JPH06160641A - Surface light source plate - Google Patents

Abstract

PURPOSE:To provide the surface light source plate which has high and uniform brightness. CONSTITUTION:This surface light source plate is an edge light type surface light source plate constituted by arranging a linear light source at one end of a light guide plate and forming a reflecting layer which has a front half part increasing coating rate per unit area or coating rate with the distance from the linear light source and a fixed-coating-rate rear half part on one surface of the light guide plate; and the reflecting layer consists of a center part which is equal in coating rate per unit area at places at an equal distance from the linear light source and side parts which are positioned on both the sides of the center part and increase in coating rate per unit area toward the side ends at a place close to the linear light source and decrease or are constant in coating rate per unit area to the side ends at a place distant from the linear light source.

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 surface light source plate having a bright and uniform brightness.

[0002]

2. Description of the Related Art In recent years, liquid crystal display devices have been remarkably developed and are used in a wide range of fields such as OA field, automobile-related field, communication device field and others. Since the liquid crystal does not emit light by itself, the display was initially viewed using reflected light, but since it is extremely unclear, transmissive display devices that use visible light to become the mainstream have become widespread. It is popular. A so-called backlight is used as a light source of transmitted light in such a transmissive display device. In this backlight, a fluorescent tube that is a linear light source is placed below the diffuser plate, and an underlight type that uses various measures to create a uniform surface light source and a fluorescent tube that is placed on the end surface of the light guide plate are placed. Then
There is an edge light system in which light incident on the light guide plate is uniformly emitted to the upper surface by various means to be used as a surface light source. In general, the under-light type is bright but has a large thickness, and the edge-light type is dark but has a small thickness, and is used depending on the application.

[0003]

As described above, the edge light method is advantageous because it can provide a structurally thin product, but it has a problem of improving the brightness. Various proposals (Japanese Patent Laid-Open No. 2-160215, Japanese Patent Laid-Open No. 4-62519, etc.) have been made to improve this point, and some of them have been put to practical use. Each of the above proposals aims at efficiently and uniformly emitting the light incident on the light guide plate to improve the overall brightness, but it cannot be said to be sufficient for some purposes.
For example, a certain amount of light irradiation cannot be obtained from the end of the light guide plate. Specifically, when the end (electrode part) of a fluorescent tube, which is a linear light source, is dark, or the end length of the light guide plate is long. On the other hand, it is hard to say that it is sufficient when facing a short fluorescent tube.

[0004]

SUMMARY OF THE INVENTION The present invention has been proposed in view of the above, and a line light source is arranged at one end of a light guide plate, and
An edge light type surface light source plate in which a reflection layer having a first half portion and a constant second half portion where the coverage per unit area increases or the coverage increases on one surface of the light guide plate as the distance from the linear light source increases. The above-mentioned reflective layer faces the central portion where the coverage per unit area is the same at a position where the distance from the linear light source is the same, and the side edge at the positions which are located on both sides of the central portion and close to the linear light source. The surface light source plate is characterized in that the coverage per unit area increases and the coverage per unit area decreases toward the side edge at a position distant from the linear light source, or the side part is constant. It is about.

The light guide plate used in the present invention may be a transparent plate that allows light to pass therethrough, and examples thereof include an acrylic resin plate, a glass plate, a polycarbonate resin plate, and a styrene-acrylic resin plate.

The reflection layer formed on one surface of the light guide plate may be a dot pattern formed by dot printing or the like, or the dot shape may be a circle, an ellipse, a polygon, a heart, a star, or the like. Alternatively, it may have a continuous mesh shape (for example, a honeycomb shape). As the reflective / diffusible pigment contained in the reflective layer, titanium oxide, silica, glass beads, urea / formalin resin powder, or the like can be used. Among them, when titanium oxide is used, the brightness is high due to the high reflectance, but high printing accuracy is required because printing bleeding and the like cause uneven brightness, and when silica or glass beads are used, the reflectance is high. Since it is low, it does not require high printing accuracy like the above-mentioned titanium oxide, but the overall brightness is low. On the other hand, when the urea / formalin resin powder is used, it has a reflectance between these values, and it is possible to obtain bright and uniform brightness without high printing accuracy.

The reflection layer has a first half portion in which the coverage per unit area increases as the distance from the linear light source increases, or a second half portion in which the coverage increases. A reflective part (eg, white ink is applied or a white polyester film is pasted) on the other end (hereinafter referred to as the rear end) facing one end facing the line light source, or the reflection on the inner wall surface of the frame is used. Is also possible.) Since light is also incident from the reflection part at the back end, the coverage per unit area is increased from one end to the middle and from that middle to the back end. The rate of increase may be reduced or may be constant, and when the reflection portion is not provided at the back end, the coverage rate per unit area may be increased from one end side to the back end side.

Further, the reflecting layer has a central portion extending from the middle of the length direction of the linear light source on one end side to the rear end side, and from the end portion (near the electrode portion) of the linear light source on the one end side to the rear end side. For example, the central portion and the side portions may both have a constant width and extend from one end side to the rear end side, or may have a constant width halfway and a width length from the middle. You may make it increase and decrease. When the central portion and the side portion are formed to have a constant width, the width ratio varies depending on the width and thickness of the light guide plate used and the effective light emission length of the linear light source. : Central part: (right) side =
1: 1: 1 to 1: 10: 1, preferably 1: 2:
It is 1 to 1: 5: 1. Further, in the central portion, the coverage rate per unit area is the same at a position where the distance from the linear light source is equal.

