Dielectric heating device and printing system

Abstract

To provide a technique that can heat both an ink containing carbon black and an ink not containing carbon black, which are attached to a medium, while preventing uneven heating.SOLUTION: A dielectric heating device is provided which heats a first ink containing carbon black and a second ink not containing carbon black, which are attached to a medium. The dielectric heating device comprises, as an electrode unit for heating the first ink and the second ink, a first electrode unit that has a first electrode and a second electrode facing the medium, and a first voltage application section that applies AC voltage with a frequency of 300 MHz or more and 300 GHz or less to the first electrode and the second electrode.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Regarding dielectric heating devices, Patent Document 1 discloses a technique in which a first liquid attached to a substrate such as recording paper is dried using a first drying device, which is a dielectric heating device, and then a second liquid is attached to the substrate and 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 technique can suppress uneven heating of the substrate, which is caused by a sudden temperature rise when a liquid containing carbon black is heated by dielectric heating. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-119395 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in Patent Document 1, the first liquid adhered to the object is first dried using a dielectric heating device, and then the second liquid is applied to the object. As a result, the second liquid cannot be applied to the object at a position corresponding to the first liquid already applied, which can result in a discrepancy between the positions of the first liquid and the second liquid. [Means for solving the problem]

[0005] According to a first aspect of the present disclosure, there is provided a dielectric heating device for heating a first ink containing carbon black and a second ink not containing carbon black that are adhered to a medium, the dielectric heating device including a first electrode unit having a first electrode and a second electrode facing the medium as an electrode unit for heating the first ink and the second ink, and a first voltage application unit for applying an AC voltage having 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 the present disclosure, there is provided a printing system including a discharge unit having a first discharge unit that discharges and deposits the first ink onto the medium and a second discharge unit that discharges and deposits the second ink onto the medium, and a transport unit that transports the medium along a transport path. The electrode unit heats the first ink and the second ink downstream of a position on the transport path where the discharge unit deposits the first ink and the second ink onto the medium. [Brief explanation of the drawings]

[0007] [Figure 1] FIG. 1 is a schematic diagram illustrating a general configuration of a printing system. [Figure 2] FIG. 1 is a perspective view showing a schematic configuration of a dielectric heating device. [Figure 3] FIG. 2 is a perspective view showing a schematic configuration of a first electrode unit. [Figure 4] FIG. 4 is a perspective view showing a schematic configuration of a second electrode unit. [Figure 5] 1 is a first graph in which the horizontal axis represents the heating time for each sample and the vertical axis represents the temperature. [Figure 6] 2 is a second graph in which the horizontal axis represents the heating time for each sample and the vertical axis represents the temperature. DETAILED DESCRIPTION OF THE INVENTION

[0008] A. First embodiment: FIG. 1 is a schematic diagram showing the overall configuration of a printing system 200 according to a first embodiment. Arrows indicating mutually orthogonal X, Y, and Z directions are shown in FIG. 1. The X and Y directions are parallel to a horizontal plane, and the Z direction is a vertically 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 by "+" and the opposite direction is indicated by "-," and positive and negative signs are used in the direction notation. Hereinafter, the +Z direction is also referred to as "up" and the -Z direction is also referred to as "down." Furthermore, in this specification, "orthogonal" includes a range of 90°±10°.

[0009] The printing system 200 includes a dielectric heating device 100, a liquid ejection device 205, and a conveyance unit 320. In the printing system 200 of this embodiment, while the conveyance unit 320 conveys the medium Md, the liquid ejection device 205 ejects ink onto the medium Md to adhere to the medium Md, and the dielectric heating device 100 heats and dries the ink adhered to the medium Md.

[0010] The transport unit 320 transports the medium Md along the transport path 310. In this embodiment, the transport unit 320 includes a first roller unit 321, a second roller unit 322, a third roller unit 323, and a fourth roller unit 324, each of which is made up of a roller, and a drive unit (not shown) that includes a motor or the like for driving these units. In this embodiment, the first roller unit 321, the second roller unit 322, the third roller unit 323, and the fourth roller unit 324 are arranged in this order in the -Y direction. The transport unit 320 transports the sheet-like medium Md in the -Y direction using the first roller unit 321 to the fourth roller unit 324 in this order.

[0011] In this embodiment, the path along which the medium Md is transported by each roller unit corresponds to the transport path 310. In other embodiments, part or all of the transport path 310 may be formed by, for example, a belt. In this case, the transport unit 320 may be configured as a drive unit that drives the belt.

[0012] The first roller unit 321 and the second roller unit 322 constitute a first transport unit 325 that transports the medium Md in a first section 311 of the transport path 310. The third roller unit 323 and the fourth roller unit 324 constitute a second transport unit 326 that transports the medium Md in a second section 312 of the transport path 310. The second section 312 is a section of the transport path 310 that is downstream of the first section 311. A constant tension is applied to the medium Md in each section. In this embodiment, the tension applied to the medium Md in each section is different. Also, as shown in FIG. 1 , the first section 311 and the second section 312 are spaced apart. The first transport unit 325 in this embodiment is provided in the liquid ejection device 205 and constitutes part of the liquid ejection device 205. The second transport unit 326 is provided in the dielectric heating device 100 and constitutes part of the dielectric heating device 100.

