DEVICE AND METHOD FOR PRODUCING A DYED AND AN UNDYED PLASTIC MELT

Abstract

A device for producing a dyed plastic melt and an undyed plastic melt includes a multi-shaft screw extruder, a first metering installation, a second metering installation, and a control installation for selecting between a first operating mode for producing the dyed plastic melt and a second operating mode for producing the undyed plastic melt. The first metering installation serves for feeding an undyed plastic material through a first infeed opening into a housing of the multi-shaft screw extruder, and the second metering installation serves for feeding at least one color granulate through a second infeed opening into the housing. The plastic material is fed exclusively by way of the first infeed opening such that residual color granulate or dyeing agent contained therein, respectively, which is still located in the second metering installation or in the region of the second infeed opening does not contaminate the undyed plastic melt.

Claims

1. A device for producing a dyed plastic melt and an undyed plastic melt, the device comprising: a multi-shaft screw extruder for providing a plastic melt, the multi-shaft screw extruder having a housing, at least two mutually penetrating housing bores configured in the housing, a first infeed opening, a second infeed opening and at least two treatment element shafts disposed so as to be rotatingly drivable in the housing bores, the first infeed opening and the second infeed opening into the at least two mutually penetrating housing bores; a first metering installation for feeding an undyed plastic material through the first infeed opening into the at least two mutually penetrating housing bores; a second metering installation for feeding at least one color granulate through the second infeed opening into the at least two mutually penetrating housing bores; and a control installation for selecting between a first operating mode for producing the dyed plastic melt and a second operating mode for producing the undyed plastic melt.

2. The device as claimed in claim 1, wherein the control installation is configured such that: in the first operating mode the undyed plastic material by the first metering installation through the first infeed opening, and the color granulate by the second metering installation through the second infeed opening, are capable of being fed into the at least two mutually penetrating housing bores; and in the second operating mode the undyed plastic material by the first metering installation is capable of being fed through the first infeed opening into the at least two mutually penetrating housing bores.

3. The device as claimed in claim 1, wherein the second metering installation comprises a first metering unit for feeding the color granulate, and a second metering unit for feeding a cleaning granulate, the first metering unit and the second metering unit opening into the second infeed opening.

4. The device as claimed in claim 1, wherein the control installation is configured such that in a cleaning mode a cleaning granulate is capable of being fed through the second infeed opening into the at least two housing bores via the second metering installation.

5. The device as claimed in claim 1, wherein a gap is defined between the at least two treatment element shafts, and a width of the gap in relation to an external diameter of the at least two treatment element shafts is greater than or equal to 0.003 and less than or equal to 0.05.

6. The device as claimed in claim 1, wherein the at least two treatment element shafts and a housing internal wall of the housing define a gap, and a width of the gap in relation to an external diameter of the at least two treatment element shafts is greater than or equal to 0.004 and less than or equal to 0.03.

7. The device as claimed in claim 1, wherein the second infeed opening is disposed upstream of the first infeed opening in a conveying direction.

8. The device as claimed in claim 7, wherein each of the at least two treatment element shafts comprises one shaft to provide at least a plurality of shafts, and kneading elements are rotationally fixed on the shafts between the first infeed opening and the second infeed opening.

9. The device as claimed in claim 7, wherein each of the at least two treatment element shafts comprises one shaft to provide at least a plurality of shafts, and screw elements are rotationally fixed on the shafts between the first infeed opening and the second infeed opening.

10. The device as claimed in claim 1, wherein each of the at least two treatment element shafts comprises one shaft to provide at least a plurality of shafts, and screw elements and kneading elements are disposed so as to be rotationally fixed on the shafts downstream of the first infeed opening and the second infeed opening.

