WO2019139223A1

WO2019139223A1 - Particle collecting device

Info

Publication number: WO2019139223A1
Application number: PCT/KR2018/011916
Authority: WO
Inventors: Manabu Ono; Takashi Nakazawa
Original assignee: Hp Printing Korea Co., Ltd.
Priority date: 2018-01-10
Filing date: 2018-10-11
Publication date: 2019-07-18
Also published as: JP2019118897A

Abstract

A system includes a charging apparatus to charge airborne particles, and a vapor generator to supply vapor to the charging apparatus. The charging apparatus includes an electrode portion and a ventilation passage passing through the electrode portion. A supply rate of the vapor supplied by the vapor generator is approximately 0.20 to 0.50 mg/min per 1 cm2 of a cross-sectional area of the ventilation passage. Additionally, the system includes a collecting apparatus to collect the airborne particles charged by the charging apparatus.

Description

PARTICLE COLLECTING DEVICE

An electric dust collecting device is a device which is attached to electric appliances such as air purifiers and air conditioners to purify air by collecting contaminants such as floating fine particles. In general, such an electric dust collecting device is of a two-stage type including a "charging unit" which charges floating fine particles by discharge and a "dust collection unit" which collects the charged floating fine particles. In order to generate corona discharge, a high voltage of several kV is applied between a "discharge electrode" to which a high voltage having a positive polarity or a negative polarity is applied and a "counter electrode" which is grounded. The floating fine particles in the air introduced into the charging unit are charged to have a positive polarity or a negative polarity due to the generation of corona discharge, are further transferred along the air flow, and are collected by the dust collection unit.

FIG. 1 is a schematic cross-sectional diagram illustrating a configuration of an example electric particle (dust) collecting device.

FIG. 2(a) is a perspective diagram illustrating main portions of a charging unit of the example electric dust collecting device and FIG. 2(b) is an exploded perspective diagram.

FIG. 3 is an example diagram of a discharge electrode disposed in a charging unit.

FIG. 4(a) is a partial enlarged front diagram of an electrode illustrating current conduction deterioration of a discharge electrode and FIG. 4(b) is a diagram illustrating a state of corona discharge of the discharge electrode.

FIGS. 5(a) and 5(b) are an external diagram and a cross-sectional diagram of a honeycomb structure and a corrugated structure including a tubular ventilation passage,.

FIG. 6 is a conceptual diagram illustrating an example structure of a film split nonwoven fabric (orientation of split fibers).

FIG. 7 is a table summarizing setting conditions and test results of examples and comparative examples.

In the following description, with reference to the drawings, the same reference numbers are assigned to the same components or to similar components having the same function, and overlapping description is omitted.

An axial flow blower may be used as an "air flow generation unit" for generating an air flow for introducing floating fine particles into an electric dust collecting device, but since the air flow itself becomes a swirling flow under the influence of a propeller fan, variation occurs in the transporting speed of the floating fine particles. The floating fine particles having a high transporting speed not only is difficult to collect at the dust collection unit, but may also result in charging to be applied at the charging unit, so that the collecting efficiency is synergistically decreased. For example, in a case where the air throughput per unit time (hereinafter, simply referred to as "air throughput") is increased, the above-described tendency becomes conspicuous, and thus, the dust collecting capability of the electric dust collecting device may be greatly decreased.

Accordingly, an electric dust collecting device including a charging unit having first and second charging cells capable of being adapted to a flow rate difference of a gas and a collection unit configured with a collecting electrode to which a high voltage is applied may be used.

The electric dust collecting device provided with the first and second charging cells in the charging unit can exhibit dust collecting capability even in a case where the air throughput is large. However, electric dust collecting devices of this type may be large and/or generate ozone.

Additionally, other types of electric dust collecting devices may be provided with a thin type charger in which the tip of the serrated (sawtooth) or needle-shaped electrode crosses the ventilation direction and the electrode tip portion is disposed alternately with another adjacent electrode tip portion.

An electric dust collecting device provided with such a thin charger can also exhibit dust collecting capability while providing a miniaturization of the charging unit and suppression of ozone generation. However, in the discharge electrode having the serrated shape or the needle shape, the tip portion is reduced, or the "current conduction deterioration (energization deterioration)" such as generation of a nonconductor layer made of an oxide progresses according to the amount of current conduction or the time for current conduction. Since the state of corona discharge at the electrode tip portions disposed at a certain intervals varies with the elapse of time, the dust collecting capability of the electric dust collecting device is lowered and the amount of generated ozone is increased.

Meanwhile, with respect to a blowing device using an ion wind, a discharge electrode in which the amount of generated ions is not likely to be affected by exhaustion of the discharge electrode may be used. For example, a discharge electrode may have a protrusion which is rounded so that a radius of curvature of the tip is equal to or greater than the plate thickness.

In addition to the influence of the shape of the tip of the discharge electrode on the ratio of generated ions under a constant voltage condition (-5 kV), a decrease in electrode performance due to an amount of generated ozone and a current conduction deterioration may also occur. In addition, blowing devices using an ion wind may be associated with a ratio of generated ions.

On the other hand, the amount of ozone generated at the time of generation of an ion wind may be reduced by a discharge electrode having an arc-shaped protrusion as viewed from the thickness direction.

In this case, it is assumed that, when a high voltage having a negative polarity is applied to the discharge electrode being rounded in the thickness direction and discharging occurs under constant current condition (0.15 mA), the amount of generated ozone with respect to the total discharge time is suppressed. However, in some discharge electrodes, the amount of generated ozone may be increased within 100 hours from the start of discharge. This tendency may occur as the radius of curvature of the tip of the protrusion is smaller, and thus, it is considered to imply the influence of the current conduction deterioration. In some cases, discharge electrodes having a plurality of protrusions have different states of current conduction deterioration of the protrusions, and thus, the protrusions capable of sufficiently functioning and the protrusions incapable of functioning may exist together. When such a discharge electrode is used for the charging unit of the electric dust collecting device, and even when the amount of current conduction to the discharge electrode and the amount of generated ozone are stable with the elapse of the total discharge time, unevenness may occur in the charging of the floating fine particles, and thus, the collecting efficiency may be lowered.

Merely specifying the tip shape of the discharge electrode may not result in the suppression of the current conduction deterioration of the discharge electrode, stabilization of the amount of generated ions, and suppression of the amount of generated ozone at a high level.

Additionally, an electronic air cleaning apparatus may have a comb-shaped discharge electrode and a platinum-immersed honeycomb-shaped counter electrode made of ceramics.

In this case, although compatibility between the miniaturization and the dust collecting efficiency may be achieved by the comb-shaped electrode and the honeycomb-shaped counter electrode, the amount of air that can be processed depends on an ion wind generated between the comb-shaped electrode and the honeycomb-shaped counter electrode. Therefore, in the case of processing a large amount of air, a high voltage may be applied between the electrodes, so that ozone is generated and the life cycle of the discharge electrode is shortened.

The collection unit of the electric dust collecting device may be miniature and simplified by using a gas filter (air filter) for collecting the floating fine particles instead of a collecting electrode to which a high voltage is applied.

For example, dedicated filters such as a HEPA filter and a ULPA filter are used to collect the floating fine particles. Such filters are effective for removing the floating fine particles, but pressure loss is very high, so that other incidental devices such as a blower inevitably become large.

An air filter may be subjected to electret treatment for adsorbing and removing floating fine particles in an air flow by an electrostatic force. For example, an electret filter made of split fibers having specific fiber width and film thickness may be used.

An electret filter may be obtained by continuously folding a polymer film subjected to electret treatment and laminating the resulting polymer films so as to form a large number of continuous voids.

