JPH0895036A - Light guiding plate - Google Patents

Abstract

PURPOSE: To prevent the occurrence of moire by randomly setting pitches between patterns scattering or refracting outgoing light from a light guiding plate base body arranged on a light guiding plate principal plane in an optional direction and to provide a high display quality by incorporating the light guiding plate in a light source of a display device. CONSTITUTION: In a light guiding plate 23, a principal plane on a liquid crystal panel 10 side serves as a light emitting plane 25, and on a principal plane opposed to the light emitting plane 25, plural scattering dots 26 are arranged. These scattering dots 26 are arranged in plural lines. Dimensions of the scattering dots 26 belonging to the lines far from a cold cathode tube 21 are increased in comparison with those of the scattering dots 26 belonging to the lines close to the cold cathode ray tube 21. In this way, areas of the scattering dots 26 are increased compensating a light loss inside the light guiding plate 23, since the light loss is increased as it is separated further from the cold cathode tube 21. Pitches P=d1, d2, d3,..., dn-2, dn-1, dn between respective lines are set on the basis of a random number.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a flat light source device used as a light source for a display device such as a liquid crystal display device.

[0002]

2. Description of the Related Art The basic structure of a liquid crystal display device comprises a liquid crystal panel and a flat light source device provided on the back surface of the liquid crystal panel. In this flat light source device, a light source such as a cold cathode tube is arranged along one side surface of a flat plate-shaped optical element called a light guide plate, and light emitted from the cold cathode tube is guided to the inside of the light guide plate for surface emission. The scheme is used.

The light guide plate is made of an optically transparent resin material base such as acrylic processed into a flat plate shape, and a scattering pattern is formed in a dot shape on the main surface of the base opposite to the liquid crystal panel. There is.

This scattering pattern has a function of scattering and emitting the light guided inside the light guide plate toward the liquid crystal panel, and a material mainly containing a white pigment such as titanium oxide is attached to the surface of the substrate. Formed by.

[0005]

In the liquid crystal display device using the conventional flat light source device, moire is observed on the display screen, which causes the display quality to be remarkably deteriorated. It is considered that the cause of the moire is due to the interference between the scattering patterns of the light guide plate or the interference between the wiring inside the liquid crystal panel and the scattering pattern of the light guide plate. Therefore, the present invention eliminates such moire,
An object is to provide a flat light source device suitable as a light source for a display device using a liquid crystal panel or the like.

[0006]

A light guide plate according to a first aspect of the present invention is a plate-shaped base body and a main body surface of the base body which are arranged in a row so as to be spaced apart from each other so that light emitted from the base body is arbitrary. A plurality of row patterns that scatter or refract in the direction of
It is characterized in that the pitch of adjacent column patterns is set based on a random number.

A light guide plate according to a second aspect of the present invention is a plate-shaped base and a row of light-emitters emitted from the base that are scattered or refracted in any direction on one main surface of the base. A plurality of dot patterns to be made to belong to, and at least a part of the dot patterns belonging to different columns and adjacent to each other are formed so as to have a pitch different from the pitch of the respective columns to which they belong.

A light guide plate according to a third aspect of the present invention is a plate-shaped base and a row of light-emitters emitted from the base that are scattered or refracted in any direction on a main surface of the base so as to be spaced apart from each other. A plurality of dot patterns to be made to belong to, and the pitch of the dot patterns belonging to different columns and adjacent to each other is set based on a random number. The light guide plate according to a fourth aspect of the present invention is characterized in that the pattern is formed by a convex portion provided on the one main surface.

[0009]

According to the present invention, the pitch between the patterns provided on the main surface of the light guide plate for scattering or refracting the light emitted from the light guide plate base in an arbitrary direction is set at random, and spatial periodicity is provided by this pattern. It is something that should not happen. As a result, it is possible to visually eliminate the moire that has conventionally occurred.

The pattern having the scattering or refracting power may be scattering dots made of, for example, a white pigment printed on the main surface of the light guide plate, or may be formed by processing the light guide plate itself. It may be a protrusion.

[0011]

【Example】

(Embodiment 1) An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic sectional view of a liquid crystal display device according to the first embodiment.

That is, the liquid crystal panel 10 has a liquid crystal layer 13 sandwiched between two glass substrates 11 and 12, and an electrode for applying a voltage to the liquid crystal layer 13 is provided on the inner surface of each glass substrate. 14 and 15 are formed. A unit pixel is formed at the intersection of the electrode 14 and the electrode 15.

