JP2007001182A - Inkjet recording apparatus and recording method, as well as inkjet printing plate manufacturing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inkjet recording apparatus capable of forming a high definition image, allowing no moire to be visually recognized. <P>SOLUTION: The inkjet recording apparatus is equipped with an ejection port substrate with the ejection port for ejecting ink opened, a head substrate which is arranged away from the ejection port substrate by a prescribed distance and forms an ink passage in a space with respect to the ejection port substrate, a control means for controlling the ejection of the ink from the ejection port, an inkjet head which penetrates through substantially the center of the ejection port and has an ink guide arranged on the head substrate so that its tip end is directed toward the ejection direction of the ink, a threshold matrix generation device 176 which generates the threshold matrix for converting a multi-value image signal into a binary image signal corresponding to the image recorded on the recording medium, and a head control means for controlling the ejection of ink droplets by the inkjet head based on the binary image signal which is converted according to the threshold matrix. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an ink jet recording apparatus and a recording method for forming an image on a recording medium by discharging ink by electrostatic force, and an ink jet plate making apparatus for manufacturing a printing plate by discharging ink to a printing substrate.

There is known an electrostatic ink jet recording method in which ink is ejected toward a recording medium by using an electrostatic force. In an electrostatic ink jet recording system, electrostatic force is generated by applying a predetermined voltage (driving voltage) to an ejection electrode (driving electrode) of an ink jet head in accordance with image data using ink containing charged fine particles. In this method, ink ejection is controlled to record an image corresponding to image data on a recording medium.
As an example of such an electrostatic ink jet recording apparatus, Patent Document 1 discloses that an ink guide is installed in a through hole that functions as a nozzle for discharging ink, and an ejection electrode is provided around the through hole. An ink jet recording apparatus having an installed structure is disclosed. In this ink jet recording apparatus, an electric field is generated in the vicinity of the through hole by applying a voltage corresponding to the recording data to the ejection electrode, and a force due to the electric field acts on the meniscus of the ink formed in the through hole. Thus, ink droplets are ejected from the through holes toward the recording medium. The ink jet head according to the electrostatic ink jet method can form micro droplets and has a simple structure, so that it is easy to make a multi-channel structure in which a plurality of discharge ports (channels) are arranged in one head. There is.

In recent years, in the field of printing, a plate making method for directly drawing an image on a printing plate original plate using such an electrostatic ink jet recording method has been proposed. That is, based on the image data signal, an electrostatic inkjet head that discharges oil-based ink using an electrostatic field is used to form an image directly on the plate material, and then the image is fixed on the plate material and printed. A method of making a plate has been proposed. In such a method, since an image is formed on a plate material without using a laser, the plate making apparatus can be made compact, and it is not necessary to treat the plate material after being exposed to a laser with a developer. Therefore, it is preferred for environmental conservation.
Also, in the field of printing, halftone dots are used to express the shading of an image, and as a halftone dot conversion method, an amplitude modulation method (a modulation method that modulates the size of dots in accordance with a multilevel image signal ( AM method) was the mainstream. In such a system, since dots are regularly arranged, a periodic striped pattern called moire may occur. As a method for preventing the occurrence of such moire, a frequency modulation method (FM method) in which the dot size is the same and the density is modulated in accordance with the multi-value image signal is known, and a mesh screen in accordance with the FM method is created. Various methods for achieving this have been studied (see, for example, Patent Document 2).

JP 10-138493 A JP 2001-270071 A

By the way, the conventional inkjet method has low accuracy of the landing position of the ink droplet, and it is difficult to obtain a high-resolution color image. In order to increase the resolution of the color image, it is conceivable to make the ink droplets minute and improve the accuracy of the landing position. Similarly, when an electrostatic ink jet system is applied to a plate making apparatus, in order to obtain a high-resolution printed matter, it is necessary to reduce the size of ink droplets ejected from the ink jet head and improve the accuracy of the landing position. desired. The present applicant disclosed in Japanese Patent Application No. 2004-357186 an ink jet head and an ink jet recording apparatus in which ink droplets are miniaturized and the landing positions of the ink droplets are improved. By using such an ink jet head, an extremely high-definition color image having a resolution of 1200 dpi or more can be formed on a recording medium.
However, when forming a high-definition color image using this inkjet head or making a printing plate for printing a high-definition color image, because the accuracy of the landing position of the ink droplet is high, There is a possibility that an unsightly regular pattern (moire) may be visually recognized in the color image.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide an ink jet recording apparatus and a recording method capable of forming a high-definition image in which moire is not visually recognized, and ink jet plate making. To provide an apparatus.

  In order to solve the above-described problem, a first aspect of the present invention is an inkjet recording apparatus that ejects ink droplets toward a recording medium, the ejection port for ejecting the ink, and the ejection port An ink jet head having a control means for controlling the ejection of the ink, and a threshold value for creating a threshold value matrix for converting a multi-value image signal corresponding to an image recorded on the recording medium into a binary image signal An inkjet recording apparatus comprising: a matrix creation device; and a head control unit that controls ejection of the ink droplets by the inkjet head based on a binary image signal converted according to the threshold matrix.

In the first aspect of the present invention, the opening shape of the ejection port of the inkjet head is preferably a shape having an aspect ratio between the length in the ink flow direction and the length in the direction perpendicular to the ink flow direction, which is greater than 1. .
The inkjet head includes a discharge port substrate in which the discharge port is opened, a head substrate that is disposed at a predetermined interval from the discharge port substrate, and forms an ink flow path between the discharge port substrate; It is preferable that the ink guide has an ink guide disposed on the head substrate so as to penetrate substantially the center of the ejection port and have a tip thereof facing the ink ejection direction.
The inkjet head further includes a discharge electrode that is disposed so as to surround the discharge port and discharges ink droplets by applying an electrostatic force to the ink, and discharges ink droplets from the discharge electrodes. It is preferable that the effective portion that contributes has a substantially symmetric shape with respect to the discharge port.

In the ink jet recording apparatus according to the first aspect of the present invention, the threshold value matrix creating device includes another threshold value matrix having the same configuration arranged around the threshold value matrix when determining the threshold values in ascending order or descending order. It is preferable that the position of the new threshold value is determined so that the distance between the already determined threshold position and the threshold position to be newly arranged is most separated.
Alternatively, when determining threshold values in ascending or descending order, including a threshold matrix having the same configuration arranged around the threshold matrix, a predetermined weighting filter is applied around the determined threshold position. By obtaining a weighting distribution by the weighting filter in the threshold matrix by cumulatively adding or subtracting a weighting value, and setting a position corresponding to a minimum value or a maximum value of the weighting distribution as a new threshold position, It is preferable to sequentially determine the position of the threshold value.
Alternatively, when the threshold values are determined in ascending order or descending order, they are already determined on the highlight side and the shadow side of the threshold value constituting the threshold value matrix, including another threshold value matrix having the same configuration arranged around the threshold value matrix. The position of the new threshold value is determined so that the distance between the threshold value position and the threshold value position to be newly arranged is farthest from each other, and in the middle part of the threshold value, from the same configuration arranged around the threshold value matrix Including the other threshold matrix, the weighting distribution by the weighting filter in the threshold matrix is obtained by applying a predetermined weighting filter centering on the position of the already determined threshold, and cumulatively adding or subtracting the weighted value. And a position corresponding to the minimum value or maximum value of the weight distribution is set as a new threshold value position. It is preferable to determine the position of the sequential threshold.

In addition, the threshold value matrix creating apparatus previously forms a plurality of combinations of test patterns in which a target pixel and its surrounding pixels are turned on / off on a desired output medium, and the density or halftone dot area ratio of each test pattern. , The correction value depending on the on / off state of the surrounding pixels is obtained, and then, including other threshold matrixes having the same configuration arranged around the threshold matrix, have already been determined. After making the correction value correspond to the threshold value position, it is preferable that the weighting filter is applied to the correction value centering on the already determined threshold value position.
When using a weighting filter, the weighting filter is preferably a point spread function obtained from visual characteristics.
Further, it is preferable that the test pattern is formed as a desired printed material, and the correction value is obtained by measuring a density or a dot area ratio of the printed material.
The position is preferably determined in ascending order, descending order of threshold values, or alternately in ascending order and descending order.

  According to a second aspect of the present invention, there is provided an ink jet recording method in which an ink droplet is ejected toward a recording medium to record an image on the recording medium, wherein the ejection opening for ejecting the ink is opened. A head substrate that is disposed at a predetermined interval from the outlet substrate and the ejection port substrate and forms an ink flow path between the outlet substrate and a control for controlling ejection of the ink from the ejection port And an image recorded on the recording medium using an inkjet head having an ink guide disposed on the head substrate so that the leading end of the ejection port substantially passes through the center of the ejection port and the front end faces the ejection direction of the ink. A threshold matrix for converting a multi-value image signal corresponding to the binary image signal is created, and the inkjet head is applied to the inkjet head based on the binary image signal converted according to the threshold matrix. By controlling the ejection of the ink droplets to provide an ink jet recording method for recording an image on the recording medium that.

  According to a third aspect of the present invention, there is provided an ink jet plate making apparatus comprising the ink jet recording apparatus according to the first aspect of the present invention and a holding means for holding the recording medium, and using a printing substrate as the recording medium.

According to the ink jet recording apparatus and the recording method of the present invention, a minute ink droplet can be landed on a recording medium with high accuracy, and an ink liquid by an ink jet head based on a binary image signal converted according to a threshold matrix. Droplet ejection can be controlled, so even if a high-definition color image of 1200 dpi or higher is formed on a recording medium, moire which is an unsightly regular pattern is not visually recognized, and an image is formed satisfactorily. can do.
In addition, according to the inkjet plate making apparatus of the present invention, it is possible to produce a printing plate for printing a high-definition color image of 1200 dpi or more without observing moire which is an unsightly regular pattern.

Hereinafter, an ink jet recording apparatus, a recording method, and an ink jet plate making apparatus according to the present invention will be described in detail based on preferred embodiments shown in the accompanying drawings.
First, a preferred embodiment when the ink jet recording apparatus of the present invention is used as an ink jet printer will be described in detail. FIG. 1A shows a schematic configuration of an ink jet recording apparatus according to the present invention. The ink jet recording apparatus of the present invention (hereinafter referred to as the printer 60) is an apparatus that performs printing of four colors on one side of a recording medium P, and transports the recording medium P, and records an image on the recording medium P. Image recording means and solvent recovery means for carrying out the above, and these are housed in a casing 61.
The conveying means includes a feed roller pair 62, a guide 64, rollers 66 (66a, 66b and 66c), a conveying belt 68, a conveying belt position detecting means 69, an electrostatic adsorption means 70, a static eliminating means 72, a peeling means 74, fixing and conveying. Means 76 and guide 78 are included. The image recording unit includes a head unit 80, an ink circulation system 82, a head driver 84, and a recording medium position detection unit 86. The solvent recovery means includes a discharge fan 90 and a solvent recovery device 92.
Hereinafter, the conveying means, the image recording means, and the solvent recovery means constituting the ink jet recording apparatus will be described in detail. First, the image recording means will be described.

  The image recording means of the printer 60 includes a head unit 80 that ejects ink as droplets, an ink circulation system 82 that supplies and recovers ink Q to the head unit 80, a computer (not shown), and an external device such as a RIP (Raster Image Processor). And a recording medium position detecting means 86 for detecting the recording medium P in order to determine the image recording position in the recording medium P.

