JP6319660B2 - Microwave electrodeless lamp and light irradiation device using the same - Google Patents

Description

  The present invention relates to a microwave electrodeless microwave electrodeless lamp and a light irradiation apparatus using the same.

  In recent years, a microwave electrodeless lamp has been developed as a discharge lamp that emits visible light or ultraviolet light. A light irradiation apparatus equipped with a microwave electrodeless lamp typically includes a microwave oscillator, a microwave cavity, and an electrodeless lamp that is a discharge tube (light emitting tube). The electrodeless lamp is detachably supported in the microwave cavity. The microwave cavity is provided with a reflecting mirror for guiding visible light or ultraviolet light from the electrodeless lamp to the light exit. The light exit is provided with a conductive mesh that is impermeable to microwaves but transmissive to visible light or ultraviolet light.

  In the discharge tube, a starting rare gas or an inert gas and a luminescent material are enclosed. By appropriately selecting the luminescent substance, visible light or ultraviolet light having a desired wavelength can be obtained. Ultraviolet rays with a wavelength of 254 nm are used for sterilization, and ultraviolet rays with a wavelength of 315 to 400 nm (UV-A region) are used for curing treatment of paints, resins, and the like. Mercury, iron group elements, metal halides, and the like are known as luminescent materials.

  Patent Document 1 describes an electrodeless discharge lamp in which mercury and halogen, and an element selected from iron, nickel, cobalt, and palladium are encapsulated as a luminescent material. Patent Document 2 describes that in order to ensure lamp life and discharge stability in an electrodeless discharge lamp, the amount of mercury and iron enclosed as a luminescent material is appropriately selected.

JP 57-172650 A JP-A-6-13052 (Patent No. 3496033)

  There is an increasing demand for ultraviolet rays having a wavelength of 315 to 400 nm (UV-A region) used for curing treatment of paints, resins, and the like. In an electrodeless discharge lamp that generates ultraviolet rays in the UV-A region, conventionally, mercury is used as a luminescent material. In recent years, mercury tends to avoid its use as an environmentally hazardous substance. On the other hand, there is an increasing demand for a light irradiation device that stably emits ultraviolet rays in the UV-A region.

  An object of the present invention is to provide a microwave electrodeless lamp capable of stably emitting the emission intensity of ultraviolet rays in the UV-A region without using mercury as a luminescent material, and a light irradiation apparatus using the same. It is in.

According to the present invention, in a microwave electrodeless lamp that emits light by receiving microwave energy,
A tubular discharge vessel made of quartz glass;
A rare gas and a luminescent material enclosed in the discharge vessel,
The luminescent material includes cobalt iodide and nickel alone, and the enclosure density of cobalt iodide is 4.0 to 6.5 μmol / cc, and the enclosure density of nickel is 15.0 μmol / cc or less. .

  According to this embodiment of the present invention, in the microwave electrodeless lamp, the nickel sealing density may be 4.0 to 8.0 μmol / cc.

According to this embodiment, in the microwave electrodeless lamp,
The discharge vessel has a reduced diameter central portion, a tapered portion connected to both sides of the reduced diameter central portion, and a cylindrical portion connected to each outer end of the tapered portion, and the reduced diameter central portion The outer diameter of the cylindrical portion is smaller than the outer diameter of the cylindrical portion, and the central portion of the reduced diameter is formed at a position corresponding to a low temperature region formed corresponding to a standing wave node of a plasma region generated by microwave energy. It is good to be.

In a light irradiation apparatus having a microwave oscillator, an antenna attached to the microwave oscillator, and an electrodeless lamp that emits light by receiving microwave energy from the antenna,
The electrodeless lamp has a discharge vessel filled with an inert gas and a luminescent material,
The luminescent material includes cobalt iodide and nickel alone, and the enclosure density of cobalt iodide is 4.0 to 6.5 mol / cc, and the enclosure density of nickel is 15.0 μmol / cc or less. .

  According to this embodiment, in the light irradiation apparatus, the nickel sealing density may be 4.0 to 8.0 μmol / cc.

  ADVANTAGE OF THE INVENTION According to this invention, the microwave electrodeless lamp which can radiate | emit the ultraviolet-ray of a UV-A area | region stably, and a light irradiation apparatus using the same can be provided.

