JP2005193595A - Inkjet head and inkjet recording apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inkjet head and an inkjet recording apparatus which can stably form dots of a desired size to a recording medium even at high-speed drawing, by improving the ink feedability to ink discharge openings. <P>SOLUTION: Discharge electrodes 18 are formed to inner walls of channel separation walls 17 which constitute a passage 30, and to a region held between the channel separation walls of a head substrate upper face. When a predetermined voltage is impressed to the discharge electrodes 18, electrostatic force acts to color material particles present in the ink passage below the discharge openings 28, and the color material particles are halted and held at the position. Since the discharge electrodes 18 do not exist at a discharge opening substrate 16, generation of a repulsive electric field which obstructs movement of the color material particles to the discharge openings 28 is prevented, and the discharge opening substrate 16 can be thinned more. Accordingly, the color material particles quickly move to the discharge openings 28, and the feedability of the color material particles is improved. Dots of the desired size can be stably formed to the recording medium even if liquid droplets are continuously discharged at a high speed. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an inkjet head that ejects ink to fly toward a recording medium, and an inkjet recording apparatus that records an image corresponding to image data on the recording medium using the inkjet head.

  The ink jet recording apparatus ejects ink from an ejection port and records an image corresponding to image data on a recording medium. As an ink jet recording apparatus, an electrostatic type, a thermal type, a piezo type or the like is known according to a difference in ink ejection control means.

  Among these ink jet recording apparatuses, the electrostatic ink jet recording apparatus uses ink containing charged color material particles (colored charged particles) and applies a predetermined voltage to each ejection portion of the ink jet head in accordance with image data. As a result, an electrostatic force is generated in the ejection unit, the ejection of ink is controlled using this electrostatic force, and an image corresponding to the image data is recorded on the recording medium. As such an electrostatic ink jet recording apparatus, for example, an ink jet recording apparatus disclosed in Patent Document 1 is known.

  FIG. 6 shows a schematic configuration diagram of an example of an ink jet head of the electrostatic ink jet recording apparatus disclosed in Patent Document 1. The inkjet head 50 shown in the figure conceptually represents only one ejection part of the inkjet head disclosed in Patent Document 1, and includes a head substrate 51, an ink guide 52, an ejection port substrate (insulating substrate). ) 53, a discharge electrode (control electrode) 54, a counter electrode 55, a DC bias voltage source 58, and a pulse voltage source 59.

JP 10-138493 A

  In the conventional electrostatic ink jet head as shown in Patent Document 1, since the discharge electrode 54 is provided on the discharge port substrate 53, when a driving voltage is applied to the discharge electrode 54, not only from the upper surface of the discharge electrode 54. The electric field Ed is also generated from the lower surface of the ejection electrode 54. That is, the electric field Ed in the direction from the ejection electrode 54 toward the head substrate surface 51 acts on the ink Q circulating in the flow path 57. An electric field Ed (hereinafter referred to as a repulsive electric field) generated in the direction from the lower surface of the ejection electrode 54 toward the head substrate 51 causes the colorant particles contained in the ink Q circulating in the main flow path 98 to the ejection port (through hole) 56. For this reason, when the inkjet head 50 is driven and a drive voltage is applied to the discharge electrode 54, the colorant particles are prevented from concentrating at the discharge port 56, and the discharge port 56 is colored. A certain amount of time is required until the material particles are sufficiently concentrated. For this reason, when drawing is performed at high speed using such an ink jet head, a desired recording medium is obtained due to the inhibition of the colorant particle supply to the ejection port due to the repulsive electric field from the ejection electrode provided on the head substrate. There is a problem that it is impossible to stably form dots having a size of. Furthermore, as the number of channels increases, there is a problem in that the discharge ports are accumulated at a high density, thereby causing fluid interference with adjacent channels and making the dot diameter formed on the recording medium unstable.

  Further, in the electrostatic ink jet head, when a multi-channel head is configured by arranging a plurality of ejection openings in a matrix, it is gradually difficult to connect signal wirings to ejection electrodes of each ejection section. For this reason, when the number of channels is large, it is conceivable to form a multilayer wiring structure for the discharge port substrate and connect the signal wiring to the discharge electrode. When the number of channels is further increased in the future, It is necessary to increase the thickness further. However, as the discharge port substrate becomes thicker, its length becomes longer than the opening diameter of the discharge port, so that the resistance between the ink and the inner wall of the discharge port increases, and it becomes difficult for ink to be discharged from the discharge port. . In addition, when the discharge port substrate becomes thick, depending on the speed of the ink flow, the ink flowing on the lower surface of the discharge port substrate may stay in the discharge port, thereby supplying the ink to the tip portion of the ink guide. It becomes difficult. As a result, there is a problem that the responsiveness to the discharge frequency is deteriorated and the dot diameter is gradually reduced as the drawing frequency is increased.

  In addition to the electrostatic type, when the discharge port substrate becomes thick, that is, when the length of the discharge port becomes long, the same problem occurs in an ink jet recording apparatus using various types of ink jet heads. .

  The present invention has been made to solve the above-described problems, and an object of the present invention is to improve the ink supply performance to the ejection port, and even if ink droplets are ejected continuously at high speed, It is an object of the present invention to provide an ink jet head and an ink jet recording apparatus capable of stably forming dots having a size of 1 on a recording medium.

  In order to solve the above-described problems, a first aspect of the present invention is an ink jet head that ejects ink as ink droplets from an ink flow path through an ejection port using electrostatic force and flies toward a recording medium. And an ejection electrode that controls ejection of the ink, an ejection port that is connected to the ejection port, stores the ink, and partitions the ink storage unit into a plurality of ink paths, and each of the inks An inkjet head comprising a separation wall arranged to connect a plurality of the discharge ports to a path.

  In the ink jet head according to the first aspect of the present invention, it is preferable that a plurality of the separation walls are provided, and the plurality of separation walls are arranged at positions facing each other.

  The ink jet head according to the first aspect of the present invention may further include a discharge port substrate having the discharge port, a predetermined distance from the discharge port substrate, and the ink between the discharge port substrate. It is preferable to include a head substrate that forms a flow path. In this case, the separation wall is preferably provided on at least one of the discharge port substrate and the head substrate, and the separation wall is formed substantially perpendicular to the surface of the head substrate. preferable. The ejection electrode is preferably provided on at least one of a surface of the head substrate facing the ejection port substrate (a surface of the head substrate) and the separation wall, and the surface of the head substrate and It is preferable to be provided on both side walls of the separation wall.

  In order to solve the above-described problem, a second aspect of the present invention is an inkjet head that ejects ink as ink droplets using electrostatic force and flies toward a recording medium. A head substrate formed in parallel with the side of the head substrate on which the groove is formed is arranged, and a plurality of ejection openings for ejecting the ink droplets are connected to the groove of the head substrate. An ink jet head is provided that includes the discharge port substrate thus opened and a discharge electrode for controlling the discharge of the ink from the discharge port.

  In the ink jet head according to the second aspect of the present invention, it is preferable that the discharge electrode is provided on at least one of a side wall and a bottom surface of the groove of the head substrate at a position corresponding to the discharge port.

