The Heart of It All

The magnetophoretic display panel is what makes the Magna Doodle unique.

Magnetophoretic display

This magnetic display has the following structure:

• Front - A piece of transparent or semi-transparent plastic
• Middle - A honeycombed or hexagonal plastic lattice
• Back - A piece of transparent or semi-transparent plastic

Close-up of the honeycombed structure of the display

The walls of the middle, honeycombed lattice are less than 0.02 inches (0.5 mm) thick. Each cell of the lattice is filled with a thick liquid suspension or dispersion medium filled with tiny magnetic particles. The liquid dispersion medium is designed so that the particles can be pulled through the liquid in response to magnetic force applied by the pen or eraser, but they will not change their position (float or sink) due to gravity. To do this, the liquid has special properties:

• The liquid is thick - This prevents the magnetic particles from sinking, so what you have written stays at the front of the display over time. The liquid is water, glycol or organic solvent/oil-based, and has particulate thickeners:
  • waxes - olefinic polymer, olefinic copolymer, wax
  • fatty acid derivatives - fatty acid amide, dextrin fatty acid ester
  • metal soap

• The magnetic particles are dark, small and fine (about 10 microns) - This allows them to be seen easily, to stack up and to be nearly unaffected by gravity.
  • magnetic oxides - black magnetite, gamma-hematite, chromium oxide, ferrite
  • magnetic alloys - iron, cobalt, nickel

• Dye is mixed in - This provides high contrast to the dark magnetic particles.
  • white pigment - most effective (concentrations of 3 to 10 percent) and most commonly used
  • colored pigments - in some Magna Doodles

The middle layer is latticed so that there is always an even distribution of the magnetic particles across the entire surface of the display.

Now that we have seen the display, let's look at the pen.