JP4802757B2 - Inkjet printer - Google Patents

Description

  In the present invention, for example, minute characters of liquid inks of a plurality of colors are ejected from a plurality of nozzles to form fine particles (ink dots) on a print medium, thereby drawing a predetermined character or image. The present invention relates to a head driving device and a head driving method for an ink jet 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.
Such an ink jet printer generally has an ink jet head head while a moving body called a carriage, which is integrally provided with an ink cartridge and an ink jet head, reciprocates on a print medium in a direction intersecting the transport direction. By ejecting (injecting) liquid ink droplets from the nozzles to form minute ink dots on the print medium, a predetermined character or image is drawn on the print medium to create a desired printed matter. ing. The carriage is equipped with four color (yellow, magenta, cyan) ink cartridges including black (black) and a print 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).

  Further, in this type of ink jet printer in which printing is executed while the ink jet head on the carriage is reciprocated in the direction intersecting the conveyance direction of the print medium, the ink jet head is set to 10 in order to print the entire page cleanly. It is necessary to reciprocate several times to several tens of times. In contrast, in an inkjet printer of a type in which a long inkjet head (not necessarily integrated) having the same dimensions as the width of the print medium is disposed and the carriage is not used, the inkjet head is moved in the width direction of the print medium. This is not necessary, and so-called one-pass printing is possible, so that high-speed printing similar to a laser printer is possible. The former inkjet printer is generally referred to as a “multi-pass (serial) inkjet printer”, and the latter inkjet printer is generally referred to as a “line head inkjet printer”.

In such an ink jet printer, an electric charge is applied to the transport belt to charge it, and the print medium made of almost an insulator is electrostatically adsorbed to the transport belt and transported, and ink droplets are ejected from the ink jet head onto the transported print medium. Some of them print. Such a print medium conveying method is particularly effective in a line head type ink jet printer. On the other hand, in Patent Document 1 described below, this type of electrostatic adsorption conveyance belt is divided into an upstream side and a downstream side, and ink droplets are ejected at an interval provided between the two, thereby leading the front end portion of the print medium. A configuration is disclosed that enables printing with no blank space from the rear edge to the rear edge. Further, in Patent Document 2 below, a printing medium printed on one side is reversed by a reversing conveyance unit, and the reversed printing medium is electrostatically attracted again to the conveyance belt and conveyed, and printing is performed on an unprinted printing surface. An ink jet printer capable of performing duplex printing is disclosed.
JP 2005-306515 A Japanese Patent Laid-Open No. 2003-154643

  By the way, a printing medium that can be regarded as an insulator is essentially an insulating material except for a special printing medium such as a photographic paper. If the resistance value of the print medium decreases, the electrostatic adsorption force of the print medium by the conveyance belt increases even if the print medium is conveyed at high speed. For example, the conveyance belt is divided in the print medium conveyance direction and the charging potentials of both conveyance belts. Are equal to each other, the electrostatic adsorption force of the downstream conveying belt becomes excessive, and the printing medium is reversed to perform double-sided printing, and the charged potential of the conveying belt is the same when printing on either printing surface. If they are equivalent, the electrostatic attraction force of the conveyor belt when printing the other printing surface in a state where one printing surface is printed becomes excessive. If the electrostatic adsorption force of the conveyor belt is excessive, not only wasteful power is consumed, but also the amount of ozone generated by discharge increases, and the durability of the conveyor belt and the like deteriorates.

  The present invention has been made paying attention to the above-described problems, and by preventing the electrostatic adsorption force of the conveyor belt from becoming excessive, the power consumption can be reduced and the durability of the conveyor belt can be improved. An object of the present invention is to provide an ink jet printer that can be improved.

