Oce's VarioStream 9000 series of high-performance digital production printers features a non-contact fusing unit with unique properties. The printer's dual-engine architecture and simultaneous-duplex capability posed a challenge for the selection of the best suited fusing technology. Another challenge were the printer's changing paper movement modes due to its multi-pass operation. Monochrome printing runs with steady web motion, while dual, triple, and full-color print modes require the web to run, stop and retract in a multitude of fashions depending on the actual document content. The process speed must be adaptable to the requirements of light and heavy paper stock and special media. Traditional hot-roll fusing in combination with contact preheating was ruled out for the obvious reason of process incompatibility and high running cost. Contactless infrared fusing held the promise to meet the abovementioned challenges. Other pros were its durability, wide operating range, and low TCO figures. Shutter curtains allow for waste-free printing in continuous and noncontinuous printing modes, even when the web starts and stops periodically every few seconds. A web cooling section effectively suppresses hot offset on drive rolls and blocking of printed material. While the printed web runs through hot and cold process sections the respective atmospheres are kept separate by means of support rollers. If required, these can be actively engaged to smoothen the surface of the soft toner image. Process control employs preset parameters in start-up situations and a bunch of non-contacting sensors for infrared power and web temperature control. The fusing unit is able to process papers from 40 g/m~2 to 160 g/m~2 with full speed (1 m/sec) and up to 240 g/m~2 with reduced speed. Toners with tailored rheological properties have been developed to achieve good balance between power consumption, process time, and web dehydration. The fusing process delivers excellent toner adhesion and crease resistance for a wide range of media. This paper also gives a breakdown of the physics involved in design and operation of the fusing system. Radiator types, print media, toner properties, and heat transfer are discussed. Engineering aspects like shutter movement, power control, safety concept round off the picture.
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