  In the ink jet head according to the first and second aspects of the present invention, it is preferable that a guard electrode for shielding an electric field generated from the ejection electrode is further provided at a position closer to the recording medium than the ejection electrode.

  The inkjet head according to the first and second aspects of the present invention further includes a wiring connected to the ejection electrode, and the wiring is on the opposite side of the head substrate to the side facing the ejection port substrate. It is preferably formed on the surface.

  In order to solve the above problems, a third aspect of the present invention provides an ink jet recording apparatus including the ink jet head according to the first or second aspect of the present invention.

  In the ink jet head according to the first aspect of the present invention, an ink storing portion that stores ink is separated by a separation wall and divided into a plurality of ink paths, and an ejection port is connected to each ink path. Therefore, even if the discharge ports are densely integrated with an increase in the number of channels, dots having a stable size can be drawn on the recording medium.

  In the ink jet head according to the first aspect of the present invention, when the discharge port substrate and the head substrate are provided, the discharge electrode for controlling the discharge of the ink is provided on the separation wall and the surface of the head substrate (on the discharge port substrate). Therefore, it is not necessary to provide a discharge electrode on the discharge port substrate. As a result, the discharge port substrate can be made thinner than the conventional one, and the length of the discharge port can be reduced. (Depth) can be made shorter (shallow) than in the past. For this reason, resistance acting between the ink and the inner wall of the ejection port is also reduced, and ink can be ejected quickly from the ejection port. Further, the ink is prevented from staying in the discharge port due to the flow rate of the ink circulating under the discharge port.

  Further, by providing the discharge electrode on at least one of the separation wall and the surface of the head substrate (the surface on the side facing the discharge port substrate), the ink flow from the discharge port substrate, which inhibits the supply of the color material particles to the discharge port, is prevented. A repulsive electric field in the direction toward the inside of the path is not generated, and the colorant particles in the ink can be quickly supplied to the ejection port. Therefore, the response of the ejection frequency during image recording is improved, and even if dots are drawn continuously at high speed, the dot diameter can be prevented from becoming smaller, so that dots of a desired size can be drawn stably. can do.

  The ink jet head according to the first aspect of the present invention causes the colorant particles in the ink flow path to be below the discharge port by the electrostatic force generated from the discharge electrode formed on at least one of the separation wall and the head substrate surface. Since the ink can be stopped, the concentrated ink can be quickly supplied to the ejection port. In particular, the discharge electrode is formed on both the separation wall and the upper surface of the head substrate sandwiched between the discharge electrodes formed on the separation wall, and an electric field is generated from these discharge electrodes, so that it is fixed below the discharge port. Since the obtained color material particles can be moved to the discharge port more rapidly, the supply property of the color material particles can be further improved.

  The ink jet head according to the second aspect of the present invention uses a plurality of grooves formed on the head substrate as ink flow dew, and suppresses fluid interference with adjacent channels by connecting discharge ports to each ink flow path. Alternatively, even if the discharge ports are densely integrated with an increase in the number of channels, dots having a stable size can be drawn on the recording medium.

  Further, in the ink jet head according to the second aspect of the present invention, the discharge electrode can be formed on at least one of the side wall and the bottom surface of the groove of the head substrate. Since the color material particles can be kept below the discharge port, the concentrated ink can be quickly supplied to the discharge port. In particular, the discharge electrode is formed on both the side wall and the bottom surface of the groove of the head substrate, and an electric field is generated from the discharge electrode, so that the colorant particles held below the discharge port can be made to the discharge port more quickly. Since it can be moved, the supply property of a color material particle further improves.

  In the ink jet head according to the first and second aspects of the present invention, the signal wiring connected to the ejection electrode can be formed on the back surface of the head substrate (the surface opposite to the surface facing the ejection port substrate). When a multi-channel head is configured by arranging a plurality of ejection portions in a matrix, signal wiring connected to ejection electrodes of each ejection portion can be formed in a multilayer structure on the back surface of the head substrate. A multi-channel head can be realized with the outlet substrate kept thin.

  Since the ink jet recording apparatus of the present invention includes the ink jet heads of the first and second aspects of the present invention, dots of a desired size can be stably formed at high speed on a recording medium, and a high quality image can be obtained. Can be drawn at high speed.

  Hereinafter, an ink jet head and an ink jet recording apparatus of the present invention will be described in detail based on preferred embodiments shown in the accompanying drawings.

  FIG. 1A is a schematic cross-sectional view showing a schematic configuration of an example of the ink jet head of the present invention, and FIG. 1B is a diagram in which the ejection port substrate of the ink jet head shown in FIG. 1A is removed. The schematic plan view when the state of the case is viewed from above is shown. FIG. 2 is a perspective view showing a schematic configuration of an example of the ink jet head of the present invention. 3A shows a partial schematic plan view of the inkjet head of the present invention as viewed from the discharge substrate side, and FIG. 3B further shows a state when the discharge port substrate is removed. A schematic plan view is shown.

  As shown in FIGS. 1A and 2, the electrostatic inkjet head 10 of the present invention mainly includes a head substrate 12, an ink guide 14, and an ejection port substrate 16 having ejection ports 28. In addition, a counter electrode 24 that supports the recording medium P and a charging unit 26 of the recording medium P are disposed so as to face a surface (upper surface in the drawing) of the ink jet head 10.

As shown in FIG. 3, the inkjet head 10 has a multi-channel structure in which each discharge portion (nozzle (discharge port 28)) is two-dimensionally arranged in order to perform higher density image recording at high speed. However, in FIG. 1, only one ejection part is shown in order to clearly show the configuration.
In the inkjet head 10 of the present invention, the number of discharge electrodes, the physical arrangement, and the like can be freely selected. For example, not only a multi-channel structure as shown in FIG. 3 but also a single discharge section may be provided. Further, a so-called (full) line head having a row of ejection units corresponding to the entire area of the recording medium P may be used, or a so-called serial head (shuttle type) that is scanned in a direction orthogonal to the direction of the nozzle row. Good. The ink jet head of the present invention can be used for both monochrome and color recording apparatuses.

  Such an ink jet head 10 includes an ink Q formed by dispersing fine particles (hereinafter referred to as color material particles) containing a color material component such as a pigment in an insulating liquid (carrier liquid). The ink is ejected by electrostatic force, and the ink droplet is modulated and ejected according to the image data by turning on / off the driving voltage applied to the ejection electrode 18 according to the image data (ejection on / off). Then, an image is recorded on the recording medium P.

  As shown in FIG. 1A, the head substrate 12 and the discharge port substrate 16 are arranged in a state of facing each other with a predetermined distance therebetween. The space formed by the head substrate 12 and the discharge port substrate 16 functions as an ink storage unit for storing ink. A plurality of separation walls (hereinafter referred to as channel separation walls) 17 are formed between the head substrate 12 and the discharge port substrate 16 so as to be in contact therewith, and the respective channel separation walls 17 are arranged in parallel to each other. Yes. That is, the channel separation wall 17 divides the ink storage section into a plurality of ink paths. The channel separation wall 17, the head substrate 12, and the discharge port substrate 16 form a main flow path (ink path) 30 for supplying ink to each discharge port 28. As shown in FIGS. 3A and 3B, the channel separation wall 17 includes at least two discharge ports 28 in which the main flow paths 30 defined by the channel separation wall 17 are formed in the discharge port substrate 16. Is arranged to connect with. That is, the channel separation wall 17 is arranged so that a plurality of discharge ports 28 arranged in a certain direction are connected to one main flow path 30. An ink channel is formed by the main channel 30 and the ejection port 28 (up to the opening end on the ejection side). The main channel 30 is an ink reservoir (ink) for supplying ink Q to the ejection port 28 (ink guide 14). Function as a room).

