JPH0566404A - LCD lighting device - Google Patents

Abstract

(57) [Summary] [Purpose] To increase the brightness of the illumination surface. [Structure] Light guide plate 11 (refractive index n2) and reflection sheet 13
Between the rear translucent film 16 (1 <n1 <
n2) is provided to increase the critical angle on the rear surface of the light guide plate 11. Light emitted to the outside of the display area L1 of the light guide plate 11 is effectively reflected inside the light guide plate 11 by the front reflection film 15. A front light-transmitting film 17 (1 <n1 <n2) having a refractive index of n1 is provided between the front reflection film 15 and the light guide plate 11 to increase the critical angle of the front reflection film 15. [Effect] The total reflection ratio of the light flux on the rear surface of the light guide plate and outside the display area L1 is increased, and the loss of the light flux is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an edge light type lighting device used for back lighting of a light receiving liquid crystal display device.

[0002]

2. Description of the Related Art Conventionally, as a lighting device used in a liquid crystal display device, as shown in FIGS. 4 and 5, an edge light type lighting device using a light guide plate tends to be mainly used from the standpoint of thinning.

A discharge tube such as a cold cathode tube or a hot cathode tube is used as a light source 1 of this illuminating device, and the discharge tube is arranged on both sides of a light guide plate 2 made of a translucent material. As the light guide plate 2, polymethylmethacrylate (PMM) having excellent light transmittance is used.
Acrylic resins such as A) are mainly used.

Further, in order to improve the utilization efficiency of the light emitted from the light source 1 and to make the brightness of the illumination surface uniform, the rear surface of the light guide plate 2 has a light scattering treatment function such as TiO ₂ system or BaS.
Patterning the O ₄ ink 3 by silk printing,
A diffusion sheet 4 made of a milky white synthetic resin plate is provided on the front surface of the light guide plate 2 in order to improve the diffusion uniformity in the display area. Further, the light emitted from the light source 1 and directed to the back surface is reflected by the reflection sheet 5 and guided to the front surface, thereby improving the light utilization efficiency.

In the figure, 6 is a light source reflector for reflecting the light from the light source 1 to the outside toward the light guide plate 2, and 7 is a liquid crystal display plate.

[0006]

The conventional edge light type illuminator using the light guide plate has the following problems.

1) The refractive index of the light guide plate 2 is 1.49,
When the light in the light guide plate 2 is reflected on the rear surface, the critical angle θ
c = sin ⁻¹ (1 / 1.49) = 42 °.

Therefore, when the light in the light guide plate 2 is incident on the rear surface at an angle of θ> θc, the loss of the light flux when the light is reflected at the reflectance ρ (= 0.9) of the reflection sheet 5. Accordingly, the effective light utilization efficiency that can be used on the diffusion sheet 4 is reduced accordingly.

2) Further, as described above, in order to load the light scattering function on the rear surface of the light guide plate 2, the pattern 3 having a high scattering effect such as TiO ₂ or BaSO ₄ is silk-printed. Support area L for supporting the light plate 2
s is at least 3 outside the display area L1 (hatched area in the figure)
It was necessary to have a width of mm or more.

From the above, in an illuminating device having the same tube surface brightness of the light source 1 and the same light incident end face area of the light guide plate 2, the light guide plate 2 has a larger vertical and horizontal dimension than the display region L1. As the light plate 2 becomes larger, the light display area L1
The light loss is large. Therefore, the brightness of the illumination surface (light emission surface) on the diffusion sheet 4 is lowered, and there is a problem in realizing a particularly high-luminance and thin specification liquid crystal illumination device.

In view of the above problems, it is an object of the present invention to provide a thin liquid crystal illuminating device capable of increasing the brightness of an illuminating surface.

[0012]

The means for solving the problems according to claim 1 of the present invention is to illuminate the liquid crystal display panel 10 from the rear side as shown in FIGS. 1 to 3 and is arranged in parallel with the liquid crystal display panel 10. A light guide plate 11, a light source 12 arranged at an end portion of the light guide plate 11, and a reflection sheet 13 for reflecting backward light in the light guide plate 11 on the rear surface of the light guide plate 11 toward the liquid crystal display plate 10 side.
In a liquid crystal lighting device provided with a diffusion sheet 14 for making the brightness of the illumination surface uniform over the entire surface, a light-transmitting film 16 is in close contact with both of the light guide plate 11 and the reflection sheet 13. The light-transmitting film 16 has a refractive index n1 of 1 <n1 <n2, where n2 is the refractive index of the light guide plate 11.

