TRANSMISSION BELT
FIG3 is a schematic view for explaining a measurement method of bending stress of power transmission belts obtained in Examples  FIG4 is a schematic view for explaining a durability running test of power transmission belts obtained in Examples
Each rubber composition shown in Table 1 was press vulcanized at a temperature of 170°C for 20 minutes to prepare a vulcanized rubber body (60 mm × 25 mm × 6.5 mm thick). Short fibers were oriented in parallel to a longitudinal direction of the vulcanized rubber body. As shown in FIG3, the vulcanized rubber body 21 was placed on a pair of rotatable rolls (diameter 6 mm) having a distance of 20 mm and supported thereon. Metal pressing member 23 was put on a central portion of the upper surface of the vulcanized rubber body 21 in a width direction (direction orthogonal to the orientation direction of the short fibers). The tip of the pressing member 23 has a semicircular shape having a diameter of 10 mm, and the tip can smoothly press the vulcanized rubber body 21. When pressing, frictional force acts between the lower surface of the vulcanized rubber body 21 and rolls 22a, 22b with compressive deformation of the vulcanized rubber body 21. However, the influence by friction is reduced by making rolls 22a, 22b rotatable. The state that the tip of the pressing member 23 is brought into contact with the upper surface of the vulcanized rubber body 21 and does not press is an initial position, and the pressing member 23 presses downward the upper surface of the vulcanized rubber body 21 from this state in a speed of 100 mm/min. Stress when bending strain reached 8% was measured as bending stress. By measuring bending stress in the direction orthogonal to the orientation direction of the short fibers, it can be judged that resistance force to buckling deformation called dishing during belt running is high when bending stress is increased, and the bending stress can be used as indexes of high load transmission and high durability. Assuming the belt temperature during running, the measurement temperature was 120°C.  Durability running test was conducted using a biaxial running tester containing a driving (Dr.) pulley 32 having a diameter of 110 mm and a driven (Dn.) pulley 33 having a diameter of 240 mm as shown in FIG4. Raw edge cogged V-belt 31 was bridged over each pulley, load of number of revolutions: 6000 rpm of the driving pulley and 25 kW was applied to the belt and the belt was run at an ambient temperature of 80°C for 70 hours. The side surface (surface contacting pulley) of the belt after running was visually measured. Presence or absence of peeling between the compression rubber layer and the cord and the presence or absence of cracks in valley parts of the lower cogs were examined. Those were evaluated by the following criteria.
schematic view
2
preferably
33
pulley
31
Raw edge cogged V-belt
21
vulcanized rubber body
3
Example
32
pulley
['14. The power transmission belt according to any one of claims 1 to 13, which is a raw edge cogged V-belt used for CVT driving.']