Patent Publication Number: US-2011051392-A1

Title: Light management assembly

Description:
BACKGROUND 
     The present invention is directed to optical displays, and more particularly to an approach for assembling light management optical films used in optical displays. Optical displays, such as liquid crystal displays (LCDs) are becoming increasingly commonplace, finding use, for example in mobile telephones, hand-held computer devices ranging from personal digital assistants (PDAs) to electronic games, to larger devices such as laptop computers, and LCD monitors and 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, illumination uniformity, viewing angle, and overall system efficiency. Such improved operating characteristics make the device easier to use and may also increase battery life. 
     The light management films are stacked, one by one, into the display frame between a backlight assembly and the flat panel display. 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, inter alia, the excess time required to remove protective liners from individual optical films, along with the increased chance of damaging a film when removing the liner. In addition, the insertion of multiple individual sheets to 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. Additionally, discrete film pieces need to independently withstand environmental conditions and are therefore designed with materials and thicknesses that accomplish requirements, adding cost to the individual films. 
     SUMMARY 
     In one aspect, the invention provides a light management assembly comprising a light-transmissive plate having a light input surface and a light output surface, a cover film having inside and outside surfaces covering at least one major surface of the light-transmissive plate, and an optical film adjacent to the outside surface of the cover film. 
     In one embodiment, the above light management assembly further comprises a second optical film between the light-transmissive plate and the cover film. 
     In another embodiment, the second optical film is between the light output surface of the light-transmissive plate and the cover film. 
     In another embodiment, the optical film is attached to the outside surface of the cover film that is nearest to the light input surface of the light-transmissive plate. 
     In another embodiment, the above light management assembly further comprises a a second cover film covering at least a major surface of the optical film. 
     In another embodiment, the second cover film encapsulates the above light management assembly. 
     In another aspect, the invention provides a light management assembly comprising a light-transmissive plate having a light input surface and a light output surface, a cover film covering at least one major surface of the light-transmissive plate, a first optical film between the cover film and the light-transmissive plate, wherein the light-transmissive plate and the optical film each have a major surface, and wherein at least one of the major surfaces of the light-transmissive plate or of the optical film is a structured surface. 
     In one embodiment, the above light management assembly further comprises a second optical film on an outside surface of the cover film. 
     In another embodiment, the light management assembly comprises first and second optical films between the cover film and the light-transmissive plate. 
     In another embodiment, the first optical film between the light-transmissive plate and the cover film is between the light input surface of the light-transmissive plate and the cover film. 
     In other embodiments, the cover film encapsulates the light-transmissive plate. 
     In other embodiments, the cover film covers one major surface of the light-transmissive plate. 
     In another aspect, the invention provides a light management assembly comprising a light-transmissive film having a light input surface and a light output surface, a cover film covering at least one of the light input or light output surfaces of the light-transmissive film, and a first optical film between the cover film and the light-transmissive film, wherein the light-transmissive film and the optical film each have a major facing surface, and wherein at least one of the major facing surfaces of the light-transmissive film or of the optical film, is a structured surface. 
     In other embodiments, light management assemblies of the invention have multiple optical films within the cover film, positioned between the output surface of a light-transmissive plate or film and the input surface of the cover film; multiple optical films on an outside surface of the cover film; or a combination of either. 
     In other embodiments, the optical film(s) on an outside surface of the cover film may be attached to the outside surface of the cover film or may be freestanding on the outside surface of the cover film. 
     In another aspect, the invention provides a light management assembly consisting essentially of a light-transmissive plate having a light input surface and a light output surface, a cover film having inside and outside surfaces covering at least one major surface of the light-transmissive plate, and an optical film attached to the outside surface of the cover film. 
     In another aspect, the invention provides a light management assembly consisting essentially of a light-transmissive plate a light input surface and a light output surface, a cover film covering at least one major surface of the light-transmissive plate, a first optical film between the cover film and the light-transmissive plate, wherein the light-transmissive plate and the optical film each have a major surface and wherein at least one of the major surfaces of the light-transmissive plate or of the optical film is a structured surface. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  schematically illustrates a back-lit liquid crystal display device that incorporates one embodiment of a light management assembly according to the present invention; 
         FIG. 2  illustrates an embodiment of a light management assembly of the invention; 
         FIG. 3  illustrates another embodiment of a light management assembly of the invention; 
         FIG. 4  illustrates another embodiment of a light management assembly of the invention; 
         FIG. 5  illustrates another embodiment of a light management assembly of the invention; 
