Dielectric heating device

Abstract

To prevent a medium from being excessively dried on the downstream in a conveyance direction of the medium in a dielectric heating device.SOLUTION: A dielectric heating device comprises: a conveying unit that conveys a medium in a conveyance direction; first electrodes 31 and second electrodes 32 that face the medium conveyed by the conveying unit; an electrode unit 30 that dries the medium by dielectric heating; a voltage application unit 80 that applies AC voltage to the first electrodes and second electrodes; and a control unit 250 that controls the conveying unit. The second electrode has a first portion and a second portion that sandwich the first electrode in the conveyance direction. The first portion is arranged upstream of the second portion in the conveyance direction. The first electrode and second electrode are formed such that the amount of heat applied to the medium by an electric field formed between the first electrode and the first portion is large compared to the amount of heat applied to the medium by an electric field formed between the first electrode and the second portion.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a dielectric heating device. [Background technology]

[0002] Regarding dielectric heating devices, Patent Document 1 describes a device that applies a high-frequency electric field to a transported object by a plurality of electrodes, thereby heating and drying the transported object by a dielectric heating method. [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] In an apparatus for heating and drying a transported object as in Patent Document 1, for example, when the transport speed is relatively slow or the size of the electrodes is relatively large, the transported object may become excessively dry downstream in the transport direction. [Means for solving the problem]

[0005] According to one aspect of the present disclosure, a dielectric heating device is provided. The dielectric heating device includes a transport section that transports a medium in a transport direction, an electrode unit having a first electrode and a second electrode facing the medium transported by the transport section and drying the medium by dielectric heating, a voltage application section that applies an AC voltage to the first electrode and the second electrode, and a control section that controls the transport section. The second electrode has a first portion and a second portion that sandwich the first electrode in the transport direction, the first portion is disposed upstream of the second portion in the transport direction, and the first electrode and the second electrode are formed such that the amount of heating of the medium caused by an electric field formed between the first electrode and the first portion is greater than the amount of heating of the medium caused by an electric field formed between the first electrode and the second portion. [Brief description of the drawings]

[0006] [Figure 1] FIG. 1 is a schematic diagram showing a schematic configuration of a dielectric heating device. [Diagram 2] FIG. 2 is a perspective view showing a schematic configuration of an electrode unit according to the first embodiment. [Diagram 3] FIG. 4 is a top view showing the first electrode, the second electrode, and the medium. [Figure 4] FIG. 4 is a schematic diagram for explaining the thickness of a first portion and the thickness of a second portion. [Diagram 5] FIG. 4 is a schematic diagram illustrating a circuit formed by an electrode unit and a medium. [Figure 6] FIG. 13 is a perspective view showing a schematic configuration of an electrode unit according to a second embodiment. [Figure 7] FIG. 4 is a schematic diagram for explaining the width of a first portion and the width of a second portion. [Figure 8] FIG. 13 is a perspective view showing a schematic configuration of an electrode unit according to a third embodiment. [Figure 9] FIG. 4 is a schematic diagram for explaining a first distance and a second distance. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0007] A. First embodiment: FIG. 1 is a schematic diagram showing a schematic configuration of a dielectric heating device 100 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 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°. In addition, the plane along the X and Y directions is also referred to as the "XY plane".

[0008] The dielectric heating device 100 includes a transport unit 320 that transports the medium Md, an electrode unit 30 that dries the medium Md by dielectric heating, a voltage application unit 80 that applies an AC voltage to the electrode unit 30, and a control unit 250. The dielectric heating device 100 dries the medium Md by heating the medium Md with an AC electric field generated by the electrode unit 30 while transporting the medium Md with the transport unit 320. When it is said that the medium Md is "heated with an AC electric field," it includes not only heating the medium Md itself with an AC electric field, but also heating any adhering matter such as a liquid or solid adhering to the medium Md with an AC electric field. The electrode unit 30 is also called a heater.

[0009] The medium Md may be, for example, paper, cloth, or film. The cloth used as the medium Md is formed by weaving fibers such as cotton, hemp, polyester, silk, or rayon, or fibers that are a blend of these. In this embodiment, a sheet-like cotton cloth is used as the medium Md.

[0010] In this embodiment, the dielectric heating device 100 dries the medium Md on which a liquid discharged by a liquid discharge device (not shown) has been applied. For example, various inks containing water as a main component are used as such liquid. In this embodiment, an aqueous ink containing water as a main component is used as the liquid. In this specification, the main component of the liquid refers to a substance that has a mass fraction of 50% or more among the substances contained in the liquid. In other embodiments, in addition to ink, any liquid may be used as the liquid, such as various coloring materials, electrode materials, samples such as biological organic matter and inorganic matter, lubricating oils, resin liquids, and etching liquids.

[0011] 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.