FIG. 1A is a schematic perspective view showing an example of a light irradiation apparatus using the microwave electrodeless lamp according to the present embodiment. FIG. 1B is a schematic front view of the light irradiation device of FIG. 1A as viewed from the front. FIG. 2 is a diagram illustrating a cross-sectional configuration of the front side inside of the housing of the light irradiation apparatus according to the present embodiment. FIG. 3 is a diagram illustrating an example of an electrodeless lamp according to the present embodiment. FIG. 4 is a diagram illustrating dimensions of an example of the electrodeless lamp according to the present embodiment. FIG. 5 is a diagram illustrating the structure and dimensions of another example of the electrodeless lamp according to the present embodiment. FIG. 6 is a diagram for explaining the relationship between the nickel encapsulation density and the ultraviolet (UV-A) emission intensity in the electrodeless lamp according to the present embodiment. FIG. 7 is a diagram for explaining the spectral characteristics of ultraviolet (UV-A) emission intensity when nickel is enclosed in the electrodeless lamp according to the present embodiment.

  Hereinafter, an electrodeless lamp according to the present invention and a light irradiation apparatus using the same will be described in detail with reference to the accompanying drawings. It should be noted that this embodiment is an exemplification and does not limit the present invention in any way.

  1A and 1B are diagrams illustrating an example of a light irradiation apparatus using a microwave electrodeless lamp according to the present embodiment. FIG. 1A is a perspective view of the light irradiation device 10. FIG. 1B is a schematic front view of the light irradiation device 10 of FIG. 1A as viewed from the front. As shown in the figure, the X axis is set along the lamp axis direction of the light irradiation device 10, the Z axis is set along the light emission direction (arrow direction) from the light irradiation device 10, and the Y axis is set in the direction perpendicular to the XZ plane. .

  The light irradiation device 10 has a rectangular housing 4, and a microwave oscillator 3 (not shown) is provided inside the rear side of the housing 4. The light irradiation device 10 further includes an antenna 8 attached to the microwave oscillator 3, an electrodeless lamp 12 that emits light upon receiving microwave energy from the antenna 8, and a reflection disposed along the axis of the electrodeless lamp 12. It has a mirror 14. A space surrounded by the reflecting mirror 14 forms a microwave cavity 5. The electrodeless lamp 12 is disposed in the microwave cavity 5.

  The light irradiation device 10 further includes a cooling air supply mechanism that cools the electrodeless lamp 12. The cooling air supply mechanism has a cooling air source (not shown) and a cooling air duct 6 (not shown in FIG. 1B) mounted on the upper side of the housing 4.

  A microwave indicates an electromagnetic wave having a wavelength of 1 m to 100 μm and a frequency of 300 MHz to 3 THz, and is the shortest wavelength region among radio waves. Examples of the microwave oscillator 3 include a circuit using a magnetron, a klystron, a traveling wave tube (TWT), a gyrotron, and a Gunn diode. In this embodiment, a magnetron is used as the microwave oscillator. A magnetron is a type of oscillation vacuum tube that generates powerful non-coherent microwaves. In familiar places, magnetrons are used in radar and microwave ovens. In this embodiment, a magnetron used in a microwave oven, preferably a commercial microwave oven, is used. Note that the microwave oven uses a frequency of 2,450 MHz, but this is not due to technical limitations but due to legal restrictions.

  FIG. 2 shows a cross-sectional configuration inside the front side of the housing 4 of the light irradiation apparatus 10 according to the present embodiment. Typically, the reflecting mirror 14 includes an ellipsoidal reflecting mirror for condensing on the irradiated surface, a parabolic reflecting mirror that applies parallel light to the irradiated surface, and the like. Both the ellipsoid and the paraboloid have at least one focal point. In the embodiment of FIG. 2, the reflecting mirror 14 is a saddle-type ellipsoidal reflecting mirror, the electrodeless lamp 12 is a straight tube type, and is arranged so that its central axis is located at the focal point of the ellipsoidal reflecting mirror. Note that the center (center axis) of the electrodeless lamp does not necessarily coincide with the focal position of the reflector, and the central portion of the lamp body is located at the position including the focal point in consideration of the positional error of the lamp. It only has to be arranged.

  A light exit 2 is formed on the front surface of the housing 4 of the reflecting mirror 14, and the light exit is covered with a conductive mesh 16. The conductive mesh 16 is impermeable to microwaves but is transmissive to irradiation light 18 from the microwave cavity, that is, visible light and ultraviolet rays.

