Inkjet printing method and apparatus

Abstract

The present invention provides an inkjet printing method and apparatus that prevents ink from becoming thicker or drying out, enabling stable and continuous ink ejection. [Solution] In an inkjet printing method in which an inkjet head having ink ejection nozzles for ejecting ink is moved in a main scanning direction perpendicular to the transport direction of the printing medium and inkjet printing is performed under predetermined printing conditions, the idle time, which is the time during which the inkjet head is moved in the main scanning direction without ejecting ink from at least some of the ink ejection nozzles of the inkjet head, is calculated based on the initial printing conditions and the printing width in the main scanning direction, and the printing conditions are changed so that the idle time is less than or equal to a preset threshold.

Description

Technical Field

[0001] The present invention relates to an inkjet printing method and apparatus for performing printing processing by ejecting ink from an inkjet head onto a printing medium.

Background Art

[0002] Conventionally, inkjet printing apparatuses have been proposed that perform printing processing by ejecting ink from an inkjet head onto printing media such as paper and film.

[0003] As an inkjet printing apparatus, there is a so-called shuttle type inkjet printing apparatus that performs printing processing while moving a head unit (also referred to as a carriage) equipped with an inkjet head relative to a printing medium.

[0004] In order to increase the productivity of the shuttle type inkjet printing apparatus, the number of inkjet heads mounted on the head unit may be increased. When productivity is increased, the amount of ink ejected per unit area per unit time also increases, and the drying time of the ink may become insufficient. To avoid this, there is a method of changing the arrangement of the inkjet heads mounted on the head unit from an in-line arrangement in which they are arranged side by side to a staggered arrangement. The staggered arrangement is known as a method that can ensure the drying time of the ink while maintaining productivity.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, in the case of a staggered arrangement, the time until printing starts will differ depending on the position of the inkjet head. For example, as shown in Figure 3, if the head unit 10 has a staggered arrangement of a first head 11 and a second head 12, the first head 11, which is located upstream in the transport direction of the printing medium (rear side as shown in Figure 1), will start the printing process first, while the second head 12, which is located downstream in the transport direction of the printing medium (front side as shown in Figure 1), will idle for a while before printing starts. Idle running refers to the state in which the inkjet head is scanned without ejecting ink. Similarly, at the end of printing, the first head 11, which has completed the printing process first, will idle. Note that idle running occurs not only when the inkjet heads are arranged in a staggered arrangement, but also in an inline arrangement if there are colors that are not ejected or areas that are not printed.

[0007] Another known method for increasing productivity involves widening the width of the printing medium and tiling the image data to be printed in the width direction of the printing medium. However, widening the width of the printing medium also increases the aforementioned idle time.

[0008] Inkjet head idle can cause the ink near the ejection nozzle to thicken or dry, making normal continuous ejection impossible. This risk increases as the width of the printing medium increases.

[0009] Patent Document 1 proposes a method to prevent clogging of an inkjet head that is running idle by performing a pre-ejection operation in which ink droplets are pre-ejected. However, there are concerns that performing such a pre-ejection operation may accelerate the rise in head temperature by applying voltage to nozzles that are not involved in image formation, and the configuration of the device itself becomes complicated because a place is needed for pre-ejection.

[0010] Furthermore, Patent Document 2 proposes an ultraviolet-curing inkjet device that performs printing by scanning a carriage equipped with an inkjet head and an ultraviolet irradiation device. In Patent Document 2, when ultraviolet irradiation is added to areas where there was insufficient irradiation, ink is not ejected from the inkjet head, resulting in idle movement. However, by increasing the reciprocating speed at this time, the time required for printing can be shortened, and clogging of the inkjet head can be prevented.

[0011] However, as mentioned above, in a head unit composed of multiple inkjet heads, changing the reciprocating speed midway through image formation requires changing parameters that adjust the targeting accuracy, making the process more complex. Furthermore, it also worsens the ink's drying time.

