JP2011110730A - Liquid delivering head, liquid delivering apparatus using the same, and recording apparatus - Google Patents

Abstract

A liquid discharge head that is not easily affected by standing waves generated in a common flow path, a liquid discharge apparatus using the liquid discharge head, and a recording apparatus are provided.
A common flow path 205a that is long in one direction and closed at both ends, a liquid supply path 205c that is connected to a portion other than both ends of the common flow path 205a, and a plurality of liquid additions respectively in the middle of the common flow path. A liquid discharge head having a plurality of liquid discharge holes connected via the pressure chambers 210 and a plurality of pressurization units that pressurize the liquid in the plurality of liquid pressurization chambers 210, respectively, A liquid discharge head is used in which the cross-sectional area of both end portions is smaller than the cross-sectional area of the central portion.
[Selection] Figure 6

Description

  The present invention relates to a liquid discharge head that discharges droplets, a liquid discharge apparatus that uses the liquid discharge head, and a recording apparatus that prints an image using the liquid discharge head.

  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 liquid discharge holes for discharging the droplets formed in the liquid discharge head must be increased. There is a need to.

  Therefore, a liquid discharge head is provided so as to cover the liquid pressurization chamber and a flow path member having a liquid discharge hole connecting the manifold (common flow path) and the manifold via a plurality of liquid pressurization chambers, respectively. A structure in which an actuator unit having a plurality of displacement elements is laminated is known (for example, see Patent Document 1). In this liquid ejection head, the liquid pressurizing chambers connected to the plurality of liquid ejection holes are arranged in a matrix, and the displacement elements of the actuator unit provided so as to cover the chambers are displaced so that each liquid ejection chamber Ink is ejected and printing is possible at a resolution of 600 dpi in the main scanning direction.

JP 2003-305852 A

  However, in the liquid ejection head described in Patent Document 1, for example, an attempt is made to increase the driving frequency for driving the displacement element, to increase the displacement amount of the displacement element, or to connect to the common flow path in order to further increase the resolution. If the interval between the liquid pressurizing chambers is narrowed or the cross-sectional area of the common flow path is reduced in order to reduce the size, the pressure applied to the liquid in the liquid pressurizing chamber is applied to the common flow path. In some cases, the liquid in the common flow path resonates and a standing wave is generated in the common flow path.

  When a standing wave occurs, the pressure is transmitted to the liquid pressurizing chamber, and the discharge characteristics may fluctuate. In particular, fluctuations in the ejection characteristics caused by the influence of standing waves may be periodic, and there is a possibility that the image when used for printing will be periodically affected and noticeable.

  Accordingly, an object of the present invention is to provide a liquid discharge head that is not easily affected by standing waves generated in a common flow path, a liquid discharge apparatus using the liquid discharge head, and a recording apparatus.

  The liquid discharge head according to the present invention includes a common channel that is long in one direction and closed at both ends, a liquid supply channel that is connected to a portion other than both ends of the common channel, and a plurality of channels in the middle of the common channel. A liquid discharge head having a plurality of liquid discharge holes connected through the liquid pressurization chambers and a plurality of pressurization units that pressurize the liquid in the plurality of liquid pressurization chambers, respectively, The cross-sectional area of the both end parts is smaller than the cross-sectional area of the center part.

  When the length of the common flow path is L (mm), the average cross-sectional area from both ends of the common flow path to the portion of length L / 4 is the central length L of the common flow path. It is preferable that it is not more than half of the average cross-sectional area of the portion of / 2.

  It is preferable that the change in the cross-sectional area of the common channel is smooth.

  The liquid discharge apparatus of the present invention is a liquid discharge apparatus including the liquid discharge head and a control unit that controls driving of the plurality of pressurizing units, and the control unit includes the common flow path. Control is performed so that the pressurization unit is driven with a driving cycle of 0.53 times or less of a vibration cycle in which the liquid in the primary resonance vibrates.

  Furthermore, the recording apparatus of the present invention includes the liquid ejecting apparatus and a transport unit that transports a recording medium to the liquid ejecting apparatus.

