JPH0636001U - Liquid crystal display - Google Patents

Abstract

(57) [Abstract] [Purpose] To obtain uniform and bright surface illumination without uneven brightness. [Structure] A light guide plate 1 having a wedge shape in a side view is arranged on the back surface side of a liquid crystal display plate 14. The back surface of the light guide plate 1 has different inclination angles 2
The two slopes 3A and 3B are provided, and the LED 2 held by the holder 16 is arranged opposite to the thick portion 1A of the light guide plate 1.
The LED 2 is arranged so as to be displaced by Δd from the center 31 of the light guide plate 1 in the plate thickness direction on the back surface side of the light guide plate.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a liquid crystal display device that employs a backlight method using a light guide plate and LEDs.

[0002]

[Prior art]

 In general, liquid crystal display devices used for OA equipment, watches, blood pressure monitors, water heaters, various other devices, and device display devices illuminate the display section from the inside 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 bulb) is illuminated to illuminate only when a user needs it. This is because, depending on the capacity of the battery built into the device, the power that can be used at all times is as small as 60 mW to 100 mW, and the bulb cannot always light. Therefore, recently, an LED (light emitting diode), which is one of low power consumption light emitters, is used as a light source to illuminate by a backlight method. LEDs consume less power (20 mW / 1 unit) than bulbs, have high brightness and long life, and are readily available in various emission colors such as green and yellow in addition to red. It is suitable as a light source. However, simply using LEDs cannot illuminate a large area uniformly over the entire surface because the directivity of the light emission output is high. Therefore, as shown in FIG. 6, a flat panel combining the light guide plate 1 and the LEDs 2 is used. The mold light emitter is used as a light source. In this flat panel type light emitter, the light guide plate 1 is formed into a wedge shape in a side view by using a transparent resin such as acrylic resin having a high light transmittance, and the back surface is a slope 3 and the light 4 emitted from the LED 2 is guided by the light guide plate 1. The end face 5 of the thick-walled portion forming the light-incident surface is guided to the inside thereof, and is reflected by the back surface 3 of the light guide plate to emit light from the front surface 6, thereby obtaining uniform surface illumination. Electroluminescence, optical fiber, etc. Compared with other flat panel type light emitting devices using, it has the advantages of simple structure and low cost. 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 vapor deposition of aluminum, attachment of the reflection sheet 9 or the like.

[0003]

[Problems to be solved by the device]

 However, in the above-mentioned conventional liquid crystal display device using the light guide plate 1 and the LED 2, the reflection surface 3 of the light guide plate 1 is formed on one slope having the same inclination angle over the entire length, so that the amount of light and There is a problem that it is difficult to finely control the reflection direction and the visibility from the front is poor. Further, the LED 2 usually has an outer diameter substantially equal to the thickness of the light incident portion, and is disposed with the optical axis L substantially coincident with the center of the light incident surface 5 of the light guide plate 1 in the thickness direction. There is also a problem that the entire display area cannot be uniformly irradiated. That is, a part 4a of the light emitted from the LED D2 and incident on the inside of the light guide plate 1 is reflected by the reflection surface 3 and emitted from the surface 6 to the outside (direct reflection light), and a part 4b is the surface 6 of the light guide plate. After being totally reflected, the light is reflected by the reflection surface 3 and emitted from the surface 6 (total reflection light), but the reflection surface 3 is divided into, for example, three areas in the optical axis direction. Assuming that B and the farthest region are C, the light amount of the directly reflected light 4a per unit area differs from that of the totally reflected light 4b depending on each region. Therefore, as shown in Table 1 below, the regions A and C are bright. Area B becomes darker and uneven brightness occurs.

[0004]

[Table 1]

In the area A closest to the LED 2, the direct reflection light 4a is irregularly reflected, so that sufficient brightness is secured even if the total reflection light 4b is scarce. The reason why the intermediate area B becomes relatively darker than the area C is that light having an incident angle larger than the critical angle with respect to the surface 6 of the light guide plate 1 is directly transmitted and emitted to the outside, and light having a small incident angle. The total reflected light 4b is small because it is totally reflected and most of it goes to the region C, and the light amount as a whole becomes smaller than that in the region C.

