JP2013215943A - Printing apparatus and printing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress staying of ink in a common ink chamber.SOLUTION: A printing apparatus includes: a head; an ink accumulation part for accumulating ink; a first channel that connects the head and the ink accumulation part; a second channel that connects the head and the ink accumulation part or the first channel; a pressure-supplying part that is provided at one of the first channel and the second channel, and pressure-supplies the ink in the channel; and a control part that controls the pressure-supplying part. The control part controls the pressure-supplying part so that the ink is flown in from the first channel to the head and flown out from the head to the second channel when a first mode is set, and the ink is flown in from the second channel to the head and flown out from the head to the first channel when a second mode is set.

Description

  The present invention relates to a printing apparatus and a printing method.

  As an example of a printing apparatus, there is an ink jet printer (hereinafter referred to as a printer) that prints an image on a printing material by ejecting ink from a plurality of nozzles provided in the head (see, for example, Patent Documents 1 and 2). ). In such a printer, first, ink is supplied from the ink tank to the common ink chamber in the head, and then the ink is supplied from the common ink chamber to a plurality of pressure chambers communicating with the plurality of nozzles. Then, each pressure chamber gives a pressure fluctuation to the ink inside, whereby ink is ejected from the corresponding nozzle.

  In addition, in order to remove bubbles and the like from the ink in the common ink chamber, a printer that circulates ink between the ink tank and the common ink chamber has also been proposed (see, for example, Patent Documents 3 to 4).

JP 2009-178951 A JP 2009-255316 A JP 2008-207371 A JP 2009-247938 A

For example, even when using ink such as white ink where the color material tends to settle, the color material in the white ink is uniformly dispersed by circulating the ink between the ink tank and the common ink chamber as described above. Can be made. However, when the ink is circulated only in one direction, the ink always stays in the same region in the common ink chamber. If it does so, a color material will settle in the area | region where the ink stays, and it will become easy to solidify ink. As a result, ink ejection from the head may be adversely affected.
Accordingly, an object of the present invention is to suppress the retention of ink in the common ink chamber.

The main invention for solving the above-described problems includes a head for ejecting ink, an ink reservoir for storing the ink, a first flow path connecting the head and the ink reservoir, and the head and the ink reservoir. Or a second flow path connecting the first flow path, a pressure feed section that is provided in at least one of the first flow path and the second flow path, and pumps the ink in the flow path, and the pressure feed section A control unit that controls the ink, wherein the control unit causes the ink to flow from the first flow path to the head when the first mode is set, When the second mode is set by controlling the pumping unit so that the ink flows out to the second flow path, the ink flows from the second flow path to the head, and the head flows from the head. So that the ink flows into the first flow path. Controlling the pumping unit, it is a printing apparatus according to claim.
Other features of the present invention will become apparent from the description of this specification and the accompanying drawings.

1 is a block diagram illustrating an overall configuration of a printing system. 2A is a schematic perspective view of the printer, and FIG. 2B is a diagram illustrating a flow path for supplying ink. 3A and 3B are diagrams illustrating a common ink chamber and a white ink circulation method according to a comparative example. 4A and 4B are diagrams illustrating a common ink chamber for white ink and a method for circulating white ink in the first embodiment. It is a figure explaining the flow of the printing method in 1st Example. FIG. 6A is a diagram for explaining a white ink circulation method in the second embodiment, and FIG. 6B is a graph showing a change in the flow rate passing through the flow rate adjustment valve. It is a figure explaining the circulation method of the white ink in 3rd Example. 8A and 8B are diagrams illustrating a white ink circulation method in the fourth embodiment. 9A and 9B are diagrams illustrating a white ink circulation method in the fifth embodiment.

=== Summary of disclosure ===
At least the following will become apparent from the description of the present specification and the accompanying drawings.

That is, a head that discharges ink, an ink storage part that stores the ink, a first flow path that connects the head and the ink storage part, and the head and the ink storage part or the first flow path. A second flow path to be connected; a pressure feed section that is provided in at least one of the first flow path and the second flow path and that feeds the ink in the flow path; and a control section that controls the pressure feed section. In the printing apparatus, when the first mode is set, the control unit causes the ink to flow from the first flow path to the head and the ink to flow from the head to the second flow path. When the second mode is set by controlling the pumping unit, the ink flows from the second flow path to the head, and the ink flows from the head to the first flow path. To control the pumping unit to A printing apparatus for the butterflies.
According to such a printing apparatus, it is possible to suppress the ink from always staying in the same region in the common ink chamber, to suppress the progress of ink solidification, and to remove the solidified ink from the common ink chamber. Can be removed.

In such a printing apparatus, the ink is a white ink.
According to such a printing apparatus, it is possible to suppress the ink from always staying in the same region in the common ink chamber, to suppress the progress of ink solidification, and to remove the solidified ink from the common ink chamber. Can be removed.

In this printing apparatus, the control unit switches between the setting of the first mode and the second mode during a period in which printing of an image on the printing material is stopped.
According to such a printing apparatus, during printing of an image, for example, it is possible to prevent the nozzle from being clogged by the ink solidified in the previous mode or the image from being printed with the solidified ink. it can.

In this printing apparatus, the control unit switches between the setting of the first mode and the second mode during a period in which the ink is ejected from the head to clean the head.
According to such a printing apparatus, the ink solidified in the previous mode can be removed from the common ink chamber.

In this printing apparatus, ink in the flow path is pumped by the pressure feeding section provided in the flow path for flowing the ink into the head among the first flow path and the second flow path, and the pressure feeding section And a flow rate adjusting valve for adjusting the flow rate of the ink flowing in the flow path is provided between the head and the head, and the control unit is configured to stop the printing of the image on the printing material during the period when the head is stopped. Controlling the flow rate adjusting valve so that the flow rate of the ink flowing into the ink changes.
According to such a printing apparatus, it is possible to cause the ink to flow into the common ink chamber vigorously, and it is possible to eliminate the ink retention area.

In this printing apparatus, ink in a flow path is pressure-fed by the pressure-feeding portion provided in the flow path for flowing the ink into the head among the first flow path and the second flow path, and the first flow path A flow rate adjusting valve that adjusts the flow rate of the ink flowing in the flow channel is provided in a flow channel that causes the ink to flow out of the head out of the flow channel and the second flow channel. The printing apparatus is characterized in that the flow rate adjusting valve is controlled so that the flow rate of the ink flowing out of the head changes during a period in which printing of the image is stopped.
According to such a printing apparatus, it is possible to cause ink to flow out of the common ink chamber vigorously, and it is possible to eliminate the ink retention area.

