Optical diffusion film and optical system including same

Abstract

An optical diffusion film includes a plurality of particles dispersed in a binder. The particles and the binder have respective refractive indexes n1b and n2b along a light blocking direction in the same plane of the optical diffusion film and respective refractive indexes n1p and n2p along a light transmitting direction in a plane orthogonal to the light blocking direction, such that for at least a first wavelength in the visible wavelength range extending from about 420 nm to about 680 nm: the magnitude of the difference between n1b and n2b is greater than about 0.04; and the magnitude of the difference between n1p and n2p is less than about 0.05. The optical diffusion film may have respective total optical transmittances TT (B) and TT (P) and respective optical diffuse transmittances TD (B) and TD (P) for the visible wavelength range and polarization states along the light blocking direction and the light transmitting direction for substantially collimated substantially vertical incident light, with TD (B) / TT (B) > = 0.7 and TD (P) / TT (P) > = 0.15.

Description

Summary of the invention

[0001] The present specification generally relates to an optical diffuser film including particles dispersed in a binder, and to an optical system including a display and an optical diffuser film. The optical diffuser film may have a higher optical diffusivity for light polarized in a blocking direction, and may have a lower optical diffusivity for light polarized in an orthogonal transmission direction. The optical diffuser film may more strongly scatter light polarized in the blocking direction in a plane parallel to the transmission direction, and less scatter light polarized in the blocking direction in a plane parallel to the blocking direction.

[0002] In some aspects, the present specification provides an optical diffuser film, which includes a plurality of particles dispersed in a binder. The particles and the binder have corresponding refractive indices n1b and n2b along the blocking direction in the same plane of the optical diffuser film and corresponding refractive indices n1p and n2p along the light-transmitting direction in a plane orthogonal to the blocking direction, so that for at least a first wavelength in the visible wavelength range extending from about 420 nm to about 680 nm: the magnitude of the difference between n1b and n2b is greater than about 0.04; and the magnitude of the difference between n1p and n2p is less than about 0.05. For substantially collimated substantially vertical incident light, for the visible wavelength range and polarization states along the blocking direction and the light-transmitting direction, the optical diffuser film may have corresponding total optical transmittances TT(B) and TT(P) and corresponding diffuse optical transmittances TD(B) and TD(P), wherein TD(B) / TT(B)≥0.7 and TD(P) / TT(P)≥0.15.

[0003] In some aspects, the present specification provides an optical diffusion film, the optical diffusion film comprising a plurality of particles dispersed in a binder and extending along an in-plane light-blocking direction orthogonal to the in-plane light-transmitting direction and the thickness direction of the optical diffusion film. The particles have average lengths Lb and Lz along the corresponding light-blocking direction and thickness direction, wherein Lb / Lz may be greater than about 10. For at least a first wavelength in a visible wavelength range extending from about 420 nm to about 680 nm, the magnitude of the difference between the refractive index of the particles and the binder along the light-blocking direction is at least about 0.04, and the magnitude of the difference between the refractive index of the particles and the binder along the light-transmitting direction is less than about 0.05. For substantially collimated substantially vertical incident light and for the visible wavelength range: for incident light polarized along the light-transmitting direction, the optical diffuser film has an optical mirror transmittance with respect to wavelength having a standard deviation greater than about 2%; and for incident light polarized along the light-blocking direction, the optical diffuser film has corresponding optical diffuse transmittance TD(B) and optical mirror transmittance TS(B), wherein TD(B) / TS(B) may be greater than about 2.

[0004] In some aspects, the present specification provides an optical diffusion film, which includes a plurality of particles dispersed in a binder and extending along an in-plane light-blocking direction orthogonal to the in-plane light-transmitting direction and the thickness direction of the optical diffusion film. The particles have average lengths Lb and Lz along the corresponding light-transmitting direction and thickness direction, wherein Lb / Lz may be greater than about 10. For at least a first wavelength in a visible wavelength range extending from about 420 nm to about 680 nm, the magnitude of the difference between the refractive index of the particles and the binder along the light-blocking direction is at least about 0.04, and the magnitude of the difference between the refractive index of the particles and the binder along the light-transmitting direction is less than about 0.05. For substantially collimated substantially vertical incident light polarized along the light-blocking direction and for the first wavelength, the optical transmittance of the optical diffusion film that varies with the transmission angle includes a substantially linear segment extending from at least about 10 degrees to about 60 degrees. The substantially linear segment may have a best linear fit with an r-squared value greater than about 0.8.

[0005] In some aspects, the present specification provides an optical system, the optical system including a display configured to emit an image for viewing by a viewer; and an optical diffuser film disposed between the display and the viewer for diffusely transmitting the emitted image primarily along a viewing direction substantially parallel to the display, so that the transmitted image has full viewing angles A(p) and A(b) along the corresponding viewing direction and a non-viewing direction orthogonal to the viewing direction and substantially parallel to the display, wherein A(p) / A(b)≥2. For substantially collimated substantially vertical incident light and for a visible wavelength range extending from about 420 nm to about 680 nm: for incident light polarized along the corresponding non-viewing direction and the viewing direction, the optical diffuser film has a total optical transmittance TT(B) greater than about 40% and a total optical transmittance TT(P) greater than about 60%; and for incident light polarized along the non-viewing direction and for a first wavelength in the visible wavelength range, the optical diffuser film may have an average normalized optical transmittance greater than about 0.2 at a transmission angle between about 5 degrees and about 20 degrees.

[0006] These and other aspects will become apparent from the following detailed description.This brief summary, however, should not be construed in any way as limiting the claimed subject matter. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 is a schematic top view of an optical diffuser film according to some embodiments.

[0008] Figure 2 is a schematic cross-sectional view of an optical diffusion film according to some embodiments.

[0009] Figure 3is a schematic top perspective view of an optical diffuser film according to some embodiments.

[0010] Figures 4 to 5 Graphs of optical reflectivity versus wavelength for exemplary and comparative optical diffuser films for substantially normally incident light having polarization states along block and pass directions, respectively.

[0011] Figure 6 to Figure 7 Graphs of optical transmittance versus wavelength for exemplary and comparative optical diffuser films for substantially normally incident light having polarization states along block and pass directions, respectively.

[0012] Figure 8 is a graph of normalized optical transmittance versus transmission angle for exemplary and comparative optical diffuser films.

[0013] Fig. 9 Shows Figure 8 A portion of a graph of optical transmittance.

[0014] Fig.10 is a schematic cross-sectional view of an optical system according to some embodiments.

[0015] Fig.11 is a schematic process flow diagram of a method for preparing an optical diffuser film according to some embodiments. DETAILED DESCRIPTION

[0016] In the following description, reference is made to the accompanying drawings, which form a part of the present invention and in which various embodiments are shown by way of example. The drawings are not necessarily drawn to scale. It should be understood that other embodiments may be conceived and carried out without departing from the scope or essence of the present specification. Therefore, the following specific embodiments should not be considered to have a limiting meaning.

