Roll-fusing apparatus

DETAILED DESCRIPTION It is an object of the present invention to equalize the characteristic of contact pressure exerted by the pressure roller on the fusing roller in a fusing apparatus of the above-described type, such that the formation of wrinkles or buckles is prevented in copies of DIN A4 through DIN A1 sizes.
It is another object of the present invention to provide a fusing apparatus as above which may readily process different copy materials such as opaque papers, transparent papers or films, without wrinkling or buckling, even though they show different behaviors in their passage through the fusing apparatus.
Still another object of the present invention is to provide a fusing apparatus as above wherein large size copies may be produced without the occurrence of a so-called "smearing effect" or double printing.
In accomplishing the foregoing objects, there has been provided in accordance with the present invention a roll-fusing apparatus comprising a pressure roller and an internally heated fusing roller disposed substantially parallel to each other so that a gap is formed therebetween, for fusing a toner image on a copy support, wherein the pressure roller comprises a coated hollow roller core supported on a shaft, and the roller core comprises a substantially cylindrical inner surface and a radially symmetrical outer surface comprising alternating regions of greater and lesser circumferences.
The roller core may comprise three longitudinally oriented zones, such that a middle zone is axially symmetrical about the midpoint of the roller, one end of each external zone borders the middle zone at a relative maximum diameter of the roller core, and the other ends of the external zones are defined by the end faces of the roller.
The roller core is coated with a silicone elastomer which conforms on its inner surface to the shape of the roller and has a substantially cylindrical outer configuration.
Finally, a film tubing having a substantially uniform thickness is shrunk onto the outside of the coating layer