JPH0636085U - Planar light emitter - Google Patents

Abstract

(57) [Summary] [Purpose] To reliably prevent the generation of bubbles and obtain a uniform and bright surface illumination without uneven brightness. [Structure] A reflection sheet 9 is adhered and fixed to the back surface of the light guide plate 1 via an adhesive 10. Air vent hole 27 in reflection sheet 9
By this, the air between the light guide plate 1 and the adhesive 10 is discharged to the outside, and the generation of bubbles 11 is prevented.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a planar light emitter suitable for use in a small liquid crystal display device or the like.

[0002]

[Prior art]

 In general, liquid crystal display devices used for OA equipment, watches, and other various display devices employ a backlight system to improve the visibility of displayed characters. In this case, generally, in a battery-powered small liquid crystal display device, reflection type illumination is performed because of low power consumption, and a bulb (incandescent light bulb) is turned on only when the user needs it. This depends on the capacity of the battery built into the device, but the power that can be used for constant lighting is as small as 60 mW to 100 mW, and it is impossible for the bulb to always light. Therefore, recently, an LED (light emitting diode), which is one of low power consumption light emitters, is used as a light source and illumination is performed by a backlight method. The LED consumes less power (20mW / 1 piece) than a bulb, has high brightness and long life, and can easily obtain various emission colors such as green and yellow in addition to red. It is suitable as a light source for illumination. However, it is not possible to uniformly illuminate a large area over a large area due to the high directivity of the light emission output by simply using LEDs. Therefore, as shown in FIG. 8, a flat panel type light emission combining the light guide plate 1 and the LED 2 is used. The body is used as a light source. In this flat panel type light emitter, the light guide plate 1 is formed in a wedge shape in a side view with a transparent resin such as acrylic resin having excellent light transmittance, and the back surface is formed as a slope 3, and the light 4 emitted from the LED 2 is guided by the light guide plate 1. A uniform surface illumination is obtained by guiding the light from the end surface 5 of the thick part of the light guide plate 5 to the inside, reflecting the light from the back surface 3 of the light guide plate, and emitting the light from the front surface 6. Other than that using electroluminescence, optical fiber, etc. It has the advantages of a simpler structure and lower cost than a flat panel type light emitter. As the LED 2, a semiconductor chip 8 molded with a transparent resin 7 having a dome-shaped tip is used. The inclined back surface 3 of the light guide plate 1 forms a reflection surface by the reflection sheet 9 being adhered and fixed via the adhesive 10.

[0003]

[Problems to be solved by the device]

 However, in the conventional planar light-emitting body using the light guide plate 1 and the LED 2 described above, when the reflection sheet 9 is adhesively fixed to the back surface 3 of the light guide plate 1, the space between the back surface 3 of the light guide plate and the adhesive 10 is fixed. It is difficult to completely remove the air. Therefore, as shown in FIG. 9, when the bubble 11 is generated, the light 4 from the LED 2 that hits the bubble 11 is diffusely reflected, which causes uneven brightness and uniform illumination can be obtained. There was a problem of not having. There is also a problem that the reflection sheet 9 is wrinkled due to the remaining air bubbles 11.

Therefore, the present invention has been made in view of the above-mentioned conventional problems, and an object thereof is to reliably prevent the generation of bubbles and to obtain a uniform and bright image without uneven brightness. Another object of the present invention is to provide a planar light emitter capable of obtaining surface illumination.

[0005]

[Means for Solving the Problems]

 In order to achieve the above-mentioned object, the present invention provides a light guide plate having a wedge shape in side view, a thick part side being a light entrance part, a front surface being an emitting surface and a back surface being a reflecting surface, and a light entering part of the light guide plate. It is provided with a light source arranged correspondingly and a reflection sheet adhered and fixed to the back surface of the light guide plate, and an air vent hole is formed in this reflection sheet.

[0006]

[Action]

 In the present invention, the air vent hole allows the air between the back surface of the light guide plate and the adhesive to escape to the outside when the reflection sheet is adhered and fixed to the back surface of the light guide plate, thereby preventing generation of air bubbles.

