JP2006015640A - Inkjet recorder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inkjet recorder in which ink can be circulated stably and supplied to an ejection head even if ink is ejected continuously from the ejection head by preventing evaporation of solvent. <P>SOLUTION: The recorder 10 comprises an ejection head 12 and an ink circulation system 20. The ink circulation system 20 comprises a main tank 14, a supply subtank 16 for supplying ink to the ejection head by a static pressure system, a supplement liquid tank 22, and interconnecting piping 50. A passage for circulating ink of the ink circulation system 20 is formed to be sealed hermetically from the atmosphere. At least a part of the ink circulation system 20 is provided with a pressure regulator for regulating the inner pressure of the ink circulation system. The pressure regulator is formed of a soft material exhibiting flexibility. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an ink jet recording apparatus that performs recording by ejecting ink toward a recording medium, and more specifically to an ink jet recording apparatus that performs recording by supplying ink to an ejection head by a static pressure method.

  An electrostatic drive system, a thermal head system, an electromechanical transducer (piezo) system, or the like is used for a recording apparatus (inkjet recording apparatus) using an inkjet recording system. As a recording material (ink) used in the ink jet recording apparatus, generally, a recording material in which colored particles are dispersed in a solvent is used. Recording (printing) is performed by using the recording method described above and causing ink to fly onto a recording medium such as recording paper.

In an electrostatic ink jet recording apparatus, normally, ink is circulated between a main ink tank (main tank) that stores ink and an ejection head, and a certain amount of ink is supplied to the ejection head. Drawing is performed by discharging ink onto a recording medium.
As a method of circulating ink between an ink tank and an ejection head, a method of circulating ink using a height difference between the ejection head and the ink tank is known. For example, Patent Document 1 discloses an ink jet recording apparatus that performs ink supply and recovery with a difference in height of ink chamber arrangement positions.

FIG. 6 shows a schematic configuration of an ink circulation device of the ink jet recording apparatus disclosed in Patent Document 1.
The ink circulation device 120 includes an ink recovery container 114, an ink flow rate adjustment chamber 116, pipes 123a to 123d connecting them, a filter 125, electromagnetic valves 126a and 126b, and a pump 124. The ink flow rate adjustment chamber 116 is an ink chamber for adjusting the flow rate of the ink supplied to the ink ejection unit 112, and the ink recovery container 114 is an ink chamber for storing the circulating ink. The filter 125 is provided for removing contaminants in the ink, and the electromagnetic valves 126a and 126b are provided for controlling the flow of ink. In the ink circulation device 120, ink stored in the ink recovery container 114 is sucked up by the pump 124, passes through the filter 125, and is sent into the ink flow rate adjustment chamber 116. The ink stored in the ink flow rate adjustment chamber 116 naturally flows toward the ink discharge portion 112 with a pressure based on potential energy determined by the difference in height between the ink liquid level in the ink liquid amount adjustment chamber 116 and the ink discharge portion 112.

The ink that has passed through the ink discharge unit 112 naturally flows toward the ink recovery container 114 due to the height difference between the ink discharge unit 112 and the ink recovery container 114. In this ink circulation device, a stable amount of ink is supplied to the ink discharge unit 112 due to the difference in height between the ink flow rate adjustment chambers 116 provided above and below the ink discharge unit 112 and the ink recovery container 114, and the ink recovery container 114 is supplied. The ink is collected stably.
When the ink amount in the ink collection container is insufficient, ink is supplied from the replenishment ink tank 122 to the ink collection container 114 through the pipes 129 and 131 by the pump 128.

JP 2001-219580 A

  However, in the ink jet recording apparatus disclosed in Patent Document 1, since the ink circulation path of the ink circulation device 120 is sealed, the ink ejected when ink is ejected continuously from the ink ejection unit 112. The internal pressure of the ink collection container 114 or the ink flow rate adjustment chamber 116 is reduced by the amount. For this reason, a pressure difference is generated between the atmospheric pressure and the internal pressure of the ink recovery container 114, or between the atmospheric pressure and the internal pressure of the ink flow rate adjusting chamber 116, and ink is discharged from the ink discharge unit 112 by this differential pressure. There is a problem that it becomes difficult to be done.

  Further, when the drive of the pump 124 is stopped and the supply of ink to the ink flow rate adjustment chamber 116 is stopped in a state where such a differential pressure is generated, the internal pressure of the ink recovery container 114 or the ink flow rate adjustment chamber is There is also a possibility that air may enter from the ink discharge portion 112 of the recording head due to the pressure difference from the atmospheric pressure.

  The present invention has been made to solve the above-described problems of the prior art, and an object thereof is to prevent evaporation of the solvent and to circulate the ink stably even when ink is continuously ejected from the ejection head. Another object of the present invention is to provide an ink jet recording apparatus that can be supplied to an ejection head.

  In order to achieve the above object, the present invention provides an ink jet recording apparatus having an ejection head for ejecting ink, wherein the ink is stored in a main tank, and ink is supplied to the ejection head in a static pressure manner. Between the main tank, the supply sub-tank, and the discharge head, the supply sub-tank for communicating with the main tank and a communication pipe that communicates the space formed above the ink liquid level of the supply sub-tank. An ink circulation system for circulating ink, wherein the ink circulation system is formed so as to be sealed from the atmosphere, and at least a part of the ink circulation system is sealed with the ink circulation system. Provided is an ink jet recording apparatus comprising a pressure adjusting body for adjusting an internal pressure.

  In the present invention, the pressure adjusting body preferably adjusts the internal pressure of the ink circulation system to be equal to the atmospheric pressure, and has a flexible member that absorbs fluctuations in the internal pressure of the ink circulation system. Is preferred.

  Preferably, at least one of the main tank, the supply sub-tank, and the communication pipe is provided with the pressure adjusting body, and the supply sub-tank is disposed at a position higher than the discharge head in the vertical direction, and is pressurized by overflow. It is preferable to supply ink to the ejection head while keeping the head constant.

  In the ink jet recording apparatus of the present invention, the ink circulation system further includes a replenishing liquid tank for replenishing the main tank with ink, and is formed above the liquid surface of the ink replenished in the replenishing liquid tank. It is preferable that the space to be connected is connected to the communication pipe, and it is preferable that at least the replenisher tank is provided with the pressure adjusting body.

  In the ink jet recording apparatus of the present invention, the ink circulation system further includes a recovery subtank that recovers and stores ink that does not contribute to ejection from the ejection head, and the recovered ink tank is disposed in the vertical direction in the ejection head. The ink is collected from the ejection head while keeping the pressure head constant by overflow, and the communication pipe is connected to a space above the liquid level of the ink stored in the collection sub tank. It is preferable that the pressure adjusting body is provided at least in the recovery sub tank.

  In the present invention, the ink is an ink obtained by dispersing charged fine particles including at least a coloring material in an insulating dispersion medium, and the discharge head discharges the ink using electrostatic force. The inkjet head is preferably used.

