Dielectric heating device and printing system

Abstract

The present application relates to a dielectric heating device and a printing system. The present application provides a technology capable of suppressing uneven heating while heating both a carbon black-containing ink and a non-carbon black-containing ink attached to a medium. The dielectric heating device of the present application heats a first carbon black-containing ink and a second non-carbon black-containing ink attached to a medium. The dielectric heating device includes a first electrode unit having a first electrode and a second electrode facing the medium as an electrode unit for heating the first and second inks, and a first voltage application unit applying an alternating voltage of a frequency of 300 MHz or more and 300 GHz or less to the first and second electrodes.

Description

Technical Field

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

[0002] Regarding dielectric heating devices, Patent Document 1 discloses the following technology: After drying a first liquid adhering to a substrate such as recording paper using a first drying device that functions as a dielectric heating device, a second liquid is applied to the substrate, and the applied second liquid is dried using a second drying device. The second liquid is black ink containing carbon black, and the first liquid is an ink of a color other than black ink. This suppresses uneven heating of the substrate caused by a rapid temperature rise when heating the carbon black-containing liquid using dielectric heating.

[0003] Patent Document 1: Japanese Patent Application Publication No. 2017-119395

[0004] However, in Patent Document 1, after the first liquid adhering to the substrate is temporarily dried by a dielectric heating device, the second liquid is further adhering to the substrate. Therefore, sometimes the second liquid cannot be adhering to the position corresponding to the already adhering first liquid, resulting in a misalignment between the adhering positions of the first and second liquids. Summary of the Invention

[0005] According to a first aspect of this disclosure, a dielectric heating device is provided for heating a first ink containing carbon black and a second ink not containing carbon black attached to a medium. The dielectric heating device includes a first electrode unit and a first voltage application unit. The first electrode unit, serving as an electrode unit for heating the first ink and the second ink, has a first electrode and a second electrode facing the medium. The first voltage application unit applies an alternating voltage with a frequency of 300 MHz or more and 300 GHz or less to the first electrode and the second electrode.

[0006] According to a second aspect of this disclosure, a printing system is provided. The printing system includes an ejection unit and a conveying unit. The ejection unit has a first ejection section that ejects a first ink onto a medium to allow the first ink to adhere to the medium, and a second ejection section that ejects a second ink onto the medium to allow the second ink to adhere to the medium. The conveying unit conveys the medium along a conveying path. An electrode unit heats the first ink and the second ink at a position downstream of the position where the ejection unit allows the first ink and the second ink to adhere to the medium in the conveying path. Attached Figure Description

[0007] Figure 1 This is a schematic diagram showing the general structure of a printing system.

[0008] Figure 2 This is a perspective view showing the general structure of a dielectric heating device.

[0009] Figure 3 This is a three-dimensional view showing the general structure of the first electrode unit.

[0010] Figure 4 This is a three-dimensional diagram showing the general structure of the second electrode unit.

[0011] Figure 5 The first graph is plotted with the heating time of each sample on the horizontal axis and the temperature on the vertical axis.

[0012] Figure 6 The second chart uses the heating time of each sample as the horizontal axis and temperature as the vertical axis.

[0013] Explanation of reference numerals in the attached figures

[0014] 20…Electrode unit, 30…First electrode unit, 31…First electrode, 32…Second electrode, 33…Connecting member, 34…First coil, 35…First wire, 40…Second electrode unit, 41…Third electrode, 42…Fourth electrode, 43…Second connecting member, 44…Second coil, 45…Second wire, 80…Voltage applying part, 81…First voltage applying part, 82…Second voltage applying part, 100…Dielectric heating device, 110…Substrate, 150…Conveying part, 1 80…Heating control unit, 200…Printing system, 205…Liquid ejection device, 210…Ejection unit, 211…First ejection section, 212…Second ejection section, 230…Media conveying section, 250…Ejection control unit, 310…Conveying path, 311…First section, 312…Second section, 320…Conveying section, 321…First roller section, 322…Second roller section, 323…Third roller section, 324…Fourth roller section, 325…First conveying section, 326…Second conveying section. Detailed Implementation

[0015] A. First implementation method:

[0016] Figure 1 This is a schematic diagram showing the general configuration of the printing system 200 as a first embodiment. Figure 1 The diagram shows arrows representing the X, Y, and Z directions, which are mutually orthogonal. The X and Y directions are parallel to the horizontal plane, and the Z direction is vertically upward. The arrows representing the X, Y, and Z directions are also shown in the diagram in the same direction. Figure 1The corresponding diagrams are illustrated appropriately. In the following description, when a direction is specified, the direction indicated by the arrow in each diagram is marked as "+", and the opposite direction is marked as "-", and the direction is indicated by positive and negative symbols in the diagram. Hereinafter, the +Z direction is also referred to as "up", and the -Z direction is also referred to as "down". In addition, in this specification, orthogonality includes a range of 90° ± 10°.

[0017] The printing system 200 includes a dielectric heating device 100, a liquid ejection device 205, and a conveying unit 320. In this embodiment, the printing system 200 conveys a medium Md through the conveying unit 320, ejects ink onto the medium Md through the liquid ejection device 205 to make it adhere to the medium Md, and heats the ink adhered to the medium Md through the dielectric heating device 100 to dry it.

[0018] The conveying unit 320 conveys medium Md along the conveying path 310. In this embodiment, the conveying unit 320 includes a first roller section 321, a second roller section 322, a third roller section 323, and a fourth roller section 324, each composed of rollers, and a drive unit (not shown) composed of a motor or the like for driving these roller sections. In this embodiment, the first roller section 321, the second roller section 322, the third roller section 323, and the fourth roller section 324 are arranged sequentially facing the -Y direction. The conveying unit 320 conveys the sheet-like medium Md sequentially through the first roller section 321 to the fourth roller section 324 along the -Y direction.

