Diffuse multilayer optical assembly

An optical assembly includes a light diffusing layer attached to a reflective polarizing layer. An intermediate region between the light diffusing layer and the reflective polarizing layer includes an intermediate structure that defines voids between the light diffusing layer and the reflective polarizing layer.

BACKGROUND

The present invention relates to optical films and optical displays incorporating the optical films. In particular, the present invention relates to a multilayer optical assembly comprising a reflective polarizing layer attached to a light diffusing layer with voids defined in an intermediate region therebetween.

Optical displays, such as liquid crystal displays (LCDs), are becoming increasingly commonplace, finding use for example in mobile telephones, in hand-held computer devices such as personal digital assistants (PDAs) and electronic games, and in larger devices such as laptop computers, LCD monitors, and LCD television screens. The incorporation of light management films into optical display devices results in improved display performance. Different types of films, including prismatically structured films, reflective polarizers, and diffuser films are useful for improving display parameters such as output luminance, luminance uniformity, viewing angle, and overall system efficiency. Such improved operating characteristics make devices easier to use and may also increase battery life.

Light management films incorporated into optical displays are typically stacked, one by one, into the display frame between a light source and a light gating device. The stack of films can be optimized to obtain a particular desired optical performance. From a manufacturing perspective, however, several issues can arise from the handling and assembly of several discrete film pieces. These problems include the excess time required to remove protective liners from individual optical films, along with the increased chance of damaging a film when removing a liner. In addition, the insertion of multiple individual sheets into the display frame is time consuming and the stacking of individual films provides further opportunity for the films to be damaged. All of these problems can contribute to diminished overall throughput or to reduced yield, which leads to higher system cost.

SUMMARY

In a first aspect, the present invention is an optical assembly including a light diffusing layer attached to a reflective polarizing layer. An intermediate region between the light diffusing layer and the reflective polarizing layer includes an intermediate structure that defines voids between the light diffusing layer and the reflective polarizing layer.

In a second aspect, the present invention is an optical assembly including a light management film and a light diffusing layer having a non-uniform major surface. A bonding layer bonds the light management film to the light diffusing layer such that voids between adjacent topographical features on the non-uniform major surface define air gaps between the light management film and the light diffusing layer.

In a third aspect, the present invention is an optical display assembly including a light gating device, a light source, and an optical assembly positioned between the backlight assembly and the light gating device. The optical assembly including a light diffusing layer attached to a light management layer. An intermediate region between the light diffusing layer and the light management layer includes an intermediate structure that defines voids between the light diffusing layer and the light management layer.

The above summary is not intended to describe each disclosed embodiment or every implementation of the present invention. The figures and the detailed description which follow more particularly exemplify illustrative embodiments.

The above-identified drawing figures set forth several embodiments of the invention. Other embodiments are also contemplated, as noted in the discussion. In all cases, this disclosure presents the invention by way of representation and not limitation. It should be understood that numerous other modifications and embodiments can be devised by those skilled in the art which fall within the scope and spirit of the principals of this invention. The figures may not be drawn to scale. Like reference numbers have been used throughout the figures to denote like parts.

DETAILED DESCRIPTION

FIG. 1is a schematic cross-sectional view of an optical assembly10according to an embodiment of the present invention. Optical assembly10includes light diffusing layer12, bonding layer14, reflective polarizing layer16, and optional polymeric layer18. Reflective polarizing layer16is attached to light diffusing layer12via bonding layer14. Polymeric layer18is optionally attached to reflective polarizing layer16on the surface opposite bonding layer14. Assembly10is typically incorporated in a display system between a light source and a light gating device.

Light diffusing layer12is used to diffuse light received from light sources, which results in an increase in the uniformity of the illumination light incident on the light gating device. Consequently, this results in an image perceived by the viewer that is more uniformly bright. In the embodiment shown inFIG. 1, light diffusing layer12is a diffuser plate having a non-uniform or textured surface. In one embodiment, light diffusing layer12has a transmission value in the range of about 40-90%, a haze value of greater than about 90%, and a half angle of greater than about 25°. Transmission and haze levels are defined according to ASTM-D1003-00, “Standard Test Methods for Haze and Transmittance for Transparent Plastics.” Half angle is defined according to a test method that measures the luminance distribution as a collimated beam passes through an optical article at normal incidence. Under such conditions, the peak luminance is observed normal to the surface of the article. “Half angle” is the angle, relative to normal, where half the peak luminance is measured.

In another embodiment, the transmission is between about 50-75%, haze is greater than about 90%, and half-angle is greater than about 40°. In yet another embodiment, the transmission is between about 55-65%, haze is greater than about 90%, and half angle is greater than about 50°. A plurality of topographical features20forms the non-uniform surface of light diffusing layer12. Topographical features20may be spaced periodically or aperiodically, may have similar or differing heights, and may have curved or pointed contours to form a matte or textured surface. In one embodiment, the average roughness (Ra) of the non-uniform surface is in the range of about 0.5-50 μm. The non-uniform surface of light diffusing layer12may be formed by, inter alia, coextrusion of a bead-filled layer, microreplication, roughening, or sandblasting of the surface.

In one embodiment, light diffusing layer12includes topographical features20that are non-uniformly spaced rounded beads or posts. The features20have a width along the non-uniform surface in the range of about 5-200 μm, and the height of the features relative to the non-uniform surface is in the range of about 25-100 μm. The distance between adjacent features20is in the range of about 10-200 μm. The average roughness (Ra) of the entire non-uniform surface is approximately 5.0 μm.

