JP2014233885A - Liquid discharge head, and recording device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid discharge head which is hardly affected by bubbles in the liquid, and to provide a recording device using the same.SOLUTION: The liquid discharge head comprises: a flow channel member 4 having plural partial flow channels 7 whose one ends are discharge holes 8, plural compression chambers 10, and a common flow channel 5; and plural compression parts 50. The flow channel member 4 is formed by laminating plates 22-31 having a flow channel hole serving as a flow channel, and at least part of the partial flow channels 7 are formed on the plates 26-29 on which the common flow channel 5 is formed. Among these plates, first plates 26, 29 disposed on outermost positions in the lamination direction have thickness T of 75-150 μm, and the flow channel holes of the first plates 26, 29 have a shape that a cross section becomes smaller from a surface of a central part side of the common flow channel 5 in the lamination direction toward opposite side surfaces, and opening diameter W1a of the flow channel holes is 200-450 μm.

Description

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

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

  Therefore, the liquid discharge head is configured to cover the manifold (common flow path), the metal flow path member having discharge holes connected to the manifold through the plurality of pressure chambers and partial flow paths, and the pressure chamber, respectively. A structure in which a ceramic piezoelectric actuator substrate having a plurality of displacement elements provided is laminated is known (see, for example, Patent Document 1). In this liquid ejection head, the pressurizing chambers connected to the plurality of ejection holes are arranged in a matrix, and the displacement element of the piezoelectric actuator substrate provided so as to cover it is displaced by deformation of the piezoelectric body, Ink is ejected from each ejection hole, and printing is possible in the main scanning direction at a resolution of 600 dpi. The manifold has a square cross-sectional shape.

JP 2003-305852 A

In the liquid discharge head as described in Patent Document 1, the corners of the four corners in the cross section of the quadrilateral manifold are 90 degrees. With such a cross-sectional shape, small bubbles may adhere to the corners, and some of them gather together as they continue to be used and flow into the manifold as relatively large bubbles. When such bubbles flow into the flow path connected to the pressurizing chamber, the pressure propagation of the liquid is hindered, or the state of pressure propagation is changed, so that the liquid cannot be discharged or the discharge characteristics are changed. was there.

  Accordingly, an object of the present invention is to provide a liquid discharge head that is not easily affected by bubbles in the liquid, and a recording apparatus using the liquid discharge head.

  The liquid discharge head of the present invention includes a plurality of partial flow paths having one end serving as a discharge hole, a plurality of pressure chambers connected to the other ends of the plurality of partial flow paths, and the plurality of pressure chambers A liquid discharge head including a flow path member having a common flow path connected to the plurality of pressure chambers and pressurizing the plurality of pressure chambers, and the flow path member includes the partial flow A plurality of plates having a channel hole including a channel, a pressurizing chamber, and a hole serving as the common channel, and the common channel includes a plurality of the channel holes. And extending in a direction intersecting with the stacking direction of the flow path members, and the partial flow path is at least in the stacking direction in the plate constituting the common flow path. The channel hole that extends and constitutes the common channel is open Among the plates, the first plate, which is the plate located at the end in the stacking direction, has a thickness of 75 to 150 μm, and the flow path hole of the first plate has the common flow The flow path hole has a shape in which the cross-sectional area decreases from the surface on the central side in the stacking direction of the path toward the surface on the opposite side, and the flow path hole constituting the partial flow path in the first plate The opening diameter on the central portion side in the stacking direction is 200 to 450 μm.

  The recording apparatus of the present 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 liquid discharge head.

  According to the liquid ejection head of the present invention, large bubbles are unlikely to accumulate in the common flow path, and therefore, liquid non-ejection and variation in ejection characteristics due to the bubbles are unlikely to occur.

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 of a flow path member and a piezoelectric actuator substrate that constitute 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. 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 view of the principal part of (a).

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

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

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

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

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

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

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

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

  The four liquid discharge heads 2 are arranged close to each other along the conveyance direction by the conveyance belt 111. Each liquid discharge head 2 has a head body 13 at the lower end. A number of ejection holes 8 for ejecting liquid are provided on the lower surface of the head body 13 (see FIGS. 4 and 5).

