JP2014175227A - Ultraviolet light generator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an energy saving ultraviolet light generator which can cure a coating film uniformly from the surface to the depths, while suppressing light curing failure due to oxygen in air, and to provide an ultraviolet light generator in which the ultraviolet radiation distribution is made uniform in the length direction by controlling discharge plasma emission in the length direction.SOLUTION: A mixture gas containing oxygen (O2) of 0-18 for nitrogen (N2) of 100, at a pressure ratio of normal temperature, is enclosed in a discharge space. Furthermore, argon (Ar) of 0.5-5 is added to the mixture gas 1, at a pressure ratio of normal temperature. The discharge space is formed in the shape of a cylindrical body, and electrode is arranged in the length direction thereof while being divided. A multi-phase AC power supply, adjusting the voltage being applied to these electrodes by phase setting, is connected with these electrodes.

Description

  The present invention relates to an ultraviolet ray generator suitable for photocuring.

  Today, energy and global environmental issues are of great concern both at home and abroad. The photo-cured coating film has a low odor and is cured in units of seconds. Therefore, the photo-cured coating film has been widely used in various applications in recent years. However, the use of a high-pressure mercury lamp that consumes a large amount of power and contains a large amount of mercury during photocuring is a major problem. Development of a new lamp is anxious from the viewpoint of energy saving and mercury removal.

  In the patent document 1, the present inventors have found that when a molecular mixed gas composed of nitric oxide gas diluted with nitrogen gas is used, strong ultraviolet radiation can be emitted in a wavelength range of 200 nm to 300 nm. However, there is a problem that molecular gas easily dissociates in the discharge plasma, and it is necessary to always take measures such as whether to keep a large amount of new gas flowing or to synthesize the original gas from the dissociated gas. .

  In the photo-curing field, acrylate-based curing solutions that are widely used are greatly hindered by the oxygen in the air dissolved in the solution, and in order to overcome it, very strong UV irradiation is required. There is a problem. In order to solve this problem, a method has been proposed in which a photocuring treatment is performed in a state where there is no or little oxygen such as a nitrogen atmosphere, or a thin cover sheet that does not allow air to pass through is applied on the coating film solution. However, it is not used much because it requires new equipment.

  On the other hand, long straight tube type ultraviolet lamps are widely used to irradiate a wide irradiation object with ultraviolet rays. Normally, the discharge lamp has a spatial distribution in which the central portion in the length direction is strong and weakens toward the end. For this reason, when irradiating ultraviolet rays while moving the irradiated object on a belt conveyor or the like, there is a problem that the irradiation intensity near the left and right sides of the belt conveyor becomes insufficient. Therefore, conventionally, measures such as installing a new ultraviolet lamp at the end have been taken.

JP 2011-23112 A

  Therefore, the present invention controls an energy-saving ultraviolet ray generator capable of suppressing photocuring inhibition by oxygen in the air and uniformly curing the coating film to be photocured from the surface to the back, and discharge plasma emission in the length direction. Thus, an object of the present invention is to provide an ultraviolet generator that makes the ultraviolet radiation distribution in the longitudinal direction uniform.

Therefore, the ultraviolet generator of the present invention is characterized in that a mixed gas containing oxygen (O2) 0-18 with respect to nitrogen (N2) 100 is sealed in a discharge space at a normal temperature pressure ratio.
The second feature is that 0.5 to 5 argon (Ar) is added to the mixed gas 1 at a normal pressure ratio.
Further, a discharge space is formed in the cylinder, and a mixed gas of nitrogen (N2) and oxygen (O2) is sealed. The electrodes are divided and arranged along the length direction of the cylinder, and the electrodes are connected to these electrodes. A third feature is that a multiphase AC power source in which the voltage applied between them is adjusted by phase setting is connected.

