JP2011135001A - Piezoelectric element, and ink jet head and ink jet recording device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a piezoelectric element capable of proofing use of long period of time by suppressing deterioration of drying agent and power consumption, and to provide an ink jet head and ink jet recording device. <P>SOLUTION: The ink jet head 303 includes a piezoelectric material 30, electrodes 20 and 40 applying an electric field to the piezoelectric material 30 in a predetermined direction, and a humidity maintaining means which maintains the humidity near the piezoelectric material 30 at constant. The ink jet head further has a control means 222 which does not actuate the humidity maintaining means while un-driving the piezoelectric material 30, and actuates the humidity maintaining means while driving the piezoelectric material 30. By opening an on-off valve 236, the drying agent 238 provided to a drying agent housing chamber 240 absorbs moisture in a piezoelectric material housing chamber 232, and by lowering the humidity of the atmosphere near the piezoelectric material 30, the humidity can be controlled. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a piezoelectric element, an inkjet head, and an inkjet recording apparatus, and more particularly to a piezoelectric element, an inkjet head, and an inkjet recording apparatus that can suppress power consumption and suppress deterioration of a piezoelectric body.

  In general, as a general-purpose image forming apparatus, an ink jet recording apparatus that forms a desired image by ejecting ink droplets from an ink jet head onto a recording medium is widely used. In an ink jet recording apparatus, a piezoelectric element (piezoelectric actuator) is preferably used as pressure applying means for ejecting ink droplets from an ink jet head.

  This piezoelectric element is known to deteriorate in the presence of moisture, and many methods have been proposed as methods for suppressing the deterioration.

  For example, the following Patent Documents 1 to 4 describe a technique for preventing deterioration by sufficiently drying a piezoelectric body.

JP 2008-210924 A JP 2004-322605 A JP 2005-022191 A JP 2005-022192 A

  However, the methods described in Patent Documents 1 to 4 are techniques for drying a piezoelectric body regardless of whether or not it is driven. When a desiccant is used, the use period of the desiccant is shortened and drying air is supplied. In this case, there is a problem that the power consumption increases due to the flow of the dry air even when the piezoelectric element is not driven.

  The present invention has been made in view of such circumstances, and provides a piezoelectric element, an ink jet head, and an ink jet recording apparatus that can suppress deterioration of a desiccant and power consumption and can withstand long-term use.

  According to a first aspect of the present invention, in order to achieve the above object, a piezoelectric body, an electrode that applies an electric field to the piezoelectric body in a predetermined direction, and a humidity retention that maintains a constant humidity near the piezoelectric body And a control means for operating the humidity holding means when the piezoelectric body is driven without operating the humidity holding means when the piezoelectric body is not driven. .

  In order to suppress the deterioration of the piezoelectric body, it has been conventionally known to reduce the humidity in the atmosphere near the piezoelectric body. However, the present applicant has found that the deterioration of the piezoelectric material due to moisture does not occur simply by being exposed to water vapor, but is caused by driving the piezoelectric element in the presence of water vapor. It was. Therefore, by operating the humidity holding means when the piezoelectric body is driven and not driving the humidity holding means when the piezoelectric body is not driven, deterioration of the piezoelectric body can be suppressed and excessive power consumption can be suppressed.

  A second aspect of the present invention is characterized in that, in the first aspect, the humidity is equal to or lower than a critical humidity which is a humidity for suppressing deterioration of the piezoelectric body.

  Further, the present applicant has found that there is humidity at which the durability of the piezoelectric body deteriorates rapidly. Therefore, sufficient durability can be obtained by maintaining the humidity near the piezoelectric body so as not to exceed this humidity. In addition, since it is not necessary to set the humidity to an extremely low humidity, it is possible to further suppress excessive power consumption.

  The cause of the ability to withstand deterioration by maintaining a predetermined humidity is unknown, but is considered to be due to capillary condensation. The piezoelectric body has microcracks, but it is presumed that when water vapor abruptly undergoes capillary condensation at a certain humidity and the liquid exists in the microcracks, the deterioration rapidly proceeds. That is, there is no problem when moisture is present as a gas, but deterioration proceeds when it is present as a liquid. Therefore, deterioration of the piezoelectric element can be prevented by controlling so as not to exceed the predetermined humidity.

  According to a third aspect of the present invention, in the second aspect, the critical humidity is measured by performing a durability test of the piezoelectric element while changing a humidity condition.

