JP2006044032A - Inkjet recorder - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inkjet recorder capable of stably conveying a recording medium without lowering quality of an image even when the image is recorded in a multipass manner. <P>SOLUTION: A voltage to be applied to a sheet from a charge roll is determined such that the voltage to be applied to at least one of a top end region or a bottom end region of the sheet is greater than the voltage to be applied to the other region (an intermediate region) at the first pass in the multipass. In the second or following pass, a constant voltage is applied over the whole length of the sheet in order to compensate an attenuated level of the charge potential at the first pass. As a result, the top end or the bottom end of the sheet is charged to be attracted by a conveyance belt, thereby preventing floating of the sheet. In the second or following pass, the sheet is surely charged to be attracted to the conveyance belt. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an ink jet recording apparatus, and more particularly to an ink jet recording apparatus compatible with so-called multi-pass that allows a recording medium to pass through an ink droplet ejection region from an ink jet recording head a plurality of times.

  Some inkjet recording apparatuses perform image recording by ejecting ink droplets from an inkjet recording head by so-called multi-pass by rotating a recording medium while being held on a drum or the like. In this configuration, since the recording medium is held on the drum while being curved in the thickness direction, it may be difficult to stably convey the recording medium, for example, the leading end portion or the trailing end portion of the recording medium is lifted or displaced. is there.

  In order to stably convey the recording medium, for example, in a configuration in which the recording medium is electrostatically attracted to a drum or the like, it is conceivable to increase the charging potential by increasing the voltage applied to the recording medium. However, when the voltage applied to the recording medium is increased as described above, the ink droplets ejected from the ink jet recording head are affected, and the image quality may be degraded.

  On the other hand, for example, in Patent Document 1, in an ink jet printer that electrostatically attracts a print medium to a drum, the front side and the rear end side of the print medium are charged more strongly than other parts, thereby lifting the print medium. The structure which prevents is described. Also, Patent Document 2 discloses an electrostatic adsorption drum printer in which the front end portion and the rear end portion of the printing medium can be strongly electrostatically adsorbed to a rotating drum and can be weakly adsorbed therebetween.

  However, in multi-pass image recording, at the time of the second and subsequent image recordings, since the ink from the image recording has adhered to the recording medium before that, the charged potential of the recording medium is lowered under the influence. There is.

Japanese Patent Application Laid-Open No. H10-228667 describes an ink jet printer provided with a replenishment charging unit capable of replenishing the amount of adsorption charge attenuated by color printing. However, it is difficult to effectively prevent the recording medium from being lifted up simply by replenishing the charge for adsorption.
Japanese Patent Laid-Open No. 10-175336 JP 2001-3278 A JP-A-10-138777

  In view of the above facts, an object of the present invention is to obtain an ink jet recording apparatus that can stably convey a recording medium and that does not deteriorate image quality even when an image is recorded by multipass.

  According to the first aspect of the present invention, an inkjet recording head that discharges ink droplets to the discharge area in accordance with image information, and a plurality of the discharge areas while rotating around a predetermined rotation path while holding the recording medium. Medium circulating means for passing the recording medium and charging means for charging the recording medium and attracting and holding the recording medium to the medium circulating means. A first charging mode in which a voltage higher than the intermediate portion is applied to at least one of the front end portion and the rear end portion, and a potential drop due to the passage of the first discharge region before the second and subsequent passes of the discharge region. And a second charging mode in which a voltage is applied to the recording medium so as to compensate.

  Therefore, the recording medium charged by the charging unit is attracted and held by the medium turning unit. Then, when the medium circulation means circulates while holding the recording medium, the recording medium passes through the ink droplet ejection area from the ink jet recording head, and an image is recorded on the recording medium. A multi-pass that passes through the ejection area a plurality of times is also possible. With this multi-pass, it is possible to record a high-resolution image with a higher resolution, or to prevent a failure of the ink jet recording head from being reflected in the recording result. It becomes possible.

  When the recording medium is circulated by the medium circulator, the recording medium is curved in the thickness direction, so that the front end portion and the rear end portion are likely to be lifted from the medium circulator. Here, the charging unit has a first charging mode and a second charging mode. In the first charging mode, the leading end portion and the trailing end portion of the recording medium are passed at least before the first ejection region. A voltage higher than that of the intermediate portion is applied to at least one of them. Therefore, local lifting of the recording medium can be prevented. In addition, since a relatively low voltage is applied to the middle portion of the recording medium, the influence on the ink droplets ejected from the ink jet recording head can be reduced (preferably without influence), and the image quality can be maintained high. It becomes possible.

