Liquid crystal cells – elements and systems – Liquid crystal system – Liquid crystal window
Reexamination Certificate
1999-06-09
2002-11-26
Ton, Toan (Department: 2871)
Liquid crystal cells, elements and systems
Liquid crystal system
Liquid crystal window
C349S122000, C349S165000
Reexamination Certificate
active
06486928
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to electrically controllable systems having variable optical properties, and more specifically to glazing units in which the light scattering and/or the light transmission can be modified due to the effect of a suitable electrical supply.
2. Discussion of the Background
There is in fact a growing demand for so-called “smart” glazing, certain properties of which can be modulated as required. Controlling or modifying the level of light scattering of glazing thus allows the degree of visibility through the glazing to be controlled, especially so that it is transparent or, on the contrary, scattering, thus preventing individuals or objects on the other side of the glazing from being identified. There are various applications for such glazing: it is thus possible to consider equipping the internal partitions between rooms in a building, especially in offices, or between two areas/compartments of means of land, air or maritime locomotion with such glazing, or for equipping shop windows or display cabinets, or any type of container. In general, such glazing can also be used for equipping any window in a building or in means of locomotion (windows on trains, cabin portholes on boats or cabin windows on aircraft).
At the present time there are various families of functional systems having electrically controllable light scattering/transmission (hereafter referred to as “functional systems”).
A first family of functional systems is known by the term liquid-crystal glazing. This is based on the use of a film based on a polymer material and placed between two conducting layers, droplets of liquid crystals, especially nematic liquid crystals having positive dielectric anisotropy, being dispersed in the said material. When a voltage is applied to the film, the liquid crystals orient in a preferred direction, thereby allowing vision. With no voltage applied, the crystals not being aligned, the film becomes diffusing and prevents vision. Examples of such films are described especially in European Patent EP 0,238,164 and U.S. Pat. Nos. 4,435,047, 4,806,922 and 4,732,456. This type of film, once laminated and incorporated between two glass substrates, is sold by Saint-Gobain Vitrage under the brand name “Priva-Lite” in fact, it is possible to use any device based on liquid crystals known as “NCAP” (Nematic Curvilinearly Aligned Phase) or “PLDC” (Polymer Dispersed Liquid Crystal) crystals.
Another family is that commonly referred to by the term optical valve: this generally involves films comprising a polymer matrix, optionally crosslinked, in which microdroplets are dispersed, these microdroplets containing particles which have the property of moving in a preferred direction under the action of an electric or magnetic field. Depending in particular on the potential applied to the terminals of the conducting layers placed on either side of these films and on the concentration and nature of the orientable particles, the films have variable optical properties. For example, Patent WO 93/09460 discloses an optical valve based on a film comprising a crosslinkable polyorganosiloxane matrix 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 a voltage is not applied: this system therefore makes it possible to obtain glazing with variable light transmission, generally associated with light scattering that can also be varied.
Whether optical valves or liquid-crystal systems are used, these systems are usually in the form of a polymer film. To supply it with electrical power, it is usually placed between two electrically conducting layers, which in particular are transparent, for example made of doped metal oxide of the tin-doped indium oxide (ITO) type or the fluorine-doped tin oxide (F:SnO
2
) type. Furthermore, the film with its two conducting layers is usually provided on at least one of its sides, and thus each of its sides, with a carrier/protector substrate. This is generally transparent. It may be chosen so as to be rigid or semi-rigid and made of inorganic or organic material, for example made of glass, or an acrylic polymer of the polymethyl methacrylate (PMMA) type. It may also be flexible, especially made of polyethylene terephthalate PET it is thus possible to have a structure of the PET/ITO/functional film/ITO/PET type, which is in the form of a flexible sheet that can be easily handled. This assembly (polymer+electrically conducting layers+at least one carrier substrate) can then be laminated to at least one transparent rigid substrate of the glass type using at least one joining layer of organic polymer of the polyvinyl butyral PVB or ethylene-vinyl acetate EVA type or certain polyurethanes PU.
Attempts have been made to add other functionalities to liquid-crystal glazing, especially in order to be able to vary not only its level of light scattering but also its level of light transmission, by making use of dyes. Patents EP 0,156,615 and EP 0,121,415 thus describe, for example, dyes of the pleochroic type, which are dissolved in the liquid crystal droplets, thereby making it possible to obtain glazing which is both dark/colored and diffusing when no voltage is applied, and both clear and non-diffusing when voltage is applied. Thus, a “screen” effect can be obtained, making the use of such glazing more attractive in the case of outside applications, for example as glazing for building facades or as car sunroofs.
However, these outdoor applications subject the glazing to considerable stress, and it has turned out that the functional systems with additional dyes (such as liquid-crystal glazing) or functional systems having polarizing particles which themselves provide a dye effect, especially by being of the dichroic type, have tended to have a markedly shorter lifetime than those which were devoid thereof, this being even more striking when they were used on the outside.
The object of the invention was therefore to remedy this drawback, by improving functional systems having electrically controllable light scattering/transmission, most particularly those using dichroic dyes or polarizing particles with a dye effect, the improvement being aimed especially at increasing their lifetime and increasing their durability.
SUMMARY OF THE INVENTION
The subject of the invention is firstly an electrically controllable system having variable light scattering/transmission, which comprises a functional film provided with electrically conducting layers. This film has so-called “active” elements either in the form of particles, in particular polarizing particles (optical-valve system) or in the form of liquid crystals (liquid-crystal system) which are associated with dichroic dyes, and in suspension in a medium. The invention also provides the system with one or more means for preventing/compensating for degradation by photoreduction of at least some of the active elements, especially that of the dichroic dyes (in the case of liquid-crystal systems) or of the polarizing particles themselves (in the case of optical-valve systems).
This is because the invention has discovered the mechanism which caused the systems to age prematurely, this being a photoreduction mechanism which tended to irreversibly degrade the dichroic dyes and the polarizing particles when the systems were subjected to intense and/or prolonged ultraviolet radiation. The solution therefore consisted in using means for combating this degradation, these means being aimed either at preventing this photoreduction or, preferably, at allowing the dyes, in reduced/degraded form, to be as it were “regenerated” by permanently re-oxidizing them, thus “compensating” for the photochemical reduction that they undergo.
According to a first variant, the means preventing degradation by photoreduction comprises the use of at least one of the two electrically conducting layers in the form of a multicomponen
Lin Xue Yun
Papret Corinne
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Saint-Gobian Glass France
Schechter Andrew
Ton Toan
LandOfFree
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