Liquid droplets (ink) of the same color are ejected from the ejection holes 8 provided in one liquid ejection head 2. Each liquid discharge head 2 is supplied with liquid from an external liquid tank (not shown). The ejection holes 8 of each liquid ejection head 2 are open to the ejection hole surface, and are 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). Since they are arranged at equal intervals, 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 the alternate long and short dash line in FIG. 2, and a part of the flow paths are omitted. FIG. 4 is an enlarged perspective view of the same position as in FIG. 3, in which some flow paths different from those in FIG. 3 are omitted so that the positions of the discharge holes 8 can be easily understood. 3 and 4, in order to make the drawings easy to understand, the pressurizing chamber 10 (pressurizing chamber group 9), the squeezing chamber 12, the discharge hole 8, and the like that are to be drawn by broken lines below the piezoelectric actuator substrate 21 are illustrated. It is drawn with solid lines. FIG. 5A is a longitudinal sectional view taken along the line VV in FIG. 3, and FIG. 5B is an enlarged view of the main part of FIG. Although details will be described later, each flow path is formed by etching, and thus has a cross-sectional shape as shown in FIG. In FIG. 5A, only the flow paths of the plates 26 and 29 having a large difference in opening shape between both surfaces are drawn in the same manner as in FIG. 5B, and the schematic rectangular cross section is shown for the other flow paths. It is drawn in shape.

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

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

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

  The corner G of the vertical cross-sectional shape of the sub-manifold 5a has a round shape, or the angle is larger than 90 even if there is a corner. The shape of the corner portion G will be described in detail later.

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

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

  As a whole, the pressurizing chambers 10 connected from the manifold 5 constitute rows of the pressurizing chambers 10 arranged in the longitudinal direction of the flow path member 4 at equal intervals, and the rows are arranged in 16 rows parallel to each other in the short side direction. ing. The number of pressurizing chambers 10 included in each pressurizing chamber row is arranged so as to gradually decrease from the long side toward the short side corresponding to the outer shape of the displacement element 50 that is an actuator. . The discharge holes 8 are also arranged in the same manner. As a result, it is possible to form an image with a resolution of 600 dpi in the longitudinal direction as a whole.

That is, when the discharge hole 8 is projected so as to be orthogonal to the virtual straight line parallel to the longitudinal direction of the flow path member 4, the four sub-manifolds 5a are connected in the range of R of the virtual straight line shown in FIG. Four discharge holes 8, that is, a total of 16 discharge holes 8 are arranged at equal intervals of 600 dpi. Moreover, the individual flow paths 32 are connected to the sub manifolds 5a at intervals corresponding to 150 dpi on average. This is because when the discharge holes 8 for 600 dpi are divided and connected to the four sub-manifolds 5a, the individual flow paths 32 connected to the sub-manifolds 5a are not always connected at equal intervals. In other words, the individual flow paths 32 are formed at intervals of an average of 170 μm (25.4 mm / 150 = 169 μm intervals if 150 dpi) in the main scanning direction.

  Individual electrodes 35 are formed on the upper surface of the piezoelectric actuator substrate 21 at positions overlapping the pressurizing chambers 10 respectively. That is, the individual electrode 35 is formed on the upper surface of the piezoelectric actuator substrate 21 in a direction different from the first direction and the first direction. The individual electrode 35 includes an individual electrode body 35a and an extraction electrode 35b that is extracted from the individual electrode 35a. The individual electrode main body 35 a is slightly smaller than the pressurizing chamber 10 and has a shape substantially similar to the pressurizing chamber 10, so that the individual electrode main body 35 a fits in a region facing the pressurizing chamber 10 on the upper surface of the piezoelectric actuator substrate 21. Has been placed.