[0017] According to some embodiments of the present specification, the optical diffusion film has a higher haze for light polarized in a first direction (also referred to as a "light blocking" direction) than in an orthogonal second direction (also referred to as a "light transmitting" direction), and may have greater scattering in a plane defined by the second direction and the thickness direction than in a plane defined by the first direction and the thickness direction. The optical diffusion film can be used, for example, in display or sensor applications. For example, a display can be constructed in which light passes through a liquid crystal display (LCD) panel (e.g., after passing through a cross prism film) with a narrow viewing angle, and on the exit side of the LCD panel, the optical diffusion film can be arranged in a horizontally oriented second direction to widen the viewing angle in the horizontal plane. As another example, an optical diffuser film may be used with a quarter wave retarder on an optical device (e.g., an optical sensor) such that when light polarized in a blocking direction is incident on the device with a wide angle distribution and any such light reflected from the device back toward the optical diffuser film is incident on the optical diffuser film in a less scattered light-transmitting state, and / or such that when light polarized in a light-transmitting direction is incident on the device with a narrow angle distribution and any such light reflected from the device back toward the optical diffuser film is incident on the optical diffuser film in a blocking state and substantially transmits the light-transmitting optical diffuser film with a wider angle distribution.

[0018] According to some embodiments of the present specification, an optical diffusion film includes a plurality of particles dispersed in a binder, wherein the particles are substantially optically isotropic (for example, for at least one wavelength in the range of about 400 nm to about 1000 nm, the difference between the maximum refractive index and the minimum refractive index of the particles may 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 wherein the binder is birefringent (for example, for at least one wavelength in the range of about 400 nm to about 1000 nm, the difference between the maximum refractive index and the minimum refractive index of the binder may be greater than about 0.04, or greater than about 0.045, or 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, and the difference may be, for example, at most about 0.35, or at most about 0.3, or at most about 0.25). The difference in the refractive index of the binder and the particles can be substantially different along a first direction (e.g., the difference is 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, and the difference can be, for example, at most about 0.35, or at most about 0.3, or at most about 0.25), and substantially matched along an orthogonal second direction (e.g., the difference 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). The at least one wavelength can be or include at least a first wavelength in the visible wavelength range extending from about 420 nm to about 680 nm. For example, the first wavelength can be about 631 nm or about 633 nm. The particles can be elongated along the first direction, which can result in greater scattering in the second direction (i.e., in a scattering plane including the second direction) than in the first direction.

[0019] The optical properties of the optical diffusion film can be adjusted by selecting a binder and a particulate material to have different refractive indices in the desired range along the light-blocking axis and the light-transmitting axis, adjusting the number or volume of the particles, and adjusting the shape of the particles. Increasing the refractive index difference in the light-blocking direction generally increases scattering in the light-blocking polarization state. Increasing the number of particles (e.g., by coextruding a larger volume of the secondary phase material in an immiscible blend of the secondary phase material and the primary phase material) also increases scattering. For example, the refractive index difference and the number of particles can be selected to cause predominantly forward scattering. It has been found that when, for example, the refractive index difference and the aspect ratio are appropriately selected (e.g., Lb / Lz is greater than about 100 or within the range described elsewhere herein), the optical transmittance of the optical diffusion film for the transmission angle may have a linear section, as further described elsewhere herein, which may be desirable in some applications, such as providing a desired full viewing angle in display applications. It has also been found that, for example, by appropriate selection of refractive index differences and aspect ratios, the averages, standard deviations and / or ratios of total transmittance, diffuse transmittance and / or specular transmittance and / or reflectance can be controlled within desired ranges of block states and polarization states that have been found to be useful for display applications.

[0020] As further described elsewhere herein, an optical diffusion film can be formed by extrusion followed by stretching. The stretch ratio used in the stretching can affect the refractive index of the binder (e.g., for positive birefringent polymers, increasing in the stretching direction) and the shape of the particles (e.g., causing the particles to elongate along the stretching direction). The stretch ratio may 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 may be at most about 30:1, or at most about 20:1, or at most about 15:1, or at most about 10:1, or at most about 8:1, or at most about 7:1. The stretch ratio may 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. It has been found that elongating the particles along the stretching direction (which may also be the light blocking direction) can result in increased scattering in a scattering plane orthogonal to the stretching direction. The stretching direction may be a longitudinal direction (MD), which may be substantially parallel to the extrusion direction. The particles can be extruded such that the particles are already elongated along the longitudinal portion upon extrusion and then stretched to substantially further increase the elongation of the particles, resulting in high aspect ratio particles (e.g., Lb / Lz greater than about 100 or within the ranges described elsewhere herein).

[0021] Figure 1 to Figure 21 and 2 are schematic top views and schematic cross-sectional views of an optical diffusion film 100 including particles 10 dispersed in a binder 20 according to some embodiments. The film 100 extends along a first direction (light blocking direction or b direction) and a second direction (light transmission direction or p direction) in orthogonal planes, and has a thickness along a z direction orthogonal to the b direction and the p direction. The particles 10 are elongated along the b direction. The particles may have an average length Lb along the light blocking direction or stretching direction, an average length Lp along the light transmission direction, and an average length Lz along the thickness direction (z direction). The particles 10 may have a thickness substantially higher than Figure 1 A to Figure 1 B schematically shows Lb / Lp ratio and / or Lb / Lz ratio. In some embodiments, Lb / Lz is greater than about 10, or 20, or 30, or 40, or 50, or 60, or 70, or 80, or 90, or 100, or 125, or 150, or 175, or 200, or 225, or 250, or 275. For example, Lb / Lz may be up to about 1000, 700, 500, or 400. When stretched in the b direction, the film typically shrinks in the thickness direction, which increases Lb / Lz. For example, when the film is constrained in the transverse direction (TD or p direction) and stretched in the longitudinal direction (MD or b direction), the thickness shrinks with a stretch ratio that is approximately the same as the stretch ratio used to stretch the film in the longitudinal direction, so that Lb / Lz increases by the approximate square of the stretch ratio. In some embodiments, Lb / Lp is greater than about 5, or 10, or 20, or 30, or 40. For example, Lb / Lp may be up to about 200, 150, or 100.

[0022] The film 100 has a length L along the light blocking 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. The length L can be substantially greater than Figure 1 or Figure 3 100. For example, the film 100 can be formed by extrusion along the b direction, and can be formed in a continuous roll-to-roll process, wherein the length L can be, for example, tens of yards or hundreds of yards. The film 100 can have an average thickness in the range of, for example, about 30 microns to about 250 microns, or about 40 microns to about 200 microns, or about 50 microns to about 150 microns.

