JP2005041053A - Liquid discharging device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a printing head with small displacement fluctuation between piezoelectric displacement elements. <P>SOLUTION: In the printing head in which a piezoelectric actuator 1 is provided via a connecting layer to a flow channel member 3 including a liquid pressurizing chamber 3a, a liquid introduction inlet for introducing a liquid into the liquid pressurizing chamber 3a, and a liquid discharging port 8 for discharging the liquid, the piezoelectric actuator 1 has a plurality of surface electrodes on the surface, and has a difference in thermal expansion coefficient between the piezoelectric actuator 1 and the flow channel member 3 of less than 3×10<SP>-6</SP>/°C. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【００５３】
本発明の試料Ｎｏ．２〜８は、残留応力のばらつきが１０％以下、静電容量のばらつきが１０％以下であった。
【００５４】
一方、熱膨張係数差の大きなポリプロピレンを用いた試料Ｎｏ．１は、残留応力のばらつきが１８％、静電容量のばらつきが２０％と大きかった。
【００５５】
【発明の効果】
本発明は、前記流路部材の少なくとも一部が、熱膨張係数が９×１０^−６／℃以下の樹脂からなる低熱膨張樹脂を用いた流路部材を採用したため、樹脂と圧電アクチュエータに熱膨張係数差があっても樹脂が応力を緩和し、特に、熱膨張係数差の小さな液晶ポリマーを用いることによって、圧電アクチュエータに発生する残留応力を顕著に低減し液体吐出装置を得ることができ、その結果、圧電アクチュエータの圧電特性を十分に発揮させることができる。
【００５６】
特に、本発明の液体吐出装置は、インクジェットヘッドとして好適に採用することができ、高速・高精彩プリンタを容易に得ることができる。
【図面の簡単な説明】
【図１】本発明に用いるインクジェットヘッドの構造を示すもので、（ａ）は概略断面図、（ｂ）は平面図である。
【図２】本発明に用いる他のインクジェットヘッドの構造を示す概略断面図である。
【符号の説明】
１・・・圧電アクチュエータ
２・・・振動板
３・・・流路部材
３ａ・・・液体加圧室
３ｂ・・・隔壁
４・・・圧電セラミック層
５・・・共通電極
６・・・個別電極
７・・・圧電変位素子
７ａ・・・変位領域
８・・・液体吐出口
９・・・接着層[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a droplet discharge device, and in particular, for example, various printers, recorders, facsimiles for printing characters and images by discharging ink droplets from fine ink discharge holes, or pattern formation in the textile and ceramic industries. The present invention relates to a liquid droplet ejection apparatus suitably used for a print head suitably used for a recording apparatus such as a printing machine used for printing, a pump used for precision ejection / liquid conveyance of an adhesive, ink, or the like.
[0002]
[Prior art]
Conventionally, products using piezoelectric ceramics include, for example, piezoelectric actuators, filters, piezoelectric resonators (including oscillators), ultrasonic vibrators, ultrasonic motors, piezoelectric sensors, pressure pumps, and the like.
[0003]
Among them, the piezoelectric actuator has a very high response speed with respect to an electric signal of the order of 10 ⁻⁶ seconds, so that the piezoelectric actuator used for positioning the XY stage of a semiconductor manufacturing apparatus or the print head of an inkjet printer Etc.
[0004]
A print head using an ink jet system includes a piezoelectric displacement element made of perovskite ceramics including Pb such as PZT, and uses a displacement of the piezoelectric displacement element when a drive voltage is applied to the piezoelectric displacement element from both sides. Liquid droplets are discharged from a liquid discharge port (for example, Patent Document 1).
[0005]
Specifically, a piezoelectric actuator provided with a plurality of piezoelectric displacement elements is rolled over a flow path member having a liquid inlet, a liquid pressurizing chamber, and a liquid discharge port, and directly rolled onto the liquid pressurizing chamber. It is comprised so that an element may be arrange | positioned.
[0006]
As the flow path member, a metal such as stainless steel is used, and is heat-bonded to the piezoelectric actuator using an adhesive or the like (see, for example, Patent Document 2).
