JP2006103230A - Inkjet recorder and inkjet recording method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inkjet recorder which can record stable and high image-quality images in electrostatic inkjet recording, and is also inexpensive, and to provide an inkjet recording method. <P>SOLUTION: The inkjet recorder includes a transfer means which has an insulating carry part that carries a recording medium to be recorded with the image, and which transfers the recording medium carried on the insulating carry part; an inkjet head which is set at a position opposed to the transfer means and has a discharging part that discharges ink liquid droplets to the recording medium by acting an electrostatic force to the ink according to an image signal; and a strong electric field generating means which applies to the discharging part an electric field strength stronger than an electric field strength formed at the discharging part at the time of ink liquid droplet non-discharge during image recording to the recording medium immediately before the recording medium and the inkjet head are relatively moved to an image recordable position. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention belongs to the field of electrostatic ink jet recording systems, and more particularly relates to an ink jet recording apparatus and an ink jet recording method for recording on a recording medium by discharging ink with an electrostatic force.

  The electrostatic ink jet recording method is a method in which an electrostatic force is applied to ink in accordance with an image signal to eject ink droplets to form an image on a recording medium. It has the characteristics that droplet formation is possible and high resolution drawing is possible. As such an electrostatic ink jet recording method, for example, in JP-A No. 2004-151867, mainly related to an ink jet recording method in which charged particles in an ink flow path are electrophoresed to increase an ink density near an opening and discharge is performed. An inkjet recording apparatus having an inkjet head that discharges ink droplets by electrostatic attraction caused by a recording medium or a counter electrode disposed on the back of the recording medium is disclosed.

FIG. 13 is a schematic configuration diagram showing the configuration of the multichannel inkjet head disclosed in Patent Document 1, and shows a cross section of the ejection electrode corresponding to the recording dots. In the drawing, oil-based ink Q is supplied between a head substrate 202 and a discharge electrode substrate 203 from a circulation mechanism 211 including a pump through an ink supply channel 212 connected to the head block 201, and is also formed in the head block 201. The ink is recovered by the ink circulation mechanism 211 through the ink recovery flow path 213. The discharge electrode substrate 203 includes an insulating substrate 204 having a through hole 207 and a discharge electrode 209 formed on the recording medium P side around the through hole 207.
On the other hand, a convex ink guide 208 is disposed on the head substrate 202 at a substantially central position of the through hole 207. The convex ink guide 208 is made of an insulating member such as plastic resin or ceramics, and is arranged at the same row interval and pitch so that the center is equal to the through hole 207, and is held on the head substrate 202 by a predetermined method. Yes. Each of the convex ink guides 208 has a shape obtained by cutting out the tip of a flat plate having a constant thickness into a triangle or a trapezoid, and the tip thereof becomes the ink droplet flying position 210. An ink meniscus is formed between the ink guide 208 and the inner wall surface of the through hole 207. A recording medium 221 is disposed on the conveyance belt 222 so as to face the tip of the convex ink guide 208. A migration electrode 205 is formed at the bottom of the space formed between the head substrate 202 and the discharge electrode substrate 203.

In such an inkjet head, during recording, the ink Q supplied from the ink circulation mechanism 211 via the ink supply channel 212 is supplied from the through hole 207 to the ink flying position 210 at the tip of the convex ink guide 208, and A part is recovered by the ink circulation mechanism 211 via the ink recovery flow path 213. Here, for example, a pulse voltage of +500 V is applied to the ejection electrode 209 as a signal voltage corresponding to the image signal from the signal voltage source 223 when the discharge electrode 209 is turned on. At this time, a voltage of +300 V is applied to the migration electrode 205. On the other hand, the recording medium 221 is charged to a voltage of −1.7 kV by a corona charging unit. Now, when the discharge voltage 209 is in an ON state (a state in which 500 V is applied), the ink droplet R is ejected from the ink droplet ejection position 210 at the tip of the convex electrode 208 and is ejected toward the recording medium P to form an image. Form.
JP 2004-82689 A

The ink jet recording apparatus disclosed in Patent Document 1 has no paper bleeding due to absorption of ink, has few restrictions on the recording medium, and can record images on various recording media.
In addition, the colored particles are discharged at a high density, and a clear image with high density without bleeding is formed, and an image with high resolving power is formed not only on inkjet dedicated paper but also on ordinary offset printing paper or plastic film. Can be formed.

However, the electrostatic ink jet recording apparatus disclosed in Patent Document 1 has the excellent characteristics as described above, but the ink meniscus state formed at the ejection port during ejection changes according to the ejection history, and the dots formed There is a problem that the diameter changes, that is, the ejection characteristics of the ink droplets have ejection frequency dependence (ejection frequency dependence), and the ejection characteristics may change depending on the ejection frequency of each ejection section.
When the ejection characteristics become unstable in this way, there is a problem that the image formed on the recording medium is not constant and a high-quality image cannot be formed.
Such a problem can be solved by controlling the ejection signal based on the ejection history. However, such a method has a problem that the driver becomes complicated and expensive.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above-described problems of the prior art, and in an electrostatic ink jet recording, an inexpensive ink jet recording apparatus capable of stably recording a high quality image. And providing an ink jet recording method.

To achieve the above object, according to a first aspect of the present invention, there is provided an insulating mounting portion on which a recording medium on which an image is recorded is mounted, and the first mounting portion is mounted on the insulating mounting portion. An ink jet head having a transport unit that transports a recording medium and an ejection unit that is disposed at a position facing the transport unit and ejects ink droplets onto the recording medium by applying an electrostatic force to ink according to an image signal. When,
Immediately before the recording medium and the inkjet head are relatively moved to a position where an image can be recorded, an electric field strength stronger than an electric field strength formed in the ejection portion when ink droplets are not ejected during image recording on the recording medium. There is provided an ink jet recording apparatus characterized by comprising a strong electric field generating means for applying a high pressure to the discharge section.
Here, it is preferable that the strong electric field forming unit gives a strong electric field strength to the ejection unit immediately before the recording medium is transported by the transport unit to a position where an image can be recorded by the inkjet head.
The ink jet head is capable of scanning in at least one direction with respect to the recording medium, and the strong electric field generating means immediately before the ink jet head is scanned to a position where an image can be recorded with respect to the recording medium. It is also preferable to give a strong electric field strength to the ejection part.
In addition, it is preferable that the strong electric field generating unit instantaneously forms a strong electric field in the ejection unit immediately before the recording medium and the inkjet head are relatively moved to a position where an image can be recorded.

  Here, the conveying means has a conveying belt for fixing the recording medium, and the strong electric field generating means charges at least one of the recording medium and the conveying belt, and the recording medium, the conveying belt, A charging unit that electrostatically adsorbs the charging unit and a charging unit control unit that controls the charging unit, and the charging unit control unit includes at least one of the conveyance belt on the upstream side in the conveyance direction from the fixing position of the recording medium. It is preferable to control to charge the portion to a higher potential than the recording medium.

In addition, the transport unit includes a transport belt including an insulating layer that forms a contact surface with the recording medium, and a conductive layer provided on a surface opposite to the contact surface of the insulating layer with the recording medium. It is preferable.
The strong electric field generating means includes a voltage control unit that controls a voltage applied to the conductive layer, and the voltage control unit is relatively moved to a position where the recording medium and the inkjet head can record an image. It is preferable that a predetermined voltage is applied to the conductive layer immediately before.
In addition, the transport unit includes a transport belt formed of an insulating member, and the strong electric field generating unit is provided on a surface of the transport belt opposite to the inkjet head side at a position facing the inkjet head. A conductive plate-like member disposed in contact with the conveyor belt; and a voltage control unit that controls a voltage applied to the conductive plate-like member, wherein the voltage control unit includes the recording medium and It is preferable that a predetermined voltage is applied to the conductive plate-like member immediately before the inkjet head is relatively moved to a position where an image can be recorded.

The inkjet head may include an ejection port for ejecting ink droplets, and an ink guide that passes through the ejection port and has a leading end protruding toward the recording medium from the opening surface of the ejection port. preferable.
Further, the ink jet head is disposed with a discharge port substrate having the discharge port opened, and spaced apart from the discharge port substrate by a predetermined distance, and forms an ink flow path between the discharge port substrate and the discharge port. A head substrate on which the ink guide is formed at a position opposite to the arrangement of the ejection ports on the surface on the substrate side, and disposed around the ejection ports of the ejection port substrate, and ejects ink droplets from the ejection ports. It is preferable to have a discharge electrode to be controlled.

In order to achieve the above object, according to a second aspect of the present invention, the inkjet head causes an electrostatic force to act on ink in accordance with an image signal on a recording medium conveyed to a position facing the inkjet head by a conveying means. An inkjet recording method for recording an image on the recording medium by ejecting ink droplets from the ejection unit onto the recording medium, immediately before the recording medium and the inkjet head are relatively moved to a position where the image can be recorded. Furthermore, the present invention provides an ink jet recording method characterized in that an electric field strength stronger than an electric field strength formed on the ejection portion is given to the ejection portion when ink droplets are not ejected during image recording on the recording medium.
In addition, it is preferable that the strong electric field strength is instantaneously applied to the ejection unit before the recording medium is conveyed to a position facing the inkjet head.

Further, it is preferable that the upstream side of the transport unit in the transport direction with respect to the fixing position of the recording medium is charged to a higher potential than the recording medium, and the strong electric field strength is given to the ejection unit.
Further, it is preferable that a predetermined voltage is applied to the transport unit to give the strong electric field strength to the ejection unit.
Further, the inkjet head may include an ejection port that ejects ink droplets, and an ink guide that passes through the ejection port and has a leading end protruding toward the recording medium from the opening surface of the ejection port. preferable.

According to the present invention, immediately before the recording medium and the ink-jet head are relatively moved to a position where image recording is possible, an electric field formed in the ejection unit when ink droplets are not ejected during image recording on the recording medium. By applying an electric field strength stronger than the strength to the ejection unit, the state of each ejection unit immediately before starting recording of an image on a recording medium can be made constant regardless of the ejection history, and the ejection characteristics are made constant. be able to. Thereby, the stability of drawing can be increased, and a high-quality image can be stably formed.
In addition, since the ejection characteristics can be made constant without controlling the ejection signal, it is possible to stably control the ejection of ink droplets with a simple driver, and to provide an inexpensive inkjet recording apparatus. it can.

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

FIG. 1 conceptually shows an example of the ink jet recording apparatus of the first aspect for carrying out the ink jet recording method of the second aspect of the present invention.
An ink jet recording apparatus (hereinafter referred to as a recording apparatus 10) 10 shown in FIG. 1 is obtained by dispersing charged fine particles containing a color material (hereinafter referred to as color material particles) in an insulating carrier liquid (dispersion medium). This is an image recording apparatus that uses ink Q and discharges ink droplets by applying an electrostatic force to the ink to record an image on a recording medium P. The recording apparatus 10 basically conveys the recording medium P through a predetermined path having a movable conveying belt 20 for fixing the recording medium P to the surface thereof and belt rollers 22 and 24 for driving the conveying belt 20. A strong electric field generating means 13 having a conveying means 12, a charging means 14 for charging at least one of the recording medium P and the conveying belt 20 to a predetermined potential, and a voltage controller 15 for controlling a voltage applied to the charging means 14, and an ink And an ejection head (inkjet head) 16 that ejects ink droplets by applying an electrostatic force.

  FIG. 1 mainly shows the characteristic portions of the present invention, but the recording apparatus 10 of the present invention is not limited to the conveying means 12, strong electric field generating means 13, and ejection head 16 shown in the figure. For example, a driver for driving the discharge head 16 to discharge ink droplets, a charge removing unit for discharging the charged recording medium P and the conveyance belt 20, supply of ink to the discharge head 16 and ink used in the discharge head 16 Various constituent elements of a known electrostatic ink jet recording apparatus, such as a circulation means for performing recovery, a sensor for detecting the transported recording medium P, a solvent recovery means for recovering a carrier liquid staying in the apparatus, etc. Of course it has.

