JP2006043895A - Image forming apparatus and image formation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which prevents discharge failures due to a viscosity increase of ink near nozzles in the case of using the ink that has the electroviscous effect, and also which can prevent the striking interference of ink droplets on a recording medium, penetration bleeding, bleeding between colors, etc., and to provide an image formation method. <P>SOLUTION: The image forming apparatus is equipped with a discharge head for discharging liquid droplets with the electroviscous effect towards the recording medium, a holding means disposed at a position opposed to a discharge face of the discharge head via the recording medium to hold the recording medium, an electrode pair consisting of a first and a second electrodes set at the holding means, and a voltage applying means for applying a voltage to the electrode pair. At the time of applying a predetermined voltage to the electrode pair by the voltage applying means, an electric field strength on the recording medium is of a level such that struck liquid droplets on the recording medium are prevented from interfering with other liquid droplets, or of a level such that a penetration speed to the recording medium of the struck liquid droplets becomes not larger than a predetermined value. At the same time, an electric field strength on the discharge face of the discharge head is of a level which prevents effects to the liquid droplet discharge of the discharge head. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus and an image forming method, and more particularly to an image forming apparatus and an image forming method for forming an image on a recording medium by discharging droplets from nozzles.

  Inkjet image forming apparatuses form an image on a recording medium by ejecting ink from nozzles provided in a print head. In such an image forming apparatus, when the second ink droplet is landed on the first ink droplet that has landed first on the recording medium so as to overlap the first ink droplet, If the first ink droplets remain unfixed on the recording medium, the droplets mix with each other at the portion where the second ink droplets and the unfixed first ink droplets overlap, The dot shape may be lost, or in the case of inks of different colors, color mixture may occur, causing image degradation. Note that mixing of ink droplets that are ejected in layers on a recording medium is called “landing interference” or “droplet interference”.

  Therefore, a technique using an electrorheological fluid has been proposed in order to prevent landing interference on the recording medium, ink bleeding, color mixing, and the like (see Patent Documents 1 to 3).

  In Patent Document 1, after a recording liquid having an electrorheological effect is attached to a recording medium, an electric field is applied to the recording medium to which the recording liquid is attached, thereby suppressing penetration of recording dots and reducing bleeding and density. A technique for preventing the above is disclosed.

  In Patent Document 2, a recording liquid having an electrorheological effect is formed into droplets by a recording head (printing head) and attached to an intermediate transfer medium having an electric field formed on the surface thereof. A technique is disclosed in which the viscosity is increased and the thickened droplets are transferred to a transfer medium (recording medium) to prevent excessive spreading or color mixing of the recording dots. In this document, in order to stably discharge the droplets of the recording head, the strength of the electric field applied to the recording liquid in the recording head is zero, or the viscosity of the recording liquid when the electric field is applied is less than a predetermined value. It is described that it is necessary to adjust.

  In Patent Document 3, a recording liquid having an electrorheological effect is formed into droplets by a recording head and adhered onto a transfer medium on which an electric field is formed, thereby instantaneously increasing the viscosity or yield value of the recording droplets. A technique for preventing bleeding, beard, and color mixing of recording dots is disclosed. This document describes that, as in Patent Document 2, it is necessary to adjust the strength of the electric field applied to the recording liquid in the recording head.

Further, in these documents, a charging device such as a corotron device is used as the electric field forming means, a charge is applied to the recording liquid adhesion surface of the transfer medium or intermediate transfer medium, and an electric field is formed on the surface. Alternatively, a method of forming an electric field by providing an electrode pair so as to sandwich the transfer medium and applying a DC voltage to the electrode pair is exemplified.
JP-A-2-212149 JP-A-5-4342 Japanese Patent Laid-Open No. 5-4343

  However, even if the electric field is formed by the electric field forming means disclosed in Patent Documents 1 to 3, the viscosity of the landing droplets on the recording medium does not sufficiently increase, and the landing of the droplets on the recording medium It has been clarified by experiments of the inventors that interference, penetrating blur, intercolor blur, and the like that have penetrated into the recording medium of the landing droplets and become blurred.

  In addition, the viscosity of the recording liquid that causes the ejection failure of the recording head is much smaller than the viscosity that can prevent landing interference between droplets on the recording medium, and is necessary for the droplets on the recording medium to avoid landing interference. It is about 1 / 1,000th of the viscosity. Therefore, when an electric field is applied to the landing droplet on the recording medium, the image forming apparatus must be designed in consideration of the thickening of the recording liquid in the recording head. However, Patent Document 2 and Patent Document 3 describe the necessity of adjusting the strength of the electric field applied to the recording liquid in the recording head, but the specific means is not clarified.

  The present invention has been made in view of such circumstances. When ink having an electrorheological effect is used, ejection failure due to thickening of ink in the vicinity of the nozzle is prevented and ink droplet landing on a recording medium is achieved. It is an object of the present invention to provide an image forming apparatus and an image forming method capable of preventing interference, permeation bleeding, intercolor bleeding, and the like.

  In order to achieve the object, the invention according to claim 1 is directed to an ejection head that ejects droplets having an electrorheological effect toward a recording medium, and an ejection surface of the ejection head across the recording medium. A holding means for holding the recording medium, arranged at opposing positions, an electrode pair disposed on the holding means and comprising a first electrode and a second electrode, and a voltage application for applying a voltage to the electrode pair And when the predetermined voltage is applied to the electrode pair by the voltage applying means, the electric field strength on the recording medium causes the landing droplet on the recording medium to interfere with other droplets. Or the permeation speed of the landing droplets to the recording medium is less than a predetermined value, and the electric field strength on the ejection surface of the ejection head does not affect the ejection of the droplets of the ejection head. There is To provide an image forming apparatus according to claim.

  According to the present invention, when a predetermined voltage is applied to the electrode pair, an electric field having a substantially arc-shaped electric field line connecting the electrode pair is applied to the droplet that has landed on the recording medium. At this time, since the electric field strength on the recording medium and the electric field strength on the ejection surface of the ejection head are configured within a predetermined range, ejection failure on the ejection surface of the ejection head is prevented, and the landing liquid on the recording medium It is possible to prevent droplet landing interference, penetrating bleeding, mixed color bleeding, and the like.

  Further, since the electrode pair is disposed on the back side of the droplet landing surface of the recording medium, when a voltage is applied to the electrode pair, an electric field is applied to the droplet on the recording medium, and the droplet A small current flows through Such an action is suitable for increasing the viscosity of a droplet having an electrorheological effect, and can reliably prevent landing interference, penetrating bleeding, intercolor bleeding, and the like.

  The “electrode pair composed of the first electrode and the second electrode” is a peripheral portion of the electrode pair when a relative potential difference is given to the first electrode and the second electrode (that is, when a voltage is applied). An electric field having a predetermined electric field strength is generated. Therefore, in the electrode pair consisting of the first electrode and the second electrode, not only positive and negative electrodes in which one electrode has a positive potential and the other electrode has a negative potential, both electrodes are positive or negative. Such electrode pairs are also included.

  The “predetermined value of the permeation speed” refers to the speed at which the droplets that have landed on the recording medium penetrate and penetrate into the recording medium before fixing.

  “A degree that does not affect droplet ejection” means that ejection failure such as non-ejection of ink, displacement of ejection position, displacement of ejection amount, and delay of ejection time does not occur.

