JP3985231B2 - Surface lighting device - Google Patents

Description

  The present invention relates to a planar illumination device used as illumination means such as a liquid crystal display device, and more particularly to a sidelight type planar illumination device using a point light source.

  Conventionally, liquid crystal display devices have been widely used as display devices for electronic devices such as personal computers and mobile phones. Since a liquid crystal is not a self-luminous display element unlike a cathode ray tube or the like, for example, in a transmissive liquid crystal display device, illumination means for irradiating light to the liquid crystal panel is indispensable, and reflection using external light is required. In many cases, the liquid crystal display device of the type and the transflective type is also provided with auxiliary illumination means to enable use in a dark place. A sidelight type planar illumination device having a light guide plate and a light source disposed on the side of the light guide plate as main components has an advantage that it can be easily thinned. It is suitably used as an illuminating means, and a cold cathode tube or the like that is a linear light source has been used as the light source. However, in recent years, with the improvement in performance of white light emitting diodes (LEDs), in order to further reduce the size and thickness and reduce power consumption, planar lighting devices using white LEDs as point light sources as light sources have increased. Yes.

  Fig.5 (a) is a top view which shows the principal part of such a sidelight type planar illuminating device, FIG.5 (b) is the AA sectional view taken on the line. In FIG. 5A, the planar illumination device 100 includes a light guide plate 101 and a point light source 102. The point light source 102 is mounted on a flexible printed circuit board (FPC) 105 so as to be lateral to the light guide plate 101. Are arranged. Here, the light guide plate 101 is a transparent member formed by injection molding of, for example, methacrylic resin or polycarbonate resin, and the point light source 102 is a white LED. In addition, an adhesive layer 106 such as a double-sided adhesive tape is interposed between one main surface 101 b of the light guide plate 101 and the FPC 105, whereby the FPC 105 is fixed to the light guide plate 101.

  Such a planar illumination device 100 causes the light emitted from the point light source 102 to enter the inside of the light guide plate 101 from the light incident surface 101c, and the incident light is incident between the one main surface 101a and the other main surface 101b. In the process of repeatedly reflecting between them and propagating through the light guide plate 101, a part of the light is emitted from the light exit surface (for example, the main surface 101a) to irradiate the liquid crystal panel. Therefore, in order to ensure sufficient luminance of the planar illumination device 100, it is important to first improve the utilization efficiency of the emitted light from the point light source 102. In this regard, the above-described planar illumination device 100 is advantageous in that the positional deviation of the point light source 102 with respect to the light incident surface 101c is small because the FPC 105 is fixed to the light guide plate 101. Have a problem.

That is, since the refractive index (n ₂ ) of the adhesive layer 106 generally made of a resin material such as methacrylic resin has a value close to the refractive index (n ₁ ) of the light guide plate 101 formed of a similar resin material, Most of the light that reaches the boundary between the main surface 101b and the adhesive layer 106 from the light source 102 enters the adhesive layer 106 side as transmitted light, and is reflected at this boundary and propagates into the light guide plate 101. As a result, the luminance of the surface illumination device 100 is reduced. In particular, as shown in FIG. 5B, even if the light (B) reaches the principal surface 101b with an incident angle equal to or greater than the critical angle (α) at the boundary between the light guide plate 101 and air, _{When 1} > n ₂ , the incident angle is smaller than the critical angle (β) at the boundary between the light guide plate 101 and the adhesive layer 106, or when n ₁ <n ₂ , regardless of the incident angle. Since total reflection does not occur, transmitted light (D) is also generated in addition to reflected light (C), and efficient use of light emitted from the point light source 102 is hindered. As a means for coping with such a problem, it has been proposed to form an adhesive layer using a material having a low refractive index such as an adhesive material containing a fluorine compound (for example, see Patent Document 1).
JP 2003-315792 A

  However, the means as described in Patent Document 1 limits the degree of freedom of material selection for the adhesive layer and the light guide plate, may increase the manufacturing cost, and has a certain refractive index as the adhesive layer. Therefore, it is not an optimal means for suppressing the generation of transmitted light at the boundary between the light guide plate and the adhesive layer, and there is room for improvement in terms of the efficiency of use of light emitted from the light source. There is.