In this printing apparatus, the head ejects the ink and is arranged in a predetermined direction, and communicates with the plurality of nozzles and applies pressure fluctuations to the ink inside so as to eject ink from the nozzles. A plurality of pressure chambers to be discharged; a plurality of pressure chambers; a common ink chamber communicating with the first flow path and the second flow path; and the first flow of the surfaces of the common ink chamber. The distance from the surface on which the path and the second flow path are provided to the surface facing the surface is shorter at the end in the predetermined direction in the common ink chamber than the central portion in the predetermined direction. Of the surfaces of the ink chamber, the distance from the surface provided with the plurality of pressure chambers to the surface facing the surface is such that the end in the predetermined direction in the common ink chamber is more than the center in the predetermined direction. Also short.
According to such a printing apparatus, the ink retention area can be reduced.

A printing method for printing an image on a printing material by ejecting ink from a head, wherein when the first mode is set, the head is connected to an ink storage unit that stores the ink. A step in which the ink flows into the head from one flow path, and the previous ink flows out from the head to a second flow path connecting the head and the ink storage section or the first flow path; And a step of causing the ink to flow into the head from the second flow path and to flow out of the ink from the head to the first flow path when set. .
According to such a printing method, it is possible to prevent the ink from always staying in the same region in the common ink chamber, to suppress the progress of ink solidification, and to remove the solidified ink from the common ink chamber. Can be removed.

=== Printing system ===
The embodiment will be described with reference to an example of a printing system in which a “printing apparatus” is an inkjet printer (hereinafter referred to as a printer) and the printer and a computer are connected.
FIG. 1 is a block diagram showing the overall configuration of the printing system. FIG. 2A is a schematic perspective view of the printer 1, and FIG. 2B is a diagram illustrating a flow path for supplying ink from the ink tank 42 to the head 41. 2B also shows a cross section of the head 41 as viewed from the conveyance direction of the printing material S.

  The printer 1 includes a controller 10, a transport unit 20, a carriage unit 30, a head unit 40, and a detector group 50. The printer 1 is communicably connected to the computer 60, and a printer driver installed in the computer 60 uses the hardware resources of the computer 60 to create print data for causing the printer 1 to print an image. Or output print data to the printer 1. Note that the printer driver may be stored in a storage medium such as a CD-ROM (Compact Disk-Read Only Memory) or downloaded via the Internet.

A controller 10 in the printer 1 is for performing overall control in the printer 1. The interface unit 11 transmits and receives data to and from the computer 60 that is an external device. A CPU 12 (Central Processing Unit) is an arithmetic processing device for performing overall control of the printer 1, and controls each unit via a unit control circuit 14. The memory 13 is for securing an area for storing a program of the CPU 12, a work area, and the like.
The detector group 50 is for monitoring the situation in the printer 1 and outputting the detection result to the controller 10.

The transport unit 20 feeds the printing material S such as paper, cloth, and film to a printable position, and transports the printing material S in the transport direction.
The carriage unit 30 is for moving the head 41 mounted on the carriage 31 along the guide rail 32 in a moving direction that is a direction that intersects the conveying direction of the printing material S (in addition, intersects). The direction is generally an orthogonal direction).

  The head unit 40 is for ejecting ink onto the printing material S and has a head 41. As shown in FIG. 2B, a number of nozzles 43 that eject ink are provided on the lower surface of the head 41, and the nozzles 43 are arranged at regular intervals in the transport direction (corresponding to a predetermined direction) for each color of ejected ink. A nozzle row is formed by the above. In the present embodiment, from the left side in the moving direction, a white nozzle row Nw that discharges white ink W, a cyan nozzle row Nc that discharges cyan ink C, a magenta nozzle row Nm that discharges magenta ink M, and a yellow ink A yellow nozzle row Ny that discharges Y and a black nozzle row Nk that discharges black ink K are arranged side by side.

  The head 41 includes a “common ink chamber 44” for each color of ink to be ejected, and a “pressure chamber 45” and a “piezo element PZT” for each nozzle 43. The common ink chamber 44 and the pressure chamber 45 are always filled with ink. Each pressure chamber 45 communicates with a corresponding one nozzle 43 and a common ink chamber 44. The common ink chamber 44 communicates with a plurality of pressure chambers 45 and communicates with an ink tank 42 (corresponding to an ink reservoir) that stores ink via a supply tube 46.

  By driving a pump P provided in the middle of the supply tube 46, ink is supplied from the ink tank 42 that stores each color ink to the corresponding common ink chamber 44 through the supply tube 46. Thereafter, ink is supplied from the common ink chamber 44 to each pressure chamber 45. During printing, the piezo element PZT expands and contracts based on the drive signal output from the controller 10, and the pressure chamber 45 connected to the piezo element PZT expands and contracts, so that the ink in the pressure chamber 45 is expanded. A pressure fluctuation is applied, and ink is ejected from the nozzle 43 communicating with the pressure chamber 45. The ink discharge method from the nozzle is not limited to this, and for example, a thermal method in which bubbles are generated in the nozzle using a heating element and ink is discharged from the nozzle by the bubbles may be used.

  In the printer 1 having such a configuration, the controller 10 causes the carriage 41 to move the head 41 in the moving direction while discharging ink from the nozzles, and the transport unit 20 moves the printing material S downstream in the transport direction. The conveying operation for conveying is repeated alternately. As a result, since dots are formed by the subsequent ejection operation at positions different from the positions of the dots formed by the previous ejection operation, a two-dimensional image is printed on the printing material S.

=== Circulation of white ink ===
In the printer 1 of the present embodiment, white ink (white ink) can be ejected. As the white ink, for example, an ink containing a white pigment such as titanium oxide (for example, one described in JP-A-2002-38063) or an ink containing a hollow polymer (for example, described in JP-A-2003-313481). Are listed). In such white ink, the color material is likely to settle compared to other color inks, and as a result, the density may become non-uniform or the ink may solidify and cause clogging of the nozzles 43. .