[0023] Substantially collimated light 43 incident substantially vertically on the optical diffuser film 100 is schematically shown at Figure 2For example, substantially vertical incident light can be within 30 degrees, or 20 degrees, or 10 degrees of the normal, or can be the nominal normal. For oblique incident light, when the polarization state projected onto the bp plane is along the corresponding blocking direction and the transmission direction, the light can be described as polarized along the blocking direction and the transmission direction. Substantially collimated light can have a divergence / convergence angle of, for example, less than about 30 degrees, or 20 degrees, or 10 degrees, or 5 degrees. For example, the divergence / convergence angle can be substantially less than the transmission angle of interest. Blocking polarization state 31 and transmission polarization state 32 are schematically shown. At least for blocking polarization state 31, light 43 can be scattered at least in the pz plane. α schematically shows the scattering angle.

[0024] Figure 3 is a schematic top perspective view of an optical diffuser film 100 according to some embodiments. For block polarization state 31, substantially normally incident light is scattered more along the p-direction (in a scattering plane 111 defined by the p-direction and the thickness direction) and less along the b-direction. Transmitted light cones 150 and 151 along the respective p-directions and b-directions are schematically shown.

[0025] The optical diffusion film 100 may be characterized by one or more of total optical transmittance or total optical reflectance, diffuse optical transmittance or diffuse optical reflectance, or specular optical transmittance or specular optical reflectance. The total optical reflectance may be determined by measuring the reflectance using an integrating sphere to collect all reflected light of a given wavelength or wavelength range. Diffuse optical reflectance may also be referred to as excluding specular reflectance, and may be determined by measuring the reflectance using an integrating sphere, wherein light corresponding to specular reflection is allowed to escape from the integrating sphere. Alternatively, in some embodiments, the total optical reflectance and the diffuse optical reflectance may be approximated as 100% minus the total transmittance and the diffuse transmittance, respectively, which may be determined according to the ASTM D1003-13 test standard. The specular optical reflectance may be determined as the difference between the total optical reflectance and the diffuse optical reflectance.

[0026] The binder 20 and the particles 10 have a refractive index along each of the illustrated b-direction, p-direction, and z-direction. In some embodiments, the optical diffusion film 100 includes a plurality of particles 10 dispersed in the binder 20, wherein the particles and the binder have a corresponding refractive index n1b and a refractive index n2b along a light-blocking direction (b-direction) in the same plane (pb plane) of the optical diffusion film 100, and a corresponding refractive index n1p and a refractive index n2p along a light-transmitting direction (p-direction) in a plane orthogonal to the light-blocking direction, such that for a visible wavelength range extending from about 420 nm to about 680 nm (e.g., Figures 4 to 7 At least a first wavelength (eg, Figures 4 to 7In some such embodiments, or in other embodiments, for at least a first wavelength, the magnitude of the difference between n1b and n2b is greater than about 0.04, or greater than about 0.045, or greater than about 0.05, or greater than about 0.055, or greater than about 0.06, or greater than about 0.065, or greater than about 0.07, or greater than about 0.075. In some such embodiments, or in other embodiments, for at least a first wavelength, the magnitude of the difference between n1p and n2p is less than about 0.05, or less than about 0.045, or less than about 0.04, or less than about 0.035, or less than about 0.03, or less than about 0.025, or less than about 0.02. For example, in some embodiments, the magnitude of the difference between n1b and n2b is greater than about 0.055, and the magnitude of the difference between n1p and n2p is less than about 0.04. At least the first wavelength can, for example, include one or more of about 532nm, about 550nm, about 631nm, about 633nm, or about 650nm. Typically, the magnitude of the difference between n1b and n2b is at least about 0.005, or at least about 0.01, or at least about 0.015, or at least about 0.02, or at least about 0.025, or at least about 0.03, or at least about 0.035 greater than the magnitude of the difference between n1p and n2p.

[0027] Figures 4 to 5 Graphs of optical reflectivity versus wavelength for exemplary and comparative optical diffuser films for substantially normally incident light having polarization states along block and pass directions, respectively. Figure 6 to Figure 7 Graphs of optical transmittance versus wavelength for exemplary and comparative optical diffuser films for substantially vertically incident light with polarization states along the block and transmittance directions, respectively. The curves in these figures are indicated by labels of reflectance (R) or transmittance (T); total (T), diffuse (D), or specular (S); and, in parentheses, labels of block (B) or transmittance (P) polarization states. Curves for the exemplary optical diffuser film and for a comparative optical diffuser film made by stretching the film in the transverse direction rather than the longitudinal direction are shown. The curve for the comparative film is labeled with C after polarization state.

[0028] In some embodiments, for substantially collimated substantially normal incident light 43, for the visible wavelength range 40 and the polarization state 32 along the light transmission direction, the optical diffuser film 100 has a total optical transmittance TT(P) and an optical diffuse transmittance TD(P), wherein TD(P) / TT(P)≥0.15, 0.2, 0.25, or 0.3. For example, TD(P) / TT(P) may be at most 0.5 or 0.4. In some embodiments, for substantially collimated substantially normal incident light 43, for the visible wavelength range 40 and the polarization state 31 and the polarization state 32 along the light blocking direction and the light transmission direction, the optical diffuser film 100 has a corresponding total optical transmittance TT(B) and a total optical transmittance TT(P) and a corresponding optical diffuse transmittance TD(B) and an optical diffuse transmittance TD(P), wherein TD(B) / TT(B)≥0.7, 0.75, 0.8, 0.85, or 0.9; and TD(P) / TT(P) may be as described above. In some embodiments, TD(B) / TT(B) is at least 0.1, or 0.2, or 0.3, or 0.4, or 0.5, or 0.6 greater than TD(P) / TT(P). For example, TD(B) / TT(B) may be at most about 0.9 or 0.8 greater than TD(P) / TT(P).

[0029] In some embodiments, for substantially collimated substantially vertical incident light 43, for an infrared wavelength range 42 extending from about 700 nm to about 1000 nm and polarization states 31 and 32 along the block direction and the transmittance direction, the optical diffuser film 100 has a corresponding total optical transmittance TT'(B) and total optical transmittance TT'(P) and a corresponding diffuse optical transmittance TD'(B) and diffuse optical transmittance TD'(P), wherein TD'(B) / TT'(B) is at least 0.4, or 0.45, or 0.5, or 0.55, or 0.6, or 0.65, or 0.7 greater than TD'(P) / TT'(P). For example, TD'(B) / TT'(B) may be at most about 0.9 or 0.8 greater than TD'(P) / TT'(P).

