JP5101966B2 - Liquid discharge head and manufacturing method thereof - Google Patents

Description

  The present invention relates to a liquid discharge head configured by sequentially arranging at least a lower electrode, a piezoelectric body, and an upper electrode on a pressure chamber communicating with a liquid discharge port, and a manufacturing method thereof.

  In Patent Document 1, the upper electrode width in the arrangement direction of the liquid chamber (pressure chamber) is Lu, the length of the piezoelectric body in the arrangement direction of the liquid chamber is Lp, and the lower electrode width in the arrangement direction of the liquid chamber is L1. In which Lu ≦ Lp <L1 is described.

  Patent Document 2 describes that the outer circumference of the piezoelectric transducer has a size and a position that overlap with a chamber opening (pressure chamber).

  In Patent Document 3, when the width of the pressure chamber in the short direction is L and the width of the drive electrode in the same direction as the width L is δ, 0.1 mm ≦ L and 0.29 ≦ (δ / L) ≦ 1 and further an optimum condition of 0.57 ≦ (δ / L) ≦ 0.77 is described.

In Patent Document 4, the planar shape of the individual electrode is formed in a shape substantially similar to the planar shape of the opening of the recess serving as the pressurizing chamber (pressure chamber), and the area A _{1 of the} individual electrode and the area of the opening of the recess are formed. A ₂ is defined as A ₂ × 0.6 ≦ A ₁ ≦ A ₂ × 0.9.

In Patent Document 5, the piezoelectric active region is formed smaller than the corresponding pressurizing chamber in the plane direction parallel to the piezoelectric film, and the entire circumference is formed between the pressurizing chamber and the peripheral edge in the plane direction. Are arranged at intervals.
JP 2002-370353 A JP 2003-25573 A JP 2003-165214 A JP 2004-351878 A JP 11-34321 A

  There is a demand to appropriately select the aspect ratio of the pressure chamber (the ratio CWy / CWx when the width in the longitudinal direction of the pressure chamber is CWy and the width in the short direction is CWx) according to the required performance of the liquid ejection head. . Specifically, for example, when pursuing a high density nozzle arrangement in a single row, it is preferable that the aspect ratio of the pressure chamber is large. However, if the aspect ratio of the pressure chamber is increased, the flow path in the pressure chamber is increased. Since resistance increases, when pursuing high-frequency discharge of a highly viscous liquid, the aspect ratio of the pressure chamber is preferably closer to “1”.

  On the other hand, there is a need for a liquid discharge head with high discharge efficiency. There is also a need for a liquid ejection head with less variation in ejection force between nozzles. In addition, there is a need for a highly reliable liquid discharge head that is less susceptible to fluctuations in discharge amount over time and failure.

  By the way, as shown in FIG. 17, since the longitudinal direction of the pressure chamber 52 coincides with the ink flow direction, the electrodes 91 and 93 sandwiching the piezoelectric body 92 extend to a position near the edge of the pressure chamber 52. The displacement profile 98 does not become an efficient and smooth displacement profile, but a vibration mode having a harmonic period is generated in the pressure chamber 52, and the bubbles 99 are likely to be accumulated, and the ink ejection force from the nozzle 51 is reduced. There is also a problem of adverse effects such as residual vibration.

  The present invention has been made in view of such circumstances, and provides a liquid discharge head having high discharge efficiency, low discharge variation, and high reliability in accordance with an aspect ratio of a selected pressure chamber, and a manufacturing method thereof. The purpose is to provide.

In order to achieve the object, the invention according to claim 1 is configured such that at least a lower electrode, a piezoelectric body, and an upper electrode are sequentially arranged on a pressure chamber communicating with a liquid discharge port, and the pressure chamber has a surface. The cross section of the concave portion along the surface direction of the piezoelectric body has a short direction and a long direction, and the area of the piezoelectric body is larger than the concave cross sectional area of the pressure chamber, and the lower portion of the piezoelectric body The area of the active region sandwiched between the electrode and the upper electrode and contributing to the displacement of the piezoelectric body is smaller than the sectional area of the concave portion of the pressure chamber, and the width CWx in the short direction of the pressure chamber and the pressure chamber the aspect ratio of the longitudinal width cwy if (cWy / CWx) is 2 to 5, before Symbol of the lateral direction of the width DWx and the pressure chamber of the active region of the piezoelectric said lateral direction of the Ratio to width CWx (DWx / CWx It is 0.4 to 0.75, and the ratio between the longitudinal width cwy of said longitudinal width DWy and the pressure chamber of the active region of the piezoelectric (DWy / CWy) is the Ln The natural logarithm is within a range of ± 0.05 with the aspect ratio (CWy / CWx) of the pressure chamber as a variable x and a central value of 0.133 × Ln (x) +0.7312. A liquid discharge head is provided.

  Here, the aspect ratio of the pressure chamber is arbitrarily selected within the range of 2 to 5 according to the required performance of the liquid ejection head.

  According to the present invention, even when the aspect ratio of the pressure chamber is arbitrarily selected within the range of 2 to 5, a high displacement volume in the vicinity of the maximum value can be obtained, so that the discharge efficiency is good. In addition, since the variation of the displacement volume with respect to the manufacturing variation of the electrode width becomes very small, the discharge variation between the nozzles becomes extremely low. In addition, the displacement profile becomes an efficient and smooth displacement profile, and it is difficult to generate harmonic components in the pressure chamber, bubbles are not easily generated in the pressure chamber, and no residual vibration remains during liquid discharge, so that the reliability is high. Therefore, it is possible to provide a liquid discharge head having high discharge efficiency, low discharge variation, and high reliability corresponding to the aspect ratio of the selected pressure chamber.