  Therefore, in the printer 1 of the present embodiment, as shown in FIG. 2B, the white ink is circulated between the common ink chamber 44 for the white ink (W) and the ink tank 42. Therefore, in the vicinity of the head 41, a first tube 71 (corresponding to the first flow path) connecting the common ink chamber 44 of white ink and the ink tank 42, and the common ink chamber 44 and ink tank 42 of white ink are also provided. A second tube 72 (corresponding to the second flow path) that connects the two, and a pump P (corresponding to a pressure feeding unit) are provided in the middle of the first tube 71. The pump P is a pump that pumps (transfers) the ink in the tube, and examples thereof include a tube pump and a gear pump. The pump P is not limited to the first tube 71, but the pump P may be provided only to the second tube 72, or the pump P may be provided in the middle of both the tubes 71 and 72.

  Thus, white ink is always stirred by circulating white ink between the common ink chamber 44 and the ink tank 42. Therefore, sedimentation of the color material can be suppressed and the color material can be uniformly dispersed in the white ink. Therefore, the density of the white ink can be made uniform, and the occurrence of clogging of the nozzle 43 due to the solidification of the white ink can be suppressed.

=== Comparative Example ===
3A and 3B are diagrams illustrating a common ink chamber 80 for white ink and a method for circulating white ink in a comparative example. 3A is a schematic view of the periphery of the common ink chamber 80 of the comparative example as viewed from above, and FIG. 3B is a schematic view of the periphery of the common ink chamber 80 of the comparative example as viewed from the moving direction. In the drawing, the ink flow in the common ink chamber 80 is indicated by a dotted arrow. Further, for the sake of explanation, the number of nozzles 43 belonging to the white nozzle row Nw is 180, and numbers are assigned in order from the nozzles 43 on the downstream side in the transport direction (# 1, # 2...). In FIG. 3B, the positions of the pressure chamber 45 and the nozzle 43 with respect to the common ink chamber 80 are indicated by dotted lines.

  180 pressure chambers 45 are attached to the side surface 80a on the left side in the movement direction of the common ink chamber 80. In addition, an opening end 71 a of the first tube 71 and an opening end 72 a of the second tube 72 are attached to the upper surface 80 e of the common ink chamber 80 at a position close to the right side in the moving direction. The first tube 71 is attached at a position close to the downstream side in the transport direction, and the second tube 72 is attached at a position close to the upstream side in the transport direction.

  In the comparative example, the common ink chamber 80 has a rectangular parallelepiped shape. Accordingly, the length X1 of the common ink chamber 80 in the moving direction is constant regardless of the position in the transport direction, and the vertical height X2 of the common ink chamber 80 is also constant regardless of the position in the transport direction.

  In the comparative example, the controller 10 in the printer 1 rotates (drives) the pump P provided in the middle of the first tube 71 only in the first direction, so that the common ink chamber 80 and the ink tank 42 Circulate white ink between them. That is, in the comparative example, white ink is circulated only in one direction between the common ink chamber 80 and the ink tank 42. Specifically, the white ink in the ink tank 42 is supplied to the common ink chamber 80 via the first tube 71, and the white ink in the common ink chamber 80 is returned to the ink tank 42 via the second tube 72. .

  Therefore, in the area where the white ink flow is generated in the common ink chamber 80, the white ink is circulated to prevent the color material from being settled, and the solidification of the white ink can be suppressed. However, in the comparative example, since the white ink is circulated only in one direction, the way in which the white ink flows is always the same. Accordingly, the flow of white ink is always generated in a certain area in the common ink chamber 80, but the flow of white ink is not always generated in another area, and the ink stays (ink stagnates). That is, white ink always stays in the same region in the common ink chamber 80.

  For example, as shown in FIG. 3A, in the downstream portion of the common ink chamber 80 in the transport direction, the white ink flows from the opening end 71a (inlet) of the first tube toward the pressure chamber 45 located on the left side in the movement direction. Arise. Therefore, the ink tends to stay at the corner A1 formed by the side surface 80c on the downstream side in the transport direction of the common ink chamber 80 and the side surface 80b on the right side in the movement direction. On the other hand, in the upstream portion of the common ink chamber 80 in the transport direction, white ink flows only near the pressure chamber 45 and the opening end 72a (outlet) of the second tube. Therefore, the ink tends to stay in the corner portion A2 formed by the side surface 80d on the upstream side in the transport direction of the common ink chamber 80 and the side surface 80b on the right side in the moving direction and the central portion A3 in the moving direction.

  Further, as shown in FIG. 3B, in the downstream portion of the common ink chamber 80 in the transport direction, the white ink flows from the inflow port 71a toward the pressure chamber 45 positioned below. Therefore, ink tends to stay at the corner A4 formed by the side surface 80c and the upper surface 80e on the downstream side in the transport direction of the common ink chamber 80. On the other hand, white ink flows only in the vicinity of the pressure chamber 45 and the outflow port 72a at the upstream side of the common ink chamber 80 in the transport direction. Therefore, the ink tends to stay in the corner portion A5 formed by the side surface 80d and the upper surface 80e on the upstream side in the transport direction of the common ink chamber 80 and the central portion A6 in the vertical direction.

As described above, when the areas A1 to A6 in which the white ink flow is poor and the ink stays in the common ink chamber 80, the color material settles in the area and the color material is not uniformly dispersed. Ink is easily solidified. Then, the nozzle 43 is clogged by the solidified ink (ink that has started to solidify or ink that has solidified), and ink ejection failure occurs. In particular, as in this comparative example, when white ink is circulated only in one direction, the ink always stays in the same area A1 to A6 in the common ink chamber 80, so that the ink is more easily solidified. End up. For example, in the common ink chamber 80 shown in FIG. 3, the ink retention area is larger in the upstream portion in the transport direction (outlet 72 a side) than in the downstream portion in the transport direction (inlet 71 a side). Therefore, the ink is always easily solidified at the upstream side of the common ink chamber 80 in the transport direction.
Therefore, an object of the present embodiment is to suppress stagnation of ink in the common ink chamber.

=== First Embodiment ===
4A and 4B are diagrams illustrating a common ink chamber 44 for white ink and a method for circulating white ink in the first embodiment. 4A is a schematic view of the periphery of the common ink chamber 44 as viewed from above, and FIG. 4B is a schematic view of the periphery of the common ink chamber 44 as viewed from the moving direction. The mounting positions of the pressure chamber 45, the first tube 71, and the second tube 72 are the same as those of the common ink chamber 80 (FIG. 3) of the comparative example.

