具体实施方式：
[0024]FIG. 1 is a split front-side elevation cross-section of an exemplary optical film. Optical film 100 includes top structured surface 110 with microstructure 112, and bottom structured surface 120 with microstructures with first face 122 and second face 124.
[0025]In FIG. 1, the structured surfaces (top structured surface 110 and bottom structured surface 120) are disposed such that a length direction of the microstructures are generally not parallel. In some embodiments, the length direction of the microstructures are oriented orthogonally from one another. However, in order to more easily depict a simultaneous cross-section of both the top and bottom structured surfaces, FIG. 1 (along with other figures in this application so-annotated) are split front-side elevation cross-sections; that is, as the reference coordinate systems to the left of each structured surface suggest, the figures are actually two perspectives spliced together. The orientation of other components in reference to these structured surfaces is described as is necessary.
[0026]Top structured surface 110 includes microstructure 112. In some embodiments, the structured top surface includes a plurality of parallel microstructures. In some embodiments, the parallel microstructures may be linear microstructures. By linear, it is meant that a peak of one of the microstructures is a line across the top structured surface (when viewed, for example, from a top plan view). In some embodiments, and for practical reasons including the limits of manufacturing processes, linear microstructures may include small deviations from precisely linear. In some embodiments, the microstructures may be linear but for a periodic or nonperiodic variation in pitch. In some embodiments, the microstructures may be linear but may vary in height, either periodically or nonperiodically. In some embodiments, there may be space or “land” between adjacent microstructures. In some embodiments, top structured surface 110 includes spacing between adjacent microstructures in a range from about 0.5 μm to about 5 μm. The spacing may be constant or varying.
[0027]Microstructure 112 may be substantially curved. In some embodiments, microstructure 112 has a substantially cylindrical or semi-cylindrical shape. In some embodiments, microstructure 112 is a semi-circle or a semi-ellipse along a cross-section orthogonal to the length of the microstructure. In some embodiments, microstructure 112 is characterized by a height h, measured from the peak of microstructure 112 to the base of microstructure 112, along a line orthogonal to the base of microstructure 112. The lowest points on top structured surface 110 may be used to determine the base of microstructure 112. Microstructure 112 may also be characterized by a radius of curvature R, and the ratio of h/R may be any suitable value. In some embodiments, h/R is not greater than 0.4.
[0028]Top structured surface 110 may be formed from any suitable method and from any suitable material. For example, top structured surface 110 may be selectively etched or ground. In some embodiments, top structured surface 110 may be formed at least in part through a two-photon mastering process. In some embodiments, top structured surface 110 relies on a cast-and-cure process utilizing an inversely shaped tool. In some cases, top structured surface may be formed from a UV-crosslinkable or UV-curable resin such that appropriate light exposure causes the resin to harden, separate from the mold or tool, and permanently retain its shape. In some embodiments, top structured surface 110 may be formed through an additive process, such as 3D-printing. In some embodiments, top structured surface 110 may be injection molded. Top structured surface 110 may be formed in a monolithic piece of material or it may be formed in a top layer of material disposed on a substrate or a dimensionally stable or warp resistant layer. The material or materials may be selected for their material, physical, or optical properties, such as clarity, scratch or abrasion resistance, warp resistance, birefringence or lack thereof, ability to be microreplicated in, haze, Tg (glass transition temperature), potential to be bonded to other surfaces, or any other suitable characteristic.
[0029]Bottom structured surface 120 includes microstructures, each with first face 122 and second face 124. As for top structured surface 110, the microstructures may be linear microstructures; however, recall that the perspective is split in FIG. 1, such that in the exemplary configuration shown in this figure, the microstructures of the top and bottom structures run generally orthogonally to one another. Bottom structured surface 120 may include spaced apart adjacent structures, with a spacing being—in some embodiments—between 0.5 μm and 3 μm.
[0030]First face 122 is substantially flat, in that from a cross-section orthogonal to the length of the microstructure, it appears as a straight line. Second face 124 is curved, in that from a cross-section orthogonal to the length of the microstructure, it appears as an arc or curve. In some embodiments, the microstructures may include more than two faces, or two faces and a peak or joining portion, for example. In some embodiments, second face 124 may have a constant curvature, or it may have a piecewise curvature. In some embodiments, second face 124 may have a continuously varying curvature. In some embodiments, each first face may be the same or substantially the same shape and size. In some embodiments, each second face may be the same or substantially the same shape and size. In some embodiments, one or more of the first and second faces may vary in one or more of shape or size, either periodically, non-periodically, or in a gradient.
