, which is fastened to the inner wall 16 of the container 1 and acts as a guide element which guides the circulating mass into the pull-in gap 23. For this purpose, the end of this deflector 50 which emits the plastic material expediently lies at least approximately at the level of the insertion gap 23 of the upper gear wheel 20.

It is expedient to adjust the temperature of the processed plastic material both in the space 38 and in the container space part located above the upper disc 11 40 monitor. For this purpose, a temperature sensor 26 is provided for each of these rooms 38, 40. The signals supplied by them are connected to the control device 28 via lines 27 and thereby suitably control the motor 14. While in the previously described embodiments, the plasticizer

19 had only a single pair of gears, according to FIG. 4 a further pair of gears 41, 42 is arranged in the housing 31 of the plasticizing member 19, which serves as a pair of mixing gears and ensures a higher melt quality in the discharge channel 25. Since the gear pair 41, 42 must rotate in the direction of arrows 43 and meshes with the gear wheels 20, 21 in order to achieve the required discharge direction (arrow 39), the gear wheels 20, 21 must rotate (arrows 22) such that a single one is centered between the two gear wheels 20, 21 lying intake gap 23 of the gear pump results. The tools 12 of the lower disk 11, which are approximately at its height, convey into this feed gap 23 in the manner already described. The embodiment according to FIG. 5 has a third pair of gearwheels 44, 45 in the housing 31 of the plasticizing member 19, which meshes with the gearwheels 41, 42 and conveys it into the discharge channel 25 in the direction of arrow 39. The directions of rotation of the three gear pairs are indicated by arrows 22. Such an embodiment enables the generation of higher pressures to overcome resistances of plant parts connected to the discharge channel 25, such as melt filters, extruder nozzles, etc. Also in such an embodiment, a deflector 50 can be provided, which acts in the same way as the deflector 50 in the embodiment 3, and the circumferential softened plastic material in the interior of the container 1 passes into the feed gap 23 of the upper gear 20 of the first pair of gears. As shown in FIG. 5, a wide feed angle α or β applies to both feed gaps 23, so that sufficient feeding of the first gear pair 20, 21 is ensured.

If more than one gear pair is provided, the delivery of the plasticized material into the discharge channel 25 could be blocked and the gear pump or gear extruder could break if adjacent gear pairs meshed strictly with one another and there was no freedom from blocking , Such freedom from blocking can be achieved in a simple manner in that the teeth 46 of the intermeshing gear wheels 41, 42 and 44, 45 are designed as stub teeth, that is, they do not mesh strictly with one another, but only in the area of the tooth tips. As shown in FIG. 7, gaps 47 then form between the teeth 46 of the two mixing gears 41, 42, through which the processed material can flow. 6, the teeth 46 of meshing gears can be interrupted by grooves 48 running in the circumferential direction of the gears. This results in a kneading of the processed material, which favors the plasticization of the same. Slots provided on teeth 46 may act in a similar manner.

Another way of preventing the material from blocking on meshing gears 41, 42 is to cut a thread 49 (FIG. 8) over the teeth of these gears, which can be carried out in a simple manner in terms of production. In all of these cases, the processed thermoplastic material has the possibility of flowing through the free spaces formed, that is, of "running over" the gear pair in question.

The conveying effect of the gears and possibly also the mentioned alternative for the processed plastic can also be supported in that at least one of the gear pairs 20, 21 or 41, 42 or 44, 45 has a helical toothing or an arrow toothing.

The design variants shown in the figures consist of gears, the axes of which are directed horizontally. This is not absolutely necessary. Rather, these axes can also be arranged at an incline or, if necessary, even be vertical.

In all embodiments, it is possible to connect a melt filter and / or nozzles of a granulating device to the discharge channel 25.

Claims

1 patent claims:

1. A process for plasticizing plastic material, the plastic material being plasticized in a gear extruder or in a gear pump, thereby

5 characterized in that the thermoplastic material is processed in a container (1) by moving tools (12) located in this container (1) and heated to a temperature below the plasticizing temperature and thereby softened and only in this softened state through a discharge opening ( 17) of the container (1) is inserted into the gear extruder or the gear pump and is only plasticized there.

2. The method according to claim 1, characterized in that the plastic material is largely homogeneously heated to a temperature close to the plasticizing temperature. 5

3. The method according to claim 1 or 2, characterized in that the plastic material in the container (1) by at least one vertical axis rotating tools (12) is processed. 0

4. The method according to any one of claims 1 to 3, characterized in that the plastic material by means of the tools (12) through the in the side wall (16) of the container (1) arranged discharge opening (17) of the container (1) in the gear extruder or the gear pump is pushed in. 5

5. The method according to any one of claims 1 to 4, characterized in that in the container (1) circulating plastic material by means of at least one deflector (50) is introduced into the gear extruder or the gear pump.

