JP2007331186A - Inkjet image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To markedly reduce an amount of ink adhering to a nozzle face, and to prevent stability of forming an image from being degraded even when printing is continuously carried out for a long time period. <P>SOLUTION: This inkjet image forming apparatus comprises a plurality of pressurizing chambers, a pressure generating means (diaphragm) for raising the inner pressure of each pressurizing chamber, and a nozzle plate that has a plurality of nozzles respectively corresponding to the pressurizing chambers and forms dots on a medium 19 by ejecting ink droplets from the nozzles on an on-demand fashion by virtue of the pressures of the pressurizing chambers. The inkjet image forming apparatus further comprises an electric potential control device (rubbing device) 8 for controlling an electric potential of the nozzle plate so as to allow the medium 19 to have an electric potential. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an ink jet image forming apparatus that ejects ink droplets from a nozzle on demand by pressure generated by a pressure chamber, forms dots on a medium by the ejected ink droplets, and forms an image.

  Conventionally, as a general printer device that prints on a medium such as recording paper, there are various types such as a serial printer that prints for each character, a line printer that prints for each line, and a page printer that collectively prints for each page. Things have been proposed. Furthermore, in recent years, it has become possible to print clear images with high resolution along with technological progress of printer devices.

  A conventional ink jet image forming apparatus will be described below with reference to the drawings.

  FIG. 17 is a schematic cross-sectional view of a conventional ink jet image forming apparatus. In FIG. 17, 201Y, 201M, 201C, and 201K are head boxes each equipped with a head that ejects each color ink, and the symbols Y, M, C, and K denote yellow and magenta ink colors ejected from the respective boxes. , Cyan and black. 202A, 202B and 202C are guide rollers for feeding paper, 203A, 203B and 203C are guide rollers for winding paper, 204A, 204B and 204C are positioning rollers, 205A and 205B are transport rollers, and 206 is printing. It is paper.

  FIG. 18 is a continuous schematic cross-sectional view of an ink droplet ejection process of a conventional ink jet image forming apparatus. In FIG. 18, 208 is a nozzle hole, 209 is an ink column, 210 is a main ink drop, and 211 is a sub ink drop separated from the main ink drop.

The operation of the conventional ink jet image forming apparatus having such a configuration will be described below. When a print command enters the image forming apparatus, the conveyance rollers 205A and 205B rotate to convey the printing paper 206 at a predetermined speed and tension. In accordance with the sheet conveyance speed and the distance of the head BOX of each color in the sheet feeding direction, ink is ejected and an image is formed on the sheet at the same timing.
JP 2003-54069 A JP 2001-199071 A

  However, in the ink jet image forming apparatus having the above-described configuration, if the printing paper 206 is charged, the sub ink droplets adhere to, coalesce, and grow on the nozzle surface at the rear of the paper conveyance direction during continuous operation, resulting in a large ink reservoir. As a result of this contact, the image surface is smudged, and an ink pool is generated near the meniscus of the nozzle at the rear of the printing paper conveyance direction, causing instability of the meniscus by communicating. In particular, when the polarities of the potentials of the printing paper 206 and the sub ink droplets 211 coincide with each other, the printing paper 206 is difficult to adhere to the printing paper 206 and easily rebounds.

  This problem will be described with reference to FIG.

  As shown in FIGS. 18 (1) to 18 (5), a positive potential is generated on the printing paper 206. FIG. As shown in FIG. 18A, when the internal pressure is transmitted to the nozzle hole 208 in the standby state, the meniscus rises as shown in FIG. 18B, and as shown in FIG. 209 is formed.

  Next, as shown in FIG. 18 (4), the ink column 209 is cut and the main ink droplets are cut by the surface tension between the ink traveling forward due to the inertial force and the ink whose speed is low or the ink which is forcibly pulled back. 210 is generated. The main ink droplet 210 often has a thin ink portion such as a tail when separated from the ink column 209. When the printing paper 206 is positively charged and has a high potential, negative charges are accumulated in the main ink droplet portion and positive charges are accumulated in the tail portion due to dielectric polarization.

  Next, as shown in FIG. 18 (5), the tail portion is also cut by the surface tension into sub ink droplets 211. At this time, the main ink droplet 210 remains negative and the sub ink droplet 211 remains positive. The sub-ink droplet 211 generally has a lower initial velocity than the main ink droplet 210 and has a small volume, so even a slightly charged amount of charge often does not reach the printing paper 206 and is bounced back to the positive-potential printing paper surface in the transport direction. It moves downstream by riding on the air flow generated by being dragged by the moving printing paper 206.

  And it drifts in the air as it is, and often adheres to the nozzle surface. The higher the potential of the printing paper 206 is, and the slower the sub ink droplet 211 is, the more the ink adheres to the nozzle plate. Needless to say, the above problem occurs even when the potential of the printing paper 206 is negative.

  As a countermeasure against the above problems, conventionally, as shown in, for example, (Patent Document 1), a recording sheet is neutralized by using a neutralizing brush so that the electrostatic charge amount becomes a predetermined value or less, and an ink is applied to the neutralized recording sheet. There has been proposed a recording head that performs recording by discharging the ink. The method proposed in this (Patent Document 1) attempts to prevent paper smearing by discharging the paper, but does not mention the problem of ink ejection due to dirt on the nozzle surface.

  As another countermeasure, for example, as shown in (Patent Document 2), the sheet is attracted by electrostatic force using the sheet and suction conveyance means, and the charged polarity of the charged sheet and the charged polarity of the ink are reversed. Thus, there has been proposed a method for obtaining an image by sucking ink to form dots on a sheet. However, since the method proposed in (Patent Document 2) separates ink by electrostatic force due to electric field and electric charge and adheres it to paper as ink droplets, special special ink must be used for ink viscosity and chargeability. In other words, it is not an inkjet image forming apparatus targeted by the present invention. Furthermore, since the dot diameter on the paper easily changes depending on the charge amount of the paper, in order to obtain a desired dot diameter, the setting value of the charger is changed in consideration of humidity, temperature, and printing speed. A means for eliminating the above potential unevenness was necessary. Further, as the printing speed increases, the amount of charge per unit time that must be generated from the charger also increases, resulting in an increase in the cost of the charger. Furthermore, as the humidity decreases, the charge generated on the media due to drying tends to increase, but the generated charge decreases in the ion generation type charger. It is not complicated and does not solve the problem of the conventional configuration.

  Further, in the ink jet image forming apparatus having the above-described conventional configuration, as another problem, when the impedance of the nozzle plate is high, the ink droplet is a meniscus stretched from the nozzle plate before being separated from the nozzle plate. Since the ink droplets are separated immediately after the electrostatic polarization occurs, the electric charge of the same polarity as the medium remains in the meniscus, which makes the potential of the nozzle plate unstable, and a weak current flows between the nozzle plate and the vibration plate. . Due to this weak current, micro bubbles may be generated and grow in the pressure chamber. As a result, discharge pressure absorption is generated by the bubbles and ink discharge may become unstable.

  The present invention has been made to solve the above-described problems, and can greatly reduce the amount of ink adhering to the nozzle surface. Even when continuous printing over a long period of time is performed, the stability of image formation is improved. An object of the present invention is to provide an ink jet image forming apparatus in which the ink is not damaged.

  In order to solve the above-described problem, an ink jet image forming apparatus according to the present invention defines a potential of a nozzle plate, and provides a friction member that takes into account a charged row of the media to rub the media, thereby The medium is charged so that the polarity is opposite to that of the medium. As a result, the main ink droplet and the sub ink droplet are charged with the opposite polarity to the media, and the main and sub ink droplets are sucked to the medium side, so that the ink does not adhere to the nozzle plate even if it is ejected continuously for a long time. Image formation can be performed.

  Further, in another ink jet image forming apparatus according to the present invention, the potentials of the vibration plate and the nozzle plate provided on the wall surface of the pressure chamber are made substantially equal. Therefore, stable image formation can be performed.

  According to the ink jet image forming apparatus of the present invention, since the same image formation as the initial stage can be performed for a long time even when continuously operating, it is possible to provide an ink jet image forming apparatus having a high operation rate, that is, high productivity. it can.

  In the ink jet image forming apparatus according to the first aspect of the present invention, the pressure chamber includes a plurality of pressure chambers, a pressure generating means for increasing the internal pressure of the pressure chamber, and a plurality of nozzles provided for each pressure chamber. An ink jet image forming apparatus including a nozzle plate that discharges ink droplets from a nozzle by pressure to form dots on a medium, and includes a potential control device that controls the potential of the nozzle plate so that the medium has a potential. . With this configuration, the ink droplets ejected from the nozzles adhere to the media without being pulled back to the nozzle plate, and the amount of ink adhering to the nozzle surface can be greatly reduced. The image forming stability is not impaired.

  In the ink jet image forming apparatus according to the second aspect of the present invention, the potential control device is a friction device that applies a charge to the medium by rubbing the medium with a member having a different charge column from the medium. With this configuration, the member is selected in consideration of the charge train of the media, so the potential can be set so that it can be negative or negative, and because friction is used, the amount of charge changes according to the media transport speed. Has the effect of being able to

  In the ink jet image forming apparatus according to the third aspect of the present invention, the friction device is equipped with a positive electrode side member of a charging column of media, and the positive electrode side member and the medium are rubbed to give a negative charge to the medium. With this configuration, a stable negative charge is generated in the media by rubbing in the transport direction at the contact surface between the friction device having a member on the positive electrode side with respect to the charged row of the media member and the media, It has the effect of being able to be a negative potential.

  In the ink jet image forming apparatus according to the fourth aspect of the present invention, the friction device is equipped with a negative electrode side member of a charging train of media, and the positive electrode side member and the media are rubbed to give a positive charge to the media. With this configuration, even when the media is replaced, a stable positive charge can be obtained by rubbing in the transport direction at the contact surface between the friction device having the negative electrode side member relative to the charged column of the media member and the media. Is generated in the medium, and the medium can be set to a positive potential.

  In the ink jet image forming apparatus according to the fifth aspect of the present invention, the friction device has a substantially cylindrical shape and contacts the medium on the side surface of the cylindrical shape, and the potential control device changes the contact portion area of the cylindrical shape. By doing so, the charge amount of the medium is controlled. With this configuration, it is possible to adjust the amount of charge on the medium by contacting the medium with a cylindrical side surface and controlling the amount of charge by the area of the contact portion, and obtain a desired potential even if the charge column order is separated. Therefore, the number of types of members provided on the surface of the friction device can be reduced, and the cost can be reduced.

  In the ink jet image forming apparatus according to the sixth aspect of the present invention, the friction device is provided with at least two kinds of members having different charge trains on the side surface, and increases or decreases the ratio of the contact areas of the two kinds of members. To control the charge amount. With this configuration, there is an effect that only the generated potential can be easily changed without changing the tension of the printing paper.

  In the ink jet image forming apparatus according to the seventh aspect of the present invention, the friction device performs friction between the medium and a member having a different charge train and the medium so that the friction direction has a medium width direction component. With this configuration, by causing friction in the width direction at the same time as the conveyance direction of the medium, it is possible to increase the contact length and to efficiently rub.

  In the ink jet image forming apparatus according to the eighth aspect of the present invention, the friction device has a friction component in the media width direction due to friction in a direction parallel to the central axis of the roller surface rotatable relative to the central axis. With this configuration, the roller rotates by feeding the media, and the portion that frictions with the media is switched. Therefore, uneven wear of the friction member on the roller surface can be prevented, and the time until replacement of the friction member, that is, the part life can be extended. Has an effect.

  In the ink jet image forming apparatus according to the ninth aspect of the present invention, a predetermined friction device is selected based on the type, speed, humidity and temperature of the media, and the friction device is detachable from the apparatus. ing. With this configuration, if the amount of generated charge does not show a desired value due to environmental changes, etc., it can be easily handled by changing to a friction device with a different contact area with a member or medium with a different charge train. Has an effect.

  In the ink jet image forming apparatus according to the tenth aspect of the present invention, the potential control device controls the potential of the medium so as to have a polarity opposite to the charge of the ink droplet. With this configuration, electrostatic attraction is generated between the ejected ink droplets and the medium, and the ink droplets do not return to the nozzle plate and can be adhered to the medium to form dots. .

  In the ink jet image forming apparatus according to the eleventh aspect of the present invention, the pressure generating means increases the pressure in the pressure chamber by the displacement of the vibrating member forming at least one surface of the pressure chamber. With this configuration, the shape and ejection timing of the generated ink droplet are stable, and the reproducibility of the potential of the ink droplet is high.

