JP2009103483A - Piezoelectric element using piezoelectric composition pressure-sensitive body - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem in hitherto manufacturing of a piezoelectric composition pressure-sensitive body by mixing fine piezoelectric ceramic powder with organic polymer, wherein it is difficult to acquire the pressure-sensitive body which varies less in a mixed state, in a dispersed state, and in the characteristics. <P>SOLUTION: This piezoelectric element is formed of the piezoelectric composition pressure-sensitive body 1 made, by mixing piezoelectric ceramic powder B5 with flexible organic polymer. The ceramic powder B5 has fine domains of 50 nm or smaller and a mean particle size of 2 μm or smaller, with a coating layer 6 formed on each of particle surfaces with a titanium coupling agent covalently bonding thereto. This enables provision of the piezoelectric element having high sensitivity, less varying in characteristics, further, is capable of preventing the electrical characteristics from changing, such as, the electrical resistance and capacitance, piezoelectric characteristics from changing, and the mechanical strength from lowering, even if the element is used at high temperature and high humidity, making it possible to realize superior durability and reliability. <P>COPYRIGHT: (C)2009,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, 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-shaped piezoelectric element is prepared by first forming a piezoelectric composition pressure-sensitive body, in which a coupling agent, piezoelectric powder, and chlorinated polyethylene are mixed and kneaded with a roll into a sheet by hot pressing, and silver paste is applied to both sides of the sheet. An electrode is formed by fusing a conductive sheet in which carbon is dispersed in a coating process or rubber, and then a poling process is performed by applying a DC voltage of several tens of kV between both electrodes in order to develop piezoelectricity. Can be obtained by: When a pressure is applied to a part or the entire surface of the electrode, the piezoelectric composition pressure-sensitive body in that part is distorted. As a result, a charge is induced between both electrodes, and the pressure is detected using the induced charge. Therefore, it is applied as a pressure sensor. In addition, nano-sized barium titanate synthesized recently in the hydrothermal environment is used for microwave sintering, which consists of ceramic particles with a fine particle size, has a fine domain of about 50 nm, and exhibits high piezoelectric performance. Although it has been reported, a composite piezoelectric material with a resin related to this has not been reported.
Japanese Patent Laid-Open No. 11-201835 Journal of Applied Physics 45, 2006, 7405 pages

  However, although the piezoelectric ceramic having the fine particle size and the fine domain described in Non-Patent Document 1 has a large piezoelectric constant, it is very difficult to form a composite with an organic polymer because of the fine particle size. For this reason, there has been a problem that the characteristic variation as a piezoelectric element also increases. Even when a composite piezoelectric body is formed, when the conventional piezoelectric element with a piezoelectric body is used in a high-temperature and high-humidity environment, water vapor passes through the electrode, and the piezoelectric composition pressure-sensitive body constituting the piezoelectric element is formed. To reach. Therefore, when the temperature inside the piezoelectric composition pressure-sensitive body is lower than the outside or when the water vapor is supersaturated on the surface of the piezoelectric composition pressure-sensitive body, the diffused water vapor condenses to produce water, and the piezoelectric composition A phenomenon occurs in which components and impurities of the piezoelectric ceramic powder constituting the material pressure sensitive body are eluted by water. 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 the durability is inferior. There has been a problem that the circuit for the circuit becomes complicated.

  In addition, when the piezoelectric element absorbs water, the piezoelectric composition pressure-sensitive body itself softens, and the relationship between the pressure and the distortion of the piezoelectric element changes. Since there is a possibility of detection, there is a problem that a complicated detection circuit is required.

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

  In particular, a piezoelectric ceramic powder containing a group I, group II alkali metal or alkaline earth metal of the periodic table has a low specific resistance and is likely to be eluted into water, so that a reduction in electric resistance becomes a problem.

  The present invention solves the above-mentioned conventional problems, greatly reduces the variation in piezoelectric characteristics of the composite piezoelectric body, and suppresses changes in electrical characteristics and softening even when used in a high-temperature and high-humidity environment, and is always stable. An object of the present invention is to provide a piezoelectric element that realizes the piezoelectric characteristics and strength.

  In order to solve the above-described conventional problems, a piezoelectric element using the piezoelectric composition pressure-sensitive body of the present invention is a piezoelectric element in which a coating layer is formed by covalently bonding a titanium coupling agent as the piezoelectric composition pressure-sensitive body. It is obtained by mixing ceramic powder with a flexible organic polymer using ceramic powder. At this time, the piezoelectric ceramic powder includes a domain of approximately 50 nm or less, and the piezoelectric ceramic powder has an average particle diameter of 2 μm or less.

  By covalently bonding the titanium coupling agent directly to the surface of the piezoelectric ceramic powder, the compatibility between the piezoelectric ceramic powder and the organic polymer is improved, the composite state is stabilized, and the characteristic variation as a piezoelectric element is reduced. The In addition, since the piezoelectric ceramic powder has minute domains, high piezoelectric performance is realized and sensitivity is increased. For this reason, noise becomes relatively small, and a complicated circuit for reducing noise is not necessary.

  Furthermore, even if the piezoelectric element is used in a high-temperature and high-humidity environment, water is generated by condensation of water vapor in the piezoelectric composition pressure-sensitive body constituting the piezoelectric element. Since the coating layer is formed, the absorption of water into the piezoelectric ceramic powder is suppressed, and an increase in the capacitance and electrical resistance of the piezoelectric element can be prevented.

  In addition, since the piezoelectric ceramic powder does not absorb water, 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, and the initial piezoelectric characteristics can be maintained. .

