JP2003062047A - Method and apparatus for sanitazing container - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and apparatus for sanitizing suitable for sanitizing containers at normal temperature and pressure. SOLUTION: A discharge electrode 3 is inserted into a container 2 to be sanitized positioned under normal temperature and pressure condition and at the same time a dielectric 5 and a counter electrode 6 are arranged in such a manner that they surround the container 3. A corona discharge is generated between both electrode 3, 6, applying a pulse high voltage having a pulse width of 10 nsec or more, an electric field intensity from 4 to 100 kV/cm and a pulse frequency of 10 pps or more between the discharge electrode 3 and the counter electrode 6. At least one kind of gas selected from the group comprising oxygen, nitrogen, hydrogen, carbon dioxide, air, argon and helium is introduced into the corona discharge.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for sterilizing a container by generating a corona discharge by a pulsed high voltage under normal temperature and pressure.

[0002]

2. Description of the Related Art As a method of sterilizing various packaging containers such as PET bottles with plasma, a container for sterilization and an electrode are housed in a vacuum container, and a high frequency power source is supplied while supplying argon gas or the like into the vacuum container. There is known a method of sterilizing by supplying a high frequency to the electrode from the electrode (for example, JP-A-7-18).
4618 gazette). A microwave power source may be used instead of the high frequency power source as a power source for generating plasma in a vacuum.

On the other hand, a method has also been proposed in which plasma is generated at room temperature and atmospheric pressure for sterilization. For example, JP-A-11-
Japanese Patent No. 187872 discloses a method in which a pulse high voltage is applied between a discharge electrode and a counter electrode set to atmospheric pressure to generate corona discharge, and an article is exposed to the corona discharge to sterilize the article. There is.

[0004]

The conventional method of performing sterilization at room temperature and atmospheric pressure is superior in terms of work efficiency because the burden on the equipment is lighter than the method using a vacuum container and no vacuum exhaust is required. ing. However, JP-A-11-187872
The publication only discloses a method of disposing an article to be sterilized in a space (discharge area) between a discharge electrode having a spherical shape, a brush shape or a knife edge shape and a counter electrode having a plate shape, and is particularly suitable for sterilizing a container. The disclosed device or method is not specifically disclosed.

Therefore, an object of the present invention is to provide a sterilizing method and a sterilizing apparatus suitable for sterilizing a container under normal temperature and normal pressure.

[0006]

According to the sterilization method of the present invention, a discharge electrode is inserted into a container to be sterilized placed at room temperature and normal pressure, and a counter electrode is arranged so as to surround the container, and a pulse width is 10 nsec. Above, electric field strength 4-100k
The problem described above is solved by applying a pulsed high voltage of V / cm and a pulse frequency of 10 pps or more between the discharge electrode and the counter electrode to generate corona discharge between both electrodes.

According to the sterilization method of the present invention, with the discharge electrode inserted in the container and the counter electrode arranged so as to surround the container, the pulse width is 10 nsec or more between both electrodes and the electric field strength is 4 to 100 kv. High energy corona discharge is generated by applying a pulsed high voltage of 10 pps / cm or more and a pulse frequency of 10 pps or more, so even under normal temperature and pressure, the inner surface of the container is reliably exposed to the discharge and a high sterilization effect can be obtained. .
Moreover, in the present invention, although the discharge having the intensity effective for sterilization is generated, since the pulse waveform as described above is selected, it does not exert a thermal action on the container.

The excellent bactericidal action of the present invention is that corona discharge generated from a pulsed high voltage characterized by a steep rise and a high peak value causes bacteria and mold to adhere to a container inserted in the discharge region. It is obtained on the basis of applying a strong electric field to the spores and generating an active atmosphere of ozone and active ions inside or near the surface of the container. A strong bactericidal action occurs due to the synergistic action of these electric fields and the active atmosphere.

