Dai Nippon Toryo Co., Ltd.

Haruhiro Kato

Masachika Yaguchi

Shigeo Fujino

Shigetaro Furuta

An electrochromic display device composed of a pair of oppositely disposed electrode plates at one of which is transparent, and an electrochromic composition sealed between the pair of electrode plates. The electrochromic composition is composed of an electrochromic compound coloring in a reduced state and a solvent. The electrochromic compound coloring in a reduced state is sealed between the electrode plated in a reducing atmosphere. The solubility of the electrochromic compound to the solvent is 10.sup.-2 mol/(100 g solvent) or more in a reduced state and 10.sup.-1 mol/(100 g solvent) or more in an oxidized state. The solvent is preferably composed of water and at least 70% by weight of alcohol. The alcohol is desirably polyhydric alcohol.

Electrochromic display device

The display in a diffusion type electrochromic display device is turned off with high response by applying an A.C. input voltage having a frequency of one to ten times as high as the cut-off frequency. The diffusion type electrochromic display device is an EC display device which uses an EC composition consisting of an EC compound coloring in a reduced state and a solvent in which the solubility of the compound to the solvent is 10.sup.-2 mol/(100 g solvent) or more in a reduced state and 10.sup.-1 mol/(100 g solvent) or more in an oxidized state. The cut-off frequency is a critical frequency at a freqency higher than which the oxidization or reduction of the EC compound cannot follow the change in the input voltage, which is normally 20 to 50 Hz.

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Kawasaki, Japan

Haruhiro Kato