JP4730155B2 - Inkjet printer - Google Patents

Description

  The present invention adsorbs and conveys a printing medium such as recording paper onto the surface of a conveying belt, and discharges, for example, fine particles (dots) of liquid ink of a plurality of colors onto the printing medium to draw predetermined characters and images. The present invention relates to an inkjet printer.

Such an inkjet printer is generally inexpensive and can easily obtain a high-quality color printed matter. Accordingly, along with the widespread use of personal computers and digital cameras, it has become widespread not only in offices but also in general users.
In such an ink jet printer, generally, a moving body called a carriage or the like, which is integrally provided with an ink cartridge and an ink discharge head (generally called an ink jet head), runs on a print medium in a direction intersecting the transport direction. By driving the actuator while reciprocating, the liquid ink particles are ejected (jetted) from the nozzles formed on the ink jet head, thereby forming minute ink dots on the print medium, thereby forming predetermined characters and images. Is drawn to create a desired printed matter. The carriage is equipped with four color (yellow, magenta, cyan) ink cartridges including black (black) and an inkjet head for each color, so that not only monochrome printing but also full-color printing combining each color is easy. (Furthermore, 6 colors, 7 colors, or 8 colors in which light cyan, light magenta, etc. are added to these colors are also put into practical use).

  In addition, in an ink jet printer that performs printing while reciprocating the ink jet head on the carriage in the direction intersecting the print medium transport direction (width direction of the print medium), the entire page is printed neatly. Therefore, it is necessary to reciprocate the inkjet head several tens of times to 100 times or more. In contrast, in an inkjet printer of a type that does not use a carriage with a long (not necessarily integral) inkjet head having the same dimensions as the width of the print medium, the inkjet head is moved in the width direction of the print medium. Therefore, it is possible to perform printing in a so-called one pass, so that high-speed printing is possible. The former inkjet printer is generally referred to as a “multi-pass inkjet printer”, and the latter inkjet printer is generally referred to as a “line head inkjet printer”.

  By the way, in this type of line head type ink jet printer, a configuration is often used in which a print medium is electrostatically adsorbed and conveyed on an endless belt for conveyance. In order to electrostatically attract the print medium with the conveyance belt, it is necessary to apply a charge to the conveyance belt to charge it, but the electric field due to this charge acts on the ink droplets, and there are problems with ink ejection such as flight bending. May occur. The flight curve means that the ink droplets ejected from the nozzle do not fly on the ideal trajectory and deviate from the ideal output position (also referred to as the landing position). In particular, in a line head type ink jet printer, since printing is performed in a so-called one pass, a printing result is remarkably lowered only by an ink ejection failure occurring in one of a large number of nozzles.

Therefore, in the ink jet printer described in Patent Document 1 below, an electrode is provided in the vicinity of the gap between the ink jet head and the print medium, and the charging of the flying ink droplet is forcibly neutralized by applying an AC voltage to the electrode. Has been proposed. In addition, the inkjet printer described in Patent Document 2 below performs so-called AC charging in which the polarity is alternately reversed along the moving direction of the transport belt, and transports so that the lines of electric force draw a minute loop between the positive and negative charging portions. An electric field is generated in the vicinity of the belt, and the print medium is electrostatically adsorbed by using an electric field that does not extend far from the conveyor belt. Further, in the ink jet printer described in Patent Document 3 below, a control electrode is provided around the nozzle for ejecting ink droplets, and a voltage is applied to the control electrode at the timing of ejecting ink droplets, so that an electric field between the transport belt and the ink jet head is applied. We are trying to weaken or reverse.
JP-A-4-83644 JP 2003-103857 A JP 2000-25249 A

  However, in the prior art, the charging of the ink droplet is removed or the influence of the electric field of the flying portion of the ink droplet is alleviated, and the ink droplet is not intended to land more aggressively at the target landing position. Absent. In addition, flying bends of ink droplets also have causes such as paper dust and ink mist adhering to the vicinity of the nozzles, and individual differences in the ink drop ejection direction of the nozzles themselves. The ink droplet cannot be landed at the target landing position by correcting the above.