  The “recording medium” is a medium (which can be called a printing medium, an image forming medium, a recording medium, an image receiving medium, or the like) that receives an image recorded by the action of an inkjet head, and is a continuous sheet, a cut sheet, a seal sheet, A variety of media are included regardless of the material and shape, such as a resin sheet such as an OHP sheet, a film, a cloth, a printed circuit board on which a wiring pattern or the like is formed by an inkjet head.

  The invention according to claim 2 is the image forming apparatus according to claim 1, wherein the first electrode and the second electrode apply a predetermined voltage to the electrode pair by the voltage applying unit. In this case, the electric field intensity on the recording medium is such that the landing droplet on the recording medium does not interfere with other droplets, or the penetration speed of the landing droplet to the recording medium is not more than a predetermined value. In addition, the electric field strength on the ejection surface of the ejection head is arranged at a distance that does not affect the droplet ejection of the ejection head.

  According to the aspect of the second aspect, by disposing the first electrode and the second electrode at a predetermined distance, similarly to the first aspect, the ejection failure on the ejection surface of the ejection head can be prevented, and It is possible to prevent landing interference, penetrating bleeding, mixed color bleeding, and the like of landing droplets on the recording medium.

  A third aspect of the present invention is the image forming apparatus according to the second aspect, wherein each of the first electrode and the second electrode has a substantially comb-like planar shape having a plurality of comb-tooth portions. The comb teeth of the first electrode and the comb teeth of the second electrode are alternately arranged, and the comb teeth of the first electrode and the comb teeth of the second electrode The electric field intensity on the recording medium when the predetermined voltage is applied to the electrode pair by the voltage applying means is such that the landing droplet on the recording medium does not interfere with other droplets or the A distance such that the permeation speed of the landing droplets with respect to the recording medium is not more than a predetermined value, and the electric field strength on the discharge surface of the discharge head does not affect the droplet discharge of the discharge head. It is characterized by being arranged.

  According to the aspect of the third aspect, when a predetermined voltage is applied to the electrode pair, the comb-tooth portion of the positive electrode and the comb-tooth portion of the negative electrode are connected to the droplet landed on the recording medium. An electric field having a substantially arc-shaped electric field line is applied. By arranging the comb teeth of the positive electrode and the comb teeth of the negative electrode at a predetermined distance, the ejection failure on the ejection surface of the ejection head can be prevented and the recording medium can be It is possible to prevent landing interference, penetrating bleeding, mixed color bleeding, and the like of landing droplets.

  A fourth aspect of the present invention is the image forming apparatus according to the second aspect, wherein each of the first electrode and the second electrode has a plurality of electrode pieces, and the first electrode The electrode pieces and the electrode pieces of the second electrode are alternately arranged in a matrix, and the electrode pieces of the first electrode and the electrode pieces of the second electrode are predetermined on the electrode pair by the voltage applying means. Is applied to the recording medium such that the landing droplet on the recording medium does not interfere with other droplets or the penetration speed of the landing droplet into the recording medium is predetermined. The electric field intensity on the ejection surface of the ejection head is arranged at a distance that does not affect the droplet ejection of the ejection head. .

  According to the fourth aspect of the present invention, when a predetermined voltage is applied to the electrode pair, the positive electrode piece and the negative electrode piece are connected to the droplet that has landed on the recording medium. An electric field having an arc-shaped electric field line is applied. By arranging the positive electrode piece and the negative electrode piece at a predetermined distance, the same effect as in the second aspect can be obtained. In carrying out the present invention, the planar shape of the electrode piece is not particularly limited, and may be any shape such as a substantially square shape, a substantially rectangular shape, a substantially circular shape, or a substantially elliptical shape.

  The present invention also provides a method invention for achieving the above object. That is, the image forming method in the image forming apparatus according to the present invention opposes the ejection surface of the ejection head with the ejection head ejecting droplets having an electrorheological effect toward the recording medium and the recording medium interposed therebetween. A holding means arranged at a position for holding the recording medium; an electrode pair disposed on the holding means and comprising a first electrode and a second electrode; and a voltage applying means for applying a voltage to the electrode pair; An image forming method for an image forming apparatus comprising: an electric field intensity on the recording medium when a predetermined voltage is applied to the electrode pair by the voltage applying unit; Is not to interfere with other droplets or the penetration speed of the landing droplets to the recording medium is not more than a predetermined value, and the electric field strength on the discharge surface of the discharge head is So as not to affect the de droplet ejection, and sets the distance of the first electrode and the second electrode.

  According to the present invention, when a voltage is applied to the electrode pair, an electric field having a substantially arc-shaped electric field line connecting the electrode pair is applied to the droplet landed on the recording medium. At this time, since the electric field strength on the recording medium and the electric field strength on the ejection surface of the ejection head are configured within a predetermined range, ejection failure on the ejection surface of the ejection head is prevented, and the landing liquid on the recording medium It is possible to prevent droplet landing interference, penetrating bleeding, mixed color bleeding, and the like.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[Overall configuration of inkjet recording apparatus]
[First Embodiment: Overall Configuration of Inkjet Recording Apparatus]
FIG. 1 is an overall configuration diagram of an ink jet recording apparatus according to a first embodiment of the present invention. As shown in the figure, the inkjet recording apparatus 10 supplies a plurality of print heads 12K, 12M, 12C, and 12Y corresponding to each ink color, and the print heads 12K, 12M, 12C, and 12Y. An ink storage / loading unit 14 for storing ink (in this example, an ultraviolet curable ink having an electrorheological effect), and an ultraviolet light source disposed downstream of the print head 12Y in the paper conveyance direction (left direction in FIG. 1). (UV light source) 16, a medium supply unit 22 for supplying a medium (recording medium) 20, a decurling unit 24 for removing curl of the medium 20, and nozzle surfaces (ink ejection) of the print heads 12K, 12M, 12C, and 12Y Surface) and the light emitting surface of the UV light source 16, and a conveyance unit 26 that conveys the medium 20 while maintaining the flatness of the medium 20, and recording A paper discharge unit 28 for discharging Mino recording paper (printed matter) to the outside, and a.

  The ink storage / loading unit 14 includes ink tanks 14K, 14M, 14C, and 14Y that store inks of colors corresponding to the print heads 12K, 12M, 12C, and 12Y. The print heads 12K, 12M, 12C, and 12Y communicate with each other. Further, the ink storage / loading unit 14 includes notifying means (display means, warning sound generating means) for notifying when the ink remaining amount is low, and has a mechanism for preventing erroneous loading between colors. ing.

  In this embodiment, an electrorheological fluid obtained by giving an electrorheological effect to an ultraviolet curable ink is used as the drawing ink. The electrorheological fluid is a liquid whose apparent viscosity instantaneously increases when an electric field is applied (voltage application), and the viscosity reversibly changes when the electric field is turned on / off. There are two types of such electrorheological fluids, a dispersion type and a homogeneous system.

  In the dispersion type, dielectric fine particles are dispersed in a liquid in an electrically insulating solvent. When no electric field is applied, the fine particles remain dispersed and the viscosity is low. When the is added, the polarized particles form a chain structure (bridge) connected in the direction of the electric field, and this bridge acts to increase the viscosity of the fluid, so that the behavior of the fluid increases in viscosity. . Dispersed electrorheological fluids include a hydrous system and a non-hydrous system.

