Dielectric heating device and liquid spraying system

Abstract

This application provides a dielectric heating device and a liquid ejection system, wherein the dielectric heating device uniformly heats a medium. The dielectric heating device includes: a conveying section for conveying the medium; an electrode unit having a first electrode and a second electrode facing the medium in a first direction and subjected to an alternating current voltage, the electrode unit heating the medium by dielectric heating; and a control section for controlling the conveying section. The second electrode is configured to surround the first electrode when viewed along the first direction. The first electrode has a first conductor and a second conductor protruding from the first conductor toward the medium. When projected onto a plane perpendicular to the first direction, the second conductor is covered by the first conductor.

Description

Technical Field

[0001] This disclosure relates to dielectric heating devices and liquid ejection systems. Background Technology

[0002] Regarding dielectric heating devices, Patent Document 1 discloses a device comprising a planar first electrode and a cylindrical second electrode. The first electrode has a circular aperture, and the second electrode has an end located within the region of the aperture when viewed from the vertical direction of the first electrode. Patent Document 1 describes a method for uniformly heating an object by radially generating an electric field from the second electrode onto the first electrode.

[0003] Patent Document 1: Japanese Patent Application Publication No. 2017-16742

[0004] However, in the device of Patent Document 1, uneven heating sometimes occurs due to a localized area of ​​extremely weak electric field strength directly below the second electrode. Therefore, there is room for further improvement in terms of uniformly heating the object to be heated. Summary of the Invention

[0005] According to a first aspect of this disclosure, a dielectric heating device is provided. The dielectric heating device includes: a conveying section for conveying a medium; an electrode unit having a first electrode and a second electrode facing the medium in a first direction and subjected to an alternating current voltage, the electrode unit heating the medium by dielectric heating; and a control section for controlling the conveying section. The second electrode is configured to surround the first electrode when viewed along the first direction, the first electrode having a first conductor and a second conductor protruding from the first conductor toward the medium, and when projected onto a plane perpendicular to the first direction, the second conductor is covered by the first conductor.

[0006] According to a second aspect of this disclosure, a liquid ejection system is provided. The liquid ejection system includes: a dielectric heating device as described above; and a liquid ejection section for coating the medium with liquid. Attached Figure Description

[0007] Figure 1 This is a schematic diagram showing the general configuration of the liquid ejection system as a first embodiment.

[0008] Figure 2 This is a perspective view showing the schematic configuration of the dielectric heating device in the first embodiment.

[0009] Figure 3 This is a perspective view showing the schematic configuration of the electrode unit in the first embodiment.

[0010] Figure 4 It is shown Figure 3 A diagram of the IV-IV cross section of the first conductor in the image.

[0011] Figure 5 It is shown Figure 3 A diagram of the VV cross-section of the first conductor in the image.

[0012] Figure 6 This is a perspective view showing a portion of the first electrode in the first embodiment.

[0013] Figure 7 This is a first side view of the first electrode.

[0014] Figure 8 This is a second side view of the first electrode.

[0015] Figure 9 This is a first explanatory diagram showing the distribution of heating energy in the first embodiment.

[0016] Figure 10 This is an illustrative diagram showing the distribution of heating energy in other methods.

[0017] Figure 11 This is a three-dimensional view of the electrode unit in other configurations.

[0018] Figure 12 This is a perspective view showing a portion of the first electrode of the electrode unit in the second embodiment.

[0019] Figure 13 This is a first explanatory diagram showing the distribution of heating energy in the second embodiment.

[0020] Figure 14 This is a second explanatory diagram showing the distribution of heating energy in the first embodiment.

[0021] Figure 15 This is a second explanatory diagram showing the distribution of heating energy in the second embodiment.

[0022] Figure 16 This is a perspective view showing the schematic configuration of the electrode unit in the third embodiment.

[0023] Figure 17 This is a top view of the electrode unit in the third embodiment.

[0024] Figure 18 This is a diagram schematically illustrating a first example of an electrode unit in other embodiments.

[0025] Figure 19 This is a diagram schematically illustrating a second example of an electrode unit in another embodiment.

[0026] Figure 20This is a diagram schematically illustrating a third example of an electrode unit in other embodiments.

[0027] Explanation of reference numerals in the attached figures

[0028] 20, 20b, 20c, 20d, 20e, 20f, 20p…electrode unit, 21…first electrode unit column, 22…second electrode unit column, 30, 30b, 30c, 30d, 30e…first electrode, 30p…electrode, 31…first conductor, 32, 32b, 32c…second conductor, 33…first end, 34…second end, 35…middle part, 36…one end, 37…one end, 38…the other end, 3 9…the other end, 40…the second electrode, 50…coil, 55…wire, 56…connecting component, 80…voltage application part, 90…third electrode, 100…dielectric heating device, 110…substrate, 180…second control part, 200…liquid ejection system, 205…liquid ejection device, 210…liquid ejection part, 250…first control part, 320…conveying part, 321…first conveying part, 322…second conveying part, 323…roller. Detailed Implementation

[0029] A. First implementation method:

[0030] Figure 1 This is a schematic diagram showing the general configuration of the liquid ejection system 200 as a first embodiment. Figure 1 The diagram shows arrows indicating the X, Y, and Z directions, which are orthogonal to each other. The X and Y directions are parallel to the horizontal plane, and the Z direction is vertically upward. In other diagrams, the arrows indicating the X, Y, and Z directions are also aligned with the directions shown in the diagram. Figure 1 The corresponding methods are illustrated appropriately. In the following explanation, when a direction is specified, the direction indicated by the arrow in each diagram is designated as "+", and its opposite direction as "-", and positive and negative signs are used in the direction description. Hereinafter, the +Z direction will be referred to as "up", and the -Z direction as "down". Furthermore, in this specification, orthogonality includes a range of 90° ± 10°. Additionally, the plane along the X and Y directions will be referred to as the "XY plane".

[0031] The liquid ejection system 200 includes a dielectric heating device 100 with an electrode unit 20, a liquid ejection device 205, and a conveying unit 320. In this embodiment, the liquid ejection system 200 conveys a medium Md through the conveying unit 320 while simultaneously ejecting liquid onto the medium Md via the liquid ejection device 205 for coating. The liquid coated on the medium Md is then heated and dried by the electrode unit 20 of the dielectric heating device 100. Alternatively, the liquid ejection device 205 can be described as coating the medium Md with liquid heated by the electrode unit 20. The electrode unit 20 is also referred to as a heater.

[0032] As the medium Md, materials such as paper, cloth, and film are used. The cloth used as the medium Md is formed by weaving fibers such as cotton, linen, polyester, silk, and rayon, or fibers blended from these. In this embodiment, sheet-like cotton cloth is used as the medium Md. Various inks are used as the liquid applied to the medium Md. In this embodiment, a water-based ink with water as its main component is used as the liquid. In this specification, the main component of a liquid refers to a substance whose mass fraction is 50% or more in the substances contained in the liquid. In other embodiments, in addition to inks, any liquid other than various coloring materials, electrode materials, samples of organic or inorganic matter from living organisms, lubricating oils, resin solutions, etching solutions, etc., can be used as the liquid.

