JP4881249B2 - Plasma sterilization apparatus and plasma sterilization method - Google Patents

Description

  The present invention relates to a plasma sterilization apparatus and a plasma sterilization method particularly suitable for medical use.

In recent years, infectious diseases caused by pathogenic microorganisms such as norovirus and avian influenza have spread worldwide and have become a serious social problem. In order to prevent such infections, it is necessary to perform sterilization and disinfection without fail, and it is extremely important to establish a sterilization method that can be realized safely and easily, especially for elderly people and infants with low immunity. is there.
The sterilization method is a treatment method that kills all microorganisms. The level of microbial contamination after sterilization required in the medical field is 10 ⁻⁶ , which means that when 1,000,000 identical forceps are sterilized, one of them is contaminated with microorganisms. This is called sterility assurance level (SAL).

In contrast to the sterilization method, the disinfection method is a treatment method with a certain antibacterial spectrum, and the target microorganisms are killed, but there are microorganisms that always protrude from the antibacterial spectrum of one disinfection method. It is not effective against other microorganisms. Taking a disinfectant as an example, there is always a resistant microorganism in one disinfectant, and in some cases it may grow in that disinfectant.

There are four sterilization methods: heating method (high pressure steam sterilization, dry heat sterilization), gas method (ethylene oxide gas sterilization, hydrogen peroxide low temperature gas plasma sterilization), irradiation method (radiation sterilization), and filtration method. Among these sterilization methods, the most widely used method is a heating method, which refers to a method of sterilization using high-temperature wet heat, air, flame or the like.
Among them, high-pressure steam sterilization is particularly used. High-pressure steam sterilization is performed using saturated steam. The reason why this method is frequently used is that (1) a large amount of water that is close and inexpensive is used, (2) vapor, which is a gas, holds and releases a large amount of heat, (3) Condensed and returned to water, harmless and no side effects, (4) Water is a scientifically stable molecule and easy to handle, (5) Vapor penetrates well into fine spaces It is because it has. In particular, when water condenses from a gas to a liquid, it releases a large amount of heat, and the energy can be used for sterilization. In addition, about high pressure steam sterilization, it describes in the nonpatent literature 1, for example.
Kobayashi, K. (eds.), Sterilization at medical sites, Japan Society for Medical Instrumentation, 2000.

  However, high-pressure steam sterilization requires (1) a sealed container for generating high-pressure steam. (2) Steam pressure rises as the pressure increases, and steam temperature rises accordingly. There is also a problem that it cannot be used for sterilized products. Therefore, it is desired to develop a sterilization technique that can be applied at a low cost and can be widely applied so as to enable sterilization at a lower temperature under conditions of atmospheric pressure that does not require decompression or pressurization.

  The present invention has been devised in view of such a demand, and provides a plasma sterilization apparatus and a plasma sterilization method capable of generating a plasma flow in an atmospheric water vapor flow and sterilizing by the plasma flow. The purpose is to provide.

In order to achieve the above object, a plasma sterilization apparatus according to the first aspect of the present invention comprises a tube made of a dielectric material, one end of which is opened to the atmosphere, and an object to be sterilized is disposed therein, A water vapor generating part connected to the other end of the tube for generating water vapor to flow into the tube, a discharge part provided in the middle of the tube and causing a dielectric barrier discharge inside the tube; A voltage generating unit for applying an AC voltage related to dielectric barrier discharge to the discharge unit, the discharge unit being disposed on the outer periphery of the tube and grounded, the first electrode inserted in the tube A second electrode, the voltage generator applies the alternating voltage between the first electrode and the second electrode, the tube is formed in a cylindrical shape, the second electrode, It is arranged on the outer periphery of the tube in a cylindrical shape, and the first electrode is formed in a linear shape and is opposed to the cylinder axis of the second electrode. When the alternating current voltage of the rectangular wave applied to the discharge unit rises, the voltage generation unit is arranged eccentrically, and then a current larger than the maximum value of the discharge current instantaneously flows after the discharge current flows. An AC voltage equal to or higher than a predetermined voltage in a discharge state is applied to the discharge part, and the water vapor generation part fills the inside of the tube with water vapor .

Ie, first, be those discharge current has a discharge state flowing short time (during the fluctuation of the discharge voltage value) upon application of voltage, the micro discharge type of dielectric barrier discharge characteristic of a discharge form If it defines, the plasma sterilization apparatus of this invention of Claim 1 will apply the alternating voltage of the magnitude | size which a discharge current far larger than the maximum value of the discharge current of this micro discharge flows to a discharge part to a discharge part. It is characterized by that.

