JP2003279972A - Liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display device for improving luminance without generating luminance irregularities by improving the reflection efficiency inside a light transmission plate of light emitted from a backlight light source in the liquid crystal display device provided with a backlight structure in which the backlight light source such as an LED is disposed on the side face of the light transmission plate. <P>SOLUTION: In the liquid crystal display device 21 with a backlight provided with the light transmission plate 28, a frame body 24 holding the light transmission plate 28 and the light source (LED 27) emitting the light to the light transmission plate 28, a reflection sheet 29 is disposed so as to surround the back surface 28a and side faces 28b, 28c, 28d and 28e of the light transmission plate 28. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device having a backlight light source.

[0002]

2. Description of the Related Art In recent years, display devices using liquid crystal cells have been installed in all kinds of electronic equipment such as watches, telephones and personal computers. Among such electronic devices, in particular, clocks, mobile phones and the like are used at night or in a dark place, and therefore, many of them have a backlight for illuminating a liquid crystal cell.

FIG. 5 shows the structure of a conventional liquid crystal display device 1 having a backlight function. The liquid crystal display device 1 includes a liquid crystal cell unit 2 and a backlight unit 3,
These are housed in the same frame body 4 in a stacked state. The liquid crystal cell part 2 has a structure in which a liquid crystal substance is sandwiched between two glass substrates having a transparent electrode film formed thereon.
And two polarizing plates (not shown) disposed on the upper surface and the lower surface of the liquid crystal cell 5. The backlight unit 3 includes an LED 7 as a light source and a light guide plate 8 for guiding the light emitted by the LED 7. The light guide plate 8
Is formed of a transparent acrylic material having a quadrangular shape having substantially the same area as the liquid crystal cell 5, and one side surface thereof serves as the light receiving surface 13. The LED 7 is mounted on a substantially central portion of the circuit board 6 on which electronic components and electrode patterns are formed, and the LED 7 is mounted on the light emitting surface 1.
1 is disposed in the side wall of the frame body 4 with the light guide plate 1 facing the light receiving surface 13 of the light guide plate 8. In some cases, a light shielding sheet 12 for preventing light leakage is arranged above the LEDs 7, and a reflection sheet 9 is spread on the back surface of the light guide plate 8. A diffusion sheet 10 is arranged between the upper surface of the light guide plate 8 and the liquid crystal cell 5 to scatter the reflected light from the light guide plate 8 to illuminate the liquid crystal cell 5. Further, the frame 4 may be formed of a resin material mixed with a white pigment or dye, or a white paint may be applied to the inner wall surface to enhance the reflection effect.

In the liquid crystal display device 1 having the above structure, the light from the LED 7 incident on the light receiving surface 13 of the light guide plate 8 is
In addition to going straight through the light guide plate 8 as it is, the light is reflected by the reflection sheet 9 and the inner wall surface of the frame body 4 provided on the back surface. As a result, the light guide plate 8 is made to uniformly emit light, and the liquid crystal cell 5 arranged above is illuminated.

[0005]

However, in the above-mentioned conventional liquid crystal display device 1, the reflection sheet 9 is spread on the bottom surface of the frame body 4 on which the light guide plate 8 is mounted, and the reflection sheet 9 is reflected upward. Although the efficiency is improved, since the reflection efficiency on the inner wall surface of the frame body 4 is low, the brightness at the outer peripheral portion of the light guide plate 8 is low,
This was a cause of uneven brightness.

Therefore, an object of the present invention is to provide a liquid crystal display device having a backlight structure in which a backlight light source such as an LED is arranged on the side surface of the light guide plate, and the light guide plate for the light emitted from the backlight light source is provided. It is intended to provide a liquid crystal display device which improves brightness and prevents uneven brightness by increasing internal reflection efficiency.

[0007]

In order to solve the above problems, a liquid crystal display device according to claim 1 of the present invention is directed toward a light guide plate, a frame body for holding the light guide plate, and the light guide plate. A liquid crystal display device with a backlight including a light source that emits light is characterized in that a reflection sheet is arranged so as to surround a side surface of the light guide plate.

