Optical: systems and elements – Optical modulator – Light wave temporal modulation
Reexamination Certificate
2001-03-05
2003-07-29
Ben, Loha (Department: 2873)
Optical: systems and elements
Optical modulator
Light wave temporal modulation
C359S275000, C428S583000, C428S426000, C514S334000, C544S347000, C546S257000
Reexamination Certificate
active
06600589
ABSTRACT:
The present invention relates to a light-stabilized electrochromic device and new electrochromic substances.
Electrochromic devices are already known, for example from D. Theis in Ullmann's Encyclopedia of Industrial Chemistry, Vol. A 8, p. 622, Verlag Chemie 1987 and WO-A 94/23333. A distinction is made between two basic types:
Type 1: full-area electrochromic device.
Type 2: electrochromic display devices having structured electrodes.
Type 1 is employed, for example, in electrically dimmable window panes or electrically dimmable automobile mirrors. Such devices are known, for example, from U.S. Pat. No. 4,902,108.
Type 2 is used in segmented and matrix displays. Such display devices have been proposed, for example, in DE-A 196 31 728. Such devices can be viewed in transmission or reflectively in the case of mirroring.
WO-A 94/23333 compares electrochromic materials of different constructions; however, these are not used as display devices:
Construction a: The electrochromic substances are fixed as a film or layer on the electrodes (Ullmann, see above).
Construction b: The electrochromic substances are deposited as a layer on the electrodes during the redox process (Ullmann, see above).
Construction c: The electrochromic substances remain permanently in solution.
For construction a), the best-known electrochromic material is the paír tungsten oxide/palladium hydride.
For construction b), viologens have been described as electrochromic substances. These devices are not self-extinguishing, so the image generated remains even after switching off the electric power and can only be extinguished again by reversing the polarity. Such devices are not particularly stable and do not allow a large number of switching cycles.
In addition, cells constructed using, in particular, tungsten oxide/palladium hydride cannot be operated using transmitted light because of the light scattering of these electrochromic layers, but can only be operated reflectively.
Elektrokhimiya 13, 32-37 (1977), 13, 404-408, 14, 319-322 (1978), U.S. Pat. Nos. 4,902,108 and 5,140,455 disclose an electrochromic system of this latter construction type c). In an electrochromic cell which is made up of conductively coated glass plates, a solution of a pair of electrochromic substances in an inert solvent is present.
As pair of electrochromic substances, use is made of one electrochemically reversibly reducible substance and one reversibly oxidizable substance. Each is colourless or only slightly coloured in the base state. 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 revert to the base state, with decolouration of lightening of colour occurring.
It is known from U.S. Pat. No. 4,902,108 that suitable pairs of redox substances are those whose 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.
However, according to WO-A 94/23333, such solution systems of construction c) have serious disadvantages.
The diffusion of electrochromic substances in the solution results in diffuse colour boundaries and causes a high power consumption to maintain the coloured state, since the coloured substances are continually being converted back to the uncoloured state by recombination and reaction at the opposite electrode.
Nonetheless, various applications have been described for such electrochromic cells of construction c). For example, they can be configured as automobile rear view mirrors which, during night driving, can be darkened by application of an electrical potential and thus prevent dazzling by the headlights of vehicles behind (U.S. Pat. Nos. 3,280,701, 4,902,108, EP-A 0 435 689). Furthermore, such cells can also be used in windows or automobile sunroofs where they dim the sunlight after application of an electric potential. The use of such devices as electrochromic display devices, for example in segmented or matrix displays having structured electrodes, has likewise been described (DE-A 196 31 728).
The electrochromic cells normally comprise a pair of glass plates of which, in the case of an automobile mirror, one is mirrored. One side of these plates is coated with a light-transparent, electrically conductive layer, for example indium-tin oxide (ITO) where, in the case of display devices, this conductive coating is divided into electrically separate segments which are individually provided with contacts. A cell is built up from these plates by joining them via a sealing ring with their electrically conductive sides facing one another to form a cell. An electrochromic liquid is then introduced into the cell via an opening and the cell is tightly sealed. The two plates are connected to a power source via the ITO layers.
The above-described electrochromic devices are generally sensitive to light, in particular UV light. For this reason, U.S. Pat. No. 5,280,380, for example, describes electrochromic devices containing UV absorbers. Electrochromic automobile mirrors which contain such absorbers in an antisplinter coating have also been described (U.S. Pat. No. 5,073,012).
The UV protection known from the prior art effects an improvement in the light stability of the electrochromic devices in the unswitched, zero-current state. This is sufficient for use in automobile rear view mirrors since they are always unswitched during the day when the light is strong and are only switched, i.e. darkened, at night when there is little light.
For other applications of electrochromic devices, for example windows or display devices, this protection is not sufficient since it is precisely when the light is strong that they are switched.
It is an object of the present invention to improve the light stability of electrochromic devices in the switched state.
It has now surprisingly been found that protection of the electrochromic device in the wavelength region from 350 to 450 nm by means of a yellow filter considerably improves its light stability in the switched-on state.
The invention accordingly provides a light-stabilized electrochromic 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, are provided on one side each with an electrically conductive coating, where at least one plate or film and its conductive coating is transparent, where the other can be mirrored and where the electrically conductive layer of at least one of the two plates or films can be divided into separate, individually contacted area segments, where the plates or films are joined via a sealing ring on the sides of their conductive coating and the volume formed by the two plates or films and the sealing ring is filled with an electrochromic medium, characterized in that the electrochromic device contains a yellow filter for which the wavelength at which the absorbance in the long-wavelength flank reaches half of the longest-wavelength maximum absorbance is in the range from 370 to 500 nm, preferably from 380 to 470 nm.
Particularly preferably, the wavelength at which the absorbance in the long-wavelength flank reaches half of the longest-wavelength maximum absorbance is in the range from 380 to 450 nm, very particularly preferably from 390 to 430 nm.
The absorption maximum is preferably in the range from 355 to 430 nm, particularly preferably from 360 to 410 nm, very particularly preferably from 370 to 405 nm. Very particular preference is given to substances and materials for which the width at half height of the absorption band, i.e. the width of the band at half its maximum absorbance, is less than 100 nm, in particular less than 80 nm, very particularly preferably less than 60 nm. The long-wavelength fall-off of the absorption band is preferably steeper than that on the short-wavelength side.
Preference is likewise given to materials which additionally filter out wavelengths below 350 nm. They then hav
Berneth Horst
Michaelis Stephan
Neigl Ralf
Womelsdorf Hermann Jens
Akorli Godfried R.
Bayer Aktiengesellschaft
Ben Loha
Eyl Diderico van
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