Plasma sterilization apparatus of the present invention described in claim 2 provides the plasma sterilizing device according to claim 1 Symbol placement, the voltage generating unit, 3-4 frequency within kHz energy per unit due to discharge time is more than 3.0W The AC voltage is applied to the discharge part.
The plasma sterilization method of the present invention according to claim 3 is a first step of placing an object to be sterilized in a tube made of a dielectric material and having one end opened to the atmosphere, and from the other end of the tube. Supplying water vapor to the inside of the tube, filling the inside of the tube with the water vapor, and applying an AC voltage between the electrodes, causing dielectric barrier discharge inside the tube to turn the water vapor into plasma And in the first step, the first electrode is inserted into the tube, and the grounded second electrode is disposed on the outer periphery of the tube. An AC voltage is applied between the first electrode and the second electrode to cause the dielectric barrier discharge. In the first step, the tube is formed into a cylindrical shape, and the second electrode is formed into a cylindrical shape. Formed and arranged on the outer periphery of the tube, and the first electrode is formed in a linear shape and is opposed to the cylinder axis of the second electrode. In the third step, a current larger than the maximum value of the discharge current instantaneously flows after the discharge current flows when the AC voltage of the rectangular wave applied to the discharge section rises in the third step. The dielectric barrier discharge is caused by applying an AC voltage equal to or higher than a predetermined voltage in a discharge state .

The plasma sterilization method of the present invention according to claim 4 is the plasma sterilization method according to claim 3 , wherein in the third step, the frequency per unit time by discharge is 3.0 W or more, and the frequency within 3 to 4 kHz. The AC barrier voltage is applied to cause the dielectric barrier discharge.

  According to the plasma sterilization apparatus and the plasma sterilization method of the present invention, water vapor in the tube is turned into plasma under atmospheric pressure by dielectric barrier discharge. Therefore, it is possible to sterilize with a plasma flow of water vapor without the need for decompression or pressurization. In addition, because it is under atmospheric pressure, the ambient temperature in the tube is constant at 100 ° C. For example, it can be sterilized at a temperature 21 ° C lower than high-pressure steam sterilization pressurized to 2 atm. It is possible to sterilize the object. Furthermore, since water vapor under atmospheric pressure is used, a sealed container is unnecessary, and the apparatus configuration can be made inexpensive and simple.

Also, if the first electrode is arranged eccentrically with respect to the second electrode, the plasma generation position in the tube cross-sectional direction is biased to form a plasma flow that flows in the tube cross-sectional direction, and the plasma is evenly distributed in the tube. Water vaporized can be distributed. Therefore, the sterilization effect can be further enhanced.
Further, the sterilization effect can be further enhanced by applying to the discharge part an AC voltage having a magnitude that causes a discharge in which a current larger than the maximum value of the discharge current of the micro discharge defined as described above flows in a pulsed manner. Furthermore, the sterilization effect can be further enhanced by applying an AC voltage having a frequency within 3 to 4 kHz at which the energy per unit time by discharge is 3.0 W or more to the discharge part.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram showing a plasma sterilization apparatus according to an embodiment of the present invention. 2 to 28 show the results of experiments conducted using the plasma sterilization apparatus of FIG. 1, and FIGS. 2 to 5 show the case where plasma is generated in a water vapor flow by changing the applied voltage. 6 to 9 are graphs showing discharge waveforms when plasma is generated in the air by changing the applied voltage, and FIGS. 10 to 13 are graphs showing the discharge waveform when the applied frequency is changed. 14 is a graph showing the discharge waveform when plasma is generated in FIG. 14, FIG. 14 is a graph showing the maximum value of the discharge current in each condition calculated from the discharge waveforms of FIGS. 2 to 13, and FIGS. FIG. 17 is a graph showing the discharge power in each condition calculated from the discharge waveform of FIG. 13, FIG. 17 is a graph showing the discharge power when plasma is generated in the water vapor flow and air by changing the applied voltage, FIG. FIG. 20 shows the applied voltage. Fig. 21 is a cross-sectional photograph of the discharge portion when plasma is generated in the water vapor stream, Fig. 21 is a cross-sectional photograph of the discharge portion when plasma is generated in the air, and Figs. FIG. 26 to FIG. 28 are tables showing sterilization results when plasma is generated in the water vapor flow, with the cross-sectional photographs of the discharge section when plasma is generated in the water vapor flow by changing.

[1. Plasma sterilizer]
As shown in FIG. 1, the plasma sterilization apparatus 1 includes a tube 10, a discharge unit 20, a water vapor generation unit 30, and a voltage generation unit 40. The plasma sterilization apparatus 1 is installed in a draft (not shown) in consideration of secondary products in the discharge unit 20.
The tube 10 is formed in a cylindrical shape from quartz glass, and one end thereof is opened to the atmosphere so that an object to be sterilized is placed inside. Here, one end of the tube 10 is connected to the silicon tube 11 here, and the tip of the silicon tube 11 is inserted into the beaker 12 and is opened to the atmosphere via the silicon tube 11.

  The discharge part 20 is inserted into the tube 10 in an eccentric manner, and is made of a linear stainless steel wire electrode (first electrode) 21 and an aluminum ground electrode (first electrode) disposed on the outer periphery of the tube 10 and grounded. Two electrodes) 22. The ground electrode 22 has a cylindrical shape and is bonded to the outer periphery of the tube 10. The tube 10 functions as a dielectric, and forms a dielectric barrier discharge inside the tube 10 to generate atmospheric pressure non-equilibrium plasma. In FIG. 1, dots are attached to the ground electrode 22 for easy visual recognition.