  According to the liquid ejection head of the present invention, a common flow path that is long in one direction and closed at both ends, a liquid supply path that is connected to a portion other than both ends of the common flow path, and in the middle of the common flow path, A liquid discharge head having a plurality of liquid discharge holes connected via a plurality of liquid pressurization chambers, and a plurality of pressurization units that pressurize the liquid in the plurality of liquid pressurization chambers, respectively, When the cross-sectional area of the both end portions of the flow path is smaller than the cross-sectional area of the central part, the frequency of the standing wave generated in the liquid in the common flow path becomes high and the standing wave is hardly generated.

  When the length of the common flow path is L (mm), the average cross-sectional area from both ends of the common flow path to the portion of length L / 4 is the central length L of the common flow path. When the ratio is less than half of the average cross-sectional area of the / 2 portion, the frequency of the standing wave generated in the liquid in the common flow path becomes higher, and the standing wave is less likely to be generated.

  When the change in the cross-sectional area of the common flow path is smooth, it is difficult for large fluctuations to occur in the discharge characteristics of the liquid discharge elements connected before and after the portion where the cross-sectional area changes rapidly.

  The liquid discharge apparatus of the present invention is a liquid discharge apparatus including the liquid discharge head and a control unit that controls driving of the plurality of pressurizing units, and the control unit includes the common flow path. By controlling so that the pressurizing unit is driven at a driving cycle of 0.53 times or less of the vibration cycle in which the liquid in the primary resonance vibrates, the driving cycle is such that both ends of the common channel are antinodes. Thus, the standing wave has the lowest frequency and is sufficiently lower than the vibration period of the primary resonance vibration that is most likely to occur, and the standing wave is difficult to be excited.

  Furthermore, the recording apparatus of the present invention includes the liquid ejecting apparatus and a transport unit that transports the recording medium to the liquid ejecting apparatus. As a result, the recording accuracy can be increased.

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 head body that constitutes the liquid ejection head of FIG. 1. 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) are samples No. 6 is a graph showing a discharge speed from a nozzle connected to one sub-manifold in the liquid discharge heads 1 and 2; (A) is the schematic diagram which showed the form of the periphery of a common flow path. (B) And (c) is the schematic diagram which showed the standing wave which arises in the common flow path shown to (a). (A)-(f) is the schematic diagram which showed the shape of the common flow path of a liquid discharge head. (A)-(e) is the schematic diagram which showed the shape of the common flow path of a liquid discharge head.

  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.

  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. A number of liquid ejection holes 8 for ejecting liquid are provided on the lower surface of the head body 13 (see FIG. 4).

  Liquid droplets (ink) of the same color are ejected from the liquid ejection holes 8 provided in one liquid ejection head 2. Since the liquid 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), Printing can be performed 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 plan view showing the head main body 13 shown in FIG. FIG. 3 is an enlarged plan view of a region surrounded by a one-dot chain line in FIG. 2 and is a part of the head main body 13. In both cases, some of the flow paths are omitted. 2 and 3, in order to make the drawings easier to understand, the manifold 5 and the liquid pressurizing chamber which are located below the piezoelectric actuator unit 21 and which should be drawn with a broken line because of the internal structure of the flow path member 4. 10, the squeeze 12 and the liquid discharge hole 8 are drawn by solid lines. 4 is a longitudinal sectional view taken along the 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 rectangular shape, and is disposed on the upper surface of the flow path member 4 so that a pair of parallel opposing sides of the rectangle are parallel to the longitudinal direction of the flow path member 4.

  A manifold 5 that is a part of the liquid flow path is formed inside the flow path member 4. The four manifolds 5 extend along the longitudinal direction of the flow path member 4, and a liquid supply path 5 c that connects the sub-manifold 5 a having an elongated shape and the opening 5 b of the manifold 5 on the upper surface of the flow path member 4 from the sub-manifold 5 a. Including. The manifold 5 is supplied with liquid from a liquid tank (not shown) through the opening 5b.

