Although toner formulations are often proprietary and diverse, they are all typically manufactured by a sequence of milling operations to produce finely divided powder. With an average size <10 μm, the particles are often very small, which can make them prone to agglomeration due to their high cohesivity. As toner is required to flow freely in a well-dispersed, near-fluidised state, additives may be used to inhibit this agglomeration, or to promote adhesion to the paper.
In laser printing process, toner particles are drawn from a reservoir via a charged drum that has been selectively discharged by a laser with a latent image of the text or graphics to be printed. The particles are then transferred to the substrate by direct contact and thermally fused. Excess particles are removed by a blade and the drum is recharged for re-exposure to the laser.
A study available from Freeman Technology, uses the multivariate approach of the FT4 Powder Rheometer® (a universal powder tester), to show how the test methodologies provided by the instrument are ideally suited to characterising the range of process-relevant powder properties that will influence the toner’s flowability in different printing processes.
By specifically testing the samples under the low-stress, highly aerated conditions present in laser printing operations, process-relevant data is generated that can be correlated with printing performance. The correlations can then be used to define a design space of properties that pertain to high quality performance in the printer, against which new formulations and outgoing products, can be assessed.
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