  Microwaves generated from the microwave oscillator 3 are radiated through the antenna 8 and supplied to the microwave cavity 5 where a standing wave is formed. Plasma is excited inside the electrodeless lamp 12 disposed in the microwave cavity 5. Visible rays or ultraviolet rays radiated from the plasma are reflected from the reflecting mirror 14 as the irradiation light 18 or directly emitted toward the light exit 2 and pass through the conductive mesh 16 to be irradiated on the irradiated surface. The

  Cooling air 17 from a cooling air source (not shown) is supplied to the microwave cavity 5 through the cooling air duct 6 (FIG. 1A) and through the hole 14 </ b> A of the reflecting mirror 14. The cooling air 17 collides with the outer peripheral surface of the electrodeless lamp 12 and cools the electrodeless lamp 12.

  An example of a straight tube type electrodeless lamp according to the present embodiment will be described with reference to FIG. The electrodeless lamp 12 is a straight tube type having a cylindrical discharge vessel 12A, and has protrusions 12B at both ends thereof. The electrodeless lamp 12 is held in the microwave cavity by engaging the protrusions 12B on both ends of the discharge vessel with the engaging portions on the inner walls on both sides of the casing.

  When the magnetron is oscillated, microwave energy of 2,450 MHz is supplied to the microwave cavity 5 to form a standing wave. The microwave is combined with the discharge vessel 12A of the electrodeless lamp 12 to excite plasma inside. Visible light or ultraviolet light is emitted from the luminescent material.

When the electrodeless lamp 12 is turned on, two plasma regions 13 are formed inside the discharge vessel 12A as indicated by broken lines. The plasma region 13 forms a standing wave having an antinode 131 and nodes 132 on both sides thereof. The wavelength of this standing wave is λ = propagation speed / frequency = 2.99 × 10 ⁸ (m / s) /2.45 GHz≈123 mm. The length in the axial direction of the discharge vessel 12A of the electrodeless lamp is formed substantially equal to the length of one wavelength.

  The portion of the antinode 131 of the standing wave has a relatively high temperature and emits relatively strong light. This is called the high temperature region (hot zone) 12a, 12b. The portion of the standing wave node 132 is relatively cool and emits relatively weak light. This is called a low temperature region (cold zone) 12c, 12d, 12e. In the discharge vessel 12A, the standing wave is formed symmetrically. Therefore, the lowest temperature position in the center is at the center position in the axial direction of the discharge vessel 12A. In the low temperature regions 12c, 12d, and 12e, the evaporation of the encapsulated material may be inhibited or recondensation may occur. Therefore, the temperature distribution in the discharge vessel 12A of the electrodeless lamp 12 becomes non-uniform along the axial direction.

  The dimensions of the straight tube type electrodeless lamp according to the present embodiment will be described with reference to FIG. The electrodeless lamp 12 according to this embodiment includes a cylindrical discharge vessel 12A and protrusions 12B and 12B on both sides. The dimension in the axial direction of the electrodeless lamp is L1, the dimension in the axial direction of the discharge vessel 12A is L, and the dimension in the axial direction of the protrusions 12B and 12B is Lt. L1 = L + 2Lt = 146-158 mm, L = 130-140 mm, Lt = 8.0-9.0 mm. Let D be the outer diameter of the discharge vessel 12A. D = 10-14 mm.

  The electrodeless lamp 12 is made of quartz glass. The discharge vessel 12A is formed of a sealed vessel made of quartz glass. The protrusions 12B and 12B are quartz glass rods. The discharge vessel 12A is filled with a starting rare gas or inert gas and a luminescent material.

  Another example of the electrodeless lamp according to the present embodiment will be described with reference to FIG. The electrodeless lamp 12 according to this embodiment includes a cylindrical discharge vessel 12A and protrusions 12B and 12B on both sides. As shown in the figure, the discharge vessel 12A has a cylindrical reduced diameter central portion 122, tapered portions 124 on both sides thereof, and cylindrical portions 121 and 121 on the outer sides thereof. End portions 123 and 123 are formed outside the cylindrical portion. The reduced diameter central portion 122 is formed in the low temperature region 12c (FIG. 3) in the center of the discharge vessel, and the tapered portion 124 is formed between the reduced diameter central portion 122 and the cylindrical portions 121 and 121 so as to connect them. ing. The end portions 123 and 123 are formed in the low temperature regions 12d and 12e on both sides of the discharge vessel. Similar to both ends of the discharge vessel 12A of the conventional straight tube type electrodeless lamp, the end portions 123 and 123 are rotated in a spherical shape, an elliptical spherical shape, or the like. It may be formed in a curved surface shape.