[0033] The conveying unit 320 conveys the medium Md. In this embodiment, the conveying unit 320 is configured as a roller mechanism that conveys the medium Md by a drive roller 323. The conveying unit 320 has a first conveying unit 321 provided in the liquid dispensing device 205 and a second conveying unit 322 provided in the dielectric heating device 100. The first conveying unit 321 and the second conveying unit 322 each have: a roller 323; and a drive unit (not shown), which is configured by a motor or the like for driving the roller 323. In other embodiments, the conveying unit 320 may also be configured as a belt mechanism that conveys the medium Md by a drive belt.

[0034] The first conveying unit 321 is positioned in the +Y direction of the second conveying unit 322. In this embodiment, the first conveying unit 321 and the second conveying unit 322 intermittently convey the sheet-like medium Md in the -Y direction. More specifically, the first conveying unit 321 and the second conveying unit 322 alternately and repeatedly perform moving and stationary operations. In the moving operation, the roller 323 is moved to move the medium Md in the -Y direction, and in the stationary operation, the roller 323 is not moved to keep the medium Md stationary.

[0035] In this embodiment, the liquid ejection device 205 is configured as an inkjet printer that prints by coating a medium Md with liquid ink ejected from it. Therefore, the liquid ejection system 200 can also be described as a printing system equipped with an inkjet printer. The liquid ejection device 205 includes: a liquid ejection unit 210 for coating the medium Md with liquid ejected from it; a first control unit 250; and the aforementioned first transport unit 321.

[0036] The liquid ejection section 210 is configured as a piezoelectric or thermal liquid ejection head, for example, and has one or more head chips (not shown). Each head chip has a flow path for liquid flow and a nozzle for ejecting liquid. The ink ejected from each head chip may be the same color or different color. In addition, the liquid ejection section 210 may be configured to move back and forth relative to the medium Md in a direction orthogonal to the Z direction and intersecting the Y direction via a carriage (not shown), or it may be configured as a so-called linear head that does not move back and forth relative to the medium Md and is fixed in position.

[0037] In this embodiment, the ink used as a liquid is a pigment ink containing resin. The resin contained in the ink has the function of firmly fixing the pigment to the medium Md by itself. Such a resin is used, for example, in a state in which a resin that is sparingly soluble or insoluble in solvents such as water is dispersed in the solvent in the form of microparticles, i.e., in an emulsion state or a suspension state. As such a resin, examples include acrylic resin, styrene acrylic resin, fluorene resin, urethane resin, polyolefin resin, rosin-modified resin, terpene resin, polyester resin, polyamide resin, epoxy resin, vinyl chloride resin, vinyl chloride-vinyl acetate copolymer, ethylene vinyl acetate resin, etc. Two or more of these resins may also be used in combination. Such a resin is also referred to as resin.

[0038] The first control unit 250 is configured as a computer, which includes one or more processors, a storage device, and an input / output interface for signal input and output to the outside. In this embodiment, the first control unit 250 controls the liquid ejection unit 210 and the first conveying unit 321 to intermittently convey the medium Md in the -Y direction while ejecting liquid and adhering it to the medium Md. More specifically, the first control unit 250 prints on the medium Md while repeatedly ejecting liquid from the medium Md during the stationary operation of the first conveying unit 321 and moving the medium Md in the -Y direction through the moving operation of the first conveying unit 321. In other embodiments, the first control unit 250 may be configured, for example, by a combination of multiple circuits. The first control unit 250 is also referred to as the ejection control unit.

[0039] Figure 2 This is a perspective view showing the schematic configuration of the dielectric heating device 100 in the first embodiment. Figure 1 and Figure 2As shown, the dielectric heating device 100 includes: an electrode unit 20 for heating a dielectric medium Md via dielectric heating; a voltage application unit 80 for applying an alternating current voltage to the electrode unit 20; a second control unit 180; and the aforementioned second conveying unit 322. In this embodiment, the dielectric heating device 100 conveys the dielectric medium Md via the second conveying unit 322 while simultaneously heating the dielectric medium Md using an alternating current electric field generated by the electrode unit 20, thereby drying the dielectric medium Md. When described as "heating the dielectric medium Md using an alternating current electric field," this includes not only heating the dielectric medium Md itself using an alternating current electric field but also heating liquids, solids, or other adhering substances attached to the dielectric medium Md using an alternating current electric field.

[0040] The voltage application unit 80 is electrically connected to the first electrode 30 and the second electrode 40 of the electrode unit 20 (described later), and applies an AC voltage with a predetermined driving frequency f0 to the first electrode 30 and the second electrode 40. In this embodiment, the voltage application unit 80 is configured as a high-frequency power supply including a high-frequency voltage generation circuit, and has a crystal oscillator (not shown), a PLL (Phase-Locked Loop) circuit, and a power amplifier, respectively. In other embodiments, the voltage application unit 80 may also be configured as an inverter with a switching circuit, which has switching elements such as transistors. The potential applied to the first electrode 30 or the second electrode 40 may also be a reference potential. The reference potential is a constant potential that serves as a reference for the high-frequency voltage, such as a ground potential.

[0041] In this embodiment, a high-frequency voltage is applied to each electrode of the electrode unit 20. In this specification, "high frequency" refers to a frequency of 1 MHz or higher. More specifically, in this embodiment, 13.56 MHz, one of the Industrial Scientific and Medical Bands (ISM), is used as the driving frequency f0. It should be noted that since the dielectric loss tangent of water is maximum around 20 GHz, applying high-frequency voltages of 2.45 GHz and 5.8 GHz in the ISM band to each electrode of the electrode unit 20 allows for more efficient heating of the liquid attached to the medium Md. On the other hand, even at relatively low driving frequencies f0, such as 13.56 MHz and 40.68 MHz, good heating efficiency can be obtained when heating ink. This is because at driving frequencies f0 of 13.56 MHz and 40.68 MHz, the dielectric loss tangent of water in the ink is low, and Joule heating is easily generated by the resistance of pigment components in the ink.

[0042] The second control unit 180, like the first control unit 250, is configured using a computer. The second control unit 180 controls the second conveying unit 322 to convey the medium Md. In this embodiment, regardless of whether the second conveying unit 322 is moving or stationary, an AC voltage is applied to the electrode unit 20 to heat the medium Md. Hereinafter, the second control unit 180 will be simply referred to as the control unit.