By applying a pulsed high voltage having a unique waveform shown in FIG. 3, a stable corona discharge is maintained between the discharge electrode and the counter electrode. In this discharge, since a high voltage is applied in a pulse shape with an extremely short rise time, molecular motion is not induced in the container to be sterilized and only electrons are accelerated to create an active atmosphere. The amount of heat generated due to the heat generation is small, so that the temperature of the container to be sterilized hardly rises. The maximum pulse voltage used for main discharge is 20
Since the voltage reaches 0 kV or more, the space (distance between electrodes) in which the active atmosphere is generated can be made larger than that in a normal corona discharge. Note that FIG. 3 shows an example of a pulse high voltage waveform by changing the time axis, and the waveform on the left side of the figure corresponds to an enlarged waveform of one pulse included in the pulse waveform on the right side. .

In the sterilization method of the present invention, corona discharge may be generated in a state where the container is surrounded by a dielectric material arranged inside the counter electrode. In this case, it is possible to prevent the occurrence of sparks between the discharge electrode and the counter electrode and to continue the corona discharge stably. Further, in the sterilization method of the present invention, at least one gas selected from the group consisting of oxygen, nitrogen, hydrogen, carbon dioxide, air, argon and helium may be introduced into the corona discharge.
By continuing the discharge while introducing these gases, it is possible to continue the active atmosphere and further enhance the sterilization effect.

The sterilizing apparatus of the present invention comprises a discharge electrode arranged in a space at normal temperature and pressure and having a shape capable of being inserted into a container to be sterilized, and a counter electrode arranged so as to surround the discharge electrode in the space. A pulsed voltage of 10 nsec or more, an electric field strength of 4 to 100 kV / cm, and a pulse high voltage of 10 pps or more of pulse frequency is provided between the discharge electrode and the counter electrode.

According to this sterilizing apparatus, the above-described sterilizing method of the present invention can be realized. In the sterilization method of the present invention, a dielectric may be arranged inside the counter electrode so as to surround the discharge electrode. A gas introduction tube having a shape that can be inserted into the container may be provided. In this case,
The various gases described above can be introduced into the container via the gas introduction pipe. The counter electrode may be adhered to the outer periphery of the dielectric. In this case, since the gap between the counter electrode and the dielectric is eliminated, the distance between the discharge electrode and the counter electrode is not unnecessarily increased.

In the present invention, the counter electrode or the dielectric does not necessarily have to completely surround the entire circumference of the container, and a region not covered with the counter electrode or the dielectric may remain in a part of the container. On the other hand, when the dielectric is provided, it is desirable that the inner circumference of the counter electrode is completely covered with the dielectric. That is, it is desirable that the counter electrode be hidden behind the dielectric over the entire surface thereof as viewed from the discharge electrode.

[0014]

FIG. 1 shows an embodiment of the sterilizing apparatus of the present invention. This sterilizer 1 is arranged around the discharge electrode 3, a discharge electrode 3 that can be inserted into the container 2 to be sterilized, a gas introduction pipe 4 that is arranged side by side with the discharge electrode 3 and that can be inserted into the container 2. The dielectric 5 and the counter electrode 6 arranged outside the dielectric 5. The discharge electrode 3 is connected to a high voltage power source 7 that generates a pulsed high voltage for plasma generation, and the counter electrode 6 is grounded. The gas introduction pipe 4 is connected to a gas cylinder 8 as a gas supply source. Gas cylinder 8 for monitoring the gas flow rate from gas cylinder 8
A flowmeter 9 is provided between the gas introduction pipe 4 and the gas introduction pipe 4. A flow rate adjusting valve may be further provided. The container 2 to be sterilized is placed on the substantially center of a stage 10 made of a dielectric (for example, acrylic resin), and the dielectric 5 and the counter electrode 6 are also arranged on the stage 10. The above-mentioned container 2, discharge electrode 3,
Gas introduction tube 4, dielectric 5, counter electrode 6, and stage 10
All of them are placed in a space at normal temperature and pressure, and it is not necessary to store them in a vacuum container.

In FIG. 1, the container 2 is, for example, a bottle-shaped container having a narrowed mouth portion 2a, a body portion 2b, and a shoulder portion 2c arranged between them, the diameter of which gradually changes. ing. However, the present invention is not limited to the bottle-shaped container, and various containers may be sterilized.

