JP2011216275A - Backlight unit and liquid crystal display device including the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a backlight unit for further reducing width of a front frame even though it includes an erroneous lamination prevention unit of an optical sheet.SOLUTION: The backlight unit 10 includes: a casing 12; a light guide plate 36 that is stored in the casing 12 and is square as a whole; a plurality of optical sheets 38, 40, 42 that are put on the light guide plate 36 and have the same size as that of the light guide plate 36; the erroneous lamination prevention unit for preventing the optical sheets 38, 40, 42 from being put on the light guide plate 36 in the wrong order of both sides thereof and in the wrong lamination order; and the front frame 78 tightened to the periphery of the casing 12 for covering the periphery of the light guide plate 36. The erroneous lamination prevention unit, namely cutout units 46A to 46E, cutout units 48A to 48E, cutout units 50A to 50E, and cutout units 52A to 52E, are provided inside the square.

Description

  The present invention relates to a backlight unit and a liquid crystal display device using the same, and more particularly to an edge light type backlight unit and the like.

In recent years, as liquid crystal display devices such as liquid crystal televisions have become widespread, the demand for backlight units equipped therein has been further expanded.
The backlight unit is roughly divided into an edge light system and a direct light system, but from the viewpoint of reducing the thickness of the entire apparatus, an edge light system is often used.

  FIG. 7 shows an exploded perspective view of a conventional backlight unit 200 according to the edge light system. As shown in FIG. 7, the backlight unit 200 includes a rectangular housing 202, and includes a reflection sheet 204, a light guide plate 206, a diffusion sheet 208, a prism sheet 210, and a polarization sheet 212 (hereinafter, these three sheets). Etc. are collectively referred to as an “optical sheet”), the optical sheet group 214 is housed in this order from the bottom of the housing 202. Light sources such as LED arrays 216, 218, 220, and 222 are arranged on the side surface of the light guide plate 206, and the optical sheet group 214 has a peripheral portion at the periphery of the light guide plate 206 by a front frame 224 that is fastened to the housing 202. Pressed and fixed.

  By the way, when a plurality of optical sheets are used in an overlapping manner, the optical sheets 208, 210, and 212 are prevented from being mistakenly stacked on the optical sheet 208, 210, and 212 with respect to the light guide plate 206. Means (hereinafter referred to as “misstacking prevention means”) may be provided. Hereinafter, conventional erroneous stacking prevention means will be described.

  Tabs 226A to 226C, 228A to 228C, 230A to 230C, and 232A to 232C are extended from two opposite sides (two sides where no LED array is provided) in each of the optical sheets 208, 210, and 212. Through holes 234A to 234C, 236A to 236C, 238A to 238C, and 240A to 240C are opened in 226A to 226C, 228A to 228C, 230A to 230C, and 232A to 232C, respectively. Further, the lower the optical sheet (an optical sheet closer to the light guide plate 206), the larger the tab width.

  On the other hand, pins 242, 244, 246, and 248 are erected from the bottom of the housing 202 so as to correspond to the through holes 234 A to 234 C, 236 A to 236 C, 238 A to 238 C, and 240 A to 240 C, respectively. The optical sheets 208, 210, and 212 are inserted into the pins 242, 244, 246, and 248 following the reflection sheet 204 and the light guide plate 206, and the through holes 234 A to 234 C, 236 A to 236 C, 238 A to 238 C, and 240 A to 240 C are fitted. Thus, it is stored in the housing 202.

FIG. 8A shows a cross section of the pin 248 and the vicinity thereof in a state where the front frame 224 is fastened to the housing 202.
The front frame 224 is fastened to the flange portion 252 of the housing 202 by screws 250 (not shown in FIG. 7), and the optical sheet group 214 is pressed and fixed to the light guide plate 206 at the inner peripheral edge of the front frame 224. ing. The portion where the front frame 224 overlaps the light guide plate 206 has the following purposes in addition to pressing the optical sheet group 214 against the light guide plate 206. That is, the region of constant width inside from the side surface of the light guide plate 206 (peripheral portion of the light guide plate) is not very good in luminance uniformity, so this portion cannot be used effectively, and the front frame 224 is effectively used. One of the purposes is to cover (hide) the unused area.

