Inkjet printing device

Abstract

An inkjet printing device according to an embodiment of the present invention includes: a print head that ejects ink onto a substrate and includes a first heater that heats the ink; a reservoir that stores ink; a first piping that supplies ink from the reservoir to the print head; a second piping that recovers the remaining ink from the print head to the reservoir; a mixing unit that is arranged on the first piping and includes a second heater that heats the ink and mixes the ink; a pump that is arranged on the second piping and pressurizes the remaining ink to supply it to the reservoir; a temperature sensor that is arranged on the first piping between the mixing unit and the print head and senses the temperature of the ink; and a control unit that controls the temperature of at least one of the first heater and the second heater in accordance with information received from the temperature sensor. The print head also includes: a heat insulating unit that blocks the heat that is dissipated from the first heater to between the substrate and the first heater.

Description

Technical Field

[0001] The present invention relates to an inkjet printing device. Background Art

[0002] With the development of information society, the demand for display devices for displaying images is increasing in various forms. For example, display devices are applicable to various electronic devices such as smart phones, desktop PCs, digital cameras, laptops, navigators, monitors and TVs. The display device can be a flat panel display device such as a liquid crystal display device (Liquid Crystal Display Device), a field emission display device (Field Emission Display Device), an organic light emitting display device (Organic Light Emitting Display Device), a quantum dot light emitting display device (Quantum Dot Light Emitting Display Device), etc.

[0003] Among them, in the process of manufacturing a thin film such as a light-emitting layer of an organic light-emitting display device, an inkjet printing process can be used to form a thin film of a desired shape by ejecting ink onto the surface of an object. The inkjet printing device generates individual ink droplets through the nozzles of a print head and ejects them to a predetermined position of a substrate as an object, thereby printing a thin film of a desired pattern on the substrate.

[0004] The inkjet printing device can have, as needed: a discontinuous inkjet printing method, in which ink droplets are generated discontinuously from the print head; and a continuous inkjet printing method, in which ink droplets are generated continuously from the print head and only selected ink droplets are ejected to the substrate side, and un-ejected ink droplets are recycled to the ink supply unit.

[0005] Inkjet printing apparatuses using the continuous inkjet printing method have a problem in that the temperature and viscosity of the ink fluctuate as the undischarged ink is recirculated, and the discharge amount becomes uneven. Summary of the invention

[0006] An object of the present invention is to provide an inkjet printing device that can maintain a uniform ink discharge amount.

[0007] In addition, an inkjet printing device is provided that can print a thin film of a pattern at a desired position on the substrate by maintaining a uniform temperature distribution on the substrate.

[0008] In addition, an inkjet printing device capable of maintaining a uniform ink concentration is provided.

[0009] However, the purpose of the present invention is not limited to the above-mentioned purpose, and various extensions can be made without departing from the scope of the idea and field of the present invention.

[0010] An inkjet printing device according to an embodiment of the present invention for solving the above-mentioned problem includes: a print head that ejects ink onto a substrate and includes a first heater that heats the ink; a reservoir that stores the ink; a first piping that supplies the ink from the reservoir to the print head; a second piping that recovers excess ink from the print head to the reservoir; a mixing unit that is disposed on the first piping, includes a second heater that heats the ink, and mixes the ink; a pump that is disposed on the second piping and pressurizes the excess ink to supply it to the reservoir; a temperature sensor that is disposed on the first piping between the mixing unit and the print head and senses the temperature of the ink; and a control unit that controls the temperature of at least one of the first heater and the second heater in accordance with information received from the temperature sensor.

[0011] The print head further includes a heat insulating portion that blocks heat dissipated from the first heater to between the substrate and the first heater.

[0012] The print head may include a nozzle portion for ejecting the ink, and the heat insulating portion may include an opening portion overlapping with the nozzle portion in a thickness direction.

[0013] The invention may further include a cooling unit which is disposed on the second pipe between the pump and the reservoir and cools the excess ink.

[0014] The cooling unit may include a Peltier element.

[0015] The cooling unit may maintain the temperature of the remaining ink at a temperature when the ink is first supplied from the tank to the print head.

[0016] The control unit may maintain the temperature of the print head by the first heater to be the same as the temperature of ink heated by the second heater.

[0017] The second heater may include a Peltier element or a silicone rubber heater.

[0018] The mixing unit may include a static mixer or a mixer using a surface acoustic wave.

[0019] The method may further include: a first pressure sensor disposed on the first pipe between the mixing unit and the print head, and sensing the pressure of the ink.

[0020] The control unit may heat the ink to a preset temperature corresponding to the sensed pressure by the first heater when the pressure sensed by the first pressure sensor is higher than a preset pressure.

[0021] The system may further include: a second pressure sensor, which is disposed on the second pipe between the print head and the pump and senses the pressure of the remaining ink.

[0022] The control unit may heat the ink in proportion to the pressure difference by the first heater when the pressure difference between the pressure sensed by the first pressure sensor and the pressure sensed by the second pressure sensor exceeds a preset range.

[0023] Another embodiment of the present invention for solving the above-mentioned problems relates to an inkjet printing device including: a print head for ejecting ink; a solvent circulation unit for supplying a solvent included in the ink to the print head; and a particle circulation unit for supplying a particle-containing liquid included in the ink to the print head.

[0024] The solvent circulation unit includes a first tank storing the solvent, a first pipe supplying the solvent from the first tank to the print head, and a second pipe collecting a surplus solvent included in surplus ink from the print head to the first tank.

[0025] The particle circulation section includes: a particle supply section, which supplies the particle-containing liquid to the first piping; a second liquid reservoir, which is arranged on the second piping and stores the residual ink remaining after being ejected from the print head; a third piping, which recovers the residual particle-containing liquid separated from the residual solvent in the residual ink from the second liquid reservoir to the particle supply section; a concentration sensor, which is arranged on the first piping between the particle supply section and the print head and senses the concentration of the ink; and a supply control section, which controls the supply amount of the particle-containing liquid corresponding to the information received from the concentration sensor.

[0026] The particle supply unit may include: a third liquid reservoir storing the recovered excess particle-containing liquid; and a first pump supplying the excess particle-containing liquid from the third liquid reservoir to the first pipe.

[0027] The supply control unit may increase the supply amount of the particle-containing liquid through the first pump when the concentration of the ink sensed by the concentration sensor is lower than a preset concentration.

[0028] The method may further include: a second pump disposed on the third pipe and pressurizing the excess particle-containing liquid to supply the excess particle-containing liquid to the particle supplying unit.

