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Carbon black contributes to a breakthrough in tire labelling
Orion Engineered Carbons will contribute to performance enhancement of tires by carbon black innovations
by Bernhard Schwaiger
Sustainable mobility is a major challenge facing the Community in the light of climate change and soaring oil prices. Tires, mainly because of their rolling resistance, account for 20% to 30% of the fuel consumption of vehicles. A reduction of the rolling resistance of tires may therefore contribute significantly to the energy efficiency of road transport and thus to the reduction of consumption and emission. For this reason reducing tire rolling resistance is now a major development goal for new tire lines. However, tires are characterized by a great number of parameters, which are in some cases interrelated. Improving one parameter such as rolling resistance may have an adverse impact on other parameters such as wet grip. To achieve progress in environmental aspects (CO2 emission, noise) and safety aspects of the tire (wet grip) and to encourage end-users to purchase more fuel-efficient tires, tire labeling classifications are or will be introduced around the world.
The tire regulation of the European Parliament, becoming effective of as November 2012, is a good example for tire labeling. This regulation sets out minimum requirements for the rolling resistance, and by also labeling wet grip tire manufacturers are encouraged to optimize all parameters beyond the standards already achieved. As third category in Europe tire noise is in the focus, whereas in North America the tire wear is labeled for PCT. Similar principles will be applied in Asian countries, for example Japan and China, and for nearly all types of vehicles and tires (PCT, TBR, Retreading).
Manufacturers of modern passenger car tires succeeded in reducing rolling resistance and improving wet grip by replacing carbon black in the tread, by silica and silane. However, not only is mixing technology much more complex for the silica-silane system, but wear resistance also may deteriorate. Especially for truck tread cap compounds, there is no silica-silane solution, which achieves reasonable mileage compared to carbon black. Due to this excellent performance level in wear and cut resistance carbon black is the filler of choice in this application. However improvements are needed to best balance wear resistance and rolling resistance. Surface activation of carbon blacks improves the interaction between carbon black particles and polymer, leading to reduction of rolling resistance, without deterioration of wear properties. Additionally there is an increased flexibility to adjust carbon black morphology in the furnace production process to optimize the performance of truck tread compounds.
With the combination of surface activation and optimized carbon black morphology a new class of tread blacks has been developed, which outclasses silica-silane systems in truck tires. The replacement of standard ASTM blacks by corresponding carbon black innovations results in significant reduction of rolling resistance. Figure 1 demonstrates the performance enhancement achieved on a truck tire used in the driving axle of a trailer truck. Especially in long haul application with constant high speed, the benefit in fuel economy is high.
Figure 1: Rolling resistance improvement by ECORAX grades measured on the test drum
Additionally, a significant part of a tire’s rolling resistance is caused by the tire body. Yet optimizing only a single compound of the tire, for example the tread, will not provide a breakthrough in the overall tire classification for energy efficiency. An integral approach taking into account all tire compounds that significantly contribute to rolling resistance is necessary to realize a performance jump. The carbon black industry offers a wide portfolio of standard carbon blacks; however carbon black innovations are needed to reduce hysteresis losses of various parts of a tire.
Figure 2: Contribution of tire components to rolling resistance of PCT (above) and TBR (below)
Optimizing the whole tire casing will provide more flexibility to adjust and balance tread compound performance. To achieve a breakthrough in tire labeling for rolling resistance, carbon black innovations are needed aimed at tire body compounds. Orion Engineered Carbons has developed process technologies to step-in, in areas of specific surface and degree of aggregation, which were not accessible in the past. These ultra-high structure or extremely low specific-surface-area blacks are suitable to improve the energy efficiency of body compounds. More exceptional is the fact that a well-balanced hysteresis/ stiffness compromise can be attained. Figure 4 demonstrates the progress made with the furnace black technology by OEC comparing structure (COAN) and specific surface area (STSA).
Figure 3: Breakthrough in furnace black process technology
In the frame the classical ASTM soft blacks normally used in tire body compounds are shown. The process technology of Orion Engineered Carbons creates the ability to produce soft blacks with ultra low specific surface area. The size of the primary particle is double in size compared to the standard ASTM grades. A well-balanced hysteresis/ stiffness compromise can be achieved. There is excellent incorporation during mixing and the processing of compounds containing these blacks.
It is possible to achieve a high structure expressed as OAN for soft blacks, but this carbon black innovation shows a remarkable high structure expressed as COAN. This is a prerequisite to realize a high dynamic stiffness in rubber compounds. A significant reduction of the carbon black filler volume fraction is now possible by maintaining or even increasing compound stiffness. The consequence of reduction in carbon black loading is a win in hysteresis performance. Due to the excellent rubber reinforcement of ECORAX S 247 even a replacement of classical N300 ASTM blacks in applications like sub tread, sidewall or soft apex is now possible. Figure 5 gives an insight in the performance of ECORAX S 247 used in a soft apex compound. The reduction in hysteresis expressed as tan δ by 40% is a real breakthrough. The simultaneous increase of stiffness is even more exceptionally.
Figure 4: Breakthrough in soft apex application using ECORAX S 247
Today Orion Engineered Carbons has the technology to reach new areas in the carbon black portfolio of specific surface area and structure especially in the soft black area. Especially in truck tread application tailor made carbon black innovations, can balance rolling resistance and wear performance. These product innovations will support the tire industry achieving their ambitious goals for tire labeling in a competitive environment.