Fillers

Fillers are – alongside the rubber itself – the most important components of a rubber compound in terms of quantity. They are added specifically to control the processability, mechanical properties and functional behaviour of an elastomer – from hardness and abrasion resistance to electrical conductivity.

• Carbon black – reinforcing fillers for high tensile strength, abrasion resistance and crack resistance
• Filled and pyrogenic silica – reinforcing, often used in light-coloured compounds or in seals and tyre treads subject to high dynamic stress
• Mineral fillers such as talc, kaolin, chalk or barite – predominantly semi-reinforcing to inactive; they influence density, stiffness, dimensional stability and cost structure

Fillers characterise the central material properties of an elastomer. Among other things, they influence:

• Hardness (e.g. Shore A) and modulus
• Tensile strength, elongation at break and resistance to tear propagation
• Abrasion resistance and resilience
• Damping behaviour and compression set
• Processability of the compound (viscosity, flow behaviour during extrusion and injection moulding)

Depending on the type and quantity of filler, a rubber compound can be made softer or harder, more flexible or stiffer, more resistant to abrasion or more shock-absorbent. In many applications, fillers also help to improve heat ageing or media resistance, for example in seals, O-rings, profiles or moulded parts that must function reliably under pressure, temperature and chemicals. Conductive carbon black types and special fillers (e.g. graphite, metal or fibre fillers) play a special role: they can significantly increase electrical conductivity and are used in antistatic or conductive components, ESD profiles or safety-relevant seals.