Soft phase engineering in brake pad binder to reduce stiffness control and device noise

Brake pad noise reduction is one of the key challenges in disc brake systems and is directly influenced by the mechanical and tribological properties as well as the damping behavior of friction materials. In this context, the binder plays a decisive role in controlling hardness, wear and consequently the tendency to generate noise. Phenolic resin, as the primary binder, provides adequate mechanical strength; however, its inherently high hardness can lead to increased wear, intensified disc corrosion, and a higher likelihood of noise generation. In this study, a practical and industrially applicable approach based on soft-phase engineering is proposed without applying any chemical modification to the resin. To this end, controlled amounts of nitrile-butadiene rubber (NBR) were introduced into the formulation as a secondary soft phase, and frictional behavior was investigated. Furthermore, the synergistic role of mineral fillers, including talc, mica and alumina, was evaluated at different NBR contents. The results revealed that high NBR contents cause a severe reduction in hardness and mechanical instability, whereas the addition of lower amounts of NBR leads to a controlled decrease in hardness while maintaining shear strength within the standard range. The investigation of filler-containing systems demonstrated that their effectiveness strongly depends on the soft-phase content and does not necessarily result in property enhancement under all conditions. The optimized formulation exhibited stable friction behavior without a noticeable decline in performance. Overall, precise control of the soft-phase content proved to be more effective than increasing formulation complexity and can indirectly reduce the tendency for noise generation by decreasing wear and aggressive contact at the pad-disc interface. This approach offers a simple, economical, and industrially feasible pathway for the development of stable, low-noise brake pads.

Keywords:

Friction materials , NBR , Brake pad , Soft-phase engineering , Hardness control , Brake noise reduction