JPH0980236A - Directional back light and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the back light which has superior luminance uniformity as to the structure and manufacture of the directional back light. SOLUTION: The directional back light has at least a plurality of comic transparent bodies 44, a pinhole plate 43 which has a plurality of pinholes, and a light source; and the conic transparent bodies 44 guide light from a small- diameter incidence surface to a large-diameter projection surface, the pinhole plate 43 has a reflecting film provided on its reverse surface and also has the conic transparent bodies 44 inserted into the pinholes from the top surface side so that the incidence surfaces of the conic transparent bodies 44 project from the reverse surface, and the light source is arranged opposite the reverse surface of the pinhole plate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-display device, and more particularly to a directional backlight used in the multi-display device.

In recent years, there has been a demand for a large-screen image device for public use such as public facilities such as public offices, museums, museums, hotels, event halls, amusement parks, etc. for providing images to a large number of viewers indoors and outdoors. It is rising. However, from the current state of manufacturing technology, C
Currently, it is impossible to realize a direct-viewing type such as RT.

As a main large-screen image device that meets such a demand, a projection-type display device for enlarging and projecting and displaying an image on a screen, and a multi-screen for arranging a plurality of small display units in a matrix to increase a screen size are provided. Examples include display devices. Since the multi-display device has a matrix of small display units, it is possible to reduce the depth with respect to the screen size and make it thinner compared to the magnifying projection type device, but on the other hand, the frame around the screen of each display unit is It has the drawback of becoming a grid-like joint on a multi-screen.

Therefore, as a method of making the best use of the thinness feature and minimizing the seam, as shown in FIG. 5, a transmissive display unit such as an LCD is provided with a short optical path consisting of an erecting imaging lens array and a Fresnel lens. By combining the projection optical system,
A multi-display method has been proposed in which a plurality of display screens are arrayed on the same screen by slightly enlarging them so as to sufficiently include a frame. In FIG. 5, 1 is a transmissive panel such as LCD, 2 is a microlens array that forms an erecting equal-magnification image, 3 is a concave Fresnel lens for enlarging an erecting equal-magnification image, 4 is a backlight, and 5 Is the screen. Further, the backlight is devised so that the emitted light beam has directivity so as to match the aperture angle of the erecting image forming lens array.

Under the circumstances as described above, there is a demand for realizing a backlight configuration in which directivity characteristics can be set reliably and easily.

[0006]

2. Description of the Related Art The structure of a conventional backlight will be described with reference to FIG. In the figure, 41 is a tubular light source such as a cold cathode tube or a hot cathode tube, 42 is a diffusing plate for uniformizing the distribution of light rays, 43 is a pinhole plate provided with many pinholes, and 44 is a pinhole inserted into each pinhole. An array of truncated conical transparent bodies, and 45 is a housing.

The inner wall surface of the housing and the surface of the pinhole plate facing the inside of the housing have a reflecting surface that specularly or diffusely reflects light. As shown in FIG. 6, among the light rays emitted from the light source, the light rays that obliquely enter the incident surface 441 of the transparent body after passing through the diffusion plate repeatedly undergo total reflection on the side surface of the transparent body, but each time The slope decreases with each increase. And
When the light is emitted from the emission surface 442 of the transparent body, the light is emitted at an angle that is a substantially normal direction with respect to the bottom surface.

As shown in FIG. 6, between the diameter D of the exit surface of the transparent body and the light exit angle θ _o , and between the diameter d of the entrance surface and the light entrance angle θ _i , there is roughly: D · sin θ _o = d・ There is a relationship of sin θ _i . Therefore, for example, the incident angle of 0 to the incident surface
In order to enter a ray of 90 degrees and give it a directivity of an angle within 20 degrees from the normal, it is necessary to make the ratio of D and d approximately 3: 1. Further, in order for this formula to hold, the height h of the transparent body must be long to some extent, and it has been experimentally found that h needs to be ten times as long as D or more.

[0009]

In the structure of the conventional backlight described above, the height h of the transparent body must be long to some extent, and h must be ten times as long as D or more. Therefore, the apex angle φ of this transparent body has a very sharp shape of about several degrees. Therefore, even if there is a slight error in the diameter of the pinhole plate, the insertion amount of the transparent body may be different, and a step may occur on the emitting surface when the array is constructed.

