US Patent 11868020 Electrophoretic display device

An electrophoretic medium comprises a fluid and first, second, third and fourth types of particles (W, Y, R, B) having four different colors. The first and third particles have charges of one polarity and the second and fourth particles charges of the opposite polarity; the first particles have a greater zeta potential or electrophoretic mobility than the third particles, and the second particles a greater zeta potential or electrophoretic mobility than the fourth particles. One particle is white (W), one non-white particle (B) is partially light-transmissive, and the remaining two non-white particles (R, Y) are light-reflective. A third light-reflective particle (G) may be added to create a five particle medium.