In another embodiment, the width of the features20is in the range of about 100-200 μm, the height of the features is in the range of about 25-50 μm, and the distance between adjacent features is in the range of about 10-200 μm. In yet another embodiment, the width of the features20is in the range of about 50-100 μm, the height of the features is in the range of about 50-75 μm, and the distance between adjacent features is in the range of about 10-200 μm. In still yet another embodiment, the width of the features20is in the range of about 5-50 μm, the height of the features is in the range of about 75-100 μm, and the distance between adjacent features is in the range of about 10-200 μm.

Reflecting polarizing layer16is used to increase the fraction of light emitted by the light sources in the optical system that passes through the light gating device, and so the image produced by the display system is brighter. Reflective polarizing layer16is attached to light diffusing layer12via bonding layer14. In one embodiment, bonding layer14is laminated onto reflective polarizing layer16, and subsequently attached to the non-uniform surface of light diffusing layer12. Reflective polarizing layer16is attached to light diffusing layer12such that reflective polarizing layer16is bonded with topographical features20of the non-uniform surface. In one embodiment, bonding layer14has a thickness that is less than a height of topographical features20. In another embodiment, bonding layer14has a thickness that is about 5-75% of a height of topographical features20. When reflective polarizing layer16is attached to light diffusing layer12via bonding layer14according to the present invention, air gaps or voids25are defined between adjacent topographical features on the non-uniform surface of light diffusing layer12. Bonding layer14, topographical features20, and voids25form an intermediate region between light diffusing layer12and reflective polarizing layer16.

Optional polymeric layer18may provide a variety of functions, such as improved mechanical stability, scratch resistance, and optical function. For example, polymeric layer18may be a light directing layer to improve optical function by redirecting off-axis light in a direction closer to the axis of the display. If polymeric layer18is a light directing layer, the optical performance of the optical system is related to, inter alia, the fractional surface area of light diffusing layer12that is exposed to an air gap between light diffusing layer12and reflective polarizing layer16. In particular, the on-axis brightness, gain, and contrast ratio of the optical system are affected by these parameters. However, providing a full air gap requires the separate assembly of the light diffusing layer and the reflective polarizing layer when assembling the optical system. This is time consuming and the stacking of individual layers provides opportunity for the layers to be damaged.

Assembly10allows the installation of all of these layers into the optical system at the same time. Voids25that are defined by adjacent topographical features20function to provide a partial air gap between light diffusing layer12and reflective polarizing layer16. If the thickness of bonding layer14is less than the height of topographical features20, reflective polarizing layer16is prevented from completely bonding with light diffusing layer12(i.e., complete optical coupling is avoided). Voids25allow assembly10to have an optical performance substantially similar to that of an assembly including a full air gap between light diffusing layer12and reflective polarizing layer16. This performance is related to the surface area of the non-uniform surface of light diffusing layer12that is exposed to the air gap as defined by the height and shape of topographical features20.

In addition, with voids25defined between light diffusing layer12and reflective polarizing layer16, assembly10performs well from an environmental durability standpoint. In particular, assembly10performs substantially similarly before and after accelerated aging protocols, such as thermal shock (rapidly varying ambient temperature between −40° C. and 85° C.), high temperature with humidity (ambient temperature of 65° C. at 95% humidity for an extended period of time), and high temperature (ambient temperature of 85° C. for an extended period of time). Also, substantially fewer visual defects, such as blisters or dimples, form at the junction between light diffusing layer12and reflective polarizing layer16after accelerated aging compared to constructions formed without voids25.

Light diffusing layer12may comprise one or more polymeric layers. Examples of polymers useful in the one or more polymeric layers include poly(meth)acrylics, poly(meth)acrylates, polycarbonates, polyurethanes, polyesters, polyolefins, polystyrenes, polycyclo-olefins, epoxy polymers, polyamides, polyimides, polysulfones, poly(vinyl chlorides), polysiloxanes, or silicone polymers, or copolymers or blends thereof. Examples include acrylic copolymers; polymethylmethacrylate; an acrylonitrile butadiene styrene copolymer; a styrene acrylonitrile copolymer, poly(vinylcyclohexane); polymethyl methacrylate/poly(vinylfluoride) blends; poly(ethylene); poly(propylene); PET; PEN; a poly(phenylene oxide) blend; a styrenic block copolymer; a polycarbonate/PET blend; a vinyl acetate/polyethylene copolymer; a cellulose acetate; a fluoropolymer; a poly(styrene)-poly(ethylene) copolymer, or copolymers or blends thereof. In one embodiment, the polymeric layer comprises an acrylic sheet having the ACRYLITE® brand (from Cyro Industries, Rockaway, N.J.). In another embodiment, the polymeric layer comprises polymethylmethacrylate or a copolymer of methyl methacrylate and styrene.

Light diffusing layer12may comprise inorganic materials such as float glass, high-quality LCD glass, and/or borosilicate. In addition, light diffusing layer12may comprise organic, inorganic, or hybrid organic/inorganic particles, or combinations thereof that are useful for diffusing light. The particles may be solid, porous, or hollow, and they may be in the form of beads, shells, spheres, or clusters. The particles may be transparent. Examples of useful particles include polystyrene beads, polymethyl methylacrylate beads, polysiloxane beads, or combinations thereof. Other examples include titanium dioxide (TiO2), calcium carbonate (CaCO3), barium sulphate (BaSO4), magnesium sulphate (MgSO4), glass beads, and combinations thereof. Light diffusing layer12may also comprise voids or bubbles that may or may not be filled with a gas such as air or carbon dioxide. Furthermore, light diffusing layer12may be made diffuse by surface treatment such as roughening.