         FIG. 6  illustrates another embodiment of a light management assembly of the invention; 
         FIG. 7  illustrates another embodiment of a light management assembly of the invention; 
         FIG. 8  illustrates an alternate embodiment of a cover film attached to a light-transmissive plate; and 
         FIG. 9  illustrates another embodiment of a light management assembly of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention is applicable to displays, such as liquid crystal displays (LCDs or LC displays), and is useful for reducing the number of steps required for making such a display. For example, a light management assembly of the invention may be simply combined with an LC panel and backlight in a frame. One of the advantages of the light management assemblies of the invention is that they are expected to be robust, for example, able to withstand packing and shipping. Additionally, since attachment points between an optical film and a light-transmissive plate are minimized or not required, the effects of thermal expansion differences between the optical film and the light-transmissive plate are reduced. 
     Another advantage of the light management assemblies of the invention is that such assemblies may be handled robotically in the assembly of an LC display device. Another benefit of the light management assemblies of the invention is that thinner optical films may be used in combination with a light-transmissive plate to minimize assembly thickness and cost. Due to the support provided by the invention, robustness during typical environmental conditions can still be maintained even from films that would not otherwise meet such requirements. Some embodiments may exclude an LC panel within a cover film. The cover films may be used as a permanent enclosure or cover and used in a device, or may be used as a temporary cover or enclosure, that is, the cover film maybe removed before placing the light management assembly into a device. 
     For the purpose of this application, a “structured surface” includes surfaces having local surface height maxima having random, pseudo-random, irregular, or regular heights and having random, pseudo-random, irregular, or regular separations between such height maxima. A “matte” surface is also a structured surface for the purpose of this application. Matte surfaces include monolithic matte surfaces, for example cast or extruded and then formed directly on the film, and matte surfaces made by coating beads or a bead composition onto a film. Examples of such structured surfaces include “anti-wet-out” surfaces described in U.S. Pat. No. 6,322,236 B1, incorporated by reference for its description of anti-wet-out surfaces, and surfaces having prismatic structures or ridges, for example, such as those described in U.S. Pat. No. 5,056,892, incorporated by reference for its description of prismatic structures. 
     A schematic exploded view, not drawn to scale, of an exemplary embodiment of a direct-lit LC display device  100  is presented in  FIG. 1 . Such a display device  100  may be used, for example, in an LCD monitor or LCD-TV. The display device  100  is based on the use of an LC panel  102 , which typically comprises a layer of LC  104  disposed between panel plates  106 . The plates  106  are 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 the LC layer  104 . 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 the plates  106  for imposing color on the image displayed. 
     An upper absorbing polarizer  108  is positioned above the LC layer  104  and a lower absorbing polarizer  110  is positioned below the LC layer  104 . In the illustrated embodiment, the upper and lower absorbing polarizers are located outside the LC panel  102 . The absorbing polarizers  108 ,  110  and the LC panel  102  in combination control the transmission of light from the backlight  112  through the display  100  to the viewer. In some LC displays, the absorbing polarizers  108 ,  110  may be arranged with their transmission axes perpendicular. When a pixel of the LC layer  104  is not activated, it may not change the polarization of light passing therethrough. Accordingly, light that passes through the lower absorbing polarizer  110  is absorbed by the upper absorbing polarizer  108 , when the absorbing polarizers  108 ,  110  are 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 the lower absorbing polarizer  110  is also transmitted through the upper absorbing polarizer  108 . Selective activation of the different pixels of the LC layer  104 , for example by a controller  114 , results in the light passing out of the display at certain desired locations, thus forming an image seen by the viewer. The controller may include, for example, a computer or a television controller that receives and displays television images. One or more optional layers  109  may be provided over the upper absorbing polarizer  108 , for example to provide mechanical and/or environmental protection to the display surface. In one exemplary embodiment, the layer  109  may include a hardcoat over the absorbing polarizer  108 . 
     It will be appreciated that some type of LC displays may operate in a manner different from that described above. For example, the absorbing polarizers may be aligned parallel and the LC panel may rotate the polarization of the light when in an unactivated state. Regardless, the basic structure of such displays remains similar to that described above. 
     The backlight  112  includes a number of light sources  116  that generate the light that illuminates the LC panel  102 . The light sources  116  used in a LCD-TV or LCD monitor are often linear, cold cathode, fluorescent tubes that extend across the display device  100 . Other types of light sources may be used, however, such as filament or arc lamps, light emitting diodes (LEDs), flat fluorescent panels or external fluorescent lamps. This list of light sources is not intended to be limiting or exhaustive, but only exemplary. 
     The backlight  112  may also include a reflector  118  for reflecting light propagating downwards from the light sources  116 , in a direction away from the LC panel  102 . The reflector  118  may also be useful for recycling light within the display device  100 , as is explained below. The reflector  118  may be a specular reflector or may be a diffuse reflector. One example of a specular reflector that may be used as the reflector  118  is 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, incorporated herein by reference. 
