CA1049171A

CA1049171A - Vulcanizable rubber mixtures for tire treads

Info

Publication number: CA1049171A
Application number: CA74211285A
Authority: CA
Inventors: Kurt Burmester; Siegfried Wolff; Erhard Klotzer; Friedrich Thurn
Original assignee: Deutsche Gold und Silber Scheideanstalt
Current assignee: Evonik Operations GmbH
Priority date: 1973-10-11
Filing date: 1974-10-11
Publication date: 1979-02-20
Also published as: NO142310B; NO142310C; JPS5652057B2; CH612886A5; LU71076A1; FR2247501A1; FI63050B; FI63050C; FR2247501B1; ES430050A1; SE414406B; DE2447614C2; NL7412353A; FI272074A; IE40183B1; NO743298L; DD114269A5; SE7412797L; NL178513B; BE821015A

Abstract

ABSTRACT OF THE DISCLOSURE
The present invention provides a vulcanizable rubber mixture for tire treads which is based on rubbers capable of being cross-linked, silica filler, processing oil, sulphur-con-taining organosilanes and accelerator, said mixture comprising one or two polybutadiene rubbers in amounts of 20 to 100% by weight of the proportion of elastomer, one or two rubbers other than polybutadiene selected from synthetic rubbers and natural rubbers in amounts of 80 to 0% by weight of the proportion of elastomer in the rubber mixture, active silica filler in amounts of more than 80 parts by weight per 100 parts by weight of rubber, processing oil in amounts of 40 to 100 parts by weight per 100 parts of rubber, at least one bis-[-alkoxy silyl alkyl]-oligosulphide in amounts of 0.1 to 25% by weight per 100 parts by weight of rubber, sulphur in amounts totalling approximately 0.2 to 8 parts by weight per 100 g of rubber and at least one vulcanization accelerator in amounts of approximately 0.1 to 8 parts by weight per 100 parts by weight of rubber The present invention also includes a tire tread formed from said mixture.

Description

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The present invention relates to special vulcanizable rubber mixtures for producing tire treads, which are intended for vehicle tires with marked resistance to skidding on wet, snow-covered roads and particularly on icy roads.
The automobile tires which are most frequently used at present to permit vehicles from skidding and planing on roads covered with ice and compacted snow are the snow tires studded with hard steel spikes, i.e., the so-called studded tires. -~
The use of studded tires, particularly the large num-ber of motor vehicles fitted with s-tudded tires has resulted in substantial disadvantages. Intense and widespread damage to the road surfaces has been caused by formation of grooves which ~
has in turn resulted in new dangers, as for example, the known ~ -aqua-planing. Moreover the studded tire has disadvantages .
insofar as driving is concerned resulting in longer stopping distances and having a more unfavourable stability on curves.
The speed limitations which were decreed for vehicles fitted with studded tires in order to reduce the damage to road covers do not remove the damages mentioned or at least not to an appreciable extent. Moreover the use of studded tires during the warm seasons, of the year is not only useless but it also results in dangers to vehicles and passengers and causes the damage to road covers described hereinbefore.

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Numerous tests were carried out to increase the co-' efficient of friction of tire treads in order to improve the adhesion of tires on wet roads, on ice and on compacted snow.
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It was obvious to solve the problem by obtaining a mechanical ! effect on ice. Thus, for example, coarsely divided foreign substances such as small pebbles, cement particles, walnut shells, hard rubber, steel chips and steel wool were incorporated in the tread mixture. However, these measures were of little or no use -1- ~' ;

