JP2008192671A - Piezoelectric element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problems, wherein a piezoelectric composition pressure sensitive element constituting a piezoelectric element absorbs water, electrical resistance, capacitance, and piezoelectric characteristics changes, and the durability and reliability deteriorate, when a conventional piezoelectric element is used under a high-temperature and high-humidity environment. <P>SOLUTION: The piezoelectric element comprises the piezoelectric composition pressure sensitive element 1, containing a first coating layer 6 by a water-repellent material, piezoelectric ceramic powder 3 where a second coating layer 7 by a coupling agent is formed, and an organic polymer 4; a first electrode 2A, connected to the piezoelectric composition pressure-sensitive element 1; and a second electrode 2B that is connected to the piezoelectric composition pressure-sensitive element 1 and is insulated from the first electrode 2A. Thus, since the penetration of water to the piezoelectric composition pressure-sensitive element 1 is suppressed, even under high temperature and high humidity, the softening of the piezoelectric composition pressure-sensitive element 2 is prevented, and elution of the constituent of the piezoelectric ceramic powder 3 can be prevented, thus preventing electrical characteristics, such as electrical resistance and capacitance from changing, preventing mechanical strength from decreasing and realizing improved durability and reliability. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a piezoelectric composition pressure-sensitive body obtained by blending a piezoelectric ceramic powder in an organic polymer, and more particularly to a piezoelectric element used as a flexible pressure-sensitive sensor.

  Conventionally, this type of piezoelectric composition pressure-sensitive body is constituted by mixing and kneading a material containing a titanium coupling agent, a piezoelectric ceramic powder, and at least one of chlorinated polyethylene or chlorosulfonated polyethylene. (For example, refer to Patent Document 1).

  This piezoelectric composition pressure-sensitive body is obtained by uniformly dispersing and kneading the above materials using a processing machine such as a kneader or a roll, and is flexible because it contains a thermoplastic elastomer such as chlorinated polyethylene. Therefore, it is processed into a sheet shape or a cable shape and used as a piezoelectric element.

  A sheet-like piezoelectric element is prepared by first forming a piezoelectric composition pressure-sensitive body in which piezoelectric powder, chlorinated polyethylene and a coupling agent are mixed and kneaded with a roll into a sheet shape by hot pressing, and silver paste is applied to both sides of the sheet. A pair of electrodes is formed by fusing a conductive sheet in which carbon is dispersed in a coating process or rubber, and then a tens of kV DC voltage is applied between both electrodes in order to develop piezoelectricity. Can be obtained by doing When pressure is applied to a part or the whole of this electrode surface, the piezoelectric composition pressure-sensitive body in that part is distorted, and as a result, a voltage is induced between both electrodes, and the pressure is detected using this induced voltage. Therefore, it is applied as a pressure sensor.

  In addition, there is a piezoelectric composition pressure-sensitive body as described above in which a coating layer is formed on a piezoelectric ceramic powder containing lead, and this is dispersed and mixed in an organic polymer (see, for example, Patent Document 2).

This coating layer is intended to prevent environmental pollution by suppressing the elution of lead from the piezoelectric ceramic powder even when the piezoelectric composition pressure-sensitive body containing the piezoelectric ceramic containing lead is discarded and exposed to the environment such as acid rain. To do. The material of the coating layer is composed of a coating film made of an inorganic or organic compound, or an organic monomolecular film, and any material can prevent the elution of lead from the piezoelectric ceramic powder.
Japanese Patent Laid-Open No. 11-201835 JP 2003-106910 A

  However, when the conventional piezoelectric element shown in Patent Document 1 is used in a high-temperature and high-humidity environment, water vapor passes through the electrode and reaches the piezoelectric composition pressure-sensitive body constituting the piezoelectric element. When the temperature inside the piezoelectric composition pressure-sensitive body is lower than the outside or when the water vapor becomes supersaturated on the surface of the piezoelectric composition pressure-sensitive body, the diffused water vapor condenses to produce water, Softening due to water absorption of the pressure body and a phenomenon in which components and impurities of the piezoelectric ceramic powder constituting the piezoelectric composition pressure sensitive body are eluted by water occur. As a result, there is a problem that the electrical characteristics change, such as an increase in the capacitance of the piezoelectric element and a decrease in electrical resistance, and there is a problem that durability is inferior. There is a problem that the circuit for control and control becomes complicated.

In addition, when the piezoelectric element absorbs water and the piezoelectric composition pressure sensitive body itself softens, the relationship between the pressure and the distortion of the piezoelectric element changes, so signal processing according to the change in the softness of the piezoelectric element is required. Because of the possibility of erroneous detection, there is a problem that it becomes a complicated detection circuit.

  Further, since the tensile strength of the piezoelectric element is reduced by the softening of the piezoelectric element, there is a problem that durability is inferior.

  In particular, a piezoelectric ceramic powder containing a group 1 or group 2A alkali metal or alkaline earth metal in the periodic table has a low specific resistance and is easily eluted into water, so that a reduction in electrical resistance becomes a problem.

  Although the above-described problem has been described with respect to the sheet-like piezoelectric element, the same problem exists in the case of a cable or other shapes.

  On the other hand, when the piezoelectric element having a coating layer formed on the piezoelectric ceramic powder shown in Patent Document 2 is exposed to an environment such as acid rain, elution of lead and the like from the piezoelectric ceramic powder is suppressed by the coating layer. Although the electrical resistance change caused by the metal ions is prevented, the absorption of water into the piezoelectric composition pressure-sensitive body cannot be suppressed, and the piezoelectric characteristics change due to the softening of the piezoelectric composition pressure-sensitive body. The above-mentioned problem has not been solved because a change in electrostatic capacity caused by a decrease in the tensile strength and the absorption of water cannot be prevented.

  The reason why the piezoelectric composition pressure-sensitive body of Patent Document 2 absorbs water is considered as follows. Inorganic materials such as alumina, silica, zirconia, and lithium silicate are used as materials to suppress lead elution from piezoelectric ceramic powder, but these are hydrophilic and have no water repellent action. . Therefore, the covering layer of these materials acts as a barrier layer, that is, acts to prevent contact between water and the piezoelectric ceramic powder. Thereby, elution of lead can be suppressed, but since the coating layer does not have water repellency, it is considered that the piezoelectric composition pressure-sensitive body itself absorbs water.

  On the other hand, organic materials and monomolecular films that use organic compounds as coating layer materials are not hydrophilic, but the amount of lead elution is comparable or rather inferior when compared to inorganic compounds. Therefore, it is considered that the elution of lead is suppressed by the action of the above-described barrier layer in all of the inorganic compound, the organic compound, and the monomolecular film. Therefore, it is considered that the structure provided with the coating layer of Patent Document 2 absorbs equivalent water and is softened regardless of the material of the coating layer.

  The present invention solves the above-described conventional problems, suppresses changes in electrical characteristics and softening even when used in a high-temperature and high-humidity environment, and always realizes stable piezoelectric characteristics and strength, and a complicated circuit. An object of the present invention is to provide a piezoelectric element using a piezoelectric composition pressure-sensitive body that does not require the above.

  In order to solve the above-described conventional problems, the piezoelectric element of the present invention is connected to a piezoelectric composition pressure-sensitive body including a piezoelectric ceramic powder and a flexible organic polymer, and the piezoelectric composition pressure-sensitive body. A first electrode, a second electrode connected to the piezoelectric composition pressure-sensitive body and insulated from the first electrode, and a first electrode provided on a surface of the piezoelectric ceramic powder to suppress moisture absorption into the piezoelectric ceramic powder; A coating layer is provided on the surface of the first coating layer, and is composed of a ceramic coating powder and a second coating layer made of a coupling agent that suppresses the familiarity of the organic polymer and the absorption of moisture. .

As a result, even when the piezoelectric element is used in a high temperature and high humidity environment, water is generated by condensation of water vapor inside the piezoelectric element, so that the piezoelectric ceramic powder constituting the piezoelectric element is made of a material that suppresses water absorption. Since one coating layer is formed, absorption of water into the piezoelectric composition pressure-sensitive body and the piezoelectric ceramic powder is suppressed. As a result, the capacitance of the piezoelectric element increases, the electrical resistance decreases,
In addition, the softening of the piezoelectric composition pressure sensitive body is suppressed, a large change in the piezoelectric characteristics caused by the softening can be prevented, and the initial piezoelectric characteristics can be maintained.

  In addition, since the second coating layer formed on the surface of the first coating layer also has an action of suppressing moisture absorption, the effect of preventing the above-described change in piezoelectric characteristics can be further enhanced, and the second coating layer Since the coating layer is composed of a coupling agent, the familiarity between the piezoelectric ceramic powder and the flexible polymer is improved, and the piezoelectric ceramic powder can be uniformly dispersed and mixed in the flexible organic polymer. It is possible to stabilize the polarization treatment for expressing the piezoelectric characteristics and stabilize the piezoelectric characteristics.

  Further, since the softening of the piezoelectric composition pressure sensitive body can be suppressed by the first coating layer and the second coating layer, a decrease in tensile strength can be prevented and the initial strength can be maintained.

  A piezoelectric element using the piezoelectric composition pressure sensitive body of the present invention is provided on a piezoelectric ceramic powder, a first coating layer that suppresses absorption of moisture into the piezoelectric ceramic powder, and a surface of the first coating layer. The penetration of water into the piezoelectric ceramic powder and the piezoelectric composition pressure sensitive body is improved by providing a second coating layer made of a coupling agent that improves the familiarity of the ceramic piezoelectric powder and the organic polymer and suppresses moisture absorption. Since it can be suppressed, the initial electrical characteristics, piezoelectric characteristics, mechanical tensile strength, and other characteristics can be maintained, changes over time can be prevented, and excellent durability and reliability can be achieved. can do. Further, since the kneadability between the piezoelectric ceramic powder and the organic polymer can be improved by the second coating layer, stable piezoelectric characteristics can be obtained at all times.

  According to a first aspect of the present invention, there is provided a piezoelectric composition pressure sensing element including piezoelectric ceramic powder and a flexible organic polymer, a first electrode connected to the piezoelectric composition pressure sensing element, and the piezoelectric composition feeling. A second electrode connected to a pressure body and insulated from the first electrode; a first coating layer provided on a surface of the piezoelectric ceramic powder; and suppressing absorption of moisture into the piezoelectric ceramic powder; The piezoelectric element is provided on the surface of the coating layer by including a second coating layer made of a coupling agent that suppresses the absorption of moisture and absorption of ceramic piezoelectric powder and organic polymer. Even if water vapor is generated in the portion of the piezoelectric composition pressure-sensitive body that is used in a high-temperature, high-humidity environment and forms water, water is not added to the piezoelectric ceramic powder in the piezoelectric composition pressure-sensitive body. Since the first coating layer that does not absorb is formed, the piezoelectric assembly Is suppressed absorption of water into the objects pressure sensitive substance and piezoelectric ceramic powder, it is possible to prevent an increase in the capacitance of the piezoelectric element, the decrease in electrical resistance. As a result, it is possible to maintain the initial electrical characteristics of the piezoelectric element, prevent changes over time, and achieve excellent durability and reliability.

