JP2012196905A - Inkjet head, and recording apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inkjet head that can increase driving frequency.SOLUTION: A head 6 has a vibrating plate 37, a common electrode 39, a piezoelectric body 41, and an individual electrode 43 sequentially laminated from a pressurizing chamber 31 side. The piezoelectric body 41 has a driving unit 41a with which an individual electrode body 44 overlaps and a non-driving unit 41b provided on the outer periphery. The driving unit 41a is polarized in a thickness direction. In comparison with the driving unit 41a, the non-driving unit 41b is not polarized in the thickness direction. A driving signal output unit 8 applies a voltage between the common electrode 39 and the individual electrode 43 at a higher frequency than the maximum driving frequency fc in a discharge element 19 in a state before shape change occurs when it is assumed that tensile stress is applied to the non-driving unit 41b in a state in which the non-driving unit 41b is polarized similarly to the driving unit 41a, whereby domain switching and the shape change accompanying the domain switching occur.

Description

  The present invention relates to an inkjet head and a recording apparatus.

  A piezo-type ink jet head that discharges ink droplets by applying pressure to ink using deformation of a piezoelectric element is known (for example, Patent Document 1). Ink droplet ejection is continuously performed at a predetermined driving frequency. For example, when one dot (halftone dot) on the marking screen is formed by landing a plurality of ink droplets on the same position on the marking screen, the plurality of ink droplets are ejected at a constant ejection interval.

JP 2006-123397 A

  From the viewpoint of speeding up printing, it is desired to shorten the discharge interval, that is, to increase the drive frequency. However, if the drive frequency is increased, the residual ink pressure fluctuation for one ejection affects the ink pressure fluctuation for the next ejection. Drop volume changes. As a result, stable ink droplet ejection cannot be performed, and image quality is degraded.

  An object of the present invention is to provide an ink jet head and a recording apparatus capable of increasing the driving frequency.

  An inkjet head according to an aspect of the present invention includes an ejection element that ejects ink droplets, and a drive signal output unit that applies a voltage to the ejection element, and the ejection element is a recess formed on a predetermined surface. A substrate having a pressurizing chamber formed by the substrate, a diaphragm stacked on the predetermined surface so as to close the pressurizing chamber, a common electrode stacked on the diaphragm, and a piezoelectric body stacked on the common electrode And an individual electrode having an individual electrode body on the pressurizing chamber in a plan view, and the piezoelectric body includes a driving unit on which the individual electrode body overlaps, and a non-circumferential outer periphery thereof. A drive unit, the drive unit is polarized in the thickness direction, the non-drive unit is not polarized in the thickness direction compared to the drive unit, the drive signal output unit, A state where the non-driving part is polarized similarly to the driving part. At a frequency higher than the maximum driving frequency in the discharge device when it is assumed that there is applied a voltage between the individual electrode and the common electrode.

  Preferably, the non-driving part has a large proportion of domains that are polarized in a direction along the direction toward the driving part.

  Preferably, the material of the diaphragm has a lower elastic modulus than the material of the piezoelectric body.

  Preferably, the diaphragm is made of a piezoelectric material having a coercive electric field smaller than that of the piezoelectric material constituting the piezoelectric body.

  Preferably, the material of the non-driving part has a higher elastic modulus than the material of the driving part.

  Preferably, the non-driving part is formed of a material in which a dopant that increases the elastic modulus of the piezoelectric material is mixed with a piezoelectric material similar to the piezoelectric material constituting the driving part.

  An ink jet head according to an aspect of the present invention includes a base body in which a pressurizing chamber is configured by a recess formed on a predetermined surface, a diaphragm stacked on the predetermined surface so as to close the pressurizing chamber, and the diaphragm A common electrode overlaid on the common electrode, and an individual electrode overlaid on the piezoelectric body and having an individual electrode body on the pressurizing chamber in plan view. The body includes a driving unit on which the individual electrode bodies overlap and a non-driving unit on the outer periphery thereof, and the material of the non-driving unit has a higher elastic modulus than the material of the driving unit.

  A recording apparatus according to one embodiment of the present invention includes an ejection element that ejects ink droplets, and a drive signal output unit that applies a voltage to the ejection element, and the ejection element includes a recess formed on a predetermined surface. A base body configured with a pressurizing chamber; a diaphragm overlaid on the predetermined surface so as to close the pressurizing chamber; a common electrode overlaid on the diaphragm; a piezoelectric body overlaid on the common electrode; And an individual electrode having an individual electrode main body on the pressurizing chamber in a plan view, and the piezoelectric body includes a driving unit on which the individual electrode main body overlaps and a non-drive of the outer periphery thereof The drive unit is polarized in the thickness direction, the non-drive unit is not polarized in the thickness direction as compared to the drive unit, and the drive signal output unit is When the drive unit is subjected to the same polarization as the drive unit, tensile stress is applied. As a result, it is assumed that domain switching and the accompanying shape change have occurred, and the common electrode and the common electrode at a frequency higher than the highest drive frequency of the ejection element in a state before the shape change occurs. A voltage is applied between the individual electrodes.

  Preferably, a base body in which a pressurizing chamber is configured by a recess formed on a predetermined surface, a diaphragm stacked on the predetermined surface so as to close the pressurizing chamber, and a common electrode stacked on the diaphragm A piezoelectric body overlaid on the common electrode, and an individual electrode overlaid on the piezoelectric body and having an individual electrode body of the pressurizing chamber in a plan view, the piezoelectric head comprising: A step of applying a direct-current voltage in the thickness direction to the drive unit overlapping the individual electrode of the body to polarize in the thickness direction, and between the common electrode and the individual electrode sandwiching the piezoelectric body polarized in the thickness direction And applying an alternating voltage that forms an electric field having a strength exceeding the coercive electric field of the piezoelectric body in the polarization direction of the piezoelectric body.

  Preferably, the alternating voltage is applied at a temperature higher than room temperature.

  According to said structure, a drive frequency can be made high.

