Optically Diffusive Film and Method of Making Same

An optically diffusive film comprising a plurality of particles dispersed in a binder, the particles and the binder comprising respective indices n1b and n2b along a same in-plane block-direction of the optically diffusive film, and respective indices nip and n2p along an in-plane pass-direction orthogonal to the block-direction, such that for at least a first wavelength in a first wavelength range extending from about 400 nm to about 1000 nm:

• a magnitude of a difference between n1b and n2b is greater than about 0.05;
• and
• a magnitude of a difference between nip and n2p is less than about 0.05;
• wherein, for a substantially normally incident light having the first wavelength, the optically diffusive film has:
• a total optical transmittance TTb and a total optical reflectance RTb when the incident light is polarized along the block-direction, TTb/RTb≥2;
• and
• a total optical transmittance TTp and a total optical reflectance RTp when the incident light is polarized along the pass-direction, TTp/RTp≥6.

An extruded optically diffusive film extruded along a pass-direction and comprising:

• a plurality of particles dispersed in a binder, the particles elongated along substantially a same in-plane block-direction orthogonal to the pass-direction and having an average aspect ratio of greater than about 5;
• and
• a plurality of substantially parallel extrusion die-lines making an angle of less than about 20 degrees with the pass-direction;
• wherein, for a substantially normally incident light having a first wavelength in a first wavelength range extending from about 400 nm to about 1000 nm, the optically diffusive film has:
• a diffuse optical transmittance TDb and a diffuse optical reflectance RDb when the incident light is polarized along the block-direction, TDb/RDb≥4;
• and
• a total optical transmittance TTp and a diffuse optical reflectance RDp when the incident light is polarized along the pass-direction, TTp/RDp≥10.

A method of making an optically diffusive film, comprising:

• extruding an immiscible blend of a minor phase material and a major phase material through a die and along a pass-direction at a first temperature greater than glass transition temperatures of the minor and major phase materials resulting in an extruded mixture at substantially the first temperature and comprising a plurality of substantially spherical domains;
• and
• stretching the extruded mixture along a block-direction, substantially orthogonal to the pass-direction, at a second temperature less than the first temperature resulting in a plurality of particles dispersed in a binder, wherein the binder and each of at least a majority of the particles comprise respective indices n2b and n1b along the block-direction and respective indices n2p and nip along the pass-direction, such that for at least a first wavelength in a first wavelength range extending from about 400 nm to about 1000 nm:
• a magnitude of a difference between n1b and n2b is greater than about 0.05;
• and
• a magnitude of a difference between nip and n2p is less than about 0.05.