JPH03239737A - Pneumatic tire - Google Patents

Abstract

PURPOSE:To prepare a pneumatic tire which gives a satisfiable resistance to wet skid, rolling, and abrasion by compounding a specific styrene-butadiene copolymer rubber with a silica filler and, if necessary, a carbon black. CONSTITUTION:100 pts.wt. rubber component comprising a styrene-butadiene copolymer rubber or a blend of 30wt.% or more copolymer rubber with 70wt.% or less other diene rubber is compounded with 10-150 pts.wt. silica filler and 0-100 pts.wt. carbon black to give a rubber compsn., which is used for a tread of a pneumatic tire. The copolymer rubber, prepd. by copolymerizing styrene with butadiene in the presence of an organolithium compd., has a glass transition point of -50 deg.C or higher and contains 20-50wt.% combined styrene units, wherein 40wt.% or higher exist as units each of which comprises a single styrene unit and is not linked to other styrene units, and 10wt.% or lower exist as styrene chains each of which comprises 8 or more styrene units.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a pneumatic tire, and more particularly to a pneumatic tire that can simultaneously satisfy wet skid resistance, rolling resistance, and abrasion resistance.

(Prior Art) In recent years, research into reducing the rolling resistance of tires has become important in order to save fuel consumption of automobiles due to social demands for energy and resource conservation.

In other words, it is generally well known that reducing the rolling resistance of a tire will reduce the amount of fuel consumed by a car, resulting in a so-called fuel-efficient tire.In order to reduce the rolling resistance of a tire, materials with low hysteresis loss are used in the tread rubber. It is common to use

Additionally, rubber materials with high frictional resistance (wet skid resistance) on wet road surfaces have become strongly desired due to demands for driving safety.

However, there is an antinomic relationship between low rolling resistance and frictional resistance on wet road surfaces, and it has been extremely difficult to satisfy both characteristics.

Recently, it has been theoretically demonstrated that the wet skid resistance and rolling resistance of a tire correspond to the viscoelastic properties of a rubber composition.In order to reduce the rolling resistance of a tire when running, it is necessary to reduce the hysteresis loss of the tread rubber. In terms of viscoelastic properties, it has been shown that lowering the loss coefficient (tan δ) at temperatures of 50 to 70° C. at which tires are used for running is effective in producing fuel-efficient tires.

On the other hand, it is known that wet skid resistance is well correlated with the coefficient near O''C'C (tan δ) under a frequency of 10 to 20H2. It is necessary to increase the lapse coefficient near CC.

As a method of reducing this hysteresis loss, it is common to use a material with a low glass transition temperature, such as high-cis varivitadiene rubber, or a material with high impact resilience, such as natural rubber.

However, these rubbers have an extremely low wet skid resistance, making it extremely difficult to achieve both running stability and rolling resistance.

Furthermore, due to recent advances in anionic polymerization, many inventions that satisfy the above-mentioned contradictory characteristics have been published.

For example, JP-A-55-12133, JP-A-56-
In JP-A No. 127650, high vinyl polybutadiene rubber is disclosed in JP-A-57-55204 and JP-A-57-73.
Publication No. 030 proposes a high vinyl styrene butadiene copolymer rubber.

Also, JP-A-59-117514, JP-A-61-
No. 103902, Japanese Patent Application Laid-open No. 14214/1983,
JP-A-61-141741 discloses that heat generation can be reduced by using a modified polymer in which a functional group such as benzophenone or isocyanate is introduced into the molecular chain of the polymer.

However, none of these methods fully satisfies the recent low drying resistance.

As a result of intensive studies aimed at further improving the wet skid resistance, rolling resistance, and wear resistance of tires, the present inventors developed (S)BR with a specific microstructure and Tg polymerized using a lithium-based initiator. The present invention was achieved by discovering that a tire whose tread is made of a rubber composition containing a silica filler is excellent in the above-mentioned properties.

