Dielectric heating device and liquid discharge system

Abstract

To provide a technique capable of uniformly drying liquid adhering to a medium without providing a sensor that measures a water content in a dielectric heating device.SOLUTION: A dielectric heating device comprises: a first heater which has a first electrode and a second electrode that are opposed to a medium to which liquid containing water adheres and a first coil that is electrically serially connected to the first electrode, and heats the liquid to dry the liquid; and a voltage application part which applies AC voltage at a predetermined drive frequency to the first electrode and the second electrode. The first heater is configured such that a difference between the resonant frequency and the drive frequency of the first heater in a case where the water content of the medium is within a first range becomes smaller than a difference between the resonant frequency and the drive frequency of the first heater in a case where the water content is within a second range smaller than the first range, and a heating amount in a case where the water content is within the first range becomes greater than a heating amount in a case where the water content is within the second range.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to a dielectric heating device and a liquid dispensing system. [Background technology]

[0002] Regarding dielectric heating devices, Patent Document 1 discloses a technique for measuring the moisture content of the transported goods by multiple sensors, and individually controlling the power of the high-frequency electric field applied to multiple electrodes provided at positions corresponding to the multiple sensors according to the results of each measurement. This technique makes it possible to uniformly dry the transported goods. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2018-9754 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, the technique of Patent Document 1 requires the provision of a sensor for measuring the moisture content of the transported goods in order to control the power of the high-frequency electric field applied to the electrodes. [Means for solving the problem]

[0005] According to a first aspect of the present disclosure, there is provided a dielectric heating device. The dielectric heating device includes a first heater having a first electrode and a second electrode facing a medium to which a water-containing liquid is attached, a first coil electrically connected in series with the first electrode, and configured to heat and dry the liquid, and a voltage application unit configured to apply an AC voltage of a predetermined drive frequency to the first electrode and the second electrode. The first heater is configured such that the difference between the resonant frequency of the first heater and the drive frequency when the moisture content of the medium is in a first range is smaller than the difference between the resonant frequency of the first heater and the drive frequency when the moisture content is in a second range that is smaller than the first range, and the amount of heat when the moisture content is in the first range is larger than the amount of heat when the moisture content is in the second range.

[0006] According to a second aspect of the present disclosure, there is provided a liquid ejection system including the dielectric heating device of the above aspect and a liquid ejection unit that ejects and applies the liquid to the medium, and the first heater heats the medium onto which the liquid has been applied by the liquid ejection unit. [Brief description of the drawings]

[0007] [Figure 1] FIG. 1 is a schematic diagram showing a schematic configuration of a liquid ejection system. [Diagram 2] FIG. 1 is a perspective view showing a schematic configuration of a dielectric heating device. [Diagram 3] FIG. 2 is a perspective view showing a schematic configuration of a heater. [Figure 4] FIG. 2 is an explanatory diagram showing the circuit configuration of a dielectric heating device. [Diagram 5] FIG. 4 is a schematic diagram illustrating a circuit formed by a heater and a liquid on a medium. [Figure 6] Equivalent circuit diagram of a dielectric heating device. [Figure 7] FIG. 4 is an explanatory diagram showing the relationship between the degree of dryness and a first resonance frequency. [Figure 8] FIG. 4 is an explanatory diagram showing the relationship between the degree of dryness and the amount of heat applied by a first heater. [Figure 9]5A to 5C are schematic diagrams illustrating adjustment of the thickness of a first electrode and a second electrode. [Figure 10] 5A and 5B are schematic diagrams illustrating adjustment of the distance between a first electrode and a second electrode. [Figure 11] 5A to 5C are schematic diagrams illustrating adjustment of the width of a first electrode and the width of a second electrode. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] A. First embodiment: FIG. 1 is a schematic diagram showing a schematic configuration of a liquid ejection system 200 as a first embodiment. In FIG. 1, arrows indicating mutually orthogonal X, Y, and Z directions are shown. The X and Y directions are parallel to a horizontal plane, and the Z direction is a direction along a vertical upward direction. The arrows indicating the X, Y, and Z directions are also shown in other figures as appropriate so that the illustrated directions correspond to those in FIG. 1. In the following description, when specifying the direction, the direction indicated by the arrow in each figure is indicated as "+" and the opposite direction is indicated as "-", and positive and negative signs are used in combination to indicate the direction. Hereinafter, the +Z direction is also referred to as "upper", and the -Z direction is also referred to as "lower". In addition, in this specification, orthogonal includes a range of 90°±10°.

[0009] The liquid ejection system 200 includes a dielectric heating device 100 having a heater 20, a liquid ejection device 205, and a conveying unit 320. In the liquid ejection system 200 of this embodiment, while conveying the medium Md by the conveying unit 320, the liquid ejection device 205 ejects and applies a liquid containing water onto the medium Md, and the heater 20 of the dielectric heating device 100 heats and dries the liquid applied to the medium Md. It can also be said that the liquid ejection device 205 applies the liquid heated by the heater 20 onto the medium Md.

[0010] As the medium Md, for example, paper, cloth, film, etc. are used. The cloth used as the medium Md is formed by weaving, for example, fibers such as cotton, hemp, polyester, silk, rayon, etc., or fibers blended with these. In this embodiment, a sheet-shaped cotton cloth is used as the medium Md. As the liquid applied to the medium Md, for example, various inks containing water as a main component are used. In this embodiment, as the liquid, an aqueous ink containing water as a main component is used. In this specification, the main component of the liquid refers to a substance contained in the liquid whose mass fraction is 50% or more. In other embodiments, as the liquid, in addition to the ink, any liquid may be used, such as various coloring materials, electrode materials, samples such as biological organic matter and inorganic matter, lubricating oil, resin liquid, etching liquid, etc.

[0011] 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 driving a roller 323. The conveying unit 320 has a first conveying unit 321 provided in the liquid ejection 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) configured by a motor or the like for driving the roller 323. The first conveying unit 321 is disposed at a position in the +Y direction of the second conveying unit 322. In this embodiment, the first conveying unit 321 and the second conveying unit 322 convey the sheet-like medium Md in the -Y direction. In other embodiments, the conveying unit 320 may be configured as a belt mechanism that conveys the medium Md by driving a belt, for example.

[0012] In this embodiment, the liquid ejection device 205 is configured as an inkjet printer that performs printing by ejecting and applying ink as a liquid to the medium Md. Therefore, it can be said that the liquid ejection system 200 is configured as a printing system equipped with an inkjet printer. The liquid ejection device 205 has a liquid ejection unit 210 that ejects and applies liquid to the medium Md, and a first control unit 250. Hereinafter, the first control unit 250 will also be simply referred to as a control unit.

