Optical films, backlights and displays

Abstract

The optical film includes a light diffusing layer including a plurality of nanoparticles dispersed between and across opposing first and second major surfaces thereof. The plurality of nanoparticles have a nanoparticle size distribution including distinct first and second peaks at respective nanoparticle sizes d1 and d2, where 1.5≦d2 / d1≦10. The light diffusing layer includes a polymeric material that bonds the nanoparticles together. For substantially collimated, substantially normally incident light, the optical film has an average specular transmittance VTs and an average total transmittance VTt in the visible wavelength range, and an average total transmittance ITt and an average specular transmittance ITs in the infrared wavelength range, where 0.3≦(VTs / VTt)≦0.7, (VTs / ITs)≦0.25, and (ITs / ITt)≧0.7.

Description

[Technical Field]

[0001] The present disclosure relates generally to optical films. Specifically, the present disclosure relates to optical films including a light diffusing layer. The present disclosure also relates to backlights including the optical films and displays including the backlights. [Background technology]

[0002] Light diffusing layers are commonly used in display devices to generate optical haze to reduce optical artifacts such as reflective moiré, however, the optical haze of a light diffusing layer can change non-uniformly due to aging in environments with high humidity and temperature. Summary of the Invention

[0003] In a first aspect, the present disclosure provides an optical film including a light-diffusing monolayer. The light-diffusing monolayer has an average thickness of about 0.5 microns to about 5 microns. The light-diffusing monolayer includes first and second major surfaces that are opposite each other. The light-diffusing monolayer further includes a plurality of nanoparticles dispersed between and across the first and second major surfaces. The nanoparticles include silica. The plurality of nanoparticles have a nanoparticle size distribution including at least two distinct first and second peaks at respective nanoparticle sizes d1 and d2, where 1.5≦(d2 / d1)≦10. Among the plurality of nanoparticles, nanoparticles within a full width at half maximum (FWHM) of the first peak and within a full width at half maximum (FWHM) of the second peak form W1 and W2 weight percent of the plurality of nanoparticles, respectively, where 1.1≦(W1 / W2)≦2. The light-diffusing monolayer further includes a polymeric material that bonds the nanoparticles to each other to form a plurality of nanoparticle aggregates that define a plurality of voids therebetween. For substantially collimated, substantially normally incident light, and in the visible wavelength range of about 420 nm (nanometers) to about 680 nm and the infrared wavelength range of about 900 nm to about 1000 nm, the optical film has an average specular transmittance VTs and an average total transmittance VTt in the visible wavelength range. Furthermore, for substantially collimated, substantially normally incident light, and in the visible and infrared wavelength ranges, the optical film has an average total transmittance ITt and an average specular transmittance ITs in the infrared wavelength range, where 0.3≦(VTs / VTt)≦0.7, (VTs / ITs)≦0.25, and (ITs / ITt)≧0.7.

[0004] In a second aspect, the present disclosure provides an optical film including a light diffusing layer bonded to a reflective polarizer. The light diffusing layer includes a plurality of nanoparticles dispersed between first and second opposing major surfaces of the light diffusing layer, occupying more than 80% of the volume defined therebetween. The nanoparticles form nanoparticle aggregates that define voids therebetween. The first and second major surfaces are spaced at least 2 microns apart. The nanoparticles have a nanoparticle size distribution including at least two distinct first and second peaks in nanoparticle sizes d1 and d2, respectively, where 1.5≦(d2 / d1)≦10. The reflective polarizer includes a plurality of polymer layers, totaling at least 10. Each polymer layer has an average thickness of less than about 500 nm. The optical film has an optical haze greater than about 30%, and the optical haze of the optical film decreases by less than about 10% when exposed to a relative humidity of about 95% and a temperature of about 65°C for at least 200 hours.

[0005] In a third aspect, the present disclosure provides a backlight including a back reflector. The backlight further includes the optical film of the second aspect disposed on the back reflector. The backlight further includes a light guide disposed between the back reflector and the optical film. For substantially collimated, substantially normally incident light, in the visible wavelength range of about 420 nm to about 680 nm, the infrared wavelength range of about 800 nm to about 1500 nm, and for first and second orthogonal polarization states, the back reflector reflects at least 60% of the incident light for each wavelength in the visible wavelength range and transmits at least 30% of the incident light for at least one wavelength in the infrared wavelength range.

[0006] In a fourth aspect, there is provided a display comprising the backlight of the third aspect arranged between a liquid crystal panel and an infrared-sensitive detector, wherein when an infrared radiation source that emits infrared radiation within the infrared wavelength range is arranged in proximity to the liquid crystal panel, the infrared-sensitive detector detects at least a portion of the emitted infrared radiation.

[0007] In a fifth aspect, the present disclosure provides an optical film including a reflective polarizer. The reflective polarizer includes a plurality of polymer layers, the total number of which is at least 10. Each of the polymer layers has an average thickness of less than about 500 nm. The reflective polarizer includes a plurality of first protrusions on its first major surface. The optical film further includes a light diffusing layer disposed on the first major surface of the reflective polarizer. The light diffusing layer includes a plurality of nanoparticles, the nanoparticle sizes d1 and d2 of which include at least two distinct first and second peaks, and the nanoparticle size distribution is 1.5≦(d2 / d1)≦10. The light diffusing layer substantially conforms to the first protrusions to form a plurality of concentric portions substantially concentric with the first protrusions. The light diffusing layer substantially conforms to the first protrusions to form a plurality of parallel portions substantially parallel to the polymer layer of the reflective polarizer. Furthermore, the light diffusing layer substantially conforms to the first protrusions to form a plurality of transition portions that provide a gradual transition between the concentric portions and the parallel portions. For each primary protrusion, the length of the transition portion corresponding to the primary protrusion is less than three times the width of the primary protrusion.

[0008] In a sixth aspect, the present disclosure provides an optical film including a reflective polarizer. The reflective polarizer includes a plurality of polymer layers, the total number of which is at least 10. Each of the polymer layers has an average thickness of less than about 500 nm. The reflective polarizer includes a plurality of first protrusions on its first major surface. The optical film further includes a light diffusing layer disposed on the first major surface of the reflective polarizer. The light diffusing layer includes a plurality of nanoparticles, the nanoparticle sizes d1 and d2 of which include at least two distinct first and second peaks, and the nanoparticle size distribution is 1.5≦(d2 / d1)≦10. The light diffusing layer substantially conforms to the first protrusions to form a plurality of concentric portions substantially concentric with the first protrusions. Furthermore, the light diffusing layer substantially conforms to the first protrusions to form a plurality of connecting portions connecting the plurality of concentric portions. The thickness variation of the light diffusing layer across at least 80% of the total surface area of ​​the light diffusing layer occupied by the connecting portions is less than about 30%.

[0009] In a seventh aspect, the present disclosure provides an optical film including a reflective polarizer. The reflective polarizer includes a plurality of polymer layers, the total number of which is at least 10. Each of the polymer layers has an average thickness of less than about 500 nm. The reflective polarizer includes a plurality of first protrusions on its first major surface. The optical film further includes a light diffusing layer disposed on the first major surface of the reflective polarizer. The light diffusing layer includes a plurality of nanoparticles having a nanoparticle size distribution that includes at least two distinct first and second peaks in respective nanoparticle sizes d1 and d2, and in which 1.5≦(d2 / d1)≦10. The light diffusing layer substantially conforms to the first protrusions to form a plurality of concentric portions substantially concentric with the first protrusions, and a plurality of connecting portions connecting the plurality of concentric portions. For substantially collimated, substantially normally incident light, and for the visible wavelength range of about 420 nm to about 680 nm and the infrared wavelength range of about 900 nm to about 1000 nm, the diffuse reflectance of the optical film versus wavelength has a global minimum at a first wavelength located between the visible and infrared wavelength ranges. [Brief explanation of the drawings]

[0010] The exemplary embodiments disclosed herein will be more fully understood upon consideration of the following Detailed Description in conjunction with the following figures. The figures are not necessarily drawn to scale. Like numbers used in the figures indicate like components. However, it will be understood that the use of a number to refer to a component in a particular figure is not intended to limit the component in another figure bearing the same number.

