METHOD FOR THE DEVULCANIZATION OF A VULCANIZED RUBBER MIXTURE, DEVICE FOR CARRYING OUT THE METHOD AND USE OF THE DEVICE FOR THE DEVULCANIZATION OF A VULCANIZED RUBBER MIXTURE

Abstract

The invention relates to a process for devulcanizing a vulcanized rubber mixture, comprising the following steps: A) providing or producing a vulcanized rubber mixture, B) comminuting the vulcanized rubber mixture to a granular material composed of vulcanized rubber particles, where the vulcanized rubber particles have a maximum particle diameter of 100 mm, C) extruding the vulcanized rubber particles produced in step B) in a twin-screw extruder at a shear rate of less than 100 s.sup.−1, where the temperature of the vulcanized rubber particles during extrusion is less than 200° C., to give a devulcanized rubber mixture having a temperature above 100° C., D) cooling the devulcanized rubber mixture in a further kneading unit, so as to give a devulcanized rubber mixture having a temperature in the range from 50° C. to 100° C. The invention further relates to an apparatus for performing the process and to the use of the apparatus for devulcanization of a vulcanized rubber mixture.

Claims

1.-15. (canceled)

16. A process for devulcanizing a vulcanized rubber mixture, the process comprising: A) providing a vulcanized rubber mixture, B) comminuting the vulcanized rubber mixture to a granular material composed of vulcanized rubber particles (2), wherein the vulcanized rubber particles (2) have a maximum particle diameter of 100 mm, C) extruding the vulcanized rubber particles (2) produced in step B) in a twin-screw extruder (3) at a shear rate of less than 100 s.sup.−1, wherein the temperature of the vulcanized rubber particles (2) during extrusion is less than 200° C., to give a devulcanized rubber mixture (8) having a temperature above 100° C., D) cooling the devulcanized rubber mixture (8) in a further kneading unit (4), so as to give a devulcanized rubber mixture (8) having a temperature in the range of from 50° C. to 100° C.

17. The process as claimed in claim 16, wherein, during the extruding in step C), a specific energy input of from 0.01 to 5 kWh/kg per screw (14) is introduced into the vulcanized rubber particles (2), based on the total mass of the vulcanized rubber particles (2) extruded in step C).

18. The process as claimed in claim 16, wherein, during the extruding in step C), a specific energy input of from 0.01 to 2.5 kWh/kg per screw (14) is introduced into the vulcanized rubber particles (2), based on the total mass of the vulcanized rubber particles (2) extruded in step C).

19. The process as claimed in claim 16, wherein the further kneading unit (4) in step D) comprises a single-screw extruder (5).

20. The process as claimed in claim 16, wherein the further kneading unit (4) in step D) comprises a gear pump (6).

21. The process as claimed in claim 16, wherein, after the cooling in step D) that takes place in the further kneading unit (4), the devulcanized rubber mixture (8), in a step E), is heated to a temperature of from 50° C. to 150° C.

22. The process as claimed in claim 16, wherein, after the cooling in step D) that takes place in the further kneading unit (4), the devulcanized rubber mixture (8), in a step E), is pushed through a filter unit (7) comprising a sieve and/or a perforated plate, wherein the devulcanized rubber mixture (8), on account of the pushing through the filter unit (7), is heated to a temperature of from 50° C. to 150° C.

23. The process as claimed in claim 16, wherein, during the extruding in step C), a means of controlling the temperature of the extruded rubber particles (2) is added to the twin-screw extruder (3), wherein the means of controlling the temperature of the extruded rubber particles (2) does not react chemically with the rubber particles (2) within the temperature range of from 10° C. and 200° C.

24. The process as claimed in claim 16, wherein, during the extruding in step C), the means of controlling the temperature of the extruded rubber particles (2) has a specific heat transfer coefficient to EN ISO 6946 in the range of from 100 to 5000 W/(m.sup.2*K) and a specific heat capacity in the range of from 3 to 5 kJ/(kg.Math.K).