6. The method according to any one of claims 1 to 5, characterized in that the plastic material is also dried and / or crushed during processing by means of the moving tools (12).

7. The method according to any one of claims 1 to 6, characterized in that a direct temperature measurement in the container (1) and / or that of the drive motor (14) of the tools (12) for monitoring the achievement or compliance with the heated state of the plastic material ) absorbed energy and / or the Material supply in the container (1) is used.

8. The method according to any one of claims 1 to 7, characterized in that the

Processing of the plastic material in the container (1) is carried out under vacuum.

9. The device for carrying out the method according to one of claims 1 to 8, with a plasticizing material carrying out gears (20, 21) having plasticizing member (19), to which the plastic material to be plasticized through an inlet opening (18) of the gearwheels ( 20, 21) having a housing (31), characterized in that the inlet opening (18) is in flow connection with the discharge opening (17) of a container (1) in which tools moved by at least one drive (14) are arranged, which for processing and softening the plastic material introduced into the container (1) by heating the same to a level below

Plasticizing temperature serving temperature.

10. The device according to claim 9, characterized in that at least one monitoring device or control device (28) is provided for the temperature of the plastic material located in the container (1).

11.Device according to claim 10, characterized in that the control device

(28) with at least one temperature sensor (26) arranged in the container (1) and / or a sensor for the energy absorbed by the motor (14) of the tools (12) and / or a sensor for the amount of the in the container (1) contributed

Plastic material is connected.

12. Device according to one of claims 9 to 11, characterized in that some tools (12) are attached to a carrier disc (11) which is driven by the motor (14) for rotation about a vertical axis and at least their tools (12) are arranged approximately at the level of the discharge opening (17) of the container (1).

13. The apparatus according to claim 12, characterized in that additional tools (12) are attached to at least one further, driven for rotation about a vertical axis support plate (11), which are at a distance above that of the discharge opening

(17) associated carrier disc (11) is arranged in the container (1).

14. Device according to one of claims 9 to 13, characterized in that at the At least one deflector (50) designed as a guide element is provided on the inner wall of the container (1) and guides the plastic material moved in the container (1) into the discharge opening (17) of the container (1).

15. Device according to one of claims 9 to 14, characterized in that the container (1) is connected to an evacuation device (5) and a lock (6) is connected to the filling opening (2) of the container (1).

16. Device according to one of claims 9 to 15, characterized in that the inlet opening (18) of the housing (31) of the plasticizing member (19) directly to the

Discharge opening (18) of the container (1) is connected.

17. Device according to one of claims 9 to 16, characterized in that the plasticizing member (19) has at least two gear pairs (20, 21 or 41, 42 or 44, 45) arranged one behind the other in the flow direction of the plastic material.

18. Device according to one of claims 14 to 17, characterized in that a feed gap (23) of the lower gear (21) of the pair of gears (20, 21) adjacent to the inlet opening (18) at the level of the lowest in the container (1) rotating Tools (12) and the pull-in gap of the upper gear (20) of this gear pair (20, 21) are at the level of the end of the deflector (50) which releases the plastic material.

19. The apparatus according to claim 18, characterized in that in at least two intermeshing gears (41, 42 or 44, 45) their teeth (46) mesh without blocking with respect to the plastic material conveyed.

20. The apparatus according to claim 19, characterized in that in order to achieve freedom from blocking, the teeth of the gear wheels (41, 42 or 44, 45) at least one

Gear pair are designed as stub teeth and / or have slots or channels and / or a thread (49) cut over the teeth (46) and / or mesh only over the tooth tips.

2 I.Device according to one of claims 9 to 20, characterized in that the direction of the axes of the gears (20,

21, 41, 42, 44, 45) deviates from the horizontal, possibly directed vertically.

22. Device according to one of claims 9 to 21, characterized in that at least one heating device (30) and / or cooling device for the container (1) and / or for the housing (31) of the plasticizing member (19) is provided.

23. The device according to any one of claims 9 to 22, characterized in that at least one pair of gears has helical teeth or arrow teeth.

24. Device according to one of claims 9 to 23, characterized in that a melt filter and / or at least one pelletizing nozzle is connected to discharge channels (25) of the plasticizing member (19).