Here, the dielectric barrier discharge will be briefly described. The dielectric barrier discharge is a method of discharging by inserting at least one dielectric between two electrodes, and can generate a stable plasma with low power. It is possible.
The steam generation unit 30 is connected to the other end of the tube 10, and includes a flask 31 having a predetermined capacity, a heater 32 for heating the flask 31, and a silicon tube 33 for supplying the generated steam to the discharge unit 20. I have. That is, the silicon tube 33 is connected to the other end of the tube 10. Then, the flask 31 containing pure water is heated by the heater 32 to generate water vapor, and the generated water vapor is supplied to the discharge unit 20 via the silicon tube 33.

Here, after plasma is generated in the discharge unit 20, all water vapor including water droplets is released to the atmosphere. Therefore, the water vapor generating unit 30 and the discharge unit 20 are at atmospheric pressure, and the water vapor temperature is constant at 100 ° C.
As shown in FIG. 3, the voltage generator 40 includes a function generator 41, a digital oscilloscope 42, and a high voltage power amplifier 43. Then, an AC voltage is generated by the function generator 41, the AC voltage is amplified 1000 times by the high voltage power amplifier 43, and the amplified AC high voltage is applied to the discharge unit 20. When discharging, the digital oscilloscope 42 is used to measure the applied voltage V, the discharge voltage, and the discharge current.

[2. Experiments with plasma sterilizer]
An experiment using the plasma sterilizer 1 will be described. By this experiment, it is clarified how the discharge waveform, the discharge power P and the state of discharge change by changing the applied voltage V and the applied frequency f by generating a water vapor plasma flow under atmospheric pressure conditions. Its plasma and sterilization characteristics are revealed.

In this experiment, the plasma sterilizer 1 uses a tube 10 having an inner diameter of φ8 mm and an outer diameter of φ10 mm, a stainless wire electrode 21 having a diameter of φ0.28 mm, and a ground electrode 22 having a long length. The length L = 57 mm and the electrode area S = 4475 mm ² and the length L = 80 mm and the electrode area S = 6280 mm ² are used.
In addition, a flask 31 having a capacity of 500 ml is used, a heater 32 using a mantle heater with a rated output of 250 W (AFR-5, Taishin Electric Co., Ltd.), and a silicon tube 33 having an inner diameter of φ10 mm. The one with an outer diameter of φ13 mm is used.

  Furthermore, the function generator 41 uses the Wave Factory WF1943B manufactured by NF Circuit Design Block Co., Ltd., and the digital oscilloscope 42 uses the Wave Surfer 434 manufactured by Le Croy and uses a square wave for the waveform. The voltage power amplifier 43 uses a 10 kVA AC / DC amplifier HVA 4321 manufactured by NF Circuit Design Block Co., Ltd.

[2.1 Plasma characteristics verification method]
In elucidating the plasma characteristics, first, the flow rate and flow rate of the water vapor flow in the tube 10 are measured. The water vapor generated from the water vapor generating unit 30 flows into the tube 10 and is cooled at the outlet of the tube 10, whereby the water vapor is condensed and water droplets are generated. When water changes from a liquid to a gas, the volume increases by 1700 times. Therefore, the average flow rate of water vapor flowing in the pipe 10 can be obtained by measuring the amount of increase in water droplets. Further, when the obtained average flow rate is divided by the cross-sectional area of the pipe 10, the average flow velocity of the water vapor flow in the pipe is obtained.
Measurement is performed three times by the above method, and the average flow rate and average flow velocity in the pipe are obtained from the average.

[2.1.1 Measurement of discharge waveform and calculation of discharge power]
The discharge waveform is measured with an oscilloscope 42. The length L, the applied frequency f, and the applied voltage V of the discharge unit 20 are changed, and the discharge waveform at an arbitrary moment is measured under each condition. From the waveform obtained at that time, the discharge power P is calculated by the equation (1).
P = VI… (1)
The measurement is performed three times for each condition, and the discharge power P is calculated as an average value.

[2.1.2 Observation of discharge section]
Observation of the discharge unit 20 is performed by taking a tube cross-sectional photograph. It is observed how the state of discharge changes when the applied voltage V is changed with the applied frequency f kept constant, and when the applied frequency f is changed with the applied voltage V kept constant. A digital SLR camera (D50, Nikon Corporation) is used for shooting.

[2.2 Method of verifying sterilization characteristics]
Sterilization experiments are performed using a short-term biological indicator (Attest 1291, Sumitomo 3M Limited). In this experiment, Geobacillus stearothermophilus (ATCC 7933, hereinafter referred to as “spore bacterium”) is used as a sample for sterilization (an object to be sterilized). Also, the instruments used in the experiment should be used after disinfecting with alcohol.

