JPH0451449A - Low pressure discharge lamp - Google Patents

Abstract

PURPOSE:To prevent a low pressure discharge lamp, in which alternate discharge is made by the use of a coil-form anode electrode, from unintentional extinction due to premature blackening of the bulb or rise of the re-arc voltage by specifying the weight of the first turn at the tip of the anode coil. CONSTITUTION:A discharge lamp concerned 1 is equipped with a U-form light emitting tube 2, and its anode electrode 4 is formed from a circular two-layer coil. A cathode 5 is made in such an arrangement that the filament axis intersects perpendicularly to the bulb axis, and is located back of the tip of the anode 4, which is connected with one of the leads 6 in connection with the cathode 5. Rectangular waves are flowed between the anode on one end and the cathode on the other end in inverted waveforms alternately, and lighting-up is made through repetition of discharging at each reversal of the polarity. If the power of this lamp is represented by PKW, the weight Mg of a W wire at its first turn at the tip of the anode coil is set as 0.6<=M/P<=20. A decrease in this weight M will lessen the thermal capacity for the corresponding portion to cause temp. rise, which brings about sputter of the wire substance. An increase in the weight should enlarge the thermal capacity, and the anode temp. does not sink during the off period of polarity judgement, and an ion barrier is formed on the facade of the anode to hinder the function.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a low-pressure discharge lamp used as a light source for ultraviolet photochemical reactions and the like.

(Prior Art) Photochemical reaction devices using ultraviolet light sources are used in various fields, such as photoCVD (Chemical Vacuum
It is widely used in semiconductor manufacturing, including the synthesis of Si thin films by the por deposition method, photo-curing of resists, photo-ashing, and photo-cleaning, and its application fields are rapidly expanding.

Furthermore, research and development of technologies for irradiating short-wavelength ultraviolet rays are rapidly progressing for purposes such as water purification, sterilization, and meat sterilization.

In these fields, there is a desire to develop a light source that efficiently irradiates short-wavelength ultraviolet rays, and for this reason, low-pressure mercury ultraviolet discharge lamps are used.

A low-pressure mercury discharge lamp consists of an arc tube made of quartz glass or the like that transmits ultraviolet rays, with electrodes sealed at both ends, mercury and rare gases sealed inside the arc tube, and this mercury-based vapor discharged at low pressure. It is designed to efficiently emit light in the short wavelength ultraviolet region including the mercury resonance line of 254 nm and 185 nm.

However, recently there has been a growing demand for higher output from low-pressure mercury discharge lamps, and attempts are being made to put ultra-high output lamps into practical use.

Special Publication No. 6349340 as an ultra-high output type lamp
As described in the publication, an anode and a cathode are separately provided at both ends of a quartz glass arc tube, and there is a gap between the anode on one end and the cathode on the other end, and A lamp has been proposed in which discharge is alternately generated between the anode and the anode at the end. By providing the anode and cathode separately from each other in this way, the cathode can be made smaller to reduce heat radiation, and conversely, the anode can be made larger to increase heat radiation.
Since the loss of these electrodes can be reduced, that is, the electrode efficiency can be increased, there is an advantage that the luminous efficiency can be improved.

That is, in the figure, 32 is an arc tube made of quartz glass with high ultraviolet transmittance, and both ends of this arc tube 1 are sealed with stems 33 and 33 (only one of which is shown). An anode 34 and a cathode 35 are sealed in each of these stems 33,33. The anode 34 is made of tungsten W.
A cathode 35 made of a coiled tungsten filament is placed behind the anode 34. A disk-shaped anode 3 is located in front of the cathode 35 on the discharge space side.
4 is arranged to protect the cathode 35 from high-speed electrons that rush into the anode 34.

Note that 36 is a lead wire.

This arc tube 32 is filled with a predetermined amount of mercury or amalgam and argon gas for starting.

Such a low-pressure mercury ultraviolet discharge lamp is connected to an AC power source, and a half-wave current component is caused to flow between the anode 34 on one end and the cathode 35 on the other end to cause discharge between them, and then A reverse half-wave current component is caused to flow between the cathode 35 and the anode 34 on the other end side to cause discharge between them, and the discharge is repeated alternately in this way to continue lighting.

Such discharge excites mercury-based vapor in a low pressure state, and as a result, it emits light in the short wavelength ultraviolet region including mercury resonance lines of 254 nm and 185 nm.

However, in order to increase the discharge current in order to increase the output, it is necessary to increase the size of the electrode, and the following problems arise in the conventional electrode structure.

