Optical diffusion film and its manufacturing method

Abstract

The optical diffusion film (200) includes a plurality of particles (10) dispersed within a binder (20). The particles (10) and binder (20) have respective refractive indices n1b and n2b along the same in-plane block direction of the optical diffusion film (200) and respective refractive indices n1p and n2p along an in-plane pass direction perpendicular to the block direction, where the magnitude of the difference between n1b and n2b is greater than about 0.05 and the magnitude of the difference between n1p and n2p is less than about 0.05 for at least a first wavelength in a first wavelength range spanning from about 400 nm to about 1000 nm. For substantially normally incident light, and for at least the first wavelength, the optical diffusion film (200) can have high optical diffusion for light polarized along the block direction (b) and low optical diffusion for light polarized along the orthogonal pass direction (p).

Description

Summary of the Invention

[0001] This specification relates generally to optically diffusive films that include particles dispersed in a binder, and methods of making optically diffusive films that include extruding an immiscible blend, which can have high optical diffusion for light polarized along a block direction and low optical diffusion for light polarized along an orthogonal pass direction.

[0002] In some aspects, the present disclosure provides an optical diffusion film comprising a plurality of particles dispersed within a binder. The particles and binder have respective refractive indices n1b and n2b along the same in-plane block direction of the optical diffusion film, and respective refractive indices n1p and n2p along an in-plane pass direction perpendicular to the block direction, and the magnitude of the difference between n1b and n2b is greater than about 0.05 and the magnitude of the difference between n1p and n2p is less than about 0.05 for at least a first wavelength within a first wavelength range spanning from about 400 nm to about 1000 nm. In some embodiments, for light having a first wavelength and substantially normally incident, the optical diffusion 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 transmittance TDp when the incident light is polarized along the pass direction, TTp / TDp≧1.1. In some such embodiments, or in other embodiments, for substantially normally incident light having a first wavelength, the optical diffusing film has a total optical transmittance TTb and a total optical reflectance RTb when the incident light is polarized along the block direction, where 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, where TTp / RTp≧6. In some such embodiments, or in other embodiments, for substantially normally incident light having a first wavelength, the optical diffusing film has specular optical transmittance TSp and TSb when the incident light is polarized along the pass direction and block direction, respectively, where TSp / TSb≧2.

[0003] In some aspects, the present disclosure provides an extruded optical diffusion film extruded along a pass direction, the film comprising a plurality of particles dispersed in a binder, the particles being elongated substantially along the same in-plane block direction perpendicular to the pass direction and having an average aspect ratio greater than about 5, and a plurality of substantially parallel extrusion die lines that form an angle of less than about 20 degrees with the pass direction. In some embodiments, for substantially normally incident light having a first wavelength within a first wavelength range spanning from about 400 nm to about 1000 nm, the optical diffusion film has a diffuse optical transmittance TDb and a diffuse optical reflectance RDb when the incident light is polarized along the block direction, where 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, where TTp / RDp≧10. In some such embodiments, or in other embodiments, for light having a first wavelength and substantially normally incident, the optical diffusion film has positive optical transmittances TSp and TSb, where TSp / TSb≧2, when the incident light is polarized along the pass direction and block direction, respectively.

[0004] In some embodiments, the present disclosure provides a method of making an optical diffusion film. The method includes extruding an immiscible blend of a minor phase material and a major phase material through a die along a pass direction at a first temperature higher than the glass transition temperature of the minor phase material and the glass transition temperature of the major phase material to obtain an extruded mixture having a plurality of substantially spherical regions at substantially the first temperature, and stretching the extruded mixture along a block direction substantially perpendicular to the pass direction at a second temperature lower than the first temperature to obtain a plurality of particles dispersed within a binder. At least a majority of the binder and particles each have respective refractive indices n2b and n1b along the block direction and respective refractive indices n2p and n1p along the pass direction, and the magnitude of the difference between n1b and n2b is greater than about 0.05 and the magnitude of the difference between n1p and n2p is less than about 0.05 for at least a first wavelength in a first wavelength range spanning from about 400 nm to about 1000 nm.

[0005] These and other aspects will become apparent from the following detailed description, but in no way should this brief summary be construed as limiting the claimed subject matter. [Brief description of the drawings]

[0006] [Figure 1A] 2A and 2B are schematic top and cross-sectional views, respectively, of an optical diffusing film according to some embodiments. [Figure 1B] 2A and 2B are schematic top and cross-sectional views, respectively, of an optical diffusing film according to some embodiments. [Figure 2A] 3A and 3B are schematic top and cross-sectional views, respectively, of another optical diffusing film according to some embodiments. [Figure 2B] 3A and 3B are schematic top and cross-sectional views, respectively, of another optical diffusing film according to some embodiments. [Diagram 3] 1 is a plot of the ratio of diffuse optical transmittance to diffuse optical reflectance in the block state and the ratio of total optical transmittance to diffuse optical transmittance in the pass state versus wavelength in accordance with some embodiments. [Figure 4] 1 is a plot of the ratio of total optical transmittance to diffuse optical reflectance in the pass state and the ratio of total optical transmittance to total optical reflectance in the pass state versus wavelength according to some embodiments. [Diagram 5] 1 is a plot of the intensity distribution of the optical transmittance of an optical diffusion film versus scattering angle in two orthogonal planes for light in a blocked state according to some embodiments. [Figure 6] 1 is a plot of the ratio of total optical transmittance to total optical reflectance in the block state and the ratio of total optical transmittance to total optical reflectance in the pass state versus wavelength in accordance with some embodiments. [Figure 7] 1 is a plot of the ratio of the positive optical transmittance in the pass state to the positive optical transmittance in the block state, and the ratio of the total optical transmittance in the pass state to the total optical transmittance in the block state versus wavelength, according to some embodiments. [Figure 8]FIG. 2 is a schematic process flow diagram of a method for making an optical diffusing film, according to some embodiments. [Figure 9A] 1 is a photomicrograph of a cross section of an exemplary extruded mixture. [Figure 9B] 1 is a photomicrograph of a cross section of an exemplary extruded mixture. [Figure 10A] 1 is a photomicrograph of a cross section of another exemplary extruded mixture. [Figure 10B] 1 is a photomicrograph of a cross section of another exemplary extruded mixture. [Figure 11] 1 is a plot of the intensity distribution of the optical transmission of an exemplary optical diffusing film versus the scattering angle in the plane orthogonal to the block direction, for light polarized along the block direction. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] In the following description, reference is made to the accompanying drawings, which form a part hereof, and in which various embodiments are shown by way of illustration. The drawings are not necessarily to scale. It is to be understood that other embodiments are contemplated and may be made without departing from the scope or spirit of the present disclosure. Accordingly, the following detailed description is not to be taken in a limiting sense.