  In the present embodiment, since the reduced diameter central portion 122 is formed in the low temperature region 12c at the center of the discharge vessel, the internal space becomes small in the central low temperature region 12c, and recondensation of the encapsulated material is avoided.

  The dimension in the axial direction of the electrodeless lamp is L1, the dimension in the axial direction of the discharge vessel 12A is L, and the dimension in the axial direction of the protrusions 12B and 12B is Lt. The dimension in the axial direction of the reduced diameter central portion 122 is La, the dimension in the axial direction of the tapered portion 124 is Lb, and the dimension in the axial direction of the cylindrical portions 121 and 121 is Lc. L1 = L + 2Lt = 146-158 mm, L = 130-140 mm, Lt = 8.0-9.0 mm. La = 15-25 mm, Lb = 15-25 mm, Lc = 30-40 mm.

  The outer diameter of the reduced diameter central portion 122 is Da, the outer diameter of the cylindrical portions 121 and 121 is Dc, and the outer diameter of the projecting portions 12B and 12B is Dt. The outer diameter Da of the reduced diameter central portion 122 is smaller than the outer diameter D of the discharge vessel 12A of the straight tube type electrodeless lamp of FIG. That is, Da <D. The outer diameter Dc of the cylindrical portions 121, 121 is equal to the outer diameter D of the discharge vessel 12A of the straight tube type electrodeless lamp of FIG. That is, Da = D. The outer diameter of the inner end of the tapered portion 124 is equal to the outer diameter Da of the reduced diameter central portion 122, and the outer diameter of the outer end of the tapered portion 124 is equal to the outer diameter Dc of the cylindrical portions 121 and 121.

  Below, the experiment which the inventor of this application performed is demonstrated. First, an example of the electrodeless lamp used in the experiment will be described in detail. In an experiment conducted by the inventors of the present application, a straight tube type electrodeless lamp shown in FIGS. 3 and 4 was used. The dimensions of the discharge vessel 12A are as follows. L1 = L + 2Lt = 155 mm, L = 138 mm, Lt = 8.5 mm, D = 11 mm, Dt = 3 mm. The thickness of the discharge vessel 12A was 1 mm. The internal volume of the discharge vessel 12A was 8.8 cc. The discharge vessel was filled with argon gas of 15 ± 5 Torr as a starting rare gas or inert gas.

  Next, the luminescent material sealed in the electrodeless lamp used in the experiment conducted by the inventors of the present application will be described in order. In this embodiment, mercury is not used as the luminescent material. That is, the microwave electrodeless lamp according to the present embodiment is a mercury-free lamp. Table 1 shows the outline and results of experiments conducted by the inventors of the present application. The input power was fixed at 1.8 kW.

The inventors have paid attention to cobalt iodide (CoI ₂₎ and iron iodide (FeI ₂₎ as a light emitting material to substitute for mercury. Experiment 1 and Experiment 2 will be described. In Experiment 1, cobalt iodide was encapsulated as a luminescent material. In Experiment 2, iron iodide was encapsulated as a luminescent material. The enclosure density of cobalt iodide in Experiment 1 and the enclosure density of iron iodide in Experiment 2 are both 6.4 μmol / cc. In Experiment 1 and Experiment 2, the emission intensity in the UV-A region was measured and compared. In Table 1, the emission intensity in the UV-A region of another experiment was compared with the emission intensity in the UV-A region of Experiment 1 as a reference. That is, the emission intensity in the UV-A region in Experiment 1 was set to 100%, and the emission intensity in the UV-A region in other experiments was displayed as a percentage. The emission intensity in the UV-A region of Experiment 2 was about 66%. Therefore, it can be seen that cobalt iodide is preferable to iron iodide as the luminescent material.

