Display systems, such as liquid crystal display (LCD) systems, are used in a variety of applications and commercially available devices such as, for example, computer monitors, personal digital assistants (PDAs), mobile phones, miniature music players, and thin LCD televisions. Many LCDs include a liquid crystal panel and an extended area light source, often referred to as a backlight, for illuminating the liquid crystal panel. Backlights typically include one or more lamps and a number of light management films such as, for example, light guides, mirror films, light redirecting films (including brightness enhancement films), retarder films, light polarizing films, and diffusing films. Diffusing films are typically included to hide optical defects and improve the brightness uniformity of the light emitted by the backlight. Diffusing films can also be used in applications other than display systems.
According to embodiments of the disclosure, a microstructured surface may include a plurality of irregularly arranged planar portions forming greater than about 10% of the microstructured surface. The microstructured surface may be configured such that, when the microstructured surface is placed on an emission surface of a lightguide extending along a first direction with a first luminous distribution of a cross-section of light exiting the lightguide from the emission surface in a first plane perpendicular to the emission surface and parallel to the first direction, the light emitted by the lightguide is transmitted by the microstructured surface at a second luminous distribution of a cross-section of the transmitted light in the first plane. The first luminous distribution includes a first peak making a first angle greater than about 60 degrees with a normal to the microstructured surface. The second luminous distribution includes a second peak making a second angle in a range from about 5 degrees to about 35 degrees with the normal to the microstructured surface.
In another embodiment, a microstructured surface includes a plurality of irregularly arranged facets and opposing first and second major sides. The microstructured surface may be configured such that, when normally incident collimated light is incident on the first major side, the microstructured surface has a first total transmission, and when normally incident collimated light is incident on the second major side, the microstructured surface has a second total transmission. The second total transmission is greater than the first total transmission. The second total transmission has a luminous distribution having an on-axis value along the normal direction and a peak value. A ratio of the peak value to the on-axis value is greater than about 1.2.
In another embodiment, a microstructured surface includes a plurality of irregularly arranged facets. The microstructured surface may be configured to reduce a contrast of a resolution target. In one embodiment, the resolution target is an object. When the microstructured surface is spaced at a spacing of about 1 mm from the object having a spatial frequency of D line pairs per millimeter, a contrast of the object viewed through the microstructured surface is less than about 0.1 when D is 1.5 and less than about 0.05 when D is 2.5. In one embodiment, the resolution target is a knife-edge target having an edge. When the microstructured surface is spaced at a spacing of about 1 mm from the knife-edge target having, a modulation transfer function of the edge viewed through the microstructured surface is less than about 0.1 when D is 1.5 and less than about 0.5 at a spatial frequency of about 0.5 line pairs per millimeter. In one embodiment, the resolution target is an opaque circle of a diameter D on a transparent background. When the microstructured surface is spaced at a spacing of about 1 mm from the opaque circle, a contrast of the circle viewed through the microstructured surface is less than about 0.25 when D is about 0.8 millimeters and less than about 0.05 when D is about 0.4 millimeters. In one embodiment, the resolution target is an opaque circular band on a transparent background and defining an inner transparent circular region surrounded by an opaque ring region having an inner diameter D and an outer diameter D1 of about 0.2 millimeters. When the microstructured surface is spaced at a spacing of about 1 mm from the opaque circular band, and when the opaque circular band is viewed through the microstructured surface, the circular region has an average intensity of I1, the ring region has an average intensity of I2, and a contrast of the circular band defined as (I1−I2)/(I1+I2) is less than zero for D in a range from about 0.15 millimeters to about 0.8 millimeters.
In another embodiment, an edge-lit optical system includes a light source, a lightguide, a microstructured surface, and a reflective polarizer. The lightguide includes a side surface and an emission surface. Light emitted by the light source entering the lightguide at the side surface and exiting the lightguide from the emission surface has a first luminous peak at a first angle greater than about 60 degrees with a normal to the emission surface. The microstructured surface is disposed on the emission surface and includes a plurality of irregularly arranged facets. Each facet includes a central portion defining a slope relative to a plane of the microstructured surface. Less than about 20% of the central portions of the facets have slopes less than about 40 degrees. The reflective polarizer is disposed between the microstructured surface and the emission surface. The reflective polarizer is configured to substantially reflect light having a first polarization state and substantially transmit light having a second polarization state orthogonal to the first polarization state. At least a portion of the light emitted from the light source exits the optical system with a second luminous peak making a second angle less than about 50 degrees with the normal to the emission surface.
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.
Like symbols in the drawings indicate like elements. Dotted lines indicate optional or functional components, while dashed lines indicate components out of view.
Various embodiments of the invention have been described. These and other embodiments are within the scope of the following claims.
Microstructured films may include microstructures with angled sides to collimate light by refracting light at particular incidence angles and reflecting light at other incidence angles back into the film to undergo further processing. To promote consistent brightness across the surface of the microstructured film, the microstructures may be patterned with surfaces oriented at a variety of angles. In some instances, the microstructures may be elongated prismatic microstructures that have flat sides angled in opposing directions. For example, two films of elongated prismatic microstructures may be stacked at perpendicular angles to collimate light along a single axis each. The surface of films having these microstructures may be covered by angled sides. However, the patterned structure of these films may not spatially distribute light evenly across the entire surface due to a limited azimuthal distribution of side angles. In other instances, microstructures may have circular or oval base profiles that have radial surfaces that distribute light in all directions. For example, microstructures may be spherical lenses or cones. However, the circular profiles of these circular base microstructures may not substantially cover the surface of films using these microstructures, leaving flat or unstructured areas in between the circular base microstructures. Further, microstructured films with a regular pattern of microstructures may be subject to negative effects, such as a moiré effect.