[0008] According to some embodiments herein, the optical diffusion film may have a higher haze for light polarized along a first direction (which may be referred to as a "block" direction) than for light polarized along an orthogonal second direction (which may be referred to as a "pass" direction), and may have a greater scattering in a plane defined by the second direction and a thickness direction than in a plane defined by the first direction and a thickness direction. The optical diffusion film may be useful, for example, in display or sensor applications. For example, a display may be constructed such that light passes through a liquid crystal display (LCD) panel at a narrow viewing angle (e.g., after passing through a crossed prism film), and an optical diffusion film may be placed on the exit side of the LCD panel in a horizontally oriented second direction to widen the viewing angle in the horizontal plane. As another example, an optical diffusion film can be used in conjunction with a quarter-wave retarder in an optical device (e.g., an optical sensor) such that when light polarized along the block direction enters the device with a wide angular distribution, any light that reflects from the device back through the retarder toward the optical diffusion film enters the optical diffusion film in a pass state with less scattering, and / or when light polarized along the pass direction enters the device with a narrow angular distribution, any light that reflects from the device back through the retarder toward the optical diffusion film enters the optical diffusion film in a block state and is substantially transmitted through the optical diffusion film with a wider angular distribution.

[0009] According to some embodiments herein, an optical diffusion film comprises a plurality of particles dispersed within a binder, the particles being substantially optically isotropic (e.g., the difference between the maximum and minimum refractive index of the particles for at least one wavelength within the range of about 400 nm to about 1000 nm can be less than about 0.05, or less than about 0.04, or less than about 0.03, or less than about 0.02, or less than about 0.01), and the binder being birefringent (e.g., the difference between the maximum and minimum refractive index of the binder for at least one wavelength within the range of about 400 nm to about 1000 nm can be greater than about 0.05, or greater than about 0.06, or greater than about 0.07, or greater than about 0.08, or greater than about 0.09, or greater than about 0.1, e.g., the difference can be up to about 0.35, or up to about 0.3, or up to about 0.25). The difference between the refractive index of the binder and the refractive index of the particles can be substantially different along a first direction (e.g., by more than about 0.05, or more than about 0.06, or more than about 0.07, or more than about 0.08, or more than about 0.09, or more than about 0.1, and the difference can be, for example, up to about 0.35, or up to about 0.3, or up to about 0.25) and can be substantially consistent along an orthogonal second direction (e.g., by less than about 0.05, or less than about 0.04, or less than about 0.03, or less than about 0.02, or less than about 0.01). The particles can be elongated along the first direction, which can result in greater scattering in the second direction (i.e., the scattering plane including the second direction) than in the first direction.

[0010] The optical properties of the optical diffusion film can be adjusted by selecting binder and particle materials to have a desired range of refractive index difference along the block and pass axes, adjusting the number or volume of particles, and adjusting the shape of the particles. In general, increasing the refractive index difference in the block direction increases scattering in the block polarization state. Increasing the number of particles also increases scattering. The refractive index difference and particle number can be selected, for example, to provide primarily forward scattering. Optical diffusion films can be formed by extrusion followed by stretching (e.g., using a standard (linear) tenter or a non-linear tenter such as a parabolic tenter), as further described elsewhere herein. The stretch ratio used in stretching can affect the refractive index of the binder (e.g., increasing in the stretch direction for positively birefringent polymers) and can also affect the shape of the particles (e.g., resulting in elongated particles along the stretch direction). The stretch ratio can be, for example, at least about 1:1, or at least about 2:1, or at least about 3:1, or at least about 4:1, or at least about 4.5:1, and can be up to about 30:1, or up to about 20:1, or up to about 15:1, or up to about 10:1, or up to about 8:1, or up to about 7:1. The stretch ratio can be, for example, in the range of about 3:1 to about 10:1, or about 4:1 to about 8:1, or about 4.5:1 to about 7:1. The stretch direction can be the block direction, and it has been found that stretching the particles along this direction can increase scattering in the scattering plane perpendicular to the stretch direction.

[0011] 1A-1B are schematic top and cross-sectional views, respectively, of an optical diffusion film 200 including particles 10 dispersed within a binder 20, according to some embodiments. FIG. 2A-2B are schematic top and cross-sectional views, respectively, of an optical diffusion film 201 including particles 11 dispersed within a binder 20, according to some embodiments. The films 200, 201 extend along orthogonal in-plane first (block or b) and second (pass or p) directions and have a thickness along a z direction orthogonal to the b and p directions. In FIG. 2B, the particles 11 are elongated along the b direction. The particles 11 can have a substantially higher Lb / Lp ratio than that shown diagrammatically in FIG. 2A. FIG. 2B illustrates diagrammatically a substantially normally incident light 30b polarized along the block direction (polarization state 31) and a substantially normally incident light 30p polarized along the pass direction (polarization state 32). A portion 131t of the light 30b is transmitted and a portion 131r of the light 30b is reflected. A portion 132t of the light 30p is transmitted and a portion 132r of the light 30p is reflected. Each portion 131t, 131r, 132t, 132r is shown diagrammatically as including a specular and a diffuse reflection component. Total optical reflectance can be measured by using an integrating sphere to collect all reflected light of a given wavelength or range of wavelengths and measure the reflectance. Diffuse optical reflectance, also referred to as specular-removed reflectance, can be measured by measuring the reflectance using an integrating sphere that allows light corresponding to specular reflection to escape the integrating sphere. Alternatively, in some embodiments, total optical reflectance and diffuse optical reflectance may be approximated as 100% minus the total transmittance and diffuse transmittance, respectively, measured according to the ASTM D1003-13 test standard. Specular reflectance can be measured as the difference between the total optical reflectance and the diffuse optical reflectance. The films 200, 201 have a length L along the pass direction that can be greater than about 40 inches, or greater than about 45 inches, or greater than about 50 inches, or greater than about 55 inches, or greater than about 60 inches. For example, the films 200, 201 can be formed by extrusion along the p direction and may be formed in a continuous roll-to-roll process, where the length L can be, for example, tens or hundreds of yards.Films 200, 201 may have an average thickness in the range of, for example, from about 30 to about 250 micrometers, or from about 40 to about 200 micrometers, or from about 50 to about 150 micrometers.

