Patent Grant
9947526
The present invention relates to a gas discharge device and a flat light source using the same, and more particularly to an external electrode type discharge tube, which includes a thin glass tube as a main component, for an ultraviolet or visible light source, a flat surface light source using the same, and a driving method therefor.
There have conventionally been known a high-pressure mercury lamp, an excimer discharge lamp, and the like as a light source device using gas discharge. There has also been known a gas discharge device using an ultraviolet light-emitting phosphor as an ultraviolet light source (for example, see Patent Document 1). Also, an external electrode type gas discharge device having a thin tube configuration suitable for a configuration of a flat light source has been known (for example, see Patent Documents 2, 3, and 4).
A conventional excimer discharge lamp of UV-C band using an ultraviolet phosphor has problems of requiring an expensive quartz glass envelope and requiring a high-voltage rectangular-wave alternating-current power source for drive. Further, a conventional gas discharge device for ultraviolet light emission using a gas discharge tube has a complicated electrode structure, and has not yet been developed to a practical level from a viewpoint of luminous efficiency and emission intensity.
In view of this, the present invention provides an inexpensive gas discharge device for a light source, particularly for an ultraviolet light source, with a simple configuration and excellent luminous efficiency. The present invention also provides a plasma tube type gas discharge device that can easily configure a flat light source for ultraviolet or visible light emission with high luminous efficiency and large emission intensity.
The present invention provides a novel external electrode type gas discharge device for a light source generating at least two types of discharges between a pair of long electrodes. Specifically, the present invention is based on an idea in which first and second discharge electrodes extending toward either side along the longitudinal direction of a thin glass tube containing a discharge gas sealed therein are provided with a discharge gap being interposed therebetween, trigger discharge is initially generated between the adjacent ends of the electrodes as a result of a voltage increase when an alternating-current voltage with a sine waveform or an inclined waveform is applied between both electrodes, and the trigger discharge is gradually grown so as to expand in each longitudinal direction of the electrodes. The pair of discharge electrodes is disposed to extend to either side with the discharge gap formed by the adjacent ends being interposed therebetween.
More specifically described, the first aspect of the present invention lies in the configuration of the gas discharge device comprising: a transparent envelope that has a front side and a back side which face each other on a transverse section thereof, the transparent envelope containing a discharge gas sealed therein; and first and second electrodes which are provided outside of the envelope at the back side, the first and second electrodes including: trigger electrode portions that constitute a trigger discharge portion at a position where the trigger electrode portions are adjacent to each other on the outside of the envelope at the back side; and main electrode portions extending in a direction of being away from each other with the trigger discharge portion being interposed therebetween.
It is preferable that a transparent thin glass tube having a circular, oval, flat-oval, rectangular, or trapezoidal transverse section with a major axis of 5 mm or less is used. The length of the thin glass tube is appropriately from 2 cm to 10 cm, and the thin glass tube may be longer than this size according to practical application. Further, even if a thin borosilicate glass tube that is more inexpensive and popular than a quartz tube is used for an envelope composing an ultraviolet light source, sufficient ultraviolet transmission light can be obtained by setting the thickness of the tube at a front side, serving as a light-emitting surface, to be 300 μm or less.
The first and second electrodes extend toward either end with a gap interposed therebetween in the longitudinal direction of the envelope made of the thin glass tube, wherein the adjacent ends thereof at the gap constitute trigger electrode portions and the extended portions thereof at either side constitute main electrode portions.
In this configuration, the first and second electrodes may be provided on a straight line along the longitudinal direction of the envelope composed of the thin glass tube, or on different lines. Further, on an end of one of the first and second electrodes, a trigger electrode member facing an end of the other may be provided. In addition, a plurality of the first and second electrodes may alternately be provided along the longitudinal direction of the thin glass tube.
An ultraviolet phosphor layer, which is excited by vacuum ultraviolet light mainly generated due to xenon gas discharge to emit light, a visible phosphor layer, or a mixed phosphor layer of these phosphors, is provided on the inner surface of the bottom part of the envelope at the back side, whereby emission of light with a desired wavelength can be obtained from the front side of the envelope.
Further, according to the present invention, a flexible flat surface light source can be configured by arraying a plurality of the thin glass tubes on a common electrode of the gas discharge device having the thin tube configuration mentioned above.
According to the gas discharge device of the present invention, high-efficient light emission can be achieved by a simple electrode configuration composed of the first and second electrodes arranged along the longitudinal direction of the envelope. In addition, with the configuration in which an ultraviolet light-emitting phosphor layer is formed in a thin glass tube serving as the envelope, emission of ultraviolet light having UV-B band or UV-C band can be performed with high intensity and high efficiency, compared to a conventional ultraviolet LED or the like.
