Stacked microvoided light diffuser
View Patent ↗The invention relates to a light diffuser comprising a polymeric film wherein the film comprises a plurality of layers having void geometry in which the x/y/z size or frequency varies by at least 28% between at least two layers.
1. A light diffuser comprising a polymeric film wherein the film comprises a plurality of layers having microvoids in which the average length of the microvoid in the x, y, or z direction or the frequency varies by at least 28% between at least two layers, and the variation is sufficient to increase the diffuse light transmission efficiency by at least 10% at 500 nm compared to a single voided layer of the same thickness as the layers but with only one frequency or void size, wherein the diffuse light transmission efficiency of the diffuser is greater than 80% at 500 nm.
2. The light diffuser of claim 1 wherein the polymeric film comprises exactly two voided layers.
3. The light diffuser of claim 1 wherein the polymeric film contains at least two voided layers and at least one non-voided layer.
4. The light diffuser of claim 3 wherein the voided and non-voided layers are integral.
5. The light diffuser of claim 3 wherein the polymeric film the non-voided layer further comprises addenda.
6. The light diffuser of claim 1 wherein the polymeric film contains at least two voided layers that are separated by a non-voided layer.
7. The light diffuser of claim 1 wherein the said plurality of voided layers that vary in geometry or frequency improve the diffuse light transmission efficiency compared to a single voided layer of the same thickness and either void geometry or frequency by at least 10% at 500 nm.
8. The light diffuser of claim 1 wherein the microvoids have a substantially circular cross-section in a plane perpendicular to the direction of light travel.
9. The light diffuser of claim 1 wherein the x/y/z size or frequency of the voids vary by between 28% and 300% between at least two layers.
10. The light diffuser of claim 1 wherein the x/y/z size or frequency of the voids vary by at least 60% between at least two layers.
11. The light diffuser of claim 1 wherein the voided layers are arranged in order of increasing size of voids in reference to the light passing through the film.
12. The light diffuser of claim 1 wherein the voided layers are arranged in order of decreasing size of voids in reference to the light passing through the film.
13. The light diffuser of claim 1 wherein the voided layers are arranged in order of increasing frequency of voids in reference to the light passing through the film.
14. The light diffuser of claim 1 wherein the voided layers are arranged in order of decreasing frequency of voids in reference to the light passing through the film.
15. The light diffuser of claim 1 wherein the film contains at least one polymeric skin layer.
16. The light diffuser of claim 1 wherein the difference in refractive index between the thermoplastic polymeric material and the microvoids is greater than 0.2.
17. The light diffuser of claim 1 wherein said microvoids are formed by organic microspheres.
18. The light diffuser of claim 1 wherein the microvoids contain cross-linked polymer beads.
19. The light diffuser of claim 1 wherein the microvoids contain a gas.
20. The light diffuser of claim 1 wherein the elastic modulus of the light diffuser is greater than 500 MPa.
21. The light diffuser of claim 1 wherein said diffuse light transmission efficiency is greater than 87% at 500 nm.
22. The light diffuser of claim 1 wherein said microvoids have a major axis diameter to minor axis diameter ratio of less than 2.0.
23. The light diffuser of claim 1 wherein said microvoids have a major axis diameter to minor axis diameter ratio of between 1.0 and 1.6.
24. The light diffuser of claim 1 wherein said thermoplastic layers contain greater than 4 index of refraction changes greater than 0.20 parallel to the direction of light travel.
25. The light diffuser of claim 1 wherein said microvoids have an average volume of between 8 and 42 cubic micrometers.
26. The light diffuser of claim 1 wherein the said light diffuser has a thickness less than 250 micrometers.
27. The light diffuser of claim 1 wherein said thermoplastic layer comprises polyolefin polymer.
28. The light diffuser of claim 1 wherein said thermoplastic layer comprises polyester polymer.
29. The light diffuser of claim 18 wherein said cross linked polymer beads have a mean particle size less than 2.0 micrometers.
30. The light diffuser of claim 18 wherein said cross linked polymer beads have a mean particle size between 0.30 and 1.7 micrometers.
31. The light diffuser of claim 1 wherein the total light transmission is at least 65% at 500 nm.