Multi-cell or multi-array plasma and surface treatment method using the same

Abstract

A plasma device (1) comprising at least two plasma cells (Cx) and a control unit (2), in which the first and second electrodes of a given plasma cell are independent of the corresponding first and second electrodes of an adjacent plasma cell, the electrodes of the adjacent plasma cells being independently connected to the control unit, and the control unit including a high-voltage pulse generator and a radio-frequency generator, which are mutually protected by a filtering element.

Description

[Technical field]

[0001] The present invention relates to a method for surface treatment with plasma in high definition, as well as to a plasma device used therefor. More specifically, the plasma device comprises a plurality of plasma cells arranged in an array and adapted to be individually controlled. The present invention also relates to a specific control circuit adapted to precisely and independently control the plasma cells. [Background technology]

[0002] Plasma has already been known for some time to treat surfaces and modify their surface tension or their surface properties. Plasma is used for example to modify the surface composition or surface structure for the deposition of layers or for the partial removal of material. Treating a surface with plasma is for example a well-known step before applying paints, inks, adhesives or any other material that would not otherwise adhere reliably to the surface. Materials with low surface tension are generally subjected to plasma treatment to increase their surface tension and allow better adhesion of additional layers of material.

[0003] Several types of plasma have been developed to date, including atmospheric or air plasma, flame plasma, and atmospheric chemical plasma. In practice, a gas is fed through two high voltage electrodes and directed towards the surface to be treated to generate ionized species. Most plasma applications involve the continuous feeding of ionized species onto a surface in such a way that a large surface is covered. Because plasma sources have small surfaces, some devices use rotating heads to allow larger surfaces to be treated.

[0004] The above mentioned plasma devices, regardless of their characteristics, are designed to provide plasma continuously and are applied to large surfaces. However, these devices are not adapted to be precisely directed to small areas of the surface. Moreover, these devices are designed for continuous and regular application and are therefore not adapted for fast on / off cycles. In particular, fast and precise control is cumbersome due to the high voltages used for plasma generation. The high voltages are usually not adapted for rapid activation and deactivation of the plasma cell.

[0005] Some arrays of plasma cells have also been developed, such as the array of plasma cells described in US Pat. No. 6,528,947. In this document, a cathode assembly is described that includes multiple cells in order to provide a uniform plasma. Although the plasma is provided through multiple cells rather than through one cell, this type of device suffers from the same drawbacks as mentioned above for the localized treatment of a surface. In particular, all the plasma cells are activated simultaneously, covering a large surface area.

[0006] Additionally, plasma treatment of surfaces typically requires a vacuum, which requires at least one pump and an enclosed environment, as well as expensive equipment surrounding the plasma device.

[0007] Surface treatments are widely used in industry for coatings or paints. However, they cannot be used to paint two-dimensional representations on surfaces or to mark parts due to their low definition and accuracy. For the purpose of marking manufactured articles, it is rather necessary to include an inkjet step, which can be added to the treatment step with plasma.

[0008] Thus, a need exists for further development of plasma devices and methods of use. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] U.S. Patent No. 6,528,947 Summary of the Invention [Problem to be solved by the invention]

[0010] It is an object of the present invention to provide a plasma device which allows to modify a surface with a two-dimensional motif, in particular to print, etch, deposit material, color shift a surface, decontaminate or clean, or a combination of two or more of these surface treatments.

[0011] Another object of the present invention is to provide a plasma device that can be used directly as a 2D printing device on a surface.

[0012] It is a further object of the present invention to provide a multi-cell or multi-array plasma cell device in which the plasma cells can be activated individually and independently. The term "multi-cell" refers to an array containing a plurality of individual cells. The term "multi-array" refers to multiple arrays each containing a plurality of individual cells.

[0013] Another object of the present invention is to provide a multi-cell or multi-array plasma cell apparatus which allows fast and accurate independent control of each of the plasma cells, in particular the object is to provide control means adapted to cause individual cells of a multi-cell or multi-array plasma cell apparatus to generate plasma independently, quickly and accurately.

[0014] It is also an object of the present invention to provide a control method for a multi-cell or multi-array plasma cell apparatus for 2D printing operations.