The present disclosure includes an optical film having a microstructured surface for collimating light. The microstructured surface includes an irregular distribution of a plurality of prismatic structures that include a plurality of facets angled from a reference plane of the microstructured surface. While the prismatic structures may be individually irregular or random, the facets of the prismatic structures may be sized, angled, and distributed such that the surface azimuthal distribution of facets may be substantially uniform along the reference plane, while the surface polar distribution of facets may fall substantially within a polar range that correlates with a peak transmission of light normally incident to the reference plane. This distribution of facets may result in optical distribution properties of the microstructured surface that approximate conical optical distribution properties, such as the optical distribution properties of an ensemble of conical prismatic structures having an equivalent distribution of base angles, while covering substantially the entire major surface with prismatic structures. The use of interconnected facet surfaces may enable substantially the entire surface of the optical film to be covered by the microstructured surface. The irregular distribution of the prismatic structures may reduce moiré effects that appear in patterned or regular films.
Microstructured surface 111 may be structured to produce substantially collimated light from uncollimated light produced by light source 130 and processed through optical article 100. Factors affecting collimation of light at microstructured surface 111 may include, for example, a refractive index of optical film 110, a refractive index of media contacting microstructured surface 111, and an angle of incident light on microstructured surface 111. Factors affecting the angle of incident light on microstructured surface 111 may include, for example, a refractive index of substrate 120, a refractive index of media between bottom major surface 121 of substrate 120 and light source 130, and an angle of incident light emitted from light source 130.
In some examples, optical article 100 may polarize and collimate light from light source 130. As may be described in further detail below, optical film 110 may be a collimating film and substrate 120 may be a reflective polarizer. By combining a collimating optical film described herein with a reflective polarizer, an optical article may operate to increase collimation and brightness in a single backlight film.
Optical film 210 may be attached to a substrate 220 at a flat major surface 212. In this embodiment, optical article 200 includes two layers: substrate 220 and optical film 210. However, optical film 210 may have one or more layers. For example, in some cases, optical article 200 can have only a single layer of optical film 210 that includes microstructured surface 211 and bottom major surface 212. In some cases, optical article 200 can have many layers. For example, substrate 220 may be composed of multiple distinct layers. When optical article 200 includes multiple layers, the constituent layers may be coextensive with each other, and each pair of adjacent constituent layers may comprise tangible optical materials and have major surfaces that are completely coincident with each other, or that physically contact each other at least over 80%, or at least 90%, of their respective surface areas.
Substrate 220 may have a composition suitable for use in an optical product designed to control the flow of light. Factors and properties for use as a substrate material may include sufficient optical clarity and structural strength so that, for example, substrate 220 may be assembled into or used within a particular optical product, and may have sufficient resistance to temperature and aging such that performance of the optical product is not compromised over time. The particular chemical composition and thickness of substrate 220 for any optical product may depend on the requirements of the particular optical product that is being constructed, e.g., balancing the needs for strength, clarity, temperature resistance, surface energy, adherence to the microstructured surface, ability to form a microstructured surface, among others. Substrate 220 may be uniaxially or biaxially oriented.
Useful substrate materials for substrate 220 may include, but are not limited to, styrene-acrylonitrile, cellulose acetate butyrate, cellulose acetate propionate, cellulose triacetate, polyether sulfone, polymethyl methacrylate, polyurethane, polyester, polycarbonate, polyvinyl chloride, polystyrene, polyethylene naphthalate, copolymers or blends based on naphthalene dicarboxylic acids, polycyclo-olefins, polyimides, and glass. Optionally, the substrate material can contain mixtures or combinations of these materials. In an embodiment, substrate 220 may be multi-layered or may contain a dispersed phase suspended or dispersed in a continuous phase. For some optical products, such as brightness enhancement films, examples of desirable substrate materials may include, but are not limited to, polyethylene terephthalate (PET) and polycarbonate.
Some substrate materials can be optically active and act as polarizing materials. Polarization of light through a film may be accomplished, for example, by the inclusion of dichroic polarizers in a film material that selectively absorbs passing light, or by the inclusion of reflective polarizers in a film material that selectively reflects passing light. Light polarization can also be achieved by including inorganic materials such as aligned mica chips or by a discontinuous phase dispersed within a continuous film, such as droplets of light modulating liquid crystals dispersed within a continuous film. As an alternative, a film can be prepared from microtine layers of different materials. The polarizing materials within the film may be aligned into a polarizing orientation, for example, by employing methods such as stretching the film, applying electric or magnetic fields, and coating techniques.
Examples of polarizing films include those described in U.S. Pat. Nos. 5,825,543 and 5,783,120, each of which are incorporated herein by reference. The use of these polarizer films in combination with a brightness enhancement film has been described in U.S. Pat. No. 6,111,696, incorporated by reference herein. A second example of a polarizing film that can be used as a substrate are those films described in U.S. Pat. No. 5,882,774, also incorporated herein by reference. Films available commercially are the multilayer films sold under the trade designation DBEF (Dual Brightness Enhancement Film) from 3M. The use of such multilayer polarizing optical film in a brightness enhancement film has been described in U.S. Pat. No. 5,828,488, incorporated herein by reference. This list of substrate materials is not exclusive, and as will be appreciated by those of skill in the art, other polarizing and non-polarizing films can also be useful as the base for the optical products of the invention. These substrate materials can be combined with any number of other films including, for example, polarizing films to form multilayer structures. A short list of additional substrate materials can include those films described in U.S. Pat. Nos. 5,612,820 and 5,486,949, among others. The thickness of a particular base can also depend on the above-described requirements of the optical product.
In some examples, optical article 200 may be a free floating or backlight film, and substrate 220 may be a reflective polarizer. Optical film 210 may be attached to substrate 220 at bottom major surface 212, with microstructured surface 211 facing a display component, such as a liquid crystal display. With respect to a path of light travelling through a system using optical article 200, optical film 210 may be located “above” substrate 220 in a film stack of the system. Optical article 200 having a reflective polarizer and collimating optical film may offer both collimating and brightness increasing properties in the same film.
