FR2669934A1 - Rubber composition - Google Patents

Abstract

Rubber composition which includes from 35 to 100 parts by weight of a furnace carbon black which has a nitrogen adsorption specific surface (N2 AS) of between 60 and 100 m<2>/g and a modal diameter of interaggregate pores (Dp) which satisfies the following formula (1) and 100 parts by weight of a rubber component; in which Dp denotes the modal diameter at the maximum frequency in an interaggregate pore diameter distribution of carbon black, determined by employing a differential scanning calorimeter (DSC), and Dst denotes the Stokes modal diameter of the carbon black aggregates, determined by employing a disc centrifuge (DCF).

Description

RUBBER COMPOSITION
BACKGROUND OF THE INVENTION
The present invention relates to a rubber composition intended for use in the preparation of treads for tires for passenger cars or light trucks. More particularly, the present invention relates to a rubber composition exhibiting both excellent abrasion resistance and low heat formation, simultaneously with high impact resilience.

Carbon blacks for reinforcing rubber are divided into many different types depending on their properties. The properties of carbon blacks are an essential factor which determines the various characteristics of the rubber composition when carbon blacks are introduced into a rubber to form a rubber composition. Consequently, generally, during the introduction of the carbon black into a rubber, one chooses a carbon black capable of imparting to the rubber composition the properties suitable for the use which is intended for it.

For example, in recent years, intensive development efforts have been made to find tires with low fuel consumption, in accordance with the needs of society for saving resources and energy.

A low heat forming rubber composition exhibiting high impact resilience, in which a carbon black of a class having a relatively large particle size is introduced with a component of the rubber in a relatively low proportion, is useful for preparing products. low fuel consumption tires. Although the introduction of a large particle size, low specific surface area carbon black with a rubber component is effective in reducing the fuel consumption of tires, it makes it difficult to avoid lowering traction when braking. on wet road surface and abrasion resistance.

While it is possible to impart high abrasion resistance and high impact resilience, all with low heat formation, to a rubber component by the use of a carbon black with a small particle size and Having a large specific surface area, a factor known to effectively improve abrasion resistance, the rubber composition obtained will be ideal as a rubber composition for treads.

Some proposals have already been made for carbon blacks capable of imparting simultaneously to a rubber component high abrasion resistance and low heat formation which are two contradictory properties. We can mention, for example, the following propositions (a) - - (f)
(a) a carbon black having a nitrogen adsorption surface area (N2SA) of 60 m2 / g or more, a dibutylphthalate absorption number of the compressed sample (24M4DBP) of 112 ml / 100 g or greater, with both the Stokes modal diameter of the aggregates and the Stokes modal distribution of the aggregates being maintained above a specific value, thereby simultaneously imparting high reinforcing properties and high impact resilience to a rubber containing this carbon black (Japanese patent application published under No. 64-53978)
(b) a rubber composition having simultaneously high abrasion resistance and high impact resistance and containing a carbon black which has an N2SA of 60 m2 / g or more, a DBP of 108 ml / 100 g or more , a true density for a predetermined specific surface area maintained within a significantly lower specific range than that of conventional carbon blacks, and a coloring power (Tint) and distribution width for a modal distribution of aggregates which are maintained above 'a specific value (Japanese Patent Application Laid-Open No. 59-140241)
(c) a carbon black having an N2SA of between 65 and 84 m2 / g and a ratio of N2SA to the iodine adsorption number (IA) of between 1.10 and 1.35, wherein the value of a formula whose variables are 24M4DBP, darkness, iodine adsorption index and modal diameter of aggregate is maintained above a specific value, which can simultaneously confer resistance to l high abrasion and high impact resilience to a rubber containing this carbon black (Japanese Patent Application Laid-Open No. 62-58792)
(d) a carbon black having an N2SA of between 75 and 105 m2 / g, a 24M4DBP of 110 ml / 100 g or more, a true density for a predetermined specific surface area set in a specific range significantly lower than that of blacks of conventional carbon, the inter-aggregate pore diameter as well as the distribution width for a modal diameter of the aggregates being kept above a specific value, which simultaneously confers high abrasion resistance and resilience high impact to a rubber containing this carbon black (Japanese patent application published under No. 64-201367) ;;
(e) a carbon black for use in rubber for tire treads, which has a
N2SA between 85 and 95 m2 / g, a 24M4DBP between 100 and 104 ml / 100 g, a Tint between 95 and 105% and a Stokes modal diameter distribution of aggregate A D50 of 180 m or more, this which achieves high abrasion resistance and high impact resilience (United States patent
No. 4,360,627; and
(f) a carbon black for energy saving tire tread rubbers, having an N2SA of 75 to 105 m2 / g, satisfying the relationships: N2SA - Ira 2 15;
N2SA - CTAB (specific surface area for cetyltrimethylammonium bromide) <5; 24M4DBP 4110; Tint = 90 to 110; and ss Tint (-3; which is capable of imparting low rolling resistance and high wet traction quality to a rubber component (United States Patent No. 4,548,980).