The channel separation wall 17 may be configured integrally with the head substrate 12 or the discharge port substrate 16 or may be configured independently of them. For example, when it is configured integrally with the head substrate 12, a plurality of grooves parallel to the head substrate 12 having a predetermined thickness may be formed, and a wall that partitions adjacent grooves may be used as the channel separation wall 17. That is, a head substrate in which a plurality of grooves are formed in parallel is manufactured, and the discharge port substrate is disposed facing the side of the head substrate where the grooves are formed, so that the structure as shown in FIG. May be. In this case, the groove of the head substrate is formed so that a plurality of discharge ports formed in the discharge port substrate are connected to each groove of the head substrate. An independent main flow path is formed by the groove formed on the head substrate and the discharge port substrate. Thus, the inkjet head of the present invention may be configured to include a head substrate and an ejection port substrate in which a plurality of grooves are formed.
The ink Q in the main flow path 30 is printed at a predetermined speed (for example, in the illustrated example, from the right to the left in the figure in the main flow path 30) by an ink circulation mechanism (not shown) during image recording. The ink is circulated at an ink flow of 200 mm / s.
In the illustrated example, the channel separation wall 17 is configured to be in contact with both the lower surface of the discharge port substrate 16 and the upper surface of the head substrate 12. However, the channel separation wall 17 is provided on either the upper surface of the discharge port substrate 16 or the lower surface of the head substrate 12. You may comprise so that it may touch only.

The discharge port substrate 16 includes an insulating substrate 32, a guard electrode 20, and an insulating layer 34, as shown in FIG. A guard electrode 20 and an insulating layer 34 are sequentially stacked on the upper surface of the insulating substrate 32 in the drawing (the surface opposite to the side facing the head substrate 12).
Further, the discharge port substrate 16 is formed with a discharge port 28 for discharging the ink droplet R penetrating the insulating substrate 32. The ink guides 14 are inserted into the respective ejection ports 28 of the ejection port substrate 16 with their tips protruding upward. In the discharge port substrate 16 having such a structure, for example, the guard electrode 20 is formed on the upper surface of the insulating substrate 32 made of an insulating material, and the upper surface of the guard electrode 20 and a part of the upper surface of the insulating substrate 32 are covered. The insulating layer 34 is formed on the surface, and the discharge port 28 is formed by a laser processing machine or the like.
As shown in FIGS. 1 and 2, the inkjet head 10 of the present invention does not have the discharge electrode 18 provided on the discharge port substrate 16, so that the insulating substrate 32 constituting the discharge port substrate 16 is conventionally used. Also, a thin insulating substrate can be used. For this reason, since the length (depth) of the ejection port 28 can be made shorter than before, the resistance acting between the ink present in the ejection port 28 and the inner wall of the ejection port 28 is reduced. Thus, it is possible to quickly eject ink from the ejection port 28. Further, the ink is prevented from staying in the ejection port 28 due to the flow velocity of the ink flowing below the ejection port 28.

  The ink guide 14 of the illustrated ink jet head 10 is made of a ceramic flat plate having a predetermined thickness having a protruding tip portion 14a, and is disposed on the head substrate 12 corresponding to each discharge port 28 (discharge portion). . Further, the ink guide 14 passes through the ejection port 28, and the tip end portion 14 a of the surface on the recording medium P side of the ejection port substrate 16 (the upper surface in the drawing of the insulating layer 34 (hereinafter, this side is referred to for convenience) The upper part protrudes upward from the other side)).

In the illustrated example, the end portion 14a side of the ink guide 14 is formed into a substantially triangular shape (or trapezoid) that gradually becomes thinner toward the counter electrode 24 side. The shape of the ink guide 14 is not particularly limited as long as the ink Q, in particular, the charged fine particle component in the ink Q can be concentrated through the discharge port 28 of the discharge port substrate 16 to the tip portion 14a. For example, the tip portion 14a may be changed as appropriate, such as not having a protrusion, or may have a conventionally known shape. For example, a cutout serving as an ink guide groove for collecting the ink Q in the front end portion 14a may be formed in the center portion of the ink guide 14 in the vertical direction in the drawing by capillary action.
Here, it is preferable that the metal is deposited on the most distal portion of the ink guide 14. By depositing metal on the most distal portion, the dielectric constant of the tip portion 14 a of the ink guide 14 is substantially increased, It becomes easy to generate a strong electric field, and ink ejection properties can be improved.

As shown in FIG. 1A, a shield plate 22 for shielding electric field noise from the outside is disposed on the lower surface of the head substrate 12 (the surface opposite to the surface facing the discharge port substrate 16). . The shield plate 22 is a grounded conductive flat plate, can eliminate the adverse effect on the electric field formation of the discharge portion, and can maintain a stable drawing performance.
Further, as described above, the ink guide 14 is substantially at a position on the upper surface of the head substrate 12 (the surface on the side facing the ejection port substrate 16) facing the ejection port 28 with respect to the surface of the head substrate 12. They are connected vertically.

As shown in FIGS. 1 to 3, ejection electrodes 18 a and 18 b for controlling the ejection of ink are formed on the opposite side walls of the two channel separation walls 17 forming the main flow path 30. Yes. The discharge electrodes 18 a and 18 b are disposed at positions corresponding to the discharge ports 28. As a preferable mode, the discharge electrodes 18 (18a and 18b) formed on the channel separation wall 17 are more preferable than the center of the discharge port 28 of the discharge port substrate 16 in the ink flow direction (length direction of the channel separation wall 17). It is formed so as to be located slightly downstream.
However, the position of the ejection electrode 18 formed on the channel separation wall 17 is not particularly limited, and may be disposed at substantially the same position as the center of the ejection port 28 in the ink flow direction. Further, in FIG. 1B, the upstream end portions 18c and 18d of the discharge electrode 18 may be further upstream than the center of the discharge port 28, and more than the outer edge portion of the discharge port 28 on the upstream side. Further, it may be located upstream. In the illustrated example, the discharge electrode 18 is formed so as to cover from the lower end of the channel separation wall 17 (connection portion with the head substrate 12) to the upper end (connection portion with the discharge port substrate 16). The discharge electrode 18 may be formed on the upper half surface or the lower half surface of the wall 17.
In the illustrated example, the discharge electrode 18 is formed on the channel separation wall 17 as a preferred mode. However, in the present invention, the channel separation wall 17 and the bottom surface of the ink flow path sandwiched between the channel separation walls 17 (head) It is preferably formed on at least one of the upper surfaces of the substrate 12.