  The ink jet recording apparatus of the present invention adjusts the internal pressure in the ink circulation system when the ink circulation system is sealed in at least a part of the components of the ink circulation system having the ink circulation path formed so as to be sealed from the atmosphere. Since the pressure regulator is provided, even if ink is continuously ejected and the total amount of ink in the ink circulation system is reduced, the internal pressure in the ink circulation system is adjusted by the pressure regulator so that the internal pressure of the ink tank is always maintained. Since the pressure can be equal to the atmospheric pressure, even if ink is continuously ejected, the ink can be circulated stably in the ink circulation system, and the ink can be ejected stably from the ejection head.

  Further, since the ink circulation path of the ink circulation system is a sealed space cut off from the atmosphere, the evaporated ink solvent is hardly discharged outside the ink circulation system, and the ink concentration can be kept uniform over a long period of time. it can.

  Hereinafter, the ink jet recording apparatus of the present invention will be described in detail based on a preferred embodiment shown in the accompanying drawings.

  FIG. 1 conceptually shows one structural example of the ink jet recording apparatus of the present invention. As shown in FIG. 1, an ink jet recording apparatus (hereinafter referred to as a recording apparatus 10) 10 basically includes an ejection head (ink jet recording head) 12 and an ink circulation system 20. The ink circulation system 20 of the recording apparatus 10 uses an ink Q formed by dispersing charged fine particles containing color material (hereinafter referred to as color material particles) in an insulating carrier liquid (dispersion medium). This is an ink circulation system of an electrostatic ink jet recording apparatus that discharges ink droplets by applying electric power. The ink circulation system 20 basically includes a main tank 14, a supply sub tank 16, a recovery sub tank 18, a replenisher tank 22, and an ink circulation pump 24. In the illustrated example, the case where the upper lid 22a of the replenisher tank 22 is formed of a pressure adjusting body is shown, and this pressure adjusting body can adjust the internal pressure of the ink circulation system 20. In the illustrated example, the internal pressure of the ink circulation system 20 is adjusted to be equal to the atmospheric pressure with the upper lid 22a that is a pressure adjusting body, and at least the internal pressure of the main tank 14 and the supply sub tank 16 is always adjusted to be equal to the atmospheric pressure. The ink in the ink circulation system 20 is stably circulated by a static pressure method. The replenisher tank 22 and the pressure adjusting body will be described in detail later.

The ink circulation path of the ink circulation system 20 mainly includes an ink supply path that supplies the ink Q in the main tank 14 to the ejection head 12 and an ink collection path that collects the ink Q that has not been ejected from the ejection head 12. Is done. The ink supply path mainly includes an ink circulation pump 24, a supply sub tank 16, and ink supply channels 32, 34, and 36. The ink recovery path is mainly composed of the recovery sub-tank 18 and the ink recovery flow paths 38 and 44. The inside of the ink circulation system 20 is formed so as to be sealed from the atmosphere. Here, the sealing means a state in which the gas or liquid in the system is not substantially permeated to the outside of the system. In this way, the ink circulation path is sealed and substantially blocked from the atmosphere, so that volatile components in the ink are prevented from being exhausted outside the ink circulation path.
The ink supply flow path and the ink recovery flow path that constitute the ink circulation system can be formed of, for example, a pipe or a flexible tube.

  The recording apparatus shown in FIG. 1 is an example of the configuration as described above, and the recording apparatus 10 of the present invention has, for example, the ejection head 12 in addition to the ejection head 12 and the ink circulation system 20 shown in the figure. Is a driver for ejecting ink droplets by driving and a scanning for transporting (scanning transporting) the recording medium P in a direction orthogonal to the nozzle row direction (row direction), which will be described later, through a predetermined path facing the ejection head 12. Prior to image recording by the conveying means, the ejection head 12, a charging means for charging the recording medium P with a predetermined bias voltage (or an opposite electrode to the control electrode of the ejection head 12), and for neutralizing the charged recording medium P Static elimination means, transport means for transporting the recording medium P along a predetermined path, sensor for detecting the transported recording medium P, solvent exhaust for discharging carrier liquid etc. remaining in the apparatus Means such as, for has various components inkjet recording device of the known electrostatic is matter of course.

In addition, the inkjet recording apparatus of the present invention may be a monochrome recording apparatus that records an image of one color such as K (black) alone, and Y (yellow), M (magenta), C (cyan). And a recording apparatus that draws a full-color image on a recording medium using four colors of inks K and K.
The ejection head 12 is not limited to an electrostatic ink jet head, and may be various types such as a thermal ink jet head, a so-called piezo type ink jet head that ejects ink by vibrating a vibration plate of an ink chamber by a piezo element, a micromachine, or the like. An inkjet head can be suitably used.

  The main tank 14 is a sealed ink tank for mainly storing ink that circulates in the ink circulation system 20 of the recording apparatus 10. The main tank 14 preferably has a stirring means for preventing the sedimentation / deposition of the color material particles and a temperature adjusting means for improving the stability of ink ejection. A filter 28 for removing contaminants in the ink is disposed in the main tank 14, and the filter 28 is connected to an ink supply channel 32 connected to the ink circulation pump 24. The ink in the main tank 14 is sucked up by the pump 24 through the filter 28 and supplied to the supply sub tank 16. The amount of liquid fed by the ink circulation pump 24 is set to be larger than the amount of ink Q supplied from the supply sub tank 16 to the ejection head 12.

  As shown in FIG. 1, the supply sub tank 16 is disposed above the ejection head 12 in the vertical direction. The other end of the ink supply channel 36 connected to the supply sub tank 16 is connected to the ink inlet 12 a of the ejection head 12. In the supply sub tank 16, the ink Q supplied from the main tank 14 by the ink supply flow paths 32 and 34 is stored, and the stored ink Q is supplied to the ejection head 12 through the ink supply flow path 36. A filter 29 is provided in the middle of the ink supply flow path 36 between the supply sub tank 16 and the ejection head 12. The filter 29 can remove foreign matters contained in the ink supplied to the ejection head 12.

  An overflow pipe 62 is disposed in the supply sub tank 16. The overflow pipe 62 maintains a constant amount of ink in the supply sub tank 16. The connection position of the ink supply flow path 36 to the supply sub tank is below the upper end of the overflow pipe 62. In the illustrated example, a connection portion with the ink supply flow path 36 is provided on the bottom surface of the supply sub tank 16.

The ink stored in the supply sub tank 16 is supplied to the discharge head 12 from the ink supply flow path 36 by gravity drop at a pressure corresponding to the height difference (drop) between the supply sub tank 16 and the discharge head 12 (or the recovery sub tank 18). The Further, in the supply subtank 16, even if the ink supplied by the circulation pump 24 exceeds the height of the overflow pipe 62, the ink overflows from the overflow pipe 62 and is discharged. Therefore, the height of the ink level in the supply subtank is It is kept constant. As a result, the supply amount and supply pressure (pressure head) of the ink Q from the supply sub tank 16 to the ejection head 12 are kept constant, and ink is supplied in a so-called static pressure system. That is, the ink in the supply subtank flows down to the ejection head at a constant pressure by the pressure head.
The ink Q discharged from the overflow pipe 62 in the supply sub-tank 16 is returned to the main tank 14 from the ink recovery flow path 42 and is again circulated.

