JPH0530857B2 - - Google Patents

Description

[Detailed description of the invention]

"Field of Industrial Application" The present invention relates to a rubber composition that has a high degree of wear resistance for use in tire retards, and in particular has excellent abrasion resistance that is suitable for use as treads for large tires such as trucks and buses. The present invention relates to a rubber composition comprising: ``Prior Art'' Furnace blacks for rubber reinforcement are available in a variety of varieties depending on their characteristics, and are usually classified based on characteristics such as average particle diameter, specific surface area, and structure. The characteristics of these furnace blacks are important factors that determine the performance of the rubber composition to which they are blended, so they are appropriately selected and used depending on the intended use. For example, for application fields that require a high degree of wear resistance, such as those used in tire tread parts,
Varieties such as SAF (N110) and ISAF (N220) are being applied. These furnace blacks are characterized by having a small average particle size and a large specific surface area, but it is generally difficult to homogeneously disperse such blacks in a rubber component. In other words, a rubber composition containing furnace black with a large specific surface area and a small particle size can provide a high degree of wear resistance, but the hardness of the kneaded product increases during the kneading process into the rubber component. This makes it difficult to achieve homogeneous dispersion.
Therefore, not only kneading energy and kneading time increase, but also the kneading and dispersion processability is poor, resulting in serious problems such as quality deterioration. "Problems to be Solved by the Invention" The present invention aims to solve the above-mentioned problems that occur when a furnace black with a small particle size and a large specific surface area is mixed and kneaded with a rubber component for the purpose of improving wear resistance. It is something to be measured. In other words, by blending furnace black with the same specific surface area without making the average particle size finer, a rubber composition with higher wear resistance is provided, without compromising kneading processability. The key point is to use a furnace black that can provide a high degree of wear resistance without causing damage. "Means for Solving the Problem" The inventors have conducted various studies on the relationship between the physical properties of the furnace black to be blended in order to improve the abrasion resistance of the rubber composition.
The present invention was conceived based on the knowledge that the true specific gravity of the furnace black and the Stokes mode diameter of the aggregate are important factors. That is, the present invention has a nitrogen adsorption specific surface area (N ₂ SA) of 145 m ² /g or more and a true specific gravity value of (1.8379
−0.0006× _N2SA ), and the Stokes mode diameter st of the aggregate obtained by centrifugal sedimentation is calculated from the formula {4.35×electron microscope particle diameter (dn)−10.0}. Furnace black with selective properties less than or equal to the rubber component
This is a rubber composition characterized in that it is blended in a ratio of 25 to 150 parts by weight per 100 parts by weight. The true specific gravity value of furnace black can be understood as a characteristic element different from particle size and structure. Furnace black is produced through a thermal decomposition reaction by injecting raw material hydrocarbon oil into a high-temperature turbulent air stream of combustion gas formed by burning fuel oil.The raw material hydrocarbon oil undergoes a complex polycondensation reaction and becomes carbon black. converts into In this production process, the true specific gravity value of the furnace black can be considered as a parameter indicating the degree of formation of the carbon microcrystalline structure inside each particle constituting the furnace black. is in a state where the carbon microcrystalline structure is insufficiently formed,
This shows that the constituent particle surfaces are rich in chemically active radicals. Therefore, this true specific gravity value is
It is closely related to the production reaction temperature, production reaction time, etc. in the production process of the furnace black, and as a result, it is correlated with the specific surface area or particle size of the furnace black. In the present invention, by setting the true specific gravity value to be equal to or less than the true specific gravity relation value calculated by the formula (1.8379-0.0006×N ₂ SA), it is possible to provide a unique surface texture with high surface activity. Next, the stalk mode diameter st of the aggregate is a parameter that indicates the properties of the aggregate in which furnace black particles are firmly fused and bonded, and is a parameter that indicates the properties of the aggregate, such as the formation reaction temperature in the furnace black generation process and the degree of disturbance of combustion gas. It is closely related to the formation conditions of As a result, the Stokes mode diameter of the aggregate st
is correlated with the particle size or specific surface area of the furnace black, and the inventors found that st is (4.35
It was confirmed that when the value is lower than the value calculated from the formula (x electron microscope particle size - 10.0), the effect of improving the abrasion resistance of the rubber composition is significant. This is characterized by the fact that the size of the aggregates is relatively small when the electron microscopic average particle diameter (dn) is constant. By specifying the true specific gravity value and the size of the aggregates of the furnace black as described above, the interfacial reaction with the rubber component can proceed smoothly and the wear resistance can be improved without deteriorating the kneading processability. I can't help it. In other words, when the specific surface areas are the same, it is possible to provide relatively high wear resistance. These effects are remarkable in rubber compositions that require excellent wear resistance, especially when the nitrogen adsorption specific surface area is