[0019] In this embodiment, the trajectory of the medium Md conveyed by each roller corresponds to the conveying path 310. In other embodiments, part or all of the conveying path 310 may be formed, for example, by a belt. In this case, the conveying unit 320 may also be configured as a drive unit for driving the belt.

[0020] The first roller section 321 and the second roller section 322 constitute a first conveying section 325 that conveys the medium Md in the first interval 311 of the conveying path 310. The third roller section 323 and the fourth roller section 324 constitute a second conveying section 326 that conveys the medium Md in the second interval 312 of the conveying path 310. The second interval 312 is the interval in the conveying path 310 that is further downstream than the first interval 311. In each interval, a certain tension is applied to the medium Md. In this embodiment, the tension applied to the medium Md in each interval is different. In addition, as Figure 1 As shown, the first section 311 and the second section 312 are separated. In this embodiment, the first conveying section 325 is provided on the liquid ejection device 205 and constitutes a part of the liquid ejection device 205. The second conveying section 326 is provided on the dielectric heating device 100 and constitutes a part of the dielectric heating device 100.

[0021] As a medium Md, for example, paper, cloth, film, etc. Cloth used as a medium Md is formed, for example, by weaving fibers such as cotton, linen, polyester, silk, rayon, etc., or fibers blended from them.

[0022] The liquid ejection device 205 in this embodiment is configured as an inkjet printer. The liquid ejection device 205 includes an ejection unit 210 that ejects ink to a medium Md to adhere it to the medium Md, the aforementioned first transport section 325, and an ejection control section 250. The ejection unit 210 includes a first ejection section 211 and a second ejection section 212. The first ejection section 211 ejects a first ink In1 containing carbon black to the medium Md to adhere it to the medium Md. The second ejection section 212 ejects a second ink In2 that does not contain carbon black to the medium Md to adhere it to the medium Md. In this embodiment, the ejection unit 210 adheres the first ink In1 and the second ink In2 to the medium Md within the aforementioned first interval 311.

[0023] The ejection unit 210 is configured, for example, as a piezoelectric or thermal liquid ejection head. The first ejection section 211 is configured as a head chip in the ejection unit 210, for example, having a flow path for the flow of first ink In1 and a nozzle for ejecting the first ink In1. The second ejection section 212 is configured as a head chip in the ejection unit 210, for example, having a flow path for the flow of second ink In2 and a nozzle for ejecting the second ink In2. The ejection unit 210 can also be configured to reciprocate relative to the medium Md in a direction intersecting the Y direction via, for example, a carriage (not shown), or it can be configured as a so-called linear head with a fixed position and no reciprocating movement relative to the medium Md.

[0024] In this embodiment, the first ink In1 and the second ink In2 are pigment inks containing resin. The resin contained in the ink has the function of firmly fixing the pigment onto the medium Md by itself. Such resins are used, for example, in a state in which resins that are sparingly soluble or insoluble in solvents such as water are formed into particulates and dispersed in the solvent, i.e., in an emulsion state or a suspension state. Examples of such resins include acrylic resins, styrene acrylic resins, fluorene resins, polyurethane resins, polyolefin resins, rosin-modified resins, terpene resins, polyester resins, polyamide resins, epoxy resins, vinyl chloride resins, vinyl chloride-vinyl acetate copolymers, ethylene vinyl acetate resins, etc. Two or more of these resins may be used simultaneously. Such resins are also referred to as resins.

[0025] As the first ink In1, for example, black ink containing carbon black, gray ink containing carbon black, etc., can be used. As a gray ink containing carbon black, for example, an ink made by dispersing a pigment made by mixing carbon black with pigments of cyan, magenta, and yellow in a solvent such as water can be used. It should be noted that as a black ink containing carbon black, an ink made by dispersing a pigment made by mixing pigments in a solvent such as water can also be used. Hereinafter, black ink made by dispersing a pigment made by mixing carbon black with pigments other than carbon black, such as cyan, magenta, and yellow, in a solvent such as water will also be referred to as "mixed-color black ink". As the second ink In2, for example, inks of cyan, magenta, yellow, blue, white, and light magenta that do not contain carbon black can be used. It should be noted that the first ink In1 can also be an ink that does not contain carbon black, as long as the rate of temperature increase per unit time when the ink is heated by dielectric heating is more than 1.5 times that of the second ink In2.

[0026] The ejection control unit 250 is configured as a computer having one or more processors, storage devices, and input / output interfaces for signal input and output to the outside. The ejection control unit 250 controls the ejection unit 210 and the first delivery unit 325 to simultaneously deliver the medium Md and eject liquid onto the medium Md to allow it to adhere to the medium Md. In other embodiments, the ejection control unit 250 may also be configured as a combination of multiple circuits.

[0027] Figure 2 This is a perspective view showing the schematic configuration of the dielectric heating device 100 in the first embodiment. Figure 1 and Figure 2 As shown, the dielectric heating device 100 includes: an electrode unit 20 for heating a first ink In1 and a second ink In2 attached to a dielectric Md, a voltage application unit 80 for applying an AC voltage to the electrode unit 20, the aforementioned second delivery unit 326, and a heating control unit 180.

[0028] In this embodiment, the dielectric heating device 100 simultaneously conveys the medium Md through the second conveying section 326 and heats the first ink In1 and the second ink In2 attached to the medium Md in the second interval 312 using an electric field generated by the electrode unit 20, thereby drying the first ink In1 and the second ink In2. In other words, in this embodiment, as... Figure 1 As shown, the electrode unit 20 heats the first ink In1 and the second ink In2 at a position downstream of the position where the ejection unit 210 attaches the first ink In1 and the second ink In2 to the medium Md.

[0029] like Figure 1 and Figure 2As shown, the dielectric heating device 100 includes a first electrode unit 30 and a second electrode unit 40 as electrode unit 20. Figure 1 As shown, the first electrode unit 30 has a first electrode 31 and a second electrode 32 opposite to the dielectric Md. The second electrode unit 40 has a third electrode 41 and a fourth electrode 42 opposite to the dielectric Md.