The discharge electrode 3 may have any shape as long as it can be inserted into the container 2, and may have a spherical shape, a tree shape or the like in addition to the rod shape shown in FIG. When the rod-shaped discharge electrode 3 is used, a diameter of about 1 mm is sufficient. The material of the discharge electrode 3 may be copper, for example. The insertion amount of the discharge electrode 3 into the container 2 may be changed according to the shape of the container 2 and the degree of sterilization effect, but it is preferable that the insertion length of the discharge electrode 3 into the container 2 is 50% of the total height of the container 2. It is desirable to set the above.

The dielectric 5 is provided to stabilize the corona discharge generated between the discharge electrode 3 and the counter electrode 6.
As the material of the dielectric 5, for example, acrylic resin, glass or ceramics, and various other materials known as insulating materials (dielectric materials) can be used. The dielectric 5 has a tubular shape, for example, and its cross-sectional shape can be circular or polygonal. The thickness of the dielectric 5 is 0.1
It is desirable to set in the range of 10 mm.

The inner surface shape of the dielectric 5 may be similar to the outer shape of the container 2 or may be non-similar. In the case of a similar shape (for example, when the dielectric 5 is formed in a cylindrical shape with respect to the container 2 having a circular cross section), the gap between the dielectric 5 and the container 2 can be set uniformly. The height of the dielectric 5 is set higher than that of the container 2. However, it suffices that the entire counter electrode 6 is hidden behind the dielectric 5 when viewed from the discharge electrode 3, and it is not necessary that the container 2 is completely hidden inside the dielectric 5. That is, there is no portion where the discharge electrode 3 and the counter electrode 6 directly face each other without sandwiching the dielectric 5 between them, and the dielectric 5 always exists between the electrodes 3 and 6. It is enough if the condition can be maintained. The dielectric 5 is not essential in the present invention, and the dielectric 5 may be omitted as long as corona discharge sufficient for sterilization can be generated.

The counter electrode 6 is made of, for example, stainless steel wire mesh. The counter electrode 6 can be wrapped around the outer periphery of the dielectric 5, so that the dielectric 5 and the counter electrode 6 can be brought into close contact with each other. Although there may be a gap between the dielectric 5 and the counter electrode 6, the discharge electrode 3 and the counter electrode 6
It is preferable that the gap between the dielectric 5 and the counter electrode 6 is as small as possible in order to reduce the distance required for sterilization and save energy required for sterilization. The material of the counter electrode 6 is not limited to the metal mesh, and a metal plate or the like may be used. However, if you use wire mesh,
There is an advantage that the discharge state inside the counter electrode 6 can be observed from the outside through the counter electrode 6. When the dielectric 5 is used, it is more convenient to observe the discharge state if at least a part of the dielectric 5 is made of a transparent material.

The counter electrode 6 is preferably provided, for example, from the bottom of the container 2 to the shoulder 2c or a height higher than that. If the container 2 and the counter electrode 6 are represented by the height ratio, the height of the counter electrode 6 is preferably 70% or more of the total height of the container 2. The counter electrode 6 may be configured, for example, in a cylindrical shape that completely surrounds the entire circumference of the container 2, or as shown in FIG. 2, an electrode curved in a semicircular shape or an arc shape having a shorter circumferential length. Using two or more plates 6a, 6a, the container 2
The counter electrode 6 may be formed so as to surround the. The counter electrode 6 may be formed by means such as forming a metal film on the outer periphery of the dielectric 5. Alternatively, the counter electrode 6 may be formed of a metal plate, and a dielectric film may be formed on the inner circumference of the counter electrode 6 by using a fixing means such as thermal spraying.

Sterilization of the container 2 using the sterilizer 1 is performed as follows. First, as a preparation for sterilization, stage 10
The container 2 is arranged on the upper side, the dielectric 5 and the counter electrode 6 are arranged around the container 2, and the discharge electrode 3 and the gas introduction pipe 4 are inserted into the inside of the container 2. After the preparation is completed, a predetermined gas is supplied from the gas cylinder 8 to the gas introduction pipe 4 so that the predetermined gas is introduced into the container 2 from the lower end of the gas introduction pipe 4, and in that state, the high voltage power supply 7 directs the discharge electrode 3 to the discharge electrode 3. By continuously applying a predetermined pulse high voltage for a predetermined time, corona discharge is generated between the discharge electrode 3 and the counter electrode 6. The introduction of the gas from the gas introduction pipe 4 is continuously performed at a predetermined flow rate while the pulse high voltage is applied. That is,
During the discharge, the gas in the container 2 is constantly replaced by the gas introduced from the gas introduction pipe 4. The gas used here is at least one selected from the group consisting of oxygen, nitrogen, hydrogen, carbon dioxide, air, argon, and helium. Two or more kinds of gases may be mixed and supplied.

