Patent Abstract:
Pre-aligned optical layers are stacked and arranged such that an adhesive layer, which is stacked onto the optical layers, contacts at least the uppermost layer and lowermost layer. The resulting subassemblies can be assembled into an optical display without individual handling of the layers, which reduces installation time and manufacturing costs.

Full Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates to optical displays. In particular, the present invention relates to pre-stacked optical films for assembly into an optical display.  
         [0002]     Optical displays, such as backlit liquid crystal displays (LCDs), are used in a wide variety of applications including mobile telephones, personal digital assistants (PDAs), electronic games, laptop computers, monitors, and television screens. Optical films are stacked within an optical display in order to enhance brightness and improve display performance without sacrificing battery life.  
         [0003]     Presently, films used in displays are provided as individual films to display manufacturers. The films include tabs that are useful in orienting and positioning the films, and cover sheets to protect the surfaces of the films. During assembly of a display, the cover sheets of the films are removed, and the films are stacked, one by one, into a frame that fits between a backlight assembly and an LCD panel. Double-coated rim tape is placed over the stacked films, which seals the edges of the films. A cover sheet is then placed over the rim tape. To finish the display, the cover sheet is removed, and the LCD panel is adhered to the rim tape.  
         [0004]     This process is difficult and costly in terms of time and material. Creating tabs on the films increases the amount of waste material that is produced and increases the width of the bezel, or edge, that must extend around the perimeter of the display to cover the tab. Because the tabs extend to the edge of the rim tape, a path is created that allows debris to enter and settle between the films. Removing cover sheets from individual films increases assembly time and the possibility of damaging the films. In addition, as optical films become thinner and thinner, it becomes increasingly difficult to handle an individual optical film. Thus, resolving these problems would increase product output by increasing assembly efficiency and reducing the number of damaged films.  
       BRIEF SUMMARY OF THE INVENTION  
       [0005]     The present invention is an optical subassembly for use in an optical display that includes a plurality of stacked optical films and an adhesive layer. The adhesive layer contacts the uppermost and lowermost films of the stack to hold the stack as a unit, so that the stack can be assembled into an optical display without individual handling of the optical films of the stack. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]      FIGS. 1   a - 1   c  are exploded views of representative embodiments of optical displays.  
         [0007]      FIGS. 2   a  and  2   b  are top and side views of a first representative embodiment of an optical film unit.  
         [0008]      FIGS. 2   c  and  2   d  are top views of second and third representative embodiments of an optical film unit.  
         [0009]      FIGS. 3   a  and  3   b  are top and side views of a fourth representative embodiment of an optical film unit.  
         [0010]      FIG. 3   c  is a top view of a fifth representative embodiment of an optical film unit.  
         [0011]      FIGS. 4   a  and  4   b  are top and side views of a sixth representative embodiment of an optical film unit.  
         [0012]      FIG. 4   c  is a top view of a seventh representative embodiment of an optical film unit.  
         [0013]      FIG. 5  is a cross-sectional view of an optical film unit installed in a chassis.  
         [0014]      FIG. 6  is a cross-sectional view of an optical film package installed in a chassis. 
     
    
     DETAILED DESCRIPTION  
       [0015]      FIG. 1   a  shows a schematic diagram of optical display  10   a,  which is not drawn to scale. Optical display  10   a  includes chassis  12 ; backlight unit  14  with reflector  16 , light guide  18 , and light source  20 ; diffuser  22 ; prismatic films  24  and  26 ; diffuser  28 ; reflective polarizer  30 ; adhesive layer  32 ; display panel  34 ; optical film unit  36  (formed by elements  22 - 32 ); and optical film package  38  (formed by optical film unit  36  and light guide  18 ).  
         [0016]     Chassis  12  is typically a plastic frame for supporting components of optical display  10 . In this embodiment, backlight unit  14  includes one or more layers of reflector  16 , along with light guide  18 , and light source  20 . Light guide  18  may include special features for directing light and can take the form of a slab as shown or other forms such as a wedge.  
         [0017]     Light source  20  may be any suitable type of light source such as a fluorescent lamp, light emitting diodes, or direct lit. Light from light source  20  is directed toward display panel  34  via light guide  18 .  
