JP2012030440A - Method of wiping liquid discharge head - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of wiping a liquid discharge head preventing variation of liquid discharge after wiping even when the liquid having high wetness with respect to a liquid discharge hole face is used.SOLUTION: The wiping method is used when the liquid 210 having 60° or less of a contact angle with respect to the liquid discharge hole face is discharged by using the liquid discharge head which is composed of a flow passage member including the liquid discharge hole face with a plurality of liquid discharge holes 8 opened thereon and a plurality of liquid pressurizing chambers and a plurality of pressurizing parts. After a pressurizing process of applying positive pressure to the liquid 210 in a flow passage from the plurality of liquid discharge holes 8 to a supply flow passage to discharge the liquid 210 from the plurality of liquid discharge holes 8 is performed, a cleaning process of making a cleaning member 220 abut on the liquid discharge hole face and moving the cleaning member 220 while making it come into contact with the liquid discharge hole face with no pressure applied to the liquid 210 within the flow passage from outside is performed. Then, a process of applying negative pressure to the liquid 210 within the flow passage is performed.

Description

  The present invention relates to a method of wiping a liquid discharge hole surface of a liquid discharge head that discharges droplets, and particularly to a method of wiping when using a liquid having high wettability with respect to the liquid discharge hole surface.

  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.

  When such a liquid discharge head is used, foreign matter or ink adheres to the surface where the ink discharge holes are opened, and the droplets are no longer discharged, or the speed and amount of the droplets change. There was a case. In such a case, it is known to wipe the surface of the ink discharge hole (see, for example, Patent Document 1).

JP 2002-234172 A

  When a liquid having low wettability with respect to the liquid discharge hole surface is used, even if the discharge is performed after wiping as described in Patent Document 1, it is difficult to cause a problem in the printing state. However, when a liquid having high wettability with respect to the liquid discharge hole surface is discharged, there is a case where the printing state is poor after wiping, although foreign matter and ink are not attached to the liquid discharge hole surface.

  Accordingly, an object of the present invention is to provide a liquid ejection head wiping method in which liquid ejection variation hardly occurs after wiping even when a liquid having high wettability with respect to the liquid ejection hole surface is used. It is in.

The liquid ejection head wiping method of the present invention includes a flow path member including a liquid ejection hole surface in which a plurality of liquid ejection holes are open and a plurality of liquid pressurization chambers connected to the plurality of liquid ejection holes, respectively. A wiping method associated with discharging a liquid having a contact angle with respect to the liquid discharge hole surface of 60 degrees or less in a liquid discharge head having a plurality of pressurizing units that pressurize each of the plurality of liquid pressurizing chambers, A pressurizing step of applying a positive pressure to the liquid in the flow path from the plurality of liquid ejection holes to the plurality of liquid pressurizing chambers to eject the liquid from the plurality of liquid ejection holes; In a state where no pressure is applied to the liquid in the flow path from the outside, a cleaning member is applied to the surface of the liquid discharge hole and moved while contacting the liquid, and after the cleaning process, the liquid in the flow path is Negative pressure Characterized by comprising the step of adding.

  It is preferable to use a liquid discharge hole having an opening diameter of 18 to 30 μm.

  According to the wiping method for a liquid ejection head of the present invention, it is possible to reduce variations in liquid ejection after wiping.

1 is a schematic configuration diagram of a printer that is a recording apparatus according to an embodiment of the present invention. (A) is a top view of the 1st flow path member and piezoelectric actuator which comprise the liquid discharge head of FIG. 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. It is a schematic diagram explaining a water head difference. (A)-(c) is a schematic diagram of the cross section when wiping is performed by methods other than the wiping of this invention, when the liquid with low wettability with respect to the liquid discharge hole surface is used, (d) (F) is a schematic diagram of a cross section when wiping is performed by a method other than the wiping of the present invention when a liquid having high wettability with respect to the liquid discharge hole surface is used. (A)-(e) is a schematic diagram of the cross section when the wiping method of this invention is performed.