That is, the electrons emitted from the cathode 35 bypass the disk-shaped anode 34 placed in front of the cathode 35 and head toward the anode at the other end. 34 forms a narrow space between the tube wall of the arc tube 32 and the electrons pass through this narrow space. At this time, in a lamp in which the input power per unit length is increased, for example, 1.5 W/cm or more, most of the electrons collide with the tube wall, causing the tube wall to be negatively charged. As a result, mercury ions are attracted to the tube wall and enter the tube wall, coloring the tube wall a grayish color, and absorbing high-power ultraviolet rays for a long period of time, generating microscopic racks in the quartz glass and causing mechanical damage. There is a problem that reduces the strength of the target.

As a result, there is concern that the arc tube bulb will darken, resulting in a decrease in ultraviolet output, and that the lamp may be damaged in the reaction tank, contaminating the cleaning system, and other problems.

In view of this, the present inventors proposed a lamp having a structure in which the anodes provided at both ends of the arc tube are formed into a coil shape, and the cathode is arranged behind the tip of the coil-shaped anode. .

With this configuration, the electrons emitted from the cathode will fly out from the front opening of the coiled anode in front of it toward the anode at the other end, thereby preventing the electrons from colliding with the tube wall at the end of the bulb. Therefore, mercury ions are prevented from being attracted to the tube wall, and early blackening of the tube wall and reduction in mechanical strength are prevented.

Additionally, if the cathode is surrounded by a coiled anode, even if the cathode material scatters or the emitter held by the cathode scatters, the surrounding coiled anode prevents it from adhering to the tube wall. Blackening of the tube wall is also prevented. Furthermore, since the cathode is kept warm by the anode surrounded by it, there are advantages such as less heating current and improved electrode efficiency.

(Problems to be Solved by the Invention) However, even in lamps using such coiled anodes, the bulb may darken prematurely, or the bulb may become unstable due to re-ignition and may easily go out. It has been found.

In other words, in the case of a lamp in which discharge occurs alternately between one anode and the other cathode, and between one cathode and the other anode, as described above, thermionic electrons are constantly emitted from the cathode. However, the temperature of the anodes that operate alternately also increases. For this reason, it has been found that the heat capacity of the first turn of the most advanced coil facing the discharge space side, especially in the anode formed by the coil, affects the function of the anode.

In order to reduce this temperature rise, if the weight of the wire is increased by increasing the coil diameter of the first turn at the tip of the coil, the heat capacity increases and the temperature rise can be reduced. A problem occurs in which the arc voltage increases by 1, and it disappears due to a drop in the power supply voltage.

Furthermore, when the restriking voltage is reached, if the weight of the wire is reduced by configuring the coil diameter of one turn "I" at the tip of the coil not to be made small, the heat capacity of this part will decrease and the temperature will increase excessively. This can cause wire material to fly off and stick to the valve wall, causing premature darkening.

The present invention was made based on the above circumstances, and its purpose is to prevent early blackening of the knob and increase in re-ignition voltage in a lamp that uses a coiled anode to alternately discharge discharge. The purpose of the present invention is to provide a low-pressure discharge lamp that can prevent the lamp from going out due to

[Structure of the Invention] (Means for Solving the Problems) The present invention provides an arrangement in which, when the lamp power is P (KW=e) and the weight of the first turn of the coil tip of the coiled anode is M (g), 0. It is characterized in that 6≦M/P≦20.

(Function) According to the configuration of the present invention, the heat capacity at the first turn of the coil tip, which affects the operating characteristics of the anode, is regulated to an optimal range, and the bulb may darken early or turn off due to an increase in the restriking voltage. can be prevented.

(Example) The present invention will be described below based on an example shown in FIGS. 1 to 3.

In FIG. 2, reference numeral 1 denotes a low-pressure mercury discharge lamp, and the discharge lamp 1 of this embodiment is equipped with an arc tube 2 made of quartz glass and bent into a U-shape.
It consists of a synthetic quartz glass tube of mm.

The end of the arc tube 2 has the structure shown in FIG. 1, with 3 being a stem, 4 an anode, 5 a cathode, and 6 a lid wire.

The anode 4 is formed by a circular two-layer coil, for example, a tungsten wire with a wire diameter of 1.2 mm and an outer diameter of 20 m.
m, formed into a tightly wound first layer coil with 8 turns,
In addition to this, a second layer coil with 3 turns is unwound and formed.

Further, the cathode 5 is arranged so that the filament axis is perpendicular to the bulb axis, and the cathode 5 is arranged so as not to protrude further into the discharge space than the front end of the anode 4.

The coiled anode 4 is connected to one of the tortograph wires 6 which is connected to the cathode 5.

This arc tube 2 contains, for example, 50 mg of mercury and 0,0
5-0. 8 torr, specifically 0, 5 torr
r argon gas is sealed. Note that 7 is a reinforcing member inserted between the straight parts of the U-shaped arc tube 1.

