阅读说明：本技术 喷墨打印装置 (Ink jet printing apparatus ) 是由 吉田太 闵淸玩 韩旼我 朴宰范 李正浩 郑兴铁 许明洙 于 2020-12-22 设计创作，主要内容包括：本发明的一实施例涉及的喷墨打印装置包括：打印头,向基板上喷出墨液,并包括对墨液进行加热的第一加热器；储液器,存储墨液；第一配管,从储液器向打印头供给墨液；第二配管,从打印头向储液器回收剩余墨液；混合部,配置在第一配管上,包括对墨液进行加热的第二加热器,并对墨液进行混合；泵,配置在第二配管上,并对剩余墨液进行加压来供给至储液器；温度传感器,配置在混合部与打印头之间的第一配管上,并感知墨液的温度；以及控制部,与从温度传感器接收的信息对应地,控制第一加热器和第二加热器中的至少一个的温度。打印头还包括：隔热部,阻断从第一加热器散出到基板与第一加热器之间的热。(An inkjet printing apparatus according to an embodiment of the present invention includes: a print head which ejects ink onto a substrate and includes a first heater which heats the ink; a reservoir storing ink; a first pipe for supplying ink from the reservoir to the print head; a second pipe for recovering surplus ink from the print head to the reservoir; a mixing unit that is disposed in the first pipe, includes a second heater that heats the ink, and mixes the ink; a pump disposed in the second pipe and configured to supply the surplus ink to the reservoir by pressurizing the surplus ink; a temperature sensor disposed in a first pipe between the mixing section and the print head, and configured to sense a temperature of the ink; and a control section that controls a temperature of at least one of the first heater and the second heater in correspondence with information received from the temperature sensor. The printhead further comprises: and a heat insulating part for blocking heat emitted from the first heater to a space between the substrate and the first heater.)

1. An inkjet printing apparatus comprising:

a print head that ejects ink onto a substrate and includes a first heater that heats the ink;

a reservoir storing the ink;

a first pipe for supplying the ink from the reservoir to the print head;

a second pipe for recovering surplus ink from the print head to the reservoir;

a mixing unit that is disposed in the first pipe, includes a second heater that heats the ink, and mixes the ink;

a pump that is disposed in the second pipe and supplies the remaining ink to the reservoir by pressurizing the remaining ink;

a temperature sensor that is disposed in the first pipe between the mixing unit and the print head and senses the temperature of the ink; and

a control section that controls a temperature of at least one of the first heater and the second heater in correspondence with information received from the temperature sensor,

the printhead further comprises: and a heat insulating part blocking heat emitted from the first heater to a space between the substrate and the first heater.

2. Inkjet printing apparatus according to claim 1,

the printhead includes a nozzle portion that ejects the ink,

the heat insulating portion includes an opening portion overlapping the nozzle portion in a thickness direction.

3. Inkjet printing apparatus according to claim 1, further comprising:

and a cooling unit disposed in the second pipe between the pump and the reservoir, and configured to cool the surplus ink.

4. Inkjet printing apparatus according to claim 3,

the cooling portion includes a peltier element.

5. Inkjet printing apparatus according to claim 3,

the cooling unit maintains the temperature of the remaining ink at a temperature at which the ink is first supplied from the reservoir to the print head.

6. Inkjet printing apparatus according to claim 1,

the control unit maintains the temperature of the print head to be equal to the temperature of the ink heated by the second heater by the first heater.

7. Inkjet printing apparatus according to claim 1,

the second heater comprises a peltier element or a silicone rubber heater.

8. Inkjet printing apparatus according to claim 1,

the mixing section includes a static mixer or a mixer using surface acoustic waves.

9. An inkjet printing apparatus comprising:

a print head that ejects ink onto a substrate and includes a first heater that heats the ink;

a reservoir storing the ink;

a first pipe for supplying the ink from the reservoir to the print head;

a second pipe for recovering surplus ink from the print head to the reservoir;

a mixing unit that is disposed in the first pipe, includes a second heater that heats the ink, and mixes the ink;

a pump that is disposed in the second pipe and supplies the remaining ink to the reservoir by pressurizing the remaining ink;

a temperature sensor that is disposed in the first pipe between the mixing unit and the print head and senses the temperature of the ink;

a first pressure sensor that is disposed in the first pipe between the mixing unit and the print head and senses the pressure of the ink; and

a control section that controls a temperature of at least one of the first heater and the second heater in correspondence with information received from the temperature sensor,

the printhead further comprises: and a heat insulating part blocking heat emitted from the first heater to a space between the substrate and the first heater.

10. Inkjet printing apparatus according to claim 9,

the control unit heats 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.

11. Inkjet printing apparatus according to claim 9 further comprising:

and a second pressure sensor disposed in the second pipe between the print head and the pump, and configured to sense the pressure of the remaining ink.

12. Inkjet printing apparatus according to claim 11,

the control unit heats the ink in proportion to a pressure difference between the pressure sensed by the first pressure sensor and the pressure sensed by the second pressure sensor by the first heater when the pressure difference exceeds a preset range.

13. An inkjet printing apparatus comprising:

a print head which ejects ink;

a solvent circulation unit configured to supply a solvent included in the ink to the print head; and

a particle circulation unit configured to supply a particle-containing liquid included in the ink liquid to the print head,

the solvent circulation section includes:

a first reservoir storing the solvent;

a first pipe for supplying the solvent from the first reservoir to the print head; and

a second pipe for recovering the residual solvent contained in the residual ink from the print head to the first reservoir,

the particle circulation section includes:

a particle supply unit configured to supply the particle-containing liquid to the first pipe;

a second reservoir that is disposed in the second pipe and stores a remaining ink remaining after being ejected from the print head;

a third pipe that collects, from the second reservoir to the particle supply unit, a surplus particle-containing liquid separated from the surplus solvent, among the surplus ink;

a density sensor disposed in the first pipe between the particle supply unit and the print head, and configured to sense a density of the ink; and

and a supply control unit that controls the supply amount of the particle-containing liquid in accordance with information received from the concentration sensor.