FIG. 3 is a perspective view schematically illustrating a main part of the recording apparatus according to the embodiment of the invention. FIG. 2 is a cross-sectional view of a part of an ink jet head of the recording apparatus of FIG. 1. 3A and 3B are a cross-sectional view and a plan view showing the actuator of the head of FIG. FIG. 4A and FIG. 4B are schematic diagrams illustrating details of the actuators of the embodiment and the comparative example. 5A and 5B are diagrams for explaining drive signals in the recording apparatus of FIG. The figure explaining an example of the prescription | regulation method of the highest drive frequency. FIGS. 7A to 7D are cross-sectional views illustrating an example of a method for manufacturing the actuator. The figure which shows an example of the voltage applied to a piezoelectric material in the orientation process of FIG.7 (d). Fig.9 (a) and FIG.9 (b) are figures which show AL of an Example.

  FIG. 1 is a perspective view schematically showing a main part of a recording apparatus 1 according to an embodiment of the present invention.

  The recording device 1 and the inkjet head 5 to be described later may be either upward or downward, but hereinafter, for convenience, the orthogonal coordinate system xyz is defined and the z-direction normal direction is defined. The term “upper surface” or “lower surface” may be used with the side (upper side in FIG. 1) as the upper side.

  The recording apparatus 1 includes, for example, a transport unit 3 that transports a medium (for example, paper) 101 in a direction indicated by an arrow y1, a head 5 that ejects ink droplets toward the transported medium 101, and the transport unit 3 and the head. 5 and a control unit 7 for controlling the operation of 5.

  For example, the transport unit 3 transports a plurality of media 101 stacked on a supply stack (not shown) one by one to a discharge stack (not shown). The transport unit 3 may have a known appropriate configuration. In FIG. 1, the conveyance path is a straight path, and a conveyance unit provided with a roller 9 that contacts the medium 101 and a motor 11 that rotates the roller 9 is illustrated.

  The head 5 is disposed in the middle of the conveyance path of the medium 101 and faces the medium 101 from the positive side in the z direction. The head 5 may be a serial head that performs a shuttle motion in a direction (main scanning direction, x direction) orthogonal to the printing screen and the conveyance direction of the medium 101, or a line fixed (substantially) in the orthogonal direction. It may be a head. In the present embodiment, the case where the head 5 is a line head will be described as an example.

  The head 5 ejects and attaches ink droplets to the medium 101 at a plurality of positions in the x direction. By repeating this operation as the medium 101 is conveyed, a two-dimensional image is formed on the medium 101.

  The control unit 7 includes, for example, a CPU, a ROM, a RAM, and an external storage device. The controller 7 applies a desired voltage to the motor 11 by outputting a control signal to the motor driver 13 to control the motor 11. Similarly, the control unit 7 outputs a control signal to the head driver 15 to apply a desired voltage to the head 5 to control the head 5.

  The head driver 15 or a part of the head driver 15 and the control unit 7 generates a drive signal (voltage applied to the head 5) including a drive pulse (drive waveform) having a predetermined drive frequency to generate the head 5 The drive signal output unit 8 is configured to output. The drive signal output unit 8 is configured by, for example, a driver IC or a circuit board.

  In FIG. 1, the drive signal output unit 8 and the head 5 are illustrated as being separate from each other. However, part or all of the drive signal output unit 8 may be mounted on the head 5. In this case, the whole of the head 5 and the part (part or all) of the drive signal output unit 8 mounted on the head 5 may be regarded as constituting the head 6 in a broad sense.

  FIG. 2 is a schematic cross-sectional view showing a part of the head 5 in an enlarged manner. 2 is the side facing the medium 101. In FIG.

  The head 5 is a piezo-type head that applies pressure to ink by mechanical distortion of a piezoelectric element. The head 5 has a plurality of ejection elements 19 that eject ink droplets, and FIG. 2 shows one ejection element 19. For example, the plurality of ejection elements 19 are arranged in the xy plane, and each ejection element 19 corresponds to one dot on the medium 101.

  In another aspect, the head 5 includes a base 21 that forms a space for storing ink, and an actuator 23 that applies pressure to the ink stored in the base 21. The plurality of ejection elements 19 includes a base 21 and an actuator 23.

  A plurality of individual channels 25 (one is shown in FIG. 2) and a common channel (reservoir) 27 communicating with the plurality of individual channels 25 are formed inside the base 21. The individual flow path 25 is provided for each ejection element 19, and the common flow path 27 is provided in common for the plurality of ejection elements 19.

  Each individual flow path 25 includes a descender (partial flow path) 29 including a discharge hole 29 a facing the medium 101, a pressurization chamber 31 that communicates with the descender 29, and a supply that communicates the pressurization chamber 31 and the common flow path 27. And a path 33.

  The plurality of individual channels 25 and the common channel 27 are filled with ink. When the volumes of the plurality of pressurizing chambers 31 change and pressure is applied to the ink, the ink is sent from the plurality of pressurizing chambers 31 to the plurality of descenders 29, and a plurality of ink droplets are ejected from the plurality of ejection holes 29a. Is discharged. In addition, the plurality of pressurizing chambers 31 are replenished with ink from a common flow path 27 via a plurality of supply paths 33.

  The cross-sectional shape or planar shape of the plurality of individual channels 25 and the common channel 27 may be set as appropriate. In the present embodiment, the pressurizing chamber 31 is formed with a constant thickness in the z direction and is generally formed in a rhombus (see FIG. 3) in plan view. One corner of the rhombus is in communication with the descender 29, and the opposite corner is in communication with the supply path 33. A part of the supply path 33 has a smaller cross-sectional area perpendicular to the flow direction than the common flow path 27 and the pressurizing chamber 31.

  The base body 21 is configured, for example, by stacking a plurality of substrates 35. The substrate 35 is formed with through holes constituting a plurality of individual channels 25 and a common channel 27. The thickness and the number of layers of the plurality of substrates 35 may be appropriately set according to the shapes of the plurality of individual channels 25 and the common channel 27. The plurality of substrates 35 may be formed of an appropriate material, for example, formed of metal, ceramic, or silicon.

  3A is a cross-sectional view of the vicinity of the actuator 23 in a direction different from that of FIG. 2, and FIG. 3B is a plan view of the vicinity of the actuator 23.