[0029] The second liquid tank may separate the remaining ink into the remaining solvent and the remaining particle-containing liquid using a surface acoustic wave.

[0030] The print head may include a first heater for heating the ink.

[0031] The invention may further include a mixing unit disposed on the first pipe between the particle supply unit and the concentration sensor, wherein the mixing unit includes a second heater for heating the ink and mixes the solvent and the particle-containing liquid.

[0032] The method may further include: a temperature sensor disposed on the first pipe between the mixing unit and the print head, and sensing the temperature of the ink.

[0033] The method may further include: a control unit that maintains the temperature of the print head, through the first heater, to be the same as the temperature of the ink heated by the second heater.

[0034] The mixing unit may include a static mixer or a mixer using a surface acoustic wave.

[0035] The method may further include: a cooling unit disposed on the second pipe between the second liquid storage container and the third liquid storage container, and configured to cool the remaining solvent.

[0036] The cooling unit may maintain the temperature of the remaining solvent at a temperature when the solvent is first supplied from the first tank to the print head.

[0037] (Effects of the Invention)

[0038] According to the inkjet printing device according to an embodiment of the present invention, the ejection amount of ink can be maintained constant by maintaining the temperature and viscosity of the ink constant.

[0039] Furthermore, according to the inkjet printing device according to an embodiment of the present invention, by preventing the heat generated by the print head from being transferred to the substrate, the temperature distribution of the substrate can be maintained uniform, and a thin film of a pattern can be printed at a desired position on the substrate.

[0040] Furthermore, according to the inkjet printing apparatus according to an embodiment of the present invention, the concentration of the ink can be maintained uniform by preventing the sedimentation of particles included in the ink.

[0041] The effects of each embodiment are not limited to the above examples, and more effects are included in this specification. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 This is a schematic perspective view for explaining an inkjet printing device according to an embodiment of the present invention.

[0043] Figure 2 It is along Figure 1 A cross-sectional view of the substrate taken along line II'.

[0044] Figure 3 It is a diagram for explaining an inkjet printing device according to an embodiment of the present invention.

[0045] Figure 4 It is a three-dimensional diagram of a print head according to an embodiment of the present invention.

[0046] Figure 5 It is along Figure 4 A cross-sectional view of the print head taken along line II-II'.

[0047] Figure 6 It is a perspective view of a liquid storage device according to an embodiment of the present invention.

[0048] Figure 7 yes Figure 6 A cross-sectional view of the reservoir is shown.

[0049] Figure 8 It is a cross-sectional view for explaining a mixing portion according to an embodiment of the present invention.

[0050] Fig. 9 It is a diagram for explaining a cooling unit according to an embodiment of the present invention.

[0051] Fig.10 It is a diagram for explaining an inkjet printing device according to another embodiment of the present invention.

[0052] Fig.11 It is a perspective view of a print head according to another embodiment of the present invention.

[0053] Fig.12 It is along Fig.11 A cross-sectional view of the print head taken along line III-III'.

[0054] Figures 13 to 16 It is a diagram for explaining an inkjet printing device according to another embodiment of the present invention. DETAILED DESCRIPTION

[0055] References and Attachments Figure 1 The advantages, features and methods of achieving the advantages and features of the present invention will become clear from the detailed description of the embodiments below. However, the present invention is not limited to the embodiments disclosed below and can be implemented in different forms. The embodiments are only provided to make the disclosure of the present invention complete and to fully inform the scope of the invention to those skilled in the art. The present invention should be defined only by the scope of the claims.

[0056] Throughout the specification, the same symbols refer to the same components. The shapes, sizes, ratios, angles, numbers, etc. disclosed in the drawings for explaining the embodiments are examples, and the present invention is not necessarily limited to the drawings.

[0057] Although the terms "first", "second" and the like can be used to describe various components, the components are certainly not limited to the terms. The terms are only used to distinguish one component from another component. Therefore, the first component mentioned below can certainly be the second component within the technical concept of the present invention.

[0058] The various features of the various embodiments of the present invention may be partially or wholly combined or coupled with one another, various linkages and drives are technically possible, and the various embodiments may be implemented independently of one another or together in an associated relationship.

[0059] Hereinafter, specific embodiments will be described with reference to the drawings.

[0060] Figure 1 This is a schematic perspective view for explaining an inkjet printing device according to an embodiment of the present invention. Figure 2 It is along Figure 1 A cross-sectional view of the substrate taken along line II'.

[0061] Reference Figure 1 and Figure 2 An inkjet printing device 1 according to an embodiment of the present invention may include a workbench 10, a print head 20 for ejecting ink (eg, organic light-emitting ink) onto a substrate 30, and a driving unit (not shown) for moving the workbench 10 or the print head 20.

[0062] The workbench 10 supports the substrate 30 and may be formed of a rigid material. However, the material of the workbench 10 is not limited thereto. In the exemplary embodiment, the workbench 10 may be in a rectangular parallelepiped shape, but the shape of the workbench 10 is not limited thereto.

[0063] A substrate 30 may be disposed on the workbench 10. The substrate 30 may include a base substrate, a thin film transistor, an insulating layer, etc. The base substrate may be formed of materials such as transparent glass, a plastic sheet, or silicon, but the material of the base substrate is not limited thereto.

[0064] The substrate 30 may be a unit display substrate or a mother substrate before being cut and divided into a plurality of unit display substrates. The substrate 30 may be a single substrate 30 or may include a plurality of laminated substrates.

[0065] like Figure 2 As shown, the substrate 30 according to an embodiment of the present invention may have a buffer layer 33 formed on a base substrate 30 a , and a thin film transistor 31 and an organic light emitting element 32 may be formed on the buffer layer 33 .

[0066] The thin film transistor 31 may include an active layer 31 a , a gate insulating film 34 formed to cover the active layer 31 a , and a gate electrode 31 b on an upper portion of the gate insulating film 34 .

[0067] An interlayer insulating film 35 may be formed to cover the gate electrode 31 b , and a source electrode 31 c and a drain electrode 31 d may be formed on an upper portion of the interlayer insulating film 35 .

[0068] The source electrode 31 c and the drain electrode 31 d may be in contact with the source region and the drain region of the active layer 31 a through contact holes formed in the gate insulating film 34 and the interlayer insulating film 35 , respectively.