Since the ultraviolet ray generator of the present invention seals a mixed gas of nitrogen (N2) and oxygen (O2) in the discharge space, part of the nitrogen (N2) and oxygen (O2) in the discharge space is dissociated by the plasma. N and O are generated, and NO in the excited state can be generated from the N and O. The short wavelength component (200 to 300 nm) from the nitrogen monoxide gas (NO) and the medium wavelength component (300 from the nitrogen gas (N2)) UV light of ~ 400nm) is generated.
Ultraviolet rays with a short wavelength range in this radiation spectrum are absorbed in a very shallow and narrow region of the coating film and cause a photocuring reaction, which prevents the penetration of oxygen in the air into the coating film. Curing proceeds quickly. The radiation intensity in the short wavelength region from NO can be changed by adjusting the O2 partial pressure (concentration) for N2.
Further, when Ar is added to the mixed gas, a metastable Ar having a long lifetime is generated by discharge, which acts on N2 and suppresses the emission of ultraviolet rays having a radiation spectrum of N2 in the middle wavelength region.
By adjusting the oxygen partial pressure (concentration) with respect to nitrogen and the Ar partial pressure (concentration) with respect to these mixed gases, the relative intensity ratio between short-wavelength radiation from NO and medium-wavelength radiation from N2 can It can be varied to suit the coating film to be cured. Moreover, Ar lowers the discharge start voltage, so that the life of the discharge tube can be extended.
In addition, by arranging the electrodes in the length direction of the straight tube type lamp and supplying multiphase AC power with the voltage applied between the electrodes adjusted by phase setting to the electrodes, discharge plasma in the length direction By controlling the light emission, the ultraviolet radiation distribution in the length direction can be made uniform.

  Embodiments of the present invention will be described below.

FIG. 1 shows a cross-sectional view of a photocuring ultraviolet ray generating apparatus embodying the present invention.
In the ultraviolet curing device for photocuring, twelve sheet-like divided electrodes 1 are embedded in the barrier layer 2 with a slight gap a, and are closely fixed to the substrate 31 on the bottom surface of the flat container 3.
The opposing surface of the substrate 31 is covered with a light extraction window 32, and the flat vessel 3 is sealed to form a low-pressure discharge chamber. The divided electrodes 1 are arranged so as to cover the entire substrate 31 with as large an area as possible.
The barrier layer 2 is made of a material having good electrical insulation and thermal conductivity, such as quartz glass or boron nitride, to form an insulator layer.

On the outside of the substrate 31, 12 + 1 bar-shaped magnets 4 arranged with the adjacent polarities reversed are closely fixed along the gap a and fixed. The arrow of the magnet 4 indicates the direction of the magnetic pole. As a result, a multipolar magnetic field is formed so that the magnetic lines of force 4 a cover the surface of the split electrode 1.
The outside of the substrate 31 to which the magnet 4 is attached is covered with a magnetic shield plate 5 so that the lines of magnetic force are concentrated inside without diverging outside.

The magnet 4 with a multipolar magnetic field may use an electromagnetic coil instead of a permanent magnet.
Alternatively, a sheet-like magnet 4 such as a rubber magnet may be sandwiched between the barrier layer 2 and the substrate 31 or may be attached to the outside of the substrate 31 to form a multipolar magnetic field. Thereby, the shape of the ultraviolet ray generator can be made thin and compact as the thickness of the magnet 4 is reduced.

Here, the positional relationship between the magnet 4 and the divided electrode 1 is arbitrary, but FIG. 1 shows a case where the magnet 4 is placed immediately behind the gap a between the divided electrode 1 and the divided electrode 1. At this time, since the multipolar magnetic field is formed so that the surface of the split electrode 1 is covered with the lines of magnetic force, the plasma P is effectively confined in the vicinity of the surface of the split electrode 1.

As shown in FIG. 2, the twelve divided electrodes 1 have 12-phase AC power supplies having the same amplitude, the phases of which are shifted by 1/12 period via a feed terminal 11 attached to one end of the divided electrode 1. 6 is connected. The 12-phase AC power supply 6 is composed of a low-frequency AC power supply whose frequency, amplitude and phase (including waveform) are controlled in a star connection, and the entire power supply is left at a floating potential by an insulating transformer or the like. Is generated only between the divided electrodes 1.
If the number of phases of the power supply is 4 or more, the uniform region of the potential distribution, that is, the uniform region of the electric field increases as the number of phases increases. Is a practical category.

