Patent Application
20070139574
The present invention generally relates to the field of liquid crystal displays. In particular, the invention relates to a system for supporting optical film stacks within liquid crystal display devices.
Liquid crystal displays (LCDs) are optical displays used in devices such as laptop computers, hand-held calculators, digital watches, and televisions. Some LCDs include a light source that is located to the side of the display, with a light guide positioned to guide the light from the light source to the back of the LCD panel. Other LCDs, for example, some LCD monitors and LCD televisions (LCD-TVs), are directly illuminated using a number of light sources positioned behind the LCD panel. This arrangement is increasingly common with larger displays because to achieve a certain level of display brightness, the light power requirements increase with the square of the display size, whereas the available real estate for locating light sources along the side of the display only increases linearly with display size. In addition, some LCD applications, such as LCD-TVs, require that the display be bright enough to be viewed from a greater distance than other applications, and the viewing angle requirements for LCD-TVs are generally different from those for LCD monitors and hand-held devices.
Some LCD monitors and most LCD-TVs are commonly illuminated from behind by a number of fluorescent tubes. These light sources are linear and stretch across the full width of the display, with the result that the back of the display is illuminated by a series of bright stripes separated by darker regions. Such an illumination profile is not desirable, and so a diffuser layer is used to smooth the illumination profile at the back of the LCD device. When the layer is thin, a uniform luminance distribution cannot be obtained easily due to warp and undulation of the layer. As the scale of LCD devices has become greater in recent years, warp and undulation of the diffuser layer has become more likely to occur and the thickness of the diffuser layer itself has been increased to suppress such problems. However, the increased weight of the diffuser layer resulting from increased thickness and area of the layer has become another problem.
In addition, the diffuser layers can have problems with distortion due to the high temperature exposure of the backlight systems, as well as from moisture absorption.
Directly illuminated liquid crystal display (LCD) units are disclosed that include an LCD panel, a backlight cavity, a film stack disposed between the LCD panel and the backlight cavity, and a supporting structure disposed to maintain the film stack in a substantially flat condition. The film stack comprises at least one flexible optical film, and can include a flexible diffuser film. The film stack itself is also flexible. The supporting structure includes at least one flexible support held taut in at least one dimension, and/or at least one rigid elongated support covering only a portion of a useful area of the film stack.
These and other aspects of the present application will be apparent from the detailed description below. In no event, however, should the above summaries be construed as limitations on the claimed subject matter, which subject matter is defined solely by the attached claims, as may be amended during prosecution.
In the figures, like reference numbers have been used to denote like parts.
Unless otherwise indicated, all numbers expressing feature sizes, amounts, and physical properties used in the specification and claims are to be understood as being modified by the term “about.” Accordingly, unless indicated to the contrary, the numerical parameters set forth in the present specification and claims are approximations that can vary depending upon the desired properties sought to be obtained by those skilled in the art utilizing the teachings disclosed herein.
Optical film stack 14 is positioned between LCD panel 12 and backlight cavity 16 and affects the light propagating from backlight cavity 16 so as to improve the operation of LCD system 10. Optical film stack 14 can include, but is not limited to: light-directing films, diffuser-type films, turning films, brightness-enhancing films, multi-layer polymer films, reflective polarizing films, and absorbing polarizers. For example, optical film stack 14 may include a diffuser film so as to enhance the uniformity of the illumination light incident on LCD panel 12. This in turn can provide a uniformly bright image on LCD panel 12 when perceived from a viewer in front of LCD system 10. Typically, each component of optical film stack 14 (i.e., the diffuser film, if present, the reflective polarizing film, if present, the brightness enhancing film, if present, and so forth) is a film that can flex, bend, and the like if manipulated by hand, and that sags under its own weight if removed from LCD system 10 and held at only one end or corner. Such flexibility also typically characterizes entire optical film stack 14, which can comprise a plurality of flexible optical films or can consist essentially of a single flexible optical film, if desired. Optical film stack 14 and each of its component film(s) is preferably sized, in both a length dimension and a width dimension, to at least fill the aperture of backlight cavity 16 and/or to at least fill the viewable area of LCD panel 12.
LCD system 10 can be or comprise an LCD-TV or any other LCD display system. Although LCD system 10 may in some cases include a thick, rigid diffuser plate, preferably any necessary diffusing function between the backlight cavity 16 and the LCD panel 12 is provided by one or more films in optical film stack 14, thus avoiding the need for any such diffuser plate, and enabling an LCD system 10 having a thinner overall profile and lighter weight. In order for optical film stack 14 to provide LCD system 10 with an optimal output brightness distribution, it is maintained in a substantially flat condition even though it is inherently flexible, and thus may be susceptible to warping, curling, sagging, and so on. Various low-profile supporting structures capable of holding optical film stack 14 in a flat condition, yet typically thinner and lighter weight than conventional diffuser plates, are described further below. One type of supporting structure includes a post that contacts the film stack at an isolated point or area. Another type of supporting structure extends across at least one lateral dimension of the backlight cavity aperture and/or of the viewable area of the LCD panel, and contacts the film stack along the length of the supporting structure. Some of these extended structures utilize thin components such as filaments, ribbons, or films that are inherently flexible but that are held taut to provide rigidity. Other extended structures utilize thin elongated components that are inherently rigid.