[0012] The present invention aims to provide an inkjet printing method and apparatus that prevents ink from becoming thicker or drying out, and enables stable, continuous ink ejection. [Means for solving the problem]

[0013] The present invention relates to an inkjet printing method in which an inkjet head having ink ejection nozzles for ejecting ink is moved in a main scanning direction perpendicular to the transport direction of the printing medium while performing inkjet printing under predetermined printing conditions. In this method, based on the initial printing conditions and the printing width in the main scanning direction, a idle time is calculated, which is the time during which the inkjet head is moved in the main scanning direction without ejecting ink from at least some of the ink ejection nozzles of the inkjet head. The printing conditions are then changed so that the idle time is less than or equal to a preset threshold. [Effects of the Invention]

[0014] According to the inkjet printing method of the present invention, the idle time is calculated based on the initial printing conditions and the printing width in the main scanning direction, and the printing conditions are changed so that the idle time is below a preset threshold. This prevents ink from becoming thicker or drying out, and enables stable continuous ink ejection. [Brief explanation of the drawing]

[0015] [Figure 1] This figure shows a schematic configuration of an inkjet printing apparatus body using one embodiment of the inkjet printing method of the present invention. [Figure 2] Figure 1 shows the main body of the inkjet printing device, viewed from the direction of arrow A. [Figure 3] Diagram showing a schematic configuration of an example head unit. [Figure 4] Block diagram showing the configuration of the control system for an inkjet printing device. [Figure 5] Flowchart illustrating a method for setting printing conditions in one embodiment of the inkjet printing apparatus of the present invention. [Figure 6] Table showing examples and comparative examples of nozzle clogs, drying time, and idle time when performing inkjet printing with varying print width, print direction conditions, nozzle utilization rate, and head main scan speed. [Modes for carrying out the invention]

[0016] Hereinafter, an inkjet printing apparatus using one embodiment of the present invention will be described in detail with reference to the drawings. The inkjet printing apparatus of this embodiment is characterized by an inkjet printing method that takes into account the idle time of the inkjet head, but first, the overall configuration of the inkjet printing apparatus body will be described. Figure 1 is a schematic configuration diagram of the inkjet printing apparatus body 1 of this embodiment. Figure 2 is a view of the inkjet printing apparatus body 1 shown in Figure 1 from the direction of arrow A. In the description of the embodiment below, the up, down, left, right, front, and back directions indicated by arrows in Figure 1 will be referred to as the up, down, left, right, front, and back directions in the inkjet printing apparatus body 1.

[0017] As shown in FIG. 1, the inkjet printing apparatus main body 1 of the present embodiment includes a base 2, a pedestal 3, a platen 4, a rail portion 5, a head unit 10, and a capping unit 20.

[0018] The base 2 is a columnar member extending in the front-rear direction and is arranged in parallel at intervals in the left-right direction. Two wheels 2a are provided on the bottom surfaces of the two bases 2, respectively.

[0019] A pedestal 3 is erected on each base 2. The platen 4 is supported on the upper surfaces of the two pedestals 3 facing each other.

[0020] A front paper guide 4a and a rear paper guide 4b formed in an arc shape extend in front of and behind the platen 4. Further, as shown in FIG. 2, a vacuum chamber 4c in which a fan 4d is installed is provided below the platen 4. In FIG. 1, the vacuum chamber 4c is not shown.

[0021] When the fan 4d in the vacuum chamber 4c rotates, the inside of the vacuum chamber 4c becomes a negative pressure, and a suction force is generated in the suction holes (not shown) formed in the platen 4. The printing paper P is adsorbed on the platen 4 by the suction force generated in the suction holes of the platen 4.

[0022] Also, as shown in FIG. 2, a drive roller 6 and a pressure roller 7 are provided facing each other behind the platen 4. In FIG. 1, the drive roller 6 and the pressure roller 7 are not shown.

[0023] The drive roller 6 is a long roller extending in the extending direction of the platen 4 and is rotated by a conveyance drive motor 61 (see FIG. 4) described later.

[0024] Similar to the drive roller 6, the pressure roller 7 is a long roller extending in the extending direction of the platen 4 and is supported so as to be able to move up and down by a lifting mechanism (not shown).

[0025] Then, the printing paper P on the rear paper guide 4b is held between the drive roller 6 and the pressure roller 7, and as the drive roller 6 rotates while the printing paper P is pressed by the pressure roller 7, the printing paper P is fed forward.

[0026] The front side of the base 2 of the inkjet printing apparatus body 1 is provided with a winding-side core holder 8 that detachably holds a core 8a for winding the printing paper P. The winding-side core holder 8 is linked to a winding drive motor 81 (see Figure 4) via a torque limiter (not shown), and is configured to rotate the winding-side core holder 8 by the winding drive motor 81.

