Resolution, printer blockages, smudging

Particle size is critically important in determining the performance of a toner, affecting not only the resolution of the final image, but also its overall handling and performance. When laser printers were first available, for example, the toner particles were on average 12 microns in diameter. Achieving resolutions of 600 dpi required particles around 8 microns, and the pressure now is to produce particles that are smaller and smaller in size.

Off-line QC

Traditionally, the standard particle sizing methodology in the toner industry for off-line quality control (QC) has been the electrozone counter method. This required off-line collection of samples and measurement at specified intervals. A typical measurement protocol might involve sampling and measurement once every 2 hours, with measurements based on 5g of material and each taking around 20 minutes. Should a first measurement indicate any deviation from specifications, then a confirmatory measurement would be necessary to ensure that this is not the result of a measurement error. Thus there is a considerable lag time before any process adjustments can be made with confidence.

Real-time particle sizing

On-line particle sizing facilitates the real-time optimization of process parameters and configurations. Laser diffraction-based systems, as exemplified by the Malvern Insitec, offer benefits in that the technique requires no calibration, nor does it need long data acquisition intervals which can mask true process behavior.

QC benefits for the toner manufacturer are:

• On-line particle sizing in statistical process control allows continual monitoring of product quality.
  
• Greater precision than using laboratory-based particle sizing.
  
• Tightening the tails of the particle size distribution improves toner performance.
  
• Continuous measurement reduces batch-to-batch variation and eliminates within batch anomalies.
  
  

More about electrozone method versus on-line particle sizing.