Process for regenerating sulfur-crosslinked rubber vulcanizates to give regenerates

Abstract

A process for regenerating sulfur-crosslinked rubber vulcanizates to regenerates, wherein at least one regenerating agent is used in the regeneration. The regenerating agent is selected from the group consisting of dithiophosphoryl polysulfides and/or silanes having a polysulfane group. Regenerates which have been produced by means of the process lead to improved or equal rolling resistance indicators and a lower compression set in vulcanized rubber mixtures compared to regenerates known in the prior art.

Claims

1. A process for regenerating sulfur-crosslinked rubber vulcanizates to give regenerates comprising: providing at least one regenerating agent for regenerating sulfur-crosslinked rubber vulcanizates, wherein the regenerating agent is selected from the group consisting of dithiophosphoryl polysulfides and silanes having a polysulfane group, and mixing a mixture of the at least one regenerating agent and sulfur-crosslinked rubber vulcanizates for a period of time of from 5 to 35 minutes.

2. The process as claimed in claim 1, wherein the dithiophosphoryl polysulfide has the general formula I ##STR00002## where R.sup.1 and R.sup.2 are identical or different and are selected from among linear or branched C.sub.3-C.sub.20-alkyl radicals and x=1 to 6.

3. The process as claimed in claim 2, wherein the dithiophosphoryl polysulfide is a bis(O,O-2-ethylhexyl)thiophosphoryl polysulfide.

4. The process as claimed in claim 1, wherein the silane having a polysulfane group has the general formula II
(R.sup.2O).sub.3-yR.sup.3.sub.ySiR.sup.1S.sub.xR.sup.1Si(OR.sup.2).sub.3-zR.sup.3.sub.z(II) where x=1 to 8 and the radicals R.sup.1 in a molecule are identical or different and are selected from among linear or branched C.sub.1-C.sub.18-alkyl radicals, the radicals R.sup.2 and R.sup.3 in a molecule are identical or different and are selected from among linear or branched or cyclic saturated C.sub.1-C.sub.30-alkyl radicals and y and z are identical or different and are each from 0 to 3, wherein the radicals R.sup.2 and/or R.sup.3 optionally contain from 1 to 10 nitrogen atoms (N) and/or oxygen atoms (O) as heteroatoms in the carbon chain.

5. The process as claimed in claim 4, wherein the silane having a polysulfane group is a bis(trialkoxysilyl)propyl polysulfane.

6. The process as claimed in claim 4, wherein the radicals R.sup.2 and/or R.sup.3 additionally contain from 1 to 10 nitrogen atoms (N) and/or oxygen atoms (0) as heteroatoms in the carbon chain.

7. The process as claimed in claim 1, wherein the silane having a polysulfane group has the general formula V
(R.sup.2O).sub.3-yR.sub.3ySiR.sup.1S.sub.xR.sup.1Si(O.sub.2R.sup.2)R.sup.3(V) where x=1 to 8 and the radicals R.sup.1 in a molecule are identical or different and are selected from among linear or branched C.sub.1-C.sub.18-alkyl radicals, the radicals R.sup.2 in a molecule are identical or different and are selected from among linear or branched or cyclic saturated C.sub.1-C.sub.30-alkyl radicals and y and z are identical or different and are each from 0 to 3 and the radicals R.sup.3 in a molecule are identical or different and are selected from among linear or branched C.sub.1-C.sub.10-alkyl or alkoxy radicals.

8. The process as claimed in claim 1, wherein the silane having a polysulfane group has the general formula VI
(R.sup.2O.sub.2)R.sup.3SiR.sup.1S.sub.xR.sup.1Si(O.sub.2R.sup.2)R.sup.3(VI) where x=1 to 8 and the radicals R.sup.1 in a molecule are identical or different and are selected from among linear or branched C.sub.1-C.sub.18-alkyl radicals, the radicals R.sup.2 in a molecule are identical or different and are selected from among linear or branched or cyclic saturated C.sub.1-C.sub.30-alkyl radicals and the radicals R.sup.3 in a molecule are identical or different and are selected from among linear or branched C.sub.1-C.sub.10-alkyl or alkoxy radicals.

9. A process for regenerating sulfur-crosslinked rubber vulcanizates to give regenerates, comprising: placing the sulfur-crosslinked rubber vulcanizate to be regenerated in amounts of from 68 to 98% by weight in a mechanical mixer; heating the sulfur-crosslinked rubber vulcanizate to be regenerated to a temperature of from 50 to 70 C.; adding at least one dithiophosphoryl polysulfide and/or at least one silane having a polysulfane group in amounts of from 2 to 15% by weight to form a mixture; and, mixing the mixture for a period of time of from 5 to 35 minutes at a temperature of from 80 to 150 C.