[0012] The binder 20 and particles 10, 11 have refractive indices along each of the illustrated b, p, and z directions. In some embodiments, the optical diffusion film 200, 201 includes a plurality of particles 10, 11 dispersed within the binder 20, the particles and binder having respective refractive indices n1b and n2b along a block direction (b direction) in the same in-plane (pb plane) of the optical diffusion film 200, 201 and respective refractive indices n1p and n2p along an in-plane pass direction (p direction) perpendicular to the block direction, the magnitude of the difference between n1b and n2b being greater than about 0.05 and the magnitude of the difference between n1p and n2p being less than about 0.05 for at least a first wavelength in a first wavelength range spanning from about 400 nm to about 1000 nm. In some embodiments, for at least the first wavelength, the magnitude of the difference between n1b and n2b may be greater than about 0.05, greater than about 0.06, greater than about 0.07, greater than about 0.08, greater than about 0.09, or greater than about 0.1. In some such embodiments, or in other embodiments, for at least the first wavelength, the magnitude of the difference between n1p and n2p is less than about 0.05, or less than about 0.04, or less than about 0.03, or less than about 0.02, or less than about 0.01.

[0013] The at least first wavelength may include one or more wavelengths in a second wavelength range narrower than the first wavelength range. For example, the at least first wavelength may include one or more wavelengths in a second wavelength range, for example, about 400 nm to about 700 nm, or about 420 nm to about 680 nm, or about 450 nm to about 650 nm. Alternatively, the first wavelength range may be narrower than about 400 nm to about 1000 nm (for example, the first wavelength range may be any of the ranges described for the second wavelength range). Wavelength ranges spanning λ1 to λ2 (for example, corresponding to the first or second wavelength range) are shown diagrammatically in FIG. 1B. λ1 may be, for example, about 400 nm, or about 420 nm, or about 450 nm. λ2 may be, for example, about 1000 nm, or about 850 nm, or about 700 nm, or about 680 nm, or about 650 nm. The at least first wavelength may include, for example, one or more of about 532 nm, about 550 nm, about 631 nm, about 633 nm, or about 900 nm.

[0014] In some embodiments, for substantially normally incident light 30 having a first wavelength, the optical diffusion film 200, 201 has a diffuse optical transmittance TDb and a diffuse optical reflectance RDb (TDb / RDb≧4) when the incident light is polarized along the block direction, and a total optical transmittance TTp and a diffuse optical transmittance TDp (TTp / TDp≧1.1) when the incident light is polarized along the pass direction. In some applications, low backscattering (e.g., quantified by a TDb / RDb of at least 4) may be desired for light polarized along the block direction, and limited diffuse transmittance relative to the total transmittance (e.g., quantified by a TTp / TDp of 1.1 or greater) may be desired for light polarized along the pass direction. Figure 3 is a plot of TDb / RDb and TTp / TDp versus wavelength, according to some embodiments. Typically, TDb / RDb generally increases when the number of particles included in the binder is reduced and / or the difference in refractive index along the block direction between the particles and the binder is reduced, resulting in less backscattering. Typically, TTp / TDp generally increases when the number or volume of particles contained in the binder is decreased and / or the difference in refractive index between the particles and the binder along the pass direction is decreased. In some embodiments, TDb / RDb≧4, or TDb / RDb≧5, or TDb / RDb≧6, or TDb / RDb≧7, or TDb / RDb≧7, or TDb / RDb≧9, or TDb / RDb≧10, or TDb / RDb≧11. In some such embodiments, or in other embodiments, TTp / TDp≧1.1, or TTp / TDp≧1.25, or TTp / TDp≧1.5, or TTp / TDp≧1.75, or TTp / TDp≧2, or TTp / TDp≧2.25, or TTp / TDp≧2.5. TDb / RDb may be, for example, up to about 25, or up to about 20, or up to about 18. TTp / TDp may be, for example, up to about 5, or up to about 4, or up to about 3. The peak occurring near 850 nm in FIG. 3 and other plots of ratio versus wavelength is believed to be due to a detector switch in the spectrophotometer used for the measurements.

[0015] Substantially normally incident light may be, for example, within 30 degrees, or 20 degrees, or 10 degrees of normal, or may be nominally normal. For obliquely incident light, light may be described as polarized along the block direction or pass direction when the polarization state projected onto the bp plane is along the block direction or pass direction, respectively.

[0016] In some embodiments, for substantially normally incident light 30 having a first wavelength, the optical diffusion film 200, 201 has a diffuse optical reflectance RDp when the incident light is polarized along the pass direction. In some applications, low backscatter (e.g., as quantified by a TTp / RDp of at least 10 and / or as described elsewhere herein, as quantified by a TTp / RTp of at least 6) for light polarized along the pass direction may be desired. In some embodiments, TTp / RDp≧10, or TTp / RDp≧15, or TTp / RDp≧20, or TTp / RDp≧25, or TTp / RDp≧30, or TTp / RDp≧35. In some such embodiments, or in other embodiments, for substantially normally incident light 30 having a first wavelength, the optical diffusion film 200, 201 has a total optical reflectance RTp when the incident light is polarized along the pass direction, where TTp / RTp≧6, or TTp / RTp≧7, or TTp / RTp≧8, or TTp / RTp≧9. Typically, TTp / RDp and TTp / RTp generally increase when the number or volume of particles contained within the binder is reduced and / or the difference in refractive index along the pass direction between the particles and the binder is reduced. TTp / RDp can be, for example, up to about 100, or up to about 80, or up to about 70. TTp / RTp can be, for example, up to about 25, or up to about 20, or up to about 18. FIG. 4 is a plot of the ratio TTp / RDp and the ratio TTp / RTp versus wavelength, according to some embodiments.

[0017] FIG. 5 is a plot of the intensity distribution of the optical transmittance of an optical diffusion film versus scattering angle in the bz plane (e.g., scattering angle α1 in the bz plane in FIG. 1B) and scattering angle in the pz plane (e.g., scattering angle α2 in the pz plane in FIG. 2B) for light in the blocked state, according to some embodiments. The intensity distribution is normalized to have a maximum value of 1.0. The plot in FIG. 5 was measured using a collimated white light emitting diode (LED) light source. In some embodiments, for substantially normally incident light 30b polarized along the block direction, the total optical transmittance of the optical diffusion film 200, 201 has a first intensity distribution 34 and a second intensity distribution 35 in the first and second scattering planes (bz and pz planes) that include the block and pass directions, respectively. The scattering planes are generally planes defined by the direction of the incident light and the direction of the scattered light. In some applications, it may be desirable for the second intensity distribution to be broader than the first intensity distribution (e.g., quantified by a ratio of the full width at half maximum (FWHM) of the distribution of at least 1.5). In some embodiments, this different FWHM results, for example, from grains that are substantially elongated along the same in-plane block direction and have an average aspect ratio greater than about 5 (or within another range described elsewhere herein). In some embodiments, the first intensity distribution and the second intensity distribution have full widths at half maximum F1 and F2, respectively, where F2 / F1≧1, or F2 / F1≧1.5, or F2 / F1≧2, or F2 / F1≧2.5, or F2 / F1≧3, or F2 / F1≧3.5, or F2 / F1≧4, or F2 / F1≧10, or F2 / F1≧50, or F2 / F1≧100. F1 can be small (e.g., less than 1 degree) in some cases (e.g., when large stretch ratios are utilized), resulting in a large F2 / F1 ratio. F2 / F1 can be, for example, up to about 500. In other embodiments, F2 / F1 is, for example, not more than about 200, or not more than about 100, or not more than about 50, or not more than about 20. In some embodiments, F1 is, for example, in the range of about 0.5 degrees to about 10 degrees, or about 1 degree to about 8 degrees, or about 1.5 degrees to about 6 degrees, or about 2 degrees to about 5 degrees.In some such embodiments, or in other embodiments, F2 is, for example, up to about 60 degrees, or up to about 40 degrees, or up to about 30 degrees, or up to about 25 degrees.

