JP2012071594A - Liquid ejection head and recorder using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid ejection head suitable for high frequency driving, and a recorder using the same.SOLUTION: The liquid ejection head has a flow channel member which is constituted by stacking tabular plates 22 to 31 and which has a plurality of liquid ejection holes 8, a plurality of liquid pressurizing chambers 10 connected with the plurality of liquid ejection holes 8, and a manifold 5 connected with the plurality of liquid pressurizing chambers 10 through a plurality of orifices 12 and a plurality of pressurizing portions 50 for changing the volume of the liquid pressurizing chambers. The orifice 12 is constituted by the wall surface of a hole formed on one plate 23 and the principal surfaces of the plates 22 and 24 stacked on and under the plate 23. The opening of the orifice 12 at a manifold 5 side is narrower than the opening of the orifice 12 at a liquid pressurizing chamber 10 side or the orifice 12 has a narrow segment.

Description

  The present invention relates to a liquid discharge head such as an ink jet recording head and a recording apparatus using the same.

  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 system that ejects droplets from the ink ejection holes, and a part of the walls 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 to eject ink. A piezoelectric method for discharging liquid droplets from 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 orthogonal to the conveyance direction of the recording medium, and a state in which the liquid discharge head that is longer in the main scanning direction than the recording medium is fixed Alternatively, there is a line type in which recording is performed on a recording medium conveyed in the sub-scanning direction in a state where a plurality of liquid ejection heads are arranged and fixed so that the recording range is wider than the recording medium. 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, as shown in FIG. 8, the liquid discharge head 513 is connected to the liquid discharge hole 508 via the manifold 505 and the manifold 505 in order from the common flow path 506, the throttle 512, the liquid pressurization chamber 510, and the communication path 507. It is known that a flow path member 504 having an individual flow path 532 and an actuator unit 521 having a plurality of displacement elements 550 provided so as to cover the liquid pressurizing chamber 510 are stacked. (For example, refer to Patent Document 1). In the liquid discharge head 513, the throttle 512 has a constant cross-sectional area, and the liquid pressurizing chambers 510 respectively connected to the plurality of liquid discharge holes 508 are arranged in a matrix and are actuators provided so as to cover them. By displacing the displacement element 550 of the unit 521, the volume of each liquid pressurizing chamber 510 is changed, and droplets are ejected from each liquid ejection hole 508, so that printing can be performed at a resolution of 600 dpi in the main scanning direction. . The flow path member 504 is a laminate of metal plates 522 to 531, and the piezoelectric actuator 521 includes a piezoelectric ceramic layer 521 a, a common electrode 534, a piezoelectric ceramic layer 521 b, and individual electrodes 535 in order from the flow path member 504 side. Laminated.

JP 2003-305852 A

  However, when performing ejection using the natural vibration of the liquid from the liquid ejection hole 508 to the manifold 505 such as striking, if the natural vibration period of the liquid is long, the time required for one ejection becomes long. Furthermore, the residual vibration of the liquid in the flow channel remaining after the discharge also has this natural vibration period. Therefore, when the natural vibration period is long, the time for damping until the influence of the residual vibration on the next discharge becomes small becomes long. . That is, if the natural vibration period is long, the time required for the discharge itself becomes long, and the time until the next discharge can be performed becomes long. Therefore, it is desirable that the natural vibration period is short, and when driving at a high frequency, it is desirable that the flow path resistance is large in order to attenuate the residual vibration quickly. However, in the case of a rectangular parallelepiped shape like the liquid discharge head described in Patent Document 1, these characteristics are contradictory characteristics, so that the natural vibration period is shortened and the flow resistance is increased. There was a problem that could not be done.

  Accordingly, an object of the present invention is to provide a liquid discharge head suitable for high-frequency driving and a recording apparatus using the same.