25. The process as claimed in claim 16, wherein, during the extruding in step C), the screw speed of the screws (14) of the twin-screw extruder (3) is at least mainly within the range of from 10 to 500 revolutions per minute.

26. The process as claimed in claim 16, wherein the vulcanized rubber particles (2) produced in step B) are extruded in step C) in the twin-screw extruder (3) at a shear rate in the range of from 10 to 80 s.sup.−1.

27. The process as claimed in claim 16, wherein the twin-screw extruder (3) in step C) has a length of less than 60 D.

28. The process as claimed in claim 16, wherein the temperature of the vulcanized rubber particles (2) during the extruding in step C) is in the range of from 105 to 180° C.

29. The process as claimed in claim 16, wherein the temperature of the vulcanized rubber particles (2) during the extruding in step C) is in the range of from 110 to 150° C.

30. The process as claimed in claim 16, wherein the resulting proportion of comminuted rubber particles (2) in step B) that passes through a 44 mesh sieve in a sieving test according to Japanese industrial standard JIS P-8207 is at least 80% by weight of the resulting total mass of comminuted rubber particles (2) in step B).

31. The process as claimed in claim 16, wherein the average particle diameter of the resulting rubber particles (2) in step B) is in the range of from 0.1 mm to 20 mm.

32. The process as claimed in claim 16, wherein the rubber mixture provided in step A) comprises natural rubber, butadiene rubber and/or SBR rubber, wherein there is from 50 phr to 100 phr of a natural rubber in the rubber mixture provided in step A), and wherein the rubber mixture provided in step A) comprises carbon black, where the carbon black is present in an amount of from 10 to 150 phr.

33. The use of a rubber mixture devulcanized according to claim 16 for production of a vehicle tire.

34. An apparatus for performing a method of claim 16, the apparatus comprising: a twin-screw extruder (3), preferably having a length of less than 60 D, a further kneading unit (4), preferably comprising a single-screw extruder (5) and/or a gear pump (6), a filter unit (7) comprising a sieve and/or a perforated plate, and optionally a particle comminution unit (11) for comminuting a vulcanized rubber mixture to a granular material composed of vulcanized rubber particles (2) having a maximum particle diameter of 100 mm and/or having an average particle diameter in the range from 0.1 mm to 20 mm.

35. The use of the apparatus as claimed in claim 34 for devulcanization of a vulcanized rubber mixture.

Description

DESCRIPTION OF FIGURES

[0098] The Figures Show:

[0099] FIG. 1: A schematic cross section through an apparatus of the invention comprising a twin-screw extruder, a single-screw extruder and a gear pump, and a strainer with a sieve and a perforated plate, wherein the rubber mixture is transferred from the twin-screw extruder without a nozzle and without a further hopper directly into the single-screw extruder;

[0100] FIG. 2: A schematic cross section through an apparatus of the invention comprising a twin-screw extruder, a single-screw extruder and a gear pump, and a strainer with a sieve and a perforated plate, wherein the rubber mixture is transferred from the twin-screw extruder with a nozzle and via a further hopper into the single-screw extruder;

[0101] FIG. 3: A schematic cross section through an apparatus of the invention comprising a twin-screw extruder, a gear pump and a strainer with a sieve and a perforated plate, wherein the rubber mixture is transferred from the twin-screw extruder with a nozzle via a material loop into the gear pump.

[0102] FIG. 1 shows a schematic diagram of an inventive apparatus 1 in a first embodiment comprising [0103] a hopper 10 for feeding vulcanized rubber particles 2 having a maximum particle diameter of 100 mm and having an average particle diameter in the range from 0.1 mm to 20 mm into a twin-screw extruder 3, [0104] a twin-screw extruder 3 having a length of less than 60 D, [0105] a further kneading unit 4 comprising a single-screw extruder 5 and a gear pump 6, [0106] and finally [0107] a filter unit 7 comprising a sieve and/or a perforated plate.