Despite the above proposals, the need for low fuel consumption tires continues to increase and there is still in the prior art a strong demand for the development of low heat forming rubber compositions exhibiting. high resilience to shocks.

SUMMARY OF THE INVENTION
The object of the invention is to provide a rubber composition suitable for the tire treads of passenger vehicles and light trucks, which exhibits both high abrasion resistance and low heat formation, simultaneously. high impact resilience. This object of the present invention can be achieved by a rubber composition which comprises from 35 to 100 parts by weight of a kiln carbon black having a nitrogen adsorption specific surface area. (N2SA) of between 60 and 100 m2 / g and an inter-aggregate pore modal diameter (Dp) which satisfies the following formula (1) and 100 parts / weight of a rubber component;
Dp <1.543 Dst - 55.0 (1) where Dp represents the modal diameter at the maximum frequency in an inter-aggregate carbon black pore diameter distribution determined using a differential scanning calorimeter (DSC) and Dst represents the Stokes modal diameter of the carbon black aggregates determined using a disc centrifuge (DCF).

DESCRIPTION OF THE PREFERRED EMBODIMENTS
The properties of the carbon blacks which are used in the present invention are the values obtained according to the following methods.

Nitrogen adsorption specific surface area (N2SA): measured in accordance with ASTM D3037-88 "Standard test method for the specific surface area of carbon black by nitrogen adsorption" Method B. The
N2SA of a conventional sample of IRB No. 6 industrial carbon black measured by this method was 76 m2 / g.

Dp: represents the modal diameter at maximum frequency in an inter-aggregate carbon black pore diameter distribution, determined using a differential scanning calorimeter (DSC), and measured by the following method described in an article by BRUN et al.

A sample of carbon black dried according to JIS K 6221 (1982) 5 "How to prepare a dry sample" is carefully weighed and then mixed with distilled water to prepare a paste having a carbon black concentration of 0.250 g. / cm3. The paste is treated by supersonic wave to obtain a satisfactory dispersion. Immediately after the ultrasonic wave dispersion, about 3-5 mg of carbon black paste is weighed exactly and put into an aluminum sample container, sealed, and placed in a differential scanning calorimeter (DSC 30 manufactured by METTLER) in order to carry out the measurement according to the following steps
(1) rapid cooling from room temperature to -80 C;
(2) heating from -80 C to -5 C at a rate of 10 C / min;
(3) heating from -50C to -0.1 C at a rate of 1 "C per minute, followed by maintaining at -0.1 C (a temperature 0.1 C below the freezing point of water distilled) for 10 minutes; and
(4) Gradual cooling from -0.1 C to 8 "C at a rate of -0.1 C / min to record the freezing thermogram on a recording apparatus.

dans lesquelles Wa est la chaleur de solidification de l'eau distillée ; et K représente un facteur tenant compte de la sensibilité du DSC et de la quantité d'échantillon.Then, the depression width of the freezing point AT of the distilled water is read from the temperature on the x-axis of the freezing thermogram and we read y (in mm) by 0.1 0C on the axis ordinates. The values obtained are substituted for AT and y in the following formulas (A) and (B) to obtain a pore distribution (tV / Dp):

where Wa is the heat of solidification of distilled water; and K represents a factor taking into account the sensitivity of the DSC and the amount of sample.

