JPH0634818A - Light diffusing waveguide plate and light diffusing device using the same - Google Patents

Abstract

(57) [Summary] [Object] To provide a light diffusing light guide plate having high brightness on the light diffusing surface and having a uniform brightness distribution over the entire surface. A light diffusing light guide plate which uses one surface of a transparent plate-like body as a light-dissipating surface and its opposite surface as a light-reflecting surface, and introduces light from at least one side end surface of four side end surfaces excluding these surfaces. In the above, the light diffusing light guide plate is provided with a large number of holes penetrating the transparent plate in the normal direction of the light radiating surface as the light diffusing means. In addition, a diffuse translucent film or sheet is arranged outside the light diffusing light guide plate and the light radiating surface, and a light reflecting flat body is arranged outside the light reflecting surface. To form a light diffusing device. [Effect] Although this light diffusion light guide plate has a simple structure,
Since a light from a light source is efficiently diffused and emitted from a light radiating surface, when used in an edge light type light diffusing device, a light diffusing device having high brightness on the display surface and having a uniform brightness distribution is provided. You can

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light diffusing light guide plate made of a transparent material and a light diffusing device using the same. The light diffusing light guide plate of the present invention is a light diffusing device that is a surface light source for receiving light from a light source and uniformly illuminating it over a relatively large area, for example, illumination of advertising signs, indoor guide signs, liquid crystal display. Used for back lighting of equipment.

[0002]

2. Description of the Related Art In recent years, a so-called edge light type light guide plate, which introduces light for illumination from a side end surface of a transparent plate, has been widely used for illumination of advertising signs, indoor signboards, rear illumination of liquid crystal display devices, etc. Has been done. The most distinctive advantage of these flat lighting devices is that they can form an extremely thin display device, and when a tubular lamp such as a fluorescent lamp is used as a light source, the device can be thinned to a thickness close to the outer diameter of the lamp. Therefore, it is possible to provide a space-saving and compact device, and the device often has an excellent appearance. On the other hand, the edge-light type display device is inferior in brightness of the display surface (which can be measured as brightness) and inferior in uniformity of brightness of the display surface (can be measured as brightness uniformity). Despite these drawbacks, the reason why edge-light type display devices continue to spread and spread is due to the above advantages and various techniques for overcoming these drawbacks.

When the light from the tubular lamp is introduced into the end face on one side without processing the upper body of the transparent plate as it is, only the portion near the end face on the four side has high brightness, and most of the incident light is Since the light is emitted from the end surface on the fourth side and the light emitting surface close to the end surface on the four side, only the vicinity of the end surface on the four side has high brightness, and the central portion of the light emitting surface has extremely low brightness. Even if the light-reflecting material is applied or adhered to the other 3 side end surfaces except the 1 side end surface which introduces light, or the amount of light directed to the light emitting surface is increased, the unevenness of the brightness on the light emitting surface remains Substantially unchanged.
A number of methods have been proposed for uniforming the brightness on the light-dissipating surface (see, for example, JP-A-57-128383 and JP-A-1-245220). In these known methods, although the brightness is made uniform, the brightness itself is at a low level, and even if the back lighting of the monochrome liquid crystal display device is satisfactory, the back lighting of the color liquid crystal display device or The brightness of the billboard was not enough to be used for lighting the billboards.

[0004]

Therefore, the present invention corrects the above-mentioned drawbacks of the light diffusing light guide plate in the prior art, and enables the use of an inexpensive light source such as a fluorescent lamp.
An object of the present invention is to provide a light diffusing light guide plate which has a high brightness on the light radiating surface and can realize a uniform brightness distribution over the entire surface, and a light diffusing device using the light diffusing light guide plate.