[0108] Also shown in FIG. 1 is the particle comminution unit 11 for comminuting a vulcanized rubber mixture to a granular material composed of vulcanized rubber particles 2 having a maximum particle diameter of 100 mm and having an average particle diameter in the range from 0.1 mm to 20 mm, in order then to feed these via the hopper 10 into the twin-screw extruder 3.

[0109] The twin-screw extruder 3 has a barrel 18 with an inner surface 24, two screws 14 each having a screw rotation axis 23, and a supply and removal unit 16, 17. The screws 14 of the twin-screw extruder 3 here comprise a screw core 29 having an outer surface 25 and multiple screw segments 28 with screw flights 30. Additionally shown is the distance 26 that constitutes the parameter h in formula 1.

[0110] The single-screw extruder 5 has a barrel 19 with an inner surface 24 and one screw 15 each having a screw rotation axis 23, and a. The screw 14 of the single-screw extruder 3 here comprises a screw core 29 having an outer surface 25 and multiple screw segments 28 with screw flights 30.

[0111] The gear pump 6 has two gears that rotate in direction 22, and in FIG. 1 follows after the single-screw extruder 5. Finally, the devulcanized rubber mixture 8 is pushed by the gear pump 6 through the filter unit 7.

[0112] The construction shown in FIG. 1, compared to the construction indicated in FIGS. 2 and 3, has greater temperature control and more automatable production. The latter is advantageous for continuous processes in particular.

[0113] FIG. 2 shows a schematic diagram of an inventive apparatus 1 in a further embodiment, wherein, by contrast with FIG. 1, the devulcanized rubber mixture 8 is pushed through a nozzle 9 at the end of the twin-screw extruder 3 and then supplied to the single-screw extruder 5 via a further hopper 12. One advantage of this construction is that further rubber mixture constituents, for example plasticizers or fillers, can be added in order to reduce or increase the shear forces in the single-screw extruder and hence to achieve an optimal temperature profile along the screw of the single-screw extruder for preservation of the rubber polymer chains.

[0114] The twin-screw extruder 3 has a final nozzle 9, a barrel 18 with an inner surface 24, two screws 14 each having a screw rotation axis 23, and a supply and removal unit 16, 17. The screws 14 of the twin-screw extruder 3 here comprise a screw core 29 having an outer surface 25 and multiple screw segments 28 with screw flights 30. Additionally shown is the distance 26 that constitutes the parameter h in formula 1.

[0115] The single-screw extruder 5 has a further hopper 12, a barrel 19 with an inner surface 24 and one screw 15 each having a screw rotation axis 23, and a. The screw 14 of the single-screw extruder 3 here comprises a screw core 29 having an outer surface 25 and multiple screw segments 28 with screw flights 30.

[0116] The gear pump 6 has two gears that rotate in direction 22, and in FIG. 2 follows after the single-screw extruder 5. Finally, the devulcanized rubber mixture 8 is pushed by the gear pump 6 through the filter unit 7.

[0117] FIG. 3 shows a schematic diagram of an inventive apparatus 1 in a further embodiment, wherein, by contrast with FIG. 1, the devulcanized rubber mixture 8 does not pass through a single-screw extruder, but is transferred directly from the twin-screw extruder 3 via what is called a material loop 13 into the gear pump 6. The adjustment of the material loop 13 is achieved with a known loop unit 27 for forming a material loop 13 and for adjusting the length of the material loop 13, including intermediate storage means for a rubber mixture belt.

[0118] The advantage of the material loop 13 is that, according to the length of the material loop 13, the temperature on entry into the gear pump 6 can be determined accurately, and hence better temperature control and especially compliance of the temperatures within the range from 50° C. to 100° C. in step D) of the process of the invention can be guaranteed.

[0119] One advantage of this construction without a single-screw extruder is that it is possible via the choice of loop length to adjust the exact temperature of the rubber mixture coming from the twin-screw extruder rapidly to the respective process or the respective rubber mixture to be devulcanized, hence leading to short lifetimes in a continuous process in an apparatus of the invention.

