Summary

In some aspects of the present description, a reflective polarizer is provided, including a plurality of polymeric layers numbering at least 200 in total. The plurality of polymeric layers may be disposed between and co-extruded and co-stretched with opposing first and second outer layers. Each of the polymeric layers may have an average thickness of less than about 350 nm, a thinnest polymeric layer in the plurality of polymeric layers disposed closer to the first outer layer and a thickest polymeric layer in the plurality of polymeric layers disposed closer to the second outer layer. The first outer layer may include a plurality of first particles partially protruding from a first major surface thereof at a surface density of between about 4 to about 250 first particles per square mm to form a first structured major surface facing away from the polymeric layers. The second outer layer may include a plurality of second particles partially protruding from a second major surface thereof at a surface density of between about 150 to about 250 first particles per square mm to form a second structured major surface facing away from the polymeric layers. The first particles may have an average size of greater than about 7 microns, and the second particles may have an average size of less than about 6 microns. For a substantially normally incident light and a first wavelength range extending from about 400 nanometers (nm) to about 800 nm and a second wavelength range extending from about 950 nm to about 1300 nm, the plurality of polymeric layers may reflect greater than about 80% of the incident light having a first polarization state in the first wavelength range, may transmit greater than about 40% of the incident light having a second polarization state orthogonal to the first polarization state in the first wavelength range, may transmit greater than about 60% of the incident light in the second wavelength range for each of the first and second polarization states, and an optical transmittance of the reflective polarizer versus wavelength for the first polarization state may have a band edge between about 800 nm and about 1100 nm, wherein a best linear fit to the band edge correlating the optical transmittance to the wavelength at least across a wavelength range where the optical transmittance along the band edge increases from about 10% to at least about 80%, may have a slope of greater than about 3% per nm.

In some aspects of the present description, a display system for sensing a finger of a user applied to the display system is provided, including a display panel configured to generate an image for viewing by the user, a lightguide for providing illumination to the display panel, a reflective polarizer as described above disposed between the display panel and the lightguide, the first structured major surface disposed between the display panel and the plurality of polymeric layers, a sensor for sensing the finger of the user disposed proximate the lightguide opposite the reflective polarizer, a mirror disposed between the lightguide and the sensor, and an infrared light source configured to emit an infrared light toward the finger of the user, the sensor configured to receive at least a portion of the infrared light reflected by the finger. Brief Description of the Drawings

FIGS. 1A-1C provide side, schematic views of a display system, in accordance with an embodiment of the present descnption;

FIG. 2A-2B provide side, schematic views of a reflective polarizer, in accordance with an embodiment of the present descnption;

FIGS. 3A-3B are charts showing the layer thickness profiles for a reflective polarizer, in accordance with an embodiment of the present description;

FIGS. 4A-4B are charts showing plots of percent transmission versus wavelength for a reflective polarizer, in accordance with an embodiment of the present description;

FIG. 5 is a plot providing additional detail for the plot of FIG. 4A, in accordance with an embodiment of the present description;

FIG. 6 is an image of an optically diffusive layer of a reflective polarizer, in accordance with an embodiment of the present description;

FIG. 7 is an illustration of a coordinate system reference used for the Examples, in accordance with an embodiment of the present description;

FIGS. 8A shows representative transmission spectra for Example Film 1, in accordance with an embodiment of the present description;

FIG. 8B shows a layer profile of individual layers in the example packets as a function of layer count, in accordance with an embodiment of the present description;

FIG. 9 shows representative transmission spectra for Example Film 2, in accordance with an embodiment of the present description;

FIG. 10A provides a schematic of a cross-section of Example Film 4, in accordance with an embodiment of the present description;

FIG. 10B shows representative transmission spectra for Example Film 4, in accordance with an embodiment of the present description;

FIG. 11 A provides a schematic of a cross-section of Example Film 5 with conformal diffuser, in accordance with an embodiment of the present description; and

FIG. 1 IB shows representative transmission spectra for Example Film 5, in accordance with an embodiment of the present description.

Detailed Description

In the following description, reference is made to the accompanying drawings that form a part hereof and in which various embodiments are shown by way of illustration. The drawings are not necessarily to scale. It is to be understood that other embodiments are contemplated and may be made without departing from the scope or spint of the present description. The following detailed description, therefore, is not to be taken in a limiting sense. As new and advanced technologies emerge, displays for mobile devices are trending larger in an effort to provide higher information content. There is increasing motivation to maximize display dimensions and to integrate additional functionalities in mobile devices. Recent trends in mobile devices include reducing the bezel size in displays (or eliminating it completely) and integrating biometric authentication capabilities (e.g., fingerprint sensing) into the displays.