[0030] like Figure 2 As shown, the dielectric heating device 100 in this embodiment includes a total of 60 first electrode units 30 and a total of eight second electrode units 40. More specifically, the dielectric heating device 100 has a first unit column UC1 and a second unit column UC2. The first unit column UC1 consists of 30 first electrode units 30 arranged along the X direction, and two first unit columns UC1 are arranged along the Y direction. The second unit column UC2 consists of four second electrode units 40 arranged along the X direction, and two second unit columns UC2 are arranged along the Y direction.

[0031] like Figure 1 and Figure 2 As shown, each first unit column UC1 is positioned in the -Y direction relative to each second unit column UC2. That is, in the transport path 310, the position where the first electrode unit 30 heats the medium Md is further downstream than the position where the second electrode unit 40 heats the medium Md. Therefore, the first electrode unit 30 heats the first ink In1 and the second ink In2 after they have been heated by the second electrode unit 40.

[0032] In this embodiment, the dielectric heating device 100 includes a first voltage application unit 81 and a second voltage application unit 82 as the aforementioned voltage application unit 80. The first voltage application unit 81 applies an AC voltage with a frequency of 300 MHz or higher and 300 GHz or lower to the first electrode 31 and the second electrode 32 of the first electrode unit 30. The second voltage application unit 82 applies an AC voltage with a frequency of 100 kHz or higher and 300 MHz or lower to the third electrode 41 and the fourth electrode 42 of the second electrode unit 40. More specifically, in this embodiment, the first voltage application unit 81 applies a high-frequency voltage of 1 GHz to the first electrode 31 and the second electrode 32. The second voltage application unit 82 applies a high-frequency voltage of 40.68 MHz to the third electrode 41 and the fourth electrode 42. It should be noted that, in this specification, high-frequency voltage refers to an AC voltage with a frequency of 1 MHz or higher.

[0033] In this embodiment, the first voltage application unit 81 is configured as a high-frequency power supply including a high-frequency voltage generation circuit, outputting a high-frequency voltage. The first voltage application unit 81 is, for example, composed of a crystal oscillator, a PLL (Phase Locked Loop) circuit, and a power amplifier. The first voltage application unit 81 amplifies the high-frequency signal generated by the PLL circuit using the power amplifier and supplies power to the first electrode unit 30 via a coaxial cable, thereby applying a high-frequency voltage to the first electrode 31 and the second electrode 32. The potential applied to either the first electrode 31 or the second electrode 32 can also be a reference potential. The reference potential is a constant potential that serves as a reference for the high-frequency voltage, such as a ground potential. It should be noted that the configuration of the second voltage application unit 82 is the same as that of the first voltage application unit 81, except that the second voltage application unit 82 applies an AC voltage to the third electrode 41 and the fourth electrode 42; therefore, its description is omitted.

[0034] The heating control unit 180, like the ejection control unit 250 described above, is also computer-based. The heating control unit 180 controls various units such as the second delivery unit 326 and the voltage application unit 80 to heat the first ink In1 and the second ink In2 adhered to the medium Md within the dielectric heating device 100. The heating control unit 180 is sometimes simply referred to as the control unit.

[0035] Figure 3 This is a perspective view showing the schematic configuration of the first electrode unit 30 in this embodiment. As described above, the first electrode unit 30 has a first electrode 31 and a second electrode 32. Furthermore, the first electrode unit 30 in this embodiment has a first coil 34.

[0036] The first electrode 31 and the second electrode 32 are conductors, such as those formed of metals, alloys, or conductive oxides. The first electrode 31 and the second electrode 32 can be formed of the same material or different materials. For example, to maintain their orientation and strength, the first electrode 31 and the second electrode 32 can be disposed on a substrate or other material formed of a material with a dielectric loss tangent and low conductivity, or supported by other components.

[0037] The first electrode 31 and the second electrode 32 are configured such that the shortest distance between them is less than one-tenth of the wavelength of the electromagnetic field output from the first electrode unit 30. In this embodiment, the first electrode 31 and the second electrode 32 have a flat, plate-like shape in the X and Y directions. When viewed along the Z direction, the first electrode 31 and the second electrode 32 have a rectangular shape with the Y direction as the longer side and the X direction as the shorter side. When viewed along the Z direction, the second electrode 32 is configured to surround the first electrode 31. More specifically, the first electrode 31 is disposed within a rectangular opening extending through the second electrode 32 along the Z direction, and this opening is located at the center of the second electrode 32 in both the X and Y directions.

[0038] Both the first electrode 31 and the second electrode 32 are disposed on a substrate 110 arranged parallel to the X and Y directions. More specifically, the first electrode 31 is configured such that its lower surface contacts the upper surface of the substrate 110. The second electrode 32 is configured such that its lower surface contacts the upper surface of the substrate 110. Therefore, in this embodiment, the central 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. It should be noted that in this embodiment, the substrate 110 is shared by all the first electrode units 30 and the second electrode units 40.

[0039] Both the first electrode 31 and the second electrode 32 are configured to face the medium Md, which is conveyed in the -Y direction via the second conveying section 326, in the second interval 312 in the Z direction. In this embodiment, the first electrode 31 and the second electrode 32 are disposed above the second interval 312. That is, in this embodiment, the lower surfaces of the first electrode 31 and the second electrode 32 face the upper surface of the medium Md. Furthermore, the aforementioned substrate 110 is disposed between the medium Md and the first electrode 31 and the second electrode 32.