[0007]
[Patent Document 1]
Japanese Patent Laid-Open No. 11-34321 FIG.
[0008]
[Patent Document 2]
Japanese Patent Laid-Open No. 2003-118103
[Problems to be solved by the invention]
However, since a metal material is used as the flow path member, the thermal expansion coefficient of this metal is larger than the thermal expansion coefficient of the ceramic member having the piezoelectric drive unit. Due to the difference in thermal expansion between the two members below, there is a problem that compressive stress remains in the piezoelectric actuator, and this residual stress significantly reduces the piezoelectric characteristics of the piezoelectric drive unit.
[0010]
Moreover, since the metal material used for the flow path member uses a rolled plate, a difference occurs in the thermal expansion coefficient between the rolling direction and the direction perpendicular thereto. The flow path member is formed by forming a pattern based on the flow path design on this metal plate, and laminating and bonding them. For this reason, the stress state between the ceramic members having the piezoelectric drive unit is further complicated, and there is a problem that residual stress in an unpredictable direction is applied to the piezoelectric ceramic and causes deterioration and fluctuation of the piezoelectric characteristics.
[0011]
Accordingly, an object of the present invention is to provide a liquid ejection device in which residual stress between a piezoelectric ceramic and a metal flow path member is small and piezoelectric characteristics are stable.
[0012]
[Means for Solving the Problems]
The present invention reduces the residual stress generated in the flow path member and the piezoelectric actuator by using a low thermal expansion material containing resin as the flow path member, and remarkably reduces the residual stress generated in the piezoelectric actuator due to stress relaxation by the resin. This is based on the novel finding that the piezoelectric characteristics of the piezoelectric actuator can be sufficiently exhibited by using a liquid crystal polymer having a small difference in thermal expansion coefficient and anisotropy.
[0013]
That is, the liquid droplet ejection apparatus of the present invention is a liquid ejection apparatus in which a piezoelectric actuator having a piezoelectric drive unit is provided on a flow path member having a liquid introduction port, a liquid pressurizing chamber, and a liquid ejection port. The flow path member contains a resin, and its thermal expansion coefficient is 9 × 10 ⁻⁶ / ° C. or less.
[0014]
As a result, even if it is a combination with a metal member, the stress strain of the entire flow path member is reduced by arranging the resin in a direction that suppresses the difference in thermal expansion coefficient, and between the piezoelectric ceramic and the flow path member. It is possible to reduce the residual stress generated in.
[0015]
In particular, the thermal expansion coefficient of the resin has anisotropy, one direction is 2 × 10 ⁻⁶ / ° C. or less, and the other direction perpendicular to the one direction is 6 × 10 ⁻⁶ / ° C. or more, The flow path member is preferably a laminate of a resin layer made of the resin and a metal layer. By having such a structure, the thermal expansion consistency in the droplet discharge device is improved, and the stress generated due to the difference in thermal expansion coefficient is also reduced by the resin, so the stress generated in the actuator is small. Therefore, even if a metal layer is used for a part of the flow path member, sufficient piezoelectric characteristics can be exhibited.
[0016]
Furthermore, it is preferable that the thermal expansion coefficient of the resin layer is larger than the thermal expansion coefficient of the piezoelectric actuator and smaller than the metal layer. Thereby, the generated residual stress can be further reduced.
[0017]
Furthermore, it is preferable that the resin comprises a liquid crystal polymer. The thermal expansion coefficient of the liquid crystal polymer is 2 to 10 × 10 ⁻⁶ / ° C. and has anisotropy. The rolled plate used for the metal plate has different α in the rolling direction. For example, 6 × ^{10 -6} / ℃ of PZT, 3 × ^{10 -6} / ℃ of PMN, is similar to the 4 × ^{10 -6} / ℃ of PNN, can provide a small thermal expansion coefficient difference.
[0018]
It is preferable that the piezoelectric actuator is provided on the flow path member via an adhesive layer. Thereby, the residual stress generated in the piezoelectric actuator can be significantly reduced.