[0043] like Figure 2 As shown, in this embodiment, the dielectric heating device 100 has seven electrode units 20. More specifically, in this embodiment, the dielectric heating device 100 has a first electrode unit column 21 and a second electrode unit column 22. The first electrode unit column 21 is composed of four electrode units 20 arranged at equal intervals in the X direction. The second electrode unit column 22 is composed of three electrode units 20 arranged at equal intervals in the X direction. The second electrode unit column 22 is positioned in the Y direction opposite to the first electrode unit column 21. The first electrode unit column 21 and the second electrode unit column 22 are arranged to be separated by a distance D in the Y direction. In this embodiment, the distance D is approximately the same as the distance that the medium Md moves by one movement operation of the first conveying unit 321 and is approximately the same as the size of the electrode unit 20 in the Y direction. In other embodiments, for example, the number of electrode units 20 may be six or less, or eight or more. Furthermore, the arrangement of each electrode unit 20 can be arbitrary.

[0044] Figure 3 This is a perspective view showing the schematic configuration of the electrode unit 20 in this embodiment. Figures 1-3 As shown, the electrode unit 20 has a first electrode 30 and a second electrode 40. Additionally, the electrode unit 20 in this embodiment has a coil 50.

[0045] The first electrode 30 and the second electrode 40 are conductive materials, such as those formed from metals, alloys, or conductive oxides. The first electrode 30 and the second electrode 40 can be formed from the same material or from different materials. For example, to maintain their orientation and strength, the first electrode 30 and the second electrode 40 can be disposed on a substrate formed from a material with a low dielectric loss tangent and low conductivity, or they can be supported by other components.

[0046] The first electrode 30 and the second electrode 40 are opposite to the medium Md in a first direction. The first direction includes a direction along one side of the same axis and both its opposite directions; in this embodiment, it is the Z direction.

[0047] The first electrode 30 has a first conductor 31 and a second conductor 32. The second conductor 32 protrudes from the first conductor 31 toward the dielectric Md and is covered by the first conductor 31 when projected onto the XY plane. The first conductor 31 and the second conductor 32 can be separate or integrated.

[0048] The first conductor 31 in this embodiment has an elongated shape, having a long side direction along a second direction and a short side direction along a third direction. The second direction is orthogonal to the first direction. The second direction includes a direction along one side of the same axis and both its opposite directions, which is the X direction in this embodiment. The third direction is orthogonal to both the first and second directions. The third direction includes a direction along one side of the same axis and both its opposite directions, which is the Y direction in this embodiment.

[0049] In this embodiment, the first conductor 31 is generally plate-shaped with a curved surface that convexes in the -Z direction. When viewed along the Z direction, the first electrode 30 has an elongated shape with the X direction as its long side and the Y direction as its short side. Alternatively, the first conductor 31 in this embodiment can be described as having a boat-shaped shape extending along the X direction.

[0050] Figure 4 It is shown Figure 3 A diagram of the IV-IV cross section of the first conductor 31 in the diagram. Figure 5 It is shown Figure 3 A cross-sectional view of the first conductor 31 in the diagram. (See diagram below.) Figure 3 and Figure 5 As shown, the first conductor 31 has an arc shape that bulges in the -Z direction when viewed along the X direction. Similarly, as Figure 3 and Figure 4 As shown, the first conductor 31 has an arc shape that bulges in the -Z direction when viewed along the Y direction.

[0051] like Figures 3-5 As shown, the first conductor 31 in this embodiment has an overall curved shape and few sharp corners. This helps to suppress the concentration of the electric field at specific locations such as the ends of the first conductor 31. Furthermore, in this embodiment, because the first conductor 31 has a boat-shaped shape, the distance in the Z-direction between the ends of the first conductor 31 in the long and short directions and the dielectric Md is longer than the distance in the Z-direction between the center of the first conductor 31 in the long and short directions and the dielectric Md. This further helps to suppress the concentration of the electric field at the ends of the first electrode 30. Additionally, Figure 5 The radius of curvature R of the end of the first conductor 31 in the X direction shown is compared to Figure 4The radius of curvature r of the end of the first conductor 31 in the Y direction is large. As a result, in particular, it is possible to more effectively suppress the concentration of the electric field at the end of the long side of the first conductor 31.

[0052] Figure 6 This is a perspective view showing a portion of the first electrode 30. Figure 7 This is a first side view of the first electrode 30. Figure 8 This is a second side view of the first electrode 30. Figure 7 The first electrode 30 is shown as viewed along the X direction. Figure 8 The first electrode 30 is shown as viewed along the Y direction.

[0053] like Figure 6 As shown, in this embodiment, the second conductor 32 has an elongated shape when viewed along the Z direction, and this elongated shape has a long side direction along the X direction and a short side direction along the Y direction. Additionally, as... Figure 7 As shown, in this embodiment, the second conductor 32, when viewed along the X direction, has a shape symmetrical in the Y direction with respect to the straight line L1 passing through the center of the first conductor 31 in the Y direction. Therefore, when viewed along the X direction, the center position of the first conductor 31 in the Y direction coincides with the center position of the second conductor 32 in the Y direction. Furthermore, as... Figure 8 As shown, the second conductor 32 has a shape that is symmetrical in the X direction with respect to the straight line L2 passing through the center of the first conductor 31 in the X direction when viewed along the Y direction. Therefore, when viewed along the Y direction, the center position of the first conductor 31 in the X direction coincides with the center position of the second conductor 32 in the X direction.

[0054] like Figures 6 to 8 As shown, the second conductor 32 has the following in the Z direction: a first end portion 33 connected to the first conductor 31; a second end portion 34 on the opposite side of the first conductor 31; and a middle portion 35 disposed between the first end portion 33 and the second end portion 34. In this embodiment, the second end portion 34, the middle portion 35, and the first end portion 33 are arranged sequentially from bottom to top. Figure 7 As shown, the width Wm of the middle portion 35 in the Y direction is wider than the width W1 of the first end portion 33 in the Y direction and the width W2 of the second end portion 34 in the Y direction. Furthermore, when projected onto the XY plane perpendicular to the Z direction, the first end portion 33 and the second end portion 34 are covered by the middle portion 35. That is, when projected onto the XY plane, the entire first end portion 33 and the entire second end portion 34 overlap with the middle portion 35. It should be noted that in this embodiment, the widths W1 and W2 are the same.

[0055] like Figure 7As shown, in this embodiment, when viewed along the X direction, the second conductor 32 has a cross shape. More specifically, the second conductor 32 has: a plate-shaped first portion P1 extending along the X and Z directions; a rectangular plate-shaped second portion P2 extending along the X and Y directions, protruding from the central portion Pc of the first portion P1 in the Z direction towards the +Y direction; and a rectangular plate-shaped third portion P3 extending along the X and Y directions, protruding from the central portion Pc towards the -Y direction. The first portion P1 is configured to extend downward from the central portion of the first conductor 31 in the Y direction when viewed along the X direction. The first end portion 33 is formed from the upper end portion of the first portion P1. The second end portion 34 is formed from the lower end portion of the first portion P1. The middle portion 35 is formed by the central portion Pc, the second portion P2, and the third portion P3.