[0013] The medium Md may be, for example, paper, cloth, film, etc. The cloth used as the medium Md is formed by weaving fibers such as cotton, linen, polyester, silk, rayon, etc., or fibers made by blending these fibers.

[0014] The liquid ejection device 205 in this embodiment is configured as an inkjet printer. The liquid ejection device 205 has a ejection unit 210 that ejects and deposits ink onto the medium Md, the first transport section 325 described above, and an ejection control section 250. The ejection unit 210 has a first ejection section 211 and a second ejection section 212. The first ejection section 211 ejects and deposits a first ink In1 containing carbon black onto the medium Md. The second ejection section 212 ejects and deposits a second ink In2 that does not contain carbon black onto the medium Md. In this embodiment, the ejection unit 210 deposits the first ink In1 and the second ink In2 onto the medium Md in the first section 311 described above.

[0015] The ejection unit 210 is configured, for example, by a piezoelectric or thermal liquid ejection head. The first ejection section 211 is configured, for example, as a head chip in the ejection unit 210 having a flow path through which the first ink In1 flows and nozzles for ejecting the first ink In1. The second ejection section 212 is configured, for example, as a head chip in the ejection unit 210 having a flow path through which the second ink In2 flows and nozzles for ejecting the second ink In2. The ejection unit 210 may be configured to be able to move back and forth relative to the medium Md in a direction intersecting the Y direction by, for example, a carriage (not shown), or may be configured as a so-called line head whose position is fixed and does not move back and forth relative to the medium Md.

[0016] The first ink In1 and the second ink In2 in this embodiment are pigment inks containing a resin. The resin contained in the ink acts to firmly fix the pigment to the medium Md. Such a resin is used, for example, in a state where the resin, which is poorly soluble or insoluble in a solvent such as water, is dispersed in the solvent in the form of fine particles, i.e., in an emulsion or suspension state. Examples of such resins 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, and ethylene-vinyl acetate resin. Two or more of these resins may be used in combination. Such resins are also called "resins."

[0017] The first ink In1 may be, for example, a black ink containing carbon black or a gray ink containing carbon black. The gray ink containing carbon black may be, for example, a mixture of carbon black and cyan, magenta, and yellow pigments dispersed in a solvent such as water. Similarly, the black ink containing carbon black may be a mixture of the pigments dispersed in a solvent such as water. Hereinafter, such a black ink may be a mixture of carbon black and a pigment other than carbon black, such as cyan, magenta, or yellow, dispersed in a solvent such as water, and may be referred to as a "mixed black ink." The second ink In2 may be, for example, a cyan, magenta, yellow, blue, white, or light magenta ink that does not contain carbon black. The first ink In1 may be an ink that does not contain carbon black, as long as the temperature increase rate per unit time when heated by dielectric heating is 1.5 times or more that of the second ink In2.

[0018] The discharge control unit 250 is configured by a computer equipped with one or more processors, a storage device, and an input / output interface for inputting and outputting signals from and to the outside. The discharge control unit 250 controls the discharge unit 210 and the first transport unit 325 to discharge and adhere liquid to the medium Md while transporting the medium Md. In other embodiments, the discharge control unit 250 may be configured, for example, by a combination of multiple circuits.

[0019] 2 is a perspective view showing a schematic configuration of the dielectric heating device 100 in the first embodiment. As shown in FIGS. 1 and 2, the dielectric heating device 100 includes an electrode unit 20 for heating the first ink In1 and the second ink In2 attached to the medium Md, a voltage application unit 80 for applying an AC voltage to the electrode unit 20, the second transport unit 326 described above, and a heating control unit 180.

[0020] The dielectric heating device 100 in this embodiment dries the first ink In1 and the second ink In2 adhered to the medium Md by heating them with an electric field generated by the electrode unit 20 in the second section 312 while transporting the medium Md by the second transport section 326. That is, in this embodiment, as shown in FIG. 1 , the electrode unit 20 heats the first ink In1 and the second ink In2 in the transport path 310 downstream of the position where the discharge unit 210 adheres the first ink In1 and the second ink In2 to the medium Md.

[0021] 1 and 2, the dielectric heating device 100 includes an electrode unit 20, which includes a first electrode unit 30 and a second electrode unit 40. As shown in Fig. 1, the first electrode unit 30 has a first electrode 31 and a second electrode 32 that face the medium Md. The second electrode unit 40 has a third electrode 41 and a fourth electrode 42 that face the medium Md.

[0022] As shown in Fig. 2, 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 row UC1 and a second unit row UC2. The first unit row UC1 is made up of 30 first electrode units 30 arranged side by side in the X direction, and two first unit rows UC1 are arranged side by side in the Y direction. The second unit row UC2 is made up of four second electrode units 40 arranged side by side in the X direction, and two second unit rows UC2 are arranged side by side in the Y direction.

[0023] 1 and 2, each first unit column UC1 is disposed at a position in the -Y direction of each second unit column UC2. That is, on the transport path 310, the position at which the first electrode unit 30 heats the medium Md is downstream of the position at which the second electrode unit 40 heats the medium Md. As a result, 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.