  The third aspect defines a method for measuring the critical humidity, and the deterioration can be effectively suppressed by performing a durability test in advance and driving at a withstandable humidity.

A fourth aspect is characterized in that, in any one of the first to third aspects, the humidity is 15 g / m ³ or less.

  According to the fourth aspect of the present invention, deterioration of the piezoelectric element can be effectively suppressed by setting the humidity to be equal to or lower than the above numerical value.

  According to a fifth aspect of the present invention, in any one of the first to fourth aspects, the humidity holding unit includes a piezoelectric body chamber that houses the piezoelectric body, and a dry air supply unit that supplies dry air to the piezoelectric body chamber. The humidity is adjusted depending on whether or not the dry air supply means is activated.

  The fifth aspect specifies the configuration of the humidity holding means, and suppresses the humidity in the vicinity of the piezoelectric body by supplying dry air when the piezoelectric body is driven.

  A sixth aspect of the present invention is the method according to any one of the first to fourth aspects, wherein the humidity holding unit includes a piezoelectric body housing chamber that houses the piezoelectric body, and a desiccant housing chamber that communicates with the piezoelectric body housing chamber and houses a desiccant. And an open / close valve that opens and closes between the piezoelectric body storage chamber and the desiccant storage chamber, and the humidity is adjusted by driving the open / close valve.

  Claim 6 defines other means for maintaining the humidity, and the desiccant is installed in a room different from the piezoelectric body, and the room in which the desiccant is installed is opened and closed by an on-off valve. Only humidity adjustment can be made. In addition, humidity adjustment is not performed when the piezoelectric element is not driven, and moisture is absorbed by the desiccant only when the piezoelectric element is driven, so that the desiccant can be used for a long period of time, and deterioration of the piezoelectric body can be suppressed for a long period of time. it can.

  A seventh aspect of the present invention is the solid polymer electrolyte membrane according to any one of the first to fourth aspects, wherein at least a part of a wall of the piezoelectric material accommodation chamber for accommodating the piezoelectric material is sandwiched between porous electrodes. The humidity is adjusted by applying a voltage between the porous electrodes.

  The seventh aspect defines other means for maintaining the humidity, and the wall of the piezoelectric body accommodating chamber is a solid polymer electrolyte membrane sandwiched between the porous electrodes, and only when the piezoelectric body is driven between the porous electrodes. The humidity can be adjusted by applying a voltage to.

  According to an eighth aspect of the present invention, in order to achieve the above object, the piezoelectric element according to any one of the first to seventh aspects, a liquid storage chamber in which a liquid is stored, and the liquid from the liquid storage chamber to the outside. An ink-jet head comprising: a liquid storage and discharge member having a liquid discharge port to be discharged.

  According to a ninth aspect of the present invention, there is provided an ink jet recording apparatus comprising the ink jet head according to the eighth aspect to achieve the above object.

  According to the eighth and ninth aspects, since the piezoelectric element of the present invention is provided, an ink jet head and an ink jet recording apparatus that can be used for a long period of time can be provided.

  According to the piezoelectric element, the ink jet head, and the ink jet recording apparatus of the present invention, by performing humidity adjustment when necessary, it is possible to suppress deterioration of the desiccant, power consumption, and deterioration of the piezoelectric body.

It is sectional drawing which shows the structure of the inkjet head provided with the piezoelectric element. It is a figure which shows an example of the PE hysteresis characteristic of a piezoelectric material. It is a schematic block diagram of the inkjet recording device provided with the inkjet head of FIG. 1 is a schematic view of an inkjet head including a piezoelectric element according to a first embodiment of the present invention. It is the schematic of the inkjet head provided with the piezoelectric element which concerns on 2nd Embodiment of this invention. It is the schematic of the inkjet head provided with the piezoelectric element which concerns on 3rd Embodiment of this invention. It is a graph which shows the result of an Example.

  Preferred embodiments of a piezoelectric element, an ink jet head, and an ink jet recording apparatus according to the present invention will be described below with reference to the accompanying drawings.

[Piezoelectric element and inkjet head]
With reference to FIG. 1, the structure of a piezoelectric actuator provided with a piezoelectric element and an inkjet head (liquid ejecting apparatus) will be described.