Although these gas filters can suppress the pressure loss to a very low level, the collecting capability by "inertial collision" and "interception effect" becomes small, so that the collecting of floating fine particles is mainly performed by "diffusion" or "electrostatic attraction". Therefore, as compared with a HEPA filter and a ULPA filter, a large amount of air may be treated with a small blower, but the collecting efficiency becomes significantly low. For example, in a case where the passing speed of the floating fine particles is high or in a case where the charged state is weak, the collecting efficiency of floating fine particles becomes extremely low. In some examples, the performance of the gas filter may be improved through compatibility between a low pressure loss and a high collecting efficiency.

Examples disclosed herein include a compact electric dust collecting device which is excellent in balance between collecting efficiency of floating fine particles existing in the air and air throughput.

In addition, the example electric dust collecting device may be used to suppress or reduce performance deterioration and ozone generation caused by current conduction deterioration of the discharge electrode.

The current conduction deterioration in the discharge electrode of the charging unit not only accelerates the ozone generation but also influences the collecting efficiency of floating fine particles, and in some examples, this tendency became apparent in an electric dust collecting device provided with a charging unit being disposed to a flat-plate-shaped counter electrode. For example, since a ventilation portion of the charging unit is partitioned by the counter electrode, even if only a portion of the discharge electrode is deteriorated by discharging, floating fine particles pass without being charged, which results in a decrease in collecting efficiency.

Example electric dust collecting device configurations may be implemented based on one or more of these considerations.

For example, the electric dust collecting device may include at least a "charging unit" which charges floating fine particles in an air, a "water vapor generation unit" which supplies water vapor to the charging unit, and a "dust collection unit" which is disposed on a downstream side in a ventilation direction of the charging unit and collects the floating fine particles charged by the charging unit. In some examples, a supply rate of the water vapor supplied from the water vapor generation unit to the charging unit is approximately 0.20 to 0.50 mg/min per 1 cm² of a cross-sectional area of a ventilation passage passing through an electrode portion of the charging unit.

By providing a water vapor generation unit on the upstream side in the ventilation direction of the charging unit and evaporating water vapor in the air flow, the water vapor is supplied to the charging unit at a specific speed, and thus, the amount of ozone generated from the charging unit can be largely suppressed. Accordingly, the current conduction deterioration of the discharge electrode can be suppressed.

In addition, in some example electric dust collecting devices, the charging unit is configured to include at least a "discharge electrode" to which a high voltage is applied by a high voltage power supply and a flat-plate-shaped "counter electrode" which is grounded. The discharge electrode may have a plurality of "protrusions" for discharging at pitches P (mm) (hereinafter, simply referred to as "protrusion pitch P"), and the counter electrode may be disposed in parallel with maintaining a gap G (mm) on both side surfaces of the discharge electrode (hereinafter, referred to as "electrode gap G"). Additionally, the protrusion pitch P and the electrode gap G may satisfy a relationship of 0.5 ≤ P/G ≤ 1.5.

By using the shapes of the discharge electrode and the counter electrode, the opening (aperture) of the charging unit may be partitioned. By specifying the relationship between the electrode gap G and the protrusion pitch P, charging may be uniformly and efficiently applied to the floating fine particles in the air passing through the charging unit. In addition, the water vapor supplied to the charging unit also works efficiently.

In some example electric dust collecting devices, the dust collection unit is provided with an air filter medium made of a sheet-shaped or film-shaped polymer material subjected to electret treatment, in which a contact angle of the polymer material to water is approximately 75° or more. Additionally, a thickness of the air filter medium is approximately 3 mm or more, and pressure loss at a wind speed of 0.2 m/sec is approximately 60 Pa or less.

By minimizing the influence of the water vapor supplied from the water vapor generation unit, the current conduction deterioration of the discharge electrode may be suppressed without lowering the dust collecting efficiency, contributing to cost reduction by thinning and simplification of the collection unit.

In some examples, the air filter medium is a structure including a tubular ventilation passage (tubular ventilation flue) formed by laminating at least polymer sheets (hereinafter, simply referred to as "a structure including a tubular ventilation passage"). Additionally, the structure may include an opening of the tubular ventilation passage located on a plane perpendicular to the ventilation direction of the air filter medium is 60% by area or more, in which an opening diameter d (mm) of the tubular ventilation passage and a ventilation passage length L (mm) satisfies a relationship of 0.025 ≤ d/L ≤ 0.2.

Use of the air filter medium as a structure including a tubular ventilation passage may be used to achieve compatibility between the air throughput and the collecting efficiency of floating fine particles at a high level. In addition, as a result of preventing condensation of water vapor supplied from the water vapor generation unit, a decrease in the effect of electret treatment on the polymer sheet forming the tubular ventilation passage may be suppressed, contributing to miniaturization of the collection unit and the air flow generation unit.

In some examples, the air filter medium may comprise a nonwoven fabric (hereinafter, simply referred to as "film split nonwoven fabric) containing approximately 50% by mass or more of a film split fiber obtained by processing a polymer film into a split, and a fiber width w (mm) and a fiber thickness k (mm) of the film split fiber satisfy a relationship of 2 ≤ w/k ≤ 5.

By using the air filter medium as the nonwoven fabric, a decrease in the effect of the electret treatment under the water vapor atmosphere supplied from the water vapor generation unit may be suppressed while suppressing the increase in pressure loss due to the water vapor supplied from the water vapor generation unit to a low level, not only to efficiently collect the floating fine particles but also to contribute to thinning of the collection unit.

The compact electric dust collecting device may therefore provide a balance between collecting efficiency of floating fine particles existing in the air and air throughput. Furthermore, the electric dust collecting device may be used to reduce or suppress performance deterioration and ozone generation caused by current conduction deterioration of a discharge electrode of a charging unit, from the time of the start of use.

FIG. 1(a) is a cross-sectional diagram illustrating a schematic configuration of a main portion 100 of an example electric particle (dust) collecting device. The direction of the ventilation is the direction of the arrow (as illustrated). In the main portion 100, with a charging unit 110 for charging floating fine particles in the air as the center, a water vapor generation unit 120 for supplying water vapor to the charging unit 110 is disposed on the upstream side in the ventilation direction, and a dust collection unit 130 for collecting the floating fine particles charged by the charging unit 110 is disposed on the downstream side in the ventilation direction. The main portion 100 is installed in an air flow inside the duct or is connected through a duct. The floating fine particles moving from a suction direction is charged by the charging unit 110, and after that, the floating fine particles are collected by the dust collection unit 130. In addition, the main portion 100 not only can be used by being installed in the air flow but also, in some examples, can be connected to the air flow generation unit 140 so that the amount of air introduced into the main portion 100 is increased or decreased. In a case where the main portion 100 is installed inside a household appliance or an office machine, the floating fine particles in the air discharged to the outside of the machine can be removed by an electric dust collection unit. In addition, in a case where an axial flow blower having a propeller fan as the air flow generation unit 140 is connected to the main portion 100, a stand-alone indoor electric dust collecting device can be implemented (refer to FIG. 1(b)).

FIG. 2 is a perspective diagram (a) and an exploded perspective diagram (b) of a main portion of the charging unit 110. The charging unit 110 includes at least a discharge electrode 111 to which a high voltage is applied by a high voltage power supply (not illustrated) and a grounded counter electrode 112 having a flat plate shape. The counter electrode 112 is disposed on both side surfaces of the discharge electrode 111 in parallel with maintaining the gap G (mm) and is installed in an electrode case 113.

