JPH0689268B2 - Soft carbon black - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is classified into Medium Reinforcement (SRF) to General Purpose (GPF).
More specifically, it relates to a carbon black belonging to, and more specifically, it imparts relatively high reinforcement to a rubber composition containing the carbon black while maintaining excellent impact resilience, and also has vulcanization properties and exothermic properties. It relates to an SRF or GPF grade carbon black that can be improved.

Carbon black for rubber compounding is roughly classified into hard carbon black mainly used for tire tread and soft carbon black used for carcass, in which abrasion resistance, workability, The most suitable carbon black is selected and used in consideration of various rubber compounding characteristics such as processability, heat generation and extrudability.

It is well known that each item of the above-mentioned rubber properties is greatly influenced by the physicochemical properties of the carbon black compounded in the rubber. Among them, as the basic physical properties of carbon black, the particle diameter (or surface area) and the connection between particles (structure) are typical.

The surface area can be evaluated by direct observation with an electron microscope, nitrogen adsorption specific surface area (N ₂ SA) by BET method, iodine adsorption amount (IA) and specific surface area by adsorption of macromolecules such as cetyltrimethylammonium bromide (CTAB). Etc. are selected according to the measurement purpose, and the smaller the particle size and the larger the surface area, the more the reinforcing properties thereof increase, while the hysteresis properties such as heat generation property decrease. It is well known that the structure is usually evaluated by the dibutyl phthalate absorption (DBPA) and has a great influence on the extrusion characteristics and the tensile strength.

However, the above-mentioned carbon black characteristics are only macroscopic ones in which the carbon black is regarded as one lump, and in the carbon black that only specifies this basic characteristic, the characteristics of the rubber composition containing this are grasped. Is difficult to do.

The present inventors have extensively studied microscopic colloidal properties rather than macroscopically capturing carbon black, and as a result of studying these properties and the physical properties of compounded rubber, aggregates have been investigated for their dynamic properties. The present invention has been completed by finding that the size distribution is a major factor, and that the contribution of the toluene coloring permeability to the vulcanization characteristics is large in the carbon black in which the aggregate size distribution is in a certain range. Is. In addition to this, it was also found that an unexpected effect of improving heat generation characteristics, which is considered to be due to the synergistic action of the above-mentioned two characteristics, is exhibited.

Carbon black is produced by spraying and introducing raw oil into a furnace (furnace) at a strictly controlled high temperature, and is pyrolyzed for several tens of milliseconds to combine 10 ⁴ to 10 ⁹ carbon atoms into a unit. Particles, and those formed by fusing several tens to several hundreds of these unit particles with each other are aggregates that are the minimum dispersion units in the elastomer.

This aggregate is very small and usually a few
It has a size of 100 nm (1 nm = 10 ⁻⁹ m). There is a method of direct observation with an electron microscope to evaluate this, but there are difficulties in measuring equipment, measurement time, analysis method, etc., and it is usually evaluated by centrifugal sedimentation analysis.

This is based on the principle that the larger the particles in the suspension, the faster they settle, and the more difficult it is to settle by increasing the settling speed by increasing the settling speed. It measures the height.

Actually, the diluted solution of carbon black is irradiated with ultrasonic waves to disperse it sufficiently, and this solution is poured on a disk that rotates at high speed, and the amount of carbon black that passes a certain point at each elapsed time. Is continuously measured as the absorbance. An example of this measurement curve is shown in FIG.

Using this measurement curve, the Stokes equivalent diameter of the carbon black aggregate is calculated by the following equation.

Where d: Stokes equivalent diameter of the aggregate (nm) k: Constant determined by the measurement conditions t: Elapsed time (minutes) The Stokes equivalent diameter of the carbon black aggregate d is also a function of the time which changes continuously. By plotting the absorbance as the concentration of the carbon black aggregate at time t, a smooth curve showing the relationship between the equivalent diameter of the aggregate and the carbon black concentration at that diameter can be obtained.