  The collection sub tank 18 is an ink tank for storing ink that has not been ejected from the ejection head 12, and is disposed below the ejection head 12 in the vertical direction. An overflow pipe 64 is provided inside the collection sub tank 18, and the lower end of the overflow pipe 64 is connected to the ink collection flow path 44 on the bottom surface of the collection sub tank 18. Further, the collection sub tank 18 is connected to the ink discharge port 12 b of the ejection head 12 through the ink collection flow path 38.

The ink Q discharged from the ink discharge port 12b of the discharge head 12 without being discharged from the discharge head 12 has a pressure corresponding to the height difference (drop) between the discharge head 12 (or the supply sub tank 16) and the recovery sub tank 18. The ink is supplied from the ink recovery flow path 38 to the recovery sub-tank 18 by gravity drop. In the recovery sub-tank 18, the ink Q that has exceeded the overflow pipe 64 is returned to the main tank 14 from the ink recovery flow path 44 and is again circulated.
Further, the ink liquid level in the recovery sub-tank 18 is kept constant by the overflow pipe 64. As a result, a certain amount of pressure corresponding to the height of the liquid level in the recovery sub tank 18 is also applied to the ink discharge port 12b from the ejection head 12. That is, a constant static pressure can be applied to the discharge port 12b of the discharge head 12.

  In the recording apparatus 10, ink is supplied from the supply sub tank 16 to the discharge head 12 with a constant pressure head in this way, and a constant pressure is also applied to the ink supply from the discharge head 12 to the recovery sub tank 18. As a result, the pressure relating to the ink flow path formed inside the ejection head 12, that is, the ink supply and ejection to the ejection head 12, can be made completely static and formed at the ejection port of the ejection head 12, which will be described later. The meniscus of the ink Q to be used can be stabilized.

The replenisher tank 22 is used to replenish the main tank 14 with ink consumed by ejection. The replenisher tank 22 is connected to the main tank 14 by an ink supply channel 46. A switching valve 48 is provided in the middle of the ink supply channel 46, and the ink in the replenisher tank 22 can be replenished to the main tank 14 by opening the switching valve 48.
The replenishing liquid tank 22 may be composed of two tanks, a concentrated ink replenishing tank that stores high-concentration ink and a dilution liquid replenishing tank that stores ink dilution liquid. As the diluting liquid, for example, an ink carrier liquid as described later may be used.

  A density sensor 26 is provided in the middle of the ink supply passage 32 between the main tank 14 and the ink circulation pump 24. The density sensor 26 is provided for detecting the density of ink circulating in the ink circulation system. The ink density is constantly monitored by the density sensor 28, and when the ink density is high or low, the ink is replenished from the replenisher tank 22 to the main tank 14, or the high density ink is supplied from the concentrated ink replenishment tank or the dilution liquid tank. In addition, by supplying the dilution liquid to the main tank 14 and optimizing the ink density, it is possible to always form an image on the recording medium with the optimum density.

In the recording apparatus 10 shown in FIG. 1, the upper cover 22a of the replenisher tank 22 is configured as a pressure regulator. The upper lid 22a formed from this pressure adjusting body can adjust the internal pressure of the ink circulation system, whereby the internal pressure in the ink circulation path can be maintained at the same pressure as the atmospheric pressure.
The pressure adjusting body is a flexible material having flexibility, and is a highly airtight material that does not substantially allow ink and a volatile component of a solvent contained in the ink to pass through. As such a pressure adjusting body, for example, a plastic film thin film is preferable, polyester, polybutylene terephthalate, polycarbonate, polyethylene, polyethylene terephthalate, polymethyl acrylate, polypropylene, polytetrafluoroethylene, polyurethane, polyvinyl chloride, poly Vinylidene chloride and polyvinylidene fluoride are preferred.

  The upper lid 22a covers the upper surface of the replenisher tank 22 in a bent state. Thereby, it is possible to follow the volume change of the space above the ink liquid surface of the replenishing liquid tank 22. In other words, when the amount of air in the space above the ink liquid level in the replenisher tank 22 changes, the upper lid 22a can contract or expand in accordance with the change. Since the upper lid 22a is formed of a flexible material, it cannot be restored to its original state after contraction or expansion. Therefore, as long as the amount of air in the replenisher tank 22 does not change, the upper lid 22a is maintained in a contracted or expanded state, and the internal pressure of the replenisher tank is always maintained at the same pressure as the atmospheric pressure.

  As shown in FIG. 1, spaces formed above the ink liquid level of the replenishing liquid tank 22, the main tank 14, the supply sub tank 16, and the recovery sub tank 18 are connected by a communication pipe 50. As a result, the respective pressures (internal pressures) in the space above the ink liquid level in the replenishing liquid tank 22, the main tank 14, the supply sub tank 16, and the recovery sub tank 18 are maintained the same, and are maintained at the same pressure as the atmospheric pressure. As described above, since the top cover 22a of the replenisher tank 22 is formed by the pressure adjusting body, even when the space above the ink liquid surface is depressurized by the amount of ejected ink due to continuous ejection of ink. The upper cover 22a of the replenisher tank 22 is plastically deformed according to the reduced pressure. For this reason, the internal pressures of the replenisher tank 22, the main tank 14, the supply sub-tank 16 and the recovery sub-tank 18 are always kept equal to the atmospheric pressure. As described above, the upper lid 22a formed by the pressure adjusting body allows the pressure in the space above the ink liquid level of the replenisher tank 22, the main tank 14, the supply sub-tank 16 and the recovery sub-tank 18, that is, the internal pressure of each tank to be atmospheric pressure. Since it is always adjusted so as to be balanced, even if ink is ejected continuously, the ejection of the ink can be stabilized.

Further, in the recording apparatus 10 of the present invention, since the ink circulation system 20 is a sealed system so that the ink in the path does not come into contact with the outside, the solvent evaporated in the ink circulation system is discharged outside through the ink circulation system. It will not be done. Since the portion where the solvent evaporates is only the discharge port (nozzle) of the discharge head, evaporation of the solvent can be suppressed to a minimum. Further, in the present invention, it is preferable that the nozzle port of the ejection head 12 is closed with the cap 52 when the recording apparatus is not driven, thereby preventing ink from evaporating from the nozzles of the ejection head. can do. By preventing such evaporation of the solvent, environmental pollution can be reduced.
Further, such a cap 52 hermetically seals all the ejection ports of the ejection head 12 when the ink circulation is stopped or when drawing is not performed for a long time, so that the dry fixing due to evaporation of ink remaining in the ejection ports is performed. It can also be prevented.