It has great practical effects when applied to furnace blacks of 145 m ² /g or more. For each characteristic value of the furnace black applied to the present invention, values determined by the following measurement method are used. (1) Nitrogen adsorption specific surface area (N ₂ SA) ASTM D3037−78 “Standard Methods of
Testing Carbon Black−Surface Area by
Nitrogen Adsorption"Method B. The value of IRB#5 measured using this method is 80.3m ² /g
It was hot. (2) True specific gravity value Place the carbon black sample in a crucible with a lid.
After degassing for 5 minutes at a temperature of 650±25°C, "Industrial Chemistry Magazine" Vol. 66, No. 12 (1963),
Measure according to method B published on page 1758. That is, an appropriate amount of the degassed sample is weighed into a pycnometer, immersed in a small amount of benzene, and then
Degas under reduced pressure of 5 mmHg until no bubbles are observed. Next, fill the pycnometer with benzene, keep it in a constant temperature water bath at 25±0.1°C for 30 minutes, and then weigh it. The true specific gravity value is calculated by the following formula. True specific gravity value = (D-A) / (D-A) - (E-C) x d ^2
5 ₄ However, A is the mass of the pycnometer, C is the mass of the pycnometer + benzene, D is the mass of the pycnometer + carbon black sample, E is the mass of the pycnometer + carbon black sample + benzene, and d ²⁵ ₄ is the mass of the benzene. It is specific gravity. The value of IRB #4 measured by this method was 1.7780. (3) Electron microscopy particle size (dn) After dispersing a carbon black sample in chloroform using an ultrasonic cleaner at a frequency of 28 KHz for 30 seconds, the dispersed sample is fixed on a carbon support membrane. [For details, see, for example, "Illustrated Illustration of Powder Physical Properties" (edited by Powder Technology Study Group and others), page 68 (c) "Water surface film method." ] Direct magnification of 20,000x and total magnification of 80,000~ using an electron microscope.
Take a photo at 100,000x magnification and randomly select from the obtained photos
Measuring the diameter of 1000 carbon black particles,
The arithmetic mean particle diameter (dn) is determined from the histogram created by dividing the particles into 3 mμ increments. (4) Stokes mode diameter of aggregate st A carbon black sample, which was accurately weighed after drying based on JIS K6221 (1975) Section 6.2.1 Method A, was mixed with a 20% aqueous ethanol solution containing a small amount of surfactant. Prepare a dispersion liquid with a carbon black concentration of 50 mg/distance and thoroughly disperse it using ultrasonic waves. Disk centrifuge device (manufactured by Joyes Loebl, UK)
The rotation speed is set to 8000 rpm, and after adding 10 to 20 ml of spin liquid (2% glycerin aqueous solution), 1 ml of buffer liquid (ethanol aqueous solution) is injected. Next, 0.5 to 1.0 ml of the sample solution is added using a syringe to start centrifugal sedimentation, and at the same time a recorder is activated to optically create an aggregate distribution curve. st reads the Stokes equivalent diameter (mμ) of the maximum frequency (maximum absorbance) in the aggregate distribution curve. A furnace black having these characteristics can be produced by appropriately setting and controlling the thermal decomposition reaction conditions using a normal oil furnace reactor. For example, it can be obtained by adjusting various conditions such as production reaction temperature, production reaction time, combustion gas flow rate, and atomization of feedstock oil.
In particular, to reduce the true specific gravity value, shorten the production reaction time, and to reduce the Stokes mode diameter of aggregates, apply conditions such as increasing the production reaction temperature and increasing the combustion gas flow rate. This is effective. Furnace black having the above characteristics is mixed with natural rubber or various synthetic rubbers together with other rubber compounding agents by a conventional method. In this case, it is desirable to mix and knead the furnace black in a proportion of 25 to 150 parts by weight, particularly 40 to 80 parts by weight, per 100 parts by weight of the rubber component. "Function" The present invention maintains the true specific gravity value at a relatively lower level than the value corresponding to the nitrogen adsorption specific surface area.
Increases the chemical activity of the furnace black surface,
This aims to increase the affinity with the rubber component. Further, when the electron microscope particle size is at a certain level, the abrasion resistance of the rubber composition can be improved by setting the Stokes mode diameter of the aggregate to a low level. Therefore, in order to create a rubber composition with excellent abrasion resistance, these functions act synergistically and a furnace black having the same level of specific surface area is blended to achieve relatively high abrasion resistance. can be granted. "Example" A combustion chamber (diameter 400 mm, length 500 mm) having a tangential air supply port, a combustion burner inserted in the axial direction of the furnace, and a raw oil injection nozzle in the furnace head, coaxial with the combustion chamber. Connecting narrow diameter reaction chambers (diameter 160mm,
Using an ordinary oil furnace consisting of a narrow-diameter reaction chamber (1500 mm in length) and a wide-diameter reaction chamber (300 mm in diameter) following a narrow-diameter reaction chamber, the feedstock oil, fuel oil, air supply amount, and wide-diameter reaction chamber Various carbon black samples were manufactured by adjusting the cooling water introduction position. In order to set the combustion gas temperature to a high temperature, the combustion chamber was lined with a zirconia refractory material instead of the normally used high alumina refractory material. Specific gravity (15/4℃) 1.073, viscosity (Engler 40/20℃) 2.10, toluene insoluble content as raw material oil
0.03%, correlation coefficient (BMCI) 140, initial boiling point 103℃
Aromatic hydrocarbon oil with a specific gravity (15/4℃) of 0.903, viscosity (CST50℃) of 16.1, residual coal content of 5.4%, sulfur content of 1.8%, and flash point of 96℃ was used as fuel oil. there was. Carbon black was produced using the above-mentioned oil furnace, raw material oil, and fuel oil, and the production conditions and characteristics of each carbon black sample are compared and shown in Table 1.

