JP2003207778A - Back light device for liquid crystal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a back light device for liquid crystal which enables uniform surface illumination and can properly reflect external light. <P>SOLUTION: A light guide part 32 composed of a scatter type liquid crystal display element is arranged opposedly to a reflecting-surface 31A side of a reflecting plate 31 and arranged on a one-flank 32A side of a light guide part 32 to make illumination light incident from the light guide part 32. The light guide part 32 is placed in a transparent state and then the external light can be reflected by the reflecting surface 31A of the reflecting plate 31 and made incident on a liquid crystal display element 10. The light guide part 32 is placed in a scattering state and then the illumination light from a light source part 33 can be scattered by the light guide part 32 to place the light guide part 32 in a uniform surface illumination state. <P>COPYRIGHT: (C)2003,JPO

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal backlight device. 2. Description of the Related Art A conventional liquid crystal display element used for a liquid crystal display device such as a mobile phone is provided with a pair of front and rear transparent glass substrates facing each other with a liquid crystal layer interposed therebetween. A liquid crystal cell provided with an electrode for applying an electric field;
It comprises a front polarizing plate and a rear polarizing plate arranged so as to sandwich the liquid crystal cell. As described above, since the liquid crystal display element is not a self-luminous element, external light is required to read the display content in the liquid crystal cell,
In a transmissive liquid crystal display device and a transflective liquid crystal display device, a backlight device is used. A conventional backlight device of this type has a reflection function for reflecting light incident from the front of a liquid crystal display element and transmitted through the liquid crystal display toward the liquid crystal display element, and illumination from a built-in light source. It has a light-emitting function that emits light toward the liquid crystal display element.In environments where external light with sufficient brightness can be obtained, the reflective function works, and in environments where external light with sufficient brightness cannot be obtained. Has a configuration in which the light emitting function works. FIG. 3 shows a conventional backlight device 100.
Is shown in a sectional view. Backlight device 1
Reference numeral 00 denotes a light guide plate 101 which is a plate-shaped member made of a transparent resin such as an acrylic resin, and has a main surface 101A formed flat. On the back surface of the light guide plate 101, an inclined surface 101B continuously formed into a scalene triangle is formed as a reflective surface, and the reflective plate 102 is arranged so as to be close to and along the inclined surface 101B of the light guide plate 101. Is established. On one end face 101C side of the light guide plate 101, a cold cathode tube 103 serving as a line light source and a holder 104 for holding the cold cathode tube 103 are provided.
3 is made to enter the light guide plate 101 from one end face 101C, and the light is reflected by the inclined surface 101B on the back surface of the light guide plate 101 to be uniformly emitted from the main surface 101A. Accordingly, in an environment where external light of sufficient brightness can be obtained, external light that has passed through the liquid crystal display element passes through the light guide plate 101 and strikes the reflective plate 102, which is generated. The reflected light enters the liquid crystal display element again, and as a result, reflective display can be performed. On the other hand, when external light of sufficient brightness cannot be obtained, illumination light from the cold cathode tube 103 is incident on the light guide plate 101 from one end face 101C,
The light is reflected by the inclined surface 101B in the direction of the main surface 101A of the light guide plate 101, so that the opposite surface of the liquid crystal display element arranged to face the light guide plate 101 can be uniformly illuminated. [0007] However, in the conventional backlight device, when performing a reflective display using external light, the external light transmitted through the liquid crystal display element and entering the light guide plate. Since a part of the light is reflected on the inclined surface formed on the back surface of the light guide plate before being reflected on the reflection plate, there is a problem that the reflection efficiency is not good. Further, in the peripheral portion of the light guide plate, for example, as shown by a dotted line X in FIG. 3, the reflected light on the inclined surface escapes from the side surface of the light guide plate. Some have a tendency to be darker than the center. As a result, there is a problem that the display quality of the liquid crystal display element is deteriorated due to external light. The surface of the reflector must have a small surface roughness in order to efficiently reflect the incident external light, but if the surface roughness is good, the scattering component of the reflected light is small. Therefore, there is a problem that the angle of the line of sight suitable for viewing the display content on the main surface of the liquid crystal display element is considerably limited, and the usability is not good. When illuminating light from a backlight device is applied to a liquid crystal display element, it is required that the light guide plate has a uniform surface emission state. However, illumination light from a light source is applied to the back surface of the light guide plate. There is a problem that it is difficult to reflect the light on the formed inclined surface and uniformly emit the reflected light from the surface, and it is difficult to obtain a uniform surface emitting state. An object of the present invention is to provide a liquid crystal backlight device which can solve the above-mentioned problems in the prior art. In order to solve the above problems, according to the present invention, instead of the light guide plate, a scattering type liquid crystal display element is provided so as to face the reflection surface of the reflection plate. By making the scattering type liquid crystal display element transparent, external light is efficiently reflected by the reflecting surface of the reflector and made incident on the required liquid crystal display element. On the other hand, when external light cannot be expected, the scattering type liquid crystal is used. The display element is set in a scattering state, and illumination light from a light source unit for illumination is scattered by a scattering type liquid crystal display element, so that the scattering type liquid crystal display element is brought into a plane emission state. In addition, by appropriately adjusting the degree of the light scattering state in the scattering type liquid crystal display element, it is possible to appropriately scatter the light reflected from the reflector when using external light. Can be displayed easily. According to the present invention, in a backlight device for a liquid crystal, a reflection plate, a scattering type liquid crystal display element arranged to face a reflection surface side of the reflection plate, and a side portion of the scattering type liquid crystal display element And a light-emitting source for causing illumination light to be incident on the scattering-type liquid crystal display element. Here, the scattering type liquid crystal display element is configured so as to function as a surface light emitting element.