The ultraviolet ray generator according to the present invention has the above-described configuration, and the inside of the flat vessel 3 is evacuated by an exhaust device (not shown), discharged and cleaned, and then pre-treated with oxygen discharge plasma (conditioning). I do. Thereby, the inner wall of the flat container 3 is oxidized, and a trace amount of oxygen is adsorbed on the inner wall. Next, after removing the oxygen used for the pretreatment, a mixed gas containing oxygen 0 to 18 with respect to nitrogen 100 is introduced at a normal temperature pressure ratio to seal the inside of the flat container 3. Here, oxygen 0 (zero) means that oxygen (O2) adsorbed on the inner wall is knocked out when nitrogen plasma is generated by confining only nitrogen (N2) after pretreatment, so oxygen (O2) is not added. It also means that there are good cases.

Next, a phase control 12 output AC power source of 1 kW or less is connected to the 12 divided electrodes 1 to supply discharge electric energy. Thereby, as shown in FIG. 1, plasma P is generated by stable alternating current glow discharge along the surface of the divided electrode 1 covered with the barrier layer 2.
When a 12-phase AC voltage is applied to the 12 divided electrodes 1, the discharge makes one turn between the divided electrodes 1 during one cycle, so that the discharge rotates by the applied frequency per second. For this reason, discharge occurs between any of the divided electrodes 1 at any time, and continuous discharge such as high-frequency lighting occurs regardless of low-frequency AC discharge. The plasma P generated as a result of the discharge is confined in a narrow and thin region by a multipolar magnetic field, and collision excitation by the plasma of an electrically neutral mixed gas becomes active, and the emission density and emission efficiency from the excited mixed gas are increased. Rise.

The emission spectrum at this time is shown in FIG. When plasma discharge occurs in a mixed gas of N2, O2, and Ar, N is dissociated from a part of N2, O is dissociated from a part of O2, and NO is excited from this N and O, and this NO is short. Light is emitted in a wavelength range of 200 to 300 nm to become ground state NO, and further dissociated by plasma to return to N and O. The short-wavelength radiation intensity from NO can be changed by adjusting the O2 partial pressure (concentration) with respect to N2. In addition, the metastable Ar having a long lifetime is generated by the discharge, and this acts on N2 to suppress ultraviolet radiation having a radiation spectrum of N2 in the middle wavelength range of 300 to 400 nm. By adjusting the oxygen partial pressure (concentration) with respect to nitrogen and the Ar partial pressure (concentration) with respect to these mixed gases, the relative intensity ratio of radiation in the short wavelength region from NO is changed. Ar lowers the discharge start voltage, so the life of the discharge tube can be extended.

  According to the experiment, the ultraviolet radiation intensity in the short wavelength region (200 to 300 nm) from nitric oxide can be changed by changing the amount of oxygen to be enclosed in the flat container 3 after the pretreatment from 0 to 18 with respect to nitrogen 100. It was found that the ultraviolet radiation intensity ratio with the mid-wavelength range can be changed from the minimum value to the maximum value. The optimum mixed gas pressure at this time is 0.2 to 2 Torr. Further, it was found that the ultraviolet radiation intensity in the medium wavelength region (300 to 400 nm) from nitrogen gas decreases as the amount of argon (Ar) added increases, and at the same time, the discharge start voltage decreases.

  When the partial pressure ratio of oxygen (O 2) gas and nitrogen (N 2) gas is 1: 6 and the total gas pressure is 0.5 Torr, when the same amount of argon (Ar) gas is added, in the middle wavelength region (300 to 400 nm) The ultraviolet component was reduced to about half compared to when no argon (Ar) gas was added. At this time, the discharge start voltage decreased to about 700 to 500V. When the added argon (Ar) gas was doubled, the ultraviolet component in the medium wavelength region (300 to 400 nm) was further reduced to about half thereof, and the discharge start voltage was reduced to about 450V. It was found that the optimum value of the partial pressure of argon (Ar) gas to be mixed is 1 to 3 times the total partial pressure of oxygen (O 2) nitrogen (N 2) gas.