  The inventor of the present application conducted an experiment to measure the emission intensity in the UV-A region by changing the encapsulation density of cobalt iodide. As a result, if the cobalt iodide encapsulation density is less than 4.0 μmol / cc, the emission intensity in the UV-A region cannot be remarkably improved, but the cobalt iodide encapsulation density is 4.0 μmol / cc or more. The emission intensity in the UV-A region was found to be good. On the other hand, it was observed that the arc became unstable when the enclosure density of cobalt iodide exceeded 6.5 μmol / cc. Therefore, in this embodiment, the enclosure density of cobalt iodide is set to 4.0 to 6.5 μmol / cc.

Furthermore, the inventor of the present application examined a luminescent material additionally encapsulated in cobalt iodide (CoI ₂ ). The inventor of the present application focused on simple nickel and simple iron. Experiment 3 and Experiment 4 will be described. In Experiment 3, nickel alone was enclosed in addition to cobalt iodide, and in Experiment 4, iron alone was enclosed in addition to cobalt iodide. The enclosure density of simple nickel in Experiment 3 and the enclosure density of simple iron in Experiment 4 correspond approximately. The enclosure density of cobalt iodide in Experiment 3 and the enclosure density of cobalt iodide in Experiment 4 are both 6.4 μmol / cc.

  The results of Experiment 3 and Experiment 4 are compared. The emission intensity in the UV-A region in Experiment 3 is about 109%, and the emission intensity in the UV-A region in Experiment 4 is about 95 to 99%. Therefore, it can be seen that nickel alone is preferable as the light emitting material to be encapsulated in addition to cobalt iodide.

  The results of experiments conducted by the inventors of the present application will be described with reference to FIG. The inventor of the present application measured the spectral characteristics of the emission intensity at a wavelength of 315 to 400 nm (UV-A region) by changing the enclosure density of nickel. The enclosure density of cobalt iodide is 6.4 μmol / cc. In this experiment, the electrodeless lamp according to the present embodiment shown in FIG. 4 was used, and the input power was fixed at 1.8 kW. The horizontal axis in FIG. 6 is the nickel density of inclusion (μmol / cc), and the vertical axis is the relative value (unit:%) of the integrated value of the emission intensity at wavelengths of 315 to 400 nm (UV-A region). In other words, the emission intensity when the encapsulation density of nickel alone is zero is 100%.

  From the graph of FIG. 6, when the enclosure density of nickel alone is 15.0 μmol / cc or less, the emission intensity in the UV-A region increases, but when the enclosure density of nickel alone is greater than 15.0 μmol / cc, UV− The emission intensity in the A region decreases. Therefore, the enclosure density of nickel alone should be 15.0 μmol / cc or less, and preferably 4.0 to 8.0 μmol / cc.

  The result of the experiment conducted by the inventors of the present application will be described with reference to FIG. FIG. 7 shows the emission intensity and spectral characteristics of Experiment 1 and Experiment 3 in Table 1. The horizontal axis is the wavelength of 315 to 400 nm in the UV-A region, and the vertical axis is the relative value (unit:%) of the emission intensity. In the case of Experiment 1, that is, the vicinity of the wavelength of 353 nm when the density of nickel alone is zero The emission intensity is set to 100%.

  The solid line shows the spectral characteristics when the nickel density in Experiment 3 is 8.0 μmol / cc. The dotted line shows the spectral characteristics when the enclosure density of nickel alone in Experiment 3 is 4.0 μmol / cc. The broken line indicates the spectral characteristics in Experiment 1, that is, in the case where the enclosure density of nickel alone is zero. At wavelengths of 315 to 380 nm, the solid line and the dotted line are clearly above the broken line. Accordingly, it can be seen that the emission intensity and spectral characteristics at wavelengths of 315 to 380 nm are remarkably improved by enclosing nickel alone in addition to cobalt iodide. Note that, at wavelengths of 315 to 380 nm, the solid line is partially slightly above the dotted line, but in general, it can be said that the two substantially overlap. Therefore, although the encapsulation density of nickel alone is preferably 8.0 μmol / cc rather than 4.0 μmol / cc, the difference in emission intensity and spectral characteristics is slight.

  On the other hand, at wavelengths of 380 to 400 nm, the broken line of Experiment 1 is on the uppermost side, followed by the dotted line of Experiment 3, and the solid line of Experiment 3 is on the lowermost side. Therefore, at a wavelength of 380 to 400 nm, the emission intensity is the best when the enclosure density of nickel alone is zero. Further, the case where the enclosure density of nickel alone is 4.0 μmol is better than the case where it is 8.0 μmol / cc. In this experiment, the input power was fixed at 1.8 kW, but it was found that when the input power was increased to 2.5 kW, a light emission intensity comparable to that of a mercury-containing lamp was obtained.