Optical film 210 may directly contact substrate 220 at bottom major surface 212 or be optically aligned to substrate 220, and can be of a size, shape, and thickness that allows microstructured surface 211 to direct or concentrate the flow of light. Optical film 210 may be integrally formed with substrate 220 or can be formed from a material and adhered or laminated to substrate 220.
Optical film 210 may have any suitable index of refraction. Factors for selection of an index of refraction may include, but are not limited to, the direction of incoming light into optical film 210, surface properties of microstructured surface 211, and desired direction of outgoing light from microstructured surface 211. For example, in some cases, optical film 210 may have an index of refraction in a range from about 1.4 to about 1.8, or from about 1.5 to about 1.8, or from about 1.5 to about 1.7. In some cases, optical film 210 may have an index of refraction that is not less than about 1.5, or not less than about 1.55, or not less than about 1.6, or not less than about 1.65, or not less than about 1.7.
Optical film 210 may have a composition suitable for use in an optical product designed to control the flow of light. Materials useful for optical film 210 include, but are not limited to: poly(carbonate) (PC); syndiotactic and isotactic poly(styrene) (PS); C1-C8 alkyl styrenes; alkyl, aromatic, and aliphatic ring-containing (meth)acrylates, including poly(methyl methacrylate) (PMMA) and PMMA copolymers; ethoxylated and propoxylated (meth)acrylates; multifunctional (meth)acrylates; acrylated epoxies; epoxies; and other ethylenically unsaturated materials; cyclic olefins and cyclic olefinic copolymers; acrylonitrile butadiene styrene (ABS); styrene acrylonitrile copolymers (SAN); epoxies; poly(vinylcyclohexane); PMMA/poly(vinyl fluoride) blends; poly(phenylene oxide) alloys; styrenic block copolymers; polyimide; polysulfone; poly(vinyl chloride); poly(dimethyl siloxane) (PDMS); polyurethanes; unsaturated polyesters; poly(ethylene), including low birefringence polyethylene; poly(propylene) (PP); poly(alkane terephthalates), such as poly(ethylene terephthalate) (PET); poly(alkane napthalates), such as poly(ethylene naphthalate)(PEN); polyamide; ionomers; vinyl acetate/polyethylene copolymers; cellulose acetate; cellulose acetate butyrate; fluoropolymers; poly(styrene)-poly(ethylene) copolymers; PET and PEN copolymers, including polyolefinic PET and PEN; and poly(carbonate)/aliphatic PET blends.
Optical film 210 may include microstructured surface 211. Microstructured surface 211 may represent a structured surface for transmission of substantially collimated light from optical article 200. Microstructured surface 211 may be configured to refract light that contacts microstructured surface 211 at particular range(s) of incidence angles and reflect light outside these range(s). These range(s) may be dependent on, for example, the refractive indices of optical film 210 and any material contacting microstructured surface 211, such as air.
Microstructured surface 211 may include a plurality of prismatic structures 230. Prismatic structures 230 may represent configurations of microstructured surface 211 that characterize the desired function of optical film 210 having prismatic structures 230, such as collimating light. In general, prismatic structures 230 are capable of redirecting light by, for example, refracting a portion of incident light and recycling a different portion of the incident light. Prismatic structures 230 may be designed to redirect light that is incident on facets 231 of prismatic structures 230, along a desired direction, such as along the positive z-direction. In some examples, prismatic structures 230 may redirect light in a direction substantially parallel to z-axis 243 and normal to a reference plane formed by x-axis and y-axis. Prismatic structures 230 may cover substantially all microstructured surface 211 of optical film 210, such as greater than 90% of a surface area of microstructured surface 211.
Prismatic structures 230 of microstructured surface 211 may be substantially irregularly or randomly arranged across microstructured surface 211. A substantially irregular or random arrangement may include a spatial distribution of prismatic structures 230 across microstructured surface 211 that is locally unpatterned or irregularly patterned, but may exhibit particular properties, ranges of properties, or probabilities of properties in the aggregate. For example, as the plurality of prismatic structures 230 increases, an average of properties of the plurality of prismatic structures 230 may exhibit less deviation; however, a first spatial area of prismatic structures 230 and a second spatial area of prismatic structures 230 may not have a similar distribution of properties.
Discontinuities, e.g., projections, in microstructured surface 211 of optical article 200 may deviate in profile from the average center line drawn through prismatic structures 230 such that the sum of the areas embraced by the surface profile above the center line is equal to the sum of the areas below the line, said line being essentially parallel to the nominal surface (bearing the microstructure) of the article. The heights of prismatic structures 230 may be about 0.2 to 100 micrometers, as measured by an optical or electron microscope, through a representative characteristic length of the surface, for example, 1-30 cm. Said average center line can be planar, concave, convex, aspheric or combinations thereof. Prismatic structures 230 may have a pitch defined as the furthest distance between two intersecting facets. The pitch of prismatic structures 230 may be not more than 250 micrometers and may vary from 0 (intersecting) to 250 micrometers. The pitch may be related to factors such as base angle 233 of facets 231 on prismatic structures 230 and height of prismatic structures 230. In some examples, height and pitch may be selected to reduce sparkle. Sparkle may refer to an optical artifact that appears as a grainy texture (texture mura) that consists of small regions of bright and dark luminance in what appears to be a random pattern. The position of the bright and dark regions can vary as the viewing angle changes, making the texture especially evident and objectionable to a viewer. To minimize sparkle, prismatic structures 230 may have a height less than about 100 micrometers, and preferably less than 20-30 micrometers, may have very little periodicity, may not form micro-images of the proximate structure, or any combination of these attributes.