     A light management assembly  120  is positioned between the backlight  112  and the LC panel  102 . The light management assembly affects the light propagating from backlight  112  so as to improve the operation of the display device  100 . In this embodiment, the light management assembly  120  includes a light-transmissive plate  122 , a cover film  124 , an optical film  126  adjacent to the outside or output surface  125  of the cover film, and voids  128  between the light-transmissive plate  122  and the cover film  124 . In this embodiment, the light-transmissive plate has matte output and input surfaces. In other embodiments described in this application, the optical film  126  may be attached to the cover film or may be freestanding on top of the cover film. 
     A “void” is a space between output and input surfaces of optical elements having a desirable index of refraction differential with an input surface. For example, the void may be occupied with air, one or more gases other than air, or a combination of air and other gases. The voids in the light management assemblies of the current invention inhibit optical coupling between adjacent surfaces of the optical films of the assembly. If an optical film is allowed to couple or “wet-out” with the adjacent film, undesirable optical artifacts can occur, such as Newton Rings, localized brightness non-uniformities, or reduced overall display brightness. 
     For certain types of brightness enhancement films, a refractive index change is necessary for proper function of the optical film. For example, in order for a prismatic structured surface film to most efficiently direct light into a narrower angular exit profile toward the user, the film often includes a planar or nearly planar entry surface (on the opposite side of the film from the prisms) that includes an interface with air or another material with a sufficiently low index of refraction. The entry surface generally prohibits light from entering the film at internal angles greater than about 40 degrees from a normal direction defined by the entry surface. 
     Optical films may be attached to the outside surface of a cover film using an adhesive. Useful adhesives include UV or thermally cured adhesives and pressure sensitive adhesives. 
     The light-transmissive plate  122  is or comprises a self supporting substrate having two major surfaces that is light-transmissive or clear and provides support to any cover films or optical films. The light-transmissive plate may typically be comprised of a diffuser plate, clear plate, or a lightguide plate. The light-transmissive plate may comprise a single layered substrate or may have multiple layers, for example, may be a composite of multiple layers of materials such as films. The light-transmissive plate should have sufficient rigidity such that it remains substantially planar singularly or as part of an assembly within a cover film. A diffuser plate is used to diffuse the light received from the light sources (light input surface), which results in an increase in the uniformity of the illumination light incident on the LC panel  102  from the light output surface. Consequently, this results in an image perceived by the viewer that is more uniformly bright. A lightguide plate is used to direct and disperse light from a linear light source located near one edge of the lightguide plate. Light is dispersed in a relatively regular pattern over the area of the lightguide plate. Typically a lightguide plate is used in devices employing edge-lit backlights. In other embodiments, light management assemblies of the invention may include two or more light-transmissive plates and may contain optical film(s) between the two or more light-transmissive plates. 
     The cover film  124  covers at least one major surface of the light-transmissive plate  122 . In this embodiment, the cover film  124  encapsulates the light-transmissive plate  122 . The cover film in this embodiment is used to provide a void  128  to prevent or inhibit “wet-out” between the surfaces of the light-transmissive plate and the optical film. In some embodiments, a cover film that encapsulates at least a light-transmissive plate may have a vent hole in the cover film. 
     Voids also prevent adjacent surfaces from sticking together and thus, decouple thermal expansion differences between layers. The separation of optical surfaces is in some cases, required to provide desirable optical and mechanical performance over a wide range of environmental conditions. Voids can be created by separating two adjacent surfaces—through the use of structured surfaces or pressure. 
     The cover film also provides support for the optical film(s) and keeps the optical film(s) flat. The cover film also confines the optical film(s) during any thermal expansion of the optical film(s). The support provided by the cover film is particularly useful when a display is subjected to varied environmental conditions. The cover film allows for the use of thinner optical films that will not otherwise meet environmental requirements as independent films due to physical deformation. 
     The cover film may typically be polymeric, is light transmissive, and capable of remaining substantially flat when used in an LC display device. Useful cover films include those films comprising amorphous polymers and semicrystalline polymers. Useful cover films include those that comprise or are selected from the group consisting of polyolefins such as polyethylene and polypropylene; polyesters such as polyethylene terephthalate and polyethylene naphthalate; polycarbonates, acrylics, such as polymethylmethacrylate; and polystyrenes. In certain embodiments of the present invention, the cover film is or may comprise any light-transmissive films that are heat-shrinkable. In certain other embodiments of the present invention, for example, where a reflective polarizer is placed between a light-transmissive plate and a cover film, cover films having minimal birefringence are desirable. The cover films may also have desirable properties such as being antistatic, germicidal, UV light absorbing, or combinations thereof. 