FIG. 8B shows a plan view of only the pin 248, the tabs 232A to 232C, and the vicinity thereof.
When the order in which the optical sheets 208, 210, and 212 are stacked is correct, the lower tab is wider, so that all three tabs are visible as shown in FIG. 8B. On the other hand, if the order of stacking even one sheet is wrong, the number of tabs that can be visually checked is one or two. That is, whether or not the stacking order of the optical sheets 208, 210, and 212 is correct can be confirmed based on the number of visible tabs.

  Further, as shown in FIG. 7, pins 242, 244, 246, 248 and through holes 234A to 234C, 236A to 236C, 238A to 238C, 240A to 240C (tabs 226A to 226C, 228A to 228C, 230A to 230C, 232A ˜232C) are provided symmetrically with respect to the center point (intersection of diagonal lines) of the optical sheets 208, 210, 212, and therefore the through holes 234A to 234C, 236A˜ 236C, 238A to 238C, 240A to 240C do not fit into the corresponding pins 242, 244, 246, 248. Thereby, it can prevent that the front and back of the optical sheets 208, 210, and 212 are mistakenly stacked.

JP 2006-004751 A

  By the way, in a liquid crystal display device, it is important to reduce the width of so-called frame portions on the left and right sides of the screen as much as possible (narrow frame) and to have a compact design as a whole.

  The front frame 224 of the backlight unit 200 is hidden on the back side of the frame portion. Therefore, if the width W2 of the front frame 224 can be shortened, the width of the frame portion can be shortened accordingly.

  For that purpose, if there is no erroneous stacking prevention means such as tabs 226A to 226C, 228A to 228C, 230A to 230C, 232A to 232C, the housing 202 can be shortened by the space, so the width W2 of the front frame 224 is also It can be shortened. However, it goes without saying that necessary optical characteristics cannot be obtained in a state where the optical sheets 208, 210, and 212 are mistakenly laminated. In addition, if the optical sheet is definitely stacked without the erroneous stacking prevention means, it is necessary to be very careful, as compared with the case where the erroneous stacking prevention means is provided. It takes a lot of time.

  In view of the above-described problems, the present invention provides a backlight unit capable of further reducing the width of the front frame while having means for preventing erroneous stacking of optical sheets, and a liquid crystal display including such a backlight unit. An object is to provide an apparatus.

  In order to achieve the above object, a backlight unit according to the present invention includes a housing, a light guide plate that is housed in the housing and has a generally rectangular shape, and the light guide plate overlaid on the light guide plate. A plurality of optical sheets of the same size, an erroneous stacking prevention means for preventing the optical sheets from being stacked on the light guide plate by mistake in the front and back and the stacking order, and the peripheral edge of the housing A backlight unit having a front frame that covers a peripheral edge of the light guide plate, wherein the erroneous stacking prevention means is provided inside the square.

  Further, the erroneous stacking prevention means is a notch provided in each of the plurality of optical sheets, and the plurality of optical sheets communicated in the stacking direction in a properly stacked state, and The closer to the light guide plate, the smaller the cutout portion.

Further, the front frame is characterized in that a peripheral portion of the optical sheet is slidably held with respect to the light guide plate.
In order to achieve the above object, a liquid crystal display device according to the present invention includes a liquid crystal display panel and the backlight unit disposed on the back surface of the liquid crystal display panel.

  According to the backlight unit having the above-described configuration, the light stacking plate having a square shape as a whole is provided with the erroneous stacking prevention means for preventing a plurality of optical sheets from being mistakenly stacked on the light guide plate. Therefore, the gap between the side surface of the light guide plate and the inner side wall of the housing can be narrowed as compared with the conventional case provided outside the square. As a result, the width of the front frame can be shortened by the narrowing.