  In the common ink chamber 44 of the first embodiment, as shown in FIG. 4A, the cross-sectional shape seen from above is a trapezoidal shape. That is, in the common ink chamber 80 (FIG. 3A) of the comparative example, the right corner (the corner formed by the downstream side surface 80c and the right side surface 80b, and the upstream side surface 80d and the right side surface 80b is formed. The shape is eliminated. Specifically, the width in the movement direction gradually decreases from the opening end 71a of the first tube toward the downstream side in the conveyance direction, and the width in the movement direction decreases from the opening end 72a of the second tube toward the upstream side in the conveyance direction. It is getting shorter gradually.

  As described above, in the first embodiment, the surface (the side surface 44a on the left side in the movement direction) provided with the plurality of pressure chambers 45 among the surfaces of the common ink chamber 44 (the side surface on the right side in the movement direction) is opposed to the surface 44a. 44b) (ie, the width in the moving direction), the distance x1 at the end in the transport direction in the common ink chamber 44 is shorter than the distance x2 at the center. By doing so, it is possible to eliminate the regions A1 and A2 where the ink has accumulated at the corner on the right side in the movement direction in the common ink chamber 80 (FIG. 3A) of the comparative example. Therefore, in the common ink chamber 44 of the first embodiment, the ink retention area can be reduced and the amount of ink solidified in the common ink chamber can be reduced as compared with the common ink chamber 80 of the comparative example. As a result, the occurrence of defective ink discharge from the nozzles 43 can be suppressed.

  Similarly, in the common ink chamber 44 of the first embodiment, as shown in FIG. 4B, the cross-sectional shape viewed from the moving direction is a trapezoidal shape. That is, the upper corner (the corner formed by the downstream side surface 80c and the upper surface 80e, and the corner formed by the upstream side surface 80d and the upper surface 80e in the common ink chamber 80 (FIG. 3B) of the comparative example. ) Has been removed. Specifically, the height in the vertical direction gradually decreases as the distance from the first tube 71 decreases in the transport direction, and the height gradually decreases as the distance from the second tube 72 increases in the transport direction.

  Thus, the distance from the surface (upper surface 44e) provided with the end portions of the first tube 71 and the second tube 72 among the surfaces of the common ink chamber 44 to the surface (lower surface 44f) facing the surface 44e. With regard to (that is, height), the distance x3 at the end in the transport direction in the common ink chamber 44 is made shorter than the distance x4 at the center. By doing so, it is possible to eliminate the regions A4 and A5 where the ink stays in the upper corner of the common ink chamber 80 (FIG. 3B) of the comparative example. Therefore, in the common ink chamber 44 of the first embodiment, the ink retention area can be reduced and the amount of ink solidified in the common ink chamber can be reduced as compared with the common ink chamber 80 of the comparative example. As a result, the occurrence of defective ink discharge from the nozzles 43 can be suppressed.

  Furthermore, in the first embodiment, the controller 10 (corresponding to the control unit) in the printer 1 controls the driving of the pump P provided in the middle of the first tube 71 (here, the rotation direction is controlled), and the first The rotation mode and the second rotation mode are performed. When the first rotation mode (corresponding to the first mode) is set, the controller 10 rotates the pump P in the first direction as in the comparative example, and the ink in the ink tank 42 is discharged from the first tube 71. Control is performed so that the ink flows into the common ink chamber 44, the ink flows out of the common ink chamber 44 into the second tube 72, and returns to the ink tank 42. On the other hand, when the second rotation mode (corresponding to the second mode) is set, the controller 10 rotates the pump P in the second direction, which is opposite to the first direction, and the ink tank 42. The inside ink flows into the common ink chamber 44 from the second tube 72, and the ink is controlled to flow out from the common ink chamber 44 into the first tube 71 and return to the ink tank 42.

  The left diagram in FIG. 4A and the top diagram in FIG. 4B are diagrams showing the flow of white ink in the first rotation mode. When the first rotation mode is set, as shown in the left diagram of FIG. 4A, for example, in order to supply ink to be used for image printing, the first ink mode is supplied to the downstream side of the common ink chamber 44 in the transport direction. White ink flows from the open end 71a (inlet) of one tube toward the pressure chamber 45 located on the left side in the movement direction. Therefore, no ink retention area occurs. On the other hand, in the upstream portion of the common ink chamber 44 in the transport direction, the white ink flows only near the pressure chamber 45 and the open end 72a (outlet) of the second tube. Therefore, the ink tends to stay in the central portion a1 in the moving direction of the common ink chamber 44.

  Further, as shown in the upper diagram of FIG. 4B, white ink flows from the inflow port 71a toward the pressure chamber 45 located below at the downstream side of the common ink chamber 44 in the transport direction. Therefore, no ink retention area occurs. On the other hand, white ink flows only in the vicinity of the pressure chamber 45 and the outflow port 72a in the upstream portion of the common ink chamber 44 in the transport direction. Therefore, the ink tends to stay in the central portion a3 in the vertical direction of the common ink chamber 44.

  As described above, in the common ink chamber 44 of the first embodiment, the ink retention areas a1 and a3 are generated. However, in the first embodiment, not only the first rotation mode but also the second rotation mode is performed. That is, the white ink is circulated not only in one direction but also in the reverse direction.

  The right diagram in FIG. 4A and the lower diagram in FIG. 4B are diagrams showing the flow of white ink in the second rotation mode. When the second rotation mode is set, as shown in the right diagram of FIG. 4A, for example, ink that is ejected in the cleaning process of the head 41 is supplied to the upstream portion of the common ink chamber 44 in the transport direction. Therefore, the white ink flows from the opening end 72a (inlet) of the second tube toward the pressure chamber 45 located on the left side in the movement direction. Therefore, in the second rotation mode, the ink can flow to the area a1 where the ink has accumulated in the first rotation mode. As a result, it is possible to prevent the ink solidification in the stay region a1. Further, the solidified ink can be returned to the ink tank 42 via the first tube 71, or the solidified ink can be ejected from the nozzle 43 during the cleaning process of the head 41. That is, the solidified ink can be removed from the common ink chamber 44, and the nozzle 43 can be prevented from being clogged during printing.

  Further, as shown in the lower diagram of FIG. 4B, white ink flows from the inflow port 72a toward the pressure chamber 45 located below at the upstream side of the common ink chamber 44 in the transport direction. Therefore, in the second rotation mode, the ink can flow to the area a3 where the ink has accumulated in the first rotation mode. As a result, the progress of ink solidification in the stay region a3 can be prevented, and the solidified ink can be removed from the common ink chamber 44. As described above, in the second rotation mode, it is possible to eliminate the regions a1 and a3 where the ink has accumulated in the first rotation mode.

