JPH0562644A - Cold cathode fluorescent lamp - Google Patents

Abstract

PURPOSE:To provide a cold cathode fluorescent lamp improved in the liminance maintenance factor and increased in the service life. CONSTITUTION:A fluorescent material coating 2 is formed on the inner surface of a bulb 1 sealed, at its ends, with cold cathodes 4, respectively, in a sealed state, a fluorescence being given forth from the effective fluorescent surface at one side of the mentioned bulb. In this cold cathode fluorescent lamp, when the mentioned cold cathodes are disposed biased toward the non-effective fluorescing surface side from a center line O-O of the bulb, since the cold cathodes are biased toward the non-effective fluorescing surface side from the bulb center line, the cold cathodes are spaced apart from the bulb of the effective fluorescing surface side. As a result, the occurrence of glow discharge is decreased, splashing of the electrode materials is prevented, and blackening of the bulb is lessened.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cold cathode fluorescent lamp in which light is emitted from an effective light emitting surface provided on one side surface of a bulb.

[0002]

2. Description of the Related Art Recently, a small-sized liquid crystal display device has been developed as a color viewfinder for a VTR, which is designed to illuminate a liquid crystal display panel having a size of about 23 mm × 18 mm with a backlight from its back surface. But
If a straight tube fluorescent lamp or a U-shaped or W-shaped fluorescent lamp is used as the backlight, it cannot be used because it is too large. For this reason, extremely small flat-type cold cathode fluorescent lamps are used.

With a flat type cold cathode fluorescent lamp, a flat light emitting surface having an area equivalent to that of the above liquid crystal display panel can be formed, and the liquid crystal display panel can be omitted without using a diffusion plate or a reflection plate. It can be irradiated evenly. Further, since the lamp can be made thin, there is an advantage that the thickness of the entire display device can be made thin.

By the way, a conventional structure of this type of flat cold cathode fluorescent lamp will be described with reference to FIG.

In FIG. 3 and FIG. 4, reference numeral 1 denotes a flat valve having a tubular shape with an oval cross section.
A phosphor coating 2 is formed on the inner surface of the. The flat valve 1 is air-tightly closed at both end openings by flat plate-shaped stems 3 as a closing member. Since the stems 3 and 3 are made of glass plates and have a flat plate shape, they belong to so-called button stems. Cold cathodes 4 and 4 are attached to such flat plate-shaped stems 3 and 3, respectively.

For the cold cathodes 4 and 4, for example, a getter 5 made of zircon-aluminum is applied to one side of a strip of nickel-plated iron plate, and a mercury emission structure 6 made of a mercury-titanium alloy is attached to the other side. Is configured. The cold cathodes 4, 4 facing each other are such that the surfaces coated with the getters 5 face each other.

One end of the plate type cold cathode 4 is joined to the wells 7 as a power supply terminal,
The wells 7 are hermetically penetrated through the stem 3 and led out to the outside.

A dummy wells 8 is hermetically penetrated through the stem 3 at a position apart from the wells 7,
The dummy wells 8 are provided to maintain a thermal balance with the wells 7 when the valve 1 and the stem 3 are heated. Of course, the plate-shaped cold cathode 4 may be supported by the two wells 7 and 8.

On the inner surface of the stem 3, the stem 3
Bosses 9 and 9 are provided for positioning when the flat valve 1 is applied to both end openings of the flat valve 1, and the wells 7 and 8 are arranged so as to penetrate the bosses 9 and 9. ing.

The stems 3 and 3 having the cold cathodes 4 and 4 as described above are made of glass adhesive, that is, frit glass 10,
It is joined by 10 to the open end of the valve 1.
The frit glasses 10 and 10 have a thin plate shape of an oval ring so as to match the opening surface of the bulb 1. Such frit glasses 10 and 10 are sandwiched between the opening surface of the bulb 1 and the inner surfaces of the stems 3 and 3, and are heated from the outside in this state. This heating causes frit glass 10,
Since 10 melts and wets across the opening end surface of the valve 1 and the inner surfaces of the stems 3 and 3, the stems 3 and 3 are joined to the opening portion of the valve 1.

The mercury-releasing structure 6 attached to the cold cathodes 4 and 4 is adapted to be vaporized and discharged into the bulb by heating from outside with high-frequency dielectric heating after the bulb is sealed. There is.