[0013] The liquid ejection unit 210 is configured as, for example, a piezoelectric or thermal liquid ejection head, and has one or more head chips (not shown). Each head chip has a flow path through which liquid flows and a nozzle for ejecting liquid. The colors of ink ejected from each head chip may be the same or different. In addition, the liquid ejection unit 210 may be configured to be capable of reciprocating in a direction perpendicular to the Z direction and intersecting with the Y direction relative to the medium Md by a carriage (not shown), or may be configured as a so-called line head whose position is fixed without reciprocating relative to the medium Md.

[0014] The ink used as the liquid in this embodiment is a pigment ink containing a resin. The resin contained in the ink has the effect of firmly fixing the pigment on the medium Md through itself. Such a resin is used in a state where, for example, a resin that is poorly soluble or insoluble in a solvent such as water is made into fine particles and dispersed in the solvent, that is, in an emulsion state or suspension state. Examples of such a resin 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 be used in combination. Such a resin is also called a resin.

[0015] The first control unit 250 is configured by a computer including one or more processors, a storage device, and an input / output interface for inputting and outputting signals from and to the outside. In this embodiment, the first control unit 250 controls the liquid ejection unit 210 and the second transport unit 322 to eject and adhere liquid to the medium Md while transporting the medium Md. In other embodiments, the first control unit 250 may be configured by, for example, a combination of multiple circuits.

[0016] FIG. 2 is a perspective view showing a schematic configuration of the dielectric heating device 100 in the first embodiment. As shown in FIG. 1 and FIG. 2, the dielectric heating device 100 includes a heater 20 that heats and dries the liquid applied to the medium Md, a voltage application unit 80 that applies an AC voltage to the heater 20, and a second control unit 180. The dielectric heating device 100 in this embodiment dries the liquid attached to the medium Md by heating the liquid attached to the medium Md with an AC electric field generated by the heater 20 while transporting the medium Md by the second transport unit 322. The dielectric heating device 100 may be provided with, for example, a blower for generating an air flow. By providing such a blower, it is possible to promote drying of the liquid attached to the medium Md and to promote cooling of the medium Md after drying is completed.

[0017] 2, the dielectric heating device 100 in this embodiment has a first heater 30 and a second heater 40 as the heater 20. The first heater 30 has a first electrode 31, a second electrode 32, and a first coil 34. The second heater 40 has a third electrode 41, a fourth electrode 42, and a second coil 44. Hereinafter, the first heater 30 and the second heater 40 may not be distinguished from each other and may be simply referred to as the heater 20.

[0018] The first electrode 31 and the second electrode 32 face the media Md. The third electrode 41 and the fourth electrode 42 also face the media Md. In this embodiment, the first electrode 31 and the second electrode 32, and the third electrode 41 and the fourth electrode 42, face the media Md transported in the first direction in a second direction perpendicular to the first direction. In this embodiment, the first direction is the -Y direction. The second direction is a direction that includes both a direction on one side along the same axis and the opposite direction, and is the Z direction in this embodiment. That is, in this embodiment, the first electrode 31 and the second electrode 32, and the third electrode 41 and the fourth electrode 42 face the media Md transported in the -Y direction by the second transport unit 322 in the Z direction.

[0019] In this embodiment, the first heater 30 and the second heater 40 are arranged side by side along the third direction. The third direction is a direction that is perpendicular to the first direction and intersects with the second direction. The third direction is a direction that includes both one direction along the same axis and the opposite direction, and is the X direction in this embodiment.

[0020] The voltage application unit 80 is electrically connected to the first heater 30 and applies an AC voltage of a predetermined driving frequency f0 to the first electrode 31 and the second electrode 32. In the present embodiment, the voltage application unit 80 is electrically connected to the second heater 40 and applies an AC voltage of a driving frequency f0 to the third electrode 41 and the fourth electrode 42. In the present embodiment, the first heater 30 and the second heater 40 are electrically connected in parallel to each other. One of the potentials applied to the first electrode 31 or the second electrode 32, or one of the potentials applied to the third electrode 41 or the fourth electrode 42 may 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.

[0021] In this embodiment, a high-frequency voltage is applied to each electrode of each heater 20. In this specification, "high frequency" refers to a frequency of 1 MHz or more. More specifically, in this embodiment, 13.56 MHz, which is one of the Industrial Scientific and Medical (ISM) bands, is used as the driving frequency f0. Since the dielectric tangent of water is maximum at around 20 GHz, the liquid attached to the medium Md can be heated more efficiently by applying a high-frequency voltage of 2.45 GHz or 5.8 GHz in the ISM band to each electrode of each heater 20. On the other hand, from the viewpoint of heating the ink, good heating efficiency can be obtained even if the driving frequency f0 is relatively low, for example, 13.56 MHz or 40.68 MHz. The reason for this is that when the driving frequency f0 is 13.56 MHz or 40.68 MHz, while the dielectric tangent of water in the ink is low, Joule heat is easily generated by the pigment components in the ink as electrical resistance.

[0022] The second control unit 180 is configured by a computer, similar to the above-mentioned first control unit 250. In this embodiment, the second control unit 180 controls the above-mentioned second transport unit 322.

[0023] Fig. 3 is a perspective view showing a schematic configuration of the heater 20 in this embodiment. More specifically, Fig. 3 shows a schematic configuration of the first heater 30. As described above, the first heater 30 has the first electrode 31, the second electrode 32, and the first coil 34. Although not shown in the drawings, in this embodiment, the third electrode 41, the fourth electrode 42, and the second coil 44 of the second heater 40 described above have the same configurations as the first electrode 31, the second electrode 32, and the first coil 34, respectively.

[0024] The first electrode 31 and the second electrode 32 are conductors and are formed of, for example, a metal, an alloy, a conductive oxide, or the like. The first electrode 31 and the second electrode 32 may be formed of the same material or different materials. For example, the first electrode 31 and the second electrode 32 may be disposed on a substrate or the like formed of a material with low dielectric tangent or conductivity, or may be supported by another member, in order to maintain their posture and strength.