  In view of the above problems, an object of the present invention is to provide a sidelight type planar illumination device that improves the utilization efficiency of light emitted from a point light source using an easy and inexpensive means.

In order to achieve the above object, a planar lighting device according to the present invention includes a light guide plate having one or more end faces as a light incident surface, and a spot-like shape disposed so as to face the light incident surface of the light guide plate. In a planar lighting device comprising a light source, a flexible printed circuit board on which the point light source is mounted, and a frame-shaped housing frame that holds the light guide plate , the flexible printed circuit board is arranged on the light guide plate via an adhesive layer. The adhesive layer is provided in a region excluding the front of the point light source.

  In another aspect, in the planar lighting device according to the present invention, the housing frame has a plurality of protrusions extending from a side wall facing the light incident surface of the light guide plate, and the point light source is The adhesive layer is disposed in a space between the adjacent protruding portions, and the adhesive layer includes a portion that fixes the flexible printed circuit board to the protruding portion.

  In another aspect, in the planar illumination device according to the present invention, the light guide plate has a plurality of protrusions extending from a light incident surface of the light guide plate, and the point light source is the light guide plate. The front end of the adhesive layer is disposed substantially in the same plane as the light emitting surface of the point light source or behind the light emitting surface. To do.

  According to the planar illumination device of the present invention, since the flexible printed circuit board on which the point light source is mounted is fixed to the light guide plate by the adhesive layer, the point light source is disposed on the light incident surface of the light guide plate without displacement. In addition, since the adhesive layer is provided in a region excluding the front of the point light source, the light emitted from the point light source does not enter the adhesive layer, and the light guide plate and the air It is possible to guide the inside of the light guide plate with high efficiency by normal reflection at the boundary, and it is possible to improve the utilization efficiency of the emitted light by an easy and inexpensive means.

  Furthermore, in the planar lighting device according to the present invention, the flexible printed circuit board is also fixed to the housing frame on the frame holding the light guide plate, thereby eliminating the adhesive area due to the removal of the adhesive layer in front of the point light source. The decrease is compensated, and the positional deviation of the point light source with respect to the light incident surface of the light guide plate can be effectively suppressed, and the utilization efficiency of the light emitted from the light source is improved. In particular, by extending a plurality of protrusions from the side facing the light incident surface of the light guide plate of the housing frame and fixing the flexible printed circuit board and the housing frame including these protrusions, the contact area increases. For this reason, the flexible printed circuit board and the housing frame are more closely fixed to each other, and the effect of suppressing the displacement is increased. Also, at this time, by arranging each point light source in the space between the adjacent protrusions, even if there is leakage light emitted from the point light source to the side or rear, the leakage light is turned on. The light is reflected by the wall surrounding the light source, can be changed in the direction of the light incident surface and incident on the light guide plate, and the utilization efficiency of the light emitted from the light source can be further improved.

  Further, in the planar illumination device according to the present invention, the adhesive layer is formed by extending a plurality of protrusions from the light incident surface of the light guide plate and disposing the point light source in a space between the adjacent protrusions. By arranging the front end of the light source approximately on the same plane as the light exit surface of the point light source or behind it, the light is emitted from the light exit surface in a wide angle in the horizontal direction regardless of the directivity characteristics of the light emitted from the point light source. As for light, it is possible to reliably avoid entering the adhesive layer and guide the light into the light guide plate with high efficiency.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. Fig.1 (a) is a top view which shows the principal part of the planar illuminating device 10 in the reference example of this invention, FIG.1 (b) is the sectional view on the AA line. The planar illumination device 10 includes a light guide plate 11 and a plurality of (three in this reference example ) point light sources 12 to 14. The point light sources 12 to 14 are mounted on a flexible printed circuit board (FPC) 15. Thus, the light emitting surface is disposed on the side of the light guide plate 11 so as to face the light incident surface 11 c that is one end surface of the light guide plate 11. In addition, adhesive layers 16 to 19 are interposed between the one principal surface 11 b of the light guide plate 11 and the FPC 15, whereby the FPC 15 is fixed to the light guide plate 11.