[0030] In some embodiments, for substantially collimated substantially vertical incident light 43 and for a visible wavelength range 40 extending from about 420 nm to about 680 nm: for incident light polarized along the pass direction (p direction), the optical diffuser film 100 has an optical specular transmittance TS(P) with respect to wavelength that may have a standard deviation greater than about 2%; and for incident light polarized along the block direction, the optical diffuser film has a corresponding optical diffuse transmittance TD(B) and optical specular transmittance TS(B), wherein TD(B) / TS(B) is greater than about 2. The standard deviation of the optical specular transmittance TS(P) with respect to wavelength may be greater than about 3%, or 4%, or 5%, or 6%, or 7%. For example, the standard deviation may be at most 15%, 12%, or 10%. TD(B) / TS(B) may be greater than about 4, or 6, or 8, or 10, or 12, or 14. For example, TD(B) / TS(B) may be at most 25, 20, or 18.

[0031] The total optical transmittance, diffuse optical transmittance, and / or optical specular transmittance within a specific wavelength range (e.g., 420 nm to 680 nm or 700 nm to 1000 nm) may be the average total optical transmittance, average diffuse optical transmittance, and / or average specular optical transmittance averaged within the specific wavelength range, respectively. For the visible and infrared wavelength ranges, Figures 4 to 7 The average optical transmittance (in percent) and standard deviation of the optical transmittance (in percent) of exemplary optical diffuser films are shown in the table below.

[0032] Wavelength range (nm) TT(B) TD(B) TS(B) TT(P) TD(P) TS(P) 420-680 (average): 56.8 53.0 3.8 80.7 25.6 55.1 420-680(standard): 2.3 1.7 0.7 3.7 3.9 7.6 700-1000 (average): 62.4 56.4 6.0 87.8 16.0 71.8 700-1000(standard): 1.0 1.4 1.6 0.7 1.8 2.5

[0033] For the visible and infrared wavelength ranges, Figures 4 to 7 The optical transmittance (in percent) and the standard deviation of the optical transmittance (in percent) of the comparative optical diffuser films are shown in the following table.

[0034] Wavelength range (nm) TT(B) TD(B) TS(B) TT(P) TD(P) TS(P) 420-680 (average): 85.4 40.6 44.8 90.1 7.8 82.3 420-680(standard): 1.1 5.0 6.1 0.6 1.3 1.8 700-1000 (average): 87.7 28.6 59.1 91.3 5.0 86.3 700-1000(standard): 0.3 2.1 2.4 0.1 0.5 0.6

[0035] Figure 8 is the transmission angle of the exemplary and comparative optical diffusers for substantially collimated, substantially normal incident light 43 polarized along the block direction (b-direction) (eg, corresponding to Figure 2The transmission angle is along the direction indicated by lowercase p or b, while the polarization state is indicated by uppercase P or B. For example, T(B,p) represents the transmittance for the block (B) polarization state for a transmission angle along the p direction (or in the pz plane). The results for a comparative optical diffuser film (denoted by C) stretched in the transverse direction are also shown. The normalized optical transmittance is the normalized total optical transmittance (scaled by a constant factor) so that the maximum value of the normalized optical transmittance is unity. The light source was determined using a collimated white light emitting diode (LED) Figure 8 Data shown. In some embodiments, for substantially collimated substantially vertical incident light 43 polarized along the blocking direction and for the first wavelength 41, the optical transmittance 50 of the optical diffuser film 100 that varies with the transmission angle (e.g., along the light transmission direction and / or in a plane defined by the light transmission direction and the thickness direction of the optical diffuser film 100) includes a substantially linear segment 52 extending from at least about 10 degrees to about 60 degrees. For example, the substantially linear segment 52 can extend down to about 7.5 degrees or 5 degrees. For example, the substantially linear segment 52 can extend up to about 65 degrees, or 70 degrees, or 75 degrees, or 80 degrees. The substantially linear segment can be understood to behave as approximately linear and have a coefficient of determination (commonly referred to as r-squared or R 2 ) is a segment for which the best linear fit (e.g., a linear least squares fit) is at least about 0.8. Fig. 9 Shows Figure 8 In some embodiments, the substantially linear segment 52 has an r-squared value R 2 A best linear fit 53 of greater than about 0.8, 0.85, 0.9 or 0.95.

[0036] In some embodiments, for substantially collimated substantially vertical incident light 43 polarized along a block direction and for a first wavelength 41, the optical diffuser film 100 diffusely transmits the incident light as a transmission light cone 50, 51 having respective full widths A(p) and A(b) at 30% maximum along respective transmission and block directions, wherein A(p) / A(b) ≥ 2, or 3, or 4, or 5, or 6, or 7, or 8, or 9, or 10, or 11, or 12, or 13, or 14. For example, A(p) / A(b) may be at most 25 or 20. Figure 8In the illustrated embodiment, A(p) is about 57 degrees, while A(b) is about 4 degrees. A(p) and A(b) may alternatively be determined for a visible wavelength range (e.g., for white light). In some embodiments, for incident light polarized along the blocking direction and for a first wavelength 41 within the visible wavelength range 40, the optical diffusion film 100 has an average normalized optical transmittance greater than about 0.2, or 0.25, or 0.3, or 0.35, or 0.4 at a transmission angle between about 5 degrees and about 20 degrees. For example, the average normalized optical transmittance at a transmission angle between about 5 degrees and about 20 degrees may be at most about 0.6 or 0.5. In some embodiments, for incident light polarized along the blocking direction and for a first wavelength 41, the optical diffusion film 100 has an average normalized optical transmittance greater than about 0.1, or 0.15, or 0.2, or 0.25 at a transmission angle between about 20 degrees and about 50 degrees. For example, the average normalized optical transmittance at a transmission angle between about 20 degrees and about 50 degrees may be at most about 0.5 or 0.4. For example, the average normalized optical transmittance at a transmission angle between about 20 degrees and about 50 degrees may be at least about 0.05, 0.08, or 0.1 less than the average normalized optical transmittance at a transmission angle between about 5 degrees and about 20 degrees. Figure 8 In an embodiment of the present invention, the optical diffuser film 100 has an average normalized optical transmittance of about 0.41 at a transmission angle between about 5 degrees and about 20 degrees, and an average normalized optical transmittance of about 0.27 at a transmission angle between about 20 degrees and about 50 degrees.

