Discharge sterilization method and discharge sterilization device

Abstract

To provide a sufficient sterilization treatment device that, according to a discharge sterilization method and sterilization device of crop of the present invention, without inviting complexity and large size of a structure of a sterilization device, can generate a sterilization effect in a short time, without lowering the value of a fruit and the like to be sterilized.SOLUTION: A discharge sterilization device wherein a first electrode (11) and a second electrode (13) are arranged facing each other across a predetermined space (25), and at least one surface of the first electrode (11) and the second electrode (13) is covered with a dielectric (12), an object (20) to be sterilized is arranged in a space (25), using a predetermined power supply (14), between a first electrode (11) and a second electrode (13), a pulse voltage is applied for a predetermined period of time to generate a barrier discharge, and a rise time of the pulse voltage is set to 3.25 μs or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a discharge sterilization method and an electric discharge sterilization device, and more particularly to a discharge sterilization method and an electric discharge sterilization device for crops. [Background technology]

[0002] It has been known for some time that stem rot occurs in fruits such as citrus fruits after harvest due to the influence of fungi that invade parts of the fruit such as the stem during the growing period. Therefore, in order to prevent stem rot in fruits, it is generally assumed that chemicals are used to disinfect the fruit.

[0003] On the other hand, Patent Document 1 discloses a method for sterilizing an item contained in a sealed container. Specifically, the packaging container in which the item to be treated is sealed is brought into close contact with an electrode, and a barrier discharge is generated inside the packaging using a high AC voltage to eliminate leaked ozone.

[0004] Patent Document 2 shows a sterilization device that uses barrier discharge. It also shows that the surface of the object to be sterilized is wetted with water or hydrogen peroxide, and then a high voltage is applied between the electrodes to perform the sterilization process, thereby promoting the generation of OH radicals and improving the sterilization effect.

[0005] Furthermore, Patent Document 3 discloses that a sterilization effect is achieved by covering at least one of a pair of electrodes arranged opposite each other across a space in which an object to be sterilized, such as fruit, with a solid dielectric, and applying a pulse or AC voltage between the electrodes to generate a barrier discharge. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-209188 [Patent Document 2] Japanese Patent Application Laid-Open No. 2006-239230 [Patent Document 3] Japanese Patent Publication No. 2020-81227 Summary of the Invention [Problem to be solved by the invention]

[0007] However, the methods described in Patent Documents 1 and 2 are not designed for use by workers in sterilizing crops such as fruit. When sterilizing crops, the target objects are relatively large and vary in size and shape. Furthermore, sterilizing the entire crop may result in the treatment of areas that do not require sterilization, resulting in a decrease in quality and commercial value. In other words, there is a concern that damage such as surface damage may occur to the fruit. Furthermore, promoting the generation of OH radicals, as described in Patent Document 2, is harmful to the human body.

[0008] In contrast, the method described in Patent Document 3 can sterilize crops such as fruits, but it takes a long time to sterilize, so it is not efficient for sterilizing a large number of crops one after another. Also, when the target object is a crop, there is a problem that the sterilization effect does not last for a long time.

[0009] The present invention has been made in consideration of the above-mentioned circumstances, and its object is to provide an electric discharge sterilization method and an electric discharge sterilization device which can produce a sterilization effect in a short time without complicating the structure or increasing the size of the sterilization device, and which can perform sufficient sterilization treatment while preventing a decrease in the commercial value of the fruit or other object to be sterilized. [Means for solving the problem]

[0010] In order to achieve the above-mentioned object, the discharge sterilization method and discharge sterilization device according to the present invention are characterized as follows.

[0011] The first electrode and the second electrode are arranged to face each other with a predetermined space therebetween, a surface of at least one of the first electrode and the second electrode is covered with a dielectric; An object to be sterilized is placed in the space; a predetermined power supply is used to apply a pulsed voltage between the first electrode and the second electrode for a predetermined period of time to generate a barrier discharge; The rise time of the pulse voltage is set to 3.25 μs or less. The pulse period of the pulsed voltage is set to 10 kHz or more and 30 kHz or less, the applied voltage of the pulsed voltage is set to 13 kVp-p, and the application time of the pulsed voltage is set to 30 s. Discharge sterilization method.

