JPH06349406A - Formation of powder film in high-pressure discharge lamp - Google Patents

Abstract

PURPOSE:To prevent stripping, etc., by applying a mixture of power, fine-particle hydrophobic silica and low-melting-point inorganic compound on the inner surface of an outer bulb and then baking, thereby increasing adhesive strength of the film. CONSTITUTION:Powder, such as phosphor powder, in a powder supply device 1, is jetted out from tip of a powder jetting spray gun 2, so that the powder is attached electrostatically on the inner surface of an outer bulb 3, and a powder film is formed. A static electricity generating device 4 is connected to the gun 2, and the bulb 3 is grounded. To increase adhesive strength of the film, hydrophobic silica as fine particles (silica made hydrophobic by covering the surface with methyl group CH3) and a low-melting-point inorganic compound are mixed to powder, as of phosphor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a powder coating, and a powder coating such as a fluorescent substance is electrostatically applied to the inner surface of an outer bulb of a high pressure discharge lamp such as a fluorescent high pressure mercury lamp, a metal halide lamp and a high pressure sodium lamp. The present invention relates to improvement of a powder film forming method applied by a coating method.

[0002]

2. Description of the Related Art A powder coating method for forming a powder coating such as a phosphor on the inner surface of an outer bulb of a fluorescent high pressure mercury lamp is generally a wet method as shown in FIG. A coating liquid consisting of powder such as a phosphor, a solvent, and an adhesive is stored in the coating liquid tank 11, and pressure is applied to the coating liquid to open / close the valve 1.
2. The coating liquid 15 is sprayed onto the inner surface of the outer bulb valve 14 through the nozzle 13, and then the outer bulb valve 14 is ejected as shown in FIG.
The inner surface of is dried by the hot air 17 through the hot air nozzle 16 to form the powder coating film 18. In general, butyl acetate / nitrocellulose or xylene / ethylcellulose is used as the above solvent and adhesive. According to the above method, since the solvent is used, it is possible to form a powder coating having a large adherence. However, when an organic solvent is used, there are problems that it is highly flammable and harmful to the human body, and that it is expensive.

[0003]

In order to solve this,
An electrostatic coating method has been developed in which powder such as phosphor is directly attached to the inner surface of the outer bulb. This is as shown in Figure 1.
Powder such as phosphor in the powder supply device 1 is sprayed from the tip of the powder spray gun 2 and electrostatically adhered to the inner surface of the outer bulb valve 3 to form a powder coating. . An electrostatic generator 4 is connected to the powder spray gun 2,
The outer bulb valve 3 is grounded. In addition, 5 is a burner for heating a valve. In this method, fine particles of silica, alumina, etc. may be mixed in order to improve the fluidity of the powder. According to this method, since no organic solvent is used, the problems of flammability, influence on the human body, and high price are solved.
However, the powder coating on the inner surface of the outer bulb produced by this method has a drawback that it is inferior in adherence to the wet method and is easily peeled off.

The present invention has been made in view of the above, and provides a method for forming a powder coating film of a high pressure discharge lamp, which has a high coating strength and does not peel off in the method of forming a powder coating film by an electrostatic coating method. The purpose is to

The powder film forming method according to the present invention is characterized in that a mixture of powder such as phosphor and fine particles of hydrophobic silica and a low melting point inorganic compound is applied to the inner surface of the outer bulb by electrostatic coating. And Further, the low melting point inorganic compound is B ₂ O ₃
And H ₃ BO ₃ . Further, the low melting point inorganic compound is powder glass having a softening point of 300 to 700 ° C.
Characterized in that it is a _{2 O · ZnO · B 2 O} 3 · SiO 2 based glass powder.

[0006]

In order to increase the adhesion strength of the coating, fine particles of hydrophobic silica (hydrophobic silica whose surface is coated with methyl group CH ₃ ) and a low melting point inorganic compound are added to powder such as phosphor. The above objects can be achieved by mixing.

There are two methods for evaluating the adherence of the powder coating. The first is the strength (blowing strength) with respect to the gas filling of the outer bulb during the manufacture of the discharge lamp, and the second is the strength with respect to foreign matter (foreign body strength) when foreign matter enters the outer bulb. . In the method according to the present invention, since the fine particles of hydrophobic silica are mixed with the powder, the flowability of the powder is improved and a good coating film is obtained, and a bond due to the decomposition of methyl groups occurs during film firing. The spray strength is improved. Further, since the low melting point inorganic compound is mixed in the powder coating, the low melting point inorganic compound is melted or softened during firing of the coating, whereby the powder and the glass surface adhere to each other and the foreign matter strength is improved.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. The electrostatic coating apparatus according to the present invention is as shown in FIG. 1, in which powder such as phosphor in the powder supply apparatus 1 is sprayed from the tip of the powder spray gun 2, and the powder is injected into the outer bulb valve. 3 is electrostatically adhered to the inner surface of 3 to form a powder coating.
An electrostatic generator 4 is connected to the powder spray gun 2, and the outer bulb valve 3 is grounded. In addition, 5 is a burner for heating a valve.