[0019]
The liquid ejection device is preferably an inkjet head. Since the liquid discharge apparatus uses a material having excellent chemical resistance for the flow path member, it can be suitably used as an ink jet head.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a liquid ejection apparatus according to an embodiment of the present invention will be described in detail with respect to a case where an inkjet head is used with reference to the drawings.
[0021]
FIG. 1 is a schematic cross-sectional view showing the piezoelectric actuator of the present embodiment. As shown in the figure, the ink jet head is obtained by bonding the piezoelectric actuator 1 to the surface of the flow path member 3 via an adhesive layer 9.
[0022]
The piezoelectric actuator 1 includes a diaphragm 2, a common electrode 5 provided on the diaphragm 2, a piezoelectric ceramic layer 4 provided on the common electrode, and a plurality of surfaces arranged on the piezoelectric ceramic layer 4. The piezoelectric displacement element 7 is formed by the common electrode 5, the piezoelectric ceramic layer 4, and the surface electrode 6.
[0023]
The flow path member includes a plurality of liquid pressurizing chambers 3a arranged in parallel, and a partition wall 3b is formed as a wall that partitions the liquid pressurizing chamber 3a. Since the piezoelectric actuator 1 and the flow path member 3 are joined so that the individual electrode 6 is disposed immediately above the opening of the liquid pressurizing chamber 3a, a driving voltage is applied between the internal electrode 5 and the individual electrode 6. When applied, the piezoelectric layer 4 sandwiched between the internal electrode 5 and the individual electrode 6 is deformed, the piezoelectric displacement element 7 is displaced, and the displacement region 7a is displaced. As a result, the volume of the liquid pressurizing chamber 3a is changed. Therefore, the liquid (ink) in the liquid pressurizing chamber 3a is discharged from the liquid discharge port 8 with the pressure generated at that time.
[0024]
The thickness T of the piezoelectric actuator 1 indicates the total thickness of the diaphragm 2 and the piezoelectric displacement element 7 and is important to be 100 μm or less. By using such a thin layer, a large displacement can be obtained, and high-efficiency driving can be realized at a low voltage. In particular, it is preferably 80 μm or less, more preferably 65 μm or less, and even more preferably 50 μm or less in that the characteristics as the piezoelectric actuator 1 can be sufficiently exhibited. On the other hand, the lower limit value of the thickness T is 3 μm, preferably 5 μm, more preferably 10 μm, and still more preferably 20 μm in order to have sufficient mechanical strength and prevent breakage during handling and operation.
[0025]
As the piezoelectric ceramic layer 4, ceramics exhibiting piezoelectricity can be used. Specifically, a Bi layered compound (layered perovskite type compound), a tungsten bronze type compound, and an Nb-based perovskite type compound (such as sodium Nb acid) Nb acid alkali compound (NAC), Nb acid alkaline earth compound (NAEC) such as barium Nb acid), lead magnesium niobate (PMN), lead nickel niobate (PNN), zirconate titanate containing Pb Examples thereof include substances containing perovskite type compounds such as lead (PZT) and lead titanate.
[0026]
Of these, a perovskite compound containing at least Pb is particularly preferable. For example, lead magnesium niobate (PMN), nickel niobate (PNN), lead zirconate titanate (PZT) containing Pb, lead titanate and the like are preferable. In particular, a crystal containing Pb as the A site constituent element and Zr and Ti as the B site constituent element is preferable. With such a composition, the piezoelectric ceramic layer 4 having a high piezoelectric constant can be obtained. Among these, lead zirconate titanate and lead titanate containing Pb are suitable for adding a large displacement.
[0027]
As an example of the perovskite crystal, PbZrTiO ₃ can be preferably used. Further, other oxides may be mixed, and as a subcomponent, other elements may be substituted at the A site and / or the B site as long as the characteristics are not adversely affected. For example, it may be a solid solution of Pb (Zn _1/3 Sb _2/3 ) O ₃ and Pb (Ni _1/2 Te _1/2 ) O ₃ to which Zn, Sb, Ni and Te are added as subcomponents. .
