Hot roll fusing

At the end of the process, the loose toner image is melted to fix it to the paper. We shall illustrate the interfaces involved for hot roll fusing, a process of choice for modern high volume duplicators. Radiant heaters, flash lamps, and cold pressure roll systems have all been incorporated in low volume copiers, whose intermittent mode favors instant start-up and low standby power. In continuous use, on the other hand, hot roll fusers have an approximately threefold advantage over their competitors in terms of power economy (.98) The toner comes into contact with more toner, with paper, and with the fusing roll. The first important interaction is one which must be avoided, and which therefore sets a temperature threshold for the materials and process it is a premature sintering ("blocking") of... 

FIGURE 19.77 Schematic of the electrophotographic process. Dual component development is shown with hot roll fusing and coronas for charging and cleaning. Source Durbeck, R.C. and Sherr, S. 1988. Hardcopy Output Devices. 

Pigmented resins are applied as dry powders and then fused by heating to 220°C or higher. The process is effective with lightweight metal components and pipework. It is likely to remain uneconomic for use on heavy sections, e.g. hot-rolled steel universal beams and columns. 

Step 6 Fixing or fusing. The toner image is permanently fixed to the paper using either a heat-and-pressure mechanism (hot-roll fuser) or a radiant fusing technology (oven fuser) to melt and bond the toner particles into the medium (usually paper) being printed on. 

For the above reasons, processes that involve combinations of heat and pressure are the most widely used. This is normally accomplished by hot-roll pressure devices in which at least one roll is heated with a quartz lamp (Lee, 1975 Prime. 1983 Kuo. 1984 Hiraoka et al.. 1993). Offset of the toner to the fuser roll can be avoided by the use of special oils wicked onto the surface of the roll. Most roller fusing devices use heated rolls coated with silicone or fluorocarbon elastomers. Composite layer structures with multiple layers for improved process lifetime are becoming more common. Figure 17 shows a cross-section of a typical fuser roller and Fig. 18 shows a typical fusing process. For a review of fusing materials, see Gruber et al. (1989). For a discussion of the effects of paper properties on fusing, see Sanders et al. (1996). 

Figure 18 shows a typical roll fusing configuration (100). A 100>m thick sheet of bond paper, bearing an approximately 30 m thick toner pattern enters the zone between a pair of rolls, one of which is compressible, the other rigid. The hot roll briefly presses the toner into... 

In summary, the interfacial relationships required to form an efficient roll fusing system are highly complex. The toner must interact weakly with the hot roll and strongly with the paper. Sintering and flow must be avoided right up to the moment of fusing, and then forced to occur in milliseconds. Heat transfer must be optimized, and mechanical drives kept stable and reliable under difficult conditions. 

Pressure treatment by a hot roll at 110-120 = (fusing treatment of synthetic fibers)... 

The 121 sample films were formulated into a replicate series. Those utilizing emulsion polymerized PVC were cast from plastisol onto glass plates and fused in a circulating hot air oven. Those incorporating suspension polymerized PVC were fluxed via a Banbury and two-roll compounding mill and finished on an inverted L 8-inch X 16-inch four-roll calender. Plastisol films were of nominal 8-mil thickness calendered film was 4 mils. 

The additive was added gradually to the polymer fused on a two-roll mill at 170°-174°C. After addition, polymer sheets were taken off the mill and put back on the mill endwise. Several such passes were made until the sample was thoroughly mixed. The specimen was removed from the mill in thin sheets and, while hot, cut into small pieces. The polymer was compression molded at 700 p.s.i.g. and a temperature of ca. 155°C. into a 6 X 6-inch sheet of about 0.045-inch thickness. This sheet was cut into the 5 X 1/2 X 0.045-inch specimens for burning in the modified D635 test. The sample was initially evaluated with 25% additive. If the compound was effective, lower concentrations were used until the additive would not confer fire retardant activity, or until the supply of additive was exhausted. With poly (methyl methacrylate), PMMA, cast samples also were prepared. 

Carbon nanotubes were discovered in 1991 and consist of elongated cages, best thought of as rolled graphite-like sheets, i.e. in contrast to the fullerenes, nanotubes consist of networks of fused 6-membered rings. Nanotubes are very flexible and have great potential in materials science. As a result, research in this area is a hot topic but is beyond the scope of this book the end-of-chapter reading list provides an entry into the area. 

These in edients are preblended with small quantities of pigments and lubricants, then fused ti ether on hot differential mixing rolls. The densi-fied material is removed from the rolls, cooled, and ground to the correct particle size and distribution. 

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