JP2002109943A - Backlight device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a backlight to reduce a leak current and a power consumption without lowering a brightness. SOLUTION: For the backlight device comprising an almost rectangular light guide plate having one main plane as a light outgoing plane, a pipe-shaped light source arranged at least at one side surface of the light guide plate having electrodes at its both end parts, a reflector arranged at the side opposite to the side that the tube-shaped light source is facing, the reflector has a plurality of reflection films separated from each other with a prescribed distance in the direction of discharge between the electrodes of the pipe-shaped light source.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a backlight device.

[0002]

2. Description of the Related Art Currently, notebook PCs (Personal Compute
r) and liquid crystal display devices widely used for monitors are P
DP (Plasma Display Panel) and EL (Electrolumines
This is not a self-luminous display system such as a flat display device such as a cence), but a system in which light from a light source of a backlight device is modulated by a liquid crystal display element to perform display.

The general structure of the above-described backlight device will be described with reference to FIGS. FIG. 5A is an exploded perspective view of the backlight device, and FIG. 5B is a longitudinal sectional view of a state where these components are assembled. Here, the reflection plate 4, the light guide 2, the diffusion plate 5, and the lens sheet 6 are sequentially laminated on the frame 7, and the light source 1 and the reflector 3 are mounted on one side of the light guide 2. Among them, as the light source 1, a cold cathode fluorescent tube (CCFL tube) having high luminous efficiency, excellent luminance uniformity, and emitting light by discharge between the electrodes is used. The reflector 3 allows light from the light source 1 to effectively enter the light guide 2, and the reflector 4 transmits light transmitted through the light guide 2 toward the light emitting surface. The diffusion plate 5 is for improving the uniformity of luminance, and the lens sheet 6
Is for distributing light in a direction perpendicular to the light exit surface of the light guide plate.

[0006] Of the constituent elements of the backlight device shown in FIG.
Is bent so that its middle part has, for example, a cylindrical surface or a parabolic surface, and both ends are formed substantially in parallel. FIG. 6A is a development view of the reflector 3 before molding, and FIG.
(B) is a sectional view taken along the line CC in FIG. Here, an insulating film is used as the substrate 10.
The reflection film 20 is formed by coating Ag or the like over the entirety of one main surface (surface) of the P.O.

[0005]

In order to turn on the cold cathode fluorescent tube used as the light source 1, it is necessary to apply a high frequency high voltage to both ends. Therefore, if there is a conductor, that is, a reflective film 20 of a metal film near the cold cathode fluorescent tube, a leak current flows. This leakage current consumes wasteful power.

In order to solve this problem, for example, FIG.
(C) As shown only in the cross section, PET (Polyet
In some cases, the reflector 3A is made of an insulating film such as hylene terephthalate). However, the reflector 3A consisting of only the insulating film is made of Al or Ag.
Inferior reflectivity to metal films such as, etc., to obtain the same brightness as a metal film with an insulating film, extra power is supplied to the cold-cathode discharge tube to reduce the leakage current to improve brightness And the power consumption of the backlight device is increased.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and provides a backlight device capable of reducing leakage current and power consumption without lowering luminance. The purpose is to:

[0008]

The invention according to claim 1 is
A light guide plate that is substantially rectangular and has one main surface as a light emission surface; a tubular light source that is disposed on at least one side surface of the light guide plate and has electrodes formed at both ends; and a side of the tubular light source that faces the light guide plate Wherein the reflector comprises a plurality of reflective films divided with a predetermined gap in a discharge direction between the electrodes of the tubular light source. .

According to a second aspect of the present invention, in the backlight device according to the first aspect, the reflector has the other reflective film laminated on the reflective film via an insulating substrate.

According to a third aspect of the present invention, in the backlight device according to the second aspect, the reflector is configured such that the reflection film is divided and arranged with a predetermined gap, and the reflector is arranged to correspond to the predetermined gap via the insulating member. A plurality of reflection films are further provided at the positions where the reflection films are formed.

According to a fourth aspect of the present invention, in the backlight device according to the first aspect, the reflection film of the reflector has a higher arrangement density of the gap at a central portion than at both ends of the tubular light source. It is characterized by being arranged as follows.

According to a fifth aspect of the present invention, a fluorescent tube is used as a light source, and the light distribution of the fluorescent tube is changed by using the reflector according to any one of the first to fourth aspects. A backlight device characterized in that it is a backlight.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The principle of the present invention will be described below with reference to FIG. FIG.
As shown in (a), the end is an AC voltage supply end,
In a backlight device having a configuration in which a light source 1 composed of a cold cathode discharge tube having a tube wall as a light emitting surface is surrounded over a substantially half circumference by a reflector 3 on which a metal film is adhered as a reflection film, When the high-frequency power supply 8 is connected to both ends, a capacitance is formed between the light source and the metal film. A model represented by the equivalent circuit of FIG. 7B was devised for this configuration. Here, the light source 1 has many resistors R
, The interconnection points of these resistors R are grounded via the capacitors C, respectively, to form a distributed constant circuit of the resistors R and the capacitors C.