[0040] In this embodiment, the substrate 110 is formed of glass. The substrate 110 suppresses the following: the first ink In1 and the second ink In2 coated on the dielectric Md adhere to the first electrode 31 and the second electrode 32; and, if the dielectric Md is cloth, the fibers of the dielectric Md adhere to the first electrode 31 and the second electrode 32. In this embodiment, the substrate 110 also suppresses the adhesion of inks and fibers to the third electrode 41 and the fourth electrode 42 in the same manner as described above. In other embodiments, the substrate 110 may, for example, be formed of alumina.

[0041] In this embodiment, the first electrode 31 is electrically connected to the first voltage application unit 81 via the first wire 35, the first coil 34, and the inner conductor IC1 of the coaxial cable. The second electrode 32 is electrically connected to the first voltage application unit 81 via the connecting member 33 disposed on the upper part of the second electrode 32, the outer conductor of the coaxial cable (not shown), etc.

[0042] By applying an alternating current voltage to the first electrode 31 and the second electrode 32, an electromagnetic field with a wavelength λ1 corresponding to the frequency f1 of the applied alternating current voltage 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 at a distance. In this specification, the electromagnetic field generated near the first electrode 31 and the second electrode 32 by applying an alternating current voltage is also referred to as the "nearby electromagnetic field". "Nearby" of the first electrode 31 and the second electrode 32 refers to a range where the distance from the first electrode 31 and the second electrode 32 is less than 1 / 2π of the wavelength of the generated electromagnetic field. A range farther than "nearby" is also referred to as "distant". In addition, in this specification, the electromagnetic field generated at a distance from the first electrode 31 and the second electrode 32 by applying an alternating current voltage is also referred to as the "distant electromagnetic field". The distant electromagnetic field is equivalent to the electromagnetic field used in communication based on ordinary communication antennas, etc.

[0043] As described above, the first electrode 31 and the second electrode 32 are configured such that the shortest distance between them is less than one-tenth of the wavelength of the electromagnetic field. This allows the electric field density of the electromagnetic field generated from the first electrode 31 and the second electrode 32 to attenuate near 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, it is possible to efficiently heat the first ink In1 and the second ink In2 attached to the medium Md using the electric field generated near the first electrode 31 and the second electrode 32, while suppressing the radiation of distant electromagnetic fields from the first electrode 31 and the second electrode 32. In particular, in this embodiment, when viewed along the Z-direction, the second electrode 32 is configured to surround the first electrode 31, thus further suppressing the radiation of distant electromagnetic fields from the first electrode 31 and the second electrode 32.

[0044] It should be noted that, according to preliminary experiments conducted by the inventors, even when microwaves are irradiated onto a sheet of material with ink adhering to it inside a microwave oven, it is almost impossible to heat the ink adhering to the sheet. This is believed to be because, since microwaves penetrate the thin ink film, very little of the electrical power of the irradiated microwaves is converted into heat within the ink. On the other hand, through the electrode unit 20 in this embodiment, an electromagnetic field in a direction intersecting the film pressure direction of the ink can be irradiated onto the ink adhering to the dielectric Md, thus effectively heating the ink.

[0045] In this embodiment, one end of the first coil 34 is electrically connected in series with the first electrode 31 via the first wire 35, and the other end is electrically connected in series with the first voltage application unit 81. In this embodiment, the first coil 34 is composed of a solenoid coil, configured such 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 to, for example, form a resonant circuit with the first electrode 31 and the second electrode 32 resonating at a frequency f1, and to achieve impedance matching between the first electrode unit 30 and the first voltage application unit 81.

[0046] An alternating voltage is applied to the first electrode unit 30 by the first voltage application unit 81, generating a high voltage at one end of the first coil 34. This increases the strength of the electric field generated from the first electrode 31 and the second electrode 32. It should be noted that the first coil 34 is preferably configured such 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 wire 35 and the second electrode 32, that is not conducive to heating the dielectric Md, potentially reducing the effectiveness of increasing the strength of the electric field generated from the first electrode 31 and the second electrode 32. In contrast, by bringing the distance between one end of the first coil 34 and the first electrode 31 closer, the generation of such an electric field that is not conducive to heating the dielectric Md can be suppressed, thus effectively increasing the strength of the electric field generated from the first electrode 31 and the second electrode 32. It should be noted that in other embodiments, for example, the first electrode 31 can be formed into a tortuous shape, so that the first electrode 31 can perform the same function as the first coil 34.

[0047] Figure 4 This is a perspective view showing the schematic configuration of the second electrode unit 40 in this embodiment. As described above, the second electrode unit 40 has a third electrode 41 and a fourth electrode 42. Furthermore, the second electrode unit 40 in this embodiment has a second coil 44.

[0048] The third electrode 41 and the fourth electrode 42 are also conductors, just like the first electrode 31 and the second electrode 32. The third electrode 41 and the fourth electrode 42 are configured such that the shortest distance between them is less than one-tenth of the wavelength of the electromagnetic field output from the second electrode unit 40. In this embodiment, the third electrode 41 has a boat-shaped form with the Y direction as its longer side and the X direction as its shorter side. The lower surface of the third electrode 41 has a curved shape that convexes in the -Z direction. When viewed along the Z direction, the third electrode 41 has an elongated oval shape that is longer in the Y direction. The fourth electrode 42 has a ring-shaped form that is flat in both the X and Y directions and longer in the Y direction. When viewed along the Z direction, the fourth electrode 42 is configured to surround the third electrode 41. In this embodiment, the dimension of the fourth electrode 42 in the Y direction is approximately 6 times the dimension of the second electrode 32 in the Y direction. Furthermore, the dimension of the fourth electrode 42 in the X direction is approximately 8.5 times the dimension of the second electrode 32 in the X direction.

[0049] The third electrode 41 and the fourth electrode 42 are disposed on the substrate 110 in the same manner as the first electrode 31 and the second electrode 32. More specifically, the third electrode 41 is configured such that the central portion of its lower surface in the X and Y directions contacts the upper surface of the substrate 110. The fourth electrode 42 is configured such that its lower surface contacts the upper surface of the substrate 110. Therefore, in this embodiment, the central portion of the lower surface of the third electrode 41 and the lower surface of the fourth electrode 42 are disposed on the same plane.