By appropriately adjusting the applied voltage, the light scattering state there can be adjusted steplessly. Thereby, an arbitrary scattering state can be generated in the reflected light generated when the external light hits the reflector. In the case where light from a built-in light source for illumination is used, the degree of scattering is adjusted so that the scattering type liquid crystal display element is most effectively brought to a uniform surface emission state by the light for illumination. Can be. Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a sectional view showing an embodiment of a liquid crystal display device using the liquid crystal backlight device according to the present invention, and FIG. 2 is an external view of the liquid crystal backlight device shown in FIG. FIG. The liquid crystal display device 1 includes a liquid crystal display element 10 and a backlight device 30 disposed behind the liquid crystal display element 10. The liquid crystal display element 10 is provided with a liquid crystal cell 11, a front polarizer 12 and a rear polarizer 13 disposed so as to sandwich the liquid crystal cell 11, and a liquid crystal cell 11 between the front polarizer 12 and the liquid crystal cell 11. And a diffusion plate 14. The liquid crystal cell 11 is provided on the inner surfaces of a pair of transparent substrates 16 and 17 facing each other with the liquid crystal layer 15 interposed therebetween.
Transparent electrodes 18 and 1 for applying an electric field to the liquid crystal layer 15
9 is provided. Further, the transparent substrate 1 on the front side of the liquid crystal cell 11
6, a color filter 20 is provided on the inner surface,
The electrode 18 is formed on the inner surface of the color filter 20. In addition, alignment films 21 and 22 are provided on the inner surfaces of the pair of transparent substrates 16 and 17 so as to cover the electrodes 18 and 19, respectively. The configuration of the liquid crystal display element 10 has been described above. However, since the configuration of the liquid crystal display element 10 is known per se, further detailed description is omitted here. Next, the backlight device 30 according to the present invention for illuminating the liquid crystal display device 10 will be described. The backlight device 30 includes the liquid crystal display element 1
A reflection function of reflecting light incident on the liquid crystal display element 10 from the front of the liquid crystal display element 10 toward the liquid crystal display element 10;
A lighting function of emitting illumination light toward the liquid crystal display element 10. The backlight device 30 shown in FIG.
Is a sidelight type. Backlight device 3
Reference numeral 0 includes a reflection plate 31 and a plate-shaped light guide portion 32 made of a scattering-type liquid crystal display element disposed so as to face and contact the reflection surface 31A of the reflection plate 31. On one side surface 32 </ b> A of the light guide 32, there is provided a light source 33 which is a light emitting source for causing illumination light to enter the light guide 32. The light source unit 33 includes a cold cathode fluorescent lamp 3 inside a holder 33A having a U-shaped cross section extending along one side surface 32A of the light guide unit 32 and having a light shielding property.
3B, so that light from the cold-cathode tube 33B enters the light guide 32 from one side surface 32A of the light guide 32. Referring to FIG. 2, the light guide section 32 configured as a scattering type liquid crystal display element has a pair of terminals T1 and T2 for applying a voltage, and a variable DC power supply E is provided between the terminals T1 and T2. , A DC voltage is applied via a switch SW. The basic configuration of the scattering type liquid crystal display element constituting the light guide section 32 is the same as that of the conventional scattering type liquid crystal display element of this type, and the DC voltage level applied to the terminals T1 to T2 is zero. The light guide section 32 is in a transparent state, and when the DC voltage level applied to the terminals T1-T2 is at a predetermined level, the light guide section 32 is in a completely scattered and reflected state. When the level of the DC voltage applied to the terminals T1-T2 is between zero and the predetermined level, the state is a scattering reflection state corresponding to the level. Therefore, by appropriately adjusting the DC voltage level applied to the terminals T1 and T2, the scattered reflection state of the light guide 32 can be set arbitrarily and steplessly from the transparent state to the completely scattered reflection state. Can be. When the liquid crystal display device 1 performs reflection display using external light using the backlight device 30 configured as described above, it is assumed that the DC voltage level applied to the terminals T1-T2 is zero. The light part 32 is in a transparent state, and as a result, the external light that has entered the light guide part 32 reaches the reflecting surface 31A of the reflecting plate 31 without being scattered by the scattering type liquid crystal display element and efficiently. reflect. The reflected light generated by this reflection is also hardly scattered by the scattering type liquid crystal display element of the light guide part 32 and the light guide part 3 is hardly scattered.
