Optical film and method of making
An optical film includes a structured film and a light control film formed on the structured film. The structured film includes a substrate and a plurality of polymeric microstructures formed on a major surface of the substrate. Each microstructure includes an optical facet and a sidewall meeting the optical facet at a ridge of the microstructure. The light control film includes an optically transparent material disposed on and covering the plurality of polymeric microstructures, and a plurality of optically absorptive louvers formed in the optically transparent material opposite the structured film. The louvers extend along a longitudinal direction and are spaced apart along an orthogonal transverse direction. The louvers have an average depth D into the optically transparent material and have an average width W in the transverse direction. D/W can be greater than 2. The optical film is integrally formed.
1. An optical film comprising:
a structured film comprising a substrate and a plurality of polymeric microstructures formed on a major surface of the substrate, each microstructure comprising an optical facet and a sidewall meeting the optical facet at a ridge of the microstructure; and
a light control film formed on the structured film, the light control film comprising:
an optically transparent material disposed on and covering the plurality of polymeric microstructures; and
a plurality of optically absorptive louvers formed in the optically transparent material opposite the structured film, the louvers extending along a longitudinal direction and spaced apart along an orthogonal transverse direction, each of the louvers having an average depth D into the optically transparent material and an average width W in the transverse direction, D/W>2,
wherein the optical film is integrally formed.
2. The optical film of claim 1 , wherein for each microstructure in at least a majority of the microstructures, an optically absorptive layer is disposed on and substantially covers the sidewall, the optically absorptive layer having an average thickness t, 100 nm<t<1 micrometer.
3. The optical film of claim 2 , wherein for each microstructure in at least a majority of the microstructures, the sidewall of the microstructure has a height H from a base of an adjacent microstructure to the ridge of the microstructure, H/t>15.
4. The optical film of claim 1 , wherein the plurality of polymeric microstructures is conformally coated with an inorganic optically transparent layer.
5. The optical film of claim 4 , wherein for each microstructure in at least a majority of the microstructures, an optically absorptive layer is disposed on and substantially covers the inorganic optically transparent layer disposed on the sidewall.
6. The optical film of claim 5 , wherein for each microstructure in at least the majority of the microstructures, a first layer is disposed between the inorganic optically transparent layer and the optically absorptive layer, the first layer having an extinction coefficient k 1 , the optically absorptive layer having an extinction coefficient k 2 , k 2 -k 1 >0.05.
7. The optical film of claim 1 , wherein for each microstructure, the ridge of the microstructure extends along the longitudinal direction across at least a majority of a length of the optical film.
8. The optical film of claim 1 , wherein each microstructure in the plurality of polymeric microstructures is a linear prism having a substantially same angle between the optical facet and the sidewall.
9. The optical film of claim 1 , wherein each microstructure in the plurality of polymeric microstructures is a linear Fresnel element.
10. The optical film of claim 1 , wherein the plurality of polymeric microstructures has a refractive index n 1 , the optically transparent material has a refractive index n 2 , and n 1 -n 2 >0.05.
11. An optical stack comprising the optical film of claim 1 laminated to a second substrate, the light control film facing the second substrate.
12. A method of making an optical film, the method comprising the steps of:
providing a structured film comprising a substrate and a plurality of polymeric microstructures formed on a major surface of the substrate, each microstructure comprising an optical facet and a sidewall meeting the optical facet at a ridge of the microstructure;
forming a light control film on the structured film, the light control film comprising:
an optically transparent material disposed on and covering the plurality of polymeric microstructures; and
a plurality of optically absorptive louvers formed in the optically transparent material opposite the structured film, the louvers extending along a longitudinal direction and spaced apart along an orthogonal transverse direction, each of the louvers having an average depth D into the optically transparent material and an average width W in the transverse direction, D/W>2,
wherein forming the light control film on the structured film comprises disposing a resin on the plurality of polymeric microstructures and curing the resin to provide the optically transparent material.
13. The method of claim 12 , wherein curing the resin comprises at least partially curing the resin while the resin is in contact with a structured tool surface such that a plurality of substantially parallel grooves is formed in the optically transparent material opposite the structured film, the method further comprising at least partially filling the grooves with optically absorptive material to provide the plurality of optically absorptive louvers.
14. The method of claim 12 , further comprising, between the providing and forming steps, the steps of:
disposing an optically absorptive layer on the plurality of polymeric microstructures; and
removing the optically absorptive layer from the optical facets.
15. The method of claim 14 , further comprising, prior to the disposing the optically absorptive layer step, disposing an inorganic optically transparent layer on the plurality of polymeric microstructures.