[0050] The third electrode 41 and the fourth electrode 42 are configured in the same way as the first electrode 31 or the second electrode 32, so that they are opposite the medium Md conveyed in the Z direction through the second conveying section 326 in the second interval 312.

[0051] In this embodiment, the third electrode 41 is electrically connected to the second voltage application unit 82 via the second wire 45, the second coil 44, and the inner conductor IC2 of the coaxial cable. The fourth electrode 42 is electrically connected to the second voltage application unit 82 via the second connecting member 43 disposed on the upper part of the fourth electrode 42, the outer conductor of the coaxial cable (not shown), etc. By applying an alternating current voltage to the third electrode 41 and the fourth electrode 42, an electromagnetic field with a wavelength λ2 corresponding to the frequency f2 of the applied alternating current voltage is generated from the third electrode 41 and the fourth electrode 42.

[0052] In this embodiment, one end of the second coil 44 is electrically connected in series with the third electrode 41 via the second wire 45, and the other end is electrically connected in series with the second voltage application unit 82. In this embodiment, the second coil 44 is composed of a solenoid coil, configured such that its length direction is along the Z direction. The shape, length, cross-sectional area, number of turns, material, etc., of the second coil 44 are selected, for example, to form a resonant circuit with the third electrode 41 and the fourth electrode 42 resonating at a frequency f2, and to achieve impedance matching between the second electrode unit 40 and the second voltage application unit 82. The second coil 44 is preferably configured such that the distance between one end of the second coil 44 and the third electrode 41 is as small as possible.

[0053] Figure 5 This is the first graph, which shows the heating time of each sample with each ink attached when the sample is heated by dielectric heating, with the temperature of each sample as the vertical axis. Figure 6 This is the second chart, which also uses the heating time of each sample as the horizontal axis and the temperature of each sample as the vertical axis. Figure 5 The relationship between the temperature of each sample and the heating time is shown when each sample is heated by an electromagnetic field with a frequency of 1 GHz. Figure 6 The relationship between the temperature of each sample and the heating time is shown when each sample is heated by an electromagnetic field with a frequency of 40.68 MHz.

[0054] Samples s1 to s4 were prepared as samples heated by an electromagnetic field with a frequency of 1 GHz. Samples s11 to s15 were prepared as samples heated by an electromagnetic field with a frequency of 40.68 MHz. Samples s1 and s11 were prepared by attaching a black water-based pigment ink containing carbon black and resin to a rectangular piece of cotton cloth and leaving it at room temperature for 30 days. Sample s12 was prepared by attaching a mixed-color black water-based pigment ink containing carbon black and resin to the same cloth and leaving it at room temperature. Samples s2 and s13 were prepared by attaching a cyan water-based pigment ink containing resin to the same cloth and leaving it at room temperature. Samples s3 and s14 were prepared by attaching a magenta water-based pigment ink containing resin to the same cloth and leaving it at room temperature. Samples s4 and s15 were prepared by attaching a yellow water-based pigment ink containing resin to the same cloth and leaving it at room temperature. Samples s1, s11, and s12 correspond to a medium Md with only the first ink In1 adhering to it, while the other samples correspond to a medium Md with only the second ink In2 adhering to it. It should be noted that, when viewed along the Z-direction, the fabric used in the fabrication of samples s1–s4 has dimensions corresponding to the external dimensions of the second electrode 32 in the X and Y directions. Similarly, when viewed along the Z-direction, the fabric used in the fabrication of samples s11–s15 has dimensions corresponding to the external dimensions of the second electrode 32 in the X and Y directions. Furthermore, each ink used in the fabrication of each sample contains glycerin.

[0055] Samples s1 to s4 were heated using the first electrode unit 30 described above. More specifically, each sample was positioned opposite the first electrode 31 and the second electrode 32 of the first electrode unit 30, and a high-frequency voltage of 1 GHz was applied to the first electrode 31 and the second electrode 32 to heat each sample. The temperature of each sample was measured using an infrared camera. Similarly, samples s11 to s15 were heated one by one using the second electrode unit 40 described above. During the heating of each sample, the applied power to the first electrode unit 30 was set to 2 W, and the applied power to the second electrode unit 40 was set to 50 W. Figure 5 and Figure 6 The “heating time” shown refers to the time elapsed since the high-frequency voltage was first applied to the first electrode 31 and the second electrode 32, and the “temperature” refers to the highest in-plane temperature of each sample at a certain point in time, as measured by an infrared camera.

[0056] like Figure 6As shown, when sample s11 was heated by an electromagnetic field with a frequency of 40.68 MHz, its temperature rose sharply and could not be measured until the heating time reached 10 seconds. In contrast, at the 10-second heating time, the temperature of sample s13 was approximately 120°C, the temperature of sample s14 was approximately 90°C, and the temperature of sample s15 was approximately 110°C. Furthermore, at the 20-second heating time, the temperature of sample s12 was approximately 250°C, while the temperature of sample s13 was approximately 150°C, and the temperatures of samples s14 and s15 were approximately 130°C.

