Stock material or miscellaneous articles – All metal or with adjacent metals – Intermediate article
Reexamination Certificate
1999-03-31
2001-03-27
Lorin, Francis J. (Department: 1775)
Stock material or miscellaneous articles
All metal or with adjacent metals
Intermediate article
C359S265000, C252S301350
Reexamination Certificate
active
06207292
ABSTRACT:
The present invention relates to an electrochromic display device.
Electrochromic display devices have been disclosed previously, for example by D. Theis in UIllmann's Encyclopedia of Industrial Chemistry, Vol. A 8, p. 622, Verlag Chemie 1987. Such display devices comprise a pair of glass panes which, on the side facing one another, are coated with a transparent, conductive layer. As a rule, the electrochromic substances are permanently bound to said conductive layer or are deposited thereon during operation. Among electrochromic substances, the couple tungsten oxide/palladium hydride is the best-known. Viologens have also been proposed. These display devices are not self-erasing, i.e. the generated image persists after the current has been switched off and can only be erased again by voltage reversal. Such devices are not particularly stable and do not allow a large number of switching cycles. Moreover, cells built from tungsten oxide/palladium hydride in particular cannot, because of light scattering on these electrochromic layers, be operated in transmitted light, but only reflectively.
WO-94/23333 compares variously constructed electrochromic cells, which are not used as display devices, however:
a) cells in which the electrochromic substances, in the form of a film or layer, permanently lie on the electrodes (cf. Ullmann, see above),
b) cells in which the electrochromic substances are deposited on the electrodes as a layer during the redox process (cf. Ullmann, see above),
c) cells in which the electrochromic substances remain permanently in solution.
With the latter type, two serious drawbacks are emphasized, inter alia:
1) the diffusion of electrochromic substances in the solution,
2) the high current consumption to maintain the color, since said color, owing to diffusion, is decaying all the time by recombination and reaction at the opposite electrode.
U.S. Pat. No. 4,902,108 discloses an electrochromic system of said last-mentioned type c). An electrochromic cell likewise comprising glass plates having conductive coatings contains a solution of a couple of electrochromic substances in an inert solvent.
Used as a redox couple is one reducible and one oxidizable substance. Both are colorless or only weakly colored. Under the influence of an electric voltage, one of the substances is reduced and the other is oxidized, at least one becoming colored in the process. After the voltage is switched off, the two original redox substances are formed once more, accompanied by bleaching or fading of the color.
U.S. Pat. No. 4,902,108 discloses that those redox couples are suitable in which the reducible substance exhibits at least two chemically reversible reduction waves in the cyclic voltammogram and the oxidizable substance correspondingly exhibits at least two chemically reversible oxidation waves.
Various applications have been described for such electrochromic cells. For example, they may take the form of a car rear view mirror which during a journey at night can be darkened by a voltage being applied and thus prevents dazzling by the headlights of vehicles following behind (compare e.g. U.S. Pat. No. 3,280,701, U.S. Pat. No. 4,902,108, EP-A-0,435,689). Such cells may further also be employed in window panes or car canopies where, after a voltage has been applied, they black out the sunlight.
Such electrochromic cells normally comprise a pair of glass panes, one of which is mirrored in the case of the car mirror. One side of these panes is coated areally with a transparent, electroconductive layer, e.g. indium tin oxide (ITO). These panes are then used to construct a cell by being joined together, via a sealing ring, with their electroconductively coated sides facing one another, to form a cell. This cell is then, via a port, filled with an electrochromic fluid and is tightly sealed. Via the ITO layers the two panes are connected to a voltage source.
Electrochromic cells of the type just outlined have been described exclusively for constructing components which can be colored over their entire area, such as the car mirrors, window panes or car canopies just mentioned. Such components which could be colored over their entire area were also used as a basis for deriving electrochromic displays of a very simple design, in which a two-dimensional electrochromic cell was either covered with an opaque plate from which the symbols to be represented had been cut out or in which the symbols made of opaque material were applied to the two-dimensional electrochromic cell. In both cases the symbols became visible when the cell was de-energized and thus bright, and invisible when the cell was live and therefore dark. Edge definition problems owing to diffusion are thus reliably prevented or do not play a significant role. The edge definition is provided by the masks.
From what was known, in particular on the basis of the drawbacks mentioned in WO-94/23333 it was reasonable to apprehend that electrochromic display devices in which information can be represented variably, e.g. via individually driven segments, bars or points, on the basis of the design just described of U.S. Pat. No. 4,902,108 would not be possible. In particular it seemed likely that the edge definition of the segments to be displayed would be unsatisfactorily poor, since the electrochromic substances are freely mobile in the electrochromic fluid and therefore, in particular in the event of prolonged operation, because of diffusion would color even those areas of the display device which are not actually energized.
The invention then relates to an electrochromic display device comprising at least two transparent substrates, preferably panes of glass or plastic, which are joined to one another via a spacer ring and of which at least one has an electrically conductive, transparent coating on the side facing the other and one of the substrates may be mirrored, wherein at least one of the substrates having a conductive coating is subdivided into segments which are electrically separated from one another and can be contacted singly, and there is contained, between the substrates,
a) a solvent,
b) dissolved in this solvent at least one oxidizable substance RED
1
which, by releasing electrons at an anode, is converted into its respective form OX
1
with a change in absorbance in the visible region of the spectrum, and at least one reducible substance OX
2
which by accepting electrons at a cathode, is converted into its respective form RED
2
with a change in absorbance in the visible region of the spectrum, the original forms RED
1
and OX
2
each being recovered after charge equalization,
c) optionally a conductive salt.
The change in absorbance in the visible region of the spectrum may refer to
a) OX
2
and/or RED
1
being colorless or only weakly colored, whereas the forms RED
2
and/or OX
1
formed at the cathode and anode, respectively, are colored, preferably strongly colored,
b) at least one of the two electrochromic substances OX
2
or RED
1
being colored, while their forms RED
2
or OX
1
respectively, formed at the cathode or anode, respectively, are not colored or only weakly colored or have a different color.
These special embodiments under a) and b) likewise form part of the subject matter of the invention.
Involved in particular are single-cell display devices in which the cathode compartment and anode compartment are not separated from one another by, for example, ion-permeable membranes or the like.
The subdivision of the plates having conductive coatings into segments electrically separated from one another can be effected in various ways:
a) by direct driving, where:
aa) only one of the two plates is subdivided into segments, whereas the other plate is not patterned, i.e. its entire area have a conductive coating,
ab) both plates are subdivided into segments, or
ac) only one of the two plates has a conductive coating and is subdivided into segments, whereas the other one does not have a conductive coating, or
b) multiplexed driving, in which the segments are combined into groups of which each has a dif
Berneth Horst
Claussen Uwe
Haarer Dietrich
Schaller Jochen
Bayer Aktiengesellschaft
Foley & Lardner
Lorin Francis J.
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