Rubber blends containing silicic acid and comprising additives containing sulphur

Abstract

The present invention relates to a silica-containing rubber mixture produced from at least one rubber, one sulphur-containing alkoxysilane, one crosslinking agent, one filler, and optionally further rubber auxiliary products and from 0.1 to 15 phr of a polysulphide additive of the formula (I)
A-S—(S).sub.x—S—Y—S—(S).sub.x—S-A  (I)
where x is 0, 1 or 2, Y is an aliphatic, cycloaliphatic or aromatic group that is optionally substituted or else comprises heteroatoms and A is an optionally substituted hydroxyethyl, carboxyaryl, hydroxyaryl, carboxyalkyl or thionamide moiety,
and comprises from 0.1 to 15 parts by weight, based on 100 parts by weight of rubber used, of 1,6-bis(N,N-dibenzylthiocarbamoyldithio)hexane (CAS No.: 151900-44-6).

Claims

1. A silica-containing rubber mixture produced from at least one rubber, one sulphur-containing alcoxysilane, one crosslinking agent, one filler, and optionally further rubber auxiliary products, the mixture comprising: 0.1 to 15 parts by weight, based on 100 parts by weight of rubber used, of 1,6-bis(N,N-dibenzylthiocarbamoyldithio)hexane (CAS No.: 151900-44-6); and 0.1 to 15 parts by weight, based on 100 parts by weight of rubber used, of a polysulphide additive of the formula (I)
A-S—(S).sub.x—S—Y—S—(S).sub.x—S-A  (I) where x is 0, 1 or 2, Y is an aliphatic, cycloaliphatic or aromatic group that is optionally substituted or else comprises heteroatoms and A is a moiety ##STR00023## where R.sup.1 to R.sup.2 are identical or different and are hydrogen, C.sub.1-C.sub.6-alkyl, C.sub.5-C.sub.6-cycloalkyl, C.sub.6-C.sub.10-aryl or a group —CH.sub.2—OR.sup.5, —CH.sub.2—CH.sub.2—OR.sup.5, —NHR.sup.5, —COR.sup.5, —COOR.sup.5, —CH.sub.2COOR.sup.5, where R.sup.5=hydrogen, C.sub.1-C.sub.6-alkyl, C.sub.5-C.sub.6-cycloalkyl, C.sub.6-C.sub.10-aryl or C.sub.1-C.sub.6-acyl, or A is a moiety ##STR00024## in which R.sup.1 and R.sup.2 are identical or different and are hydrogen, C.sub.1-C.sub.6-alkyl, C.sub.5-C.sub.6-cycloalkyl, C.sub.6-C.sub.10-aryl or a group —CH.sub.2—OR.sup.5, —CH.sub.2—CH.sub.2—OR.sup.5, —NHR.sup.5, —COR.sup.5, —COOR.sup.5, —CH.sub.2COOR.sup.5, where R.sup.5=hydrogen, C.sub.1-C.sub.6-alkyl, C.sub.5-C.sub.6-cycloalkyl, C.sub.6-C.sub.10-aryl or C.sub.1-C.sub.6-acyl, or A is a moiety ##STR00025## in which R.sup.1 to R.sup.2 are identical or different and are hydrogen, C.sub.1-C.sub.6-alkyl, C.sub.5-C.sub.6-cycloalkyl, C.sub.6-C.sub.10-aryl or a group —CH.sub.2—OR.sup.5, —CH.sub.2—CH.sub.2—OR.sup.5, —NHR.sup.5, —COR.sup.5, —COOR.sup.5, —CH.sub.2—COOR.sup.5, where R.sup.5=hydrogen, C.sub.1-C.sub.6-alkyl, C.sub.5-C.sub.6-cycloalkyl, C.sub.6-C.sub.10-aryl or C.sub.1-C.sub.6-acyl and R.sup.6 is hydrogen, C.sub.1-C.sub.6-alkyl, C.sub.5-C.sub.6-cycloalkyl, C.sub.6-C.sub.10-aryl or a group —CH.sub.2—OR.sup.5, —CH.sub.2—CH.sub.2—OR.sup.5, —NHR.sup.5, —COR.sup.5, —COOR.sup.5, —CH.sub.2—COOR.sup.5, where R.sup.5=hydrogen, C.sub.1-C.sub.6-alkyl, C.sub.5-C.sub.6-cycloalkyl, C.sub.6-C.sub.10-aryl or C.sub.1-C.sub.6-acyl and y is 0, 1 or 2, or, if Y is —(CH.sub.2).sub.6— and x is 0, A is ##STR00026## in which R.sup.8 and R.sup.9 are mutually independently hydrogen, C.sub.1-C.sub.6-alkyl, C.sub.5-C.sub.6-cycloakyl, C.sub.6-C.sub.10-aryl or a group —CH.sub.2—OR.sup.5, —CH.sub.2—CH.sub.2—OR.sup.5, —CH.sub.2—COOR.sup.5, —CH.sub.2—CH.sub.2—COOR.sup.5 and R.sup.8 and R.sup.9 can also optionally form a ring together with the respective nitrogen atom, and R.sup.5 is defined as above, where both moieties A of the compound of the formula I can be identical or different, and at least one of the moieties R.sup.8 and R.sup.9 on one of the moieties A comprises one or more oxygen atoms.

