JP2014008684A - Printing method and recording apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a printing method and a recording apparatus, in which a stripe is hardly caused.SOLUTION: In the printing method related to the present invention, when the highest density area is printed, pixels 60 constitutes a plurality of pixel arrays A-D in which the pixels 60 are aligned at substantially equal intervals on a recording medium, the plurality of pixel arrays A-D are landed so as to be aligned at substantially equal intervals, the pixels 60 which are belong to adjacent pixel arrays (for example, A and C to B) are landed so as to be shifted to a direction in which the pixels 60 are aligned in the pixel arrays A-D, a liquid amount to be one of the pixels 60 can be set to three or more stages of different amount, the liquid amount to be each of the pixels 60 on the recording medium is to be the liquid amount different from all of six pixels (B2, B4, A3, A5, C3 and C5 to B4) adjacent to each (for example, B4) of the pixels.

Description

  The present invention relates to a printing method and a recording apparatus that perform printing using a liquid discharge head or the like.

  In recent years, printing apparatuses using inkjet recording methods such as inkjet printers and inkjet plotters are not only printers for general consumers, but also, for example, formation of electronic circuits, manufacture of color filters for liquid crystal displays, manufacture of organic EL displays It is also widely used for industrial applications.

  In such an ink jet printing apparatus, a liquid discharge head for discharging liquid is mounted as a print head. This type of print head includes a heater as a pressurizing unit in an ink flow path filled with ink, heats and boiles the ink with the heater, pressurizes the ink with bubbles generated in the ink flow path, A thermal head system that ejects ink as droplets from the ink ejection holes, and a part of the wall of the ink channel filled with ink is bent and displaced by a displacement element, and the ink in the ink channel is mechanically pressurized, and the ink A piezoelectric method for discharging liquid droplets from discharge holes is generally known.

  In addition, in such a liquid discharge head, a serial type that performs recording while moving the liquid discharge head in a direction (main scanning direction) orthogonal to the conveyance direction (sub-scanning direction) of the recording medium, and main scanning from the recording medium There is a line type in which recording is performed on a recording medium conveyed in the sub-scanning direction with a liquid discharge head that is long in the direction fixed. The line type has the advantage that high-speed recording is possible because there is no need to move the liquid discharge head as in the serial type.

  In order to print droplets at a high density in any of the serial type and line type liquid discharge heads, the density of the discharge holes for discharging the droplets formed in the liquid discharge head is increased. There is a need.

  In view of this, the liquid discharge head includes a manifold and a flow path member having discharge holes connected to the manifold via a plurality of pressurization chambers, a plurality of individual electrodes and a plurality of individual electrodes provided so as to cover the plurality of pressurization chambers. There is known a structure in which a piezoelectric actuator substrate having a plurality of displacement elements including a common electrode facing each individual electrode and a piezoelectric ceramic layer sandwiched between them is laminated (for example, patent document) 1). In this liquid discharge head, the pressurizing chambers connected to the plurality of discharge holes are arranged in a matrix, and the displacement element of the actuator unit provided so as to cover it is displaced by deformation of the piezoelectric body, so that each discharge Ink is ejected from the holes and printing is possible in the main scanning direction at a resolution of 600 dpi.

JP 2003-305852 A

When performing solid (highest density) printing with the liquid discharge head described in Patent Document 1, the recording medium has pixels 60 of approximately the same size in a grid-like position as shown in FIG. To land. Note that in solid printing, the entire area of the surface of the recording medium where the pixels 60 spread may be covered, or as shown in FIG. In the former, since the boundary of the pixel 60 is almost unknown and the landing position cannot be indicated, FIG. 7 shows a state where the pixel 60 has landed so as not to overlap. Solid printing may be performed in either case.

  In the pixel 60 as shown in FIG. 7, if the pixel 60 arranged in a straight line has a variability with a tendency such as a small pixel size (droplet amount) or a landing position deviating in a certain direction, A part with a small amount of overlap or a part with a large amount of overlapping may appear streak-like.

  Accordingly, an object of the present invention is to provide a printing method and a recording apparatus in which streaks are unlikely to occur.

  The printing method of the present invention is a printing method in which a liquid is landed on a recording medium to form and print pixels, and when printing a region having the highest density, the pixels are printed on the recording medium, A plurality of pixel columns in which pixels are arranged at substantially equal intervals are configured to land so that the plurality of pixel columns are arranged at approximately equal intervals, and the pixels belonging to the adjacent pixel columns are arranged in the pixel columns. The pixels are landed so as to be shifted in the direction in which the pixels are arranged, and the amount of the liquid to be one pixel can be set to three or more different amounts. The amount of liquid that becomes each pixel excluding the pixel at the end belongs to the same pixel column as the pixel, the two pixels adjacent to the pixel, and the two pixel columns adjacent to the pixel Belongs to one of the images Column every two fold, characterized in that the one and the amounts of different liquid also of the pixel adjacent to a total of six of the pixels combined the pixels adjacent to the pixel.

  Further, the recording apparatus of the present invention controls the liquid ejection head having a plurality of ejection holes, a transport unit that transports the recording medium to the liquid ejection head, and the liquid ejection head to perform the printing method. It is characterized by having a control part which performs.