[0037] For some applications, a higher haze is desired for light polarized in the block direction than for light polarized in the transmit direction. In some embodiments, the optical diffusion film 100 has an optical haze Hb for substantially vertical incident light 43 polarized in the block direction, and an optical haze Hp for substantially vertical incident light 40 polarized in the transmit direction, wherein Hb / Hp≥1.4, or Hb / Hp≥1.5, or Hb / Hp≥1.8, or Hb / Hp≥2, or Hb / Hp≥2.2, or Hb / Hp≥2.4, or Hb / Hp≥2.5. The optical haze of a film of a specific polarization state can be measured using a haze meter (e.g., a Haze-Gard haze meter available from BYK Corporation, Wiesel, Germany), wherein an absorbing linear polarizer disposed on the film faces the light source of the haze meter, and the transmittance axis of the polarizer is aligned with the specific polarization state. Optical haze can be measured as described in the ASTM D1003-13 test standard, except that the test sample includes an absorbing linear polarizer disposed on the film. In general, the optical haze Hb increases as the difference in refractive index between the particles and the binder increases along the light blocking direction and / or as the number of particles increases. For example, when the refractive index of the particles and the binder differs significantly along the light blocking direction (e.g., differs by at least about 0.08 or at least about 0.1), the optical haze Hb can be high (e.g., greater than about 75% or greater than about 80%). For example, when the refractive index of the particles and the binder is closely matched along the light transmission direction (e.g., within about 0.02 or about 0.01), the optical haze Hp can be low (e.g., less than about 2% or less than about 1%). For example, Hb / Hp can be at most about 100, or at most about 50, or at most about 25, or at most about 20, or at most about 15, or at most about 10. 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 25% to about 90%. In some such embodiments, or in other embodiments, Hp is in the range of about 0% to about 65%, or about 1% to about 60%, or about 2% to about 55%, or about 5% to about 50%, or about 10% to about 45%.

[0038] Any optical properties described herein for a visible wavelength range extending from about 420 nm to about 680 nm may be applicable to other visible wavelength ranges. For example, a visible wavelength range extending from about 400 nm to about 700 nm or from about 450 nm to about 650 nm may be used to determine average optical transmittance or other optical properties.

[0039] Any optical diffusion film of the present specification can be used in a display. Fig.10is a schematic cross-sectional view of an optical system 200 according to some embodiments. The optical system 200 includes: a display 60 configured to emit an image 61 for viewing by a viewer 70; and an optical diffuser film 100 disposed between the display 60 and the viewer 70 for diffusely transmitting the emitted image primarily along a viewing direction (v direction) substantially parallel (e.g., parallel within about 30 degrees, 20 degrees, 10 degrees, 5 degrees, or 3 degrees, or nominally parallel) to the display 60, so that the transmitted image has a full viewing angle A(p) and A(b) along the corresponding viewing direction and a non-viewing direction (nv direction) orthogonal to the viewing direction and substantially parallel to the display 60, wherein A(p) / A(b)≥2 or A(p) / A(b) may be within any range described elsewhere herein. A(p) and A(b) may be determined as the full width at 30% of the maximum value of the transmitted light, as further described elsewhere herein. The viewing and non-viewing directions may be substantially parallel to the corresponding light-transmitting and light-blocking directions. Any optical properties specified for light polarized along the transmit and block directions may also apply to light polarized along the viewing and non-viewing directions, respectively. Similarly, any optical properties specified for light polarized along the non-viewing and viewing directions may also apply to light polarized along the transmit and block directions, respectively.

[0040] In some embodiments, for incident light polarized along the corresponding non-viewing direction and the viewing direction (and / or along the corresponding light transmission direction and the light blocking direction), the optical diffusion film 100 has a total optical transmittance TT(B) greater than about 40% and a total optical transmittance TT(P) greater than about 60%. TT(B) may be greater than about 40%, 45%, 50%, or 55%. For example, TT(B) may be at most about 90%, 80%, 70%, or 65%. TT(P) may be greater than about 60%, 65%, 70%, 75%, or 80%. For example, TT(P) may be at most about 100%, 95%, 90%, or 85%. In some embodiments, for incident light polarized in a non-view direction and for a first wavelength 41 in the visible wavelength range, the optical diffuser film 100 has an average normalized optical transmittance greater than about 0.2, or 0.25, or 0.3, or 0.35, or 0.4 at a transmission angle between about 5 degrees and about 20 degrees. In some embodiments, for incident light polarized in a non-view direction and for a first wavelength 41, the optical diffuser film 100 has an average normalized optical transmittance greater than about 0.1, or 0.15, or 0.2, or 0.25 at a transmission angle between about 20 degrees and about 50 degrees.

[0041] The display can be oriented to extend along horizontal and vertical directions (e.g., generally in a plane defined by the horizontal and vertical directions) to display images to a viewer spaced apart from the display generally along a direction substantially orthogonal to the horizontal and vertical directions. The viewing direction can be substantially parallel to the horizontal direction. In some embodiments, the display has a horizontal width along the viewing direction (v direction) and a vertical height along the non-viewing direction (nv direction), wherein the horizontal width is greater than the vertical height.

[0042] In some embodiments, the binder 20 includes a first thermoplastic polymer and the particles 10 include a different second thermoplastic polymer. In some embodiments, the first thermoplastic polymer and the second thermoplastic polymer are immiscible at a temperature higher than the melting temperature of the first thermoplastic polymer and the second thermoplastic polymer (i.e., at a temperature higher than each of the melting temperature of the first thermoplastic polymer and the melting temperature of the second thermoplastic polymer). In some such embodiments, or in other embodiments, the first thermoplastic polymer is birefringent and the second thermoplastic polymer is substantially optically isotropic.

[0043] Suitable materials for the binder 20 include, for example, polyethylene naphthalate (PEN), coPEN (co-polyethylene naphthalate terephthalate copolymer), polyethylene terephthalate (PET), polyethylene hexyl 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 be optionally blended with sPS (e.g., about 5 wt % to about 30 wt % aPS) to adjust the refractive index of the resulting layer and / or 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, South Carolina). PETG can be described as PET, wherein some of the glycol units in the glycol units of the polymer are replaced by different monomer units, typically those derived from cyclohexanedimethanol. For example, PETG can be prepared by replacing part of the ethylene glycol (e.g., about 15 mol % to about 60 mol % or about 30 mol % to about 40 mol %) used in the transesterification reaction of producing polyester with cyclohexanedimethanol. Suitable PETG copolyesters include GN071 purchased from Eastman Chemical Company (Kingsport, TN, Tennessee). PEN and coPEN can be manufactured as described in U.S. Patent No. 10,001,587 (Liu). A glycol-modified polyethylene naphthalate (PENG) may be described as a PEN in which some of the glycol units of the polymer are replaced by different monomer units, and may be prepared by, for example, replacing a portion of the ethylene glycol (e.g., about 15 mol % to about 60 mol % or about 30 mol % to about 40 mol %) used in the transesterification reaction to produce the polyester with cyclohexanedimethanol. PHEN may be prepared, for example, as described in U.S. Pat. No. 10,001,587 (Liu) for PEN, except that a portion of the ethylene glycol (e.g., about 15 mol % to about 60 mol %, or about 30 mol % to about 50 mol %, or about 40 mol %) used in the transesterification reaction is replaced by hexanediol. In some embodiments, the binder 20 includes one or more of a polyester and a copolyester. For example, the binder may include a blend of a polyester and a copolyester. In some embodiments, the binder 20 includes one or more of polyethylene terephthalate, glycol-modified polyethylene terephthalate, polyethylene naphthalate, and glycol-modified polyethylene naphthalate.