(Means for solving the problems) The present invention was invented with the above-mentioned objectives, and its gist is that styrene and butadiene are copolymerized using an organic lithium compound, ) 20 to 50% by weight of bound styrene; II) less than 40% by weight of a single chain of 1 styrene unit of the total bonded styrene, and 10% of the total bonded styrene of long styrene chains of 8 or more styrene units. % by weight or less, and the glass transition temperature is -5
A styrene-butadiene copolymer having a molecular weight of 0"C or more, or 30 parts by weight or more of this rubber and 70 parts by weight of other diene rubber.
10 to 150 parts by weight of silica filler and 0 to 150 parts by weight of carbon black per 100 parts by weight of blended rubber.
The present invention relates to a pneumatic tire characterized in that a rubber composition comprising 100 parts by weight is used for the tire tread.

The styrene-butadiene copolymer used in the present invention is
It is obtained by copolymerizing styrene and butadiene using a lithium-based polymerization initiator, but a more preferred embodiment uses a cocatalyst consisting of an organolithium compound and a specific organometallic.

By using this cocatalyst, the process of the invention allows control of the polymerization reaction to produce copolymers with optimal properties.

The bound styrene content in the styrene-butadiene copolymer used in the present invention is 20 to 50% by weight, preferably 25% by weight.
~45% by weight. If the bound styrene content is less than 20%, the wear resistance will be poor and the desired pneumatic tire cannot be obtained. If the amount of bound styrene exceeds 50% by weight, the rolling resistance will be poor, which is not preferable.

In order to obtain the pneumatic tire of the present invention having excellent wear resistance, it is important to keep the bound styrene chains in the styrene-butadiene copolymer within a certain range.

The chain distribution of styrene in the above-mentioned styrene-butadiene is analyzed by gel permeation chromatogram after decomposing the material with ozone (Society of Materials Science and Polymer Science, Proceedings (9), p. 2055).

In such a styrene-butadiene copolymer, the proportion of short chains with one styrene unit is less than 40%, preferably less than 35%, and the long styrene chains with 8 or more styrene units are preferably less than 10% by weight of the total bonded styrene. is 5% by weight
It is as follows. If the styrene short chains are 40% or more, wear resistance and tear strength will be poor, and if the styrene long chains are more than 10%, the rolling resistance will be poor, making it difficult to obtain the desired pneumatic tire.

The glass transition temperature of such a styrene-buckene copolymer is -50°C or higher, preferably -40°C or higher. If the glass transition temperature is lower than -50°C, the wet skid resistance will be poor and this is not preferable.

The styrene-butadiene copolymer used in the present invention is
Although it is possible to use it alone in the tread, it may be used as needed in an amount of up to 70 parts by weight, preferably up to 50 parts by weight, based on 100 parts by weight of natural rubber, polybutadiene rubber, synthetic polyisoprene rubber, butadiene-acrylonitrile copolymer. Rubber, diene rubber such as styrene-butadiene copolymer rubber other than the above-mentioned copolymer rubber may be blended.

Representative examples of the organolithium polymerization initiators used in the production of the styrene-butadiene copolymer of the present invention are as follows. That is, ethyllithium, propyllithium, n-butyllithium, 5ec-lithium,
Alkyllithium represented by tert-butyllithium, allyllithium such as phenyllithium, tolyllithium, alkenyllithium such as vinyllithium, propenyllithium; tetramethylene dilithium, pentamethylene dilithium, hexamethylene dilithium, decamethylene Alkylene dilithium such as dilithium.

Examples of organometallic potassium used as a cocatalyst with this organolithium include potassium dodecylbenzenesulfonate, potassium tetradecylbenzenesulfonate, potassium hexadecylbenzenesulfonate, potassium octadecylsulfonate, etc. There are compounds described in .

Further, a small amount of alcohol or secondary amine may be added to these compounds.

This organometallic potassium can be used in an amount of 0.01 to 0.5 mol per gram atom equivalent of lithium.

As the polymerization solvent, n-hexane, cyclohexane, heptane, benzene, etc. can be used.

The polymerization reaction for obtaining the polymer of the present invention can be carried out by either a batch polymerization method or a continuous polymerization method.

The polymerization temperature used is O@C-130°C.

Moreover, any polymerization method such as isothermal polymerization, temperature-programmed polymerization, or adiabatic polymerization can be used.