The pore diameter (Dp) giving the maximum tV / Dp value in the pore distribution tV / Dp = f (Dp), obtained according to the above formula (B), is defined as Dp (modal Dp diameter).

The article by BRUN et al. mentioned above appeared in THERMOCHIMICA ACTA, 21, (1977), 59 - 88 "new method for the simultaneous determination of the size and shape of the pores: thermoporometry".

The Dp of the standard reference carbon black
C-3 (N234) of ASTM D 24 measured with this method is 77.6 nm.

Dst: A sample of dry carbon black is mixed with a 20% aqueous ethanol solution containing a small amount of a surfactant to prepare a dispersion having a carbon black concentration of 50 mg / ml. This dispersion is dispersed satisfactorily by ultrasound treatment to thereby obtain a sample. The speed of rotation of a disc centrifuge (manufactured by Joyes Lobel, United Kingdom) is fixed at 8000 rpm, and 10 ml of a liquid of rotation ("spin") (an aqueous solution of glycerin) is added. at 2%). In addition, 1 ml of buffer (aqueous ethanol solution) is injected therein.

Then, 0.5 ml of the sample is added with a syringe to start the centrifugation, and simultaneously a recorder is turned on to optically prepare a distribution curve of the diameters of.
Stokes of aggregates. The Stokes diameter at the maximum frequency in the resulting distribution curve is defined as Dst. Standard Reference Carbon Black Dst C-3 (N234) according to the standard
ASTM D 24 measured by this method is 80 nm.

The baked carbon black according to the present invention having the characteristic properties mentioned above can be produced by controlling various manufacturing conditions such as the feed oil, fuel oil and fuel feed rate. air, and the oxygen gas supply conditions, for example using an oil furnace. This oil furnace comprises an air supply inlet disposed in the tangential direction in its head part, a combustion chamber equipped with a burner and a feed oil spray nozzle both inserted in the axial direction of the furnace, a narrow reaction chamber extending from the combustion chamber, and a wide reaction chamber extending from the narrow reaction chamber and internally provided with a water spray nozzle cooling.

According to the usual process, the carbon black according to the present invention can be incorporated into a rubber component, such as natural rubber or synthetic diene rubbers such as styrene-butadiene rubber, polybutadiene rubber, isopropene rubber, butyl rubber, and various other elastomers such as various synthetic rubbers and compound rubbers which can be reinforced with ordinary carbon blacks. The amount of carbon black incorporated is 35 to 100 parts by weight based on 100 parts by weight of the rubber component and the carbon black can be incorporated simultaneously with any other necessary ingredient such as vulcanizing agents, vulcanization accelerators, antioxidants, vulcanizing aids, softeners and plasticizers, in order to obtain the rubber composition in accordance with the present invention.

Among the properties described above, of the baked carbon black for use in the present invention, the nitrogen adsorption specific surface area (N2SA) which is between 60 to 100 m2 / g indicates a carbon black. hard carbon, which is necessary to give the rubber component high abrasion resistance and proper heat formation. When the N2SA is less than 60 m2 / g, the abrasion resistance is not satisfactory. On the other hand, if it exceeds 100 m2 / g, the heat formation becomes excessive and makes it difficult to use especially as carbon black for low fuel consumption tires.

The inter-aggregate pore modal diameter <Dp) is a parameter which indicates the size of the pores created by the complex morphology of the aggregates resulting from the solid fusion of the first carbon black particles. It is closely related to the conditions of formation of carbon black, such as the reaction temperature and the degree of turbulence of the flue gas, therefore, there is a correlation between Dp and the structure and specific surface area, and , according to the results of the inventor's studies, it is confirmed that the following formulas (C) and (D) are valid for ordinary commercially available carbon blacks
Dp = [75.2 x (DBP) / <N2SA)) t 3.0 ----- (C)
Dp = (1.543 Dst - 42.8) t 8.0 ----- (D)
The Dp for example of the standard reference carbon black C-3 (N234) of the standard ASTM D 24 measured by this method is between 72.6 and 88.6 nm by substituting the value obtained for Dst in the formula (D ). The measured values for Dp fall within this range. On the contrary, the p of the carbon black used in the present invention is a smaller value than that obtained by substituting Dst in the above formula (D), and is the same or less than the value obtained in the above formula (1). This means that in the carbon black for the present invention, the intra-aggregate pore size is relatively small compared to the size (Stokes modal diameter) of the aggregate itself. By virtue of this characteristic property, heat formation can be minimized without a negative effect on the abrasion resistance of the rubber component, and the impact resilience for a given specific surface area can be greatly increased. In accordance with the invention, a rubber composition simultaneously exhibiting excellent abrasion resistance and low heat formation, as well as high impact resilience, can be obtained by the synergy of the various properties described above.

