JP2012109103A - Plane light source device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain generation of an emission line due to light leakage from an edge of an opening of a shading sheet.SOLUTION: A diffusion sheet 28 and prism sheets 29a, 29b are sequentially laminated on a light guide plate 24 housed in a frame 23, and a shading sheet 30 is adhered to the frame 23 over the prism sheet 29b. The shading sheet 30 includes an opening 31 opposed to an effective light-emitting area of the light guide plate 24. At an opening edge of a side positioned at a light source side of the shading sheet 30, at least a pair of concave parts 32 parallel to the side 34 are provided, and a tip part of a flap part 33 which is made between the concave parts 32 is adhered to an upper surface of an end part of the prism sheet 29b.

Description

  The present invention relates to a surface light source device, for example, a surface light source device used as a backlight for illuminating a liquid crystal panel.

  In a liquid crystal display unit of a cellular phone, a surface light source device (backlight) for illumination is disposed behind a liquid crystal panel. As such a surface light source device, for example, one disclosed in Patent Document 1 is known.

  FIG. 1A is a plan view showing a part of a conventional surface light source device (portion close to the light source), and FIG. 1B is a sectional view thereof. In the surface light source device 11, a light guide plate 13 and a light source 14 are housed in a frame 12, and a diffusion sheet 15 and two optical sheets 16 a and 16 b are overlapped on the upper surface (light emission surface) of the light guide plate 13. And the light shielding sheet 17 which consists of a black double-sided adhesive sheet etc. is affixed on the flame | frame 12 from the optical sheet 16b. The light shielding sheet 17 has a frame shape, and the effective light emitting area of the light guide plate 13 is exposed from the opening portion 19, while covering the periphery of the effective light emitting area and the light source 14.

  By the way, in the liquid crystal display device for incorporation, the demand for thinning has become strict, and accordingly, the thickness of the light guide plate used in the surface light source device has gradually decreased. On the other hand, since it is difficult to reduce the thickness (height) of the light source, in recent surface light source devices, the upper surface of the light source 14 or the flexible printed circuit board 18 on which the light source 14 is mounted and the upper surface of the light guide plate 13 are used. The level difference between is large.

  Therefore, as illustrated in FIG. 1B, a gap is easily generated between the upper surface of the end portion of the optical sheet 16 b and the opening edge of the light shielding sheet 17. In such a surface light source device 11, as indicated by an arrow in FIG. 1B, when the light L incident from the light source 14 into the light guide plate 13 leaks from a position closer to the light source than the end of the optical sheet 16b. The light is repeatedly reflected between the lower surface of the light shielding sheet 17 and the upper surface of the optical sheet 16 b and emitted from the edge of the opening 19 of the light shielding sheet 17. The light leaked from the edge of the opening 19 of the light shielding sheet 17 in this manner causes the edge of the effective light emitting region of the surface light source device 11 to shine brightly as shown by hatching in FIG. High brightness area), and the optical quality of the surface light source device 11 is reduced.

  Further, in order to eliminate the gap under the light shielding sheet 17 as described above, when the opening edge of the light shielding sheet 17 is pressed and adhered to the end of the optical sheet 16b as shown in FIG. The optical sheet 16b is pulled up due to the elastic restoring force. Therefore, as shown in FIG. 2, the light L leaked from the upper surface of the light guide plate 13 at a position near the light source is repeatedly reflected between the lower surface of the optical sheet 16 b and the upper surface of the optical sheet 16 a to open the light shielding sheet 17. The light is emitted from the edge of the portion 19. As a result, the edge of the effective light emitting region of the surface light source device 11 is also brightly lit to generate the bright line α, and the optical quality of the surface light source device 11 is deteriorated.

  In order to reduce such a problem, the protruding length (distance D shown in FIG. 1A) from the flexible printed circuit board 18 to the opening edge of the light shielding sheet 17 is increased, and the opening edge of the light shielding sheet 17 is What is necessary is just to make it easy to hang down on the optical sheet 16b.