  In addition, the inkjet recording apparatus of the present invention may be a monochrome recording apparatus that records an image of only one color such as K (black), and Y (yellow), M (magenta), and C (cyan). And a recording apparatus that records a full-color image on a recording medium using four colors of inks K and K.

  Here, examples of the recording medium P used in the inkjet recording apparatus of the present invention include high-quality paper, fine-coated paper, and coated paper, which are printing papers that are normally used as recording media. Further, for example, polyolefin-laminated paper having a resin film layer on the surface, and plastic film such as polyester film, vinyl chloride film, polyolefin film, and the like can be used. Furthermore, a plastic film, a processed paper, a printing plate for printing, or the like in which a metal is deposited on the surface or a metal foil is laminated can also be used. Of course, exclusive paper and film for inkjet can also be used.

As shown in FIG. 1, the transport unit 12 includes a transport belt 20 and belt rollers 22 and 24.
The conveyance belt 20 is configured to place the recording medium P on the surface and convey the recording medium P in a predetermined direction. The conveyor belt 20 is a ring-shaped endless belt and is stretched by belt rollers 22 and 24. The conveyor belt 20 is composed of an insulating layer 30 and a conductive layer 32, and the insulating layer 30 is provided on the surface (surface) in contact with the recording medium P, and the conductive layer 32 is the recording medium P of the insulating layer 30. Is provided on the surface opposite to the surface in contact with the belt, that is, on the surface (back surface) in contact with the belt rollers 22 and 24.

The insulating layer 30 is made of an insulating material such as polyimide resin or fluororesin. The fluororesin includes tetrafluoroethylene resin (PTFE), tetrafluoroethylene / perfluoroalkoxyethylene copolymer resin (PFA), tetrafluoroethylene / hexafluoropropylene copolymer resin (FEP), Ethylene / ethylene copolymer resin (ETFE), trifluoroethylene chloride resin (PCTFE), trifluoroethylene chloride / ethylene copolymer resin (ECTFE), vinylidene fluoride resin (PVDF), vinyl fluoride resin (PVF) Is exemplified.
Here, the insulating layer 30 preferably has an intrinsic volume resistivity of 10 ¹⁴ Ω · cm or more and an intrinsic surface resistance of 10 ¹⁵ Ω or more. By setting the specific resistance value and the specific surface resistance value in the above ranges, the surface of the transport belt becomes highly insulating, and a local change in the charged potential charged by the charging means 14 described later becomes possible.
The thickness of the insulating layer 30 is preferably 10 μm to 500 μm, and the surface roughness of the insulating layer is preferably an average surface roughness Ra ≦ 20 μm. By setting the thickness and the surface roughness of the insulating layer within the above ranges, excellent charge retention and durability can be obtained.

The conductive layer 32 is made of a conductive material, such as a flexible metal, specifically a stainless thin film.
The thickness of the conductive layer 32 is preferably 10 μm to 200 μm. By setting the thickness of the conductive layer in the above range, it is possible to obtain excellent charge retention and durability of the transport belt.
The production method of the transport belt 20 is not particularly limited, and is a method of forming the metal layer by coating the resin, a method of pasting a resin sheet with an adhesive, or the like, or a metal layer by vapor deposition on the back surface of the insulating layer. It can create by the method of providing.

At least one of the belt rollers 22 and 24 is connected to a drive source (not shown), and is driven to rotate at a predetermined speed during recording. Thereby, the conveyance belt 20 is rotated clockwise in the figure.
The belt roller 22 is grounded. As a result, the potential of the conductive layer 32 in contact with the belt roller 22 is held at the reference potential of 0V.

The strong electric field generating unit 13 includes a charging unit 14 that charges the recording medium P and the insulating layer 30 of the transport belt 20 with a predetermined potential, and a voltage control unit 15 that controls a voltage applied to the charging unit 14.
The charging unit 14 is disposed to face a surface of the transport belt 20 on the insulating layer 30 side, that is, a surface on which the recording medium P is placed, and includes a scorotron charger 40 and a high-voltage power source 42. The scorotron charger 40 is disposed at a position facing the surface of the conveyor belt 20 on the insulating layer 30 side. The scorotron charger 40 is connected to the negative terminal of the high voltage power source 42, and the positive terminal of the high voltage power source 42 is grounded.

The charging unit 14 charges the surface of the recording medium P and / or the insulating layer 32 of the transport belt 20 to a predetermined potential by a scorotron charger 40 connected to a high-voltage power source 42 (negative high potential in this embodiment). . Here, as described above, the potential of the conductive layer 32 of the transport belt is held at the reference potential. Thereby, the electric potential charged in the recording medium P and the insulating layer 30 is stabilized.
In the present embodiment, the scorotron charger is used as the charging means. However, the present invention is not limited to this, and various charging means such as a corotron charger, a solid charger, and a discharge needle can be used.

The voltage controller 15 is connected to the scorotron charger 40 and controls the grit voltage of the scorotron charger 40. In the present invention, the grit voltage is controlled by the voltage control unit 15 to control the voltage charged to the recording medium P and the conveyance belt 20.
Control of the voltage charged to the recording medium P and the conveyor belt 20 by the strong electric field generating means 13 will be described in detail later.

  The ejection head 16 ejects ink droplets according to an image signal to form an image on the recording medium P, and is a conveyance belt on the downstream side (right side in FIG. 1) of the recording medium P with respect to the charging unit. It is arranged at a position facing 20.

FIG. 2A schematically shows a cross-section of the schematic configuration of the ejection head, and FIG. 2B shows a view taken along the line IIB-IIB in FIG. As shown in FIG. 2A, the ejection head 16 includes a head substrate 72, an ink guide 74, and an ejection port substrate 76 on which ejection ports 82 are formed. A discharge electrode 78 is disposed on the discharge port substrate 76 so as to surround the discharge port 82.
In addition, the head substrate 72 and the discharge port substrate 76 are arranged at a predetermined interval while facing each other. An ink flow path 84 that supplies ink to each ejection port 82 is formed by a space formed between the head substrate 72 and the ejection port substrate 76.

  The discharge head 16 has a multi-channel structure in which a plurality of discharge ports 82 (nozzles) are two-dimensionally arranged in order to perform higher density image recording at high speed. FIG. 3 schematically shows a state in which a plurality of discharge ports 82 are two-dimensionally arranged on the discharge port substrate 76 of the discharge head 16. In FIGS. 2A and 2B, only one of the plurality of discharge ports is shown in order to easily understand the configuration of the inkjet head.

  In the ejection head 16 of the present embodiment, the number of ejection ports 82 and the physical arrangement position thereof can be freely selected. For example, not only a multi-channel structure as shown in FIG. 3 but also a single discharge port may be provided. Further, a so-called (full) line head having a row of ejection openings corresponding to the entire area of the recording medium P may be used, or a so-called serial head (shuttle type) 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.

FIG. 3 shows an arrangement of the ejection ports of a part of the multi-channel structure (3 rows and 3 columns). As a preferred mode, the ejection ports 82 in the downstream column are arranged in the upstream column in the ink flow direction. The nozzles are arranged so as to be shifted by a predetermined pitch in the direction perpendicular to the ink flow with respect to the ejection ports. In this way, by disposing the discharge ports in the downstream row in a direction perpendicular to the ink flow direction with respect to the discharge ports in the upstream row, it is possible to satisfactorily supply ink to the discharge ports. In the inkjet head of the present invention, n rows and m columns (n and m are positive) are arranged such that the discharge ports in the downstream column are shifted in the direction perpendicular to the ink flow direction with respect to the discharge ports in the upstream column. May be configured such that each of the discharge ports is perpendicular to the ink flow with respect to the discharge ports located on the upstream side. It may be arranged so as to be continuously shifted in the direction (downward or upward in FIG. 3). The number, pitch, repetition period, and the like of the discharge ports can be appropriately set according to the resolution and the feed pitch.
Further, in FIG. 3, as a preferred mode, in the ink flow direction, the discharge ports in the downstream row are shifted in the direction perpendicular to the ink flow with respect to the discharge ports in the upstream row, but this is not limitative. Instead, the downstream outlet and the upstream outlet may be arranged on the same straight line in the ink flow direction. In this case, it is preferable to dispose each ejection port in each row in the ink flow direction with respect to each ejection port in a row adjacent to the row in a direction perpendicular to the ink flow.

  In such an ejection head 16, an ink Q is used, which includes a coloring material such as a pigment and is dispersed in an insulating liquid (carrier liquid) with charged fine particles (hereinafter referred to as coloring material particles). . Then, a drive voltage is applied to the discharge electrode 78 provided on the discharge port substrate 76 to generate an electric field at the discharge port 82, and the ink in the discharge port 82 is discharged by electrostatic force. Further, by turning on / off the drive voltage applied to the ejection electrode 78 in accordance with the image data (ejection on / off), ink droplets are ejected from the ejection port 82 in accordance with the image data, and the recording medium P Record the image on top.

  Hereinafter, the structure of the ejection head 16 of the present invention shown in FIGS. 2A and 2B will be described in more detail.

  As shown in FIG. 2A, the discharge port substrate 76 of the discharge head 16 includes an insulating substrate 86, a guard electrode 80, a discharge electrode 78, and an insulating layer 88. A guard electrode 80 and an insulating layer 88 are sequentially stacked on the upper surface of the insulating substrate 86 in the drawing (the surface opposite to the side facing the head substrate 72). A discharge electrode 78 is formed on the lower surface of the insulating substrate 86 in the drawing (the surface facing the head substrate 72).

Further, a discharge port 82 for discharging the ink droplet R is formed in the discharge port substrate 76 through the insulating substrate 86. As shown in FIG. 2B, the ejection port 82 is a bowl-shaped opening (slit) elongated in the ink flow direction in which both short sides of the rectangle are semicircular, and has a length L in the ink flow direction. And the length D in the direction perpendicular to the ink flow has an aspect ratio (L / D) of 1 or more.
In this embodiment, as described above, the ejection port 82 has an opening having an aspect ratio (L / D) between the length L in the ink flow direction and the length D in the direction perpendicular to the ink flow of 1 or more (in the ink flow direction). By making it a shape having long side shape anisotropy and a long hole shape having the long side in the ink flow direction, the ink can easily flow into the ejection port 82. That is, it is possible to improve the ink particle supply to the ejection port 82, improve the frequency response, and prevent clogging. This will be described in detail later together with the action of discharging ink droplets.

  In this embodiment, the ejection port 82 is formed as an elongated bowl-shaped opening. However, the present invention is not limited to this, and ink can be ejected from the ejection port 82, and the length in the direction perpendicular to the ink flow is the length in the direction perpendicular to the ink flow. As long as the aspect ratio is 1 or more, any shape such as a substantially circular shape, an elliptical shape, a rectangular shape, a rhombus shape, or a parallelogram shape can be used. For example, a rectangular shape having a long side in the ink flow direction, or an ellipse or a rhombus having a long axis in the ink flow direction can be used. Alternatively, the upstream side of the ink flow may be an upper base, the downstream side may be a lower bottom, and the height in the ink flow direction may be longer than the lower base. In this case, the upstream side may be lengthened or the downstream side may be lengthened. Alternatively, a shape in which a circle having a diameter larger than the short side of the rectangle is connected to both short sides of the rectangle having the long side in the ink flow direction. Further, the discharge port 82 may have a symmetric shape or an asymmetric shape on the upstream side and the downstream side with respect to the center thereof. For example, the discharge port may be formed by making a semicircular shape at least one of the upstream and downstream ends of the rectangular discharge port.

  The ink guide 74 of the discharge head 16 is made of a ceramic flat plate having a predetermined thickness, and is disposed on the head substrate 72 corresponding to each discharge port 82 (discharge portion). The ink guide 74 is formed to be wide according to the length of the bowl-shaped discharge port 82 in the long side direction. As described above, the ink guide 74 passes through the ejection port 82, and the tip end portion 74 a protrudes above the surface of the ejection port substrate 76 on the recording medium P side (the surface of the insulating layer 88).