  The shape of the cross section of the concave portion of the pressure chamber may be a rectangular shape, a parallelogram shape, or may have an R at a corner. Even when the parallelogram shape or the corner has R, the excluded volume does not change much when the aspect ratio (CWy / CWx) is 2 or more.

  In the case of a rectangular shape, the aspect ratio is the width of the short side of the rectangle, the width of the long side is the length of the long side of the rectangle, and the parallelogram shape. The width in the short direction means the shorter one of the heights of the parallelogram, and the width in the longitudinal direction means the length of the long side of the parallelogram.

  According to a second aspect of the present invention, in the first aspect of the present invention, the piezoelectric body is formed of a single plate structure, and the minimum value Lmin [the creepage distance from the edge of the upper electrode along the surface of the piezoelectric body] [mu] m] and a drive electric field E [V] of the piezoelectric body satisfy a relationship of E / Lmin≤1.

  According to the present invention, dielectric breakdown due to creeping discharge can be prevented, and the reliability of the liquid discharge head can be further improved.

According to a third aspect of the present invention, in the method of manufacturing a liquid discharge head in which at least a lower electrode, a piezoelectric body, and an upper electrode are sequentially formed on a pressure chamber communicating with a liquid discharge port, the pressure chamber has the planar piezoelectric element. A cross section of the concave portion along the surface direction of the body has a short side direction and a long side direction, and an area of the piezoelectric body is larger than a cross sectional area of the concave portion of the pressure chamber, and the lower electrode and the upper portion of the piezoelectric body The area of the active region sandwiched between the electrodes and contributing to the displacement of the piezoelectric body is made smaller than the cross-sectional area of the concave portion of the pressure chamber, and the width CWx in the short direction of the pressure chamber and the pressure chamber the aspect ratio of the longitudinal width cWy (cWy / CWx) is in the case of 2 to 5, before Symbol said the lateral direction of the lateral direction of width DWx the pressure chamber width of the active region of the piezoelectric CWX Ratio (DWx / CW ) Is a 0.4 to 0.75, and the ratio between the said longitudinal width DWy active region before Symbol piezoelectric body and the pressure chamber longitudinal width CWy (DWy / CWy) is Ln Is a natural logarithm, the aspect ratio (CWy / CWx) of the pressure chamber is a variable x, and is within a range of ± 0.05 centered on 0.133 × Ln (x) +0.7312. A method for manufacturing a liquid discharge head is provided.

  The invention described in claim 4 is the invention described in claim 3, wherein the piezoelectric body is formed by sputtering, AD (aerosol deposition) method, sol-gel method, screen printing, MOCVD (metal organic chemical vapor deposition) method, laser. Provided is a method for manufacturing a liquid discharge head, wherein a thin film is formed by any one of an ablation method and a hydrothermal synthesis method.

  According to a fifth aspect of the present invention, there is provided an image forming apparatus comprising the liquid ejection head according to the first or second aspect.

  According to the present invention, high discharge efficiency, low discharge variation, and high reliability can be provided in accordance with the aspect ratio of the selected pressure chamber.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a plan perspective view showing an overall configuration of an example of a liquid discharge head.

  A head 50 shown as an example in FIG. 1 is a so-called full-line head, and is a direction (arrow in the figure) perpendicular to the relative movement direction of the recording medium 16 with respect to the head 50 (sub-scanning direction indicated by arrow S in the figure). A structure in which a large number of nozzles 51 for ejecting ink toward the recording medium 16 are two-dimensionally arranged over a length corresponding to the maximum recording area width Wm of the recording medium 16 in the main scanning direction indicated by M). Have.

  In the liquid ejection head 50, a plurality of ejection elements 54 including a nozzle 51, a pressure chamber 52 communicating with the nozzle 51, and a liquid supply port 53 have a predetermined acute angle with respect to the main scanning direction M and the main scanning direction M. They are arranged along two oblique directions forming θ (0 degrees <θ <90 degrees). In FIG. 1, only a part of the ejection elements 54 is illustrated for convenience of illustration.

  Specifically, the nozzles 51 are arranged at a constant pitch d in an oblique direction that forms a predetermined acute angle θ with respect to the main scanning direction M, and thus, “on a straight line along the main scanning direction M” d × cos θ ”can be handled equivalently.

  Although FIG. 1 shows an example of a full-line type liquid discharge head, the liquid discharge head of the present invention is not particularly limited to such an example. For example, a single full-line liquid discharge head may be configured by combining a plurality of strip-shaped head units. Further, for example, a shuttle type (serial type) liquid discharge head that is reciprocally scanned in the main scanning direction (a direction orthogonal to the conveyance direction of the recording medium) may be used.

  FIG. 2A is an enlarged plan view showing a part of the liquid discharge head 50 of FIG. FIG. 2B is a cross-sectional view taken along line BB in FIG. 2 (A) and 2 (B), only two ejection elements 54 are shown, but in reality, a large number of ejection elements 54 are two-dimensionally arranged in the liquid ejection head 50 as shown in FIG. ing.