  As shown in FIG. 1, the piezoelectric element 1 has a piezoelectric film 30 on the back surface of the substrate 10 of the piezoelectric element 1 in which the lower electrode 20, the piezoelectric film 30 and the upper electrode 40 are sequentially stacked on the substrate 10. A diaphragm 50 that vibrates due to expansion and contraction is attached. In the piezoelectric element 1, an electric field is applied to the piezoelectric film 30 in the film thickness direction by the lower electrode 20 and the upper electrode 40, and the piezoelectric actuator 2 is controlled to drive the piezoelectric element 1. Control means (not shown) such as a drive circuit is also provided.

  The lower electrode 20 is formed on substantially the entire surface of the substrate 10, and a piezoelectric film 30 having a pattern in which convex portions 31 on the line are arranged in a stripe shape is formed thereon, and the upper electrode is formed on each convex portion 31. 40 is formed.

  The pattern of the piezoelectric film 30 is not limited to that shown in the figure, and is appropriately designed. The piezoelectric film 30 may be a continuous film. However, the piezoelectric film 30 is not a continuous film, but is formed by a pattern composed of a plurality of protrusions 31 separated from each other, so that the expansion and contraction of the individual protrusions 31 occurs smoothly, so that a larger displacement amount can be obtained. ,preferable.

The substrate 10 is not particularly limited, and examples thereof include substrates such as silicon, silicon oxide, stainless steel (SUS), yttrium stabilized zirconia (YSZ), alumina, sapphire, SiC, and SrTiO ₃ . As the substrate 10, a laminated substrate such as an SOI substrate in which a SiO ₂ film and a Si active layer are sequentially laminated on a silicon substrate may be used.

The composition of the lower electrode 20 is not particularly limited, and examples thereof include metals or metal oxides such as Au, Pt, Ir, IrO ₂ , RuO ₂ , LaNiO ₃ , and SrRuO ₃ , and combinations thereof. The composition of the upper electrode 40 is not particularly limited, and examples thereof include the materials exemplified for the lower electrode 20, electrode materials used in general semiconductor processes such as Al, Ta, Cr, and Cu, and combinations thereof. The thickness of the lower electrode 20 and the upper electrode 40 is not particularly limited and is preferably 50 to 500 nm.

  The piezoelectric film 30 has coercive electric field points on the negative electric field side and the positive electric field side as shown in FIG. 2, and the absolute value of the coercive electric field on the negative electric field side and the coercive electric field value on the positive electric field side are It has different asymmetric bipolar polarization-electric field hysteresis characteristics. If it is such a piezoelectric film 30, the piezoelectric film 30 is not particularly limited. The piezoelectric film 30 was formed on the substrate 10 by sputtering using plasma. Examples thereof include a piezoelectric film (which may contain inevitable impurities) made of one or more perovskite oxides represented by the following general formula (P). Such a piezoelectric film has a piezoelectric characteristic in which the polarity of the coercive electric field having a small absolute value is negative and the PE hysteresis is biased toward the positive electric field.

General formula A _a B _b O ₃ (P)
(In the formula, A is an A site element mainly composed of Pb, B is an element of B site, and Ti, Zr, V, Nb, Ta, Cr, Mo, W, Mn, Sc, Co, Cu, In , Sn, Ga, Zn, Cd, Fe, and Ni, at least one element selected from the group consisting of O and oxygen, where a ≧ 1.0 and b = 1.0 are standard, (These numerical values may deviate from 1.0 within a range where a perovskite structure can be taken.)
Examples of the perovskite oxide represented by the general formula (P) include lead titanate, lead zirconate titanate (PZT), lead zirconate, and lead niobate zirconium titanate. The piezoelectric film may be a mixed crystal system of perovskite oxides represented by the above general formula (P).

  The ink jet head (liquid ejecting apparatus) 3 is roughly composed of an ink chamber (liquid storing chamber) 61 for storing ink and an ink ejecting port (liquid ejecting) for ejecting ink from the ink chamber 61 to the back surface of the piezoelectric actuator 2. The ink nozzle (liquid storing and discharging member) 60 having the chamber 62 is attached. A plurality of ink chambers 61 are provided corresponding to the number and pattern of the convex portions 31 of the piezoelectric film 30. In the ink jet head 3, the electric field strength applied to the piezoelectric element 1 is increased or decreased to expand and contract the piezoelectric element 1, thereby discharging ink from the ink chamber 61 and suppressing the discharge amount.

