JPH1152138A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To lessen the loss of light by light reflection of a back light panel of a liquid crystal display device and to improve the luminance to be applied on the liquid crystal panel by the same light source throwing power. SOLUTION: A cold cathode tube 3 arranged along the end face 4a of the light transmission body 4 of the back light panel 2 radiates light which transmits an optical adhesive 5 packed between the light transmission body 4 and the cold cathode tube 3 and is further made incident on the light transmission body 4. The optical adhesive 5 is packed between the light transmission body 4 and the cold cathode tube 3 in such a manner and since there is no air layer and since the refractive index of the optical adhesive 5 is nearly the same as the refractive index of the cold cathode tube 3 and the light transmission body 4, partial reflection and total reflection hardly arise and the incident rate of the light transmission body at the time of the light is made incident on the light transmission body 4 may be enhanced. The luminance applied on the liquid crystal panel 17 is this improved with the same light source throwing power and the visibility is enhanced.

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, and more particularly to a liquid crystal display device having a backlight panel for irradiating uniform light over the entire surface of a liquid crystal panel.

[0002]

2. Description of the Related Art In recent years, liquid crystal display devices have been used in various fields as display devices for displaying images based on various types of image information. An example of such a liquid crystal display device will be described with reference to the drawings.

FIG. 5 is a sectional view showing a section of the liquid crystal display device 50. The liquid crystal display device 50 includes a liquid crystal panel 17 with the display surface 17a facing upward in the drawing and the backlight panel 2. The backlight panel 2 includes a plate-shaped light guide 53 made of acrylic resin and a light guide 53. The cold cathode tube 3 which is a linear light source arranged along the end face 53 a of the light body 53, and the cold cathode tube 3 and the light guide 53 from the back of the light guide 17 so as to open toward the liquid crystal panel 17. , A light reflector 7 for condensing light emitted from the cold cathode tube 3 on the light guide 53, a light diffusion sheet 13 for diffusing light emitted from the light guide 53, A prism sheet 15 for condensing the light diffused by the diffusion sheet 13 in a direction normal to the display surface 17a of the liquid crystal panel 17; And
A dot-shaped light diffusion print 19 is formed on the bottom surface 53b of the light guide 53 so as to prevent light incident on the light guide 53 from returning to the cold cathode tube 3 again. In addition, the cold cathode tube 3 is obtained by applying a phosphor 3a to the inside of an outer diameter glass 3b.

The light reflector 7 is formed so as to surround the cold cathode tube 3 and reflects light from the cold cathode tube 3 to reflect the light from the light guide 53.
A light reflecting cover 7a for condensing light on an end face 53a of the light guide 5;
3 includes a bottom light reflecting sheet 7b provided on the bottom surface and an end light reflecting sheet 7c surrounding three end faces other than the end face 53a of the light guide 53. Although FIG. 5 is a cross-sectional view of the liquid crystal display device 50, oblique lines indicating the cross-section are omitted for clarity of the drawing (the same applies hereinafter).

In the above-mentioned backlight panel 2, when the generated ultraviolet rays are exposed to the fluorescent material 3a inside the cold cathode tube 3, light having a peak at three wavelengths is emitted from the fluorescent material 3a through the outer diameter glass 3b. Radiated to Then, the emitted light enters the light guide 53 from the air layer through the end face 53a, or is reflected by the light reflecting cover 7a and is reflected by the end face 53a.
The light enters the light guide 53 from a. The light incident on the light guide 53 is refracted and radiated to the light diffusion sheet 13 or radiated to the light diffusion sheet 13 by being reflected by the bottom light reflection sheet 7b and the end light reflection sheet 7c. . Then, the emitted light is diffused by the light diffusion sheet 13 and emitted to the prism sheet 15. Further, the emitted light is applied to the display surface 17 a of the liquid crystal panel 17 by the prism sheet 15.
And reaches the liquid crystal panel 17. In this way, the backlight panel 51 irradiates uniform light over the entire surface of the liquid crystal panel 17.