[0005]

The above object is to use one surface of a transparent plate-like body as a light-diffusing surface and the opposite surface thereof as a light-reflecting surface, and at least one of four side end surfaces excluding these surfaces. In a light diffusing light guide plate for introducing light from an end face, it is achieved by a light diffusing light guide plate characterized in that a large number of holes penetrating the transparent plate-like body are provided as a light diffusing means in a direction normal to the light emitting surface. It

The above object is to use the light diffusing light guide plate, and dispose a diffuse translucent film or sheet on the light radiating surface side of the light diffusing light guide plate and a light reflecting flat body on the light reflecting surface side thereof. It is also achieved by a light diffusing device characterized by:

[0007]

The present invention will now be described in more detail with reference to the drawings.

FIG. 1 is a plan view showing an embodiment of a light diffusing light guide plate according to the present invention, and FIG. 2 is a sectional view taken along the line A--A in FIG.
It is sectional drawing which follows the line. In the figure, the transparent plate-like body 1 has one surface as a light emitting surface 4 and the opposite surface as a light reflecting surface 5,
At least one side end surface of the four side end surfaces excluding these surfaces is a side end surface 2 through which light is incident, and the remaining side end surfaces are side end surfaces 3 through which light is reflected. The light diffusing light guide plate is provided with a large number of holes 6 penetrating the transparent plate 1 in the normal direction.

The transparent plate 1 is preferably made of a material having a high degree of transparency, for example, a transparent synthetic resin such as methacrylic resin, polycarbonate resin, polystyrene resin, or glass.

Since the side end surface 2 on which light is incident is required to efficiently introduce light, it is preferable that the surface 2 be smoothed by cutting, polishing or the like. The side end surface 3 for reflecting light may be a rough surface or a smooth surface, but is preferably a smooth surface, and a white paint is applied to this surface or a reflective white film or the like is applied. Therefore, a surface having increased light reflectivity is used.

The light emitting surface 4 is preferably a smooth mirror surface. The light reflection surface 5 is a surface parallel to the light diffusion surface 4,
A smooth mirror surface or a metal thin film may be vapor-deposited on the mirror surface or a white paint may be applied to increase the light reflectivity.

The planar shape of the through-hole 6 is preferably circular in view of easy processing, but square, elliptical, etc. can be used and is not limited to circular. The cross-sectional shape of the through hole 6 may be a through hole in which the central axis of the hole is perpendicular to the surface of the light diffusion surface 4 or the light reflection surface 5 and the hole diameter is constant. It may be a changing tapered hole. In addition, in order to avoid troubles caused by penetration such as scattering of cutting chips and burrs during machining, or to obscure the outline of the hole, a substantial penetration of about 1/10 of the plate thickness is left. Even a hole
Such a substantial through hole may be used because the function as the light guide plate of the present invention can be exhibited.

FIG. 3 is a diagram showing the relationship between the depth of the hole and the brightness, and the depth of the hole has a close relationship with the value of the brightness. The brightness increases with the depth of the hole, and at 80% of the thickness of the plate, the brightness reaches a saturated state, but becomes maximum in the through hole. That is, it is presumed that the light incident from the side end surface increases the diffusion amount having directivity in the normal direction of the light emitting surface with the depth of the hole, and the most effective normal direction diffusion is performed in the case of a through hole. It

The relationship between the thickness of the plate and the brightness of the through hole is 2 m.
Since there is almost no difference between the m plate and the plate having a thickness exceeding it, the plate thickness may be at least 2 mm, and may be increased in consideration of warpage and the like.

As a method of forming the through holes, cutting and laser processing accompanied by numerical control can be performed, but casting, compression molding and injection molding with higher productivity are more preferable. The hole diameter and the hole distribution of the through holes are closely related to the performance of the light diffusing light guide plate, and there is a suitable range depending on the application purpose. When displaying characters or simple figures such as guide signs in a series of through holes, a strict luminance uniformity is not necessarily required, and therefore a hole diameter of 3 mm can be used. On the other hand, when it is used as an illumination of an advertising signboard or as a back illumination of a liquid crystal, a strict luminance uniformity is required, and it is difficult to make the entire surface uniform with a constant hole diameter. However, when the hole area ratio is 1% or less, the hole diameter is 0.7 mm.
The purpose can be achieved for the time being by using the following small-diameter holes. When the hole area ratio is larger or when a higher degree of luminance uniformity is required, the purpose can be achieved by increasing the hole diameter along with the distance from the light incident side end face. However, the hole diameter to be changed cannot be selected without limitation, and it is not preferable to use the hole diameter in FIG. 4 in a range in which the brightness is attenuated as the hole diameter increases, because the effect is low. Due to the above restriction on the hole diameter, it is preferable that the through hole as the light diffusing means has a hole diameter in the range of 0.1 to 3 mm, particularly 0.5 to 2 mm, and more preferably away from the side end surface for introducing light. According to the above, the hole diameter is gradually increased.

