JP2016107476A - Ink jet head and ink jet printer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve piezoelectric adjustment with a simple structure and thereby easily reduce piezoelectric variations between different substrates or in one substrate in a structure including a substrate 22 supporting multiple piezoelectric elements 27.SOLUTION: An ink jet head includes: piezoelectric elements 27; and a substrate 22 supporting the piezoelectric elements 27. The substrate 22 includes a curved substrate 41 in which at least part thereof is deflected. The curved substrate 41 is deflected so that only one curve shape which protrudes or is recessed to the piezoelectric elements 27 arrangement side is formed on the entire substrate in one direction that the piezoelectric elements 27 are arranged.SELECTED DRAWING: Figure 5

Description

  The present invention relates to an inkjet head in which a plurality of piezoelectric elements are supported by a support substrate, and an inkjet printer including the inkjet head.

  Conventionally, piezoelectric materials such as lead zirconate titanate (PZT) have been used as electromechanical conversion elements such as drive elements and sensors. In recent years, MEMS (Micro Electro Mechanical Systems) elements using a silicon (Si) substrate are increasing in response to demands for downsizing, high density, and low cost of devices. In order to apply a piezoelectric body to a MEMS element, it is desirable to make the piezoelectric body thin. By reducing the thickness of the piezoelectric body, high-precision processing using semiconductor process technology such as film formation and photolithography can be performed, and miniaturization and high density can be realized. Further, since the elements can be collectively processed on a large-area wafer, the cost can be reduced. Furthermore, there is an advantage that the conversion efficiency of mechanical electricity is improved and the characteristics of the drive element and the sensitivity of the sensor are improved.

  As an application example of a device using such a MEMS element, an ink jet printer is known. In an inkjet printer, a two-dimensional image is recorded on a recording medium by controlling the ejection of ink while moving an inkjet head having a plurality of channels for ejecting liquid ink relative to the recording medium such as paper or cloth. Formed.

  Ink can be ejected using a pressure actuator (piezoelectric, electrostatic, thermal deformation, etc.) or by generating bubbles in the ink in the tube by heat. Among them, the piezoelectric actuator has advantages such as high output, modulation, high responsiveness, and choice of ink, and has been frequently used in recent years. In particular, in order to realize a small-sized and low-cost printer with high resolution (small droplets may be used), it is suitable to use an inkjet head using a thin film piezoelectric body.

In recent years, inkjet printers are required to form high-definition images at higher speeds. For this purpose, the ink jet head is required to increase the droplet velocity and to apply high viscosity ink. In order to realize these, the piezoelectric thin film (ferroelectric thin film) needs to have high piezoelectric characteristics (piezoelectric constant d ₃₁ ).

  On the other hand, as a method of forming a piezoelectric material such as PZT on a substrate such as Si, a chemical film forming method such as a CVD (Chemical Vapor Deposition) method, a physical method such as a sputtering method or an ion plating method, a sol gel The growth method in the liquid phase such as the method is known. The upper limit of the thickness of the thin film obtained by these manufacturing methods is about 10 μm. If the film thickness exceeds that, cracks and film peeling occur, and desired characteristics cannot be obtained.

The deposited PZT exhibits a good piezoelectric effect when the crystal has a perovskite structure. The perovskite structure ideally has a cubic unit cell, and is arranged at each vertex of the cubic A, metal B arranged at the body center, and arranged at each face center of the cubic crystal. It is an ABO ₃ type crystal structure composed of oxygen O. Crystals having a perovskite structure include tetragonal crystals, orthorhombic crystals, rhombohedral crystals and the like in which cubic crystals are distorted.

  The PZT thin film formed on the electrode on the Si substrate becomes a polycrystal composed of an aggregate of a plurality of crystals due to the difference in lattice constant from the crystal of the electrode. Depending on the production method, this polycrystal is composed of granular crystals (granular crystals) with a particle size of several hundreds of nanometers, or a width of several hundreds of nanometers and one elongated crystal grain in the film thickness direction. A certain columnar crystal is gathered together.

  By the way, since the output of the ink jet head is determined by the voltage of the piezoelectric element × piezoelectricity, the drive voltage of the piezoelectric element is increased in order to increase the output (increase the droplet velocity or eject a higher viscosity ink). Or it is necessary to increase the piezoelectricity. However, a polycrystalline film piezoelectric body (piezoelectric thin film) made up of a plurality of crystals tends to generate a leakage current between the upper electrode and the lower electrode, and has a low voltage resistance. There is. For this reason, in order to increase the output, it is necessary to increase the piezoelectricity.

  Several methods have been proposed for increasing the piezoelectricity of a piezoelectric thin film. For example, there are a method of increasing the piezoelectricity by optimizing the film formation conditions and increasing the crystallinity of the sputtered film, and a method of increasing the piezoelectricity by sputtering PZT added with niobium or lanthanum. However, any of these methods has severe process conditions and tends to deteriorate film formation stability.

  On the other hand, in Patent Document 1, for example, in a configuration in which a diaphragm and a piezoelectric element are formed on a substrate on which a pressure chamber is formed, bent portions are formed on both sides in the width direction of the piezoelectric element in a region opposite to the pressure chamber of the diaphragm. Is provided. Thus, when the piezoelectric element is driven to bend and deform, the force that the diaphragm resists against the displacement of the piezoelectric element is reduced, and the displacement amount of the piezoelectric element is increased.

JP 2009-29012 A (see claim 1, paragraphs [0010], [0011], [0032], [0033], FIG. 2, etc.)

  However, when the bending portion is provided on the diaphragm as in Patent Document 1, the processing for bending the diaphragm is complicated (many processes), resulting in high costs and a decrease in yield and reliability. Moreover, it is difficult to process the diaphragm uniformly. Therefore, the configuration of Patent Document 1 cannot easily improve the piezoelectricity of the piezoelectric element.

  Further, as shown in FIG. 22, a plurality of piezoelectric elements are collectively formed on the same wafer 100, and a substrate 101 that supports the plurality of piezoelectric elements is cut out from a region near the outer periphery of the wear 100, and the wafer 100 is centered. When the substrate 102 supporting a plurality of piezoelectric elements is cut out from the vicinity, the substrate 101 generally has a relatively high piezoelectricity and the substrate 102 tends to have a relatively low piezoelectricity. This is considered to be because when the piezoelectric thin film is formed by vacuum film formation, the closer to the outer peripheral side than the center of the wafer 100, the easier the crystal grows and the in-plane unevenness of crystallinity occurs. In this case, if the substrate 101 and the substrate 102 are used for one head, the piezoelectricity varies depending on the position of the head (the positions of the substrates 101 and 102), so that ink ejection unevenness occurs and an image with good image quality is recorded. It cannot be formed on top. Further, in the case where unevenness (variation) in piezoelectricity occurs in a single substrate 103 cut out from the wafer 100, uneven ink ejection occurs in the substrate 103.

  Therefore, in an inkjet head having a substrate that supports a plurality of piezoelectric elements, the piezoelectricity can be adjusted with a simple configuration in order to suppress ink discharge unevenness, and the piezoelectricity between different substrates or within the same substrate can be reduced. It is desirable to make it possible to easily reduce variations.