11. A method for producing a dyed and an undyed plastic melt, the method comprising the following method steps: providing a multi-shaft screw extruder having a housing, at least two mutually penetrating housing bores configured in the housing a first infeed opening, a second infeed opening and at least two treatment element shafts rotatingly drivable in the at least two mutually penetrating housing bores, the first infeed opening and the second infeed opening into the at least two mutually penetrating housing bores; providing a first metering installation and a second metering installation; selecting between a first operating mode for producing the dyed plastic melt and a second operating mode for producing the undyed plastic melt via a control installation, wherein in the first operating mode an undyed plastic material via the first metering installation through the first infeed opening, and a color granulate via the second metering installation through the second infeed opening, are fed into the at least two mutually penetrating housing bores, wherein in the second operating mode the undyed plastic material via the first metering installation is fed through the first infeed opening into the at least two mutually penetrating housing bores; and operating the multi-shaft screw extruder, the first metering installation and the second metering installation in a selected operating mode.

12. The method as claimed in claim 11, wherein the second metering installation comprises a first metering unit for feeding the color granulate, and a second metering unit for feeding a cleaning granulate, the first metering unit and the second metering unit opening into the second infeed opening.

13. The method as claimed in claim 11, wherein the control installation is configured such that in a cleaning mode a cleaning granulate is capable of being fed through the second infeed opening into the at least two housing bores via the second metering installation.

14. The method as claimed in claim 11, wherein a gap is defined between the at least two treatment element shafts, and a width of the gap in relation to an external diameter of the at least two treatment element shafts is greater than or equal to 0.003 and less than or equal to 0.05.

15. The method as claimed in claim 11, wherein the at least two treatment element shafts and a housing internal wall of the housing define a gap, and a width of the gap in relation to an external diameter of the at least two treatment element shafts is greater than or equal to 0.004 and less than or equal to 0.03.

16. The method as claimed in claim 11, wherein the second infeed opening is disposed upstream of the first infeed opening in a conveying direction.

17. The device as claimed in claim 1, wherein a gap is defined between the at least two treatment element shafts, and a width of the gap in relation to an external diameter of the at least two treatment element shafts is greater than or equal to 0.004 and less than or equal to 0.035.

18. The device as claimed in claim 1, wherein a gap is defined between the at least two treatment element shafts, and a width of the gap in relation to an external diameter of the at least two treatment element shafts is greater than or equal to 0.011 and less than or equal to 0.02.

19. The device as claimed in claim 1, wherein the at least two treatment element shafts and a housing internal wall of the housing define a gap, and a width of the gap in relation to an external diameter of the at least two treatment element shafts is greater than or equal to 0.005 and less than or equal to 0.025.

20. The device as claimed in claim 1, wherein the at least two treatment element shafts and a housing internal wall of the housing define a gap, and a width of the gap in relation to an external diameter of the at least two treatment element shafts is greater than or equal to 0.012 and less than or equal to 0.019.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In the drawings:

[0022] FIG. 1 is a partial sectional view of a device for producing a dyed and an undyed plastic melt according to a first exemplary embodiment;

[0023] FIG. 2 is a partially sectional plan view of a multi-shaft screw extruder of the device in FIG. 1;

[0024] FIG. 3 is a sectional view of the multi-shaft screw extruder along a section line III-III in FIG. 2;

[0025] FIG. 4 is a partial sectional view of a device for producing a dyed and an undyed plastic melt according to a second exemplary embodiment; and

[0026] FIG. 5 is a partially sectional plan view of a multi-shaft screw extruder of the device in FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] A first exemplary embodiment of the invention is described hereunder by means of FIGS. 1 to 3. A device 1 for producing a dyed plastic melt S.sub.1 and an undyed plastic melt S.sub.2 comprises a multi-shaft screw extruder 2, a first metering installation 3, a second metering installation 4, and a control installation 5. The multi-shaft screw extruder 2 has a housing 6 in which two mutually penetrating housing bores 7, 8 are configured. Treatment element shafts 9, 10 are disposed so as to be rotatable about associated rotation axes 11, 12 in the housing bores 7, 8. The treatment element shafts 9, 10 by means of a drive motor 13, and by way of a transfer gearbox 14, are rotatingly drivable in the same direction, thus in identical directions. A clutch 15 is disposed between the drive motor 13 and the transfer gearbox 14.

[0028] A first infeed opening 16 and a second infeed opening 17 which open into the housing bores 7, 8 are configured in the housing 6. The second infeed opening 17 in a conveying direction 18 is disposed upstream of the first infeed opening 16. The first metering installation 3 opens into the first infeed opening 16 and serves for feeding an undyed plastic material M through the first infeed opening 16 into the housing bores 7, 8. The first metering installation 3 is configured as gravimetric metering unit, for example.