In the example shown in FIGS. 1 to 3, the discharge electrode 18 e is formed on the upper surface of the head substrate 12 (the bottom surface of the main flow path 30) sandwiched between the discharge electrodes 18 a and 18 b, and the discharge electrode 18 e is connected to the channel separation wall 17. The discharge electrodes 18a and 18b formed on the side wall surface are electrically connected. Therefore, the ejection electrode 18e also functions as the ejection electrode 18 for ejecting ink. As shown in FIG. 1B, the ejection electrode 18e is formed in a curved shape on the upstream side so as to avoid the root portion of the ink guide 14. The shape of the ejection electrode 18e formed on the upper surface of the head substrate 12 is arbitrary, and may be rectangular, for example.
As described above, when the discharge electrode 18e uses a head substrate in which a plurality of grooves are formed in parallel to each other, and a wall that partitions the grooves formed in the head substrate is used as a channel separation wall, What is necessary is just to form in the bottom face of the groove | channel pinched | interposed by the discharge electrode formed in the inner wall. By electrically connecting the discharge electrode 18e and the discharge electrode formed on the inner wall of the groove, the discharge electrode 18e can function in the same manner as the discharge electrode.

  In addition, the length of the discharge electrode 18 formed on the channel separation wall 17 is not particularly limited, and may be any length as long as the discharge electrode 18 is formed for each discharge port arranged in a matrix. It can be formed.

  The discharge electrode 18 formed on the side wall surface of the channel separation wall 17 is connected to the signal voltage source 33, and when a predetermined voltage is applied from the signal voltage source 33, a flow path sandwiched between the discharge electrodes 18a and 18b. An electric field is formed inside. Therefore, by applying a predetermined bias voltage to the ejection electrode 18, electrostatic force is applied to the color material particles of the ink passing through the flow path surrounded by the ejection electrodes 18a and 18b, so that the color material particles It can be pushed into the flow path.

  As shown in FIG. 3, the inkjet head 10 of this embodiment has a multi-channel structure in which the discharge ports 28 are two-dimensionally arranged. Therefore, the discharge electrodes 18 are also two-dimensionally corresponding to the discharge ports 28. Are arranged. The wiring provided for connecting the ejection electrode 18 to the signal voltage source 33 can be formed, for example, on the back surface of the head substrate 12 (the surface opposite to the side facing the ejection port substrate 16). For example, the wiring can be easily formed by laminating a layer having wiring on the back surface of the head substrate 12.

  In the present invention, the distance between the discharge electrodes formed on the opposing surfaces of the two channel separation walls forming the main flow path and the distance from the upper surface of the discharge electrode to the tip of the ink guide are from 1: 0.7 to It is preferably in the range of 1: 2.8, and more preferably in the range of 1: 1.0 to 1: 2.4. That is, as shown in FIG. 1B, the interval between the discharge electrode 18a and the discharge electrode 18b respectively formed on the two channel separation walls 17 partitioning the main flow path 30 is X, and these discharge electrodes 18a and 18b. More preferably, L / X is in the range of 0.7 to 2.8, where L is the distance from the top surface of the ink guide 14 to the tip of the ink guide 14. It is preferable to adjust at least one of the distance X between the ejection electrode 18a and the ejection electrode 18b and the distance L from the upper surface of the ejection electrode 18 to the tip of the ink guide so as to be within the range. This is because the electric field formed by the ejection electrode 18 converges and the region where the strongest electric field is formed is within the above range, and the tip of the ink guide, which is the ejection position, is arranged at a position that satisfies the above range. Thus, even when the voltage applied to the ejection electrode 18 is lower than that in the prior art, it is possible to reliably eject droplets from the tip of the ink guide. That is, the voltage applied to the ejection electrode can be reduced.

In the inkjet head 10 shown in FIG. 1, a guard electrode is formed on the discharge port substrate 16. The guard electrode 20 is provided at a position closer to the recording medium P than the discharge electrode 18, and the electric lines of force generated from the discharge electrode 18 are arranged at the discharge port close to the discharge port 28 corresponding to the discharge electrode 18. The ink guide is positioned so as not to reach the front end of the ink guide. Here, the guard electrode 20 is formed on the upper surface of the discharge port substrate 16, and the surface thereof is covered with the insulating layer 34. FIG. 4 shows an AA arrow view of FIG. As shown in FIG. 4, the guard electrode 20 is a sheet-like electrode common to each discharge electrode such as a metal plate, and an opening 36 corresponding to each discharge port 28 arranged in a two-dimensional manner is perforated. ing.
The guard electrode 20 can shield electric field lines between the adjacent ejection electrodes 18 and suppress electric field interference between the adjacent ejection electrodes. A predetermined voltage is applied to the guard electrode 20 (including 0 V due to grounding), and in the illustrated example, the guard electrode 20 is grounded to 0 V.

Here, the guard electrode 20 is a front end portion of an ink guide (hereinafter referred to as “own channel” for convenience) arranged in an ejection port 28 corresponding to the ejection electrode 18 among electric lines of force generated from the ejection electrode 18. And the electric lines of force from the other discharge electrodes 18 and the tip of the ink guide 14 disposed in the other discharge ports 28 (referred to as “other channels”). It is necessary to provide it so as to shield the electric lines of force.
Considering the above points, the diameter of the opening 36 of the guard electrode 20 does not block the projection line from the discharge electrode 18 to the own channel and projects to another channel according to the discharge electrode 18 arranged. It is preferable to set so as to block the line.
By having the above-described configuration, the ejection stability from the ejection port 28 is sufficiently ensured, and variations in the ink landing position due to electric field interference between adjacent channels are suitably suppressed, and the stability can be increased. It is possible to perform image recording with high image quality.

  In the above example, the guard electrode 20 is a sheet-like electrode. However, the present invention is not limited to this, and the guard electrode 20 may be provided so as to shield the electric lines of force of the other channels between the discharge units. Anything is acceptable. For example, the guard electrode 20 may be provided in a mesh shape between the respective discharge units, or may not be provided in a portion that is sufficiently distant from the discharge unit so as not to cause electric field interference. It may be provided only between.

As described above, in FIG. 1A, the counter electrode 24 is disposed so as to face the ejection surface of the ink droplet R of the inkjet head 10.
The counter electrode 24 is disposed at a position facing the front end portion 14a of the ink guide 14, and is disposed on the grounded electrode substrate 24a and the lower surface of the electrode substrate 24a in the drawing, that is, the surface on the inkjet head 10 side. The insulating sheet 24b is used.
The recording medium P is supported by, for example, electrostatic adsorption on the lower surface of the counter electrode 24 in the drawing, that is, the surface of the insulating sheet 24b, and the counter electrode 24 (insulating sheet 24b) serves as a platen of the recording medium P. Function.

The recording medium P held on the insulating sheet 24b of the counter electrode 24 has a predetermined negative high voltage having a polarity opposite to that of the drive voltage (for example, pulse voltage) applied to the ejection electrode 18 by the charging unit 26 at least during recording. For example, it is charged to -1.5 kV.
As a result, the recording medium P is negatively charged and biased to a negative high voltage, acts as a substantial counter electrode with respect to the ejection voltage 18, and is electrostatically adsorbed to the insulating sheet 24 b of the counter electrode 24.