[0006]

By the way, when light is radiated from the outer diameter glass 3b to the air layer or when light enters the light guide 53 from the air layer, the light is incident on the light incident surface where different substances come into contact. It is known that reflection occurs, which causes a loss of light and causes a decrease in luminance of the display device.

This light reflection occurs because the refractive index of the outer diameter glass (n = 1.5) and the refractive index of the acrylic resin light guide 53 (n = 1.5) are inconsistent with the cold cathode tube 3. This is because the refractive index (n = 1.0) of air interposed between the light body 53 and the light body 53 is significantly different. Light reflection based on the above-mentioned causes includes light reflection (hereinafter, this light reflection is referred to as partial reflection) in which light incident on the light incident surface always reflects at a certain rate (hereinafter, this light reflection is referred to as partial reflection). And total reflection in which light incident at an angle of incidence equal to or greater than the angle is completely reflected at the light incident surface.

In order to solve such light reflection, Japanese Patent Application Laid-Open No.
No. 15699 proposes reducing the light reflection by attaching a transparent dielectric having a refractive index between air and the light guide on the light guide light incident surface. However, even if MgF2 (refractive index n = 1.3), which has the lowest refractive index, is used as the transparent dielectric, since there is still a difference in refractive index between the linear light source and the transparent dielectric and the air layer, partial reflection occurs. And total reflection occurred, and the loss due to this could not be reduced much.

Accordingly, an object of the present invention is to improve the visibility of a backlight panel by reducing the loss of light due to light reflection and improving the luminance given to the liquid crystal panel with the same light source input power.

[0010]

Means for Solving the Problems and Effects of the Invention In order to achieve the above object, in the liquid crystal display device according to the first aspect of the present invention, first, a plate-like light guide of a backlight panel is provided. A linear light source arranged along the end surface emits light, passes through a transparent body filled so that there is no air layer between the light guide and the linear light source, and further enters the light guide. Irradiates the liquid crystal panel.

As described above, the space between the light guide and the linear light source is filled with the transparent body, and there is no air layer. Since the refractive index of the light guide can be made almost the same as that of the light guide, the occurrence of partial reflection or total reflection can be greatly reduced, and the incidence rate of the light guide when light enters the light guide can be increased. .

Here, a description will be given of how the incidence rate of the light guide is increased by the above-mentioned transparent body with reference to FIG.
FIG. 1 is an enlarged sectional view of a linear light source and a light guide. The incidence rate of the light guide to the light guide located at a certain distance H from the linear light source increases as the thickness t of the light guide increases. However, in the prior art, a linear light source (here, the refractive index n =
A cold-cathode tube having an outer diameter glass of 1.5) and a light guide (here, acrylic resin, refractive index n1 = 1.5)
The light layer having an incident angle equal to or larger than the critical angle θ is totally reflected from the refractive index difference between the air layer and the light guide.
The thickness T2 of the light guide that totally reflects the light (here, referred to as the maximum thickness of the light guide) is smaller than the critical angle at which the ray B in the direction normal to the outer diameter of the linear light source reflects. Given. The maximum thickness T1 that transmits light without causing total reflection (hereinafter, referred to as a light guide minimum thickness) is a critical thickness at which a light ray A in the tangential direction of the outer diameter of the linear light source reflects. Given from the position of the corner.

[0013]

(Equation 1)

Therefore, for example, as shown in FIG. 2, the outer diameter d of the linear light source is 2.6 mm, and the distance H between the light guide and the linear light source is 5 m.
m, the light guide incident rate increases in proportion to the thickness of the light guide on the light incident surface of the light guide up to the light guide minimum thickness T1 = 4 mm, and gradually exceeds the light guide minimum thickness T1. The incident light quantity saturates, and then the maximum thickness of the light guide T2 = 9 mm
Is reached, the light guide incidence is completely saturated and does not rise any further. The light guide incidence rate at the time of saturation is about 17%.