[0018] In some applications, a higher haze is desired for light polarized along the block direction than for light polarized along the pass direction. In some embodiments, the optical diffusion film 200, 201 has an optical haze Hb for substantially normally incident light 30, 30b polarized along the block direction and an optical haze Hp for substantially normally incident light 30, 30p polarized along the pass direction, where Hb / Hp≧1.5, or Hb / Hp≧2, or Hb / Hp≧2.5, or Hb / Hp≧3, or Hb / Hp≧3.5. The optical haze of the film for a specified polarization state can be measured using a haze meter (e.g., a Haze-Gard haze meter available from BYK Corporation, Wesel, Germany) by placing an absorbing linear polarizer on the film facing the light source of the haze meter and aligning the pass axis of the polarizer to the specified polarization state. Optical haze can be measured as described in the ASTM D1003-13 test standard, except that the test specimen includes an absorbing linear polarizer disposed on the film. Typically, optical haze Hb generally increases when the difference in refractive index between the particles and the binder along the block direction is increased and / or when the number of particles is increased. Optical haze Hb can be high (e.g., greater than about 80% or greater than about 90%), for example, when the refractive index between the particles and the binder along the block direction is substantially different (e.g., differs by at least about 0.08 or at least about 0.1). Optical haze Hp can be low (e.g., less than about 2% or less than about 1%), for example, when the refractive index between the particles and the binder along the pass direction is closely matched (e.g., within about 0.02 or within about 0.01). Hb / Hp can be, for example, up to about 100, or up to about 50, or up to about 25, or up to about 20. In some embodiments, Hb is in the range of about 10% to about 100%, or about 15% to about 99%, or about 20% to about 98%, or about 20% to about 90%. In some such embodiments, or in other embodiments, Hp is in the range of about 0% to about 65%, or about 0.5% to about 60%, or about 1% to about 55%, or about 1.2% to about 50%, or about 5% to about 45%, or about 10% to about 40%.The higher haze for light 30b than for light 30p is shown, for example, diagrammatically in FIG. 2B.

[0019] In some embodiments, for light 30 having a first wavelength and incident substantially normally, the optical diffusion film 200, 201 has a total optical transmittance TTb when the incident light is polarized along the block direction. TTb may be similar to TTp (e.g., both may be greater than about 60%, or greater than about 70%), and the regular optical transmittance TSp when the incident light is polarized along the pass direction may be substantially greater than the regular optical transmittance TSb when the incident light is polarized along the block direction (e.g., a substantially greater diffuse transmittance and correspondingly substantially less regular transmittance may be desired for light polarized along the block direction than for light polarized along the pass direction). Figure 7 is a plot of TSp / TSb and TTp / TTb versus wavelength, according to some embodiments. In some embodiments, for light 30 having a first wavelength and incident substantially normally, 0.5≦TTp / TTb≦2. In some such or other embodiments, for substantially normally incident light 30 having a first wavelength, the optical diffusion films 200, 201 have positive optical transmissions TSp and TSb when the incident light is polarized along the pass and block directions, respectively, where TSp / TSb > 2. In some such or other embodiments, 0.5 < TTp / TTb, or 0.6 < TTp / TTb, or 0.7 < TTp / TTb, or 0.8 < TTp / TTb, or 0.9 < TTp / TTb, or 1 < TTp / TTb. In some such embodiments, or in other embodiments, TTp / TTb≦2, or TTp / TTb≦1.9, or TTp / TTb≦1.8, or TTp / TTb≦1.7, or TTp / TTb≦1.6, or TTp / TTb≦1.5, or TTp / TTb≦1.4, or TTp / TTb≦1.3, or TTp / TTb≦1.25, or TTp / TTb≦1.2. In some such embodiments, or in other embodiments, TSp / TSb≧2, or TSp / TSb≧2.5, or TSp / TSb≧3, or TSp / TSb≧3.5, or TSp / TSb≧4, or TSp / TSb≧4.5, or TSp / TSb≧5, or TSp / TSb≧5.5, or TSp / TSb≧6.Typically, TSp / TSb generally increases when the difference in refractive index between the particle and the binder along the block direction is increased and / or when the difference in refractive index between the particle and the binder along the pass direction is decreased. TSp / TSb may be, for example, up to about 150, or up to about 100, or up to about 75, or up to about 50, or up to about 30.

[0020] In some embodiments, for substantially normally incident light 30 having a first wavelength, the optical diffusion film 200, 201 has a total optical transmittance TTb and a total optical reflectance RTb when the incident light is polarized along the block direction, where 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, where TTp / RTp≧6. In some applications, low backscattering (e.g., quantified by a TTb / RTb of at least 2 and / or by a TTp / RTp of at least 6) may be desired. FIG. 6 is a plot of the ratios TTb / RTb and TTp / RTp versus wavelength, according to some embodiments. In some embodiments, TTb / RTb≧2, or TTb / RTb≧3, or TTb / RTb≧3.5, or TTb / RTb≧4, or TTb / RTb≧4.5. In some such embodiments, or in other embodiments, TTp / RTp≧6, or TTp / RTp≧7, or TTp / RTp≧8, or TTp / RTp≧9, or TTp / RTp≧10, or TTp / RTp≧11. Typically, TTb / RTb generally increases when the number of particles in the binder is reduced and / or the difference in refractive index between the particles and the binder along the block direction is reduced, resulting in less backscattering. TTb / RTb can be, for example, up to about 15, or up to about 12, or up to about 10. TTp / RTp can be large when the refractive index along the pass direction of the particles and the binder is closely matched. TTp / RTp can be, for example, up to about 100, or up to about 75, or up to about 50, or up to about 30. In some embodiments, for substantially normally incident light 30 having a first wavelength, RTb is less than about 25%, or less than about 20%, or less than about 17%, or less than about 15%. In some such embodiments, or in other embodiments, for substantially normally incident light 30 having a first wavelength, RTp is less than about 20%, or less than about 15%, or less than about 10%, or less than about 8%.