  The present invention has been made in order to solve the above-described problems, and an object of the present invention is to realize adjustment of piezoelectricity with a simple configuration in a configuration including a substrate that supports a plurality of piezoelectric elements. Accordingly, it is an object of the present invention to provide an ink jet head that can easily reduce piezoelectric variations between different substrates or within the same substrate, and an ink jet printer including the ink jet head.

  An ink jet head according to an aspect of the present invention is an ink jet head including a plurality of piezoelectric elements and a support substrate that supports the plurality of piezoelectric elements, and the support substrate is bent at least partially. The curved substrate includes only one curved shape that is convex or concave on the arrangement side of the plurality of piezoelectric elements in the whole substrate in one direction in which the plurality of piezoelectric elements are arranged side by side. Is bent.

  According to the above configuration, if the curved substrate has a curved shape (convex shape) that protrudes toward the plurality of piezoelectric elements, when the piezoelectric elements are driven, the piezoelectric elements are vertically expanded due to horizontal expansion and contraction. Directional displacement (particularly displacement to the opposite side of the piezoelectric element with respect to the curved substrate) is difficult to occur. For this reason, in the portion where the curved shape is formed (for example, the whole substrate in one direction or a part thereof), the piezoelectricity of the piezoelectric element is lower than when the support substrate is flat. On the other hand, when a curved shape (concave shape) that is concave on the side of a plurality of piezoelectric elements is formed on the curved substrate, when the piezoelectric element is driven, the piezoelectric element is opposite to the piezoelectric element with respect to the curved substrate. Displacement to the side is easy. For this reason, in the part in which the said curved shape was formed, the piezoelectricity of a piezoelectric element improves compared with the case where a support substrate is flat form. In addition, a curved substrate in which only one curved shape is formed in one direction in which a plurality of piezoelectric elements are arranged is, for example, the attachment of a substrate to a holding plate having a curved surface portion or a line between the holding plate and the substrate. It can be easily obtained by changing the expansion coefficient to give a temperature change.

  Therefore, the piezoelectricity can be adjusted in the whole or a part of the curved substrate with a simple configuration in which a curved substrate in which at least a part is bent is used as the support substrate for supporting the plurality of piezoelectric elements. As a result, variations in piezoelectricity between different support substrates or within the same support substrate (curved substrate) can be easily reduced.

  The curved substrate may be bent so that one curved shape is formed on the entire substrate in the one direction. In this case, the piezoelectricity can be adjusted over the entire substrate of the curved substrate to reduce the variation in piezoelectricity between different support substrates.

  The curved substrate may be bent so that one curved shape is formed in a part of the one direction and the rest is a flat plate shape. In this case, the piezoelectricity of the piezoelectric element can be adjusted in a part of the curved substrate to reduce the variation in piezoelectricity within the same curved substrate.

  The curvature radius of the curved shape of the curved substrate may be 150 mm or greater and 1000 mm or less in absolute value. If the absolute value of the radius of curvature is below the lower limit, the curved substrate may be bent too much and be broken (cracked). On the other hand, if the absolute value of the radius of curvature exceeds the upper limit, the degree of curvature of the curved substrate is too small and the piezoelectric adjustment range becomes small (the piezoelectricity cannot be increased or decreased greatly). Therefore, by setting the radius of curvature within the above range, it is possible to reliably obtain an effect of reducing piezoelectric variation while avoiding damage to the curved substrate.

  The curved shape of the curved substrate may be a concave shape on the arrangement side of the plurality of piezoelectric elements. In this case, as described above, the piezoelectricity of the piezoelectric element is improved, so that the output (ink discharge amount) of the head can be increased.

  The inkjet head includes a plurality of the support substrates, and the curved substrate included in the plurality of support substrates so that variations in piezoelectricity of the piezoelectric elements between the plurality of support substrates are within a predetermined range. The curvature of the curved shape may be set. Even if the head includes a plurality of support substrates, variations in piezoelectricity among the plurality of support substrates are reduced, so that the output of the head can be made uniform.

  The ink jet head further includes a holding plate that has a curved portion and holds the support substrate, and the curved substrate is formed by bending at least a part of the support substrate along the curved portion. May be. By using a holding plate having a curved surface portion, a curved substrate having at least a part thereof can be easily realized.

  The holding plate may be positioned on the side of the plurality of piezoelectric elements with respect to the support substrate, and may hold the curved substrate outside a formation region of the plurality of piezoelectric elements. In this configuration, the curved substrate can be held by the holding portion without the plurality of piezoelectric elements of the curved substrate interfering with the holding plate (curved surface portion).

  The inkjet head further includes a holding plate that is located on the opposite side of the support substrate from the plurality of piezoelectric elements and holds the support substrate, and the holding plate has a linear expansion coefficient with the support substrate. May be made of different materials. Since the linear expansion coefficient is different between the holding plate and the support substrate, a curved substrate that is at least partially bent can be easily realized by the difference in the degree of contraction from the holding plate due to temperature change.

  The support substrate may be bonded to a nozzle substrate having ink ejection holes via the holding plate. In the configuration in which the support substrate (curved substrate) and the nozzle substrate are bonded together via the intermediate plate, the curved substrate can be realized by using the holding plate as the intermediate plate.

  The inkjet head further includes a holding plate that is positioned on the side of the plurality of piezoelectric elements with respect to the support substrate and holds the support substrate, and the holding plate is made of a material having a linear expansion coefficient different from that of the support substrate. It may be formed. Since the linear expansion coefficient is different between the holding plate and the support substrate, a curved substrate that is at least partially bent can be easily realized by the difference in the degree of contraction from the holding plate due to temperature change.

  The support substrate is formed corresponding to the formation positions of the plurality of piezoelectric elements, and applies pressure to the ink in the pressure chambers by vibrating by driving the plurality of piezoelectric elements and a pressure chamber containing the ink. You may have a diaphragm to do. As described above, in the configuration in which the pressure is applied to the ink in the pressure chamber by displacing (vibrating) the vibration plate by driving the piezoelectric element, the above-described effects can be obtained.

  An ink jet printer according to another aspect of the present invention may include the above-described ink jet head and eject ink from the ink jet head toward a recording medium. According to the configuration of the ink jet head described above, it is possible to easily reduce piezoelectric variation between different support substrates and piezoelectric variation within the same curved substrate. It can be easily suppressed. Thereby, in the ink jet printer, it is possible to easily suppress the deterioration of the image quality due to the uneven ejection of ink.

  The piezoelectricity of the piezoelectric element can be easily adjusted for the whole or a part of the curved substrate with a simple configuration in which a curved substrate having at least a part thereof is used as the support substrate. As a result, it is possible to easily reduce piezoelectric variation between different support substrates or within the same curved substrate.