[0069] In addition, the pixel electrode 32a of the organic light-emitting element 32 can be connected to the drain electrode 31d. The pixel electrode 32a is formed on the upper part of the planarization film 36, and a pixel definition film (Pixeldefining layer) 37 that divides the sub-pixel area is formed on the pixel electrode 32a. In addition, the light-emitting layer 32b of the organic light-emitting element 32 is formed in the opening of the pixel definition film 37, and the counter electrode 32c is deposited on them. That is, the opening surrounded by the pixel definition film 37 becomes the area of ​​a sub-pixel such as a red pixel R, a green pixel G, and a blue pixel B, and the light-emitting layer 32b of the corresponding color is formed therein. Here, one sub-pixel is shown, but in fact, a plurality of such sub-pixels can be arranged in the row and column directions in the display unit.

[0070] The plurality of sub-pixels may be in a rectangular shape. The plurality of sub-pixels may be arranged in a matrix of n×m (where n and m are integers greater than 1). Figure 1 In the exemplary embodiment shown, when the row direction is set to the y direction and the column direction is set to the x direction, sub-pixels may be arranged in a 6×6 matrix on the substrate 30. However, Figure 1The arrangement of the sub-pixels is an example, and a larger number of sub-pixels can actually be arranged on the substrate 30. In addition, the sub-pixels can be arranged in various forms such as stripe form or pentile form in addition to the matrix form.

[0071] Such a thin film of an organic light emitting display device can be formed by printing using the above-mentioned print head 20 . For example, by ejecting ink at a position corresponding to the light emitting layer 32 b , a light emitting layer 32 b having a desired pattern can be formed.

[0072] To explain the inkjet printing device 1 in more detail, refer to Figures 3 to 9 .

[0073] Figure 3 It is a diagram for explaining an inkjet printing device according to an embodiment of the present invention. Figure 4 It is a three-dimensional diagram of a print head according to an embodiment of the present invention. Figure 5 It is along Figure 4 A cross-sectional view of the print head taken along line II-II'. Figure 6 It is a perspective view of a liquid storage device according to an embodiment of the present invention. Figure 7 yes Figure 6 A cross-sectional view of the reservoir is shown. Figure 8 It is a cross-sectional view for explaining a mixing portion according to an embodiment of the present invention. Fig. 9 It is a diagram for explaining a cooling unit according to an embodiment of the present invention.

[0074] Reference Figures 3 to 9 The inkjet printing device 1 may include a print head 20 , a reservoir 40 , a first pipe P1 , a second pipe P2 , a mixing unit 50 , a pump PU, a cooling unit 60 , a temperature sensor TS, and a control unit 70 .

[0075] According to an embodiment of the present invention, the print head 20 can eject ink onto the substrate 30 .

[0076] Reference Figure 4 and Figure 5 The print head 20 involved in this embodiment may include a main body 21 serving as a shell of the print head 20 , a driving unit 22 disposed on a side of the main body 21 , an ink storage unit 23 , a nozzle unit 24 , and a first heater H1 .

[0077] The body 21 may function as a housing of the print head 20. The body 21 may have various shapes. The body 21 may have a quadrangular prism shape.

[0078] The main body 21 may include an injection port IN1 disposed on one side of the main body 21 and an ink flow outlet OUT1 disposed on the other side. The injection port IN1 and the ink flow outlet OUT1 may be formed by forming a hole on the main body 21. Various ink compositions, cleaning agents, etc. may be injected through the injection port IN1. The ink compositions and cleaning agents, etc. may flow out through the ink flow outlet OUT1. For example, the ink stored in the reservoir 40 may be supplied to the ink storage portion 23 through the injection port IN1, and ink droplets are continuously generated from the nozzle portion 24, from which only selected ink droplets are ejected to the substrate 30 side, and the ink droplets that are not ejected may be recovered to the reservoir 40 through the ink flow outlet OUT1, whereby the ink may be circulated again.

[0079] The body 21 may include a coupling hole 21 a for coupling with the nozzle part 24. The coupling holes 21 a may be disposed at both sides of the body 21.

[0080] The driving unit 22 may be disposed on both sides of the main body 21, and applies power to the nozzle unit 24 to drive the nozzle unit 24. The driving unit 22 may be electrically connected to the printed circuit substrate 22b via the flexible circuit substrate 22a.

[0081] Although not shown, the driving unit 22 may include a circuit in which a plurality of transistors, resistors, capacitors, etc. are integrated on a silicon substrate. The driving unit 22 may apply power to the nozzle unit 24 to eject ink.

[0082] The flexible circuit substrate 22a may be disposed outside the main body 21 and electrically connected to the driving unit 22. The flexible circuit substrate 22a may apply power to the driving unit 22 for discharging ink.

[0083] The flexible circuit board 22a is a board having a circuit formed on a soft insulating film, and a heat-resistant plastic film such as polyester or polyimide can be used as a flexible material. A plurality of flexible circuit boards 22a can be formed as needed.

[0084] The printed circuit substrate 22b may generate a signal for driving the driving unit 22. The printed circuit substrate 22b may be disposed on an upper portion of the print head 20 and electrically connected to the driving unit 22 via the flexible circuit substrate 22a.

[0085] The driving unit 22 and the flexible circuit board 22a, and the flexible circuit board 22a and the printed circuit board 22b may be connected to each other through the connecting element 22c. For example, the connecting element 22c may be formed of a conductive material such as copper (Gu) or aluminum (Al).

[0086] The main body 21 may include an ink storage portion 23 that stores ink supplied from the injection port IN1 .

[0087] The ink storage unit 23 may be disposed inside the main body 21 and may be disposed below the injection port IN1 . The ink storage unit 23 may receive the supply of ink from the injection port IN1 and allow the ink to flow toward the nozzle unit 24 .

[0088] The main body 21 may include a nozzle unit 24 that receives ink from the ink storage unit 23 and discharges the ink to the outside of the main body 21. The nozzle unit 24 may be disposed at a lower portion of the ink storage unit 23.

[0089] Although not shown, a plurality of dispersion holes (not shown) for dispersing the ink discharged from the nozzle portion 24 may be formed on the lower surface of the main body 21. For example, 128 or 256 dispersion holes may be formed.

[0090] The nozzle unit 24 may be provided at the bottom of the print head 20 and may discharge ink of a desired size upon receiving the supply of ink from the print head 20 .

[0091] A plurality of nozzle upper holes 24a may be formed on the upper surface of the nozzle portion 24. The nozzle portion 24 may be supplied with ink from the print head 20. For example, 128 or 256 nozzle upper holes 24a may be formed. The ink may be ejected through the inside of the nozzle portion 24 and through the lower surface of the nozzle portion 24 formed with a plurality of nozzle lower holes 24b of a desired size.