[Table] (Note) * Residence time of generated carbon black-containing gas to water cooling point Among the comparative examples, sample No. 4 has st, sample No. 5 has true specific gravity, and samples No. 6 and No. No. 7 is an example in which both the true specific gravity value and st are outside the characteristic range regulated by the present invention. Next, these carbon black samples are shown in Table 2.
It was blended into natural rubber at the blending ratio shown below.

【table】

[Table] Various rubber properties were measured for the rubber composition obtained by vulcanizing this compound at a temperature of 145°C for 40 minutes, and the results were compared with sample No. in Table 1.
Shown in 3.

[Table] Among the various rubber properties, the amount of wear was measured using a Lambourne abrasion tester (mechanical slip mechanism).
Measurements were made under the following conditions. Test piece: Thickness 10mm, outer diameter 44mm, Emery wheel: GC type, grain size 80, hardness H Added carbon random: Grain size 80 mesh, addition amount approx. 9g/min Relative slip rate with emery wheel surface: 12% Test piece rotation Number: 660rpm, Test load: 4Kg All other rubber properties are JIS
Based on K6301 "General Rubber Test Method". From the results in Table 3, it can be seen that samples Nos. 1 to 3 that satisfy the characteristic requirements of the present invention all have nitrogen adsorption specific surface areas at the same level as the comparative examples.
It is found that it has a high degree of wear resistance and also has excellent mechanical strength properties. "Effects of the Invention" As is clear from the above explanation, a rubber composition containing furnace black as a reinforcing agent, which has the selective property requirements regulated by the present invention, can be effectively used without increasing the specific surface area for nitrogen adsorption. can improve wear resistance. Therefore, a rubber composition having high wear resistance can be obtained without reducing kneading and dispersion processability, and can be particularly useful as a tread for large tires.

Claims (1)

[Claims] 1 Nitrogen adsorption specific surface area (N ₂ SA) is 145 m ² /g or more, true specific gravity value is equal to or less than the true specific gravity relationship value calculated by the formula (1.8379-0.0006×N ₂ SA), and aggregates obtained by centrifugal sedimentation. Stokes mode diameter st
Furnace black, which has selective properties less than the value calculated from the formula {4.35 x electron microscope particle diameter (dn) - 10.0}, is added at a rate of 25 to 25 parts per 100 parts by weight of the rubber component.
A rubber composition containing 150 parts by weight.