  The indicator contains a piece of paper soaked with spore bacteria. A piece of paper is installed along the tube wall of the discharge unit 20, and three pieces are used for each condition. The sterilization process is performed after the discharge unit 20 is sufficiently filled with water vapor and the temperature of the discharge unit 20 becomes constant. The discharge is started after confirming that the stainless wire electrode 21 is stretched in a straight line so that there is no slack. The start of the discharge is regarded as the start of the sterilization process, and the paper piece is exposed to the plasma for the set sterilization time t.

  As soon as the sterilization process is finished, the discharge is terminated and a piece of paper is taken out from the discharge unit 20. At this time, since the temperature of the discharge part 20 has risen to 100 ° C., the work should be performed after sufficiently dissipating heat so as not to burn. Since the taken-out paper piece contains a large amount of moisture, the paper waste is absorbed before returning to the indicator. This is because the determination of sterilization may be affected if a piece of paper contains a large amount of moisture. As the paper waste, one made by Nippon Paper Crecia Co., Ltd. is used.

When the sterilized paper piece is returned to the indicator, sterilization is determined. For determination, a sterilization determination device (Attest Auto-Reader, Sumitomo 3M Limited) 50 is used.
The sterilization determination device 50 determines the success or failure of sterilization by reading the fluorescence of the enzyme produced when the spore germ grows. In judging, the glass ampule in the indicator is squeezed. The ampoule contains a culture solution, and spore bacteria are cultured by immersing a piece of paper in the culture solution. When it is confirmed that the piece of paper is sufficiently immersed in the culture solution, the indicator is put on the sterilization determination device 50. The sterilization determination device 50 performs fluorescence determination for 1 hour, and determines the success or failure of sterilization. Positive (+) indicates incomplete sterilization and negative (-) indicates completion of sterilization. At this time, an indicator that has not been sterilized is also subjected to determination as a positive control. If the positive control does not show positive correctly, check the storage status of the incubator with the indicator. An indicator that has been judged to be sterilized should be discarded after being fully sterilized by an autoclave.

The above operation is performed by changing the applied frequency f, the applied voltage V, and the sterilization treatment time t to verify the sterilization effect for each condition.
[3. Experimental results and discussion]
[3.1 Plasma characteristics]
In this experiment, when the plasma flow was generated in the water vapor flow at atmospheric pressure, the flow rate and flow velocity of the water vapor flow flowing in the pipe were measured. It is clarified how the discharge state changes by changing the applied voltage V and the applied frequency f in the water vapor flow to generate a plasma flow. The results and discussion are shown below.

[3.1.1 Measurement of average pipe flow rate and average flow velocity]
The output of the mantle heater 32 used in this experiment is 250 W, and the enthalpy difference between liquid water and gaseous water at 100 ° C is 2259 J / g. Assuming that all was used only for evaporation, the average flow rate in the pipe was 11.3 l / min and the average flow velocity was 3.7 m / s. However, since there is heat loss and some water vapor condenses, the actual flow rate is slower.
In the experiment, an average pipe flow rate of 8.1 l / min was obtained from the average of three measurement results. When this is converted into a flow velocity, the average pipe flow velocity is 2.7 m / s. In other words, it can be said that 67 W of heat loss exists.

[3.1.2 Discharge waveform measurement]
FIGS. 2 to 5 show the case where plasma is generated in the water vapor flow by changing the applied voltage V from 11 kV _{pp to} 14 kV _pp with the applied frequency f = 3 kHz and the discharge length L = 80 mm. A discharge waveform is shown.

Under each condition, the discharge current increases at the rising edge of the voltage. This is a phenomenon called micro discharge, which is a typical discharge state of dielectric barrier discharge. That is, here, micro discharge is defined as a kind of discharge form in which a discharge current having a substantially constant maximum value flows for a short time when the discharge voltage rises (when voltage is applied). However, as shown in FIGS. 4 and 5, when the applied voltage V ≧ 13 kV _pp , it is possible to confirm a characteristic discharge state in which a larger current instantaneously flows after the micro discharge has occurred. That is, it is possible to confirm a pulsed discharge state in which a current much larger than the maximum value of the discharge current of the micro discharge flows following the discharge current of the micro discharge in a short time when the discharge voltage rises. it can. Such a discharge state is not formed when the voltage is low, and can be confirmed by increasing the applied voltage V. On the other hand, FIGS. 6 to 9 show waveforms when the working gas is discharged as air under the same conditions, but such a discharge state is not formed in the air.

10 to 13, the applied voltage V = 13 kV _pp , the discharge length L = 80 mm, the applied frequency f was changed to 1, 2, 4, 5 kHz, and plasma was generated in the water vapor flow. The discharge waveform is shown.
Comparing these four conditions and f = 3 kHz in FIG. 4, it can be seen that the maximum value of the current is higher at the high frequency than at the low frequency.