Furthermore, an allene compound such as 1,2-butadiene may be added to prevent the formation of gel in the reaction vessel during polymerization.

The styrene-butadiene copolymer of the present invention is washed by adding naphthenic oil, highly aromatic oil, softener, or liquid polymer as necessary, and separating the rubber and solvent by direct drying or steam stripping. and can be dried.

Note that the copolymer rubber is manufactured, for example, as follows. Cyclohexane 25K in a 50 liter reaction vessel
g, styrene 1.8Kg, 1.3-butadiene 4.4K
g, 125 g of tetrahydrofuran, 0.4 ml of potassium dodecylbenzenesulfonate. n-butyllithium 4m
After polymerization is carried out at an elevated temperature of 50 to 100° C., the catalyst is removed and the product is dried.

For the amount of bound styrene in the copolymer, the styrene monomer was changed, and for the introduction of styrene chains, the amount of potassium dodecylbenzenesulfonate used was changed.
The amount of 1,2-coupled gold can be controlled to a desired ratio by varying the polymerization temperature and the amount of tetrahydrofuran.

The silica filler blended in the present invention is rubber component 2.
10 to 150 parts by weight per 00 parts by weight, preferably 15 to 150 parts by weight
It is 100 parts by weight. If the amount is less than 10 parts by weight, the filling reinforcement effect is small and the wear resistance is poor, while if it exceeds 150 parts by weight, the workability and fracture properties are poor.

The rubber composition used in the present invention may also contain 0 to 100 parts by weight of carbon black as a filler, and has better processability, abrasion resistance, and cut resistance than silica alone. can be improved. In this case, the weight ratio of carbon to silica is preferably in the range of about 9515 to 10/90 in view of the balance between wet skidding properties, rolling resistance, and abrasion resistance.

As the silica, dry process silica or wet process silica is used, especially Nip Seal VN3 (manufactured by Nippon Silica).
, Tokusil U, UR (manufactured by m-sansoda), Ultrasil V
Wet process silica such as N3 (manufactured by Degussa, West Germany) is preferred.

As the carbon black, conventional carbon black for tread rubber compositions, such as HAF (N330.N
332 etc.), HAF-N3 (N339 etc.), ■・l
5AF, 15AF%SAF, etc. are used.

The rubber composition used in the present invention may further contain powdered fillers such as magnesium carbonate, calcium carbonate, and clay, and fibrous fillers such as glass fiber and whiskers, as well as zinc white and aging. Conventional vulcanized rubber compounding agents such as inhibitors, vulcanization accelerators, and vulcanizing agents can be added.

(Example) Example 1 The present invention will be explained in more detail below with reference to Examples.
The present invention is not limited to the following examples in any way unless it exceeds the gist thereof.

Further, various measurements in the examples were carried out by the following methods.

The microstructure of the butadiene moiety was determined using infrared absorption spectroscopy (
Morello method). The styrene content was measured by the absorption of phenyl group at 699 cm-' by infrared absorption spectroscopy using a predetermined calibration curve.

Further, the vulcanized physical properties were measured according to JTSK6301.

The Lambourn friction index, which is a wear resistance test, was measured by the Lambourn friction method. The measurement conditions were a load of 4.
5Kg, surface speed of the grindstone is 100m/sec, test speed is 1
The speed was 30 m/sec, the slip rate was 30%, the amount of falling sand was 20 g/min, and the measurement temperature was room temperature.

The internal loss (tan δ) was measured using a mechanical spectrometer manufactured by Rheometrics, and the dynamic shear strain was measured with an amplitude of 1.0.
%, vibration 15H2, and each measurement temperature.

The rolling resistance index is calculated by placing the tire in contact with a drum with an outer diameter of 1.7 m, rotating the drum, and increasing it to a certain speed.
The drum was coasted and evaluated using the following formula from the value calculated from the moment of inertia at a predetermined speed.

The skid resistance on a wet road surface (wet skid resistance) is 80 km/h on a wet concrete road surface with a water depth of 3 mm.
The skid resistance of the test tire was evaluated using the formula below, by measuring the distance from when the wheels locked up to when the wheels came to a stop.