  FIG. 1 is a schematic configuration diagram of a color ink jet printer which is a recording apparatus including a liquid discharge head 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. This long direction is sometimes called the longitudinal direction.

  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 head body 13 at the lower end. The lower surface of the head body 13 is a liquid discharge hole surface 4a provided with a large number of liquid discharge holes 8 for discharging liquid (see FIGS. 4, 5 and 6).

  Liquid droplets (ink) of the same color are ejected from the liquid ejection holes 8 provided in one liquid ejection head 2. Each liquid discharge head 2 is supplied with liquid from an external liquid tank (not shown). The liquid discharge hole 8 of each liquid discharge head 2 is opened in the liquid discharge hole surface 4a, and is in one direction (a direction parallel to the print paper P and perpendicular to the transport direction of the print paper P, and the longitudinal direction of the liquid discharge head 2). (Direction) at equal intervals, it is possible to print without gaps in one 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 ejection head 2 is disposed with a slight gap between the lower surface of the head 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 head main 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 head main body 13 constituting the liquid discharge head of the present invention will be described. FIG. 2 is a top view showing the 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 head main body 13. FIG. 4 is an enlarged perspective view of the same position as in FIG. 3, in which some of the flow paths are omitted so that the position of the liquid discharge holes 8 can be easily understood. 3 and 4, for easy understanding of the drawings, a liquid pressurizing chamber 10 (liquid pressurizing chamber group 9), a squeeze 12 and a liquid discharge hole which are to be drawn by broken lines below the piezoelectric actuator unit 21 are shown. 8 is drawn with a solid line. FIG. 5 is a longitudinal sectional view taken along line VV in FIG.

The head body 13 includes a flat plate-like flow path member 4 and a piezoelectric actuator unit 21 that is an actuator unit on the flow path member 4. The piezoelectric actuator unit 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. Further, two piezoelectric actuator units 21 are arranged on the flow path member 4 as a whole in a zigzag manner, two along each of two virtual straight lines parallel to the longitudinal direction of the flow path member 4. Yes. The oblique sides of the piezoelectric actuator units 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 units 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 units 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 unit 21 and is disposed so as to intersect with the longitudinal direction of the flow path member 4. In a region sandwiched between two piezoelectric actuator units 21, one manifold 5 is shared by adjacent piezoelectric actuator units 21, and the sub-manifold 5 a branches off from both sides of the manifold 5. These sub-manifolds 5 a extend in the longitudinal direction of the head main body 13 adjacent to each other in regions facing the piezoelectric actuator units 21 inside the flow path member 4.

The flow path member 4 has four liquid pressurizing chamber groups 9 in which a plurality of liquid pressurizing chambers 10 are formed in a matrix (that is, two-dimensionally and regularly). The liquid pressurizing chamber 10 is a hollow region having a substantially rhombic planar shape with rounded corners. The liquid pressurizing chamber 10 is formed so as to open on the upper surface of the flow path member 4. These liquid pressurizing chambers 10 are arranged over almost the entire surface of the upper surface of the flow path member 4 facing the piezoelectric actuator unit 21. Accordingly, each liquid pressurizing chamber group 9 formed by these liquid pressurizing chambers 10 occupies a region having almost the same size and shape as the piezoelectric actuator unit 21. Further, the opening of each liquid pressurizing chamber 10 is closed by adhering the piezoelectric actuator unit 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 liquid pressurizing chambers 10 connected to 5a constitute a row of liquid 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 short direction. Yes. Two rows of liquid pressurizing chambers 10 connected to the sub-manifold 5a are arranged on both sides of the sub-manifold 5a.