  The actuator 23 shown in FIGS. 2 and 3 is composed of, for example, a unimorph type piezoelectric element that is displaced in a bending mode. Specifically, for example, the actuator 23 includes a diaphragm 37, a common electrode 39, a piezoelectric body 41, and a plurality of individual electrodes 43 that are stacked in order from the pressurizing chamber 31 side.

  The diaphragm 37, the common electrode 39, and the piezoelectric body 41 are provided in common to the plurality of pressurizing chambers 31 so as to cover the plurality of pressurizing chambers 31, for example. On the other hand, the individual electrode 43 is provided for each pressurizing chamber 31.

  The vibration plate 37 is overlaid on the upper surface of the base body 21, thereby closing the pressurizing chamber 31 formed by a recess formed on the upper surface of the base body 21. The individual electrode 43 is generally similar to the pressurizing chamber 31 (in the present embodiment, rhombus), and is slightly smaller than the area of the pressurizing chamber 31 (expands in the center of the pressurizing chamber 31). And an extraction electrode 45 connected to a corner of the individual electrode main body 44.

  The diaphragm 37, the common electrode 39, the piezoelectric body 41, and the individual electrode 43 may be formed of an appropriate material. For example, the diaphragm 37 is made of ceramic, silicon oxide, or silicon nitride. The common electrode 39 and the individual electrode 43 are made of, for example, platinum or palladium. The piezoelectric body 41 is made of ceramic such as PZT (lead zirconate titanate).

  The piezoelectric body 41 has a thickness direction (z direction) as a polarization direction at least in a region overlapping with the individual electrode main body 44. Therefore, when a voltage is applied to the common electrode 39 and the individual electrode 43 to cause an electric field to act on the piezoelectric body 41 in the polarization direction, the piezoelectric body 41 contracts in the plane (in the xy plane). Due to this contraction, the diaphragm 37 is bent so as to protrude toward the pressurizing chamber 31, and as a result, the volume of the pressurizing chamber 31 changes.

  FIG. 4A is a schematic diagram illustrating the details of the actuator 23 and showing the same cross section as FIG. FIG. 4B is a diagram corresponding to FIG. 4A of the actuator 123 of the comparative example.

  4A, the piezoelectric body 41 has a drive part 41a that overlaps the individual electrode main body 44 and a non-drive part 41b on the outer periphery thereof. Although the outer edge of the non-driving unit 41b may be appropriately defined, in the description of the present embodiment, the position overlapping the edge of the pressurizing chamber 31 is defined as the outer edge of the non-driving unit 41b.

  The drive unit 41a is polarized in the thickness direction (z direction) as indicated by an arrow y3. The direction of the polarization direction may be either the positive side or the negative side in the z direction, but FIG. 4A illustrates the case where the direction of the polarization direction is the negative side in the z direction.

  On the other hand, the non-driving part 41b is not polarized in the thickness direction as compared with the driving part 41a. For example, in the non-driving unit 41b, as compared with the driving unit 41a, the ratio of the domain whose polarization direction is the thickness direction is small and the ratio of the domain whose polarization direction is the direction along the xy plane is large. More preferably, the non-driving unit 41b has a higher proportion of domains polarized in a direction along the direction toward the driving unit 41a. However, in this case, the domain direction increases in the domain aligned in the direction toward the drive unit 41a, but the polarization directions may not be aligned. That is, either one of the polarization domain directed toward the drive unit 41a and the polarization domain in the opposite direction may be large, and the polarization domain in the opposite direction may be approximately the same amount, and on average, the polarization domain is not polarized. There may be.

  In addition, as indicated by an arrow y5, the non-driving unit 41b has a length from the inner peripheral side to the outer peripheral side that is longer than the distance between the individual electrode main body 44 and the edge of the pressurizing chamber 31 in the direction parallel to the xy plane. Is also getting longer. On the other hand, the position of the outer edge of the non-driving part 41b is fixed by the base 21 or the like. As a result, as indicated by an arrow y7, a compressive stress is applied from the non-driving unit 41b to the driving unit 41a, and the driving unit 41a is slightly located on the pressurizing chamber 31 side.

  The drive part 41a shows the same property as the elasticity modulus became high by giving compressive stress from the non-drive part 41b compared with the case where compressive stress is not given. For example, the drive unit 41a has a higher resonance frequency than when no compressive stress is applied.

  The non-driving part 41b is made of a material in which a dopant 42 that increases the elastic modulus is dispersed with respect to a piezoelectric material similar to the piezoelectric material that constitutes the driving part 41a. That is, the elastic modulus (Young's modulus E2) of the piezoelectric material of the non-driving part 41b is higher than the elastic modulus (Young's modulus E1) of the piezoelectric material of the driving part 41a.

  As the dopant 42 (acceptor) that increases the elastic modulus, for example, if the piezoelectric material is PZT, an element having an ion valence smaller than that of the main component of the B site may be used. For example, when the main component of the B site is Zr, examples of the dopant 42 include Al or Mn.

  The diaphragm 37 is made of a material having a smaller elastic modulus (Young's modulus E3) than that of the material constituting the piezoelectric body 41 (drive unit 41a). Here, in the piezoelectric material, if the composition is substantially the same, the smaller the coercive electric field Ec, the lower the elastic modulus. Therefore, the diaphragm 37 is formed of, for example, a piezoelectric material having a coercive electric field Ec3 having a lower strength than the coercive electric field Ec1 of the piezoelectric material constituting the driving unit 41a.

  Note that the piezoelectric body 141 of the comparative example shown in FIG. 4B is polarized in the thickness direction over the entire body (including the driving unit 141a and the non-driving unit 141b). The non-driving unit 141b has a length from the inner peripheral side to the outer peripheral side that is equal to the distance between the individual electrode main body 44 and the edge of the pressurizing chamber 31 in the direction parallel to the xy plane. No compressive stress is applied from 41b to the drive unit 41a (or smaller compared to FIG. 4A), and the piezoelectric body 41 is flat (compared to FIG. 4A) ( The drive part 41a is not located on the pressurizing chamber 31 side.) The dopant 42 is not dispersed in the non-driving portion 141b, the vibration plate 137 has the same composition as the piezoelectric body 41, and the elastic modulus of the driving portion 141a, the non-driving portion 141b and the vibration plate 137 is the same.

