The tread is the part of a tire that comes into contact with the road surface and must meet three basic requirements: first, it must have high wet grip or good traction on wet roads to ensure the safety of the vehicle and passengers; second, it must have low rolling resistance to save fuel. Generally speaking, reducing the rolling resistance of a tire by 3% to 4% can reduce fuel consumption by 1%. Based on the fact that the rolling resistance of the tread accounts for about 50% of the tire's total rolling resistance, reducing its rolling resistance is an important way to save fuel. Third, it must be wear-resistant and have a long service life. To achieve these performance requirements, precipitated silica, especially highly dispersed precipitated silica, is essential.
Passenger tire tread
According to reports, using precipitated silica in passenger tire tread rubber filled with carbon black can greatly improve the various performance characteristics of the tire. By using highly dispersed precipitated silica together with special solution polymers and silane coupling agents, and with the best mixing process, it is possible to overcome the drawback of reduced wet grip performance due to the lagging loss of tread rubber. Tread rubber that is entirely filled with precipitated silica as a filler can reduce tire rolling resistance by 20%, which means that the lagging loss of the tread is reduced by about 50%, and fuel consumption is reduced by at least 3%.
Using 36 parts of precipitated silica and adding a mercapto functionalized silane coupling agent equivalent to 3% of the amount of precipitated silica, a filler system with a total amount of 72 parts was formed. Testing showed that the rolling resistance of the passenger car tire's styrene-butadiene rubber/polybutadiene rubber tread compound decreased by about 25%, while the dry and wet traction performance remained unchanged.
When filling the tread compound with 20 parts of precipitated silica and 40 parts of N339 carbon black and using TESPT coupling agent, a balanced vulcanization effect can be obtained, and the rolling resistance of the tire decreases by 9%, with minimal changes in tread wear performance.
By partially replacing carbon black with precipitated silica (accounting for 40%-60% of the original carbon black amount) and using a coupling agent (accounting for 13.6% of the amount of precipitated silica), experimental results showed that the ice traction of the passenger car tire tread compound mainly composed of oil-extended natural rubber/polybutadiene rubber increased by 5%, while the rolling resistance decreased by 18% and the wet traction was equivalent to the comparison tire. The tread wear performance remained almost unchanged. In the study of natural rubber/styrene-butadiene rubber/polybutadiene rubber tread compound, it was found that increasing the amount of precipitated silica and using an organic silane while reducing the amount of carbon black can significantly reduce the loss tangent value of the tread compound at 60℃. This value has always been considered as an indicator of expected rolling resistance.
In the study of filling natural rubber with carbon black and precipitated silica, using 3,3'-dithiodipropionic acid disulfide as the silane coupling agent, the 300% modulus, rebound resilience, and hardness values were improved, and the loss tangent value of the tread rubber at 60°C was reduced. Using 2-amino-2-propanol salt as the coupling agent and using cis-1,4-polyisoprene synthetic rubber instead of natural rubber in the original formula, it was found that the elongation at break increased and the loss tangent value decreased.
In the study of filling precipitated silica in styrene-isoprene-butadiene rubber (SIBR)/polybutadiene rubber (BR) tread rubber and SIBR/BR/isoprene-butadiene rubber (IBR) tread rubber, laboratory test results showed that compared with the tread rubber filled with carbon black/precipitated silica, the tread rubber filled with only precipitated silica had a lower loss tangent value at 50°C and a higher loss tangent value at -20°C, indicating that the rolling resistance was reduced and the wet skid resistance was improved.
In summary, tire performance is directly related to the amount of precipitated silica in the tread rubber, and its performance improves as the amount of the latter increases. The best results are achieved when it completely replaces carbon black. Currently, the amount of precipitated silica used in passenger tire tread rubber is 65 parts.