1 is an explanatory diagram illustrating a schematic configuration of an inkjet printer according to an embodiment of the present invention. FIG. FIG. 2 is a plan view showing a schematic configuration of an actuator of an ink jet head provided in the ink jet printer, and a cross-sectional view taken along line A-A ′ in the plan view. It is sectional drawing which shows the structure of the said inkjet head. It is sectional drawing which shows the manufacturing process of the said inkjet head. It is sectional drawing which shows one structural example of the curved board | substrate used for the said inkjet head. FIG. 6 is a simplified cross-sectional view of an inkjet head having a plurality of substrates including the curved substrate of FIG. 5. It is sectional drawing which shows the other structural example of the said curved board | substrate. FIG. 8 is a simplified cross-sectional view of an inkjet head having a plurality of substrates including the curved substrate of FIG. 7. It is a graph which shows the relationship between the curvature radius of the said curved substrate, and piezoelectricity. It is sectional drawing which shows the further another structural example of the said curved board | substrate. It is sectional drawing which shows the further another structural example of the said curved board | substrate. It is a perspective view of the holding plate holding a some board | substrate. It is a top view of the said holding plate. It is a top view which shows the state which hold | maintained the said several board | substrate with the said holding plate. FIG. 15 is a cross-sectional view taken along line B-B ′ of FIG. 14. FIG. 15 is a cross-sectional view taken along line C-C ′ in FIG. 14. It is sectional drawing which shows the other structure of the said inkjet head. It is explanatory drawing which shows an example of a mode that a board | substrate bends by the difference in a linear expansion coefficient with a holding plate. It is explanatory drawing which shows the other example of a mode that a board | substrate bends by the difference in a linear expansion coefficient with a holding plate. It is explanatory drawing which shows the further another example of a mode that a board | substrate bends by the difference in a linear expansion coefficient with a holding plate. It is explanatory drawing which shows the further another example of a mode that a board | substrate bends by the difference in a linear expansion coefficient with a holding plate. It is explanatory drawing which shows the relationship between the position of the some board | substrate cut out from the same wafer, and piezoelectricity.

  An embodiment of the present invention will be described below with reference to the drawings. In the present specification, when the numerical range is expressed as A to B, the numerical value range includes the values of the lower limit A and the upper limit B.

[Configuration of inkjet printer]
FIG. 1 is an explanatory diagram illustrating a schematic configuration of an inkjet printer 1 according to the present embodiment. The ink jet printer 1 is a so-called line head type ink jet recording apparatus in which an ink jet head 21 is provided in a line shape in the width direction of a recording medium in the ink jet head unit 2.

  The ink jet printer 1 includes an ink jet head unit 2, a feed roll 3, a take-up roll 4, two back rolls 5 and 5, an intermediate tank 6, a liquid feed pump 7, a storage tank 8, and a fixing tank. And a mechanism 9.

  The ink jet head unit 2 ejects ink from the ink jet head 21 toward the recording medium P to perform image formation (drawing) based on image data, and is disposed in the vicinity of one back roll 5. Details of the inkjet head 21 will be described later.

  The feed roll 3, the take-up roll 4 and the back rolls 5 are members each having a cylindrical shape that can rotate about its axis. The feeding roll 3 is a roll that feeds the long recording medium P wound around the circumferential surface toward the position facing the inkjet head unit 2. The feeding roll 3 is rotated by driving means (not shown) such as a motor, thereby feeding the recording medium P in the X direction in FIG.

  The take-up roll 4 is taken out from the take-out roll 3 and takes up the recording medium P on which the ink is ejected by the inkjet head unit 2 around the circumferential surface.

  Each back roll 5 is disposed between the feed roll 3 and the take-up roll 4. One back roll 5 located on the upstream side in the conveyance direction of the recording medium P is opposed to the inkjet head unit 2 while winding the recording medium P fed by the feeding roll 3 around and supporting the recording medium P. Transport toward The other back roll 5 conveys the recording medium P from a position facing the inkjet head unit 2 toward the take-up roll 4 while being wound around and supported by a part of the peripheral surface.

  The intermediate tank 6 temporarily stores the ink supplied from the storage tank 8. The intermediate tank 6 is connected to a plurality of ink tubes 10, adjusts the back pressure of ink in each inkjet head 21, and supplies ink to each inkjet head 21.

  The liquid feed pump 7 supplies the ink stored in the storage tank 8 to the intermediate tank 6 and is disposed in the middle of the supply pipe 11. The ink stored in the storage tank 8 is pumped up by the liquid feed pump 7 and supplied to the intermediate tank 6 through the supply pipe 11.

  The fixing mechanism 9 fixes the ink ejected to the recording medium P by the inkjet head unit 2 on the recording medium P. The fixing mechanism 9 includes a heater for heat-fixing the discharged ink on the recording medium P, a UV lamp for curing the ink by irradiating the discharged ink with UV (ultraviolet light), and the like. Yes.

  In the above configuration, the recording medium P fed from the feeding roll 3 is transported to a position facing the inkjet head unit 2 by the back roll 5, and ink is ejected from the inkjet head unit 2 to the recording medium P. Thereafter, the ink ejected onto the recording medium P is fixed by the fixing mechanism 9, and the recording medium P after ink fixing is taken up by the take-up roll 4. As described above, in the line head type inkjet printer 1, ink is ejected while the recording medium P is conveyed while the inkjet head unit 2 is stationary, and an image is formed on the recording medium P.

  The ink jet printer 1 may be configured to form an image on a recording medium by a serial head method. The serial head method is a method of forming an image by ejecting ink by moving an inkjet head in a direction orthogonal to the transport direction while transporting a recording medium.

[Configuration of inkjet head]
Next, the configuration of the inkjet head 21 will be described. FIG. 2 is a plan view showing a schematic configuration of an actuator 21a (piezoelectric actuator) of the inkjet head 21 and a cross-sectional view taken along the line AA ′ in the plan view. FIG. 3 is a cross-sectional view showing the configuration of the inkjet head 21 in which the nozzle substrate 31 is joined to the actuator 21a of FIG.

  The inkjet head 21 has a thermal oxide film 23, a lower electrode 24, a piezoelectric thin film 25, and an upper electrode 26 in this order on a substrate 22 having a plurality of pressure chambers 22a (openings).

  The substrate 22 is configured by a semiconductor substrate made of a single crystal Si (silicon) single-piece having a thickness of, for example, about 100 to 300 μm or an SOI (Silicon on Insulator) substrate. For example, a substrate having a thickness of about 300 to 750 μm is prepared, and a PZT layer is formed on the substrate 22 as described later, and then the substrate 22 is made to have a thickness of 100 to 300 μm by polishing or the like. . Note that FIG. 2 shows a case where the substrate 22 is configured by an SOI substrate. The SOI substrate is obtained by bonding two Si substrates through an oxide film. The upper wall of the pressure chamber 22a in the substrate 22 (the wall positioned on the side where the piezoelectric thin film 25 is formed with respect to the pressure chamber 22a) constitutes a vibration plate 22b serving as a driven film. Along with this displacement (vibration), pressure is applied to the ink in the pressure chamber 22a. The substrate 22 constitutes a support substrate that supports a plurality of piezoelectric elements 27 described later. In the substrate 22, the pressure chambers 22 a are formed corresponding to the positions where the plurality of piezoelectric elements 27 are formed.

The thermal oxide film 23 is made of, for example, SiO ₂ (silicon oxide) having a thickness of about 0.1 μm, and is formed for the purpose of protecting and insulating the substrate 22.