[0027] Furthermore, a supply-side core holder 9 is provided on the rear side of the base 2 of the inkjet printing device body 1, which detachably holds the core 9a of the roll paper in which the printing paper P is wound into a roll. The supply-side core holder 9 is linked to a supply drive motor 91 (see Figure 4) via a torque limiter (not shown), and the supply-side core holder 9 is configured to rotate by the supply drive motor 91.

[0028] As shown in Figure 2, the roll paper (printing paper P) held in the supply-side core holder 9 is pulled out and wound onto the core 8a held in the winding-side core holder 8, passing through the rear paper guide 4b, between the drive roller 6 and the pressure roller 7, on the platen 4, and the front paper guide 4a.

[0029] A rail section 5 is mounted on the upper part of the two leg bases 3 via support members (not shown). The rail section 5 includes a rail (not shown) extending in the left-right direction and a main scanning drive motor 54 (see Figure 4) that moves the head unit 10 back and forth in the left-right direction on the rail.

[0030] Figure 3 shows a schematic configuration of the head unit 10. As shown in Figure 3, the head unit 10 of this embodiment includes a first head 11 and a second head 12. The first head 11 and the second head 12 each include four inkjet heads 13 to 16.

[0031] The four inkjet heads 13-16 are inkjet heads that eject ink of different colors, for example, C (cyan), M (magenta), Y (yellow), and K (black). The four inkjet heads 13-16 are arranged in a direction perpendicular to the transport direction of the printing paper P (main scanning direction), and each inkjet head 13-16 is equipped with multiple ink ejection nozzles arranged in the transport direction of the printing paper P.

[0032] The first head 11 and the second head 12 are arranged in the main scanning direction, and some of the ink ejection nozzles of the inkjet heads 13-16 are arranged in a staggered configuration so as to overlap in the transport direction.

[0033] The capping unit 20 includes capping members that cap the ink ejection surfaces of the inkjet heads 13-16 of the first head 11 and the inkjet heads 13-16 of the second head 12, respectively. When printing is not being performed, the head unit 10 is positioned above the capping unit 20 and is capped by the capping members contacting the ink ejection surfaces of each inkjet head 13-16. When printing is performed, the capping members separate from each inkjet head 13-16 and the head unit 10 moves to the initial printing position.

[0034] Figure 4 is a block diagram showing the configuration of the control system of the inkjet printing apparatus according to this embodiment. The inkjet printing apparatus body 1 operates each of the controlled parts shown in Figure 4 in accordance with the control signals from the print control device 17. In this embodiment, the print control device 17 corresponds to the control unit of the present invention.

[0035] The print control device 17 and the inkjet printer unit 1 are connected by a communication line such as a LAN (Local Area Network) or an internet connection, and are configured to communicate with each other. The communication line may be wired or wireless.

[0036] The print control device 17 consists of a computer equipped with a CPU (Central Processing Unit), semiconductor memory, and a hard disk. Based on the input print job, the print control device 17 executes a print control program pre-stored in a storage medium such as semiconductor memory or a hard disk, and controls the various parts shown in Figure 4 by operating electrical circuits.

[0037] In particular, the print control device 17 of this embodiment performs tiling processing using image data of the print target included in a print job, etc., to arrange multiple images of that image data in directions corresponding to the main scanning direction and the transport direction. For example, 50 cm of image data is arranged to a print width of 1 m to 2 m and then tiled. By performing inkjet printing on a wide printing paper P in the main scanning direction based on the tiled image data in this way, productivity can be improved.

[0038] In this embodiment, the head unit 10 of the inkjet printing apparatus body 1 has a first head 11 and a second head 12 arranged in a staggered configuration, as described above. When the two heads are arranged in a staggered configuration in this way, as described above, there is a idle time for the second head 12 at the start of printing, and an idle time for the first head 11 at the end of printing.

[0039] As mentioned above, prolonged idle time can lead to increased viscosity and drying of the ink near the ink ejection nozzle, making normal continuous ejection impossible. This risk is particularly high when performing inkjet printing on wide printing paper P that has undergone tiling of image data, as in this embodiment, because the idle time is longer.

[0040] Therefore, the print control device 17 of this embodiment calculates the idle time based on the initial print conditions and the print width in the main scanning direction, and changes the print conditions so that the idle time is less than or equal to a preset threshold.

[0041] In this embodiment, the initial print conditions are the print conditions set for the image data before tiling, and are the print conditions set within the print job. However, the system is not limited to these, and other pre-set initial print conditions may be used.

