JPH039304A - Backlight device - Google Patents

Abstract

PURPOSE:To make a device thin and light and to maintain the uniformity of brightness in the device even when large area is accomplished by disposing a light source on the side surface of a transparent substrate, forming alight irregular reflection layer on the back surface thereof in a pattern in which density gets high in accordance with a distance from the light source so that the layer may have specified occupation factor and providing a light diffusion layer on the front surface thereof. CONSTITUTION:The light source 2 is disposed on at least one of four sides of the transparent substrate, the light irregular reflection layer 3 is formed on the back surface of the substrate 1 in the pattern in which the density gets high in accordance with the distance from the light source so that it may have 5-50% occupation factor with respect to the light emitting area of the surface of the substrate 1 and the light diffusion layer 4 is provided on the surface of the substrate. When light radiated from the light source 2 is made incident on the light irregular reflection layer 3, it is irregularly reflected on the layer 3 and becomes equal to or below an critical angle in a boundary between the substrate 1 and air to be radiated to the outside through the light diffusion layer 4 on the front surface of the substrate 1. In such a case, the light is uniformly emitted to the outside on all the light emitting area of the surface of the substrate 1. Thus, the device is made thin and light, and furthermore the excellent uniformity of brightness is obtained in the device even when the large area is accomplished.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a backlight device that is disposed on the back side of a liquid crystal display (LCD) and illuminates the liquid crystal display.

"Prior Art" In recent years, liquid crystal displays have excellent characteristics such as being thin, lightweight, and low power consumption, and there are great expectations for their use in various products as flat displays that can fully demonstrate these characteristics. It is being However, liquid crystal displays are based on C, which is currently widely used for industrial and consumer purposes.
It is inferior in image quality compared to RT (Cathode RayTube), and a backlight type liquid crystal display has been developed to improve this image quality.

This type of backlight device is desired to be thin and lightweight, and is also required to have uniform brightness over the entire screen area. Various proposals have already been made as techniques for improving the uniformity of brightness in backlight devices. For example, in the device described in JP-A-57-13478, a milky white light scattering body is provided on the top of a linear light source, and the layer thickness of the milky white light scattering body is thick at the center and becomes thinner toward the ends. This eliminates uneven illumination and allows for a thinner and more compact design. Furthermore, in the one described in JP-A No. 60-264039,
Using a serpentine cold cathode lamp, JP-A-61-21998
The one described in Publication No. 0 utilizes the ultraviolet lamp 1 and the phosphor coating layer disposed around the purple + cotton dump,
In the device described in JP-A No. 62-10621, a light source is built into the light guide plate, and in the device described in JP-A-62-12771/1989, concave-convex lenses are arranged on the upper and lower surfaces of a plurality of light sources. , JP-A No. 63-12597525975 uses a J-shaped lamp, which eliminates uneven illumination and makes the brightness uniform.Furthermore, in order to make the brightness uniform, transparent lamps are used. JP-A-54-10556, in which a light scattering material is placed in a substrate so that the a concentration increases on the light source side and increases as the distance from the light source increases.
2, or a backlight device described in JP-A No. 1-309918, in which a light reflecting means is depicted on a coated transparent substrate with a density distribution that is inversely proportional to the distance from the illumination light source and the illuminance. Nowadays, it becomes known.

``Problem to be Solved by the Invention'' 7 However, the above conventional method has the following problems.

(1) When placing the light source on the bottom surface of the light f1,
There is a problem that the entire backlight device becomes thick and expensive.

(2) Use lamps to equalize brightness? If several lamps are provided, there is a problem that the larger the area, the more lamps are required, resulting in a one-stroke quotient.

(3) When using a serpentine lamp, there is a problem in that if a lamp with a large area is used, mass production becomes difficult.

(4) When a light scattering body is placed in a transparent substrate, there is a problem in that it is not easy to produce uniform brightness with good reproducibility.

(5) Coated transparent substrate - When depicting light reflecting means, there is a problem in that the cost is higher than when using a transparent substrate that is not coated.

SUMMARY OF THE INVENTION The present invention has been made to overcome the above-mentioned problems, and aims to provide a backlight device that is thin, lightweight, and can maintain uniformity of brightness even when the area is increased.

"Means for Solving the Problems" The present invention has been made to achieve the above object, and in claim (1), a light source is disposed at at least one of the four circumferences of the transparent substrate, and the transparent substrate On the rear surface, a light scattering reflection layer is formed with a pattern whose density increases according to the distance from the light source and has an occupation rate of 5 to 50% of the light output area on the surface of the transparent substrate. is characterized by a backlight device provided with a light diffusion layer. Furthermore, in claim (2), the light scattering reflection layer has a ratio of 1.5 to 1 to the light emitting area.
It is characterized by a backlight device formed with an occupancy rate of 5-40%.