  FIGS. 5A and 5B are diagrams illustrating the drive signal Sd output from the drive signal output unit 8 to the head 5.

  The drive signal Sd is, for example, a signal whose signal level is a change in potential with respect to the reference potential. Further, a reference potential is applied to the common electrode 39. Then, when the drive signal Sd is input to the individual electrode 43, a voltage is applied between the common electrode 39 and the individual electrode 43.

  Specifically, FIG. 5A shows the waveform of the drive signal Sd in one ejection and the change (dotted line Ln) of the meniscus displacement q of the ink in the ejection holes 29a, and FIG. The waveform of the drive signal Sd in each ejection is shown. 5 (a) and 5 (b), the horizontal axis indicates time, and in FIG. 5 (a), the vertical axis indicates voltage V and displacement q (the direction toward the outside of the inkjet head 5 is positive), In FIG. 5B, the vertical axis indicates the voltage V.

  The driving method of the ejection element 19 may be appropriately selected from known driving methods such as a so-called pulling method and a pushing method, but FIG. 5 will be described using the pulling method as an example.

  As shown in FIG. 5 (a), in the stroke type, in the standby state (time t0 to t1) in which ejection is not performed, the signal level of the drive signal Sd is a voltage in the polarization direction with respect to the drive unit 41a. The applied potential V1 is maintained. Accordingly, the drive unit 41a contracts in the xy plane, and the actuator 23 is bent in a direction protruding toward the pressurizing chamber 31 side. That is, the pressurizing chamber 31 is in a state where the volume is reduced.

  When the ejection timing arrives (time t1), the drive signal output unit 8 outputs a drive pulse Ps for temporarily stopping voltage application to the individual electrode 43 (included in the drive signal Sd). As a result, the reduction of the drive unit 41a is released, and hence the bending of the actuator 23 is also released. That is, the volume of the pressurizing chamber 31 is increased. As the volume of the pressurizing chamber 31 is increased, the ink in the descender 29 and the supply path 33 is drawn into the pressurizing chamber 31 (the meniscus is displaced to the negative side).

  The volume of the pressurizing chamber 31 is reduced and reflected at the timing before and after the pressure wave from the discharge hole 29a generated at this time is reflected by the squeezing and corresponding to the rise of the pulse (time point t2). Ink is sent from the pressurizing chamber 31 so that the pressure wave generated by the contraction of the pressure wave and the pressure wave generated by the volume contraction is sent from the pressurizing chamber 31 (the meniscus is displaced to the positive side). As a result, ink droplets are ejected from the ejection holes 29a (near time t4).

  Thereafter, in the pressurizing chamber 31 and the like, the ink pressure gradually attenuates while fluctuating at the natural frequency (resonance frequency). In other words, the pressure fluctuation that vibrates at the natural frequency remains in the pressurizing chamber 31 and the like, and the meniscus causes undershoot (around time t6 and the like) and overshoot (around time t8 and the like).

  AL (Acoustic Length), which is the time for the pressure wave to travel from the ejection hole 29a to the squeezing (more precisely, the end of the squeezed pressure chamber 31), is half the natural vibration period of the ink from the ejection hole 29a. . The natural vibration period of the ink in the discharge element 19 includes the natural vibration of the ink itself in the flow path from the discharge hole 29a to the squeezed (the natural vibration of the ink having the same shape as the ink in the flow path), and the pressurizing chamber 31. The natural vibration of the displacement element (the vibration plate 37, the common electrode 29, the piezoelectric body 41, and the individual electrode main body 44) directly above becomes a synthesized vibration cycle. Therefore, even if the shape of the flow path does not change and the natural vibration period of the ink itself in the flow path does not change, if the natural vibration period of the displacement element changes, the natural vibration period of the ink changes and AL also changes. Become. The influence of the displacement element on the AL varies depending on the displacement method of the displacement element. However, since the displacement element that performs flexural vibration as in this embodiment is easily deformed, the contribution to the AL is large. It is necessary to consider the impact. Note that the width of the drive pulse Ps is, for example, about AL in the stroke type.

  As shown in FIG. 5B, the drive pulse Ps is continuously input to the ejection element 19 at a constant drive cycle Ta (a constant drive frequency f). Thereby, for example, a plurality of ink droplets are ejected when one dot (halftone dot) is formed on the mark screen. Note that gradation is expressed by increasing or decreasing the number of the plurality of ink droplets.

  FIG. 6 is a diagram for explaining an example of a method for defining the maximum drive frequency of the drive pulse Ps. In FIG. 6A, the horizontal axis represents the driving frequency f (1 / Ta), and the vertical axis represents the predetermined number when ejecting a predetermined number (two or more) of ink droplets at the driving frequency f. The ink amount D of the entire ink droplet is shown.

  A solid line Lp indicates the ink amount D in the present embodiment, and a dotted line Lc indicates the ink amount D of the comparative example illustrated in FIG. It is assumed that the ink amount D when the driving cycle Ta is sufficiently large (when the driving frequency f is sufficiently low) is the same in the embodiment and the comparative example.

  Regarding the solid line Lp, when the drive frequency f is lower than the predetermined drive frequency fp, the ink amount D is constant. On the other hand, when the drive frequency f exceeds the predetermined drive frequency fp, the ink amount D varies according to the change of the drive frequency f. This is because as the drive frequency f increases, the drive cycle Ta decreases, and the pressure wave generated by one drive pulse Ps affects the pressure wave generated by the next drive pulse Ps.

  Therefore, for example, in order to realize stable ink ejection in which the number of ink droplets is proportional to the amount of ink, the driving frequency fp (the maximum of the range in which the ink amount D of the driving frequency f is maintained constant). Value) is defined as the maximum drive frequency, and the actual drive frequency f is preferably set within a range equal to or less than the maximum drive frequency fp.