  In particular, since the piezoelectric ceramic powder and the piezoelectric composition pressure-sensitive body do not absorb water due to the first coating layer, softening of the piezoelectric composition pressure-sensitive body is suppressed, and a large change in piezoelectric characteristics caused by the softening is prevented. The initial piezoelectric characteristics can always be maintained. As a result, it is possible to design a highly reliable detection and control circuit that can prevent erroneous detection because signal processing corresponding to changes in piezoelectric characteristics is not required even at the same applied pressure.

  In addition, since the second coating layer is composed of a coupling agent, familiarity between the piezoelectric ceramic powder and the flexible polymer is improved, and the piezoelectric ceramic powder is uniformly dispersed and mixed in the flexible organic polymer. It is possible to stabilize the polarization treatment for expressing the piezoelectric characteristics, stabilize the piezoelectric characteristics, and improve the familiarity of the piezoelectric ceramic powder and the flexible polymer, thereby kneading. Processing time can be shortened and productivity can be improved.

  In addition, the second coating layer is not as effective in suppressing water absorption as the first coating layer, but has a water repellent action, so that the water penetration into the piezoelectric ceramic powder is suppressed more than in the first coating layer alone. be able to.

  In the second invention, in particular, the first coating layer of the first invention is made of a water-repellent material, so that the water-repellent action can be made into a thin film coating layer. In addition to preventing changes in piezoelectric properties due to prevention of permeation, the loss of applied voltage can be reduced in the poling process performed to express piezoelectricity, and excellent piezoelectric properties are exhibited even at low voltages. Can be made.

  Moreover, since the first coating layer is formed on the surface of the piezoelectric ceramic powder, the first coating layer of the water repellent material is applied to each particle of the piezoelectric ceramic powder, so The contact can be extremely reduced, and the effect of preventing a decrease in electrical resistance caused by the dissolution of the components of the piezoelectric ceramic powder into water is great.

  In addition, since a large number of piezoelectric ceramic powders on which the first coating layer is formed are present on the surface of the piezoelectric composition pressure-sensitive body, excellent water repellency can be expressed on the surface of the piezoelectric composition pressure-sensitive body. Since the penetration of water into the composition pressure-sensitive body can be suppressed, softening of the piezoelectric composition pressure-sensitive body can be suppressed, and a large change in piezoelectric characteristics caused by the softening can be prevented. Characteristics can be maintained. As a result, it is possible to design a highly reliable detection and control circuit that can prevent erroneous detection because signal processing corresponding to changes in piezoelectric characteristics is not required even at the same applied pressure.

  In addition, by applying water-repellent treatment to the piezoelectric ceramic powder in advance, even if the shape and size of the piezoelectric element changes, there is no need for a corresponding water-repellent treatment step, and the productivity of the piezoelectric element can be increased. Regardless of the shape and size of the piezoelectric element, a stable water repellent effect can always be realized.

  In particular, the third invention uses a material having a contact angle with respect to distilled water of 125 ° or more and less than 180 ° as the first coating layer formed by performing the water repellent treatment of the first or second invention. Excellent water repellency can be achieved, so that changes in the electrical characteristics, piezoelectric characteristics, and mechanical strength of the initial piezoelectric element can be further reduced, and more excellent durability and reliability of the piezoelectric element can be realized. be able to.

  In the fourth aspect of the invention, particularly, the first coating layer of the first to third aspects of the invention can be realized with at least one of fatty acid, fatty acid salt, and monomolecular layer, thereby realizing excellent water repellency. . In particular, when the first coating layer is formed of a monomolecular layer, when the thickness of the coating layer is a monomolecular layer of several nanometers, a single DC layer is applied during poling to apply a high DC voltage in order to develop piezoelectric characteristics. The voltage drop that occurs in the molecular layer is reduced, and the poling efficiency can be improved, and the polling processing time can be shortened or excellent piezoelectric characteristics can be realized.

  Further, since the amount of the water repellent material used can be reduced by making the first coating layer a monomolecular layer, the cost of the water repellent piezoelectric element can be reduced.

  In the fifth invention, in particular, by forming the second coating layer of the first to fourth inventions with a titanium coupling agent, the familiarity with the piezoelectric ceramic powder can be improved. The kneadability of the organic polymer having flexibility can be improved. This is because the titanium coupling agent has high affinity with the organic compound.

  In the sixth invention, in particular, by using a material containing at least one of isopropoxytriisostearoyl titanate and isopropoxytris (dioctylpyrophosphate) titanate as the second coating layer of the first to fifth inventions. The kneadability (mixing / dispersion) between the piezoelectric ceramic powder and organic polymer can be further improved, shortening the kneading process time, improving the piezoelectric properties, stabilizing the piezoelectric properties, and improving the flexibility And can be easily molded into an arbitrary shape such as a sheet shape or a cable shape.

  According to a seventh aspect of the present invention, in particular, the piezoelectric ceramic powder according to the first to sixth aspects is a compound having a perovskite structure including at least one element of Group 1A of the periodic table and Group 2A of the periodic table. Originally, alkali metals and alkaline earth metals of Group 1A of the periodic table and Group 2A of the periodic table are easily eluted by water, but the elution of these alkali components contained in the piezoelectric ceramic powder can be suppressed. Therefore, a significant decrease in electrical resistance can be suppressed. In particular, a piezoelectric element containing an alkali component has a low specific resistance, and if the electric resistance value is further lowered, it may not be used as a piezoelectric element. Preventing a decrease in the electric resistance of a piezoelectric element containing an alkali component is highly practical. Have.

  In the eighth aspect of the invention, in particular, the piezoelectric ceramic powder of the first to seventh aspects contains at least one of bismuth sodium titanate, barium titanate, sodium niobate, and potassium niobate. Even if the device is disposed of and exposed to the environment such as acid rain, lead is not eluted and there is no possibility of environmental pollution. In addition, since the piezoelectric ceramic powder is provided with the first coating layer and the second coating layer to prevent elution of the piezoelectric ceramic powder components, the elution of metals other than lead can be suppressed and safety can be further improved. it can.

  In the ninth invention, in particular, the first electrode and the second electrode of the first to eighth inventions are made of an elastic body containing at least one of a thermoplastic resin, a thermoplastic elastomer and rubber, and a conductive layer of conductive powder. As a result, it is possible to obtain an extended outer electrode with excellent flexibility, and thus excellent bending resistance can be realized.

  In a tenth aspect of the invention, in particular, the first electrode and the second electrode of the first to eighth aspects are formed as a coating film of a conductive paint or conductive paste whose main component is a mixture of conductive powder and organic polymer. The adhesion between the piezoelectric composition pressure-sensitive body and the first electrode and the second electrode can be increased, and the air layer is less interposed between the first electrode, the second electrode and the piezoelectric composition pressure-sensitive body. Therefore, the voltage drop between the piezoelectric composition pressure sensitive bodies during the poling process can be suppressed, and the effective voltage of the poling process can be increased.

  In the eleventh aspect of the invention, in particular, the first electrode and the second electrode can be formed as a thin film by using the first electrode and the second electrode of the first to eighth inventions as vapor-deposited films of a conductive material. Therefore, the excellent flexibility of the piezoelectric composition pressure-sensitive body can be maintained, and the deterioration of the piezoelectric characteristics of the piezoelectric composition pressure-sensitive body can be prevented.

  In a twelfth aspect of the invention, in particular, the conductive material or conductive powder of the eleventh to thirteenth aspects of the invention contains at least one of C, Pt, Au, Pd, Ag, Cu, Al, and Ni. Particularly excellent electrical conductivity and corrosion resistance can be realized.

  In the thirteenth aspect of the invention, in particular, by using the flexible organic polymer of the first to twelfth aspects of the invention as a material containing at least one of a thermoplastic elastomer and rubber, the piezoelectric element has excellent elasticity and flexibility. Since flexibility can be imparted, the piezoelectric element can obtain a large repulsive force and displacement with respect to the applied pressure, and can improve the piezoelectric characteristics.

In a fourteenth aspect of the invention, in particular, the thermoplastic elastomer of the thirteenth aspect of the invention is chlorinated polyethylene,
By using at least one material of chlorosulfonated polyethylene, the content of the piezoelectric ceramic powder in the piezoelectric composition pressure-sensitive body can be increased, so that the piezoelectric characteristics of the piezoelectric element can be improved.

  In the fifteenth aspect of the invention, in particular, the first electrode, the second electrode, and the protective layer that covers the piezoelectric composition pressure-sensitive body constituting the piezoelectric element of the first to fourteenth aspects of the invention are formed. Thus, the protective layer itself prevents the diffusion of water vapor and can suppress the penetration of water into the piezoelectric composition pressure-sensitive body, so that changes in the electrical characteristics and piezoelectric characteristics of the piezoelectric element can be further reduced.

  In the sixteenth aspect of the invention, in particular, the protective layer of the fifteenth aspect of the invention is made of a material containing at least one of an electrically insulating thermoplastic elastomer and rubber, thereby improving the adhesion between the piezoelectric composition pressure-sensitive body and the electrode. Therefore, the sensitivity of the sensor can be improved, and damage to the piezoelectric element due to an external mechanical force can be prevented.

  In the seventeenth aspect of the invention, in particular, by using a piezoelectric ceramic powder of the first to sixteenth aspects of the invention having a relative dielectric constant of more than 0 and 1,000 or less, a direct current high voltage is applied in order to make the piezoelectric element exhibit piezoelectricity. When the poling process is applied, the ratio of the voltage applied to the piezoelectric ceramic powder can be increased, so that the voltage output constant of the piezoelectric element can be increased and the sensitivity of the piezoelectric element can be increased.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the embodiments.

(Embodiment 1)
FIG. 1 is a cross-sectional view of a sheet-like piezoelectric element according to the first embodiment of the present invention. In FIG. 1, a sheet-like piezoelectric element is configured by forming an electrode 2 </ b> A as a first electrode and an electrode 2 </ b> B as a second electrode on both surfaces of a sheet-like piezoelectric composition pressure-sensitive body 1.

  FIG. 2 is a schematic diagram showing a partial cross section of the piezoelectric composition pressure-sensitive body 1. In FIG. 2, a sheet-like piezoelectric composition pressure-sensitive body 1 is composed of a piezoelectric ceramic powder 3 on which first and second coating layers are formed, and a flexible organic polymer 4 to form a coating layer. The piezoelectric ceramic powder 3 is in a state of being uniformly dispersed in the organic polymer 4.