This step becomes a black streak and impairs the brightness uniformity of the backlight. In particular, since the height of the transparent body directly affects the thickness of the backlight, it is necessary to make the transparent body as small as possible, but if it is made smaller, the incident surface becomes smaller and the tolerance of the pinhole diameter becomes more severe. There was a point.

For example, if D = 6 mm, d = 2 mm, and h = 75 mm, then φ = 2 × tan ⁻¹ (D−d) / 2h = 3 °. Further, the change in the insertion amount due to the error in the pinhole diameter is 25 mm for an error of 1 mm. According to this,
When drilling a pinhole with a drill, the accuracy is ± 0.
Since there is only about 1 mm, a step difference of 2.5 mm will occur.

This change in insertion amount does not change as long as the conical transparent body has the same shape (that is, a similar shape). Therefore, the size of the example is the reduction limit, and the height of the backlight is very high. growing. In addition, an error in the distance between adjacent pinholes also becomes a problem, and the insertion of the transparent body becomes insufficient in a narrow place, which also causes a step.

Further, since it is necessary to provide a large number of pinholes, there is a problem that processing takes a very long time. Regarding the processing time, a method such as punching may be adopted, but it is difficult because the number of pinholes is extremely large and the punching pressure becomes excessive.

In view of the above circumstances, the present invention aims to provide a backlight having excellent brightness uniformity simply and easily by forming a large number of pinholes at a time with high precision without using a drill. It is what

[0015]

To achieve the above object, the present invention has at least a plurality of truncated cone-shaped transparent bodies, a pinhole plate provided with a plurality of pinholes, and a light source. The frustoconical transparent body guides light from an incident surface with a small diameter to an exit surface with a large diameter, and the pinhole plate is provided with a reflective film on the back surface, and the conical-shaped transparent body is transparent. The light source is inserted into the pinhole from the front surface side so that the incident surface of the body projects to the rear surface, and the light source is the backlight arranged so as to face the rear surface of the pinhole plate. It can be realized by such a configuration.

That is, the pinhole plate is a resin layer integrated with a transparent body, and is a truncated cone transparent so that a reflecting film is formed on the surface of the resin layer on the side where the incident surface projects. Or the pinhole plate has a structure in which a number of thin metal plates are stacked, and a cone is formed so that a reflection film is formed on the surface of the pinhole plate on the side where the incident surface projects. A trapezoidal transparent body array is constructed.

According to the structure of the present invention as described above, a large number of pinholes can be accurately formed at once without using a drill or the like, so that it is possible to provide a backlight having excellent brightness uniformity. Becomes

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to FIGS. 1 (a) to 3 (c).

FIGS. 1 (a) to 1 (e) show a first embodiment, and a large number of conical transparent bodies 44 are arranged in the gauge 6 as shown in FIG. 1 (a). The gauge is provided with a positioning hole 61 at the top of the transparent body. In this state, when a resin having a very good flowability such as monomeric acrylic is poured to form a resin layer 62 and the resin layer is cured, the shape after curing becomes as shown in FIG. 1 (b).

After forming a reflective surface of Ag, Al, etc. on the lower surface of this resin layer as shown in FIG. 1 (c), only the apex of the protruding transparent body is cut as shown in FIG. 1 (d). Flattening,
If polishing is performed, a truncated cone shape can be obtained and the reflection film 431 on the incident surface can be removed.

An enlarged view of the vicinity of the incident surface is shown in FIG. 1 (e).
Since there is an interface between the transparent body and the resin layer, the incident light ray is totally reflected at the interface, and does not pass through the resin layer as shown by the broken line.

According to this embodiment, the apex diameter error of the conical transparent body itself is also absorbed, and the pinhole plate is very easily formed. Further, FIG. 2D shows the second embodiment, which has a structure in which very thin metal plates are stacked. Each metal plate is perforated by etching. After applying resist as shown in FIGS. 2 (a) to 2 (c), a mask is overlaid, resist is removed by exposure, plate material etching is performed, and then bonding is performed. Completed by laminating and attaching a reflective film. According to the present embodiment, the hole diameter and the spacing error are determined by the mask accuracy, but they are 1/10 that of the conventional drilling.
It can be suppressed to the extent.