[0015] It is also an object of the present invention to make it possible to print a surface in a convenient and inexpensive way. In particular, it is an object of the present invention to make it possible to print a surface with a multi-cell or multi-array plasma device without the generation of a vacuum. By not generating a vacuum it is meant that the printing of the surface is carried out at atmospheric pressure. It is also an object of the present invention to make it possible to print a surface with a multi-cell or multi-array plasma device under a moderate vacuum. By moderate vacuum it is meant a pressure slightly below atmospheric pressure, for example from about 1 bar to about 800 mbars, or from about 1 bar to about 500 mbars, or from about 1 bar to about 100 mbars.

[0016] It is an object of the present invention to provide a surface treatment, by which is meant one or more of modifying surface properties such as surface tension, adding material such as deposition, and removing material such as etching, which surface treatment is localized and / or allows for the formation of patterns on the surface. [Means for solving the problem]

[0017] These objects are achieved by means of an apparatus and a method as defined in the independent claims and further detailed by the dependent claims.

[0018] Thus, the claimed invention advantageously enables fast and accurate drawing of 2D markings on a surface.

[0019] Examples and embodiments of the invention are explained in more detail below with the aid of the following drawings: [Brief description of the drawings]

[0020] [Figure 1] FIG. 2 is a schematic diagram showing a marking process using a multi-cell plasma device according to the present invention. [Diagram 2] 1 shows a detail of an array of plasma cells. [Diagram 3] 1 shows details of a given plasma cell. [Figure 4a]1 illustrates details of a given cell according to an embodiment. [Figure 4b] 1 illustrates details of a given cell according to an embodiment. [Figure 4c] 1 illustrates details of a given cell according to an embodiment. [Figure 4d] 1 illustrates details of a given cell according to an embodiment. [Diagram 5] FIG. 2 is a schematic diagram of a control unit. [Figure 6] FIG. 1 is a schematic diagram of pulse control. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] As shown in FIG. 1, a manufactured article M having at least one surface M1 can be the subject of a surface treatment using a plasma device 1. The treatment of the surface M1 results in a mark M2 located in a predetermined area of ​​the surface M. The surface M1 of the article M can be made of any material, including a material with a low surface tension. It can be made of glass, synthetic polymers, metals such as iron, stainless steel, or metal alloys. The mark M2 provided on the surface can be any kind of 2D representation, including letters, numbers, geometric figures or any other inscription. The surface M1 is thus treated to locally modify its properties, in particular its surface tension, or to locally add or remove material to provide a pattern. The marking process using the plasma device 1 can be performed in-line, in the production flow or in stages, after a short period of immobilization of the manufactured article. The staged approach can be used as a batch process.

[0022] In the present invention, the term "surface treatment" refers to the modification of the physical properties of the treated surface, in particular its surface tension, wettability and / or polarity. Surface treatment thus induces a direct change in the material of the treated surface, such as oxidation. Surface treatment also includes, where applicable, localized coatings or material depositions, such as chemical products. Such product depositions may or may not be simultaneous with the physical change of the surface. The deposited product locally provides the treated surface with a different surface tension, wettability and / or polarity. Alternatively, the deposited product itself has different properties than the surface to which it is deposited. Surface treatment also includes the removal of material, commonly known as etching.

[0023] The plasma device 1 comprises a head 4 arranged to be placed in the vicinity of a surface M1 to be treated. The head 4 comprises a number of plasma cells Cx, each of which is adapted to generate a plasma Px once activated by a control unit 2. The control unit makes it possible to supply a voltage Vx independently to each plasma cell Cx of the head 4. In particular, the control unit 2 makes it possible to supply a time-varying voltage or an intermittent voltage or a combination thereof. The plasma device 1 also comprises a plasma precursor unit 3 connected to each of the cells Cx by a pipe 31 for injecting a plasma precursor through the cells.

[0024] The plasma precursor may be any material that can be used to provide a plasma. It may be a gas, such as oxygen, a mixture of gases, a solution containing one or more components, or a mixture of gas and vaporized components. The plasma precursor may also or alternatively include an aerosol. The plasma precursor unit 3 includes, separately or together, if applicable, one or more tanks adapted to store the plasma precursor. Such tanks include gas containers or gas supply lines. Such tanks thus refer to any suitable reservoir adapted to store the plasma precursor, whether liquid or gaseous. The plasma precursor unit 3 may also include an aerosol generator.