  FIG. 3 is a schematic view showing a cross section of one particle of the piezoelectric ceramic powder 3 on which a coating layer is formed. In FIG. 3, the piezoelectric ceramic powder 3 on which the coating layer is formed includes a first coating layer 6 made of a water-repellent material that suppresses water absorption on the surface of the piezoelectric ceramic powder 5, and the surface of the first coating layer 6. Further, a second coating layer 7 made of a coupling agent is formed.

The sheet-like piezoelectric element according to the first embodiment is manufactured as follows. This manufacturing process is shown in FIG. First, the piezoelectric ceramic powder 5 is diluted with a suitable solvent and immersed in a solution containing a water repellent material adjusted to a predetermined concentration, stirred and mixed, and then dried or heated to a melting temperature. The piezoelectric ceramic powder 5 is subjected to a water repellent treatment by either being immersed in a solution and then cooled, or by mixing the piezoelectric ceramic powder 5 with a predetermined amount of water repellent powder. The coating layer 6 is formed (S1). Next, the piezoelectric ceramic powder 5 on which the first coating layer 6 is formed is diluted with an appropriate solvent and immersed in a solution containing a coupling agent adjusted to a predetermined concentration and stirred and mixed, or dried. The surface of the first clothing layer 6 is made of a coupling agent by any method of stirring and mixing the piezoelectric ceramic powder 5 on which one clothing layer 6 is formed and a predetermined amount of a coupling agent with a stirrer such as a mixer. The 2nd coating layer 7 is formed (S2), and the piezoelectric ceramic powder 3 in which the 1st clothing layer 6 and the 2nd clothing layer 7 were formed is produced. Next, the piezoelectric ceramic powder 3 on which the coating layer is formed is flexible by using the piezoelectric ceramic powder 3 on which the respective coating layers are formed and the organic polymer 4 having flexibility using a processing machine such as a kneader or a roll. The organic polymer 4 having a property is kneaded so as to be uniformly mixed and dispersed (S3). After kneading, it is processed using a processing machine such as a roll or a hot press to produce a sheet-like piezoelectric composition pressure-sensitive body 1 (S4). Next, a conductive paste or conductive paint in which conductive powder and an organic polymer are mixed is applied to both surfaces of the sheet-like piezoelectric composition pressure-sensitive body 1, and the conductive powder is made of flexible material such as rubber or thermoplastic elastomer. Electrodes 2A and 2B insulated from each other are formed by fusing a conductive sheet mixed / dispersed in an organic polymer having the above, and depositing the conductive material by any material and forming method (S5). Thereafter, a poling process is performed by applying a DC high voltage between the electrodes 2A and 2B in the air or in a silicon oil bath in order to develop piezoelectricity (S6), and a sheet-like piezoelectric element is manufactured. The polling process (S6) is performed after the electrodes 2A and 2B are formed (S5). However, after the sheet-shaped piezoelectric composition pressure-sensitive body 1 is fabricated (S4), two pseudo electrodes are used. You may go.

  The operation and action of the sheet-like piezoelectric element configured as described above will be described below.

  As described above, the piezoelectric characteristics of the sheet-like piezoelectric element are manifested by applying a high direct-current voltage between the electrodes 2A and 2B and poling the piezoelectric composition pressure-sensitive body 1. When a temporally changing pressure is applied to a part or the entire surface of a sheet-like piezoelectric element that exhibits piezoelectric characteristics, vibration corresponding to the acceleration generated in that part is applied between the first electrode 2A and the second electrode 2B. A voltage is induced. The pressure can be detected using this induced voltage. Therefore, the invention of the present application is a sensor installed on a car door to prevent pinching, a touch sensor installed on a door handle to control unlocking, a sensor installed on a care bed to detect body movement, a handrail on a veranda, etc. It can be used as a pressure-sensitive sensor such as a sensor that is arranged and detects intrusion from the outside.

  Pressure sensors such as those mentioned above may be used outdoors or when installed in automobiles, in high-temperature steam environments during rainy seasons or in the rain in summer, and incontinence or sweat when installed in nursing beds. If it is mounted on bedding, there is a high possibility that it will be used in a high-temperature and high-humidity environment such as washing and cleaning to maintain sanitation.

  When a conventional piezoelectric element is used as a pressure-sensitive sensor in such a high temperature and high humidity environment, water vapor passes through the electrode and diffuses into the sheet-like piezoelectric element. When the temperature of the piezoelectric composition pressure-sensitive body is lower than the outside or when the water vapor becomes supersaturated on the surface of the piezoelectric composition pressure-sensitive body, the diffused water vapor condenses to produce water, and this water is Penetration into the pressure body causes a phenomenon in which components and impurities of the piezoelectric ceramic powder are eluted. As a result, the capacitance of the sheet-like piezoelectric element increases and the electrical characteristics change, such as a decrease in electrical resistance. This results in inferior durability and detection when used as a pressure sensor. In addition, it is necessary to make it possible to cope with the initial change in electrical characteristics of the control circuit, which makes the circuit a complicated configuration.

When the sheet-like piezoelectric element of the present embodiment is used in a high-temperature and high-humidity environment, water vapor passes through the electrodes 2A and 2B, and the water vapor is aggregated on the surface of the piezoelectric composition pressure-sensitive body 1 to generate water. To do. However, the sheet-like piezoelectric element of the present embodiment as shown in FIG. 3 is coupled to the first coating layer 6 formed by subjecting the piezoelectric ceramic powder 5 constituting the piezoelectric composition pressure-sensitive body 1 to a water repellent treatment. By forming the second coating layer 7 made of an agent, even if water vapor is generated by the piezoelectric composition pressure-sensitive body 1 and water is generated, the piezoelectric composition feels due to the water-repellent action of the first coating layer 6. Since water does not penetrate into the pressure body 1, elution of the components and impurities of the piezoelectric ceramic powder 5 is suppressed, and an increase in capacitance and a decrease in electrical resistance as a sheet-like piezoelectric element can be prevented. As a result, the initial electrical characteristics of the sheet-like piezoelectric element can be maintained, and excellent durability and reliability can be realized. Further, since it is possible to prevent an initial change in electrical characteristics, a highly reliable pressure-sensitive sensor can be realized without the need for a circuit configuration for correcting the change in electrical characteristics.

  In particular, since the first coating layer 6 formed by performing the water repellent treatment is formed on each particle of the piezoelectric ceramic powder 5, contact with water can be extremely reduced. The effect of preventing the decrease in electrical resistance caused by the elution of components into water is great.

  The piezoelectric composition pressure-sensitive body 1 is composed of a piezoelectric ceramic powder 3 having a coating layer formed thereon and an organic polymer 4. In order to develop excellent piezoelectric properties, the piezoelectric ceramic powder having a coating layer formed thereon 3 is increased in composition. With this configuration, the piezoelectric composition pressure-sensitive body 1 can have a surface having excellent water repellency since there are a large number of piezoelectric ceramic powders 3 on which a coating layer is formed. Penetration of condensed water can be suppressed, and softening of the piezoelectric composition pressure-sensitive body 1 can be prevented. In particular, since the piezoelectric pressure-sensitive composition 1 exhibits excellent water repellency, the first coating layer 6 formed on the surface of the piezoelectric ceramic powder 3 requires a material having excellent water repellency.

  In addition, as disclosed in Patent Document 2, there is a piezoelectric composition pressure-sensitive body produced by forming a coating layer on lead-containing piezoelectric ceramic powder and dispersing and mixing it with an organic polymer. The material of the coating layer is composed of a coating made of an inorganic or organic compound, or an organic monomolecular film, and any material can prevent the elution of lead from the piezoelectric ceramic powder. The composition pressure-sensitive body itself cannot prevent water absorption. The reason is considered as follows.

  In Patent Document 2, the material of the coating layer uses an inorganic compound of alumina, silica, zirconia, or lithium silicate, but these show hydrophilicity, have no water repellent action, This acts as a barrier layer that prevents contact between the piezoelectric ceramic powder and the piezoelectric ceramic powder. Thereby, elution of lead can be suppressed, but since the coating layer does not have water repellency, it is considered that the piezoelectric composition pressure-sensitive body itself absorbs water.

  Further, according to Patent Document 2, materials using an organic compound or a monomolecular film as a material for the coating layer are not hydrophilic, but when the lead elution suppression effect is compared with an inorganic compound, is the amount of lead elution equivalent? Since the results are rather inferior, it is considered that the elution of lead is suppressed by the action of the above-described barrier layer in the inorganic compound, the organic compound, and the monomolecular film. Further, there are descriptions of materials such as acrylic resin, silicon resin, and fluorine resin as organic compounds, and organic silicon compounds and organic titanium compounds as monomolecular films, but the organic compounds and monomolecular films used in Patent Document 2 are the present invention. Thus, it is presumed that the compound does not have excellent water repellency and is a compound having a different composition or molecular structure, or the properties of the coating layer are different.

  Therefore, the structure provided with the coating layer of Patent Document 2 is considered to absorb the equivalent water and soften the piezoelectric composition pressure sensitive body regardless of the material of the coating layer. Since there is no description that the layer has water repellency, the elution of the components of the piezoelectric ceramic powder is not prevented by the water repellency as in the present invention. In addition, the coating layer of Patent Document 2 cannot prevent a change in piezoelectric characteristics due to softening of the piezoelectric composition pressure-sensitive body, a decrease in mechanical tensile strength, and a change in capacitance caused by water absorption. It seems that the problem cannot be solved.

Further, in the conventional piezoelectric element, when water penetrates, the piezoelectric composition pressure-sensitive body softens and the relationship between the pressure and the distortion of the piezoelectric element changes. In order to eliminate erroneous detection, signal processing corresponding to the change in the softness of the piezoelectric composition pressure-sensitive body 1 is necessary. However, when the sheet-like piezoelectric element of the present embodiment is used as a pressure-sensitive sensor. Since the first coating layer 6 formed by performing the water repellent treatment covering the piezoelectric ceramic powder 5 can prevent water absorption into the piezoelectric composition pressure-sensitive body 1, the piezoelectric composition pressure-sensitive body. 1 is suppressed, and the initial piezoelectric characteristics can always be maintained. As a result, it is possible to design a highly reliable detection and control circuit, such as preventing erroneous detection because signal processing corresponding to changes in piezoelectric characteristics is not required even at the same applied pressure.

  In addition, since the first coating layer 6 is made of a water repellent material, it can be formed into a thin film, so that it is possible to prevent a change in piezoelectric characteristics due to prevention of penetration into the piezoelectric composition pressure-sensitive body 1. At the same time, in the poling process performed to develop the piezoelectric characteristics, the loss of the applied voltage can be reduced, and excellent piezoelectric characteristics can be exhibited even at a low voltage.