One approach to improving display properties and integrating additional functionality is to replace traditional components with multilayer optical films which are thinner, and which can be designed to have the desired optical properties. For example, display components (e.g., a reflective polarizer, or a backlight reflector) can be designed as multilayer optical films which reflect some wavelengths and/or polarizations of light while transmitting other wavelengths and/or polarizations.

Some display systems may allow certain wavelengths of infrared light to pass through the layers of an optical stack, such that an infrared light source and infrared sensor may be used to read a fingerprint above the glass, while not significantly effecting the human-visible performance of the display.

When these films are assembled in an optical system (e.g., a display, or a backlight unit), adjacent films may come in contact and create wet-out on the display (unwanted optical patterns on the display caused by changes in refractive index when the two films touch), or air gaps between adjacent films may cause interference “fringe” patterns on the display (e.g., Newton’s rings, moire patterns). Wet-out effects may be reduced or eliminated by coating one or more films in the stack with small beads to reduce physical contact between layers. Ffowever, the size of the beads used to eliminate wet-out can introduce air gaps between adjacent films which can result in interference fringe patterns which may manifest as defects on the display resembling wet-out patterns.

According to some aspects of the present description, a reflective polarizer is described including an “optimal” bead size to provide improved display performance. In some embodiments, a reflective polarizer includes a plurality of polymeric layers numbering at least 200 in total. In some embodiments, the plurality of polymeric layers may be disposed between, and co-extruded and co-stretched with, opposing first and second outer layers. Each of the polymeric layers may have an average thickness of less than about 350 nm, and a thinnest polymeric layer in the plurality of polymeric layers may be disposed closer to the first outer layer and a thickest polymeric layer in the plurality of polymeric layers may be disposed closer to the second outer layer. In some embodiments, a layer profile showing the thickness of the plurality of polymeric layers may exhibit a substantially monotonic increase from polymeric layers disposed closer to the first outer layer toward polymeric layers disposed closer to the second outer layer.

In some embodiments, the first outer layer may include a plurality of first particles (e.g., beads) partially protruding from a first major surface thereof at a surface density of between about 4 to about 250 first particles per square millimeter (mm) to form a first structured major surface facing away from the polymeric layers. In some embodiments, the first outer layer may include a plurality of first particles at a surface density of between about 10 to about 250, or between about 50 to about 250, or between about 75 to about 250, or between about 100 to about 250, or between about 125 to about 250, or between about 150 to about 250, first particles per square mm to form the first structured major surface. In some embodiments, first particles and the second particles may include, but not be limited to, an acrylic material.

In some embodiments, the second outer layer may include a plurality of second particles partially protruding from a second major surface thereof at a surface density of between about 150 to about 250 first particles per square mm to form a second structured major surface facing away from the polymeric layers. In some embodiments, the first particles may have an average size of greater than about 7 microns, and the second particles may have an average size of less than about 6 microns. In some embodiments, an average size of the first particles may be greater than about 7 microns and the average size of the second particles may be greater than about 3 microns. In some embodiments, at least some of the first particles may have a size between about 15 microns and about 50 microns. In some embodiments, the first and second outer layers may have different compositions.

In some embodiments, for a substantially normally incident light and a first wavelength range extending from about 400 nm to about 800 nm and a second wavelength range extending from about 950 nm to about 1300 nm, the plurality of polymeric layers may reflect greater than about 80%, or about 85%, or about 90%, of the incident light having a first polarization state (e g., linear s-polarized light) in the first wavelength range, may transmit greater than about 40%, or about 45%, or about 50%, of the incident light having a second polarization state orthogonal to the first polarization state (e g., linear p-polarized light) in the first wavelength range, may transmit greater than about 60% of the incident light in the second wavelength range for each of the first and second polarization states, and an optical transmittance of the reflective polarizer versus wavelength for the first polarization state may have a band edge between about 800 nm and about 1100 nm, wherein a best linear fit to the band edge correlating the optical transmittance to the wavelength at least across a wavelength range where the optical transmittance along the band edge increases from about 10% to at least about 80%, may have a slope of greater than about 3% per nm. In some embodiments, the best linear fit to the band edge may have an r-squared value of greater than about 0.8, or about 0.85, or about 0.9, or about 0.95.

In some embodiments, for substantially normally incident light and in a third wavelength range extending from a smaller wavelength LI to a greater wavelength L2, the difference L2 - LI is between about 30 nm and about 50 nm. In some embodiments, LI may be greater than and within about 20 nm of a wavelength corresponding to an optical transmittance of about 50% along the band edge. In some embodiments, the optical transmittance may have an average value of greater than about 75%, or about 80%, or about 85%.