         [0018]     Next, diffuser  22  is stacked onto light guide  18 . Diffuser  22  homogenizes the intensity of the light from light guide  18 .  
         [0019]     Prismatic films  24  and  26  are stacked onto diffuser  22 . Films  24  and  26  contain arrays of prisms for directing light toward display panel  34 . Relative to each other, films  24  and  26  may be arranged such that their prism arrays run parallel, or more typically, the prism arrays run non-parallel. As shown in this embodiment, the prism arrays run perpendicular relative to each other.  
         [0020]     Diffuser  28  is stacked onto prismatic film  26 . Diffuser  28  is typically a relatively weak diffuser and, as described in regard to diffuser  22 , homogenizes the light intensity so that it is more uniform.  
         [0021]     The last film shown stacked is reflective polarizer  30 . Reflective polarizer  30  may be any of a number of types of reflective polarizers including a multi-polymer film, a cholesteric polarizer, or a wire-grid polarizer. Reflective polarizer  30  recycles light that is in the wrong polarization state and will not be transmitted as image light.  
         [0022]     Typically, reflective polarizer  30  is laminated to the back of panel  34 . However, as in the case shown here and in the following embodiments, reflective polarizer  30  may be stacked with the other layers.  
         [0023]     The next layer is adhesive layer  32  (in bold). Adhesive layer  32  is typically double-coated rim tape or shading frame, but it may also be an adhesive coating. One surface of adhesive layer  32  is black and contacts display panel  34 . The opposite surface is colored white or silver and contacts a portion of each of the layers underneath it. Light tends to leak around the film layers, and the reflective surface of adhesive layer  32  recycles the leaked light for redirection. The black surface reduces a “halo effect” around the optical display, which is a bright line that sometimes forms along its perimeter. Suitable rim tapes that may be used include 3M Company&#39;s Black and White Double Coated Polyester Tape 4003S, 4003T, 4007, 4037, and 4040 and Black and Silver Double Coated Polyester Tape 5173. If desired, 3M Company&#39;s Black and White Single Coated Polyester Tape 4038 and 4039 may also be used.  
         [0024]     It should be noted that layers  22  through  30  represent one embodiment. Depending on needs and desires, some of layers  22  through  30  may be omitted, added to, or substituted. For example, a turning film with its prisms facing either up or down may replace prismatic films  24  and  26 , or a Vikuiti BEF-RP 90/24 reflective polarizer with prisms may be added. In addition, each layer becomes progressively smaller, and their edges or perimeters are serially recessed such that portions of the layers contact adhesive layer  32 , which will be explained in more detail below.  
         [0025]     Adhesive layer  32  may contact layers  22  through  30  to form optical film unit  36 . Alternatively, adhesive layer  32  may additionally contact light guide  18  to form optical film package  38 . Optical film unit  36  and optical film package  38  may be referred to as optical subassemblies. Unit  36  and package  38  are assembled prior to delivery to a manufacturer for assembly of optical display  10 . The layers are pre-aligned, so no tabs are needed. Adhesive layer  32  seals the edges of the layers, which removes any entry point for debris. However, as will be shown below, it is unnecessary for adhesive layer  32  to completely circumscribe the perimeters of the included layers.  
         [0026]      FIG. 1   b  is a schematic diagram of optical display  10   b.  Display  10   b  includes the same layers as display  10   a  but additionally includes adhesive layer  25 .  
         [0027]     Light guide  18 , diffuser  22 , and prismatic film  24  become serially smaller as previously shown. Adhesive layer  25  is stacked onto prismatic film  24  and sized similarly to adhesive layer  32  such that one surface of adhesive layer  25  contacts and secures each of layers  18  through  24  or  22  through  24 . Next, prismatic film  26 , diffuser  28 , and reflective polarizer  30  are stacked. Instead of continuing to decrease in size as in  FIG. 1   a,  however, each layer becomes serially larger. Adhesive layer  32 , which is sized identically to that shown for display  10   a,  is then stacked onto reflective polarizer  30 . The remaining surface of adhesive layer  25  contacts layers  26  through  32 .  