FIG. 1B is a perspective view schematically showing the head unit 80 and the conveying means for the recording medium P around it.
The head unit 80 has four inkjet heads 80a corresponding to ink ejection of four colors of cyan (C), magenta (M), yellow (Y), and black (K) for recording a full color image. Then, in accordance with a signal from the head driver 84 to which the image data is supplied, the ink Q supplied by the ink circulation system 82 is ejected as an ink droplet R, and the recording medium P being conveyed by the conveying belt 68 at a predetermined speed. Record an image on The inkjet heads 80 a for the respective colors are arranged in the conveyance direction of the conveyance belt 68.

In the illustrated example, each inkjet head 80a is a line head in which nozzles for ejecting ink are arranged in the entire width direction of the recording medium P, and a multi-channel head having a structure in which a plurality of nozzles are arranged in a staggered manner. is there.
Therefore, in the illustrated example, the recording medium P is held by the transport belt 68 and the recording medium P is simply passed through the head unit 80 once by transport, that is, only one scanning transport is performed. An image is formed on the entire surface of the recording medium P. Accordingly, image recording (drawing) can be performed at a higher speed than when the ejection head is serially scanned.

  Thus, the image formed on the entire surface of the recording medium P by the head unit 80 is fixed by the recording medium P being nipped and conveyed by the fixing / conveying means 76 described later.

Here, the configuration of the inkjet head of the head unit 80 will be described in detail with reference to the drawings.
2A schematically shows a cross-section of the schematic configuration of the inkjet head, and FIG. 2B shows a view taken along the line IB-IB in FIG. 2A. As shown in FIG. 2A, the inkjet head 10 includes a head substrate 12, an ink guide 14, and a discharge port substrate 16 on which discharge ports 28 are formed. On the discharge port substrate 16, discharge electrodes 18 are arranged so as to surround the discharge port 28. A counter electrode 24 that supports the recording medium P and a charging unit 26 of the recording medium P are disposed at a position facing the ink discharge side surface (upper surface in the drawing) of the inkjet head 10.
In addition, the head substrate 12 and the discharge port substrate 16 are arranged at a predetermined interval while facing each other. An ink flow path 30 that supplies ink to each ejection port 28 is formed by a space formed between the head substrate 12 and the ejection port substrate 16.

  The inkjet head 10 has a multi-channel structure in which a plurality of ejection ports 28 (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 28 are two-dimensionally arranged on the discharge port substrate 16 of the inkjet head 10. 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 inkjet head 10, the number of ejection ports 28, the physical arrangement position thereof, and the like can be freely selected. For example, not only a multi-channel structure as shown in FIG. 3 but also a single discharge 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. In addition, the inkjet head can be used for both monochrome and color recording apparatuses.

FIG. 3 shows a part of the multi-channel structure (3 rows and 3 columns), and as a preferred mode, in the ink flow direction, the downstream side ejection ports 28 are arranged in the upstream side. 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. Further, the vertical direction shown in FIG. 3 may be the ink flow direction.

  In such an ink jet head 10, 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 driving voltage is applied to the ejection electrode 18 provided on the ejection port substrate 16 to generate an electric field at the ejection port 28, and the ink in the ejection port 28 is ejected by electrostatic force. Further, by turning on / off the drive voltage applied to the ejection electrode 18 according to the image data (ejection on / off), the ink droplets are ejected from the ejection port 28 according to the image data, and the recording medium P Record the image on top.

  Hereinafter, the structure of the inkjet head 10 shown in FIGS. 2A and 2B will be described in more detail.

  As shown in FIG. 2A, the discharge port substrate 16 of the inkjet head 10 includes an insulating substrate 32, a guard electrode 20, a discharge electrode 18, and an insulating layer 34. A guard electrode 20 and an insulating layer 34 are sequentially stacked on the upper surface of the insulating substrate 32 in the drawing (the surface opposite to the side facing the head substrate 12). In addition, the discharge electrode 18 is formed on the lower surface of the insulating substrate 32 in the figure (the surface facing the head substrate 12).

Further, the discharge port substrate 16 is formed with a discharge port 28 for discharging the ink droplet R penetrating the insulating substrate 32. As shown in FIG. 2B, the ejection port 28 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 an aspect ratio (L / D) between the length D in the direction orthogonal to the ink flow and a shape of 1 or more.
In the present invention, in this way, the opening 28 has an aspect ratio (L / D) between the length L in the ink flow direction and the length D in the direction orthogonal to the ink flow of 1 or more (the ink flow direction is long). By making the side a shape having anisotropy and a long hole shape having the ink flow direction as a long side), the ink easily flows into the ejection port 28. That is, it is possible to improve the ink particle supply to the ejection port 28, improve the frequency response, and prevent clogging. This will be described in detail later along with the action of discharging ink droplets.

  In the present embodiment, the ejection port 28 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 28, 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 28 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 14 of the inkjet head 10 is made of a ceramic flat plate having a predetermined thickness, and is disposed on the head substrate 12 corresponding to each ejection port 28 (ejection unit). The ink guide 14 is formed wide according to the length in the long side direction of the bowl-shaped discharge port 28. As described above, the ink guide 14 passes through the ejection port 28, and the tip end portion 14 a protrudes above the surface of the ejection port substrate 16 on the recording medium P side (the surface of the insulating layer 34).

The leading end portion 14a of the ink guide 14 is formed into a substantially triangular shape (or trapezoid) that gradually becomes thinner toward the counter electrode 24 side. The ink guide 14 is disposed so that the inclined surface of the tip portion 14a intersects the ink flow direction. As a result, the ink flowing into the ejection port 28 reaches the apex of the leading end portion 14 a along the inclined surface of the leading end portion 14 a of the ink guide 14, so that an ink meniscus is stably formed at the ejection port 28.
Further, by forming the ink guide 14 wider in the long side direction of the ejection port 28, the width in the direction perpendicular 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 14 is not particularly limited as long as the colorant particles in the ink Q can be concentrated in the tip portion 14a through the discharge port 28 of the discharge port substrate 16, and for example, the tip portion 14a. The shape does not have to be thinned toward the counter electrode, and can be changed as appropriate. For example, a cutout serving as an ink guide groove that collects the ink Q in the front end portion 14a may be formed in the center portion of the ink guide 14 in the vertical direction in the drawing by capillary action.
Further, it is preferable that a metal is deposited on the most advanced portion of the ink guide 14. By depositing metal on the leading edge of the ink guide 14, the dielectric constant of the tip portion 14a of the ink guide 14 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, the discharge electrode 18 is formed on the lower surface of the insulating substrate 32 (the surface facing the head substrate 12). The ejection electrode 18 is arranged in a U-shape in which one side on the upstream side of the ink flow is cut out along the peripheral edge of the ejection port 28 so as to surround the periphery of the rectangular ejection port 28. In FIG. 2B, the ejection electrode 18 is formed in a U-shape, but may be any shape as long as it is an electrode arranged so as to face the ink guide, for example, a square electrode, Various shapes such as a ring-shaped circular electrode, an elliptical electrode, a divided circular electrode, a parallel electrode, and a substantially parallel electrode can be used depending on the shape of the discharge port 28.

As described above, since the inkjet head 10 has a multi-channel structure in which the discharge ports 28 are two-dimensionally arranged, the discharge electrode 18 corresponds to each discharge port 28 as schematically shown in FIG. They are arranged two-dimensionally.
The ejection electrode 18 is exposed to the ink flow path 30 and is in contact with the ink Q flowing through the ink flow path 30. 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 18 is not necessarily exposed to the ink flow path 30 and in contact with the ink. That is, the discharge electrode 18 may be formed inside the discharge port substrate 16, or the exposed surface of the discharge electrode 18 may be covered with a thin insulating layer or the like.

  As shown in the figure, the discharge electrode 18 is connected to the control unit 33. The controller 33 can control the voltage applied to the ejection electrode 18 when ink is ejected and when ink is not ejected.

The guard electrode 20 is formed on the surface of the insulating substrate 32, and the surface of the guard electrode 20 is covered with an insulating layer 34. FIG. 4 schematically shows a planar structure of the guard electrode 20. FIG. 4 is a view taken along the line IV-IV in FIG. 2A and schematically shows a planar structure of the guard electrode 20 in the case of a multi-channel inkjet head. As shown in FIG. 4, the guard electrode 20 is a sheet-like electrode common to each discharge electrode such as a metal plate, and the discharge electrode 18 formed around each discharge port 28 arranged two-dimensionally. Has an opening 36 at a position corresponding to. The opening 36 is formed in a rectangular shape. The length and width of the opening 36 of the guard electrode 20 are formed larger than the length and width of the discharge port.
The guard electrode 20 can shield electric lines of force between the adjacent ejection electrodes 18 to suppress electric field interference, and a predetermined voltage is applied to the guard electrode 20 (including 0 V due to grounding). In the illustrated example, the guard electrode 20 is grounded to 0V.

As a preferred embodiment, the guard electrode 20 is formed in a layer different from the ejection electrode 18 as shown in FIG. 2A, and the entire surface is covered with an insulating layer 34.
By having such an insulating layer 34, electric field interference between the adjacent ejection electrodes 18 can be suitably prevented, and the color material particles of the ink Q are coated between the ejection electrodes 18 and the guard electrodes 20 to cause discharge. Can also be prevented.

Here, the guard electrode 20 secures the electric lines of force that act on the corresponding discharge ports 28 (hereinafter referred to as “own channels” for convenience) among the electric lines of force generated from the discharge electrodes 18. Therefore, it is necessary to shield the electric lines of force of the discharge electrode 18 provided in the discharge port 28 (also referred to as “other channel”) and the electric lines of force to the other channel.
When the guard electrode 20 is not provided, the electric lines of force generated from the end on the discharge port side of the discharge electrode 18 (hereinafter referred to as the inner edge of the discharge electrode) when discharging ink droplets are inside the discharge electrode 18, that is, the discharge It converges in a region surrounded by the inner edge of the electrode 18 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 18 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 18 and affect other channels. Cause electric field interference.

In consideration of the above points, the width and length of the rectangular opening 36 of the guard electrode 20 are such that the discharge of the self-channel is not observed when viewed from the plane of the substrate so as not to shield the lines of electric force to the self-channel. It is preferable to make it larger than the electrode 18. In other words, the end of the guard electrode 20 on the discharge port 28 side is preferably separated (retreated) from the discharge port 28 rather than the inner edge of the discharge electrode 18 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 36 of the guard electrode 20 are set so that the discharge electrode 18 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 20 is closer (advanced) to the discharge port 28 than the outer edge portion of the discharge electrode 18 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 28 is sufficiently ensured, and variations in the ink landing position due to electric field interference between adjacent channels are suitably suppressed, and the stability can be increased. It is possible to perform image recording with high image quality.

  The opening 36 of the guard electrode 20 is substantially similar to the shape formed by the inner edge or the outer edge of the ejection electrode 18, and the inner edge of the guard electrode 20 is more ejected than the inner edge of the ejection electrode 18 of its own channel. The guard electrode 20 may be provided so as to be separated from (retracted from) 28 and closer to (advance) the discharge port 28 than the outer edge of the discharge electrode (that is, the opening 36 of the guard electrode 20 may be formed). Good).

In the above example, the guard electrode 20 is a sheet-like electrode. However, the present invention is not limited to this, and the guard electrode 20 may be provided so as to shield the electric lines of force of other channels between the discharge ports. Any shape or structure may be used. For example, the guard electrode 20 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 discharge ports.
Even in such a case, the inner edge portion of the guard electrode 20 is further away from the discharge port 28 than the inner edge portion of the discharge electrode 18 with respect to the discharge electrode 18 of the own channel, and the discharge port 28 is separated from the outer edge portion of the discharge electrode 18. The guard electrode 20 may be formed so as to be close to the electrode.
Here, the shape of the opening 36 of the guard electrode 20 is substantially the same as the shape of the discharge port 28, but is not limited to this, and the lines of electric force between the adjacent discharge electrodes 18 are shielded. As long as electric field interference can be prevented, it can be formed in an arbitrary shape. For example, the shape may be a circle, an ellipse, a square, a rhombus, or the like.