  The liquid discharge head according to the present invention includes a plurality of liquid discharge holes that are formed by laminating flat plates and open to one main surface, and are connected to the plurality of liquid discharge holes, respectively, and the other A plurality of liquid pressurizing chambers opened in the main surface, a flow path member having manifolds respectively connected to the plurality of liquid pressurizing chambers via a plurality of squeezes, and the liquid pressurizing chambers, respectively. A liquid discharge head having a plurality of pressurizing portions for applying pressure, wherein the squeezing is made up of a wall surface of a hole formed in one plate and a main surface of the plate stacked above and below the plate. In addition, the opening on the manifold side is narrower than the opening on the liquid pressurizing chamber side or has a constricted portion.

  The recording apparatus of the invention includes the liquid discharge head, a transport unit that transports a recording medium to the liquid discharge head, and a control unit that controls the plurality of pressure units. .

  According to the liquid ejection head of the present invention, the natural vibration period of the liquid in the flow path can be reduced and the flow path resistance of the squeezed can be increased compared to a rectangular parallelepiped-shaped squeezing, so that high-frequency driving is possible.

1 is a schematic configuration diagram illustrating a printer that is an example of a recording apparatus 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. 2. FIG. 3 is an enlarged view of a region surrounded by an alternate long and short dash line in FIG. (A) is a longitudinal cross-sectional view along the VV line of FIG. 3, (b) is an enlarged plan view of the aperture plate in which the aperture is formed. (A)-(e) is the planar shape of a squeezing. (A), (b) is the planar shape of a squeezing. It is a longitudinal cross-sectional view of a conventional liquid discharge head.

FIG. 1 is a schematic configuration diagram showing a color ink jet printer which is an example of a recording apparatus 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 recording paper P that is a recording medium, 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 recording 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 feed unit 114 includes a paper storage case 115 that can store a plurality of recording papers P, and a paper supply roller 145. The paper feed roller 145 can send out the uppermost recording paper P among the recording 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 recording paper P. The recording paper P sent out from the paper supply unit 114 is guided by these feed rollers 118 a, 118 b, 119 a and 119 b 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 the two belt rollers 106 and 107. As a result, the conveyor belt 111 is stretched without slack along two parallel planes including the common tangent lines of the two belt rollers 106 and 107, respectively. Of these two planes, the plane closer to the liquid ejection head 2 is a conveyance surface 127 that conveys the recording 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 recording 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 recording paper P is pressed against the transport surface 127 of the transport belt 111 and is fixed on the transport surface 127. Then, the recording 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 recording paper P can be reliably 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 large number of liquid ejection holes 8 for ejecting liquid are provided on the lower surface of the head body 13 (see FIG. 3).

  Liquid droplets (ink) of the same color are ejected from the liquid ejection holes 8 provided in one liquid ejection head 2. The liquid discharge holes 8 of each liquid discharge head 2 are arranged at equal intervals in one direction (a direction parallel to the recording paper P and perpendicular to the conveyance direction of the recording paper P and the longitudinal direction of the liquid discharge head 2). Therefore, it is possible to record without a gap 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 recording paper P transported by the transport belt 111 passes through a gap between the recording belt P and the transport belt 111 on the lower surface side of the liquid ejection head 2. At that time, droplets are ejected from the head body 13 constituting the liquid ejection head 2 toward the upper surface of the recording 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 recording 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 recording paper P on which the color image is recorded is transported from the transport belt 111 to the peeling plate 140. At this time, the recording paper P is peeled from the transport surface 127 by the right end of the peeling plate 140. Then, the recording paper P is sent out to the paper receiving unit 116 by the feed rollers 121a, 121b, 122a and 122b. In this way, the recorded recording 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 on the most upstream side in the conveyance direction of the recording 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 recording 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 transport motor 174, and the like based on the detection result sent from the paper surface sensor 133 so that the transport of the recording paper P and the image recording are synchronized.

  Next, the head main body 13 constituting the liquid discharge head 2 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 view of a region surrounded by a one-dot chain 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 and 4, in order to make the drawings easy to understand, the liquid pressurizing chamber 10 (liquid pressurizing chamber group 9), the squeezing 12, and the liquid discharge holes which are to be drawn by broken lines below the piezoelectric actuator unit 21. 8 is drawn with a solid line. 5A is a longitudinal sectional view taken along the line VV in FIG. 3, and FIG. 5B is an enlarged plan view of the aperture plate 24 in which the aperture 12 is formed. FIG. 5B also shows the liquid pressurization chamber 10 formed in the cavity plate 22 so that the relationship with the liquid pressurization chamber 10 can be understood.