  The lower electrode 24 is a common electrode provided in common to the plurality of pressure chambers 22a, and is configured by laminating a Ti (titanium) layer and a Pt (platinum) layer. The Ti layer is formed in order to improve the adhesion between the thermal oxide film 23 and the Pt layer. The thickness of the Ti layer is, for example, about 0.02 μm, and the thickness of the Pt layer is, for example, about 0.1 μm.

  The piezoelectric thin film 25 is composed of a ferroelectric thin film made of, for example, PZT (lead zirconate titanate), and is provided corresponding to each pressure chamber 22a. The film thickness of the piezoelectric thin film 25 is, for example, not less than 1 μm and not more than 10 μm.

  The upper electrode 26 is an individual electrode provided corresponding to each pressure chamber 22a, and is configured by laminating a Ti layer and a Pt layer. The Ti layer is formed in order to improve the adhesion between the piezoelectric thin film 25 and the Pt layer. The thickness of the Ti layer is about 0.02 μm, for example, and the thickness of the Pt layer is about 0.1 to 0.2 μm, for example. The upper electrode 26 is provided so as to sandwich the piezoelectric thin film 25 from the film thickness direction with the lower electrode 24. Note that a layer made of gold (Au) may be formed instead of the Pt layer.

  The lower electrode 24, the piezoelectric thin film 25, and the upper electrode 26 constitute a thin film piezoelectric element 27 for discharging the ink in the pressure chamber 22a to the outside. The piezoelectric element 27 is driven based on a voltage (drive signal) applied from the drive circuit 28 to the lower electrode 24 and the upper electrode 26. The inkjet head 21 is formed by arranging the piezoelectric element 27 and the pressure chamber 22a vertically and horizontally. In the present embodiment, the piezoelectric element 27 particularly refers to a portion of the lower electrode 24, the piezoelectric thin film 25, and the upper electrode 26 that is positioned corresponding to each pressure chamber 22a (above each pressure chamber 22a). .

  A nozzle substrate 31 is bonded to the opposite side of the pressure chamber 22a from the diaphragm 22b. The nozzle substrate 31 is formed with an ink discharge hole (nozzle hole) 31a for discharging the ink stored in the pressure chamber 22a to the outside as ink droplets. Ink supplied from the intermediate tank 6 is stored in the pressure chamber 22a.

  In the above configuration, when a voltage is applied from the drive circuit 28 to the lower electrode 24 and the upper electrode 26, the piezoelectric thin film 25 is in a direction perpendicular to the thickness direction (substrate) according to the potential difference between the lower electrode 24 and the upper electrode 26. (Direction parallel to the surface of 22). Then, due to the difference in length between the piezoelectric thin film 25 and the diaphragm 22b, a curvature is generated in the diaphragm 22b, and the diaphragm 22b is displaced (curved or vibrated) in the thickness direction.

  Therefore, if ink is stored in the pressure chamber 22a, the pressure wave is propagated to the ink in the pressure chamber 22a due to the vibration of the vibration plate 22b described above, and the ink in the pressure chamber 22a is transferred from the ink discharge hole 31a to the ink. It is discharged to the outside as a drop.

[Inkjet head manufacturing method]
Next, the manufacturing method of the inkjet head 21 of this embodiment is demonstrated below. FIG. 4 is a cross-sectional view showing the manufacturing process of the inkjet head 21. In the manufacture of the inkjet head 21, a plurality of piezoelectric elements 27 and pressure chambers 22a are formed on one substrate 22. Here, a case where one piezoelectric element 27 and pressure chambers 22a are formed is representatively shown. Show.

First, a single wafer-shaped substrate 22 is prepared. As the substrate 22, crystalline silicon (Si) often used in MEMS (Micro Electro Mechanical Systems) can be used. Here, two Si substrates 22 c and 22 d are bonded via an oxide film 22 e. An SOI structure is used. Subsequently, the substrate 22 is put into a heating furnace and held at about 1500 ° C. for a predetermined time, and thermal oxide films 23a and 23b made of SiO ₂ are formed on the surfaces of the Si substrates 22c and 22d, respectively.

  Next, Ti and Pt layers are sequentially formed on one thermal oxide film 23a by a sputtering method to form the lower electrode 24. Subsequently, a piezoelectric thin film 25 having a perovskite structure such as PZT is formed on the lower electrode 24. More specifically, the substrate 22 is reheated to about 600 ° C., and a PZT layer 25a serving as a displacement film is formed by sputtering. Next, a photosensitive resin 35 is applied onto the layer 25a by a spin coating method, and unnecessary portions of the photosensitive resin 35 are removed by exposure and etching through a mask, and the shape of the piezoelectric thin film 25 to be formed is changed. Transcript. Thereafter, using the photosensitive resin 35 as a mask, the shape of the layer 25 a is processed using a reactive ion etching method to form the piezoelectric thin film 25.

  Next, Ti and Pt layers are sequentially formed on the lower electrode 24 by a sputtering method so as to cover the piezoelectric thin film 25, thereby forming a layer 26a. Subsequently, a photosensitive resin 36 is applied onto the layer 26a by a spin coating method, and unnecessary portions of the photosensitive resin 36 are removed by exposure and etching through a mask, and the shape of the upper electrode 26 to be formed is transferred. To do. Thereafter, using the photosensitive resin 36 as a mask, the shape of the layer 26a is processed using a reactive ion etching method to form the upper electrode 26.

  Next, a photosensitive resin 37 is applied to the back surface (thermal oxide film 23b side) of the substrate 22 by a spin coat method, and unnecessary portions of the photosensitive resin 37 are removed by exposure and etching through a mask. The shape of the pressure chamber 22a to be formed is transferred. Then, using the photosensitive resin 37 as a mask, the substrate 22 is removed using a reactive ion etching method to form a pressure chamber 22a to be an actuator 21a.

  Thereafter, a wafer having a predetermined size is cut out from the wafer-shaped substrate 22 (hereinafter, the cut-out substrate is referred to as the substrate 22), and the substrate 22 of the actuator 21a and the nozzle substrate 31 having the ink discharge holes 31a are bonded. Joining using an agent or the like. Thereby, the inkjet head 21 is completed. The intermediate glass having a through hole at a position corresponding to the ink discharge hole 31a is used, the thermal oxide film 23b is removed, and the substrate 22 and the intermediate glass, and the intermediate glass and the nozzle substrate 31 are anodically bonded. May be. In this case, the three parties (substrate 22, intermediate glass, nozzle substrate 31) can be joined without using an adhesive.

[About the board]
Next, details of the substrate 22 of the inkjet head 21 will be described. FIG. 5 is a cross-sectional view showing a configuration example of the curved substrate 41 used as the substrate 22. In the present embodiment, a curved substrate 41 that is at least partially bent is used as the substrate 22, and a plurality of (for example, three) piezoelectric elements 27 are supported by the curved substrate 41. A method of bending the curved substrate 41 will be described later. The length of the white arrow shown in FIG. 5 corresponds to the amount of displacement in the thickness direction of each piezoelectric element 27 when the curved substrate 41 is used (the same applies to the subsequent drawings).