It is a disassembled perspective view of the backlight unit which concerns on embodiment. It is a fragmentary sectional view of the said backlight unit. It is a fragmentary sectional view of the said backlight unit. It is the schematic diagram which planarly viewed only the optical sheet and press pin in the said backlight unit. (A) is the fragmentary sectional view of the said backlight unit, (b) is the figure which planarly viewed only the positioning pin, the notch part, and these vicinity. It is sectional drawing of the liquid crystal television which concerns on embodiment. It is a disassembled perspective view of the backlight unit which concerns on a prior art. (A) is the fragmentary sectional view of the backlight unit which concerns on the said prior art, (b) is the figure which planarly viewed only a pin, a tab, and these vicinity.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is an exploded perspective view of a backlight unit 10 according to an embodiment. In addition, the scale between each member is not unified in all the figures including this figure.

  As shown in FIG. 1, the backlight unit 10 has a casing 12 that is rectangular (in this example, a horizontally long rectangle) and has a flat box shape. The casing 12 is formed by pressing a steel plate made of stainless steel or the like. The periphery of the opening of the housing 12 is formed in a flange portion 14 having a rectangular frame shape. The flange portion 14 is provided with screw holes 16, 18, 20, and 22 for fastening a front frame 78 described later. In addition, the bottom portion 24 of the housing 12 is formed with a portion that protrudes one step higher by drawing. This is mainly for increasing the rigidity of the housing 12. Furthermore, a plurality of (four in this example) columnar pins 26, 28, 30, and 32 are erected from the bottom 24 of the housing 12. The role of the positioning pins 26, 28, 30, 32 will be described later.

  The housing 12 includes a reflection sheet 34, a light guide plate 36, a diffusion sheet 38, a prism sheet 40, and a polarizing sheet 42 (hereinafter, these three sheets are collectively referred to as an “optical sheet”). The optical sheet group 44 is housed in this order from the bottom 24.

For the reflection sheet 34, for example, a polyethylene terephthalate (PET) sheet is used.
The light guide plate 36 is made of polycarbonate (PC), for example, and is a daylighting element for causing incident light to be emitted from the light emission surface on the reflection sheet 34 side main surface facing the light emission surface (one side main surface). A dot pattern (not shown) is printed. As a lighting element, a light scattering element such as a light scattering structure formed by printing, molding, etc. and a prism shape, or formed inside the light guide plate with respect to the main surface facing the light exit surface of the light guide plate However, the present invention is not particularly limited. In addition to this, an optical element that changes the light guiding direction can also be used as the daylighting element.

For the diffusion sheet 38, for example, a PET film or a PC film is used.
The prism sheet 40 is formed, for example, by forming a regular prism pattern with an acrylic resin on one side of a polyester sheet material. For the polarizing sheet 42, for example, a polyethylene naphthalate film is used.

  The thicknesses of the reflection sheet 34, the light guide plate 36, the diffusion sheet 38, the prism sheet 40, and the polarizing sheet 42 are 0.33 [mm], 4 [mm], 0.16 [mm], 0.3 [mm], respectively. It is 0.3 [mm].

  Moreover, the reflection sheet 34, the light guide plate 36, and the optical sheets 38, 40, and 42 are all rectangular in shape, and all have the same size. Here, “having a rectangular shape as a whole” means that the shape is a square, except for a local notch which will be described later. Therefore, from any of the reflection sheet 34, the light guide plate 36, and the optical sheets 38, 40, and 42, a square in which all four sides are straight lines can be considered. Therefore, in the present specification, when referring to the inside of the rectangular shape of the reflecting sheet 34, the light guide plate 36, and the optical sheets 38, 40, and 42 that are generally rectangular, the inside of the rectangular shape in which all the four sides are straight lines. Shall.

  In each of the reflection sheet 34, the light guide plate 36, and the optical sheets 38, 40, and 42, cutout portions 46A to 46E cut into a square shape from end edges corresponding to both short sides thereof, and cutout portions 48A to 48E, notches 50A to 50E, and notches 52A to 52E are established.

  Each of the cutout portions 46A to 46E, the cutout portions 48A to 48E, the cutout portions 50A to 50E, and the cutout portions 52A to 52E is the width of the lower optical sheet (an optical sheet close to the light guide plate 36), and its width. (Notch width) is increased. Note that the depth of the notch is the same.