  Further, in the second rotation mode, contrary to the first rotation mode, as shown in the right diagram of FIG. 4A, the ink in the region a2 at the downstream side in the transport direction of the common ink chamber 44 and in the central portion in the movement direction. Tends to stay. Further, as shown in the lower diagram of FIG. 4B, the ink tends to stay in a region a4 in the central portion in the vertical direction, which is the downstream side of the common ink chamber 44 in the transport direction. However, when the second rotation mode is switched to the first rotation mode, the ink flows in these ink retention areas a2 and a4, so that the progress of ink solidification can be prevented, and the common ink chamber 44 is used. From this, solidified ink can be removed. That is, in the first rotation mode, it is possible to eliminate the areas a2 and a4 where the ink has accumulated in the second rotation mode.

  As described above, in the first embodiment, the white ink is circulated not only in one direction but also in the reverse direction between the common ink chamber 44 and the ink tank 42. By doing so, the flow of ink in the common ink chamber 44 can be changed in accordance with the mode even when using white ink in which the color material easily settles and solidifies. It is possible to prevent the white ink from always staying in the same area. As a result, the progress of ink solidification can be suppressed, and the solidified ink can be removed from the common ink chamber 44, so that it is possible to prevent the occurrence of ejection failure due to clogging of the nozzles 43.

  FIG. 5 is a diagram for explaining the flow of the printing method in the first embodiment. Upon receiving the print job (S01), the controller 10 repeats the ejection operation for ejecting ink while moving the head 41 in the movement direction and the conveyance operation for conveying the printing material S in the conveyance direction, thereby printing the printing material. An image is printed on S (S02). It is assumed that white ink is circulated during image printing, and in the first embodiment, the first rotation mode is set during image printing.

  When the printing of the image on the printing material S is completed, the controller 10 performs a cleaning process of the head 41 (S03). In the nozzle 43 that is not frequently used during printing, the ink solvent evaporates from the nozzle 43 and the ink thickens, or foreign matter (such as paper dust or dust) adheres to it, resulting in ejection failure. There is a fear. For example, there is a possibility that a predetermined amount of ink is not ejected from the nozzle, or the flying direction of the ink droplet ejected from the nozzle is deviated. Therefore, when printing of the image is completed, the controller 10 performs a cleaning process of the head 41 so that ink is normally ejected from the defective nozzle.

  Specifically, the controller 10 moves the head 41 to the home position, causes the nozzle surface of the head 41 and the cap 47 (see FIG. 2A) to face each other, and forcibly ejects ink from the nozzle 43. By doing so, thickened ink and foreign matter are ejected from the nozzle 43, and the defective nozzle can be restored to a normal nozzle. Further, after the cap 47 and the head 41 are brought into close contact with each other so that the nozzle 43 is surrounded by the concave portion of the cap 47, the air in the sealed space formed between the concave portion of the cap 47 and the nozzle surface of the head 41 is pumped. The thickened ink or the foreign matter may be ejected from the nozzle 43 by suctioning with a negative pressure in the sealed space.

  During the cleaning process of the head 41, the controller 10 switches the setting from the first rotation mode to the second rotation mode (S03). That is, the white ink is circulated in the direction opposite to the direction in which the white ink was circulated during image printing. By doing so, it is possible to cause ink to flow in the areas (a1 and a3 in FIG. 4) that have stayed in the common ink chamber 44 during image printing. After a predetermined time has elapsed since the change to the second rotation mode, the controller 10 switches the setting to the first rotation mode (S04) and waits for the next print job. When the standby time is long, the rotation mode (white ink circulation direction) may be switched every predetermined time.

  As described above, the controller 10 switches the setting between the first rotation mode and the second rotation mode while the printing of the image on the printing material S is stopped. Immediately after switching the rotation mode, the solidified ink staying in the previous rotation mode may flow in the common ink chamber 44 and move to the pressure chamber 45 in some cases. As a result, the nozzle 43 may be clogged by the solidified ink, or the solidified ink may be discharged from the nozzle 43. Therefore, if the rotation mode is switched during image printing, dot dropout occurs or the image is printed with solidified ink, and the image quality of the image deteriorates. Therefore, it is possible to suppress image quality deterioration by switching the rotation mode while the image printing is stopped.

  Further, the controller 10 switches the setting between the first rotation mode and the second rotation mode during a period in which ink is ejected from the head 41 in order to clean the head 41. By doing so, the solidified ink flowing in the common ink chamber 44 immediately after switching the rotation mode can be ejected from the nozzle 43. As a result, the solidified ink can be removed from the common ink chamber 44, and the solidified ink can be prevented from returning to the ink tank. Therefore, the nozzle 43 is not clogged with the solidified ink or the image is not printed with the solidified ink during image printing, and image quality deterioration of the image can be suppressed.

<Modification of the first embodiment>
In the above embodiment, the first rotation mode is set during image printing. However, the present invention is not limited to this. For example, the second rotation mode may be set during image printing. The rotation mode may be switched for each print job. That is, the first rotation mode may be set during a certain print job, and the second rotation mode may be set for the next print job.

  In the flow of FIG. 5, the rotation mode is switched every time one print job is completed, but the present invention is not limited to this. For example, the rotation mode may be switched every time a plurality of print jobs are completed. Further, the rotation mode may be switched every predetermined time (for example, every other day). The rotation mode may be switched during image printing.

  In the above embodiment, the rotation mode is switched after the cleaning process of the head 41 is started. However, the present invention is not limited to this. For example, the rotation mode may be switched simultaneously with the start of the cleaning process, or the cleaning process may be started after the rotation mode is switched.

=== Second Embodiment ===
FIG. 6A is a diagram for explaining a white ink circulation method in the second embodiment, and FIG. 6B is a graph showing a change in the flow rate passing through the flow rate adjustment valves V1, V2. In the second embodiment, the first pump P1 is provided in the middle of the first tube 71, the first flow rate adjusting valve V1 is provided between the first pump P1 and the common ink chamber 44, and the second tube 72 is in the middle. The second pump P2 is provided, and the second flow rate adjusting valve V2 is provided between the second pump P2 and the common ink chamber 44. The flow rate adjusting valves V1, V2 are for adjusting the flow rate of ink flowing in the flow path.