         [0028]     Adhesive layer  25 , unlike adhesive layer  32  is not rim tape but is any type of suitable double-coated tape. With this embodiment, the layers may be more secure, and the smallest layer of display  10   b  is larger than the smallest layer of display  10   a.  Thus, a larger viewing area is provided without increasing the overall size of the layers.  
         [0029]      FIG. 1   c  is a schematic diagram of optical display  10   c.  Again, display  10   c  includes the same layers as display  10   a.    
         [0030]     Here, light guide  18  is larger than layers  22  through  30 . Layers  22  through  30  are the same size, and adhesive layer  32  only contacts a portion of light guide  18  and reflective polarizer  30 . The remaining layers are trapped between light guide  10  and reflective polarizer  30 , and the edges of each layer are sealed to prevent debris from entering.  
         [0031]     Note that in order to form unit  36 , diffuser  22  would be sized larger than the remaining layers to adhere to adhesive layer  32 . As with display  10   b,  the smallest layers are larger than the smallest layer of display  10   a,  which provides a larger viewing area without increasing the films&#39; overall size.  
         [0032]      FIGS. 2   a  and  2   b  are top and side views, respectively, of optical film unit  36 . Unit  36  includes adhesive layer  32  having outer perimeter  32   p ′ and inner perimeter  32   p ″, diffuser  28  having outer perimeter  28   p,  and reflective polarizer  30  having outer perimeter  30   p.  Recess distances d 1 , d 2 , and d 3  are also shown in  FIG. 2   a.  Only two layers,  28  and  30 , are shown for simplicity. However, any number and type of film used in managing light for an optical display, such as those described for  FIGS. 1   a - 1   c,  may be used.  
         [0033]     Diffuser  28  is the bottom layer with reflective polarizer  30  being stacked on top. As is evident in  FIGS. 2   a  and  2   b,  diffuser  28  is larger than reflective polarizer  30 , and the films are arranged such that outer perimeter  30   p  is recessed by distance d 1  from outer perimeter  28   p.    
         [0034]     In this embodiment, adhesive layer  32  has a frame-type shape and is stacked over diffuser  28  and reflective polarizer  30 . Inner perimeter  32   p ″ is recessed by distance d 2  from outer perimeter  30   p,  while outer perimeter  32   p ′ extends beyond outer perimeter  28   p  by distance d 3 . Thus, a portion of each of diffuser  28  and reflective polarizer  30  contacts and adheres to adhesive layer  32 . Ideally, a protective cover sheet (not shown) is stacked over adhesive layer  32  and under the lowermost layer. The cover sheets are removed prior to attaching panel  34  to unit  36  to create a display module. Suitable protective cover sheets and their method of attachment are described in Ser. No. 10/750,553, filed on Dec. 31, 2003.  
         [0035]     Distances d 1 , d 2 , and d 3  are about 2.0 mm or less or, more typically, about 1.0 mm or less. Distances d 1 -d 3  may not be identical to each other and may not be uniform along any of the entire perimeters of the layers.  
         [0036]     As evident in  FIG. 2   b,  adhesive  32  must conform to the geometry of the staggered edges of the layers in order to contact a portion of each layer. It is shown exaggerated for purposes of illustration. The films are thin, and adhesive layer  32  would not normally require such a conformation.  
         [0037]     Unit  36  is much easier to handle than each film individually and is sealed, which prevents debris from accumulating between films. The films have no tabs, because they are pre-aligned and the manufacturer need only align outer perimeter  32   p ′ within a chassis in order to correctly position optical film unit  36 . In addition, tab-less films result in narrower borders around the viewing area. This allows manufacturers to increase the size of the viewing area without increasing the overall size of the device. This is especially significant for small devices such as mobile phones and PDAs.  
         [0038]      FIG. 2   c  is a top view of optical unit  36   a,  which is similar to unit  36  but includes holes  40  and slots  42  within reflective polarizer  30 . Holes  40  may have any of a number of types of shapes such as circles or squares. Although two are shown here, there may be one or more along any portion of or all of outer perimeter  30   p.  Holes  40  should measure less than about 2 mm across, but will typically measure about 0.5 mm to about 1.0 mm.  
