JP2002116705A - Backlight device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a backlight device capable of reducing tubular display unevenness on an illuminated surface of an LCD(liquid crystal display) panel. SOLUTION: In the backlight device 6, in which at least one or more cylindrical light sources 3 and a light reflector 2 are arranged inside a flat casing 1 with an opened upper surface and a light transmission diffusion plate 4 is arranged on the opening part 19 of the casing 1, a pattern 10 whose reflectance is different from that of the light reflector 2 is provided on at least a part of the inside surface of the casing 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backlight device used for a liquid crystal display, and more particularly to a backlight device having reduced unevenness of a backlight tube.

[0002]

2. Description of the Related Art LCs used as display devices for electronic devices such as microcomputers and television receivers.
Since D (liquid crystal display) is non-luminous, it requires a light source for external irradiation such as a backlight device.

[0003] As such a backlight device, a small-diameter fluorescent tube such as a cold cathode tube or a hot cathode tube is generally used as a cylindrical light source, and the fluorescent tube is arranged on the side surface of a light guide plate. Edge light type, a reflector (hereinafter, referred to as a reflector) and a fluorescent tube are housed in the housing, and a light transmitting diffuser disposed in the housing opening directs light from the fluorescent tube and light from the fluorescent tube. There is known a direct type in which light reflected by a reflection plate is incident and diffused by a light transmission / diffusion plate to emit uniform planar light.

The above direct type or edge light type is L
It is selected according to the required performance of the CD, but the direct type uses the direct light of the fluorescent tube, so the light use efficiency is higher than the edge light type, and high brightness for monitors, television receivers, etc. Suitable for required applications.

FIG. 10 is a plan view showing a conventional direct type backlight device, FIG. 11 is a sectional view taken along the line AA 'of FIG. 10, and FIGS. 12 (A) and 12 (B) are B of FIG. FIG. 12B shows a light quantity distribution on the light transmitting / diffusing plate.

[0006] A housing 1 serving as a lamp house for a backlight.
Is formed in a box shape having a trapezoidal cross section having an opening 1a on the upper surface, and is integrally molded with a white high-reflection grade molding resin, or is produced by combining a metal plate or a metal plate and a molding resin.

A high-reflection paint is applied to the inside of the housing 1 or a high-reflection film material or the like is adhered to the housing 1 to form a reflection plate
To form

The cylindrical light source 3 such as a fluorescent tube is held at a position spaced from the bottom surface of the housing 1 by about 1 to 2 mm.
(In FIG. 10 to FIG. 12, it is integrated with the side plate of the housing 1), and the number to be arranged is determined by the required luminance.

A backlight device 6 is constructed by assembling the above components and disposing a light transmitting / diffusing plate 4 using a milky white acrylic material or the like on the upper surface so as to cover the opening 1.
Light emitted radially from the cylindrical light source 3 is reflected directly or on the reflection plate 2 in the housing 1 to reach the light transmission / diffusion plate 4, and is converted into surface light by the light transmission / diffusion plate 4.

An important factor indicating the display quality of the LCD is the uniformity of the brightness of the illuminated surface of the backlight device 6. One of the elements representing the brightness uniformity is tube unevenness. As shown in FIG. 12B, the tube unevenness is adjacent at a luminance change rate when light on the illuminating surface emitted from the light transmission / diffusion plate 4 is compared between an upper portion of the cylindrical light source 3 and an intermediate portion of the adjacent cylindrical light source 3. It is defined as (maximum luminance−minimum luminance) / maximum luminance × 100% of the cylindrical light source value.

If there is a luminance change on the illuminated surface of the diffusion plate 4 of the backlight device, that portion is visually recognized as tube unevenness.

Therefore, the fixing position of the cylindrical light source 3 and the housing 1
Although it is necessary to design the structure such as the shape to minimize the tube unevenness as much as possible, the above-mentioned conventional backlight device 6 cannot suppress the tube unevenness to 3 to 4% or less.

[0013]

In the backlight device 6 having the above-described structure, the light emitted from the cylindrical light source 3 spreads radially, and the amount of light emitted from the light transmitting diffuser 4 is as shown in FIG.
As shown in FIG. 7, a single peak curve 7 decreases as the distance from the cylindrical light source 3 increases.

When a plurality of cylindrical light sources 3 are arranged at a fixed interval, the amounts of light from the respective cylindrical light sources 3 are integrated and the amount of light emitted from the light transmission / diffusion plate 4 is shown in FIGS.
5, a multi-peak curve 8 in which the luminance decreases as the distance from the cylindrical light source 3 increases, similarly to the above.