[0016]

EXAMPLES The present invention will be described in more detail with reference to Examples and Comparative Examples.

FIG. 5 is a sectional view of a light diffusing device used for back lighting of a liquid crystal display device, and the performance of the light diffusing light guide plate was evaluated using this device.

First, a tubular lamp 51 is provided on one end surface (light incident side end surface) of the light diffusing light guide plate 53, a diffusion film 52 is provided on the light emitting surface, a reflecting film 54 is provided on the light reflecting surface, and a reflecting film 55 is provided on the light reflecting side end surface. Further, reflective films 56 were provided around the tubular lamps, respectively. As the tubular lamp 51, a cold cathode fluorescent tube having a tube diameter of 5.6 mm (center brightness: 16000 cd
/ M ² ) was used. The diffusing film 52 scatters and transmits light from the light diffusing surface 4 of the light diffusing light guide plate 53 and reflected light from the light reflecting surface 5 and the reflecting films 54 and 56, and is a roughened polyester film ( Kimoto Co., Ltd. D104) was used.

As the light diffusion light guide plate 54, a transparent methacrylic resin plate having a thickness of 2 mm (extruded plate Cosmo Glass manufactured by Kuraray Co., Ltd.) was used. The reflection film 54 is the light diffusion light guide plate 5.
A white reflective polyester film (W900 manufactured by Kimoto Co., Ltd.) was used in order to reflect the light dissipated from the light reflecting surface of No. 3 and to improve the light utilization efficiency. The reflection film 55 is for reflecting the light scattered from the side end surface of the light diffusing light guide plate 53, and the reflection film 56 is for reflecting the light scattered from the tubular lamp 51 to the outside of the device, thereby improving the utilization efficiency of the light. The same material was used.

FIG. 6 shows the luminance distribution of the embodiment on the surface of the diffusion film of the light diffusion device shown in FIG. The brightness distribution on the surface of the diffusion film was measured in a direction orthogonal to the longitudinal direction at approximately the center of the longitudinal direction of the lamp, and the focus was placed on the center of the through hole. This value is illustrated, and the brightness uniformity ratio k% [k = (minimum brightness / maximum brightness) × 100] is added to the brightness curve. In the figure, the brightness curves with symbols A, B and C are curves when using a light diffusion light guide plate in which through holes having a constant hole diameter are provided in a grid pattern at an equal pitch of 10 mm as in FIG. hand,
A, B and C correspond to the light diffusion light guide plate provided with circular through holes having hole diameters of 2 mm, 1 mm and 0.7 mm, respectively.

It can be seen from FIG. 6 that the larger the hole diameter is, the more severe the attenuation of the brightness with the light entrance distance becomes, and the lower the brightness uniformity becomes. If the hole diameter is reduced to 0.7 mm or less, the brightness uniformity is improved to a level at which it can be put to practical use. However, when the pitch of the grating is made finer, the uniformity of the holes decreases with a hole diameter of 0.7 mm, and a through hole with a smaller diameter is required, but there is a drawback that the brightness decreases as shown in FIG.

As means for maintaining high brightness and enhancing brightness uniformity, which is a feature of the present invention, there is a means for providing through-holes having a continuously changing hole diameter instead of a constant hole diameter. That is, as shown in the example in FIG. 7, a hole diameter is used that gradually increases as the distance from the side end surface for introducing light increases.