  2B, the liquid discharge head 50 mainly includes a nozzle plate 21 in which nozzles 51 are formed, a communication channel plate 22 in which nozzle communication channels 51a communicating with the nozzles 51 are formed, and pressure. A pressure chamber plate 23 in which the chamber 52 is formed, a diaphragm 24 constituting the upper wall surface of the pressure chamber 52, an insulating layer 25, and a piezoelectric actuator 60 as means for generating pressure in the pressure chamber 52, , Including. The ejection element 54 mainly includes a nozzle 51, a pressure chamber 52, a piezoelectric actuator 60, and a liquid supply port (not shown) for supplying liquid to the pressure chamber 52.

The diaphragm 24 is made of, for example, a metal material such as SUS (stainless steel), Ni, or Cr, Si, ZrO ₂ , or a piezoelectric material.

  The thickness of the diaphragm 24 is 5 μm, for example.

The insulating layer 25 is made of an insulating material such as SiO ₂ or ZrO ₂ . In the present invention, the material of the insulating layer 25 is not particularly limited to SiO ₂ and ZrO ₂ .

  The insulating layer 25 has a thickness of 1 μm, for example.

  The piezoelectric body 62 is made of a piezoelectric material such as PZT (lead zirconate titanate). In the present invention, the material of the piezoelectric body 62 is not particularly limited to PZT.

  The thickness of the piezoelectric body 62 is, for example, 4 to 5 μm.

  The lower electrode 61 and the upper electrode 63 are made of a conductive material such as Pt, Ir, or Au, for example. In the present invention, the material of the lower electrode 61 and the upper electrode 63 is not particularly limited to Pt, Ir, and Au.

  The thicknesses of the lower electrode 61 and the upper electrode 63 are, for example, 0.2 μm.

  The upper electrode 63 is a common electrode (common electrode) in the plurality of piezoelectric actuators 60 and is grounded. On the other hand, the lower electrode 61 is an individual electrode (individual electrode) for each piezoelectric actuator 60. When a predetermined drive signal is individually applied to the lower electrode 61, that is, when a predetermined drive voltage is individually applied between the electrodes 61 and 63 by the piezoelectric actuators 60, the lower electrode 61 is sandwiched between the electrodes 61 and 63. The piezoelectric body 62 is displaced (deformed), the pressure in the pressure chamber 52 is changed via the vibration plate 24, and the liquid is discharged from the nozzle 51.

  2A and 2B show an example of a groove separation structure in which the piezoelectric body 62 is separated by the groove 64 between the ejection elements 54. FIG. The piezoelectric body in the present invention is not particularly limited to the groove separation structure, and may be a structure in which the ejection elements 54 are physically completely separated, or a physical structure in which there is no groove 64 between the ejection elements 54. May have a non-separable structure.

  The area of the piezoelectric body 62 in each ejection element 54 is larger than the recess cross-sectional area of the pressure chamber 52 (the area of the opening cross section parallel to the diaphragm 24, also referred to as “opening cross-sectional area”). That is, the piezoelectric body 62 is formed so as to cover the pressure chamber 52 via the diaphragm 24. As a result, damage to the diaphragm 24 at the boundary between the diaphragm 24 and the partition wall 23a of the pressure chamber 52 is prevented, reliability is improved, and stress applied to the piezoelectric body 62 is reduced.

  In this example, in each ejection element 54, the area of the upper electrode 63 is smaller than the recess sectional area of the pressure chamber 52. On the other hand, the area of the lower electrode 61 is larger than the cross-sectional area of the concave portion of the pressure chamber 52. In addition, the lower electrode and the upper electrode in the present invention are not particularly limited when the area of one electrode is smaller than the sectional area of the concave portion of the pressure chamber. Both the area of the lower electrode 61 and the area of the upper electrode 63 may be smaller than the cross-sectional area of the recess of the pressure chamber 52.

  FIG. 3A is a cross-sectional view used for explaining the active region 62 a of the piezoelectric body 62. As shown in FIG. 3A, the piezoelectric body 62 has an active region 62a (which contributes to displacement (deformation) of the piezoelectric body 62 when a predetermined drive voltage is applied between the lower electrode 61 and the upper electrode 63. A non-active region 62b (also referred to as a “non-driving region”) that does not contribute to the displacement (deformation) of the piezoelectric body 62 when a driving voltage is applied between the lower electrode 61 and the upper electrode 63. It is divided into and. Specifically, when the piezoelectric actuator 60 is viewed from the vertical direction indicated by the arrow Z in FIG. 3A (the direction perpendicular to the diaphragm 24), the upper electrode 63, the piezoelectric body 62, and the lower electrode 61 are viewed. The region where all of these overlap is the active region 62a, and the other region is the non-active region 62b.

  FIG. 3B shows the pressure chamber 52 and the active region 62a of the piezoelectric body 62 seen through from the vertical direction Z in FIG. The pressure chamber 52 has a short side direction and a long side direction in a concave cross section parallel to the surface direction of the planar piezoelectric body 62 shown in FIG. In other words, the pressure chamber 52 has a lateral direction and a longitudinal direction in the concave cross section parallel to the lower electrode 61, the piezoelectric body 62, and the upper electrode 63.