  As a whole, the liquid pressurizing chambers 10 connected from the manifold 5 constitute rows of the liquid pressurizing chambers 10 arranged in the longitudinal direction of the flow path member 4 at equal intervals, and the rows are 16 rows parallel to each other in the short direction. It is arranged. The number of liquid pressurizing chambers 10 included in each liquid 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. ing. The liquid 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, when the liquid discharge hole 8 is projected so as to be orthogonal to a virtual straight line parallel to the longitudinal direction of the flow path member 4, each sub-manifold 5a is connected to the range R of the virtual straight line shown in FIG. Two liquid discharge holes 8, that is, a total of 16 liquid discharge holes 8 are equally spaced at 600 dpi. Moreover, the individual flow paths 32 are connected to the sub manifolds 5a at intervals corresponding to 150 dpi on average. This is because the individual flow paths 32 connected to the sub-manifolds 5a are not always connected at equal intervals when the 600 dpi liquid discharge holes 8 are divided and connected to the four sub-manifolds 5a. This means that 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 extending direction of 5a, that is, the main scanning direction.

  Individual electrodes 35 to be described later are formed at positions facing the liquid pressurizing chambers 10 on the upper surface of the piezoelectric actuator unit 21. The individual electrode 35 is slightly smaller than the liquid pressurizing chamber 10, has a shape substantially similar to the liquid pressurizing chamber 10, and fits in a region facing the liquid pressurizing chamber 10 on the upper surface of the piezoelectric actuator unit 21. Is arranged.

  A large number of liquid discharge holes 8 are formed in the liquid discharge surface on the lower surface of the flow path member 4. These liquid discharge holes 8 are arranged at a position avoiding a region facing the sub-manifold 5 a arranged on the lower surface side of the flow path member 4. Further, these liquid discharge holes 8 are arranged in a region facing the piezoelectric actuator unit 21 on the lower surface side of the flow path member 4. These liquid discharge hole groups 7 occupy an area having almost the same size and shape as the piezoelectric actuator unit 21, and the liquid discharge holes 8 are made to drop liquid by displacing the displacement element 50 of the corresponding piezoelectric actuator unit 21. Can be discharged. The arrangement of the liquid discharge holes 8 will be described in detail later. The liquid 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 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 head main body 13 has a liquid pressurizing chamber 10 on the upper surface of the flow path member 4, the sub-manifold 5a on the inner lower surface side, and the liquid discharge holes 8 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 liquid discharge hole 8 are connected via the liquid pressurizing chamber 10. The lower surface of the flow path member 4 is a liquid discharge hole surface 4a in which the liquid discharge holes 8 are opened.

  The holes formed in each plate will be described. These holes include the following. First, the liquid pressurizing chamber 10 formed in the cavity plate 22. Second, there is a communication hole that forms a flow path that connects from one end of the liquid 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 liquid 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 that constitutes a flow channel that communicates from the other end of the liquid pressurizing chamber 10 to the liquid discharge hole 8, and this communication hole is referred to as a descender (partial flow channel) in the following description. . The descender is formed on each plate from the base plate 23 (specifically, the outlet of the liquid pressurizing chamber 10) to the nozzle plate 31 (specifically, the liquid discharge hole 8). Fourthly, there is a communication hole constituting the sub-manifold 5a. The communication holes are formed in the manifold plates 27 to 29.

  Such communication holes are connected to each other to form an individual flow path 32 from the liquid inflow port (the outlet of the submanifold 5a) from the submanifold 5a to the liquid discharge hole 8. The liquid supplied to the sub manifold 5a is discharged from the liquid 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 liquid pressurizing chamber 10 upward. Further, the liquid pressurizing chamber 10 proceeds horizontally along the extending direction of the liquid pressurizing chamber 10 and reaches the other end of the liquid pressurizing chamber 10. While moving little by little in the horizontal direction from there, it proceeds mainly downward and proceeds to the liquid discharge hole 8 opened on the lower surface.

