To provide a wet friction material having a high coefficient of friction and good μ-V characteristics and suppressing the opponent aggresiveness and sufficiently exhibiting friction increasing effects with a filler while suppressing falling off of the filler.
The filler of the wet friction material is an oxide consisting essentially of aluminum and composed of granulated particles formed of hollow powder particles having ≤1 μm average particle diameter and ≤20 nm shell thickness and bonded with a granulating binder. The average particle diameter of the granulated particles is larger than the average fiber diameter of a fiber substrate. A method for producing the wet friction material comprises the following steps. A powder particle producing step of providing the hollow powder particles which are an oxide consisting essentially of the aluminum and having ≤1 μm average particle diameter and ≤20 nm shell thickness, a granulating step of affording the granulated particles obtained by bonding the powder particles with the granulating binder and having the larger average particle diameter than the average fiber diameter of the fiber substrate and a forming step of forming the wet friction material from a raw material containing the filler composed of the granulated particles, fiber substrate and binder.
TAKATORI KAZUMASA
TOYAMA MAMORU
OKUYAMA MASARU
OMORI SHUNEI
OTA TAKASHI
KAWABATA MASATAKA
TOYOTA MOTOR CORP