JPS5968165A - High pressure sodium lamp - Google Patents

Abstract

PURPOSE:To obtain highly-heat-insulating heat-protecting films which are formed easily and in which any cracks and separations are prevented by heating an alumina emission tube after a suspension composed of colloidal solution of a metal oxide, aluminosilicate glass powder, and the like is applied to the outer surfaces of the end sections of the emission tube. CONSTITUTION:An emission tube 3 is made of polycrystal alumina and charged with 4mg sodium, 11mg mercury and xenon gas at 40Torr. Electrodes are installed at the ends of the emission tube 3. White heat-protecting films 4 are formed on the outer surfaces of the end sections of the emission tube 3. The heat-protecting films 4 are about 0.3mm. in thickness and formed by preparing a suspension, then applying the suspension to the outer surfaces of the end sections of the emission tube 3, followed by sintering it at 500 deg.C in an atmosphere of argon; the suspension is prepared by mixing 100g of zirconium oxide which has a grain diameter of 1mu and is used as a white heat-resisting powder, 100g of alumina sol which contains 25wt% aluminum oxide and is used as colloidal solution of a metal oxide, and 20g of alminosilicate glass.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a high-pressure sodium lamp, and particularly to a thermal protection film for keeping the coldest point of the arc tube warm.

Conventional structure and its problems High-pressure sodium lamps, in which buffer gas metals such as sodium and mercury and starting inert gas are sealed in an arc tube made of alumina, are highly efficient and have become energy-saving for a long time. It is attracting attention as a suitable lamp. In particular, high-pressure sodium lamps with improved color rendering properties, such as those shown in Japanese Patent Publication No. 50-34871, are said to have a light color similar to that of a light bulb and to increase the saturation of illuminated objects. Due to its unique features, it is attracting attention as a new light source that can replace low-efficiency light bulbs.

The arc tube of a high-pressure lithium lithium lamp with improved color rendering has a thermal protection film attached to the outer wall of its end in order to increase the temperature at its coldest point.

The thermal protection film that has traditionally been used is metal foil, but
Since it takes a relatively long time to install, it is not necessarily the best method.

As shown in Japanese Patent Application Laid-Open No. 57-53059, in a lamp having a structure in which the ends of the arc tube are narrower than the center, there is a problem in that it is difficult to attach the metal foil. Incidentally, in metal halide lamps and the like, white powder is attached to the end of the arc tube made of glass, but if one inch of that powder is used in an arc tube made of alumina, there is a problem that it will peel off during the movement.

OBJECTS OF THE INVENTION The present invention aims to provide a high-pressure sodium lamp in which a heat-retaining film is formed on the outer end wall of an arc tube made of alumina, which is easy to produce, has no cracks or peeling, and has good workability. This is the purpose.

Structure of the Invention The present invention involves applying a suspension consisting of a white powder, a colloidal solution of metal oxide, and aluminosilicate glass powder to the outer end wall of an arc tube made of alumina, and reducing the softening point of the aluminosilicate glass. In order to avoid heating to low temperatures, a thermal protective film is formed on the outer wall of the end of the arc tube without being fused.
Both objectives have been fully realized.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 shows a high-pressure sodium lamp that is an embodiment of the present invention. In the figure, 1 is an outer tube, 2 is a stem wire, and 3 is an arc tube. This arc tube 3 has a diameter of 9.6 mm and a total length of 54 mm. A colored thermal protection film 4 is formed from polycrystalline alumina. This thermal protection film 4 was formed as follows. That is, 100 g of zirconium oxide with an average menarche of 1 μ as a grain heat-resistant white powder, 100 g of alumina sol containing 26% by weight of aluminum oxide as a colloidal solution of metal oxide, and 20 g of aluminosilicate glass were mixed together to prepare a suspension. After this was applied to the outer wall of the end of the arc tube, it was fired at a temperature of 50° C. in an argon atmosphere to form a thermal protection film 4 with a thickness of about 0.3 mm.

A getter 6 maintains the vacuum inside the outer tube 1.

6 is a cap.

A lamp with this configuration was turned on continuously at an input of 150W, turned on for 30 minutes and then turned off for 30 minutes.The lamp was turned on and the changes during operation (9000 hours and 2000 times) were investigated, but cracks in the thermal protection film and arc tubes were detected. No peeling occurred from No. 3.

Here, the reason why cracks did not occur in the thermal protection film was that the above suspension was applied to the outer end wall of the arc tube made of alumina and heated to a temperature lower than the softening point of aluminosilicate glass. Therefore, the thermal protection film could be formed without being fused to the outer wall of the end of the arc tube. If fusion occurs, cracks will occur in the thermal protection film due to the difference in thermal expansion coefficient between alumina and aluminosilicate glass.

Unfortunately, the rise in lamp voltage was the same as with the thermal protection film made of a metal cylinder. Furthermore, the changes during the movement of the getter 4 are almost the same as in the lamp when metal T3'ff is used, so it can be concluded that no abnormal gas was generated from thermal protection.

”-, the case where the weight ratio of zirconium oxide and aluminosilicate glass powder was 100=20 was explained, but the same effect could be obtained if this weight ratio was in the range of 93 nia to 66:35. .

Figures 2(a) and (b) show other embodiments of the present invention-1
-L, the shape of the arc tube 3 made of alumina is different from that shown in FIG. The thermal protection film 4 was formed in the same manner as in the above.

According to the present invention, a thermal protection film can be easily formed even on such a specially shaped arc tube.

Although zirconium oxide was used as the white powder in the above embodiment, the same effect can be obtained by using alumina, silica, magnesia, or the like.

Further, as the colloidal solution of the metal oxide, not only alumina sol but also silica sol and the like can be used.

DETAILED DESCRIPTION OF THE INVENTION As described in detail, the present invention involves applying a suspension consisting of a white powder, a colloidal solution of a metal oxide, and aluminosilicate glass powder to the outer wall of the end of an arc tube; By heating to a temperature lower than the softening point (915°C) and forming a thermal protective film, it has good heat retention, no cracks, no peeling from the arc tube, and the outer wall of the end of the arc tube. It is possible to provide a high-density thorium lamp that is equipped with an excellent thermal protection film that is easy to form.

[Brief explanation of the drawing]

FIG. 1 is a front view of a high-pressure sodium lamp according to one embodiment of the present invention, and FIGS. 2(a) and 2(b) are front views of essential parts of high-pressure sodium lamps according to other embodiments of the present invention. 1...Outer tube, 2...Stem wire, 3...
... Arc tube, 4 ... Thermal protection film, 5 ...
・Ge, ri, 6...Base. Name of agent: Patent attorney Toshio Nakao and 1 other person 1st
Figure 2

Claims (1)

[Claims] A suspension consisting of white powder, a colloidal solution of metal oxide, and aluminosilicate glass powder is completely applied to the outer end wall of an arc tube made of alumina, and heated at a temperature lower than the softening point of the aluminosilicate glass. A high-pressure sodium lamp characterized in that it has a thermal protection film formed by.