When the logarithm of the equivalent diameter of this aggregate is plotted on the horizontal axis and the absorbance (concentration or frequency) is plotted on the vertical axis, it has been confirmed that carbon black exhibits a nearly lognormal distribution, and the equivalent of the aggregate calculated from FIG. 1 is confirmed. The diameter-absorbance curve is shown in FIG.

In the measurement curve of FIG. 1, when the time in the maximum absorbance A _P t _P, 1 / 2A time in _P a and t _L and _{t S (t L <t S} ), aggregate which is converted by Equation (1) The Stokes equivalent diameters of Dst, D ^L ₅₀ and D _{S 50} are shown in Fig. 2 respectively.
It corresponds to.

Here, the aggregate size distribution index s of carbon black is defined by the following equation.

s = 0.84932 x log (D ₅₀ / Dst) (2) If the average aggregate size of carbon black (usually represented by the most frequent Stokes diameter of the aggregate, called Dst) is large, the rubber composition has high repulsive elasticity. While giving a material, there is a tendency for the specific surface area to decrease and, consequently, the wear resistance to decrease, and to combine the dynamic characteristics and wear resistance means that the average aggregate size, that is, the size of Dst. It was almost impossible to control only Sasaki.

In the laboratory, in order to solve this problem, research has been conducted to mix two or more kinds of carbon blacks so that the desired performance can be exhibited, but it is a large-scale industrial scale such as tire manufacturing. In order to be compatible with the use of carbon black, not only can there be no device that mixes two or more kinds of carbon black in a large amount and in an accurate compounding ratio, but also due to the difference in dispersibility due to the characteristics of carbon black, uniformity of There is a drawback that a product having the above cannot be obtained.

Regarding the influence of the aggregate size on the dynamic properties of a rubber composition containing a single product of carbon black, the inventors of the present invention have set the above-mentioned trade-off condition in which the amount of aggregates larger than the most frequent aggregate size is the above-mentioned. It is an important factor to solve, and the aggregate size value (D ^L ₅₀ ) that has the most frequent aggregate size value (Dst) and the aggregate size side that is larger than Dst and has a frequency value of 1/2 of Dst. ), The aggregate size distribution index s calculated from the two numerical values of
It has been found that by keeping it at 0.15, it is possible to impart a high reinforcing property to the rubber while maintaining the impact resilience of the conventional carbon black of the same grade.

Defining such an aggregate size distribution index s has the following technical meaning. That is, when an aggregate, which is a unit of minimum variance formed by binding carbon black particles to each other, is evaluated by a centrifugal sedimentation analysis method, conventionally, the most frequent value (Dst) of the aggregate and its distribution (usually ΔD ₅₀ = D ^L ₅₀ −D _{S 50 (} see FIG. 2), the larger the value of the other is, the larger the value of the other is. It was impossible to evaluate how the distribution changed.

Therefore, using the fact that the logarithmic value and the absorbance (frequency) of the carbon black aggregate show a nearly normal distribution as described above, using the numerical values of Dst and D ^L ₅₀ , it has the meaning of being close to the standard deviation of the distribution. It is the basis of the present invention to introduce a completely new concept of evaluating the distribution state by defining the aggregate size distribution index (s), and the introduction of this s leads to the distribution shape. For the first time, the criteria for determining what the That is, by defining this evaluation criterion of s, even if the value of ΔD ₅₀ simply increases, the value of s, which is a function of Dst, decreases conversely, and so on.

Furthermore, the other specific requirement, the toluene coloring permeability, is the transmittance (%) measured according to JIS K 6221 6.2.4, and the lower this value, the greater the amount of toluene extractable substances contained in carbon black. To do.

For this toluene extractable substance, it has hitherto been considered that the smaller the amount, that is, the larger the toluene coloring permeability, the more desirable, but, surprisingly, in addition to the specific requirements described above, the present inventors have found that the toluene coloring permeability is further improved. It was found that the vulcanization characteristics of the compounded rubber are remarkably improved when the degree is lowered.