[0011] [Figure 1] 1 shows a detailed schematic cross-sectional view of an optical film including a light diffusing layer according to one embodiment of the present disclosure. [Figure 2] 2 shows a scanning electron microscope (SEM) image showing a top view of the light diffusing layer of FIG. 1 according to one embodiment of the present disclosure. [Figure 3] 1 shows a schematic cross-sectional view of a reflective polarizer according to one embodiment of the present disclosure. [Figure 4]2 shows a plot illustrating the nanoparticle size distribution of the plurality of nanoparticles in the light diffusing layer of FIG. 1 according to one embodiment of the present disclosure. [Figure 5] 2 shows a plot illustrating the optical properties of the optical film of FIG. 1 according to one embodiment of the present disclosure. [Figure 6A] 2 shows a detailed schematic cross-sectional view of a display including the optical film of FIG. 1 according to one embodiment of the present disclosure. [Figure 6B] 6B shows a schematic cross-sectional view of a back reflector of the display of FIG. 6A according to one embodiment of the present disclosure. [Figure 7A] 1 shows an SEM image depicting a detailed cross-sectional view of an optical film according to another embodiment of the present disclosure. [Figure 7B] 7B shows another SEM image showing a detailed cross-sectional view of the optical film of FIG. 7A according to one embodiment of the present disclosure. [Figure 7C] 1 shows an SEM image depicting a top view of an optical film according to an embodiment of the present disclosure. [Figure 8A] 1 shows a schematic cross-sectional view of an optical film according to one embodiment of the present disclosure. [Figure 8B] 8B shows a plot illustrating the optical properties of the optical film of FIG. 8A according to one embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0012] In the following description, reference is made to the accompanying drawings, which form a part hereof, and in which are shown by way of illustration various embodiments. 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.

[0013] In the disclosure that follows, the following definitions will be adopted:

[0014] All numbers used herein shall be deemed to be modified by the term "about." As used herein, "a," "an," "the," "at least one," and "one or more" are used interchangeably.

[0015] As used herein as a modifier to a characteristic or attribute, the term "generally" means, unless otherwise specified, that the characteristic or attribute would be readily recognized by one of ordinary skill in the art, but does not require absolute precision or perfect agreement (e.g., within ±20% for quantifiable characteristics).

[0016] The term "substantially" means, unless otherwise specified, a close degree of approximation (e.g., within ±10% for quantifiable properties), but again does not require absolute precision or perfect agreement.

[0017] The term "about," unless otherwise specified, means a high degree of approximation (e.g., within ±5% for quantifiable properties), but again does not require absolute precision or exact agreement.

[0018] As used herein, the terms "first" and "second" are used as identifiers. Therefore, such terms should not be construed as limiting the present disclosure. When used in conjunction with features or elements, the terms "first" and "second" can be interchanged throughout the embodiments of the present disclosure.

[0019] As used herein, when a first material is said to be "similar" to a second material, at least 90% by weight of the first and second materials are identical, and if there is variation between the first and second materials, the variation is less than about 10% by weight of each of the first and second materials.

[0020] As used herein, "at least one of A and B" should be understood to mean "A only, B only, or both A and B."

[0021] As used herein, the term "film" generally refers to a material with a very high ratio of length or width to thickness. A film has two major surfaces defined by length and width. Films typically have good flexibility and can be used in a variety of applications, including displays. Films can also be of a thickness or material composition that makes them semi-rigid or rigid. The films described in this disclosure can be composed of various polymer materials. Films can be monolayer, multilayer, or blends of different polymers.

[0022] As used herein, the term "layer" generally refers to a thickness of material in a film that has a relatively consistent chemical composition. A layer may be of any type of material, including polymeric, cellulose, metal, or a blend thereof. A given polymer layer may comprise a single polymer type or a blend of polymers, and may include additives. A given layer may be combined or connected with other layers to form a film. A layer may be partially or completely continuous with an adjacent layer or film. A given layer may be partially or completely coextensive with an adjacent layer. A layer may contain sublayers.

[0023] As used herein, the term "specular transmittance" generally refers to the transmission of light through a body where the angular distribution of the transmitted light is substantially the same as the angular distribution of the incident light incident on the body.

[0024] As used herein, the term "diffuse transmittance" generally refers to the transmittance of light through a body where the angular distribution of the transmitted light differs from the angular distribution of the incident light incident on the body.

[0025] As used herein, the term "total transmittance" generally refers to the combined transmittance of all light, including that due to specular and diffuse transmittance.

[0026] As used herein, the term "diffuse reflectance" generally refers to the reflection of light off a body where the angular distribution of the reflected light differs from the angular distribution of the incident light incident on the body.

[0027] As used herein, the term "about" generally refers to an inclusive or closed range unless otherwise specified. For example, if parameter X is between about A and B, then A≦X≦B.

[0028] As used herein, the term "dry thickness" generally refers to the thickness of a coating or film after any solvent present in the coating or film has dried.

[0029] The present disclosure relates to an optical film including a light diffusing layer. The present disclosure further relates to a backlight including the optical film. The backlight including the optical film can be used in a display. In some examples, the optical film can be used to backlight a display device. The display device can be incorporated into an electronic device such as a computer monitor, a television, a mobile phone, a personal digital assistant (PDA), a wearable device, or any other portable device. In some other examples, the optical film can be used to backlight an optical biometric scanning device such as a fingerprint scanner, a retinal scanner, etc.

[0030] Display devices with liquid crystal panels generally have a backlight because the liquid crystal panel itself is not self-luminous. Light emitted from the backlight passes through the liquid crystal panel to reach the viewer. However, such display devices may be susceptible to optical artifacts such as reflective moiré. To reduce such optical artifacts, the backlight of such display devices may include an optical film including a porous coating to impart optical haze to the display device. However, conventional porous coatings may be susceptible to aging. Specifically, optical films including conventional porous coatings may generate non-uniform optical haze after approximately 200 hours of continuous exposure to high temperatures and / or high humidity, such as 95% relative humidity and 65 degrees Celsius (°C). In some cases, the optical haze of conventional porous coatings may substantially decrease after continuous exposure to high temperatures and / or high humidity. Therefore, conventional porous coatings may perform poorly in environmental durability tests, particularly high temperature or high humidity tests.

[0031] One way to mitigate the effects of aging is to increase the dry thickness of the conventional porous coating. This can be achieved by including nanoparticles with a size of approximately 75 nm (nanometers) in the conventional porous coating. However, such increased dry thickness can adversely affect the cohesive strength of the conventional porous coating, leading to premature mechanical failure of the conventional porous coating.