The pulse width of the pulse high voltage applied by the high-voltage power supply 7 is 10 nsec (nanosecond) or more, preferably 50 nsec or more. If it is 10 nsec or less, good corona discharge is unlikely to occur, and a sufficient bactericidal effect cannot be obtained. On the other hand, as the pulse width becomes wider, the effective discharge energy increases and the bactericidal action becomes stronger. As a result, the processing efficiency is improved, and the desired bactericidal effect can be achieved in a short time. Further, when the pulse width is large, even if the distance between the discharge electrode 3 and the counter electrode 6 is widened, corona discharge with sufficient strength can be generated, and a good sterilization effect is achieved.
However, if the pulse width becomes too long, harmful sparks are likely to occur and the power supply capacity also increases.
It is preferably set to μsec or less.

The voltage of the pulse high voltage is 4 to 100 k expressed by the average electric field strength (applied voltage (peak value)) / distance between poles.
The range is V / cm. When the average electric field strength is lower than 4 kV / cm, good corona discharge is unlikely to occur. Desirably, the average electric field strength is set to 15 kV / cm or more, and more preferably 30 kV / cm or more. On the other hand, when the average electric field strength is higher than 100 kV / cm, it is easy to shift to the spark discharge, and the insulating means is complicated and expensive for the effect. When the container 2 is made of a thermoplastic resin, the average electric field strength is 100 kV / c depending on the duration of discharge.
If it exceeds m, thermal influence such as thermal deformation may occur in the container 2.

The pulse frequency of the pulsed high voltage is 10 pps or higher, preferably 50 pps or higher, more preferably 10 pps or higher.
Set to 0 pps or higher. If it is less than 10 pps, good corona discharge is unlikely to occur, effective treatment energy is insufficient, and sterilization treatment takes time. On the other hand, if the pulse frequency is too high, the container 2 may be thermally affected. Therefore, it is desirable to set the pulse frequency to 2000 pps or less. Further, it is technically difficult to generate a high voltage pulse having a pulse frequency exceeding 2000 pps with the above pulse width and average electric field strength. Attempting to obtain a pulse frequency of 2000 pps or higher is not preferable, because the high voltage generator becomes very large, the equipment cost becomes excessive, and the profit becomes industrially unprofitable.

In the present invention, introduction of gas during discharge is not essential. Instead of inserting the gas introduction pipe 4, the discharge may be continued in the air staying in the container 2 for a predetermined time. Prior to the start of the discharge, the gases mentioned above: oxygen, nitrogen, hydrogen, carbon dioxide, air, argon,
And at least one kind of gas selected from the group consisting of helium may be introduced into the container 2 to replace the air in the container 2 with these gases, and then the introduction of the gas may be stopped to start the discharge. . However, the sterilization effect is enhanced by continuing the discharge while constantly introducing the gas into the container 2. A plurality of gas introduction pipes 4 may be provided.

[0026]

EXAMPLE The sterilizing method of the present invention was carried out using the sterilizing apparatus 1 shown in FIG.

As the container to be sterilized, a PET bottle for 500 mL was used. Spores of Bacillus subtilis, Aspergilus niger, or chaetomium globosum were evenly attached to the inner surface of the PET bottle. The number of bacteria was adjusted to 10 ⁵ per bottle.

As a sterilization method, the discharge electrode and the gas introduction tube were inserted into a PET bottle which had been sterilized, and the dielectric and the counter electrode were installed on the outer circumference of the bolt. While continuously supplying a predetermined gas at a predetermined flow rate from the gas introduction tube, a pulse high voltage was applied between the electrodes for a predetermined time to continue the corona discharge. After the discharge was completed, sterile air was supplied into the bottle at a flow rate of 9 L / min for 30 seconds in order to remove impurities such as ozone gas.