That is, the present invention has a nitrogen adsorption specific surface area (N ₂ SA) of 20 to
35m ² / g, dibutyl phthalate absorption (DBPA) 50-100m
It is intended to provide a carbon black having a specific physical property of an aggregate size distribution index s of 0.12 to 0.15 and a toluene coloration transmittance of 20 to 60% in the carbon black having a characteristic of 1/100 g.

When the present inventors measured the aggregate size distribution of many commercially available SRF-class and GPF-class carbon blacks, the aggregate size distribution index s was mostly concentrated at 0.16 to 0.17, These commercially available carbon blacks cannot satisfy the condition of having both impact resilience and reinforcement.

In the present invention, the aggregate distribution index s is 0.12 to
By holding it on the narrow side of 0.15, it is almost the same.
Compared with carbon black having N ₂ SA and DBPA values, it is possible to significantly improve the reinforcing property while maintaining the impact resilience at the same level.

However, when s of the carbon black exceeds 0.15, an increase in impact resilience is recognized, but it is not preferable because the level of the conventional carbon black having N ₂ SA having the same reinforcing properties such as tensile strength cannot be maintained. Also, s is 0.
If it does not reach 12, the improvement of the reinforcing property is satisfactory, but the impact resilience is lowered. Therefore, when considering both the properties of the reinforcing property and the impact resilience, s is in the range of 0.12 to 0.15. Need to hold.

Furthermore, the above-mentioned aggregate size distribution index is specified in a narrow range, and the toluene coloring transmittance in the range of 75 to 100% in the conventional product is 20 to 60% in the carbon black of the present invention, preferably 35 to 50. %, Which can significantly reduce the vulcanization characteristics of the compounded rubber composition, such as Mooney scorch time.

This improvement in the vulcanization characteristics makes it possible to prevent the mold flow at the time of molding the compounded rubber composition and to greatly improve the workability in the vulcanization process.

When the transmittance of toluene coloring exceeds 60%, no improvement in vulcanization properties was observed, and it was similar to the conventional product. When it was below 20%, too much toluene extractable substance was added and blended. Staining from the rubber, that is, staining, occurs, which is not preferable.

When N ₂ SA is 20 m ² / g or less, it becomes difficult to maintain the required reinforcing property, and when it exceeds 35 m ² / g, the impact resilience decreases, which is not preferable. Further, when the DBPA value exceeds 95 ml / 100 g, Mooney viscosity increases, which may cause adverse effects such as decrease in adhesiveness, which is not preferable, and when less than 50 ml / 100 g, poor dispersion due to particle aggregation or the like occurs. Is seen, which is not preferable.

Furthermore, the ratio of the iodine adsorption amount (IA) expressed in mg / g and the nitrogen adsorption specific surface area (N ₂ SA) expressed in m ² / g, IA / N ₂ SA
Is considered to have some correlation with the surface chemical activity of carbon black, but when this ratio is less than 0.95, it exhibits more preferable properties for dynamic properties and reinforcing properties.

However, the soft carbon black tends to have a smaller difference between IA and N ₂ SA than the hard carbon black, and the surface area of N ₂ SA is IA / N ₂ SA in the range of ²⁰ to 35 m ² / g.
It is difficult to produce carbon black having a ratio of less than 0.75, so this value is made the lower limit.

The carbon black of the present invention has both reinforcing and impact resilience properties, and provides a rubber composition capable of improving vulcanization characteristics and heat generation characteristics, and is an aggregate size distribution index of SRF or GPF class carbon black. By maintaining s at 0.12 to 0.15 and specifying the toluene coloring transmission rate at 20 to 60%, a remarkably improved reinforcing property is maintained for a carbon black compounded rubber composition while maintaining the same impact resilience as conventional products. While achieving this, it is possible to improve vulcanization characteristics and heat generation characteristics.

The production examples of the carbon black of the present invention are shown below.