In some embodiments, the reflective polarizer may further include an optically diffusive layer conformably disposed on the first structured major surface of the first outer layer so that opposing first and second major surfaces of the optically diffusive layer substantially conform to the first structured major surface and define an average spacing of between about 200 to about 5000 nm, or about 4000 nm, or about 3000 nm, or about 2000 nm, or about 1500 nm, therebetween. In some embodiments, the optically diffusive layer may include a plurality of nanoparticles dispersed between and across the first and second major surfaces of the optically diffusive layer. In some embodiments, the nanoparticles may have an average size of between about 10 nm to about 150 nm, which may define a plurality of voids between them. In some embodiments, for substantially normally incident light and for a visible (i.e., human-visible) wavelength range extending from about 450 nm to about 650 nm and for an infrared wavelength range extending from about 930 nm to about 970 nm, the reflective polarizer may have an average specular transmittance, Ys, in the visible wavelength range and an average specular transmittance, Is, in the infrared wavelength range, such that the ratio Is/Vs is greater than about 2.5. In some embodiments, the average spacing between the first and second major surfaces of the optically diffusive layer is between about 0.5 and about 5 microns.

In some aspects of the present description, a display system for sensing a finger (e.g., the ridges of a fingerprint) of a user applied to the display system (e.g., pressed to or placed near the bezel glass of the display) includes a display panel (e.g., a liquid crystal display) configured to generate an image for viewing by the user, a lightguide for providing illumination to the display panel, a reflective polarizer as described above disposed between the display panel and the lightguide (such that the first structured major surface of the reflective polarizer disposed between the display panel and the plurality of polymeric layers), a sensor for sensing the finger of the user disposed proximate the lightguide opposite the reflective polarizer, a mirror (e.g., an infrared-transmissive mirror film) disposed between the lightguide and the sensor, and an infrared light source configured to emit an infrared light toward the finger of the user, the sensor configured to receive at least a portion of the infrared light reflected by the finger. In some embodiments, for substantially normally incident light and for each of the first and second polarization states, the mirror may reflect greater than about 80%, or about 85%, or about 90%, of the incident light in the first wavelength range and transmits greater than about 40%, or about 45%, or about 50%, of the incident light in the second wavelength range.

In some embodiments, the lightguide may include a lightguide plate and at least one light source configured to inject light into the lightguide plate. In some embodiments, the injected light may propagate through the lightguide plate via total internal reflection before impinging on an interior surface of the lightguide plate at an angle which allows some or all of the light to exit the lightguide plate. In some embodiments, the display system may further include an optical diffuser disposed between the reflective polarizer and the lightguide.

In some embodiments of the display system, the infrared light source may be directly or indirectly disposed below a cover glass (e.g., bezel glass) of the display system. In some embodiments, the infrared light source may be disposed below the mirror (i.e., such that light passes up through the mirror to illuminate the finger or other object on or above the display, is reflected, and passes back through the mirror to a sensor). In some embodiments, the infrared light source may be disposed adjacent to one or more layers of the display system (e.g., to the side of the reflective polarizer) or may be disposed between two layers of the display system (e.g., between the optical diffusive layer, if present, and the reflective polarizer).

In some embodiments, the reflective polarizer may include two “packets” of polymeric layers so that the plurality of polymeric layers include a plurality of first polymeric layers spaced apart along a thickness direction (e.g., the z axis) of the reflective polanzers from a plurality of second polymeric layers by one or more middle layers. In some embodiments, each of the pluralities of first and second polymeric layers may number at least 200. In some embodiments, the pluralities of first and second polymeric layers may be disposed between, and co-extruded and co-stretched with, the opposing first and second outer layers, where each of the first and second polymeric layers may have an average thickness of less than about 350 nm, and where each of the one or more middle layers may have an average thickness of greater than about 500 nm. In some embodiments, the reflective polarizer may include a single packet of polymeric layers so that each layer between the opposing first and second outer layers has an average thickness of less than about 350 nm.

Turning now to the figures, FIGS. 1A-1C provide side, schematic views of alternate embodiments of a display system of the present description. Each of FIGS. 1A-1C share common components and, as such, refer to these components using the same reference designator. The following discussion applies equally to each of FIGS. 1A-1C unless noted otherwise.

FIG. 1A shows a display system 300 which, in some embodiments, includes a display panel 90, a lightguide 100, a reflective polarizer 200 disposed between display panel 90 and lightguide 100, a sensor (e.g., an infrared sensor) 110, a mirror 120 disposed between the lightguide 100 and sensor 110, and an infrared light source 130.

In some embodiments, light guide 100 includes at least one light source 102 configured to inject light 103 into a lightguide plate 101, where light 103 is redirected by total internal reflection through lightguide plate 101 until it impinges on an internal surface of lightguide plate 101 at an angle allowing light 103 to escape lightguide plate as illumination 107. Illumination 107 passes up through reflective polarizer 200, and through display panel 90 in order to illuminate an image 91 on display panel 90 for viewing by viewer 302. When light 103 exits the side of lightguide plate 101 facing mirror 120, at least a portion of the light is reflected by mirror 120 (recycled) and passed back into lightguide plate 101 (or transmitted through) such that it eventually becomes illumination 107.