The plurality of prismatic structures 230 may include a plurality of facets 231. Each prismatic structure 230 may include a plurality of facets 231 meeting at a peak 237. Each facet 231 may represent a surface of prismatic structure 230 and microstructured surface 211 that defines at least one slope relative to a reference plane formed by x-axis 241 and y-axis 242, each facet 231 and corresponding slope forming a non-zero base angle 233.
The at least one slope of the plurality of facets 231 may define a slope magnitude distribution and a slope magnitude cumulative distribution. The slope magnitude distribution may represent a normalized frequency of slope angles, such as base angle 233. The slope magnitude cumulative distribution may represent a cumulative normalized frequency of slope angles, such as base angle 233, for each degree over microstructured surface 211. The cumulative slope magnitude distribution may include a rate of change that represents a change in cumulative normalized frequency for a slope angle. See, for example,
Microstructured surface 211 may define a plurality of slopes relative to the reference plane. In some examples, about 10% of the microstructured surface has slopes less than about 10 degrees and about 15% of the microstructured surface has slopes greater than about 60 degrees. See, for example,
Each facet 231 may have a surface area and a facet normal direction that represents an average surface direction of facet 231. A surface area of each facet 231 may represent an area through which light passing through optical film 210 may contact the facet and refract at lower incidence angles or reflect at higher incidence angles. In examples where facet 231 is curved, the facet normal direction may be a normal direction of an average degree of curvature, a tangent of curvature, a plane across peaks of the facet 231, or other functional surface that represents an averaged refractive surface of the facet 231.
Facets 231 may cover substantially all of microstructured surface 211. In some examples, facets 231 may cover greater than 90% of microstructured surface 211. Surface coverage of microstructured surface 211 may be represented as percent microstructured surface per solid angle in units of square degrees for particular gradient magnitude ranges or limits. In some examples, less than 0.010% of the microstructured surface 211 per solid angle in units of square degrees has gradient magnitudes of about 10 degrees, while less than about 0.008% of the microstructured surface 211 per solid angle in units of square degrees have gradient magnitudes of about 30 degrees. See, for example,
A sub-plurality of the plurality of prismatic structures 230 may include facets 231 that comprise a substantially planar central portion surrounded by a substantially curved peripheral portion. In some examples, less than about 20% of the planar central portions of the facets have slopes less than about 40 degrees, less than about 10% of the microstructured surface 211 having slopes less than about 20 degrees.
Facets 231 may be substantially flat. Substantial flatness may be indicated or determined by, for example, a radius of curvature or average curvature of the flat facet 231, such as a radius of curvature greater than ten times an average height of the prismatic structures 230. In some examples, a particular portion of facets 231 of microstructured surface 211 may be substantially flat, such as greater than 30%.
The plurality of prismatic structures 230 may include a plurality of peaks 237 formed at an intersection of two facets 231. Two facets 231 forming a peak 237 may have an associated apex angle 232. Each peak 237 may have an associated radius of curvature that represents the angular sharpness of the peak. For example, peak 237 may have a radius of curvature less than one tenth of an average height of prismatic structures 230. Peak 237 may be substantially defined or sharp, such that a surface area of peak 237 contributes insignificantly to microstructured surface 211. In some examples, surface area of the plurality of peaks 237 is less than 1% of total surface area of microstructured surface 211. A microstructured surface 211 having defined peaks 237 may increase the surface area of facets 231, increase optical gain for a desired transmission range from optical film 210, and reduce wet-out caused near on-axis transmission angles.
Microstructured surface 211 may have a surface normal distribution of facets 231. The surface normal distribution of facets may represent the normal distribution of facets 231, such as a probability or concentration of a facet 231 having a particular polar angle 235 or azimuthal angle 236. The surface normal distribution of facets 231 includes a surface polar distribution of facets 231 and a surface azimuthal distribution of facets 231.
The surface polar distribution represents a normal distribution of facets 231 at particular polar angles 236. In some examples, the surface polar distribution may be represented as a percentage of facets within a range of polar angles. For example, substantially all facets 231, such as greater than 90%, may have a polar angle within a particular range of polar angles. A particular range of polar angles may include a range of polar angles that produce substantially collimated light, such as within five degrees of the z-axis 243. In some examples, substantially all of facets 231 may have a polar angle 236 of approximately 45 degrees, such as 90% of facets 231 having a polar angle 236 between 40 degrees and 50 degrees. In some examples, the surface polar distribution may be represented as a probability of flat facet 231 having particular polar angles 236.
The surface polar distribution of the plurality of facets 231 may include a peak polar distribution associated with a polar angle or range of polar angles that represent a peak distribution of the plurality of facets 231. The peak polar distribution may be off-axis; that is, the peak polar distribution may not be substantially normal to the reference plane of microstructured surface 211. In some examples, the surface polar distribution has an off-axis peak polar distribution that is at least twice as high as an on-axis polar distribution.
Prismatic structures 230 may be distributed across optical film 210 and their facets oriented across microstructured surface 211 so that the surface polar distribution of facets increases the optical gain of optical film 210 for a particular range of polar angles. In some examples, the surface polar distribution may be configured to create a polar transmission distribution, where the polar transmission distribution represents the transmission of axial collimated light through microstructured surface 211 into an intensity distribution over polar angles θ to □/2. The polar transmission distribution may be associated with the collimated light transmission properties of aggregate conical microstructures. For example, conical microstructures may distribute light with a peak luminance at particular polar angles for particular refractive indices, and the peak luminance may be a particular ratio higher than an on-axis polar transmission, such as twice as high. The surface polar distribution of microstructured surface 211 may include substantially all facets in a polar range that produces collimated light from light at particular incidence angles associated with peak luminance. In some examples, the polar range is selected for peak luminance for light at incidence angles between 32 and 38 degrees. Facets 231 may be oriented throughout a range of polar angles 236, such as 30 to 60 degrees, such that the light transmitted from microstructured surface 211 is substantially collimated.