[Inkjet recording apparatus]
With reference to FIG. 3, the structural example of the inkjet recording device provided with the inkjet head 3 is demonstrated. FIG. 3 is an overall view of the apparatus.

  The inkjet recording apparatus 100 includes a plurality of colors from inkjet heads 172M, 172K, 172C, and 172Y on a recording medium 124 (sometimes referred to as “paper” for convenience) held on the impression cylinder (drawing drum 170) of the drawing unit 116. This is an impression cylinder direct drawing type ink jet recording apparatus that forms a desired color image by ejecting ink, and a treatment liquid (here, a coagulation treatment liquid) is applied onto the recording medium 124 before ink ejection. This is an on-demand type image forming apparatus to which a two-liquid reaction (aggregation) method for forming an image on a recording medium 124 by reacting a liquid and an ink liquid is applied.

  As shown in the figure, the ink jet recording apparatus 100 mainly includes a paper feeding unit 112, a treatment liquid application unit 114, a drawing unit 116, a drying unit 118, a fixing unit 120, and a discharge unit 122.

(Paper Feeder)
The paper feeding unit 112 is a mechanism that supplies the recording medium 124 to the processing liquid application unit 114, and the recording medium 124 that is a sheet is stacked on the paper feeding unit 112. The paper feed unit 112 is provided with a paper feed tray 150, and the recording medium 124 is fed from the paper feed tray 150 to the processing liquid application unit 114 one by one.

(Processing liquid application part)
The processing liquid application unit 114 is a mechanism that applies the processing liquid to the recording surface of the recording medium 124. The treatment liquid contains a color material aggregating agent that agglomerates the color material (pigment in this example) in the ink applied by the drawing unit 116, and the ink comes into contact with the treatment liquid and the ink. And the solvent are promoted.

  As shown in FIG. 3, the treatment liquid application unit 114 includes a paper feed cylinder 152, a treatment liquid drum 154, and a treatment liquid application device 156. The treatment liquid drum 154 is a drum that holds and rotates the recording medium 124. A processing liquid coating device 156 is provided outside the processing liquid drum 154 so as to face the peripheral surface thereof. The processing liquid coating device 156 includes a processing liquid container in which the processing liquid is stored, an anix roller partially immersed in the processing liquid in the processing liquid container, and the recording medium 124 on the anix roller and the processing liquid drum 154. And a rubber roller that transfers the measured processing liquid to the recording medium 124. According to the processing liquid coating apparatus 156, the processing liquid can be applied to the recording medium 124 while being measured.

  The recording medium 124 to which the processing liquid is applied by the processing liquid applying unit 114 is transferred from the processing liquid drum 154 to the drawing drum 170 of the drawing unit 116 via the intermediate transport unit 126.

(Drawing part)
The drawing unit 116 includes a drawing drum (second transport body) 170, a sheet pressing roller 174, and ink jet heads 172M, 172K, 172C, and 172Y.

  The inkjet heads 172M, 172K, 172C, and 172Y are preferably full-line inkjet recording heads (inkjet heads) each having a length corresponding to the maximum width of the image forming area on the recording medium 124. On the ink ejection surface, a nozzle row in which a plurality of nozzles for ink ejection are arranged over the entire width of the image forming area is formed. Each inkjet head 172M, 172K, 172C, 172Y is installed so as to extend in a direction orthogonal to the conveyance direction of the recording medium 124 (the rotation direction of the drawing drum 170).

  The droplets of the corresponding color ink are ejected from the inkjet heads 172M, 172K, 172C, and 172Y toward the recording surface of the recording medium 124 held in close contact with the drawing drum 170, whereby the processing liquid application unit 114 performs the processing. The ink comes into contact with the treatment liquid previously applied to the recording surface, and the color material (pigment) dispersed in the ink is aggregated to form a color material aggregate. Thereby, the color material flow on the recording medium 124 is prevented, and an image is formed on the recording surface of the recording medium 124.

  The recording medium 124 on which an image is formed by the drawing unit 116 is transferred from the drawing drum 170 to the drying drum 176 of the drying unit 118 via the intermediate conveyance unit 128.

(Drying part)
The drying unit 118 is a mechanism for drying moisture contained in the solvent separated by the color material aggregating action, and includes a drying drum (conveying body) 176 and a solvent drying device 178 as shown in FIG.