[0028]
According to the present invention, it is desirable that an alkaline earth element is further contained as the A site constituent element in the perovskite crystal. Examples of the alkaline earth element include Ba, Sr, and Ca, and Ba and Sr are particularly preferable because high displacement can be obtained. As a result, the dielectric constant is improved, and as a result, a higher piezoelectric constant can be obtained.
[0029]
_{Specifically, Pb 1-x-y Sr} x Ba y (Zn 1/3 Sb 2/3) a (Ni 1/2 Te 1/2) b Zr 1-a-b-c Ti c O 3 + α Mass% Pb _1/2 NbO ₃ (0 ≦ x ≦ 0.14, 0 ≦ y ≦ 0.14, 0.05 ≦ a ≦ 0.1, 0.002 ≦ b ≦ 0.01, 0.44 ≦ c ≦ 0.50, α = 0.1 to 1.0).
[0030]
The diaphragm 2 only needs to have a high insulating property, but is preferably a piezoelectric body, and particularly has a thermal expansion coefficient substantially the same as that of the piezoelectric ceramic layer 4 in order to reduce residual stress. More preferably, the composition is substantially the same as that of the piezoelectric ceramic layer 4. As a result, simultaneous firing becomes possible, and it becomes easy to prevent warping and distortion from being caused by thermal stress generated during firing due to a difference in thermal expansion.
[0031]
The diaphragm 2 may be a single layer, but is preferably a laminate in order to control the thickness and suppress compositional variation and characteristic variation after sintering. In addition, a conductor layer may be provided inside for the purpose of increasing rigidity or removing charges generated inside the diaphragm.
[0032]
Any material may be used for the surface electrode 6 as long as it has conductivity, and Au, Ag, Pd, Pt, Cu, Al, and alloys thereof are used. The thickness of the surface electrode 6 needs to be conductive and not to prevent displacement, and is generally about 0.5 to 5 μm, particularly preferably 1 to 4 μm.
[0033]
The common electrode 5 preferably contains Ag, and more preferably an Ag—Pd alloy. In the case of an Ag—Pd alloy, the ratio of Ag in the electrode material is preferably 90% by volume or more, and the balance is Pd. Thereby, the contraction of the electrode is suppressed, and the compressive residual stress at the time of firing the piezoelectric actuator can be suppressed.
[0034]
In particular, by increasing the Ag ratio of the Ag—Pd alloy, Ag is appropriately diffused in the piezoelectric ceramic layer 4 to lower the firing temperature of the piezoelectric ceramic layer 4, thereby improving the density of the piezoelectric ceramic layer 4. Can do. The thickness of the common electrode 5 needs to be conductive and not to prevent displacement, and is generally about 0.5 to 5 μm, preferably 1 to 4 μm.
[0035]
According to the present invention, it is important to use a material containing a resin having a thermal expansion coefficient of 9 × 10 ⁻⁶ / ° C. or less as the flow path member. This is because when the thermal expansion coefficient exceeds 9 × 10 ⁻⁶ / ° C., the difference in thermal expansion coefficient from the piezoelectric ceramics increases, resulting in a problem that residual stress between the flow path member and the piezoelectric ceramics increases. It is preferably 8 × 10 ⁻⁶ / ° C. or lower, more preferably 7 × 10 ⁻⁶ / ° C. or lower.
[0036]
Furthermore, since the resin is used, the residual stress generated due to the thermal expansion coefficient can be reduced. Therefore, even if the residual stress due to the difference in thermal expansion coefficient occurs, it can be suppressed to a small extent, and the piezoelectric characteristics can be sufficiently exhibited. A possible liquid ejection device can be provided.
[0037]
The thermal expansion coefficient of the resin is not uniform and preferably has anisotropy. This is because the anisotropy can suppress the influence of the anisotropy of the thermal expansion coefficient of the metal plate when combined with the metal plate. In particular, it is preferable that one direction is 2 × 10 ⁻⁶ / ° C. or lower and the direction perpendicular to this is 6 × 10 ⁻⁶ / ° C. or higher. Needless to say, even when such anisotropy is present, when the flow path member is formed using a resin, it has a thermal expansion coefficient of 9 × 10 ⁻⁶ / ° C. or less at least in the plane direction.