  Although details will be described later, both ends of the sub-manifold (common flow path) 5a are closed, and the liquid supply path 5c is connected to portions other than both ends of the sub-manifold (common flow path) 5a. The cross-sectional area of both ends of the flow path) 5a is smaller than the cross-sectional area of the central part. The cross-sectional area is changed by changing the depth of the sub-manifold (common flow path) 5a. The cross-sectional area of the liquid supply path 5c is smaller than the cross-sectional area of the end of the sub-manifold (common flow path) 5a.

  The flow path member 4 has a plurality of liquid pressurizing chambers 10 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. Therefore, each liquid pressurizing chamber group formed by these liquid pressurizing chambers 10 occupies an area 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. 2, the sub-manifolds 5 a are arranged in four rows arranged in parallel to each other in the short direction of the flow path member 4. The liquid pressurizing chambers 10 connected to the sub-manifolds 5a through the squeezing 12 constitute a row of liquid pressurizing chambers 10 arranged in the longitudinal direction of the flow path member 4 at equal intervals, and the row is a short direction. Are arranged in four rows parallel to each other. Two rows of liquid pressurizing chambers 10 connected to the sub-manifold 5a through the squeezing 12 are arranged on both sides of the sub-manifold 5a.

  As a whole, the liquid pressurizing chambers 10 connected to the sub-manifold 5a constitute a row of liquid pressurizing chambers 10 arranged at equal intervals in the longitudinal direction of the flow path member 4, and the rows are parallel to each other in the short direction. It is arranged in a column. 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. This is because, when projected so as to be orthogonal to a virtual straight line parallel to the longitudinal direction shown in FIG. 3, four liquid discharge holes 8 connected to each sub-manifold 5a in the range of R of the virtual straight line, that is, a total of 16 That is, the liquid discharge holes 8 are equally spaced at 600 dpi. This means that the liquid pressurizing chamber 10 is connected to one sub-manifold 5a at an interval of 150 dpi on the average in the longitudinal direction via the throttle 12. In FIG. 3, the liquid ejection holes 8 that are not projected onto the range R of the imaginary straight line and the flow paths that connect the liquid ejection holes 8 to the liquid pressurizing chamber are omitted.

  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 holes occupy an area having almost the same size and shape as the piezoelectric actuator unit 21 as one group, and the liquid discharge holes 8 are displaced by displacing the displacement elements 50 of the corresponding piezoelectric actuator units 21. Droplets can be discharged from 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 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. Depending on the position of the sub-manifold 5a, the manifold plate 29 may have a portion where no hole is formed, whereby the cross-sectional area of the sub-manifold 5a is changed.

  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, silver-palladium 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 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 referred to as an active portion, and the piezoelectric ceramic in that portion is polarized. 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 as pressurizing portions. 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.

  In the piezoelectric actuator unit 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. 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 the actual driving procedure in this 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.

  In gradation printing, gradation expression is performed by the number of droplets ejected continuously from the liquid ejection holes 8, that is, the droplet amount (volume) adjusted by the number of droplet ejections. For this reason, the number of droplet discharges corresponding to the specified gradation expression is continuously performed from the liquid discharge hole 8 corresponding to the specified dot region. In general, when liquid ejection is performed continuously, it is preferable that the interval between pulses supplied to eject liquid droplets is AL. As a result, the period of the residual pressure wave of the pressure generated when discharging the previously discharged liquid droplet coincides with the pressure wave of the pressure generated when discharging the liquid droplet discharged later, and these are superimposed. Thus, the pressure for discharging the droplet can be amplified.