14. Inkjet printing apparatus according to claim 13,

the particle supply section includes:

a third reservoir for storing the recovered residual particle-containing liquid; and

and a first pump that supplies the surplus particle-containing liquid from the third reservoir to the first pipe.

15. Inkjet printing apparatus according to claim 14,

the supply control unit increases the supply amount of the particle-containing liquid by the first pump when the concentration of the ink sensed by the concentration sensor is lower than a preset concentration.

16. Inkjet printing apparatus according to claim 13 further comprising:

and a second pump that is disposed in the third pipe and supplies the surplus particle-containing liquid to the particle supply unit by pressurizing the surplus particle-containing liquid.

17. Inkjet printing apparatus according to claim 13,

the second reservoir separates the remaining ink liquid into the remaining solvent and the remaining particle-containing liquid using surface acoustic waves.

18. Inkjet printing apparatus according to claim 13,

the printhead includes a first heater that heats the ink.

19. Inkjet printing apparatus according to claim 18 further comprising:

a mixing section disposed in the first pipe between the particle supply section and the concentration sensor,

the mixing unit includes a second heater that heats the ink liquid, and mixes the solvent and the particle-containing liquid.

20. Inkjet printing apparatus according to claim 19 further comprising:

and a temperature sensor disposed in the first pipe between the mixing unit and the print head, and configured to sense a temperature of the ink.

21. Inkjet printing apparatus according to claim 19 further comprising:

and a control unit that maintains the temperature of the print head by the first heater to be equal to the temperature of the ink heated by the second heater.

22. Inkjet printing apparatus according to claim 19,

the mixing section includes a static mixer or a mixer using surface acoustic waves.

23. Inkjet printing apparatus according to claim 14 further comprising:

and a cooling unit disposed in the second pipe between the second tank and the third tank, and configured to cool the surplus solvent.

24. Inkjet printing apparatus according to claim 23,

the cooling unit maintains the temperature of the remaining solvent at a temperature at which the solvent is first supplied from the first reservoir to the print head.

Technical Field

The present invention relates to an inkjet printing apparatus.

Background

With the development of information-oriented society, demands for display devices for displaying images are increasing in various forms. For example, the display device is suitable for use in various electronic apparatuses such as a smart phone, a desktop PC, a digital camera, a notebook computer, a navigator, a monitor, and a TV. The Display Device may 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), or the like.

Among these, in a thin film manufacturing process for forming a light-emitting layer of an organic light-emitting display device, an ink jet printing (Inkjet printing) process for ejecting ink onto the surface of an object to form a thin film of a desired form can be used. The inkjet printing apparatus generates individual ink droplets from nozzles of a print head and ejects the ink droplets to predetermined positions on a substrate as an object, thereby printing a thin film of a desired pattern on the substrate.

The inkjet printing apparatus may have, as necessary: a discontinuous ink jet printing system in which ink droplets are discontinuously generated from a print head; and a continuous inkjet printing method in which ink droplets are continuously generated from a print head, only selected ink droplets are ejected to the substrate side, and ink droplets that are not ejected are recycled to an ink supply unit.

In the inkjet printing apparatus of the continuous inkjet printing method, there is a problem that the temperature and viscosity of the ink fluctuate as the ink that is not ejected is recirculated, and the ejection amount becomes uneven.

Disclosure of Invention

The present invention addresses the problem of providing an inkjet printing apparatus that can maintain a uniform ink ejection amount.

Further, an inkjet printing apparatus is provided which is capable of printing a thin film of a pattern at a desired position on a substrate by maintaining a uniform temperature distribution of the substrate.

Further, an inkjet printing apparatus capable of maintaining the density of ink uniform is provided.

However, the object of the present invention is not limited to the above object, and various extensions can be made without departing from the spirit and scope of the present invention.

An inkjet printing apparatus according to an embodiment of the present invention for solving the above-described problems includes: a print head that ejects ink onto a substrate and includes a first heater that heats the ink; a reservoir storing the ink; a first pipe for supplying the ink from the reservoir to the print head; a second pipe for recovering surplus ink from the print head to the reservoir; a mixing unit that is disposed in the first pipe, includes a second heater that heats the ink, and mixes the ink; a pump that is disposed in the second pipe and supplies the remaining ink to the reservoir by pressurizing the remaining ink; a temperature sensor that is disposed in the first pipe 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 printhead further comprises: and a heat insulating part blocking heat emitted from the first heater to a space between the substrate and the first heater.

The print head may include a nozzle portion that ejects the ink, and the thermal insulating portion may include an opening that overlaps the nozzle portion in a thickness direction.

May, further include: and a cooling unit disposed in the second pipe between the pump and the reservoir, and configured to cool the surplus ink.

The cooling part may include a peltier element.

The cooling unit may maintain the temperature of the remaining ink at a temperature at which the ink is first supplied from the reservoir to the print head.

The control unit may maintain the temperature of the print head to be equal to the temperature of the ink heated by the second heater by the first heater.

It may be that the second heater comprises a peltier element or a silicone rubber heater.

The mixing section may include a static mixer (static mixer) or a mixer using a surface acoustic wave (surface acoustic wave).

May, further include: and a first pressure sensor disposed in the first pipe between the mixing unit and the print head, and configured to sense the pressure of the ink.

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.

May, further include: and a second pressure sensor disposed in the second pipe between the print head and the pump, and configured to sense the pressure of the remaining ink.

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

An inkjet printing apparatus according to another embodiment of the present invention for solving the above-described problems includes: a print head which ejects ink; a solvent circulation unit configured to supply a solvent included in the ink to the print head; and a particle circulation unit configured to supply a particle-containing liquid included in the ink to the print head.

The solvent circulation section includes: a first reservoir storing the solvent; a first pipe for supplying the solvent from the first reservoir to the print head; and a second pipe for recovering the residual solvent included in the residual ink from the print head to the first reservoir.

The particle circulation section includes: a particle supply unit configured to supply the particle-containing liquid to the first pipe; a second reservoir that is disposed in the second pipe and stores a remaining ink remaining after being ejected from the print head; a third pipe that collects, from the second reservoir to the particle supply unit, a surplus particle-containing liquid separated from the surplus solvent, among the surplus ink; a density sensor disposed in the first pipe between the particle supply unit and the print head, and configured to sense a density of the ink; and a supply control unit that controls the supply amount of the particle-containing liquid in accordance with information received from the concentration sensor.