  However, recently, it has been required to increase the ratio of the area of the effective light emitting region to the planar size of the surface light source device. For this reason, the width of each side (edge piece) of the light shielding sheet is also narrowed, and the overhanging length D from the flexible printed circuit board 18 to the opening edge of the light shielding sheet 17 cannot be increased. When bonded to the end of 16 b, the optical sheet 16 b is lifted by the elastic restoring force of the light shielding sheet 17.

JP 2008-123931 A

  The present invention has been made in view of the technical problems as described above, and an object thereof is a surface light source capable of suppressing generation of bright lines due to light leaking from the edge of the opening of the light shielding sheet. To provide an apparatus.

  In the surface light source device according to the present invention, a light guide plate and a light source arranged to face the light incident end face of the light guide plate are accommodated in a frame, and one or more optical sheets are stacked on the light guide plate. A surface light source in which a light shielding sheet having an opening corresponding to an effective light emitting area of the light guide plate is overlaid on the optical sheet, and the light source is mounted on the lower surface and the light shielding sheet is bonded to the upper surface of the frame. The apparatus is characterized in that at least a pair of recesses or slits are provided on the light source side edge of the opening of the light shielding sheet. The concave portion is a cut portion having a certain width, which is obtained by cutting the light shielding sheet into a concave shape, and the slit is a cut portion which is linearly cut and has almost no width.

  In the surface light source device of the present invention, since at least a pair of recesses or slits is provided at the light source side edge of the opening of the light shielding sheet, both ends of the portion between the recesses or slits of the light shielding sheet are the other parts of the light shielding sheet. It becomes easy to bend by being separated from the part of. Therefore, even if the portion between the concave portion or the slit of the light shielding sheet is bonded to the optical sheet, the optical sheet is hardly lifted by the elastic restoring force of the portion. For this reason, light hardly leaks from the opening edge on the light source side of the light shielding sheet, and generation of bright lines can be suppressed.

  An embodiment of the surface light source device according to the present invention is characterized in that a pair of recesses are provided at a light source side edge of the opening of the light shielding sheet, and a slit is provided from the recess toward the light source side. . According to this embodiment, light leakage can be reduced as compared with the case where the entirety is a recess, and the portion sandwiched between the recess and the slit is easier to move than when the entirety is a slit.

  Another embodiment of the surface light source device according to the present invention is characterized in that a bent portion for facilitating bending of the region between the concave portion or the slit of the light shielding sheet is provided between the concave portion or the slit. The bent portion can be formed by, for example, perforated cut or half cut. According to this embodiment, it becomes easier to bend the part between the recessed part or slit of a light shielding sheet.

  In another embodiment of the surface light source device according to the present invention, the recess or slit is provided in a range not overlapping the wiring board. Since the light shielding sheet is supported by the wiring board and cannot bend at the part that overlaps the wiring board, it is necessary and sufficient if the recess or slit is provided in a range that does not overlap the wiring board, and excess light from the recess or slit. Leakage can be eliminated.

  The means for solving the above-described problems in the present invention has a feature in which the above-described constituent elements are appropriately combined, and the present invention enables many variations by combining such constituent elements. .

FIG. 1A is a partially broken plan view of a surface light source device according to a conventional example. FIG. 1B is a partially broken cross-sectional view of the surface light source device. FIG. 2 is a partially broken sectional view showing a state in which the light shielding sheet is bonded to the surface of the optical sheet in the surface light source device shown in FIG. FIG. 3 is an exploded perspective view of the surface light source device according to Embodiment 1 of the present invention. FIG. 4 is a partially broken plan view of the surface light source device according to the first embodiment. FIG. 5 is a partially broken sectional view of the surface light source device according to the first embodiment. FIG. 6 is a partially cutaway plan view of a surface light source device according to Embodiment 2 of the present invention. FIG. 7 is a partially broken sectional view of the surface light source device according to the second embodiment. FIG. 8 is a partially broken plan view of a surface light source device according to Embodiment 3 of the present invention. FIG. 9 is a partially broken sectional view of the surface light source device according to the third embodiment. FIG. 10 is a partially cutaway plan view of a surface light source device according to Embodiment 4 of the present invention.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. However, the present invention is not limited to the following embodiments, and various design changes can be made without departing from the gist of the present invention.