  In the ink jet image forming apparatus according to the twelfth aspect of the present invention, the potential control device defines the polarity of the charge of the ink droplet by defining the potential of the nozzle plate. With this configuration, the electric potential does not accumulate on the nozzle plate and the potential is stable even when continuous printing is performed, so the potential of the ink droplets ejected into the air is stable, and the adhesion to the media is also stable. Has the effect of being performed.

  In the ink jet image forming apparatus according to the thirteenth aspect of the present invention, the ink droplets generated from the nozzles by the pressure in the pressure chamber are the main ink droplets constituting most of the dots formed on the medium, It consists of at least one sub ink droplet constituting the remaining part. With this configuration, even if the ejection system conditions change due to changes in ink viscosity due to temperature, etc., the number and size of the sub-ink droplets only need to change slightly. It is possible to perform stable dot formation.

  In the ink jet image forming apparatus according to the fourteenth aspect of the present invention, the media potential is set higher than the nozzle potential when the nozzle potential is negative, and the potential difference between the media potential and the nozzle potential is 200V. When the nozzle potential is positive, it is set lower than the nozzle potential, and the potential difference between the media potential and the nozzle potential is 200 V to 2 kV. This configuration prevents ink mist from adhering to the media due to electrostatic force and returning to the nozzle plate, and does not discharge between the media and the nozzle plate or meniscus. It has the effect that it can be formed.

  In the ink jet image forming apparatus according to the fifteenth aspect of the present invention, a plurality of pressure chambers, pressure generating means for increasing the internal pressure of the pressure chambers, and a plurality of nozzles provided for each pressure chamber, In an inkjet image forming apparatus including a nozzle plate that ejects ink droplets from a nozzle by pressure to form dots on a medium, at least one of the pressure chambers includes a vibrating member that forms at least one surface, and a pressure chamber. A piezoelectric element provided; a first electrode provided on an arbitrary surface of the piezoelectric element; and a second electrode provided on a surface opposite to the first electrode of the piezoelectric element; The shape of the piezoelectric element is changed by controlling the potential of the first electrode to increase the pressure in the pressure chamber to eject ink droplets from the nozzle, electrically connecting the first electrode and the vibrating member, and the nozzle plate Vibration member The electrically conductive is not to the first electrode vibration member and the nozzle plate at the same potential. With this configuration, the ink potential in the pressure chamber can be made equal to the nozzle potential, so that the ink potential reaching the nozzle plate can be stably set to a desired value. In addition, since electricity does not flow through the ink between the vibration plate and the nozzle plate, there is an effect that stable ink discharge can be performed without generating microbubbles due to electrolysis and without causing retention in the pressure chamber. .

  In the ink jet image forming apparatus according to the sixteenth aspect of the present invention, the potential of the medium is opposite to the polarity of the nozzle plate potential when the ink droplet is separated from the nozzle plate. With this configuration, even if the voltage applied to the piezoelectric element during ejection changes from a positive voltage to a negative voltage, the media potential is determined in accordance with the potential of the nozzle plate when the ink droplet is separated from the nozzle plate. Therefore, the ink mist does not adhere to the medium and does not return to the nozzle plate.

  In the ink jet image forming apparatus according to the seventeenth aspect of the present invention, the media potential is set higher than the nozzle potential when the nozzle potential is negative, and the potential difference between the media potential and the nozzle potential is 200V. When the nozzle potential is positive, it is set lower than the nozzle potential, and the potential difference between the media potential and the nozzle potential is 200 V to 2 kV. This configuration prevents ink droplets from adhering to the media by electrostatic force and returning to the nozzle plate, and does not discharge between the media and the nozzle plate or meniscus, so that the ink droplets are stably ejected to form the desired image. Has the effect of being

(Embodiment 1)
Hereinafter, a first embodiment of the present invention will be described with reference to FIGS.

  FIG. 1 is a schematic cross-sectional view of an ink jet image forming apparatus according to Embodiment 1 of the present invention. In FIG. 1, 1Y, 1M, 1C, and 1K are head boxes equipped with heads for ejecting inks of respective colors, 2A, 2B, and 2C are guide rollers for winding paper, 3A, 3B, and 3C are positioning rollers, 4A and 4B are transport rollers. 5A and 5B are friction guide rollers, 6 is a rotating plate whose rotating shaft is the same as that of the friction guide roller 5A, 7 is a tension holding roller whose shaft is fixed to the rotating plate 6 and is rotatable, and 8 is a friction attached to the rotating plate 6. An instrument (potential control device) 19 is a printing paper to which a predetermined tension is applied by the transport rollers 4A and 4B, ink droplets adhere, and an image is generated on the surface thereof.

  FIG. 2 is an attachment diagram of the charger in the first embodiment of the present invention. In FIG. 2, 9 is a fixed plate that holds the friction device 8 in the shape of a groove, and 10 is a rotating mechanism that changes the angle of the fixed plate 9 by a worm gear mechanism by appropriately applying forward and reverse voltages. The friction device 8 has a cylindrical shape, and both bottom surfaces have a quadrangular prism shaft at the center of the shaft, and are rotatably supported on the fixed plate 9 by the quadrangular prism shaft. For example, as shown in FIG. 19, the negative electrode member 11 which is the negative side of the charging train represented by Teflon (registered trademark) is attached to the side surface of the cylinder. As shown in FIG. 19, a positive electrode member 12 which is a plus side of a charged column represented by nylon is attached.

  FIG. 3 is a side view of line type heads of the ink jet image forming apparatus according to the first embodiment of the present invention, and is an arrangement as viewed from the printing paper side. In FIG. 3, reference numeral 13 denotes a single head, and the heads are arranged so as to be equally spaced when the nozzle holes are projected in the conveyance direction of the printing paper 19. Although FIG. 3 shows an arrangement with 20 heads, it goes without saying that the effect of the present embodiment can be obtained even with any other arrangement number.

  FIG. 4 is a perspective view of main parts of the single head according to Embodiment 1 of the present invention. In FIG. 4, 21 is a piezoelectric element, 22 is an upper electrode, 23 is a diaphragm (pressure generating means) that also serves as a lower electrode, 25 is a laminated flow path member, and 14 is an ink tube connection hole. The diaphragm 23 serves as a lower electrode common to the piezoelectric elements 21. The piezoelectric element 21 and the upper electrode 22 form a pair. In FIG. 4, the number of piezoelectric elements is 20. However, the effect of the present embodiment can be obtained even if the number of piezoelectric elements is arbitrary. Needless to say, it can be obtained.

  FIG. 5 is a plan view of the main part of the single head according to Embodiment 1 of the present invention. In FIG. 5, 15 is a common ink flow path. FIG. 6 is a longitudinal sectional view taken along the line A-A in FIG. 5 in Embodiment 1 of the present invention, and a nozzle plate having a plurality of nozzles provided corresponding to the pressure generating means for increasing the internal pressure of the pressure chamber and the pressure chamber. FIG. 6 is a structural diagram of a portion corresponding to one nozzle of a structure in which an ink droplet is ejected from a nozzle on demand with an increased pressure in the pressure chamber.

  In FIG. 6, 24 is an insulating adhesive layer, 31 is a pressure chamber provided in the flow path member 25 corresponding to the piezoelectric element 21, and 26 is a nozzle plate, and a potential is regulated to 35 V from a DC power source. The nozzle hole 27 penetrates the nozzle plate 26 and is tapered on the outlet side in the ink flow direction, and is provided corresponding to the pressure chamber 31. 28 is an insulating adhesive layer for bonding the flow path member 25 and the nozzle plate 26, 29 is a main ink droplet ejected from the nozzle hole 27, and 30 is a sub ink droplet separated from the main ink droplet.

  Inkjet image forming apparatuses are roughly classified into a continuous type and an on-demand type. In the continuous type, ink is always ejected, and the ink is ejected toward the printing paper by applying a charge as necessary. On-demand systems, on the other hand, cause ink to fly only when printing. The ink jet image forming apparatus according to the present embodiment is an on-demand system. However, the ink jet image forming apparatus according to the present invention is not limited to this.

  FIG. 7 is a continuous schematic cross-sectional view of the ink droplet ejection process of the ink jet image forming apparatus according to Embodiment 1 of the present invention. In FIG. 7, 27 is a nozzle hole, 32 is an ink column, 29 is a main ink drop, and 30 is a sub ink drop separated from the main ink drop.

  The operation of the ink jet image forming apparatus according to the present embodiment will be described below. When paper is selected as the printing medium, the friction device 8 is attached to the fixed plate 9 so that the friction surface with the printing paper 19 is nylon before the paper is set in the image forming apparatus. Next, the rotating plate 6 is tilted and stopped at an appropriate position near the center of the movable region. The printing paper 19 is wound around each roller in a predetermined order to adjust the tension. When a paper transport command enters the image forming apparatus, the transport rollers 4A and 4B rotate to transport the printing paper 19 at a predetermined speed and tension. At this time, friction occurs between the printing paper 19 and the positive electrode member 12 on the friction device 8, and an electrostatic charge due to the friction is generated. As shown in FIG. 19, in the case of paper and nylon in the charging row, the paper is the negative electrode and the nylon is the positive electrode, so the printing paper 19 is charged with a negative charge and the surface of the printing paper 19 becomes a negative potential.

  At this time, the potential of the printing paper 19 is measured on the upstream side in the transport direction of the head box 1Y with a potential measuring instrument (not shown), and the friction instrument is rotated by the rotation mechanism unit 10 so as to be −200 V or −2 kV. The angle at which the rotating plate 6 is tilted is adjusted. When the deviation from the adjustment range does not reach −200 V, the diameter of the friction device 8 is increased. When the deviation is outside the adjustment range and becomes lower than −2 kV, the friction device 8 is rotated by the rotation mechanism unit 10 so that nylon and Teflon (registered trademark) simultaneously rub against the printing paper 19. The surface potential is adjusted to about −1 kV.

  When the adjustment is completed, printing is possible. When a print command enters the image forming apparatus, the transport rollers 4A and 4B rotate and transport the printing paper 19 at a predetermined speed and tension. At the same time, the potential of the nozzle plate 26 is fixed to + 35V from a DC power source (not shown). When the paper conveyance speed reaches a preset value of the user in advance, the drive voltage waveform is supplied to the lower electrode 23 from an amplifier (not shown) in accordance with the paper conveyance speed and the distance in the paper feed direction of the head BOX of each color. Applied. The upper electrode 22 selected corresponding to the formed image is connected to GND by a drive driver (not shown), and an electric field is applied to the piezoelectric element 21. The piezoelectric element 21 shrinks in the plane direction, the diaphragm 23 is bent by the bimetal effect with the diaphragm 23, the internal pressure of the pressure chamber 31 is increased, and the increased internal pressure ejects ink droplets 29 and 30 from the nozzle hole 27. An image is formed on the printing paper 19.

  The behavior of the sub ink droplet 30 as the ink mist at this time will be described with reference to FIG. As shown in FIG. 7 (1), when the internal pressure is transmitted to the nozzle hole in the standby state, the meniscus rises as shown in FIG. 7 (2), and as shown in FIG. It is formed. Since the potential of the nozzle plate is fixed at 35V, a positive charge is generated on the surface of the ink column.

  Next, as shown in FIG. 7 (4), the ink column 32 is cut and the main ink droplet is cut by the surface tension between the ink traveling forward due to the inertial force and the ink whose speed is slow or the ink which is forcibly pulled back. 29 is generated. The main ink droplet 29 often has a thin ink portion such as a tail when separated from the ink column 32. When the printing paper 19 is negatively charged and the potential is low, the main ink droplet 29 is positively charged due to dielectric polarization. , Try to generate a negative charge in the tail. However, since a positive charge is charged in the main ink droplet 29 in advance, a large positive charge remains in the main ink droplet 29 and a small positive charge remains in the tail portion.

  Next, as shown in FIG. 7 (5), the tail portion is also cut by the surface tension to become the sub ink droplet 30, and a small positive charge remains in the sub ink droplet 30. 30 adheres to the printing paper 19 without adhering to the nozzle plate 26. At this time, since the printing paper potential difference is 200 V or more with respect to GND, the printing paper 19 potential does not become 0 V due to discharge due to ink ejection or natural discharge into the air even at the end of printing of the fourth head box 1K. The sub ink droplet 30 does not repel the printing paper 19. Further, since the potential of the printing paper 19 is set so as to be 2 kV or less, a discharge is not generated between the nozzle plate 26 and the ink column 32, and the main ink droplets 29 are not scattered, and the image formation is stabilized. Can continue.

(Embodiment 2)
A second embodiment of the present invention will be described below with reference to FIGS. 1 to 3 and FIGS. 1 to 3 are the same as those described in the first embodiment, and a description thereof will be omitted.

  FIG. 8 is a perspective view of a main part of the single head according to the second embodiment of the present invention. In FIG. 8, 51 is a piezoelectric element, 54 is a diaphragm, 56 is a laminated flow path member, 44 is an ink tube connection hole, and 63 is a head base. The diaphragm 54 is common to each piezoelectric element 51. Although the piezoelectric element 51 has a configuration with 20 piezoelectric elements in FIG. 8, it goes without saying that the effect of the present embodiment can be obtained even if the number of piezoelectric elements is arbitrary.

  FIG. 9 is a plan view of an essential part of the single head according to the second embodiment of the present invention. In FIG. 9, 65 is a common ink flow path. FIG. 10 is a longitudinal sectional view taken along the line BB in FIG. 9 according to the second embodiment of the present invention, and a nozzle plate having a plurality of nozzles provided corresponding to the pressure generating means for increasing the internal pressure of the pressure chamber and the pressure chamber. FIG. 5 is a longitudinal sectional view of a portion corresponding to one nozzle of a structure in which ink droplets are ejected from a nozzle on demand with an increased pressure chamber pressure. In FIG. 10, reference numeral 51 denotes a piezoelectric element stacked in multiple layers, 52 denotes an upper electrode inserted every other layer of the multilayer piezoelectric element 51, and 53 denotes an upper electrode every other layer of the multilayer piezoelectric element 51. The lower electrodes 54 are inserted alternately with each other, 54 is a diaphragm that is electrically connected to the lower electrode, 55 is an insulating adhesive layer, 56 is a flow path member, and 57 is provided in the flow path member 56 corresponding to the piezoelectric element 51. The pressure chamber 58, which is a nozzle plate, has a potential regulated to -30V from a DC power source. Reference numeral 59 denotes a nozzle hole that passes through the nozzle plate 58 and is tapered on the outlet side in the ink flow direction, and is provided corresponding to the pressure chamber 57. 60 is an insulating adhesive layer for bonding the flow path member 56 and the nozzle plate 58, 61 is a main ink droplet discharged from the nozzle hole 59, and 62 is a sub ink droplet separated from the main ink droplet. The piezoelectric element 51 is fixed to the flow path member 56 by the head base 63 so that the extended deformation force does not escape.

  FIG. 11 is a continuous schematic cross-sectional view of the ink droplet ejection process of the ink jet image forming apparatus according to Embodiment 2 of the present invention. In FIG. 11, 59 is a nozzle hole, 66 is an ink column, 61 is a main ink drop, and 62 is a sub ink drop separated from the main ink drop.

  The operation of the ink jet image forming apparatus according to the present embodiment will be described below. When paper is selected as the printing medium, the friction device 8 is attached to the fixed plate 9 so that the friction surface with the printing paper 19 becomes Teflon (registered trademark) before the paper is set in the image forming apparatus. It is done. Next, the rotating plate 6 is tilted and stopped at an appropriate position near the center of the movable region. The printing paper 19 is wound around each roller in a predetermined order to adjust the tension. When a paper transport command enters the image forming apparatus, the transport rollers 4A and 4B rotate to transport the printing paper 19 at a predetermined speed and tension. At this time, friction occurs between the printing paper 19 and the negative electrode member 11 on the friction device 8, and an electrostatic charge due to the friction is generated. As shown in FIG. 19, in the case of paper and Teflon (registered trademark) in the charging row, the paper is a positive electrode and the Teflon (registered trademark) is a negative electrode. Becomes a positive potential.

  At this time, the potential of the printing paper 19 is measured on the upstream side in the transport direction of the head box 1Y with a potential measuring instrument (not shown), and the angle at which the rotating plate 6 is tilted is adjusted to +200 V or +2 kV. If the deviation from the adjustment range does not reach +200 V, the diameter of the friction device 8 is increased. When the deviation exceeds the adjustment range and becomes higher than +2 kV, the friction device 8 is rotated by the rotation mechanism unit 10 so that nylon and Teflon (registered trademark) simultaneously rub against the printing paper 19. Adjustment is made so that the potential is about +1 kV.

  When the adjustment is completed, printing is possible. When a print command enters the image forming apparatus, the transport rollers 4A and 4B rotate to transport the printing paper 19 at a predetermined speed and tension. At the same time, the potential of the nozzle plate 58 is fixed to -30 V from a DC power source (not shown). When the paper conveyance speed reaches a preset value of the user in advance, the drive voltage waveform is supplied to the lower electrode 53 from an amplifier (not shown) in accordance with the paper conveyance speed and the distance in the paper feed direction of the head BOX of each color. Applied. Then, the upper electrode 52 selected corresponding to the formed image is connected to GND by a drive driver (not shown), and an electric field is applied to the piezoelectric element 51. The piezoelectric element 51 extends in the vertical direction, pushes down the diaphragm 54 in the direction of the pressure chamber 57, increases the internal pressure of the pressure chamber 57, and the increased internal pressure ejects ink droplets 61 and 62 from the nozzle 59, thereby printing on the printing paper 19. An image is formed on.

  The behavior of the sub ink droplet 62 as the ink mist at this time will be described with reference to FIG. FIG. 12 is a continuous schematic cross-sectional view of an ink droplet discharge process of the ink jet image forming apparatus described in FIG. 11. When the internal pressure is transmitted to the nozzle hole in the standby state as shown in FIG. 11 (1), the meniscus rises as shown in FIG. 11 (2), and as shown in FIG. 11 (3), the ink column 66 Is formed. Since the potential of the nozzle plate 58 is fixed at −30V, a negative charge is generated on the surface of the ink column 66. Next, as shown in FIG. 11 (4), the ink column 66 is cut and the main ink droplet is cut by the surface tension between the ink traveling forward by the inertial force and the ink having a low speed or the ink which is forcibly pulled back. 61 is generated. When the main ink droplet 61 is separated from the ink column 66, the main ink droplet 61 often has a thin ink portion such as a tail. When the printing paper 19 is positively charged and the potential is high, the main ink droplet portion has a negative charge due to dielectric polarization. A positive charge is generated at the tail. However, since negative charges are charged in advance on the ink droplets, a large negative charge remains on the main ink droplet 61 and a small negative charge remains on the tail portion.

  Next, as shown in FIG. 11 (5), the tail portion is also cut by the surface tension into sub ink droplets 62. A small negative charge remains in the sub-ink droplet 62 and attracts the printing paper potential, so that the sub-ink droplet adheres to the printing paper 19 without adhering to the nozzle plate. At this time, since the printing paper potential difference is 200 V or more with respect to GND, the printing paper 19 potential does not become 0 V due to discharge due to ink ejection or natural discharge into the air even at the end of printing of the fourth head box 1K. The sub ink droplet 62 does not repel the printing paper 19. Further, since the potential of the printing paper is set so as to be 2 kV or less, discharge does not occur between the nozzle plate 58 and the ink column 66, and the main ink droplet 61 does not scatter, and image formation is stable. Can continue.

(Embodiment 3)
The third embodiment of the present invention will be described below with reference to FIGS. 3 to 6, 12, 13, and 14. FIG. FIG. 12 is a schematic cross-sectional view of an ink jet image forming apparatus according to Embodiment 3 of the present invention.

  In FIG. 12, 71Y, 71M, 71C and 71K are head boxes equipped with heads for ejecting the respective color inks, 72A, 72B and 72C are guide rollers for winding the paper, 73A, 73B and 73C are positioning rollers, and 74A. And 74B are transport rollers, and 83 is a media charger (potential control device) that also serves as a printing paper reversing unit.

  FIG. 13 is a perspective view showing a main part of the media charger according to the third embodiment of the present invention. In FIG. 13, 91 is a take-up-side vertical roller, 92 is a feed-side vertical roller that adjusts printing paper tension together with 91, 93 and 94 are guide rollers, and 95 is a slant attached at an angle of 45 degrees with respect to the printing plane. The roller 96 is attached to the printing plane at an angle of 45 degrees and the oblique roller 95 at an angle of 90 degrees, has a cylindrical shape, and is rotatable around the center line as a rotation axis. A friction charging roller having an acrylic positive member 97 attached thereto.

  3 and 4 are the same as those in the first embodiment, and a description thereof will be omitted. The operation of the ink jet image forming apparatus according to the present embodiment will be described below. When paper is selected as the print medium, a friction charging roller 96 having an acrylic positive member 97 on the friction surface with the print paper 19 is attached before the paper is set in the image forming apparatus. Next, the printing paper 19 is wound around each roller in a predetermined order to adjust the tension. As shown in FIG. 13, the printing paper 19 enters the two rollers attached at an angle of 45 degrees and 135 degrees at an angle of 45 degrees and exits at 135 degrees. As a result, the printing paper 19 is twisted by 180 degrees, Will be reversed. In FIG. 13, in order to improve the visibility, one side of the printing paper 19 is hatched to help explain.

  When a paper transport command enters the image forming apparatus, the transport rollers 74A and 74B rotate to transport the printing paper 19 at a predetermined speed. The conveying rollers 74A and 74B described above, the winding side vertical roller 91 and the feeding side roller 92 in the charging device 83 are interlocked to adjust the tension of the printing paper 19.

  Since the printing paper 19 is wound around the frictional charging roller 96 at an angle of 45 degrees with respect to the central axis of the frictional charging roller 96 and the frictional charging roller 96 is rotatable around the central axis, the circumferential direction of the frictional charging roller 96 The friction between the positive electrode member 97 and the printing paper 19 occurs only in the direction parallel to the central axis of the friction charging roller 96. Static charge is generated by friction.

  In the case of paper and acrylic in the charging row, since the paper is a negative electrode and the acrylic is a positive electrode, the printing paper 19 is charged with a negative charge, and the surface of the printing paper 19 has a negative potential. At this time, the potential of the printing paper 19 is measured on the upstream side in the transport direction of the Y head box 71A with a potential measuring instrument (not shown). When the voltage does not reach −200 V, the material of the positive electrode member 97 is replaced with a material that is further away from the charged column such as nylon. When the voltage is lower than −2 kV, the material of the positive electrode member 97 is changed to a closer one to a charged column such as aluminum, and the surface potential of the printing paper 19 is adjusted to be about −1 kV. Needless to say, it is possible to adjust the printing paper potential in combination with the first and second embodiments.

  When the adjustment is completed, printing is possible. When a print command enters the image forming apparatus, the transport rollers 74A and 74B rotate to transport the printing paper 19 at a predetermined speed. The conveying rollers 74A and 74B described above, the winding side vertical roller 91 and the feeding side roller 92 in the charging device 83 are interlocked to adjust the tension of the printing paper 19.

  At the same time, the potential of the nozzle plate 26 is fixed to + 35V from a DC power source (not shown). When the paper conveyance speed reaches a preset value of the user in advance, the drive voltage waveform is supplied to the lower electrode 23 from an amplifier (not shown) in accordance with the paper conveyance speed and the distance in the paper feed direction of the head BOX of each color. Applied. The upper electrode 22 selected corresponding to the formed image is connected to GND by a drive driver (not shown), and an electric field is applied to the piezoelectric element 21. The piezoelectric element 21 shrinks in the plane direction, the diaphragm 23 is bent by the bimetal effect with the diaphragm 23, the internal pressure of the pressure chamber 31 is increased, and the increased internal pressure ejects ink droplets 29 and 30 from the nozzle hole 27. An image is formed on the printing paper 19.

  Since the behavior of the sub ink droplet 30 as the ink mist at this time is the same as that of the first embodiment, the description thereof is omitted.

(Embodiment 4)
Hereinafter, Embodiment 4 of the present invention will be described with reference to FIG. 14, FIG. 15, and FIG.

  FIG. 14 is a longitudinal sectional view of the main part of the single head according to the fourth embodiment of the present invention. In FIG. 14, reference numeral 101 denotes a piezoelectric element, 102 denotes an upper electrode, and 103 denotes a diaphragm that also serves as a lower electrode, which serves as a lower electrode common to a plurality of piezoelectric elements. 104 is a conductive adhesive layer, 105 is a flow path member made of stainless steel, 111 is a pressure chamber provided in the flow path member 105 corresponding to the piezoelectric element 101, 106 is a nozzle plate, 107 is penetrating the nozzle plate 106. A nozzle hole that is tapered on the outlet side in the ink flow direction is provided corresponding to the pressure chamber. 108 is a conductive adhesive layer for bonding the flow path member 105 and the nozzle plate 106, 109 is a main ink droplet discharged from the nozzle hole 107, and 110 is a sub ink droplet separated from the main ink droplet.