[0032] In one aspect, the present disclosure provides an optical film including a light-diffusing monolayer. The light-diffusing monolayer has an average thickness of about 0.5 microns to about 5 microns. The light-diffusing monolayer includes first and second major surfaces that are opposite each other. The light-diffusing monolayer further includes a plurality of nanoparticles dispersed between and across the first and second major surfaces. The nanoparticles include silica. The plurality of nanoparticles have a nanoparticle size distribution including at least two distinct first and second peaks at respective nanoparticle sizes d1 and d2, where 1.5≦(d2 / d1)≦10. Among the plurality of nanoparticles, nanoparticles within a full width at half maximum (FWHM) of the first peak and within a full width at half maximum (FWHM) of the second peak form W1 and W2 weight percent of the plurality of nanoparticles, respectively, where 1.1≦(W1 / W2)≦2. The light-diffusing monolayer further includes a polymeric material that bonds the nanoparticles to each other to form a plurality of nanoparticle aggregates that define a plurality of voids therebetween. For substantially collimated, substantially normally incident light, and in the visible wavelength range of about 420 nm to about 680 nm and the infrared wavelength range of about 900 nm to about 1000 nm, the optical film has an average specular transmittance VTs and an average total transmittance VTt in the visible wavelength range. Further, for substantially collimated, substantially normally incident light, and in the visible and infrared wavelength ranges, the optical film has an average total transmittance ITt and an average specular transmittance ITs in the infrared wavelength range, where 0.3≦(VTs / VTt)≦0.7, (VTs / ITs)≦0.25, and (ITs / ITt)≧0.7.

[0033] The light-diffusing layer of the optical film can produce optical haze in the visible wavelength range due to the presence of nanoparticles and voids. However, the light-diffusing layer can provide substantially high specular transmittance in the infrared wavelength range. Therefore, the optical film can be suitable for use with optical sensors operating in the infrared wavelength range or in display devices that use such optical sensors for various applications, such as fingerprint detection.

[0034] Furthermore, a plurality of nanoparticles having a nanoparticle size distribution including at least two distinct first and second peaks at respective nanoparticle sizes d1 and d2, such that 1.5≦(d2 / d1)≦10, and respective weight percentages W1 and W2 of nanoparticles within the FWHMS of the respective first and second peaks, such that 1.1≦W1 / W2≦2, can result in an increase in the dry thickness of the light diffusing layer without adversely affecting the cohesive strength of the light diffusing layer. The increased dry thickness of the light diffusing layer can reduce the adverse effects of aging, i.e., non-uniform optical haze upon continued exposure to high temperatures and / or humidity, without compromising the cohesive strength of the light diffusing layer. Specifically, the optical haze of the optical film decreases by less than about 10% upon exposure to about 95% relative humidity and a temperature of about 65°C for at least 200 hours.

[0035] Furthermore, the optical haze produced by the light diffusing layer can be controlled by varying the weight percentages W1 and W2 of the nanoparticles and / or the nanoparticle sizes d2 and d1.

[0036] Referring now to the figures, FIG. 1 shows a detailed schematic cross-sectional view of an optical film 300 according to one embodiment of the present disclosure.

[0037] The optical film 300 defines mutually orthogonal x-, y-, and z-axes. The x- and y-axes correspond to in-plane axes of the optical film 300, while the z-axis is a transverse axis disposed along the thickness of the optical film 300. In other words, the x- and y-axes are disposed along the plane of the optical film 300 (i.e., the xy-plane), and the z-axis is perpendicular to the plane of the optical film 300. The z-axis may be referred to interchangeably as the "thickness direction."

[0038] The optical film 300 includes a light diffusing monolayer 10, which may be interchangeably referred to as a "light diffusing layer 10." The light diffusing layer 10 includes a first major surface 11 and a second major surface 12 that are opposite each other. The light diffusing layer 10 has an average thickness t. The light diffusing layer 10 defines the average thickness t along the z-axis. As used herein, the term "average thickness" refers to the average thickness along the plane of the light diffusing layer 10 (i.e., the xy plane). In some embodiments, the average thickness t of the light diffusing layer 10 may be measured between the opposite first major surface 11 and second major surface 12. In some embodiments, the light diffusing layer 10 has an average thickness t of about 0.5 microns to about 5 microns.

[0039] In some embodiments, first major surface 11 and second major surface 12 may be referred to interchangeably as "major first and second surfaces 11, 12." In some embodiments, first and second major surfaces 11 and 12 are spaced apart by at least 2 microns. In some embodiments, first and second major surfaces 11 and 12 are spaced apart by at least 4 microns, at least 6 microns, or at least 8 microns. In other words, in some embodiments, light diffusing layer 10 has an average thickness of at least 2 microns, at least 4 microns, at least 6 microns, or at least 8 microns.

[0040] FIG. 2 shows an exemplary scanning electron microscope (SEM) image 200 showing a top view of the light diffusing layer 10.

[0041] 1 and 2, the light diffusing layer 10 further includes a plurality of nanoparticles. Specifically, the plurality of nanoparticles includes a plurality of first nanoparticles 20 and a plurality of second nanoparticles 30. In some embodiments, the plurality of first nanoparticles 20 and the plurality of second nanoparticles 30 may be collectively referred to as "a plurality of nanoparticles 20 and 30." The plurality of nanoparticles 20 and 30 are dispersed between and across the first major surface 11 and the second major surface 12.

[0042] In some embodiments, the plurality of nanoparticles 20 and 30 occupy more than 80% of the volume defined between the first and second opposing major surfaces 11 and 12 of the light diffusing layer 10. In some embodiments, the plurality of nanoparticles 20 and 30 occupy more than about 85%, or more than about 90%, of the volume defined between the first and second opposing major surfaces 11 and 12 of the light diffusing layer 10.

[0043] Nanoparticles 20 and 30 comprise silica. In some embodiments, nanoparticles 20 and 30 comprise functionalized silica. In some embodiments, nanoparticles 20 and 30 are substantially spherical. Furthermore, in some embodiments, nanoparticles 20 and 30 are substantially circular in a cross-sectional plane of the light diffusing layer 10 along the thickness direction (i.e., the zx plane). Furthermore, in some embodiments, nanoparticles may be substantially circular in a cross-sectional plane of the light diffusing layer 10 along the xy plane.

[0044] The nanoparticles 20 and 30 form nanoparticle aggregates 60. Specifically, the light diffusing layer 10 includes a polymer material 50 that bonds the nanoparticles 20 and 30 to one another to form the nanoparticle aggregates 60. The nanoparticle aggregates 60 define voids 70 therebetween. In some embodiments, the polymer material 50 includes pentaerythritol triacrylate.

[0045] 1, in some embodiments, optical film 300 further includes a substrate 190 disposed on light diffusing layer 10. In some embodiments, light diffusing layer 10 is bonded to substrate 190. In some embodiments, light diffusing layer 10 is bonded to substrate 190 via an optically clear adhesive or epoxy layer.

[0046] In some embodiments, the substrate 190 comprises one or more of polyethylene terephthalate (PET), polycarbonate, polymethyl methacrylate (PMMA), polyvinyl chloride (PVC), polyvinyl alcohol (PVA), polyolefin, polyethylene, polyethylene naphthalate, cellulose acetate, polystyrene, and polyimide.

[0047] Substrate 190 has an average thickness ts. The average thickness ts is defined along the z-axis. As used herein, the term "average thickness" refers to the average thickness along the plane of substrate 190 (i.e., the xy plane). In some embodiments, substrate 190 has an average thickness ts of about 20 microns to about 500 microns. In some embodiments, substrate 190 has an average thickness ts of about 20 microns to about 300 microns, about 20 microns to about 200 microns, or about 20 microns to about 100 microns.

[0048] In some embodiments, the light diffusing layer 10 may be deposited on the substrate 190 in the form of a wet coating. In such cases, the average thickness t of the light diffusing layer 10 may be measured after the wet coating has dried. In other words, the average thickness t of the light diffusing layer 10 may be a dry thickness.

[0049] FIG. 1 also illustrates substantially collimated, substantially normally incident light 80 incident on optical film 300. In other words, substantially collimated, substantially normally incident light 80 is incident at an angle of about 0 degrees with respect to a normal N to optical film 300. In some embodiments, normal N may be substantially along the z-axis of optical film 300. Furthermore, as used herein, the term "substantially collimated" refers to a total divergence angle of the light being less than about 20 degrees. Thus, substantially collimated, substantially normally incident light 80 incident on optical film 300 may have a total divergence angle (not shown) of less than about 20 degrees. Substantially collimated, substantially normally incident light 80 may be referred to interchangeably as "incident light 80."