10. The process as claimed in claim 1, wherein the sulfur-crosslinked rubber vulcanizates originate from used tires or conveyor belts or vulcanized waste obtained in the production of industrial rubber articles or pneumatic vehicle tires.

11. A regenerate produced as claimed in the process as claimed in claim 1.

12. The regenerate as claimed in claim 11 for producing pneumatic vehicle tires.

13. A process of regenerating sulfur-crosslinked rubber vulcanizates comprising adding dithiophosphoryl polysulfides as regenerating agents, and mixing the resulting mixture for a period of time of from 5 to 35 minutes.

14. A process for regenerating sulfur-crosslinked rubber vulcanizates comprising adding silanes having a polysulfane group as regenerating agents, and mixing the resulting mixture for a period of time of from 5 to 35 minutes.

Description

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

(1) The disclosure will now be illustrated with the aid of comparative examples and working examples.

(2) Regenerates were firstly produced, namely regenerates ER1 and ER2, according to the disclosed process using two different regenerating agents and the regenerates RG3 and RG4 by means of regenerating agents known from the prior art.

(3) The production of the regenerate ER1 from vulcanized rubber vulcanizates was carried out using the process steps in the following order: comminution of the sulfur-crosslinked rubber vulcanizate by means of a cryogenic milling process (pin mill) to give a granulated material having a particle size of from 0.001 to 0.5 mm placing of 90.7% by weight of the comminuted sulfur-crosslinked rubber vulcanizate to be regenerated in a mechanical mixer heating of the comminuted sulfur-crosslinked rubber vulcanizate to be regenerated to 60 C. addition of 2% by weight of carbon black (N121) addition of 5.5% by weight of regenerating agent (bis(triethoxysilyl)propyl tetrasulfane (TESPT), addition of 2% by weight of TDAE oil (TDAE=treated aromatic extract) mixing of the abovementioned constituents to give a mixture for a period of 20 minutes at a temperature of 100 C. cooling of the mixture.

(4) Production of the regenerates ER2 and also RG3 and RG4 was carried out analogously, in these cases with addition of the following regenerating agents:

(5) ER2: 5.5% by weight of bis(O,O-2-ethylhexylthiophosphoryl) polysulfide, Rhenocure SDT 50, from Rheinchemie GmbH

(6) RG3: 5.5% by weight of CBS (N-cyclohexyl-2-benzothiazole-sulfenamide),

(7) RG4: 5.5% by weight of dioctyl pentasulfide, Aktiplast GE1979, from Rheinchemie GmbH

(8) The regenerates produced using the various regenerating agents were in each case added in amounts of 60 phr to a rubber mixture (base mixture) B1, in each case added in amounts of 82 phr to a rubber mixture (base mixture) B2 and in each case added in amounts of 43 phr to a rubber mixture (base mixture) B3, the compositions of which are shown in Table 1.

(9) TABLE-US-00001 TABLE 1 Constituents of base mixture Unit B1 B2 B3 NR phr 100 30 40 IR phr 10 BR phr 3 20 SBR phr 30 SSBR phr 67 Carbon black N121 phr 47 Carbon black N339 phr 18 30 Silica, BET: 200 m.sup.2/g phr 85 Silane, TESPD phr 7.4 Plasticizer TDAE phr 2 37 8 Aging inhibitor phr 6 7.8 8 Zinc oxide phr 3 4.5 2.5 Stearic acid phr 2 1 2.25 Accelerator DPG* phr 2.2 Accelerator CBS* phr 2.5 1 Accelerator TBBS* phr 0.75 Sulfur* phr 1.65 1.7 2.2 *Adaptation in accordance with Gibala D, Hamed GR.: Cure and mechanical behavior of rubber compounds containing ground vulcanizates - Parte I - Cure behavior, Rubber Chemistry and Technology, 1997; 67(1): 636-648 may be appropriate and advantageous.

(10) Production of the mixture was carried out under conventional conditions in a plurality of stages in a tangential laboratory mixer. Test specimens were produced from all mixtures by 20 minute vulcanization under pressure at 160 C. and materials properties typical of the rubber industry were determined on these test specimens using the test methods indicated below. Shore A hardness at room temperature (RT) and 70 C. in accordance with DIN 53 505 Rebound resiliencies at room temperature (RT) and 70 C. in accordance with DIN 53 512 Tensile strength at room temperature in accordance with DIN 53 504 Elongation at break at room temperature in accordance with DIN 53 504 Stress at 300% elongation at room temperature (modulus 300) in accordance with DIN 53 504 Compression set using a method based on DIN ISO 815-1 Abrasion at room temperature in accordance with DIN/ISO 4649 Relative degree of crosslinking of 5% or 10% (t5, t10 partial vulcanization time) by means of rotor-less vulcameter (MDR=Moving Disc Rheometer) in accordance with DIN 53 529

(11) Furthermore, vulcanizates of the rubber mixtures were stored in air for 14 days at 70 C. and their physical properties were likewise determined.