This low-pressure mercury discharge lamp 1 is connected to an AC power source 11 via a lighting circuit device 10, as shown in FIG. Lighting circuit device] 0 is rectifier smoothing circuit] 2, power FET (
Square wave inverter circuit 1 including field effect transistors
It has 3. In addition, the power FET 13 has the following:
Variable resistor for frequency adjustment and current adjustment] 4.15
is provided.

The AC power supply 11 is, for example, a 200V commercial power supply,
In addition to the rectifying and smoothing circuit 12 and the rectangular wave inverter circuit 13, a heater transformer 16.16 is connected to this power source 11.

The heater transformers 16.16 are each connected to a cathode 5.5, so that the cathodes 5.5 are hot cathodes that constantly generate heat and emit thermoelectrons.

Although not shown in FIG. 2, a starting circuit is incorporated in the rectangular wave inverter circuit means, and this starting circuit superimposes a rectified rectified voltage of 300 V on the power supply voltage at the time of starting, and applies it to the electrodes. It is designed to be applied. After the lamp is started, this starting circuit detects a voltage drop between both poles of the lamp and activates a relay (not shown) to be electrically disconnected from the rectangular wave inverter circuit.

The low-pressure mercury discharge lamp 1 in this embodiment is designed to be lit with a light emission length of 670 mm, a rated human power of 500 W, and a discharge current of 17 amperes, so that the input per unit length is :I-, 5W/c
m or more, that is, 7.4 W/cm.

This lamp has a lamp power of P (KW-),
When the weight of the first tungsten wire at the tip of the coil of the coiled anode is M (g), it is set as 屹6≦M/P≦20.

In this example, the rated input is 500W, so 0.3(g)
It is set as ≦M≦10 (g).

The operation of such a lamp and the reason for the numerical limitations will be explained.

When the lamp 1 is connected to the lighting circuit [power supply]] through the lighting circuit and lit, the cathode 5.5 is connected to the heater transformer 16.16.
Since the cathodes 5.5 are connected to the AC power source 11- through the 11-, the cathodes 5.5 constantly generate heat and emit thermoelectrons, thus serving as hot cathodes.

Then, by the action of the rectifier smoothing circuit 12 and the rectangular wave inverter circuit 3 including the power FET, the sine wave of the power supply is converted into the rectangular wave shown in FIG. 3, and this rectangular wave is used for frequency adjustment and current adjustment. is adjusted by variable resistors 14 and 15 and provided between each anode 4 and cathode 5.

Therefore, in a low-pressure mercury discharge lamp, a rectangular current of 1t in a rectangular or trapezoidal wave is passed between the anode 4 at one end and the cathode 5 at the other end, and a discharge occurs between them. A reverse rectangular or trapezoidal wave half-wave rectified current is passed between the cathode 5 on one end and the anode 4 on the other end, and a discharge occurs between them. In this way, each anode 4 and cathode 5 alternately discharge each other every time the polarity is reversed to continue lighting.

Such a discharge excites mercury-based vapor at low pressure, and therefore the mercury resonance lines], 85 nm and 2
It emits light in the short wavelength ultraviolet region including 54 nm.

According to the configuration of the above embodiment, the weight M of one turn of the most advanced coil of the coiled anode 4 facing the discharge space side is 0.
3g≦M≦1. Og, that is, the lamp power is P
(KW), since 0.6≦M/P≦20, it is possible to prevent early blackening of the bulb, and also to prevent the lamp from turning off due to a 1-increase in the restriking voltage.

These effects were confirmed through experiments by the present inventors, and will be explained below. When the lamp current is increased to meet the demand for increased output, the load on the electrodes increases. In particular, in an anode whose polarity changes alternately, it is expected that the heat capacity of the frontmost end of the coil will affect the characteristics.

In other words, in the case of a lamp in which discharge is performed alternately between the cathode and anode, the cathode is operated so that thermionic electrons are constantly emitted, but the temperature of the anode that operates alternately also rises by 1.

In this case, it is presumed that the heat capacity of the first turn at the leading end facing the discharge space side of the coil influences the anode action.

To explain further, if the weight of the wire is reduced by reducing the diameter of the first turn of the coil at the tip of the coil,
The heat capacity of this part is reduced and the temperature rises excessively, causing the wire material to scatter and adhere to the bulb wall, causing early blackening.