[0038]
Among the resins having such thermal expansion, liquid crystal polymers are preferable in terms of the absolute value of thermal expansion coefficient and anisotropy. In addition, by using a liquid crystal polymer, a liquid ejection device having excellent acid resistance can be obtained, and a strong acid or strong alkali liquid such as a strongly acidic ink can be handled.
[0039]
According to the invention, it is preferable that the flow path member is composed of a resin layer and a metal layer. By using a metal layer, the Young's modulus of the flow path member can be expected, and crosstalk that occurs when a piezoelectric actuator in which piezoelectric displacement elements are arranged in a lattice or staggered pattern on the diaphragm is formed. It can be expected to suppress. Further, when the thermal expansion coefficient of the metal layer is larger than the thermal expansion coefficient of the resin layer, the piezoelectric actuator, the resin layer, and the metal layer are provided in this order to suppress the generated stress, and the generated stress is also reduced to the resin layer. Can be removed.
[0040]
For example, as shown in FIG. 2, the inkjet head has a piezoelectric actuator 11 bonded to the surface of a flow path member 13 via an adhesive layer 19, and the flow path member 13 includes a resin layer 13b and a metal layer 13c. Consists of A metal layer 13 c is provided on the surface of the inkjet head including the liquid discharge port, and a resin layer 13 b is provided so as to be sandwiched between the metal layer 13 c and the piezoelectric actuator 11.
[0041]
In particular, it is preferable to set the coefficient of thermal expansion to decrease in the order of the metal layer, the resin layer, and the piezoelectric actuator. For example, it is desirable that the resin layer has a larger thermal expansion coefficient than that of the metal layer, and that the difference in thermal expansion coefficient is 8 × 10 ⁻⁶ or less, the resin layer is larger than the thermal expansion coefficient of the piezoelectric actuator, and The difference in thermal expansion coefficient is preferably 3 × 10 ⁻⁶ or less. By setting such a range, it is possible to effectively eliminate the influence of the generated stress.
[0042]
As the metal layer, stainless steel is preferable in terms of excellent corrosion resistance, and 42 alloy is preferable in terms of thermal expansion coefficient. Further, when the resin has anisotropy, it is easy to reduce the thermal expansion coefficient anisotropy of the metal layer.
[0043]
For such a flow path member, an adhesive such as a thermosetting epoxy adhesive is applied to the flow path member in advance, a pressure of 2 MPa is applied to the piezoelectric actuator, and after bonding at a temperature of 150 ° C., cooling and solidification is performed. Can be joined.
[0044]
Moreover, when it has a metal layer, it can join by the procedure of laminating | stacking a metal layer and a resin layer alternately.
[0045]
When the liquid ejection apparatus of the present invention is used in an inkjet head, it has the effect of suppressing displacement variation of the piezoelectric actuator by reducing the variation of residual stress and improving the displacement by reducing the residual stress, and to realize a high-speed, high-definition printer. It becomes very effective.
[0046]
【Example】
First, as a raw material, a piezoelectric powder containing lead zirconate titanate having a purity of 99.9% or more is prepared, and milled with a zirconia ball having a diameter of 2 mm to obtain an average particle size of 0.3 to 0.5 μm. The raw material powder was obtained by making a mesh pass after adjustment.
[0047]
Next, the obtained raw material powder was molded to produce a green sheet and an internal electrode paste. Next, the internal electrode paste was printed on the surface of some green sheets with a thickness of 4 μm to form internal electrodes. Furthermore, the green sheet on which the internal electrode was printed and the green sheet on which the internal electrode paste was not printed were laminated and pressed to create a laminated molded body, which was fired.
[0048]
A plurality of surface electrodes were formed on the surface of the obtained piezoelectric actuator laminate. As the surface electrode, Au paste was applied by screen printing to form 600 rectangular surface electrodes. This was baked in the atmosphere of 600 to 800 ° C. to obtain a piezoelectric drive unit.
