JP2012187225A - Plasma generating apparatus and plasma generating method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase amount of active species and to hardly make dew formation or moisture attachment be generated on a dielectric layer.SOLUTION: A plasma generating apparatus includes a pair of electrodes, wherein a dielectric layer is arranged on at least one of surfaces of the electrodes facing each other, plasma discharge occurs as a predetermined voltage is applied to the electrodes, and a coating film is arranged on a surface of the dielectric layer.

Description

  The present invention relates to a plasma generation apparatus and a plasma generation method.

  The need for air quality control in the living environment, such as sterilization and deodorization, is increasing due to the increase in infectious risk seen in the recent epidemic of atopy, asthma and allergy symptoms and the outbreak of new influenza. In addition, as the life becomes richer, the amount of stored foods has increased and the chances of storing uneaten foods have increased, and environmental control in storage devices represented by refrigerators has also become more important.

  As for the prior art aiming at air quality control of living environment, physical control represented by a filter is generally used. Physical control can capture relatively large dust and dirt floating in the air and bacteria and viruses depending on the size of the filter hole. Moreover, when there are innumerable adsorption sites such as activated carbon, malodorous odor molecules can be captured. However, in order to capture it, it is necessary to pass the air in the controlled space evenly through the filter, which increases the size of the device and increases maintenance costs such as filter replacement. There is no. Therefore, as a means for enabling sterilization and deodorization of the deposit, it is possible to release chemically active species to a space where sterilization and deodorization are desired. In the spraying of chemicals and the release of fragrances and deodorants, it is necessary to prepare active species in advance, and regular replenishment is essential. On the other hand, means for attempting to sterilize and deodorize by generating plasma in the atmosphere and using chemically active species generated there has been increasing in recent years.

Technologies for generating plasma in the atmosphere by discharge and performing sterilization and deodorization with ions or radicals (hereinafter referred to as active species) generated therein can be classified into the following two types.
(1) A so-called passive plasma generator that reacts bacteria and viruses floating in the atmosphere (hereinafter referred to as floating bacteria) or malodorous substances (hereinafter referred to as odor) with active species within a limited volume in the device ( For example, Patent Document 1)
(2) The active species generated in the plasma generator are discharged into a closed space (for example, a living room, a toilet, a passenger car, etc.) having a volume larger than that of (1), and the active species, airborne bacteria and odors in the atmosphere So-called active-type plasma generator that reacts by collision with the plasma

  The advantage of the passive plasma generator of (1) is that a high concentration of active species is generated by generating plasma in a small volume, so that a high sterilizing effect and deodorizing effect are expected. On the other hand, since it is necessary to introduce airborne bacteria and odors into the device, the size of the device is increased, and ozone is likely to be generated as a by-product from the generation of plasma. Alternatively, it is necessary to install a separate filter for disassembly.

  Next, the advantage of the active plasma generator of (2) is that the device can be made relatively small. In addition to sterilization of airborne bacteria and decomposition of odors in the air, bacteria attached to the surface of clothing and household goods (hereinafter referred to as In addition, sterilization of adhering bacteria) and decomposition of odor adsorbed on the surface can be expected. On the other hand, the disadvantage is that active species are diffused in a very large closed space compared to the volume of the device, so the concentration is low, so that only active species with a long life expectation of sterilization and deodorizing effects can be expected. It is a point that cannot be obtained. As a result, a deodorizing effect can hardly be expected in a space with a high odor concentration (a concentration about 10,000 times higher than the active species concentration).

  From the above, in the passive plasma generator, the effect is limited only to airborne bacteria and odors contained in the air flow flowing into the apparatus, and in the active plasma generator, low concentration of airborne bacteria and adhesion You can only expect effects on bacteria and odors. That is, what can be realized by using the prior art is limited to either “sterilization and deodorization of airborne bacteria” or “sterilization of airborne bacteria with low concentration, adhesion bacteria, and deodorization of adhesion odor”.