The surface azimuthal distribution represents a distribution of facets 231 at particular azimuthal angles. For example, at high sample sizes, substantially a 360th of all flat facets, such as between 0.1% and 0.5%, or 0.25% and 0.3%, may have an azimuthal angle between a particular angular degree. Prismatic structures 230 may be distributed across optical film 210 and their flat facets oriented across microstructured surface 211 so that the surface azimuthal distribution of facets 231 may create a uniform azimuthal transmission distribution, where the azimuthal transmission distribution represents a transmission of light through microstructured surface 211 at azimuthal angles. The azimuthal transmission of light may be associated with the collimated light transmission properties of aggregate conical microstructures. For example, conical microstructures may distribute light evenly across a full azimuthal range. The surface azimuthal distribution of facets 231 may be uniform within a particular angular resolution across a full 360 degrees. In some examples, the angular resolution is selected based on manufacturing accuracy. The aggregate surface area or number of facets 231 may be substantially the same for each azimuthal angle 235 and the average of the azimuthal angles 235 may be rotationally symmetric. In some examples, the aggregate surface area or number of facets 231 may be evaluated as substantially the same at a particular sample size or resolution of facets 231, such as greater than 10,000 flat facets, as there may be local variation in the azimuthal angles 235.
While prismatic structures 230 may be irregularly distributed and oriented across optical film 210, the aggregate effect of flat facets 231 of prismatic structures 230 is microstructured surface 211 that has a surface area that is evenly distributed over a full range of azimuthal angles on the reference plane to evenly distribute light and a limited range of polar angles to substantially collimate light.
In step 310, a base may be provided to serve as a foundation upon which metal layers can be electroplated. The base can take one of numerous forms, e.g. a sheet, plate, or cylinder. For example, circular cylinders may be used to produce continuous roll goods. The base may be made of a metal, and exemplary metals include nickel, copper, and brass; however, other metals may also be used. The base may have an exposed surface (“base surface”) on which one or more electrodeposited layers may be formed in subsequent steps. The base surface may be smooth and flat, or substantially flat. The curved outer surface of a smooth polished cylinder may be considered to be substantially flat, particularly when considering a small local region in the vicinity of any given point on the surface of the cylinder.
In step 320, electroplating conditions may be selected for electroplating the base surface. The composition of the electroplating solution, such as the type of metal salt used in the solution, as well as other process parameters, such as current density, plating time, and substrate moving speed, may be selected so that the electroplated layer is not formed smooth and flat, but instead has a major surface that is structured, and characterized by irregular flat-faceted features, such as features that correspond to desired prismatic structures 230. Selection of a current density, selection of a plating time, and selection of a base exposure rate, such as substrate moving speed, may determine the size and density of the irregular features. Selection of a metal template, such as the type of metal salt used in the electroplating solution, may determine the geometry of the features. For example, the type of metal salt used in the electroplating process may determine the geometry of the deposited metal structures, and thus, may determine the shape of the prismatic structures, such as prismatic structures 230, on the microstructured surface, such as microstructured surface 211.
In step 330, a layer of a metal may be formed on the base surface of the substrate using an electroplating process. Before this step is initiated, the base surface of the substrate may be primed or otherwise treated to promote adhesion. The metal to be electroplated may be substantially the same as the metal of which the base surface is composed. For example, if the base surface comprises copper, the electroplated layer formed in step 330 may also be made of copper. To form a layer of the metal, the electroplating process may use an electroplating solution. The electroplating process may be carried out such that the surface of the electroplated layer has a microstructured surface having irregular faces that corresponds to the microstructured surface 211. Metal may accrete inhomogeneously on the microstructured surface of the roll, forming protuberances. The microstructured surface of the optical film replicates with peaks or valleys, etc., relative to the microstructured surface of the roll. The location and disposition of the deposited metal structures on the microstructured roll is random. The structured character and roughness of a representative first major surface can be seen in the SEM image of an optical film of
After step 330 is completed, the substrate with the electroplated layer(s) may be used as an original tool with which to form optical diffusing films. In some cases, the structured surface of the tool, which may include the structured surface of the electroplated layer(s) produced in step 330, may be passivated or otherwise protected with a second metal or other suitable material. For example, if the electroplated layer(s) are composed of copper, the structured surface can be electroplated with a thin coating of chromium. The thin coating of chromium or other suitable material is preferably thin enough to substantially preserve the topography of the structured surface.
Rather than using the original tool itself in the fabrication of optical diffusing films, one or more replica tools may be made by microreplicating the structured surface of the original tool, and the replica tool(s) may then be used to fabricate the optical films. A first replica made from the original tool will have a first replica structured surface which corresponds to, but is an inverted form of, the structured surface. For example, protrusions in the structured surface correspond to cavities in the first replica structured surface. A second replica may be made from the first replica. The second replica will have a second replica structured surface which corresponds to, and is a non-inverted form of, the structured surface of the original tool.
After the structured surface tool is made, for example, in step 330, optical films, such as optical film 210, having the same structured surface (whether inverted or non-inverted relative to the original tool) can be made in step 340 by microreplication from the original or replica tool. The optical film may be formed from the tool using any suitable process, including e.g. embossing a pre-formed film, or cast-and-curing a curable layer on a carrier film. For example, optical film 210 having microstructured surface 211 may be prepared by: (a) preparing a polymerizable composition; (b) depositing the polymerizable composition onto a master negative structured surface of the structured surface tool formed in step 330 in an amount sufficient to fill the cavities of the master; (c) filling the cavities by moving a bead of the polymerizable composition between a substrate, such as substrate 220, and the master; and (d) curing the polymerizable composition. In the embodiment above, optical film 210 and substrate 220 may be separate layers bonded together. Another method may include directly replicating the mold onto an extruded or cast substrate material, resulting in a substrate 220 and optical film 210 that is monolithic.
