JP2732174B2 - Surface light source plate - Google Patents

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 luminance.

[0002]

2. Description of the Related Art In recent years, the development of liquid crystal display devices has been remarkable, and they have been used in the OA field, the automobile-related field, the communication device field, and other wide fields. Since the liquid crystal does not emit light by itself, the display was initially viewed using reflected light.However, since the display was extremely unclear, a transmissive display device that viewed using transmitted light became mainstream, Widespread. A so-called backlight is used as a light source of transmitted light in such a transmission type display device. This backlight has a fluorescent tube, which is a linear light source, disposed below the diffuser plate, and is underdeveloped by various measures to provide a uniform surface light source, and a fluorescent tube, which is disposed at an end surface of the light guide plate. And
There is an edge light method using a surface light source that uniformly reflects light incident on the light guide plate to the upper surface by various means. In general, the underlight type is bright but thick, and the edge light type is dark but thin.

[0003]

As described above, the edge light method is advantageous because it can provide a structurally thin product, but has a problem in improving the luminance. Various proposals have been made to improve this point (JP-A-57-128383, JP-A-2-26983, JP-A-3-118594, JP-A-2-1265).
No. 01, JP-A-2-160215, JP-A-4
No.-62519) and some of them have been put to practical use. The above proposals relate to a device for efficiently and uniformly reflecting light incident on the light guide plate, and a reflection layer provided on the light guide plate includes titanium oxide (TiO 2).
₂ ), barium sulfate (BaSO ₄ ), glass beads and the like are contained, but it is still not enough depending on the use. In particular, when the reflection layer contains titanium oxide, the reflectance of titanium oxide is high, so that the reflection is increased from the set reflection amount due to the printing blur of the unit dot, and uniform brightness cannot be obtained. Become. Therefore, there is a problem that extremely high-precision print management is required and the yield is low. On the other hand, since glass beads have a low reflectance, printing blur does not cause the above-described problem, but there is a problem that high luminance cannot be obtained.

[0004]

SUMMARY OF THE INVENTION The present invention has been proposed in view of the above.
The present invention relates to a surface light source plate in which a reflection layer is formed on one surface of a light guide plate with an ink containing urea / formalin resin powder.

As the light guide plate used in the present invention, a transparent plate for transmitting light is used. The material of the light guide plate is not limited, but acrylic, polycarbonate, polystyrene, glass and the like can be used. In general, it is desirable to use an acrylic plate in view of cost, workability, and the like.

The urea-formalin resin powder used in the present invention is a spherical powder of a polycondensate of urea and formaldehyde, and various commercial products have already been provided.
In general formula _{- (CH 2 NHCONHCH 2) n} - (CH 2
NHCONHCH ₂ O) _m - is represented by. This urea
Formalin resin powder has the same light scattering ability as titanium oxide (refractive index 2.7) despite its small refractive index of 1.5.

In the ink containing the urea-formalin resin powder, various resins can be used for the vehicle component, and the vehicle component is not particularly limited. Therefore, it is necessary that the content be contained in the range of 0.1 to 1.0 by weight. 0.1
If the amount is less than the above, no optical characteristics are exhibited, and if the amount is more than 1.0, the printability of the ink deteriorates. In addition, in the same manner as general-purpose inks, in consideration of printability and the like, an antifoaming agent (eg, silicon type), a leveling agent (eg, fine powder silica), a thixotropic agent (eg, aluminum stearate), a curing accelerator (eg, For example, manganese naphthenate), a solvent (eg, isophorone, xylene, ethyl acetate) and other additives can be appropriately blended. Furthermore, various organic pigments and inorganic pigments can be contained in a range that does not impair the above-mentioned optical characteristics (at least, in a range not more than the urea-formalin resin powder). As the organic pigment, for example, a nylon resin, a silicone resin, Resin powders such as polystyrene resin, polyethylene resin, benzoguanamine resin, acrylic resin, and fluororesin can be used.Examples of inorganic pigments include diamond, aluminum oxide, silica powder, and mica powder coated with titanium oxide. I can give it.