The opening of the charging unit 110 is partitioned by a counter electrode 112 having a shape of a flat plate at every length (G × 2) which is twice the electrode gap G. As a result, the floating fine particles may be uniformly charged in the air flow. In some examples, the electrode gap G may be set within a range of approximately 2 to 15 mm. In a case where the electrode gap G is less than 2 mm, the influence of the thickness of the discharge electrode 111 and the counter electrode 112 may make it difficult to sufficiently secure the opening of the charging unit 110. an electrode gap exceeds 15 mm may operate to remove the effect of partitioning the opening of the charging unit 110 with the flat-plate-shaped counter electrode 112, and may be associated with the application of a high voltage. Additionally, the electrode gap may be associated with an increase in current conduction deterioration of the electrode. By adjusting the number of the counter electrodes 112 in order to set the electrode gap G within the above-mentioned range, the opening of the charging unit 110 may be partitioned in a manner which contributes to applying the charging to the floating fine particles.

In some examples, the discharge electrode has a plurality of "protrusions" for discharging at pitches P (mm), and the protrusion pitch P and the electrode gap G (mm) are set to satisfy a relationship of 0.5 ≤ P/G ≤ 1.5. In a case where the P/G value is less than approximately 0.5, the control range of the inter-electrode current conduction amount (energization amount) for maintaining floating fine particles collecting well becomes narrow. In addition, a P/G value which exceeds approximately 1.5 may be associated with a non-uniform charging to the floating fine particles, which may cause a decrease in collecting efficiency and the like.

A protrusion processed into a serrated shape or a needle shape may be used. FIG. 3 is an external diagram of the discharge electrode 111 having serrated protrusions, in which the discharge electrode 111 is formed by providing the serrated protrusions having a height h at pitches P in a flat-plate-shaped "base portion".

A predetermined voltage is applied to the base portion of the discharge electrode 111 from a high voltage power supply (not illustrated) to form a corona at the tip of the protrusion (hereinafter, referred to as "electrode tip"), and thus, the charging is applied to the floating fine particles in the air flow. The degree of applying the charging to the floating fine particles can be controlled by the amount of current conduction between the discharge electrode and the counter electrode (hereinafter, simply referred to as "inter-electrode current conduction amount").

When the charging is applied to the floating fine particles in the air flow, the electrode tip is depleted while being rounded, and an increase in resistance due to oxidation of the constituent material of the electrode tip and adhesion of chemical substances mixed in the air flow progresses. The progression of the "current conduction deterioration" may be associated with a larger applied voltage to maintain initial corona formation. In addition, the shape of the electrode tip may be related to the amount of generated ozone. For example, in the case of a serrated shaped discharge electrode, if the radius of tip curvature R of the electrode tip exceeds the half of the thickness of the electrode plate the amount of generated ozone doubles. Therefore, the shape of the electrode tip is set such that the radius of tip curvature R of the electrode does not exceed half of the thickness of the electrode plate even if the current conduction deterioration progresses. The shapes of the electrode tip and the entire protrusions may be designed accordingly.

The degree of the current conduction deterioration of the discharge electrode may be influenced by the inter-electrode current conduction amount, the current conduction time, the impurity amount in the constituent material of the electrode, the processing state, the frequency of attachment of chemical substances, and the like, and any combination thereof. Accordingly, the degree of the current conduction deterioration may be different for each electrode tip.

In some examples, the discharge electrode has a plurality of protrusions through the base portion on the flat plate. Accordingly, if there occurs a protrusion in which current conduction deterioration has progressed as compared with the surroundings, the amount of current conduction is decreased, so that a portion where corona formation is partially unstable occurs (refer to (a) and (b) of FIG. 4). Since the opening of the charging unit is partitioned by the flat-plate-shaped counter electrode, sufficient charging is not applied to the floating fine particles passing through the portion where protrusions in which current conduction deterioration has progressed exist, and as a result, the dust collecting efficiency is decreased. However, in some examples, since the water vapor is supplied from the water vapor generation unit 120 to the charging unit 110, not only the ozone generation can be suppressed, but also the progression of current conduction deterioration can be suppressed to prevent the dust collecting efficiency from being decreased.

The electric dust collecting device may be provided with the water vapor generation unit 120 for supplying the water vapor to the charging unit 110, and the water vapor may be supplied to the charging unit 110, in order to reduce the current conduction deterioration of the discharge electrode 111 while greatly suppressing the amount of ozone generated from the charging unit 110. When a high voltage having positive polarity is applied to the discharge electrode 111, the amount of generated ozone may be significantly reduced.

For a humidifying device 121 configured for use with the water vapor generation unit 120, a compact humidifier such as a steam type, an ultrasonic type, a vaporizing type (a heaterless type), a hybrid type or the like can be applied. In addition, in the case of installing in household electric appliances or office machines, a water vapor generation source existing in those devices can also be used. For example, in the case of installing in a printer using an electrophotographic method, moisture contained in a printing paper is evaporated by using a heating/fixing device in the printer, and water vapor is supplied to the charging unit. Accordingly, the electric dust collecting device may be operated without a dedicated water vapor generation source and for that matter without a water supply, which can contribute to miniaturization of the whole apparatus and improvement of usability.

In some examples, the supply rate of the water vapor supplied from the water vapor generation unit 120 to the charging unit 110 is set to approximately 0.20 to 0.50 mg/min per 1 cm² of the cross-sectional area of the ventilation passage passing through the electrode portion of the charging unit 110. In a case where the supply rate of water vapor is less than approximately 0.20 mg, the effect of supplying the water vapor may not be sufficient. In a case where the supply rate of water vapor exceeds approximately 0.50 mg/min, the dust collection unit 130 is over-humidified (occurrence of clogging or the like due to condensation), so that the collecting efficiency is decreased.

In some examples, the supply rate of water vapor may be defined as a value obtained by dividing an evaporation amount of water put into a humidifying device by an operation time of the humidifying device, and by further dividing the obtained value by a cross-sectional area of a ventilation passage passing through the electrode portion of the charging unit.

Most of the water vapor supplied to the charging unit 110 reaches the dust collection unit 130 together with the air flow. However, since an air filter medium made of a sheet-shaped or film-shaped polymer material subjected to electret treatment is used for the dust collection unit 130, the influence of the water vapor may be minimized and the collecting efficiency and air throughput may be maintained. In some examples, an air filter medium may be processed so that the contact angle of the polymer material subjected to electret treatment to water is approximately 75° or more, the filter medium thickness of the air filter medium is approximately 3 mm or more, and the pressure loss at a wind speed of 0.2 m/sec is approximately 60 Pa or less.

The electret treatment is a process of forming a structure that retains charging in a polymer material by solidifying a heated and melted polymer material or an intermediate structure of the polymer material while applying a high voltage to the heated and melted polymer material or the intermediate structure of the polymer material. Through the electret treatment, the polymer material can be formed to be in a semi-permanently charged state.

Even if the polymer sheet or polymer film subjected to electret treatment is humidified by the water vapor evaporated from the water vapor generation unit 120, the polymer sheet or polymer film can be restored to the charged state simply by drying under an air flow. In addition, in a case where the polymer material is immersed in an insoluble organic solvent such as isopropyl alcohol, only the structure for retaining the charges formed in the polymer material may be changed, and the electret treatment may be nullified.

The charged state of the polymer sheet or polymer film subjected to electret treatment may be checked by, for example, an electrostatic analyzer (FMX-004) manufactured by Simco-Ion, Kelvin probe force microscope (Dimension Edge) manufactured by Bruker, or the like.