[0044] In some embodiments, the particles in the plurality of particles 10 include styrene-based polymers or copolymers (polymers or copolymers containing styrene groups). In some embodiments, the particles in the plurality of particles 10 include one or more of styrene butadiene, styrene acrylonitrile, styrene methyl methacrylate, and impact-modified styrene acrylic. As known in the art, impact-modified styrene acrylic introduces monomer groups to improve impact resistance and / or toughness. Suitable impact-modified styrene acrylics include, for example, products provided by Ineos Americas, League City, TX, under the trade name ZYLAR. Other suitable styrene-based copolymers include, for example, products provided by Ineos Americas, League City, TX, under the trade names STYROLUX, STYROLUTION, and NAS. Other types of materials that can be used as particles in the plurality of particles include polycarbonate polymers, including bisphenol A; nylon polymers, such as polyhexamethylene adipamide (nylon 6,6) and polycaprolactam (nylon 6); and methacrylate polymers, such as poly (2-phenylethyl methacrylate). In selecting polymers for use as particles in the plurality of particles, selection is generally made by selecting a polymer that substantially matches the refractive index of the birefringent binder in the non-stretched in-plane direction, and selecting a polymer that is immiscible with the binder polymer system, remains non-birefringent during stretching, and does not degrade during the melt processing stage.

[0045] Fig.112 is a schematic process flow chart of a method for preparing an optical diffusion film according to some embodiments. In some embodiments, the method for preparing an optical diffusion film 100, 265 includes: extruding (step 301) an immiscible blend 263 of a main phase material 320 and a secondary phase material 310 through a die and along a light-blocking direction (b direction) at a first temperature T1 higher than the glass transition temperature (Tg) of the main phase material 320 and the secondary phase material 310, thereby obtaining an extruded mixture 264 substantially at the first temperature T1 (e.g., within about 10°C of T1 or at about 5°C); and stretching (step 302) the extruded mixture along the light-blocking direction (b direction) at a second temperature T2 lower than the first temperature T1 264, thereby obtaining a plurality of particles 10 dispersed in a binder 20, wherein each of the binder 20 and at least a majority of the particles 10 has a respective refractive index n2b and n1b along a light-blocking direction and a respective refractive index n2p and n1p along a light-transmitting direction in a plane orthogonal to the light-blocking direction, such that for at least a first wavelength in a first wavelength range extending from about 420 nm to about 680 nm, or in any wavelength range described elsewhere herein, the magnitude of the difference between n1b and n2b may be greater than about 0.05 and the magnitude of the difference between n1p and n2p may be less than about 0.05. The magnitude of the difference between n1b and n2b may be any range described elsewhere herein. The magnitude of the difference between n1p and n2p may be any range described elsewhere herein. At least a majority of the particles 10 may include at least about 60%, or at least about 70%, or at least 80%, or at least about 90%, or substantially all of the particles 10 (by number). At least a majority of the particles 10 may include at least about 60%, or at least about 70%, or at least 80%, or at least about 90%, or substantially all of the mass of the total mass of the particles 10. The secondary phase material of the immiscible blend typically occupies less than half of the total volume of the immiscible blend and typically defines a discontinuous phase. The primary phase material of the immiscible blend typically occupies more than half of the total volume of the immiscible blend and typically defines a continuous phase. In some embodiments, the extruded mixture 264 (before stretching) includes a plurality of discrete domains 10' having average lengths Lb' and Lz' along the light blocking direction and thickness direction (z direction) of the extruded mixture, wherein, for example, Lb' / Lz' is in the range of about 3 to about 15, or about 4 to about 12, or about 5 to about 10. Lb' and Lz' may typically be as follows: Figure 1 to Figure 2, respectively, as schematically shown for Lb and Lz, although Lb is greater than Lb' and Lz is generally less than Lz'. It has been found that by providing a higher shear rate during extrusion, the domain can be further elongated. This is accomplished, for example, by using a smaller die gap with a higher extrusion rate and / or using a higher viscosity main phase material 320 (e.g., at a given temperature) and / or a lower extrusion temperature (e.g., to increase the viscosity of the main phase material 320). In some embodiments, after stretching, the particles have an average length Lb and Lz along the light blocking direction and the thickness direction, wherein, for example, Lb / Lz is in the range of about 100 to about 500, or about 150 to about 450, or about 200 to about 400. Lb / Lz may be in any range described elsewhere herein. Fig.11 It is schematically shown in FIG. 1 that Lb' increases to Lb and Lz' decreases to Lz during stretching.

[0046] In some embodiments, the first temperature T1 is greater than the melting temperature of the secondary phase material 310 and the primary phase material 320. In some embodiments, the first temperature T1 is, for example, greater than about 200 degrees Celsius, or greater than about 220 degrees Celsius, or greater than about 240 degrees Celsius, or greater than about 260 degrees Celsius, or greater than about 270 degrees Celsius. In some embodiments, the first temperature is less than, for example, about 400 degrees Celsius. In some embodiments, the second temperature is about 5 degrees Celsius to about 50 degrees Celsius, or about 5 degrees Celsius to about 40 degrees Celsius, or about 5 degrees Celsius to about 30 degrees Celsius, or about 5 degrees Celsius to about 20 degrees Celsius, or about 8 degrees Celsius to about 30 degrees Celsius higher than the glass transition temperature of the primary phase material and the secondary phase material. In some such embodiments, or in other embodiments, the extruded mixture 264 is stretched in the light-blocking direction at the second temperature T2, before which 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 on a casting wheel (sometimes referred to as a cooling roll or casting roll in the art) to quickly cool the mixture 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 degrees Celsius).

[0047] In some embodiments, the discrete domains 10' in the extruded mixture are at least predominantly comprised of the secondary phase material. For example, the secondary phase material may comprise at least about 80% by weight of the domain, or at least about 90%, or at least about 95%. In some embodiments, the discrete domains in the extruded mixture are dispersed in a material that is at least predominantly comprised of the primary phase material. For example, the primary phase material may comprise at least about 70%, or at least about 80%, or at least about 90%, or at least about 95% by weight of the material in which the domains are dispersed.

[0048] Example

[0049] Table 1: Materials used in the examples

[0050]

[0051]

[0052] Optical diffusion films of Comparative Examples C1 to C5 and Example 1 were prepared by coextrusion and batch orientation using the materials shown in Table 2. The temperature of the extruder was about 277 degrees Celsius.

[0053] Table 2

[0054]

[0055] Material #1 and material #3 (when included) are polyester phase materials, and material #2 is a copolystyrene phase material. The weight percentages and pounds per hour (pph) of these materials in the extruder feed are shown in Table 2. The polyester phase and the copolystyrene phase are immiscible and exhibit two distinct phases after extrusion and after stretching.