"Function" In the above configuration, the present invention provides that in claim (1), the emitted light from the light source enters the inside from the end surface of the transparent substrate, and most of the radiation light is incident on the inside from the end face of the transparent substrate, and most of the light is emitted due to the difference in optical density at the interface between the transparent substrate and the air. The light travels while being reflected. If the light enters the diffuse reflection layer during this process, it will be diffusely reflected by the light diffusion layer (7. At the interface C, '1' between the transparent substrate and air, the angle becomes below the critical angle and passes through the light diffusion layer on the front side of the transparent substrate. The light is emitted to the outside.The light scattering reflection layer becomes a pattern with higher density as it moves away from the light source, and has a density of 5 to 50% of the light emitting area of the surface of the transparent substrate.
Therefore, the light is uniformly radiated to the outside over the entire light output area on the surface of the transparent substrate. The light diffusion layer is
By diffusing the emitted light from inside the transparent substrate to the outside, uneven irradiation is prevented between the light-diffusing reflection layer and the area at the pattern interval where the light-diffusing reflection layer is not formed.

In claim (2), the light-scattering reflective layer has a ratio of 1. de1
When the occupancy is 5 to 40%, the uniformity of brightness is the best and the loss of light incident from the end face of the transparent substrate is minimized.

Embodiment J Below, embodiments of the backlight Wl according to the present invention will be explained based on the drawings. Figures 1 and 2 are block diagrams of the backlight device in each embodiment. First, the configuration will be explained. 1 in the figure is a transparent substrate. The transparent substrate 1 is a thin plate with good light transmittance, and is made of an inorganic or synthetic resin such as a glass plate, an acrylic resin plate, a polycarbonate resin plate, etc. A light source 2 is disposed on one side edge of the four peripheries of the transparent substrate 1.

In addition to the generally widely used fluorescent lamp, the light source 2 uses a cold cathode tube with a narrow tube diameter because it can make the entire backlight device thinner and suppress the influence of temperature on the liquid crystal display (LCD) panel. It is advantageous. Further, as the light source 2, an aperture type lamp may be used. On the back surface of the transparent substrate 1, a light-diffusing reflection layer 3 that diffusely reflects the light emitted from the light source 2 is drawn in a pattern whose density increases in proportion to the distance from the light source 2. The light-scattering reflection layer 3 uses a volatile-curable or ultraviolet-curable white ink containing titanium oxide as reflective particles, or a colored ink of a color according to the wishes of the user. As a method of forming the light scattering reflection N3 on the back surface of the transparent substrate 1, a known technique such as screen printing or a stamp method is used. When forming the light scattering reflection layer 3 on the back surface of the transparent substrate 1, as shown in FIG. The occupancy rate of the light-scattering reflective layer 3 per unit area of the transparent substrate 1 is changed.

The diameter of the points on the light-scattering reflective layer 3 is set to 1 to 3000 microns, preferably 10 to 1000 microns.

On the other hand, a light diffusing layer N4 is attached to the surface of the transparent substrate 1.

For the light diffusion N4, so-called frosted glass or a plastic film with a roughened surface is used, and a polyester film having a light diffusion layer with a roughened surface is preferable from the viewpoint of cost and durability.

The transparent substrate 1 on which the light scattering reflection layer 3 is formed, the light diffusion layer 4, and the light source 2 are surrounded by a housing 5 except for the front side. The housing 5 has a function of returning light leaking from the transparent substrate 1 or the light source 2 to the transparent substrate 1, a function of blocking light to prevent leakage of light from other than the front surface, and a function of dissipating heat generated from the light source 2 to the outside. It has a heat dissipation function, and is made of metal or plastic with a highly light-reflecting treatment on the inner surface. For example, as the housing 5, an aluminum case coated with a white paint with high light reflectance or an aluminum case coated with metal vapor deposition with high reflectance is suitable. Further, a reflective tape 6 may be attached to an end surface of the transparent substrate 1 other than the end surface through which the light from the light source 2 enters, to prevent light from leaking from the periphery of the transparent substrate 1.