[0092] The nozzle portion 24 may be a silicon nozzle portion or a metal nozzle portion. Preferably, it may be a silicon nozzle portion. Generally, the nozzle portion 24 may be formed using silicon by a MEMS (Micro Electro Mechanical Systems) method. Alternatively, the nozzle portion 24 may be implemented by a known nozzle portion in order to adjust the size and amount of ink.

[0093] The first heater H1 may be configured to overlap the ink storage portion 23 in the thickness direction. The first heater H1 may include a coil that generates heat when current flows therethrough. The first heater H1 may be physically in contact with the ink storage portion 23, so that the heat generated by the first heater H1 may be transferred to the ink stored in the ink storage portion 23 by heat conduction.

[0094] The tank 40 may store ink and supply the ink in response to a request from the print head 20 .

[0095] Reference Figure 6 and Figure 7, the reservoir 40 may include an ink tank 41 and a preheating unit 42. For the ink stored in the reservoir 40 and flowing out therefrom, for the sake of detailed description, it is divided into newly injected ink INK0 and stored ink INK1 for description. The newly injected ink INK0 is ink stored in an external ink storage place (not shown) and newly injected into the ink tank 41 through the injection port 41a, and the stored ink INK1 is ink that has been stored in the ink tank 41 before the newly injected ink INK0 is injected into the ink tank 41. Therefore, the temperature of the newly injected ink INK0 may be different from the temperature of the stored ink INK1.

[0096] The ink tank 41 may include a storage area 41b for storing stored ink INK1, an injection port 41a for receiving injection of newly injected ink INK0 from the outside, an outflow port OUT2 for allowing the stored ink INK1 to flow out from the storage area 41b to the outside, and a recovery port IN2 for recovering the ink that has not been ejected from the nozzle portion 24 to the substrate 30 side. The ink tank 41 may have a certain volume of empty space inside it so that the stored ink INK1 can be stored. The ink tank 41 may be made of a material with high thermal conductivity. It is preferably formed of a metal such as aluminum or an aluminum alloy.

[0097] The injection port 41a is formed on the upper side of the preheating unit 42. Specifically, the injection port 41a is formed on the upper surface of the edge of the ink tank 41, is connected to an external ink storage, and receives injection of new ink INK0 from the ink storage into the interior.

[0098] The stored ink INK1 is temporarily stored in the storage area 41b of the ink tank 41. A level sensor (not shown) is provided inside the reservoir 40 to recognize the height of the stored ink INK1 which has been lowered due to the outflow, so that the newly injected ink INK0 is injected to maintain a certain amount of the newly injected ink INK0 and the stored ink INK1 stored in the storage area 41b. The storage area 41b is defined at the lower side of the preheating section 42. Therefore, it is possible to maintain that the stored ink INK1 is stored only at the lower side of the preheating section 42.

[0099] The outflow port OUT2 is formed at the lower side of the preheating unit 42. Specifically, it is formed at the lower side of the ink tank 41. However, the invention is not limited thereto, and the outflow port OUT2 may also be formed at the lower surface of the ink tank 41. The stored ink INK1 in the storage area 41b may reach the print head 20 through the outflow port OUT2, and the stored ink INK1 reaching the print head 20 may be ejected to the substrate 30 side.

[0100] The one side 41s of the ink tank 41 can be formed in a detachable manner. When the user uses the reservoir 40 for a long time and the inside of the reservoir 40 is contaminated or foreign matter is generated, the detachable one side 41s can be separated to clean the inside of the reservoir 40. However, this is only one embodiment and is not limited thereto. The ink tank 41 may not include the detachable one side 41s.

[0101] The preheating unit 42 is disposed between the injection port 41a and the storage area 41b. Newly injected ink INK0 injected into the ink tank 41 from the injection port 41a can reach the preheating unit 42. The preheating unit 42 has one surface in contact with the inner side surface of the ink tank 41, and can receive heat from the inner side surface.

[0102] The preheating unit 42 may be formed of a material with high thermal conductivity, and is preferably formed of aluminum or an aluminum alloy.

[0103] The preheating section 42 may include a base plate BS having a flat plate shape. The base plate BS allows the newly injected ink INK0 injected from the injection port 41a to move along its upper surface, thereby transferring the newly injected ink INK0 to the storage area 41b. The preheating section 42 may include a preheating wall WA formed along the edge position of the base plate BS so that the newly injected ink INK0 is preheated in a state of being enclosed in the preheating section 42 and transferred to the storage area 41b. However, this is not limited to this, and the shape of the preheating section 42 may be deformed for implementation. Specifically, the preheating section 42 may not include the preheating wall WA but only include the base plate BS.

[0104] The newly injected ink INK0 can be transferred to one end BS_E of the base plate BS along the upper surface of the base plate BS. The newly injected ink INK0 injected through the injection port 41a can reach the preheating unit 42. The preheating unit 42 is in contact with the inner side of the ink tank 41, so the preheating unit 42 can receive the heat of the stored ink INK1 transferred to the inner side of the ink tank 41 to achieve thermal balance.

[0105] The newly injected ink INK0 has a low initial temperature and a high density, so the injected newly injected ink INK0 is diffused while sinking in the preheating section 42. The sunken newly injected ink INK0 can be heated by the preheating section 42 to increase the temperature and decrease the density. The newly injected ink INK0 whose temperature and density reach a normal state will float up and diffuse to one end BS_E as shown by the first arrow Da, and the newly injected ink INK0 diffused to one end BS_E moves from one end BS_E of the base plate BS to the storage area 41b, thereby merging with the stored ink INK1. The preheating wall WA at one end BS_E is formed to be lower than other preheating walls WA, so that the newly injected ink INK0 moves from one end BS_E to the storage area 41b as shown by the second arrow Db. However, it is not limited to this, for example, the shape of the preheating wall WA at one end BS_E can be deformed to implement it.

[0106] The initial temperature of the newly injected ink INK0 injected into the ink tank 41 may be lower than that of the stored ink INK1, but it is preheated to the same temperature as that of the stored ink INK1 by the preheating unit 42, so that the temperature of the ink in the storage area 41b can be uniformly maintained even after the newly injected ink INK0 and the stored ink INK1 are merged. Therefore, the viscosity of the stored ink INK1 stored in the reservoir 40 is also uniformly maintained, so that a uniform amount of the stored ink INK1 can flow out through the outflow port OUT2.

[0107] However, the liquid storage device 40 may not include the preheating unit 42 but may include only the storage area 41 b .

[0108] The first pipe P1 may connect the inlet IN1 of the print head 20 and the outlet OUT2 of the tank 40. The ink stored in the tank 40 may be supplied to the print head 20 via the first pipe P1.