  The curved substrate 41 has a curved shape that protrudes toward the arrangement side of the plurality of piezoelectric elements 27 (in this case, a convex shape) in one direction in which the plurality of piezoelectric elements 27 are arranged side by side (left and right in FIG. 5). The whole is bent so that only one is formed. In particular, in the configuration of FIG. 5, the curved substrate 41 is bent so that only one convex shape is formed over the entire substrate in the one direction. Therefore, in the one direction of the curved substrate 41, there is no inflection point that changes from a convex shape to a concave shape, and each piezoelectric element 27 is located at any position on the curved substrate 41 (even at a position that supports each piezoelectric element 27). (Even at a position between) is convex. The one direction corresponds to the long side direction of the rectangular substrate 22 in plan view.

  When the piezoelectric element 27 is driven by applying a voltage, the piezoelectric element 27 is displaced in the vertical direction (particularly on the side opposite to the piezoelectric element 27 with respect to the curved substrate 41) by expansion and contraction in the horizontal direction (direction perpendicular to the thickness direction). To do. When the curved substrate 41 is convex toward the plurality of piezoelectric elements 27, the initial bending direction of the curved substrate 41 (the protruding direction toward the piezoelectric element 27) is the direction in which the piezoelectric elements 27 are displaced in the thickness direction (ink). Therefore, the piezoelectric element 27 is less likely to be displaced in the thickness direction. For this reason, compared with the case where the board | substrate 22 is flat form, the piezoelectricity of the piezoelectric element 27 falls (the displacement amount when a drive voltage is made constant) falls.

  When a plurality of piezoelectric elements are collectively formed on one wafer, in-plane distribution occurs in the piezoelectricity of the piezoelectric elements within the wafer surface, and the piezoelectricity tends to be high on the outer peripheral side of the wafer and low on the central side of the wafer. It is as described above. However, as shown in FIG. 6, even when the inkjet head 21 is configured by cutting out a relatively high piezoelectric substrate 51 and a relatively low piezoelectric substrate 52 from the wafer, the flat substrate 52 is By using the substrate 51 as it is and bending the substrate 51 so as to have a convex shape toward the plurality of piezoelectric elements 27 to form the curved substrate 41, the piezoelectricity of each piezoelectric element 27 in the curved substrate 41 is reduced. The piezoelectricity of 52 can be brought close to each other.

  On the other hand, FIG. 7 is a cross-sectional view showing another configuration example of the curved substrate 41. The curved substrate 41 has a curved shape that is concave on the arrangement side of the plurality of piezoelectric elements 27 (in this case, a concave shape) in one direction (left and right direction in FIG. 7) in which the plurality of piezoelectric elements 27 are arranged side by side. You may bend so that only an individual may be formed. In particular, in the configuration of FIG. 7, the curved substrate 41 is bent so that only one concave shape is formed over the entire substrate in the one direction. Therefore, in the one direction of the curved substrate 41, there is no inflection point that changes from a concave shape to a convex shape, and each piezoelectric element 27 is located at any position on the curved substrate 41 (even at a position that supports each piezoelectric element 27). (Even at a position between) is concave.

  When the curved substrate 41 has a concave shape on the side of the plurality of piezoelectric elements 27, the initial bending direction of the curved substrate 41 (the protruding direction to the side opposite to the piezoelectric element 27) is displaced in the thickness direction. Since the direction is the same as the direction, the piezoelectric element 27 is easily displaced in the thickness direction when driven by voltage application. For this reason, compared with the case where the board | substrate 22 is flat shape, the piezoelectricity of the piezoelectric element 27 improves (the displacement amount when a drive voltage is made constant increases).

  Therefore, as shown in FIG. 8, even when the inkjet head 21 is configured by cutting out a relatively low piezoelectric substrate 53 and a relatively high piezoelectric substrate 54 from one wafer, a flat substrate 54 is used as it is, and the substrates 53 are curved so as to have a concave shape toward the plurality of piezoelectric elements 27 to form the curved substrates 41, whereby the piezoelectric properties of the piezoelectric elements 27 in the curved substrates 41 are improved and the both substrates 53. -The piezoelectricity of 54 can be brought close to each other. Further, the substrate 53 is curved so as to be concave toward the plurality of piezoelectric elements 27 to improve the piezoelectricity, and the substrate 54 is curved so as to be convex toward the plurality of piezoelectric elements 27 to be piezoelectric. The piezoelectricity of both substrates 53 and 54 can be made closer to each other by lowering.

  Thus, with the simple configuration of using the curved substrate 41 as the substrate 22 that supports the plurality of piezoelectric elements 27, the piezoelectricity of the piezoelectric element 27 can be improved or decreased, and the output of the piezoelectric element 27 can be reduced. The (displacement amount) can be set to a desired size. Therefore, even when the inkjet head 21 is configured using a plurality of substrates 22, it is possible to adjust piezoelectricity for at least one substrate 22 and easily reduce variations in piezoelectricity between different substrates 22. Become. As a result, the ink discharge unevenness in the ink jet head 21 can be easily suppressed, and the ink jet printer 1 can form a good image on the recording medium while suppressing the deterioration of the image quality due to the ink discharge unevenness. Can do.

  In particular, as shown in FIGS. 5 and 7, the curved substrate 41 is formed so that one curved shape (convex shape or concave shape) is formed on the entire substrate in the arrangement direction of the plurality of piezoelectric elements 27 (the one direction). By bending, the piezoelectricity of the piezoelectric element 27 can be lowered or improved in the entire curved substrate 41, and variations in piezoelectricity between different substrates can be reduced.

  Further, as shown in FIG. 7, since the curved shape of the curved substrate 41 is a concave shape that is concave on the arrangement side of the plurality of piezoelectric elements 27, the piezoelectricity of the piezoelectric elements 27 on the curved substrate 41 is improved. In the inkjet head 21 provided with the curved substrate 41, the output (ink discharge amount) can be adjusted to increase.

  Conventionally, when a piezoelectric element is applied to an inkjet head, the size of one substrate is limited in order to keep the piezoelectric variation between different substrates of the inkjet head within an allowable range. On the other hand, since the variation in piezoelectricity between different substrates can be reduced by using the curved substrate 41 as in the present embodiment, the inkjet head is configured with a larger substrate size than before. You can also

[Relationship between radius of curvature and piezoelectricity of curved substrate]
FIG. 9 shows the relationship between the curvature radius of the curved substrate 41 and the piezoelectricity. The curvature radius of the horizontal axis in FIG. 9 is positive when the curved substrate 41 is concave with respect to the piezoelectric element 27, and the curved substrate 41 is attached to the curved surface portion 62 of the holding plate 60 (see FIG. 12) described later. This is indicated by the value of the radius of curvature of the curved surface portion 62 when attached. The piezoelectricity on the vertical axis is measured by measuring the amount of displacement in the thickness direction when a piezoelectric element formed on a flat substrate that is not curved (applied voltage is constant) using a laser Doppler device. The reference value is shown as a relative value of the displacement amount of the piezoelectric element formed on the curved substrate 41 with respect to the reference value.