[0049]
Next, the obtained piezoelectric actuator was bonded to the flow path member. As a channel member, sample No. 1 to 7 are bonded to a piezoelectric actuator using a liquid crystal polymer as a resin layer, and bonded to a resin layer as shown in FIG. 2 using SUS316 steel, SUS430 steel (both stainless steel) or 4-2 alloy as a metal layer. Used. Sample No. As a comparison, a piezoelectric actuator was directly joined to SUS316 steel.
In addition, the adhesion | attachment used 150 degreeC and the heat processing for 4 hours, using the epoxy-type adhesive agent as an adhesive agent.
[0050]
The thermal expansion coefficient was measured by measuring the linear expansion coefficient from room temperature to 150 ° C. Further, the residual stress was calculated from the amount of strain using X-ray diffraction.
[0051]
Capacitance was measured using 30 impedance displacement elements using an impedance analyzer, and variations in capacitance were calculated. That is, when the average capacitance value is Av and the maximum variation from Av is D, D / Av is displayed as a percentage as a variation.
[0052]
[Table 1]

[0053]
Sample No. of the present invention. In Nos. 2 to 8, variation in residual stress was 10% or less, and variation in capacitance was 10% or less.
[0054]
On the other hand, Sample No. using polypropylene having a large difference in thermal expansion coefficient. No. 1 had a large variation in residual stress of 18% and a variation of capacitance of 20%.
[0055]
【The invention's effect】
In the present invention, since at least a part of the flow path member employs a flow path member using a low thermal expansion resin made of a resin having a thermal expansion coefficient of 9 × 10 ⁻⁶ / ° C. or less, the resin and the piezoelectric actuator are thermally expanded. Even if there is a coefficient difference, the resin relaxes the stress, and in particular, by using a liquid crystal polymer with a small difference in thermal expansion coefficient, the residual stress generated in the piezoelectric actuator can be significantly reduced, and a liquid ejection device can be obtained. As a result, the piezoelectric characteristics of the piezoelectric actuator can be sufficiently exhibited.
[0056]
In particular, the liquid discharge apparatus of the present invention can be suitably employed as an ink jet head, and a high-speed and high-definition printer can be easily obtained.
[Brief description of the drawings]
1A and 1B show the structure of an inkjet head used in the present invention, in which FIG. 1A is a schematic sectional view, and FIG. 1B is a plan view;
FIG. 2 is a schematic sectional view showing the structure of another inkjet head used in the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Piezoelectric actuator 2 ... Diaphragm 3 ... Flow path member 3a ... Liquid pressurization chamber 3b ... Partition 4 ... Piezoelectric ceramic layer 5 ... Common electrode 6 ... Individual Electrode 7 ... Piezoelectric displacement element 7a ... Displacement region 8 ... Liquid discharge port 9 ... Adhesive layer

Claims (7)

In a liquid discharge apparatus in which a piezoelectric actuator having a piezoelectric drive unit is provided on a flow path member including a liquid introduction port, a liquid pressurization chamber, and a liquid discharge port, the flow path member includes a resin, A liquid ejection apparatus having a thermal expansion coefficient of 9 × 10 ⁻⁶ / ° C. or less. The thermal expansion coefficient of the resin has anisotropy, one direction is 2 × 10 ⁻⁶ / ° C. or less, and the other direction perpendicular to the one direction is 6 × 10 ⁻⁶ / ° C. or more. The liquid ejection device according to claim 1. The liquid discharge apparatus according to claim 1, wherein the flow path member is formed of a laminate of a resin layer made of the resin and a metal layer. The liquid ejection apparatus according to claim 3, wherein a thermal expansion coefficient of the resin layer is larger than a thermal expansion coefficient of the piezoelectric actuator and smaller than the metal layer. The liquid discharge apparatus according to claim 1, wherein the resin is made of a liquid crystal polymer. The liquid ejecting apparatus according to claim 1, wherein the piezoelectric actuator is provided on the flow path member via an adhesive layer. The liquid ejecting apparatus according to claim 1, wherein the liquid ejecting apparatus is an inkjet head.

Images