  When the pixels are arranged in a grid, there are four adjacent pixels. However, when the pixels in the adjacent pixel column are shifted as in the present invention, the adjacent pixels are six, and further, The amount of liquid (pixel size or spread) is different between the pixel and the center pixel, and each pixel is in such a state, so the size of the pixels arranged on the left and right of the boundary of the pixel column Because of the difference, the state of the boundary of the pixel row is difficult to be constant, and it is difficult to be recognized as a streak by human eyes.

1 is a schematic configuration diagram of a printer that is a recording apparatus according to an embodiment of the present invention. FIG. 2 is a plan view showing a liquid discharge head main body constituting the liquid discharge head of FIG. 1. FIG. 3 is an enlarged view of a region surrounded by an alternate long and short dash line in FIG. FIG. 3 is an enlarged view of a region surrounded by an alternate long and short dash line in FIG. It is a longitudinal cross-sectional view along the VV line of FIG. (A) And (b) is the top view which showed typically the pixel on the recording medium which performed printing of temporary embodiment of this invention. It is the top view which showed typically the pixel on the recording medium which performed the conventional printing.

  FIG. 1 is a schematic configuration diagram of a color inkjet printer which is a recording apparatus according to an embodiment of the present invention. This color inkjet printer 1 (hereinafter referred to as printer 1) has four liquid ejection heads 2. These liquid discharge heads 2 are arranged along the conveyance direction of the printing paper P and are fixed to the printer 1. The liquid discharge head 2 has an elongated shape in a direction from the front to the back in FIG.

  In the printer 1, a paper feed unit 114, a transport unit 120, and a paper receiver 116 are sequentially provided along the transport path of the printing paper P. In addition, the printer 1 is provided with a control unit 100 for controlling the operation of each unit of the printer 1 such as the liquid discharge head 2 and the paper feeding unit 114.

  The paper supply unit 114 includes a paper storage case 115 that can store a plurality of printing papers P, and a paper supply roller 145. The paper feed roller 145 can send out the uppermost print paper P among the print papers P stacked and stored in the paper storage case 115 one by one.

  Between the paper feed unit 114 and the transport unit 120, two pairs of feed rollers 118a and 118b and 119a and 119b are arranged along the transport path of the printing paper P. The printing paper P sent out from the paper supply unit 114 is guided by these feed rollers and further sent out to the transport unit 120.

  The transport unit 120 includes an endless transport belt 111 and two belt rollers 106 and 107. The conveyor belt 111 is wound around belt rollers 106 and 107. The conveyor belt 111 is adjusted to such a length that it is stretched with a predetermined tension when it is wound around two belt rollers. Thus, the conveyor belt 111 is stretched without slack along two parallel planes each including a common tangent line of the two belt rollers. Of these two planes, the plane closer to the liquid ejection head 2 is a transport surface 127 that transports the printing paper P.

  As shown in FIG. 1, a conveyance motor 174 is connected to the belt roller 106. The transport motor 174 can rotate the belt roller 106 in the direction of arrow A. The belt roller 107 can rotate in conjunction with the transport belt 111. Therefore, the conveyance belt 111 moves along the direction of arrow A by driving the conveyance motor 174 and rotating the belt roller 106.

  In the vicinity of the belt roller 107, a nip roller 138 and a nip receiving roller 139 are arranged so as to sandwich the conveyance belt 111. The nip roller 138 is urged downward by a spring (not shown). A nip receiving roller 139 below the nip roller 138 receives the nip roller 138 biased downward via the conveying belt 111. The two nip rollers are rotatably installed and rotate in conjunction with the conveyance belt 111.

  The printing paper P sent out from the paper supply unit 114 to the transport unit 120 is sandwiched between the nip roller 138 and the transport belt 111. As a result, the printing paper P is pressed against the transport surface 127 of the transport belt 111 and is fixed on the transport surface 127. The printing paper P is transported in the direction in which the liquid ejection head 2 is installed according to the rotation of the transport belt 111. The outer peripheral surface 113 of the conveyor belt 111 may be treated with adhesive silicon rubber. Thereby, the printing paper P can be securely fixed to the transport surface 127.

  The four liquid discharge heads 2 are arranged close to each other along the conveyance direction by the conveyance belt 111. Each liquid discharge head 2 has a liquid discharge head main body 13 at the lower end. A number of ejection holes 8 for ejecting liquid are provided on the lower surface of the liquid ejection head body 13 (see FIG. 3).

  Liquid droplets (ink) of the same color are ejected from the ejection holes 8 provided in one liquid ejection head 2. The ejection holes 8 of each liquid ejection head 2 are arranged at equal intervals in one direction (a direction parallel to the printing paper P and perpendicular to the conveyance direction of the printing paper P, and the longitudinal direction of the liquid ejection head 2). Can print without gaps in the direction. The colors of the liquid ejected from each liquid ejection head 2 are magenta (M), yellow (Y), cyan (C), and black (K), respectively. Each liquid discharge head 2 is arranged with a slight gap between the lower surface of the liquid discharge head main body 13 and the transport surface 127 of the transport belt 111.

  The printing paper P transported by the transport belt 111 passes through the gap between the liquid ejection head 2 and the transport belt 111. At that time, droplets are ejected from the liquid ejection head body 13 constituting the liquid ejection head 2 toward the upper surface of the printing paper P. As a result, a color image based on the image data stored by the control unit 100 is formed on the upper surface of the printing paper P.