  The homogeneous system is an anisotropy in which molecules and domains are aligned in the electric field direction, such as liquid crystal. Since a homogeneous electrorheological fluid has little change in viscosity at present, it is considered that a distributed electrorheological fluid is suitable for an inkjet printer application.

  In this embodiment, the ultraviolet curable ink is made to have an electrorheological effect. As a method for producing such an ink, for example, a liquid containing at least a radiation curable monomer and a polymerization initiator in a solid fine particle ( Silica gel, starch, dextrin, carbon, gypsum, gelatin, alumina, cellulose, mica, zeolite, kaolinite, etc.), a method of using pigment fine particles themselves as a dispersant for electrorheological effect, and a dye or pigment micro A method of encapsulating and insulating the surface thereof to use as a dispersant for the electrorheological effect, or a method of mixing a homogeneous electrorheological fluid can be considered.

  In FIG. 1, a roll paper (continuous paper) magazine 32 is shown as an example of the media paper supply unit 22, but a plurality of magazines with different paper widths, paper qualities, and the like may be provided side by side. Further, instead of the roll paper magazine or in combination therewith, the paper may be supplied by a cassette in which cut papers are stacked and loaded.

  When multiple types of media can be used, an information recording body such as a barcode or wireless tag that records the media type information is attached to the magazine, and the information on the information recording body is read by a predetermined reader. It is preferable to automatically determine the type of media to be used and perform ink ejection control so as to realize appropriate ink ejection according to the media type.

  The media 20 delivered from the media supply unit 22 retains curl due to having been loaded in the magazine 32. In order to remove the curl, heat is applied to the medium 20 by the heating drum 34 in the direction opposite to the curl direction of the magazine 32 in the decurling unit 24. At this time, it is more preferable to control the heating temperature so that the printed surface is slightly curled outward.

  In the case of an apparatus configuration using roll paper, as shown in FIG. 1, a cutter 38 is provided, and the roll paper is cut into a desired size by the cutter 38. The cutter 38 includes a fixed blade 38A having a length equal to or longer than the conveyance path width of the medium 20 and a round blade 38B that moves along the fixed blade 38A. The fixed blade 38A is provided on the back side of the print. The round blade 38B is disposed on the printing surface side with the conveyance path interposed therebetween. Note that the cutter 38 is not necessary when cut paper is used.

  After the decurling process, the cut medium 20 is sent to the transport unit 26. The transport unit 26 has a structure in which an endless belt-like electrode unit (electrostatic adsorption belt) 43 is wound between rollers 41 and 42, and faces at least the nozzle surfaces of the heads 12K, 12M, 12C, and 12Y. The portion to be formed is a horizontal surface (flat surface).

  When a DC high voltage is applied to the roller 41 by the DC high voltage generator 100, the belt-like electrode unit 43 wound around the roller 41 is charged, and the medium 20 is placed on the belt-like electrode unit 43 by the electrostatic adsorption effect. Is adsorbed and retained.

  When the power of a motor (not shown in FIG. 1, described as reference numeral 134 in FIG. 7) is transmitted to at least one of the rollers 41 and 42 around which the belt-like electrode unit 43 is wound, the belt-like electrode unit 43 is 1 is driven in the counterclockwise direction, and the medium 20 held on the belt-like electrode unit 43 is conveyed from right to left in FIG.

  Each of the print heads 12K, 12M, 12C, and 12Y has a length corresponding to the maximum paper width of the medium 20 targeted by the inkjet recording apparatus 10, and the nozzle surface thereof exceeds at least one side of the maximum size medium 20. This is a full-line type head in which a plurality of nozzles for ejecting ink are arranged over the length (full width of the drawable range).

  The print heads 12K, 12M, 12C, and 12Y are arranged in the order of black (K), magenta (M), cyan (C), and yellow (Y) from the upstream side along the feeding direction of the medium 20, and each print The heads 12K, 12M, 12C, and 12Y are fixedly installed so as to extend along a direction substantially orthogonal to the conveyance direction of the medium 20.

  A color image can be formed on the medium 20 by ejecting different colors of ink from the print heads 12K, 12M, 12C, and 12Y while the medium 20 is being conveyed by the conveyance unit 26.

  As described above, according to the configuration in which the full-line type print heads 12K, 12M, 12C, and 12Y having nozzle rows that cover the entire width of the paper are provided for each color, the medium 20 is printed in the paper feed direction (sub-scanning direction). An image can be recorded on the entire surface of the medium 20 by performing the operation of moving relative to 12K, 12M, 12C, and 12Y only once (that is, by one sub-scan). Such a single-pass image forming apparatus can perform high-speed printing as compared with the shuttle scan method in which drawing is performed while reciprocating the print head in the main scanning direction, and can improve print productivity.

  In this example, the configuration of KMCY standard colors (four colors) is illustrated, but the combination of ink colors and the number of colors is not limited to this embodiment, and light ink and dark ink may be added as necessary. . For example, it is possible to add a print head that discharges light ink such as light cyan and light magenta. Further, the arrangement order of the print heads for each color is not particularly limited.

  Similar to the print heads 12K, 12M, 12C, and 12Y, the UV light source 16 disposed downstream of the print head 12Y has a length corresponding to the maximum paper width of the medium 20, and is substantially orthogonal to the conveyance direction of the medium 20. It is fixed so as to extend in the direction. For example, the UV light source 16 has a configuration in which ultraviolet LED elements or ultraviolet LD elements are arranged in a line. According to this configuration, light emission control can be selectively performed for each light emitting element, so that the light emitting element to be turned on and the amount of emitted light can be easily adjusted, and a desired irradiation range and light intensity (intensity) distribution can be realized for the ultraviolet irradiation area. it can.

  The UV light source 16 emits ultraviolet rays for promoting the curing of the landing ink droplets by the upstream print heads 12K, 12M, 12C, and 12Y. The ink droplets irradiated with ultraviolet rays from the UV light source 16 are preferably cured and fixed to such an extent that image deterioration does not occur due to handling in the downstream process. Handling here means [1] rubbing between the roller, the conveying guide and the image surface in the downstream conveying process of the UV light source 16, [2] rubbing between prints in the print stacking unit, and [3] finished print. It means rubbing by various objects when actually handled.

  Thus, the medium 20 (generated printed matter) that has passed through the UV light source 16 is discharged from the paper discharge unit 28 via the nip roller 47. Although not shown in FIG. 1, the paper discharge unit 28 is provided with a sorter for collecting images according to orders.

[Print head structure]
Next, the structure of the print head will be described. Since the structures of the print heads 12K, 12M, 12C, and 12Y provided for each ink color are common, the print heads are represented by the reference numeral 50 in the following.

  FIG. 2A is a plan perspective view showing an example of the structure of the print head 50, and FIG. 2B is an enlarged view of a part thereof. 3 is a perspective plan view showing another example of the structure of the print head 50, and FIG. 4 is a cross-sectional view showing a three-dimensional configuration of one droplet discharge element (an ink chamber unit corresponding to one nozzle 51). 4 is a cross-sectional view taken along line 4-4 in FIG.

  In order to increase the dot pitch printed on the medium 20, it is necessary to increase the nozzle pitch in the print head 50. As shown in FIGS. 2 to 4, the print head 50 of this example includes a plurality of ink chamber units (droplets) including nozzles 51 serving as ink droplet ejection openings, pressure chambers 52 corresponding to the nozzles 51, and the like. The ejection elements 53 are arranged in a zigzag matrix (two-dimensionally), and are thus projected so as to be arranged along the print head longitudinal direction (direction perpendicular to the paper feed direction). High density of substantial nozzle interval (projection nozzle pitch) is achieved.

  Further, instead of the configuration of FIG. 2, as shown in FIG. 3, a short head unit 50 ′ in which a plurality of nozzles 51 are two-dimensionally arranged is arranged in a staggered manner and joined together to achieve the full width of the medium 20. You may comprise the full line head which has a nozzle row of corresponding length.

  The pressure chamber 52 provided corresponding to each nozzle 51 has a substantially square planar shape (see FIGS. 2A and 2B), and is supplied with the nozzle 51 at both corners on a diagonal line. An ink inflow port (supply port) 54 is provided.

  As shown in FIG. 4, the pressure chamber 52 communicates with a common flow channel 55 through a supply port 54. The common channel 55 communicates with an ink tank (not shown in FIG. 4, not shown in FIG. 6 and indicated by reference numeral 60) serving as an ink supply source, and the ink supplied from the ink tank 60 passes through the common channel 55 in FIG. Then, it is distributed and supplied to each pressure chamber 52.

  An actuator 58 having an individual electrode 57 is joined to a pressure plate (common electrode) 56 constituting the top surface of the pressure chamber 52, and an actuator is applied by applying a drive voltage to the individual electrode 57 and the common electrode 56. 58 is deformed to change the volume of the pressure chamber 52, and ink is ejected from the nozzle 51 due to the pressure change accompanying this. For the actuator 58, a piezoelectric body such as a piezoelectric element is preferably used. After ink discharge, new ink is supplied from the common channel 55 to the pressure chamber 52 through the supply port 54.

  As shown in FIG. 5, a large number of ink chamber units 53 having such a structure are arranged in a row direction along the main scanning direction and an oblique column direction having a constant angle θ that is not orthogonal to the main scanning direction. The structure is arranged in a lattice pattern.

  That is, with a structure in which a plurality of ink chamber units 53 are arranged at a constant pitch d along a certain angle θ with respect to the main scanning direction, the pitch P of the nozzles projected so as to be aligned in the main scanning direction is d × cos θ. Thus, in the main scanning direction, each nozzle 51 can be handled equivalently as a linear arrangement with a constant pitch P. With such a configuration, it is possible to realize a nozzle configuration in which nozzle rows projected so as to be aligned in the main scanning direction have a high density.

  When the nozzles are driven by a full line head having a nozzle row having a length corresponding to the entire printable width, (1) all the nozzles are driven simultaneously, (2) the nozzles are sequentially moved from one side to the other. (3) The nozzles are divided into blocks, and each block is sequentially driven from one side to the other, etc., and one line or one in the sheet width direction (direction perpendicular to the sheet conveyance direction) Nozzle driving for printing individual strips is defined as main scanning.

  In particular, when driving the nozzles 51 arranged in a matrix as shown in FIG. 5, the main scanning as described in (3) above is preferable. That is, nozzles 51-11, 51-12, 51-13, 51-14, 51-15, 51-16 are made into one block (other nozzles 51-21,..., 51-26 are made into one block, Nozzles 51-31,..., 51-36 as one block,...), And the nozzles 51-11, 51-12,. Print one line in the width direction.

  On the other hand, by moving the full line head and the paper relative to each other, it is possible to repeatedly print one line formed by the main scanning described above (a line composed of a single row of dots or a line composed of a plurality of rows of dots). This is defined as sub-scanning.

  In implementing the present invention, the nozzle arrangement structure is not limited to the illustrated example. In this embodiment, a method of ejecting ink droplets by deformation of an actuator 58 typified by a piezo element (piezoelectric element) is employed. However, the method of ejecting ink is particularly limited in the implementation of the present invention. Instead of the piezo method, various methods such as a thermal jet method in which ink is heated by a heating element such as a heater to generate bubbles and ink droplets are ejected by the pressure can be applied.

[Configuration of ink supply system]
FIG. 6 is a schematic diagram showing the configuration of the ink supply system in the inkjet recording apparatus 10. The ink tank 60 is a base tank for supplying ink to the print head 50, and is installed in the ink storage / loading unit 14 described with reference to FIG. In the form of the ink tank 60, there are a system that replenishes ink from a replenishing port (not shown) and a cartridge system that replaces the entire tank when the remaining amount of ink is low. When the ink type is changed according to the usage, the cartridge system is suitable. In this case, it is preferable that the ink type information is identified by a barcode or the like, and ejection control is performed according to the ink type. The ink tank 60 in FIG. 6 is equivalent to the ink storage / loading unit 14 in FIG. 1 described above.

  As shown in FIG. 6, a filter 62 is provided between the ink tank 60 and the print head 50 in order to remove foreign substances and bubbles. The filter mesh size is preferably equal to or smaller than the nozzle diameter. Although not shown in FIG. 6, a configuration in which a sub tank is provided in the vicinity of the print head 50 or integrally with the print head 50 is also preferable. The sub-tank has a function of improving a damper effect and refill that prevents fluctuations in the internal pressure of the head.

  Further, the inkjet recording apparatus 10 is provided with a cap 64 as a means for preventing the nozzle 51 from drying or preventing an increase in ink viscosity near the nozzle, and a cleaning blade 66 as a means for cleaning the nozzle surface 50A. The maintenance unit including the cap 64 and the cleaning blade 66 can be moved relative to the print head 50 by a moving mechanism (not shown), and is moved from a predetermined retracted position to a maintenance position below the print head 50 as necessary. The

  The cap 64 is displaced up and down relatively with respect to the print head 50 by an elevator mechanism (not shown). The cap surface 64A is covered with the cap 64 by raising the cap 64 to a predetermined raised position when the power is turned off or during printing standby, and bringing the cap 64 into close contact with the print head 50.

  The cleaning blade 66 is made of an elastic member such as rubber, and can slide on the nozzle surface 50A of the print head 50 by a blade moving mechanism (not shown). When ink droplets or foreign matter adheres to the nozzle surface 50A, the nozzle plate surface is wiped by sliding the cleaning blade 66 on the nozzle surface 50A to clean the nozzle surface 50A.

  During printing or standby, when a specific nozzle 51 is used less frequently and the ink viscosity in the vicinity of the nozzle increases, preliminary ejection is performed toward the cap 64 to discharge the deteriorated ink.

  Further, when air bubbles are mixed into the ink (pressure chamber) in the print head 50, the cap 64 is applied to the print head 50, and the ink in the pressure chamber (ink mixed with air bubbles) is removed by suction with the suction pump 67, and suction is performed. The removed ink is sent to the collection tank 68. In this suction operation, the deteriorated ink having increased viscosity (solidified) is sucked out when the initial ink is loaded into the print head 50 or when the ink is used after being stopped for a long time.

  If the print head 50 is not ejected for a certain period of time, the ink solvent near the nozzle evaporates and the viscosity of the ink near the nozzle increases. Ink will not be ejected. Therefore, before this state is reached (within the viscosity range in which ink can be discharged by the operation of the actuator 58), the actuator 58 is operated toward the ink receiver to discharge ink in the vicinity of the nozzle whose viscosity has increased. “Preliminary discharge” is performed. Further, after the dirt on the nozzle surface 50A is cleaned by a wiper such as a cleaning blade 66 provided as a cleaning means for the nozzle surface 50A, the foreign matter is prevented from being mixed into the nozzle 51 by this wiper rubbing operation. Also, preliminary discharge is performed. Note that the preliminary discharge may be referred to as “empty discharge”, “purge”, “spitting”, or the like.

  In addition, if bubbles are mixed into the nozzle 51 or the pressure chamber 52 or if the viscosity increase of the ink in the nozzle 51 exceeds a certain level, ink cannot be ejected by the preliminary ejection, and the suction operation described below is performed.

  That is, when bubbles are mixed in the ink in the nozzle 51 or the pressure chamber 52, or when the ink viscosity in the nozzle 51 rises to a certain level or more, the ink can be ejected from the nozzle 51 even if the actuator 58 is operated. Disappear. In such a case, the pump 67 is used to suck ink or thickened ink in which bubbles in the pressure chamber 52 are mixed by applying the cap 64 to the nozzle surface of the print head 50.

  However, since the above suction operation is performed on the entire ink in the pressure chamber 52, the ink consumption is large. Therefore, when the increase in viscosity is small, it is preferable to perform preliminary discharge as much as possible.

[Explanation of control system]
Next, the control system of the inkjet recording apparatus 10 will be described.

  FIG. 7 is a principal block diagram showing the system configuration of the inkjet recording apparatus 10. The inkjet recording apparatus 10 includes a communication interface 110, a system controller 112, an image memory 114, a motor driver 116, a heater driver 118, a voltage control unit 129, a print control unit 120, an image buffer memory 122, a head driver 124, a media detection unit 126, A light source control unit 128 and the like are provided.

  The communication interface 110 is an interface unit that receives image data sent from the host computer 130. As the communication interface 110, a serial interface such as USB, IEEE1394, Ethernet, and wireless network, and a parallel interface such as Centronics can be applied. In this part, a buffer memory (not shown) for speeding up communication may be mounted.

  Image data sent from the host computer 130 is taken into the inkjet recording apparatus 10 via the communication interface 110 and temporarily stored in the image memory 114. The image memory 114 is a storage unit that temporarily stores an image input via the communication interface 110, and data is read and written through the system controller 112. The image memory 114 is not limited to a memory made of a semiconductor element, and a magnetic medium such as a hard disk may be used.

  The system controller 112 is a control unit that controls each unit such as the communication interface 110, the image memory 114, the motor driver 116, the heater driver 118, and the voltage control unit 129. The system controller 112 includes a central processing unit (CPU) and its peripheral circuits, and performs communication control with the host computer 130, read / write control of the image memory 114, and the like, as well as a transport system motor 134 and a heater 136. And a control signal for controlling the DC high voltage generator 100 is generated.

  The motor driver 116 is a driver (drive circuit) that drives the motor 134 in accordance with instructions from the system controller 112. The heater driver 118 is a driver that drives the heater 136 of the heating drum 34 and other parts in accordance with instructions from the system controller 112.

  The voltage control unit 129 controls the voltage generated by the DC high voltage generator 100 in accordance with an instruction from the system controller 112.

  The print control unit 120 has a signal processing function for performing various processes and corrections for generating a print control signal from the image data in the image memory 114 under the control of the system controller 112, and the generated print A control unit that supplies a control signal (dot data) to the head driver 124. The required signal processing is performed in the print control unit 120, and the ejection amount and ejection timing of the ink droplets of the print heads 12K, 12M, 12C, and 12Y for each color are controlled via the head driver 124 based on the image data. Done. Thereby, a desired dot size and dot arrangement are realized.

  The print control unit 120 includes an image buffer memory 122, and image data, parameters, and other data are temporarily stored in the image buffer memory 122 when image data is processed in the print control unit 120. In FIG. 7, the image buffer memory 122 is shown as being attached to the print control unit 120, but it can also be used as the image memory 114. Also possible is an aspect in which the print control unit 120 and the system controller 112 are integrated to form a single processor.

  The head driver 124 drives the ejection driving actuators 58 of the print heads 12K, 12M, 12C, and 12Y based on the dot data given from the print control unit 120. The head driver 124 may include a feedback control system for keeping the print head drive condition constant.

  Image data to be printed is input from the outside via the communication interface 110 and stored in the image memory 114. At this stage, for example, RGB image data is stored in the image memory 114. The image data stored in the image memory 114 is sent to the print control unit 120 via the system controller 112, and the print control unit 120 converts it into dot data for each ink color by a known dither method, error diffusion method, or the like. Converted.

  In this way, the print heads 12K, 12M, 12C, and 12Y are driven and controlled based on the dot data generated by the print control unit 120, and ink is ejected from the print heads 12K, 12M, 12C, and 12Y. An image is formed on the recording paper 20 by controlling the ink ejection from the print heads 12K, 12M, 12C, and 12Y in synchronization with the conveyance speed of the recording paper 20.

  The media detection unit 126 is means for detecting the paper type and size of the recording paper 20. For example, means for reading information such as a bar code attached to the magazine 32 of the paper supply unit 22, sensors (paper width detection sensors, sensors for detecting the thickness of the paper, papers) disposed at appropriate locations in the paper conveyance path A sensor for detecting the reflectance of the light source is used, and an appropriate combination thereof is also possible. Further, in place of or in combination with these automatic detection means, it is possible to specify information such as paper type and size by input from a predetermined user interface.

  Information acquired by the media detection unit 126 is notified to the system controller 112 and / or the print control unit 120 and used for ink ejection control and the like.

  The light source control unit 128 controls lighting (ON) / extinguishing (OFF) of the UV light source 16 and a light emission amount at the time of lighting in accordance with a command from the print control unit 120.

[Structure of belt-shaped electrode unit]
Next, the structure of the belt-like electrode unit 43 will be described.

  FIG. 8 is a plan perspective view showing the configuration of the electrode layer of the belt-like electrode unit. 9 is a sectional view taken along line 9-9 in FIG. 8, and FIG. 10 is a sectional view taken along line 10-10 in FIG. In FIG. 8 to FIG. 10, parts that are the same as those in FIG.

  The belt-like electrode unit 43 is formed wider than the medium 20 indicated by a broken line in FIG. 8 and is configured to be able to reliably adsorb the medium 20. The region excluding both ends in the main scanning direction shown in FIG. 8 of the belt-like electrode unit 43 is composed of three layers as shown in FIG. 9, and in order from the lowest layer on the side opposite to the media 20, the support layer 90, An electrode layer 92 and a slightly conductive layer 94 are disposed.

  As shown in FIG. 8, the electrode layer 92 is provided with a comb-like positive electrode 96 and a negative electrode 98, and a non-conductive member 95 is provided between the positive electrode 96 and the negative electrode 98. Provided.

  The positive electrode 96 is formed at a plurality of comb teeth 96a substantially parallel to the main scanning direction and one end of the belt-like electrode unit 43 in the main scanning direction, and is connected to the ends of the comb teeth 96a. It has an electrode part 96b. Similarly, the negative electrode 98 is formed at a plurality of comb tooth portions 98a substantially parallel to the main scanning direction and the other end portion of the belt-shaped electrode unit 43 in the main scanning direction. Each has a common electrode portion 98b to be connected.

  The comb teeth portions 96a and 98a are alternately arranged in the sub-scanning direction shown in FIG. As shown in FIG. 9, a slightly conductive layer 94 is disposed on the top surfaces of the comb teeth portions 96a and 98a that are alternately arranged in this manner, and the medium 20 is held on the top surface.

  As shown in FIG. 10, both end portions in the main scanning direction of the belt-like electrode unit 43 have a two-layer configuration of a slightly conductive layer 94 and common electrode portions 96b and 98b. That is, the exposed portions 96b1 and 98b1 of the common electrode portions 96b and 98b are formed on the surface of the belt-like electrode unit 43 opposite to the medium 20 side.

  As shown in FIG. 10, the roller 41 includes an insulating roller 197 formed of a non-conductive member, and metal rollers 196b and 198b formed at both ends of the insulating roller 197 in the vertical direction in FIG. It is supported by metal shafts 206b and 208b. The insulating roller 197 is provided to prevent a short circuit from occurring when a voltage is applied to the metal shafts 206b and 208b from a DC high voltage generator 100 described later.

  The metal shaft 206b and the metal roller 196b, and the metal shaft 208b and the metal roller 198b are electrically connected. Further, the exposed portions 96b1 and 98b1 of the common electrode portions 96b and 98b are configured to contact the metal rollers 196b and 198b of the roller 41, respectively, and are electrically connected. Further, as shown in FIG. 8, a DC high voltage generator 100 is connected to the metal shafts 206b and 208b that support the roller 41. Thus, the common electrode portions 96b and 98b in the present embodiment obtain electrical continuity by a simple method.

  When a predetermined voltage is applied from the DC high voltage generator 100 to the positive and negative electrodes 96 and 98, the comb tooth portion 96a of the positive electrode 96 and the comb tooth portion 98a of the negative electrode 98 adjacent to each other in the sub-scanning direction A substantially arc-shaped electric field line (two-dot chain line in FIG. 9) is formed.

  As shown in FIG. 9, the slightly conductive layer 94 provided on the medium 20 side of the electrode layer 92 is a thin layer having minute conductivity. When a predetermined voltage is applied from the DC high voltage generator 100 to the positive and negative electrodes 96, 98, a minute current flows through the landing ink droplets on the medium 20.

  That is, when a predetermined voltage is applied to the positive and negative electrodes 96 and 98, an electric field is applied to the landing ink droplet on the medium 20, and a small current is applied to the landing ink droplet via the microconductive layer 94. Flows. Such an action is suitable for increasing the viscosity of a landed ink droplet having an electrorheological effect, thereby preventing landing interference, penetrating bleeding, intercolor bleeding, and the like.

[How to set the distance between electrodes]
FIG. 11 is an explanatory diagram illustrating a schematic configuration of the electrode layer illustrated in FIG. 8. FIG. 12 is an explanatory diagram showing the relationship between the print head and the ink droplets on the medium 20 at the 12-12 cross-sectional position in FIG. In FIG. 11 and FIG. 12, the same reference numerals are given to portions common to FIG. 8 and FIG. 11 and 12, the support layer 90 and the non-conductive member 95 shown in FIG. 9 are omitted for convenience of explanation.

  In the present embodiment, the distance (hereinafter referred to as interelectrode distance) between the comb tooth portion (hereinafter referred to as positive comb tooth portion) 96a of the positive electrode 96 and the comb tooth portion (hereinafter referred to as negative comb tooth portion) 98a of the negative electrode 98. W) is set so as to prevent landing interference, permeation bleeding, intercolor bleeding, and the like, and to prevent ejection failure due to thickening of ink near the nozzle. Below, the setting method of such interelectrode distance W is demonstrated.

  As shown in FIG. 12, in the positive comb teeth portion 96a and the negative comb teeth portion 98a, the landing positions of the ink droplets 59a on the medium 20 are positioned substantially above the center portions of the positive comb teeth portion 96a and the negative comb teeth portion 98a. The condition parameter of the electric field strength is set based on the state in which this occurs. Here, when the distance between the landing ink droplet 59a on the medium 20 and the center portion of the positive comb tooth portion 96a or the center portion of the negative comb tooth portion 98a (hereinafter referred to as an electrode distance) is x, the inter-electrode distance W is the electrode distance. x twice.

  In addition, the height (hereinafter referred to as electrode height) when the center portion of the positive comb tooth portion 96a and the negative comb tooth portion 98a is set as h, and the electrode height of the landing ink droplet 59a on the medium 20 is hA. The electrode height of the nozzle surface 50A of the print head 50 is hB.

  When a voltage is applied to the positive comb teeth portion 96a and the negative comb teeth portion 98a, the electric field lines 104 (104A, 104B) having a substantially arc shape that connects the positive comb teeth portion 96a and the negative comb teeth portion 98a. , 104C) are formed innumerably. At the same time, a minute current flows to the landing ink droplet 59 a on the medium 20 through the minute conductive layer 94.

  In FIG. 12, the electric force line 104A passes through the landing ink droplet 59a on the medium 20, the electric force line 104B passes through the lower side of the flying ink drop 59b in FIG. 12, and the electric force line 104C is printed. Passes near the nozzle 51 of the head 50.

  FIG. 13 is a graph showing the relationship between the strength of the electric field applied to the electrorheological fluid and the viscosity of the electrorheological fluid. As shown in the figure, the relation that the viscosity of the electrorheological fluid increases when the strength of the electric field applied to the electrorheological fluid having the initial viscosity η0 is gradually increased is described in JP-A-5-4342. As is well known.

  When the electric field strength at the landing position (point A in FIG. 12) of the ink droplet 59a on the medium 20 is gradually increased from 0, the viscosity of the ink droplet 59a on the medium 20 gradually increases. The critical viscosity when it becomes difficult to cause landing interference, permeation bleeding, or intercolor bleeding is ηA0, and the critical electric field strength at that time is EA0.

  Further, when the electric field strength in the vicinity of the nozzle 51 of the print head 50 (point B in FIG. 12) is gradually increased from 0, the viscosity of the ink in the vicinity of the nozzle gradually increases. The critical viscosity when an ejection failure such as a non-ejection of the nozzle 51, a displacement of the ejection position, a displacement of the ejection amount, a delay of the ejection time or the like is caused is ηB0, and the critical electric field strength at that time is EB0.

  Such critical electric field strengths EA0 and EB0 vary depending on the type of electrorheological fluid, the configuration and specifications of the print head 50, and so are determined through experiments.

  If the electric field strength at the point A of the electrode height hA is E (hA, x) and the electric field strength at the point B of the electrode height hB is E (hB, x), the ejection failure of the nozzle 51 is prevented and the medium 20 In order to prevent landing interference, penetrating bleeding, and mixed color bleeding, the following equation (1) must be satisfied.

E (hA, x)> EA0 and E (hB, x) <EB0 (1)
That is, the electric field strength E (hA, x) must be larger than the critical electric field strength EA0, and the electric field strength E (hB, x) must be smaller than the critical electric field strength EB0.

