Water plasma sterilizer

Abstract

Provided is a water plasma sterilizer that is capable of stably supplying water molecules into a treatment chamber for performing treatment with plasma and of effectively recovering and reusing the water molecules used in the treatment chamber and moisture in the air in a living and operating space for an operator.　The water plasma sterilizer comprises a treatment chamber 1 for holding an object to be sterilized, an exhaust means 2 for exhausting gas from the treatment chamber, and a plasma generation means (an antenna 3 and a power source 4) for generating water plasma by converting water molecules in the treatment chamber into plasma, and sterilizes the object with the water plasma. The water plasma sterilizer is characterized in that an adsorbent (5) having adsorbed water molecules is used as a supply source for supplying water molecules into the treatment chamber.

Description

Water plasma sterilization device

[0001] The present invention relates to a water plasma sterilization apparatus, and more particularly to a water plasma sterilization apparatus comprising a processing chamber for containing an object to be sterilized, an exhaust means for exhausting gas from the processing chamber, and a plasma generating means for generating water plasma by plasmaizing water molecules in the processing chamber, wherein the object is sterilized by the water plasma.

[0002] Traditional sterilization technologies have utilized high-pressure steam (autoclaves), ultraviolet light, gamma rays, and ethylene oxide gas. In recent years, "plasma sterilization," which utilizes active species in plasma, has been attracting attention. Plasma sterilization has the advantage of enabling high-speed, low-temperature sterilization without the need for high-temperature, high-pressure environments or carcinogenic gases, compared to conventional methods. This is due to the non-thermal equilibrium nature of plasma and the reactions of many active radical species, and since it is already being used in some products, the foundational technology is being established.

[0003] As shown in Non-Patent Documents 1 and 2, various sterilization devices (sterilizers) utilizing plasma have been proposed. Furthermore, Patent Document 1 proposes the use of water plasma, which uses water as a raw material. When vaporized water is turned into plasma, reactive oxygen species (ROS) such as OH radicals and O radicals can be efficiently generated. These reactive oxygen species enable sterilization of bacteria, fungi, fungal spores, and spores, as well as the decomposition of allergens. Moreover, since the gas in a radical state is rapidly deactivated and does not remain at 1 atmosphere in the human living environment, it can be safely used even in enclosed spaces.

[0004] Plasma-based sterilization devices require a near-vacuum environment within the processing chamber to generate plasma. Therefore, the processing gas to be plasma-generated is gradually introduced into the chamber, and the pressure within the chamber is adjusted to generate the plasma. However, since water is a liquid at room temperature, introducing liquid water into a vacuum-filled processing chamber causes it to instantly vaporize, expanding in volume and rapidly changing the pressure within the chamber. Pressure within the processing chamber is a crucial parameter in plasma generation, and such rapid pressure changes make it difficult to generate plasma stably.

[0005] Patent Document 1 describes a system that uses water stored in a tank, vaporizes the water in a vaporizer, and introduces the vaporized water into the processing chamber (enclosure) via a mass flow controller and valves. In the plasma sterilization apparatus of Patent Document 1, water is heated to generate steam when vaporizing water in the vaporizer. The vaporized water is then transported via a mass flow controller and other components, and it is essential to take additional measures to prevent the water from liquefying along the way. For example, it is necessary to constantly heat the mass flow controller, valves, and the part that introduces steam into the processing chamber to over 100 degrees Celsius, or to take measures in advance to prevent liquefied water from flowing into the processing chamber. As a result, the apparatus becomes more complex, and problems such as longer preparation times for operating the plasma sterilization apparatus arise.

