JP2003302636A - Front light device and liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display device capable of uniform surface light emission. <P>SOLUTION: A light guide plate 32 having an entrance face of external light which transmits external light to introduce into the light guide plate, one side face where the light from a light source enters, and an illumination face 32B opposing to a liquid crystal display element and emitting the light from the light source and external light is disposed in the front side of the liquid crystal display element. A reflecting layer to reflect the light propagating from the inside of the light guide plate to the outside to the inside of the light guide plate is applied on at least a part of the side face of the light guide plate. <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 front light device and a liquid crystal display device having the front light device.

[0002]

2. Description of the Related Art A conventional liquid crystal display element used in a liquid crystal display device such as a mobile phone is provided with electrodes for applying an electric field to a pair of substrates facing each other with a liquid crystal layer interposed therebetween. A liquid crystal cell and a front polarizing plate and a rear polarizing plate that are arranged so as to sandwich the liquid crystal cell are provided. As described above, since the liquid crystal display element is not a self-luminous element, light from the outside is necessary to read the display content in the liquid crystal cell, and in the transmissive liquid crystal display device and the transflective liquid crystal display device, A front light device is used.

A conventional front light device of this type has a transmissive function for transmitting external light incident from the outside and guiding it to the liquid crystal display element, and emits illumination light from a built-in light source toward the liquid crystal display element. It has a light-emitting function that enables the light-transmitting function to work in an environment where sufficient external light is obtained, and the light-emitting function to work in an environment where sufficient external light cannot be obtained. There is.

FIG. 3 shows an example of a cross section showing a schematic configuration of a conventional front light device 100. The front light device 100 includes a light guide plate 101 which is a plate member made of a transparent resin such as acrylic resin, and the main surface 101A is formed into a flat surface. Inside the surface facing the main surface of the light guide plate 101, the inclined surface 10 continuously processed into an isosceles triangle is provided.
1B is formed as a reflecting surface. Cage, light guide plate 10
The transmission plate 1 is arranged so as to approach the inclined surface 101B of No. 1 and follow.
02 is provided.

On one end surface 101C side of the light guide plate 101, a cold cathode tube 103 forming a linear light source and a holder 104 for holding the cold cathode tube 103 are provided.
Light from No. 3 is made to enter the light guide plate 101 from one end surface 101C, is reflected by the inclined surface 101B of the light guide plate 101, and is uniformly emitted from the main surface 101A.

Therefore, when external light of sufficient brightness cannot be obtained and light from the light source is used, the illumination light from the cold cathode tube 103 enters the light guide plate 101 from the one end surface 101C and is inclined by the inclined surface 101B. Main surface 101 of light guide plate 101
The light is reflected in the A direction, so that the facing surface of the liquid crystal display element arranged facing the light guide plate 101 can be uniformly illuminated. On the other hand, when the environment is such that outside light of sufficient brightness can be obtained, the outside light passes through the transmission plate 102 and the light guide plate 101 and is incident on the liquid crystal display element, and as a result, display can be performed.

[0007]

However, in the conventional front light device, the illumination light that has entered the light guide plate from the cold cathode fluorescent lamp is, for example, as shown in FIG.
By following the path indicated by the dotted arrow in the figure, the light leaks from the side surface of the light guide plate to the outside of the light guide plate, the peripheral part of the light guide plate becomes darker than the central part, and uniform brightness is provided over the entire main surface of the light guide plate. Hard to get. Therefore, when the liquid crystal display element is illuminated by the conventional front light device, the display state of the liquid crystal display element becomes darker in the peripheral portion than in the central portion, which causes a problem of poor display quality. is doing.

Therefore, the present invention realizes a configuration of a liquid crystal front light device and a liquid crystal display device which can solve the above-mentioned problems in the prior art.

[0009]

In order to solve the above problems, the front light device of the present invention has the following configuration. That is, the light guide plate includes an incident surface on which light from the light source is incident, an external light incident surface that transmits external light and guides the light to the inside of the light guide plate, and a main surface that emits light from the light source and external light. At least a part of the remaining side surface of the light guide plate is provided with a reflection layer for reflecting light traveling from the inside of the light guide plate to the outside toward the inside of the light guide plate.

As described above, by providing the reflection layer on the side surface of the light guide plate, the light which is going to go out from the side surface of the light guide plate is reflected by the reflection layer and returns to the inside of the light guide plate to be emitted from the main surface thereof. As a result, it is possible to improve the illumination efficiency, prevent the illuminance from being lower than the central portion of the light guide plate, and ensure uniform brightness over the entire main surface. .