In the inkjet head 10 of this embodiment, as a preferred embodiment, an ink guide weir 40 that guides ink to the ejection port 28 is provided on the head substrate 12. Hereinafter, the ink guide weir 40 will be described.
FIG. 5A is a partial cross-sectional perspective view showing the configuration in the vicinity of the ejection portion in the inkjet head 10 of FIG. In the drawing, in order to clearly show the structure of the ink guide weir 40, the discharge port substrate 16 is shown cut along the ink flow direction at a substantially central position of the ink guide 14.

  The ink guide weir 40 is located upstream and downstream in the ink flow direction of the ink guide 14 disposed at a position corresponding to the ejection port 28 on the ink channel 30 side surface of the head substrate 12, that is, the bottom surface of the ink channel 30. The surface is provided on the side and is inclined so as to gradually approach the discharge port substrate 16 from the vicinity of the position corresponding to the discharge port 28 toward the position corresponding to the center of the discharge port 28 with respect to the ink flow direction. have. That is, the ink guide weir 40 has a shape that is inclined toward the ejection port 28 along the ink flow direction.

  In addition, the ink guide weir 40 has a shape having a width substantially the same as the ejection port 28 in the direction orthogonal to the ink flow and having a wall surface extending from the bottom surface. In addition, the ink guide weir 40 does not block the discharge port 28 and secures a flow path for the ink Q from the surface on the ink flow channel 30 side of the discharge port substrate 16, that is, from the upper surface of the ink flow channel 30. It is provided at intervals. Such an ink guide weir 40 is provided in each discharge part.

  Thus, by providing the ink guide weir 40 that is inclined toward the ejection port 28 along the ink flow direction on the bottom surface of the ink flow path 30, an ink flow toward the ejection port 28 is formed, and the ink Q The discharge port 28 is guided to the opening on the ink flow path 30 side. Therefore, the ink Q can be suitably flown into the discharge port 28, 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 40 in the ink flow direction may be set as appropriate so that the ink Q can be suitably guided to the ejection port 28 within a range that does not interfere with the adjacent ejection unit. As shown in FIG. 4, the height h of the highest part of the ink guide weir 40 is preferably 3 times or more (l / h ≧ 3), more preferably 8 times or more (l / h ≧ 8). preferable.

  The width of the ink guide weir 40 in the direction perpendicular to the ink flow is preferably equal to or slightly wider than the ejection port 28. Further, the width of the ink guide weir 40 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 guide weir 40 may be a shape suitable for guiding the ink Q to the ejection port 28, and may be a slope having a certain tilt angle. It may be a changing surface or a curved surface. 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 28.
Further, the vicinity of the contact portion of the upper part of the ink guide weir 40 with the ink guide 14 may have a smoothly connected shape without a step as in the illustrated example.

  In the illustrated example, the ink guide weir 40 is arranged on the upstream side and the downstream side of the ink guide 14, but a trapezoidal ink guide weir 40 having slopes on the upstream side and the downstream side of the ejection port 28 is provided. The ink guide 14 may be erected on the upper portion, or the ink guide 14 and the ink guide weir 40 may be integrally formed. As described above, the ink guide weir 40 may be formed separately or integrally with the ink guide 14 and attached to the head substrate 12, or the head substrate 12 is shaved by a conventionally known excavation means. It may also be formed.

  The ink guide weir 40 may be provided on the upstream side of the ejection port 28, but the height in the ejection direction of the ink droplets R is also ejected on the downstream side of the ejection port 28 as shown in the illustrated example. It is preferable to be provided so as to become lower as the distance from the outlet 28 increases. As a result, the ink Q guided toward the discharge port 28 by the upstream ink guide weir 40 flows smoothly to the downstream side, so that the ink Q does not become turbulent and the ink flow can be kept stable. , Discharge stability can be maintained.

In the example of FIG. 5, the ink guide weir 40 is disposed on the upper surface of the head substrate 12. 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 passing through a position corresponding to the ejection port 28 is provided along the ink flow direction, and is inclined toward the ejection port 28 along the ink flow direction at a position corresponding to the ejection port. An ink guide weir having a surface is provided. Thus, by providing the ink flow groove, most of the ink Q flowing through the ink flow path 30 can be selectively flowed to the ink flow groove. By providing the ink flow path weir, the ink Q is discharged from the ejection port 28. The ink can be preferably introduced into the interior of the ink guide, and the ink supply to the ink guide tip portion 14a can be improved.

As shown in FIG. 2A, the counter electrode 24 is disposed so as to face the ejection surface of the ink droplet R of the inkjet head 10.
The counter electrode 24 is disposed at a position facing the front end portion 14a of the ink guide 14, and is disposed on the grounded electrode substrate 24a and the lower surface of the electrode substrate 24a in the drawing, that is, the surface on the inkjet head 10 side. The insulating sheet 24b is used.
The recording medium P is held on the lower surface of the counter electrode 24 in the drawing, that is, the surface of the insulating sheet 24b by, for example, electrostatic adsorption, and the counter electrode 24 (insulating sheet 24b) is used as a platen of the recording medium P. Function.

At least during recording, the recording medium P held on the insulating sheet 24b of the counter electrode 24 is charged by the charging unit 26 to a predetermined negative high voltage having a polarity opposite to the drive voltage applied to the ejection electrode 18.
As a result, the recording medium P is negatively charged and biased to a negative high voltage, acts as a substantial counter electrode with respect to the ejection voltage 18, and is electrostatically adsorbed to the insulating sheet 24 b of the counter electrode 24.

  The charging unit 26 includes a scorotron charger 26a for charging the recording medium P to a negative high voltage, a high voltage power source 26b for supplying a negative high voltage to the scorotron charger 26a, and a bias voltage source 26c. Yes. The corona wire of the scorotron charger 26a is connected to the negative terminal of the high voltage power supply 26b, and the positive terminal of the high voltage power supply 26b and the metal shield case of the scorotron charger 26a are grounded. The negative terminal of the bias voltage source 26c is connected to the grit electrode of the scorotron charger 26a, and the positive terminal is grounded.

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

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

As shown in FIG. 2A, in the inkjet head 10, a color charged to the same polarity as the voltage applied to the ejection electrode 18 during recording, for example, positive (+), by an ink circulation mechanism including a pump or the like (not shown). Ink Q containing material particles circulates in the ink flow path 30 in the direction of the arrow (from the left to the right in the figure).
On the other hand, at the time of recording, the recording medium P is supplied to the counter electrode 24 and charged by the charging unit 26 to a polarity opposite to that of the color material particles, that is, negative high voltage (for example, −1500 V) and charged with a bias voltage. Thus, it is electrostatically attracted to the counter electrode 24.
In this state, while the recording medium P (counter electrode 24) and the inkjet head 10 are relatively moved, the controller 33 applies a pulse voltage (hereinafter referred to as a drive voltage) to the ejection electrode 18 in accordance with the supplied image data. ) Is applied. Basically, the ink droplets R are modulated and ejected according to the image data by ejecting on / off by applying the drive voltage on / off, and the image is recorded on the recording medium P.

Here, in a state where the drive voltage is not applied to the ejection electrode 18 (or in a state where the applied voltage is at a low voltage level), that is, in a state where only the bias voltage is applied, the ink Q has a bias voltage and The Coulomb attractive force with the charge of the color material particles (charged particles) of the ink Q, the Coulomb repulsion force between the color material particles, the viscosity of the carrier liquid, the surface tension, the dielectric polarization force, and the like are acting. These are coupled to move the color material particles and the carrier liquid. As shown conceptually in FIG. 1A, the ink Q has a meniscus shape slightly raised from the ejection port 28 and is balanced. It is taken.
Further, the color material particles are aggregated in the discharge port 28 by the electric field generated from the discharge electrode 18. 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. Accordingly, the ink Q is concentrated in the meniscus formed at the ejection port 28.

  From this state, a driving voltage is applied to the ejection electrode 18. 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 18. The electrostatic force causes the colorant particles and the carrier liquid to be pulled to the bias voltage (counter electrode) side, that is, the recording medium P side, so that the meniscus formed at the ejection port grows upward and substantially above the ejection port 28. A conical ink liquid column 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 18, a force (Coulomb force) mainly acting on the color material particles at the tip portion of the meniscus having a high electric field strength due to movement of the color material particles or the like. Etc.) and the surface tension of the carrier liquid are lost, and the meniscus is abruptly stretched to form an elongated ink liquid column having a diameter of several μm to several tens of μm, which is called a kite string.
Further, when a finite time has passed, the silk thread grows, and the growth of the silk thread, vibration caused by Rayleigh / Weber instability, uneven distribution of coloring material particles in the meniscus, uneven distribution of the electrostatic field applied to 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 ejection port of the inkjet head has an elongated slit shape elongated in the ink flow direction. As described above, the ejection port 28 is formed in a long and narrow slit-like 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 orthogonal to the ink flow is 1 or more, so that the ink is ejected from the ejection port. It becomes easy to flow inside, and the ink particle supply property to the ejection port 28 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 ejection port to 1 or more, the flow of ink becomes smooth and clogging at the ejection port can be prevented.
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, the ejection port preferably has an aspect ratio of 1.5 or more between the ink flow direction and the direction orthogonal thereto.
By setting the aspect ratio to 1.5 or more, the ink supply performance to the ink guide is further improved, and even when continuous large dots are formed, dots can be formed more stably, with higher frequency. Drawing can be performed at a drawing frequency.

  Here, as in the above-described embodiment, the above-described effect is more preferable by making the opening shape of the ejection port 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. In addition, it is possible to make the flow of ink smooth and prevent clogging at the discharge port by making the opening shape of the discharge port the aspect ratio of the major axis and minor axis of the aperture to 1 or more. it can.

  Further, it is preferable that the ejection electrode has a shape in which a part of the upstream side in the ink flow direction is missing as in the present embodiment. Accordingly, since an electric field that prevents the inflow of the color material particles from the upstream side in the ink flow direction to the ejection port is not formed, the color material particles can be efficiently supplied to the ejection port. Further, by disposing the ejection electrode on the downstream side of the ink, an electric field is formed in a direction in which the color material particles flowing into the ejection port are retained at the ejection 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.

Here, another form of the ejection electrode will be described.
6A to 6F are schematic views showing various forms of the ejection electrode. In FIGS. 6A to 6F, it is assumed that ink flows from the left to the right in the drawing.
As shown in FIG. 6A, the discharge electrode is symmetrical with respect to a plane (X-ray in FIG. 6A) passing through the center of the discharge port and parallel to the major axis direction of the discharge port. The longitudinal portion of the discharge electrode formed in the major axis direction of the outlet, that is, the surface excluding the hatched portion S in FIG. 6A passes through the center of the ejection port and is orthogonal to the major axis direction of the ejection port. It is preferable to have a symmetric shape with respect to (Y line in FIG. 6A).
Since the discharge part has a high contribution to the electric field formation and works substantially effectively, it is the longitudinal part of the discharge electrode. By forming the discharge electrode as described above, it passes through the center of the discharge port and the discharge port. An electric field that is substantially symmetrical with respect to a plane parallel to the major axis direction and a plane perpendicular to the longitudinal direction is formed, the ejection position is stable, the landing position of the ink droplet can be made constant, and more stable image formation is possible. Thus, a high-quality image can be formed.
Further, since the discharge electrode shown in FIG. 6A has a shape in which a part of the upstream side of the ink is cut out, as described above, the particle supply property to the discharge port is improved and the ink droplet is discharged. The position can be stabilized.