  A separation plate 140 and two pairs of feed rollers 121a and 121b and 122a and 122b are arranged between the transport unit 120 and the paper receiver 116. The printing paper P on which the color image is printed is conveyed to the peeling plate 140 by the conveying belt 111. At this time, the printing paper P is peeled from the transport surface 127 by the right end of the peeling plate 140. Then, the printing paper P is sent out to the paper receiving unit 116 by the feed rollers 121a to 122b. In this way, the printed printing paper P is sequentially sent to the paper receiving unit 116 and stacked on the paper receiving unit 116.

  Note that a paper surface sensor 133 is installed between the liquid ejection head 2 and the nip roller 138 that are the most upstream in the transport direction of the printing paper P. The paper surface sensor 133 includes a light emitting element and a light receiving element, and can detect the leading end position of the printing paper P on the transport path. The detection result by the paper surface sensor 133 is sent to the control unit 100. The control unit 100 can control the liquid ejection head 2, the conveyance motor 174, and the like so that the conveyance of the printing paper P and the printing of the image are synchronized based on the detection result sent from the paper surface sensor 133.

  Next, the liquid discharge head main body 13 constituting the liquid discharge head of the present invention will be described. FIG. 2 is a top view showing the liquid discharge head main body 13 shown in FIG. FIG. 3 is an enlarged top view of a region surrounded by the alternate long and short dash line in FIG. 2 and is a part of the liquid discharge head main body 13. FIG. 4 is an enlarged perspective view of the same position as FIG. 3, in which some of the flow paths are omitted so that the positions of the discharge holes 8 can be easily understood. 3 and 4, in order to make the drawings easy to understand, the pressurizing chamber 10 (pressurizing chamber group 9), the squeezing chamber 12, and the discharge hole 8 that are to be drawn by broken lines below the piezoelectric actuator substrate 21 are shown by solid lines. It is drawn in. FIG. 5 is a longitudinal sectional view taken along line VV in FIG.

The liquid discharge head body 13 includes a flat plate-like flow path member 4 and a piezoelectric actuator substrate 21 that is an actuator unit on the flow path member 4. The piezoelectric actuator substrate 21 has a trapezoidal shape, and is disposed on the upper surface of the flow path member 4 so that a pair of parallel opposing sides of the trapezoid is parallel to the longitudinal direction of the flow path member 4. In addition, two piezoelectric actuator substrates 21 are arranged on the flow path member 4 as a whole in a zigzag manner, two along each of the two virtual straight lines parallel to the longitudinal direction of the flow path member 4. Yes. The oblique sides of the piezoelectric actuator substrates 21 adjacent to each other on the flow path member 4 partially overlap in the short direction of the flow path member 4. In the area printed by driving the overlapping piezoelectric actuator unit 21, the droplets ejected by the two piezoelectric actuator substrates 21 are mixed and landed.

  A manifold 5 that is a part of the liquid flow path is formed inside the flow path member 4. The manifold 5 has an elongated shape extending along the longitudinal direction of the flow path member 4, and an opening 5 b of the manifold 5 is formed on the upper surface of the flow path member 4. A total of ten openings 5 b are formed along each of two straight lines (imaginary lines) parallel to the longitudinal direction of the flow path member 4. The opening 5b is formed at a position that avoids a region where the four piezoelectric actuator substrates 21 are disposed. The manifold 5 is supplied with liquid from a liquid tank (not shown) through the opening 5b.

  The manifold 5 formed in the flow path member 4 is branched into a plurality of branches (the manifold 5 at the branched portion may be referred to as a sub-manifold 5a). The manifold 5 connected to the opening 5 b extends along the oblique side of the piezoelectric actuator substrate 21 and is disposed so as to intersect with the longitudinal direction of the flow path member 4. In the region sandwiched between the two piezoelectric actuator substrates 21, one manifold 5 is shared by the adjacent piezoelectric actuator substrates 21, and the sub-manifold 5 a is branched from both sides of the manifold 5. These sub-manifolds 5 a extend in the longitudinal direction of the liquid discharge head main body 13 adjacent to each other in regions facing the piezoelectric actuator substrates 21 inside the flow path member 4.

  The flow path member 4 has four pressure chamber groups 9 in which a plurality of pressure chambers 10 are formed in a matrix (that is, two-dimensionally and regularly). The pressurizing chamber 10 is a hollow region having a substantially rhombic planar shape with rounded corners. The pressurizing chamber 10 is formed so as to open on the upper surface of the flow path member 4. These pressurizing chambers 10 are arranged over almost the entire surface of the upper surface of the flow path member 4 facing the piezoelectric actuator substrate 21. Therefore, each pressurizing chamber group 9 formed by these pressurizing chambers 10 occupies an area having almost the same size and shape as the piezoelectric actuator substrate 21. Further, the opening of each pressurizing chamber 10 is closed by adhering the piezoelectric actuator substrate 21 to the upper surface of the flow path member 4.

  In the present embodiment, as shown in FIG. 3, the manifold 5 branches into four rows of E1-E4 sub-manifolds 5a arranged in parallel with each other in the short direction of the flow path member 4, and each sub-manifold The pressurizing chambers 10 connected to 5a constitute a row of the pressurizing chambers 10 arranged in the longitudinal direction of the flow path member 4 at equal intervals, and the four rows are arranged in parallel to each other in the lateral direction. Two rows of the pressure chambers 10 connected to the sub-manifold 5a are arranged on both sides of the sub-manifold 5a.