For the driving method of the liquid crystal panel, two kinds of methods are abbreviated. The first method is a so-called multiplex method. In this case, the electrodes 14 and 15 are band-shaped transparent electrodes, and these band-shaped electrodes are combined so as to be orthogonal to each other to form a pixel. The second method is the so-called active matrix method, in which case the electrode 14
Alternatively, one of the electrodes 15 is a dot-shaped display pixel electrode arranged in a matrix. A thin film transistor (TFT) is connected to each display pixel electrode as a switching element for controlling the display pixel electrode. And this TF
A scanning line and a signal line for controlling T are arranged orthogonal to each other so as to surround the display pixel electrode. The other electrode functions as a counter electrode formed on the entire surface of the substrate.

In this embodiment, an active matrix type liquid crystal panel is used. The display pixel electrodes are arranged such that the mutual electrode pitch is 300 μm in the vertical direction and 100 μm in the horizontal direction.

On the back surface of the liquid crystal panel 10, a flat light source device 20 having a shape substantially the same as that of the liquid crystal panel 10 is arranged close to the liquid crystal panel 10. This flat light source device 20
Is composed of a light guide plate 23 and a cold cathode tube 21 provided facing one end of the light guide plate 23. The main surface of the light guide plate 23 on the liquid crystal panel 10 side is a light emitting surface 25, and a plurality of scattering dots 26 are provided on the main surface facing the light emitting surface 25. Although not shown, a diffusion sheet may be interposed between the liquid crystal panel 10 and the light guide plate 23.

Further, a reflecting plate 22 may be provided so as to cover the surface of the cold cathode tube 21 other than the surface facing the light guide plate 23. Further, the reflecting plate 22 may be provided close to the surface of the light guide plate 23 opposite to the liquid crystal panel 10. The plate 24 may be arranged.

Next, the operation of this liquid crystal display device will be described. When the light emitted from the cold cathode tube 21 enters the inside of the light guide plate 23, the incident light is transmitted through the inside of the light guide plate 23 while repeating total reflection. When the transmitted light reaches any of the scattering dots 26, the light is scattered there. Of the scattered light, the light that reaches the light emitting main surface 25 under the condition that the total reflection condition is broken is the liquid crystal panel 10.
It is emitted toward.

On the other hand, in the liquid crystal panel 10, the electrodes 14 (display pixel electrodes) arranged in a matrix are line-sequentially selected for each row and a predetermined potential is written. Then, the transmittance of the liquid crystal layer 13 is modulated for each pixel according to the potential difference between the electrode 14 and the electrode 15 (counter electrode). And the light guide plate 2
Display is performed by controlling the amount of transmitted light emitted from 3 for each pixel according to this transmittance.

FIG. 2 is a schematic perspective view of the light guide plate 23. The light guide plate 23 of the present embodiment is made of an optically transparent acrylic resin flat plate, and a white pigment containing titanium oxide as a main component is attached in a dot shape on one of its main surfaces.
A large number of circular scattering dots 26 are formed.

These scattering dots 26 are arranged so as to form a plurality of rows. The scattering dots 26 belonging to the row farther from the cold cathode tubes 21 are formed to be larger than the scattering dots 26 belonging to the row closer to the cold cathode tubes 21. This is because the light loss inside the light guide plate 23 increases as the distance from the cold cathode tube increases, and in order to compensate for this, the area of the scattering dots 26 is increased to increase the amount of light emission per unit dot. Then, the pitch P between the columns P = d1, d2, d3, ..., dn-2, dn-
1, dn are set based on random numbers. Specifically, these pitches P are

[0021]

## EQU1 ## It is set so that P = P0 + Pr × (1 + r). In the above equation, P0 is a reference pitch between columns, which is set to a value such that the column pattern is not visually recognized through the liquid crystal panel. Specifically, it is about half the thickness of the light guide plate, and in the case of this embodiment, it is set to 1.5 mm.