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~ Attempts were also made to increase the adhesion of . tires on icy roads by way of the mixture composition of the tread. However, decisive, i.e., the desired improvements could not be obtained. The antiskid properties of the studded tires on icy roads could not be obtained heretofore, that is to say, not even remotely. Therefore, the most important problem of --developing a vehicle tire which is non-skidding in the winter and in inbetween seasons, particularly on ice-covered and snow-covered roads, still remained to be solved.
A tire txead made of a vulcanized rubber mixture con-sisting of a rubber, a finely divided reinforcing silica pigment ' and a coupling agent is also known (British Patent No. 1,310,379).
A very large number of coupling agents are mentioned along with-general formulae but only a few individual coupling agents which ;~1 are silanes containing sulphur in the molecule are mentioned.
The mercapto propyl trimethoxy silane and the mercapto propyl triethoxy silane tested according to the examples obviously are the only ones tried in practice. Apart from the coupling agent and the silica pigment the rubber mixtures used for producing - the treads have no specific mixture ingredients and proportions.
Reduced curing time and improvements with respect to the viscos-ity, the modulers values, the permanent set and hysteresis or the heat build-up~are cited as favourable properties of the disclosed mixtures as compared with those of the prior art.
Surprisingly, a tread mixture and a tread produced therefrom and a tire provided with this tread have now been discovered. Said tread has a skid resistance which equals that - 30 of a studded tire having a projecting length of the steel .~
spikes .. . .
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of 1.2 mm and it even surpasses the studded tire in some of its properties.
~ ~he novel vulcanizable rubber mixture for tire treads is based on rubber (which can be cross-linked preferably with sulphur) silica filler, processing oil, organosilane, sulphur and accelerator and is characterized in that the rubber mixture consists of one or two polybutadiene rubbers in amounts of 20 to 100~ by weight of the proportion of elastomer, one or two rubbers ~ (other than polybutadiene) from the groups of synthetic rubbers and natural rubbers in amounts of 80 to 0% by weight of the proportion of elastomer in the rubber mixture, active silica filler in amounts of at least 60 parts and preferably more than 80 parts by weight per 100 parts by weight of rubber, processing ~; oil in amounts of 40 to 100 parts by weight per 100 parts by weight of rubber, at least one bis-[alkoxy silyl alkyl]-oligosulphide in amounts of 0.1 to 25 parts by weight per 100 -` parts by weightof rubber, sulphur and, if required, sulphur donors in amounts totalling approximately 0.2 to 8 parts by weight per 100 g of rubber and at least one vulcanization 20 accelerator in amounts of approximately 0.1 to 8 parts by weight per 100 parts by weight of rubber as well as, if required, the ~' usual amounts of further mixture ingredients used in the tire -~- ... .
industry such as age resisters, fatigue resisters, antiozonants, antioxidants, dyes, pigments, adhesive additives, activators and waxes. If required, the mixture can also contain reinforcing ;~ carbon black in amounts of 0.1 to 50 parts by weight per 100 parts by weight of rubber.
Contrary to expectations, i.e., surprisingly, this rubber mixturé according to thé invention, despite its extremely high proportion of filler, has such a low viscosity that it can be readily processed and particularly is extrudable and therefor can be used in conventional machinery in tire plants because of its properties. It is equally surprising that despite the very .

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~9~71 high proportion of filler and the additionally high proportion of processing oil, the mixture can be successfully vulcanized such that the vulcanizate has the required properties with respect to tensile strength, tear resistance and the like, and this, despite the fact that the presence of carbon black is not required, and that the treads or tires produced from the novel mixture show an excellent and unexpectedly favourable behavior on wet, ice-covered and/or slippery snow-covered roads despite the unusual composition of the mixture.
These outstanding properties could be obtained, in particular only by the concomitant use of the oligosulphidic silanes, which are known per se. Silanes having the general formula Z - Alk - Sn - Alk - Z
are a substantial component of the rubber mixtures. In this formula Z represents the groupings Rl Rl R2 - Si / R , - Si / R and - Si - ~2 \R2 \R2 \R2 " ,, 2Q wherein R represents an alkyl yroup containing 1 to 4 carbon atoms, a cycloalkyl group containing 5 to 8 carbon atoms or the phenyl radical and R2 represents an alkoxy group containing 1 to 8 carbon atoms or a cycloalkoxy group containing 5 to 8 carbon atoms and all the symbols Rl and R2 can have the same or a different meaning, Alk represents a divalent, straight or branched hydrocarbon radical containing 1 to 8 carbon atoms, preferably on alkylene radical containing 2 to 4 carbon atoms and n repre-sents a number from 2.0 to 6.0, preferably from 2.0 to 4Ø Alk can also represent, an unsaturated or a cyclic hydrocarbon radical.
These bis-Calkoxy silyl alkyl]-oligolsulphides can be produced according to the Belgian Patent 787.,691. For example, ' ' . ' ~4~
according to the invention the following silanes can be used with advantage: bis - [3-trimethoxy silyl propyl]-trisulphide, bis -[3-triethoxy silyl propyl]-trisulphide, bis - [3-trimethoxy silyl propyl]- tetrasulphide, bis - ~3-triethoxy silyl propyl]- tetra-sulphide, bis - [3-diethoxy-methyl silyl propyl]- tetrasulphide, bis - ~3-diethoxy-phenyl silyl propyl]- tetrasulphide, bis -~3-tricyclohexoxy silyl propyl]- tetrasulphide, and bis - ~2-tri~
ethoxy silyl ethyl]- tetrasulphide. With respect to their sulphur content the applicable silanes can differ from the content deter-mined stoichiometrically so that "n" in the general formula I can also represent fractions of integers, for example, or advantageously between 2.8 and 4.2.
Polybutadiene rubber (BR) must be present in the rubber mixture as a polymer component, if required even a mixture of two polybutadienes. In most cases it is required to use one or even two additional kinds of rubber as mixture ingredients. For this purpose rubbers having a vitrification point as low as possible are particularly well suited. In this connection natural rubbers (NR), synthetic rubbers of isoprene (IR) and trans-poly-pentanamers are preferable mentioned. Rubbers made from styrene and butadiene (SRB), particularly co-polymers of so-called "low Mooney" quality, i.e., SRB types having low Mooney viscosity (see DIN 53523, ASTM D1646-62 or BS 1673:3:1951) which can be obtained commercially and are characterized as such, nitrile rubbers, ha-logen-butyl rubbers such as chloro- or bromo-butyl rubber, ethylene-propylene-diene terpolymers or similar rubbers, which preferably can be cross-linked with sulphur, are also suitable.
Among the BR types particularly those having average molecular weights are used. Those having a high cis-1,4 content are pre-ferred.

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In the novel rubber mixtures two rubber types, for example, BR and SBR or BR and N~ or BR and IR, are preferably used. The amounts of BR are 20 to 100% by weight, particularly 30 to 90, preferably 50 to 85% by weight of the proportion of elastomer proportion, i.e., 80 to 0~ by weight, is provided by the other rubber types mentioned, i.e., by the synthetic rubbers, with the exception of BR and/or natural rubbers.
The selection of the active fillers their high proportion are particularly important. The silica known in the rubber-processing industry is primarlly suited as the filler, preferably an active or reinforcing silica in a highly dispersed form which consists for the most part or substantially of silicon dioxide. This means particularly precipitated silicas of great purity and activity and haviny BET surface areas between approx-imately 50 and 300 sg m per gram and average primary particle sizes of more than approximately 10 millimicrons, for example, between 10 and 50 millimicrons. Other applicable silica fillers are the known pyrogenically produced silicas. Mixtures of silica fillers can also be used with advantage.
This silica filler must be used in amounts of at least 60 parts and preferably more than 80 parts by weight per 100 parts by weight of rubber in order to assure the desired good wet skid resistance of the finished tire despite the high pro-portion of polybutadiene in the mixture. The amounts of silica filler thus are larger than the amounts of carbon black used in tire treads heretofore, whereby, per se t the processability of the rubber mixture with respect to its viscosity would no longer be assured and the rubber-technological value level of the vul- ~ -canizate (tensile strength, tear strength, etc.) would no longer be attainable if it were not for the presence of a bis - [alkoxy silyl alkyl]-oligosulphide in the rubber .. . . . .
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mixture. The upper limit of the proportion of silica can vary depending on the desired properties of both the ~ixture and the .
vulcanizate. It can be determined by a person skilled in the art. The amounts of filler are suitably in the range from approx-imately 80 and 130 parts by weight, preferably between > 90 and 120 parts by weight per 100 parts by weight of rubber.
mAny In ~ffl~ cases it was found to be expedient to first thoroughly mix the oligosulphidic sllanes with a portion of the active silica, for example, in equal portions (by weight), where-upon this silane-silica mixture is added to the other ingredients of the rubber mixture, thus to mix it with the rubher and the processing oil, for example, in the first stage of mixing.
It can be particularly advantageous if activators are present in the rubher mixture according to the invention. These substances referred to as basic activators or also as filler activators are, for example, diphenyl guanidine, hexamethylene tetramine, o-tolyl guanidine, triethano amine, cycohexyl amine, diethylene glycol and other known useful guanidines, amines or polyhydric alcohols. The amounts in which these basic activators are used must be chosen relative to the amounts of fillers and are between approximately 0.2 and 8 parts by weight per 100 parts by weight of the white filler.
If desired, carbon black can also be present in the rubber mixture according to the invention, for example, for the purpose of coloring it. The carbon black can usually be incor porated in the mixture in amounts between approximately 0.1 and 50 parts by weight per 100 parts by weight of rubber, if required even in smaller amounts. Any type of carbon black, particularly the types of carbon black conventionally used for treads in the rubber industry are suitable. For example, HAF carbon blacks and ISAF carbon blacks are particularly mentioned.
The processing oil to be concomitantly used according . -. :: . : ... .. .. . . ........... . . ....... .
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to the invention is an important ingredient of the rubber mixture and so is the proportion of the processing oil in the mixture.
The proportion must be within the limits of approximately ~0 to approximately 100 parts by weight per 100 parts by weight of rubber, preferably within the limits between 50 and 80 parts by weight per 100 parts by weight of rubber. Processing oils of the type of the ~ oils are preferably used. Processing oils having a setting point between 0 and -60C, preferably between -10 and -55C are particularly favourable. However, processing oils of a highly aromatic nature can also be used and, if re~uired, even those of an aromatic nature A Even mixtures of different processing oils can be used with advantage. The pro- -;
cessing oils usually are petroleum fractions, which can also be chemically modified if required.
The bis - ~alkoxy silyl alkyl~-oligosulphides are usually incorporated in the rubber mixture in amounts of 0.1 to 25 parts by weight, preferably in amounts of 1.0 to 15 parts by weight per 100 parts by weight of rubber.
By adhesive additives are meant known substances or mixtures of substances which, during the vulcanization, bring ~-about a good adhesion (binding) of the rubber mixture to the ma-terials concomitantly used in the manufacture of tires such as metals or textiles, as for example, steel cord, textile~fibre cord, glass-fibre cord, and bead wire. They are applied in the usual amounts.
For the vulcanization the novel rubber mixtures contain preferably sulphur, if required, also sulphur donors such as the known N,NI - dithio-bis-hexahydro-2H-azepinone - (2) and 2-benz-thiazyl-dithio-N-morpholide, both counted together in usual ~ 30 amounts of approximately 0~2 to approximately 5 parts by weight .' . ' . ' , ., ' . ~ . :
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per lO0 parts by weight of rubber as well as at least one vulcanization accelerator likewise in the usual amounts of - approximately 0.1 to 8 parts by weight per 100 parts by weight of i rubber. For special purposes the vulcanization can also be carried out with peroxides, for example, with dicumyl peroxide.
According to the invention it is particularly favour-; able to use as accelerators in the vulcanization with sulphur, sulphur-containing triazine derivatives, which are described in - French Patent 1564 112 or British Patent 1201862 for example, bis -[(2-ethyl-amino-~-diethyl-amino-triazinyl-6)]-disulphide, possibly in combinationwith other known accelerators, for example, diphenyl guanidine.
An organic acld, as for example, stearic acid, benzoic acid or salicylic acid, and, if required, zinc oxide or lead -. .
; oxide, is preferably used in the mixture according to the inven-tion in the usual amounts. It is also favourable in incorporate in the mixtures according to the invention auxiliary agents which are known per se such as protective agents against oxida-tive influences and fatique resisters and age resisters and/or antiozidants in the usual amounts. If required, fur-ther additives known in the rubber-proeessing industry sueh as pigments, dyes and other known agents, whieh improve the adhesion of fillers, waxes, aetivators and the like ean be added to the mixture in the usual amounts.
The production of the rubber mixtures as well as the 'r,~ moulding, for example, by extrusion, and the vuleanization are earried out aeeording to known methods and with the aid of known devices used in the rubber industry.
The inven:tion also includes the mixing process. Said - proeess for produeing vulcanizable rubber mixtures for tire ~I treads, _g_ ' ~ , , .
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i.e., mixtures based on rubbers which can be cross-linked preferably with sulphur, and based on silica filler, processing oils, sulphur-containing organosilane, sulphur and accelerator, is characterized in that one or, if required, two polybutadiene rubbers in amounts of 20 to 100% by weight of the proportion of elastomer, one or tworubbers (other than polybutadiene) from the group of synthet;c rubbers and natural rubbers in amounts of 80 to 0~ by weight of the elastomer proportion in the rubber mixture,active silica filler in amounts of at least 60~ and preferably more than 80~ by weight per 100 parts by weight of rubber, processin~ oil in amounts of 40 to 100 parts by weight per 100 parts by weight of rubber, at least one bis - [alkoxy silyI alkyl]-oligosulphide in amounts of 0.1 to 25 parts by weight per 100 parts by weight of rubber, sulphur and if required , sulphur donors in total amounts of approximately 0.2 to 8 parts by weight per 100 g of rubber and at least one vulcanization accelerator in amounts of approximately 0.1 to 8 parts by weight per 100 parts by weight of rubber and, if required, the usual amounts of further additives used in the tire industry such as age resisters, fati~ue resisters, antiozidants, antioxidants, dyes, pigments, adhesive additives, activators and waxes are mixed until they are homogeneously dlstributed.