The reflective layer can be provided at an appropriate position on the side surface of the light guide plate by a known appropriate means using a known reflective material. Further, it is particularly effective to provide the reflective layer on the side surface of the light guide plate facing the light emitting source, but it is preferable to provide the reflective layer on the entire side surface of the light guide plate except for the portion where the light from the light emitting source enters. .

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION A liquid crystal display element, an irradiation surface arranged on the front side of the liquid crystal display element and facing each other with the liquid crystal display element, and external light incident on which the external light is transmitted to guide the external light into the light guide plate. A light guide plate having a surface, and a light source that allows light to enter from one side surface of the light guide plate. At least a part of the side surface of the light guide plate reflects light traveling from the inside to the outside of the light guide plate. A reflective layer is provided for this purpose.

As described above, by providing the reflection layer on the side surface of the light guide plate, the light that is going to go out from the side surface of the light guide plate is reflected by the reflection layer, returns to the inside of the light guide plate, and is emitted from the main surface thereof. As a result, it is possible to improve the illumination efficiency, prevent the illuminance from being lower than the central portion of the light guide plate, and ensure uniform brightness over the entire main surface. .

[0014]

Embodiments of the liquid crystal display device according to the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a sectional view showing an embodiment of a liquid crystal display device having a liquid crystal front light device according to the present invention, and FIG. 2 is a perspective view showing the appearance of the liquid crystal front light device shown in FIG. is there. The liquid crystal display device 1 includes a liquid crystal display element 10 and a front light device 30 arranged on the front side of the liquid crystal display element 10.

The liquid crystal display element 10 includes a liquid crystal cell 11, a front polarizing plate 13 and a rear polarizing plate 14 which are arranged so as to sandwich the liquid crystal cell 11, and a reflecting plate 12 behind the rear polarizing plate 14.
Are arranged.

The liquid crystal cell 11 is formed on the inner surfaces of a pair of front and rear transparent substrates 16 and 17 which face each other with the liquid crystal layer 15 in between.
Transparent electrodes 18, 1 for applying an electric field to the liquid crystal layer 15.
9 is provided.

Further, a pair of transparent substrates 1 of the liquid crystal cell 11
Electrodes 18 and 19 and alignment films 21 and 22 are provided on the inner surfaces of 6 and 17, respectively. Further, when performing color display, a color filter is generally provided on the front transparent substrate 17.

Although the configuration of the liquid crystal display element 10 has been described above, the configuration itself of the liquid crystal display element 10 is publicly known, and a detailed description thereof will be omitted here.

Next, the front light device 30 for illuminating the liquid crystal display element will be described.

The front light device 30 has an incident function of transmitting external light incident from the outside and making it enter the liquid crystal display element 10, and an illumination function of guiding illumination light to emit it toward the liquid crystal display element 10. Have

The front light device 3 shown in FIG.
0 is a side light type. The front light device 30 includes a transmission plate 31 and a light guide plate 32 arranged so as to be in contact with the transmission plate 31. On one side surface 32A of the light guide plate 32, a light source unit 33, which is a light emission source for causing the light for illumination to enter the light guide plate 32, is provided. The light source unit 33 is configured by accommodating a cold cathode tube 33B in a holder 33A having a U-shaped cross section and extending along one side surface 32A of the light guide plate 32, and light from the cold cathode tube 33B is emitted from the light guide plate 32. It has a well-known configuration in which light is efficiently incident on the light guide plate 32 from the one side surface 32A.

The light guide plate 32 is made of a transparent plate material such as an acrylic resin plate, and a plurality of prism portions 32C are provided on the entire surface of the light guide plate 32 in contact with the transmission plate 31 at a predetermined pitch as shown in the figure. Are closely arranged in parallel with each other. The main surface 32B of the light guide plate 32 is a flat emission surface.

The prism portion 32C reflects the incident light from the cold cathode fluorescent lamp 33B toward the main surface 32B, whereby the incident light is reflected.
Almost all the light that has entered the light guide plate 32 from the one side surface 32A is configured to be emitted from the main surface 32B. As a result, the main surface 32B is in a state of emitting surface light, and the main surface 32B
It is possible to uniformly illuminate the liquid crystal display element 10 which is arranged so as to face the above.

In order to prevent the light incident on the light guide plate 32 from the light source section 33 from being emitted to the outside from the side surfaces 32D, 32E, 32F of the light guide plate 32, the side surfaces 32D, 32E, 32.
Reflective layers 34, 35, and 36 are provided on each of F.

The reflective layers 34, 35 and 36 are formed on the respective side surfaces 32D, 32E and 32F by aluminum (A
l), silver (Ag), or a metal such as an Ag alloy can be electrodeposited. In addition, magnesium fluoride (Mg
F ₂ ) and zinc dioxide (ZnO ₂ ) may be provided by adhering a dielectric reflection sheet formed by laminating a plurality of thin films made of materials having different refractive indexes, or the second aluminum oxide ( Al ₂ O ₃ ) and lead oxide (Pb
It may be provided by applying an oxide powder such as O).