  Further, in the second charging mode of the charging means, a voltage is applied to the recording medium so as to compensate for the potential drop due to the passage of the first discharge area before the second and subsequent discharge areas. Accordingly, in the second and subsequent image recordings, the ink drops adhering to the recording medium and the charging potential attenuated by the circulation of the recording medium are compensated, so that the recording medium can be reliably held by the medium circulation means. Thus, the recording medium can be stably conveyed.

  In the second charging mode of the charging means, if a constant voltage is applied to the recording medium from the leading end to the trailing end of the recording medium as described in claim 2, charging control is facilitated.

  Further, the voltage applied to the recording medium in the first charging mode can be changed according to the type of the recorded image, for example, as described in claim 3, or the type of the recording medium, as described in claim 4. Or, depending on the type of ink in the ink droplets, as described in claim 5, it is possible to change the recording medium more appropriately according to each case. Lifting can be suppressed.

  The invention according to claim 6 is characterized in that the charging means controls the timing of voltage application to the recording medium in accordance with the size of the recording medium.

  As a result, it is possible to apply the voltage in the first charging mode or the second charging mode to a necessary and sufficient range according to the size of the recording medium and cause the recording medium to be attracted and held by the medium rotating means.

  According to a seventh aspect of the present invention, there is provided the recording medium according to any one of the first to sixth aspects, wherein the ink jet recording head is perpendicular to a moving direction of the recording medium by the medium turning means. It has a width capable of ejecting ink droplets with respect to the entire width.

  Since it is not necessary to move the ink jet recording head in a direction orthogonal to the moving direction of the recording medium, it is possible to speed up image recording. Of course, the inkjet recording head is moved in a direction perpendicular to the moving direction of the recording medium, and the effect of multi-pass image recording (obtaining a high-resolution image with high resolution, or using the inkjet recording head as a result of recording) Etc.) may be obtained.

  According to an eighth aspect of the invention, there is provided the recording medium according to any one of the first to seventh aspects, wherein the recording medium is passed through the ejection area by the medium circulating means a plurality of times. Has reversing means for reversing the surface facing the ink jet recording head.

  Thus, by inverting the recording medium with the inverting means, it is possible to easily perform image recording on both sides of the recording medium.

  Since the present invention has the above-described configuration, the recording medium can be stably conveyed even when an image is recorded by multipass, and the image quality is not deteriorated.

  FIG. 1 shows an ink jet recording apparatus 12 according to a first embodiment of the present invention. A paper feed tray 16 is provided in the lower part of the casing 14 of the ink jet recording apparatus 12, and the sheets P stacked in the paper feed tray 16 can be taken out one by one by a pickup roll 18. The taken paper P is transported by a plurality of transport roller pairs 20 constituting a predetermined transport path 22. Hereinafter, the “conveying direction” simply refers to the conveying direction of the paper P that is a recording medium, and the “upstream” and “downstream” refer to upstream and downstream in the conveying direction, respectively.

  Above the paper feed tray 16, an endless transport belt 28 stretched around a drive roll 24 and a driven roll 26 is disposed. A recording head array 30 is disposed above the conveyor belt 28 and faces the flat portion 28F of the conveyor belt 28. This opposed area is an ejection area SE where ink droplets are ejected from the recording head array 30. The sheet P transported along the transport path 22 is held by the transport belt 28 and reaches the discharge area SE, and ink droplets corresponding to image information are attached from the recording head array 30 in a state of facing the recording head array 30. The

  Then, by rotating the paper P while being held by the transport belt 28, the paper P can be passed through the discharge region SE a plurality of times, and so-called multipass image recording can be performed. Therefore, the surface of the conveyance belt 28 is a circulation path of the paper P in the present invention. Hereinafter, for convenience, passing the ejection region SE n times is simply referred to as “n-pass”, and the n-th passage is referred to as “n-th pass”.

For example, the transport belt 28 is made of a semiconductive polyimide material (surface resistance value 10 ¹⁰ to 10 ¹³ Ω / □, volume resistance value 10 ⁹ to 10 ¹² Ω · cm), thickness 75 μm, width 380 mm, circumference What was shape | molded in length 1000mm can be used. Moreover, as the drive roll 24 and the driven roll 26, as an example, a φ50 mm SUS roll can be used.