In addition, light diffusing layer12may comprise a combination of a substantially non-diffusing rigid substrate attached to a diffusing layer. Examples of light diffusing layers are described in U.S. Pat. No. 6,723,772, WO 2003/064526, and WO 2004/111692, the disclosures of which are incorporated herein by reference.

The light diffusing layer,12, may be subjected to various treatments that modify the surfaces, or any portion thereof, as by rendering them more conducive to subsequent treatments such as coating, dying, metallizing, or lamination. This may be accomplished through treatment with primers, such as polyvinylvinylidene chloride, polymethylmethacrylate, epoxies, and aziridines, or through physical priming treatments such as corona, flame, plasma, flash lamp, sputter-etching, e-beam treatments, or amorphizing the surface layer to remove crystallinity, such as with a heated contacting roll.

The properties of light diffusing layer12may be tailored to provide particular optical and physical performance features depending on the application. For example, light diffusing layer12may be designed to exhibit a particular light transmission and haze value. Physical properties of light diffusing layer12may be adjusted by the choice of the polymeric material. The thickness of the layers, and the particular choice of particles, such as their size, shape, and amount, may be varied in order to adjust optical properties.

Additional components may be added to any one of the layers of the assembly10. Examples include UV absorbers such as benzotriazoles, benzatriazines, and benzophenones, or combinations thereof. Light stabilizers such as hindered amine light stabilizers may also be added, and also heat stabilizers, optical brighteners, antistat materials, and phosphors. For a further description of components that may be added to the layers of assembly10, see U.S. Pat. Nos. 6,723,772 and 6,613,619, which are incorporated herein by reference.

Any suitable type of reflective polarizer16may be used, for example, multi-layer optical film (MOF) reflective polarizers, diffuse reflective polarizer film (DRPF) such as continuous/disperse phase polarizers, wire grid reflective polarizers, or cholesteric reflective polarizers.

Both the MOF and continuous/disperse phase reflective polarizers rely on the difference in refractive index between at least two materials, usually polymeric materials, to selectively reflect light of one polarization state while transmitting light in an orthogonal polarization state. Some examples of MOF reflective polarizers are described in co-owned U.S. Pat. No. 5,882,774, incorporated herein by reference. Commercially available examples of a MOF reflective polarizers include Vikuiti™ DBEF-D200 and DBEF-D440 multi-layer reflective polarizers that include diffusive surfaces, available from 3M Company, St. Paul, Minn.

Examples of DRPF useful in connection with the present invention include continuous/disperse phase reflective polarizers as described in co-owned U.S. Pat. No. 5,825,543, incorporated herein by reference, and diffusely reflecting multi-layer polarizers as described in e.g. co-owned U.S. Pat. No. 5,867,316, also incorporated herein by reference. Other suitable types of DRPF are described in U.S. Pat. No. 5,751,388.

Some examples of wire grid polarizers useful in connection with the present invention include those described in U.S. Pat. No. 6,122,103. Wire grid polarizers are commercially available from, inter alia, Moxtek Inc., Orem, Utah.

Some examples of cholesteric polarizer useful in connection with the present invention include those described in, for example, U.S. Pat. No. 5,793,456, and U.S. Patent Publication No. 2002/0159019. Cholesteric polarizers are often provided along with a quarter wave retarding layer on the output side, so that the light transmitted through the cholesteric polarizer is converted to linear polarization.

In one embodiment, bonding layer14comprises an adhesive material, such as a pressure sensitive adhesive. A pressure sensitive adhesive refers to a viscoelastic material that displays aggressive tackiness and adheres well to a wide variety of substrates after applying only light pressure (e.g., finger pressure). An acceptable quantitative description of a pressure sensitive adhesive is given by the Dahlquist criterion, which indicates that materials having a storage modulus (G′) of less than about 4.0×105Pascals (measured at room temperature) have pressure sensitive adhesive properties.

The pressure sensitive adhesive polymer may comprise a copolymer of one or more acrylate or methacrylate monomers, collectively referred to as (meth)acrylate monomers or reinforcing monomers, that have the formula:

wherein R1is H or CH3, and R2is a linear, branched, aromatic, or cyclic hydrocarbon group, for example, an alkyl group comprising from about 1 to about 20 carbon atoms. R2may also include heteroatoms such as nitrogen, oxygen or sulfur.

The pressure sensitive adhesive polymer may comprise a (meth)acrylate monomer that, as a homopolymer, has a Tg of less than about 0° C.; and a reinforcing monomer that, as a homopolymer, has a Tg of at least about 20° C. The pressure sensitive adhesive polymer may comprise a (meth)acrylate monomer that, as a homopolymer, has a Tg of less than about −20° C.; and the reinforcing monomer that, as a homopolymer, has a Tg of at least about 50° C.

The pressure sensitive adhesive polymer may comprise the (meth)acrylate monomer in an amount of from about 40% by weight to about 98% by weight.

The pressure sensitive adhesive polymer may comprise the reinforcing monomer in an amount of up to about 20% by weight, or up to about 10% by weight. These reinforcing monomers can contain acidic or basic functionalities.

The pressure sensitive adhesive polymer comprises acid or base functionality which may be obtained by randomly polymerizing acidic or basic monomers, respectfully. In either case, the pressure sensitive adhesive polymer may comprise additional neutral monomers, referred to as non-acidic and non-basic monomers, respectively.