2. The silica-containing rubber mixture according to claim 1, wherein Y is one of the groups: ##STR00027##

3. The silica-containing rubber mixture according to claim 1, wherein the polysulphide additive comprises at least one compound of the formulae (II), (III), (IV), (IVa), (V), (Va), (VI) or (VIa) ##STR00028##

4. The silica-containing rubber mixture according to claim 1, wherein the polysulphide additive comprises at least one compound of the formula (VII) ##STR00029##

5. The silica-containing rubber mixture according to claim 1, wherein the quantity of sulphur-containing alkoxysilanes is greater than or equal to the quantity of polysulphide additives of the formula (I).

6. The silica-containing rubber mixture according to claim 1, wherein the rubber mixture comprises 1 to 15 parts by weight of one or more sulphur-containing alkoxysilanes, based on 100 parts by weight of rubber used, where the ratio by weight of sulphur-containing alkoxysilane to polysulphide additive of the formula (I) is 1.5:1 to 20:1.

7. The silica-containing rubber mixture according to claim 1, wherein the rubber mixture comprises 0.3 to 7 parts by weight of one or more polysulphide additives of the formula (I), based on 100 parts by weight of rubber used, and 0.3 to 7 parts by weight based on 100 parts by weight of rubber used, of 1,6-bis(N,N-dibenzylthiocarbamoyldithio)hexane (CAS No.: 151900-44-6).

8. The silica-containing rubber mixture according to claim 1, wherein the polysulphide additive comprises at least one compound of the formula (VIII) ##STR00030## in which R.sup.8, R.sup.9, R.sup.10 and R.sup.11 are mutually independently hydrogen, C.sub.1-C.sub.6-alkyl, C.sub.5-C.sub.6-cycloalkyl, C.sub.6-C.sub.10-aryl or a group —CH.sub.2—OR.sup.5, —CH.sub.2—CH.sub.2—OR.sup.5, —CH.sub.2—COOR.sup.5, —CH.sub.2—CH.sub.2—COOR.sup.5 and R.sup.8 and R.sup.9 and, respectively, R.sup.10 and R.sup.11 can also optionally form a ring together with the respective nitrogen atom, and R.sup.5 is as defined above, and at least one of the moieties R.sup.8, R.sup.9, R.sup.10 and R.sup.11 comprises one or more oxygen atoms.

9. The silica-containing rubber mixture according to claim 8, wherein the polysulphide additive comprises at least one compound of the formulae (IX), (X) or (XI) ##STR00031##

10. The silica-containing rubber mixture according to claim 1, wherein the rubber comprises at least one SBR rubber and at least one BR rubber.

11. The silica-containing rubber mixture according to claim 10, wherein the rubber further comprises at least one NR rubber.

12. The silica-containing rubber mixture according to claim 1, wherein the rubber mixture comprises 50 to 200 parts by weight of one or more inorganic and/or organic fillers based on 100 parts by weight of rubbers used.