Here, in the above embodiment, the ejection electrode has a U-shape in which one side on the upstream side of the ink flow is cut out, but the present invention is not limited to this. For example, an elongated saddle-shaped shape in which both short sides of a rectangle obtained by cutting out a part of the upstream side of the ink flow as shown in FIG. 6B are semicircular may be used, as shown in FIG. An elliptical shape in which a long axis and a direction parallel to the ink flow direction are formed and a part on the upstream side of the ink flow is cut off may be used. Furthermore, a parallel electrode in which rectangular electrodes as shown in FIG. 6D are arranged in parallel to the major axis direction of the discharge port can also be suitably used.
In this way, with respect to a plane (X-ray in FIGS. 6A to 6D) passing through the center of the discharge port and parallel to the longitudinal direction of the discharge port as shown in FIGS. In addition, the longitudinal portion of the discharge electrode, that is, the discharge electrode shown in FIGS. 6 (A), 6 (B), and 6 (C) is shown in FIG. 6 (D) except for the hatched portion S. The discharge electrode has a shape that is symmetric with respect to a plane that passes through the center of the discharge port and that is parallel to the direction perpendicular to the major axis direction of the discharge port (the Y line in FIGS. 6A to 6D). As a result, the landing position of the ink droplet can be stabilized, and a higher quality image can be formed.
Also, the discharge electrodes shown in FIGS. 6B to 6D have a shape in which a part on the upstream side of the ink flow is cut out, similarly to the discharge electrodes shown in FIG. The particle supply property can also be improved.

  Here, the shape of the discharge port is not limited to a long and narrow bowl shape, and may be a shape in which the aspect ratio of the major axis and the minor axis of the opening is 1 or more. For example, as shown in FIG. In this case, as described above, it is symmetric with respect to a plane passing through the center of the ejection port and parallel to the longitudinal direction of the ejection port (X-ray in FIG. 6E), and further, the longitudinal portion of the ejection electrode (FIG. 6 (E), the portion excluding the hatched portion S) is symmetric with respect to a plane that passes through the center of the discharge port and is perpendicular to the longitudinal direction (Y line in FIG. 6E). The ejection position of the ink droplet can be stabilized. As a result, the landing position of the ink droplet on the recording medium is stabilized, and a higher quality image can be formed on the recording medium.

  Also, the major axis direction of the ejection port is not limited to the direction parallel to the ink flow, and the major axis direction of the ejection port may be any direction, and the shape of the ejection electrode with respect to the opening shape of the ejection port passes through the center of the ejection port. Further, it is symmetric with respect to a plane parallel to the major axis direction of the discharge port, and further, the longitudinal part of the discharge electrode has a symmetrical shape with respect to a plane that passes through the center of the discharge port and is orthogonal to the major axis direction of the discharge port. As a result, the ink droplet ejection position can be stabilized. Therefore, the landing position of the ink droplet on the recording medium is stabilized, and a higher quality image can be formed on the recording medium.

  Further, the shape of the discharge electrode is symmetrical with respect to a plane that passes through the center of the discharge port and is parallel to the major axis direction of the discharge port from the point that a substantially symmetric electric field can be easily formed on the discharge port. Furthermore, it is preferable that the longitudinal portion of the ejection electrode has a symmetric shape with respect to a plane that passes through the center of the ejection port and is orthogonal to the major axis direction of the ejection port. The effective part which contributes to the discharge of a droplet should just be a shape substantially symmetrical with respect to the discharge outlet. As an example, as shown in FIG. 6 (F), the ink upstream side is rectangular and the ink downstream side is semicircular, and the longitudinal part (the part excluding the hatched part S in FIG. 6 (F)). ) Is not symmetrical with respect to a plane (Y line in FIG. 6 (F)) that passes through the center of the discharge port and is orthogonal to the major axis direction of the discharge port. That is, an electric field that is substantially point-symmetric with respect to the center of the ejection port or an electric field that is substantially symmetrical with respect to a plane that passes through the center of the ejection port and is perpendicular to the major axis direction of the ejection port. The droplet discharge position can be stabilized. Therefore, as described above, the landing positions of the ink droplets on the recording medium are stable, and a higher quality image can be formed on the recording medium.

  6 (A) to 6 (F), the discharge electrode has a cut-out shape. However, the present invention is not limited to this. For example, a circular electrode or an elliptical shape with no cut-out formed. The electrode, the rectangular electrode, etc. also have an effective portion that contributes to the ejection of the ink droplets of the ejection electrode in a shape that is substantially symmetrical with respect to the ejection port, preferably the center of the ejection port and the major axis direction of the ejection port. The ink droplets are symmetrical with respect to a parallel plane, and the longitudinal portion of the discharge electrode is symmetrical with respect to a plane that passes through the center of the discharge port and is orthogonal to the major axis direction of the discharge port. The discharge position can be stabilized.

  Further, the shape of the discharge electrode is not limited to the above shape, and the discharge electrode is symmetrical with respect to a plane passing through the center of the discharge port and parallel to the major axis direction, and is formed in the longitudinal direction formed in the major axis direction of the ejection port. A shape in which the length of the part is longer than the length in the major axis direction of the ejection port, or the ejection electrode is symmetric about a line passing through the center of the ejection port and parallel to the major axis direction, and the major axis direction of the ejection port A shape in which the center of the longitudinal part formed on the surface passes through the center of the discharge port and is perpendicular to the major axis direction, or the discharge electrode is symmetrical with respect to a plane that passes through the center of the discharge port and is parallel to the major axis direction In addition, it is possible to stabilize the ejection position of the ink droplets by forming the center of the longitudinal portion formed in the major axis direction of the ejection port on the plane passing through the center of the ejection port and perpendicular to the major axis direction. Can do.

In the inkjet head 10 shown in FIGS. 2A and 2B, the ejection electrode 18 is exposed to the ink flow path 30. That is, the ejection electrode 18 is in contact with the ink Q in the ink flow path 30.
As described above, when the drive voltage is applied to the discharge electrode 18 in contact with the ink Q in the ink flow path 30 (discharge is turned on), a part of the charge supplied to the discharge electrode 18 is injected into the ink Q, and the discharge port 28. The conductivity of the ink Q located between the discharge electrode 18 and the discharge electrode 18 is increased. Therefore, in the inkjet head 10 of the present embodiment, the ink Q is in a state in which the ink droplet R is easily ejected when the driving voltage is applied to the ejection electrode 18 (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 18 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. As a result, the conductivity of the ink can be further increased, and the charged color material particles floating in the ink flowing from the upstream side can be reliably held down by the discharge port 28 by the electrostatic force generated by the discharge electrode 18.

Here, the ink used for the inkjet head 10 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. Further, a carrier liquid having a low electrical resistance is not suitable because there is a concern that electrical conduction between adjacent control electrodes may occur.

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

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

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

As the color material, any pigments and dyes that have been conventionally used in inkjet ink compositions, printing (oil-based) ink compositions, or electrophotographic liquid developers can be used.
As the pigment used as the color material, regardless of inorganic pigments or organic pigments, those generally used in the technical field of printing can be used. Specifically, for example, carbon black, cadmium red, molybdenum red, chrome yellow, cadmium yellow, titanium yellow, chromium oxide, viridian, cobalt green, ultramarine blue, Prussian blue, cobalt blue, azo pigment, phthalocyanine pigment , Conventionally known pigments such as quinacridone pigments, isoindolinone pigments, dioxazine pigments, selenium pigments, perylene pigments, perinone pigments, thioindigo pigments, quinophthalone pigments, metal complex pigments, and the like are 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 can be used if necessary), the chargeant is added to the carrier liquid to charge the colorant particles, and the charged colorant The ink Q is obtained by dispersing particles in a carrier liquid. When dispersing the colorant particles, a dispersion medium may be added as necessary.
As an example of the charge control agent, various materials used in electrophotographic liquid developers can be used. In addition, “Recent development and commercialization of electrophotographic development systems and toner materials”, pages 139 to 148, Electrophotographic Society edited by “Basics and Applications of Electrophotographic Technology” pages 497 to 505 (Corona, 1988), Yuji Harasaki Various charge control agents described in “Electrophotography” 16 (No. 2), page 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 is determined using an LCR meter (AG-4311 manufactured by Ando Electric Co., Ltd.) and a liquid electrode (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 the 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 addition, the ink used in the inkjet of the present invention is not limited to the above-described insulating ink, and a conductive ink having an electric conductivity of 10 ^{−8 to} 100 pS / cm can also be used.
Moreover, in the said Example, although the color material was made to contain a color material, it is not necessary to make a color material contain, for example, the microparticles | fine-particles comprised only by the dispersion resin particle can also be used.

The configuration of the inkjet head of the image recording unit and the ink ejection principle have been described in detail above.
Returning to FIG. 1, other components of the image recording means will be described.
As shown in FIG. 1, a head driver 84 is connected to the head unit 80. The head driver 84 can receive image data from the system control unit and drive the head unit 80 based on the image data. FIG. 7 shows a block diagram of the control system 170 of the image recording means including the head unit 80, the head driver 84, and the system control unit 172.
As shown in FIG. 7, the system control unit 172 is connected to a RIP (raster image processor) 174, and performs color separation, division calculation into an appropriate number of pixels and gradations, and the like on image data received from the RIP 174. The head driver 84 generates image data for driving the head unit 80 (inkjet head). Further, the system control unit 172 can control the ink ejection timing by the head unit 80 in accordance with the conveyance timing of the recording medium P by the conveyance belt 68. The discharge timing is controlled by using the output from the recording medium position detecting unit 86 shown in FIG. 1 and the output signal from the encoder disposed on the conveying belt 68 or the driving unit of the conveying belt 68. Further, the system control unit 172 can perform various processes on image data received from an external device such as a computer, an image scanner, a magnetic disk device, or an image data transfer device.

The RIP 174 is connected to an external device such as a computer, an image scanner, a magnetic disk device, and an image data transfer device, and a threshold value matrix creating device. The RIP 174 includes a comparator 180, a selection unit 182, a threshold matrix storage unit 184, and a test pattern data file 186. The multi-value image signal I supplied from the external device to the raster image processor (RIP) 174 is selected by the selection unit 182 according to the output conditions such as the number of screen lines and the output medium, and output from the threshold matrix storage unit 184. Is compared with the threshold signal TH to be converted into a binary image signal B. The threshold value signal TH is created in the threshold value matrix creating device 176 as described later, but this threshold value matrix creating device 176 may be integrated with the RIP 174.
Next, the binary image signal B is supplied to the system control unit 172, the ink ejection timing of the head unit 80 is controlled via the head driver 84, and a halftone image is formed on the recording medium. A method for creating the threshold matrix (mesh screen) will be described in detail later.

In FIG. 1, a recording medium position detection means 86 is for detecting the recording medium P conveyed to the ink droplet ejection position by the head unit 80, and uses a known detection means such as a photosensor. be able to.
Here, the head driver 84 divides the drawing when there are a large number of ejection units (number of channels) to be controlled, such as when a line head is applied, and a known resistance matrix driving method or resistance diode matrix driving method. May be used. Thereby, the number of ICs used by the head driver 84 can be reduced, and the cost can be reduced and the control circuit size can be suppressed.

  The ink circulation system 82 is for flowing ink into the ink flow paths provided in the ink jet heads 80a of the respective colors of the head unit 80, and is an ink tank for each of four colors (C, M, Y, K), An ink circulation device 82a having a pump, a replenishment ink tank (not shown), and the like, and an ink supply for supplying the ink Q of each color from the ink tank of the ink circulation device 82a to the ink flow path of each color inkjet head of the head unit 80 A system 82b, and an ink collection system 82c that collects ink from the ink flow paths of the ink jet heads of the respective colors of the head unit 80 to the ink circulation device 82a.