  The behavior of the sub ink droplet 110 which is the ink mist at this time will be described with reference to FIGS.

  FIG. 15 is a voltage waveform diagram of the ink jet image forming apparatus according to the fourth embodiment of the present invention. In FIG. 15, a pull-push-pull voltage waveform is applied to the piezoelectric element 101 between the vibration plate 103 and the upper electrode 102. Since the vibration plate 103 is a common electrode, the ink near all the nozzles has the same potential. It has become. Corresponding to the time timing of the voltage waveform, symbols from T1 to T6 are given, and each potential of the voltage waveform is set to V1 and V2.

  FIG. 16 is a continuous schematic cross-sectional view of the ink droplet ejection process of the ink jet image forming apparatus according to Embodiment 4 of the present invention. In FIG. 16, 106 is a nozzle hole, 112 is an ink column, 109 is a main ink drop, 110 is a sub ink drop separated from the main ink drop, and 19 is a printing paper. A negative potential of -2 kV is generated.

  The operation of the ink jet image forming apparatus according to the present embodiment will be described below. As shown in FIG. 15, in the interval from the standby state to T1, the applied voltage is held in the state of V1, so that the piezoelectric element 101 is reduced in the planar direction, and the diaphragm 103 is caused by the bimetal effect with the diaphragm 103. The pressure chamber 111 is bent and held in a reduced state.

  Next, in the section from T1 to T2, since the applied voltage V1 gradually decreases from GND, the bimetal effect decreases, and the pressure chamber 111 gradually expands. At this time, as shown in FIG. 16A, the meniscus of the nozzle hole 107 is slightly retracted and drawn into a concave shape.

  Next, after the voltage is held in the section from T2 to T3, the applied voltage is increased from GND to V2 in the section from T3 to T4, and the pressure chamber 111 further decreases than in the standby state. At this time, the meniscus rises as shown in FIG. 16 (2), and the ink column 112 is formed as shown in FIG. 16 (3). Since the nozzle plate 106 is electrically connected to the vibration plate 103 through the conductive adhesive layers 104 and 108 and the flow path member 105, the potential of the nozzle plate 106 is equal to that of the vibration plate 103. A positive charge is generated on the surface of the ink column 112.

  Next, after holding the voltage in the section from T4 to T5, the applied voltage is gradually lowered from V2 to V1 in the section from T5 to T6, and the volume of the pressure chamber 111 is expanded to return to the standby state. At this time, as shown in FIG. 16 (4), the ink column 112 is cut and the main ink is cut by the surface tension between the ink that advances forward due to the inertial force and the ink that is slow or forcibly pulled back. Although the droplet 109 is generated, since the potential of the nozzle plate 106 is maintained at V1, the main ink droplet 109 has a positive charge. The main ink droplet 109 often has a thin ink portion such as a tail when separated from the ink column 112. When the printing paper 19 is negatively charged and the potential is low, the main ink droplet 109 is positively charged due to dielectric polarization. , Try to generate a negative charge in the tail. However, since the main ink droplet 109 has a positive charge in advance, a large positive charge remains in the main ink droplet 109 and a small positive charge remains in the tail portion.

  Next, as shown in FIG. 16 (5), the tail portion is also cut by the surface tension to become the sub ink droplet 110. As a result, a small positive charge also remains in the sub ink droplet 110 and attracts the printing paper potential, so that the sub ink droplet adheres to the printing paper without adhering to the nozzle plate. At this time, since the printing paper potential is negative by −200 V or more with respect to GND, the electric charge does not suddenly disappear due to discharge due to ink ejection or natural discharge. In addition, since the potential of the printing paper is set so as to be a negative potential smaller than −2 kV, no discharge is generated between the nozzle surface and the discharge between the nozzle plate 106 and the ink column 111. The main ink droplets 109 are not scattered and the image formation can be stably continued.

  Further, since the nozzle plate 106 and the diaphragm 103 are electrically connected, no current flows between the nozzle plate and the diaphragm. Therefore, stable printing can be realized without microbubbles caused by electrolysis staying in the pressure chamber. In the fourth embodiment, the description has been made with the combination of the voltage waveform on the positive electrode side and the printing paper on the negative electrode side. Yes.

  Naturally, the fourth embodiment can be performed simultaneously with the first and third embodiments or simultaneously with the second and third embodiments.

  Hereinafter, specific contents of the present invention will be described with reference to examples.

Example 1
FIG. 20 is a table showing the initial potential and the relative humidity dependence of the post-printing potential when ink is applied to the printing paper surface. The printing paper is plain paper (Oji Paper's OKH-J OFF 70), the environmental temperature is 30 ° C., the printing speed is 60 m / min, and the relative humidity is 20% RH and 80% RH. From FIG. 19, even at 20% RH, no discharge occurs if the initial potential is 2 kV or less, and even at 80% RH, if the initial potential is 200 V or more, it does not drop to GND, and the effect of the present invention can be obtained.

  Since the ink jet image forming apparatus according to the present invention can be operated continuously for a long time, the field of paper printing such as newspaper printing and direct mail, the label of PET bottles, the field of resin printing such as DVD, the field of cloth printing such as textile printing, and the outer wall, etc. It can be used in the panel printing field.

