JP2005186526A - Ink jet head and ink jet recorder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an ink jet head and an ink jet recorder capable of forming a dot of desired size stably on a recording medium even in case of high speed writing by enhancing ink supply performance to an ink ejection port. <P>SOLUTION: A first ejection electrode 18 is formed on an ejection port substrate 16 in which an ink ejection port 28 is formed, and a second ejection electrode 19 is formed at a position of a head substrate 12 facing the ejection port 28. When a predetermined voltage is applied to the second ejection electrode 19, the second ejection electrode generates an electric field reversely to a repulsion electric field being generated from the lower surface of the first ejection electrode 18. Consequently, effect of the repulsion electric field on ink particles is reduced, and the ink particles move quickly to the ejection port 28 thus filling the ejection port 28 with ink of a desired concentration. A dot of desired size can be formed stably on a recording medium even if liquid drops are ejected continuously 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 this electrostatic ink jet recording apparatus, for example, an ink jet recording apparatus disclosed in Patent Document 1 is known.

FIG. 5 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

  Since the conventional electrostatic ink jet head as shown in Patent Document 1 has the discharge electrode 54 provided on the discharge port substrate 53, when a drive 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 is that ink particles contained in the ink Q circulating through the main flow path 98 are directed to the ejection port (through hole) 56. Therefore, when the inkjet head 50 is driven and a drive voltage is applied to the discharge electrode 54, the ink particles are prevented from concentrating at the discharge ports 56, and the ink particles are collected at the discharge ports 56. A certain amount of time is required until it is sufficiently concentrated. For this reason, when drawing is performed at high speed using such an ink jet head, a desired recording medium is formed on the recording medium due to the inhibition of ink 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 dots of a size cannot be formed stably.

  The present invention has been made to solve the above problems, and an object of the present invention is to prevent ink particles from being supplied to the ejection port due to a repulsive electric field from the ejection electrode, and to prevent ink from being discharged to the ejection port. It is an object to provide an ink jet head and an ink jet recording apparatus that can improve the supply performance and can stably form dots of a desired size on a recording medium even when ink droplets are ejected continuously at a high speed.

  In order to solve the above problems, a first aspect of the present invention is an ink jet head that ejects ink as ink droplets using electrostatic force and flies toward a recording medium. A discharge port substrate in which a discharge port to be discharged is opened; a head substrate which is disposed at a predetermined interval from the discharge port substrate and forms an ink flow path between the discharge port substrate; and the discharge port substrate A first discharge electrode to which a drive voltage for controlling ink discharge from the discharge port is applied, and a position on the head substrate facing the discharge port, to which a predetermined voltage is applied. An inkjet head comprising a second ejection electrode is provided.

In the ink jet head according to the aspect of the invention, it is preferable that a voltage value of a voltage applied to the second ejection electrode is higher than a voltage value of a driving voltage applied to the first ejection electrode.
In addition, it is preferable that the phase of the voltage applied to the second ejection electrode is ahead of the phase of the drive voltage applied to the first ejection electrode. In addition, it is preferable that the application time of the voltage applied to the second discharge electrode is different from the application time of the drive voltage applied to the first discharge electrode.

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

  The ink jet head of the present invention generates an electric field opposite to the repulsive electric field generated from the first discharge electrode functioning as the discharge electrode from the second discharge electrode provided on the head substrate, to the ink particles by the repulsive electric field. Therefore, the ink particles (coloring material particles) in the ink can be promptly supplied to the ejection port. Thereby, even if dots are drawn continuously at high speed, dots of a desired size can be stably drawn. In addition, by providing the second discharge electrode on the head substrate, the ink particles can be supplied to the discharge port while maintaining the optimum positional relationship between the discharge electrode and the discharge port in forming the electric field at the discharge port. Can be improved.

  Since the ink jet recording apparatus of the present invention includes the ink jet head of the present invention, dots of a desired size can be formed on a recording medium at high speed and stably, and high quality images can be drawn at high speed. It is.