  The solvent drying device 178 is disposed at a position facing the outer peripheral surface of the drying drum 176 and includes an IR heater 182 and a hot air jet nozzle 180 disposed between the IR heaters 182.

  Various drying conditions can be realized by appropriately adjusting the temperature and air volume of the hot air blown from the hot air jet nozzle 180 toward the recording medium 124 and the temperature of each IR heater 182.

  The recording medium 124 that has been dried by the drying unit 118 is transferred from the drying drum 176 to the fixing drum 184 of the fixing unit 120 via the intermediate conveyance unit 130.

(Fixing part)
The fixing unit 120 includes a fixing drum 184, a halogen heater 186, a fixing roller 188, and an inline sensor 190. With the rotation of the fixing drum 184, the recording medium 124 is conveyed with the recording surface facing outward. The recording surface is preheated by the halogen heater 186, fixing processing by the fixing roller 188, and by the inline sensor 190. Inspection is performed.

  The halogen heater 186 is controlled to a predetermined temperature (for example, 180 ° C.). Thereby, preheating of the recording medium 124 is performed. The fixing roller 188 is a roller member that heats and pressurizes the dried ink to weld the self-dispersing thermoplastic resin fine particles in the ink to form a film of the ink, so that the recording medium 124 is heated and pressed. Composed. The in-line sensor 190 is a measuring unit for measuring a check pattern, a moisture content, a surface temperature, a glossiness, and the like for an image fixed on the recording medium 124, and a CCD line sensor or the like is applied.

(Discharge part)
Subsequent to the fixing unit 120, a discharge unit 122 is provided. The discharge unit 122 includes a discharge tray 192, and a transfer drum 194, a conveyance belt 196, and a stretching roller 198 are provided between the discharge tray 192 and the fixing drum 184 of the fixing unit 120 so as to be in contact therewith. It has been. The recording medium 124 is sent to the conveyor belt 196 by the transfer drum 194 and discharged to the discharge tray 192.

  Although the drum conveyance type inkjet recording apparatus has been described with reference to FIG. 3, the present invention is not limited to this, and the invention can also be used in a belt conveyance type inkjet recording apparatus.

<< First Embodiment >>
FIG. 4 is a schematic diagram of the inkjet head 3 including the piezoelectric element according to the first embodiment of the present invention. The inkjet head 3 shown in FIG. 4 includes a piezoelectric film 30 and a humidity holding unit 210 that adjusts the humidity around the piezoelectric film 30. The humidity holding means includes a piezoelectric body chamber 212, humidity detection means 214, dry air supply means 216, supply port 218 for taking in dry gas, and discharge port 220.

  The humidity in the piezoelectric body chamber 212 is adjusted by the dry air supplied by the dry air supply means 216. The dry air supplied by the dry air supply means 216 is low-humidity air such as dry air, nitrogen gas, or argon gas. Examples of the drying air supply unit 216 include an air dryer that can generate a dry gas, and a cylinder in which the dry gas is sealed. In addition, about an air dryer, it is preferable to have a filter which removes the water | moisture content in gas.

  It is known that a piezoelectric body deteriorates in the presence of moisture. However, the present applicant has found that the deterioration due to moisture does not occur simply by being exposed to water vapor, but the deterioration proceeds by driving the piezoelectric body in the presence of water vapor. In the present invention, it is possible to suppress the consumption of extra power by adjusting the humidity around the piezoelectric body only when the piezoelectric body is driven.

  Therefore, the driving of the dry air supply means 216 is performed when the piezoelectric body is driven. By performing the driving at the time of driving the piezoelectric body, deterioration can be suppressed. Further, when the dry air supply means 216 is operated simultaneously with the driving of the piezoelectric body, the piezoelectric body is driven in a high humidity state in the initial driving of the piezoelectric body, so that the deterioration of the piezoelectric body is caused. It will progress. By supplying dry air before driving the piezoelectric body and lowering the humidity so that the humidity in the vicinity of the piezoelectric body is low when the piezoelectric body is driven, deterioration in the initial driving of the piezoelectric body can be suppressed. preferable.

  In addition, the piezoelectric body has a humidity (hereinafter referred to as “critical humidity” in the present invention) in which the durability of the piezoelectric body is abruptly deteriorated by setting the humidity to a certain level or higher without extremely reducing the humidity. By preventing the humidity in the vicinity of the piezoelectric body from exceeding the critical humidity, deterioration of the piezoelectric body can be suppressed, and extra power can be prevented from being applied.