[0056] like Figure 8 As shown, in this embodiment, one end 37 of the second conductor 32, including one end 36 in the X direction, has a shape in which the distance between it and the dielectric Md in the Z direction gradually increases in the X direction from the opposite side of one end 36 toward one end 36. Similarly, in this embodiment, the other end 39 of the second conductor 32, including the other end 38 in the X direction, has a shape in which the distance between it and the dielectric Md in the Z direction gradually increases in the X direction from the opposite side of the other end 38 toward the other end 38. More specifically, the portion of the first portion P1 located below the second portion P2 and the third portion P3 is formed as a generally trapezoidal plate that convexes downwards.

[0057] like Figure 3 As shown, the second electrode 40 is configured to surround the first electrode 30 when viewed along the Z direction. In this embodiment, the second electrode 40 has a flattened elliptical ring shape in both the X and Y directions. Similar to the first electrode 30, when viewed along the Z direction, the second electrode 40 has an elongated shape with the X direction as its long side and the Y direction as its short side. The first electrode 30 and the second electrode 40 are configured such that the shortest distance between them is less than one-tenth of the wavelength of the electromagnetic field output from the electrode unit 20.

[0058] In other embodiments, the second electrode 40 may also have a circular, rectangular, or polygonal ring shape, for example. Furthermore, when stated as "the second electrode 40 is configured to surround the first electrode 30 when viewed along the Z direction," it is sufficient that the second electrode 40 surrounds more than half of the first electrode 30 when viewed along the Z direction; it is not necessary for the second electrode 40 to surround the entire area of ​​the first electrode 30 without gaps. Therefore, in other embodiments, the second electrode 40 may, for example, have a so-called C-shaped or U-shaped shape when viewed along the Z direction. Additionally, the second electrode 40 may, for example, have a shape that surrounds the first electrode 30 entirely while being intermittently interrupted when viewed along the Z direction. In this case, the second electrode 40 is configured such that when an AC voltage is applied to both the first electrode 30 and the second electrode 40, each portion of the second electrode 40 is given the same potential.

[0059] like Figure 1 and Figure 2 As shown, both the first electrode 30 and the second electrode 40 are disposed on a substrate 110 arranged parallel to the X and Y directions. More specifically, the first electrode 30 is configured such that the lower end face of the first end 33 of the first conductor 31 contacts the upper surface of the substrate 110. The second electrode 40 is configured such that the lower surface of the second electrode 40 contacts the upper surface of the substrate 110. Therefore, in this embodiment, the shortest distance in the Z direction between the first electrode 30 and the dielectric Md is equal to the shortest distance in the Z direction between the second electrode 40 and the dielectric Md. Alternatively, the lower end face of the first end 33 and the lower surface of the second electrode 40 are disposed on the same plane.

[0060] The substrate 110 prevents liquids such as ink coated on the dielectric Md from adhering to the first electrode 30 and the second electrode 40, and, in the case of a cloth dielectric Md, prevents the lint of the dielectric Md from adhering to the first electrode 30 and the second electrode 40. In this embodiment, a single substrate 110 formed of glass is used for all electrode units 20. In other embodiments, the substrate 110 may also be formed of alumina, for example. Alternatively, the substrate 110 may be individually provided corresponding to each electrode unit 20.

[0061] return Figure 3 The following explanation is provided. In this embodiment, the first electrode 30 is electrically connected to the voltage application unit 80 via a wire 55, a coil 50, and the inner conductor IC1 of a coaxial cable. The second electrode 40 is electrically connected to the voltage application unit 80 via a connecting member 56 disposed on the upper part of the second electrode 40, the outer conductor of a coaxial cable (not shown), etc.

[0062] In this embodiment, one end of the coil 50 is electrically connected in series with the first electrode 30 via a wire 55, and the other end of the coil 50 is connected to... Figure 1 and Figure 2 The voltage application section 80 shown is electrically connected in series. In this embodiment, the coil 50 is composed of a solenoid coil and is configured such that its length direction is along the Z direction. The shape, length, cross-sectional area, number of turns, material, etc. of the coil 50 are selected, for example, according to the driving frequency f0, to achieve impedance matching between the electrode unit 20 and the voltage application section 80. In other embodiments, one end of the coil 50 may be connected in series with the second electrode 40 instead of the first electrode 30.

[0063] By applying an alternating voltage with a driving frequency f0 to the first electrode 30 and the second electrode 40, an electromagnetic field with a wavelength corresponding to the driving frequency f0 is generated from the first electrode 30 and the second electrode 40. The intensity of this electromagnetic field is extremely strong near the first electrode 30 and the second electrode 40, and becomes extremely weak at a distance. In this specification, the electromagnetic field generated near the first electrode 30 and the second electrode 40 by applying an alternating voltage is also referred to as the "nearby electromagnetic field". "Nearby" of the first electrode 30 and the second electrode 40 refers to a range of distances from the first electrode 30 and the second electrode 40 that is less than 1 / 2π of the wavelength of the generated electromagnetic field. A range farther than "nearby" is also referred to as "far away". In addition, in this specification, the electromagnetic field generated far from the first electrode 30 and the second electrode 40 by applying an alternating voltage is also referred to as the "far-field electromagnetic field". The far-field electromagnetic field is equivalent to the electromagnetic field used in communication via a general communication antenna, etc.

[0064] As described above, by ensuring that the shortest distance between the first electrode 30 and the second electrode 40 is less than one-tenth of the wavelength of the electromagnetic field, the density of the electromagnetic field generated from the first electrode 30 and the second electrode 40 can be attenuated near the first electrode 30 and the second electrode 40. Therefore, by appropriately maintaining the distance between the medium Md and the first electrode 30 and the second electrode 40, it is possible to efficiently heat the liquid attached to the medium Md using the electric field generated near the first electrode 30 and the second electrode 40, while suppressing the radiation of electromagnetic fields from distant locations near the first electrode 30 and the second electrode 40. In particular, in this embodiment, since the second electrode 40 is configured to surround the first electrode 30 when viewed along the Z direction, the radiation of electromagnetic fields from distant locations near the first electrode 30 and the second electrode 40 can be further suppressed.

[0065] By applying an alternating current voltage to the electrode unit 20, a high voltage is generated at one end of the coil 50. This increases the strength of the electric field generated from the first electrode 30 and the second electrode 40. It should be noted that the coil 50 is preferably configured such that the distance between one end of the coil 50 and the first electrode 30 is as small as possible. If the distance between one end of the coil 50 and the first electrode 30 is large, the high voltage generated at one end of the coil 50 will cause an electric field that does not contribute to the heating of the dielectric Md to be generated between the coil 50 and the first electrode 30, or between the wire 55 and the second electrode 40, potentially reducing the effectiveness of increasing the strength of the electric field generated from the first electrode 30 and the second electrode 40. Conversely, by bringing the distance between one end of the coil 50 and the first electrode 30 closer, the generation of such an electric field that does not contribute to the heating of the dielectric Md can be suppressed, thus effectively increasing the strength of the electric field generated from the first electrode 30 and the second electrode 40. It should be noted that in other embodiments, the electrode unit 20 may not have a coil 50; for example, the first electrode 30 may be formed in a meandering shape to perform the same function as the coil 50.

