NO142310B - VULCANIZABLE RUBBER MIXTURES FOR THE PREPARATION OF TIRE WEAVES WITH REDUCED TENSION SLIDING AND WITH A RELATIVE HIGH CONTENT OF POLYBUTADIA RUBBER - Google Patents

Description

The invention relates to special rubber compounds for the production of tire eUte surfaces, which treads are distinguished by a distinct slip resistance of

wet, snow-covered and especially icy roads.

The most used car tires to prevent slipping on streets covered with ice or stuck snow are winter tires equipped with hard steel studs, the so-called studded tires.

However, the use of studded tires and especially the large number of cars equipped with such tires entails significant disadvantages. Very widespread road damage occurs due to the formation of wheel ruts with a new danger, such as the well-known aquaplaning. Studded tires also have driving technical disadvantages, they cause longer braking distances and unfavorable cornering stability.

There has been no shortage of attempts to improve road grip on wet streets, on ice and stuck snow. It was obvious to solve the problem by achieving a mechanical effect. Thus, for example, roughly divided foreign bodies were incorporated into the tread, such as e.g. pebbles, cement particles, walnut shells, hard rubber.. steel shavings or

-wool, etc. These precautions, however, helped little or nothing. They even partially led to a reduction in driving characteristics. Attempts have also already been made to increase the adhesion of the tires to icy streets by changing the composition of the treads. However, no decisive improvements could be achieved. The studded tires' slip resistance on icy streets could not be achieved. It therefore remained to solve the important task of finding a non-slip car tire without spikes for icy and snowy streets. A tire wearing surface of a vulcanized rubber mixture containing finely divided silicic acid and a coupling agent is also known (BRD Off.Schr. no. 2,062,883). However, only a few coupling agents are mentioned which are sulphur-containing silanes. Mercaptopropyl-trimethoxysilane and -triethoxysilane are obviously the only silanes investigated in practice.

Surprisingly, a rubber compound has now been found which provides the same slip resistance as a studded tire with a steel pin protrusion of 1.2 mm, and which even surpasses the studded tires in some respects.

The invention relates to a vulcanizable rubber mixture for the production of tire treads with a reduced tendency to slip on ice, consisting of a) one or more polybutadiene rubbers, preferably with a high cis-1,4 content b) one or more other rubbers in such an amount that the sum of a) and b) make up 100 parts

c) 80-200 parts silicic acid filler

d) 40-100 parts softening oil, preferably a naphthenic process oil e) 0.1-25 parts of at least one organosilane of formula in which Z means the groupings: in which R means an alkyl group with 1-4 carbon atoms, a cycloalkyl group with 5-8 carbon atoms or 2 phenyl, and R means an alkoxy group with 1-8 carbon atoms or a cycloalkyl group with 5-8 carbon atoms, all 12 symbols R and R can have the same or different meanings, Alk means a divalent hydrocarbon residue with 1-8 carbon atoms and n means a number from 2 to 6, f) sulfur and possibly sulfur donors in an amount of a total of 0.2-8 parts, g ) " at least one vulcanization accelerator in an amount of 0.1-8 parts h) zinc oxide and stearic acid in the usual amounts for rubber compounds, as well as possibly

i) up to 50 parts of soot and/or

j) a basic activator in amounts from 0.2 to 8

parts to 100 parts silicic acid filler

besides other, common additions i

usual amounts

in that all parts of mixture components c) to i) are referred to 100 parts rubber mixture, and

the mixture being characterized in that the polybutadiene rubber or rubbers make up at least 50 parts of the 100 parts total rubber content.

In the above as well as in the patent claim, "parts" shall mean parts by weight.

What is stated here in the introduction of the claim,

is obvious in the preceding application no. 4286/73 which, however, had not become widely available on the priority date for the present invention.

The silanes specified in point e) are known as coupling agents ("Haftvermitler") in rubber compounds containing silicate filler from BRD Off.Schr. No. 2,141,159 and 2,141,160.

This rubber mixture according to the invention surprisingly has, despite the high filler content, such a low viscosity that it is easy to process. It is sprayable and can therefore be used on the usual machines in tire factories. It is equally surprising that, despite the high content of filler and plasticizer oil, the mixture can be vulcanized with good results so that the vulcanized material has the necessary properties with regard to tear resistance, wear resistance and the like, and this, although they do not must have added soot. The treads made from the new compound show an excellent and unexpectedly favorable condition on wet, icy or slush streets.