In FIG. 14, in the single peak curves 7a and 7b of the cylindrical light sources 3a and 3b, respectively,
The light quantity at the point is the sum of the light quantity at the point a and the light quantity at the point b, and the light quantity at the valley e point of the multi-peak curve 8 is twice the light quantity at the d point.

FIG. 15 shows a luminance distribution of a multi-peak curve 8 obtained by synthesizing single-peak curves 7a to 7g when seven cylindrical light sources (fluorescent tubes) 3a, 3b 並 3g are juxtaposed in the housing 1. The difference between the peaks and valleys of the multi-peak curve 8 appears as tube unevenness. The luminance distribution diagram on the light transmission / diffusion plate 4 of the actual backlight device 6 is orthogonal to the tube axis direction of the cylindrical light source 3. FIG. 16 shows the luminance distribution in the direction (Y axis). In the figure, the X axis is the tube axis direction of the cylindrical light source 3, and in the multi-peak curve 8, 8a is the luminance on the cylindrical light source 3 and 8b is the luminance between the cylindrical light sources.

As described above, the brightness decreases as the distance from the cylindrical light source 3 increases, so that a portion 8b having a low light amount always exists in the housing 1.

For this reason, the backlight device 6 of the direct type has a problem that a tube unevenness which is visually recognized as dark on the illuminated surface occurs.

The present invention has been made in order to solve the above-mentioned problems. In order to reduce the amount of light in a portion where tube unevenness is high, patterns having different reflectances along the tube axis direction of a fluorescent tube 3 which is a cylindrical light source are provided. Is formed on the reflection plate 2 so as to reduce the unevenness of the tube.

[0020]

According to the first aspect of the present invention, a light transmitting / diffusing plate 4 is provided so as to cover an opening 1a of a casing 1, and a light reflecting plate 2 and at least one A backlight device 6 provided with the cylindrical light source 3 described above, wherein a pattern having a different reflectance is formed on the light reflecting plate 2 along both side surfaces of the cylindrical light source 3 in the tube axis direction. It is a device.

The present invention according to claim 2 is characterized in that the pattern shapes having different reflectivities formed on the light reflecting plate 2 are straight lines, waveforms and curves along the tube axis direction of the cylindrical light source 3. A backlight device according to claim 1 is provided.

According to a third aspect of the present invention, in the backlight device according to the first or second aspect, the shapes of the patterns 10 having different reflectances formed on the light reflecting plate 2 are formed as dotted lines. 6.

According to a fourth aspect of the present invention, the patterns 10 having different reflectivities formed on the reflection plate 2 are diffuse reflection materials. This is a backlight device 6.

According to a fifth aspect of the present invention, there is provided the back according to any one of the first to fourth aspects, wherein the patterns 10 having different reflectances formed on the reflecting plate 2 are formed by printing. This is a light device 6.

According to the configuration of the present invention according to claims 1 to 5, the light transmission / diffusion plate 4 of the backlight device is provided.
The brightness (light amount) of the light on the illuminating surface is determined by the change in the amount of light reflected by the reflecting plate and the reflection angle by the patterns 10 having different reflectances arranged on both sides of the cylindrical light source when viewed from above the reflecting plate. Work in the direction of uniformity, thereby reducing tube unevenness.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of a backlight device according to the present invention will be described below in detail with reference to FIGS.

FIG. 1 is a plan view of a backlight device showing one embodiment of the present invention, FIG. 2 is a sectional view taken along line AA 'of FIG. 1, and FIG. 3 is a sectional view taken along line BB' of FIG. FIG. 4 is a luminance distribution curve in the Y-axis direction to which the present invention is applied. 10 to 1
2 are denoted by the same reference numerals and described.

Referring to FIG. 1, a housing 1 serving as a lamp housing of a backlight device 6 has a reflecting plate 2 adhered inside the housing 1 and a reflecting sheet or a light reflector or a housing coated with a reflecting member. 1 itself is integrally molded with a white high-reflection grade molding resin. The housing 1 is formed in a box shape with an opening 1a provided at the top.

The left, right, front and rear sides of the housing 1 are shown in FIG.
2 and 3 are sectional views taken along arrows A 'and BB', each having a trapezoidal cross section, and a cylindrical light source support 5 formed of high-reflection grade resin (not shown) fixed to the left and right sides. A cylindrical light source 3 composed of at least one or more cold-cathode tubes, hot-cathode tubes, or the like is mounted at a position about 1 to 2 mm away from the surface of the reflector 2 on the bottom surface of the housing 1.

By arranging the light transmitting / diffusing plate 4 made of milky white acrylic resin or the like so as to cover the opening 1a of the housing 1, the light emitted from the cylindrical light source 3 can be directly or cylindrically illuminated. The light transmitted from the light source 3 to the light transmitting / diffusing plate 4 together with the light reflected by the lower reflecting plate 2 is converted into planar light by the light transmitting / diffusing plate 4 to form a planar light source.