  The present invention has been made paying attention to the above-described problems, and provides an ink jet printer that can more positively land ink droplets at a target landing position and reduce the time required for printing. It is for the purpose.

  [Invention 1] In order to solve the above-described problems, the ink jet printer of Invention 1 carries a print medium by placing the print medium on the surface of the conveyance belt, and ejecting ink droplets from the nozzles of the ink jet head onto the print medium for printing. In the ink jet printer that performs the above, an ink charging unit that charges the ink to a predetermined polarity, and a non-contact arrangement of the ink jet head on the opposite side of the nozzle of the ink jet head across the transport belt and the reverse of the charging potential of the ink A landing auxiliary electrode having a polar potential is provided, and the landing auxiliary electrode is arranged so as to be shifted downstream of the nozzle position of the inkjet head in the print medium conveyance direction.

  According to the ink jet printer according to the first aspect of the invention, the ink is charged to a predetermined polarity by the ink charging means, and a potential having a polarity opposite to the charging potential of the ink is provided on the opposite side of the nozzle of the ink jet head across the transport belt. By placing the landing auxiliary electrode in a non-contact manner on the conveyor belt, the ink droplets fly toward the landing auxiliary electrode by electrostatic force. Therefore, the position of the landing auxiliary electrode can be set more appropriately. In addition, the ink droplets can be landed on the target landing position, and the flying speed of the ink droplets can be increased, so that the time required for printing can be shortened. In addition, by arranging the landing auxiliary electrode so as to be shifted downstream of the nozzle position of the inkjet head in the print medium conveyance direction, the ink droplets ejected from the nozzles of the inkjet printer when the conveyance speed of the print medium is equal to or higher than a predetermined value. Is affected by the air flow accompanying the conveyance of the print medium, it is possible to prevent the influence of the air flow from being suppressed and land the ink droplets at the target landing position.

[Invention 2] The ink jet printer according to Invention 2 is the ink jet printer according to Invention 1, wherein the landing auxiliary electrode is ink-jetted only by the influence of the ink droplets ejected from the nozzles of the ink-jet head from the air flow accompanying the printing medium conveyance. It is characterized by being arranged shifted from the nozzle position of the head to the downstream side in the print medium conveying direction.
According to the ink jet printer according to the second aspect of the present invention, the ink droplets ejected from the nozzles of the ink jet head are shifted from the nozzle position of the ink jet head to the downstream side in the print medium transport direction by the amount affected by the air flow accompanying the print medium transport. By providing the landing auxiliary electrode, it is possible to reliably suppress and prevent the influence of the air flow and land the ink droplet at the target landing position.

Next, an embodiment of an inkjet printer according to the present invention will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram of an ink jet printer according to the present embodiment. Reference numeral 1 in the figure denotes a conveyance belt for conveying a printing medium 2 such as printing paper. The print medium 2 is a sheet material made of a high resistance material such as printing paper or an OHP sheet. The conveyor belt 1 is an endless belt made of a medium / high resistance material made of a material as described later. The conveyor belt 1 is wound around a driving roller 3 disposed at the left end portion in the figure and a driven roller 4 disposed at the right end portion in the figure.

  The drive roller 3 is driven to rotate in the direction of the arrow in the figure by a drive source (not shown), and the print medium 2 is sucked from the right side of the figure in a state where the print medium 2 is attracted to the conveyance belt 1 charged by the charging roller described later. Transport to the left, that is, in the direction of the arrow. The drive roller 3 is grounded so as to remove charges from the conveying belt 1, so-called static elimination. The tension of the conveyor belt 1 is adjusted by a configuration such as using a tension roller (not shown) to expand the belt downward in the figure, or pulling either the driving roller 3 or the driven roller 4 outward with a spring, etc. It's not going out.