  Hereinafter, more specific examples will be described. The length of the drive pulse for ejecting one drop by striking is about AL. In addition, when n droplets are ejected continuously (one dot is formed by landing on an adjacent place on the medium), the second and subsequent drive pulses are matched to the natural vibration of the ink. Since it is sent every 2 ALs for transmission, the length of the entire drive waveform is about (2n−1) AL. Furthermore, after the drive waveform for forming one dot is finished, the residual vibration of the ink is large for about one natural vibration period (2AL) of the ink. Therefore, even if the next drive waveform is sent, the effect of the residual vibration It is considered that the discharge characteristics are not stable. Therefore, in the strike, when there are n drive pulses for ejecting ink in the drive waveform for forming one dot, the drive frequency is preferably set so that the period is greater than (2n + 1) AL, and the maximum drive The frequency is preferably 1 / (2n + 1) AL.

  Similarly, in a more general case, after the drive signal for performing the ink ejection operation is sent, the residual vibration of the ink is large for about one natural vibration period (2AL), and even if the next drive signal is sent, It is considered that the next discharge is not stable. Therefore, the maximum drive frequency is preferably 1 / (longest drive signal + 2AL).

  Similarly, in the comparative example indicated by the dotted line Lc, the driving frequency fc, which is the highest value in the range in which the ink amount D is constant, of the driving frequency f is defined as the highest driving frequency, and in the range below the highest driving frequency fc, It is preferable that the actual driving frequency f is set.

  Here, in the actuator 23 of the present embodiment, as described with reference to FIG. 4, the elastic modulus is substantially increased by applying a compressive stress to the drive unit 41a from the non-drive unit 41b. Therefore, in the embodiment, the compliance becomes smaller and the AL becomes shorter than in the comparative example. As a result, in the embodiment, the driving cycle Ta can be shortened. That is, the maximum drive frequency fp of the embodiment is higher than the maximum drive frequency fc of the comparative example.

  In the recording apparatus 1 (head 6) of the embodiment, a frequency exceeding the maximum drive frequency fc of the comparative example can be set as an actual drive frequency. As will be described later, in the recording apparatus 1 of the present embodiment, a drive frequency fq higher than the current maximum drive frequency fp can be set as the actual drive frequency.

  The maximum drive frequency can also be obtained by simulation using each dimension of the flow path, the viscosity of the ink to be used, and the physical properties of the vibration plate 37 and the piezoelectric body 41, especially the piezoelectric body 41 including the polarization state.

  FIG. 7A to FIG. 7D are cross-sectional views for explaining an example of a method for manufacturing the actuator 23. However, for convenience of explanation, hatching of the cross section of the piezoelectric body 41 may be omitted. Moreover, although a specific composition etc. change with progress of a manufacturing process, the same code | symbol shall be used before and after the change.

  First, a green sheet to be the piezoelectric body 41 and a green sheet to be the diaphragm 37 are prepared. A conductive paste to be the common electrode 39 and the individual electrode 43 is printed on these green sheets (for example, a green sheet to be the piezoelectric body 41), and the green sheets are laminated and fired. Thereby, as shown in FIG. 7A, a laminated body of the diaphragm 37, the common electrode 39, the piezoelectric body 41 and the individual electrode 43 is formed.

  Next, as shown in FIG. 7B, the dopant 42 is dispersed in the piezoelectric material to be the non-driving portion 41b by an ion implantation method or the like. In the ion implantation method, the individual electrode 43 functions as a mask, but a resist mask may be formed separately from the individual electrode 43. Further, the dopant 42 may or may not be dispersed in a portion outside the non-driving portion 41b of the piezoelectric body 41 (a portion that is outside the pressurizing chamber 31 in plan view).

  Next, as shown in FIG. 7C, a voltage is applied between the individual electrode 43 and the common electrode 39 by the DC power source 53 to perform a polarization process on the drive unit 41a. By this polarization treatment, polarization with the thickness direction as the polarization direction indicated by the arrow y3 is performed. The polarization may be performed on the entire piezoelectric body 41. In that case, first, a polarization electrode is formed by applying and drying a conductive paste on substantially the entire surface of the piezoelectric body 41 including the drive unit 41a and the non-drive unit 41b. Then, a DC voltage is applied between the polarization electrode and the common electrode 39 by the DC power source 53. In this polarization process, polarization is performed with the thickness direction being the polarization direction in both the drive unit 41a and the non-drive unit 41b. Thereafter, the polarization electrode 51 is removed by ultrasonic cleaning or the like in an organic solvent.

  Next, as shown in FIG. 7D, an AC voltage is applied between the individual electrode 43 and the common electrode 39 by the AC power supply 55. This voltage application is performed at a temperature higher than room temperature (room temperature), for example.

  In addition, the polarization process by a direct current voltage as shown in FIG.7 (c) is generally performed at normal temperature (it may be performed above normal temperature in this embodiment). In the Japanese Industrial Standard, the normal temperature is defined as 5-35 ° C. 7D is performed at a temperature of 40 ° C. or higher, for example, and is preferably 45 ° C. or higher and the Curie temperature of the piezoelectric body 41 or lower. If the piezoelectric body 41 is PZT, it may be performed at a temperature of about 100 ° C.

  FIG. 8 is a diagram illustrating an example of voltages applied to the common electrode 39 and the individual electrodes 43 in the alignment process of FIG. The horizontal axis indicates time, and the vertical axis indicates voltage.

  A voltage is applied to the common electrode 39 and the individual electrode 43 in the same direction as the polarization direction. That is, a voltage for reducing the drive unit 41a in the xy plane (a voltage in the same direction as the voltage applied to the drive unit 41a by the typical drive signal output unit 8; a positive voltage in this embodiment) is applied.

  The maximum value of the AC voltage is a voltage Von that forms an electric field having a strength exceeding the coercive electric field Ec of the piezoelectric body 41 (drive unit 41a). The voltage Voff when the voltage drops is, for example, a reference potential (0 V). That is, in the piezoelectric body 41, application of an electric field having a strength exceeding the coercive electric field and release thereof are repeated. The voltage Voff may not be 0V.

  The time Ton when the electric field having a strength exceeding the coercive electric field is applied to the piezoelectric body 41 is set longer than the time Toff when the electric field is released, for example.

