JPH0553176B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an advantageous rubber composition for tires, which improves the high-temperature fracture properties of the rubber composition by incorporating carbon black having an improved higher-order structure, thereby improving the separation resistance of the tire. In order to improve the separation resistance of tires,
Although it is important to improve the heat generation properties of the tread surface, which occupies the largest volume in the tire, it is also necessary to improve the fracture characteristics at high temperatures of each member other than the tread surface. Among the fracture properties of tire carcass, belts, and other components at high temperatures, important properties for improving separation resistance include peel resistance at high temperatures and crack growth at high temperatures. In ordinary carbon black, if the particle size is made smaller, the crack growth properties at high temperatures are improved, but the peel resistance at high temperatures is reduced, and it has been difficult to achieve both. Therefore, conventionally, soft carbon blacks, which are cheaper than hard carbon blacks such as HAF, have been used, and FEF is particularly preferred. If crack growth (at high temperatures) could be improved without impairing FEF's high peel resistance (at high temperatures), it would be possible to improve the separation resistance of tires, which has long been strongly desired. In view of the above, the present inventors have conducted extensive research into the correlation between the various properties of carbon black to be blended and the physical properties of the resulting rubber composition, and have found that even if carbon black has a particle size in the soft range, The present inventors have discovered that the crack growth properties of a rubber composition can be improved by adjusting the aggregate distribution state to a specific region, and have achieved the present invention. That is, the present invention applies to natural rubber and/or synthetic rubber.
A tire rubber composition comprising 30 to 80 parts by weight of carbon black per 100 parts by weight, wherein the carbon black has an arithmetic mean particle diameter dn of 40 to 50 mμ and a standard deviation thereof as measured by an electron microscope. S is 10 to 20 mμ, and the half-width ΔD ₅₀ (D _st ) of carbon black aggregate distribution by centrifugal sedimentation is
The present invention relates to a rubber composition for tires, characterized in that the mode D _st (mode) of the aggregate distribution is 80 to 110 mμ, and the mode D st (mode) of the aggregate distribution is 130 to 160 mμ. Here, "arithmetic mean particle diameter (dn) determined by electron microscopy" refers to the carbon black sample that is dispersed in chloroform by ultrasonic cleaning (dispersion conditions may be, for example, ultrasonic cleaning at a frequency of 28 KHz for 30 minutes). The dispersed sample was fixed on a carbon support membrane, and this sample was directly examined under an electron microscope at a magnification of 20,000 times.
Photographs were taken at a total magnification of 80,000 to 100,000 times, and the diameters of 1,000 carbon black particles were measured from the obtained electron micrographs, and the average particle diameter (dn) was determined by an arithmetic average from a histogram of 3 mμ divisions. The carbon black aggregate distribution by the centrifugal sedimentation method was measured by the following method using a disk centrifuge manufactured by Joys Lebre. In other words, accurately weigh the carbon black, add it to a 20% ethanol aqueous solution, and adjust the carbon black concentration.
After reducing the concentration to 0.01% by weight, disperse it using ultrasound (for example, for 10 minutes) and use this as a sample solution. Set the rotation speed of the disk centrifuge to 6000 RPM,
A sample solution (0.25 ml to 1.00 ml) was injected into 30 ml of a spin solution (2% aqueous glycerin solution) using a syringe, centrifugal sedimentation was started all at once, and an aggregate distribution curve was created by photoelectroprecipitation. Half width ΔD ₅₀ (D _st ) and mode
D _st (mode) was determined from Figure 1. Note that the broken line portions in the drawing have the same length, and the half width is the length of the solid line portion shown in the drawing. The carbon black according to the present invention having the above characteristics has a narrower distribution of aggregates and is more homogeneous in quality than conventional FEF. This carbon black can be manufactured in a conventional FEF manufacturing process using a manufacturing furnace for soft carbon black, as long as care is taken not to expose it to excessively high temperatures so as to cause a homogeneous reaction. That is, highly aromatic heavy oils such as creosote oil and ethylene bottom oil are mixed with high-temperature combustion gas through an atomizing injection nozzle to obtain a highly homogeneous mixture.
