JPH0140458B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for forming a phosphor layer on the inner surface of a bulb of a fluorescent lamp, mercury lamp, or the like.

Conventionally, in order to form a phosphor layer on the inner surface of a glass bulb such as a fluorescent lamp or mercury lamp, the phosphor and phosphor adhesive powder are first dispersed in a lacquer in which an organic binder is dissolved in water or an organic solvent. The method is to prepare a phosphor coating liquid, apply it to the inner surface of the bulb, dry the solvent, form a phosphor coating, and then sinter it to burn off the organic binder remaining in the coating. It is being said. However, such conventional methods require a large amount of equipment for the drying process and the firing process, and there are problems in that they require a huge amount of thermal energy.

In order to solve this problem and save energy in the manufacturing process of fluorescent lamps and the like, various so-called electrostatic powder coating methods have been studied in recent years, in which phosphor powder is applied using static electricity. This method (1) does not require a coating liquid preparation process because it directly applies the phosphor powder, (2) does not require a drying process because it does not use a solvent, and (3) does not require a baking process because it does not use an organic binder. It has the advantage that it is unnecessary, but on the other hand, it has the disadvantage that the adhesion of the phosphor is weaker than that of the solvent method.

On the other hand, phosphor powders generally used in fluorescent lamps have a fairly large average particle size of 5 to 10 microns, and have a high specific gravity of 3 to 5. It tends to fall off easily. Therefore, for the purpose of increasing adhesion, a phosphor layer is usually formed by mixing an inorganic substance such as fine aluminum oxide powder or barium borate into phosphor powder. However, in the case of a solvent coating method, the phosphor and the phosphor adhesive can be mixed sufficiently uniformly by stirring during the coating liquid preparation process, but in the case of a powder coating method, the powders are mixed together, so it is difficult to achieve uniform mixing. Even if they are mixed uniformly, the phosphor and adhesive tend to separate due to the transport of air flow during coating, so the formed phosphor layer is free from contamination with the phosphor adhesive. The concentration becomes non-uniform and sufficient adhesion strength cannot be obtained, so a decrease in adhesion strength compared to the solvent method is unavoidable.

The present invention has been made to improve the above-mentioned drawbacks, and aims to provide a method for forming a phosphor layer having sufficient adhesion strength using an electrostatic powder coating method.

In the present invention, after charging the phosphor powder and applying it to the inner surface of the bulb, a boric acid aqueous solution is sprayed onto the phosphor layer in the form of a mist, and then the bulb is heated to remove moisture in the phosphor layer. It is characterized by the following.

The present invention will be explained below based on examples.

Antimony and manganese-activated calcium halophosphate phosphor is sprayed from an electrostatic powder coating nozzle to which a voltage of 70KV is applied, and coated on the inner surface of a 32mmφ 20W fluorescent lamp bulb. Next, a boric acid aqueous solution having a concentration of 3% by weight is atomized using an ultrasonic atomizer and is blown into the bulb to adhere to the phosphor coated thereon.
The attached boric acid aqueous solution penetrates between the laminated phosphor particles by capillary action and is uniformly adsorbed onto the entire coated phosphor. The amount of boric acid injected should be adjusted to 0.3cc per bulb. Next, the bulb is heated to about 400°C to remove the moisture adsorbed on the phosphor. In this process, the boric acid adsorbed on the surface of the phosphor particles is dehydrated and becomes boric anhydride (boron oxide).
In the process, it melts and strengthens the adhesion between the phosphor particles and between the phosphor and the glass surface.

The phosphor layer thus obtained had adhesion strength equivalent to that of a phosphor layer formed by a conventional solvent method. In the above examples, there is a correlation between the adhesion strength, the concentration of the boric acid aqueous solution, and the adsorbed amount, and the higher the concentration and the larger the adsorption amount, the better the adhesion strength. Since the addition of an agent can only be a negative factor for the luminous efficiency of the phosphor and not a positive factor, the amount added should be kept to the minimum necessary amount. In the present invention, boric acid (finally in the form of boron oxide)
The amount of boron oxide acting as a phosphor adhesion enhancer is approximately the same as in the above example, that is, the amount of boron oxide ultimately remaining in the phosphor is approximately 0.3% by weight.

As described above, the present invention sprays a boric acid aqueous solution atomized by an ultrasonic fog generator onto a phosphor layer applied electrostatically, and then removes water in the phosphor layer. Therefore, it is possible to form a phosphor layer with sufficient adhesion strength even when using a powder coating method using static electricity.

Claims (1)

[Claims] 1. A step of electrostatically applying a charged phosphor powder to the inner surface of a glass tube, and blowing a boric acid aqueous solution into the glass tube in the form of a mist using an ultrasonic fog generator, and turning the boric acid aqueous solution into a phosphor. A method for forming a phosphor layer, comprising the steps of adsorption, and then heating a glass tube to remove moisture in the phosphor layer.