[0056] After extrusion and before stretching, the extruded mixture was cooled by casting the extruded mixture against a casting wheel. For Example 1 and Comparative Examples C1 to C4, a two-layer coextrusion was performed, wherein the layer already described (blend layer) was located on the air side during the casting process, and the wheel-side layer consisted of the same composition as the polyester phase in the blend layer and was fed at the same rate as the total blend layer. For Comparative Example C5, a 3-layer coextrusion was used, wherein the center layer was the blend layer, 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 a rate half the rate of the total blend layer. An 8" extrusion die was used for all examples. The die gap for Example 1 and Comparative Examples C1 to C4 was 60 mils, while the die gap for Comparative Example C5 was 100 mils.

[0057] All of these film stretching processes were performed on a batch orienter (Karo IV from Brueckner Group, Portsmouth, NH). The preheat and stretching temperature utilized was 95°C. For Comparative Examples C1 to C5, the stretching was a constrained stretch with a stretch ratio of about 6:1 in the transverse direction (TD) orthogonal to the machine direction (MD). For Example 1, the stretching was a constrained stretch with a stretch ratio of about 6:1 in the machine direction. The PET stretched under these conditions had a refractive index of about 1.66 in the stretch direction (TD), a refractive index of 1.56 in the in-plane direction perpendicular to the stretch direction (MD direction), and a refractive index of 1.53 in the thickness direction, which was measured at 631 nm using a refractometer (Metricon Corporation, Pennington, NJ, USA). The thickness of the films after stretching is given in Table 2.

[0058] The tendency of the film to scatter polarized light was characterized using Haze Gard (BYK Corporation, Wesel, Germany). The haze of light polarized in the block direction (TD) was determined by placing a high contrast ratio absorbing polarizer (whose clear state transmission axis was aligned with the stretch direction of the exemplary film) on the incident light side of the exemplary film, and applying a transparent tape (3M375 from 3M, Saint Paul, MN) to the air side of the film to reduce scattering from the surface roughness of the exemplary film. The sample was oriented so that the wheel side of the film faced the incident light. For clear state haze, the absorbing polarizer was aligned with the non-stretch direction (MD) of the exemplary film. The polarization haze measurement results are provided in Table 3.

[0059] The angular distribution of scattered light was measured using a conoscope with a cone angle of 80 degrees (ELDIM Corporation, Hérouville-Saint-Clair, France). A collimated white light (LED) light source was used, and an absorbing polarizer was placed between the light source and the exemplary film. The transmission axis polarized in the block direction was measured, and the full width at half maximum (FWHM) of the scattered pattern along the MD and TD directions was determined and reported in Table 3.

[0060] Table 3

[0061]

[0062]

[0063] The reflective properties of the exemplary film are determined by measuring the reflectivity of the film in an integrating sphere. The total reflectivity (also referred to as the reflectivity including specular reflection (RSIN)) is measured by collecting all the light reflected by the exemplary film irradiated from all angles, while the diffuse reflectivity (also referred to as the reflectivity excluding specular reflection (RSEX)) is measured by allowing light to escape the integrating sphere and produce specular reflection. A LAMBDA 1050 spectrophotometer (PerkinElmer, Inc., Waltham, MA, USA) was used in the measurement. The average transmittance obtained in the wavelength range of 450nm to 650nm is shown in Table 4.

[0064] Table 4

[0065]

[0066] The average aspect ratio of the particles before stretching the cast film was determined using an optical microscope to examine the cross-sections in the bz plane and the pz plane. The Lp / Lz ratio and the Lb / Lz ratio of the particles in the cross-section were determined, and the average value of the ratios was determined. The results are provided in Table 5.

[0067] Table 5

[0068] Example Lp / Lz Lb / Lz C1 2.16 1.51 C2 2.42 1.33 C3 3.61 1.50 C4 15.50 1.54 C5 1.27 1.30 1 1.13 7.72

[0069] When calculating the corresponding aspect ratio of the stretched film, it was assumed that a stretch ratio of about 6 resulted in a stretch of 6 times in the stretch direction and a thinning of 6 times in the thickness direction, as expected for the constrained stretching used in the Examples and Comparative Examples. The results are provided in Table 6.

[0070] Table 6

[0071] Example Lp / Lz Lb / Lz C1 12.94 54.51 C2 14.51 47.98 C3 21.63 54.00 C4 93.01 55.40 C5 7.62 46.97 1 6.77 278

[0072] exist Figures 4 to 9 Further results for Example 1 and Comparative Example C5 are shown in .

[0073] Terms such as "about" will be understood by one of ordinary skill in the art in the context of use and description in this specification. If it is not clear to one of ordinary skill in the art in the context of use and description in this specification that "about" should be used to express the amount of feature size, quantity, and physical properties, then "about" will be understood to mean within 10% of the specified value. A quantity given as about a specified value may be exactly the specified value. For example, if it is not clear to one of ordinary skill in the art in the context of use and description in this specification, a quantity having a value of about 1 means that the quantity has a value between 0.9 and 1.1, and the value may be 1.

[0074] All references, patents, and patent applications cited above are hereby incorporated by reference in their entirety in a consistent manner. In the event of inconsistencies or conflicts between an incorporated reference portion and the present application, the information in the foregoing description shall prevail.

[0075] Unless otherwise indicated, the description of the elements in the drawings should be understood to be equally applicable to the corresponding elements in the other drawings. Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that the specific embodiments shown and described may be replaced with a variety of alternative and / or equivalent implementations without departing from the scope of the present disclosure. The present application is intended to cover any modification or variation or combination of the specific embodiments discussed herein. Therefore, the present disclosure is intended to be limited only by the claims and their equivalents.

Claims

1. An optical diffuser film, comprising a plurality of particles dispersed in a binder, the particles and the binder having respective refractive indices n1b and n2b along a light blocking direction in a same plane of the optical diffuser film and respective refractive indices n1p and n2p along a light transmitting direction in a plane orthogonal to the light blocking direction, such that for at least a first wavelength in a visible wavelength range extending from about 420 nm to about 680 nm: The magnitude of the difference between n1b and n2b is greater than about 0.04; and The magnitude of the difference between n1p and n2p is less than about 0.05; Wherein, for substantially collimated substantially vertical incident light, for the visible wavelength range and the polarization state along the light blocking direction and the light transmitting direction, the optical diffusion film has corresponding total optical transmittance TT(B) and TT(P) and corresponding optical diffuse transmittance TD(B) and TD(P), TD(B) / TT(B)≥0.7, TD(P) / TT(P)≥0.

15. 2 . The optical diffuser film of claim 1 , wherein TD(B) / TT(B) is at least 0.1 greater than TD(P) / TT(P).