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. 1 is a schematic cross-sectional view showing a schematic configuration of an example of the ink jet head of the present invention. FIGS. 2A and 2B are views taken along arrows AA and BB in FIG. Are shown respectively.
The electrostatic inkjet head 10 shown in FIG. 1 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. 2, 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. 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 the figure but also one having only one row of ejection portions may be used. 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 droplets are ejected by an electrostatic force, and the ink droplets are modulated according to the image data by turning on / off (ejection on / off) the drive voltage applied to the first ejection electrode 18 according to the image data. The ink is discharged and an image is recorded on the recording medium P.

  As shown in FIG. 1, 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 head substrate 12 and the ejection port substrate 16 form an ink main channel 30 for supplying ink to each ejection port 28. The main channel 30 and the ejection port 28 (up to the opening end on the ejection side) form an ink channel. Is formed. The main channel 30 functions as an ink reservoir (ink chamber) for supplying the ink Q to the ejection port 28 (ink guide 14).

The ink Q is recorded at a predetermined speed (for example, an ink flow rate of 200 mm / s) from the right to the left in the drawing in a predetermined direction, in the illustrated example, in the main flow path 30 by an ink circulation mechanism (not shown) during image recording. ).
As shown in FIG. 1, the discharge port substrate 16 includes an insulating substrate 32, a guard electrode 20, a first insulating layer 34, a first discharge electrode 18, and a second insulating layer 35. A guard electrode 20 and an insulating layer 34 are sequentially stacked on the upper surface of the insulating substrate 32 (the surface opposite to the side facing the head substrate 12), and the first ejection electrode 18 and the second insulating layer are stacked on the lower surface of the insulating substrate 32. 35 is formed.

  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. The discharge port substrate 16 having such a structure can be manufactured as follows, for example. First, the guard electrode 20 is formed on the upper surface of the insulating substrate 32 made of an insulating material, and the first insulating layer 34 is formed so as to cover the upper surface of the guard electrode 20 and a part of the upper surface of the insulating substrate 32. Next, the first discharge electrode 18 is formed around the discharge port 28 on the lower surface side of the insulating substrate 32, and the lower surface of the insulating substrate 32 covers the region other than the region where the first discharge electrode 18 is formed. Two insulating layers 35 are formed. Thereafter, the discharge port 28 is formed by a laser processing machine or the like. Thus, the discharge port substrate 16 having the structure shown in FIG. 1 can be manufactured.

  On the lower surface of the discharge port substrate 12 (the surface on the side facing the head substrate 16), the first discharge electrodes 18 are formed as ring-shaped circular electrodes surrounding the discharge port. The first ejection electrode 18 is positioned so that the central axis thereof is substantially coaxial with the ink guide 14 and the ejection port 28. The first ejection electrode 18 is connected to a signal voltage source 33. The signal voltage source 33 is a drive voltage (for example, a pulse) having a predetermined potential corresponding to ejection data (ejection signal) such as image data and print data. Voltage) can be generated.

  Here, the first discharge electrode 18 is formed on the lower surface of the discharge port substrate 12 so as to be exposed to the main flow path 30 and in contact with the ink Q, thereby greatly improving the discharge property of the ink droplets. It is improving. However, the present invention is not limited to such a structure, and the discharge port substrate 12 is substantially coaxial with the discharge port so that the first discharge electrode 18 is not exposed to the main flow path 30. The first discharge electrode 18 may be formed at the position. In this case, for example, the discharge port substrate 12 may be manufactured so as to cover the first discharge electrode 18 with the second insulating layer.

  Further, the first ejection electrode 18 is not limited to a ring-shaped circular electrode, and electrodes having various shapes can be used. Preferably, the surrounding electrode disposed so as to surround each discharge port 28 formed in the insulating substrate 32 is exemplified, and among them, a substantially circular electrode is preferable, and a circular electrode is more preferable. Further, the first ejection electrode 18 may have an arc shape (C-shape) in which a part of the upstream side of the ink flow of the circular electrode is cut out.

Further, as described above, since the illustrated example has a multi-channel structure in which the discharge ports 28 are two-dimensionally arranged, the first discharge electrode 18 has each discharge port 28 as shown in FIG. Are two-dimensionally arranged. The wiring connected from the first ejection electrode 18 to the signal voltage source 33 can be formed on the lower surface of the head substrate 12, for example.
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. 1, 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.
A flow path bottom electrode as the second ejection electrode 19 is formed on the top surface of the head substrate 12, that is, on the bottom surface of the ink flow path.