The wear resistance index was evaluated by driving the tire for 40,000 km, measuring the depth of remaining grooves at 10 locations, and using the average value of the measurements using the formula below.

Rubber compositions were prepared using the various polymers shown in Table 1 in the basic blending ratios (parts by weight) shown in Table 2. In addition, in Table 2, all chemicals other than the copolymer and filler are the same for the Examples and Comparative Examples and are as shown in Table 2.

These rubber compositions were evaluated for breaking strength (Tb) and Lambourn wear tan δ.

These rubber compositions were then applied to tire size 165SR1.
A tire was prepared using the tread of No. 3, and wet skid resistance, rolling resistance, and abrasion resistance were evaluated. The results are shown in Table 3.

That is, among the various polymers shown in Table 1 produced here, copolymers No. 1 and 2 have structures suitable for use in the present invention, and copolymers No. 1 and 7 have one polymer. The amount of styrene short chains greatly exceeds the specified amount, and N014
The number of long styrene chains of 8 or more exceeds the specified amount.

Furthermore, in No. 5, the bound styrene content is less than the specified amount, and N
No. 0 and No. 6 have a glass transition temperature below a specified value.

Now, in Table 3, Comparative Example 1 using copolymer No. 7 is t! Example 1 using copolymers N011 and 2 used in the present invention will be discussed as a reference.
and No. 2, both the physical property test and the tire performance test far exceeded the standards, and it can be seen that good results were achieved that cleared both of the contradictory objectives of the present invention.

On the other hand, in Comparative Examples 2 to 5 using N013 to 6 which deviate from the structural regulations as a copolymer as described above,
- It has not been possible to completely satisfy all items in physical property tests and tire performance tests.

This proves how important the structural characteristics of the copolymer are in achieving the objectives of the present invention.

Furthermore, in Examples N013 and 4, copolymer N01
This is an example of using Samples No. 1 and No. 2 and changing the blending composition, and the results are good, far exceeding the standard values mentioned above.

On the other hand, in Comparative Example 6, in which copolymer No. 1 was used, which met the regulations, but the silica filler was blended below the specified amount, both physical properties and tire performance tests were below the standard values. It can be seen that in order to achieve the object of the present invention, it is necessary to consider not only the structure of the copolymer but also the formulation composition.

As is clear from Table 3, the pneumatic tires of the present invention are excellent in wet skid resistance, rolling resistance, and abrasion resistance.

Example 2 Next, a rubber composition having the formulation shown in Table 4 was prepared,
The same study as in Example 1 was conducted.

The same chemicals as in Example 1 were used except for the copolymer and filler.

Comparative Example 1 shown in Table 4 is the same as Comparative Example 1 shown in Table 3, but Comparative Example 7 uses copolymer N011 that meets the provisions of the present invention, but the formulation as a rubber is This is an example in which the amount was out of specification (20 parts by weight compared to NR).

Now, in Examples 5 and 6, the amount of rubber compounded was varied, and in comparison with NR, these Examples used 30 to 70 parts by weight, which is the limit of the predetermined amount.

Comparing these results with Comparative Example 1, it can be seen that both results are excellent.

Furthermore, in comparison with Comparative Example 7, this example is superior in most of the test items, and from the future it can be seen that not only a copolymer with a specific structure is used, but also the rubber formulation It can be seen that this must be considered in order to achieve the objective.

Table 2 Standard recipe (parts by weight) Table 4

Claims (1)

[Claims] (1) Obtained by copolymerizing styrene and butadiene with an organolithium compound, I) 20 to 50% by weight of bound styrene, II) A single chain with one styrene unit is 4% of fully bound styrene.
A styrene-butadiene copolymer which is less than 0% by weight, has a long styrene chain consisting of 8 or more styrene units, is 10% by weight or less of the total bonded styrene, and has a glass transition temperature of -50°C or higher, A rubber composition consisting of 10 to 150 parts by weight of silica filler and 0 to 100 parts by weight of carbon black, based on 100 parts by weight of rubber alone or a blend of 30 parts by weight or more of this rubber and 70 parts by weight or less of other diene rubber. A pneumatic tire characterized by using for the tire tread.