The outstanding properties could only be achieved by the combined use of the known per se oligosulphide silanes, cf. the above item e). ;

The preparation of these bis-/Alkoxysilylalkyl/- oligosulfides can take place according to what is stated in the above-mentioned BDR Off.Schr. no. 2,141,159 and 2,141,160, as well as no. 2,212,239. For example, the following silanes can be advantageously used: bis-[3-trimethoxysilylpropyl]-trisulfide bis-[3-triethoxysilylpropyl]-trisulfide

bis-[3-trimethoxysilylpropyl]-tetrasulfide bis-[triethoxysilylpropyl]-tetrasulfide

bis-[3-diethoxymethylsilylpropyl]-tetrasulfide bis-[3-diethoxyphenylsilylpropyl]-tetrasulfide bis-[3-tricyclohexoxysilylpropyl]-tetrasulfide and bis-[2-triethoxysilylethyl]-tetrasulfide.

With respect to sulfur content, the usable silanes may deviate from the stoichiometrically calculated content, so that "n" in the general formula I may also mean fractions of whole numbers, preferably between 2.8 and 4.2. .As said, polybutadiene rubber (BR), possibly a mixture of two polybutadienes, must be present in the new rubber mixture. In most cases, it is also necessary to use one or two additional types of rubber as a mixture component. One should then use rubbers with the lowest possible glass transition temperature, preferably natural rubber (NR), synthetic rubbers from isoprene (IR) and trans-poly-pentenamer. Furthermore, styrene and butadiene rubbers are suitable.

(SBR), especially copolymers of so-called "Low-Mooney" quality, i.e. SBR types with low Mooney viscosity (see DIN 53 523, ASTM D 1646-62 or BS 1673:3:1951), which are available

in trade under this designation; nitrile rubbers, halo-butyl rubbers such as chloro or bromobutyl rubber, ethylene/propylene/diene terpolymers or similar synthetic rubbers which are preferably vulcanizable with sulphur. Of the BR types, those with an average molecular weight are used in particular, preferably at the same time as having a high cis-1,4 content.

In the new rubber compounds, two types of rubber are preferably used, for example BR and SBR, or BR and NR, or BR and IR. As said, the amount of BR constitutes 50-100% by weight, preferably 50-85% by weight, of the total rubber content.

The choice of silicic acid and its high content is particularly important. Primarily, an active or reinforcing silicic acid is used in highly dispersed form, which essentially consists of silicon dioxide. Precipitated silicic acid of high purity and activity and with a BET surface area between 50 and 300 m<2>/g and an average primary particle size of over approx. 10 nanometers, for example between 10 and 50 nanometers. Other usable silicic acid fillers are the known pyrogenically produced types. Mixtures of silicic acid fillers can also be used with advantage.

This silicic acid filler must be used in quantities of at least 80 parts by weight per 100 parts by weight of rubber, so that the finished tire will have the desired high level of safety against ice slipping. The amount of silicic acid filler in the mixture is thus greater than the amounts of soot that have hitherto been common in tire tracks:. Such a mixture would not have been possible to process if it had not been added to a bis-[alkoxysilylalkyl]-oligosulphide. The upper limit for the amount of silicic acid can vary according to the desired properties of the mixture and the vulcanizate and can be determined by a person skilled in the art. Appropriately, the amount of filler is between 80

and 130 parts by weight, preferably between 90 and 120 parts by weight per 100 parts by weight rubber.

In many cases, it has proven appropriate to mix the oligosulfidic silanes beforehand with a part of the active silicic acid, for example in equal parts (by weight), and then to add this silane/silicic acid mixture to the other components of the mixture.

It can be particularly beneficial to add activators. The substances referred to as "basic activators" or "filler f-activators" are, for example, diphenylguanidine, hexamethylenetetramine, o-tolylguanidine, triethanolamine, cyclohexylamine, diethylene glycol and other commonly known guanidines, amines or polyhydric alcohols. The amounts of these are chosen in accordance with the amount of filler and are between 0.2 and 8 parts by weight per 100 parts by weight of "the white filler" (silicic acid).