[0042] In this embodiment, the printing conditions are set as the printing direction condition, nozzle utilization rate, and head main scanning speed.

[0043] The printing direction condition indicates whether the printing process is unidirectional scanning, where ink is ejected and printing is performed only when the head unit 10 is scanned in one direction of the main scanning direction (left or right as shown in Figure 1), or bidirectional scanning, where ink is ejected and printing is performed when the head unit 10 is scanned in both directions of the main scanning direction (left and right as shown in Figure 1). Bidirectional scanning results in a shorter printing time for a predetermined scanning range than unidirectional scanning, thus reducing idle time, while unidirectional scanning results in a longer idle time. However, in the case of bidirectional scanning, when moving from one scan to the next, the ink ejection interval becomes shorter at the print edge in the main scanning direction, making ink bleeding more likely.

[0044] Nozzle utilization rate refers to the utilization rate of the nozzles per scan of the head unit 10. When the head unit 10 is scanned once, it is the ratio of the number of nozzles that eject ink to the total number of ink ejection nozzles of each inkjet head 13-16 of the head unit 10. A higher nozzle utilization rate indicates that more nozzles are ejecting ink. For example, in bidirectional scanning printing, as mentioned above, the ink ejection interval becomes shorter at the print edge in the main scanning direction, making the ink prone to bleeding. This bleeding can be suppressed by lowering the nozzle utilization rate. On the other hand, if the nozzle utilization rate is lowered, the positions of the unused nozzles that do not eject ink need to be filled in later by printing, which increases the number of scans of the head unit 10, and as a result, the idle time increases.

[0045] The head main scanning speed is the scanning (movement) speed of the head unit 10 in the main scanning direction. The faster the head main scanning speed, the shorter the idle time; the slower the head main scanning speed, the longer the idle time.

[0046] In this embodiment, the print width in the main scanning direction is the print width of the image data after tiling. As mentioned above, the longer the print width, the longer the idle time.

[0047] The print control device 17 of this embodiment calculates the idle time based on the initial print conditions and the print width in the main scanning direction, and modifies the print conditions so that the idle time is below a preset threshold and blurring at the print edge in the main scanning direction is suppressed.

[0048] Next, the method for setting the printing conditions in the inkjet printing apparatus of this embodiment will be explained with reference to the flowchart shown in Figure 5.

[0049] First, the print control device 17 calculates the idle time based on the initial printing conditions and the print width in the main scanning direction, and also calculates the number of print dots per unit time at the print edge in the main scanning direction based on the image data after tiling (S10). The print resolution is set to the same setting as before tiling.

[0050] Then, if the idle time calculated in S10 is less than or equal to a preset threshold and the number of print dots per unit time is less than or equal to a preset upper limit (S12, YES), the print control device 17 sets the print conditions that were set for the image data before tiling (S14).

[0051] On the other hand, in S12, if the idle time exceeds a preset threshold or the number of printed dots per unit time exceeds a preset upper limit (S12, NO), the printing direction condition is changed and the idle time and number of printed dots per unit time are recalculated (S16). For example, if the printing direction condition is unidirectional scanning printing, it is changed to bidirectional scanning printing and the idle time and number of printed dots per unit time are recalculated. Also, if the printing direction condition is bidirectional scanning printing, it is changed to unidirectional scanning printing and the idle time and number of printed dots per unit time are recalculated.

[0052] Then, if the idle time recalculated in S16 is below a preset threshold and the number of print dots per unit time is below a preset upper limit (S18, YES), the print control device 17 issues a warning to the user prompting them to change the print direction conditions (S20). The warning may be, for example, a message.

[0053] On the other hand, if the idle time calculated in S16 exceeds a preset threshold (S18, NO, S22, idle time NG), the print control device 17 increases the nozzle utilization rate (S24), and recalculates the idle time and the number of print dots per unit time using the changed print direction conditions and nozzle utilization rate (S26). It then determines whether the idle time is below the preset threshold and whether the number of print dots per unit time is below the preset upper limit (S28). The nozzle utilization rate may be increased gradually up to the upper limit.

[0054] Furthermore, if the number of print dots per unit time calculated in S16 exceeds a preset upper limit (S18, NO, S22, Smudge NG), the print control device 17 reduces the nozzle utilization rate (S30), and then recalculates the idle time and the number of print dots per unit time using the changed print direction conditions and nozzle utilization rate. It then determines whether the idle time is below a preset threshold and whether the number of print dots per unit time is below a preset upper limit (S28). Note that the nozzle utilization rate may be gradually reduced up to the upper limit.

