JPH0380175B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a tire tread rubber composition, and more particularly to a tread rubber composition for passenger car radial tires, which has improved heat generation properties, grip, and handling performance, and is a styrene-butadiene rubber obtained by a solution polymerization method. The intrinsic viscosity in °C toluene solution is 1.7 or more and 3.0 or less, the amount of bound styrene is 30% by weight or more and 40% by weight or less, and the amount of vinyl bonds in the butadiene moiety is 37% or more and 45% by mole.
The main rubber component is styrene-butadiene rubber in which the proportion of polymer chains modified with a tri- or tetrafunctional binder is 50% by weight or more and 65% by weight or less, and the average particle diameter is 20% by weight. ~30mμ of carbon black per 100 parts by weight of the rubber component.
Contains 40 to 70 parts by weight and has a loss modulus (E″) of 16
Kg/cm ² or less, loss compliance (E″/|E ^* | ² ) is 3.5×10 ^-3 (Kg/cm ² ) ^-1 or less, and the humidity ranges from -30℃ to -15℃. The present invention relates to a tire tread rubber composition having an integral value of loss coefficient (tan δ) of 6 or more.In recent years, with the development of expressway networks and improvements in the driving performance of automobiles, tires are required to have low heat generation properties during high-speed driving. In order to drive more safely, there is a demand for tires with handling characteristics that can fully bring out the driving performance of automobiles.If we look at the history of tires for passenger cars,
There has been a shift from bias tires to radial tires with an aspect ratio of 82%, then to radial tires with an aspect ratio of 70%, and in recent years, radial tires with an aspect ratio of 60% and 50% have also appeared. Attempts have been made to improve grip and maneuverability. In addition, from the viewpoint of compounding tread rubber, rubber components mainly composed of emulsion polymerized styrene-butadiene rubber and containing a large amount of carbon black have been used. That is, the former was selected because it has superior grip properties compared to various conventional rubbers, such as natural rubber and butadiene rubber.
Especially the so-called high styrene, which has a large amount of styrene bonds.
The SBR had excellent wet grip characteristics and maneuverability. In addition, the latter is due to improved reinforcing properties.
It increases the stickiness when the rubber deforms, improving maneuverability and improving wear resistance. However, although these conventional formulations are good in terms of the above-mentioned characteristics, they are inferior in terms of heat generation characteristics and rolling resistance performance, and the former not only deteriorates high-speed durability performance but also has an adverse effect on maneuverability. is giving. That is, as the tread rubber generates heat, the rigidity decreases and the vehicle becomes stiff during cornering, resulting in unstable and undesirable behavior. Regarding the latter, since polymer species and carbon content that have a large energy loss are used, rolling resistance performance deteriorates. Therefore, as a result of detailed research, the inventors found that
The following conclusions were reached. That is, by applying the styrene-butadiene rubber prepared as described below as a treaded rubber composition, not only the grip and maneuverability are dramatically improved, but also the fatal disadvantages of conventional rubber distribution can be improved. By overcoming the heat generation characteristics and poor rolling resistance that had previously existed, we were able to create an extremely well-balanced tire. SBR here is styrene-butadiene rubber obtained by solution polymerization, and has an intrinsic viscosity of 1.7 in toluene solution at 30°C.
or more and 3.0 or less, and the amount of bound styrene is 30% or more and 40% or less by weight, and the amount of vinyl bonds in the butadiene moiety is 37% or more and 45% or less, and 3.
A styrene-butadiene rubber in which the proportion of polymer chains modified with a tetrafunctional binder is 50% by weight or more and 65% by weight or less. The intrinsic viscosity of the styrene-butadiene rubber measured in toluene at 30°C is closely related to the heat generation properties and rolling resistance performance, and if it is less than 1.7, these properties are undesirably deteriorated. In addition, if the intrinsic viscosity is large, the workability during processing such as rubber kneading and extrusion will be significantly reduced, so it needs to be 3.0 or less, but it is necessary to add the necessary amount of process oil after polymerization is completed. That is, by using an oil-extended polymer, workability is significantly improved. In addition, the amount of bound styrene and the amount of vinyl bonds in the butadiene moiety are deeply related to wet grip performance, handling performance, and wear resistance. If this is the case, the performance of the former two may deteriorate, which is undesirable. Furthermore, if the bound styrene content exceeds 40% by weight or the vinyl bond content exceeds 45 mol%, the physical properties of the latter will be greatly reduced, and in particular, tires with a large vinyl bond content may suffer from damage to the tread area at the end of tire vulcanization, so-called demolding. This is not preferable because splitting occurs. These values are particularly preferred because
The bound styrene content is in the range of 30% by weight or more and 35% by weight or less. In addition, in the present invention, in order to obtain a rubber composition with excellent processability, the polymer chains modified with a trifunctional or tetrafunctional binder are used in the styrene-butadiene rubber. It is controlled so that it accounts for at least 50% by weight of the polymer chains. In this case, a polymer chain modified with a trifunctional or tetrafunctional binder means that there is a polymer chain that is bonded by chemical bonds in three or four directions from atoms or atomic groups in the polymer chain. It means a polymer chain having a shape like that. As a method for producing a polymer containing such a modified branched polymer chain, a known living anionic polymerization method using an alkali metal compound as a polymerization initiator is effective. A method may be adopted in which the activated polymer terminals are bonded together by causing the active polymer to act on the active polymer. In this case, the weight ratio of the polymer chains having bonded branches in the polymer can be read from the molecular weight distribution measured by gel permeation chromatography (GPC). In other words, the weight of each polymer chain is determined by the relative ratio of the peak height corresponding to the average molecular weight of polymer chains with connected branches and the peak height corresponding to the average molecular weight of polymer chains without branches. Define as ratio. In the styrene-butadiene rubber, the bonded polymer chains can have a shape modified by either a trifunctional or tetrafunctional binder, or a mixture thereof. The higher the proportion of the modified polymer chains, the better the roll