A current flowing from the high frequency power supply 8 to both ends of the light source and flowing to the ground potential via the capacitor C, that is, a current that does not contribute to the light emission of the light source 1 will be referred to as a leak current. Therefore, it is considered that the leakage current can be reduced by cutting the portion where the capacitor C is connected to each other and cutting off the portion from the ground point. It can be seen that for this purpose, the reflection film 20 applied to the substrate 10 may be divided and arranged with a gap in the axial direction of the light source 1. The present invention has been made in accordance with these principles. Hereinafter, the present invention will be described in detail based on preferred embodiments shown in the drawings.

FIG. 1 shows the configuration of a reflector according to a first embodiment of the present invention. FIG. 1A is a plan view of a reflector that has been developed before bending according to a light source 1.
FIG. 1B is a cross-sectional view taken along line AA in FIG. In the figure, an insulator having a high light transmittance such as a PET film is used for a substrate 10, for example, and a width W for realizing the reflector 3 whose sectional shape is shown in FIG. And has a length L substantially equal to the dimension. A reflection film 21 made of a layered metal film having a width W and a length X made of, for example, Ag is provided on the surface of the substrate 10 (the surface facing the light source 1).
, 2n are divided and arranged in the direction of the length L with an interval d. In this case, the width W of the substrate 10 is 10
mm, length L is 200mm, thickness T is 0.7mm PE
Using a T film, the width W of the reflective films 21, 22,.
Is set to 10 mm, the length X is set to 5 mm, and the interval d is set to 0.2 mm, it is possible to reduce the leak current while maintaining substantially the same luminance as the conventional device.

As described above, since the conductor constituting the reflection film, in this case, the metal film is formed in the shape of an island divided in the direction of the electrode of the light source, the leakage current not contributing to light emission can be suppressed.
In addition, power consumption can be reduced without a decrease in luminance.

In the embodiment shown in FIG. 1, the substrate 1
Even if white PET is used as 0, light may leak to the back surface from the portion at the interval d, though very slightly.

FIG. 2 shows the configuration of a reflector according to a second embodiment of the present invention. FIG. 2 (a) is a developed plan view, and FIG. It is sectional drawing of the B line. This reflector is formed in a substrate 10 made of a PET film that is translucent and high in light transmittance, and is formed in an island shape divided on the surface of the substrate 10 facing the light source 1 in the electrode axis direction of the light source. An island-shaped reflection film provided on a side of the first reflection film of the metal film opposite to the first reflection film of the substrate 10 and having the same size as the surface at a portion corresponding to the distance d between the island-shaped first reflection films. , 3 (n-1).

As described above, by forming the conductor constituting the reflector, here, the reflection film into a shape divided in the electrode axis direction of the light source, it is possible to suppress the leak current to the reflector. Furthermore, by arranging the divided reflective films on both surfaces of the reflector substrate, light transmitted through the reflective film on one surface can be emitted to the light source side by the reflective film on the other surface,
Light extraction efficiency can be improved.

Here, the reflector shown as the embodiment of FIG. 2 and the reflector described as a conventional device will be compared in terms of power consumption.

First, FIGS. 6A and 6B show a conventional apparatus.
A PET film is used as the substrate 10 shown in FIG. 1, a reflector made of one layer of Ag is used as a reflective film, and a substantially rectangular shape having a short side (longitudinal direction of the light source 1) of 20 cm and a long side of 25 cm is used. When a backlight device was formed using the light guide and the luminance in the front direction was 70 cd / m ² , the power consumption of the backlight was 1.1 W. This power consumption includes a leak current.

Next, a white PE is used as a reflector 3A consisting of only an insulating film whose cross section is shown only in FIG.
When using a T film and setting the luminance in the front direction to 70 cd / m ² under the same other conditions, the power consumption of the backlight was 1.0 W. This is presumably because even though the leakage current could be kept low, the input current had to be increased because the reflectance was low, and there was no large difference in power consumption.

On the other hand, when the reflector according to the second embodiment shown in FIG. 2 is used and the luminance in the front direction is 150 cd / m ² under the same other conditions, the power consumption of the backlight is 0. .9W.

In the first embodiment shown in FIG. 1, the reflectivity of light is slightly inferior because the reflective film has a single-layer structure, but the reflectivity of Ag itself is high and the interval is 0.2 mm. Therefore, it is considered that the power consumption is substantially the same as that of the embodiment shown in FIG.

As is clear from the results of these experiments,
According to the first and second embodiments, the leak current can be reduced without lowering the luminance.
Power consumption can be reduced.

FIG. 3 is a cross-sectional view similar to FIG. 1 or FIG. 2 for explaining the structure of a reflector according to a third embodiment of the present invention. The description is omitted here. In this embodiment, the substrate 1
, 2n are dispersed on the surface of
, 3 (n +
1) are dispersed and another substrate 11 is superimposed on these reflective film surfaces, and the reflective films 31, 32,..., 3 (n +
Reflecting films 41, 42,
, 4n constitute a reflector having three reflective layers. As a result, a light leakage to the back surface is reduced as compared with the embodiment shown in FIG. 2, and a reflector with low power consumption and a backlight device using the same can be obtained.

