Patent ID: 8431629

Claim:
A wet friction member comprising: a core metal of a flat ring shape; and a friction material substrate formed by impregnating a thermosetting resin with a paper body containing a fiber component and a filler component and hardening it by heat, wherein one or more kinds of an inorganic filler are included in the filler component within a range of 5% by weight to 40% by weight to a total weight of the paper body, wherein the inorganic filler consists of filler having an average particle size within a range of 0.3 to 10 μm, an absolute specific gravity within a range of 4 to 6, and Moh's hardness within a range of 3 to 8, wherein the friction material substrate being joined onto one or both surfaces of the core metal of the flat ring shape; wherein the peak of the pore diameter distribution of the friction material substrate measured by a mercury intrusion technique is set within a range of 1 μm to 20 μm, and the porosity of the friction material substrate is set within a range of 30% to 70%, and wherein the particles of the one or more kinds of the inorganic filler attach to the fiber component of the paper body of the friction material substrate so as to interconnect the fibers of the friction material substrate.