In FIG. 1, the upper lid 22a of the replenisher tank 22 is configured as a pressure adjuster, but the replenisher tank 22 main body may be used as a pressure adjuster. Further, a pressure adjusting body may be provided in the upper lid portion of at least one of the supply sub tank 16, the recovery sub tank 18 and the main tank 14, or a part of the tank, and these tank bodies may be used as the pressure adjusting body.
Further, as shown in FIG. 2, an air bag 51 as a pressure adjusting body is connected in the middle of the communication pipe 50 that connects the space above the ink liquid level of each ink tank of the ink circulation system 20. The air bag 51 can also maintain the internal pressure of each ink tank to be the same as the atmospheric pressure. Further, such an airbag may be connected to at least one of the main tank 14, the supply sub tank 16, the recovery sub tank 18, and the replenisher tank 22. Further, the communication pipe 50 itself may be used as a pressure adjusting body.
As described above, in the present invention, it is sufficient that at least one of the main tank 14, the supply sub tank 16, the recovery sub tank 18, the replenisher tank 22, and the communication pipe 50 includes a pressure adjusting body. For example, the upper lid of the tank, a part of the tank, the tank body, the whole or a part of the communication pipe, the air bag connected to the tank or the communication pipe, or the connection part of the communication pipe and the air bag may be used.

  By the way, when the ink circulation system 20 is configured without using the pressure regulator as described above, and the inside of the ink circulation path of the ink circulation system 20 is a sealed space that does not communicate with the atmosphere, for example, from the replenisher tank 22 When the main tank 14 is refilled with ink, the inside of the replenisher tank 22 is depressurized by the amount of the refilled ink, and a differential pressure is generated in the internal pressure of each tank included in the ink circulation system 20. Also, when the ink circulation pump 24 is started, the pressure in the main tank 14 is reduced immediately after the start, so that a differential pressure is generated in the internal pressure of each tank included in the ink circulation system 20. Such a differential pressure causes pulsation of the ink circulating in the ink circulation system 20 to make the ink discharge unstable, or the discharge port of the discharge head 12 becomes higher in pressure, so that the ink is discharged from the discharge port. There is a risk that it may not be discharged.

  Even in such a case, according to the present invention, a part of the ink circulation system 20, for example, the upper surface of at least one of the main tank 14, the supply sub tank 16, the recovery sub tank 18, and the replenisher tank 22, those tanks. The communication pipes 50 connecting the air chambers above the ink liquid level in these tanks are configured using a pressure regulator, and the air in each tank is supplied to the air chamber portion of the replenisher tank 22 or the main tank. Since the air can be quickly supplied to the air chamber portion 14 while maintaining the atmospheric pressure and the equal pressure state, the ink in the ink circulation path can be circulated stably, and the ink can be stably supplied from the ejection head 12. Can be discharged.

In the recording apparatus 10 of the present invention, the height of the meniscus of the ink Q formed at the ejection port of the ejection head 12 can be freely increased by appropriately setting the height of the supply sub tank 16 and / or the recovery sub tank 18. It is also possible to select in degrees. Accordingly, it is preferable to have a height adjusting means for adjusting the height of the supply sub tank 16 and / or the recovery sub tank 18 so that the state and height of the meniscus can be controlled.
As the height adjusting means, various methods capable of adjusting the height in the vertical direction, such as a method using a screw shaft and a nut that are screwed together, a method using a cylinder or an actuator, and a method using a cam can be used.

Next, the structure of the ejection head 12 will be described in detail with reference to FIGS.
The ejection head 12 is an electrostatic inkjet head that ejects ink droplets by applying an electrostatic force to the ink.
In the illustrated example, the ejection head 12 is a so-called line head having a row of ejection portions (so-called nozzle rows) corresponding to the entire area with respect to the width of the corresponding recording medium (size in a direction orthogonal to the scanning conveyance direction). Thus, the columns of the ejection units (row direction, which will be described later) are aligned with the width direction of the recording medium P, and are arranged in the conveyance direction (column direction, which will be described later) of the recording medium.
The ink jet recording apparatus of the present invention is not limited to the one using such a line head, and the recording head is intermittently transported, and the recording head is orthogonal to the transport direction in synchronization with the transport. It may be an ink jet recording apparatus that uses a so-called shuttle type recording head that scans in the direction of movement.

FIG. 3 shows a conceptual diagram of the ejection head 12. 3A is a partially sectional perspective view, and FIG. 3B is a sectional view.
In the recording apparatus 10, a recording image, that is, a supplied image is supplied while scanning and conveying the recording medium P charged to a negative high voltage (charging a bias voltage) in a direction perpendicular to the arrangement direction (row direction described later) of the ejection units. In accordance with the image data, each ejection unit of the ejection head 12 is modulated and driven to turn ejection on / off, thereby ejecting ink droplets R on demand and recording a target image on the recording medium P. .

  As described above, the ejection head 12 is a line head having a row of ejection openings corresponding to the width of the recording medium P. As shown conceptually in FIG. FIG. 3 shows only a part of the ejection unit in order to clearly show the structure.

The discharge head 12 is an electrostatic ink jet head that discharges ink droplets R by applying an electrostatic force to ink Q formed by dispersing color material particles (including color material and charged fine particles) in a carrier liquid. Thus, a head substrate 72, a discharge substrate 74, and an ink guide 76 are provided.
In the ejection head 12, the head substrate 72 and the ejection substrate 74 face each other and are spaced apart from each other by a predetermined distance, and an ink flow path 78 for supplying the ink Q to each ejection port 96 is formed therebetween. . The ink Q is circulated through a predetermined path including the ink flow path 78 by the ink circulation system. At the time of recording, the ink Q is circulated through the ink flow path 78 in a predetermined direction at a predetermined speed (for example, an ink flow of 200 mm / s), for example. , In the direction of the arrow in the figure.

The head substrate 72 is a sheet-like insulative substrate common to all ejection units, and a floating conductive plate 80 that is in an electrically floating state is provided on the surface thereof.
The floating conductive plate 80 generates an induced voltage that is induced in accordance with a drive voltage applied to a first control electrode 82 and a second control electrode 84 described later during image recording. In addition, the voltage value of the induced voltage automatically changes according to the number of operating channels. By this induced voltage, the color material particles contained in the ink Q in the ink flow path 78 are energized and migrate to the discharge substrate 74 side, that is, the concentration of the ink Q at the discharge port 96 described later is more preferably performed. Is called.

  The floating conductive plate 80 is not an essential component and is preferably provided as necessary. The floating conductive plate 80 may be disposed on the head substrate 72 side with respect to the ink flow path 78, and may be disposed, for example, inside the head substrate 72. The floating conductive plate 80 is preferably arranged on the upstream side of the ink flow path 78 from the position where the ejection unit is arranged. Further, a predetermined voltage may be applied to the floating conductive plate 80.