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

Further, the ink tank is preferably provided with a stirring device for suppressing precipitation / concentration of the solid component of the ink and an ink temperature management device for suppressing temperature change of the ink. The reason for this is that if the temperature is not controlled, the ink temperature will change due to changes in the environmental temperature, etc., and the dot diameter will change due to changes in the ink properties, making it impossible to stably form high-quality images. Because there is.
A rotating blade, an ultrasonic vibrator, a circulation pump, or the like can be used as the stirring device.
As the ink temperature control device, a known method such as a method in which a heating element such as a heater or a Peltier element or a cooling element is arranged in the head unit 80, ink tank, ink piping system, etc., and control is performed by a temperature sensor, for example, a thermostat. Can be used. When the temperature control device is arranged in the ink tank, it is preferable to arrange the temperature control device 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 ink jet head can also be used for a so-called serial head (shuttle type), and therefore the printer 60 may also be in this mode.
In this case, the head unit 80 is configured by aligning the nozzle rows (single row or multi-channel) of each ink jet head with the transport direction of the transport belt 68, and the head unit 80 is set in the transport direction of the recording medium P. A scanning means for scanning in the orthogonal direction can be provided. As the scanning means, known scanning means can be used.

The image recording apparatus has been described in detail above. Subsequently, the conveying means of the ink jet recording apparatus will be described in detail.
As described above, the conveying means includes the feed roller pair 62, the guide 64, the rollers 66 (66a, 66b and 66c), the conveying belt 68, the conveying belt position detecting means 69, the electrostatic attraction means 70, the static eliminating means 72, and the peeling means. 74, a fixing / conveying means 76 and a guide 78.
In the conveyance means for the recording medium P, the feed roller pair 62 is a conveyance roller pair provided adjacent to the carry-in port 61 a provided on the side surface of the housing 61. The feed roller 62 feeds the recording medium P supplied from a stocker (not shown) to the transport belt 68 (portion supported by the roller 66a). The guide 64 is provided between the feed roller pair 62 and a roller 66 a that supports the conveyance belt 68, and guides the recording medium P to the conveyance belt 68.

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

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

In the illustrated example, since the recording medium P is held on the conveyance belt 68 by electrostatic attraction, the conveyance belt 68 is insulative on the side (front surface) holding the recording medium P and is in contact with the roller 66 (back surface). ) Has conductivity. In the illustrated example, the roller 66a is a conductive roller, and the back surface of the transport belt 68 is grounded via the roller 66a.
That is, the conveyance belt 68 functions as the counter electrode 24 composed of the electrode substrate 24a and the insulating sheet 24b shown in FIG. 2A when holding the recording medium P.

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

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

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

The electrostatic attraction means 70 applies a predetermined bias voltage to the head unit 80 (the ink jet head of the present invention) to the recording medium P and attracts it to the conveying belt 68 by electrostatic force to hold it. Is charged to a predetermined potential.
In the illustrated example, the electrostatic attraction unit 70 includes a scorotron charger 70a that charges the recording medium P, a high-voltage power source 70b connected to the scorotron charger 70a, and a bias voltage source 77c. The corona wire of the scorotron charger 70a is connected to the negative terminal of the high voltage power source 70b, and the positive terminal of the high voltage power source 70b and the metal shield case of the scorotron charger 70a are grounded. The negative terminal of the bias voltage source 70c is connected to the grit electrode of the scorotron charger 70a, and the positive terminal is grounded.
While the recording medium P is conveyed by the feed roller pair 62 and the conveying belt 68, the recording medium P is charged with a negative bias voltage by the scorotron charger 70a connected to the negative high voltage power source 70b, and is applied to the insulating layer of the conveying belt 68. It is electrostatically attracted.

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

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

The recording medium P charged by the electrostatic attraction means 70 is transported to the position of the head unit 80 described later by the transport belt 68.
The head unit 80 records an image on the recording medium P by ejecting ink droplets according to the image data using an inkjet head. Here, the ink jet head uses the charging potential of the recording medium P as a bias voltage, and applies the driving voltage to the ejection electrode 18, thereby superimposing the driving voltage on the bias voltage and ejecting the ink droplets R. The image is recorded in the same manner as described above. At this time, by providing a heating means for the conveying belt 68 and increasing the temperature of the recording medium P, fixing of the ink droplets R on the recording medium P can be promoted, and bleeding is further suppressed and image quality is improved. Can be achieved.

The recording medium P on which the image is recorded is discharged by the discharging unit 72, peeled off from the transport belt 68 by the peeling unit 74, and transported to the fixing / transporting unit 76.
In the example of illustration, the static elimination means 72 is what is called AC corotron static elimination provided with the corotron static elimination 72a, the alternating voltage source 72b, and the high voltage power supply 72c. The corona wire of the corotron static eliminator 72a is connected to the high voltage power source 72c via the AC voltage source 72b, and the other end of the high voltage power source 72c and the metal shield case of the corotron static eliminator 72a are grounded. In addition to the above, as the static elimination means, various means and methods such as a scorotron static eliminator, a solid charger, a discharge needle, etc. can be used, and a conductive roller, A configuration using a conductive platen is also preferably used.
As the peeling means 74, a known technique such as a peeling blade, a reverse rotation roller, an air knife or the like can be used.

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

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

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

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

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

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

  Here, the ink jet head of the present invention is preferably used in the electrostatic ink jet recording method described above, but is not limited to this, and can be used in various ink jet recording methods such as a piezo method and a thermal method.

The configuration of the ink jet recording apparatus of the present invention has been described in detail above.
Next, an example of creating a threshold matrix (mesh screen) will be described in detail with reference to the drawings. In the present invention, the threshold value matrix is created in accordance with the threshold value matrix creation method described below, and the ink ejection is controlled based on the threshold value matrix. Therefore, an inkjet head capable of ejecting minute ink droplets with high accuracy Can be used, it is possible to obtain a good binary image in which the dot pattern does not shift and to record a high-resolution image without moire on a recording medium.

[Example 1]
8 to 10 are flowcharts showing the processing procedure of creation example 1. In this creation example, by setting a threshold value matrix so that threshold values close to each other are not arranged close to each other, the dot pattern of the image formed by the threshold value matrix is not locally offset, thereby reducing the graininess. In addition, by arranging the threshold values in consideration of another threshold matrix set adjacent to the threshold matrix, appearance of a regular pattern due to repetition of the threshold matrix can be reduced.

First, as shown in FIG. 11, threshold doors with array T _5, the threshold phased array T ₅ the surrounding of the same configuration as the threshold phased array T ₁ through T ₄ is the desired threshold value matrix, T ₆ to define and ~T _9. Each of the 25 threshold values t (P _kl ) (k = 1 to 9, l = 1 to 25, t = 1 to 25) constituting each of the threshold arrays T _k (k = 1 to 9). Pixel point _Pkl is defined (step S100). The x and y coordinates of each pixel point P _kl are x _kl and y _kl .

Therefore, after setting all threshold values t (P _kl ) of each threshold array T _k to 0 (step S102), two pixel points P _k1 and P _k2 that are appropriately separated from each threshold array T _k are obtained. The threshold values t (P _k1 ) = 1 and t (P _k2 ) = 2 are set as initial values (step S104, see FIG. 11).

Next, a pixel point P _kl for setting a threshold value t (P _kl ) from 3 to 25 is obtained.

First, z = 3, the maximum distance R _max = 0 between the two pixel points P _kl , the random number RND = 0, and i = 1 (steps S106, S108, S112, S114, S116), and the threshold t (P _5i ) Is 0 (step S120), the minimum value R _min (i) of the distance between the pixel point P _5i and the surrounding pixel point P _kl for which the threshold value t (P _kl ) has already been set is obtained. Obtained (step S122).

The minimum value R _min (i) can be obtained according to the flowchart shown in FIG. That is, after setting the initial value of the minimum value R _min (i) to 99999 (step S150), through steps S152, S154, S156, S158, S160, S162, threshold t (P _kl) other than 0 is set and which extracts the pixel point P _kl (step S164), obtains the distance RR between the pixel point P _kl and the pixel point P _5i according to the following equation (1) (step S166).

RR = √ ((x _kl −x _5i ) ² + (y _kl −y _5i ) ² ) (1)
Then, the distance RR obtained as described above is compared with the minimum value R _min (i) (step S168), and if RR <R _min (i), R _min (i) = RR is set (step S168). S170). By performing this process for all pixel points P _kl for which the threshold value t (P _kl ) of all threshold arrays T _k is not 0, the pixel point P _5i and the surrounding threshold value t (P _kl ) are already set. The minimum value R _min (i) of the distance between the pixel point P _kl thus determined can be obtained.

Next, returning to FIG. 9, the minimum value R _min (i) obtained as described above is compared with the maximum value R _max (steps S124 and S130). In this case, when i = 1, the maximum value R _max is 0 (step S112). Therefore, R _max = R _min (i) is set (step S126), and x _5z = x _5i and y _5z = y _5i. (Step S128). Then, i is updated (step S116), the minimum value R _min (i) is obtained again (step S122), and the minimum value R _min (i) is compared with the maximum value R _max updated in step S126. (Steps S124 and S130).

Here, as long as R _min (i)> R _max (step S124), the coordinates x _5z and y _5z for setting the threshold value t (P _5i ) = 3 (z = 3) are sequentially updated. That is, by this processing, coordinates x _5z and y _5z that are separated from any pixel point P _kl for which the threshold value t (P _kl ) has already been set can be obtained.

If it is determined in step S130 that R _min (i) = R _max , as shown in FIG. 12, the distance from the pixel point P _kl for which the threshold value t (P _kl ) has already been set is equal. comprising pixel point P _5i is that there are two or more (e.g., if the threshold t (P _5i) = 3 and comprising pixel point P _5i is 3A, the two points 3B). In this case, a random number NEWRND having a value of either 0 or 1 is obtained (step S132), the random number NEWRND is compared with the random number RND set in step S112 (step S134), and if NEWWRND> RND, RND = a NEWRND (step S136), the coordinates x _5i determined later, threshold _{y 5i t (P 5i) =} 3 (z = 3) coordinates to set the x _5z, and y _5z (step S138). If NEWWRND ≦ RND, the coordinates x _5i and y _5i obtained first are set as coordinates x _5z and y _5z for setting the threshold t (P _5i ) = 3 (z = 3). As a result, any one of 3A and 3B shown in FIG. 11 is randomly selected as coordinates x _5z and y _5z for which the threshold value t (P _5i ) = 3 (z = 3) should be set.

In this way, among all the pixel points P _5l of the threshold array T ₅ , the pixel point P that is located farthest from the other pixel points P _kl for which the threshold value t (P _kl ) has already been set. _5Z can be extracted. Therefore, a threshold value t (P _kz ) = 3 (z = 3) is set for the pixel point P _{kz of} each threshold array T _k including the pixel point P _5Z (steps S118 and S140).

Similarly, by repeating the processing from step S108 and setting threshold value t (P _kl ) = 4 to 25, threshold value t (P) for all pixel points P _kl in threshold _array T _k . _kl ) is set (step S110).

From the threshold array T _k determined as described above, only the central threshold array T ₅ is extracted and set as a threshold matrix in the threshold matrix storage unit 184 shown in FIG.