[0055] Furthermore, if the idle time calculated in S16 exceeds a preset threshold and the number of print dots per unit time calculated in S16 exceeds a preset upper limit (S22, idle time NG and smudging NG), the print control device 17 proceeds to S36, which will be described later.

[0056] Then, if the print control device 17 determines in S28 that the idle time is below a preset threshold and the number of print dots per unit time is below a preset upper limit, it issues a warning to the user prompting them to change to the modified print direction conditions and modified nozzle utilization rate (S32).

[0057] On the other hand, if the print control device 17 determines in S28 that the idle time exceeds a preset threshold (S28, NO, S34, idle time NG), or if the head main scanning speed is "Low" (S36, YES), it changes the head main scanning speed to "High" (S38), and then calculates the idle time again based on the changed printing direction conditions, changed nozzle utilization rate, and changed head main scanning speed (S40), and determines whether the idle time is less than or equal to a preset threshold (S42).

[0058] Then, in S42, if the print control device 17 determines that the idle time is below a preset threshold (S42, YES), it issues a warning to the user prompting them to change the modified print direction conditions, modified nozzle utilization rate, and head main scanning speed to "High" (S44).

[0059] On the other hand, the print control device 17, as determined in S28, if the number of print dots per unit time exceeds a preset upper limit (S28, NO, S34, Smudge NG), if the idle time exceeds a preset threshold and the number of print dots per unit time exceeds a preset upper limit (S28, NO, S34, Idle time NG and Smudge NG), if the head main scanning speed is "High" in S36 (S36, NO), and if it is determined in S42 that the idle time exceeds a preset threshold (S42, NO), will issue a warning to the user indicating that printing is not possible and will display the following three options, requesting the user to select one of them (S46). 1. Print even if nozzle clogging / image blurring occurs. 2. Re-verify whether printing is possible after reducing the number of tiles. 3. Re-verify whether printing is possible with a lower print resolution.

[0060] If "1" is selected, the print control device 17 sets the initial print conditions as they are. If "2" is selected, the print control device 17 accepts the user's changed tiling count, calculates the print width in the main scanning direction based on the changed tiling count, and then repeats the processes from S10 to S36. If "3" is selected, the print control device 17 accepts the user's changed print resolution and repeats the processes from S10 to S46 using the changed print resolution.

[0061] Ultimately, the printing conditions are determined in one of steps S14, S20, S32, S44, or S46, and the print control device 17 sets those printing conditions. In this embodiment, a warning is issued to the user prompting them to change the printing conditions, but the print control device 17 may also be configured to change the printing conditions automatically.

[0062] Next, the printing operation of the inkjet printing apparatus body 1 of the above embodiment will be described. The printing operation described below uses the printing conditions set by the flowchart shown in Figure 5 above.

[0063] First, as shown in Figure 2, a roll of paper is placed in the supply-side core holder 9, and the roll of paper (printing paper P) is pulled out and wound around the core 8a held in the winding-side core holder 8, passing through the rear paper guide 4b, between the drive roller 6 and the pressure roller 7, on the platen 4, and the front paper guide 4a.

[0064] The printing control device 17 then feeds out the printing paper P by rotating the supply-side core holder 9, the winding-side core holder 8, and the drive roller 6, and stops feeding out the printing paper P when it reaches the initial printing position.

[0065] Next, the print control device 17, in the capping unit 20, separates the caps from the inkjet heads 13-16 of the first head 11 and the second head 12, then operates the main scanning drive motor 54 to move the head unit 10 to the right in the main scanning direction on the rail section 5, and positions it at the initial position of the right end.

[0066] The print control device 17 then moves the head unit 10 to the left in the main scanning direction and operates the inkjet heads 13-16 of the head unit 10 to eject ink onto the first scanning line and perform printing. At this time, of the first head 11 and second head 12 of the head unit 10, only the first head 11, which is located upstream in the transport direction of the printing paper P, has reached the initial printing position. Therefore, ink is ejected only from the first head 11, and no ink is ejected from the second head 12.

[0067] Next, if bidirectional scanning printing is set as the printing condition, the print control device 17 feeds out the printing paper P for one scanning line and moves the head unit 10 to the right in the main scanning direction on the rail section 5. The amount of printing paper P fed out for one scanning line at this time varies depending on the printing resolution. The higher the printing resolution, the less printing paper P is fed out.

