JP2010218972A - Planar lighting system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a planar lighting system which improves yellowing without deteriorating luminance of emitted light. <P>SOLUTION: This planar lighting system 10 includes a light guide plate 11 and a white light source 12 disposed on the side end face of the guide plate 11. The surface 11a of the light guide plate 11 is used as a light emitting surface, a white reflection layer 13 is disposed on the back surface 11b side of the light guide plate 11, and a blue reflection layer 14 is disposed on the back surface side of the white reflection layer 13. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a planar lighting device, and more particularly, to a side light type planar lighting device including a light guide plate and a light source disposed on a side of the light guide plate.

  In general, in a so-called sidelight type planar illumination device having a light guide plate and a primary light source disposed on the side of the light guide plate as main components, the light guide plate material has a high value for high illumination brightness. Transparency is required, and from this viewpoint, an acrylic resin is preferably used. On the other hand, from the viewpoint of cost reduction, it is preferable to use a polycarbonate (PC) resin that is less expensive than an acrylic resin.

  However, since the PC resin has a larger blue light absorption rate than the acrylic resin, in the light guide plate made of PC resin, the blue light component is generated in the process in which the white light incident from the side end surface propagates through the light guide plate. It is known that there is a problem that the phenomenon that the light emitted from the light guide plate is yellowed is significantly absorbed and is yellowed.

  In addition, white light emission in LEDs that are currently widely used as light sources for planar lighting devices is a phosphor that emits blue light from a blue light emitting element and yellow light that is a complementary color by absorbing the blue light. The mainstream is a method of mixing yellow light from, etc., and yellowing of the emitted light as described above becomes a problem particularly when such a white LED is used as a light source.

  In order to cope with this problem, conventionally, a planar illumination device has been proposed in which the light reflecting material of the light emitting region formed on the light guide plate is made of a material including a correction material for the color component of light absorbed by the light guide plate. (For example, refer to Patent Document 1). FIGS. 3A and 3B are diagrams showing an example of such a conventional planar illumination device, in which FIG. 3A is a top view and FIG. 3B is a side view showing a part thereof enlarged.

  A planar illumination device 100 shown in FIG. 3 includes a light guide plate 112 made of a transparent resin, and a white LED 102 disposed on one end face A of the light guide plate 112, and is provided on one main surface B of the light guide plate 112. Are provided with light emitting regions 111 a to 111 c that diffusely reflect light incident on the main surface B in the process of propagating through the light guide plate 112. In the planar lighting device 100, the light emitting regions 111a to 111c are formed by mixing a blue pigment with a white material, thereby suppressing the absorption of the blue component in the light emitting regions 111a to 111c, and the light emitted from the main surface B. It is intended to prevent yellowing.

JP 2008-177106 A

  However, the planar illumination device 100 as shown in FIG. 3 increases the blue reflectance of the light emitting regions 111a to 111c arranged on the main surface B of the light guide plate 112. In other words, this is a light emitting region 111a. If ~ c is composed only of a white material, it increases the absorptance of other color light components (for example, yellow light components) that should become the emitted light, so that there is a problem that the luminance of the emitted light as a whole decreases. is there. Furthermore, in the planar illumination device 100 as shown in FIG. 3, the structure of the light guide plate 112 becomes complicated in order to improve the yellowing of the emitted light, which increases the manufacturing cost of the planar illumination device 100. There is also a problem.

  In view of the above problems, an object of the present invention is to provide a planar illumination device that improves yellowing without reducing the luminance of emitted light by simple and inexpensive means.

  The following aspects of the present invention exemplify the configuration of the present invention, and will be described separately for easy understanding of various configurations of the present invention. Each section does not limit the technical scope of the present invention, and some of the components of each section are replaced, deleted, or further, while referring to the best mode for carrying out the invention. Those to which the above components are added can also be included in the technical scope of the present invention.

(1) A light guide plate and a white light source disposed on a side end surface of the light guide plate, the surface of the light guide plate as a light emitting surface, and a white reflective layer disposed on the back side of the light guide plate; A planar illumination device comprising a blue reflective layer disposed on the back side of the white reflective layer (Claim 1).

  According to the planar illumination device described in this section, by providing the blue reflective layer on the back side of the white reflective layer, only the blue light component of the leaked light from the white reflective layer is reflected with high efficiency, and the light guide plate Because it can be reused as light emitted from the light guide plate, it is possible to improve the yellowing of the emitted light by correcting the absorption of the blue light component by the light guide plate with simple and inexpensive means. become.