[0012] The transport unit 320 is configured as a roller mechanism that transports the medium Md by driving rollers 323. Under the control of the control unit 250, the transport unit 320 drives the rollers 323 by the driving force of a drive unit (not shown) configured by a motor or the like. In this embodiment, the transport unit 320 transports the medium Md in the -Y direction. In other embodiments, the transport unit 320 may be configured as a belt mechanism that transports the medium Md by driving a belt, for example.

[0013] The 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 other embodiments, the control unit 250 may be configured by, for example, a combination of multiple circuits.

[0014] The voltage application section 80 is electrically connected to the electrode unit 30, and applies an AC voltage of a predetermined driving frequency f0 to the first electrode 31 and the second electrode 32 of the electrode unit 30 described later. In this embodiment, the voltage application section 80 is configured as a high-frequency power supply including a high-frequency voltage generating circuit, and each of the high-frequency voltage generating circuits has a crystal oscillator, a PLL (Phase Locked Loop) circuit, and a power amplifier, which are not shown. In other embodiments, the voltage application section 80 may be configured as an inverter including a switching circuit having a switching element such as a transistor, for example. One of the potentials applied to the first electrode 31 or the second electrode 32 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.

[0015] In this embodiment, a high-frequency voltage is applied to each electrode of the electrode unit 30. 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 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 the electrode unit 30. 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, such as 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, the dielectric tangent of water in the ink is low, while Joule heat is easily generated by the pigment components in the ink as electrical resistance.

[0016] FIG. 2 is a perspective view showing a schematic configuration of the electrode unit 30 in this embodiment. As shown in FIG. 1, in this embodiment, the dielectric heating device 100 has two electrode units 30 arranged side by side along the X direction. As shown in FIGS. 1 and 2, the electrode unit 30 has a first electrode 31 and a second electrode 32. Moreover, the electrode unit 30 in this embodiment has a coil 34. In other embodiments, the number of electrode units 30 may be one, or may be three or more. Moreover, the electrode units 30 do not have to be arranged side by side along the X direction, and may be arranged arbitrarily.

[0017] The first electrode 31 and the second electrode 32 face the medium Md transported in the transport direction. In this embodiment, the transport direction is the -Y direction. Therefore, in this embodiment, the +Y direction side corresponds to the upstream side of the transport direction, and the -Y direction side corresponds to the downstream side of the transport direction. Hereinafter, the direction in which the first electrode 31 and the second electrode 32 face the medium Md is also referred to as the facing direction. The facing direction includes both a direction on one side along the same axis and the opposite direction, and is the Z direction in this embodiment.

[0018] 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.

[0019] 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 electrode unit 30. As shown in FIG. 2, the first electrode 31 in this embodiment has a boat-shaped shape with the Y direction as the longitudinal direction and the X direction as the transverse direction. The lower surface of the first electrode 31 has a curved shape that is convex in the -Z direction. When viewed along the Z direction, the first electrode 31 has an elliptical shape that is elongated in the X direction. The second electrode 32 has an elliptical ring shape that is flat in the X direction and the Y direction and is elongated in the X direction. When viewed along the Z direction, the second electrode 32 is arranged so as to surround the periphery of the first electrode 31. The second electrode 32 has a first portion 36 and a second portion 37 that sandwich the first electrode 31 in the transport direction, as described later.

[0020] 1 and 2, the first electrode 31 and the second electrode 32 are both disposed on a substrate 110 disposed parallel to the XY plane. More specifically, the first electrode 31 is disposed such that the center portion in the X direction and the Y direction of the lower surface of the first electrode 31 contacts the upper surface of the substrate 110. The second electrode 32 is disposed such that the lower surface of the second electrode 32 contacts the upper surface of the substrate 110. Therefore, in this embodiment, the center portion of the lower surface of the first electrode 31 and the lower surface of the second electrode 32 are disposed on the same plane.

[0021] 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.

[0022] 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 the medium Md, in the case where the medium Md is a cloth, from adhering to the first electrode 31 and the second electrode 32. In other embodiments, the substrate 110 may be made of, for example, alumina.

[0023] Returning to Fig. 2, in this embodiment, the first electrode 31 is electrically connected to the voltage application unit 80 via the electric wire 35, the 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 part of the second electrode 32, an outer conductor of the coaxial cable (not shown), and the like.

[0024] 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. Hereinafter, the electromagnetic field generated near the first electrode 31 and the second electrode 32 by the application of the AC voltage is also called the "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 the "far". 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 the "far electromagnetic field". The far electromagnetic field corresponds to an electromagnetic field used for communication by a general communication antenna or the like. The electric field formed in the vicinity of the first electrode 31 and the second electrode 32 is also called a near electric field.

[0025] 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 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 periphery of 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.

[0026] In this embodiment, one end of the coil 34 is electrically connected in series to the first electrode 31 via the electric wire 35, and the other end is electrically connected in series to the voltage application unit 80 shown in FIG. 1. In this embodiment, the 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 coil 34 are selected, for example, according to the drive frequency f0 and so as to realize impedance matching between the electrode unit 30 and the voltage application unit 80. In other embodiments, one end of the coil 34 may be connected in series to the second electrode 32 instead of the first electrode 31.

[0027] When the voltage application unit 80 applies an AC voltage to the electrode unit 30, a high voltage is generated at one end of the coil 34. This can increase the intensity of the electric field generated from the first electrode 31 and the second electrode 32. The coil 34 is preferably disposed so that the distance between one end of the coil 34 and the first electrode 31 is as small as possible. If the distance between one end of the coil 34 and the first electrode 31 is large, the high voltage generated at one end of the coil 34 may generate an electric field between the coil 34 and the first electrode 31 or between the 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 nearby electric field generated from the first electrode 31 and the second electrode 32 may decrease. In contrast, by shortening the distance between one end of the 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 that contributes to heating the medium Md can be effectively increased. In another embodiment, for example, the first electrode 31 may be formed in a meandering shape so that the first electrode 31 has the same function as the coil .

[0028] 3 is a top view showing the first electrode 31, the second electrode 32, and the medium Md in this embodiment. In FIG. 3, the substrate 110 is omitted. As shown in FIG. 2 and FIG. 3, the first portion 36 of the second electrode 32 described above is disposed upstream of the second portion 37 in the transport direction. More specifically, in this embodiment, the first portion 36 is a portion of the second electrode 32 formed in a ring shape surrounding the first electrode 31 as described above, which is located on the +Y direction side of the first electrode 31. The second portion 37 is a portion of the second electrode 32 located on the -Y direction side of the first electrode 31.

[0029] In this embodiment, the thickness t1 of the first portion 36 is thicker than the thickness t2 of the second portion 37. In this specification, the thickness t1 refers to the average thickness of the first portion 36, and the thickness t2 refers to the average thickness of the second portion 37. The average thickness of a certain portion is measured by measuring the thickness at 10 or more points in the portion and calculating the arithmetic average of the thicknesses. In this embodiment, the first portion 36 and the second portion 37 are each formed so that their thicknesses in the Z direction are uniform.

[0030] The first electrode 31 and the second electrode 32 are formed such that a first heating amount of the electrode unit 30 is greater than a second heating amount of the electrode unit 30. The first heating amount refers to the heating amount of the medium Md by a first electric field representing a near electric field formed between the first electrode 31 and the first portion 36. The second heating amount refers to the heating amount of the medium Md by a second electric field representing a near electric field formed between the first electrode 31 and the second portion 37.

[0031] When comparing the first and second heating amounts, for example, a cotton cloth with a liquid applied to the entire surface with a substantially uniform thickness is prepared as the medium Md, and the temperature in the first media portion Mp1 and the temperature in the second media portion Mp2 are compared when the medium Md is heated by the electrode unit 30 without being transported. More specifically, when the first heating amount is larger than the second heating amount, the temperature in the first media portion Mp1 when the medium Md is heated in this manner is higher than the temperature in the second media portion Mp2. The first media portion Mp1 refers to a portion of the medium Md that is located between the first electrode 31 and the first portion 36 when viewed along the Z direction, as shown by the dashed line and hatching in FIG. 3. Similarly, the second media portion Mp2 refers to a portion of the medium Md that is located between the first electrode 31 and the second portion 37 when viewed along the Z direction.

[0032] The amount of heat when a certain portion of the medium Md is heated by the electrode unit 30 increases as the strength of the near electric field acting on that portion increases. Therefore, the first amount of heat can be made larger relative to the second amount of heat by increasing the strength of the electric field acting on the liquid attached to the first media portion Mp1 or decreasing the strength of the electric field acting on the liquid attached to the second media portion Mp2. Increasing the strength of the near electric field acting on the liquid attached to a certain portion of the medium Md corresponds to increasing the density of the electric field lines passing through the liquid when the near electric field is expressed by electric field lines. In particular, since the liquid attached to the sheet-like medium Md is usually distributed so as to spread on the medium Md along the surface direction of the medium Md, the amount of heat in that portion can be effectively increased by increasing the density of the electric field lines along the surface direction of the medium Md in the vicinity of the certain portion of the medium Md.

[0033] FIG. 4 is a schematic diagram for explaining the thickness t1 of the first portion 36 and the thickness t2 of the second portion 37. FIG. 4 is a schematic diagram showing a state when the liquid Lq attached to the medium Md is heated by the electrode unit 30. In FIG. 4, the electric field Eq1 acting on the liquid Lq attached to the first media portion Mp1 and the electric field Eq2 acting on the liquid Lq attached to the second media portion Mp2 are represented by dashed lines. In FIG. 4, the thicker the dashed line is, the stronger the intensity of the electric field represented by the dashed line is. As shown in FIG. 2 and FIG. 4, in this embodiment, the second electrode 32 is formed so that the thickness t1 of the first portion 36 in the Z direction is thicker than the thickness t2 of the second portion 37 in the Z direction, thereby realizing that the first heating amount is larger than the second heating amount. More specifically, as shown in FIG. 4, in this embodiment, the thickness t1 is thicker than the thickness t2, so that the intensity of the electric field Eq1 is stronger than the intensity of the electric field Eq2.