[0012] a first electrode and a second electrode arranged opposite to each other with a predetermined space therebetween; a power source that generates a discharge plasma between the first electrode and the second electrode, a surface of at least one of the first electrode and the second electrode is covered with a dielectric; the power supply applies a pulsed voltage between the first electrode and the second electrode for a predetermined time to generate a barrier discharge, thereby sterilizing a predetermined object placed in the space; The power supply is configured so that the rise time of the pulse voltage is 3.25 μs or less. The pulse period of the pulsed voltage is set to 10 kHz or more and 30 kHz or less, the applied voltage of the pulsed voltage is set to 13 kVp-p, and the application time of the pulsed voltage is set to 30 s. Electric discharge sterilizer. [Effects of the Invention]

[0013] The method and apparatus for discharge sterilization of crops of the present invention can produce a sterilization effect in a short time without complicating the structure or increasing the size of the sterilization apparatus, and can perform sufficient sterilization treatment while preventing a decrease in the commercial value of the fruits and other products to be sterilized.

[0014] The present invention has been briefly described above. The details of the present invention will become clearer by reading the following detailed description of the invention (hereinafter referred to as "embodiments") with reference to the accompanying drawings. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a block diagram showing the basic configuration and usage state of a discharge sterilization device according to an embodiment of the present invention. [Figure 2] FIG. 2 is a block diagram showing a high-voltage pulse generator according to an embodiment of the present invention. [Figure 3] FIG. 3 is a graph showing an example of the waveform of the applied pulse. [Figure 4] FIG. 4 is a graph showing the incidence of disease when the waveform shown in FIG. 3 is applied to the electrodes. [Figure 5] FIG. 5 is a graph of a sine wave waveform applied to an electrode as a comparative example. [Figure 6] FIG. 6 is a graph showing the incidence of disease when the sine wave waveform shown in FIG. 5 is applied as a comparative example. [Figure 7] FIG. 7 is a graph of pulse waveforms with different pulse periods. [Figure 8] FIG. 8 is a graph showing a comparison of the incidence of disease when each of the pulse waveforms shown in FIG. 7 is applied to the electrodes. DETAILED DESCRIPTION OF THE INVENTION

[0016] Specific embodiments of the present invention will be described below with reference to the accompanying drawings.

[0017] <Example of the principle configuration and usage of a discharge sterilization device> FIG. 1 shows the basic configuration and usage state of a discharge sterilization device 10 according to an embodiment of the present invention.

[0018] The discharge sterilization device 10 shown in Fig. 1 has a first electrode 11, a solid dielectric 12, a second electrode 13, and a high-voltage pulse generating power supply 14. The first electrode 11 and the second electrode 13 are each formed of, for example, a conductive metal plate, and the first electrode 11 and the second electrode 13 are arranged facing each other with a predetermined space 25 between them. The periphery of the first electrode 11, particularly the lower surface facing the second electrode 13, is covered with a solid dielectric 12.

[0019] The power supply 14 is capable of outputting a high-voltage pulse voltage. One output terminal of the high-voltage pulse generating power supply 14 is electrically connected to the first electrode 11 via an electric cable 16, and the other output terminal is connected to the ground. The second electrode 13 is also connected to the ground via an electric cable 17.

[0020] The space 25 between the first electrode 11 and the second electrode 13 is large enough to accommodate the object to be sterilized 20. In this embodiment, the space 25 is large enough to accommodate crops such as fruits. When sterilizing the object to be sterilized 20, an operator places the object to be sterilized 20 in the space 25 as shown in Fig. 1. The operator then aligns the first electrode 11 and the area to be sterilized 20a so that they face each other.

[0021] The second electrode 13 has an area that is sufficiently larger than the presumed size of the object to be sterilized 20. On the other hand, the area of the first electrode 11 is approximately the same as the area to be sterilized 20a (sufficiently smaller than the entire object to be sterilized 20 and the second electrode 13), and the shape of the first electrode 11 is, for example, circular. When the object to be sterilized 20 is a fruit, the area to be sterilized 20a is, for example, the area around the stem or the stem of the fruit.

[0022] FIG. 2 is a block diagram showing a high-voltage pulse generating power supply 14 according to an embodiment of the present invention. The high-voltage pulse generating power supply 14 includes a DC power supply 31, a signal generator 32, drive circuits 33 and 34, and a transformer 35.

