JP4965724B2 - Piezoelectric actuator and print head - Google Patents

Description

  The present invention relates to an actuator composed of a thin layer sintered body mainly composed of a piezoelectric ceramic layer containing Pb, Zr and Ti, a method for manufacturing the actuator, and a piezoelectric material suitably used for an ink jet recording apparatus used for printing characters and images. The present invention relates to an actuator, a manufacturing method thereof, and a print head.

  In recent years, with the spread of personal computers and the development of multimedia, the use of ink jet recording apparatuses as recording apparatuses that output information to recording media is rapidly expanding.

  Such an ink jet recording apparatus is equipped with a print head, and this type of print head includes a heater as a pressurizing unit in an ink flow path filled with ink, and heats the ink with the heater. A thermal head system that boiles and pressurizes ink with bubbles generated in the ink flow path and discharges it as an ink flow from the ink discharge hole, and a part of the wall of the ink flow path filled with ink is bent by a displacement element A piezoelectric method is generally known that displaces, pressurizes ink in an ink flow path mechanically, and discharges the ink as an ink flow from an ink discharge hole.

  For example, as shown in FIG. 4A, a print head used in an ink jet recording apparatus using a piezoelectric method has a plurality of grooves arranged in parallel as ink flow paths 23a, and a partition wall as a wall for partitioning each ink flow path 23a. The piezoelectric actuator 21 is provided on the flow path member 23 in which the 23b is formed.

  That is, an actuator in which an internal electrode 25 (common electrode) is formed on one main surface of the piezoelectric ceramic layer 24, a plurality of individual electrodes 26 are formed on the other main surface, and a plurality of displacement elements 27 are provided. Then, the actuator and the flow path member 23 are bonded so that the individual electrode 26 is disposed immediately above the ink flow path 23 a that is the opening of the flow path member 23.

  By applying a voltage between the internal electrode 25 and the individual electrode 26 to vibrate the displacement element 27, the ink in the ink flow path 23 a is pressurized, and the ink discharge hole 28 opened on the bottom surface of the flow path member 23. It is structured to eject ink droplets. In FIG. 4A, reference numeral 10 denotes a via conductor.

  Further, as shown in FIG. 4B, a print head in which a large number of individual electrodes 26 are arranged in parallel on the piezoelectric ceramic layer 24 at an equal pitch and a large number of displacement elements 27 are provided. Further, by independently controlling each displacement element 27, it is possible to contribute to speeding up and high accuracy of the ink jet printer. (See Patent Document 1)

  For example, lead zirconate titanate (PZT) is used as the piezoelectric ceramic layer 24 of the piezoelectric actuator 21 used in the inkjet printer. In Patent Document 2, a part of Pb in PZT is replaced with Ba, Sr or Ca, and the composition is controlled, so that even when co-fired with an internal electrode containing Ag, it has a high piezoelectric constant and is dense. It is disclosed that a simple piezoelectric ceramic can be obtained.

  In such a piezoelectric actuator, when the piezoelectric ceramic layer and the internal electrode containing silver are simultaneously fired, lead evaporates from the piezoelectric ceramic layer and silver diffuses from the internal electrode to the piezoelectric ceramic layer in the sintering stage. It is generally known that happens. Non-Patent Document 1 reports that when the amount of silver-doped piezoelectric ceramics is large, a low melting point compound of silver-lead precipitates at crystal grain boundaries and the insulation resistance decreases.

  That is, as described in Non-Patent Document 1, in a piezoelectric actuator having a piezoelectric ceramic doped with silver, when a voltage is repeatedly applied, the insulation resistance gradually decreases, so that current increases and heat is generated. This further accelerates the insulation degradation and causes dielectric breakdown. As a result, the piezoelectric actuator has a short life and is not practical.

Japanese Patent Laid-Open No. 10-151739 JP 2004-137106 A

JOURNAL OF MATERIAL SCIENCE 35 (2000) 5433-5436

  An object of the present invention is to provide a piezoelectric actuator and a print head in which deterioration of insulation resistance of piezoelectric ceramics is suppressed in a piezoelectric actuator composed of an internal electrode containing silver and a piezoelectric ceramic layer containing lead.