[0050] In some cases, incident light 80 may have a first polarization state. In some embodiments, the first polarization state may refer to polarization along the x-axis. In some cases, incident light 80 may have an orthogonal second polarization state. In some embodiments, the orthogonal second polarization state may refer to polarization along the y-axis. In some embodiments, incident light 80 may include a mixture of the first and second polarization states.

[0051] In some embodiments, substrate 190 includes an absorbing polarizer. In some embodiments, for substantially collimated, substantially normally incident light 80 and a visible wavelength range 81 of about 420 nm to about 680 nm (shown in FIG. 5 ), the absorbing polarizer has an average light transmittance of at least 40% for a first polarization state. In other words, for incident light 80 and visible wavelength range 81, the absorbing polarizer has an average light transmittance of at least 40% for light polarized along the x-axis. In some embodiments, for incident light 80 and visible wavelength range 81, the absorbing polarizer has an average light transmittance of at least 50%, at least 60%, at least 70%, at least 80%, or at least 90% for a first polarization state.

[0052] In some embodiments, for substantially collimated, substantially normally incident light 80 and visible wavelength range 81, the absorbing polarizer has an average optical absorptance of at least 60% for the orthogonal second polarization state. In other words, for incident light 80 and visible wavelength range 81, the absorbing polarizer has an average optical absorptance of at least 60% for light polarized along the y-axis. In some embodiments, for incident light 80 and visible wavelength range 81, the absorbing polarizer has an average optical absorptance of at least 70%, at least 80%, at least 90%, or at least 95% for the orthogonal second polarization state.

[0053] Thus, for incident light 80 and a visible wavelength range 81, the absorbing polarizer can substantially transmit incident light 80 having a first polarization state and substantially absorb incident light 80 having an orthogonal second polarization state. In other words, for incident light 80 and a visible wavelength range 81, the absorbing polarizer can substantially pass incident light 80 having a first polarization state and substantially block incident light 80 having an orthogonal second polarization state.

[0054] In some other embodiments, substrate 190 comprises an optical mirror. In these embodiments, for substantially collimated, substantially normally incident light 80 and visible wavelength range 81, the optical mirror has an average optical reflectivity of at least 60% for each of first and second, orthogonal polarization states. In other words, for incident light 80 and visible wavelength range 81, the optical mirror has an average optical reflectivity of at least 60% for polarizations along each of the x-axis and y-axis, which are orthogonal to each other. In some embodiments, for incident light 80 and visible wavelength range 81, the optical mirror has an average optical reflectivity of at least 70%, at least 80%, at least 90%, or at least 95% for each of the first and second, orthogonal polarization states. Thus, the optical mirror can selectively transmit or reflect light regardless of the polarization of incident light 80.

[0055] FIG. 3 shows a detailed schematic cross-sectional view of a reflective polarizer 90 according to one embodiment of the present disclosure.

[0056] 1 and 3, in some embodiments, the substrate 190 includes a reflective polarizer 90. In some embodiments, the light diffusing layer 10 is bonded to the reflective polarizer 90. A reflective polarizer relies on the difference in refractive index between at least two materials, usually polymeric materials, to selectively reflect light of one polarization state while transmitting light of the orthogonal polarization state.

[0057] The reflective polarizer 90 defines x1, y1, and z1 axes that are orthogonal to each other. The x1 and y1 axes correspond to the in-plane axes of the reflective polarizer 90, while the z1 axis is a horizontal axis disposed along the thickness of the reflective polarizer 90. In other words, the x1 and y1 axes are along the plane of the reflective polarizer 90 (i.e., the x1-y1 plane), and the z1 axis is perpendicular to the plane of the reflective polarizer 90, i.e., along the thickness of the reflective polarizer 90. In some embodiments, the x1, y1, and z1 axes of the reflective polarizer 90 may correspond to the x, y, and z axes, respectively, of the optical film 300 (shown in FIG. 1 ).

[0058] The reflective polarizer 90 includes multiple polymer layers. In the illustrated embodiment of FIG. 3 , the reflective polarizer 90 includes multiple alternating first and second polymer layers 91 and 92. The multiple alternating first and second polymer layers 91 and 92 may be referred to interchangeably as "multiple polymer layers 91, 92" or "polymer layers 91, 92." In some embodiments, the multiple polymer layers 91, 92 are disposed adjacent to one another along the z1 axis. The total number of the multiple polymer layers 91, 92 is at least 10. In some embodiments, each of the polymer layers 91, 92 has an average thickness tr. The average thickness tr is defined along the z1 axis. As used herein, the term "average thickness" refers to the average thickness of the polymer layers 91, 92 along their respective planes (i.e., the x1-y1 plane). Each of the polymer layers 91, 92 has an average thickness tr of less than about 500 nm.

[0059] In some embodiments, for substantially collimated, substantially normally incident light 80 and visible wavelength range 81 (shown in FIG. 5 ), reflective polarizer 90 has an average light transmittance for a first polarization state of at least 40%. In other words, for incident light 80 and visible wavelength range 81, reflective polarizer 90 has an average light transmittance for light polarized along the x-axis of at least 40%. In some embodiments, for incident light 80 and visible wavelength range 81, reflective polarizer 90 has an average light transmittance for a first polarization state of at least 50%, at least 60%, at least 70%, at least 80%, or at least 90%.

[0060] In some embodiments, for substantially collimated, substantially normally incident light 80 and visible wavelength range 81, reflective polarizer 90 has an average light reflectance of at least 40% for the orthogonal second polarization state. In other words, for incident light 80 and visible wavelength range 81, reflective polarizer 90 has an average light reflectance of at least 40% for light polarized along the y-axis. In some embodiments, for incident light 80 and visible wavelength range 81, reflective polarizer 90 has an average light reflectance of at least 50%, at least 60%, at least 70%, at least 80%, or at least 90% for the orthogonal second polarization state.

[0061] Thus, for incident light 80 and visible wavelength range 81, reflective polarizer 90 can substantially transmit incident light 80 having a first polarization state and substantially reflect incident light 80 having an orthogonal second polarization state. In other words, for incident light 80 and visible wavelength range 81, reflective polarizer 90 can substantially pass incident light 80 having a first polarization state and substantially block incident light 80 having an orthogonal second polarization state.

[0062] In some embodiments, in the first polarization state and visible wavelength range 81, the reflective polarizer 90 has a greater average light transmittance for light incident at smaller angles of incidence and a lesser average light transmittance for light incident at larger angles of incidence. Specifically, in the first polarization state and visible wavelength range 81, the reflective polarizer 90 has a greater average light transmittance for light having smaller angles of incidence relative to the normal N (e.g., incident light 80) and a lesser average light transmittance for light incident at larger angles of incidence (not shown) relative to the normal N. In other words, in the first polarization state and visible wavelength range 81, the average light transmittance of the reflective polarizer 90 for the incident light 80 decreases as the angle of incidence of the incident light 80 relative to the normal N increases. Thus, in the first polarization state and visible wavelength range 81, the reflective polarizer 90 can have a greater on-axis light transmittance than an off-axis light transmittance.

[0063] 4 illustrates an exemplary plot 210 showing a nanoparticle size distribution 40 of the plurality of nanoparticles 20, 30 (shown in FIGS. 1 and 2). Specifically, the plot 210 shows the nanoparticle size distribution 40 of the plurality of first nanoparticles 20 and the plurality of second nanoparticles 30. Additionally, the plot 210 shows the nanoparticle size of the plurality of nanoparticles 20, 30 as the diameter of the substantially spherical nanoparticles 20, 30. The nanoparticle count is shown on the vertical axis in arbitrary units (au) and the nanoparticle diameter is shown on the horizontal axis in nm (nanometers).