[0031]Optical film 100 may be, overall, formed from any suitable material or combination of materials and have any suitable dimensions. In some embodiments, optical film 100 may be sized or shaped for the particular display or lighting application. The structures on the structured surfaces of optical film 100 may run orthogonally as described, or they may extend or run simply in a first direction and a second direction, where the first direction and the second direction are different from one another. For example, an angle between the first and second direction may be between 78 and 90 degrees. In some embodiments, the top structured surface and the bottom structured surface cover the same area. In some embodiments, top structured surface 110 and bottom structured surface 120 are two sides of the same monolithic film. In some embodiments, the two structured surfaces or their respective substrates are laminated to or attached to each other.
[0032]FIG. 2 is a split front-side elevation cross-section of another optical film. Optical film 200 includes top structured surface 210 with microstructure 212, bottom structured surface 222 with microstructures with first face 222 and second face 224 and characterized in part by line 225. Intermediate layers 230 and 232 may or may not be included.
[0033]As described with respect to optical film 100 in FIG. 1, optical film 200 includes top structured surface 210 and bottom structured surface 220. The microstructures of the top and bottom structured surface may have some or all of the properties described in conjunction with FIG. 1. The structures of the top and bottom surface extend orthogonally with respect to one another, as is shown with their respectively oriented coordinate systems of this split view.
[0034]Disposed between top structured surface 210 and bottom structured surface 220 are intermediate layers 230 and 232. In some embodiments, intermediate layers 230 and 232 may be a single layer. In some embodiments, one or both of intermediate layers 230 and 232 may not be present.
[0035]In some embodiments, intermediate layer 230 is a reflective polarizer. The reflective polarizer may be adhered to the top structured surface layer and the bottom structured surface layer. Reflective polarizers are characterized by the at least partial—or in many cases substantial—reflection of a first polarization while largely transmitting a second, orthogonal polarization. In some embodiments, the first polarization may be a linear polarization along a third direction, and the second polarization may be a linear polarization along a fourth direction. The third direction may be the same as the first or second direction, and the fourth direction may be the same as the other one of the first or second directions. In some embodiments, and for some applications, it may be acceptable for the third direction or fourth direction and either the first or second direction to make an angle between 0 and 12 degrees.
[0036]In some embodiments, intermediate layer 230 may be a reflective polarizer and intermediate layer 232 may be a quarter wave plate, quarter wave layer, or quarter wave retarder. The quarter wave layer and the reflective polarizer may be stacked or attached in either order and may be referred to together as a polarization management optical stack. In some embodiments, additional layers such as adhesives, protective layers, or diffusion layers may be present. Effectively, the combination of intermediate layers 230 and 232 may function as a circular reflective polarizer, in that the combination at least partially reflects light having a first polarization handedness while largely transmitting the other polarization handedness. The quarter wave plate may be or include, in some embodiments, a liquid crystal polymer. In some embodiments the reflective polarizer may not be present, and the intermediate layers may include only a quarter wave layer.
[0037]Reflective polarizers may be multilayer reflective polarizers. Multilayer reflective polarizers are formed from coextruded packets of alternating high and low index layers that, when oriented appropriately, possess internal index of refraction interfaces having appropriate thickness to reflect light of certain polarizations through constructive interference. Examples of reflective polarizers include DBEF and APF, (available from 3M Company, St. Paul, Minn.).
[0038]In some embodiments, one or both of intermediate layers 230 and 232 may be birefringent. In some embodiments, one of both of intermediate layers 230 and 232 may include bulk scattering or hazy elements, such as beads, particles, bubbles, or voids. In some embodiments, one or both of intermediate layers 230 and 232 may be a diffuse reflective polarizer. Diffuse reflective polarizers may be formed from an oriented immiscible blend of two polymers, where at least one of the polymers is capable of developing birefringence when stretched. One or both of intermediate layers 230 and 232 may be laminated or adhered to one another. Intermediate layers 230 and 232 may be attached, laminated, or adhered to one or both of the layers including top structured surface 210 and bottom structured surface 220.