  As a result of intensive studies to solve the above problems, the present inventors have included a specific amount of sulfur in the piezoelectric ceramic layer containing lead, so that the lead and sulfur precipitated from the piezoelectric ceramic particles during firing are grains. The new fact that it precipitates as a compound at the triple point of the boundary, suppresses the precipitation of the silver-lead compound between the two faces of the piezoelectric ceramic particles, and can suppress the deterioration of the insulation resistance of the piezoelectric ceramic layer. The invention has been completed.

That is, the piezoelectric actuator of the present invention has the following configuration.
(1) as well as sandwiched between the pair of electrodes of the piezoelectric ceramic layer containing lead, viewed including the at least one electrode silver among the pair of electrodes, said and one said electrode including at least the silver piezoelectric ceramic layer In the piezoelectric actuator formed by simultaneously firing the piezoelectric ceramic layer, the piezoelectric ceramic layer contains lead and sulfur and contains a different phase having an average diameter of 0.05 to 2.5 μm.
(2) The piezoelectric actuator according to (1), wherein the piezoelectric ceramic layer contains barium or strontium.
(3) The piezoelectric actuator according to (1) or (2), wherein the number of the different phases observed in an area of 400 μm ² by an EPMA wavelength dispersion analysis method is 1 to 5.

  In the printing head of the present invention, the piezoelectric actuator according to any one of the above (1) to (3) is mounted on a flow path member in which a plurality of ink flow paths having ink discharge holes are arranged. Features.

  According to the configuration of the above (1) of the present invention, in the piezoelectric actuator comprising the piezoelectric ceramic layer containing lead and the internal electrode containing silver, the piezoelectric ceramic layer contains a different phase containing lead and sulfur. It is possible to suppress the deterioration of the insulation resistance and to increase the product life. Further, by setting the average diameter of the different phase to 0.05 to 2.5 μm, the size of the different phase is obtained while having the effect of concentrating the lead-containing low melting point compound that may exist between the two faces of the piezoelectric ceramic particles in the different phase part. The variation in the piezoelectric characteristics of the piezoelectric ceramic layer resulting from the distribution can be suppressed.

  In particular, according to the configuration of (2) above, by containing barium or strontium in the heterogeneous phase, the low melting point compound containing lead precipitated between the piezoelectric ceramic particles is more selectively concentrated in the heterogeneous portion of the triple point. It can be made. As a result, the formation of silver-lead precipitates between the two surfaces of the piezoelectric ceramic particles can be prevented, and the insulation resistance can be maintained over a long period of time even when a voltage is continuously applied for a long period of time.

According to the configuration of (3) above, by setting the number of different phases to 1 to 5 in the region of 400 μm ² , the lead-containing low melting point compound that can exist between the two faces of the piezoelectric ceramic particles is further reduced. While having the effect of concentrating on the different phase part, it is possible to further suppress variations in the piezoelectric characteristics of the piezoelectric ceramic layer resulting from the size and distribution of the different phase.

  According to the printing head of the present invention, the provision of the piezoelectric actuator has an effect of extending the product life.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows an embodiment of a piezoelectric actuator of the present invention, where (a) is a schematic cutaway perspective view, and (b) is a schematic cross-sectional view. 1 shows a structure of a print head of the present invention, in which (a) is a schematic broken perspective view, and (b) is a schematic cross-sectional view. FIG. 4 shows another embodiment of the piezoelectric actuator of the present invention, in which (a) is a schematic cutaway perspective view, and (b) is a schematic cross-sectional view. 1 shows a structure of a conventional print head, in which (a) is a schematic broken perspective view, and (b) is a schematic cross-sectional view.