  Further, the medium circulating means of the present invention is not limited to the conveyor belt 28. For example, the recording medium (paper P) may be sucked and held on the outer periphery of a conveyance roller formed in a cylindrical shape or a columnar shape and rotated. However, when the conveyor belt 28 is used as in the present embodiment, the flat portion 28F is formed, so that the recording head array 30 can be arranged corresponding to the flat portion 28F, which is preferable.

  In this embodiment, the recording head array 30 has a long shape in which the effective recording area is equal to or larger than the width of the paper P (the length in the direction orthogonal to the transport direction), and is yellow (Y) and magenta (M). , Four ink jet recording heads 32 corresponding to four colors of Sian (S) and black (K) are arranged along the transport direction, and a full color image can be recorded. The method for ejecting ink droplets in each inkjet recording head 32 is not particularly limited, and a known method such as a so-called thermal method or piezoelectric method can be applied.

  Each inkjet recording head 32 is controlled by recording head control means (not shown). For example, the recording head control means determines the ink droplet ejection timing and the ink ejection port (nozzle) to be used according to the image information, and sends a drive signal to the inkjet recording head 32.

  The recording head array 30 may be stationary in a direction orthogonal to the transport direction. However, if the recording head array 30 is configured to move as necessary, an image with higher resolution can be obtained by multi-pass image recording. Or failure of the ink jet recording head 32 is not reflected in the recording result.

  Four maintenance units 34 corresponding to the respective ink jet recording heads 32 are arranged in the vicinity of the recording head array 30 (in this embodiment, both sides in the transport direction). When maintenance is performed on the inkjet recording head 32, the recording head array 30 moves upward as shown in FIG. 2, and the maintenance unit 34 moves to a gap formed between the conveyance belt 28 and the maintenance unit 34. Get in. Then, a predetermined maintenance operation (vacuum, dummy jet, wiping, capping, etc.) is performed while facing the nozzle surface 32N (see FIG. 3).

  In this embodiment, the four maintenance units 34 are divided into two sets of two, and the recording head array 30 is arranged on the upstream side and the downstream side of the recording head array 30 at the time of image recording. .

  As shown in detail in FIG. 3, a charging roll 36 to which a power source 38 is connected is disposed on the upstream side of the recording head array 30. The charging roll 36 is driven while sandwiching the conveyance belt 28 and the paper P with the driven roll 26, and moves between a pressing position for pressing the paper P against the conveyance belt 28 and a separation position separated from the conveyance belt 28. It is possible. At the pressing position, a predetermined potential difference is generated between the grounded driven roll 26 and the sheet P can be charged and electrostatically attracted to the transport belt 28.

As the charging roll 36, for example, a roll having a diameter of 14 mm can be used in which conductive rubber is coated on the surface of silicone rubber and the volume resistance value is adjusted to about 10 ⁶ to 10 ⁷ Ω · cm.

  As the power source 38, a DC power source is shown in FIG. 3, but an AC power source may be used as long as the paper P can be charged to a predetermined potential.

  A registration roll (not shown) is provided further upstream than the charging roll 36, and the paper P is aligned before reaching between the conveyance belt 28 and the charging roll 36.

  A peeling plate 40 is disposed on the downstream side of the recording head array 30, and the paper P can be peeled from the transport belt 28. As the peeling plate 40, for example, an aluminum plate having a thickness of 0.5 mm, a width of 330 mm, and a length of 100 mm can be used.

  The peeled paper P is transported by a plurality of discharge roller pairs 42 that constitute a discharge path 44 on the downstream side of the peeling plate 40, and is discharged to a paper discharge tray 46 provided on the top of the housing 14.

  Below the peeling plate 40, a cleaning roll 48 capable of sandwiching the conveying belt 28 with the driving roll 24 is disposed, and the surface of the conveying belt 28 is cleaned.

  A reversing path 52 composed of a plurality of reversing roller pairs 50 is provided between the paper feed tray 16 and the conveying belt 28 as a reversing means of the present invention, and the paper P on which an image is recorded on one side is reversed. Thus, the image can be easily recorded on both sides of the paper P by being held on the transport belt 28.