Such a flat cold cathode fluorescent lamp is connected to a pulse generating circuit 20 and applies pulse power to the cold cathodes 4 and 4 at both ends to generate glow discharge. This glow discharge ionizes and excites the mercury atoms in the bulb 1 to emit ultraviolet rays. This ultraviolet ray is converted into visible light by the phosphor coating 6 formed on the inner surface of the bulb and is emitted to the outside.

In this case, the light which goes to the outside is radiated in the direction shown by the arrow in FIG. 3B from this effective light emitting surface, with one surface having a large area of the bulb 1 as the effective light emitting surface. The liquid crystal display plate (not shown) is irradiated.

In this case, as for the film thickness of the phosphor coating 6 formed on the inner surface of the bulb 1, as shown in FIG. 3B, the film thickness t ₁ on the effective light emitting surface side is the film thickness t ₁ on the ineffective light emitting surface side. It is formed to be smaller than the film thickness t ₂ (t ₁ <t ₂ ).

That is, since it is not necessary for the phosphor coating on the side of the ineffective light emitting surface to transmit light in this direction, it is desirable that it converts ultraviolet rays emitted from mercury into visible light and has a high reflection function. The larger the film thickness t _{2, the} higher the reflection function and the higher the brightness seen from the effective light emitting surface. On the other hand, the phosphor coating on the effective light emitting surface side must have the function of converting the ultraviolet rays emitted from mercury into visible light and transmitting the visible light to the outside, however, the absorption of ultraviolet rays and visible light And since there is scattering, there exists an optimum value of film thickness t ₁ as shown in FIG. It is generally said that maximum efficiency can be obtained by keeping the total light linear transmittance on the effective light emitting surface side at 50 to 60% and the total light linear transmittance on the ineffective light emitting surface side at about 10%.

Therefore, when the light is extracted only on the effective light emitting surface side, the film thickness t ₁ on the effective light emitting surface side is formed smaller than the film thickness t ₂ on the ineffective light emitting surface side.

The pulse lighting method has an advantage that the discharge is apparently uniform and the brightness uniformity is improved.

[0018]

However, in the case of the flat type cold cathode fluorescent lamp having the above-mentioned structure, the luminance maintenance factor may be lower than that of a general fluorescent lamp. In particular, a phenomenon in which blackening occurs on the effective light emitting surface is seen near the electrodes.

As a result of investigating the cause, it was found that the electrode material was attached to the bulb wall by sputtering because the distance between the electrode and the bulb on the effective light emitting surface side was short.

That is, in the case of the strip-plate type cold cathode, the electric field is concentrated at the corners thereof, and spot-like glow discharge is generated between the edge part and the phosphor film near the edge part. For this reason, the electrode material scatters and adheres to the bulb wall, and the solarization (photosensitivity) of the glass is promoted by the irradiation of ultraviolet rays, which causes the bulb to blacken.

Further, in the case of pulse lighting, the electrode is in the cathode mode, and when the pulse voltage peaks, the electrode sputters remarkably.

Further, as described above, when the thickness of the phosphor coating 2 formed on the inner surface of the bulb is thinner on the effective light emitting surface side than on the ineffective light emitting surface side, the blackening immediately leads to the brightness. The decrease in the brightness maintenance ratio appears early, reflecting the decrease.

For this reason, as can be understood from the characteristics of the luminance maintenance ratio shown in FIG. 2, the luminance drops relatively early. Therefore, there is a drawback that the life is shortened.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a cold cathode fluorescent lamp having an improved luminance maintenance rate and a long life.

[0025]

According to the present invention, a phosphor coating is formed on the inner surface of a bulb having cold cathodes sealed at both ends, and light is emitted from an effective light emitting surface on one side of the bulb. The cold cathode fluorescent lamp is characterized in that the cold cathode is arranged so as to be offset from the center line of the bulb toward the ineffective light emitting surface side.

[0026]

According to the present invention, since the cold cathode is deviated to the non-effective light emitting surface side from the bulb center line, the cold cathode is separated from the bulb and the phosphor coating on the effective light emitting surface side to prevent glow discharge. It is possible to reduce the generation, prevent the electrode material from scattering, and reduce the blackening of the bulb on the effective light emitting surface side.

[0027]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on an embodiment shown in FIGS. In the figure, members that may be the same as those in the case of FIGS. 3 and 4 described above are denoted by the same reference numerals, and description thereof will be omitted.

In this embodiment, the cold cathodes 4 and 4 are shown in FIG.
As shown in FIG. 6B, the bulb 1 is arranged on the non-effective light emitting surface side with respect to the center line OO.