At least one light-collecting sheet 9 is adhered to the surface of the light-transmitting / diffusing plate 4 to condense light in a direction normal to the illuminating surface to increase the brightness.

On the upper surface of the light-condensing sheet 6, a C, a polarizing plate, a color filter and the like, which are arranged between glass substrates, are integrated.
A liquid crystal display device is configured by attaching an LCD housing serving as a D panel unit.

In the backlight device 6 of this embodiment, the cylindrical light source 3
For example, a linear pattern 10 having a predetermined width is printed on both sides of the cold cathode tube along the tube axis direction.

The printing color is selected to be a predetermined color and a material having a different reflectance from the white color of the reflection plate 2. Also, the shape can be appropriately selected.

The unevenness of the tube on the illuminating surface of the light transmitting / diffusing plate 4 is different from that of the conventional light transmitting / diffusing plate 4 with respect to the single peak curves 7a and 7b corresponding to the respective cylindrical light sources 3 and 3, as shown in FIG. , The level of the light amount becomes low as a whole, like the single peak curves 7a 'and 7b' when the pattern 10 is provided. Therefore, in the multiple peak curve 8 'obtained by combining the single peak curves 7a' and 7b ', the light amount difference between the point c and the point e is much smaller than that of the curve 8 similar to that of FIG. I understand that

[Embodiments] The shapes of various patterns 10 formed on the reflection plate 2 along the tube axis direction of the cylindrical light source 3 of the present invention and the method of forming the same will be described below.

[Embodiment 1] FIG. 5A shows a straight line on a reflecting plate 2 corresponding to both sides of a lamp 3 along the tube axis direction of a plurality of cylindrical light sources (cold cathode tubes: hereinafter referred to as lamps). And a silver paint pattern 10 is formed by printing. Al (aluminum) powder or the like is mixed in the silver paint. The tube diameter of the lamp 3 is 3φ, the height from the surface of the reflector 2 to the center of the lamp is 3.5 mm, and the center line of the lamp 3 in the tube axis direction coincides with the reference line CL in FIG. Let it. The right and left straight lines 10L and 10R having a width of 1.5 mm around the reference line CL are printed at intervals of 5 mm. In this case, the length of the pattern corresponds to the length of the lamp 3.

FIG. 5B shows a luminance distribution diagram of the first embodiment and a luminance distribution curve 8 'in the Y-axis direction (the direction orthogonal to the tube axis direction of the juxtaposed lamps 3). In the case where the pattern 10 shown in FIG.
Improvements of 8% and 2.0% were made. In such a pattern shape, the tube unevenness can be adjusted and controlled by changing the distance a between the patterns 10L and 10R, the pattern width b, and the color of the pattern 10.

[Embodiment 2] FIG. 6A shows the pattern 10 as a dotted line, and the dimension a between the left and right dotted lines 10L and 10R.
= 5 mm, line width b = 1 mm, dotted line length c = 5 mm, dotted line interval d = 5 mm, and silver paint is printed on the reflector 2 on both sides of the lamp 3 along the tube axis direction. The length of the pattern 3 may correspond to the length of the lamp 3 or may be printed only at a predetermined portion at a predetermined length.

FIG. 6B shows a luminance distribution diagram of the first embodiment and a luminance distribution curve 8 'in the Y direction. Also in this case, FIG.
In the case where the pattern 10 shown in FIG. 3 was not formed, the unevenness of the tube was 2.8%, which was reduced to 1.4% and 1.4%, and the improvement was achieved. In this case, the tube unevenness can be controlled by changing the dotted line width b, the dotted line length c, the dotted line interval d, and the color of the pattern 10.

[Embodiment 3] FIG. 7 (A) shows a pattern 10 having a triangular wave, an interval e = 4 mm between the center positions of the left and right triangular waves 10L and 10R, and a line width b =
This is a case where black paint is printed on the reflector 2 along both sides of the lamp 3 along the tube axis direction, with 0.5 mm, wavelength f = 5 mm, and wave height g = 1.4 mm. The length of the pattern may correspond to the length of the lamp 3, or may be printed at a predetermined length only on a predetermined portion.

FIG. 7B shows a luminance distribution diagram of the first embodiment and a luminance distribution curve 8 'in the Y direction. Also in this case, FIG.
In the case where the pattern 10 is not formed as shown in FIG. 2, the unevenness of the tube was 2.8%, which was reduced by 1.2% to 1.6%, and the improvement was achieved. In this case, the tube unevenness can be changed and controlled by changing the wavelength f, the wave height g, the interval e between the left and right triangular wave patterns 10L and 10R, the line width b, the color of the paint, and the like.

