JP4860127B2 - Backlight device for liquid crystal display device - Google Patents

Description

  The present invention relates to a direct-type backlight device used as a light source device of a liquid crystal display device, and more particularly to a direct-type backlight device that has high light utilization efficiency and can uniformly irradiate a liquid crystal panel with no unevenness.

As a backlight device of a liquid crystal panel of a liquid crystal display device, a sidelight system in which light from a light source arranged on the side of the liquid crystal panel is applied to the back surface (irradiation surface) of the liquid crystal panel via a light guide plate, etc. There is known a direct type system in which light from a light source disposed facing the back surface is directly applied to the back surface. In recent years, due to the increase in the size of liquid crystal display devices, a direct type that facilitates high brightness has come to be adopted. A direct-type backlight device, that is, a direct-type backlight device includes a light source that illuminates the rear surface of the liquid crystal panel and a reflector that reflects light emitted from the light source toward the rear surface. A long fluorescent tube is used as the light source. In particular, in the case of a large-sized liquid crystal display device, a plurality of fluorescent tubes are arranged in parallel at equal intervals on the back side of the liquid crystal panel. In the following Patent Documents 1 and 2, a reflector for uniformly guiding light from a plurality of light sources to the back of a large liquid crystal panel is repeatedly refracted according to the number of light sources and the distance between the light sources. Is formed.
JP-A-5-100223 JP-A-5-159609

  An object of the present invention is to propose a direct-type backlight device for a liquid crystal display device that has higher light utilization efficiency than that of the prior art and that can uniformly irradiate a liquid crystal panel.

  In order to solve the above-described problems, a direct backlight device of a liquid crystal display device according to the present invention includes a plurality of linear light sources arranged in parallel at regular intervals with respect to an irradiation surface of a liquid crystal panel, and the linear light source. And a reflection plate for reflecting the emitted light toward the irradiation surface, and the reflected light from the reflection plate is reflected on the irradiation surface at an angle within about 35 degrees with respect to the normal of the irradiation surface. The reflection surface shape of the reflection plate is set so as to be incident.

  Here, it is conceivable to adopt an elliptical surface, a hyperboloid, or the like as the reflecting surface of the reflecting plate. However, by using a parabolic surface, the amount of light is uniform and the light utilization efficiency can be increased. In the present invention, the reflecting plate is characterized in that a polygonal reflecting surface composed of a plurality of planar reflecting surfaces arranged along a paraboloid surface is arranged corresponding to each linear light source.

  By adopting a parabolic surface as the reflecting surface, the amount of light is uniform and the light utilization efficiency can be increased. Moreover, since the reflecting surface is formed by a plurality of planar reflecting surfaces arranged along the paraboloid, it is possible to realize a reflecting plate that is easy to manufacture and that has a uniform amount of light and high light utilization efficiency.

  In the present invention, the boundary between the adjacent polygonal reflecting surfaces is such that the edge of the planar reflecting surface on one side and the edge of the planar reflecting surface on the other side are abutted at an acute angle. It is said.

  When the boundary of the reflection surface of each linear light source is the tip, it can be suppressed that the light reflected by the reflection surface wraps around and interferes with the adjacent reflection surface. In addition, when a flat surface or the like is formed at the boundary portion, the illuminance unevenness occurs due to a galling on the liquid crystal panel side of this portion. According to the present invention, such an uneven illuminance is suppressed. it can.

  Next, the polygonal reflecting surface of the present invention can be formed by bending along a plurality of folds extending in parallel and formed on the reflecting plate. In addition, the crease corresponding to the boundary is provided with a perforation having a constant width that is alternately cut at an angle of 45 degrees with respect to the thickness direction of the reflector at regular intervals along the crease. A pointed boundary can be formed by bending the portion.

  On the other hand, the direct type backlight device of the present invention has an optical characteristic such as a light diffusion characteristic between the irradiation surface of the liquid crystal panel and the linear light source and the reflecting plate in addition to the above configuration. A film or an optical sheet is arranged. According to this configuration, light from the light source can be uniformly applied over a wide range to the back surface (irradiation surface) of the liquid crystal panel.

  In the present invention, in the direct type backlight device of the liquid crystal display device, the reflected light from the reflecting plate is incident on the irradiation surface at an angle of about 35 degrees or less with respect to the normal of the irradiation surface (back surface) of the liquid crystal panel. As described above, the shape of the reflecting surface of the reflecting plate is set. Therefore, the amount of light can be made uniform and the utilization efficiency of reflected light can be increased.