  Between the conveyance belt 28 and the paper discharge tray 46, an ink tank 54 for storing each of the four color inks is provided. The ink in the ink tank 54 is supplied to the recording head array 30 through an ink supply pipe (not shown). As the ink, various known inks such as water-based ink, oil-based ink, and solvent-based ink can be used.

  As shown in FIG. 4, the entire inkjet recording apparatus 12 is controlled by a control unit 56 so that operations including image recording, discharging, and maintenance are performed after the paper P is taken out. Various data relating to the recorded image is sent from the image control unit 58 to the control unit 56. For example, as will be described later, the applied voltage and the like in the first charging mode and the second charging mode are controlled by the control unit 56 according to the data of the recorded image. Similarly, the timing of voltage application in the first charging mode and the second charging mode (when voltage application starts, when it ends, when the voltage changes, etc.) is the size of the paper P (for example, A3, A4, B4, B5, Letter , Postcards, etc.). Note that the size of the paper P may be detected by, for example, a sensor (not shown) provided in the paper feed tray 16 or the transport path 22 or the like, or input from the outside to the control unit 56 (in the inkjet recording device 12). You may make it know by the input from a user, or the input from external apparatuses, such as a computer connected to the inkjet recording device 12. Further, the control unit 56 and the charging roll 36 are supplied with power from a power source 38.

  In the ink jet recording apparatus 12 of the present embodiment configured as described above, the paper P taken out from the paper feed tray 16 is transported to the transport belt 28 as described above. Then, it is pressed against the conveyor belt 28 by the charging roll 36 and is held by being attracted (contacted) to the conveyor belt 28 by the voltage applied from the charging roll 36. In this state, while the paper P passes through the ejection area SE by circulation of the transport belt, ink droplets are ejected from the recording head array 30 and an image is recorded on the paper P. When recording an image in only one pass, the paper P is peeled from the transport belt 28 by the peeling plate 40, transported by the discharge roller pair 42, and discharged to the paper discharge tray 46. On the other hand, when performing image recording by multi-pass, after the paper P is circulated until it reaches the required number of times and passed through the ejection region SE, the paper P is peeled off from the transport belt 28 by the peeling plate 40, The paper is conveyed by the discharge roller pair 42 and discharged to the paper discharge tray 46.

FIG. 5 illustrates the voltage applied from the charging roll 36 in the first pass when the image recording is performed only in one pass and the image recording is performed in the multi-pass in the inkjet recording apparatus 12 of the present embodiment, and the paper P An example of the charging potential of the conveyor belt 28 is shown as time passes (first charging mode). FIG. 6 also shows an example of the voltage applied from the charging roll 36 and the charging potentials of the paper P and the conveying belt 28 in the second and subsequent passes of the multi-pass, with the passage of time (No. 1). (2 charging mode)
As can be seen from FIG. 5A, in the first charging mode, among the time corresponding to the entire area (full length) of the paper P, the time corresponding to the paper leading edge area and the paper trailing edge area is relatively low. The applied voltage is relatively lowered in the region between these (intermediate region). Therefore, as can be seen from FIG. 5B, the charging potential of the front and rear end regions of the paper P in the transport direction is higher than the charging potential of the intermediate region. As a result, the leading end region and the trailing end region of the paper P are electrostatically attracted to the transport belt 28 more strongly than the intermediate region.

  In general, in an inkjet recording apparatus capable of multi-pass, for example, the recording paper is held on an endless conveying belt 28, a cylindrical conveying drum, or the like as in the present embodiment, and the paper P is circulated. It will be curved in the thickness direction. In addition, because the sheet P itself has a so-called stiffness, the leading end area and the trailing end area of the sheet P are likely to be lifted from the conveying belt 28 (or the conveying drum). In the present embodiment, since the leading end region and the trailing end region of the paper P are electrostatically attracted to the transport belt 28 more strongly than the intermediate region, such lifting can be prevented.

  In order to simply prevent the leading edge or trailing edge of the paper P from being lifted, the applied voltage may be increased over the entire area of the paper P. However, when the applied voltage is increased over the entire area of the paper P, the charging potential at the intermediate portion where the ink droplets are attached also increases, which affects the ink droplets and makes it difficult to record high-quality images. In the present embodiment, it is possible to maintain the image quality high by setting the applied voltage (charging potential) in the intermediate region so as to have little influence (preferably no influence) on the ink droplets.