On the other hand, the ejection substrate 74 is a sheet-like insulating substrate that is common to all ejection sections, like the head substrate 72, and includes an insulating substrate 86, a first control electrode 82, a second control electrode 84, and a guard. An electrode 88 and insulating layers 90, 92, and 94 are provided. In addition, ink discharge ports 96 are opened through the discharge substrate 74 at positions corresponding to the respective ink guides 76, and the leading end portion 98 of the ink guide protrudes from the surface of the discharge substrate 74 to form the ink guide 76. Is inserted. As described above, the head substrate 72 and the discharge substrate 74 are arranged apart from each other, and the ink flow path 78 is formed therebetween.
In the ejection head 12, the first control electrode 82, the second control electrode 84, the ejection port 96, the ink guide 76, and the like that correspond to each other constitute one ink ejection unit.

The first control electrode 82 and the second control electrode 84 are circular electrodes provided in a ring shape on the surfaces of the upper surface and the lower surface of the insulating substrate 86 in the drawing so as to surround the periphery of the corresponding discharge ports 96, respectively. Yes (see FIG. 4 and FIG. 5). The surfaces of the insulating substrate 86 and the first control electrode 82 are coated with an insulating layer 92 that protects and planarizes the surface, and similarly, the surfaces of the insulating substrate 86 and the second control electrode 84 are covered with the insulating layer 92. An insulating layer 90 for planarizing the surface is covered. Further, a guard electrode 88 is formed on the insulating layer 92, and an insulating layer 94 for planarizing the surface is formed on the guard electrode 88 and the insulating layer 92.
Note that the first control electrode 82 and the second control electrode 84 are not limited to ring-shaped circular electrodes, and may be substantially circular electrodes, divided circular electrodes, parallel electrodes, for example, as long as the electrodes are disposed so as to face the ink guide 76. Any shape such as a substantially parallel electrode may be used.

  As shown in FIGS. 4 and 5, in the ejection head 12, each ejection unit including the ink guide 76, the first control electrode 82 and the second control electrode 84, the ejection port 96, and the like is two-dimensionally arranged in a matrix. Is arranged. Here, FIG. 4A is a plan view in the case of cutting along a plane parallel to the insulating substrate 86 including the guard electrode 88 in FIG. FIG. 4B is a plan view of FIG. 3A in which the first control electrode 82 is included and cut along a plane parallel to the insulating substrate 86. FIG. 4C is a plan view in the case of cutting along a plane parallel to the insulating substrate 86 including the second control electrode 84 in FIG.

Specifically, as shown in FIGS. 4B and 4C, the ejection head 12 is arranged in the column direction (scanning conveyance direction (FIG. 4)) in the row of ejection units arranged in the row direction (lateral direction in FIG. 4). 5 vertical directions)) and 3 rows (A row, B row, C row). Note that FIG. 4 shows a total of 15 discharge units arranged in a matrix of 5 (1 column, 2 columns, 3 columns, 4 columns, 5 columns) in the row direction.
The ejection head 12 is a line head, and has a row of ejection portions (nozzle row) corresponding to the entire size of the recording medium P in the row direction. Therefore, in the recording apparatus 10, the recording medium P is drawn by electrostatic ink jet while being scanned and conveyed in the column direction orthogonal to the row direction (arrangement direction of the discharge units (discharge ports 96) = nozzle column direction).
The ejection units in each row are arranged at a predetermined interval in the column direction. In addition, each row is arranged so that the ejection units are shifted from each other by 1/3 pitch in the row direction so that their ejection units are located between the ejection units of other rows (between the row directions).

As shown in FIG. 4A, the guard electrode 88 is a sheet-like electrode in which regions corresponding to the discharge port 96 and the control electrode open in a circular shape. That is, the guard electrode 88 is formed between the control electrodes.
As shown in FIG. 4B, the first control electrodes 82 of the ejection units arranged in the same column are connected to each other and arranged in the same row as shown in FIG. The second control electrodes 84 of the discharge unit are connected to each other.
Further, although not shown, the first control electrode 82 and the second control electrode 84 are each applied with a drive voltage (pulse voltage), and each electrode is modulated to drive ejection of the ink droplet R. It is connected to a pulse power supply for turning off.

At the time of image recording, the first control electrodes 82 arranged in the same column are simultaneously applied (on) with a driving voltage of the same voltage level. Similarly, the drive voltages are applied (on) to the second control electrodes 84 arranged in the same row simultaneously and at the same voltage level.
In addition, one row recorded on the recording medium P is divided into three groups corresponding to the number of rows of the second control electrodes 84 in the column direction, and each row of A row, B row, and C row It is recorded sequentially by dividing.
For example, in the example shown in FIG. 3, the A line, the B line, and the C line of the second control electrode 84 are sequentially turned on at a predetermined timing. Corresponding to this driving, the first control electrode 82 is modulated and driven (on / off) according to image data (recorded image), so that one line on the recording medium P is recorded by three times of time-divided recording. Is drawn. As described above, since the recording medium P is conveyed in the column direction, it is possible to perform drawing with a recording density three times the recording density (discharge portion density) of each row in the row direction (sub-scanning direction). .

  The control electrode is not limited to the two-layer electrode structure of the first control electrode 82 and the second control electrode 84, and may be a single-layer electrode structure or an electrode structure having three or more layers.

As described above, the guard electrode 88 has a ring-shaped portion corresponding to the first control electrode 82 and the second control electrode 84 formed around each discharge port 96 as shown in FIG. It is a sheet-like electrode common to all the discharge parts. That is, the guard electrode 88 is an electrode disposed between the control electrodes. The surfaces of the insulating layer 92 and the guard electrode 88 are covered with an insulating layer 94 that protects and flattens the surfaces.
A predetermined voltage is applied to the guard electrode 88 and plays a role of suppressing electric field interference generated between the ink guides 76 of the adjacent ejection portions.
The guard electrode 88 is not an essential component. Further, in order to shield the repulsive electric field from the first control electrode 82 or the second control electrode 84 toward the ink flow path 78, the discharge substrate 74 has a shield electrode on the ink flow path 78 side from the second control electrode 84. May be provided.

  The ink guide 76 is a ceramic flat plate having a convex end portion 98 having a predetermined thickness. In the illustrated example, the ink guides 76 of the ejection units in the same row are disposed at a predetermined interval on the same support disposed on the floating conductive plate 80 on the head substrate 72. The ink guide 76 passes through the ejection port 96 opened in the ejection substrate 74, and the tip end portion 98 is above the outermost surface of the ejection substrate 74 on the recording medium P side (the upper surface in the drawing of the insulating layer 94). It protrudes.

The leading end portion 98 of the ink guide 76 is formed in a substantially triangular shape (or trapezoidal shape) that gradually becomes thinner toward the holding means (not shown) of the recording medium P.
In addition, it is preferable that the tip portion 98 (the most advanced portion) is deposited with metal. Although metal deposition of the tip portion 98 is not an essential element, this has an effect that the dielectric constant of the tip portion 98 is substantially increased and a strong electric field can be easily generated.

  The shape of the ink guide 76 is not particularly limited as long as the colorant particles in the ink Q can be migrated toward the tip portion 98 (that is, the ink Q is concentrated). For example, the tip portion 98 is convex. You may change freely, such as not having to. Further, in order to promote the concentration of ink, a notch serving as an ink guide groove for collecting the ink Q in the tip end portion 98 by capillary action may be formed in the central portion of the ink guide 76 along the vertical direction in the drawing. .

