Optical film, backlight, and display
An optical film includes an optically diffusive layer including a plurality of nanoparticles dispersed between and across opposing first and second major surfaces thereof. The plurality of nanoparticles has a nanoparticle size distribution including distinct first and second peaks at respective nanoparticle sizes d1 and d2, wherein 1.5≤d2/d1≤10. The optically diffusive layer includes a polymeric material bonding the nanoparticles to each other. For a substantially collimated substantially normally incident light, the optical film has, in a visible wavelength, an average specular transmittance VTs and an average total transmittance VTt, and in an infrared wavelength range, an average total transmittance ITt and an average specular transmittance ITs, wherein 0.3≤(VTs/VTt)≤0.7, (VTs/ITs)≤0.25, and (ITs/ITt)≥0.7.
1 . An optical film comprising an optically diffusive single layer having an average thickness of between about 0.5 and about 5 microns and comprising:
opposing first and second major surfaces;
a plurality of nanoparticles dispersed between and across the first and second major surfaces, the nanoparticles comprising silica, the plurality of nanoparticles having a nanoparticle size distribution comprising at least two distinct first and second peaks at respective nanoparticle sizes d1 and d2, 1.5≤d2/d1≤10, wherein the nanoparticles in the plurality of nanoparticles within a full width at half maximum (FWHM) of the first peak and within a FWHM of the second peak form respective W1 and W2 percent by weight of the plurality of nanoparticles, 1.1≤W1/W2≤2; and
a polymeric material bonding the nanoparticles to each other to form a plurality of nanoparticle aggregates defining a plurality of voids therebetween,
wherein, for a substantially collimated substantially normally incident light and a visible wavelength range from about 420 nanometers (nm) to about 680 nm and an infrared wavelength range from about 900 nm to about 1000 nm, the optical film has:
in the visible wavelength range, an average specular transmittance VTs and an average total transmittance VTt; and
in the infrared wavelength range, an average total transmittance ITt and an average specular transmittance ITs, 0.3≤VTs/VTt≤0.7, VTs/ITs≤0.25, ITs/ITt≥0.7.
2 . The optical film of claim 1 , wherein 50 nm≤d2≤100 nm and 5 nm≤d1≤50 nm.
3 . The optical film of claim 1 further comprising a substrate disposed on the optically diffusive single layer and comprising: (a) a reflective polarizer, and wherein for the substantially collimated substantially normally incident light and the visible wavelength range, the reflective polarizer has an average optical transmittance of at least 40% for a first polarization state and an average optical reflectance of at least 40% for an orthogonal second polarization state; (b) an absorbing polarizer, and wherein for the substantially collimated substantially normally incident light and the visible wavelength range, the absorbing polarizer has an average optical transmittance of at least 40% for a first polarization state and an average optical absorption of at least 60% for an orthogonal second polarization state; or (c) an optical mirror, such that for the substantially collimated substantially normally incident light and the visible wavelength range, the optical mirror has an average optical reflectance of at least 60% for each of mutually orthogonal first and second polarization states.
4 . The optical film of claim 1 , wherein in a plane of a cross-section of the optically diffusive single layer in the thickness direction of the optically diffusive single layer, the nanoparticles are substantially circular.