Lubricant composition and sealed bearing thereof

#The present invention relates to a lubricant composition and a sealed bearing thereof. More particularly, the present invention relates to the lubricant composition which is used by sealing it into a rolling bearing for motors for use in household appliances and apparatuses for industrial use. The rolling bearing is used at high temperatures and rotational speeds and required to have a high degree of quietness, a long life at high temperatures, a low torque, and excellent fretting property. The present invention also relates to the sealed bearing thereof.

#The lubricant composition is sealed into the rolling bearing incorporated in apparatuses for industrial use and vehicles to impart lubricant property thereto. The lubricant composition is obtained by kneading a base oil, a thickening agent, and additives used as necessary. As the base oil, mineral oil and synthetic oil such as, ester oil, silicon oil, and ether oil are used. As the thickening agent, metal soap such as lithium soap and urea compounds are used. As the additives, an antioxidant, a rust preventive, a metal deactivator, and a viscosity index improver are added to the base oil as necessary.

#In recent years, motor bearings which are used for household appliances and apparatuses for industrial use are rotated at high temperatures and rotational speeds. The motor bearings are demanded to have a high degree of quietness, a high durability at high temperatures and rotational speeds, a low torque, and excellent fretting property.

#FIG. 1 is a sectional view showing a ball bearing having a small diameter.

#The present inventors have examined the lubricant composition that allows the rolling bearing to satisfy all the necessary characteristics of having a high degree of quietness, an excellent durability at high temperatures and rotational speeds, a low torque, and excellent fretting property when the lubricant composition is sealed into rolling bearings, for motors of household appliances and apparatuses for industrial use, which are used at high temperatures and rotational speeds.

#The present inventors have found that the use of thickening agents excellent in dispersibility improve the degree of quietness. The present inventors have found that owing to contribution of the straight-chain alkyl group of the urea compound shown by the formula (1), the urea compound shown by the formula (1) is more dispersible in a base oil consisting of a mixed oil of a synthetic hydrocarbon oil and an ester oil than other thickening agents excellent in the dispersibility in the base oil and that the use of the urea compound shown by the formula (1) improves the degree of the quietness of the rolling bearing.

#The present inventors have examined the kind and characteristic of the base oil excellent in durability at high temperatures and rotational speeds. As a result, they have found that it is possible to improve the durability of the lubricant composition at high temperatures and rotational speeds to the highest extent by using the mixed oil, consisting of the synthetic hydrocarbon oil and the ester oil, having a specific kinematic viscosity characteristic and a specific mixing ratio. They have also found that it is possible to reduce the torque of the bearing and improve the fretting property of the lubricant composition by using the above-described mixed oil.