[0039]The faces of the microstructures of bottom structured surface 220 may be characterized by an angle. The angle is measured between the base (e.g., a line or plane normal to the thickness direction and even with the lowest (or highest, depending on perspective—in any case the base is on the opposite side of the structured surface from the peak) points of bottom structured surface 220) and a line 225 connecting a point on the base nearest the face and the peak of the microstructure. In some embodiments, this angle is between 60 degrees and 80 degrees for curved second face 224 and between 50 degrees to about 70 degrees for flat first face 222. For flat faces, line 225 may be largely or completely coincident with the face, depending on the geometry of the peak. Alternatively, curved faces such as second face 224 may be characterized by one or more radii of curvature. In some embodiments, the curved face may have a single value for its radius of curvature. In some embodiments, the curved face may have two or more sections, each with a different value for its radius of curvature. In some embodiments, the curved face may have a continuously varying radius of curvature. The value or values for the radii of curvature may be within a range from about 40 μm to about 100 μm, or from about 60 μm to about 100 μm.
[0040]FIG. 3 is a cross-section of an exemplary configuration for the bottom microstructure of the optical films of FIGS. 1 and 2. The bottom microstructure has first face 302, second face 304, and base 306. Second face 304 is piecewise curved and characterized in a first part by first circle 310 having first center of curvature 312 and in a second part by second circle 320 having second center of curvature 322. Line 330 connects the intersection of second face 304 and base 306 with the peak of the microstructure. Bisecting line 340 orthogonally bisects line 330.
[0041]The two centers of curvature, first center of curvature 312 and second center of curvature 322, are offset from bisecting line 340 that perpendicularly bisects line 330. In some embodiments, there is one center of curvature, and it is offset from bisecting line 340. In some embodiments, there are two or more centers of curvature, and at least one center of curvature is offset from bisecting line 340. In some embodiments, there are many centers of curvature, and at least some are offset from bisecting line 340. In some embodiments, all centers of curvature are offset from bisecting line 340.
[0042]In some embodiments, each microstructure on a structured surface of an optical film have faces with centers of curvature that meet certain of the criteria outlined herein. In some embodiments, a plurality of microstructures on a structured surface of an optical film have faces with centers of curvature that meet certain of the criteria.
[0043]FIG. 4 is a cross section of another configuration for a bottom microstructure. The bottom microstructure has first face 402, second face 404, base 406, and peak 408. FIG. 4 illustrates that the microstructure design may not necessarily have a sharp peak, in contrast to those depicted in FIGS. 1-3. Peak 408 may be rounded, curved, or flat, and may be characterized by its geometry, including its width and radius of curvature. Peak 408, when curved, may be simply curved, or may be piecewise or continuously curved. In some embodiments, the peak is an arc having a radius of curvature in a range from 0.1 μm to 5 μm.
[0044]FIG. 5 is a split front-side elevation cross-section of another exemplary optical film. Optical film 500 includes top structured surface 510 with microstructures having first face 512 and second face 514. Bottom structured surface 520 has microstructures having first face 522 and second face 524. FIG. 5 is similar to FIG. 1, except that top structured surface 510 has microstructures including first face 512 and second face 514. The top faces are flat or substantially flat (e.g., within manufacturing tolerances for flatness). The top faces, first face 512 and second face 514, meet at a peak of the microstructure forming a peak angle therebetween. In some embodiments, the peak angle is within five degrees of 90 degrees. In some embodiments, the peak angle is in a range from 90 degrees to 110 degrees. The microstructures of top structured surface 510 may have a rounded, faceted, or shaped peak.
[0045]FIG. 6 is a split front-side elevation cross-section of a backlight including an optical film. Backlight 600 includes optical film 602 having top structured surface 610 with microstructure 612, bottom structured surface 620 including first face 622 and second face 624, and optional intermediate layer 630. Backlight 600 further includes buffer layer 640, lightguide 650, reflector 660, and light source 670.
[0046]Optical film 602 is similar to those depicted in FIGS. 1 and 2, including top structured surface 610 with microstructure 612 and bottom structured surface 620 facing the output surface of the lightguide and including microstructures with first face 622 and second face 624. Optical film 602 also includes intermediate layer 630, which correspond with intermediate layers 230 and 232 as shown in and described in conjunction with FIG. 2. In this sense, intermediate layer 630 in FIG. 6 is simplified and, as such, may represent both the quarter wave plate and the linear reflective polarizer although these are treated as separate layers in FIG. 2. Optical film 602 may be a monolithic layer or it may be formed from several laminated portions or layers. Any other optical films described herein may be substituted for or features thereof incorporated in optical film 602.