  In a state where the reflection sheet 34, the light guide plate 36, and the optical sheets 38, 40, and 42 are correctly overlapped, the notches 46A to 46E, the notches 48A to 48E, the notches 50A to 50E, and the notches 52A to 52A Each of 52E communicates.

  Further, in each of the optical sheets 38, 40, 42, notches 54A to 54C, notches 56A to 56C, which are cut in an “U” shape inwardly from end edges corresponding to both short sides thereof, Notch parts 58A-58C and notch parts 60A-60C are established. In a state where the optical sheets 38, 40, 42 are correctly overlapped, the notches 54A to 54C, the notches 56A to 56C, the notches 58A to 58C, and the notches 60A to 60C 40 and 42 are communicated in the stacking direction.

  In the assembly process of the backlight unit 10, each of the reflection sheet 34, the light guide plate 36, and the optical sheets 38, 40, and 42 has a notch 46A to 46E, a notch 48A to 48E, and a notch 50A to 50E. The notches 52 </ b> A to 52 </ b> E are accommodated in the corresponding positioning pins 26, 28, 30, 32, and are accommodated in the housing 12. In this case, the notch portions 46D, 48D, 50D, and 52D provided in the light guide plate 36 and the corresponding positioning pins 26, 28, 30, and 32 are arranged in the vertical and horizontal directions in the housing 12 of the light guide plate 36. Functions as positioning means. The positioned light guide plate 36 is laminated using an assembly jig (not shown) so that the four sides of each of the optical sheets 38, 40, 42 are exactly overlapped with the four sides of the light guide plate 36.

LED array units 62, 64, 66, and 68, which are linear light sources, are provided so as to face each of both side surfaces corresponding to both long sides of the light guide plate 36. The LED array units 62, 64, 66, and 68 have the same configuration. The LED array units 62 and 64 are formed by mounting a plurality of white LEDs 62B and 64B in the longitudinal direction of the elongated metal base printed wiring boards 62A and 64A. The LED array units 66 and 68 are the same.
The LED array units 62, 64, 66, and 68 are held by heat sinks 70, 72, 74, and 76, respectively.

The heat sinks 70, 72, 74, 76 are made of an aluminum drawing material (angle material) having a substantially “L” -shaped cross section.
The LED array units 62, 64, 66, and 68 are attached to the LED array units 62, 64, 66, and 68 by a heat conductive double-sided tape (not shown) on the back surface of the metal base printed wiring boards 62A, 64A, 66A, and 68A. Being held.

  The actual assembly order is that the heat sinks 70, 72, 74, 76 holding the LED array units 62, 64, 66, 68 are each fixed to the bottom of the housing 12 with screws (not shown), and then the reflective sheet 34. The light guide plate 36, the diffusion sheet 38, the prism sheet 40, and the polarizing sheet 42 are accommodated in the housing 12 in this order.

  Thereafter, the front frame 78 having a square shape (rectangular shape in this example) is fastened to the flange portion 14 which is the peripheral portion of the housing 12 by screws 80, 82, 84 and 86. The front frame 78 fixes the light guide plate 36 to the casing bottom 24 in the thickness direction, and holds the periphery of the optical sheets 38, 40, 42 slidably between the light guide plate 36 as will be described later. To do.

FIG. 2 shows a sectional view of the screw 86 and the vicinity thereof in the assembled backlight unit 10.
As described above, the front frame 78 is fastened with the flange portion 14 of the housing 12 and the screw 86. The front frame 78 has a pressing pin 88 that is a pressing member protruding from the inner surface 78A facing the peripheral edge of the light guide plate 36. The pressing pin 88 lightly presses the light guide plate 36 and restrains it in the thickness direction. Here, the size T1 of the gap between the main surface 36A of the light guide plate 36 and the inner surface 78A of the front frame 78 in the fastening state is larger than the total thickness T2 of the optical sheets 38, 40, 42 by a predetermined size ( T1> T2). For this reason, the optical sheets 38, 40, 42 can slide in the direction along the main surface 36 </ b> A of the light guide plate 36 within a range described later.

