Low layer count reflective polarizer with optimized gain

摘要

Multilayer reflecting polarizing films are disclosed having increased in-plane refractive index differences between adjacent microlayers along both the pass and block axis, and having negative refractive index differences between adjacent microlayers along the thickness or z-axis. Major front and back surfaces of the film exposed to air provide a Fresnel reflectivity component to the pass axis reflectivity, and the microlayers provide a microlayer component to the pass axis reflectivity, such microlayer component preferably having a reflectivity of p-polarized light that increases with incidence angle faster than the Fresnel reflectivity component decreases so as to substantially avoid off-axis gain peaks for p-polarized light. The films preferably utilize a relatively small total number of microlayers, arranged in a single coherent stack with monotonic optical repeat unit thickness profile, and at least some microlayers preferably include polyethylene naphthalate or a copolymer thereof.

主权项

1. A reflective polarizer having a block axis and a pass axis corresponding respectively to an x-axis and a y-axis, the reflective polarizer comprising:
first and second opposed major surfaces exposed to air and therefore exhibiting Brewster angle reflection minima, the major surfaces being disposed perpendicular to a z-axis which is itself perpendicular to the x- and y-axes, the z-axis and the y-axis forming a y-z plane; and a stack of microlayers disposed between the major surfaces and arranged into pairs of adjacent microlayers that exhibit refractive index differences along the x-, y-, and z-axes of Δnx, Δny, and Δnz respectively, where Δnx>Δny>0>Δnz, the stack of microlayers having a total number N of said microlayers; wherein the number N and the index difference Δnx in combination are large enough to provide the polarizer with a high reflectivity for normally incident light polarized along the x-axis, said high reflectivity referred to as Rblocknormal, said Rblocknormal being at least 80%; wherein the number N and the index difference Δny in combination are small enough to provide the polarizer with a low reflectivity for normally incident light polarized along the y-axis, said low reflectivity referred to as Rpassnormal, said Rpassnormal being 25% or less; and wherein Δny is responsible for an incremental portion Rpassinc of said Rpassnormal, and a corresponding portion of Δnx equal to Δny is responsible for an incremental portion Rblockinc of said Rblocknormal, and the number N is small enough so that said Rblockinc is at least half of Rpassinc, and wherein said Rpassnormal, Rpassinc, Rblocknormal, and Rblockinc are all averages over a same wavelength range.