  In the present invention, the reflecting surface corresponding to each light source is formed so that the light beams of adjacent light sources do not interfere with each other. Furthermore, the boundary between adjacent reflecting surfaces has a pointed shape. Therefore, luminance unevenness can be reduced and the liquid crystal panel can be illuminated uniformly, so that uniform screen illuminance can be ensured.

  Hereinafter, a direct backlight device of a liquid crystal display device to which the present invention is applied will be described with reference to the drawings.

  FIG. 1 is a schematic configuration diagram of a direct type backlight device of the liquid crystal display device of this example. FIG. 2A is a configuration diagram of the reflecting plate, and FIG. 2B is an explanatory diagram showing a state in which the reflecting plate is developed on a plane.

  The direct type backlight device 1 is disposed on the back side of the liquid crystal panel 101 of the liquid crystal display device 100, and a plurality of direct backlight devices 1 are arranged in parallel with the back side irradiation surface 102 of the liquid crystal panel 101 at a predetermined interval. It has the linear light source 2 and the reflecting plate 3 provided with the reflective surface part corresponding to each linear light source 2. FIG. In addition, a plurality of light diffusing means 4 are disposed in a position between the liquid crystal panel 101 and the linear light source 2 and the reflection plate 3 so as to face the irradiation surface 102 of the liquid crystal panel in parallel. The light diffusing unit 4 includes, for example, two diffusion sheets 41 and 42 and one diffusion panel 43.

  As the linear light source 2, a long tubular cold cathode fluorescent tube or the like can be used. In this example, a plurality of linear light sources 2 arranged in parallel to the irradiation surface 102 of the liquid crystal panel are arranged at regular intervals.

  The reflector 3 has a reflecting surface portion 31 having a parabolic shape as a whole when viewed from the axial direction of the linear light source 2 parallel to the irradiation surface 102 of the liquid crystal panel, corresponding to each linear light source 2. It becomes the composition. Each reflecting surface portion 31 is a polygonal reflecting surface in which a plurality of planar reflecting surfaces, in the illustrated example, nine planar reflecting surfaces 32 (1) to 32 (9) are arranged along a parabolic surface. Yes.

  Each reflecting surface portion 31 of this example approximates a paraboloid of focal length f = a / 4, radius of curvature R = a / 2, and curvature C = 2a. In the example shown in the drawing, a = 18.4 mm, f = Z = 4.8 mm, and R = ρ = 9.6 mm. The paraboloid is approximated by nine planar reflecting surfaces, and a linear light source is obtained. 2 is arranged at the focal position. As a result, the reflected light 5 of the reflecting plate 3 of this example is incident on the irradiation surface 102 at an angle of approximately 35 degrees or less with respect to the perpendicular drawn on the irradiation surface 102 of the liquid crystal panel 101.

  In addition, at the boundary 33 of each parabolic reflecting surface portion 31, the plane reflecting surface 32 (1) of one reflecting surface portion 31 and the plane reflecting surface 32 (9) of the other reflecting surface portion 31. The angle formed is an acute angle, in this example, an angle of about 47 degrees. That is, the boundary of each reflecting surface portion 31 is a pointed end (33) protruding toward the liquid crystal panel.

  Here, the reflecting plate 3 of this example is formed using a material that performs diffuse reflection with high reflectivity, for example, a microcellular plastic-based reflecting material. As such a reflective material, for example, MCPET-RB (manufactured by Furukawa Electric Co., Ltd.) can be used.

  Further, the reflecting plate 3 can be formed by bending a reflecting plate having the respective flat reflecting surfaces 32 (1) to 32 (9) along the fold line 34. As shown in FIG. 2 (b), perforations (cut portions) 36 having a predetermined width are alternately formed in the crease 35 at the boundary 33 of the reflecting surface portion 31 with a length of several mm from the direction of 45 degrees to the left and right. It is attached along this crease 35 to form a pointed boundary 33 of approximately 47 degrees. In addition, the reflecting plate 3 can be comprised by connecting the reflecting plate provided with each planar reflective surface at a predetermined angle. Instead of this, it is also possible to perform integral molding by injection molding so as to have a parabolic shape.

  As described above, the reflector 3 of the direct type backlight device 1 of this example employs a parabolic surface, the light source 2 is disposed at the focal position, and the reflected light 5 of the reflector 3 is a liquid crystal panel. 101 is incident on the irradiation surface 102 at an angle of approximately 35 degrees or less with respect to a perpendicular drawn on the irradiation surface 102.

