Patent ID: 8528980

Claim:
A seat back unit to be connected to a seat of a chair, the seat back unit comprising a main frame, a supporting member and a backrest member; wherein the main frame is a L-shaped member having a vertical section and a horizontal section, a top end of the vertical section has a first hinge portion, a resting seat having an embedded concave portion is fixed to a middle segment of the vertical section, and connection projections are disposed on a junction between the vertical section and the horizontal section; the supporting member, which is a plate member having one end formed with a second hinge portion, and the other end formed with a crossing portion, which is embedded into the embedded concave portion of the resting seat; and the backrest member is composed of a vertical arch section and transversal curved sections, wherein the vertical arch section has a third hinge portion and a fourth hinge portion corresponding to the first hinge portion of the main frame and the second hinge portion of the supporting member, respectively.