Rubber mixtures containing silicic acid and sulfur-containing additives

Abstract

A silica-containing rubber mixture includes at least one rubber, a sulphur-containing alkoxysilane, a crosslinking agent, a filler, and optionally further rubber auxiliaries, and the mixture also includes from 0.1 to 15 parts by weight, based on 100 parts by weight of rubber used, of a silicon-free 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 optionally substituted or heteroatom-containing aliphatic, cycloaliphatic or aromatic group, and A may include hydroxy, carboxy, or carboxyphenyl groups.

Claims

1. A silica-containing rubber mixture comprising at least one SBR rubber and at least one BR rubber in an SBR:BR ratio by weight of 60:40 to 90:10, a sulphur-containing alkoxysilane, a crosslinking agent, a filler, and 0.1 to 15 parts by weight, based on 100 parts by weight of the rubber used, a silicon-free 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 optionally substituted or heteroatom-containing aliphatic, cycloaliphatic or aromatic group, and A is a moiety ##STR00024##

2. The silica-containing rubber mixture according to claim 1, wherein the polysulphide additive is at least one compound of the formula (VII) ##STR00025##

3. The silica-containing rubber mixture according to claim 1, wherein the mixture comprises 1 to 15 parts by weight of the sulphur-containing alkoxysilanes, based on 100 parts by weight of rubber used.

4. The silica-containing rubber mixture according to claim 1, wherein the mixture comprises 0.3 to 7 parts by weight of the silicon-free polysulphide additives, based on 100 parts by weight of rubber used.

5. The silica-containing rubber mixture according to claim 1, wherein a ratio of the sulphur-containing alkoxysilane to the silicon-free polysulphide additive is 1.5:1 to 20:1.

6. The silica-containing rubber mixture according to claim 1, wherein the mixture comprises 0.5 to 5 parts by weight, based on 100 parts by weight of rubber used, of the silicon-free polysulphide additive.

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

8. The silica-containing rubber mixture according to claim 7, wherein the one or more fillers are selected from the group of oxidic and silicate fillers, carbon blacks, and mixtures of these.

9. The silica-containing rubber mixture according to claim 8, wherein at least one filler is selected from the group of precipitated silicas and/or silicates with a specific surface area of 20 to 400 m.sup.2/g.

10. The silica-containing rubber mixture according to any of claim 1, 2 or 6 wherein a ML 1+4 viscosity of the mixture at 100° C. is less than 150.

11. Vulcanizates and rubber mouldings comprising the silica-containing rubber mixtures according to claim 1.

12. The silica-containing rubber mixture according to claim 1, wherein a loss factor tan delta of a vulcanizate produced therefrom by heating at 170° C./t95 is <0.2 at 60° C., the Shore A hardness thereof is simultaneously >67 at 23° C., and the 300 modulus value thereof is >12 MPa.

13. The silica-containing rubber mixture according to claim 1, wherein a loss factor tan delta of a vulcanizate produced therefrom by heating at 170° C./t95 is <0.17 at 60° C., the Shore A hardness thereof is simultaneously >70 at 23° C., and the 300 modulus value thereof is >15 MPa.

14. The silica-containing rubber mixture according to claim 1, wherein a loss factor tan delta of a vulcanizate produced therefrom by heating at 170° C./t95 is less than 0.17 at 60° C., and its scorch time is simultaneously greater than 1000 seconds.

15. The silica-containing rubber mixture according to claim 1, wherein a loss factor tan delta of a vulcanizate produced therefrom by heating at 170° C./t95 is less than 0.17 at 60° C., and its full vulcanization time is simultaneously less than 2000 seconds.

16. The silica-containing rubber mixture according to claim 1, wherein a scorch time of a vulcanizate produced therefrom by heating at 170° C./t95 is greater than 1000 seconds and its full vulcanization time is simultaneously less than 2000 seconds.

17. A silica-containing rubber mixture comprising at least one NA rubber, at least one SBR rubber, at least one BR rubber, a sulphur-containing alkoxysilane, a crosslinking agent, a filler, and 0.1 to 15 parts by weight, based on 100 parts by weight of the rubber, a silicon-free 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 optionally substituted or heteroatom-containing aliphatic, cycloaliphatic or aromatic group, and A is a moiety ##STR00026##

18. The silica-containing rubber mixture according to claim 17, wherein the mixture comprises the at least one SBR rubber and the at least one BR rubber and the at least one NA rubber in amounts of at least 60 and at most 85 percent by weight of SBR, based on rubber, and at least 10 and at most 35 percent by weight of BR, based on rubber, and at least 5 and at most 20 percent by weight of NR, based on rubber.

19. A silica-containing rubber mixture comprising: at least one rubber, a sulphur-containing alkoxysilane, a crosslinking agent, 50 to 200 parts by weight, based on 100 parts by weight of the rubber, of one or more fillers selected from the group of precipitated silicas and/or silicates with a specific surface area of 20 to 400 m.sup.2/g, and 0.1 to 15 parts by weight, based on 100 parts by weight of the rubber, of a silicon-free 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 optionally substituted or heteroatom-containing aliphatic, cycloaliphatic or aromatic group, and A is a moiety ##STR00027##

20. The silica-containing rubber mixture according to claim 1, wherein Y is one of the following groups:
—(—CH.sub.2—).sub.a— where a=2 to 12, ##STR00028## where a=2 to 12, ##STR00029## where b=1 to 4, and ##STR00030## where b=1 to 4.

21. The silica-containing rubber mixture according to claim 19, wherein an amount of sulphur-containing alkoxysilanes in the mixture is greater than or equal to an amount of silicon-free polysulphide additives in the mixture.

