Shape and tone(r) this New Year!
Written by: Steve Ward-Smith
I hope you all had a fabulous holiday season and that 2011 finds you happy and healthy! However, I’m also sure that following the festivities a fair number of us are giving more than a passing thought to our size and shape distributions, and if you are following a new fitness regime that it’s still working for you a month into 2011! Now, despite the fact that they say the camera adds ten pounds (or should that be 4.536 kgs?), I am going to recommend that one of the most effective ways to size up your shape this New Year is to take as many images as you can! *GASP*
I am, of course, referring to applying the automated Sysmex FPIA-3000 particle analyzer to capturing images of your sample and converting the information into particle size and shape distributions!
Watch your toner flow!
In the toner industry both particle size and shape are important characteristics in the quality of the final product. A toner’s flow properties and charging capability are both primarily influenced by the physical properties of the constituent particles: the mobility of the toner in the supply reservoir mechanism; the transferability performance to paper; and, the property of peeling from the drum are all affected.
Toner manufacturers using both traditional and newer polymerisation techniques need to target very specific size and shape to achieve the performance they want. They aim for:
- Tight particle size distribution
- Particle size towards 8 microns or even less
- Optimum circularity (0.95 to 0.96)
Sysmex FPIA-3000 automated particle imaging
Using a charge-coupled device (CCD) camera, the Sysmex FPIA-3000 produces images of every particle. Each individual particle is illuminated by strobe as it passes through a sheath flow cell and its image captured and analysed in real time.
The numerical value of the particle shape is obtained by measuring the area of the particle. From this, its perimeter, circularity and circle equivalent diameter can also be determined.
Picture your powder particles – how circular are they?
Figure 2: Using the Sysmex FPIA-3000 it becomes straight forward to distinguish between: (left) Good toner circularity and (right) poor toner circularity
In terms of shape, the main characteristic that affects performance is the circularity of the toner powder. The more perfectly circular your particles, the better they will flow – no jagged bits sticking out to catch on each other. However, if they are too perfectly circular the particles will act like a lubricant and not transfer to the print medium properly. The optimal shape distribution for toners is therefore centered around a mean circularity of 0.95-0.96.
Circularity is defined as the ratio between the perimeter of a circle of equivalent area to the particle and the perimeter of the particle itself. Circularity can be viewed as an index of the degree of irregularities on the surface of a particle. Therefore, if the circularity were 1, the shape would be perfectly spherical. As this value decreases, the surface shape becomes increasingly complicated.
Not too big, not too small, but not too perfect either!
So, don’t get worked up about your toner shape in 2011, the idea is to aim for imperfection! Not to big, not too small and almost, but not quite, perfectly circular!
Of course, having defined your specifications, laser diffraction then comes into its own, especially for routine on-line particle size measurements, but that’s a topic I plan to cover in another blog…