[0109] The second pipe P2 can connect the outlet port OUT1 of the print head 20 and the recovery port IN2 of the tank 40. The excess ink remaining without being ejected through the nozzle portion 24 of the print head 20 can be recovered in the tank 40 through the second pipe P2.

[0110] The mixing unit 50 may be disposed in a region of the first pipe P1. The mixing unit 50 may include a static mixer SM and a second heater H2 for heating the ink.

[0111] like Figure 8 As shown, a static mixer SM according to an embodiment of the present invention may include blades 52 arranged along the length direction of a mixer tube 51. Figure 8As shown, the blade 52 may include blade elements 53 and 54 so that the ink is transferred to the lower part by switching directions every 1 pitch. The blade elements 53 and 54 may have a screw shape, and the screw directions of the blade elements 53 and the blade elements 54 may be opposite to each other. However, the shape of the blade elements 53 and 54 is not limited thereto, and various changes may be made corresponding to the type and viscosity of the ink passing through the mixing section 50. In addition, the number of blade elements 53 and 54 may also be variously changed corresponding to the amount of ink passing through the mixing section 50.

[0112] Ink can be injected into the static mixer SM through the first pipe P1. For the injected ink, while passing through the blades 52 provided along the length direction of the mixer tube body 51, as the blade elements 53 and 54 change the feeding direction every 1 pitch, the particles and solvent included in the ink can be uniformly mixed with each other. In particular, bubbles generated during the mixing process can be removed, and the physical property efficiency of the ink can be improved.

[0113] The mixing part 50 may include a second heater H2 surrounding a mixer tube 51 of the static mixer SM.

[0114] The second heater H2 according to an embodiment may be a silicone rubber heater. The second heater H2 may include a heater pad 55 and a heat insulating cover 56.

[0115] The heater pad 55 may be attached to be in direct contact with the outer surface of the mixer tube 51. The heat generated by the heater pad 55 may be directly transferred to the mixer tube 51 mainly by conduction.

[0116] The heat insulating cover 56 may extend radially outward from the heater pad 55 and substantially surround the heater pad 55, and include a heat insulating material having a lower thermal conductivity than the mixer tube 51 and the heater pad 55. Since the heat insulating cover 56 has a lower thermal conductivity than the mixer tube 51, the heat generated by the heater pad 55 mainly flows radially inward from the mixer tube 51 toward the mixer tube 51 rather than flowing radially outward. Thus, the heat of the second heater H2 can be effectively transferred to the ink passing through the mixer tube 51.

[0117] However, the type of the second heater H2 is not limited thereto, and for example, the second heater H2 may be an element utilizing the Peltier Effect described later.

[0118] The cooling unit 60 may be disposed in a region of the second pipe P2 . For example, the cooling unit 60 may be disposed between the pump PU and the reservoir 40 .

[0119] The cooling unit 60 can cool the excess ink that has passed through the pump PU.

[0120] Reference Fig. 9 The cooling unit 60 may include a thermoelectric element 61. The thermoelectric element 61 is an element that utilizes the Peltier effect, which generates heat or absorbs heat at the junction of two metals when two metals are connected and current flows through the two metals. That is, in different types of metals, the potential of electrons in the metals is different. Therefore, in order to transfer electrons from a metal in a state of low potential energy to a metal in a state of high potential energy, it is necessary to obtain energy from the outside, thereby obtaining heat energy from the contact point. In the opposite case, heat energy will be dissipated. According to the direction of the current provided to this thermoelectric element 61, the direction of heat generation or heat absorption can be determined.

[0121] For example, in Fig. 9 When the current flows in the direction of the arrow, heat absorption occurs on the first metal 61a side and heat dissipation occurs on the second metal 61b side. Fig. 9 When the heat flows in the direction opposite to the direction of the arrow shown, heat is dissipated on the first metal 61 a side and heat is absorbed on the second metal 61 b ​​side.

[0122] Therefore, in the present invention, in order to lower the temperature of the remaining ink passing through the second piping P2, there is no need to use a fan-type cooler that takes up a large space when installed. Instead, a thermoelectric element 61 that has a cooling effect when current is applied is used, and the required installation space is relatively small, thereby improving the overall effective utilization of space.

[0123] The thermoelectric element 61 may be arranged to surround the second piping P2. When the cooling unit 60 senses that the temperature of the remaining ink passing through the second piping P2 has increased through a temperature sensor (not shown), the cooling unit 60 may quickly dissipate heat through the thermoelectric element 61. At this time, the cooling unit 60 may control the operation of the thermoelectric element 61 through an independent control unit (not shown) or through a control unit 70 described later.

[0124] For example, the cooling unit 60 can maintain the temperature of the remaining ink passing through the second pipe P2 at the ambient temperature (e.g., about 23° C.). In other words, the cooling unit 60 can maintain the temperature of the remaining ink recovered in the reservoir 40 at the temperature when the ink is first supplied from the reservoir 40 to the print head 20.

[0125] That is, the temperature of the ink initially stored in the reservoir 40 may be equal to the atmospheric temperature (or the ambient temperature of the inkjet printing device) because the ink has not yet circulated in the inkjet printing device 1. Therefore, when the temperature of the remaining ink is maintained at the atmospheric temperature, the temperature of the remaining ink recovered to the recovery port IN2 of the reservoir 40 may be equal to the temperature when the ink is initially supplied from the reservoir 40 to the print head 20.

[0126] Thus, the excess ink recovered into the tank 40 can maintain a physical property state similar to that of the newly injected ink INK0 injected from the external ink storage (not shown) in terms of temperature and viscosity.

[0127] However, the cooling unit 60 is not limited to the thermoelectric element 61. For example, cooling water or cooling liquid may be constantly flowed through the second pipe P2 to maintain the temperature of the excess ink passing through the second pipe P2 constant.

[0128] The pump PU may be disposed in a region of the second pipe P2 . For example, the pump PU may be disposed between the print head 20 and the cooling unit 60 .

[0129] The pump PU can pressurize the remaining ink and supply it to the reservoir 40. The remaining ink passing through the pump PU is the ink before passing through the cooling unit 60, so its viscosity is lower than the remaining ink after passing through the cooling unit 60. Therefore, since the remaining ink with low viscosity is supplied to the reservoir 40 through the pump PU, it can be expected that the durability and operability of the pump PU will be improved.