Next, a comparative experiment between the lamp according to the present invention and the conventional lamp will be described. Tables 1 and 2 show the results of investigating the spraying strength and foreign matter strength with respect to the type of silica mixed in the powder and the mixing amount of the low melting point inorganic compound.
Here, the finely divided hydrophilic silica is Nippon Aerosil Co., Ltd.
Aerosil 200 manufactured by Nippon Aerosil Co., Ltd. and Aerosil R972 manufactured by Nippon Aerosil Co., Ltd. are used as the fine particle hydrophobic silica, and the amount of silica mixed is 2.5 wt%. Also, powdered glass has a softening point of 560 ° C. of Na ₂ O.ZnO.B ₂ O.
₃ · SiO ₂ powder glass (Nippon Electric Glass Co., Ltd. powder glass GA12) is used.

Then, the coating is measured by measuring the mixed powder with 0.8 to
The film was applied to the outer bulb bulb (BT116) with a film thickness of 1.2 mg / cm ² by electrostatic coating and baked at 600 ° C. for 5 minutes. The spraying strength for evaluating the adherence of the coating was measured by spraying N ₂ gas for 0.2 seconds from a distance of 10 mm from the coating surface and measuring the maximum diameter of the peeled portion. Further, the foreign matter strength for evaluating the adherence of the coating is measured by inserting a 0.2 g metal piece (20 mm × 5 mm) into the valve and scratching the film when the valve is rotated sideways. Whether done or not.

[0011]

[Table 1]

[0012]

[Table 2]

As is clear from Table 1, in the lamp without silica and the lamp in which hydrophilic silica is mixed, in order to satisfy the spraying strength, the mixing amount of the low melting point inorganic compound must be 20 wt% or more. On the other hand, the lamp mixed with the hydrophobic silica has good spraying strength regardless of the mixing amount of the low melting point inorganic compound. Also, Table 2
As is apparent from the above, the strength of the foreign matter is good if the low-melting inorganic compound is mixed in an amount of 1 wt% or more, regardless of the presence or absence of silica and the type. From the above, if a mixture of powder such as a phosphor and fine particles of hydrophobic silica and a low melting point inorganic compound is applied to the inner surface of the outer bulb by electrostatic coating, both the spraying strength and the foreign matter strength are improved. Recognize.

Next, Table 3 shows the results of investigating the spraying strength and foreign matter strength with respect to the types of silica and low melting point inorganic compound mixed in the powder. Here, the amount of silica mixed is 2.5 wt% and the amount of low-melting inorganic compound is 2.0 wt%.
%, And other conditions are the same as in the above experiment. As is clear from Table 3, when the fine particles of hydrophobic silica and the low melting point inorganic compound are mixed with the powder such as the phosphor, the spraying strength and the foreign matter strength are both good.

[0015]

[Table 3]

In the above experimental example, B ₂ O ₃ was explained as the low melting point inorganic compound, but H ₃ BO ₃ or powdered glass having a softening point of 300 to 700 ° C., especially a softening point of 5
Almost the same effect was observed for powder glass of Na ₂ O.ZnO.B ₂ O ₃ .SiO ₂ system at 60 ° C.

[0017]

As is apparent from the above description, the method for forming a powder coating film according to the present invention is an outer bulb valve in which a mixture of powder and fine particles of hydrophobic silica and a low melting point inorganic compound is electrostatically coated. Since it is applied to the inner surface and fired, there are advantages that the adherence of the coating (spraying strength and foreign matter strength) is good, and peeling of the coating does not occur.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an example of an electrostatic coating device according to the present invention.

FIG. 2 is an explanatory view showing a conventional coating device.

FIG. 3 is an explanatory view showing a drying process of the conventional coating device.

[Explanation of symbols]

 1 Powder Supply Device 2 Powder Spray Gun 3 Outer Ball Valve 4 Electrostatic Generator 5 Valve Heating Burner 11 Coating Liquid Tank 12 Open / Close Valve 13 Nozzle 14 Outer Ball Valve 15 Coating Liquid 16 Hot Air Nozzle 17 Hot Air 18 Powder Film

Claims (5)

[Claims] 1. A method for forming a powder film of a high pressure discharge lamp, which comprises applying a mixture of a powder such as a phosphor and fine particles of hydrophobic silica and a low melting point inorganic compound to the inner surface of an outer bulb by an electrostatic coating method. 2. The method for forming a powder coating of a high pressure discharge lamp according to claim 1, wherein the low melting point inorganic compound is B ₂ O ₃ . 3. The method for forming a powder coating of a high pressure discharge lamp according to claim 1, wherein the low melting point inorganic compound is H ₃ BO ₃ . 4. The softening point of the low melting point inorganic compound is 300.
The method for forming a powder film of a high-pressure discharge lamp according to claim 1, wherein the powder glass is a glass having a temperature of from to 700 ° C. 5. The low melting point inorganic compound is Na ₂ O.Zn
The method for forming a powder film of a high pressure discharge lamp according to claim 1, wherein the powder film is an O.B ₂ O ₃ .SiO ₂ powder glass.