As described above, the microstructured surfaces described herein may be configured to collimate light, diffuse light, and increase gain in optical systems. Correspondingly, a microstructured surface having a plurality of irregularly arranged facets or planar portions as described herein may be characterized by an ability of the microstructured surface to collimate light, diffuse light, or increase gain. The aforementioned optical properties may be correlated to structural properties of the microstructured surfaces previously described, such as irregularity of the distribution of facets, definition of apex angle between facets, planarity of facets, and the like. While the optical properties of the microstructured surfaces may be advantageous for optical systems incorporating the microstructured surfaces, such optical properties may also indicate and characterize the presence and configuration of the structural properties.
In some examples, a microstructured surface having a plurality of planar portions may be characterized by an ability of the microstructured surface to collimate light from a lightguide.
Lightguide 20 may be configured to receive light from a light source 90 through a side surface 22 and emit light 30 from an emission surface 21 of lightguide 20. Emission surface 21 may extend along a first direction (x) of lightguide 20. Light 30 may exit lightguide 20 in a first plane 40 perpendicular to the emission surface and parallel to the first direction (x). Light 30 exiting lightguide 20 may have a luminous distribution 31 (“first luminous distribution 31”) of a cross-section of light 30. First luminous distribution 31 may be characterized by a peak 32 (“first peak 32”) at an angle θ1 (“first angle θ1”) from normal 41 to the first direction (x).
Optical film 50 may have a first major surface 52 configured to transmit light and a second major surface 54 configured to receive light, such as light 30 from lightguide 20. First major surface 52 may include a microstructured surface 10 configured with a plurality of irregularly arranged planar portions 11, as described in
When microstructured surface 10 is placed on or near emission surface 21, microstructured surface 10 may be characterized by second angle θ2 of second luminous distribution 33 with respect to first angle θ1 of first luminous distribution 31. When first angle θ1 of first luminous distribution 31 is greater than about 60 degrees, or greater than about 70 degrees, or greater than about 75 degrees, second angle θ2 of second luminous distribution 33 may be in a range from about 5 degrees to about 35 degrees, or in a range from about 5 degrees to about 30 degrees, or in a range from about 10 degrees to about 25 degrees, respectively.
The reduction in the peak angle of the luminous distribution of light from lightguide 20 to microstructured surface 10 may represent collimation of light along at least first plane 40. Collimation of light may be due to the refraction of light on the slopes turning the high angle light angles toward normal, which may indicate a substantially restricted distribution of facet slopes at particular angles, such as base angle 233 of
In some examples, a microstructured surface having a plurality of irregularly arranged facets may be characterized by a higher transmission of collimated light from the microstructured surface than from an opposing flat surface (delta transmission).
When forward collimated light 15 is incident on first major side 13 of microstructured surface 10, light transmitted from microstructured surface may have a first total transmission. When backward collimated light 16 is incident on second major side 14 of microstructured surface 10, light transmitted from microstructured surface 10 may have a second total transmission that is larger than the first total transmission.
An ability of microstructured surface 10 to receive collimated light at a transmission surface of microstructured surface 10 and transmit the light at a higher total transmission may indicate a greater ability to recycle light, and may correspondingly indicate the presence of facet slopes and an index of refraction of optical film 50 for restricting transmitted light to collimated light. A higher delta transmission may also indicate a higher gain or greater ability to hide defects.
In some examples, a microstructured surface having a plurality of irregularly arranged facets may be characterized by a luminous distribution that has a peak value higher than an on-axis value.
In some examples, a microstructured surface having a plurality of irregularly arranged facets may be configured to diffuse light. A light guide may emit light that is unevenly distributed or contains optical defects. The irregular arrangement of the facets on the microstructured surface may diffusely process light while maintaining substantial collimation of transmitted light.
The ability of the microstructured surface to diffuse light may be correlated with the ability of the microstructured surface to hide defects. In some examples, the microstructured surface may be characterized by a degree of reduced contrast of a resolution target. Light from the resolution target may be processed through the optical film, transmitted from the microstructured surface, and detected as an image. The reduction in contrast of the resolution target in the image may represent the ability of the microstructured film to diffuse light. See, for example,
Microstructured surfaces described herein may be used to collimate light in a variety of optical applications. One particularly useful application is in backlights of edge-lit optical systems, such as televisions and monitors. In some examples, a microstructured surface having a plurality of irregularly arranged facets may be used in an edge-lit optical system.
Microstructured surface 10 may be disposed on emission surface 21. Microstructured surface 10 may include a plurality of irregularly arranged facets 12. Each facet may include a central portion 52 defining a slope relative to a plane 40 of microstructured surface 10. In some examples, less than about 20% of central portions 52 may have slopes less than about 40 degrees.
Reflective polarizer 96 may be disposed between microstructured surface 10 and emission surface 21. Reflective polarizer 96 may be configured to substantially reflect light having a first polarization state and substantially transmit light having a second polarization state orthogonal to the first polarization state. At least a portion of the light emitted from light source 90 may exit optical system 95 as light 35 in a second luminous distribution 33 with a second luminous peak 34. Second luminous peak may make a second angle θ2. In some examples, second angle θ2 may be less than about 50 degrees with the normal of emission surface 21. In some examples, a diffuse reflector may be disposed on lightguide 20 opposite reflective polarizer 96, such that second angle θ2 is less than about 45 degrees with the normal of emission surface 21. In some examples, a specular reflector may be disposed on lightguide 20 opposite reflective polarizer 96, such that second angle θ2 is less than about 40 degrees with the normal to emission surface 21. See, for example,
In some examples, edge-lit optical system 95 may have reflective polarizer 96 directly coupled to a second major surface 54, opposite a first major surface 52, of an optical film 50. For example, optical film 50 and reflective polarizer 96 may be manufactured as a single article having advantageous light distribution properties as discussed herein. The article may have other layers, such as a PET substrate laminated to a major surface of reflective polarizer 96 opposite second major surface 54 of optical film 50 that may act as a diffuser sheet. The resulting article may have improved diffusion, clarity, collimation, and gain properties.