[0066] Figure 9 This is a first explanatory diagram showing the distribution of heating energy in the first embodiment. Figure 9 The results of simulating heating of dielectric Md using electrode unit 20 via electromagnetic field simulation are shown. More specifically, Figure 9 Simulation results are shown for the power consumption density in region Rs when a sheet-like dielectric Md with its upper surface uniformly coated with ink is positioned opposite a first electrode 30 and a second electrode 40 of an electrode unit 20, and a high-frequency voltage of 13.56 MHz is applied to the first electrode 30 and the second electrode 40. Region Rs is a rectangular area on the upper surface of the dielectric Md that overlaps with the first electrode 30 and the second electrode 40 when viewed along the Z direction. In this simulation, the distribution of power consumption density in region Rs is shown in 15 levels using color differences. For example, dark navy blue represents the area with the lowest power consumption density, and red represents the area with the highest power consumption density. Figure 9 In a given system, a higher power consumption density in a certain part means that more heating energy is required in that part.

[0067] Figure 10 This is an illustrative diagram showing the distribution of heating energy in other methods. Figure 11 This is a three-dimensional view of electrode unit 20p in other configurations. Figure 10 The results of simulating the heating of medium Md using electrode unit 20p are shown by electromagnetic field simulation. Figure 10 The simulation conditions, in addition to using electrode unit 20p, were the same as... Figure 9 The simulation is the same. Additionally, Figure 10The display format of the simulation results and Figure 9 The simulation is the same. For example... Figure 11 As shown, the configuration of electrode unit 20p is equivalent to the configuration after the first electrode 30 of electrode unit 20 is replaced by electrode 30p. Electrode 30p is composed only of a portion having the same shape as the first conductor 31, and the lower surface of its central portion is disposed on the same plane as the lower surface of the second electrode 40 of electrode unit 20p. Hereinafter, the electrode that is surrounded by the second electrode 40 when viewed in the Z direction, like the first electrode 30 and electrode 30p, will also be referred to as the inner electrode. The central portion of the inner electrode in the X and Y directions is disposed on the same plane as the lower surface of the second electrode 40 of electrode unit 20p. Figure 9 and Figure 10 The central part of the region Rs shown overlaps.

[0068] exist Figure 9 and Figure 10 In the simulation results, heating regions Ht1 and Htp, which expand in a roughly elliptical shape to surround the empty region described later, were observed within region Rs. The outer edges of heating regions Ht1 and Htp roughly coincide with the positions where they overlap with the outer edge of the second electrode 40 on the upper surface of the dielectric Md. Figure 9 and Figure 10 In the simulation results, the power consumption density is at level four in most of the heating regions Ht1 and Htp. For example, Figure 9 Location Pt1 shown Figure 10 Location Pt2 shown is a site with an energy consumption density of level four.

[0069] exist Figure 9 and Figure 10 In the process, empty regions BR1 and BRp are generated in the central part of region Rs. The empty region is a locally generated area on the upper surface of dielectric Md, overlapping with the central electrode, when viewed along the Z direction, where the nearby electric field strength is extremely weak. Therefore, in the empty region, dielectric Md is almost not heated. Figure 9 and Figure 10 In the simulation results, the power consumption density in empty regions BR1 and BRp is at level one. Level one power consumption density is less than one-third of the power consumption density at level four mentioned above. Empty regions BR1 and BRp can also include areas with almost zero power consumption density.

[0070] Figure 9 The area ratio of the empty region BR1 shown Figure 10 The area of ​​the empty region BRp shown is narrow. The reason for this is that, in this embodiment, by forming an electric field between the second conductor 32 and the second electrode 40 that facilitates the heating of the dielectric Md, the area where the electric field strength is extremely weak is reduced.

[0071] It should be noted that, although the illustration is omitted, assuming that the inner electrode is formed only by a portion having the same shape as the second conductor 32, the deviation of heating energy near the empty region increases compared to the case where the inner electrode is formed by the first conductor 31 and the second conductor 32. Furthermore, in this embodiment, by making the width of the middle portion 35 of the second conductor 32 wider than the widths of the first end portion 33 and the second end portion 34, the deviation of heating energy near the empty region BR1 can be further suppressed. In particular, in this embodiment, since the first end portion 33 and the second end portion 34 are covered by the middle portion 35 when projected onto the XY plane, the deviation of the electric field strength near the empty region BR1 can be further suppressed.

[0072] Unlike this embodiment, in the use of Figure 11 When the electrode unit 20p is used to heat the medium Md, uneven heating may sometimes occur on the medium Md due to insufficient heating in the empty region BRp. In particular, when the medium Md is intermittently transported as in this embodiment, insufficient heating is likely to occur in the areas of the medium Md that become empty regions BRp during stationary operation. In addition, insufficient heating from the empty regions BRp can also easily occur, for example, when the moving speed of the medium Md relative to the electrode unit 20p is relatively high. Therefore, when using the electrode unit 20p to heat the medium Md, it is necessary, for example, to configure the electrode unit 20p to compensate for insufficient heating, to transport the medium Md sufficiently slowly relative to the electrode unit 20p, and to move the medium Md back and forth little by little relative to the electrode unit 20p to prevent the areas of the medium Md that become empty regions BRp from becoming fixed, etc. In contrast, in this embodiment, since the area of ​​the empty region can be made smaller, the degree of freedom in the configuration of the electrode unit 20 and the transport mode of the medium Md can be increased. More specifically, for example, even when the moving speed of the medium Md relative to the electrode unit 20 is relatively fast, the possibility of uniformly heating the medium Md will be improved. Furthermore, even when the medium Md is moved back and forth little by little relative to the electrode unit 20 to compensate for insufficient heating, as described above, its movement amplitude can be made smaller.

[0073] According to the dielectric heating device 100 in the first embodiment described above, the first electrode 30 has a first conductor 31 and a second conductor 32 protruding from the first conductor 31 toward the dielectric Md. When projected onto an XY plane perpendicular to the Z direction, the second conductor 32 is covered by the first conductor 31. In this way, the area of ​​the empty region can be reduced by the second conductor 32. That is, the second conductor 32 can suppress the local generation of extremely weak electric fields in the region of the dielectric Md that overlaps with the first electrode 30. Therefore, the possibility of uniformly heating the dielectric Md is improved.

[0074] Furthermore, in this embodiment, when viewed along the Z direction, the first conductor 31 and the second conductor 32 have elongated shapes, with a long side along the X direction and a short side along the Y direction. Therefore, with the first conductor 31 having an elongated shape, the area of ​​the empty region can be effectively reduced by using the second conductor 32, which also has an elongated shape.

