Apparatus for printing on opposite surfaces of a strip of printing paper

Abstract

An apparatus for printing on opposite surfaces of a strip of printing paper using two electrophotographic printing units wherein each printing operation is of high quality and thermal damage to the printing is minimized. The apparatus includes a first electrophotographic printing unit for printing on the front surface of the printing paper, a buffer unit for temporarily holding the printing paper discharged outside of the first electrophotographic printing unit, a turn unit for turning over the printing paper, and a second electrophotographic printing unit for printing the reverse surface of the printing paper. A toner having a low melting temperature is employed for each of the first and second electrophotographic printing units so that developing treatment is conducted only with the aid of a heat roll but without any use of a preheating plate. A back-up roll adapted to cooperate with the heat roll is coated with a tetrafluoroethylene-based synthetic resin. The second electrophotographic printing unit is provided with a paper presser for squeezing the printing paper against a photosensitive drum only within the printing width range. A retract mechanism is operatively connected to the paper presser.