  As shown in FIG. 5, the piezoelectric actuator unit 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 unit 21 is about 40 μm. Each of the piezoelectric ceramic layers 21a and 21b extends so as to straddle the plurality of liquid pressurizing 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 unit 21 includes 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 liquid pressurizing chamber 10 on the upper surface of the piezoelectric actuator unit 21. One end of the individual electrode 35 is drawn out of a region facing the liquid pressurizing chamber 10 to form a connection electrode 36. 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). Although details will be described later, a drive signal (drive voltage) is supplied to the individual electrode 35 from the control unit 100 through the FPC. The drive signal is supplied in a constant cycle in synchronization with the conveyance speed of the print medium P.

  The common electrode 34 is formed over almost the entire surface in the area between the piezoelectric ceramic layer 21a and the piezoelectric ceramic layer 21b. That is, the common electrode 34 extends so as to cover all the liquid pressurizing chambers 10 in the region facing the piezoelectric actuator unit 21. The thickness of the common electrode 34 is about 2 μm. The common electrode 34 is grounded in a region not shown, and is held at the ground potential. In the present embodiment, a surface electrode (not shown) different from the individual electrode 35 is formed on the piezoelectric ceramic layer 21b at a position avoiding the electrode group composed of the individual electrodes 35. The surface electrode is electrically connected to the common electrode 34 through a through-hole formed in the piezoelectric ceramic layer 21b, and is connected to another electrode on the FPC in the same manner as many individual electrodes 35. ing.

  As shown in FIG. 5, the common electrode 34 and the individual electrode 35 are disposed so as to sandwich only the uppermost piezoelectric ceramic layer 21b. A region sandwiched between the individual electrode 35 and the common electrode 34 in the piezoelectric ceramic layer 21b is called an active portion, and the piezoelectric ceramic in that portion is polarized in the thickness direction. In the piezoelectric actuator unit 21 of the present embodiment, only the uppermost piezoelectric ceramic layer 21b includes an active portion, and the piezoelectric ceramic 21a does not include an active portion and functions as a diaphragm. The piezoelectric actuator unit 21 has a so-called unimorph type configuration.

  As will be described later, when a predetermined drive signal is selectively supplied to the individual electrode 35, pressure is applied to the liquid in the liquid pressurizing chamber 10 corresponding to the individual electrode 35. As a result, droplets are discharged from the corresponding liquid discharge ports 8 through the individual flow paths 32. That is, the portion of the piezoelectric actuator unit 21 that faces each liquid pressurizing chamber 10 corresponds to an individual displacement element 50 (actuator) corresponding to each liquid pressurizing chamber 10 and the liquid discharge port 8. That is, in the laminate composed of two piezoelectric ceramic layers, the displacement element 50 having a unit structure as shown in FIG. 5 is provided immediately above the liquid pressurizing chamber 10 for each liquid pressurizing chamber 10. Are formed by a diaphragm 21a, a common electrode 34, a piezoelectric ceramic layer 21b, and individual electrodes 35, and the piezoelectric actuator unit 21 includes a plurality of displacement elements 50. In the present embodiment, the amount of liquid ejected from the liquid ejection port 8 by one ejection operation is about 5 to 7 pL (picoliter).

  A large number of individual electrodes 35 are individually electrically connected to the actuator control means via contacts and wirings on the FPC so that potentials can be individually controlled.

An example of a driving method at the time of liquid ejection of the piezoelectric actuator unit 21 in the present embodiment will be described with respect to a driving voltage (drive signal) supplied to the individual electrode 35. When an electric field is applied to the piezoelectric ceramic layer 21b in the polarization direction by setting the individual electrode 35 to a potential different from that of the common electrode 34, the portion to which the electric field is applied functions as an active portion that is distorted by the piezoelectric 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. In other words, the piezoelectric actuator unit 21 uses the upper piezoelectric ceramic layer 21b (that is, the side away from the liquid pressurizing chamber 10) as a layer including the active portion and the lower side (that is, close to the liquid pressurizing chamber 10). This is a so-called unimorph type configuration in which the piezoelectric ceramic layer 21a on the side) is an inactive layer.
In this configuration, when the individual electrode 35 is set to a predetermined positive or negative potential with respect to the common electrode 34 by the actuator controller 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 liquid pressurizing chamber 10 (unimorph deformation). .