[0064] As can be seen from plot 210, the plurality of nanoparticles 20 and 30 have a nanoparticle size distribution 40 including at least two distinct first and second peaks 41 and 42 at respective nanoparticle sizes d1 and d2. Thus, the majority of the plurality of nanoparticles 20 and 30 have nanoparticle sizes d1 and d2. Specifically, the majority of the plurality of first nanoparticles 20 have nanoparticle size d1, and the majority of the plurality of second nanoparticles 30 have nanoparticle size d2. The ratio of nanoparticle size d2 to nanoparticle size d1 is 1.5 or greater and 10 or less, i.e., 1.5≦(d2 / d1)≦10. In other words, nanoparticle size d2 is approximately 1.5 times or greater and approximately 10 times or less than nanoparticle size d1. In some embodiments, nanoparticle size d1 is approximately 5 nm or greater and approximately 50 nm or less, i.e., 5 nm≦d1≦50 nm. In some embodiments, the nanoparticle size d2 is greater than or equal to about 50 nm and less than or equal to about 100 nm, i.e., 50 nm≦d2≦100 nm. In plot 210, the value of nanoparticle size d1 (i.e., at first peak 41) is about 18 nm, and the value of nanoparticle size d2 (i.e., at second peak 42) is about 56 nm. Therefore, (d2 / d1) is about 3.1. In some other examples, the nanoparticle size d1 is about 20 nm, and the nanoparticle size d2 is about 75 nm. Therefore, (d2 / d1) is 3.75.

[0065] Furthermore, nanoparticles within a full width at half maximum (FWHM) 43 of a first peak 41 and a full width at half maximum (FWHM) 44 of a second peak 42 of the plurality of nanoparticles 20, 30 constitute the W1 and W2 weight percents of the plurality of nanoparticles 20, 30, respectively. In other words, nanoparticles within the FWHM 43 of the first peak 41 constitute the W1 weight percent of the plurality of nanoparticles 20, 30, and nanoparticles within the FWHM 44 of the second peak 42 constitute the W2 weight percent of the plurality of nanoparticles 20, 30. In plot 210, FWHM 43 is between about 17 nm and about 22 nm, and FWHM 44 is between about 56 nm and about 72 nm. Thus, nanoparticles having a particle size between about 17 nm and about 22 nm constitute the W1 weight percent of the plurality of nanoparticles 20, 30, and nanoparticles having a particle size between about 56 nm and about 72 nm constitute the W2 weight percent of the plurality of nanoparticles 20, 30.

[0066] The ratio of W1 to W2 is greater than or equal to about 1.1 and less than or equal to about 2, i.e., 1.1≦(W1 / W2)≦2. In other words, the weight percentage of the plurality of first nanoparticles 20 (i.e., W1) is greater than or equal to about 1.1 times and less than or equal to about 2 times the weight percentage of the plurality of second nanoparticles 30 (i.e., W2). In some embodiments, 1.1≦(W1 / W2)≦1.8, or 1.1≦(W1 / W2)≦1.6. In some examples, W1 is about 60% and W2 is about 40%. Thus, (W1 / W2) is 1.5.

[0067] 5 shows a plot 500 illustrating the optical properties of the optical film 300 shown in FIG. 1 according to one embodiment of the present disclosure. Specifically, plot 500 shows the specular transmittance, diffuse transmittance, and total transmittance of the optical film 300 for incident light 80 (shown in FIG. 1), where total transmittance = (specular transmittance + diffuse transmittance). Wavelength is represented in nm (nanometers) on the abscissa, and transmittance is represented as percent transmittance on the left ordinate.

[0068] 1 and 5, plot 500 includes curve 501 showing the total transmittance of optical film 300, curve 502 showing the specular transmittance of optical film 300, and curve 503 showing the diffuse transmittance of optical film 300. Specifically, curve 501 shows the change in total transmittance of optical film 300 with respect to the wavelength of incident light. Curve 502 shows the change in specular transmittance of optical film 300 with respect to the wavelength of incident light. Furthermore, curve 503 shows the change in diffuse transmittance of optical film 300 with respect to the wavelength of incident light.

[0069] As shown by curve 501, for substantially collimated, substantially normally incident light 80, and a visible wavelength range 81 and an infrared wavelength range 82 of about 900 nm to about 1000 nm, optical film 300 has an average total transmittance VTt in the visible wavelength range 81.

[0070] As shown by curve 502, for substantially collimated, substantially normally incident light 80 and a visible wavelength range 81 and an infrared wavelength range 82, optical film 300 has an average specular transmittance VTs in the visible wavelength range 81.

[0071] Furthermore, as shown by curve 503, for substantially collimated, substantially normally incident light 80 and a visible wavelength range 81 and an infrared wavelength range 82, optical film 300 has an average diffuse transmittance VTd in the visible wavelength range 81.

[0072] In some embodiments, the ratio of the average specular transmittance VTs to the average total transmittance VTt is greater than or equal to about 0.3 and less than or equal to about 0.7, i.e., 0.3≦(VTs / VTt)≦0.7. In other words, for the visible wavelength range 81, the average specular transmittance VTs of the optical film 300 may be greater than or equal to about 30% and less than or equal to about 70% of the average total transmittance VTt of the optical film 300. Accordingly, for the visible wavelength range 81, the average diffuse transmittance VTd of the optical film 300 may be less than or equal to about 70% and greater than or equal to about 30% of the average total transmittance VTt of the optical film 300 (i.e., the remaining portion of the average total transmittance VTt of the optical film 300). In other words, for the visible wavelength range 81, a portion of the incident light 80 exits the optical film 300 as diffuse light, thereby generating optical haze in the visible wavelength range 81. In some embodiments, 0.3≦(VTs / VTt)≦0.65, 0.3≦(VTs / VTt)≦0.6, or 0.3≦(VTs / VTt)≦0.55. In other words, in some embodiments, the ratio of the average total transmittance, VTt, to the average specular transmittance, VTs, is about 0.3 or more and about 0.65 or less, about 0.3 or more and about 0.6 or less, about 0.3 or more and about 0.55 or less, or about 0.3 or more and about 0.5 or less.

[0073] Based on the value of VTd of the optical film 300, the amount of incident light 80 that exits the optical film 300 as diffused light may vary, and therefore, the optical haze of the optical film 300 may correspondingly vary depending on the desired application attributes. The diffuse transmittance of the optical film 300 may be due to scattering of the incident light 80 due to the presence of the nanoparticles 20, 30 and the voids 70 in the light diffusing layer 10. The optical haze of the optical film 300 may be directly proportional to the amount of incident light 80 scattered by the nanoparticles 20, 30. Furthermore, the amount of incident light 80 scattered by the nanoparticles 20, 30 may depend on at least one of d2 / d1 and W1 / W2, and can be varied by correspondingly varying at least one of d2 / d1 and W1 / W2 depending on the desired application attributes. In other words, by controlling at least one of d2 / d1 and W1 / W2 of the nanoparticles 20, 30 in the light diffusing layer 10, the optical haze of the optical film 300 can be varied depending on the desired application attributes.

[0074] In some examples, for a light diffusing layer 10 having an average thickness t of about 2.7 microns, VTt is about 26.5%, VTs is about 14.1%, and VTd is about 12.4%. In this example, (VTs / VTt) is about 0.53. Furthermore, VTd is about 47% of VTt, thereby imparting optical haze to the optical film 300.

[0075] As shown by curve 501, for substantially collimated, substantially normally incident light 80 and a visible wavelength range 81 and an infrared wavelength range 82, optical film 300 has an average total transmittance ITt in the infrared wavelength range 82.

