JPH06148630A - Surface light source plate - Google Patents

Abstract

PURPOSE:To make possible the production of the liquid crystal display device of an edge light system which is bright, has uniform brightness, is of a thin type and has high brightness by forming a reflection layer consisting of ink contg. urea formalin resin powder on a light transmission plate. CONSTITUTION:The reflection layer consisting of the ink contg. the urea formalin resin powder is formed on one surface of the light transmission plate of the surface light source plate of the edge light system. A transparent plate for allowing the transmittance of light is used for this light transmission plate, for which acryl, glass, etc., are usable. The urea formalin resin powder is the spherical powder of the polycondensate of the urea and formaldehyde and is expressed by formula -(CH2 NHCONHCH2)n (CH2 NHCONHCH2O)m-. This ink contains the urea formalin resin powder in a 0.1 to 1.0 range by weight of the total solid content. The reflection layer is obtd. by applying this ink on the one surface of the light transmission plate and drying the coating.

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 various types of devices are used to provide a surface light source that uniformly reflects light incident on a light guide plate to the upper surface. 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. In order to improve this point, various proposals have heretofore been made (JP-A-57-128383, JP-A-2-26983, JP-A-3-118594, JP-A2-1265).
No. 01, No. 2-160215, No. 4
No. 62519, etc.) has been made, and a part thereof has been put to practical use. Each of the above proposals relates to a device for efficiently and uniformly reflecting the light incident on the light guide plate, and the reflection layer provided on the light guide plate is made of titanium oxide (TiO 2).
₂ ), barium sulphate (BaSO ₄ ), glass beads, etc. are contained, but it is still not sufficient depending on the application. In particular, those containing titanium oxide in the reflective layer have a high reflectance of titanium oxide, so that it is impossible to obtain uniform brightness by reflecting more than the set reflection amount due to print bleeding of unit dots. Become. Therefore, there is a problem that extremely high precision print management is required and the yield is low. In that respect, since glass beads have a low reflectance, printing bleeding does not cause the above-mentioned problems, but there is a problem that high brightness cannot be obtained.

[0004]

The present invention has been proposed in view of the above, and in an edge light type surface light source plate,
The present invention relates to a surface light source plate having a reflective layer formed on one surface of a light guide plate with an ink containing urea / formalin resin powder.

The light guide plate used in the present invention is a transparent plate for transmitting light, and the material thereof is not limited, but acrylic, polycarbonate, polystyrene, glass or the like can be used. Generally, it is desirable to use an acrylic plate because of its price and workability.

Further, the urea / formalin resin powder used in the present invention is a spherical powder of a polycondensation product 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
Although the formalin resin powder has a small refractive index of 1.5, it has a light-scattering ability similar to that of titanium oxide (refractive index 2.7).

In the ink containing the above urea / formalin resin powder, various resins can be used as the vehicle component, and although not particularly limited, the urea / formalin resin powder is based on the total solid content. Therefore, it is necessary to add it in a weight ratio of 0.1 to 1.0. 0.1
If it is less, the optical properties will not be exhibited, and if it is more than 1.0, the printability of the ink will deteriorate. Also, as with general-purpose inks, defoaming agents (eg, silicon-based), leveling agents (eg, fine powder silica), thixotropy imparting agents (eg, aluminum stearate), curing accelerators (in consideration of printing suitability, etc.) (Eg, manganese naphthenate), a solvent (eg, isophorone, xylene, ethyl acetate), and other additives can be appropriately blended. Further, various organic pigments and inorganic pigments can be contained in a range that does not impair the above-mentioned optical properties (at least in a range that does not exceed the amount of urea / formalin resin powder), and examples of the organic pigment include nylon resin, silicone resin, Resin powders such as polystyrene resin, polyethylene resin, benzoguanamine resin, acrylic resin, and fluororesin can be cited.Examples of inorganic pigments include diamond, aluminum oxide, silica powder, and titanium oxide coated mica powder. I can give you.

The reflective layer in the present invention is obtained by applying the above ink to one surface of the light guide plate and drying it. The means for applying the ink may be various printing methods or other coating methods, and is not particularly limited, but as described above, it is possible to form a high reflective layer containing titanium oxide. Precision print management is not particularly necessary.

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

[0010]

EXAMPLES Examples of the present invention will be shown below.

Examples 1 to 9 and Comparative Examples 1 to 7 Inks containing urea / formalin resin powder were prepared,
Pre-designed dot pattern for uniform brightness is screen-printed, and the light guide plate (acrylic transparent plate, 2 × 153 ×
(216 mm), a reflective layer was formed by screen printing using the above ink, and the surface light source plates of Examples 1 to 9 were produced. 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 downward, and a diffusion sheet (matte-treated polyester film) is placed on the surface light source plate. ) Was laminated.
One hour after turning on the fluorescent tube, a luminance meter (manufactured by Topcon. BM
-7) was used to measure the luminance in the vertical direction at every 1.0 mm distance from the end (fluorescent tube). For the measurement, the surface light source plate is placed and supported on the XY table, and the luminance meter is fixed at a position 40 cm vertically above the surface light source plate. In this state, the XY table is set to the length of the surface light source plate. The brightness was measured by moving in the direction. Table 1 shows the composition and average brightness of Examples 1 to 9.
Are summarized in. Further, the surface light source plates of Comparative Examples 1 to 7 were prepared in the same manner as above except that the above-mentioned various pigments were used in place of the urea / formalin resin powder, and the brightness was measured in the same manner. Table 1 also shows the composition and average brightness of Comparative Examples 1 to 7. Furthermore, for Examples 1 and 6 and Comparative Examples 1 and 2, graphs showing the luminance distribution were prepared by plotting the measured values, and shown in FIGS. The range of the measurement surface in FIGS. 1 to 4 is 250 mm in total length, but since the surface light source plate has a lateral width of 216 mm as described above, the substantial measurement portion of the surface light source plate is the central portion (2
16 mm range). Of course, the average luminance in Table 1 is calculated from the measurement portion of this surface light source plate.

[0012]

[Table 1]

[0013]

As described above, the surface light source body of the present invention has a reflective layer containing urea formalin / resin powder formed on one surface of the light guide plate, and has a bright and 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 luminance distribution according to an embodiment of the present invention.

FIG. 2 is a graph showing a luminance distribution of 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)

[Claims] 1. An edge light type surface light source plate,
A surface light source plate characterized in that a reflective layer is formed on one surface of a light guide plate with an ink containing urea / formalin resin powder.