[0024] In this embodiment, the dielectric heating device 100 includes a first voltage application unit 81 and a second voltage application unit 82 as the voltage application unit 80. The first voltage application unit 81 applies an AC voltage having a frequency of 300 MHz or more and 300 GHz or less 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 having a frequency of 100 kHz or more and 300 MHz or less 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. Note that in this specification, a high-frequency voltage refers to an AC voltage having a frequency of 1 MHz or more.

[0025] In this embodiment, the first voltage application unit 81 is configured as a high-frequency power supply including a high-frequency voltage generation circuit and outputs a high-frequency voltage. The first voltage application unit 81 is configured, for example, with a crystal oscillator, a PLL (Phase Locked Loop) circuit, and a power amplifier. The first voltage application unit 81 amplifies a high-frequency signal generated by the PLL circuit using the power amplifier and supplies the amplified signal to the first electrode unit 30 via a coaxial cable or the like, thereby applying a high-frequency voltage to the first electrode 31 and the second electrode 32. 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. The second voltage application unit 82 has the same configuration as 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, and therefore a description thereof will be omitted.

[0026] The heating control unit 180 is configured by a computer, similar to the above-described discharge control unit 250. The heating control unit 180 controls each unit, such as the above-described second transport unit 326 and voltage application unit 80, to heat the first ink In1 and the second ink In2 attached to the medium Md in the dielectric heating device 100. The heating control unit 180 may also be simply referred to as the control unit.

[0027] 3 is a perspective view showing a schematic configuration of the first electrode unit 30 in this embodiment. As described above, the first electrode unit 30 has the first electrode 31 and the second electrode 32. Furthermore, the first electrode unit 30 in this embodiment has a first coil 34.

[0028] 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, in order to maintain their posture and strength, the first electrode 31 and the second electrode 32 may be placed on a substrate or the like formed of a material with low dielectric tangent or conductivity, or may be supported by another member.

[0029] The first electrode 31 and the second electrode 32 are arranged so that the shortest distance between them is one-tenth or less 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 shape that is flat 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 longitudinal direction and the X direction as the lateral direction. When viewed along the Z direction, the second electrode 32 is arranged to surround the periphery of the first electrode 31. More specifically, the first electrode 31 is arranged in a rectangular opening that is provided in the center of the second electrode 32 in the X and Y directions and that penetrates the second electrode 32 in the Z direction.

[0030] The first electrode 31 and the second electrode 32 are both disposed on a substrate 110 that is disposed parallel to the X and Y directions. More specifically, the first electrode 31 is disposed so that its lower surface is in contact with the upper surface of the substrate 110. The second electrode 32 is disposed so that its lower surface is in contact with the upper surface of the substrate 110. Therefore, in this embodiment, the center of the lower surface of the first electrode 31 and the lower surface of the second electrode 32 are disposed on the same plane. Note that in this embodiment, the substrate 110 is provided in common to all of the first electrode units 30 and second electrode units 40.

[0031] The first electrode 31 and the second electrode 32 are both arranged in the second section 312 so as to face in the Z direction the media Md being transported in the −Y direction by the second transport section 326. In this embodiment, the first electrode 31 and the second electrode 32 are arranged above the second section 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 media Md. In addition, the above-mentioned substrate 110 is arranged between the media Md and the first electrode 31 and the second electrode 32.

[0032] In this embodiment, the substrate 110 is made of glass. The substrate 110 prevents the first ink In1 and the second ink In2 applied to the medium Md from adhering to the first electrode 31 and the second electrode 32, and prevents fluff from the medium Md from adhering to the first electrode 31 and the second electrode 32 when the medium Md is a cloth. In this embodiment, the substrate 110 also prevents the inks and fluff from adhering to the third electrode 41 and the fourth electrode 42, as described above. In other embodiments, the substrate 110 may be made of, for example, alumina.

[0033] In this embodiment, the first electrode 31 is electrically connected to the first voltage application unit 81 via the first electric wire 35, the first coil 34, and the inner conductor IC1 of the coaxial cable. The second electrode 32 is electrically connected to the first voltage application unit 81 via a connection member 33 arranged above the second electrode 32, an outer conductor of the coaxial cable (not shown), etc.

[0034] When an AC voltage is applied to the first electrode 31 and the second electrode 32, an electromagnetic field having a wavelength λ1 corresponding to the frequency f1 of the applied AC 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 farther away. In this specification, the electromagnetic field generated near the first electrode 31 and the second electrode 32 by the application of an AC voltage is also referred to as the "near electromagnetic field." The "near" 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 ½π or less of the wavelength of the generated electromagnetic field. A range farther away than the "near" is also referred to as the "far" range. In this specification, the electromagnetic field generated far from the first electrode 31 and the second electrode 32 by the application of an AC voltage is also referred to as the "far electromagnetic field." The far electromagnetic field corresponds to the electromagnetic field used in communication using a general communication antenna, etc.