In some embodiments, display system 300 may be configured to sense a finger 301 applied to the display system 300 (e.g., the ridges of a fingerprint for biometric security purposes) of a user 302. In some embodiments, infrared light source 130 may be configured to emit an infrared light 131 toward the finger 301 of the user. Infrared light 131 may be reflected from finger 301 and be redirected into display system 300, passing through reflective polarizer 200, lightguide 100, and mirror 120, where at least a portion 132 of the infrared light 131 impinges on sensor 110.

In some embodiments, reflective polanzer 200 may include a plurality of polymeric layers 10, 11 (FIGS. 2A-2B provide additional detail on polymeric layers 10, 11 and are discussed elsewhere herein). Polymeric layers 10, 11 may be co-extruded and co-stretched with opposing first outer layer 20 and second outer layer 30. In some embodiments, first outer layer 20 may include a plurality of first particles 40 partially protruding from first major surface 21. In some embodiments, second outer layer 30 may include a plurality of second particles 50 partially protruding from first major surface 31.

In some embodiments, reflective polanzer 200 may further include an optically diffusive layer 80 disposed on the first major surface 21 of first outer layer 20. In some embodiments, optically diffusive layer 80 may have opposing first 81 and second 82 major surfaces which substantially conform to the first major surface 21. In some embodiments, the first 81 and second 82 major surfaces have an average spacing therebetween of about 200 nm to 5000 nm, or about 200 nm to about 4000 nm, or about 200 nm to about 3000 nm, or about 200 nm to about 2000 nm, or about 200 nm to about 1500 nm. Additional detail on optically diffusive layer 80 is provided in FIG. 6 and discussed elsewhere herein.

In the embodiment of FIG. 1A, infrared light source 130 is disposed above reflective polarizer 200 and below display panel 90, near an edge of the optical stack forming display system 300. As infrared light source 130 is typically not used as an illumination source for display panel 90, it may for convenience or to meet certain design requirements be placed in alternate locations. Two additional embodiments are provided in FIGS. IB and 1C, in which the location of the infrared light source 130 is changed. The locations of infrared light source 130 shown in FIGS. 1A-1C are intended to be exemplary only and not limiting in any sense. In FIG. IB, infrared light source 130’ is shown located beside (i.e., at one edge) of display panel 90, underneath cover glass 92 (e g., the glass screen of a mobile device). Infrared light 131 is emitted by infrared light source 130’ and is reflected by finger 301, and at least a portion 132 of infrared light 131 passes through the layers of display system 300 to impinge on sensor 110. In FIG. 1C, infrared light source 130” is located beneath mirror 120, adjacent to infrared sensor 110. Infrared light 103 is emitted by infrared light source 130”, passed up through the optical stack of display system 300, reflected by finger 301, and passed back through display system 300 such that at least a portion 132 of infrared light 131 impinges on sensor 110.

In some embodiments, the various layers of display system 300 may be at least partially transmissive in an infrared wavelength band, such that infrared light 131 may be passed up to finger 301 and be reflected back through the display system 300 to sensor 101. For example, in some embodiments, for a substantially normally incident light and a first wavelength range extending from about 400 nm to about 800 nm and a second wavelength range extending from about 950 nm to about 1300 nm, the plurality of polymeric layers may reflect greater than about 80% of the incident light having a first polarization state in the first wavelength range, may transmit greater than about 40%, or about 45%, or about 50%, of the incident light having a second polarization state orthogonal to the first polarization state, in the first wavelength range, and may transmit greater than about 60% of the incident light in the second wavelength range for each of the first and second polarization states. In some embodiments, an optical transmittance of the reflective polarizer versus wavelength for the first polarization state may include a band edge between about 800 nm and about 1100 nm, wherein a best linear fit to the band edge correlating the optical transmittance to the wavelength at least across a wavelength range where the optical transmittance along the band edge increases from about 10% to at least about 80% has a slope of greater than about 3%/nm. Additional detail on the optical characteristics of the reflective polarizer are described elsewhere herein.

As another example, the optically diffusive layer 80 may be configured such that light in a first, human-visible wavelength range is scattered (i.e., diffused) more than light in an infrared range. In some embodiments, for example, for substantially normally incident light and a visible wavelength range extending from about 450 nm to about 650 nm and an infrared wavelength range extending from about 930 nm to about 970 nm, the reflective polarizer (with optically diffusive layer 80) may have an average specular transmittance, Vs, in the visible wavelength range and an average specular transmittance, Is, in the infrared wavelength range, such that the ratio of Is/Vs is greater than or equal to about 2.5.