If desired, e.g. for the sake of color, maybe

soot may also be present in the mixture. The; can usually be incorporated in amounts between 0.1 and 50 parts by weight per

100 parts by weight of rubber, possibly in even smaller quantities.

All types of soot come into play here. Examples should be mentioned

HAF soot and especially ISAF soot.

The plasticizer oil to be used in accordance with the invention is an important component of the new rubber mixture, as is the amount of this oil. The amount must be from 40 to 100 parts by weight per 100 parts by weight rubber, preferably between 50 and 80 parts by weight. Preferably, the oil designated as process oil of the naphthenic oil type is used. Particularly advantageous are oils with a "stock" point (DIN 51583) between 0 and -60°C, preferably between -10 and -55°C. However, plasticizer oils of a highly aromatic nature can also be used. Mixtures of different oils can also be used with advantage. Plasticizer oils or processing oils

are usually petroleum fractions which may possibly be chemically modified.

The bis-[alkoxysilylalkyl]-oligosulphides are incorporated in amounts from 0.1 to 25 parts by weight, preferably in amounts from 1.0 to 15 parts by weight per 100 parts by weight rubber.

By "adhesive additives" is meant known substances or substance mixtures, which during vulcanization cause a good adhesion (bonding) of the rubber mixture to the materials used in the tire manufacture, i.e. e.g. steel cord, tek ss p til fiber cord, glass fiber cord, beaded wire and the like; they are used in normal amounts.

The new mixtures preferably contain sulfur for vulcanization, possibly also sulfur donors such as the known N,N'-dithiobis-hexahydro-2H-azepinone-(2) and 2-benz-thiazyldithio-N-morpholide, both together calculated in normal amounts from 0 ,-2 to 8 parts by weight per 100 parts by weight of rubber, as well as at least 'teii "vulcanization accelerator, likewise in the usual amounts from 0.1 to 8 parts by weight per 100 parts by weight of rubber.

According to the invention, there are special advantages when sulfur-containing triazine derivatives are used as accelerators during the vulcanization, which are known from Norwegian patent no. 127,352, for example bis-(2-ethyl-amino-4-diethylamino-triazinyl-6)-disulfide, possibly in combination with other known accelerators, such as diphenylguahidin.

In addition, stearic acid and zinc oxide are also added to the mixture according to the invention in normal amounts. It is also advantageous to incorporate in and of itself known aids, such as protective agents against oxidative influence and anti-fatigue agents as well as anti-ageing agents and ozone protective agents in normal quantities. Optionally, pigments, dyes, waxes and the like can be added to the mixture in normal quantities.

The production of the rubber compounds as well as the shaping, e.g. by injection molding, and the vulcanization takes place in the usual way and with the help of devices that are common in the rubber industry.

The mixing itself is preferably carried out after

the so-called "upside-down" method in a pinch.

The subsequent shaping and vulcanization can be carried out at normal temperatures in the range between approx. 100' and approx. 300°C, preferably at 130-240°C. As mentioned, the usual vulcanization devices are used for this.

Examples

Two mixtures according to the invention have the following compositions (in parts by weight):

These two compounds and their vulcanizates were compared with a normal winter tire compound "A" for a tread of a commercially available tire of German manufacture, and with the following soot-containing compound "B" and its vulcanizates.

The following abbreviations were used for the examinations and the declarations of the resulting test results:

Sample standards

The physical tests were carried out at room temperature according to the following standard regulations:

The vulcanizates were always produced in a steam-heated floor press at the specified vulcanization temperatures.

Properties of the vulcanized mixtures.

The vulcanization took place at 160°C.

Goodrich flexornet surveys.

Vulcanization temperature l60°C Vulcanization duration 40 minutes

Of the four mixtures (1 and 2 according to the invention A

and B according to the state of the art) treads were produced and with these again tires. These tires were then examined on a

passenger car on an artificial ice track, as well as on the wet road surface of a street equipped with a raw asphalt surface, and the results compared. The investigations took place with the same car and the tire sets all had the same profile. It was first driven on a circular track with a diameter of 20 meters (circular track test, 4 measurement laps, driving time measurements).