[0035] As described above, the first electrode 31 and the second electrode 32 are arranged so that the shortest distance between them is one-tenth the wavelength of the electromagnetic field or less. This allows the electric field 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 maintaining an appropriate distance between the medium Md and the first electrode 31 and the second electrode 32, the first ink In1 and the second ink In2 attached to the medium Md can be efficiently heated by the electric field generated in the vicinity of the first electrode 31 and the second electrode 32, while suppressing radiation of the far electromagnetic field from the first electrode 31 and the second electrode 32. In particular, in this embodiment, the second electrode 32 is arranged to surround the first electrode 31 when viewed along the Z direction, which further suppresses radiation of the far electromagnetic field from the first electrode 31 and the second electrode 32.

[0036] Preliminary experiments conducted by the inventors have shown that irradiating microwaves onto a sheet with ink attached in a microwave oven barely heats the ink attached to the sheet. This is thought to be because microwaves penetrate the thin ink film, resulting in a very low amount of microwave power being converted into heat inside the ink. On the other hand, the electrode unit 20 of this embodiment can irradiate the ink attached to the medium Md with an electromagnetic field in a direction intersecting the ink film thickness direction, thereby effectively heating the ink.

[0037] In this embodiment, one end of the first coil 34 is electrically connected in series to the first electrode 31 via the first electric wire 35, and the other end is electrically connected in series to the first voltage application unit 81. In this embodiment, the first coil 34 is configured as a solenoid coil and is disposed so that its length direction is along the Z direction. The shape, length, cross-sectional area, number of turns, material, etc. of the first coil 34 are selected, for example, so as to form a resonant circuit that resonates with the first electrode 31 and the second electrode 32 at frequency f1, and so as to achieve impedance matching between the first electrode unit 30 and the first voltage application unit 81.

[0038] When the first voltage application unit 81 applies an AC voltage to the first electrode unit 30, a high voltage is generated 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. The first coil 34 is preferably positioned so that the distance between one end of the first coil 34 and the first electrode 31 is as small as possible. If the distance between one end of the first coil 34 and the first electrode 31 is large, the high voltage generated at one end of the first coil 34 may generate an electric field between the first coil 34 and the first electrode 31 or between the first electric wire 35 and the second electrode 32 that does not contribute to heating the medium Md, thereby reducing the effect of increasing the strength of the electric field generated from the first electrode 31 and the second electrode 32. In contrast, by reducing the distance between the one end of the first coil 34 and the first electrode 31, the generation of such an electric field that does not contribute to heating the medium Md can be suppressed, thereby effectively increasing the strength of the electric field generated from the first electrode 31 and the second electrode 32. In other embodiments, the first electrode 31 may be formed in a meandering shape, so that the first electrode 31 performs the same function as the first coil .

[0039] 4 is a perspective view showing a schematic configuration of the second electrode unit 40 in this embodiment. As described above, the second electrode unit 40 has the third electrode 41 and the fourth electrode 42. Furthermore, the second electrode unit 40 in this embodiment has the second coil 44.

[0040] The third electrode 41 and the fourth electrode 42 are conductors, similar to the first electrode 31 and the second electrode 32. The third electrode 41 and the fourth electrode 42 are arranged so that the shortest distance between them is one-tenth or less of the wavelength of the electromagnetic field output from the second electrode unit 40. In this embodiment, the third electrode 41 has a boat-like shape with the Y direction as the longitudinal direction and the X direction as the transverse direction. The lower surface of the third electrode 41 has a curved shape that is convex in the -Z direction. When viewed along the Z direction, the third electrode 41 has an elliptical shape that is elongated in the Y direction. The fourth electrode 42 is flat in the X and Y directions and has an elliptical ring shape that is elongated in the Y direction. When viewed along the Z direction, the fourth electrode 42 is arranged to surround the third electrode 41. In this embodiment, the dimension of the fourth electrode 42 in the Y direction is approximately six times the dimension of the second electrode 32 in the Y direction. 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.

[0041] The third electrode 41 and the fourth electrode 42 are disposed on the substrate 110, similar to the first electrode 31 and the second electrode 32. More specifically, the third electrode 41 is disposed so that the central portions of the lower surface of the third electrode 41 in the X and Y directions are in contact with the upper surface of the substrate 110. The fourth electrode 42 is disposed so that the lower surface of the fourth electrode 42 is in contact with 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.

[0042] Similar to the first electrode 31 and the second electrode 32, the third electrode 41 and the fourth electrode 42 are arranged in the second section 312 so as to face the media Md in the Z direction, which is transported in the -Y direction by the second transport section 326.

[0043] In the present embodiment, the third electrode 41 is electrically connected to the second voltage application unit 82 via the second electric 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 a second connection member 43 disposed above the fourth electrode 42, an outer conductor of the coaxial cable (not shown), and the like. When an AC voltage is applied to the third electrode 41 and the fourth electrode 42, an electromagnetic field having a wavelength λ2 corresponding to the frequency f2 of the applied AC voltage is generated from the third electrode 41 and the fourth electrode 42.