  In the piezoelectric actuator of the present invention, for example, as shown in FIG. 1, the piezoelectric ceramic layer 4 is sandwiched between the internal electrode 5 (internal common electrode) made of Ag—Pd and the individual electrode 6 made of Au on the surface of the substrate 2. Displacement element 7 provided as described above is formed.

  It is important that the piezoelectric ceramic layer 4 constituting the displacement element 7 is mainly composed of a perovskite crystal containing at least Pb, Zr and Ti. For example, it is a crystal containing Pb as an A site constituent element and Zr and Ti as a B site constituent element. With such a composition, the piezoelectric ceramic layer 4 having a high piezoelectric constant can be obtained. .

Specific examples of the perovskite crystal include PbZrTiO ₃ . Further, other oxides may be mixed, and further, other elements may be substituted at the A site and / or the B site as a subcomponent within a range not affecting the characteristics. For example, Zn, Sb, Ni, and Te may be added as accessory components, and a solid solution of Pb (Zn _1/3 Sb _2/3 ) O ₃ and Pb (Ni _1/2 Te _1/2 ) O ₃ may be used. .

  Further, it is desirable to further contain an alkaline earth element as the A site constituent element in the perovskite crystal. Examples of alkaline earth elements 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 exhibited.

Specifically, the compound represented by the following formula can be exemplified.

  In addition, perovskite-type crystals containing Pb, Zr and Ti such as lead magnesium niobate (PMN series) and lead nickel niobate (PNN series) can be used.

  In the present invention, a piezoelectric ceramic layer 4 made of piezoelectric ceramic and an internal electrode 5 made of Ag-Pd or the like constitute a laminated body, and a displacement element 7 comprising a piezoelectric ceramic layer 4 and a pair of electrodes 5 and 6 sandwiching the piezoelectric ceramic layer 4. In the piezoelectric actuator 1 provided with the above, the piezoelectric ceramic layer 4 is dotted with different phases having an average diameter of 0.3 to 2 μm.

  If the average diameter of the different phases exceeds 2 μm, the partial piezoelectric characteristics will vary. Conversely, if the average diameter is less than 0.3 μm, it will be insufficient to capture Pb at the grain boundaries. Will remain. From this, it is more preferable that the average diameter of the different phase is in the range of 0.5 to 1 μm.

  As a result, when the piezoelectric ceramic layer 4 and the internal electrode 5 made of Ag—Pd are simultaneously fired, the low melting point compound containing lead precipitated between the piezoelectric ceramic particles in the sintering stage is selectively concentrated on the heterogeneous portion of the triple point. It can be made. As a result, the low melting point compound can be prevented from remaining between the two surfaces of the piezoelectric ceramic particles, and the portion where the continuous insulation resistance tends to deteriorate between the piezoelectric ceramic layers 4 sandwiched between the electrodes can be eliminated. Therefore, even if a voltage is continuously applied for a long time, the insulation resistance does not deteriorate for a long time.

  Moreover, this hetero phase contains at least sulfur. This is because sulfur combines with lead and easily forms a liquid layer, and is stable even at a sintering temperature of 900 to 1000 ° C., so that it easily remains in the piezoelectric ceramic grain boundary and works suitably.

  Furthermore, the number of the different phases is preferably at least one when an area of 20 μm × 20 μm is observed using an EPMA wavelength dispersion type. Thereby, precipitation of Pb to the grain boundary can be suppressed more suitably, and a decrease in insulation resistance can be suppressed.

  Similar to the above-mentioned different phase size, if there is no different phase in the area, there is no effect of suppressing the decrease in insulation resistance. Conversely, if there are three or more different phases in the area, there will be partial variations in piezoelectric characteristics. End up. By setting the number of different phases within the above range, it effectively works to suppress a decrease in insulation resistance and also suppresses variations in piezoelectric characteristics. Therefore, when such a piezoelectric actuator is used as an inkjet printer head, an inkjet printer head that exhibits stable ink ejection performance and excellent long-term reliability can be provided.

Next, the manufacturing method of the actuator 1 of the present invention will be described by taking as an example a case where a PbZrTiO ₃ -based perovskite crystal is specifically applied to a print head of an ink jet printer.