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

  The flow path member 4 included in the 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, a supply plate 25, manifold plates 26 to 29, a cover plate 30 and a nozzle plate 31 in order from the upper surface of the flow path member 4. These plates are formed with a large number of flow path holes (hereinafter sometimes simply referred to as holes). 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 body 13 has the pressurizing chamber 10 on the upper surface of the flow path member 4, the sub-manifold 5 a on the inner lower surface side, and the discharge holes 8 on the lower surface. Are arranged close to each other at different positions, and the sub-manifold 5 a and the discharge hole 8 are connected via the pressurizing chamber 10.

  The holes formed in each plate will be described. These holes include the following. First, the pressurizing chamber 10 formed in the cavity plate 22. Secondly, there is a communication hole that constitutes a flow path that connects from one end of the pressurizing chamber 10 to the sub-manifold 5a. This communication hole is formed in each plate from the base plate 23 (specifically, the inlet of the pressurizing chamber 10) to the supply plate 24 (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, there is a communication hole that constitutes the partial flow path 7 that communicates from the other end of the pressurizing chamber 10 to the discharge hole 8. The partial flow path 7 is formed in each plate from the base plate 23 (specifically, the outlet of the pressurizing chamber 10) to the nozzle plate 31 (specifically, the discharge hole 8). Fourthly, there is a communication hole constituting the sub-manifold 5a. The communication holes are formed in the manifold plates 27 to 29.

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

  As shown in FIG. 5, the piezoelectric actuator substrate 21 has a laminated structure including two piezoelectric ceramic layers 21a and 21b. Each of these piezoelectric ceramic layers 21a and 21b has a thickness of about 20 μm. The thickness of the laminated body of the piezoelectric ceramic layers 21a and 21b of the piezoelectric actuator substrate 21 is about 40 μm, and the displacement can be increased by being 100 μm or less. The piezoelectric actuator substrate 21 is laminated on the planar surface of the flow path member 4 where the pressurizing chamber 10 is open, and the piezoelectric ceramic layers 21 a and 21 b straddle the plurality of 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 substrate 21 has a common electrode 34 made of a metal material such as Ag—Pd and an individual electrode 35 made of a metal material such as Au. If necessary, a connection electrode 36 made of an Ag-based metal material formed on the individual electrode 35 may be formed. The individual electrode 35 is disposed at a position overlapping the pressurizing chamber 10 on the upper surface of the piezoelectric actuator substrate 21, and the extraction electrode is drawn from the individual electrode main body 35 a to a position not overlapping the pressurizing chamber 10. 35b. A connection electrode 36 is formed at a position of the extraction electrode 35b where the pressurizing chamber 10 is not provided. The thickness of the individual electrode 35 is 0.3 to 1 μm. The connection electrode 36 is made of, for example, silver containing glass frit, and has a thickness of about 1 to 15 μm and is formed in a convex shape. Further, the connection electrode 36 is not shown in FPC (Flexible).
It is electrically joined to the electrode provided in the printed circuit. Although details will be described later, a drive signal (drive voltage) is supplied to the individual electrode 35 from the control unit 100 through the FPC. The drive signal is supplied in a constant cycle in synchronization with the conveyance speed of the print medium P.

  The common electrode 34 is formed over almost the entire surface in the region between the piezoelectric ceramic layer (ceramic diaphragm) 21a and the piezoelectric ceramic layer (piezoelectric layer) 21b. That is, the common electrode 34 extends so as to cover all the pressurizing chambers 10 in the region facing the piezoelectric actuator substrate 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 in the external wiring, like the large number of individual electrodes 35. Has been.

  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 called an active portion, and the piezoelectric ceramic in that portion is polarized in the thickness direction. In the piezoelectric actuator substrate 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 substrate 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 pressurizing chamber 10 corresponding to the individual electrode 35. As a result, droplets are discharged from the corresponding discharge holes 8 through the individual flow paths 32. That is, the portion of the piezoelectric actuator substrate 21 that faces each pressurizing chamber 10 has the pressurizing chambers 10 and the discharge holes 8.
It corresponds to the individual displacement element 50 corresponding to. 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 positioned immediately above the pressurizing chamber 10 for each pressurizing chamber 10. The ceramic diaphragm 21a, the common electrode 34, the piezoelectric ceramic layer 21b, and the individual electrode 35 are formed, and the piezoelectric actuator substrate 21 includes a plurality of displacement elements 50. In the present embodiment, the amount of liquid discharged from the discharge hole 8 by one discharge operation is about 5 to 7 pL (picoliter).