Conversely, if the weight of the wire is increased by increasing the diameter of the first turn of the coil at the tip of the coil, the heat capacity increases. In this case, if the heat capacity is made too large,
During the rest period when the polarity is reversed, the temperature of the anode does not drop, and then when the polarity is reversed and the anode has to perform its original function, thermionic electrons are emitted from this anode, and these thermionic electrons are transferred to the other hot cathode. inhibits the entry of thermionic electrons emitted from the In other words, during the rest period when the polarity is reversed, an ion barrier is created on the front side of the anode, and this barrier blocks the uptake of ions from the cathode, shields the positive potential, and inhibits the anode's original function. Therefore, the discharge current is temporarily cut off, and a back electromotive force is generated due to the actance of the lighting circuit, and this is superimposed on the discharge voltage, increasing the restriking voltage. This back electromotive force is accompanied by damped oscillations and makes the discharge unstable.

For this reason, it is important to regulate the heat capacity of the coil in the first turn at the tip of the coil, and for this reason it is necessary to select the weight of the wire.

The heat capacity of such a wire is also related to the lamp power P.

Therefore, the results of experiments conducted on lamps with a rated human power P of 0.5 KW are shown in the table below.

In addition, the table below examines the blackening and fading of the arc tube after 3000 hours of lighting, and the wavelength is 254 nm.
A case where the ultraviolet radiation intensity of 75% or more of the initial value was maintained was evaluated as good.

From the above table, it can be seen that for a lamp with a rated human power P of 0.5KW, it is sufficient if 0.3≦M≦10, and 0.6≦
It is confirmed that it is sufficient to regulate M/P≦20.

Also, for lamps with other rated inputs, 0.6≦M/P≦2
It has been confirmed that the initial objective can be achieved by setting it in the range of 0.

Note that the present invention is not limited to the above embodiments.

That is, in the above embodiment, the filament axis of the cathode 5 was housed in the coil-shaped anode 3 with the filament axis perpendicular to the bulb axis.
The cathode 5 may be housed in the anode with its filament axis on the bulb axis or parallel to the bulb axis, and in this case, the bulb diameter can be reduced.

Furthermore, the shape of the arc tube 2 is not limited to a U-shape, but also a straight tube shape or a W-shape.
It may also have a bent shape such as a letter shape.

Further, in the above embodiment, the cathode 5 is replaced with the coiled anode 4.
Although shown in the figure, the cathode 5 may be placed in the hollow part of the coiled anode 4, as shown as a modification in FIG. 4, for example.

In this case, the electrons emitted from the cathode 5 do not jump out from the front opening of the coiled anode 4 surrounding the cathode toward the discharge space, that is, the anode at the other end, so that the electrons are not emitted from the end of the arc tube bulb 2. Collision with the wall of the tube is prevented. Therefore, mercury ions are prevented from being attracted to the tube wall, preventing the tube wall from turning gray and causing early blackening, and also preventing a decrease in mechanical strength.

In addition, the cathode material and the emitter coated on the cathode 5 may scatter during lighting, but since the cathode 5 is surrounded by the coiled anode 4, the coiled anode 4 prevents the scattered material from hitting the bulb wall. adhesion is prevented. Also in this respect, blackening of the tube wall is prevented.

Furthermore, since the cathode 5 is surrounded by the coiled anode 4, it is kept warm, which improves the rate of temperature rise, and therefore requires less heating current, reducing power consumption at the electrode. , the electrode efficiency is improved.

[Effects of the Invention] As explained above, according to the present invention, since the weight of the first turn of the coil tip, which affects the operating characteristics of the anode, is determined, the heat capacity is in the optimum range, and early blackening of the bulb is prevented. It is possible to prevent the power from going out due to a rise in the re-ignition voltage.

[Brief explanation of the drawing]

1 to 3 show an embodiment of the present invention, FIG. 1 is a configuration diagram showing an end of a low-pressure mercury discharge lamp, FIG. 2 is a configuration diagram showing a low-pressure mercury discharge lamp and its lighting circuit, Fig. 3 is a waveform diagram of a rectangular wave showing the current applied to the lamp, Fig. 4 is a configuration diagram of the end of a low-pressure mercury discharge lamp showing another embodiment of the present invention, and Fig. 5 is a conventional low-pressure mercury ultraviolet ray. It is a block diagram which shows the edge part of a discharge lamp. ]...low-pressure mercury discharge lamp, 2...luminous tube, 3...stem, 4...coiled anode, 5...cathode. ]-〇・・・Lighting circuit device. Applicant's agent Patent attorney Takehiko Suzue

Claims (1)

[Claims] An anode and a cathode are sealed at both ends of the arc tube, and the anode at one end and the cathode at the other end are sealed, and the cathode at one end and the anode at the other end are alternately sealed. In a low-pressure discharge lamp in which the anode is formed into a coil shape and the cathode is arranged behind the tip of the coil-shaped anode, the lamp power of the discharge lamp is P (KW = kilowatt), and the above-mentioned A low-pressure discharge lamp characterized in that, where the weight of the first turn of the anode coil tip is M (g), 0.6≦M/P≦20.