Example materials for applying the electret treatment may include thermoplastic resins (acrylic resin, polyethylene resin, ABS resin, and the like) and thermosetting resins (polyester resin, epoxy resin, and the like) which may generally be associated with relatively low electrical conductivity. However, since the dust collection unit 130 is affected by the water vapor supplied to the charging unit 110, as a polymer material used for the air filter medium, in order not to reduce the effect of the electret treatment, the polymer material having a low affinity to water may be used, and in some examples, the polymer material is selected from polymer materials having a contact angle of approximately 75° or more with respect to water. In particular, a polymer material having a contact angle of approximately 80° or more with respect to water may be used because water particles can be quickly dried by ventilation even if the water particles adhere to the surface of the polymer material and the polymer material can return to the original state. As such a polymer material, polypropylene, polyethylene, polyvinylidene fluoride, a fluorinated resin, a silicone resin, and the like may be used alone or in combination. In addition, in order to increase a charge holding amount, voids may be provided in the polymer material and/or a charge control agent may be incorporated. The charge control agent may be selected from, for example, a negatively chargeable charge control agent such as metal compounds of carboxylic acids such as salicylic acid, naphthoic acid, and dicarboxylic acid; polymer type compounds having a sulfonic acid group or a carboxylic acid group in a side chain thereof; a boron compound; a urea compound; a silicon compound; and calixarene or a positively chargeable charge control agent such as a quaternary ammonium salt; a polymer type compound having the quaternary ammonium salt in a side chain thereof; a guanidine compound; an imidazole compound; and an azine compound; or any combination thereof.

The polymer material subjected to electret treatment is processed into a polymer sheet, a polymer film, or the like, and the resulting material is applied to the air filter medium. A filter medium thickness of the air filter medium of approximately 3 mm or more and a pressure loss at the wind speed of approximately 0.2 m/sec is 60 Pa or less may be used to achieve compatibility between the electrostatic collection using electret treatment and the moisture permeability. When the filter medium thickness of the air filter medium is less than approximately 3 mm, sufficient collecting efficiency may not be obtained, and in a case where the pressure loss exceeds approximately 60 Pa, moisture condensation and a decrease in wind speed may occur.

In a case where the polymer sheet subjected to electret treatment is used as the air filter medium, a polymer sheet may be laminated and processed into a structure including a tubular ventilation passage.

For example, a honeycomb structure, a corrugated structure, or the like as illustrated in FIG. 5 can be applied as a structure including a tubular ventilation passage. By using the structure including a tubular ventilation passage for the dust collection unit 130, the air flow in the electric dust collecting device is uniformly distributed and rectified by the structure including the tubular ventilation passage, to control the amount of charge applied to the floating fine particles in the charging unit 110. As a result, even if the discharge electrode is deteriorated in current conduction, the influence of the floating fine particles on the collecting efficiency may be minimized. In addition, as compared with a two-stage type electrostatic collecting apparatus in which a high voltage is applied to both the charging unit and the collection unit, the polymer sheet subjected to electret treatment may be used to electrostatically collect the floating fine particles in the air flow with a simplified configuration.

The structure including the tubular ventilation passage can be manufactured as a honeycomb structure, in which case adhesives may be applied and laminated in a linear shape to both sides of a polymer sheet subjected to electret treatment to form a block shape. A honeycomb structure can be obtained by cutting the block-shaped polymer sheet in a direction perpendicular to the application direction of the adhesive and expanding the resulting sheet in the vertical direction. At this time, an arbitrary opening diameter d can be obtained by changing the application width, the application interval, or a degree of expansion of the adhesive applied linearly. In addition, in the case of manufacturing a corrugated structure, the corrugated structure can be manufactured by using a corrugator. While shaping the polymer sheet subjected to electret treatment into a corrugated shape, the top portion thereof is adhered to a polymer sheet subjected to electret treatment, which is separately prepared, so that a single-faced cardboard shape is formed. The corrugated structure can be manufactured by laminating and bonding the single-faced cardboards, and after that, by cutting. At this time, when shaping the polymer sheet into a corrugated shape, an arbitrary opening diameter d may be obtained by adjusting the shape and molding conditions. casein some examples, instead of or in addition to the adhesive, welding can be used for bonding the polymer sheets. In addition, an electret treatment may be applied immediately before adhesion.

In the structure including the tubular ventilation passage, the opening of the tubular ventilation passage located on a plane perpendicular to the ventilation direction of the air filter medium may be approximately 60% by area or more, and the opening diameter d (mm) of the tubular ventilation passage and the ventilation passage length L (mm) (refer to FIG. 5) satisfies a relationship of approximately 0.025 ≤ d/L ≤ 0.2, to achieve a high level of compatibility between the air throughput and the collecting efficiency of floating fine particles. In some examples, the opening diameter d of the structure including the tubular ventilation passage is approximately 0.5 to 5 mm. In a case where the opening diameter d is less than approximately 0.5 mm, the pressure loss becomes large which may make it difficult to increase the air throughput. In addition, in a case where the opening diameter d exceeds approximately 5 mm, the amount of the floating fine particles in the air approaching the polymer sheet forming the tubular ventilation passage may be decreased, so that the collecting efficiency is decreased.

In some examples, the length L of the ventilation passage of the structure including the tubular ventilation passage is approximately 3 mm or more, and in other examples approximately 5 to 50 mm, to maintain the stable collecting efficiency. In a case where the length L is less than approximately 5 mm, the life cycle of the dust collection unit 130 may be shortened, and the replacement frequency is increased. In addition, in a case where the length L exceeds approximately 50 mm, the water vapor supplied by the humidifying device 121 is cooled, so that condensation may occur.

The length L of the ventilation passage of the structure including the tubular ventilation passage is set so as to satisfy the relationship of L > d with respect to the opening diameter d. In the case of L ≤ d, since the floating fine particles floating in the air are diffused into the tubular ventilation passage and are difficult to electrostatically adsorb, sufficient collecting efficiency cannot be obtained.

The thickness t (mm) of the polymer sheet comprising the ventilation passage of the structure including the tubular ventilation passage is approximately 0.1 to 1.5 mm. In a case where the polymer sheet thickness t is less than approximately 0.1 mm, the strength for configuring the tubular ventilation passage may be insufficient, and thus, it is difficult to apply the electret treatment. In addition, in a case where the polymer sheet thickness exceeds approximately 1.5 mm, the ratio of the opening portion of the tubular ventilation passage occupying on the wind receiving surface becomes small, so that the collecting capability is lowered.

In some examples, the polymer sheet thickness t and the opening diameter d forming the structure including the tubular ventilation passage can be determined by taking an enlarged photograph of a vertical cross section of the tubular ventilation passage (refer to FIG. 5). For example, by a method in which an enlarged photograph of a vertical cross section of a tubular ventilation passage is taken into a personal computer or the like and measurement is performed by using image measurement software (e.g. machine readable instructions). In other examples, by a method in which the enlarged photograph is printed out and then direct measurement is performed by using a measuring instrument, and the like, the sheet thickness t and the opening diameter d can be determined by averaging the thicknesses and the opening diameters of 20 points or more randomly extracted, respectively. The opening diameter d of the tubular ventilation passage may be defined as a diameter of a circle inscribed in the inner wall of the tubular ventilation passage.

In some examples, the opening diameter d is selected and combined so as to satisfy d/G = approximately 0.05 to 1 with respect to the gap G between the discharge electrode 111 and the flat plate-shaped counter electrode 112. In a case where d/G is less than approximately 0.05, the charge applying to the floating fine particles may be insufficient, so that the collecting ability is lowered. In addition, in a case where d/G exceeds approximately 1, the number of tubular ventilation passages with respect to the space partitioned by the flat-plate-shaped counter electrodes is decreased, so that the influence of current conduction deterioration of the discharge electrode 111 is likely to occur.

In a case where the structure including the tubular ventilation passage is applied to the dust collection unit 130 of the electric dust collecting device, the length L of the ventilation passage of the structure including the tubular ventilation passage is set so as to satisfy the relationship of L/(V × 1,000) ≥ 0.005 with respect to the ventilation speed V (m/sec) of the air introduced into the structure including the tubular ventilation passage, in order to secure sufficient air throughput. For example, in a case where the area of the wind receiving surface of the dust collection unit 130 is set to approximately 100 cm², about 750 L to 1 cubic meter per minute of air may be processed.