In some embodiments, display system 300 may further include an optical diffuser 140 disposed between reflective polarizer 200 and lightguide 100.

FIG. 2A-2B provide side, schematic views of two separate embodiments of a reflective polarizer construction, according to the present description. FIG. 2A illustrates a reflective polarizer 200 created with a single-packet construction (i.e., a single packet multilayer optical film), and FIG. 2B illustrates an alternate embodiment of a reflective polarizer 200 created with two packets. Looking first at FIG. 2A, a reflective polarizer 200 may include a single optical packet 205 including a plurality of alternating polymeric layers 10, 11. In some embodiments, the total number of polymeric layers 10, 11 may be equal to or greater than 200, and each of the polymeric layers 10, 11 may have an average thickness of less than about 350 nm.

The plurality of polymeric layers 10, 11 may be disposed between, and co-extruded and co stretched with, opposing first 20 and second 30 outer layers. In some embodiments, the first outer layer 20 may include a plurality of first particles 40 partially protruding from a first major surface 21 thereof at a surface density of between about 4 to about 250, or about 10 to 250, or about 50 to 250, or about 75 to 250, or about 100 to 250, or about 125 to 250, or about 150 to 250, first particles 40 per square mm to form a first structured major surface 22 facing away from the polymeric layers. In some embodiments, the second outer layer 30 may include a plurality of second particles 50 partially protruding from a second major surface 31 thereof at a surface density of between about 150 to 250 second particles 50 per square mm to form a first structured major surface 32 facing away from the polymeric layers. In some embodiments, the composition of the first outer layer 20 and the composition of the second outer 30 layer may be different.

In some embodiments, the thickness of the polymeric layers 10, 11 may exhibit a substantially monotonic increase from polymeric layers 10, 11 disposed closer to the first outer layer 20 toward polymeric layers 10, 11 disposed closer to the second outer layer 30. For example, a thinnest polymeric layer 12 in the plurality of polymeric layers 10, 11 may be disposed closer to the first outer layer 20, while a thickest polymeric layer 13 in the plurality of polymeric layers 10, 11 may be disposed closer to the second outer layer 30 (i.e., a comparison of polymeric layer 12 to polymeric layer 13 may show polymeric layer 13 to be thicker than polymeric layer 12). In some embodiments, the first particles 40 may have an average size of greater than about 7 microns, and the second particles 50 may have an average size of less than about 6 microns. In some embodiments, at least some of the first particles 40 may have a size between about 15 microns and about 50 microns.

The thicknesses of the individual polymeric layers 10, 11, as well as the selection of the refractive indices of layers 10 versus layers 11, may be chosen so as to configure the reflective polarizer 200 to achieve a specific target for optical performance (e.g., specific wavelength ranges to transmit or reflect). For example, in one embodiment, for a substantially normally incident light 60 and a first wavelength range extending from about 400 nm to about 800 nm and a second wavelength range extending from about 950 nm to about 1300 nm, the plurality of polymeric layers may reflect greater than about 80% of the incident light 60 having a first polarization state in the first wavelength range, may transmit greater than about 40%, or greater than about 50%, of the incident light 60 having a second polarization state orthogonal to the first polarization state, in the first wavelength range, and may transmit greater than about 60%, or greater than about 65%, or greater than about 70%, of the incident light in the second wavelength range for each of the first and second polarization states. Additional details on the optical performance of one embodiment of a reflective polarizer are provided in FIGS. 4A-4B, discussed elsewhere herein.

The embodiment of FIG. 2B is similar to the embodiment of FIG. 2A in most aspects, but differs in that the reflective polarizer 200’ of FIG. 2B is created with two packets, a first packet 210 and a second packet 220. The two packets 210 and 220 each include a plurality of alternating polymeric layers 10,

11, and spaced apart from each other along a thickness direction of the reflective polarizer (the z- axis as shown in FIG. 2B) by one or more middle layers 23, 24. Each of the middle layers 23, 24 may have an average thickness of greater than about 500 nm. As with the embodiment of FIG. 2A, the total number of polymeric layers 10, 11 may be at least 200, and the polymeric layers 10, 11 may be co-extruded and co-stretched with the opposing first 20 and second 30 outer layers. In some embodiments, the thickness of first packet 210 may be less (e.g., may contain fewer polymeric layers 10, 11) than the thickness of second packet 220.