  As described above, the second control electrode 84 is sequentially turned on (driven (high voltage level (for example, 400 to 600 V) or high impedance state)) one row at a time at a predetermined timing, and all the remaining second electrodes are driven. The control electrode 84 is turned off (non-driven (ground level (ground state)). Further, the first control electrode 82 is turned on (on a column basis) in accordance with image data (recorded image) in all the columns at the same time. By setting the high voltage level or the ground level, ink ejection / non-ejection (ink ejection on / off) in each ejection unit is controlled.

That is, when the second control electrode 84 is on and the first control electrode 82 is on, the ink Q is ejected (ejection on) as the ink droplet R, and the first control electrode 82 and the second control electrode 84 are When at least one is off, ink is not ejected (ejection off).
Then, the ink droplets R ejected from each ejection unit are attracted to the recording medium P charged with a negative bias voltage, and adhere to a predetermined position of the recording medium P to form an image.

  As described above, when the row of the second lower control electrode 84 is sequentially turned on and the upper first control electrode 82 is turned on / off according to the image data, the first control electrode 82 is turned on according to the image data. Therefore, the first control electrode 82 frequently changes to the high voltage level or the ground level at the discharge portions on both sides of each discharge portion in the column direction. In this case, by biasing the guard electrode 88 to a predetermined guard potential, for example, the ground level, at the time of image recording, it is possible to eliminate the influence of the electric field of the adjacent ejection unit.

  In the ejection head 12, whether the on / off control of ink ejection is performed by one or both of the first control electrode 82 and the second control electrode 84 is not limited. That is, ink is ejected when the difference between the voltage value at the time of ink on / off on the control electrode side and the voltage value on the recording medium P side is larger than a predetermined value, and ink is discharged when the difference is smaller than the predetermined value. What is necessary is just to set the voltage of the control electrode side and the recording medium P side suitably so that it may not discharge.

Accordingly, in the ejection head 12, the first control electrode 82 is sequentially turned on for each column and the second control electrode 84 is turned on in accordance with the image data. It is also possible to turn off / off.
In this case, the column direction is turned on for each column of the first control electrodes 82, and the first control electrodes 82 of the discharge units in the columns on both sides thereof are always at the ground level with the respective discharge units in the column direction as the center. The first control electrodes 26 of the ejection portions in the rows on both sides serve as the guard electrode 88. As described above, when each column is sequentially turned on by the upper first control electrode 82 and the lower second control electrode 84 is driven in accordance with the image data, the adjacent ejection can be performed without providing the guard electrode 88. It is possible to improve the recording quality by eliminating the influence of the part.

  In this embodiment, the color material particles in the ink Q are positively charged and the recording medium side is charged to a negative high voltage. However, the present invention is not limited to this, and conversely, the color material particles in the ink are negatively charged. The recording medium P side may be charged to a positive high voltage. As described above, when the polarity of the color material particles is reversed from that of the present embodiment, the applied voltage to the counter electrode, the charging unit of the recording medium P, and the first control electrode 82 and the second control electrode 84 of each discharge unit. What is necessary is just to make polarity etc. reverse to said example.

In the electrostatic ink jet using the ink Q containing the colorant particles as described above, the force is applied to the entire ink to cause the ink to fly toward the recording medium as in the conventional ink jet system. Instead, a force is applied to the colorant particles, which are solid components dispersed in the carrier liquid, to cause the ink to fly. Hereinafter, the operation of discharging the ink droplet R in the discharge head 12 will be described.
In the following example, the color material particles are positively charged. Therefore, when ejection is on, a positive drive voltage is applied to the first control electrode 82 and the second control electrode 84, and the recording medium P has A negative high voltage (bias voltage) is charged.

At the time of image recording, the ink Q is circulated by the above-described ink circulation system and the ink circulation system, and flows in the ink flow path 78 from the right side to the left side (in the direction of the arrow in FIG. 3B) at a predetermined speed.
Further, as described above, the recording medium P is charged to a negative high voltage, and is scanned and conveyed facing the ejection head 12.
The negative high voltage charged on the recording medium P acts as a bias voltage in electrostatic ink jet, and the charged recording medium P having this bias voltage acts as a counter electrode for the control electrode of the ejection head 12. This is as described above.

  When the recording medium P is transported to a predetermined position, a drive signal is supplied to the ejection head 12 according to the transport timing of the recording medium P and the image data, and each ejection head 12 responds accordingly to each row. The second control electrodes 84 are sequentially driven, the first control electrodes 82 in each column are modulated and driven according to the image data, and the ink ejection is modulated and turned on / off according to the image data.

Here, when at least one of the first control electrode 82 and the second control electrode 84 is off, that is, in a state where only the bias voltage is applied, the ink Q has the bias voltage and the color material particles (charge) of the ink Q. Particle) and the Coulomb repulsive force between the coloring material particles, the coulomb repulsive force between the coloring material particles, the viscosity of the carrier liquid, the surface tension, the dielectric polarization force, etc., which are coupled to move the coloring material particles and the carrier liquid. As conceptually shown in FIG. 3 (B), a meniscus shape slightly raised from the discharge port 96 is balanced.
In addition, the colorant particles move toward the recording medium P charged with a bias voltage by so-called electrophoresis due to the Coulomb attractive force or the like. That is, the ink Q is concentrated in the meniscus of the discharge port 96.

  From this state, a driving voltage (pulse voltage) for ejecting the ink droplet R is applied. That is, in the illustrated example, when both the first control electrode 82 and the second control electrode 84 are turned on, the drive voltage is superimposed on the bias voltage, and the previous coupling is further performed by the superposition of the drive voltage. The formed movement occurs, the colorant particles and the carrier liquid are pulled by the electrostatic force to the bias voltage (counter electrode) side, that is, the recording medium P side, the meniscus grows, and a so-called conical ink liquid column is so-called from the upper part. A tailor cone is formed. Similarly to the above, the color material particles are moved to the meniscus by electrophoresis, and the ink Q of the meniscus is concentrated and is in a substantially uniform high density state having a large number of color material particles.

  When a finite time has passed after the start of the application of the drive voltage, the balance between the color material particles and the surface tension of the carrier liquid mainly breaks at the tip of the meniscus with high electric field strength due to the movement of the color material particles, The meniscus grows abruptly to form an elongated ink liquid column having a diameter of about several to several tens of μm, which is called a kite string.

Further, when a finite time elapses, the silk thread grows, and the growth of the silk thread, vibration caused by Rayleigh / Weber instability, uneven distribution of colorant particles in the meniscus, uneven distribution of electrostatic field on the meniscus, etc. As a result of this interaction, the kite string is divided, ejected / flyed as ink droplets R, and pulled by the bias voltage to land on the recording medium P.
The growth and splitting of the kite string, and further the movement of the color material particles to the meniscus (punch kite) occur continuously during the application of the drive voltage. When the application of the drive voltage is finished (at least one of the first control electrode 82 and the second control electrode 84 is turned off), the state returns to the meniscus state in FIG. 3B where only the bias voltage is applied.
One dot of ink on the recording medium P is usually obtained by applying the drive voltage once (one pulse). Therefore, one dot is separated from the string by applying the drive voltage once. Formed by a plurality of ink droplets R ejected in this manner.

