Thirty years ago, Continental used silica for the very first time in its tread compounds for car tyres. The properties of this filler revolutionised the driving safety and energy efficiency of tyres. Rolling resistance has been significantly reduced, and braking distances have since been cut by nearly 50 percent. This was made possible by the special surface properties of silica, which can form chemical bonds with the rubber polymer. During vulcanisation – the process in which the tyre obtains its shape – silica, as well as other components, is responsible for the formation of a very strong network between the rubber molecules. The result is an elastic tyre with excellent safety properties. Today, silica has largely replaced carbon black in the tyre tread and has become indispensable in many rubber compounds for car, van and two-wheeled vehicle tyres. Its production is also becoming increasingly sustainable: Continental is already using a particularly sustainable silica that is obtained from rice husk ashes.
“Silica in rubber compounds was a revolution in tyre technology, enabling us to almost halve braking distances on wet road surfaces. This is still an enormous safety gain today,” says Prof. Burkhard Wies. In the mid-1990s, he worked on developing the first tyres with silica in the rubber compound at Continental. He now heads the Applied Research and Innovation department. “Silica compounds are also good for the environment, as they reduce the rolling resistance of tyres. This means less fuel consumption for combustion engines and increased range for today’s electric cars,” explains Wies.
In the mid-1990s, the first production tyres containing silica were launched on the market
Silica is used as a filler in many industries. In construction, for example, it is used in the production of concrete and bricks. Silica is primarily obtained from quartz sand. However, this crystalline silica is unsuitable for use in tyre production. A technically prepared “amorphous” silica is used instead.
In the mid-1990s, Continental was one of the first tyre manufacturers in the world to recognise the potential of silica as a filler for the tyre industry. At the beginning of the decade, the Hanover-based company conducted the first very promising experiments. Its properties are activated during the mixing process, whereby the silica reacts with the binding agent silane. In the next step, the vulcanisation process, the rubber mixture is then pressurised at temperatures of 120°C to 160°C. The tyre obtains its characteristic appearance thanks to special tyre moulds.
At the same time, sulphur is used to turn the rubber compound and silica into a flexible and elastic rubber. This is because the sulphur forms bridges between the long-chain molecular strands of the rubber during vulcanisation. The silica – supported by silane – forms additional bonds between individual rubber polymers, creating a very strong network between the rubber molecules. This gives the tyre physical properties such as outstanding wet grip, good abrasion resistance and excellent rolling resistance. At the same time, it can withstand extreme stresses.
The first road tests using the new filler in the tyre compounds back in 1994 demonstrated huge improvements in braking on wet roads and rolling resistance compared with carbon black. A year later, Continental used silica for the very first time in a production tyre, the ContiEcoContact CP. In 1996, this was followed by the launch of the ContiWinterContact TS 770, the first winter tyre with silica in the tyre rubber compound. “Together with the introduction of passive safety equipment such as seat belts and the anti-lock brake system, the use of silica in tyres has helped to significantly reduce the number of road casualties,” says Wies.
Greater sustainability with silica made from rice husk ashes
Continental’s developers are constantly working on making tyres safer and more sustainable while delivering even greater performance, both when it comes to the tyre assembly and the materials used. For example, the company is researching the use of alternative, more sustainable silica with comparable properties and safety benefits. Rice husks have proven to be a reliable base material for sustainably manufactured silica. Rice husks are a by-product of rice production that cannot be used as food or animal feed. Manufacturing silica out of rice husk ashes is more energy-efficient than conventional materials such as quartz sand. Silica from rice husk ashes is already used in Continental’s most sustainable production tyre to date – the UltraContact NXT.