Further, in the side portion, the coverage per unit area increases toward the side end at a position near the linear light source on one end side, and the unit ratio goes toward the side end at a position far from the linear light source at the back end side. The coverage per area decreases or becomes constant. That is, the same reflection parts as the back end are provided at both ends of the light guide plate, but when the tube length of the line light source is shorter than the end part of the light guide plate at a position close to the line light source on one end side, Since the amount of incident light is small, the amount of light emitted upwards is increased by increasing the coverage toward the side edge, and at the location far from the line light source on the back edge side, it is incident by the reflection part at the back edge and light diffusion. Since the amount of light is large, the coverage is reduced or made constant toward the side edge, and the amount of light emitted upward is adjusted and made uniform.

In order to form the reflection layer according to the present invention, the material, size and shape of the light guide plate, the tube length and the amount of light emission of the linear light source, the diffusion sheet or the reflection sheet to be used, etc. are determined based on the above-mentioned change of the coverage. Accordingly, the coverage of each place may be set appropriately. For example, by computer analysis or the like, light can be efficiently and uniformly emitted based on the guideline of the coverage change of the present invention to improve the overall brightness.

The present invention does not particularly describe other structures attached to the surface light source plate, such as a reflection sheet, but may be appropriately selected and added.

[0012]

EXAMPLES Examples of the present invention will be shown below.

Example 1, Comparative Examples 1 and 2; The light guide plate (transparent acrylic plate: 2 × 155 × 215 mm) has the change in coverage shown in FIG. 1, and the side part: central part: side part = 1:
A pattern (FIG. 2) that reproduces the 3: 1 reflective layer was screen-printed to obtain a printed light guide plate. The ink used was one containing urea / formalin resin powder. Then, a fluorescent tube having a diameter of 3.0 mmφ and a length of 155 mm (effective emission length: 12 mm) is arranged on one end surface of the printed light guide plate,
A reflector made of white polyester film was provided, which was wrapped around this fluorescent tube and attached at both ends to a printed light guide plate with double-sided tape. Further, the light guide plate is laminated on the reflection sheet (white polyester film) with the printing surface facing downward, and the diffusion sheet (polycarbonate film having fine irregularities) is further laminated on the upper surface, and thus the surface light source plate of Example 1 And An inverter was connected to this and turned on, and 1 hour later, the luminance at the measurement position shown in FIG. 3 was measured using a luminance meter (BN-7, manufactured by Topcon). Table 1 shows the measured values at each measurement position.
It was shown to. Here, the average luminance is an average value of 9 measured values, and the luminance unevenness is a value calculated as (average luminance) / (maximum luminance) × 100. On the other hand, the surface light source plate of Comparative Example 1 was prepared in exactly the same manner as in Example 1 except that the pattern of only the central portion (FIG. 4) without the side portions in Example 1 was printed. Further, a surface light source plate of Comparative Example 2 was produced in exactly the same manner as in Example 1 except that the pattern (FIG. 5) of only the side portion not provided with the central portion in Example 1 was printed. Then, the luminance was measured according to each of the above methods, and the results are also shown in Table 1.

[0014]

[Table 1]

Example 2, Comparative Examples 3 to 4; Pattern for Reproducing Reflective Layer with Coverage Change Shown in FIG. 6 (FIG. 7)
A surface light source plate of Example 2 was manufactured in exactly the same manner as in Example 1 except that the above was screen-printed. Example 2
The surface light source plate of Comparative Example 3 was prepared in exactly the same manner as in Example 1 except that the pattern of only the side portion where the central portion was not provided was printed, and the pattern of only the side portion where the central portion was not provided in Example 2 was used. A surface light source plate of Comparative Example 4 was produced in exactly the same manner as in Example 1 except that was printed.
Then, the brightness was measured according to each of the above methods, and the results are shown in Table 2.

[0016]

[Table 2]

[0017]

As described above, the surface light source body of the present invention is bright and has uniform brightness. Therefore, it is possible to manufacture a thin liquid crystal display device of the edge light system with high brightness.

[Brief description of drawings]

FIG. 1 is a graph showing a change in coverage of a reflective layer of Example 1.

FIG. 2 is a plan view showing a pattern of a reflective layer of Example 1.

FIG. 3 is a plan view showing a luminance measurement position.

FIG. 4 is a plan view showing a pattern of a reflective layer of Comparative Example 1.

5 is a plan view showing a pattern of a reflective layer of Comparative Example 2. FIG.

FIG. 6 is a graph showing changes in the coverage of the reflective layer of Example 2.

FIG. 7 is a plan view showing a pattern of a reflective layer of Example 2.

Claims (1)

[Claims] 1. A linear light source is arranged at one end of the light guide plate, and
An edge light type surface light source plate in which a reflection layer having a first half portion and a constant second half portion where the coverage per unit area increases or the coverage increases on one surface of the light guide plate as the distance from the linear light source increases. The above-mentioned reflective layer faces the central portion where the coverage per unit area is the same at a position where the distance from the linear light source is the same, and the side edge at the positions which are located on both sides of the central portion and close to the linear light source. The surface light source plate is characterized in that the coverage per unit area increases and the coverage per unit area decreases toward the side edge at a position distant from the linear light source, or the side part is constant. .