  As shown in FIG. 3B, the area of the active region 62 a of the piezoelectric body 62 is smaller than the cross-sectional area of the concave portion of the pressure chamber 52. Specifically, in the short direction of the pressure chamber 52 (hereinafter simply referred to as “short direction”), the width DWx of the active region 62 a is smaller than the width CWx of the pressure chamber 52. In the longitudinal direction of the pressure chamber 52 (hereinafter simply referred to as “longitudinal direction”), the width DWy of the active region 62 a is smaller than the width CWy of the pressure chamber 52.

  In this example, since the area of the upper electrode 63 is the smallest among the lower electrode 61, the piezoelectric body 62, and the upper electrode 63, the area of the active region 62 a of the piezoelectric body 62 is equal to the area of the upper electrode 63. Specifically, the width DWx of the active region 62a is equal to the width of the upper electrode 63 in the short direction, and the width DWy of the active region 62a is equal to the width of the upper electrode 63 in the longitudinal direction. .

  FIG. 4 shows the relationship between the generated pressure and the aspect ratio CWy / CWx of the pressure chamber 52 (the ratio of the width CWy in the longitudinal direction of the pressure chamber 52 to the width CWx in the short direction of the pressure chamber 52).

  In FIG. 4, the generated pressure increases as the aspect ratio CWy / CWx of the pressure chamber 52 increases. If the generated pressure is small, the pressure chamber 52 is not suitable for discharging a high-viscosity liquid. Therefore, the aspect ratio of the pressure chamber 52 is set to “2” or more. Further, the larger the aspect ratio CWy / CWx of the pressure chamber 52, the more suitable the nozzles 51 are arranged with high density. On the other hand, as the aspect ratio CWy / CWx of the pressure chamber 52 increases, the flow path resistance in the pressure chamber 52 increases and becomes unsuitable for high-frequency discharge. Therefore, the aspect ratio of the pressure chamber 52 is set to “5” or less. .

  Hereinafter, when the aspect ratio of the pressure chamber 52 is arbitrarily selected within the range of 2 to 5, a preferable size of the active region 62a of the piezoelectric body 62 will be described in detail.

  FIG. 5 shows the relationship between the width DWx of the upper electrode 63 in the lateral direction, the displacement volume ΔV, and the main stress when the aspect ratio CWy / CWx of the pressure chamber 52 is “4”.

  In FIG. 5, the horizontal axis represents the electrode width ratio DWx / CWx in the short direction (that is, the ratio of the upper electrode width DWx to the width CWx of the pressure chamber 52 in the short direction). The vertical axis on the left is the displacement volume ΔV (unit: [pl]). The vertical axis on the right is the main stress generated in the piezoelectric body 62 (unit is [MPa]).

  FIG. 6 shows the relationship between the width DWy of the upper electrode 63 in the longitudinal direction and the displacement volume ΔV when the aspect ratio CWy / CWx of the pressure chamber 52 is “4”.

  In FIG. 6, the horizontal axis represents the electrode width ratio DWy / CWy in the longitudinal direction (that is, the ratio of the width DWy of the upper electrode 63 to the width CWy of the pressure chamber 52 in the longitudinal direction). The vertical axis represents the displacement volume ΔV (unit: [pl]).

  Each of the curves 601, 602, 603, 604, 605, 606, and 607 in FIG. 6 indicates an electrode width ratio DWx / CWx in the short direction (the width DWx of the upper electrode 63 with respect to the width CWx of the pressure chamber 52 in the short direction). Ratio) was “0.4”, “0.43”, “0.6”, “0.65”, “0.7”, “0.73”, “0.75”, and obtained by plotting the displacement volume ΔV against DWy / CWy, respectively. .

  When DWx / CWx = 0.6 (that is, a curve indicated by reference numeral 603), when DWx / CWx has values of 0.4, 0.43, 0.65, 0.7, 0.73, and 0.75 (that is, reference numerals 601, 602, 604, 605, 606, The displacement volume ΔV is larger than each curve 607). Further, even if DWx / CWx is different (that is, curves 601 to 607 are different), the value of DWy / CWy at which the displacement volume ΔV becomes a maximum value (referred to as “optimum value of DWy / CWy”) is set as a central value. In the vicinity of the “optimum value of DWy / CWy”, the shapes of the curves 601 to 607 are substantially the same.

  In order to keep the lower limit value of the displacement volume ΔV within 10% with the maximum value of the displacement volume ΔV (that is, the maximum value of the curve 603) as a reference (100%), the electrode width ratio DWx / CWx in the short direction is 0.4˜ The electrode width ratio DWy / CWy in the longitudinal direction is within a range of 0.75, and the optimum value (approximately “0.91”) of DWy / CWy is a central value of −0.05 to +0.05. Range.

  5 and 6, when the aspect ratio of the pressure chamber 52 is “4”, a preferable size of the active region 62a of the piezoelectric body 62 (a preferable size of the upper electrode 63 in this example) was obtained. Below, the case where the aspect ratio of the pressure chamber 52 is expanded to the range of 2-5 is demonstrated.

  FIG. 7 shows the relationship between the aspect ratio CWy / CWx of the pressure chamber 52 and the width DWy of the upper electrode 63 in the longitudinal direction.

  In FIG. 7, the x-axis as the horizontal axis is the aspect ratio CWy / CWx of the pressure chamber 52. The y axis as the vertical axis is the electrode width ratio DWy / CWy in the longitudinal direction (ratio of the width DWy of the upper electrode 63 to the width CWy of the pressure chamber 52 in the longitudinal direction).