  Thus, the length of the leading end region and the trailing end region where the applied voltage is increased is not particularly limited as long as the length capable of preventing the sheet P from being lifted can be secured. For example, it may overlap with a recordable area where an image can be recorded on the paper P. However, as described above, there is a possibility that the ink droplets are affected in the portion where the charged potential of the paper P is high. Therefore, from the viewpoint of reducing the area that affects the ink droplets, for example, it can be set within a range of about 10 mm from the leading edge and the trailing edge of the paper P. Moreover, even if it is either the front end area or the rear end area of the paper P, there is an effect of preventing the floating.

  Further, if the strength of the voltage applied to each region is, for example, −4 kv in the front end region and the rear end region, it can be reliably electrostatically adsorbed to the transport belt 28. Further, in the intermediate region, for example, about -3 kv, it is possible to prevent the influence on ink droplets (ink repulsion, etc.).

  By the way, in general, when ink droplets adhere to the paper P, the charged potential of the paper P may be lowered. For this reason, in multi-pass image recording, as indicated by a broken line in FIG. 6B, the sheet P is circulated with the charged potential attenuated after the second pass.

  On the other hand, in this embodiment, as can be seen from FIG. 6A, a constant voltage is applied from the charging roll 36 over the entire length of the paper P even in the second charging mode after the second pass. For this reason, since the decrease in the potential of the paper P is compensated and recharged, the charged potential in the second pass and thereafter approaches the charged potential in the first pass as shown by the solid line in FIG. As a result, the suction force of the paper P to the transport belt 28 in the second and subsequent passes also returns to the same level as in the first pass, so that the paper P is securely attracted to the transport belt 28 and can be stably transported without causing lifting. Is possible.

  In FIG. 6A, the applied voltage in the second charging mode (from the second pass) is constant regardless of the time. However, as in the first pass, for example, the paper leading edge region and the paper trailing edge region are strongly strengthened. May be. However, since the potential drop due to ink adhesion to the paper P often occurs almost uniformly over the entire area of the paper P, the applied voltage after the second pass is made constant regardless of the time, and the control is easy. It is preferable to do. If the applied voltage at this time is, for example, about −2 kv, the potential drop due to the ink droplet adhering to the paper P can be compensated without excess or deficiency.

  Further, not only in the case of four passes, but in all cases of multi-pass, it is preferable to apply a constant voltage from the charging roll 36 so as to compensate for the potential drop of the paper P as described above in the second and subsequent passes. .

  The timing of voltage application in the first charging mode and the second charging mode is controlled according to the size of the paper P. For this reason, it is possible to apply the voltage in the first charging mode and the second charging mode to the necessary and sufficient range according to the size of the paper P, and to hold the paper P on the conveyance belt 28 by suction.

  The applied voltages in the first charging mode and the second charging mode are preferably controlled to preferable values depending on the type of recorded image, the number of passes, the type of paper P, the type of ink, and the like. Hereinafter, it demonstrates individually.

1. <Applied voltage control according to the type of recorded image>
In many cases, the amount of ink droplets attached to the paper P can be considered to change according to the type of recorded image. For example, if the recorded image is A.E. Only letters,
B. Only photos (including graphs and charts)
C. A mix of text and photos,
In general, the amount of ink droplets attached to the paper P is the smallest for A, the largest for B, and the middle between these. The paper P is more likely to lift from the conveyor belt 28 as more ink droplets adhere.

  Therefore, as shown in FIG. 7A, the applied voltage in the first pass is low in the case of A, relatively high in the case of B, and intermediate in the case of C. As a result, depending on the type of the recorded image, in other words, depending on the assumed amount of ink droplets adhering to the paper P, a necessary and sufficient voltage is applied and charged to effectively lift the conveyor belt 28. Can be prevented.

  Note that, as shown in FIG. 7B, in the second and subsequent passes when multipass is performed, the charge potential that is attenuated while the paper P circulates is the same as in the example shown in FIG. 6A. It is preferable to apply a voltage that compensates for the above, and return the adsorption force of the paper P to the transport belt 28 to the same level as in the first pass.

  In this case, recorded image data is sent from the image control unit 58 shown in FIG. 4 to the control unit 56, and the control unit 56 controls the applied voltage based on this.