  The charging unit 26 includes a scorotron charger 26a for charging the recording medium P to a negative high voltage, and a bias voltage source 26b for supplying a negative high voltage to the scorotron charger 26a. The charging means of the charging unit 26 used in the present invention is not limited to the scorotron charger 26a, and various discharging means such as a corotron charger, a solid charger, and a discharge needle can be used.

In the illustrated example, the counter electrode 24 includes an electrode substrate 24a and an insulating sheet 24b, and the recording medium P is charged to a negative high voltage by the charging unit 26, whereby a bias voltage is applied to the counter electrode. However, the present invention is not limited to this, and the counter electrode 24 is constituted only by the electrode substrate 24a, and the counter electrode 24 (electrode substrate 24a itself) is formed. May be connected to a negative high voltage bias voltage source so as to be constantly biased to a negative high voltage so that the recording medium P is electrostatically attracted to the surface of the counter electrode 24.
Further, the electrostatic adsorption of the recording medium P to the counter electrode 24 and the charging of the recording medium P to a negative high voltage or the application of a negative bias high voltage to the counter electrode 24 are separate negative high voltage sources. The support of the recording medium P by the counter electrode 24 is not limited to the electrostatic adsorption of the recording medium P, and other support methods and support means may be used.

  Hereinafter, the present invention will be described in more detail by explaining the operation of ejecting ink droplets R in the inkjet head 10.

As shown in FIG. 1A, the inkjet head 10 is charged to the same polarity as the voltage applied to the ejection electrode 18, for example, positive (+), by an ink circulation mechanism including a pump (not shown) during recording. The ink Q containing color material particles is circulated in the main flow path 30 in the direction of the arrow (from the right to the left in the figure).
On the other hand, at the time of recording, the recording medium P is supplied to the counter electrode 24 and charged by the charging unit 26 to the opposite polarity of the color material particles, that is, negative high voltage (for example, −1500 V) and charged with the bias voltage. Thus, it is electrostatically attracted to the counter electrode 24. The shield plate 22 is grounded.
In this state, the recording medium P (counter electrode 24) and the inkjet head 10 are relatively moved, and a driving voltage (pulse voltage) is applied from the signal voltage source 33 to each ejection electrode 18 according to the supplied image data. And the ink droplet R is modulated and ejected according to the image data, and the image is recorded on the recording medium P.

Here, in a state where the drive voltage is not applied to the ejection electrode 18 (or in a state where the applied voltage is at a low voltage level), that is, in a state where only the bias voltage is applied, the ink Q has a bias voltage and The Coulomb attractive force with the charge of the color material particles (charged particles) of the ink Q, the Coulomb repulsion force between the color material particles, the viscosity of the carrier liquid, the surface tension, the dielectric polarization force, etc. act, and these are coupled to produce the color. The material particles and the carrier liquid move and are balanced in a meniscus shape slightly raised from the discharge port 28 as conceptually shown in FIG.
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 at the meniscus of the discharge port 28.

  From this state, a drive voltage is applied to the ejection electrode 18. As a result, the drive voltage is superimposed on the bias voltage, and the movement coupled by the superposition of the drive voltage further occurs in the previous coupling, and the color material particles and the carrier liquid are biased (counter electrode) side by the electrostatic force. That is, when pulled to the recording medium P side, the meniscus grows to form a substantially conical ink liquid column so-called tailor cone from its upper part. 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 a slender ink liquid column having a diameter of about several μm 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. It should be noted that the growth and splitting of the kite and the movement of the color material particles to the meniscus (spinner) occur continuously during the application of the drive voltage.
Further, when the application of the driving voltage is finished (discharge is turned off), the state returns to the state of the meniscus to which only the bias voltage is applied.

Here, in the inkjet head 10 of the present invention, the ejection electrode 18 is exposed to the main flow path 30, that is, in contact with the ink Q in the main flow path 30.
In this way, when a drive voltage is applied (discharge on) to the discharge electrode 18 that is in contact with the ink Q in the ink flow path formed by the main flow path 30 and the discharge port 28 (up to the opening end), the discharge electrode 18. A part of the electric charge supplied to the ink Q is injected into the ink Q, and the conductivity of the ink Q located between the discharge port 28 and the discharge electrode 18 is increased. In addition, the charged color material particles floating in the ink flowing from the upstream flow from the discharge electrode 18 formed on the channel separation wall 17 and the discharge electrode 18e formed on the upper surface of the head substrate 12 (bottom surface of the ink flow path). While being held down in the region below the discharge port 28 by the electrostatic force, it is pushed up toward the discharge port 28. As a result, in the ink jet head 10 of the present invention, the ink Q is remarkably easy to eject the ink droplet R only when the drive voltage is applied to the ejection electrode 18 (when ejection is on) (ejection). Improved).

  The electrostatic ink jet having the above configuration stably discharges ink droplets even when the driving voltage applied to the discharge electrode 18 for discharging ink droplets is significantly lower than that of the conventional case. Can do. According to the study of the present inventor, as an example, even if a conventional electrostatic ink jet head has a bias voltage of −1500 V and a drive voltage of 1000 V is required, For example, the ink droplet R can be stably discharged with a driving voltage of about 400V. Therefore, according to the ink jet head shown in the present embodiment, it is possible to stably control the ejection of ink droplets on / off by using an inexpensive power source and on / off of a low driving voltage.

  In addition, by improving the discharge property, the bias voltage applied to the recording medium P (counter electrode 24) is lowered and / or even when using a low discharge property ink (for example, low conductivity ink) Without increasing the drive voltage, it is possible to perform stable ejection while ensuring sufficient ink droplet ejection properties when ejection is on. That is, it is possible to reduce the discharge performance when the discharge is turned off while ensuring the discharge performance when the discharge is turned on. Therefore, according to the present invention, it is possible to greatly increase the difference in dischargeability between when discharge is on and when discharge is off, and to discharge ink droplets more stably.

  In addition, according to the present invention, since the drive voltage can be lowered, the electric field interference between the adjacent ejection electrodes 18 can also be reduced. Furthermore, according to the above configuration, it is possible to prevent a short circuit and a discharge between the discharge electrode 18 and the guard electrode 20 due to the coating of the color material particles of the ink.

  Next, the ink used for the inkjet head of the present invention will be described.

The ink Q (ink composition) ejected by the inkjet head 10 described above is obtained by dispersing color material particles (including color material and charged fine 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 electric resistance is not suitable for the present invention 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 color material, any pigments and dyes that have been conventionally used in inkjet ink compositions, printing (oil-based) ink compositions, or electrophotographic liquid developers 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 phenolic 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.

In addition, the color material particles may be charged with either a positive charge or a negative charge as long as it has the same polarity as the driving voltage applied to the ejection 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 ejection 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 ejection electrode does not become extremely high, and the ink does not leak around the head and become 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.

In the present invention, it is a solid component mainly dispersed in a carrier liquid, rather than causing the ink to fly toward the recording medium by applying a force to the entire ink as in the conventional ink jet system. A force is applied to the color material particles to fly.
As a result, images can be recorded on various recording media P such as plain paper and non-absorbing films (for example, PET film), and bleeding and flow are generated on the recording media P. Therefore, high-quality images can be obtained on various recording media.