[0025] The first electrode 31 and the second electrode 32 are arranged so that the shortest distance between the first electrode 31 and the second electrode 32 is equal to or less than one tenth of the wavelength of the electromagnetic field output from the first heater 30. The first electrode 31 in this embodiment has a boat shape having a longitudinal direction and a lateral direction. The lower surface of the first electrode 31 has a curved shape that is convex in the -Z direction. The first electrode 31 has an elliptical shape when viewed along the Z direction. The second electrode 32 has an annular shape that is flattened in the X direction and the Y direction. The second electrode 32 is arranged so as to surround the periphery of the first electrode 31 when viewed along the Z direction. The first electrode 31 and the second electrode 32 are arranged so that the longitudinal direction of the first electrode 31 and the longitudinal direction of the second electrode 32 are parallel to each other.

[0026] As shown in FIG. 1 and FIG. 2, the first electrode 31 and the second electrode 32 are both disposed on a substrate 110 disposed parallel to the X direction and the Y direction. More specifically, the first electrode 31 is disposed so that the center of the lower surface of the first electrode 31 in the X direction and the Y direction contacts the upper surface of the substrate 110. The second electrode 32 is disposed so that the lower surface of the second electrode 32 contacts the upper surface of the substrate 110. Therefore, in this embodiment, the center of the lower surface of the first electrode 31 and the lower surface of the second electrode 32 are disposed on the same plane. In this embodiment, the substrate 110 is provided in common to the first heater 30 and the second heater 40.

[0027] 1, in this embodiment, the first electrode 31 and the second electrode 32 are disposed above the medium Md. Therefore, in this embodiment, the lower surfaces of the first electrode 31 and the second electrode 32 face the upper surface of the medium Md. The above-mentioned substrate 110 is disposed between the medium Md and the first electrode 31 and the second electrode 32. Similarly, the third electrode 41 and the fourth electrode 42 are disposed above the medium Md so as to face the medium Md in the Z direction.

[0028] In this embodiment, the substrate 110 is made of glass. The substrate 110 prevents liquid such as ink applied to the medium Md from adhering to the first electrode 31 and the second electrode 32, and prevents fluff from adhering to the first electrode 31 and the second electrode 32 when the medium Md is a cloth. In this embodiment, the substrate 110 also prevents liquid and fluff from adhering to the third electrode 41 and the fourth electrode 42 of the second heater 40, in the same manner as described above. In other embodiments, the substrate 110 may be made of, for example, alumina.

[0029] Returning to Fig. 3, in this embodiment, the first electrode 31 is electrically connected to the voltage application unit 80 via the first electric wire 35, the first coil 34, and the inner conductor IC1 of the coaxial cable. The second electrode 32 is electrically connected to the voltage application unit 80 via a connection member 33 disposed on the upper portion of the second electrode 32, an outer conductor of the coaxial cable (not shown), and the like.

[0030] When an AC voltage of a drive frequency f0 is applied to the first electrode 31 and the second electrode 32, an electromagnetic field having a wavelength according to the drive frequency f0 is generated from the first electrode 31 and the second electrode 32. The intensity of this electromagnetic field is very strong near the first electrode 31 and the second electrode 32, and very weak far away. In this specification, the electromagnetic field generated near the first electrode 31 and the second electrode 32 by the application of the AC voltage is also called a "near electromagnetic field". The "near" of the first electrode 31 and the second electrode 32 refers to a range in which the distance from the first electrode 31 and the second electrode 32 is 1 / 2π or less of the wavelength of the generated electromagnetic field. A range farther than the "near" is also called a "far" range. In this specification, the electromagnetic field generated far away from the first electrode 31 and the second electrode 32 by the application of the AC voltage is also called a "far electromagnetic field". The far electromagnetic field corresponds to an electromagnetic field used in communication by a general communication antenna or the like.

[0031] As described above, the first electrode 31 and the second electrode 32 are arranged so that the shortest distance between them is equal to or less than one tenth of the wavelength of the electromagnetic field. This allows the density of the electromagnetic field generated from the first electrode 31 and the second electrode 32 to be attenuated in the vicinity of the first electrode 31 and the second electrode 32. Therefore, by appropriately maintaining the distance between the medium Md and the first electrode 31 and the second electrode 32, the liquid attached to the medium Md can be efficiently heated by the electric field generated in the vicinity of the first electrode 31 and the second electrode 32, while suppressing radiation of the far electromagnetic field from the first electrode 31 and the second electrode 32. In particular, in this embodiment, the second electrode 32 is arranged so as to surround the first electrode 31 when viewed along the Z direction, so that radiation of the far electromagnetic field from the first electrode 31 and the second electrode 32 can be further suppressed.

[0032] In this embodiment, one end of the first coil 34 is electrically connected in series to the first electrode 31 via the first electric wire 35, and the other end is electrically connected in series to the voltage application unit 80 shown in FIG. 1 and FIG. 2. In this embodiment, the first coil 34 is configured by a solenoid coil and is arranged so that its length direction is along the Z direction. The shape, length, cross-sectional area, number of turns, material, etc. of the first coil 34 are selected, for example, according to the driving frequency f0 and so as to realize impedance matching between the first heater 30 and the voltage application unit 80. Although not shown in the figures, in this embodiment, one end of the second coil 44 is electrically connected to the third electrode 41 via the second electric wire, and the other end is electrically connected in series to the voltage application unit 80. In other embodiments, one end of the first coil 34 may be connected in series to the second electrode 32 instead of the first electrode 31. Similarly, one end of the second coil 44 may be connected in series to the fourth electrode 42 instead of the third electrode 41.

[0033] When the voltage application unit 80 applies an AC voltage to the first heater 30, a high voltage is generated at one end of the first coil 34. This can increase the intensity of the electric field generated from the first electrode 31 and the second electrode 32. The first coil 34 is preferably disposed so that the distance between one end of the first coil 34 and the first electrode 31 is as small as possible. If the distance between one end of the first coil 34 and the first electrode 31 is large, the high voltage generated at one end of the first coil 34 may generate an electric field between the first coil 34 and the first electrode 31 or between the first electric wire 35 and the second electrode 32 that does not contribute to heating the medium Md, and the effect of increasing the intensity of the electric field generated from the first electrode 31 and the second electrode 32 may be reduced. In contrast, by shortening the distance between one end of the first coil 34 and the first electrode 31, the generation of such an electric field that does not contribute to heating the medium Md can be suppressed, and the intensity of the electric field generated from the first electrode 31 and the second electrode 32 can be effectively increased. Similarly, the second coil 44 can increase the intensity of the electric field generated from the third electrode 41 and the fourth electrode 42. In other embodiments, for example, the first electrode 31 and the third electrode 41 may be formed in a meandering shape, so that the first electrode 31 and the third electrode 41 have the same function as a coil.