  The second discharge electrode 19 is formed on the upper surface of the head substrate 12 at a position facing the discharge port 28 of the discharge port substrate 16. The second ejection electrode 19 has a ring shape surrounding the periphery of the connection portion of the ink guide 14 formed on the head substrate 12 with the head substrate 12. The second ejection electrode 19 is connected to a signal voltage source 37, and the signal voltage source 37 can generate a pulse voltage with various waveform patterns. A pulse voltage is applied to the second ejection electrode 19 in various waveform patterns by the signal voltage source 37 in accordance with the drive voltage applied to the first ejection electrode 18.

  The second discharge electrode 19 generates an electric field having a predetermined intensity in a direction toward the discharge port substrate 16 when a predetermined pulse voltage is applied from the signal voltage source 37. Due to the electric field generated in the direction toward the discharge port substrate 16, the repulsive electric field from the first discharge electrode 18 is hardly formed in the main channel 30. For this reason, the repulsive electric field from the first ejection electrode 18 is reduced or prevented from acting on the ink particles existing in the main flow path 30, and the ink particles existing in the main flow path 30 are quickly supplied to the discharge ports 28. .

Here, the optimum waveform as the pulse waveform of the pulse voltage applied to the second ejection electrode 19 will be described. FIG. 3 shows an example of an optimum pulse waveform as a pulse voltage applied to the second ejection electrode 19.
3A is an example of a pulse waveform of the drive voltage applied to the first ejection electrode 18, and FIGS. 3B to 3E are pulse waveforms applied to the second ejection electrode 19. It is an example. FIG. 3B shows a pulse waveform having the same phase as the pulse voltage applied to the first ejection electrode 18 and a large voltage value. When a pulse voltage is applied to the second ejection electrode 19 with such a pulse waveform, a repulsive electric field is not generated from the lower surface side of the first ejection electrode 18, and the surface is directed from the upper surface of the second ejection electrode 19 to the ejection port substrate 16. An electric field is formed in the direction. Therefore, the ink particles present in the main flow path 30 are promptly supplied to the ejection port 28.

  FIG. 3C shows a pulse waveform having a phase earlier than the pulse voltage applied to the first ejection electrode 18 and the same pulse width. In this pulse waveform, since the pulse voltage applied to the second ejection electrode 19 is advanced more than the pulse voltage applied to the first ejection electrode 18, before the repulsive electric field is generated from the lower surface side of the first ejection electrode 18. In addition, an electric field is generated in a direction from the upper surface of the second discharge electrode 19 toward the discharge port substrate 16. For this reason, before the ink is ejected from the ejection port 28, the ink particles are quickly supplied to the ejection port 28 by the electric field generated from the upper surface side of the second ejection electrode 19, and the ink sufficiently concentrated in the ejection port is obtained. Supplied.

In FIG. 3D, the pulse width of the pulse voltage applied to the second ejection electrode 19 is the same as the pulse width of the voltage applied to the first ejection electrode 18, but as shown in FIG. In addition, the pulse width of the pulse voltage applied to the second ejection electrode 19 may be shorter than the pulse width of the voltage applied to the first ejection electrode 18.
FIG. 3E shows a pulse waveform in which one pulse of the first ejection electrode 18 is included in one pulse applied to the second ejection electrode 19. That is, a pulse voltage having a phase earlier than the pulse voltage applied to the first ejection electrode 18 and having a long pulse width is applied to the second ejection electrode 19. When a pulse voltage is applied to the second discharge electrode 19 with such a pulse waveform, an electric field in a direction from the second discharge electrode 19 toward the discharge port substrate 16 before and after the drive voltage is applied to the first discharge electrode 18. Acts on the ink particles, so that the ink particles are quickly supplied to the ejection port 28.

  Regardless of the pulse voltage of any of the pulse waveforms shown above, when the application of the drive voltage to the first discharge electrode 18 is started, the repulsive electric field from the first discharge electrode 18 is reversed. Since the electric field from the second discharge electrode 19 is generated in the direction, the ink particles existing in the main flow path 30 can be reliably and promptly supplied to the discharge port 28, and the ink supply property to the discharge port 28 is possible. Can be further enhanced.