Therefore, in the RIP, the threshold matrix (threshold array T ₅ ) is selected from the threshold matrix storage unit 184 by the selection means 182 and the threshold signal TH (corresponding to the threshold t (P _5l )) is _sent to the comparator 180. The binary image signal B is generated by being supplied and compared with the multi-value image signal I. The binary image signal is output to the head driver 84 via the system control unit 172. A halftone image is formed on the recording medium P by the head driver 84 driving the head unit 80 based on the binary image signal.

In this case, since the threshold value matrix is arranged so that the threshold values close to each other are not close to each other, the dot pattern of the image formed by the threshold value matrix is not shifted, and a good halftone dot where the graininess is not conspicuous An image can be obtained. Further, the threshold matrix is arranged in consideration of other threshold matrices arranged in the vicinity, such as threshold arrays T _{1 to} T ₄ and T _{6 to} T ₉ shown in FIG. Therefore, a regular pattern due to repetition of the threshold matrix does not appear on the halftone dot image, and a better image can be obtained.

[Example 2]
In creation example 1, the threshold value t (P _kl ) is set in ascending order, such as 1, 2,..., But in this case, when setting a large value threshold value t (P _kl ), most pixels are already set. since the threshold t (P _kl) is set for the point P _kl, there is a concern that becomes the pixel points P _kl close to each other and selectively forced state.

Therefore, in creation example 2, as shown in FIG. 13, four pixel points P _k1 , P _k2 , P _k24 , and P _k25 that are appropriately spaced from each threshold _array T _k are selected, and a threshold value t is set as an initial value. (P _k1 ) = 1, t (P _k2 ) = 2, t (P _k24 ) = 24, t (P _k25 ) = 25 are set. Next, in the same manner as in the first embodiment, after _obtaining the pixel point P _k3 for setting the threshold value t (P _k3 ) = 3, the pixel point P _k23 for setting the threshold value t (P _k23 ) = 23 is obtained. In this way, the threshold array T ₅ is obtained by alternately setting the threshold value t (P _kl ) one by one from the highlight side and the shadow side.

In the threshold array T ₅ set as described above, the threshold value t (P _kl ) is sufficiently separated on the highlight side and the shadow side. Therefore, when forming a halftone dot image using the threshold matrix of the threshold phased array T _5, it is possible to obtain good halftone images without roughness in both the highlight side and the shadow side.

[Example 3]
FIG. 14 and FIG. 15 are flowcharts showing the processing procedure of creation example 3. In this example, the point spread function shown in FIG. 16 is obtained by two-dimensional Fourier transform of the visual spatial frequency characteristic (MTF) shown in FIG. 21, and the point spread function is applied to the position corresponding to the threshold position. By adding or subtracting cumulatively, the virtual density distribution of the image obtained from the threshold value is obtained, and the threshold value matrix is set so as to minimize the variation, thereby suppressing annoying graininess to a minimum. In addition, by arranging threshold values in consideration of another threshold matrix set adjacent to the threshold matrix, appearance of a regular pattern due to discontinuous repetition of the threshold matrix can be reduced.

First, as in creation example 1, a threshold array T _k and pixel points P _kl (k = 1 to 9, l = 1 to 25) are defined (step S200), and all threshold values t (P _kl ) are defined. After setting to 0 (step S202), two pixel points P _k1 and P _k2 that are appropriately separated from each threshold array T _k are selected, and threshold values t (P _k1 ) = 1 and t (P _k2 ) are set as initial values. ) = 2 is set (see step S204, FIG. 10).

Next, z = 2 (step S206), the weighting filter f _kl (P _kz ) shown in FIG. 17 is applied to the threshold array T _k shown in FIG. 11, and the weighted threshold array T shown in FIG. _{A k} density distribution _Dkl is obtained (step S208).

That is, the weighting filter f _kl (P _kz ) shown in FIG. 17 represents the distribution characteristics of the point spread function shown in FIG. 16 as a two-dimensional density distribution consisting of a 5 × 5 matrix, and this weighting filter f _{By applying kl} (P _kz ) to the pixel point P _{kl for} which the threshold value t (P _kl ) of the threshold array T _k is set and adding them, the density distribution D _kl shown in FIG. 18 is obtained. Obtainable. In this case, by setting the threshold value t (P _kl ) sequentially so that the variation in the density distribution D _kl is minimized (in this case, it corresponds to the minimum value), it is possible to suppress annoying graininess to a minimum. it can.

First, z = 3, the minimum value Dmin = 99999 density distribution D _kl, and a random number RND = 0, i = 1 (step S210, S214, S216, S218) , if the threshold t (P _5i) 0 (step S222), and compares the density distribution D _5i and the minimum value D _min of the pixel point P _5i (step S224, S230). In this case, when i = 1, the minimum value D _min is 99999 (step S214), so that D _min = D _5i is set (step S226), and x _5z = x _5i and y _5z = y _5i ( Step S228). Then, i is updated (step S218), and the density distribution _D5i and the minimum value _Dmin are compared again (steps S224 and S230).

Thereafter, processing is performed in the same manner as in Steps S124 to S138 of Preparation Example 1 (Steps S224 to S238), and the pixel point P _5Z having the lowest density in the density distribution D _kl shown in FIG. Corresponding to the position) can be extracted. Therefore, a threshold value t (P _kz ) = 3 (z = 3) is set for the pixel point P _{kz of} each threshold array T _k including the pixel point P _5Z (steps S220 and S240).

Similarly, by repeating the processing from step S208 and setting threshold value t (P _kl ) = 4 to 25, threshold value t (P) for all pixel points P _kl in threshold _array T _k . _kl ) is set (step S212).

As the threshold array T _k set as described above, only the central threshold array T ₅ is extracted and the threshold value matrix storage unit shown in FIG. 184 is set.

  Since the threshold value matrix set in this way has threshold values arranged so as to minimize annoying graininess, a good dot image can be obtained. In addition, since threshold values are arranged in consideration of other threshold matrixes arranged in the vicinity, a regular pattern based on repetition of the threshold value matrix is displayed on the halftone image as in the case of creation example 1. A better image can be obtained without appearing.

Note that in this creation example 3, as in creation example 2, a better halftone image can be formed by alternately setting the threshold values one by one from the highlight side and the shadow side. Is possible. Further, weighting filters f _kl a (P _kz) instead of obtaining the density distribution D _kl by cumulatively adding, may be obtained density distribution D _kl cumulative subtraction.

[Example 4]
By the way, in creation example 3, the weighting filter f _kl (P _kz ) corresponding to vision has a finite size, and the threshold is separated from the range in which this weighting filter f _kl (P _kz ) acts. / In the shadow area, even if the density distribution _Dkl is obtained, the minimum value and the maximum value are not uniquely determined, and there is a possibility that an appropriate threshold position cannot be determined.

Therefore, in creation example 4, the highlight side (0 <t (P _kl ) ≦ TH _W ) of the threshold value t (P _kl ) is set using the method of creation example 1 (FIGS. 8 and 9). The intermediate value of threshold value t (P _kl ) (TH _W <t (P _kl ) ≦ TH _B ) is set using the method of creation example 3 (see FIGS. 14 and 15). Further, for the shadow side (TH _B <t (P _kl ) ≦ TH _MAX ) of the threshold value t (P _kl ), the setting of the creation example 1 is used again. Note that 0 <TH _W <TH _B <TH _MAX , and TH _MAX represents the maximum value of the threshold value t (P _kl ).

  In this case, it is possible to obtain a threshold value matrix capable of forming an image in which graininess and periodic patterns are not conspicuous in the entire range from highlight to shadow.

  In this creation example 4, as in creation example 2, a better halftone image can be formed by alternately setting the threshold values one by one from the highlight side and the shadow side. Is possible.

[Creation Example 5]
In this creation example 5, in consideration of the influence of the dot gain of the recording medium P, the threshold value matrix is created by correcting the weighting filter f _kl (P _kz ) in the creation example 3, thereby correcting the dot gain of the dot gain. An image can be obtained.

First, a method for obtaining the dot gain correction amount Cor (Q ₁ , Q ₂ , Q ₃ , Q ₄ ) will be described.

In this case, as shown in FIG. 7, using the output device 20, based on the test data T supplied from the test pattern data file 186 of the RIP 174, as shown in FIG. A test pattern composed of the pixels is created. Then, each of the test patterns is measured using a density measuring device 178, and from the measured values, as shown in FIG. 20, the peripheral pixels Q ₁ , Q ₂ , Q ₃ , Q ₄ are turned on (black dots) / off ( The correction amount Cor (Q ₁ , Q ₂ , Q ₃ , Q ₄ ) is obtained based on the density difference when the central pixel Q, which is the target pixel, is turned on from the off state with respect to the (white point) state. However, in the nine pixels of FIG. 20, the on / off states of four pixels excluding the pixels Q, Q ₁ , Q ₂ , Q ₃ , and Q ₄ are constant. In FIG. 19, when the pixel Q and the peripheral pixels Q ₁ , Q ₂ , Q ₃ , and Q ₄ are off, 0 is set, and when the pixel Q is turned on, 1 is set, and [Q ₁ Q ₂ Q ₃ Q ₄ −Q] = It shall be expressed as [0000-1].

Therefore, first, the concentration D1 of [Q ₁ Q ₂ Q ₃ Q ₄ −1] and the concentration D 0 of [Q ₁ Q ₂ Q ₃ Q ₄ −0] are measured using the concentration measuring device 178. Next, in the threshold value matrix creating device 176, the difference between the densities D1 and D0 is obtained as a half-tone difference Δ (%) of each test pattern. That is, assuming that the base density before image recording of the film F or the printed matter P is Db and the maximum density when the whole is blackened is Dmax, the halftone difference Δ (%) is

Can be obtained as In this case, an ideal halftone difference R without dot gain or the like in the test pattern shown in FIG. 19 is R = 100/9 (%) (3)
Therefore, the correction amount Cor (Q ₁ , Q ₂ , Q ₃ , Q ₄ ) is
Cor (Q ₁ , Q ₂ , Q ₃ , Q ₄ ) = Δ / R−1 (4)
Can be obtained as

The correction amounts Cor (Q ₁ , Q ₂ , Q ₃ , Q ₄ ) obtained as described above are supplied to the threshold matrix creation device 176, and the threshold value matrix is obtained in substantially the same manner as in creation example 3.

That is, the correction amount Cor (Q ₁ , Q ₂ , Q ₃ , Q ₄ ) is the threshold value t (P _k1 ) = 1 set as the initial value in the processing immediately before step S208 in FIG. It acts on the weighting filter f _kl (P _kz ) for P _k2 ) = 2. In this case, the threshold value t (P _k1), the threshold value t (P _k2), because as shown in FIG. 11, the threshold value for forming the surrounding pixels is 0, the threshold t (P _k1), the threshold value t (P _The dot gain correction amount Cor (Q ₁ , Q ₂ , Q ₃ , Q ₄ ) when only the pixel corresponding to _k2 ) is blackened on the recording medium P is the test pattern [0000-0] in FIG. And the correction amount Cor (0, 0, 0, 0) obtained from [0000-1].

Therefore, 1 + Cor (0,0,0,0) is, by being multiplied by each element of the weighting filters f _kl (P _kz) shown in FIG. 17, weighting filter the corrected dot gain is taken into account f _kl ( P _kz ) is obtained.

Next, using the weighting filter f _kl (P _kz ) in consideration of the dot gain obtained as described above, the processing from step S208 shown in FIG. 14 and FIG. 15 is performed, and the threshold value t (P _k3 ) = A pixel point P _kl for setting 3 is obtained (step S240). Similarly, the weighting filter f _kl (P _kz ) of each pixel point P _kl for which the threshold value t (P _kl ) is set is corrected in consideration of the dot gain, and the processing after step S208 is performed again to obtain the desired value. Threshold matrix is created.