The particle supply unit may include: a third reservoir for storing the recovered residual particle-containing liquid; and a first pump that supplies the surplus particle-containing liquid from the third reservoir to the first pipe.

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

May, further include: and a second pump that is disposed in the third pipe and supplies the surplus particle-containing liquid to the particle supply unit by pressurizing the surplus particle-containing liquid.

The second reservoir may separate the remaining ink liquid into the remaining solvent and the remaining particle-containing liquid using a surface acoustic wave (saw wave).

The printhead may include a first heater that heats the ink.

May, further include: and a mixing unit that is disposed in the first pipe between the particle supply unit and the concentration sensor, includes a second heater that heats the ink liquid, and mixes the solvent and the particle-containing liquid.

May, further include: and a temperature sensor disposed in the first pipe between the mixing unit and the print head, and configured to sense a temperature of the ink.

May, further include: and a control unit that maintains the temperature of the print head by the first heater to be equal to the temperature of the ink heated by the second heater.

The mixing section may include a static mixer (static mixer) or a mixer using a surface acoustic wave (surface acoustic wave).

May, further include: and a cooling unit disposed in the second pipe between the second tank and the third tank, and configured to cool the surplus solvent.

The cooling unit may maintain the temperature of the remaining solvent at a temperature at which the solvent is first supplied from the first reservoir to the print head.

(effect of the invention)

According to the inkjet printing apparatus according to the embodiment of the present invention, the temperature and viscosity of the ink are maintained constant, so that the ejection amount of the ink can be maintained constant.

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

Further, 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 precipitation of particles included in the ink.

The effects according to the embodiments are not limited to those exemplified above, and further effects are included in the present specification.

Drawings

Fig. 1 is a schematic perspective view for explaining an inkjet printing apparatus according to an embodiment of the present invention.

Fig. 2 is a cross-sectional view of the substrate taken along line I-I' of fig. 1.

Fig. 3 is a diagram for explaining an inkjet printing apparatus according to an embodiment of the present invention.

Fig. 4 is a perspective view of a printhead according to an embodiment of the present invention.

Fig. 5 is a cross-sectional view of the printhead taken along line II-II' of fig. 4.

Fig. 6 is a perspective view of a reservoir according to an embodiment of the present invention.

Fig. 7 is a cross-sectional view of the reservoir shown in fig. 6.

Fig. 8 is a sectional view for explaining a mixing section according to an embodiment of the present invention.

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

Fig. 10 is a diagram for explaining an inkjet printing apparatus according to another embodiment of the present invention.

Fig. 11 is a perspective view of a printhead according to another embodiment of the present invention.

Fig. 12 is a cross-sectional view of the printhead taken along line III-III' of fig. 11.

Fig. 13 to 16 are views for explaining an inkjet printing apparatus according to another embodiment of the present invention.

Detailed Description

The advantages and features of the present invention and methods of accomplishing the same will become apparent by reference to the following detailed description of the embodiments taken in conjunction with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but may be implemented in various forms different from each other, and the embodiments are only provided to make the disclosure of the present invention complete and to fully inform the scope of the present invention to those skilled in the art, and the present invention should be defined only by the scope of the claims.

Like reference numerals refer to like elements throughout the specification. The shapes, sizes, ratios, angles, numbers, and the like disclosed in the drawings for describing the respective embodiments are examples, and the present invention is not necessarily limited to the illustrated cases.

Although the terms first, second, etc. may be used to describe various components, the components are not limited to the terms. The above-described terms are used only for the purpose of distinguishing one constituent element from another. Therefore, the first component mentioned below may be a second component within the technical idea of the present invention.

The various features of the embodiments of the invention can be combined or combined with each other, partly or wholly, technically various linkages and drives are possible and the embodiments can be implemented independently of each other or together in a linked relationship.

Specific embodiments are described below with reference to the drawings.

Fig. 1 is a schematic perspective view for explaining an inkjet printing apparatus according to an embodiment of the present invention. Fig. 2 is a cross-sectional view of the substrate taken along line I-I' of fig. 1.

Referring to fig. 1 and 2, an inkjet printing apparatus 1 according to an embodiment of the present invention may include a table 10, a print head 20 that ejects ink (e.g., organic light-emitting ink) onto a substrate 30, and a driving unit (not shown) that moves the table 10 or the print head 20.

The table 10 may be made of a rigid material to support the substrate 30. However, the material of the table 10 is not limited thereto. In the exemplary embodiment, the table 10 may be a rectangular parallelepiped shape, but the shape of the table 10 is not limited thereto.

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

The substrate 30 may be a unit display substrate, or may be a mother substrate before being cut into a plurality of unit display substrates. The substrate 30 may be a single substrate 30, or may include a plurality of stacked substrates.

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

The thin film transistor 31 may have an active layer 31a, a gate insulating film 34 formed to cover the active layer 31a, and a gate electrode 31b on the gate insulating film 34.

An interlayer insulating film 35 covering the gate electrode 31b may be formed, and a source electrode 31c and a drain electrode 31d may be formed on the interlayer insulating film 35.

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

Further, the pixel electrode 32a of the organic light emitting element 32 may be connected to the drain electrode 31 d. A Pixel electrode 32a is formed on an upper portion of the planarization film 36, and a Pixel defining film (Pixel defining layer)37 for dividing a sub-Pixel region is formed on the Pixel electrode 32 a. Further, the light-emitting layer 32b of the organic light-emitting element 32 is formed in the opening of the pixel defining film 37, and the counter electrode 32c is deposited on the opening. That is, the opening surrounded by the pixel defining film 37 is a region of one sub-pixel such as the red pixel R, the green pixel G, and the blue pixel B, and the light emitting layer 32B of the corresponding color is formed therein. Here, one sub-pixel is shown, and a plurality of such sub-pixels may be actually arranged in the row and column directions in the display portion.