  In addition, in the electrode constituting the plasma generation unit, for example, a porous dielectric film is often used at the plasma generation site of the electrode, and therefore, under high humidity, the dielectric film itself absorbs moisture due to its hygroscopic action. The characteristics change, and the generation of plasma is hindered. In particular, in an environment where the temperature and humidity change greatly, such as in a refrigerator, the dielectric film itself of the electrode tends to condense, the generation of plasma stops, and the sterilization and deodorization performance deteriorates. Therefore, it is difficult to maintain sterilization performance when the inside of the refrigerator remains in a high humidity state.

JP 2002-224211 JP 2003-79714 A

  Therefore, the present invention is a technology that realizes both sterilization and deodorization of attached bacteria at the same time, and generates a plasma to generate a passive type function that deodorizes with active species and releases the active species to the outside of the device. The main objective is to increase the amount of active species generated and to make it difficult for condensation and moisture to occur on the dielectric film in order to simultaneously have two active functions for sterilizing bacteria.

  That is, the plasma generator according to the present invention has a pair of electrodes provided with a dielectric film on at least one of the opposing surfaces, and a plasma discharge is performed by applying a predetermined voltage between the electrodes. A coating layer is provided on the surface.

  In such a case, since the coating film is provided on the surface of the dielectric film, it is difficult for condensation and moisture to occur on the dielectric film. For example, the sterilization performance is reduced even under high humidity in the refrigerator. This can prevent sterilization performance for a long time. In addition, if the fluid flow holes are provided at the corresponding positions of the electrodes so that they can penetrate, the amount of plasma generated in the corresponding fluid through holes can be increased as much as possible. The contact area between the plasma and the fluid can be increased as much as possible. As a result, the production amount of active species such as ions and radicals can be increased, and the function of deodorizing with the active species and the function of releasing the active species outside the apparatus to sterilize the floating bacteria and attached bacteria are sufficient. Will be able to demonstrate. Note that the corresponding part in this specification means that each fluid flow hole formed in both electrodes is substantially at the same position when viewed from the direction of the face plate of the electrode. When a pair of electrodes having an xy plane shape is seen from the direction, it means that the coordinate positions are substantially the same (x, y) in both electrodes.

  When the dielectric film is formed by a thermal spraying method, the formed dielectric film is easily affected by humidity because it has a porous or fine concavo-convex structure, as in the present invention. The effect of providing the coating film becomes more remarkable.

  In order to further prevent dew condensation and moisture adhesion at the plasma generation site, it is desirable that the coating film has water repellency.

  It is desirable that the thickness of the coating film is 0.01 μm or more and 100 μm or less. Here, if the coating film is 100 μm or more, the physical properties of the dielectric film itself are impaired, and the unevenness formed on the surface of the dielectric film is buried, so that the plasma generation effect is lowered.

  It is desirable to have a spacer having a thickness of 500 μm or less between the pair of electrodes. If it is this, since the distance between electrodes can be enlarged and a deodorization reaction field can be enlarged, the deodorizing efficiency of an odor can be improved. In addition, since the distance between the electrodes is increased by the spacer, even if moisture adheres, the water droplets are fine and can be easily removed from between the electrodes. Here, spacer formation methods include thin film formation methods such as vapor deposition, CVD (Chemical Vapor Deposition), sputtering, and ion plating, or plating, thermal spraying, spray coating, spin coating, and coating. And so on.

  In order to prevent condensation and moisture adhesion in the spacer, it is desirable that a coating layer is provided on the surface of the spacer.

  In order to promote the generation of active species by allowing the fluid to efficiently pass through the fluid circulation hole and to increase the deodorizing effect, it has a blower mechanism that forcibly sends air toward the fluid circulation hole. Is desirable.

  Here, it is desirable that the flow velocity of the wind passing through the fluid circulation hole by the air blowing mechanism is in the range of 0.1 m / s to 30 m / s.

  In order to increase the number of active species contained in the fluid that has passed through the fluid through-hole as much as possible, and to suppress the concentration of generated ozone, the voltage applied to each of the electrodes has a pulse shape, and its peak value Is preferably in the range of 100 V to 5000 V, and the pulse width is preferably in the range of 0.1 μs to 300 μs.

  Further, the plasma generation method according to the present invention uses a pair of electrodes provided with a dielectric film on at least one of the opposing surfaces, and plasma discharge is performed by applying a predetermined voltage between the electrodes. Is provided with a coating layer.