[0034] 5 is a schematic diagram illustrating a circuit formed by the electrode unit 30 in this embodiment and the liquid Lq attached to the medium Md. As shown in Fig. 5, the first electrode 31 and the second electrode 32 of the electrode unit 30 can each be considered as an electrode plate that constitutes a capacitor.

[0035] The resistor R shown in Figure 5 a represents the resistance of the electrode unit 30. Resistance R a includes the internal resistance of the voltage application unit 80 and the parasitic resistance of the coil 34. a represents the inductance of the electrode unit 30. Inductance L a includes the inductance of the coil 34 and the parasitic inductance of each electrode of the electrode unit 30. a represents the capacitance of the electrode unit 30. Capacitance C a includes the parasitic capacitance of the coil 34 and the capacitance between the electrodes of the electrode unit 30. b represents the electrical resistance of the liquid Lq deposited on the medium Md. Capacitance C 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 capacitance C b1 and C b2 It is expressed as the sum of the capacitance C a and capacitance C b The sum of these corresponds to the capacitance of the electrode unit 30.

[0036] The resonant frequency f1 of the electrode unit 30 when the liquid applied to the medium Md is dried is expressed as the resonant frequency of the electrode unit 30 in the circuit formed by the electrode unit 30 and the liquid Lq attached to the medium Md shown in Figure 5. The capacitance C aSince the driving frequency f0 of the medium Md decreases, the resonant frequency f1 increases as the drying progresses. Hereinafter, such a change in the resonant frequency f1 as the drying progresses is also referred to as a shift in the resonant frequency f1. The shift in the resonant frequency f1 changes the difference between the driving frequency f0 and the resonant frequency f1, and the impedance of the electrode unit 30 changes. Therefore, the shift in the resonant frequency f1 affects the amount of heat generated by the entire electrode unit 30. For example, if the driving frequency f0 is set to match the resonant frequency f1 when the moisture content of the medium Md is sufficiently large, the shift in the resonant frequency f1 increases the difference between the resonant frequency f1 and the driving frequency f0, and the impedance of the electrode unit 30 increases. Therefore, in this case, the shift in the resonant frequency f1 contributes to a decrease in the amount of heat generated by the entire electrode unit 30.

[0037] In this embodiment, the electrode unit 30 is configured so that the first sensitivity of the resonant frequency f1 is higher than the second sensitivity. The first sensitivity refers to the sensitivity of the resonant frequency f1 to the change in the moisture content of the medium Md between the first electrode 31 and the first portion 36. The second sensitivity refers to the sensitivity of the resonant frequency f1 of the electrode unit 30 to the change in the moisture content of the medium Md between the second electrode 32 and the second portion 37. More specifically, the first sensitivity corresponds to the sensitivity of the resonant frequency f1 to the change in the moisture content of the first media portion Mp1. The second sensitivity corresponds to the sensitivity of the resonant frequency f1 to the change in the moisture content of the second media portion Mp2. As described above, the shift of the resonant frequency f1 affects the amount of heat generated by the entire electrode unit 30. Therefore, by making the first sensitivity higher than the second sensitivity, the sensitivity of the amount of heat generated by the entire electrode unit 30 to the change in the moisture content of the first media portion Mp1 can be made higher than the sensitivity to the change in the moisture content of the second media portion Mp2.

[0038] In this embodiment, the water content of a certain portion of the medium Md is expressed as the mass of water contained per unit volume of that portion. In other embodiments, for example, the water content of a certain portion may be expressed as the volume of water contained per unit volume of that portion, or as a ratio of the mass or volume of water to a reference value for the mass or volume.

[0039] When comparing the first sensitivity and the second sensitivity, first, a cotton cloth with a liquid applied to the entire surface in a substantially uniform thickness is prepared as a first sample, and a first step is performed to measure the resonance frequency ft0 when the first sample is heated by the electrode unit 30 without being transported. Next, a cotton cloth with a liquid applied to the entire surface except for the portion corresponding to the first media portion Mp1 is prepared as a second sample, and a resonance frequency ft1 is measured when the second sample is heated by the electrode unit 30 without being transported. The difference between this resonance frequency ft1 and the resonance frequency ft0 corresponds to the first sensitivity. Similarly, a cotton cloth with a liquid applied to the entire surface except for the portion corresponding to the second media portion Mp2 is prepared as a medium Md, and a resonance frequency ft2 is measured when the cotton cloth is heated by the electrode unit 30 in a similar manner. The difference between this resonance frequency ft2 and the resonance frequency ft0 corresponds to the second sensitivity. Note that, when ink is used as the liquid Lq as in this embodiment, the above-mentioned first sample can be prepared by, for example, printing the liquid solidly on the entire surface of the cotton cloth using an inkjet printer. Solid printing refers to forming dots on all pixels that make up an image, so that no part of the background color of the medium Md remains. Similarly, the second and third samples can be prepared by solid printing a liquid on the surface of the cotton cloth excluding the parts corresponding to the first media part Mp1 and the second media part Mp2. The resonance frequencies ft0 to ft2 are calculated based on the inductance and capacitance of the electrode unit 30 measured using a network analyzer, for example.

