JP2014065184A - Liquid discharge head and recording device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid discharge head including a reservoir in which a difference between pressures of liquid to be supplied to a head body is small, and to provide a recording device using the same.SOLUTION: A liquid discharge head 2 includes: a head body having a plurality of discharge holes arranged along one direction; and a reservoir 40 having a reservoir channel 42 that is extended along the one direction and supplies liquid to the head body. The reservoir channel 42 supplies the liquid to the head body via a plurality of connection channels 42d arranged along the one direction and has a supply hole 42b through which the liquid is supplied from the outside. The connection channels 42d is formed such that channel resistance becomes smaller, as a distance along the one direction from the supply hole 42b is longer.

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.

  Further, such a liquid discharge head is known to include a reservoir in addition to the head main body in order to cope with an increase or decrease in the amount of ink discharged, and is provided along the liquid discharge head in one direction. There is known one in which ink is supplied from a reservoir channel in a reservoir (see, for example, Patent Document 1).

JP 2006-256342 A

  However, in the liquid discharge head described in Patent Document 1, since the liquid is supplied to the head body from a plurality of locations in the middle of the reservoir channel that is long in one direction, the liquid is supplied from the reservoir channel to the head body. The pressure applied to the liquid varies depending on the position where the liquid is applied, and the liquid ejection characteristics vary depending on the position of the ejection hole in the head body.

  Accordingly, it is an object of the present invention to provide a liquid discharge head having a reservoir capable of reducing the difference in pressure of liquid supplied to the head body, and a recording apparatus using the same.

  A liquid discharge head according to the present invention includes a head body having a plurality of discharge holes arranged along one direction, and a reservoir having a reservoir channel extending in the one direction for supplying liquid to the head body. The liquid discharge head, wherein the reservoir flow path supplies liquid to the head main body via a plurality of connection flow paths arranged along the one direction and is supplied with liquid from the outside The plurality of connection channels are characterized in that the channel resistance decreases as the distance along the one direction from the supply hole increases.

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 discharge head of the present invention, the difference in the pressure of the liquid flowing from the reservoir to the head body through the plurality of connection flow paths depending on where the connection flow path is located in the liquid discharge head is unlikely to occur. Variations in ejection characteristics within the head can be reduced.

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 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. FIG. 3 is an enlarged view of a region surrounded by an alternate long and short dash line in FIG. It is a longitudinal cross-sectional view along the VV line of FIG. FIG. 2 is a longitudinal sectional view of the liquid ejection head in FIG. 1.

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

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

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

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

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

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

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

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

  The four liquid discharge heads 2 are arranged close to each other along the conveyance direction by the conveyance belt 111. Each liquid discharge head 2 has a head body 13 at the lower end. The lower surface of the head body 13 is a discharge hole surface 4-1 provided with a large number of discharge holes 8 for discharging liquid (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. The ejection hole 8 of each liquid ejection head 2 is in one direction (a direction parallel to the printing paper P and not parallel to the conveyance direction of the printing paper P (typically, an orthogonal direction 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 liquid discharge head 2 of the present invention will be described. FIG. 6 is a longitudinal sectional view of the liquid discharge head 2. The liquid discharge head 2 is long in one direction (left-right direction in FIG. 6). The liquid discharge head 2 includes a head body 13 including a flow path member 4 and a piezoelectric actuator unit 21 having a discharge hole surface 4-1 in which discharge holes 8 are arranged along the longitudinal direction, and a reservoir 40. . The liquid discharge head 2 further includes a housing 90. In FIG. 6, the internal structure of the flow path member 4 is omitted. In the cross section of FIG. 6, the piezoelectric actuator unit 21 is not visible, and the piezoelectric actuator unit 21 is joined to the flow path member 4 and accommodated in a recess provided in the plate 40e.

  In the head body 13, a reservoir 40 is stacked on the flow path member 4, and a piezoelectric actuator unit 21 is accommodated therebetween. The reservoir 40 is provided with a reservoir channel 42 extending in the longitudinal direction, and a plurality of liquids that are introduced into the reservoir channel 42 from the outside through the supply holes 42 b are arranged along the longitudinal direction of the reservoir channel 42. It flows into the head main body 13 through the connecting flow path 42d.