[0029] The second metering installation 4 comprises a first metering unit 19 and a second metering unit 20. A color granulate G by means of the first metering unit 19, and a cleaning granulate R by means of the second metering unit 20, are capable of being fed through the second infeed opening 17 into the housing bores 7, 8. The metering units 19, 20 are configured as gravimetric metering units, for example.

[0030] The screw extruder 2 in the conveying direction 18 has in succession a drawing-in zone 21, a melting and mixing zone 22, and a discharge zone 23. The housing 6 at the end side of the discharge zone 23 has a discharge opening 24. The infeed openings 16, 17 are disposed in the drawing-in zone 21. The treatment element shafts 9, 10 comprise in each case an associated shaft 25, 26 on which screw elements 27, 27 and kneading elements 28, 28 in succession in the conveying direction 18 are disposed in pairs side by side so as to be rotationally fixed on said shafts 25, 26. Screw elements 27, 27 are exclusively disposed so as to be rotationally fixed on the shafts 25, 26 in the drawing-in zone 21. Screw elements 27, 27 and kneading elements 28, 28 are disposed so as to be rotationally fixed on the shafts 25, 26 in the melting and mixing zone 22. Screw elements 27, 27 are in turn exclusively disposed so as to be rotationally fixed on the shafts 25, 26 in the discharge zone 23. The kneading elements 28, 28 are configured, for example, as individual kneading disks and/or as kneading blocks having a plurality of integrally interconnected kneading disks.

[0031] The treatment element shafts 9, 10 are configured so as to mutually mesh in a tight manner and so as to scrape a housing internal wall 29 of the housing 6. To this end, the treatment element shafts 9, 10 are mutually disposed in such a manner that a gap 30 delimited by the treatment element shafts 9, 10, when viewed in the cross section, has a width A.sub.1, where the width A.sub.1 in relation to an external diameter D of the treatment element shafts 9, 10 is: 0.003A.sub.1/D0.05, in particular 0.004A.sub.1/D0.035, and in particular 0.011A.sub.1/D0.02.

[0032] Furthermore, the treatment element shafts 9, 10, conjointly with the housing internal wall 29, form a respective gap 31 which, when viewed in the cross section, has an associated width A.sub.2, where the width A.sub.2 to external diameter D ratio is: 0.004A.sub.2/D0.03, in particular 0.005A.sub.2/D0.025, and in particular 0.012A.sub.2/D0.019.

[0033] The control installation 5 serves for selecting between a first operating mode B.sub.1 for producing the dyed plastic melt S.sub.1 and a second operating mode B.sub.2 for producing the undyed plastic melt S.sub.2. To this end, the control installation 5 in terms of signaling is connected to the multi-shaft screw extruder 2, the first metering installation 3, and the second metering installation 4. The control installation 5 is configured in such a manner that in the first operating mode B.sub.1 the undyed plastic material M by means of the first metering installation 3 is capable of being fed through the first infeed opening 16, and the color granulate G by means of the second metering installation 4, or the first metering unit 19, respectively, is capable of being fed through the second infeed opening 17. The control installation 5 is furthermore configured in such a manner that in the second operating mode B.sub.2 the undyed plastic material M by means of the first metering installation 3 is capable of being fed through the first infeed opening 16 into the at least two housing bores 7, 8. No color granulate G is capable of being fed into the housing bores 7, 8 by means of the second metering installation 4 in the second operating mode B.sub.2. The control installation 5 is furthermore configured in such a manner that the device 1 in a conversion from the first operating mode B.sub.1 to the second operating mode B.sub.2 is initially operated in a cleaning mode B.sub.3. In the cleaning mode B.sub.3, the cleaning granulate R by means of the second metering installation 4, or by means of the second metering unit 20 respectively, is capable of being fed through the second infeed opening 17 into the housing bores 7, 8. The first metering unit 19 is deactivated in the cleaning mode B.sub.3. In the cleaning mode, plastic material M by means of the first metering installation 3 can additionally be fed through the first infeed opening 16 so as to improve or accelerate, respectively, self-cleaning of the multi-shaft screw extruder 2 downstream of the first infeed opening 16.