The head main body 13 includes a flat plate-like channel member 4 and a piezoelectric actuator unit 21 that is an actuator unit and is disposed on the channel member 4. As shown in FIG. 5A, the piezoelectric actuator unit 21 is formed by laminating a piezoelectric ceramic layer (vibrating plate) 21, a common electrode 34, a piezoelectric ceramic layer 21b, and individual electrodes 35 in order from the flow path member 4 side. Is. The piezoelectric actuator unit 21 has a trapezoidal planar shape, and the upper surface of the flow path member 4 so that the pair of parallel opposing sides of the trapezoidal shape is parallel to the longitudinal direction of the flow path member 4. Is arranged. 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 when the short direction of the flow path member 4 is viewed. In the area recorded by driving the piezoelectric actuator unit 21 in the overlapping portion, the liquid droplets discharged 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. In other words, two rows of the 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 piezoelectric actuator actuator unit 21. Yes. 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, each sub-manifold 5a has an individual flow path 32 at intervals corresponding to 150 dpi on average.
Is connected. This is because the individual flow paths 32 connected to the sub-manifolds 5a are not necessarily connected at equal intervals when the 600 dpi liquid discharge holes 8 are divided and connected to the four rows of sub-manifolds 5a. In other words, the individual flow paths 32 are formed at intervals of an average of 170 μm (25.4 mm / 150 = 169 μm intervals if 150 dpi) in the main scanning direction.

  Individual electrodes 35 are formed at positions facing the respective liquid pressurizing chambers 10 on the upper surface of the piezoelectric ceramic layer 21 b constituting the piezoelectric actuator unit 21. The individual electrode 35 has a plane shape slightly smaller than that of the liquid pressurizing chamber 10, has a shape substantially similar to the liquid pressurizing chamber 10, and opposes the liquid pressurizing chamber 10 on the upper surface of the piezoelectric ceramic layer 21b. Arranged to fit within the area.

  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 occupy an area having almost the same size and shape as the piezoelectric actuator unit 21, and the liquid discharge hole is displaced by displacing the displacement element (pressurizing unit) 50 of the corresponding piezoelectric actuator unit 21. A droplet can be ejected from 8. 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 constituting the head body 13 has a laminated structure in which a plurality of plates are laminated. These plates are a cavity plate 22, a base plate 23, an aperture (squeezing) plate 24, a supply plate 25, manifold plates 26, 27, 28, 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. 5A, the head main body 13 has the 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 hole 8 on the lower surface. In addition, each part constituting the individual flow 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.

  Next, 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). Note that the communication hole includes the aperture 12 formed in the aperture plate 24 and the individual supply flow path 6 formed in the supply plate 25. Third, a communication hole that forms a flow path that connects the other end of the liquid pressurizing chamber 10 to the liquid discharge hole 8.

The squeezing 12 is a part of the flow path connecting from one end of the liquid pressurizing chamber 10 to the sub-manifold 5a, and the base plate 23 and the supply plate laminated on the wall surface of the aperture plate 24 and the aperture plate 24. It consists of 25 main surfaces. FIG. 5 (b) shows a hole that becomes the aperture 12 that is opened in the aperture plate 24. Both ends of the hole to be the aperture 12 are connected to a hole larger than the width of the aperture 12. The opening 12a on the liquid pressurizing chamber side of the squeezing 12 and the opening 12b on the manifold side are boundaries with the large holes. The opening 12a on the liquid pressurizing chamber side of the squeezing 12 is a flow channel that is connected from one end of the liquid pressurizing chamber 10 to the lower side in the stacking direction, and the cross-sectional area perpendicular to the liquid flow in this portion of the flow channel Is the area in the planar direction. Accordingly, the flow path in this portion is not narrow with respect to the vertical cross-sectional area of the liquid pressurizing chamber 10, which is a cross-sectional area perpendicular to the liquid flow in the liquid pressurizing chamber 10. Absent.

