JP2002367561A - Cold cathode fluorescent lamp - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a cold cathode fluorescent lamp starting without the existence of outside light and generating no variation of characteristics during the duration of life by making the shape of a cold cathode 3 cylindrical, forming a metal film 5 comprising an exoelectron emissive material at only the inner end part on the outer circumferential surface, and specifying a gap h to a glass bulb 1. SOLUTION: A pair of cylindrical cold cathode 3 is sealed to both end insides of the glass bulb 1. The gap h between the outer circumferential surface of the cylindrical cold cathode 3 and the inner circumferential surface of the glass bulb 1 is set so as to keep the relation of 0<h<=0.15 mm. The metal film 5 comprising the exoelectron emissive material is formed over the whole circumference of the inner end part on the outer circumferential surface. The metal film 5 comprising the exoelectron emissive material is composed of one kind of a Cs compound or a mixture of two or more kinds of Cs compounds. The forming amount of the metal film 5 is 0.1-1.2 mg.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used as a backlight or a small illuminating light source of a liquid crystal display device such as a liquid crystal television, a personal computer, a word processor and the like. The present invention relates to a cold cathode fluorescent lamp serving as a cathode, and more particularly to a cold cathode fluorescent lamp in which the structure of an internal electrode is improved in order to improve startability.

[0002]

2. Description of the Related Art In a fluorescent lamp, if there are no initial electrons in the discharge space to trigger discharge, ionization cannot be carried out smoothly, and starting is impossible or extremely difficult. The initial electrons include thermoelectrons, photoelectrons, and cosmic rays in the natural world emitted by a high electric field, but only when the fluorescent lamp is placed in a dark atmosphere without external light, which makes starting difficult. . In particular, a cold cathode fluorescent lamp in which the electrodes are cold cathodes does not have a structure that emits thermoelectrons at the time of starting, and therefore, the starting characteristics in darkness is not preferable. Various proposals have been made to improve the startability of the cold cathode fluorescent lamp. A cold cathode fluorescent lamp of this type having a characteristic in the electrode portion will be described below.

FIGS. 9 and 10 show a specific example of a cold cathode fluorescent lamp in which a Cs compound is provided on the electrode surface. First, in FIG. 9, a pair of bottomed cylindrical cold cathodes 101 are disposed and sealed inside both ends of a glass bulb 100 such that their openings face each other. Are electrically connected to each other, and are air-tightly penetrated through the end wall of the glass bulb 100 and led out to the outside. On the inner and outer surfaces of the bottomed cylindrical cold cathode 101, a metal film 103 of a Cs compound, which is an exo-electron emitting material, is formed. In FIG. 10, a cylindrical conductive member 105 is inserted and attached from the outer end side opening of a cylindrical cold cathode 104 having electrodes opened at both ends, and a lead wire 106 is electrically connected to the cylindrical conductive member 105. Connected to the glass bulb 10
No. 0 end wall (bead glass 107) is airtightly penetrated to the outside. Outer peripheral surface of cylindrical cold cathode 104, inner end surface of cylindrical conductive member 105, and cylindrical cold cathode 104
A metal film 103 of a Cs compound, which is an exoelectron emitting material, is formed on a portion of the inner peripheral surface exposed to the discharge space. The cold-cathode fluorescent lamps shown in FIGS. 9 and 10 increase the overcurrent aging and the aging time, forcibly sputter the electrode portion, blacken the inner surface of the glass bulb near the electrode, and improve the startability. ing. Also, 0.7-2.5 mg of Ca on the surface of the bottomed cylindrical cold cathode,
A metal film made of Sr, Ba, Y, La, and Ce is deposited to extend the life (see, for example, JP-A-11-120).
No. 958), and a cup-shaped second electrode section surrounding the first electrode section is provided outside the first electrode section connected to the lead wire, and the cup-shaped second electrode section is provided. A metal film made of one of Ag-Cs and Cs-Sb or a mixture thereof is formed on the inner surface of the first electrode, and the electron emission function of the second electrode is enhanced to increase the discharge current and increase the luminance. (For example, see JP-A-6-13032) or a cold cathode formed by molding a mixture of a predetermined base material and a predetermined ratio of an electron-emitting substance into a bottomed cylindrical shape Is used as an electrode to uniformly disperse an electron-emitting substance in a base material to obtain stable light emission and suppress evaporation of the electron-emitting substance to reduce the degree of blackening at the bulb end (for example, Japanese Patent Laid-Open No. 4-27210 And Japanese Patent Application Laid-Open No. H11-15064) and a material in which the porosity of the surface located on the discharge space side is higher than that of the surface on the opposite side to improve the starting characteristics. See Japanese Unexamined Patent Publication No. Hei.
Also, without improving the electrode itself, the inner surface of the glass bulb near the electrode (the inner surface of the glass bulb end near the electrode)
There is a cold cathode fluorescent lamp in which an exo-electron emitting material such as ₂ O ₃ or CaO is applied and exo-electrons are emitted as initial electrons at the time of starting (for example, Japanese Patent Laid-Open No.
-345594, JP-A-5-28961).