FIG. 14 shows the maximum value of the discharge current I under each condition obtained from the above discharge waveform. When the applied voltage V is 12 kV _pp or less, the discharge current value I is approximately 2.8 mA at each applied frequency f, and is substantially constant. In addition, when the working gas is air, the current value is almost the same. However, when the applied voltage V is 13 kV _pp or more, the discharge current I increases. The rate of increase is greater at higher frequencies than at lower frequencies, and when the applied frequency f is 3 kHz or higher, the discharge current I increases nearly twice as the applied voltage V increases from 12 kV _pp to 13 kV _pp. 6 mA. However, when the applied voltage V is 14 kV _pp , there is almost no difference depending on the applied frequency f.

[3.1.3 Calculation of discharge power]
FIG. 15 shows the discharge power value P under each condition calculated from the discharge waveform. As described above, it has been clarified that when V = 13 kV _pp , the maximum current almost doubled as compared with the case of V = 12 kV _pp flows, but the discharge power P does not increase so significantly. It is considered that this is because the moment when a large current flows is momentary, and thus the discharge power value P is not significantly affected.

However, in reality, a large amount of energy is instantaneously released as the current increases.
When the applied voltage V is changed from 11 kV _pp to 14 kV _pp at f = 3 kHz, the discharge power P increases to 1.9, 2.1, 3.0, and 4.2 W.
FIG. 16 shows the discharge power value P when the frequency f is on the horizontal axis using the same result. Since the number of discharges increases as the applied frequency f increases, it can be estimated that the discharge power P increases accordingly. However, when the applied voltage V is 14 kV _pp , the frequency f is increased when the applied frequency f is 3 kHz or more. The difference in the discharge power P due to is hardly seen. This indicates that the energy per discharge is larger in the case of f = 3 kHz than in the case of f = 5 kHz.

  FIG. 17 shows the discharge power P in the water vapor flow and in the air when the applied voltage V is changed with the applied frequency f = 3 kHz and the length L = 80 mm. Even under the same conditions, the discharge power P is larger when discharged in a water vapor flow than when discharged in air.

[3.1.4 Observation of discharge section]
18 to 20, the applied frequency f is set to a constant value of 3 kHz, and the applied voltage V is changed to 16 to 18 kV _pp (f = 3 kHz, V = 16 to 18 kV _pp ). The tube cross-sectional photograph of the discharge part 20 when plasma is generated is shown in gray scale. When plasma is generated in water vapor, a faint white discharge area can be confirmed. The tube cross-sectional photographs in FIGS. 18 to 20 are shown in gray scale, but when this is viewed in color scale, it can be confirmed that the discharge region emits light blue. As the applied voltage V increases, the discharge region gradually expands to the tube wall. That is, when V = 16 kV _pp shown in FIG. 18, the discharge region observed only near the wire electrode 21 reaches the tube wall of the tube 10 when V = 18 kV _pp shown in FIG. 20. .

FIG. 21 shows a gray cross-sectional photograph of the tube when discharged in air when the applied frequency f is 3 kHz and the applied voltage V is 13 kV _pp (f = 3 kHz, V = 13 kV _pp ). Shown in scale. In air, since the discharge reaches the tube wall even at V = 13 kVpp, it can be said that the ionization potential is higher in water vapor than in air. This is because air is mainly composed of nitrogen, which is easier to discharge than water vapor. Further, when the tube cross-sectional photograph of FIG. 21 is viewed on a color scale, the color of the discharge region is purple in the air. This is because the composition of water vapor is only H and O, whereas since various gases are contained in the air, it is considered that the difference is due to their influence, particularly the presence or absence of nitrogen.

22 to 25, the applied voltage V is set to a constant value of 18 kV _pp , and the applied frequency f is changed to 1 to 5 kHz (f = 1 to 5 kHz, V = 18 kV _pp ). The tube cross-section photograph of the discharge part 20 when plasma is generated is shown. By increasing the applied frequency f, the discharge region diffuses in the tube circumferential direction. This is because the number of discharges per unit time increases as the applied frequency f increases.

[3.2 Sterilization characteristics]
In conducting the sterilization experiment, the spore bacteria used in this experiment were sterilized only with water vapor at 100 ° C. This spore bacterium is said not to be sterilized with water vapor at 100 ° C., and sterilization was not confirmed after 100 minutes of sterilization.
In this experiment, the sterilization experiment was performed by changing the applied voltage V, the applied frequency f, and the length L of the discharge unit 20 to generate a plasma flow in the atmospheric water vapor flow, and sterilization using the atmospheric water vapor plasma flow. The possibility of the system was examined. The results and discussion are shown below.

[3.2.1 Effect of applied voltage]
26, when the applied frequency f is 3 kHz, the length L of the discharge part 20 is 57 mm, and the applied voltage V is changed to 11 to 15 kVpp (f = 3 kHz, L = 57 mm, V = 11). The results of sterilization with an atmospheric water vapor plasma flow of ~ 15 kVpp) are shown. When the applied voltage V is relatively small at 12 kVpp, the sterilization effect is hardly confirmed. When the applied voltage V is 13 kVpp or more, the sterilization effect begins to appear by increasing the sterilization time t, and when the applied voltage V is 15 kV _pp , the sterilization effect is confirmed by setting the sterilization time t to 20 minutes or more. can do.