Suitable diffuser films have at least a first polymeric resin phase and a second phase such as beads, particles, voids, or the like that provide in combination a diffusing function. Suitable polymer materials may be amorphous or semi-crystalline, and may include homopolymer, copolymer, or blends thereof. Polymer foams may also be used. Examples of polymer materials include, but are not limited to: polycarbonate (PC), polystyrene (PS), acrylates, polypropylene (PP), poly(ethylene terephthalate) (PET), PET copolymers, polyethylene (PE), polymethyl methacrylate (PMMA), PMMA copolymers, poly(ethylene naphthalate) (PEN), PEN copolymers, cycloolefins, cycloolefin copolymers, acrylonitrile butadiene styrene (ABS), styrene acrylonitrile copolymers (SAN), epoxies, poly(vinylcyclohexane), PMMA/poly(vinylfluoride) blends, a tactic PP, poly(phenylene) oxide alloys, styrenic block copolymers, polyimide, polysulfone, poly(vinyl chloride), poly(dimethyl siloxane) (PDMS), polyurethanes, and poly(carbonate)/aliphatic PET blends. In some embodiments, the diffuser film can be made from a modified Acrylic Foam Tape, product number 4643, available from 3M Company, Saint Paul, Minn.
Backlight cavity 16 includes surface 18, light sources 20, and support posts 22. Surface 18 forms the perimeter of backlight cavity 16 proximate optical film stack 14 and has sides 26, 28, 30, and 32, which can be arranged to form a rectangle, if desired.
Backlight cavity 16 includes light sources 20 that illuminate LCD panel 12. Light sources 20 used in LCD system 10 are typically linear, cold cathode fluorescent tubes that extend across the length or width of LCD system 10. Other types of light sources may also be used, such as filament or arc lamps, light emitting diodes (LEDs), flat fluorescent panels (FFL), or external electrode fluorescent lamps (EEFL). In the case of LEDs, arrays of multicolored LEDs (such as red/green/blue) can be used, and the LEDs can be packaged or unpackaged, forward-emitting or side-emitting. Although
Support posts 22 of LCD system 10 are preferably mounted in or on backlight cavity 16 to help minimize gravitational sagging of optical film stack 14. Support posts 22 extend from backlight cavity 16 and contact optical film stack 14 at numerous points to provide support for optical film stack 14. Due to this support, optical film stack 14 is prevented from warping, sagging, curling, and the like. While optical film stack 14 is in contact with support posts 22, optical film stack 14 is preferably slightly distanced from LCD panel 12 by a thin air gap of between one millimeter and twenty-five millimeters. Alternatively, in some embodiments, optical film stack 14 may contact LCD panel 12. Although
A plurality of elongated supports 34 each include filaments 34a-34c. Filaments 34a-34c extend across LCD system 10 such that a first end 36 of filaments 34a-34c contacts one side 26 of surface 18 and a second end 38 of filaments 34a-34c contacts the opposed side 30 of surface 18. Elongated supports 34 can be arranged along surface 18 in a parallel array, as shown, or they can be non-parallel to each other, whether slightly skewed or intersecting, including intersecting at right angles. For example, at least one elongated support 34 can extend from side 26 to side 30 of surface 18, and at least another elongated support 34 can extend from side 28 to side 32 of surface 18. Elongated supports 34 are positioned such that they contact optical film stack 14, preventing optical film stack 14 from sagging into backlight cavity 16 and maintaining optical film stack 14 in a substantially flat condition, thus avoiding warping, sagging, curling, or the like of optical film stack 14 caused by gravity or other influences. In some cases, each elongated support 34 and its component filaments 34a-34c are so thin and long as to be flexible, bendable, and non-self-supporting, i.e., if removed from LCD system 10 and held at one end they would sag and bend under their own weight. Nevertheless, by mounting filaments 34a-34c in tension and holding them taut across at least one dimension of backlight cavity 16 and/or of the viewable area of LCD panel 12, a sufficient stiffness or rigidity is achieved to enable them to prevent optical film stack 14 from sagging into backlight cavity 16, thus holding optical film stack 14 in a substantially flat condition. The contact between elongated support(s) 34 and optical film stack 14 maintains the flatness of optical film stack 14. Optical film stack 14 is thus supported by support posts 22 and elongated supports 34 such that optical film stack 14 remains in a substantially flat condition and is resistant to warping or sagging.