[0021] In some embodiments, the optical diffusion film 200, 201 includes a plurality of particles 10, 11 dispersed within a binder 20. The particles 10, 11 and the binder 20 have respective refractive indices n1b and n2b along the same in-plane (pb-plane) block direction (b-direction) of the optical diffusion film 200, 201, and respective refractive indices n1p and n2p along the in-plane pass direction (p-direction) perpendicular to the block direction, and the magnitude of the difference between n1b and n2b is greater than about 0.05 and the magnitude of the difference between n1p and n2p is less than about 0.05 for at least a first wavelength within a first wavelength range spanning from about 400 nm to about 1000 nm (or any wavelength range described elsewhere herein). The magnitude of the difference between n1b and n2b can be within any range described elsewhere herein. The magnitude of the difference between n1p and n2p can be within any range described elsewhere herein. In some embodiments, for substantially normally incident light 30 having a first wavelength, the optical diffusion film 200, 201 has a total optical transmittance TTb and a total optical reflectance RTb when the incident light is polarized along the block direction, and a total optical transmittance TTp and a total optical reflectance RTp when the incident light is polarized along the pass direction. In some embodiments, TTb / RTb≧2, or TTb / RTb can be within any of the ranges described elsewhere herein. In some or other embodiments, TTp / RTp≧6, or TTp / RTp can be within any of the ranges described elsewhere herein. In some embodiments, for substantially normally incident light having a first wavelength, 0.5≦TTp / TTb≦2, and the optical diffusion film 200, 201 has a positive optical transmittance TSp and TSb when the incident light is polarized along the pass direction and the block direction, respectively, and TSp / TSb≧2. TTp / TTb and TSp / TSb can be within any of the respective ranges described elsewhere herein.

[0022] In some embodiments, the optical diffusion film 200, 201 is formed by an extrusion process, as further described elsewhere herein. In some embodiments, the optical diffusion film 200, 201 includes a plurality of substantially parallel (e.g., within about 20 degrees, or within about 15 degrees, or within about 10 degrees, or within about 6 degrees, or within about 4 degrees of parallel) extrusion die lines 40 that form an angle θ of less than about 20 degrees, or less than about 15 degrees, or less than about 10 degrees, or less than about 6 degrees, or less than about 4 degrees with respect to the pass direction. Die lines are marks or structures (e.g., ridges or grooves) left in the film from the die used to extrude the film. The die lines may be spaced apart a greater distance along the b direction than the corresponding features of the die, since the film may be stretched in a direction substantially perpendicular to the die lines after extrusion. In some embodiments, at least some of the extrusion die lines 40 form ridges 41. In some embodiments, the ridges 41 of the die lines have an average height h (e.g., see FIG. 1B) of, for example, about 0.1 to about 8 microns, or about 0.2 to about 4 microns, or about 0.4 to 2 microns. In some embodiments, at least some of the extrusion die lines 40 form groove lines 42. In some embodiments, the groove lines 42 of the die lines have an average depth d (e.g., see FIG. 1B) of, for example, about 0.1 to about 8 microns, or about 0.2 to about 4 microns, or about 0.4 to 2 microns. In some embodiments, the die lines are sufficiently large (e.g., wide and / or high / deep) that the die lines can be easily seen by the naked eye (e.g., of a person with normal vision) when light from a light source point (e.g., polarized along the pass direction) is transmitted through the film to form a projected image (e.g., when viewed from a distance of about 1 m from the projected image).

[0023] In some embodiments, an extruded optical diffusion film 201 extruded along a pass direction (p-direction) includes a plurality of particles 11 dispersed within a binder 20, the particles 11 being elongated substantially along the same in-plane block direction (b-direction) perpendicular to the pass direction. For example, the particles 11 can be elongated along directions within about 20 degrees, or within about 10 degrees, or within about 5 degrees of the same direction (b-direction). The particles can have an average aspect ratio, for example, greater than about 5, or greater than about 10, or greater than about 15, or greater than about 20, or greater than about 40, or greater than about 45, or greater than about 50. The average aspect ratio can be, for example, up to about 1000, or up to about 600, or up to about 400, or up to about 200, or up to about 100, or up to about 80. Unless otherwise stated, the aspect ratio of a particle is the length of the particle along the stretch direction (Lb) divided by the length of the particle along the thickness direction (z-direction) of the film (Lz). The average aspect ratio is the average (e.g., unweighted average) of the particle aspect ratios for a plurality of particles. In some embodiments, for example, one or both of Lb / Lp and Lp / Lz can have an average in the ranges described herein for the average particle aspect ratio (average Lb / Lz). The optical diffusion film 201 can include a plurality of substantially parallel extrusion die lines 40 that make an angle θ of less than about 20 degrees with respect to the pass direction, or the angle θ can be within any of the ranges described elsewhere herein. In some embodiments, for substantially normally incident light 30 having a first wavelength within a first wavelength range spanning from about 400 nm to about 1000 nm, or another range described elsewhere herein, the optical diffusion film 201 has a diffuse optical transmittance TDb and a diffuse optical reflectance RDb when the incident light is polarized along the block direction, where 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, where TTp / RDp≧10. TDb / RDb and TTp / RDp can be within any of the respective ranges described elsewhere herein.In some embodiments, the extruded optical diffusion film 201 has a length L along the pass direction that is greater than about 40 inches, or the length L can be within another range described elsewhere herein.

[0024] In some embodiments, the binder 20 comprises a first thermoplastic polymer and the particles 10, 11 comprise a second thermoplastic polymer that is different therefrom. In some embodiments, the first thermoplastic polymer and the second thermoplastic polymer are immiscible at temperatures higher than the melting temperature of the first thermoplastic polymer and the melting temperature of the second thermoplastic polymer (i.e., at temperatures higher than the melting temperature of the first thermoplastic polymer and the melting temperature of the second thermoplastic polymer, respectively). In some such or other embodiments, the first thermoplastic polymer is birefringent and the second thermoplastic polymer is substantially optically isotropic.