27, when the applied frequency f is 3 kHz, the length L of the discharge part 20 is 80 mm, and the applied voltage V is changed from 11 to 14 kV _pp (f = 3 kHz, L = 80 mm, V = The sterilization result by the water vapor plasma flow of 11-14 kV _pp ) is shown. In this case, the sterilization effect cannot be confirmed when the applied voltage V is 12 kV _pp or less, and can be confirmed when the applied voltage V is 13 kVpp or more and the sterilization treatment time t is 30 minutes or more.

It is considered that the clear difference in the sterilization effect caused by the applied voltage value V is due to a large pulse-like current confirmed at 13 kV _pp or higher. An increase in the discharge current is an increase in the discharge power P. Along with this, the electron energy in the plasma also increased, and it was considered that the sterilization effect that could not be obtained at 12 kV _pp or less could be obtained at 13 kV _pp or higher due to the increase in the amount of radicals generated or ultraviolet intensity. Moreover, the result of FIG. 27 represents the sterilization result of the sample installed in the upstream, the center, and the downstream of the discharge part 20 in order from the left for each condition. That is, [+-] represents upstream (+), center (-), and downstream (-). From this result, it became clear that the sterilization effect is greater on the downstream side than on the upstream side even in the same discharge part 20. This is because the radicals generated by the plasma in the discharge unit 20 are transported downstream by the water vapor flow, so that the amount of radicals irradiated to the spore bacteria is larger on the downstream side than on the upstream side. Conceivable.

[3.2.2 Effect of applied frequency]
28, when the applied voltage V is 13 kV _pp , the length L of the discharge part 20 is 80 mm, and the applied frequency f is changed from 1 to 5 kHz (f = 1 to 5 kHz, L = 80 mm, The sterilization result by the water vapor plasma flow of V = 13 kV _pp ) is shown. The sterilization effect can be confirmed at f = 3 kHz and 4 kHz, but the sterilization effect cannot be confirmed under other conditions.

This result seems to be related to the discharge power P.
That is, when f = 3 kHz and f = 5 kHz at V = 13 kV _pp , the discharge power P is 3.0 W and 3.5 W, respectively, and the energy per discharge is f = 3 kHz. It can be said that the case is larger. Thereby, the energy of electrons in the plasma is increased, and it is considered that a higher sterilization effect can be obtained when f = 3 kHz than when f = 5 kHz.

From the above results, when sterilization is performed using an atmospheric pressure water vapor plasma flow, discharge is performed at an appropriate applied voltage V and an appropriate applied frequency f, and in this experiment, V = 13 kV _pp or more and f = 3 kHz. It was found that a high sterilization effect can be obtained even in atmospheric pressure, that is, 100 ° C. water vapor.
The results obtained are summarized below.

(1) When an atmospheric pressure water vapor plasma flow is generated by a dielectric barrier discharge, a large current that cannot be seen in a discharge in air flows instantaneously. In this experiment, such a discharge state was formed when the applied voltage V was 13 kV _pp or more. When the applied voltage V increases from 12 kV _pp to 13 kV _pp at an applied frequency f = 3 kHz, the maximum discharge current I increases from 2.7 mA to 6.2 mA.

(2) Although the discharge power P increases with the applied voltage V, no significant change is observed when the applied frequency f is changed. In particular, when the applied voltage V = 14 kV _pp , the difference due to the applied frequency f is hardly seen when the applied frequency f is 3 kHz or more. That is, the energy at one discharge is larger at 3 kHz than at 5 kHz. When f = 3 kHz, V = 14 kV _pp , L = 80 mm and an atmospheric pressure water vapor plasma flow is generated, the discharge power P is 3.0 W.

(3) When sterilization is performed using an atmospheric pressure water vapor plasma flow, sterilization is performed at an applied voltage V of 13 kV _pp or more and a sterilization treatment time t of 30 minutes or more under the conditions of f = 3 kHz and L = 80 mm. An effect is obtained. The sterilization effect is affected by the applied frequency f, and the sterilization effect cannot be confirmed at frequencies other than f = 3 kHz and 4 kHz. In addition, in the same water discharge portion 20 in the water vapor flow, the sterilization effect is greater on the downstream side than on the upstream side.

[Others]
As mentioned above, although one embodiment of the plasma sterilization apparatus of the present invention, its experimental method, and the experimental result have been described, the plasma sterilization apparatus of the present invention is not limited to the above-described embodiment and is within the scope of the present invention. Various modifications are possible.
For example, in the above embodiment, the tube 10 is made of quartz glass. However, the tube 10 may be made of a material other than quartz glass as long as it functions as a dielectric. For example, the tube 10 may be made of a fluororesin such as PFA or FEP, an insulating polymer such as polyimide resin, or an insulating inorganic material such as DLC or barium titanate.