  By forming the wall surface of the hole of one plate of the aperture 12 and the main surface of the upper and lower plates, the formation accuracy is higher than that when the aperture 12 is formed by communicating holes formed in a plurality of plates. wear.

  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 described above, 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 and the flow path member 4 are bonded through, for example, an adhesive layer. As the adhesive layer, in order not to affect the piezoelectric actuator unit 21 and the flow path member 4, at least one kind selected from the group of epoxy resin, phenol resin, and polyphenylene ether resin having a thermosetting temperature of 100 to 150 ° C. A thermosetting resin adhesive is used. The reason why the thermosetting resin adhesive is used is that the room temperature curing adhesive may not ensure sufficient ink resistance. For this reason, the piezoelectric actuator unit 21 is in a state in which a stress generated by a difference in thermal expansion coefficient between the flow path member 4 and the piezoelectric actuator unit 21 is applied by being cooled from the thermosetting temperature to room temperature. When the stress is large, the piezoelectric actuator unit 21 may be broken, and even if the stress is not so high that the piezoelectric actuator unit 21 is broken, the characteristics of the piezoelectric actuator unit 21 vary depending on the applied stress. Specifically, in a state where compressive stress is applied, the piezoelectric constant is lowered, but the influence of the phenomenon of drive deterioration in which the amount of displacement is reduced when the drive is repeated for a very long time is reduced. Conversely, in a state where tensile stress is applied, the piezoelectric constant increases, but the influence of drive deterioration increases. In any case, the difference in coefficient of thermal expansion between the flow path member 4 and the piezoelectric actuator unit 21 needs to be reduced. It is preferable that a small compressive stress is weakly applied. Therefore, when PZT ceramics are used for the piezoelectric actuator unit 21, it is preferable to use 42 alloy as the material of the flow path member 4.

The piezoelectric actuator unit 21 has a common electrode 34 made of a metal material such as Ag—Pd and an individual electrode 35 made of a metal material such as Au. As described above, the individual electrode 35 is disposed at a position facing the 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 is supplied to the individual electrode 35 from the control unit 100 through the FPC. The drive signal is supplied at a constant period in synchronization with the conveyance speed of the recording paper 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. 5A, 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 layer 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, pressurizing unit) corresponding to each liquid pressurizing chamber 10 and the liquid discharge port 8. That is, in the laminated body composed of the two piezoelectric ceramic layers 21a and 21b, the displacement element 50 having a unit structure as shown in FIG. The piezoelectric ceramic layer 21 a as a vibration plate located directly above the pressurizing chamber 10, the common electrode 34, the piezoelectric ceramic layer 21 b, and the individual electrodes 35 are formed. The piezoelectric actuator unit 21 includes a plurality of displacement elements 50. ing. 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 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, this is referred to as a low potential), and then the potential is set again at a predetermined timing. Thereby, the piezoelectric ceramic layers 21a and 21b return to their original shapes 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 21 a and 21 b are deformed so as to protrude toward the liquid pressurizing chamber 10. Becomes a positive pressure, the pressure on the liquid rises, and droplets are ejected from the liquid ejection holes 8. 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, the liquid pressurizing chamber 1
When the inside of the zero is reversed from the negative pressure state to the positive pressure state, the pressures of the two are combined, and the droplets can be ejected at a stronger pressure.

  When recording with gradation, gradation expression is performed by the number of droplets ejected continuously from the liquid ejection hole 8, that is, the droplet amount (volume) adjusted by the number of droplet ejections. It is. 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.

  In such a printer 1, by adjusting the cycle of the recording paper P at the conveyance speed and the drive signal, it is possible to record an image having a resolution of 600 dpi in the longitudinal direction and 600 dpi in the conveyance direction. For example, if the drive signal is 20 kHz and the transport speed is 0.85 m / s, the ejected droplets can be landed on the recording paper P every about 42 μm in the transport direction, and the resolution in the transport direction is 600 dpi. .