  Here, the pressing pin 88 also serves as a spacer for ensuring at least the T1 between the main surface 36A of the light guide plate 36 and the inner surface 78A of the front frame 78. That is, as described above, since the casing 12 is manufactured by press molding, there is a possibility that the inclination of the flange portion 14 may vary due to its processing accuracy. Therefore, if the pressing pin 88 is not provided, the inner edge of the front frame 78 may press the optical sheets 38, 40, and 42 when the screw 86 is completely tightened depending on the direction of inclination of the flange portion 14. As a result, if the movement of the peripheral portions of the optical sheets 38, 40, 42 in the direction along the main surface 36A of the light guide plate 36 is constrained, the following problems of the prior art occur. On the other hand, when the pressing pin 88 is provided, the size of the gap between the main surface 36A of the light guide plate 36 and the inner surface 78A of the front frame 78 does not become shorter than the height from the inner surface 78A of the pressing pin 88. .

  The flange portion 14 and the front frame 78 lightly press the optical sheet 38, 40, 42 toward the light guide plate 36 by the inner edge of the front frame 78 when the screw 86 is tightened without the pressing pin 88. It can also be intentionally formed in such a shape. Thus, the tip of the pressing pin 88 is surely brought into contact with the light guide plate 36 to press the light guide plate 36, and the size of the gap between the main surface 36A of the light guide plate 36 and the inner surface 78A of the front frame 78 is the above. This is because it becomes T1 (height from the inner surface 78A of the pressing pin 88). However, in any case, there is no difference that the pressing pin 88 functions as a spacer.

  Further, as in this example, the pressing pin 88 is preferably positioned in the vicinity of the screw 86. This is because it is possible to effectively prevent the inner edge of the front frame 78 from pressing the optical sheets 38, 40, 42 toward the light guide plate 36 by tightening the screws 86. In addition to the pressing pin 88, the pressing pin is also provided in the vicinity of the screws 80, 82, and 84 (the pressing pins 83, 85, and 87 (FIG. 4)).

The number and position of screws for fastening the front frame 78 to the housing 12 and the number and position of the pressing pins are not limited to the above example, and can be appropriately increased or decreased.
Further, the pressing member is not limited to the pressing pin, and for example, may be constituted by a rib (pressing rib) formed integrally with the front frame 78 and extending from the inner surface 78A.

  The size T1 of the gap between the inner surface 78A of the front frame 78 and the main surface of the light guide plate 36 is maintained not only at the position shown in FIG. 2 (the short side portion of the front frame 78) but also over the entire circumference thereof. Yes. For example, FIG. 3 shows a partial cross-sectional view cut at a position where the LED module 66 (FIG. 1) exists (long side portion of the front frame 78). In this figure, the LED module 66 is not cut.

  Here, the difference between T1 and T2 is a so-called state in which the optical sheets 38, 42 at both ends of the laminated optical sheets 38, 40, 42 are in contact with the inner surface 78A of the front frame 78 and the main surface of the light guide plate 36, respectively. A size that is in a sliding contact state is preferable. This is because such a dimensional relationship can prevent the optical sheets 38, 40, 42 from floating from the main surface of the light guide plate 36 as much as possible.

  As shown in FIG. 3, long side peripheral portions of the reflection sheet 34, the light guide plate 36, and the optical sheets 38, 40, 42 are supported on the bottom of the housing 12 via a heat sink 74. The LED 66B is disposed opposite to the side surface of the light guide plate 36, and light emitted from the LED 66B enters from the side surface.

  The LED 66B generates heat during lighting, and the optical sheets 38, 40, and 42 tend to expand under the influence of the heat. In particular, the portion of the optical sheet close to the LED module tends to stretch well. Conventionally, since the peripheral edge portion of the optical sheet is pressed and restrained by the light guide plate by the front frame, expansion of the restrained region is suppressed. Therefore, a difference in expansion occurs between the area near the front frame and, as a result, the optical sheet undulates near the front frame. When undulation occurs, uneven brightness occurs in this portion.