2. <Applied voltage control according to the number of passes>
In general, the necessary amount of ink on the paper P for obtaining a desired recorded image is substantially constant regardless of the number of passes. Therefore, as the number of passes to the paper P increases, the amount of ink adhering to the paper P per pass can be reduced. Conversely, when image recording on the paper P is completed in only one pass, the pass 1 The amount of ink adhering to the paper P per round is greater than in the case of multipass. Therefore, in the case of multi-pass, it is possible to prevent lifting from the conveyor belt 28 even if the applied voltage in the first pass is lower than in the case of recording an image in only one pass.

  Therefore, as shown in FIG. 8A, when the number of passes is larger (in this example, 4 passes), the applied voltage for the first pass (shown by a solid line) is applied for the first pass when the number of passes is small. Lower than voltage (indicated by broken line). As a result, when the number of passes is large, the sheet P can be prevented from floating without excessively increasing the applied voltage in the first pass. Further, since the applied voltage is not increased, the influence on the ink droplet is further reduced, and a higher quality image can be recorded.

  As shown in FIG. 8B, in the second and subsequent passes when multipass is performed, a voltage that compensates for the charging potential that is attenuated while the paper P circulates is applied to transport the paper P. The suction force on the belt 28 can be returned to the same level as in the first pass.

3. <Applied voltage control according to the stiffness of the paper>
As the stiffness of the paper P, that is, the elasticity in the thickness direction is stronger, the paper P is less likely to be deformed even in the state where ink is absorbed, and therefore, the possibility that the paper P will be lifted from the transport belt 28 becomes lower. Therefore, this stiffness is stronger for cardboard than for so-called plain paper.

  Therefore, as shown in FIG. 9A, the applied voltage for the first pass (shown by a solid line) for thick paper is set lower than the applied voltage for the first pass (shown by a broken line) for plain paper. Accordingly, it is possible to prevent the stiff paper P from being lifted without excessively increasing the applied voltage in the first pass. Further, since the applied voltage is not increased, the influence on the ink droplet is further reduced, and a higher quality image can be recorded.

  Note that, as shown by the solid line in FIG. 9B, even in the case where the stiffness of the paper P is strong, in the second charging mode, a voltage that compensates for the charging potential that is attenuated while the paper P circulates. Is preferably applied to return the adsorption force of the paper P to the conveyance belt 28 to the same level as in the first pass. However, even in the second charging mode, the applied voltage is lower in the case of thick paper than in the case of plain paper indicated by a broken line.

4). <Voltage control according to ink absorbency of paper>
The paper P has different ink absorbability depending on the type or the presence / absence or type of surface processing. For example, so-called glossy paper has lower ink absorbability than plain paper. And the lower the ink absorptivity, the less deformation occurs when ink is deposited. In addition, there is little decrease in charging potential due to ink adhesion.

  Therefore, as shown in FIG. 10A, the applied voltage in the first pass (shown by a solid line) for glossy paper is lower than the applied voltage (shown by a broken line) in the first pass for plain paper. To do. Thereby, in the case of glossy paper, the paper P can be prevented from being lifted without excessively increasing the applied voltage. Further, since the applied voltage is not increased, the influence on the ink droplet is further reduced, and a higher quality image can be recorded.

  Further, in the second and subsequent passes, in the case of glossy paper, as described above, the decrease in the charging potential is small, and as shown by the solid line in FIG. In comparison, the applied voltage is lowered.

5. <Voltage control according to ink type>
The permeability of the ink varies depending on the type of the ink. Ink with lower permeability is less absorbed by the paper P, so deformation of the paper P is reduced. In addition, there is little decrease in charging potential due to ink adhesion. For example, when inks are roughly classified into water-based inks and oil-based inks, oil-based inks are less permeable to the paper P than water-based inks, and the deformation amount of the paper P is small.

  Therefore, as shown in FIG. 11A, the applied voltage in the first pass (shown by a solid line) when oil-based ink is used is compared to the applied voltage (shown by a broken line) in the first pass in the case of water-based ink. Also lower. Thereby, in the case of oil-based ink, the sheet P can be prevented from being lifted without excessively increasing the applied voltage. Further, since the applied voltage is not increased, the influence on the ink droplet is further reduced, and a higher quality image can be recorded.

  Also in the second and subsequent passes, in the case of oil-based ink, as described above, the decrease in the charging potential is small, and as shown by the solid line in FIG. In comparison, the applied voltage is lowered.