Here, the liquid in the flow path from the liquid discharge hole 8 to the orifice 12 will be described in detail. Assuming that the natural vibration period Tn of this portion of the liquid is Tn (s, the unit may be omitted below), it can be expressed as Tn = 2π {(Ms + Mn) / (1 / Cv + 1 / Cc)} ^1/2 . Here, the compliance of the displacement element 50 is Cv (m ⁵ / N, the unit may be omitted below), and the compliance from the liquid pressurizing chamber 10 and the liquid pressurizing chamber 10 to the end of the liquid discharge hole 8 is Cc. The inertance of the squeezing 12 is Ms (kg / m ⁴ , and the unit may be omitted below), and the inertance from the liquid discharge hole 8 and the liquid discharge hole 8 to the end of the liquid pressurizing chamber 10 is Mn. This formula for calculating Tn ignores some of the factors that have little influence. For example, the compliance of the squeezing 12 is ignored because its volume is small compared to other parts, and the inertance of the liquid pressurizing chamber 10 is ignored because its cross-sectional area is large compared to other parts. is doing. Furthermore, Ms is represented by ρL {ln (W _C / W _M )} / {d (W _C −W _M )}. Here, ρ (kg / m ³ , unit may be omitted below) is the density of the liquid, L (m, unit may be omitted below) is the length of the squeezing 12, d (m, below) Is the height of the orifice 12, and W _C (m, which may be omitted hereinafter) is the width of the opening 12 a on the liquid pressurizing chamber side of the orifice 12, W _M ( m, the unit may be omitted below) is the width of the opening 12b on the manifold side of the aperture 12. Note that when W _C = W _M , Ms = ρL / (dW _C ).

Further, the squeezing flow path resistance Rs (Ns / m ⁵ , the unit may be omitted below) can be calculated by ΔP / U. ΔP (N / m ² , unit may be omitted below) is the difference between the inflow pressure and the outflow pressure obtained by simulation, and U (m ³ / s, unit may be omitted below) ) Is the flow rate at that time.

  In the squeezing 12, the manifold-side opening 12b is made narrower than the opening 12a on the liquid pressurizing chamber side or a constricted portion is provided, so that the inertance is not changed, that is, the natural vibration period Tn is not changed. Since the flow resistance from the liquid pressurizing chamber 10 toward the manifold 5 can be increased, the attenuation of the residual vibration can be increased. If the opening 12b on the manifold side is narrowed and a constriction is provided in the middle, the flow path resistance can be further increased.

Even if the opening 12a on the liquid pressurizing chamber side is narrowed, the flow resistance from the liquid pressurizing chamber 10 toward the manifold 5 can be increased if the opening is extremely narrowed. However, by doing so, the flow resistance from the manifold 5 to the liquid pressurizing chamber 10 becomes extremely large, and it becomes difficult for the liquid to flow from the manifold 5 to the liquid pressurizing chamber 10. In the present invention, the opening 12b on the manifold side is made narrower than the opening 12a on the liquid pressurizing chamber side.

  Since the length of the portion where the cross-sectional area decreases from the liquid pressurizing chamber 10 toward the manifold 5 with respect to the length of the squeezing 12, the flow from the manifold 5 to the pressurizing chamber 10 is reduced. The flow path resistance from the liquid pressurizing chamber 10 toward the manifold 5 can be increased without increasing the flow path resistance too much. It is preferable that the width of the portion other than the portion where the cross-sectional area decreases from the liquid pressurizing chamber 10 toward the manifold 5 does not change. Furthermore, it is preferable that the entire squeeze 12 is formed of a portion where the cross-sectional area becomes substantially smaller from the liquid pressurizing chamber 10 toward the manifold 5.