Since the reflection layers 34, 35, and 36 are provided on the three side surfaces 32D, 32E, and 32F except the one side surface 32A of the light guide plate 32 in this manner, the illumination incident on the inside of the light guide plate 32 from the one side surface 32A. Some of the light is
The side surface 32 passes through the transmission path as indicated by the dotted arrow in
Even toward D, it is reflected by the reflection layer 34 and returned to the inside of the light guide plate 32, so that the illumination light does not leak from the side surface 32D to the outside of the light guide plate 32. Similarly, of the illumination light taken into the light guide plate 32, the other side surfaces 32E, 32
Even the illumination light directed to F is reflected by one of the corresponding reflection layers 35 and 36 and returned to the inside of the light guide plate 32. As a result, the illumination light from the light source section 33 is transmitted to the light guide plate 32.
Almost all the light incident on the light guide plate 32 is emitted from the main surface 32B without leaking to the outside from the side surface. As a result, the non-uniformity of the illumination due to the light guide plate 32, which is caused by the light leaking from the side surface of the light guide plate 32, is significantly improved, and the main surface 32B of the light guide plate 32 is improved.
It is possible to secure a substantially uniform illuminance over the entire surface, and it is possible to uniformly illuminate the liquid crystal display element 10 arranged so as to face the entire surface.

In this embodiment, the light guide plate 32 has the three side surfaces 32D, 32E, 32F except the one side surface 32A provided with the reflection layers 34, 35, 36. However, the present invention is not limited to this. , The three side surfaces 32D, 32E,
A reflective layer may be provided on any two side surfaces of 32F. In addition, the three side faces 32D, 32E, 3
A reflective layer may be provided on any one side surface of 2F. However, when the reflective layer is provided on any one of the three side surfaces, it is most effective to provide it on the side surface 32D facing the light source unit 33.

The liquid crystal display element 10 illuminated by the front light device 30 is not limited to the liquid crystal display element having the configuration shown in FIG. 1, but may be used for illuminating other types of liquid crystal display elements. Of course, it can be used. Further, the light source is not limited to the line light source, and may be configured using a point light source.

[0030]

According to the present invention, since the reflecting layer is provided on at least a part of the side surface of the light guide plate, the illumination light taken into the light guide plate from the light source is outside the light guide plate from the side surface of the light guide plate. Can be prevented from leaking to. Therefore, it is possible to prevent the peripheral portion of the light guide plate from being darker than the central portion, and it is possible to bring the brightness of the entire main surface of the light guide plate closer to a uniform state. As a result, when the liquid crystal display element is illuminated by the front light device, the display state of the liquid crystal display element can be made to have the same brightness in the peripheral portion and the central portion, and the display quality can be improved.

[Brief description of 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 showing the external appearance of the liquid crystal front light device shown in FIG.

FIG. 3 is a sectional view showing an example of a conventional liquid crystal front light device.

[Explanation of symbols]

1 Liquid crystal display 10 Liquid crystal display element 11 Liquid crystal cell 12 Reflector 13 Front polarizing plate 14 Rear polarizing plate 30 front light device 31 Transparent plate 32 light guide plate 32A One side 32B main surface 32C prism part 32D, 32E, 32F Side surface 33 Light source 34, 35, 36 Reflective layer

Claims (5)

[Claims] 1. A front light device having a light source and a light guide plate, wherein the light guide plate has an incident surface on which light from the light source is incident, an external light incident surface that transmits external light and guides the light to the inside of the light guide plate, A light source and a main surface that emits the external light are provided, and at least a part of a side surface of the light guide plate is used to reflect light traveling from the inside of the light guide plate to the outside toward the inside of the light guide plate. A front light device having a reflective layer. 2. A liquid crystal display element, an irradiation surface arranged on the front surface side of the liquid crystal display element, facing the liquid crystal display element, and external light incident on the liquid crystal display element to guide the external light into the light guide plate. A light guide plate having a surface; and a light source that allows light to enter from one side surface of the light guide plate, wherein at least a part of a side surface of the light guide plate receives light from the inside of the light guide plate to the outside. A liquid crystal display device comprising a reflective layer for reflecting the light toward the display. 3. The liquid crystal display device according to claim 2, wherein the reflective layer is a metallic material having light reflectivity formed on the side surface by electrodeposition means. 4. The liquid crystal display device according to claim 2, wherein the reflective layer is a dielectric reflective sheet. 5. The liquid crystal display device according to claim 2, wherein the reflective layer is a light-reflecting material formed on the side surface by coating.