Plasma surface sanitizer and method therefor

Abstract

To provide a process for generating plasma on a surface to be sanitized or directly on the surface and a plasma rail device for this purpose.SOLUTION: A plasma rail device is a novel method and device for generating plasma in the immediate vicinity of a surface or slightly above the surface for surface treatment, specifically surface disinfection. The device generally includes a pair of electrodes held together by a frame. A feature of the device is a fan for holding and positioning the electrode in close proximity to the surface during treatment. By generating electrical discharge in a space surrounded by the electrode and generating plasma on and above the surface to be treated, the device can be placed outside an object during treatment.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to the application of cold plasma for surface treatment and sterilization, and more particularly to a plasma device for surface sterilization, and further to a method for generating a controllable and uniform plasma directly on a treatment surface to produce desired surface properties, including sterilization. [Background technology]

[0002] Cross-contamination and cross-infection can occur through the air or through commonly touched surfaces, which can harbor bacteria. For example, some bacterial species, such as methicillin-resistant Staphylococcus aureus (MRSA), can survive on dry surfaces for more than four to five months, and viruses, such as norovirus, can survive for up to a week.

[0003] In recent years, plasma technology has proven to be very effective for air disinfection (see, for example, patent US8361402 B2, Apparatus for Air Purification and Disinfection, Tsui). Plasma, called the fourth substance, is a partially ionized gas consisting of freely moving ions, electrons, and neutral particles. Plasma is electrically neutral overall, but electrically conductive. This property allows the injection of electrical energy into the space it occupies. Depending on the operating conditions, plasma can consist of charged particles (electrons and ions), excited species, free radicals, ozone, and ultraviolet photons, which can decompose chemical compounds or destroy microorganisms. The energy of the electrons can be utilized to excite atoms and molecules, which then undergo chemical reactions and / or emit radiation. These emissions, especially in the ultraviolet spectral range, can initiate photophysical and photochemical processes by breaking molecular bonds. High-energy electrons break some chemical bonds in molecules, collide with background molecules to break molecular chains, cause ionization and excitation, and generate free atoms and radicals such as O, OH, or HO2. Radicals can attack harmful organic molecules and help break down airborne pollutants. Dissociation of O2 gives the O needed to combine with O2 to produce ozone. Low-energy electrons can also attach to neutral atoms or molecules to form negative ions, which can accelerate reactions in the breakdown of pollutants and the destruction of microorganisms. In addition, to be effective, a delivery mechanism is usually required to deliver the charged particles and active species to the surface to be treated.

[0004] Plasma can be created by electrical means by creating a gaseous discharge, whereby a high voltage is applied to a set of electrodes, the anode and the cathode. When the applied voltage is high enough and exceeds the breakdown voltage, arcing begins to occur between the anode and the cathode electrodes. With long-term use, this can cause problems with electrode degradation and overheating.

[0005] Several approaches to disinfect surfaces using plasma have been proposed, some of which involve the delivery of charged particles and other active species from a plasma generating device to the treatment surface. For example:

[0006] · Patent application publication US 20040005261 A1 (Plasma Sterilization Apparatus, Ko) describes sterilizing items in a vacuum chamber by drawing in plasma and active species generated in a separate chamber.

[0007] Patent US 7633231 B2 (Harmonic Cold Plasma Device And Associated Methods, Watson) describes the use of a plasma gun device with helium gas injection and a magnetic system to deliver plasma and active species to the surface to be treated.

[0008] Patent US9236227 B2 (Cold Plasma Treatment Devices and Associated Methods, Watson et al.) describes the use of a plasma gun device to deliver highly charged ions and reactive species to be inhaled by the patient.

[0009] Patent US 9623132 B2 (Plasma-generated Gas Sterilization Method, Krohmann et al.) describes the generation of plasma from air to produce reactive nitrogen and oxygen species, which are contacted with water to form a mixture that is then directed at the object to be sterilized.

[0010] Patent EP 2052097 B1 (Plasma Surface Treatment Using Dielectric Barrier Discharges, Boulos et al.) describes a surface coating treatment using a plasma torch, which supplies the coating material to the plasma torch.