[Invention 1] In order to solve the above problems, an ink jet printer according to Invention 1 includes an upstream conveyance belt provided upstream in the print medium conveyance direction for conveying a print medium, and printing for conveying the print medium. a downstream transport belt provided in the medium conveyance direction downstream side, and an upstream side ink jet head for printing by ejecting ink droplets onto the printing medium conveyed by the upstream conveying belts, is conveyed by the downstream conveyor belt and downstream inkjet head for printing by ejecting ink droplets onto the print medium that, upstream charging means for charging the upstream conveyor belt to convey electrostatically adsorbing the print medium by the upstream transport belt , and a downstream charging means for charging the downstream transport belt for conveying electrostatically adsorbing the print medium by the downstream transport belt, the upstream conveyor belt Printing is performed by ejecting ink droplets from the upstream inkjet head onto a print medium that is electrostatically attracted and conveyed, and then the downstream inkjet head is printed on the print medium that is electrostatically adsorbed and conveyed on the downstream conveyance belt. When performing printing by ejecting ink droplets from the downstream charging means, the charging potential of the downstream conveying belt by the downstream charging means is made smaller than the charging potential of the upstream conveying belt by the upstream charging means. .

  In the ink jet printer according to the first aspect of the invention, the upstream conveying belt is charged by the upstream charging unit and the downstream conveying belt is charged by the downstream charging unit, and is electrostatically adsorbed and conveyed by the upstream conveying belt. When printing is performed by ejecting ink droplets from the upstream inkjet head onto the print medium, and then ejecting ink droplets from the downstream inkjet head onto the print medium that is electrostatically attracted to the downstream transport belt and then transported In addition, since the charging potential of the downstream conveying belt by the downstream charging unit is made smaller than the charging potential of the upstream conveying belt by the upstream charging unit, the static of the downstream conveying belt that electrostatically attracts the printed print medium is set. The electroadsorption force does not become excessive, and the power consumption can be reduced, and the durability of the conveyor belt and the like can be improved.

[Invention 2] The ink jet printer of the invention 2, the ink jet head for a conveyor belt for transporting the print medium, the printing by ejecting ink droplets onto the print medium transported by the transport belt, the conveyor belt in a charging unit that charges the conveyor belt to convey the printing medium by electrostatic adsorption, comprising an inverting means for inverting the print medium in order to perform double-sided printing, and is electrostatically attracted to the conveyor belt after printing by ejecting ink droplets from the inkjet head on one printing surface of the printing medium conveyed, by inverting the print medium in the reversing means, electrostatic the inverted print medium to the conveyor belt in performing printing by ejecting ink droplets from the inkjet head to the other printing surface of the printing medium while conveying by suction, the printing on the other printing surface of the printing medium Characterized by less than the charging potential of the transfer belt when performing the printing charge potential of the transfer belt Utoki on one printing surface of the printing medium.

According to the ink jet printer according to the second aspect of the invention, the transport belt is charged by the charging unit, and ink droplets are ejected from the ink jet head onto one print surface of the print medium that is electrostatically attracted to the transport belt and printed. Then, the printing medium is reversed by the reversing means, and the reversed printing medium is electrostatically adsorbed to the conveying belt and conveyed to eject the ink droplets from the inkjet head onto the other printing surface of the printing medium. When performing printing, since the charging potential of the conveyance belt when performing printing on the other printing surface of the printing medium is configured to be smaller than the charging potential of the conveyance belt when performing printing on one printing surface of the printing medium, The electrostatic attraction force of the conveyor belt when electrostatically attracting printed print media is not excessive, reducing power consumption and improving the durability of the conveyor belt, etc. It can be.
The printed print medium referred to in these inventions means a print medium in which the ink droplets ejected from the inkjet nozzles are not yet completely dried.

Next, a first embodiment of the inkjet printer of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram of the ink jet printer of the present embodiment, FIG. 1a is a plan view thereof, and FIG. 1b is a front view thereof. In FIG. 1, a print medium 1 is a line head type ink jet printer that is transported in the direction of the arrow in the figure from the upper right to the lower left of the figure, and is printed in the print area in the middle of the conveyance. However, the ink jet head of the present embodiment is arranged not only at one place but also at two places.

  Reference numeral 2 in the figure denotes a first inkjet head (upstream inkjet head) provided upstream in the conveyance direction of the print medium 1, and reference numeral 3 denotes a second inkjet head (downstream inkjet head) also provided downstream. The first transport unit 4 for transporting the print medium 1 is provided below the first ink jet head 2, and the second transport unit 5 is provided below the second ink jet head 3. The first transport unit 4 includes five first transport belts (upstream transport belts) arranged at predetermined intervals in a direction intersecting with the transport direction of the print medium 1 (hereinafter also referred to as nozzle row direction). 6, and the second transport unit 5 includes six second transport belts (downstream transport) disposed at predetermined intervals in the same direction (nozzle row direction) that intersects the transport direction of the print medium 1. Belt) 7.

  The six second conveyor belts 7 as well as the five first conveyor belts 6 are arranged in a so-called staggered pattern so as to be alternately adjacent to each other. A driving roller 8 is disposed in the overlapping portion of the first conveying belt 6 and the second conveying belt 7, a first driven roller 9 is disposed on the upstream side, and a second driven roller 10 is disposed on the downstream side. It is installed. The first conveying belt 6 is wound around the driving roller 8 and the first driven roller 9, and the second conveying belt 7 is wound around the driving roller 8 and the second driven roller 10. The motor is connected. Therefore, when the drive roller 8 is rotationally driven by the electric motor, the first transport unit 4 configured by the first transport belt 6 and the second transport unit 5 configured by the second transport belt 7 are synchronized with each other and at the same speed. Move with.

  The first ink jet head 2 and the second ink jet head 3 are shifted in the transport direction of the printing medium 1 for each of six colors, for example, yellow (Y), magenta (M), cyan (C), and black (K). Arranged. Ink is supplied to each inkjet head 2 and 3 from an ink tank of each color (not shown) via an ink supply tube. Each inkjet head 2, 3 is formed with a plurality of nozzles in the direction intersecting with the conveyance direction of the print medium 1 (that is, in the nozzle row direction), and a necessary amount of ink droplets are simultaneously applied from the nozzles to necessary locations. By discharging, minute ink dots are formed and output on the printing medium 1. By performing this for each color, it is possible to perform so-called one-pass printing by passing the print medium 1 conveyed by the first conveyance unit 4 and the second conveyance unit 5 once. That is, the area where the inkjet heads 2 and 3 are disposed corresponds to the printing area.

  As a method for discharging and outputting ink from each nozzle of the ink jet head, there are an electrostatic method, a piezo method, a film boiling ink jet method, and the like. In the electrostatic system, when a drive signal is given to the electrostatic gap, which is an actuator, the diaphragm in the cavity is displaced, causing a pressure change in the cavity, and ink drops are ejected from the nozzle by the pressure change. It is. In the piezo method, when a drive signal is given to a piezo element that is an actuator, the diaphragm in the cavity is displaced to cause a pressure change in the cavity, and ink droplets are ejected from the nozzle by the pressure change. . In the film boiling ink jet method, there is a minute heater in the cavity, the ink is instantaneously heated to 300 ° C. or more, the ink becomes a film boiling state, bubbles are generated, and ink droplets are ejected from the nozzle by the pressure change. That's it. The present invention can be applied to any ink output method, but is particularly suitable for a piezo element that can adjust the ejection amount of ink droplets by adjusting the peak value of the drive signal and the voltage increase / decrease slope.

  The first inkjet head 2 is formed only between the five first conveyance belts 6 of the first conveyance unit 4 and at both ends thereof, and the second inkjet head 3 is composed of six second conveyance belts of the second conveyance unit 5. It is formed only between the conveyor belts 7. This is because the inkjet heads 2 and 3 are cleaned by a cleaning unit, which will be described later, but in this way, one-pass printing cannot be performed with only one of the inkjet heads. For this reason, the first ink jet head 2 and the second ink jet head 3 are arranged so as to be shifted in the transport direction of the print medium 1 in order to compensate for the portions that cannot be printed with each other. All nozzles have independent actuators, each of which is provided with a selection switch.