FIG. 5A shows a conceptual diagram of an embodiment of the ink jet recording apparatus of the present invention using the ink jet head of the present invention.
An ink jet recording apparatus 60 (hereinafter referred to as a printer 60) shown in the figure is an apparatus that performs four-color printing on one side of a recording medium P, and includes a conveying means for the recording medium P, an image recording means, and a solvent recovery means. Yes, these are housed in a housing 61.
The conveying means includes a feed roller pair 62, a guide 64, rollers 66 (66a, 66b and 66c), a conveying belt 68, a conveying belt position detecting means 69, an electrostatic adsorption means 70, a static eliminating means 72, a peeling means 74, and a fixing. -It has the conveyance means 76 and the guide 78. The image recording forming unit includes a head unit 80, an ink circulation system 82, a head driver 84, and a recording medium position detecting unit 86. Further, the solvent recovery means includes a discharge fan 90 and a solvent recovery device 92.

  In the conveyance means for the recording medium P, the feed roller pair 62 is a conveyance roller pair provided adjacent to the carry-in port 61 a provided on the side surface of the housing 61. The feed roller 62 feeds the recording medium P supplied from a stocker (not shown) to the transport belt 68 (portion supported by the roller 66a). The guide 64 is provided between the feed roller pair 62 and a roller 66 a that supports the conveyance belt 68, and guides the recording medium P to the conveyance belt 68.

It should be noted that a foreign matter removing means for removing foreign matter such as dust and paper dust adhering to the recording medium P is preferably provided in the vicinity of the feed roller pair 62.
As the foreign matter removing means, one or more of non-contact methods such as known suction removal, blow-off removal, electrostatic removal, and contact methods using brushes, rollers, etc. may be used in combination. Alternatively, the feed roller pair 62 may be a slightly adhesive roller, and a cleaner for the feed roller pair 62 may be provided to remove foreign matters such as dust and paper powder when the recording medium P is fed by the feed roller pair 62.

The conveyor belt 68 is an endless belt stretched around the three rollers 66. At least one of the rollers 66a, 66b, and 66c is connected to a drive source (not shown), and rotates the conveyor belt 68.
The conveyance belt 68 functions as a platen for holding the recording medium P in addition to the scanning conveyance means for the recording medium P during image recording by the head unit 80, and further conveys the image to the fixing / conveyance means 76 after image recording. Therefore, the transport belt 68 is preferably formed of a material having excellent dimensional stability and durability. For example, the transport belt 68 is formed of a metal, a polyimide resin, a fluororesin, another resin, or a composite thereof.

In the illustrated example, since the recording medium P is held on the conveyance belt 68 by electrostatic attraction, the conveyance belt 68 is insulative on the side (front surface) that holds the recording medium P and is in contact with the roller 66 (back surface). ) Has conductivity. In the illustrated example, the roller 66a is a conductive roller, and the back surface of the transport belt 68 is grounded via the roller 66a.
That is, the conveyance belt 68 functions as the counter electrode 24 composed of the electrode substrate 24a and the insulating sheet 24b shown in FIG. 1 when holding the recording medium P.

As such a conveyor belt 68, a resin sheet and a metal belt are bonded to each other with a belt coated with any of the above resin materials, an adhesive, etc. A belt having a metal layer and an insulator layer manufactured by various methods such as a metal belt or a belt formed by metal vapor deposition on the back surface of a belt made of the above resin may be used.
Further, it is preferable that the surface of the conveying belt 68 that contacts the recording medium P is smooth, and thereby, good adsorbability of the recording medium P can be obtained.

  The conveyor belt 68 is preferably suppressed from meandering by a known method. As a meandering suppression method, for example, the roller 66c is a tension roller, and the axis of the roller 66c is adjusted between the roller 66a and the roller 66b in accordance with the output of the conveying belt position detecting means 69, that is, the detecting position in the width direction of the conveying belt 68. A method of suppressing meandering by changing the tension at both ends in the width direction of the conveyor belt by tilting with respect to the axis is exemplified. Further, the meandering may be suppressed by forming the roller 66 in a tapered shape, a crown shape, or other shapes.

  Here, as described above, the conveying belt position detecting unit 69 suppresses the meandering of the conveying belt and regulates the position of the recording medium P in the scanning conveying direction at the time of image recording to a predetermined position. 68 is used to detect the position in the width direction, and known detection means such as a photosensor is used.

The electrostatic attraction means 70 applies a predetermined bias voltage to the head unit 80 (the ink jet head of the present invention) to the recording medium P and attracts it to the conveying belt 68 by electrostatic force to hold it. Is charged to a predetermined potential.
In the illustrated example, the electrostatic attraction unit 70 includes a scorotron charger 70a that charges the recording medium P, and a negative high-voltage power supply 70b that is connected to the scorotron charger 70a. While the recording medium P is conveyed by the feed roller pair 62 and the conveying belt 68, the recording medium P is charged with a negative bias voltage by the scorotron charger 70a connected to the negative high voltage power source 70b, and is applied to the insulating layer of the conveying belt 68. It is electrostatically attracted.

In addition, the conveyance speed of the conveyance belt 68 when charging the recording medium P may be in a range that can be stably charged, and may be the same as or different from the conveyance speed at the time of image recording. Alternatively, the recording medium P may be rotated a plurality of times so that the electrostatic adsorption means acts on the same recording medium P a plurality of times to perform uniform charging.
In the illustrated example, the electrostatic adsorption unit 70 performs electrostatic adsorption and charging of the recording medium P. However, the electrostatic adsorption unit and the charging unit may be provided separately.

  The electrostatic attraction means is not limited to the illustrated scorotron charger 70a, and various other means and methods such as a corotron charger, a solid charger, and a discharge needle can be used. Further, as will be described in detail later, at least one of the rollers 66 is a conductive roller, or a conductive platen is provided on the back surface side (opposite side of the recording medium P) of the conveying belt 68 at the recording position on the recording medium P. By arranging and connecting this conductive roller or conductive platen to a negative high voltage power source, the electrostatic attraction means 70 may be configured, or the conveying belt 68 is an insulating belt and the conductive roller is grounded. The conductive platen may be connected to a negative high voltage power source.

The recording medium P charged by the electrostatic attraction means 70 is transported to the position of the head unit 80 described later by the transport belt 68.
The head unit 80 records an image on the recording medium P by ejecting ink droplets according to the image data using the inkjet head of the present invention. Here, the ink jet head of the present invention discharges the ink droplet R by superimposing the drive voltage on the bias voltage by applying the drive voltage to the discharge electrode 18 with the charging potential of the recording medium P as the bias voltage, The image is recorded on the recording medium P as described above. At this time, by providing a heating means for the conveying belt 68 and increasing the temperature of the recording medium P, fixing of the ink droplets R on the recording medium P can be promoted, and bleeding is further suppressed and image quality is improved. Can be achieved.
The image recording by the head unit 80 or the like will be described in detail later.