  According to the present invention configured as described above, it is possible to realize both sterilization and deodorization of the attached bacteria at the same time by increasing the generation amount of active species, and it is difficult for condensation and moisture adhesion to occur on the dielectric film. It is possible to prevent a decrease in sterilization performance over a long period of time.

The perspective view which shows one Embodiment of the plasma generator of this invention. The schematic diagram which shows the effect | action of a plasma generator. The top view which shows an electrode part. Sectional drawing which shows an electrode part and an explosion-proof mechanism. The expanded sectional view which shows the structure of the opposing surface of an electrode part. The partial enlarged plan view and sectional view which show a fluid circulation hole and a penetration hole typically. The figure which shows the pulse width dependence of ion number density and ozone concentration. The figure which shows the relationship between the condensation cycle of conventional products and this invention, and ion number density. The conceptual diagram which shows the difference in the deodorizing effect by the magnitude of the distance between electrodes. The figure which shows the dependence of the spacer thickness in deodorizing performance. An example of temperature and humidity changes in the refrigerator.

  An embodiment of the present invention will be described below with reference to the drawings.

  The plasma generator 100 according to the present embodiment is used for home appliances such as a refrigerator, a washing machine, a clothes dryer, a vacuum cleaner, an air conditioner, or an air cleaner, and the inside or outside of the home appliance. It is intended to sterilize airborne odors and adhering bacteria inside or outside of these products.

  Specifically, as shown in FIGS. 1 and 2, the plasma electrode unit 2 generates active species such as ions and radicals by micro gap plasma (Micro Gap Plasma), and the outside of the plasma electrode unit 2 A blower mechanism 3 that is provided and forcibly sends wind (air flow) to the plasma electrode unit 2 and a flame that is provided outside the plasma electrode unit 2 and that is generated in the plasma electrode unit 2 does not propagate to the outside. An explosion-proof mechanism 4 and a power source 5 for applying a high voltage to the electrode part are provided.

  Hereinafter, each part 2-5 is demonstrated with reference to each figure.

  As shown in FIGS. 2 to 6, the plasma electrode unit 2 includes a pair of electrodes 21 and 22 having dielectric films 21 a and 22 a provided on opposite surfaces, and a predetermined voltage is applied between the electrodes 21 and 22. Plasma discharge. As shown in FIG. 3 in particular, each of the electrodes 21 and 22 has a substantially rectangular shape in plan view (when viewed from the face plate direction of the electrodes 21 and 22), and is made of stainless steel such as SUS403, for example. Yes. In addition, the application terminal 2T to which the voltage from the power supply 5 is applied is formed in the edge part of the electrodes 21 and 22 of the electrode part 2 (refer FIG. 3).

  Here, the voltage application method to the plasma electrode unit 2 by the power source 5 is such that the voltage applied to each of the electrodes 21 and 22 has a pulse shape, the peak value is in the range of 100 V to 5000 V, and the pulse width is 0.1 μm. It is within the range of not less than seconds and not more than 300 μsec. As shown in FIG. 7, when the pulse width is 300 μsec or less, the ion number density is measured, and the ozone concentration is decreased. As the pulse width is decreased, the ion number is increased and the ozone concentration is decreased. As a result, the amount of ozone generated is suppressed, and the active species generated in the plasma can be efficiently released without losing it with a filter or the like that is often found in the prior art. Can be realized in a short time.

  Further, as shown in FIG. 5, dielectric films 21 a and 22 a are formed on the opposing surfaces of the electrodes 21 and 22 by applying a dielectric such as barium titanate. The surface roughness (calculated average roughness Ra in the present embodiment) of the dielectric films 21a and 22a is not less than 0.1 μm and not more than 100 μm. Other surface roughness may be defined using the maximum height Ry and the ten-point average roughness Rz. Note that the surface roughness of the dielectric films 21a and 22a can be controlled by a thermal spraying method. Dielectrics applied to the electrodes include aluminum oxide, titanium oxide, magnesium oxide, strontium titanate, silicon oxide, silver phosphate, lead zirconate titanate, silicon carbide, indium oxide, cadmium oxide, bismuth oxide, and zinc oxide. Iron oxide, carbon nanotubes, etc. may be used.