[0004]

Among the above-mentioned conventional cold-cathode fluorescent lamps, the cold-cathode fluorescent lamps shown in FIGS. 9 and 10 have an overcurrent aging or a long aging time in which the electrode portion is forcibly sputtered. To blacken the inner surface of the glass bulb near the electrode, the amount of light at the time of the initial drop is remarkably reduced, and the Cs compound applied to the electrode during the life is scattered. 100 characteristics
There is a problem that there is a so-called characteristic change with time during the life, that is, change within 0 hours. JP-A-11-120958
Patent Publication and the invention disclosed in Japanese Patent Application Laid-Open No. 6-13032,
Since a metal film having a high electron emission property is formed on the inner surface of the cylindrical cold cathode, there is a problem that the lamp snakes after 15 seconds of aging. In the invention disclosed in Japanese Patent Application Laid-Open No. 4-272109, a cold cathode is formed by molding a mixture of a base material and an electron-emitting substance into a cylindrical shape. Since it contains a radioactive substance, there is a problem that the lamp snakes after aging lighting. In addition, a cold cathode fluorescent lamp in which an exo-electron emitting material is coated on the inner surface of a glass bulb near an electrode does not emit electrons unless external light is present, and thus does not light well in a complete dark atmosphere and has poor reliability. There was a problem.
The present invention has been made in order to solve the above-mentioned problems of the prior art, in which an exo-electron emitting material is provided at the inner end of the outer surface of a cylindrical cold cathode, and the outer surface of the electrode and the inner surface of the glass bulb are provided. By setting the gap in a predetermined range, it is possible to provide a cold-cathode fluorescent lamp that can be started without external light and that does not change over time during life.

[0005]

In order to achieve the above object, according to the first aspect of the present invention, a phosphor film is formed on an inner surface, and a discharge medium is provided in a glass bulb having an inner diameter of φ1 to φ4 mm. And a gap is formed between the inner surface of the glass bulb and a pair of cylindrical cold cathodes disposed opposite to each other on the inner side of both ends and sealed. It is characterized in that a metal film made of an exo-electron-emitting substance is provided at the inner end of the outer peripheral surface of the cathode. The invention according to claim 2 of the present invention is characterized in that the metal film made of an exoelectron emitting substance is made of one kind of Cs compound selected from metal compounds made of Cs or a mixture of two or more kinds of Cs compounds. Features. The invention according to claim 3 of the present invention is characterized in that the amount of the metal film formed of an exo-electron-emitting substance is 0.1 to 1.2 mg. The invention according to claim 4 of the present invention is characterized in that, when a gap between the outer peripheral surface of the cylindrical cold cathode and the inner peripheral surface of the glass bulb is h, the gap h is 0 <h ≦ 0.15 mm. .

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a partially cutaway sectional view showing a main part of a cold cathode fluorescent lamp, and FIG. 2 is a sectional view taken along line AA of FIG. In these figures, the inner surface of a straight tube-shaped glass bulb 1 having an outer diameter of 2.6 mm, an inner diameter of 2.0 mm, and a total length of 320 mm and having a substantially perfect circular cross section has red, green, and blue colors.
A phosphor film 2 is formed by applying a three-wavelength phosphor obtained by mixing a red phosphor, a green phosphor, and a blue phosphor so as to have an emission peak in a wavelength region. The glass bulb 1 is filled with a rare gas such as a neon gas and an argon gas and mercury. Inside the both ends of the glass bulb 1, the distance between the electrodes is 306 mm, and the vertical distance between the outer peripheral surface of these electrodes and the inner peripheral surface of the glass bulb 1, that is, the gap h is 0 <h ≦ 0.15 mm. A pair of cylindrical cold cathodes 3 are arranged facing each other and sealed. The cold cathode 3 is
The cylindrical body is formed in a bottomed cylindrical body in which an inner end face is opened and an outer end face is closed, and a lead wire 4 is electrically connected to the outer end face. The lead wire 4 penetrates the end wall of the glass bulb 1 in an airtight manner, is led out to the outside, and is configured to be supplied with power from an external power supply (not shown). A metal film 5 made of an exo-electron-emitting substance is formed on the entire outer periphery of the cylindrical cold cathode 3 at the inner end of the outer peripheral surface. The metal film 5 made of an exo-electron-emitting substance is composed of one selected from Cs compounds.
It is composed of a kind of Cs compound or a mixture of two or more kinds of Cs compounds. The Cs compound is used because of high reactivity among all elements. As the Cs compound, for example, Cs ₂ CrO ₄ , CsCl, or the like is used. The metal film 5 made of an exo-electron-emitting substance is obtained by converting a fine powder of a Cs compound obtained by a coprecipitation method or the like into a fine powder of several μm or less, and adjusting the fine powder into a paste by a known method. 3 is formed by coating, drying and sintering the entire periphery of the inner end portion on the outer peripheral surface. In this embodiment, 0.8 mg of C per one cold cathode 3 is used.
The s compound is applied, and the Cs compound is applied in an amount of 0.1 to 1.2 mg depending on conditions such as the size of the cold cathode 3 and the like. Metal film 5 made of an exo-electron emitting material on cylindrical cold cathode 3
May be formed by vapor deposition or sputtering in addition to the above coating method.