[0076] As shown by curve 502, for substantially collimated, substantially normally incident light 80 and a visible wavelength range 81 and an infrared wavelength range 82, optical film 300 has an average specular transmittance ITs in the infrared wavelength range 82.

[0077] Furthermore, as shown by curve 503, for substantially collimated, substantially normally incident light 80 and a visible wavelength range 81 and an infrared wavelength range 82, the optical film 300 has an average diffuse transmittance ITd in the infrared wavelength range 82.

[0078] In some embodiments, the ratio of the average specular transmittance ITs to the average total transmittance ITt is about 0.7 or greater, i.e., (ITs / ITt)≧0.7. In other words, the average specular transmittance ITs of the optical film 300 may be about 70% or greater of the average total transmittance ITt of the optical film 300. Accordingly, the average diffuse transmittance ITd of the optical film 300 may be less than about 30% of the average total transmittance ITt of the optical film 300 (i.e., the remaining portion of the average total transmittance ITt of the optical film 300). In other words, for the infrared wavelength range 82, the optical film 300 can provide substantial specular transmission of the incident light 80. In some embodiments, (ITs / ITt)≧0.75, or (ITs / ITt)≧0.8. In other words, the ratio of the average specular transmittance ITs to the average total transmittance ITt is about 0.75 or greater, or about 0.8 or greater.

[0079] In some examples, for a light diffusing layer 10 having an average thickness t of about 2.7 microns, ITt is about 87.5% and ITs is about 75%. In this example, (ITs / ITt) is about 0.85. In other words, ITs is about 85% of ITt, i.e., for the infrared wavelength range 82, the optical film 300 can provide substantial specular transmission of incident light 80.

[0080] Thus, optical film 300 can be used in applications requiring substantial specular transmission in the infrared wavelength range, such as optical biometric scanning applications including fingerprint scanning, retinal scanning, and the like.

[0081] Furthermore, the ratio of the average specular transmittance VTs of optical film 300 to the average specular transmittance ITs of optical film 300 is 0.25 or less, i.e., (VTs / ITs)≦0.25. In other words, optical film 300 has a substantially greater average specular transmittance in the infrared wavelength range 82 compared to the visible wavelength range 81. Thus, optical film 300 may be suitable for use in applications that may require substantial specular transmittance in the infrared wavelength range 82 and optical haze in the visible wavelength range 81. In some embodiments, (VTs / ITs)≦0.22, or (VTs / ITs)≦0.2. In some examples, for a light diffusing layer 10 having an average thickness t of about 2.7 microns, VTs is about 14.1% and ITs is about 75%. In this example, (VTs / ITs) is about 0.18.

[0082] 1, 4 and 5, the light diffusing layer 10 can create optical haze in the visible wavelength range 81 and provide substantially high specular transmittance in the infrared wavelength range 82 in the optical film 300.

[0083] Furthermore, due to the nanoparticle size distribution 40 of the plurality of first and second nanoparticles 20, 30, the light diffusing layer 10 can have an increased dry thickness compared to conventional porous coatings without adversely affecting the cohesive strength of the light diffusing layer 10. Increasing the dry thickness of the light diffusing layer 10 can reduce the adverse effects of aging, i.e., non-uniform optical haze upon continued exposure to high temperatures and / or high humidity. Increasing the dry thickness can reduce non-uniform changes in the optical haze of the optical film 300 due to aging. Specifically, in some embodiments, the optical film 300 has an optical haze greater than about 30%, and the optical haze of the optical film 300 decreases by less than about 10% upon exposing the optical film 300 to about 95% relative humidity and a temperature of about 65°C for at least 200 hours. In some examples, the optical film 300 has an optical haze of about 45%.

[0084] 6A shows a detailed schematic cross-sectional view of a display 120 including an optical film 300 according to one embodiment of the present disclosure. The display 120 includes a backlight 110. In some embodiments, the backlight 110 includes a back reflector 111 and an optical film 300 disposed on the back reflector 111. In some embodiments, the optical film 300 and the back reflector 111 can form a recycling optical cavity therebetween.

[0085] In some embodiments, the backlight 110 further includes a light guide 112 disposed between the back reflector 111 and the optical film 300. In some embodiments, the light guide 112 may be a solid light guide. In some embodiments, the light guide 112 may be a step-wedge light guide. In some embodiments, the light guide 112 may use total internal reflection (TIR) ​​to transport or direct light incident on the light guide 112 toward the optical film 300. In some cases, the light guide 112 may improve the uniformity of the light incident on the optical film 300. In some embodiments, the light guide 112 may include a diffusing layer or a light redirecting layer to provide a desired angular distribution of light incident on the optical film 300.

[0086] The backlight 110 is disposed between the liquid crystal panel 121 and the infrared-sensitive detector 122. When an infrared radiation source 123 emitting infrared light 124 within an infrared wavelength range (e.g., infrared wavelength range 82 shown in FIG. 5 ) is disposed proximate to the liquid crystal panel 121, the infrared-sensitive detector 122 detects at least a portion of the emitted infrared light 124. In some applications, the display 120 may include a fingerprint scanner. The infrared light 124 emitted by the infrared radiation source 123 passes through the liquid crystal panel 121 and may be reflected from a finger (not shown) positioned on the liquid crystal panel 121. Thus, the light reflected from the finger may include a portion of the emitted infrared light 124. The light reflected from the finger may pass through the optical film 300 and the back reflector 111 and be detected by the infrared-sensitive detector 122.

[0087] 6B shows a schematic cross-sectional view of the back reflector 111 of the display 120 shown in FIG. 6A, according to one embodiment of the present disclosure. FIG. 6B further shows substantially collimated, substantially normally incident light 601 incident on the back reflector 111, i.e., the substantially collimated, substantially normally incident light 601 is incident at an angle of about 0 degrees with respect to a normal N1 to the back reflector 111. In some embodiments, the normal N1 may be substantially parallel to the normal N (shown in FIG. 1). The substantially collimated, substantially normally incident light 601 may be referred to interchangeably as "incident light 601."

[0088] In some cases, the incident light 601 may have first and second polarization states that are orthogonal to each other. In some embodiments, the first and second orthogonal polarization states may refer to polarization along the x-axis and y-axis, respectively.

[0089] 6A and 6B, in some embodiments, for substantially collimated, substantially normally incident light 601 in the visible wavelength range of about 420 nm to about 680 nm and the infrared wavelength range of about 800 nm to about 1500 nm, and for each of first and second orthogonal polarization states, the back reflector 111 reflects at least 60% of the incident light 601 for each wavelength in the visible wavelength range. In some embodiments, for the incident light 601, the visible wavelength range and the infrared wavelength range, and for each of the first and second orthogonal polarization states, the back reflector 111 reflects at least 70%, at least 80%, at least 90%, or at least 95% of the incident light 601 for each wavelength in the visible wavelength range. In other words, for each of the first and second orthogonal polarization states, the back reflector 111 substantially reflects the incident light 601 for each wavelength in the visible wavelength range.

[0090] In some embodiments, for substantially collimated, substantially normally incident light 601 in the visible and infrared wavelength ranges and for each of the first and second orthogonal polarization states, the back reflector 111 transmits at least 30% of the incident light 601 for at least one wavelength in the infrared wavelength range. In some embodiments, for the incident light 601 in the visible and infrared wavelength ranges and for each of the first and second orthogonal polarization states, the back reflector 111 transmits at least 30%, at least 40%, at least 50%, at least 60%, at least 70%, or at least 80% of the incident light 601 for at least one wavelength in the infrared wavelength range. In other words, for each of the first and second orthogonal polarization states, the back reflector 111 transmits at least a portion of the incident light 601 for at least one wavelength in the infrared wavelength range.