[0023] The DC power supply 31 is connected to a midpoint 36 on the primary side of the transformer 35. A drive circuit 33 is connected to one end of the primary side of the transformer 35, and a drive circuit 34 is connected to the other end. A first electrode 11 is connected to one end of the secondary side of the transformer 35, and a second electrode 13 is connected to the other end.

[0024] The signal generator 32 controls the drive circuits 33 and 34 to generate a pulse signal according to conditions input by an operator via input means (not shown). In the present embodiment, the signal generator 32 can set the pulse period (pulse frequency) within a range of at least 10 to 30 kHz, and the pulse rise time within a range of at least 0 to 3.25 μs. The pulse rise time refers to the time required for the high-voltage pulse voltage to rise from 0 V to the peak voltage.

[0025] <Sterilization procedure> An operator places object 20 to be sterilized in space 25 as shown in Fig. 1, and after determining the position of first electrode 11 and area 20a to be sterilized, starts high-voltage pulse generating power supply 14 by operation of the operator in the state shown in Fig. 1. This causes high-voltage pulse generating power supply 14 to output a high-voltage pulse voltage having a waveform such as that shown in Fig. 3, and this high-voltage pulse voltage is applied between first electrode 11 and second electrode 13. At this time, the pulse rise time is set to be shorter than 3.25 [μs].

[0026] As a result, in an atmospheric pressure environment, a discharge occurs between the first electrode 11 and the second electrode 13. Here, since the first electrode 11 is covered with the solid dielectric 12, a barrier discharge occurs between the first electrode 11 and the second electrode 13.

[0027] Furthermore, due to the barrier discharge, plasma is formed near the first electrode 11, and this plasma generates energy due to local discharge. Furthermore, the amount of ozone generated at this time is very small, so it does not affect the bodies of workers and other personnel. The energy from the generated discharge is irradiated onto the sterilization target area 20a of the sterilization target object 20 located opposite the first electrode 11. This achieves a sterilization effect. In particular, since the discharge sterilization device 10 can locally apply energy from the discharge, it can sterilize not only the surface but also the interior of the sterilization target area 20a. Furthermore, since the energy from the discharge is not irradiated onto unnecessary areas other than the sterilization target area 20a opposite the first electrode 11, deterioration in the quality of fruits and the like can be prevented.

[0028] Furthermore, since the first electrode 11 is formed relatively small and the second electrode 13 is connected to the earth 15, it is possible to prevent the operator from receiving an electric shock due to the high voltage output from the power supply 14. Of course, the discharge sterilization device 10 may have a case with a door that encloses the space 25, and a switch that detects the closed state of the door may be attached to the door, so that the power supply 14 generates a high voltage pulse only when the switch detects the closed state.

[0029] The sterilization process of the sterilization target area 20a is carried out continuously for a certain period of time, and after the certain period of time has elapsed, the output of the power supply 14 is shut off to terminate the discharge. In this embodiment, as will be described later, the sterilization process is set to a time period that is significantly shorter than conventional times.

[0030] Alternatively, the discharge sterilization device 10 may be installed so that the conveyor path for transporting multiple crops to be sterilized 20 passes through the space 25, and the multiple crops are automatically placed in the space 25 one after another, and after a predetermined period of plasma irradiation, the crops are transported from the space 25 to the area for the next work process. In this case, it is preferable to fix the orientation of the crops in advance using a jig or the like when placing the crops on the conveyor so that the sterilization target area 20a of the crops transported into the space 25 faces the first electrode 11.

[0031] <Experiment 1: Change in incidence rate with exposure time> In order to confirm the effect of the discharge sterilization method according to this embodiment, an experiment was carried out under the following conditions.

[0032] First, to examine the change in disease incidence rate with irradiation time, plasma was irradiated onto the stem of the fruit, which was the sterilization target 20, using the high-voltage pulse voltage shown in Figure 3, and the disease incidence rate of the sterilization target 20 was calculated. The disease incidence rate was calculated by determining that individuals with discoloration on the surface of the fruit from the stem of the sterilization target were diseased, and then calculating the ratio of diseased individuals to the number of samples.