  A charging roller 7 as a charging unit is in contact with the conveyor belt 1 so as to face the driven roller 4, and a positive (+) pole DC power supply 8 is connected to the charging roller 7. The arrangement of the charging roller 7 corresponds to immediately before the feeding position of the printing medium 2. The charging roller 7 is charged by applying a positive (+) pole charge to the surface of the conveyance belt 1, generates dielectric polarization in the print medium 2 by the charge, and the print medium 2 side of the print medium 2 by the dielectric polarization is charged. The print medium 2 is attracted to the surface of the conveyor belt 1 by electrostatic force due to the electric charge of the toner and the charge on the surface of the conveyor belt 1. The charging roller 7 is pressed against the conveyor belt 1 by a spring (not shown).

  A pressure roller 9 may be disposed above the driven roller 4 as shown. The pressure roller 9 is urged downward by a spring (not shown) and has a function of pressing the print medium 2 against the conveyance belt 1 on the driven roller 4. Since the printing medium 2 has irregularities of about 10 to several tens of μm, and there are wrinkles, warping, sagging, and bending, the printing medium 2 can be transferred to the conveying belt 1 just by feeding the printing medium 2 onto the conveying belt 1. It does not adhere to.

  Therefore, after the printing medium 2 is mounted on the outer peripheral surface of the charged conveyance belt 1, when the printing medium 2 is pressed against the conveyance belt 1 by the pressure roller 9, it is attracted to the outer peripheral surface of the conveyance belt 1 by the dielectric polarization as described above. The printed print medium 2 is further closely adhering and transported with increased suction force, and improves the surface smoothness of the print medium 2 and improves the uniformity of the gap with the head nozzle. improves. A gate roller (not shown) is arranged on the upstream side of the pressure roller 9 in the conveyance direction of the print medium 2. This gate roller is used to adjust the timing at which the print medium 2 fed from the paper feed unit is fed onto the transport belt 1 and to bend the print medium 2 in the transport direction, so as to correct a so-called skew.

  Reference numeral 11 in FIG. 1 is a line-type inkjet head. The inkjet head 11 is shifted in the transport direction of the printing medium 2 for each of a plurality of necessary combinations of colors such as four colors of yellow (Y), magenta (M), cyan (C), and black (K). Arranged. Ink is supplied to each inkjet head 11 from an ink tank of each color (not shown) via an ink supply tube.

Each inkjet head 11 is formed with a plurality of nozzles in a direction intersecting with the transport direction of the print medium 2, and by ejecting a necessary amount of ink droplets from these nozzles to necessary places as appropriate, the print medium 2. A minute ink dot is formed and output on the top. By performing this for each color, it is possible to perform so-called one-pass printing by passing the print medium 2 adsorbed on the conveyor belt 1 once. That is, the area where the inkjet head 11 is disposed corresponds to the print area. In the present embodiment, the conveyance speed of the print medium 2 is set to 600 mm / s in order to cope with high-speed printing. The gap between the nozzles of the inkjet head 11 and the printing medium 2 is 1 mm, and the ink droplet ejection speed is 5 m / s.

  There are various methods for ejecting and outputting ink from each nozzle of the ink jet head, such as a piezo method and a thermal method, and any ink output method can be applied to the present invention. The in-type inkjet head of the present embodiment literally has a “single row” nozzle configuration. However, as described in, for example, Japanese Patent Application Laid-Open No. 7-81049, a relatively short nozzle row module is inclined or staggered. It may be arranged in a shape. In this embodiment, it is important that the inkjet head is fixed.

  A plane forming portion 12 is provided below the inkjet head 11 constituting the printing area so as to face the inkjet head 11. The plane forming unit 12 is generally called a platen, and regulates the flat surface of the print medium 2 via the transport belt 1 when ejecting ink droplets from the inkjet head 11. Details of the plane forming portion 12 will be described later.

The conveyor belt 1 uses nylon, polyester, polyurethane, PET, polycarbonate, fluorine-based resin such as silicon-based or PVDF-based resin as a base resin, carbon black or conductive filler is mixed into this, Volume resistivity is 10 ⁸ to 10 ¹⁵ Ω · cm
The degree is adjusted to about 10 ⁹ to 10 ¹² Ω · cm. The thickness of the conveyor belt 1 is
Considering durability and flexibility, charging at high speed and static elimination characteristics, etc., that is, from the viewpoint of compatibility between static elimination / power feeding efficiency and mechanical strength, 0.05 to 0.5 mm, more preferably 0.1 to 0. Select about 2mm.

