JPH07225377A - Light guide device for light source of liquid crystal display element - Google Patents

Abstract

PURPOSE:To efficiently perform coating operation for reflective paint by adhering a flexible thin film, on which the reflective paint is printed so that desired reflection characteristics are obtained, to the back of a light guide plate with a transparent adhesive. CONSTITUTION:The light of a lamp 1 is reflected by a lamp reflecting sheet 2, entered into a light guide plate 4, and reflected by a reflecting sheet 6 and diffused by a diffusion sheet 3 to irradiate the back of a display element. The reflecting sheet 6 is constituted by printing glass beads, which have a refractive index equal to or larger than the refractive index of the light guide plate 4 and white paint 5, obtained by mixing titanium white with a large reflection factor and the transparent adhesive, on a transparent acryl plate which is thin enough and flexible. The surface of the reflecting sheet 6 on which the reflecting paint 5 is printed is adhered to the light guide plate 4 in contact by using the transparent adhesive. The part where the white paint is printed is circular and larger in diameter with the distance from the light source and higher in distribution density per area with the distance from the light source.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light guide device for a light source of a liquid crystal display device, which is particularly excellent in mass productivity.

[0002]

2. Description of the Related Art As a light source of a liquid crystal display element, that is, a so-called backlight, some fluorescent lamps are arranged behind the liquid crystal display element, and the back surface of the liquid crystal display element is illuminated through a diffusion plate. The structure may be deeper,
It is not used except when particularly high brightness is required, and usually a rod-shaped light source (usually a cold cathode fluorescent lamp if you want to reduce the thickness) is placed on the side of both ends or one end behind the liquid crystal display element. The light guide device guides the light so that the back surface of the liquid crystal display element is illuminated with uniform illuminance.

As this light guide plate (apparatus), the thickness of the end portion in contact with the light source has been thick, becomes thinner as the distance from the light source increases, and fine unevenness (light is refracted and emitted to the liquid crystal display element side) on the surface. A transparent acrylic resin plate (a glass plate was shunned because it is difficult to process, heavy, etc.) was used, but a light guide plate shaped on the surface of such an acrylic resin plate was used. Is inconvenient in terms of process control, such as when the type (specification) of the display device increases, so in recent years, a transparent acrylic plate with a uniform thickness and a flat surface is used for the light guide plate itself. On the other hand, it has come to be used that a reflection means is provided on the back so that the area average reflectance near the portion becomes higher as the distance from the light source increases. Specifically, for example, a reflective coating (ink) obtained by mixing glass powder (refractive material), titanium white (titanium oxide having a high reflectance), and a transparent adhesive is circularly applied to a thickness of a predetermined value or more. Then, the light reaching the back surface of the light guide plate and leaking out from the light guide plate is reflected toward the back surface of the liquid crystal display element, and the diameter of the circular portion and its distribution density are changed to change the back surface of the liquid crystal display element. Illumination by the backlight is made uniform over the entire surface. If the above method is used, the material used is always the same, and it suffices to change only how to apply the reflective paint according to the specifications.

FIG. 2 is a side sectional view of the above conventional example.
FIG. 2A shows an example in which the light source is arranged only on one side end portion behind the liquid crystal display element, and FIG. 2B shows an example in which the light source is arranged on both side end portions behind the liquid crystal display element. In the figure, 1 is a lamp (cold cathode fluorescent lamp), 2 is a lamp reflection sheet, 3 is a diffusion sheet, 4 is a transparent plate (light guide plate), 5 is a reflective paint, and 6 is a reflection sheet. Each of the reflective paints 5 has a circular shape, and its size and number (distribution density) are as expected (the illuminance on the back surface of the liquid crystal display element (not shown) disposed on the diffusion sheet 3 is uniform over the entire surface). It is printed by the silk screen printing method. When viewed from above without passing through the diffusion sheet 3, the portion where the reflective paint 5 is printed looks brighter than the surrounding area. The reflection sheet is for making the display bright by using all the light as little as possible.

[0005]

However, not only when glass is used as the material of the light guide plate, but also when the acrylic resin is used in the usual case or when the plate thickness is actually thin, it is 1 m.
If the thickness is m, the thickness is 10 mm, and the light guide plate is thick and hard. Therefore, the work of applying the reflective paint to such a light guide plate is not easy in mass production. In the case of this reflective paint, there is no problem if the thickness is a predetermined value or more, but if you try to mass-produce a product with the shape of the circular part coated with the reflective paint and the distribution density of the applied parts as accurate as possible, use printing technology However, since the light guide plate is thick and hard as described above, only the most primitive silk screen printing method can be used as a printing technique, and even if this method is used, the productivity is low. Remain.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a light guide device for a liquid crystal display element light source, which solves the problems of the conventional light guide device described above and enables the application work of the reflective paint to be efficiently performed.