Acid functionality may be incorporated into the pressure sensitive adhesive polymer by copolymerizing acidic monomers such as ethylenically unsaturated carboxylic acids, ethylenically unsaturated sulfonic acids, ethylenically unsaturated phosphonic acids, and mixtures thereof. Ethylenically unsaturated carboxylic acids are useful because they are readily available. Sulfonic and phosphonic acid derivatives provide a strong interaction with basic functionality, which is useful when high cohesive strength, temperature resistance, and solvent resistance required. Particularly useful acidic monomers are acidic (meth)acrylates. Examples of acidic monomers are (meth)acrylic acid, itaconic acid, fumaric acid, crotonic acid, citraconic acid, maleic acid, oleic acid, B-carboxyethyl acrylate, 2-sulfoethyl methacrylate, styrene sulfonic acid, 2-acrylamido-2-methylpropane sulfonic acid, vinyl phosphonic acid, and mixtures thereof.

When the pressure sensitive adhesive polymer comprises acid functionality, the acidic monomers described above may be polymerized with non-acidic monomers. The amount of acid and non-acidic monomers may vary, and may depend on the desired properties of the pressure sensitive adhesive polymer, such as its cohesive strength. For example, acidic monomers may comprise from about 2% by weight to about 30% by weight, preferably from about 2% by weight to about 15% by weight.

In one embodiment, the pressure sensitive adhesive polymer comprises isooctyl acrylate and acrylic acid, prepared using methods described in U.S. Pat. No. 4,074,004.

The adhesive layer may comprise a crosslinker in order to provide cohesive strength of the layer. The crosslinker may be a thermal crosslinker such as a multifunctional aziridine, an isocyanate, or an epoxy. One example is 1,1′-(1,3-phenylene dicarbonyl)-bis-(2-methylaziridine). The crosslinker may also be a chemical crosslinker such as a peroxide, e.g., benzoyl peroxide. The crosslinker may also be a photosensitive crosslinker which is activated by high intensity ultraviolet light, e.g., benzophenone and copolymerizable aromatic ketone monomers as described in U.S. Pat. No. 4,737,559, or triazines, e.g., 2,4-bis(trichloromethyl)-6-(4-methoxy-pheynl)-s-triazine. The crosslinker may also be hydrolyzable, such as monoethylenic ally unsaturated mono-, di-, and trialkoxy silane compounds including, but not limited to, methacryloxypropyltrimethoxysilane (available from Gelest, Inc., Tullytown, Pa.), vinyldimethylethoxysilane, vinylmethyl diethoxysilane, vinyltriethoxysilane, vinyltrimethoxysilane, and vinyltriphenoxysilane. Crosslinking may also be achieved using high energy electromagnetic radiation such as gamma or e-beam radiation.

The particular choice and amount of crosslinker used in the blend may depend on the other polymers present in the blend, as well as the other layers in the optical assembly, and the application in which the optical assembly is used. Typically, the crosslinker is present in amounts of less than about 5 parts based on the total dry weight of the blend, and more specifically, from about 0.01 parts to 1 part.

The pressure sensitive adhesive polymer may be prepared by any conventional free radical polymerization method, including solution, radiation, bulk, dispersion, emulsion, and suspension processes. Free radical initiators and photoinitiators, chain transfer agents. Details of these processes may be found in, for example, WO 97/23577.

The adhesive layer may comprise additives such as tackifiers, plasticizers, UV absorbers, etc., such as that shown and described in WO 97/23577.

The dry thickness of the adhesive layer may be from about 0.05 micrometers to about 100 micrometers.

The pressure sensitive adhesive may be applied to reflective polarizing layer16or light diffusing layer12using conventional coating methods such as gravure coating, curtain coating, slot coating, spin coating, screen coating, transfer coating, brush coating, or roller coating. The blend may also be hot-melt coated. For most coating methods, the blend may additionally comprise a solvent which may be removed after the coating operation. The percent solids of the blend may vary depending on the coating method and the particular chemical identities of the pressure sensitive adhesive polymer and the crosslinker. The blend may also be coated onto a release liner such as paper and film liners coated with release agents such as silicones, fluorocarbons, etc. An example is the T-30 liner available from CPFilms Inc., Martinsville, Va. The release liner may then be removed. Whether applied directly to the reflective polarizing layer, the light diffusing layer, or a release liner, the remaining layers of the optical assembly may then be laminated to the adhesive layer.

It is desirable that the adhesive layer maintains a consistent optical performance over the useful life of optical assembly10. The adhesive layer should also maintain bond strength, integrity, and stability, and not exhibit delamination or bubbling over time and under a variety of environmental conditions, as may be estimated using accelerated aging tests. Such test conditions may include thermal shock (−40 C to 85 C, 100 cycles), temperature extremes (−40 C, 85 C), high heat/humidity, and heat/ultraviolet exposure.

In one embodiment, the adhesive layer comprises a blend of a majority of a pressure sensitive adhesive polymer having acid or base functionality, a high Tg polymer having a Tg of greater than about 20° C. and having acid or base functionality, and a crosslinker, such as that shown and described in U.S. patent application Ser. No. 10/411,933, the disclosure of which is herein incorporated by reference. The functionality of the pressure sensitive adhesive polymer and the functionality of the high Tg polymer form an acid-base interaction when mixed. The adhesive crosslink density, modulus, and tack properties are designed so that adequate bond is maintained between the layers over the lifetime of the device. In addition, the adhesive properties are controlled so that the adhesive does not flow into voids25during operation, which would detrimentally affect the optical performance of optical assembly10.

In another embodiment, the pressure sensitive adhesive polymer may comprise a polyurethane, a polyolefin, a tackified natural rubber, a synthetic rubber, a tackified styrene block copolymer, a silicone, a polyvinyl ether, or a combination thereof. The pressure sensitive adhesive polymer may comprise a copolymer of one or more vinyl esters (e.g., vinyl acetate), styrene, substituted styrene (e.g., a-methyl styrene), vinyl halide, vinyl propionate, and mixtures thereof. Other useful vinyl monomers include macromeric (meth)acrylates such as (meth)acrylate-terminated styrene oligomers and (meth)acrylate-terminated polyethers, such as are described in WO 84/03837. The pressure sensitive adhesive polymer may be a waterborne emulsion or dispersion.