[0075] Furthermore, in this embodiment, the second conductor 32 has the following in the Z direction: a first end portion 33 connected to the first conductor 31; a second end portion 34 opposite to the first end portion 33; and a middle portion 35 disposed between the first end portion 33 and the second end portion 34, and its width in the Y direction is wider than that of the first end portion 33 and the second end portion 34. Therefore, for example, compared to a configuration without the middle portion 35 which is wider than the first end portion 33 and the second end portion 34, deviations in the electric field strength near empty areas can be more effectively suppressed. Consequently, the possibility of uniformly heating the dielectric Md is further increased.

[0076] Furthermore, in this embodiment, when projected onto the XY plane, the first end portion 33 and the second end portion 34 are covered by the middle portion 35. Therefore, deviations in the electric field intensity near the empty region can be further suppressed.

[0077] Furthermore, in this embodiment, the second conductor 32 has a cross shape when viewed along the X direction. Therefore, with a simple configuration, the area of ​​the empty region can be reduced and deviations in the electric field strength near the empty region can be suppressed.

[0078] Furthermore, in this embodiment, the end 37 of the second conductor 32, including one end 36 in the X direction, has a shape in which the distance between it and the dielectric Md in the Z direction gradually increases in the X direction from the opposite side of one end 36 toward one end 36. Therefore, it is possible to suppress the concentration of the electric field at one end 36.

[0079] Furthermore, in this embodiment, the radius of curvature R of the end portion of the first conductor 31 in the long side direction is larger than the radius of curvature r of the end portion of the first conductor 31 in the short side direction. Therefore, it is possible to suppress the concentration of the electric field at the end portion of the first conductor 31 in the long side direction.

[0080] Furthermore, in this embodiment, the shortest distance in the Z direction between the first electrode 30 and the dielectric Md is equal to the shortest distance in the Z direction between the second electrode 40 and the dielectric Md. Therefore, the possibility of uniformly heating the dielectric Md is further increased. In addition, when heating a sheet-like dielectric Md as in this embodiment, since an electric field along the surface direction of the dielectric Md is easily generated between the first electrode 30 and the second electrode 40, the dielectric Md can be heated more efficiently.

[0081] B. Second implementation method:

[0082] Figure 12 This is a partial perspective view showing the first electrode 30b of the electrode unit 20b in the second embodiment. In this embodiment, the second conductor 32b of the first electrode 30b differs from that in the first embodiment; it does not have a cross shape when viewed along the X direction. In the configuration of the electrode unit 20b and the dielectric heating device 100 in the second embodiment, the parts not specifically described are the same as in the first embodiment.

[0083] The second conductor 32b has a flat plate shape along both the X and Z directions. Therefore, when viewed along the X direction, the second conductor 32b has a so-called "I-shaped" shape that extends linearly along the Z direction. More specifically, in this embodiment, the shape of the second conductor 32b is such that the width Wm of the middle portion 35 of the second conductor 32 is the same as the width W1 of the first end portion 33 and the width W2 of the second end portion 34.

[0084] Figure 13 This is a first explanatory diagram showing the distribution of heating energy in the second embodiment. Figure 13 The results of simulating the heating of medium Md using electrode unit 20b are shown by electromagnetic field simulation. Figure 13 The simulation conditions, except for the use of electrode unit 20b, are the same as those described in the first embodiment. Figure 9 The simulation is the same. Additionally, Figure 13 The display format of the simulation results and Figure 9 The simulation is the same.

[0085] exist Figure 13 In the simulation results, with Figure 9 , Figure 10 Similarly, the heating region Ht2 was observed within region Rs. Figure 13In the simulation results, the power consumption density is at level four in most of the heating region Ht2. For example, Figure 9 The location shown, Pt3, represents a level four energy consumption density. Additionally, in... Figure 13 The central part of region Rs, with Figure 9 , Figure 10 Similarly, an empty region BR2 was generated. The area of ​​the empty region BR2 is... Figure 10 The area of ​​the empty region BRp shown is narrow. Therefore, in the second embodiment, similar to the first embodiment, it is assumed that the portion where the intensity of the nearby electric field is extremely weak is reduced.

[0086] Figure 14 This is a second explanatory diagram showing the distribution of heating energy in the first embodiment. Figure 15 This is a second explanatory diagram showing the distribution of heating energy in the second embodiment. Figure 14 It is magnification Figure 9 The graph shows the area near the empty region BR1 in region Rs. Figure 15 It is magnification Figure 13 The graph shows the empty region BR2 in region Rs. Figure 14 and Figure 15 The approximately identical ranges in medium Md are shown.

[0087] exist Figure 14 and Figure 15 In the diagram, areas with relatively high heating energy are marked with shaded lines. More specifically, areas with power consumption densities of levels 15 to 11 are marked with upward-right shaded lines, while areas with power consumption densities of levels 6 to 10 are marked with downward-right shaded lines. For example... Figure 14 and Figure 15 As shown, in the second embodiment, compared to the first embodiment, the regions with relatively higher heating energy are widely distributed near the empty region BR2. Thus, it can be seen that, compared to the second embodiment, the deviation in heating energy near the empty region is smaller in the first embodiment.

[0088] It should be noted that, in the second embodiment, for example, the insufficient heating in the empty region BR2 can also be compensated by making the parts with relatively large heating energy more widely distributed near the empty region BR2.

[0089] According to the second embodiment described above, the second conductor 32b has a flat plate shape along the Z and X directions. Therefore, the area of ​​the empty region can be reduced through a simpler configuration.

[0090] C. Third implementation method:

[0091] Figure 16This is a perspective view showing the schematic configuration of the electrode unit 20c in the third embodiment. Figure 17 This is a top view of electrode unit 20c. Figure 17 The connecting component 56 is omitted. The electrode unit 20c differs from the first embodiment in that it includes a third electrode 90. In the configuration of the electrode unit 20c and the dielectric heating device 100 in the third embodiment, the parts not specifically described are the same as in the first embodiment.

[0092] The third electrode 90 is a conductor and is disposed between the first electrode 30 and the second electrode 40. The third electrode 90 is not electrically connected to the power supply or voltage application part 80 and is electrically insulated from the first electrode 30 and the second electrode 40. The third electrode 90 is supported, for example, by an insulator (not shown). The third electrode 90 can be formed of the same material as the first electrode 30 and the second electrode 40, or it can be formed of a different material. The third electrode 90 is also referred to as a floating electrode.

[0093] More specifically, in this embodiment, the third electrode 90 is configured to surround the first electrode 30 when viewed along the Z direction. The third electrode 90 has a flattened elliptical ring shape in both the X and Y directions. Similar to the first electrode 30 and the second electrode 40, when viewed along the Z direction, the third electrode 90 has an elongated shape with the X direction as its long side and the Y direction as its short side. The second electrode 40 is configured to surround the third electrode 90 and the first electrode 30 surrounded by the third electrode 90 when viewed along the Z direction. It should be noted that in other embodiments, if the third electrode 90 is disposed between the first electrode 30 and the second electrode 40, it may not be configured to surround the first electrode 30 when viewed along the Z direction.