  The center value curve 700 in FIG. 7 shows the optimum value of DWy / CWy for each value (“1”, “2”, “3”, “4”, “5”) of the aspect ratio CWy / CWx of the pressure chamber 52. (Corresponding to 610 in FIG. 6), and the obtained optimum values of DWy / CWy were plotted. When an approximate expression of the obtained center value curve 700 was obtained, it was y = 0.1334 × Ln (x) +0.7312. Here, Ln is a natural logarithm. x is CWy / CWx.

  If one aspect ratio CWy / CWx (in the range of 2 to 5) of the pressure chamber 52 is selected, as shown in FIG. 6, even if DWx / CWx is different, the displacement volume ΔV is the maximum value. DWy / CWy (ie, the optimum value of DWy / CWy) is substantially constant, and the shape of the curve in the vicinity of the optimum value of DWy / CWy with the optimum value of DWy / CWy as the center value is also substantially constant. . Moreover, if the optimal value of DWy / CWy is within the range of -0.05 to +0.05 with the center value as the center value, a high displacement volume can be obtained, and since the maximum value is the center, the displacement volume is assumed to vary in size. The impact on is low. Such a relationship is the same even when the aspect ratio of the pressure chamber 52 is switched within the range of 2 to 5. Therefore, in FIG. 7, “−0” is set in the y direction with respect to the center value curve 700 including the optimum value of DWy / CWy. .05 ”shifted to an allowable range is a region between a lower limit curve 701 configured by shifting and an upper limit curve 702 configured by shifting“ +0.05 ”in the y direction with respect to the center value curve 700. .

  In short, the aspect ratio (CWy / CWx) of the pressure chamber 52 is arbitrarily selected within the range of 2 to 5, and DWx / CWx (the width of the active region 62a with respect to the width of the pressure chamber 52 in the short side direction) is In the range of 0.4 to 0.75, and DWy / CWy (the width of the active region 62a with respect to the width of the pressure chamber 52 in the longitudinal direction), Ln is a natural logarithm, and the aspect ratio of the pressure chamber 52 ( CWy / CWx) is a variable x, and is within a range of ± 0.05 with 0.133 × Ln (x) +0.7312 as the center value. Thus, by defining the width of the active region 62a with respect to the width of the pressure chamber 52, the displacement volume can be maximized even if the aspect ratio of the pressure chamber 52 is arbitrarily selected within the range of 2 to 5. A high displacement volume in the vicinity of the displacement volume ΔV in the optimum value 610 of 6) can be obtained, so that the discharge efficiency is good. Further, since the variation of the displacement volume with respect to the manufacturing variation of the width of the upper electrode 63 becomes very small, the discharge variation between the nozzles 51 becomes extremely low.

  Further, according to the liquid discharge head 50 of the present embodiment, the width of the active region 62 a of the piezoelectric body 62 is smaller than the width of the pressure chamber 52 in the longitudinal direction of the pressure chamber 52, and in the short direction of the pressure chamber 52. Since the width of the active region 62 a of the piezoelectric body 62 is smaller than the width of the pressure chamber 52, the displacement profile 800 becomes an efficient and smooth displacement profile as shown in FIG. It is difficult to generate, bubbles are not easily generated in the pressure chamber 52, and no residual vibration is left during liquid discharge.

  FIG. 9A shows the creeping distance L along the surface of the piezoelectric body 62 from the edge of the upper electrode 63 in the liquid ejection head 50 shown in FIGS. 2A and 2B.

  In FIG. 9A, since the lower electrode 61 is covered with the piezoelectric body 62 and the edge of the lower electrode 61 is shielded by the non-conductive piezoelectric body 62, the creepage distance L is the edge of the upper electrode 63. To the vibration plate 24 (provided that the vibration plate 24 is a conductive material) along the surface of the piezoelectric body 62. Since the insulating layer 25 is very thin, its thickness can be ignored.

  FIG. 9B shows a main part of another example of the liquid ejection head 500 in which the lower electrode 61 is exposed. In FIG. 9B, the creepage distance L is the distance from the edge of the upper electrode 63 to the lower electrode 61 along the surface of the piezoelectric body 62.

  In any case, the liquid ejection head is such that the relationship between the shortest value (shortest creepage distance) Lmin [μm] of the creepage distance L and the drive electric field E [V] of the piezoelectric body 62 satisfies E / Lmin ≦ 1. 50, 500 are configured. Thereby, the dielectric breakdown of the piezoelectric actuator 60 due to creeping discharge can be prevented, and the reliability of the liquid discharge heads 50 and 500 can be further improved.

  In the liquid ejection heads 50 and 500 of the present embodiment, the vibration plate 24, the insulating layer 25, the lower electrode 61, the piezoelectric body 62, and the upper electrode 63 are sequentially formed on the pressure chamber 52 that communicates with the nozzle 51. Manufactured.

  Here, the area of the active region 62a that is sandwiched between the lower electrode 61 and the upper electrode 63 in the piezoelectric body 62 and contributes to the displacement of the piezoelectric body 62 is formed smaller than the cross-sectional area of the concave portion of the pressure chamber 52, and When the aspect ratio (CWy / CWx) of the width CWx in the short direction of the pressure chamber 52 and the width CWy in the longitudinal direction of the pressure chamber 52 is arbitrarily selected within the range of 2 to 5, The ratio (DWx / CWx) of the width DWx of the upper electrode 63 in the short direction (that is, the width of the active region 62a of the piezoelectric body 62 in the short direction) and the width CWx in the short direction of the pressure chamber 52 is 0.4. The width DWy of the upper electrode 63 in the longitudinal direction of the pressure chamber 52 (that is, the width of the active region 62a of the piezoelectric body 62 in the longitudinal direction) and the width CWy of the pressure chamber 52 in the longitudinal direction. Ratio (DWy / Wy) is set within a range of ± 0.05 centered on 0.133 × Ln (x) +0.7312 with Ln as a natural logarithm and the aspect ratio (CWy / CWx) of the pressure chamber 52 as a variable x. Manufactured.