(12) The results of the measurements and also the assignment of the regenerates used to the variants are summarized in Tables 2 and 3. Here, the rubber mixture E1 contains 60 phr of the regenerate ER1, E2 contains 60 phr of the regenerate ER2, E3 contains 82 phr of TESPD and E4 contains 43 phr of TESPD.

(13) The rubber mixtures V1 and V2 contain 60 phr of the regenerate RG3 and 60 phr of the regenerate RG4, respectively. The rubber mixture V4 contains 82 phr of the regenerate RG4 and the rubber mixture V5 contains 43 phr of the regenerate RG4.

(14) As further comparative example, the rubber mixture V3 contains 60 phr of the regenerate RG5 which is a regenerate which is commercially available under the trade name ECORR RNR 30 from RubberResources.

(15) The rubber mixtures Ref1, Ref2 and Ref3 which do not contain any regenerate and therefore have the compositions indicated in Table 1 serve as reference.

(16) TABLE-US-00002 TABLE 2 Ref1 V1 V2 V3 E1 E2 Regenerate Unit RG3 RG4 RG5 ER1 ER2 Physical properties before aging Shore Shore 62 63 60 60 62 57 hardness A at RT Shore Shore 57 58 55 54 58 52 hardness A at 70 C. Rebound % 46 44.5 41 40.5 45 46 resilience at RT Rebound % 61 59 55 54 58 59 resilience at 70 C. Tensile MPa 23 20 20 18 20 17 strength Modulus 300 MPa 13 13 11 11 12 11 Elongation at % 496 452 506 494 467 434 break Abrasion mm.sup.3 104 117 122 130 117 117 Compression % 28 35 37 36 33 35 set at 70 C. t10 min 2.2 1.0 1.7 2.1 2.2 0.72 t5 min 1.63 0.6 0.2 1.7 1.9 0.17 Physical properties after aging for 14 days at 70 C., air Shore Shore A 67 69 67 67 68.5 hardness at RT Shore Shore A 64 66 63 63 65 hardness at 70 C. Rebound % 47 47 43 43 46 resilience at RT Rebound % 63 61 58 59 60 resilience at 70 C. Tensile MPa 24 18 18 16 18 strength Modulus 300 MPa 17 17 15 15 17 Elongation at % 438 338 389 359 346 break

(17) TABLE-US-00003 TABLE 3 Ref2 V4 E3 Ref3 E4 V5 Regenerate Unit RG4 TESPD RG4 TESPD Physical properties before aging Shore Shore 73 77 74 48.8 51 47.3 hardness A at RT Shore Shore 67 70 66 45.9 46.7 42.7 hardness A at 70 C. Rebound % 15.8 15.5 15 58.7 53.8 51.2 resilience at RT Rebound % 38 37.5 34 68 64 61.2 resilience at 70 C. Modulus 200 MPa 6.1 7.2 4.8 Modulus 300 MPa 4.4 5.4 3.9 Tensile MPa 12.7 10.9 11.5 13.8 9.2 8.7 strength Elongation at % 394 294 396 610 461 519 break Abrasion mm.sup.3 95 102 106 t10 min 0.69 0.34 0.22 2.7 1.8 1.7 t5 min 0.32 0.23 0.16 2.4 1.6 1.5 Physical properties after aging for 14 days at 70 C., air Shore Shore 77.2 81.1 78.4 55.7 58.4 55.3 hardness A at RT Shore Shore 73.6 77.4 74.8 53.8 55.8 52.1 hardness A at 70 C. Rebound % 16.1 16.4 15.7 63.3 57.3 56 resilience at RT Rebound % 39.6 38.5 37.6 72 68.1 67.4 resilience at 70 C. Tensile MPa 10.9 9.9 11.3 11 8.4 8.4 strength Modulus 200 MPa 8.3 9.9 7.2 4.4 5.2 4.1 Modulus 300 MPa Elongation at % 280 216 306 401 305 354 break
As can be seen from Tables 2 and 3, the vulcanizates of the rubber mixtures E1, E2, E3, and E4 which contain the regenerates according to the disclosure TSPD, ER1 and ER2 have higher rebound resiliencies than rubber mixtures containing regenerates known from the prior art. The rebound resilience at 70 C. represents a rolling resistance indicator, so that pneumatic vehicle tires containing the regenerates according to the invention in at least one rubber mixture are expected to give rise to a lower fuel consumption than tires containing regenerates known from the prior art. Furthermore, the rubber mixtures E1 and E2 display a comparatively low compression set compared to the mixtures V1, V2 and V3. At the same time, it can be seen that the process reliability generally increases in the case of the mixtures according to the disclosure.

(18) It is understood that the foregoing description is that of the preferred embodiments of the invention and that various changes and modifications may be made thereto without departing from the spirit and scope of the invention as defined in the appended claims.