  On the other hand, in the present embodiment, since the peripheral portions of the optical sheets 38, 40, 42 are slidably held, the degree of expansion difference as described above can be reduced, so that the swell is prevented as much as possible. it can.

  Since the optical sheet 38, 40, 42 is only slidably held along the main surface of the light guide plate 36, the entire optical sheet 38, 40, 42 slides relative to the front frame 78. For this reason, it is necessary to prevent the optical sheets 38, 40, 42 from sliding so that the edge of the optical sheet 38, 40, 42 is viewed from the opening window of the front frame 78, that is, the edge does not move into the opening window of the front frame 78. It is necessary to do so. In this example, the restricting means for restricting the slide are notches 54A to 54C, notches 56A to 56C, notches 58A to 58C, and notches 60A corresponding to the pressing pins 83, 85, 87, 88. It consists of ~ 60C.

  Here, the relationship in plan view of the optical sheet (38, 40, 42) and the pressing pins 83, 85, 87, 88 will be described with reference to FIG. FIG. 4 is a schematic view of only the optical sheet (38, 40,) 42 and the pressing pins 83, 85, 87, 88 viewed in plan. In FIG. 4, for the sake of convenience, the optical sheets 38, 40, and 42 are only the polarizing sheet 42, and the notches 54A to 54C, the notches 56A to 56C, the notches 58A to 58C, and the notches 60A to 60A. Each of 60C is indicated by only a number (54, 56, 58, 60). In the drawing, a two-dot chain line indicates the inner edge of the front frame 78, that is, the opening window 90. Further, an orthogonal coordinate system is set in which the X axis is parallel to the long side of the aperture window 90 and the Y axis is parallel to the short side, and the X axis direction is the horizontal direction and the Y axis direction is the vertical direction.

The dimensional relationships between the pressing pins 83, 85, 87, and 88 and the corresponding notches 54, 56, 58, and 60 are all the same. FIG. 4 shows a state in which the pressing pins 83, 85, 87, 88 are located in the middle of the notches 54, 56, 58, 60, respectively. Exactly middle means a state in which the center of the semicircle at the bottom of the notches 54, 56, 58, 60 coincides with the center of the cylindrical pressing pins 83, 85, 87, 88.
In this state, the size of the clearance (clearance) in the Y-axis direction between the pressing pins 83, 85, 87, and 88 and the notches 54, 56, 58, and 60 is d1, and the clearance (clearance) in the X-axis direction. Let the magnitude be d2. The distance in the Y-axis direction between the long side of the opening window 90 and the long side of the optical sheet 42 is D1, and the shortest distance in the X-axis direction between the short side of the opening window 90 and the notches 54, 56, 58, 60 is D2. And In such a case, in this example, the dimensions of each part are determined so that d1, d2, D1, and D2 have a relationship of D1> d1 and D2> d2. Due to this relationship, even if the optical sheet 42 is slid until the inner periphery of the notches 54, 56, 58, 60 abuts against the pressing pins 83, 85, 87, 88, the short edge of the optical sheet 42 has the opening window 90. The edge of the optical sheet does not move into the opening window 90.

FIG. 5A is a partial cross-sectional view of the backlight unit 10 cut at the position of the positioning pin 32 (FIG. 1).
As shown in FIG. 5A, a positioning pin 32, which is a columnar member standing from the bottom of the housing 12, passes through the notches 52A to 52E.

  Here, the dimensional relationship between the positioning pins 26, 28, 30, 32 and the notches 46D, 48D, 50D, 52D of the light guide plate 36 is as follows. That is, the clearances between the positioning pins 26, 28, 30, 32 and the corresponding notches 46D, 48D, 50D, 52D are extremely small. Specifically, with the notches 46D, 48D, 50D, and 52D fitted into the positioning pins 26, 28, 30, and 32, the light guide plate 36 is almost fully struck in the vertical and horizontal directions with respect to the housing 12. The clearance is set to a certain level (see FIG. 5). This is because it is necessary to accurately position the side surface (light introduction surface from the LED array) of the light guide plate 36 with respect to the light emission surface of each LED.