  In FIG. 2, the detail of the plane formation part 12 is shown. In the present embodiment, two plane regulation bodies 13 are disposed for each of the four color nozzle rows of the inkjet head 11 described above, and landing auxiliary electrodes 14 are disposed therebetween. The circles in the figure represent the nozzles of the inkjet head 11. In other words, the plane regulating body 13 and the landing auxiliary electrode 14 are disposed on the opposite side of the nozzle of the inkjet head 11 with the conveyance belt 1 interposed therebetween. In this embodiment, the landing auxiliary electrode 14 is used as the nozzle of the inkjet head 11. On the other hand, it is slightly arranged on the downstream side in the print medium conveyance direction.

  FIG. 3 shows the plane restricting body 13 and the landing auxiliary electrode 14 that are arranged to face one nozzle row. The plane regulating body 13 is called the platen described above, is made of an insulating material such as plastic, and is formed with a plane portion 13a that contacts the back surface (inner circumferential surface) of the transport belt 1. In addition, on the upstream side of the landing auxiliary electrode 14 in the print medium conveyance direction, the static elimination electrode 15 is disposed so as to be in close contact with the plane regulation body 13 with the plane regulation body 13 interposed therebetween. Further, a recharging electrode 16 is disposed on the downstream side of the landing auxiliary electrode 14 in the print medium conveying direction so as to be in close contact with the plane regulating body 13.

FIG. 4 shows details of the landing auxiliary electrode 14, the inkjet head 11, the charge removal electrode 15, and the recharging electrode 16. The landing auxiliary electrode 14 is disposed between the two plane regulating bodies 13 so as to be sandwiched between the two but is not in contact with the transport belt 1. The landing auxiliary electrode 14 has a negative (−) pole and is configured by a thin blade (thin plate) in the print medium conveyance direction. As will be described later, this is to limit the landing position of the ink droplets to a narrow range. By using the blade, it is possible to easily cope with the above-described inclined or staggered inkjet head nozzles. On the other hand, a positive (+) electrode charge is applied to the inkjet head 11 as ink charging means, and the inkjet head 11 and the ink inside the inkjet head 11 are also charged to the positive (+) electrode. The static elimination electrode 15 is for removing the charge (charge) of the transport belt 1, is composed of a negative (−) electrode, and is in contact with the transport belt 1. The recharging electrode 6 is for recharging the conveyor belt 1 and is composed of a positive (+) pole blade electrode and is in contact with the conveyor belt 1.

The landing auxiliary electrode 14 uses a conductive plastic blade in which resistance is adjusted by mixing carbon black or conductive filler with various plastics, and its volume resistance value is 10 ⁹ to 10 ¹² Ω · Adjust to medium or high resistance of about cm. The clearance between the landing auxiliary electrode 14 and the conveyor belt 1 is in a non-contact state within a range not exceeding 1 mm. The dimension in the height direction of the landing auxiliary electrode 14, that is, the thickness in the energizing direction is about 3 mm or more. Further, if the shape of the landing auxiliary electrode 14 on the ink jet head nozzle side is sharp, it is easy to discharge. Therefore, the tip of the landing auxiliary electrode 14 on the ink jet head nozzle side has an R shape, the radius of curvature of the R shape is 2 mm or less, and 0.5 mm or less when performing high-density mounting.

  The potential of the inkjet head 11 is set to +500 V to +1000 V, and the potential of the landing auxiliary electrode 14 is set to −1000 V to −1500 V so that the overall potential difference does not exceed 2000 V. (If it exceeds 2000 V, there is a risk of leak discharge). When ink droplets are ejected from the nozzles of the inkjet head 11, the ink droplets charged to the positive (+) electrode are repelled by the electrostatic force with the inkjet head 11 and are attracted by the electrostatic landing force to the negative (−) electrode landing auxiliary electrode 14. To fly.

