JP2863584B2 - Pneumatic tire - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a pneumatic tire, and more particularly to a pneumatic tire capable of simultaneously satisfying wet skid resistance, rolling resistance, and abrasion resistance.

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

In other words, it is generally well known that reducing the rolling resistance of the tire reduces the consumption of automobiles, so-called low fuel consumption tires. It is common to use

In addition, there has been a strong demand for a rubber material having a large friction resistance (wet skid resistance) on a wet road surface due to a demand for running safety.

However, these low rolling resistance and friction resistance on a wet road surface have a trade-off relationship, and it is very difficult to satisfy both characteristics.

Recently, the association between the wet skid resistance and rolling resistance of the tire and the viscoelastic properties of the rubber composition has been theoretically shown, and the rolling resistance during tire running is reduced by reducing the hysteresis loss of the tread rubber. In terms of viscoelasticity, it has been shown that lowering the loss factor (tan δ) at a temperature of 50 to 70 ° C. at which the tire is used for traveling is effective for low fuel consumption.

On the other hand, it is known that the wet skid resistance correlates well with the loss factor (tan δ) around 0 ° C. at a frequency of 10 to 20 HZ. It is necessary to increase the loss factor of the

As a method of reducing the hysteresis loss, it is common to use a material having a low glass transition temperature such as high cis polybitadiene rubber or a material having a high rebound resilience such as natural rubber.

However, these rubbers extremely reduce wet skid resistance, and it is extremely difficult to achieve both running stability and rolling resistance.

Further, in recent years, many inventions satisfying the above contradictory characteristics have been made with the progress of anionic polymerization.

For example, JP-A-55-12133, JP-A-56-127650
Japanese Patent Application Publication No.
JP-A-55204 and JP-A-57-73030 propose a high vinylstyrene butadiene copolymer rubber.

JP-A-59-117514, JP-A-61-103902, JP-A-61-14214, and JP-A-61-141741 disclose benzophenone, isocyanate and the like in the polymer molecular chain. This shows that the exothermic property is reduced by using a modified polymer into which a functional group is introduced.

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

The present inventors have conducted intensive studies with the aim of further improving the wet skid resistance, rolling resistance, and wear resistance of a tire. As a result, the (S) BR having a specific microstructure and Tg polymerized using a lithium-based initiator has been developed. The present invention has been found that a tire using a rubber composition containing a silica filler for a tread is excellent in the above-mentioned various properties, and has reached the present invention.

(Means for Solving the Problems) The present invention was invented with the above objects, and the gist of the present invention is to obtain styrene and butadiene with an organolithium compound, ) 20 to 50% by weight of bound styrene, II) a single chain of one styrene unit is less than 40% by weight of the total bound styrene, and a styrene long chain having 8 or more styrene units is 10% of the total bound styrene. Styrene-butadiene copolymer having a glass transition temperature of -50 ° C. or higher, alone or 30 parts by weight or more of the rubber and 100 parts by weight of a blend rubber of 70 parts by weight or less of another diene rubber, The present invention relates to a pneumatic tire, wherein a rubber composition comprising 10 to 150 parts by weight of a silica filler and 0 to 100 parts by weight of carbon black is used for a tread of the tire.

The styrene-butadiene copolymer used in the present invention is obtained by copolymerizing styrene and butadiene using a lithium-based polymerization initiator. In a more preferred embodiment, a copolymer comprising an organolithium compound and a specific organic metal is used. A catalyst is used. By using this cocatalyst, the process of the present invention allows for control of the polymerization reaction to produce a copolymer having optimal properties.

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

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

The chain distribution of styrene in the styrene-butadiene is analyzed by gel permeation chromatogram after decomposing the sample with ozone (Tanaka et al., The Society of Polymer Science, ( 9 ), p. 2055).

The short chain of one styrene unit in the styrene-butadiene copolymer is less than 40%, preferably 35% or less;
In addition, the styrene long chain in which eight or more styrene units are linked is 10% by weight or less, preferably 5% by weight or less of the total bound styrene. If the styrene short chain is at least 40%, the wear resistance and tear strength will be poor, and if the styrene long chain exceeds 10%, the rolling resistance will be poor, making it difficult to obtain the desired pneumatic tire.

