JPH07262817A - Back light unit - Google Patents

Abstract

PURPOSE:To provide a specific brightness uniformity and a specific illumination even though a conductive sheet hangs down on a fluorescent lamp, by forming the transparent conductive sheet to cover the upper side of the fluorescent lamp in a lamp house, out of an insulating sheet and a transparent conductive film, and providing the insulating sheet on the fluorescent lamp side. CONSTITUTION:A slender and a small diameter of fluorescent lamp 3 is set in parallel in a flat lamp house 2 having an upper side opening, and its ends are fixed and held to the receptacles 5 of a circuit 4. The fluorescent lamp 3 is lighted by a high-frequency lighting circuit 6 of the circuit case 4, and the lamp light is radiated evenly from a liquid crystal display device 9 through a light transmissive diffusion plate 8. In this case, the opening of the lamp house 2 is blocked by a transparent conductive sheet 12 which consists of a transparent conductive film 12a and an insulating sheet 12b, and the insulating sheet 12b is positioned on the fluorescent lamp 3 side. Consequently, even though the transparent conductive sheet 12 hangs down on the fluorescent lamp 3, the transparent conductive film 12a is insulated from the bulb wall surface of the fluorescent lamp 3, and a leaking current is not leaked to the transparent conductive sheet 12.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has a light-transmitting diffuser plate which is formed on the opening of a lamp house in which a light source lamp is arranged and whose inner wall surface is made to reflect light, and which is arranged on the upper surface side of the lamp house. Regarding a direct-type backlight unit that uniformly illuminates the display device from the back side, in particular, a long and thin fluorescent lamp is used as a light source lamp, and in a backlight unit of a liquid crystal display device that is turned on at a high frequency, a lamp house The present invention relates to a backlight unit in which a transparent conductive sheet is provided in an opening to shield radiation noise emitted from a fluorescent lamp.

[0002]

2. Description of the Related Art This type of direct-type backlight unit has a higher light output efficiency than an edge-light type unit in which a light source lamp is arranged on the end surface of a light guide plate, and by using a long and narrow fluorescent lamp as a light source, It is excellent as a backlight unit of a liquid crystal display device because a thin display device, a large display surface, high luminance, and low power consumption can be achieved.

For example, FIG. 2 shows a backlight unit 1 of a liquid crystal display device which incorporates such an elongated fluorescent lamp having a small diameter.
FIG. 7 is a cross-sectional view showing a conventional example of FIG.

That is, in the figure, 2 is a flat lamp house formed of an aluminum plate and having an upper opening. Although not shown, white coating is applied to the inner wall surface, or a mirror-finished silver vapor-deposited sheet is attached to the inner surface. The walls are formed with good light reflectivity. Reference numeral 3 is a long and thin fluorescent lamp arranged in parallel in the lamp house 2, and both ends where electrodes are arranged are arranged outside the lamp house 2. Reference numeral 4 denotes a circuit case arranged so as to be connected to the lamp house 2, and houses a socket 5 for supporting both ends of the fluorescent lamp 3, a high frequency lighting circuit 6 for lighting the fluorescent lamp 3 at a high frequency, and the like. Reference numeral 7 denotes a transparent conductive sheet arranged in the opening of the lamp house 2 so as to close the opening.
Radiation noise emitted from the fluorescent lamp 3 is shielded. The transparent conductive sheet 7 is, for example, a transparent conductive film 7 on the surface of a PET (polyethylene terephthalate) resin sheet.
The transparent conductive film 7a is formed so as to face the fluorescent lamp 3 and is grounded together with the lamp house 2. Reference numeral 8 denotes a light transmission diffusion plate which is arranged on the upper surface side (non-fluorescent lamp side) of the transparent conductive sheet 7 and which diffuses and transmits light from the fluorescent lamp 3.

In the backlight unit 1 thus constructed, when the fluorescent lamp 3 is lit at a high frequency by the high frequency lighting circuit 6, a part of the light is directly reflected and the remaining light is reflected on the inner surface of the lamp house 2. The liquid crystal display device 9 arranged on the diffusion plate 7 is uniformly illuminated through the light transmission diffusion plate 8.

The fluorescent lamp 3 emits radiant noise when it is lit at a high frequency, but since it is covered and shielded by the transparent conductive sheet 7 provided in the opening of the lamp house 2, it is outside the backlight unit 1. The amount of radiation to the diffusion plate 7 is suppressed, and the liquid crystal display device 9 arranged on the diffusion plate 7 is prevented from malfunctioning.

[0007]

However, in the backlight unit 1 in which the transparent conductive sheet 7 is arranged in the opening of the lamp house 2 as described above, the temperature of the transparent conductive sheet 7 in the lamp house rises during use. However, there is a problem in that the transparent conductive film hangs down on the fluorescent lamp 3 and the transparent conductive film comes into contact with the fluorescent lamp, resulting in a reduction in the luminance uniformity of the surface of the diffusion plate 7 and a reduction in illuminance.