  As a whole, the pressurizing chambers 10 connected from the manifold 5 constitute rows of the pressurizing chambers 10 arranged in the longitudinal direction of the flow path member 4 at equal intervals, and the rows are arranged in 16 rows parallel to each other in the short side direction. ing. The number of pressurizing chambers 10 included in each pressurizing chamber row is arranged so as to gradually decrease from the long side toward the short side corresponding to the outer shape of the displacement element 50 that is an actuator. Yes. The discharge holes 8 are also arranged in the same manner. As a result, it is possible to form an image with a resolution of 600 dpi in the longitudinal direction as a whole. That is, the individual flow paths 32 are connected to each sub-manifold 5a at intervals corresponding to 150 dpi on average. This is because when the discharge holes 8 for 600 dpi are divided and connected to the four sub-manifolds 5a, the individual flow paths 32 connected to the sub-manifolds 5a are not always connected at equal intervals. In other words, the individual flow paths 32 are formed at intervals of an average of 170 μm (25.4 mm / 150 = 169 μm intervals if 150 dpi) in the main scanning direction.

Individual electrodes 35 to be described later are formed at positions facing the pressurizing chambers 10 on the upper surface of the piezoelectric actuator substrate 21. The individual electrode 35 is slightly smaller than the pressurizing chamber 10, has a shape substantially similar to the pressurizing chamber 10, and is disposed so as to be within a region facing the pressurizing chamber 10 on the upper surface of the piezoelectric actuator substrate 21. ing.

  A large number of discharge holes 8 are formed in the lower surface of the flow path member 4. These discharge holes 8 are arranged at positions avoiding the area facing the sub-manifold 5a arranged on the lower surface side of the flow path member 4. Further, these discharge holes 8 are arranged in a region facing the piezoelectric actuator substrate 21 on the lower surface side of the flow path member 4. These discharge hole groups 7 occupy regions of almost the same size and shape as the piezoelectric actuator substrate 21, and droplets are discharged from the discharge holes 8 by displacing the corresponding displacement elements 50 of the piezoelectric actuator substrate 21. it can. The arrangement of the discharge holes 8 will be described in detail later. The discharge holes 8 in each region are arranged at equal intervals along a plurality of straight lines parallel to the longitudinal direction of the flow path member 4.

  The flow path member 4 included in the liquid discharge head body 13 has a stacked structure in which a plurality of plates are stacked. These plates are a cavity plate 22, a base plate 23, an aperture (squeezing) plate 24, supply plates 25 and 26, manifold plates 27, 28 and 29, a cover plate 30 and a nozzle plate 31 in order from the upper surface of the flow path member 4. is there. A number of holes are formed in these plates. Each plate is aligned and laminated so that these holes communicate with each other to form the individual flow path 32 and the sub-manifold 5a. As shown in FIG. 5, the liquid discharge head body 13 is configured such that the pressurizing chamber 10 is on the upper surface of the flow path member 4, the sub-manifold 5 a is on the inner lower surface side, and the discharge holes 8 are on the lower surface. Each portion constituting the path 32 is disposed close to each other at different positions, and the sub-manifold 5 a and the discharge hole 8 are connected via the pressurizing chamber 10.

  The holes formed in each plate will be described. These holes include the following. First, the pressurizing chamber 10 formed in the cavity plate 22. Secondly, there is a communication hole that constitutes a flow path that connects from one end of the pressurizing chamber 10 to the sub-manifold 5a. This communication hole is formed in each plate from the base plate 23 (specifically, the inlet of the pressurizing chamber 10) to the supply plate 25 (specifically, the outlet of the sub-manifold 5a). The communication hole includes the aperture 12 formed in the aperture plate 24 and the individual supply flow path 6 formed in the supply plates 25 and 26.

  Third, there is a communication hole constituting a flow path communicating from the other end of the pressurizing chamber 10 to the discharge hole 8, and this communication hole is referred to as a descender (partial flow path) in the following description. The descender is formed on each plate from the base plate 23 (specifically, the outlet of the pressurizing chamber 10) to the nozzle plate 31 (specifically, the discharge hole 8). Fourthly, there is a communication hole constituting the sub-manifold 5a. The communication holes are formed in the manifold plates 27-30.

  Such communication holes are connected to each other to form an individual flow path 32 extending from the liquid inflow port (the outlet of the submanifold 5a) from the submanifold 5a to the discharge hole 8. The liquid supplied to the sub-manifold 5a is discharged from the discharge hole 8 through the following path. First, from the sub-manifold 5a, it passes through the individual supply flow path 6 and reaches one end of the aperture 12. Next, it proceeds horizontally along the extending direction of the aperture 12 and reaches the other end of the aperture 12. From there, it reaches one end of the pressurizing chamber 10 upward. Furthermore, it progresses horizontally along the extending direction of the pressurizing chamber 10 and reaches the other end of the pressurizing chamber 10. While moving little by little in the horizontal direction from there, it proceeds mainly downward and proceeds to the discharge hole 8 opened in the lower surface.

As shown in FIG. 5, the piezoelectric actuator substrate 21 has a laminated structure including two piezoelectric ceramic layers 21a and 21b. Each of these piezoelectric ceramic layers 21a and 21b has a thickness of about 20 μm. The total thickness of the piezoelectric actuator substrate 21 is 4
The displacement amount can be increased by being about 0 μm and 100 μm or less. Each of the piezoelectric ceramic layers 21a and 21b extends so as to straddle the plurality of pressure chambers 10 (see FIG. 3). The piezoelectric ceramic layers 21a and 21b are made of a lead zirconate titanate (PZT) ceramic material having ferroelectricity.

  The piezoelectric actuator substrate 21 has a common electrode 34 made of a metal material such as Ag—Pd and an individual electrode 35 made of a metal material such as Au. As described above, the individual electrode 35 is disposed at a position facing the pressurizing chamber 10 on the upper surface of the piezoelectric actuator substrate 21. One end of the individual electrode 35 is drawn out of a region facing the pressurizing chamber 10 to form a lead electrode 35b, and a connection electrode 36 is formed on the lead electrode 35b. The connection electrode 36 is made of, for example, gold containing glass frit, and has a convex shape with a thickness of about 15 μm. The connection electrode 36 is electrically joined to an electrode provided in an FPC (Flexible Printed Circuit) (not shown).

  In the piezoelectric actuator substrate 21 in the present embodiment, when an electric field is applied in the polarization direction to the piezoelectric ceramic layer 21b by setting the individual electrode 35 to a potential different from that of the common electrode 34, the portion to which this electric field is applied is piezoelectric. It works as an active part that is distorted by the effect. At this time, the piezoelectric ceramic layer 21b expands or contracts in the thickness direction, that is, the stacking direction, and tends to contract or extend in the direction perpendicular to the stacking direction, that is, the surface direction, due to the piezoelectric lateral effect. On the other hand, since the remaining piezoelectric ceramic layer 21a is an inactive layer that does not have a region sandwiched between the individual electrode 35 and the common electrode 34, it does not spontaneously deform. That is, the piezoelectric actuator substrate 21 has the piezoelectric ceramic layer 21b on the upper side (that is, the side away from the pressurizing chamber 10) as a layer including the active portion and the lower side (that is, the side close to the pressurizing chamber 10). This piezoceramic layer 21a is a so-called unimorph type structure having an inactive layer.

  In this configuration, when the control unit 100 sets the individual electrode 35 to a predetermined positive or negative potential with respect to the common electrode 34 so that the electric field and the polarization are in the same direction, a portion sandwiched between the electrodes of the piezoelectric ceramic layer 21b. (Active part) contracts in the surface direction. On the other hand, the piezoelectric ceramic layer 21a, which is an inactive layer, is not affected by an electric field, so that it does not spontaneously shrink and tries to restrict deformation of the active portion. As a result, there is a difference in strain in the polarization direction between the piezoelectric ceramic layer 21b and the piezoelectric ceramic layer 21a, and the piezoelectric ceramic layer 21b is deformed so as to protrude toward the pressurizing chamber 10 (unimorph deformation).

The actual driving procedure in the present embodiment is such that the first electrode V1V (volt, which may be omitted hereinafter) is set in advance so that the individual electrode 35 has a higher potential than the common electrode 34, and every time there is a discharge request. The individual electrode 35 and the common electrode 34 are once set to a low potential, for example, the same potential by applying a second voltage lower than the first voltage V1, and then set to a high potential again at a predetermined timing. As a result, the piezoelectric ceramic layers 21a and 21b return to their original shapes at the timing when the individual electrodes 35 become low potential, and the volume of the pressurizing chamber 10 increases compared to the initial state (the state where the potentials of both electrodes are different). To do. At this time, a negative pressure is applied to the pressurizing chamber 10 and the liquid is sucked into the pressurizing chamber 10 from the manifold 5 side. Thereafter, at the timing when the individual electrode 35 is set to a high potential again, the piezoelectric ceramic layers 21a and 21b are deformed so as to protrude toward the pressurizing chamber 10, and the pressure in the pressurizing chamber 10 is reduced due to the volume reduction of the pressurizing chamber 10. The pressure becomes positive and the pressure on the liquid rises, and droplets are ejected. That is, a drive signal including a pulse based on a high potential is supplied to the individual electrode 35 in order to eject a droplet. This pulse width is ideally AL (Acoustic Length), which is the length of time during which the pressure wave propagates from the manifold 5 to the discharge hole 8 in the pressurizing chamber 10. According to this, when the inside of the pressurizing chamber 10 is reversed from the negative pressure state to the positive pressure state, both pressures are combined, and the liquid droplets can be discharged at a stronger pressure.

In order to control the amount of droplets to be ejected, and hence the size and spread amount of the pixel 60, for example, the following is performed. By making the pulse width shorter than AL, the liquid discharge amount can be reduced. Also, by sending pulses at short intervals, droplets are continuously ejected so that they become one during flight, or land at close positions on the recording medium to become one pixel. More methods than can be combined may be combined.

  When recording is performed using such a drive signal, crosstalk may occur. The main crosstalk is that when the pressure displacement element 50 is displaced, the displacement element 50 contracts, so that the stress affects the adjacent displacement element, and the vibration of the liquid in the pressurizing chamber 10 is a flow path. What is transmitted to the adjacent pressurizing chamber 10 through the member 4, and vibrations of the liquid in the pressurizing chamber 10 are transmitted to the sub manifold 5a through the squeezing 12, and further transmitted to the pressurizing chamber 10 connected to the sub manifold 5a. There is. In order to suppress such crosstalk, it is conceivable to delay the drive signal by a delay time and send it to the displacement element 50. This is where a drive signal is sent at a time (t + delay time) when a drive signal is sent at a certain time t, and a displacement connected to an adjacent pressurization chamber among the pressurization chambers 10 arranged in a matrix. By not sending drive signals to the element 50 at the same time, it is effective to suppress the first two crosstalks among the main crosstalks described above.