3. The optical diffuser film of claim 1 , wherein for substantially collimated substantially normal incident light, for an infrared wavelength range extending from about 700 nm to about 1000 nm and polarization states along the block direction and the transmittance direction, the optical diffuser film has corresponding total optical transmittances TT'(B) and TT'(P) and corresponding diffuse optical transmittances TD'(B) and TD'(P), wherein TD'(B) / TT'(B) is at least 0.4 greater than TD'(P) / TT'(P).

4. The optical diffuser film of claim 1, wherein for substantially collimated substantially vertical incident light polarized along the light-blocking direction and for the first wavelength, the optical diffuser film diffusely transmits the incident light as a transmitted light cone, the transmitted light cone having respective full widths A(p) and A(b) at 30% of maximum along the respective light-transmitting direction and the light-blocking direction, and A(p) / A(b)≥2. 5 . The optical diffuser film of claim 1 , wherein the particles are elongated along the light-blocking direction and have an average length Lb along the light-blocking direction and an average width Lz along a thickness direction of the optical diffuser film, and Lb / Lz is greater than about 10.

6. The optical diffuser film of claim 1 , wherein for substantially collimated substantially normally incident light polarized along the block direction and for the first wavelength, the optical transmittance of the optical diffuser film as a function of transmission angle in a plane defined by the pass direction and a thickness direction of the optical diffuser film comprises a substantially linear segment extending from at least about 10 degrees to about 60 degrees, the substantially linear segment having a best linear fit with an r-squared value greater than about 0.

8.

7. An optical diffuser film, comprising a plurality of particles dispersed in a binder and extending along an in-plane light-blocking direction orthogonal to the in-plane light-transmitting direction and the thickness direction of the optical diffuser film, wherein the average lengths of the particles along the respective light-blocking and thickness directions are Lb and Lz, Lb / Lz is greater than about 10, and for at least a first wavelength in a visible wavelength range extending from about 420 nm to about 680 nm, the magnitude of the difference between the refractive index of the particles and the binder along the light-blocking direction is at least about 0.04, and the magnitude of the difference between the refractive index of the particles and the binder along the light-transmitting direction is less than about 0.05; where for substantially collimated, substantially vertically incident light and for the visible wavelength range: The optical diffuser film has an optical specular transmittance with respect to wavelength having a standard deviation greater than about 2% for the incident light polarized along the transmission direction; and For the incident light polarized along the light-blocking direction, the optical diffusion film has a corresponding optical diffuse transmittance TD(B) and an optical specular transmittance TS(B), TD(B) / TS(B) is greater than about 2.

8. The optical diffuser film of claim 7, wherein for the substantially collimated substantially vertical incident light, for the visible wavelength range and the polarization state along the transmission direction, the optical diffuser film has a total optical transmittance TT(P) and an optical diffuse transmittance TD(P), TD(P) / TT(P)≥0.

15.

9. The optical diffuser film of claim 1, wherein for substantially collimated substantially normally incident light polarized along the block direction and for the first wavelength, the optical transmittance of the optical diffuser film as a function of transmission angle in a plane defined by the pass direction and a thickness direction of the optical diffuser film comprises a substantially linear segment extending from at least about 10 degrees to about 60 degrees, the substantially linear segment having a best linear fit with an r-squared value greater than about 0.

8.

10. An optical diffuser film, comprising a plurality of particles dispersed in a binder and extending along an in-plane light-blocking direction orthogonal to the in-plane light-transmitting direction and the thickness direction of the optical diffuser film, wherein the average lengths of the particles along the respective light-transmitting direction and the thickness direction are Lb and Lz, Lb / Lz is greater than about 10, and for at least a first wavelength in a visible wavelength range extending from about 420 nm to about 680 nm, the magnitude of the difference between the refractive index of the particles and the binder along the light-blocking direction is at least about 0.04, and the magnitude of the difference between the refractive index of the particles and the binder along the light-transmitting direction is less than about 0.05; Wherein for substantially collimated substantially vertically incident light polarized along the light-blocking direction and for the first wavelength, the optical transmittance of the optical diffuser film as a function of transmission angle includes a substantially linear segment extending from at least about 10 degrees to about 60 degrees, the substantially linear segment having a best linear fit with an r-squared value greater than about 0.

8.

11. The optical diffuser film according to claim 10, wherein for the substantially collimated substantially vertical incident light, for the visible wavelength range and the polarization state along the light transmission direction, the optical diffuser film has a total optical transmittance TT(P) and an optical diffuse transmittance TD(P), TD(P) / TT(P)≥0.

15.

12. An optical system, comprising: a display configured to emit an image for viewing by a viewer; as well as The optical diffuser film according to any one of claims 1 to 11, wherein the optical diffuser film is disposed between the display and the viewer, and is used to diffusely transmit the emitted image mainly along a viewing direction substantially parallel to the display, so that the transmitted image has full viewing angles A(p) and A(b) along the corresponding viewing direction and a non-viewing direction orthogonal to the viewing direction and substantially parallel to the display, A(p) / A(b)≥2, and the viewing direction and the non-viewing direction are substantially parallel to the corresponding light-transmitting direction and the light-blocking direction.

13. An optical system, comprising: a display configured to emit an image for viewing by a viewer; as well as An optical diffusion film, the optical diffusion film being disposed between the display and the viewer and configured to diffusely transmit the emitted image mainly along a viewing direction substantially parallel to the display, so that the transmitted image has full viewing angles A(p) and A(b) along the corresponding viewing direction and a non-viewing direction orthogonal to the viewing direction and substantially parallel to the display, and A(p) / A(b)≥2; Wherein for substantially collimated, substantially normally incident light and for the visible wavelength range extending from about 420 nm to about 680 nm: The optical diffuser film has a total optical transmittance TT(B) greater than about 40% and a total optical transmittance TT(P) greater than about 60% for the incident light polarized along the corresponding non-view direction and the view direction; as well as The optical diffuser film has an average normalized optical transmittance greater than about 0.2 at transmission angles between about 5 degrees and about 20 degrees for the incident light polarized along the non-view direction and for a first wavelength in the visible wavelength range.

14. The optical system of claim 13, wherein the optical diffuser film has an average normalized optical transmittance greater than about 0.1 at transmission angles between about 20 degrees and about 50 degrees for the incident light polarized along the non-view direction and for the first wavelength.

15. The optical system according to claim 13, wherein the optical diffusion film comprises a plurality of particles dispersed in a binder and elongated along an in-plane light-blocking direction orthogonal to an in-plane light-transmitting direction and a thickness direction of the optical diffusion film, the particles having average lengths Lb and Lz along the corresponding light-transmitting direction and the thickness direction, Lb / Lz being greater than about 10, and the light-transmitting direction and the light-blocking direction being substantially parallel to the corresponding viewing direction and the non-viewing direction.

Images