  The waveform of the voltage applied to the second ejection electrode 19 is not limited to the waveform shown in FIGS. 3B to 3E, and the pulse width, voltage value, and phase are appropriately changed according to the ejection performance of the inkjet head. It is possible. That is, in the present invention, the discharge electrodes are provided as the first discharge electrode 18 and the second discharge electrode 19 on the discharge port substrate 16 and the flow path bottom surface, respectively. The same signal is applied according to the image data. However, the present invention is not limited to this, and it is preferable to adjust at least one of a voltage value, a phase, and a pulse width of a signal applied to the two ejection electrodes according to the ejection performance of the inkjet head.

  Here, the shape of the second discharge electrode 19 is circular, but the shape of the second discharge electrode 19 is not particularly limited, and the influence of the repulsive electric field from the first discharge electrode 18 on the ink particles is reduced. If it can, it can be made into an arbitrary shape. Preferably, a surrounding electrode surrounding each discharge port 28 formed in the insulating substrate 32 is exemplified, and among them, a substantially circular electrode is preferable, and a circular electrode is more preferable. Further, the second ejection electrode 19 may have an arcuate shape (C shape) in which a part of the circular electrode on the upstream side of the ink flow is cut away.

Further, the shape of the second ejection electrode 19 can be changed according to the shape of the first ejection electrode 18. For example, the first ejection electrode 18 has an arcuate shape in which the upstream side of the ink flow is cut away. In this case, the second ejection electrode 19 may be similarly formed in an arc shape with the upstream side of the ink flow notched or a circular electrode.
In the inkjet head 10 shown in FIG. 1, the second discharge electrode 19 is disposed so as to be exposed to the main flow path 30 and in contact with the ink Q, but is formed inside the head substrate 12 and is not exposed to the main flow path 30. You may form as follows. Alternatively, for example, an insulating layer may be formed so as to cover the second discharge electrode 19 so that the second discharge electrode 19 is not exposed to the main flow path 30.

  In the present invention, the inner diameter of the first ejection electrode 18 and the distance from the surface of the first ejection electrode 18 to the tip of the ink guide 14 are preferably in the range of 1: 0.5 to 1: 2. : It is still more preferable to exist in the range of 0.7-1: 1.7. That is, as shown in FIG. 1, when the inner diameter of the first ejection electrode 18 is r and the distance from the surface of the first ejection electrode 18 to the tip of the ink guide 14 is h, h / r is 0. The ink guide from the inner diameter of the first ejection electrode 18 and the surface of the first ejection electrode 18 so as to be within the range of 5 to 2, more preferably within the range of 0.7 to 1.7. It is preferable to adjust at least one of the distances to the tip. This is because the electric field formed by the first ejection electrode 18 converges, and the region where the strongest electric field is formed is within the range, and the tip of the ink guide, which is the ejection position, is positioned so as to satisfy the range. By disposing, even if the voltage applied to the first ejection electrode 18 is lower than the conventional voltage, 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.

Here, as the inner diameter of the surrounding electrode that is not a constant inner diameter, such as a substantially circular electrode, an effective inner diameter such as an average inner diameter that can be regarded as a substantially inner diameter may be used. Further, when a parallel electrode is used as the discharge electrode, the inner diameter of the discharge electrode may be the interval between the parallel electrodes, and when a substantially parallel electrode is used, it can be regarded as a substantially interval such as an average interval. The effective interval may be used.
The guard electrode 20 is provided at a position closer to the recording medium P than the first discharge electrode 18, and the electric lines of force generated from the first discharge electrode 18 are adjacent to the discharge port 28 corresponding to the first discharge electrode 18. The ink guide is positioned so as not to reach the front end of the ink guide disposed at the discharge port. 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. As shown in FIG. 2A, the guard electrode 20 is a sheet-like electrode common to each discharge electrode such as a metal plate, and the opening 36 corresponding to each discharge port 28 arranged two-dimensionally. Is perforated.