  In addition, the adjacent pressurization chamber 10 said here is the pressurization chamber 10 with the shortest distance between them, More specifically, it is a substantially rhombus (more generally a substantially parallelogram-shaped). It is the pressurization chamber 10 which a side opposes and adjoins. Then, for example, such a drive sends a non-delayed drive signal to the displacement element 50 corresponding to the pressurization chamber row of F1, F3, F5, F7, F9, F11, F13, and F15 in FIG. , F6, F8, F10, F12, F14, and F16 may be transmitted to the displacement element 50 corresponding to the pressurizing chamber row.

  Also in cases other than those described above, in the liquid ejection head 2 having a plurality of pressurizing chamber rows, a drive signal is simultaneously sent to the displacement elements 50 corresponding to the pressurizing chambers 10 belonging to one pressurizing chamber row (hereinafter referred to as In some cases, the drive signal is sent to the pressurization chamber row simply), and the drive signal is not sent simultaneously to the adjacent pressurization chamber row by sending a delayed drive signal to at least one of them. As a result, the driving method can be simplified (this makes the structure of the driver IC for controlling the driving signal simple and inexpensive), and the crosstalk can be reduced. Here, in order to print an image, in addition to sending a drive signal for ejecting droplets having a voltage change, a signal for not ejecting a droplet without voltage change is also sent. It expresses sending a drive signal to the column. In addition to a signal that does not cause a change in voltage and does not eject a droplet, a signal that causes a change in voltage but does not eject a droplet may be sent.

  Further, if the drive signal is delayed, the landing position of the ejected liquid droplet is shifted until it is left as it is. As long as the delay time value allows the impact of the landing position deviation on the image quality to be acceptable, it can be used as it is, or the placement of the ejection holes can be shifted according to the delay time, and the accuracy of the landing position can be changed. May be raised.

  When solid (highest density) printing is performed using such a liquid discharge head 2, the recording medium is provided with pixels 60 of approximately the same size at a grid-like position as shown in FIG. When landing, streaks may be noticeable. This is due to the following reasons, for example. The pixels 60 in the pixel row arranged in the vertical direction in FIG. 7 are formed by ejecting liquid from one ejection hole 8 (ejection element), and the pixels 60 in the pixel row adjacent to the pixel 60 are separated from each other. It is discharged from the hole 8 (discharge element). Accordingly, even if the pixels 60 of the same size are ejected to land on the grid-like points, the pixels 60 of the respective pixel columns become larger in size or the landing positions are shifted in one direction. Therefore, the overlapping method of the pixels 60 may be different between adjacent pixel rows, which may appear streaks.

  In particular, in the liquid discharge head 2 described above, since the discharge elements are arranged close to each other in a matrix, crosstalk between the discharge elements is relatively large, and the discharge holes 8 are the same during solid printing. Since the amount of liquid droplets is ejected, the operation of the surrounding ejection elements is also in the same state, so that the same crosstalk state continues and there is a possibility that the variation in the pixels 60 for each pixel column described above becomes large. In particular, in the liquid discharge head 2 described above, since the piezoelectric ceramic layer 21b of the displacement element 50 is connected between the adjacent displacement elements 50, the expansion and contraction that drives the piezoelectric ceramic layer 21b is transmitted to the adjacent displacement element 50. There is an influence of talk. This is the same even when the above-described delay is added to reduce the influence of crosstalk.

  Even if the pixels 60 belonging to one pixel column are not ejected from one ejection hole 8, the same streak may occur due to other factors.

  Therefore, when performing solid printing, as shown in FIGS. 6A and 6B, the pixels 60 are arranged and the size is adjusted. In solid printing, the entire area of the surface of the recording medium on which the pixels 60 spread may be covered, or as shown in FIGS. 6A and 6B, the area may be covered at a constant rate. Good. In the former case, the boundary of the pixel 60 is almost unknown, and the landing position cannot be indicated. FIGS. 1A and 1B show a state where the pixel 60 is landed so as not to overlap. However, the solid printing mentioned here may be used in either case.

  In FIG. 6A, the pixel 60 is landed along virtual lines A to D indicating the pixel column. In FIG. 6A, the pixels 60 on the same imaginary lines A to D are ejected from the same ejection hole 8. If so, the effect of suppressing the streaks of the above-described factors is enhanced, but otherwise, the effect of suppressing the streaks is effective.

  The pixels 60 on the virtual lines A to D are arranged at substantially equal intervals. Here, the point where the pixel 60 is arranged is considered as the point of the area centroid. Further, “substantially equidistant” means that each interval is within ± 30%, particularly within 15% of the average value of the interval. Even if the intervals of the pixels 60 are set at equal intervals in the design of the discharge control, there are variations in the discharge direction and the discharge speed. Therefore, the intervals on the recording medium vary to some extent. In addition, in a droplet ejected with one pulse, the larger the droplet size, the greater the velocity of the droplet. Furthermore, when one pixel 60 is configured by ejecting a plurality of droplets with a plurality of pulses, drive control is simplified if the landing positions of the droplets ejected with the first pulse are set at equal intervals. The position of the pixel 60 where a plurality of droplets are combined is deviated from the position. Further, although the above-described delay control is performed, the interval between the pixels 60 also changes when the position of the ejection hole 8 is not adjusted in accordance with the delay.