[0011] In another known approach, the treatment object is placed close to where the plasma generating electrodes are placed. Typically, the electrodes are arranged in a sandwich or woven configuration, as illustrated in the following documents:

[0012] · Published patent application US 20120039747 A1 (Treating Device for Treating a Body Part of a Patient with a Non-thermal Plasma, Morfill et al) discloses a plasma generating electrode configuration with a dielectric insulator sandwiched between two electrodes, one in the form of a plate and the other in the form of a wire mesh. A surface discharge is generated at the surface of the dielectric insulator in the gaps of the wire mesh. A similar sandwich electrode configuration is also disclosed in published patent application US 20180206321 A1 (Electrode Assembly and Plasma Source for Generating a Non-Thermal Plasma, and Method for Operating a Plasma Source, Morfill et al), where the outermost electrodes (top and bottom) are covered with additional dielectric insulators to form a five-layer structure.

[0013] Also, published patent application US 20120039747 A1 discloses another configuration in which one set of electrodes is insulated and another set is bare or insulated. This configuration is also disclosed in patent US 7037468 B2 (Decontamination of Fluids or Objects contaminated with Chemical or Biological Agents Using a Distributed Plasma Reactor, Hammerstrom et al) and published patent application US 2005 / 0249646 A1 (Gas Treatment Apparatus, Iwama et al). In this configuration, plasma-generating discharges occur at the intersections of the crossed electrodes.

[0014] Yet another known approach places the object to be treated between a high voltage electrode and a ground electrode, as shown in the following example.

[0015] Patent US9295280 B2 (Method and Apparatus for Cold Plasma Food Contact Surface Sanitation, Jacofsky et al.) describes the use of plasma for surface sanitation, where the treated surface acts as a ground electrode or a ground rod assembly is placed under the treated surface (i.e. the treated surface is sandwiched between a high voltage electrode and a ground electrode).

[0016] These prior approaches require additional mechanisms for delivering charged particles and other active species to the surface being treated, either by sandwiching the object being treated between a high voltage electrode and a grounded electrode, or by confining the plasma generating discharge to the intersection of a dielectric surface and an electrode pair. It would therefore be desirable to develop a method and device that can simply generate plasma directly on or on the surface being disinfected, without requiring special delivery and configurational arrangements, and without entangling the surface being treated with the device. Summary of the Invention

[0017] In view of the above-mentioned shortcomings existing in the prior art, and based on the above-mentioned principles, the method and device of the present invention provide a process for generating plasma directly on or above the surface to be disinfected. This objective is achieved by using a plasma trail device.

[0018] The plasma rail device of the present invention embodies a novel method and device designed to generate plasma in the immediate vicinity or slightly above a surface for surface treatment, specifically sterilization of the surface. The device generally includes a pair of high voltage and ground electrodes arranged in alternating polarity, i.e., alternating high voltage and ground electrodes, and is powered by an AC power source. The high voltage electrode is covered with an insulating dielectric. The ground electrode can be bare or covered with an insulating dielectric. The pair of electrodes is powered by an AC power source with the high voltage electrode connected to the high voltage end of the power source and the ground electrode connected to the low voltage end of the power source. An electrical discharge is generated in the space between the pair of electrodes and on the surface of the object to be treated.

[0019] In a first preferred embodiment, a system for surface treatment and disinfection is provided, comprising: (a) at least one pair of electrodes, a high voltage electrode and a ground electrode, where the high voltage electrode is covered with a dielectric material providing electrical insulation and the ground electrode is bare or covered with a dielectric material; (b) a frame for holding and positioning the electrodes at a predetermined, preferably adjustable, distance towards the surface to be treated; (c) a power source for supplying a high voltage alternating current to the electrodes; The electrodes thereby generate a plasma in the space between the electrodes and on the surface of the object being treated.

[0020] The power supply may be adjustable to adjust the amplitude, waveform period, and shape of the voltage applied to the electrodes to maximize plasma activity and minimize the production of unwanted by-product gases. The electrode insulator may be in the form of a dielectric tube made of glass or plate.

[0021] The electrode conductors may be made from conductive sheets, meshes, or deposits.

[0022] The voltage supplied may range from 10 kilovolts to 50 kilovolts.

[0023] The waveform period is 10 -1ms~10 2 It may be in the range of ms.

[0024] The distance between the pair of electrodes is preferably within a range of 1 mm to about 20 mm. The distance between the electrodes and the surface to be treated is preferably within a range of 0 mm to 20 mm.