In an actual driving procedure in the present embodiment, the individual electrode 35 is set to a potential higher than the common electrode 34 (hereinafter referred to as a high potential) in advance, and the individual electrode 35 is temporarily set to the same potential as the common electrode 34 every time there is a discharge request. (Hereinafter referred to as a low potential), and then set to a high potential again at a predetermined timing. As a result, the piezoelectric ceramic layers 21a and 21b return to the original shape at the timing when the individual electrode 35 becomes low potential, and the volume of the liquid pressurizing chamber 10 is compared with the initial state (the state where the potentials of both electrodes are different). To increase. At this time, a negative pressure is applied to the liquid pressurizing chamber 10 and the liquid is sucked into the liquid 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 liquid pressurizing chamber 10, and the volume of the liquid pressurizing chamber 10 is reduced so that the inside of the liquid pressurizing chamber 10 Becomes a positive pressure, 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. The ideal pulse width is AL (Acoustic Length), which is the length of time during which the pressure wave propagates from the manifold 5 to the liquid discharge hole 8 in the liquid pressurizing chamber 10. According to this, when the inside of the liquid pressurizing chamber 10 is reversed from the negative pressure state to the positive pressure state, both pressures are combined, and the liquid droplet can be ejected with a stronger pressure.

  When the liquid discharge head 2 as described above is used for printing or the like, foreign matter is clogged in the flow path, or foreign matter or liquid adheres to the liquid discharge hole surface 4a. The discharge speed and the discharge amount may change. In such a case, wiping is performed. Further, when the liquid discharge head 2 is used for the first time, it is necessary to put the liquid into the flow path of the flow path member 4, but the liquid discharge from the liquid discharge hole 8 almost inevitably causes the liquid discharge. Since the liquid is attached to the hole surface 4a, wiping is performed.

  Before explaining the wiping method, the water head difference will be explained. FIG. 6 is a schematic diagram illustrating the water head difference. The external liquid tank 201 is connected to the flow path member 4 (the internal flow path is omitted) having the liquid multiple discharge hole surface 4a in which the liquid discharge holes 8 are opened via the tubes 203a and 203b. Yes. An external tube 207 is connected between the tubes 203a and 203b via a valve 205 that can be opened and closed. The external liquid tank 201 contains the liquid 210, and the liquid level 210 a is the upper surface of the liquid 210 in the external liquid tank 201. The liquid 210 fills the flow path in the flow path member 4 through the tubes 203 a and 203 b, and the liquid 210 has a meniscus 210 b extending inside the liquid discharge hole 8. The external liquid tank 201 is connected to the atmosphere by a pipe 209. Such a meniscus 210b is obtained by subjecting the liquid discharge hole surface 4a to a water repellent treatment with respect to the liquid 210, and becomes easier to stabilize by making the contact angle with respect to the liquid 210 larger than the inner wall of the liquid discharge hole 8. The water repellent treatment may also be performed on a portion of the inner wall of the liquid discharge hole 8 close to the liquid discharge hole surface 4a.

In the liquid discharge head 2 as described above, negative pressure is applied to the liquid in the flow path when discharging. When a positive pressure is applied, the liquid leaks out from the liquid discharge hole 8, and when no negative force is applied or when the negative pressure is low, the shape of the meniscus 210b is not stable. Conversely, when the negative pressure is large, the meniscus 210b is drawn into the flow path member 4, and the shape is not stable. In order to obtain an appropriate negative pressure, the liquid surface 210a is lowered with respect to the liquid discharge hole surface 4a, and the difference in height from the liquid discharge hole surface 4a to the liquid surface 210a is referred to as a water head difference. . The water head difference at the time of discharging is set to a negative value so as to apply a negative pressure. In the liquid discharge head described above, the water head difference during discharge is -20 to -120 mm. It is important to apply a negative pressure to the meniscus. Therefore, the meniscus 210b may be maintained by applying a pressure corresponding to the water head difference from the outside.