  As described above, when an electric field for reducing the drive unit 41a in the xy plane is applied to the drive unit 41a, the non-drive unit 41b receives a tensile force from the drive unit 41a. When such a tensile force is repeatedly received, domain switching occurs in the non-driving unit 41b, and the proportion of domains in which the polarization direction is oriented in the direction toward the driving unit 41a increases. Thereby, in the non-driving part 41b, the ratio of the domain which makes a polarization direction other than the thickness direction of the piezoelectric material 41 increases compared with the driving part 41a. Further, the non-driving unit 41b is deformed into a stretched state.

  In addition, the ratio of the domain in which the polarization direction is oriented in the direction toward the drive unit 41a is oriented in the direction toward the drive unit 41a using a scanning microscope capable of measuring the polarization state on the surface of the piezoelectric body 41. And the domain oriented in the direction orthogonal to the direction toward the drive unit 41a are divided into an angle of 45 degrees with respect to the direction toward the drive unit 41a and head toward the drive unit 41a. It can be obtained by measuring the ratio of the area of the domain oriented in the direction to the whole.

  In addition, the application of such an electric field is performed at a strength exceeding the coercive electric field Ec, at a high temperature, and / or by setting the time Ton longer than the time Toff. Domain switching occurs quickly.

  In the manufacturing process of the embodiment, in the case where only the driving unit 41a is polarized, the non-driving unit 41b is extended compared to the state where the domain of the non-driving unit 41b is randomly polarized. Has occurred. Further, in the manufacturing process of the embodiment, in the case where the entire piezoelectric body 41 is once polarized, the non-driving portion 41b has the same thickness as the driving portion 41a as in the comparative example shown in FIG. There is a state in which the direction is polarized and the non-driving portion 41b is extended (FIG. 7C). As can be understood from this, the matter that the maximum drive frequency fp of the embodiment described above with reference to FIG. 6 is higher than the maximum drive frequency fc of the comparative example is that the non-drive unit 41b performs domain switching and this. In other words, it can be said that the highest drive frequency fp is higher than the highest drive frequency fc in the ejection element 19 in a state before the change in shape is assumed.

  Further, the driving of the head 5 after the shipment of the head 5 may have the effect of extending the non-driving portion 41b, similarly to the orientation process of FIG. 7D, and the non-driving portion 41b is extended. Later, the driving frequency fq higher than the maximum driving frequency fp at the time of shipment shown in FIG. 6 can be set as the maximum driving frequency.

  In general heads, it is necessary to drive the heads a considerable number of times in order for domain switching of the non-driving unit 41b to start to occur by driving the heads after shipment. In general, the head is set as a period of use until such domain switching occurs and discharge characteristics start to be affected. The drive frequency is set based on the state before domain switching occurs. That is, in a general head, the driving frequency is set to be equal to or lower than the maximum driving frequency fc of the comparative example shown in FIG.

  According to the embodiment described above, the head 6 includes the ejection element 19 that ejects ink droplets and the drive signal output unit 8 that applies a voltage to the ejection element 19. The discharge element 19 includes a base 21 in which a pressurizing chamber 31 is configured by a recess formed on the upper surface, a vibration plate 37 that is stacked on the upper surface of the base 21 so as to close the pressurization chamber 31, and a vibration plate 37. A common electrode 39, a piezoelectric body 41 overlaid on the common electrode 39, and an individual electrode 43 that is overlaid on the piezoelectric body 41 and has an individual electrode body 44 that extends in the center of the pressurizing chamber 31 in plan view. Have. The piezoelectric body 41 has a drive unit 41a on which the individual electrode main body 44 overlaps and a non-drive unit 41b on the outer periphery thereof.

  The drive unit 41a is polarized in the thickness direction, and the non-drive unit 41b is not polarized in the thickness direction as compared to the drive unit 41a. The drive signal output unit 8 assumes that the non-drive unit 41b has undergone domain switching and a shape change associated therewith when a tensile stress is applied from a state where the same polarization as the drive unit 41a is applied. Sometimes, a voltage is applied between the common electrode 39 and the individual electrode 43 at a frequency higher than the maximum drive frequency fc in the ejection element 19 in a state before the shape change occurs.

  Therefore, ink can be ejected at a higher driving frequency than a head that can use a state where domain switching has not occurred in the non-driving unit 41b. As a result, it is possible to meet the demand for higher printing speed. Further, since the state in which domain switching has occurred is set to the usable state, the occurrence of domain switching does not mean the end of the use period of the head 5, and the use period is expected to be prolonged.

  The drive signal output unit 8 may apply a voltage between the common electrode 39 and the individual electrode 43 at a frequency fq that is higher than the highest drive frequency fp of the current ejection element 19.

  In this case, ink can be ejected at a higher driving frequency in accordance with the shortening of AL accompanying the use of the head 5. Further, depending on the characteristics of the head 5, it is expected that a high driving frequency corresponding to AL is maintained over a longer period than when the driving frequency is set to the maximum driving frequency fp at the time of shipment.

  The material of the diaphragm 37 has a lower elastic modulus than the material of the piezoelectric body 41. Accordingly, an increase in the reaction force received by the non-driving unit 41b from the diaphragm 37 is suppressed, and a compressive force can be efficiently applied from the non-driving unit 41b to the driving unit 41a. As a result, the effect of shortening AL and the accompanying increase in drive frequency increases.

  The diaphragm 37 is made of a piezoelectric material having a coercive electric field smaller than that of the piezoelectric material constituting the piezoelectric body 41. Therefore, it is possible to realize the diaphragm 37 having a low elastic modulus while making the diaphragm 37 and the piezoelectric body 41 have substantially the same composition, and it is expected that the manufacturing process is simplified and the cost is reduced.

  The material of the non-driving part 41b has a higher elastic modulus than the material of the driving part 41a. Accordingly, the elastic modulus of the drive unit 41a and the non-drive unit 41b as a whole is increased, and the compressive stress applied to the drive unit 41a due to the extension of the non-drive unit 41b is increased, the AL is shortened, and the drive frequency associated therewith is increased. Increase effect increases.

  The non-driving unit 41b is formed of a material in which a dopant 42 that increases the elastic modulus of the piezoelectric material is mixed with a piezoelectric material similar to the piezoelectric material constituting the driving unit 41a. Therefore, the non-driving part 41b whose elastic modulus is higher than that of the driving part 41a is simply realized.