The styrene-butadiene copolymer has a glass transition temperature of -50 ° C or higher, preferably -40 ° C or higher. If the glass transition temperature is lower than -50 ° C, the wet skid resistance is inferior, which is not preferable.

The styrene-butadiene copolymer used in the present invention may be used alone in the tread, but if necessary, 70 parts by weight or less, preferably 50 parts by weight or less of natural rubber or polybutadiene rubber in 100 parts by weight of rubber. A diene rubber such as synthetic polyisoprene rubber, butadiene-acrylonitrile copolymer rubber, and styrene-butadiene copolymer rubber other than the above-mentioned copolymer rubber may be blended.

Typical examples of the organolithium polymerization initiator used for producing the styrene-butadiene copolymer of the present invention are as follows. That is, ethyl lithium, propyl lithium, n-butyl lithium, sec-lithium, t
alkyllithium represented by ert-butyllithium; allyllithium such as phenyllithium and tolyllithium; alkenyllithium such as vinyllithium and propenyllithium; tetramethylenedilithium, pentamethylenedilithium, hexamethylenedilithium, decamethylene It is an alkylenedilithium such as dilithium.

Examples of the organic metal potassium used as a cocatalyst with the organic lithium include potassium dodecylbenzenesulfonate, potassium tetradecylbenzenesulfonate, potassium hexadecylbenzenesulfonate, potassium octadecylsulfonate, and the like. And the compounds described in

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

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

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

The polymerization reaction for obtaining the polymer of the present invention can be performed by any of a batch polymerization system and a continuous polymerization system.

 The polymerization temperature is in the range of 0 ° C to 130 ° C.

Further, the polymerization can be carried out by any polymerization method such as isothermal polymerization, elevated temperature polymerization, or adiabatic polymerization.

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

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

In addition, the said copolymer rubber is manufactured as follows, for example. 25 kg of cyclohexane in a 50 liter reaction vessel,
1.8 kg of styrene, 4.4 kg of 1.3-butadienene, 1.25 g of tetrahydrofuran, potassium dodecylbenzenesulfonate
It is obtained by adding 0.4 ml and 4 ml of n-butyllithium, performing polymerization at an elevated temperature of 50 to 100 ° C., removing residual catalyst, and drying the product.

For the amount of bound styrene in the copolymer, the styrene monomer was changed, for the introduction of the styrene chain, the amount of potassium dodecylbenzenesulfonate was changed, and for the 1,2 bond content, the polymerization temperature and tetrahydrofuran By changing the amount, each can be controlled to a desired ratio.

Silica filler compounded in the present invention is a rubber component
It is 10 to 150 parts by weight, preferably 15 to 100 parts by weight, per 200 parts by weight. If it is less than 10 parts by weight, the effect of filling and reinforcing is small, resulting in inferior abrasion resistance.

Incidentally, the rubber composition used in the present invention, as a filler, 0 to 100 parts by weight of carbon black may be used in combination, compared with silica alone use, processability, abrasion resistance, cut resistance. Can be improved. In this case, the weight ratio of carbon to silica is preferably in the range of about 95/5 to 10/90 in terms of the balance between wet skid properties, rolling resistance and abrasion resistance.

As the silica, dry method silica or wet method silica is used. In particular, Nip Seal VN3 (manufactured by Nippon Silica),
Toksil U, UR (made by Tokuyama Soda), Ultrasil VN3
Preferred is wet-process silica such as Degussa (West Germany).

Examples of the carbon black include carbon black for general tread rubber compositions, for example, HAF (N330, N332
Etc.), HAF-HS (N339 etc.), I • ISAF, ISAF, SAF etc. are used.

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

(Examples) Example 1 Hereinafter, the present invention will be described more specifically with reference to Examples. However, the present invention is not limited to the following Examples at all without departing from the gist thereof.

 Various measurements in the examples were performed by the following methods.

The microstructure of the butadiene portion was determined by an infrared absorption spectrum method (Morello method). The styrene content was measured by an absorption of a phenyl group at 699 cm ^-1 by infrared absorption spectroscopy using a previously determined calibration curve.

 The vulcanization properties were measured according to JISK6301.

The Lambourn friction index, which is a wear resistance test, was measured by the Lambourn friction method. The measurement conditions were a load of 4.5 kg, a wheel speed of 100 m / sec, and a test speed of 130 m / sec.
Second, 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 determined by using a mechanical spectrometer manufactured by Rheometrics Co., Ltd. with a dynamic shear strain of amplitude 1,0.
%, Vibration 15HZ and each measurement temperature.