[0057] like Figure 5 As shown, when sample s1 was heated by an electromagnetic field with a frequency of 1 GHz, its temperature was higher than that of samples s2 to s4 when heated for the same duration. On the other hand, no abnormalities were observed in sample s1. Figure 5 The temperature rise was as rapid as that of sample s11. More specifically, for example, at a heating time of 10 seconds, the temperature of sample s1 was approximately 67°C, the temperature of sample s2 was approximately 59°C, the temperature of sample s3 was approximately 55°C, and the temperature of sample s4 was approximately 58°C. Therefore, the temperature difference between sample s1 and the other samples was approximately 8°C to 12°C. Furthermore, at a heating time of 30 seconds, the temperature difference between sample s1 and the other samples was also to the same extent, approximately 10°C to 13°C. This is believed to be because, when the ink containing carbon black is heated by an electromagnetic field at a frequency of 40.68 MHz, the heat generated by the conductivity of the carbon black primarily contributes to the temperature rise of the ink; in contrast, when the ink is heated by an electromagnetic field at a frequency of 1 GHz, the heat generated by the dielectric loss tangent of the ink primarily contributes to the temperature rise of the ink. Therefore, if the first ink In1 and the second ink In2 are heated by the first electrode unit 30, it is possible to suppress the rapid rise in temperature of the first ink In1 while heating both the first ink In1 and the second ink In2 to dry them.

[0058] As mentioned above Figure 6As shown, at a frequency of 40.68 MHz, for example, at a heating time of 10 seconds, the temperature of sample s14 did not reach 100°C, while the temperature of sample s11 exceeded 240°C. Therefore, when the first ink In1 and the second ink In2 attached to the medium Md are continuously heated only by the second electrode unit 40, during the period when the solvent such as water near the location where the second ink In2 is attached to the medium Md has not sufficiently evaporated or volatilized, the possibility of scorching of the medium Md (described later) near the location where the first ink In1 is attached to the medium Md is high. On the other hand, by heating the first ink In1 and the second ink In2 after being heated by the second electrode unit 40 by the first electrode unit 30 as in this embodiment, both inks can be heated efficiently, and uneven heating can be suppressed. More specifically, when the first ink In1 attached to the medium Md contains a sufficient amount of solvent such as water, the heat caused by the conductivity of the carbon black is removed by the solvent. Therefore, by heating the two inks through the second electrode unit 40 while the solvent content of the two inks is sufficient, and then heating the two inks through the first electrode unit 30 before the solvent disappears due to evaporation, the two inks can be heated and dried efficiently and uniformly. It should be noted that, in this case, solvent vapors contained in each ink are more easily generated near the second electrode unit 40 compared to the vicinity of the first electrode unit 30; therefore, for example, a fan or similar device for generating airflow can be provided near the second electrode unit 40.

[0059] In this embodiment, the heating control unit 180 of the dielectric heating device 100 controls the power applied to the first electrode 31 and the second electrode 32 by controlling the first voltage application unit 81, thereby heating the first ink In1 and the second ink In2 to a temperature of 150°C or higher and 240°C or lower, respectively. More specifically, the heating control unit 180 performs feedback control on the power applied to the first electrode 31 and the second electrode 32, for example, by referring to the temperatures of the two inks obtained by an infrared camera (not shown) or a temperature sensor disposed near the first electrode unit 30. It should be noted that, in this case, the heating control unit 180 may also use the temperature of the medium Md as a reference for the temperatures of the two inks.

[0060] By heating the two inks to a temperature of 150°C or higher, the pigment can be firmly fixed to the medium Md by the resin contained in the two inks. In particular, in this embodiment, since the resin contained in the two inks can be heated to 150°C or higher by the first electrode unit 30 after the solvent contained in the two inks is dried by the second electrode unit 40, the two inks can be dried efficiently while the pigment is firmly fixed to the medium Md by the resin. Furthermore, by heating the two inks to a temperature of 240°C or lower, scorching of the medium Md can be suppressed, for example, when the medium Md is paper with cellulose as its main component, or cotton or linen cloth with cellulose as its main component. Additionally, melting of the medium Md can be suppressed when the medium Md is polyester cloth, and color decomposition of the medium Md can be suppressed when the medium Md is rayon cloth.

[0061] It should be noted that, as described above, the frequency of the AC voltage applied to the first electrode 31 and the second electrode 32 by the first voltage application unit 81 can be either 1 GHz or a frequency equivalent to a general microwave frequency of 300 MHz or higher and 300 GHz or lower. Generally, in this frequency range, the dielectric loss tangent of substances such as water is large, and the AC resistance of carbon black increases due to the skin effect. Therefore, by heating the first ink In1 and the second ink In2 using an electromagnetic field in this frequency range, the heating caused by the dielectric loss tangent of the two inks can primarily contribute to the temperature rise of the two inks. In this case, a frequency of 300 MHz or higher and 30 GHz or lower, equivalent to a frequency generally used in microwave heating, is particularly preferred. For example, frequencies of 915 MHz, 2.45 GHz, 5.8 GHz, and 24.125 GHz, which are specified as ISM (Industrial Scientific and Medical Band) frequencies, can also be used.

[0062] Furthermore, as described above, in addition to a frequency of 40.68 MHz, frequencies above 100 kHz and below 300 MHz can be used as the frequency of the AC voltage applied to the third electrode 41 and the fourth electrode 42 by the second voltage application unit 82. Generally, in this frequency range, the dielectric loss tangent of substances such as water is small, and the effect of the skin effect is minimal. Therefore, by heating the first ink In1 using an electromagnetic field in this frequency range, the heat generated by the conductivity of carbon black can primarily contribute to the temperature rise of the first ink In1 or the second ink In2. Thus, as described above, the rapid heating of the first ink In1 can be utilized for heating both the first ink In1 and the second ink In2. For example, frequencies other than 40.68 MHz, such as 13.56 MHz and 27.12 MHz, can also be used within the ISM band.

[0063] The dielectric heating apparatus 100 according to the first embodiment described above includes a first electrode unit 30 having a first electrode 31 and a second electrode 32 as an electrode unit 20 for heating the first ink In1 and the second ink In2 attached to the dielectric Md, and a first voltage application unit 81 applying an AC voltage with a frequency of 300MHz or higher and 300GHz or lower to the first electrode 31 and the second electrode 32. Therefore, the first electrode unit 30 can suppress uneven heating while heating both the carbon black-containing first ink In1 and the carbon black-free second ink In2 attached to the dielectric Md. Thus, after drying only the second ink In2 attached to the dielectric Md by dielectric heating, it is not necessary to further attach the first ink In1 to the dielectric Md, thereby suppressing the shift in the attachment positions of the first ink In1 and the second ink In2.