Therefore, the distance s ₁ between the cold cathode 4 and the bulb 1 on the effective light emitting surface side is larger than the distance s ₂ between the cold cathode 4 and the bulb 1 on the ineffective light emitting surface side (s ₁ > s). ₂ ) Formed.

According to this structure, since the cold cathode 4 is separated from the bulb 1 on the effective light emitting surface side, even if the electric field is concentrated at the corner of the cold cathode 4, this edge portion and the fluorescent light near this edge portion The occurrence of glow discharge with the body coating is reduced. For this reason, the scattering of the electrode substance is reduced, and the ratio of the electrode substance adhering to the valve wall is reduced. Therefore, blackening of the bulb is prevented, and the luminance retention rate is increased.

In the case of pulse lighting, the electrode is in the cathode mode, and electrode sputtering easily occurs when the pulse voltage peaks, but the cold cathode 4 is far away from the wall surface of the bulb 1 on the effective light emitting surface side. Therefore, the ratio of electrode spatter adhering to the valve wall is reduced.

In this case, glow discharge is generated between the cold cathode 4 and the bulb 1 on the side of the ineffective light emitting surface where the cold cathode 4 approaches, and blackening is likely to occur on this side. However, since the phosphor coating 2 on the non-effective light emitting surface side has a large film thickness t _{2, the} reflectance is only slightly decreased, and it does not affect the decrease in brightness on the effective light emitting surface side.

From the above, as can be seen from the characteristics of the brightness maintenance ratio shown in FIG. 2, the brightness maintenance ratio is improved in the case of the present invention as compared with the conventional case, and therefore the life is extended.

The present invention is not limited to the above embodiment.

That is, in the above embodiment, the case of the bulb 1 cold cathode fluorescent lamp having a flat cross section has been described, but the present invention has a flat cold cathode fluorescent lamp having an oval cross section or a circular cold cathode fluorescent lamp. It may be a cold cathode fluorescent lamp, or may be a straight tube type or a U-shaped or W-shaped bent lamp.

Further, the film thickness of the phosphor coating 2 is not necessarily made thicker on the ineffective light emitting surface side than on the effective light emitting surface side, and a reflection film may be formed on the ineffective light emitting surface. Since they may be present, they may have the same film thickness.

Further, the present invention is not limited to the case of using the liquid crystal display panel, but may be the case of using a normal translucent display panel.

[0038]

As described above, according to the present invention, since the cold cathode is arranged deviated to the non-effective light emitting surface side from the bulb center line, the cold cathode is on the effective light emitting surface side of the bulb and the phosphor coating. Away from the glow discharge is reduced,
It is possible to prevent the electrode material from scattering and reduce the blackening of the bulb on the effective light emitting surface side. For this reason, the luminance maintenance rate is improved and the life is extended.

[Brief description of drawings]

FIG. 1 shows an embodiment of the present invention, in which (A) is an exploded perspective view of a flat cold cathode fluorescent lamp, and (B) is a sectional view of a bulb.

FIG. 2 is a characteristic diagram showing a luminance maintenance ratio in the example.

FIG. 3 shows a conventional example, FIG. 3A is an exploded perspective view of a flat type cold cathode fluorescent lamp, and FIG. 3B is a sectional view of a bulb.

FIG. 4 is a transverse sectional view of the conventional fluorescent lamp.

FIG. 5 is a luminance characteristic diagram of the phosphor film in the conventional case.

[Explanation of symbols]

1 ... Flat bulb, 2 ... Fluorescent film, 3 ... Stem, 4 ...
Cold cathode, 20 ... Pulse lighting circuit.

Claims (4)

[Claims] 1. A cold cathode fluorescent lamp in which a phosphor film is formed on the inner surface of a bulb having cold cathodes sealed at both ends and light is emitted from an effective light emitting surface on one side of the bulb. A cold cathode fluorescent lamp characterized in that the cold cathode is arranged so as to be offset from the center line of the bulb toward the ineffective light emitting surface side. 2. The valve has a flat cross section,
The cold cathode fluorescent lamp according to claim 1, wherein one surface having a large area is an effective light emitting surface. 3. The cold cathode fluorescent lamp according to claim 1, wherein the phosphor coating has a thickness on the ineffective light emitting surface side larger than that on the effective light emitting surface side. .. 4. The cold cathode fluorescent lamp according to claim 1, wherein a pulse voltage is applied to the cold cathode.