[0025] Suitable materials for the binder 20 include, for example, polyethylene naphthalate (PEN), coPEN (copolyethylene naphthalate terephthalate copolymer), polyethylene terephthalate (PET), polyhexylethylene naphthalate copolymer (PHEN), glycol modified PET (PETG or PETg), glycol modified PEN (PENG), syndiotactic polystyrene (sPS), or blends thereof. Suitable sPS can be obtained, for example, from Idemitsu Kosan Co., Ltd. (Tokyo, Japan). Atactic polystyrene (aPS) can optionally be blended with sPS (e.g., at about 5 to about 30 weight percent aPS) to adjust the refractive index of the resulting layer and / or to reduce the haze of the layer (e.g., by reducing the crystallinity of the layer). Suitable PET can be obtained, for example, from Nan Ya Plastics Corporation, America (Lake City, SC). PETG can be described as PET in which some of the glycol units of the polymer have been replaced with different monomer units, typically monomer units derived from cyclohexanedimethanol. PETG can be produced by replacing a portion (e.g., about 15 to about 60 mole percent or about 30 to about 40 mole percent) of the ethylene glycol used in the transesterification reaction to produce the polyester with, for example, cyclohexanedimethanol. Suitable PETG copolyesters include GN071 available from Eastman Chemical Company (Kingsport, TN). PEN and coPEN can be produced, for example, as described in U.S. Pat. No. 10,001,587 (Liu). Glycol-modified polyethylene naphthalate (PENG) can be described as PEN in which some of the glycol units of the polymer have been replaced with different monomer units, for example, by replacing a portion (e.g., about 15 to about 60 mole percent or about 30 to about 40 mole percent) of the ethylene glycol used in the transesterification reaction to produce the polyester with, for example, cyclohexanedimethanol.PHEN can be prepared, for example, as described for PEN in U.S. Pat. No. 10,001,587 (Liu), except that a portion of the ethylene glycol used in the transesterification reaction (e.g., about 15 to about 60 mole percent, or about 30 to about 50 mole percent, or about 40 mole percent) is replaced with hexanediol. In some embodiments, the binder 20 comprises one or more of a polyester and a copolyester. For example, the binder may comprise a blend of a polyester and a copolyester. In some embodiments, the binder 20 comprises one or more of polyethylene terephthalate, glycol-modified polyethylene terephthalate, polyethylene naphthalate, and glycol-modified polyethylene naphthalate.

[0026] In some embodiments, the particles in the plurality of particles 10, 11 include a styrenic polymer or copolymer (a polymer or copolymer containing a styrene group). In some embodiments, the particles in the plurality of particles 10, 11 include one or more of styrene butadiene, styrene acrylonitrile, styrene methyl methacrylate, and impact modified styrene acrylic. Impact modified styrene acrylics can incorporate monomeric groups to improve impact resistance and / or toughness, as known in the art. Suitable impact modified styrene acrylics include, for example, those available under the trade name ZYLAR from Ineos Americas (League City, TX). Other suitable styrenic copolymers include, for example, those available under the trade names STYROLUX, STYROLUTION, and NAS from Ineos Americas (League City, TX). Other classes of materials useful as particles of the plurality include, for example, polycarbonate polymers containing bisphenol A, nylon polymers such as poly(hexamethylene adipamide) (nylon 6,6) and poly(caprolactam) (nylon 6), and methacrylate polymers such as poly(2-phenylethyl methacrylate). Selecting a polymer useful as a particle of the plurality may generally be guided by selecting a polymer to substantially match the refractive index of the birefringent binder in the non-stretched in-plane direction, and by selecting a polymer that is immiscible with the binder polymer system, remains non-birefringent during the stretching process, and does not degrade during the melt processing step.

[0027] 8 is a schematic process flow diagram of a method for making an optical diffusion film, according to some embodiments. In some embodiments, a method for making an optical diffusion film 201, 265 includes extruding an immiscible blend 263 of a secondary phase material 310 and a primary phase material 320 through a die along a pass direction (p-direction) at a first temperature T1 that is higher than the glass transition temperature (Tg) of the secondary phase material 310 and the glass transition temperature (Tg) of the primary phase material 320 to obtain an extruded mixture 264 substantially at the first temperature T1 (e.g., within about 10° C. or within 5° C. of T1) (step 301), and extruding the extruded mixture 264 in a block direction (b-direction) substantially perpendicular to the pass direction (e.g., within about 20 degrees, or within about 10 degrees, or within about 5 degrees of perpendicular). and stretching the binder 20 along the block direction at a second temperature T2 lower than the first temperature T1 to obtain a plurality of particles 11 dispersed within the binder 20 (step 302), wherein the binder 20 and at least a majority of the particles 11 each have respective refractive indices n2b and n1b along the block direction and respective refractive indices n2p and n1p along the pass direction, and the magnitude of the difference between n1b and n2b is greater than about 0.05 and the magnitude of the difference between n1p and n2p is less than about 0.05 for at least a first wavelength within a first wavelength range spanning from about 400 nm to about 1000 nm or any wavelength range described elsewhere herein. The magnitude of the difference between n1b and n2b can be within any range described elsewhere herein. The magnitude of the difference between n1p and n2p can be within any range described elsewhere herein. At least a majority of the particles 11 can include at least about 60 percent, or at least about 70 percent, or at least about 80 percent, or at least about 90 percent, or substantially all (by number) of the particles 11. At least a majority of the particles 11 can include at least about 60 percent, or at least about 70 percent, or at least about 80 percent, or at least about 90 percent, or substantially all of the total mass of the particles 11. The minor phase material of the immiscible blend generally comprises less than half of the total volume of the immiscible blend and typically defines a discontinuous phase.The major phase material of the immiscible blend generally comprises more than half of the total volume of the immiscible blend and typically defines the continuous phase.

[0028] 9A-9B are micrographs of the pz and bz cross sections of the extruded mixture (Example 1) before stretching. FIG. 10A-10B are micrographs of the pz and bz cross sections of the extruded mixture (Example 2) before stretching. In some embodiments, the extruded mixture 264 (before stretching) includes a plurality of discrete regions 410. In some embodiments, the extruded mixture includes a plurality of substantially spherical regions 510. For example, the discrete regions 410 can include a plurality of substantially spherical regions 510. In some embodiments, the discrete regions 410 can also include regions that are not substantially spherical. A substantially spherical region is a region where the largest sphere that can be inscribed in the region has a diameter Di, the smallest sphere that can contain the region has a diameter Do, and Do / Di is less than about 4. In some embodiments, at least a portion (e.g., at least a majority) of the substantially spherical regions have a Do / Di of less than about 3.5, or less than about 3, or less than about 2.5. It has been found that the domains can be made more spherical by using a larger die (e.g., a larger die gap) at a slower extrusion rate and / or by using a less viscous (e.g., at a given temperature) primary phase material 320 and / or a higher extrusion temperature (e.g., to reduce the viscosity of the primary phase material 320). Having substantially spherical domains in the extruded mixture has been found to result in particles with larger aspect ratios, e.g., after stretching along the b-direction, as opposed to being substantially elongated along the p-direction, and has been found to result in desirable scattering properties (e.g., high F2 / F1 as described elsewhere herein).