13. The silica-containing rubber mixture according to claim 12, wherein the at least one filler is selected from the group of precipitated silicas and/or silicates with specific surface area of 20 to 400 m.sup.2/g.

14. The silica-containing rubber mixture according to claim 12, wherein the rubber mixture comprise 60 to 120 parts by weight of the filers and the filler is selected from the group of precipitated silicas and/or silicates with specific surface area of 100 to 200 m.sup.2/g.

15. The silica-containing rubber mixture according to claim 1, wherein Y is —(CH.sub.2).sub.6—.

16. The silica-containing rubber mixture according to claim 15, wherein the rubber mixture comprises: at least one SBR rubber and at least one BR rubber in a ratio by weight SBR:BR of 60:40 to 90:10; 1 to 15 parts by weight of one or more sulphur-containing alkoxysilanes, based on 100 parts by weight of the rubber used, where the ratio by weight of the sulphur-containing alkoxysilane to the polysulphide additive of the formula (I) is 1.5:1 to 20:1; 0.3 to 7 parts by weight of the one or more polysulphide additives of the formula (I), based on 100 parts by weight of rubber used, and 0.3 to 7 parts by weight, based on 100 parts by weight of rubber used, of the 1,6-bis(N,N-dibenzylthiocarbamoyldithio)hexane (CAS No.: 151900-44-6); and 50 to 200 parts by weight, based on 100 parts by weight of the rubbers used, of one or more inorganic and/or organic fillers.

17. The silica-containing rubber mixture according to claim 16, wherein: Y is —(CH.sub.2).sub.6—; the rubber further comprises at least one NR rubber; the ratio by weight of the sulphur-containing alkoxysilane to the polysulphide additive of the formula (I) is 5:1 to 15:1; the rubber mixture comprises 0.5 to 5 parts by weight, of the one or more polysulphide additives of the formula (I), based on 100 parts by weight of rubber used, and 0.5 to 5 parts by weight, based on 100 parts by weight of rubber used, of the 1,6-bis(N,N-dibenzylthiocarbamoyldithio)hexane (CAS No.: 151900-44-6); the rubber mixture comprises 60 to 120 parts by weight, based on 100 parts by weight of rubbers used, of the one or more inorganic and/or organic fillers; and the fillers are selected from the group of oxidic, silicatic filers and carbon blacks and mixtures of these.

18. Vulcanisates and rubber mouldings comprising the silica-containing rubber mixtures according to claim 1.

19. A process for the production of the silica-containing rubber mixture according to claim 1, the process comprising, in a mixing process which has a plurality of mixing stages, where these can optionally be subdivided into a plurality of component steps, mixing: one or more rubbers, one or more hydroxylated oxidic fillers, one or more sulphur-containing alkoxysilanes, one or more vulcanization additives, one or more rubber additives, the at least one polysulphide additive according to claim 1, and the 1,6-bis(N,N-dibenzylthiocarbamoyldithio)hexane (CAS No.: 151900-44-6) wherein the polysulphide additive and the 1,6-bis(N,N-dibenzylthiocarbamoyldithio)hexane are incorporated by mixing in a first mixing stage of the plurality of mixing stages.

20. An additive mixture comprising, based on 100 parts by weight of additive mixture, 10 to 90 parts by weight of one or more polysulphide additives of the formula (I) according to claim 1, and 10 to 90 parts by weight of 1,6-bis(N,N-dibenzylthiocarbamoyldithio)hexane (CAS No.: 151900-44-6.

Description

POLYSULPHIDE ADDITIVE EXAMPLES

Example 1

(1) ##STR00013## Apparatus: 2000 ml four-necked flask with thermometer, dropping funnel with pressure equalization, reflux condenser with gas-discharge attachment (bubble counter) and tubing, stirrer Initial charge: 79.3 g=0.2 mol of Duralink HTS from Flexsys (98.48%) 480 ml of demineralized water 33.6 g=0.4 mol of sodium hydrogencarbonate 32.5 g=0.4 mol of about 37% formaldehyde solution 960 ml of toluene Feed: 31.6 g=0.4 mol of 2-mercaptoethanol (Aldrich, ≧99%)

(2) Duralink HTS and water are used as initial charge in the nitrogen-flushed apparatus. The stirrer is switched on, and then first sodium hydrogencarbonate is added, followed by formaldehyde and toluene.