The mixing is carried out with advantage according to the so-called upside-down process in a kneader. The rubber mix-ture is then further processed, suitably by extruding with the aid of known extruders.
The subsequent moulding and vulcanization are carried out at the usual temperatures, ranging from approximately 100 and approximately 300C, preferably between 130 and 240C. For this purpose the vulcanizing devices used in the tire industry are applied.

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The present invention will be further illustrated by way of the following Examples.
Example 1 . ~
Two mixtures according to the invention have the follow-ing compositions (in parts by weight):

~ixture 1 Mixture 2 . ~
low Mooney styrene - butadiene rubber 30 3 n polybutadiene rubber having a high cis-1,4 content 70 70 precipitated active silica, surface area as measured according to BET: 130sg m/g; 95 114 average primary particle size:
28 millimicrons; ::~
Ultrasil VN 2 of DEGUSSA

bis - 3-triethoxy-silyl- ~
propyl -tetrasulphide 5 6 :
zinc oxide 3 3 :-stearic acid highly aromatic processing oil 48 69 age resister N-isopropyl-N' -phenyl-p-phenylene diamine 1.2 1.2 age resister phenyl-B-naph-thylamine 1.2 1.2 benzthiazolyl~2-cyclohexyl -sulphene amide 1.2 1.2 .
diphenyl guanidine 3.15 2.8 tetramethylthiuran monosulphide - 0.1 sulphur 2 2 ;
260.75 301.5 The two mixtures and their vulcanizates were compared with a conventional snow-tire mixture "A" for a tread of a current tire produced in Germany and with the following carbon-black-containing mixture "B" and its vulcanizates.