[0040] 4, the first sensitivity can be increased by increasing the ratio of the intensity of the electric field Eq1 acting on the first media portion Mp1 to the intensity of the electric field En1 not acting on the first media portion Mp1, among the first electric field. Increasing the ratio of the electric field Eq1 to the intensity of the electric field En1 corresponds to increasing the proportion of the electric field lines that pass through the liquid Lq attached to the first media portion Mp1, among the electric field lines that represent the first electric field, when the first electric field is represented by electric field lines. Moreover, the second sensitivity can be decreased by decreasing the ratio of the intensity of the electric field Eq2 acting on the second media portion Mp2 to the intensity of the electric field En2 not acting on the second media portion Mp2, among the second electric field.

[0041] In this embodiment, the second electrode 32 is formed so that the thickness t1 shown in FIG. 2 and FIG. 4 is thicker than the thickness t2, thereby realizing that the first sensitivity to the resonance frequency f1 is higher than the second sensitivity. In general, by making the thickness t1 thicker, the density of the electric field lines passing through the liquid Lq on the first media portion Mp1 can be increased, and the ratio of the electric field Eq1 to the intensity of the electric field En1 can be increased. However, if the thickness t1 is made too thick, the number of electric field lines that do not pass through the liquid Lq on the first media portion Mp1 increases, which may reduce the ratio of the electric field Eq1 to the intensity of the electric field En1. In this embodiment, the thickness t1 is preferably 1.5 times or more than the thickness t2, and more preferably 3 times or more. Moreover, the thickness t1 is preferably 10 times or less than the thickness t2, and more preferably 8 times or less than the thickness t2.

[0042] According to the dielectric heating device 100 in the first embodiment described above, the electrode unit 30 has a first portion 36 and a second portion 37 that sandwich the first electrode 31 in the transport direction of the media Md, the first portion 36 is disposed upstream of the second portion 37 in the transport direction, and the first electrode 31 and the second electrode 32 are formed so that a first heating amount representing the amount of heating of the media Md by the first electric field formed between the first electrode 31 and the first portion 36 is larger than a second heating amount representing the amount of heating of the media Md by the second electric field formed between the first electrode 31 and the second portion 37. This makes the amount of heating of the media Md by the electrode unit 30 larger upstream in the transport direction of the media Md, and makes the amount of heating of the media Md by the electrode unit 30 smaller downstream in the transport direction. Therefore, it is possible to prevent the media Md from being overly dried by heating by the electrode unit 30 downstream in the transport direction. Furthermore, since there is no need to measure the moisture content of the media Md, for example, even if a sensor for measuring the moisture content is not provided near the first electrode 31 or the second electrode 32, the media Md can be prevented from becoming too dry further downstream in the transport direction.

[0043] In the present embodiment, the electrode unit 30 is configured such that the first sensitivity of the resonant frequency f1 of the electrode unit 30 to the change in the moisture content of the medium Md heated by the electric field formed between the first electrode 31 and the first portion 36 is higher than the second sensitivity to the change in the moisture content of the medium Md heated by the electric field formed between the first electrode 31 and the second portion 37. In this manner, the sensitivity of the heating amount of the entire electrode unit 30 to the change in the moisture content of the first media portion Mp1 can be made higher than the sensitivity to the change in the moisture content of the second media portion Mp2. As a result, for example, by setting the driving frequency f0 to coincide with the resonant frequency f1 when the moisture content of the medium Md is sufficiently large, when the moisture content of the first media portion Mp1 is relatively large, the heating amount in the first media portion Mp1 can be made larger, and the moisture content of the first media portion Mp1 can be reduced. Conversely, if the moisture content of the first media portion Mp1 is smaller, the amount of heat applied to the first media portion Mp1 can be reduced, and the first media portion Mp1 can be prevented from being overdried. When the medium Md is heated while being transported, the portion that is first heated by the electrode unit 30 as the first media portion Mp1 becomes the second media portion Mp2. Therefore, by doing as described above, the second media portion Mp2 can be dried just right, regardless of whether the moisture content of the first media portion Mp1 is relatively high or low. Therefore, the medium Md can be dried more uniformly.

[0044] In this embodiment, the thickness t1 of the first portion 36 is greater than the thickness t2 of the second portion 37. Therefore, by making the thickness t1 greater than the thickness t2, it is possible to easily realize that the first amount of heating is greater than the second amount of heating. In addition, by making the thickness t1 greater than the thickness t2, it is also possible to easily realize that the first sensitivity to the resonant frequency f1 is greater than the second sensitivity.