[0034] FIG. 4 is an explanatory diagram showing the circuit configuration of the dielectric heating device 100 in this embodiment. In FIG. 4, in order to facilitate understanding of the technology, some components of the circuit configuration of the dielectric heating device 100 are omitted. As shown in FIG. 4, the voltage application unit 80 is configured as an inverter having a switching circuit 81. The switching circuit 81 is electrically connected to the DC power supply 150, the first heater 30, and the second heater 40. The switching circuit 81 switches the DC voltage of the DC power supply 150 to convert it into an AC voltage with a driving frequency f0, and outputs the AC voltage to the first heater 30 and the second heater 40.

[0035] The switching circuit 81 in this embodiment is configured as a full-bridge inverter, and has four switching elements 82 and Zener diodes 83 for overvoltage protection provided corresponding to each switching element 82. In this embodiment, the switching elements 82 are configured by N-channel metal-oxide-semiconductor field-effect transistors (MOSFETs). In other embodiments, the switching elements 82 may be configured by, for example, bipolar transistors, insulated gate transistors, gate turn-off thyristors, or the like. In addition to the Zener diodes 83, or instead of the Zener diodes 83, the switching circuit 81 may have a PN junction diode or the like as appropriate. In addition, the switching circuit 81 may be configured as, for example, a phase-shift full-bridge inverter, or a half-bridge inverter.

[0036] Each switching element 82 repeatedly opens and closes a part of the switching circuit 81 in response to a control signal input to the gate of the switching element 82. The switching circuit 81 converts the DC voltage of the DC power supply 150 into an AC voltage with a drive frequency f0 through the operation of the switching elements 82. As a result, the AC voltage with the drive frequency f0 is applied to the first heater 30 and the second heater 40.

[0037] In this embodiment, AC voltages with phases reversed by 180° are applied to the first heater 30 and the second heater 40. More specifically, as shown in Fig. 4, the first electrode 31 of the first heater 30 and the fourth electrode 42 of the second heater 40 are connected to the switching circuit 81 so as to be in phase with each other, and the second electrode 32 of the first heater 30 and the fourth electrode 42 of the second heater 40 are connected to the switching circuit 81 so as to be in phase with each other, so that AC voltages with phases reversed by 180° are applied to the first heater 30 and the second heater 40. In this way, by applying AC voltages with phases reversed by 180° to the adjacent heaters 20, radiation waves from the adjacent heaters 20 that do not contribute to heating the medium Md can be weakened by each other.

[0038] FIG. 5 is a schematic diagram illustrating a circuit formed by the heater 20 and the liquid Lq attached to the medium Md in this embodiment. FIG. 6 is an equivalent circuit diagram of the dielectric heating device 100 in this embodiment. More specifically, FIG. 5 shows a circuit formed by the first heater 30 and the liquid Lq. Also, FIG. 6 corresponds to a circuit when only the first heater 30 of the first heater 30 and the second heater 40 is focused on. In the circuits shown in FIG. 5 and FIG. 6, the first electrode 31 and the second electrode 32 of the first heater 30 can be regarded as electrode plates constituting one capacitor. Although not shown, a circuit similar to the circuit shown in FIG. 5 is also formed by the second heater 40 and the liquid Lq. Also, the circuit when only the second heater 40 of the first heater 30 and the second heater 40 is focused on is similar to the circuit shown in FIG. 6.

[0039] R shown in Figs. a represents the resistance of the first heater 30. Resistance R a includes the internal resistance of the voltage application unit 80 and the parasitic resistance of the first coil 34. a represents the inductance of the first heater 30. Inductance L a In FIG. 5, the inductance L cand the parasitic inductance of each electrode of the first heater 30. a represents the capacitance of the first heater 30. Capacitance C a includes the parasitic capacitance of the first coil 34 and the capacitance between the electrodes of the first heater 30. b represents the electrical resistance of the liquid Lq deposited on the media Md. b1 represents the parasitic capacitance between the first electrode 31 and the liquid Lq. b2 represents the parasitic capacitance between the second electrode 32 and the liquid Lq. b is the parasitic capacitance C b1 and C b2 The capacitance C a and capacitance C b The sum of these corresponds to the capacitance of the first heater 30.

[0040] As the liquid Lq on the medium Md is heated and dried, the moisture content of the medium Md decreases, and the capacitance C a and the resistance R of the liquid Lq b In more detail, the thickness of the water contained in the liquid Lq on the medium Md decreases due to the decrease in the water content as the drying progresses, and the capacitance of the capacitor formed by the first electrode 31 and the second electrode 32 decreases, so that the capacitance C a decreases. This is because the dielectric constant of the water contained in the liquid Lq is higher than that of a vacuum. In addition, the mass fraction of water contained in the liquid Lq decreases due to the decrease in the water content as the drying progresses, and the electrical conductivity of the liquid Lq decreases, so the resistance R b In reality, the capacitance C increases as the liquid L dries. b The capacitance C a The decrease in resistance R b This increase is very small compared to the increase in

[0041] The resonant frequency of the heater 20 when drying the liquid applied to the medium Md is expressed as the resonant frequency of the heater 20 in the equivalent circuits shown in Figures 5 and 6. Therefore, the resonant frequency of the heater 20 changes as the drying progresses. More specifically, as described above, the capacitance C a decreases, so that the resonant frequency of the heater 20 increases as the drying progresses. Hereinafter, such a change in the resonant frequency of the heater 20 as the drying progresses is also referred to as a resonant frequency shift. Moreover, the amount of change in the resonant frequency due to the resonant frequency shift is also referred to as a resonant frequency shift amount. Moreover, the resonant frequency of the first heater 30 when drying the liquid applied to the medium Md is also referred to as a first resonant frequency f1. Similarly, the resonant frequency of the second heater 40 when drying the liquid applied to the medium Md is also referred to as a second resonant frequency f2.

[0042] The first heater 30 is configured to satisfy a first condition that the difference between the first resonance frequency f1 and the drive frequency f0 when the moisture content of the medium Md is in a first range is smaller than the difference between the first resonance frequency f1 and the drive frequency f0 when the moisture content is in a second range that is smaller than the first range. The moisture content of the medium Md is in the first range or the second range refers to the amount of water contained per unit volume of the first portion of the medium Md, which is a portion that forms the above-mentioned equivalent circuit with the first heater 30, being in the first range or the second range. In this case, the "amount of water" is represented by the mass of water in this embodiment, but in other embodiments, it may be represented by, for example, the volume of water or the ratio of the mass or volume of water to a reference value of the mass or volume. Hereinafter, the "moisture content of the first portion" refers to the "moisture content per unit volume of the first portion" unless otherwise specified. In this embodiment, the first portion corresponds to a portion located between the first electrode 31 and the second electrode 32 when viewed along the Z direction. This "portion between the first electrode 31 and the second electrode 32" includes the portion where the first electrode 31 and the second electrode 32 are provided.