  An example of a driving method at the time of liquid ejection of the piezoelectric actuator substrate 21 in the present embodiment will be described with respect to a driving voltage (drive signal) supplied to the individual electrode 35. When an electric field is applied to the piezoelectric ceramic layer 21b in the polarization direction by setting the individual electrode 35 to a potential different from that of the common electrode 34, the portion to which the electric field is applied functions as an active portion that is distorted by the piezoelectric effect. At this time, the piezoelectric ceramic layer 21b expands or contracts in the thickness direction, that is, the stacking direction, and tends to contract or extend in the direction perpendicular to the stacking direction, that is, the plane direction, due to the piezoelectric lateral effect. On the other hand, since the remaining piezoelectric ceramic layer 21a is an inactive layer that does not have a region sandwiched between the individual electrode 35 and the common electrode 34, it does not spontaneously deform. That is, the piezoelectric actuator substrate 21 has the piezoelectric ceramic layer 21b on the upper side (that is, the side away from the pressurizing chamber 10) as a layer including the active portion and the lower side (that is, the side close to the pressurizing chamber 10). This piezoceramic layer 21a is a so-called unimorph type structure having an inactive layer.

  In this configuration, when the 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 pressurizing chamber 10 (unimorph deformation).

In an actual driving procedure in the present embodiment, the individual electrode 35 is set to a potential higher than the common electrode 34 (hereinafter referred to as a high potential) in advance, and the individual electrode 35 is temporarily set to the same potential as the common electrode 34 every time there is a discharge request. (Hereinafter referred to as a low potential), and then set to a high potential again at a predetermined timing. As a result, the piezoelectric ceramic layers 21a and 21b return to their original shapes at the timing when the individual electrodes 35 become low potential, and the volume of the pressurizing chamber 10 increases compared to the initial state (the state where the potentials of both electrodes are different). To do. At this time, a negative pressure is applied to the pressurizing chamber 10 and the liquid is sucked into the pressurizing chamber 10 from the manifold 5 side. Thereafter, at the timing when the individual electrode 35 is set to a high potential again, the piezoelectric ceramic layers 21a and 21b are deformed so as to protrude toward the pressurizing chamber 10, and the pressure in the pressurizing chamber 10 is reduced due to the volume reduction of the pressurizing chamber 10. The pressure becomes positive and the pressure on the liquid rises, and droplets are ejected. That is, a drive signal including a pulse based on a high potential is supplied to the individual electrode 35 in order to eject a droplet. The ideal pulse width is AL (Acoustic Length), which is the length of time that the pressure wave propagates from the orifice 12 to the discharge hole 8. According to this, the pressure chamber 10
When the inside is reversed from the negative pressure state to the positive pressure state, both pressures are combined, and the liquid droplets can be ejected at a stronger pressure.

  In the liquid flowing through the manifold 5, gas is dissolved or bubbles are mixed. If the angle of the cross section of the manifold 5 is equal to or less than a right angle, bubbles are attached or dissolved gas tends to be generated as bubbles. A plurality of these bubbles may gather together and become larger, or may become larger due to a gas generated from the liquid, and may drift into the manifold 5. When the bubbles enter the individual supply path 6, if the bubbles are large, the pressure propagation of the liquid in the individual flow path 32 is obstructed, so that the liquid cannot be discharged or even if it is small, the pressure of the liquid in the individual flow path 32. The state of propagation changes, and fluctuations in ejection characteristics such as a slower ejection speed and a smaller ejection amount are caused.