  As described above, the mixing ratio of oxygen (O 2), nitrogen (N 2), and argon (Ar) gas is adjusted, and the radiation intensity ratio in the short wavelength region (200 to 300 nm) and medium wavelength region (300 to 400 nm) of ultraviolet light is controlled. Thus, it is possible to realize energy-saving photocuring that suppresses photocuring inhibition by oxygen in the air and that can uniformly effect the coating film from the surface to the back.

The emission spectrum from nitric oxide (NO) is in a short wavelength range of 200 to 300 nm (short wavelength range). Ultraviolet rays in the short wavelength region are absorbed in a very narrow region on the surface of the coating film, and the energy density is high. Therefore, even if there is inhibition of photocuring by oxygen in the air, the photocuring reaction (crosslinking) in this region is likely to proceed.
As shown in FIG. 4, when the photocuring reaction proceeds on the surface of the coating film, oxygen in the air hardly passes (diffuses) through the surface to the depth of the coating film. That is, a barrier (air-coating film blocking layer in FIG. 4) that suppresses the permeation (diffusion) of oxygen in the air is generated on the surface area of the coating film by irradiation with ultraviolet rays having a short wavelength component, and the medium wavelength that is the main component Oxygen inhibition with respect to photocuring by ultraviolet rays in the region is suppressed, and the coating film is photocured in a short time (about 30 seconds). By adjusting the concentration of O2 with respect to N2, the radiation intensity in the short wavelength region from NO can be changed. If the component in the short wavelength region is too strong, the properties of the surface region of the coating film and the cured film inside are not good (if only the surface region is solidified, small wrinkles are formed on the surface and the transparency of the coating film is lowered). If the short wavelength component is weak, it will not harden.

In the discharge plasma, the wavelength of ultraviolet rays emitted from N2 is longer than that of NO, and the ultraviolet rays in the middle wavelength range are transmitted to the depth of the coating film, so that the entire coating film is photocured. If the ratio of the intensity of the short wavelength and medium wavelength is appropriate, it can be photocured with the same properties to the inside while creating a barrier that does not allow oxygen in the air to enter the surface of the coating film, so it is short and short Photocuring with good properties can be achieved with power consumption.
It is to be noted that the combination of a medium wavelength LED and a short wavelength LED in photocuring is effective, but the discharge tube can be manufactured at a lower cost than the LED.

Next, an ultraviolet generator capable of adjusting the light intensity in the width direction will be described.
When this ultraviolet ray generator is conceptually described, as shown in FIG. 5a, a plurality of rod-shaped (120 cm, thickness 1 cm) quartz tubes 8 are arranged in a direction perpendicular to the traveling direction above the conveyor C. And irradiate the irradiated object L. Alternatively, as shown in FIG. 5b, a plurality of quartz tubes 8 are arranged in the length direction of the inner wall of the container D having an arched cross section, and the irradiated object L in the container D is irradiated. If the light intensity of the quartz tubes 8 arranged in this way is made stronger at both ends from the center, the illuminance of the irradiated surface can be averaged in the width direction. The example in FIG. 5a is suitable for a flat plate having a large area to be irradiated, and the example in FIG. 5b is suitable for a solid shape.

6 and 7 show a front view and a cross-sectional view of an ultraviolet ray generator capable of adjusting the light intensity in the width direction.
In this ultraviolet ray generator, a lamp house LH is formed by a magnetic shield plate 7, a quartz tube 8 is fitted into the lamp house and attached, and both ends of the lamp house are pushed into a fixture 9 to fix the quartz tube 8.

The electrode 1 is formed by sputtering or vapor-depositing aluminum on the outer half of the quartz tube 8.
The surface of the electrode 1 on the quartz tube 8 side serves as a mirror surface and also serves as an ultraviolet reflecting surface. This reflecting surface effectively acts on radiation components from nitric oxide (NO) in the center of the discharge plasma.
The reason is that nitric oxide (NO) synthesized from nitrogen (N) and oxygen (O) in the discharge plasma is immediately dissociated into nitrogen (N) and oxygen (O) by the discharge plasma after emitting ultraviolet rays. Like the excimer lamp, it is considered that there is no self-absorption (there is no NO that absorbs radiation from NO).
As a result, almost all ultraviolet rays radiated from deep inside the discharge plasma and directed to the reflection surface are reflected to the light extraction side. Actually, in the case where the mirror-like sputter electrode 1 is used and the case where it is not, the short wavelength region component from NO has changed more than twice.

