JPH04487A - Backlighting type illuminator in display device - Google Patents

Abstract

PURPOSE:To realize a face light source which has uniform brightness without making the device thick nor sacrificing the brightness by arranging an optical scattering sheet which has specific unevenness at least on the side of a diffusion plate between the diffusion plate and a light source. CONSTITUTION:The optical scattering plate 9 is provided between the light source 4 and diffusion plate 5. The surface of the sheet 9 at least on the side of the diffusion plate 5 is made uneven to a depth and a pitch of 0.1-1.0mm. The unevenness may be uniform or variable in size within this range. Consequently, the light emitted by the light source 4 is securely scattered in all directions of the diffusion plate when transmitted through the sheet 9. Consequently, light from light and dark parts is mixed in the case of reaching respective positions of the diffusion plate 5 to obtain uniform brightness over than entire surface. Further, the diffusion plate 5 and a display panel are arranged at an interval, so the brightness is made further uniform by the scattering effect of the diffusion plate.

Description

[Detailed Description of the Invention] [Summary] This invention relates to a backlight type illumination device suitable for thin display devices such as liquid crystal display devices in word processors and personal computers. The aim is to realize a surface light source with uniform brightness without sacrificing brightness. Backlight type lighting illuminates the display panel from the back using a lighting device with a light source placed behind a diffuser plate. In the device, at least the surface on the diffuser plate side has a depth and pitch of 0.1
An optical scattering sheet having irregularities of mm to 1.01 mm is arranged between a diffuser plate and a light source.

[Industrial Application Field] In recent years, thin display devices using liquid crystal display devices have become popular in word processors, personal computers, and the like. The present invention relates to a backlight type illumination device suitable for such a thin liquid crystal display device.

[Conventional technology]

FIGS. 8 and 9 are cross-sectional views showing backlight type illumination devices in conventional display devices. FIG. 8 shows a crawling curtain type illumination device, and FIG. 9 shows a free-form surface type illumination device.

In FIG. 8, reference numeral 1 denotes a display panel made of a liquid crystal display (LCD), and is illuminated by a backlight type illumination device 2 of a lighting curtain type arranged at the back thereof. A drive circuit is connected to each electrode of the liquid crystal display panel l.

3 is a casing called a backlight mold, and a fluorescent tube 4 serving as a light source is disposed at the bottom of the casing.

A diffusion plate 5 made of acrylic or the like is disposed at the opening of the casing 3, that is, in front of the fluorescent tube 4.
In a device consisting only of the fluorescent tube 4 and the diffuser plate 5, only the vicinity of the fluorescent tube 4 becomes bright, and there is a large difference in brightness from the surrounding area.

Therefore, a lighting curtain 6 made of a transparent film such as polyester is placed between the diffuser plate 5 and the fluorescent tube 4, and aluminum foil or the like is attached intensively to the area directly above the fluorescent tube 4. Light shielding and reflection are performed.

In this structure, the combined light of direct light from the fluorescent tube 4 (solid line arrow) and reflected light from the casing 3 (dashed line arrow) passes through the lighting curtain 6.
By correcting the amount of transmitted light, a surface light source with uniform brightness is obtained.

In the free-form surface type device shown in FIG. 9, the inner surface of the casing 3 is modified to have a special curved shape, and a concave mirror surface 7 is provided by pasting aluminum foil or the like. Further, as shown in FIG. 10, a striped light intensity correction pattern 8 is provided on the surface of the diffuser plate 5 of the fluorescent tube 4 by a method such as printing carbon on a curved surface.

In this way, by correcting the amount of direct light from the fluorescent tube 4 and combining it with the reflected light from the free-form surface, the first
It is designed to provide a uniform surface light source as shown by the solid line ■ in Figure 1.

(Problem to be Solved by the Invention) However, there are individual differences in the brightness of fluorescent tubes, and in particular, there are large variations in brightness between manufacturing lofts.Therefore, as shown in the figure, a plurality of fluorescent tubes 4. 4, one side is bright and the other is dark, which may cause uneven brightness on the display panel 1.

Furthermore, even if the same fluorescent tube deteriorates over time, there will be individual differences in the degree of reduction in brightness, and even the same fluorescent tube may have different brightness from the beginning or due to changes over time. There is also. Furthermore, due to assembly manufacturing errors of the backlight type lighting device or the diffusion plate 5
The brightness may also be uneven due to warpage or warping of the inner surface of the casing.

Such variations in brightness cannot be resolved with conventional backlight type illumination devices as shown in FIGS. 8 and 9. In other words, if the fluorescent tube 4 is too bright or is mounted too close to the diffuser plate 5, and the area directly above the fluorescent tube 4 is brighter than the designed value, the brightness will be as shown by the thick line ■ in Figure 11. distribution. Furthermore, if the amount of light becomes insufficient due to changes in the fluorescent tube 4 over time, or if it is installed too quickly from the diffuser plate 5, only the vicinity of the fluorescent tube 4 will become dark, as shown by the broken line ■.