         [0039]     Slot  42  is also shown. Slot  42  may have any of a number of elongated shapes such as a rectangle or oval. There may be one or more of slot  42  along outer perimeter  30   p  and can be in any combination with holes  40 . Slot  42  may have any length, but its width should be less than 2 mm, typically between about 0.5 mm and 1.0 mm.  
         [0040]     Holes  40  and slot  42  should be about 0.50 mm or less from outer perimeter  30   p  and inner perimeter  32   p ″. Typically, additional layers sized the same as reflective polarizer  30  and also having holes  40  and/or slot  42  would be included. Only the lowermost layer is sized larger and does not include holes  40  or slot  42 . Thus, each of the layers is secured and sealed from entry of any debris.  
         [0041]     The use of slot  42  secures the layers as a unit, but also allows some movement of the layers in the direction of the width of slot  42 . Thus, this embodiment may better tolerate any adjustments between the layers should it be necessary.  
         [0042]      FIG. 2   d  is a top view of optical unit  36   b,  which is also similar to unit  36  but includes notches  30   n  on reflective polarizer  30 . Here, outer perimeter  30   p  extends out to outer perimeter  28   p  except where notches  30   n  are recessed by distance d 1 . There may be any number notches  30   n  having any size along outer perimeter  30   p.  Notches  30   n  may have any type of shape such as, for example, a triangular shape, and it is not necessary that perimeter  30   p  extend out to outer perimeter  28   p.    
         [0043]      FIGS. 3   a  and  3   b  are top and side views, respectively, of optical film unit  36   c.  Unit  36   c  includes diffuser  28  having edges  28   a  and  28   b,  reflective polarizer  30  having edges  30   a  and  30   b,  adhesive layer  32 ′ having outer edge  32 ′ o  and inner edge  32 ′ i,  and adhesive layer  32 ″ having outer edge  32 ″ o  and inner edge  32 ″ i.  Recessed distances d 1 , d 2 , and d 3  are also included. Edge  28   a  is opposite edge  28   b,  and likewise, edge  30   a  is opposite edge  30   b.    
         [0044]     Unlike the embodiment of unit  36 , the full perimeter of the films and adhesive layer are not staggered relative to one another. In addition, the adhesive layer is in the form of only a portion of a frame-type shape. Edges  30   a  and  30   b  are recessed from edges  28   a  and  28   b,  respectively, by distance d 1 . Edges  32 ′ i  and  32 ″ i  are recessed from edges  30   a  and  30   b,  respectively, by distance d 2 . Edges  32 ′ o  and  32 ″ o  extend beyond edges  28   a  and  28   b,  respectively, by distance d 3 . Again, distances d 1 -d 3  need not be identical to each other or uniform along each edge.  
         [0045]     Though unit  36   c  has two remaining edges of each layer that are not staggered and have no adhesive layer, unit  36   c  is still assembled and installed as a unit. The advantage is that a device into which it is installed will require only a minimal bezel to cover the two remaining edges. Thus, unit  36   c  provides a maximum viewing area in one dimension.  
         [0046]     Any two edges along the perimeters of diffuser  28  and reflective polarizer  30  may be staggered and secured with adhesive layers  32 ′ and  32 ″. In addition, it may be desirable to stagger and secure a third edge of unit  36   c.    
         [0047]      FIG. 3   c  is a top view of optical unit  36   d,  which is similar to unit  36   c  but includes adhesive layer  32  and shows outer perimeter  30   p.  Here, adhesive layer  32  has a frame-type shape that extends around the entire perimeter of the layers. Edges  28   a  and  30   a  are staggered relative to each other, and edges  28   b  and  30   b  are also staggered relative to each other as shown in unit  36   c.  The remaining two edges of films  28  and  30  are not staggered, and inner perimeter  32   p ″ is recessed from outer perimeter  30   p  by distance d 2 . The remaining edges of diffuser  28  do not contact adhesive layer  32 .  