According to the above-described first to third embodiments, since the reflecting film of the reflector is formed with substantially uniform and equally-spaced gaps, it is formed so as to substantially uniformly reflect light in the axial direction of the light source. You.

In a backlight device in which a light source is disposed on one side of a light guide plate, electrodes and the like are formed at both ends of the light source. In some cases, island-like light emission from the light plate was not uniform.

FIG. 4 is a sectional view similar to FIG. 2 for explaining the structure of the fourth embodiment based on this concept. In the figure, the same elements as those in FIG. The description is omitted here. In this embodiment, an equal interval is provided between the reflective films 21, 22,..., 2n directly facing the light source 1, but the axial length X of the reflective films 21, 22,.
Are sequentially shortened from the end to the center. That is, the length of the reflective film at the center is X ₁ , and the length from the center to the end is X ₂ ,
When X ₃ , X ₄ ,..., X _n are set, X ₁ <
Reflective film 2 having a relationship of X ₂ <X ₃ <X ₄ <... <X _n
.., 2n are formed. In other words, the arrangement density of the interval d at the center is increased. Then, on the rear surface of the substrate 10, at portions corresponding to the gaps between the reflective films 21, 22,..., 2 n, the reflective films 31, 32,
.., 3 (n + 1) are arranged.

With this configuration, the light source 1
Since the average reflectance of light at the center in the longitudinal direction is relatively lower than the average reflectance at the ends, the amount of light incident on the light guide plate is substantially uniform in the axial direction of the light source, and therefore,
A light guide plate having excellent luminance uniformity on the light emitting surface can be achieved.

In each of the above embodiments, the description has been made of the case where the number of reflective films is three or less. However, it goes without saying that a reflector having four or more reflective films can be formed.

Further, even if the axial length of each reflective film from the axial end to the central portion is gradually reduced, the power consumption can be further reduced by forming the reflective films in a plurality of layers. can do.

In each of the above embodiments, the substrates 10, 11, and 12 for forming the multilayer reflective film are made of PET.
Although a film is used, light leaking from an interval can be collected with high efficiency even if other materials are used as long as they have excellent light transmission characteristics. Further, it is clear that a metal other than Ag can be used as a material for forming the reflection film. Further, the reflective film may be a laminated film of a plurality of metal films, for example, a laminated film of Al / Ag, stainless steel / Ag, or the like.

Further, in each of the above embodiments, the backlight device is constituted by using a cold cathode fluorescent tube as a light source. However, the present invention is not limited to this, and various light sources such as a hot cathode fluorescent tube can be used.

In the above-described embodiment, the reflector is formed in a sheet shape in a state where the reflection film is formed and then formed by bending. However, the present invention is not limited to this. The reflection film is plated on the formed insulator. May be arranged.

[0036]

As is apparent from the above description, according to the present invention, the reflector which can reduce the leakage current and reduce the power consumption without lowering the luminance, and the use of the reflector. A backlight device can be provided.

[Brief description of the drawings]

FIG. 1 is a developed plan view and a sectional view of a reflector according to a first embodiment of the present invention.

FIG. 2 is a developed plan view and a sectional view of a reflector according to a second embodiment of the present invention.

FIG. 3 is a sectional view of a reflector according to a third embodiment of the present invention.

FIG. 4 is a sectional view of a reflector according to a fourth embodiment of the present invention.

FIG. 5 is an exploded perspective view of a conventional backlight device and a longitudinal sectional view showing an assembled state thereof.

FIG. 6 is a plan view and a cross-sectional view of a reflector included in a conventional backlight device.

FIG. 7 is a diagram showing an electrical connection state of a light source, a reflector, and a high-frequency power supply, and an equivalent circuit diagram for explaining the principle of the present invention.

[Description of Signs] 1 Light source 2 Light guide 3 Reflector 4 Reflector 5 Diffusion plate 6 Lens sheet 7 Frame 8 High frequency power supply 10, 11 Substrate 20-2n, 31-3 (n-1), 41-4n Reflective film

Claims (5)

[Claims] 1. A light guide plate which is substantially rectangular and has one main surface as a light exit surface, a tubular light source disposed on at least one side of the light guide plate and having electrodes formed at both ends, and a light guide for the tubular light source. A reflector disposed on a side facing the light plate, wherein the reflector includes a plurality of reflective films divided at a predetermined gap in a discharge direction between the electrodes of the tubular light source. Backlight device. 2. The backlight device according to claim 1, wherein the reflector has the other reflective film laminated on the reflective film via an insulating substrate. 3. The reflector according to claim 1, wherein the reflection film is divided and arranged with a predetermined gap, and a plurality of reflection films are further provided at positions corresponding to the predetermined gap via the insulating member. Item 3. The backlight device according to Item 2. 4. The reflector according to claim 1, wherein the reflection film of the reflector is arranged such that the arrangement density of the gaps at the center is higher than at both ends of the tubular light source.
The backlight device as described in the above. 5. The light source according to claim 1, wherein a fluorescent tube is used as a light source.
A backlight device for a liquid crystal display device, wherein the light distribution of the fluorescent tube is changed using the reflector described in any one of the above.