The leading end portion 74a of the ink guide 74 is formed into a substantially triangular shape (or trapezoidal shape) that gradually becomes thinner toward the recording medium P (conveying belt 20). The ink guide 74 is disposed such that the inclined surface of the tip end portion 74a intersects the ink flow direction. As a result, the ink flowing into the ejection port 82 reaches the apex of the leading end portion 74 a along the inclined surface of the leading end portion 74 a of the ink guide 74, so that the ink meniscus is stably formed at the ejection port 82.
Further, by forming the ink guide 74 wider in the long side direction of the ejection port 82, the width in the direction orthogonal to the ink flow can be shortened, and the influence on the ink flow can be reduced, and A meniscus described later can be formed stably.

The shape of the ink guide 74 is not particularly limited as long as the colorant particles in the ink Q can be concentrated to the tip portion 74a through the discharge port 82 of the discharge port substrate 76. For example, the shape of the ink guide 74 is not limited. However, the shape does not have to be thinner toward the recording medium P side, and can be changed as appropriate. For example, a cutout serving as an ink guide groove for collecting the ink Q in the tip end portion 74a by capillary action may be formed in the center portion of the ink guide 74 in the vertical direction in the drawing.
Further, it is preferable that a metal is deposited on the most distal portion of the ink guide 74. By depositing metal on the leading edge of the ink guide 74, the dielectric constant of the tip portion 74a of the ink guide 74 is substantially increased. Thereby, it becomes easy to generate a strong electric field, and the discharge property of ink can be improved.

As shown in FIG. 2B, a discharge electrode 78 is formed on the lower surface of the insulating substrate 86 (the surface facing the head substrate 72). The discharge electrode 78 is arranged in a U-shape in which one side on the upstream side of the ink flow is cut out along the periphery of the discharge port 82 so as to surround the periphery of the rectangular discharge port 82. By forming the ejection electrode 78 into a shape in which a part of the upstream side in the ink flow direction is missing, an electric field that prevents the flow of the color material particles from the upstream side in the ink flow direction to the ejection port is not formed, and the color material is efficiently produced. Particles can be supplied to the discharge port. Further, by disposing the discharge electrode 78 on the downstream side of the ink, an electric field is formed in a direction in which the color material particles flowing into the discharge port are retained at the discharge port. As described above, by making the ejection electrode into a shape in which the upstream side in the ink flow direction is partially missing, it is possible to further improve the ability to supply particles to the ejection port.
Further, in the present embodiment, the discharge electrode 78 is formed in a U shape from the viewpoint that the above-described effect can be obtained. However, any shape can be used as long as the electrode is disposed so as to face the ink guide. For example, it can be changed to various shapes according to the shape of the discharge port 82, such as a ring-shaped circular electrode, an elliptical electrode, a divided circular electrode, a parallel electrode, and a substantially parallel electrode.

As described above, since the ejection head 16 has a multi-channel structure in which the ejection ports 82 are two-dimensionally arranged, the ejection electrodes 78 correspond to the ejection ports 82 as schematically shown in FIG. They are arranged two-dimensionally.
Further, the ejection electrode 78 is exposed to the ink flow path 84 and is in contact with the ink Q flowing through the ink flow path 84. Thereby, the discharge property of ink droplets can be greatly improved. This point will be described later together with the action of discharge. However, the ejection electrode 78 is not necessarily exposed to the ink flow path 84 and in contact with the ink. That is, the discharge electrode 78 may be formed inside the discharge port substrate 76, or the exposed surface of the discharge electrode 78 may be covered with a thin insulating layer or the like.

  As shown in the figure, the discharge electrode 78 is connected to the control unit 92. The controller 92 can control the voltage applied to the ejection electrode 78 during ink ejection and during non-ejection.

The guard electrode 80 is formed on the surface of the insulating substrate 86, and the surface of the guard electrode 80 is covered with an insulating layer 88. FIG. 4 schematically shows the planar structure of the guard electrode 80. FIG. 4 is a view taken along the line IV-IV in FIG. 2A, and schematically shows a planar structure of the guard electrode 80 in the case of an inkjet head having a multi-channel structure. As shown in FIG. 4, the guard electrode 80 is a sheet-like electrode common to each discharge electrode such as a metal plate, and is a discharge electrode 78 formed around each discharge port 82 arranged two-dimensionally. Has an opening 90 at a position corresponding to. The opening 90 is formed in a rectangular shape. The length and width of the opening 90 of the guard electrode 80 are formed larger than the length and width of the discharge port.
The guard electrode 80 can shield electric lines of force between the adjacent ejection electrodes 78 to suppress electric field interference, and a predetermined voltage is applied to the guard electrode 80 (including 0 V due to grounding). In the illustrated example, the guard electrode 80 is grounded to 0V.

As a preferred embodiment, the guard electrode 80 is formed in a layer different from the ejection electrode 78 as shown in FIG. 2A, and the entire surface is covered with an insulating layer 88.
By having such an insulating layer 88, electric field interference between the adjacent ejection electrodes 78 can be suitably prevented, and the color material particles of the ink Q form a film between the ejection electrodes 78 and the guard electrode 80, thereby discharging. Can also be prevented.

Here, the guard electrode 80 secures the electric lines of force acting on the corresponding discharge ports 82 (hereinafter referred to as “own channel” for convenience) among the electric lines of force generated from the discharge electrodes 78, and the like. It is necessary to provide the electric lines of force of the discharge electrode 78 provided at the discharge port 82 (also referred to as “other channels”) and the electric lines of force to the other channels.
In the absence of the guard electrode 80, the electric lines of force generated from the end of the discharge electrode 78 on the discharge port side (hereinafter referred to as the inner edge of the discharge electrode) when discharging ink droplets are inside the discharge electrode 78, that is, the discharge It converges in a region surrounded by the inner edge of the electrode 78 and acts on its own channel to generate an electric field necessary for discharging ink droplets. On the other hand, electric lines of force generated from the end of the discharge electrode 78 opposite to the discharge port (hereinafter referred to as the outer edge of the discharge electrode) diverge further outward than the outer edge of the discharge electrode 78 and affect other channels. Cause electric field interference.

In consideration of the above points, the width and length of the rectangular opening 90 of the guard electrode 80 are such that the discharge of the self-channel is not observed when viewed from the substrate plane so as not to block the electric lines of force to the self-channel. The electrode 78 is also preferably made larger. That is, it is preferable that the end of the guard electrode 80 on the discharge port 82 side is separated (retracted) from the discharge port 82 rather than the inner edge of the discharge electrode 78 of the own channel.
Further, in order to efficiently shield the lines of electric force to other channels, the length and width of the rectangular opening 90 of the guard electrode 80 are set such that the discharge electrode 78 of the own channel when viewed in the substrate plane. It is preferable to make it smaller than the interval between the outer edge portions. That is, it is preferable that the inner edge portion of the guard electrode 80 is closer (advanced) to the discharge port 82 than the outer edge portion of the discharge electrode 78 of the own channel. According to the study of the present inventor, this proximity amount is preferably 5 μm or more, particularly preferably 10 μm or more.
By having the above-described configuration, the ejection stability from the ejection port 82 is sufficiently ensured, and variations in the ink landing position due to the electric field interference between adjacent channels are suitably suppressed to stably increase the ejection stability. It is possible to perform image recording with high image quality.

  The opening 90 of the guard electrode 80 is substantially similar to the shape formed by the inner edge or the outer edge of the discharge electrode 78, and the inner edge of the guard electrode 80 has a discharge port more than the inner edge of the discharge electrode 78 of its own channel. The guard electrode 80 may be provided so as to be separated (retracted) from 82 and to be closer (advanced) to the discharge port 82 than the outer edge of the discharge electrode (that is, the opening 90 of the guard electrode 80 may be formed). Good).

In the above example, the guard electrode 80 is a sheet-like electrode. However, the present embodiment is not limited to this, and is provided so as to shield the electric lines of force of other channels between the discharge ports. Any shape or structure may be used. For example, the guard electrode 80 may be provided in a mesh shape between the discharge ports. In addition, in a plurality of discharge ports arranged in a matrix, for example, when the intervals between adjacent discharge ports in the row direction and the column direction are different, between the discharge ports sufficiently separated so as not to cause electric field interference. May not be provided with a guard electrode, but may be provided only between adjacent outlets.
Even in such a case, the inner edge portion of the guard electrode 80 is further away from the discharge port 82 than the inner edge portion of the discharge electrode 78 with respect to the discharge electrode 78 of the own channel, and the discharge port 82 from the outer edge portion of the discharge electrode 78. The guard electrode 80 may be formed so as to be close to.
Here, the shape of the opening 90 of the guard electrode 80 is substantially the same as the shape of the discharge port 82, but is not limited to this, and the lines of electric force between the adjacent discharge electrodes 78 are shielded. As long as the electric field interference can be prevented, it can be formed into an arbitrary shape. For example, the shape may be a circle, an ellipse, a square, a rhombus, or the like.

In addition, as a preferable embodiment, the discharge head 16 of the present embodiment is provided with an ink guide weir 94 that guides ink to the discharge port 82 on the head substrate 72. Hereinafter, the ink guide weir 94 will be described.
FIG. 5A is a partial cross-sectional perspective view showing the configuration in the vicinity of the ejection portion in the ejection head 16 of FIG. In the drawing, in order to clearly show the structure of the ink guide weir 94, the ejection port substrate 76 is shown cut along the ink flow direction at a substantially central position of the ink guide 74.

  The ink guide weir 94 is located upstream and downstream in the ink flow direction of the ink guide 74 disposed at a position corresponding to the ejection port 82 on the ink channel 84 side surface of the head substrate 72, that is, the bottom surface of the ink channel 84. The surface is provided on the side and is inclined so as to gradually approach the discharge port substrate 76 from the vicinity of the position corresponding to the discharge port 82 toward the position corresponding to the center of the discharge port 82 with respect to the ink flow direction. have. That is, the ink guide weir 94 has a shape that is inclined toward the ejection port 82 along the ink flow direction.

  In addition, the ink guide weir 94 has a shape that has substantially the same width as the ejection port 82 in the direction orthogonal to the ink flow and has a wall surface that hangs from the bottom surface. In addition, the ink guide weir 94 does not block the ejection port 82 and secures a channel for the ink Q from the surface on the ink channel 84 side of the ejection port substrate 76, that is, from the upper surface of the ink channel 84. It is provided at intervals. Such an ink guide weir 94 is provided in each ejection part.

  As described above, by providing the ink guide weir 94 inclined toward the discharge port 82 along the ink flow direction on the bottom surface of the ink flow path 84, an ink flow toward the discharge port 82 is formed, and the ink Q The discharge port 82 is guided to the opening on the ink flow path 84 side. Therefore, the ink Q can be suitably flown into the discharge port 82, and the ink particle supply property can be further improved. Furthermore, clogging can be prevented more reliably.

  The length l of the ink guide weir 94 in the ink flow direction may be set as appropriate so that the ink Q can be suitably guided to the ejection port 82 within a range that does not interfere with the adjacent ejection unit. FIG. As shown in FIG. 4, it is preferable that the height h of the highest part of the ink guide weir 94 is 3 times or more (l / h ≧ 3), more preferably 8 times or more (l / h ≧ 8). preferable.

  The width of the ink guide weir 94 in the direction orthogonal to the ink flow is preferably equal to or slightly wider than that of the ejection port 82. Further, the width of the ink guide weir 94 is not limited to a uniform one as shown in the drawing, and may be one in which the width gradually decreases or one in which the width gradually increases. Further, the wall surface is not limited to a vertical surface, and may be an inclined surface or the like.

  The inclined surface (ink guiding surface) of the ink guiding weir 94 may be a shape suitable for guiding the ink Q to the ejection port 82, and may be a slope having a certain inclination angle. It may be a changing surface or a curved surface. Further, the surface is not limited to a smooth surface, and one or more wrinkles, grooves, or the like may be formed in the ink flow direction or radially toward the center of the ejection port 82.

  Further, the vicinity of the contact portion with the ink guide 74 at the top of the ink guide weir 94 may have a shape that is smoothly connected without having a step as in the illustrated example.