[0007]

In order to solve the above-mentioned problems, in the present invention, light from a rod-shaped light source arranged at a lateral end portion behind a liquid crystal display element is arranged behind a liquid crystal display element. The light incident on the light guide plate made of a material with high transmittance and having a uniform thickness, of the light incident on the light guide plate that reaches the back surface of the plate and leaks out, is displayed on the liquid crystal display at each part of the back surface of the light guide plate. A means for reflecting the area back surface of the liquid crystal display element was provided so that the area average reflectance of the area gradually increased as the area became farther from the light source toward the back surface of the element. In the light guide device for a liquid crystal display element light source, the means for reflecting is provided with a layer of a reflective coating material having a high reflectance and having a thickness of a predetermined value or more, which is brought into close contact with or close to the back surface of the light guide plate, and is arranged at each portion. You can get the reflectivity of the period In order to distribute the reflective paint layer in close contact with or close to the back surface of the light guide plate, it is not necessary to directly print on the light guide plate by another method. A flexible thin film is pre-printed with reflective paint so that the desired reflectance distribution can be obtained, and a transparent adhesive is used so that the printed surface of the reflective paint will adhere to the back surface of the light guide plate. After bonding or applying a reflective coating on the entire inner surface of the bottom plate of the device, the reflective coating should be distributed so that the desired reflectance can be obtained at each site before the coating dries and solidifies. At the position, a light-shielding thin film having a through hole pre-drilled is pressure-bonded to the inner surface of the bottom plate, and the reflective coating material applied at a position other than the position of the through hole is extruded into the through hole, so that the bottom plate Reflective paint on the inner surface through the light-shielding thin film To form those applied in distribution density of Nozomu, the light-shielding thin film surface has to be bonded with a transparent adhesive so as to be in close contact with the rear light guide plate.

[0008]

According to the present invention, the flexible thin film different from the light guide plate is much easier to handle in the printing technique, avoiding the direct application of the reflective paint to the thick and hard light guide plate by the printing method. For example, by printing a reflective coating on paper or Saran wrap to obtain the desired distribution of reflective characteristics, and then bonding it to the back surface of the light guide plate with a transparent adhesive, the workability and efficiency of printing are significantly improved. Not only is it possible to improve the number of units to be manufactured per hour, but also the printing accuracy itself is generally improved and the quality is improved. Also, due to the nature of the reflective paint, or because the coating thickness of the reflective paint is slightly thick,
If the contour of the area coated with the reflective coating cannot be accurately formed by the normal printing method, through holes are pre-drilled in the light-shielding thin film, for example, black thin paper, at the location corresponding to the location where the reflective coating is to be applied. Then, after uniformly applying the reflective coating on the entire inner surface of the bottom plate of the light guide device, before the coating is dried and solidified, the light-shielding thin film is uniformly applied with the reflective coating on the bottom plate. The inner surface of the light-shielding film is pressure-bonded to the surface of the light-guiding plate so that the surface of the light-shielding thin film is brought into close contact with the back surface of the light-guide plate. According to this method
It is possible to accurately form the positions of the through holes drilled in the light-shielding thin film and the contour line of the peripheral portion thereof, and if the coating thickness of the reflective coating is a predetermined value or more, there may be some difference in thickness. Therefore, there is an advantage that the contour of the region coated with the reflective paint can be accurately formed.

[0009] Although the patent publication has already disclosed a technique relating to a light guide plate and a light guide device suitable for many light sources of liquid crystal display elements, in all of them, a diffuse reflection layer is provided (attached) on the light guide plate itself. .

[0010]

1 (a) is a side sectional view of a first embodiment of the present invention, in which 1 is a lamp (cold cathode fluorescent lamp), 2 is a lamp reflection sheet, 3 is a diffusion sheet, and 4 is transparent. A light guide plate made of an acrylic plate, 5 is a reflective paint, and 6 is a reflective sheet. In the first embodiment, the reflection sheet 6 is sufficiently thin and flexible, and the inner surface thereof has glass beads having a refractive index equal to or higher than that of the light guide plate 4, and titanium white (titanium oxide) having a high reflectance. ) And a transparent adhesive mixed with a white paint 5 so that the desired reflectance distribution can be obtained (the white paint printing spot is circular, and the diameter is larger at the part farther from the light source, and the distribution density per area is Is printed closer to the part farther from the light source). The surface of the reflective sheet 6 on which the reflective coating 5 is printed is adhered to the light guide plate 4 with a transparent adhesive. In this embodiment, the lamp 1 serving as the light source is installed only on one side, but it is of course possible to install the lamp 1 on both sides to enhance the display brightness of the liquid crystal display element.

