Thermoscattering materials and devices

Details Thermoscattering materials and devices Thermoscattering materials and devices

2000-05-19

2002-03-26

Gorr, Rachel (Department: 1711)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

From reactant having at least one -n=c=x group as well as...

C528S083000, C116S216000, C116S217000, C428S067000, C428S913000, C525S176000, C525S440030, C525S454000, C525S458000, C525S460000, C525S931000, C525S932000

Reexamination Certificate

active

06362303

ABSTRACT:

BACKGROUND
A number of reversibly variable light transmission technologies based on changes between light scattering and less or non-light scattering conditions have been proposed or commercialized for a variety of intended uses. These technologies generally involve electrically induced and/or thermally induced changes. The materials with thermally induced, reversible changes between light scattering and less or non light scattering states can be termed thermally reversible light scattering, (TRLS), materials.
Polymer dispersed liquid crystal, (PDLC), technologies generally have involved liquid crystal droplets either physically dispersed in a polymer matrix, see for example U.S. Pat. Nos. 5,089,904; 5,082,351; 4,838,660; 4,815,826 and 4,435,047 or liquid crystal droplets formed by phase separation during curing of a reactive monomer/liquid crystal solution and/or by solvent removal, see for example U.S. Pat. Nos. 5,530,566; 5,087,387; 5,021,188; 4,888,126; 4,688,900; 4,685,771; 4,673,255 and 4,671,618. Droplet formation in the later case is due to decreased solubility of the liquid crystal material in the polymer being formed as compared to a higher solubility of the liquid crystal material in the monomer prior to curing. Droplet formation may also be due the polymer and the liquid crystal both being soluble in a solvent whereas the liquid crystal is insoluble or immiscible in the polymer and forms droplets within the polymer as the solvent is removed.
In general with PDLC materials, the index of refraction of the liquid crystal droplets is different from the polymer matrix material and a layer of the droplet containing material is light scattering and thus appears translucent, frosted or white. When a layer of PDLC is provided between two transparent electrode layers, a voltage can be applied to change the index of refraction of the liquid crystal droplets. As the index of refraction of the droplets approaches that of the polymer matrix the PDLC layer decreases in light scattering and with a high enough applied voltage the PDLC materials can become quite clear. Thus these devices are electrically operated or electrooptic variable light scattering devices although thermally induced changes from light scattering to clear or TRLS changes have been described for these material in U.S. Pat. Nos. 5,087,387; 5,021,188 and 4,888,126.
A more recently proposed electrooptic variable light scattering technology is based on what is called polymer stabilized cholesteric texture, (PSCT). With this technology a cholesteric liquid crystal is mixed with a small amount of a reactive monomer, placed in a very thin film between conducting layers and the monomer is allowed to react while an applied electric field holds the liquid crystal material in a clear or low light scattering state known as the homeotropic texture. Thus, the small amount of polymer matrix formed during the curing process favors or stabilizes this texture to some extent and the liquid crystal returns to it in the future when voltages of adequate strength are applied across the liquid crystal layer. In the absence of an applied voltage the liquid crystal material goes to a light scattering, focal conic texture. Devices with this technology rapidly switch between light scattering with no applied voltage to fairly low light scattering with an applied voltage. Examples of these materials and devices are given in U.S. Pat. Nos. 5,847,798; 5,695,682; 5,691,795; 5,644,330 and 5,570,216. Reverse mode device are also possible in which there is relatively little light scattering in the no voltage applied condition and the device becomes light scattering when a voltage is applied. PSCT technology lends itself to TRLS as heating a PSCT material from its mesomorphic phase with focal conic texture to it isotropic phase causes the polymer stabilized material to change from light scattering to less light scattering or clear.
One type of variable light scattering technology, that depends exclusively on temperature changes to cause changes in the light scattering nature of the materials, is based on the phenomenon know as lower critical solution temperature, (LCST), see for example U.S. Pat. Nos. 5,615,040; 5,525,430; 5,404,245; 4,952,035; 4,877,675; 4,832,466; 4,816,518; 4,772,506; and 4,260,225. With this technology, as the temperature is raised, a clear, transparent solution of a polymer in a solvent reaches a critical point at a particular temperature at which the polymer comes out of solution or phase separates to form a highly scattering material. Layers of this type of material have been proposed for use in window or roof situations where increases in ambient, outdoor temperature are enough to cause the transition from clear to frosted. The amount of backward scattered light is significant enough to have such windows and roof elements considered for providing energy savings in buildings that use this technology. They have also been described for use in displays and thermal recording materials in U.S. Pat. Nos. 4,952,035; 4,832,466 and 4,734,359. A reverse mode system which is reported to have materials with upper critical solution temperature, (UCST), behavior is described in U.S. Pat. No. 4,900,135. Both the materials based on LCST and those based on UCST qualify as TRLS materials.
Another type of thermally controlled, variable light scattering technology is suggested for use as thermally reversible recording media. Generally a low melting, relatively low molecular weight material is contained in a polymer matrix in these TRLS materials. In most cases, at low temperatures this composite material is light scattering. As the temperature is raised, above a certain point the material turns clear. To be useful as a recording media, this clear state is maintained by cooling the cleared material immediately after the temperature for clearing is reached. To erase a recorded image, the material is heated to a temperature significantly above the clearing temperature and cooling from this temperature regenerates the light scattering state of the material. Thus the preferred materials are bistable since they are stable in either the light scattering or the clear state at normal room temperature depending on their thermal history. For examples of this technology, see U.S. Pat. Nos. 5,965,484; 5,780,387; 5,747,413; 5,700,746; 5,298,476; 5,278,128; 4,917,948 and 4,695,528. Similar bistable, TRLS behavior has been described for liquid crystal polymers in U.S. Pat. Nos. 5,589,237 and 5,426,009 and for liquid crystals contained in an inorganic polymer matrix formed from fumed silica, see U.S. Pat. No. 5,729,320.
Thermally reversible light attenuating materials for various display and window applications are described in U.S. Pat. No. 4,268,413 to Dabisch. The TRLS materials of this invention are reported to comprise a polymeric or resinous matrix material and at least one organic substance embedded in the matrix material as a discrete phase. The organic substances embedded in the matrix material are relatively low molecular weight materials with melting points near or slightly above the desired transition between states with more and with less “light-absorbance”. The change in the way the material attenuates light involves a change of the dispersed, embedded organic substance from a solid which is at least partially insoluble in the matrix material to a liquid which has an index of refraction that matches the index of refraction of the matrix. Alternatively, the change in light attenuation involves a change in the dispersed, embedded material from solid particles which have an index of refraction that matches that of the matrix to liquid droplets which are not soluble in the matrix and have an index of refraction that differs from that of the matrix.
Descriptions of electrooptic devices that are suggested for changes between clear and light scattering states are given by Beni, et al “Anisotropic Suspension Display” Appl. Phys. Lett. 39(3), 195-197 (1981) and “Electro-wetting Displays” Appl. Phys. Lett. 38(4), 207-209 (1981).
No description has been fou

Affiliated with

Also associated with

Rating

Thermoscattering materials and devices does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Thermoscattering materials and devices, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Thermoscattering materials and devices will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2869235