[0091] Thus, the back reflector 111 can be highly reflective for wavelengths within the visible wavelength range. Such high reflectivity for wavelengths within the visible wavelength range can reduce the amount of loss within the recycling cavity defined between the optical film 300 and the back reflector 111. Furthermore, such high reflectivity for wavelengths within the visible wavelength range can include both specular and diffuse reflection. In some embodiments, the back reflector 111 can be a predominantly specular reflector, a diffuse reflector, or a combination specular / diffuse reflector, whether spatially uniform or patterned. In some embodiments, the back reflector 111 can be a semi-specular reflector. In some cases, the back reflector 111 can include a rigid metal substrate with a highly reflective coating or a highly reflective film laminated to a supporting substrate. In some embodiments, the back reflector 111 can include one or more elements such as silver, aluminum, a white coating, a non-conductive coating, etc.

[0092] 7A and 7B show scanning electron microscope (SEM) images 701 and 702, respectively, illustrating a detailed cross-sectional side view of an optical film 300′ according to another embodiment of the present disclosure. The optical film 300′ shown in FIGS. 7A and 7B is substantially similar to the optical film 300 of FIG. 1 . However, the optical film 300′ includes a reflective polarizer 90′ and a light diffusing layer 10′. Common components between the optical film 300′ and the optical film 300 are indicated using the same reference numerals.

[0093] The reflective polarizer 90' is substantially similar to the reflective polarizer 90 shown in Figure 3. However, the reflective polarizer 90' includes a plurality of first protrusions 100 on the first major surface 93 thereof.

[0094] Light diffusing layer 10' is disposed on first major surface 93 of reflective polarizer 90'. Light diffusing layer 10' is substantially similar to light diffusing layer 10 of FIG. 1. However, light diffusing layer 10' substantially conforms to first protrusion 100.

[0095] The light diffusing layer 10' substantially conforms to the first protrusions 100 to form a plurality of concentric portions 13 that are substantially concentric with the first protrusions 100. In the illustrated embodiment of Figures 7A and 7B, one of the first protrusions 100 is shown for clarity.

[0096] Furthermore, the light diffusing layer 10' forms a plurality of parallel portions 14 that substantially conform to the first protrusions 100 and are substantially parallel to the polymer layers 91, 92 of the reflective polarizer 90'.

[0097] Additionally, the light diffusing layer 10′ forms a plurality of transition portions 15 that substantially conform to the first protrusions 100 to provide a gradual transition between the concentric portions 13 and the parallel portions 14. For each first protrusion 100, the length L1 of the transition portion 15 corresponding to the first protrusion 100 is less than three times the width L2 of the first protrusion 100, i.e., L1<3L2.

[0098] FIG. 7C shows an SEM image 703 illustrating a top view of the optical film 300' of FIGS. 7A and 7B, according to one embodiment of the present disclosure.

[0099] 7A-7C, in some embodiments, for at least two adjacent first protrusions 100-1 and 100-2, the light diffusing layer 10' substantially conforms to the two adjacent first protrusions 100-1 and 100-2 to form two concentric portions 13-1 and 13-2, and the light diffusing layer 10' is substantially concentric with the two adjacent first protrusions 100-1 and 100-2 but does not form a parallel portion between the two concentric portions 13-1 and 13-2.

[0100] In some embodiments, for at least one of the first protrusions, the concentric portion 13 of the light diffusing layer 10' exposes the peak of at least one of the first protrusions.

[0101] In the illustrated embodiment of FIG. 7C, for the first protrusion 100-1, the concentric portion 13-1 of the light diffusing layer 10' exposes the peak 76 of the first protrusion 100-1.

[0102] In some embodiments, at least one of the first protrusions having an exposed peak (e.g., first protrusion 100-1) comprises at least 1% of the plurality of first protrusions 100. In some embodiments, at least one of the first protrusions comprises at least 2%, at least 3%, at least 4%, or at least 5% of the plurality of first protrusions 100.

[0103] Furthermore, the light diffusing layer 10' substantially conforms to the first protrusions 100 to form a plurality of connecting portions 16 connecting the plurality of concentric portions 13. In the illustrated embodiment of Figure 7C, the light diffusing layer 10' substantially conforms to the first protrusions 100-1, 100-2, 100-3 to form connecting portions 16-1 connecting concentric portions 13-1 and 13-2 and connecting portions 16-2 connecting concentric portions 13-1 and 13-3.

[0104] Furthermore, the thickness variation of the light diffusing layer 10' across at least 80% of the total surface area of ​​the light diffusing layer 10' occupied by the connecting portions 16 (e.g., 16-1, 16-2) is less than about 30%. In other words, the thickness of the light diffusing layer 10' across at least 80% of the total surface area of ​​the light diffusing layer 10' occupied by the connecting portions 16 may not vary by more than 30%. In some embodiments, the thickness variation of the light diffusing layer 10' across at least 80% of the total surface area of ​​the light diffusing layer 10' occupied by the connecting portions 16 is less than about 25%, less than about 20%, less than about 15%, or less than about 10%. Thus, the thickness of the light diffusing layer 10' across at least 80% of the total surface area of ​​the light diffusing layer 10' occupied by the connecting portions 16 may be substantially constant.

[0105] 8A shows a schematic cross-sectional view of the optical film 300′ shown in FIGS. 7A-7C, according to one embodiment of the present disclosure. FIG. 8A further shows substantially collimated, substantially normally incident light 801 incident on the optical film 300′, i.e., the substantially collimated, substantially normally incident light 801 is incident at an angle of about 0 degrees with respect to the normal N2 to the optical film 300′. The substantially collimated, substantially normally incident light 801 may be referred to interchangeably as “incident light 801.”

[0106] 8B shows a plot 800 illustrating the optical properties of the optical film 300′ shown in FIG. 8A according to one embodiment of the present disclosure. Specifically, plot 800 shows the diffuse reflectance of the optical film versus wavelength 83. The diffuse reflectance of the optical film versus wavelength 83 may be interchangeably referred to as the “diffuse reflectance versus wavelength 83.” The diffuse reflectance versus wavelength 83 indicates the variation in diffuse reflectance of the optical film 300′ versus the wavelength of incident light 801 incident on the optical film 300′. Wavelength is expressed in nm (nanometers) on the abscissa, and diffuse reflectance is expressed as percent reflectance on the left ordinate.

[0107] 8A and 8B, it is evident from plot 800 that for substantially collimated, substantially normally incident light 801 and a visible wavelength range 81 and an infrared wavelength range 82, the diffuse reflectance for wavelength 83 has a global minimum 84 at a first wavelength 85 located between the visible wavelength range 81 and the infrared wavelength range 82. In some embodiments, first wavelength 85 is between about 750 nm and about 880 nm. In some embodiments, global minimum 84 is between about 30% and about 50%. In plot 800, first wavelength 85 is about 820 nm and global minimum 84 is about 32%.

[0108] 1-8B, the light diffusing layer 10, 10′ of each optical film 300, 300′ can generate optical haze in the visible wavelength range 81 and can also provide substantially high specular transmittance in the infrared wavelength range 82 due to the presence of the nanoparticles 20, 30 and the voids 70. In other words, the nanoparticles 20, 30 and the voids 70 can be substantially transparent to incident light in the infrared wavelength range 82. Furthermore, a plurality of nanoparticles 20 and 30 having a nanoparticle size distribution 40 including at least two distinct first and second peaks 41 and 42 at respective nanoparticle sizes d1 and d2, such that 1.5≦(d2 / d1)≦10, and respective weight percentages W1 and W2 of nanoparticles within the FWHMS of the first and second peaks 41 and 42, such that 1.1≦W1 / W2≦2, can result in an increase in the dry thickness of the light diffusing layers 10 and 10′ without adversely affecting the cohesive strength of the light diffusing layers 10 and 10′. Accordingly, the light diffusing layers 10 and 10′ of the present disclosure can reduce the adverse effects of aging, i.e., non-uniform optical haze upon continued exposure to high temperatures and / or humidity, without compromising the cohesive strength of the light diffusing layers 10 and 10′. Specifically, exposing the optical film 300, 300′ to a relative humidity of about 95% and a temperature of about 65° C. for at least 200 hours reduces the optical haze of the optical film 300, 300′ by less than about 10%. Furthermore, the optical haze produced by the light diffusing layer 10, 10′ can be controlled by varying the respective weight percentages W1 and W2 of the plurality of nanoparticles 20, 30 and / or the respective nanoparticle sizes d2 and d1.

