Patent ID: 8568052

Claim:
A one-piece plastic binder for binding sheets of paper, comprising: a plastic back part; and a plurality of plastic rings arranged at certain intervals along a longitudinal axis of the back part to align with holes punched in the sheets of paper, each of the rings being formed of ring parts on respective sides of the back part, and each of the rings being openable and closable, wherein the plurality of rings are coupled together through the back part being disposed between side surfaces of the respective adjacent rings, and at least one of the plastic rings is formed with only one, unbroken unitary penetration hole that intersects the longitudinal axis of the plastic back part and absorbs a linear expansion of the binder in a longitudinal direction thereof along the longitudinal axis of the back part to maintain the plurality of rings aligned with the holes punched in the sheets of paper, wherein the penetration hole extends in a radial direction of the at least one of the rings from a radially inner surface to a radially outer surface of the at least one of the rings.