As a method for evaluating the bactericidal effect, after the above-mentioned aseptic air supply is completed, an agar medium is injected into a PET bottle, the mouth of each bottle is sealed with a sterile cap, and the bacteria are cultured under the following conditions. . After culturing, the number of surviving bacteria in the bottle was counted. Condition 1: For the bottle to which Bacillus subtilis was attached, the bacteria were cultured for 6 days in an environment of standard agar medium and 36 ° C. Condition 2: For a bottle to which Aspergillus niger or ketodium glopossum was attached, the bacteria were cultured for 6 days in an environment of potato dextrose agar and 25 ° C. (Example 1) Table 1 shows the number of surviving bacteria after discharge and the presence or absence of thermal deformation of the PET bottle after discharge when sterilization was performed by changing the electric field strength. The test strain was Aspergillus niger, the initial number of bacteria was 2.0 × 10 ⁵ , and the pulse width was 80 nse.
c, pulse frequency is 400 pps, discharge time is 30 sec
Then, discharge was performed in the air in the bottle.

[0030]

[Table 1]

Example 2 Table 2 shows the number of surviving bacteria after discharge and the presence or absence of thermal deformation of the PET bottle after discharge when sterilization was performed by changing the pulse width. The test strain was Aspergillus niger, the initial number of bacteria was 2.0 × 10 ⁵ , the electric field strength was 60 kV / cm, the pulse frequency was 400 pps, the discharge time was 30 sec, and the discharge was performed in the air in the bottle.

[0032]

[Table 2]

Example 3 Table 3 shows the number of surviving bacteria after discharge and the presence or absence of thermal deformation of the PET bottle after discharge when sterilization was performed by changing the pulse frequency. The test strain was Aspergillus niger, the initial number of bacteria was 2.0 × 10 ⁵ , the electric field intensity was 60 kV / cm, the pulse width was 80 nsec, and the discharge time was 30 sec, and discharging was performed in the air in the bottle.

[0034]

[Table 3]

(Embodiment 4) The number of surviving bacteria after discharge and P after discharge when various gases were introduced into the bottle for sterilization
Table 4 shows whether or not the ET bottle was thermally deformed. The test strain was Aspergillus niger, and the initial number was 2.0 × 1.
0 ⁵ , electric field strength 60 kV / cm, pulse width 80 ns
ec, pulse frequency 400 pps, discharge time 30 sec
c. 9L / m of various gases before generating discharge
It was introduced into the bottle at a flow rate of in for 30 seconds to replace the air in the bottle with the target gas. Then, the introduction of the gas was stopped and the discharge was immediately performed.

[0036]

[Table 4]

Example 5 Table 5 shows the number of surviving bacteria after discharge and the presence or absence of thermal deformation of the PET bottle after discharge when sterilization was performed by changing the flow rate of gas to be introduced. The test strain was Aspergillus niger, and the initial number of bacteria was 2.0 × 10.
⁵ , electric field strength is 60 kV / cm, pulse width is 80 nse
c, pulse frequency is 400 pps, discharge time is 10 sec
And Argon gas 9L / m before generating discharge
It was introduced into the bottle at a flow rate of in for 30 seconds to replace the air in the bottle with argon gas. After that, the flow rate of the argon gas was adjusted to a predetermined value, and the discharge was performed while continuing the introduction.

[0038]

[Table 5]

(Example 6) Table 6 shows the number of surviving bacteria after discharge and the presence or absence of thermal deformation of the PET bottle after discharge when two kinds of gases were mixed and sterilized. The test strain was Aspergillus niger, the initial number of bacteria was 2.0 × 10 ⁵ , the electric field strength was 60 kV / cm, the pulse width was 80 nsec, the pulse frequency was 400 pps, and the discharge time was 10 sec.
Before generating a discharge, a mixed gas of argon gas and air (mixing ratio: 0.5: 0.5) was used at a flow rate of 9 L / min for 3 times.
The mixture was introduced into the bottle for 0 seconds to replace the air in the bottle with the mixed gas. Then, discharging was performed while supplying the mixed gas (mixing ratio was as described above) into the bottle at a flow rate of 1 L / min.