[0006] Until now, research and development of plasma sterilization equipment has mainly focused on the medical and food sectors. Meanwhile, with the progress of space exploration and development, the frequency of human activity in outer space, on extraterrestrial planets and moons is increasing. For this reason, there is a growing need for "planetary protection," which involves preventing contamination of the Earth's environment by organisms originating from other celestial bodies during extraterrestrial planet exploration, while simultaneously preventing contamination of extraterrestrial environments by organisms originating from Earth. There are various methods for sterilizing and removing organisms, but since some bacteria on Earth are resistant to heat and radiation, there is a need for methods with higher sterilization effectiveness. Furthermore, not only is sterilization of organisms important, but the removal and inactivation of dead bacterial debris such as proteins and amino acids that make up organisms is also of great importance from the perspective of planetary protection. Plasma sterilization has the advantage of being safer than conventional methods because it is non-toxic, and it can sterilize at low temperatures.

[0007] If sterilization using water plasma were to be performed outside of Earth, such as on a space station or satellite base, securing "water," the raw material for the plasma, would be essential. However, in outer space (inside a spacecraft), water, along with air, is a precious resource, and its wasteful use must be avoided. Moreover, in order to ensure the stable operation of a water plasma sterilization device even in environments where it is difficult to supply sufficient water from the outside, securing the water necessary for sterilization by some means is also a crucial factor.

[0008] Japanese Patent Publication No. 2022-75126

[0009] Takayuki Watanabe, "2. Sterilization and Disinfection Using Discharge Plasma," Journal of the Japan Society of Plasma and Nuclear Fusion Science 75(6), 651-658, 1999. Kaoru Tamazawa, "Characteristics and Problems of Plasma Sterilization and Future Prospects of New Plasma Sterilization," Antimicrobial and Antifungal Research Association, 32(1), pp. 13-30, 2004.

[0010] The present invention was made to solve the above-mentioned problems, and aims to provide a water plasma sterilization device that can stably supply water molecules to a processing chamber where plasma processing is performed, and can effectively recover and reuse water molecules used in the processing chamber and moisture in the air within the operator's living and working space.

[0011] To solve the above-mentioned problems, the water plasma sterilization apparatus of the present invention has the following features: (1) A water plasma sterilization apparatus comprising a processing chamber for containing an object to be sterilized, an exhaust means for exhausting gas from the processing chamber, and a plasma generating means for generating water plasma by plasmaizing water molecules in the processing chamber, wherein the object is sterilized by the water plasma, and the supply source for supplying water molecules to the processing chamber is characterized in that an adsorbent material on which water molecules have been adsorbed is used.

[0012] (2) In the water plasma sterilization apparatus described in (1) above, the adsorbent is characterized in that it is one of silica gel, zeolite, activated carbon, clay, alumina, superabsorbent polymer, or a combination of several of these.

[0013] (3) The water plasma sterilization apparatus described in (1) above is characterized in that the adsorbent is placed inside the processing chamber.

[0014] (4) In the water plasma sterilization apparatus described in (1) above, the adsorbent container for containing the adsorbent is located outside the processing chamber, and is configured such that water molecules in the adsorbent container are introduced into the processing chamber by utilizing the differential pressure formed between the processing chamber and the exhaust means.

[0015] (5) The water plasma sterilization apparatus described in (1) above is characterized in that another adsorbent is placed in a part of the flow path of the gas exhausted by the exhaust means.

[0016] According to the present invention, in a water plasma sterilization apparatus comprising a processing chamber for containing an object to be sterilized, an exhaust means for exhausting gas from the processing chamber, and a plasma generating means for generating water plasma by plasmaizing water molecules in the processing chamber, an adsorbent material containing water molecules is used as the supply source for supplying water molecules into the processing chamber. Therefore, even if the area around the adsorbent material is in a vacuum state, water molecules are gradually released from the adsorbent material into the processing chamber, making it possible to maintain a constant pressure of water molecules in the processing chamber and to generate plasma stably. Moreover, by using an adsorbent material, it is possible to effectively recover water molecules used in the processing chamber and moisture in the air within the operator's living and operating space and reuse them in the water plasma sterilization apparatus.