[First Embodiment]
FIG. 3 is an exploded perspective view of the surface light source device 21 according to Embodiment 1 of the present invention. FIG. 4 is a partially cutaway plan view of the surface light source device 21. FIG. 5 is a partially broken cross-sectional view of the surface light source device 21.

  First, components of the surface light source device 21 will be described with reference to FIG. The surface light source device 21 includes a reflective sheet 22, a frame 23, a light guide plate 24, a plurality of light sources 26 mounted on the lower surface of a flexible printed circuit board 25 (wiring board), a diffusion sheet 28 (optical sheet), and prism sheets 29a and 29b. (Optical sheet) and a light shielding sheet 30.

  The reflection sheet 22 is a smooth sheet made of a white resin sheet or metal foil having a high light reflectance. Each of the plurality of light sources 26 is an LED white light source that emits white light, and is mounted on the lower surface of the flexible printed circuit board 25 at a predetermined interval.

  The light guide plate 24 is formed of a resin having a high refractive index and translucency, such as polycarbonate resin or polymethyl methacrylate resin (PMMA). The light guide plate 24 is provided with a wedge-shaped light introducing portion 35b whose upper surface is inclined at the end of a plate-shaped light guide plate body 35a having a uniform thickness. A large number of minute optical patterns 36 are formed on the lower surface of the light guide plate main body 35a (see FIG. 5), and the upper surface of the light guide plate main body 35a is a light emitting surface 24b (light emitting surface). The light introducing portion 35b has a light incident end surface 24a for taking in light of the light source 26 at the end surface on the larger thickness side, and is continuous with the light guide plate body 35a at the end on the smaller thickness side. The light source 26 is arranged so that the light emission window faces the light incident end surface 24a of the light guide plate 24 with a small gap therebetween or in close contact therewith.

  The diffusion sheet 28 is a translucent resin film for diffusing the light emitted from the light emitting surface 24b of the light guide plate 24 to widen the directivity characteristic (viewing angle) of the illumination light. The prism sheets 29a and 29b are transparent resin films having a triangular prism-like fine pattern formed on the upper surface, and the directions of the patterns are orthogonal to each other when viewed from the vertical direction.

  The light shielding sheet 30 is a flexible black adhesive sheet (rim sheet) whose upper and lower surfaces are adhesive surfaces. The light shielding sheet 30 has a frame shape, and has an opening 31 in a region corresponding to the effective light emitting region of the light guide plate 24. The light shielding sheet 30 is generally in the shape of a frame, but there is also a sheet that covers only two sides that are not the side on the light source side and the side opposite to the light source.

  At least a pair of concave portions 32 (cut portions) are cut out at the opening edge on the light source side of the light shielding sheet 30 in parallel with the both sides 34 of the light shielding sheet 30. Here, the concave portion 32 is a cut portion having a certain width, obtained by cutting the light shielding sheet 30 into a concave shape. The concave portion 32 may be formed at the same time when the black sheet is punched out with a press device or the like to produce the light shielding sheet 30, and may be punched out later or cut with a cutter or the like. The recess 32 is provided at a position that does not overlap the side 34 of the light shielding sheet 30 and is not bonded to the frame 23, the flexible printed circuit board 25, or the like. Therefore, a portion between the recesses 32 (hereinafter, this portion is referred to as a flap portion 33) has a tip (free end) that is easily bent up and down.

  The frame 23 is a member that surrounds the periphery of the light guide plate 24, the diffusion sheet 28, the prism sheets 29a and 29b, and the wiring passage portion 27 is partially cut away. The frame 23 is generally formed of a white resin. The frame 23 functions as a casing of the surface light source device 21 together with the reflection sheet 22 and the light shielding sheet 30.

  Next, the structure when the surface light source device 21 is assembled will be described with reference to FIGS. 4 and 5 are a plan view and a cross-sectional view of the surface light source device 21 on the light source arrangement side.