<Example>
(Examples 1-3)
Examples 1 to 3 having different piezoelectric materials constituting the diaphragm 37 were set, and AL was estimated.

Specifically, PZT whose composition is represented by ABO ₃ was assumed as the piezoelectric material of the piezoelectric body 41 and the diaphragm 37 of Examples 1 to 3. Compositions 1 to 3 having different specific composition contents were set for this PZT, and the following combinations of the piezoelectric bodies 41 and the diaphragms 37 of Examples 1 to 3 were assumed.
Piezoelectric body Diaphragm Example 1 Composition 1 Composition 1
Example 2 Composition 1 Composition 2
Example 3 Composition 1 Composition 3

Specific contents of Compositions 1 to 3 are as follows.
Composition 1 (diaphragm of Example 1, piezoelectric material of Examples 1 to 3):
A site: Pb _0.92 Ba _0.08
B site: (Zn _1/3 Sb _2/3 ) _0.105 Zr _0.435 Ti _0.460
Additives: Pb _1/2 NbO ₃ (0.3 wt%), Bi ₂ O ₃ (0.2 wt%)
Composition 2 (diaphragm of Example 2):
A site: Pb _0.92 Ba _0.08
B site: (Zn _1/3 Sb _2/3 ) _0.105 Zr _0.465 Ti _0.430
Additives: Pb _1/2 NbO ₃ (0.3 wt%), Bi ₂ O ₃ (0.2 wt%)
Composition 3 (diaphragm of Example 3):
A site: Pb _0.88 Ba _0.08 B site:
(Zn _1/3 Sb _2/3 ) _0.18 (Co _1/3 Sb _2/3 ) _0.02 (Zr _0.500 Ti _0.500 ) _0.800
Additives: Pb _1/2 NbO ₃ (0.3 wt%), Bi ₂ O ₃ (1.0 wt%)

  The composition of the A site and the B site indicates that the atoms contained in those compositions are mainly located at the corresponding site, and that all the atoms are located at the corresponding site. is not.

The characteristics of the diaphragm 37 and the trial calculation results such as AL in Examples 1 to 3 are as follows.
Ec Er d31 AL
Example 1 1.5 3200 250 7.0
Example 2 1.0 3800 300 5.2
Example 3 0.8 5760 330 4.8

  In the above, Ec represents the coercive electric field (V / μm) of the diaphragm 37, Er represents the dielectric constant of the diaphragm 37, and d31 represents the displacement (pm / V) of the actuator 23. The unit of AL is μs.

  In Example 1, the coercive electric field Ec of the diaphragm 37 is equivalent to the coercive electric field Ec of the piezoelectric body 41. In Examples 2 and 3, the coercive electric field Ec of the diaphragm 37 is greater than the coercive electric field Ec of the piezoelectric body 41. Is also small. In Examples 2 and 3, AL is shorter than that in Example 1. Therefore, according to this trial calculation example, it was confirmed that by using a piezoelectric material having a coercive electric field Ec smaller than that of the piezoelectric body 41 as the material of the diaphragm 37, the AL can be shortened and, consequently, the driving frequency can be increased.

(Examples 1, 5 and 6)
In the head 5 of Example 1 described above, Examples 5 and 6 in which ion implantation was performed on the non-driving unit 41b were set, and AL was estimated.

Specifically, the following combinations were assumed for the piezoelectric body 41 (non-driving unit 41b).
Piezoelectric material Example 1 Composition 1
Example 5 Composition 1 + Al Ion Implantation Example 6 Composition 1 + Mn Ion Implantation Note that the piezoelectric material of the diaphragm 37 in Examples 5 and 6 is the composition 1 as in Example 1.

The characteristics of the piezoelectric body 41 (non-driving portion 41b) in Examples 1, 5, and 6 and the trial calculation results of AL and the like are as follows. The meanings and units of Ec, Er, d31, and AL are the same as in Examples 1 to 3.
Ec Er d31 AL
Example 1 1.5 3200 250 7.0
Example 5 2.0 2800 230 4.8
Example 6 2.3 2500 200 4.0

  From this trial calculation example, it was confirmed that by ion implantation, the AL can be shortened and, consequently, the drive frequency can be increased.

(Examples 7 to 9)
Examples 7 to 9 having different AC voltage application times described with reference to FIGS. 7D and 8 were set, and experimental values of the resonance frequency and AL of the actuator 23 were obtained. Specifically, the application time of the alternating voltage in Examples 7 to 9 was set to 0.5 hour, 1 hour, and 5 hours.

  Fig.9 (a) is a figure which shows AL of Examples 7-9. The horizontal axis represents the resonance frequency fr (kHz) of the actuator 23, and the vertical axis represents AL (μs). Points P7 to P9 indicate the resonance frequencies fr and AL of the seventh to ninth embodiments. A solid line L1 indicates an approximate straight line of the points P7 to P9.

  From this experimental result, it was confirmed that when the application time of the AC voltage is increased, the resonance frequency is increased and the AL is shortened.

(Examples 10 to 12)
Resonance frequency, AL, etc. were estimated about Examples 10-12 which made the application time of alternating voltage longer than Examples 7-9. Specifically, the application time of the alternating voltage in Examples 10 to 12 was set to 24 hours, 45 hours, and 100 hours.

  FIG. 9B is the same diagram as FIG. Points P7 to P9 indicate the resonance frequencies fr and AL of Examples 7 to 9 as in FIG. 9A, and points P10 to P12 indicate the resonance frequencies fr and AL of Examples 10 to 12, respectively. A solid line L3 indicates an approximate straight line of the points P7 to P12.

  The approximate straight line indicated by the solid line L3 matches the points P7 to P9 on which the experimental values are plotted and the points P10 to P12 on which the estimated values are plotted, and the validity of the estimated values of the resonance frequencies fr and AL in Examples 10 to 12 are appropriate. Showing sex.

  And it was confirmed by the points P10 to P12 in FIG. 9B that the actuator 23 expected to be driven at a considerably high frequency can be obtained by sufficiently increasing the AC voltage application time.