The plurality of sub-pixels may be rectangular in shape. The plurality of sub-pixels may be arranged in a matrix form of n × m (here, n and m are integers of 1 or more). In the exemplary embodiment shown in fig. 1, when the row direction is the y direction and the column direction is the x direction, the sub-pixels may be arranged in a 6 × 6 matrix on the substrate 30. However, the arrangement of the sub-pixels in fig. 1 is an example, and a larger number of sub-pixels than this may be actually arranged on the substrate 30. In addition to the matrix form, the subpixels may be arranged in various forms such as Stripe (Stripe) form and Pentile form.

Such a thin film of the organic light emitting display device can be formed by printing with the print head 20, and for example, if ink is ejected at a position corresponding to the light emitting layer 32b, the light emitting layer 32b having a desired pattern can be formed.

To explain the inkjet printing apparatus 1 more specifically, refer to fig. 3 to 9.

Fig. 3 is a diagram for explaining an inkjet printing apparatus according to an embodiment of the present invention. Fig. 4 is a perspective view of a printhead according to an embodiment of the present invention. Fig. 5 is a cross-sectional view of the printhead taken along line II-II' of fig. 4. Fig. 6 is a perspective view of a reservoir according to an embodiment of the present invention. Fig. 7 is a cross-sectional view of the reservoir shown in fig. 6. Fig. 8 is a sectional view for explaining a mixing section according to an embodiment of the present invention. Fig. 9 is a diagram for explaining a cooling unit according to an embodiment of the present invention.

Referring to fig. 3 to 9, the inkjet printing apparatus 1 may include a print head 20, a reservoir (reservoir)40, a first pipe P1, a second pipe P2, a mixing part 50, a pump PU, a cooling part 60, a temperature sensor TS, and a control part 70.

According to an embodiment of the present invention, the printhead 20 can eject ink onto the substrate 30.

Referring to fig. 4 and 5, the print head 20 according to the present embodiment may include a main body 21 that functions as a housing of the print head 20, a driving portion 22 disposed on a side surface of the main body 21, an ink storage portion 23, a nozzle portion 24, and a first heater H1.

The body 21 may function as a housing for the printhead 20. The body 21 may have various shapes. The body 21 may have a quadrangular prism shape.

The main body 21 may include an injection port IN1 disposed at one side of the main body 21 and an ink outflow port OUT1 disposed at the other side. The injection port IN1 and the ink flow outlet OUT1 may be formed by forming holes IN the main body 21. Various ink compositions, cleaning agents, and the like can be injected through the injection port IN 1. The ink composition, the cleaning agent, and the like can be discharged through the ink outlet OUT 1. For example, ink stored IN the reservoir 40 may be supplied to the ink storage unit 23 through the injection port IN1, ink droplets are continuously generated from the nozzle unit 24, 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 outflow port OUT1, whereby the ink may be circulated again.

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

The driving unit 22 may be disposed on both sides of the body 21, and may drive the nozzle unit 24 by applying power to the nozzle unit 24. The driver 22 may be electrically connected to the printed circuit board 22b via the flexible circuit board 22 a.

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

The flexible circuit board 22a may be disposed outside the main body 21 and electrically connected to the driving unit 22. The flexible circuit board 22a can apply power to the drive unit 22 for discharging ink.

The flexible circuit board 22a is a board in which a circuit is formed on a flexible insulating film, and a heat-resistant plastic film such as polyester (polyester) or polyimide (polyimide) which is a flexible material can be used. A plurality of flexible circuit boards 22a may be formed as necessary.

The printed circuit substrate 22b may generate a signal for driving the driving part 22. The printed circuit board 22b may be disposed above the print head 20 and electrically connected to the driving unit 22 through the flexible circuit board 22 a.

The drive unit 22 and the flexible circuit board 22a, and the flexible circuit board 22a and the printed circuit board 22b can be connected to each other by the connecting element 22 c. For example, the connection element 22c may be formed of a conductive substance such as copper (Gu), aluminum (Al), or the like.

The main body 21 may include an ink storage portion 23 that stores ink supplied from the injection port IN 1.

The ink storage unit 23 may be disposed inside the main body 21 and below the inlet IN 1. The ink storage unit 23 can receive the supply of ink from the injection port IN1 and can cause the ink to flow to the nozzle unit 24.

The main body 21 may include a nozzle portion 24 that receives supply of ink from the ink storage portion 23 and discharges the ink to the outside of the main body 21. The nozzle portion 24 may be disposed below the ink storage portion 23.

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

The nozzle 24 can receive the supply of ink from the print head 20 and discharge ink of a desired size. The nozzle portion 24 may be disposed at a lower portion of the print head 20.

A plurality of nozzle upper holes 24a may be formed on an upper surface of the nozzle portion 24. The nozzle portion 24 can receive ink supply from the print head 20. For example, 128 or 256 nozzle upper holes 24a may be formed. The ink can be ejected through the inside of the nozzle portion 24 and through the lower surface of the nozzle portion 24 in which the plurality of nozzle lower holes 24b of a desired size are formed.

The nozzle portion 24 may be a silicon nozzle portion or a metal nozzle portion. Preferably a silicon nozzle section. Generally, the nozzle portion 24 may be formed using silicon by a Micro Electro Mechanical Systems (MEMS) method. In contrast, the nozzle unit 24 may be realized by a known nozzle unit for adjusting the size, amount, and the like of ink.

The first heater H1 may be disposed so as 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 in physical contact with the ink storage portion 23, so that heat generated by the first heater H1 may be transferred to ink stored in the ink storage portion 23 by thermal conduction.

The reservoir 40 may store ink and supply the ink in correspondence with a request of the printhead 20.

Referring to fig. 6 and 7, the reservoir 40 may include an ink tank 41 and a preheating part 42. For the purpose of detailed description, the INK stored in the reservoir 40 and discharged therefrom is described as being divided into the newly injected INK0 and the stored INK 1. The newly injected INK0 is INK stored in an external INK storage (not shown) and newly injected into the INK tank 41 through the injection port 41a, and the stored INK inj 1 is INK stored in the INK tank 41 before the newly injected INK0 is injected into the INK tank 41. Therefore, the temperature of the newly injected INK0 may be different from the temperature of the stored INK 1.