  As shown in the figure, it can be seen that the smaller the radius of curvature of the curved substrate 41 is, the better the piezoelectricity is. However, if the radius of curvature is less than 150 mm, the curved substrate 41 is too curved and broken (breaks). ) On the other hand, if the radius of curvature exceeds 1000 mm, the degree of curvature of the curved substrate 41 is too small, and the piezoelectric adjustment range becomes small (the piezoelectricity cannot be increased greatly). That is, the piezoelectricity is almost close to 1, which is not much different from the case where the substrate is flat, and the effect of improving the piezoelectricity is reduced.

  When the curvature radius of the curved substrate 41 is a negative value, that is, when the curved substrate 41 has a convex shape with respect to the piezoelectric element 27, the direction in which the absolute value of the curvature radius increases decreases the piezoelectricity. In this case, it can be considered in the same manner as above (when the absolute value of the radius of curvature exceeds 1000 mm, the curved substrate 41 approaches a flat plate shape, so that the piezoelectricity cannot be greatly reduced).

  Therefore, by setting the absolute value of the radius of curvature of the curved shape of the curved substrate 41 to 150 mm or more and 1000 mm or less, it is possible to reliably obtain an effect of reducing piezoelectric variation while avoiding damage to the curved substrate 41.

  From FIG. 9, when the curvature radius of the curved shape of the curved substrate 41 is set to 1000 mm, the piezoelectricity varies by about 5%. That is, when the substrate is flat, the piezoelectricity is 1, and when the curved shape is concave, the piezoelectricity is 1.05, and when the substrate is convex, the piezoelectricity is 0.95. On the other hand, when the curvature radius of the curved shape is set to 150 mm, the piezoelectricity fluctuates by about 20%. That is, when the curved shape is concave, the piezoelectricity is 1.20, and when the curved shape is convex, the piezoelectricity is 0.8.

  Further, when the inkjet head 21 includes a plurality of substrates 22, the curved substrate 41 included in the plurality of substrates 22 is arranged so that the piezoelectric variation of the piezoelectric elements 27 between the plurality of substrates 22 is within a predetermined range. The curvature of the curved shape (= 1 / curvature radius) may be set. As the predetermined range, for example, a range of ± 10% with respect to the average value of piezoelectricity of each substrate 22 can be considered. Note that all of the plurality of substrates 22 may be the curved substrate 41, or only a part thereof may be the curved substrate 41 (the rest may be a flat substrate).

  As described above, by setting the curvature of the curved substrate 41, the piezoelectric variation among the plurality of substrates 22 falls within a predetermined range, and the variation is reduced. It can be made uniform.

[Other configurations of curved substrate]
FIG. 10 is a cross-sectional view showing still another configuration example of the curved substrate 41. As shown in the figure, the curved substrate 41 is formed with one curved shape (convex shape) that protrudes toward the piezoelectric element 27 in a part of one direction in which the plurality of piezoelectric elements 27 are arranged side by side. The remaining portion may be bent so as to have a flat plate shape. In this case, in the curved substrate 41, the surface on the piezoelectric element 27 side in the curved portion and the surface on the piezoelectric element 27 side in the flat plate portion are each composed of a curved surface and a flat surface. It is composed of a tangential plane and is a surface that is continuous with the curved surface.

  For example, when the substrate 22 is cut out from one wafer, a piezoelectric in-plane distribution may occur in the same substrate 22 depending on the region of the wafer to be cut out. As shown in FIG. 10, when the piezoelectricity of some of the piezoelectric elements 27 is relatively higher than that of the other piezoelectric elements 27 and the piezoelectricity of the other piezoelectric elements 27 is substantially uniform, Only the portion having relatively high piezoelectricity is convex toward the piezoelectric element 27 side, and the others are left flat so that the piezoelectricity of the piezoelectric element 27 can be increased only at a part of the curved portion of the curved substrate 41. It is possible to reduce the piezoelectric variation within the same curved substrate 41.

  FIG. 11 is a cross-sectional view showing still another configuration example of the curved substrate 41. As shown in the figure, the curved substrate 41 is bent so that, in a part of the one direction, one curved shape (concave shape) is formed on the piezoelectric element 27 side, and the rest is a flat plate shape. It may be. When the piezoelectricity of only some of the piezoelectric elements 27 is relatively lower than that of the other piezoelectric elements 27 within the same substrate 22 and the piezoelectricity of the other piezoelectric elements 27 is substantially uniform, the curved substrate as described above. 41, by making only the relatively low piezoelectric portion concave on the piezoelectric element 27 side, the piezoelectricity of the piezoelectric element 27 is improved only in the curved portion, so that the inside of the same curved substrate 41 is improved. Piezoelectric variation can be reduced.

  Therefore, in the inkjet head 21 and the inkjet printer 1 including the curved substrate 41 of FIGS. 10 and 11, ink discharge unevenness due to piezoelectric variation in the same curved substrate 41 is suppressed, and deterioration in image quality is suppressed. Can do.

[About the method of bending the curved substrate]
Next, a method for bending the above-described curved substrate 41 will be described. As a method of bending the curved substrate 41, (1) a method of attaching the substrate to the curved surface of the holding plate and bending the substrate, and (2) a method of bending the substrate using a difference in linear expansion coefficient between the substrate and the holding plate. There are two ways. Hereinafter, it demonstrates in order.

(Method of attaching the substrate to the curved surface of the holding plate and bending it)
FIG. 12 is a perspective view of the holding plate 60 that holds the plurality of substrates 22, and FIG. 13 is a plan view of the holding plate 60. The holding plate 60 has a main body 61 having a substantially rectangular parallelepiped shape. The main body 61 may be formed of a material having rigidity so as to hold the plurality of substrates 22. For example, the main body 61 can be composed of silicon, glass, metal (for example, stainless steel, aluminum), resin, or the like.

  A curved surface portion 62 and a flat surface portion 63 are provided side by side on the surface of the main body 61. One of the plurality of substrates 22 is attached to the curved surface portion 62, and another substrate 22 is attached to the flat surface portion 63. The curvature or radius of curvature of the curved surface portion 62 can be easily adjusted by blasting the surface of the holding portion 60. The holding plate 60 (main body 61) and the board | substrate 22 are affixed, for example using an adhesive agent.

  When the substrate 22 is attached to the holding plate 60, strictly speaking, between the holding plate 60 and the substrate 22, the thermal oxide film 23 and the lower electrode 24 (corresponding to each pressure chamber 22a) shown in FIG. Except for the portion constituting the piezoelectric element 27). Therefore, “attaching the substrate 22 to the holding plate 60” includes a case where the substrate 22 is attached to the holding plate 60 via the thermal oxide film 23 and the lower electrode 24.

  The main body 61 is formed with a rectangular opening 61a in plan view that penetrates in the thickness direction (direction perpendicular to the flat plate portion 63). In the present embodiment, two openings 61 a are formed in the main body 61, but it is only necessary to be formed corresponding to the number of substrates 22 to be held. The opening area of the opening 61 a is larger than the formation area of the plurality of piezoelectric elements 27 supported by the substrate 22 (area including each piezoelectric element 27) and smaller than the outer shape of the substrate 22. As a result, as shown in FIG. 14, each substrate 22 can be attached to the main body 61 (the curved surface portion 62 and the flat surface portion 63) outside the region where the plurality of piezoelectric elements 27 are formed. A plurality of piezoelectric elements 27 supported by one substrate 22 can be positioned together in the opening 61a. Therefore, the plurality of substrates 22 can be held by the holding plate 60 without causing the plurality of piezoelectric elements 27 and the holding plate 60 (main body 61) to interfere with each other.