(3) At a reaction temperature of from 20 to 25° C., 2-mercaptoethanol is then added dropwise within about 30 min, with nitrogen blanketing.

(4) Once addition has ended, stirring is continued at 20-25° C. overnight. The mixture is transferred to a 21 separating funnel. After addition of 8.8 g of sodium chloride, the phases can be separated. The aqueous phase is then extracted twice, in each case with 300 ml of toluene. The combined organic phases are extracted three times, in each case with 300 ml of demineralized water, dried over sodium sulphate, and isolated by filtration.

(5) The product is extracted by freezing at −6° C., isolated by way of a D4 frit, and dried in a vacuum drying oven at 25° C.

(6) Yield: 30.2 g (50%) of a substance of the idealized formula

(7) ##STR00014##

Example 2

(8) ##STR00015## Batch size: 0.25 mol Apparatus: 2000 ml four-necked flask with thermometer, dropping funnel with pressure equalization, reflux condenser with gas-discharge attachment (bubble counter) and tubing, 250 rpm stirrer, pH meter Initial charge: 99.1 g=0.25 mol of Duralink HTS from Flexsys (98.48%) 600 ml of demineralized water 42 g=0.5 mol of about 37% formaldehyde solution 42 g=0.5 mol of sodium hydrogencarbonate 50 ml of toluene Feed: 54.4 g=0.5 mol of thioglycerol (99.4%, Bruno Bock)

(9) Duralink HTS and water are used as initial charge in the nitrogen-flushed apparatus. The stirrer is switched on, and then first sodium hydrogencarbonate is added, followed by formaldehyde and then toluene.

(10) At a reaction temperature of from 20 to 25° C., the thioglycerol is then added dropwise within about 30 min, with nitrogen blanketing. Once addition has ended, a further 200 ml of demineralized water are added so that the mixture is easier to stir. Stirring is then continued at from 20 to 25° C. for 22 h, and the solid is then isolated by suction filtration by means of a D4 frit. The product is then washed six times, in each case with 500 ml demineralized water (conductivity<0.3 millisiemens). The product is then dried to constant weight at 25° C. in a vacuum drying oven.

(11) Yield: 80.4 g (90.6%) of a substance of the idealized formula

(12) ##STR00016##

Example 3

(13) ##STR00017## Apparatus: 2000 ml four-necked flask with thermometer, dropping funnel with pressure equalization, reflux condenser with gas-discharge attachment (bubble counter) and tubing, 250 rpm stirrer, Dulcometer Initial charge: 88.6 g=0.22 mol of Duralink HTS from Flexsys 600 ml of demineralized water 42 g=0.5 mol of about 37% formaldehyde solution 42 g=0.5 mol of sodium hydrogencarbonate Feed: 53.61 g=0.5 mol of 3-mercaptopropionic acid (Aldrich, ≧99%) Auxiliaries: 15% NaOH 37% HCl

(14) Duralink HTS and water are used as initial charge in the nitrogen-flushed apparatus. The stirrer is switched on, and then first sodium hydrogencarbonate is added, followed by formaldehyde.

(15) At a reaction temperature of from 20 to 25° C., the 3-mercaptopropionic acid is then added dropwise within about 1 h, with nitrogen blanketing. During the reaction, a Dulcometer is used to maintain the pH value at pH 8 (±0.2), with 15% NaOH.

(16) Once addition has ended, pH is adjusted to pH 2 with 37% hydrochloric acid, under nitrogen blanketing, with cooling, at 22 (±1)° C.

(17) The reaction suspension is then subjected to suction filtration by means of a D4 frit. The product is then washed six times, in each case with 300 ml of demineralised water (conductivity<0.3 millisiemens). The product is dried to constant weight at 25° C. in a vacuum drying oven.