[0017] This is a schematic diagram illustrating an example of a water plasma sterilization apparatus according to the present invention. This figure shows an example of a method for controlling the amount of water molecules released from the adsorbent in the water plasma sterilization apparatus of Figure 1. This is a schematic diagram illustrating another example of a water plasma sterilization apparatus according to the present invention. This is a graph showing an example of the spectral spectrum of light emitted from the water plasma sterilization apparatus. This is a graph showing the correlation between the pressure in the processing chamber and the OH radical intensity. This is a graph showing the relationship between water plasma irradiation time and the number of viable bacteria. This is a graph showing the relationship between the protein removal characteristics by water plasma irradiation. This is a graph showing the relationship between water plasma irradiation time and the amide I removal rate.

[0018] The water plasma sterilization apparatus according to the present invention will be described in detail below. The features of the present invention are that, as shown in Figure 1 or 3, the water plasma sterilization apparatus comprises a processing chamber 1 for containing an object to be sterilized, an exhaust means 2 for exhausting gas from the processing chamber, and a plasma generating means (antenna 3, power supply 4) for generating water plasma by plasmaizing water molecules in the processing chamber, and the object is sterilized by the water plasma, wherein an adsorbent (5, 7) on which water molecules have been adsorbed is used as the supply source for supplying water molecules into the processing chamber.

[0019] In this invention, "water plasma" refers to water (H ２This refers to a gaseous plasma containing charged particles (electrons and ions), radicals, and excited species produced by the ionization, dissociation, or excitation of water molecules, using water as a raw material. It also refers to a plasma using water alone or in a mixture with other substances, where energy is applied through discharge, electromagnetic waves, heat, light irradiation, or a combination thereof. ＋ , OH － , H ２ O ＊ , H ２ O ＋ These are generated. Even if gases other than water are present, if the active species derived from water play the main role, they are considered to be included in the water plasma.

[0020] The adsorbent used in the water plasma sterilization apparatus of the present invention can be, for example, silica gel, zeolite, activated carbon, clay, alumina, or superabsorbent polymer. These adsorbents only adsorb and retain water molecules, and when the adsorbent is placed in a vacuum environment, the adsorbed water molecules are gradually released. Thus, the method of supplying moisture (water molecules) in the present invention is completely different from methods using a vaporizer, such as heating liquid water to vaporize it, as described in Patent Document 1. Another example of an adsorbent is to use melamine foam as the hygroscopic material, and to use a hygroscopic material layer with a sponge-like layered structure. Such a hygroscopic material layer takes in moisture using capillary action and releases vaporized moisture by air (blowing) in contact with the surface of the hygroscopic material layer. The water molecules taken into the adsorbent by capillary action do not evaporate all at once, the evaporation rate can be controlled, and the pressure inside the processing chamber does not fluctuate significantly.

[0021] In this invention, the term "water molecule" refers to both a state in which water molecules are captured by the adsorbent through hydrogen bonds, and a state in which water molecules are incorporated into the adsorbent as an aggregate of water molecules (liquid) through capillary action. Furthermore, when released into a vacuum such as a processing chamber, the term encompasses not only individual water molecules (gas) but also the state of water particles and water vapor, which are aggregates of water molecules (agglomerated states).

[0022] As described above, the adsorbent releases water molecules adsorbed onto a carrier such as silica gel (including water molecules taken into the adsorbent by capillary action) into a vacuum, so the release of water molecules proceeds slowly. Therefore, the pressure inside the processing chamber does not change rapidly, and plasma generation is stabilized. In particular, the release of water molecules adsorbed onto the carrier of the adsorbent is slow.

[0023] The adsorbent of the present invention not only releases water molecules but also has the function of recovering excess moisture (water molecules) from the air. In outer space (inside a spacecraft), water is one of the precious resources, but if there is moisture floating in the living space, the water molecules can be adsorbed onto the adsorbent and reused as a water molecule supply source for a water plasma sterilization device.