In the above-described backlight device, first, the emitted light from the light source 2 enters from one end surface of the transparent substrate 1. The emitted light from the light source 2 that enters the transparent substrate 1 travels while being repeatedly reflected depending on the incident angle due to the optical density difference at the interface between the transparent substrate 1 and the air. As this progresses, when the light reaches the diffuse reflection layer 3 and enters it, it is diffusely reflected by the titanium oxide contained inside, and as a result, the diffusely reflected light becomes less than the critical angle with respect to the interface between the surface of the transparent substrate 1 and the air. Then, the transparent substrate 1
radiates outward from the surface of the At this time, the light diffusely reflected by the light diffuser reflection layer 3 passes through the light diffuser N4 on the surface of the transparent substrate 1, but since the light diffuser layer 4 has minute dots or irregularities, the light is further diffused. and radiates to the outside. The light diffused reflection N3 increases as the occupancy rate per unit area of the transparent substrate 1 increases as the distance from the light source 2 increases.
It is possible to prevent non-uniformity of light due to the distance between the lights, and to obtain a uniform amount of diffusely reflected light over the entire surface from the vicinity of the light source 2 where there is a large amount of light to a location at a distance where there is little amount of light. The light diffusing layer 4 eliminates the change in the amount of light between the light diffused reflection N3 and the area other than the pattern of the light diffused reflection layer 3, that is, the so-called "occurrence of shadows", and makes it possible to obtain uniform brightness. The light leaking from the transparent substrate 1, especially the light leaking from the spacing between the light-scattering reflective layers 3, is reflected on the inner surface of the housing 5 and returns to the transparent substrate 1, and as it is repeatedly reflected within the transparent substrate 1, it is reflected as described above. Similarly, the light is diffusely reflected by the light diffuser layer 3 and radiated to the outside via the light diffuser layer 4. Heat generated from the light source 2 is dissipated to the outside through the housing 5.

Next, to explain the first embodiment, an acrylic resin plate having a length of 200 mm, a width of 150 mm, and a tail of 5 mm is used as the transparent substrate 1. The light scattering reflection layer 3 formed on the surface of the transparent substrate 1 has a length of the rear surface of the transparent substrate 1], 90 mm.
, is drawn using white ink containing titanium oxide by screen printing in a 140 mm wide area. In the light scattering reflection layer 3, the pitch between each point is fixed at 1 tnm, and the diameter of the points is changed, and the diameter of the points near the light source 2 is set to 0.2 tnm.
mm, the diameter of the point becomes larger as the distance from the light source 2 increases, and the diameter of the point farthest from the light source 2 is set to 0.9 rmn. At this time, the degree of change in the diameter of the point was adjusted so that the drawing area of the light scattering reflection means was 25% of the light output area.

The light emission area is the area where light is emitted from the front surface of the transparent substrate 1 to the outside, and is the same as the area where the diffused light reflection N3 on the back surface of the transparent substrate 1 is depicted. On the other hand, the light source 2 is a cold cathode tube with a tube diameter of 8 mm and a length of 250 mm, and is disposed at one end of the transparent substrate 1 in the longitudinal direction.

In the first embodiment, the brightness of the backlight device is set at the center position 1. The luminance was measured using a luminance meter at three locations: a position closer to the light source 2 side by 70 valences from the center, and a position farther away from the light source side by 70 mm from the center.

According to this measurement value, the brightness at all three locations is 160±20
It was within the range of c and d/l a, and no unevenness in brightness could be observed with the naked eye, and good uniformity and quality of brightness could be obtained.

Next, referring to the second embodiment, the second embodiment is the same as the first embodiment except that the depiction form of the light-scattering reflective layer 3 is changed. , the pitch between the points of the light scattering reflective layer 3 is fixed at lll1ll+, j, 7°, the diameter of the points near the light source 2 is 0.2 mm and 1,2, the diameter of the points increases as the distance from the light source 2 increases, and the light source The diameter of the point at the farthest position from the point was (,), 5 mi. ,,
The depiction area of the light scattering reflective layer at the time of is 8? of the light output area? '6L
: Adjusted the degree of change in point diameter so that

The eight light device of this example also has the same characteristics as the first actual hOi example 2.
The brightness was measured at the position and using a brightness meter. In this meter, ll
(According to trl, the brightness at all three locations is 1.140±3
It was within the range of 0c, d/'bo, and T brightness unevenness could be observed visually, but it was not significant.

Next, a comparative example was set up to compare with the first and second embodiments, and the luminance was measured.

The first comparative example is the same as the first example except that the depiction form of the light-scattering reflective layer 3 of the first example is changed. In other words, in the first comparative example, the pitch between points of the light scattering reflective layer 3 is fixed at one pitch, and the diameter of the point near the light source 2 is set to 0.
．． 15m, and the diameter of the point increases as it moves away from the light source.21. The diameter of the point farthest from light source 2 is 0.3
It was set as tnrn. At this time, the depiction area of the light scattering reflection layer 3 is
The degree of change in the diameter of the dots was adjusted so that it was 4% of the light emission area. In this comparative example, when measured using the same position and luminance meter as in the first embodiment, the luminance was 100±5 at all three locations.
The result was within the range of 0ed/rrr, and was insufficient to allow brightness unevenness to be determined visually. Further, the absolute value of the brightness is lower than that of the first example and the second example.
Light usage efficiency is poor.