  When the first rotation mode is set (upper diagram in FIG. 6A), the controller 10 circulates white ink by driving (rotating) the first pump P1 that supplies ink to the common ink chamber 44. The driving of the second pump P2 is stopped. It is assumed that the first pump P1 and the second pump P2 are configured not to block the flow path even when the driving is stopped, and in this case also, it is assumed that ink flows downstream of the second pump P2. And the controller 10 changes the flow volume which passes the 1st flow regulating valve V1 in the period which has stopped printing of the image to the to-be-printed material S. FIG. That is, the first flow rate adjustment valve V1 is controlled so that the amount of ink flowing from the first tube 71 into the common ink chamber 44 changes.

  For example, as illustrated in FIG. 6B, the controller 10 controls so that a relatively large amount of flow q1 passes through the first flow rate adjustment valve V1 at time t1 to t2, and at time t2 to t3 thereafter, Control is performed so that the flow rate passing through the flow rate adjustment valve V1 is a small flow rate q2 (or control is performed so that no ink flows). Note that the second flow rate adjustment valve V2 is always in a state in which a large flow rate q1 can pass. As a result, during the period from time t2 to time t3, the pressure of the ink in the flow path on the upstream side (that is, the first pump P1 side) from the first flow rate adjustment valve V1 is downstream from the first flow rate adjustment valve V1. It becomes higher than the pressure of the ink in the flow path on the side (that is, the common ink chamber 44 side). Therefore, when the controller 10 controls so that a large flow rate q1 passes through the first flow rate adjustment valve V1 at the subsequent times t3 to t4, the controller 10 enters the common ink chamber 44 from the first tube 71 (inlet). A large amount of ink can flow in vigorously. As a result, the ink that has been solidified in the previous second rotation mode can be more reliably put on the ink flow, the progress of the ink solidification is prevented, and the solidified ink is removed from the common ink chamber 44. be able to. That is, it is possible to eliminate a region where ink has accumulated in the second rotation mode (a2 and a4 in FIG. 4).

  Conversely, when the second rotation mode is set (the lower diagram in FIG. 6A), the controller 10 circulates white ink by driving the second pump P2 on the side that supplies ink to the common ink chamber 44, The driving of the first pump P1 is stopped. Then, the controller 10 changes the flow rate passing through the second flow rate adjustment valve V2 during the printing stop period. That is, the second flow rate adjustment valve V2 is controlled so that the amount of ink flowing from the second tube 72 into the common ink chamber 44 changes. It is assumed that the first flow rate adjustment valve V1 is always in a state where a large flow rate q1 can pass therethrough.

  By doing so, during the period when the flow rate passing through the second flow rate adjustment valve V2 is reduced (time t2 to t3 in FIG. 6B), it is upstream of the second flow rate adjustment valve V2 (that is, the second pump P2 side). The pressure of the ink in the flow path can be higher than the pressure of the ink in the flow path on the downstream side (that is, the common ink chamber 44 side) from the second flow rate adjustment valve V2. For this reason, when the controller 10 thereafter (time t3 to t4) controls so that a large amount of flow q1 passes through the second flow rate adjustment valve V2, the second tube 72 (inlet) enters the common ink chamber 44. A large amount of ink can flow in vigorously. As a result, the ink that has been solidified in the previous first rotation mode can be more reliably put on the ink flow, the progress of the ink solidification can be prevented, and the solidified ink can be removed from the common ink chamber 44. be able to. That is, it is possible to eliminate a region where ink has accumulated during the first rotation mode (a1 and a3 in FIG. 4).

=== Third embodiment ===
FIG. 7 is a diagram illustrating a white ink circulation method in the third embodiment. In the third embodiment, similarly to the second embodiment, pumps P1 and P2 are provided in the middle of the first tube 71 and the second tube 72, respectively, and the flow rates are respectively set between the pumps P1 and P2 and the common ink chamber 44. Adjusting valves V1 and V2 are provided.

  When the first rotation mode is set (upper diagram in FIG. 7), the controller 10 circulates white ink by driving (rotating) the first pump P1 on the side that supplies ink to the common ink chamber 44. The driving of the second pump P2 is stopped. Then, the controller 10 changes the flow rate passing through the second flow rate adjustment valve V2 during the printing stop period as shown in FIG. 6B described above. That is, the second flow rate adjustment valve V2 is controlled so that the amount of ink flowing out from the common ink chamber 44 to the second tube 72 changes. It is assumed that the first flow rate adjustment valve V1 is always in a state where a large flow rate q1 can pass therethrough.

  By doing so, during the period when the flow rate passing through the second flow rate adjustment valve V2 is reduced (time t2 to t3 in FIG. 6B), the upstream side of the second flow rate adjustment valve V2, that is, in the common ink chamber 44. The pressure of the ink can be higher than the pressure of the ink in the flow path on the downstream side of the second flow rate adjustment valve V2, that is, on the second pump P2 side. For this reason, when the controller 10 thereafter (time t3 to t4) controls so that a large flow rate q1 passes through the second flow rate adjustment valve V2, a large amount of ink is supplied from the common ink chamber 44 to the second tube 72. It can be drained vigorously. By doing so, it is possible to generate an ink flow in a region (a1 or a3 in FIG. 4) in which the ink tends to stay in the first rotation mode. As a result, it is possible to suppress the progress of ink solidification in the ink retention areas a1 and a3.

  Conversely, when the second rotation mode is set (the lower diagram in FIG. 7), the controller 10 drives (rotates) the second pump P2 on the side that supplies ink to the common ink chamber 44, thereby supplying white ink. It circulates and the driving of the first pump P1 stops. And the controller 10 changes the flow volume which passes the 1st flow regulating valve V1 in a printing stop period. That is, the first flow rate adjustment valve V1 is controlled so that the amount of ink flowing out from the common ink chamber 44 to the first tube 71 changes. Note that the second flow rate adjustment valve V2 is always in a state in which a large flow rate q1 can pass.