[0024] The water molecules that serve as raw materials for reactive oxygen species in the plasma are recovered from the air using an adsorbent composed of one or more of the following: silica gel, zeolite, activated carbon, clay, alumina, superabsorbent polymer, etc., and recycled as a raw material gas for generating water plasma. Since the hygroscopic action of adsorbents such as silica gel, zeolite, activated carbon, clay, alumina, and superabsorbent polymer is reversible, the water adsorption performance is maintained even after water is removed, so the hygroscopic material (adsorbent) can be recycled and reused repeatedly. Water plasma has excellent sterilization properties and can be easily generated in a processing chamber (in a vacuum chamber on Earth). Moreover, as will be described later, when processing gases such as water plasma are discharged from the processing chamber, it is possible to recover them as water again, making it possible to circulate the precious water inside the spacecraft more efficiently.

[0025] Figure 1 is a schematic diagram showing an example of the water plasma sterilization apparatus of the present invention. The processing chamber 1 houses the object to be sterilized and is subjected to plasma treatment. The air inside the processing chamber is discharged to the outside from arrow F1 to F2 by an exhaust means 2 such as a vacuum pump.

[0026] As a means of generating plasma, the water plasma sterilization apparatus of the present invention assumes plasma generation under a low-pressure environment. It utilizes a high-frequency power supply 4 (RF power supply, microwave power supply) and a power supply antenna 3 to convert water molecules, which are gases in the processing chamber, into plasma, thereby generating water plasma.

[0027] In Figure 1, the adsorbent 5 is placed inside the processing chamber 1. When the vacuum state inside the processing chamber is set to a predetermined pressure, water molecules are continuously released from the adsorbent 5. Figure 2 shows an example of a method for controlling the amount of water molecules released from the adsorbent. The case CA containing the adsorbent 5 has an opening that opens into the processing chamber, and means are provided to vary the area of ​​the opening. The method for changing the opening area is to move a member (shutter SH, which has plate-like members attached according to the number of openings) that closes the openings (slits, which may be one or more) provided in a part of the case CA, as shown by arrow S, thereby changing the width (area) of the opening. When the opening becomes smaller, the number of water molecules released from the case CA decreases. On the other hand, the concentration of water molecules released from the adsorbent inside the case CA increases, so the release of water molecules from the adsorbent also gradually decreases. In Figure 2, the case CA also serves as the container for the adsorbent. However, it is also possible to create a closed space partitioned by a wall within a portion of the processing chamber, place a tray or other container containing the adsorbent inside this space, and configure the opening area of ​​the wall to be adjustable.

[0028] The shape of the opening and the number and shape of the shutters can be arranged in various ways. Furthermore, by providing a means to heat the adsorbent inside the case, it is possible to control the release of water molecules supported by the adsorbent.

[0029] In Figure 1, an electromagnetic shield ES can be provided surrounding the adsorbent. Specifically, the electromagnetic shield can have openings large enough for water molecules to enter and exit, while being made of conductive material to prevent damage to the adsorbent from electromagnetic fields and plasma generated in the processing chamber. This can include a grid-like plate-like member or wire mesh.

[0030] Furthermore, in the water plasma sterilization apparatus shown in Figure 1, another adsorbent 6 is placed in the middle of the gas flow path discharged from the exhaust means 2. If the plasma-generated gas subsequently reverts to water molecules, the exhausted gas will contain water molecules. The adsorbent 6 can efficiently recover the water molecules in the exhaust. Naturally, the adsorbent 6 that has adsorbed water molecules can be reused as the adsorbent 5 that supplies water molecules into the processing chamber 1.

[0031] Figure 3 shows an embodiment in which the adsorbent container containing the adsorbent 7 is located outside the processing chamber 1. Water molecules in the adsorbent container are introduced into the processing chamber 1 using the differential pressure formed between the processing chamber 1 and the exhaust means 2. For this reason, gas passages f1 and f2 are provided as shown in Figure 3.