[0094] According to the third embodiment described above, a third electrode 90 is provided, which is disposed between the first electrode 30 and the second electrode 40 and is electrically insulated from the first electrode 30 and the second electrode 40. In this manner, the third electrode 90 can reduce the deviation in the intensity of the electric field generated between the first electrode 30 and the second electrode 40. Therefore, the possibility of uniformly heating the medium Md is further increased.

[0095] D. Other implementation methods:

[0096] (D-1) Figure 18 This is a diagram that schematically illustrates an example of electrode unit 20d in another embodiment. Figure 18In the electrode unit 20d, the second conductor 32 of the first electrode 30c is configured such that, when viewed along the X direction, the center position of the second conductor 32 in the Y direction is located on the -Y direction side compared to the center position of the first conductor 31 in the Y direction. The first electrode 30 can also be configured in this way. Alternatively, for example, when viewed along the Y direction, the center position of the second conductor 32 in the X direction can be located on the +X direction side and the -X direction side compared to the center position of the second conductor 32 in the X direction.

[0097] (D-2) Figure 19 This is a diagram schematically illustrating an example of electrode unit 20e in another embodiment. Figure 19 The first electrode 30d of the electrode unit 20e has two second conductors 32. More specifically, when viewed along the X direction, one second conductor 32 is positioned closer to the -Y direction side than the center position of the first conductor 31 in the Y direction, and the other second conductor 32 is positioned closer to the +Y direction side than the center position of the first conductor 31 in the Y direction. Thus, the first electrode 30d can also have two second conductors 32. Alternatively, the first electrode 30d can also have three or more second conductors 32.

[0098] (D-3) Figure 20 This is a diagram schematically illustrating an example of electrode unit 20f in another embodiment. Figure 20 The second conductor 32c of the first electrode 30e in the electrode unit 20f has a so-called V-shaped shape when viewed along the X direction. Thus, the second conductor 32c can also have a shape different from the cross-shaped or I-shaped shape when viewed along the X direction.

[0099] (D-4) In the above embodiment, the first conductor 31 has a boat-shaped shape, but it may not have a boat-shaped shape. For example, it may have a flat plate shape, a rod shape, or a plate shape with a V-shaped cross-section. In addition, in the above embodiment, the first conductor 31 has an elliptical shape when viewed along the Z direction, but it may not have an elliptical shape. For example, it may have a circular shape, a rectangular shape, or other polygonal shapes.

[0100] (D-5) In the above embodiment, the first conductor 31 and the second conductor 32 have an elongated shape with the X direction as their long side when viewed along the Z direction. Conversely, for example, the first conductor 31 and the second conductor 32 may not have an elongated shape. In this case, for example, the first conductor 31 and the second conductor 32 may have a circular shape or a square shape when viewed along the Z direction. Alternatively, when viewed along the Z direction, either the first conductor 31 or the second conductor 32 may have an elongated shape, while the other may not. Furthermore, for example, the first conductor 31 and the second conductor 32 may have elongated shapes with their long sides in different directions.

[0101] (D-6) In the above-described manner, if the second conductor 32 is configured in the same manner as in the first embodiment, such that the first end 33 and the second end 34 are covered by the middle portion 35 when projected onto a plane perpendicular to the Z direction, the second conductor 32 may not be configured to have a cross shape when viewed along the X direction. Alternatively, the second conductor 32 may not be configured such that the first end 33 and the second end 34 are covered by the middle portion 35 when projected onto a plane perpendicular to the Z direction.

[0102] (D-7) In the above embodiment, one end 37 of the second conductor 32 in the X direction has a shape in which the distance between it and the dielectric Md in the Z direction gradually increases in the X direction from the side opposite to the end 36 toward the end 36. Conversely, one end 37 of the second conductor 32 may not have such a shape. Similarly, the other end 39 may not have a shape in which the distance between it and the dielectric Md in the Z direction gradually increases in the X direction from the side opposite to the other end 38 toward the other end 38. In this case, the second conductor 32 may, for example, be formed to have a rectangular shape, an upwardly convex trapezoidal shape, etc., when viewed along the Y direction.

[0103] (D-8) In the above embodiment, the radius of curvature R of the end in the long side direction of the first conductor 31 is larger than the radius of curvature r of the end in the short side direction of the first conductor 31. Conversely, the radius of curvature R may be smaller than the radius of curvature r, or it may be the same as the radius of curvature r.

[0104] (D-9) In the above embodiment, the shortest distance in the Z direction between the first electrode 30 and the dielectric Md is equal to the shortest distance in the Z direction between the second electrode 40 and the dielectric Md. Conversely, the shortest distance in the Z direction between the first electrode 30 and the dielectric Md may not be equal to the shortest distance in the Z direction between the second electrode 40 and the dielectric Md. In this case, for example, the lower end of the first conductor 31 of the first electrode 30 may be located above or below the lower end of the second electrode 40.

[0105] (D-10) In the above embodiment, the medium Md is conveyed intermittently. In contrast, the medium Md may also be conveyed in the -Y direction at a certain speed by the first conveying unit 321 and the second conveying unit 322 without stopping midway.

[0106] (D-11) In the above embodiment, the medium Md is continuously conveyed from the liquid ejection device 205 to the dielectric heating device 100. When the medium Md is continuously conveyed from the liquid ejection device 205 to the dielectric heating device 100 in this manner, the conveying unit 320 may, for example, only have a conveying unit shared by the dielectric heating device 100 and the liquid ejection device 205. Alternatively, the medium Md may not be continuously conveyed from the liquid ejection device 205 to the dielectric heating device 100. For example, after the medium Md coated with liquid by the liquid ejection device 205 is temporarily wound into a roll, it may be moved to the dielectric heating device 100 by a robot or the like. In this case, in the dielectric heating device 100, for example, it is possible to heat the medium Md while it is being conveyed through the second conveying unit 322, etc., while unwinding the rolled medium Md.

[0107] (D-12) In the above embodiment, a frequency of 13.56 MHz was used as the driving frequency f0. Conversely, the driving frequency f0 may not be 13.56 MHz; for example, other frequencies such as 40.68 MHz, 2.45 GHz, and 5.8 GHz, which are part of the ISM band, may be used. Furthermore, if the driving frequency f0 is a frequency capable of heating the medium Md, it may not be high-frequency. In this case, the driving frequency f0 is preferably, for example, 100 kHz or higher and less than 1 MHz.

[0108] (D-13) In the above embodiment, the dielectric heating device 100 is assembled to the liquid ejection system 200. In contrast, the dielectric heating device 100 may not be assembled to the liquid ejection system 200, for example, the dielectric heating device 100 may be used alone.