[0025] The plasma precursors are fed to the cells Cx of the head 4 at one of the ends of these cells and are ejected at their opposite end towards the surface M1 to be treated. Meanwhile, for a time Tx, called the ignition duration for a given cell, a high voltage Vx is applied to the electrodes of the cells Cx in which plasma is desired. In the references Cx and Tx, x represents an integer between 1 and 10000 or more, preferably between 10 and 1000, and corresponds to the rank of the given cell Cx. In other words, the number of plasma cells can be as high as necessary, such as 10, 100, 1000, 10000 or more. The plasma device 1 is therefore a multi-cell plasma, in which the plasma cells Cx are adjacent to one another and are organized in the form of a line or a cluster or an array. Other geometrical arrangements of the cells may be envisaged. The plasma cells may preferably be organized in the form of one or several parallel lines, each containing 2-200, 20-200 or 20-2000 plasma cells. The plasma cells can be arranged in multiple arrays or clusters to provide a multi-array arrangement.

[0026] For 2D printing operations, each of the plasma cells Cx can be activated individually and independently, meaning that a plasma Px is generated for each cell independently and for an independent ignition time Tx. For this purpose, each cell of the device 1 includes an independent electrode E1, E2.

[0027] The plasma device 1 may contain only one plasma cell, which is switched on and off through the control unit 2 at different times and for different durations. The successive ignition and stopping of the plasma while a relative movement between the head 4 and the surface to be treated M1 occurs makes it possible to print a predetermined figure M2 on the surface. However, this may require both lateral and longitudinal movement of the head 4 in relation to the surface to be treated M1. This is time-consuming and requires a suitable mechanical arrangement. Therefore, the plasma device 1 preferably contains a number of cells Cx in the form of rows. In this way, a relative movement between the head 4 and the surface to be treated M1 may only be required in one direction. If the rows of plasma cells Cx are transverse to the direction of movement of the surface to be treated M1, the successive individual activation of the plasma cells Cx allows a 2d marking. The more plasma cells that are arranged, the faster the printing operation. If the plasma cells Cx are arranged in an array, it may even be possible to print the surface M1 without any relative movement between the article M and the head 4. It may still be possible to move the head 4, which includes multiple plasma cells organized in an array, in relation to the article M in order to print multiple different 2D representations in multiple areas of a given article M. It should therefore be understood that the number of plasma cells Cx, their relative arrangement and the relative movement of the head 4 and the article M can be adapted to the needs without departing from the invention.

[0028] FIG. 3 shows the details of a given plasma cell Cx. Each of the plasma cells Cx of the head comprises a gas inlet 6 having a core 61 and a central through hole 62. The gas inlet 6 is installed at the rear end of the plasma cell Cx and allows the plasma precursor to be fed to the plasma cell. The through hole 62 is connected to the internal chamber 7 of the plasma cell Cx. The internal chamber is bounded by side walls 71. Such side walls 71 can be of any shape, such as circular, elliptical, square, rectangular, hexagonal or polygonal. Opposite the gas inlet 6 in relation to the internal chamber 7, the plasma cell comprises a front wall 8 having a front opening 81 through which gas can flow from the internal chamber 7 to the outside of the plasma cell. The front opening 81 is surrounded by a first electrode E1 and a second electrode E2 separated by an insulating layer 9. The electrodes E1, E2 of each plasma cell Cx are connected in an independent manner to the control unit 2. As a result, it is possible to place the independent electrodes at different potentials. The term "independently" here refers to the fact that each cell includes an independent electrode E1, E2, meaning that two different plasma cells Cx, whether adjacent or not, do not share any common electrode. In particular, the side walls 71 of the plasma cells are preferably not used as electrodes.

[0029] Although one example of a plasma cell arrangement is described, it is understood that the invention is not limited to this particular arrangement. For example, the gas inlet 6 can be located on the side wall of the plasma cell.

[0030] The insulating layer 9 may be made of any kind of insulating material, such as a dielectric polymer, ceramic or any other known material.

[0031] The side walls 71 of the plasma cells Cx may correspond to the overall structure of the head 4. For this purpose, the head 4 includes a frame 41 having a number of adjacent holes, each corresponding to one plasma cell Cx, the frame itself defining the side walls 71 of each plasma cell Cx. The frame 41 is preferably made of an insulating material so as not to conduct any voltage to the plasma cells Cx. In other words, the frame only serves as a physical structure. Alternatively, the side walls 71 of the plasma cells can be defined by an independent layer maintained on the frame of the head 4. This is the case, for example, when the frame 41 is made of or includes a conductive material. In this specific case, an additional insulating layer can be used to provide the side walls of the plasma cells Cx.