Since the light is emitted from the second main surface 32B, the back surface of the liquid crystal display element 10 for viewing the display content can be illuminated with increased luminance. Also, by appropriately adjusting the level of the DC voltage applied to the terminals T1-T2, the light guide 32 can be brought into an appropriate scattered reflection state, so that the light is emitted from the main surface 32B of the light guide 32. The reflected light can appropriately contain a scattering component, and the liquid crystal display element 10
Can be illuminated with reflected light containing a moderately scattered component. When light-emitting display is performed using illumination light from the light source unit 33 in an environment where external light cannot be expected, the terminal T1-
When the DC voltage level applied to T2 is set to a predetermined level, the light guide 32 is in a completely scattered reflection state.
Is in a state where incident light can be scattered and reflected. As a result, the illumination light that has entered the light guide unit 32 from the light source unit 33 is scattered and reflected, and the scattered reflected light is reflected on the main surface 3 of the light guide unit 32.
The light emitted from 2B can illuminate the liquid crystal display element 10. At this time, since the level of the DC voltage applied to the terminals T1-T2 can be adjusted steplessly, the illumination light travels through the light guide 32 to the other side surface 32C, and The light guide portion 32 can be set to an appropriate scattered reflection state so that the illumination light is scattered and reflected in the inside 32 and exits from the main surface 32B. As a result, the scattered reflected light can be uniformly emitted from the entire main surface 32B of the light guide portion 32, and the main surface 32B of the light guide portion 32 can be in a uniform surface emission state. The provided liquid crystal display element 10 can be uniformly illuminated over the entire surface. In the backlight device 30, the light source unit 33
In the case of performing light-emitting display using illumination light from, the brightness of the illumination light by the cold-cathode tube 33B may be increased or decreased in accordance with the luminance of the external light to suppress the power consumption used for illumination. The liquid crystal display element illuminated by the backlight device 30 is not limited to the liquid crystal display element having the configuration shown in FIG. 1, but may be used to illuminate other appropriate liquid crystal display elements. Of course, it can also be used. According to the present invention, in a backlight device for a liquid crystal display, a reflection plate, a scattering type liquid crystal display element disposed to face the reflection surface side of the reflection plate, and a scattering type liquid crystal display element And a light-emitting source for allowing illumination light to enter the scattering-type liquid crystal display element, which is arranged on the side of the scattering-type liquid crystal display element.Since no inclined surface is formed on the back surface of the scattering-type liquid crystal display element, In the case of performing reflection display using external light, external light incident into the scattering type liquid crystal display element is not reflected on the inclined surface, and the problem of reflection efficiency can be solved. Further, since the scattering type liquid crystal display element is disposed on the reflection surface side of the reflection plate so as to appropriately include a scattered reflection component in the reflected light, the main surface of the liquid crystal display element can be viewed. The range of angles can be widened, and usability can be improved. Further, by disposing the scattering type liquid crystal display element on the reflection surface side of the reflection plate, the illumination light from the backlight device is applied to the liquid crystal display element for viewing the display contents. Uniform surface light emission can be performed in the scattering type liquid crystal display element arranged opposite to the reflection surface side, and the illumination light from the light source can be uniformly emitted from the surface of the scattering type liquid crystal display element. Surface light emission can be performed, and the display quality of the liquid crystal display element for viewing display contents can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view showing an example of an embodiment of a liquid crystal display device using a liquid crystal backlight device according to the present invention. FIG. 2 is a perspective view showing the appearance of the liquid crystal backlight device shown in FIG. FIG. 3 is a cross-sectional view illustrating an example of a conventional backlight device. [Description of Signs] 1 Liquid crystal display device 10 Liquid crystal display element 11 Liquid crystal cell 30 Backlight device 31 Reflector 31A Reflective surface 32 Light guide 32A One side 32B Main surface 32C Other side 33 Light source

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme court ゛ (Reference) // F21Y 103: 00 F21Y 103: 00 (72) Inventor Yoshio Iwata 1-8 Nakase Nakase, Mihama-ku, Chiba-shi, Chiba Address Seiko Instruments Co., Ltd. (72) Inventor Shigeru Senbonmatsu 1-8-1, Nakase, Mihama-ku, Chiba-shi F term in Seiko Instruments Inc. (reference) 2H042 BA08 BA13 BA20 2H091 FA14Z FA23Z FA31Z FA42Z FB02 FC10 FC23 FC29 FC30 HA06 JA02 LA03 LA11 LA12 LA13 LA18

Claims (1)

Claims: 1. A backlight device for a liquid crystal device, comprising: a reflecting plate; a scattering type liquid crystal display element disposed to face a reflecting surface side of the reflecting plate; A light-emitting source disposed on a side portion for causing illumination light to be incident on the scattering-type liquid crystal display element.