  The control unit 100 can print an image by repeatedly sending such a drive signal to each displacement element 50 of the liquid ejection head 2. Each displacement element 50 is sent at a constant cycle, and a drive signal when ejecting a droplet and a non-ejection drive signal when not ejecting a droplet (including a case where no signal is sent) are sent. Is called a drive cycle, and its frequency is called a drive frequency. For example, when the entire surface is printed with the same color, each liquid ejection element 50 is driven every driving cycle. Note that the actual drive signal reduces the residual vibration remaining in the liquid in the individual flow channel 32 after the strike signal, in addition to the ejection signal of one droplet by the one strike signal described above. In some cases, a cancel signal is added, or a plurality of strike signals are included so that a plurality of liquid droplets are landed at one place for gradation expression. Of course, ejection by pushing may be performed. In any case, when discharge is continuously performed from the liquid discharge element 50, a drive signal is applied every drive cycle.

  In such a printer 1, when the displacement element 50, which is a pressurizing unit, is driven, a droplet is ejected from the liquid ejection hole 8. At this time, the pressure of the liquid is reduced from the liquid pressurizing chamber 10. Then, it is also transmitted to the sub-manifold 5a which is a common flow path. That is, in the common flow path, pressure is transmitted from the plurality of pressurization units connected to the common flow path for each driving cycle, and thus standing waves may be generated by the pressure.

  FIG. 5A shows the velocity of the droplets ejected at the first and tenth times from the stopped state. As the driving is repeated, the ejection speed of the liquid droplets ejected from the respective liquid ejection holes varies, and the tendency of the ejection speed differs between the first ejection and the tenth ejection. This is due to the influence of the standing wave pressure generated in the common channel through the squeezing. From the 10th time onward, almost the same tendency of the discharge speed continues, and this distribution is periodic in relation to the position in the common flow path. The distribution of the discharge speed at the tenth time in FIG. 5 (a) has a minimum value at one place and a maximum value at two places, but the discharge speed of the liquid is high if the pressure received from the common flow path is large. This distribution is not a simple one, and this distribution is considered to be a result of the occurrence of a standing wave of the first-order (fundamental) resonance described later.

  Here, standing waves generated in the common flow path will be described. FIG. 6A is a schematic diagram of the common channel 205a and the surrounding structure.

  Both ends of the common flow path 205a are closed and connected to the liquid supply path 205c at the center. The cross-sectional area of the liquid supply path 205c is smaller than the cross-sectional area of the common flow path 205a. Since the cross-sectional area of the liquid supply path 205c is small, the pressure of the liquid in the common flow path 205a is easily transmitted to the liquid supply path 205, and the position where the liquid supply path 205c is connected is within the common flow path 205a. Does not affect the standing wave of Further, since both ends of the common flow path 205a are closed, it becomes an antinode of the standing wave where the fluctuation of the pressure vibration is maximized. The liquid supply path 205c is preferably not provided at both ends so as not to affect the state where both ends become abdomen, and is preferably provided in the range of L / 2 in the center of the common flow path 205a.

Hereinafter, the length of the common flow path 205a will be described as Lmm (hereinafter, the unit mm may be omitted). The common flow path 205a does not need to be linear, may be curved, and may have a corner that bends in the middle. In these cases, the length L of the common flow path 205a is the total length of the line segments that can connect the area centers of the cross sections. The cross-sectional area of the common flow path 205a is constant and is Bmm ² (hereinafter, the unit mm ² may be omitted).

  A plurality of liquid pressurizing chambers 10 are connected to each other through a squeezing 212 in the common flow path 205a over the length direction. Although not particularly limited, the intervals at which the apertures 212 are connected are equal intervals or intervals at which a constant pattern is repeated, such as alternating intervals of 0.1 mm and 0.2 mm. Although not shown, the liquid pressurizing chamber 10 is adjacent to a pressurizing unit that changes its volume, and a flow path that connects the liquid pressurizing chamber 10 to the liquid discharge hole is formed.

  Although not limited to the structure in which the aperture 212 is connected over the entire length L of the common flow path 205a, the structure for suppressing standing waves of the present invention has a range in which the aperture 212 is connected in the common flow path. It is more useful when it is more than half the length L of 205a, and particularly useful when it is connected to the entire length L.