The guard electrode 20 can shield the electric lines of force between the adjacent first discharge electrodes 18 and suppress electric field interference between the adjacent discharge 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) disposed in a corresponding ejection port 28 which is an ejection portion among electric lines of force generated from the first ejection electrode 18. ”), While securing the electric lines of force acting on the other first discharge electrodes 18 and the tip portions of the ink guides 14 disposed in the other discharge ports 28 (the“ other channels ”). It is necessary to provide so as to shield the electric lines of force to

When the guard electrode 20 is not provided, the electric lines of force generated from the inner periphery of the first discharge electrode 18 converge on the inside of the first discharge electrode 18 and act on the own channel to generate a necessary electric field. On the other hand, the lines of electric force generated from the outer peripheral portion of the first ejection electrode 18 diverge to the outside and affect other channels, resulting in electric field interference.
Considering the above points, it is preferable that the diameter of the opening 36 of the guard electrode 20 is larger than the inner diameter of the first ejection electrode 18 of the own channel so as not to block the electric lines of force to the own channel. That is, the end of the guard electrode 20 on the discharge port 28 side (hereinafter, the discharge port side end of each member is referred to as “inner edge” and the opposite end is referred to as “outer edge”) is the first discharge of the own channel. It is preferable that the electrode 18 is separated (retracted) from the discharge port 28 rather than the inner edge portion of the electrode 18.

In order to efficiently shield the lines of electric force to other channels, it is preferable that the diameter of the opening 36 of the guard electrode 20 is smaller than the outer diameter of the first discharge electrode 18 of the own channel. That is, it is preferable that the inner edge portion of the guard electrode 20 is closer (advanced) to the discharge port 28 than the outer edge portion of the first discharge electrode 18 of the own channel.
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 first discharge electrode 18 is described as a circular electrode. However, when the first discharge electrode 18 is not a circular electrode, an effective diameter that can be regarded as a substantial diameter, such as an average diameter, is considered depending on the shape. do it. Alternatively, the opening 36 of the guard electrode 20 is substantially similar to the shape of the inner periphery or the outer periphery of the first discharge electrode 18, and the inner edge of each of the positions in the circumferential direction of the first discharge electrode 18 is self-adjusted. The guard electrode 20 may be provided so as to be separated (retracted) from the discharge port 28 rather than the inner edge portion of the first discharge electrode 18 of the channel and to approach (advance) the discharge port 28 from the outer edge portion (that is, the guard electrode 20). An opening 36 of the electrode 20 may be formed).

  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.

  Even in such a case, the inner edge of the first discharge electrode 18 of the own channel is further away from the discharge port 28 than the inner edge of the first discharge electrode 18, and the outer edge of the first discharge electrode 18. The guard electrode 20 may be formed so as to be close to the discharge port 28.

As described above, in FIG. 1, 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 polarity opposite to the drive voltage (for example, pulse voltage) applied to the first ejection electrode 18 by the charging unit 26 at least during recording. It is charged to a high voltage, for example -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.

In the ink jet head 10 shown in FIG. 1, during recording, an ink circulation mechanism including a pump (not shown) or the like has the same polarity as the voltage applied to the first ejection electrode 18, for example, positive (+) charged color material particles. The contained ink Q is circulated in the main flow path 30 in the arrow direction (right to 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 first discharge electrode 18 and the second discharge electrode 19 from the signal voltage source 33 according to the supplied image data while relatively moving the recording medium P (counter electrode 24) and the inkjet head 10. A driving voltage (pulse voltage) is applied to the recording medium, and the ejection is turned on / off by applying the driving voltage on / off, whereby the ink droplet R is modulated and ejected according to the image data. Record an image.

  Here, in a state where the driving voltage is not applied to the first ejection electrode 18 and the second ejection electrode 19 (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 is affected by the Coulomb attractive force between the bias voltage and the charge of the color material particles (charged particles) of the ink Q, the Coulomb repulsive force between the color material particles, the viscosity of the carrier liquid, the surface tension, the dielectric polarization force, and the like. These are coupled to move the color material particles and the carrier liquid, 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 driving voltage is applied to the first ejection electrode 18 and the second ejection electrode 19. 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 first discharge electrode 18 and the second discharge electrode 19 are partially exposed to the main flow path 30, that is, in the main flow path 30, they are in contact with the ink Q. doing.