[0044] In this embodiment, one end of the second coil 44 is electrically connected in series to the third electrode 41 via the second electric wire 45, and the other end is electrically connected in series to the second voltage application unit 82. In this embodiment, the second coil 44 is configured as a solenoid coil and is disposed so that its longitudinal 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, so as to form a resonant circuit that resonates with the third electrode 41 and the fourth electrode 42 at 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 disposed so that the distance between one end of the second coil 44 and the third electrode 41 is as small as possible.

[0045] Figure 5 is a first graph in which the horizontal axis represents the heating time of each sample and the vertical axis represents the temperature of each sample when the samples with each ink attached were heated by dielectric heating. Figure 6 is a second graph in which the horizontal axis represents the heating time of each sample and the vertical axis represents the temperature of each sample. Figure 5 shows the relationship between the temperature of each sample and the heating time when the samples were heated by an electromagnetic field with a frequency of 1 GHz. Figure 6 shows the relationship between the temperature of each sample and the heating time when the samples were heated by an electromagnetic field with a frequency of 40.68 MHz.

[0046] Samples s1 to s4 were prepared as samples heated by an electromagnetic field with a frequency of 1 GHz. Samples s11 to s15 were also prepared as samples heated by an electromagnetic field with a frequency of 40.68 MHz. Samples s1 and s11 were prepared by applying a black aqueous pigment ink containing carbon black and resin to a rectangular cotton cloth and leaving it at room temperature for 30 days. Sample s12 was prepared by applying a mixed black aqueous pigment ink containing carbon black and resin to the same cloth and leaving it at room temperature in the same way. Samples s2 and s13 were prepared by applying a cyan aqueous pigment ink containing resin to the same cloth and leaving it at room temperature in the same way. Samples s3 and s14 were prepared by applying a magenta aqueous pigment ink containing resin to the same cloth and leaving it at room temperature in the same way. Samples s4 and s15 were prepared by applying a yellow aqueous pigment ink containing resin to the same cloth and leaving it at room temperature in the same way. Samples s1, s11, and s12 correspond to media Md to which only the first ink In1 is applied, and the other samples correspond to media Md to which only the second ink In2 is applied. The cloth used to prepare samples s1 to s4 has dimensions, when viewed along the Z direction, that correspond to the outer dimensions of the second electrode 32 in the X and Y directions. The cloth used to prepare samples s11 to s15 has dimensions, when viewed along the Z direction, that correspond to the outer dimensions of the second electrode 32 in the X and Y directions. The inks used to prepare each sample contain glycerin.

[0047] Samples s1 to s4 were heated using the first electrode unit 30 described above. More specifically, each sample was placed facing the first electrode 31 and the second electrode 32 of one of the first electrode units 30, and a 1 GHz high-frequency voltage 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 using the second electrode unit 40 described above. During heating of each sample, the power applied to the first electrode unit 30 was 2 W, and the power applied to the second electrode unit 40 was 50 W. The "heating time" shown in FIGS. 5 and 6 represents the time elapsed since the application of the high-frequency voltage to the first electrode 31 and the second electrode 32 began, and the "temperature" represents the maximum temperature within the surface of each sample measured using an infrared camera at a given point in time.

[0048] As shown in Figure 6, when sample s11 was heated by an electromagnetic field with a frequency of 40.68 MHz, its temperature rose rapidly and became unmeasurable before the heating time reached 10 seconds. In contrast, at the 10-second heating time, the temperatures of sample s13 were approximately 120°C, sample s14 was approximately 90°C, and sample s15 was approximately 110°C. Furthermore, at the 20-second heating time, the temperatures of sample s12 were approximately 250°C, while the temperatures of sample s13 were approximately 150°C, and the temperatures of samples s14 and s15 were approximately 130°C.

[0049] As shown in FIG. 5, when sample s1 was heated by an electromagnetic field with a frequency of 1 GHz, its temperature was higher than when samples s2 to s4 were heated in the same manner, even for the same heating time. On the other hand, sample s1 did not exhibit the same rapid temperature increase as sample s11 in FIG. 5. More specifically, for example, after 10 seconds of heating, 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, even after 30 seconds of heating, the temperature difference between sample s1 and the other samples was approximately the same as above, approximately 10°C to 13°C. This is thought to be because, when ink containing carbon black is heated by an electromagnetic field with a frequency of 40.68 MHz, the heat generated by the conductivity of the carbon black contributes predominantly to the temperature rise of the ink, whereas, when this ink is heated by an electromagnetic field with a frequency of 1 GHz, the heat generated by the dielectric loss tangent of the ink contributes predominantly to the temperature rise of the ink. Therefore, by heating the first ink In1 and the second ink In2 using the first electrode unit 30, it is possible to heat and dry both the first ink In1 and the second ink In2 while suppressing a sudden temperature rise of the first ink In1.