  When the humidity becomes low, the supply of the dry air by the dry air supply means 216 is terminated. The humidity is measured by the humidity detection means 214, and when the humidity is high, the control means 222 supplies the dry air by the dry air supply means 216 to lower the humidity in the piezoelectric body chamber 212. Then, when the humidity in the piezoelectric body storage chamber 212 decreases, the humidity in the piezoelectric body storage chamber 212 is maintained by stopping the supply of the drying air. Thereby, since it is not necessary to make humidity extremely low, power consumption can be suppressed.

  The critical humidity is determined in advance by performing a durability test under each humidity condition. In the durability test, for example, a trapezoidal wave of −12.5 V ± 12.5 V 100 kHz is applied, voltage application is turned off every predetermined time, and 1 V, 1 kHz tan δ (dielectric loss tangent of vibration surface) is measured with an LCR meter. Measure. When tan δ exceeded 0.1, it was considered that the product had deteriorated and was regarded as the life. The critical humidity was defined as the humidity at which the lifetime did not deteriorate even after 100 billion cycle driving.

Specifically, the critical humidity is preferably 15 g / m ³ or less, more preferably 12 g / m ³ or less, and still more preferably 10 g / m ³ or less. By setting the humidity within the above range, deterioration of the piezoelectric body can be suppressed. The lower limit is preferably 6.2 g / m ³ or more, more preferably 8 g / m ³ or more, and still more preferably 9 g / m ³ or more. Even if it is lower than the above range, the effect of suppressing the deterioration of the piezoelectric body does not increase, and extra power is consumed.

<< Second Embodiment >>
FIG. 5 is a schematic view of an inkjet head 303 including a piezoelectric element according to the second embodiment of the present invention. The inkjet head 303 shown in FIG. 5 includes a piezoelectric film 30 and a humidity holding unit 230 that adjusts the humidity around the piezoelectric film 30. The humidity holding unit 230 includes a piezoelectric body storage chamber 232, a humidity detection unit 234, a desiccant 238, and a desiccant storage chamber 240 that encloses the desiccant 238 and can be opened and closed by an on-off valve 236. By opening the on-off valve 236, the desiccant 238 provided in the desiccant storage chamber 240 absorbs moisture in the piezoelectric body storage chamber 232, and the humidity is adjusted by lowering the humidity in the vicinity of the piezoelectric body. be able to.

  Also in the second embodiment, the temperature in the piezoelectric body accommodating chamber 232 is adjusted by opening and closing the on-off valve 236 only when the piezoelectric body is driven or at a predetermined humidity during driving. The humidity in the piezoelectric material chamber 232 is measured by the humidity detecting means 234, and when the humidity is high, the control means 242 opens the on-off valve 236 to absorb moisture into the desiccant 238, and the humidity around the piezoelectric material. Lower. When the humidity around the piezoelectric body decreases, the on-off valve 236 is closed to maintain the humidity around the piezoelectric body.

  Examples of the desiccant that can be used include silica gel, humidity control silica gel controlled to have a predetermined humidity, gypsum, carbon materials (wood, charcoal, etc.), and humidity control paper.

  The method for measuring the critical humidity can be performed in the same manner as in the first embodiment. The same numerical range as in the first embodiment can also be used for the preferable absolute humidity value.

<< Third Embodiment >>
FIG. 6 is a schematic view of an inkjet head 403 provided with a piezoelectric element according to the third embodiment of the present invention. The ink jet head 403 shown in FIG. 6 includes a piezoelectric film 30 and a wall of the piezoelectric body chamber 250 that houses the piezoelectric film 30 as a humidity holding unit 252 that adjusts the humidity around the piezoelectric film 30 and the porous film 256. By using the solid polymer electrolyte membrane 254 sandwiched between 256 ′, the moisture in the piezoelectric body chamber 250 is removed.

Removal of moisture in the piezoelectric body chamber 250 is performed as follows. By applying a voltage between the porous electrodes 256 and 256 ′, moisture in the piezoelectric body chamber 250 is electrolyzed with hydrogen ions (H ⁺ ) by the porous electrode 256 that forms the inner wall of the piezoelectric body chamber 252. It is decomposed into oxygen molecules (O ₂ ) and electrons (e ⁻ ).