  By doing so, during a period in which the flow rate passing through the first flow rate adjustment valve V1 is reduced (time t2 to t3 in FIG. 6B), upstream of the first flow rate adjustment valve V1, that is, in the common ink chamber 44. The pressure of the ink can be higher than the pressure of the ink in the flow path on the downstream side of the first flow rate adjustment valve V1, that is, on the first pump P1 side. Therefore, when the controller 10 adjusts so that a large amount of flow q1 passes through the first flow rate adjustment valve V1 thereafter (time t3 to t4), a large amount of ink is supplied from the common ink chamber 44 to the first tube 71. It can be drained vigorously. By doing so, it is possible to generate an ink flow in a region (a2 or a4 in FIG. 4) in which the ink tends to stay in the second rotation mode. As a result, it is possible to suppress the progress of ink solidification in the ink retention areas a2 and a4.

=== Fourth Embodiment ===
8A and 8B are diagrams for explaining a white ink circulation method in the fourth embodiment. FIG. 8A is a schematic view of the periphery of the common ink chamber 44 as viewed from above, and FIG. 8B is a schematic view of the periphery of the common ink chamber 44 as viewed from the moving direction. In the fourth embodiment, three flow paths connecting the common ink chamber 44 and the ink tank 42 are provided, and the third tube 73 is provided between the first tube 71 and the second tube 72 (that is, in the central portion in the transport direction). Is provided. Moreover, although the pump P is provided in the middle of the 3rd tube 73, you may provide the pump P in the middle of not only this but the 1st tube 71 and the 2nd tube 72, or in the middle of all the tubes 71-73. A pump P may be provided.

  When the first rotation mode is set, the controller 10 causes the ink in the ink tank 42 to flow from the first tube 71 and the second tube 72 into the common ink chamber 44 and from the common ink chamber 44 to the third tube. Control is performed so that the ink flows out to 73 and returns to the ink tank.

  The left diagram in FIG. 8A and the upper diagram in FIG. 8B are diagrams showing the flow of white ink in the first rotation mode. When the first rotation mode is set, as shown in the left diagram of FIG. 8A, the opening ends 71 a and 72 a of the first tube and the second tube at the downstream side and the upstream side of the common ink chamber 44 in the transport direction. White ink flows from the (inlet) toward the pressure chamber 45 located on the left side in the moving direction. Therefore, no ink retention area occurs. On the other hand, in the central portion of the common ink chamber 44 in the transport direction, white ink flows only near the pressure chamber 45 and the open end 73a (outlet) of the third tube. Therefore, the ink tends to stay at the central portion a5 in the moving direction of the common ink chamber 44.

  Further, as shown in the upper diagram of FIG. 8B, in the downstream side and upstream side of the common ink chamber 44 in the transport direction, the white ink is directed from the first tube 71 and the second tube 72 to the pressure chamber 45 positioned below. A flow occurs. Therefore, no ink retention area occurs. On the other hand, in the central portion of the common ink chamber 44 in the transport direction, white ink flows only near the pressure chamber 45 and the opening end 73a of the third tube. Therefore, the ink tends to stay in the central portion a8 in the vertical direction of the common ink chamber 44.

  However, after that, the controller 10 switches the setting to the second rotation mode, the ink in the ink tank 42 flows into the common ink chamber 44 from the third tube 73, and the first tube 71 and the first tube from the common ink chamber 44. Control is performed so that ink flows out into the two tubes 72 and returns to the ink tank 42.

  As a result, as shown in the right diagram of FIG. 8A, in the central portion in the transport direction of the common ink chamber 44, the white ink heading from the open end 73a (inlet) of the third tube toward the pressure chamber 45 located on the left side in the moving direction. The flow of Further, as shown in the lower diagram of FIG. 8B, in the central portion of the common ink chamber 44 in the transport direction, white ink flows from the opening end 73a (inflow port) of the third tube toward the pressure chamber 45 positioned below. . Therefore, it is possible to cause the ink to flow in the regions a5 and a8 where the ink has accumulated in the previous first rotation mode. Accordingly, the progress of ink solidification in the regions a5 and a8 where the ink has accumulated during the first rotation mode can be prevented, and the solidified ink can be removed from the common ink chamber 44.

  Further, in the second rotation mode, as shown in the right diagram of FIG. 8A, the ink stays in the regions a6 and a7 in the central portion in the moving direction at the downstream and upstream portions of the common ink chamber 44 in the transport direction. It becomes easy. Further, as shown in the lower diagram of FIG. 8B, the ink tends to stay in the regions a <b> 9 and a <b> 10 in the central portion in the vertical direction at the downstream and upstream portions of the common ink chamber 44 in the transport direction. However, when the second rotation mode is switched to the first rotation mode, the ink flows into the ink retention areas a6, a7, a9, and a10, so that the ink solidification can be prevented and the common ink chamber is prevented. Solidified ink can be removed from 44.

=== Fifth embodiment ===
9A and 9B are diagrams illustrating a white ink circulation method in the fifth embodiment. In the embodiment shown in FIG. 9A, the white ink is circulated between the two ink tanks 421 and 422 for storing the white ink and the common ink chamber 44. Of the two ink tanks, one first tank 421 is connected to the common ink chamber 44 via the first tube 71, and the other second tank 422 is connected to the common ink chamber 44 via the second tube 72. .

  Also in this case, the controller 10 causes the ink in the first tank 421 to flow into the common ink chamber 44 from the first tube 71 and the ink in the common ink chamber 44 from the second tube 72 in the first rotation mode. In the second rotation mode, the ink in the second tank 422 flows into the common ink chamber 44 from the second tube 72, and the ink in the common ink chamber 44 flows from the first tube 71. Control is performed to return to the first tank 421.

  9B, one end of the second tube 72 is connected to the common ink chamber 44, and the other end of the second tube 72 is connected to the first tube 71. Specifically, the first tube 71 and the other end of the second tube are connected between the pump P provided in the first tube 71 and the check valve V3. The check valve V3 limits the flow of ink in one direction, and blocks the ink that has flowed out of the common ink chamber 44 from returning to the ink tank 42.

  Also in this case, the controller 10 causes the ink in the ink tank 42 to flow into the common ink chamber 44 from the first tube 71 and the ink in the common ink chamber 44 through the second tube 72 in the first rotation mode. In the second rotation mode, the ink in the ink tank 42 flows from the second tube 72 into the common ink chamber 44, and the ink in the common ink chamber 44 causes the first tube 71 to return to the first tube 71. And control to return to the second tube 72. That is, white ink is circulated only between the common ink chamber 44 and the ink flow path (the first tube 71 and the second tube 72).