[0043] In this embodiment, the second heater 40 is configured in the same manner as the first heater 30, and is configured to satisfy a third condition that the difference between the second resonance frequency f2 and the drive frequency f0 when the moisture content of the medium Md is in the third range is smaller than the difference between the second resonance frequency f2 and the drive frequency f0 when the moisture content is in a fourth range that is smaller than the third range. The moisture content of the medium Md in the third or fourth range refers to the moisture content per unit volume of the second portion of the medium Md, which is a portion that forms the above-mentioned equivalent circuit with the second heater 40, being in the third or fourth range. Hereinafter, the "moisture content of the second portion" refers to the "moisture content per unit volume of the second portion" unless otherwise specified. In this embodiment, the second portion corresponds to the portion located between the third electrode 41 and the fourth electrode 42 when viewed along the Z direction. The "portion between the third electrode 41 and the fourth electrode 42" includes the portion where the third electrode 41 and the fourth electrode 42 are provided.

[0044] FIG. 7 is an explanatory diagram showing the relationship between the degree of dryness and the first resonance frequency f1. FIG. 7 shows a schematic graph in which the horizontal axis represents the degree of dryness and the vertical axis represents the first resonance frequency f1. The "degree of dryness" in FIG. 7 represents the difference between the current moisture content in the first portion of the medium Md and the moisture content at the start of drying. The moisture content at a certain start of drying is calculated, for example, as the difference between the mass per unit volume of the first portion at the start of drying and the dry mass representing the mass per unit volume of the first portion at the end of drying. The dry mass is calculated, for example, as the mass when the medium Md is sufficiently dried. The first resonance frequency f1 is calculated, for example, based on the inductance and capacitance of the first heater 30 measured using a network analyzer.

[0045] Since the degree of dryness in FIG. 7 has a negative correlation with the moisture content in the first portion, it can be said that FIG. 7 shows the relationship between the moisture content in the first portion and the first resonance frequency f1. Since the moisture content and the degree of dryness are correlated in this way, the magnitude of the moisture content at two timings at which the progress of drying is different can be determined by comparing the magnitude of the degree of dryness at each timing, rather than directly comparing the magnitude of the moisture content at each timing. Note that the "degree of dryness" may be expressed, for example, by the ratio of the current moisture content in the first portion to the moisture content at the start of drying, the reciprocal of the current moisture content in the first portion, or the drying time when the liquid applied to the first portion is dried under certain conditions.

[0046] In this embodiment, the first heater 30 is configured so that the first resonance frequency f1 and the drive frequency f0 coincide when the moisture content in the first portion of the medium Md is a moisture content equivalent to a moisture content when the medium Md is coated with a liquid in a solid state. When the medium Md is coated with a liquid in a solid state, the liquid is applied without gaps to at least a part of one surface of the medium Md. More specifically, the moisture content equivalent to a solid state in this embodiment is defined as the moisture content per unit volume in the first portion of the medium Md immediately after the liquid ejection unit 210 performs solid printing of multiple colors on the medium Md. Solid printing refers to printing in which dots are formed in all pixels that make up an image, so that no part of the background color of the medium Md remains. In FIG. 7, the moisture content when the degree of dryness is zero, that is, the moisture content at the start of drying, corresponds to the moisture content equivalent to a solid state. As a result, in this embodiment, when the moisture content in the first portion of the medium Md at the start of drying is equal to or less than the moisture content equivalent to solid printing, the difference between the first resonance frequency f1 and the drive frequency f0 increases as the drying progresses, that is, as the moisture content in the first portion decreases. When the first resonance frequency f1 and the drive frequency f0 are said to match, the first resonance frequency f1 and the drive frequency f0 do not have to match completely. More specifically, the first resonance frequency f1 and the drive frequency f0 may match within a range of ±1.0% as long as the ratio of the difference between the first resonance frequency f1 and the drive frequency f0 to the drive frequency f0 matches within a range of ±0.5%, and more preferably matches within a range of ±0.1%. In another embodiment, the moisture content equivalent to solid printing may be defined as the moisture content per unit volume in the first portion of the medium Md immediately after the liquid ejection unit 210 performs solid printing of a single color such as black on the medium Md.

[0047] FIG. 8 is an explanatory diagram showing the relationship between the degree of dryness and the amount of heat by the first heater 30. FIG. 8 shows a schematic graph in which the horizontal axis indicates the degree of dryness and the vertical axis indicates the amount of heat by the first heater 30. The first heater 30 is configured to satisfy a second condition that the amount of heat when the moisture content in the first portion is in a first range is greater than the amount of heat when the moisture content in the first portion is in a second range. More specifically, in this embodiment, as shown in FIG. 8, the amount of heat by the first heater 30 decreases as the drying progresses, that is, as the moisture content in the first portion decreases. Note that the magnitude of the amount of heat by the first heater 30 in each of the cases where the moisture content is in the first range and the second range can be compared, for example, by comparing the high and low temperatures when cotton cloths with moisture contents in the first and second ranges are heated from the same temperature and with the same power output for the same time. Furthermore, in this embodiment, the second heater 40 is configured similarly to the first heater 30, and is configured to satisfy a fourth condition that the amount of heating when the moisture content in the second portion is in the third range is greater than the amount of heating when the moisture content in the second portion is in the fourth range.

[0048] The increase in the shift of the first resonance frequency f1 that accompanies the progress of drying contributes to a decrease in the amount of heat generated by the first heater 30. This is because the impedance of the first heater 30 increases as the difference between the first resonance frequency f1 and the drive frequency f0 increases. On the other hand, the resistance R of the liquid Lq on the medium Md decreases due to the increase in the water content that accompanies the progress of drying, as described with reference to Figs. 5 and 6. b The increase in resistance R b In this embodiment, the amount of heat generated by the shift in the first resonant frequency f1 is reduced by the increase in the resistance R b The second condition is met by configuring the first heater 30 so that the increase in the amount of heat generated by the first heater 30 exceeds the increase in the amount of heat generated by the first heater 30 due to the increase in the amount of heat generated by the first heater 30 .

[0049] The shift amount of the first resonant frequency f1 is calculated by subtracting the capacitance C b The capacitance C of the first heater 30 can be increased by increasing the ratio of b Increasing this ratio corresponds to increasing the influence of the dielectric constant of the liquid Lq on the near electric field formed in the region near the first electrode 31 and the second electrode 32, and corresponds to increasing the proportion of electric field lines that pass through the liquid Lq when the near electric field is represented by electric field lines.

