Rubber mixtures containing silicic acid and sulfur-containing additives

Abstract

A silica-containing rubber mixture is produced from a rubber, a sulphur-containing alkoxysilane, a crosslinking agent, a silica-containing filler, 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-B
where x is 0-4, and A and B are the same or different, are alkyl or aryl, and contain at last one oxygen, which may be in the form of a carboxyl group.

Claims

1. Silica-containing rubber mixture comprising: rubber, a sulphur-containing alkoxysilane, a crosslinking agent, a silica-containing filler, and 0.1 to 15 parts by weight, based on 100 parts by weight of the rubber used, of a silicon-free polysulphide additive of the formula (I)
A-S-(S).sub.x-S-B(I) in which: x is 1, 2, 3 or 4 and A and B are independently one of CH.sub.2CH.sub.2COOCH.sub.3 or CH.sub.2COOCH.sub.3, or and A and B are ##STR00012##

2. The silica-containing rubber mixture according to claim 1, wherein the polysulphide additive comprises at least one compound of the formula (II), ##STR00013##

3. The silica-containing rubber mixture according to claim 1, wherein the polysulphide additive comprises at least one compound of the formula (IIa), ##STR00014##

4. The silica-containing rubber mixture according to claim 1, wherein the polysulphide additive comprises at least one compound of the formulae (III), ##STR00015## in which x is 1, 2, 3 or 4.

5. The silica-containing rubber mixture according to claim 1, wherein the mixture comprises an amount of sulphur-containing alkoxysilanes that is greater than or equal to an amount of silicon-free polysulphide additives.

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

7. The silica-containing rubber mixture according to claim 6, wherein the mixture comprises an SBR:BR ratio by weight of from 60:40 to 90:10.

8. The silica-containing rubber mixture according to claim 7, further comprising at least one NR rubber.

9. The silica-containing rubber mixture according to claim 8, wherein the mixture comprises a ratio 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.

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

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

12. The silica-containing rubber mixture according to claim 1, wherein the mixture comprises a ratio by weight of from 1.5:1 to 20:1 of the sulphur-containing alkoxysilane in relation to the silicon-free polysulphide additive.

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

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

15. The silica-containing rubber mixture according to claim 14, wherein the fillers are selected from the group of oxidic and silicatic fillers, and carbon blacks, or a mixture of these.

16. The silica-containing rubber mixture according to claim 15, wherein at least one filler is selected from the group of precipitated silicas and/or silicates with a specific surface area of from 20 to 400 m.sup.2/g.

17. 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. and a Shore A hardness thereof is simultaneously >67 at 23 C., and a 300 modulus value thereof is >12 MPa.

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

19. The silica-containing rubber mixture according to claim 1, where 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 a scorch time of the vulcanizate is simultaneously greater than 1000 seconds.

20. The silica-containing rubber mixture according to claim 1, where 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 a full vulcanization time of the vulcanizate is simultaneously less than 2000 seconds.

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

22. The silica-containing mixture according to claim 1, wherein an ML 1+4 viscosity of the mixture at 100 C. is less than 150.

23. A method for producing vulcanizates and rubber moulding, the method comprising producing vulcanizates and rubber mouldings from the rubber mixture according to claim 1.

24. Vulcanizates and rubber mouldings comprising the rubber mixtures according to claim 1.

Description

EXAMPLES

Example 1

(1) ##STR00007## Apparatus: 500 ml four-necked flask with thermometer, dropping funnel with pressure equalization, reflux condenser with gas-discharge attachment (bubble counter) and tubing, stirrer Initial charge: 91.75 g=0.75 mol of methyl 3-mercaptopropionate (Acros, 98%) of 250 ml cyclohexane (p.A., Merck, dried over molecular sieve) Feed: 51.15 g=0.375 mol of disulphur dichloride (99%, Merck)

(2) Dried cyclohexane and methyl 3-mercaptopropionate are used as initial charge in the nitrogen-flushed apparatus. Once the methyl 3-mercaptopropionate has been completely dissolved, the disulphur dichloride is added dropwise within about 1 h with nitrogen blanketing at a temperature of from 5 to 10 C. The feed rate is to be adjusted so as to avoid exceeding a temperature of 10 C.