Production Example Carbon blacks of the present invention and comparative carbon blacks were produced using the carbon black production furnaces shown in FIGS. 5, 6 and 7.

Cylindrical combustion chamber 1 (inner diameter 450 mmφ, length 300 mm) and two first air inlets (2 and 3: inner diameter 100 m having a central axis in the tangential direction installed in the first half of the combustion chamber)
mφ) and six radial second natural gas inlets (4,5, 6, 7, 8, and 9: inner diameter 25 mmφ) independent of the first air inlet and connected to the combustion chamber. Narrowest inner diameter 250mm
φ, a venturi portion having a length of 255 mm, and also provided on the downstream side of the venturi portion and provided so as to be introduced in the forward direction (tangent) or the reverse direction (reverse contact) with respect to the turning direction of the first inlet. Two sets of third air and / or natural gas inlets (11 to 14 of No. 1 and No. 1) passing through the upper and lower ends of the same section.
2 15 to 18: inner diameter 40 mmφ) is installed, and a plurality of cooling water injection sprayers (a to g) are installed in the space on the downstream side of the third inlet.
A continuous reaction and cooling chamber (19: inner diameter 500 mmφ, length 40
00mm) and a carbon black manufacturing furnace entirely covered with a refractory, the feed position of the feedstock, the air and natural gas supply conditions from the first and second inlets, and the third inlet The specific surface area (N ₂ S
SR with different A), structure (DBPA), aggregate most frequent value and aggregate size distribution index (s)
F grade or GPF grade carbon black was produced.

More specifically, the surface area (N ₂ SA) was adjusted by adjusting the ratio of the amount of introduced air to the amount of air, and when the surface area was increased, the amount of introduced air was increased, and when it was decreased, it was controlled by decreasing it. .

The aggregate size distribution was controlled mainly by the flow state in the reaction chamber. That is, the distribution is narrowed (smaller than s) by increasing the amount of air introduced into the reaction chamber, especially the amount of air introduced from the tangent, and widened by increasing the amount of reverse connection. The effect of this flow change becomes large when the upstream side, that is, 11 to 14 is used. Furthermore, it becomes an effective means for controlling the size distribution to be small by adding not only air but fuel. In addition to this, the introduction position of the feedstock oil is also a major control factor. That is, when the feedstock oil is introduced at a position close to the inlet of the venturi, it is introduced in a state in which the flow velocity and density of the combustion gas are increased by the venturi, which causes the size distribution index to move to the smaller side and vice versa. This index increases when moving to the upstream side.

Also, the toluene color transmission and the desired requirement IA
The control of the ratio of / N ₂ SA was controlled depending on which of the cooling water injection spraying devices a to g which were installed in the rapid cooling chamber for continuing the reaction was used. That is, when controlling the toluene color permeability to a low value, or to control the IA / N ₂ SA value to the low side, use an upstream device to increase the color permeability, and _{2 When} large control of SA was made, adjustment was made by using a device on the downstream side.

Inventive carbon blacks and comparative carbon blacks were produced by combining the control conditions described above. The structure was controlled mainly by adjusting the amount of alkali metal added to the feed oil.

The production conditions of various carbon blacks and the physicochemical properties of the produced carbon blacks are shown in Table 1.

SRF-LM (trade name: Asahi # 3)
5), SRF (Product name: Asahi # 50) and GPF (Product name: Asahi # 5)
The properties of carbon black in 5) are also shown.

Specific gravity (15/4 ℃) 1.130 as raw material oil, kinematic viscosity 16.8 cSt
(50 ° C), residual carbon 9.5%, initial boiling point 202 ° C A highly aromatic hydrocarbon having the properties of BMCI160 was used and spray-introduced in the axial direction.

Each characteristic of the carbon black according to the present invention is measured as follows.

DBP absorption (DBPA): According to JIS K 6221-1982A method.

Iodine absorption (IA): According to JIS K 6221-1982.

Coloring power: According to JIS K 6221-1982A method.