[0047]The rest of backlight 600 includes buffer layer 640 disposed between optical film 602 and lightguide 650, lightguide 650 itself, reflector 660, and light source 670.
[0048]Buffer layer 640 may be formed from optically transparent polymeric materials and may have any suitable dimensions. In some embodiments, buffer layer 640 may cover substantially all of the area of lightguide 650 or optical film 602. In some embodiments, buffer layer 640 may be designed to prevent physical damage to lightguide 650 or the peaks of bottom structured surface 620. Damage may include scratching or even bending or breaking of portions of the structured surface, for example after experiencing a shock, such as an impact or collision. In certain applications buffer layer 640 may have physical properties that make it advantageous for shock absorption, such as characteristics that make it appropriately cushioning.
[0049]In some embodiments, buffer layer 640 may have a structured surface. In some embodiments, buffer layer 640 may have two structured surfaces. Buffer layer 640 may include a bottom structured surface that imparts very low haze, such as less than 10%, less than 5%, or even less than 1%. Haze as used herein is the value reported through the proper operation of a HAZE-GARD PLUS hazemeter, (available from BYK-Gardner USA, Columbia, Md.). In some embodiments, this low-haze structured surface may provide advantageous anti-wetout properties to the buffer layer vis-à-vis the lightguide.
[0050]In some embodiments, buffer layer 640 may have a structured surface that diffuses light or imparts some haze. In some embodiments, the hazy structured surface may cover a portion of the top surface. In some embodiments, the hazy structured surface may only cover a small portion (in some embodiments, no more than 10%) of the top surface nearest the edge closest to the light source. The haze of the small edge portion may be greater than 30%, 50%, or 70%. In some embodiments, the structured surface has a hazy portion covering a small portion of a surface and another portion with lower haze covering some or all of the rest of the surface.
[0051]The structured surface may be formed from any suitable process, including a cast-and-cure method against a tool. The tool may be formed from any process or combination of processes including, for example, masking and etching, reactive ion etching, diamond turning, electroplating, coating a tool with beads, or photolithography including one- and two-photon processes.
[0052]In some embodiments, buffer layer 640 may be laminated or attached to one or more of lightguide 650 and optical film 602. Buffer layer 640 may be attached to lightguide 650, for example, with a layer of pressure sensitive or optically clear adhesive, or through one or more pieces of edge or rim tape. In some embodiments, buffer layer 640 may be bonded to lightguide 650 with a low index adhesive layer. Such a low index adhesive layer may include a plurality of voids.
[0053]In some embodiments, buffer layer 640 may include an antireflection coating or surface structure (such as a moth's eye structure) on one or both sides. Particularly in configurations where there is an air gap between buffer layer 640 and an adjacent layer or layers, such an antireflection treatment may reduce Fresnel reflections and may increase the overall brightness of backlight 600.
[0054]Buffer layer 640 is optional in many configurations, and its removal naturally allows for thinner backlight designs. Without the buffer layer, light may be specularly transmitted from the output surface of lightguide 650 to the bottom structured surface of optical film 602.
[0055]Lightguide 650 may be any suitable size or shape, and may be formed from any suitable material. In some embodiments, lightguide 650 may be formed from an injection molded monolithic piece of acrylic, for example, or it may be formed from any other suitable material. Lightguide 650 may have its material selected for advantageous optical characteristics, such as high transmission, low absorption, or low scattering, or physical characteristics such as rigidity, flexibility, or temperature and warp resistance. In some embodiments, lightguide 650 may be a wedge lightguide. In some embodiments, lightguide 650 may include or contain extraction features, such as printed dots, negative microfeatures (i.e., indentations where the air/lightguide interface tends to defeat total internal reflection by scattering or reflecting light at subcritical angles, which then passes through the other surface of the lightguide), or positive microfeatures. The extraction features may be arranged in a gradient pattern so that light is evenly extracted over the area of the lightguide (and, ultimately, backlight 600 overall). In other words, the extraction features may be less densely packed in portions of the lightguide that have more overall light, such as the area proximate the light source. Alternatively, for some applications, the extraction features may be more densely packed in areas where greater light output is desired, such as under the numbers or buttons on a phone keypad or the like. The extraction features may vary in size, shape, and number either periodically, in a gradient, or non-periodically.