Further, a film-type flat light source can easily be configured by arraying a plurality of ultraviolet light-emitting tubes on a common electrode sheet. Therefore, industrial practical use, such as medial application or sterilization application, is significantly expanded.
Preferable embodiments of the present invention will be described below in detail with reference to the drawings. It is to be noted that, for simplifying the description, the same components are identified by the same reference numerals. Further, in the description below, an electrode extending in a longitudinal direction of a glass tube is referred to as a “long electrode” for characterizing an electrode structure of the present invention.
The glass tube 1 serving as the envelope is formed such that a pipe-like preform of a borosilicate glass including silicon oxide (SiO2) and boron oxide (B2O3) as main components is redrawn to be formed into a thin tube with an outer diameter of 5 mm or less and a thickness of 500 μm or less.
The transverse section of the glass tube 1 may be circular, flat-oval, rectangular, or trapezoidal as shown in
Even if the borosilicate glass is used, the transmittance of 90% or more can be obtained with respect to ultraviolet light with a wavelength band of UV-B by setting its thickness to 300 μm or less. In this case, the thickness at the back side of the glass tube 1 where electrodes are disposed may be set larger than the thickness at the front side to enhance mechanical strength as in the example of the transverse section illustrated in
In the configuration shown in
The long electrodes 2 and 3 may be directly formed on the outer surface of the glass tube 1 by printing a silver paste or the like, or may be formed by pasting a metal foil such as a copper foil or an aluminum foil or a metal mesh pattern formed on a base film made of a resin onto the outer surface of the glass tube 1. Alternatively, the pair of long electrodes 2 and 3 may be formed on the outer surface of the glass tube through an insulating layer or an insulating film.
In
Further, the angular positions of the pair of the long electrodes 2 and 3 relative to the tube axis may differ on the side face of the glass tube 1. In the case where the pair of long electrodes 2 and 3 is formed on the light-emitting surface of the glass tube 1, a known transparent electrode such as ITO or a metal electrode with a mesh pattern has to be used for allowing the long electrodes 2 and 3 to transmit the emission light. However, in an ultraviolet light-emitting tube using an ultraviolet phosphor, the electrodes are preferably disposed on the back side except the light-emitting surface in order to prevent emission loss.
When a voltage v1 in the increasing process of the sine wave voltage exceeds a discharge start voltage Vf between the trigger electrode portions 2a and 3a at a timing t1, discharge occurs in the trigger discharge portion 5. Due to this trigger discharge, a lot of space charges are supplied to the adjacent gas space, so that a sort-of pilot fire effect occurs, and thus, the discharge extends toward the main electrode portions 2b and 3b of the long electrodes with the increase in the sine wave voltage and grows to so-called long-distance discharge.
Simultaneously, charges (electrons (−) and plus ions (+)) having a polarity opposite to the polarity of the applied voltage are accumulated as wall charges on an inner wall surface of the glass tube 1 corresponding to the trigger electrode portions 2a and 3a that initially generate the trigger discharge, and the electric field caused by this wall charges cancels the electric field caused by the applied voltage. Thus, the discharge in the trigger discharge portion 5 is stopped.
It can be understood from this model that the discharge generated in the trigger discharge portion 5 between the trigger electrode portions 2a and 3a at the timing t1 is extended to the main discharge portion 6 along the extending direction of the main electrode portions 2b and 3b at the timings t2 and t3 during the increasing process of the applied voltage, accompanied by the accumulation of the wall charges.
At the timing t4 during the voltage dropping process after the applied sine wave voltage reaches one of the crest values, the wall charges are in the accumulation state shown in
To cause combined discharge by utilizing the increasing process of the applied voltage, a voltage with a saw-tooth waveform (ramp waveform) can be used instead of the sine wave voltage described above. Further, since the discharge tube having the external electrode configuration according to the present invention becomes a capacitive load, the combined discharge can be generated by utilizing the inclination at a rise time, even if a voltage with a rectangular waveform is used. Therefore, if an alternating-current voltage having a rise time is applied between the pair of long electrodes, the similar drive can be performed. However, it is desirable to use a sine wave voltage from the viewpoint of easiness in generating a waveform. A brightness can be adjusted by changing the frequency of the sine wave voltage or the inclination angle of the saw-tooth waveform voltage.