         [0048]     Unit  36   d  also maximizes the viewing area in one dimension. In addition, additional layers may be added between films  28  and  30  that are sized the same as reflective polarizer  30  giving a configuration similar to that shown in  FIG. 1   c.    
         [0049]      FIGS. 4   a  and  4   b  are top and side views of optical film unit  36   e.  Unit  36   e  includes diffuser  28  having edge  28   a,  reflective polarizer  30  having edge  30   b,  and adhesive layer  32 ′ having outer edge  32 ′ o  and inner edge  32 ′ i.  Again, recessed distances d 1 , d 2 , and d 3  are shown.  
         [0050]     In this embodiment, only one edge is secured. Diffuser  28  is at the bottom of the stack followed by reflective polarizer  30  and then adhesive layer  32 ′. Edge  30   a  is recessed from edge  28   a  by distance d 1 . Edge  32 ′ i  is recessed from edge  30   a  by distance d 2 . Edge  32 ′ o  extends beyond edge  28   a  by distance d 3 . The advantages of unit  36   e  are that unit  36   e  is still handled as a unit instead of as single films, but if necessary, the films may be fanned out in order to remove any debris that may settle between the films.  
         [0051]      FIG. 4   c  is a top view of optical unit  36   f,  which is similar to unit  36   e  but includes adhesive layer  32  and outer perimeter  30   p.  Edges  28   a  and  30   a  are staggered relative to each other. The remaining edges are not staggered, and inner perimeter  32   p ″ is recessed from outer perimeter  30   p  by distance d 2 . The remaining edges of diffuser  28  do not contact adhesive layer  32 .  
         [0052]     Additional layers may also be added to any of the previous embodiments. For example, additional film layers and an additional adhesive layer such as shown in  FIG. 1   b  may be combined with the embodiment of unit  36   f.  In this example, only one edge of each layer would be serially staggered. In all embodiments, recessed distances d 1 -d 3  are typically 2.0 mm, but preferably 1.0 mm or less.  
         [0053]     The films and adhesive layers shown in these embodiments can have any geometric shape, including circular and oval shapes. In addition, these embodiments also apply to optical film package  38  ( FIGS. 1   a - 1   c ) simply by adding a light guide to the bottom of the plurality of stacked films.  
         [0054]      FIG. 5  shows optical film unit  36   e  as assembled into chassis  12 , which are not drawn to scale.  FIG. 5  includes chassis  12 , reflector  16 , light guide  18 , and unit  36   c  with adhesive layer  32 ′ and plurality of stacked optical films  44 . Films  44  are shown having three films, but it may include any number of films such as those shown in and described in reference to  FIGS. 1   a - 1   c.    
         [0055]     Light guide  18  is attached to chassis  12 . Unit  36   e  is installed by positioning the edge of adhesive layer  32 ′ within chassis  12 . Adhesive layer  32 ′ adheres to chassis  12  to secure unit  36   e.  As shown in  FIG. 5 , adhesive layer  32 ′ must conform to the geometry of the staggered layers and attachment to chassis  12 .  
         [0056]      FIG. 6  shows optical film package  38   a  as assembled into chassis  12   a,  which are not drawn to scale.  FIG. 6  includes chassis  12   a,  reflector  16 , and package  38   a  with light guide  18   a,  adhesive layer  32 ′, and plurality of stacked optical films  44 .  
         [0057]     In this embodiment, package  38   a  is installed by positioning adhesive layer  32 ′ within chassis  12   a.  Chassis  12  and chassis  12   a  and light guides  18  and  18   a  are slightly different to accommodate installation of an optical film unit or an optical film package, respectively. Again, adhesive layer  32 ′ conforms to the geometry needed to contact portions of light guide  18   a,  optical films  44 , and chassis  12   a.    
         [0058]     The present invention provides a more efficient and less costly product for installation into an optical display. The optical layers may be pre-aligned and stacked in bulk by means of a continuous web, which is more efficient and effective than stacking each layer individually as is presently done. Because the layers are not individually stacked, they no longer require peripheral tabs for positioning and orienting nor protective cover sheets. In addition, the films may be sealed to prevent any debris from entering between the layers.  
         [0059]     Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.

Technology Classification (CPC): 1