Chemistry of inorganic compounds – With additive – Additive contains metal – boron – or silicon
Reexamination Certificate
1999-09-03
2002-05-21
Hendrickson, Stuart L. (Department: 1754)
Chemistry of inorganic compounds
With additive
Additive contains metal, boron, or silicon
C423S449100, C423S450000, C524S495000
Reexamination Certificate
active
06391274
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to carbon blacks, a process for the production of these carbon blacks, as well as their use, in particular as reinforcing carbon blacks in rubber mixtures.
BACKGROUND OF THE INVENTION
Carbon blacks are known from Ullmanns Enzyklopädie der technischen Chemie, 4th Edition (1977), Vol. 14, pp. 633 to 648.
The most important processes for producing carbon blacks are based on the oxidative pyrolysis of carbon-containing carbon black raw materials. In these processes the carbon black raw materials are incompletely burnt at high temperatures in the presence of oxygen. These carbon black production processes include for example the furnace carbon black process, the gas carbon black process and the flame carbon black process. Predominantly polynuclear aromatic carbon black oils are used as carbon black raw materials.
Carbon blacks are used as fillers and as reinforcing agents in the preparation of rubber mixtures for the tire industry. In addition to natural and/or synthetic rubber, typical rubber mixtures also include carbon black, mineral oil and further additives as well as sulfur as vulcanization agent.
Carbon blacks influence the abrasion resistance, rolling resistance as well as the wet skidding behavior of tires produced from these rubber mixtures. For rubber mixtures that serve as tire treads, tread mixtures having a high abrasion resistance and, at the same time, as low a rolling resistance as possible combined with good wet skidding behavior are required. A low rolling resistance leads to low fuel consumption of the vehicle.
Rolling resistance and wet skidding properties are influenced by the viscoelastic behavior of the tread mixture. With periodic deformation the viscoelastic behavior can be described by the mechanical loss factor tan &dgr; and, in the case of stretching or compression, by the dynamic modulus of elasticity |E*|. Both quantities are strongly temperature-dependent.
The wet skidding behavior of the tread mixture is correlated with the loss factor tan &dgr;
0
at 0° C., while the rolling resistance is correlated with the loss factor tan &dgr;
60
at 60° C. The higher the loss factor at the low temperature, the better usually is the wet skidding behavior of the tire mixture. In order to reduce the rolling resistance, as small a loss factor as possible at the high temperature is required.
The abrasion resistance and the viscoelastic properties, and thus also the loss factor of the tread mixtures, are essentially determined by the properties of the reinforcing carbon blacks that are used.
An important index for the rubber-active surface proportion of the carbon black is the specific surface, in particular the CTAB surface or STSA surface. With increasing CTAB surface or STSA surface both the abrasion resistance and tan &dgr; increase.
Further important carbon black parameters are the DBP absorption as a quantitative measure of the initial structure, and the 24M4-DBP absorption as a measure of the residual structure still remaining after the carbon black has been subjected to mechanical stress.
For tread mixtures, carbon blacks are suitable that have CTAB surfaces between 80 and 180 m
2
/g and 24M4-DBP absorption values between 80 and 140 ml/100 g.
It is known that ASTM carbon blacks are unable to influence the temperature dependence of the loss factor tan &dgr; in such a way that the tread mixture has a lower rolling resistance with the same or better wet skidding behavior. As is known, the desired reduction of the rolling resistance is directly coupled to a deterioration of the wet skidding behavior. Carbon blacks that have a low rolling resistance are termed so-called “low hysteresis” carbon blacks.
It is furthermore known that the rolling resistance of tires can be reduced by replacing the carbon black by silica (see EP 0 447 066 A1). In order to bind the silica to the polymer building blocks of the rubber, silane coupling reactants are used. Silica-containing rubber mixtures have a loss factor tan &dgr;
60
that is reduced by up to 50%.
SUMMARY OF THE INVENTION
The object of the present invention is to provide carbon blacks that impart to rubber mixtures of natural rubber or synthetic rubber or mixtures thereof a reduced rolling resistance with at the same time the same or an improved wet skidding behavior and abrasion resistance.
The present invention provides a carbon black that has a STSA surface of between 20 and 180 m
2
/g, a 24M4-DBP absorption of between 40 and 140 ml/100 g, a specific BET surface of between 20 and 250 m
2
/g and a content of 0.01 to 20 wt. % of silicon, referred to its overall weight, which is characterized in that in rubber mixtures it has a tan &dgr;
0
/tan &dgr;
60
ratio of greater than 3.37−0.0068 STSA.
In an embodiment of the invention the carbon black may contain, in addition to silicon, 0.01 to 1 wt. % of nitrogen.
The silicon is incorporated into the carbon black aggregates during the production process. For this purpose silicon-containing compounds may, for example, be mixed into the carbon black raw material. Suitable silicon-containing compounds may be organosilicon compounds such as organosilanes, organochlorosilanes, siloxanes and silazanes. In particular silicone oils, silicon tetrachloride, siloxanes and silazanes may be used. Silanes and silicone oils may preferably be used.
The starting compound has only a slight influence on the incorporation of the silicon atoms into the carbon black aggregates. It can be shown by X-ray photoelectron spectrometry (XPS) and secondary ion mass spectrometry (SIMS) that the silicon atoms are oxidically bound and distributed in the carbon black aggregates. The oxidic bonding consists predominantly of silicon dioxide. Other silicon atoms form silanol groups. Whereas the silanol groups are mainly located on the surface of the carbon black aggregates, silicon dioxide is distributed uniformly over the cross-section of the aggregates.
In one embodiment of the invention the silicon may be concentrated in the sub-surface regions of the carbon black aggregates.
After incorporation into rubber mixtures, the silicon-containing groups on the surface of the carbon black aggregates influence the interaction of the filler with the rubber polymer components. To effect a covalent bonding of the silanol groups of the carbon blacks to the polymer mixture bifunctional silanes, for example Si69 (Bis(3-triethoxysilylpropyl)-tetrasulfane) from Degussa-Hüls A G, Germany, may be added to the rubber mixtures as a silane coupling reagent.
The tread mixtures produced with the silicon-containing carbon blacks according to the invention exhibit an increased value of tan &dgr;
0
and a reduced value of tan &dgr;
60
compared to known carbon blacks having the same specific surface and structure, without the need to add a coupling reagent. These values correspond to a substantially improved wet skidding behavior combined with a substantially reduced rolling resistance of the tread. The rolling resistance of the rubber mixtures can be improved still more, i.e. reduced further, by adding bifunctional silanes.
The carbon blacks according to the invention may be produced by the furnace carbon black process according to DE 195 21 565 A1.
According to the furnace carbon black process the oxidative pyrolysis of the carbon black raw material is carried out in a reactor lined with highly refractory material. In such a reactor three zones, disposed one following the other along the reactor axis and through which the reaction media flow in succession, may be distinguished.
The first zone, the so-called combustion zone, essentially comprises the combustion chamber of the reactor. A hot process gas is produced in this zone by burning a fuel, generally hydrocarbons, with an excess of preheated combustion air or other oxygen-containing gases. Natural gas may be used as fuel. Liquid hydrocarbons such as light and heavy heating oil may also be used.
In a preferred embodiment of the invention carbon black raw material (carbon black oil) may also be used as fuel.
T
Forster Frank
Freund Burkhard
Vogel Karl
Vogler Conny
Degussa Huls Aktiengesellschaft
Hendrickson Stuart L.
Pillsbury & Winthrop LLP
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