[0064] Furthermore, according to the dielectric heating device 100 in this embodiment, the first ink In1 and the second ink In2 are resin-containing pigment inks. The ejection control unit 250 heats the first ink In1 and the second ink In2 to a temperature of 150°C or higher and 240°C or lower by controlling the first voltage application unit 81. Therefore, since each ink is heated to a temperature of 150°C or higher, the resin contained in each ink can firmly fix the pigment to the medium Md, thereby improving the abrasion resistance of the pigment in the medium Md. In addition, since each ink is heated to a temperature of 240°C or lower, scorching, melting, discoloration, etc., of the medium Md caused by heating can be suppressed.

[0065] Furthermore, according to the dielectric heating device 100 in this embodiment, the electrode unit 20 further includes a second electrode unit 40 having a third electrode 41 and a fourth electrode 42, and a second voltage application unit 82 applying an AC voltage with a frequency of 100 kHz or higher and less than 300 MHz to the third electrode 41 and the fourth electrode 42. The first electrode unit 30 heats the first ink In1 and the second ink In2 after they have been heated by the second electrode unit 40. This allows for efficient and uniform heating and drying of the first ink In1 and the second ink In2. Additionally, as in this embodiment, when the first ink In1 and the second ink In2 are resin-containing pigment inks, it is possible to efficiently dry both inks while simultaneously fixing the pigment firmly to the medium Md using the resin.

[0066] Furthermore, according to the printing system 200 in this embodiment, the ejection unit 210 applies the first ink In1 and the second ink In2 to the medium Md in the first section 311 of the transport path 310, and the electrode unit 20 of the dielectric heating device 100 heats the first ink In1 and the second ink In2 in the second section 312, which is further downstream of the first section 311. Therefore, compared with the case where the application and heating of each ink are performed in the same section of the transport path 310, the flexibility of the arrangement of the electrode unit 20 and the ejection unit 210 in the printing system 200 can be improved. For example, in the first embodiment, the medium Md is transported in the -Y direction in both the first section 311 and the second section 312, but the medium Md can also be transported in different directions in the two sections. For example, after the medium Md is transported in the -Y direction in the first section 311, it can be transported in the +Y direction in the second section 312 after a direction change by a roller (not shown). As a result, the printing system 200 can be miniaturized in the Y direction.

[0067] Furthermore, according to the printing system 200 of this embodiment, the first section 311 and the second section 312 are separated. Therefore, the degree of freedom in the arrangement of the electrode unit 20 and the ejection unit 210 in the printing system 200 can be further improved. For example, in the first embodiment, the medium Md is continuously conveyed from the liquid ejection device 205 to the dielectric heating device 100, but it is also possible not to continuously convey the medium Md from the liquid ejection device 205 to the dielectric heating device 100. In this case, for example, the medium Md with the first ink In1 and the second ink In2 ejected by the liquid ejection device 205 is temporarily wound into a roll, and after the wound medium Md is moved to the dielectric heating device 100 by a robot or the like, the wound medium Md can be unwound and conveyed while being heated in the dielectric heating device 100. In this way, for example, the liquid ejection device 205 and the dielectric heating device 100 can be easily separated in the printing system 200.

[0068] B. Other implementation methods:

[0069] (B-1) In the above embodiment, the first ink In1 and the second ink In2 are pigment inks containing resin. In contrast, the first ink In1 and the second ink In2 may, for example, not contain resin, or may not be pigment inks but dye inks. Furthermore, the heating control unit 180 may not heat the first ink In1 and the second ink In2 to a temperature of 150°C or higher and 240°C or lower. For example, if the first ink In1 and the second ink In2 are water-based inks that do not contain resin, the heating control unit 180 may heat both inks to a temperature of 100°C or higher and less than 150°C.

[0070] (B-2) In the above embodiment, when viewed along the Z-direction, the second electrode 32 is configured to surround the first electrode 31. Alternatively, when viewed along the Z-direction, the second electrode 32 may not surround the first electrode 31. For example, when viewed along the Z-direction, the first electrode 31 and the second electrode 32 may be configured to be adjacent to each other. In this case, the shapes of the first electrode 31 and the second electrode 32 can be arbitrary, and can be circular, oblong, rectangular, polygonal, etc. Furthermore, when viewed along the Z-direction, the areas of the first electrode 31 and the second electrode 32 may be the same or different. Preferably, when viewed along the Z-direction, the first electrode 31 and the second electrode 32 are configured not to overlap. Similarly, when viewed along the Z-direction, the fourth electrode 42 may not be configured to surround the third electrode 41; for example, when viewed along the Z-direction, the third electrode 41 and the fourth electrode 42 may be configured to be adjacent to each other.

[0071] (B-3) In the above embodiment, in addition to the first electrode unit 30, a second electrode unit 40 is also provided as the electrode unit 20. Alternatively, the second electrode unit 40 may not be provided.

[0072] (B-4) In the above embodiment, the dielectric heating device 100 includes two first unit columns UC1 and two second unit columns UC2, and has a total of 60 first electrode units 30 and a total of 8 second electrode units 40. Alternatively, the number of first unit columns UC1 and second unit columns UC2 can be one or more. Furthermore, when multiple first unit columns UC1 and multiple second unit columns UC2 are provided, the number of first electrode units 30 and second electrode units 40 can be different in each column. Additionally, the number of first electrode units 30 and second electrode units 40 provided in the dielectric heating device 100 can be arbitrary, for example, it can be one.