  Here, the point light sources 12 to 14 are white LEDs, and the light guide plate 11 is a plate-like light guide formed by molding a transparent resin material. Transparent resin materials suitable for the light guide plate include methacrylic resin, polycarbonate resin, polystyrene resin, polyolefin resin, amorphous polyolefin resin, polyester resin, polystyrene resin, transparent fluororesin, epoxy resin and the like. The pressure-sensitive adhesive layer in the present invention is formed of any appropriate pressure-sensitive adhesive or adhesive. Preferably, for example, an acrylic or silicone pressure-sensitive adhesive is provided on both surfaces of a substrate such as a PET film. It is a so-called double-sided adhesive tape that is applied. In this case, in this specification, it shall call an adhesion layer also including the base material part of a center.

As shown to Fig.1 (a), in this reference example , the adhesion layers 16-19 are intermittently provided only in the area | region except the front of the point light sources 12-14, ie, a light-projection direction. Therefore, in front of each point light source, there is only an air layer between the FPC 15 and the main surface 11b, which is a fixed surface with the FPC 15 of the light guide plate 11, and therefore in front of the point light sources 12-14. Light that is emitted and incident on the light incident surface 11c and reaches the main surface 11b is guided by normal reflection at the boundary between the light guide plate 11 and air without entering the adhesive layers 16 to 19 with a large transmittance. Guided into the interior of the light plate 11. In particular, as shown in FIG. 1B, light (B) having an incident angle equal to or greater than the critical angle (α) at the boundary between the light guide plate 11 and air reaches the main surface 11b is totally reflected light ( All of them are guided to the inside of the light guide plate 11 as C).

Next, a first embodiment of the present invention will be described with reference to FIG. In the following description of each embodiment, the same parts as those in the reference example described above are denoted by the same reference numerals, and the description thereof is omitted. FIG. 2A is a plan view showing a main part of the planar illumination device 20 having a housing frame 21 in addition to the configuration of the planar illumination device 10 shown in FIG. FIG. 2B is a plan view showing the planar illumination device 20 shown in FIG. 2A with the housing frame 21 omitted for explanation. Here, the housing frame 21 is a frame-like member having a region for accommodating the light guide plate 11 in the center thereof, and holds the planar illumination device 20 as an integral unit. The housing frame 21 is usually molded from a resin material mixed with a white pigment and has high light reflectivity, and suitable materials include polycarbonate resin mixed with titanium oxide as a white pigment. The light guide plate 11 can be fixed to the housing frame 21 by any joining or locking means.

  As shown in FIG. 2A, in the present embodiment, the side wall 21a of the housing frame 21 facing the light incident surface 11c has projecting portions 22 to 25 extending toward the opposite light incident surface 11c. Each of the point light sources 12 to 14 is disposed in each of the sections 26 to 28 each including a space between adjacent protrusions. Moreover, as shown in FIG.2 (b), the adhesion layer 30 is the area | regions 31-34 provided in the side of each point light source 12-14, and the area | region provided in the back of the point light source 12-14. 35, the tip portions 31a to 34a of the side regions 31 to 34 are on the light guide plate 11, the remaining portions of the side regions 31 to 34 are on the protrusions 22 to 25, and the rear region 35 is the side wall 21a. Correspond to each. The FPC 15 is fixed to both the light guide plate 11 and the housing frame 21 by the adhesive layer 30 so that the light incident surface 11c of the light guide plate 11 and the side wall 21a of the housing frame 21 are connected and integrated.