FIG. 5B shows a plan view of only the positioning pin 32, the notches 52A to 52C, and the vicinity thereof.
When the order in which the optical sheets 38, 40, and 42 are stacked is correct, the notch portion of the upper optical sheet has a larger notch width (in other words, the notch portion of the lower optical sheet has a smaller notch width), As shown in FIG. 5B, all of the three optical sheets 38, 40, and 42 can be visually observed around the positioning pin 32. On the other hand, if even one sheet is overlaid in the wrong order, the visible optical sheet (part) will be one sheet or two sheets. That is, whether or not the stacking order of the optical sheets 38, 40, and 42 is correct can be confirmed by the number of optical sheets that can be visually checked.

  Further, as shown in FIG. 1, the positioning pins 26, 28, 30, 32, the notches 46A to 46E, the notches 48A to 48E, the notches 50A to 50E, and the notches 52A to 52E are optical sheets. 38, 40 and 42 are provided symmetrically with respect to the center point (intersection of diagonal lines), so that the cutout portions 46A to 46E, the cutout portions 48A to 48E, The notches 50A to 50E and the notches 52A to 52E do not fit into the corresponding positioning pins 26, 28, 30, and 32. Thereby, it can prevent that the front and back of the optical sheets 38, 40, and 42 are mistakenly stacked.

  Note that the positioning pins 26, 28, 30, and 32 are not necessarily required as means for preventing the optical sheets 38, 40, and 42 from being mistakenly stacked. Even when the optical sheets 38, 40, and 42 are laminated without the positioning pin, whether or not all the front and back sides of the three optical sheets are set correctly is determined by the notches 46A to 46E and the notches. This is because it can be confirmed whether or not all (a part) of the three optical sheets 38, 40, and 42 are visible through 48A to 48E, the notches 50A to 50E, and the notches 52A to 52E.

  Returning to FIG. 5, the notch portions 52 </ b> A to 52 </ b> E which are means for preventing erroneous stacking are present inside the rectangular shape of the light guide plate 36 having a rectangular shape as a whole. Located inside the rectangle. By doing in this way, compared with the conventional backlight unit 200 (FIG. 8) in which the tabs 232 </ b> A to 232 </ b> C are arranged on the outside of the square, the side surface (notch portion) of the light guide plate 36 by the space of the tabs 232 </ b> A to 232 </ b> C. And the inner wall surface of the housing 12 can be brought closer to each other. As a result, the width W1 of the front frame 78 can be made shorter than the conventional width W2 (FIG. 8), and as a result, the so-called frame width of the liquid crystal display device can be shortened.

  In the present embodiment, the notches 46D, 48D, 50D, and 52D are provided on the side surface of the light guide plate 36, but the performance of the light guide plate 36 is hardly adversely affected. This is because, as described above, the region having a constant width from the main side surface of the light guide plate 30 originally does not have a good luminance uniformity, so this portion is not used effectively. One of the installation purposes of the front frame 78 is to cover (hide) this area that is not used effectively (periphery of the light guide plate 36). Incidentally, for example, the length of the light guide plate 36 in the longitudinal direction is 700 to 800 [mm], and the depth of the notch is about 5 [mm].

  Further, the positioning pin 32 protrudes larger than the uppermost polarizing sheet 42. This is to prevent the optical sheets 38, 40, 42 from inadvertently getting on the tip of the positioning pin 32 when the front frame 78 is attached to the housing 12. That is, when the protrusion height of the positioning pin 32 from the uppermost polarizing sheet 42 is low, even if the optical sheets 38, 40, 42 are positioned just superimposed on the light guide plate 36, in the direction along the surface. When an external force is unexpectedly applied, the optical sheets 38, 40, 42 may ride on the positioning pins 32. If the front frame 78 is fastened to the housing 12 in such a state, the optical sheets 38, 40, and 42 may be damaged. Accordingly, the positioning pin 32 is secured to a height from the main surface (upper surface) of the uppermost polarizing sheet 42, and the optical sheets 38, 40, 42 are once positioned and then run on the positioning pin 32. Is prevented from occurring. The end portion of the positioning pin 32 that has been raised is provided with a recess 92 in the front frame 78 and is housed (entered) into the recess 92. Or it is good also as not only the recessed part 92 but opening a through-hole (not shown) and inserting the said edge part into the said through-hole.