  Further, in the above embodiment, the ground electrode 22 is formed in a cylindrical shape and bonded to the entire outer periphery of the tube 10. However, for example, the cross section is formed in a semicircular shape, and a part of the entire outer periphery of the tube 10 is formed. It may be adhered to.

It is a typical lineblock diagram showing the plasma sterilization device concerning one embodiment of the present invention. 1 is a graph showing a discharge waveform when plasma is generated in a water vapor flow with an applied frequency f = 3 kHz, a discharge length L = 80 mm, and an applied voltage V = 11 kV _pp in the plasma sterilization apparatus shown in FIG. is there. 1 is a graph showing a discharge waveform when plasma is generated in a water vapor flow in the plasma sterilization apparatus shown in FIG. 1 with an applied frequency f = 3 kHz, a discharge length L = 80 mm, and an applied voltage V = 12 kV _pp. is there. 1 is a graph showing a discharge waveform when plasma is generated in a water vapor flow in the plasma sterilization apparatus shown in FIG. 1 with an applied frequency f = 3 kHz, a discharge length L = 80 mm, and an applied voltage V = 13 kV _pp. is there. 1 is a graph showing a discharge waveform when plasma is generated in a water vapor flow in the plasma sterilization apparatus shown in FIG. 1 with an applied frequency f = 3 kHz, a discharge length L = 80 mm, and an applied voltage V = 14 kV _pp. is there. 2 is a graph showing a discharge waveform when plasma is generated in air with an applied frequency f = 3 kHz, a discharge portion length L = 80 mm, and an applied voltage V = 11 kV _pp in the plasma sterilization apparatus shown in FIG. . In the plasma sterilization apparatus shown in FIG. 1, it is a graph which shows the discharge waveform when plasma is generated in the air by applying frequency f = 3 kHz, discharge part length L = 80 mm, and applied voltage V = 12 kV _pp. . 2 is a graph showing a discharge waveform when plasma is generated in air with an applied frequency f = 3 kHz, a discharge part length L = 80 mm, and an applied voltage V = 13 kV _pp in the plasma sterilization apparatus shown in FIG. . In the plasma sterilization apparatus shown in FIG. 1, it is a graph which shows the discharge waveform when plasma is generated in the air by applying frequency f = 3 kHz, discharge part length L = 80 mm, and applied voltage V = 14 kV _pp. . 1 is a graph showing a discharge waveform when plasma is generated in a water vapor flow in the plasma sterilization apparatus shown in FIG. 1 with an applied frequency f = 1 kHz, a discharge length L = 80 mm, and an applied voltage V = 13 kV _pp. is there. 1 is a graph showing a discharge waveform when plasma is generated in a water vapor flow in the plasma sterilization apparatus shown in FIG. 1 with an applied frequency f = 2 kHz, a discharge length L = 80 mm, and an applied voltage V = 13 kV _pp. is there. 1 is a graph showing a discharge waveform when plasma is generated in a water vapor flow with an applied frequency f = 4 kHz, a discharge length L = 80 mm, and an applied voltage V = 13 kV _pp in the plasma sterilization apparatus shown in FIG. is there. 1 is a graph showing a discharge waveform when plasma is generated in a water vapor flow in the plasma sterilization apparatus shown in FIG. 1 with an applied frequency f = 5 kHz, a discharge length L = 80 mm, and an applied voltage V = 13 kV _pp. is there. It is a graph which shows the maximum value of the discharge current I in each condition calculated by the discharge waveform of FIGS. FIG. 14 is a graph showing discharge power P calculated under the discharge waveforms in FIGS. 2 to 13 under various conditions with the applied voltage V on the horizontal axis. It is a graph which shows the discharge power P in each condition calculated from the discharge waveforms of FIGS. 2 to 13 with the applied frequency f on the horizontal axis. In the plasma sterilization apparatus shown in FIG. 1, when plasma is generated in a water vapor flow and in air with an applied frequency f = 3 kHz, a discharge length L = 80 mm, and an applied voltage V = 11 kV _{pp to} 14 kV _pp It is a graph which shows the discharge electric power P of. In the plasma sterilization apparatus shown in FIG. 1, it is a pipe | tube cross-sectional photograph of the discharge part when plasma is generated in water vapor | steam flow by setting applied frequency f = 3 kHz and applied voltage V = 16 kV _pp . In the plasma sterilization apparatus shown in FIG. 1, it is a pipe | tube cross-sectional photograph of the discharge part when plasma is generated in water vapor | steam flow by setting application frequency f = 3 kHz and application voltage V = 17 kV _pp . In the plasma sterilization apparatus shown in FIG. 1, it is a pipe | tube cross-sectional photograph of the discharge part when plasma is generated in water vapor | steam flow with the applied frequency f = 3 kHz and the applied voltage V = 18 kV _pp . In the plasma sterilization apparatus shown in FIG. 1, it is a pipe | tube cross-sectional photograph of the discharge part when plasma is generated in air by applying frequency f = 3 kHz and applying voltage V = 13 kV _pp . In the plasma sterilization apparatus shown in FIG. 1, it is a pipe | tube cross-sectional photograph of the discharge part when plasma is generated in water vapor | steam flow by setting applied frequency f = 1kHz and applied voltage V = 18 kV _pp . In the plasma sterilization apparatus shown in FIG. 1, it is a pipe | tube cross-sectional photograph of the discharge part when plasma is generated in water vapor | steam flow by setting application frequency f = 2kHz and application voltage V = 18 kV _pp . In the plasma sterilization apparatus shown in FIG. 1, it is a pipe | tube cross-sectional photograph of the discharge part when plasma is generated in the water vapor | steam flow by applying frequency f = 4 kHz and applying voltage V = 18 kV _pp . In the plasma sterilization apparatus shown in FIG. 1, it is a pipe | tube cross-sectional photograph of the discharge part when plasma is generated in water vapor | steam flow by making application frequency f = 5 kHz and application voltage V = 18 kV _pp . In the plasma sterilization apparatus shown in FIG. 1, sterilization results when plasma is generated in a steam flow with an applied frequency f = 3 kHz, a discharge length L = 57 mm, and an applied voltage V = 11 kV _pp to 15 kV _pp It is a table | surface which shows. In the plasma sterilization apparatus shown in FIG. 1, sterilization results when plasma is generated in a steam flow with an applied frequency f = 3 kHz, a discharge length L = 80 mm, and an applied voltage V = 11 kV _{pp to} 14 kV _pp It is a table | surface which shows. In the plasma sterilization apparatus shown in FIG. 1, the sterilization result when plasma is generated in a water vapor flow with an applied frequency f = 1 kHz to 5 kHz, a discharge length L = 80 mm, and an applied voltage V = 13 kV _pp is shown. It is a table | surface which shows.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Plasma sterilizer 10 Tube 11 Silicon tube 12 Beaker 20 Electric discharge part 21 Wire electrode (1st electrode)
22 Ground electrode (second electrode)
30 Water Vapor Generation Unit 31 Flask 32 Heater 33 Silicon Tube 40 Voltage Generation Unit 41 Function Generator 42 Digital Oscilloscope 43 High Voltage Power Amplifier 50 Auto-Reader (Sterilization Judgment Device)