[0050] As shown in FIG. 6 , when the frequency is 40.68 MHz, for example, after 10 seconds of heating, the temperature of sample s14 does not reach 100°C, while the temperature of sample s11 exceeds 240°C. Therefore, if the first ink In1 and the second ink In2 attached to the medium Md are continuously heated only by the second electrode unit 40, there is a high possibility that the medium Md will be burned near the position of the first ink In1 before the solvent, such as water, has sufficiently evaporated or volatilized near the position of the medium Md where the second ink In2 is attached. On the other hand, in this embodiment, by heating the first ink In1 and the second ink In2 by the first electrode unit 30 after being heated by the second electrode unit 40, both inks can be heated efficiently and uneven heating can be suppressed. More specifically, if the first ink In1 attached to the medium Md contains a sufficiently large amount of solvent, such as water, the heat resulting from the conductivity of the carbon black described above is absorbed by the solvent. Therefore, by heating both inks with the second electrode unit 40 while the solvent contained in each ink is still sufficient, and then heating both inks with the first electrode unit 30 before the solvent disappears due to evaporation, both inks can be heated and dried efficiently and evenly. In this case, since vapor of the solvent contained in each ink is more likely to be generated near the second electrode unit 40 than near the first electrode unit 30, for example, a blower fan or the like for generating airflow may be provided near the second electrode unit 40.

[0051] Furthermore, in this embodiment, the heating control unit 180 of the dielectric heating device 100 controls the first voltage application unit 81 to control the power applied to the first electrode 31 and the second electrode 32, thereby heating the first ink In1 and the second ink In2 to a temperature of 150°C or higher and 240°C or lower. More specifically, the heating control unit 180 performs feedback control of the power applied to the first electrode 31 and the second electrode 32, while referring to the temperatures of both inks acquired by, for example, an infrared camera or a temperature sensor (not shown) disposed near the first electrode unit 30. In this case, the heating control unit 180 may refer to the temperature of the medium Md as the temperature of both inks.

[0052] By heating both inks to a temperature of 150°C or higher, the pigment can be firmly fixed to the medium Md via the resin contained in both inks. In particular, in this embodiment, after the solvent contained in both inks is dried by the second electrode unit 40, the resin contained in both inks can be heated to 150°C or higher by the first electrode unit 30. This allows the pigment to be firmly fixed to the medium Md via the resin while efficiently drying both inks. Furthermore, by heating both inks to a temperature of 240°C or lower, for example, when the medium Md is paper whose main component is cellulose, or cloth made of cotton or linen, which also has cellulose as its main component, scorching of the medium Md can be suppressed. Furthermore, when the medium Md is a cloth made of polyester, melting of the medium Md can be suppressed, and when the medium Md is a cloth made of rayon, color decomposition of the medium Md can be suppressed.

[0053] 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 1 GHz or higher, or a frequency between 300 MHz and 300 GHz, which corresponds to microwave frequencies in a broad sense. 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 using an electromagnetic field in this frequency range to heat the first ink In1 and the second ink In2, heat generated by the dielectric loss tangent of the inks can be the dominant contributor to the temperature rise of both inks. In this case, it is particularly preferable to use a frequency between 300 MHz and 30 GHz, which corresponds to frequencies commonly used in microwave heating. For example, frequencies of 915 MHz, 2.45 GHz, 5.8 GHz, and 24.125 GHz, which are defined as the ISM (Industrial Scientific and Medical) band, may be used.

[0054] As described above, the frequency of the AC voltage applied to the third electrode 41 and the fourth electrode 42 by the second voltage application unit 82 can be 40.68 MHz or higher, or a frequency greater than 100 kHz and less than 300 MHz. Generally, in this frequency range, the dielectric loss tangent of substances such as water is small and the skin effect is minimal. Therefore, by using an electromagnetic field in this frequency range to heat the first ink In1, heat generated by the conductivity of the carbon black can be made to predominantly contribute to the temperature rise of the first ink In1 and the second ink In2. As a result, as described above, the sudden heat generation of the first ink In1 can be used to heat 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, which are frequencies defined as ISM bands, may be used.

[0055] The dielectric heating device 100 in the first embodiment described above includes a first electrode unit 30 having a first electrode 31 and a second electrode 32 as the electrode unit 20 for heating the first ink In1 and the second ink In2 adhered to the medium Md, and a first voltage application unit 81 that applies an AC voltage of a frequency of 300 MHz or more and 300 GHz or less to the first electrode 31 and the second electrode 32. This allows both the first ink In1 containing carbon black and the second ink In2 not containing carbon black adhered to the medium Md to be heated by the first electrode unit 30 while suppressing heating unevenness. Therefore, after only the second ink In2 adhered to the medium Md is dried by dielectric heating, there is no need to further adhere the first ink In1 to the medium Md, and therefore misalignment of the adhered positions of the first ink In1 and the second ink In2 can be suppressed.

[0056] Furthermore, according to the dielectric heating device 100 of this embodiment, the first ink In1 and the second ink In2 are pigment inks containing resin, and the discharge control unit 250 controls the first voltage application unit 81 to heat the first ink In1 and the second ink In2, respectively, to a temperature of 150°C or higher and 240°C or lower. Because each ink is heated to a temperature of 150°C or higher, the pigment can be firmly fixed to the medium Md via the resin contained in each ink, thereby improving the abrasion resistance of the pigment in the medium Md. Furthermore, because each ink is heated to a temperature of 240°C or lower, scorching, melting, discoloration, and the like of the medium Md due to heating can be suppressed.