  FIG. 6 shows a liquid crystal television 100 as an example of a liquid crystal display device including the backlight unit 10 having the above configuration. FIG. 6 is a cross-sectional view showing a schematic configuration of the liquid crystal television 100. The liquid crystal television 100 includes a liquid crystal display panel 102 and a backlight unit 10 disposed on the back surface of the liquid crystal display panel 102, and the liquid crystal display panel 102 and the backlight unit 10 are housed in a housing 104. ing.

As described above, the backlight unit according to the present invention has been described based on the embodiment. However, the present invention is not limited to the above-described form, and may be, for example, the following form.
(1) In the above embodiment, when the optical sheet is slid, its edge is not looked into from the opening window of the front frame (so that the edge is not moved into the opening window of the front frame). The restricting means for restricting the slide range includes notches 46A to 46C, notches 48A to 48C, notches 50A to 50C, notches 52A to 52C provided on the optical sheet, and positioning pins corresponding thereto. However, the present invention is not limited to this and may be as follows. That is, the gap between the casing (inner wall) and other members existing in the vertical and horizontal directions of the optical sheet and the edge of the optical sheet may be set to a predetermined size, or the light guide plate side (inner surface) of the front frame may be used. ) May be provided with protrusions (ribs) to restrict the movement of the optical sheet. The predetermined size is, for example, the gap between the edge of the optical sheet in one direction in the longitudinal direction and the inner wall of the casing even if the edge slides until it contacts the inner wall of the casing, for example. Is sufficiently short so that it cannot be seen through the opening window of the front frame (so that it does not move into the opening window). The same applies to the horizontal direction.
(2) In the above embodiment, the notches 46A to 46E, 48A to 48E, 50A to 50E, and 52A to 52E are all formed in a “U” shape, but are not limited thereto. A U-shape may be used. Further, the positioning pin is not limited to a cylindrical shape, and may be an elliptical column shape or a prism shape.
(3) Although the LED array unit is arranged on the two side surfaces of the light guide plate, the present invention is not limited to this, and the present invention can also be applied to a backlight unit configured to arrange the LED array unit only on one side surface of the light guide plate. It is.
(4) In the above embodiment, the front frame and the housing are fastened with screws, but the fastening means is not limited to this, and for example, rivets may be used. Alternatively, welding may be used.

  The backlight unit according to the present invention can be suitably used as a planar light source disposed on the back surface of a liquid crystal panel of a liquid crystal display device such as a liquid crystal television.

DESCRIPTION OF SYMBOLS 10 Backlight unit 12 Case 36 Light guide plate 38 Diffusion sheet 40 Prism sheet 42 Polarizing sheet 46A-46E, 48A-48E, 50A-50E, 52A-52E Notch

Claims (4)

A housing,
A light guide plate that is housed in the housing and is generally rectangular;
A plurality of optical sheets of the same size as the light guide plate, overlaid on the light guide plate;
Erroneous stacking prevention means for preventing the optical sheet from being stacked on the light guide plate by mistake in its front and back and stacking order;
A front frame that is fastened to the peripheral edge of the housing and covers the peripheral edge of the light guide plate;
A backlight unit having
The backlight unit, wherein the erroneous stacking prevention means is provided inside the square.   The erroneous stacking prevention means is a notch provided in each of the plurality of optical sheets, communicated in the stacking direction in a state where the plurality of optical sheets are correctly stacked, and the guide The backlight unit according to claim 1, wherein the closer to the light plate, the smaller the notch.   2. The backlight unit according to claim 1, wherein the front frame holds a peripheral portion of the optical sheet so as to be slidable with respect to the light guide plate. A liquid crystal display panel;
The backlight unit according to any one of claims 1 to 3, disposed on a back surface of the liquid crystal display panel,
A liquid crystal display device comprising:

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