In another embodiment, the adhesive layer may comprise a heat-activated adhesive. In addition, the adhesive layer may comprise a radiation-curable adhesive as described in U.S. application Ser. No. 10/914,555, filed Aug. 9, 2004, the disclosure of which is herein incorporated by reference.

In other embodiments, light diffusing layer12may be bonded to reflective polarizing layer16around a periphery of the layers by perimeter or edge bonding. That is, rather than providing bonding layer14to completely coat a major surface of reflective polarizing layer16, bonding layer14may bond light diffusing layer12to reflective polarizing layer16around a periphery of these layers outside of the optically active portions of the layers. Alternatively, rather than bonding light diffusing layer12to reflective polarizing layer16using an adhesive, light diffusing layer12may be bonded to reflective polarizing layer16around a periphery of the layers using solvent bonding, ultrasonic welding, or laser welding. In essence, light diffusing layer12may be bonded to reflective polarizing layer16using any bonding method that does not affect the performance of the optically active area of assembly10.

Polymeric layer18is an optional layer that is attached to reflective polarizing layer16on a surface opposite bonding layer14. In one embodiment, polymeric layer18is a light directing film that includes a surface structure that redirects off-axis light in a direction closer to the axis of the display. This increases the amount of light propagating on-axis through the display, thus increasing the brightness of the image seen by the viewer. One example of a light directing layer is a prismatic brightness enhancing layer, which has a number of prismatic ridges that redirect the illumination light, through refraction and reflection. Examples of prismatic brightness enhancing layers that may be used in optical assembly10include the Vikuiti™ BEFII and BEFIII family of prismatic films available from 3M Company, St. Paul, Minn., including BEFII 90/24, BEFII 90/50, BEFIIIM 90/50, and BEFIIIT. The 90/24 refers to a prism peak angle of 90 degrees and a prism peak spacing of 24 micrometers, while the 90/50 refers to a prism peak angle of 90 degrees and a prism peak spacing of 50 micrometers. In another embodiment, polymeric layer18is a gain diffusing layer, for example, a layer containing micrometer-size particles that provides diffusion and directing of light. In further embodiments, polymeric layer18is a flat film (e.g., a protective film) or has a structured or microstructured surface including any of regular or irregular prismatic patterns, an annular prismatic pattern, a cube-corner pattern, any lenticular microstructure, or combinations thereof.

FIG. 2is a schematic cross-sectional view of exemplary direct-lit display device100. Display device100includes liquid crystal (LC) panel102comprising LC layer104disposed between panel plates106. Display device100also includes upper polarizer108with optional layer109attached thereto, lower polarizer110, light source region112including light sources114and reflector116, and controller118. Controller118is connected to LC layer104of LC panel102. Optical assembly10is incorporated into display device100and is disposed between light source region112and LC panel102.

Display device100may be used, for example, in an LCD monitor or LCD-TV. The operation of display device100is based on the use of LC panel102, which typically comprises an LC layer104disposed between panel plates106. Plates106are often formed of glass, and may include electrode structures and alignment layers on their inner surfaces for controlling the orientation of the liquid crystals in LC layer104. The electrode structures are commonly arranged so as to define LC panel pixels, areas of the LC layer where the orientation of the liquid crystals can be controlled independently of adjacent areas. A color filter may also be included with one or more of plates106for imposing color on the image displayed.

Upper absorbing polarizer108is positioned above LC layer104and lower absorbing polarizer110is positioned below LC layer104. In the illustrated embodiment, the upper and lower absorbing polarizers are located outside LC panel102. Absorbing polarizers108and110and LC panel102in combination control the transmission of light from light source region112through display100to the viewer. In some LC displays, absorbing polarizers108and110may be arranged with their transmission axes perpendicular. When a pixel of LC layer104is not activated, it does not change the polarization of light passing therethrough. Accordingly, light that passes through lower absorbing polarizer110is absorbed by upper absorbing polarizer108when absorbing polarizers108and110are aligned perpendicularly. When the pixel is activated, on the other, hand, the polarization of the light passing therethrough is rotated, so that at least some of the light that is transmitted through lower absorbing polarizer110is also transmitted through upper absorbing polarizer108. Selective activation of the different pixels of LC layer104, for example by controller118, results in the light passing out of the display at certain desired locations, thus forming an image seen by the viewer. Controller118may include, for example, a computer or a television controller that receives and displays television images. One or more optional layers109may be provided over upper absorbing polarizer108, for example to provide mechanical and/or environmental protection to the display surface. In one exemplary embodiment, layer109may include a hardcoat over absorbing polarizer108.

It will be appreciated that some types of LC displays may operate in a manner different from that described above. For example, the absorbing polarizers may be aligned parallel and LC panel102may rotate the polarization of the light when a pixel is in an unactivated state. Regardless, the basic structure of such displays remains similar to that described above.

Light source region112includes a number of light sources114that generate the light that illuminates LC panel102. Light sources114used in a LCD-TV or LCD monitor are often linear, cold cathode fluorescent tubes that extend across display device100. Other types of light sources may be used, however, such as filament or arc lamps, light emitting diodes (LEDs), non-linear cold cathode fluorescent tubes, flat fluorescent panels, or external electrode fluorescent lamps. This list of light sources is not intended to be limiting or exhaustive, but only exemplary.

