Abstract: A rubber composition containing a rubber forming a continuous phase of 100 weight parts; a nylon fiber with fine diameter of 1-15 weight parts by the fiber, the nylon fiber being grafted with a molecular of a rubber capable of co-crosslinking to the rubber forming the continuous phase; and a short fiber of 1-30 weight parts is used to at least a part of a rubber of a transmission belt. Thus, high anisotropy in modulus of elasticity in the transmission belt is maintained. Further, stress concentration at an interface of the short fiber and the rubber is distributed to enhance the strength, elasticity and flex fatigue resistance.

Abstract: There is provided a synchronous belt with excellent heat resistance and excellent abrasion resistance, in which a backing rubber is composed of a rubber composition obtained by vulcanizing hydrogenated nitrile rubber with an organic peroxide. At least the lowermost layer of a tooth rubber is composed of a hydrogenated nitrile rubber composition obtained through both sulfur vulcanization and peroxide vulcanization. The coating rubber on a facing fabric is composed of a rubber composition obtained through sulfur vulcanization. The above rubber composition of the tooth rubber is obtained by adding, to every 100 g of hydrogenated nitrile rubber, 0.3 to 10 g of sulfur-containing vulcanizing agent and 0.002 to 0.025 mol of organic peroxide.