In addition, the ventilation speed V (m/sec) of the air introduced into the structure including the tubular ventilation passage is determined by the surface wind speed of the wind receiving surface. For example, the surface wind speed may be measured by a portable anemometer (Climomaster model 6501-00, probe; 6543-21, manufactured by KANOMAX JAPAN INCORPORATED), or the like.

In addition, in a case where the polymer film subjected to electret treatment is used as the air filter medium, a film split nonwoven fabric may be used. The film split nonwoven fabric may be obtained, for example, by forming the polymer film into a split fiber and, after that, processing the split fiber. By using a nonwoven fabric for the air filter medium, the floating fine particles may be efficiently collected while suppressing an increase in pressure loss due to water vapor supplied from the water vapor generation unit to be low. Additionally, use of a nonwoven fabric may also contribute to thinning of the dust collection unit.

As a film split nonwoven fabric as illustrated in FIG. 6(a), a web in which a portion of the film split fiber is disposed in a direction in which it is not difficult for the air to be introduced to pass is applied. By using such a film split nonwoven fabric for the dust collection unit 130, the influence of the water vapor supplied from the water vapor generation unit 120 may be minimized.

In some examples, a film split fiber may be manufactured by finely cutting a polymer film as a raw material with a fiber opening cutter or the like. Therefore, the film width (hereinafter, referred to as "fiber width w") is likely to be larger than the film thickness (hereinafter, referred to as "fiber thickness k"). In addition, in a case where electret treatment is applied to a polymer film, polarization occurs on the front and back of the film surface. Therefore, if such a film split fiber is laminated and formed into a web, the film surface of the fiber may be arranged parallel to the surface of the nonwoven fabric, and it becomes easy to hinder the passing of air (refer to FIG. 6(b)). Furthermore, since adjacent polarization surfaces tend to cancel electrostatic force therebetween, the water vapor supplied from the water vapor generation unit 120 may cause a reduction in the effect of electret treatment, or in some cases, condensation may occur.

However, in the film split nonwoven fabric used in an example air filter medium, the composition ratio and cross-sectional shape of the film split fiber forming the film split nonwoven fabric may be specified.

The film split nonwoven fabric may contain at least 50% by weight or more of a film split fiber obtained by processing a polymer film into a split form, and in some examples contains approximately 50 to 90% by weight. In a case where the composition ratio of film split fiber is less than approximately 50% by weight, the existing amount of the polymer film subjected to electret treatment is decreased, so that sufficient collecting efficiency may not be obtained. In addition to the issues of air permeability, a composition ratio of film split fiber that exceeds approximately 90% by weight may affect the ability to maintain strength and the like as the air filter medium.

In addition, a film split fiber which has a specific flat or rectangular shape may be used to efficiently collect the floating fine particles while suppressing the increase in pressure loss due to the water vapor supplied from the water vapor generation unit to a low level. In some examples, the fiber width w (㎛) and the fiber thickness k (㎛) of the film split fiber satisfy the relationship 2 ≤ w/k ≤ 5. In a case where w/k is less than approximately 2, the influence of the processing surface by the fiber opening cutter becomes large, so that the dust collecting efficiency may be lowered. In a case where w/k exceeds 5, the pressure loss is increased, which may affect the ability to secure air permeability.

In some examples, the cross-sectional shape of the film split fiber is flat or rectangular. In addition, the length of the major axis (hereinafter, referred to as "fiber width") of the film split fiber may be two to five times the length of the minor axis (hereinafter, referred to as "film thickness") of the polymer film and the composition ratio of the film split fiber occupying in the whole fibers of the film split nonwoven fabric is approximately 50 to 90%. In a case where the fiber width is less than twice the film thickness, the influence of the processing surface by the fiber opening cutter becomes large, so that the dust collecting efficiency may be lowered. In addition, in a case where the fiber width exceeds five times the film thickness, the pressure loss becomes large, which may affect the ability to secure the air permeability.

In order to reduce the pressure loss, aggregates or spacers may additionally be used for the film split nonwoven fabric within a range where the composition ratio of film split fibers satisfies approximately 50 to 90%. In a case where the composition ratio of film split fiber is less than approximately 50%, the existing amount of the polymer film subjected to electret treatment is decreased, so that sufficient collecting efficiency may not be obtained. In addition, a composition ratio of film split fiber that exceeds approximately 90% may affect the ability to maintain the strength and the like as the air filter medium.

In some examples, the film split fiber has a fiber thickness k of approximately 3 to 15 ㎛. By mixing one or more types of polymer fibers selected from nylon, rayon, and acetate within a range not exceeding 10% by weight, the film thickness of the film split fiber is set to approximately 3 to 15 ㎛. Furthermore, by mixing one or more types of polymer fibers selected from nylon, rayon, acetate into the above-mentioned film split fiber, the film split fiber can be used for holding the electret while fulfilling the role of aggregates and spacers. In some examples, the nonwoven fabric is made of a plurality of polymer fibers having different charging sequences, in order to compensate for the loss of the electret effect by rubbing at the time of ventilation.

In some example, the main portion 100 of the electric dust collecting device can be used not only by being installed in the air flow but also can be connected to the air flow generation unit 140 so that the amount of air introduced into the main portion 100 is increased or decreased (refer to FIG. 1(b)). For example, in a case where the main portion 100 is installed inside a household appliance or an office machine, the floating fine particles in the air discharged to the outside of the machine can be removed by an electric dust collection unit. In addition, in a case where an axial flow blower having a propeller fan as the air flow generation unit 140 is connected to the main portion 100, a stand-alone indoor electric dust collecting device can be implemented.

At this time, the ventilation direction is the direction of the arrow in the figure, the air containing the floating fine particles is introduced into the main portion 100 by suction with the air flow generation unit 140, and after the dust collection, the air is exhausted. Unlike the swirling flow generated on the discharge side of the blower, the air flow generated on the suction side of the blower is relatively uniform in order to remove the floating fine particles in the air flow. As a result, the swirling flow caused by the propeller fan is made uniform, so that the floating fine particles in the air flow passing through the charging unit 110 can be uniformly subjected to the ion application.

The air flow generation unit 140 may comprise an axial flow blower having a propeller fan, a centrifugal blower having a multi-blade fan and a turbo fan, a diagonal flow blower having a diagonal flow fan, a transverse flow blower having a cross flow fan, or the like, or any combination thereof. When the ventilation direction is the direction of the arrow in the figure, the air containing the floating fine particles can be introduced into the main portion 100 by suction with a blower.

Hereinafter, additional examples and comparative examples are provided by way of providing further illustration.

Example 1

The stand-alone electric dust collecting device illustrated in FIG. 1(b) was used to evaluate the collecting efficiency of floating fine particles in the air and the emission rate of ozone.

In the charging unit 110, a flat-plate-shaped counter electrode was disposed in parallel on both side surfaces of the serrated discharge electrode. By setting the size of the opening of the charging unit 110 to 80 mm in length and 80 mm in width and setting the gap G between the discharge electrode and the counter electrode to 5.0 mm, the opening was divided into eleven counter electrodes (and ten discharge electrodes). The discharge electrode was obtained by etching a flat plate (SUS 304) having a thickness of 0.3 mm. The pitch P of the serrated protrusions was set to 5.0 mm (P/G = 1.0), and the radius of tip curvature R of the electrode tip was set to 50 ㎛.

A corrugated structure obtained by laminating a polypropylene sheet (sheet thickness t = 0.1 mm, contact angle 94°) subjected to electret treatment was used for the dust collection unit 130. The opening diameter d of the tubular ventilation passage of the corrugated structure was set to 0.9 mm, the ventilation passage length L (filter medium thickness) was set to 20 mm (d/L = 0.045, opening ratio = 70%, pressure loss = 3 Pa), and the area of the wind receiving surface was set to 64 cm² (same as the opening of the charging unit 110).