     In this embodiment, the optical film  126  may comprise a reflective polarizer or a brightness enhancement layer. The light sources  116  typically produce unpolarized light but the lower absorbing polarizer  110  only transmits a single polarization state, and so about half of the light generated by the light sources  116  is not transmitted through to the LC layer  104 . The optical film  126 , however, may be used to reflect the light that would otherwise be absorbed in the lower absorbing polarizer, and so this light may be recycled by reflection between the optical film  126  and the reflector  118 . At least some of the light reflected by the optical film  126  may be depolarized, and subsequently returned to the optical film  126  in a polarization state that is transmitted through the reflecting polarizer  124  and the lower absorbing polarizer  110  to the LC layer  104 . In this manner, the optical film  126  may be used to increase the fraction of light emitted by the light sources  116  that reaches the LC layer  104 , and so the image produced by the display device  100  is brighter. 
     Any suitable type of reflective polarizer may be used, for example, multilayer optical film (MOF) reflective polarizers; diffusely reflective polarizing film (DRPF), such as continuous/disperse phase polarizers, wire grid reflective polarizers, fiber reflective polarizers such as those described in US 2005/0193577, 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 MOF reflective polarizers include Vikuiti™ DBEF-D200 and DBEF-D440 multilayer 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 multilayer 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 this embodiment, the optical film  126  may also comprise a brightness enhancing layer. A brightness enhancing layer is one 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 LC layer  104 , thus increasing the brightness of the image seen by the viewer. One example 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 the display device include 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. 
     Depending upon needs and desires, other useful optical films for use in the light management assemblies of the invention include absorbing polarizers, turning films (such as light redirecting films having prisms facing towards the light guide), diffuser films (such as a film having hemispherical structures facing towards the liquid crystal panel), and composite optical films (fiber reinforced optical films such as those described in US 2006/0257678). 
     In other embodiments different types of optical films are desirably placed in the structure or outside of the structure of the light management assemblies of the invention. For example, compensation films, retardation films, absorbing polarizers and reflective polarizers may be desirably used above the output surface of the cover film; reflective films may be desirably placed below the light-transmissive plate; and prismatic films, diffusion films, multifunctional films, collimation films, transmissive films, and lens sheets may be desirably placed anywhere inside or outside of the light assemblies of the invention. 
     Another embodiment of a light management assembly of the invention is shown in  FIG. 2 . In this embodiment, light management assembly  200  includes a light-transmissive plate  202 , a cover film  204  encapsulating the light-transmissive plate, a first optical film  206  attached to the outside or output surface  205  of the cover film, a second optical film  208  between the output surface  210  of the light-transmissive plate and the input surface  212  of the cover film, a void  214  between the light-transmissive plate and the second optical film, and a void  215  between the second optical film  208  and cover film input surface  212 . In this embodiment, output surface  210  of the light-transmissive plate  202  has a structured surface facing the input surface  211  of the second optical film and the second optical film has a structured output surface  217  facing input surface  212  of the cover film. Alternatively, the input surface  211  of the optical film may be a structured surface in addition to, or, in place of, the structured output surface  210  of the light-transmissive plate. The voids  214 ,  215  inhibit “wet-out” between the second optical film and the light-transmissive plate and the second optical film and the cover film. In this embodiment, for example, the first optical film may comprise, but is not limited to, a reflective polarizer and the second optical film may comprise, but is not limited to, a brightness enhancement layer. 
     Another embodiment of a light management assembly of the invention is shown in  FIG. 3 . In this embodiment, light management assembly  300  includes a light-transmissive plate  302 , a cover film  304  encapsulating the light-transmissive plate, an optical film  306  between the output surface  308  of the light-transmissive plate and the input surface  310  of the cover film, and voids  312 ,  313  between the light-transmissive plate and the optical film and the optical film and the input surface  310  of the cover film. In this embodiment, light-transmissive plate has a structured output surface  308  facing the input surface  314  of the optical film and the optical film  306  has a structured output surface  315  facing input surface  310  of the cover film. Alternatively, the light transmissive plate could have a smooth output surface  308  facing a structured input surface  314  of the optical film. In this embodiment, for example, the optical film may comprise, but is not limited to, a reflective polarizer or a brightness enhancement layer. 
     Another embodiment of a light management assembly of the invention is shown in  FIG. 4 . In this embodiment, light management assembly  400  includes a light-transmissive plate  402 , a cover film  404  encapsulating the light-transmissive plate  402 , a first optical film  406 , a second optical film  408  between the output surface  410  of the light-transmissive plate and the input surface  412  of the first optical film, and an void  414  between the light-transmissive plate and the second optical film  408 . Further, this embodiment includes voids  415 ,  417  between the first and second optical films and between the first optical film  406  and the input surface  419  of the cover film  404 . Output surface  410  of the plate has a structured (matte) surface and output surfaces  413 ,  420  of optical films  406 ,  408  are structured surfaces. In this embodiment, for example, the first optical film may comprise, but is not limited to, another brightness enhancement layer having a prismatic surface and the second optical film may comprise, but is not limited to, a brightness enhancement layer having a prismatic surface on the output surface. 