  Further, as shown in FIGS. 3, 4, and 6, fluid flow holes 21 b and 22 b are provided in corresponding portions of the electrodes 21 and 22, respectively, and are configured to communicate with and penetrate the electrodes 21 and 22. When viewed from the direction of the face plate 22 (in plan view), at least a part of the contour of each corresponding fluid through-hole 21b, 22b is configured to be different from each other. That is, the plan view shape of the fluid circulation hole 21 b formed in one electrode 21 and the plan view shape of the fluid circulation hole 22 b formed in the other electrode 22 are different from each other.

  Specifically, the fluid circulation holes 21b and 22b respectively formed in the corresponding portions of the electrodes 21 and 22 have a substantially circular shape in plan view (see FIGS. 3 and 6). The opening size (opening diameter) of the fluid circulation hole 21b formed in the first electrode 21 is smaller than the opening size (opening diameter) of the fluid circulation hole 22b formed in the other electrode 22 (for example, the opening diameter is 10 μm or more smaller). Has been.

  Similarly, as shown in FIGS. 3 and 6, the fluid circulation hole 21 b formed in one electrode 21 and the fluid circulation hole 22 b formed in the other electrode 22 are formed concentrically. In the present embodiment, the plurality of fluid circulation holes 21b formed in one electrode 21 all have the same shape, and the plurality of fluid circulation holes 22b formed in the other electrode 22 all have the same shape. All of the fluid circulation holes 21 b formed in one electrode 21 are formed smaller than the fluid circulation holes 22 b formed in the other electrode 22. In the present embodiment, the effect is shown as a substantially circular shape, but the opening is not limited to a circle, and may have any shape, and at least a part of the contour of each corresponding fluid through-hole is different from each other in plan view. It suffices to be configured.

  Furthermore, the total opening area of the fluid circulation holes 21 b and 22 b formed in each electrode 21 and 22 is in the range of 2% to 90% with respect to the total area of each electrode 21 and 22. Specifically, the total opening area of the fluid circulation holes 22 b formed in the other electrode 22 is in the range of 2% to 90% with respect to the total area of the electrode 22. The total opening area of the fluid circulation holes 21b formed in one electrode 21 may be in the range of 2% to 90%.

  As shown in FIGS. 3 and 6, the plasma electrode portion 2 of the present embodiment is provided with a through hole 21c in one electrode 21 separately from the fluid circulation holes 21b and 22b, and this through hole 21c is the other electrode. The opening on the opposite surface side is closed by 22. In addition, what consists of the fluid circulation holes 21b and 22b formed in each said electrodes 21 and 22 may be hereafter called a complete opening, but what is formed by the through-hole 21c in comparison with this is a half opening. That's it.

  The opening size of the through hole 21c is formed to be 10 μm or more smaller than the opening size of the fluid circulation hole 21b. The through hole 21c is formed by replacing a part of the regularly provided fluid circulation hole 21b, and the through hole 21c is provided around the fluid circulation hole 21b (see FIG. 3).

  The blower mechanism 3 is disposed on the other electrode 22 side of the plasma electrode unit 2 and forcibly sends air toward the fluid circulation holes 21b and 22b (completely open portions) formed in the plasma electrode unit 2. It has a blower fan. Specifically, in this blower mechanism 3, the flow velocity of the wind passing through the fluid circulation holes 21b and 22b is set in the range of 0.1 m / s to 30 m / s.

  As shown in FIG. 4, the explosion-proof mechanism 4 has a protective cover 41 disposed outside the pair of electrodes 21, 22, and a flame generated by plasma when combustible gas flows into the fluid circulation holes 21 b, 22 b. However, it is configured not to propagate outside the protective cover 41. Specifically, the explosion-proof mechanism 4 has a protective cover 41 having a metal mesh 411 disposed outside the pair of electrodes 21 and 22, and the wire diameter of the metal mesh 411 is within a range of 1.5 mm or less. And the aperture ratio of the metal mesh 411 is 30% or more.

