Optical: systems and elements – Optical modulator – Light wave temporal modulation
Reexamination Certificate
2001-03-26
2003-10-07
Dang, Hung Xuan (Department: 2873)
Optical: systems and elements
Optical modulator
Light wave temporal modulation
C359S267000, C359S900000, C204S192220
Reexamination Certificate
active
06631023
ABSTRACT:
The invention relates to an electrochromic display device having display segments which are individually connected to a power source and whose electric leads are insulated from the electrochromic medium. The invention also relates to a method of producing such a display device.
Electrochromic devices containing an electrochromic system are already known. Electrochromic systems alter their spectral absorption under the action of an electric field.
In WO-A 94/23333, electrochromic materials of different constructions are compared but are not used as display devices:
Construction a: The electrochromic substances are present in solid form as a film or layer on the electrodes (cf. D. Theis in Ullmann's Encyclopedia of Industrial Chemistry, Vol. A8, p. 622, Verlag Chemie 1987)
Construction b: The electrochromic substances are deposited on the electrodes as a layer during the redox process (cf. Ullmann, see above).
Construction c: The electrochromic substances remain permanently in solution.
For construction a), the pair tungsten oxide/palladium hydride is the best known electrochromic material.
For construction b), viologens have been described as electrochromic substances. These devices are not self-extinguishing, so the image produced remains after the electric potential has been switched off and can be extinguished again only by reversing the polarity. Such devices are not particularly stable and do not allow a large number of switching cycles.
In addition, particularly cells based on tungsten oxide/palladium hydride cannot be operated in transmitted light because of light scattering from these electrochromic layers, but can only be operated using reflected light.
Elektrokhimiya, 13, 32-37 (1977), 13, 404-408, 14, 319-322 (1978), U.S. Pat. No. 4,902,108 and U.S. Pat. No. 5,140,455 disclose an electrochromic system having the last-named construction c). An electrochromic cell which is built up of glass plates having a conductive coating contains a solution of a pair of electrochromic substances in an inert solvent.
The pair of electrochromic substances used comprises one electrochemically reversibly reducible substance and one reversibly oxidizable substance. In their ground state, both are colourless or only slightly coloured. Under the action of an electric potential, one substance is reduced and the other is oxidized, with both becoming coloured. After switching off the potential both substances return to the ground state, resulting in decolouration or lightening of the colour.
It is known from U.S. Pat. No. 4,902,108 that pairs of redox substances in which the reducible substance has at least two chemically reversible reduction waves in the cyclic voltammogram and the oxidizable substance correspondingly has at least two chemically reversible oxidation waves are suitable.
However, according to WO-A 94/23333, such solution systems of construction c) have serious disadvantages.
The diffusion of the electrochromic substances in the solution results in fuzzy colour boundaries and causes high power consumption for maintaining the coloured state, since the coloured substances are permanently being removed by recombination and reaction at the respective opposite electrode.
Nevertheless, various applications have been described for such electrochromic cells of the construction c). Thus, for example, they can be configured as an automobile rearview mirror which can be dimmed during night driving by application of a voltage and thus prevents dazzling by headlights of following vehicles (cf., for example, U.S. Pat. No. 3,280,701, U.S. Pat. No. 4,902,108, EP-A 0 435 689). Furthermore, such cells can also be used in window panes or automobile sunroofs where they dim sunlight after application of a voltage. The use of such devices as electrochromic display devices, for example in segmented or matrix displays with structured electrodes, has likewise been described (DE 196 31 728).
Electrochromic devices comprise a pair of glass or plastic plates which are each provided on one side with an electrically conductive coating, e.g. indium-tin oxide (ITO). At least one of these plates is transparent. In the case of an automobile mirror, one of the plates is mirrored. A cell is constructed from these plates by joining them, preferably adhesively bonding them, by means of a circular or rectangular sealing ring with their conductively coated sides facing one another. The sealing ring establishes a uniform spacing between the plates of, for example, from 0.01 to 0.5 mm. This cell is filled with an electrochromic medium. The two plates can be separately connected to a power source via the electrically conductive layers.
In electrochromic display devices, at least one of the two electrically conductive layers is divided into segments which are individually connected to a power source and are electrically insulated from one another. These segments are provided with power via electric leads which each lead to an edge of the respective plate and are there connected to a power source by means of, for example, clips, soldered points, conductive paint or other electrically conductive connections.
During operation of the electrochromic device, an electric potential between the conductively coated plates is applied to selected segments, so that the desired information is displayed by colouration of the electrochromic medium. However, the potential is likewise present at the power leads, as a result of which an electrochromic reaction also takes place along these and the leads likewise become coloured. This is undesirable since the image defined by the segments is considerably disrupted thereby.
It was an object of the invention to produce an electrochromic display device having segments which are individually connected to a power source, in which device the power leads to the segments to which a potential is being applied do not cause a colour reaction.
The object of the invention is achieved by an electrochromic display device comprising a pair of glass or plastic plates or plastic films of which at least one plate or film, preferably both plates or films, is/are provided on one side each with an electrically conductive coating and of which at least one plate or film and its conductive coating is transparent and of which the other can be mirrored and in which the electrically conductive layer of at least one of the two plates or films is divided into separate segments which are individually connected to a power source and each has an electric lead from one edge of the respective plate or film, where the plates or films are joined via a sealing ring on the sides on which they are conductively coated and the volume formed by the two plates or films and the sealing ring is filled with an electrochromic medium, characterized in that the electric leads to the segments are electrically insulated from the electrochromic medium. Due to different demands upon the electrochromic display device the division into seperate segments can be carried out differently. If only one sign or symbol shall be displayed, only one segment is prepared. Alternatively several segments can be prepared. The shape and number of the said several segments can be chosen, so that with the combination of these segments all kinds of signs like letters, figures, symbols, words, numbers and combinations thereof can be displayed. The shape of a single segment can be that of the sign itself or that of a rectangle, square, multiangle, circle, oval and/or other geometric object or combinations thereof.
The insulation can be achieved, for example, by the electric leads to the areas being coated with an electrically insulating layer. Preferably said electrically insulating layer is transparent.
As electrically conductive coatings on the glass plates or plastic plates or plastic films from which the electrochromic display device is constructed, it is in principle possible to use any electrically conductive materials. However, a transparent plate or film has to have a conductive coating which is itself transparent. Suitable, preferably transparent, ma
Berneth Horst
Claussen Uwe
Haarer Dietrich
Jacobsen Wolfgang
Neigl Ralf
Dang Hung Xuan
Tra Tuyen
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