  The threshold value matrix set as described above is created according to the head unit 80 and the recording medium, and is set in the threshold value matrix storage unit 184 shown in FIG. The selection unit 182 selects a desired threshold matrix from the threshold matrix storage unit 184, and a binary image signal B is generated from the multi-value image signal I using this threshold matrix. The binary image signal is output as a halftone dot image on the recording medium P by the head unit 80.

  In this case, as in the case of Creation Example 3, the threshold value matrix has threshold values arranged according to visual characteristics, so that it is possible to obtain a good halftone image in which an unobtrusive graininess is not visually recognized. it can. In addition, since threshold values are arranged in consideration of other threshold matrixes arranged in the vicinity, a regular pattern based on repetition of the threshold value matrix is displayed on the halftone image as in the case of creation example 1. A better image can be obtained without appearing. Furthermore, since the dot gain depending on the output medium such as the film F or the printed matter P can be corrected, a halftone image with no more granularity can be obtained with higher accuracy.

  In this creation example 5, as in creation example 2, it is possible to form a better halftone dot image by alternately setting the threshold values one by one from the highlight side and the shadow side. .

  In each of the above-described creation examples, two or more initial threshold values are set, but it is needless to say that the initial value may be one.

  As described above, in the present invention, by setting the threshold values in the order in which the distances between the threshold values constituting the threshold value matrix are separated, it is possible to obtain a good binary image in which the dot pattern is not offset. Further, since the threshold values are also considered in determining the threshold value, periodicity due to repetition of the threshold matrix does not appear on the created binary image.

  In the present invention, when the threshold value is determined, for example, a point spread function obtained from visual characteristics is used as a weighting filter, and this weighting filter is operated centering on the position of the predetermined threshold value. It is also possible to sequentially determine the threshold value from the portion where the weighting distribution obtained by subtraction is minimized. In this case, it is possible to obtain a good binary image in which the graininess and the periodic pattern are not conspicuous.

  In addition, for the highlight side and the shadow side of the threshold value, the position is set in consideration of the distance between the threshold values, and the intermediate part is set using a predetermined weighting filter, so that the entire image obtained is set. The graininess and the visibility of the periodic pattern can be reduced in the range.

  Further, a correction amount for the dot gain is obtained by creating a test pattern using a desired output device or a desired output medium, and after correcting the point spread function with the correction amount, the threshold matrix is set as described above. As a result, it is possible to correct the dot gain and create a more accurate binary image.

  Here, in order to investigate the effect of the above-described mesh screen (threshold matrix), using an inkjet recording apparatus according to the present invention, a color with a resolution lower than 1200 dpi and a higher resolution of 1200 dpi or higher is used according to a normal mesh screen creation method. An image was formed on a recording medium. As a result, moire was not visually recognized in a low-resolution color image up to 1200 dpi, but moire was visually recognized in a high-resolution color image of 1200 dpi or higher. Next, when a color image was similarly formed on the recording medium at a resolution lower than 1200 dpi and a resolution higher than 1200 dpi using the inkjet recording apparatus according to the present invention in accordance with the method for creating a mesh screen described above, the color image was lower than 1200 dpi. Moire was not visually recognized in the resolution color image or in the high resolution color image of 1200 dpi or higher.

Also, for printing a color image having a resolution lower than 1200 dpi and a higher resolution of 1200 dpi or higher, using an inkjet plate making apparatus according to the present invention, which will be described later, in accordance with a normal mesh screen creation method and the mesh screen creation method described above. When printing plates were prepared and printed using these printing plates, the same results as described above were obtained.
Therefore, if a mesh screen is produced and a color image is formed in accordance with the method for creating a mesh screen, the occurrence of moire can be prevented even at high resolution.

The embodiment using the ink jet recording apparatus of the present invention as an ink jet printer has been described above.
Next, a preferred embodiment of an ink jet plate making apparatus using the ink jet recording apparatus of the present invention will be described.

FIG. 22 shows a conceptual diagram of an embodiment of an ink jet plate making apparatus using the ink jet recording apparatus of the present invention.
An ink jet plate making apparatus 200 shown in the figure is a device that uses a printing substrate (plate material) as a recording medium P and forms an image on the plate material to produce a printing plate. The ink jet plate making apparatus includes an ink jet recording apparatus 204, a drum 202 for supporting the recording medium P, a control system 206, and an automatic supply apparatus (not shown) for automatically supplying the recording medium P to the drum 202. The automatic supply device is a known automatic supply device that automatically supplies the recording medium P to the drum 202.

The drum 202 is a rotating body having a cylindrical shape for supporting the recording medium P, as shown in FIG.
The drum 202 is formed of a metal such as aluminum or stainless steel, has a function as a counter electrode of the ink jet head 110 of the ink jet recording apparatus 204, is connected to a high voltage power source (not shown), and has a high surface on the surface during image recording. A voltage is applied.
The recording medium P supplied from an automatic supply device (not shown) is fixed to the surface of the drum 202 by fixing means (not shown). As the fixing means, a plurality of suction holes communicating with the suction port of the suction device are formed in the drum 202, and the recording medium P is fixed to the surface of the drum 202 by the suction force from the suction holes, the tip of the recording medium P, and Examples include a mechanical method of fixing the recording medium P to the surface of the drum 202 by a device for holding the rear end or a roller device for pressing, or a method of fixing the recording medium P to the surface of the drum 202 by an electrostatic method. Is done.

The ink jet recording apparatus 204 includes an ink jet head 210 as ink ejection means, an ink supply means 212, a head separation / contact means 214, and a head sub-scanning means 216.
The ink jet head 210 is disposed at a position facing the drum 202 and ejects ink droplets toward the recording medium P fixed on the surface of the drum 202 to form an image on the recording medium P. Here, since the inkjet head 210 has the same configuration as the inkjet head described above, detailed description thereof is omitted. The ink jet head 210 is a small and safe ink jet head as described above.
Here, the inkjet head 210 of the present embodiment is a multi-channel head having a plurality of ejection units, and a plurality of ejection units are arranged extending in the axial direction of the drum 202.

  The ink supply unit 212 includes an ink density control unit 220, an ink tank 222, and an ink delivery unit 224. Inside the ink tank 222, an agitation unit 226 and an ink temperature management unit 228 are provided.

  The ink in the ink tank 222 is supplied to the inkjet head 210 by the ink delivery device 224 via the ink supply pipe 230. The ink delivery device 224 can be configured using a pump, for example. The ink supplied to the inkjet head 210 is collected in the ink tank 222 via an ink collection tube (not shown). That is, the ink circulates within the inkjet 210. As described above, the ink supply tube 230 and the ink recovery tube (not shown) connected to the inkjet head 210 are constituted by flexible tubes.

  The stirring unit 226 can suppress precipitation and aggregation of the solid component of the ink. This reduces the need to clean the ink tank 222. As the stirring means 226, a rotary blade, an ultrasonic vibrator, and a circulation pump can be used, and these are used in combination or in combination.

  The ink temperature management means 228 can detect the temperature of the ink in the ink tank 222 and maintain the ink at a constant temperature. Thereby, it is possible to prevent the physical properties of the ink from changing due to a change in ambient temperature, and it is possible to prevent the dot diameter formed on the plate material from changing. Thereby, a high-quality image can be stably formed on the plate material. The ink temperature management means 228 can be composed of, for example, a heating element such as a heater or a Peltier element, or a temperature control element such as a cooling element, and a temperature sensor such as a thermostat. Further, the agitation unit 226 may be disposed together with the temperature control element so that the temperature distribution in the ink tank 222 is constant. The ink temperature in the ink tank 222 is desirably 15 ° C. or higher and 60 ° C. or lower, and more preferably 20 ° C. or higher and 50 ° C. or lower. Further, the stirring means for keeping the temperature distribution in the ink tank 222 constant may be shared with the stirring means for the purpose of suppressing precipitation and aggregation of the solid component of the ink.

  Further, the ink jet recording apparatus 204 in the present embodiment has an ink density control unit 220 in order to perform high-quality drawing. As a result, it is possible to effectively suppress the occurrence of bleeding on the plate due to a decrease in the solid content concentration in the ink, the jumping or blurring of the printed image, or the change in the dot diameter on the plate due to the increase in the solid content concentration. The ink density is measured by optical detection, conductivity measurement, physical property measurement such as viscosity measurement, or management based on the number of drawn images. In the case of management by physical property measurement, an optical detector, a conductivity measuring device, and a viscosity measuring device are provided alone or in combination in the ink tank 222 or in the ink flow path. When managing by the number of sheets, liquid supply from a replenishment concentrated ink tank or dilution ink carrier tank (not shown) to the ink tank 222 is controlled according to the number of plates and the frequency.

  The head separation / contact means 214 moves the inkjet head 210 in a direction perpendicular to the axial direction of the drum 202, that is, a direction away from / contacting the drum 202, and the head sub-scanning means 216 The inkjet head 210 is moved in a direction parallel to the axial direction.

The control system 206 has basically the same configuration as the control system of the image recording means of the ink jet printer described above. The control system 206 receives image data from an image scanner, a magnetic disk device, an image data transmission device, etc., performs color separation as necessary, and sets an appropriate number of pixels and gradations for the separated data. Divide operation. Further, in order to draw an image with halftone dots using the inkjet head 210, calculation of a halftone dot area ratio, that is, creation of a halftone screen (threshold matrix) is performed. Since the method described above can be applied to the method of creating the mesh screen, the description thereof is omitted.
The control system 206 controls the movement of the inkjet head and the ejection timing of the ink droplets, and also controls the operation timing of the drum 202 and the like as necessary.
The control system 206 rotates the drum 202 to bring the inkjet head 210 closer to the position close to the drum 202 by the head separation / contact means 214. The distance between the inkjet head 210 and the recording medium P on the drum 202 is a predetermined distance during drawing by controlling the mechanical distance such as a butting roller, or by controlling the head separating apparatus by a signal from an optical distance detector. Controlled. By performing the distance control in this way, the dot diameter becomes non-uniform due to the floating of the recording medium P, etc., and especially when the vibration is applied to the plate making apparatus, the dot diameter does not change, and good plate making is possible. It can be carried out.

  The control system 206 causes the inkjet head 210 to move on the surface of the recording medium P fixed to the drum 202 by a predetermined distance in the axial direction of the drum 202 every time the drum 202 makes one revolution, and to obtain a discharge position obtained by calculation. Ink is ejected at a dot area ratio. A halftone image corresponding to the density of the printed document is drawn on the surface of the recording medium P by the ink thus ejected. This operation continues until an ink image for one color of the printed document is formed on the surface of the recording medium P. By performing main scanning by rotating the drum 202 in this way, the positional accuracy in the main scanning direction can be improved and high-speed drawing can be performed.

In this embodiment, the inkjet head is a multi-channel head. However, the present invention is not limited to this, and a full-line head in which the inkjet head 210 has substantially the same length as the width of the drum 202 is also preferably used. it can.
When a full line head is used as the ink jet head, an ink image for one color of the print document is formed on the printing original plate wound around the surface of the drum 202 by rotating the drum 202 once.
Further, in the present invention, the recording medium is mounted on the drum for recording, but the present invention is not limited to this, and a flatbed transport system that performs recording while transporting the recording medium on the mounting table, In addition, a known recording apparatus configuration such as a roller nip conveyance method in which recording is performed while a recording medium is nip-conveyed by a roller can also be suitably used.