  Further, the supply of the liquid to the liquid discharge head 2 is performed as follows. The liquid 210 flows from the external tube 207 to the tube 203b through the valve 205, and the liquid 210 is put into the external liquid tank 201 by a pump or the like. The liquid 210 is allowed to flow from the external tube 207 to the tube 203a through the valve 205, and the liquid 210 is put into the flow path of the flow path member 4. In order to apply a positive pressure to the liquid 210 in the flow path, the liquid 205 is allowed to flow from the external tube 207 to the tube 203a and the liquid is sent from the external tube 207 by a pump or the like, or the valve 205 is transferred from the tube 203b to the tube 203b. The liquid 210 may flow to 203a, and the water head difference may be made positive. When discharging, the valve 205 is allowed to flow from the tube 203b to the tube 203a, and a negative pressure is applied by setting the water head difference within a certain range of negative values. The liquid 210 may flow from the tube 203a to the tube 203a, and a negative pressure such as a pump may be used.

  When wiping is performed, cleaning is performed by pressing a cleaning member 220 made of an elastic material such as resin or rubber, which deforms to some extent, against the liquid multiple discharge hole surface 4a and moving it in contact therewith. At this time, the range in which the portion where the cleaning member 220 and the liquid ejection surface 4 a are in contact with is moved larger than the entire area where the liquid ejection hole 8 is opened, so that foreign matter or The liquid can hardly remain.

  First, a wiping method other than the wiping method of the present invention in the case where a liquid having a low wettability with respect to the liquid discharge surface 4a and a contact angle with respect to the liquid discharge surface 4a of greater than 60 degrees is used will be described. FIGS. 7A to 7C are schematic views of each step of the wiping method. In FIG. 7A, a positive pressure is applied to the liquid 210 in the flow path member 4, and the liquid 210 overflows from the liquid discharge hole 8. In the figure, it only spreads around the liquid discharge hole 8, but actually, it protrudes from the liquid discharge head 2 to the outside. At this time, the process may be performed with a cover attached so that the bottom of the liquid discharge head 2 and the like are not wetted. Thereafter, when a water head difference is applied, the liquid 210 is drawn into the liquid discharge hole 8 as shown in FIG. However, the liquid 210 remains in a portion (not shown) such as between the opening of the liquid discharge hole 8 on the liquid discharge hole surface 4a and the opening of the adjacent liquid discharge hole 8. Thereafter, the cleaning member 220 is pressed against the liquid discharge hole surface 4a and is moved while being brought into contact, as shown in FIG. 7C. In this way, wiping is performed.

  If the same process is performed when a liquid having a high wettability with respect to the liquid discharge surface 4a and a contact angle with respect to the liquid discharge surface 4a of 60 degrees or less is used, foreign matter or liquid on the liquid discharge hole surface 4a is removed. Even though 210 is removed, the liquid discharge variation after wiping may increase. This is considered to be due to the cause described with reference to FIGS.