  Disposed below the first inkjet head 2 is the first cleaning cap 12 for cleaning the first inkjet head 2, and disposed below the second inkjet head 3 is the second inkjet head. 2 is a second cleaning cap 13 that cleans 3. Each of the cleaning caps 12 and 13 has such a size that it can pass between the five first conveying belts 6 of the first conveying unit 4 and between the six second conveying belts 7 of the second conveying unit 5. It is formed. These cleaning caps 12 and 13 are, for example, a rectangular bottomed cap body that covers the nozzles formed on the lower surfaces of the inkjet heads 2 and 3, that is, the nozzle surfaces and can be in close contact with the nozzle surfaces, and is disposed at the bottom thereof. And a tube pump connected to the bottom of the cap body, and a lifting device that lifts and lowers the cap body. Therefore, the cap body is raised by the lifting device and is brought into close contact with the nozzle surfaces of the inkjet heads 2 and 3. In this state, when the cap body is made negative pressure by the tube pump, ink droplets and bubbles are sucked out from the nozzles established on the nozzle surfaces of the ink jet heads 2 and 3, and the ink jet heads 2 and 3 can be cleaned. . When the cleaning is completed, the cleaning caps 12 and 13 are lowered. In some cases, the nozzle surface may be stroked with a wiper to adjust the meniscus of each nozzle.

  An upstream side of the first driven roller 9 is provided with a pair of two gate rollers 14 that adjust the paper feed timing of the print medium 1 supplied from the paper feed unit and correct the skew of the print medium 1. Yes. The skew is a twist of the print medium 1 with respect to the transport direction. Further, two pairs of feed rollers 16 for supplying the print medium 1 are provided in the paper feeding unit. Reference numeral 15 in the drawing denotes a pressure roller that presses the print medium 1 against the first driven roller 15 and electrostatically attracts the print medium 1 to the first conveying belt 6 as will be described later.

  Below the first driven roller 9, a first belt charging device 21 is disposed as upstream belt charging means. The first belt charging device 21 includes a first charging roller 22 that contacts the first conveying belt 6 with the first driven roller 9 interposed therebetween, and an AC power source that alternately applies positive and negative charges to the first charging roller 22. The first charging roller 22 alternately applies positive and negative charges to the first conveying belt 6 to charge the outer peripheral surface of the first conveying belt 6 in a striped manner. A second belt charging device 24 as a downstream belt charging unit is disposed below the driving roller 8. The second belt charging device 24 includes a second charging roller 25 that is in contact with the second conveying belt 7 with the driving roller 8 interposed therebetween, and an AC power supply 26 that alternately applies positive and negative charges to the second charging roller 25. The positive and negative charges are alternately applied from the second charging roller 25 to the second conveying belt 7 to charge the outer peripheral surface of the second conveying belt 7 in a striped manner. In general, these belts are composed of a medium / high resistance body or an insulator. Therefore, when charged by a belt charging device, the electric charge applied to the outer peripheral surface is also composed of a high resistance body or an insulator. The print medium 1 is caused to generate dielectric polarization, and the print medium 1 can be adsorbed to the belt by an electrostatic force generated between the charge generated by the dielectric polarization and the charge on the outer peripheral surface of the belt. The charging means may be a direct current power source or a so-called corotron that drops the charge. Further, as will be described later, the charging potential of the second conveying belt 7 by the second charging roller 25 in this embodiment is smaller (lower) than the charging potential of the first conveying belt 6 by the first charging roller 22. The charging roller 25 may be in contact with the first conveying belt 6.

  Therefore, according to this ink jet printer, the first belt charging device 21 charges the outer peripheral surface of the first conveying belt 6 and the second belt charging device 24 charges the outer peripheral surface of the second conveying belt 7. When the printing medium 1 is fed from the gate roller 14 and pressed against the first conveying belt 6 by the pressure roller 15, the printing medium 1 is attracted to the outer peripheral surface of the first conveying belt 6 by the action of the dielectric polarization described above. Is done. In this state, when the driving roller 8 is rotationally driven by the electric motor, the rotational driving force is transmitted to the first driven roller 9 via the first conveying belt 6.

  In this way, the first conveyance belt 6 is moved downstream in the conveyance direction while the print medium 1 is adsorbed, and the print medium 1 is moved below the first inkjet head 2 to be formed on the first inkjet head 2. Printing is performed by ejecting ink droplets from the nozzles. When the printing by the first ink jet head 2 is completed, the print medium 1 is moved downstream in the transport direction and transferred onto the second transport belt 7 of the second transport unit 5. As described above, since the outer peripheral surface of the second transport belt 7 is also charged by the second belt charging device 24, the print medium 1 is attracted to the outer peripheral surface of the second transport belt 7 by the action of the dielectric polarization described above. .