[0056]Reflector 660 is any suitable layer that is a broadband reflector of light. In some embodiments, reflector 660 is a metallic reflector, such as aluminum or silver, or a substrate with a metallic reflecting surface deposited thereon. In some embodiments, reflector 660 is a multilayer optical film.
[0057]Similarly to the multilayer optical film reflective polarizer described herein, the multilayer optical film reflector includes alternating high and low index layers of polymeric materials carefully selected and capable of developing birefringence when oriented. The layers are coextruded and oriented such that a broad spectrum of light is reflected by the interfaces between the layers through constructive interference. The optical thickness of each layer pair is designed such that different layer pairs contribute to the reflection of different wavelengths of light. An exemplary multilayer optical film reflector is Enhanced Specular Reflector, or ESR (available from 3M Company, St. Paul, Minn.). Suitable reflectors may reflect at least 90% of light, 95%, 98% of light, or even 99%. The reflector may provide a reflection pattern characterized as diffuse (or even Lambertian), specular, or semi-specular.
[0058]Light source 670 may be any suitable light source or combination of light sources. Conventional light sources such as light emitting diodes (LEDs), cold cathode fluorescent lamps (CCFLs), and even incandescent bulbs may be used. In some embodiments, although light source 670 is depicted as a single object in FIG. 6, combinations of LEDs may be used to provide a sufficiently white input light, but, depending on the application, any suitable spectra or combination of spectra may be utilized. In some embodiments, the LEDs may use phosphors or other downconverting elements. Light source 670 may include suitable injection or collimation optics to aid in coupling light into lightguide 650 or to help shape the light input for the lightguide. Light source 670 may be disposed on either side of lightguide 650: for example, it may be disposed such that light from light source 670 exiting the lightguide is incident first on the flat first faces, or, alternatively, light from light source 670 exiting the lightguide is incident first on the curved second faces. The rest of the components of backlight 600 can be adjusted accordingly.
[0059]Depending on the application, certain characteristics of the overall design of backlight 600 may have a significant impact on its performance. In particular, the design of the bottom structured surface 620 of optical film 602 and the output distribution of lightguide 650. The design of lightguide 650 may take into account that optical film 602 may have certain input angles that provide a more desirable output than certain other input angles; in other words, the lightguide and backlight overall may be designed to provide optical film 602 with these input angles. The opposite is also possible: optical film 602 may be designed to have the output angle of the lightguide be an input angle that provides a desirable output.
[0060]In some embodiments, some level of diffusion or haze is desirable for the hiding of visual defects from manufacturing, assembly, or through use and environmental exposure or for visual interference such as moiré patterns. Optical film 602 may include a surface diffusing structure on the bottom structured surface or on the top structured surface. Such a surface diffusing structure may be on all or only some of the structured surfaces; for example, a surface diffusing structure may be on only one side of the structures. In some embodiments, the surface diffusing structure may be between the structured surface and the underlying substrate. Alternatively or additionally, any of the structures of the structured surfaces, their substrates, or any intermediate layers may have a bulk diffusing or scattering element. In some embodiments, optical film 602 may include an embedded matte layer; i.e., a diffusing layer between the structured surface and the underlying substrate having an index of refraction different than at least one of the structured surface layer and its underlying substrate.
[0061]A quantity for characterizing either the surface diffusing structure is the slope distributions of the surface. Slope distributions provide a particularly useful characterization of the surface diffusing structure in embodiments where it is desired to have relatively shallow slopes (for example, most slopes less than 40 degrees). In some embodiments, no more than about 20 percent, or no more than about 10 percent, or no more than about 7 percent, or no more than about 5 percent, or no more than about 3 percent of the surface diffusing structure has a slope magnitude that is greater than about 20 degrees, greater than about 15 degrees, greater than about 10 degrees, or greater than about 7 degrees, or greater than about 5 degrees, or greater than about 3.5 degrees. In some embodiments, the surface diffusing structure may have steeper slopes. For example, in some embodiments, no more than about 20 percent, no more than about 10 percent, no more than about 7 percent of the surface diffusing structure has a slope magnitude that is greater than about 20 degrees, or greater than about 30 degrees, or greater than about 35 degrees or greater than about 40 degrees. In some embodiments, a substantial fraction of surface diffusing structure has a slope magnitude greater than 1 degree and a substantial fraction of the second major surface has a slope magnitude less than 10 degrees or less than 15 degrees. In some embodiments, at least about 50 percent, or at least about 70 percent, or at least about 80 percent, or at least about 85 percent, or at least about 90 percent of the surface diffusing structure has a slope magnitude that is greater than 1 degree. In some embodiments, no more than about 85 percent, or no more than about 80 percent, of the surface diffusing structure has a slope magnitude that is greater than about 15 degrees, or that is greater than about 10 degrees.
