JPH0676935U - Backlight device - Google Patents

Abstract

(57) [Summary] [Object] To provide a backlight device which is thin and which can obtain uniform illuminance without lowering the illuminance of the entire surface. A light guide plate (1) illuminated by a light source (2) arranged on at least one side surface, a reflection plate (4) arranged on the back surface of the light guide plate, and a diffusion plate arranged on the entire surface of the light guide plate. (6), and illuminates the illuminated body in front of the diffuser plate. A light transmission layer (5) having a refractive index substantially equal to that of the light guide plate and having a density afterimage depending on the distance from the light source is provided between the light guide plate and the reflection plate. The light transmitting layer (5) is made of an adhesive material and is formed by the dot pattern (5a).

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a backlight device that illuminates an illuminated object such as a liquid crystal display panel from the back surface.

[0002]

[Prior art]

 In recent years, in the case of a device equipped with a liquid crystal display panel, in particular, a device such as a portable personal computer or a word processor, there is a strong demand for downsizing and weight reduction of the device. Directional thinning is required.

Generally, as a structure of a backlight device for irradiating light on the entire surface of a liquid crystal display panel, a reflecting plate is arranged on the back side of a light guide plate, and light from a fluorescent tube is incident from the side of the light guide plate. A so-called edge light type backlight device that emits light to an illuminated object through a diffusion plate disposed on the front surface of the light guide plate has been conventionally used. The edge light system has been widely used in recent years because it has an advantage that the thickness of the backlight device is only the diffuser plate, the light guide plate, and the reflector plate, and the device can be made extremely thin.

[0004]

[Problems to be solved by the device]

 However, this edge-light type backlight device has a problem that the illuminance decreases on the side closer to the light source, whereas the illuminance decreases on the side farther from the light source. It wasn't easy to get.

Therefore, in order to solve this problem conventionally, for example, the front surface or the back surface of the light guide plate is formed to have a satin finish, the thickness of the light guide plate is made thinner as the distance from the light source is increased, and a plurality of light guide plates are stacked. By doing so, the light is evenly distributed from the light source to the opposite side, and the illuminance on the entire surface is made uniform.

However, in the case of a backlight device having a certain thickness or more, it was possible to measure the uniformity of illuminance by performing these treatments, but to achieve the above-mentioned treatment and structure, it is possible to obtain a certain degree. The above-mentioned thickness of the light guide plate is required, and it is difficult to form the thickness of the light guide plate to, for example, 5 mm or less due to the demand for thinning, and there is a limit to the uniformity of illuminance.

As another method, there has been proposed a method of forming a dot pattern of white ink or the like on the back surface of the light guide plate so that the density of the dot pattern changes. However, the unevenness of irradiation can be suppressed by the density distribution of the dot pattern, but the light loss due to the dot pattern itself is large, and the overall illuminance loss of the liquid crystal display panel illuminates against the illuminance of the light emitted from the light source. It had the drawback of becoming larger.

It is an object of the present invention to solve the above problems and provide a backlight device which is thin and which can obtain uniform illumination without lowering the illuminance of the entire surface.

[0009]

[Means for Solving the Problems]

 In order to achieve the above-mentioned object, the present invention provides a light guide plate illuminated by a light source arranged on at least one side surface, a reflector plate arranged on the back surface of the light guide plate, and a light guide plate arranged on the front surface of the light guide plate. In a backlight device having a light plate and illuminating an illuminated object in front of the diffusion plate,

This is achieved by providing a light transmission layer between the light guide plate and the reflection plate, the refractive index of which is substantially equal to that of the light guide plate and the density of which gradually increases according to the distance from the light source.

[0011]

[Action]

 The operation of the above configuration will be described with reference to FIG.

On the side surface of the light guide plate 1, the lights (a), (b) and (c) incident from the light source into the light guide plate 1 travel toward the opposite side of the light source while repeating reflection inside the light guide plate 1. As shown in FIG. 4, it reaches the back surface 1b of the light guide plate 1. At that time, in the back surface 1b of the light guide plate 1, the light (a) reaching the portion where the adhesive layer 3 is formed has the refractive index of the light guide plate 1 and that of the light transmission layer 3 substantially equal to each other. The light travels into the light transmitting layer 5 without being reflected, and is reflected by the reflecting plate 4 toward the surface side of the light guide plate 1. Further, the light (b) that has reached at an angle equal to or larger than the critical angle in the portion where the light transmission layer 5 is not formed is almost totally reflected and further proceeds to the opposite side of the light guide plate 1 from the light source. Further, the light (c) arriving at an angle smaller than the critical angle in the portion where the light transmission layer 5 is not formed travels to the surface 4a of the reflection plate 4, where it is reflected and reflected to the surface side of the light guide plate 1. . The three optical paths shown here are examples, and the light emitted from the front surface of the light guide plate 1 to the outside after being reflected a number of times inside the light guide plate 1 through other complicated optical paths is particularly important. Not shown.

Therefore, the light transmission layer 5 is formed so that the density increases according to the distance from the light source, so that the amount of light emitted from the front surface through the optical path (a) depends on the density. It is possible to obtain almost uniform illuminance over the entire surface and to allow light from the light source to reach the opposite side of the light guide plate without losing most of the light.

By using the light transmitting layer as an adhesive layer, the light guide plate and the reflection plate can be fixed by using another fixing member.

[0015]

【Example】

 An embodiment of the present invention will be described in detail below with reference to the drawings. FIG. 1 is a sectional view showing the backlight device of this embodiment, and FIG. 2 is a plan view of the backlight device shown in FIG.