Light Transmission Characterization
Samples (Sample 1, Sample 2, and Sample 3) of optical films according to the current disclosure were fabricated according to techniques described herein, including
The optical films were tested with a collimated light transmission probe to determine the optical properties of the optical film, such polar transmission distribution and azimuthal transmission distribution.
Surface Characterization
Four samples (Sample 6A/B, Sample 7A/B, Sample 8, and Sample 9) of optical films according to the current disclosure were fabricated according to techniques described herein, including
The AFM images were analyzed for flatness and angular orientation. Code was written to add a facet analysis functionality to a slope analysis tool. The facet analysis functionality was configured to identify a core region of a facet for analysis of the flatness and orientation of the facets of a sample. Prefilter height maps were selected to minimize noise (e.g. media 3 for AFM and Fourier low pass for confocal microscopy) and shift the height map so that the zero height is a mean height.
A gcurvature and tcurvature were calculated at each pixel. The gcurvature at a pixel is the surface curvature calculated in the gradient direction using the heights of the following three points: Z(x, y), Z(x−dx, y−dy), and Z(x+dx, y+dy), where (dx,dy) is parallel to the gradient vector and the magnitude of (dx, dy)=Sk/Skdivosor, where Sk is the core roughness depth and Skdivisor is a unitless parameter set by the user. The magnitude of (dx,dy) may be rounded to the nearest pixel and set to be at a minimum, such as 3 pixels. The tcurvature is the same as the gcurvature except that the direction transverse to the gradient is used in the calculation of the curvature, instead of parallel.
Thresholds for each pixel were used to obtain a binary map of the flat facets. The thresholds include: (1) max (gcurvature, tcurvature)<rel_curvecutoff/R, where R=min (xcrossingperiod, ycrossingperiod)/2 and xcrossingperiod and ycrossingperiod are the mean distances between zero crossings in the x,y direction, respectively; and (2) gslope<facetslope_cutoff.
Image processing steps may be applied to clean up the binary image. The image processing steps may include: erode, remove facets less than N pixels, dilate twice, erode, where N=ceil(r*r*minfacetcoeff) pixels, r is the magnitude of (dx,dy) in pixels, and ceil is a function that rounds up to the nearest integer. The images were then generated and the statistics and distributions of the facet regions calculated.
A fourth sample optical film (Sample 4) as disclosed herein was prepared according to
An optical conical structure was modeled to determine the optical properties of the optical conical structure. The optical conical structure simulated, for example, refraction and Fresnel reflection at surfaces of the optical conical structure.
The optical properties of a sample (Sample 5) of the optical film were compared with the optical properties of the conical structure model.
Defect Hiding
A sample of an optical film according to the present disclosure was fabricated according to techniques discussed herein. Comparative examples of: (1) an optical film having round-peaked irregular prisms and (2) an optical film having a packed array of partial spheres were also provided. Photographs of the samples were taken and used for image analysis, as will be described below.
The optical films were tested with a camera and a Lambertian light source to determine the defect hiding properties of the optical film and, correspondingly, diffusing properties of the optical film.
Contrast of the photographs of
Modulation transfer functions of the photographs of
Device Gain and Turning Characteristics
A test system similar to
The following are embodiments of the present disclosure
Embodiment 1 is a microstructured surface comprising: a plurality of irregularly arranged planar portions forming greater than about 10% of the microstructured surface, wherein when the microstructured surface is placed on an emission surface of a lightguide extending along a first direction with a first luminous distribution of a cross-section of light exiting the lightguide from the emission surface in a first plane perpendicular to the emission surface and parallel to the first direction, the light emitted by the lightguide is transmitted by the microstructured surface at a second luminous distribution of a cross-section of the transmitted light in the first plane, wherein the first luminous distribution comprises a first peak making a first angle greater than about 60 degrees with a normal to the microstructured surface, and wherein the second luminous distribution comprises a second peak making a second angle in a range from about 5 degrees to about 35 degrees with the normal to the microstructured surface.
Embodiment 2 is the microstructured surface of embodiment 1, wherein the first angle is greater than about 70 degrees with the normal to the microstructured surface.
Embodiment 3 is the microstructured surface of embodiment 1, wherein the first angle is greater than about 75 degrees with the normal to the microstructured surface.
Embodiment 4 is the microstructured surface of embodiment 1, wherein the second angle is in a range from about 5 degrees to about 30 degrees with the normal to the microstructured surface.
Embodiment 5 is the microstructured surface of embodiment 1, wherein the second angle is in a range from about 10 degrees to about 30 degrees with the normal to the microstructured surface.
Embodiment 6 is an optical film comprising opposing first and second major surfaces, the first major surface comprising the microstructured surface of claim 1.
Embodiment 7 is a microstructured surface comprising: a plurality of irregularly arranged facets; opposing first and second major sides; wherein when normally incident collimated light is incident on the first major side, the microstructured surface has a first total transmission, wherein when normally incident collimated light is incident on the second major side, the microstructured surface has a second total transmission and a luminous distribution having an on-axis value along the normal direction and a peak value, wherein the second total transmission is greater than the first total transmission, and wherein a ratio of the peak value to the on-axis value is greater than about 1.2.
Embodiment 8 is the microstructured surface of embodiment 7, wherein the ratio of the peak value to the on-axis value is greater than about 1.5.
Embodiment 9 is the microstructured surface of embodiment 7, wherein the ratio of the peak value to the on-axis value is greater than about 2.
Embodiment 10 is the microstructured surface of embodiment 7, wherein the ratio of the peak value to the on-axis value is greater than about 15.
