JP6180312B2 - LED backlight - Google Patents

Description

  The present invention relates to an LED backlight used in a liquid crystal panel or the like, and more particularly to a sidelight type LED backlight in which light emitted from an LED is incident on a side end surface of a light guide plate and is emitted from an exit surface of the light guide plate.

  In a liquid crystal display device, a sidelight that causes light emitted from an LED to be incident on a side end face of a light guide plate (hereinafter referred to as a light incident end face) in order to illuminate the liquid crystal panel from the back, and to be emitted from an exit face of the light guide plate facing the liquid crystal panel. A type of LED backlight may be employed. The LED backlight often includes an optical sheet such as a diffusion sheet or a prism sheet in addition to the light source LED and the light guide plate. In addition, since the light guide plate used in this LED backlight is required to have a thin LED backlight, the light emitting plate is thinned in the vicinity of the light incident end surface, and the light emitting plate is formed between the light incident end surface and the light emitting surface. In some cases, slopes are provided.

  However, if the light guide plate is provided with a slope, a part of the light that is to propagate through the light guide plate leaks out of the slope. The leaked light may be incident on the side end face of an optical sheet such as a diffusion sheet or a prism sheet, resulting in uneven brightness called a so-called hot spot. As a countermeasure, light shielding may be provided between the inclined surface and the side end surface of the optical sheet (for example, FIG. 2 of Patent Document 1). Then, FIG. 2 of patent document 1 is re-displayed in FIG. 3, and the structure etc. are demonstrated.

  FIG. 3 is a sectional view of a conventional planar illumination device (LED backlight). In the planar illumination device shown in FIG. 3, the light guide plate 11 includes a light incident end surface 14, an exit surface 12, the other main surface 13 facing the exit surface 12, and an inclined surface 16 (inclined surface), and an inclined portion start position. The thickness is reduced from 33 toward the emission surface 12. A diffusion sheet 17 and prism sheets 18 and 19 are laminated on the light guide plate 11.

  The LED 22 is attached to an FPC 21 (flexible printed circuit board), and the light emitting surface 22 a faces the light incident end surface 14. In the FPC 21, a wiring layer 24 and a base film 25 are laminated on a cover film 23, and the wiring layer 24 includes adhesive layers 24a and 24c and a conductive pattern 24b (copper foil layer). The FPC 21 has a mounting portion 21a on which the LED 22 is mounted and a bent portion 21b. The bent portion 21 b has a thickness of only the base film 25, and the tip thereof is sandwiched between the light guide plate 11 and the diffusion sheet 17.

 Since the surface illumination device covers the inclined surface 16 with the base film 25 of the FPC 21 and blocks light that is about to leak from the inclined surface 16, light is incident from the side end surfaces of the diffusion sheet 17 and the prism sheets 18 and 19. In this case, uneven brightness such as hot spots can be suppressed.

JP 2013-37846 A (FIG. 2)

However, in the LED backlight (planar illumination device) as shown in FIG. 3, since the light shielding property of the base film 25 made of polyimide is not sufficient, the light leaking from the base film 25 is an optical sheet (diffusion sheet 17, prism sheet). 18, 19). As a result, this LED backlight has a problem that luminance unevenness cannot be sufficiently suppressed.

  Further, the FPC 21 is deformed so that a part of the base film 25 is extended. Therefore, the LED backlight as shown in FIG. 3 has a problem that it is difficult to manufacture, and when the shape of the light guide plate 11 or the optical sheet is changed, the FPC 21 itself needs to be changed. There is also a problem that it cannot respond to.

  Therefore, the present invention has been made in view of the above problems, and provides an LED backlight that is easy to manufacture and can flexibly cope with design changes while sufficiently suppressing unevenness in luminance due to light leaking from the slope of the light guide plate. For the purpose.

In order to achieve the above object, an LED backlight according to the present invention includes an LED, a light guide plate having a light incident end surface and an output surface, and an inclined surface provided between the light input end surface and the light output surface, and the light guide plate. In a sidelight type LED backlight including an optical sheet laminated on the emission surface, an FPC to which the LED is attached, a tape that is attached to the FPC and partially extends from the FPC, and an extension of the tape A light-shielding sheet with one end affixed to the part, and a rim sheet that covers a part of the LED, the slope and the emission surface , the optical sheet includes a diffusion sheet in the bottom layer, the light-shielding sheet , covering the slope, a vicinity of a portion where the exit surface and the inclined surface intersects the other end on the exit surface is sandwiched between the diffusion sheet and the light guide plate, Serial other end, and being covered in the rim seats.