  In the illustrated example, the ink guide weirs 94 are arranged on the upstream side and the downstream side of the ink guide 74, but a trapezoidal ink guide weir 94 having inclined surfaces on the upstream side and the downstream side of the ejection port 82 is provided. The ink guide 74 may be erected on the upper portion, or the ink guide 74 and the ink guide weir 94 may be integrally formed. As described above, the ink guide weir 94 may be formed separately or integrally with the ink guide 74 and attached to the head substrate 72, or the head substrate 72 is shaved by a conventionally known excavation means. It may also be formed.

  The ink guide weir 94 only needs to be provided on the upstream side of the ejection port 82, but the height in the ejection direction of the ink droplet R is also ejected on the downstream side of the ejection port 82, as shown in the illustrated example. It is preferable to be provided so as to become lower as the distance from the outlet 82 increases. As a result, the ink Q guided toward the ejection port 82 by the upstream ink guide weir 94 flows smoothly downstream, so that the ink Q can be kept stable without being turbulent. , Discharge stability can be maintained.

  In the example of FIG. 5, the ink guide weir 94 is disposed on the upper surface of the head substrate 72. However, the present invention is not limited to this. An ink guide weir may be provided.

  For example, an ink flow groove having a predetermined depth that passes through a position corresponding to the ejection port 82 is provided along the ink flow direction, and is inclined toward the ejection port 82 along the ink flow direction at a position corresponding to the ejection port. An ink guide weir having a surface is provided. As described above, by providing the ink flow groove, most of the ink Q flowing through the ink flow path 84 can be selectively flowed to the ink flow groove. By providing the ink flow path weir, the ink Q is ejected from the ejection port 82. The ink can be suitably flown into the ink guide, and the ink supply to the ink guide tip 74a can be improved.

  In the electrostatic ink jet using the ink Q containing the colorant particles as described above, the force is applied to the entire ink to cause the ink to fly toward the recording medium as in the conventional ink jet system. Instead, a force is applied to the colorant particles, which are solid components dispersed in the carrier liquid, to cause the ink to fly. Hereinafter, the ejection action of the ink droplet R in the ejection head 16 will be described.

As shown in FIG. 2A, in the ejection head 16, a color charged to the same polarity as the voltage applied to the ejection electrode 78 during recording, for example, positive (+), by an ink circulation mechanism including a pump or the like (not shown). The ink Q containing material particles circulates in the ink flow path 84 in the direction of the arrow (from the left to the right in the figure).
On the other hand, during recording, as described above, the recording medium P is charged by the charging unit 14 to a polarity opposite to that of the color material particles, that is, to a negative high voltage (for example, -2.2 kV), and charged with a bias voltage. In this state, it is electrostatically attracted to the conveyor belt 20.
In this state, while the recording medium P (conveying belt 20) and the ejection head 16 are relatively moved, the controller 92 applies a pulse voltage (hereinafter referred to as drive voltage) to the ejection electrode 78 in accordance with the supplied image data. ) Is applied. Basically, the ink droplet R is modulated and ejected according to the image data by ejecting on / off by applying the drive voltage on / off, and an image is recorded on the recording medium P.

Here, in a state where the drive voltage is not applied to the ejection electrode 78 (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 Coulomb attractive force with the charge of the color material particles (charged particles) of the ink Q, Coulomb repulsive force between the color material particles, carrier liquid viscosity, surface tension, dielectric polarization force, and the like are acting. These are coupled to move the colorant particles and the carrier liquid. As shown conceptually in FIG. 2A, the ink Q has a meniscus shape slightly raised from the discharge port 82 and is balanced. It is taken.
Further, the color material particles are aggregated in the discharge port 82 by the electric field generated from the discharge electrode 78. The colorant particles move toward the recording medium P charged with a bias voltage by so-called electrophoresis due to the above-described Coulomb attractive force or the like. Therefore, the ink Q is concentrated in the meniscus formed at the ejection port 82.

  From this state, a drive voltage is applied to the ejection electrode 78. As a result, the drive voltage is superimposed on the bias voltage, and the motion coupled by the superposition of the drive voltage further occurs in the previous coupling. An electrostatic force acts on the colorant particles and the carrier liquid by an electric field generated by applying a drive voltage to the ejection electrode 78. The electrostatic force causes the color material particles and the carrier liquid to be pulled toward the bias voltage (conveying belt 20), that is, the recording medium P, and the meniscus formed at the ejection port grows upward, and above the ejection port 82. A substantially conical ink liquid column, a so-called tailor cone is formed. Similarly to the above, the color material particles are moved to the meniscus by electrophoresis and the electric field from the discharge electrode, and the meniscus ink Q is concentrated and has a large number of color material particles. It is in a state.

When a finite time has passed after the start of application of the drive voltage to the discharge electrode 78, the surface tension of the colorant particles and the carrier liquid mainly at the tip of the meniscus having a high electric field strength due to the movement of the colorant particles, etc. Is lost, the meniscus grows rapidly, and a slender ink liquid column having a diameter of about several μm to several tens of μm is formed.
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. The silk thread is broken by the interaction. Then, the divided string is ejected as ink droplets R, flies toward the recording medium, and is 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. Therefore, by adjusting the time during which the drive voltage is applied, the ink droplet ejection amount per pixel can be adjusted.
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, as shown in FIG. 2, the discharge port of the ink jet head of the present embodiment has an elongated slit shape elongated in the ink flow direction. In this way, the ejection port 82 is formed into a long and narrow slit-like long hole shape, that is, a shape in which the aspect ratio between the length in the ink flow direction and the length in the direction perpendicular to the ink flow is 1 or more, so that the ink is ejected from the ejection port 82. It becomes easy to flow inside, and the ink particle supply property to the ejection port 82 becomes high. Thereby, the ink particle supply property to the ink guide tip 14a can be improved. Therefore, the ejection frequency at the time of image recording is improved, and a dot of a desired size can be stably drawn even if dots are drawn continuously at a high speed. Furthermore, by setting the aspect ratio of the discharge port to 1 or more, the flow of ink becomes smooth and clogging at the discharge port can be prevented, and by setting the aspect ratio to 1.5 or more, the ink When the ink supply to the guide is further improved, and continuous large dots are formed, dots can be formed more stably, and drawing can be performed at a higher drawing frequency.
In consideration of the image output time, it is desired that the ejection frequency can be drawn at 5 kHz, preferably at 10 kHz, more preferably at 15 kHz.

  Here, as described above, the above-described effect can be obtained more suitably by setting the opening shape of the ejection port to a shape in which the aspect ratio between the length in the ink flow direction and the length in the direction perpendicular to the ink flow is 1 or more. However, the ink jet head of the present embodiment is not limited to this, and by setting the opening shape of the discharge port to an aspect ratio of the major axis and the minor axis of the opening of 1 or more, the flow of ink is made smooth, and the ejection port Clogging can be prevented.

In the ejection head 16 shown in FIGS. 2A and 2B, the ejection electrode 78 is exposed to the ink flow path 84. That is, the ejection electrode 78 is in contact with the ink Q in the ink flow path 84.
As described above, when a drive voltage is applied to the discharge electrode 78 in contact with the ink Q in the ink flow path 84 (discharge is turned on), a part of the charge supplied to the discharge electrode 78 is injected into the ink Q, and the discharge port 82. The conductivity of the ink Q positioned between the discharge electrode 78 and the discharge electrode 78 is increased. Therefore, in the ejection head 16 of the present embodiment, the ink Q is in a state in which it is easy to eject the ink droplet R when the drive voltage is applied to the ejection electrode 78 (when ejection is on) (the ejection performance is improved). To do).
Further, by applying a voltage having the same polarity as that of the color material particles to the U-shaped ejection electrode 78 at the time of non-ejection, that is, when no driving voltage is applied, electric charge is injected into the ink even at the time of non-ejection. Thus, the electrical conductivity of the ink can be further increased, and the charged color material particles floating in the ink flowing from the upstream side are surely held by the ejection port 82 by the electrostatic force by the ejection electrode 78.

Here, the ink used for the ejection head 16 of this embodiment will be described.
Ink Q is obtained by dispersing colorant particles in a carrier liquid. The carrier liquid is preferably a dielectric liquid (nonaqueous solvent) having a high electric resistivity (10 ⁹ Ω · cm or more, preferably 10 ¹⁰ Ω · cm or more). If the electric resistance of the carrier liquid is low, the carrier liquid itself is charged by charge injection due to the drive voltage applied to the control electrode, and the colorant particles do not concentrate. In addition, a carrier liquid having a low electrical resistance is not suitable because there is a concern of causing electrical conduction between adjacent control electrodes.

The relative dielectric constant of the dielectric liquid used as the carrier liquid is preferably 5 or less, more preferably 4 or less, and still more preferably 3.5 or less. By setting the relative dielectric constant in such a range, an electric field effectively acts on the colorant particles in the carrier liquid, and migration easily occurs.
Note that the upper limit value of the specific electric resistance of such a carrier liquid is desirably about 10 ¹⁶ Ω · cm, and the lower limit value of the relative dielectric constant is desirably 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 and metal complex pigments are used without particular limitation. be able to.
As dyes used as coloring materials, azo dyes, metal complex dyes, naphthol dyes, anthraquinone dyes, indigo dyes, carbonium dyes, quinoneimine dyes, xanthene dyes, aniline dyes, quinoline dyes, nitro dyes, nitroso dyes, benzoquinone dyes, naphthoquinone dyes And oil-soluble dyes such as phthalocyanine dyes and metal phthalocyanine dyes.

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

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

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

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

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

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

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

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

  In the electrostatic ink jet recording apparatus, normally, the recording medium P is ejected from the ejection head 16 in accordance with the image signal while the recording medium P is transported by the transport belt 20 as described above. An image is formed. However, in such an electrostatic ink jet recording apparatus, the ejection characteristics change due to the ejection history of the ejection head, the ejection of ink droplets becomes unstable, and a high-quality image cannot be formed. There has been a problem that the ejection of ink droplets has ejection frequency dependency.

  As a result of diligent investigations on this point, the present inventor has found that the discharge characteristics (frequency dependency and discharge frequency dependency) are caused by the wet state of the discharge portion, particularly the wet state of the ink guide, and the discharge frequency is low, that is, the discharge It has been found that when the frequency is low (the discharge time interval is large), the discharge portion, particularly the tip portion of the ink guide, is dried.

  Therefore, in the present invention, in order to prevent the discharge portion such as the tip portion of the ink guide from drying, the discharge is performed before the recording medium P is conveyed to a position facing the discharge head and an image is formed on the recording medium P. A strong electric field generating means 13 having a function of forming a strong electric field in the ejection portion of the head, supplying ink to the tip portion of the ink guide, and making the tip portion of the ink guide wet with ink is disposed.

  The strong electric field generating means 13 of the present embodiment is composed of the charging means 14 and the voltage controller 15 as described above. The voltage control unit 15 controls the voltage for charging the insulating layer 30 on the surface of the transport belt 20 by controlling the grit voltage of the scorotron charger 40 of the charging unit 14.

  Hereinafter, the control of the charging unit 14 by the voltage control unit 15 will be described in detail with reference to FIG. 6A is an enlarged view around the strong electric field generating means 13, and FIG. 6B is a grit voltage applied to the scorotron charger 40 by the position of the conveyor belt 20 and the voltage controller 44. FIG. FIG. 6C is a graph showing the relationship between the position of the conveyor belt 20 and the potential charged on the conveyor belt (potential on the conveyor belt). Further, FIG. ) Is a graph showing the relationship between the grid voltage applied to the scorotron charger 40 by the voltage controller 15 and time.

First, the conveyance belt 20 to which the recording medium P is fixed starts moving together with the recording medium P (t = 0).
A predetermined position (A _{1 in} FIG. 6A) on the upstream side in the transport direction with respect to the leading end of the fixing position of the recording medium P (A _{3 in} FIG. 6A) is a position facing the scorotron charger 40. When the conveyor belt 20 is moved (t = t ₁ ), the voltage control unit 15 applies −2.7 kV as the grit voltage and −6.5 kV as the wire discharge voltage to the scorotron charger 40.