On the other hand, in the present invention, a transparent body is filled so that there is no air layer between the light guide and the linear light source, and the refractive index of the transparent body is close to n2 = 1.5. By using a transparent material (for example, an optical adhesive having a refractive index of n2 = 1.5 or a silicone oil having a refractive index of n2 = 1.4), refraction at the light incident surface of the light guide can be used. The rate difference is reduced, and the decrease in the amount of incident light due to light reflection can be suppressed.

Therefore, as shown in FIG. 2, for example, when a transparent body having a refractive index n2 = 1.45 is used, the incidence rate of the light guide is:
The light guide minimum thickness T1 rises in proportion to the thickness up to 10 mm in the same manner as in the prior art, and thereafter, the incident light quantity gradually becomes saturated, but becomes saturated when the light guide maximum thickness T2 reaches 38 mm. . Then, the light guide incidence rate at the time of saturation is about 45%, and the present invention can realize a higher light guide incidence rate as compared with the prior art.

Thus, the conventional light guide maximum thickness T
2 is 10 mm, the maximum thickness T2 of the light guide of the present invention.
Is 38 mm, so that the present invention, compared to the prior art,
By increasing the thickness of the light guide, the incidence rate of the light guide can be significantly improved. Furthermore, in the present invention, since the difference in the refractive index of the light incident surface between the linear light source and the air layer is reduced, light reflection is less likely to occur than in the conventional example, which contributes to keeping the light guide incident rate high. I have.

As a result, according to the liquid crystal display device of the first aspect, since the transparent body is filled between the light guide of the backlight panel and the linear light source so as to eliminate the air layer, the light guide is provided. Light loss due to light reflection on the light incident surface of the light body can be reduced, and in addition, light reflection on the light incident surface between the linear light source and the transparent body can be reduced. Therefore, the brightness given to the liquid crystal panel with the same light source input power can be improved, and the visibility can be improved.

Further, when the light guide is formed of an acrylic resin and the transparent member is an optical adhesive as described in claim 2, an optical adhesive (for example, Toa Gosei Co., Ltd. LUXTRACK LCR063, Inc.
(2, refractive index n2 = 1.5) is liquid until solidified, so that it can be filled without gaps between the linear light source and the light guide, and light reflection due to the presence of the air layer can be easily eliminated. Further, since the refractive index of the light guide is very close to the refractive index of the acrylic resin, light reflection due to a difference in the refractive index of the light incident surface can be reduced. It is suitable.

According to a third aspect of the present invention, in the liquid crystal display device according to the second aspect, a concave portion corresponding to the shape of the linear light source is formed on an end surface of the light guide, and the linear light source is formed in the concave portion. By using an optical adhesive, the gap between the linear light source and the light guide can be reduced, and the amount of the optical adhesive used to fill the gap can be reduced. Therefore, there is an effect that the above-described effects can be obtained without increasing the cost much compared to the conventional technique.

According to a fourth aspect of the present invention, there is provided a light reflecting cover which is formed so as to surround the linear light source, reflects light from the linear light source, and condenses the light on the end face of the light guide. When silicone oil is filled as a body between the reflection cover and the end face of the light guide, the silicone oil is filled in a space surrounded by the light reflection cover and the light guide (for example, Toray Industries, Ltd. , Silicon SH200, refractive index n2
= 1.4) is filled, so that there is no air layer between the linear light source and the light guide, and the same effect as described in claim 1 is achieved,
Further, the light emitted from the linear light source to the light reflecting cover side is reflected by the light reflecting cover without passing through the air layer, enters the light guide, and is irradiated on the liquid crystal panel.

Therefore, according to the liquid crystal display device of the fourth aspect, since the gap between the light guide of the backlight panel and the linear light source is filled with the silicone oil so as to eliminate the air layer, the light guide is provided. Light loss due to light reflection on the light incident surface of the body can be reduced, light reflection on the light incident surface between the linear light source and the transparent body is also small, and light radiated to the light reflection cover side is also efficiently used Since it can be used, the luminance given to the liquid crystal panel with the same light source input power can be improved, and the visibility can be improved.