The INK tank 41 may include a storage area 41b that stores the stored INK1, an injection port 41a that receives injection of newly injected INK0 from the outside, an outflow port OUT2 that allows the stored INK1 to flow OUT from the storage area 41b to the outside, and a recovery port IN2 that recovers INK that is not ejected from the nozzle portion 24 to the substrate 30 side. The INK tank 41 may be provided with a certain volume of empty space inside thereof so as to be able to store the stored INK 1. The ink tank 41 may be made of a material having high thermal conductivity. Preferably formed of a metal such as aluminum or an aluminum alloy.

The injection port 41a is formed on the upper side of the preheating part 42. Specifically, the injection port 41a is formed on the upper surface of the edge of the INK tank 41, and is connected to an external INK reservoir to receive the newly injected INK0 from the INK reservoir and inject it into the interior.

The stored INK1 is temporarily stored in the storage area 41b of the INK tank 41. A level sensor (not shown) is present inside the reservoir 40, and the height of the stored INK1 that has decreased due to the outflow is recognized, so that the newly injected INK0 is injected, and a certain amount of the newly injected INK0 and the stored INK1 are maintained in the storage region 41 b. The storage area 41b is defined on the lower side of the preheating part 42. Therefore, the stored INK1 can be maintained to be stored only on the lower side of the preheating section 42.

The outlet port OUT2 is formed below the preheating section 42. Specifically, the ink tank 41 is formed on the lower side surface thereof. However, the present invention is not limited to this, and the outlet OUT2 may be formed on the lower surface of the ink tank 41. The stored INK1 in the storage area 41b can reach the printhead 20 through the outflow port OUT2, and the stored INK1 reaching the printhead 20 can be ejected to the substrate 30 side.

The one surface 41s of the ink tank 41 can be formed detachably. 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 inside of the reservoir 40 can be cleaned by separating the detachable surface 41 s. However, this is merely an example, and the ink tank 41 is not limited to this, and the detachable surface 41s may not be included.

The preheating section 42 is disposed between the inlet 41a and the storage region 41 b. The newly injected INK0 injected from the injection port 41a into the INK tank 41 can reach the preheating section 42. The preheating section 42 can receive heat from the inner side surface by contacting the inner side surface of the ink tank 41.

The preheating section 42 may be formed of a material having high thermal conductivity, and is preferably formed of aluminum or an aluminum alloy.

The preheating section 42 may include a base plate BS having a flat plate shape. The base plate BS moves the newly injected INK0 injected from the injection port 41a along the upper surface thereof, thereby transferring the newly injected INK0 to the storage region 41 b. The preheating part 42 may include a preheating wall WA formed along an edge position of the substrate sheet BS so that the newly injected INK0 is preheated in a state of being enclosed in the preheating part 42 and transferred to the storage region 41 b. However, the present invention is not limited to this, and the preheating section 42 may be modified in form. In particular, the preheating section 42 may not comprise the preheating wall WA but only the base panel BS.

The newly injected INK0 may be transferred to one end portion BS _ E of the substrate board BS along the upper surface of the substrate board BS. The newly injected INK0 injected through the injection port 41a can reach the preheating section 42. Since the preheating unit 42 is in contact with the inner side surface of the INK tank 41, the preheating unit 42 can receive the supply of heat of the stored INK1 transferred to the inner side surface of the INK tank 41, and thereby achieve thermal balance.

Since the initial temperature of the newly injected INK0 is low and the density is high, the newly injected INK0 is diffused while sinking in the preheating section 42. The newly injected INK0 that has fallen down can be heated by the preheating section 42 to become higher in temperature and lower in density. The newly injected INK0, which has reached the normal state in temperature and density, floats up and spreads to the one end portion BS _ E as indicated by the first arrow Da, and the newly injected INK0, which has spread to the one end portion BS _ E, moves from the one end portion BS _ E of the base plate BS toward the storage area 41b, thereby achieving merging with the already stored INK 1. The preheating wall WA at one end BS _ E is formed lower than the other preheating walls WA, so that the newly injected INK0 moves from the one end BS _ E to the storage area 41b across the preheating wall WA as indicated by the second arrow Db. However, the present invention is not limited to this, and may be implemented by modifying the form of the preheating wall WA at the one end BS _ E, for example.

The initial temperature of the newly injected INK0 injected into the INK tank 41 may have a lower temperature than the temperature of the already-stored INK1, but is preheated to the same temperature as the temperature of the already-stored INK1 by the preheating section 42, so that the temperature of the INK in the storage region 41b can be uniformly maintained even after the newly injected INK0 and the already-stored INK1 are merged. Therefore, the viscosity of the stored INK1 stored in the reservoir 40 is also uniformly maintained, so that a uniform amount of the stored INK1 can be caused to flow OUT through the outflow port OUT 2.

However, the reservoir 40 may not include the preheating section 42 but include only the storage region 41 b.

The first pipe P1 can connect the inlet IN1 of the print head 20 and the outlet OUT2 of the reservoir 40. The ink stored in the reservoir 40 can be supplied to the print head 20 via the first pipe P1.

The second pipe P2 can connect the outflow port OUT1 of the print head 20 and the recovery port IN2 of the reservoir 40. The remaining ink that has not been discharged through the nozzle portion 24 of the print head 20 can be recovered to the reservoir 40 through the second pipe P2.

The mixing section 50 may be disposed in a region of the first pipe P1. The mixing section 50 may include a static mixer (static mixer) SM and a second heater H2 that heats the ink.

As shown in fig. 8, a static mixer SM according to an embodiment of the present invention may include blades 52 arranged along the length of a mixer tube 51. As shown in fig. 8, the blade 52 may include blade elements 53 and 54 for transferring the ink to the lower portion by changing the direction of the ink with each other at every 1 pitch (pitch). The blade elements 53, 54 may have a spiral (screen) shape, and the spiral directions of the blade element 53 and the blade element 54 may be opposite to each other. However, the shape of the blade elements 53 and 54 is not limited to this, and various modifications may be made in accordance with the type and viscosity of the ink passing through the mixing section 50. The number of the blade elements 53 and 54 may be variously changed according to the amount of ink passing through the mixing unit 50.