  An example of the manufacturing process of the liquid discharge head will be described in detail.

  10, FIG. 11 and FIG. 12 are process diagrams showing the manufacturing process of the first embodiment.

First, as shown in FIG. 10A, an SOI substrate 20 having an insulating layer 25 on the surface is prepared. The SOI substrate 20 is formed by laminating an Si layer 23 (pressure chamber plate), an SiO ₂ layer 241 and an Si layer 242 (vibrating plate 24), and an SiO ₂ layer 25 (insulating layer).

  A lower electrode 61 is formed by sputtering on the SOI substrate 20 shown in FIG. 10A as shown in FIG. 10B. Of course, the film forming method is not limited to sputtering, but may be CVD (Chemical Vapor Deposition), vapor deposition, or screen printing. The film forming material may be Ti, Ir, Pt, Au, Cu, a laminate thereof, or an oxide.

  Next, as shown in FIG. 10C, the lower electrode 61 is etched. Here, RIE (Reactive Ion Etching) processing is performed using a gas obtained by adding a small amount of Ar to a fluorine-based or chlorine-based gas. Of course, the processing method is not limited to RIE, and may be wet etching or sand blasting.

  In this embodiment, the case where the lower electrode 61 is processed is described as an example. However, the lower electrode 61 may not be processed, and only the upper electrode may be individualized.

  Next, as shown in FIG. 10D, a piezoelectric body 62 (for example, PZT) is formed as a thin film. The film forming method is not limited to sputtering, and may be an aerosol deposition method, a sol-gel method, screen printing, a metal organic chemical vapor deposition (MOCVD) method, a laser ablation method, or a hydrothermal synthesis method.

  Next, as shown in FIG. 11E, the upper electrode 63 is formed. This may be the same as the method and material for forming the lower electrode 61.

  Next, as shown in FIG. 11F, the upper electrode 63 is processed. RIE processing is performed using a gas obtained by adding a small amount of Ar to a fluorine-based or chlorine-based gas. Of course, the processing method is not limited to RIE, and may be wet etching or sand blasting. The electrode size at this time is such that the ratio of the dimensions is within a predetermined range when the lateral width is DWx and the longitudinal width is DWy with respect to the aspect ratio (CWy / CWx) of the pressure chamber to be processed later. And Here, as described above, DWx / CWx and DWy / CWy are set within a predetermined range.

  Next, as shown in FIG. 11G, the piezoelectric body 62 is processed. Either dry etching in which Ar gas is added to a fluorine-based or chlorine-based gas for processing, or wet etching using an acid may be used. Also, sand blasting may be used.

  Next, as shown in FIG. 12H, the pressure chamber 52 is etched into the Si layer 23 corresponding to the pressure chamber plate of the SOI substrate 20. RIE and anisotropic wet etching methods can be used.

  Finally, as shown in FIG. 12 (I), the nozzle plate 21 and the communication flow path plate 22 are joined or bonded to the SOI substrate 20. Thereby, the liquid discharge head 50 is obtained.

  Although the case where the etching of the upper electrode 63 and the etching of the piezoelectric body 62 are performed separately has been described as an example, the upper electrode 63 and the piezoelectric body 62 may be etched simultaneously.

  13 and 14 are process diagrams showing the manufacturing process of the second embodiment.

  First, as shown in FIG. 13A, an opened substrate 200 is prepared. The substrate 200 includes a nozzle plate 21 in which a nozzle 51 is formed, a communication flow path plate 22 in which a nozzle communication path 51 a is formed, a pressure chamber plate 23 in which a pressure chamber 52 is formed, and a vibration plate 24. And an insulating layer 25. The pressure chamber plate 23, the vibration plate 24 and the insulating layer 25 constitute an SOI substrate 20.

  A lower electrode 61 is formed by sputtering on the substrate 200 shown in FIG. 13A as shown in FIG. Of course, the film forming method is not limited to sputtering, and CVD, vapor deposition, or screen printing may be used. The film forming material may be Ti, Ir, Pt, Au, Cu, a laminate thereof, or an oxide.

  Next, as shown in FIG. 13C, the lower electrode 61 is etched. Here, RIE processing is performed using a gas obtained by adding a small amount of Ar to a fluorine-based or chlorine-based gas. Of course, the processing method is not limited to RIE, and may be wet etching or sand blasting.

  In this embodiment, the case where the lower electrode 61 is processed is described as an example. However, the lower electrode 61 may not be processed, and only the upper electrode may be individualized.

  Next, as shown in FIG. 13D, a piezoelectric body 62 (for example, PZT) is formed as a thin film. Note that the film forming method is not limited to sputtering, and may be an aerosol deposition method, a sol-gel method, screen printing, a metal organic chemical vapor deposition method (MOCVD), a laser ablation method, or a hydrothermal synthesis method.

