Switchable light-collimating layer with reflector
A method for collimating light using a film including elongated chambers of bistable electrophoretic fluids. The light-collimating films are suitable to control the amount and/or direction of light incident to a transmissive substrate. Such films may be integrated into devices, such as LCD displays, to provide a zone of privacy for a user viewing the LCD display. Because the light-collimating film is switchable, it allows a user to alter the collimation of the emitted light on demand. Because the films are bistable, they do not require additional power after they have been switched to a display state.
1. A method for collimating a light source, comprising:
providing a switchable light-collimating film between a viewer and a light source, the switchable light-collimating film including:
a first light-transmissive electrode layer,
a collimating layer having a thickness of at least 20 μm, and comprising a plurality of elongated chambers, with a portion of collimating layer between elongated chambers, each elongated chamber having an opening,
a bistable electrophoretic fluid comprising pigment particles disposed in each elongated chamber,
a sealing layer including light-reflective materials that seals the bistable electrophoretic fluid within at least one of the plurality of elongated chambers by spanning the opening of the elongated chamber, wherein the sealing layer provides a light-reflective surface aligned with the opening of each elongated chamber, and wherein the light-reflective surface does not substantially overlap with the portion of the collimating layer between elongated chambers, and
a second light-transmissive electrode layer, wherein the first and second light transmissive layers are disposed on either side of the collimating layer;
providing a voltage source operably coupled between the first light-transmissive electrode layer and the second light-transmissive electrode layer; and
providing a voltage impulse between the first light-transmissive electrode layer and the second light-transmissive electrode layer to cause the pigment particles to move from a first position adjacent the first light-transmissive electrode layer or adjacent the second light-transmissive electrode layer to a second position in which the pigment particles are dispersed throughout the volume of the elongated chambers, thereby collimating the light source as viewed by the viewer.
2. The method for collimating a light source of claim 1 , wherein the collimating layer has a thickness of less than 500 μm.
3. The method for collimating a light source of claim 1 , wherein a height of the elongated chambers is equal to or less than the thickness of the collimating layer, a width of the elongated chambers is between 5 μm and 150 μm, and a length of the chambers is between 200 μm and 5 mm.
4. The method for collimating a light source of claim 1 , wherein the collimating layer comprises a polymer including acrylate monomers, urethane monomers, styrene monomers, epoxide monomers, silane monomers, thio-ene monomers, thio-yne monomers, or vinyl ether monomers.
5. The method for collimating a light source of claim 1 , wherein sealing layer comprises a metal or a light-reflective metal oxide.
6. The method for collimating a light source of claim 5 , wherein the sealing layer comprises metal flakes or titanium dioxide.
7. The method for collimating a light source of claim 1 , wherein the bistable electrophoretic fluid comprises polymer-functionalized pigment particles and free polymer, not bonded to the pigment particles, dispersed in a non-polar solvent.
8. The method for collimating a light source of claim 7 , wherein the free polymer comprises polyisobutylene or copolymers including ethylene, propylene, or styrene monomers.
9. The method for collimating a light source of claim 7 , wherein the pigment is functionalized with a polyacrylate, polystyrene, polynaphthalene, or polydimethylsiloxane.
10. The method for collimating a light source of claim 1 , wherein the sealing layer comprises cellulose, gelatin, a polyacrylate, a polyvinyl alcohol, a polyethylene, a poly(vinyl) acetate, a poly(vinyl) pyrrolidone, a polyurethane, or a copolymer of any of the aforementioned polymers.
11. The method for collimating a light source of claim 1 , further comprising a providing a diffusion layer and a prism film between the switchable light-collimating film and the light source.