Below, the experimental value and estimated value of the various parameters of Examples 7-12 are shown.
Tm fr AL fp
Example 7 0.5 498 7.1 25
Example 8 1 550 7.0 28
Example 9 5 602 6.8 30
Example 10 24 740 6.4 37
Example 11 45 816 6.2 41
Example 12 100 925 5.9 45

  Tm represents the application time (h) of the alternating voltage, fr represents the resonance frequency (kHz), and fp represents the maximum drive frequency (see FIG. 6, kHz). The unit of AL is μs.

  The present invention is not limited to the above embodiment, and may be implemented in various aspects.

  The drive frequency need not always be constant, and may be changed according to the content of the image, for example. The drive frequency is always the highest drive frequency fc (the non-drive unit is subjected to the domain switching and the shape change caused by the tensile stress applied from the state where the polarization is the same as that of the drive unit. Assuming that the frequency is higher than the highest drive frequency of the ejection element in the state before the shape change occurs. A head that is temporarily driven at a drive frequency higher than the maximum drive frequency fc according to the contents of the image or according to other appropriate circumstances is also included in the present invention.

  The material of the diaphragm may have an elastic modulus equal to or higher than that of the piezoelectric material, and the material of the non-driving part has an elastic modulus equal to or lower than that of the material of the driving part. May be.

  The manufacturing method shown in FIG. 7 is merely an example, and may be changed as appropriate. For example, after sintering a laminated body of a piezoelectric body, a common electrode, and a diaphragm, a conductive paste serving as an individual electrode may be printed and heat-treated, or ion implantation for dispersing a dopant in a non-driving part may be performed on the individual electrode. It may be done before placement.

DESCRIPTION OF SYMBOLS 1 ... Recording device, 5 ... Head (a drive signal output part is not included), 6 ... Head (a drive signal output part is included), 8 ... Drive signal output part, 19 ... Discharge element, 21 ... Base | substrate, 37 ... Diaphragm, 39 ... Common electrode, 41 ... Piezoelectric body, 41a ... Drive unit, 41b ... Non-drive unit, 43 ... Individual electrode, 44 ... Individual electrode body.

Claims (10)

An ejection element for ejecting ink droplets;
A drive signal output unit for applying a voltage to the ejection element;
Have
The ejection element is
A base body in which a pressurizing chamber is constituted by a recess formed on a predetermined surface;
A diaphragm overlaid on the predetermined surface so as to close the pressurizing chamber;
A common electrode overlaid on the diaphragm;
A piezoelectric body overlaid on the common electrode;
An individual electrode superimposed on the piezoelectric body and having an individual electrode body on the pressurizing chamber in plan view;
The piezoelectric body has a drive unit on which the individual electrode main body overlaps, and a non-drive unit on the outer periphery thereof,
The drive part is polarized in the thickness direction,
The non-driving part is not polarized in the thickness direction compared to the driving part,
The drive signal output unit has a frequency higher than a maximum drive frequency of the ejection element when the non-drive unit is assumed to be in a state where polarization similar to that of the drive unit is performed. Inkjet head that applies voltage between individual electrodes. The inkjet head according to claim 1, wherein the non-driving unit has a large proportion of domains polarized in a direction along the direction toward the driving unit. The inkjet head according to claim 1, wherein the vibration plate material has a lower elastic modulus than the piezoelectric material. The inkjet head according to claim 3, wherein the diaphragm is made of a piezoelectric material having a coercive electric field smaller than that of the piezoelectric material constituting the piezoelectric body. The inkjet head according to claim 1, wherein the material of the non-driving unit has a higher elastic modulus than the material of the driving unit. The inkjet according to claim 5, wherein the non-driving unit is formed of a material in which a dopant that increases the elastic modulus of the piezoelectric material is mixed with a piezoelectric material similar to the piezoelectric material constituting the driving unit. head. A base body in which a pressurizing chamber is constituted by a recess formed on a predetermined surface;
A diaphragm overlaid on the predetermined surface so as to close the pressurizing chamber;
A common electrode overlaid on the diaphragm;
A piezoelectric body overlaid on the common electrode;
An individual electrode superimposed on the piezoelectric body and having an individual electrode body on the pressurizing chamber in plan view;
The piezoelectric body has a drive unit on which the individual electrode main body overlaps, and a non-drive unit on the outer periphery thereof,
The material of the non-driving part is an inkjet head having a higher elastic modulus than the material of the driving part. An ejection element for ejecting ink droplets;
A drive signal output unit for applying a voltage to the ejection element;
Have
The ejection element is
A base body in which a pressurizing chamber is constituted by a recess formed on a predetermined surface;
A diaphragm overlaid on the predetermined surface so as to close the pressurizing chamber;
A common electrode overlaid on the diaphragm;
A piezoelectric body overlaid on the common electrode;
An individual electrode superimposed on the piezoelectric body and having an individual electrode body on the pressurizing chamber in plan view;
The piezoelectric body has a drive unit on which the individual electrode main body overlaps, and a non-drive unit on the outer periphery thereof,
The drive part is polarized in the thickness direction,
The non-driving part is not polarized in the thickness direction compared to the driving part,
The drive signal output unit has a frequency higher than a maximum drive frequency of the ejection element when the non-drive unit is assumed to be in a state where polarization similar to that of the drive unit is performed. A recording device that applies voltage between individual electrodes. A base body in which a pressurizing chamber is configured by a recess formed on a predetermined surface, a diaphragm overlaid on the predetermined surface so as to close the pressurizing chamber, a common electrode overlaid on the diaphragm, and the common A method of manufacturing an ink jet head, comprising: a piezoelectric body overlaid on an electrode; and an individual electrode overlaid on the piezoelectric body and having an individual electrode body on the pressurizing chamber in plan view,
Applying a direct current voltage in the thickness direction to the drive unit overlapping the individual electrodes of the piezoelectric body to polarize in the thickness direction;
An alternating voltage is applied in the polarization direction of the piezoelectric body between the common electrode and the individual electrode sandwiching the piezoelectric body polarized in the thickness direction, forming an electric field whose strength exceeds the coercive electric field of the piezoelectric body. And a process of
A method of manufacturing an inkjet head having The inkjet head manufacturing method according to claim 9, wherein the application of the AC voltage is performed at a temperature higher than room temperature.

Images