JPH038524B2 - - Google Patents

Description

Claim 1: An electrochromic display cell capable of assuming multiple visually distinguishable optical states at temperatures below -11°C with a response time of 50 milliseconds or less, comprising: a transparent electrically conductive display electrode; , a counter electrode for applying a potential difference to the display electrode, a layer of electrochromic material made of a rare earth diphthalocyanine complex disposed on the display electrode, and a counter electrode for passing an ion flow through the display electrode. an electrolyte material interposed between the upper layer and the counter electrode, and the electrolyte material is a highly concentrated aqueous solution of metal chloride that solidifies at a temperature of -11°C or lower. An electrochromic display cell.

2 The rare earth of the rare earth diphthalocyanine complex is a lanthanide series rare earth element, yttrium,
2. The display cell of claim 1, wherein the display cell is selected from the group consisting of: and scandium.

3. The display cell according to claim 1, wherein the electrolyte material contains an aqueous calcium chloride solution.

4. The display cell according to claim 1, wherein the electrolyte material contains an aqueous lithium chloride solution.

5 The calcium chloride is 30% by weight of the solution.
The display cell according to claim 3, characterized in that:

6. Display cell according to claim 4, characterized in that the lithium chloride is 25% by weight of the solution.

FIELD OF THE INVENTION This invention relates generally to the field of electrically controllable displays, and more particularly to the field of electrochromic displays.

BACKGROUND OF THE INVENTION Many types of electrically controllable display devices exist. A number of such devices have been commercially available for some time and include liquid crystal displays, light emitting diode displays, plasma displays, and the like. Light emitting diodes and plasma display panels are active light emitting devices that require extra power to operate. Additionally, it is difficult, if not impossible, to fabricate light emitting diode displays that are easily visible under bright ambient lighting. Liquid crystal displays operate only over a limited temperature range and have virtually no memory within the liquid crystal material. Additionally, the visibility of many liquid crystal displays decreases when the viewer moves a few degrees off-axis.

Electrochromic displays have been developed to display information through changes in the colored portions of the display by electrochemical reactions of active materials to achieve color changes. In the well-known case of tungsten oxide electrochromic materials, this color change is from white to blue. For viologen electrochromic materials, the change is from white to violet. Because of their specific electrochemical mechanisms, such displays require substantial power and time to write or erase the displayed information. The amount of power required is undesirably large, especially when powered by batteries, and the time required to change the displayed information makes such materials undesirable for many display applications. shall be taken as a thing.
None of these known displays provide more than one color to the background.

It is known from previous publications that rare earth diphthalocyanines have electrochromic properties. In those publications, the color of diphthalocyanine changes over about 8 seconds when a potential difference is applied to an electrochemical cell having a diphthalocyanine film on one electrode. As an example, P.N.
Moskalev and ISKirin, “Effect of the
Electrode potential on the absorption
Spectrum of a Rare-Earth Diphthalo-
cyanine layer，”Opt.i Spektrosk，29414
(1970) and P.N.Moskalev and ISKirin,
“The Electrochromism of Lanthanide
Diphthalocyanines”Russian J.Phys Chem,
46, 1019 (1972). Although diphthalocyanine does not require large amounts of power to change color, the long time required to change color may make the performance characteristics of diphthalocyanine unfavorable when evaluated for display requirements. let

However, electrochromic display devices with faster switching characteristics
Phthalocyanine by MM Nicholson
January 22, 1980 entitled Electroctromic Display
US Pat. No. 4,184,751, issued in This display device contains an electrolyte solution of potassium chloride (KCl). This device has an operating temperature range of approximately 100°C to -11°C. As a result, many applications for using electrochromic displays are precluded due to their limited operating temperature range.

The above-mentioned US patent (corresponding to Japanese Patent Application Laid-Open No. 53-77494) further discloses a configuration capable of achieving a response time of 50 milliseconds or less.

SUMMARY OF THE INVENTION This invention provides a display that utilizes a metal diphthalocyanine complex as a material with electrochromic activity and a low freezing point metal chloride as an electrolyte in an electrolyte solution in an electrochromic display cell. This overcomes many of the problems of prior art displays. Rapid color changes of less than 50 milliseconds have been achieved to alleviate the slow switching times previously reported for rare earth metal diphthalocyanine complexes. Power consumption is low because the display material has low power consumption, high optical absorption, and the display exhibits an open circuit memory of minutes to hours depending on its configuration. Polychromatic, ie, two or more color, displays are achieved using a range of voltages applied between the display electrode and the counter electrode. Color reversal of the displayed information and the background on which the information is displayed is achieved by using display electrodes in the background portion of the viewing area as well as in the character segments. The use of an aqueous solution of the selected metal chloride as the electrolyte solution extends the operating range to very low temperatures, for example on the order of -80 DEG C. if the electrolyte solution is a highly concentrated solution of lithium chloride.