Further, since the silicone oil is in a liquid state, it can be filled without a gap between the linear light source and the light reflecting cover, and light reflection due to the presence of the air layer can be easily eliminated. Further, when replacing the exhausted linear light source, the silicone oil is in a liquid state, so that it can be easily removed, and once it is removed, the linear light source can be easily replaced.

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the liquid crystal display device of the present invention will be described below with reference to the drawings. First, the liquid crystal display device 1 according to the first embodiment will be described with reference to FIG. Note that the liquid crystal display device 50 described in the section of the related art is used.
The same parts as those described above are denoted by the same reference numerals, and detailed description thereof will be omitted.

The liquid crystal display device 1 includes a liquid crystal panel 17 and a backlight panel 2 like the liquid crystal display device 50. The backlight panel 2 has a configuration different from that of the liquid crystal display device 50. A plate made of an acrylic resin (refractive index n = 1.5) having a concave portion 4b conforming to the shape of the cold cathode tube 3 formed on the end surface 4a. The light guide 4 is provided.
An optical adhesive 5 is provided between the cold cathode tube 3 and the recess 4b.
(For example, Toa Gosei Co., Ltd., LUXTRACK LCR
0632, refractive index n = 1.5) and bonded without an air layer.

In the liquid crystal display device 1 configured as described above, since there is almost no difference in the refractive index of the light incident surface between the outer diameter glass 3b and the optical adhesive 5, the light is radiated from the phosphor 3a of the cold cathode tube 3. The emitted light is emitted to the optical adhesive 5 with high efficiency.
The light transmitted through the optical adhesive 5 has almost no difference in refractive index even on the surface of the concave portion 4b which is the light incident surface of the light guide 4,
As shown in FIG. 2, the light enters the light guide 4 at a high light guide incidence rate.

As described above, according to the liquid crystal display device 1 of the first embodiment, the light guide 4 of the backlight panel 2 and the cold cathode fluorescent lamp 3
Is filled with an optical adhesive 5 having the same refractive index as that of the light guide 4, so that the concave portion 4 which is the light incident surface of the light guide 4 is filled.
Light loss due to light reflection on the surface b can be reduced, and light loss due to light reflection on the light incident surface between the outer diameter glass 3b and the optical adhesive 5 can also be reduced. Therefore, the luminance given to the liquid crystal panel 17 with the same light source input power can be improved, and the visibility can be improved.

Since the optical adhesive 5 is in a liquid state until it is solidified, the space between the cold cathode tube 3 and the light guide 4 can be filled without gaps. A concave portion corresponding to the cold-cathode tube 3 is formed in the light guide 4, and the cold-cathode tube 3 is incorporated in the concave portion, so that the gap between the cold-cathode tube 3 and the light guide 4 can be reduced. The amount of the optical adhesive 5 used to fill the gap can be reduced. Therefore, the above-described effects can be obtained without increasing the cost much in comparison with the conventional technique.

Next, a liquid crystal display device 30 according to a second embodiment will be described with reference to FIG. The same parts as those of the liquid crystal display device 50 described in the section of the related art are denoted by the same reference numerals, and detailed description will be omitted. The liquid crystal display device 30 has a liquid crystal panel 17 similar to the liquid crystal display device 50.
And a backlight panel 2. The backlight panel 2 has a configuration different from that of the liquid crystal display device 50, and a silicone oil 33 (for example, a space between the light reflection cover 7 a and the end surface 53 a of the light guide 53), which has conventionally been an air space. , Toray Industries, Inc., Silicon SH20
0, refractive index n = 1.4). Then, the light guide 53 is formed using the airtight packing 35 so that the silicone oil 33 does not leak from the backlight panel 2.
And the light reflection cover 7a have an airtight structure.