  A part of the inner wall of the reservoir channel 42 is a damper 46 made of an elastically deformable material. The surface of the damper 46 opposite to the reservoir channel 42 is a space so that the damper 46 can be deformed, and the volume of the reservoir channel 42 can be changed by elastically deforming the damper 46. Thereby, when the liquid discharge amount changes, the liquid can be stably supplied. The damper 46 is not necessarily provided.

  Next, the flow path member 4 constituting the liquid discharge head 2 of the present invention will be described. FIG. 2 is a plan view of the head main body 13. FIG. 3 is an enlarged plan view of a region surrounded by a one-dot chain line in FIG. 2 and is a part of the head main body 13. In FIG. 3, some flow paths are omitted for easy understanding of the arrangement. FIG. 4 is an enlarged plan view of the same position as FIG. 3, and the flow path different from FIG. 3 is omitted so that the position of the discharge hole 8 can be easily understood. In FIGS. 3 and 4, for easy understanding of the drawings, the liquid pressurizing chamber 10 (pressurizing chamber group 9), the squeeze 12 and the discharge holes 8 which are to be drawn by broken lines below the piezoelectric actuator unit 21 are shown. Is drawn with a solid line. FIG. 5 is a longitudinal sectional view taken along line VV in FIG.

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

A manifold 5 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. Liquid is supplied to the manifold 5 from the reservoir channel 42 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 is sometimes referred to as a sub-manifold 5a, and the manifold 5 from the opening 5b to the sub-manifold 5a is referred to as a liquid supply path). 5c). The liquid supply path 5 c 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. That is, both ends of the sub-manifold 5a are connected to the liquid supply path 5c.

  The flow path member 4 has four pressure chamber groups 9 in which a plurality of liquid pressure 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 to open to a pressurizing chamber surface 4-2 that is the upper surface of the flow path member 4. These liquid pressurizing chambers 10 are arranged over almost the entire surface of the upper surface of the flow path member 4 facing the piezoelectric actuator unit 21. Therefore, each pressurizing chamber group 9 formed by these liquid pressurizing chambers 10 occupies an area having almost the same size and shape as the piezoelectric actuator unit 21. Further, the opening of each liquid pressurizing chamber 10 is closed by adhering the piezoelectric actuator unit 21 to the upper surface of the flow path member 4.

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

  As a whole, the liquid pressurizing chambers 10 connected from the manifold 5 constitute rows of the liquid pressurizing chambers 10 arranged in the longitudinal direction of the flow path member 4 at equal intervals, and the rows are 16 rows parallel to each other in the short direction. It is arranged. The number of liquid pressurizing chambers 10 included in each 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 the pressurizing unit. Has been. 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.

  In other words, when the ejection holes 8 are projected so as to be orthogonal to a virtual straight line parallel to the longitudinal direction of the liquid ejection head 2, 4 is connected to each sub-manifold 5 a within the range of R of the virtual straight line shown in FIG. 3. One discharge hole 8, that is, a total of 16 discharge holes 8, is equally spaced at 600 dpi. Moreover, the individual flow paths 32 are connected to the sub manifolds 5a at intervals corresponding to 150 dpi on average. This is because 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. The individual flow paths 32 are formed at intervals of an average of 170 μm (25.4 mm / 150 = 169 μm intervals if 150 dpi) in the extending direction, that is, the main scanning direction.

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

  A large number of discharge holes 8 are formed in the liquid discharge surface on 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 disposed in a region facing the piezoelectric actuator unit 21 on the lower surface side of the flow path member 4. These discharge holes 8 occupy a region having substantially the same size and shape as the piezoelectric actuator unit 21 as one group, and the displacement element 50 of the corresponding piezoelectric actuator unit 21 is displaced from the discharge hole 8. Droplets can be ejected.

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

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

  Third, there is a communication hole constituting a flow path communicating from the other end of the liquid pressurizing chamber 10 to the discharge hole 8, and this communication hole is referred to as a descender (partial flow path) in the following description. The descender is formed on each plate from the base plate 23 (specifically, the outlet of the liquid 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. Depending on the position of the sub-manifold 5a, the manifold plate 29 may have a portion where no hole is formed, whereby the cross-sectional area of the sub-manifold 5a is changed.

  Such communication holes are connected to each other to form an individual flow path 32 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 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 discharge hole 8 opened in the lower surface.