[Brief explanation of drawings]

FIG. 1 illustrates a cross-section of a typical transmissive display cell shape.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Display cells according to the present invention fall into two major types. One type includes reflective display cells that are designed to be viewed by reflected light only. The other type includes a transmissive display cell that is designed to be viewed again by light transmitted through it.

The configuration of a transmissive display cell is indicated generally at 10 in FIG. Display cell 10 includes a case or similar structure (not shown) that supports a transparent face plate 14 that constitutes the viewing surface or area of the display cell. The rear plate 12 is also transparent (in transmissive cells). Back plate 12 and front plate 14 together with spacers 18 and seals 20 form a chamber 16 containing the electrochromic material, cell electrodes and electrolyte solution therein.

A plurality of transparent electrically conductive display electrodes are preferably disposed on the inner surface of the face plate 14. The display electrodes include character segments 28 or other patterned areas, the number and arrangement of which is determined by the amount and type of information the cell is intended to display. A thin layer 30 of electrochromic metal diphthalocyanine is present in an electrolyte solution 11.
8 is placed on the character segment 28 of the display electrode. A thin layer of metal diphthalocyanine 30 contains the electrochromic material of the display cell. The counter electrode 22 is arranged on a part of the rear plate 12 forming the back surface of the cavity 16 . The cell also includes another reference electrode 24 when an electrostatic potential drive system is used. Typical display cell 1
The configuration of 0 is merely an example. Reference is made to the Nicholson application mentioned above in the discussion of the prior art, the contents of which are incorporated herein by reference for details of the structure of the cell.

The present invention is directed to electrochromic displays that utilize metal diphthalocyanine materials and improved electrolytes that provide improved operation.
Specifically, the electrolyte solution is a highly concentrated aqueous solution of metal chlorides that solidifies well below the freezing point of water. A particularly desirable electrolyte solution is a solution containing 30 weight percent calcium chloride in water. This composition is close to that of a eutectic mixture that freezes at approximately -55°C. As a result, low temperature and fast response time cell operation is achieved. This electrolyte solution was used with a lutetium diphthalocyanine display cell and was successfully operated at approximately -50°C for at least 900 cycles. Multicolor electrochromic switching occurred with excellent color quality in this display cell under these conditions. Furthermore, no visually detectable changes were observed during the switching time. Color transformation in the electrochromic material continued to occur within 50 milliseconds as the solution was cooled from about room temperature to -50°C.

It is proposed that other low melting point electrolytes replace the aqueous potassium chloride solution used in some known display cells. For example, aqueous lithium chloride solutions are also suitable. In this chemistry, the eutectic mixture contains 25 weight percent lithium chloride and has a melting point of approximately -80°C.

In producing electrolyte solutions, the ionized material need not be made from chloride salts, although metal chloride solutions are the lowest melting point systems that are particularly inert and can be used as aqueous electrolytes. However, it should be understood that ternary systems or other types of mixtures containing two or more salts in water may also be used.

Even if these low melting point electrolytes are not available, rare earth metal diphthalocyanine displays (M.
(see U.S. Pat. No. 4,184,751 to M. Nicholson) offer a number of advantages over other electrochromic materials and liquid crystals, such as tungsten oxide or viologen. However, the very low temperature capabilities achieved by the electrolytes described in this application are not achievable by other display technologies.

In the display cell in which the experiment was conducted, a nickel counter electrode is used in the circuit that drives the three electrodes. More suitable counter electrode materials for display cells with two or three electrode drivers in highly concentrated chloride media are electrochromic metals in the form of silver-silver chloride, lead-lead chloride and oxidants and reductants. Contains a solid mixture of dyes. The counter electrode is typically kept away from the field of view to improve maneuverability and visibility. Diphthalocyanine electrochromic counter electrodes are preferred over metal-metal chlorides because diphthalocyanine materials exhibit fast electrode response at low temperatures.

Thus, an electrochromic display cell has been shown and described. This display cell is characterized by a suitable structural shape that is similar to existing cells known in the art.
However, this cell includes new and unique electrochromic material improvements that allow the cell to operate at extremely low temperatures without sacrificing the desirable operating characteristics normally found in electrochromic display cells.