Filaments 34a-34c can be wires, ribbons, or similar thin, long structures, and can comprise organic or inorganic materials, such as carbon, nylon, plastic, metal, and the like. Although
To mount optical film stack 14 onto backlight cavity 18, optical film stack 14 preferably includes alignment tabs 43 located at one or more of its edges or boundaries. Perforations 45 extend through tabs 43 of optical film stack 14 and are sized and spaced to mate with corresponding protrusions 47 in an adjacent component such as surface 18 of backlight cavity 16. As shown in
Rather than mounting elongated supports 34 directly to backlight cavity 16, elongated supports 34 can alternatively be mounted to a separate mounting frame or structure which is then attached or otherwise connected to backlight cavity 16. This is shown in the perspective view of
Mounting frame 44 has sides 46, 48, 50, and 52, which can be arranged to form a rectangle or other desired shape. As with backlight cavity 16, mounting frame 44 can utilize any known materials of construction and can utilize any design features that provide a low profile rigid body. The thickness of mounting frame 44 will depend on the size and thickness of LCD display 12 and the materials of construction. In some embodiments, mounting frame 44 has a thickness of 100 mm or less. Exemplary materials of construction include without limitation plastics, such as polypropylene, poly(ethylene terephthalate), polymethyl methacrylate, polycarbonate, and polyethylene, and metals, such as aluminum or stainless steel.
Mounting frame 44 can include posts 42 along some or all of its perimeter, as shown in
Elongated supports 56 each have a first end 58 and a second end 60. As shown, first ends 58 attach to side 26 of surface 18, and second ends 60 attach to opposite side 30 of surface 18. As mentioned above, elongated supports 56 can, but need not be arranged in a parallel array. Skewed arrangements, intersecting arrangements, and other arrangements can also be used, but preferably the array of elongated supports 56 provides enough support to maintain optical film stack 14 in position relative to LCD panel 12.
The number of elongated supports 56 can range from one to tens, hundreds, or even one thousand or more. The thickness of each of elongated supports 56 will depend on the size and thickness of LCD display 12. The cross-sectional shape of the elongated supports 56 can be circular, elliptical, rectangular, polygonal, or any other desired shape.
Elongated supports 56 can be made of organic or inorganic materials, plastics, or metals. Exemplary supports 56 that are positioned within the display area are either transparent or sufficiently narrow (from the perspective of the observer in front of LCD system 100) as to not substantially interfere with the visual display as seen by the observer. Any elongated supports 56 not located within the display area need not be transparent, and can be formed of wider plastic or metal. Exemplary plastics include, but are not limited to: polypropylene, poly(ethylene terephthalate), polymethyl methacrylate, polycarbonate, and polyethylene. An exemplary metal includes, but is not limited to, aluminum.
Elongated supports 56 can be attached to backlight cavity 16 using any conventional techniques. For example, holes can be formed in the first and second ends 58, 60 of elongated supports 56 to engage corresponding posts in surface 18. Altematively, elongated supports 56 can be attached to surface 18 or to a separate mounting frame by an adhesive or mechanical means.
Stretched film 62 is or comprises a flexible sheet of light-transmissive material that is stretched across surface 18a or across some other frame or structure within LCD system 200. Stretched film 62 may be made of any material that is substantially transparent to visible light, including without limitation plastic materials such as polypropylene, poly(ethylene terephthalate), and polyethylene. In exemplary embodiments, stretched film 62 is or comprises a thermal shrinkage film. Such a film can be readily incorporated into LCD system 200 by: (1) bonding stretched film 62 (in an unstretched condition) to surface 18a, or to a separate mounting frame or similar structure, with an adhesive or other conventional bonding mechanism; and (2) applying heat to stretched film 62 such that it permanently contacts enough to become uniformly taut within surface 18a. Such a shrinkage film is considered to be a “stretched film” for purposes of this application because the film is held in tension, even though such tension results from shrinkage instead of an expansion of the film. Of course, stretched film 62 can also be made by mechanically stretching a film (e.g., by holding the film in a gripping mechanism and pulling apart the jaws that hold opposing edges of the film) and then mounting the stretched film on a frame to maintain the tension in the film. If desired, stretched film 62 can be laminated to one or more films of optical film stack 14a, including in some cases to a diffuser film in optical film stack 14a. Stretched film 62 can also provide optical functionality. For example, stretched film 62 can be or comprise a diffuser film or other optical film suitable for use in optical film stack 14a.
The present application contemplates LCD systems that incorporate any combination of features disclosed in the various LCD systems discussed above. For example, an LCD system can include one or more elongated supports 56 extending across the width of the backlight cavity as well as one or more elongated supports 34 extending across the length of surface 18, the latter elongated supports 34 intersecting and optionally perpendicular to elongated supports 56.
The disclosed LCD systems preferably comprise an LCD panel, an optical film stack, and a backlight cavity. The systems also include a supporting structure that supports the optical film stack with respect to the LCD panel of the LCD unit. The supporting structure applies pressure to the optical film stack to prevent the optical film stack from sagging into the backlight cavity and to maintain the optical film stack in a substantially flat condition.
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.
