Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
1999-06-10
2001-06-26
Cain, Edward J. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C525S495000, C423S449100
Reexamination Certificate
active
06251983
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to improved inversion carbon blacks as well as a method for their manufacture.
Carbon blacks are used extensively as reinforcement carbon blacks in rubber compounds used in the tire industry. The proper-ties of carbon blacks in this context have an influence, together with the properties of the rubber compounds used, on the performance properties of the completed tires.
The required properties are high abrasion resistance, low rolling resistance, and good adhesion in the case of wet road conditions. The last two properties are influenced essentially by the viscoelastic behavior of the tread compound. In the case of periodic deformation, the viscoelastic behavior can be described by the mechanical loss factor tan &dgr;, and in the case of elongation or compression, the viscoelastic behavior can be described by the dynamic elongation modulus |E* |. Both magnitudes of these values are strongly temperature dependent. The adhesion to wet roads is, in this context, directly correlated with the loss factor tan &dgr;
0
at approximately 0° C., and the rolling resistance with the loss factor tan &dgr;
60
at approximately 60° C. The higher the loss factor is at low temperature, the better the adhesion of the tire composition to a wet road usually is. To reduce the rolling resistance, in contrast, a loss factor which is as small as possible at high temperature is required.
The abrasion resistance and the viscoelastic properties, and thus also the loss factor of the tread compounds, are essentially determined by the properties of the reinforcement carbon blacks used. Here, the essential parameter is the specific surface area, particularly the CTAB surface area, which is a measure of the rubber active surface area portion of the carbon black. As the CTAB surface area increases, the abrasion resistance and tan &dgr; increase.
Other important carbon black parameters are the DBP absorption and the 24M4-DBP absorption as measured numbers for the starting structure, respecting the residual structure which still remains after mechanically stressing the carbon black, as well as the specific surface area (BET-surface area) of the carbon black as determined according to DIN 66132.
The identified carbon black parameters are dependent on the form of the carbon black particles. In the course of carbon black preparation, there is formed first the so-called primary particles with a diameter of 10 to 500 nm, which then grow into solid three dimensional aggregates. The spatial structure and the particle size distribution as parameters to be measured are exhibited in the precipitation.
For tread compounds, the suitable carbon blacks present a CTAB surface area of 20-190 m
2
/g and 24M4-DBP absorption values of 40-140 mL/100 g.
The average particle diameter of the carbon black aggregate is used for the classification of the carbon blacks according to ASTM D-1765. This classification consists of a four-digit alphanumerical nomenclature, where the first letter (an N or an S) provides information regarding the vulcanization properties, and the first number of the subsequent three-digit number provides information regarding the average particle size. However, this ASTM classification is very rough. Thus, within one ASTM classification range, considerably deviating viscoelastic properties of the tread compounds can occur.
DE 19 521 565 describes inversion carbon blacks which to a large extent satisfy the requirements of low rolling resistance and improved adhesion. These are carbon blacks for which the ratio tan &dgr;
0
/ tan &dgr;
60
during incorporation into an SSBR/BR rubber compound satisfies the relation
tan &dgr;
0
/ tan &dgr;
60
>2.76-6.7×10
−3
×CTAB,
and the value of tan &dgr;
60
is always lower than the corresponding value for ASTM carbon blacks with identical CTAB surface area and 24M4-DBP absorption.
The carbon blacks according to DE 19 521 565 are manufactured according to the furnace carbon black method, which is used today to produce the overwhelming majority of the carbon blacks used in the tire industry. These methods were specially modified for the manufacture of the inversion carbon blacks.
The furnace carbon black method is based on the principle of oxidative pyrolysis; that is, the incomplete combustion of carbon black raw materials in a reactor which is coated with a highly fire-resistant material. As the carbon black raw material, so-called carbon black oils are used, but gaseous hydrocarbons can also be used alone or simultaneously with carbon black oil. Independently of the special construction design of the reactors, three zones can be distinguished in the carbon black reactor, which correspond to the different steps of the carbon black production. The zones are present successively along the reactor axis, and the reaction medium flows through them in succession.
The first zone, the so-called combustion zone, essentially comprises the combustion chamber of the reactor. Here a hot combustion chamber exhaust gas is generated, by burning a fuel, as a rule a hydrocarbon fuel, with an excess of preheated combustion air or other oxygen-containing gases. Natural gas is predominately used today as the fuel, but it is also possible to use liquid hydrocarbons such as heating oils. The combustion of the fuel usually occurs under conditions with an excess of oxygen. According to the book “Carbon Black” second edition, Marcel Dekker Inc., New York, 1993, page 20, it is very important, for the purpose of obtaining optimal use of the energy, that the conversion of the fuel to carbon dioxide and water occurs as completely as possible in the combustion chamber. In this process, the excess air promotes the complete conversion of the fuel. The fuel is usually introduced by means of one or more combustion lances into the combustion chamber.
The K factor is frequently used as an index number to characterize the excess air. The K factor is the ratio of the quantity of air required for the stoichiometric combustion of the fuel to the quantity of air which is in fact fed to the combustion. A K factor of 1 thus means that the combustion is stoichiometric. If there is an excess of air, the K factor is smaller than 1. Usually K factors of 0.3-0.9 are used.
In the second zone of the carbon black reactor, called the reaction zone, carbon black formation takes place. For this purpose, the carbon black raw material is injected and admixed in the hot combustion gas stream. With respect to the oxygen quantity which is not completely reacted in the combustion zone, there is an excess hydrocarbon quantity introduced into the reaction zone. Therefore, under normal conditions, carbon black formation starts here.
Carbon black oil can be injected into the reactor in different manners. For example, an axial oil injection lance, or one or more radial oil lances which are arranged on the circumference of the reactor, in a plane which is vertical with respect to the direction of flow, are suitable. A reactor can have several planes with radial oil lances along the direction of flow. At the tip of the oil lances, either spray or injection nozzles are provided, by means of which the carbon black oil is admixed in the combustion gas stream.
In the case of simultaneous use of carbon black oil and gaseous hydrocarbons, such as, for example, methane, as the carbon black raw material, the gaseous hydrocarbons can be injected separately from the carbon black oil through a special set of gas lances into the hot combustion gas stream.
In the third zone of the carbon black reactor, called the termination zone (quenching zone), carbon black formation is stopped by a rapid cooling of the carbon black-containing process gas. This process prevents any undesired secondary reactions. Such secondary reactions would lead to porous carbon blacks. The reaction is usually stopped by spraying in water using appropriate spray nozzles. Usually there are several points along the carbon black reactor for water spraying, for example, for “quenching” so that the
Freund Burkhard
Messer Paul
Niedermeier Werner
Vogel Karl
Vogler Conny
Cain Edward J.
Degussa - Hüls Aktiengesellschaft
Smith , Gambrell & Russell, LLP
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