[0120] The twin-screw extruder 3 has a barrel 18 with an inner surface 24, two screws 14 each having a screw rotation axis 23, and a supply and removal unit 16, 17. The screws 14 of the twin-screw extruder 3 here comprise a screw core 29 having an outer surface 25 and multiple screw segments 28 with screw flights 30. Additionally shown is the distance 26 that constitutes the parameter h in formula 1.

[0121] The gear pump 6 has two gears that rotate in direction 22, and in FIG. 3 follows after the loop unit 27. Finally, the devulcanized rubber mixture 8 is pushed by the gear pump 6 through the filter unit 7.

Experimental Examples

[0122] Test Methods [0123] 1. Mooney Viscosity [0124] The results were ascertained in accordance with the DIN 53523 (ML1+3) method at 100° C. (Mooney units M. U.). [0125] 2. Shore A hardness [0126] The results were ascertained in accordance with the DIN method at room temperature by means of a durometer to DIN ISO 7619-1. [0127] 3. Resilience [0128] The results were ascertained in accordance with the DIN 53 512 method at room temperature. [0129] 4. 300 modulus [0130] The stress value results were ascertained in accordance with DIN 53 504 method at 300% static strain at room temperature. [0131] 5. Maximum (max) loss factor tan 5 (tangent delta) [0132] The results were ascertained in accordance with the DIN 53 513 method from dynamic-mechanical measurement, strain sweep at 55° C.

[0133] Production:

[0134] Production of a rubber mixture devulcanized in accordance with the invention and not in accordance with the invention: The devulcanized rubber mixture was produced in steps B), C) and D). In the first process step B), rubber from used car tire treads was comminuted by means of a particle comminution unit to vulcanized rubber particles having a maximum particle diameter and having an average particle diameter as shown in table A. Subsequently, the rubber particles thus comminuted were processed with the aid of an apparatus of the invention as shown in FIG. 1 to give a devulcanized rubber mixture. The parameters established here in the single-screw and twin-screw extruder are those shown in tab. A. The procedure here was such that the rubber mixture extruded in the twin-screw extruder did not experience any higher shear forces in the single-screw extruder and in the gear pump than in the twin-screw extruder.

TABLE-US-00001 TABLE A Experimental data of the devulcanizates VD1, ED1 and ED2 produced in accordance with the invention and not in accordance with the invention in an apparatus of the invention Designation VD1 ED1 ED2 Property Non-inv. Inv. Inv. Unit Parameter Twin-screw extruder Temperature in the ° C. 250 170 130 barrel Shear forces 1/s 80 80 80 Single-screw extruder Temperature on exit ° C. 150 94 86 Properties Rubber particles Average particle size mm 2 2 2 Maximum particle size mm 5 5 5

[0135] Production of the Specimens:

[0136] The devulcanized rubber mixture VD1, ED1 and ED2 was produced by the above-described process of the invention. The finished mixture is produced by addition of NR, BR, SBR, the respective devulcanized rubber mixture and further additives as specified in table 1 to a mixer in a first mixing stage and by subsequent addition of the vulcanization system in a second mixing stage.

[0137] This is followed by further processing by vulcanization of the finished mixture, wherein sulfur crosslinking takes place due to the vulcanization system added in the context of the present invention. The finished mixture was vulcanized at 160° C. for 12 min.