The reason why the gap h is formed so that 0 <h ≦ 0.15 mm is that the flicker occurrence rate during the life of the lamp is reduced to 0%.
In order to keep it. FIG. 3 is a diagram showing the results of measuring the flicker occurrence rate for each length of the gap h. 25 ° C
Under the temperature environment, the inner diameter is 2.0 mm and the outer diameter is 2.6 m
m, distance between cold cathodes is 306 mm, lamp length is 320 mm,
Under the condition that the lamp current is 8 mA, the length of the gap h is 0.05
mm, 0.10mm, 0.15mm, 0.20mm,
0.25mm, 0.30mm, 0.40mm, 0.50
Using 100 cold-cathode fluorescent lamps for each mm, the flicker occurrence rate after the lighting time of 5000 hours was examined. As shown in FIG. 3, when the gap h exceeds 0.15 mm, the light is turned on 5000.
It can be seen that flickering starts to occur after a lapse of time. From these results, in the cold cathode fluorescent lamp according to the present invention, the gap h was set to 0 <h ≦ 0.15 mm.

The reason why the amount of the exo-electron emitting material applied is 0.1 to 1.2 mg per cold cathode is to shorten the discharge start delay time and to prevent the cold cathode fluorescent lamp from flickering. . FIG. 4 is a diagram showing the discharge start delay time for each application amount of the exo-electron-emitting material per cold cathode. Cs ₂ CrO ₄ was used as the exo-electron-emitting substance, and the fluorescent lamp was left in a dark atmosphere at room temperature for 96 hours. As shown in FIG. 4, when the application amount of the exo-electron-emitting substance is 0.1 mg or more, the discharge start delay time is reduced to 3.5 msec or less, and the discharge delay becomes good. FIG. 5 is a graph showing the relationship between the application amount of the exo-electron emitting substance and the flicker occurrence rate. 2.0m inside diameter
m, an outer diameter of 2.6 mm, a lamp length of 320 mm, and a lamp current of 8 mA, an experiment was carried out using 100 cold cathode fluorescent lamps for each coating amount of the exo-electroactive substance. From FIG. 5, it can be seen that when the applied amount of the exo-electron-emitting substance exceeds 1.3 mg, the flicker occurrence rate after aging becomes extremely high. From the results shown in FIGS. 4 and 5, 1
The exo-emissive substance applied to each cold cathode is 0.1
The amount of about 1.2 mg is optimal from the viewpoint of shortening the discharge start delay time of the cold cathode fluorescent lamp and preventing flicker.

In the present invention, the reason why the metal film 5 made of an exo-electron emitting substance is applied only to the inner end portion of the outer peripheral surface of the cylindrical cold cathode 3 and not applied to the inner peripheral surface is that the aging time is shortened. FIG. 6 is a diagram showing the relationship between the aging time and the relative luminance value. Inner diameter 2.0 mm, outer diameter 2.6 mm, lamp length 32
0 mm, aging current 8 mA, distance between electrodes 306 mm
The relationship between aging time and luminance was measured for a cold cathode fluorescent lamp provided with 0.8 mg of Cs ₂ CrO ₄ over the entire inner periphery of the pair of bottomed cylindrical cold cathodes. The result is indicated by A in FIG. FIG. 9 for comparison
Was measured under the same conditions for the conventional cold-cathode fluorescent lamp shown in FIG. 1, and the result is shown by B in FIG. FIG. 6 shows that the cold-cathode fluorescent lamp of this embodiment has a shorter aging time and an improved initial luminance. or,
Under a temperature environment of 25 ° C. and a lamp current of 8 mA, the lamp lighting state after 15 minutes of aging was examined. The snaking occurrence rate of the cold cathode fluorescent lamps of the examples shown in FIGS. 1 and 2 was 0%. For comparison, a cold cathode fluorescent lamp using an electrode having a metal film of Cs ₂ CrO ₄ formed on the inner peripheral surface and inner peripheral surface of the bottomed cylindrical cold cathode under the same conditions was used for aging 15. A minute later, the lamp lighting state was examined. The result is that the snake occurrence rate is 100%
Met. From the results of the snake occurrence rate and FIG. 6, it was found that it is not preferable to form a metal film of an exo-electron emitting substance on the inner peripheral surface of the bottomed cylindrical cold cathode. FIG. 7 is a characteristic diagram showing the relationship between the lighting time and the tube voltage. The test was performed under conditions of an ambient temperature of 25 ° C. and a lamp current of 8 mA. 7, the solid line is the cold cathode fluorescent lamp of this embodiment shown in FIGS. 1 and 2, the dashed line is the cold cathode fluorescent lamp shown in FIG. 8, and the dotted line is the conventional cold cathode fluorescent lamp shown in FIG. Indicates a lamp. Since the conventional cold cathode fluorescent lamp shown in FIG. 8 has a small surface area inside the electrode, the outer surface of the electrode is covered with glow, the Cs compound is scattered during the life and the tube voltage rises rapidly after about 1000 hours of lighting. In the cold-cathode fluorescent lamp of the embodiment, since the electrode surface is not covered with glow, there is no scattering of Cs, and the same tube voltage maintaining characteristics as the tube voltage of the conventional cold-cathode fluorescent lamp shown in FIG. 10 can be obtained. Therefore, it is possible to cope with long-life applications such as large monitors and televisions.

A second embodiment of the present invention will be described with reference to FIG. The cold cathode 6 has a metal film 5 made of an exo-electron emitting material all around the inner end portion of the outer peripheral surface of a cylindrical sleeve 7 made of nickel, for example, having both ends opened and having inner and outer ends having different diameters. Is formed. A gap h between the outer peripheral surface of the large-diameter portion on the inner end side of the cylindrical sleeve 7 and the inner peripheral surface of the glass bulb 1 is formed such that 0 <h ≦ 0.15 mm. A rod 8 having conductivity is inserted and fixed from the outer end side opening of the cylindrical sleeve 7. The cylindrical sleeve 7 is integrally fixed to the conductive rod 8 by means such as caulking. The conductive rod 8 is electrically connected to the lead wire 4, and is hermetically penetrated through a bead glass 9 constituting an end wall of the glass bulb 1 and is led to the outside. Other configurations are the same as those of the embodiment shown in FIGS.

[0011]

According to the present invention, since the Cs compound is provided only on the inner end of the outer peripheral surface of the cylindrical cold cathode, the startability is improved, and the start can be performed without external light. This has the effect. The aging time can be shortened, the amount of light at the time of initial increases, and the effective light emission length increases, so that there is an effect that a fluorescent lamp of a stable quality that does not change with time during the life of the lamp can be provided.
Also, the gap h between the electrode and the glass bulb is defined as 0 <h ≦ 0.1.
By setting the distance to 5 mm, there is an effect that the characteristics do not change (degrade) during the life of the fluorescent lamp.

[Brief description of the drawings]

FIG. 1 is a partially cutaway sectional view showing a main part of a cold cathode fluorescent lamp.

FIG. 2 is a sectional view taken along line AA of FIG.

FIG. 3 is a characteristic diagram showing a flicker occurrence rate with respect to a length of a gap h.

FIG. 4 is a characteristic diagram showing a discharge start delay time for each application amount of an exo-electron emitting material.

FIG. 5 is a characteristic diagram showing an application amount of an exo-electron emitting substance and a flicker occurrence rate of a lamp.

FIG. 6 is a characteristic diagram showing aging time and relative luminance.

FIG. 7 is a characteristic diagram showing a lighting time and a tube voltage.

FIG. 8 is a partially cutaway sectional view showing a main part of the cold cathode fluorescent lamp.

FIG. 9 is an explanatory diagram showing a conventional example.

FIG. 10 is an explanatory diagram showing a conventional example.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 glass bulb 2 phosphor coating 3, 6 cold cathode 5 metal film made of exo-emissive substance

Claims (4)

[Claims] 1. A phosphor film is formed on an inner surface and has an inner diameter of φ1.
A discharge medium is sealed in a glass bulb having a diameter of about 4 mm, and a gap is formed between the discharge medium and the inner peripheral surface of the glass bulb. In the cathode fluorescent lamp, a metal film made of an exo-electron emitting material is provided at an inner end of an outer peripheral surface of the cylindrical cold cathode. 2. The method according to claim 1, wherein the metal film made of the exo-electron-emitting substance is one kind of C selected from metal compounds made of Cs.
2. The cold cathode fluorescent lamp according to claim 1, comprising an s compound or a mixture of two or more Cs compounds. 3. The cold cathode fluorescent lamp according to claim 1, wherein an amount of the metal film made of the exo-electron emitting substance is 0.1 to 1.2 mg. 4. When the gap is h, the gap h is 0 <
3. The structure of claim 1, wherein h.ltoreq.0.15 mm.
Or the cold cathode fluorescent lamp according to 3.