  As shown in FIGS. 4 and 5, the outer periphery of the reflection sheet 22 is bonded to the lower surface of the frame 23 by the double-sided adhesive tape 37, and the space in the frame 23 is closed by the reflection sheet 22 on the lower surface. The light guide plate 24 is placed in the frame 23 and placed on the reflection sheet 22. The light source 26 is housed in the frame 23 so that the light emitting window faces the light incident end surface 24a of the light guide plate 24, and the lower surface of the flexible printed circuit board 25 is bonded to the frame 23 using a double-sided adhesive tape or the like. The wiring lead-out part of the flexible printed circuit board 25 passes through the wiring passage part 27 of the frame 23 and is drawn to the outside of the frame 23. Further, a diffusion sheet 28 and prism sheets 29a and 29b are sequentially stacked on the light emitting surface 24b of the light guide plate 24.

  The light shielding sheet 30 is overlaid on the frame 23 from above the prism sheet 29 b and adhered to the upper surface of the frame 23 and the flexible printed circuit board 25. Further, the front end portion of the flap portion 33 is pressed against the prism sheet 29b and bonded to the end portion of the prism sheet 29b. As a result, the periphery of the light guide plate 24, the diffusion sheet 28, and the prism sheets 29a and 29b is covered with the light shielding sheet 30, and only the region corresponding to the effective light emitting region of the light guide plate 24 in the prism sheet 29b is exposed from the opening 31. It is done.

  In the surface light source device 21 assembled in this way, the light guide plate 24, the flexible printed circuit board 25 and the light source 26, the diffusion sheet 28, and the prism sheets 29 a and 29 b housed in the frame 23 are the light shielding sheet 30 and the reflection sheet 22. Held between.

  Although not shown, a liquid crystal panel (not shown) and other members are arranged on the surface light source device 21 to constitute a liquid crystal display device.

  In the surface light source device 21 having such a structure, since the height of the light incident end face 24a is larger than the thickness of the light guide plate body 35a, the thickness of the light guide plate body 35a is thinner than the height of the light source 26. Even in this case, the light emitted from the light source 26 can be efficiently taken into the light introducing portion 35b, and the light emission luminance of the surface light source device 21 can be increased. As indicated by a broken line arrow in FIG. 5, the light Ls that has entered the light introducing portion 35b from the light incident end surface 24a is guided to the light guide plate body 35a while being reflected by the upper and lower surfaces of the light introducing portion 35b. Further, the light Ls guided to the light guide plate body 35 a is guided through the light guide plate 24 while being totally reflected by the upper and lower surfaces of the light guide plate 24, and spreads throughout the light guide plate 24. On the lower surface of the light guide plate 24, there are minute prism-shaped optical patterns 36 (triangular columnar minute patterns in which the lower surface of the light guide plate 24 is recessed, or triangular columnar minute patterns protruding from the lower surface of the light guide plate 24). Many are formed. Therefore, when the light Ls guided in the light guide plate 24 enters the optical pattern 36 and is totally reflected by the optical pattern 36, the incident light is smaller than the critical angle of total reflection among the light Ls totally reflected by the optical pattern 36. Light incident on the light exit surface 24b at the corner exits from the light exit surface 24b to the outside. In this way, the directivity characteristic of the light emitted from the light exit surface 24b is relatively narrow, so that the light is gently diffused by transmitting through the diffusion sheet 28, thereby widening the directivity characteristic. Further, the direction of the light is bent by transmitting through the prism sheets 29a and 29b so that the maximum luminance direction is close to the direction perpendicular to the light emitting surface 24b.

  On the other hand, the flap portion 33 of the light shielding sheet 30 is bonded to the prism sheet 29b so that no gap is generated between the flap portion 33 and the prism sheet 29b. Further, although the flap portion 33 is bonded to the prism sheet 29b, the flap portion 33 is provided with the concave portions 32 at both ends, and the elastic restoring force is weak. Therefore, the flap portion 33 is weak and easily follows the surface of the prism sheet 29b. Therefore, the prism sheet 29b is hardly lifted upward by the flap portion 33, and a gap is not easily generated between the prism sheet 29a and the prism sheet 29b. Therefore, as shown by the solid line arrow in FIG. 5, even if the light L incident in the light guide plate 24 leaks from the upper surface of the light guide plate 24 on the light source side with respect to the prism sheet 29 b, the leaked light L remains on the light shielding sheet 30. It is possible to improve the optical quality of the surface light source device 21 without leaking from the edge, making it possible to brighten the edge of the effective light emitting region of the surface light source device 21 and making it difficult to generate a partial bright line (high luminance region). it can.