  When the liquid discharge head having such a common flow path 205a is driven, the pressure generated from the pressurizing unit as described above is transmitted to the common flow path 205a, and a standing wave may be generated. FIG. 6B is a diagram in which the pressure fluctuation of the standing wave 280a generated by the primary (basic) resonance among the standing waves is schematically superimposed on the common channel 205a. The standing wave 280a has an antinode where the pressure fluctuation becomes maximum at both closed ends of the common flow path 205a, and the pressure fluctuation gradually decreases toward the center of the common flow path 205a. In the center, the pressure fluctuation is zero.

  FIG. 6C is a diagram in which the pressure fluctuation of the standing wave 280b generated by the secondary resonance among the standing waves is schematically superimposed on the common channel 205a. The standing wave 280b has an antinode where the pressure fluctuation becomes maximum at both closed ends and the center of the common flow path 205a, and the pressure fluctuation is 0 at L / 4 and 3L / 4 from one end of the common flow path 205a. It has become a clause.

  Although the standing wave depends on the driving period, a standing wave having a primary resonance with the lowest energy required for excitation is likely to be generated. Further, when there is a standing wave having a resonance period close to the period of the drive signal or a resonance period close to an integral multiple of the period of the drive signal, the standing wave is likely to be generated. And when a standing wave arises and the influence is large, there exists a possibility that the fluctuation | variation of the periodic discharge speed as shown to Fig.5 (a) may arise.

  In order to make it difficult to generate a standing wave, it is preferable to set the frequency of the primary standing wave higher than the drive frequency. As a result, the first-order standing wave, which is most likely to be generated, is less likely to be generated when the driving frequency is higher than the driving frequency, and the higher-order standing wave is also higher than the driving frequency. Standing waves are less likely to occur. This makes it difficult for periodic discharge speed fluctuations to occur due to the period of higher-order standing waves.

Such standing waves are likely to occur when the cross-sectional area of the common flow path 205a is small. Increasing the frequency of the primary standing wave is the case of a common flow path with an average cross-sectional area of 0.5 mm ² or less. It is more useful when it is 0.3 mm ² or less. In addition, standing waves are more likely to occur as the density of the squeezing 212 connected to the common flow path 205a is higher. Increasing the frequency of the primary standing wave is more useful when five or more squeezing 212 are connected per 1 mm. Thus, it is particularly useful when ten or more squeezed 212 are connected per 1 mm. Further, when the common flow path 205a having a constant cross-sectional area is used, the resonance period when the liquid in the common flow path 205a vibrates at the primary resonance frequency is shorter than 1 / 0.53 times the drive period. In this case, the cross-sectional shape is changed so that the resonance period when the liquid in the common flow path 205a vibrates at the primary resonance frequency is 1 / 0.53 times the drive period or more. Is useful.

  In order to increase the resonance frequency of the primary standing wave, the cross-sectional area of the common flow path 205a at the antinode of the primary standing wave is reduced, or the node of the primary standing wave node is reduced. What is necessary is just to enlarge the cross-sectional area of the common flow path 205a. That is, the cross-sectional area of the closed both ends of the common channel 205a may be made smaller than the central cross-sectional area. More specifically, in order to further increase the resonance frequency of the primary standing wave, from both ends of the common channel 205a corresponding to the antinodes of the primary standing wave of the common channel 205a. What is necessary is just to make the average cross-sectional area to the part of length L / 4 smaller than the average cross-sectional area of the part of the center length L / 2 in the common flow path 205a. A larger cross-sectional area ratio is more effective and is preferably 3/4 or less, particularly preferably half or less.

  Here, the average cross-sectional area is an average cross-sectional area of a portion for calculating the average cross-sectional area. That is, the value obtained by integrating the cross-sectional area of the pipe of the part to be calculated in the length direction divided by the length of the pipe of the part to be calculated, and the volume of the pipe of the part to be calculated is the value of the pipe of the part to be calculated. It is the value divided by the length.