Therefore, in the present embodiment, as shown in FIG. 5, a single coating film 23 is provided on the surfaces of the dielectric films 21 a and 22 a of the electrodes 21 and 22. This coating film 23 has water repellency and is made of glass, fluororesin, silicon, diamond-like carbon (DLC), fluorine-containing DLC, SiO ₂ , ZrO ₂ , TiO ₂ , SrO ₂ , MgO, or That combination. In addition, the coating film 23 is formed almost uniformly on the top surfaces of the dielectric films 21a and 22a, so that a thin film forming method such as a vapor deposition method, a CVD method (Chemical Vapor Deposition), a sputtering method, or an ion plating method, or , Plating, thermal spraying, spray coating, spin coating, coating, and the like.

  FIG. 8 shows the relationship between the condensation cycle and the ion number density in the plasma generator 100 (invention) in which the coating film 23 is formed and the plasma generator (conventional product) in which the coating film 23 is not formed. As can be seen from FIG. 8, in the conventional product, the ion number density gradually decreases from the second condensation cycle, but in the present invention, the ion number density does not decrease regardless of the condensation cycle. I understand.

  Further, in the electrodes 21 and 22 of this embodiment, a gap of a predetermined distance is formed between the electrodes 21 and 22 by a spacer 24 made of an insulating material. As shown in FIG. 3, the spacers 24 are provided at a plurality of locations on the periphery of the electrodes 21 and 22. Note that the position of the spacer is not limited to that shown in FIG. 3. For example, the spacer may be provided over the entire peripheral edge, or may be provided at any position that does not block the fluid circulation holes 21 b and 22 b and the through hole 21 c, such as the center of the electrode. It may be provided. The thickness of the spacer 24 is desirably 500 μm or less. This is because if it is larger than 500 μm, the voltage for generating plasma increases, and ozone is easily generated. Further, the spacer 24 is any one of fluorine resin, epoxy, polyimide, alumina, glass, or a combination thereof. The spacer 24 of the present embodiment is formed by a thermal spraying method in the same manner as the dielectric films 21a and 22a. More specifically, a member that becomes the spacer 24 is formed on the dielectric films 21a and 22a of the electrodes 21 and 22 with a thickness of, for example, 250 μm or less, and the spacers 24 are 500 μm or less by overlapping them. Yes. In addition, the spacer 24 may be formed on the dielectric film 21a (dielectric film 22a) of one electrode 21 (or electrode 22).

  The coating film 23 of this embodiment is formed after the dielectric films 21a and 22a are formed by a thermal spraying method, and a member to be the spacer 24 is formed on the dielectric films 21a and 22a by the thermal spraying method. Thereby, the spacer 24 is also covered with the coating film 23, and the dew condensation and moisture adhesion which occur in the spacer 24 can be prevented. The spacers 24 may be formed after the dielectric films 21a and 22a are formed and the coating film 23 is formed.

  By providing the spacer 24 in this way, the distance between the electrodes can be increased by the thickness of the spacer 24, and as shown in FIG. 9, the deodorization reaction field is increased and the contact volume between air and plasma is increased. Therefore, the deodorization efficiency is improved. Here, the dependency of the deodorizing performance and the thickness of the spacer 24 is shown in FIG. The deodorizing efficiency when the spacer 24 is not provided is 20%, whereas the deodorizing efficiency when the spacer 24 having a thickness of 10 μm is provided is 30%, 32% at 20 μm, and 35% of the maximum at 50 μm. Efficiency has improved. Further, the deodorization efficiency at 100 μm is 30%, and the improvement in the deodorization rate is remarkable at 10 μm to 100 μm. In addition, the deodorization efficiency deteriorates as the thickness of the spacer 24 exceeds 100 μm, but it is 20% or more up to 500 μm. On the other hand, when the thickness of the spacer 24 exceeds 500 μm, the deodorizing efficiency is deteriorated as compared with the case where the spacer 24 is not provided.

  The plasma generator 100 configured as described above can be suitably used in a refrigerator. As shown in FIG. 11, the inside of the refrigerator is in a high humidity state during the defrosting operation, and condensation is likely to occur between the electrodes 21 and 22 or moisture tends to adhere. On the other hand, in the plasma generating apparatus 100 of the present embodiment, the water-repellent coating film 23 is provided on the surfaces of the dielectric films 21a and 22a between the electrodes 21 and 22, so that condensation and moisture adhesion hardly occur. . In addition, since the distance between the electrodes 21 and 22 is increased by the spacer 24, even if condensation occurs, the condensed water easily escapes to the outside between the electrodes 21 and 22.

<Effect of this embodiment>
According to the plasma generating apparatus 100 according to the present embodiment configured as described above, it is possible to increase the amount of plasma generated in the corresponding fluid through holes 21b and 22b as much as possible. The contact area can be increased as much as possible. As a result, the production amount of active species such as ions and radicals can be increased, and the function of deodorizing with the active species and the function of releasing the active species outside the apparatus to sterilize the floating bacteria and attached bacteria are sufficient. Will be able to demonstrate. In addition, since the water-repellent coating film 23 is provided on the surfaces of the dielectric films 21a and 22a, the dielectric films 21a and 22a are less likely to form dew condensation and moisture, and are sterilized even under high humidity in a refrigerator, for example. It is possible to prevent the performance from being lowered and to exhibit the bactericidal performance for a long time.

<Other modified embodiments>
The present invention is not limited to the above embodiment.
For example, in the above-described embodiment, the coating film is provided on the dielectric film of each electrode.

  In the above embodiment, the plurality of fluid circulation holes 21b of the electrode 21 have the same shape, and the plurality of fluid circulation holes 22b of the electrode 22 have the same shape, but each has a different shape. May be.

  In the embodiment, all the fluid circulation holes 21 b of the electrode 21 are formed smaller or larger than the plurality of fluid circulation holes 22 b of the electrode 22, but some of the fluid circulation holes 21 b of the electrode 21 are formed in the electrode 22. The other fluid circulation hole 21 b may be formed larger than the fluid circulation hole 22 b of the electrode 22.

  Furthermore, in the embodiment, the through hole is formed in either one of the electrodes 21 or the other electrode 22, but a through hole (half opening) may be formed in both.

  In addition, in the above-described embodiment, the fluid circulation hole has an equal cross-sectional shape, but in addition, the fluid circulation hole formed in each electrode has a tapered surface, a mortar shape or a bowl shape, that is, The diameter may be reduced or increased from one opening to the other opening.

  In addition, the fluid flow hole may be elliptical, rectangular, linear slit, concentric slit, corrugated slit, crescent, comb, honeycomb, or star, in addition to a circular shape. .

  In addition, it goes without saying that the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention.

DESCRIPTION OF SYMBOLS 100 ... Plasma generator 21 ... One electrode 22 ... The other electrode 21a, 22a ... Dielectric film | membrane 21b, 22b ... Fluid flow hole 23 ... Coating film 24 ... Spacer 3 ... Blower mechanism

Claims (11)

  Plasma having a pair of electrodes provided with a dielectric film on at least one of the opposing surfaces, and a plasma discharge is performed by applying a predetermined voltage between the electrodes, and a plasma having a coating layer provided on the surface of the dielectric film Generator.   The plasma generating apparatus according to claim 1, wherein the dielectric film is formed by a thermal spraying method.   The plasma generating apparatus according to claim 1, wherein the coating film has water repellency.   The plasma generator according to any one of claims 1 to 3, wherein a thickness of the coating film is 0.01 µm or more and 100 µm or less.   The plasma generator according to claim 1, further comprising a spacer having a thickness of 500 μm or less between the pair of electrodes.   The plasma generating apparatus according to claim 5, wherein the spacer is formed by a thermal spraying method.   The plasma generator according to claim 5 or 6, wherein a coating layer is provided on a surface of the spacer.   A plasma generation method using a pair of electrodes provided with a dielectric film on at least one of the opposing surfaces, and applying a predetermined voltage between the electrodes for plasma discharge, and providing a coating layer on the surface of the dielectric film .   9. The plasma generation method according to claim 8, wherein the dielectric film is formed by a thermal spraying method.   The plasma generation method according to claim 8 or 9, wherein the coating film has water repellency.   The plasma generation method according to claim 8, wherein the coating film has a thickness of 0.01 μm to 100 μm.