Here, the ink used for the recording apparatus 10 of the present invention will be described.
Ink Q is obtained by dispersing colorant particles in a carrier liquid. The carrier liquid is preferably a dielectric liquid (nonaqueous solvent) having a high electric resistivity (10 ⁹ Ω · cm or more, preferably 10 ¹⁰ Ω · cm or more). If the electric resistance of the carrier liquid is low, the carrier liquid itself is charged by charge injection due to the drive voltage applied to the control electrode, and the colorant particles do not concentrate. In addition, a carrier liquid having a low electrical resistance is not suitable because there is a concern of causing electrical conduction between adjacent control electrodes.

The relative dielectric constant of the dielectric liquid used as the carrier liquid is preferably 5 or less, more preferably 4 or less, and still more preferably 3.5 or less. By setting the relative dielectric constant in such a range, an electric field effectively acts on the colorant particles in the carrier liquid, and migration easily occurs.
The upper limit value of the specific electric resistance of such a carrier liquid is preferably about 10 ¹⁶ Ωcm, and the lower limit value of the relative dielectric constant is preferably about 1.9. The reason why it is desirable that the electric resistance of the carrier liquid is in the above range is that if the electric resistance is low, ink ejection under a low electric field is deteriorated, and the reason why the relative dielectric constant is preferably in the above range is the reason. This is because, when the dielectric constant increases, the electric field is relaxed by the polarization of the solvent, and the color of the dots formed thereby becomes thin or causes blurring.

  The dielectric liquid used as the carrier liquid is preferably a linear or branched aliphatic hydrocarbon, alicyclic hydrocarbon, or aromatic hydrocarbon, and halogen-substituted products of these hydrocarbons. For example, hexane, heptane, octane, isooctane, decane, isodecane, decalin, nonane, dodecane, isododecane, cyclohexane, cyclooctane, cyclodecane, benzene, toluene, xylene, mesitylene, Isopar C, Isopar E, Isopar G, Isopar H, Isopar L, Isopar M (isopar: trade name of Exxon), Shellsol 70, Shellsol 71 (shellsol: trade name of Shell Oil), Amsco OMS, Amsco 460 Solvent (trade name of Amsco: Spirits), Silicone oil (for example, KF-96L manufactured by Shin-Etsu Silicone) or the like can be used alone or in combination.

  The colorant particles dispersed in such a carrier liquid may be dispersed in the carrier liquid as the colorant itself as colorant particles, but preferably contain dispersed resin particles for improving fixability. When the dispersed resin particles are included, the pigment is generally coated with the resin material of the dispersed resin particles to form resin-coated particles, and the dye is colored with the dispersed resin particles to form colored particles. Is common.

As the coloring material, any of conventional pigments and dyes used in a flow channel kujet ink composition, a printing (oil-based) ink composition, or an electrophotographic liquid developer can be used.
As the pigment used as the color material, regardless of inorganic pigments or organic pigments, those generally used in the technical field of printing can be used. Specifically, for example, carbon black, cadmium red, molybdenum red, chrome yellow, cadmium yellow, titanium yellow, chromium oxide, viridian, cobalt green, ultramarine blue, Prussian blue, cobalt blue, azo pigment, phthalocyanine pigment Conventionally known pigments such as quinacridone pigments, isoindolinone pigments, dioxazine pigments, selenium pigments, perylene pigments, perinone pigments, thioindigo pigments, quinophthalone pigments, metal complex pigments, and the like are not particularly limited. Can be used.
As dyes used as coloring materials, azo dyes, metal complex dyes, naphthol dyes, anthraquinone dyes, indigo dyes, carbonium dyes, quinoneimine dyes, xanthene dyes, aniline dyes, quinoline dyes, nitro dyes, nitroso dyes, benzoquinone dyes, naphthoquinone dyes And oil-soluble dyes such as phthalocyanine dyes and metal phthalocyanine dyes.

Further, as dispersed resin particles, for example, rosins, rosin-modified phenol resins, alkyd resins, (meth) acrylic polymers, polyurethane, polyester, polyamide, polyethylene, polybutadiene, polystyrene, polyvinyl acetate, polyvinyl alcohol, polyvinyl alcohol, acetal-modified Products, polycarbonate and the like.
Among these, from the viewpoint of ease of particle formation, the weight average molecular weight is in the range of 2,000 to 1,000,000 and the polydispersity (weight average molecular weight / number average molecular weight) is 1.0 to 5 Polymers in the range of 0.0 are preferred. Furthermore, from the viewpoint of ease of fixing, a polymer having any one of a softening point, a glass transition point, and a melting point within a range of 40 ° C. to 120 ° C. is preferable.

  In the ink Q, the content of the color material particles (the total content of the color material particles or further dispersed resin particles) is preferably contained in the range of 0.5 to 30% by weight with respect to the whole ink, and more preferably. Is preferably contained in the range of 1.5 to 25% by weight, more preferably 3 to 20% by weight. If the content of the colorant particles is reduced, problems such as insufficient printed image density or difficulty in obtaining a strong image due to difficulty in obtaining the affinity between the ink Q and the surface of the recording medium P are likely to occur. On the other hand, when the content is increased, it becomes difficult to obtain a uniform dispersion liquid, or the ink Q is easily clogged with an inkjet head or the like, and it is difficult to obtain stable ink discharge. is there.

  The average particle diameter of the colorant particles dispersed in the carrier liquid is preferably 0.1 to 5 μm, more preferably 0.2 to 1.5 μm, and still more preferably 0.4 to 1.0 μm. . This particle size is determined by CAPA-500 (trade name, manufactured by Horiba, Ltd.).

After the colorant particles are dispersed in the carrier liquid (a dispersant may be used if necessary), the chargeant is added to the carrier liquid to charge the colorant particles, and the charged colorant The ink Q is obtained by dispersing particles in a carrier liquid. When dispersing the colorant particles, a dispersion medium may be added as necessary.
As an example of the charge control agent, various materials used in electrophotographic liquid developers can be used. Also, “Recent development and commercialization of electrophotographic development systems and toner materials”, pages 139 to 148, “The Basics and Applications of Electrophotographic Technology” edited by Electrophotographic Society, pages 497 to 505 (Corona Inc., published in 1988), Yuji Harasaki Various charge control agents described in “Electrophotography” 16 (No. 2), p. 44 (1977) can also be used.

The color material particles may be positively charged or negatively charged as long as they have the same polarity as the drive voltage applied to the control electrode.
The charge amount of the color material particles is preferably in the range of 5 to 200 μC / g, more preferably 10 to 150 μC / g, and still more preferably 15 to 100 μC / g.