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Mixture B

oil-extended styrene-butadiene rubber 95.5 cis-1,4-polybutadiene 30 ISAF carbon black (Corax 6 of Degussa) 75 zinc oxide 4 stearic acid 1.2 highly aromatic processing oil 15 ::
age resister N-isopropyl N'- ~ -phenyl-p-phenylene diamine 1.5 age resister phenyl-B-naphthyl amine 1.5 benzthiazolyl-2-cyclohexyl sulphene amide 1.2 -~
sulphur 1.6 227.5 In the tests and in the results resulting there~rom the following abbreviations were used:
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Abbreviation Term Measured In .. _ . . .. _ ~ t5 Mooney scorch time minutes , t35 Mooney cure time minutes ML 4 MooneyOplasticity at 100 C, standard rotor, testing time 4 minutes -speg. Gew. specific gravity g/cu m VZ vulcanizing time minutes VT vulcanizing temperature C

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Continuation of Page 1'2' -- - ~
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Abbreviation ~Term - Mea'sured'In ZF tensile strength kp/sq cm M 300 tension value at 300% elongation kp/sq cm BD elongation at break %
bl.D. permanent elongation upon break %
E shock elasticity SH Shore A hardness - ' :.,' ' EF resistance to tear -propagation kp/cm A abrasion (also "DIN
abrasion") mm3 ~ ' ' ~T rise of temperature ' ' (see Goodrich flexo-meter) C
~.. ._ , -Testing Standards - '~
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` The physical tests were carried out at room temperature '. ~.
~' according to the following standard specifications~
tensile strength, elongation at ,.
break, tension value on rings of ''' 6 mm thickness DIN 53504 resistance to tear propagation DIN 53507 shock elasticity DIN 53512 :-Shore A hardness DIN 53505 specific gravity DIN 53550 Mooney test DIN 53524 . Goodrich flexometer (determination of the heat ~.
build-up ~T) ASTM D 623-62 abrasion DIN 53516 , The vulcanizates were always produced in a steam-heated platen press at the vulcanization temperatures mentioned hereinbefore. ~ -:, :
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Properties of the Unvu'lca~iz`ed`Mixtur`es Mixture A 'B' 1 2 t5 (130C) 18,5 29,6 15,4 14,0 t35 22,2 33,3 20,1 17,4 ML 4 60 64 60 67 .
specific :.
gravity 1,16 1,15 1,21 1,23 _ Properties of the Vulcanized Mixtures The vulcanization was carried out at 160C

_ -Mix*ure VZ ZF M 300 BD _ bl.D. E SH EF A

40 166 65 620 29 58 19 i :
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169 56 690 23 i7 56 14 ' '~

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2 20 121 42 715 50 24 67 28 111 ~' ' 40 113 43 677 40 25 70 ~7 ~ '~

Good~ich Flexometer Tests vulcanization temperature 160C ~ curiny time 40 minutes stroke 0.250 frequency 30 Hz.
specific ~ load 11 kg.

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Continuation from page 1`4- `````
Test temperature: room temperature Duration of test: 25 minutes . _-- - --- , :

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~T O static/dynamic permanent Mixture in C compression in % set in %
.._ A 136 15,6 36,0 25,8 B 149 16,1 36,2 27,3 1 79 15,4 32,0 25,9 2 87 19,4 3?~5 34,2 From the four mixtures (1 and 2 according to the inven-tion, A and B according to the prior art) treads were produced and tires were in turn produced from the treads. These tires were then tested on a motor car on an aritificial ice rink and on the wet lane of a road provided with a rough asphalt cover and the results were compared with one another. The testing was carried out with the same motor car. All the sets of tires had the same -engraving. The car was first driven on a circular path having an effective diameter of 20 metres (circular path test, 4 runs - of measurement, driving-time measurement).
Second, in a brake test at an initial speed of 30 km per hour full-blocking measurements were carried out (braking retardation by measuring the stopping distance in metres).
Third, the acceleration test was carried out by driving a measuring section of 22 metres with dead start at a maximum of possible acceleration (timing in seconds and measurement of the final speed after 25 metres). The artificial ice had a tempera-ture of 0 - 3.5C on the surface. The air temperature at a ,' ~0493L-~
height of 0.8 m above the surface of the ice was 2 to 4C.
The testing of the tires on a wet roadwa~ was carried out on a watered circular path (asphalt). At an effective diameter of 67 metres 4 runs of measurement were driven. The driving time in seconds was measured with the aid of a light barrier. In the brake tests on a wet roadway the car was driven at an initial speed of 50 km/h and 80 km/h, respectively, and on the watered rough asphalt path full blocking measurements were then carried out. The stopping distance was measured in metres and the average retardation was determined.
The temperature on the surface of the roadway was 11 to 20C and the air temperature was 9 to 19C.
From all the measured values average values for accel-eration, circular acceleration and retardation can be determined and therefrom the ~ values (also called coefficients of friction~.
For the evaluation the coefficient of friction concerned (as an average) for the tires produced from the mixture A was equated to 100. The following evaluations were obtained from the other measured coefficients of friction:

Testing On Ice On a Wet_~oadway Mixture Circular Path Braking Acceleration Circular Path Braking B 95 95 96 100104 ~
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2 129 1~1 121 98 95 ; : :, The following results can be deduced from these figures.