22. The silica-containing rubber mixture according to claim 19, wherein the mixture comprises at least one SBR rubber and at least one BR rubber.

Description

EXAMPLES

Example 1

(1) ##STR00014## Apparatus: 2000 ml four-necked flask with thermometer, dropping funnel with pressure equalization, reflux condenser with gas-discharge attachment (bubble counter) and tubing, stirrer

(2) TABLE-US-00001 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%)

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

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

(5) Once addition has ended, stirring is continued at 20-25° C. overnight. The mixture is transferred to a 2 l 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.

(6) 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.

(7) Yield: 30.2 g (50%) of the idealized formula

(8) ##STR00015##

Example 2

(9) ##STR00016##
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

(10) TABLE-US-00002 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)

(11) 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.

(12) 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 milli siemens). The product is then dried to constant weight at 25° C. in a vacuum drying oven.

(13) Yield: 80.4 g (90.6%) of the idealized formula

(14) ##STR00017##

Example 3

(15) ##STR00018## 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

(16) TABLE-US-00003 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

(17) 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.

(18) 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.

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

(20) 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 milli siemens). The product is dried to constant weight at 25° C. in a vacuum drying oven.

(21) Yield: 50.8 g (64.4%) of the idealized formula

(22) ##STR00019##

Example 4

(23) ##STR00020## 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

(24) TABLE-US-00004 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

(25) 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.

(26) 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 the pH is adjusted to pH 2 with 37% hydrochloric acid, under nitrogen blanketing, at from 20 to 25° C.

(27) 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 milli siemens). The product is then dried to constant weight at 25° C. in a vacuum drying oven.

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

(29) ##STR00021##

Example 5

(30) ##STR00022## 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

(31) TABLE-US-00005 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%)

(32) 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.

(33) 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 milli siemens). The product is then dried to constant weight at 35° C. in a vacuum drying oven.

(34) Yield: 35.9 g (38%) of the idealized formula

(35) ##STR00023##
Results:

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

(37) 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).

(38) 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.).

(39) TABLE-US-00006 TABLE 1 Rubber formulation Reference Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 BUNA CB 24 30 30 30 30 30 30 (oil-extended rubber from Lanxess Deutschland GmbH) BUNA VSL 5025-1 96 96 96 96 96 96 (Lanxess Deutschland GmbH) CORAX N 339 6.4 6.4 6.4 6.4 6.4 6.4 (commercially available carbon black) VULKASIL S 80 80 80 80 80 80 (precipitated silica from Lanxess Deutschland GmbH) TUDALEN 1849-1 8 8 8 8 8 8 (mineral oil) EDENOR C 18 98-100 1 1 1 1 1 1 VULKANOX 4020/LG 1 1 1 1 1 1 VULKANOX HS/LG 1 1 1 1 1 1 ROTSIEGEL ZINC 2.5 2.5 2.5 2.5 2.5 2.5 WHITE ANTILUX 654 1.5 1.5 1.5 1.5 1.5 1.5 SI 69 6.4 6.4 6.4 6.4 6.4 6.4 VULKACIT D/C 2 2 2 2 2 2 VULKACIT CZ/C 1.5 1.5 1.5 1.5 1.5 1.5 CHANCEL 1.5 1.5 1.5 1.5 1.5 1.5 90/95 GRIND SULPHUR Example 1 1 Example 2 1 Example 3 1 Example 4 1 Example 5 1

(40) TABLE-US-00007 TABLE 2 Collation of results Parameter Unit DIN Reference Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Mooney viscosity [MU] 53523 95 90 86 94 89 83 (ML 1 + 4) Mooney scorch time sec acc. to 1253 1060 638 1573 1495 1305 at 130° C. (t5) ASTM D 5289-95 Full vulcanization at sec 53529 1417 1520 1320 1798 1588 1369 170° C./t95 Shore A hardness at [Shore A] 53505 66 67 67 69 72 68 23° C. 300 modulus MPa 53504 15 15 16 15 15 15 Elongation at break % 53504 349 361 361 384 338 371 Tensile strength MPa 53504 19 19 20 21 18 20 Abrasion mm.sup.3 53516 74 85 83 80 76 82 Wet grip (tan d (0° C.)) — 0.463 0.351 0.393 0.432 0.407 0.433 Rolling resistance — 0.133 0.151 0.146 0.151 0.145 0.146 (tan d (60° C.))

(41) Surprisingly, as shown by the results in Table 2, hardness (Shore A) measured in all of the examples was higher in comparison with the reference. The mechanical properties, such as tensile strength, elongation at break and 300 modulus, remained almost unaltered here. All of the vulcanizates tested exhibit comparable good wet grip and comparable good rolling resistance when compared with the reference (tan delta at 0° C.>0.35 and tan delta at 60° C.<0.2) and likewise very advantageous abrasion values (<100 mm.sup.3).

(42) Testing of the Rubber Mixture and of the Vulcanizates:

(43) Mooney Viscosity Measurement:

(44) 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.

(45) 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).

(46) The viscosities of the rubber mixtures specified in table 1 are measured by means of a Mooney shearing-disk viscometer.

(47) Scorch Performance (t5 Scorch Time):

(48) 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).

(49) Rheometer (Vulcameter) 170° C./t95 Full Vulcanization Time:

(50) 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.

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

(52) Determination of Hardness:

(53) 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).

(54) Tensile Test:

(55) 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).

(56) Table 2 lists the test results.

(57) Dyn. Damping:

(58) 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.

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