[Second Embodiment]
FIG. 6 is a partially broken plan view of the surface light source device 41 according to Embodiment 2 of the present invention. FIG. 7 is a partially broken cross-sectional view of the surface light source device 41. In the surface light source device 41, a slit 42 is provided as a cut portion of the light shielding sheet 30 instead of the concave portion 32 of the first embodiment. Here, the slit 42 is a cut portion that is linearly cut and has almost no width. In other words, the recess 32 is a cutting method in which cut pieces (debris) are generated, and the slit 42 is a cutting method in which cut pieces are not generated. The slit 42 may be formed at the same time when the black sheet is punched out with a press device or the like to produce the light shielding sheet 30, or may be cut later with a cutter or the like.

  Even when such a slit 42 is provided, since the elastic restoring force of the flap portion 33 between the slits 42 is weakened, the flap portion 33 can easily follow the upper surface of the prism sheet 29b, and the flap portion 33 can be attached to the prism sheet 29b. When bonded, the prism sheet 29 b is hardly lifted by the flap portion 33. Therefore, also in this embodiment, it is possible to prevent the bright line α from being generated by brightly shining the edge of the effective light emitting region of the surface light source device 41.

  When Embodiment 1 and Embodiment 2 are compared, there are the following features. In the case of Embodiment 1, since the notch part is the recessed part 32 with a width | variety, there exists a possibility that light may leak a little from this notch part (notch 32). Therefore, the length of the concave portion 32 cannot be made too long. In the first embodiment, the concave portion 32 is stopped in the middle between the front end of the flap portion 33 and the end of the flexible printed circuit board 25. There is a possibility that the upper surface of the prism sheet 29b is somewhat difficult to copy. On the other hand, in the case of Embodiment 2, since the cut portion is the slit 42, it is difficult for light to leak from the cut portion (slit 42). Therefore, in the case of the slit 42, the length can be lengthened, and in the second embodiment, the slit 42 can be extended to the vicinity of the end of the flexible printed circuit board 25. Therefore, using the slit 42 can weaken the elastic restoring force of the flap portion 33 and the flap portion 33 can easily follow the upper surface of the prism sheet 29 b, and the prism sheet 29 b is less likely to be lifted by the flap portion 33.

  On the other hand, in the case of the slit 42, both sides of the slit 42 rub against each other, so that there is a risk that wrinkles may occur in the light shielding sheet 30 at the slit 42.

[Third Embodiment]
FIG. 8 is a partially cutaway plan view of a surface light source device 51 according to Embodiment 3 of the present invention. FIG. 9 is a partially broken cross-sectional view of the surface light source device 51. In the surface light source device 51, on the light source side, the opening edge of the light shielding sheet 30 is provided with a recess 32 parallel to both sides 34, and the slit 42 is provided continuously from the tip of the recess 32 and parallel to both sides. For example, the recess 32 has a length up to the middle between the tip of the flap portion 33 and the end of the flexible printed board 25, and the slit 42 further extends from the tip of the slit 42 to the end of the flexible printed board 25. And the center part of the flap part 33 is adhere | attached on the upper surface of the diffusion sheet 28 or the light-guide plate 24, and the front-end | tip part of the flap part 33 is adhere | attached on the upper surface of the prism sheet 29b. In this embodiment, even if the length of the cut portion is increased, the slit 42 is provided at a location close to the light source 26, so that it is difficult to leak light from the cut portion. Further, since the concave portion 32 is formed at the distal end portion of the flap portion 33, the distal end portion of the flap portion 33 is not easily caught on both sides of the concave portion 32 when the distal end portion of the flap portion 33 is bonded to the prism sheet 29b. 33 becomes easy to adhere. Furthermore, by bonding the upper surface of the flap portion 33 to the upper surface of the diffusion sheet 28 or the light guide plate 24, the prism sheet 29 b can be pressed down by the flap portion 33.