[0029] In some embodiments, the first temperature T1 is higher than the melting temperature of the minor phase material 310 and the melting temperature of the major phase material 320. In some embodiments, the first temperature T1 is, for example, greater than about 200° C., or greater than about 220° C., or greater than about 240° C., or greater than about 260° C., or greater than about 270° C. In some embodiments, the first temperature is, for example, less than about 400° C. In some embodiments, the second temperature is about 5 to about 50° C., or about 5 to about 40° C., or about 5 to about 30° C., or about 5 to about 20° C., or about 8 to about 30° C. higher than the glass transition temperature of the minor phase material and the glass transition temperature of the major phase material. In some such embodiments, or in other embodiments, prior to stretching the extruded mixture 264 along the block direction at the second temperature T2, the temperature of the extruded mixture 264 is reduced to a third temperature T3 that is lower than the second temperature T2. For example, the extruded mixture can be cast onto a casting wheel (sometimes referred to in the art as a chill roll or casting drum) and the mixture can be rapidly cooled to obtain a cast film. In some embodiments, the third temperature T3 is about room temperature (e.g., a temperature in the range of about 18 to about 30° C.).

[0030] In some embodiments, the discrete regions in the extruded mixture and / or the substantially spherical regions in the extruded mixture comprise at least mostly the minor phase material. For example, the minor phase material can comprise at least about 80 weight percent, or at least about 90 weight percent, or at least about 95 weight percent of the regions. In some embodiments, the discrete regions in the extruded mixture and / or the substantially spherical regions in the extruded mixture are dispersed in a material that comprises at least a majority of the major phase material. For example, the major phase material can comprise at least about 70 weight percent, or at least about 80 weight percent, or at least about 90 weight percent, or at least about 95 weight percent of the material in which the regions are dispersed. EXAMPLES

[0031] [Table 1] The optical diffusion films of Examples 1-5 were made by coextrusion and batch orienting using the materials shown in Table 2. The extruder temperature was about 277°C. [Table 2]

[0032] Material #1 and Material #3 (when included) were polyester phase materials and Material #2 was the copolystyrene phase material. The weight percent and pounds per hour (pph) of these materials in the extruder feed are shown in Table 2. The polyester and copolystyrene phases were immiscible and showed two separate phases after extrusion and stretching.

[0033] After extrusion and prior to stretching, the extruded mixture was cooled by casting the extruded mixture onto a casting wheel. In Examples 1-4, a two-layer coextrusion was performed, where the layer already described (the blend layer) was on the air side during the casting process, and the layer on the wheel side was composed of the same composition as the polyester phase in the blend layer and was fed at the same rate as the entire blend layer. In Example 5, a three-layer coextrusion was used, where the center layer was the blend layer, and the other two layers had the same composition as the polyester phase of the blend layer, and each of the two streams was fed at half the rate of the entire blend layer. An 8-inch extrusion die was used for all examples. The die gap was 60 mils for Examples 1-4 and 100 mils for Example 5.

[0034] For all of these films, the stretching process was carried out in a batch stretcher (Karo IV manufactured by Brueckner Group, Portsmouth, NH). A preheat and stretch temperature of 95°C was used. Stretching was a constrained stretch with a stretch ratio of about 6:1 in the transverse direction (TD) perpendicular to the machine direction (MD). PET stretched under these conditions has a refractive index of about 1.66 in the stretch direction (TD), 1.56 in the in-plane direction (MD) perpendicular to the stretch direction, and 1.53 through the thickness direction, as measured at 631 nm using a refractometer (Metricon Corporation, Pennington, NJ). The thicknesses of the films after stretching are shown in Table 2.

[0035] The tendency of the films to scatter polarized light was characterized using Haze Gard (BYK Corporation, Wesel, Germany). Haze for light polarized in the block direction (TD) was measured by placing a high contrast ratio absorbing polarizer (with the pass state transmission axis aligned in the stretch direction of the example film) on the incident light side of the example film and applying a transparent tape (3M 375 from 3M, Saint Paul, Minn.) to the air side of the film to reduce scattering from the surface roughness of the example film. The samples were oriented so that the wheel side of the film faced the incident light. For pass state haze, the absorbing polarizer is aligned in the non-stretch direction (MD) of the example film. The results of the polarized haze measurements are shown in Table 3.

[0036] The angular distribution of scattered light was measured using a conoscope (ELDIM Corporation, Herouville-Saint-Clair, France) at a cone angle of 80 degrees. A collimated white (LED) light source was used with an absorbing polarizer placed between the light source and the example film. Measurements were performed with the polarized transmission axis in the block direction, and the full width at half maximum (FWHM) of the scattering pattern along the MD and TD directions was measured and is reported in Table 3. [Table 3]

[0037] The reflective properties of the example films were measured by measuring the film reflectance in an integrating sphere. Total reflectance, also known as Reflectance with the Specular Included (RSIN), was measured by collecting all light reflected from the example film, incident from all angles, and diffuse reflectance, also known as Reflectance with the Specular Excluded (RSEX), was measured by allowing light that produces specular reflection to escape the integrating sphere. A LAMBDA 1050 spectrophotometer (PerkinElmer, Inc., Waltham, Mass.) was used for the measurements. Table 4 shows the resulting reflectances averaged over the wavelength range of 450 nm to 650 nm. [Table 4]

[0038] The scattering of the exemplary films for block state polarized light (normalized by the maximum counts achieved) in the plane defined by the machine and thickness directions (pz plane) is shown in Figure 11. An example of asymmetric scattering of these films is shown in Figure 5 for Example 5. Photomicrographs of cross sections of the example films before stretching are shown in Figures 9A-B for Example 1 and Figures 10A-B for Example 2.

[0039] The average aspect ratio of the particles before stretching the cast film was measured by examining the cross-sections in the bz and pz planes using an optical microscope. The ratios Lp / Lz and Lb / Lz were measured for the particles in the cross-sections and the average of the ratios was determined. The results are shown in Table 5. [Table 5]

[0040] The corresponding aspect ratios of the stretched films were calculated assuming a stretch ratio of about 6 would result in a 6x stretch in the TD and a 6x thinning in the Ctch direction, as would be expected if a standard tenter were used in the examples, and the results are shown in Table 6. [Table 6]

[0041] The aspect ratio that would be obtained if the cast film were stretched using a parabolic tenter with a stretch ratio of 6 was calculated assuming a stretch of 6 times in the TD and a shrinkage and thinning by the square root of 6 in the MD and thickness directions, respectively. The results are shown in Table 7. [Table 7]

[0042] Terms such as "about" will be understood by those of skill in the art in the context in which they are used and described herein. Where the use of "about" as applied to quantities describing feature sizes, quantities, and physical properties is not otherwise clear to those of skill in the art in the context in which it is used and described herein, "about" will be understood to mean within 10 percent of the particular value. A quantity given as about a particular value may be exactly that particular value. For example, where the use of "about" as applied to quantities describing feature sizes, quantities, and physical properties is not otherwise clear to those of skill in the art in the context in which it is used and described herein, a quantity having a value of about 1 means that the quantity has a value between 0.9 and 1.1, and may even be 1.