Therefore, the present invention has been made in view of the above-mentioned conventional problems, and an object thereof is to obtain a uniform and bright surface illumination without thinning and miniaturization and causing uneven brightness. It is to provide a liquid crystal display device capable of

[0007]

[Means for Solving the Problems]

 In order to achieve the above object, the present invention forms a liquid crystal display panel disposed in a case and a reflective surface having a substantially wedge shape in a side view and disposed on the back surface side of the liquid crystal display panel, and the back surface is inclined. The light guide plate has a light-incident part on the thick-walled side, and an LED arranged so as to face the light-incident part of the light guide plate. The back surface of the light guide plate has a plurality of slopes with different inclination angles. The LED is arranged such that the optical axis is displaced toward the front surface or the back surface side of the light guide plate with respect to the center of the light entrance surface of the light guide plate.

[0008]

[Action]

 In the present invention, the back surface of the light guide plate is formed with a plurality of reflective surfaces each having a different inclination angle to finely control the light quantity and the reflective direction. If the LED is displaced toward the front surface or the back surface side of the light guide plate with respect to the center of the light entrance surface of the light guide plate, the reflection position of the total reflected light that hits the surface of the light guide plate and is totally reflected is displaced even if the output angle from the LED is the same. When the LED is displaced to the back surface side of the light guide plate, the reflection position shifts to the thin portion side, the emission angle is large, and the light quantity of the total reflection light that hits the surface of the light guide plate and is totally reflected and goes to the intermediate area on the back surface of the light guide plate increases . On the contrary, when the LED is displaced to the light guide plate surface side, the reflection position shifts to the thick part side, the emission angle is small, and the light amount of the total reflected light that hits the light guide plate surface and is totally reflected and goes to the intermediate area on the back surface of the light guide plate. Will increase. Therefore, the brightness of the intermediate region is increased regardless of the displacement to any side, and the brightness of the back surface of the light guide plate is made uniform over the entire surface.

[0009]

【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 of a liquid crystal display device according to the present invention, FIG. 2 is a perspective view of main constituent members, and FIG. 3 is a view showing light reflection. In the figure, the same components as those in FIG. 6 are designated by the same reference numerals. In these figures, a liquid crystal display device 11 includes a case 12 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 14 housed and arranged in the case 12 facing the opening 13. A surface plate 15 made of a transparent plate that protects the surface of the liquid crystal display plate 14 or a light diffusing plate having a milky white translucency; a light guide plate 1 disposed on the back side of the liquid crystal display plate 14; A holder 16 for holding the LED 2, a substrate 17 arranged along the inner bottom surface of the case 12 and located behind the light guide plate 1, a liquid crystal display plate 14 and a power source section 19 for the LED 2, and an upper surface of the case 12. A plurality of operation switches 20 and the like are provided.

The liquid crystal display panel 14 is well known, and has a plurality of terminals 21 arranged on one side surface in the longitudinal direction, and these terminals 21 are formed on the substrate 17 by lead wires 22. It is connected to a driving circuit (not shown). A diffusion sheet 23 is adhesively fixed to the back surface of the liquid crystal display plate 14.

The light guide plate 1 is formed in a wedge shape in a side view by a transparent resin having a high light transmission property such as acrylic resin, 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 fitted and held in the holder 16. Further, the thick portion 1A of the light guide plate 1 constitutes a light incident portion by facing the LED 2, and the recesses 26 are provided at predetermined intervals in the width direction, for example, three recesses are provided. The LEDs 2 are housed in the recesses 26, respectively. The back surface of the light guide plate 1 has a reflecting surface 3 formed by sticking a white sheet 9 that has been subjected to a high reflection treatment, and if necessary, a minute unevenness is formed by embossing to form a diffuse reflecting surface. Be done. In this case, the back surface 3 of the light guide plate is composed of two slopes 3A and 3B having different inclination angles (α, β), and the inclination angle α of the slope 3A on the thick portion 1A side is the slope 3B on the thin portion 1B side. Is smaller than the inclination angle β of.