Thoroughly homogeneous atomization and dispersion into uniform fine oil droplets and prolonged exposure to excessively high temperatures should be avoided to avoid recycling of carbon aggregates suspended in the combustion products. This narrows the distribution size of the aggregate distribution and prevents the formation of large aggregates. It is also important to increase the linear velocity in the reaction zone and change the position of water quenching to make the quenching more effective. The arithmetic mean diameter dn of the electron microscope according to the present invention is 40 to 50 mμ, and its standard deviation S is 10 to 20 m.
If the half-value width ΔD ₅₀ (D _st ) of carbon black aggregate distribution obtained by centrifugal sedimentation is less than 80 mμ, the heat resistance of the rubber composition, which is a characteristic of conventional FEF, will be significantly reduced. When it exceeds 110 mμ, the fatigue resistance of the rubber composition begins to decrease, and the fracture strength and crack growth resistance, which is an important improvement property, decrease. Furthermore, if the mode value D _st (mode) is less than 130 mμ, the elastic modulus of the rubber composition blended with it will decrease significantly, making it difficult to use as a tire frame material, and if it exceeds 160 mμ, peeling from adjacent members may occur. It is not used because it reduces drag. In the present invention, synthetic rubbers include styrene-butadiene copolymer rubber, polybutadiene rubber, synthetic polyisoprene rubber, chloroprene rubber, ethylene-propylene-diene ternary copolymer rubber, ethylene-propylene copolymer rubber, butyl rubber, halogenated butyl rubber, It is a butadiene-acrylonitrile copolymer rubber, etc., and may be a blend rubber of one or more of these. In the present invention, if 30 to 80 parts by weight of the carbon black is added to 100 parts by weight of rubber, the objective of the present invention, which is to improve crack growth without impairing the peel resistance, can be achieved. If heat generation is important, the carbon black according to the present invention should be
It is preferable to mix 60% by weight. In addition, the rubber composition of the present invention may contain, in addition to carbon black, a vulcanizing agent such as sulfur, a vulcanization accelerator,
It may contain a vulcanization accelerator, an anti-aging agent, a tackifier, a softener, a filler, etc. As described above, the rubber composition for tires of the present invention containing carbon black having properties in the specified range can be used for carcass ply coating rubber, breaker coating rubber, inner liner rubber, stiffener rubber, It is applied to the frame members of large and small tires, such as bead filler rubber, sidewall rubber, and base tread rubber, and advantageously improves the separation resistance of pneumatic tires. It is also used in rubber industrial products. This will be explained in more detail below with reference to Examples. Example 1 As shown in Tables 1 and 2, rubber compounds containing various types of carbon black were kneaded and heated at 145°C.
Vulcanization was performed for 30 minutes to obtain a vulcanized product. This vulcanizate was evaluated for peel resistance (100°C), crack growth (70°C), and impact resilience (room temperature). The obtained results are also listed in Tables 1 and 2. The evaluation method is as follows. Peel resistance After kneading various carbon black-containing rubber compounds, sheet them into approximately 2 mm sheets before vulcanization.
The sheets are pasted together and vulcanized at 145°C for 30 minutes. The sample after vulcanization (thickness approx. 4 mm) is 11 mm wide.
After punching out a rectangular shape of cm with a blade die and repeatedly elongating it using an Instron type tensile tester at a strain of 200% and a tensile speed of 100 mm/min, it was immediately stretched along the pasting surface at a tensile speed of 100 mm/min. A tear test was carried out at 30 minutes, and the drag force obtained at that time was
The force divided by is taken as the peeling force. The test was repeated twice, and the average value of the two tests was recorded. Unit is Kg・f/cm
It is. Crack growth: Punch out a 2 mm thick vulcanized rubber sheet with a JIS No. 1 blade die, and use a razor blade to make an initial cut (scar) with a width of 0.3 mm in the area of maximum strain (center) of the dumbbell-shaped specimen. . Distort this by 30%, 40%, 50%, 60%
Stretch the material repeatedly and measure the life until rupture at each strain. At the same time, the energy applied to the sample at each strain was determined from the following equation, and the rupture life at the same energy was compared. The numerical values of crack growth properties in Tables 1 and 2 are the fracture life (number of times) at input energy T=50 g/mm, and the larger the numerical value, the better. T=σ/2×ε×π/√1+ε ε: Strain, σ: Stress, π: Pi, Repulsion Resilience Measured at room temperature using a Dunlop tripsometer.