[0109] Unless otherwise indicated, all numbers expressing feature sizes, quantities, and physical properties used in the specification and claims are to be understood as modified by the term "about." Accordingly, unless specifically indicated to the contrary, the numerical parameters set forth in the foregoing specification and appended claims are approximations that may vary depending upon the desired properties sought to be obtained by those of ordinary skill in the art using the teachings disclosed herein.

[0110] While specific embodiments have been illustrated and described herein, those skilled in the art will recognize 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. This application is intended to cover any adaptations or variations of the specific embodiments discussed herein. Accordingly, it is intended that the present disclosure be limited only by the claims and equivalents thereof.

Claims

1. 1. An optical film comprising a light diffusing monolayer having an average thickness of about 0.5 microns to about 5 microns, said light diffusing monolayer comprising: Opposite first and second major surfaces; a plurality of nanoparticles dispersed between and across the first and second major surfaces, the nanoparticles comprising silica, the plurality of nanoparticles having a nanoparticle size distribution including at least two distinct first and second peaks at respective nanoparticle sizes d1 and d2, where 1.5≦d2 / d1≦10, the nanoparticles of the plurality of nanoparticles within a full width at half maximum (FWHM) of the first peak and within a full width at half maximum (FWHM) of the second peak form a W1 and W2 weight percent, respectively, of the plurality of nanoparticles, where 1.1≦W1 / W2≦2; a polymeric material that bonds the nanoparticles together to form a plurality of nanoparticle aggregates that define a plurality of voids therebetween; For substantially collimated, substantially normally incident light, and the visible wavelength range of about 420 nm (nanometers) to about 680 nm and the infrared wavelength range of about 900 nm to about 1000 nm, the optical film: In the visible wavelength range, an average specular transmittance VTs and an average total transmittance VTt, and An optical film having an average total transmittance ITt and an average specular transmittance ITs in the infrared wavelength range, wherein 0.3≦VTs / VTt≦0.7, VTs / ITs≦0.25, and ITs / ITt≧0.

7.

2. 2. The optical film of claim 1, wherein 50 nm≦d2≦100 nm and 5 nm≦d1≦50 nm.

3. 2. The optical film of claim 1, further comprising a substrate disposed on the light diffusing monolayer, the substrate comprising: (a) a reflective polarizer having an average light transmittance of at least 40% for a first polarization state and an average light reflectance of at least 40% for an orthogonal second polarization state for the substantially collimated, substantially normally incident light and the visible wavelength range; (b) an absorbing polarizer having an average light transmittance of at least 40% for a first polarization state and an average light absorbance of at least 60% for an orthogonal second polarization state for the substantially collimated, substantially normally incident light and the visible wavelength range; or (c) an optical mirror having an average light reflectance of at least 60% for each of the first and second orthogonal polarization states for the substantially collimated, substantially normally incident light and the visible wavelength range.

4. The optical film of claim 1 , wherein in a plane of a cross section of the light diffusing monolayer in a thickness direction of the light diffusing monolayer, the nanoparticles are substantially circular.

5. 1. An optical film comprising a light diffusing layer coupled to a reflective polarizer, the light diffusing layer comprising a plurality of nanoparticles dispersed between and occupying greater than 80% of a volume defined between first and second opposed major surfaces of the light diffusing layer, the nanoparticles forming a plurality of nanoparticle aggregates defining a plurality of voids therebetween, the first and second major surfaces being spaced at least 2 microns apart, the nanoparticles having a nanoparticle size distribution comprising at least two distinct first and second peaks in respective nanoparticle sizes d1 and d2, and 1.5≦d2 / d1≦10, the reflective polarizer comprising a plurality of polymer layers totaling at least 10, each of the polymer layers having an average thickness less than about 500 nm, the optical film having an optical haze greater than about 30%, and wherein exposing the optical film to a relative humidity of about 95% and a temperature of about 65° C. for at least 200 hours reduces the optical haze of the optical film by less than about 10%.

6. 6. The optical film of claim 5, wherein the reflective polarizer has an average light transmission of at least 40% for a first polarization state and an average light reflectance of at least 40% for an orthogonal second polarization state for substantially collimated, substantially normally incident light and a visible wavelength range of about 420 nm to about 680 nm.

7. 7. The optical film of claim 6, wherein in the first polarization state and in the visible wavelength range, the reflective polarizer has a greater average light transmission for light incident at smaller angles of incidence and a lesser average light transmission for light incident at larger angles of incidence.

8. 6. The optical film of claim 5, wherein 50 nm≦d2≦100 nm and 5 nm≦d1≦50 nm.

9. A back reflector; 6. The optical film of claim 5 disposed on the back reflector; and a light guide disposed between the back reflector and the optical film, wherein for substantially collimated, substantially normally incident light, a visible wavelength range of about 420 nm to about 680 nm, an infrared wavelength range of about 800 nm to about 1500 nm, and each of first and second mutually orthogonal polarization states, the back reflector reflects at least 60% of the incident light for each wavelength in the visible wavelength range and transmits at least 30% of the incident light for at least one wavelength in the infrared wavelength range.

10. 10. A display comprising a backlight according to claim 9, disposed between a liquid crystal panel and an infrared-sensitive detector, wherein when an infrared radiation source emitting infrared radiation within the infrared wavelength range is disposed proximate to the liquid crystal panel, the infrared-sensitive detector detects at least a portion of the emitted infrared radiation.

11. a reflective polarizer including a plurality of polymer layers totaling at least 10 in number, each of the polymer layers having an average thickness of less than about 500 nm, the reflective polarizer including a plurality of first protrusions on a first major surface thereof; a light diffusing layer disposed on the first major surface of the reflective polarizer, the light diffusing layer comprising a plurality of nanoparticles having a nanoparticle size distribution including at least two distinct first and second peaks in respective nanoparticle sizes d1 and d2, where 1.5≦d2 / d1≦10, wherein the light diffusing layer substantially conforms to the first protrusions; a plurality of concentric portions substantially concentric with the first protrusion; a plurality of parallel portions, the parallel portions being substantially parallel to the polymer layer of the reflective polarizer; and a plurality of transition sections providing a gradual transition between the concentric portion and the parallel portion, wherein for each first protrusion, the length of the transition section corresponding to the first protrusion is less than three times the width of the first protrusion; Forming an optical film.

12. 12. The optical film of claim 11, wherein for at least two adjacent first protrusions, the light diffusing layer substantially conforms to the two adjacent first protrusions to form two concentric portions, and the light diffusing layer is substantially concentric with the two adjacent first protrusions but does not form a parallel portion between the two concentric portions.

13. 12. The optical film of claim 11, wherein 50 nm≦d2≦100 nm and 5 nm≦d1≦50 nm.

14. 12. The optical film of claim 11, wherein for at least one of the first protrusions, the concentric portion of the light diffusing layer exposes a peak of the at least one of the first protrusions.

15. The optical film of claim 14 , wherein at least one of the first protrusions comprises at least 1% of the plurality of first protrusions.

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