Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2002-04-08
2004-02-24
Chowdhury, Tarifur R. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S115000, C349S176000
Reexamination Certificate
active
06697133
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates generally to reflective polarizing films where the reflectivity may be varied by impressing an electric field across the film. Such films may be used to great advantage in electro-optical glazing structures having reflection, semi-transparent, and/or transparent modes of operation which are electrically-switchable for use in dynamically controlling electromagnetic radiation flow in diverse applications. In particular, the present invention relates to reflective polarizing films where the bandwidth of the reflectivity may be controlled by impressing an electric field across the film.
2. Brief Description of the Literature
Broadband reflecting polarizers were introduced in copending application Ser. No. 08/550,022 (now U.S. Pat. No. 5,691,789) entitled “Single Layer Reflective Super Broadband Circular Polarizer and Method of Fabrication Therefor” by Sadeg M. Faris and Le Li which was filed Oct. 30, 1995. Such broadband polarizers are made by producing a single layer having cholesteric liquid crystal order where the pitch of the liquid crystal order varies in a non linear fashion across the layer. A narrow band, switchable polarizing single layer reflector is disclosed in European patent application 0 643 121 A, published Mar. 15, 1995. A switchable polarizing single layer reflector having a broader bandwidth is disclosed in PCT application WO97/2358, published Jul. 3, 1997. General references on polymer dispersed liquid crystals may be found in detail in “Polymer Dispersed Liquid crystal displays”, by J. W. Doane, a chapter in “Liquid Crystals”, Ed. B. Bahadur, World Scientific Publishing, Singapore, and “CLC/polymer dispersion for haze-free light shutters, by D. Yang et al. Appl. Phys. Lett. 60, 3102 (1992). Smart Window Design is treated in “Electrochromism and smart window design”, by C. Granqvist, Solid State Ionics 53-56 (1992) and “large scale electochromic devices for smart windows and absorbers”, by T. Meisel and R. Baraun, SPIE 1728, 200 (1992). The above identified US patents and other references are hereby incorporated by reference.
OBJECTS OF THE PRESENT INVENTION
It is an object of the invention to provide a reflective polarizing film having a bandwidth which is controllable by an electric field.
It is an object of the invention to provide a “smart window” using a polarizing reflective film having a very wide bandwidth which is controllable by an electric field.
SUMMARY OF THE PRESENT INVENTION
The present invention provides a single layer polarizing reflective film comprising a crosslinked polymer matrix mixed with low molecular weight liquid crystal molecules. The low molecular weight liquid crystal molecules are oriented with respect to the surface of the film and to each other in cholesteric order. The ratio of the amount of liquid crystal molecules to the amount of cross-linked polymer is chosen so that the liquid crystal molecules may move reversibly in an electric field. The movement of the low molecular weight molecules perturbs the cholesteric liquid crystalline order responsible for the reflectivity of the polarized light. If the composition of the film is uniform, the polarized reflectivity of the film has a very narrow bandwidth when there is no electric field impressed in the film. As the electric field is increased, the bandwidth of the polarized reflectivity increases. There is sufficient high molecular weight cross linked polymer material to ensure that the film is not liquid, and to ensure that the low molecular weight material does not diffuse after manufacture of the film, and to ensure that the low molecular weight material returns to the cholesteric liquid crystal ordered state when the field is removed.
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A Single-Layer Super Broadband Reflective Polarizer by Lee Li, et al., SID 96 Digest, vol. XXXVII, May 17, 1996, P. 111-113.
Fan Bunsen
Faris Sadeg
Li Jian-feng
Li Le
Chowdhury Tarifur R.
Crispino Esq. Ralph J.
Hodgson Rodney T.
Reveo Inc.
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