  Moreover, since the softening of the piezoelectric composition pressure-sensitive body 1 constituting the sheet-like piezoelectric element can be suppressed, a decrease in the tensile strength of the piezoelectric composition pressure-sensitive body 1 can be prevented and the initial strength can be maintained. And excellent durability can be realized.

  Further, by forming the first coating layer 6 on the piezoelectric ceramic powder 5 by water repellent treatment in advance, even if the shape and size of the sheet-like piezoelectric element changes, there is no need for a corresponding water repellent treatment step. The productivity of the piezoelectric element can be increased, and a stable water-repellent effect can always be provided regardless of the shape and size of the sheet-like piezoelectric element.

  Examples of the water repellent material of the first coating layer 6 of the present embodiment include fatty acids, fatty acid salts, fatty acid amides, fluorine-based resins, silicon-based resins, acrylic resins, and silane compounds.

  In particular, the fatty acids include caprylic acid, pelargonic acid, capric acid, undecyl acid, lauric acid, tridecyl acid, myristic acid, pentadecylic acid, palmitic acid, heptadecylic acid, stearic acid, nonadencanic acid, arachic acid, behenic acid, lignoceric acid , Serotic acid, heptacosanoic acid, montanic acid, acrylic acid, crotonic acid, isocrotonic acid, undecylenic acid, oleic acid, elaidic acid, cetreic acid, erucic acid, pracidic acid, sorbic acid, linoleic acid, linolenic acid.

  Examples of the fatty acid salt include compounds of the above-described fatty acids and calcium, zinc, sodium, potassium, magnesium, copper, and lead metal elements, and at least one of these fatty acid salts.

  Examples of fatty acid amides include caprylic acid, pelargonic acid, capric acid, undecylic acid, lauric acid, tridecylic acid, myristic acid, pentadecylic acid, palmitic acid, heptadecylic acid, stearic acid, nonadencanic acid, arachic acid, behenic acid, lignoserine. Acid, serotic acid, heptacosanoic acid, montanic acid, acrylic acid, crotonic acid, isocrotonic acid, undecylenic acid, oleic acid, elaidic acid, cetoleic acid, erucic acid, pracidic acid, sorbic acid, linoleic acid, linolenic acid What substituted the hydrogen group by the amino group is used.

  In addition, as a fluorine-based resin, polytetrafluoroethylene (PTFE), perfluoroalkylethyl acrylate, as a silicon-based resin, dimethylpolysiloxane, diethylpolysiloxane, a silicon-acrylic block copolymer, and as an acrylic resin, Examples include methacrylic acid esters and acrylic acid ester polymers.

  Examples of the silane compound include dialkylsilane compounds and fluorosilane compounds having at least a siloxane bond on the surface of the piezoelectric ceramic powder 5 and having at least an alkyl group or a fluoroalkyl group.

  The above-described silane compound can form the first coating layer 6 formed by applying a water repellent material as a monomolecular layer. Since the monomolecular layer is an ultra-thin film having a thickness of several nanometers, after the piezoelectric composition pressure-sensitive body 1 is produced, when a high DC voltage is applied in a poling process performed to develop piezoelectric characteristics, the monomolecular layer Since the voltage drop in the layer can be reduced, the efficiency of polling can be improved, the processing time can be shortened, and excellent piezoelectric characteristics can be realized. Moreover, since the amount of the water-repellent material used can be remarkably reduced by making the first coating layer 6 formed by performing the water-repellent treatment into a monomolecular layer, the cost of the sheet-like piezoelectric element can be reduced. Can do.

  According to the present embodiment, the first covering layer 6 of the water repellent material is formed on the surface of the piezoelectric ceramic powder 5. Piezoelectric composition in order to suppress the penetration of water into the piezoelectric composition pressure-sensitive body 1 and to significantly reduce the changes in electrical characteristics, piezoelectric characteristics, and mechanical strength of the sheet-like piezoelectric element in a high temperature and high humidity environment It is necessary to develop an excellent water repellency on the entire surface of the pressure-sensitive body 1, and for this purpose, the water repellency of the first coating layer 6 needs to be remarkably increased. Therefore, the first coating layer 6 is preferably a water repellent material having a contact angle with distilled water of 125 ° or more. In other words, if the contact angle of the first coating layer 6 with distilled water is 125 ° or more, the surface of the piezoelectric composition pressure-sensitive body 1 has high water repellency with respect to condensed water even in a high temperature environment. It is possible to increase the effect of suppressing the penetration of water into the piezoelectric composition pressure-sensitive body 1. Since the contact angle is less than 180 ° by definition, a water repellent material having a contact angle with distilled water of 125 ° or more and less than 180 ° is preferable. Desirably, a super water-repellent material having a contact angle with distilled water of 150 ° or more is preferable.

  In particular, as the water repellent material having a contact angle with respect to distilled water of the first coating layer 6 formed by performing the water repellent treatment of 150 ° or more, the above-mentioned fatty acid, fatty acid salt, fatty acid amide, fluorine resin, silicon resin And silane compounds.

  In S1, the first coating layer 6 formed by performing the water repellent treatment is prepared by immersing the piezoelectric ceramic powder 5 after heating the water repellent material and melting it, or in a solvent suitable for the water repellent material. Put the water repellent material and immerse the piezoelectric ceramic powder 5 in a solution adjusted to an appropriate concentration, and then dry or mix the water repellent material powder and the piezoelectric ceramic powder 5 if the water repellent material is solid. Formed by any of the methods. Moreover, the water repellent material may be used alone or in combination of two or more.

  As a solvent suitable for the silane compound, a non-aqueous solvent containing no active hydrogen is preferably used, and a hydrocarbon solvent, a fluorocarbon solvent, a silicon solvent, or the like not containing water is used. In addition to petroleum-based solvents, those that can be specifically used include petroleum naphtha, solvent naphtha, petroleum ether, petroleum benzine, isoparaffin, normal paraffin, decalin, industrial gasoline, kerosene, ligroin, dimethyl silicone, phenyl silicone, Examples thereof include alkyl-modified silicon and polyester silicon. In addition, the fluorocarbon solvent includes a fluorocarbon solvent, perfluorooctane, tris-perfluoron-butylamine solvent, and the like. In addition, these may be used individually by 1 type and may be used in combination of 2 or more type as long as it mixes well.

  Even if the piezoelectric ceramic powder 5 and the organic polymer 4 having flexibility are added with a water-repellent material and mixed and dispersed using a processing machine such as a kneader or a roll, the particles of the piezoelectric ceramic powder 5 are one by one. Cannot be completely covered with a water-repellent material, so that excellent water repellency cannot be obtained. Therefore, in order to realize excellent water repellency, it is necessary to provide the first coating layer 6 of the water repellent material on the surface of each particle of the piezoelectric ceramic powder 5.

The second coating layer 7 shown in this embodiment is formed of a coupling agent. In particular,
The titanium coupling agent used as the coupling agent covers the surface of the first coating layer 6 formed by subjecting the piezoelectric ceramic powder 5 to water repellency treatment as shown in FIG. 2, and has a hydrophobic side chain organic functional group on the outside. By providing a group, the piezoelectric ceramic powder 3 with improved flexibility (wetting) with the organic polymer 4 having flexibility, lowering the overall viscosity, workability, flexibility, and a coating layer is further formed. By improving the dispersibility, the expression of piezoelectric characteristics can be remarkably improved.

  Also, when isopropoxytriisostearoyl titanate, isopropoxytris (dioctylpyrophosphate) titanate is used as the titanium coupling agent, and chlorinated polyethylene or chlorosulfonated polyethylene is used as the flexible organic polymer, the coating layer Since the familiarity with the piezoelectric ceramic powder 3 on which is formed is further improved, the kneading process time can be shortened, the piezoelectric characteristics can be improved, the piezoelectric characteristics can be stabilized, and the flexibility can be improved. It can be easily molded into an arbitrary shape such as a cable shape.

  The reason why the above-mentioned familiarity is good is that the SP value (solubility parameter) of isopropoxytriisostearoyl titanate, isopropoxytris (dioctyl pyrophosphate) titanate has a value of 8 to 9, while chlorinated polyethylene, The SP value of chlorosulfonated polyethylene is 9 to 9.5, which is considered to have a similar SP value. For that reason, not only a titanium coupling agent but also a coupling agent having an SP value similar to a flexible organic polymer such as a silica coupling agent is applicable as a coupling agent.

  Further, the second coating layer 7 is not as effective in suppressing moisture absorption as the first coating layer 6 but has a water repellent effect, so that the water to the piezoelectric ceramic powder 5 is more than the first coating layer 6 alone. Penetration can be suppressed, and even better durability and reliability can be realized.

  The compound of the piezoelectric ceramic powder 5 used in this embodiment is a compound having a perovskite structure such as lead titanate, lead zircon, lead zirconate titanate, bismuth sodium sodium titanate, barium titanate, alkali niobate, etc., bismuth Examples thereof include a ceramic material that exhibits piezoelectricity by poling treatment, such as a compound having a layered structure and a compound having a tungsten bronze structure.

  When these piezoelectric ceramic powders 5 come into contact with an electrolyte such as water, the components of the piezoelectric ceramic powder 5 and impurities contained in the piezoelectric ceramic powder 5 are eluted. In particular, compounds having a perovskite structure including at least one element of Group 1A of the periodic table and Group 2A of the periodic table, among them compounds of bismuth sodium titanate, barium titanate, sodium niobate, potassium niobate are Since an alkaline component that is easily eluted in water is contained, the alkaline component is largely eluted in an environment of high temperature and high humidity, and the change in electrical characteristics becomes large. Furthermore, the piezoelectric ceramic containing an alkali component has a lower specific resistance than, for example, lead zirconate titanate. Therefore, when the alkali component is eluted, the absolute value of the electrical resistance is further reduced, and a constant voltage is always applied to the sheet-like piezoelectric element. There is a possibility that it cannot be used as a pressure-sensitive sensor in a circuit configuration in which pressure is detected by applying.

  In the present embodiment, a compound having a perovskite structure including at least one element of Group 1A of the periodic table, Group 2A of the periodic table containing an alkali component, or a main component thereof is bismuth sodium titanate, barium titanate, A first coating layer 6 formed by subjecting a piezoelectric ceramic powder 5 made of a compound containing at least one of sodium niobate and potassium niobate to a water repellent treatment and a second coating layer 7 made of a coupling agent are formed. As a result, elution of alkali components can be suppressed, and a significant decrease in electrical resistance can be prevented. In addition, pressure is detected even in a circuit configuration in which a constant voltage is constantly applied to a sheet-like piezoelectric element to detect pressure. It can be used as a sensor and has high practicality.