In the figure, the light guide plate 1 is a transparent member having a high transmittance such as acrylic. The fluorescent tube 2 is arranged on one side surface thereof, and the surface of the fluorescent tube 2 other than the portion facing the light guide plate 1 is covered with a cover 3 having high reflectance, so that the fluorescent tube 2 emits light. All are configured to enter the light guide plate. A diffuser plate 6 made of frosted glass or the like is arranged on the upper surface of the light guide plate 1, diffuses light emitted from the upper surface 1a of the light guide plate 1, and illuminates a liquid crystal display panel (not shown) with the light emitting surface 6a.

A portion other than the upper surface 1 a of the light guide plate 1 and the one end surface of the light entering the fluorescent tube 2 is covered with the reflection plate 4. The diffuse reflection layer 4a is formed on the surface of the reflection plate 4 by applying white ink. The diffused reflection layer 4a is not limited to the application of white ink, and may be directly cut so as to diffusely reflect the surface of a fluorescent paint, a paint of another color, or a highly reflective reflector such as aluminum. I don't mind.

On the lower surface 1 b of the light guide plate 1, an adhesive layer 5 having a refractive index substantially the same as that of the light guide plate 1 is formed. The adhesive layer 5 is preferably made of an adhesive having a relatively high hardness. Then, the light guide plate 1 and the diffuse reflection layer 4a are fixed by the adhesive layer 5, so that the light guide plate and the reflection plate 4 are fixed. The adhesive layer 3 is applied to the lower surface 1a of the light guide plate 1 by drawing a large number of substantially circular dot patterns 5a. As shown in FIG. 2, the dot patterns 5a are evenly spaced from each other. The radius of the circular dot pattern is smaller toward the portion closer to, and the radius gradually increases as the distance from the light source increases, and the area covering the lower surface 1b increases as the distance from the light source increases. In FIG. 2, the dot pattern in the central portion is omitted.

In this embodiment, the light guide plate has a length of 200 mm, a width of 135 mm, and a thickness of about 2 mm, and the total thickness including the diffusion layer, the light guide plate, the adhesive layer, and the irregular reflection layer is about 2.5 mm. It has become possible to make it thin.

The operation of the above embodiment will be described. All the light generated from the light source 2 enters the light guide plate 1, including the light reflected in the cover 3. Then, a part of the light in the light guide plate 1 passes through the diffusion plate 6 from the surface 1a and is emitted from the surface 6a while being diffused. The light that has not been emitted from the front surface 1a proceeds further in the direction opposite to the light source 2 of the light guide plate 1 while repeatedly reflecting, but the adhesive layer 5 is formed on the back surface 1a so that the density gradually increases. As a result, the light incident on the adhesive layer 5 is more likely to be diffusely reflected by the irregular reflection layer 4a on the lower surface of the portion farther from the light source 2 than the portion closer to the light source 2, so that the light is substantially uniform as a whole. It is possible to obtain a high illuminance.

FIG. 3 is a plan view showing the second embodiment.

While the dot pattern 5 a is formed so that the size thereof is gradually increased in the above-described first embodiment, in the second embodiment, each of the dot patterns 7 a of the adhesive layer 7 is formed. The size is the same, and the number of dots per unit area is increased as the distance from the light source increases. The dot pattern in the central portion is omitted in FIG. As a result, the density of the dot patterns 7a increases as the distance from the light source increases, similarly to the first embodiment described above, and it is possible to obtain uniform illumination as a whole.

In the above-mentioned first and second embodiments, there is one fluorescent tube as a light source, but the light source may be arranged at two opposing ends of the light guide plate. In this case, the density of the dot pattern may be gradually increased from both ends close to the two light sources toward the center.

[0024]

【effect】

 As described above, according to the backlight device of the present invention, the overall illuminance can be made uniform and the device can be made thin without taking a complicated configuration.

[Brief description of drawings]

FIG. 1 is a sectional view showing a first embodiment of a backlight device of the present invention.

FIG. 2 is a plan view of the backlight device shown in FIG.

FIG. 3 is a plan view showing a second embodiment of the backlight device of the present invention.

FIG. 4 is a sectional view of an essential part for explaining the operation of the backlight device of the present invention.

[Explanation of symbols]

 1 Light guide plate 2 Light source 3 Cover 4 Reflector 4a Diffuse reflection layer 5 Adhesive layer 5a Dot pattern 6 Diffuser

Claims (5)

[Scope of utility model registration request] 1. A light guide plate illuminated by a light source arranged on at least one side surface, a reflector plate arranged on the back surface of the light guide plate, and a light guide plate arranged on the front surface of the light guide plate. In a backlight device for illuminating an object to be illuminated in front of the diffusion plate, a refractive index between the light guide plate and the reflection plate is approximately equal to that of the light guide plate, and a density is gradually increased according to a distance from a light source. Backlight device having a transparent light transmission layer. 2. The backlight device according to claim 1, wherein the light transmission layer is an adhesive layer. 3. The backlight device according to claim 1, wherein the light-transmitting layer is formed by arranging substantially circular dot patterns at equal intervals so that the radius increases according to the distance from the light source. 4. The backlight device according to claim 1, wherein the light transmitting layer is arranged so that dot patterns having a substantially circular shape and having the same diameter are increased in number depending on a distance from a light source. 5. The backlight device according to claim 1, wherein an irregular reflection layer is formed on the surface of the reflection plate.