[0033] Sterilization conditions: Period of high-voltage pulse voltage applied between electrodes 11 and 13: 10 [kHz] Applied voltage: 13[kVp-p] Pulse rise time: 3.25 [μs] Sterilization time: 0, 10, 20, 30 [s] Conditions for observation of results: The state of the sterilization object 20 after sterilization treatment for each sterilization treatment time and the state of the non-sterilized sterilization object 20 were observed every day.

[0034] The results of this experiment are shown in Figure 4. In Figure 4, disease incidence data D1 represents the change in disease incidence rate for fruit that was not subjected to sterilization treatment. Disease incidence data D2, D3, and D4 represent the change in disease incidence rate for fruit that was sterilized under the above conditions with sterilization times of 10 [s], 20 [s], and 30 [s], respectively. In Figure 4, the horizontal axis represents the number of days elapsed, and the vertical axis represents the disease incidence rate [%].

[0035] As shown in Figure 4 as disease incidence data D1, for fruit that was not sterilized, diseased individuals appeared six days after inoculation with stem-end rot fungus, and the disease incidence reached 50%. Then, after nine days, the disease incidence reached 100%. Also, as shown in Figure 4 as disease incidence data D5, when the fruit was irradiated with plasma generated by high-voltage pulse voltage for 10 seconds, diseased individuals appeared six days after the inoculation, and the disease incidence reached 100% after eight days.

[0036] On the other hand, as shown as disease incidence data D6 in Figure 4, when plasma generated by high-voltage pulse voltage was irradiated for 20 [s], some individuals developed the disease after 6 days, but the increase in the disease incidence rate over the number of days passed became gradual, and after 10 days the disease incidence rate had dropped to 80 [%].

[0037] As shown in Figure 4 as disease incidence data D7, when plasma generated by high-voltage pulse voltage was irradiated for 30 seconds, some individuals developed the disease after six days, but the disease incidence rate was suppressed to 20%. Furthermore, the increase in disease incidence rate over the number of days passed became even more gradual, dropping to 40% after 10 days. In other words, it was confirmed that sterilizing fruit and the like for 30 seconds using the method of this embodiment effectively sterilizes fruit and the like, thereby preventing stem rot disease in a short period of time.

[0038] <Comparative Example> As a comparative example, the sinusoidal wave voltage shown in Figure 5 was applied to the stem of a fruit, which was the object to be sterilized 20, and the disease incidence rate of the object to be sterilized 20 was determined at predetermined time intervals. The applied voltage was set to the same value as the high-voltage pulse voltage shown in Figure 3.

[0039] Sterilization conditions: Frequency of the sinusoidal voltage applied between the electrodes 11 and 13: 10 kHz Applied voltage: 13[kVp-p] Sine wave voltage rise time: 25 μs Sterilization time: 0, 10, 20, 30 [s]

[0040] The results of this experiment are shown in Figure 6. Note that disease incidence data D1 is the same as disease incidence data D1 in Figure 4. Disease incidence data D2 to D4 show the progression of disease incidence in fruit sterilized for sterilization times of 10 [s], 20 [s], and 30 [s], respectively, when the above-mentioned sinusoidal voltage was applied between electrodes 11 and 13 to generate plasma. In Figure 6, the horizontal axis represents the number of days elapsed, and the vertical axis represents the disease incidence [%]. In Figure 6, the horizontal axis represents the number of days elapsed, and the vertical axis represents the disease incidence [%].

[0041] As shown by disease incidence data D2 to D4 in Figure 6, for fruit sterilized using the sine wave voltage of the comparative example, individuals developed the disease six days after inoculation with stem-end rot fungus. In all cases of disease incidence data D2 to D4, the disease incidence reached 100% after 10 days. Note that disease incidence data D2 and D3 produced the same results, so they are shown overlapping in Figure 6.

[0042] That is, when sterilization was performed using the sine wave voltage of the comparative example, an irradiation time of about 30 [s] was not sufficient to suppress the onset of disease, even though plasma was generated using the same applied voltage as the high-voltage pulse voltage shown in Figure 3. In contrast, when plasma was irradiated using a high-voltage pulse voltage with a pulse rise time shortened to 3.25 [μs] as shown in Figure 3, it was confirmed that a sterilization effect could be obtained with a short irradiation time of about 30 [s].