Thereafter, a predetermined position (A in FIG. 6 (A)) between the leading end of the recording medium P (A _{3 in} FIG. 6 (A)) and the grit voltage application start position (A _{1 in} FIG. 6 (A)). ₂ ) is moved to a position facing the scorotron charger 40 (t = t ₂ ), −2.7 kV is applied to the scorotron charger 40 as a grit voltage.

Thereafter, a predetermined position (A in FIG. 6 (A)) between the leading end of the recording medium P (A _{3 in} FIG. 6 (A)) and the grit voltage application start position (A _{1 in} FIG. 6 (A)). ₂ ) After passing through the position facing the scorotron charger 40 (after t = t ₂ ), -2.2 kV is applied to the scorotron charger 40 as a grit voltage.
When the recording medium P passes through the position facing the scorotron charger 40, that is, after the front end of the recording medium P (A _{3 in} FIG. 6A) passes through the position facing the scorotron charger 40 (t = t ₍ After ₃ ), -2.2 kV is applied to the scorotron charger 40 as the grit voltage.

As described above, the voltage controller 15 controls the grit voltage applied to the scorotron charger 40 according to the position of the conveyor belt 20 as shown in FIG. Further, as shown in FIG. 6D, the voltage control unit 15 of the strong electric field generating means 13 applies -2.7 kV as a grit voltage to the scorotron charger 40 between t1 and t2, and after- Apply 2.2 kV.
As a result, the recording medium P and the insulating layer 30 of the transport belt 20 have approximately a portion between A ₁ and A ₂ on the insulating layer 30 of the transport belt 20 as shown in FIG. 6C. -2.7 kV is charged, and the conveying belt 20 and the recording medium P on the recording medium P side from A ₂ are charged with about -2.2 kV. That is, a predetermined portion on the upstream side in the transport direction from the fixing position of the recording medium P on the transport belt 20 is charged to a higher potential than the other portions of the recording medium P and the transport belt 20.
Further, in the present embodiment, by forming the transport belt with the above-described highly insulating member, the potential charged by the scorotron charger 40 as shown in FIG. 6C is suitably applied to the transport belt. Retained.

Portion between the A ₁ and A ₂ of the conveyance belt 20 (hereinafter referred to as strongly charged portion) has been conveyed to the position opposite to the ejection head 16, other portions of the recording medium P and the conveyance belt 20 ( A stronger electric field is formed between the ejection head 16 and the conveying belt 20 than when the portion other than the strong charging portion faces the ejection head 16. That is, the strong charging portion of the transport belt 20 has an electric field strength stronger than the electric field strength formed at the discharge portion of the discharge head 16 when ink droplets are not discharged during image recording on the recording medium P. In other words, a strong electric field is formed in the discharge portion.

  When the strong charging portion of the transport belt 20 is transported to a position facing the discharge head 16 and a strong electric field is formed between the discharge head 16 and the transport belt 20, the ink at the discharge port 96 of the discharge head 16 is transferred to the transport belt. As a result, the ink is moved to the front end portion 98 of the ink guide 76 of the ejection head 16 and the front end portion 98 of the ink guide 76 is wetted by the ink.

  In this way, a predetermined portion on the upstream side of the conveyance direction of the conveyance belt with respect to the recording medium is charged to a high potential, and immediately before recording on the recording medium, that is, a position where the recording medium and the ejection head can record an image. Immediately before being moved relatively, the portion charged at a high potential is passed through a position facing the discharge head, so that the tip portion of the ink guide of the discharge portion of the discharge head is recorded before image recording on the recording medium. Can be made wet with ink. As a result, regardless of the discharge history and the discharge interval, the wet state of the discharge portion (the tip portion of the ink guide) of the discharge head during recording becomes constant, and ink droplets can be discharged with constant discharge characteristics.

As described above, according to the present invention, the wet state of the discharge portion can be made constant, the drawing stability can be increased, and a high-quality image can be stably formed on the recording medium. In addition, the ejection characteristics can be made constant without controlling the ejection head. As a result, the ejection of ink droplets can be controlled with a simple driver, and the apparatus cost can be reduced.
In addition, even if there is an ejection part that does not eject ink droplets for a long time, every time the strong charging part of the transport belt passes, all the ejection parts become wet, so that no ink droplets are ejected for a long time. It is possible to prevent the clogging of the discharge port generated by the above.

  Further, even when ink droplets are ejected from the ejection head 16 when the strong charging portion of the conveyor belt 20 passes through the position facing the ejection head 16, there is no effect on the image recorded on the recording medium P. The strong charging portion of the transport belt 20 may be charged to a potential that forms an electric field through which ink droplets are ejected. In addition, by ejecting ink droplets from the ejection head 16 when passing through the strong charging portion of the transport belt 20, the tip portion of the ink guide can be reliably wetted. In this case, it is preferable to provide a transport belt cleaning mechanism.

The strong charging portion of the transport belt preferably has a width in a direction orthogonal to the transport direction of the recording medium longer than the width of the ejection head. That is, in the case of the line head as in the present embodiment, it is preferable to provide the entire area in the width direction of the transport belt, that is, in the entire direction orthogonal to the transport direction.
By making the width in the direction perpendicular to the conveyance direction of the strong charging unit longer than the width in the direction orthogonal to the conveyance direction of the ejection head, only the movement of the strong charging unit by the conveyance belt is performed without moving the ejection head. Thus, it is possible to generate a strong electric field in all of the ejection portions of the ejection head, so that the ejection portion (tip portion of the ink guide) is wetted with ink.

If the tip of the ink guide of the ejection head is wet with ink before recording, the time for forming a strong electric field on the ejection part by the strong electric field generating means is not particularly limited. For example, a strong electric field may be generated in the ejection head, and the tip portion of the ink guide may be wetted.
Even when the strong electric field generating means forms an electric field with a strength for ejecting ink droplets by making the time for forming the strong electric field in the ejection portion instantaneous, that is, a short time by the strong electric field generating means. The ejection of droplets can be minimized, and ink consumption can be suppressed.

In the present embodiment, the portion that becomes the strong charging portion of the transport belt may be formed of a material that has higher chargeability than other portions of the transport belt.
Thus, even if the voltage applied to the strong charging portion by the charging means is lower than that in the above embodiment by forming the portion to be the strong charging portion with a highly chargeable material, as in the above embodiment, The strong charging portion of the transport belt can be charged to a higher potential than other portions of the transport belt, and a strong electric field can be formed in the discharge head.

  Further, in the above-described embodiment, the strong charging unit is moved together with the conveying belt 20 to pass the position facing the discharge head 16. However, the present invention is not limited to this, and the recording medium P and the discharge head 16 are used for image recording. Just before the relative movement to a possible position, the strong electric field forming unit 18 may apply a strong electric field strength to the discharge unit at a position facing the discharge head, or the discharge head 16 may be moved.

  In this embodiment, the electrostatic charging and charging of the recording medium and the charging to the conveying belt are performed by the charging unit. However, they may be provided separately. For example, the electrostatic charging and charging to the recording medium P may be performed. A charging unit that charges a uniform potential and a charging unit that selectively charges a strong charging portion of the transport belt may be provided as separate charging units.

Hereinafter, the operation of the recording apparatus 10 will be described.
In the recording apparatus 10, the recording medium P is supplied to the conveyance belt 20 from a paper feed tray (not shown) at the time of image recording. The conveyance belt 20 on which the recording medium P is placed at a predetermined position is predetermined by belt rollers 22 and 24. Moved in the direction. In synchronization with the movement of the conveyor belt 20, the recording medium P placed on the conveyor belt 20 is also conveyed in a predetermined direction.

When the transport belt 20 moves, strongly charged portion of the conveyor belt 20 (between FIG. 6 (A) Medium A ₁ and A ₂₎ is moved to a position facing the scorotron charger 40 charging means 14, the voltage control unit 15, a high voltage (for example, −2.7 kV) is applied as a grit voltage to the scorotron charger 40 (t _{1 to} t ₂ in FIG. 6D), and the strong charging portion is charged to a high potential.
Thereafter (after elapse of t ₂ ), a predetermined voltage (for example, −2.2 kV) is applied as a grit voltage to the scorotron charger 40 by the voltage controller 15.
Thereafter, after the leading end portion (A _{3 in} FIG. 6) of the recording medium P placed on the downstream side in the transport direction by a predetermined distance from the strong charging portion of the transport belt 20 is transported to a position facing the scorotron charger 40 (FIG. 6 (D) medium t ₃ after) also predetermined voltage is applied as a grid voltage, the recording medium P is charged to a predetermined potential.

In this way, the strong charging portion of the conveying belt 20 charged to a high potential and the recording medium P charged to a predetermined potential by the strong electric field generating means 13 are in order of the strong charging portion of the conveying belt 20 and the recording medium P. It is moved to a position facing the ejection head 16.
When the strong charging portion of the transport belt 20 passes through the position facing the discharge head 16, a strong electric field is formed on the discharge head 16, and the discharge portion of the discharge head, particularly the tip portion of the ink guide, is wet with ink. .

  Thereafter, the recording medium P is transported to a position facing the ejection head, and an image corresponding to image data is formed on the surface of the recording medium P by the ejection head 16 while being transported at a predetermined constant speed as the transport belt 20 moves. Is done.

  The recording medium P on which the image is formed is fixed by an unillustrated fixing device, and the recording medium P on which the image is fixed is discharged to a discharge tray (not shown).

FIG. 7 is a schematic configuration diagram showing another example of the present invention.
An ink jet recording apparatus (hereinafter referred to as a recording apparatus 50) 50 shown in FIG. 7 has the same configuration as that of the recording apparatus 10 shown in FIG. Accordingly, the same reference numerals are given to the same constituent elements in both, and detailed description thereof will be omitted. Hereinafter, points peculiar to the recording apparatus 50 will be mainly described.

The strong electric field generating unit 51 of the recording apparatus 50 includes the charging unit 14 and a voltage control unit 52.
The charging unit 14 has the same configuration as described above, and includes a scorotron charger 40 and a high-voltage power source 42, and charges the surface of the recording medium P and / or the insulating layer 32 of the transport belt 20 to a predetermined potential (this book). Negative high potential in the examples). Here, in the present embodiment, the charging unit 14 charges the recording medium P and the insulating layer 32 of the transport belt with a predetermined uniform potential (in this embodiment, −2.2 kV).

  The voltage control unit 52 is connected to the belt roller 22, and a predetermined voltage is applied to the conductive layer 32 of the conveying belt 20 that is in contact with the belt roller 22 by applying a predetermined voltage to the belt roller 22. To. In addition, the voltage control unit 52 controls the voltage applied to the conductive layer 32 and forms a strong electric field in the discharge part of the discharge head 16.

  Hereinafter, the control of the voltage applied to the belt roller 22 and the conductive layer 32 of the transport belt 20 by the voltage controller 52 will be described in detail with reference to FIG. 8A is an enlarged view of the periphery of the ejection head 16, and FIG. 8B is applied to the belt roller 22 and the conductive layer 32 by the position on the conveying belt 20 and the voltage controller 52. It is a graph which shows the relationship with a voltage to be.

First, the conveyance belt 20 to which the recording medium P is fixed starts moving together with the recording medium P. Here, in this embodiment, the conveyance belt 20 and the recording medium P are charged to a predetermined potential (in this embodiment, −2.2 kV) by the scorotron charger 40 of the charging unit 14.
A predetermined position (B _{1 in} FIG. 8A) on the upstream side in the transport direction with respect to the transport direction leading end portion (B _{3 in} FIG. 8A) of the recording medium P at a position facing the discharge head 16 is the discharge head 16. When the transport belt 20 is moved to the opposing position, the voltage control unit 52 applies a predetermined voltage (−500 V (−0.5 kV) in this embodiment) to the belt roller 22 and the conductive layer 32.

Thereafter, a predetermined position (B _{2 in} FIG. 8A) between the leading end of the recording medium P (B _{3 in} FIG. 8A) and the voltage application start position (B _{1 in} FIG. 8A). ) Is moved to a position facing the ejection head 16, a predetermined voltage is applied to the belt roller 22 and the conductive layer 32.