[0025] The method may further include adjusting the amplitude, waveform period, and shape of the voltage applied to the electrodes to maximize plasma activity and minimize the generation of unwanted by-product gases.

[0026] The device of the present invention has a high voltage AC power source for controlling the amplitude, waveform period, and shape of the voltage applied to the electrodes, so that it operates at a plasma discharge of selected conditions. The high voltage AC power source can be a high voltage generator. The amplitude, waveform period, and shape of the voltage applied to the electrodes can be adjusted according to the desired treatment intensity and treatment time in the multiple reactors. The system generally consists of multiple reactors arranged with alternating high voltage electrodes and ground electrodes, and the configuration and overall size can be designed to provide the appropriate treatment intensity and time.

[0027] The high voltage electrode is covered with an insulator. The ground electrode may be bare or covered with an insulator. The insulated electrode includes an insulator that may be in the form of a dielectric tube or plate.

[0028] The system may further include a blower unit for driving air over the object being treated to reduce heating of the object surface.

[0029] The generation of plasma for the direct treatment of surfaces takes advantage of the generation of an electrical discharge on the surface of the object to be treated.

[0030] Another advantage is that the discharge occurs directly above the surface of the object to be treated to generate a plasma for directly treating the surface.

[0031] A further advantage of at least one embodiment of the present invention is that it provides a method and device for generating plasma directly on or above the surface of an object to be treated (including sterilized) without requiring the delivery or structural arrangement of charged ions and reactive species, thereby overcoming the shortcomings of the prior art.

[0032] The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages, and certain objects attained by its uses, reference should be made to the drawings and following descriptive matter in which preferred embodiments of the invention are shown and described. [Brief description of the drawings]

[0033] Specific embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:

[0034] [Figure 1] FIG. 2 shows components of the surface treatment device of the present invention. [Diagram 2] FIG. 2 illustrates an electrode and frame assembly according to a preferred embodiment. [Diagram 3] FIG. 2 illustrates an electrode configuration according to a preferred embodiment. [Figure 4] FIG. 13 illustrates an electrode assembly according to another embodiment. [Diagram 5] FIG. 13 illustrates another embodiment of an electrode assembly having an insulated electrode disposed within a circular cutout in a ground plate. [Figure 6] FIG. 13 illustrates another embodiment of an electrode assembly having an insulated electrode disposed within a hexagonal cutout in a ground plate. [Figure 7] 7a and 7b show another embodiment in which the position of the electrodes is adjustable. [Figure 8] 1A-1C show prototype devices fabricated in accordance with the present invention, illustrating the effect of surface treatment. [Figure 9] FIG. 9 is a diagram showing the results of an experiment using the prototype of FIG. 8. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0035] Reference will now be made in detail to the preferred embodiments of the present invention.

[0036] Referring now to the drawings, FIG. 1 generally illustrates system components of a surface treatment system 1 including an electrode assembly 10 with a high voltage electrode 20, a low voltage electrode 30, and associated power supply 4 and controller 5. The power supply and controller generate and maintain a discharge having specific plasma parameters predetermined and controlled by a high voltage AC power supply. As shown in FIG. 1, the electrodes 20, 30 may be connected to a high voltage AC power supply 4 having an electronic control unit 5. The power supply 4 may provide a voltage sufficient to cause dielectric breakdown and plasma generation directly or on the surface of the object to be treated (including sterilization) without the need for delivery of charged ions and active species. The voltage provided to the electrodes 20, 30 may be controlled within a range of 10 kilovolts to 50 kilovolts. The waveform period may be 10 to 200 Hz. -1 ms~10 2 It can be controlled within the range of ms.

[0037] FIG. 2 shows a preferred embodiment of an electrode assembly 10 including a high voltage electrode 20, a low voltage electrode 30. The electrodes are held in place by holders 11 and 12. Besides planar forms, the assembly may take other forms such as a cylinder or a sphere. As shown in FIG. 3, the high voltage electrode 20 has a conductor 21 covered with an insulator 22 and a wire connection 23 to a power source. The low voltage electrode 30 has a conductor 31, which may be bare or covered with an insulator 32, and a wire connection 33 to a power source. The insulators may be made of a dielectric material such as glass or ceramic in the form of a cylindrical tube, as in this preferred embodiment. They may also be in the form of a plate or made from any insulating or dielectric material. The insulators may also be in the form of a dielectric coating. The electrode conductors 21, 31 of the electrodes 21, 31 may be made from a conductive sheet, mesh, or deposit. The distance between a pair of electrodes 20, 30 may be in the range of about 1 mm to about 20 mm. A discharge is generated in the space surrounded by the electrodes, generating plasma on and above the surface of the object to be treated.