  The findings obtained from experiments conducted by the inventors of the present application will be summarized.

  (1) In a mercury-free discharge lamp, encapsulating cobalt iodide is more effective in improving the emission intensity in the UV-A region than encapsulating iron iodide.

  (2) In the mercury-free discharge lamp, the enclosure density of cobalt iodide is preferably 4.0 to 6.5 mol / cc. If the enclosure density of cobalt iodide is less than 4.0 mol / cc, the emission intensity cannot be improved sufficiently. On the other hand, when the enclosure density of cobalt iodide is more than 6.5 mol / cc, the arc becomes unstable.

  (3) In the mercury-free discharge lamp, the emission intensity in the UV-A region can be improved by further enclosing nickel alone in addition to cobalt iodide. The enclosure density of nickel alone may be 15.0 μmol / cc or less, but is preferably 4.0 to 8.0 μmol / cc.

  (4) The normal straight tube type shown in FIGS. 3 and 4 may be used as the discharge vessel, but preferably, the discharge vessel has a shape having a reduced diameter central portion in the central low temperature region (cold zone) shown in FIG. Use a good one.

  Although the embodiments of the present invention have been described above, the scope of the present invention is not limited by these embodiments, and various modifications can be made within the scope of the invention described in the claims. This will be readily appreciated by those skilled in the art.

  In the present invention, a light irradiation apparatus equipped with a microwave electrodeless lamp can be suitably used for, for example, surface hardening treatment of a surface coated with ink, coating, or the like.

DESCRIPTION OF SYMBOLS 2 ... Light emission port, 3 ... Microwave oscillator, 4 ... Housing | casing, 5 ... Microwave cavity, 6 ... Cooling air duct, 8 ... Antenna, 10 ... Light irradiation apparatus, 12 ... Electrodeless lamp, 12A ... Discharge vessel , 12B ... projections, 12a, 12b ... high temperature region (hot zone), 12c, 12d, 12e ... low temperature region (cold zone), 13 ... plasma region, 14 ... reflector, 14A ... hole, 16 ... conductive mesh, 17 ... cooling air, 18 ... irradiation light, 121 ... cylindrical portion, 122 ... center of reduced diameter, 123 ... end portion, 124 ... tapered portion, 131 ... belly, 132 ... node

Claims (5)

In microwave electrodeless lamps that emit light upon receiving microwave energy,
A tubular discharge vessel made of quartz glass;
A rare gas and a luminescent material enclosed in the discharge vessel,
The luminescent material includes cobalt iodide and nickel alone, and the enclosure density of cobalt iodide is 4.0 to 6.5 μmol / cc, and the enclosure density of nickel is 15.0 μmol / cc or less. Microwave electrodeless lamp. The microwave electrodeless lamp according to claim 1, wherein
A microwave electrodeless lamp having an enclosure density of nickel of 4.0 to 8.0 μmol / cc. The microwave electrodeless lamp according to claim 1, wherein
The discharge vessel has a reduced diameter central portion, a tapered portion connected to both sides of the reduced diameter central portion, and a cylindrical portion connected to each outer end of the tapered portion, and the reduced diameter central portion The outer diameter of the cylindrical portion is smaller than the outer diameter of the cylindrical portion, and the central portion of the reduced diameter is formed at a position corresponding to a low temperature region formed corresponding to a standing wave node of a plasma region generated by microwave energy. Microwave electrodeless lamp characterized by being made. In a light irradiation apparatus having a microwave oscillator, an antenna attached to the microwave oscillator, and an electrodeless lamp that emits light by receiving microwave energy from the antenna,
The electrodeless lamp has a discharge vessel filled with an inert gas and a luminescent material,
The luminescent material includes cobalt iodide and nickel alone, and the enclosure density of cobalt iodide is 4.0 to 6.5 mol / cc, and the enclosure density of nickel is 15.0 μmol / cc or less. , Light irradiation device. In the light irradiation apparatus of Claim 4,
The nickel irradiation density is 4.0 to 8.0 μmol / cc.

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