  The reservoir 40 is obtained by a rolling method or the like in the same manner as the flow path member 4, etched plates 40 a and c, a damper plate 40 b that is an elastic material, a plate 40 d that is manufactured by plastic injection molding, and a metal plate Is laminated with a plate 40e produced by cutting. The plate 40d may be manufactured by cutting a metal plate and the plate 40e by plastic injection molding.

  As shown in FIG. 5, the piezoelectric actuator unit 21 has a laminated structure including two piezoelectric ceramic layers 21a and 21b. Each of these piezoelectric ceramic layers 21a and 21b has a thickness of about 20 μm. The total thickness of the piezoelectric actuator unit 21 is about 40 μm. Each of the piezoelectric ceramic layers 21a and 21b extends so as to straddle the plurality of liquid pressurizing chambers 10 (see FIG. 3). The piezoelectric ceramic layers 21a and 21b are made of a lead zirconate titanate (PZT) ceramic material having ferroelectricity.

  The piezoelectric actuator unit 21 includes a common electrode 34 made of a metal material such as Ag—Pd and an individual electrode 35 made of a metal material such as Au. As described above, the individual electrode 35 is disposed at a position facing the liquid pressurizing chamber 10 on the upper surface of the piezoelectric actuator unit 21. One end of the individual electrode 35 is drawn out of a region facing the liquid pressurizing chamber 10 to form a connection electrode 36. The connection electrode 36 is formed by, for example, applying a mixture of silver particles, resin particles, a solvent, and the like, drying and fixing, and has a convex shape with a thickness of about 15 μm. In addition, a signal transmission unit is connected to the connection electrode 36, and a drive signal is supplied from the control unit 100 through the signal transmission unit. The drive signal is supplied in a constant cycle in synchronization with the conveyance speed of the print medium P.

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

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

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

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

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

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

  In gradation printing, gradation expression is performed by the number of droplets ejected continuously from the ejection holes 8, that is, the droplet amount (volume) adjusted by the number of droplet ejections. For this reason, the number of droplet discharges corresponding to the designated gradation expression is continuously performed from the discharge holes 8 corresponding to the designated 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 this case, it is considered that the speed of the liquid droplets ejected later increases, but this is preferable because the landing points of a plurality of liquid droplets are close.

  In such a liquid discharge head 2, the reservoir flow path 42 extends along the longitudinal direction of the liquid discharge head 2, and as shown in FIG. 2, the liquid is supplied to the opening 5 b of the common flow path provided along the longitudinal direction. Supply. The reservoir channel main body 42a has a shape such as a rectangular parallelepiped or a shape in which the cross-sectional area in the direction orthogonal to the longitudinal direction is substantially constant, or a plurality of the reservoir channel main body 42a and the common channel opening 5b are connected. Assuming that the shapes of the connection flow paths 42d are all the same, the closer the opening 5b of the common flow path is to the supply hole 42b, the stronger the liquid pressure and the greater the liquid supply amount. As a result, the amount of droplets ejected from the ejection holes close to the supply holes 42b increases, and the variation in ejection characteristics within the liquid ejection head 2 increases, for example, darker printing. In the present embodiment, the liquid in the liquid discharge head 2 is basically set to a negative pressure so that a meniscus is formed in the nozzle shape portion of the discharge hole 8. That is, the absolute value of the negative pressure value of the liquid pressure becomes smaller.

  Therefore, the shape of the connection flow path 42d is set such that the flow path resistance of the connection flow path 42d decreases as the distance along the longitudinal direction from the supply hole 42b increases. By doing so, the difference in the pressure of the liquid depending on the position of the opening 5b of the common flow path can be reduced, and the variation in the discharge characteristics in the liquid discharge head 2 can be reduced. For example, in the liquid discharge head 2 of the present embodiment, although it varies depending on what is printed, 0.6 to 1 mL / s of liquid is discharged, and the same amount of liquid flows in the reservoir flow path. The pressure applied to the liquid at the opening 5b of each common flow path can be calculated or simulated from the flow velocity, the shape of the reservoir flow path 42, and the characteristics of the liquid to be used. The flow path resistance of the connection flow path 42d may be adjusted as described.

  In order to simplify the examination content, it is better to consider the reservoir 42 alone. The reservoir channel main body 42a has a width (19 mm) and a length (140 mm) that are the same as the range in which the opening 5b of the common channel is arranged when the head main body 2a is viewed in plan view. When the simulation is performed with 4 mm, the liquid flows at 0.09 mL / s in the connection flow path 42d closest to the supply hole 42b, and the liquid flows at 0.03 mL / s in the connection flow path 42d farthest. The flow path resistance of the farthest connection flow path 42d may be made smaller than the closest connection flow path 42d so that this flow rate difference is reduced.