Examples of the present invention will now be described by comparison with Comparative Examples.

Examples - comparative examples - reference examples
An oil furnace was used which included a combustion chamber (800 mm in diameter and 600 mm in length) having an air supply orifice disposed in the tangential direction in the head of the furnace, and provided with a burner of combustion and a feed oil spray nozzle both inserted in the axial direction of the furnace, a narrow reaction chamber (160 mm in diameter and 1200 mm in length) coaxially connected to the combustion chamber, and a Wide reaction chamber (400 mm in diameter) coaxially connected to the narrow reaction chamber.

As the feed oil, a hydrocarbon oil having a density (15/4 "C) of 1.073, a viscosity (Engler 40/20" C) of 2.10, a toluene insoluble matter content of 0, was used. 03% and a correlation coefficient of the Bureau of Mines (BMCI) of 140. We used as combustion oil a hydrocarbon oil having a density (15/4 "C) of 0.903, a viscosity (cSt / 500C) of 16, 1, a residual carbon content of 5.4% and a flash point of 96%
Using the reaction furnace, feed oil and combustion oil described above, five kinds of carbon black (Examples 1-3 and Comparative Examples 1 and 2) were prepared under conditions which been varied with respect to feed oil, combustion oil, rate of introduction of air and addition or absence of addition of oxygen. The properties of the carbon blacks obtained are shown in Table 1 as well as the preparation conditions.

In the Reference Examples in Table 1, commercially available hard carbon blacks were used. In Reference Example 1, we used the
N 351 [manufactured by TOKAI CARBON KK, SEAST NH, (registered trademark)]; in Reference Example 2, N 347 (manufactured by TOKAI CARBON KK, SEAST 3H, (registered trademark)) was used; and in Reference Example 3, N 339 [manufactured by TOKAI CARBON KK,
SEAST KH, (registered trademark)].

These carbon black samples were incorporated into a styrene-butadiene rubber [manufactured by NIPPON GOSEI GOMU K.K. JSR 1712 (brand)] according to the composition shown in Table 2.

The compounds of Table 3 were vulcanized at 145 ° C for 50 minutes to thereby obtain rubber compositions which were subjected to various rubber-related tests. The results are shown in Table 3.

The methods and conditions for measuring rubber properties are described below. Among the parameters, the parameter tan 8 (loss factor) is the index of heat formation. The smaller its value, the lower the heat build-up.

From the results of Table 3, it can be seen that the rubber compositions of Examples 1-3 according to the present invention show a significantly lowered tan 8, which measures heat formation, and significantly improved impact resilience. marked, while having the same or improved abrasion resistance as compared to Comparative Examples and Reference Examples which have the same level of N2SA but fall outside the characteristics of the present invention. In addition, it can be seen that the quality of reinforcement remains maintained at a high level.

As described above, according to the present invention, there is obtained a low heat forming rubber composition exhibiting both excellent abrasion resistance and high impact resilience, by selecting and controlling the microscopic properties of the blacks. carbon in a different way from the prior art. As a result, effective fuel consumption reduction can be achieved in applications of the invention to tire treads for passenger cars and light trucks.

NOTE
The methods and conditions used for the measurement of rubber properties were as follows
1 ") amount of LAMBOURNE abrasion loss.

The measurement was made using a LAMBOURNE abrasion tester (with mechanical sliding mechanism) under the following conditions
specimens: 10 mm thick and 44 mm outside diameter.

Emery wheel: type GC, abrasive grain size of n 80, hardness of H.

Carborundum powder added: grain size of n 80., Amount added about 9 grams per minute.

