US Patent 7240398 Opening and closing damping apparatus

An annular groove part with a predetermined depth is formed in a rotation body, and a wall surface of the annular groove part is sealed by a second protrusion elongated annular part formed in an inner circumference of a rotor attached to the annular groove part, and a wall surface of the annular groove part is sealed by a first protrusion elongated annular part formed in an outer circumference of the rotor, and grease is sealed in the inside. When the rotor is engaged in a support body and the rotation body is rotated, rotation of the rotor is regulated, so that the rotation body is damped by fluid resistance of the grease and is slowly rotated. The rotation body is supported by a support shaft inserted into a shaft hole.