FABRICATION METHOD OF NITROGEN DISCHARGE LAMP

Abstract

A method of fabricating a nitrogen discharge lamp includes: a first evacuation step for evacuating the gas in a glass tube, a first gas introduction step for introducing nitrogen gas into the glass tube that has undergone the first evacuation step, a preliminary discharge step for producing electric discharge in the glass tube that has undergone the first gas introduction step, a second evacuation step for evacuating the gas inside the glass tube that has undergone the preliminary discharge step, and a second gas introduction step for introducing at least nitrogen gas and a noble gas into the glass tube that has undergone the second gas introduction step.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a process chart showing an example of the fabrication method of the nitrogen discharge lamp of the present invention;

FIG. 2 is a schematic sectional view showing one step of the fabrication method of the nitrogen discharge lamp of the present invention; and

FIG. 3 is a schematic sectional view showing a step of the fabrication method of the nitrogen discharge lamp of the present invention.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENT

Explanation next regards the details regarding an example of the fabrication method of the nitrogen discharge lamp of the present invention with reference to FIGS. 1 to 3. FIG. 1 is a process chart of the fabrication method of the nitrogen discharge lamp of the present example. FIG. 2 is a schematic sectional view showing a step of the fabrication method of the present example, and FIG. 3 is a schematic sectional view showing another step.

Glass tube 2 is first prepared as shown in FIG. 2 with electrodes 1a and 1b arranged in the interior at the two opposite ends with one end already sealed in an airtight state. In FIG. 2, the left side of glass tube 2 has already been sealed in an airtight state. Electrode 1b arranged on the right side may be only provisionally secured, and the same right end may still be unsealed. In the present explanation, the left end of glass tube 2 that is already sealed at this stage is identified as the “sealed end” and the unsealed right end is identified as the “unsealed end.”

Glass tube 2 shown in FIG. 2 is set in an electric furnace (not shown), and further, the unsealed end of glass tube 2 is connected to an air intake and exhaust system (not shown), whereby unnecessary gas inside glass tube 2 is evacuated (FIG. 1: Step 1). Simultaneous with the start of Step 1, the above-described electric furnace is placed in operation to heat glass tube 2 (FIG. 1: Step 2). In other words, unnecessary gas is evacuated while glass tube 2 is being heated. This heating is for the purpose of volatilizing the unnecessary gas component contained in glass tube 2, glass tube 2 being heated to 450° C. in the present example.

When the temperature of glass tube 2 reaches 450° C., the electric furnace is turned off and glass tube 2 is allowed to cool naturally to normal temperature (room temperature) (FIG. 1: Step 3). The intake and exhaust system is then switched to gas supply, and a mixed gas (aging gas) of argon (Ar) and nitrogen (N₂) is introduced into glass tube 2 from the unsealed end (FIG. 1: Step 4). In the present example, a mixed gas in which Ar:N₂=9:1 is introduced to 20 [Torr] (≈2.666×10³ [Pa]).

Next, as shown in FIG. 3, provisional electrode 3 is formed near the unsealed end of glass tube 2 into which a prescribed amount of aging gas has been introduced. In the present example, aluminum foil is wrapped around the outside of glass tube 2 to form provisional electrode 3. A high-frequency voltage is then applied across provisional electrode 3 and electrode l a that is arranged at the sealed end of glass tube 2 to produce a discharge (preliminary discharge) inside glass tube 2 (FIG. 1: Step 5). In the present example, a high-frequency voltage is applied continuously over four hours.

After the passage of a prescribed time interval, the application of voltage between electrode la and provisional electrode 3 is halted and provisional electrode 3 is removed (FIG. 1: Step 6). The intake and exhaust system connected to the unsealed end of glass tube 2 is then again switched to exhaust, and the electric furnace is again placed in operation while the interior of glass tube 2 is being evacuated to heat glass tube 2 to a prescribed temperature (in the present example, 450° C.) (FIG. 1: Step 7). When the temperature of glass tube 2 reaches the prescribed temperature (in the present example, 450° C.), the electric furnace is turned off and glass tube 2 is allowed to naturally cool to normal temperature (room temperature) (FIG. 1: Step 8).

After the temperature of glass tube 2 has fallen to normal temperature, the intake and exhaust system is switched to a gas supply and a mixed gas (discharge gas) of argon (Ar) and nitrogen (N₂) is introduced into glass tube 2 (FIG. 1: Step 9), following which the unsealed end of glass tube 2 is sealed in an airtight state (FIG. 1: Step 10).

The method of evacuating glass tube 2 and the method of introducing the aging gas and discharge gas into glass tube 2 are equivalent to methods used in the related art, and explanation of these methods is therefore here omitted. The method of sealing the unsealed end is equivalent to methods used in the related art, and explanation of the method is therefore here omitted.

The nitrogen discharge lamp is completed by means of the procedures described hereinabove. Lighting tests carried out for the completed nitrogen discharge lamp confirmed that the continuous lighting time was longer than for a nitrogen discharge lamp of the related art. In addition, examination of a section of the tube walls of the glass tube after continuous lighting confirmed the presence of nitrides on the inner surface and within a range of depth of from several nm to ten and several nm from the inner surface. Based on these phenomena, it is believed that the absorption of nitrogen into the glass tube due to the above-described preliminary discharge prevents the absorption of nitrogen into the glass tube during lighting, whereby a lengthening of lighting time was obtained.