[0130] The temperature sensor TS may be disposed in a region of the first pipe P1. For example, the temperature sensor TS may be disposed between the mixing unit 50 and the injection port IN1 of the print head 20. The temperature sensor TS may sense the temperature of the ink that has passed through the mixing unit 50.

[0131] The control portion 70 may control the temperature of the first heater H1 and / or the second heater H2 corresponding to information received from the temperature sensor TS.

[0132] For example, the control unit 70 may increase the temperature of the ink passing through the mixing unit 50 by the second heater H2 in order to maintain a constant amount of ink ejected from the print head 20. However, if the length of the first pipe P1 from the mixing unit 50 to the print head 20 is long, the temperature of the ink heated by the second heater H2 may decrease again. If the expected temperature of the ink changes due to the external environment, the printing quality of the inkjet printer 1 may be reduced.

[0133] Therefore, when the control unit 70 determines that the temperature of the ink sensed by the temperature sensor TS is different from the temperature of the ink heated by the second heater H2, the control unit 70 can maintain the temperature of the ink stored in the ink storage unit 23 to the same temperature as the temperature of the ink heated by the second heater H2 through the first heater H1.

[0134] In the following embodiments, the same configurations as those in the previously described embodiments are omitted or simplified, and the differences are mainly described.

[0135] Fig.10 It is a diagram for explaining an inkjet printing device according to another embodiment of the present invention. Fig.11 It is a perspective view of a print head according to another embodiment of the present invention. Fig.12 It is along Fig.11 A cross-sectional view of the print head taken along line III-III'.

[0136] Reference Figures 10 to 12 Other embodiments of the present invention relate to an inkjet printing device 1_1 and Figure 3 The inkjet printing device 1 shown is different in that it further includes a heat insulating portion 25 for blocking heat dissipated from the first heater H1 to between the substrate 30 and the first heater H1. Therefore, the description of the reservoir 40, the mixing portion 50, the cooling portion 60, the first pipe P1, the second pipe P2, and the pump PU, which have substantially the same configuration and operation, is omitted, and the print head 20_1 is described below.

[0137] Specifically, the print head 20_1 may further include a heat insulating portion 25 that blocks heat dissipated from the first heater H1 to between the substrate 30 and the first heater H1 .

[0138] The heat insulating part 25 may be disposed on the lower surface of the body 21. The nozzle part 24 may be disposed between the heat insulating part 25 and the body 21. The heat insulating part 25 may be disposed at a certain distance from the nozzle part 24. For example, the heat insulating part 25 may be mutually supported by the nozzle part 24 and a plurality of spacers SPC.

[0139] The heat insulating portion 25 may be formed in an integral shape to surround the nozzle portion 24. Fig.11 As shown, the heat insulating portion 25 may include a rectangular parallelepiped shaped receiving portion 25a and a fastening portion 25b for connecting the receiving portion 25a to the lower surface of the body 21. The bottom surface of the receiving portion 25a may include an opening 25c overlapping the nozzle portion 24 (or the nozzle lower hole 24b) in the thickness direction.

[0140] The heat insulation part 25 preferably has an emissivity of less than 0.2. At this time, the emissivity refers to the energy ratio of an object that absorbs external light energy and transmits part of it or causes surface reflection phenomenon and re-radiates it. In theory, an object that radiates 100% of the external energy without surface reflection after absorbing it is called a black body, and the emissivity value at this time can be defined as "1". That is, when the emissivity is 0.2, it means that only 20% of the heat dissipated from the first heater H1 is re-radiated. In other words, when the emissivity is 0.2, it means that 80% of the heat dissipated from the first heater H1 is reflected by the surface or partially transmitted. For example, the heat insulation part 25 may include at least one of stainless steel (SUS), gold (Au), silver (Ag), copper (Cu) and aluminum (Al). According to one embodiment of the present invention, the gasket SPC may include the same material as the above-mentioned heat insulation part 25.

[0141] The control unit 70 controls the temperature of the ink through the first heater H1, so that the ejection amount of the ink can be maintained constant. However, the temperature of the ink heated by the first heater H1 can usually be higher than the atmospheric temperature (e.g., about 23° C.). For example, the heat dissipated by the first heater H1 can be about 40° C.

[0142] The heat dissipated by the first heater H1 may be transferred to the substrate 30. In this case, non-uniform temperature distribution may occur on the surface of the substrate 30 facing the first heater H1. If non-uniform temperature distribution occurs on the substrate 30, the flatness of the substrate 30 may change due to thermal expansion, and thus the printing quality may be degraded.

[0143] The print head 20_1 according to an embodiment of the present invention includes a heat insulating portion 25, thereby blocking the heat transferred to the substrate 30 and maintaining a uniform temperature distribution on the substrate 30. In addition, since the degree to which the heat dissipated from the first heater H1 is dissipated to the outside is reduced, the effect of preventing the temperature of the ink stored in the ink storage portion 23 from decreasing can be expected.

[0144] Fig.13 It is a diagram for explaining an inkjet printing device according to another embodiment of the present invention.

[0145] Reference Fig.13 Other embodiments of the present invention involve inkjet printing devices 1_2 and Figure 3 The inkjet printing device 1 shown is different in that it includes a plurality of pressure sensors (PS1, PS2). Therefore, the description of the liquid storage 40, the mixing unit 50, the cooling unit 60, the first pipe P1, the second pipe P2, and the pump PU, which have substantially the same structure and operation, is omitted, and the plurality of pressure sensors (PS1, PS2) are described below.

[0146] Specifically, the first pressure sensor PS1 may be disposed on the first pipe P1 between the mixing unit 50 and the print head 20. The first pressure sensor PS1 may sense the pressure of the ink in a state after passing through the mixing unit 50 and before flowing into the print head 20.

[0147] When the pressure sensed by the first pressure sensor PS1 is higher than a preset pressure, the control unit 70 may heat the ink to a preset temperature corresponding to the sensed pressure through the first heater H1 .

[0148] When the ink is repeatedly circulated, the concentration of the ink may change as the solvent contained in the ink evaporates, or when the ink is repeatedly heated and cooled, the physical properties of the ink may change. Even if the ink is heated to a temperature similar to that of the newly injected ink INK0 (see Figure 6 and Figure 7 ) may be the same, or may have different viscosities.

[0149] In the first pipe P1 , the pressure loss and the viscosity may have a relationship as shown in the following formula 1.

[0150] [Formula 1]

[0151] Pressure loss = a × viscosity × pipe length × average flow rate / pipe inner diameter

[0152] (Where a is a proportionality constant.)