Anode (dehumidification side) H ₂ O → 2H ⁺ + (1/2) O ₂ + 2e ⁻
The hydrogen ions pass through the solid polymer electrolyte membrane 254, move to the porous electrode 256 ′ side that forms the outer wall of the piezoelectric body chamber 250, and combine with oxygen molecules in the air to form water, Released into.

Cathode (moisture release side) 2H ⁺ + (1/2) O ₂ + 2e ⁻ → H ₂ O
That is, dehumidification is performed on the porous electrode 256 side inside the piezoelectric body chamber 250, and humidification is performed on the outer porous electrode 256 ′.

  Also in the third embodiment. As in the first and second embodiments, the piezoelectric body chamber is obtained by applying a voltage between the porous electrodes 256 and 256 ′ so that the predetermined humidity is obtained only when the piezoelectric body is driven or when the piezoelectric body is driven. Adjust humidity in 250. The method for measuring the critical humidity and the preferable numerical range of the absolute humidity can also be performed in the same manner as in the first embodiment and the second embodiment.

  EXAMPLES Next, the present invention will be described more specifically with reference to examples, but the present invention is not limited thereto.

<Setting critical humidity>
The humidity dependence of the piezoelectric element was confirmed for a normal sample (without a humidity control mechanism).

Using a Pb _1.3 (Zr _0.52 Ti _0.48 ) _0.88 Nb _0.12 O _X sintered compact target having a diameter of 120 mm, film formation was performed at an RF input power of 500 W and a distance of TS = 60 mm. The film thickness was about 4 μm. As the film formation substrate, an electrode in which Ti 20 nm and Ir 150 nm were stacked on a Si substrate was used. The Ir (111) plane was the main component.

  A Ti / Pt electrode was formed on top of the produced PZT thin film. A trapezoidal wave of −12.5 V ± 12.5 100 kHz is applied to these films at 80 ° C. or less at 80% or less, and every 1 billion cycles (ie, 100 kHz × 1 billion cycles = 16.7 minutes). With the LCR meter turned off, 1 V, 1 kHz tan δ (dielectric loss tangent of the vibration surface) was measured with an LCR meter, and durability was evaluated. The measurement was performed at 20 locations, and the point at which tan δ first exceeded 0.1 at one location was defined as the point at which the piezoelectric element deteriorated and was regarded as the lifetime. Those exceeding 100 billion were measured once every 5 billion cycles.

  The environment at 40 ° C. was performed using a high-temperature and high-humidity tank. The environment of 25 ° C. and 55% humidity was evaluated in a room conditioned with a normal air conditioner. Moreover, 25 degreeC humidity 1% evaluated in the environment which made dry air flow. The results are shown in Table 1 and FIG.

As shown in Table 1 and FIG. 7, in the sample having an absolute humidity of less than 15 g / m ³ , the durability was drastically improved, and no deterioration was observed even when it was driven for 500 billion cycles. Thus, it was confirmed that sufficient driving durability was obtained by adjusting the piezoelectric element to a water vapor amount of about 12 g / m ³ .

<Driving durability test>
The sample was held for 1 week in an environment of humidity 20 g / m ³ (25 ° C., 60%) without driving the piezoelectric element. Thereafter, the piezoelectric element was driven while operating the humidity holding means under the following conditions. As the humidity maintaining means, the dry air supply means was used, and the humidity was adjusted by controlling the strength of the dry air.

[Example 1]
The humidity holding means was activated and waited until the humidity was stabilized at 1 g / m ³ (25 ° C. 3%), and the driving of the piezoelectric element was started.

[Example 2]
When the humidity holding means was activated and the humidity dropped to 12 g / m ³ (25 ° C., 25%), driving of the piezoelectric element was started. The humidity holding means continued to operate while the piezoelectric element was driven. The humidity gradually decreased to 1 g / m ³ over 100 minutes.

[Example 3]
When the humidity holding unit was activated and the humidity dropped to 12 g / m ³ , driving of the piezoelectric element was started. When driving the piezoelectric element, the humidity was kept at 12 g / m ³ .

[Example 4]
Simultaneously with the operation of the humidity holding means, the driving of the piezoelectric element was started without waiting for the humidity to drop to 12 g / m ³ . After starting to drive the piezoelectric element, it reached 12 g / m ³ in about 20 minutes.

[Comparative Example 1]
The driving of the piezoelectric element was started in an environment where the humidity holding means was not operated and the humidity was 20 g / m ³ .