[0032] The frame 41 has a rear face and a front face, the rear face being adapted to accommodate the gas inlets 6 of each of the cells Cx. The gas inlets may be made of a metallic material, such as stainless steel or a metal alloy adapted to withstand corrosive and / or oxidative products. Alternatively, the gas inlets 6 may be made of a polymeric material or a mixture of polymeric materials, such as the polymers used in 3D printing processes. The gas inlets 6 are connected to the frame 41 by a connecting element 10. The connecting element thus allows to maintain the gas inlets 6 in a desired position at the rear end of a given plasma cell Cx. The connecting element 10 is preferably made of an insulating material. Each hole of the frame 41 is provided with a first electrode E1 on the front face. The first electrode E1 may be directly linked to the frame 41 or separated from the frame 41 by an insulating layer. The first layer E1 is at least partially in direct contact with the internal space of the inner chamber 7 of the plasma cell. However, it is possible to coat the part of the first layer E1 in contact with the internal space of the internal chamber 7 with a protective layer (not shown), provided that the potential of the first electrode E1 still provides its effect on the contents of the internal chamber 7. The first electrode E1 may have the shape of a plate close to the front end of the plasma cell and with a geometric edge adapted to the side wall 71 of the plasma cell. In that case, the first electrode E1 comprises a central opening through which the plasma precursor can be ejected from the internal chamber. Alternatively, the first electrode E1 may take the form of a metal grid or any other shape adapted to apply a voltage to the internal contents of the internal chamber 7. The first electrode E1 of a given plasma cell Cx is electrically insulated from the first electrodes E1 of the adjacent plasma cells Cx. Furthermore, the first electrode E1 of each plasma cell is electrically insulated from one of the adjacent plasma cells Cx by an insulating layer. The first electrode E1 of each plasma cell is individually connected to the control unit 2 to receive control electric pulses.

[0033] Each hole of the frame 41 is provided with a second electrode E2 on its front face. The second electrode E2 is electrically insulated from the first electrode E1 by means of one or more insulating layers 9. The second electrode E2 may have the shape of a plate and overlap the first electrode E1. The second electrode E2 then comprises a central opening through which the plasma precursor can be ejected from the internal chamber 7. The insulating layer 9 also comprises an opening. According to one specific arrangement, the first electrode E1, the second electrode E2 and the insulating layer 9 are each provided with an opening that coincides with one another and is adapted to provide the front opening 81 of the plasma cell Cx. Both the first electrode E1 as well as the second electrode E2 are in direct contact with the material stored in the internal chamber 7, at least at the level of the front opening 81 of the plasma cell Cx. Here, and in line with the present disclosure, direct contact of the electrodes with the material stored in the internal chamber 7 is understood to mean the situation in which the potential of the electrodes remains active towards the contents of the internal chamber 7. Thus, a protective layer without any effect on the electrical potential is possible. The second electrode E2 of a given plasma cell Cx can be physically separated and electrically insulated from the second electrodes E2 of adjacent plasma cells Cx. Furthermore, the second electrode E2 of each plasma cell is electrically insulated from one of the adjacent plasma cells Cx by an insulating layer. The second electrode E2 of each plasma cell is individually connected to the control unit 2 to receive control electrical pulses.

[0034] According to one embodiment, the first electrodes E1 of two or more plasma cells receive a common potential, while the second electrodes E2 of these two or more plasma cells remain independent and receive independent ignition and shutdown pulses. The reverse configuration is also possible, where the second electrodes E2 of two or more plasma cells receive a common potential, while the first electrodes E1 of these two or more plasma cells remain independent and receive independent ignition and shutdown pulses. Although the electrodes receiving a given common potential may be physically and electrically independent, they are advantageously connected to provide a single electrode common to two or more plasma cells. Such an arrangement can simplify the electrical circuit.

[0035] The insulating layer 9 may be common to all the plasma cells of the head 4. Alternatively, the insulating layer 9 may be specific to each plasma cell and independent from the insulating layers 9 of adjacent plasma cells.