The reference pitch P0 may be changed in the plane of the light guide plate depending on its position. That is, as described above, the light that has entered the light guide plate from the light source undergoes loss inside the light guide plate. Therefore, depending on the position (x, y) on the main surface of the light guide plate, that is, the distance from the light source, the intensity of light emitted from the light guide plate has a distribution. By increasing the density of the scattering pattern from the side closer to the light source to the side farther from this, the scattering area per unit area is substantially increased,
Can be compensated. That is, the reference pitch P0 may be set so that the light emitted from the light guide plate becomes uniform and increases as the distance from the side closer to the light source increases.

On the other hand, Pr is the maximum value of the deviation amount from the reference pitch, and in this embodiment, it is set to 150 μm. Further, r is a random number and is selected so that −1 ≦ r ≦ 1. Also in the row direction, the pitches h1, h2, h3, ..., hm between the respective scattering dots are determined based on random numbers.

The light guide plate 23 in this embodiment is manufactured by using a so-called screen printing method. The outline is shown in Fig. 3.
As shown in. That is, a photosensitive photoresist material is applied on the entire surface of a screen mesh 31 formed by orthogonally crossing metal thin wires, and this is exposed and developed to be patterned into a predetermined shape. Then, a white pigment containing titanium oxide as a main component is printed on the surface of the acrylic resin plate serving as the light guide plate base through the openings 33 formed by this patterning.

By the way, in the screen printing method,
The resist may partially adhere and remain on the mesh 31 in the openings 33. In particular, the resist at the portions where the metal thin lines forming the mesh intersect cannot be completely removed at the time of development, and the resist is likely to remain in areas other than the desired pattern shape, as shown by hatching in the figure. As a result, the scattering pattern is not a perfect circle, but has an indefinite shape that reflects the shape of the remaining resist.

Since the pitch of the mesh 31 and the pitch of the mask for exposing the resist do not necessarily match, the shape of the scattering dots formed by this also differs from place to place. A predetermined periodicity occurs due to the pitch relationship. It has been found that this causes interference fringes in the scattered light from the scattering dots, which causes moire to be visually recognized in the emitted light from the light guide plate.

Therefore, in this embodiment, the pitch of the holes 33 formed by patterning is determined based on a random number. Specifically, as described above, the pitch of the holes 33 is determined so that the formed pattern becomes the pattern shown in FIG. At this time, it has been found that setting the value of Pr for determining the pitch to about the thickness of the screen mesh line is more effective in eliminating moire. In the present embodiment, a No. 250 to No. 300 screen mesh is used, and Pr is 150 μm in accordance with this.
m.

When a liquid crystal display device was assembled using the light guide plate manufactured as described above, and was actually turned on and observed, it was confirmed that moire was not visually recognized. In the liquid crystal display device of the present example, no moire was observed and good display quality could be realized. Further, in the method of manufacturing the light guide plate of the present embodiment, moire due to the influence of the undesired resist remaining on the mesh pitch can be avoided, so that the manufacturing yield can be significantly improved.

The arrangement of the scattering dots may be modified. For example, in the above light guide plate, the scattering dots belonging to each row are arranged so that the centers of the dots coincide with the reference line shown by the broken line in FIG. 2, but the invention is not limited to this.
The scattering dots may be formed so that the center of the scattering dots deviates from the reference line. That is, the scattering dots in each row may be formed so as to overlap the reference line and to have a region where the pitch between adjacent reference lines (row pitch) is different from the pitch between the scattering dots. If the regularity of the scattering dots is disturbed excessively, a distribution of brightness due to this may newly occur, but by regulating the displacement amount of the dots so as to be surely superimposed on an arbitrary reference line in this way, The regularity of the scattering dots could be disturbed without generating a luminance distribution, and moire could be made inconspicuous as in the light guide plate shown in FIG. (Embodiment 2) FIG. 5 is a schematic perspective view of a light guide plate according to a second embodiment of the present invention.

In this embodiment, a projection is formed on the light-emitting main surface of the light guide plate by molding this light guide plate,
The light is refracted / reflected by the projections to allow surface emission.

In the flat light source device of this embodiment, a cold cathode tube 41 is arranged so as to face one end of the light guide plate 43. The light guide plate 43 is made of an acrylic resin flat plate as a base, and a plurality of rows of projections 46 are formed on the light emitting main surface by molding this base. The projection 46 has an inclined surface on the cold cathode tube 41 side, and has a substantially vertical surface on the side opposite to the cold cathode tube 41. The inclination of the slope of the projection 46 is set so that the light transmitted inside the light guide plate 43 is totally reflected. On the other hand, the substantially vertical surface connected to this is inclined so that the condition of total reflection is broken. It is set.

