Liquid crystal cells – elements and systems – Particular structure – Having significant detail of cell structure only
Reexamination Certificate
2000-05-16
2003-12-16
Kim, Robert H. (Department: 2871)
Liquid crystal cells, elements and systems
Particular structure
Having significant detail of cell structure only
C349S086000, C359S253000, C359S259000
Reexamination Certificate
active
06665042
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to electrically switchable particle devices employing a system of flakes or platelets of either polymer liquid crystals (PLC) or birefringent polymers (BP) suspended in a fluid host medium. The devices in accordance with the invention are useful in information display, optics, and photonics, including but not limited to, reflective or transmissive information displays capable of color switching and as flexible media for information display applications on either flat or curved surfaces (e.g. large-area signs, automobile dashboards, heads-up displays, and “electronic paper”. The invention also provides improved switchable and tunable devices for color manipulation (i.e. switchable or tunable color filters), switchable and tunable optical retardation or modulation elements for polarized light at desired wavelengths or bandwidth, switchable micropolarizers, switchable “smart windows” for either energy or privacy control, switchable conformal coatings for use in decorative applications, and switchable coatings for applications in military security, camouflage, substrate reflectance control, document security, anti-counterfeiting, and object tagging and identification.
BACKGROUND
Considerable research effort has been focused on technologies for information display such as liquid crystal devices, field-emissive devices, plasma devices, and most recently, particle-based image displays. Particle-based displays, initially investigated over 30-40 years ago, rely on the motion of particles suspended in a fluid host medium. The particles respond to an applied electric or magnetic field to produce either a change in reflectivity or color of incident reflected light or to modulate or change the polarization state of transmitted light. Such effects are induced by either translation or rotation of the suspended particles and are based on physical phenomenon such as magnetic polarization, electrophoresis, dielectric polarization or other forms of current-induced effects. C. R. Tate, U.S. Pat. No. 3,406,363 issued Oct. 15, 1968 describes multicolored “micromagnets” of varying magnetic strength made of materials such as barium ferrite, in a liquid suspending medium, and the manipulation thereof by an external magnetic force to produce color displays. W. E. Haas et al, U.S. Pat. No. 4,076,387, issued Feb. 28, 1978 describes metal flakes, such as aluminum, of <325 mesh size (~45 &mgr;m) dispersed in either a water-based or a hydrocarbon-based ferrofluid to construct a reflective display device switched by an electromagnet for use in ambient lighting conditions. In addition, I. Ota, U.S. Pat. No. 3,668,106, issued Jun. 6, 1972, describes an electrophoretic display or recording device based on charged particles manipulated by an electric field that altered the device reflectivity.
C. W. Jacob, U.S. Pat. No. 3,967,265, issued Jun. 29, 1976, describes a light gating display consisting of small conductive particles (aluminum or graphite) dispersed in a continuously circulated dielectric fluid. The device of the Jacob patent is addressed indirectly using an electric field generated by selective illumination of an integral photoconductor, and functions as an image relay or image converter, whether in reflection or transmission. Jacobs mentions that the particle dispersion can be replaced by a pure, particle-free liquid crystal fluid host to produce a device that functions in a similar manner.
U.S. Pat. No. 5,650,872, issued to R. L. Saxe et al. on Jul. 22, 1997, describes a “Suspended Particle Device” (SPD) that relies on sub-micron, anisometric, light-polarizing particles dispersed in a host medium for its function. Application of an electric field causes the particles to reorient. Two-color switching is possible, but very large cell path lengths (125-825 &mgr;m) and high drive voltages (>2000V) are required, and the contrast difference between on and off states is low.
More recently, particle-based devices employing microencapsulation techniques have come to the forefront due to great interest in their use as new forms of flexible, re-writeable, re-usable electronic storage media that could take the place of newspapers or other printed material. Such paper-like information storage media that could be updated electronically from the Internet or other source of stored information is projected to have a large economic impact due to the wide scope of potential applications and market areas that such a device could address. These devices consist of a particle/fluid host dispersion that itself is microencapsulated in a polymeric, film-forming binder material to form a flexible, electrically-addressable sheet with bistable switching characteristics that can retain text and graphics images for prolonged periods of time.
In this connection, N. K. Sheridon et al. in U.S. Pat. Nos. 4,143,103, 4,126,854, 5,344,594, 5,389,945, 5,708,525, 5,739,801, 5,751,268, 5,760,761, 5,767,826, J. M. Crowley in U.S. Pat. Nos. 5,754,332 and 5,825,529, D. K. Biegelsen et al. in U.S. Pat. No. 5,717,283 and J. D. Mackinlay et al. in U.S. Pat. No. 5,737,115, describe various forms of a “Gyricon” device consisting of 50-500 &mgr;m “bi-chromal” glass or polymeric spheres contained within fluid-filled cavities that are themselves encapsulated in a flexible polymer matrix. Each sphere is formed such that its opposing hemispheres are of different colors, and can be made to rotate from 90-180° in the presence of an electrical field applied across the film because the two hemispheres bear opposing surface charges. Drive voltages increase with increasing diameter of the rotating spheres and the cavities containing them, and produce bistable switching. The Gyricon device functions in reflective mode.
Another microencapsulated particle display technology is E-Ink™, described in U.S. Pat. No. 5,961,804 issued to J. Jacobson et al. and by J. D. Albert et al, U.S. Pat. No. 6,017,584. This technology is based on an encapsulated “electrophoretic dispersion” of negatively and positively charged microparticles (<1 &mgr;m in diameter) in an isotropic, dielectric host fluid that in turn is encapsulated in a polymer binder. According to Jacobsen and Albert, microencapsulation of the electrophoretic dispersion is an essential element for avoiding the particle agglomeration and sedimentation that commonly occurs in conventional electrophoretic displays. Unlike the Gyricon device, the E-Ink device functions by translation of particles towards the top or bottom of the microcapsule, depending on the sign of the applied voltage. The particles are generally composed of inorganic or metallic particles that are coated with a polymeric coating. Other pigments, metallic flakes or retroreflectors are added to the electrophoretic dispersions either to produce switching between colors or to producing changes in reflectivity, respectively. A nematic liquid crystal fluid can be used in place of the isotropic, dielectric host fluid in the dispersion to modify the switching threshold and bistability of the device. A. Somlyody et al, U.S. Pat. No. 4,305,807 issued Dec. 15, 1981, reports the use of a nematic liquid crystal as a fluid host for charged-particle displays to provide a threshold response characteristic in a similar manner as the devices of the Jacobsen and Albert patents.
Although many examples abound in both the patent and open literature of particle-based devices employing inorganic or metallic particles, instances of reported electro-optical particle devices that employ birefringent polymers or polymeric liquid crystals as the active particles are nearly non-existent. One example is the use of in-situ polymerized nematic liquid crystal spheres prepared by polymerizing a UV-curable liquid crystal reactive monomer dispersed in glycerol in the presence of an appropriate photoinitiator as reported by D. Cairns et al. in the Society for Information Display (SID) Digest of Technical Papers, XXX, p725-728 (1999). This device differs substantially from those described in the patents described above in that (1) t
Faris Sadeg M.
Jacobs Stephen D.
Kosc Tanya Z.
Li Le
Marshall Kenneth L.
Chung David
Kim Robert H.
LuKacher Kenneth J.
LuKacher Martin
The University of Rochester
LandOfFree
Electrically switchable polymer liquid crystal and polymer... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Electrically switchable polymer liquid crystal and polymer..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Electrically switchable polymer liquid crystal and polymer... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3167262