[0068] Then, as the head unit 10 moves to the right in the main scanning direction, the print control device 17 ejects ink from the inkjet heads 13-16 to print on the second scanning line.

[0069] On the other hand, if unidirectional scanning printing is set as the printing condition, the print control device 17 moves the head unit 10 to the right side in the main scanning direction on the rail section 5 before feeding out the printing paper P. Then, after the head unit 10 returns to its original position, the print control device 17 feeds out one scan line's worth of printing paper P, and then moves the head unit 10 to the left side in the main scanning direction, while simultaneously ejecting ink from the inkjet heads 13-16 to print on the second scanning line.

[0070] Thereafter, the print control device 17 performs the printing process by alternately feeding out one scan line's worth of printing paper P and moving the head unit 10 to the right and left in the main scanning direction on the rail section 5, as described above.

[0071] Then, the print control device 17 starts ejecting ink from the second head 12 of the head unit 10 when the second head 12 reaches the initial printing position, and starts printing with both the first head 11 and the second head 12.

[0072] Then, the print control device 17, after all the ink ejection nozzles of the inkjet heads 13-16 of the first head 11 of the head unit 10 have passed the print completion position and printing by the first head 11 has finished, ejects ink only from the second head 12 and does not eject ink from the second head 12.

[0073] Then, after printing by the second head 12 is completed, the print control device 17 moves the head unit 10 to the capping unit 20 and brings the capping member into contact with each of the inkjet heads 13-16 of the first head 11 and the second head 12 to perform capping.

[0074] According to the inkjet printing apparatus of the above embodiment, the idle time is calculated based on the initial printing conditions and the printing width in the main scanning direction, and the printing conditions are changed so that the idle time is below a preset threshold. This prevents ink from becoming thicker or drying out, and enables stable continuous ink ejection.

[0075] Furthermore, in the inkjet printing apparatus of the above embodiment, the printing conditions include at least one of the printing direction conditions, nozzle utilization rate, and head main scanning speed, so that the printing conditions related to idle time can be changed.

[0076] Furthermore, in the inkjet printing apparatus of the above embodiment, the idle time is determined by changing the printing direction conditions, nozzle utilization rate, and head main scanning speed in that order, so that the printing conditions can be changed starting with the printing conditions, which are easy to control.

[0077] Furthermore, in the inkjet printing apparatus of the above embodiment, when the inkjet head is arranged in a staggered configuration, the idle time at the start of printing and the idle time at the end of printing are calculated, which allows for more appropriate changes to the printing conditions.

[0078] Furthermore, in the inkjet printing apparatus of the above embodiment, since the image data is tiled, productivity is increased, ink viscosity and drying are prevented, and stable continuous ink ejection is possible.

[0079] Furthermore, in the inkjet printing apparatus of the above embodiment, if the idle time does not fall below a threshold even after changing the printing conditions, the number of image data to be tiled is reduced and inkjet printing is performed, the printing resolution is lowered and inkjet printing is performed, or inkjet printing is performed with the initial printing conditions, thereby avoiding a situation where printing cannot be performed.

[0080] Furthermore, although the above embodiment described the case where the inkjet heads are arranged in a staggered pattern, the invention is not limited to this, and for example, the idle time and number of printed dots may be calculated for the case of an inline arrangement and the printing conditions may be changed accordingly.

[0081] Next, we will describe an example of inkjet printing performed in the inkjet printing apparatus of the above embodiment based on the set printing conditions (printing direction conditions, nozzle utilization rate, and head main scanning speed), and a comparative example that serves as a comparison between these two.

[0082] Figure 6 is a table showing Examples 1-4 and Comparative Examples 1-4, which evaluate nozzle clogs, drying time, and idle time when inkjet printing is performed with varying print width, print direction conditions, nozzle utilization rate, and head main scanning speed.

[0083] In this document, the inkjet printing device 1 used was a roll-type inkjet printer manufactured by DGI Corporation (product name: Perseus). The roll paper used was Mitsubishi Paper Mills Ltd.'s offset paper, DF Color M, FSC certified-MX, 157 g / m². 2 A 700mm x 30m sheet of paper was used. Printing was performed while heating the platen 4 so that the surface temperature of the printing paper P reached 43°C. The print resolution was set to 720dpi x 2400dip. The image data to be printed consisted of a natural image with dimensions of 500mm wide x 500mm long, used as the image data before tiling. This was used as one unit, and the print width was increased by tiling in the width direction (main scanning direction).