[0036] In one embodiment, the combination of the first electrode E1, the second electrode E2 and the insulating layer 9 forms the front wall 8 of the plasma cell Cx. Alternatively, the front wall 8 of the plasma cell Cx includes, in addition to the first electrode E1 and the second electrode E2 and the insulating layer 9, a sealing material adapted to contain and maintain the mentioned components. Such a sealing material can be, for example, a molded polymer, a hard or soft polymer, an insulating polymer or any suitable coating material. The insulating layer 9 can also cover the surface of the electrode in contact with the internal chamber 7, provided that it does not negatively affect the effect of the potential of the electrodes.

[0037] The first electrode E1 and the second electrode E2 are made of a conductive material. These electrodes may have a thickness of about 1 μm to about a few mm, or about 0.05 mm to about 1 mm, preferably 0.1 to 0.8 mm. The thickness of each electrode may be, for example, about 0.5 mm. However, it should be understood that the thickness is not as critical for pixel resolution as the diameter of the plasma cell.

[0038] In this specification, the term "adjacent" and related terms refer to the proximity of two items, such as plasma cells Cx. Thus, two adjacent plasma cells means that the two plasma cells are directly and immediately adjacent to each other, with no intermediate plasma cell between them. Thus, the term "adjacent" is understood as "adjacent," "in close proximity to," "beside," "nearby," or "having a common boundary." The relative positions of the plasma cells remain independent of their relative electrical states and electrical insulation and any other parameters.

[0039] The distance separating the front openings 81 of two adjacent plasma cells Cx is preferably less than 5 mm, more preferably less than 3 mm, and more preferably approximately 1 mm or less. In a preferred arrangement, the distance separating the front openings 81 of two adjacent plasma cells Cx is preferably less than 0.5 mm, or less than 0.1 mm.

[0040] Optionally, the plasma cell Cx may be defined by one or more of the diameter of the front opening 81, the diameter of the inner chamber 7, the diameter of the gas inlet through-hole 62, and the height of the inner chamber 7. Figures 4a, 4b, 4c and 4d better show different examples of possible arrangements of the plasma cell Cx.

[0041] The diameter of the through hole 62 of the gas inlet 6 may be about 0.005 mm to 0.8 mm, preferably about 0.1 to 0.5 mm. It may also be about 0.2 mm.

[0042] The height of the inner chamber 7, which separates the gas inlet 6 from the inner surface of the front wall 8, may be from about 0.1 mm to about 20 mm. The inner chamber 7 may be short in length, for example as shown in FIG. 4a, in which case the height may be about 0.1-0.5 mm. Alternatively, the inner chamber 7 may be long in length, in which case the height may be about 0.5-1 to 3 mm, preferably up to 20 mm. The terms "short" and "long" in length are not intended to be limited to the above dimensions, but rather correspond to adjustable parameters of the plasma cell.

[0043] Independently of the diameter of the through-hole 62 and the height of the internal chamber 7, the diameter of the internal chamber 7 can vary between a minimum and a maximum value depending on the intensity of the plasma to be delivered to the surface M1. The diameter of the internal chamber 7 can be of the same order of magnitude as the diameter of the through-hole 62 of the gas inlet 6 (FIG. 4c). It can even be thinner, as shown in FIG. 4d. For example, the diameter of the internal chamber 7 can correspond to one tenth, or one half or one third, of the diameter of the through-hole 62. Alternatively, the diameter of the internal chamber 7 can be larger than the through-hole 62. It can correspond, for example, to two or three or ten times the value of the diameter of the through-hole 62.

[0044] According to one embodiment, the plasma cell may be of short length, where the diameter of the inner chamber corresponds to 3-5 times the diameter of the through-hole 62 .

[0045] According to another embodiment, the plasma cell may be long in length, where the diameter of the inner chamber corresponds to 3 to 5 times the diameter of the through-hole 62 .

[0046] According to alternative embodiments, the plasma cell can be short or long in length, where the diameter of the inner chamber is on the same order of magnitude as the diameter of the through-hole 62 .

[0047] According to alternative embodiments, the plasma cell may be short or long in length, where the diameter of the inner chamber corresponds to one-half to one-fifth of the diameter of the through-hole 62 .

[0048] It will be appreciated that any other suitable ratio between the height and diameter of the inner chamber 7 and the diameter of the through hole 62 may be determined.