Embodiment 11 is the microstructured surface of embodiment 7, wherein a difference between the first total transmission and the second total transmission is greater than about 10%.
Embodiment 12 is the microstructured surface of embodiment 7, wherein a difference between the first total transmission and the second total transmission is greater than about 20%.
Embodiment 13 is the microstructured surface of embodiment 7, wherein a difference between the first total transmission and the second total transmission is greater than about 30%.
Embodiment 14 is an optical film comprising opposing first and second major surfaces, the first major surface comprising the microstructured surface of embodiment 7.
Embodiment 15 is a microstructured surface comprising: a plurality of irregularly arranged facets, wherein when the microstructured surface is spaced at a spacing of about 1 mm from an object having a spatial frequency of D line pairs per millimeter, a contrast of the object viewed through the microstructured surface is less than about 0.1 when D is 1.5 and less than about 0.05 when D is 2.5.
Embodiment 16 is the microstructured surface of embodiment 15, wherein a contrast of the object viewed absent the microstructured surface is greater than about 0.7 when D is 1.5 and when D is 2.5.
Embodiment 17 is the microstructured surface of embodiment 15, wherein a contrast of the object viewed absent the microstructured surface is greater than about 0.8 when D is 1.5 and when D is 2.5.
Embodiment 18 is the microstructured surface of embodiment 15, wherein when the microstructured surface is spaced at a spacing of about 1 mm from the object, the object is illuminated by a Lambertian light source.
Embodiment 19 is the microstructured surface of embodiment 18, wherein the object is disposed between the microstructured surface and the Lambertian light source.
Embodiment 20 is the microstructured surface of embodiment 15, wherein the spacing of about 1 mm between the microstructured surface and the object is substantially filled with an optically transparent plate-like substrate.
Embodiment 21 is the microstructured surface of embodiment 20, wherein the optically transparent plate-like substrate is made of optically transparent glass.
Embodiment 22 is a microstructured surface comprising: a plurality of irregularly arranged facets, wherein when the microstructured surface is spaced at a spacing of about 1 mm from a knife-edge target having an edge, a modulation transfer function of the edge viewed through the microstructured surface is less than about 0.1 when D is 1.5 and less than about 0.5 at a spatial frequency of about 0.5 line pairs per millimeter.
Embodiment 23 is the microstructured surface of embodiment 22, wherein the modulation transfer function of the edge viewed through the microstructured surface is less than about 0.1 at a spatial frequency of about 1 line pair per millimeter.
Embodiment 24 is the microstructured surface of embodiment 22, wherein the modulation transfer function of the edge viewed through the microstructured surface is less than about 0.8 at a spatial frequency of about 0.5 line pairs per millimeter.
Embodiment 25 is a microstructured surface comprising: a plurality of irregularly arranged facets, wherein when the microstructured surface is spaced at a spacing of about 1 mm from a target that includes an opaque circle of a diameter D on a transparent background, a contrast of the circle viewed through the microstructured surface is less than about 0.25 when D is about 0.8 millimeters and less than about 0.05 when D is about 0.4 millimeters.
Embodiment 26 is the microstructured surface of embodiment 25, wherein the contrast of the circle viewed in the absence of the microstructured surface is greater than about 0.7 when D is about 0.8 millimeters and when D is about 0.4 millimeters.
Embodiment 27 is a microstructured surface comprising: a plurality of irregularly arranged facets, wherein when the microstructured surface is spaced at a spacing of about 1 mm from a target that includes an opaque circular band on a transparent background and defining an inner transparent circular region surrounded by an opaque ring region having an inner diameter D and an outer diameter D1 of about 0.2 millimeters, and when the opaque circular band is viewed through the microstructured surface, the circular region has an average intensity of I1, the ring region has an average intensity of I2, and a contrast of the circular band defined as (I1−I2)/(I1+I2) is less than zero for D in a range from about 0.15 millimeters to about 0.8 millimeters.
Embodiment 28 is the microstructured surface of embodiment 27, wherein the contrast of the circular band viewed in the absence of the microstructured surface is greater than zero for D in the range from about 0.15 millimeters to about 0.8 millimeters.
Embodiment 29 is the microstructured surface of embodiment 27, wherein a magnitude of the contrast of the circular band increases as D decreases from about 0.8 millimeters to at least about 0.4 millimeters.
Embodiment 30 is an edge-lit optical system, comprising: a light source; a lightguide having a side surface and an emission surface, wherein light emitted by the light source entering the lightguide at the side surface and exiting the lightguide from the emission surface with a first luminous peak making a first angle greater than about 60 degrees with a normal to the emission surface; a microstructured surface disposed on the emission surface and comprising a plurality of irregularly arranged facets, each facet comprising a central portion defining a slope relative to a plane of the microstructured surface, wherein less than about 20% of the central portions of the facets have slopes less than about 40 degrees; and a reflective polarizer disposed between the microstructured surface and the emission surface, the reflective polarizer configured to substantially reflect light having a first polarization state and substantially transmit light having a second polarization state orthogonal to the first polarization state, such that at least a portion of the light emitted from the light source exits the optical system with a second luminous peak making a second angle less than about 50 degrees with the normal to the emission surface.
Embodiment 31 is the optical system of embodiment 30, further comprising a diffuse reflector disposed on the lightguide opposite the reflective polarizer, wherein the second angle is less than about 45 degrees with the normal to the emission surface.
Embodiment 32 is the optical system of embodiment 30, further comprising a specular reflector disposed on the lightguide opposite the reflective polarizer, wherein the second angle is less than about 40 degrees with the normal to the emission surface.
Various embodiments of the invention have been described. These and other embodiments are within the scope of the following claims.
Filing Document | Filing Date | Country | Kind |
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PCT/IB2018/055084 | 7/10/2018 | WO | 00 |
Number | Date | Country | |
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62531395 | Jul 2017 | US |