  The results are shown in Table 2.

As shown in Examples 1 to 3, when driving the piezoelectric element, the critical humidity (12 g / m ³ for this sample) or less is used to drive the piezoelectric element under high humidity while not driving the piezoelectric element. It was confirmed that sufficient durability could be obtained even after storage. On the other hand, Comparative Example 1 in which the piezoelectric element was driven at the same humidity without adjusting the humidity deteriorated in 30 billion cycles.

Further, Example 4 in which the humidity holding means and the piezoelectric element were driven simultaneously had durability superior to that of Comparative Example 1, but performance was inferior to Examples 1 to 3. This is considered to be because the deterioration proceeds within 20 minutes until the critical humidity of 12 g / m ³ is reached. Therefore, it was confirmed that it is preferable to drive when the humidity becomes lower than the critical humidity.

  DESCRIPTION OF SYMBOLS 1 ... Piezoelectric element, 2 ... Piezoelectric actuator, 3, 303, 403 ... Inkjet head (liquid ejection apparatus), 10 ... Substrate, 20 ... Lower electrode, 30 ... Piezoelectric film, 40 ... Upper electrode, 50 ... Vibration plate, 60 ... ink nozzle (liquid storage and discharge member), 61 ... ink chamber (liquid storage chamber), 62 ... ink discharge port (liquid discharge chamber), 100 ... ink jet recording apparatus, 112 ... paper feed section, 114 ... treatment liquid application section, DESCRIPTION OF SYMBOLS 116 ... Drawing part, 118 ... Drying part, 120 ... Fixing part, 122 ... Ejection part, 124 ... Recording medium, 155, 171, 177, 185 ... Holding means (gripper), 170 ... Drawing drum, 172M, 172K, 172C, 172Y ... Inkjet head, 176 ... Drying drum, 184 ... Fixing drum, 188 ... Fixing roller, 192 ... Discharge tray, 196 ... Conveyor belt, 2 0, 230, 252 ... humidity holding means, 212, 232, 250 ... piezoelectric housing chambers, 214, 234, 258 ... humidity detecting means, 216 ... dry air supply means, 218 ... supply port, 220 ... discharge port, 222, 242 ... Control means, 236 ... On-off valve, 238 ... Desiccant, 240 ... Desiccant storage chamber, 254 ... Solid polymer electrolyte membrane, 256, 256 '... Porous electrode

Claims (9)

A piezoelectric body, an electrode that applies an electric field to the piezoelectric body in a predetermined direction, and humidity holding means that maintains a constant humidity near the piezoelectric body,
A piezoelectric element comprising control means for operating the humidity holding means when the piezoelectric body is driven, without operating the humidity holding means when the piezoelectric body is not driven.   2. The piezoelectric element according to claim 1, wherein the humidity is equal to or lower than a critical humidity which is a humidity for suppressing deterioration of the piezoelectric body.   The piezoelectric element according to claim 2, wherein the critical humidity is measured by performing a durability test of the piezoelectric element while changing a humidity condition. The piezoelectric element according to any one of claims 1 to 3, wherein the humidity is 15 g / m ³ or less. The humidity holding means comprises a piezoelectric body housing chamber for housing the piezoelectric body, and a drying air supply means for supplying drying air to the piezoelectric body housing chamber;
The piezoelectric element according to any one of claims 1 to 4, wherein the humidity is adjusted depending on whether or not the dry air supply means is activated. The humidity holding means includes: a piezoelectric material storage chamber that stores the piezoelectric material; a desiccant storage chamber that communicates with the piezoelectric material storage chamber and stores a desiccant; and the piezoelectric material storage chamber and the desiccant storage chamber. An on-off valve that opens and closes
The piezoelectric element according to claim 1, wherein humidity is adjusted by driving the on-off valve. The humidity holding means is a solid polymer electrolyte membrane in which at least a part of a wall of a piezoelectric material storage chamber for storing the piezoelectric material is sandwiched between porous electrodes,
The piezoelectric element according to claim 1, wherein the humidity is adjusted by applying a voltage between the porous electrodes. A piezoelectric element according to any one of claims 1 to 7,
An ink-jet head comprising: a liquid storage chamber in which liquid is stored; and a liquid storage / discharge member having a liquid discharge port through which the liquid is discharged from the liquid storage chamber.   An ink jet recording apparatus comprising the ink jet head according to claim 8.

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