Switchable light-collimating layer including bistable electrophoretic fluid
A switchable light-collimating film can be used as a privacy filter for computer monitors or other display devices. The film comprises a plurality of elongated chambers having pigment particles, the position of which can be controlled by the applied electric field. Distribution of the pigment particles throughout the elongated chambers, as opposed to their concentration on one side of the chambers, narrows the viewing angle to the light passing through the film and provides privacy of the viewing images to the user.
1. A method of fabrication of a switchable light-collimating film comprising the steps:
providing a first light-transmissive electrode layer;
depositing an embossing composition on the surface of the first light-transmissive electrode layer, creating a layer of embossing composition;
embossing the embossing composition at a temperature higher than the glass transition temperature of the layer of the embossing composition material, using a pre-patterned embossing tool, creating a patterned layer;
releasing the patterned layer from the embossing tool, creating a collimating layer having a plurality of elongate chambers, each elongated chamber having an opening, each elongated chamber having height, length (L), and width (W), the collimating layer having a thickness of at least 20 μm, the plurality of the elongated chambers being arranged in rows and columns when the collimating layer is viewed from above, the longer dimension of the elongated chambers running along rows, first row of elongated chambers including a gap between elongated chambers of first column and second column, second row of elongated chambers including a gap between elongated chambers of first column and second column, third row of elongated chambers including a gap between elongated chambers of first column and second column, the gap between elongated chambers of first column and second column in the first row being offset horizontally from the gap between elongated chambers of first column and second column in the second row, the gap between elongated chambers of first column and second column in the second row being offset horizontally from the gap between elongated chambers of first column and second column in the third row, the gap between elongated chambers of first column and second column in the first row being offset horizontally from the gap between elongated chambers of first column and second column in the third row,
filling each chamber of the plurality of the elongated chambers through their opening with a bistable electrophoretic fluid comprising pigment particles;
sealing the openings of the plurality of filled elongated chambers with a sealing composition, forming a sealing layer spanning the opening of each of the plurality of the elongated chambers;
laminating the sealed elongated chambers to a second light-transmissive electrode layer, wherein the first and second light-transmissive electrode layers are disposed on either side of the collimating layer.
2. The method of fabrication of a switchable light-collimating film according to 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.
3. The method of fabrication of a switchable light-collimating film according to claim 1 , wherein the bistable electrophoretic fluid comprises polymer-functionalized pigment particles and free polymer in a non-polar solvent.
4. The method of fabrication of a switchable light-collimating film according to claim 3 , wherein the pigment particles are functionalized with a polyacrylate, polystyrene, polynaphthalene, or polydimethylsiloxane.
5. The method of fabrication of a switchable light-collimating film according to claim 3 , wherein the free polymer comprises polyisobutylene or copolymers including ethylene, propylene, or styrene monomers.
6. The method of fabrication of a switchable light-collimating film according to claim 1 , wherein the first row is separated from the second row by at least three times the width of the elongated chambers.
7. The method of fabrication of a switchable light-collimating film according to claim 1 , wherein the adjacent elongated chambers within the first row are separated by a gap of less than 30 μm.
8. The method of fabrication of a switchable light-collimating film according to claim 1 , wherein the collimating layer has a thickness of less than 500 μm.
9. The method of fabrication of a switchable light-collimating film according to claim 1 , wherein the collimating layer comprises a polyacrylate.
10. The method of fabrication of a switchable light-collimating film according to claim 1 , wherein the first or second light-transmissive electrode layer comprises indium-tin-oxide.
11. The method of fabrication of a switchable light-collimating film according to 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.
12. The method of fabrication of a switchable light-collimating film according to claim 1 , wherein a height of the plurality of the elongated chambers is equal to or less than thickness of the collimating layer, the width of the plurality of the elongated chambers is between 5 μm and 150 μm, and the length of the plurality of elongated chambers is between 200 μm and 5 mm.
13. The method of fabrication of a switchable light-collimating film according to claim 1 , wherein the bistable electrophoretic fluid comprises polymer-functionalized pigment particles and free polymer in a non-polar solvent.
14. A method of fabrication of a switchable light-collimating film comprising the steps:
providing a first light-transmissive electrode layer;
depositing an embossing composition on the surface of the first light-transmissive electrode layer, creating a layer of embossing composition;
embossing the embossing composition at a temperature higher than the glass transition temperature of the layer of the embossing composition material, using a pre-patterned embossing tool, creating a patterned layer;
releasing the patterned layer from the embossing tool, creating a collimating layer having a plurality of elongate chambers, each elongated chamber having an opening, each elongated chamber having height, length (L), and width (W), the collimating layer having a thickness of at least 20 μm, the plurality of the elongated chambers being arranged in rows and columns when the collimating layer is viewed from above, the longer dimension of the elongated chambers running along rows, first row of elongated chambers including a gap between elongated chambers of first column and second column, second row of elongated chambers including a gap between elongated chambers of first column and second column, third row of elongated chambers including a gap between elongated chambers of first column and second column, the gap between elongated chambers of first column and second column in the first row being offset horizontally from the gap between elongated chambers of first column and second column in the second row, the gap between elongated chambers of first column and second column in the second row being offset horizontally from the gap between elongated chambers of first column and second column in the third row, the gap between elongated chambers of first column and second column in the first row being offset horizontally from the gap between elongated chambers of first column and second column in the third row,
filling each chamber of the plurality of the elongated chambers through their opening with a bistable electrophoretic fluid comprising pigment particles;
sealing the openings of the plurality of filled elongated chambers with a sealing composition, forming a sealing layer spanning the opening of each of the plurality of the elongated chambers;
attaching an optically clear adhesive layer and a release layer onto the sealing layer, wherein the optically clear adhesive layer is disposed between the sealing layer and the release layer.