[0038] The electrodes can take other shapes, for example, a wavy voltage electrode 120 as shown in FIG. 4, as well as the low voltage electrode 130. The electrode assembly is not limited to the form of a rail. In the embodiment shown in FIG. 5, the ground electrode 230 is a conductive sheet with a circular cutout to accommodate the insulated high voltage electrode 220. FIG. 6 shows another embodiment in which the insulated high voltage electrode 320 is placed in a hexagonal cutout in the ground electrode plate 330. Although the embodiment is shown in planar form, the assembly can take other forms, such as a cylinder or a sphere. An additional feature shown in FIG. 7a and FIG. 7b is that the high voltage electrodes 220 attached to the support 221 can be recessed behind the ground electrode plate 230 when not in use, as shown in FIG. 7a, and can be moved to an operating position when they are used for surface treatment and disinfection, as shown in FIG. 7b. Another embodiment includes moving the ground electrode plate 230 to be flush with the high voltage electrode when used for surface treatment.

[0039] The superior surface disinfection performance of the prototype device of the present invention (see FIG. 8) over the prototype device of the prior art has been confirmed in comparative tests. In the tests, Petri dishes were preloaded with bacteria and treated with the corresponding device operating at comparable plasma conditions. In the photograph of FIG. 9, each "dot" on the Petri dish represents a bacterial colony. FIG. 9c is a "control" where the Petri dish was not treated with any device and shows the initial concentration of bacteria. FIG. 9a shows the results of a Petri dish treated with the device of the present invention (the device shown in FIG. 8). FIG. 9b shows the results of a Petri dish treated with a device according to the prior art. Comparing FIG. 9a and FIG. 9b, FIG. 9a shows a much lower number of bacterial colonies, indicating that the device of the present invention disinfects surfaces more effectively.

[0040] The electrode and frame assembly (e.g., according to the preferred embodiment of FIG. 2) can be applied to a smooth surface with the surfaces of the electrodes (20, 30) resting on the surface to be treated or overlying the surface to be treated at a distance not greater than the separation between the electrodes (20, 30). In the preferred embodiment shown in FIG. 2, the separation between the electrodes (20, 30) can range from 1 mm to 20 mm. The distance between the electrode surface and the surface to be treated can range from 0 mm to 20 mm. Typical treatment times are from a fraction of a second to a few seconds. The device of the present invention can simultaneously sterilize the air by blowing air (e.g., using a fan) into the gap space between the electrode surface and the surface to be treated.

[0041] In an alternative embodiment as shown in FIG. 5, a high voltage electrode 220 can be mounted on a movable support 221 to optimize the distance between the electrode tip and the surface being treated.

[0042] Surface treatment is not limited to surfaces smaller than the size of the electrode assembly. The electrode assembly can be used to treat large surfaces by sliding or moving the electrode assembly over the surface to be treated. Alternatively, the surface to be treated can be moved under the electrode assembly, for example, the electrode assembly can be placed on the rubber handrail of an escalator and moved continuously under the electrode assembly. Since the electrode is placed over the moving surface, physical contact can be avoided, and mechanical wear and tear can be eliminated.

[0043] The treatment time to disinfect the surface beneath the electrode assembly is a matter of seconds, and a small laptop-sized electrode assembly can effectively disinfect a desk surface in minutes. By attaching the electrode assembly to a mobile device (robot or drone), the mobile electrode assembly can disinfect a room surface in minutes. By blowing air through the interstitial space between the electrode surface and the surface to be treated (e.g., using the motion or fan of the mobile device), the device can simultaneously disinfect the air.