Claims (4)

A pipe made of a dielectric material, one end of which is opened to the atmosphere, and an object to be sterilized is placed inside,
A water vapor generating part connected to the other end of the pipe for generating water vapor to be circulated into the pipe;
A discharge part provided in the middle of the tube and causing a dielectric barrier discharge inside the tube;
A voltage generation unit that applies an AC voltage related to the dielectric barrier discharge to the discharge unit ;
The discharge part has a first electrode inserted into the tube, and a second electrode arranged on the outer periphery of the tube and grounded,
The voltage generator applies the alternating voltage between the first electrode and the second electrode;
The tube is formed in a cylindrical shape;
The second electrode is arranged on the outer periphery of the tube in a cylindrical shape;
The first electrode is formed in a linear shape and is arranged eccentrically with respect to the cylinder axis of the second electrode,
The voltage generator is in a discharge state in which a current larger than the maximum value of the discharge current instantaneously flows after the discharge current flows when the AC voltage of the rectangular wave applied to the discharge unit rises. Apply an alternating voltage of a predetermined voltage or higher to the discharge part,
The plasma sterilization apparatus, wherein the water vapor generating unit fills the inside of the tube with water vapor . The voltage generating unit, an alternating voltage with a frequency of 3 to 4 kHz the energy per unit due to discharge time is more than 3.0W and applying to said discharge unit, according to claim 1 Symbol placement of the plasma sterilizer . A first step of disposing an object to be sterilized in a tube made of a dielectric material and having one end open to the atmosphere;
A second step of supplying water vapor from the other end of the pipe to the inside of the pipe, and filling the inside of the pipe with the water vapor ;
A third step of applying an AC voltage between the electrodes, causing a dielectric barrier discharge inside the tube to turn the water vapor into plasma, and
In the first step, a first electrode is inserted into the tube, and a grounded second electrode is disposed on the outer periphery of the tube,
In the third step, an alternating voltage is applied between the first electrode and the second electrode to cause the dielectric barrier discharge,
In the first step, the tube is formed in a cylindrical shape, the second electrode is formed in a cylindrical shape and disposed on the outer periphery of the tube, and the first electrode is formed in a linear shape to form the first electrode. Placed eccentric to the cylinder axis of the two electrodes,
In the third step, after the discharge current flows when the AC voltage of the rectangular wave applied to the discharge portion rises, a discharge state in which a current larger than the maximum value of the discharge current instantaneously flows is obtained. A plasma sterilization method, wherein an AC voltage higher than a predetermined voltage is applied to cause the dielectric barrier discharge . In said third step, the energy per unit due to discharge time is greater than or equal to 3.0 W, 3 by applying an AC voltage of a frequency within to 4 kHz, and wherein the causing dielectric barrier discharge, claim 3 The plasma sterilization method described.