Reflective cholesteric liquid crystal display with complementary light-absorbing layer
View Patent ↗A display sheet comprising a substrate carrying layers of material; including a polymer-dispersed cholesteric liquid-crystal layer having a first high reflection state within a portion of the visible light spectrum and a second less-reflective state in said spectrum, said states being changeable by electric field between the two states which states can be maintained in the absence of an electric field; a first transparent conductor disposed over the polymer-dispersed cholesteric liquid-crystal layer; a complementary light-absorbing layer below the polymer-dispersed cholesteric liquid-crystal layer having relatively high light absorption within the spectrum of the high-reflection state of the polymer-dispersed cholesteric liquid-crystal layer and having relatively less light absorption in the spectrum complementary to that of the high reflection state of the polymer-dispersed cholesteric liquid-crystal layer; and a reflective second conductor under said complementary light-absorbing layer reflecting light received from the complementary light-absorbing layer back through the complementary light-absorbing layer.
1. A display sheet comprising:
a) a substrate for carrying layers of material;
b) an imaging layer comprising polymer-dispersed cholesteric liquid-crystal material, such imaging layer having a first relatively higher reflection state within a portion of the visible light spectrum defining an operating spectrum and a second relatively less reflective state in said operating spectrum, wherein said states are capable of being changed by an electric field between the two states, which states are capable of being maintained in the absence of an electric field;
c) a first transparent conductor disposed on one side of the imaging layer;
d) a colored complementary light-absorbing layer on the other side of the imaging layer having relatively lower transmission of light within the operating spectrum of the imaging layer and having relatively greater transmission of light outside of the operating spectrum; and
e) a reflective surface, optionally part of a second electrode, that reflects light transmitted through the colored complementary light-absorbing layer back to the complementary light-absorbing layer, wherein the colored complementary light-absorbing layer is capable of operating in conjunction with the reflective surface to provide a substantially neutral reflective image when the imaging layer is in the first relatively higher reflection state; and
f) a second electrode.
2. The display sheet of claim 1 wherein reflected light from the display sheet when the imaging layer is in the first relatively higher reflection state has CIE tristimulus values X, Y and Z that are within 20 percent of each other.
3. The display of claim 1 wherein the display sheet comprises polymer-dispersed cholesteric liquid-crystal material with a peak reflected wavelength between 570 and 590 nanometers.
4. The display of claim 1 wherein the colored complementary light-absorbing layer comprises sub-micrometer pigment particles in a polymeric binder.
5. The display of claim 1 wherein the reflective surface is on the second conductor that is formed of printed silver ink.
6. The display of claim 1 wherein the reflective surface is on the second conductor that is formed of vacuum deposited metal.