[0153] For example, when the viscosity of the ink increases, the resistance of the ink passing through the nozzle portion 24 will increase, and thus the pressure value sensed by the first pressure sensor PS1 may increase. In this case, the control unit 70 may heat the ink to a preset temperature corresponding to the sensed pressure value through the first heater H1. At this time, the relationship between the viscosity and temperature of the ink can be obtained through experiments, based on which a lookup table can be generated in advance. According to one embodiment, the higher the sensed pressure value, the higher the preset temperature. Therefore, when the viscosity of the ink increases, the first heater H1 may be heated to a higher temperature to reduce the viscosity of the ink, thereby maintaining the viscosity of the ink at a constant level.

[0154] As a result, even if the physical properties of the ink vary, the viscosity of the ink can be maintained constant, and an effect of maintaining the ejection amount of the ink uniform can be expected.

[0155] On the other hand, the second pressure sensor PS2 may be disposed on the second pipe P2 between the print head 20 and the pump PU. The second pressure sensor PS2 may sense the pressure of the ink in the state after passing through the print head 20 and before flowing into the pump PU.

[0156] When the pressure difference between the pressure sensed by the first pressure sensor PS1 and the pressure sensed by the second pressure sensor PS2 exceeds a preset range, the control unit 70 may heat the ink in proportion to the pressure difference through the first heater H1 .

[0157] For example, when the viscosity of the ink increases, the resistance of the ink passing through the nozzle portion 24 may increase, so the pressure value sensed by the first pressure sensor PS1 may increase, and the pressure difference between the pressure value sensed by the first pressure sensor PS1 and the pressure value sensed by the second pressure sensor PS2 may also increase. The ink may be heated in proportion to the pressure difference by the first heater H1. That is, the greater the pressure difference, the higher the temperature at which the first heater H1 is heated. At this time, the relationship between the viscosity and temperature of the ink can be obtained through experiments, and based on this, a lookup table can be generated in advance.

[0158] Thus, even if the physical properties of the ink change, the viscosity of the ink can be maintained constant, and the effect of maintaining the ejection amount of the ink uniform can be expected. Fig.13 Although an embodiment not including a temperature sensor is described in the embodiment, pressure sensors (PS1, PS2) and temperature sensors may also be used together.

[0159] Fig.14 It is a diagram for explaining an inkjet printing device according to another embodiment of the present invention.

[0160] Reference Fig.14 , inkjet printing device 2 and Figure 3 The inkjet printing apparatus 1 shown is different in that the particle-containing liquid and the solvent included in the ink are separated and supplied to the print head 20. In this case, the particle-containing liquid included in the ink may include an inorganic substance.

[0161] Specifically, the inkjet printing device 2 can be divided into a solvent circulation unit that supplies a solvent included in the ink and a particle circulation unit that supplies a particle-containing liquid included in the ink.

[0162] The solvent circulation unit may include: a first liquid reservoir 40_1a for storing a solvent; a first piping P1 for supplying the solvent from the first liquid reservoir 40_1a to the print head 20; a mixing unit 50_1 arranged on the first piping P1 and mixing the particle-containing liquid of the ink supplied from the particle supply unit 80 described later and the solvent supplied from the first liquid reservoir 40_1a; a second piping P2_1a for supplying the residual ink remaining after being ejected from the print head 20 to the second liquid reservoir 40_1b; a second piping P2_1b for recovering the residual solvent separated from the ink by the second liquid reservoir 40_1b to the first liquid reservoir 40_1a (hereinafter, the second piping P2_1a and the second piping P2_1b are sometimes collectively referred to as the second piping P2); and a cooling unit 60 arranged on the second piping P2_1b.

[0163] The first liquid reservoir 40_1a corresponds to Figure 3 The first pump PU1 corresponds to the reservoir 40. Figure 3 The pump PU, print head 20, temperature sensor TS and cooling unit 60 are substantially the same in structure and operation as Figure 3 The embodiment is the same as that of the embodiment, so the mixing unit 50_1 is described below.

[0164] like Fig.14 As shown, the mixing unit 50_1 can uniformly mix the particle-containing liquid and the solvent included in the ink by a mixer SAW using a surface acoustic wave (SAW). Here, the surface acoustic wave is a type of ultrasonic wave and has a characteristic that its wave energy is concentrated on the surface of a sphere and propagates.

[0165] The particle circulation unit may include: a particle supply unit 80 that supplies a particle-containing liquid of ink to the first piping P1 between the first liquid reservoir 40_1a and the mixing unit 50_1; a second liquid reservoir 40_1b that is disposed in an area of ​​the second piping P2_1a, P2_1b and stores the residual ink remaining after being ejected from the print head 20; a third piping P3 that recovers the residual particle-containing liquid separated from the residual solvent in the residual ink from the second liquid reservoir 40_1b to the particle supply unit 80; a concentration sensor PC that is disposed on the first piping P1 between the particle supply unit 80 and the print head 20 and senses the concentration of particles; and a supply control unit 90 that controls the supply amount of the particle-containing liquid in accordance with the information received from the concentration sensor PC. The third liquid reservoir 40_1c may be configured and operated in the same manner as the first piping P1 between the particle supply unit 80 and the print head 20. Figure 3 The particle supply unit 80, the concentration sensor PC, and the second liquid storage unit 40_1b are mainly described below.

[0166] The second liquid tank 40_1b can separate the remaining ink that is not ejected from the print head 20 and is recovered into the remaining solvent and the remaining particle-containing liquid using a surface acoustic wave.

[0167] The second pump PU2 is disposed on the third pipe P3 between the second liquid reservoir 40_1 b and the particle supply unit 80 , and pressurizes the excess particle-containing liquid separated from the excess ink and supplies it to the particle supply unit 80 .

[0168] The particle supply unit 80 may include a third liquid reservoir 40_1c for storing the recovered excess particle-containing liquid and a third pump PU3 for supplying the excess particle-containing liquid from the third liquid reservoir 40_1c to the first pipe P1 in the region between the first liquid reservoir 40_1a and the mixing unit 50_1.

[0169] The concentration sensor PC according to an embodiment of the present invention may be a particle counter that counts the number of particles contained in a unit volume of ink.

[0170] When the concentration of particles included in the ink sensed by the concentration sensor PC is lower than a preset concentration, the supply control unit 90 may increase the supply amount of the particle-containing liquid in the ink through the third pump PU3 .

[0171] In the case where the ink includes a particle-containing liquid containing an inorganic substance, the particles may separate from the solvent and precipitate due to the size and weight of the particles. In particular, when the length of the first pipe P1 between the mixing unit 50_1 and the print head 20 is long, the particles may separate from the solvent and precipitate while the mixed ink reaches the print head 20. In this case, the concentration of the ink ejected from the print head 20 becomes uneven, and thus the printing quality may be reduced.