[0043] All references, patents, or patent applications referenced above are hereby incorporated by reference in their entirety. In the event of any inconsistency or contradiction between any of the incorporated references and this application, the information in the foregoing description shall prevail.

[0044] Descriptions of elements in the drawings should be understood to apply equally to corresponding elements in other drawings unless otherwise indicated. Although specific embodiments have been illustrated and described herein, those skilled in the art will appreciate that the specific embodiments illustrated and described may be replaced by various alternative and / or equivalent embodiments without departing from the scope of the present disclosure. The present application is intended to cover any adaptations, or variations, or combinations of the specific embodiments discussed herein. Accordingly, the present disclosure is intended to be limited only by the claims and the equivalents thereof.

Claims

1. 1. An optical diffusing film comprising a plurality of particles dispersed within a binder, the particles and the binder having respective refractive indices n1b and n2b along the same in-plane block direction of the optical diffusing film, and respective refractive indices n1p and n2p along an in-plane pass direction orthogonal to the block direction, and for at least a first wavelength within a first wavelength range spanning from about 400 nm to about 1000 nm: the magnitude of the difference between n1b and n2b is greater than about 0.05; the magnitude of the difference between n1p and n2p is less than about 0.05; for light having the first wavelength and substantially normally incident, the optical diffusing film: when the incident light is polarized along the block direction, it has a diffuse optical transmittance TDb and a diffuse optical reflectance RDb, where TDb / RDb≧4; When the incident light is polarized along the pass direction, it has a total optical transmittance TTp and a diffuse optical transmittance TDp, where TTp / TDp≧1.

1. Optical diffusion film.

2. 2. The optical diffusion film of claim 1, wherein for light having the first wavelength and incident substantially normally, the optical diffusion film has a diffuse optical reflectance RDp when the incident light is polarized along the pass direction, where TTp / RDp≧10.

3. 2. The optical diffusion film of claim 1, wherein for substantially normally incident light polarized along the block direction, the total optical transmittance of the optical diffusion film has a first intensity distribution and a second intensity distribution in a first scattering surface and a second scattering surface that include the block direction and the pass direction, respectively, the first intensity distribution and the second intensity distribution having full widths at half maximum F1 and F2, respectively, where F2 / F1≧1.

5.

4. The optical diffusion film of any one of claims 1 to 3, wherein the optical diffusion film is formed by an extrusion process including a plurality of substantially parallel extrusion die lines that form an angle of less than about 20 degrees with the pass direction.

5. 4. The optical diffusion film of claim 1, wherein the binder comprises a birefringent first thermoplastic polymer, the particles comprise a substantially optically isotropic second thermoplastic polymer, and the first and second thermoplastic polymers are immiscible at temperatures above the melting temperatures of the first and second thermoplastic polymers.

6. 4. The optical diffusion film of claim 1, having an optical haze Hb for substantially normally incident light polarized along the block direction and an optical haze Hp for substantially normally incident light polarized along the pass direction, where Hb / Hp≧1.

5.

7. The optical diffusing film of any one of claims 1 to 3, wherein the particles are elongated along the in-plane block direction and have an average aspect ratio of greater than about 10.

8. 1. An optical diffusing film comprising a plurality of particles dispersed within a binder, the particles and the binder having respective refractive indices n1b and n2b along the same in-plane block direction of the optical diffusing film, and respective refractive indices n1p and n2p along an in-plane pass direction orthogonal to the block direction, and for at least a first wavelength within a first wavelength range spanning from about 400 nm to about 1000 nm: the magnitude of the difference between n1b and n2b is greater than about 0.05; the magnitude of the difference between n1p and n2p is less than about 0.05; for light having the first wavelength and substantially normally incident, the optical diffusing film: when the incident light is polarized along the block direction, it has a total optical transmittance TTb and a total optical reflectance RTb, where TTb / RTb≧2; When the incident light is polarized along the pass direction, it has a total optical transmittance TTp and a total optical reflectance RTp, where TTp / RTp≧6. Optical diffusion film.

9. For the light having the first wavelength and substantially normally incident, 0.5≦TTp / TTb≦2, When the incident light is polarized along the pass direction and the block direction, respectively, the optical diffusion film has a positive optical transmittance TSp and a positive optical transmittance TSb, and TSp / TSb≧2. The optical diffusion film of claim 8.

10. For at least the first wavelength, the magnitude of the difference between n1b and n2b is greater than about 0.06; the magnitude of the difference between n1p and n2p is less than about 0.04; The optical diffusion film according to claim 8 or 9.

11. 1. An extruded optical diffusion film extruded along a pass direction, comprising: a plurality of particles dispersed within a binder, said particles being elongated substantially along a same in-plane block direction perpendicular to said pass direction and having an average aspect ratio of greater than about 5; a plurality of substantially parallel extrusion die lines that form an angle of less than about 20 degrees with the pass direction; for substantially normally incident light having a first wavelength within a first wavelength range spanning from about 400 nm to about 1000 nm, the optical diffusing film: when the incident light is polarized along the block direction, it has a diffuse optical transmittance TDb and a diffuse optical reflectance RDb, where TDb / RDb≧4; When the incident light is polarized along the pass direction, it has a total optical transmittance TTp and a diffuse optical reflectance RDp, where TTp / RDp≧10. Extruded optical diffusion film.

12. 12. The extruded optical diffusing film of claim 11 having a length along said pass direction greater than about 40 inches.

13. 1. A method of making an optical diffusion film, comprising: extruding an immiscible blend of a minor phase material and a major phase material through a die along a pass direction at a first temperature greater than a glass transition temperature of the minor phase material and a glass transition temperature of the major phase material to obtain an extruded mixture having a plurality of substantially spherical domains at substantially the first temperature; stretching the extruded mixture along a block direction substantially perpendicular to the pass direction at a second temperature lower than the first temperature to obtain a plurality of particles dispersed within a binder, wherein the binder and at least a majority of the particles each have respective refractive indices n2b and n1b along the block direction and respective refractive indices n2p and n1p along the pass direction, and for at least a first wavelength within a first wavelength range spanning from about 400 nm to about 1000 nm: the magnitude of the difference between n1b and n2b is greater than about 0.05; the magnitude of the difference between n1p and n2p is less than about 0.05; method.

14. 14. The method of claim 13, wherein the second temperature is about 5 to about 50° C. higher than the glass transition temperature of the minor phase material and the glass transition temperature of the major phase material, and the temperature of the extruded material is reduced to a third temperature lower than the second temperature prior to stretching the extruded mixture along the block direction at the second temperature.

15. 15. The method of claim 13 or 14, wherein the substantially spherical regions within the extruded mixture comprise at least a majority of the secondary phase material.

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