In order to solve this problem, it is effective to increase the distance between the fluorescent tube 4 and the diffuser plate 5, but in this case, the bank light type illumination device itself becomes thicker (as described above). This is not suitable for thin display devices.Moreover, since the distance between the light source and the display panel l increases, the overall brightness decreases.

The technical problem of the present invention is to address these problems and to realize a surface light source with uniform brightness without increasing the thickness of the backlight type lighting device or sacrificing brightness. be.

[Means to solve the problem]

FIG. 1 is a sectional view illustrating the basic principle of a bank light type illumination device in a display device according to the present invention. 1 is an object to be illuminated, such as a liquid crystal display panel, and 2a is a bank light type illumination device according to the present invention.

The backlight type illumination device 2a has a light source 4 disposed at the back of the diffuser plate 5, and is configured to illuminate the display panel 1 from the back.

An optical scattering sheet 9 is disposed between the diffuser plate 5 and the light source 4. The optical scattering sheet 9 covers at least the diffusion plate 5.
On the surface of the example, the depth and pitch are 0゜1mm-1, Omm.
It is a sheet-like member having rough irregularities, and is characterized in that the direction of reflection or scattering on each irregular surface is random and the amount of diffused light is large.

It is more effective to use the optical scattering sheet 9 together with the lighting curtain 6 shown in FIG. 8 or the reflective concave mirror surface or light shielding pattern printed fluorescent tube 4 shown in FIG. 9.

[Effect]

Since the optical scattering sheet 9 is present between the light source 4 and the diffuser plate 5, the light emitted from the light source 4 is scattered by the unevenness of the optical scattering sheet 9 when passing through the optical scattering sheet 9.

If the unevenness of the optical scattering sheet 9 is minute, scattering will occur only in the vicinity, but the unevenness of the optical scattering sheet 9 of the present invention is formed at least on the surface on the side of the diffuser plate 5, and the depth and pitch are It has rough irregularities of 0.1 mm to l, Omm. Therefore, the amount of scattered light on each uneven surface is large, and the light is scattered far away, and is reliably scattered in all directions of the diffuser plate 5. As a result, when the light reaches each part of the diffuser plate 5, the light scattered from a bright place and the light scattered from a dark place are mixed, and the brightness on the diffuser plate 5 is made uniform. , the brightness is uniform over the entire surface.

Moreover, since there is a gap between the diffuser plate 5 and the display puff l, when the light reaches the display panel 1, the brightness is further made uniform due to the scattering effect of the diffuser plate 5.

[Example] Next, how the hasycrite lighting device in the display device according to the present invention is actually implemented will be explained using an example. FIG. 2 is a cross-sectional view showing an embodiment of the optical scattering sheet 9, in which both sides of a transparent or translucent polycarbonate film have triangular irregularities. The pitch of this uneven mountain and the depth from the top of the mountain to the bottom of the valley are 0.1 m.
It has rough irregularities of m-1.0 mm.

This [depth and pitch of unevenness is 0.1 to 1.0 mm]
J means (1) The depth and pitch of the unevenness is 0.1 mm to 1.0 m.
(2) If the depth and pitch of the unevenness are uniform within a certain value within the range of m, or (2) the depth and pitch of the unevenness are within the range of 0.1 mm to 1.0 mm, respectively. If the depth and pitch of the unevenness are not uniform, but are mixed in size, this includes both of the following. Further, in either case, the scattering effect is excellent.

As the optical scattering sheet (1), Lexan film 8B36 manufactured by General Electric Company, USA, etc. are suitable.

Note that the unevenness may be formed only on the surface on the side of the diffusion plate 5, or may be formed on both surfaces.

FIG. 3 shows another embodiment of the optical scattering sheet 9, which is a cloth made by weaving transparent or translucent silk threads such as polycarbonate into a woven fabric. In this case, the pitch of adjacent threads and the thickness from one side to the other should be 0.1 mm to 1.0 m.
m.

It is desirable to weave tightly so that there are no meshes. The cross-sectional shape of the vertical and horizontal threads may be circular or angular.

FIG. 4 shows an embodiment of a backlight type illumination device using both the optical scattering sheet 9 and the lighting curtain 6 of the present invention. The optical scattering sheet 9 may be arranged parallel to each other between the fluorescent tube 4 and the lighting curtain 6 as shown in the figure, but it may be arranged parallel to each other between the lighting curtain 6 and the diffusion plate 5. You can also do that. Alternatively, they may be provided on both sides of the lighting curtain 6.

When an optical scattering sheet 9 is disposed between the lighting curtain 6 and the fluorescent tubes 4 as shown in the figure, the light emitted from the fluorescent tubes 4 is scattered in all directions of the lighting curtain 6 by the optical scattering sheet 9. , and multiple reflections occur in the surrounding area. Since the lighting curtain 6 has an aluminum pattern concentrated only in the area directly above the fluorescent tubes 4, variations in brightness are further suppressed.