  The LED backlight of the present invention can block light that leaks from the slope of the light guide plate by the light shielding sheet that can improve the light shielding performance, so that the light leaked from the slope of the light guide plate is transmitted from the end surface of the optical sheet to the optical sheet. Luminance unevenness caused by incidence can be sufficiently suppressed. Further, FPC is easy to manufacture because it is not necessary to perform a deforming process for extending only the base film. Furthermore, even if the shape of the light guide plate or the optical sheet changes, if the shape of the tape or the light shielding sheet is changed, it is possible to cope with a wide range of design changes, and the burden of redesign is reduced.

  As described above, the LED backlight of the present invention can be easily manufactured and can flexibly cope with a design change while sufficiently suppressing luminance unevenness due to light leaking from the inclined surface of the light guide plate.

The external view of the LED backlight shown as embodiment of this invention. Sectional drawing of the LED backlight shown in FIG. Sectional drawing of the LED backlight shown as a prior art example.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to FIGS. In the description of the drawings, the same or equivalent elements will be denoted by the same reference numerals, and redundant description will be omitted. For the sake of explanation, the scale of the members is changed as appropriate.

  First, the external appearance of the LED backlight 30 of this embodiment will be described with reference to FIG. 1A and 1B are external views of the LED backlight 30. FIG. 1A is a plan view and FIG. 1B is a side view.

As shown in FIG. 1A, when the LED backlight 30 is viewed from above, a frame-shaped rim sheet 31 and a light emitting portion 32 surrounded by the rim sheet 31 are observed. The left side of the rim sheet 31 is thick, and a light incident end face 44 (see FIG. 2) and an inclined surface 45 (see FIG. 2) of the LED 50 (see FIG. 2) and the light guide plate 41 (see FIG. 2) are provided below the rim sheet 31. The light emitting unit 32 includes a light guide plate 41 and a diffusion sheet 47 (see FIG. 2), and emits light in a direction perpendicular to the paper surface. As shown in FIG. 1B, when the LED backlight 30 is viewed from the side, it is observed that the frame 34 and the rim sheet 31 are stacked on the reflection sheet 36. The frame 34 is a frame-shaped member. The LED 50, the light guide plate 41, the diffusion sheet 47, and the like are housed inside the frame 34, and the rim sheet 31 and the reflection sheet 36 are attached to the top and bottom.

  Next, the laminated structure of the LED backlight 30 will be described in detail with reference to FIG. FIG. 2 is a cross-sectional view of the LED backlight 30 drawn along the line AA in FIG. In the LED backlight 30 shown in FIG. 2, the light guide plate 41 includes a light incident end surface 44, an output surface 42, the other main surface 43 facing the output surface 42, and a slope 45, and emits light from the vicinity of the light incident end surface 44. It becomes thinner toward the surface 42. A diffusion sheet 47 and prism sheets 48 and 49 are stacked on the light guide plate 41.

  The LED 50 is attached to the lower surface of the FPC 51 (flexible printed circuit board), and the light emitting surface 50 a faces the light incident end surface 44. The tape 52 attached to the upper surface of the FPC 51 extends from the FPC 51 in the right direction in the figure, and one end of a light shielding sheet 53 is attached to the extended portion. The light shielding sheet 53 covers the slope 45 of the light guide plate 41, and the other end is sandwiched between the light guide plate 41 and the diffusion sheet 47. In FIG. 3, the gap between the diffusion sheet 47 and the light exit surface 42 of the light guide plate 41 is drawn. However, the actual diffusion sheet 47 overlaps with the light guide plate 41 so that the light shielding sheet 53 and Deformed at the overlapping part. This deformation is the same for the prism sheets 48 and 49.

 In addition, a reflective sheet 36 is attached to the main surface 43 which is the lower surface of the light guide plate 41. The rim sheet 31 is attached to the upper surface of the tape 52 and a part of the upper surface of the prism sheet 49. 1 is the opening of the rim sheet 31 as described above, and the light guide plate 41, the diffusion sheet 47, and the prism sheets 48 and 49 are laminated on the reflection sheet. In FIG. 2, the frame 34 (see FIG. 1) is not shown.

  The light guide plate 41 is made of PET (polyethylene terephthalate), has a thickness in the vicinity of the light incident end face 44 of 400 μm, a thickness of the emission face 42 of 300 μm, and a length of the slope 45 of 1.5 mm. The LED 50 is a package product in which an LED die is mounted on a lead frame or a submount substrate or the like and is covered with a fluorescent resin. The LED 50 includes a reflecting member for emitting light only in the direction of the light guide plate 41 and has a thickness of 0.4 mm. A plurality of them are arranged in a direction perpendicular to. The FPC 51 is a flexible printed circuit board in which Cu wiring is formed on a polyimide sheet, has a thickness of 70 to 90 μm, has flexibility, has a power supply unit (not shown), and supplies power from the outside by this power supply unit. Receive.

  The diffusion sheet 47 is made of PET and has a thickness of 30 to 40 μm. The prism sheets 48 and 49 have a base material of PET, a microprism array made of acrylic resin, and a thickness of 60 to 70 μm. In the prism sheets 48 and 49, the ridge lines of the respective microprisms are orthogonal to each other, and the viewing angle characteristics in the direction perpendicular to the paper surface and the direction parallel to the paper surface are adjusted.

  The tape 52 is made of black PET and has a thickness of 20 μm and has an adhesive on one side. The light shielding sheet 53 is also made of black PET and has a thickness of 80 μm. The reflection sheet 36 is also made of PET and has a thickness of 60 to 70 μm. The rim sheet 31 is a so-called double-sided tape whose upper and lower surfaces are black, has a base material of PET, and a thickness of 30 μm. Until the LED backlight 30 is incorporated in a product such as a liquid crystal display device, a separator (not shown) is attached to the upper surface of the rim sheet 31.

In the LED backlight 30, the light shielding sheet 53 covers the slope 45 and blocks light that is about to leak from the slope 45, so that light does not enter from the side end surfaces of the diffusion sheet 47 and the prism sheets 48 and 49, and diffuses. Luminance unevenness such as hot spots caused by light incident from the side end surfaces of the optical sheets such as the sheet 47 and the prism sheets 48 and 49 does not occur.

  Since the tape 52 and the light shielding sheet 53 included in the LED backlight 30 are black, the light shielding property can be improved. On the other hand, if the tape 52 or the light shielding sheet 53 is silver and has a reflection characteristic, the light emission efficiency of the LED backlight 30 can be improved. In addition, since the FPC 51 is expensive and it is not easy to change the thickness, the tape 52 and the light-shielding sheet 53, which are relatively inexpensive and can be prepared in various thicknesses, have their own shape and thickness even if the design of the LED backlight 30 is changed. In many cases, it is possible to respond flexibly by making changes.

30 ... LED backlight,
31 ... Rim seat,
32 ... light emitting part,
34 ... Frame,
36 ... reflective sheet,
41. Light guide plate,
42 .. exit surface,
43 ...
44. Incident light end face,
45 ... Slope,
47 ... diffusion sheet,
48, 49 ... Prism sheet,
50 ... LED,
50a: light emitting surface,
51 ... FPC (flexible printed circuit board),
52 ... tape,
53: A light shielding sheet.

Claims (1)

A sidelight system comprising: an LED; a light guide plate having a light incident end surface and an output surface; and a light guide plate provided with an inclined surface between the light input end surface and the output surface; and an optical sheet laminated on the output surface of the light guide plate In LED backlight,
An FPC to which the LED is attached;
A tape attached to the FPC and partially extending from the FPC;
A light-shielding sheet with one end attached to the extended portion of the tape ;
A rim sheet covering the LED, the inclined surface, and a part of the emission surface ;
The optical sheet includes a diffusion sheet in the lowermost layer,
The light shielding sheet covers the slope, a vicinity of a portion where the exit surface and the inclined surface intersects the other end on the exit surface is sandwiched between the diffusion sheet and the light guide plate,
The LED backlight , wherein the other end is covered with the rim sheet .

Images