Relative slip ratio between the surface of the grinding wheel and the specimen: 24%, 60%
Rotation speed of the specimens: 535 rpm.

Load on the specimens: 4 daN.

2 ") Tan S (hysteresis loss factor).

The measurement was made using a viscoelastic spectrometer (manufactured by IWAMOTO SEISAKUSHO CO.) Under the following conditions
specimens: 2 mm thick, 30 mm long, 5 mm wide.

Frequency: 50 Hz,
Dynamic stress e: +/- 1.2%
Temperature: 60 "C.

3) Others
All other tests were made in accordance with JIS K 6301 "Physical test methods for vulcanized rubber".

TABLE 1

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<tb><SEP> W <SEP> CO
<tb><SEP> flow <SEP> of supply <SEP> in <SEP> oxygen
<tb> N <SEP> (Nm3 / h) <SEP> 105 <SEP> 105 <SEP> 105 <SEP> H <SEP>'s<SEP> H <SEP>
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<tb><SEP> Dst <SEP> (nm) <SEP> N <SEP> o <SEP> 109 <SEP> m <SEP> o <SEP> 113 <SEP> 106 <SEP> 93
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<tb> cn <SEP> 0 <SEP> 0 <SEP> Value <SEP> of <SEP> (1.543
<tb><SEP> Dst <SEP> ri <SEP> 55.0) <SEP> 164.1 <SEP> 127.1 <SEP> 113.2 <SEP> rlH <SEP> H
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TABLE 2

<tb> Components <SEP> Parts <SEP> in <SEP> weight
<tb> Rubber <SEP> Styrene
<tb> butadiene <SEP> (SBR) <SEP> 137.5
<tb> Black <SEP> of <SEP> carbon <SEP> 68.75
<tb> Stearic acid <SEP><SEP> (adjuvant
<tb> of <SEP> vulcanization <SEP> and <SEP> of
<tb> dispersion) <SEP> 1.0 <SEP>
<tb> Oxide <SEP> of <SEP> zinc <SEP> (adjuvant
<tb> of <SEP> vulcanization <SEP> 3.0
<tb> Nt-butyl-2-benzothiazyl
<tb> sulfeneamide <SEP> sulfide <SEP> (promoter <SEP> 1.38
<tb> from <SEP> vulcanization)
<tb> Sulfur <SEP> (vulcanizing <SEP> agent) <SEP> 1.75
<tb> TABLE 3

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<tb><SEP> 24 <SEP>% <SEP> of <SEP> slip <SEP> 87 <SEP> 40 <SEP> 99 <SEP> ç <SEP> 93 <SEP> 87 <SEP> 96 <SEP> 100
<tb><SEP> 60 <SEP> of <SEP> sliding <SEP> 90 <SEP> 97 <SEP> 102 <SEP> o <SEP> o <SEP> 91 <SEP> 95 <SEP> 100
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<tb> Tan (<SEP> factor of <SEP> loss) <SEP> 0.183 <SEP> 0.202 <SEP>, 211 <SEP> w <SEP> 0.228 <SEP> 0.209 <SEP> 0.233 <SEP> 0.244
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<tb><SEP> Hardness <SEP><<SEP> Us) <SEP> 65 <SEP><<SEP> GD <SEP> O <SEP> CS
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<tb> Resilience <SEP> to <SEP> shocks <SEP> OD <SEP>42> 8 <SEP> Cn <SEP> O <SEP> H <SEP> 36.9 <SEP> 38.9 <SEP> 37 , 1 <SEP> 35.3
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Claims (1)

CLAIM A rubber composition which comprises from 35 to 100 parts by weight of a kiln carbon black having a nitrogen adsorption surface area (N2SA) of between 60 and 100 m2 / g and a modal pore diameter between. aggregate (Dp) which satisfies the following formula (1) and 100 parts / weight of a rubber component; Dp <1.543 Dst - 55.0 (1) where Dp represents the modal diameter at the maximum frequency in an inter-aggregate carbon black pore diameter distribution determined using a differential scanning calorimeter (DSC) and Dst represents the Stokes modal diameter of the carbon black aggregates determined using a disc centrifuge (DCF).