According to the present invention, since the reflection sheet is arranged so as to surround the side surface of the light guide plate, which has not been sufficiently obtained in reflection efficiency, the light hitting the inner wall surface of the frame body from the side surface of the light guide plate. Is reflected again in the light guide plate by the reflection sheet, so that the brightness of the outer peripheral portion of the light guide plate is increased and the uneven brightness with the center part of the light guide plate is eliminated.

Further, a liquid crystal display device according to a second aspect of the present invention has a backlight provided with a light guide plate, a frame body for holding the light guide plate, and a light source for emitting light toward the light guide plate. In the liquid crystal display device, a reflection sheet is arranged so as to surround the back surface and the side surface of the light guide plate.

According to the present invention, the reflection efficiency can be further improved by disposing the reflection sheet so as to surround the back surface and the four side surfaces of the light guide plate. In this case, by integrally forming the reflection sheets provided on the back surface side and the side surface side of the light guide plate, the mounting work inside the frame becomes extremely easy.

Further, a cutout window is formed in one of the side walls of the reflection sheet, and the light source is arranged so as to project into the reflection sheet from the cutout window, so that the light emitted from the light source is not leaked inside the reflection sheet. Can be irradiated.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a liquid crystal display device according to the present invention will be described below in detail with reference to the accompanying drawings. Figure 1
2 is a sectional view of a liquid crystal display device according to the present invention, and FIG. 2 is an exploded perspective view of the liquid crystal display device.

As shown in FIGS. 1 and 2, the liquid crystal display device 21 according to this embodiment has a frame 24 and a frame 24.
Backlight part 23 and liquid crystal cell part 2 laminated inside
2 and. The frame body 24 is formed by processing a plastic material into a rectangular box shape.
The first accommodating part 30a for accommodating 3 and the second accommodating part 30b for accommodating the circuit board 26 on which the LED 27 are mounted are provided. A step portion 31 for mounting the liquid crystal cell portion 22 is provided on the first storage portion 30a, and the second storage portion 30 is provided.
A partition wall 37 is formed at the boundary with b.

The backlight unit 23 includes a light guide plate 28.
And a light source (LED 27) arranged on one side surface 28b side of the light guide plate 28, and a reflection sheet 29 covering the back surface 28a of the light guide plate 28 and the four side surfaces 28b, 28c, 28d, 28e. The light guide plate 28 is a rectangular thin plate made of a transparent acrylic material, and a concave portion 32 serving as a light receiving portion by incorporating the LED 27 is formed on one side surface 28b. The LED 27 is mounted on a substantially central portion of the circuit board 26, and is fitted and fixed in the second storage portion 30b with its light emitting surface 33 facing the recess 32 side of the light guide plate 28. A wiring 38 extends from the circuit board 26 for electrical connection with the outside. The reflection sheet 29 has substantially the same size as the light guide plate 28, and has a back surface 28 of the light guide plate 28.
a bottom wall 29a having a rectangular shape that covers a, and side walls 29b and 2b that stand up by bending four sides of the bottom wall 29a.
It is integrally formed with 9c, 29d, and 29e. Then, slits 35 are formed at the four corners of each side wall 29b to 29e, and L is formed on the side wall 29b on the LED 27 side.
A cutout window 34 into which the ED 27 is inserted is formed. Further, a light shielding sheet 12 for preventing leakage of light is disposed above the circuit board 26, and further, on the upper surface of the light guide plate 28, the emitted light is evenly propagated to the liquid crystal cell unit 22, A diffusion sheet 10 is provided.

Since the reflecting sheet 29 is provided with a cutout window 34 for inserting the LED 27 and a slit 35 for facilitating bending of the side walls 29b to 29e,
According to the shape and size of the light guide plate 28, the light guide plate 28 can be covered without any gap, and sufficient adhesion can be maintained. If the adhesion with the light guide plate 28 can be ensured, the reflection sheet can be formed by separately forming the bottom wall 29a and the side walls 29b to 29e and joined together.

As is well known, the liquid crystal cell section 22 has a liquid crystal cell 25 having a structure in which a liquid crystal substance is sandwiched between two glass substrates on which transparent electrode films are formed, and the liquid crystal cell 25 has an upper surface and a lower surface. It is composed of two polarizing plates (not shown) arranged.