[0040]

[Table 6]

(Example 7) Table 7 shows the number of surviving bacteria after discharge and the presence or absence of thermal deformation of the PET bottle after discharge when sterilization was performed by changing the bacterial species. The electric field strength is 60 kV.
/ Cm, pulse width 80 nsec, pulse frequency 400
The pps and discharge time were 10 sec. Before generating a discharge, argon gas was introduced into the bottle at a flow rate of 9 L / min for 30 seconds to replace the air in the bottle with the argon gas. Then, discharge was performed while supplying argon gas into the bottle at a flow rate of 2 L / min.

[0042]

[Table 7]

As is clear from the above results, according to the sterilization method of the present invention, the container can be surely sterilized in a short time even at room temperature and normal pressure.

[0044]

As described above, according to the sterilization method and device of the present invention, corona discharge based on pulse high voltage is generated between the discharge electrode and the counter electrode arranged inside and outside the container. Thus, the container can be surely sterilized under normal temperature and normal pressure. In particular, when the dielectric is arranged inside the counter electrode, corona discharge can be stably continued and a high sterilization effect can be obtained. Moreover, by introducing a specific gas into the corona discharge, the sterilizing effect can be surely exhibited by maintaining the activated atmosphere.

[Brief description of drawings]

FIG. 1 is a diagram showing an outline of a sterilizing apparatus according to an embodiment of the present invention.

FIG. 2 is a perspective view in which a counter electrode of the sterilizer of FIG. 1 is changed.

FIG. 3 is a diagram showing an example of a waveform of a high voltage pulse used in the present invention.

[Explanation of symbols]

1 sterilizer 2 containers 3 discharge electrodes 4 Gas introduction pipe 5 Dielectric 6 Counter electrode 7 High voltage power supply 8 gas cylinders 9 Flowmeter 10 stages

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Ryo Hayashi             1-1-1, Ichigaya-Kagacho, Shinjuku-ku, Tokyo             Dai Nippon Printing Co., Ltd. (72) Inventor Akutsu Akiko             19-17 Ikedanaka-cho, Neyagawa-shi, Osaka Japan             Into Inc. (72) Inventor Akinori Iwata             19-17 Ikedanaka-cho, Neyagawa-shi, Osaka Japan             Into Inc. F-term (reference) 4C058 AA16 AA25 BB06 KK06 KK22

Claims (7)

[Claims] 1. A discharge electrode is inserted into a container to be sterilized, which is placed under normal temperature and normal pressure, and a counter electrode is arranged so as to surround the container, a pulse width of 10 nsec or more, an electric field intensity of 4 to 100 kV / cm, and a pulse. A method for sterilizing a container, characterized in that a high pulse voltage having a frequency of 10 pps or more is applied between the discharge electrode and the counter electrode to generate corona discharge between both electrodes. 2. The sterilization method according to claim 1, wherein the corona discharge is generated in a state where the container is surrounded by a dielectric material arranged inside the counter electrode. 3. Oxygen, nitrogen, hydrogen, carbon dioxide, air,
The sterilization method according to claim 1 or 2, wherein at least one gas selected from the group consisting of argon and helium is introduced into the corona discharge. 4. A discharge electrode arranged in a space at normal temperature and pressure and having a shape capable of being inserted into a container to be sterilized, a counter electrode arranged so as to surround the discharge electrode in the space, and a pulse width of 10 nsec or more. , Electric field strength 4 to 100 kV /
cm, a high voltage power source capable of applying a pulsed high voltage having a pulse frequency of 10 pps or more between the discharge electrode and the counter electrode. 5. The sterilizer according to claim 4, wherein a dielectric is arranged inside the counter electrode so as to surround the discharge electrode. 6. The sterilizer according to claim 4, further comprising a gas introduction pipe having a shape that can be inserted into the container. 7. The sterilizer according to claim 4, wherein the counter electrode is in close contact with the outer periphery of the dielectric.