The static mixer SM can be injected with ink through the first pipe P1. The particles included in the ink and the solvent can be uniformly mixed with each other as the feeding direction of the blade elements 53 and 54 is switched every 1 pitch while the injected ink passes through the blade 52 provided in the mixer tube 51 along the longitudinal direction. In particular, bubbles generated during the mixing process can be removed, and the physical efficiency of the ink can be improved.

The mixing section 50 may include a second heater H2 surrounding the mixer tube 51 of the static mixer SM.

One embodiment relates to a second heater H2 that may be a silicone rubber heater. The second heater H2 may include a heater mat 55 and an insulating cover 56.

The heater mat 55 may be attached in direct contact with the outer surface of the mixer tube 51. The heat generated by the heater mat 55 can be transferred directly to the mixer body 51, primarily by conduction.

The heat insulating cover 56 may extend radially outward from the heater mat 55, substantially surround the heater mat 55, and include a heat insulating material having a lower thermal conductivity than the mixer body 51 and the heater mat 55. Since the heat insulating cover 56 has a lower thermal conductivity than the mixer tube 51, the heat generated by the heater mat 55 flows more mainly radially inward from the mixer tube 51 toward the mixer tube 51 than radially outward. This makes it possible to efficiently transfer the heat of the second heater H2 to the ink passing through the mixer tube 51.

However, the kind of the second heater H2 is not limited thereto. For example, the second heater H2 may be an element utilizing the Peltier Effect (Peltier Effect) described later.

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.

The cooling unit 60 can cool the remaining ink that has passed through the pump PU.

Referring to fig. 9, the cooling part 60 may include a thermoelectric element 61. The thermoelectric element 61 is an element utilizing the Peltier Effect (Peltier Effect) in which heat is generated or heat is absorbed at a junction between two metals when the two metals are connected and current flows. That is, since the Potential (Potential) of electrons in metals differs among different metals, electrons are transferred from a metal having a low Potential to a metal having a high Potential, but energy must be obtained from the outside, and thus thermal energy is obtained from a contact, and conversely, thermal energy is dissipated. Depending on the direction of the current supplied to such a thermoelectric element 61, the direction in which heat is generated or absorption of heat is generated can be determined.

For example, in fig. 9, when a 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, whereas when a current flows in the direction opposite to the direction of the arrow shown in fig. 9, heat dissipation occurs on the first metal 61a side and heat absorption occurs on the second metal 61b side.

Therefore, in the present invention, in order to reduce the temperature of the remaining ink via the second pipe P2, it is not necessary to use a fan cooler which occupies a large space during installation, but the thermoelectric element 61 having a cooling effect when current is applied is used, and the installation space required is relatively small, whereby the space availability as a whole can be improved.

The thermoelectric element 61 may be disposed so as to surround the second pipe P2. The cooling unit 60 can quickly dissipate heat from the thermoelectric element 61 when a temperature sensor (not shown) senses that the temperature of the remaining ink via the second pipe P2 is high. At this time, the cooling unit 60 may control the operation of the thermoelectric element 61 by an independent control unit (not shown) or control the operation of the thermoelectric element 61 by a control unit 70 to be described later.

For example, the cooling unit 60 may maintain the temperature of the remaining ink passing through the second pipe P2 at the atmospheric temperature (e.g., about 23 ℃). 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.

That is, since the ink initially stored in the reservoir 40 is when the ink has not been circulated in the inkjet printing apparatus 1, the temperature thereof may have an atmospheric temperature (or a peripheral temperature of the inkjet printing apparatus). Therefore, IN the case of maintaining the temperature of the remaining ink 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 first supplied from the reservoir 40 to the print head 20.

This allows the remaining INK collected in the reservoir 40 to maintain the physical state similar to the temperature and viscosity of the newly injected INK0 injected from the external INK storage (not shown).

However, the cooling unit 60 is not limited to the thermoelectric element 61. For example, the temperature of the remaining ink passing through the second pipe P2 may be maintained constant by always flowing cooling water or cooling liquid through the second pipe P2.

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 portion 60.

The pump PU can pressurize the remaining ink to supply it to the reservoir 40. Since the ink remaining after passing through the pump PU is ink before passing through the cooling unit 60, the viscosity thereof is lower than that of ink remaining after passing through the cooling unit 60. Therefore, since the surplus ink having a low viscosity is supplied to the reservoir 40 by the pump PU, an effect of improving the durability and the operability of the pump PU can be expected.

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 section 50 and the injection port IN1 of the print head 20. The temperature sensor TS can sense the temperature of the ink passing through the mixing section 50.

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

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 extending from the mixing section 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 ink temperature varies depending on the external environment, the printing quality of the inkjet printing apparatus 1 may be degraded.

Therefore, when determining 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 may maintain the temperature of the ink stored in the ink storage unit 23 at the same temperature as the temperature of the ink heated by the second heater H2 by the first heater H1.

Other embodiments are described below. In the following embodiments, the same configurations as those of the embodiments described above are omitted or simplified, and the differences will be mainly described.

Fig. 10 is a diagram for explaining an inkjet printing apparatus according to another embodiment of the present invention. Fig. 11 is a perspective view of a printhead according to another embodiment of the present invention. Fig. 12 is a cross-sectional view of the printhead taken along line III-III' of fig. 11.

Referring to fig. 10 to 12, an ink jet printing apparatus 1_1 according to another embodiment of the present invention is different from the ink jet printing apparatus 1 shown in fig. 3 in that it further includes a heat insulating portion 25 that blocks heat radiated from the first heater H1 to between the substrate 30 and the first heater H1. Therefore, the reservoir 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 configuration and operation, are omitted from description, and the printhead 20_1 will be described below.

Specifically, the printhead 20_1 may further include a heat insulating portion 25 that blocks heat radiated from the first heater H1 to between the substrate 30 and the first heater H1.

