JP4329705B2 - Inkjet printer - Google Patents

Description

  The present invention relates to an ink jet printer that draws predetermined characters and images by discharging and outputting fine particles (dots) of liquid ink of a plurality of colors onto a printing medium (printing paper), for example.

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 integrally provided with an ink cartridge and an ink jet head (generally called an ink jet head) has a paper feed direction on a printing paper (recording paper). By driving the actuator while reciprocating in the orthogonal direction, the liquid ink particles are ejected (jetted) from the nozzles formed in the ink jet head, thereby outputting minute ink dots on the recording paper to obtain a predetermined value. A desired printed matter is created by drawing characters and images. 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 this type of ink jet printer in which printing is executed while the ink jet head on the carriage is reciprocated in the direction orthogonal to the paper feed direction (the width direction of the print paper), the entire page is printed neatly. In addition, since it is necessary to reciprocate the inkjet head several tens of times to 100 times or more, it takes much printing time compared with other types of printing apparatuses such as laser printers and copying machines using electrophotographic technology. There are drawbacks.

  On the other hand, in an ink jet printer of a type in which a long ink jet head having the same dimensions as the width of the printing paper is arranged and a carriage is not used, it is not necessary to move the ink jet head in the width direction of the printing paper, so-called one pass. Therefore, high-speed printing similar to that of the laser printer is possible. The former inkjet printer is generally referred to as a “multi-pass printer”, and the latter inkjet printer is generally referred to as a “line head printer”.

 By the way, in this type of line head type ink jet printer, the flatness of the printing paper in the printing region is important in order to improve the printing quality. In line head type ink jet printers, a configuration in which printing paper is sucked and conveyed by an endless belt for conveyance is often used. In other words, the flatness of the conveyance belt in the printing area is important for improving print quality. Will be. For example, if the distance between the printing paper and the ink jet head fluctuates due to vibration of the conveying belt, the ink droplets may be displaced in the paper conveying direction (generally also referred to as the landing position) or the distance from the nozzle may increase when the distance increases. As a result, a slight shift at the time of ink droplet ejection is amplified, resulting in a decrease in print quality. When a full-color image is output by ejecting ink from a plurality of color line-type inkjet heads that are grounded at different positions in the paper conveyance direction, this is recognized as a color shift. Furthermore, the distance from the nozzle surface of the line-type inkjet head to the printing paper is about 1 mm, and if a large vibration occurs, the printing paper or the conveyance belt comes into contact with the nozzle surface, and the ink in the nozzles contacts the printing paper or the conveyance belt Adhering causes problems such as deterioration in print image quality and ink color mixing.

 As a technique for suppressing and preventing the vibration of the conveying belt, there is a method of supporting the back surface of the conveying belt with a support member in a printing region. As an example, in Patent Document 1 listed below, a plane forming portion called a platen is disposed below a printing area while applying tension to a conveying belt for conveying printing paper, and a flat surface of the platen is arranged. By contacting the inner peripheral surface of the conveyor belt, the conveyor belt is pressed against the platen to regulate the flat surface of the conveyor belt. Further, there is also disclosed a belt pressing force generated in the entire contact area between the conveying belt and the platen, with the belt contact surface of the platen convexly curved upward.

Moreover, in patent document 2 mentioned below, the belt curved surface similar to the said patent document 1 is comprised with the roller. In addition, an electrode divided in the printing paper conveyance direction is arranged on the inner circumferential surface of the conveying belt, that is, the back surface side of the surface on which the printing paper is mounted, and the printing area contacts the inner circumferential surface of the conveying belt. A belt suction unit that contacts and sucks the belt with electrostatic force is disposed, and the printing paper is adsorbed by applying a potential difference to the adjacent electrodes also received on the inner peripheral surface of the transport belt, and the surface of the belt suction unit A configuration in which the belt is sucked by the potential and the belt inner peripheral surface electrode potential is also disclosed.
Japanese Patent No. 2755960 JP 2002-145474 A

 However, in the prior art described in Patent Document 1, the flat surface of the platen is restricted by pressing the transfer belt against the platen by bringing the flat surface of the platen into contact with the inner peripheral surface of the transfer belt. Then, the tension applied to the conveying belt acts as a force for pressing the conveying belt against the platen, in the contact area between the conveying belt and the platen, the front and rear end portions in the moving direction of the conveying belt, That is, there are only the most upstream part and the most downstream part in the paper transport direction, and the intermediate belt cannot effectively press the transport belt against the platen, and as a result, the flat surface of the printing paper cannot be regulated.

 Among the prior arts described in Patent Document 1, the curved surface of the platen is brought into contact with the inner peripheral surface of the transport belt, and among the conventional techniques described in Patent Document 2, the roller is used for transporting. In the case of bending the belt, the tension and the pressing force against the platen are stable, but in the case of so-called strong printing paper, the printing paper can not follow the shape of the platen or roller and the printing paper floats up, For example, a so-called jam that causes biting between the inkjet head and the ink jet head is likely to occur. Further, in order to make the gap between the inkjet head and the printing paper constant, it is necessary to adjust the height of the inkjet head in accordance with the shape of the platen or roller. Further, in order to prevent belt vibration during high-speed printing, it is necessary to apply a sufficient tension to the conveying belt, but this tension may shorten the life of the conveying belt. In addition, when the conveyance belt is not driven, the conveyance belt is liable to generate habits, and the habit of the belt changes the interval between the inkjet head and the printing paper, and the ink droplets are not ejected to the target position. There is a risk of causing a shift and degrading the image quality.

 In the prior art described in Patent Document 2, a divided electrode is disposed on the inner peripheral surface of the conveying belt, and the print area is in contact with the inner peripheral surface of the conveying belt and is charged with electrostatic force. In the case where the belt suction means for sucking the belt is arranged, the conveying belt suction force by the belt suction means is not constant because of the structure, and the conveying belt load fluctuates, which adversely affects the belt feeding accuracy. In addition, for example, by disposing a divided electrode on the inner peripheral surface of the conveyor belt, the flexibility and flexibility of the belt become non-uniform, and the electrode life due to a decrease in wear resistance, ink adhesion, etc. There is concern about the decline.

In other words, none of the above-described conventional techniques can reliably adsorb the printing paper to the conveyance belt, and cannot reliably regulate the flat surface of the conveyance belt and the printing paper in the printing area below the inkjet head.
The present invention has been made by paying attention to the above-described problems, and can reliably adsorb the printing paper to the endless belt for conveyance and reliably regulate the flat surface of the printing paper in the printing area. An object of the present invention is to provide a simple inkjet printer.

  [Invention 1] In order to solve the above-described problem, an inkjet printer of Invention 1 includes a plurality of endless belts that convey a print medium in a predetermined direction and nozzles that output ink in a direction intersecting the print medium conveyance direction. A line-type inkjet head provided; charging means for forming a stripe-shaped charging pattern parallel to a conveyance direction of a printing medium on an outer periphery of the endless belt; and the endless belt disposed in a printing region by the line-type inkjet head. A flat surface forming portion that abuts the inner periphery of the belt and regulates the flat surface of the endless belt, and the flat surface forming portion has a center that coincides with the polarity boundary portion of the striped charging pattern formed on the endless belt. In this manner, a plurality of protrusions protruding toward the endless belt are formed.

  The ink jet head referred to in the present invention refers to an ink droplet output portion in which nozzles for ink output used in, for example, an ink jet printer are formed. By using a known electrostatic method, piezo method, film boiling ink jet method, etc., fine particle ink droplets are used. Is generically used to form minute round ink dots by discharging the ink onto the recording paper. In addition, the stripe-shaped charging pattern is a charging pattern in which a charging area of one polarity and a charging area of the other polarity are alternately formed, and that it is parallel to the transport direction means that each polarity This means that the charged region is parallel to the transport direction or continuous in the longitudinal direction in the transport direction.

 According to the ink jet printer of the first aspect of the present invention, in the line head type ink jet printer including the line type ink jet head in which a plurality of nozzles for outputting ink are arranged in a direction intersecting the print medium transport direction, the print medium transport A striped charging pattern parallel to the transport direction of the print medium is formed on the outer periphery of the endless belt for use in suction, and the print medium is adsorbed and transported. Although the flat surface of the print medium is regulated, a plurality of protrusions are formed on the endless belt side from the flat surface forming portion, and the center thereof coincides with the boundary of the polarity of the striped charging pattern formed on the endless belt. The belt suction force is expressed by the electrostatic force between the charge on the outer peripheral surface of the endless belt and the charge on the belt side end surface of the protrusion generated by dielectric polarization. It is possible to reliably restrict the flat surface of the endless belt and the printing medium reliably adsorb the print medium to an endless belt for conveying and printing region.

[Invention 2] The ink jet printer of Invention 2 is characterized in that, in the ink jet printer of Invention 1, the protrusion and the flat surface forming portion are made of an insulator having a relative dielectric constant larger than that of the print medium. It is.
According to the ink jet printer according to the second aspect of the present invention, the protrusion and the flat surface forming portion are made of an insulator having a relative dielectric constant larger than the relative dielectric constant of the print medium. Even if the contact area between the protrusion and the endless belt is small, even if the contact area between the protrusion and the endless belt is small, the endless belt and the printing medium are flat in the printing area. The surface can be reliably regulated.

[Invention 3] The inkjet printer of Invention 3 is characterized in that, in the inkjet printer of Invention 1 or 2, the protrusion is disposed at a position facing the inkjet head.
According to the ink jet printer according to the third aspect of the present invention, since the protrusion is disposed at a position facing the ink jet head, the belt suction force effectively acts on the portion having the protrusion, that is, the position facing the ink jet head. The flatness of the medium is regulated, and a printing medium suction force by belt charging acts effectively at a portion where there is no protrusion, that is, a position not facing the ink jet head, thereby ensuring stable conveyance of the printing medium.

[Invention 4] The inkjet printer according to Invention 4 is the inkjet printer according to any one of Inventions 1 to 3, wherein there is at least one polarity boundary portion of the striped charging pattern between the protrusions. The protrusion is formed.
According to the ink jet printer according to the fourth aspect of the present invention, the protrusion is formed by forming the protrusion so that there is at least one polarity boundary portion of the striped charging pattern between the protrusion that expresses the belt suction force and the protrusion. It is possible to secure a printing medium suction force due to belt charging in a portion where there is no gap.

[Invention 5] The inkjet printer according to Invention 5 is the inkjet printer according to any one of Inventions 1 to 4, wherein one end in the width direction of the endless belt is brought into contact with a belt positioning surface formed in the flat surface forming portion. It is characterized by that.
In the ink jet printer according to the fifth aspect of the invention, since one end in the width direction of the endless belt is brought into contact with the belt positioning surface formed on the flat surface forming portion, the belt suction force of the protrusion on the flat surface forming portion and the belt The positional relationship with the print medium suction force due to charging can be ensured.

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 an ink jet printer according to the present embodiment. Reference numeral 1 in the figure denotes an endless belt for conveying a recording paper 2 as a printing medium. The endless belt 1 is wound around a driving roller 3 disposed at the left end portion in the figure, a driven roller 4 disposed at the right end portion in the figure, and a tension roller 5 disposed below the center portion thereof. It has been turned. The driving roller 3 is rotationally driven in the direction of the arrow in the figure by a driving source (not shown), and the recording paper 2 is attracted to the endless belt 1 charged by a charging roller, which will be described later. Transport to the left, that is, in the direction of the arrow. The driven roller 4 is grounded in order to discharge surplus charges from a charging roller described later. The tension roller 5 is urged downward by a spring 6, thereby applying tension to the endless belt 1.

 Two charging rollers 7 and 8 as charging means are in contact with the endless belt 1 so as to face the driven roller 4. The arrangement of the charging rollers 7 and 8 corresponds to immediately before the feeding position of the recording paper 2. Each of the charging rollers 7 and 8 includes a conductive portion 7a and 8a at the center and dielectric portions 7b and 8b at the outer periphery thereof. The dielectric portions 7b and 8b of each charging roller 7 and 8 are made of a medium / high resistance material. For example, as shown by the solid line in FIG. 1a, the dielectric portion 7b of one charging roller 7 has a cylindrical shape with a constant width and Assuming that the gap is spaced apart by a width, the dielectric portion 8b of the other charging roller 8 corresponds to the gap between the dielectric portions 7b of the one charging roller 7, as shown by the two-dot chain line in FIG. It is arranged at the position to do.

 A direct current positive (+) potential is applied to the conductive portion 7 a of one charging roller 7, and a direct current negative (−) potential is applied to the conductive portion 8 a of the other charging roller 8. Accordingly, the dielectric portion 7b of one charging roller 7 is charged with a positive polarity, and the dielectric portion 8b of the other charging roller 8 is charged with a negative polarity. When the endless belt 1 is rotated in this state, as shown in FIG. 1a, the outer peripheral surface of the endless belt 1 is charged so that the charged state of the dielectric portions 7b and 8b of the charging rollers 7 and 8 is transferred. . That is, on the outer peripheral surface of the endless belt 1, a positive polarity charging region and a negative polarity charging region are alternately formed in a direction intersecting the recording paper conveyance direction, and this charging pattern is referred to as a stripe charging pattern. In other words, the striped charging pattern of the present embodiment is parallel to the conveyance direction of the recording paper 2. As described above, the stripe-shaped charging pattern parallel to the conveyance direction of the recording paper 2, that is, parallel to the rotation direction of the endless belt 1, even if the endless belt 1 rotates, In the case of this embodiment, there is an advantage that the electric field form with the projection of the flat surface forming portion to be described later does not change. Note that the charging pitch of the striped charging pattern, that is, the width of the dielectric portions 7b and 8b of the charging rollers 7 and 8, the width of the recording paper 2 (size in the conveyance direction and the orthogonal direction), the recording paper suction force described later, and the like. From this point, it is desirable that the thickness is about 4 to 20 mm.

The endless belt 1 uses a polyamide-based synthetic fiber, polyester, polyurethane, PET, polycarbonate, a fluororesin such as silicon-based or PVDF-based resin as a base resin, and has a volume resistance of 10 ⁹ Ω · cm or more, More preferably, it is 10 ¹⁵ Ω · cm or more. Further, if necessary, carbon black or conductive filler is mixed into these resin bases to adjust the resistance value, so that at the time of recharging around the end, that is, at the next charging after the endless belt 1 rotates once. The amount of retained charge may be adjusted. Further, the thickness is selected to be 0.05 to 0.5 mm, more preferably about 0.1 to 0.2 mm, from the viewpoint of durability and flexibility, charging at high speed, and static elimination characteristics.

 A paper pressing roller 9 is disposed above the driven roller 4. The paper pressing roller 9 is biased downward by a spring 10 and has a function of pressing the recording paper 2 against the endless belt 1 on the driven roller 4. As described above, when the recording paper 2 is mounted on the outer peripheral surface of the endless belt 1 charged in stripes and the recording paper 2 is pressed against the endless belt 1 by the paper pressing roller 9, the recording paper 2 is endless by so-called dielectric polarization. Adsorbed to the outer peripheral surface of the belt 1.

 Reference numeral 11 in FIG. 1b denotes an inkjet head. The ink jet head 11 transports the recording paper 2 for each of the six colors of yellow (Y), magenta (M), cyan (C), light magenta (Lm), light cyan (Lc), and black (K). It is arranged to be shifted. Ink is supplied to each inkjet head 11 from an ink tank of each color (not shown) via an ink supply tube. Each ink jet head 11 is formed with a plurality of nozzles in a direction intersecting with the conveyance direction of the recording paper 2, and by ejecting a necessary amount of ink droplets from these nozzles to a required location at the same time, the recording paper 2 A minute ink dot is formed and output on the top. By performing this for each color, printing by so-called one-pass can be performed only by passing the recording paper 2 adsorbed to the endless belt 1 once. That is, the area where the inkjet head 11 is disposed corresponds to the print 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. Any ink output method can be applied to the present invention.

 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 flat surface forming unit 12 regulates the flat surface of the recording paper 2 when ejecting ink droplets from the inkjet head 11. The plane forming portion 12 of the present embodiment is composed of a dielectric having a relative dielectric constant greater than the relative dielectric constant 1.2 to 2.6 of the recording paper 2, that is, an insulator. A plurality of rib-shaped protrusions 13 that are long in the recording paper transport direction are provided on the flat surface forming portion 12 in a direction intersecting the recording paper transport direction, and the upper end surface of the protrusion 13 is the inner peripheral surface of the endless belt 1. The flat surface of the endless belt 11, that is, the flat surface of the recording paper 2 is regulated. Note that a belt positioning projection 15 protrudes upward at one end of the flat surface forming unit 12 in the direction intersecting the recording paper conveyance direction, and is in the direction intersecting the recording paper conveyance direction of the endless belt 1. One end surface (one end portion in the width direction) is in contact with the belt positioning surface 16 of the belt positioning protrusion 15.

 Details of the positional relationship between the protrusion 13 and the endless belt 1, the recording paper 2, and the ink jet head 11 are shown in FIG. 2a. Further, FIG. 2B shows details of the plane forming portion 12 including the CC cross section of FIG. As shown in FIG. 2 b, the center of the protrusion 13 coincides with the boundary portion of the polarity of the striped charging pattern of the endless belt 1 described above. Further, the arrangement pitch of the projections 13 in the direction intersecting the recording paper conveyance direction is wider than the charging pitch of the stripe-shaped charging pattern formed on the outer peripheral surface of the endless belt 1, as shown in FIG. 2b. In other words, at least one boundary between the polarities of the striped charging pattern of the endless belt 1 exists between the projections 13.

 According to this ink jet printer, for example, as shown in FIG. 2a, the endless belt 1 is fed with the endless belt 1 in accordance with the feed timing from a gate roller (not shown) in a state where the outer peripheral surface of the endless belt 1 is charged with a positive polarity. When the recording paper 2 is pressed against the endless belt 1 by the paper pressing roller 9, the electric field due to the surface charge on the outer peripheral surface of the endless belt 1 causes dielectric polarization, and the endless belt of the recording paper 2 is placed. One side surface is negative, and the surface opposite to the endless belt 1 is positive polarity. The recording paper 2 is attracted to the outer peripheral surface of the endless belt 1 by attracting the electric charge of the recording paper 2 generated by the dielectric polarization and the electric charge of the outer peripheral surface of the endless belt 1 by electrostatic force. The electric field generated at this time corresponds to the electric field in the portion without the protrusion 13 in FIG. As is clear from the figure, the electric field of electrostatic force between charges due to dielectric polarization is stronger at the boundary portion of the charge polarity than the other portions.

 Further, in the portion where the inner peripheral surface of the endless belt 1 abuts on the protrusion 13 of the flat surface forming portion 12, the center of the protrusion 13 coincides with the polarity boundary portion of the striped charging pattern of the endless belt 1. The electric field due to the surface charge on the outer peripheral surface of 1 causes dielectric polarization on the belt side surface of the protrusion 13 of the plane forming portion 12. The charge on the belt side surface of the protrusion 13 and the charge on the outer peripheral surface of the endless belt 1 generated by this dielectric polarization Are attracted by the electrostatic force, and the endless belt 1 is attracted to the protrusion 13, that is, the plane forming portion 12. At this time, since the relative permittivity of the plane forming portion 12 and the protrusion 13 is larger than the relative permittivity of the recording paper 2, the endless belt 1 attracts the recording paper 2 at least at the portion where the protrusion 13 and the endless belt 1 abut. The protrusion 13, that is, the belt suction force that the flat surface forming portion 12 sucks the endless belt 1 is larger than the recording paper suction force to be performed. However, on the other hand, as shown in FIG. 2b, since at least one polarity boundary portion of the striped charging pattern exists between the protrusion 13 and the protrusion 13 that expresses the belt suction force, the protrusion It is possible to secure the recording paper suction force due to the belt charging in the portion without 13 and to simultaneously adsorb the recording paper 2 and suck the belt, that is, to regulate the flat surfaces of the endless belt 1 and the recording paper 2 at the same time.

 FIG. 3 shows the electric field characteristics when the flat surface of the flat surface forming portion 12 is in direct contact with the inner peripheral surface of the endless belt 1 without forming protrusions on the flat surface forming portion 12 as in this embodiment. . As is apparent from the figure, an electric field is generated both on the recording paper 2 side and on the endless belt 1 side at the polarity boundary of the striped charging pattern of the endless belt 1. If the relative dielectric constant of the flat surface forming portion 12 is larger than the relative dielectric constant of the recording paper 2, the recording paper 2 is lifted from the endless belt 1 because the belt suction force exceeds the recording paper suction force. On the contrary, if the relative dielectric constant of the recording paper 2 is larger than the relative dielectric constant of the flat surface forming portion 12, the recording paper suction force exceeds the belt suction force and the flat surfaces of the endless belt 1 and the recording paper 2 cannot be regulated. In other words, the protrusion 13 is formed on the flat surface forming portion 12, the belt suction force is expressed between the protrusion 13 and the endless belt 1, and the recording paper suction force is ensured in the portion without the protrusion 13. The trade-off described above cannot be resolved.

 That is, a striped charging pattern parallel to the conveyance direction of the recording paper 2 is formed on the outer periphery of the endless belt 1 for conveying the recording paper 2 to suck and convey the recording paper 2, and the flat surface forming unit 12 passes through the endless belt 1. The flat surface of the recording paper 2 and the flat surface of the recording paper 2 are regulated by contact with the inner periphery of the belt, but a plurality of projections 13 are formed on the endless belt 1 side from the flat surface forming portion 12, and the center thereof is formed on the endless belt 1. The belt attracting force is expressed by the electrostatic force between the electric charge on the outer peripheral surface of the endless belt 1 and the electric charge on the belt side end surface of the protrusion 13 generated by dielectric polarization, because it coincides with the boundary of the polarity of the striped charging pattern. As a result, the recording paper 2 can be reliably attracted to the conveying endless belt 1 and the flat surfaces of the endless belt 1 and the recording paper 2 can be reliably regulated in the printing region.

