The Influence of Physical and Environmental Factors on the Flow Properties of Toner Powders
Toner formulations are diverse and often proprietary but are all typically manufactured by a series of milling operations to produce finely divided powder. The particles are often very small, with an average size <10 μm, which can make them highly cohesive and prone to agglomeration. As the toner is required to flow freely in a well-dispersed, near-fluidised state, additives may be employed to inhibit agglomeration, or to promote adhesion to the paper.
In laser printing, toner particles (typically copolymers) 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 (paper) by direct contact and thermally fused. Excess particles are removed by a blade and the drum is recharged for re-exposure to the laser.
Advances in laser printing technology over the last forty years have developed toner manufacturing into a multi-billion-dollar industry, with the requirement for robust quality control balancing the commercial benefits of increased output. A method of correlating primary toner properties with printing performance, enabling criteria to be defined that predict performance, can therefore deliver significant commercial advantages in terms of increased productivity and reduced waste.
Successful printing demands that a toner consistently meets exacting criteria to ensure that it delivers high-quality and repeatable performance. The wide range of printing techniques, and the diverse conditions that a toner is subjected to in any one process, means that no single parameter, or even a single technique, will be sufficient to define the properties of a toner that dictate performance. A multivariate approach that delivers process relevant information is required.
The study available below, using the multivariate approach of the FT4 Powder Rheometer, shows 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.