A DC axial flow blower (80 mm × 80 mm × 15 mm) provided with a propeller fan was used as the air flow generation unit 140, and the passing wind speed of the air being introduced into the structure including a tubular ventilation passage is set to 0.5 m/sec (L/(V × 1,000) = 0.04). The air throughput at this time was 192 L/min.

When the electric dust collecting device was in operation, a positive polarity voltage was applied to the discharge electrode, and the inter-electrode current conduction amount was set to 90 ㎂. In addition, a compact ultrasonic humidifier was used for the water vapor generation unit 120, and the supply rate of the water vapor supplied from the water vapor generation unit 120 to the charging unit 110 was adjusted so as to be 0.35 mg/min per cross-sectional area 1 cm² of the ventilation passage (same as the opening) passing through the electrode portion of the charging unit 110.

The collecting efficiency of floating fine particles in the air and the emission rate of ozone were evaluated with favorable results, including a collecting efficiency of floating fine particles in the air of 99% by number, and an emission rate of ozone of less than 1.0 mg/hour.

Furthermore, in order to carry out the influence test of current conduction deterioration of the discharge electrode, the current conduction deterioration of the discharge electrode was accelerated with the inter-electrode current conduction amount of 180 ㎂. After the current conduction deterioration of the discharge electrode, the collecting efficiency of floating fine particles in the air and the emission rate of ozone were evaluated in the same manner as described above. The evaluation again indicated favorable results, including a collecting efficiency of floating fine particles in the air of 98% by number, and an emission rate of ozone of 1.0 mg/hour.

Additional details of the above results are summarized in the table of FIG. 7. The example method of measuring the collecting efficiency of floating fine particles in the air and the emission rate of ozone, the evaluation criteria of measurement results, and the example method for the influence test of current conduction deterioration of the discharge electrode are provided below.

1. Evaluation of Collecting Efficiency of Floating Fine Particles

The collecting efficiency of floating fine particles in the air collected by the electric dust collecting device is determined by measuring the number concentration of the atmospheric dust in the air suctioned into the electric dust collecting device and number concentration of the atmospheric dust in the air exhausted from the electric dust collecting device for 3 minutes each and calculating the rate of reduction of atmospheric dust. The calculated collecting efficiency of floating fine particles was evaluated according to the following criteria. For measurement of the number concentration of atmospheric dust in the air, a compact UFP measuring instrument (NANOSCAN SMPS NANOPARTICLE SIZER Model 3910, manufactured by TSI Incorporated) was used.

A: 98% by number or more (very favorable)

B: 95% by number or more, and less than 98% by number (favorable)

C: 80% by number or more, and less than 95% by number (acceptable level)

D: less than 80% by number (unacceptable level)

2. Evaluation of Emission Rate of Ozone

The emission amount of ozone emitted to the outside of the electric dust collecting device was obtained by measuring the change in concentration of generated ozone emitted by the electric dust collecting device installed in the clean booth at the time of operation and calculating the emission rate of ozone. The calculated emission rate of ozone was evaluated according to the following criteria. For the measurement of the concentration of ozone emitted at the time of operation, an ultraviolet absorption type ozone densitometer for low concentration (Model 1100, manufactured by Dylec Inc.) was used.

A: less than 1.0 mg/hour (very favorable)

B: 1.0 mg/hour or more, and less than 2.0 mg/hour (favorable)

C: 2.0 mg/hour or more, and less than 3.0 mg/hour (acceptable level)

D: 3.0 mg/hour or more (unacceptable level)

3. Influence Test of Current Conduction Deterioration of Discharge Electrode

After the current conduction deterioration of the discharge electrode was accelerated by carrying out current conduction for a cumulative time of 700 hours with 1.5 times the inter-electrode current conduction amount of the time of normal use, the measurement and evaluation disclosed in the above 1. Evaluation of Collecting Efficiency of Floating Fine Particles, and 2. Evaluation of Emission Rate of Ozone, were carried out.

Example 2

The discharge electrode of the charging unit 110 was exchanged, and the radius of curvature of the electrode tip was changed to 75 ㎛. In addition, a film split nonwoven fabric (filter medium thickness = 3.0 mm, composition ratio of film split fiber = 70% by mass, pressure loss = 20 Pa) obtained by processing a film split fiber (fiber width w = 43 ㎛, w/k = 4.3) formed from a polypropylene film (film thickness (fiber thickness k) = 10 ㎛, contact angle 94°) subjected to electret treatment was used as an air filter medium of the dust collection unit 130. The same settings were made as in Example 1 except that, since the filter medium thickness of the air filter medium used for the dust collection unit 130 became thinner than that of Example 1, the inter-electrode current conduction amount was readjusted to 120 ㎂. And then, the emission test was carried out.

As a result, although the inter-electrode current conduction amount was increased, since the water vapor was supplied to the charging unit 110, it was possible to greatly reduce the emission amount of floating fine particles without increasing the emission amount of ozone. In addition, as a result of carrying out the influence test of current conduction deterioration of the discharge electrode, since the radius of curvature of the electrode tip was made larger than that in Example 1, even if the inter-electrode current conduction amount was increased, the floating fine particles can be stably collected. However, a slight increase in the emission amount of ozone was seen.

Example 3

The discharge electrode of the charging unit 110 was exchanged, and the pitch P of the serrated protrusion was changed to 3.5 mm (P/G = 0.7). In addition, a film split nonwoven fabric (filter medium thickness = 3.0 mm, composition ratio of film split fiber = 53 % by mass, pressure loss = 15 Pa) obtained by processing a film split fiber (fiber width w = 35 ㎛, w/k = 2.3) formed from a polyethylene film (film thickness (fiber thickness k) = 15 ㎛, contact angle 101°) subjected to electret treatment was used as an air filter medium of the dust collection unit 130. In addition, the same settings were made as in Example 2 except that the supply rate of water vapor to be supplied to the charging unit 110 was readjusted to 0.22 mg/min. And then, the emission test was carried out.

As a result, as compared with Example 2, as the supply rate of water vapor supplied to the charging unit 110 became lower, the emission amount of ozone was increased. In addition, the influence test of current conduction deterioration of the discharge electrode was carried out. As a result, the collecting efficiency of floating fine particles was decreased, and the emission amount of ozone was further increased. However, the pitch P of the protrusion of the charging unit 110 was adjusted to 3.0 mm, so that it was possible to achieve compatibility between the collecting efficiency of floating fine particles and the emission amount of ozone at an acceptable level.

Example 4

The same settings were made as in Example 3 except that a film split nonwoven fabric (filter medium thickness = 4.0 mm, composition ratio of film split fiber = 80 % by mass, pressure loss = 55 Pa) obtained by processing a film split fiber (fiber width w = 60 mm, w/k = 5.0) formed from a polyethylene terephthalate film (film thickness (fiber thickness k) = 12 ㎛, contact angle = 79°) subjected to electret treatment was used as the air filter medium of the dust collection unit 130. And then, the emission test was carried out.

As a result, the collecting efficiency of floating fine particles was slightly reduced by the increased affinity of the air filter medium to water as compared with Example 3. However, the result of the influence test of current conduction deterioration of the discharge electrode was included, and it was possible to achieve compatibility between the collecting efficiency of floating fine particles and the emission amount of ozone at an acceptable level.

Example 5

The discharge electrode of the charging unit 110 was exchanged, and the pitch P of the serrated protrusion was changed to 7.0 mm (P/G = 1.4). In addition, the same settings were made as in Example 3 except that the supply rate of water vapor to be supplied to the charging unit 110 was readjusted to 0.47 mg/min.