FIGS. 3A-3B are charts showing the layer thickness profiles for one embodiment of a reflective polarizer of the present description. The charts plot the thickness of each of the individual polymeric layers 10, 11 (see FIGS. 2A-2B) versus their relative position in the packet(s) (their layer number). The relative positions of thinnest polymeric layer 12 and the thickest polymeric layer 13, as discussed with FIG. 2A elsewhere herein, are marked on FIGS. 3A and 3B. FIG. 3A shows the layer profile for a single packet, and FIG. 3B shows the layer profile of a combined dual-packet configuration (such as that shown in FIG. 2B). Both FIGS. 3 A and 3B show a substantially monotonic increase from polymeric layers (10,

11) disposed closer to the first outer layer 20 (the left side of FIGS. 3A/3B) toward polymeric layers (10,

11) disposed closer to the second outer layer 30 (the right side of FIGS. 3A/3B). FIGS. 4A-4B are charts showing plots of percent transmission versus wavelength for a reflective polarizer according to the present description. FIG. 4A provides a plot of optical transmittance 70 for substantially normally incident light (see 60, FIGS. 2A-2B) for the reflective polarizer versus wavelength of light for the first polarization state. The plot shows that light with the first polarization state from about 400 nm up to about 900 nm is substantially reflected (i.e., not transmitted), and has a band edge 71 between about 800 nm and about 1100 nm, such that wavelengths of light above the band edge 71 are substantially transmitted. FIG. 4B provides a plot of the band edge 71 at a closer scale, showing that, in some embodiments, a best linear fit 72 to the band edge 71 correlating the optical transmittance to the wavelength at least across a wavelength range where the optical transmittance along the band edge increases from about 10% to at least about 80% has a slope 73 of greater than about 3%/nm. In some embodiments, the best linear fit 72 to the band edge 71 has an r-squared value 74 of greater than about 0.8, or greater than about 0.85, or greater than about 0.9, or greater than about 0.95.

FIG. 5 is a plot providing additional detail for the plot of FIG. 4A, showing the optical transmittance 70 for substantially normally incident light (see 60, FIGS. 2A-2B) versus wavelength of light. For a third wavelength range 75 extending from a smaller wavelength LI to a greater wavelength L2, the difference L2 - LI may be greater than or equal to about 30 nm and less than or equal to about 50 nm. In some embodiments, wavelength LI may be greater than and within about 20 nm of a wavelength 76 which corresponds to an optical transmittance of about 50% along the band edge 71. In some embodiments, the optical transmittance 70 within the third wavelength range 75 may have an average value of greater than about 75%, or greater than about 80%, or greater than about 85%.

FIG. 6 is a magnified image of optically diffusive layer 80 of FIG. 1, according to the present description. FIG. 6 shows optically diffusive layer 80 (disposed on the first major surface 21 as shown in FIG. 1) with opposing first 81 and second 82 major surfaces. In some embodiments, there is an average spacing between opposing first 81 and second 82 major surfaces of between about 0.5 and 5 microns. In some embodiments, the optically diffusive layer 80 includes a plurality of nanoparticles 83 between and across the first major surface 81 and second major surface 82. In some embodiments, the nanoparticles 83 may have an average size of between about 10 nm to about 150 nm, and may define a plurality of voids 84 therebetween. In some embodiments, for the substantially normally incident light and a visible wavelength range extending from about 450 nm to about 650 nm and for an infrared wavelength range extending from about 930 nm to about 970 nm, the reflective polarizer may have an average specular transmittance, Vs, in the visible wavelength range and an average specular transmittance, Is, in the infrared wavelength range, such that the ratio Is/Vs is greater than or equal to about 2.5. EXAMPLES

Multilayered optical films (MOFs) with specific alternate layers of polymeric materials with different refractive indices were prepared and coated with different acrylic beads during the manufacturing of the MOF films described herein. The bead diameters and distribution were optimized to eliminate the interference fringes that appeared due to multiple reflection between the MOF surface and the reflecting polarizing film used in display devices such as a smart phone.

All parts, percentages, ratios, etc., in the examples and the rest of the specification are by weight, unless noted otherwise. The following abbreviations are used herein: g = gram, mol = molar, mm = millimeters; cm = centimeters; um = micrometers, kPa = kilo Pascals, °C = Degree Celsius, mins = minutes, hrs = hours, mg = milligram, ft = feet, s = seconds, nm = nanometer, psi = per square inch, ° = degrees, IR = Infra-Red, UV = Ultraviolet, md = machine direction, td = transverse direction, ppm = parts per million, g = gram, DSC = Differential Scanning Calorimeter. A summary of the materials used in the examples herein is provided in Table 1. Table 1: Materials Used in the Examples. Preparation of Bead Coating Mixtures:

First, a precursor mixture WB50 was prepared as follows. A one-gallon polyester kettle was charged with 111.9 g (5.5 mol %) 5-sodiosulfoisophthalic acid, 592.1 g (47.0 mol %) terephthalic acid, 598.4 g (47.5 mol %) isophthalic acid, 705.8 g ethylene glycol, 599 g neopentyl glycol, 0.7 g antimony oxide, and 2.5 g sodium acetate. The mixture was heated with stirring to 230 °C at 345 kPa (50 psi) under nitrogen for 2 hours, during which time water evolution was observed. The temperature was increased to 250 °C and the pressure was then reduced, vacuum was applied (0.2 torr), and the temperature was increased to 270 °C. The viscosity of the material increased over a period of 45 minutes, after which time a high molecular weight, clear, viscous sulfopolyester was drained. This sulfopolyester was found by DSC to have a Tg of 70.3 °C. The theoretical sulfonate equivalent weight was 3847 g polymer per mole of sulfonate. 500 g of the polymer was dissolved in a mixture of 2000 g water and 450 g isopropanol at 80 °C. The temperature was then raised to 95 °C in order to remove the isopropanol (and a portion of the water). The final dispersion consisted of an aqueous 20 wt. % solids dispersion.

Coating mixtures were prepared by mixing the inputs detailed in Table 2 and agitating until homogeneous.

Table 2: Mixture Inputs.

Example Film 1. A multilayer optical (MOF) film was manufactured with two sequential (stacked) packets of microlayers, with 325 individual microlayers layers in each packet enclosed by packet bonding layers. The microlayers in each packet were arranged as alternating layers of material A and material B. Material A is a birefringent polyester PEN, and material B is a blend of PC :PCTG and PETg (GN017) in the ratio of 85: 15. The microlayer packet was designed to have a reflection band that spans the regions of visible and near-IR wavelengths. The films were then stretched continuously in a standard tenter with a draw ratio of 6: 1 in the transverse direction and constrained in the machine direction (no orientation or relaxation). The oven temperature used for the orientation was 270 degrees Fahrenheit. The process conditions for the manufacture of this film were chosen so that the measured spectra matched the calculated spectra using the wavelength-dependent refractive index values, as shown in the Table 3. Respective refractive indices of materials n _x , n _y , and n _z are along three orthogonal directions as defined in the coordinate system in FIG 7. ni _S0 is the refractive index of the isotropic phase of PC:PCTG:PETg(GN071) blend.

Table 3: Calculated Spectra Values.

Representative spectra for Example Film 1 were measured and are shown in FIG. 8A. The layer thicknesses were measured using an Atomic Force Microscope (Dimension ICON from Bruker Instruments, Billerica, MA) and is shown in FIG. 8B.

Example Film 2. The surface of the packet 1 of unoriented cast web was continuously coated with mixture A using a gravure roll in a reverse kiss configuration. The coated web then passed through a coating oven for at least 5 seconds with the temperature of the oven maintained above 65° C. The beads were observed under a microscope on the unoriented cast web to be not grouped together and the beads appeared to be delivered to the surface of the web at the same concentration as in the coating mixture. This bead coated cast film was stretched and oriented to yield bead coated MOF as described in Example Film 1.

A Keyence microscope was used to count the number of beads per unit area and it was found to be -175 beads/mm2. Representative spectra for Example Film 2 were measured and are shown in FIG. 9.

Example Film 3. The surface of the packet 1 of unoriented cast web was continuously coated with mixture A using a gravure roll in a reverse kiss configuration. The coated web then passed through a coating oven for at least 5 seconds with the temperature of the oven maintained above 65° C. The other side (surface of packet 2) of the cast web coated with mixture A was then continuously coated with mixture B and dried in the same manner as with mixture A. The beads were observed under a microscope on the unoriented cast web to be not grouped together and the beads appeared to be delivered to the surface of the web at the same concentration as in the coating mixture. This bead coated cast film was stretched and oriented to yield both side bead coated MOF as described in Example Film 1. A Keyence microscope was used to count the number of beads per unit area and it was found to be -175 beads/mm2.

Example Film 4: Example Film 4 was prepared very similar to Example Film 3 except the coating mixture B was replaced by coating mixture C. A Keyence microscope was used to count the number of beads per unit area and it was found to be -182 beads/mm2. Schematic of the cross-section of the Example Film 4 is shown in FIG 10A. Representative spectra for Example Film 4 were measured and are shown in FIG. 10B. Example Film 5. The surface of the thick packet of the MOF film as described in Example Film 4 was coated with a conformal diffuser using a slurry of silica nanoparticles in acrylic monomer dissolved in its solvent as described below.