In the liquid crystal display device 21 having the above structure, as shown in FIG. 2, the reflection sheet 2 in which the four side walls 29b to 29e are previously bent in the first housing portion 30a of the frame 24.
9 is placed, and the back surface 28a and the side surfaces 28b to 28e of the light guide plate 28 are placed thereon so as to be wrapped therewith. Then, the light emitting surface 33 of the LED 27 is connected to the concave portion 3 of the light guide plate 28.
The circuit board 26 is mounted and fixed to the second accommodating portion 30b of the frame body 24 in the state of being oriented toward 2. After that, the light shielding sheet 12 is covered over the circuit board 26 to shield the gap between the light guide plate 28 and the frame 24 from light. Finally, the diffusion sheet 1 is placed on the light guide plate 28.
0 is placed, and the outer peripheral portion of the liquid crystal cell 25 is placed and fixed on the step portion 31 provided on the frame body 24.

FIG. 3A shows the light reflecting action when the backlight unit 23 is viewed from directly above, and FIG. 3B shows the light reflecting action when the backlight unit 23 is viewed from the side. It is shown. As shown in FIG. 3A, the LED 2
The light emitted from the light emitting front surface of No. 7 is reflected by the side wall 29d of the reflection sheet 29 located on the front surface, and the light radially emitted from the LED 27 is reflected by the side walls 29c and 29e. In addition, the light that circulates behind the LED 27 is reflected by the rear side wall 29b. Furthermore, the side wall 29b-
The primary reflection light at 29e is reflected again toward the other side wall, so that the inside of the light guide plate 28 can be brightly illuminated in every corner.

On the other hand, as shown in FIG. 3B, the bottom wall 29 of the reflection sheet 29 covering the back surface 28a of the light guide plate 28.
At a, the light emitted mainly downward from the LED 27 is reflected upward. By the light reflecting action on the side walls 29b to 29e and the bottom wall 29a of the reflection sheet 29, light is incident from all surfaces of the light guide plate 28 except the surface on which the liquid crystal cell 25 is mounted. Light is evenly distributed to every corner and emits light with high brightness. In addition, since the reflection sheet 29 has a structure in which the frame body 24 and the light guide plate 28 are brought into close contact with each other without a gap, it is not necessary to join them using an adhesive agent for joining or the like. Therefore, the light emitted from the LED 27 can be reflected to the light guide plate 28 without leakage.

In order to demonstrate the above effect, a liquid crystal display device 21 including a backlight portion 23 using the reflection sheet 29, a reflection sheet on the back surface of the light guide plate, and a frame on which other side surfaces are painted white. The brightness and the brightness unevenness were measured with the liquid crystal display device 1 having a conventional backlight unit that reflects on the inner wall surface of the body. The reflection sheet 29 has a thickness of 8
The product of Kimoto Co., Ltd. having a silver (Ag) vapor deposition film formed on the surface of 4 μm was used. In this measurement, as shown in FIG. 4A, in addition to the liquid crystal display devices 1 and 21 to be measured,
Drive power supply 15 for liquid crystal display devices 1 and 21, drive signal device 1
6 and luminance meter 17 (RISA-C manufactured by HI-LAND)
D) is used. The liquid crystal display device sample used in this measurement has a liquid crystal cell surface of 35 × 41.5 mm,
Two EDs were set on one side of the light guide plate. As shown in FIG. 4B, 5 × 5 measurement points were set uniformly in the vertical and horizontal directions with the center point of the liquid crystal cell as P0. The measurement point located on the outer peripheral portion is set to be inside about 10% of the entire width from the outer periphery of the liquid crystal cell.

The luminance is measured by setting the drive signal in advance so that the optimum contrast can be obtained when viewed from the front in a dark room in which no incident light from the surroundings enters, and then the drive signal device 1
The entire white (total transmission signal) is displayed by 6 and the central portion of the liquid crystal cell portion 22 shown in FIG. 4 (b) is installed at a position separated by a distance L (50 cm) with the maximum brightness (dimming maximum). The brightness is measured by the brightness meter 17.