[0084] The nozzle usage rate is shown as Custom〇%, which is the notation used by the DGI roll-type inkjet printer mentioned above. The higher this number, the lower the nozzle usage.

[0085] The head main scanning speed was set to two levels, "Low" and "High," as in the above embodiment.

[0086] The evaluation method involved visual sensory evaluation immediately after printing. For nozzle cut-off, the print was rated "good" if no cut-off lines occurred in the printed image, and "poor" if cut-off lines occurred. For drying properties, the print was rated "good" if no bleeding occurred at the edges of the print in the main scanning direction, and "poor" if bleeding occurred.

[0087] The idle time is the time from when the first head 11 and the second head 12 separate from the cap member of the capping unit 20 at the start of printing until all nozzles of the second head 12 begin printing, and the time from when ink stops being ejected from at least one nozzle of the first head 11 until when ink stops being ejected from all nozzles of the second head 12 at the end of printing.

[0088] In Examples 1 to 4, the idle time was kept below 55 seconds, resulting in a "good" evaluation for nozzle clearance in all cases. Furthermore, although Examples 3 and 4 involved bidirectional scanning printing, the low nozzle utilization resulted in a "good" drying performance.

[0089] On the other hand, Comparative Example 1 had a lower nozzle utilization rate compared to Example 1, and Comparative Example 2 had a lower nozzle utilization rate compared to Example 2, resulting in a slack time exceeding the limit time and a "poor" nozzle release. Furthermore, Comparative Example 4 had a slower head main scanning speed compared to Example 4, resulting in a longer slack time and a "poor" nozzle release. Note that for Comparative Examples 1, 2, and 3, since nozzle release occurred and problems occurred with the image itself, blurring was not evaluated.

[0090] Furthermore, in Comparative Example 3, the idle time was slightly longer compared to Example 3 due to the reduced nozzle usage rate, but there were no streaks. However, because Comparative Example 3 uses bidirectional scanning printing, blurring occurred at the edges of the printed image, and the drying performance was "poor".

[0091] Furthermore, the present invention is not limited to the embodiments described above, and the components can be modified and implemented in practice without departing from the spirit of the invention. Also, various inventions can be formed by appropriate combinations of the multiple components disclosed in the embodiments. For example, all the components shown in the embodiments may be combined as appropriate. It goes without saying that various modifications and applications are possible without departing from the spirit of the invention.

[0092] The following additional information is disclosed regarding the present invention.

[0093] (Note 1) The present invention relates to an inkjet printing method in which an inkjet head having ink ejection nozzles for ejecting ink is moved in a main scanning direction perpendicular to the transport direction of the printing medium while performing inkjet printing under predetermined printing conditions. In this method, based on the initial printing conditions and the printing width in the main scanning direction, a idle time is calculated, which is the time during which the inkjet head is moved in the main scanning direction without ejecting ink from at least some of the ink ejection nozzles of the inkjet head. The printing conditions are then changed so that the idle time is less than or equal to a preset threshold.

[0094] (Note 2) In the inkjet printing apparatus described in Appendix 1, the printing conditions may include at least one of the printing direction conditions, whether it is unidirectional scanning printing or bidirectional scanning printing, the nozzle utilization rate of the ink ejection nozzles in the inkjet head per scan, and the head main scanning speed in the main scanning direction of the inkjet head.

[0095] (Note 3) In the inkjet printing method described in Appendix 2, the printing conditions include the printing direction condition, nozzle utilization rate, and head main scanning speed. By changing the printing direction condition, nozzle utilization rate, and head main scanning speed in that order, it is possible to determine whether or not the idle time falls below a preset threshold.

[0096] (Note 4) In an inkjet printing apparatus described in any of Appendix 1 to Appendix 3, if a plurality of inkjet heads are arranged in a staggered configuration with a staggered arrangement in the transport direction, the scanning time of the inkjet heads located downstream in the transport direction among the plurality of inkjet heads, in which at least some of the ink ejection nozzles do not eject ink at the start of printing, and the scanning time of the inkjet heads located upstream in the transport direction among the plurality of inkjet heads, in which at least some of the ink ejection nozzles do not eject ink at the end of printing, can be calculated as idle time.

