Multi-color electrophoretic displays

An electrophoretic display having a viewing surface and comprising a first electrophoretic layer adjacent the viewing surface and a second electrophoretic layer on the opposed side of the first electrophoretic layer from the viewing surface,

• the first electrophoretic layer comprising a first fluid, a plurality of charged white particles and a plurality of light transmissive charged particles of a first color different from white, the white and first color particles being dispersed in the first fluid, the first electrophoretic layer being provided with driving means capable of driving the white and first color particles to three different optical states, namely (a) a first optical state in which the white particles lie adjacent the viewing surface and the first color particles are spaced from the viewing surface;
• (b) a second optical state in which the first color particles lie adjacent the viewing surface and the white particles are spaced from the viewing surface;
• and (c) a third optical state in which the white and first color particles occupy only a minor proportion of the area of the first electrophoretic layer, thereby permitting light entering the first electrophoretic layer through the viewing surface to pass through the first electrophoretic layer to the second electrophoretic layer;
• and
• the second electrophoretic layer comprising a second fluid, a plurality of charged particles of a second color different from white and the first color, and a plurality of charged particles of a third color different from white and the first and second colors, the second and third color particles being dispersed in the second fluid, the second electrophoretic layer being provided with driving means capable of driving the second and third color particles to three different optical states, namely (d) a fourth optical state in which the second particles lie adjacent the first electrophoretic layer and the third color particles are spaced from this layer;
• (e) a fifth optical state in which the third particles lie adjacent the first electrophoretic layer and the second color particles are spaced from this layer;
• and (f) a sixth optical state in which the second and third color particles are intermixed within the second fluid.