[0050] FIG. 9 is a schematic diagram for explaining the adjustment of the thickness t1 of the first electrode 31 and the thickness t2 of the second electrode 32. For example, the shift amount of the first resonance frequency f1 can be adjusted by adjusting the thickness t1 and the thickness t2 as shown in FIG. 9. More specifically, in order to increase the shift amount of the first resonance frequency f1, that is, to increase the ratio of the electric field lines Eq passing through the liquid Lq, the thickness t1 and the thickness t2 are adjusted so that the number of the electric field lines Eq increases relatively to the number of the electric field lines En not passing through the liquid Lq. FIG. 9 shows an example in which the ratio of the electric field lines Eq is increased by increasing the thickness t1 and the thickness t2. In general, as shown in FIG. 9, the number of the electric field lines Eq can be increased by making the thickness t1 and the thickness t2 thicker. However, if the thickness t1 and the thickness t2 are made too thick, the ratio of the electric field lines Eq may decrease due to the increase in the number of the electric field lines En. In this embodiment, it is preferable that the thickness t1 and the thickness t2 are adjusted to, for example, 0.1 mm or more and 2.0 mm or less.

[0051] FIG. 10 is a diagram for explaining the adjustment of the distance d between the first electrode 31 and the second electrode 32. Note that the thicker dashed arrows in FIG. 10 indicate a greater number of electric field lines than the thinner dashed arrows. FIG. 10 shows an example in which the shift amount of the first resonance frequency f1 is increased by shortening the distance d within a range in which the proportion of the electric field lines Eq passing through the liquid Lq increases. The shift amount of the first resonance frequency f1 can also be adjusted by adjusting the distance d as shown in FIG. 10.

[0052] 11 is a diagram for explaining adjustment of the width W1 of the first electrode 31 and the width W2 of the second electrode 32. As shown in FIG. 11, the shift amount of the first resonant frequency f1 can also be adjusted by adjusting the width W1 and the width W2. In this case, narrowing the width W1 and the width W2 makes it easier to concentrate the electric field lines near the liquid Lq, so that the number of electric field lines En can be increased and the shift amount of the first resonant frequency f1 can be increased. FIG. 11 shows an example in which the shift amount of the first resonant frequency f1 is increased by narrowing the width W2.

[0053] In addition, the above-mentioned resistor R b The increase in the amount of heat generated by the increase in the resistance R in the equivalent circuit shown in FIG. 5 and FIG. 6 can be reduced by, for example, reducing the parasitic resistance of the first coil 34 while maintaining the inductance. a becomes smaller, the Q value in the equivalent circuit becomes larger, and the resistance R b This is because the contribution of the resistance R in the equivalent circuit shown in Figs. 5 and 6 is relatively small. In this case, for example, the parasitic resistance of the first coil 34 can be reduced by increasing the diameter of the winding of the first coil 34 or by increasing the pitch between the windings of the first coil 34. Also, as described above, by configuring the voltage application unit 80 with the switching circuit 81, the internal resistance of the voltage application unit 80 can be reduced compared to the case where the voltage application unit 80 is configured with an analog amplifier such as a class B amplifier or a high-frequency power supply circuit having a transformer. a This also reduces the resistance R b The increase in the amount of heat generated by the increase in the temperature can be reduced.

[0054] As shown above, resistor R bWhen reducing the increase in the amount of heat due to an increase in the amount of heat, it is more preferable to configure the first heater 30 so that the amount of heat of the liquid by the first heater 30 after drying of the medium Md is completed is equal to or less than the amount of cooling of the liquid. The timing at which drying of the medium Md is completed is determined, for example, as the timing at which the moisture content of the first portion of the medium Md becomes equal to or less than a predetermined moisture content. For example, if a blower is provided as described above, the amount of cooling of the liquid is the amount of cooling that takes into account the cooling by the blower. This makes it possible to suppress excessive heating of the medium Md after drying is completed.

[0055] According to the dielectric heating device 100 in the first embodiment described above, the first heater 30 is configured so that the difference between the resonance frequency and the drive frequency f0 of the first heater 30 when the moisture content of the medium Md is in the first range is smaller than the difference between the resonance frequency and the drive frequency f0 of the first heater 30 when the moisture content is in the second range that is smaller than the first range, and the heating amount of the first heater 30 when the moisture content is in the first range is larger than the heating amount when the moisture content is in the second range. As a result, even if the output of the AC power applied to the first heater 30 is not controlled based on the moisture content of the medium Md, the first heater 30 can heat the medium Md with a larger heating amount when the moisture content is in the first range that is larger than the second range, and the first heater 30 can heat the medium Md with a smaller heating amount when the moisture content is in the second range that is smaller than the first range. Therefore, the liquid attached to the medium Md can be uniformly dried without providing a sensor that measures the moisture content of the medium Md.

[0056] Moreover, in this embodiment, the voltage application unit 80 applies an AC voltage with a drive frequency f0 to the third electrode 41 and the fourth electrode 42 of the second heater 40, and the second heater 40 is configured so that the difference between the resonant frequency of the second heater 40 and the drive frequency f0 when the moisture content of the medium Md is in the third range is smaller than the difference between the resonant frequency of the second heater 40 and the drive frequency f0 when the moisture content is in a fourth range that is lower than the third range, and so that the heating amount of the second heater 40 when the moisture content is in the third range is larger than the heating amount when the moisture content is in the fourth range. As a result, in the second heater 40, as in the first heater 30, even without controlling the output of the AC power applied to the second heater 40 based on the moisture content of the medium Md, the medium Md can be heated with a larger heating amount when the moisture content is in the third range that is higher than the fourth range, and can be heated with a smaller heating amount when the moisture content is in the fourth range that is lower than the third range. Therefore, in a configuration in which a first heater 30 and a second heater 40 are provided, the liquid adhering to the medium Md can be uniformly dried without individually controlling the power output applied to the first heater 30 and the power output applied to the second heater 40.

[0057] In this embodiment, the first heater 30 and the second heater 40 are arranged side by side along a third direction that is perpendicular to the Z direction, which is the first direction, and intersects with the Y direction, which is the second direction. This makes it possible to suppress variation in the dryness of the media Md in the third direction.