The recording medium P on which the image is recorded is discharged by the discharging unit 72, peeled off from the transport belt 68 by the peeling unit 74, and transported to the fixing / transporting unit 76.
In the illustrated example, the static elimination unit 72 is a so-called AC corotron static eliminator having a corotron static eliminator 72a, an AC power source 72b, and a DC high-voltage power source 72c grounded at one end. In addition to the above, as the static elimination means, various means and methods such as a scorotron static eliminator, a solid charger, a discharge needle, etc. can be used, and a conductive roller, A configuration using a conductive platen is also preferably used.
As the peeling means 74, a known technique such as a peeling blade, a reverse rotation roller, an air knife or the like can be used.

The recording medium P peeled off from the conveying belt 68 is sent to the fixing / conveying means 76, and the image formed by ink jet is fixed. A roller pair including a heat roller 76a and a conveyance roller 76b is used as the fixing / conveying means 76, and the recorded image is heated and fixed while the recording medium P is nipped and conveyed.
The recording medium P on which the image is fixed is guided by a guide 78 and discharged to a discharge stocker (not shown).

Examples of the heat fixing means include general heat fixing such as irradiation with infrared rays or a halogen lamp or a xenon flash lamp, or hot air fixing using a heater, in addition to the heat roll fixing described above. In the heat fixing / conveying means 76, the heating means performs only heating, and the conveying means and the heat fixing means may be provided separately.
In the case of heat fixing, when coated paper or laminated paper is used as the recording medium P, a phenomenon called blistering occurs in which the water inside the paper rapidly evaporates due to a rapid temperature rise and the paper surface is uneven. May occur. In order to prevent this, it is preferable to arrange a plurality of fixing devices and change one or both of the power supply of each fixing device and the distance to the recording medium P so that the temperature of the recording medium P gradually increases.

The printer 60 is preferably configured so that nothing touches the image recording surface of the recording medium P from at least the image recording by the head unit 80 until the fixing by the fixing / conveying means 76 is completed.
Further, the moving speed of the recording medium P at the time of fixing in the fixing / conveying means 76 is not particularly limited, and may be the same as or different from the conveying speed by the conveying belt 68 at the time of image formation. . When the conveyance speed is different from that at the time of image formation, it is preferable to provide a speed buffer for the recording medium P immediately before the fixing / conveyance means 76.

Hereinafter, image recording in the printer 60 will be described in detail.
As shown in FIG. 5A, the image recording means of the printer 60 includes a head unit 80 that ejects ink jets, an ink circulation system 82 that supplies and recovers ink Q to the head unit 80, a computer (not shown), a RIP (Raster A head driver 84 for driving the head unit 80 based on an output image signal from an external device such as an image processor), a recording medium position detecting means 86 for detecting the recording medium P in order to determine an image recording position in the recording medium P, and a head A recording position control means 88 for controlling the position of the unit 80 is provided.

FIG. 5B is a perspective view schematically showing the head unit 80, the recording position control means 88, and the conveying means for the recording medium P in the vicinity thereof.
The head unit 80 has four inkjet heads 80a corresponding to ink ejection of four colors of cyan (C), magenta (M), yellow (Y), and black (K) for recording a full color image. Then, in accordance with a signal from the head driver 84 supplied with the image data, the ink Q supplied by the ink circulation system 82 is ejected as an ink droplet R, and the recording medium P being conveyed by the conveying belt 68 at a predetermined speed. Record an image on The inkjet heads 80 a for the respective colors are arranged in the conveyance direction of the conveyance belt 68.
The ink jet heads 80a of the respective colors of the head unit 80 are the ink jet heads of the present invention.

In the illustrated example, each ink jet head 80a is a line head in which the ejection ports 28 are arranged in the entire width direction of the recording medium P, and preferably has a staggered shape as shown in FIGS. It is a multichannel head which has a plurality of nozzle rows arranged in a line.
Therefore, in the illustrated example, the recording medium P is transported to the head unit 80 in a state where the recording medium P is held on the transport belt 68, and the recording medium P is passed once, that is, only one scanning transport is performed. An image is formed on the entire surface of the recording medium P. Therefore, image recording (drawing) can be performed at a higher speed than when the ejection head is serially scanned.

The ink jet head of the present invention can also be used for a so-called serial head (shuttle type). Therefore, the printer 60 may also be in this mode.
In this case, the head unit 80 is configured by aligning the row of the ejection ports 28 of each inkjet head (which may be single row or multi-channel) with the carrying direction of the carrying belt 68, and the head unit 80 is carried by the recording medium P. Known scanning means for scanning in a direction orthogonal to the direction is provided.
The image recording may be performed in the same manner as a normal shuttle type ink jet printer, and the recording medium P is intermittently conveyed by the conveying belt 68 according to the length of the row of the ejection ports 28 and is synchronized with this intermittent conveyance. Then, at the time of stop, the head unit 80 is scanned to record an image on the entire surface of the recording medium P.
The image formed on the entire surface of the recording medium P by the head unit 80 in this way is fixed by the fixing / conveying means 76 as the recording medium P is nipped and conveyed by the fixing / conveying means 76 as described above. The

The head driver 84 receives image data from an external device, receives image data from a system control unit (not shown) that performs various processes, and drives the head unit 80 based on the image data.
This system control unit performs color separation, division into appropriate numbers of pixels and gradations, etc. on image data received from external devices such as computers, RIPs, image scanners, magnetic disk devices, and thumbtack data transmission devices. This is a part that is used as image data for the head driver 84 to drive the head unit 80 (inkjet head). Further, the system control unit controls the ink ejection timing by the head unit 80 in accordance with the conveyance timing of the recording medium P by the conveyance belt 68. The discharge timing is controlled by using an output from the recording medium position detecting unit 86 and an output signal from the encoder disposed on the conveying belt 68 or the driving unit of the conveying belt 68.

The recording medium position detection means 86 is for detecting the recording medium P conveyed to the ink droplet ejection position by the head unit 80, and known detection means such as a photo sensor can be used.
Here, the head driver 84 divides the drawing when there are a large number of ejection units (number of channels) to be controlled, such as when a line head is applied, and a known resistance matrix driving method or resistance diode matrix driving method. May be used. Thereby, the number of ICs used by the head driver 84 can be reduced, and the cost can be reduced and the control circuit size can be suppressed.

  The ink circulation system 82 is for flowing the ink Q through the main flow path 30 (see FIG. 1) of the ink jet head 80a of each color of the head unit 80, and is an ink tank for each of four colors (C, M, Y, K). An ink circulating device 82a having a pump, a replenishing ink tank (not shown), and the like, and ink for supplying the ink Q of each color from the ink tank of the ink circulating device 82a to the main flow path 30 of each color inkjet head of the head unit 80 It has a supply system 82b and an ink collection system 82c that collects ink from the main flow path 30 of each color inkjet head of the head unit 80 to the ink circulation device 82a.

The ink circulation system 82 supplies ink Q for each color from the ink tank to the head unit 80 via the ink supply system 80b by the ink circulation device 82a, and for each color from the head unit 80 via the ink supply system 80c. Any ink Q can be used as long as it can be collected and circulated in the ink tank.
The ink tank stores ink Q of each color, and the ink Q is pumped out by a pump and sent to the head unit 80. As the ink is discharged from the head unit 80, the density of the ink circulating in the ink circulation system 82 is decreased. In the ink circulation system 82, the ink density is detected by the ink density detector and replenished accordingly. It is desirable to appropriately replenish ink from the ink tank and maintain the ink density within a predetermined range.

