DE4030779A1 - Rubber compsn. for fast-reacting motor tyre treads - contains mixt. of specified SBR, natural rubber and specified butadiene] rubber, with carbon black and mineral oil plasticiser - Google Patents

Abstract

Rubber compsn. (I) comprises (a) 100 pts.wt. base rubber contg. 30-80 pts.wt. mainly amorphous SBR with 3-30 wt.% styrene and above 70 wt.% 1,2-vinyl units, 10-50 pts.wt. natural rubber and 10-40 pts.wt. butadiene rubber with more than 95 wt.% cis-1,4-component (BR), (b) 80-130 pts.wt. carbon black with specific surface (nitrogen absorption method) above 100 m2/g and (c) 20-90 pts.wt. mineral oil plasticiser with viscosity-gravity constant 0.90-0.98. (I) has shear storage modulus below 500 MPa at -30 deg.C and a difference in hardness of not more than 15 determined at +60 and -10 deg.C; (c) is an aromatic extender-plasticiser oil. SBR is produced, e.g. by block copolymerisation of styrene and butadiene with a Li-based catalyst; BR is produced by polymerisation of butadiene with Li initiators. USE/ADVANTAGE - (I) is useful in motor vehicle tyre treads (claimed). Tyres made with (I) have stable running properties and fast reaction to steering movements over a wide temp. range, with superior holding properties on snow and ice.

Description

The invention relates to use in the tread of Rubber compositions suitable for car tires, in particular those that have both stable running properties of the Tire over a wide temperature range as well lead to superior grip on snow and ice.

Tires should generally be safe and economical have smooth running characteristics and comfortable driving possible. The expansion of the road network gave the impetus the requirements of the tires in terms of cornering and Increase braking properties at high speeds. Recently, the "response quality" has become an issue for the further development of high-performance tires poses. This quality describes the ability of the tire to react accordingly or, in other words, the Ab driver's view to be carried out precisely and immediately.

In order to increase road grip, there are tire runs surfaces usually made of rubber with high hysteresis loss, closely related to the frictional force on the Road surface. The hysteresis loss is caused by peri odic deformation of the tread under frictional contact  high speeds due to light waves and bumps on the street. The greater the friction force, the more Energy conducts the tread to the street in Kon clocked up top. This type of tread defor mation is according to the William Landel-Fery'schen overlay principle of temperature over a period of time a hysteresis loss depending on a 30-40 ° C lower temperature than the actual tire temperature is executable, can be determined. The one with tan δ be Loss factor of the tire serves as a measured value for the hysteresis loss. This value was found to be good with the coefficient of friction of the tire at such a low lower temperature correlates.

There have been certain types of styrene-butadiene rubber (SBR) in rubber compounds with large hysteresis losses used. The types of rubber mentioned have a high Styrene content and therefore have a high glass transition temperature (Tg). The advantage is exploited that in the frictional force of the Tire is controlled because the rubber is a loss factor gate maximum near its glass temperature corresponding to 0 ° C The running temperature is reached when the tire rolls at 30 ° C.

With increasing styrene content, SBR types are subject to a shift in the loss factor maxima to the side of higher temperatures and thus lead to a large tan δ at about 0 ° C. of the loss factor temperature curve shown in FIG. 1, the SBR types shown by emulsion polymerization variable styrene contents can be obtained. This means that tan δ depends to a large extent on the ambient temperature and that the SBR types have a steep rise in the elas modulus on the low temperature side and thus do not follow the road bumps and in particular do not deform on ice, which may be insufficient Curve and braking properties leads. In contrast, rubber grades with a low Tg temperature, embodied by butadiene rubber grades (BR) with a high cis bond content, are known to be unsurpassed in adhesion at lower temperatures, but to some extent the tan δ value is around 0 ° C and the liability is reduced at high temperatures.

Attempts have been made to come out of this conflict to mix an SBR rubber with a BR rubber or a large amount of soot particles, such as B. in "The Friction of Pneumatic Tires "by D.F. Moore, Elsevier Scientific Publishing Co. (1975), US-A-47 48 168 and JP-A- 62-12 932. According to JP-A-62-2 60 843 and JP-A-62-1 90 238 have been successfully used in the SBR-BR blends Manufacture of treads used for all-weather tires. In this case, the mixing ratios were embarrassing nau set to a good relationship between the ver tolerance of the rubber types and the Tg properties receive.