  If the number of constrictions is increased to some extent, the flow resistance can be increased.However, if the number of constrictions is very large with respect to the length, the liquid approaches the flow of the cross-sectional area of the constriction. Go. Further, although depending on the processing method of the flow path, if the processed shape is about the same as or smaller than the thickness, the processing accuracy deteriorates and the fluctuation of the discharge characteristics also increases. It is preferable to provide a plurality of constricted portions, and it is preferable to provide a large number of constricted portions in a range where the minimum interval for forming the constricted portions is 25 μm or more.

  When the opening area of the squeezing 12 on the manifold 5 side is 1/3 or less of the opening area on the liquid pressurizing chamber side 10, the flow path resistance of the squeezing 12 can be further increased.

  When the squeezing 12 has a narrowed portion having a cross-sectional area of 1/3 or less of the average cross-sectional area of the squeezing 12, the flow resistance of the squeezing 12 can be further increased. The average cross-sectional area of the squeezing 12 is a value obtained by dividing the volume of the squeezing 12 by the length of the squeezing 12.

  6 (b) to 6 (e) and FIGS. 7 (a) and 7 (b) show the planar shape of the aperture according to another embodiment of the present invention. The left side of the figure is connected to the manifold 5, and the right side is connected to the liquid pressurizing chamber 10. Any squeezing can be provided in the liquid discharge head 2 described above.

  In the squeezing shown in FIG. 6B, the opening on the liquid pressurizing chamber side and the area on the manifold side are the same, but two constricted portions are provided. The cross-sectional area before and after the narrowed portion gradually increases as the distance from the narrowed portion increases.

  In the squeezing shown in FIG. 6C, the area of the opening on the liquid pressurizing chamber side and the opening on the manifold side are the same, but one constricted portion is provided. The cross-sectional area before and after the narrowed portion gradually increases as the distance from the narrowed portion increases.

  In the squeezing shown in FIG. 6 (d), the area of the opening on the manifold side is larger than the opening on the liquid pressurizing chamber side, and three constrictions are provided. The cross-sectional area of the squeezing gradually spreads from the manifold side toward the liquid pressurizing chamber side, and abruptly narrows at the constriction (substantially zero length). This is repeated three times, and in the fourth time, the cross-sectional area gradually increases and then connects to the liquid pressurizing chamber as it is wide. In such a structure, since the cross-sectional area decreases from the liquid pressurizing chamber to the manifold except for the portion where the area changes suddenly at the constricted portion, the entire squeeze is substantially directed from the liquid pressurizing chamber to the manifold. Since the cross-sectional area becomes smaller, the flow resistance from the liquid pressurizing chamber toward the manifold increases, which is preferable.

In the squeezing shown in FIG. 6 (e), the area of the opening on the manifold side is smaller than the opening on the liquid pressurizing chamber side, but three constrictions are provided. The cross-sectional area of the squeezing gradually narrows from the manifold side toward the liquid pressurizing chamber side, and spreads abruptly (substantially zero length) at the constriction. This is repeated three times, and in the fourth time, the cross-sectional area is gradually narrowed and then connected to the liquid pressurizing chamber while remaining narrow.

  In the squeezing shown in FIG. 7A, the area of the opening on the liquid pressurizing chamber side and the opening on the manifold side are the same, but two constricted portions are provided. The narrowed portion has a constant width in the range of 1/5 of the length L of the squeezing, and the area is rapidly increased before and after that.

  In the squeezing shown in FIG. 7B, the area of the opening on the liquid pressurizing chamber side and the opening on the manifold side are the same, but one constricted portion is provided. The narrowed portion has a constant width in the range of 1/5 of the length L of the squeezing, and the area is rapidly increased before and after that. In the present embodiment, the displacement element 30 using piezoelectric deformation is shown as the pressurizing unit. However, the displacement element 30 is not limited to this, and can change the volume of the pressurizing chamber 10, that is, pressurizing. Any other device that can pressurize the liquid in the chamber 10 may be used. For example, the liquid in the pressurizing chamber 10 is heated and boiled to generate pressure, or MEMS (Micro Electro Mechanical Systems) is used. Things can be used.