The heat insulating portion 25 may be disposed on the lower surface of the main body 21. A nozzle portion 24 may be disposed between the heat insulating portion 25 and the main body 21. The heat insulator 25 may be disposed at a predetermined interval from the nozzle 24. For example, the thermal insulation portion 25 may be supported by the nozzle portion 24 and the plurality of spacers SPC.

The heat insulating portion 25 may be formed in an integrated type to surround the nozzle portion 24. For example, as shown in fig. 11, the heat insulating part 25 may include a rectangular parallelepiped housing part 25a and a fastening part 25b for connecting the housing part 25a to the lower surface of the body 21. The bottom surface of the housing portion 25a may include an opening 25c that overlaps the nozzle portion 24 (or the nozzle lower hole 24b) in the thickness direction.

The heat insulating portion 25 preferably has an Emissivity (Emissivity) of 0.2 or less. In this case, emissivity refers to a ratio of energy re-radiated when an object absorbs external light energy and then transmits a portion thereof or causes a surface reflection phenomenon. Theoretically, an object that is irradiated 100% after absorbing external energy and does not undergo surface reflection is called a black body (Blackbody), and the emissivity value at this time can be defined as "1". That is, in the case where the emissivity is 0.2, it means that only 20% of the heat radiated from the first heater H1 is radiated again. In other words, the emissivity is 0.2, which means that 80% of the heat emitted from the first heater H1 is reflected by the surface or partially transmitted. For example, the thermal insulation part 25 may include at least one of stainless steel (SUS), gold (Au), silver (Ag), copper (Cu), and aluminum (Al). According to an embodiment of the present invention, the spacer SPC may include the same substance as the thermal insulation part 25 described above.

The control unit 70 can maintain the ink ejection amount constant by controlling the temperature of the ink by the first heater H1. However, the temperature of the ink heated by the first heater H1 may generally be higher than the atmospheric temperature (e.g., about 23 ℃). For example, the heat dissipated by first heater H1 may be about 40 ℃.

The heat dissipated by the first heater H1 may be transferred to the substrate 30. In this case, there is a possibility that an uneven temperature distribution is generated on the surface of the substrate 30 facing the first heater H1. If an uneven temperature distribution occurs on the substrate 30, the flatness of the substrate 30 may fluctuate due to thermal expansion, and thus print quality may be degraded.

The print head 20_1 according to an embodiment of the present invention includes the heat insulating portion 25, so that heat transferred to the substrate 30 is blocked, and a temperature distribution on the substrate 30 can be maintained uniform. Further, since the degree to which heat emitted from the first heater H1 is emitted to the outside is reduced, an effect of preventing the temperature of the ink stored in the ink storage unit 23 from decreasing can be expected.

Fig. 13 is a diagram for explaining an inkjet printing apparatus according to another embodiment of the present invention.

Referring to fig. 13, an inkjet printing apparatus 1_2 according to another embodiment of the present invention is different from the inkjet printing apparatus 1 shown in fig. 3 in that it includes a plurality of pressure sensors (PS1, PS 2). Therefore, the accumulator 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 configuration and operation, are not described, and the plurality of pressure sensors (PS1 and PS2) will be described below.

Specifically, the first pressure sensor PS1 may be disposed in the first pipe P1 between the mixing unit 50 and the print head 20. The first pressure sensor PS1 can sense the pressure of the ink in a state before the ink passes through the mixing unit 50 and flows into the print head 20.

When the pressure sensed by the first pressure sensor PS1 is higher than the preset pressure, the controller 70 may heat the ink to a preset temperature corresponding to the sensed pressure by the first heater H1.

In the case where the ink is repeatedly circulated, the concentration of the ink may change as the solvent included in the ink is volatilized, or in the case where the ink is repeatedly heated and cooled, the physical properties of the ink may change. Such denatured INK may have different viscosities even when heated to the same temperature as the newly injected INK0 (see fig. 6 and 7) injected into the INK tank 41.

In the first pipe P1, the pressure loss and the viscosity may have a relationship of the following formula 1.

[ formula 1]

Pressure loss (a × viscosity × length of pipe × average flow rate/inner diameter of pipe)

(wherein, a is a proportionality constant.)

For example, when the viscosity of the ink increases, the resistance of the ink passing through the nozzle portion 24 increases, and therefore 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 by the first heater H1. In this case, the relationship between the viscosity of the ink and the temperature can be obtained by an experiment, and based on this, a lookup table can be generated in advance. According to an embodiment, it may be that the higher the sensed pressure value, the higher the preset temperature. Therefore, when the viscosity of the ink increases, the viscosity of the ink can be maintained constant by heating the first heater H1 to a higher temperature to lower the viscosity of the ink.

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

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

The control part 70 may heat the ink in proportion to the pressure difference between the pressure sensed by the first pressure sensor PS1 and the pressure sensed by the second pressure sensor PS2 by the first heater H1 when the pressure difference exceeds a preset range.

For example, when the viscosity of the ink increases, the resistance of the ink passing through the nozzle portion 24 may increase, and therefore, the pressure value sensed by the first pressure sensor PS1 may increase, and the 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 to which the first heater H1 is heated. In this case, the relationship between the viscosity of the ink and the temperature can be obtained by experiments, and based on this, a lookup table can be generated in advance.

This can maintain the viscosity of the ink constant even if the physical properties of the ink vary, and can be expected to maintain a uniform ejection amount of the ink. An embodiment that does not include a temperature sensor is illustrated in fig. 13, but a pressure sensor (PS1, PS2) and a temperature sensor may be applied together.

Fig. 14 is a diagram for explaining an inkjet printing apparatus according to another embodiment of the present invention.

Referring to fig. 14, the inkjet printing apparatus 2 is different from the inkjet printing apparatus 1 shown in fig. 3 in that the particle-containing liquid included in the ink and the solvent 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.

Specifically, the inkjet printing apparatus 2 may 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.