processability, and is controlled to be at least 50% by weight. When the proportion of modified polymer chains is 50% by weight or more, the wrapping stability of the rubber sheet during roll processing is good and the processing operation is easy. On the other hand, if the proportion of modified polymer chains exceeds 65% by weight, the adhesiveness of the rubber sheet becomes poor, making it difficult to bond the sheet together during tire molding, resulting in a decrease in practical moldability. In order to obtain such a preferable ratio of modified polymer chains, the molar ratio of the binder used to the active polymer terminal should be controlled during the production of styrene-butadiene rubber. If used, the amount should be from 0.175 to 0.250 mol per mol of active polymer terminal. The styrene-butadiene rubber of the present invention is polymerized by a known living anionic polymerization process as follows. That is, when styrene and butadiene are copolymerized in a hydrocarbon solvent using an organic alkali metal compound as an initiator, a Lewis basic compound such as an ether or a tertiary amine is allowed to coexist to carry out the copolymerization. can be synthesized by reacting a trifunctional or tetrafunctional binder with the so-called "living active end" in the copolymer solution. As the organic alkali metal compound, alkyl lithiums are particularly preferably used from the viewpoint of stability of the polymerization reaction, and as the trifunctional or tetrafunctional binder, methyl trichloro silicon, silicon tetrachloride, tin tetrachloride, etc. These halogen-containing compounds are preferably used from the viewpoint of controllability of the binding reaction. Next, in the present invention, in order to improve handling performance and wear resistance, the carbon black added to the composition must have an average particle diameter of 20 mμ or more and 30 mμ or less. For example, in the ASTM designation,
Carbon blacks such as N220, N234, N330, and N339 are used. When the average particle diameter exceeds 30 mμ,
This is not preferable because the reinforcing properties are lowered, the wear resistance is inferior, and the handling performance is lowered. On the other hand, if it is smaller than 20 mμ, reduction in rolling resistance cannot be achieved. Carbon black is based on 100 parts by weight of the rubber component.
It is blended in an amount of 40 to 70 parts by weight. Carbon black is
If it is less than 40 parts by weight, the abrasion resistance will be poor, while if it exceeds 70 parts by weight, heat-generating rolling resistance will deteriorate, which is not preferable. Furthermore, in the composition of the present invention, natural rubber and/or synthetic isoprene rubber, or styrene-butadiene rubber with a small amount of vinyl bonds is added to 100 to 50 parts by weight of the above-mentioned styrene-butadiene rubber.
Preferably, 50 parts by weight are mixed. Here, the amount of natural rubber and/or synthetic isoprene rubber is
If it exceeds 50 parts by weight, it is undesirable because wet braking performance deteriorates, but in order to maintain a good balance between better workability, rolling resistance performance, and wet braking performance, the content should be 5 to 40 parts by weight. things are more preferable. As described above, the prepared rubber composition includes process oils, waxes, anti-aging agents, vulcanizing agents, vulcanizing aids, and
Vulcanization accelerators and the like may be added. Furthermore, the above rubber composition is heated at a temperature of 65°C and a frequency of 10
The loss elasticity (E″) measured at Hz and 2% amplitude is 16
Kg/ ^cm2 or less, loss compliance E″/｜E ^* ｜ ²
is required to be 3.5×10 ^-3 (Kg/cm ² ) ^-1 or less. If the loss modulus and loss compliance exceed the above numerical ranges, rolling resistance cannot be reduced. Further, in the present invention, from the viewpoint of improving wet grip properties, it is necessary that the integral value of the loss coefficient be 6 or more in the temperature range of -30°C to -15°C. Conventionally, in viscoelastic polymers, the idea that frequency and temperature are equivalent, that is, temperature -
A time conversion rule has been proposed, and for existing elastomers such as natural rubber and emulsion polymerized styrene-butadiene rubber, Ferry et al. proposed the WLF formula, and empirically calculated the frequency from the glass transition temperature Tg to Tg + 100°C. It is known that it can be converted into temperature. (M L. Willlams et al., J. Am Chem.
Soc., 77 , 334 (1955)). However, it has been reported in various literature that the glass transition temperatures of natural rubber and emulsion polymerized styrene-butadiene rubber, which are generally used mainly as tire tread rubber, are around -70℃ and -50℃, respectively, and WLF Since the temperature range for which the formula holds is at most 30 to 50 degrees Celsius, the tire temperature and tire surface temperature during driving are outside this range. However, no attempt was made to consider this as a loss characteristic due to temperature dispersion. Therefore, the present inventors intentionally deviated from the range in which the WLF formula holds, but by using the idea of temperature-time conversion, high frequency and high temperature are converted into low frequency and low temperature when evaluating wet grip performance. In order to confirm the possibility of this, we investigated the correlation between the loss characteristics due to temperature dispersion and the rolling resistance and wet grip performance of actual tires. As a result, we have discovered the fact that wet grip performance has the highest correlation with the logarithm of the integral value of the loss coefficient in the range of -30°C to -15°C, a fact that was completely unknown until now. The present inventor has completed the present invention by measuring wet grip using this measurement method and studying an elastomer composition that has better tread performance than conventionally used treads. . That is, in the temperature dispersion curve of dynamic viscoelasticity at a frequency of 10 Hz measured at a heating rate of 1 °C/min, the present invention has a temperature range from -30 °C to -15 °C at a secondary strain of 0.5%.
The integral of loss coefficient (tan δ(T)) between °C ∫ ^-15 _-30 tan δ(T) dT value must be 6 or more. EXAMPLES Next, in order to make the present invention more clear, the present invention will be described with reference to examples, but the present invention is not limited thereto. Note that measurements of various physical properties in Examples and Comparative Examples were carried out under the following conditions. Intrinsic viscosity [η] Measured using an Ostwald solution viscosity meter at 30°C in toluene solvent. Measurement of the proportion of modified polymer chains in styrene-butadiene rubber Using Toyo Soda HLC-802UR, 10 ³ , 10 ⁴ , 10 ⁶ , 10 ⁷ columns were selected as distribution columns,
A refractometer was used as a detector. The molecular weight distribution of the polymer was measured at 40°C using tetrahydrofuran (THF) as a developing solvent. The relative ratio of the peak heights corresponding to the respective average molecular weights of modified and unmodified polymer chains,
Weight ratio of each polymer chain