  In FIG. 7D, a positive pressure is applied to the liquid 210 in the flow path member 4, and the liquid 210 overflows from the liquid discharge hole 8. After that, when the water head difference is applied, the liquid 210 is drawn into the liquid discharge hole 8 as shown in FIG. 7E. However, since the wettability of the liquid 210 is high, around the liquid discharge hole 8 Liquid 210 is left. Then, the remaining liquid 210 causes the liquid 210 to cover the periphery of the liquid discharge hole 8 (part A in the figure), and the formed meniscus is a liquid discharge compared to FIG. 7B. It will be deeply depressed in the hole 8. After that, when the cleaning member 220 is pressed against the liquid discharge hole surface 4a and moved while being in contact with each other as shown in FIG. 7 (f), some of the liquid discharge holes 8 out of the many liquid discharge holes 8 are discharged. In the hole 8, the air immediately below the meniscus that has fallen deeply is entrained as bubbles. The reason why the liquid discharge variation becomes large is considered to be caused by the bubble 215 entering the flow path.

  The wiping method according to an embodiment of the present invention reduces the discharge variation when using a liquid having a contact angle with respect to the liquid discharge surface 4a of 60 degrees or less, which is considered to be caused by the bubbles 215 described above. Do as follows. 8A to 8E are cross-sectional views of the process.

  First, a pressurizing step of applying a positive pressure to the liquid in the flow path in the flow path member 4 is performed. As a result, as shown in FIG. 8A, the liquid 210 overflows from the liquid discharge hole 8. After the pressurizing step, as shown in FIG. 8B, the liquid 210 is brought into a state where no pressure is applied. This can be done by closing the valve 205, or allowing the liquid 205 to flow from the external tube 207 to the tube 203a, and stopping the supply of the liquid 210 by the pump from the outside. Further, the water head difference may be substantially 0 mm. Deviation from 0 mm is acceptable if it is about ± 5 mm, although it depends on the structure of the liquid ejection head 2. Specifically, the positive pressure may be set in a range in which the liquid does not continue to overflow the liquid discharge hole surface 4a, and the negative pressure is set so that a deep meniscus as shown in FIG. 7 (e) is not formed. do it. Deep here means deeper than the meniscus when the liquid is discharged. In such a state, as shown in FIG. 8C, the cleaning member 220 is pressed against the liquid discharge hole surface 4a and moved while being in contact with the cleaning member 220, whereby the cleaning process is performed. After the cleaning process, the liquid 210 enters the liquid discharge hole 8 as shown in FIG. In the drawing, the surface of the liquid 210 is shown to be a flat surface, but depending on the surface tension of the liquid 210 or the wetness of the liquid 210 with respect to the flow path member 4, the liquid 210 has a concave or convex shape. Even if it is concave, it does not have to be drawn into the flow path member 4, and even if it becomes convex, it does not have to wet and spread to the left and right of the liquid discharge hole 8. Thereafter, a negative pressure is applied so that discharge can be performed, and a meniscus is formed as shown in FIG.

  The liquid discharge heads shown in FIGS. 2 to 5 were manufactured and printing variations were evaluated. First, the piezoelectric material used for the piezoelectric ceramic layer was lead zirconate titanate (PZT), and a slurry using PZT was prepared. From this slurry, a roll coater method was adopted as a forming method to prepare a green sheet.

  Next, through holes having a diameter of 100 μm were formed in the green sheet by die punching. Then, the electrode pattern used as a common electrode was formed in the surface of each green sheet by the screen-printing method using the conductor paste containing an Ag-Pd alloy.

  Further, a via conductor paste is prepared by adding 30% by volume of piezoelectric powder as a filler to the Ag—Pd alloy, and this is filled in the through-hole formed in the green sheet by screen printing. A via electrode was formed.

  Next, two layers of this green sheet were laminated to produce a laminated molded body having a common electrode and a via electrode inside. Thereafter, this laminated molded body was fired at a temperature of 1020 ° C. to produce a piezoelectric sintered body. The obtained piezoelectric sintered body was about 20 μm per layer.

  On the surface of this piezoelectric sintered body, individual electrodes are formed in a matrix by screen printing using a conductor paste containing a main component Au so as to be opposed to the common electrode of the portion constituting the displacement element. A piezoelectric actuator unit was manufactured by forming individual electrodes by heat treatment at ℃.