FIG. 5 is a cross-sectional view showing the assembled portion of the optical scattering sheet 9 and the lighting curtain 6. As shown in the figure, a stepped portion 10.11 is formed on the opening side of the casing 3,
By placing the optical scattering sheet 9 on the step part 10, the lighting curtain 6 on the step part 11, and the diffusion plate 5 on the top in this order, the optical scattering sheet 9, the lighting curtain 6, and the diffusion plate 5 can be arranged with high precision and Can be assembled uniformly.

FIG. 6 shows an embodiment of a hacklight type illumination device that uses the optical scattering sheet 9 of the present invention and the free-form surface method shown in FIG. 9 in combination. The optical scattering sheet 9 is disposed between the fluorescent tube 4 and the diffuser plate 5 in parallel with the diffuser plate 5, as shown in the figure.

Even when applied to a free-form backlight illumination device in this way, the light that reaches the optical scattering sheet 9 either directly from the fluorescent tube 4 or after being reflected from the concave mirror surface 7 is transmitted by the optical scattering sheet 9. The light is scattered toward the diffuser plate 5.

At this time, each part of the optical scattering sheet 9 is scattered in each direction of the diffuser plate 5, so at the time of reaching each part of the diffuser plate 5, light scattered from a bright place and light scattered from a dark place are mixed. The brightness is evened out by mixing with the other light.

Note that it is more effective to roughen the inner surface or both surfaces of the diffusion plate 5.

FIG. 7 is a diagram showing the measurement results of the luminance distribution of the conventional device and the device of the present invention, where (a) is the luminance distribution of the conventional device of the free-form type shown in FIG. This is a brightness distribution in the embodiment of FIG. 6 applied to a curved surface type device.

In the figure (a), the brightness is high at two locations indicated by 41 and 42. This is the area directly above the fluorescent tube, and it can be seen that the brightness distribution is non-uniform.

In contrast, in figure b), there is no protrusion as seen in figure (a). That is, it is recognized that in the device to which the optical scattering sheet of the present invention is applied, scattering is performed effectively and the brightness distribution is uniform. Note that the portions with low brightness at both ends are areas that are not used for display.

In addition, in conventional grasshopper light lighting devices, the thickness is 20~
Although relatively thick at 25 mm, the device of the present invention has a thickness of 14.
Can be made as thin as 5mm and has a brightness of 500cd/cr
A. We were able to achieve brightness unevenness of 6% or less.

[Effects of the Invention] As described above, according to the present invention, the depth and pitch between the light source such as a fluorescent tube and the diffuser plate 5 are 0.1 mm to 1.0 m.
Since the optical scattering sheet 9 having an unevenness of m is provided, the light is effectively scattered by the optical scattering sheet 9 towards each part of the diffuser plate 5, and the scattered light from each direction is mixed on the diffuser plate 5. The brightness is then averaged. As a result, the brightness becomes even more uniform at the position where the light passes through the diffuser plate 5 and reaches the display panel l. Therefore, a backlight type illumination device with sufficient brightness can be obtained without increasing the size, and is optimal for a thin display device.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view illustrating the basic principle of a backlight illumination device in a display device according to the present invention, FIGS. 2 and 3 are cross-sectional views showing various embodiments of the optical scattering sheet according to the present invention, and FIG. 5 is a cross-sectional view illustrating the assembled structure of the device shown in FIG. 4. FIG. 7 is a diagram showing the measurement results of the luminance distribution of the conventional device and the device of the present invention, and FIG. 8 is a cross-sectional view showing an example of a backlight type lighting device of the conventional lighting curtain type. 9 is a sectional view showing a conventional free-form backlight type lighting device, and FIG. 10 is a perspective view showing a light source formed by printing a light intensity correction pattern on a curved surface of a fluorescent tube. , FIG. 11 is a diagram showing the luminance distribution in a conventional device. In the figure, ■ is a display bar, 2.2a is a backlight type illumination device, 3 is a casing, 4 is a light source (fluorescent tube), and 5
is a diffuser plate, 6 is a lighting curtain, 7 is a concave mirror surface, 8
9 indicates a striped light intensity correction pattern, and 9 indicates an optical scattering sheet. Patent applicant Fujitsu Co., Ltd. Sub-agent Patent attorney Yasushi Fukushima Bunko 3 Figure 3 PIII! I Practical Example 1 of the Light Seduction Sheet Figure 2 'IAs Oral Confession l Kimikata'il: Kagabu 5shir-1p1 6th evil (ri) Reflection νt1 [HL'Tru 1 tremor e* ( b) 7Nt8Mv41:j-;+j”+fl!+1j4,000I
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Claims (1)

[Scope of Claims] A backlight type illumination device that illuminates a display panel (1) from the back with a light source (4) disposed behind a diffuser plate (5), which comprises at least a diffuser plate (5). ) An optical scattering sheet (9) having irregularities with a depth and pitch of 0.1 mm to 1.0 mm is disposed between the diffuser plate (5) and the light source (4). A backlight type illumination device for a display device characterized by: