JP2003045329A - Forming method of phosphor coating for cold cathode discharge tube, cold cathode discharge tube and lighting system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of applying an even phosphor coating by preventing residual liquid at the lower end of a glass tube or an uneven coating toward the circumferential direction of the glass tube or of a wind ripple pattern, a cold cathode discharge tube made of this glass tube emitting light with stable optical characteristics and also a lighting system using the discharge lamp emitting light with uniform brightness. SOLUTION: Fluorescent liquid 3, composed of a mixture of fluorescent particles of red, blue and green with a solvent, with relative gravity of 1.3 to 1.6 and viscosity of 9.8 to 161.7 mPa.s at least at 30 deg.C or higher is sucked upwards into a glass tube 1 held upright, and is let to go down naturally after the sucking operation is stopped, to complete application of a fluorescent film.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cold cathode discharge tube used, for example, as a light source for a lighting device of a liquid crystal display device,
In particular, the present invention relates to a method for forming a fluorescent coating formed on the inner surface of a glass tube, a cold cathode discharge tube using a glass tube on which a fluorescent coating is formed, and an illumination device using the same.

[0002]

2. Description of the Related Art In recent years, as is well known, cold cathode discharge tubes have been used as a light source for backlights of liquid crystal display devices used in personal computers and the like, and such cold cathode discharge tubes have particularly high brightness, low power consumption, Further, since the lighting start voltage is low, it is widely used in liquid crystal display devices.

As shown in FIG. 6, the discharge tube 7 is constructed by sealing metal bodies 9 and 11 of, for example, a tungsten metal material at both ends of a glass bulb 8 through bead glasses 14 and 15, and further, inside the glass bulb. Metal bodies 9 and 11 located in one direction
Electrodes 10 and 12 of a sintered metal obtained by sintering a metal powder of tungsten or hafnium or a mixture thereof or a hollow metal of nickel or niobium are attached to the tip of the glass bulb 8, and a fluorescent coating 22 is formed on the inner surface of the glass bulb 8. In addition, a mixed rare gas such as neon or argon is enclosed in the interior 13 and mercury is diffused and enclosed.

As a method for applying a fluorescent coating on the inner surface of the glass bulb 8, the method described in JP-A-8-281177 is known. As shown in FIG. 7, the method for applying the fluorescent coating described in the publication discloses that the lower end of the glass tube 1 is immersed in a fluorescent liquid 3 in which a fluorescent substance, a binder and a solvent are mixed in a container 2 and vacuum is applied. By operating the pump 26 and the electromagnetic valve 25, the pressure inside the glass tube 1 is reduced via the pressure reducing valve 24 and the suction head 5. When the inside of the glass tube 1 is decompressed, the fluorescent liquid 3 in the container 2 rises inside the glass tube, and when the fluorescent liquid surface reaches a predetermined height, the liquid level detection sensor 23 detects the fluorescent liquid surface and the solenoid valve 25 Is blocked to reduce the degree of vacuum in the glass tube 1 and allow the fluorescent liquid to descend naturally. Then, the applied fluorescent coating is dried and then baked at a high temperature to form the fluorescent coating.

[0005]

The fluorescent liquid is prepared in consideration of the light characteristics of the discharge tube, but red, blue and green fluorescent particles, liquid such as butyl acetate and ethyl alcohol, and nitrocellulose as an adhesive are used. It is made by mixing with a solvent consisting of, and is prepared to have an appropriate viscosity by adjusting the weight ratio of the total weight of the phosphor particles and the solvent. The viscosity of the fluorescent liquid is determined in consideration of the thickness of the fluorescent coating when applied on the inner surface of the glass tube. Further, it is preferable that the coating film of the fluorescent liquid applied to the inner surface of the glass tube is applied to a uniform thickness. Therefore, in the above method, in order to apply the fluorescent coating with the thickness of the fluorescent coating for ensuring the brightness required for the fluorescent discharge tube, the specific gravity of the fluorescent liquid needs to be 1.35 or more. However, if the glass tube 1 is a thin tube having an inner diameter of 2.0 mmφ, liquid pooling at the lower end of the glass tube 1 or film unevenness in the circumferential direction or in a wind pattern occurs, and it becomes difficult to uniformly apply the fluorescent coating. In order to prevent this, the specific gravity of the fluorescent liquid 3 may be reduced to less than 1.35, but if this is done, the coating amount of the fluorescent coating is remarkably reduced and the thickness of the fluorescent coating 22 becomes thin, resulting in a decrease in brightness. As a countermeasure, it is necessary to thicken the fluorescent coating 22 by repeatedly applying it, for example, by applying the first time and then turning the glass tube 1 upside down and applying the second time by the above method, but the application process becomes complicated. As a result, the work efficiency may decrease and the fluorescent coating applied earlier may come off during subsequent application.

Further, if the fluorescent coating 22 is manufactured as a non-uniform product, the light characteristics such as brightness and color temperature of the cold cathode discharge tube become unstable, and a lighting device using the same also emits light with uniform brightness. There is a drawback that the product value cannot be released because it cannot be released.

The present invention has been made in view of the above-mentioned conventional problems, and is a method for applying a uniform fluorescent coating while preventing liquid pool at the lower end of a glass tube and circumferential or wind pattern unevenness. An object of the present invention is to provide a cold cathode discharge tube that emits light with stable light characteristics and a lighting device that can emit light with uniform brightness by using a glass tube having a uniform fluorescent coating by the method.

[0008]

The features of the present invention as a method for forming a fluorescent film for solving the above problems are as follows:
Blue and green phosphor particles are mixed with a solvent and the specific gravity is 1.3 to
1.6, suction the fluorescent liquid that has a viscosity of 9.8 to 161.7 mPa · sec and at least 30 ° C. or higher into the upright glass tube, and naturally lower it after stopping the suction operation to apply the fluorescent coating. It is in.

A feature of the cold cathode discharge tube is that a glass tube having a fluorescent coating formed by the fluorescent coating method according to claim 1 is used, and it is possible to emit light with stable light characteristics. I can.

Further, a feature of the illuminating device is that by using the cold cathode discharge tube according to claim 2 as a light source, it is possible to emit light of uniform brightness and color temperature.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic sectional view showing a method of applying a fluorescent liquid similar to that illustrated in the above-mentioned conventional example. The same members as those in the above-mentioned conventional example are designated by the same reference numerals, a liquid level detecting sensor 23, and a pressure reducing valve. 24, the solenoid valve 25, and the vacuum pump 26 are omitted in the drawing.

As shown in FIG. 1, the lower end of the glass tube 1 is dipped in the fluorescent liquid 3 in the container 2 whose temperature is adjusted by heating with a heater 4 or the like, and the vacuum pump 26 and the electromagnetic valve 25 are operated to reduce the pressure. The pressure inside the glass tube 1 is reduced via the valve 24 and the suction head 5. When the inside of the glass tube 1 is decompressed, the fluorescent liquid 3 in the container 2 rises, and when the fluorescent liquid surface reaches a predetermined height, the liquid level detection sensor 23 detects the fluorescent liquid surface and shuts off the electromagnetic valve 25. Then, the degree of vacuum in the glass tube 1 is lowered and the fluorescent liquid is allowed to fall naturally to apply a fluorescent coating to the inner surface of the glass tube 1.

The fluorescent liquid 3 is made of a mixed liquid of red, blue and green phosphor particles, a liquid such as butyl acetate or ethyl alcohol, and a solvent composed of nitrocellulose.

The fluorescent liquid 3 used in the method for coating a fluorescent coating of the present invention has a specific gravity of 1.3 to 1.
6, the viscosity is 9.8 to 161.7 mPa · sec, and the temperature of the liquid heated by the heating element of the heater 4 is 3
The temperature is preferably 0 ° C. or higher, and under these conditions, a fluorescent film having a uniform and required thickness can be applied and formed.

Actually, the specific gravity of 1.2, 1.
3, 1.4, 1.5, 1.6, 1.7, viscosity at room temperature is 3.3, 9.8, 67.7, 161.7, 366.3 m
Fluorescent solutions with a combination of Pa · s are prepared and applied to glass tubes at 25 ° C, 30 ° C, 35 ° C and 40 ° C, respectively.
The total length is 250 mm and the inner diameter is 4.0, 3.0,
It was applied to five types of glass tubes of 2.0, 1.6 and 1.2 mmφ, and the application state of the fluorescent coating was confirmed with a magnifying lens.

At this time, the specific gravity of the fluorescent liquid is 1.3 to
1.6, the viscosity is 9.8 to 161.7 mPa · sec, and if the temperature is 30 ° C. or higher, the thickness of all glass tubes with an inner diameter of 4.0 to 1.6 mmφ is set. It was possible to secure a material with sufficient brightness and to apply it uniformly.

By the way, if the specific gravity is 1.2 or 1.7, it is difficult to obtain a desired thickness even if the viscosity is adjusted,
Further, when the viscosity was too low or too high, it was not possible to secure a sufficient fluorescent coating in terms of thickness and uniform application.

When the fluorescent coating is applied by the method as described above, the fluorescent coating 6 having a uniform thickness and no film unevenness as shown in FIG. It can be obtained with a sufficient thickness.

FIG. 3 shows a cold cathode discharge tube 7 using the glass tube 1 on which the uniform fluorescent coating 6 as shown in FIG. 2 is formed by the method shown in FIG.