[0058] Furthermore, in this embodiment, the voltage application unit 80 has a switching circuit 81 that switches the DC voltage of the DC power supply 150 to convert it into an AC voltage with a drive frequency f0. This allows the internal resistance of the voltage application unit 80 to be smaller than when the voltage application unit 80 is configured with a high-frequency power supply circuit having an analog amplifier and a transformer, increasing the possibility of improving power efficiency. Also, the resistance R of the liquid adhering to the medium Md that increases with the progress of drying bSince the increase in the amount of heat due to an increase in the moisture content can be made small, the amount of heat can be made larger when the moisture content is in the first range than when the moisture content is in the second range.

[0059] Furthermore, in this embodiment, the first heater 30 is configured so that the first resonant frequency f1 and the drive frequency f0 match when the moisture content is equivalent to a moisture content equivalent to a solid coating. As a result, when the liquid on the medium Md whose moisture content is equal to or less than the moisture content equivalent to a solid coating is dried by the first heater 30, the difference between the first resonant frequency f1 and the drive frequency f0 can be increased as the drying progresses. Therefore, the variation in the degree of dryness of the medium Md can be further suppressed.

[0060] B. Other embodiments: (B-1) In the above embodiment, the dielectric heating device 100 includes the first heater 30 and the second heater 40. In contrast, the dielectric heating device 100 may include, for example, only the first heater 30. Furthermore, the dielectric heating device 100 may include, for example, in addition to the first heater 30 and the second heater 40, one or more other heaters 20.

[0061] (B-2) In the above embodiment, an AC voltage with a driving frequency f0 is applied to the first heater 30 and the second heater 40 by a single voltage application unit 80. In contrast, for example, two voltage application units 80 configured separately from each other may apply an AC voltage with a driving frequency f0 to the first heater 30 and the second heater 40, respectively.

[0062] (B-3) In the above embodiment, the voltage application unit 80 is configured as an inverter having a switching circuit 81 that switches the DC voltage of the DC power supply 150 to convert it into an AC voltage of the drive frequency f0. In contrast, the voltage application unit 80 does not need to have the switching circuit 81, and may be configured, for example, by a high-frequency power supply circuit having an analog amplifier and a transformer.

[0063] (B-4) In the above embodiment, the first heater 30 is configured so that the first resonant frequency f1 and the drive frequency f0 match when the moisture content corresponds to the moisture content corresponding to solid painting. In contrast, the first heater 30 may not be configured so that the first resonant frequency f1 and the drive frequency f0 match when the moisture content corresponds to the moisture content corresponding to solid painting, as long as the first heater 30 is configured so as to satisfy the first and second conditions. For example, the first heater 30 may be configured so that the first resonant frequency f1 and the drive frequency f0 match when the moisture content corresponds to a moisture content lower than the moisture content corresponding to solid painting. Similarly, the second heater 40 may not be configured so that the second resonant frequency f2 and the drive frequency f0 match when the moisture content corresponds to the moisture content corresponding to solid painting, as long as the second heater 40 is configured so as to satisfy the third and fourth conditions.

[0064] (B-5) In the above embodiment, the second electrode 32 is arranged so as to surround the first electrode 31 when viewed along the Z direction. In contrast, for example, the first electrode 31 and the second electrode 32 may be arranged so as to be adjacent to each other when viewed along the Z direction, or may be arranged so as to sandwich the medium Md between the first electrode 31 and the second electrode 32 in the Z direction. In this case, the shapes of the first electrode 31 and the second electrode 32 may be any shape, and may be a circular shape, an elliptical shape, a rectangular shape, a polygonal shape, or the like. In addition, when viewed along the Z direction, the areas of the first electrode 31 and the second electrode 32 may be the same or different from each other. When viewed along the Z direction, it is preferable that the first electrode 31 and the second electrode 32 are arranged so as not to overlap each other. Similarly, the third electrode 41 and the fourth electrode 42 may be arranged so as to be adjacent to each other when viewed along the Z direction, or may be arranged so as to sandwich the medium Md between the third electrode 41 and the fourth electrode 42 in the Z direction.

[0065] (B-6) In the above embodiment, the medium Md is continuously transported from the liquid ejection device 205 to the dielectric heating device 100. When the medium Md is continuously transported from the liquid ejection device 205 to the dielectric heating device 100 in this manner, the transport unit 320 may, for example, only have a transport unit common to the dielectric heating device 100 and the liquid ejection device 205. The medium Md does not have to be continuously transported from the liquid ejection device 205 to the dielectric heating device 100. For example, the medium Md to which the liquid has been applied by the liquid ejection device 205 may be once wound into a roll, and then the medium Md 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, the medium Md wound into a roll can be unwound while the medium Md is transported by the second transport unit 322 or the like and heated.

[0066] (B-7) In the above embodiment, the heater 20 may be configured to be reciprocally movable in the third direction. For example, the heater 20 may be supported by a drive unit (not shown) configured by a belt mechanism or a ball screw mechanism and moved reciprocally in the X direction.

[0067] (B-8) In the above embodiment, a frequency of 13.56 MHz is used as the driving frequency f0. However, the driving frequency f0 does not have to be 13.56 MHz, and for example, other ISM band frequencies such as 40.68 MHz, 2.45 GHz, and 5.8 GHz may be used. Furthermore, the driving frequency f0 does not have to be a high frequency as long as it is a frequency that can heat the liquid attached to the medium Md by the heater 20. In this case, the driving frequency f0 is preferably, for example, equal to or higher than 100 kHz and lower than 1 MHz.

[0068] (B-9) In the above embodiment, the dielectric heating device 100 is incorporated into the liquid ejection system 200. In contrast, the dielectric heating device 100 does not have to be incorporated into the liquid ejection system 200, and for example, only the dielectric heating device 100 may be used alone.

[0069] C. Other forms: The present disclosure is not limited to the above-mentioned embodiment, and can be realized in various forms without departing from the spirit of the present disclosure. For example, the present disclosure can be realized in the following forms. The technical features in the above-mentioned embodiments corresponding to the technical features in each form described below can be appropriately replaced or combined in order to solve some or all of the problems of the present disclosure, or to achieve some or all of the effects of the present disclosure. Furthermore, if the technical feature is not described as essential in this specification, it can be appropriately deleted.