[0057] Furthermore, according to the dielectric heating device 100 of 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 that applies an AC voltage of a frequency of 100 kHz or more 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 the first ink In1 and the second ink In2 to be efficiently and evenly heated and dried. Furthermore, when the first ink In1 and the second ink In2 are pigment inks containing resin, as in this embodiment, the pigment can be firmly fixed to the medium Md via the resin while efficiently drying both inks.

[0058] Furthermore, according to the printing system 200 of this embodiment, the discharge 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 downstream of the first section 311. This allows for greater flexibility in the placement of the electrode unit 20 and the discharge unit 210 in the printing system 200 compared to when the application and heating of each ink are performed in the same section of the transport path 310. 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 may be transported in different directions in both sections. For example, the medium Md may be transported in the −Y direction in the first section 311, then be transported in the +Y direction in the second section 312 after being changed in direction by a roller or the like (not shown). This allows for the printing system 200 to be made more compact in the Y direction.

[0059] Furthermore, according to the printing system 200 of this embodiment, the first section 311 and the second section 312 are spaced apart. This further increases the degree of freedom in arranging the electrode unit 20 and the discharge unit 210 in the printing system 200. For example, in the first embodiment, the medium Md is continuously transported from the liquid discharge device 205 to the dielectric heating device 100. However, the medium Md does not have to be continuously transported from the liquid discharge device 205 to the dielectric heating device 100. In this case, for example, the medium Md to which the first ink In1 and the second ink In2 discharged by the liquid discharge device 205 are adhered can be temporarily wound into a roll, and the wound medium Md can be moved to the dielectric heating device 100 by a robot or the like. After that, the wound medium Md can be heated while being unwound and transported in the dielectric heating device 100. In this way, for example, in the printing system 200, the liquid discharge device 205 and the dielectric heating device 100 can be easily disposed apart from each other.

[0060] B. Other Embodiments: (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 not contain resin, or may be dye inks instead of pigment 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 aqueous inks that do not contain resin, the heating control unit 180 may heat both inks to a temperature of 100°C or higher and lower than 150°C.

[0061] (B-2) In the above embodiment, the second electrode 32 is arranged to surround the first electrode 31 when viewed along the Z direction. In contrast, the second electrode 32 does not have to be arranged to surround the first electrode 31 when viewed along the Z direction. For example, the first electrode 31 and the second electrode 32 may be arranged to be adjacent to each other when viewed along the Z direction. In this case, the shapes of the first electrode 31 and the second electrode 32 may be any shape, such as a circle, an oval, a rectangle, or a polygon. Furthermore, the areas of the first electrode 31 and the second electrode 32 when viewed along the Z direction may be the same or different. It is preferable that the first electrode 31 and the second electrode 32 are arranged so as not to overlap each other when viewed along the Z direction. Similarly, the fourth electrode 42 does not have to be arranged to surround the third electrode 41 when viewed along the Z direction. For example, the third electrode 41 and the fourth electrode 42 may be arranged to be adjacent to each other when viewed along the Z direction.

[0062] (B-3) In the above embodiment, the electrode unit 20 includes the second electrode unit 40 in addition to the first electrode unit 30. However, the second electrode unit 40 does not necessarily have to be provided.

[0063] (B-4) In the above embodiment, the dielectric heating device 100 includes two first unit rows UC1 and two second unit rows UC2, for a total of 60 first electrode units 30 and eight second electrode units 40. In contrast, the number of first unit rows UC1 and second unit rows UC2 may be one or three or more. Furthermore, when multiple first unit rows UC1 and multiple second unit rows UC2 are provided, the number of first electrode units 30 and second electrode units 40 may differ from row to row. Furthermore, the number of first electrode units 30 and second electrode units 40 provided in the dielectric heating device 100 may be any number, and may be, for example, one.

[0064] (B-5) In the above embodiment, the first electrode unit 30 and the second electrode unit 40 may be configured to be reciprocally movable in a direction intersecting the direction in which the medium Md is transported. For example, the first electrode unit 30 and the second electrode unit 40 may be supported by a drive unit (not shown) configured by a belt mechanism or a ball screw mechanism, and may be reciprocally movable in the X direction.

[0065] C. Other forms: The present disclosure is not limited to the above-described embodiments and can be realized in various forms without departing from the spirit thereof. For example, the present disclosure can also be realized in the following forms. The technical features in the above embodiments corresponding to the technical features in each form described below can be appropriately replaced or combined 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 a technical feature is not described as essential in this specification, it can be appropriately deleted.

[0066] (1) According to a first aspect of the present disclosure, there is provided a dielectric heating device for heating a first ink containing carbon black and a second ink not containing carbon black that are adhered 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 ink and the second ink, and a first voltage application unit for applying an AC voltage having a frequency of 300 MHz or more and 300 GHz or less to the first electrode and the second electrode. According to this embodiment, both the first ink containing carbon black and the second ink not containing carbon black that are adhered to the medium can be heated by the first electrode unit while suppressing uneven heating. Therefore, after only the second ink adhered to the medium is dried by dielectric heating, there is no need to apply further first ink to the medium, and therefore misalignment of the adhesion positions of the first ink and the second ink can be suppressed.