As a result, as compared with Example 3, as the P/G became large and the supply rate of water vapor supplied to the charging unit 110 became higher, the emission amount of ozone is decreased. The air filter medium having a low affinity to water was used, so that it was possible to slightly suppress a decrease in the collecting efficiency of floating fine particles. In addition, even in the influence test of the current conduction degradation of the discharge electrode, it was possible to achieve compatibility between the collecting efficiency of floating fine particles and the emission amount of ozone at an acceptable level.

Example 6

The same settings were made as in Example 5 except that the film split nonwoven fabric used in Example 4 was used as the air filter medium of the dust collection unit 130. And then, the emission test was carried out.

As a result, as compared with Example 4, as the P/G became large and the supply rate of the water vapor supplied to the charging unit 110 was increased, the collecting efficiency of floating fine particles was decreased. However, it was possible to greatly suppress the emission amount of ozone.

Subsequently, the influence test of current conduction deterioration of the discharge electrode was carried out. As a result, the collecting efficiency of floating fine particles was further decreased. However, by changing the inter-electrode current conduction amount to 150 ㎂, the collecting efficiency of floating fine particles was improved up to an acceptable level, and thus, it was possible to minimize the performance difference before and after the influence test of current conduction deterioration of the discharge electrode.

Example 7

The discharge electrode of the charging unit 110 was exchanged, and the pitch P of the serrated protrusion was changed to 2.5 mm (P/G = 0.5). In addition, the same settings were made as in Example 1 except that a corrugated structure (opening diameter d of a tubular ventilation passage = 0.5 mm, ventilation passage length L (filter medium thickness) = 5.0 mm, d/L = 0.10, opening ratio = 75%, pressure loss = 7 Pa) obtained by laminating a polyethylene terephthalate sheet (sheet thickness t = 0.1 mm, contact angle 79°) subjected to electret treatment was used as the air filter medium of the dust collection unit 130. And then, the emission test was carried out.

As a result, as compared with Example 1, as the affinity of the air filter medium to water was increased and the ventilation passage length L is shortened, the P/G and the opening diameter d were set to be decreased so that it was possible to slightly suppress a decrease of the collecting efficiency of the floating fine particles. In addition, the influence test of current conduction deterioration of the discharge electrode was carried out. As a result, it was possible to achieve compatibility between the collecting efficiency of floating fine particles and the emission amount of ozone at an acceptable level. Furthermore, although the inter-electrode current conduction amount was changed to 150 ㎂, improvement of the collecting efficiency of floating fine particles was not seen by merely increasing the emission amount of ozone.

Example 8

The discharge electrode of the charging unit 110 was exchanged, and the radius of tip curvature R of the electrode tip of the serrated protrusion was changed to 125 ㎛. In addition, the same settings were made as in Example 1 except that a corrugated structure (opening diameter d of a tubular ventilation passage = 1.2 mm, ventilation passage length L (filter medium thickness) = 45 mm, d/L = 0.027, opening ratio = 62%, a pressure loss = 2 Pa) obtained by laminating and processing a polypropylene sheet (sheet thickness t = 0.2 mm, contact angle 94°) subjected to electret treatment was used as the air filter medium of the dust collection unit 130. And then, the emission test was carried out.

As a result, as compared with Example 1, the opening diameter d of the air filter medium became larger and the sheet thickness t became thicker, so the opening ratio became lower. However, by increasing the ventilation passage length L, it was possible to slightly suppress a decrease in the collecting efficiency of floating fine particles. In addition, although the emission amount of ozone was increased due to the increase in the radius of tip curvature R of the electrode tip, it was possible to minimize the emission amount of ozone by supplying the water vapor to the charging unit 110.

In addition, the influence test of the current conduction deterioration of the discharge electrode was carried out. As a result, it was possible to achieve compatibility between the collecting efficiency of floating fine particles and the emission amount of ozone at an acceptable level, and the radius of tip curvature R of the electrode tip was increased, so that it was possible to minimize the performance difference before and after the influence test of the current conduction deterioration of the discharge electrode.

Example 9

The discharge electrode of the charging unit 110 was exchanged, the pitch P of the serrated protrusion was changed to 7.0 mm (P/G = 1.4), and the radius of tip curvature R of the electrode tip was changed to 75 ㎛. In addition, the same settings were made as in Example 1 except that a honeycomb structure (opening diameter d of a tubular ventilation passage = 5 mm, ventilation passage length L (filter medium thickness) = 25 mm, d/L = 0.20, opening ratio = 79%, pressure loss = 1 Pa) obtained by laminating and processing a polyethylene sheet (sheet thickness t = 1.5 mm, contact angle = 101°) subjected to electret treatment was used as the air filter medium of the dust collection unit 130, and inter-electrode current conduction amount was readjusted to 120 ㎂. And then, the emission test was carried out.

As a result, as compared with Example 1, the radius of curvature R of the electrode tip was increased, and the inter-electrode current conduction amount was also increased. However, since water vapor was supplied to the charging unit 110, the emission amount of ozone was slightly increased. On the other hand, the P/G and the opening diameter d of the air filter medium became large. However, by lowering the affinity of the air filter medium to water and increasing the inter-electrode current conduction amount, it was possible to maintain a decrease of the collecting efficiency of floating fine particles to an acceptable level.

Subsequently, the influence test of current conduction deterioration of the discharge electrode was carried out. As a result, the emission amount of ozone was increased. However, it was possible to achieve compatibility between the collecting efficiency of floating fine particles and the emission amount of ozone at an acceptable level, it was possible to minimize performance difference before and after the influence test of current conduction deterioration of discharge electrode.

Example 10

The discharge electrode of the charging unit 110 was exchanged, the pitch P of the serrated protrusions was 3.5 mm (P/G = 0.7), and the radius of tip curvature R of the electrode tip was changed to 10 ㎛. In addition, a meltblown nonwoven fabric (filter medium thickness = 2.0 mm, contact angle = 94°, pressure loss = 60 Pa) obtained by processing, as a main material, a polypropylene fiber subjected to electret treatment was used as the air filter medium of the dust collection unit 130. In addition, the same settings were made as in Example 1 except that the inter-electrode current conduction amount was readjusted to 120 ㎂. And then, the emission test was carried out.

As a result, since the air filter medium was changed to a meltblown nonwoven fabric, the collecting efficiency of floating fine particles was lowered. However, by using the polypropylene fiber subjected to electret treatment, it was possible to maintain the collecting efficiency of floating fine particles to an acceptable level.

Subsequently, the influence test of current conduction deterioration of the discharge electrode was carried out. As a result, since the discharge electrode having a small radius of tip curvature R of the electrode tip was used, the collecting efficiency of floating fine particles was decreased due to the current conduction deterioration, so that the inter-electrode current conduction amount was changed to 150 ㎂. As a result, although the emission amount of ozone was greatly increased, it was possible to achieve compatibility between the collecting efficiency of floating fine particles and the emission amount of ozone at an acceptable level.

The evaluation results of Examples 2 to 10 are summarized in the table of FIG. 7.

Comparative Example 1

The same settings were made as in Example 10 except that the discharge electrode of the charging unit 110 was exchanged, the pitch P of the serrated protrusions was changed to 5.0 mm (P/G = 1.0), and the supply of water vapor to the charging unit 110 was stopped. And then, the emission test was carried out. As a result, since the emission amount of ozone cannot be suppressed to an acceptable level, the emission test was restarted by readjusting the supply rate of water vapor to 0.18 mg/min.

As a result, it was possible to achieve compatibility between the collecting efficiency of floating fine particles and the emission amount of ozone at an acceptable level.

Subsequently, the influence test of current conduction deterioration of the discharge electrode was carried out. As a result, because the collecting efficiency of floating fine particles was lowered, similarly to Example 10, by changing the inter-electrode current conduction amount to 150 ㎂, the collecting efficiency of the floating fine particles was improved. However, since the supply rate of water vapor supplied to the charging unit 110 was not sufficient, it was impossible to improve the emission amount of ozone to an acceptable level.