[0070] (1) According to a first aspect of the present disclosure, there is provided a dielectric heating device. The dielectric heating device includes a first heater having a first electrode and a second electrode facing a medium to which a water-containing liquid is attached, a first coil electrically connected in series with the first electrode, and configured to heat and dry the liquid, and a voltage application unit configured to apply an AC voltage of a predetermined drive frequency to the first electrode and the second electrode. The first heater is configured such that the difference between the resonant frequency of the first heater and the drive frequency when the moisture content of the medium is in a first range is smaller than the difference between the resonant frequency of the first heater and the drive frequency when the moisture content is in a second range that is smaller than the first range, and the amount of heat when the moisture content is in the first range is larger than the amount of heat when the moisture content is in the second range. According to this embodiment, even if the output of AC power applied to the first heater is not controlled based on the moisture content of the media, the first heater can heat the media with a greater amount of heat when the moisture content is in the first range that is higher than the second range, and the first heater can heat the media with a smaller amount of heat when the moisture content is in the second range that is lower than the first range. Therefore, the liquid adhering to the media can be uniformly dried without providing a sensor that measures the moisture content of the media.

[0071] (2) In the above embodiment, a second heater is provided that has a third electrode and a fourth electrode facing the medium and a second coil electrically connected in series with the third electrode, and heats and dries the liquid, and the voltage application unit applies an AC voltage of the drive frequency to the third electrode and the fourth electrode, and the second heater is configured so that the difference between the resonant frequency of the second heater and the drive frequency when the water content is in a third range is smaller than the difference between the resonant frequency of the second heater and the drive frequency when the water content is in a fourth range that is smaller than the third range, and the amount of heat when the water content is in the third range is larger than the amount of heat when the water content is in the fourth range. According to this embodiment, in an embodiment in which a first heater and a second heater are provided, the liquid attached to the medium can be uniformly dried without individually controlling the output of the power applied to the first heater and the output of the power applied to the second heater.

[0072] (3) In the above embodiment, the first electrode, the second electrode, the third electrode, and the fourth electrode may each face the medium transported in a first direction in a second direction perpendicular to the first direction, and the first heater and the second heater may be arranged side by side along a third direction perpendicular to the first direction and intersecting the second direction. This embodiment can suppress variation in the degree of drying of the liquid on the medium in the third direction.

[0073] (4) In the above embodiment, the voltage application unit may have a switching circuit that switches the DC voltage of a DC power supply to convert it into an AC voltage of the drive frequency. According to this embodiment, the voltage application unit can be made smaller and the power efficiency can be improved, compared to a case where the voltage application unit is configured by a high-frequency power supply circuit having an analog amplifier and a transformer, for example.

[0074] (5) In the above embodiment, the first heater may be configured such that the resonant frequency of the first heater and the driving frequency match when the water content corresponds to the water content when the liquid is applied solidly to the medium. According to this embodiment, when the first heater is used to dry liquid on a medium whose water content is equal to or less than the water content when the liquid is applied solidly, the difference between the resonant frequency of the first heater and the driving frequency can be increased as the drying progresses. Therefore, the variation in the degree of drying of the liquid on the medium can be further suppressed.

[0075] (6) According to a second aspect of the present disclosure, there is provided a liquid ejection system including the dielectric heating device of the above aspect and a liquid ejection unit that ejects and applies the liquid to the medium, and the first heater heats the medium onto which the liquid has been applied by the liquid ejection unit.

[0076] (7) According to a third aspect of the present disclosure, there is provided a liquid ejection device that applies, onto a medium, the liquid that is heated by a heater configured to: face a medium having a water-containing liquid attached thereto; and include: a first electrode and a second electrode to which an AC voltage of a predetermined drive frequency is applied; and a first coil electrically connected in series with the first electrode; and to make the difference between the resonant frequency and the drive frequency smaller when the water content of the medium is in a first range than the difference between the resonant frequency and the drive frequency when the water content is in a second range that is lower than the first range; and to make the amount of heating larger when the water content is in the first range than the amount of heating larger when the water content is in the second range. This liquid ejection device includes a transport unit that transports the medium, a liquid ejection unit that ejects the liquid onto the medium, and a control unit that controls the transport unit and the liquid ejection unit. [Explanation of symbols]

[0077] 20... heater, 30... first heater, 31... first electrode, 32... second electrode, 33... connecting member, 34... first coil, 35... first electric wire, 40... second heater, 41... third electrode, 42... fourth electrode, 44... second coil, 80... voltage application section, 81... switching circuit, 82... switching element, 83... Zener diode, 100... dielectric heating device, 110... substrate, 150... DC power supply, 180... second control section, 200... liquid discharge system, 205... liquid discharge device, 210... liquid discharge section, 250... first control section, 320... conveying section, 321... first conveying section, 322... second conveying section, 323... roller

Claims

1. a first heater having a first electrode and a second electrode facing a medium to which a water-containing liquid is attached, and a first coil electrically connected in series with the first electrode, the first heater heating and drying the liquid; a voltage application unit that applies an AC voltage having a predetermined drive frequency to the first electrode and the second electrode; The first heater is a difference between the resonant frequency of the first heater and the drive frequency when the moisture content of the medium is in a first range is smaller than a difference between the resonant frequency of the first heater and the drive frequency when the moisture content of the medium is in a second range that is smaller than the first range; and The heating amount when the moisture content is in the first range is configured to be greater than the heating amount when the moisture content is in the second range. Dielectric heating device.

2. 2. The dielectric heating device according to claim 1, a second heater including a third electrode and a fourth electrode facing the medium and a second coil electrically connected in series to the third electrode, the second heater heating and drying the liquid; the voltage application unit applies an AC voltage of the drive frequency to the third electrode and the fourth electrode; The second heater is a difference between the resonant frequency of the second heater and the driving frequency when the moisture content is in a third range is smaller than a difference between the resonant frequency of the second heater and the driving frequency when the moisture content is in a fourth range that is smaller than the third range; and The heating amount when the moisture content is in the third range is configured to be greater than the heating amount when the moisture content is in the fourth range. Dielectric heating device.

3. The dielectric heating device according to claim 2, the first electrode, the second electrode, the third electrode, and the fourth electrode each face the medium transported in a first direction in a second direction perpendicular to the first direction; The dielectric heating device, wherein the first heater and the second heater are arranged side by side along a third direction that is perpendicular to the first direction and intersects with the second direction.

4. 2. The dielectric heating device according to claim 1, The voltage application unit is a dielectric heating device having a switching circuit that switches a DC voltage of a DC power supply to convert it into an AC voltage of the drive frequency.

5. 2. The dielectric heating device according to claim 1, A dielectric heating device, wherein the first heater is configured so that the resonant frequency of the first heater and the driving frequency match when the water content corresponds to the water content when the liquid is applied solidly to the medium.

6. The dielectric heating device according to any one of claims 1 to 5, a liquid ejection unit that ejects and applies the liquid to the medium, The first heater heats the medium onto which the liquid is applied by the liquid ejection unit.

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