Furthermore, in braking tests at an initial speed of 30 km/h, full stop measurements were carried out (braking delay at braking distance in metres).

Thirdly, acceleration tests took place when driving over a distance of 22 meters with a standing start with maximum acceleration (time measurement in seconds and measurement of final speed after 25 metres). The artificial ice had a surface temperature of 0 to -3.5°C. The air temperature at a height of 0.8 meters above the ice was +2 - +4°C.

The tires' test on a wet road surface took place on a watered asphalt circular track with a diameter of 67 metres. Four rounds were run each time. The running time in seconds was measured using a light beam. During the braking tests on a wet road, the vehicle was driven at an initial speed of 50 km/h or 80 km/h, and then a full-stop measurement was carried out on the watered track. Braking distances in meters were measured and the average delay determined.

The temperature of the track on the surface was 11-20°C, and the air temperature 9-19°C.

From all measured values, it is possible to determine mean acceleration, circular acceleration, resp. delay values, and from this the u-values (friction coefficients) were calculated. For comparison, the measured coefficients of friction (as an average) for the tires from mixture A were set = 100. The other measured values appear in the following table:

The following results can be derived from these figures:

The specified friction coefficients show for

the compounds according to the invention produced tires with a considerable improvement in slip resistance. This improvement can be characterized as well reproducible. Such good values of slip resistance on ice have not been measured so far. A tread quality has thus been found that is capable of replacing studded tyres.

The winter tires used for comparison have been produced for a few years and can be obtained commercially. They have a track quality described as "very good" (mixture A). This mixture A is particularly used for tires with favorable sliding properties with a balanced ratio between ice and wet slip resistance. Mixture A is, however, a mixture which only contains carbon black as a filler, just like mixture B. As B, a representative mixture was chosen which is common in the production of passenger car tyres. These "B-tyres" are slightly worse than "A-tyres" in terms of sliding on ice. Compared to mixture A, according to the invention, improvements in the sliding properties of up to 30% can be achieved. This can only be achieved with the mixtures according to the invention.

A further mixture according to the invention had the following composition:

A further mixture according to the invention had the following composition:

The properties of the unvulcanized mixtures

Properties of the vulcanized mixtures

The vulcanization took place at 150°C (mixture 3), respectively 160°C (mixture 4) and lasted 20 minutes in both cases.

Slip resistance of mix 3 tires

Measurement of friction coefficients (y-wefdier) of the above-mentioned mixture 3 compared to mixture 2 from the previous example.

Slip resistance of mixture 4- tires

The determination of the coefficient of friction of tires equipped with tread compound 4, compared to ordinary tires having a compound A or B.

From the above figures, especially from the evaluation of the friction coefficients, the clear superiority of the mixture according to the invention is evident.

Claims (1)

Patent claims Vulcanizable rubber mixture for the production of decks Outdoor surfaces with a reduced tendency to slip on ice, consisting of a) one or more polybutadiene rubbers, preferably with a high cis-1,4 content, b) one or more other rubbers, in such quantity that the sum of a) and b) amounts to 100 parts, c) 80-200 parts silicic acid filler, d) 40-100 parts softening oil, preferably a naphthenic process oil, e) . 0.1-25 parts of at least one organosilane with formula: Z - Alk - Sn - Alk - Z (I) in which Z means the groupings: in which R means an alkyl group with 1-4 carbon atoms, a cycloalkyl group with 5-8 carbon atoms or phenyl and R<2 >means an alkoxy group with 1-8 carbon atoms or a cycloalkoxy group with 5-8 carbon atoms, as all symbols 12-R bg R can have the same or different meanings, Alk means a divalent hydrocarbon residue with 1-8 carbon atoms, and n means a number from 2 to 6, f) sulfur and optionally sulfur donors in a quantity of a total of 0.2-8 parts by weight, g) at least one vulcanization accelerator in a quantity of 0.1-8 parts by weight, h) zinc oxide and stearic acid in the usual quantities for rubber compounds, as well as possibly i) up to 50 parts of carbon black and /or j) a basic activator in amounts from 0.2 to 8 parts per 100 parts silicic acid filler, all parts of the mixture components c)-i) are referred to 100 parts rubber mixture, characterized in that the polybutadiene rubber or rubbers make up at least 50 parts of the 100 parts total rubber content.