[0138] Results:

TABLE-US-00002 TABLE 1 Experimental data of the rubber composition for inventive experiments E2 and E3 and the noninventive comparative experiment V1 Comp. Exp. Exp. Mixing exp. V1 E2 E3 Constituent Unit stage Non-inv. Inv. Inv. NR phr 1 50 50 50 BR phr 1 20 20 20 SBR phr 1 30 30 30 Devulcanizate phr 1 40     VD 1 Devulcanizate phr 1   40   ED 1 Devulcanizate phr 1   40 ED 2 Carbon black phr 1 30 30 30 Plasticizer phr 1 15 15 15 Aging phr 1 4.5 4.5 4.5 inhibitor Stearic acid phr 1 2 2 2 ZnO phr 1 2.5 2.5 2.5 Sulfur phr 2 2.5 2.5 2.5 Vulcanizing phr 2 1.4 1.4 1.4 agent

TABLE-US-00003 TABLE 2 Experimental data of the finished rubber mixture comprising the devulcanizates produced in accordance with the invention and not in accordance with the invention, and of the specimens that result therefrom after vulcanization Comp. exp. V1 Exp. E1 Exp. E2 Non-inv. Inv. Inv. Property Unit V1 E1 E2 Finished rubber mixture Mooney (ML1 + 3) MU 32 34 36 Specimens of the vulcanized finished mixture Shore A hardness @ RT ShA 48.8 49.1 49.5 Resilience @RT % 45.8 47.4 48.3 300 modulus @RT MPa 4.8 5.3 5.4 tan d (max) — 0.123 0.113 0.111

[0139] The experimental data from tab. 2 show that the control of temperature and the compliance of the parameter of the vulcanized rubber particles used and of the low shear rates play an important role in order to shorten the polymer chains of the rubber molecules to a minimum degree in the course of devulcanization. The finished rubber mixture containing the devulcanizate ED1 has higher Mooney viscosity and, after vulcanization, has higher resilience, a higher 300 modulus and a low loss factor tan d(max) with virtually the same Shore A hardness. The differences were additionally increased when, in the twin-screw extruder in the experimental setup, not only a temperature of 170° but a maximum temperature of 130° C. was observed (cf. Exp. 2 with Exp. 3). This shows that the chain length of the devulcanized rubber mixture that was obtained in inventive experiment Exp. 3 were even longer than those of the devulcanized rubber mixture according to inventive experiment Exp. 2.

LIST OF REFERENCE NUMERALS

[0140] 1 inventive apparatus [0141] 2 vulcanized rubber particles; vulcanized rubber particles having a maximum diameter of 100 mm and having an average particle diameter of 0.1 mm to 20 mm [0142] 3 twin-screw extruder [0143] 4 further kneading unit [0144] 5 single-screw extruder [0145] 6 gear pump [0146] 7 filter unit comprising a sieve and a perforated plate; strainer [0147] 8 devulcanized rubber mixture [0148] 9 nozzle at the end of the twin-screw extruder [0149] 10 hopper for supply of vulcanized rubber particles to a twin-screw extruder [0150] 11 particle comminution unit for comminuting a vulcanized rubber mixture to a granular material composed of vulcanized rubber particles having a maximum particle diameter of 100 mm and having an average particle diameter in the range from 0.1 mm to 20 mm [0151] 12 further hopper for supply of vulcanized rubber particles to a single-screw extruder [0152] 13 material loop of devulcanized rubber mixture [0153] 14 screw of a twin-screw extruder [0154] 15 screw of a single-screw extruder [0155] 16 feed unit for feeding of a means of controlling the temperature of the extruded rubber particles into the twin-screw extruder [0156] 17 removal unit for removal of an added means of controlling the temperature of the extruded rubber particles from the twin-screw extruder [0157] 18 barrel of a twin-screw extruder [0158] 19 barrel of a single-screw extruder [0159] 20 extrusion direction; production direction [0160] 21 gears of the gear pump [0161] 22 rotation direction of the gears of the gear pump [0162] 23 axis of screw rotation [0163] 24 inner surface of the extrusion barrel [0164] 25 outer surface of the screw core [0165] 26 distance in a cross section at right angles to the axis of rotation of the screw between the inner face of the extrusion barrel and the outer surface of the screw core [0166] 27 loop unit for forming a material loop and for adjusting the length of the material loop; intermediate storage means for a rubber mixture belt [0167] 28 screw segment in the extruder [0168] 29 screw core [0169] 30 screw flight; screw land