  Further, in the planar illumination device described in this section, the blue light transmittance of the light guide plate itself is increased, or the blue light reflectance of the light reflection region or the white reflection layer formed on the light guide plate is increased (that is, In this case, the leakage of light from the white reflective layer, which was discarded in the conventional configuration without the blue reflective layer, is reused. It becomes possible to improve yellowing without reducing the brightness of the incident light.

(2) In the planar lighting device according to (1), the blue light reflectance of the blue reflective layer is from the side end surface side of the light guide plate on which the white light source is disposed toward the opposite side end surface side. A planar lighting device (claim 2) characterized in that it increases.

  In the surface illumination device described in this section, the color of the emitted light is increased by increasing the blue light reflectance of the blue reflective layer from the side end surface side where the white light source is disposed toward the opposite side end surface side. Can be corrected according to the increase in the absorption of the blue light component accompanying the propagation of light in the light guide plate, effectively improving the yellowing on the end face side of the light guide plate, and exiting from the light emitting surface. It is possible to make the color of the incident light uniform.

(3) The planar illumination device according to (1) or (2), wherein the blue reflective layer is made of a blue reflective sheet (Claim 3).

(4) The planar illumination device according to (1) or (2), wherein the blue reflective layer is made of a blue ink printed on the back surface of the white reflective layer. (Claim 4).

  According to the present invention, it is possible to provide a planar illumination device that improves yellowing without lowering the luminance of emitted light by the configuration as described above. In particular, the present invention has a remarkable effect in a configuration including a light guide plate made of PC resin and a light source made of white LED, thereby realizing a low-cost and high-quality planar illumination device. It becomes possible to do. Since the planar illumination device according to the present invention improves yellowing of the emitted light by simple and inexpensive means, the backlight for the keyboard of a personal computer (particularly, a notebook personal computer) that has a high cost requirement for the members. As such, it is particularly advantageous.

In one Embodiment of the planar illuminating device which concerns on this invention, it is a side view which decomposes | disassembles and shows the principal part. It is a disassembled block diagram which shows the example of the keyboard provided with the planar illuminating device in one Embodiment of this invention. It is a figure which shows an example of the conventional planar illuminating device, (a) is a top view, (b) is a side view which expands and shows a part.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is an exploded side view showing a main part of a planar illumination device 10 according to an embodiment of the present invention. The planar lighting device 10 includes a light guide plate 11 that is a plate-shaped light guide made of a transparent resin, and a white light source 12 disposed on one end face 11c of the light guide plate 11, and the white light source 12 extends to the side end face 11c. Light that enters through the light guide and propagates through the light guide plate 11 is emitted from the light emitting surface that is one main surface (surface) 11a of the light guide plate 11 to irradiate the object to be illuminated.

  The planar lighting device 10 further includes a white reflective layer 13 disposed on the other main surface (back surface) 11 b side of the light guide plate 11 and a blue reflective layer 14 disposed on the back surface 13 b side of the white reflective layer 13. ing. Note that regular reflection means or diffuse reflection means (not shown) may be provided on the back surface 11 b of the light guide plate 11.

  In the present embodiment, the white light source 12 includes a white LED, is mounted on the FPC 15, and is disposed on the light incident surface 11 c of the light guide plate 11. The light guide plate 11 is made of polycarbonate (PC) resin.

  The white reflective layer 13 is made of a white reflective sheet obtained by forming a resin material such as whitened PET into a sheet shape. Here, as means for whitening a resin material such as PET, white pigments such as barium sulfate and titanium dioxide are dispersed in the resin material, fine bubbles are contained in the resin material, or white as described above. Any means such as printing a white ink having a pigment as a component may be used. Such a white reflective layer 13 has a substantially uniform reflectance over the wavelength range of visible light.

  Further, in the present embodiment, the blue reflective layer 14 is a blue reflective sheet formed by dispersing a blue material such as a blue pigment or a dye in a synthetic resin material and forming it into a sheet shape.

  In the planar lighting device 10 configured as described above, the light emitted from the white LED 12 is repeatedly reflected between the light emitting surface 11a and the back surface 11b after entering the light guide plate 11 from the light incident surface 11c. However, in the process, a part of the light reflected by the back surface 11b (or by the regular reflection means or the diffuse reflection means provided on the back surface 11b if present) is partly emitted. It radiates | emits from 11a and irradiates to-be-illuminated bodies, such as a keyboard.