In order to prevent the transparent conductive sheet 7 from hanging down on the fluorescent lamp 3, it is conceivable to increase the thickness of the lamp house 2 and widen the gap between the transparent conductive sheet 7 and the fluorescent lamp 3. However, if the thickness of the lamp house 2 is increased, the size of the backlight unit 1 is increased,
Thinning of the entire device cannot be achieved. On the other hand, it is difficult to completely prevent the transparent conductive sheet 7 from hanging down on the fluorescent lamp 3 due to the demand for a larger display surface, and the illuminance of the backlight unit is lowered due to the hanging down of the transparent conductive sheet 7. Was required.

Therefore, the present invention has been made in view of the problems of the brightness uniformity and the illuminance decrease of the backlight unit due to the above-mentioned hanging of the transparent conductive sheet, and even if the transparent conductive sheet hangs down on the fluorescent lamp, a predetermined It is an object of the present invention to provide a backlight unit capable of obtaining a brightness uniformity and a predetermined illuminance.

[0010]

Means for Solving the Problems As a result of studying the cause of the decrease in illuminance of the backlight unit 1, the present inventor found that
The following conclusions have been reached. That is, the fluorescent lamp 3 used in the backlight unit 1 is extremely thin and thin with a bulb outer diameter of 3 to 5 mm and a bulb length of 150 to 250 mm, and a high-frequency lighting circuit 6 for driving and lighting the bulb. Is set to a high voltage of several hundred V to several thousand V. Then, both ends 3a, 3 of the fluorescent lamp 3 are
As shown in FIG. 3, the transparent conductive sheet 7 is connected to the high-voltage side terminal 6a and the low-voltage side terminal (ground side) 6b of the high-frequency lighting circuit 6, and the transparent conductive sheet 7 causes the fluorescent lamp 3 to
The transparent conductive film 7a on the surface of the valve hangs up to A on the wall surface of the valve.
When it comes into contact with or comes close to a point, the transparent conductive sheet 7 in this part
A high frequency and a high voltage of the lighting circuit 6 are applied to the transparent lamp through the bulb wall surface of the fluorescent lamp 2, and the transparent conductive film 7a is applied from the bulb wall surface.
Leakage current i flows through. As a result, it has been found that the fluorescent lamp 2 causes a decrease in brightness toward the low pressure side from this portion, resulting in a decrease in brightness uniformity and a decrease in illuminance. The decrease in the brightness of the fluorescent lamp 3 due to the leakage current i is hardly visible when the lighting frequency of the lighting circuit 6 is 15 KHz or less.
It was clearly visible when the lighting frequency was 15 KHz or higher, and a luminance reduction of 10% or higher was observed at the usual frequency of 40 to 50 KHz. Therefore, in the present invention, an insulating member is interposed between the fluorescent lamp and the transparent conductive film of the transparent conductive sheet, and is specifically configured as follows. That is, the backlight unit of the present invention includes a flat lamp house having an upper surface opening, a long and thin fluorescent lamp arranged in the lamp house, and at least 15 KHz for the fluorescent lamp.
A high-frequency lighting circuit for lighting at the above high-frequency, a transparent conductive sheet disposed in the opening of the lamp house so as to close the opening, and a light transmission disposed on the side of the opening of the transparent conductive sheet. The transparent conductive sheet is formed by forming a transparent conductive film on an insulating sheet, and the transparent conductive sheet is arranged such that the transparent conductive film is on the non-fluorescent lamp side. Further, in the backlight unit of the present invention, the transparent conductive sheet is arranged in the opening of the lamp house so that the transparent conductive film faces the fluorescent lamp, and a transparent insulation is provided between the transparent conductive film and the fluorescent lamp. It is characterized by interposing members.

[0011]

The transparent conductive sheet disposed in the opening of the lamp house in a closed shape has an insulative surface on the lower side of the fluorescent lamp. Therefore, even if the transparent conductive sheet hangs down on the fluorescent lamp, the transparent conductive film remains It is insulated from the bulb wall surface of the fluorescent lamp, and even if the fluorescent lamp is turned on at a high frequency of 15 KHz or higher, no leakage current leaks to the transparent conductive sheet through the bulb wall surface. Therefore, a decrease in the brightness of the fluorescent lamp is prevented.

[0012]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 1 is a sectional view showing a structural example of a backlight unit 11 for a liquid crystal display device according to the present invention.

Like the conventional backlight unit 1, the backlight unit 11 is also elongated and slender in a flat lamp house 2 having an upper surface opening formed of, for example, an aluminum plate (other metal plate may be used). Diameter fluorescent lamp 3
Are arranged in parallel and housed, and both ends of the fluorescent lamp 3 are led out of the lamp house 2 and fixedly supported by a socket 5 arranged in a circuit case 4 connected to the lamp house 2. is there. The fluorescent lamp 3 is lit by the high frequency lighting circuit 6 of the circuit case 4, and the liquid crystal display device 9 arranged on the upper surface side is uniformly irradiated with the lamp light through the light transmitting / diffusing plate 8 from the rear surface side. is there. Further, the opening of the lamp house 2 is closed by the transparent conductive sheet 12, and the fluorescent lamp 3 in the lamp house 2 is covered with the conductive sheet 12 from above, so that the radiation noise of the fluorescent lamp 3 radiates to the outside of the lamp house 2 as much as possible. It is configured not to.