(18) Yield: 50.8 g (64.4%) of a substance of the idealized formula

(19) ##STR00018##

Example 4

(20) ##STR00019## Apparatus: 2000 ml four-necked flask with thermometer, dropping funnel with pressure equalization, reflux condenser with gas-discharge attachment (bubble counter) and tubing, stirrer, gas-inlet tube Initial charge: 99.1 g=0.25 mol of Duralink HTS from Flexsys (98.48%) 600 ml of demineralized water 41.1 g=0.5 mol of about 36.5% formaldehyde solution 42 g=0.5 mol of sodium hydrogencarbonate Feed: 78.7 g=0.5 mol of 2-mercaptobenzoic acid (98%), dissolved in 500 ml of water at pH 8 under nitrogen via NaOH addition Auxiliary: 37% HCl

(21) Duralink HTS and water are used as initial charge in the nitrogen-flushed apparatus. The stirrer is switched on, and then first sodium hydrogencarbonate is added, followed by formaldehyde.

(22) At a reaction temperature of from 20 to 25° C., the solution of sodium salt of 2-mercaptobenzoic acid is then added dropwise within about 1 h, with nitrogen blanketing. Once addition has ended, stirring is continued for 22 h and then pH is adjusted to pH 2 with 37% hydrochloric acid, under nitrogen blanketing, at from 20 to 25° C.

(23) Stirring is continued for a further hour, and the solid is then isolated by suction filtration by means of a D4 frit. The product is then washed, in each case with 300 ml of demineralized water (conductivity<0.3 millisiemens). The product is then dried to constant weight at 25° C. in a vacuum drying oven.

(24) Yield: 113.3 (99.7%) of a polysulphide mixture of the idealized formula

(25) ##STR00020##

Example 5

(26) ##STR00021## Apparatus: 2000 ml four-necked flask with thermometer, dropping funnel with pressure equalization, reflux condenser with gas-discharge attachment (bubble counter) and tubing, stirrer, pH meter Initial charge: 79.6 g=0.2 mol of Duralink HTS from Flexsys (98.14%) 272 ml of demineralized water 32.9 g=0.4 mol of about 36.5% formaldehyde solution 33.6 g=0.4 mol of sodium hydrogencarbonate 40 ml of toluene Feed: 791.7 g=0.4 mol Na salt of morpholinedithiocarboxylic acid (11.7%)

(27) Duralink HTS and water are used as initial charge in the nitrogen-flushed apparatus. The stirrer is switched on, and then first sodium hydrogencarbonate is added, followed by formaldehyde and then toluene.

(28) At a reaction temperature of from 20 to 25° C., the Na salt of morpholinedithiocarboxylic acid (aqueous solution) is then added dropwise within about 30 min, with nitrogen blanketing. Once addition has ended, stirring is continued at from 20 to 25° C. for 22 h, and the solid is then isolated by suction filtration by means of a D4 frit. The product is then washed four times, in each case with 300 ml demineralized water (conductivity<0.3 millisiemens). The product is then dried to constant weight at 35° C. in a vacuum drying oven.

(29) Yield: 35.9 g (38%) of a substance of the idealized formula

(30) ##STR00022##
Results

(31) The examples below provide further explanation of invention, but there is no intention that the invention be restricted thereby.

(32) The following rubber formulations, listed in Table 1, were selected for the tests. Unless otherwise stated, all numeric data are based on “parts per hundred rubber” (phr).

(33) The following rubber mixtures were produced in a 1.5 L internal mixer (70 rpm), start temperature 80° C. mixing time: 5 minutes. Sulphur and accelerator were finally admixed on a roll (temperature: 50° C.).