  15 is a cross-sectional view taken along line B-B ′ in FIG. 14, and FIG. 16 is a cross-sectional view taken along line C-C ′ in FIG. 14. When the plurality of substrates 22 are held by the holding plate 60, the holding plate 60 is positioned on the side of the plurality of piezoelectric elements 27 with respect to the substrate 22, and an adhesive or the like is used to form the curved surface portion 62 and the flat surface of the holding plate 60. Each substrate 22 is attached to the portion 63. By sticking the substrate 22 to the curved surface portion 62, the substrate 22 is curved along the curved surface portion 62, whereby the curved substrate 41 in which the entire substrate is curved is obtained. On the other hand, the board | substrate 22 affixed on the plane part 63 remains flat form. In addition, the curved substrate 41 in which only a part of the substrate is curved along the curved surface portion 62 can be obtained by pasting the single substrate 22 across the curved surface portion 62 and the flat surface portion 63. However, in this case, it is necessary to adjust the size of the opening 61 a so that the plurality of piezoelectric elements 27 of the curved substrate 41 do not interfere with the main body 61.

  Thus, the curved substrate 41 is formed by attaching at least a part of the substrate 22 to the curved surface portion 62 and curving it along the curved surface portion 62. Therefore, by using the holding plate 60 having the curved surface portion 62, it is possible to easily realize the curved substrate 41 that is at least partially bent. In addition, the holding plate 60 is positioned on the side of the plurality of piezoelectric elements 27 with respect to the substrate 22, and holds the curved substrate 41 outside the formation region of the plurality of piezoelectric elements 27. The element 27 does not interfere with the holding plate 60.

  As described above, as shown in FIG. 15, the example in which the curved substrate 62 has the convex curved holding plate 60 on the substrate 22 side and the concave curved substrate 41 on the piezoelectric element 27 side is obtained. A holding plate 60 having a concave curved surface portion 62 may be used. In this case, by sticking the substrate 22 to the curved surface portion 62, the convex curved substrate 41 can be obtained on the piezoelectric element 27 side.

  In addition, on the piezoelectric element 27 side with respect to the substrate 22, a wiring substrate for driving each piezoelectric element 27 and ink common to each pressure chamber 22 a that stores ink supplied to each pressure chamber 22 a of the substrate 22 are stored. A chamber (common ink chamber) may be provided. When the wiring board is provided, the holding plate 60 is positioned between the board 22 and the wiring board, and the wiring board and each piezoelectric element 27 are electrically connected through the opening 61a of the holding plate 60 using bumps or the like. Thus, each piezoelectric element 27 can be driven. In other words, even if the curved substrate 41 is formed using the holding plate 60, each piezoelectric element 27 can be driven by providing a wiring substrate above the holding plate 60. Therefore, the holding plate 60 does not hinder the installation of the wiring board. In the case where the common ink chamber is provided, the curved substrate 41 can be obtained by providing a curved surface portion in a part of the casing constituting the common ink chamber and attaching the substrate 22 thereto. That is, in this case, the housing can be used instead of the holding plate.

  Here, in the inkjet head 21 in which the curved substrate 41 is held by the holding unit 60, as a result of various considerations including simulation, it has been found that the following effects of improving piezoelectricity can be obtained. In addition, each member which comprises the inkjet head 21 shown in FIG. 3 was set as follows. Parts of the substrate 22 other than the diaphragm 22b; Si (thickness 200 μm), diaphragm 22b; Si (thickness 5 μm), lower electrode 24; Pt (thickness 0.1 μm), piezoelectric thin film 25; PZT (thickness 5 μm), upper electrode 26; Au (thickness 0.3 μm). The piezoelectric thin film 25 was formed on the lower electrode 24 by sputtering. As a result, the piezoelectric thin film 25 was a polycrystalline film (grain size: about several tens of nm to 1 μm, crystal orientation: <100>) in which columnar crystals extending upward from the lower electrode 24 gathered.

  The surface of the substrate 22 on the piezoelectric element 27 side was attached to a holding plate 60 (material: SUS) processed to have a radius of curvature of 270 mm with an adhesive made of an epoxy resin to produce an inkjet head 21 (Example 1). . For comparison, an inkjet head was manufactured by attaching the substrate 22 to a holding plate (material: SUS) having a flat surface (Comparative Example 1). And the displacement amount of the thickness direction at the time of the drive of a piezoelectric element was measured with the laser Doppler apparatus, and this was evaluated as piezoelectricity. As a result, when the piezoelectricity in the configuration of Comparative Example 1 was used as a reference (1.00), the piezoelectricity in the configuration of Example 1 was 1.13. That is, by using the holding plate 60 and forming the curved substrate 41 that is curved so as to have a concave shape on the piezoelectric element 27 side, the piezoelectricity is improved by 13%.

  Further, the substrate 22 with uneven piezoelectricity (the substrate with the left end piezoelectricity being 1 and the right end portion being 0.9 and the piezoelectricity being inclined) and the right end portion being curved (minimum radius of curvature). The inkjet head 21 was manufactured by affixing to the holding plate 60 (material is SUS) made 300 mm) (Example 2). When the partially curved curved substrate 41 is formed as in Example 2, the piezoelectricity in the substrate that was 0.9 to 1.0 is in the range of 0.95 to 1.0, and the piezoelectric property Unevenness could be reduced.

  Further, two substrates A and B were prepared, and these substrates A and B were attached to one holding plate 60 to produce an ink jet head 21 (Example 3). Before the pasting, one substrate A was a substrate having a piezoelectricity 10% lower than the other substrate B. In addition, the portion (curved surface portion 62) to which the substrate A is attached in the holding plate 60 is processed with a curvature radius of 300 mm, and the portion to which the substrate B is attached (planar portion 63) has a flat shape without curvature. In the configuration of Example 3, the piezoelectric variation between the two substrates A and B was less than 10%. In this way, even if a plurality of substrates A and B are used, since the variation in piezoelectricity is reduced, a large inkjet head 21 can be produced, and ink is ejected onto a large recording medium. Can be easily handled.

(Method of bending the board using the difference in linear expansion coefficient between the board and the holding plate)
FIG. 17 is a cross-sectional view showing another configuration of the inkjet head 21. The substrate 22 of the inkjet head 21 may be bonded to the nozzle substrate 31 via a holding plate 70 located on the opposite side of the substrate 22 from the piezoelectric element 27. A communication hole 70 a is formed in the holding plate 70. The communication hole 70 a is a hole for communicating the pressure chamber 22 a formed in the substrate 22 and the ink discharge hole 31 a of the nozzle substrate 31.