The combined discharge described above is alternately repeated between the pair of long electrodes 2 and 3 with the application of a sine wave voltage, and at each time, cathode glow emission and positive column emission are generated along the discharge path. In the case where a gas formed by mixing a small percent of xenon (Xe) into neon (Ne) is used as a discharge gas, emission of neon orange light and vacuum ultraviolet (VUV) with a wavelength of 143 nm and 173 nm are obtained as discharge light. Therefore, if the mixture ratio of Ne and Xe is appropriately adjusted and the emission of the gas discharge is used as it is, a neon orange light-emitting tube or an ultraviolet light-emitting tube can be obtained.
In the gas discharge device according to the first embodiment shown in
On the other hand, the spread of the discharge in the extending direction of each of the long electrodes 2 and 3 varies according to the peak voltage Vp of the sine wave voltage to be applied. When the peak voltage Vp is set too high, there is a danger that the trigger discharge portion 5 is damaged. Specifically, while the size Dg of the gap between the trigger electrode portions is generally set within the range from about 0.1 mm to about 2 cm inclusive, the peak voltage Vp of the sine wave differs according to the effective length (2 EL+Dg) of the thin glass tube 1. Therefore, from the relationship between both factors, the length EL of each of the main electrode portions 2b and 3b of the long electrodes can be set to be more than three times, preferably about ten time, as large as the gap size Dg between the trigger electrode portions 2a and 3a. If the total discharge effective length of the thin glass tube 1 is 50 mm, the gap size Dg between the trigger electrode portions can be set as 3 mm, and the length EL (
Consequently, the glass tube 1 using the pair of long electrodes 2 and 3 shown in
The frequency of the sine wave voltage is set to several 10 kHz, e.g., to 40 kHz, from the relationship between the capacitance between electrodes and impedance. The peak voltage Vp is set to be higher than the discharge start voltage Vf of the trigger discharge portion 5, that is, 1000 V or higher, according to the discharge start voltage Vf. However, the upper limit is preferably determined in consideration of the length of the spread of the discharge on the long electrode and the prevention of damage on the trigger discharge portion 5.
Further, since the gas discharge device according to the present invention employs a discharge system in which discharge is extended along the long electrode while being stopped by utilizing the accumulation of wall charges, a peak current while the device is driven can be suppressed, and thus, power consumption to be required is significantly low, compared to an LED or an excimer discharge lamp.
For reference, a commercially available 5 W compact power source circuit (for example, HIU-465 manufactured by Harison Electric Co., Ltd.) including an inverter circuit that converts 10 V DC voltage (battery) into a sine wave voltage of 42 kHz and a compact transformer that raises the sine wave voltage to a peak voltage of 1000 V can be suitably used for driving the gas discharge device according to the first embodiment.
In the case where a gadolinium-activated phosphor (LaMgAl11O19:Gd) is used as one example of the phosphor layer 7, emission of ultraviolet light with 311 nm which is the wavelength range of UV-B band can be obtained. If a praseodymium-activated phosphor (YBO3:Pr or Y2SiO5:Pr) is used, emission of ultraviolet light with 261 nm or 270 nm which is the wavelength range of UV-C band can be obtained.
A known precipitation method can be used to form the phosphor layer 7 of the gas discharge tube 10. Specifically, phosphor slurry in which particles of the above-mentioned phosphor are made into a suspension state is injected into the glass tube, and the glass tube is left to stand. Then, the supernatant liquid is exhausted and the precipitates are burned, whereby the phosphor layer 7 can be formed.
If fine crystal particles of magnesium oxide (MgO) are mixed during the preparation of a suspension of an ultraviolet light-emitting phosphor material, the effect of increasing the emission of secondary electrons from the phosphor layer 7 during the discharge operation can be obtained, which contributes to the reduction in discharge voltage. In the case where a small amount of visible phosphor, such as a red phosphor, is mixed in the ultraviolet light-emitting phosphor layer 7, emission of invisible ultraviolet spectrum can be confirmed by the emission of visible red light.
In the gas discharge device according to the second embodiment using the gadolinium-activated phosphor as the ultraviolet light-emitting phosphor layer 7, the combined discharge of the trigger discharge and the long-distance discharge along the long electrodes is repeated as in the first embodiment through the application of a sine wave voltage between the pair of long electrodes 2 and 3. Consequently, the ultraviolet emission having a peak at the wavelength of 311 nm could be obtained from the phosphor layer 7 with the emission intensity of 10 mW/cm2 and luminous efficiency of 4% W/W.
An electrode sheet 20 and an electrode sheet 30 are disposed close to each other with a gap 40 (gap size Dg) constituting a trigger discharge portion interposed therebetween, and six gas discharge tubes 10 having a rectangular or flat-oval transverse section and used in the second embodiment are disposed in parallel on the upper surface of the sheets as one example.