  The flying ink droplets are received from the force ejected from the inkjet head 11, the force received from the electric field of the landing auxiliary electrode 14, the air resistance (toward the inkjet head 11), and the air flow (wind) flowing on the print medium 2. Fly in balance with the force and land on the print medium 2. Among these, the air (wind) flowing on the print medium 2 is a wind generated when an object (in this case, the print medium 2) moves at a high speed, and in the present embodiment, the print medium 2 is conveyed. Since the speed is set to 600 mm / s, this air flow affects the flight of ink droplets. Specifically, ink droplets are caused to flow in the air stream and land downstream. In this embodiment, in order to suppress and prevent the influence of the air flow accompanying the conveyance of the print medium 2, the landing auxiliary electrode 14 is arranged with a shift of 60 μm downstream from the nozzle of the inkjet head 11 in the print medium conveyance direction. Has been established. That is, the landing auxiliary electrode 14 is shifted from the nozzle position of the inkjet head 11 to the downstream side in the printing medium conveyance direction by an amount affected by the air flow accompanying the conveyance of the printing medium 2 by the ink droplets ejected from the nozzle of the inkjet head 11. By disposing the ink droplet, the influence of the air flow can be reliably suppressed and prevented, and the ink droplet can be landed on the target landing position.

The neutralization electrode 15 and the recharging electrode 16 are made of conductive plastic blades in which various plastics are mixed with carbon black or conductive filler to adjust the resistance, and the volume resistance value is about 10 ⁴ to 10 ¹⁰ Ω · cm. adjust. The static elimination electrode 15 and the recharging electrode 16 must be in contact with the conveyance belt 1 from their respective functions. Further, the dimension in the height direction of the static elimination electrode 15 and the recharging electrode 16, that is, the thickness in the energization direction is about 3 mm or more. The static elimination electrode 15 and the recharging electrode 16 do not need to limit the ink droplet landing position unlike the landing auxiliary electrode 14 and may be roller electrodes.

The electric potential of the static elimination electrode 15 is adjusted to a value at which the charge (charge) of the conveying belt 1 can be completely or almost completely removed in order to ensure the ink droplet suction effect by the landing auxiliary electrode 14 described above. If the object can be achieved, the ground potential may be used. In order to restore the print medium electrostatic adsorption force of the conveyor belt 1 removed by the static elimination electrode 15, the potential of the recharging electrode 16 is
Adjustment is made so that the outer peripheral surface potential of the conveyance belt 1 after the charge is applied is 300V to 1000V, preferably 500V to 800V.

  Further, the distance between the landing auxiliary electrode 14 and the static elimination electrode 15 and the distance between the landing auxiliary electrode 14 and the recharging electrode 16 are both larger than the distance between the landing auxiliary electrode 14 and the nozzle of the inkjet head 11. In the present embodiment, the ink droplet charged to the positive (+) electrode is easily attracted to the charge removal electrode 15 that is the negative (−) electrode, and easily repels the recharged electrode 16 that is the positive (+) electrode. By making the distance between the landing auxiliary electrode 14 and the static elimination electrode 15 and the distance between the landing auxiliary electrode 14 and the recharging electrode 16 larger than the distance between the landing auxiliary electrode 14 and the nozzle of the inkjet head 11, The influence of the static elimination electrode 15 and the recharging electrode 16 on the flight of the ejected ink droplet can be suppressed and prevented, and the ink droplet suction effect by the landing auxiliary electrode 14 can be ensured.