[0034] The functioning mode of the device 1 is as follows:

[0035] A selection between the first operating mode B.sub.1 and the second operating mode B.sub.2 is possible by means of the control installation 5. The production of the dyed plastic melt S.sub.1 is performed in the first operating mode B.sub.1, whereas the production of the undyed plastic melt S.sub.2 is performed in the second operating mode B.sub.2.

[0036] The undyed plastic material M and the color granulate G are fed to the multi-shaft screw extruder 2 in the first operating mode B.sub.1. The color granulate G in the drawing-in zone 21 makes its way through the second infeed opening 17 into the housing bores 7, 8, and by means of the screw elements 27, 27 is conveyed in the conveying direction 18 only to the first infeed opening 16. The undyed plastic material M in the drawing-in zone 21 is fed through the first infeed opening 16 into the housing bores 7, 8. The undyed plastic material M and the color granulate G are conveyed to the melting and mixing zone 22. The color granulate G and optionally the plastic material M is/are melted in the melting and mixing zone 22, and the molten plastic material M is mixed with the dyeing agent F which is contained in the infed color granulate G such that the dyed plastic melt S.sub.1 is created. The dyed plastic melt S.sub.1 is subsequently discharged through the discharge opening 24 in the discharge zone 23. The dyed plastic melt S.sub.1 is subsequently pelletized in the usual manner, and a dyed plastic granulate is generated, for example.

[0037] The undyed plastic material, thus the plastic material M of natural color, is fed as bulk material, in particular as powder and/or granulate, and/or as melt. The dyeing agent F is present in a bound form in the color granulate G. The color granulate G is, for example, a mixture from the undyed plastic material M and the dyeing agent F. The dyeing agent F is contained in a concentrated form in the color granulate G. The dyeing agent F is carbon black, for example.

[0038] The dyed plastic melt S.sub.1 comprises between 0.5% by weight and 10% by weight, in particular between 1% by weight and 6% by weight, and in particular between 1.5% by weight and 4% by weight dyeing agent F, and between 90% by weight and 99.5% by weight, in particular between 94% by weight and 99% by weight, and in particular between 96% by weight and 98.5% by weight undyed plastic material M. Additionally, other additives than the dyeing agent F can be mixed with the dyed plastic melt S.sub.1, said additives not being considered in the weight proportions stated above.

[0039] When the second operating mode B.sub.2 is subsequently selected by means of the control installation 5, a cleaning mode B.sub.3 is initially activated. In the cleaning mode B.sub.3 the cleaning granulate R by means of the second metering installation 4, or the second metering unit 20, respectively, is fed through the second infeed opening 17 into the housing bores 7, 8. No color granulate G is fed in the cleaning mode B.sub.3. In the cleaning mode B.sub.3, undyed plastic material M by means of the first metering installation 3 can additionally be fed through the first infeed opening 16 into the housing bores 7, 8. Self-cleaning of the multi-shaft screw extruder 2 takes place in a transition period after the termination of the first operating mode B.sub.1, thus during the cleaning mode B.sub.3. Residual color granulate G and/or residual dyeing agent F which are/is located in the region of the second infeed opening 17 and in housing bores 7, 8, in particular on the treatment element shafts 9, 10 and on the housing internal wall 29, by virtue of the tightly meshing configuration of the treatment element shafts 9, 10 and of the scraping of the housing internal wall 29 by means of the treatment element shafts 9, 10, are/is removed from the multi-shaft screw extruder 2. An impure plastic melt S.sub.3 which is capable of being utilized neither as a dyed plastic melt S.sub.1 nor as an undyed plastic melt S.sub.2 is created in said transition period, said impure plastic melt S.sub.3 therefore having to be separated. Self-cleaning is completed after the transition period such that the cleaning mode B.sub.3 is terminated. To this end, the second metering installation 4, or the second metering unit 20, respectively, is deactivated such that cleaning granulate R no longer makes its way through the second infeed opening 17 into the housing bores 7, 8. The undyed plastic melt S.sub.2 is subsequently generated in the second operating mode B.sub.2. To this end, the undyed plastic material M by means of the first metering installation 3 is fed through the first infeed opening 16 into the housing bores 7, 8 and conveyed to the melting and mixing zone 22 and therein is optionally melted and subsequently discharged in the discharge zone 23. The plastic material M in the second operating mode B.sub.2 is fed as bulk material, in particular as powder and/or granulate, and/or as melt.

