Electrochromic display apparatus

• US 4,309,082 A
• Filed: 11/05/1979
• Issued: 01/05/1982
• Est. Priority Date: 07/12/1976
• Status: Expired due to Term

• Current Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Inventors: Kohara, Rikusei, Komoto, Yoshihisa, Nakajima, Seizo
• Primary Examiner(s): Davie, James W.
• Application Number:
  US06/090,919
• Time in Patent Office: 792 Days
• Field of Search: 350/357, 340/763, 340/785
• US Class Current: 359/272
• CPC Class Codes: G02F 1/163 Operation of electrochromic cells, e.g. electrodeposition cells; Circuit arrangements therefor

Abstract

In a container which contains an electrochromic solution, a pair of electrodes, namely an indication electrode and a counter-electrode are disposed and an electric circuit is constituted in a manner such that a D.C. pulse is impressed across the electrodes and thereafter the electrodes are shortcircuited to each other. By means of the shortcircuiting, a color indicating substance formed on the indication electrode by the electrochemical reduction reaction or electrochemical oxidation reaction is reversably dissolved from the indication electrode into the solution so as to erase the indication, and therefore contamination of the indication electrode is less and hence a longer life is achieved in comparison with conventional apparatus where such shortcircuiting is not made and simply an inverse pulse is impressed across the electrodes for erasing.

Claims

1. An electrochromic display apparatus comprising:

(a) a display cell having an indication electrode, a polarizable counter-electrode and an electrochemical electrochromic substance filled between said indication electrode and said counterelectrode,

(b) a voltage-impressing means for impressing a predetermined voltage across said indication electrode and said counter-electrode for a predetermined time period to allow a current to flow across the electrodes to form an electrochromic reaction product for electrochromic indication on the surface of said indication electrode, and

(c) a shortcircuiting means which, each time before applying said predetermined voltage, shortcircuits said indication electrode and said counter-electrode to each other for a predetermined time period to provide an inverse current to said current across the electrodes to dissolve said electrochemical reaction product and thereby erase said electrochromic indication.

2. The electrochromic display apparatus of claim 1 wherein said counterelectrode is gold or platinum.

3. In a method of operating an electrochemical electrochromic display apparatus comprising a display cell having an indication electrode, a counter-electrode and an electrochemical electrochromic substance filled between said counter-electrode and said indication electrode,

the improvement comprising the steps of:

(a) impressing a predetermined voltage across said indication electrode and a polarizable counter-electrode for a predetermined time period to allow a current to flow across the electrodes to form at least an electrochemical reaction product for electrochromic indication on the surface of said indication electrode, and

(b) each time before applying said predetermined voltage shortcircuiting said indication electrode and said counter-electrode to each other for a predetermined time period making an inverse current to said current across the electrodes, dissolving said reaction product and thereby erasing said electrochromic indication.

4. An electrochromic display apparatus comprising:

(a) a display cell having an indication electrode, a Pt or Au counter-electrode and an electrochemical electrochromic substance filled between said indication electrode and said counter-electrode,

(b) a voltage-impressing means for impressing a predetermined voltage across said indication electrode and said counter-electrode for a predetermined time period to allow a current to flow across the electrodes to form an electrochromic reaction product for electrochromic indication on the surface of said indication electrode, and

(c) a shortcircuiting means which, each time before applying said predetermined voltage, shortcircuits said indication electrode and said counter-electrode to each other for another predetermined time period to provide an inverse current to said current across the electrodes to dissolve said electrochemical reaction product and thereby erase said electrochromic indication.

5. An electrochromic display apparatus in accordance with claim 4, wherein said electrochemical electrochromic substance is an aqueous solution containing at least one compound selected from the group consisting of hexyl viologen compounds, heptyl viologen compounds, octyl viologen compounds and benzyl viologen compounds.

6. The electrochromic display apparatus of claim 4, wherein said another predetermined time period is from 1-20 times long as said predetermined time period.

7. A method of operating an electrochemical electrochromic display apparatus including a display cell having an indication electrode, a counter-electrode and an electrochemical electrochromic substance filled between said counter-electrode and said indication electrode, said method comprising the steps of:

(a) impressing a predetermined voltage across said indication electrode and a Pt or Au counter-electrode for a predetermined time period to allow a current to flow across the electrodes to form at least an electrochemical reaction product for electrochromic indication on the surface of said indication electrode, and

(b) each time before applying said predetermined voltage short-circuiting said indication electrode and said counter-electrode to each other for another predetermined time period making an inverse current to said current across the electrodes, dissolving said reaction product and thereby erasing said electrochromic indication.

8. The method of claim 7, wherein said electrochemical electrochromic substance is an aqueous solution containing at least one compound selected from the group consisting of hexyl viologen compounds, heptyl viologen compounds, octyl viologen compounds and benzyl viologen compounds.

9. The method of claim 7, wherein said another predetermined time period is as 1-20 times long as said predetermined time period.