  As described above, according to the ink jet printer of this embodiment, the ink charging means charges the ink to a predetermined polarity, and the ink charging potential is set on the opposite side of the nozzle of the ink jet head 11 with the conveying belt 1 interposed therebetween. Since the landing auxiliary electrode 14 having a reverse polarity potential is disposed in a non-contact manner on the transport belt 1, the ink droplets fly toward the landing auxiliary electrode 14 due to electrostatic force. Therefore, the position of the landing auxiliary electrode 14 is changed. By setting appropriately, the ink droplet can be landed more actively at the target landing position, and the flight speed can be increased on the ink droplet, so that the time required for printing can be shortened. Further, since the landing auxiliary electrode 14 is disposed so as to be shifted downstream of the nozzle position of the inkjet head 11 in the printing medium conveyance direction, the conveyance speed of the printing medium 2 is equal to or higher than a predetermined value and discharged from the nozzles of the inkjet printer 11. When the ink droplets are affected by the air flow accompanying the conveyance of the printing medium, the ink droplets can be landed on the target landing position while suppressing the influence of the air flow.

Further, the landing auxiliary electrode 14 is disposed by shifting the ink droplets ejected from the nozzles of the inkjet head 11 from the nozzle position of the inkjet head 11 to the downstream side in the printing medium conveyance direction by the amount affected by the air flow accompanying the conveyance of the printing medium. By providing, it is possible to reliably suppress and prevent the influence of the air flow and land the ink droplet at the target landing position.
In addition, even if the polarity of the DC potential applied to the landing auxiliary electrode 14 and the inkjet head 11 is reversed from the setting in the above-described embodiment, the effect is the same.

  In the above-described embodiment, the static elimination electrode 15 is disposed on the upstream side of the landing auxiliary electrode 14 in the print medium conveyance direction, and the recharging electrode 16 is disposed on the downstream side in the print medium conveyance direction. The electrodes 15 and 16 are not required. In short, when the printing medium 2 is transported at a speed equal to or higher than a predetermined value, the ink droplets ejected from the nozzles of the inkjet printer are affected by the air flow accompanying the transportation of the printing medium 2. It is important that the landing auxiliary electrode 14 to be sucked is shifted to the upstream side in the print medium conveyance direction.

  The ink jet printer of the present invention is not only for electrostatically attracting and transporting the print medium 2 to the transport belt 1, but also for simply placing the print medium on the transport belt, or for applying the print medium to the transport belt by air suction. The present invention can be applied to any ink jet printer as long as the print medium is placed on the surface of the transport belt and transported, such as the one transported by suction.

1 is a front view illustrating a schematic configuration of an embodiment of an inkjet printer according to the present invention. It is explanatory drawing of the plane formation part of FIG. It is explanatory drawing of the plane control body and landing auxiliary electrode which oppose 1 row of nozzles among the plane formation parts of FIG. It is explanatory drawing which shows the relationship between a landing auxiliary electrode and an inkjet head.

Explanation of symbols

  1 is a conveying belt, 2 is a printing medium, 3 is a driving roller, 4 is a driven roller, 7 is a charging roller, 8 is a DC power supply, 9 is a pressure roller, 11 is an inkjet head, 12 is a plane forming portion, and 13 is a plane regulation. Body, 14 is an auxiliary landing electrode, 15 is a static elimination electrode, and 16 is a recharging electrode.

Claims (2)

In an inkjet printer that carries a print by placing a print medium on the surface of a conveyance belt and ejecting ink droplets from the nozzles of the inkjet head onto the print medium
Ink charging means for charging the ink to a predetermined polarity;
A landing auxiliary electrode disposed in a non-contact manner on the opposite side of the nozzle of the inkjet head across the conveyance belt and having a potential opposite to the charging potential of the ink ;
With
The landing auxiliary electrode is arranged shifted from the nozzle position of the inkjet head to the downstream side in the print medium conveyance direction ,
A static elimination electrode applied in the opposite polarity to the charging potential of the ink is disposed in contact with the transport belt via an insulating member on the upstream side of the landing auxiliary electrode,
A recharging electrode applied in the same polarity as the charging potential of the ink is disposed in contact with the transport belt via an insulating member different from the insulator on the downstream side of the landing auxiliary electrode.
An inkjet printer characterized by the above. The distance between the landing auxiliary electrode and the static elimination electrode and the distance between the landing auxiliary electrode and the recharging electrode are larger than the distance between the landing auxiliary electrode and the nozzle of the inkjet head.
The inkjet printer according to claim 1.

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