A predetermined position (B _{2 in} FIG. 8A) between the leading end of the recording medium P (B _{3 in} FIG. 8A) and the voltage application start position (B _{1 in} FIG. 8A) is After passing the position facing the ejection head 16, the voltage application from the voltage control unit 52 to the belt roller 22 and the conductive layer 32 ends, and the belt roller 22 and the conductive layer 32 are in a 0V state.
Thereafter, when the recording medium P passes through the position facing the ejection head 16, that is, after the front end portion (B _{3 in} FIG. 8A) of the recording medium P passes through the position facing the ejection head 16, the belt roller. 22 and the conductive layer 32 are in a 0V state. That is, when an image is recorded on the recording medium P, only −2.2 kV charged to the recording medium P by the scorotron charger 40 is charged on the recording medium P.

As described above, the voltage control unit 52 controls the voltage applied to the belt roller 22 and the conductive layer 30 according to the position of the transport belt.
Thus, as shown in FIG. 8 (B), while the portion between the B ₁ and B ₂ of the conveyor belt 20 is conveyed to the position opposite to the ejection head 16, a predetermined voltage by the voltage control unit 52 A stronger electric field is formed between the ejection head 16 and the conveyor belt 20 than when the recording medium P and the other part of the recording belt P and the conveyor belt 20 (parts other than the strong charging portion) are opposed to the ejection head 16. That is, a strong electric field is formed in the discharge portion of the discharge head 16.

  As in the present embodiment, the recording medium P and the insulating layer 30 of the transport belt 20 are charged to a predetermined uniform potential, and the predetermined portion on the upstream side in the transport direction of the fixing position of the recording medium P faces the ejection head 16. Even when a predetermined voltage is applied to the belt roller 22 and the conductive layer 32 by the voltage control unit 52 while the image recording medium P is being conveyed, the recording unit P is strongly applied to the discharge unit of the discharge head 16 before recording. An electric field can be formed.

  Thereby, this embodiment can also obtain the various effects of the above-mentioned present invention, can improve drawing stability, and can stably form a high-quality image on a recording medium. Further, since it is not necessary to control the discharge unit in this embodiment, the apparatus cost can be reduced.

FIG. 9 is a schematic configuration diagram showing another example of the present invention.
An ink jet recording apparatus (hereinafter referred to as a recording apparatus 60) 60 shown in FIG. 9 has the same configuration as that of the recording apparatus 10 shown in FIG. 1 except for the conveying means 62 and the strong electric field generating means 65. Therefore, the same reference numerals are given to the same constituent elements in both, and detailed description thereof will be omitted. Hereinafter, points peculiar to the recording apparatus 60 will be described mainly.

The conveyance unit 62 of the recording apparatus 60 includes a conveyance belt 64 and belt rollers 22 and 24.
In the recording apparatus 10, the transport belt 20 having a two-layer structure of the insulating layer 30 and the conductive layer 32 is used. However, the transport belt 64 of this embodiment is configured by an insulating member.

The conveyor belt 64 is a ring-shaped endless belt, like the conveyor belt 20, and is stretched by belt rollers 22 and 24. Here, the belt roller 22 of the present embodiment is not grounded.
The conveyor belt 64 can be formed of the same material as the insulating layer 30 of the conveyor belt 20, for example, a polyimide resin or a fluororesin. The fluororesin includes tetrafluoroethylene resin (PTFE), tetrafluoroethylene / perfluoroalkoxyethylene copolymer resin (PFA), tetrafluoroethylene / hexafluoropropylene copolymer resin (FEP), Ethylene / ethylene copolymer resin (ETFE), trifluoroethylene chloride resin (PCTFE), trifluoroethylene chloride / ethylene copolymer resin (ECTFE), vinylidene fluoride resin (PVDF), vinyl fluoride resin (PVF) Is exemplified.

Here, when the surface roughness Ra of the transport belt 64 is 5 μm or less, preferably 2 μm or less, the recording medium P can be uniformly sucked and transported. Further, by setting the thickness of the conveyor belt 64 to 10 to 500 μm, preferably 50 to 300 μm, sufficient durability and suitability for conveying the belt can be obtained. Further, by setting the tensile strength of the conveying belt 64 to 100 kg / cm ² or more, preferably 120 kg / cm ² or more, high conveying accuracy and high durability can be obtained. Further, by setting the volume resistivity of the conveying belt 64 to 10 ¹⁴ Ω · cm or more, preferably 10 ¹⁵ Ω · cm or more, good charge (charge potential) retention can be secured. Moreover, the conveyance accuracy with respect to a humidity fluctuation | variation can be stabilized by making the water absorption rate (based on ASTMD570) of a conveyance belt into 5% or less, Preferably it is 2% or less.

The strong electric field generating means 65 has a conductive platen 66 and a voltage control unit 68.
The conductive platen 66 is disposed in contact with the conveyor belt 20 on the inner side of the conveyor belt 64 at a position facing the ejection head 16, that is, on the belt rolls 22 and 24 side.
The voltage control unit 68 is connected to the conductive platen 66 and applies a voltage to the conductive platen. The voltage control unit 68 controls the voltage applied to the conductive platen 66 and forms a strong electric field in the discharge unit of the discharge head 16.

  Hereinafter, the control of the voltage applied to the conductive platen 66 by the voltage control unit 68 will be described in detail with reference to FIG. Here, FIG. 10A is an enlarged view of the periphery of the ejection head 16, and FIG. 10B shows the relationship between the position of the conveyor belt 20 and the voltage applied to the conductive platen 66 by the voltage controller 68. It is a graph which shows.

First, the conveyance belt 20 to which the recording medium P is fixed starts moving together with the recording medium P.
A predetermined position (C _{1 in} FIG. 10A) on the upstream side of the transport direction of the recording medium P in the position facing the discharge head 16 (C _{3 in} FIG. 10A) is the discharge head 16. When the transport belt 64 is moved to the opposing position, the voltage control unit 68 applies a high voltage (in the present embodiment, −2.7 kV) to the conductive platen 66.

Thereafter, a predetermined position (C _{2 in} FIG. 10A) between the leading end of the recording medium P (C _{3 in} FIG. 10A) and the voltage application start position (C _{1 in} FIG. 10A). ) Is moved to a position facing the ejection head 16, a high voltage (−2.7 kV) is applied to the conductive platen 68.

A predetermined position (C _{2 in} FIG. 10A) between the leading end of the recording medium P (C _{3 in} FIG. 10A) and the voltage application start position (C _{1 in} FIG. 10A) is After passing the position facing the ejection head 16, a predetermined voltage (−2.2 kV) is applied from the voltage control unit 68 to the conductive platen 68.
After that, when the recording medium P passes through the position facing the ejection head 16, that is, after the front end portion (C _{3 in} FIG. 10A) of the recording medium P passes through the position facing the ejection head 16, the conductivity is maintained. A predetermined voltage (−2.2 kV) is applied to the platen 68. Thus, in this embodiment, when an image is recorded on the recording medium P, the conductive platen 68 functions as a counter electrode, and ink is generated by an electric field formed between the conductive platen 68 and the control electrode of the ejection head 16. Droplets are ejected, and an image is recorded on the recording medium P.

  As in this embodiment, the voltage control unit 66 applies a high voltage to the conductive platen 68 while the predetermined portion on the upstream side in the conveyance direction of the fixing position of the recording medium P is conveyed at a position facing the ejection head 16. By applying a, a strong electric field can be formed in the ejection part of the ejection head 16 before recording an image on the recording medium P.

  Thereby, this embodiment can also obtain the various effects of the above-mentioned present invention, can improve drawing stability, and can stably form a high-quality image on a recording medium. Further, since it is not necessary to control the discharge unit in this embodiment, the apparatus cost can be reduced.

In the present embodiment, the bias voltage is set by applying a predetermined voltage to the conductive platen during recording.However, the present invention is not limited to this, and charging means is provided to charge the recording medium to a predetermined potential. The voltage applied to the conductive platen and the voltage charged to the recording medium P may be a bias voltage at the time of recording.
The strong electric field forming means may combine the above-described embodiments. For example, the charging means charges a predetermined area upstream of the conveyance position of the recording medium on the conveying belt in the conveying direction to a high potential. A predetermined voltage may be applied to the conductive platen, the conductive layer of the transport belt, or the like when the portion charged to the potential passes through a position facing the ejection head.

  Here, in any of the above embodiments, the strong electric field formed in the ejection unit is an electric field stronger than the electric field formed in the ejection unit when ink droplets are not ejected during image recording on the recording medium. The present invention is not limited to this, and before the recording medium is conveyed to a position facing the ejection head, the ink in the ejection section can be moved by forming a strong electric field in the ejection section, and the ejection port Thus, it is possible to prevent ink clogging generated by the ink sticking.

Next, a specific example of the ink jet recording apparatus of the present invention will be described with reference to FIG.
FIG. 11 is a schematic diagram showing a schematic overall configuration of an example of a specific embodiment of the electrostatic ink jet recording apparatus of the present invention.

  An ink jet recording apparatus (hereinafter referred to as an ink jet printer 100) 100 shown in FIG. 1 is an apparatus that performs four-color printing on one side of a recording medium P. As conveying means for the recording medium P, a feed roller pair 102, a guide 104, a roller 106a, 106b, 106c, conveyor belt 108, conveyor belt position detecting means 109, strong electric field generating means 13, neutralizing means 112, peeling means 114, fixing / conveying means 116 and guide 118, and head unit 120 as image forming means. It has an ink circulation system 122, a head driver 124, a recording medium position detection means 126, and a recording position control means 128, and further has a discharge fan 130 and a solvent recovery device 132 as solvent recovery means, including these components. A housing 101 is provided.

First, the conveyance means of the recording medium P in the inkjet printer 100 will be described.
The pair of feed rollers 102 is provided adjacent to the carry-in port 101a provided on the side surface of the casing 101, and the recording medium P is supported by the conveyance belt 108 (roller 106a) provided in the casing 101 from a stocker (not shown). It consists of a pair of rollers that feed into The guide 104 is provided between the feed roller pair 102 and the roller 106 a that supports the conveyance belt 108, and guides the recording medium P to the conveyance belt 108.

  In the vicinity of the feed roller pair 102, although not shown, it is preferable to provide a foreign matter removing means for removing foreign matter such as dust and paper powder adhering to the recording medium P. The foreign matter removing means may be used in combination with one or a plurality of known non-contact methods such as suction removal, blow-off removal, and electrostatic removal, and contact methods using brushes, rollers, and the like. Further, the feed roller pair 102 may be constituted by a slightly adhesive roller, and a cleaner for the feed roller pair 102 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 102. .

The rollers 106a, 106b, and 106c are configured to stretch and move the conveyor belt 108, and at least one of the rollers 106a, 106b, and 106c is connected to a drive source (not shown).
The conveyance belt 108 functions as a platen that holds the recording medium P when an image is formed by the ink ejected from the ejection head 120a of the head unit 120. The conveyance belt 108 moves the recording medium P and fixes and conveys the image after formation. It is for conveying to the means 116. Therefore, as the conveyor belt 108, an endless belt made of a material having excellent dimensional stability and durability is used.

  In the illustrated embodiment, the recording medium P is held on the conveyance belt 108 by electrostatic attraction, so that the conveyance belt 108 is insulative on the side (surface) holding the recording medium P, and the rollers 106a and 106b. , 106c side (rear surface) is conductive. Specifically, the conveyor belt 108 is obtained by applying a fluororesin coat on the surface side of a metal belt. In the illustrated example, the roller 106a is a conductive roller, and the back surface (metal surface) of the conveyor belt 108 is grounded via the roller 106a.

  Note that the meandering of the conveyor belt 108 is preferably suppressed by a known method. As a meandering suppression method, for example, the roller 106c is a tension roller, and the axis of the roller 106c is adjusted between the roller 106a and the roller 106b according to the output of the conveying belt position detecting means 109, that is, the detecting position in the width direction of the conveying belt 108. 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 used. Further, meandering may be suppressed by making the rollers 106a, 106b, 106c into a tapered shape, a crown shape, or other shapes.