  In this state, the second conveying belt 7 is moved downstream in the conveying direction, the printing medium 1 is moved below the second inkjet head 3, and ink droplets are ejected from the nozzles formed on the second inkjet head 3. And print. When printing by the second ink jet head is completed, the print medium 1 is further moved downstream in the transport direction, and the print medium 1 is discharged from the outer peripheral surface of the second transport belt 7 to the paper discharge unit while being separated by a separation device (not shown). Make paper.

  When the first and second inkjet heads 2 and 3 need to be cleaned, the first and second cleaning caps 12 and 13 are raised as described above to raise the nozzle surfaces of the first and second inkjet heads 2 and 3. In this state, the cap body is brought into a negative pressure so that ink drops and bubbles are sucked out from the nozzles of the first and second ink jet heads 2 and 3 and cleaned. 2 Lower the cleaning caps 12 and 13.

  Next, the charging potential of the first conveying belt 6 by the first belt charging device 21 and the charging potential of the second conveying belt 7 by the second belt charging device 24 will be described. For example, as shown in Table 1 below, the surface resistance immediately after printing is significantly smaller for both the printing medium 2 called A and the printing medium 2 called B than the surface resistance before printing.

  As described above, when the print medium is placed on the conveyance belt, for example, the electric field formed by the positive and negative stripe-shaped charging patterns on the outer circumferential surface of the conveyance belt causes the charge opposite to the charge of the conveyance belt to be charged. An electrostatic attraction force F is generated by inducing a potential difference Vg between the conveyance belt and the printing medium by inducing on the side surface of the conveyance belt (hereinafter also referred to as a conveyance surface). This potential difference Vg is caused by a transient phenomenon that charges a capacitor (also referred to as a gap capacitor) having a capacitance Cg that is formed by using an air layer between the conveyance belt and the print medium as a dielectric layer. Assuming that the thickness of the air layer constituting the gap capacitor is d, the resistance value of the printing medium is R, and the withstand potential of the conveying belt is Vb, the electrostatic attraction force F of the printing medium by the conveying belt is expressed by the following equation: The potential difference Vg of the capacitor is expressed by the following two equations using time t as a parameter.

  The change with time of the gap capacitor potential difference Vg in the first conveyor belt 6 when the gap capacitor potential difference is 800 V is indicated by a solid line in FIG. 2, and the change with time of the gap capacitor potential difference Vg in the second conveyor belt 7 is indicated by a two-dot chain line in FIG. It shows with. The positive and negative cycle length of belt charging was 20 mm. As can be seen from the figure, in the case of the second conveying belt 7, that is, the printed printing medium 1, the gap capacitor potential Vg quickly rises, and the electrostatic adsorption force F of the printing medium 1 by the second conveying belt 7 is increased. It turns out that it becomes excessive. That is, the electrostatic attraction force of the print medium by the conveyance belt only needs to reach a predetermined value during the period from when the print medium is placed on the conveyance belt to when it reaches the first inkjet head nozzle. For example, in FIG. 2, in the case of the first transport belt 6, that is, the unprinted print medium 1, the time until the gap capacitor potential difference Vg reaches 800 V is about 1 second, whereas the second transport belt 7, that is, in the case of a printed print medium, the time until the gap capacitor potential difference Vg reaches 800 V is about 0.001 second.

  For example, when the printing medium conveyance speed by the conveyance belts 6 and 7 is 500 m / sec. And the distance to the nozzles of the first inkjet heads 2 and 3 of each conveyance belt 6 and 7 is 50 mm, the required time between them is 0. 1 second. For example, when the required gap capacitor potential difference Vg when adsorbing the print medium 1 with a predetermined electrostatic attraction force is 500 V, the print medium 1 is not printed on the first conveying belt 6, that is, the print medium 1 is ink. In order to make the gap capacitor potential difference Vg reach the necessary gap capacitor potential difference Vg = 500 V in 0.1 second required time until the print medium 1 reaches the nozzle of the first first inkjet head 2 because it is not wet with the droplets. The maximum gap capacitor potential difference Vg in the first transport belt 1 must be set to 800V. On the other hand, the second transport belt 7 in which the print medium 1 has been printed, that is, the print medium 1 is wet with ink droplets, reaches the maximum gap capacitor potential difference Vg in only 0.001 seconds. 2 The maximum gap capacitor potential difference Vg in the conveyor belt 7 may also be 500V.

  As described above, according to the ink jet printer of the present embodiment, the first (upstream side) transport belt 6 is charged by the first (upstream side) charging device 21 and the second (downstream side) transport belt 7 is charged by the downstream side charging device. 24, printing is performed by ejecting ink droplets from the first (upstream side) inkjet head 2 onto the print medium 1 that is electrostatically attracted to the first conveyance belt 6 and conveyed, and then printed on the second conveyance belt 7. When printing is performed by ejecting ink droplets from the second (downstream) inkjet head 3 onto the print medium 1 that is electrostatically attracted and transported, the charging potential of the second transport belt 7 by the second charging device 24 is set to the first potential. Since the charging potential of the first conveying belt 6 by the first charging device 21 is set to be smaller than the charging potential of the second conveying belt 7 that electrostatically attracts the printed print medium 1, the electric power is not excessive. Low consumption Or, or you can improve the durability of such conveyor belts. Further, since the electrostatic attraction force of the print medium 1 by the second conveyance belt 7 does not become excessive, the paper discharge operation for peeling the print medium 1 that has become soaked by the ink droplets from the conveyance belt 7. Can be performed stably.

  Next, a second embodiment of the ink jet printer of the present invention will be described. In the present embodiment, unlike the first embodiment, there is only one conveyance belt 106 and it is wound around a driving roller 108 and a driven roller 109. Therefore, the charging device 121 exists only in one place, and the inkjet head 102 exists only in one place. In the figure, reference numeral 122 is a charging roller, 123 is an AC power source, 101 is a printing medium, 114 is a gate roller, 116 is a feed roller, and 115 is a pressure roller. It is the same as that of the embodiment.

  The ink jet printer of this embodiment is provided with a guide device 103 as a reversing unit. The guide device 103 includes a plurality of guide rollers 104 and guide rails 105, and the print medium 101 electrostatically attracted to the conveyance belt 106 is printed on one side while being conveyed from right to left in the figure. Ink droplets are ejected onto the surface, printed, and introduced into the guide device 103. In the guide device 103, the front and back surfaces of the printing medium 101 are reversed while being guided by the guide roller 104 and the guide rail 105, and are sent back to the paper feeding unit 110 as they are. The paper feeding unit 110 feeds the inverted print medium 101 to the conveyance belt 106 again, electrostatically attracts the print medium 101 with the conveyance belt 106, and conveys the print medium 101 in the middle. Double-sided printing is performed on both sides of the print medium 101 by ejecting ink droplets from the nozzles of the inkjet head 102 onto the printing surface 101, that is, the printing surface opposite to the printing surface printed last time.

  In the present embodiment, the conveyance belt is used when printing is performed by ejecting ink droplets from the nozzles of the inkjet head 102 onto the print surface (the other print surface) opposite to the previously printed print surface (the one print surface). The charging potential of 106 is made smaller than the charging potential of the conveyor belt 106 when printing on the unprinted print medium 101. The reason and effect, the charging potential (gap capacitor potential difference) setting method, and the like are the same as in the first embodiment.

  As described above, according to the inkjet printer of this embodiment, the conveyance belt 106 is charged by the charging device 121, and the inkjet head 102 is applied to one printing surface of the print medium 101 that is electrostatically attracted to the conveyance belt 106 and conveyed. After the ink droplets are discharged from the printing medium, the printing medium 101 is reversed by a guide device (reversing unit) 103, and the reversed printing medium 101 is electrostatically adsorbed to the conveying belt 106 and conveyed. When printing is performed by ejecting ink droplets from the inkjet head 102 onto the other print surface of the medium 101, the charging potential of the transport belt 106 when printing on the other print surface of the print medium 101 is set to one of the print media 101. Since the configuration is such that the charged potential of the conveyor belt 106 when printing on the print surface of the print is made, the printed print medium 101 is statically printed. Without becoming excessive electrostatic attraction force of the conveying belt 106 at the time of adsorption, or reduce power consumption, or can improve the durability of such conveyor belts. Further, since the electrostatic attraction force of the printing medium 1 when printing the other printing surface does not become excessive, the printing medium 1 that has been soaked with ink droplets and weakened so-called stiffness is peeled off from the conveying belt 106. The paper discharge operation can be performed stably.