Carbon black aggregate size analysis method by sedimentation analysis Equipment used Centrifuge (Photo sedimentomenter) (DCF) (UK) Joyce Loebl measurement method In a 30% methanol aqueous solution with some surfactant added,
Add 0.05-0.1% carbon black and sonicate to completely disperse. The rotation speed of the rotary disk (disk) to which 15 to 30 ml of 25 v / v% glycerin aqueous solution was added was set to 6000 rpm, 0.1 to 0.5 ml of pure water was added, and the buffer line was adjusted by the usual method. After forming,
Add 0.2-0.3 ml of the above dispersion.

The recorder is operated at the same time as the dispersion is added, and the amount of carbon black aggregate that passes through a fixed point near the outer circumference of the rotating disk by sedimentation is optically measured and recorded as a histogram against time. To do.

The settling time can be calculated by the following formula (the general type of Stokes' formula)
Convert to Stokes equivalent diameter and obtain a histogram of the Stokes equivalent diameter of the carbon black aggregate and its frequency.

In equation (1), d is the Stokes equivalent diameter of the carbon black aggregate that passes through the optical measurement point of the rotating disk at time t after the start of sedimentation.

The constant K is the amount of the spin liquid at the time of measurement, the viscosity, and the density difference with the carbon black (the true density of the carbon black is 1.
86 g / ml), and is a constant determined by the rotation speed of the rotating disk. For example, 25v / v% as spin liquid
When 25 ml of glycerin aqueous solution is used and the measurement temperature is 20 ° C. and the disk rotation speed is 6000 rpm, the K value is 7920, and d is nm,
t is displayed in minutes.

Definition of Dst and s In the Stokes equivalent diameter histogram of the aggregate obtained by the above measurement operation, the highest frequency (actually,
The Stokes equivalent diameter that gives the maximum absorbance) is called Dst (mode) and is used as a measure of the average size of the carbon black aggregate.

In the histogram, the Stokes equivalent diameter that is half the frequency (absorbance) of Dst (mode) and is larger than Dst (mode) is ▲ D ^L ₅₀
The triangle size distribution index s is defined as s = 0.84932 × log (▲ D ^L ₅₀ ▼ / Dst). This is a measure of the distribution width of a relatively large aggregate size.

Performance Evaluation Test In order to evaluate the performance of the carbon black shown in Table-1, a rubber composition having a compounding ratio shown in Table-2 was prepared,
It was subjected to various tests.

The performance of each rubber composition was measured and evaluated under the following rubber characteristic test conditions.

Rubber property test conditions Vulcanization condition of compound: 145 ° C, 30 minutes Abrasion resistance test: Measured at a slip ratio of 25% using a Lambourn abrasion tester, and wear resistance is calculated by the following formula.

Abrasion resistance index = (S / T) × 100 (%) Here, the volume loss of the S: IRB No. 5 test piece at a 25% slip ratio.

 T: Volume loss at 25% slip rate of test specimen.

Impact resilience test: BS (British Standard) 903: Part A8: 1 using resilience tester (manufactured by Toyo Seiki Seisakusho)
963 Heat generation characteristics: Measured according to ASTM D 623.

Other rubber properties: JIS K 6300-1974 and JIS K 6301
-Measure according to 1975.

For the rubber properties of each carbon black, see Table-
Shown together in 3.

Consideration from Tables 1-3 Reinforcing property Focusing on 300% modulus value and wear resistance as a measure of reinforcing property, DBN and N ₂ SA approximate RunN
In comparison between o.1 and the control SRF-LM (trade name: Asahi # 35), it can be seen that all the characteristics are improved by making the value of the aggregate size distribution index a small. Similarly, Run No. 2 and control SRF (trade name: Asahi # 50) and RunN
In comparison between o.4 and control GRF (trade name: Asahi # 55),
The carbon black of the present invention in which the value of s is small shows superior reinforcement.