  As a method for forming a hole in the plate, there are an etching process and a grinding process. In etching, since it is necessary to form small holes with high accuracy, double-sided etching in which etching is performed from both sides of a plate is usually performed. When holes are formed by double-sided etching or grinding, the side walls of the holes near both sides of the plate become almost perpendicular to the main surface. When the manifold 5 is constituted by such holes, the cross-sectional shape of the manifold 5 has a corner portion G of about 90 degrees, and the above-described bubbles are easily generated.

  Therefore, among the plates 26 to 29 in which the holes constituting the manifold 5 are formed, a plate (sometimes referred to as a first plate) 26 located at the end in the plate stacking direction, and a plate (first plate) In at least one of the plates 29), the holes constituting the manifold 5 are shaped so that the cross-sectional area decreases from the surface on the central side in the stacking direction toward the surface on the opposite side. The part G should not include an angle of 90 degrees or less.

  More specifically, in the manifold 5 configured by stacking a plurality of holes and stacking the other plates 25 and 30 at the upper and lower ends thereof, the first one located at the lower end of the plurality of holes. The cross-sectional area of the hole of the plate 29 is reduced from the top to the bottom, or the cross-sectional area of the hole of the first plate 26 located at the upper end is reduced from the bottom to the top. In order to form such a shape, the first plate 29 may be etched on one side from the upper side. By forming by single-sided etching, the shape of the corner portion G becomes a round shape, and at the corner portion G, the angle formed by the wall surface of the hole of the first plate 29 and the main surface of the plate 30 can be increased. Air bubbles can be more difficult to collect. Similarly, the first plate 26 may be etched on one side from the lower side.

  Although it is preferable for the manifold 5 alone to make the first plates 26 and 29 as described above, in addition to this, in the plates 26 to 29 on which the manifold 5 is formed, portions extending in the stacking direction It is necessary to design in consideration of the shape of the flow path 7.

  In order to perform printing of about 300 to 1200 dpi, if the sectional area of the partial flow path 7 is made extremely large or small, it does not function sufficiently as a flow path. Further, when the thickness (T [μm]) of the first plates 26 and 29 is increased, the opening diameter (W1a [μm]) on the larger side of the apertures of the holes of the first plates 26 and 29 is reduced to the smaller side. The difference between the opening diameter (W1b [μm]) and the large change in the cross-sectional area may deteriorate the discharge characteristics. Further, when the thickness T is increased, the opening diameter (W1a [μm]) becomes too large or the opening diameter (W1b [μm]) becomes too small, so that it does not function sufficiently as a flow path. When T becomes thin, the angle formed by the side wall of the hole and the plates 25 and 30 at the corner portion G of the manifold 5 approaches 90 degrees.

  Therefore, by setting the thickness T to 75 μm or more and 150 μm or less and the opening diameter W1a to 200 μm or more and 450 μm or less, the partial flow path 7 has a sufficiently functioning shape and the angle of the corner portion G can be increased. The thickness T is preferably 75 μm or more and 100 μm or less.

  The opening shape of the partial flow path 7 is preferably a circular shape, but may be a polygonal shape such as an elliptical shape, an oval shape, or a rectangular shape. In the case of a shape other than the circular shape, the area may be set within the range of the area of the circle within the range of the opening diameter. In the range of the thickness T as described above, the opening diameter W1b is about W1a-0.4T to W1a-0.2T, although it depends on the etching conditions. For example, if T is 100 μm and W1a is 200 μm, it is about 160 to 180 μm.

In the one-side etching, the main surface on the opening diameter W1a side is masked and etched. Then, the accuracy of the opening diameter W1a is relatively high, but the formation accuracy of the opening diameter W1b is lower than that. The opening diameter W2 [μm] on the first plate side of the partial flow path 7 in the second plates 25 and 30 stacked on the side that does not become the manifold 5 with respect to the first plates 26 and 29 is smaller than W1b. If so, the influence of the variation in the opening diameter W1b on the ejection characteristics can be reduced.

  By processing the plates other than the first plates 26 and 29 by double-sided etching, the hole forming accuracy of these plates can be increased.

  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, a via hole is formed in a part of the green sheet as necessary, and a via conductor is filled in the via hole.