[0043] <Experiment 2: Changes in incidence rate with pulse period> An experiment similar to Experiment 1 was performed as shown in Figure 7, in which the pulse period of the high-voltage pulse voltage was changed, plasma was irradiated onto the stems of fruits, which were the objects to be sterilized 20, and the disease incidence rate of the objects to be sterilized 20 was calculated. The disease incidence rate was calculated by determining the number of diseased individuals to the number of samples as the number of individuals in which the color of the fruit surface had changed from the stems of the objects to be sterilized had developed disease.

[0044] Sterilization conditions: Period of high-voltage pulse voltage applied between electrodes 11 and 13: 10, 15, 20, 30 [kHz] Applied voltage: 13[kVp-p] Pulse rise time: 3.25 [μs] Sterilization time: 30 seconds Conditions for observation of results: The state of the sterilization object 20 after sterilization treatment for each sterilization treatment time and the state of the non-sterilized sterilization object 20 were observed every day.

[0045] The results of this experiment are shown in Figure 8. When the high-voltage pulse voltage period was 10 kHz, the incidence rate was reduced to 40% after 10 days. Furthermore, when the high-voltage pulse voltage period was 15, 20, or 30 kHz, the incidence rate was reduced to 60% after 10 days. In other words, it was confirmed that if the high-voltage pulse voltage period was in the range of 10 to 30 kHz, and the pulse rise time was set to a short value, such as 3.25 μs, then irradiating the object with plasma for 30 seconds was sufficient to reduce the incidence rate.

[0046] The present invention is not limited to the above-described embodiments, and can be appropriately modified, improved, etc. The material, shape, size, number, location, etc. of each component in the above-described embodiments are arbitrary and not limited as long as they can achieve the present invention.

[0047] Here, the features of the discharge sterilization method and the discharge sterilization device according to the above-described embodiments of the present invention are briefly summarized and listed below in [1] to [5]. [1] A first electrode (11) and a second electrode (13) are arranged facing each other with a predetermined space (25) therebetween, a surface of at least one of the first electrode (11) and the second electrode (13) is covered with a dielectric (12); placing an object (20) to be sterilized in the space (25); A pulsed voltage is applied between the first electrode (11) and the second electrode (13) for a predetermined time using a predetermined power supply (14) to generate a barrier discharge; The rise time of the pulse voltage is set to 3.25 μs or less. Discharge sterilization method.

[0048] According to the discharge sterilization method described in [1] above, a voltage is applied from a power source while at least one of the first and second electrodes is covered with a dielectric, generating a barrier discharge, a type of discharge plasma, between the first and second electrodes. The energy from this discharge is irradiated onto the crops placed in the space, thereby carrying out the sterilization treatment. Furthermore, since the discharge energy can be irradiated locally onto the crops, it is possible to sterilize not only the surface but also the interior of the crops. By setting the rise time of the pulsed voltage to 3.25 μs or less, the irradiation time can be significantly shortened compared to conventional sinusoidal voltages, allowing for efficient sterilization of a large number of objects to be sterilized one after another.

[0049] [2] The size of the first electrode (11) is smaller than the overall size of the object (20) to be sterilized and is equal to or smaller than the size of the area to be sterilized of the object (20), After the area to be sterilized (20a) of the object (20) is positioned facing the first electrode (11), Applying a voltage between the first electrode (11) and the second electrode (13); The discharge sterilization method described in [1] above.

[0050] According to the discharge sterilization method configured as [2] above, the first electrode is relatively small, and the area of the object to be sterilized is positioned facing the first electrode, so sterilization can be limited to only the areas that require sterilization. This prevents the energy from the discharge from being irradiated to areas that do not require sterilization, which could reduce the quality and commercial value of the object to be sterilized. Furthermore, because the first electrode is small, discharge can be generated even with a power supply with a low power capacity. As a result, effective sterilization can be achieved without using a large power supply. Furthermore, because the first electrode is small, only a small amount of harmful ozone is generated, making it easier to ensure the safety of workers.

[0051] [3] The pulse period of the pulsed voltage is set to 10 kHz or more and 30 kHz or less. The discharge sterilization method according to [1] or [2] above.