FIG. 8 shows the luminance distribution of another embodiment using the light diffusing light guide plate provided with the through holes having the above-mentioned continuously changing hole diameters. In the figure, the brightness curves with the symbols D, E and F indicate the case where a light diffusion light guide plate is used in which through holes having continuously changing hole diameters as shown in FIG. 7 are provided in a grid pattern at an equal pitch of 5 mm. It is a curve, and in D, it is a hole diameter that increases in arithmetic series with the distance from the incident end face from a minimum of 0.8 mm to a maximum of 3.6 mm, and in E, it is a minimum of 1.3 m.
From m to 2.3 mm, the minimum is 0.9 m in F as well.
It corresponds to the hole diameter increasing from m to a maximum of 1.9 mm, respectively. As shown in FIG. 8, if a hole diameter larger than the maximum brightness hole diameter (2.1 to 2.3 mm in FIG. 4) as in D is frequently used, the brightness uniformity becomes low as in the case of a constant diameter. , E and F, by limiting the range of pore diameter, an excellent degree of uniformity can be obtained.

FIG. 9 shows an example of a luminance curve of a conventional light guide plate using white halftone dots by screen printing instead of the above-mentioned light diffusion light guide plate as a comparative example. Comparing FIG. 9 and FIG. 8, although both are about the same in luminance uniformity,
The brightness itself is much higher in the embodiment of FIG. 8 and the light utilization efficiency is excellent.

[0025]

As described above, the present invention uses one surface of the transparent plate as a light-diffusing surface and the opposite surface as a light-reflecting surface, and at least one of the four side end surfaces excluding these surfaces. In the light diffusing light guide plate for introducing light from the end face, the light diffusing plate having a simple structure is provided as a light diffusing means by providing a large number of holes penetrating the transparent plate in the normal direction of the light radiating surface. Is used to efficiently diffuse the light from the light source and emit the light from the light emitting surface. Therefore, when used in an edge light type light diffusing device, it is possible to provide a light diffusing device having high brightness on the display surface and a uniform brightness distribution.

[Brief description of drawings]

FIG. 1 is a plan view showing an embodiment of a light diffusing light guide plate of the present invention,

2 is a sectional view taken along the line AA in FIG.

FIG. 3 is a diagram showing an example of the relationship between the depth of a hole and brightness,

FIG. 4 is a diagram showing an example of the relationship between the hole diameter and brightness,

FIG. 5 is a sectional view showing an embodiment of a light diffusing device of the present invention,

FIG. 6 is a diagram showing a luminance curve in an example of the present invention,

FIG. 7 is a diagram showing an example of a continuously changing hole diameter,

FIG. 8 is a diagram showing a luminance curve in another embodiment of the present invention,

FIG. 9 is a diagram showing a luminance curve in a comparative example of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Transparent plate-shaped body, 2 ... End surface which light injects, 3 ... Side end surface which reflects light, 4 ... Light diffusion surface, 5 ... Light reflection surface, 6 ... Through hole, 51 ... Tubular lamp, 52 ... Diffusion Film, 53 ... Light diffusion light guide plate, 54/55/56 ... Reflective film.

Claims (4)

[Claims] 1. A light diffuser which uses one surface of a transparent plate as a light-diffusing surface and the opposite surface as a light-reflecting surface, and introduces light from at least one of the four end surfaces excluding these surfaces. In the light guide plate, a plurality of holes penetrating the transparent plate-like body are provided as light diffusing means in a direction normal to the light radiating surface. 2. The light diffusing light guide plate according to claim 1, wherein the diameter of the holes is in the range of 0.1 to 3 mm. 3. The light diffusing light guide plate according to claim 1 or 2, wherein the diameter of the hole is provided so as to increase gradually as the distance from the end face side on which light is introduced increases. . 4. The light diffusing light guide plate according to any one of claims 1 to 3, wherein a diffuse translucent film or sheet is provided on the light diffusing surface side of the light diffusing light guide plate, and a light reflecting flat body is provided on the light reflecting surface side thereof. A light diffusing device, characterized in that.