[0040] A conversion from the second operating mode B.sub.2 to the first operating mode B.sub.1 is possible in a simple manner since no self-cleaning of the multi-shaft screw extruder 2 is required for producing the dyed plastic melt S.sub.1.

[0041] A second exemplary embodiment of the invention is described hereunder by means of FIGS. 4 and 5. As opposed to the preceding exemplary embodiment, the multi-shaft screw extruder 2 in the conveying direction 18 configures in succession a first drawing-in zone 21, a melting zone 22, a second drawing-in zone 21, the melting and mixing zone 22, and the discharge zone 23. Screw elements 27, 27 are exclusively disposed so as to be rotationally fixed on the shafts 25, 26 in the region of the first drawing-in zone 22. By contrast, kneading elements 28, 28 are in turn exclusively disposed so as to be rotationally fixed on the shafts 25, 26 in the melting zone 22. The kneading elements 28, 28 are configured as individual kneading disks and/or as kneading blocks having a plurality of integrally interconnected kneading disks. The second infeed opening 17 is disposed in the first drawing-in zone 21, thus upstream of the first infeed opening 16. The first infeed opening 16 is disposed in the second drawing-in zone 21. The melting zone 22 is thus disposed between the infeed openings 16, 17. Accordingly, screw elements 27, 27 and kneading elements 28, 28 are disposed so as to be rotationally fixed on the shafts 25, 26 between the infeed openings 16, 17.

[0042] In the first operating mode B.sub.1 the color granulate G by means of the second metering installation 4, or the first metering unit 19, respectively, is fed through the second infeed opening 17 into the first drawing-zone 21. The color granulate G is conveyed to the melting zone 22 and melted therein by means of the kneading elements 28, 28. The undyed plastic material M by means of the first metering installation 3 is fed through the first infeed opening 16 to the molten color granulate G in the second drawing-in zone 21. The molten color granulate G, or the dyeing agent F contained therein, respectively is mixed with the plastic material M that is present as melt in the melting and mixing zone 22. The dyed plastic melt S.sub.1 is subsequently discharged in the discharge zone 23.

[0043] Accordingly, in the cleaning mode B.sub.3 the cleaning granulate R is fed through the second infeed opening 17 into the first drawing-in zone 21 and conveyed to the melting zone 22. The cleaning granulate R is melted in the melting zone 22 and is subsequently conveyed to the second drawing-in zone 21, the melting and mixing zone 22, and the discharge zone 23.

[0044] Self-cleaning of the multi-shaft screw extruder 2, in particular of the second infeed opening 17, the treatment element shafts 9, 10, and of the housing internal wall 29, is performed on account thereof. In the cleaning mode B.sub.3, plastic material M can additionally be fed through the first infeed opening 16. Reference in terms of the further construction and of the further functional mode is made to the preceding exemplary embodiment.

[0045] The device 1 according to the invention enables the selective production of a dyed plastic melt S.sub.1 and an undyed plastic melt S.sub.2 by way of only a single multi-shaft screw extruder 2. The complexity in terms of machine technology is comparatively minor on account thereof. When the first operating mode B.sub.1 is converted to the second operating mode B.sub.2, an impure plastic melt S.sub.3 is thus created during self-cleaning in a transition period, thus in the cleaning mode B.sub.3. The impure plastic granulate produced therefrom, depending on the economics, is sold or in a subsequent production of the dyed plastic melt S.sub.1 is re-fed to the multi-shaft screw extruder 2 by way of the second infeed opening 17 and is further processed. The device 1 thus enables a simple, flexible and economical production selectively of a dyed plastic melt S.sub.1 and an undyed plastic melt S.sub.2.

[0046] While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.