In the first to third embodiments, the case where silver or black paint is printed as a reflector having a different reflectance from the surface of the reflector 2 has been described.
Any color such as green, blue, and gray may be used, and the pattern forming method is not limited to printing, and a black tape or a silver tape may be attached to both sides of the lamp 3 in the length direction. .

Embodiment 4 FIGS. 8 and 9 show the pattern 10
3 shows a pattern shape when the reflector 2 is viewed from above when variously changed.

FIG. 8A shows a pattern 10 in the case where patterns 10L and 10R are formed so as to gradually expand from the center to the right and left so as to approach the approximate center of the lamp 3 in the longitudinal direction.
It is.

FIG. 8B shows a pattern printed on the left and right ends of the lamp 3 so that the patterns 10L and 10R are separated from the left and right side surfaces of the lamp 3.

FIG. 8C shows patterns 1 on both sides of the lamp 3.
The dots 0L and 10R are formed in a dot shape, and the dot diameter is reduced or reduced in a direction orthogonal to the tube axis direction of the lamp 3 to give a dot gradation.

FIG. 8D shows the left and right patterns 1 of the lamp 3.
0L and 10R are printed in parallel with the main axis direction, and the print density is printed thinner in the direction away from the lamp.

FIG. 9A shows left and right patterns 10L and 10R.
Is a sawtooth wave, and is a rectangular wave in FIG.
(C) shows a case where a stripe is formed in a direction perpendicular to the lamp.

As a reflector for forming the pattern 10 having a different reflectance from the reflector 2, a diffuse reflector in which white fine particles are mixed in a paint so as to cause diffuse reflection (diffuse reflection) can sufficiently exert the effects of the present invention. Can be played. The present invention can be used in combination with a pipe formed as a gradation as means for improving tube unevenness.

[0051]

According to the present invention, the patterns having different reflectivities are provided so as to be arranged on both side surfaces of the cylindrical light source when viewed from the upper surface of the reflector. It is possible to obtain a backlight device that works in a direction to make the light on the illuminating surface uniform, reduces tube unevenness, and can control tube unevenness by selecting a pattern tone and shape.

[Brief description of the drawings]

FIG. 1 is a plan view of a backlight device showing one embodiment of the present invention.

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

FIG. 3 is a sectional view taken along a line BB ′ in FIG. 1;

FIG. 4 is a light amount distribution curve diagram for explaining tube unevenness according to the present invention.

FIG. 5 is a diagram showing a pattern shape, a luminance distribution diagram, and a light intensity distribution curve diagram used in the present invention.

FIG. 6 is a diagram showing another pattern shape, luminance distribution and light amount distribution curve used in the present invention.

FIG. 7 is a diagram showing still another pattern shape, a luminance distribution diagram, and a light amount distribution curve diagram used in the present invention.

FIG. 8 is a plan view showing a pattern shape used in the present invention.

FIG. 9 is a plan view showing another pattern shape used in the present invention.

FIG. 10 is a plan view of a conventional backlight device.

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

12 is a sectional view taken along the line BB 'in FIG.

FIG. 13 is an explanatory diagram of the amount of light emitted from one conventional light source.

FIG. 14 is an explanatory diagram of the amount of light emitted from a plurality of conventional light sources.

FIG. 15 is a diagram showing a conventional light amount distribution characteristic curve from a plurality of light sources and a total characteristic curve thereof.

FIG. 16 shows a luminance distribution diagram and a light amount distribution characteristic curve of a conventional backlight device.

[Explanation of symbols]

1 ‥‥ case, 2 ‥‥ reflector, 3 ‥‥ cylindrical light source (cold cathode tube), 4 ‥‥ light transmission diffuser, 5 ‥‥ condenser sheet, 6 ‥‥
Backlight device, 10mm pattern

Claims (5)

[Claims] 1. A backlight device, comprising: a light transmission / diffusion plate disposed so as to cover an opening of a housing; and a light reflector and at least one or more cylindrical light sources disposed in the housing. A backlight device wherein patterns having different reflectances are formed on both sides of the body along the tube axis direction of the cylindrical light source. 2. The method according to claim 1, wherein the pattern shape having different reflectances formed on the light reflector is a straight line, a waveform, or a curve along the tube axis direction of the cylindrical light source. Backlight device. 3. The backlight device according to claim 1, wherein the pattern having different reflectances formed on the light reflector is a dotted line. 4. The backlight device according to claim 1, wherein the patterns having different reflectances formed on the reflector are diffuse reflectors. 5. The backlight device according to claim 1, wherein the patterns having different reflectances formed on the reflector are formed by printing.