     In another embodiment of a light management assembly shown in  FIG. 5 , light management assembly  500  includes a light-transmissive plate  502 , cover film  504  encapsulating the light-transmissive plate  502 , and an optical film  506  between the input surface  508  of the light-transmissive diffuser plate and the output surface  510  of cover film  504 . Voids  512 ,  513  are between the input surface  508  of the light-transmissive plate and the optical film and the output surface  510  of the cover film. In this embodiment, optical film  506  has structured input and output surfaces facing the cover film and the light-transmissive plate. In this embodiment, useful optical films may include, but are not limited to, light diverting layers, as described in U.S. patent application publication No. 20070030415 A1, prismatic brightness enhancement films (BEF), available from 3M Company, St. Paul, Minn., or diffuser films. 
     In another embodiment of a light management assembly shown in  FIG. 6 , light management assembly  600  includes a light-transmissive plate  602 , cover film  604  encapsulating the light-transmissive plate  602 , and an optical film  606  attached to the outside or input surface  607  of the cover film and an void  608  between the light-transmissive plate  602  and the cover film  604 . In this embodiment, the optical film is attached to the input surface  607  of the cover film and the input surface  610  of the light-transmissive plate is a structured surface. In this embodiment, useful optical films include, but are not limited to, diffuser films or prismatic films. 
     In another embodiment of a light management assembly shown in  FIG. 7 , light management assembly  700  includes a light-transmissive plate  702 , first cover film  704  encapsulating the light-transmissive plate, optical film  705  adjacent to the outside or output surface  706  of the first cover film  704 , and second cover film  708  encapsulating the optical film  705  and first cover film  704 . Voids  710 ,  711  are present between the optical film and the second cover film and the optical film and the first cover film. In this embodiment, optical film  705  has structured input  712  and output  714  surfaces. If the optical film were attached to the first cover film, voids would not be present between the first cover film and the optical film. It is to be understood that the illustrated second cover film shown in  FIG. 7  is applicable to any light management assemblies described or depicted in this application. 
     Other embodiments of the light management assemblies of the invention may have a window in the cover film. For example, light management assembly  800  in  FIG. 8  includes a light transmissive plate  802 , cover film  804  covering the structured input surface  803  of the light transmissive plate and an optical film  806  adjacent the output surface  805  of the light transmissive plate. The window  808  in the cover film  804  defines a cover film frame  810  and an opening  811 . The cover film frame  810  provides positioning support for the optical film  806 . In this embodiment, a void  812  is present between the cover film and the input surface  803  of the light-transmissive plate. Voids  813  may or may not be present between the optical film and the cover film frame  810  depending upon whether the ultimate viewing surface area of a device is within or without the area of the window. In this embodiment, the light-transmissive plate may have structured or matte input and output surfaces and the optical film may or may not have one or two structured surfaces. 
     In some embodiments of the light management assemblies of the invention, the cover film may be applied over the light-transmissive plate using a conventional heat-sealing process. In one embodiment of a heat sealing process, sheets of film are placed under and over a light-transmissive plate (and any optical film(s)) and the individual films are heat sealed together, and any excess film may be trimmed. Alternatively, a sufficiently large sheet of film can be cut and placed under and folded over a light-transmissive plate (and any optical film(s)) and the edges can be heat sealed together and any excess film may be trimmed. Additionally, heat-shrinkable films are shrunk taut over the light-transmissive plate in such processes. The stiffness and elasticity of these types of cover film adds stability to optical films attached to, or confined by, those cover sheets. This is especially useful during environmental conditions where the independent films may otherwise deform. Windows in the cover film may be cut into the cover film pre or post application to or over a light-transmissive plate and any optical film(s). 
     In other embodiments, a light management assembly may include a single or top sheet of cover film  902  of appropriate dimensions, placed over a light-transmissive plate  904 , and any optical film(s)  905 , and attached to the edges  906  of the light-transmissive plate. An example of such a light management assembly  900  is shown in  FIG. 9 . However, it is to be understood that the illustrated cover film attachment shown in  FIG. 9 , is applicable to any light management assemblies described or depicted in this application. 
     Although not shown, the cover film can also be attached to the edges or bottom or top surface of the light-transmissive plate by using adhesives, for example, hot melt and pressure sensitive adhesives; tapes; by heat bonding, or by mechanical means such as a securing band made of metal, plastic, or rubber, around the edges of the plate, on top of the cover film, or attached to the cover film, or a spline member that is press fit into a groove or channel, on top of the cover film and around the perimeter of the plate. The light management assemblies of the invention are useful for making or assembling display devices, for example LCDs. For example, a method of making an LCD comprises providing a light management assembly as described in this application, and then combining the light management assembly with at least a LC panel and a backlight to form a liquid crystal display device. In one embodiment of the above method, the light management assembly is assembled in one location, transported to another location, and then mated with at least an LC panel and a backlight. In another embodiment, the light management assembly, the backlight, and the LC panel are each made in a different location, and transported to another location to be assembled into and LCD device. 
     EXAMPLES 
     Test Methods 
     Visual Appearance 
     Visual appearance (VA) is a judgment as to whether the light management assembly provides a uniform appearance, that is, an appearance having no visual defects. Lack of a uniform appearance can take the form of any visual difference in the area of the display. One example of a visual defect is a noticeable wetout region. A wetout region appears different from the area around it, possibly displaying Newton Ring phenomena or a change in brightness. Other visual defects include those caused by buckling of the optical film and bubbles between laminated films. Certain conditions may cause a film to buckle, displaying regions that are raised from the bulk of the sheet. Bubbles between laminated films will cause a noticeable change in brightness. 
     Visual appearance is rated as Excellent, Good, or Unacceptable. An excellent visual appearance is defined as a flat light management assembly displaying uniform brightness at all viewing angles, showing nothing that catches the eye. A good visual appearance is defined as a light management assembly having uniform brightness at all viewing angles, but showing few small defects that catch the eye. An unacceptable visual appearance is defined as a light management assembly having a noticeable wetout region, film buckling, or bubbles between films causing noticeable changes in brightness. 
     Optical Gain Measurement 
     Although specific details are given for completeness, it should be readily recognized that similar results can be obtained using modifications of the following approach using other commercially available equipment. 
     Optical performance of the films was measured using a SpectraScan™ PR-650 SpectraColorimeter with an MS-75 lens, available from Photo Research, Inc, Chatsworth, Calif. The optical articles were placed on top of a diffusely transmissive hollow light box. The diffuse transmission and reflection of the light box can be described as Lambertian. The light box was a six-sided hollow cube measuring approximately 12.5 cm×12.5 cm×11.5 cm (L×W×H) made from diffuse PTFE plates of ˜6 mm thickness. One face of the box is chosen as the sample surface. The hollow light box had a diffuse reflectance of ˜0.83 measured at the sample surface (e.g. ˜83%, averaged over the 400-700 nm wavelength range, box reflectance measurement method described further below). During the gain test, the box is illuminated from within through a ˜1 cm circular hole in the bottom of the box (opposite the sample surface, with the light directed towards the sample surface from the inside). This illumination is provided using a stabilized broadband incandescent light source attached to a fiber-optic bundle used to direct the light (Fostec DCR-II with ˜1 cm diameter fiber bundle extension from Schott-Fostec LLC, Marlborough Mass. and Auburn, N.Y.). A standard linear absorbing polarizer (such as Melles Griot 03 FPG 007) was placed between the sample box and the camera. The camera was focused on the sample surface of the light box at a distance of ˜34 cm and the absorbing polarizer is placed ˜2.5 cm from the camera lens. 
     The luminance of the illuminated light box, measured with the polarizer in place and no sample optical article, was &gt;150 cd/m 2 . The sample luminance is measured with the PR-650 at normal incidence to the plane of the box sample surface when the sample optical articles are placed parallel to the box sample surface, the sample articles being in general contact with the box. The relative gain is calculated by comparing this sample luminance to the luminance measured in the same fashion from the light box alone. The entire measurement was carried out in a black enclosure to eliminate stray light sources. When the relative gain of optical containing reflective polarizing elements were tested, the pass axis of the reflective polarizing element was aligned with the pass axis of the absorbing polarizer of the test system. The relative optical gain of a given sample was obtained by dividing the optical gain of a sample in question by the optical gain of a reference, or control sample. 
     Shrink-Wrap Method 
     The light-transmissive plate was prepared by smoothing the edges using 400-grit sandpaper. The corners of the light-transmissive plate were rounded slightly using 400-grit sandpaper. In the case where a lightguide plate was used, no smoothing or rounding was performed. The light-transmissive plate was cleaned of debris using a tacky roller (Teknek DCR clean roller system, Inchinnan, Scotland). An oversized piece of cover film was cut from a roll of cover film. (For example, an 11 inch×22 inch (27.9 cm×55.9 cm) light-transmissive plate would require about a 30 inch (76.2 cm) long piece of pre-folded cover film from an 18″ (45.7 cm) wide roll of folded film). One side of the pre-folded film was then welded, perpendicular to the fold, using an impulse sealer (Heat Shrink Replay 55, available from Minipak-Torre Systems, Italy, to form an L-shaped pocket. The debris-free plate was slipped into the film pocket and tucked up tightly to the corner of the “L”. The film pocket containing the plate was then placed into the impulse sealer with a minimum amount of slack in the film to weld the 2 remaining open edges of the film. The film covered plate was then placed in an oven at a temperature of about 93° C. to shrink the cover film around the plate. To clean up any remaining wrinkles in the film, a hot air gun (MHT Products Inc. Model 750 Heat Gun, Plymouth, Minn.) was used to warm the “wrinkled” regions of the film, shrinking out the wrinkles. 
     Polarizing Reflector Film Preparation 3M™ Vikuiti™ Dual Brightness Enhancement Film (DBEF-Q) was coated on one side with a beaded diffuser solution and dried, substantially as described in U.S. application Ser. No. 11/427,948, filed Jun. 30, 2006. The opposite side of the film was then coated with an acrylic pressure sensitive adhesive (PSA) solution (as described below in Examples 1-9), dried, and then covered with a protective liner to protect the PSA coating. Before lamination to a substrate, the protective liner was removed. 
     GLOSSARY 
       
     
       
         
           
               
               
               
             
               
                   
               
               
                 Abbreviation 
                 Description 
                 Availability 
               
               
                   
               
             
            
               
                  75 LEG 
                 Shrink film, polyolefin, low 
                 Bemis Clysar, Inc., 
               
               
                   
                 shrink force, 75 gauge 
                 Oshkosh, WI 
               
               
                  60 LLG 
                 Linear, low density 
                 Bemis Clysar, Inc. 
               
               
                   
                 polyethylene shrink film, 
               
               
                   
                 60 gauge 
               
               
                 125 ABL 
                 Crosslinked, polyethylene, 
                 Bemis Clysar, Inc. 
               
               
                   
                 monolayer, 125 gauge 
               
               
                  75 LEFP 
                 Shrink film, polyolefin, low 
                 Bemis Clysar, Inc. 
               
               
                   
                 shrink force, 75 gauge 
               
               
                  50 VHGF 
                 Shrink film, linear low 
                 Bemis Clysar, Inc. 
               
               
                   
                 density polyolefin 50 gauge 
               
               
                 150 HPGF 
                 Shrink film, linear low 
                 Bemis Clysar, Inc. 
               
               
                   
                 density, polyolefin, 
               
               
                   
                 crosslinked, 150 gauge 
               
               
                  75 LLGF 
                 Shrink film, linear low 
                 Bemis Clysar, Inc. 
               
               
                   
                 density polyethylene, 
               
               
                   
                 monolayer, 75 gauge 
               
               
                  50 VEZ 
                 Shrink film, polyolefin, 
                 Bemis Clysar, Inc. 
               
               
                   
                 multilayer. 50 gauge 
               
               
                 Shrink Box 
                 Shrink film, polyolefin, high 
                 Bemis Clysar, Inc. 
               
               
                   
                 shrink force 
               
               
                 BEF 
                 Light directing film (ie. 
                 3M Company Saint Paul, 
               
               
                   
                 BEFII 90/50) 
                 Minnesota 
               
               
                 DBEF 
                 Polarizing reflector optical 
                 3M Company 
               
               
                   
                 film 
               
               
                   
               
            
           
         
       
     
     Examples 1-9 
     Matte finished light-transmissive plates ((Model # RM802, from Sumitomo Chemical Company, Tokyo, JP) were enveloped in various shrink-wrap cover films as described above. DBEF films were prepared as described above having a beaded diffuser coating on one side and an acrylic PSA on the other. The acrylic PSA was a copolymer of isooctylacrylate and acrylic acid (90:10), and contained 30 parts of Pinecrystal™ KE-311 (Arakawa Chemical (USA) Inc, Chicago, Ill.). The polarizing film was laminated to the cover film on the output side of the light transmissive plate. The Control did not employ the cover film, and was a layered assembly of the same matte finished light-transmissive plate and the same DBEF. The relative optical gain for each example is shown in Table 1. 
     
       
         
           
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                   
                   
                 Relative 
               
               
                   
                   
                 Optical 
               
               
                 Example 
                 Cover Film 
                 Gain 
               
               
                   
               
             
            
               
                 1 
                 Shrink Box 
                 0.97 
               
               
                 2 
                  75 LEG 
                 1.00 
               
               
                 3 
                  60 LLG 
                 0.96 
               
               
                 4 
                 125 ABL 
                 0.97 
               
               
                 5 
                  75 LEFP 
                 0.98 
               
               
                 6 
                  50 VHG 
                 0.99 
               
               
                 7 
                 150 HPG 
                 0.98 
               
               
                 8 
                  75 LLG 
                 0.96 
               
               
                 9 
                  50 VEZ 
                 0.98 
               
               
                 Control 
                 — 
                 1.00 
               
               
                   