[0049] The diameter of the front opening 81 may be approximately 0.01 mm to 1 mm, depending on the desired resolution of the pattern to be printed on the surface. The diameter of the front opening 81 is preferably about 0.01 mm to about 0.5 mm, more preferably 0.01 mm to about 0.3 mm, and even more advantageously 0.01 mm to about 0.1 mm. It is pointed out that the diameter influences the precision of the plasma jet on the surface M1. The length of the front opening 81 may correspond to the thickness of the front wall 8. Alternatively, this length may be longer, with a corresponding protrusion towards the outside of the plasma cell, in order to better direct and guide the plasma jet on the surface M1. The front wall 81 may have another geometric shape, although it may be cylindrical with parallel side walls. For example, its transverse section may be conical, where its tip has a smaller diameter than its base, or conversely, where its tip has a larger diameter than its base. For better pixel definition, the plasma jet should not be dispersed but rather focused onto a small area of ​​the surface M1, so that the pressure conditions of the incoming plasma precursor and the dimensions of the front opening 81 can be properly correlated.

[0050] In this disclosure, the terms "front" and "rear" as applied to plasma cells refer to opposite faces of a given plasma cell, where the front end or front face of the plasma cell corresponds to the face from which the plasma is ejected and the rear face corresponds to the face to which the incoming plasma precursor is delivered. Thus, the front face of the plasma cell Cx faces the surface M to be treated.

[0051] The plasma device 1 according to the present disclosure allows for individual activation of the plasma cells Cx. This is possible because the electrodes of each plasma cell Cx are independent of the other plasma cells. Furthermore, the plasma device allows for activation of the plasma cells on demand, which means that each of the plasma cells Cx can be activated for a short time Tx, which can be from approximately a few milliseconds up to hundreds of milliseconds or more. Thus, such a time Tx can be limited to 10 ms, or 100 ms, or 500 ms, or 1 second, or can be 10 ms to 100 ms, or 200 to 800 ms.

[0052] In one embodiment, a given cell Cx of the plasma device 1 may be activated for an ignition period Tx of 10 ms to 500 ms or more, and at the end of this ignition period Tx, may be deactivated for an inactivation period Ux of 100 to 500 ms or more.

[0053] In the present disclosure, the terms "cell activation" and "activated cell" or any related expression refer to the state of a plasma cell Cx receiving a high voltage Vx adapted to generate a plasma Px. A plasma cell Cx is activated when it is switched on. Thus, the terms "cell deactivation", "deactivated cell" and related expressions refer to the state of a plasma cell Cx that does not provide plasma due to the absence of a voltage Vx. A plasma cell is deactivated when it is switched off. Thus, a given plasma cell Cx alternates between one of two states, an active state and an inactive state, depending on the presence or absence of a high voltage applied to the corresponding first electrode E1 and second electrode E2.

[0054] By high voltage Vx is meant a voltage suitable for converting the plasma precursor into actual plasma. It can be approximately 800 volts or 1000 volts or 2000 volts or more, depending on parameters such as pressure, nature of the plasma precursor, distance between the first electrode E1 and the second electrode E2, and flow rate. If the pressure is low enough, a voltage Vx as low as about 100 volts can be applied. Thus, depending on the applied parameters, a voltage Vx of about 100 volts to 2000 volts or more can be used.

[0055] The activation period of the plasma cell Cx may last less than a few seconds, even less than 1 second, preferably less than 100 ms, for example 10-50 ms. Such short activation of the plasma cell allows excellent pixel definition. The activation and deactivation cycle may last for example approximately 1 or 2 seconds. In other words, the firing frequency is approximately 1 second or more. The application of high voltages at such high frequencies requires a suitable control unit 2 adapted to achieve these performances and to avoid material damage.

[0056] The control unit 2 of the plasma device is represented in FIG. 5. It comprises a high voltage generator 21 adapted to provide short pulses of high voltage. The high voltage generator 21 preferably provides pulses of high DC voltage. It is therefore understood as being a high voltage pulse generator. The pulse duration will be better explained below. The high voltage DC generator 21 may comprise several units providing high DC voltage and arranged in parallel. The number of such units may be more than 100. Each of these DC voltage units has a diameter of 50 cm so that the high voltage DC generator 21 remains sufficiently compact. 3 Less than 30cm, preferably 3Each of the DC voltage units preferably consumes less than 10 watts and provides a voltage of approximately 2000 volts. Each of the high voltage units is connected to a different plasma cell. By DC, we mean very low frequency pulses of DC origin up to a few hundred Hertz. Thus, DC may fluctuate slightly. However, it is considered direct current for the time frame of the pulse.