  Here, as described above, the conveyance belt position detecting means 109 suppresses the meandering of the conveyance belt and regulates the position of the recording medium P in the sub-scanning direction during image recording to a predetermined position. 108 is used for detecting the position in the width direction, and known detection means such as a photosensor is used.

The strong electric field generating means 13 includes the charging means 14 and the voltage control unit 15 as described above.
As described above, the charging unit 14 applies a predetermined bias voltage to the recording medium P with respect to the head unit 120 (the ejection head 120a thereof), and is attracted to and held by the conveyance belt 108 by electrostatic force. The medium P is charged to a predetermined potential, and further, a predetermined portion of the conveyance belt 108 upstream of the fixing position of the recording medium P in the conveyance direction is charged to a predetermined potential.
In the present embodiment, the charging unit 14 includes a scorotron charger 40 that charges the recording medium P, and a negative high-voltage power source 42 that is connected to the scorotron charger 40. The recording medium P is charged to a negative high voltage by the scorotron charger 40 connected to the negative high voltage power source 42 and electrostatically adsorbed to the insulating layer of the transport belt 108. Further, as described above, the charging unit 14 charges a predetermined portion upstream of the conveyance position of the recording medium P on the conveyance belt 108 in the conveyance direction to a higher potential than the recording medium P.

  Further, as described above, the charging means is not limited to the scorotron charger 40, and other various means and methods such as a corotron charger, a solid charger, and a discharge needle can be used. As in the other example described above, at least one of the rollers 106a, 106b, 106c is a conductive roller, or the charging unit 14 is a conductive roller, or the back side of the conveying belt 108 (recording at the recording position on the recording medium P). A conductive platen may be disposed on the opposite side of the medium P), and the conductive roller or the conductive platen may be connected to a negative high voltage power source. Alternatively, the conveying belt 108 may be an insulating belt, and the conductive roller. May be grounded and the conductive platen may be connected to a negative high voltage power source.

  The charging unit 14 charges a predetermined position (strongly charged portion) on the upstream side in the conveyance direction with respect to the fixing position of the recording medium P on the conveyance belt 108 to a higher potential than the recording medium P, and further, the recording medium P is electrostatically charged. Is electrostatically adsorbed to the conveying belt 108 without being lifted, and then the surface of the recording medium P is uniformly charged while driving the conveying belt 108. The conveyance speed of the conveyance belt 108 for charging the recording medium P is not limited as long as it can be stably charged, and may be the same as or different from the conveyance speed at the time of image recording. Further, by charging the recording medium P a plurality of times, the charging means may act on the same recording medium P a plurality of times to perform uniform charging.

The recording medium P charged by the charging unit 110 and the strong charging portion of the transport belt 108 are transported by the transport belt 108 to a position of a head unit 120 described later. As described above, the strong charging portion is formed on the conveyance belt 108 on the upstream side in the conveyance direction of the fixing position of the recording medium P. Thus, before the recording medium P is conveyed to the position facing the head unit 120, the recording medium P passes through the position facing the head unit 120, and all the ejection portions of the head unit 120 are wetted with ink.
The head unit 120 records an image on the recording medium P using the ejection head shown in FIGS. Here, the ejection head uses the charging potential of the recording medium P as a bias voltage, applies the recording signal voltage to the control electrode of the ejection head, superimposes the driving voltage on the bias voltage, and ejects the ink droplets R. The image is formed on P as described above. At this time, the heating means of the conveyor belt 108 is provided to increase the temperature of the recording medium, whereby the fixing of the ink droplets R on the recording medium P can be promoted, and the image quality is improved by further suppressing bleeding. be able to. The image recording by the head unit 120 will be described in detail later.

The recording medium P on which the image is formed is discharged by the discharging unit 112, peeled off from the transport belt 108 by the peeling unit 114, and transported to the fixing / transporting unit 116.
In the present embodiment, the static elimination means 112 includes a corotron static eliminator 112a, an AC power source 112b, and a DC high voltage power source 112c, and the other terminal of the DC high voltage power source 112c is grounded. The neutralization means 112 in the illustrated example uses a so-called AC corotron neutralizer that uses a corotron neutralizer 112a and an alternating current (AC) power supply 112b. In addition to this, for example, a scorotron neutralizer, a solid charger, a discharge needle, etc. In addition, a configuration using a conductive roller or a conductive platen like the above-described charging unit 110 is also preferably used. As the peeling means 114, 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 108 is sent to the fixing / conveying means 116, and the image formed by inkjet is fixed. In this embodiment, a roller pair including a heat roller 116a and a conveyance roller 116b is used as the fixing / conveying means 116, and the recording medium P is conveyed, and an image formed on the recording medium P is contact-heated and fixed. Yes. In the present invention, the fixing unit may be provided separately from the conveying unit including the conveying roller pair, and the fixing may be performed by other fixing unit or fixing method.

Examples of the heat fixing include general heat fixing such as irradiation with an infrared ray 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 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. In order to prevent this, a plurality of fixing devices are arranged, and one or both of the power supply of each fixing device and the distance to the recording medium P are changed so that the temperature of the paper gradually increases. preferable.

It should be noted that at least in the process from the image formation by the head unit 120 to the fixing by the fixing / conveying means 116, it is desirable to keep nothing in contact with the image forming surface of the recording medium P.
The moving speed of the recording medium P at the time of fixing in the fixing / conveying means 116 is not particularly limited, and may be the same as or different from the conveying speed by the conveying belt 108 at the time of image formation. If it is different from the conveyance speed 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 116.
The recording medium P on which the image is fixed is guided by a guide 118 and discharged to a discharge stocker (not shown).

Next, an image forming (drawing) unit and an image recording method in the inkjet printer 100 will be described.
As described above, the image forming unit of the ink jet printer 100 includes the head unit 120 that ejects ink jet, the ink circulation system 122 that supplies and collects ink to the head unit 120, a computer (not shown), a RIP (Raster Image Processor), and the like. A head driver 124 that drives the head unit 120 by an output image signal from an external device, a recording medium position detecting unit 126 that detects the recording medium P in order to determine an image forming (recording) position on the recording medium P, and the head unit 120. Recording position control means 128 for controlling the position of the recording medium.

FIG. 11B is a perspective view schematically showing the head unit 120, the recording position control means 128, and the conveying means for the recording medium P in the vicinity thereof.
The head unit 120 has discharge heads 120a of four colors of cyan (C), magenta (M), yellow (Y), and black (K) for recording a full color image, and according to a signal from the head driver 124. Then, the ink supplied by the ink circulation system 122 is ejected as ink droplets, and an image is formed (recorded) on the recording medium P conveyed at a predetermined speed by the conveying belt 108. The discharge heads for each color are arranged in the conveyance direction of the conveyance belt 108. The discharge heads 120a for the respective colors of the head unit 80 are the ink jet heads shown in FIGS.

In the illustrated example, each of the ejection heads 120a is a line head in which the ejection ports 96 are arranged in the entire width direction of the recording medium P, and are preferably arranged in a staggered manner as shown in FIG. And a multi-channel head having a plurality of nozzle rows.
Accordingly, in the illustrated example, the recording medium P is held by the conveying belt 108 and the recording medium P is simply passed through the head unit 120 once by conveyance, that is, only by one scanning conveyance. 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), and thus the recording apparatus 100 may also be in this mode.
In this case, the head unit 120 is configured by aligning the row of ejection ports 96 (single row or multi-channel) of each inkjet head with the carrying direction of the carrying belt 108, and the head unit 120 is carried by the recording medium P. Scanning means for scanning in a direction orthogonal to the direction is provided. As the scanning means, known scanning means can be used.
The image recording may be performed in the same manner as a normal shuttle type ink jet printer. The recording medium P is intermittently conveyed by the conveying belt 108 according to the length of the row of the discharge ports 96 and is synchronized with the intermittent conveyance. Then, the head unit 120 is scanned when stopped, and an image is recorded on the entire surface of the recording medium P.
Thus, the image formed on the entire surface of the recording medium P by the head unit 120 is fixed by the fixing / conveying means 116 as the recording medium P is nipped and conveyed by the fixing / conveying means 116 as described above. Is done.

Here, a region on the conveyor belt (hereinafter referred to as a strong electric field forming region 140) that gives a strong electric field strength to the discharge portion by the strong electric field generating means 13 when the discharge head 120a is at the opposite position will be described with reference to FIG. To do. Here, in this specific embodiment, the strong electric field forming region 140 is a strong charging portion that is charged to a high potential by a scorotron charger.
12 (A) to 12 (C) are partial enlarged views schematically showing the strong electric field forming region 140 on the conveyor belt 108. FIG. In FIGS. 12A to 12C, the recording medium P is conveyed from the lower direction to the upper direction in the drawing. 12B and 12C show the case where the head unit 120 (ejection head 120a) is a serial head, and the head unit 120 is scanned in the left-right direction in the figure.

  In the case of the line head as in the present embodiment, as shown in FIG. 12A, the strong electric field forming region 140 is disposed upstream of the recording medium P in the conveyance direction, that is, in the width direction of the conveyance belt 20, that is, in the direction orthogonal to the conveyance direction. It is as having mentioned above to provide in the length substantially the same as this length.

Further, when the head unit is a serial head as described above, it is not limited to the above example, and as shown in FIG. 12B, a strong electric field having a width at least equal to or larger than the width of the head unit 120 is formed on the conveyor belt 108. By providing the formation region 140, the effect of the present invention can be obtained.
Further, in the case of a serial head, as shown in FIG. 12C, the strong electric field forming region 140 is transported to both ends of the transport belt 108 in the direction orthogonal to the transport direction of the recording medium P. You may extend in the direction.
As described above, by providing the strong electric field forming region 140, when the ejection head 120 a is scanned in a direction orthogonal to the recording medium P and an image is recorded on the recording medium P, the ejection head 120 a is moved to the strong electric field forming region 140. By scanning to the opposite position, even when an image is recorded on the recording medium P, a strong electric field is applied to the ejection portion of the ejection head 120a immediately before the recording medium P and the ejection head 120a are relatively moved to a position where image recording is possible. The discharge characteristics of the discharge part can be made constant. Thereby, the drawing stability can be further improved.

Here, in the present invention, at least before recording on the recording medium P, it is sufficient to form a strong electric field in all the ejection portions of the head unit 120, and the head unit 120 is moved to a position facing the strong electric field forming region 140. The number, frequency, and the like of generating a strong electric field in the ejection unit of the head unit 120 are not particularly limited, and the head can be moved a predetermined number of times even if the head unit 120 is moved to a position facing the strong electric field forming region 140 each time the head unit 120 is scanned. Each time the unit 120 is scanned, the unit 120 may be moved to a position facing the strong electric field forming region 140.
Further, the length of the strong electric field forming region 140 in the longitudinal direction can be set to an arbitrary length such as substantially the same length as the recording medium P and the entire circumference of the transport belt 108.
Furthermore, in the example shown in FIG. 6C, the strong electric field forming region 140 is provided at both ends in the direction orthogonal to the conveyance direction of the conveyance belt 108, but in the direction orthogonal to the conveyance direction of the conveyance belt 108. Only one of the ends may be provided.

  Next, the ink circulation system 122 is for flowing ink sufficient for ink discharge into the ink flow paths 78 (see FIG. 2) of the discharge heads 120a of the respective colors of the head unit 120, and has four colors (C, M, Y). , K), an ink circulation device 122a having an ink tank of each color, a pump, a replenishment ink tank (not shown), and the like, and an ink flow path of each color discharge head 120a from the ink tank of the ink circulation device 122a. 78 (see FIG. 2), an ink supply system 122b including an ink supply path composed of an ink piping system for each color for supplying each color ink (from the right side in FIG. 2), and an ejection head 120a for each color of the head unit 120. An ink collection path comprising an ink piping system of each color for collecting ink from the ink flow path 78 (left side in FIG. 2) to the ink circulation device 122a. And a non-ink recovery system 122c.