  Here, since the housing frame 21 is normally formed thicker than the light guide plate 11 and has higher dimensional accuracy and dimensional stability than the light guide plate 11, the FPC 15 is not only the light guide plate 11 but also the housing frame. 21 is also advantageous in suppressing the positional deviation between the point light sources 12 to 14 mounted on the FPC and the light incident surface 11c of the light guide plate 11, and in this case, the surface in the present embodiment. In the state lighting device 20, the side wall 21 a of the housing frame 21 has protrusions 22 to 25, and the adhesive layer 30 has side regions 31 to 34 corresponding to the protrusions 22 to 25, whereby the FPC 15 and the housing frame 21. Since the contact area with each other increases, both are more closely fixed. However, the present invention is not limited to the specific mode of the region where the FPC 15 and the housing frame 21 of the adhesive layer 30 are fixed, and depending on conditions such as the shape of the FPC 15 and the housing frame 21 and the area that can be used as the adhesive region. When only the side regions 31 to 34 are provided and fixed to the protrusions 22 to 25 or the protrusions 22 to 25 and the side wall 21a, or the region fixed to the light guide plate 11 (the tip 31a of the side regions 31 to 34). To the side wall 21a by a rear region 35 provided separately from the region corresponding to .about.34a).

  Furthermore, in the planar illumination device 20 according to the present embodiment, the respective point light sources 12 to 14 are respectively accommodated in the sections 26 to 28 surrounded on three sides by the light-reflective walls forming the housing frame 21. Therefore, even when there is leakage light emitted sideways or rearward through the package or sealing material of the point light sources 12 to 14, the leakage light is reflected by the protruding portions 22 to 25 and the side walls 21 a forming each section. Thus, the path can be changed and incident on the light incident surface 11c. Here, in this embodiment, the corner portions 26a to 28a on the housing frame 21 side of the sections 26 to 28 have curved surfaces that form arcuate curves in FIG. This shape is advantageous in effectively changing the path of leakage light in the direction of the light incident surface 11c. However, the shape and size of the corner portion 20 are determined in consideration of conditions such as the light emission characteristics of the LED used. For example, it may be formed as a chamfered portion by a flat surface, or may be a corner portion that is not particularly subjected to curved surface or flattening. Further, each of the sections 26 to 28 has a light incident surface of the light guide plate 11 from the side wall 21a side of the housing frame 21 in order to further improve the reflection efficiency of the leaked light from the point light sources 12 to 14 toward the light incident surface 11c. You may form in the shape which spreads toward 11c side.

In the first embodiment described above, in general, light emitted from the LEDs that are the point light sources 12 to 14 is emitted with directivity characteristics having a certain spread from the light emission surface, and the intensity thereof has a large directivity angle ( In other words, the adhesive layer that fixes the FPC 15 and the light guide plate 11 desirably avoids light emitted in a wide angle in the horizontal direction. Therefore, in FIGS. 1 (a) and 2 (b), the length (l) of the portion where the adhesive layer protrudes from the light emitting surface of the point light sources 12-14 (the surface facing the light incident surface 11c), and The width (w) of the area where the adhesive layer is not formed in front of the point light sources 12 to 14 and the shape of the adhesive layer are the point light sources 12 to 14 used in consideration of the fixing strength between the FPC 15 and the light guide plate 11 and the like. It is set as appropriate according to the directivity characteristics.

Next, a second embodiment of the planar light source device according to the present invention will be described with reference to FIG. FIG. 3 is a plan view showing a main part of the planar illumination device 40 according to the second embodiment of the present invention. The planar illumination device 40 has the same components as those of the first embodiment described above, but the sections 51 to 53 in which the respective point light sources 12 to 14 are arranged are light guide plates 41. This is different in that it is formed by projecting portions 43 to 46 extending from the light incident surface 41 c toward the side wall 42 a of the housing frame 42. Further, the adhesive layers 47 to 50 extending to the side of the point light sources 12 to 14 have front portions corresponding to the protruding portions 43 to 46 of the light guide plate 41 and rear portions corresponding to the side walls 42 a of the housing frame 42. The FPC 15 is fixed to both the light guide plate 41 and the housing frame 42 so that the light incident surface 41c of the light guide plate 41 and the side wall 42a of the housing frame 42 are connected and integrated by the adhesive layers 47 to 50. Has been.