Run No. 8 shows a slight decrease in reinforcement than Run No. 3 due to deviation from the desired IA / N ₂ SA ratio, but is still superior to Comparative Example 6 and control SRF with large s value. .

In Run No.6, the s value is large, so the 300% module value,
A marked decrease in wear resistance is seen.

B. Dynamic characteristics Comparing the dynamic characteristics (repulsion elasticity and heat generation) of the black of the present invention and the control black in which DBPA and N ₂ SA are close to each other, there is no significant difference in repulsion elasticity, but they are almost the same, but the heat generation There is a clear difference in properties.

In Run No. 5 in which s deviates to the smaller side, the reinforcing property is improved, but the impact resilience and heat generation characteristics are reduced, and s
It is understood that the value of is lower than 0.12.

C. Other Properties There is no clear difference in Mooney viscosity between the carbon black of the present invention and the control carbon black, but there is a significant difference in the Mooney scorch time of the vulcanization properties.

Although this Mooney scorch time generally tends to extend as the particle size increases, a value close to the Mooney scorch time of a hard carbon black, although the carbon black of the present invention has a soft particle size. have.

Run No. 7 and Run No. 4 and controls with DBPA and N ₂ SA that are nearly equal because the toluene color transmission is outside the scope of the invention.
Compared to GPF, the Mooney scorch time is closer to that of the control GPF, and no significant difference is observed. Therefore, the upper limit of toluene color transmission is 60%.

As described above, DBPA50~95ml / 100g, it has a characteristic of N ^₂ SA20~35m ₂ / g, further, the aggregate size distribution index s
0.12 to 0.15 and a toluene color transmission of 20 to
The carbon black of the present invention having a specific range of 60% is
It is intended to provide a carbon black capable of attaining improvement of reinforcing property, promotion of workability and reduction of heat generation property without lowering any dynamic property (rebound resilience) with respect to a rubber composition.

[Brief description of drawings]

FIG. 1 is an example of a measurement curve showing the relationship between the elapsed time and the absorbance (frequency value) when the carbon black aggregate is measured by centrifugal sedimentation analysis. FIG. 2 is a plot of the relationship between the logarithm of the equivalent stalk diameter of the aggregate and the frequency value in the curve shown in FIG. FIG. 3 shows an aggregate distribution curve of two different carbon blacks obtained from the frequency value vs. time measurement curve shown in FIG. FIG. 4 schematically shows the difference in aggregate distribution of carbon black from the conventional product. FIG. 5 is a longitudinal sectional view showing an example of an apparatus used for producing the carbon black of the present invention, FIG. 6 is a sectional view taken along the line AA of FIG. 5, and FIG. 7 is a view taken along the line BB. FIG. 1 ... Combustion chamber, 2,3 ... Air inlet 4-9 ... Natural gas inlet 10 ... Venturi section 11-17 ... Air, natural gas inlet 19 ... Reaction continuous cooling chamber a ... g … Cooling water injection sprayer

Claims (2)

[Claims] 1. A nitrogen adsorption specific surface area (N ₂ SA) of 20 to 35 m ² / g,
In a carbon black having a characteristic of dibutyl phthalate absorption (DBPA) of 50 to 95 ml / 100 g, the aggregate size distribution index (s) calculated by the following formula is 0.12 to 0.15, and the toluene color permeability is 20 to A soft carbon black that is in the range of 60%. s = 0.84932 × log (▲ D ^L ₅₀ ▼ / Dst) where s: Aggregate size distribution index Dst: Stokes equivalent diameter of the most frequent Stokes obtained by centrifugal sedimentation analysis ▲ D ^L ₅₀ ▼: Greater than Dst , Stokes equivalent diameter with a frequency of 1/2 of Dst _2. A measured value of nitrogen adsorption specific surface area (N ₂ SA) (m ² /
g) and measured iodine adsorption (IA) (mg / g) ratio, IA / N ₂ SA
Is in the range of 0.75 to 0.95, the soft carbon black according to claim 1.