[0057] The control unit 2 further includes a radio frequency generator (RF) 22. The RF generator 22 is capable of generating a radio frequency of about 13 MHz to 15 MHz, for example about 13.56 MHz. Such an RF generator 22 enables the plasma Px of the corresponding plasma cell Cx to remain activated once the corresponding plasma cell Cx is switched on.

[0058] While the RF generator 22 is permanently on, the high voltage DC generator 21 supplies high voltage to the plasma cell Cx on demand.

[0059] The RF generator 22 and the high voltage DC generator 21 are distinct elements of the plasma control. They are mutually protected from each other by one or more filtering elements 23. The filtering element 23 protects the high voltage DC generator 21 from the RF generator 22. The filtering element 23 protects the RF generator 22 from damage caused by the high voltage DC generator 21. Furthermore, the filtering element 23 likewise protects the RF generator 23 from interference. In detail, the filtering element 23 includes a matching unit that ensures the best adaptation of the impedance of the plasma circuit to the impedance of the RF generator unit 22. This matching unit ensures that the output power of the RF generator is most efficiently coupled into the plasma itself. The output power of the RF generator depends on the number of activated cells. The more activated the cells, the greater the power from the RF generator 22 should be. This power dependency of the RF output is also guaranteed and managed by the control unit 2.

[0060] The control unit 2 described here may be fully integrated in the plasma device 1 described above and permanently connected to the plasma cell Cx. Alternatively, the control unit 2 may be independent from the plasma cell Cx. In this particular case, the plasma device 1 comprises a frame 41 of the plasma cell Cx as described above and a separate control unit 2 that can be connected to and disconnected from the plasma cell Cx. For this purpose, the frame 41 or any other suitable part of the plasma device 1 is provided with the necessary electrical plugs (not shown) that allow the connection of the electrodes of the plasma cell to the control unit 2. The control unit 2 includes the necessary connection means for plugging in the plasma cell.

[0061] According to an embodiment, the control unit 2 can be adapted to different plasma cell arrays. For example, the number of units of the high voltage DC generator 21 may be adapted depending on the number of plasma cells to be controlled. Furthermore, the power of the RF generator 22 is modulated or adapted as required. The control unit may include suitable software that allows a user to modulate at least the power of the RF generator 22.

[0062] The radio frequency generator 22 is arranged to supply all the plasma cells Cx together by means of an adapted switching device. While all the plasma cells Cx are supplied by the radio frequency generator 22, each of the plasma cells Cx can be activated or deactivated individually through the high voltage DC generator 21.

[0063] The control unit 2 may further include or be connected to one or more human machine interfaces, such as a display and a keyboard. The control unit 2 may further include a program adapted to perform the printing of the parts.

[0064] FIG. 6 shows an example of the control of the plasma cell Cx of the present plasma device 1. The first line L1 shows the activation cycle of the plasma cell, where Tx means the ignition duration of the plasma cell. Tx can be about 10 ms to 1 or 2 seconds. Tx can be about 500 ms.

[0065] Line L2 shows an activation pulse Ta applied from the control bus. The voltage is low, about 3.3 volts. The pulse duration is about 50 μs. Line L4 shows the corresponding activation pulse of the high voltage DC unit. In this way, the high voltage DC unit is only used to initiate the ignition of the plasma. The RF generator is active during the ignition period Tx.

[0066] To switch off the plasma cell Cx, a deactivation pulse Ti is initiated to the RF generator 23, as shown by line L3. Line L6 shows the profile of the RF output power when multiple plasma cells are successively activated and deactivated.

[0067] The present disclosure further describes a process for efficiently marking a manufactured article M with a local 2D representation, which in detail comprises the step of placing a surface M1 close to a plasma cell Cx of a plasma device 1. The distance between the surface M1 and the plasma cell can be, for example, about 0.3 to about 3 mm.

[0068] The process also includes the step of independently activating the plasma cells Cx of the plasma device 1. Each plasma cell is activated according to the method described above.

[0069] Activation of the plasma cell may be performed while the article of manufacture M and the head 4 of the plasma device are fixed in relation to each other.

[0070] Alternatively, any step of moving the article of manufacture M relative to the head 4 of the plasma device 1, either in one direction or in two planar directions, can be performed while the plasma cell is activated.