4 and 5 show an illuminating device using the cold cathode discharge tube shown in FIG. In such an illuminating device, the light emitted from the discharge tube 7 is incident from the side surface of the translucent light guide body 16 made of a resin material, and is disposed below the light guide body 16 and has a light reflecting surface made of a metal or a resin material. After the light is reflected by the light reflection plate 17, the light is incident again, and the light direction is controlled by the light control member including the light diffusion plate 18 and the prism sheet 19 arranged above the light guide body 16, and the light is emitted from above. It is a thing. Reference numeral 20 denotes a light reflector that reflects the light emitted from the discharge tube 7 so as to efficiently enter the light guide 16, and reference numeral 21 denotes an upper surface of the light guide 16.

In the present embodiment, after the fluorescent liquid is sucked, the fluorescent liquid is allowed to fall naturally, but air may be introduced from above the glass tube to smoothly discharge the fluorescent liquid from the glass tube.

[0023]

As described above, according to the present invention, the specific gravity of the fluorescent liquid composed of the mixed liquid of the phosphor particles and the solvent is 1.3 to 1.6,
Fluorescent liquid with viscosity of 9.8 to 161.7 mPa · sec at 30 ° C
By applying while maintaining the temperature above, it is possible to prevent the film unevenness of the fluorescent film and obtain a uniform fluorescent film while obtaining the required film thickness. In the cold cathode discharge tube using the glass tube on which the uniform fluorescent coating is formed by such a method, the fluorescent coating is uniformly applied, so that the optical characteristics are stable. Further, an illuminating device using a cold cathode discharge tube on which a uniform fluorescent film is formed by such a fluorescent film forming method can emit light with uniform brightness, and the commercial value is improved.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing a method for applying a fluorescent coating in a method for forming a fluorescent coating on a cold cathode discharge tube according to the present invention.

FIG. 2 is a sectional view of a glass tube of a cold cathode discharge tube according to the present invention, which is formed by applying a uniform fluorescent coating to the glass tube.

FIG. 3 is a sectional view of a cold cathode discharge tube using a glass tube coated with a fluorescent coating by the method for forming a fluorescent coating of the present invention.

FIG. 4 is a schematic cross-sectional view of a lighting device using the cold cathode discharge tube of the present invention.

5 is a schematic top view of the illumination device according to FIG.

FIG. 6 is a cross-sectional view of a conventional cold cathode discharge tube.

FIG. 7 is a schematic view of an apparatus for applying a fluorescent coating on a glass tube of a conventional cold cathode discharge tube.

[Explanation of symbols]

1 glass tube 2 containers 3 Fluorescent liquid 4 heater 5 suction head 6 Fluorescent film 7 Cold cathode discharge tube 8 glass bulbs 9, 11 Sealed metal body 10, 12 electrodes 13 Inside of cold cathode discharge tube 16 Light guide 17 Light reflector 18 Light diffuser 19 prism sheet 20 light reflector 23 Liquid level sensor 24 Pressure reducing valve 25 solenoid valve 26 Vacuum pump

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) H01J 61/42 H01J 61/42 L // F21Y 103: 00 F21Y 103: 00 F term (reference) 4D075 AB05 AB36 AB51 AB54 BB22Y BB24Z BB28Z CA21 CB09 DA15 DA19 DB13 DC24 DC25 EA07 EA10 EB52 EB60 EC11 EC52 5C028 EE02 EE15 5C043 AA13 BB04 CC09 CC16 CD01 DD28 EA19 EB02 EC16 EC17 EC18 EC20

Claims (3)

[Claims] 1. A fluorescent liquid, which is a mixed liquid of phosphor particles and a solvent, is raised above the inside of the glass tube, and then the fluorescent liquid is discharged from below the glass tube to apply a fluorescent coating to the inner surface of the glass tube. Then, in the method of forming a fluorescent coating of a cold cathode discharge tube using the glass tube obtained by drying and firing this fluorescent coating, the fluorescent liquid has a specific gravity of 1.3 to 1.6,
The viscosity at room temperature is 9.8 to 161.7 mPa · sec, and the temperature when the glass tube is raised upward is at least 3.
A method for forming a fluorescent coating on a cold cathode discharge tube, which is maintained at a temperature of 0 ° C or higher. 2. A glass tube having a fluorescent film formed by the method for forming a fluorescent film according to claim 1, a metal body sealed at both ends of the glass tube, and a metal body located inside the glass tube. A cold cathode discharge tube comprising an electrode attached to a tip portion, a rare gas sealed in the glass tube, and mercury diffused and sealed in the glass tube. 3. The cold cathode discharge tube according to claim 2, a light reflector that reflects light emitted from the cold cathode discharge tube, and light emitted from the cold cathode discharge tube is incident on the upper surface of the cold cathode discharge tube. Illumination including a light guide that emits light, a light reflection plate that is arranged on the lower surface of the light guide surface, and a light control member that is arranged on the upper surface of the light guide and optically controls the light emitted from the light guide. apparatus.