[0008] The reflection layer in the present invention is obtained by applying the above ink on one surface of the light guide plate and drying. The means for applying the ink may be performed by various printing methods or other coating methods, and is not particularly limited. However, as described above, a high-level method for forming a reflective layer containing titanium oxide is used. Print management of accuracy is not particularly required.

The surface light source plate of the present invention in which a reflection layer is formed on one surface of the light guide plate with the ink containing the urea / formalin resin powder is the same as the conventional surface light source plate having a reflection layer containing titanium oxide or the like. The luminance is improved as compared with the above. The reason for this is that the refractive index of the urea-formalin resin powder is 1.5 as described above, which is the same as that of an acrylic plate normally used for a light guide plate, but the fine particles having a particle size of 0.1 to 1.0 μm are used. It is presumed that certain primary particles are aggregated to form secondary particles of about 1.0 to 10 μm, so that optical characteristics of reflection and diffusion are largely exhibited. For example, the particle size of "Pergo Pack" (trademark), which is a urea-formalin resin manufactured by Lonza Japan, is 0.1 to 1.0 [mu] m for primary particles and 4 to 7 [mu] m for secondary particles. The particle size of “Organic Filler” (trademark) manufactured by Nippon Kasei Co., Ltd. is 0.1 to 0.3 μm in primary particles.
And the secondary particles are 1 to 7 μm.

[0010]

Embodiments of the present invention will be described below.

Examples 1 to 9 and Comparative Examples 1 to 7 Inks containing urea / formalin resin powder were prepared.
A screen printing is performed on a pre-designed dot pattern for brightness uniformity, and the light guide plate (acrylic transparent plate, 2 × 153 ×
A reflective layer was formed by screen printing using the ink at 216 mm) to produce the surface light source plates of Examples 1 to 9. One fluorescent tube of 3 mmφ is attached to the short end face of this surface light source plate, a reflection sheet (white polyester film) is laminated with the reflection layer facing down, and a diffusion sheet (matted polyester film) is placed on the surface light source plate. ) Were laminated.
One hour after turning on the fluorescent tube, a luminance meter (Topcon. BM
Using -7), the luminance in the vertical direction was measured every 1.0 mm from the end (fluorescent tube). For the measurement, the surface light source plate was placed and supported on an XY table, and a luminance meter was fixed at a position 40 cm vertically above the surface light source plate. The brightness was measured by moving the lens in the direction. Table 1 shows the composition and average luminance of Examples 1 to 9.
Are shown together. Also, the surface light source plates of Comparative Examples 1 to 7 were prepared in exactly the same manner as described above except that the various pigments were used in place of the urea / formalin resin powder, and the luminance was measured in the same manner. The composition and average luminance of Comparative Examples 1 to 7 are also shown in Table 1. Further, for Examples 1 and 6 and Comparative Examples 1 and 2, graphs showing the luminance distribution by plotting the measured values were produced and are shown in FIGS. The range of the measurement surface in FIGS. 1 to 4 is 250 mm in total length. However, since the surface light source plate has a width of 216 mm as described above, a substantial measurement part of the surface light source plate is a central portion (2
16 mm). Of course, the average luminance in Table 1 is calculated from the measured portion of the surface light source plate.

[0012]

[Table 1]

[0013]

As described above, the surface light source of the present invention is formed by forming a reflection layer containing urea formalin / resin powder on one surface of a light guide plate, and has a bright and uniform luminance. Therefore, an edge-light type liquid crystal display device which is thin and has high luminance can be manufactured.

[Brief description of the drawings]

FIG. 1 is a graph showing a luminance distribution according to one embodiment of the present invention.

FIG. 2 is a graph showing a luminance distribution according to another embodiment of the present invention.

FIG. 3 is a graph showing a luminance distribution of a comparative example.

FIG. 4 is a graph showing a luminance distribution of another comparative example.

Claims (1)

(57) [Claims] 1. An edge light type surface light source plate,
A surface light source plate, wherein a reflection layer is formed on one surface of a light guide plate with an ink containing urea / formalin resin powder.