The coefficients of *riction (expressed in %) and the ~ values of the skidding tests on ice su~stantiate the substantial ' ',: ' .. . .

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improvements attained in the skid resistance on ice for the tires produced from the mixtures according to the invention. The appreciable increase in the skid resistance on ice was found to be well reproducible. This was repeatedly confirmed. Such good values of the skid resistance on ice were not known heretofore.
A tread quality was thus found which can fully replace the studded tires produced and used at present insofar as their favourable behaviour on ice is concerned.
The motor-car snow tires used for the comparison tests have been produced for a number of years and are available on the market. They have a tread quality (mixture) which is regarded as very good. This mixture A was especially developed with favour-able skid properties on ice with a balanced ratio of ice-skid resistance and wet-skid resistance. However, the mixture A is a mixture which contains only carbon black as the filler like the tread mixture B, which was used for the comparison. For the mixture B a representative composition like that frequently used today in the production of motor car tires was used. In their skid behaviour on ice these mixture-B tires are slightly more unfavourable than the mixture-A tires. Compared with the mix ture A the invention can result in improvements in the skid be-haviour on ice of up to and exceeding 30%. This can be achieved only by means of the mixture compositions according to the in-vention.
Example 2 Another mixture according to the present invention had the following composition:
MIXTURE 3 Parts by Weight Natural Rubber ML 4 approx. 40 3n cis-1,4-Polybutadiene (98 ~ cis-1,4)70 , .

109~
(continuation of MIXTURE 3~
Precipitated active silica having a specific surface area measured according to BET of 200 m2/g and an average primary particle size of 18 millimicrons (Ultrasil VN 3 a trademark of Degussa) 103 HAF improved (Corax 4 a trademark of Degussa) 5 Bis-(3,3~-triethoxysilylpropyl)-tetrasulfide 8 Zinc oxide 4 , Stearic acid Naphthenic hydrocarbon plasticizer oil (setting point -28C) 70 Anti-ager, N-isopropyl-N'-phenyl-p-phenylenediamine 1,5 .
Anti-ager, phenyl-~-naphthylamine 1,5 Diphenyl guanidine 3,5 Bis-~2-ethylamino-4-diethylamino-triazine-6-yl)-disulphide 2 Sulfur 2 301,5 '~ , t5 (130C) 11,4 t35 (130C) 15,5 ' ~ :

spec. gravity 1,18 Propertie's of'the'vul'can'ized'Mlx'ture ' The vulcanization took place at 150C~20l ';
Tensile Strength kp~cm2 133 : Modulus 300 kp~cm2 62 Elongation at Break % 577 , Perm. Set after Break ~ 35 i~
Resilience ~ 34 : Shore-Hardness - 68 - Tear Resistance kp~cm 31 : Abrasion mm3 61 1~ :

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Skid~test against Mlx*ur'e'2 Mixture On Ice On Wet Roadway Circular Road Braking Braking 2 (of example 1~ la0 100 100

3 g8 94 99 Exam ~
Another mixture according to the invention had the followlng composition:
MIXTURE 4 -Par't's'by Weight Natural Rubber ML 4 approx. 40 30 cis-1,4-Polybutadiene ~98 ~ cis-1,4~ 70 Precipitated active silica having a specific surface area measured according to BET of 200 m2/g and an average primary particle si2e of 18 millimicrons (Ultrasil VN 3 a trademark of Degussa) 60 ISAF improved ~corax 7 a trademark of Degussa~ 60 Bis-~3,3'-tr.iethoxysilylpropyl)-tetrasulfide 2,5 :
Zinc oxide , 4 Stearic acid 1 2Q , Naphthenic hydrocarbon plasticizer oil (setting point -28C) 72 Anti-ager, N-isopropyl-N'-phenyl-p-phenylenediamine 1,5 .
Anti-ager, phenyl-~-naphthylamine 1,5 `~. -Diphenyl guanidine 1,5 Bis-(2-ethylamino-4-diethylamino-triazine-6-yl)disulphide 2 Sulfur 2 , ':
308,0 . ~ . .
'~ t5 (130C) 21,2 -' : 30 ` :

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t35 (130oc~ 26,0 .

spec. gravity 1,17 .
Properties of the vulcanized Mixture The vulcanization took place at 160C~20' Tensile Strength kp~cm2 80 Modulus 300 kp~cm2 48 Elongation at Break % 450 Perm. Set after Break ~ 32 Resilience % 24 Shore-Hardness - 65 Tear Resistance kp~cm 15 Abrasion mm3 76 Sk'id-test a'gain`st Mix'ture'A-and B
.
(Mixtures A and B being conventional mixtures for the production of winter tires containing carbon-black as the only ~' filler). :' Mixture On Ice On Wet Roadway Circular Road Braking Braking A 100 100 100 .,.
B 100 96 100 ~ :

4 115 116 102 : :
.:
,~ 2Q

:' ' ' ':
, ., .. ; ,.
, - 20 - , , . .