[0071] The marking process results in a local 2D marking M2 on the surface M1, where the surface properties of the marked area are different from the properties of the unmarked surface. [Explanation of symbols]

[0072] 1 Plasma equipment 2. Control unit 3. Plasma Precursor Unit 31 Pipe 4 Head 41 Frame 6 Gas inlet 61 cores 62 Through hole 7. Inner Chamber 71 Side wall 8 Front Wall 81 Opening 9 Insulating Layer 10 Connected Components Cx Plasma Cell Px Plasma in a given cell x Tx Firing period in a given cell x Vx is the voltage applied to a given cell x Ux the inactivity period of a given cell M Manufactured articles M1 Surface of manufactured article M2 treated surface E1, E2 electrode

Claims

1. 1. A plasma device (1) comprising at least two plasma cells (Cx), each plasma cell having a gas inlet (6) with a through hole (62) and a core (61), an internal chamber (7) defined by side walls (71), and a front wall (8) with a front opening (81), said gas inlet being connected to a plasma precursor unit (3), said front wall comprising a first electrode (E1) and a second electrode (E2) separated by an insulating layer (9), and further comprising a control unit (2), wherein the first and second electrodes of a given plasma cell are independent of the corresponding first and second electrodes of an adjacent plasma cell and are independently connected to the control unit (2), and wherein the control unit (2) comprises a high voltage pulse generator (21) and a radio frequency generator (22), both of which are mutually protected by one or more filtering elements (23).

2. 2. The plasma device according to claim 1, characterized in that the plasma cells (Cx) are arranged in a frame (41) and the distance separating the front openings (81) of two adjacent plasma cells is less than 1 mm.

3. 3. The plasma device according to claim 1, wherein the diameter of the through hole (62) is between about 0.005 mm and 0.8 mm.

4. 4. The plasma device according to claim 1, wherein the height of the inner chamber is about 0.1 mm to about 20 mm.

5. 5. The plasma device according to claim 1, wherein the diameter of the inner chamber (7) corresponds to 3 to 5 times the diameter of the through-hole (62), or is of the same order of magnitude as the diameter of the through-hole (62), or corresponds to one tenth, one half or one third of the diameter of the through-hole (62).

6. 6. The plasma device according to claim 1, characterized in that the output power of the radio frequency generator (22) depends on the number of activated plasma cells and that the one or more filtering elements (23) comprise a matching unit ensuring the best adaptation of the impedance of the plasma circuit to the impedance of the radio frequency generator unit (22).

7. 7. Plasma device according to any one of the preceding claims, characterized in that the power dependence of the radio frequency output is managed by the control unit (2).

8. 8. The plasma device according to claim 1, wherein the high voltage pulse generator (21) comprises a number of high voltage DC units, the number of which corresponds to the number of plasma cells.

9. 9. The plasma device according to claim 1, characterized in that a high voltage pulse generator (21) activates the plasma cell or cells independently with an initiation pulse and a radio frequency generator (23) maintains the ignition of the plasma.

10. 10. The plasma device according to claim 1, wherein the activated plasma cell is deactivated with a deactivation pulse.

11. A control unit (2) adapted to individually control plasma cells of a plasma cell array, said control unit comprising a high voltage pulse generator (21), a radio frequency generator (22), both of which are mutually protected by one or more filtering elements (23), and a coupling means adapted to plug in said plasma cell array.

12. The control unit according to claim 11, wherein the high voltage pulse generator (21) comprises a number of units, the number of which is adaptable according to the number of plasma cells to be controlled.

13. 13. A control unit according to claim 12, wherein said units of high voltage pulse generator (21) are activated and deactivated independently.

14. A control unit according to any one of claims 11 to 13, further comprising a switching device adapted to supply all said plasma cells together with said radio frequency generator (22).

15. A method for treating a surface (M1) of a product (M), comprising the steps of: - placing a surface (M1) close to a plasma cell (Cx) of a plasma device (1) according to any one of claims 1 to 10, - independently activating the plasma cells (Cx) of said plasma device (1) so as to provide a localized 2D marking (M2) on the surface (M1); The method includes:

16. 15. The method according to claim 14, characterized in that the surface of the product is treated in-line through a continuous flow or in stages.

17. Manufactured article (M) having a surface (M2), characterized in that the surface (M2) is patterned or marked according to the method of claim 12 or 13.

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