Rolling resistance index, the tire is brought into contact with a drum with an outer diameter of 1,7 m, the drum is rotated, and after rising to a certain speed,
The drum was coasted and the value calculated from the moment of inertia at a predetermined speed was evaluated by the following equation.

The skid resistance (wet skid property) of wet road surface is
Rapid braking was performed at a speed of 80 km / h on a wet concrete road surface with a depth of 3 mm, the distance from when the wheels were locked to when they stopped was measured, and the skid resistance of the test tires was evaluated by the following equation.

The abrasion resistance index was obtained by running the tire 40,000 km on an actual vehicle, measuring the depth of the remaining grooves at 10 locations, and evaluating the average value by the following equation.

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

For these rubber compositions, the breaking strength (Tb) and Lambourn abrasion tan δ were evaluated.

Next, a tire was prepared using these rubber compositions for a tread having a tire size of 165SR13, and wet skid resistance, rolling resistance, and abrasion resistance were evaluated. Third result
It is shown in the table.

That is, among the various polymers shown in Table 1 produced here, those having a structure suitable for use in the present invention are copolymers NO, 1 and 2, and NOs 3 and 7 are One styrene short chain greatly exceeds the specified amount.
More than one styrene long chain exceeds the specified amount.

Further, for NO and 5, the bound styrene content
O and 6 are those whose glass transition temperatures are below the specified value.

Now, in Table 3, Comparative Example 1 using the copolymers NO and 7 will be considered as a standard, and the results obtained using the copolymers NOs 1 and 2 used in the present invention will be considered. 1 and 2
In the above, both the physical property test and the tire performance test greatly exceeded the standards, and it can be seen that good results were achieved that clear both of the trade-offs of the present invention.

On the other hand, in Comparative Examples 2 to 5 using NO, 3 to 6 which deviated from the structural specification as a copolymer as described above,
In general, a physical property test and a performance test as a tire have not been found to completely satisfy all items.

This demonstrates how important the structural features of the copolymer are to achieve the objects of the present invention.

Further, in Examples NO, 3 and 4, the copolymers NO, 1
And 2 are examples in which the composition is changed, and these results are also good results that greatly exceed the standard values described above.

On the other hand, although NO and 1, which conform to the regulations, were used as the copolymer, in Comparative Example 6 in which the silica filler was blended in a predetermined amount or less, all of the physical properties and the tire performance tests were below the standard values. It is understood that in order to achieve the object of the present invention, not only the definition of the structure of the copolymer but also the composition of the copolymer must be taken into consideration.

As is clear from Table 3, the pneumatic tire of the present invention has excellent wet skid resistance, rolling resistance and wear resistance at the same time.

Example 2 Next, a rubber composition having the composition shown in Table 4 was prepared and examined in the same manner as in Example 1.

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

What is shown in Table 4 is the same as Comparative Example 1 shown in Table 3 in Comparative Example 1, but Comparative Example 7 uses copolymers NO and 1 which meet the requirements of the present invention. Is an example in which the blending amount is out of the specified range (20 parts by weight relative to NR).

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

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

Furthermore, in comparison with Comparative Example 7, the present example is superior in most of the test items. In view of this, not only a copolymer having a specific structure is used, but also from the viewpoint of rubber compounding. It must be understood that this must be considered in order to achieve the purpose.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ identification symbol FI // (C08K 3/00 3:04 3:36) (58) Field of investigation (Int.Cl. ⁶ , DB name) C08L 7 / 00-21/02

Claims (1)

(57) [Claims] 1. Styrene and butadiene are copolymerized with an organolithium compound. I) 20 to 50% by weight of bound styrene; II) A single chain having one styrene unit is 40% of the total bound styrene.
Less than 10% by weight of the total styrene and less than 8% by weight,
And a styrene-butadiene copolymer having a glass transition temperature of −50 ° C. or more, and a silica filler alone or with respect to 100 parts by weight of a blend rubber of 30 parts by weight or more of the rubber and 70 parts by weight or less of another diene rubber. From 10 to 150
A pneumatic tire characterized in that a rubber composition comprising 0 to 100 parts by weight of carbon black is used for a tread of a tire.