[0052] According to the discharge sterilization method configured as above in [3], the sterilization effect can be reliably achieved by irradiating the object to be sterilized with discharge plasma for a short time. Moreover, since this can be achieved by using a high-voltage pulse generating power supply with a pulse period of 30 kHz or less, there is no need to use an expensive high-frequency high-voltage power supply.

[0053] [4] The object is a crop. The discharge sterilization method according to any one of the above [1] to [3].

[0054] According to the discharge sterilization method configured as [4] above, crops can be sterilized in a short time using discharge plasma, which enables sufficient sterilization while preventing a decrease in the commercial value of the crops to be sterilized due to long-term irradiation with discharge plasma.

[0055] [5] A first electrode (11) and a second electrode (13) arranged opposite each other with a predetermined space (25) therebetween; a power source (14) that generates a discharge plasma between the first electrode (11) and the second electrode (13), At least one surface of the first electrode (11) and the second electrode (13) is covered with a dielectric (12), the power supply (14) applies a pulsed voltage between the first electrode (11) and the second electrode (13) for a predetermined time to generate a barrier discharge, thereby sterilizing a predetermined object (20) placed in the space (25); The power supply (14) is set so that the rise time of the pulsed voltage is 3.25 μs or less. Electric discharge sterilizer (10).

[0056] According to the discharge sterilization device configured as described above in [5], a voltage is applied from a power source while at least one of the first and second electrodes is covered with a dielectric, generating a barrier discharge, a type of discharge plasma, between the first and second electrodes. The energy from this discharge is irradiated onto the crops placed in the space, thereby carrying out the sterilization treatment. Furthermore, since the discharge energy can be irradiated locally onto the crops, it is possible to sterilize not only the surface but also the interior of the crops. By setting the rise time of the pulsed voltage to 3.25 μs or less, the irradiation time can be significantly shortened compared to conventional sinusoidal voltages, allowing for efficient sterilization of a large number of crops in succession. [Explanation of symbols]

[0057] 10 Electric discharge sterilizer 11 1st electrode 12 Solid Dielectrics 13 Second electrode 14 High voltage pulse generating power supply 15 Earth 16,17 Electrical cables 20 Objects to be sterilized 20a Area to be sterilized 25 Space 31 DC power supply 32 Signal Generator 33,34 Drive circuit 35 Transformer 36 Midpoint D1, D2, D3, D4, D5, D6, D7 Incidence data

Claims

1. The first electrode and the second electrode are arranged in a state where they face each other with a predetermined space therebetween, a surface of at least one of the first electrode and the second electrode is covered with a dielectric; An object to be sterilized is placed in the space; a predetermined power supply is used to apply a pulsed voltage between the first electrode and the second electrode for a predetermined period of time to generate a barrier discharge; The rise time of the pulsed voltage is set to 3.25 μs or less, the pulse period of the pulsed voltage is set to 10 kHz or more and 30 kHz or less, the applied voltage of the pulsed voltage is set to 13 kVp-p, and the application time of the pulsed voltage is set to 30 s. Discharge sterilization method.

2. The size of the first electrode is formed to be smaller than the entire size of the object to be sterilized and to be equal to or smaller than the size of the area to be sterilized of the object, After positioning the area to be sterilized of the object so as to face the first electrode, applying a voltage between the first electrode and the second electrode; The discharge sterilization method according to claim 1.

3. The pulse period of the pulsed voltage is set to 10 kHz. The discharge sterilization method according to claim 1 or 2.

4. The object is a crop. The discharge sterilization method according to any one of claims 1 to 3.

5. a first electrode and a second electrode arranged opposite to each other with a predetermined space therebetween; a power source that generates a discharge plasma between the first electrode and the second electrode, a surface of at least one of the first electrode and the second electrode is covered with a dielectric; the power supply applies a pulsed voltage between the first electrode and the second electrode for a predetermined time to generate a barrier discharge, thereby sterilizing a predetermined object placed in the space; The power supply is configured such that the rise time of the pulsed voltage is set to 3.25 μs or less, the pulse period of the pulsed voltage is set to 10 kHz or more and 30 kHz or less, the applied voltage of the pulsed voltage is set to 13 kVp-p, and the application time of the pulsed voltage is set to 30 s. Electric discharge sterilizer.

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