  The pixel columns on the virtual lines A to D (hereinafter may be referred to as pixel columns A to D) are parallel to each other and are substantially equally spaced. Here, “substantially equidistant” means that each interval is within ± 20%, particularly within 10%, with respect to the average value of the interval. This interval corresponds to the interval in which the discharge holes 8 are arranged in one direction in the liquid discharge head 2, but varies slightly due to variations in the discharge direction.

In adjacent pixel columns (for example, pixel columns A and C with respect to the pixel column B), the pixels 60 are landed by shifting in the direction in which the pixels 60 are arranged in the pixel column. This does not occur due to the above-described variation or the like, and each pixel 60 is shifted substantially uniformly. In FIG. 6A, the pixel A3 of the pixel column A is orthogonal to the pixel column B with respect to the pixel 60 (hereinafter, sometimes referred to as pixel B4) that has landed at the position B4 of the pixel column B. Landing is shifted in the direction, and this shift is almost half of the interval between the pixels B2 and B4. The average shift amount is preferably 20% or more, particularly 40% or more of the interval between the pixels 60 in the pixel row, and is preferably controlled to be 50% in terms of control. Further, the pixels 60 in adjacent pixel rows with one pixel row in between may or may not be shifted. As described above, if the shift between adjacent pixel columns is 50%, there is no leakage between adjacent pixel columns with one pixel column in between. Further, the deviation in the three aligned pixel rows may be 33% (1/3).

  As a control method for landing with 50% deviation, every other displacement element 50 to be driven in one drive cycle, and every other displacement element 50 to be driven in the pressurization chamber row (drive and not drive) In the next drive cycle, the displacement element may be different from the previous drive cycle. In this way, since the adjacent displacement elements 50 are not driven simultaneously, the occurrence of crosstalk itself can be reduced, and the printing accuracy can be increased. Further, if an amount of deviation other than 50% is to be set, for example, the drive cycle must be increased accordingly, and a driver IC having a high drive frequency is used, resulting in an increased amount of heat generation. Specifically, for example, in order to set the deviation amount to 40%, driving is performed at a frequency five times, and in order, driving of one displacement element drive, all pauses, the other displacement element drive, all pauses, all pauses, etc. Must be done.

  When the pixels 60 are shifted and landed in adjacent pixel rows, the number of pixels 60 adjacent to one pixel 60 is six. Specifically, the pixels 60 adjacent to the pixel B4 belong to the same pixel column B, are adjacent to the pixels B2 and B6, and are adjacent to the adjacent pixel column A to be adjacent to the pixels A3 and A5. And adjacent pixels C3 and C5 belonging to the adjacent pixel column C. Thus, adjacent pixels 60 are arranged in a hexagonal shape with respect to one pixel 60.

  The amount of liquid droplets (pixel size or pixel expansion) that is adjacent to the central pixel 60 is different from the amount of liquid droplets (pixel size or pixel expansion) that is adjacent to the center pixel 60, and the If the pixels 60 in the printing range are similarly configured, the sizes of the pixels 60 arranged on the left and right of the pixel column boundary are different, so that the state of the pixel column boundary is difficult to be constant, It becomes difficult to be recognized. In FIG. 6A, the droplet amount can be set to a large droplet, a medium droplet, and a small droplet, and the pixels A1, A7, B4, C1, C7, and D4 are large droplets and the pixels A5, B2, and C5. , D4 are medium drops, and pixels A3, B6, C3, and D6 are printed with small suitability. If the pixels 60 can be distinguished from each other on the recording medium, it can be understood that the area occupied by the large droplets, medium droplets, and small droplets increases according to the amount of the droplets.

  In the liquid ejection head 2 described above, the drive signal is changed in order to change the droplet amount. Therefore, when performing solid printing, the drive signal for driving the displacement elements 50 around each displacement element 50 is the same liquid. Since the drive signal for discharging the droplet amount is not limited, the situation of the crosstalk is changed, and the tendency of the discharge characteristic is changed even for the droplet discharged from the same discharge hole 8, so that the pixel 60 belonging to the same pixel column varies. The trend changes and the lines become inconspicuous. Specifically, even if the most suitable pixel B4 tends to be printed larger than the average, the medium drop pixel B2 and the small drop pixel B6 do not always have such a tendency. Since these boundaries are mixed, it is difficult to recognize the boundary as a streak.

In order to achieve such an arrangement, it is necessary that the amount of droplets can be set in three or more stages. For example, in the liquid ejection head 2, if the pulse width is adjusted to eject 3 pL small droplets and 6 pL medium droplets, 2 pulses are ejected, 2 droplets are ejected, and 13 pL large droplets are obtained. Depending on how the liquid wets and spreads, solid printing can be performed so as to cover a certain area of the recording medium. This is different from what is schematically shown in FIG. 6A, in which printing can be performed so that the pixels 50 overlap and there is no unprinted portion. In this case, if each droplet is printed alone on the recording medium, its diameter becomes 36 μm, 48 μm, or 66 μm.