 Further, since the protrusion 13 and the plane forming portion 12 are made of an insulator having a relative dielectric constant larger than that of the recording paper 2, the dielectric polarization between the recording paper 2 and the endless belt 1 is performed at a portion where the protrusion 13 is present. Even if the contact area between the protrusion 13 and the endless belt 1 is small, a dielectric polarization electric field stronger than the electric field is generated between the protrusion 13 and the endless belt 1. The flat surface of the paper 2 can be reliably regulated.

Further, by forming the protrusion 13 so that there is at least one polarity boundary portion of the stripe-shaped charging pattern between the protrusion 13 and the protrusion 13 that expresses the belt suction force, the belt in the portion without the protrusion 13 is formed. A recording paper suction force due to charging can be ensured.
Further, since one end portion in the width direction of the endless belt 1 is in contact with the belt positioning surface 16 formed on the flat surface forming portion 12, the recording paper is generated by the belt suction force of the protrusion 13 of the flat surface forming portion 12 and the belt charging. The positional relationship with the suction force can be ensured.

 Next, a second embodiment of the ink jet printer of the present invention will be described with reference to FIG. The schematic configuration of the ink jet printer of the present embodiment is the same as that of the first embodiment shown in FIG. The flat surface forming portion 12 of the present embodiment is provided only at a position facing each inkjet head 11 corresponding to each of the six colors of ink, and the same protrusion 13 as that of the first embodiment protrudes from the flat surface forming portion 12. It is installed.

 According to the ink jet printer of this embodiment, since the protrusion 13 is disposed at a position facing the ink jet head 11, the belt suction force effectively acts at a portion where the protrusion 13 is present, that is, a position facing the ink jet head 11. Thus, the flatness of the recording paper 2 is regulated, and the recording paper suction force due to the belt charging acts effectively in a portion where the projection 13 is not provided, that is, the position not facing the ink jet head 11, so that the recording paper 2 is stably conveyed. Can be secured.

BRIEF DESCRIPTION OF THE DRAWINGS It is a schematic block diagram which shows 1st Embodiment of the inkjet printer of this invention, (a) is a top view, (b) is a front view. 2A and 2B are explanatory views of a positional relationship between a projection of a flat surface forming portion and an endless belt, a recording paper (printing medium), and an inkjet head in the inkjet printer of FIG. 1, where FIG. It is -C sectional drawing. It is explanatory drawing of the positional relationship with a plane formation part, an endless belt, a recording paper (printing medium), and an inkjet head when there is no protrusion in a plane formation part, (a) is a front view, (b) is (a). It is DD sectional drawing of. It is explanatory drawing of the positional relationship of the plane formation part which shows 2nd Embodiment of the inkjet printer of this invention, an endless belt, a recording paper (printing medium), and an inkjet head.

Explanation of symbols

  1 is an endless belt, 2 is a recording paper (printing medium), 3 is a driving roller, 4 is a driven roller, 5 is a tension roller, 6 is a spring, 7 and 8 are charging rollers, 9 is a paper pressing roller, 10 is a spring, 11 is an inkjet head, 12 is a plane forming portion, 13 is a protrusion, 15 is a belt positioning protrusion, and 16 is a belt positioning surface.

Claims (5)

  An endless belt that conveys the print medium in a predetermined direction, a line-type inkjet head in which a plurality of nozzles for outputting ink are arranged in a direction intersecting the print medium conveyance direction, and conveyance of the print medium on the outer periphery of the endless belt A charging unit that forms a stripe-shaped charging pattern parallel to the direction, and a flat surface forming unit that is disposed in a printing region of the line-type ink jet head, contacts an inner periphery of the endless belt, and regulates a flat surface of the endless belt And a plurality of protrusions protruding toward the endless belt so that the centers thereof coincide with the polar boundary portions of the striped charging pattern formed on the endless belt. Inkjet printer.  2. The ink jet printer according to claim 1, wherein the protrusion and the plane forming portion are made of an insulator having a relative dielectric constant larger than that of the print medium.   The ink jet printer according to claim 1, wherein the protrusion is disposed at a position facing the ink jet head.   4. The inkjet according to claim 1, wherein the protrusion is formed such that at least one polarity boundary portion of the striped charging pattern exists between the protrusions. 5. Printer.   5. The inkjet printer according to claim 1, wherein one end of the endless belt in the width direction is in contact with a belt positioning surface formed on the flat surface forming portion.

Images