[0097] (Note 5) In the inkjet printing method described in any of Appendix 1 to Appendix 4, the image data of a single print target can be tiled in a direction corresponding to the main scanning direction and then inkjet printed.

[0098] (Note 6) In the inkjet printing method described in Appendix 5, if the idle time does not fall below a threshold as a result of changing the printing conditions, the number of tiled image data may be reduced and inkjet printing may be performed, the printing resolution may be lowered and inkjet printing may be performed, or inkjet printing may be performed with the initial printing conditions.

[0099] (Note 7) The present invention provides an inkjet printing apparatus comprising an inkjet head having ink ejection nozzles for ejecting ink, and a control unit that performs inkjet printing under predetermined printing conditions while moving the inkjet head in a main scanning direction perpendicular to the transport direction of the printing medium. The control unit calculates a idle time, which is the time during which the inkjet head is moved in the main scanning direction without ejecting ink from at least some of the ink ejection nozzles of the inkjet head, based on the initial printing conditions and the printing width in the main scanning direction, and determines printing conditions such that the idle time is less than or equal to a preset threshold. [Explanation of symbols]

[0100] 1. Inkjet printing device main unit 2 bases 2a wheels 3 pedestal 4 Platen 4a Front paper guide 4b Rear paper guide 4c Vacuum Chamber 4D Fan 5 Rail section 6 drive rollers 7 Pressure roller 8. Winding side core holding section 8a Core body 9 Supply side core holding part 9a Core body 10 Head Units 11 First Head 12 Second Head 13-16 Inkjet heads 17 Printing control device 20 capping units 54 Main scanning drive motor 61 Transport drive motor 81. Winding drive motor 91 Supply drive motor P Print paper

Claims

1. In an inkjet printing method in which an inkjet head having an ink ejection nozzle for ejecting ink is moved in a main scanning direction perpendicular to the transport direction of the printing medium while performing inkjet printing under predetermined printing conditions, An inkjet printing method that calculates a idle time, which is the time during which the inkjet head is moved in the main scanning direction without ejecting ink from at least some of the ink ejection nozzles of the inkjet head, based on the initial printing conditions and the printing width in the main scanning direction, and modifies the printing conditions so that the idle time is less than or equal to a preset threshold.

2. The inkjet printing method according to claim 1, wherein the printing conditions include at least one of a printing direction condition, whether it is unidirectional scanning printing or bidirectional scanning printing, the nozzle utilization rate of the ink ejection nozzles in the inkjet head per scan, and the head main scanning speed of the inkjet head in the main scanning direction.

3. The inkjet printing method according to claim 2, wherein the printing conditions include the printing direction condition, the nozzle utilization rate, and the head main scanning speed, and the method determines whether the idle time falls below a preset threshold by changing the printing conditions, the nozzle utilization rate, and the head main scanning speed in that order.

4. When multiple inkjet heads are arranged in a staggered configuration with a shift in the transport direction, The inkjet printing method according to claim 1, wherein the scanning time of an inkjet head, among the plurality of inkjet heads, that is located downstream in the transport direction and in which at least some of the ink ejection nozzles do not eject ink at the start of printing, and the scanning time of an inkjet head, among the plurality of inkjet heads, that is located upstream in the transport direction and in which at least some of the ink ejection nozzles do not eject ink at the end of printing, are calculated as the idle time.

5. The inkjet printing method according to claim 1, wherein image data to be printed is tiled in a direction corresponding to the main scanning direction and inkjet printing is performed.

6. The inkjet printing method according to claim 5, wherein if the idle time does not fall below the threshold as a result of changing the printing conditions, the number of tiled image data is reduced and inkjet printing is performed, the printing resolution is lowered and inkjet printing is performed, or inkjet printing is performed with the initial printing conditions.

7. An inkjet head having an ink ejection nozzle that ejects ink, An inkjet printing apparatus comprising an inkjet head and a control unit that performs inkjet printing under predetermined printing conditions while moving the inkjet head in a main scanning direction perpendicular to the transport direction of the printing medium, An inkjet printing apparatus in which the control unit calculates a idle time, which is the time during which the inkjet head is moved in the main scanning direction without ejecting ink from at least some of the ink ejection nozzles of the inkjet head, based on the initial printing conditions and the printing width in the main scanning direction, and determines the printing conditions such that the idle time is less than or equal to a preset threshold.

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