[0045] B. Second embodiment: Fig. 6 is a perspective view showing a schematic configuration of an electrode unit 30b in the second embodiment. In Fig. 6, the electric wire 35, the coil 34, and the internal conductor IC1 are omitted. In this embodiment, unlike the first embodiment, the second electrode 32b is formed so that the width w1 in the conveying direction of the first portion 36b is smaller than the width w2 in the conveying direction of the second portion 37b. Parts of the configuration of the electrode unit 30b and the dielectric heating device 100 in the second embodiment that are not particularly described are similar to those in the first embodiment.

[0046] As described above, in this embodiment, the width w1 is smaller than the width w2. In this specification, the width w1 refers to the average width of the first portion 36b, and the width w2 refers to the average width of the second portion 37b. The average width of a certain portion is measured by measuring the width of 10 or more points in the portion and calculating the arithmetic average of each width. In this embodiment, the width w1 is smaller than the width w2, so that the second electrode 32b has a shape that is asymmetrical with respect to a straight line along the X direction that bisects the first electrode 31 in the Y direction when viewed along the Z direction, and a shape that is asymmetrical with respect to the center point of the first electrode 31 in the X direction and the Y direction. In this embodiment, the width w1 is smaller than the width w2, so that the first heating amount is larger than the second heating amount. In this embodiment, the first portion 36b and the second portion 37b are formed to have uniform widths w1 and w2 in the X direction, respectively. In this embodiment, the thickness t1 of the first portion 36 and the thickness t2 of the second portion 37 are the same.

[0047] FIG. 7 is a schematic diagram for explaining the width w1 of the first portion 36b and the width w2 of the second portion 37b. FIG. 7 is a schematic diagram showing the state when the liquid Lq attached to the medium Md is heated by the electrode unit 30b, similar to FIG. 4 described in the first embodiment. In FIG. 7, the electric fields Eq1, Eq2, En1, and En2 are shown by dashed lines, similar to FIG. 4. As shown in FIG. 7, in this embodiment, the width w1 is made smaller than the width w2, so that the intensity of the electric field Eq1 is stronger than the intensity of the electric field Eq2. More specifically, the smaller width w1 causes the electric field lines from the first portion 36b to the first electrode 31 and from the first electrode 31 to the first portion 36b to be concentrated in a narrower range, so that the intensity of the electric field Eq1 is stronger. In this embodiment, the width w1 is preferably 1.5 times or more than the width w2, and more preferably 2 times or more. Moreover, the width w1 is preferably 8 times or less than the width w2, and more preferably 6 times or less.

[0048] In this embodiment, the second electrode 32 is formed so that the width w1 is smaller than the width w2, thereby realizing that the first sensitivity to the resonant frequency f1 is higher than the second sensitivity. More specifically, as described above, the smaller width w1 causes the electric field lines from the first portion 36b to the first electrode 31 and from the first electrode 31 to the first portion 36b to be concentrated in a narrower range in the first portion 36b, thereby making the strength of the electric field Eq1 stronger relative to the strength of the electric field En1.

[0049] According to the second embodiment described above, the width w1 of the first portion 36b of the second electrode 32b is smaller than the width w2 of the second portion 37b. Therefore, by making the width w1 smaller than the width w2, it is possible to easily realize that the first heating amount is larger than the second heating amount. In addition, by making the width w1 smaller than the width w2, it is also possible to easily realize that the first sensitivity to the resonant frequency f1 is higher than the second sensitivity.

[0050] C. Third embodiment: Fig. 8 is a perspective view showing a schematic configuration of an electrode unit 30c in the third embodiment. In Fig. 8, the electric wire 35, the coil 34, and the internal conductor IC1 are omitted, as in Fig. 2 described in the second embodiment. In this embodiment, unlike the first and second embodiments, the first distance d1 in the conveying direction between the first electrode 31 and the first portion 36c of the second electrode 32c is shorter than the second distance d2 in the conveying direction between the first electrode 31 and the second portion 37. Parts of the configuration of the electrode unit 30c and the dielectric heating device 100 in the third embodiment that are not particularly described are similar to those in the first embodiment.

[0051] As described above, in this embodiment, the first distance d1 is shorter than the second distance d2. In this embodiment, the first distance d1 refers to the average value of the distance between the first electrode 31 and the first portion 36c in the transport direction, and the second distance d2 refers to the average value of the distance between the first electrode 31 and the second portion 37 in the transport direction. The average value of the distance is measured by measuring the distance at 10 or more points and calculating the arithmetic mean of each distance. In this embodiment, the first distance d1 is smaller than the second distance d2, so that the second electrode 32c has a shape that is asymmetrical with respect to a straight line along the X direction that bisects the first electrode 31 in the Y direction when viewed along the Z direction, and a shape that is asymmetrical with respect to the center point of the first electrode 31 in the X direction and the Y direction. In this embodiment, the first distance d1 is smaller than the second distance d2, so that the first heating amount is larger than the second heating amount. Thus, forming the first electrode 31 and the second electrode 32c so that the first heating amount is larger than the second heating amount also includes setting the relative positions of the first electrode 31 and the second electrode 32c so that the first heating amount is larger than the second heating amount. In this embodiment, the first electrode 31 and the first portion 36c are disposed at a constant first distance d1 in the X direction, and the first electrode 31 and the second portion 37 are disposed at a constant second distance d2 in the X direction. In this embodiment, the thickness t1 of the first portion 36c and the thickness t2 of the second portion 37 are the same, and the width w1 of the first portion 36c and the width w2 of the second portion 37 are the same.