Regarding the brightness unevenness, the liquid crystal display devices 1 and 21 are placed in the same dark room state as described above, and the brightness at each measurement point (P0 to P24) on the liquid crystal cell portion 22 at the maximum brightness is measured by the brightness meter 17.
Are calculated by the following formulas.

[0023]

[Equation 1]

Table 1 below shows the results of measuring the central position luminance, the maximum luminance, the average luminance, and the luminance unevenness for three samples of the conventional liquid crystal display device 1 and the liquid crystal display device 21 of the present embodiment. is there. Here, the central position luminance is shown in FIG.
As shown in (b), P0 which is the center of the liquid crystal cell
The brightness at the point and the maximum brightness are P which is the closest to the LEDs 7 and 27.
21 and the brightness centering on P23 and the average brightness are P0 to P
It refers to the average luminance of all 24. As can be seen from Table 1, the liquid crystal display device 21 of the present embodiment has the LED 7,
Regarding the maximum brightness depending on the distance from 27, although there is not much change from the conventional liquid crystal display device 1, the central position brightness and the average brightness are high as a whole. Further, the uneven brightness was reduced from the conventional 65.75% to 55.42%, and an improvement effect of about 18% was obtained. This is an LED
The light emitted by 7, 27 is the bottom wall 29 of the reflection sheet 29.
a side wall 29b that surrounds not only a but also the four sides of the light guide plate 28
This is because the reflected light at 29e has a great influence. Therefore, the entire light guide plate 28 can be made to emit light uniformly, so that the liquid crystal cell surface can be evenly illuminated with high brightness.

[0025]

[Table 1]

[0026]

As described above, according to the liquid crystal display device of the present invention, since the reflection sheet is arranged so as to surround the side surface of the light guide plate where the reflection efficiency is not sufficiently obtained in the related art, Light that hits the inner wall surface of the frame from the side surface of the light plate is reflected back into the light guide plate by the reflection sheet,
The brightness of the outer peripheral part of the light guide plate is increased, and the uneven brightness with the center part of the light guide plate is eliminated.

Further, the reflection efficiency can be further improved by disposing the reflection sheet so as to surround the back surface and the four side surfaces of the light guide plate. In this case, by integrally forming the reflection sheets provided on the back surface side and the side surface side of the light guide plate, the mounting work inside the frame becomes extremely easy.

[Brief description of drawings]

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

FIG. 2 is an exploded perspective view of the liquid crystal display device of FIG.

FIG. 3 is an operation diagram showing a light reflection effect in a light guide plate of the liquid crystal display device.

FIG. 4 is an explanatory diagram showing a luminance measuring method of a liquid crystal display device.

FIG. 5 is a cross-sectional view of a conventional liquid crystal display device.

[Explanation of symbols]

21 Liquid Crystal Display 22 Liquid crystal cell section 23 Backlight part 24 frame 25 liquid crystal cell 26 circuit board 27 LED (light source) 28 Light guide plate 28a back side 28b-28e side surface 29 Reflective sheet 29a bottom wall 29b to 29e Side wall 34 cutout window

Claims (4)

[Claims] 1. A liquid crystal display device with a backlight, comprising: a light guide plate; a frame body holding the light guide plate; and a light source that emits light toward the light guide plate, wherein a side surface of the light guide plate is surrounded. A liquid crystal display device characterized in that a reflection sheet is disposed on the. 2. A liquid crystal display device with a backlight, comprising: a light guide plate; a frame body holding the light guide plate; and a light source that emits light toward the light guide plate. A liquid crystal display device characterized in that a reflection sheet is provided so as to surround the liquid crystal display device. 3. The liquid crystal according to claim 2, wherein the reflection sheet is integrally formed by a bottom wall that covers the back surface of the light guide plate and a side wall that rises from the peripheral portion of the bottom wall and surrounds the side surface of the light guide plate. Display device. 4. A cutout window is formed in one of the side walls,
The liquid crystal display device according to claim 3, wherein the light source is disposed so as to project from the cutout window into a reflection sheet.