  In order to reduce the channel resistance, for example, either the channel length is shortened or the cross-sectional area is increased. Further, a filter may be placed in the connection flow path 42d, and the number and the aperture ratio may be changed for adjustment.

  Further, the difference in the pressure of the liquid depending on the position of the opening 5b of the common flow path can also be reduced by increasing the area of the cross section orthogonal to the longitudinal direction of the reservoir flow path main body 42a as the distance from the supply hole 42b increases.

  A portion of the reservoir channel main body 42b on the head main body 13 side is a plate-like plate-like portion 44, and a through-hole penetrating the plate-like portion 44 is a connection flow passage 42d, which is separated from the supply hole 42b in the longitudinal direction. Therefore, if the thickness of the plate-like portion 44 is reduced, the cross-sectional area perpendicular to the longitudinal direction of the reservoir channel main body 42a is increased as the distance from the supply hole 42b in the longitudinal direction is increased, and the flow of the connection channel 42d is increased. Since the road resistance can be reduced, it can be effectively adjusted rather than adjusting each of them individually.

The (average) height of the reservoir channel main body 42a is preferably 4 to 8 mm. When the height is lowered, the flow velocity is increased, so that the pressure difference due to the position of the opening 5b of the common flow path is increased, and the volume occupied by the connection flow path 42d for adjustment is increased. Since the flow path resistance of 42a becomes large and the throughput of the liquid falls, there is a possibility that the supply of the liquid is insufficient. If the height is high, the flow rate is low and liquid stays easily, and a liquid containing particles may cause problems such as sedimentation.

  Since the (average) height of the reservoir channel body 42a is 4 mm when the flow rate is 1 mL / s, the amount of liquid is 8 seconds, and when the height is 8 mm, the flow rate is 1 mL / s and the amount is 28 seconds. The volume of the road body 42a is preferably 8 to 28 seconds of the flow rate.

  Since the supply hole 42b is provided at the end of the reservoir channel 42 in the longitudinal direction, an empty space can be provided in the upper part of the reservoir 40, and a heater, a circuit board for processing discharge signals, and the like are provided there. Can be arranged.

  Further, when the supply hole 42b is arranged at one end and the discharge hole 42e is provided at the other end, and the liquid is first supplied, the liquid is supplied from the supply hole 42b and the liquid is supplied from the discharge hole 42e. It is good to carry out while discharging. In this case, bubbles that may be contained in the liquid are not easily discharged from the discharge hole 42e without going to the flow path member 4 side. It can be difficult to be in the state of bubbles. When discharging the liquid, the discharge hole 42e is closed, and the liquid is supplied only from the supply hole 42b.

  The channel connecting the reservoir channel main body 42a to the supply hole 42b is a server channel end portion 42c having a smaller cross-sectional area perpendicular to the longitudinal direction than the reservoir channel main body 42a. Since the path end portion 42c is connected to the reservoir channel main body 42a on the side far from the discharge hole surface 4-1, gas that may be contained in the liquid hardly enters the channel member 4. it can. The liquid discharge head 2 is basically used in a state where the discharge hole surface 4-1 is directed downward. The discharge hole surface 4-1 is preferably horizontal, but when printing on the recording paper P conveyed on the drum, the discharge hole surface 4-1 is inclined to some extent in order to be arranged substantially parallel to the drum surface. May be used. In such a state, the reservoir channel end 42c is connected to the reservoir channel main body 42a on the side far from the discharge hole surface 4-1, so that the bubbles that have entered from the reservoir channel end 42c remain in the reservoir flow. It drifts in the upper part of the road body 42a and is difficult to reach the flow path member 4 side. Note that the bubbles accumulated in the upper part of the reservoir channel main body 42a may be discharged from the discharge hole 42e during maintenance or the like.

  Further, the flow path connecting the reservoir flow path main body 42a to the supply hole 42b is a server flow path end 42c having a smaller cross-sectional area perpendicular to the longitudinal direction than the reservoir flow path main body 42a. The server flow path end 42c is connected to the reservoir flow path main body 42a on the side closer to the discharge hole surface 4-1, and has an air trap part, so that the gas that may be contained in the liquid is It is difficult to enter the reservoir channel main body 42a. It is preferable that the gas accumulated in the air trap portion is removed by providing an air discharge hole in the air trap portion.