[0052] Fig. 9 is a schematic diagram for explaining the first distance d1 and the second distance d2. Fig. 9, like Fig. 4 described in the first embodiment, shows a schematic diagram of the liquid Lq attached to the medium Md being heated by the electrode unit 30b. In Fig. 9, like Fig. 4, the electric fields Eq1, Eq2, En1, and En2 are shown by dashed lines. As shown in Fig. 9, in this embodiment, the first distance d1 is made smaller than the second distance d2, so that the strength of the electric field Eq1 is stronger than the strength of the electric field Eq2.

[0053] In this embodiment, the first distance d1 is smaller than the second distance d2, so that the first sensitivity to the resonance frequency f1 is higher than the second sensitivity. In general, by shortening the first distance d1 and lengthening the second distance d2, the density of the electric field lines passing through the liquid Lq on the first media portion Mp1 can be increased, and the ratio of the intensity of the electric field Eq1 to the intensity of the electric field En1 can be increased. However, if the first distance d1 is too short compared to the second distance d2, the area of ​​the first media portion Mp1 in the XY plane becomes relatively small compared to the area of ​​the second media portion Mp2 in the XY plane, so that the first sensitivity may be lower than the second sensitivity. In this embodiment, the first distance d1 is preferably 0.25 times or more, more preferably 0.35 times or more, of the second distance d2. In addition, the first distance d1 is preferably 0.75 times or less, more preferably 0.6 times or less, of the second distance d2.

[0054] According to the third embodiment described above, the first distance d1 between the first electrode 31 and the first portion 36c is shorter than the second distance d2 between the first electrode 31 and the second portion 37. Therefore, by making the first distance d1 shorter than the second distance d2, it is possible to easily realize that the first heating amount is larger than the second heating amount. In addition, by making the first distance d1 shorter than the second distance d2, it is also possible to easily realize that the first sensitivity to the resonant frequency f1 is higher than the second sensitivity.

[0055] D. Other embodiments: (D-1) In the above embodiment, the first amount of heating may be greater than the second amount of heating by combining two or more of, for example, making the thickness t1 thicker than the thickness t2, making the width w1 smaller than the width w2, and making the first distance d1 shorter than the second distance d2.

[0056] (D-2) In the above embodiment, the first amount of heating may be greater than the second amount of heating, for example, by adjusting the thickness of the first electrode 31. For example, the first amount of heating may be greater than the second amount of heating, by making the thickness of the first electrode 31 in the +Y direction half greater than the thickness of the first electrode 31 in the -Y direction half.

[0057] (D-3) In the above embodiment, the electrode unit 30 is configured so that the first sensitivity to the resonant frequency f1 is higher than the second sensitivity, but it does not have to be configured in this way.

[0058] (D-4) In the above embodiment, the first electrode 31 has a boat-like shape, but it does not have to have a boat-like shape, and may have, for example, a flat plate shape or a rod shape. Also, in the above embodiment, the first electrode 31 has an oval shape when viewed along the Z direction, but it does not have to have an oval shape, and may have, for example, a circular shape, a rectangular shape, or another polygonal shape.

[0059] (D-5) In the above embodiment, the second electrode 32 is disposed so as to surround the periphery of the first electrode 31 when viewed along the Z direction. In contrast, the second electrode 32 does not have to be disposed so as to surround the periphery of the first electrode 31 when viewed along the Z direction. For example, the second electrode 32 may be configured by two rod-shaped electrodes or two plate-shaped electrodes having the same potential, sandwiching the first electrode 31 in the transport direction. In this case, of the portions of the electrodes constituting the second electrode 32 that sandwich the first electrode 31 in the transport direction, the portion located on the upstream side in the transport direction corresponds to the first portion 36, and the portion located on the downstream side corresponds to the second portion 37.

[0060] (D-6) In the above embodiment, the electrode unit 30 may be configured to be capable of reciprocating in the X direction, for example. For example, the electrode unit 30 may be supported by a drive unit (not shown) configured by a belt mechanism or a ball screw mechanism, and may be reciprocated in the X direction.

[0061] (D-7) 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. In addition, the driving frequency f0 does not have to be a high frequency as long as the liquid attached to the medium Md can be heated by the electrode unit 30. In this case, the driving frequency f0 is preferably, for example, equal to or higher than 100 kHz and lower than 1 MHz.

[0062] E. 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.