[0062]In some embodiments, the slope distributions may be measured separately along two orthogonal directions. These slopes may have very small magnitudes along one direction, and larger magnitudes along a second, orthogonal direction. In other words, the slope distributions may be asymmetric. In some embodiments, the slopes along one direction may have magnitude distributions as described above (except while there applied there to the entire surface, here along a single direction). In some embodiments, there may be a very narrow distribution of slopes around zero or some other constant, or no slope (e.g., a flat or constant slope) along one direction. In some embodiments, at least 50 percent, at least 70 percent, at least 80 percent, at least 85 percent, or at least 90 percent of the slope magnitudes along one direction are less than 0.5 degrees, or less than 0.1 degrees. In some embodiments, at least 50 percent, at least 70 percent, at least 80 percent, at least 85 percent, or at least 90 percent of the slope magnitudes along one direction are less than 0.5 degrees, or less than 0.1 degrees from a same non-zero slope. In some embodiments, the asymmetrically larger slope distribution direction may be orthogonal to the direction of the linearly extended direction of the top structures or the bottom structures (i.e., along the x- or y-axis) or the larger slope distribution direction may be parallel to the direction of the linearly extended direction of the top structures or the bottom structures.
[0063]The slopes of the structured surface can be characterized using atomic force microscopy (AFM) or confocal scanning laser microscopy (CSLM), for example, to determine a surface profile H(x,y) (i.e., a height, H, of the surface above a reference plane as a function of the orthogonal in-plane coordinates x and y). Slopes Sx and Sy along respective x- and y-directions can then be calculated from the following two expressions:
Sx=∂H(x,y)/∂x
Sy=∂H(x,y)/∂y.
The slope magnitude Sm can be calculated from the following expression:
Sm=√{square root over ([∂H/∂x]2+[∂H/∂y]2)}.
[0064]A cutting tool system used to cut a tool which can be microreplicated to produce a surface diffusing structure may employ a thread cut lathe turning process and includes a roll that can rotate around and/or move along a central axis by a driver, and a cutter for cutting the roll material. The cutter is mounted on a servo and can be moved into and/or along the roll along the x-direction by a driver. In general, the cutter is mounted normal to the roll and the central axis and is driven into the engraveable material of roll while the roll is rotating around the central axis. The cutter is then driven parallel to the central axis to produce a thread cut. The cutter can be simultaneously actuated at high frequencies and low displacements to produce features in the roll that when microreplicated result in surface diffusing structures. The cutter can be any type of cutter and can have any shape that may be desirable in an application. Suitable cutters are described in U.S. Pat. No. 8,657,472 (Aronson et al.) or U.S. Pat. No. 8,888,333 (Yapel et al.).
[0065]Optical film 602 may be configured such that at least some of the light emitted by light source 670 that eventually exits backlight 600 is recycled by top structured surface 610. By recycled, it is meant that the light is reflected or otherwise redirected back toward lightguide 650. Such light may be reflected by reflector 660 and directed back toward optical film 602. Because at least some of the light redirected by top structured surface 610 is not at a preferred viewing angle or may not otherwise be at a useable or desirable angle, the redirection may be referred to as recycling because the light is cycled again through the backlight. In some embodiments, at least 10% of the light emitted by light source 670 is recycled by top structured surface 610. In some embodiments, at least 20% of the light emitted by light source 670 is recycled by top structured surface 610.
[0066]FIG. 7 is a split front-side elevation cross-section of another optical film. Optical film 700 includes top structured surface 710 with microstructure 712 characterized by first top line 714 and second top line 716, bottom structured surface 720 with microstructures having first face 722 and second face 724, and characterized by first bottom line 726 and second bottom line 728. Optical film 700 may also include intermediate layer 730.
[0067]Optical film 700 of FIG. 7 is similar to optical film 200 of FIG. 2, or optical film 602 of FIG. 6, exc