  Next, as shown in FIG. 14E, the upper electrode 63 is formed. This may be the same as the method and material for forming the lower electrode 61.

  Next, as shown in FIG. 14F, the upper electrode 63 is processed. RIE processing is performed using a gas obtained by adding a small amount of Ar to a fluorine-based or chlorine-based gas. Of course, the processing method is not limited to RIE, and may be wet etching or sand blasting. The electrode size at this time is such that the ratio of dimensions with respect to the aspect ratio (CWy / CWx) of the formed pressure chamber 52 is within a predetermined range when the lateral width is DWx and the longitudinal width is DWy. And Here, as described above, DWx / CWx and DWy / CWy are set within a predetermined range.

  Next, as shown in FIG. 14G, the piezoelectric body 62 is processed. Thereby, the liquid discharge head 50 is obtained. Either dry etching in which Ar gas is added to a fluorine-based or chlorine-based gas for processing, or wet etching using an acid may be used. Also, sand blasting may be used.

  Although the case where the etching of the upper electrode 63 and the etching of the piezoelectric body 62 are performed separately has been described as an example, the upper electrode 63 and the piezoelectric body 62 may be etched simultaneously.

  As described above, the liquid discharge head and the manufacturing method thereof have been described by taking the case where the concave section of the pressure chamber 52 (the section along the surface direction of the piezoelectric body 62) has a rectangular shape as an example. As shown in FIG. 4, the cross-sectional shape of the concave portion of the pressure chamber 52 may be a parallelogram shape. In addition, as shown in FIG. 15B, corners may have R. Even in the case of a parallelogram shape or R at the corner, the excluded volume does not change much when the aspect ratio (CWy / CWx) is 2 or more.

  In the case of a rectangular shape, the aspect ratio is the width of the short side of the rectangle, the width of the long side is the length of the long side of the rectangle, and the parallelogram shape. The width in the short direction means the shorter one of the heights of the parallelogram, and the width in the longitudinal direction means the length of the long side of the parallelogram.

[Image forming apparatus]
FIG. 16 is a block diagram showing an outline of the overall configuration of an image forming apparatus 80 including the liquid ejection head 50 of FIG.

  In FIG. 16, an image forming apparatus 80 mainly includes a liquid discharge head 50, a communication interface 81, a system controller 82, memories 83a and 83b, a conveyance motor 84, a conveyance driver 840, a print control unit 85, a liquid supply unit 86, and a supply unit. The liquid control unit 860 and the head driver 87 are included.

  The image forming apparatus 80 includes a total of four liquid ejection heads 50 for each color of K (black), C (cyan), M (magenta), and Y (yellow).

  The communication interface 81 is image data input means for receiving image data transmitted from the host computer 89. A wired or wireless interface can be applied to the communication interface 81. The image data taken into the image forming apparatus 80 by the communication interface 81 is temporarily stored in the first memory 83a for storing the image data.

  The system controller 82 includes a central processing unit (CPU) and its peripheral circuits, and is main control means for controlling the entire image forming apparatus 80 according to a predetermined program. That is, the system controller 82 controls each unit such as the communication interface 81, the conveyance driver 840, the print control unit 85, and the like.

  The conveyance motor 84 applies power to a roller, a belt, or the like for conveying an ejection medium such as paper. By the conveyance motor 84, the medium to be ejected and the liquid ejection head 50 are relatively moved.

  The transport driver 840 is a circuit that drives the transport motor 84 in accordance with an instruction from the system controller 82.

  The liquid supply unit 86 includes a conduit and a pump for flowing ink from an ink tank (not shown) as ink storage means for storing ink to the liquid ejection head 50.

  The liquid supply control unit 860 performs control for supplying ink to the liquid ejection head 50 using the liquid supply unit 86.

  The print control unit 85 causes the liquid discharge head 50 to discharge (drop droplets) toward the discharge medium based on the image data input to the image forming apparatus 80 to form dots on the discharge medium. Necessary data (dot data) is generated. That is, the print control unit 85 performs image processing such as various processes and corrections for generating dot ejection dot data from the image data in the first memory 83a in accordance with the control of the system controller 82. And the generated dot data is supplied to the head driver 87.

  The print controller 85 is accompanied by a second memory 83b, and dot data and the like are temporarily stored in the second memory 83b during image processing in the print controller 85.

  In FIG. 16, the second memory 83b is shown as being attached to the print control unit 85, but it can also be used as the first memory 83a. Also possible is an aspect in which the print controller 85 and the system controller 82 are integrated and configured with one processor.

  The head driver 87 ejects a drive signal for ejection to the piezoelectric actuator 60 of the liquid ejection head 50 based on the dot data provided from the print control unit 85 (actually, the dot data is stored in the second memory 83b). Is output. By supplying the ejection drive signal output from the head driver 87 to the piezoelectric actuator 60 of the liquid ejection head 50, the liquid (droplet) is ejected from the nozzle 51 of the liquid ejection head 50 toward the ejection target medium. .

  The present invention is not limited to the examples described in the present specification and the examples illustrated in the drawings, and various design changes and improvements may be made without departing from the spirit of the present invention.