The solvent circulation section may include: a first reservoir 40_1a storing a solvent; a first pipe P1 for supplying the solvent from the first reservoir 40_1a to the print head 20; a mixing unit 50_1 that is disposed on the first pipe P1 and mixes a particle-containing liquid of ink supplied from a particle supply unit 80 described later and a solvent supplied from the first reservoir 40_1 a; a second pipe P2_1a that supplies the remaining ink after being discharged from the print head 20 to the second reservoir 40_1 b; a second pipe P2_1b that recovers the remaining solvent separated from the ink by the second reservoir 40_1b into the first reservoir 40_1a (hereinafter, the second pipe P2_1a and the second pipe P2_1b may be collectively referred to as a second pipe P2); and a cooling unit 60 disposed in the second pipe P2_1 b.

The first reservoir 40_1a corresponds to the reservoir 40 of fig. 3, the first pump PU1 corresponds to the pump PU of fig. 3, and the print head 20, the temperature sensor TS, and the cooling portion 60 are substantially the same in their constitution and operation as the embodiment of fig. 3, and therefore the mixing portion 50_1 is described below.

As shown in fig. 14, the mixing section 50_1 can uniformly mix the particle-containing liquid included in the ink and the solvent by using a mixer SAW of a surface acoustic wave (surface acoustic wave). Here, the surface acoustic wave is a kind of ultrasonic wave, and has a characteristic that wave energy propagates while being concentrated on a surface of a sphere.

The particle circulation section may include: a particle supply unit 80 that supplies a particle-containing liquid of ink to a first pipe P1 between the first reservoir 40_1a and the mixing unit 50_ 1; a second reservoir 40_1b disposed in one region of the second pipes P2_1a and P2_1b and storing the remaining ink after being discharged from the print head 20; a third pipe P3 that collects the surplus particle-containing liquid separated from the surplus solvent in the surplus ink from the second reservoir 40_1b to the particle supply unit 80; a concentration sensor PC disposed in the first pipe P1 between the particle supply unit 80 and the print head 20 and sensing the concentration of the particles; and a supply control unit 90 for controlling the supply amount of the particle-containing liquid in accordance with information received from the concentration sensor PC. The third reservoir 40_1c may be identical in construction and operation to the reservoir 40 of fig. 3. Hereinafter, the particle supply unit 80, the concentration sensor PC, and the second reservoir 40_1b will be mainly described.

The second reservoir 40_1b can separate the surplus ink that is not ejected from the print head 20 and is recovered into the surplus solvent and the surplus particle-containing liquid by a surface acoustic wave (surface acoustic wave).

The second pump PU2 is disposed in the third pipe P3 between the second reservoir 40_1b and the particle supply unit 80, and supplies the surplus particle-containing liquid separated from the surplus ink to the particle supply unit 80 by pressurizing the surplus particle-containing liquid.

The particle supplying part 80 may include: a third reservoir 40_1c that stores the recovered remaining particle-containing liquid; and a third pump PU3 that supplies the surplus particle-containing liquid from the third tank 40_1c to the first pipe P1 in the region between the first tank 40_1a and the mixing unit 50_ 1.

The concentration sensor PC according to an embodiment of the present invention may be a particle counter (particle counter) that counts the number of particles included in a unit volume of ink.

The supply control unit 90 may increase the supply amount of the particle containing liquid of the ink by the third pump PU3 when the concentration of the particles included in the ink sensed by the concentration sensor PC is lower than a preset concentration.

When the ink includes a particle-containing liquid containing an inorganic substance, the particles may be separated from the solvent and precipitated depending on the size and weight of the particles. In particular, when the length of the first pipe P1 located between the mixing unit 50_1 and the print head 20 is long, particles may be separated from the solvent and precipitated while the ink to be mixed reaches the print head 20. In this case, the density of the ink ejected from the print head 20 becomes uneven, and thus the print quality may be degraded.

The inkjet printing apparatus 2 according to an embodiment of the present invention can sense the density of the ink near the inlet IN1 of the print head 20 by the density sensor PC, and control the density of the ink to be constant by the supply control unit 90, thereby maintaining the density of the ink ejected from the print head 20 to be uniform. Further, by operating the solvent circulation portion and the particle circulation portion separately, the load on the inkjet printing apparatus 2 as a whole can be reduced.

Fig. 15 is a diagram for explaining an inkjet printing apparatus according to another embodiment of the present invention.

Referring to fig. 15, the inkjet printing apparatus 2_1 differs from the embodiment shown in fig. 14 in that the mixing section 50 includes a static mixer SM instead of a mixer SAW using a surface acoustic wave, and the particle-containing liquid and the solvent are separated in the second tank 40_2b not using a surface acoustic wave but using gravity.

The description of the static mixer SM overlaps with that described in fig. 3, and therefore, the description of the second reservoir 40_2b will be omitted. The second reservoir 40_2b can store the surplus ink collected from the print head 20 for a certain time, and the surplus ink does not flow out to the cooling unit 60 and the second pipe P2 within the certain time. In this case, the particles included in the ink may be precipitated by gravity.

Since it is not necessary to provide the second reservoir 40_2b with a device for generating a surface acoustic wave, it is possible to achieve weight reduction, which is advantageous in terms of cost.

Fig. 16 is a diagram for explaining an inkjet printing apparatus according to another embodiment of the present invention.

Referring to fig. 16, the inkjet printing apparatus 2_2 differs from the embodiment shown in fig. 14 in that a third pipe P3 connecting the second pump PU2 and the particle supply unit 80 is not included, but a particle collection unit 100 is included.

Specifically, the second reservoir 40_1b can separate the surplus ink that is not ejected from the print head 20 but is recovered into the surplus solvent and the surplus particle-containing liquid by a surface acoustic wave (surface acoustic wave). The second pump PU2 may be disposed in the third pipe P3_1 between the second reservoir 40_1b and the particle collection unit 100, and may supply the surplus particle-containing liquid separated from the surplus ink to the particle collection unit 100.

After the state of the surplus particle-containing liquid collected in the particle collecting unit 100 is checked, the surplus particle-containing liquid may be supplied to the particle supplying unit 80 if the state of the particle-containing liquid is good, or may be discarded if the state is bad. This can maintain the physical state of the ink in a good state.

While the embodiments of the present invention have been described with reference to the drawings, it will be understood by those skilled in the art that the present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. Therefore, it should be understood that the above-described embodiments are illustrative in all aspects and are not restrictive.