First, Pb ₂ O ₃ , ZrO ₂ , TiO ₂ , BaCO ₃ , ZnO, SrCO ₃ , Sb ₂ O ₃ , NiO, and TeO ₂ are prepared as raw material powders. These are adjusted to a composition corresponding to the stoichiometric composition of the perovskite crystal and mixed. At this time, BaCO ₃ containing BaSO ₄ as an impurity and containing 0.02 to 0.1% by mass with respect to the total amount of the raw material powder is used. If it is 0.02% by mass or less, a heterogeneous phase is not formed, so there is no effect of suppressing the deterioration of insulation resistance. The increase causes partial variations in piezoelectric characteristics.

In addition, compounds other than BaSO ₄ , such as K ₂ SO ₄ , Na ₂ SO ₄ , SrSO ₄ , CaSO ₄ , MgSO _4, etc., may be used as the sulfate. The sulfate may be added to the raw material powder in addition to those contained as impurities in the raw material powder.

  Here, when the laminate is fired, it is more than the Pb amount corresponding to the stoichiometric composition of the perovskite crystal, and in particular, the molar ratio A / B is adjusted to be 1.01 to 1.05. This is preferable in terms of reducing variation in characteristics and expressing more excellent piezoelectric characteristics.

  The molar ratio A / B is obtained by dividing the sum of the number of moles of all components at the A site by the sum of the number of moles of all components at the B site. The A / B ratio is 1 in the stoichiometric perovskite oxide, whereas when the A / B ratio is more than 1, the A site has a higher molar ratio than the B site. When the A / B ratio is smaller than 1, it means that the molar ratio of the B site is larger than that of the A site.

  Using the obtained mixed powder, a tape made of a piezoelectric ceramic layer and an organic composition is formed by a general tape forming method such as a roll coater method or a slit coater to produce a green sheet. In this green sheet, the Pb content is larger than the Pb amount corresponding to the stoichiometric composition of the perovskite crystal, so that the composition variation of the ceramic after firing can be greatly reduced, and the actuator 1 of the present invention can be obtained. Is important to get.

  The internal electrode 5 and the individual electrode 6 are formed on the surface of a part of the green sheet by a printing method or the like. If desired, a via hole may be formed in a part of the green sheet, and the via conductor 10 may be inserted into the via hole.

  Next, a desired green sheet is laminated to produce a laminate, and a constraining sheet obtained by adding an organic composition to piezoelectric ceramics having substantially the same composition as the green sheet is disposed on both sides or one side of the laminate. Then, press contact is performed.

  The piezoelectric ceramic 1 can be obtained by placing the laminated body after pressure contact inside a firing furnace and firing at a firing temperature of 900 ° C. or higher, particularly 940 to 1000 ° C. in a high-concentration oxygen atmosphere.

The green sheet density after pressure contact is 4.2 g / cm ² or more, especially 4.5 g / cm ² or more, which reduces Pb evaporation from the inside. It is preferable because it can be suppressed.

  The oxygen concentration in the oxygen atmosphere during firing is preferably 98% or more, particularly 99% or more. As a result, decomposition of the lead oxide can be suppressed, the amount of evaporation of Pb can be further reduced, the composition variation can be suppressed, and the displacement variation as an actuator can be further reduced.

  Here, as a method for confirming the size and distribution of the different phases, after mirror finishing with 1 μm diamond abrasive grains in the lamination cross section or in the lamination plane direction, carbon deposition was formed, and EPMA wavelength dispersion analysis was performed. The analysis area was set to 20 × 20 μm at a magnification of 5000 ×, sulfur mapping was performed at 10 locations, and the number of existences was calculated. Further, the size of the different phase was measured by SEM and TEM observation of the different phase portion.

  The print head of the present invention includes a flow path member and the actuator provided on the flow path member, and ink provided on the flow path member by displacement of the displacement element constituting the actuator. The ink filled in the flow path is ejected.