[0032] In the water plasma sterilization apparatus shown in Figure 3, the amount of water molecules supplied to the processing chamber 1 can be controlled by adjusting the amount of gas flowing through the gas channels (f1 and f2). For example, a mass flow meter MM or a valve VA can be installed in the gas channel f2 to adjust the amount of gas passing through the gas channel. In Figure 3, water molecules are supplied by utilizing the minute pressure difference formed by the processing chamber 1 and the exhaust means 2, allowing for highly precise control of the water molecule concentration.

[0033] In generating water plasma, the most difficult aspect is adjusting the supply rate of water molecules. Therefore, in the water plasma sterilization apparatus shown in Figures 1 and 3, when adjusting the supply rate of water molecules to the processing chamber 1, it is possible to precisely control the supply rate of water molecules by analyzing the optical spectrum of the generated water plasma.

[0034] Using the water plasma sterilization apparatus shown in Figure 1, we confirmed that a stable plasma can be generated by supplying water molecules using an adsorbent. Specifically, when silica gel (adsorbent) containing water molecules, which are the raw material for water plasma, was placed in the processing chamber and the exhaust system was activated, we observed that the red silica gel containing water molecules gradually lost water molecules and changed color to blue, indicating drying.

[0035] Next, when power was applied to the antenna by an RF power supply (13.56 MHz), the emission spectrum of OH radicals (309 nm) sharply rose, and the emission spectrum characteristic of water plasma was confirmed (see Fig. 4). Also, when the pressure inside the processing chamber (vacuum vessel) was changed within the range of 100 to 500 Pa, as shown in Fig. 5, it was also confirmed that the intensity of the emission spectrum of OH radicals (309 nm) tended to be higher at lower pressures.

[0036] From this, it is understood that by reducing the pressure, the vapor pressure decreases, and the water molecules supported on the silica gel evaporate, serving as the raw material for water plasma. In addition, when the dried silica gel was taken out of the processing chamber 1 and left in the atmosphere containing moisture, it was confirmed again that it returned to red and could retain moisture repeatedly.

[0037] Next, it was confirmed that sterilization treatment was possible with the water plasma sterilizer. As a sterilization treatment method, silica gel adsorbed with moisture in the atmosphere was placed in a vacuum vessel (φ21 cm, width 48 cm, capacity approximately 20 L), the input power to the antenna installed in the vacuum vessel was set to 50 W, and the pressure inside the vessel was set to the pressure shown below to generate water plasma. A sample carrying an indicator bacterium of water plasma (Bacillus atrophaeus; NBRC 13721) was placed in the vacuum vessel, and the sterilization characteristics by water plasma were evaluated.

[0038] The experimental method is as follows. (1) Spores BI (Biological indicator; indicator bacterium Bacillus atrophaeus (NBRC 13721; provided by JAXA); number of indicator bacteria 10 ６ ,10 ５ ,10 ４ ,10 ３[[CFU / mL]] and the hygroscopic silica gel (54.4 g) are sealed in a vacuum container and the pressure is reduced. (2) The pressure in the vacuum container is set to 600 Pa (start) to 200 Pa (first time: irradiation times 0, 1, 3, 6 hours), pressure 710 Pa (start) to 230 Pa (second time: irradiation times 0, 0.5, 2 hours), and the RF power to the antenna is 50 W to generate a water plasma and irradiate the sample. (3) After the water plasma treatment, the spore spots are wiped off with a wiping inspection kit (ST-25-100, Elmex), vortexed for 60 seconds, then 5 drops are dropped into a liquid medium (TSB-BP16, Mesa Labs) and 1 mL is dropped into a sheet-like medium for general viable bacteria (Acplus MC-Media Pad, JNC), and cultured at 35°C for 2 days. Among the two spots made on the slide glass, one is used as a positive control and cultured under the same conditions.