[0172] The inkjet printing device 2 according to one embodiment of the present invention can sense the concentration of ink near the injection port IN1 of the print head 20 through the concentration sensor PC, and control the concentration of the ink to be constant through the supply control unit 90, thereby maintaining a uniform concentration of the ink ejected from the print head 20. In addition, by operating the solvent circulation unit and the particle circulation unit separately, the load of the inkjet printing device 2 can be reduced as a whole.

[0173] Fig.15 It is a diagram for explaining an inkjet printing device according to another embodiment of the present invention.

[0174] Reference Fig.15 , inkjet printing device 2_1 and Fig.14The illustrated embodiment is different in that the mixing section 50 includes a static mixer SM instead of a mixer SAW using surface acoustic waves, and that the particle-containing liquid and the solvent are separated in the second liquid reservoir 40_2b using gravity instead of surface acoustic waves.

[0175] Description of the static mixer SM Figure 3 The contents described in the above are repeated, so they are omitted, and the second reservoir 40_2b is described. The second reservoir 40_2b can store the remaining ink recovered from the print head 20 for a certain period of time, and the remaining ink will not flow out to the cooling unit 60 and the second pipe P2 during the certain period of time. In this case, the particles included in the ink can be precipitated by gravity.

[0176] Since the second liquid reservoir 40_2b does not need to be provided with a device for generating surface acoustic waves, weight reduction can be achieved, which is advantageous in terms of cost.

[0177] Fig.16 It is a diagram for explaining an inkjet printing device according to another embodiment of the present invention.

[0178] Reference Fig.16 , inkjet printing device 2_2 and Fig.14 The illustrated embodiment is different in that the third pipe P3 connecting the second pump PU2 and the particle supply unit 80 is not included, but a particle recovery unit 100 is included.

[0179] Specifically, the second liquid reservoir 40_1b can use surface acoustic waves to separate the residual ink that is not ejected from the print head 20 but is recovered into the residual solvent and the residual particle-containing liquid. The second pump PU2 can be arranged on the third pipe P3_1 between the second liquid reservoir 40_1b and the particle recovery unit 100, and can supply the residual particle-containing liquid separated from the residual ink to the particle recovery unit 100.

[0180] After checking the state of the remaining particle-containing liquid accumulated in the particle recovery unit 100, if the particle-containing liquid is in a good state, it can be supplied to the particle supply unit 80, and if it is not in a good state, it can be discarded. In this way, the physical property state of the ink can be maintained in a good state.

[0181] The above embodiments of the present invention are described with reference to the accompanying drawings, but those skilled in the art should be able to understand that the present invention can be implemented in other specific forms without changing the technical concept and essential features of the present invention. Therefore, it should be understood that the embodiments described above are illustrative in all aspects and are not restrictive.

Claims

1. An inkjet printing device, comprising: A print head ejects ink onto a substrate and includes a first heater for heating the ink and a nozzle portion for ejecting the ink; A liquid reservoir for storing the ink; a first pipe for supplying the ink from the reservoir to the print head; a second pipe for recovering excess ink from the print head to the reservoir; a mixing unit, disposed on the first pipe, including a second heater for heating the ink and mixing the ink; a pump, disposed on the second pipe, and pressurizing the remaining ink to supply it to the reservoir; a temperature sensor disposed on the first pipe between the mixing unit and the print head and sensing the temperature of the ink; as well as a control unit that controls a temperature of at least one of the first heater and the second heater in response to information received from the temperature sensor, The print head also includes: a heat insulating portion, which is formed as an integral body to surround the nozzle portion and is located on the lower surface of the main body of the print head, and includes an opening portion overlapping with the nozzle portion in the thickness direction, and the heat insulating portion blocks heat dissipated from the first heater to between the substrate and the first heater.

2. The inkjet printing device according to claim 1, wherein: The heat insulating portion includes an opening portion overlapping with the nozzle portion in a thickness direction.

3. The inkjet printing device according to claim 1, further comprising: The cooling unit is disposed on the second pipe between the pump and the reservoir, and cools the excess ink.

4. The inkjet printing device according to claim 3, wherein: The cooling portion includes a Peltier element.

5. The inkjet printing device according to claim 3, wherein: The cooling unit maintains the temperature of the remaining ink at a temperature when the ink is first supplied from the tank to the print head.

6. The inkjet printing device according to claim 1, wherein: The control unit maintains the temperature of the ink in the print head by the first heater to be the same as the temperature of the ink heated by the second heater.

7. The inkjet printing device according to claim 1, wherein: The second heater includes a Peltier element or a silicone rubber heater.

8. The inkjet printing device according to claim 1, wherein: The mixing section includes a static mixer or a mixer using a surface acoustic wave.

9. An inkjet printing device, comprising: A print head ejects ink onto a substrate and includes a first heater for heating the ink and a nozzle portion for ejecting the ink; A liquid reservoir for storing the ink; a first pipe for supplying the ink from the reservoir to the print head; a second pipe for recovering excess ink from the print head to the reservoir; a mixing unit, disposed on the first pipe, including a second heater for heating the ink and mixing the ink; a pump, disposed on the second pipe, and pressurizing the remaining ink to supply it to the reservoir; a temperature sensor disposed on the first pipe between the mixing unit and the print head and sensing the temperature of the ink; a first pressure sensor disposed on the first pipe between the mixing unit and the print head and sensing the pressure of the ink; as well as a control unit that controls a temperature of at least one of the first heater and the second heater in response to information received from the temperature sensor, The print head also includes: a heat insulating portion, which is formed as an integral body to surround the nozzle portion and is located on the lower surface of the main body of the print head, and includes an opening portion overlapping with the nozzle portion in the thickness direction, and the heat insulating portion blocks heat dissipated from the first heater to between the substrate and the first heater.

10. The inkjet printing device according to claim 9, wherein: When the pressure sensed by the first pressure sensor is higher than a preset pressure, the control unit heats the ink to a preset temperature corresponding to the sensed pressure through the first heater.

11. The inkjet printing device according to claim 9, further comprising: The second pressure sensor is disposed on the second pipe between the print head and the pump, and senses the pressure of the remaining ink.

12. The inkjet printing device according to claim 11, wherein: When a pressure difference between a pressure sensed by the first pressure sensor and a pressure sensed by the second pressure sensor exceeds a preset range, the control unit heats the ink in proportion to the pressure difference using the first heater.

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