  In contrast to the third embodiment, the concave portion 32 may be provided continuously with the tip of the slit 42.

[Fourth Embodiment]
FIG. 10 is a partially cutaway plan view of a surface light source device 61 according to Embodiment 4 of the present invention. In this surface light source device 61, at least one of the concave portion 32 and the slit 42 is provided as a cut portion to form a flap portion 33, and a perforated cut or half cut is made in the flap portion 33 along the width direction thereof. Thus, a bent portion 62 is formed. Since the half cut is a cut that does not penetrate, light does not leak. In the illustrated example, one bent portion 62 is shown, but a plurality of bent portions 62 may be provided. According to this embodiment, the flap portion 33 can be bent at the position of the bent portion 62, and the flap portion 33 can be easily followed along the upper surface of the diffusion sheet 28 or the light guide plate 24. The position of the bent portion 62 may be adjusted according to the product. However, if the bent portion 62 is provided in the vicinity of the edge of the flexible printed circuit board 25 far from the light source, the flap 33 is located on the side far from the light source of the flexible printed circuit board 25. It becomes easy to bend around the edge.

  In addition, although not shown in figure, as a light-guide plate, you may use what changed the thickness in the whole wedge shape.

  In order to confirm the effect of the present invention, the emission rates of bright lines were compared using the surface light source device as in the third embodiment and the surface light source device (comparative example) having no notches such as the recess 32 and the slit 42. The light shielding sheet used in the comparative example has a vertical length of 97.54 mm, a horizontal width of 53.63 mm, an opening width of 51.94 mm, a width of the side on the light source side of 6.03 mm, and the width of the side opposite to the light source. The width was 10.03 mm, the side width was 0.85 mm, and the thickness was 0.05 mm. The light-shielding sheet used in Embodiment 3 is provided with a recess 32 having a length of 0.8 mm and a width of 1.00 mm in the light-shielding sheet used in the comparative example, and further having a length of 0.8 mm so as to be continuous with the recess 32. A slit 42 is provided.

  1270 surface light source devices of the comparative example were manufactured, 583 surface light source devices of the example 3 were manufactured, and the number of the bright lines generated was examined. In the comparative example, 343 bright lines were generated. In No. 3, 12 bright lines were generated. Therefore, in the comparative example, the generation rate of the bright line reached 27.01%, but in the third embodiment, it was only 2.06%, and a significant improvement effect could be confirmed.

21, 41, 51, 61 Surface light source device 23 Frame 24 Light guide plate 25 Flexible printed circuit board 26 Light source 28 Diffusion sheet 29a, 29b Prism sheet 30 Light shielding sheet 31 Opening portion 32 Recessed portion 33 Flap portion 34 Side edge 42 Slit

Claims (5)

A light guide plate and a light source arranged to face the light incident end face of the light guide plate are housed in a frame, and one or more optical sheets are stacked on the light guide plate, and an effective light emitting region of the light guide plate is formed. In the surface light source device in which a light shielding sheet having a corresponding opening is overlaid on the optical sheet, the light source is mounted on the lower surface of the wiring board, and the light shielding sheet is bonded to the upper surface of the frame.
A surface light source device, wherein at least a pair of recesses or slits is provided at an edge on the light source side in the opening of the light shielding sheet.   2. The surface light source device according to claim 1, wherein a pair of recesses is provided at a light source side edge of the opening of the light shielding sheet, and a slit is provided from the recess toward the light source.   2. The surface light source device according to claim 1, wherein a bent portion is provided between the recessed portions or the slits so as to facilitate folding of the region between the recessed portions or the slits of the light shielding sheet.   The surface light source device according to claim 3, wherein the bent portion is formed by a perforated cut or a half cut.   The surface light source device according to claim 3, wherein the recess or the slit is provided in a range that does not overlap the wiring board.

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