In the second comparative example, the depiction form of the light-diffusing reflection layer 3 of the first example is also changed, and the pitch between the 30 points of the light-diffusing reflection layer is fixed by IM7, and the diameter of the points near the light source 2 is set to 0.゜8
+nm, and the diameter of the point increases as the distance from the light source 2 increases.
, the diameter of the point at the farthest distance from the light source is 0.9
It was set to 5+nm. At this time, the depiction area of the light scattering reflection layer 3 is
The degree of change in the diameter of the points was adjusted so that it was 60% of the light emission area. In the backlight device 1 of this comparative example, when measured at the same position and with a luminance meter as in the first example, the luminance was within the range of 150 ± 120 cd/bore at all three locations.
There is a lot of unevenness in brightness and it cannot be put to practical use.

Incidentally, the loss of the light emitted from the light source 2 which is incident from one end of the transparent substrate 1 occurs in the following portion.

■Loss when passing through the transparent substrate.

■Loss caused by reflection at the interface between the transparent substrate and air.

■Loss caused by diffused reflection in the light-diffusing reflective layer.

■Loss due to light leaking from the rear surface of the transparent substrate.

■Loss due to light leaking from the periphery of the transparent substrate.

Regarding (2) above, is it possible to prevent light leakage by adding a light reflecting means to the periphery of the transparent substrate 1? causes brightness unevenness, so when a light reflecting means is provided at the periphery of the transparent substrate 1, it is necessary to adjust the density pattern of the diffused light reflection N3 near the periphery ζ; When the light is reflected by the light reflection η・1 means, a loss also occurs in C.The pursuit of a pattern for the light scattering reflection layer 3 that suppresses the losses described above from ■ to ■ is a backlight device with high light utilization efficiency. This is an extremely important element in obtaining

Therefore, as in the first example, the second example, the first comparative example, and the second comparative example, the light scattering reflective layer 3 The most efficient method is achieved by setting the depiction ratio to 5 to 50%, more preferably 15 to 40%, of the light emission area of the transparent substrate l, and by forming the light scattering reflection layer 3 into a pattern with a density proportional to the distance from the light source. A backlight device was obtained.

In addition, in the present invention, in addition to the above-mentioned embodiments, as the light scattering reflection layer, the number of points per unit area may be changed depending on the distance from the light source, or the diameter of the points and the unit area may be changed depending on the distance from the light source. Both the number of winning points can be changed, and not only points but also lines can be used and the thickness of the lines and the spacing between the lines can be changed.

Regarding the light source 2, in the above embodiment, it is arranged only on one end side of the transparent substrate 1, but it may be arranged in a format in which two light sources are arranged in both opposing ends, or in a format in which it is arranged in all four peripheries. The brightness can also be improved by increasing the number of light sources. In this case as well, it is possible to form a light scattering reflection layer in a pattern with a density corresponding to the distance from each light source, and to achieve a backlight device with improved light utilization and excellent uniformity of brightness.

"Effects of the Invention" As described above, according to the backlight device according to the present invention,
Since the light source is placed on the periphery of the transparent substrate rather than in the thickness direction, the total thickness of the backlight device is determined by the thickness of the transparent substrate including the diameter of the light source, the multilayer thickness of the light diffusion layer, the light scattering reflection layer, and the like. It only requires a slight clearance when assembling it into the housing, and the total thickness of other necessary parts such as the housing, and it also has excellent brightness uniformity, making it thin and lightweight, which was difficult with conventional technology. Therefore, the present invention can provide a backlight device that can obtain excellent brightness uniformity even when the area is increased and has high light utilization efficiency. By installing the backlight device of the present invention as described above behind a liquid crystal display (LCD), it is possible to realize a thin and easy-to-see screen with no uneven brightness, thereby improving the functions of the liquid crystal display (LCD). It can contribute greatly and can also be used as various other backlight devices.

[Brief Description of the Drawings] Fig. 1 is an exploded perspective view showing an embodiment of the backlight device according to the present invention, Fig. 2 is a perspective view of the banklight device when assembled, and Fig. 3 is the back side of the transparent substrate. FIG. 3 is an explanatory diagram showing a depiction form of a light-diffusing reflective layer attached to the wafer. 1...Transparent substrate 2...Light source 3...Light scattering reflection layer 4...Light diffusion layer 5...Housing Fig. 2 Fig. 3

Claims (2)

[Claims] (1) A light source is arranged at at least one of the four circumferences of the transparent substrate, and the rear surface of the transparent substrate has a pattern that increases in density according to the distance from the light source, and has a pattern that increases in density with respect to the light output area of the surface of the transparent substrate. 1. A backlight device comprising: a light scattering reflection layer formed with an occupancy of ~50%; and a light diffusion layer provided on the surface of a transparent substrate. (2) The above light scattering reflection layer is 15 to 40% of the light output area.
A claim characterized in that the claim is formed with an occupation rate of (
1) The backlight device described.