[0073] (B-5) In the above embodiment, the first electrode unit 30 and the second electrode unit 40 may also be configured to reciprocate in a direction intersecting the direction of the conveying medium Md. For example, the first electrode unit 30 or the second electrode unit 40 may be supported by a drive unit (not shown) consisting of a belt mechanism or a ball screw mechanism, and reciprocated in the X direction.

[0074] C. Other methods:

[0075] This disclosure is not limited to the embodiments described above, and can be implemented in various ways without departing from its spirit. For example, this disclosure can also be implemented in the following ways. In order to solve part or all of the problems of this disclosure, or to achieve part or all of the effects of this disclosure, the technical features in the above embodiments corresponding to the technical features in the various methods described below can be appropriately replaced or combined. In addition, as long as the technical feature is not described as an essential technical feature in this specification, the technical feature can be appropriately deleted.

[0076] (1) According to a first aspect of this disclosure, a dielectric heating device is provided for heating a first ink containing carbon black and a second ink not containing carbon black attached to a medium. The dielectric heating device includes a first electrode unit and a first voltage application unit. The first electrode unit, as an electrode unit for heating the first ink and the second ink, has a first electrode and a second electrode opposite to the medium. The first voltage application unit applies an alternating voltage with a frequency of 300 MHz or more and 300 GHz or less to the first electrode and the second electrode.

[0077] In this manner, the first electrode unit can heat both the first ink containing carbon black and the second ink not containing carbon black, which are attached to the medium, while suppressing uneven heating. Therefore, after the second ink attached to the medium is dried by dielectric heating, it is not necessary to further attach the first ink to the medium, thus suppressing the shift in the attachment positions of the first and second inks.

[0078] (2) In the above-described manner, a control unit may also be included to control the first voltage application unit. The first ink and the second ink are pigment inks containing resin. The control unit heats the first ink and the second ink to a temperature of 150°C or higher and 240°C or lower by controlling the first voltage application unit. According to this method, since each ink is heated to a temperature of 150°C or higher, the resin contained in each ink can firmly fix the pigment to the medium, thereby improving the abrasion resistance of the pigment in the medium. Furthermore, since each ink is heated to a temperature of 240°C or lower, scorching, melting, discoloration, and other phenomena in the medium caused by heating can be suppressed.

[0079] (3) In the above-described manner, a second electrode unit and a second voltage application unit may also be provided. The second electrode unit, as the electrode unit, has a third electrode and a fourth electrode facing the medium. The second voltage application unit applies an AC voltage with a frequency of 100 kHz or higher and less than 300 MHz to the third electrode and the fourth electrode. The first electrode unit heats the first ink and the second ink after they have been heated by the second electrode unit. According to this method, the first ink and the second ink can be dried efficiently and uniformly by heating them with the first electrode unit and the second electrode unit.

[0080] (4) According to a second aspect of this disclosure, a printing system is provided. The printing system includes an ejection unit and a conveying unit. The ejection unit has a first ejection section that ejects the first ink onto the medium to cause it to adhere to the medium, and a second ejection section that ejects the second ink onto the medium to cause it to adhere to the medium. The conveying unit conveys the medium along a conveying path. The electrode unit heats the first ink and the second ink at a position downstream of the position where the ejection unit causes the first ink and the second ink to adhere to the medium in the conveying path.

[0081] (5) In the second embodiment described above, the conveying unit may also have a first conveying unit and a second conveying unit. The first conveying unit conveys the medium in a first section of the conveying path, and the second conveying unit conveys the medium in a second section of the conveying path that is further downstream than the first section. The ejection unit applies the first ink and the second ink to the medium in the first section, and the electrode unit heats the first ink and the second ink in the second section. According to this embodiment, compared to the case where the application and heating of each ink are performed in the same section of the conveying path, the flexibility in configuring the electrode unit and the ejection unit in the printing system can be increased.

[0082] (6) In the second method described above, the first interval and the second interval can also be separated. According to this method, the degree of freedom in the configuration of the electrode unit and the ejection unit in the printing system can be further improved.

Claims

1. A dielectric heating device, characterized in that, The dielectric heating device is configured to heat a first ink containing carbon black and a second ink not containing carbon black adhering to a medium. The first electrode unit, as an electrode unit for heating the first ink and the second ink, has a first electrode and a second electrode opposite to the medium; The first voltage application unit applies an alternating voltage with a frequency of 300MHz or higher and 300GHz or lower to the first electrode and the second electrode. The second electrode unit, as the electrode unit, has a third electrode and a fourth electrode opposite to the medium; as well as The second voltage application unit applies an alternating voltage with a frequency of 100kHz or higher and less than 300MHz to the third and fourth electrodes. The first electrode unit heats the first ink and the second ink after they have been heated by the second electrode unit.

2. The dielectric heating device according to claim 1, characterized in that, The dielectric heating device includes a control unit for controlling the first voltage application unit. The first ink and the second ink are pigment inks containing resin. The control unit heats the first ink and the second ink to a temperature of 150°C or higher and 240°C or lower by controlling the first voltage application unit.

3. A printing system, characterized in that, have: The dielectric heating device according to claim 1 or 2; The ejection unit has a first ejection section and a second ejection section, wherein the first ejection section ejects the first ink onto the medium to make the first ink adhere to the medium, and the second ejection section ejects the second ink onto the medium to make the second ink adhere to the medium; as well as The conveying unit transports the medium along the conveying path. The electrode unit heats the first ink and the second ink at a position downstream of the position where the ejection unit attaches the first ink and the second ink to the medium in the delivery path.

4. The printing system according to claim 3, characterized in that, The conveying unit includes a first conveying unit and a second conveying unit. The first conveying unit conveys the medium in a first section of the conveying path, and the second conveying unit conveys the medium in a second section of the conveying path that is further downstream than the first section. The ejection unit causes the first ink and the second ink to adhere to the medium within the first interval. The electrode unit heats the first ink and the second ink in the second interval.

5. The printing system according to claim 4, characterized in that, The first interval is separated from the second interval.

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