Further, although the step of applying a fluorescent material to the inner surface of glass tube 2 was omitted in the previous explanation and in FIG. 1, a fluorescent material was applied to the inner surface of glass tube 2 at an appropriate stage.

In the specification, explanation regarded a case in which a mixed gas of nitrogen gas and argon gas is used as the aging gas and discharge gas, but the noble gas that is mixed with nitrogen gas is not limited to argon gas and a desired noble gas such as neon gas or helium gas can also be selected. In addition, a mixed gas in which two or more types of noble gas are mixed can also be used. Still further, the aging gas may be only nitrogen gas.

Although a nitrogen discharge lamp of the internal electrode type was described as an example of an embodiment of the present invention in the present specification, the fabrication method of the present invention can also be applied to a nitrogen discharge lamp of the external electrode type. In such a case, a provisional electrode need not be provided for the preliminary discharge, and a high-frequency voltage can be applied across a pair of external electrodes provided on the exterior of the glass tube (on the surface of the outer circumference) to produce the preliminary discharge. Of course, a provisional electrode may also be provided and a high-frequency voltage may then be applied across this provisional electrode and the other external electrode to produce the preliminary discharge.

Still further, the introduction of aging gas and the preliminary discharge may be repeated a plurality of times as necessary. For example, a series of cycles can be repeated in which, after carrying out the preliminary discharge for a prescribed time interval, the interior of the glass tube is evacuated, the aging gas again introduced, and the application of voltage resumed.

Alternatively, a series of cycles can be repeated in which the current and the voltage across the electrodes during the preliminary discharge are monitored, and upon decrease of the voltage below a prescribed value (or rise of the current above a prescribed value), the interior of the glass tube is evacuated, the aging gas again introduced, and the application of voltage resumed. Because the aging gas (nitrogen gas) is absorbed into the glass tube by the preliminary discharge and thus decreases, two or more introductions of aging gas brings about the absorption of a sufficient amount of nitrogen into the glass tube and can therefore realize more effective and more reliable prevention of the absorption of nitrogen into the glass tube during lighting.

In this case, the decrease of the voltage across the electrodes (increase in current) during the preliminary discharge indicates a state in which the amount of nitrogen in the glass tube has decreased and in which the production of discharge has become easier. Accordingly, controlling the timing or the number of instances of the reintroduction of aging gas based on the voltage across the electrodes (the current) in the preliminary discharge is extremely effective as a method for bringing about absorption of a sufficient amount of nitrogen into the glass tube.

While a preferred embodiment of the present invention has been described using specific terms, such description is for illustrative purposes only, and it is to be understood that changes and variations may be made without departing from the spirit of scope of the following claims.

Claims

1. A fabrication method of a nitrogen discharge lamp for fabricating a nitrogen discharge lamp in which electrodes are arranged at the two ends of a glass tube in which at least nitrogen gas and an noble gas are enclosed, said fabrication method comprising: a first evacuation step for evacuating gas within said glass tube;a first gas introduction step for introducing nitrogen gas into said glass tube that has undergone said first evacuation step;a preliminary discharge step for producing discharge in said glass tube that has undergone said first gas introduction step;a second evacuation step for evacuating gas within said glass tube that has undergone said preliminary discharge step; anda second gas introduction step for introducing at least nitrogen gas and an noble gas into said glass tube that has undergone said second evacuation step.

2. A fabrication method of a nitrogen discharge lamp for fabricating a nitrogen discharge lamp in which electrodes are arranged at the two ends of a glass tube in which at least nitrogen gas and an noble gas are enclosed, said fabrication method comprising: a first evacuation step for evacuating gas within said glass tube;a first gas introduction step for introducing a mixed gas of nitrogen gas and an noble gas into said glass tube that has undergone said first evacuation step;a preliminary discharge step for producing a discharge in said glass tube that has undergone said first gas introduction step;a second evacuation step for evacuating gas within said glass tube that has undergone said preliminary discharge step; anda second gas introduction step for introducing at least nitrogen gas and an noble gas into said glass tube that has undergone said second evacuation step.

3. The fabrication method of a nitrogen discharge lamp according to claim 1, wherein at least one of said first evacuation step and said second evacuation step is carried out while heating said glass tube.

4. The fabrication method of a nitrogen discharge lamp according to claim 2, wherein at least one of said first evacuation step and said second evacuation step is carried out while heating said glass tube.

5. The fabrication method of a nitrogen discharge lamp according to claim 1, wherein said preliminary discharge step is carried out by applying voltage across a pair of electrodes at least one of which is arranged outside said glass tube.

6. The fabrication method of a nitrogen discharge lamp according to claim 2, wherein said preliminary discharge step is carried out by applying voltage across a pair of electrodes at least one of which is arranged outside said glass tube.

7. The fabrication method of a nitrogen discharge lamp according to claim 1, wherein said first gas introduction step and said preliminary discharge step are repeated a plurality of times.

8. The fabrication method of a nitrogen discharge lamp according to claim 2, wherein said first gas introduction step and said preliminary discharge step are repeated a plurality of times.

9. The fabrication method of a nitrogen discharge lamp according to claim 3, wherein at least one of said first gas introduction step and said second gas introduction step is carried out after the temperature of said glass tube that has been heated is lowered to normal temperature.

10. The fabrication method of a nitrogen discharge lamp according to claim 4, wherein at least one of said first gas introduction step and said second gas introduction step is carried out after the temperature of said glass tube that has been heated is lowered to normal temperature.