  In this embodiment, the displacement element 50 using piezoelectric deformation is shown as the pressurizing unit. However, the present invention is not limited to this, and any other device that can pressurize the liquid in the liquid pressurizing chamber 10 may be used. For example, the liquid in the liquid pressurizing chamber 10 may be heated and boiled to generate pressure, or may be one using MEMS (Micro Electro Mechanical Systems).

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

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

  A well-known adhesive layer can be used as the adhesive layer, but in order not to affect the piezoelectric actuator unit 21 and the flow path member 4, an epoxy resin, phenol resin, polyphenylene having a thermosetting temperature of 100 to 150 ° C. It is preferable to use at least one thermosetting resin adhesive selected from the group of ether resins. Bonding can be performed by heating to the thermosetting temperature using such an adhesive layer.

  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.

  Similarly, the reservoir 40 includes metal plates 40a and 40c having various holes, a resin film damper plate 40b to be a damper 46, an injection-molded plastic plate 40d, and a metal plate cut plate 40e. Are laminated and bonded.

  Furthermore, the liquid discharge head 2 can be manufactured by laminating and bonding the piezoelectric actuator unit 21 to the flow path member 4 and laminating and bonding the reservoir 40 to the flow path member 4. The same adhesive layer as the adhesive layer of the flow path member 4 can be used as the adhesive layer of these laminated adhesives.

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 5a ... Sub manifold 5b ... Manifold opening 5c ... Liquid supply path 6 ... Individual supply flow path 8 ... Discharge hole 9 ... Pressurizing chamber group 10 ... Liquid pressurizing chamber 11a, b, c, d ... pressurizing chamber row 12 ... squeezing 13 ... head body 15a, b, c, d ... discharge hole row 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 40 ... Reservoir 40a, 40c-40e .. (reservoir) plate 40b ... damper plate 42 ... reservoir channel 42a ... reservoir channel body 42b ... (reservoir channel) supply hole 42c ... reservoir channel body end 42d ... Connection channel 42e ... Discharge hole (of reservoir channel) 44 ... Plate-like part 46 ... Damper 50 ... Displacement element (pressurizing part)
90 ... Case

Claims (7)

A liquid ejection head comprising: a head body having a plurality of ejection holes arranged along one direction; and a reservoir having a reservoir channel extending in the one direction for supplying liquid to the head body,
The reservoir channel includes a supply hole for supplying the liquid to the head main body via a plurality of connection channels arranged along the one direction, and for supplying the liquid from the outside.
The liquid discharge head, wherein the plurality of connection flow paths have a smaller flow path resistance as a distance from the supply hole along the one direction is longer.   2. The liquid ejection head according to claim 1, wherein an area of a cross section orthogonal to the one direction of the reservoir channel increases as the distance from the supply hole in the one direction increases.   A portion of the reservoir on the head main body side of the reservoir channel is a plate-like portion provided with a plurality of through holes that are the plurality of connection channels, and extends from the supply hole in the one direction. The liquid discharge head according to claim 2, wherein the thickness of the plate-like portion decreases as the distance from the liquid discharge portion increases.   The liquid discharge head according to claim 1, wherein the supply hole is provided at an end of the reservoir channel. The plurality of discharge holes are disposed on a discharge hole surface provided in the head body, and the reservoir is connected to the opposite side of the discharge hole surface of the head body,
The reservoir channel is connected to the reservoir channel main body and the supply hole and the reservoir channel main body at the end on the side where the supply hole is provided. A reservoir channel end having a narrow cross-sectional area perpendicular to
The liquid discharge head according to claim 4, wherein the reservoir channel end is connected to the reservoir channel main body on a side farther from the discharge hole surface. The plurality of discharge holes are disposed on a discharge hole surface provided in the head body, and the reservoir is connected to the opposite side of the discharge hole surface of the head body,
The reservoir channel is connected to the reservoir channel main body and the supply hole and the reservoir channel main body at the end on the side where the supply hole is provided. A reservoir channel end having a narrow cross-sectional area perpendicular to
The liquid discharge head according to claim 4, wherein the reservoir channel end is connected to the reservoir channel main body on a side close to the discharge hole surface and has an air trap portion.   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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