  Here, in the planar device 40 in the present embodiment, the front ends 47a to 50a of the adhesive layers 47 to 50 are substantially the same as the light emitting surfaces of the point light sources 12 to 14 (surfaces facing the light incident surface 41c of the light guide plate 41). Since it is arranged on the same surface and does not have a portion (l) protruding from the light emitting surface as shown in FIGS. 1A and 2B, it is exemplified by the point light source 13 shown in FIG. Light (A) emitted in a wide angle in the horizontal direction can be reliably avoided regardless of the directivity characteristics of the point light source used. At this time, the front ends 47a to 50a of the adhesive layers 47 to 50 are substantially flush with the light emitting surfaces of the point light sources 12 to 14 as described above in order to secure a sufficient contact area between the FPC 15 and the light guide plate 41. Although arrange | positioning is preferable, the front ends 47a-50a of the adhesion layers 47-50 may be arrange | positioned behind the light-projection surface of the point light sources 12-14.

In addition, the planar illumination device according to the present embodiment includes the projecting portions 67 to 70 facing the projecting portions 63 to 66 on the light guide plate 61 side, like the planar illumination device 60 shown in FIG. The point light sources 12 to 14 may be arranged in the sections 75 to 77 formed on the side and formed by both the projecting portions 63 to 66 and 67 to 70. Even in this case, the adhesive layers 47 to 50 can be the same as the adhesive layers 47 to 50 shown in FIG. Furthermore, in the planar lighting devices 40 and 60 shown in FIG. 3 and FIG. 4, the shape of each section 51 to 53, 75 to 77, the shape of the corner portion on the housing frame 42, 62 side of each section, the adhesive layer 47 to The shape of the 50 housing frames 42, 62 and the like can be formed in the same manner as in the first embodiment described above with reference to FIG.

  In addition, although the point light source shall be arrange | positioned at the one end surface of a substantially quadrilateral light-guide plate through all the above-mentioned embodiment, this invention is with respect to the several end surface of the light-guide plate of arbitrary shapes. This includes the case where a point light source is arranged. In the present invention, the flexible printed circuit board on which the point light source is mounted may be fixed to any main surface of the two main surfaces facing the light guide plate.

It is a figure which shows the principal part of the planar illuminating device in the reference example of this invention, (a) is a top view, (b) is the sectional view on the AA line of (a). It is a figure which shows the principal part of the planar illuminating device in the 1st Embodiment of this invention, (a) is a top view, (b) abbreviate | omitted the housing frame of the planar illuminating device shown to (a). It is the shown top view. It is a top view which shows the principal part of the planar illuminating device in the 2nd Embodiment of this invention. It is a top view which shows another aspect of the division where a point light source is arrange | positioned in the planar illuminating device in the 2nd Embodiment of this invention. It is a figure which shows typically the typical structure of the conventional planar illuminating device, (a) is a top view, (b) is the AA sectional view taken on the line.

Explanation of symbols

10, 20, 40, 60 Planar illumination device 11, 41, 61 Light guide plate 12-14 Point light source 15 Flexible printed circuit board 16-19, 30, 47-50 Adhesive layer 22-25, 67-70 Projection (housing) Frame side)
43 to 46, 63 to 66 Projection (light guide plate side)

Claims (3)

A light guide plate having one or more end faces as a light incident surface, a point light source disposed so as to face the light incident surface of the light guide plate, a flexible printed circuit board on which the point light source is mounted, and the light guide plate In a planar lighting device comprising a frame-shaped housing frame that holds
The flexible printed circuit board is fixed on one surface across the light guide plate and the housing frame via an adhesive layer,
The planar lighting device, wherein the adhesive layer is provided in a region excluding the front of the point light source. The housing frame has a plurality of protrusions extending from a side wall facing the light incident surface of the light guide plate, and the point light source is disposed in a space between the adjacent protrusions, and the adhesive layer The planar illumination device according to claim 1, further comprising a portion that fixes the flexible printed circuit board to the protruding portion . The light guide plate has a plurality of protrusions extending from a light incident surface of the light guide plate, and the point light source is disposed in a space between the adjacent protrusions of the light guide plate, and the adhesive layer the front end, spread illuminating apparatus according to claim 1 or 2, characterized in that it is arranged to the rear than approximately Domen or the light exit surface and the light emitting surface of the point light source.

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