However, the previously known SBR-BR mixtures are not too Peaceful as it is made of two different types of rubber is peculiar to their physical properties equalize, resulting in insufficient liability at low and high temperatures. The addition of soot particles in large amounts should be avoided to make a bad one Dispersibility in the rubber mixture obtained and undesired heating of the corresponding tread shut down.

JP-A-61-66 733 and JP-A-62-62 840 describe the addition of one certain plasticizer to the SBR-BR mixture for use at low temperatures. This additive is, though it effectively improves adhesion at low temperatures, sensitive to a decrease in the modulus of elasticity and therefore unstable when rolling at high temperatures.  

All of the above and belonging to the prior art Ver Publications refer to rubber for treads of car tires that help achieve all-weather properties are designed. Recently, great importance has been attached to that "React" of the tires in combination with a reliable one Liability placed. The tires should be the cars that the ent meet speaking social needs, ent speak. Due to the progress in mechanical engineering and the Electronics developed a strong demand for higher cultured cars that are not just in acceleration and curve characteristics, but also the driver make you feel left alone or detached from to feel the tire, d. H. Such cars can do well send shoes to be compared. That is why the Rei fen expects to respond to the driver's intentions without a react delay.

In these cars, hereinafter referred to briefly as "responsive Cars "shouldn't waste time generating one lateral force lost in response to the steering movement will. To put it more clearly, this type of Car quickly turning the steering wheel by even one react small angle. Research showed that langsa mes responding to steering movements from the structure of the tires and the phase lag of the tread and tread comes from. A suitable measure for the phase delay can by the difference in the hardness of the rubber at + 60 ° C and -10 ° C can be defined. It has been confirmed that the bigger the faster the difference in hardness is caused Rubber relieves tension. Thus, a Tension reduction due to a slight running fla Chen deformation does not maintain a predetermined tension will hold, or responding to a slight steering movement delivery is delayed.

The hardness difference defined above, hereinafter referred to as the "M coefficient", was found to increase in the case of SBR-BR blends having a high styrene content and a high Tg temperature, as shown in FIG. 1. This leads to the difficulty that the use of SBR-BR mixtures with a high Tg temperature to improve the adhesion leads to an increase in the M coefficient and thus the tire reacts insufficiently to steering movements.

It is the object of the present invention to create new ones Rubber compositions for use in the tread Chen provide of car tires, the rubber compound compositions are characterized by high stability in relation to road grip and responding to steering movements via distinguish a wide temperature range.

This task was solved by the surprising finding that rubber compositions with excellent loss factor (tan δ) and M coefficients by using with essentially amorphous styrene-butadiene rubbers selected styrene and 1,2-vinyl contents in combination with certain amounts of natural rubber and butadiene rubber are available with a high cis bond content. It is not Tread rubber known of use from the prior art point of reaction behavior to steering movements from off fits.

The rubber compositions according to the invention are as Tread rubber especially for use in air All-weather tires with quick responsiveness is suitable.

The invention thus relates to rubber compositions, in particular for use in treads for tires, which comprise: (a) 100 parts by weight of a base rubber containing 30 to 80 parts by weight of an essentially amorphous styrene-butadiene Rubber with a styrene content of 3 to 30 wt .-% and a 1,2-vinyl content of more than 70 wt .-%, 10 to 50 parts by weight of natural rubber and 10 to 40 parts by weight of a butadiene rubber with a cis-1,4-binding content of more than 95% by weight, (b) 80 to 130 parts by weight of carbon black with a specific surface area of more than 100 m ² / g determined by nitrogen adsorption and (c) 20 to 90 parts by weight of a petroleum plasticizer with a viscosity density constant of 0.90 to 0.98, the composition in particular a shear storage module of less than 500 MPa at -30 ° C. and a difference in hardness of not more than 15. determined at + 60 ° C and -10 ° C.

Fig. 1 shows dissipation factor-temperature curves of various styrene-butadiene rubber types obtained by emulsion polymerization with variable styrene contents.

Fig. 2 shows the points of different rubber mixtures in a shear modulus embrittlement temperature diagram.

The rubber compositions according to the invention consist essentially from a selected base rubber selected carbon black and a selected petroleum plasticizer.

The base rubbers according to the invention are of their type Mixtures and contain styrene-butadiene rubber (SBR), Na rubber (NR) and butadiene rubber (BR).