The holder 16 is formed of resin into a box shape, and has a front surface with a recess 29 into which the thick portion 1 A of the light guide plate 1 is fitted and fixed, and a back surface with which the recess 29 communicates. However, three insertion holes 30 into which each LED 2 is inserted are formed at a predetermined interval in the width direction, and small fitting holes 32 are formed on both left and right side surfaces. The axis L of the LED 2 housed in the holder 16 is, as shown in FIGS. 1 and 3, the light guide plate rear surface with respect to the center line 31 in the plate thickness direction of the thick portion 1A forming the light entrance part of the light guide plate 1. It is displaced by Δd to the side. The holder 16 is held by fitting a protrusion (not shown) protruding from the inner surface of the case 12 into the fitting hole 32. The lead wire 34 of the LED 2 is led out from the insertion hole 30 to the rear of the holder 16, bent to the back surface side of the light guide plate, and connected to the electric circuit of the substrate 17. 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 from the thick portion 1A as shown in FIG. 3, and a part of the light 4 directly strikes the reflecting surfaces 3A and 3B. The light is totally reflected forward to become a directly reflected light 4a, a part of which is totally reflected by hitting the surface 6 of the light guide plate 1 and further reflected by hitting the reflecting surfaces 3A and 3B to be totally reflected light 4b. The liquid crystal display plate 14 and the front surface plate 15 are transmitted, so that the liquid crystal display plate 14 is back-illuminated.

The substrate 17 has a liquid crystal driving circuit including the liquid crystal driving IC, various electronic components 36 such as transistors, and a constant current circuit for 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 17 so as to be positioned in a triangular gap 38 formed between the inclined back surface (3A, 3B) forming the reflection surface of the light guide plate 1 and the substrate 17. As a result, the case 2 can be made thinner.

In the liquid crystal display device 11 having such a configuration, part of the light emitted from the LED 2 which is a point light source is directly reflected on the reflecting surfaces 3 A and 3 B of the light guide plate 1 as described above, and is totally reflected forward. By doing so, it becomes the directly reflected light 4a, a part of which is totally reflected by hitting the surface 6 of the light guide plate 1 and is further reflected by hitting the reflecting surfaces 3A and 3B to be totally reflected light 4b. A surface light source is configured by transmitting illumination. Therefore, the entire surface of the liquid crystal display plate 14 can be backlit well. Here, if the back surface of the light guide plate 1 is formed into two inclined surfaces 3A and 3B having different inclination angles, it is easy to control the light amount and the reflection direction in each of the areas A, B, and C, and uniform illumination and frontal lighting can be achieved. It is possible to improve the visibility. Further, in the present invention, the axis L of the LED 2 is displaced from the center of the thick portion 1A of the light guide plate 1 in the plate thickness direction to the back side of the light guide plate, so that the brightness can be made uniform as shown in Table 2. it can.

Table 2 shows the brightness of each area A, B, C of the reflecting surface 3 when the LED 2 is displaced to the back surface side of the light guide plate.

[0016]

[Table 2]

The reason why the intermediate region B becomes bright is that when the LED 2 is displaced to the back surface side of the light guide plate, the reflection position of the totally reflected light 4b emitted from the LED 2 and reflected on the front surface of the light guide plate shifts to the thin portion 1B side. The angle of emission from the LED 2 is large, and the total reflected light that enters the light guide plate 1 and strikes the light guide plate surface 6 to be totally reflected increases. Therefore, the amount of the total reflection light 4b directed to the intermediate region B on the back surface of the light guide plate also increases by that amount. As a result, the brightness of the areas A, B, C can be made uniform.