The holding plate 70 is made of a material having a linear expansion coefficient different from that of the substrate 22. As the material of the holding plate 70, a material different from the material of the substrate 22 can be selected from, for example, silicon, glass, metal (for example, stainless steel, aluminum), resin, and the like. By the way, the linear expansion coefficient of each material is silicon: 2.4 × 10 ⁻⁶ / K, hard glass: 8.5 × 10 ⁻⁶ / K, stainless steel (SUS410): 10.4 × 10 ⁻⁶ / K K, stainless steel (SUS304): 17.3 × 10 ⁻⁶ / K, aluminum: 2.3 × 10 ⁻⁶ / K, carbon steel: 10.8 × 10 ⁻⁶ / K, acrylic resin: 4.5 to 7 × 10 ⁻⁵ / K, ABS resin: 6 to 13 × 10 ⁻⁵ / K.

  As shown in FIG. 18, when the linear expansion coefficient of the holding plate 70 is larger than the linear expansion coefficient of the substrate 22, the substrate 22 and the holding plate 70 are attached at a high temperature (with anodic bonding or an adhesive), and then When the temperature is returned to normal temperature, the holding plate 70 is more contracted than the substrate 22, so that the substrate 22 is curved so as to protrude toward the piezoelectric element 27, thereby forming the curved substrate 41. Conversely, as shown in FIG. 19, when the linear expansion coefficient of the holding plate 70 is smaller than the linear expansion coefficient of the substrate 22, the substrate 22 and the holding plate 70 are pasted at a high temperature, and then returned to room temperature. Since the contraction degree of the substrate 22 is larger than that of the holding plate 70, the substrate 22 is curved so as to be concave toward the piezoelectric element 27, thereby forming the curved substrate 41.

  Accordingly, the material of the substrate 22 and the holding plate 70 (difference in the linear expansion coefficient between the substrate 22 and the holding plate 70), the thickness (difference in the thickness of the substrate 22 and the holding plate 70), the temperature at the time of attachment, and the like are appropriately adjusted. Thus, the curved substrate 41 having a desired deflection can be obtained. In addition, the degree of bending of the curved substrate 41 can be changed (inclined) within the substrate surface by inclining the temperature at the time of attachment within the substrate surface. Furthermore, the degree of bending can be tilted in the substrate plane also by changing the thickness difference in the substrate plane.

  In this way, by configuring the holding plate 70 with a material having a linear expansion coefficient different from that of the substrate 22, at least a part of the substrate 22 is bent due to a difference in contraction between the substrate 22 and the holding plate 70 when a temperature change is applied. A curved substrate 41 can be obtained.

  The method for obtaining the curved substrate 41 by changing the linear expansion coefficient between the holding plate 70 and the substrate 22 in the configuration in which the holding plate 70 is positioned on the opposite side of the piezoelectric element 27 with respect to the substrate 22 has been described above. However, even in the configuration in which the holding plate 70 is positioned on the piezoelectric element 27 side with respect to the substrate 22, at least a part of the holding plate 70 is bent by making the coefficient of linear expansion different between the holding plate 70 and the substrate 22. The curved substrate 41 can be obtained.

  That is, as shown in FIG. 20, when the linear expansion coefficient of the holding plate 70 is larger than the linear expansion coefficient of the substrate 22, the substrate 22 and the holding plate 70 are pasted at a high temperature, and then returned to room temperature. Since the holding plate 70 is more contracted than the substrate 22, the substrate 22 is curved so as to be concave toward the piezoelectric element 27, thereby forming a curved substrate 41. Conversely, as shown in FIG. 21, when the linear expansion coefficient of the holding plate 70 is smaller than the linear expansion coefficient of the substrate 22, the substrate 22 and the holding plate 70 are attached at a high temperature, and then returned to room temperature. Since the substrate 22 contracts more than the holding plate 70, the substrate 22 is curved so as to protrude toward the piezoelectric element 27, thereby forming the curved substrate 41.

  Therefore, even when the holding plate 70 is positioned on the piezoelectric element 27 side with respect to the substrate 22, the curved substrate 41 can be obtained by changing the linear expansion coefficient between the holding plate 70 and the substrate 22 to change the temperature. it can. Such a holding plate 70 can be configured in a shape (outer shape is a rectangular parallelepiped shape) in which the curved surface portion 62 is eliminated and the entire surface is flat in the holding plate 60 shown in FIG.

  It should be noted that the inkjet head 21 and thus the inkjet printer 1 can be configured by appropriately combining the configurations shown in the drawings (including the curved substrate).

  The ink jet head of the present invention can be used in an ink jet printer.

1 Inkjet printer 21 Inkjet head 22 Substrate (support substrate)
22a Pressure chamber 22b Vibration plate 27 Piezoelectric element 31 Nozzle substrate 31a Ink discharge hole 41 Curved substrate 60 Holding plate 62 Curved portion 70 Holding plate P Recording medium

Claims (13)

An inkjet head comprising a plurality of piezoelectric elements and a support substrate that supports the plurality of piezoelectric elements,
The support substrate includes a curved substrate that is at least partially bent;
The curved substrate is bent so that only one curved shape that is convex or concave on the arrangement side of the plurality of piezoelectric elements is formed on the entire substrate in one direction where the plurality of piezoelectric elements are arranged side by side. An ink jet head characterized by comprising:   The inkjet head according to claim 1, wherein the curved substrate is bent so that one curved shape is formed on the entire substrate in the one direction.   2. The inkjet head according to claim 1, wherein the curved substrate is bent so that one curved shape is formed in a part of the one direction, and the rest is flat.   The inkjet head according to any one of claims 1 to 3, wherein a radius of curvature of the curved shape of the curved substrate is 150 mm or more and 1000 mm or less in absolute value.   5. The inkjet head according to claim 1, wherein the curved shape of the curved substrate is a shape that is concave on an arrangement side of the plurality of piezoelectric elements. A plurality of the support substrates;
The curvature of the curved shape of the curved substrate included in the plurality of support substrates is set so that the piezoelectric variation of the piezoelectric elements between the plurality of support substrates is within a predetermined range. The inkjet head according to claim 1, wherein the inkjet head is characterized in that A curved plate, further comprising a holding plate for holding the support substrate;
The inkjet head according to claim 1, wherein the curved substrate is formed by curving at least a part of the support substrate along the curved surface portion.   The said holding | maintenance board is located in the said several piezoelectric element side with respect to the said support substrate, The said curved board | substrate is hold | maintained outside the formation area of the said several piezoelectric element. Inkjet head. A holding plate for holding the support substrate, further on the opposite side of the plurality of piezoelectric elements with respect to the support substrate;
The inkjet head according to claim 1, wherein the holding plate is made of a material having a linear expansion coefficient different from that of the support substrate.   The inkjet head according to claim 9, wherein the support substrate is bonded to a nozzle substrate having an ink discharge hole via the holding plate. A holding plate that is positioned on the side of the plurality of piezoelectric elements with respect to the support substrate and holds the support substrate;
The inkjet head according to claim 1, wherein the holding plate is made of a material having a linear expansion coefficient different from that of the support substrate. The support substrate is
A pressure chamber formed corresponding to the formation position of the plurality of piezoelectric elements, and containing ink;
The inkjet head according to claim 1, further comprising a diaphragm that vibrates by driving the plurality of piezoelectric elements to apply pressure to the ink in the pressure chamber.   An ink jet printer comprising the ink jet head according to claim 1, wherein ink is ejected from the ink jet head toward a recording medium.

Images