  The flow resistance of the liquid from the liquid pressurizing chamber to the manifold 5 of the squeeze 12 having a length of 300 μm and a height of 20 μm and other dimensions shown in Table 1 was evaluated by simulation. Inertance was calculated by the above formula.

6 and 7 show plan views of the aperture 12 for which simulation was performed. In FIG. 6 (a), the width of the manifold 5a side is _{W 2,} the width of the liquid pressurizing chamber 10 side is _{W 1.} In FIG. 6 (b) ~ (e) and FIG. 7 (a), (b) , the width of the most narrow portion is the _{W 1,} which is the width of the widest portion _{W 2.}

  Sample No. The number of wedges described in the column of 10 to 12 indicates the number of wedge-shaped shapes whose width gradually changes in the aperture 12. Sample No. 10 (FIG. 6A) has a wedge number of 1, and sample No. Reference numeral 10 denotes a structure having four wedges as shown in FIG. In the simulation, the wedge shape was formed by connecting the same shape.

  Sample No. which is a structure of a squeezing within the scope of the present invention. 1 to 3 and 8 to 15, without changing the inertance, the rectangular parallelepiped sample Nos. 4, the flow path resistance from the liquid pressurizing chamber 10 toward the manifold 5 can be increased to 1.12 times or more. Furthermore, sample no. 1, 2, and 8 to 15, the opening area of the squeezing 12 on the manifold 5 side is 1/3 or less of the opening area of the liquid pressurizing chamber side 10, or 1/3 of the average cross-sectional area of the squeezing 12. Since it had a constricted portion with the following cross-sectional area, a rectangular parallelepiped sample No. The channel resistance with respect to 4 could be increased to 1.24 times or more.

  Sample No. Nos. 10 to 12 were obtained by changing the number of constrictions in the structure shown in FIG. 6D. By increasing the number of constrictions from four to ten, the channel resistance could be increased. It was confirmed that the flow path resistance was increased by providing the narrow portions at intervals of 30 μm.

DESCRIPTION OF SYMBOLS 1 ... Printer 2 ... Liquid discharge head 4 ... Flow path member 5 ... Manifold 5a ... Sub manifold 5b ... Opening 6 ... Individual supply flow path 8 ... Liquid discharge hole DESCRIPTION OF SYMBOLS 9 ... Liquid pressurization chamber group 10 ... Liquid pressurization chamber 11a, b, c, d ... Liquid pressurization chamber row | line | column 12 ... Squeeze 12a ... Opening of the liquid pressurization chamber side of squeezing 12b ... Openings on the side of the manifold 15a, b, c, d ... Liquid discharge hole array 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 ... Displacement element (pressure part)

Claims (6)

  A plurality of liquid discharge holes, a plurality of liquid pressurization chambers respectively connected to the plurality of liquid discharge holes, and a plurality of squeezes in the plurality of liquid pressurization chambers. A liquid discharge head having a flow path member having manifolds connected to each other via a plurality of pressurization units each changing the volume of the liquid pressurization chamber, wherein the squeezing is applied to one plate It is composed of the wall surface of the hole formed and the main surface of the other plate stacked above and below the plate, and the opening on the manifold side is narrower than the opening on the liquid pressurizing chamber side. Or a liquid discharge head characterized by having a narrowed portion.   2. The liquid ejection head according to claim 1, wherein the squeezing has an opening on the manifold side narrower than an opening on the liquid pressurizing chamber side and has a constricted portion in the middle.   2. The liquid ejection head according to claim 1, wherein a length of a portion of the squeezed portion whose cross-sectional area decreases from the liquid pressurizing chamber toward the manifold is longer than a half of the entire length. .   4. The liquid ejection head according to claim 1, wherein an opening area on the manifold side of the squeezing is 1/3 or less of an opening area on the liquid pressurizing chamber side.   5. The liquid discharge head according to claim 1, wherein the squeezing has a narrowed portion having a cross-sectional area of 1/3 or less of an average cross-sectional area of the squeezing.   A liquid discharge head according to claim 1, a transport unit that transports a recording medium to the liquid discharge head, and a control unit that controls the plurality of pressure units. A recording apparatus.

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