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A vulcanizable rubber mixture for tire treads which is based on rubbers capable of being cross-linked silica filler, processing oil, sulphur-containing organosilanes and accelerator, said mixture comprising one or two polybutadiene rubbers in amounts of 20 to 100% by weight of the proportion of elastomer, one or two rubbers other than polybutadiene selected from synthetic rubbers and natural rubbers in amounts of 80 to 0%
by weight of the proportion of elastomer in the rubber mixture, active silica filler in amounts of at least 60 parts by weight per 100 parts by weight of rubber, processing oil in amounts of 40 to 100 parts by weight per 100 parts of rubber, at least one bis - [alkoxy silyl alkyl]-oligosulphide in amounts of 0.1 to 25% by weight per 100 parts by weight of rubber, sulphur in amounts totalling approximately 0.2 to 8 parts by weight per 100 g of rubber and at least one vulcanization accelerator in amounts of approximately 0.1 to 8 parts by weight per 100 parts by weight of rubber.

2. A mixture according to claim 1, which contains as the rubber a mixture of polybutadiene rubber and styrene-buta-diene rubber.

3. A mixture according to claim 1, which contains as rubber a mixture of polybutadiene rubber having a high cis-1,4 content and a low Mooney styrene-butadiene rubber.

4. A mixture according to claim 1, which contains as rubber, a mixture of polybutadiene rubber and natural rubber.

5. A mixture according to the claims 1, 2 or 3, including carbon black in amounts of approximately 0.1 to 50 parts by weight per 100 parts by weight of rubber.

6. A mixture as claimed in claim 1, in which the oligo-sulphidic silane has the general formula Z - Alk - Sn - Alk - Z

where Z is selected from , , and R1 is alkyl having 1 to 4 carbon atoms; cycloalkyl having 5 to 8 carbon atoms or phenyl, R2 is alkoxy having 1 to 8 carbon atoms or cycloalkoxy having 5 to 8 carbon atoms, Alk is a divalent by hydrocarbon atoms having 1 to 8 carbon atoms and n is a number from 2.0 to 6Ø

7. A mixture as claimed in claim 6 in which Alk is an alkylene group having 2 to 4 carbon atoms.

8. A mixture as claimed in claim 7 in which n is a number from 2.0 to 4Ø

9. A mixture as claimed in claim 7 in which n is a number from 2.8 to 4.2.

10. A mixture as claimed in claim 6 in which the oligo-sulphidic silane is selected from: bis - [3-trimethoxy silyl propyl]- trisulphide, bis - [3-triethoxy silyl propyl]-trisulphide, bis - [3-trimethoxy silyl propyl]-tetrasulphide, bis -[3-trie-thoxy silyl propyl]- tetrasulphide, bis - [3-diethoxy-methyl silyl propyl]- tetrasulphide, bis - [3-diethoxy-phenyl silyl propyl]-tetrasulphide, bis - [3-tricyclohexoxy silyl propyl]- tetrasul-phide, and bis - [2-triethoxy silyl ethyl]- tetrasulphide.

11. A mixture as claimed in claim 9 in which Alk is propylene.

12. A mixture as claimed in claim 6 in whîch the silane is bis - [3-triethoxy-silyl propyl]- tetrasulphide.

13. A mixture as claimed in claim 1, 2 or 3 in which the rubbers are cross-linked with sulphur.

14. A mixture as claimed in claim 1, 2 or 3 in which the polybutadiene rubber is present in an amount from 30 - 90%
by weight of the elastomer.

15. A mixture as claimed in claim 1, 2 or 3 in which the polybutadiene rubber is present in an amount of from 50 -85% by weight of the elastomer.

16. A mixture as claimed in claim 1, 2 or 3 in which the active silica filler is a precipitated silica of large purity a BET surface area between about 50 and 300 sq. m per gm and an average primary particle size of more than 100 millimicrons.

17. A mixture as claimed in claim 1, 2 or 3 in which the active silica filler is present in an amount from 80 to 130 parts by weight per 100 parts of rubber.

18. A mixture as claimed in claim 1, 2 or 3 in which the active silica filler is present in an amount from >90 to 120 parts by weight per 100 parts of rubber.