【table】

【table】

【table】

[Table] Example 2 A rubber composition using carbon black No. 2 of the present invention was applied to a passenger car bias structure tire size 560-13,
The rubber composition was applied to 4-ply breaker coating rubber, ply coating rubber, and sidewall rubber, and an indoor drum test was conducted using a rubber composition using commercially available FEF carbon black in conjunction with a comparative tire using the same rubber composition. Above carbon black No.
No. 2 had the characteristics shown in FIG. 2 in comparison with the above-mentioned commercially available FEF. The compounding contents (parts by weight) of the rubber composition are shown in Table 3 (the only difference in the compounding recipe between the tire using the rubber composition of the present invention and the comparative tire is the carbon species).
The dry test conditions are as follows. Drum test conditions: Internal pressure of the test tire was 1.70Kg. After filling with f/cm ² , a step load test was conducted at a constant test speed of 80 Km/H. Load Running time 1st step 382.5Kg 5 hours 2nd step 405Kg 5 hours 3rd step 450Kg 30 hours 4th step 517.5Kg 5 hours ↓ From now on, add 67.5Kg every 5 hours. The test results are displayed as (number of final steps) x (running time at final step).

【table】

[Table] In the comparison tire, separation between the breaker and ply occurred after 6 steps x 1.5 hours and the tire failed, but in the tire using the rubber composition of the present invention, separation between the breaker and ply occurred after 10 steps x 0.5 hour. It can be understood that the durability has been improved just by the occurrence of this phenomenon. Example 3 Radial tire 165 for passenger cars as in Example 2
SR13, base tread rubber in 4 ply,
Belt coating rubber, sidewall rubber,
Carbon black No. 2 of the present invention (tire using the rubber composition of the present invention) and commercially available FEF (comparative tire) were applied to four types of rubber compositions of bead filler rubber, and a drum test was conducted under the same conditions as in Example 2. was carried out. The formulation (parts by weight) of the rubber composition is shown in Table 4.

[Table] Separation between the base tread and belt occurred in 8 steps x 3.0 hours for the comparison tire.
However, a similar failure occurred in the tire using the rubber composition of the present invention after 12 steps x 0.5 hours, confirming that the tire had improved durability. Example 4 Large bias tire 1000- for trucks and buses
In the 20 and 14 plies, carbon black of the present invention No. 2 (a tire using the rubber composition of the present invention) was added to the composition of four types of members: base tread rubber, breaker coating rubber, ply coating rubber, and sidewall rubber. ) and a commercially available FEF (comparison tire), and a drum test was conducted under the test conditions shown below. Rubber composition formulation (parts by weight)
are shown in Table 5.

[Table] Drum test conditions After filling the test tire with an internal pressure of 6.50Kg・f/ ^cm2 , perform a step load test at a constant test speed of 60Km/H. Load Running time 1st step 1659Kg 8 hours 2nd step 2014.5Kg 8 hours 3rd step 2370Kg 8 hours ↓ From now on, add 355.5Kg every 8 hours. The test results are displayed as (number of final steps) x (running time at final step). In the comparison tire, separation between the base tread and belt occurred in 5 steps x 1.0 hours.
However, in the tire using the rubber composition of the present invention, separation between the base tread and the belt occurred after 6 steps x 2.5 hours, and it was confirmed that the separation resistance was significantly improved by applying the carbon black of the present invention. It was done. Example 5 Large bias tire for trucks and buses
In 1000R20, 14-ply, the carbon black of the present invention was added to the composition of five types of members: base tread rubber, belt coating rubber, ply coating rubber, sidewall rubber, and stiffener rubber.
No. 2 (tire using the rubber composition of the present invention) and commercially available FEF (comparison tire) were applied, and the internal pressure was set to 7.25.
A drum test was conducted under the same test conditions as in Example 4 except that the test conditions were Kg·f/cm ² . The formulation of the rubber composition is shown in Table 6.

[Table] In the comparative tire, separation occurred between the belts at 5 steps x 6 hours and failure occurred, but in the tire using the rubber composition of the present invention, separation between the belts occurred at 7 steps x 0.5 hours, and the tire failed. Improvement in separation resistance was confirmed. As described above, the present invention provides a tire rubber composition that can improve the separation resistance of pneumatic tires at a low cost by improving the aggregate distribution of soft carbon black with a particle size of FEF class. be able to.

[Brief explanation of the drawing]

Figure 1 is an aggregate distribution curve diagram of carbon black, showing how to determine the half width and mode, and Figure 2 is an aggregate distribution curve of carbon black No. 2 according to the present invention and commercially available FEF. It is a curve diagram.

Claims (1)

[Claims] 1. A tire rubber composition comprising 30 to 80 parts by weight of carbon black to 100 parts by weight of natural rubber and/or synthetic rubber, wherein the carbon black has an arithmetic mean particle diameter dn measured by an electron microscope. is 40 to 50 mμ, and its standard deviation S is 10 to 20
mμ, and the half-width ΔD ₅₀ (D _st ) of carbon black aggregate distribution by centrifugal sedimentation method is 80 to 110 m.
μ, the mode D _st (mode) of its aggregate distribution is 130
A rubber composition for tires, characterized in that it has a particle diameter of ~160 mμ.