Plane perspective view showing the overall configuration of an example of a liquid discharge head 1A is an enlarged plan view showing a part of the liquid ejection head of FIG. 1, and FIG. 1B is an enlarged cross-sectional view showing a part of the liquid ejection head of FIG. (A) is explanatory drawing used for description of the active region of a piezoelectric body, (B) is the width CWx of the short direction of a pressure chamber, the width CWy of the longitudinal direction of a pressure chamber, and the width DWx of the short direction of an active region. And an explanatory diagram used to describe the width DWy in the longitudinal direction of the active region Diagram showing the relationship between the aspect ratio of the pressure chamber and the generated pressure in the pressure chamber Diagram showing the relationship between the electrode width ratio in the short direction and the displacement volume Diagram showing the relationship between the electrode width ratio in the longitudinal direction and the displacement volume Diagram showing the relationship between the aspect ratio of the pressure chamber and the electrode width ratio in the longitudinal direction Explanatory diagram used to explain the prevention of bubble generation (A) is explanatory drawing used for description of the creeping distance in an example of the liquid discharge head shown to FIG. 2 (A) and (B), (B) is description used for description of the creeping distance in the liquid discharge head of another example. Figure Process drawing which shows the manufacturing process of Example 1 Process drawing which shows the manufacturing process of Example 1 Process drawing which shows the manufacturing process of Example 1 Process drawing which shows the manufacturing process of Example 2 Process drawing which shows the manufacturing process of Example 2 Explanatory drawing used for explanation of lateral width and longitudinal width 1 is a block diagram illustrating an overall configuration of an example of an image forming apparatus including a liquid ejection head Explanatory drawing used to describe a conventional liquid discharge head

Explanation of symbols

  DESCRIPTION OF SYMBOLS 21 ... Nozzle plate, 22 ... Communication flow path plate, 23 ... Pressure chamber plate, 24 ... Vibration plate, 25 ... Insulating layer, 50 ... Liquid discharge head, 51 ... Nozzle, 52 ... Pressure chamber, 60 ... Piezoelectric actuator, 61 ... Lower electrode, 62 ... piezoelectric body, 63 ... upper electrode, CWx ... width in the transverse direction of the pressure chamber, CWy ... width in the longitudinal direction of the pressure chamber, DWx ... width in the transverse direction of the active region of the piezoelectric material, DWy ... Longitudinal width of the active area of the piezoelectric body

Claims (5)

At least a lower electrode, a piezoelectric body and an upper electrode are sequentially arranged on the pressure chamber communicating with the liquid discharge port,
The pressure chamber has a short side direction and a long side direction in a concave cross section along the plane direction of the planar piezoelectric body,
The area of the piezoelectric body is larger than the concave cross-sectional area of the pressure chamber,
Of the piezoelectric body, the area of the active region sandwiched between the lower electrode and the upper electrode and contributing to the displacement of the piezoelectric body is smaller than the concave cross-sectional area of the pressure chamber,
When the aspect ratio (CWy / CWx) of the width CWx in the lateral direction of the pressure chamber and the width CWy in the longitudinal direction of the pressure chamber is 2 to 5,
The ratio of the previous SL the lateral direction of the width CWX of the lateral direction of the width DWX between the pressure chamber of the active region of the piezoelectric body (DWx / CWx) is 0.4 to 0.75,
And, the piezoelectric ratio (DWy / CWy) and said longitudinal width cwy of said longitudinal width DWy active region and the pressure chamber of the Ln a natural logarithm, the aspect ratio of the pressure chamber (cwy / CWx) is a variable x, and the liquid ejection head is within a range of ± 0.05 with 0.133 × Ln (x) +0.7312 as the center value. The piezoelectric body is formed of a single plate structure,
The relationship between the minimum creepage distance Lmin [μm] along the surface of the piezoelectric body from the edge of the upper electrode and the drive electric field E [V] of the piezoelectric body satisfies E / Lmin ≦ 1. The liquid discharge head according to claim 1. In a method for manufacturing a liquid discharge head, in which at least a lower electrode, a piezoelectric body, and an upper electrode are sequentially formed on a pressure chamber communicating with a liquid discharge port.
The pressure chamber has a short side direction and a long side direction in a concave cross section along the plane direction of the planar piezoelectric body,
The area of the piezoelectric body is larger than the concave cross-sectional area of the pressure chamber,
An area of an active region that is sandwiched between the lower electrode and the upper electrode among the piezoelectric bodies and contributes to displacement of the piezoelectric body is formed to be smaller than a cross-sectional area of the concave portion of the pressure chamber,
When the aspect ratio (CWy / CWx) of the width CWx in the lateral direction of the pressure chamber and the width CWy in the longitudinal direction of the pressure chamber is 2 to 5,
The ratio of the previous SL the lateral direction of the width CWX of the lateral direction of the width DWX between the pressure chamber of the active region of the piezoelectric body (DWx / CWx) is a 0.4 to 0.75,
And the ratio between the longitudinal width cwy of said longitudinal width DWy and the pressure chamber of the active region of the previous SL piezoelectric (DWy / CWy) is a Ln a natural logarithm, the aspect ratio of the pressure chamber ( A method of manufacturing a liquid discharge head, wherein CWy / CWx) is within a range of ± 0.05 with a variable x and 0.133 × Ln (x) +0.7312 as a center value.   The piezoelectric material is formed into a thin film by any of sputtering, AD (aerosol deposition) method, sol-gel method, screen printing, MOCVD (metal organic chemical vapor deposition) method, laser ablation method, and hydrothermal synthesis method. The method of manufacturing a liquid discharge head according to claim 3.   An image forming apparatus comprising the liquid ejection head according to claim 1.

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