  In addition, it is preferable to smoothly change the cross-sectional area in the length direction of the common flow path 205a because the liquid ejection characteristics hardly change near the non-smooth portion as compared with the case where there are discontinuous steps. . The term “smooth” means that the cross-sectional area of the common flow path 205a does not change abruptly. Typically, the cross-sectional area is determined by a plane orthogonal to the length direction of the common flow path 205a. It does not change. Further, among the channels connected from the liquid pressurizing chamber 10 to the common channel 205a, the average interruption of the common channel 205a between the positions where the channels adjacent to each other in the length direction of the common channel 205a are connected. The change in area is preferably 5% or less before and after one flow path.

  The liquid discharge head 2 as described above is manufactured as follows, for example.

  A tape composed of a piezoelectric ceramic powder and an organic composition is formed by a general tape forming method such as a roll coater method or a slit coater method, and a plurality of green sheets that become piezoelectric ceramic layers 21a and 21b after firing are produced. . An electrode paste to be the common electrode 34 is formed on a part of the green sheet by a printing method or the like. Further, if necessary, a via hole is formed in a part of the green sheet, and a via conductor is inserted into the via hole.

  Next, each green sheet is laminated to produce a laminate, and pressure adhesion is performed. The laminated body after pressure contact is fired in a high-concentration oxygen atmosphere, and then the individual electrode 35 is printed on the surface of the fired body using an organic gold paste. After firing, the connection electrode 36 is printed using an Ag paste. And the piezoelectric actuator unit 21 is produced by baking.

  Next, the flow path member 4 is produced by laminating plates 22 to 31 obtained by a rolling method or the like. Holes to be the manifold 5, the individual supply flow path 6, the liquid pressurizing chamber 10, the descender, and the like are processed in the plates 22 to 31 into a predetermined shape by etching.

  These plates 22 to 31 are preferably formed of at least one metal selected from the group consisting of Fe—Cr, Fe—Ni, and WC—TiC, particularly when ink is used as a liquid. Since it is desired to be made of a material having excellent corrosion resistance against ink, Fe-Cr is more preferable.

  The piezoelectric actuator 21 and the flow path member 4 can be laminated and bonded via an adhesive layer, for example. A well-known adhesive layer can be used as the adhesive layer. However, in order not to affect the piezoelectric actuator 21 and the flow path member 4, an epoxy resin, a phenol resin, or a polyphenylene ether having a thermosetting temperature of 100 to 150 ° C. It is preferable to use at least one thermosetting resin adhesive selected from the group of resins. By heating to the thermosetting temperature using such an adhesive layer, the piezoelectric actuator 21 and the flow path member 4 can be heat-bonded. A liquid discharge head 2 is obtained.

  Thereafter, one end electrode such as FPC is joined to the connection electrode 36 on the piezoelectric actuator 21 and the other end of the FPC is connected to the control circuit 100 to obtain a liquid ejection device.

  The liquid discharge head 2 having a different shape of the common flow path 205a was produced, and the relationship between the resonance frequency of the primary standing wave and the fluctuation of the discharge speed was evaluated.

  7 (a) to 7 (f) and FIGS. 8 (a) to 8 (e) show the liquid ejection head No. 1 in which the test was performed. It is a schematic diagram of 1-11 common flow paths. These common flow paths are common flow paths in the same liquid discharge head as the liquid discharge head having the basic structure shown in FIGS. However, the adjustment of the cross-sectional area of the common flow path is performed by changing the dimension in the width direction.

  L is 24 mm, sectional area A is width 0.6 mm × thickness 0.3 mm, sectional area B is width 1.3 mm × thickness 0.3 mm, and sectional area C is width 2.0 mm × thickness 0.3 mm. . The following results are obtained by calculating the resonance frequency of the standing wave by a simulation to be described later. Regarding the fluctuation of the liquid discharge speed, the actual liquid discharge head is driven at 20 kHz and printing corresponding to solid printing is performed. The discharge speed during the tenth discharge was measured.