Light source region112may also include reflector116for reflecting light propagating downwards from light sources114, in a direction away from LC panel102. Reflector116may also be useful for recycling light within display device100, as is explained below. Reflector116may be a specular reflector or may be a diffuse reflector. One example of a specular reflector that may be used as reflector116is Vikuiti™ Enhanced Specular Reflection (ESR) film available from 3M Company, St. Paul, Minn. Examples of suitable diffuse reflectors include polymers, such as polyethylene terephthalate (PET), polycarbonate (PC), polypropylene, polystyrene and the like, loaded with diffusely reflective particles, such as titanium dioxide, barium sulphate, calcium carbonate and the like. Other examples of diffuse reflectors, including microporous materials and fibril-containing materials, are discussed in co-owned U.S. Patent Application Publication 2003/0118805 A1, which is incorporated herein by reference.

Assembly10is positioned between light source region112and LC panel102. As described above, the light management layers affect the light propagating from light source region112so as to improve the operation of display device100. It is desirable to utilize optical assemblies such as assembly10, which include reflective polarizing layer16attached to diffuser plate12on a non-uniform surface. The use of such optical assemblies decreases the assembly time for LCD televisions, for example, because there are fewer components to assemble. Also, providing assembly10as a unitary article better facilitates automated assembly of the components of the display device100.

ADDITIONAL EMBODIMENTS

While assembly10includes a non-uniform surface formed by topographical features20to define voids25, any structure may be provided in the intermediate region between the light diffusing layer and the reflective polarizing layer to define voids or air gaps. For example,FIG. 3shows optical assembly200according to another embodiment of the present invention. Assembly200may be incorporated in display system100(FIG. 2) in place of assembly10. Assembly200includes light diffusing layer212, structured intermediate layer214, reflective polarizing layer216, and optional polymeric layer218. Reflective polarizing layer216is attached to light diffusing layer212via structured intermediate layer214. Light diffusing layer212, structured intermediate layer214, and reflective polarizing layer216may be coupled to each other via an adhesive layer between each of the layers (either completely coating or around a periphery of the layers). Alternatively, reflective polarizing layer216and light diffusing layer212. may be coupled to structured intermediate film214by solvent bonding, or ultrasonic welding. Polymeric layer218is optionally attached to reflective polarizing layer216on the surface opposite structured intermediate layer214.

Structured intermediate layer214includes structures220that define voids225. Voids225provide a partial air gap between light diffusing layer212and reflective polarizing layer216. Voids225allow assembly200to have an optical performance substantially similar to that of an assembly including a full air gap between light diffusing layer212and reflective polarizing layer216. While structured intermediate layer214is shown with structures220defining voids225that extend through structured intermediate layer214, structured intermediate layer214may have any configuration that defines voids or air gaps between light diffusing layer212and reflective polarizing layer216.

Light diffusing layer212, reflective polarizing layer216, and polymeric layer218may be made of similar materials or have similar configurations as light diffusing layer12, reflective polarizing layer16, and polymeric layer218(FIG. 1), respectively, as set forth above. Structured intermediate layer214may be made of a polymeric material including poly(meth)acrylics, poly(meth)acrylates, polycarbonates, polyurethanes, polyesters, polyolefins, polystyrenes, polycyclo-olefins, epoxy polymers, polyamides, polyimides, polysulfones, poly(vinyl chlorides), polysiloxanes, or silicone polymers, or copolymers or blends thereof. Examples include acrylic copolymers; polymethylmethacrylate; an acrylonitrile butadiene styrene copolymer; a styrene acrylonitrile copolymer, poly(vinylcyclohexane); polymethyl methacrylate/poly(vinylfluoride) blends; poly(ethylene); poly(propylene); PET; PEN; a poly(phenylene oxide) blend; a styrenic block copolymer; a polycarbonate/PET blend; a vinyl acetate/polyethylene copolymer; a cellulose acetate; a fluoropolymer; a poly(styrene)-poly(ethylene) copolymer; or copolymers or blends thereof. In one embodiment, the structured intermediate layer214comprises an acrylic sheet having the ACRYLITE® brand (from Cyro Industries, Rockaway, N.J.). In another embodiment, the structured intermediate layer214comprises polymethylmethacrylate or a copolymer of methyl methacrylate and styrene. In an alternative embodiment, structured intermediate layer214is configured as an adhesive perimeter bond such that the bond and the facing major surfaces of light diffusing layer212and reflective polarizing layer216define a void between light diffusing layer212and reflective polarizing layer216.

FIG. 4shows optical assembly300according to a further embodiment of the present invention. Assembly300may be incorporated in display system100(FIG. 2) in place of assembly10. Assembly300includes light diffusing layer312, bonding layer314, reflective polarizing layer316, and optional polymeric layer318. Reflective polarizing layer316is attached to light diffusing layer312via bonding layer314. Polymeric layer318is optionally attached to reflective polarizing layer316on the surface opposite light diffusing layer312. Light diffusing layer312, bonding layer314, reflective polarizing layer316, and polymeric layer318may be made of similar materials to or have similar configurations as light diffusing layer12, bonding layer14, reflective polarizing layer16, and polymeric layer18(FIG. 1), respectively, as set forth above.

Reflective polarizing layer316includes a non-uniform or textured surface. A plurality of topographical features320form the non-uniform surface of reflective polarizing layer316. Topographical features320may be spaced periodically or aperiodically, may have similar or differing heights, and may have curved or pointed contours to form a matte or textured surface. In one embodiment, the average roughness (Ra) of the non-uniform surface is in the range of about 0.5-10 μm. The non-uniform surface of reflective polarizing layer316may be formed by, inter alia, microreplication, roughening, or sandblasting of the surface.