In addition, since the electric resistance of the dielectric solvent may change due to the addition of the charge control agent, the distribution ratio P defined below is preferably 50% or more, more preferably 60% or more, and even more preferably 70% or more. And
P = 100 × (σ1−σ2) / σ1
Here, σ1 is the electrical conductivity of the ink Q, and σ2 is the electrical conductivity of the supernatant obtained by applying the ink Q to the centrifuge. The electrical conductivity was measured using an LCR meter (AG-4311 manufactured by Ando Electric Co., Ltd.) and an electrode for liquid (LP-05 type manufactured by Kawaguchi Electric Manufacturing Co., Ltd.) under the conditions of an applied voltage of 5 V and a frequency of 1 kHz. This is the measured value. Centrifugation was performed for 30 minutes using a small high-speed cooling centrifuge (Tomy Seiko Co., Ltd. SRX-201) under conditions of a rotational speed of 14500 rpm and a temperature of 23 ° C.
By using the ink Q as described above, migration of charged particles is likely to occur, and concentration is facilitated.

The electrical conductivity of the ink Q is preferably 100 to 3000 pS / cm, more preferably 150 to 2500 pS / cm, and still more preferably 200 to 2000 pS / cm. By setting the electric conductivity in the above range, the voltage applied to the control electrode does not become extremely high, and there is no fear of causing electrical continuity between adjacent recording electrodes.
The surface tension of the ink Q is preferably in the range of 15 to 50 mN / m, more preferably 15.5 to 45 mN / m, and still more preferably 16 to 40 mN / m. By setting the surface tension within this range, the voltage applied to the control electrode does not become extremely high, and the ink does not leak around the head to be contaminated.
Furthermore, the viscosity of the ink Q is preferably 0.5 to 5 mPa · sec, more preferably 0.6 to 3.0 mPa · sec, and still more preferably 0.7 to 2.0 mPa · sec.

As an example, such an ink Q can be prepared by dispersing color material particles in a carrier liquid to form particles, and adding a charge adjusting agent to the dispersion medium to cause the color material particles to be charged. Specific methods include the following methods.
(1) A method in which a color material or further dispersed resin particles are mixed (kneaded) in advance, and then dispersed in a carrier liquid using a dispersant as required, and a charge adjusting agent is added.
(2) A method in which a coloring material, or further dispersed resin particles and a dispersing agent are simultaneously added to a carrier liquid, dispersed, and a charge adjusting agent is added.
(3) A method in which a coloring material and a charge adjusting agent, or further dispersed resin particles and a dispersing agent are simultaneously added to a carrier liquid and dispersed.

  The inkjet recording apparatus of the present invention has been described in detail above. However, the present invention is not limited to the above-described embodiment, and various improvements and modifications may be made without departing from the gist of the present invention. Of course.

  For example, in the above example, the ink jet recording apparatus of the present invention is used for a concentration type electrostatic ink jet recording apparatus that uses ink in which color material particles (charged particles including a color material) are dispersed in a carrier liquid. However, the present invention is not limited to this, and can be suitably used for a non-concentrated electrostatic ink jet recording apparatus that does not use ink containing charged particles.

It is the schematic of the example of 1 structure of the inkjet recording device of this invention. It is another example of a structure of the inkjet recording device of this invention. 2A and 2B are conceptual diagrams of an ejection head of the ink jet recording apparatus illustrated in FIG. 1, in which FIG. (A), (B) and (C) are schematic diagrams for explaining the ejection head shown in FIG. It is a schematic perspective view for demonstrating the discharge head shown in FIG. It is a schematic block diagram of the conventional inkjet recording device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 (Inkjet) recording apparatus 12 Discharge head 12a Ink inlet 12b Ink outlet 14 Main tank 16 Supply sub tank 18 Recovery sub tank 20 Ink circulation system 22 Replenisher tank 24 Ink circulation pump 26 Concentration sensor 28, 29 Filters 32, 34, 36 , 46 Ink supply flow path 38, 42, 44 Ink recovery flow path 48 Switching valve 50 Communication pipe 62, 64 Overflow pipe 72 Head substrate 74 Discharge substrate 76 Ink guide 78 Ink flow path 80 Floating conductive plate 82 First control electrode 84 First control electrode 84 2 Control electrode 86 Insulating substrate 88 Guard electrode 90, 92, 94 Insulating layer 96 Discharge port 98 End portion 114 Ink collection container 116 Ink flow rate adjustment chamber 120 Ink circulation device 122 Ink tanks for replenishment 123a, 123b, 123c, 123 d, 129, 131 Piping 125 Filter 126a, 126b Solenoid valve 124, 128 Pump

Claims (10)

An inkjet recording apparatus having an ejection head for ejecting ink,
A main tank in which the ink is stored, a supply subtank for supplying ink to the ejection head in a static pressure manner, and a space formed above the ink liquid level of the main tank and the supply subtank communicate with each other. An ink circulation system that circulates ink between the main tank, the supply sub-tank, and the ejection head.
The inside of the ink circulation system is formed so as to be sealed from the atmosphere,
An ink jet recording apparatus comprising: a pressure adjusting body that adjusts an internal pressure of the ink circulation system when the inside of the ink circulation system is sealed in at least a part of the ink circulation system.   The inkjet head recording apparatus according to claim 1, wherein the pressure adjusting body adjusts an internal pressure of the ink circulation system to be equal to an atmospheric pressure.   The ink jet recording apparatus according to claim 1, wherein the pressure adjusting body includes a flexible member that absorbs fluctuations in internal pressure of the ink circulation system.   The inkjet recording apparatus according to claim 1, wherein the pressure adjusting body is provided in at least one of the main tank, the supply sub tank, and the communication pipe.   The supply sub-tank is arranged at a position higher than the discharge head in the vertical direction, and supplies ink to the discharge head while keeping the pressure head constant by overflow. The ink jet recording apparatus according to one item.   The ink circulation system further includes a replenishing liquid tank for replenishing the main tank with ink, and a space formed above the liquid surface of the ink replenished in the replenishing liquid tank is connected to the communication pipe. The ink jet recording apparatus according to claim 1, wherein the ink jet recording apparatus is provided.   The inkjet recording apparatus according to claim 6, wherein at least the pressure adjusting body is provided in the replenisher tank. The ink circulation system further includes a collection subtank for collecting and storing ink that does not contribute to ejection from the ejection head;
The recovery ink tank is disposed at a position lower than the ejection head in the vertical direction, and collects ink from the ejection head while keeping the pressure head constant by overflow,
The ink jet recording apparatus according to claim 1, wherein the communication pipe is connected to a space above a liquid level of ink stored in the recovery sub tank.   The ink jet recording apparatus according to claim 8, wherein at least the recovery sub tank includes the pressure adjusting body. The ink is an ink obtained by dispersing charged fine particles containing at least a coloring material in an insulating dispersion medium,
The inkjet recording apparatus according to claim 1, wherein the ejection head is an electrostatic inkjet head that ejects the ink using electrostatic force.

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