Organic friction material compositions currently used in clutch and brake linings of vehicles must be capable of withstanding severe operating temperatures and dynamic pressures experienced during repeated applications. To prevent a deterioration in performance and physical degradation during an application, the linings are reinfoced by asbestos fibers randomly dispursed throughout a resin matrix. However, recent medical evidence indicates that asbestos fibers can cause health hazards of the lungs in persons exposed to asbestos fibers of the type used in the manufacture of clutch and brake lining. The health hazard is caused by the polution of the surrounding environment with small particles of asbestos during the mixing of the friction composition in a manufacturing facility.
In an effort to reduce the environment contamination by the asbestos fiber and thereby continue manufacturing asbestos based organic friction linings, a water slurry process is disclosed in U.S. patent application Ser. No. 754,477 has been evaluated. The water slurry can be transmitted throughout a manufacturing facility without contaminating the surrounding environment with asbestos fibers. However, before the friction material can be cured, the water in the slurry must be removed in order to be assured that any resulting lining has essentially the same operating characteristics as a lining made from a dry mix.
In another attempt to reduce the occupational health hazards in the manufacture of linings it has been suggested that the asbestos fiber be replaced with glass fibers.
U.S. Pat. No. 3,967,037 discloses several lining compositions utilizing fiber glass. From experimentation it has been determined that such lining compositions are acceptable, however, in admixing the ingredients the fiber glass tends to ball and thereby reduce the continuity of the friction material. In addition, when fiber glass base friction materials are mated with a steel brake rotor or drum, an unacceptable wear condition occurs.
U.S. Pat. No. 3,896,075 discloses another friction composition wherein the asbestos in an organic lining is replaced with basalt fibers. Because of the process required to reduce the mineral basalt into a fiber state, the use of such friction composition to date has not received open acceptance as a substitute for asbestos based organic friction materials.
Later as disclosed in U.S. Pat. No. 4,019,912 the reinforcing of the structure of a resulting friction lining was achieved through the use of carbon fibers. However, the pyrolysis step required to reduce the rayon or cellulose fiber to a carbon fiber would destroy the elastomers and inorganic fillers found in organic friction compositions.