(34) TABLE-US-00001 TABLE 1 Rubber formulation Rubber Rubber Reference formulation 1 formulation 2 BUNA CB 24 30 30 30 BUNA VSL 5025-1 96 96 96 CORAX N 339 6.4 6.4 6.4 VULKASIL S 80 80 80 TUDALEN 1849-1 8 8 8 EDENOR C 18 98-100 1 1 1 VULKANOX 4020/LG 1 1 1 VULKANOX HS/LG 1 1 1 ROTSIEGEL ZINC WHITE 2.5 2.5 2.5 ANTILUX 654 1.5 1.5 1.5 SI 69 6.4 6.4 6.4 VULKACIT D/C 2 2 2 VULKACIT CZ/C 1.5 1.5 1.5 CHANCEL 90/95 1.5 1.5 1.5 GROUND SULPHUR Vulcuren 1 1 Polysulphide additive of Example 4 1 Polysulphide additive of Example 3 1 Non-inventive comparisons Comparison 1 Comparison 2 Comparison 3 BUNA CB 24 30 30 30 BUNA VSL 5025-1 96 96 96 CORAX N 339 6.4 6.4 6.4 VULKASIL S 80 80 80 TUDALEN 1849-1 8 8 8 EDENOR C 18 98-100 1 1 1 VULKANOX 4020/LG 1 1 1 VULKANOX HS/LG 1 1 1 ROTSIEGEL ZINC WHITE 2.5 2.5 2.5 ANTILUX 654 1.5 1.5 1.5 SI 69 6.4 6.4 6.4 VULKACIT D/C 2 2 2 VULKACIT CZ/C 1.5 1.5 1.5 CHANCEL 90/95 1.5 1.5 1.5 GROUND SULPHUR Vulcuren 1 Polysulphide additive of Example 4 1 Polysulphide additive of Example 3 1 BUNA CB 24 BR Lanxess Deutschland GmbH BUNA VSL 5025-1 SBR Lanxess Deutschland GmbH CORAX N 339 Carbon black Degussa-Evonik GmbH VULKASIL S Silica Lanxess Deutschland GmbH TUDALEN 1849-1 Mineral oil Hansen&Rosenthal KG EDENOR C 18 98-100 Stearic acid Cognis Deutschland GmbH VULKANOX N-1,3-dimethylbutyl-N- Lanxess Deutschland GmbH 4020/LG phenyl-p-phenylenediamine VULKANOX Polymerized 2,2,4-trimethyl- Lanxess Deutschland GmbH HS/LG 1,2-dihydroquinoline ROTSIEGEL Zinc oxide Grillo Zinkoxid GmbH ZINC WHITE ANTILUX 654 Light-stabilizer wax RheinChemie Rheinau GmbH Si 69 bis(triethoxysilylpropyl) Evonik Industries tetrasulphide VULKACIT D/C 1,3-Diphenylguanidine Lanxess Deutschland GmbH VULKACIT CZ/C N-cyclohexyl-2-benzo- Lanxess Deutschland GmbH thiazole-sulphenamide CHANCEL 90/95 Sulphur Solvay Deutschland GmbH GROUND SULPHUR Vulcuren 1,6,bis(N,N-dibenzyl- Lanxess Deutschland GmbH thiocarbamoyldithio)hexane

(35) TABLE-US-00002 TABLE 2 Collation of results Rubber Refer- formu- Parameter Unit DIN ence lation 1 Mooney viscosity [MU] 53523 95 98 (ML 1 + 4) Mooney scorch at sec acc. to 1253 630 130° C. (t5) ASTM D 5289-95 Full vulcanization at s 53529 1417 301 170° C./t95 Shore A hardness at [Shore A] 53505 66 69 23° C. 300 modulus MPa 53504 15 21 Elongation at break % 53504 349 302 Tensile strength MPa 53504 19 21 Abrasion mm.sup.3 53516 74 60 Wet skid performance — 0.463 0.384 (tan d (0° C.)) Rolling resistance — 0.133 0.109 (tan d (60° C.))

(36) Surprisingly, as shown by the results in Table 2, it was found that hardness (Shore A) measured in the Inventive Example (rubber formulation 1) was higher when comparison was made with the reference. Mechanical properties such as tensile strength, elongation at break and in particular 300 modulus are very good. Wet skid performance is good (tan delta at 0° C.>0.35). There is a marked improvement in rolling resistance when comparison is made with the reference (tan delta at 60° C.<0.12). The abrasion values (<70 mm) are likewise very advantageous. There was a marked improvement in full vulcanization time (less than 500 seconds).