  The direct light applied to the liquid crystal panel from the light source 2 has a high luminance in the portion directly above the light source, and the luminance decreases toward the peripheral portion. In the reflected light 5 by the reflecting plate 3, the reflected light component reaching the liquid crystal panel irradiation surface 102 directly above the light source 2 is adjusted by the reflecting surface of the reflecting plate 3. That is, the incidence on the reflecting surface is approximately 25 degrees or less, and the amount of reflected light is suppressed. For this purpose, in this example, the angle of the reflected light incident on the irradiation surface 102 of the liquid crystal panel with respect to the perpendicular drawn on the irradiation surface is set to an angle of approximately 35 degrees or less. On the contrary, the total reflection state is formed by increasing the reflection angle of the reflection plate 3 in the reflected light component incident on the peripheral portion to be 50 degrees or more so that the amount of reflected light to the peripheral portion is increased. Also in this case, the angle of the reflected light incident on the back surface (irradiation surface) of the liquid crystal panel may be set to about 35 degrees or less. A reflection surface shape having such reflection characteristics can be realized by adopting a parabolic surface.

  Therefore, according to the present example, by reducing the reflection angle incident on the portion directly above the light source 2 and suppressing the light amount, the incident light amount in the portion directly above the light source 2 and the peripheral portion is made uniform, Uneven brightness can be suppressed.

  Moreover, in this example, the reflective surface part 31 of each linear light source 2 is prescribed | regulated from the several plane reflective surface 32 (1) -32 (9) arranged along the paraboloid, and each reflective surface part 31 is defined. The boundary 33 has a pointed shape (47 degrees in this example). Therefore, a parabolic reflecting surface can be easily formed, and the reflected light emitted from the linear light source 2 and reflected by each reflecting surface portion 31 is efficiently guided to the irradiation surface 102 of the liquid crystal panel. be able to. Further, the sharp boundary 33 prevents the reflected light of the reflecting surface portion 31 from entering and interfering with the adjacent reflecting surface portion. Furthermore, since the boundary 33 has a pointed shape, there is no adverse effect that the liquid crystal panel side is dulled and illuminance unevenness occurs on the irradiation surface 102 of the liquid crystal panel.

  As described above, according to this example, it is possible to realize a direct type backlight device that can uniformly illuminate the entire irradiation surface 102 of the liquid crystal panel.

It is a schematic block diagram of the direct type backlight apparatus of the liquid crystal display device to which this invention is applied. 2 (b) (i) is a plan view before the reflector is bent and bent, FIG. 2 (b) (ii) is a sectional view before the reflector is bent, and FIG. 2 (a) is a reflector. It is sectional drawing after bending and bending.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Direct type backlight apparatus 2 Linear light source 3 Reflector 31 Reflecting surface part 32 (1) -32 (9) Planar reflecting surface 33 Boundary 34, 35 Fold 36 Perforation 4 Light diffusing means 100 Liquid crystal display device 101 Liquid crystal panel 102 Irradiation surface

Claims (4)

A plurality of linear light sources arranged in parallel at regular intervals to the irradiation surface of the liquid crystal panel;
A reflecting plate for reflecting the emitted light of the linear light source toward the irradiation surface;
The reflecting surface shape of the reflecting plate is set so that the reflected light from the reflecting plate is incident on the irradiating surface at an angle within about 35 degrees with respect to the perpendicular of the irradiating surface,
The reflecting plate has a configuration in which a polygonal reflecting surface composed of a plurality of plane reflecting surfaces arranged along a paraboloid surface is arranged corresponding to each linear light source,
The direct-type backlight device for a liquid crystal display device, wherein the polygonal reflective surface is formed by bending along a plurality of parallel folds formed in a reflective plate. The boundary between the adjacent polygonal reflecting surfaces is such that the edge of the planar reflecting surface on one side and the edge of the planar reflecting surface on the other side are abutted at an acute angle, and the acute angle stands 47 degrees. A direct type backlight device for a liquid crystal display device according to claim 1 . 3. A perforation having a constant width, which is alternately cut at an angle of 45 degrees with respect to the thickness direction of the reflector at regular intervals, is formed on the fold corresponding to the boundary. A direct type backlight device of the liquid crystal display device according to claim. An irradiation surface of the liquid crystal panel, between the linear light source and the reflector, claim, characterized in that the optical film or optical sheet having an optical characteristic such as light diffusing characteristics are arranged 1 4. A direct type backlight device for a liquid crystal display device according to any one of items 3 to 3 .

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