Specifically, the light incident on the light guide plate 43 is
The cone has a spread depending on the refractive index of the light guide plate material. When an acrylic resin plate having a refractive index of about 1.5 is used as in this embodiment, the spread angle of the cone is about ± 42 °.
Therefore, to totally reflect the light traveling in the 42 ° direction,
The slope of the slope may be determined. Then, of the light reflected by this surface, the light that reaches a substantially vertical surface (hereinafter referred to as the light emission surface) connected to this surface is extracted to the outside, and the remaining light is directed to the inside of the light guide plate. Is reflected again and propagates inside the light guide plate. As a result, the light emitted from the light guide plate becomes convergent light whose spread angle is reduced according to the area of the light emitting surface.

The light emitted from the light guide plate is bent in such a manner that it crosses the liquid crystal panel vertically through the prism lens sheet (not shown) arranged on the light emitting main surface of the light guide plate. And is incident on the liquid crystal panel.

As a result, it is possible to reduce the component that obliquely crosses the liquid crystal panel, make the optical path length passing through the liquid crystal panel substantially constant, and reduce the viewing angle dependence of the contrast. Further, since it is not necessary to provide scattering dots and the like, light loss can be minimized and the brightness of the display device can be improved.

Further, in the present embodiment, the pitches d1, d2, ..., dn-1, dn of the projections 46 are determined based on random numbers, like the pitch of the scattering pattern in the first embodiment. When the light guide plate of this example was incorporated into a liquid crystal display device and turned on and observed, it was confirmed that moire did not occur as in Example 1. This is because the protrusions 46 and the electrodes inside the liquid crystal panel did not cause regular interference by disturbing the regularity of the arrangement of the protrusions 46. In addition, a light display with little light loss in the light source device could be obtained.

In the light guide plate of the present embodiment, it is possible to realize such high display quality and reduce the viewing angle dependence of contrast. Further, since it is not necessary to form the scattering dots, it is possible to suppress the light loss and improve the brightness of the display device, and further it is possible to reduce the number of steps and the manufacturing cost.

In the present embodiment, a plurality of rows of column-shaped projections are provided, but the present invention is not limited to this configuration. For example, island-shaped projections may be arranged in rows and a plurality of rows of projections may be provided. good. When the protrusions are arranged in rows as in the above-described embodiment, there is no regularity along the row direction, so there is an advantage that the processing for reducing moire does not become complicated.

[0038]

In the light guide plate of the present invention, it is possible to prevent the occurrence of moire due to the interference between the light guide plate body or the light guide plate and the display panel. Therefore, high display quality can be obtained by incorporating the light guide plate of the present invention into the light source of the display device.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of a liquid crystal display device according to a first embodiment of the present invention.

FIG. 2 is a schematic perspective view of a light guide plate according to the first embodiment of the present invention.

3 shows a schematic manufacturing method of the light guide plate shown in FIG.

FIG. 4 is a schematic perspective view of a light guide plate according to a second embodiment of the present invention.

[Explanation of symbols]

 10 ... Liquid crystal panel 20 ... Planar light source device 21 ... Cold cathode tube 23 ... Light guide plate 24 ... Reflector plate 26 ... Scattering dot

Claims (4)

[Claims] 1. A flat plate-shaped substrate, and a plurality of column patterns which are arranged in a row on one main surface of the substrate so as to be spaced apart from each other and scatter or refract light emitted from the substrate in an arbitrary direction, A light guide plate, wherein pitches of adjacent row patterns are set based on random numbers. 2. A flat plate-shaped substrate, and a plurality of dot patterns which are arranged on one main surface of the substrate so as to be spaced apart from each other and scatter or refract light emitted from the substrate in an arbitrary direction, A light guide plate, wherein at least some of the dot patterns belonging to different columns and adjacent to each other are formed to have a pitch different from the pitch of the columns to which they belong. 3. A flat plate-shaped substrate, and a plurality of dot patterns, which are arranged on one main surface of the substrate so as to be spaced apart from each other and scatter or refract light emitted from the substrate in an arbitrary direction, A light guide plate, wherein pitches of the dot patterns belonging to different rows and adjacent to each other are set based on a random number. 4. The light guide plate according to claim 1, wherein the pattern comprises a convex portion provided on the one main surface.