  An example of the print head of the present invention will be described with reference to FIG. A flow path member 13 having a structure in which an ink flow path 13a, which is a plurality of grooves, is partitioned by a partition wall 13b is bonded to the actuator 1 of the present invention. That is, the substrate 2 of the piezoelectric actuator 1 is bonded to the surface of the flow path member 13 with an adhesive. The piezoelectric actuator 1 is provided with a plurality of displacement elements 7 as described above. The piezoelectric actuator 1 is stacked on the flow path member 13 such that each displacement element 7 is positioned on the ink flow path 13 a that is an opening of the flow path member 13.

  In the displacement element 7, an internal electrode 5 (common electrode) is formed on one main surface of the piezoelectric ceramic layer 4, an individual electrode 6 is formed on the other main surface, and the piezoelectric ceramic layer 4 is sandwiched between a pair of electrodes 5 and 6. It has a structure.

  Further, the internal electrode 5 and the individual electrode 6 of the displacement element 7 are electrically connected to an external drive circuit, and when a voltage is applied between the internal electrode 15 and the individual electrode 6 from the drive circuit, FIG. As shown in b), the ink in the ink flow path 13 a corresponding to the displacement element 7 displaced by applying a voltage is pressurized, and ink droplets are ejected from the ink ejection holes 18 opened at one end surface of the flow path member 13. Can be discharged.

  In the printing head of the present invention, as shown in FIG. 2 (b), a plurality of displacement elements 7, 7... Are arranged on the piezoelectric actuator 1, and the individual displacement elements 7 are independently controlled to individually Is displaced. By adopting such a configuration, it is possible to stably perform high-speed and high-precision ink ejection, and it is possible to realize a print head suitable for a printer that realizes a clear image at high speed.

  Further, as shown in FIGS. 3A and 3B, the piezoelectric actuator of the present invention has a substrate 2 ′ (piezoelectric laminate) in which a plurality of piezoelectric ceramic layers 4 and 41 and internal electrodes 5, 61 and 51 are laminated. The individual electrode 6 may be formed on the surface of the body. Such a piezoelectric actuator 1 ′ is also suitably applied to the ink head in the same manner as the piezoelectric actuator 1 described above.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated, this invention is not limited to a following example.

（式中、ｘ＝０．０４、ｙ＝０．０２、ａ＝０．０７５、ｂ＝０．００５、ｃ＝０．４．２である。）
ここで、ＢａＣＯ₃原料粉末には、ＢａＳＯ₄を０．０１質量％〜０．１５質量％含むものを準備し、比較評価した。 Each raw material powder of high-purity Pb ₂ O ₃ , ZrO ₂ , TiO ₂ , BaCO ₃ , ZnO, SrCO ₃ , Sb ₂ O ₃ , NiO, TeO _{2 is used as} the raw material powder, and the sintered body is represented by the following formula. A predetermined amount was weighed so as to obtain a composition, and an excess Pb having a quantitative ratio shown in Table 1 was added to this composition.

(In the formula, x = 0.04, y = 0.02, a = 0.075, b = 0.005, and c = 0.4.2.)
Here, a BaCO ₃ raw material powder containing 0.01% by mass to 0.15% by mass of BaSO ₄ was prepared for comparative evaluation.

  The above-prepared powder was wet mixed by a ball mill for 20 hours, and then the mixture was dehydrated and dried. Thereafter, the mixture was calcined at 900 ° C. for 3 hours, and the obtained calcined product was wet pulverized again with a ball mill. The obtained pulverized product was mixed with an organic binder, water, a dispersant and a plasticizer to prepare a slurry, and a green sheet was prepared by a roll coater method generally used for forming a thin green sheet. At this time, considering the shrinkage rate of the green sheet in advance so that the thickness after firing becomes the size shown in the table

  Thereafter, the green sheet was punched into a rectangular shape using a mold to prepare a plurality of rectangular sheets. Next, an electrode was applied to the surface of the green sheet by screen printing on the rectangular sheet surface using an electrode paste made of Ag—Pd as an internal electrode and individual electrodes.