The present embodiment is effective when there is not enough space for displacing the LED 2 to the front surface side of the light guide plate and there is space on the rear surface side of the light guide plate. Further, by using a light diffusion plate as the surface plate 15 and diffusing the light from the LED 2 that has passed through the liquid crystal display plate 14, it is possible to eliminate the flicker of the light in a specific direction, and obtain uniform surface illumination without unevenness. You can

FIG. 4 is a sectional view showing another embodiment of the present invention. In this embodiment, the back surface of the light guide plate 1 is composed of two slopes 3A and 3B having different inclination angles α and β, and the axis L of the LED 2 is the thickness direction of the thick portion 1A forming the light entrance part of the light guide plate 1. The center line 31 is displaced by Δd toward the surface of the light guide plate. The inclination angle α of the slope 3A is larger than the inclination angle β of the slope 3B. In such a configuration, the reflection position of the totally reflected light 4b emitted from the LED 2 and totally reflected on the light guide plate surface 6 can be shifted to the thick portion 1A side. Therefore, in particular, it is possible to increase the light amount of the total reflected light 4b that is emitted at a small angle with respect to the optical axis L, hits the light guide plate surface 6 at the angle equal to or less than the critical angle, and is totally reflected, and travels toward the region B. Therefore, also in this case, the brightness of the areas A, B, and C can be made uniform, as in the above-described embodiment. Further, this embodiment is effective when there is no space on the back side of the light guide plate and there is sufficient space only on the front side of the light guide plate.

FIG. 5 is a sectional view showing still another embodiment of the present invention. In this embodiment, the rear surface of the light guide plate is formed by five slopes 3A to 3E that gradually change so that the inclination angles α1 to α5 increase from the thick portion 1A to the thin portion 1B. It has been displaced to the side. In such a structure, the light quantity and the reflection direction in each of the areas A, B, and C can be controlled more finely, and uniform illumination and visibility from the front can be improved.

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 may be used. Needless to say, the LEDs may be made to emit light to diversify the illumination.

[0022]

[Effect of device]

 As described above, in the liquid crystal display device according to the present invention, the light guide plate disposed on the back surface side of the liquid crystal display plate has a wedge shape in side view, and the back surface of the light guide plate has a plurality of slopes with different inclination angles. Since the LED arranged facing the thick portion of the light guide plate is configured to be displaced toward the front surface or the back surface side of the light guide plate with respect to the center of the light guide plate in the plate thickness direction, total reflection occurs when the light guide plate surface is hit. However, it is possible to increase the amount of total reflected light that goes to the intermediate area on the back surface of the light guide plate. Therefore, the brightness of the entire back surface of the light guide plate can be made uniform, and uneven brightness can be prevented. Further, in the present invention, since the back surface of the light guide plate is formed into a plurality of slopes, the light can be finely controlled and a uniform surface light source can be obtained.

[Brief description of drawings]

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

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

FIG. 3 is a diagram showing light reflection.

FIG. 4 is a sectional view showing an embodiment of the present invention.

FIG. 5 is a cross-sectional view showing another embodiment of the present invention.

FIG. 6 is a view showing a conventional flat panel type light emitting body using a light guide plate and LEDs.

[Explanation of symbols]

 1 Light guide plate 2 LED 3 Light guide plate back face 6 Light guide plate front face 12 Case 14 Liquid crystal display plate 16 Holder L Optical axis

Continued Front Page (72) Inventor Nobuo Matsukawa 500 Kitawaki, Shimizu City, Shizuoka Prefecture Koito Manufacturing Co., Ltd. Shizuoka Factory

Claims (1)

[Scope of utility model registration request] 1. A liquid crystal display panel disposed in a case, and a rear surface of the liquid crystal display panel, which is substantially wedge-shaped in side view, is disposed on the back side of the liquid crystal display panel to form an inclined reflection surface, and the thick-walled side receives light. Part of the light guide plate, and L arranged to face the light entering part of the light guide plate.
ED, and the rear surface of the light guide plate is composed of a plurality of slopes having different inclination angles, and the LED is disposed with its optical axis displaced toward the front surface or the rear surface side of the light guide plate with respect to the center of the light entrance surface of the light guide plate. A liquid crystal display device characterized by being provided.