FIG. 1 (b) is a side sectional view of a second embodiment of the present invention, in which 1 is a lamp (cold cathode fluorescent lamp), 2 is a lamp reflection sheet, 3 is a diffusion sheet, and 4 is transparent. A light guide plate made of an acrylic plate, 5 is a reflective paint, 6 is a reflective sheet, and 7 is a light-shielding film. In this embodiment, the reflection sheet 6 serves as the bottom plate of the light guide device of the backlight. Also, the viscosity of the reflective coating material 5 used in this embodiment is slightly lower than that used in the first embodiment. Through holes are formed in the light-shielding film 7 at positions corresponding to positions where the reflective coating should be applied so as to obtain a desired reflection characteristic distribution in advance. That is, a large number of relatively large holes are formed in the part far from the light source, and vice versa in the part close to the light source. Since the light-shielding film is thin, it is easy to form the through-holes exactly in the desired shape, size, density, etc. as desired. A relatively low-viscosity reflective paint 5 is evenly (solid) applied to the inner surface of a reflective sheet 6 that serves as the bottom plate of the apparatus, and the light-shielding film 7 perforated as described above is pressure-bonded to the paint before the paint dries and solidifies. To do. Then, the reflective coating material 5 applied to the place where there is no hole is extruded into the perforated portion and, in some cases, passes through the through hole and appears on the front surface side of the light shielding film 7 (back surface side of the light guide plate 4). The light-shielding film side of the reflection sheet 6 thus configured is brought into close contact with the back surface of the light guide plate 4. A transparent adhesive is usually used to bring the light-shielding film 7 into close contact with the back surface of the light guide plate 4, but the adhesive is also included in the reflective paint 5 itself, so that the light guide plate 4 side passes through the through hole. Depending on the amount of the reflective paint extruded on the sheet, it is possible to adhere the reflective paint itself without using an adhesive. As described above, in the second embodiment, the shape (contour) of the portion to which the reflective coating material 5 is applied is generally more accurate than in the case of printing in the first embodiment.

In both the first and second embodiments, in addition to the above, a vacuum packing method or a double-sided tape may be used for pressure and adhesion.

[0013]

As described above, according to the present invention, the light guided in the light guide plate for the light source of the liquid crystal display device reaches the back surface of the light guide plate and leaks to the outside. Therefore, the work of applying the reflective coating material in an appropriate distribution in accordance with the distance from the light source can be performed very easily and accurately in order to reflect it toward the rear surface of the liquid crystal display element through the light guide plate.

[Brief description of drawings]

FIG. 1 (a) is a side sectional view of a first embodiment of the present invention,
FIG. 1 (b) is a side sectional view of the second embodiment of the present invention.

FIG. 2 (a) is a conventional example in which a light source is arranged only on one side end portion behind a liquid crystal display element, and FIG. 2 (b) is a conventional example in which a light source is arranged on both side end portions behind a liquid crystal display element. It is a sectional side view shown.

[Explanation of symbols]

1 ... Lamp (cold cathode fluorescent lamp), 2 ... Lamp reflection sheet, 3 ... Diffusion sheet, 4 ... Light guide plate, 5 ... Reflective paint,
6 ... Reflective sheet, 7 ... Shading film.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shigego Takahisa 3673 Hayano, Mobara-shi, Chiba Hitachi Nisshin Electronics Co., Ltd.

Claims (2)

[Claims] 1. Light from a rod-shaped light source disposed at a side end portion behind a liquid crystal display element is made incident on a light guide plate made of a substance having a high light transmittance disposed behind the liquid crystal display element and having a uniform thickness. Of the light that has entered the light guide plate from the light source, the light that has reached the back surface of the plate and leaked is directed toward the back surface of the liquid crystal display element at each part of the back surface of the light guide plate, and as the part becomes further away from the light source, In the light guide device for a liquid crystal display element light source, which is provided with a means for reflecting so that the area average reflectance in the region gradually increases, a uniform illuminance can be obtained on the back surface of the liquid crystal display element, the reflecting means is: It is formed by placing a layer of a reflective paint having a high reflectance and having a thickness equal to or more than a predetermined value on the back surface of the light guide plate, and distributing the area ratio so that the desired reflectance is obtained at each part. , The reflective paint layer on the back of the light guide plate Instead of directly printing on the light guide plate in order to obtain a close contact distribution, a flexible coating different from the light guide plate is printed beforehand with a reflective coating so that the desired reflectance distribution can be obtained. A light guide device for a light source of a liquid crystal display element, characterized in that the deposited material is adhered with a transparent adhesive so that the surface coated with the reflective paint is in close contact with the back surface of the light guide plate. 2. In the light guide device for a liquid crystal display element light source, the means for reflecting is obtained by closely contacting or approaching a back surface of a light guide plate with a layer of a reflective paint having a high reflectance and having a thickness of a predetermined value or more. , It is formed by distributing the area ratio so that the desired reflectance is obtained in each part, and the reflective paint layer is distributed close to or close to the back surface of the light guide plate, so that it does not depend on the printing method. After applying the reflective coating on the entire inner surface of the bottom plate of the device, before the coating dries and solidifies, the reflective coating should be distributed and arranged in advance so that the desired reflectance can be obtained at each part. A light-shielding thin film having a through hole is pressure-bonded to the inner surface of the bottom plate, and the reflective coating applied to the portion other than the position of the through hole is pushed out into the through hole, so that the inner surface of the bottom plate has a reflective property. Desired distribution of paint through the light-shielding thin film To form what is applied in degrees,
A light guide device for a liquid crystal display element light source, characterized in that the surface of the light-shielding thin film is adhered to the back surface of the light guide plate with a transparent adhesive.