(3) Once the reaction has ended, stirring is continued overnight at room temperature under nitrogen blanketing.

(4) The reaction solution is then concentrated by rotating on a Rotavapor at 50 C., and is then dried to constant weight at 60 C. in a vacuum drying oven.

(5) Yield: 108.4 g (95.6%) of a polysulphide mixture of the idealized formula

(6) ##STR00008##

Example 2

(7) ##STR00009## 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: 118.0 g=0.75 mol of mercaptobenzoic acid (Aldrich, 99%) 900 ml toluene (p.A., Aldrich, dried over molecular sieve Feed: 57.15 g=0.375 mol of disulphur dichloride (99%, Merck)

(8) Dried toluene and mercaptobenzoic acid are used as initial charge in the nitrogen-flushed apparatus. The disulphur dichloride is now added dropwise to the present suspension within about 1 h with nitrogen blanketing at a temperature of from 0 to 5 C. The feed rate is to be adjusted so as to avoid exceeding a temperature of 5 C.

(9) Once the reaction has ended, stirring is continued overnight at room temperature under nitrogen blanketing.

(10) The reaction solution is the subjected to suction filtration using a D4 frit and washed twice with approx. 200 ml dry toluene. The product is dried at room temperature (approx 25 C.) in a vacuum drying oven.

(11) Yield: 144.6 g (104.1%) of a polysulphide mixture of the idealized formula

(12) ##STR00010##

Example 3

(13) ##STR00011##
Results:

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

(15) 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).

(16) 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.).

(17) TABLE-US-00001 TABLE 1 Rubber formulation Exam- Exam- Exam- Reference ple 1 ple 2 ple 3 BUNA CB 24 30 30 30 30 (oil-extended rubber from Lanxess Deutschland GmbH) BUNA VSL 5025-1 (Lanxess 96 96 96 96 Deutschland GmbH) CORAX N 339 (commercially 6.4 6.4 6.4 6.4 available carbon black) VULKASIL S (precipitated 80 80 80 80 silica from Lanxess Deutschland GmbH) TUDALEN 1849-1 (mineral oil) 8 8 8 8 EDENOR C 18 98-100 1 1 1 1 VULKANOX 4020/LG 1 1 1 1 VULKANOX HS/LG 1 1 1 1 ROTSIEGEL ZINC WHITE 2.5 2.5 2.5 2.5 ANTILUX 654 1.5 1.5 1.5 1.5 SI 69 6.4 6.4 6.4 6.4 VULKACIT D/C 2 2 2 2 VULKACIT CZ/C 1.5 1.5 1.5 1.5 CHANCEL 90/95 GRIND 1.5 1.5 1.5 1.5 SULPHUR Example 1 1 Example 2 1 Example 3 1

(18) TABLE-US-00002 TABLE 2 Collation of results Parameter Unit DIN Reference Example 1 Example 2 Example 3 Mooney viscosity [MU] 53523 95 82 92 93 (ML 1 + 4) Mooney scorch time sec acc. to 1253 1244 1228 1198 at 130 C. (t5) ASTM D 5289-95 Full vulcanization at sec 53529 1417 1617 1315 1544 170 C./t95 Shore A hardness at [Shore A] 53505 66 72 73 73 23 C. 300 modulus MPa 53504 15 17 18 17 Elongation at break % 53504 349 346 308 332 Tensile strength MPa 53504 19 20 18 19 Abrasion mm.sup.3 53516 74 95 93 82 Wet grip 0.463 0.444 0.452 0.385 (tan d (0 C.)) Rolling resistance 0.133 0.168 0.154 0.160 (tan d (60 C.))

(19) 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).

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

(21) Mooney Viscosity Measurement:

(22) 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.

(23) 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).

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

(25) Scorch Performance (t5 Scorch Time):

(26) 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).

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

(28) 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.

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

(30) Determination of Hardness:

(31) 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).

(32) Tensile Test:

(33) 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).

(34) Table 2 lists the test results.

(35) Dyn. Damping:

(36) 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.

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