  Further, as the piezoelectric ceramic powder 5, a compound having a perovskite structure including at least one element of Group 1 of the periodic table and Group 2A of the periodic table, and main components thereof are bismuth / sodium titanate, barium titanate, sodium niobate. By using a compound containing at least one kind of potassium niobate, the sheet-like piezoelectric element is discarded and lead is not eluted even when exposed to an environment such as acid rain, and there is no possibility of environmental pollution. In addition, the first coating layer 6 formed by subjecting the piezoelectric ceramic powder 5 to water repellent treatment and the second coating layer 7 made of a coupling agent are formed to prevent the components of the piezoelectric ceramic powder 5 from being eluted. Therefore, elution of metals other than lead is suppressed, and safety can be further improved.

  In addition, piezoelectric characteristics are manifested by applying a high-voltage DC voltage between both electrodes and performing a poling process. However, when the sheet-like piezoelectric element of this embodiment is used as a pressure-sensitive sensor, the important piezoelectric characteristics are This is a voltage output constant that serves as an index of the generated voltage.

  The piezoelectric composition pressure-sensitive body 1 constituting the sheet-like piezoelectric element of the present embodiment is mainly composed of a composite of a piezoelectric ceramic powder 5 and a flexible organic polymer 4. The dielectric constant (dielectric constant of material / dielectric constant of vacuum) of the piezoelectric ceramic powder 5 is several hundred to several thousands, whereas the relative dielectric constant of the organic polymer 4 having flexibility is about several tens. . The DC voltage applied during the poling process is distributed in inverse proportion to the ratio of the dielectric constant of the piezoelectric ceramic powder 5 and the organic polymer 4 having flexibility, so that the DC voltage is flexible with a low dielectric constant. A high voltage is applied to the organic polymer 4 having In other words, when the same organic polymer 4 having flexibility is used, a higher voltage is applied to the organic polymer 4 having flexibility as the dielectric constant of the piezoelectric ceramic powder 5 is higher. .

  Accordingly, when piezoelectric zirconate titanate having a relative dielectric constant of about 2000 and bismuth / sodium titanate having a relative dielectric constant of about 600 are used as the piezoelectric ceramic powder 5 of the piezoelectric composition pressure-sensitive body 1, the piezoelectric composition of both is used. When a constant DC voltage is applied to the object pressure sensing element 1, a higher voltage is applied to bismuth / sodium titanate having a lower relative dielectric constant than lead zirconate titanate, and the efficiency of poling can be increased. The voltage output constant increases. As a result, when a sheet-like piezoelectric element is used as a pressure-sensitive sensor, the output voltage of the sensor with respect to the applied pressure can be increased, so that the sensitivity can be improved and the sheet-like piezoelectric element can be improved. Since the amplification factor of the detection circuit can be lowered by increasing the sensitivity, a pressure-sensitive sensor that is strong against electrical noise can be obtained.

  The dielectric constant of the piezoelectric ceramic powder 5 is preferably as low as possible. However, if it is 1000 or less, an excellent voltage output constant of 3 times or more than that obtained when the piezoelectric ceramic powder 5 of lead zirconate titanate is used can be obtained. From this point, useful piezoelectric ceramic powder 5 includes bismuth sodium titanate, barium titanate, sodium niobate, and potassium niobate.

  That is, the relative dielectric constant of the piezoelectric ceramic powder 5 is preferably greater than 0 and 1000 or less. However, since the practically lowest relative dielectric constant is sodium niobate (relative dielectric constant is 120), the relative dielectric constant of the piezoelectric ceramic powder 5 is preferably 120 or more and 1000 or less. Such a preferable range of the relative dielectric constant is the same in other embodiments described later.

The piezoelectric ceramic powder 5 made of bismuth / sodium titanate or barium titanate contains less free alkaline components than the piezoelectric ceramic powder 5 made of sodium niobate or potassium niobate, and therefore is the first water-repellent material. The amount of the alkaline component eluted through the coating layer 6 and the second coating layer 7 can be reduced, and the change in electrical characteristics can be further reduced.

  On the other hand, the piezoelectric ceramic powder 5 made of sodium niobate and potassium niobate has a dielectric constant higher than that of the piezoelectric ceramic powder 5 made of lead titanate, lead zirconate, lead zirconate titanate, bismuth / sodium titanate, and barium titanate. Since the piezoelectric composition pressure-sensitive body 1 including the flexible organic polymer 4 is produced and the poling treatment is performed to develop the piezoelectric characteristics, the DC voltage applied to the piezoelectric ceramic powder 5 is increased. The voltage output constant can be increased.

  Therefore, the piezoelectric ceramic powder 5 is appropriately selected according to the environment in which the sheet-like piezoelectric element is used and the required sensitivity.

  The electrode 2A and the electrode 2B of the sheet-like piezoelectric element of the present embodiment can be composed of an elastic body containing at least one of a thermoplastic resin, a thermoplastic elastomer, and rubber and a conductive layer of conductive powder. In this configuration, the electrode 2A and the electrode 2B can be extended and excellent in flexibility, so that a sheet-like piezoelectric element having high bending resistance and excellent durability can be obtained. This conductive layer is formed by extruding an elastic material containing at least one of a thermoplastic resin, a thermoplastic elastomer, and a rubber and a conductive powder using a processing machine such as an extruder, so that the pressure sensitivity of the piezoelectric composition is increased. Formed on the body 1.

  Alternatively, the electrodes 2A and 2B may be formed of a conductive paint whose main component is a mixture of a conductive powder and an organic polymer, or a coating film of a conductive paste. In this configuration, the adhesiveness between the piezoelectric composition pressure-sensitive body 1 and the electrodes 2A and 2B can be increased, and an air layer is less interposed between the electrodes 2A and 2B and the piezoelectric composition pressure-sensitive body 1. Therefore, the voltage drop between the electrodes 2A and 2B and the piezoelectric composition pressure sensitive body 1 during the poling process can be suppressed, and the effective voltage of the poling process can be increased.

  Further, the electrode 2A and the electrode 2B can be formed of a vapor-deposited film of a conductive material. In this configuration, since the electrodes 2A and 2B can be formed as thin films, the excellent flexibility of the piezoelectric composition pressure-sensitive body 1 can be maintained, and the piezoelectric characteristics of the piezoelectric composition pressure-sensitive body 1 can be maintained. A decrease can be prevented. This thin film is formed on the piezoelectric composition pressure-sensitive body 1 by vapor deposition using an apparatus such as vacuum vapor deposition, sputtering, or CVD.

  The conductive powder and conductive material described above can achieve particularly excellent conductivity and corrosion resistance by using at least one of C, Pt, Au, Pd, Ag, Cu, Al, and Ni. .

  Using a conductive layer made of a conductive film in which at least one foil of C, Pt, Au, Pd, Ag, Cu, Al, and Ni is bonded to both surfaces of a polymer film such as polyethylene terephthalate and the both surfaces are made conductive. Also good.

  Examples of the flexible organic polymer 4 used in the present embodiment include a material containing at least one of a thermoplastic elastomer and rubber. The organic polymer 4 having flexibility can impart excellent elasticity and flexibility to the sheet-like piezoelectric element, so that the sheet-like piezoelectric element has a large repulsive force and displacement with respect to the applied pressure. The amount can be obtained and the piezoelectric characteristics can be improved.

  In particular, as the above-mentioned thermoplastic elastomer, chlorinated polyethylene and chlorosulfonated polyethylene can increase the content of the piezoelectric ceramic powder 3 in the piezoelectric composition pressure-sensitive body 1, so that the piezoelectric characteristics of the sheet-like piezoelectric element are increased. Can be improved.

(Embodiment 2)
FIG. 5 is a sectional view of a sheet-like piezoelectric element according to the second embodiment of the present invention. In FIG. 5, the difference from the first embodiment is that a protective layer 8 is provided to cover and protect the piezoelectric composition pressure-sensitive body 1, the electrode 2A as the first electrode, and the electrode 2B as the second electrode. It is. The same members as those in the first embodiment are denoted by the same reference numerals.

  As shown in FIG. 5, a sheet-shaped piezoelectric composition pressure-sensitive body 1 comprising a piezoelectric ceramic powder 3 on which a coating layer described in the first embodiment is formed and a flexible organic polymer 4 is formed. The electrode 2A and the electrode 2B are provided, and the protective layer 8 that covers the piezoelectric composition pressure-sensitive body 1, the electrode 2A, and the electrode 2B is further provided.

  The sheet-like piezoelectric element in the present embodiment is manufactured as follows. The manufacturing process will be described with reference to FIG. First, the piezoelectric ceramic powder 5 is diluted with a suitable solvent and immersed in a solution containing a water repellent material adjusted to a predetermined concentration, stirred and mixed, and then dried or heated to a melting temperature. The piezoelectric ceramic powder 5 is subjected to a water repellent treatment by either being immersed in a solution and then cooled, or by mixing the piezoelectric ceramic powder 5 with a predetermined amount of water repellent powder. The coating layer 6 is formed (S7). Next, the piezoelectric ceramic powder 5 on which the first coating layer 6 is formed is diluted with an appropriate solvent and immersed in a solution containing a coupling agent adjusted to a predetermined concentration and stirred and mixed, or dried. The surface of the first clothing layer 6 is made of a coupling agent by any method of stirring and mixing the piezoelectric ceramic powder 5 on which one clothing layer 6 is formed and a predetermined amount of a coupling agent with a stirrer such as a mixer. The 2nd coating layer 7 is formed (S8), and the piezoelectric ceramic powder 3 in which the 1st clothing layer 6 and the 2nd clothing layer 7 were formed is produced. Next, the piezoelectric ceramic powder 3 on which the coating layer is formed is flexible by using the piezoelectric ceramic powder 3 on which the respective coating layers are formed and the organic polymer 4 having flexibility using a processing machine such as a kneader or a roll. The organic polymer 4 having the property is kneaded so as to be uniformly mixed and dispersed (S9). After kneading, it is processed using a processing machine such as a roll or a hot press to produce a sheet-like piezoelectric composition pressure-sensitive body 1 (S10). Next, a conductive paste or conductive paint in which conductive powder and an organic polymer are mixed is applied to both surfaces of the sheet-like piezoelectric composition pressure-sensitive body 1, and the conductive powder is made of flexible material such as rubber or thermoplastic elastomer. Electrodes 2A and 2B insulated from each other are formed by fusing a conductive sheet mixed / dispersed in an organic polymer having a conductive material, and depositing the conductive material by any material and forming method (S11). Further, the material of the protective layer 8 is processed into a sheet shape using a processing machine such as a roll or a hot press, and the piezoelectric composition pressure-sensitive body 1 and the electrode 2A, which are water-repellent treated by folding or sandwiching the sheet, The electrode 2B is covered (S12). Thereafter, a poling process is performed by applying a DC high voltage between the electrodes 2A and 2B in the air or in a silicon oil bath in order to develop the piezoelectric characteristics (S13), thereby producing a sheet-like piezoelectric element. The polling process (S13) is performed after the protective layer 8 is formed (S12). However, after the sheet-shaped pressure sensitive body 1 is manufactured (S10), it may be performed using two pseudo electrodes. However, this may be performed after the electrodes 2A and 2B are formed (S11).