  Table 1 shows the test results when using a liquid having a contact angle of 40 degrees with respect to the liquid discharge hole surface 4a. The evaluation was performed after wiping was performed under conditions where printing of 600 dpi in length and breadth was possible, a straight line was printed at an interval of 300 dpi, and the variation (standard deviation) between the straight lines was measured, and the unit was μm. is there. In the wiping method other than the wiping method of the present invention in which the water head difference in the cleaning process is the same as the water head difference at the time of discharge, the deviation is larger than 5 μm and the printing accuracy may be deteriorated. In the wiping method of the present invention in which the valve was closed and no pressure was applied, the deviation was 5 μm or less, and good printing results were obtained. As the diameter of the liquid discharge hole 8 increases, the variation tends to increase. This is presumably because the larger the diameter, the deeper the meniscus tends to be and the air bubbles are more likely to be entrained, and a stable printing is possible with a diameter of 18 to 30 μm.

Table 2 shows the results of performing the same test using a liquid discharge head having a liquid discharge hole diameter of 20 μm and changing the liquid to one having a different contact angle. In the case of a liquid having a liquid contact angle with respect to the liquid discharge hole surface 4a lower than 60 degrees, in the wiping method other than the wiping method of the present invention in which the water head difference in the cleaning process is the same as the water head difference in discharging, the deviation is more than 5 μm. While the printing accuracy may be increased, the wiping method of the present invention in which the valve is closed and no pressure is applied in the cleaning process has a deviation of 5 μm or less, and a good printing result is obtained. Obtained.

DESCRIPTION OF SYMBOLS 1 ... Printer 2 ... Liquid discharge head 4 ... Flow path member 4a ... Liquid discharge hole surface 5 ... Manifold 5a ... Sub-manifold 5b ... Manifold opening 6 ... Individual Supply flow path 8 ... Liquid discharge hole 9 ... Liquid pressurization chamber group 10 ... Liquid pressurization chamber 11a, b, c, d ... Liquid pressurization chamber row 12 ... Squeeze 13 ... Liquid discharge head main body 15a, b, c, d ... Liquid discharge hole row 16 ... Liquid discharge hole opening area 21 ... Piezoelectric actuator unit 21a ... Piezoelectric ceramic layer (vibrating plate)
21b ... Piezoelectric ceramic layer 22-31 ... Plate 32 ... Individual flow path 34 ... Common electrode 35 ... Individual electrode 36 ... Connection electrode 50 ... Pressure part (displacement element)
201 ... External liquid tank 203a, 203b ... Tube 205 ... Valve 207 ... External tube 209 ... Pipe 210 ... Liquid 210a ... Liquid level in the external liquid tank 210b ... Meniscus (liquid level in the liquid discharge hole)
215 ... Bubble 220 ... Cleaning member

Claims (2)

  A flow path member including a liquid discharge hole surface in which a plurality of liquid discharge holes are open and a plurality of liquid pressurization chambers connected to the plurality of liquid discharge holes, respectively, and pressurizing the plurality of liquid pressurization chambers, respectively. A wiping method for discharging a liquid having a contact angle with respect to the surface of the liquid discharge hole of 60 degrees or less in a liquid discharge head having a plurality of pressurizing units, wherein the liquid is discharged from the plurality of liquid discharge holes. A pressurizing step of applying a positive pressure to the liquid in the flow path to the pressurizing chamber to discharge the liquid from the plurality of liquid discharge holes, and applying a pressure from the outside to the liquid in the flow path after the pressurizing step; A cleaning process in which a cleaning member is applied to the surface of the liquid discharge hole in contact with the liquid discharge hole and moved while being in contact therewith, and a negative pressure is applied to the liquid in the flow path after the cleaning process. Liquid characterized by Wiping method of the discharge head.   2. The liquid ejection head wiping method according to claim 1, wherein the liquid ejection hole has an opening diameter of 18 to 30 [mu] m.

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