Liquid crystal cells – elements and systems – Liquid crystal optical element – Antidazzle mirror formed from liquid crystal cell
Reexamination Certificate
2000-03-24
2002-10-15
Lester, Evelyn A (Department: 2873)
Liquid crystal cells, elements and systems
Liquid crystal optical element
Antidazzle mirror formed from liquid crystal cell
C349S016000, C359S265000, C359S267000, C359S241000
Reexamination Certificate
active
06466298
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to glazings with variable optical/energetic properties. It relates more precisely to glazings whose characteristics can be modified, for example, under the effect of an electrical supply, for example, light diffusion or the transmission within some wavelengths of the electromagnetic spectrum, especially in the infrared and/or in the visible, or under the effect of a particular radiation.
2. Discussion of the Background
An increasingly growing demand exists for so-called “intelligent” glazings, or glazings whose properties can be modulated at will, in order to take various changing parameters into account. It is highly advantageous to be able to control the input of sunlight through glazings fitted externally in buildings, motor vehicles, or trains, in order to avoid excessive heating of the rooms or compartments in the event of strong sunshine. Similarly, it may be useful to control the degree of vision through glazings, for example in the case of glazings employed as internal partitions between two rooms, in a building, or between two compartments in a train or an aircraft. Many other applications also exist for such glazings: for example, rearview mirrors in vehicles which, by becoming darker when required, can prevent dazzling of the driver, or road or urban sign panels displaying mileages or designs only intermittently in order to attract attention better.
The interest in such glazings accounts for the fact that many such systems have already been studied.
One of the known systems that make it possible to modulate the light transmission or absorption of glazings are especially the so-called viologen systems like those described in U.S. Pat. No. 5,239,406 or in Patent EP-A-0 612 826. The latter makes it possible to obtain a variable absorption essentially in the visible range.
For the same purpose there are also the so-called electrochromic systems, which include a layer of an electrochromic material capable of reversibly and simultaneously inserting cations and electrons, and whose oxidation states corresponding to the inserted and disinserted states have different colors, one of the states exhibiting a higher light transmission than the other. The insertion or disinsertion reaction in driven by a suitable electric supply with the aid of a current generator or a voltage generator. The electrochromic material, usually tungsten oxide-based, is placed in contact with a source of electrons, such as a transparent electrically conductive layer, and a source of cations, such as an ionically conductive electrolyte.
To ensure at least about a hundred switchings, the layer of electrochromic material must be combined with a counterelectrode, itself also capable of reversibly inserting cations, symmetrically in relation to the layer of electro-chromic material, so that, macroscopically, the electrolyte appears to be a simple medium for the cations.
The counterelectrode must consist of a layer which is either neutral in color, transparent, or weakly colored when the electrochromic layer is in the faded state. Since tungsten oxide is a cathodic electrochromic material, that is to say its colored state corresponds to the most reduced state, an anodic electrochromic material such as nickel oxide or iridium oxide is generally employed for the counterelectrode. It has also been proposed to employ a material which is optically neutral in the oxidation states involved, such as, for example, curium oxide, or organic materials like electronically conductive polymers (polyaniline, etc.) or Prussian blue.
The description of such systems will be found, for example, in European Patents EP-0 338 876, EP-0 408 427, EP-0 575 207 and EP-0 628 849.
At present these systems can be classified into two categories, according to the electrolyte type employed:
1. either the electrolyte is in the form of a polymer or of a gel, for example a proton-conducting polymer like those described in European Patents EP-0 253 713 and EP-0 670346 or a polymer conducting lithium ions, such as those described in Patents EP-0 382 623, EP-0 518 754 and EP-0 532 408; or
2. the electrolyte is an inorganic layer, ionically conductive but electronically insulating; “all-solid” electrochromic systems is the term which is then employed. For the description of an “all-solid” electrochromic system reference may be made to French Patent Application FR-96/03799 filed on Mar. 27, 1996.
These systems containing reversible-insertion material(s) are particularly advantageous in the sense that they allow the absorption to be modulated in a wider range of wavelengths than the viologen systems; they can absorb in a variable manner not only in the visible but also in the infrared, and this enables them to assume an efficacious optical and/or thermal function.
The viologenic or electrochromic systems deposited or combined with transparent substrates form glazings whose light absorption and transmission (as well as the energy transmission) can vary within given ranges. The ranges are typically determined by the choice of the electrochromic materials employed and/or their thickness.
Another type of “intelligent” glazing includes what is referred to by the term of optical valve: this is a film including a matrix of generally crosslinked polymer(s) in which are dispersed microdroplets containing particles which can orient in a preferred direction under the action of an electric or magnetic field.
The above film exhibits variable optical properties as a function of the electrical potential applied to the terminals of the conductive layers placed on both sides of the film and of the concentration and the nature of the orientable particles.
Thus, Patent WO-93/09460 discloses an optical valve based on a film including a matrix made of crosslinkable polyorganosilane and inorganic or organic orientable particles, more particularly light-absorbing particles such as polyiodide particles. When a voltage is applied to the film, the particles intercept the light much less than when there is no voltage.
A glazing which operates on a similar principle is also known under the term of liquid-crystal glazing. It is based on the use of a film placed between two conductive layers and based on a polymeric material in which are dispersed droplets of liquid crystals, especially nematic with positive dielectric anisotropy. When a voltage is applied to the film the liquid crystals orient themselves along a preferred axis, and this permits vision. With no voltage, in the absence of alignment of the crystals, the film becomes diffusing and prevents vision.
Examples of such films are described in European Patent EP-0 238 164 and U.S. Patents U.S. Pat. No. 4,435,047, U.S. Pat. No. 4.806,922 and U.S. Pat. No. 4,732,456. Films of this type, once laminated and incorporated between two glass substrates, are marketed by Saint-Gobain Vitrage under the trade name “Priva-lite”.
All the liquid-crystal devices known under the terms of “NCAP” (Nematic Curvilinearly Aligned Phases) or “PDLC” (Polymer Dispersed Liquid Crystal) can in fact be employed.
It is also possible to employ, for example, gels based on cholesteric liquid crystals containing a small quantity of crosslinked polymer, like those described in Patent WO-92/19695.
So-called photochromic glazings also exist in which the property of absorption in the visible and possibly in at least a portion of the infrared can be modulated under the effect of energetic radiation, generally situated in the ultraviolet. There are mainly two classes of these; the first employs silver salts, especially silver halides, as the active components, for example, in a glassy matrix, halides which by absorption in the ultraviolet are converted reversibly into a form of metal aggregates. The second class employs as the active components organic dyes that are generally dispersed in a polymer matrix, especially compounds derived from spiroxazines and spiropyrans. These compounds are isomerized reversibly by absorption in the ultraviolet.
However, all of the above glazin
Fix Renaud
Guiselin Olivier
Lin Xue Yun
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