  The ink jet plate making apparatus of the present invention may include an ink fixing unit in order to strengthen the ink image formed on the printing original plate. As the ink fixing means, means such as heat fixing means and solvent fixing means can be used. As the heat fixing means, irradiation with an infrared lamp, a halogen lamp or a xenon flash lamp, hot air fixing using a heater, or heat roll fixing can be used. In this case, in order to improve the fixability, a method of heating the drum, a method of preheating the recording medium, a method of drawing while applying hot air, a method of coating the drum with a heat insulating material, a drum at the time of fixing It is effective to apply a method of heating only the recording medium separately from the recording medium alone or in combination. A flash fixing method using a xenon lamp or the like is known as a method for fixing an electrophotographic toner, and has an advantage that fixing can be performed in a short time. In addition, when a paper plate material is used as a recording medium, moisture inside the recording medium rapidly evaporates due to a rapid temperature rise, and a phenomenon called blistering occurs where irregularities occur on the surface of the recording medium. It is preferable to gradually raise the temperature of the material. Similarly to the ink jet head described above, a heating device that scans the recording medium while facing the surface of the drum may be provided to heat the recording medium.

  In the solvent fixing, a solvent capable of dissolving the resin component in the ink such as methanol or ethyl acetate is sprayed or exposed to vapor, and excess solvent vapor is recovered. It should be noted that at least in the process from the ink image formation by the ink jet recording apparatus 204 to the fixing by the fixing apparatus, it is desirable to keep nothing in contact with the image on the recording medium.

  Moreover, the ink jet plate making apparatus according to the present invention can be provided with a plate surface desensitizing device for the purpose of enhancing the hydrophilicity of the surface of the recording medium, if necessary. Further, the plate making apparatus may have dust removing means for removing dust existing on the surface of the plate material before and / or during drawing on the recording medium. Accordingly, it is possible to effectively prevent the ink from adhering to the plate material through the dust that has entered between the head and the plate material during plate making, and to perform good plate making. As the dust removing means, for example, a contact method using a brush, an adhesive roller or the like can be used in addition to a non-contact method such as suction removal, blow-off removal, electrostatic removal, etc. In the present invention, air suction or air blow-off is desirable. Any one or a combination thereof can be used.

  In addition, the ink jet plate making apparatus of the present invention preferably includes an automatic plate removing apparatus that automatically removes the recording medium after drawing from the drum. By using the automatic plate discharging device, the plate making operation becomes simpler and the plate making time can be shortened.

Next, a plate making process by the ink jet plate making apparatus 200 of the present invention will be described.
First, the recording medium P is mounted on the surface of the drum 202 by an automatic plate feeder (not shown). At this time, the recording medium P is tightly fixed on the surface of the drum 202 by a fixing means (not shown). As a result, it is possible to prevent the recording medium P from being peeled off from the surface of the drum 202 and coming into contact with the ink jet head 210 at the time of drawing. In addition, a method of arranging pressing rollers upstream and downstream of the drawing position of the drum 202 is also effective. Further, when drawing is not performed, it is desirable to keep the ink jet head 210 away from the recording medium P, thereby effectively preventing problems such as contact damage in the ink jet head 210.

  The printing plate thus obtained is printed by a known lithographic printing method. That is, the printing plate on which the ink image is formed is mounted on a printing machine, printing ink and fountain solution are applied to form a printing ink image, and the printing ink image is transferred onto a blanket cylinder rotating with the plate cylinder. Then, printing for one color is performed by transferring the printing ink image on the blanket cylinder onto the printing paper passing between the blanket cylinder and the impression cylinder. The printing plate after printing is removed from the plate cylinder, and the blanket on the blanket cylinder is cleaned by the blanket cleaning device to be ready for the next printing.

As the plate material (printing substrate) used in the ink jet plate making apparatus of the present invention, a metal plate such as aluminum or a steel plate subjected to chrome plating can be used. In particular, an aluminum plate having excellent surface water retention and wear resistance by graining and anodizing treatment is preferred. As a cheaper plate material, a plate material in which an image receiving layer is provided on a water-resistant support such as water-resistant paper, plastic film, or plastic-laminated paper can be used. The thickness of the plate material is preferably in the range of 100 to 300 μm, and the thickness of the image receiving layer provided therein is preferably in the range of 5 to 30 μm.
The inkjet plate making apparatus of the present invention can form a high-definition image directly on a printing substrate using an inkjet head with extremely high accuracy of the landing position of minute ink droplets. Can be created.

  As described above, the ink jet recording apparatus, the recording method, and the ink jet plate making apparatus of the present invention have been described in detail. However, the present invention is not limited to the above embodiment, and various improvements and modifications can be made without departing from the gist of the present invention. Of course, you may do this.

(A) is a conceptual diagram of an embodiment of the ink jet recording apparatus of the present invention using the ink jet head of the present invention, and (B) is a schematic view of the head unit and the peripheral recording medium conveying means. It is a perspective view shown in FIG. (A) is the schematic diagram which showed schematic structure of the inkjet head, (B) is the IB-IB arrow directional view of (A). 2 is a schematic diagram illustrating a state in which a plurality of discharge ports are two-dimensionally arranged on the discharge port substrate 16 of the inkjet head. FIG. It is the schematic diagram which showed 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)-(F) is a schematic diagram which shows an example of the shape of a discharge electrode, respectively. It is a block diagram of the configuration of the control system of the ink jet recording apparatus according to the present invention. It is a processing flowchart of creation example 1. It is a processing flowchart of creation example 1. It is a processing flowchart of creation example 1. It is explanatory drawing of a threshold array and the initial value of the threshold value set to it. It is explanatory drawing in the case of setting the threshold value of 3 with respect to a threshold array. It is explanatory drawing in the case of Example 2 which sets a threshold value alternately with an ascending order and a descending order with respect to a threshold array. 14 is a processing flowchart of creation example 3; 14 is a processing flowchart of creation example 3; It is explanatory drawing of the point spread function in the example 3 of creation. It is explanatory drawing of the weighting filter in the example 3 of creation. In creation example 3, it is explanatory drawing at the time of making a weighting filter act with respect to a threshold array. It is explanatory drawing of the test pattern in the example 5 of creation. FIG. 10 is an explanatory diagram of a relationship between a target pixel of a test pattern and its surrounding pixels in creation example 5. It is explanatory drawing of a visual characteristic. It is a schematic diagram of the inkjet plate-making apparatus according to this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Inkjet head 12 Head substrate 14 Ink guide 14a Tip part 16 Discharge port substrate 18 Discharge electrode 20 Guard electrode 24 Counter electrode 24a Electrode substrate 24b Insulating sheet 26a Scorotron charger 26b Bias voltage source 28 Each discharge port 30 Ink flow path 32 Insulating substrate 33 Control Unit 36 Opening 40 Guide Weir 60 Inkjet Recording Device (Inkjet Printer)
62 Feed roller 64 Guide 66 Roller 66a Roller 68 Conveying belt 69 Conveying belt position detecting means 70 Electrostatic adsorption means 70a Scorotron charger 70b High voltage power supply 72 Discharge means 72a Corotron neutralizer 72b AC power supply 72c DC high voltage power supply 76 Fixing / conveying means 76a Heat roller 78 Guide 80 Head unit 80a Each inkjet head 80b, 80c Ink supply system 82 Ink circulation system 82a Ink circulation device 82b Ink supply system 82c Ink collection system 84 Head driver 86 Recording medium position detection means 90 Discharge fan 110, 210 Inkjet head 114 Head separation / contact means 122 Ink tank 170 Control system 178 Density measuring device 180 Comparator 182 Selection means 200 Inkjet plate making apparatus 202 204 Inkjet recording apparatus 206 Control system 212 Ink supply means 214 Ink separation / contact means 216 Head sub-scanning means 220 Ink density control unit 222 Ink tank 224 Ink delivery means 226 Stirring means 228 Ink temperature management means 230 Ink supply pipe P Recording medium Q Ink R Ink droplet

Claims (9)

An inkjet recording apparatus that ejects ink droplets toward a recording medium,
An inkjet head having an ejection port for ejecting the ink, and a control unit for controlling ejection of the ink from the ejection port;
A threshold value matrix creating device for creating a threshold value matrix for converting a multi-value image signal corresponding to an image recorded on the recording medium into a binary image signal;
An ink jet recording apparatus comprising: a head control unit that controls ejection of the ink droplets by the ink jet head based on a binary image signal converted according to the threshold matrix.   2. The ink jet recording apparatus according to claim 1, wherein the opening shape of the ejection port of the ink jet head is a shape having an aspect ratio of 1 in an ink flow direction and a length in a direction perpendicular to the ink flow direction, which is larger than 1.   The inkjet head includes a discharge port substrate in which the discharge port is opened, a head substrate that is disposed at a predetermined interval from the discharge port substrate, and that forms an ink flow path between the discharge port substrate and the discharge port substrate. 3. The ink jet recording apparatus according to claim 1, further comprising: an ink guide that passes through substantially the center of the outlet and is disposed on the head substrate so that a leading end of the outlet faces the ink ejection direction.   The ink jet head further includes a discharge electrode that is disposed so as to surround the discharge port and discharges an ink droplet by applying an electrostatic force to the ink, and contributes to the discharge of the ink droplet of the discharge electrode. The inkjet recording apparatus according to claim 1, wherein the effective portion has a shape that is substantially symmetrical with respect to the ejection port.   When determining threshold values in ascending order or descending order, the threshold value matrix creating apparatus includes other threshold value matrices having the same configuration arranged around the threshold value matrix, and positions of the already determined threshold values and newly arranged threshold values. The inkjet recording apparatus according to any one of claims 1 to 4, wherein the position of the new threshold value is determined so that the distance from the position is the farthest.   When determining threshold values in ascending order or descending order, the threshold value matrix creating device includes a predetermined weighting filter centering on the position of the already determined threshold value including another threshold value matrix having the same configuration arranged around the threshold value matrix. The weighting distribution by the weighting filter in the threshold matrix is obtained by accumulating or subtracting the weighting value, and the position corresponding to the minimum value or the maximum value of the weighting distribution is set as a new threshold position. The inkjet recording apparatus according to claim 1, wherein the threshold position is sequentially determined by setting.   When determining threshold values in ascending order or descending order, the threshold value matrix creating device selects other threshold value matrixes having the same configuration arranged around the threshold value matrix on the highlight side and shadow side of the threshold value constituting the threshold value matrix. In addition, the position of the new threshold is determined so that the distance between the position of the already determined threshold and the position of the threshold to be newly arranged is the most separated, and the middle of the threshold is arranged around the threshold matrix. The weighting in the threshold matrix is performed by applying a predetermined weighting filter centering on the position of the already determined threshold, including other threshold matrixes of the same configuration, and cumulatively adding or subtracting the weighted values. A weighted distribution by a filter is obtained, and a position corresponding to the minimum value or maximum value of the weighted distribution is set as a new threshold value. By setting the position, the ink jet recording apparatus according to claim 1 for determining the position of the sequential threshold. An inkjet recording method for recording an image on the recording medium by discharging ink droplets toward the recording medium,
An ejection port substrate in which ejection ports for ejecting the ink are opened; a head substrate that is disposed at a predetermined interval from the ejection port substrate and forms an ink flow path between the ejection port substrate; and A control means for controlling the ejection of the ink from the ejection port; and an ink guide disposed on the head substrate so as to pass through substantially the center of the ejection port and have a leading end directed in the ink ejection direction. Using an inkjet head having
Creating a threshold matrix for converting a multi-value image signal corresponding to an image recorded on the recording medium into a binary image signal;
An inkjet recording method for recording an image on the recording medium by controlling ejection of the ink droplets by the inkjet head based on a binary image signal converted according to the threshold matrix. An ink jet recording apparatus according to claim 1;
Holding means for holding the recording medium,
An ink jet plate making apparatus using a printing substrate as the recording medium.

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