It is the schematic which shows the inkjet recording device of one Embodiment of this invention in an image recording state. It is the schematic which shows the inkjet recording device of one Embodiment of this invention in a maintenance state. FIG. 2 is a schematic diagram illustrating a transport belt and the vicinity thereof in an ink jet recording apparatus according to an embodiment of the present invention. 1 is a block diagram illustrating a configuration for controlling a charging roll in an ink jet recording apparatus according to an embodiment of the present invention. FIG. In the ink jet recording apparatus of one embodiment of the present invention, (A) is a graph showing the voltage applied from the charging roll in the first pass, and (B) is a graph showing the charging potential of the paper in the first pass over time. In the inkjet recording apparatus of one embodiment of the present invention, (A) is a graph showing the applied voltage from the charging roll in the second pass and thereafter, and (B) is a graph showing the charging potential of the paper in the second pass and the like over time. . It is a schematic plan view which shows the bump of a drive IC. In the inkjet recording device of one embodiment of the present invention, it is a graph which shows the difference in the applied voltage according to the kind of record image, (A) is the 1st pass and (B) is after the 2nd pass. In the inkjet recording device of one embodiment of the present invention, it is a graph which shows the difference of the applied voltage according to the number of passes, (A) is the 1st pass and (B) is the 2nd pass and after. In the inkjet recording device of one embodiment of the present invention, it is a graph which shows the difference in the applied voltage according to the stiffness of paper, (A) is the 1st pass and (B) is the 2nd pass and after. In the inkjet recording apparatus of one embodiment of the present invention, it is a graph which shows the difference in the applied voltage according to the ink absorptivity of paper, (A) is the 1st pass, and (B) is after the 2nd pass. In the inkjet recording apparatus of one Embodiment of this invention, it is a graph which shows the difference in the applied voltage according to the kind of ink used, (A) is the 1st pass and (B) is the 2nd pass and after.

Explanation of symbols

DESCRIPTION OF SYMBOLS 12 Inkjet recording device 14 Housing | casing 16 Paper feed tray 18 Pickup roll 20 Conveying roller pair 22 Conveyance path 24 Drive roll 26 Driven roll 28 Conveying belt 28F Flat part 30 Recording head array 32 Inkjet recording head 32N Nozzle surface 34 Maintenance unit 36 Charging roll 38 Power supply 40 Separation plate 42 Discharge roller pair 44 Discharge path 46 Discharge tray 48 Cleaning roll 50 Reverse roller pair 52 Reverse path 54 Ink tank 56 Control unit 58 Image control unit P Paper SE Discharge area

Claims (8)

An ink jet recording head that ejects ink droplets to an ejection area in accordance with image information;
Medium circulating means for passing the ejection area a plurality of times while rotating along a predetermined circular path while holding the recording medium;
Charging means for charging the recording medium and attracting and holding the recording medium to the medium turning means;
With
The charging means is
A first charging mode in which a voltage higher than the intermediate portion is applied to at least one of the leading end portion and the trailing end portion of the recording medium before passing through the ejection region at least once
A second charging mode in which a voltage is applied to the recording medium so as to compensate for a potential drop due to the first passage of the ejection region before the second passage of the ejection region;
An ink jet recording apparatus comprising:   2. The ink jet recording apparatus according to claim 1, wherein the charging unit applies a constant voltage to the recording medium from the leading end to the trailing end of the recording medium in the second charging mode.   The inkjet recording apparatus according to claim 1, wherein the charging unit is capable of changing the applied voltage according to a type of a recorded image on a recording medium.   The inkjet recording apparatus according to claim 1, wherein the charging unit is capable of changing the applied voltage according to a type of the recording medium.   5. The inkjet recording apparatus according to claim 1, wherein the charging unit is configured to change the applied voltage according to the type of ink in the ink droplet.   The inkjet recording apparatus according to claim 1, wherein the charging unit controls a timing of voltage application to the recording medium according to a size of the recording medium.   The ink-jet recording head has a width capable of ejecting ink droplets with respect to the entire width of the recording medium in a direction orthogonal to the moving direction of the recording medium by the medium turning means. The inkjet recording apparatus according to any one of 6. Reversing means for reversing the surface of the recording medium facing the ink jet recording head during a plurality of passes of the recording medium to the ejection area by the medium turning means;
The inkjet recording apparatus according to claim 1, wherein the inkjet recording apparatus includes:

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