[0109] E. Other aspects:

[0110] This disclosure is not limited to the embodiments described above, and can be implemented in various ways without departing from its spirit. For example, this disclosure can also be implemented in the following ways. In order to solve some or all of the technical problems of this disclosure, or to achieve some or all of the effects of this disclosure, the technical features in the above embodiments corresponding to the technical features in the aspects described below can be appropriately replaced or combined. In addition, if a technical feature is not described as an essential technical feature in this specification, it can be appropriately deleted.

[0111] (1) According to a first aspect of this disclosure, a dielectric heating device is provided. The dielectric heating device includes: a conveying section for conveying a medium; an electrode unit having a first electrode and a second electrode facing the medium in a first direction and subjected to an alternating current voltage, the electrode unit heating the medium by dielectric heating; and a control section for controlling the conveying section. The second electrode is configured to surround the first electrode when viewed along the first direction, the first electrode having a first conductor and a second conductor protruding from the first conductor toward the medium, the second conductor being covered by the first conductor when projected onto a plane perpendicular to the first direction.

[0112] Based on this aspect, it is possible to suppress the extremely weak localized alternating electric field in the region of the medium overlapping with the first electrode by using the second conductor. Therefore, the possibility of uniformly heating the medium is improved.

[0113] (2) In the above aspect, it is also possible that, when viewed along the first direction, the first conductor and the second conductor have elongated shapes, the elongated shapes having a long side direction along a second direction orthogonal to the first direction and a short side direction along a third direction orthogonal to both the first and second directions. According to this aspect, in the manner in which the first conductor has an elongated shape, the portion of the alternating current field with extremely weak intensity that is locally generated can be effectively suppressed by the second conductor having the same elongated shape as the first conductor.

[0114] (3) In the above aspect, the second conductor may also have a first end, a second end opposite to the first end, and a middle portion in the first direction. The first end is connected to the first conductor, and the middle portion is disposed between the first end and the second end. The width of the middle portion in the third direction is wider than the width of the first end and the second end in the third direction. According to this aspect, deviations in the electric field strength in the medium can be more effectively suppressed. Therefore, the possibility of uniformly heating the medium is further increased.

[0115] (4) In the above aspect, when projected onto a plane perpendicular to the first direction, the first end and the second end are covered by the intermediate portion. According to this aspect, deviations in electric field strength can be further suppressed.

[0116] (5) In the above aspect, the second conductor may also have a cross shape when viewed along the second direction. According to this aspect, with a simple configuration, it is possible to suppress the localized generation of extremely weak alternating electric fields and to suppress deviations in electric field strength.

[0117] (6) In the above aspects, the second conductor may also have a plate shape along the first and second directions. According to this aspect, it is possible to suppress the localized areas of extremely weak alternating electric field with a simpler configuration.

[0118] (7) In the above aspect, it is also possible that one end of the second conductor, including one end in the second direction, has a shape in which the distance between it and the medium in the first direction gradually increases in the second direction from the opposite side toward that end. According to this aspect, it is possible to suppress the concentration of the electric field at one end in the second direction of the second conductor.

[0119] (8) In the above aspect, the radius of curvature of the end of the first conductor in the second direction may also be larger than the radius of curvature of the end of the first conductor in the third direction. According to this aspect, it is possible to suppress the concentration of the electric field at the end in the long side direction of the first conductor.

[0120] (9) In the above aspect, the shortest distance in the first direction between the first electrode and the medium is equal to the shortest distance in the first direction between the second electrode and the medium. According to this aspect, the possibility of uniformly heating the medium is further increased.

[0121] (10) In the above aspect, a third electrode may also be provided, which is disposed between the first electrode and the second electrode and electrically insulated from both the first electrode and the second electrode. According to this aspect, the deviation in the intensity of the electric field generated between the first electrode and the second electrode can be further reduced by the third electrode. Therefore, the possibility of uniformly heating the medium is further improved.

[0122] (11) According to a second aspect of the present disclosure, a liquid ejection system is provided. The liquid ejection system includes: the dielectric heating device described above; and a liquid ejection section for coating the medium with liquid.

[0123] (12) According to a third aspect of this disclosure, a liquid ejection device is provided, wherein a liquid heated by an electrode unit is coated onto a medium, the electrode unit having a first electrode and a second electrode facing the medium in a first direction and subjected to an alternating voltage, the second electrode being configured to surround the first electrode when viewed along the first direction, the first electrode having a first conductor and a second conductor protruding from the first conductor toward the medium, the second conductor being covered by the first conductor when projected onto a plane perpendicular to the first direction. The liquid ejection device includes: a conveying section for conveying the medium; a liquid ejection section for coating the medium with the liquid; and an ejection control section for controlling the conveying section and the liquid ejection section.

Claims

1. A dielectric heating device, characterized in that, have: Conveying section, conveying medium; An electrode unit having a first electrode and a second electrode facing the medium in a first direction and subjected to an alternating current voltage, wherein the first direction is vertical, and the electrode unit heats the medium by dielectric heating; and The control unit controls the conveying unit. The second electrode is configured to surround the first electrode when viewed along the first direction. The first electrode has a first conductor and a second conductor protruding from the first conductor toward the medium. When projected onto a plane perpendicular to the first direction, the second conductor is covered by the first conductor.

2. The dielectric heating device according to claim 1, characterized in that, When viewed along the first direction, the first conductor and the second conductor have an elongated shape, the elongated shape having a long side direction along a second direction orthogonal to the first direction and a short side direction along a third direction orthogonal to the first direction and the second direction.

3. The dielectric heating device according to claim 2, characterized in that, The second conductor has a first end, a second end opposite to the first end, and a middle portion in the first direction. The first end is connected to the first conductor, and the middle portion is disposed between the first end and the second end. The width of the middle portion in the third direction is wider than the width of the first end and the second end in the third direction.

4. The dielectric heating device according to claim 3, characterized in that, When projected onto a plane perpendicular to the first direction, the first end and the second end are covered by the middle portion.

5. The dielectric heating device according to claim 4, characterized in that, When viewed along the second direction, the second conductor has a cross shape.

6. The dielectric heating device according to claim 2, characterized in that, The second conductor has a plate-like shape along the first direction and the second direction.

7. The dielectric heating device according to claim 2, characterized in that, The second conductor has an end portion including one end in the second direction having a shape in which the distance between it and the medium in the first direction gradually increases in the second direction from the opposite side toward the first end.

8. The dielectric heating device according to claim 2, characterized in that, The radius of curvature of the end of the first conductor in the second direction is larger than the radius of curvature of the end of the first conductor in the third direction.

9. The dielectric heating device according to claim 1, characterized in that, The shortest distance in the first direction between the first electrode and the medium is equal to the shortest distance in the first direction between the second electrode and the medium.

10. The dielectric heating device according to claim 1, characterized in that, The dielectric heating device includes a third electrode, which is disposed between the first electrode and the second electrode and is electrically insulated from the first electrode and the second electrode.

11. A liquid ejection system, characterized in that, have: The dielectric heating device according to any one of claims 1 to 10; and The liquid ejection section applies liquid to the medium.

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