Specifically, the gas discharge tubes 10 for ultraviolet light emission shown in
The electrode sheets 20 and 30 are formed by pasting an aluminum foil on a common support body 8 composed of a resin film such as a polyimide resin or PET. Further, the pair of electrodes 20, 30 can be formed by patterning the copper foil on the common support body 8. The pair of electrode patterns may be formed as a linear divided pattern corresponding to the individual discharge tube 10, and the divided pair of electrode patterns may be connected respectively in common at both end sides.
If fifty discharge tubes 10 with a length of 100 mm are arrayed on the electrode sheets 20 and 30, each tube having a transverse section with a major axis of 2 mm in the transverse direction, a 10×10 cm ultraviolet flat light source can be obtained. This flat light source has a very simple configuration, and emits light by utilizing long-distance discharge, thereby being capable of providing extremely high luminous efficiency and brightness (emission intensity). This configuration also provides a merit in which the electrode sheets 20 and 30 implement a function of a reflection plate by automatically covering almost all effective discharge area at the back side.
Further, when the 10×10 cm flat light source configured as described above is specified as a unit light source, and a plurality of the unit light sources are arrayed adjacent to each other in the horizontal direction and vertical direction in a mosaic pattern or in a tile pattern, a large-area ultraviolet irradiation device can be implemented.
In this case, if the electrode terminal of each of the unit light sources arrayed in the mosaic pattern is individually extracted and selectively connected to a drive source, an irradiation area is selectable in a unit of a small-area light source, and this is particularly effective for a medical application or the like. In this case as well, a compact power source that is the same as described above and converts a DC voltage into a sine wave and raises the resultant voltage can be used as the drive source, whereby a very simple and inexpensive unit light source configuration can be implemented as a whole. That is, the compact drive source circuit can easily be mounted on the back side of the support body 8 of the electrode sheet 30 to which a sine wave voltage is applied for each unit light source, and with this, the flat surface light source can be formed into a module.
A fourth embodiment of the gas discharge device according to the present invention is shown in
Specifically, in the longitudinal sectional view in
In the case where multiple, e.g., six gas discharge tubes 10 are arrayed to form a flat light source, the flat light source has the configuration shown in
In this configuration, a common trigger electrode member 31a intersecting the tubes is provided to face the right end of the left electrode sheet 20 on the upper surface of the array of the gas discharge tubes, and this trigger electrode member 31a is connected to the right electrode sheet 30 with a connection conductor 42a.
The trigger electrode member 31a may be a transparent conductive film, or may be formed by applying a silver paste in a stripe pattern. Alternatively, a conductive film having a trigger electrode pattern may be formed in advance on a surface of an ultraviolet transmission acrylic resin film (for example, Kanaselite #001), and the resultant may be laminated on the upper surface of the array of the gas discharge tubes so as to also function as a protection film.
In the fourth embodiment in which the trigger discharge portion 50 has an opposed discharge cell structure, the initial trigger discharge start voltage is lower than that in the surface discharge cell structure along the longitudinal direction of the glass tube 1 as in the first or the second embodiment, whereby the trigger discharge can reliably be generated.
The operation in which the trigger discharge of the opposed discharge system becomes a supply source of space electrons to the adjacent gas discharge spaces as a pilot fire and the long-distance discharge accompanied by the wall charges is gradually extended in the tube axis direction with the increase in the sine wave voltage is the same as the operation described in the first embodiment. The trigger electrode member 31 located on the upper surface and the right electrode sheet 30 connected thereto are connected to a ground potential, and a sine wave drive voltage is applied to the left electrode sheet 20 for driving.
It is to be noted that the trigger electrode member 31a is not necessarily provided on the position facing the trigger electrode portion 2a at the end of one of the long electrodes as illustrated in
It is only sufficient to use a commercially available compact power source circuit (for example, S-05584 manufactured by Elevam Corporation) including an inverter circuit that coverts a DC voltage (battery) of 5 V into a sine wave voltage of 80 kHz and a compact transformer that raises the sine wave voltage to the peak voltage of 650 V, in order to drive a gas discharge device of a size of 3×3 cm (9 cm2) formed by arranging, with a space of 1 mm, ten tubes with a major axis of 2 mm and a length of 3 cm having the structure provided with the trigger electrode member 31a as in the fourth embodiment.
Specifically, with the structure provided with the trigger electrode member 31a, ultraviolet light emission intensity of 6 mW/cm2 and efficient of 4% W/W could be implemented with further reduced power consumption. Since the effective discharge area of this gas discharge device was 9 cm2, an ultraviolet light-emitting device with an output intensity exceeding 50 mW in total could be implemented.