According to the above embodiments, the pinhole accuracy is greatly improved. As a result, the size of the conical transparent body can be reduced to a fraction of the conventional size. Figure 3 (a) shows
6 is a configuration example of a backlight using the first embodiment or the second embodiment. When the cone light guide is reduced, the number of cone light guides required for one LCD unit increases. Therefore, as shown in FIG. 4, work is performed by forming a plurality of frustoconical transparent bodies in an array. The efficiency was improved.

The cathode tube used as the light source generally has a phosphor 4 as shown in FIG. 3 (c) due to its manufacturing process.
The film thickness unevenness of No. 11 occurs, and a certain asymmetry in the emission luminance 412 occurs. That is, the emission bright line 412 shown by the solid line is partially deviated from the symmetrical shape shown by the broken line. Therefore, as shown in FIG. 3 (b), a large number of cathode tubes are alternately arranged with reference to the inlet after gas is filled, and the luminance of the entire light emitting surface is made symmetrical.

[0025]

As is apparent from the above description, according to the present invention, it is possible to give directivity to the outgoing light beam so as to match the aperture angle of the erecting imaging lens array with an extremely simple structure, It is expected that the image will contribute to the realization of a more natural large multi-display.

[Brief description of drawings]

FIG. 1 is a diagram showing a first embodiment of the present invention.

FIG. 2 is a diagram showing a second embodiment of the present invention.

FIG. 3 is a diagram showing a configuration example of a backlight.

FIG. 4 is a view showing a truncated cone-shaped transparent body array.

FIG. 5 is a diagram showing an example of a multi-display system.

FIG. 6 is a diagram showing a relationship between light entering and exiting a transparent body.

FIG. 7 is a diagram showing a configuration example of a conventional backlight.

[Explanation of symbols]

1 is a transmissive panel such as LCD, 2 is a microlens array for forming an erecting equal-magnification image, 3 is a concave Fresnel lens for enlarging an erecting equal-magnification image, 4 is a backlight, 5 is a screen, 6 Is a gauge, 41 is a tubular light source such as a cold-cathode tube or a hot-cathode tube, 42 is a diffuser plate for uniformizing the distribution of light rays, 43 is a pinhole plate provided with a large number of pinholes, and 44 is each pinhole. An array of truncated cone-shaped transparent bodies, 45 is a housing, 61 is a positioning hole at the vertex of the transparent body, 62 is a resin layer, 411 is a phosphor, 412 is emission brightness, 431 is a reflective film, and 441 is a transparent body. An incident surface, and 442 is a transparent emitting surface.

Claims (4)

[Claims] 1. At least a plurality of truncated cone-shaped transparent bodies, a pinhole plate provided with a plurality of pinholes, and a light source, wherein the truncated cone-shaped transparent body transmits light from an incident surface having a small diameter. The pinhole plate is provided with a reflection film on the back surface, and the pinhole plate is inserted into the pinhole from the front surface side so that the incident surface of the truncated cone-shaped transparent body projects to the back surface. A directional backlight, characterized in that the light source is arranged so as to face the back surface of the pinhole plate. 2. The pinhole plate is formed by stacking a large number of metal thin films having pinholes, and has a reflection film on the back surface from which the incident surface of the truncated cone-shaped transparent body projects. The directional backlight according to 1. 3. A truncated cone-shaped transparent body, a pinhole plate having a pinhole into which the truncated cone-shaped transparent body is inserted, and a plurality of cathode tubes. Multiple frustum-shaped transparent bodies
It is a truncated cone-shaped transparent body array-like structure connected in rows, wherein the cathode tubes are arranged in parallel, and the directions of the glass tube sealing ports are alternately placed on the opposite side. Light. 4. A conical transparent body is arranged with its apex facing down in a box-shaped case provided with a positioning hole into which the apex of the conical transparent body is inserted on the bottom surface, and then in the box-shaped case. A resin layer is formed by pouring resin into the bottom of the conical transparent body to form a resin layer, then a reflecting film is formed on the side where the apex of the conical transparent body projects, and then only the conical transparent body apex is cut and flattened. Then, the method of manufacturing a directional backlight, further comprising the step of cutting only the apex of the conical transparent body so as to be flat so that the conical transparent body has a truncated cone shape.