  At that time, the white reflective layer 13 fulfills the function of reflecting light leaking from the back surface 11b and re-entering the light guide plate 11, but the reflectance of the white reflective layer 13 configured as described above is as follows. Usually, it is about 93.2%, and therefore there is leakage light from the white reflective layer 13 of about 6.8%. The planar lighting device 10 arranges the blue reflective layer 14 on the back surface 13b side of the white reflective layer 13 to reflect only the blue light component in the leaked light from the white reflective layer 13 with high efficiency, and again. The light is incident on the light guide plate 11. This corrects the absorption of the blue light component accompanying propagation in the light guide plate 11 and improves the yellowing of the emitted light.

  Thus, in the planar lighting device 10, the light guide plate 11 itself, the positive (diffuse) reflecting means formed on the light guide plate 11, and the white reflective layer 13 are increased in the absorptance of color light components other than blue light. Rather than correcting the color of the emitted light, the leakage light from the white reflective layer 13 that was discarded in the conventional configuration without the blue reflective layer 14 is reused. It is possible to improve yellowing without reducing the luminance of the emitted light.

  Here, the blue reflective layer 14 is directed from one end 14c disposed on the light incident surface 11c side of the light guide plate 11 toward the other end 14d disposed on the side end surface 11d side opposite to the light incident surface 11c, for example. The blue light reflectance may be increased by increasing the content of the blue material.

  This makes it possible to correct the emitted light from the light emitting surface 11a according to the increase in the absorption of the blue light component accompanying the propagation of the light in the light guide plate 11, and the yellow on the end surface 11d side of the light guide plate 11 The change can be effectively improved, and the color of the emitted light from the light emitting surface 11a can be made uniform.

  At this time, the blue light reflectance and the increase rate of the blue reflective layer 14 are appropriately set in consideration of the size of the light guide plate to be used, the spectral transmittance characteristics, and the like. However, the blue light reflectance is preferably set so as to change smoothly without exhibiting a rapid change.

  In the above description, the blue reflective layer 14 is configured as a blue reflective sheet separate from the white reflective layer 13, but the blue reflective layer 14 according to the present invention is a white that forms the white reflective layer 13. A blue ink having a blue pigment as a component (for example, 456 process blue manufactured by Seiko Advance Co., Ltd., CAV Meiban / CAV transparent series) may be printed on the back surface 13b of the reflection sheet.

  In this case, in order to increase the blue light reflectance of the blue reflective layer 14 from the one end 14c toward the other end 14d, for example, the blue ink is divided into a plurality of small regions (for example, dots) and printed. It can be realized by increasing the area density of the small region from one end 14c toward the other end 14d.

  As described above, the planar lighting device according to the present invention corrects the absorption of the blue light component by the light guide plate by a relatively simple and inexpensive means of providing the blue reflective layer on the back side of the white reflective layer. In order to improve the yellowing of the emitted light, it is possible to realize a low-cost but high-quality planar lighting device. The present invention can be applied particularly advantageously as a keyboard backlight for a personal computer.

  The exploded block diagram of FIG. 2 shows an example of a keyboard unit to which the planar illumination device according to the present invention is applied as a backlight. A keyboard unit 21 shown in FIG. 2 is incorporated in a notebook personal computer, and has a masking sheet on the back side of a keyboard assembly 22 having a key cap 22a and a stabilizer (not shown) for sliding the key cap up and down. A backlight 28 is arranged through the projector 23. The backlight 28 is arranged on the light guide plate 24, the plurality of LEDs 27 mounted on the flexible substrate 25, the white reflection sheet 26 arranged on the back surface side of the light guide plate 24, and the back surface side of the white reflection sheet 26. It consists of a blue reflective sheet 27 and constitutes an example of the configuration of a planar illumination device according to the present invention. Of course, the backlight 28 may be configured by performing blue printing on the back side of the white reflective sheet 26 without using the blue reflective sheet 28.

10: planar illumination device, 11: light guide plate, 12: white light source (white LED), 13: white reflective layer, 14: blue reflective layer

Claims (4)

  A light guide plate, and a white light source disposed on a side end surface of the light guide plate, the surface of the light guide plate serving as a light emitting surface, a white reflective layer disposed on the back side of the light guide plate, and the white light reflection A planar lighting device comprising a blue reflective layer disposed on the back side of the layer.   2. The planar shape according to claim 1, wherein the blue light reflectance of the blue reflective layer increases from a side end surface side of the light guide plate on which the white light source is disposed toward an opposite side end surface side. Lighting device.   The planar illumination device according to claim 1, wherein the blue reflective layer is made of a blue reflective sheet.   The planar illumination device according to claim 1, wherein the blue reflective layer is made of blue ink printed on a back surface of the white reflective layer.

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