  Next, a plate plated with soft iron is bent into a bowl shape to form the magnetic shield plate 7, and the magnet 4 is set at a fixed position by using the inner valley fold line 7a for positioning. FIG. 8 shows a perspective view of the magnetic shield plate. FIG. 8A shows the arrangement of the polarities of the magnets 4 at the center of the magnetic shield plate 7 at the same time. FIG. 8B also shows how the polarities of the magnets 4 are arranged at both ends of the magnetic shield plate 7.

  The quartz tube 8 is attached to the lamp house LH in which the barrier layer (insulator) 2 is disposed inside the set. When attached, as shown in FIG. 7, the electrode 1 of the quartz tube 8 is electrically connected to the power supply probe 10 of the lamp house. The power supply probe 10 has a diameter of 2 and protrudes toward the electrode by the force of the spring. By doing so, even if there are a plurality of electrodes, the feeding probe can be connected to all the electrodes at once by simply fitting the quartz tube 8 into the lamp house LH. The thickness of the electrode 1 is 1 to 10 μm, the barrier layer 2 is 0.1 to 0.3 mm, and the magnetic shield plate 7 is 0.8 mm. The magnet 4 is made of iron, neodymium, or boron.

Here, when discharge electric energy is supplied to the electrode 1, plasma P is generated as shown in FIG. 10, and the plasma P is confined by the magnetic lines of force of the magnet 4.
At this time, as shown in FIGS. 11A and 11B, the phase difference of the multiphase AC power source is changed from the initial equal 60 ° to V1-V2 = 105 °, V2-V3 = 60 °, V3-V4 = 30. When the angle is changed to V4-V5 = 60 ° and V5-V6 = 105 °, the potential difference between the electrodes 1 at both ends becomes larger than that at the center, and the light intensity at both ends can be easily increased from that at the center.

It is sectional drawing of the ultraviolet-ray generator for photocuring which implemented this invention. FIG. 2 is a power supply connection diagram of FIG. 1. It is a figure which shows the emission spectrum of an ultraviolet-ray. It is a figure explaining photocuring. It is a conceptual explanatory drawing of the ultraviolet-ray generator which can adjust light intensity in the width direction. It is a front view of the ultraviolet-ray generator which can adjust light intensity in the width direction. It is an expanded sectional view of FIG. (A) is the center part of FIG. 6, (b) is the perspective view of the both ends. FIG. 7 is a power supply connection diagram of FIG. 6. It is a figure which shows the mode of the plasma generation | occurrence | production in FIG. It is the electric power feeding vector diagram of FIG.

DESCRIPTION OF SYMBOLS 1 Electrode 2 Barrier layer 3 Flat container 31 Substrate 32 Light extraction window 4 Magnet 5 Magnetic shield plate 6 12-phase AC power source 7 Magnetic shield plate 8 Quartz tube 9 Fixing tool 10 Feed probe a Gap C Conveyor D Container L Irradiated object P Plasma

Claims (3)

  An ultraviolet ray generator in which a mixed gas containing oxygen (O2) 0 to 18 with respect to nitrogen (N2) 100 is sealed in a discharge space at a normal pressure ratio.   The ultraviolet ray generator according to claim 1, wherein 0.5 to 5 of argon (Ar) is added to the mixed gas 1 at a normal pressure ratio. A discharge space is formed in the cylinder, and a mixed gas of nitrogen (N2) and oxygen (O2) is sealed,
Dividing and arranging the electrodes along the length direction of this cylinder,
An ultraviolet ray generator comprising a multiphase AC power source in which the voltage applied between the electrodes is adjusted by phase setting to these electrodes.

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