19. A mixture as claimed in claim 1, 2 or 3 including at least one activator in an amount from 0.2 and 8 parts by weight per 100 parts by weight of the white filler.

20. A mixture as claimed in claim 1, 2 or 3 in which the processing oil is present in an amount from 50 to 80 parts by weight per 100 parts of the rubber.

21. A mixture as claimed in claim 1, 2 or 3 in which the processing oil has a setting point between 0 and -60°C.

22. A mixture as claimed in claim 1, 2 or 3 in which the silane is present in an amount from 1.0 to 15 parks by weight per 100 parts by weight of rubber.

23. A mixture as claimed in claim 1, 2 or 3 in which the sulphur content is made up in part by sulphur donors.

24. A mixture according to claim 1, 2 or 3 containing at least one sulphur-containing triazine derivative as the vulcanization accelerator.

25. A mixture as claimed in claim 1, 2 or 3 contain-ing at least one ingredient selected from age resisters, fatigue resisters, antiozonants, antioxidants, dyes, pigments, adhesive additives, activators and waxes.

26. A vulcanizable rubber mixture suitable for skid resistant tire treads comprising (1) a rubber, 20 to 100% of the rubber being a sulfur vulcanizable synthetic rubber other than polybutadiene or being natural rubber, (2) silica filler in an amount of at least 60 parts by weight per 100 parts of rubber, (3) plasticizer oil in an amount of 40 to 100 parts by weight per 100 parts of rubber, (4) sulfur or a sulfur donor in an amount of 0.2 to 8 parts by weight per 100 parts of rubber, (5) an accelerator in an amount of 0.1 to 8 parts by weight per 100 parts of rubber, and (6) 0.1 to 25 parts by weight per 100 parts of rubber of a sulfur containing organosilane having the formula Z - alk - Sn - alk - Z in which , , or in which R1 is alkyl of 1 to 4 carbon atoms, cycloalkyl of 5 to 8 carbon atoms or phenyl, R2 is alkoxy of 1 to 8 carbon atoms or cycloalkoxy of 5 to 8 carbon atoms, alk is a divalent hydrocarbon group of 1 to 8 carbon atoms, and n is a number of 2 to 6.

27. The mixture of claim 26, wherein said poly-butadiene is 30 to 90% of the total rubber the balance being a different sulfur vulcanizable rubber.

28. The mixture of claim 27, wherein said different sulfur vulcanizable rubber is a polymer of conjugated diene.

29. The mixture of claim 28, wherein the different sulfur vulcanizable rubber is natural rubber, polyisoprene, butadiene-styrene copolymer, butadiene-acrylonitrile copolymer, polychlorobutadiene, butyl rubber, chlorobutyl rubber, bromobutyl rubber or ethylene propylene non conjugated polyene terpolymer.

30. The mixture of claim 26, wherein n is about 2.8 to 4.2.

31. The mixture of claim 26, wherein Z is (3).

32. The mixture of claim 31, wherein R2 is alkyl of 1 to 4 carbon atoms.

33. The mixture of claim 32, wherein the organosilane includes bis-(3,3'-triethoxysilylpropyl) tetrasulfide.

34. The mixture of claim 26, wherein the accelerator includes a sulfur containing triazine compound having the formula II

wherein R1 and R3 are each selected from the group consisting of hydrogen, alkyl, alkenyl, cycloalkyl, phenyl, aralkyl and sub-stituted alkyl, alkenyl, cycloalkyl, phenyl and aralkyl wherein the substituents are selected from the group consisting of - OH, - OR and - CN, R being alkyl with up to 18 carbon atoms, R2 and R4 each selected from the group consisting of hydrogen, alkyl, alkenyl, cycloalkyl, phenyl, aralkyl and substituted alkyl, alkenyl, cycloalkyl, phenyl and aralkyl wherein the substituents are selected from the group consisting of - OH, - OR, and - CN, R
being alkyl with up to 18 carbon atoms, X is selected from the group consisting of hydrogen, III

and wherein R5 signifies alkyl, aryl, aralkyl or benzothiazole, R6 being selected from the group consisting of hydrogen, alkyl, aralkyl and cycloalkyl and R7 being selected from the group con-sisting of alkyl, aralkyl and cycloalkyl and wherein R6 and R7 together may also form a cycloaliphatic ring having from 5 to 7 carbon atoms in the ring and from 5 to 10 carbon atoms, including lower alkyl, attached to the ring or wherein R6 and R7 may be linked by a member of the group consisting of - O - , - S - and and wherein the number of carbon atoms in R1, R2, R3, R4, R6 and R7 is as follows:
alkyl up to 18 carbon atoms alkenyl up to 6 carbon atoms cycloalkyl from 5 to 7 carbon atoms aralkyl from 7 to 9 carbon atoms.

35. A tire tread formed from a vulcanized mixture as claimed in claim 1, 2 or 3.

36. A tire tread formed from a vulcanized mixture as claimed in claim 26, 27 or 28.