[0063] (1) According to one aspect of the present disclosure, there is provided a dielectric heating device. The dielectric heating device includes a transport section that transports a medium in a transport direction, an electrode unit having a first electrode and a second electrode facing the medium transported by the transport section and drying the medium by dielectric heating, a voltage application section that applies an AC voltage to the first electrode and the second electrode, and a control section that controls the transport section. The second electrode has a first portion and a second portion that sandwich the first electrode in the transport direction, the first portion is disposed upstream of the second portion in the transport direction, and the first electrode and the second electrode are formed such that an amount of heating of the medium due to an electric field formed between the first electrode and the first portion is greater than an amount of heating of the medium due to an electric field formed between the first electrode and the second portion. In this configuration, the amount of heating of the media by the electrode units is greater upstream in the media transport direction, and the amount of heating of the media by the electrode units is smaller downstream in the media transport direction, thereby preventing the media from becoming overly dry due to heating by the electrode units downstream in the media transport direction.

[0064] (2) In the above embodiment, the distance in the transport direction between the first electrode and the first portion may be shorter than the distance in the transport direction between the first electrode and the second portion. According to this embodiment, by making the distance in the transport direction between the first electrode and the first portion shorter than the distance in the transport direction between the first electrode and the first portion, it is possible to easily achieve a greater amount of heating of the medium due to the electric field formed between the first electrode and the first portion than the amount of heating of the medium due to the electric field formed between the first electrode and the second portion.

[0065] (3) In the above embodiment, the thickness of the first portion in a direction in which the first electrode and the second electrode face the medium may be greater than the thickness of the second portion in the facing direction. According to this embodiment, by making the thickness of the first portion greater than the thickness of the second portion, it is possible to easily achieve a larger amount of heating of the medium due to the electric field formed between the first electrode and the first portion than the amount of heating of the medium due to the electric field formed between the first electrode and the second portion.

[0066] (4) In the above embodiment, the width of the first portion in the transport direction may be smaller than the width of the second portion in the transport direction. According to this embodiment, by making the width of the first portion smaller than the width of the second portion, it is possible to easily achieve a larger amount of heating of the medium due to the electric field formed between the first electrode and the first portion than a larger amount of heating of the medium due to the electric field formed between the first electrode and the second portion.

[0067] (5) In the above embodiment, the electrode unit may be configured such that the sensitivity of the resonant frequency of the electrode unit to changes in the moisture content of the media heated by the electric field formed between the first electrode and the first portion is higher than the sensitivity of the resonant frequency of the electrode unit to changes in the moisture content of the media heated by the electric field formed between the first electrode and the second portion. According to this embodiment, the sensitivity of the heating amount of the entire electrode unit to changes in the moisture content of the media heated by the electric field formed between the first electrode and the first portion can be made higher than the sensitivity of the heating amount of the entire electrode unit to changes in the moisture content of the media heated by the electric field formed between the first electrode and the second portion. This increases the possibility of drying the media more uniformly. [Explanation of symbols]

[0068] 30, 30b, 30c...electrode unit, 31...first electrode, 32, 32b, 32c...second electrode, 33...connecting member, 34...coil, 35...electric wire, 36, 36b, 36c...first portion, 37, 37b...second portion, 80...voltage application section, 100...dielectric heating device, 110...substrate, 250...control section, 320...transport section, 323...roller

Claims

1. a transport unit that transports the medium in a transport direction; an electrode unit having a first electrode and a second electrode facing the medium transported by the transport section, and drying the medium by dielectric heating; a voltage application unit that applies an AC voltage to the first electrode and the second electrode; A control unit that controls the transport unit, the second electrode has a first portion and a second portion sandwiching the first electrode in the transport direction, the first portion is disposed upstream of the second portion in the conveying direction; A dielectric heating device, wherein the first electrode and the second electrode are configured so that an amount of heating of the medium due to an electric field formed between the first electrode and the first portion is greater than an amount of heating of the medium due to an electric field formed between the first electrode and the second portion.

2. 2. The dielectric heating device according to claim 1, A dielectric heating device, wherein a distance between the first electrode and the first portion in the conveying direction is shorter than a distance between the first electrode and the second portion in the conveying direction.

3. 2. The dielectric heating device according to claim 1, A dielectric heating device, wherein a thickness of the first portion in a direction in which the first electrode and the second electrode face the medium is greater than a thickness of the second portion in the direction in which the first electrode and the second electrode face the medium.

4. 2. The dielectric heating device according to claim 1, A dielectric heating device, wherein the width of the first portion in the conveying direction is smaller than the width of the second portion in the conveying direction.

5. The dielectric heating device according to any one of claims 1 to 4, A dielectric heating device, wherein the electrode unit is configured so that the sensitivity of the resonant frequency of the electrode unit to changes in the moisture content of the medium heated by the electric field formed between the first electrode and the first portion is higher than the sensitivity of the resonant frequency of the electrode unit to changes in the moisture content of the medium heated by the electric field formed between the first electrode and the second portion.

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