(37) TABLE-US-00003 TABLE 2a Collation of results of comparisons Parameter Unit DIN Comparison 1 Comparison 2 Comparison 3 Mooney viscosity [MU] 53523 106 89 94 (ML 1 + 4) Moorsey scorch at sec acc. to 551 1495 1573 130° C. (t5) ASTM D 5289-95 Full vulcanization at s 53529 262 1588 1798 170° C./t95 Shore A hardness at [Shore A] 53505 65 72 69 23° C. 300 modulus MPa 53504 19.5 15 15 Elongation at break % 53504 313 338 384 Tensile strength MPa 53504 20.5 18 21 Abrasion mm.sup.3 53516 78 76 80 Wet skid performance — 0.434 0.407 0.432 (tan d (0° C.)) Rolling resistance — 0.112 0.145 0.151 (tan d (60° C. )

(38) Surprisingly, as shown by the results in Table 2 and 2a, the vulcanisate of the invention was found to have better 300 modulus values and excellent rolling resistance (tan delta at 60° C.<0.12) in combination with high hardness. The very advantageous abrasion values (<70 mm.sup.3) of the Inventive Example are very particularly surprising. Abrasion was improved by 20% in the Inventive Example when comparison is made with the Comparative Examples and the reference.

(39) Testing of the Rubber Mixture and of the Vulcanisates:

(40) Mooney Viscosity Measurement:

(41) Viscosity can be determined directly from the resisting force exerted by the rubbers (and rubber mixtures) while they are processed. In the Mooney shearing-disc viscometer a grooved disc is surrounded above and below by sample substance and is rotated at about two revolutions per minute in a heatable chamber. The force required for this purpose is measured in the form of torque and corresponds to the respective viscosity. The specimen is generally preheated to 100° C. for 1 minute; the measurement takes a further 4 minutes, while the temperature is held constant.

(42) The viscosity is given together with the respective test conditions, an example being ML (1+4) 100° C. (Mooney viscosity, large rotor, preheat time and test time in minutes, test temperature).

(43) The viscosities of the rubber mixtures specified in Table 1 are measured by means of a Mooney shearing-disc viscometer.

(44) Scorch Performance (t5 Scorch Time):

(45) The same test can also be used as described above to measure the “scorch” performance of a mixture. The temperature selected in this Patent is 130° C. The rotor runs until, after the torque value has passed through a minimum, it has risen to 5 Mooney units relative to the minimum value (t5). The greater the value (the unit here being seconds), the slower the scorch (high scorch values here).

(46) Rheometer (Vulcameter) 170° C./t95 Full Vulcanizaton Time:

(47) The progress of vulcanization in a MDR (moving die rheometer) and analytical data therefor are measured in accordance with ASTM D5289-95 in a MDR 2000 Monsanto rheometer. Table 2 collates the results of this test.

(48) The time at which 95% of the rubber has crosslinked is measured as the full vulcanization time. The temperature selected was 170° C.

(49) Determination of Hardness:

(50) In order to determine the hardness of the rubber mixture according to the invention, milled sheets of thickness 6 mm made of the rubber mixture were produced according to formulations from Table 1. Test specimens of diameter 35 mm were cut from the milled sheets, and the Shore A hardness values were determined for these by means of a digital Shore hardness tester (Zwick GmbH & Co. KG, Ulm).

(51) Tensile Test:

(52) The tensile test serves directly to determine the loading limits of an elastomer. The longitudinal elongation at break is divided by the initial length to give the elongation at break. The force required to reach certain stages of elongation, mostly 50, 100, 200 and 300%, is also determined and expressed as modulus (tensile strength at the given elongation of 300%, or 300 modulus).

(53) Table 2 lists the test results.

(54) Dyn. Damping:

(55) Dynamic test methods are used to characterize the deformation performance of elastomers under loadings which change periodically. An external stress changes the conformation of the polymer chain.

(56) This measurement determines the loss factor tan delta indirectly by way of the ratio between loss modulus G″ and storage modulus G′.