First, a coating precursor mixture was prepared by mixing a 5.95 g of A-174 and 0.5 g of 4- hydroxy-2,2,6,6-tetramethylpiperidine 1-oxyl (5 wt. %; 4Fl-2,2,6,6-TMP 1-0) were added to the mixture of 400 g Nalco 2329 and 450 g of 1-methoxy -2 -propanol in a glass jar with stirring at room temperature for 10 mins. The jar was sealed and placed in an oven at 80° C for 16 hours. Then, the water was removed from the resultant mixture with a rotary evaporator at 60° C until the solid content of the mixture was close to 45 wt %. 200 g of l-methoxy-2 -propanol was charged into the resultant mixture, and then remaining water was removed by using the rotary evaporator at 60° C. This latter step was repeated for a second time to further remove water from the mixture. Finally, the concentration of total silica nanoparticles was adjusted to 42.5 wt. % by adding l-methoxy-2 -propanol to result in the silica mixture containing surface modified silica nanoparticles with an average size of 75 nm.

Next, a coating mixture was prepared. The coating mixture was composed of 20.96 wt. % of the clear precursor mixture described above, 5.94 wt. % of SR444, 71.55 wt. % isopropyl alcohol, 1.48 wt. % Irgacure 184 and 0.07 wt. % Irgacure 819. Coating mixture was pumped (using a pressure pot) to a slot- type coating die at a rate that produced a wet layer thickness of 7 um onto Example 4 Film.

Next, the coating was polymerized by passing the coated substrate through a UV-FED cure chamber that included a quartz window to allow passage of UV radiation. The UV-FED cure chamber included a rectangular array of UV-FEDs. The FEDs (available from Nichia Inc., Tokyo Japan) operated at a nominal wavelength of 385 nm and when run at 10 Amps, resulted in a UV-A dose of 0.035 joules per square cm. The UV-FEDs were run at 3 Amps to produce the film described in this example. The water-cooled UV-FED array was powered by a Genesys 150-22 power supply (available from TDK- Fambda, Neptune N.J.). The UV-FEDs were positioned above the quartz window of the cure chamber at approximately 2.5 cm from the substrate. The UV-FED cure chamber was supplied with a flow of nitrogen at a flow rate of 22 cubic feet per minute in order to keep the oxygen level below 50 parts ppm. The oxygen level in the UV-FED cure chamber was monitored using a Series 3000 oxygen analyzer (available from Alpha Omega Instruments, Cumberland RI).

After being polymerized by the UV-FEDs, the solvent in the cured coating was removed and dried at 66° C for 30 seconds. Next, the dried coating was post-cured using a Fusion System Model 1600 configured with a D-bulb (available from Fusion UV Systems, Gaithersburg, MD). The UV Fusion chamber was supplied with a flow of nitrogen that resulted in an oxygen concentration of approximately 50 ppm in the chamber. This resulted in a diffuser coated film with conformal coating of the beads.

Schematic of the cross-section of the Example Film 5 is shown in FIG 11A. Representative spectra for Example Film 5 were measured and are shown in FIG. 1 IB.

Terms such as “about” will be understood in the context in which they are used and described in the present description by one of ordinary skill in the art. If the use of “about” as applied to quantities expressing feature sizes, amounts, and physical properties is not otherwise clear to one of ordinary skill in the art in the context in which it is used and described in the present description, “about” will be understood to mean within 10 percent of the specified value. A quantity given as about a specified value can be precisely the specified value. For example, if it is not otherwise clear to one of ordinary skill in the art in the context in which it is used and described in the present description, a quantity having a value of about 1 , means that the quantity has a value between 0.9 and 1.1, and that the value could be 1.

Terms such as “substantially” will be understood in the context in which they are used and described in the present description by one of ordinary skill in the art. If the use of “substantially equal” is not otherwise clear to one of ordinary skill in the art in the context in which it is used and described in the present description, “substantially equal” will mean about equal where about is as described above. If the use of “substantially parallel” is not otherwise clear to one of ordinary skill in the art in the context in which it is used and described in the present description, “substantially parallel” will mean within 30 degrees of parallel. Directions or surfaces described as substantially parallel to one another may, in some embodiments, be within 20 degrees, or within 10 degrees of parallel, or may be parallel or nominally parallel. If the use of “substantially aligned” is not otherwise clear to one of ordinary skill in the art in the context in which it is used and described in the present description, “substantially aligned” will mean aligned to within 20% of a width of the objects being aligned. Objects described as substantially aligned may, in some embodiments, be aligned to within 10% or to within 5% of a width of the objects being aligned.

All references, patents, and patent applications referenced in the foregoing are hereby incorporated herein by reference in their entirety in a consistent manner. In the event of inconsistencies or contradictions between portions of the incorporated references and this application, the information in the preceding description shall control.

Descriptions for elements in figures should be understood to apply equally to corresponding elements in other figures, unless indicated otherwise. Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent implementations can be substituted for the specific embodiments shown and described 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. Therefore, it is intended that this disclosure be limited only by the claims and the equivalents thereof.