  Next, each green sheet is laminated to produce a laminate, and pressure adhesion is performed. After firing the pressure-bonded laminate in a high-concentration oxygen atmosphere, the individual electrodes 35 are printed on the surface of the fired body using a gold paste and fired, and then the individual gold thin film 38 and the same gold paste are used. The piezoelectric thin film 39 is printed and fired, and the connection electrode 36 is printed and fired using Ag paste, whereby the piezoelectric actuator substrate 21 is manufactured.

  Next, the flow path member 4 is produced by laminating plates 22 to 31 obtained by a rolling method or the like via an adhesive layer. In the plates 22 to 31 to be stacked, holes to be the manifold 5, the individual supply channel 6, the liquid pressurizing chamber 10, the partial channel 6 and the like are processed into a predetermined shape by etching. Of the holes to be the manifold 5, the first plates 26 and 29 in which holes located at the upper end and the lower end in the stacking direction are formed and etched from one side, respectively.

  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.

  Subsequently, the piezoelectric actuator substrate 21 and the flow path member 4 are laminated via an adhesive layer. After the lamination is finished, the adhesive layer is cured by heating and pressing. Thereafter, a voltage is applied between the individual electrode 35 and the common electrode 34 to polarize the piezoelectric ceramic layer 21b sandwiched between them, whereby the liquid ejection head 2 can be obtained.

DESCRIPTION OF SYMBOLS 1 ... Printer 2 ... Liquid discharge head 4 ... Flow path member 4-1 ... Discharge hole surface 4-2 ... Pressurization chamber surface 5 ... Manifold (common flow path)
5a ... Sub-manifold 5b ... Manifold opening 6 ... Individual supply channel 7 ... Partial channel 8 ... Discharge hole 9 ... Pressurizing chamber group 10 ... Pressurizing chamber 11a , B, c, d: pressurizing chamber row 12: squeezing 13 ... head body 15a, b, c, d ... discharge hole row 21 ... piezoelectric actuator substrate 21a ... piezoelectric ceramic Layer (diaphragm)
21b ... Piezoelectric ceramic layer 22-31 ... Plate 26, 29 ... 1st plate 25, 30 ... 1st plate 32 ... Individual flow path 34 ... Common electrode 35 ... -Individual electrode 35a ... Individual electrode body 35b ... Extraction electrode 36 ... Connection electrode 50 ... Displacement element (pressure part)

Claims (4)

A plurality of partial flow paths having one end serving as a discharge hole, a plurality of pressure chambers connected to the other ends of the plurality of partial flow paths, and a common flow path connected to the plurality of pressure chambers A liquid discharge head including a flow path member provided and a plurality of pressurization units that pressurize the plurality of pressurization chambers,
The flow path member is formed by laminating a plurality of plates having flow path holes including holes serving as the partial flow path, the pressure chamber, and the common flow path,
The common flow path is configured such that a plurality of the flow path holes are overlapped in the stacking direction of the flow path member, and extends in a direction intersecting the stacking direction of the flow path member,
The partial flow path extends in the laminating direction at least in the plate constituting the common flow path,
Among the plates in which the flow path holes constituting the common flow path are open, the first plate, which is the plate located at the extreme end in the stacking direction, has a thickness of 75 to 150 μm. The flow path hole of the first plate has a shape in which a cross-sectional area decreases from a surface on the central portion side in the stacking direction of the common flow path toward a surface on the opposite side. The liquid discharge head according to claim 1, wherein an opening diameter on a central side in the stacking direction of the flow path holes constituting the partial flow path in the plate is 200 to 450 μm.   In the partial flow path located at the boundary between the first plate and the second plate that is the plate that is stacked on the side that does not become the common flow path with respect to the first plate, The opening shape of the flow path hole on the second plate side of the second plate is within the opening shape of the flow path hole on the first plate side of the first plate. The liquid discharge head according to claim 1.   3. The liquid ejection head according to claim 1, wherein the flow path hole of the one plate is formed by one-side etching from a central portion side in a stacking direction.   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 liquid discharge head. Recording device.

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