  The protective layer 8 is made of an organic polymer having elasticity so as not to impair the flexibility of the piezoelectric composition pressure-sensitive body 1 and the electrodes 2A and 2B. In particular, thermoplastic elastomers and rubber materials are suitable. Although the thickness of the protective layer 8 is not limited, in order not to impair the piezoelectric characteristics of the piezoelectric composition pressure-sensitive body 1, it is preferable to set the thickness to 0.2 to 2 mm.

When the sheet-like piezoelectric element having the above configuration is used in a high-temperature and high-humidity environment as in the first embodiment, the first electrode, the second electrode, and the piezoelectric composition feeling constituting the piezoelectric element. By providing the protective layer 8 on the pressure body, the protective layer 8 itself can prevent the diffusion of water vapor and suppress the penetration of water into the piezoelectric composition pressure sensitive body. Since the first coating layer 6 and the second coating layer 7 are formed, the penetration of water into the piezoelectric ceramic powder 5 can be further suppressed, so that changes in the electrical characteristics and piezoelectric characteristics of the piezoelectric element are further reduced. be able to.

  Further, by using a material containing at least one of an electrically insulating thermoplastic elastomer and rubber as the protective layer 8, the adhesion between the piezoelectric composition pressure sensitive body 1 and the electrode can be improved, so that the sensitivity of the sensor can be improved. While being able to improve, the damage of the piezoelectric element by the external mechanical force can be prevented, and the sheet-like piezoelectric element excellent in durability and reliability can be implement | achieved.

  Further, since the electrodes 2A and 2B can also suppress water permeation, it is possible to prevent changes in the electrical resistance of the electrodes 2A and 2B, and to detect the piezoelectric characteristics of the piezoelectric composition pressure-sensitive body 1 that is always stable. Can be transmitted to the circuit.

(Embodiment 3)
FIG. 7 is a partial cross-sectional view of a cable-like piezoelectric element according to the third embodiment of the present invention. As shown in FIG. 7, the cable-shaped piezoelectric element has a flexible piezoelectric composition pressure-sensitive body 10 formed on the outer surface of the core electrode 9 that is the first electrode. A flexible outer electrode 11 as a second electrode is formed on the outer surface, and a protective layer 12 made of an electrically insulating elastic body is further formed. The core electrode 9 and the outer electrode 11 are insulated by the piezoelectric composition pressure sensitive body 10.

  The core electrode 9 has a structure in which a metal such as copper is wound around one or a plurality of metal wires, or converging wires of a large number of polyester fibers, and the piezoelectric composition pressure-sensitive body 10 is used in the first embodiment. The material having the composition described in the form is used.

  As with the electrodes 2A and 2B in the first embodiment, the outer electrode 11 has at least one of C, Pt, Au, Pd, Ag, Cu, Al, and Ni on both surfaces of a polymer film such as polyethylene terephthalate. A conductive layer formed by winding a conductive film with a seed foil attached around the pressure-sensitive body 10 in the form of a cable, and at least one type of conductive material selected from C, Pt, Au, Pd, Ag, Cu, Al, and Ni. A conductive layer formed by extrusion molding a flexible conductive composition prepared by kneading a flexible powder and a flexible organic polymer such as rubber or thermoplastic elastomer, and the conductive powder described above into an organic polymer A conductive film coated with a dispersed conductive paint (paste), at least one conductive material of C, Pt, Au, Pd, Ag, Cu, Al, and Ni is vacuum-deposited on the piezoelectric composition pressure sensitive body 10; Sputtering, C Vapor deposition film of thin film formed by a method such as D is used.

  The protective layer 12 uses the material of the protective layer 8 described in the second embodiment, and is formed by extrusion molding of this material.

The cable-shaped piezoelectric element in the present embodiment is manufactured as follows. The manufacturing process will be described with reference to FIG. First, first, the piezoelectric ceramic powder 5 is diluted with an appropriate solvent and immersed in a solution containing a water-repellent material adjusted to a predetermined concentration, stirred and mixed, and then dried or heated to a melting temperature. The piezoelectric ceramic powder 5 is subjected to a water repellent treatment by either being immersed in a solution of the material and then cooled, or by mixing the piezoelectric ceramic powder 5 with a predetermined amount of powder of the water repellent material. 1 covering layer 6 is formed (S14). Next, the piezoelectric ceramic powder 5 on which the first coating layer 6 is formed is diluted with an appropriate solvent and immersed in a solution containing a coupling agent adjusted to a predetermined concentration and stirred and mixed, or dried. The surface of the first clothing layer 6 is made of a coupling agent by any method of stirring and mixing the piezoelectric ceramic powder 5 on which one clothing layer 6 is formed and a predetermined amount of a coupling agent with a stirrer such as a mixer. The 2nd coating layer 7 is formed (S15), and the piezoelectric ceramic powder 3 in which the 1st clothing layer 6 and the 2nd clothing layer 7 were formed is produced. Next, the piezoelectric ceramic powder 3 with the coating layer and the organic polymer 4 are uniformly mixed and dispersed in the organic polymer 4 using a processing machine such as a kneader or a roll. The mixture is kneaded so as to be in a finished state (S16). Next, a sheet-shaped piezoelectric composition pressure-sensitive body is produced from the kneaded product using a roll processing machine (S17), and the sheet-shaped piezoelectric composition pressure-sensitive body is processed into a pellet using a processing machine such as a pelletizer. (S18). Next, using the core electrode 9 as a core material, a pellet-shaped piezoelectric composition pressure-sensitive body is extruded using an extrusion molding machine, and a layer of the piezoelectric composition pressure-sensitive body 10 is formed around the core electrode 9. That is, a layer of the piezoelectric composition pressure sensitive body 10 is provided around the core electrode 9 (S19). Next, the outer electrode 11 is formed using any of the materials and processing means described above (S20). Next, the protective layer 12 is formed by extrusion molding using an organic polymer such as a thermoplastic elastomer or rubber having elasticity (S21). Thereafter, a poling process is performed by applying a DC high voltage between the core electrode 9 and the outer electrode 11 in the air or in a silicon oil bath in order to develop piezoelectricity (S22), and a cable-shaped piezoelectric element is manufactured. Is done. The polling process (S22) is performed after the protective layer 12 is formed (S21). However, after the layer of the piezoelectric composition pressure sensitive body 10 is formed around the core electrode 9 (S19), the core electrode and It may be performed using a pseudo electrode corresponding to the outer electrode, or may be performed after forming the outer electrode 11 (S20).

  As shown in FIG. 7, the cable-shaped piezoelectric element thus manufactured is formed by removing the protective layer 12 and the piezoelectric composition pressure-sensitive body 10 at one end and exposing the core electrode 9 and the outer electrode 11. It is connected to the control circuit and used as a pressure sensitive sensor.

  The operation and action of the cable-shaped piezoelectric element configured as described above will be described below.

  When a time-varying pressure is applied to a part or the entire surface of the cable-shaped piezoelectric element, a gap between the core electrode 9 and the outer electrode 11 corresponds to the acceleration generated in the cable-shaped piezoelectric element of that part. An oscillating voltage is induced. The pressure can be detected using this induced voltage.

  When the cable-shaped piezoelectric element having the above configuration is used as a pressure-sensitive sensor in a high-temperature and high-humidity environment as in the first embodiment, since the protective layer 12 is present, the piezoelectric composition pressure-sensitive body 10 of water vapor is present. However, the protective layer 12 can prevent the diffusion of water vapor because the gap between the organic polymer three-dimensional network molecular structure of the protective layer 12 is larger than the size of one molecule of water vapor. In the same manner as in the first embodiment, water passes through the outer electrode 11, and water vapor is condensed on the surface of the piezoelectric composition pressure-sensitive body 10 to generate water. However, the piezoelectric ceramic powder 5 constituting the piezoelectric composition pressure sensitive body 10 is formed with a first coating layer 6 formed by water repellent treatment and a second coating layer 7 made of a coupling agent. The penetration of water into the piezoelectric composition pressure-sensitive body 10 is suppressed, and the softening of the piezoelectric composition pressure-sensitive body 10 and the elution of the components of the piezoelectric ceramic powder 5 can be reduced. Therefore, similar to the first embodiment, it is possible to reduce changes in the electrical characteristics, piezoelectric characteristics, and mechanical strength of the initial cable-shaped piezoelectric element, and the cable-shaped piezoelectric element that is excellent in durability and reliability. An element can be realized.

  Further, even when a long cable-shaped piezoelectric element having a length of several kilometers or more is processed, the piezoelectric ceramic powder 5 is subjected to water repellent treatment in advance to form the first coating layer 6, thereby repelling each particle. Since a water action can be imparted, any part of the cable shape can exhibit a water repellency, and a stable water repellency can always be realized.

  In this embodiment, the outer electrode 11 is formed by extruding a flexible conductive composition prepared by kneading a conductive powder and an organic polymer, and a conductive paint in which the conductive powder is dispersed in the organic polymer. (Paste) application, when the conductive material is formed by vapor deposition such as vacuum vapor deposition, sputtering, CVD, etc., because it has excellent adhesion to the piezoelectric composition pressure sensitive body 10, the cable-like piezoelectric element is separated from another member. If there is a means to protect with, the protective layer 12 may not be formed.

  In the above embodiment, by providing the first coating layer 6 of the water repellent material and the second coating layer 7 of the coupling agent, the piezoelectric ceramic powder and the effect of suppressing the elution of impurities by water or the piezoelectric composition The effect of suppressing the penetration of water into the pressure sensitive body and preventing the softening has been described. In addition to this, those effects can be realized with other configurations.

  That is, in addition to the first coating layer 6 and the second coating layer 7 described above, the protective layers 8 and 12 are formed thick to increase the resistance to water vapor permeation to the piezoelectric composition pressure-sensitive bodies 1 and 10. Water can be suppressed to prevent softening, and elution of the piezoelectric ceramic powder 5 and impurities can be suppressed. Alternatively, a dense film in which water vapor molecules hardly pass can be formed as a coating layer by physical vapor deposition (sputtering, vapor deposition), chemical vapor deposition, or chemical synthesis. A dense film formed by physical vapor deposition, chemical vapor deposition, or chemical synthesis treatment can suppress the intrusion of water vapor itself, so that the piezoelectric composition pressure-sensitive bodies 1 and 10 can be prevented from being softened even when provided on the outermost layer of the piezoelectric element. At the same time, the effect of preventing the elution of the piezoelectric ceramic powder 5 and impurities can be realized.