[0044] In case of curved surfaces, the frame (11, 12 in FIG. 2) holding the electrodes may be curved to match the curvature of the surface to be treated. Furthermore, the holder (11, 12 in FIG. 2) of the preferred embodiment may be made of flexible material or configured in the form of a flexible chain so that the electrode can be adapted to any curved surface. In an alternative embodiment as shown in FIG. 5, the high voltage electrode 220 is attached to a flexible support 221 together with a flexible ground electrode 230, allowing the tip of the electrode to conform to any curved surface and to provide an optimal distance between the tip of the electrode and the surface to be treated.

[0045] In the present invention, the distance between the electrode surface and the surface to be treated does not need to be fixed, but can be varied within a reasonable range of 0 mm to 20 mm. Therefore, the device can sterilize not only smooth surfaces, but also non-flat surfaces with surface irregularities of up to 20 mm.

[0046] In the device of the present invention, the structure and arrangement of the electrodes allows the disinfectant to be easily applied onto the surface of the object to be treated. Compared with the prior art devices, the device of the present invention is simple in structure, yet flexible, and more effective in treating the surface. There is no particular need to ground the surface of the object, that is, the object to be treated essentially becomes part of the electrical circuit. For the frame, the basic requirement is that it can hold and place the electrodes at the required close distance towards the treatment surface. As long as the frame can meet such requirements, it can be constructed in various ways with various shapes and materials. For example, it can be made from flexible materials to treat curved or irregular surfaces. It can also incorporate a fan mechanism to direct air to the treatment surface. It can also have wheels or slide mechanisms to facilitate moving over the surface being treated. In the present invention, plasma treatment can be applied to various objects, for example, the surfaces of elevator button panels and other structures in common areas can be treated to reduce the infection and transmission of viruses and bacteria in the community. This is because, unlike the prior art devices, there is no need to place the object between the electrodes. In addition to the uniqueness of the present invention to overcome some of the complications of prior art developments, the device of the present invention is able to disinfect surfaces better than prior art devices.

[0047] It should be understood that the expressions and terms employed herein are for the purpose of explanation and should not be considered as limiting. Although the basic novel features of the present invention as applied to the preferred embodiments of the present invention have been described and pointed out, it will be understood that various omissions and substitutions and changes can be made by those skilled in the art in the form and details of the illustrated embodiments without departing from the spirit of the present invention. The present invention is not limited by the above-described embodiments presented as examples, but can be modified in various ways within the scope of protection defined by the appended claims. It will be further understood that the present invention can be implemented without reference to these specific examples, since the essence of the present invention lies not in technical difficulty or complexity but in the novel idea itself. Once the idea is known, it is within the ordinary skill in the art to put it into practice.

Claims

1. A device for treating a surface, comprising: (a) at least one pair of electrodes arranged at a distance of 1 to 20 mm from each other and capable of generating plasma; (b) a frame for holding and positioning said electrode against a surface being treated at a distance of 0-20 mm; (c) a power source that supplies high voltage AC to the electrodes; (d) a controller for controlling the plasma generation and treatment process; The device, wherein the frame has a number of wheels for facilitating movement of the device over a surface during processing.

2. 10. The device of claim 1, wherein one electrode is at a high voltage and insulated with a dielectric material and the other electrode is at a low voltage and is either insulated or bare.

3. The device of claim 1 , wherein one electrode comprises a conductor in the form of a conductive sheet, mesh, wire, or deposit.

4. 2. The device of claim 1, wherein the frame has a flat surface parallel to a plane formed by the electrodes and a perpendicular distance to the plane between 0 mm and 20 mm determines the distance between the electrodes and the surface under treatment.

5. The device of claim 1 , wherein the frame has a curved surface that conforms to a surface during processing.

6. The device of claim 1 , wherein the frame has a flexible surface that can change shape to accommodate the surface during processing.

7. The device of claim 1 , wherein the frame houses a fan or electric fan for blowing air towards a surface during processing.

8. The device of claim 1 , wherein the frame has a sliding surface to facilitate movement of the device over a surface during processing.

9. The device of claim 1 , wherein the power source is capable of providing electricity at a voltage between 10 kv and 50 kv.

10. 10. The device of claim 1, wherein the controller adjusts the power supply to control the amplitude, waveform period and shape of the voltage applied to the electrodes to maximize plasma processing and minimize generation of unwanted by-product gases.

11. The waveform period is 10 －１ ms~10 ２ The device of claim 10, wherein the frequency is in the range of ms.

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