  It should be noted that the pixel 60 at the extreme end of the area where solid printing is performed may be printed with a droplet amount different from the above-described solid printing conditions so that the adjacent pixel 60 is not printed or gradation is expressed. As a result, the above-described condition of the droplet amount is not always satisfied. However, when viewed from the pixel 60 at the end, the pixel 60 adjacent to the side on which solid printing is performed is made to satisfy the condition of the droplet amount.

  In FIG. 6, the relationship between the droplet amounts of the respective pixels 60 is as follows. When six pixels adjacent to the pixel B4 are arranged in order so as to rotate when viewed from the pixel B4, the amount of droplets becomes B2, C3, C5, B6, A5, A3, and B2 (return to the beginning). In this case, medium drops and small drops are alternately repeated. In this way, the distribution of the surrounding droplet amount is more easily averaged than when there is an array in which the droplet amount continuously increases or decreases, and unintended voids (non-printing range) and / or occur. It can suppress that the magnitude | size of a space | gap becomes large.

  In order to facilitate discharge control, the amount of liquid droplets during solid printing is preferably three stages.

  When gradation printing is performed, the above-described droplet amount may be set as the upper limit, and smaller droplets may be printed. Specifically, the upper eye of the discharge amount (the amount of liquid droplets serving as pixels) is set over the entire area of the recording medium according to the same rules as in FIG. 6A, and the actual discharge amount is less than the upper limit. do it. As for the discharge amount for expressing the intermediate gradation, the discharge amount of all the pixels may be decreased at a rate close to a certain ratio with respect to the upper limit discharge amount. Alternatively, only the discharge amount of a pixel having a large upper limit discharge amount may be reduced. Furthermore, the discharge of pixels with a small upper limit discharge amount may be eliminated. These may be combined. The combination of the latter two is preferable because the number of drive waveforms with different discharge amounts to be prepared is small.

  FIG. 6B shows a printing state according to another embodiment of the present invention. In each of the pixel columns A to D, the pixels 60 are printed at approximately equal intervals, and the pixel columns A to D are aligned approximately at equal intervals. Pixels A1, A5, C3, and C7 are very suitable, pixels B2, B6, and D4 are printed as medium drops, pixels B4, D3, and D6 are printed as small drops, and pixels A3, A7, C1, and C5 are printed as fine drops. . Each pixel 60 is printed with a different droplet amount from the adjacent pixel 60, so that streaks are less likely to occur.

  The printing method as described above is particularly effective when printing is performed using a liquid discharge head in which a plurality of discharge holes are arranged at substantially equal intervals in one direction.

DESCRIPTION OF SYMBOLS 1 ... Printer 2 ... Liquid discharge head 4 ... Flow path member 5 ... Manifold 5a ... Sub manifold 5b ... Opening 6 ... Individual supply flow path 8 ... Discharge hole 9 ... Pressure chamber group 10 ... Pressure chamber 11a, b, c, d ... Pressure chamber row 12 ... Through 15a, b, c, d ... Discharge hole row 21 ... Piezoelectric actuator substrate 21a ... Piezoelectric ceramic layer (vibrating plate)
21b ... Piezoelectric ceramic layer 22-31 ... Plate 32 ... Individual flow path 34 ... Common electrode 35 ... Individual electrode 35a ... Individual electrode body 35b ... Extraction electrode 36 ... Connection electrode 50... Displacement element 60... Pixel A, B, C, D... Virtual lines indicating pixel columns A1 to 7, B2 to 6, C1 to C7, D2 to D6. position)

Claims (5)

A printing method in which liquid is deposited on a recording medium to form and print pixels,
When printing the area with the highest density,
The pixels constitute a plurality of pixel rows in which the pixels are arranged at substantially equal intervals on the recording medium, and landed so that the plurality of pixel rows are arranged at substantially equal intervals,
The pixels belonging to the adjacent pixel columns are landed so as to be shifted in the direction in which the pixels are arranged in the pixel columns,
In addition, the amount of liquid to be one pixel can be set to three or more different amounts, and each pixel excluding the pixel at the extreme end of the high density area on the recording medium. The amount of liquid belongs to the same pixel column as the pixel, the two pixels adjacent to the pixel, and the two pixels adjacent to the pixel belong to the pixel column, and there are two per one pixel column, A printing method, characterized in that the liquid amount is different from any of the pixels adjacent to a total of six pixels including the pixels adjacent to the pixel.   The amount of liquid to be the six pixels adjacent to each pixel excluding the pixel at the extreme end of the high-density region is sequentially changed in the direction of rotation as viewed from the pixel at the center. The printing method according to claim 1, wherein the amount is alternately increased or decreased.   The printing method according to claim 1, wherein the amount of liquid to be the pixel is set in three stages. In printing with gradation, when printing an area with a lower density than an area with the highest density,
The printing method according to any one of claims 1 to 3, wherein the upper limit is the amount of liquid determined in the same manner as in the case of printing the region with the highest density, and the pixel is printed with a smaller amount of liquid. A printing method characterized by the above. A liquid ejection head having a plurality of ejection holes, a transport unit that transports the recording medium to the liquid ejection head, and a control unit that controls the liquid ejection head to perform any one of printings 1 to 4 A recording apparatus comprising:

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