1 is a schematic cross-sectional view of an ink jet image forming apparatus according to Embodiment 1 of the present invention. Attachment diagram of charger in embodiment 1 of the present invention Arrangement of line-type heads of ink-jet image forming apparatus according to Embodiment 1 of the present invention 1 is a perspective view of main parts of a single head according to Embodiment 1 of the present invention. The principal part top view of the single head in Embodiment 1 of this invention FIG. 5 is a longitudinal sectional view taken along A-A in FIG. 5 in Embodiment 1 of the present invention. Continuous schematic sectional view of the ink droplet ejection process of the ink jet image forming apparatus according to Embodiment 1 of the present invention. The principal part perspective view of the single head in Embodiment 2 of this invention The principal part top view of the single head in Embodiment 2 of this invention FIG. 9 is a longitudinal sectional view taken along line BB in FIG. 9 in Embodiment 2 of the present invention. Continuous schematic cross-sectional view of the ink droplet ejection process of the ink jet image forming apparatus according to Embodiment 2 of the present invention Schematic sectional view of an ink jet image forming apparatus according to Embodiment 3 of the present invention. The perspective view which shows the principal part of the media charger in Embodiment 3 of this invention. Longitudinal sectional view of main part of single head according to Embodiment 4 of the present invention Voltage waveform diagram of ink jet image forming apparatus according to Embodiment 4 of the present invention Continuous schematic sectional view of the ink droplet ejection process of the ink jet image forming apparatus according to Embodiment 4 of the present invention. Schematic cross-sectional view of a conventional ink jet image forming apparatus Continuous schematic cross-sectional view of the ink droplet ejection process of a conventional inkjet image forming apparatus Figure showing a list of charged columns of typical materials The figure which shows the table | surface which showed the initial potential of the electric potential after printing at the time of printing ink on the printing paper surface, and relative humidity dependence

Explanation of symbols

4 Conveying roller 6 Rotating plate 8 Friction device (potential control device)
DESCRIPTION OF SYMBOLS 9 Fixed plate 10 Rotation mechanism part 11 Negative electrode member 12,97 Positive electrode member 13 Single head 19 Printing paper (media)
21, 51, 101 Piezoelectric element 22, 52, 102 Upper electrode 23, 53, 103 Lower electrode (diaphragm, pressure generating means)
25, 56, 105 Flow path member 26, 58, 106 Nozzle plate 27, 59, 107 Nozzle hole 29, 61, 109 Main ink droplet 30, 62, 110 Sub ink droplet 31, 57, 111 Pressure chamber 32, 66, 112 Ink pillar 63 Head base 83 Charging device 91 Feeding side vertical roller 92 Winding side vertical roller 95 Diagonal roller 96 Friction charging roller 104, 108 Conductive adhesive layer

Claims (17)

Multiple pressure chambers;
Pressure generating means for increasing the internal pressure of the pressure chamber;
A nozzle plate provided for each pressure chamber, each having a plurality of nozzles, and ejecting ink droplets from the nozzles by the pressure in the pressure chambers to form dots on the media;
In an inkjet image forming apparatus comprising:
A potential control device that controls the potential of the nozzle plate so that the media has a potential,
An ink jet image forming apparatus. The potential control device is a friction device that applies an electric charge to the medium by rubbing the medium with a member having a different charge train from the medium.
The inkjet image forming apparatus according to claim 1. The friction device is equipped with a positive electrode side member of the charging column of the medium, and friction between the positive electrode side member and the medium to give a negative charge to the medium.
The inkjet image forming apparatus according to claim 2. The friction device is equipped with a negative electrode side member of the charging train of the media, and friction between the positive electrode side member and the media to give a positive charge to the media.
The inkjet image forming apparatus according to claim 2. The friction device has a substantially cylindrical shape and contacts the medium on the side surface of the cylindrical shape, and the potential control device controls the charge amount of the medium by changing the contact portion area of the cylindrical shape. To
The inkjet image forming apparatus according to claim 3. The friction device is provided with at least two types of members having different charge trains on the side surface, and controls the amount of charge by increasing or decreasing the ratio of the contact areas of the two types of members.
An ink jet image forming apparatus according to claim 5. The friction device performs friction between the medium and a member having a different charge train and the medium such that the friction direction has a media width direction component.
The inkjet image forming apparatus according to claim 2. The friction device has a friction component in the media width direction due to friction in a direction parallel to the center axis of the roller surface rotatable with respect to the center axis.
The inkjet image forming apparatus according to claim 7. The friction device is selected based on the type, speed, humidity and temperature of the media, and the friction device is detachable from the apparatus.
The inkjet image forming apparatus according to claim 3. The potential control device controls the potential of the medium so as to have a polarity opposite to the charge of the ink droplet.
The inkjet image forming apparatus according to claim 1. The pressure generating means increases the pressure in the pressure chamber by displacement of a vibration member forming at least one surface of the pressure chamber;
The inkjet image forming apparatus according to claim 1. The potential control device defines the polarity of the charge of the ink droplet by defining the potential of the nozzle plate.
The inkjet image forming apparatus according to claim 1. The ink droplets generated from the nozzles by the pressure in the pressure chamber include a main ink droplet that constitutes a large part of the dots formed on the medium and at least one secondary ink that constitutes the remaining part of the dots. Consisting of ink drops,
The inkjet image forming apparatus according to claim 1. The media potential is set higher than the nozzle potential when the nozzle potential is negative, the potential difference between the media potential and the nozzle potential is 200 V to 2 kV, and the nozzle potential is positive. In the case of the characteristic, it is set lower than the potential of the nozzle, and the potential difference between the potential of the medium and the potential of the nozzle is 200 V to 2 kV.
The ink jet image forming apparatus according to claim 1, wherein the ink jet image forming apparatus is an ink jet image forming apparatus. Multiple pressure chambers;
Pressure generating means for increasing the internal pressure of the pressure chamber;
A nozzle plate provided for each pressure chamber, each having a plurality of nozzles, and ejecting ink droplets from the nozzles by the pressure in the pressure chambers to form dots on the media;
In an inkjet image forming apparatus comprising:
At least one of the pressure chambers is
A vibrating member forming at least one surface;
A piezoelectric element provided in the pressure chamber;
A first electrode provided on an arbitrary surface of the piezoelectric element;
A second electrode provided on a surface opposite to the first electrode of the piezoelectric element;
The shape of the piezoelectric element is changed by controlling the potential of the first electrode to increase the pressure in the pressure chamber, and the ink droplets are ejected from the nozzle.
The first electrode and the vibrating member are electrically connected, and the nozzle plate and the vibrating member are electrically connected, so that the first electrode, the vibrating member, and the nozzle plate have the same potential. To
An ink jet image forming apparatus. Making the potential of the media opposite to the polarity of the nozzle plate potential when the ink drop separates from the nozzle plate,
The inkjet image forming apparatus according to claim 15. The media potential is set higher than the nozzle potential when the nozzle potential is negative, the potential difference between the media potential and the nozzle potential is 200 V to 2 kV, and the nozzle potential is positive. In the case of the characteristic, it is set lower than the potential of the nozzle, and the potential difference between the potential of the medium and the potential of the nozzle is 200 V to 2 kV.
The inkjet image forming apparatus according to claim 16.

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