Specifically, a long electrode 22 extending from a left end to the center is provided on the upper outer surface of the gas discharge tube 10 containing a discharge gas filled therein, and a long electrode 32 extending from a right end to the center is provided on the lower outer surface. The both long electrodes have an overlapped portion serving as trigger electrode portions 22a and 32a at the center, and a trigger discharge portion 52 is formed in the gas space corresponding to the overlapped portion.
In the case where a plurality of gas discharge tubes 10 is arrayed to form a flat light source, a tube array including a plurality of (here, six) tubes is vertically sandwiched between an electrode sheet 22b and an electrode sheet 23 which commonly serve as the long electrodes 22 and the long electrodes 23 of the respective tubes. The upper electrode sheet 22b serving as a light-emitting surface has to be formed from a transparent conductive film or a metal mesh pattern in consideration of extracting radiation light. This configuration causes a transmission loss of light by one electrode, so that it is rather suitable for a visible flat light source than for an ultraviolet flat surface light source.
It is preferable that the electrode sheet 22b and the electrode sheet 32b may preliminarily be formed on a common support film in a solid pattern or a stripe pattern following the array of the gas discharge tubes.
Since the trigger discharge portion 52 has an opposite discharge system in the configuration of the fifth embodiment, initial trigger discharge can reliably be generated with a lower voltage. Further, the connection to the drive source is set such that the electrode sheet 22b located on the light-emitting surface has a ground potential and a sine wave alternating-current voltage is applied to the electrode sheet 32b at the back surface side.
In this case as well, the gas discharge device can be driven by a compact power source circuit (S-05584 manufactured by Elevam Corporation) as in the fourth embodiment.
Specifically, as illustrated in
Therefore, the gas discharge device according to the present invention generates combined discharge which is of a different system from discharge conventionally generated between display electrode pairs composing a pixel in a plasma tube array for a large-sized display. The difference in the discharge system is caused by the length of an electrode and a long increasing process of the sine wave drive voltage.
Thus, when the terminal 20C is connected to a ground potential and a sine wave alternating-current voltage from a power source AC is applied from the other terminal 30C, trigger discharge in the gap between the adjacent electrode segments and long-distance discharge along each electrode segment are repeatedly generated in each discharge tube, whereby ultraviolet light emission throughout the entire surface can be obtained.
The electrode segments in the sixth embodiment are not necessarily arrayed on a straight line on the bottom surface of the gas discharge tube 10 as shown in
Alternatively, in the configuration in
In the embodiments described above, a long and thin glass tube is used as the envelope containing a discharge gas sealed therein. However, it can be configured such that a closed discharge space is formed between two thin glass sheets, and strip electrodes extending in the longitudinal direction are provided on the outer surface with a trigger discharge gap being interposed therebetween. When a plurality of pairs of strip electrodes is arranged in parallel on the outside of the common discharge space, a flat surface light source substantially similar to the flat light source in the third embodiment can be obtained.
The above-mentioned embodiments describe the configuration in which long electrodes that make a pair are directly provided on the outer surface of a thin glass tube. However, an electrode pair may be provided through an insulating layer or an insulating film in consideration of compensation of smoothness of the glass tube wall or protection of the tube wall. In the case where a long electrode with a solid pattern formed from an aluminum foil is directly bonded to the outer surface of a thin glass tube, air bubbles are present on the bonded surface due to fine irregularities on the glass surface, and this might cause an unnecessary spark discharge while the device is driven. In order to prevent this problem, the electrodes are preferably provided through a thin polyimide insulating tape, e.g., Kapton (registered trademark). Specifically, a configuration in which the common electrodes 20 and 30 are disposed at the back of the electrode support sheet 8 in
In addition, in order to protect the surface of a thin glass tube, a heat-resistant fluoroplastic having an ultraviolet light transmission function, such as Teflon (registered trademark), may be coated on the surface of the thin tube. According to this configuration, resistance to weather and resistance to impact of the thin glass tube are enhanced, whereby practical application can be expanded. In this case as well, the electrode pair on the outer surface of the glass tube is indirectly provided on the surface of the glass tube through an insulating layer of a coating resin.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2015-019141 | Feb 2015 | JP | national |
| 2015-099146 | May 2015 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2016/052716 | 1/29/2016 | WO | 00 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2016/125708 | 8/11/2016 | WO | A |
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| Number | Date | Country | |
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| 20170186596 A1 | Jun 2017 | US |