[0007]

【Example】

 Hereinafter, the present invention will be described in detail with reference to the embodiments shown in the drawings. FIG. 1 is a sectional view showing an embodiment in which the planar light emitting device according to the present invention is applied to a liquid crystal display device, FIG. 2 is a perspective view of main constituent members, and FIG. 3 is a sectional view of essential parts. In the figure, the same components as those in FIGS. 8 and 9 are designated by the same reference numerals. In these figures, a liquid crystal display device 12 includes a case 14 formed in a rectangular thin box shape and having an opening 13 at the center of the upper surface, and a liquid crystal display plate 15 housed and arranged in the case 14 facing the opening 13. A surface plate 16 made of a transparent plate or a light diffusing plate having a milky white translucency for protecting the surface of the liquid crystal display plate 15, and a planar light-emitting body formed with the LED 2 arranged on the back side of the liquid crystal display plate 15. Light guide plate 1, a holder 17 for holding the light guide plate 1 and the LEDs 2, a substrate 18 arranged along the inner bottom surface of the case 14 and located behind the light guide plate 1, a liquid crystal display plate 15 and a power source for the LEDs 2. The unit 19 and a plurality of operation switches 20 and the like arranged on the upper surface of the case 14 are provided.

The liquid crystal display panel 15 is well known, and has a plurality of terminals 21 arranged on one side surface in the longitudinal direction, and these terminals 21 are liquid crystal formed on the substrate 18 by lead wires 22. It is connected to a driving circuit (not shown). A diffusion sheet 23 is closely attached to the back surface of the liquid crystal display plate 15.

The light guide plate 1 is formed in a wedge shape in a side view by a transparent resin such as an acrylic resin having excellent light transmittance, so that the end portion 1A on the LED 2 side has the maximum wall thickness and the opposite end portion 1B. Has a minimum thickness, and the thick portion 1A is held by the holder 17. Further, since the thick portion 1A of the light guide plate 1 constitutes the light incident portion by facing the LED 2, the concave portions 26 are provided at predetermined intervals in the width direction, for example, three concave portions are provided. The LEDs 2 are housed in the recesses 26, respectively. The slanted back surface of the light guide plate 1 has a reflective surface 3 formed by adhering a reflective sheet 9 that has been subjected to a high-reflection treatment, and if necessary, minute unevenness is formed by embossing to diffuse the light. It is used as a reflective surface.

As shown in FIG. 3, the reflection sheet 9 has a plurality of minute air vent holes 27 formed in advance and is fixed to the back surface 3 of the light guide plate by an adhesive 10. The air vent hole 27 can be easily formed by pressing a needle-shaped member against the reflection sheet 9. Although the shape of the air vent hole 27 can be made to be an appropriate shape, a straight hole causes a large amount of the adhesive 10 to squeeze out and forms a non-reflective portion. ) And (b), the opening on the light guide plate side is a conical round hole consisting of minute holes, or the opening on the light guide plate side is a slit and the pulling direction of the reflection sheet 9 (directions A and B). ), It is desirable to have a long conical slot. Such a reflection sheet 9 is pressed against the back surface of the light guide plate by the pressure roller 30 as shown in FIG. 5, and is easily adhered and fixed by being squeezed. When adhering the reflection sheet 9, the light guide plate 1 and the reflection sheet 9 may be moved in the directions of arrows C and D, and at the same time, the pressure roller 30 may be rotated in the direction of arrow E.

Referring again to FIGS. 1 and 2, the holder 17 is formed of resin into a box shape, and thus has a recess 31 on the front surface to which the thick portion 1A of the light guide plate 1 is fitted, and on the back surface. Three insertion holes 32, which communicate with the recesses 31 and into which the LEDs 2 are inserted, are formed at predetermined intervals in the width direction, and small fitting holes 33 are formed on the left and right side surfaces. The holder 17 is fixed to the thick portion 1A of the light guide plate 1 with an adhesive, a double-sided adhesive tape, or the like, and the convex portion (not shown) provided on the inner surface of the case 14 is fitted to the fitting portion. It is held by being fitted into the hole 33.

The lead wire 34 of the LED 2 is led out from the insertion hole 32 to the rear of the holder 17, bent to the back surface side of the light guide plate, and connected to the electric circuit of the substrate 18. When the LED 2 is turned on by operating the operation switch 20, the light 4 emitted from the LED 2 enters the light guide plate 1 through the thick portion 1A, and a part of the light 4 directly hits the reflecting surface 3 and is completely reflected forward to be directly reflected. The light 4a becomes a total reflection light 4b by partially reflecting the light 6a on the surface 6 of the light guide plate 1 and further reflecting on the reflecting surface 3 and passing through the liquid crystal display plate 15 and the surface plate 16. By doing so, the liquid crystal display panel 15 is back-illuminated.