Reflective polarizing layer316is attached to light diffusing layer312such that light diffusing layer312is bonded with topographical features320of the non-uniform surface. In one embodiment, bonding layer314has a thickness that is less than a height of topographical features320. In another embodiment, bonding layer314has a thickness that is about 5-75% of a height of topographical features320. When reflective polarizing layer316is attached to light diffusing layer312via bonding layer314according to the present invention, air gaps or voids325are defined between adjacent topographical features on the non-uniform surface of reflective polarizing layer316. Bonding layer314, topographical features320, and voids325form an intermediate region between light diffusing layer312and reflective polarizing layer316. Voids325provide a partial air gap between light diffusing layer312and reflective polarizing layer316. Voids325allow assembly300to have an optical performance substantially similar to that of an assembly including a full air gap between light diffusing layer312and reflective polarizing layer316.

EXAMPLES

Preparation of Optical Assemblies

The reflective polarizing layer used was ½-D400, which is a 3M™ Vikuiti™ Dual Brightness Enhancement Film (DBEF-Q) laminated to one sheet of approximately 130 μm thick polycarbonate (60% haze) using a radiation-curable adhesive. The polycarbonate had a matte surface. The light diffusing layer was a 2.0 mm light diffuser plate with a non-uniform surface which is commercially available under model RM802 from Sumitomo Chemical Company, Tokyo, Japan. The light diffusing layer comprised a copolymer of methyl methacrylate and styrene (hereinafter referred to as MS). The surface characteristics of Surface1and Surface2of the RM802 light diffusing layer measured by stylus profilometry are shown in Table 1 below. The reflective polarizing layer was attached to Surface1of the light diffusing layer using an approximately 15 μm thick layer of pressure sensitive adhesive made by 3M Corporation, Saint Paul, Minn. (Adhesive A). Adhesive A was a blend of 90% of a pressure sensitive adhesive, a copolymer of isooctylacrylate and acrylic acid (93:7), and 10% of a high Tg polymer, a copolymer of methylmethacrylate, butylmethacrylate, and DMA-EMA (69:25:6) and having a molecular weight of ˜140,000 g/mol.

Example 2 was prepared as in Example 1, except that the reflective polarizing layer included a layer of approximately 250 μm thick polycarbonate laminated to each side of the DBEF-Q film, and BEFIII 90/50, 7R (i.e., 7 μm radius of curvature) prisms coated on one of the layers of polycarbonate (DBEF-DTV).

Example 3 was prepared as in Example 1, except that the reflective polarizing layer used was a DBEF-Q film without the sheet of approximately 130 μm thick polycarbonate laminated thereto.

Example 4 was prepared as in Example 1, except that the reflective polarizing layer used was a DBEF-Q film with BEFII 90/24 prisms coated thereon.

Example 5 was prepared as in Example 1, except that the reflective polarizing layer used was a DBEF-Q film with BEFIII 90/50, 7R prisms coated thereon.

Example 6 was prepared as in Example 1, except that the reflective polarizing layer was attached to Surface1of the light diffusing layer using an approximately 12.7 μm thick layer of pressure sensitive adhesive (Adhesive A) and the reflective polarizing layer used was a DBEF-Q film with BEFII 90/24 prisms coated thereon.

Example 7 was prepared as in Example 1, except that the reflective polarizing layer was attached to Surface1of the light diffusing layer using an approximately 6.35 μm thick layer of pressure sensitive adhesive (Adhesive A) and the reflective polarizing layer used was a DBEF-Q film with BEFII 90/24 prisms coated thereon.

Example 8 was prepared as in Example 1, except that the reflective polarizing layer was attached to Surface1of the light diffusing layer using an approximately 2.54 μm thick layer of pressure sensitive adhesive (Adhesive A) and the reflective polarizing layer used was a DBEF-Q film with BEFII 90/24 prisms coated thereon.

Example 9 was prepared as in Example 1, except that the reflective polarizing layer was attached to Surface2of the light diffusing layer using an approximately 12.7 μm thick layer of pressure sensitive adhesive (Adhesive A) and the reflective polarizing layer used was a DBEF-Q film with BEFII 90/24 prisms coated thereon.

Example 10 was prepared as in Example 1, except that the reflective polarizing layer was attached to Surface2of the light diffusing layer using an approximately 6.35 μm thick layer of pressure sensitive adhesive (Adhesive A) and the reflective polarizing layer used was a DBEF-Q film with BEFII 90/24 prisms coated thereon.

Example 11 was prepared as in Example 1, except that the reflective polarizing layer was attached to Surface2of the light diffusing layer using an approximately 2.54 μm thick layer of pressure sensitive adhesive (Adhesive A) and the reflective polarizing layer used was a DBEF-Q film with BEFII 90/24 prisms coated thereon.

Comparative Example 1 was prepared as in Example 1, except that the reflective polarizing layer was free floating on the diffuser plate to provide a full air gap between the reflective polarizing layer and the light diffuser plate.

Comparative Example 2 was prepared as in Example 1, except that the reflective polarizer was completely optically coupled to the light diffuser plate using 3M 9483 adhesive from 3M Corporation, Saint Paul, Minn., which is an approximately 80 μm thick layer of acrylic pressure sensitive adhesive.

Comparative Example 3 was prepared as in Example 2, except that the reflective polarizing layer was free floating on the light diffuser plate to provide a full air gap between the reflective polarizing layer and the light diffuser plate.

Comparative Example 4 was prepared as in Example 2, except that the reflective polarizing layer was completely optically coupled to the light diffuser plate using 3M 9483 adhesive.

Comparative Example 5 was prepared as in Example 3, except that the reflective polarizing layer was free floating on the light diffuser plate to provide a full air gap between the reflective polarizing layer and the light diffuser plate.