The characteristic of the backlight unit 11 is that
Transparent conductive sheet 12 that closes the opening of the lamp house 2
Is arranged so that the transparent conductive film is located on the non-fluorescent lamp side, and further, the transparent conductive film is arranged on the fluorescent lamp side, and an insulating member is provided between the fluorescent lamp and the transparent conductive film. It is in the intervening point. Therefore, the same components are designated by the same reference numerals as those in FIG. 2 and their description is omitted.

That is, in the transparent conductive sheet 12 of the backlight unit 11, the transparent conductive film 12a formed on the surface of the insulating sheet 12b is arranged so as to be on the non-fluorescent lamp side. The lamp house 2 is bonded and fixed to the peripheral surface of the house 2 and is grounded together with the lamp house 2.

The backlight unit 11 having such a configuration
3, both ends 3a and 3b are connected to the high-voltage side terminal 6a and the low-voltage side terminal 6b of the high-frequency lighting circuit 6, and the high-frequency and high voltage is applied to the fluorescent lamp 3 to light it.

At this time, even if the transparent conductive sheet 12 hangs down on the fluorescent lamp 3 and comes into contact with or comes close to the point A on the wall surface of the bulb, the transparent conductive sheet 12 at this portion has the transparent conductive film 12a on the upper side (non-contact). It is arranged toward the fluorescent lamp) and the lower surface of the contact portion is formed insulative (insulating sheet 12b). Even if the fluorescent lamp is lit at a high frequency of 15 KHz or more, it is transparent through the bulb wall surface. No leakage current leaks to the conductive sheet 12. Therefore, the decrease in the brightness of the fluorescent lamp 3 is prevented, and the problems of the deterioration of the brightness uniformity of the backlight unit 11 and the decrease of the illuminance are solved. Further, since the gap between the transparent conductive sheet 12 and the fluorescent lamp 3 can be set to be narrow, the thickness dimension of the backlight unit 11 can be reduced, which can contribute to the thinning of the entire liquid crystal display device.

In the present invention, the transparent conductive sheet 12 is formed of a conductive sheet obtained by coating the transparent conductive film 12a on the surface of the PET resin sheet in the above embodiment, but the present invention is not limited to this. The conductive film may be arranged on the fluorescent lamp side, and an insulating member may be arranged on the surface thereof. Further, the fluorescent lamp 3 of the light source can be applied not only to a straight tube type but also to a U-shaped or curved tube type. Further, although the backlight unit 11 has an integrated structure in which the light emitting portion and the lighting circuit portion are integrally connected, the backlight unit 11 can also be applied to a structure in which this is formed separately.

[0020]

As described in detail above, according to the present invention,
Since the insulating member is interposed between the transparent conductive film of the transparent conductive sheet arranged in the opening of the lamp house and the fluorescent lamp, the radiation noise can be suppressed and the transparent conductive film hangs down on the fluorescent lamp. Even if the leakage current from the wall surface of the bulb can be prevented and the luminance of the fluorescent lamp can be prevented from lowering, a backlight unit for a liquid crystal display device having excellent luminance uniformity and illuminance can be provided.

[Brief description of drawings]

1A is a sectional view showing a configuration example of a backlight unit of the present invention, and FIG. 1B is a partially enlarged sectional view of FIG. 1A.

FIG. 2 is a perspective view showing a configuration example of a conventional backlight unit.

FIG. 3 is an operation explanatory diagram of the backlight unit of FIG.

[Explanation of symbols]

 2 Lamp house 3 Fluorescent lamp 4 Circuit case 5 Socket 6 High frequency lighting circuit 8 Light transmission diffuser plate 9 Liquid crystal display device 11 Backlight unit 12 Transparent conductive sheet 12a Transparent conductive film 12b Insulating sheet (insulating member)

Claims (2)

[Claims] 1. A flat lamp house having an upper opening, a long and narrow fluorescent lamp arranged in the lamp house, a high frequency lighting circuit for lighting the fluorescent lamp at a high frequency of at least 15 KHz, and the lamp. The opening of the house is provided with a transparent conductive sheet arranged so as to close the opening, and a light transmission diffusion plate arranged on the side of the opening of the transparent conductive sheet, and the transparent conductive sheet is insulated. A backlight unit, characterized in that a transparent conductive film is formed on a sheet, and the transparent conductive sheet is arranged so that the transparent conductive film is on the non-fluorescent lamp side. 2. The transparent conductive sheet is arranged in an opening of a lamp house so that the transparent conductive film faces the fluorescent lamp, and a transparent insulating member is interposed between the transparent conductive film and the fluorescent lamp. A backlight unit characterized by that.