The substrate 18 has a liquid crystal driving circuit including the liquid crystal driving IC, various electronic components 36 such as transistors, and a constant current circuit of the LED 2, and is electrically connected to the power source section 19 by a lead wire 37. It is connected. The constant current circuit compensates for the temperature of LED2. That is, when the diode voltage changes with temperature, the current changes because the power supply voltage is constant, and the brightness of the LED 2 also changes. In order to prevent this, a FET transistor is incorporated in series with LED2 to form a constant current circuit. In particular, it is effective when the diode voltage is as low as 3V, 4.5V, and 6V. The electronic component 36 is mounted on the substrate 18 so as to be positioned in a triangular gap 38 formed between the inclined back surface forming the reflective surface 3 of the light guide plate 1 and the substrate 18, and The case 2 can be made thinner.

In the liquid crystal display device 12 having such a structure, a part of the light emitted from the LED 2 which is a point light source directly strikes the reflecting surface 3 of the light guide plate 1 and is totally reflected forward as described above. Results in directly reflected light 4a, part of which is totally reflected by hitting the surface 6 of the light guide plate 1 and further reflected by hitting the reflecting surface 3 to be totally reflected light 4b. Configure the light source. Therefore, the entire surface of the liquid crystal display panel 15 can be back-illuminated well. Further, in the present invention, since the air vent hole 27 is formed in the reflection sheet 9 which is adhesively fixed to the back surface 3 of the light guide plate 1, the back surface 3 of the light guide plate and the adhesive 10 are adhered to each other when pressure bonding is performed by the pressure roller 30. Air between can be released to the outside. Therefore, the reflection sheet 9 can be reliably adhered without remaining as air bubbles or generating wrinkles.

FIG. 6 is a sectional view showing another embodiment of the present invention. In this embodiment, the back surface of the light guide plate 1 is formed by five slopes 3A to 3E which gradually change so that the inclination angles α1 to α5 increase from the thick portion 1A to the thin portion 1B. Other configurations are the same as those in the above-mentioned embodiment. In such a configuration, the amount of light and the reflection direction can be controlled more finely, and uniform illumination and visibility from the front can be improved.

FIG. 7 is a cross-sectional view of the essential parts showing another embodiment of the present invention. In this embodiment, LE D2 is molded in a holder 17 to integrate them, the front opening 42 of the holder 17 is fitted to the end face of the light guide plate 1 on the thick portion 1A side, and is fixed by welding, adhesive or the like. It was done. In such a configuration, since the conical recess 43 of the holder 17 that houses the LED 2 is kept airtight, when used in a high humidity atmosphere, dew condensation may occur on the end surface of the LED 2 or the thick portion 1A. In addition, since it is possible to prevent the adhesion of dust and the like, it is possible to form a good surface light emitter without affecting the brightness.

In each of the above embodiments, a plurality of LEDs 2 of the same color are used, but the present invention is not limited to this, and LEDs of two or more colors are used, for example, a normal green LED is made to emit light, and a red color is displayed when a warning is displayed. Needless to say, the LEDs may be made to emit light to diversify the illumination.

[0018]

[Effect of device]

 As described above, the planar light emitting device according to the present invention is formed by forming the air vent holes in the reflection sheet that is adhesively fixed to the back surface of the light guide plate. The air between them can be released to the outside through the air vent hole, and the generation of bubbles can be prevented. Therefore, it is possible to obtain a good surface light emitter without the occurrence of uneven brightness due to bubbles. If no bubbles are generated, no wrinkles are formed on the reflection sheet, and the appearance is good.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an embodiment of a liquid crystal display device having a planar light emitting device according to the present invention.

FIG. 2 is a perspective view of main constituent members.

FIG. 3 is an enlarged sectional view of a main part.

4A and 4B are plan views of air vent holes, respectively.

FIG. 5 is a diagram showing a method of attaching a reflection sheet.

FIG. 6 is a sectional view showing another embodiment of the light guide plate.

FIG. 7 is a cross-sectional view of essential parts showing an embodiment in which an LED and a holder are integrally formed.

FIG. 8 is a diagram showing a conventional example of a planar light-emitting body using a light guide plate.

FIG. 9 is a diagram showing generation of bubbles.

[Explanation of symbols]

 1 Light guide plate 2 LED 3 Light guide plate back surface 6 Light guide plate surface 9 Reflective sheet 10 Adhesive 15 Liquid crystal display plate 17 Holder 27 Air vent hole

Claims (1)

[Scope of utility model registration request] 1. A light guide plate, which is formed in a wedge shape in a side view and has a light-incident portion on the thick-walled side, an emission surface on the front surface, and a reflection surface on the back surface, and the light-incident portion of the light-guide plate is disposed corresponding to the light-incident portion. Light source,
A planar light-emitting body, comprising: a reflection sheet adhered and fixed to the back surface of the light guide plate; and an air vent hole formed in the reflection sheet.