Comparative Example 6 was prepared as in Example 3, except that the reflective polarizing layer was completely optically coupled to the light diffuser plate using 3M 9483 adhesive from 3M Corporation, Saint Paul, Minn., which is an acrylic pressure sensitive adhesive.

Comparative Example 7 was prepared as in Example 4, except that the reflective polarizing layer was free floating on the light diffuser plate to provide a full air gap between the reflective polarizing layer and the light diffuser plate.

Comparative Example 8 was prepared as in Example 4, except that the reflective polarizing layer was completely optically coupled to the light diffuser plate using 3M 9483 adhesive from 3M Corporation, Saint Paul, Minn., which is an acrylic pressure sensitive adhesive.

Comparative Example 9 was prepared as in Example 5, except that the reflective polarizing layer was free floating on the light diffuser plate to provide a full air gap between the reflective polarizing layer and the light diffuser plate.

Comparative Example 10 was prepared as in Example 5, except that the reflective polarizing layer was completely optically coupled to light diffuser plate using 3M 9483 adhesive from 3M Corporation, Saint Paul, Minn., which is an acrylic pressure sensitive adhesive.

A summary of the optical assemblies described above is provided in Table 2.

The effective transmission was measured for each of the optical assemblies prepared. A Teflon cube with walls about 0.6 cm thick and about 11 cm on a side was provided. The cube was illuminated from its interior via a high intensity fiber-optic light pipe. The highly diffusing translucent walls of the cube provided reference surfaces of highly uniform (Lambertian) luminance. A luminance meter, centered relative to an external cube face and positioned along a normal to the cube face, recorded the luminance on the cube face with and without each of the optical assemblies provided between the luminance meter and the cube face. The ratio of the luminance with the optical assembly included to that without the optical assembly included is the effective transmission. The results of the effective transmission measurement for each of samples prepared are provided in Table 3.

As is shown by this table, the effective transmissions of optical assemblies prepared in accordance with the present invention (Examples 1-5) are substantially similar to the effective transmissions of the corollary comparative example optical assemblies having a full air gap between the light diffusing layer and the reflective polarizing layer (Comparative Examples 1, 3, 5, 7, and 9, respectively). In addition, optical assemblies prepared in

TABLE 3ExampleEffective Transmission11.55921.78731.60441.90951.82661.82271.92781.94891.470101.809111.931C-11.619C-21.499C-31.924C-41.459C-51.608C-61.624C-71.964C-81.418C-91.972C-101.567
accordance with the present invention (Examples 1-11) generally show improved effective transmissions over the corollary comparative examples wherein the reflective polarizing layer is completely coupled to the light diffusing layer.
Speckle Test

At regions where bonding layer14optically couples light diffusing layer12and optional polymeric layer18(i.e., where the peaks of the non-uniform surface of light diffusing layer12touch bonding layer14), a difference in brightness is observed compared with regions above voids25between light diffusing layer12and bonding layer14. This speckle defect is typically more apparent to an observer at higher viewing angles where the regions above voids25appear less bright than the regions with optical coupling between light diffusing layer12and optional polymeric layer18. The speckle defect exists due to the inability of optional polymeric layer18to function as a light directing layer when optically coupled to light diffusing layer12.

Test samples of some of the above examples (examples 6-11 and comparative examples C-7 and C-8) were tested to inspect for the speckle defect. The example was tested in a display constructed with the following components starting with component furthest from the eye: (1) a light box including diffuse white light with a white acrylic bottom diffuser and a fluorescent bulb (e.g., General Electric F15T8-SP41); (2) a light box diffuser made of a white acrylic with a minimum haze of 98% and a brightness in the range of 150-300 cd/m2; (3) TEST SAMPLE; (4) a top diffuser filter (e.g., Keiwa 100-BMU1S) having nominal haze of 65%; (5) a polarizer laminated glass layer (e.g., SanRitz HLC2-5618) having a transmittance of 35-45% and polarization efficiency of ≧99.9%; and (6) an approximately 38 cm XGA black matrix layer having a pixel size of 0.298 mm by 0.100 mm, a black matrix (BM) width of 0.010 mm, and an aperture ratio of 84%. The criteria for passing the speckle test was whether the speckle defect was objectionable at a horizontal viewing angle within ±80°, a vertical viewing angle within ±80°, and a viewing distance of at least 50 cm from the example to the eye.

The speckle defect may be made less apparent by changing the spatial frequency of voids25. For example, by providing a single void25throughout the entire usable viewing area of the display, the speckle defect would not be apparent. Also, the spatial frequency of the voids could be increased to a point at which the individual regions of differing brightness are no longer discernable. With 100% contrast between the brightness above voids25and above where bonding layer14optically couples light diffusing layer12and optional polymeric layer18, a spatial frequency of approximately 40 cycles/degree (corresponding to a 100 μm distance between nearest optically coupled regions at a viewing distance of 0.25 meters) would be necessary to reduce the appearance of the speckle defect to an acceptable level based on typical contrast response functions. The required distance between nearest optically coupled regions could be increased by increasing the viewing distance or decreasing the contrast between the brightness above voids25and above the optically coupled regions.

In summary, the present invention is an optical assembly that includes a light diffusing layer attached to a reflective polarizing layer. An intermediate region between the light diffusing layer and the reflective polarizing layer includes an intermediate structure that defines voids between the light diffusing layer and the reflective polarizing layer. This configuration allows several optical layers to be incorporated into an optical system as a single assembly. This reduces the time required to assemble an optical system including these layers and decreases the possibility of damage to the individual layers during assembly of the layers and integration into the optical system.