               
            
           
         
       
     
     Example 10 
     A light management assembly was prepared as described above in Example 10, except BEF film was also added between the output surface of the light transmissive plate and the cover film. The relative optical gain was 0.98. The relative optical gain of the control assembly (separate pieces with no cover film and no PSA on the DBEF film) was 1. 
     Example 11 
     A light management assembly was prepared as described above in Example 9, except the light transmissive plate had dimensions of 49.6 cm×28.3 cm×0.2 cm. The light management assembly was placed in a frame similar to that of an actual backlight housing and placed in an environmental testing chamber (Envirotronics model# FLX900-2-6-WC, Grand Rapids Mich.). The assembly was exposed to environmental conditions of 65° C. and 95% relative humidity (RH) for 100 hours, and then 90° C. for 24 hours. During and after both environmental conditions, the assembly showed excellent visual appearance, with only minor plate deformation. 
     Example 12 
     A light management assembly was prepared by placing a matte finished diffuser film (diffuser having a double sided matte finish, from an Apple™ 12 inch diameter Mac™ Powerbook™ laptop computer) on the smooth surface of the light guide plate (from the laptop computer described above), and two pieces of BEF film on top of the matte finished diffuser film. The plate and films were enveloped in 75 LEF cover film as described above. The cover film was taut after heating and shrinking. The peaked structures on the BEF films were enough to substantially preserve the voids between the first and second BEF films, and the upper BEF film and the shrink wrap envelop. The rough pattern on the bottom of the light guide was enough to substantially preserve the void between the light guide and the cover film, therefore avoiding wetout. The sample showed excellent visual appearance. 
     Demonstrative Example 1 
     A reflective polarizing film having a beaded diffuser coating on one side, prepared as described above, was placed between two light transmissive plates having dimensions of 49.6 cm×28.3 cm×0.2 cm. The bottom or input plate had a matte finish facing the smooth side of the reflective polarizing film. This matte finish was enough to preserve the void between the bottom plate and the film. The output plate (CYRO Acrylite™ FF, CYRO Industries, Parsippany, N.Y.) had a smooth surface facing the beaded diffuser side of the polarizing film. The output plate served as the cover film. The diffuser coating was enough to preserve the void between the film and the upper cover. The light transmissive plates were glued on the edges using an epoxy adhesive (DP100, 3M Company), with the film, which was slightly smaller in dimension than the plates, floating free between the plates. The finished light management assembly showed no visual wetout. The light management assembly was placed in a frame similar to that of an actual backlight housing and was exposed to environmental conditions of 65° C. and 95% RH for 100 hours. After exposure, the light management assembly showed excellent visual appearance, with no noticeable wetout and only minor deformation of the polarizing film. The voids allowed the film to move independently in two dimensions relative the covers, therefore minimizing stress and deformation of the film. 
     Comparative Example 1 
     A light management assembly was assembled as described in Example 13 except that the bottom or input light transmissive plate (CYRO Acrylite FF, CYRO Industries) had a smooth surface facing the smooth surface of the reflective polarizing film. The smooth finish on the light-transmissive plate allowed for wetout regions between the light-transmissive plate the smooth side of the reflective polarizing film. The wetout regions were not only visible, the smooth surfaces of the light-transmissive plate and the reflective polarizing film in the wetout regions were partially bonded together such that the light-transmissive plate and the reflective polarizing film did not move independently. The light management assembly was placed in a frame similar to that of an actual backlight housing and exposed to environmental conditions of 65° C. and 95% RH for 100 hours. After exposure, the light management assembly showed an unacceptable visual appearance, with noticeable deformation of the polarizing film due to the partial bonding in some regions of the two adjacent smooth surfaces, and free movement on other regions. 
     Comparative Example 2 
     Comparative Example 2 was prepared as described above for Example 13, except that the bottom or input light transmissive plate had a smooth surface facing the smooth surface of a BEF film. The smooth finish on the diffuser plate allowed for wetout regions between the diffuser plate and the shrink film, along with wet out of the BEF film with the diffuser plate. The light management assembly was placed in a frame similar to that of an actual backlight housing and the assembly was exposed to environmental conditions of 65° C. and 95% RH for 100 hrs. After testing, the sample provided an unacceptable visual appearance due to visible wetout regions. 
     Various modifications and alterations of this invention will be apparent to those skilled in the art without departing from the scope and spirit of this invention, and it should be understood that this invention is not limited to the illustrative embodiments set forth herein. All U.S. patents, patent application publications, and other patent and non-patent documents referred to herein are incorporated by reference in their entireties, except to the extent any subject matter therein is inconsistent with the foregoing disclosure.