  However, if the coating layer is thick, the sensitivity of the piezoelectric element is lowered, so it is necessary to design it strictly. In addition, a dense film needs to be formed with high accuracy because the effect is lost if there is a pinhole.

  The cable-shaped piezoelectric element manufactured by the manufacturing method of the present invention is flexible and has a cable shape, so that the arrangement including the bent portion and the mounting width are limited. It has excellent characteristics that it can be arranged and can maintain the initial electrical characteristics, piezoelectric characteristics, and mechanical strength even when used in a high temperature and high humidity environment. Therefore, it is most suitable as a sensor for detecting pressure and vibration for outdoor use that requires such arrangement conditions and characteristics. Specifically, sensors are installed on devices and parts that require opening and closing, such as car sliding doors, hatchback doors, trunks, and power windows, and they are installed on car door handles to control door unlocking. Touch sensor.

  In addition, body motion sensors used for nursing beds and the like need to ensure a large area detection, but the cable-like piezoelectric element of the present invention has a large area by being meandered on the bed. In addition, it can be detected, and it is an optimum configuration as a body motion sensor for a nursing bed in consideration of usage conditions such as a humid environment such as incontinence and sweat and washing for hygiene maintenance.

  In addition, it can be used as a pressure-sensitive sensor such as a sensor for detecting an intrusion from the outside by placing it on a handrail of a veranda or an entrance door in an apartment or a detached house. In this case as well, the cable-shaped piezoelectric element is exposed to high-temperature and high-humidity environments because it is outdoors, but because it can maintain stable piezoelectric characteristics even in such an environment, malfunctions can be prevented and it can be used as a security sensor. can do.

  In addition, the cable-shaped piezoelectric element produced by the manufacturing method of the present invention can detect a large area by being meandered on the bed, and is optimal as a body motion sensor for a nursing bed. It is a configuration.

(Example 1)
In order to investigate the water-repellent effect of the piezoelectric ceramic powder coated with the water-repellent material, the piezoelectric ceramic powder is a solid solution of bismuth sodium titanate and barium titanate having an average particle diameter of about 1 μm (Bi _1/2 Na _1/2 ) Piezoelectric ceramic powder having a first coating layer was prepared using _0.85 Ba _0.15 TiO ₃ and the following various water materials.

  Next, a piezoelectric ceramic powder film having a first coating layer made of various water repellent materials is formed on a glass plate, and the contact angle of polka dots formed by dropping distilled water on the film is measured. did. The contact angle was measured using a contact angle meter CA-DT type manufactured by Kyowa Interface Science Co., Ltd. For comparison, the contact angle is also measured for a piezoelectric ceramic powder having only a second coating layer using isopropoxytriisostearoyl titanate as a titanium coupling agent and a piezoelectric ceramic powder only. .

  Table 1 shows the names of the water-repellent materials used for the measurement and the measurement results of the contact angle.

  As is clear from this result, it can be seen that the piezoelectric ceramic powder formed with the first coating layer of the water repellent material has a large contact angle, and that this large contact angle has a feeling of the piezoelectric composition constituting the piezoelectric element. It is considered that the effect of suppressing the penetration of water into the pressure body is expressed.

The piezoelectric ceramic powder in which only the second coating layer with the titanium coupling agent is formed is also inferior in water repellency by the first coating layer, but has improved water repellency compared to the piezoelectric ceramic powder, and water penetration. It turns out that it has the effect which suppresses.

  Referring to the results of Example 1, the water repellent material that suppresses changes in the electrical characteristics of the piezoelectric element is particularly good when the contact angle of distilled water is 125 ° or more, and more preferably 150 ° or more. More preferred.

(Example 2)
As the piezoelectric ceramic powder, (Bi _1/2 Na _1/2 ) _0.85 Ba _0.15 TiO ₃ , which is a solid solution of bismuth sodium titanate and barium titanate having an average particle diameter of about 1 μm, is used. A water material was used to form a first coating layer of the following water repellent material on the surface of the piezoelectric ceramic powder.

  As the water repellent material, four kinds of calcium oleate (fatty acid salt), polytetrafluoroethylene (fluorine resin), heptadecafluorodecyltrichlorosilane (silane compound) methacrylate ester (acrylic resin) are used. Is a solution dissolved by heating, polytetrafluoroethylene is a solution diluted with the solvent methylethylketone, heptadecafluorodecyltrichlorosilane is a solution containing the solvent hexamethyldisiloxane, and methacrylate is a solution diluted with the solvent xylene. The coating layer of the water repellent material was formed by dipping treatment and then drying.

  Next, the piezoelectric ceramic powder on which the first coating layer was formed and the isopropoxy triisostearoyl titanate used in Example 1 as a predetermined amount of titanium coupling agent were mixed and stirred with a Hensyl mixer, and the first coating layer was The 2nd coating layer of the titanium coupling agent was formed in this.

  Next, the piezoelectric ceramic powder in which the first coating layer and the second coating layer are formed so that the piezoelectric ceramic powder is about 60% by volume and the chlorinated polyethylene is about 35% by volume; A chlorinated polyethylene as a polymer was kneaded with a roll machine to produce a piezoelectric composition pressure-sensitive body, and a piezoelectric composition pressure-sensitive body sheet having a thickness of about 0.5 mm was produced using a hot press machine.

  Next, a conductive sheet having a thickness of 0.2 mm, which is obtained by filling carbon in chlorinated polyethylene and imparting conductivity, is fused to both sides of the sheet of the piezoelectric composition pressure-sensitive body to form electrodes, thereby expressing piezoelectricity. Then, a poling process was performed by applying a DC high voltage of 5 kV / mm between the electrodes in air at 100 ° C. to produce a sheet-like piezoelectric element having a width of 20 mm and a length of 120 mm.

  For the four types of sheet-shaped piezoelectric elements of the first coating layer manufactured as described above, a high-temperature and high-humidity test was performed using a high-temperature and high-humidity tank at 85 ° C. and a relative humidity of 85%. The both ends of the piezoelectric element were sandwiched and the tensile strength was measured. The tensile strength was set to the value of the force by which the sheet-like piezoelectric element extends 2 mm. As a measuring instrument, a digital force gauge DPS-50 manufactured by Imada Corporation was used. For comparison, a sheet-like piezoelectric element was also produced for a piezoelectric ceramic powder in which only the second coating layer was formed using a titanium coupling agent of isopropoxy triisostearoyl titanate, and the same test was performed. did.

  The results are shown in (Table 2).

  As is clear from this result, it can be seen that the tensile strength of the sheet-like piezoelectric element on which the first coating layer is formed is high, and the penetration of water into the piezoelectric composition pressure sensitive body can be prevented. Accordingly, it is possible to prevent the initial tensile strength from being lowered and to realize a piezoelectric element having excellent mechanical strength.

(Example 3)
Piezoelectric ceramic powder is a solid solution of bismuth sodium titanate and barium titanate with an average particle diameter of about 1 μm (Bi _1/2 Na _1/2 ) _0.85 Ba _0.15 TiO ₃ and an average particle system of about 1 μm. Pb (Zr · Ti) O ₃ , which is a solid solution of lead titanate and lead zirconate, and calcium oleate (fatty acid salt) and heptadecafluorodecyltrichlorosilane (silane compound) as water repellent materials 2 was formed on the surface of each piezoelectric ceramic powder to produce a water-repellent-treated piezoelectric ceramic powder.

  Next, in the same manner as in Example 2, the piezoelectric ceramic powder on which the first coating layer was formed and isopropoxytriisostearoyl titanate, which is a predetermined amount of titanium coupling agent, were mixed and stirred with a hensil mixer, and the first coating layer was then stirred. A second coating layer of a titanium coupling agent was formed thereon.

  Next, a predetermined amount of each water-repellent-treated piezoelectric ceramic powder so that the water-repellent-treated piezoelectric ceramic powder is about 60% by volume and chlorinated polyethylene is about 35% by volume; A chlorinated polyethylene as a molecule was kneaded with a roll machine to produce a piezoelectric composition pressure-sensitive sheet, and then a pellet was produced with a pelletizer.

  Using the piezoelectric composition pressure-sensitive pellets, a core electrode is obtained by winding a copper foil around a converging line of a number of polyester fibers having a diameter of 0.45 mm, and using an extrusion molding machine, a piezoelectric composition is formed around the core electrode. The physical pressure body was coated so as to have a thickness of about 0.6 mm. Next, a piezoelectric composition pressure-sensitive body in which a core electrode is coated with a conductive film in which an aluminum foil having a width of 3 mm and a thickness of 10 μm is bonded to both surfaces of a polymer film of polyethylene terephthalate having a width of 3 mm and a thickness of 12 μm. The outer electrode was wound by winding so that a part of the conductive film overlapped on the surface. In addition, the outer layer of the outer electrode is coated with a protective layer so that the thickness of the olefinic thermoplastic elastomer becomes about 0.5 mm by using an extrusion molding machine, to produce a cable-shaped piezoelectric element, and to express piezoelectricity. A poling treatment was performed by applying a DC voltage of 5 kV / mm to the core electrode and the outer electrode in air at 100 ° C.

Various cable-shaped piezoelectric elements produced as described above were adjusted so that the effective length was 150 mm, and a high-temperature and high-humidity test under the same conditions as in Example 2 was performed for 20 hours. After the test, the electrical resistance and capacitance were measured at room temperature. The measuring instrument was an LCR high tester 3522 manufactured by Hioki Electric Co., Ltd., and measured at a frequency of 1 kHz. For comparison, a cable-shaped piezoelectric element was also manufactured for a piezoelectric ceramic powder in which only the second coating layer was formed using a titanium coupling agent of isopropoxytriisostearoyl titanate, and the test was performed in the same manner. .

  Table 3 shows the rate of change in electrical resistance after 20 hours of high-temperature and high-humidity test, and Table 4 shows the rate of change in capacitance after 20 hours of high-temperature and high-humidity test.

  As is clear from this result, it is understood that the cable-like piezoelectric element using the piezoelectric ceramic powder on which the first coating layer and the second coating layer are formed has little change in electrical resistance and capacitance, The same effect as that of the sheet-like piezoelectric element could be obtained even with piezoelectric elements having different values.

The electrical resistance of the cable-like piezoelectric element decreases under a high temperature and high humidity environment. It is considered that this is because condensed water penetrates into the piezoelectric composition pressure-sensitive body, and the components of the piezoelectric ceramic powder dissolve in the penetrated water. In addition, the change in electric resistance is such that the cable-like piezoelectric element using the piezoelectric ceramic powder of (Bi _1/2 Na _1/2 ) _0.85 Ba _0.15 TiO ₃ has Pb (Zr · Ti) O ₃ . Although the result is larger than that of the cable-shaped piezoelectric element using the piezoelectric ceramic powder, this indicates that the alkali component contained in the piezoelectric ceramic powder is easily dissolved in water.