SBR rubbers should have a styrene content of 3 to 30 % By weight and a 1,2-vinyl content of more than 70% by weight point. With less than 70% this would result Rubber mixture a too low Tg temperature and therefore have a small loss factor (tan δ) at 0 ° C, which resulted in insufficient road grip. Higher vinylge Holds are of course desirable, but are due to the Manufacturing process limited to about 95 wt .-% as possible. The amount of SBR is 30 to 80 parts by weight of the total Base rubber. This rubber would be less than 30 Do not share its inherent properties bring and with a share of more than 80 parts  he does not have sufficient strength when using as Rubber for treads.

The SBR rubber used according to the invention can, for. B. by block copolymerization of styrene and 1,3-butadiene in the presence of a lithium-based catalyst and under Use of a hydrocarbon solvent and one polar dispersant, such as ether. The The reaction can be carried out batchwise or continuously the reaction temperature, the components ver ratios and other parameters can be set. That so block copolymer obtained can in a known manner by End group reforming or coupling reactions modified will.

Natural rubber is for the practical application of the Erfin essential. This rubber is used for elimination or reduction of tread damage the impact of a violent, bumping or cutting external force, because the tires often do not roll over paved and wavy roads. The natural rubber is in an amount of 10 to 50 parts by weight, based on the ge whole base rubber added. Less than 10 parts would not effectively prevent the impairment while more than 50 parts of the association with the SBR rubber run and cause insufficient road grip would.

The butadiene rubber should be more than 95% by weight cis-1,4- Have bond share and serves to improve Road grip at low temperatures and abrasion consistency. The proportion of BR is in the range from 10 to 40 parts by weight based on the total base rubber. From Deviations from this area would not result in any quality changes cause changes, and in particular more than 40 parts would lead to poor road grip.  

The butadiene rubber used according to the invention is in obtained in a manner known per se. 1,3-butadiene can batchwise or continuously in a hydrocarbon Solvent and in the presence of an initiator of lithium Type and using a polar compound like Ether, polymerized as a dispersant. The 1,4- Binding percentage is determined by the Morero method.

Suitable carbon black should have a specific surface area of more than 100 m ² / g and thus result in a highly abrasion-resistant and stable running surface. This ingredient is added in an amount between 80 and 130 parts by weight based on 100 parts by weight of the total base rubber. Exceeding the upper limit would lead to a rubber mixture with insufficient abrasion resistance and unwanted heating.

Carbon black with the desired physical properties can e.g. B. according to JP-A-63-1 12 638. The speci surface is determined in accordance with ASTM D-3037.

The petroleum plasticizers according to the invention should have a visco have density constant from 0.90 to 0.98. This Ingredient serves to improve workability and other quality features such as driving characteristics, noise courage and braking behavior. If the constant of the plasticizer is less than 0.90, sufficient ver cease improving road grip, and if more than 0.98, it would not act as a plasticizer and thus cause difficult processability. The amount of the added plasticizer changes with the amount of Carbon black, but is between 20 to 90 parts by weight to 100 parts by weight of the entire base rubber. Lesser Quantities would be responsible for poor stretching and thus cause breaks and cuts. Higher quantities the resulting rubber compound would mechanically weaken Chen and cause high abrasion in practical use.  

Examples of the plasticizer are extender plasticizer oils the aromatic variety. Extenders are particularly preferred. Plasticizing oils with a viscosity-density constant of about 0.98. Known ones can be used to determine these constants Procedures are applied.

A rubber assembled in this way should have a shear storage modulus of less than 500 MPa at -30 ° C. Chewy chuk-like material is usually glassy at temperatures below the Tg point and therefore brittle, with a modulus 100 times greater than that at room temperature. This means that the material breaks even under a noticeable tension. The temperature at which the fracture takes place is called the embrittlement temperature and is generally recognized in the art as a measure of certain physical properties of rubber at low temperatures. If the module is less dependent on temperature than in the rubber composition of the invention, it is difficult to simply derive the embrittlement temperature from the glass transition temperature. The shear modules G 'of different rubber mixtures are, as illustrated in Fig. 2, applied to the embrittlement temperatures. The drawing shows that all the mixtures exceed the value 500 MPa for G' and thus become brittle. The value G 'should therefore be kept below 500 MPa. The shear modulus was determined at -30 ° C because tires are rarely used at even lower temperatures.

To improve the response to small steering movements, the composition of the invention should have no value greater than 15 in the difference in hardness or M coefficient, be true at + 60 ° C and -10 ° C. Values for the M- Coefficients of more than 16 would be, even if they were one sufficient liability for these reactions and finally in relation to the overall property of the corresponding tire is not justifiable. differences in  The hardness of less than 13 are used for better results prefers.