  In the above embodiment, only an example in which the ink jet printer of the present invention is applied to a so-called line head type ink jet printer has been described in detail. However, the ink jet printer of the present invention includes a multi-pass printer and other printed prints. The present invention can be applied to all types of ink jet printers that electrostatically attract a medium with different conveyance belts.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic block diagram which shows 1st Embodiment of the line head type inkjet printer to which the inkjet printer of this invention is applied, (a) is a top view, (b) is a front view. FIG. 3 is an explanatory diagram of a gap capacitor potential difference between a first (upstream side) conveyance belt and a second (downstream side) conveyance belt in FIG. 1. It is a schematic front view which shows 2nd Embodiment of the line head type inkjet printer for double-sided printing to which the inkjet printer of this invention is applied.

Explanation of symbols

  1 is a print medium, 2 is a first (upstream) inkjet head, 3 is a second (downstream) inkjet head, 4 is a first transport unit, 5 is a second transport unit, and 6 is a first (upstream) transport. Belt, 7 is a second (downstream) conveying belt, 8 is a driving roller, 9 is a first driven roller, 10 is a second driven roller, 21 is a first (upstream) charging device, 22 and 25 are charging rollers, 23 and 26 are AC power supplies, 24 is a second (downstream) charging device, 101 is a printing medium, 102 is an ink jet head, 103 is a guide device (reversing means), 104 is a guide roller, 105 is a guide rail, and 106 is transported Belt, 108 driving roller, 109 driven roller, 121 charging device, 122 charging roller, 123 AC power supply

Claims (2)

An upstream conveyor belt provided upstream of the print medium conveyance direction for conveying the print medium;
A downstream conveying belt provided on the downstream side in the printing medium conveyance direction for conveying the printing medium;
An upstream inkjet head that performs printing by ejecting ink droplets onto a print medium conveyed by the upstream conveyance belt;
A downstream inkjet head that performs printing by ejecting ink droplets onto a print medium conveyed by the downstream conveyance belt;
An upstream charging means for charging the upstream conveyor belt to convey electrostatically adsorbing the print medium in the upstream conveyor belt,
And the downstream-side charging means for charging the downstream transport belt for conveying electrostatically adsorbing the print medium by the downstream transport belt,
With
Printing is performed by ejecting ink droplets from the upstream inkjet head onto a print medium that is electrostatically adsorbed and conveyed by the upstream conveyance belt,
Next, when printing is performed by ejecting ink droplets from the downstream inkjet head onto a print medium that is electrostatically adsorbed and conveyed by the downstream conveyance belt, the charging potential of the downstream conveyance belt by the downstream charging unit The ink jet printer is characterized in that is made smaller than the charging potential of the upstream conveying belt by the upstream charging means . A transport belt for transporting print media;
An inkjet head that performs printing by ejecting ink droplets onto a print medium conveyed by the conveyance belt;
A charging unit that charges the conveyor belt to convey electrostatically adsorbing the print medium in the conveyance belt,
Reversing means for reversing the print medium to perform duplex printing;
With
After printing by ejecting one ink droplet from the ink jet head to the printing surface of the printing medium conveyed is electrostatically adsorbed on the conveyance belt, reversing the print medium in the reversing means, it is inverted performed in performing printing by ejecting ink droplets, a print on the other printing surface of the print medium from said ink jet head to the other printing surface of the printing medium while conveying electrostatically adsorbed to the conveying belt print media the conveyor belt inkjet printer according to the feature to be smaller than the charging potential of the transfer belt when the charge potential performs printing on one printing surface of the printing medium when.

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