According to a second aspect of the present invention, the means for solving the problem is to illuminate the liquid crystal display panel 10 from the rear side, and the light guide plate 11 arranged in parallel with the liquid crystal display plate 10 and the light guide plate 11 are provided.
A light source 12 arranged at the end of the light guide plate, a reflection sheet 13 for reflecting the backward light in the light guide plate 11 to the liquid crystal display panel 10 side at the rear surface of the light guide plate 11, and the brightness of the illumination surface over the entire surface. In a liquid crystal lighting device provided with a diffusion sheet 14 for uniformization, a front reflection film 15 that reflects light from the light source 12 into the light guide plate 11 outside the display region L1 on the front surface of the light guide plate 11. Is provided, and the translucent film 17 is closely interposed between the front reflection film 15 and the light guide plate 11.
The refractive index n1 of the transparent film 17 is the refractive index n of the light guide plate 11.
2 is set to 1 <n1 <n2.

[0014]

In the means for solving the problems according to the above-mentioned claim 1, the light from the light source 12 enters the inside from the light incident end face of the light guide plate 11 and then is reflected forward by the reflection sheet 13 to be reflected by the light guide plate 11. The back surface of the liquid crystal display panel 10 is illuminated from the front surface.

At this time, if a light-transmitting film 16 having a refractive index of more than 1 is provided between the light guide plate 11 and the reflecting sheet 13, the light generally has a large refractive index and a small refractive index. Since the critical angle of light increases upon incidence, the critical angle on the rear surface of the light guide plate 11 increases and the ratio of total reflection of the light flux increases.

In the problem solving means according to the second aspect, when the outside of the display area L1 of the light guide plate 11 is large, the irradiation light to this portion is effectively reflected inside the light guide plate 11 by the front reflection film 15. ..

At this time, since the translucent film 17 having a refractive index of more than 1 is provided between the front reflection film 15 and the light guide plate 11, the critical angle of the front reflection film 15 increases, The ratio of total reflection of the light flux at this portion increases.

[0018]

1 is a principle view showing the light reflection of a liquid crystal lighting device according to an embodiment of the present invention, FIG. 2 is a plan view thereof, and FIG. 3 is a sectional view taken along the line AA.

As shown in the figure, the liquid crystal lighting device of this embodiment illuminates the liquid crystal display panel 10 from the rear by the edge light method, and includes a light guide plate 11 arranged in parallel with the liquid crystal display plate 10. Light sources 1 arranged at both ends of the light guide plate 11.
2, a reflection sheet 13 for reflecting the backward light from the light guide plate 11 to the liquid crystal display plate 10 side, a diffusion sheet 14 for uniformizing the brightness of the illumination surface over the entire surface, and the light guide plate 11 Front reflection film 15 for reflecting the light from the light source 12 into the light guide plate 11 outside the display region L1 on the front side of the front surface, and the rear light transmission film 16 for reducing light attenuation between the light guide plate 11 and the reflection sheet 13. And a front light-transmitting film 17 for reducing light attenuation between the front reflection film 15 and the light guide plate 11.

As shown in FIGS. 1 to 3, the light guide plate 11 is made of a translucent acrylic resin such as polymethylmethacrylate (PMMA) having a refractive index n = 1.49, and has a length dimension of 191 mm and a width. Dimension 147mm, thickness 6.0m
It is formed in a flat plate shape of m. On the rear surface of the light guide plate 11, TiO ₂ and BaSO ₃ are added to load a light scattering function.
_The white ink 18 having a high scattering effect such as ₄ is silk-printed. The area of the effective display area L1 (hatched portion in the figure) of the light guide plate 11 is 183 mm × 139 mm. Here, the area of the effective display area L1 is smaller than the area of the light guide plate 11 because the light guide plate 2 is printed when the ink 18 is printed.
This is because it is necessary to secure the support area Ls for supporting the display area outside the display area L1.

As the light source 12, a straight tube type cold cathode tube or the like is used, and the diameter thereof is 4.1 mm.

As the reflection sheet 13, a silver vapor deposition film or the like is used.

The diffusion sheet 14 has a thickness of 0.25 mm.
The acrylic plate or the like is used and is in close contact with the effective display area L1 on the front surface of the light guide plate 11.

The front reflection film 15 is formed of a mirror-finished sheet such as a silver vapor deposition film and is adjacent to the diffusion sheet 14 outside the effective display area L1 on the front surface of the light guide plate 11.

The rear transparent film 16 and the front transparent film 17
Are colorless LiF (refractive index 1.39), NaF (refractive index 1.31), KF (refractive index 1.32), RbF (refractive index 1.40) and the like. Here, the transparent film 1
The refractive indexes n1 of 6 and 17 are 1 <n1 <n2, where n2 is the refractive index of the light guide plate 11. This is the light guide plate 11
This is to increase the critical angle between and and to increase the total reflection ratio of the light flux. The rear light-transmitting film 16 is provided on the light guide plate 1.
1 and the reflection sheet 13 are in close contact with each other.
The front light-transmitting film 17 is interposed between the light guide plate 11 and the front reflecting film 15 so as to be in close contact with each other.

In FIG. 3, reference numeral 19 denotes a light source reflector for reflecting the light from the light source 12 to the side opposite to the light guide plate 11 to the light guide plate 11 side.

In the above structure, the light from the light source 12 is
The light guide plate 11 is directly or through the light source reflector 19.
Enters the inside from the light incident end face.