In JP-A-56-1 10 753 a certain rubber mixture is be wrote in which a styrene-butadiene rubber with high Vinyl content combined with natural rubber and one of them various diene or butadiene rubber is used. Such well-known rubber mixtures are intended to good balance between rolling resistance at low Temperatures and grip on wet roads at high To achieve temperatures. This publication does not teach the dependence of the hardness of the rubber on the tempera is still concerned with the addition of soot in a sufficient amount to respond to steering movements to achieve.

Examples

In all examples, the numerical values mean parts by weight, unless otherwise stated.

Four different test examples of styrene-butadiene rubber with changing styrene and 1,2-vinyl content were prepared in accordance with Table I and processed further in accordance with Table II. The styrene content was determined using the Hampton method using an infrared spectrometer and the vinyl content using the Morero method. For comparison, two commercially available types of SBR rubber ( 1 ) and ( 2 ) were used, which were prepared by emulsion polymerization.

The test compositions were each at 160 ° C for 20 minutes vulcanized to 2 mm thick discs. The Vulkani sat was on rubber hardness, shear modulus and loss factor under the conditions described below and the results are shown in Table II.  

Hardness (H)

The measurements were carried out in accordance with JIS K-6301.

Shear modulus (G ′) at -30 ° C

A test device for determining the flow behavior, manufactured by Rheometrics Co., was manufactured at one frequency operated at 20 Hz and a shear stress of 0.5%.

Loss factor (tan δ) at 0 ° C

The method for determining G 'was used.

Table I

Table II

As can be seen from the results in Table II, the Rubber compositions 1 to 3 according to the invention in be highly satisfied with all properties tested lend.

In Comparative Examples 4 and 5 , the comparative rubber types, ie SBR-1 and SBR-2, were examined. Comparative example 5, although its G'-value is sufficient, is insufficient in the loss factor and thus also in liability. Comparative example 4 shows exactly the opposite and leads to an insufficient G'-value.

The 1,2-vinyl-BR- not covered by the scope of the invention Rubber (Comparative Example 1) has a sufficient M coefficients, but is to some extent not too reaching tan δ and showing unacceptable roads liability. The SBR (2) NR BR system (Comparative Example 2) leads to decreased tan δ and an increased M-coefficient clients, d. H. there is no noticeable increase in the reak behavior on steering movements. Deviations from the he The amount of soot according to the invention leads to insufficient values of tan δ, as from Comparative Example 3, which is similar Rubber system such as Example 1 according to the invention points out. In Comparative Example 6, a station wagon nation from SBR-A with BR with a cis 1,4-binding fraction of 98% by weight used and leads to unacceptable tan δ.  

There were test tires in the size 196 / 65R15 with the tread Chen from the compositions of Example 1 and Ver same example 2 and 4 produced. The tires were on a 5-seater limousine made in Japan. Responding to steering movements and behavior in critical A number of jurors determined the situations Results are shown in Table III.

Table III

The tires of the invention show that they with respect to Responding to steering movements and finally in the overall ver keep improved. A comparison tire was like out Comparative example 4 can be seen in the behavior in critical Situations a little better. The larger the number in Table III, the better the properties, with the upper limit Is 10 points.

Claims (4)

1. A rubber composition comprising:

• a) 100 parts by weight of a base rubber containing 30 to 80 parts by weight of an essentially amorphous styrene-butadiene rubber with a styrene content of 3 to 30 wt .-% styrene content and a 1,2-Vi nyl content of more than 70% by weight, 10 to 50 parts by weight of natural rubber and 10 to 40 parts by weight of butadiene rubber with a cis-1,4-binding content of more than 95% by weight,
• b) 80 to 130 parts by weight of carbon black with a specific surface area of more than 100 m ² / g determined by nitrogen adsorption and
• c) 20 to 90 parts by weight of a petroleum plasticizer with a viscosity-density constant of 0.90 to 0.98.

2. Rubber composition according to claim 1, characterized ge indicates that the composition is a shear storage modulus of less than 500 MPa at -30 ° C and a hardness difference of not more than 15, determined at + 60 ° C and -10 ° C. 3. Rubber composition according to claim 1 or 2, there characterized in that the petroleum plasticizer is an aro mat extender plasticizing oil. 4. Use of the rubber composition according to claim 1, 2 or 3 in treads of car tires.