  Further, the ink tank is preferably provided with a stirring device for suppressing precipitation / concentration of the solid component of the ink and an ink temperature management device for suppressing temperature change of the ink. The reason for this is that if the temperature is not controlled, the ink temperature will change due to changes in the environmental temperature, etc., and the dot diameter will change due to changes in the ink properties, making it impossible to stably form high-quality images. Because there is. As the stirring device, a rotary blade, an ultrasonic vibrator, a circulation pump, or the like can be used.

  As the ink temperature control device, a known method such as a method in which a heating element such as a heater or a Peltier element or a cooling element is provided in the head unit 80, ink tank, ink distribution pipe system, etc., and control is performed by a temperature sensor, for example, a thermostat. Can be used. When the temperature control device is arranged in the ink tank, it is preferable to arrange it together with the stirring device so as to make the temperature distribution constant. Further, the stirring device for keeping the concentration distribution in the tank constant may be shared with the stirring device for suppressing the precipitation and concentration of the solid component of the ink.

As described above, the printer 60 has the solvent recovery means including the exhaust fan 90 and the solvent recovery device 92. The solvent recovery means recovers the carrier liquid that evaporates from the ink droplets ejected from the head unit 80 onto the recording medium P, particularly the carrier liquid that evaporates from the recording medium P when fixing the image formed by the ink droplets. To do.
The discharge fan 90 is for sucking air inside the casing 61 of the printer 60 and sending it to the solvent recovery device 92.
The solvent recovery device 92 includes a solvent vapor absorber, and adsorbs the solvent component of the gas containing the solvent vapor sucked by the exhaust fan 90 to the solvent vapor absorber, and the gas after the solvent is adsorbed and recovered. The paper is discharged out of the casing 11 of the printer 60. As the solvent vapor absorbing material, various activated carbons are preferably used.

  In the above description, an electrostatic ink jet recording apparatus that records a color image using four color inks of C, M, Y, and K has been described. However, the present invention is not limited to this, and a monochrome recording apparatus Alternatively, recording may be performed using an arbitrary number of inks of other colors, for example, light colors or special colors. In that case, the number of head units 80 and ink circulation systems 82 corresponding to the number of ink colors are used.

  In each of the above examples, the ink jet discharges ink droplets R by charging the color material particles in the ink positively and setting the opposite electrode on the back of the recording medium or recording medium P to a negative high voltage. However, the present invention is not limited to this, and conversely, the color material particles in the ink may be negatively charged, and the recording medium or the counter electrode may be set to a positive high voltage to perform image recording by inkjet. . Thus, when the polarity of the colored charged particles is reversed from the above example, the polarity of the voltage applied to the electrostatic adsorption means, the counter electrode, and the drive electrode of the inkjet head may be reversed from the above example. .

  Further, the ink jet head and the recording apparatus of the present invention are not limited to those that discharge ink containing charged color material components, and are not particularly limited as long as they are liquid discharge heads that discharge liquid containing charged particles. For example, in addition to the electrostatic ink jet recording apparatus described above, the present invention can be applied to a coating apparatus that applies charged objects by discharging droplets and applying an object.

  As described above, the electrostatic ink jet head of the present invention and the ink jet recording apparatus using the same have been described in detail. However, the present invention is not limited to the above-described embodiment, and various types can be made without departing from the gist of the present invention. Of course, improvements and changes may be made.

(A) is a schematic sectional drawing of an example of the inkjet head of this invention, (B) is a schematic plan view when the mode when the discharge port board | substrate of the inkjet head shown to (A) is removed is seen from upper direction. is there. It is a schematic perspective view of an example of the inkjet head of this invention. (A) is a partial schematic plan view when the ink jet head of the present invention is viewed from the discharge substrate side, and (B) is a partial schematic plan view of the state when the discharge port substrate is removed. It is an AA arrow directional view of the inkjet head shown in Drawing 1 (A). (A) is a schematic configuration diagram of an ink jet head recording apparatus of the present invention, and (B) is a perspective view schematically showing a head unit and a conveying means for a recording medium around the head unit. It is a schematic block diagram of the conventional inkjet head.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Inkjet head 12 Head substrate 14 Ink guide 14a Tip part 16 Discharge port substrate 17 Channel separation wall 18, 18a, 18b, 18e Discharge electrode 20 Guard electrode 22 Shield plate 24 Counter electrode 24a Electrode substrate 24b Insulating sheet 26 Charging unit 26a Scorotron charge Device 26b Bias voltage source 28 Discharge port 30 Main flow path 33 Signal voltage source 34 Insulating layer 36 Opening 60 Inkjet printer 62 Feed roller 64 Guide 66 Roller 68 Conveying belt 69 Conveying belt position detecting means 70 Electrostatic adsorption means 72 Static eliminating means 74 Peeling Means 76 Fixing / conveying means 78 Guide 80 Head unit 82 Ink circulation system 84 Head driver 86 Recording medium position detection means 90 Discharge fan 92 Solvent recovery device P Recording medium Q Click R ink droplets

Claims (11)

An ink jet head that ejects ink as ink droplets from an ink flow path through an ejection port using electrostatic force, and flies toward a recording medium,
An ejection electrode for controlling ejection of the ink;
An ink reservoir connected to the ejection port and storing the ink;
An ink jet head comprising: partitioning the ink storage section into a plurality of ink paths, and separation walls arranged so that a plurality of the ejection openings are connected to the ink paths.   The inkjet head according to claim 1, wherein a plurality of the separation walls are provided, and the plurality of separation walls are arranged at positions facing each other. A discharge port substrate having the discharge port;
The inkjet head according to claim 1, further comprising: a head substrate that is disposed at a predetermined interval from the ejection port substrate and forms the ink flow path between the ejection port substrate.   The inkjet head according to claim 3, wherein the separation wall is provided on at least one of the discharge port substrate and the head substrate.   The inkjet head according to claim 3, wherein the separation wall is formed substantially perpendicular to the surface of the head substrate.   6. The discharge electrode according to claim 3, wherein the discharge electrode is provided on at least one of a surface of the head substrate facing the discharge port substrate and the separation wall. Inkjet head.   Furthermore, it has the wiring connected to the said discharge electrode, The said wiring is formed in the surface on the opposite side to the side facing the said discharge port board | substrate of the said head substrate. The inkjet head according to item. An inkjet head that discharges ink as ink droplets using electrostatic force and flies toward a recording medium,
A head substrate having a plurality of grooves formed in parallel to each other;
A discharge port substrate that is disposed to face the grooved side of the head substrate and has a plurality of discharge ports for discharging the ink droplets that are connected to the groove of the head substrate;
An inkjet head comprising: an ejection electrode for controlling ejection of the ink from the ejection port.   9. The inkjet head according to claim 8, wherein the ejection electrode is provided on at least one of a side wall and a bottom surface of the groove of the head substrate at a position corresponding to the ejection port.   10. The inkjet according to claim 8, further comprising a wiring connected to the ejection electrode, wherein the wiring is formed on a surface of the head substrate opposite to the side facing the ejection port substrate. head.   An inkjet recording apparatus provided with the inkjet head as described in any one of Claims 1-10.

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