[0067] (2) In the above embodiment, a control unit may be provided for controlling the first voltage application unit, and the first ink and the second ink may be pigment inks containing a resin, and the control unit may control the first voltage application unit to heat the first ink and the second ink to a temperature of 150°C or higher and 240°C or lower. According to this embodiment, since each ink is heated to a temperature of 150°C or higher, the pigment can be firmly fixed to the medium via the resin contained in each ink, thereby improving the abrasion resistance of the pigment on the medium. Furthermore, since each ink is heated to a temperature of 240°C or lower, scorching, melting, discoloration, and the like of the medium due to heating can be suppressed.

[0068] (3) In the above aspect, the electrode unit may include a second electrode unit having a third electrode and a fourth electrode facing the medium, and a second voltage application unit that applies an AC voltage having a frequency of 100 kHz or more and less than 300 MHz to the third electrode and the fourth electrode, and the first electrode unit may heat the first ink and the second ink after being heated by the second electrode unit. According to this aspect, the first ink and the second ink can be efficiently and evenly heated and dried by the first electrode unit and the second electrode unit.

[0069] (4) According to a second aspect of the present disclosure, there is provided a printing system including a discharge unit having a first discharge unit that discharges and deposits the first ink onto the medium and a second discharge unit that discharges and deposits the second ink onto the medium, and a transport unit that transports the medium along a transport path. The electrode unit heats the first ink and the second ink downstream of a position on the transport path where the discharge unit deposits the first ink and the second ink onto the medium.

[0070] (5) In the second aspect, the transport unit may include a first transport unit that transports the medium in a first section of the transport path and a second transport unit that transports the medium in a second section of the transport path downstream from the first section, the ejection unit may apply the first ink and the second ink to the medium in the first section, and the electrode unit may heat the first ink and the second ink in the second section. This aspect allows for greater flexibility in the placement of electrode units and ejection units in the printing system compared to when the application and heating of each ink are performed in the same section of the transport path.

[0071] (6) In the second aspect, the first section and the second section may be spaced apart. This aspect further increases the degree of freedom in arranging the electrode units and the discharge units in the printing system. [Explanation of symbols]

[0072] 20...electrode unit, 30...first electrode unit, 31...first electrode, 32...second electrode, 33...connecting member, 34...first coil, 35...first electric wire, 40...second electrode unit, 41...third electrode, 42...fourth electrode, 43...second connecting member, 44...second coil, 45...second electric wire, 80...voltage application section, 81...first voltage application section, 82...second voltage application section, 100...dielectric heating device, 110...substrate, 150...transport section, 180...heating Control unit, 200...printing system, 205...liquid ejection device, 210...ejection unit, 211...first ejection unit, 212...second ejection unit, 230...media transport unit, 250...ejection control unit, 310...transport path, 311...first section, 312...second section, 320...transport unit, 321...first roller unit, 322...second roller unit, 323...third roller unit, 324...fourth roller unit, 325...first transport unit, 326...second transport unit

Claims

1. A dielectric heating device for heating a first ink containing carbon black and a second ink not containing carbon black, both of which are attached to a medium, comprising: a first electrode unit having a first electrode and a second electrode facing the medium as an electrode unit for heating the first ink and the second ink; a first voltage application unit that applies an AC voltage having a frequency of 300 MHz or more and 300 GHz or less to the first electrode and the second electrode; the electrode unit includes a second electrode unit having a third electrode and a fourth electrode facing the medium; a second voltage application unit that applies an AC voltage having a frequency of 100 kHz or more and less than 300 MHz to the third electrode and the fourth electrode.

2. A dielectric heating device for heating a first ink containing carbon black and a second ink not containing carbon black, both of which are attached to a medium, comprising: a first electrode unit having a first electrode and a second electrode facing the medium as an electrode unit for heating the first ink and the second ink; a first voltage application unit that applies an AC voltage having a frequency of 300 MHz or more and 300 GHz or less to the first electrode and the second electrode; the electrode unit includes a second electrode unit having a third electrode and a fourth electrode facing the medium; a second voltage application unit that applies an AC voltage having a frequency of 100 kHz or more 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 being heated by the second electrode unit.

3. The dielectric heating device according to claim 1 or 2, a control unit that controls the first voltage application unit, the first ink and the second ink are pigment inks containing a resin, The control unit controls the first voltage application unit to heat the first ink and the second ink to a temperature of 150° C. or higher and 240° C. or lower, respectively.

4. The dielectric heating device according to any one of claims 1 to 3; a discharge unit having a first discharge section that discharges the first ink onto the medium and a second discharge section that discharges the second ink onto the medium; a transport unit that transports the medium along a transport path, The electrode unit heats the first ink and the second ink downstream of a position on the transport path where the ejection unit deposits the first ink and the second ink on the medium.

5. 5. The printing system according to claim 4, the transport unit includes a first transport unit that transports the medium in a first section of the transport path, and a second transport unit that transports the medium in a second section of the transport path that is downstream of the first section; the ejection unit deposits the first ink and the second ink onto the medium in the first section; The electrode unit heats the first ink and the second ink in the second section.

6. 6. The printing system according to claim 5, The printing system, wherein the first section and the second section are spaced apart.

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