  In addition, there is a printer configured to supply ink from a main ink tank (for example, an ink cartridge) to a sub ink tank and supply ink from the sub tank to a common ink chamber 44 (not shown). In the case of such a printer, the ink may be circulated between the sub tank and the common ink chamber 44.

  Even with the above configuration, the white ink can be prevented from staying in the same region in the common ink chamber 44 by circulating the white ink not only in one direction but also in the reverse direction. As a result, the progress of ink solidification can be suppressed and the solidified ink can be removed from the common ink chamber 44.

=== Other Embodiments ===
The above-described embodiments are for facilitating the understanding of the present invention, and are not intended to limit the present invention. The present invention can be changed and improved without departing from the gist thereof, and it is needless to say that the present invention includes equivalents thereof.

<About ink>
In the above embodiment, the case where white ink is circulated between the common ink chamber and the ink tank is taken as an example, but the present invention is not limited to this. Other colored ink (YMCK) may be circulated, or metallic ink containing a metal pigment may be circulated.

<About the printer>
In the above-described embodiment, a printer that repeats the operation of ejecting ink while the head moves and the operation of transporting the printing material in the transport direction is described as an example. For example, when the printing material passes under a fixed head extending over the width of the printing material, the head ejects ink toward the printing material, thereby causing the printing material to be 2 A printer that prints a three-dimensional image may be used. Further, for example, by repeating the operation of ejecting ink while the head moves in the X direction and the operation of moving the head in the Y direction on the printing material conveyed to the printing region, the printing in the printing region is performed. A printer that prints a two-dimensional image on a material, and then conveys the printing material in the X direction to convey a new portion of the printing material to the printing region may be used.

<About white>
In the present specification, the term “white” is not limited to the white color in the strict sense that is the surface color of an object that reflects 100% of all wavelengths of visible light. It shall include a color called white. For example, “white” means (1) color measurement mode: spot colorimetry, light source: D50, backing: Black, printing medium: transparent film, using a colorimeter eye-one Pro manufactured by x-rite When the colorimetry is performed, the Lab-based mark is on the a ^* b ^* plane within the circumference of the radius 20 and the inside thereof, and the color is within the hue range represented by L ^* being 70 or more. (2) When the color is measured with the color mode CM2022 manufactured by Minolta in the measurement mode D502 ° field of view, SCF mode, and white background, the label in the Lab system is on the circumference of the radius 20 on the a ^* b ^* plane and inside Or a color within the hue range represented by L ^* of 70 or more, or (3) the color of the ink used as the background of the image as described in JP-A-2004-306591, If it is used, it is not limited to pure white.

1 Printer, 10 Controller, 11 Interface section,
12 CPU, 13 memory, 14 unit control circuit,
20 transport unit, 30 carriage unit, 31 carriage,
32 guide rails, 40 head units, 41 heads,
42 ink tanks, 43 nozzles, 44 common ink chambers, 45 pressure chambers,
46 supply tube, 47 cap,
50 detector groups, 60 computers,
71 1st tube, 72 2nd tube, 73 3rd tube,
80 Common ink chamber of comparative example

Claims (8)

A head for ejecting ink;
An ink reservoir for storing the ink;
A first flow path connecting the head and the ink reservoir;
A second flow path connecting the head and the ink reservoir or the first flow path;
A pumping unit that is provided in at least one of the first channel and the second channel and pumps the ink in the channel;
A control unit for controlling the pumping unit;
A printing apparatus comprising:
The controller is
When the first mode is set, the pressure feeding unit is controlled so that the ink flows from the first flow path to the head and the ink flows from the head to the second flow path,
When the second mode is set, the pressure feeding unit is controlled so that the ink flows into the head from the second flow path and the ink flows out from the head into the first flow path;
A printing apparatus characterized by that. The printing apparatus according to claim 1,
A printing apparatus, wherein the ink is a white ink. The printing apparatus according to claim 1 or 2, wherein
The control unit switches between the setting of the first mode and the second mode during a period in which printing of an image on the printing material is stopped.
A printing apparatus characterized by that. The printing apparatus according to claim 3,
The control unit switches the setting between the first mode and the second mode during a period in which the ink is ejected from the head to clean the head.
A printing apparatus characterized by that. The printing apparatus according to any one of claims 1 to 4, wherein:
Of the first flow path and the second flow path, the ink in the flow path is pumped by the pressure feeding section provided in the flow path for flowing the ink into the head,
A flow rate adjusting valve for adjusting the flow rate of the ink flowing in the flow path is provided between the pumping unit and the head.
The control unit controls the flow rate adjusting valve so that the flow rate of the ink flowing into the head changes during a period in which printing of an image on the printing material is stopped.
A printing apparatus characterized by that. The printing apparatus according to any one of claims 1 to 5, wherein
Of the first flow path and the second flow path, the ink in the flow path is pumped by the pressure feeding section provided in the flow path for flowing the ink into the head,
A flow rate adjusting valve for adjusting a flow rate of the ink flowing in the flow channel is provided in a flow channel that causes the ink to flow out of the head out of the first flow channel and the second flow channel,
The control unit controls the flow rate adjustment valve so that the flow rate of the ink flowing out from the head changes during a period in which printing of an image on the printing material is stopped.
A printing apparatus characterized by that. The printing apparatus according to any one of claims 1 to 6,
The head includes a plurality of nozzles that discharge the ink and are arranged in a predetermined direction, and a plurality of pressure chambers that communicate with the plurality of nozzles and that cause pressure fluctuations to the ink inside and discharge ink from the nozzles, respectively. A plurality of pressure chambers, a common ink chamber communicating with the first flow path and the second flow path,
Of the surfaces of the common ink chamber, the distance from the surface where the first flow path and the second flow path are provided to the surface facing the surface is the end of the common ink chamber in the predetermined direction. Is shorter than the central portion in the predetermined direction,
Of the surfaces of the common ink chamber, the distance from the surface provided with the plurality of pressure chambers to the surface facing the surface is such that the end in the predetermined direction in the common ink chamber is the center in the predetermined direction. Shorter than part,
A printing apparatus characterized by that. A printing method for printing an image on a printing material by discharging ink from a head,
When the first mode is set, the ink flows into the head from a first flow path that connects the head and an ink reservoir that stores the ink, and the head and the ink reservoir or the first A step of allowing the ink to flow out from the head to a second flow path connecting the flow path;
When the second mode is set, the ink flows into the head from the second flow path, and the ink flows out from the head into the first flow path;
A printing method comprising:

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