The resonance frequency was calculated using acoustic analysis software “ANSYS” using a finite element method, assuming that the density of the liquid and the speed of sound in the liquid were 1.04 kg / m ³ and 1500 m / sec of the liquid actually used. Specifically, a model is produced with the above-mentioned dimensions, a pressure at which the frequency is changed is input, a frequency analysis is performed, and the frequencies at which the pressure becomes maximum are first, second, third, in order from the lowest frequency. The resonance frequency was as follows.

  Sample No. with a constant cross-sectional dimension. In one liquid discharge head, the primary resonance frequency is 31.2 kHz, which is not so high as compared with the driving frequency of 20 kHz, and the variation in the discharge speed is as large as 20%. The distribution of the discharge speed of the liquid discharge head is as shown in FIG. 5A, and the discharge speed has a periodic distribution as described above.

  In contrast, sample no. In the liquid discharge head of No. 2, the primary resonance frequency is 51.2 kHz, which is higher than the drive frequency, and the variation in the discharge speed is as very low as 8%. As shown in FIG. 5B, the distribution of the discharge speed of the liquid discharge head is suppressed even in the tenth discharge.

  Thus, the liquid discharge head No. In Nos. 2 to 7, it was possible to reduce the fluctuation of the discharge speed by increasing the primary resonance frequency. And it turns out that the fluctuation | variation of discharge speed becomes small as a primary resonant frequency becomes high. From this result, if the drive frequency is set to the resonance frequency and the resonance frequency is set to a ratio of the drive frequency of 20 kHz to 38.4 kHz, that is, 0.53 times or less, the variation in the discharge speed can be reduced to 10% or less.

  Sample No. 8 and sample no. The common flow channel 9 is designed so that the secondary and tertiary resonance frequencies are increased. However, since the primary resonance frequency is decreased, the variation in the discharge speed is increased, and the higher-order resonance frequency is increased. It can be seen that the influence of the primary resonance frequency is greater than the resonance frequency.

DESCRIPTION OF SYMBOLS 1 ... Printer 2 ... Liquid discharge head 4 ... Channel member 5, 205 ... Manifold (common channel and liquid supply channel)
5a, 205a ... Sub manifold (common flow path)
5b ... Open 5c ... Liquid supply path 6 ... Individual supply path 8 ... Liquid discharge hole 10, 210 ... Liquid pressurizing chamber 12, 212 ... Squeezed 21 ... Piezoelectric actuator Unit 21a: Piezoelectric ceramic layer (diaphragm)
21b ... Piezoelectric ceramic layer 22-31 ... Plate 32 ... Individual flow path 34 ... Common electrode 35 ... Individual electrode 36 ... Connection electrode 50 ... Displacement element (pressure part)
L: Length of sub-manifold (common flow path)

Claims (5)

  A common channel long in one direction and closed at both ends, a liquid supply channel connected to a portion other than both ends of the common channel, and a plurality of liquid pressurizing chambers in the middle of the common channel. A liquid discharge head having a plurality of connected liquid discharge holes and a plurality of pressurization units that pressurize the liquid in the plurality of liquid pressurization chambers, respectively, wherein the cross-sectional area of both end portions of the common flow path is the center A liquid discharge head having a smaller cross-sectional area than a portion thereof.   When the length of the common flow path is L (mm), the average cross-sectional area from both ends of the common flow path to the portion of length L / 4 is the central length L of the common flow path. The liquid discharge head according to claim 1, wherein the liquid discharge head is equal to or less than a half of an average cross-sectional area of a portion of / 2.   The liquid discharge head according to claim 1, wherein a change in a cross-sectional area of the common flow path is smooth.   4. A liquid ejection apparatus comprising: the liquid ejection head according to claim 1; and a control unit that controls driving of the plurality of pressurizing units, wherein the control unit includes the common flow path. A liquid ejecting apparatus, wherein the pressurizing unit is controlled to be driven with a driving cycle of 0.53 times or less of a vibration cycle in which the liquid in the first resonance vibration occurs.   A recording apparatus comprising: the liquid ejection apparatus according to claim 4; and a transport unit that transports a recording medium to the liquid ejection apparatus.

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