Comparative Example 2

The discharge electrode of the charging unit 110 was exchanged, and the radius of curvature of the electrode tip of the serrated protrusion was changed to 150 ㎛. In addition, the same settings were made as in Comparative Example 1 except that the supply rate of water vapor to be supplied to the charging unit 110 was readjusted to 0.55 mg/min. And then, the emission test was carried out.

As a result, it was possible to achieve compatibility between the collecting efficiency of floating fine particles and the emission amount of ozone at an acceptable level. However, during the influence test of current conduction deterioration of the discharge electrode which was carried out afterwards, condensation occurred on the air filter medium, so the test was stopped.

Comparative Example 3

The same settings were made as in Comparative Example 1 except that a high performance air filter (quasi-HEPA filter, pressure loss = 200 Pa, filter medium thickness = 2.5 mm) mainly configured with glass fiber was used as the air filter medium of the dust collection unit 130. And then, the emission test was carried out.

As a result, the air throughput was greatly reduced, and condensation occurred on the air filter medium, so that the test was stopped.

Comparative Example 4

The same settings were made as in Example 5 except that the discharge electrode of the charging unit 110 was exchanged, the pitch P of the serrated protrusions was changed to 5.0 mm (P/G = 1.0), and a film split nonwoven fabric (filter medium thickness = 4.0 mm, composition ratio of film split fiber = 40% by mass, pressure loss = 12 Pa) obtained by processing a film split fiber (fiber width w = 60 ㎛, w/k = 5.0) formed from a polyethylene terephthalate film (film thickness (fiber thickness k) = 12 ㎛, contact angle = 79°) not subjected to electret treatment was used as the air filter medium of the dust collection unit 130. And then, the emission test was carried out.

As a result, the collecting efficiency of floating fine particles did not reach an acceptable level. In addition, the influence test of current conduction deterioration of the discharge electrode was stopped.

Comparative Example 5

The same settings were made as in Comparative Example 4 except that a corrugated structure (opening diameter d of a tubular ventilation passage = 0.5 mm, ventilation passage length L (filter medium thickness) = 5.0 mm, d/L = 0.10, opening ratio = 75%, pressure loss = 7 Pa) obtained by laminating a polyethylene terephthalate sheet (sheet thickness t = 0.1 mm, contact angle 79°) not subjected to electret treatment was used as the air filter medium of the dust collection unit 130. And then, the emission test was carried out.

The evaluation results of Comparative Examples 1 to 5 are summarized in the table of FIG. 7.

It is to be understood that not all aspects, advantages and features described herein may necessarily be achieved by, or included in, any one particular example. Indeed, having described and illustrated various examples herein, it should be apparent that other examples may be modified in arrangement and detail

List of Reference Numbers

110: charging unit, 111: discharge electrode, 112: counter electrode, 120: water vapor generation unit, 130: dust collection unit, 140: air flow generation unit, G: gap between discharge electrode and counter electrode, L: length of tubular ventilation passage, P: pitch of protrusions in discharge electrode, d: opening diameter of tubular ventilation passage.

Claims

A particle collecting device comprising:

a charging apparatus to charge airborne floating fine particles;

a water vapor generator to apply water vapor to the charging apparatus; and

a particle collector disposed on a downstream side in a ventilation direction of the charging apparatus, the particle collector to collect the floating fine particles charged by the charging apparatus,

wherein a supply rate of the water vapor supplied from the water vapor generator to the charging apparatus is approximately 0.20 to 0.50 mg/min per 1 cm² of a cross-sectional area of a ventilation passage passing through an electrode portion of the charging apparatus.
The particle collecting device according to claim 1,

wherein the charging apparatus includes:

a discharge electrode to be supplied with a high voltage by a high voltage power supply; and

a counter electrode to be grounded and having a shape of a flat plate,

wherein the discharge electrode has a plurality of protrusions to discharge at a pitch P,

wherein the counter electrode is disposed in parallel with the discharge electrode while maintaining a gap G on two side surfaces of the discharge electrode, and

wherein the pitch P of the protrusions and the gap G between the discharge electrode and the counter electrode satisfy a relationship of 0.5 ≤ P/G ≤ 1.5.
The particle collecting device according to claim 1,

wherein the particle collector includes an air filter medium made of a sheet-shaped or film-shaped polymer material to be subjected to electret treatment,

wherein a contact angle of the polymer material with respect to water is approximately 75° or more, and

wherein a thickness of the air filter medium is approximately 3 mm or more, and a pressure loss at a wind speed of 0.2 m/sec is approximately 60 Pa or less.
The particle collecting device according to claim 3,

wherein the air filter medium includes a tubular ventilation passage formed by laminating polymer sheets,

wherein an opening of the tubular ventilation passage located on a plane perpendicular to a ventilation direction of the air filter medium is approximately 60% by area or more, and

wherein an opening diameter d of the tubular ventilation passage and a ventilation passage length L satisfy a relationship of 0.025 ≤ d/L ≤ 0.2.
The particle collecting device according to claim 3,

wherein the air filter medium comprises a nonwoven fabric containing approximately 50% by mass or more of a film split fiber obtained by processing a polymer film into a split shape, and

wherein a fiber width w and a fiber thickness k of the film split fiber satisfies a relationship of 2 ≤ w/k ≤ 5.
A system comprising:

a charging apparatus to charge airborne particles, the charging apparatus including an electrode portion and a ventilation passage passing through the electrode portion;

a vapor generator to supply vapor to the charging apparatus, wherein a supply rate of the vapor supplied by the vapor generator is approximately 0.20 to 0.50 mg/min per 1 cm² of a cross-sectional area of the ventilation passage; and

a collecting apparatus to collect the airborne particles charged by the charging apparatus.
The system according to claim 6, wherein the collecting apparatus is located downstream from the charging apparatus in a ventilation direction of the charging apparatus.
The system according to claim 6, wherein the vapor comprises water vapor.
The system according to claim 6,

wherein the charging apparatus includes:

a discharge electrode to receive a voltage supply; and

a counter electrode,

wherein the discharge electrode has a plurality of protrusions to discharge at a pitch P,

wherein the counter electrode forms a gap G on two side surfaces of the discharge electrode, and

wherein the pitch P of the protrusions and the gap G between the discharge electrode and the counter electrode satisfy a relationship of 0.5 ≤ P/G ≤ 1.5.
The system according to claim 9, wherein the counter electrode is grounded and comprises a plurality of flat plates disposed parallel to the discharge electrode.
The system according to claim 6,

wherein the collecting apparatus includes an air filter to undergo an electret treatment,

wherein a contact angle of the air filter with respect to water is approximately 75° or more, and

wherein a thickness of the air filter is approximately 3 mm or more, and a pressure loss at a wind speed of 0.2 m/sec is approximately 60 Pa or less.
The system according to claim 11,

wherein the air filter is made of a sheet-shaped or film-shaped polymer material subjected to the electret treatment.
The system according to claim 11,

wherein the air filter includes a tubular ventilation passage formed by laminating polymer sheets, and

wherein an opening of the tubular ventilation passage is located on a plane perpendicular to a ventilation direction of the air filter.
The system according to claim 13,

wherein the air filter is approximately 60% by area or more, and

wherein an opening diameter d of the tubular ventilation passage and a length L of the ventilation passage satisfy a relationship of 0.025 ≤ d/L ≤ 0.2.
The system according to claim 11,

wherein the air filter comprises a nonwoven fabric containing approximately 50% by mass or more of a film split fiber obtained by processing a polymer film into a split shape, and

wherein a fiber width w and a fiber thickness k of the film split fiber satisfies a relationship of 2 ≤ w/k ≤ 5.