  In this manner, the drive voltage is applied (discharged) to the first discharge electrode 18 and the second discharge electrode 19 that are 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). on), a part of the electric charge supplied to the first ejection electrode 18 and the second ejection electrode 19 is injected into the ink Q, and the conductivity of the ink Q located between the ejection port 28 and the first ejection electrode 18. Becomes higher. In addition, the charged color material particles floating between the ejection port 28 and the first ejection electrode 18 are pushed up toward the ejection port 28 by the electrostatic force from the first ejection electrode 18. As a result, in the inkjet head 10 of the present invention, the ink Q significantly reduces the ink droplet R only when the drive voltage is applied to the first ejection electrode 18 and the second ejection electrode 19 (when ejection is on). It becomes a state where it is easy to discharge (the discharge property is improved).

  The electrostatic ink jet having the above-described configuration stably discharges ink droplets even when the drive voltage applied to the first discharge electrode 18 for discharging ink droplets is significantly lower than the conventional one. It can be carried out. 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 first 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 first ejection 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. In addition, “Recent development and commercialization of electrophotographic development systems and toner materials” on pages 139 to 148, “Basics and Applications of Electrophotographic Technology” on pages 497 to 505 (Corona, 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. 4 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 shaft 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 first 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 water inside the paper rapidly evaporates due to a rapid temperature rise and unevenness occurs on the paper surface. 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 described above, the image recording means of the printer 60 includes the head unit 80 that discharges the ink jet, the ink circulation system 82 that supplies and recovers the ink Q to the head unit 80, a computer (not shown), a RIP (Raster Image Processor), and the like. A head driver 84 that drives the head unit 80 by an output image signal from an external device, and a recording medium position detecting unit 86 that detects the recording medium P in order to determine the image recording position in the recording medium P are configured.

FIG. 4B is a perspective view schematically showing the head unit 80 and the conveying means for the recording medium P around it.
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, the inkjet heads 80a are line heads in which the ejection ports 28 are arranged in the entire width direction of the recording medium P, and are preferably arranged in a staggered manner as shown in FIG. A multi-channel head having a plurality of nozzle rows.

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.

It is a schematic sectional drawing of an example of the inkjet head of this invention. (A) is an AA arrow directional view of the inkjet head shown in FIG. 1, (B) is a BB arrow directional view of the inkjet head shown in FIG. (A) is an example of the pulse waveform of the drive voltage applied to the ejection electrode, and (B) to (E) are suitable examples of the pulse waveform of the pulse voltage applied to the second ejection electrode. (A) is a schematic configuration diagram of the ink jet recording apparatus of the present invention, and (B) is a perspective view schematically showing a head unit and conveying means for a recording medium in the vicinity thereof. 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 18 1st discharge electrode 19 2nd discharge electrode (flow-path bottom electrode)
20 Guard electrode 22 Shield plate 24 Counter electrode 24a Electrode substrate 24b Insulating sheet 26 Charging unit 26a Scorotron charger 26b Bias voltage source 28 Discharge port 30 Main flow path 33, 37 Signal voltage source 34, 35 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 detecting means 90 Discharge fan 92 Solvent recovery device P Recording medium Q Ink R Ink droplet

Claims (5)

An inkjet head that discharges ink as ink droplets using electrostatic force and flies toward a recording medium,
An ejection port substrate having an ejection port through which the ink droplets are ejected; and
A head substrate that is disposed at a predetermined interval from the ejection port substrate and forms an ink flow path between the ejection port substrate;
A first ejection electrode formed on the ejection port substrate and applied with a drive voltage for controlling ejection of ink from the ejection port;
An inkjet head comprising: a second ejection electrode formed at a position facing the ejection port of the head substrate and applied with a predetermined voltage.   The inkjet head according to claim 1, wherein a voltage value of a voltage applied to the second ejection electrode is higher than a voltage value of a driving voltage applied to the first ejection electrode.   The inkjet head according to claim 1, wherein the phase of the voltage applied to the second ejection electrode is advanced from the phase of the drive voltage applied to the first ejection electrode.   The inkjet head according to claim 1, wherein an application time of a voltage applied to the second ejection electrode is different from an application time of a drive voltage applied to the first ejection electrode.   An inkjet recording apparatus provided with the inkjet head in any one of Claims 1-4.

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