On the other hand, the specific resistance of both of them is (Bi _1/2 Na _1/2 ) _0.85 Ba _0.15 TiO in the cable-like piezoelectric element using the piezoelectric ceramic powder of Pb (Zr · Ti) O _{3. 3} is about twice as high as the cable-like piezoelectric element using the piezoelectric ceramic powder (Bi _{1 /
2} Na _1/2 ) _0.85 Ba _0.15 TiO ₃ piezoceramic powder using a piezoelectric ceramic powder has a low specific resistance and further decreases in a high temperature and high humidity environment. If the cable-shaped piezoelectric element becomes longer, the electrical resistance further decreases, so it may not be possible to use it as a pressure-sensitive sensor in a circuit configuration in which a constant voltage is constantly applied to the piezoelectric element to detect pressure. When a long cable-shaped piezoelectric element using a piezoelectric ceramic powder containing is used in a high-temperature and high-humidity environment, it can be said that formation of a coating layer of the piezoelectric ceramic powder is indispensable in order to prevent elution of alkali components.

In addition, the change in capacitance is also larger for the piezoelectric ceramic powder of (Bi _1/2 Na _1/2 ) _0.85 Ba _0.15 TiO _{3 than for} the piezoelectric ceramic powder of Pb (Zr · Ti) O _3. However, it is considered that there is a difference in the hygroscopicity with respect to water of the components contained in the piezoelectric ceramic powder.

  In addition, although the high temperature high humidity test was implemented for 1000 hours, it confirmed that it maintained the electrical resistance and electrostatic capacitance of the level for 20 hours, and had the outstanding water-repellent effect.

  Thus, by forming the first coating layer made of the water repellent material and the second coating layer made of the coupling agent on the piezoelectric ceramic powder, both the electric resistance and capacitance of the cable-like piezoelectric element are reduced. Can do. Since this phenomenon does not change the hardness of the piezoelectric composition pressure sensitive body, the piezoelectric ceramic powder coated with the water repellent material increases the water repellency of the piezoelectric composition pressure sensitive body, and the condensed water is removed from the piezoelectric composition. This is thought to be due to the fact that the pressure sensitive body does not absorb.

  Further, the tensile strength of the water-repellent sheet-like piezoelectric element described in Example 2 is higher than that of the sheet-like piezoelectric element not subjected to the water-repellent treatment. The piezoelectric composition pressure-sensitive body produced by forming a coating layer of the material can be determined to be softened and prevented from maintaining the initial hardness because absorption of condensed water is suppressed. Indicates that the consideration is correct.

Example 4
The cable-shaped piezoelectric element tested in Example 3 was evaluated for piezoelectric characteristics. Piezoelectric characteristics are evaluated by the amount of charge generated from the relationship between the voltage and load generated at that time, with the load being changed at a constant frequency with a constant load applied to the center of the cable-shaped piezoelectric element. did.

  Table 5 shows the rate of change in the amount of charge generated after 20 hours of the high temperature and high humidity test.

  As is clear from this result, the change in charge generation amount of the cable-shaped piezoelectric element using the piezoelectric ceramic powder in which the first coating layer by the water repellent treatment and the second coating layer by the coupling agent are formed is small, and the high temperature Stable piezoelectric characteristics could be obtained even in a high humidity environment. The piezoelectric characteristics vary depending on the elastic modulus of the piezoelectric composition pressure-sensitive body. That is, if the piezoelectric composition pressure sensitive body absorbs water and softens, the elastic modulus decreases and the piezoelectric characteristics tend to increase. In the cable-like piezoelectric element using the piezoelectric ceramic powder of only the second coating layer by the coupling agent shown in Table 5, the reason why the change in the amount of generated charge is high is that the piezoelectric composition constituting the cable-like piezoelectric element The pressure-sensitive material absorbs water and softens, whereby the elasticity is lowered, and as a result, the charge generation amount is increased. On the other hand, the charge generation amount of the cable-shaped piezoelectric element using the piezoelectric ceramic powder on which the first coating layer and the second coating layer are formed is little changed, and water is not absorbed by the piezoelectric composition pressure-sensitive body. Show.

(Example 5)
In the cable-shaped piezoelectric element, piezoelectric ceramic powders having different relative dielectric constants were used, and the voltage output constant was evaluated.

Pb (Zr · Ti) O ₃ , (Bi _1/2 Na _1/2 ) _0.85 Ba _0.15 TiO ₃ , and NaNbO ₃ are used as piezoelectric ceramic powders having different relative dielectric constants. A piezoelectric element was manufactured in the same manner as the cable-shaped piezoelectric element manufacturing method of Example 4 so that 60% by volume and chlorinated polyethylene were about 35% by volume. Next, in order to develop the piezoelectricity in the manufactured piezoelectric element, a DC voltage of 5 kV / mm was applied to the core electrode and the outer electrode in air at 100 ° C. to perform a poling process.

  The cable-shaped piezoelectric element manufactured as described above was adjusted so that the effective length was 150 mm, and the voltage output constant was evaluated. The measurement was performed using a Piezometer manufactured by Piezotest.

Table 6 shows the ratio of the voltage output constants of the cable-shaped piezoelectric elements using other piezoelectric ceramic powders based on the voltage output coefficient of the cable-shaped piezoelectric elements using Pb (Zr · Ti) O _3. .

  As is clear from this result, the lower the relative dielectric constant of the piezoelectric ceramic powder is, the higher the voltage output constant is, and the smaller the relative dielectric constant of the piezoelectric ceramic powder is, the larger voltage is applied, and the poling efficiency is improved. I understand.

  Therefore, by using ceramic powder having a low relative dielectric constant, the voltage output constant of the piezoelectric element, that is, the sensitivity as a pressure sensitive sensor can be improved.

As described above, the piezoelectric element according to the present invention can suppress water absorption of the piezoelectric composition pressure-sensitive body even when used in a high-temperature and high-humidity environment. It is possible to prevent a change in the tensile strength, and to realize excellent durability and reliability. Therefore, sensors that can be installed on the handrails and entrances of the outdoor veranda where high-temperature and high-humidity environments can occur to prevent intrusion from the outside, automobile sliding doors, hatchback doors, power windows, etc. Sensors installed on parts to detect pinching, touch sensors installed on car door handles to control unlocking of doors, sensors for pressure detection devices that detect the presence of a person by detecting the movement of a person on a nursing bed It can be applied to a wide range of uses.

Sectional drawing of the sheet-like piezoelectric element in Embodiment 1 of this invention Schematic diagram showing a partial cross-section of the piezoelectric composition pressure-sensitive body according to Embodiment 1 of the present invention. Schematic diagram showing a cross section of the piezoelectric ceramic powder on which the coating layer in Embodiment 1 of the present invention is formed The figure explaining the manufacturing process of the piezoelectric element using the piezoelectric composition pressure sensing element in Embodiment 1 of this invention. Sectional drawing of the sheet-like piezoelectric element in Embodiment 2 of this invention The figure explaining the manufacturing process of the piezoelectric element using the piezoelectric composition pressure sensing element in Embodiment 2 of this invention. Sectional drawing of the cable-shaped piezoelectric element in Embodiment 3 of this invention The figure explaining the manufacturing process of the piezoelectric element using the piezoelectric composition pressure sensing element in Embodiment 3 of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 10 Piezoelectric composition pressure sensitive body 2A 1st electrode 2B 2nd electrode 3 Piezoelectric ceramic powder in which the coating layer was formed 4 Organic polymer 5 Piezoelectric ceramic powder 6 1st coating layer 7 2nd coating layer 8, 12 Protective layer 9 Core electrode 11 External electrode

Claims (17)

Piezoelectric composition pressure-sensitive body containing piezoelectric ceramic powder and flexible organic polymer, first electrode connected to the piezoelectric composition pressure-sensitive body, and connected to the piezoelectric composition pressure-sensitive body A second electrode insulated from the first electrode; a first coating layer provided on a surface of the piezoelectric ceramic powder; and suppressing absorption of moisture into the piezoelectric ceramic powder; and a surface of the first coating layer. A piezoelectric element provided with a second coating layer comprising a coupling agent that is provided and improves the familiarity of the ceramic piezoelectric powder and the organic polymer and suppresses moisture absorption. The piezoelectric element according to claim 1, wherein the first coating layer is made of a water repellent material. The piezoelectric element according to claim 1, wherein the first coating layer has a contact angle with respect to distilled water of 125 ° or more and less than 180 °. The piezoelectric element according to claim 1, wherein the first coating layer is formed of at least one of fatty acid, fatty acid salt, and monomolecular layer. The piezoelectric element according to claim 1, wherein the second coating layer is made of a titanium coupling agent. 6. The piezoelectric element according to claim 1, wherein the second coating layer is formed of at least one of isopropoxy triisostearoyl titanate and isopropoxy tris dioctyl pyrophosphate titanate. The piezoelectric element according to claim 1, wherein the piezoelectric ceramic powder is a compound having a perovskite structure including at least one element of Group 1A of the periodic table and Group 2A of the periodic table. The piezoelectric element according to claim 1, wherein the piezoelectric ceramic powder contains at least one of bismuth sodium titanate, barium titanate, sodium niobate, and potassium niobate as a main component. The piezoelectric element according to any one of claims 1 to 8, wherein the first electrode and the second electrode are a conductive layer of an elastic body containing at least one of a thermoplastic resin, a thermoplastic elastomer, and rubber and a conductive powder. . The piezoelectric element according to any one of claims 1 to 8, wherein the first electrode and the second electrode are coating films of a conductive paint or conductive paste whose main components are a mixture of conductive powder and organic polymer. The piezoelectric element according to any one of claims 1 to 8, wherein the first electrode and the second electrode are configured by a vapor deposition film of a conductive material. The piezoelectric element according to any one of claims 9 to 11, wherein the conductive material or conductive powder contains at least one of C, Pt, Au, Pd, Ag, Cu, Al, and Ni. The piezoelectric element according to any one of claims 1 to 12, wherein the organic polymer contains at least one of a thermoplastic elastomer and rubber. The piezoelectric element according to claim 13, wherein the thermoplastic elastomer contains at least one of chlorinated polyethylene and chlorosulfonated polyethylene. The piezoelectric element according to claim 1, further comprising a protective layer that covers the first electrode, the second electrode, and the piezoelectric composition pressure-sensitive body. The piezoelectric element according to claim 15, wherein the protective layer contains at least one of an electrically insulating thermoplastic elastomer and rubber. The piezoelectric element according to any one of claims 1 to 16, wherein the dielectric constant of the piezoelectric ceramic powder is more than 0 and 1000 or less.

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