【table】

[Table] Indicates that

[Table] Expressed as percentage. Using the elastomer shown in Table 1 and the composition of the formulation shown in Table 2, tire size 185/
We prototyped a 70HR/13 steel tire and evaluated its rolling resistance, wet grip, and handling stability. These evaluation methods are as follows. The contents of the rubber composition and the performance evaluation results of tires using the same are shown in Tables 2 and 3, respectively. From Table 3, it is recognized that the examples of the present invention are excellent in various performances. Rolling resistance index Fit the above tire to a 5 1/2 J x 13 rim, 60
Speed 80Km/h on inch drum, internal pressure 2.10Kg
f/cm ² and a load of 300 kg, and the rolling resistance was measured. The table shows relative values based on Comparative Example 1. The smaller the number, the better the rolling resistance performance. Wet Grip Index Each of the above tires is fitted to a 5 1/2 J x 13 rim, mounted on a passenger car with a displacement of 1500 cc, and the speed is 60 km/h when one person is riding on a slippery concrete road surface with water sprinkled on it. The friction coefficient μ is calculated from the stopping distance from the stop distance, and is expressed as a relative value with Comparative Example 1 as a reference. Steering stability performance When the above tires are installed on a passenger car with a displacement of 1500c.c.
Air pressure 1.8Kgf/cm ² at JARI general test track, 1
The steering stability performance when driving under the name of the vehicle is shown as a relative value, with Comparative Example 1 set as a standard value of 3.0. Maneuvering stability performance includes straight-line stability, steering response, ground contact,
Evaluated based on convergence, the overall evaluation of each evaluation is shown, and the larger the value, the better. In the table, + on the right side of the numbers means slightly better, and - means slightly worse.

Claims (1)

[Claims] 1. A styrene-butadiene rubber obtained by a solution polymerization method, which has an intrinsic viscosity of 1.7 or more and 3.0 or less in a 30°C toluene solution, and has a bound styrene content of 30% or more and 40% or less by weight, Styrene-butadiene in which the amount of vinyl bonds in the butadiene moiety is 37 mol% or more and 45 mol% or less, and the proportion of polymer chains modified with a trifunctional or tetrafunctional binder is 50% or more and 65% by weight or less Using rubber as the main rubber component, carbon black with an average particle size of 20 to 30 mμ is added to 100 parts by weight of the rubber component.
Contains 40 to 70 parts by weight and has a loss modulus (E″) of 16
Kg/cm ² or less, and the loss compliance (E″/|E ^* | ² ) is 3.5×10 ^-3 (Kg/cm ² ) ^-1 or less, and the loss in the temperature range of -30℃ to -15℃ A tire tread rubber composition having an integral value of a coefficient (tan δ) of 6 or more.