  Next, the green sheet coated with the electrode and the green sheet coated with no electrode are stacked so that the structure shown in FIG. 1 is formed, that is, a plurality of displacement elements are formed on the surface of the substrate, and heat is applied. The laminated actuator molded body was manufactured by pressure bonding.

  Finally, this molded body was degreased at 400 ° C. and then fired at 1000 ° C. for 2 hours to obtain a piezoelectric actuator as a piezoelectric ceramic laminate.

  Here, in order to confirm the size and distribution of the different phases, after mirror finishing with 1 μm diamond abrasive grains in the lamination cross section and lamination plane direction, carbon deposition was formed, and EPMA wavelength dispersion type (apparatus name: JXA-8600M) The analysis was performed using. As an analysis method, the analysis area was set to 20 × 20 μm at a magnification of 5000 times, sulfur mapping was performed at 10 locations, and the number of existence was determined. Further, the size of the different phase was determined by observing the different phase portion with an SEM (device name: JSM-6340F manufactured by JEOL Ltd.). Furthermore, the grain boundary component between the two surfaces of the piezoelectric ceramic particles was analyzed by TEM (device name: 2010E made by JEOL) analysis.

  Next, the variation in the piezoelectric characteristics of the actuator obtained above was measured with an impedance analyzer (device name: HP Impedance Analyzer 4194a). Here, the d31 constant was calculated from the resonance, antiresonance frequency, and capacitance value of each element, and the percentage obtained by dividing the variation for 20 elements by the average value was displayed as a percentage.

  Further, a voltage was continuously applied at 10 KHz and 50 V under an environment of a temperature of 60 ° C., and the change over time in the insulation resistance was confirmed using an insulation resistance meter. Then, the insulation resistance value change when the displacement vibration was continued 1 billion times was confirmed, and the presence or absence of the change was judged. The test results are shown in Table 1.

  According to Table 1, in the EPMA wavelength dispersion type analysis, for sample A in which a heterogeneous phase containing lead and sulfur is not confirmed in the reference area, an amorphous lead layer is confirmed by TEM observation between the two surfaces of the piezoelectric ceramic particles. It was. In addition, a decrease in the resistance value was confirmed even with the time-dependent change in the insulation resistance.

  On the other hand, for Samples B to L of the present invention, no precipitation phase was confirmed at the grain boundary even in TEM observation between the two faces of the piezoelectric ceramic particles, and no change in insulation resistance with time was confirmed. In particular, Samples B, D, E, F, G, H, and J were confirmed to be actuators with small variations in piezoelectric characteristics and stable displacement vibration.

DESCRIPTION OF SYMBOLS 1 ... Piezoelectric actuator 2 ... Board | substrate 4 ... Piezoelectric ceramic layer 5 ... Internal electrode 6 ... Individual electrode 7 ... Displacement element 13 ... Channel member 13a ... Ink channel 13b ... partition 18 ... discharge hole 19 ... nozzle plate

Claims (4)

While sandwiching the piezoelectric ceramic layer with a pair of electrodes containing lead, it viewed including the at least one electrode silver among the pair of electrodes, and wherein at least the silver laden one the electrodes of the piezoelectric ceramic layer is simultaneously fired In the piezoelectric actuator formed,
The piezoelectric actuator, wherein the piezoelectric ceramic layer contains lead and sulfur and has a different phase having an average diameter of 0.05 to 2.5 μm.   The piezoelectric actuator according to claim 1, wherein the piezoelectric ceramic layer contains barium or strontium. 3. The piezoelectric actuator according to claim 1, wherein the number of the different phases observed in an area of 400 μm ² by an EPMA wavelength dispersion analysis method is 1 to 5. 5.   4. A print head, wherein the piezoelectric actuator according to claim 1 is mounted on a flow path member in which a plurality of ink flow paths having ink discharge holes are arranged.

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