  When an electric field as shown in FIG. 12 is applied by the voltage applied to the positive comb teeth portion 96a and the negative comb teeth portion 98a, the ink droplet flying space, that is, the approximate center between the positive comb teeth portion 96a and the negative comb teeth portion 98a. The electric field strength E (h, x) above the portion is a combination of the electric field strength E + by the positive comb tooth portion 96a and the electric field strength E− by the negative comb tooth portion 98a. Since the planar shapes of the positive comb teeth portion 96a and the negative comb teeth portion 98a are rods formed so as to extend in the main scanning direction as shown in FIGS. 8 and 11, each electric field intensity E +, E− Are inversely proportional to the distance from the positive comb teeth 96a and the negative electrode 98a, respectively. Therefore, if the constant proportional to the applied voltage to the positive comb tooth portion 96a and the negative comb tooth portion 98a is K, the electric field strength E (h, x) is as shown in the following equation (2).

図１４は、式（２）における電界強度Ｅ（ｈ，ｘ）が一定となる電極高さｈ及び電極距離ｘの組を結んだ線である。以下では、同図に示した各線２００（２００Ｐ、２００Ｑ、２００Ｒ、２００Ｓ）を等電界強度線という。

FIG. 14 is a line connecting a set of the electrode height h and the electrode distance x at which the electric field strength E (h, x) in Equation (2) is constant. Hereinafter, each line 200 (200P, 200Q, 200R, 200S) shown in FIG.

  In FIG. 14, the electric field strength E (h, x) represented by the equal electric field strength line 200P is equal to the critical electric field strength EA0 at the point A, and the electric field strength E (h, x) represented by the equal electric field strength line 200S is the point B. Is assumed to be equal to the critical electric field strength EB0. Further, the electric field strengths represented by the equal electric field strength lines 200Q and 200R located between the equal electric field strength lines 200A and 200B are Eq and Er, respectively.

  As the equivalent electric field strength line 200 (200P, 200Q, 200R, 200S) shifts in the upper right direction in FIG. 14, the electric field strength represented by the equivalent electric field curve 200 (200P, 200Q, 200R, 200S) becomes smaller. The relationship 3) is established.

EA0>Eq>Er> EB0 (3)
The electrode height hA at the point A determined by the thickness of the microconductive layer 94 and the medium 20 is as shown in FIG. From the relationship with the formula (1), the electric field strength E (hA, x) becomes larger than the critical electric field strength EA0 at the electrode height hA within the range of the electrode distance x indicated by the double arrow L in FIG. It is. In this case, since the viscosity ηA of the landing ink droplet 59a on the medium 20 is larger than the critical viscosity ηA0, it is possible to prevent landing interference, penetrating bleeding, mixed color bleeding, and the like of the landing ink droplet 59a on the medium 20.

  Further, the electrode height hB at the point B determined by the discharge performance of the print head 50 is as shown in FIG. From the relationship with the equation (1), the electric field strength E (hB, x) becomes smaller than the critical electric field strength EB0 at the electrode height hB in the range of the electrode distance x indicated by the double-headed arrow M in FIG. It is. In this case, since the viscosity ηB of the ink in the vicinity of the nozzle is smaller than the critical viscosity ηB0, the ejection failure of the nozzle 51 can be prevented.

  Therefore, the electrode distance x satisfying the expression (1) is indicated by the double arrow N in FIG. 14 that satisfies both the range indicated by the double arrow L and the range indicated by the double arrow M in FIG. Range.

  By making the inter-electrode distance W between the positive comb-tooth portion 96a and the negative comb-tooth portion 98a twice the electrode distance x thus determined, ejection failure of the nozzle 51 is prevented, and on the medium 20 Landing interference, penetration bleeding, mixed color bleeding, and the like can be prevented.

  As described above, in this embodiment, the inter-electrode distance W between the positive comb tooth portion 96a and the negative comb tooth portion 98a is set without changing the distance (clearance) between the nozzle surface 50A of the print head 50 and the medium 20. Thus, the electric field strength on the medium 20 and on the nozzle surface 50A can be optimized.

  Further, from the equation (2), the electric field intensity E (h, x) in the case of the electrode height h and the electrode distance x is proportional to the applied voltage to the positive comb tooth portion 96a and the negative comb tooth portion 98a. Therefore, by adjusting the applied voltage and setting the inter-electrode distance W between the positive comb tooth portion 96a and the negative comb tooth portion 98a, the electric field strength on the medium 20 and the nozzle surface 50A can be easily optimized.

[Second Embodiment]
Next, a second embodiment of the present invention will be described.

  FIG. 15 is an explanatory diagram illustrating a schematic configuration of an electrode layer according to the second embodiment of the present invention. FIG. 16 is an explanatory diagram showing the relationship between the print head 50 and the ink droplets on the medium 20 at the position 16-16 in FIG. In FIG. 15 and FIG. 16, parts common to those in FIG. 11 and FIG.

  As shown in FIG. 15, the electrode layer 92 (see FIG. 9) in the present embodiment includes a fine, substantially square positive electrode piece (hereinafter referred to as a positive electrode piece) 96c and a negative electrode piece (hereinafter referred to as a negative electrode piece). 98c (referred to as electrode pieces) are alternately arranged in a matrix in the main scanning direction and the sub-scanning direction.

  A positive common line 107 and a negative common line 108 connected to the DC high voltage generator 100 are disposed at both ends in the main scanning direction. Further, between each electrode piece row in which the positive electrode pieces 96c and the negative electrode pieces 98c are alternately arranged in the main scanning direction, it is connected to the positive individual wiring 109 connected to the positive common wiring 107 or the negative common wiring 108. Negative individual wiring 110 is provided.

  The positive individual wiring 109 is connected to each positive electrode piece 96c, and the negative individual wiring 110 is connected to each negative electrode piece 98c.

  In the present embodiment, the inter-electrode distance W between the positive electrode piece 96c and the negative electrode piece 98c is set to an optimum electric field that can prevent ejection failure of the nozzle 51, and prevent landing interference, permeation bleeding, intercolor bleeding, and the like. Is set so that can be applied.

  As shown in FIG. 16, when the distance (electrode distance) x between the landing ink droplet 59a on the medium 20 and the center part of the positive electrode piece 96c or the center part of the negative electrode piece 98c, the inter-electrode distance W is the electrode distance x. Twice as much. In addition, the electrode height when the height of the center part of the positive electrode piece 96c and the negative electrode piece 98c is set as h, the electrode height of the ink droplet landing surface on the medium 20 is hA, and the nozzle of the print head 50 is set. The electrode height of the surface 50A is hB.

  The electric field strength E (h, x) in the flying space of the ink droplets substantially above the center of the positive electrode piece 96c and the negative electrode piece 98 is the electric field strength E + by the positive electrode piece 96c and the electric field strength E- by the negative electrode piece 98c. It is a synthesis. Since the planar shapes of the positive electrode piece 96c and the negative electrode piece 98c are fine and substantially square, as shown in FIG. 15, the electric field strengths E + and E− are obtained from the positive electrode piece 96c and the negative electrode piece 98c, respectively. Is inversely proportional to the square of the distance. Therefore, if the constant proportional to the applied voltage to the positive electrode piece 96c and the negative electrode piece 98c is K, the electric field strength E (h, x) is as shown in the following equation (4).