  The ink circulation system 122 supplies ink for each color from the ink tank to the head unit 120 via the ink supply system 122b by the ink circulation device 122a, and for each color from the head unit 120 via the ink supply system 122c. Any ink can be used as long as it can be collected and circulated in the ink tank. The ink tank stores image recording ink, and the ink is pumped out by a pump and sent to the head unit 120. As the ink is discharged from the head unit 120, 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 the detected ink density is detected. Accordingly, it is desirable to appropriately replenish the ink from the replenishment 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.
Examples of the ink temperature control device include a head unit 120, an ink tank, an ink piping system, a heating element such as a heater, a heating means and / or a heating / absorption element such as a Peltier element, and / or a cooling means such as a cooler. A temperature control element, temperature control means, and its controller and temperature sensor are provided, and the temperature control element and temperature control means are controlled by the controller according to the ink density detected by the temperature sensor, and the temperature control element and temperature control means A well-known temperature control unit, such as one in which a temperature sensor and a controller are integrated, for example, controlled by 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.

  The head driver 124 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 120 based on the image data. This system control unit color-separates image data received from an external device such as a computer, a RIP, an image scanner, a magnetic disk device, a thumbtack data transmission device, and the like. This is head drive data corresponding to the image data for the head driver 124 to drive the head unit 120 (discharge head 120a) by dividing the logarithm and performing the screening process and dot area ratio calculation.

Further, the system control unit controls the movement of the head unit 120 (recording position control means 128) in accordance with the conveyance timing of the recording medium P by the conveyance belt 108 and the ink ejection timing by the head unit 120. The discharge timing is controlled by using the output of the recording medium position detecting means 126 and the output signal from the encoder or photo interpreter disposed on the conveying belt 108 or the driving means of the conveying belt 108.
The recording medium position detection means 126 is for detecting the recording medium P conveyed to the ink droplet ejection position by the head unit 120, and known detection means such as a photosensor can be used.

  The recording position control means 128 adjusts the image forming position in the width direction on the recording medium P by placing and fixing the head unit 120 and moving it in the width direction of the conveying belt 108. That is, the recording position control means 128 detects the conveyance belt position for fine adjustment for forming an image at a predetermined position of the recording medium P and for sub-scanning when a multichannel head is used as the head unit 120. The head unit 120 is moved in accordance with the position of the conveyor belt 108 detected by the means 109 and the image signal from the head driver 124.

Next, solvent recovery means in the inkjet printer 100 will be described.
The ink jet printer 100 includes a discharge fan 130 and a solvent recovery device 132 as solvent recovery means. From the ink droplets including the color material particles discharged from the head unit 120 onto the recording medium P and the dispersion solvent for dispersing the color material particles. The dispersed solvent that evaporates from the recording medium P when the image formed by the ink droplets is fixed is recovered.
The discharge fan 130 is for sucking the air inside the casing 101 of the inkjet printer 100 and sending it to the solvent recovery device 132.
The solvent recovery device 132 includes a solvent vapor absorber, and adsorbs the solvent component of the gas containing the solvent vapor sucked by the exhaust fan 130 onto the solvent vapor absorber, and the gas after the solvent is adsorbed and recovered. The ink is discharged out of the casing 101 of the inkjet printer 100. 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 colors of inks of C, M, Y, and K has been described. However, the present invention is not limited to this and is a monochrome recording apparatus. The recording may be performed by using an arbitrary number of inks of other colors, for example, light colors or special colors. In that case, the number of head units 120 and ink circulation systems 122 corresponding to the number of ink colors are used.

  In any of the above examples, the color material particles in the ink are positively charged, and the recording electrode or the counter electrode (conductive platen) on the back of the recording medium is set to a negative high voltage, and image recording is performed by the ejected ink jet. Although the ink jet recording apparatus is described, the present invention is not limited to this, and conversely, the color material particles in the ink are negatively charged, the recording medium or the counter electrode is set to a positive high voltage, and the ink jet recording apparatus is used. Image recording may be performed. Thus, when the polarity of the color material particles is reversed from the above example, the polarity of the voltage applied to the charging means, the counter electrode, and the drive electrode of the electrostatic ink jet head is reversed from the above example. good.

  Further, the electrostatic ink jet recording apparatus of the present invention is not limited to one that discharges ink containing charged color material components, and is not particularly limited as long as it is a liquid discharge head that discharges liquid containing color material 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 a target by discharging droplets using charged particles.

  The electrostatic ink jet recording apparatus and the recording method according to the present invention have been described in detail with reference to various embodiments. However, the present invention is not limited to the above various embodiments and does not depart from the gist of the present invention. Of course, various improvements and changes may be made in the range. For example, by charging means

1 is a schematic diagram illustrating a schematic configuration of an ink jet recording apparatus of the present invention. It is a schematic diagram of an example of the inkjet head of the inkjet recording device shown in FIG. FIG. 6 is a diagram schematically illustrating a state in which a plurality of discharge ports 82 are two-dimensionally arranged on a discharge port substrate 76 of the discharge head 16. It is the figure which showed typically the planar structure of the guard electrode of the inkjet head of a multichannel structure. (A) is a partial cross-sectional perspective view showing the configuration in the vicinity of the ejection portion in the inkjet head of FIG. 2, and (B) is a diagram for explaining the shape dimensions of the ink guide weir. (A) is an enlarged view around the strong electric field generating means shown in FIG. 1, and (B) is a graph showing the relationship between the conveyance belt position and the grit voltage applied to the scorotron charger by the voltage controller. And (C) is a graph showing the relationship between the transport belt position and the potential charged on the transport belt (potential on the transport belt), and (D) is applied to the scorotron charger by the voltage controller. It is a graph which shows the relationship between the grit voltage and time which are. It is a schematic diagram which shows schematic structure of the other example of the inkjet recording device of this invention. (A) is an enlarged view of the periphery of the ejection head shown in FIG. 7, and (B) is the relationship between the position of the ejection head on the transport belt and the voltage applied to the belt roller and the conductive layer by the voltage controller. It is a graph which shows. It is a schematic diagram which shows schematic structure of the other example of the inkjet recording device of this invention. (A) is an enlarged view of the periphery of the ejection head shown in FIG. 9, and (B) is a graph showing the relationship between the position of the conveyor belt and the voltage applied to the conductive platen by the voltage controller. It is a conceptual diagram of a specific example of the ink jet recording apparatus of the present invention. (A)-(C) are the elements on larger scale which show typically the example of the strong electric field formation area on a conveyance belt. It is a conceptual diagram which shows an example of the inkjet head of the conventional inkjet recording device.

Explanation of symbols

10, 50, 100 Inkjet recording device 12, 62 Conveying means 13, 51, 65 Strong electric field generating means 14 Charging means 15, 52, 68 Voltage control means 16 Discharge head 20, 64 Conveying belt 22, 24 Belt roller 30 Insulating layer 32 Conductive layer 40 Scorotron charger 42 High voltage source 62 Conductive platen 72 Head substrate 74 Ink guide 74a Tip portion 76 Discharge port substrate 78 Discharge electrode 80 Guard electrode 82 Each discharge port 84 Ink flow path 86 Insulating substrate 88 Insulating layer 90 Opening 92 Control unit 94 Guide weir 102 Feed roller 104 Guide 106a, 106b, 106c Roller 108 Conveying belt 109 Conveying belt position detecting means 100 Charging means 112 Static eliminating means 114 Peeling means 116 Fixing / conveying means 118 Guide 120 Head unit 120a Inkjet head 122 Ink circulation system 124 Head driver 126 Recording medium position detection means 128 Recording position control means 130 Discharge fan 132 Solvent recovery device 140 Strong electric field formation region P Recording medium Q Ink R Ink droplet

Claims (14)

A transport unit that transports the recording medium mounted on the insulating mounting unit, the insulating mounting unit mounting a recording medium on which an image is recorded;
An ink jet head that is disposed at a position facing the conveying means and has a discharge section that discharges ink droplets onto the recording medium by applying an electrostatic force to ink according to an image signal;
Immediately before the recording medium and the inkjet head are relatively moved to a position where an image can be recorded, an electric field strength stronger than an electric field strength formed in the ejection portion when ink droplets are not ejected during image recording on the recording medium. An ink jet recording apparatus, comprising: a strong electric field generating unit that supplies the discharge part to the discharge unit.   2. The strong electric field forming unit gives a strong electric field strength to the ejection unit immediately before the recording medium is conveyed by the conveying unit to a position where an image can be recorded by the inkjet head. The ink jet recording apparatus described in 1. The inkjet head is capable of scanning in at least one direction with respect to the recording medium,
3. The strong electric field generating means gives a strong electric field strength to the ejection unit immediately before the inkjet head is scanned to a position where an image can be recorded on the recording medium. The ink jet recording apparatus described in 1. The transport means has a transport belt for fixing the recording medium,
The strong electric field generating unit includes a charging unit that charges at least one of the recording medium and the conveyance belt and electrostatically attracts the recording medium and the conveyance belt, and a charging unit control unit that controls the charging unit. And
4. The control unit according to claim 1, wherein the charging unit control unit performs control to charge at least a part of the conveyance belt on the upstream side in the conveyance direction from the fixing position of the recording medium to a higher potential than the recording medium. An ink jet recording apparatus according to claim 1.   The transport means includes a transport belt including an insulating layer constituting a contact surface with the recording medium, and a conductive layer provided on a surface opposite to the contact surface of the insulating layer with the recording medium. The inkjet recording device in any one of 1-4. The strong electric field generating means has a voltage control unit for controlling a voltage applied to the conductive layer,
The ink jet recording apparatus according to claim 5, wherein the voltage control unit applies a predetermined voltage to the conductive layer immediately before the recording medium and the ink jet head are relatively moved to a position where an image can be recorded. The transport means has a transport belt formed of an insulating member,
The strong electric field generating means includes a conductive plate-like member disposed in contact with the conveyance belt on a surface opposite to the inkjet head side at a position facing the inkjet head of the conveyance belt; A voltage control unit for controlling the voltage applied to the adhesive plate member,
The voltage control unit applies a predetermined voltage to the conductive plate member immediately before the recording medium and the inkjet head are relatively moved to a position where an image can be recorded. Inkjet recording apparatus. The inkjet head includes an ejection port for ejecting ink droplets;
The ink jet recording apparatus according to claim 1, further comprising: an ink guide that passes through the discharge port and has a leading end protruding toward a recording medium from an opening surface of the discharge port. The inkjet head includes an ejection port substrate in which the ejection port is opened,
The ink guide is disposed at a predetermined interval from the discharge port substrate, forms an ink flow path between the discharge port substrate, and the ink guide is positioned at a position facing the discharge port arrangement on the surface on the discharge port substrate side. A formed head substrate;
The inkjet recording apparatus according to claim 8, further comprising: an ejection electrode that is disposed around the ejection port of the ejection port substrate and controls ejection of ink droplets from the ejection port. The ink jet head causes an electrostatic force to act on ink according to an image signal on the recording medium conveyed to a position facing the ink jet head by the conveying means, thereby ejecting ink droplets from the ejection unit onto the recording medium. An inkjet recording method for recording an image on a recording medium,
Immediately before the recording medium and the inkjet head are relatively moved to a position where an image can be recorded, an electric field strength stronger than an electric field strength formed in the ejection portion when ink droplets are not ejected during image recording on the recording medium. Is applied to the discharge section.   The inkjet recording method according to claim 10, wherein the strong electric field strength is instantaneously applied to the ejection unit before the recording medium is transported to a position facing the inkjet head.   12. The ink jet recording method according to claim 10, wherein an upstream side in the transport direction of the transport unit with respect to the recording medium is charged at a higher potential than the recording medium, and the strong electric field strength is applied to the ejection unit. .   The inkjet recording method according to any one of claims 10 to 12, wherein a predetermined voltage is applied to the conveying unit to give the strong electric field strength to the ejection unit. The inkjet head includes an ejection port for ejecting ink droplets;
14. The ink jet recording method according to claim 10, further comprising: an ink guide that passes through the ejection port and has a leading end projecting toward the recording medium from the opening surface of the ejection port.

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