Here, of the incoming light from the light incident end face,
The backward light is reflected by the reflection sheet 13 and is distributed to the front diffusion sheet 14.

At this time, if there is a light-transmitting film 16 having a refractive index of more than 1 between the light guide plate 11 and the reflection sheet 13, the light is changed from the one having the larger refractive index to the one having the smaller refractive index according to Snell's law. Since the critical angle of light increases when is incident on, the critical angle θc at the rear surface of the light guide plate 11 increases as compared with the conventional case, as shown in FIG. Then, the light toward the rear of the light guide plate 11 can be totally reflected. Specifically, when NaF is used for the translucent film 16, compared with the conventional example of FIGS. 4 and 5, Δθ = sin ⁻¹ (1.31 / 1.49) −sin ⁻¹ (1/1. 49), the critical angle increases, and the total reflection ratio of the luminous flux can be increased accordingly, and the loss of the luminous flux can be significantly reduced.

Of the light entering from the light incident end face, the light directly applied to the effective display area L1 of the light guide plate 11 is effectively reflected in the light guide plate 11 by the front reflection film 15.

At this time, since the front light-transmitting film 17 having a refractive index of more than 1 is provided between the front reflection film 15 and the light guide plate 11, the front light-transmitting film 16 has the same refractive index as the above-mentioned rear light-transmitting film 16. Reflection film 15
The critical angle at is increased, the ratio of total reflection of the light flux at this portion is increased, and the loss of the light flux can be significantly reduced.

After that, light is emitted from the front surface of the light guide plate 11 and is substantially evenly distributed to the back surface of the liquid crystal display plate 10 through the diffusion sheet 14. Then, the brightness of the illumination surface can be improved by the amount of effective use of light as described above.

The present invention is not limited to the above embodiments, and it goes without saying that many modifications and changes can be made to the above embodiments within the scope of the present invention.

For example, in the above embodiment, the rear transparent film 16 is used.
Although both the front light-transmitting film 17 and the front light-transmitting film 17 are provided, only one of them may be provided.

[0035]

As is apparent from the above description, according to claim 1 of the present invention, since the light-transmitting film having a refractive index of more than 1 is provided between the light guide plate and the reflection sheet, the light-transmitting film has a refractive index of more than 1. The critical angle at the rear surface of the light plate can be increased, and the total reflection ratio of the light flux can be increased.

According to the second aspect of the present invention, when the outside of the display area of the light guide plate is large, the irradiation light to this portion can be effectively reflected inside the light guide plate by the front reflection film.

Further, since the translucent film having a refractive index of more than 1 is provided between the front reflection film and the light guide plate, the critical angle in the front reflection film can be increased and the luminous flux of the light flux can be increased. The total reflection ratio can be increased.

From the above, the loss of luminous flux can be reduced,
If the illuminating surface of the liquid crystal lighting device can be made to have high brightness, it has an excellent effect.

[Brief description of drawings]

FIG. 1 is a principle diagram showing light reflection of a liquid crystal lighting device according to an embodiment of the present invention.

FIG. 2 is a plan view of the same.

FIG. 3 is a sectional view taken along line AA of FIG.

FIG. 4 is a plan view showing a conventional liquid crystal lighting device.

FIG. 5 is a similar BB cross-sectional view.

[Explanation of symbols]

 10 Liquid Crystal Display Plate 11 Light Guide Plate 12 Light Source 13 Reflective Sheet 14 Diffuser Sheet 15 Front Reflective Film 16, 17 Translucent Film

Claims (2)

[Claims] 1. A liquid crystal display plate is illuminated from the rear, wherein a light guide plate arranged in parallel with the liquid crystal display plate, a light source arranged at an end of the light guide plate, and a light guide plate at the rear surface thereof. In a lighting device for liquid crystal, which includes a reflection sheet for reflecting light in the rear of the light plate toward the liquid crystal display plate side, and a diffusion sheet for making the brightness of the illumination surface uniform over the entire surface, the light guide plate and A light-transmitting film is closely provided between the light-transmitting film and the reflection sheet, and the refractive index n1 of the light-transmitting film is 1 <n1 <n2, where n2 is the refractive index of the light guide plate. LCD lighting device. 2. A liquid crystal display plate is illuminated from the rear, wherein a light guide plate arranged parallel to the liquid crystal display plate, a light source arranged at an end of the light guide plate, and a light guide plate at the rear surface. In a liquid crystal lighting device comprising a reflection sheet for reflecting light in the rear of the light plate toward the liquid crystal display panel side, and a diffusion sheet for making the brightness of the illumination surface uniform over the entire surface, A front reflection film for reflecting light from the light source into the light guide plate is provided outside the front display area, and a light transmissive film is interposed between the front reflection film and the light guide plate. The refractive index n1 of the transparent film is 1 <n1 where n2 is the refractive index of the light guide plate.
A liquid crystal lighting device, wherein <n2 is satisfied.