[0039] The experimental results are shown in the graph of Fig. 6. The number of viable bacteria tended to decrease with the water plasma irradiation time. In the 6-hour treatment, colonies were not detected for samples other than 10 ６ [[CFU / mL]]. For 10 ４ [[CFU / mL]], colonies were almost zero after 2 hours of irradiation, and for 10 ３ [[CFU / mL]], colonies were almost zero after 0.5 hours of irradiation. For reference, even for the 10 ８ [[CFU / mL]] sample, the evaluation of the liquid medium was negative after 48 hours of irradiation. Also, when the 10 ８ [[CFU / mL]] sample was treated for 6 hours, colonies were detected on the sheet-like medium but there was no discoloration in the liquid medium. From the above, it was confirmed that effective sterilization treatment can be achieved with water plasma using an adsorbent.

[0040] Next, the protein inactivation or removal characteristics of water plasma were evaluated. The experimental method was as follows: (1) 1 g of bovine serum-derived albumin (017-21273, Fujifilm Wako Pure Chemical Industries, Ltd.) was dissolved in 50 ml of purified water, and 10 ml of this solution was dropped onto a calcium fluoride plate (φ25 mm, thickness 3 mm; OPCF-25C03-P, Sigma Koki) and dried. (2) The calcium fluoride plate coated with dried albumin was sealed in a vacuum container together with silica gel and the pressure was reduced. When the pressure inside the vacuum container was 510 Pa, water plasma was generated with an RF power supply of 50 W and irradiated onto the albumin. The irradiation times were 0 h, 0.5 h, 1 h, 1.5 h, 2 h, and 3 h. (3) After irradiation, the calcium fluoride plate was removed and the absorption spectrum was measured using a Fourier transform infrared spectrometer (FT-IR-6100, JASCO).

[0041] After irradiation with water plasma, the secondary structure of the protein is revealed at 1650 cm². －１ Nearby peak (amide I band; C=O stretching vibration), 1540 cm －１ Nearby peaks (Amido II band; N-H bending vibration, C-N stretching vibration), 1240 cm －１ The peaks in the vicinity (Amid III band; C-N stretching vibration, N-H bending vibration) decreased, as shown in the graph in Figure 7. Furthermore, Figure 8 shows the results of evaluating the protein removal rate based on the percentage decrease in the peak of the Amid I band.

[0042] As shown in Figures 7 and 8, the peaks related to protein structure change upon irradiation with water plasma, suggesting that albumin is being degraded or denatured by OH radicals generated in the water plasma. This also indicates that proteins can be removed or denatured by water plasma.

[0043] As described above, the present invention provides a water plasma sterilization apparatus that can stably supply water molecules to a processing chamber where plasma processing is performed, and can effectively recover and reuse water molecules used in the processing chamber and moisture in the air within the operator's living and working space.

[0044] 1. Processing chamber 2. Exhaust means (vacuum pump) 3. Antenna 4. RF power supply 5, 6, 7. Adsorbent material

Claims

1. A water plasma sterilization apparatus comprising a processing chamber for containing an object to be sterilized, an exhaust means for exhausting gas from the processing chamber, and a plasma generating means for generating water plasma by plasmaizing water molecules in the processing chamber, wherein the object is sterilized by the water plasma, characterized in that an adsorbent material containing water molecules is used as the supply source for supplying water molecules into the processing chamber.

2. A water plasma sterilization apparatus according to claim 1, characterized in that the adsorbent is silica gel, zeolite, activated carbon, clay, alumina, a superabsorbent polymer, or a combination of several of these.

3. A water plasma sterilization apparatus according to claim 1, characterized in that the adsorbent is placed in the processing chamber.

4. A water plasma sterilization apparatus according to claim 1, wherein the adsorbent container containing the adsorbent is located outside the processing chamber, and the water molecules in the adsorbent container are introduced into the processing chamber by utilizing the differential pressure formed between the processing chamber and the exhaust means.

5. A water plasma sterilization apparatus according to claim 1, characterized in that another adsorbent is placed in a part of the flow path of the gas exhausted by the exhaust means.

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