図１７は、式（４）における電界強度Ｅ（ｈ，ｘ）が一定となる電極高さｈ及び電極距離ｘの組を結んだ線である。以下では、同図に示した各線２１０（２１０Ｐ、２１０Ｑ、２１０Ｒ、２１０Ｓ）を等電界強度線という。同図において、等電界強度線２１０Ｐは、Ａ地点における臨界電界強度ＥＡ０と等しく、等電界強度線２１０Ｓは、Ｂ地点における臨界電界強度ＥＢ０と等しいとする。

FIG. 17 is a line connecting a set of the electrode height h and the electrode distance x at which the electric field intensity E (h, x) in Equation (4) is constant. Hereinafter, each line 210 (210P, 210Q, 210R, 210S) shown in FIG. In the figure, it is assumed that the equal electric field strength line 210P is equal to the critical electric field strength EA0 at the point A, and the equal electric field strength line 210S is equal to the critical electric field strength EB0 at the point B.

  In the present embodiment, similarly to the first embodiment, the electrode distance x satisfying the expression (1) is obtained. That is, at the electrode height hA at the point A shown in FIG. 16, the electric field strength E (hA, x) is larger than the critical electric field strength EA0 within the range of the electrode distance x as shown by the double arrow L in FIG. It becomes. On the other hand, at the electrode height hB at the point B shown in FIG. 16, the electric field strength E (hB, x) is smaller than the critical electric field strength EB0 within the range of the electrode distance x as shown by the double-headed arrow M in FIG. It becomes. Therefore, the electrode distance x satisfying the expression (1) is in the range indicated by the double-headed arrow N in FIG.

  The distance (clearance) between the nozzle surface 50A of the print head 50 and the medium 20 is set by making the inter-electrode distance W between the positive electrode piece 96c and the negative electrode piece 98c twice the electrode distance x thus obtained. It is possible to prevent the ejection failure of the nozzle 51 and the landing interference on the medium 20, penetrating blur, mixed color blur, and the like without affecting the above.

  Similarly to the first embodiment, by adjusting the applied voltage to the positive electrode piece 96c and the negative electrode piece 98c and setting the inter-electrode distance W, the electric field strength on the medium 20 and the nozzle surface 50A can be easily optimized. Can be.

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

1 is an overall configuration diagram showing an outline of an inkjet recording apparatus as a first embodiment of an image forming apparatus according to the present invention. (A) is a plan perspective view showing a structural example of the print head, and (b) is an enlarged view of a part thereof. FIG. 6 is a plan perspective view illustrating another example of the structure of the print head. FIG. 4 is a cross-sectional view taken along line 4-4 in FIG. FIG. 3 is an enlarged view showing a nozzle arrangement of the print head shown in FIG. 2. It is the schematic which showed the structure of the ink supply system of an inkjet recording device. It is a principal block diagram showing the system configuration of the inkjet recording apparatus It is a plane perspective view showing the structure of the electrode layer of a belt-shaped electrode unit. It is 9-9 sectional drawing in FIG. It is 10-10 sectional drawing in FIG. It is explanatory drawing showing schematic structure of the electrode layer of a belt-shaped electrode unit. FIG. 12 is an explanatory diagram illustrating a relationship between a print head and an ink droplet on a medium at a 12-12 cross-sectional position in FIG. 11. It is a graph showing the relationship between the strength of the electric field applied to the electrorheological fluid and the viscosity of the electrorheological fluid This is a line connecting a set of the electrode height h and the electrode distance x at which the electric field strength E (h, x) is constant. It is explanatory drawing showing schematic structure of the electrode layer which concerns on the 2nd Embodiment of this invention. FIG. 16 is an explanatory diagram illustrating a relationship between a print head and an ink droplet on a medium at a 16-16 cross-sectional position in FIG. 15. This is a line connecting a set of the electrode height h and the electrode distance x at which the electric field strength E (h, x) is constant.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Inkjet recording device, 12K, 12M, 12C, 12Y ... Print head, 16 ... UV light source, 20 ... Media, 41 ... Roller, 46 ... Belt electrode unit, 90 ... Support layer, 92 ... Electrode layer, 94 ... Fine Conductive layer, 96 ... positive electrode, 96a ... comb tooth portion, 96b ... common electrode portion, 96c ... electrode piece, 98 ... negative electrode, 98a ... comb tooth portion, 98b ... common electrode portion, 98c ... electrode piece, 100 ... DC high voltage generator

Claims (5)

An ejection head for ejecting droplets having an electrorheological effect toward a recording medium;
A holding means for holding the recording medium, which is disposed at a position facing the ejection surface of the ejection head across the recording medium;
An electrode pair disposed on the holding means and comprising a first electrode and a second electrode;
Voltage application means for applying a voltage to the electrode pair,
When a predetermined voltage is applied to the electrode pair by the voltage applying means,
The electric field strength on the recording medium is such that the landing droplet on the recording medium does not interfere with other droplets, or the penetration speed of the landing droplet into the recording medium is not more than a predetermined value. An image forming apparatus characterized in that the electric field strength on the ejection surface of the ejection head is such that it does not affect droplet ejection of the ejection head. The first electrode and the second electrode are:
When a predetermined voltage is applied to the electrode pair by the voltage applying means,
The electric field strength on the recording medium is such that the landing droplet on the recording medium does not interfere with other droplets, or the penetration speed of the landing droplet into the recording medium is not more than a predetermined value. 2. The image formation according to claim 1, wherein the electric field intensity on the ejection surface of the ejection head is arranged at a distance that does not affect the droplet ejection of the ejection head. apparatus. Each of the first electrode and the second electrode has a substantially comb-like planar shape having a plurality of comb teeth, and the comb teeth of the first electrode and the comb teeth of the second electrode Are arranged alternately with parts,
The comb teeth of the first electrode and the comb teeth of the second electrode are
When a predetermined voltage is applied to the electrode pair by the voltage applying means,
The electric field strength on the recording medium is such that the landing droplet on the recording medium does not interfere with other droplets, or the penetration speed of the landing droplet into the recording medium is not more than a predetermined value. 3. The image forming apparatus according to claim 2, wherein the electric field intensity on the discharge surface of the discharge head is arranged at a distance that does not affect the droplet discharge of the discharge head. apparatus. Each of the first electrode and the second electrode has a plurality of electrode pieces, and the electrode pieces of the first electrode and the electrode pieces of the second electrode are alternately arranged in a matrix,
The electrode piece of the first electrode and the electrode piece of the second electrode are:
When a predetermined voltage is applied to the electrode pair by the voltage applying means,
The electric field strength on the recording medium is such that the landing droplet on the recording medium does not interfere with other droplets, or the penetration speed of the landing droplet into the recording medium is not more than a predetermined value. 3. The image forming apparatus according to claim 2, wherein the electric field intensity on the discharge surface of the discharge head is arranged at a distance that does not affect the droplet discharge of the discharge head. apparatus. An ejection head for ejecting droplets having an electrorheological effect toward a recording medium;
A holding means for holding the recording medium, which is disposed at a position facing the ejection surface of the ejection head across the recording medium;
An electrode pair disposed on the holding means and comprising a first electrode and a second electrode;
An image forming method of an image forming apparatus comprising: a voltage applying unit that applies a voltage to the electrode pair,
When a predetermined voltage is applied to the electrode pair by the voltage applying means,
The electric field strength on the recording medium is such that the landing droplet on the recording medium does not interfere with other droplets, or the penetration speed of the landing droplet into the recording medium is not more than a predetermined value. The distance between the first electrode and the second electrode is set so that the electric field strength on the ejection surface of the ejection head does not affect the droplet ejection of the ejection head. Method.

Images