In the liquid crystal display device 30 configured as described above, since the difference in the refractive index between the outer diameter glass 3b and the silicon oil 33 is small, the light radiated from the phosphor 3a of the cold cathode tube 3 is 33 is released with high efficiency. Then, the light transmitted through the silicon oil 33 is incident on the light guide 53 at a high light guide incidence rate because the difference in the refractive index is small even at the end face 53 a which is the light incidence surface of the light guide 53. In the related art, the utilization rate of the light radiated toward the light reflection cover 7a is not good because of the presence of the air layer. However, in the liquid crystal display device 30, the light radiated toward the light reflection cover 7a also reduces the air layer. Since the light is reflected without passing through and enters the light guide 4, the light utilization rate can be increased.

As described above, the liquid crystal display device 30 of the second embodiment
According to the method, since the silicon oil 33 having a refractive index close to that of the light guide 4 is filled between the light guide 53 of the backlight panel 2 and the cold cathode tube 3, light is incident on the light guide 53. Light loss due to light reflection from the end surface 53a, which is a surface, can be reduced,
In addition, light loss due to light reflection on the light incident surface between the outer diameter glass 3b and the silicon oil 33 can be reduced, and light radiated to the light reflection cover 7a side can be used efficiently. Therefore, with the same light source input power, the liquid crystal panel 1
7 can be improved to enhance the visibility.

Since the silicone oil 33 is in a liquid state, it can be filled without any gap between the cold cathode tube 3 and the light reflecting cover 7a. Further, when replacing the exhausted cold-cathode tube 3, the silicon oil 33 is in a liquid state and can be easily removed, and once removed, the cold-cathode tube 3 can be easily replaced.

Although the embodiment of the present invention has been described above, the present invention is not limited to the above-described embodiment, and it goes without saying that the present invention may be embodied in various modes. For example, in the liquid crystal display device 30, the silicone oil 33 is used as the transparent body, but the above-described optical adhesive 5 may be used other than the silicone oil 33.

In this embodiment, the cold cathode tube 3 is used as the linear light source. However, the present invention is not limited to the cold cathode tube 3, and a hot cathode tube or the like may be used. Further, in this embodiment, the case where only one cold cathode tube 3 is used as the linear light source has been described, but the present invention may be implemented using a plurality of linear light sources.

[Brief description of the drawings]

FIG. 1 is an enlarged sectional view of a linear light source and a light guide for illustrating the operation of the present invention.

FIG. 2 is a graph comparing the light guide incidence rates of the present invention and the prior art.

FIG. 3 is a cross-sectional view illustrating a cross section of the liquid crystal display device 1 according to the first embodiment.

FIG. 4 is a sectional view showing a section of a liquid crystal display device 30 according to a second embodiment.

FIG. 5 is a cross-sectional view showing a cross section of a conventional liquid crystal display device 50.

[Explanation of symbols]

1. Liquid crystal display device 2. Backlight panel 3.
Cold cathode tube, 4 ... light guide, 4a ... end face, 4b ... recess,
5 optical adhesive, 7 light reflector, 7a light reflective cover, 17 liquid crystal panel, 30 liquid crystal display device, 33
…silicon oil

Claims (4)

[Claims] 1. A liquid crystal panel for displaying an image by transmitting or blocking light based on image information, a plate-shaped light guide disposed substantially parallel to the liquid crystal panel, and a light guide for the light guide. A liquid crystal display device comprising: a linear light source disposed along an end face; and a backlight panel for irradiating the liquid crystal panel with light from the linear light source via the light guide. A liquid crystal display device wherein a space between a body and a linear light source is filled with a transparent body so that an air layer is eliminated. 2. The liquid crystal display device according to claim 1, wherein said light guide is made of acrylic resin, and said transparent body is made of an optical adhesive. 3. The liquid crystal display device according to claim 2, wherein a concave portion corresponding to the shape of the linear light source is formed on an end surface of the light guide, and the linear light source is formed in the concave portion with the optical adhesive. A liquid crystal display device characterized by being adhered. 4. The liquid crystal display device according to claim 1, wherein the light reflecting cover is formed so as to surround the linear light source, and reflects light from the linear light source to collect light on an end face of the light guide. A liquid crystal display device comprising: a transparent body filled with silicone oil between the reflective cover and an end face of the light guide.