  Further, since the softening of the piezoelectric composition pressure-sensitive body constituting the piezoelectric element can be suppressed, a decrease in the tensile strength of the piezoelectric composition pressure-sensitive body can be prevented, and the initial strength can be maintained.

  In the piezoelectric element using the piezoelectric composition pressure sensitive body of the present invention, the composite state of the piezoelectric ceramic powder and the organic polymer is stabilized by forming a coating layer on the piezoelectric ceramic powder having a micro domain. In addition, highly sensitive and stable characteristics can be realized without complicated circuits, and further, since water penetration into the piezoelectric composition pressure sensitive body is suppressed, changes in the initial electrical characteristics, piezoelectric characteristics, and mechanical tensile strength can be achieved. Can be prevented, and excellent durability and reliability can be realized.

  In the first invention, a piezoelectric ceramic powder in which a coating layer is formed by covalently bonding a titanium coupling agent to a particle surface as a piezoelectric element, a flexible organic polymer, and a titanium coupling agent are mixed. The piezoelectric ceramic powder is composed of a piezoelectric composition pressure-sensitive body comprising a domain having a size of approximately 50 nm or less and an average particle diameter of the piezoelectric ceramic powder of 2 μm or less.

  Since the piezoelectric ceramic powder has minute domains, high piezoelectric performance is realized and sensitivity is increased. For this reason, noise becomes relatively small, and a complicated circuit for reducing noise is not necessary.

  In addition, by using the piezoelectric ceramic powder in which the coating layer is formed by covalently bonding the titanium coupling agent, kneading with the organic polymer is facilitated, and the kneading state is saturated in a short time. The dispersion of the dispersed state due to the kneading of the obtained composite piezoelectric material is reduced, the piezoelectric constant is also stabilized, and as a result, the characteristics of the piezoelectric element can be stabilized.

  In addition, even when the piezoelectric element is used in a high-temperature and high-humidity environment, even if water vapor is generated by the piezoelectric composition pressure-sensitive body constituting the piezoelectric element, the piezoelectric ceramic powder in the piezoelectric composition pressure-sensitive body is coated. Since the layer is formed, the absorption of water into the piezoelectric ceramic powder is suppressed, and an increase in the capacitance and electrical resistance of the piezoelectric element can be prevented. As a result, the initial electrical characteristics of the piezoelectric element can be maintained, and excellent durability and reliability can be realized.

  In addition, since the piezoelectric ceramic powder does not absorb water, 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, and the initial high piezoelectric characteristics can always be maintained. Can do. 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.

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

  In the second invention, in particular, by using a material having a contact angle with distilled water of 130 ° or more as the coating layer of the first invention, particularly excellent water resistance can be realized. Changes in electrical characteristics, piezoelectric characteristics, and mechanical strength can be further reduced, and more excellent durability and reliability of the piezoelectric element can be realized.

  In the third invention, in particular, by forming the coating layer of the first or second invention as a monomolecular layer, the thickness of the coating layer can be made an ultra-thin film of several nanometers level, so that piezoelectric characteristics can be expressed. The voltage drop that occurs in the monomolecular layer during the poling process in which a high DC voltage is applied can be reduced, the poling efficiency can be improved, and the processing time can be shortened or excellent piezoelectric characteristics can be realized. Moreover, since the amount of the titanium coupling agent used can be reduced by making the coating layer a monomolecular layer, the cost of the piezoelectric element can be reduced.

  The fourth invention is particularly a compound having a perovskite structure containing at least one element of Group I of the Periodic Table and Group II of the Periodic Table of the piezoelectric ceramic powder on which the coating layers of the first to third inventions are formed. By nature, alkali metals and alkaline earth metals of Group I of the periodic table and elements of Group II of the periodic table are easily eluted by water, but these alkali and alkaline earth components contained in the piezoelectric ceramic powder Can be suppressed, so that a significant decrease in electrical resistance can be suppressed.

In the fifth invention, in particular, the piezoelectric ceramic powder on which the coating layers of the first to fourth inventions are formed is a compound containing a barium titanate as a main component. Even if the device is disposed of and exposed to the environment such as acid rain, lead is not eluted and the environment is not polluted. Further, since the piezoelectric ceramic powder is provided with a coating layer to prevent the elution of the piezoelectric ceramic powder components, the elution of metals other than lead can be suppressed and the safety can be further improved.

  In the sixth invention, in particular, by using the flexible organic polymer of the first to fifth inventions 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 the seventh invention, in particular, the content of the piezoelectric ceramic powder in the piezoelectric composition pressure-sensitive body is obtained by using the thermoplastic elastomer of the sixth invention as at least one material of chlorinated polyethylene and chlorosulfonated polyethylene. Therefore, the piezoelectric characteristics of the piezoelectric element can be improved.

  In the eighth invention, in particular, by using the titanium coupling agent of the first to seventh inventions as a material containing at least one of isopropoxytriisostearoyl titanate and isopropoxytris (dioctyl pyrophosphate) titanate, The kneadability (mixing / dispersion) between the piezoelectric ceramic powder and the organic polymer can be improved, so that 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. And can be easily molded into an arbitrary shape such as a sheet shape or a cable shape.

  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 electrodes 2 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 A3 having a coating layer formed by covalently bonding a titanium coupling agent, and a flexible organic polymer 4. The piezoelectric ceramic powder A3 on which the coating layer is formed is in a state of being uniformly dispersed with the organic polymer 4. At this time, among the piezoelectric ceramic powder A3 formed with the coating layer, the average particle size of the piezoelectric ceramics (piezoelectric ceramic powder B5 in FIG. 3 below) excluding the coating layer is 2 μm or less, and a fine particle size of about 50 nm or less. It has the feature of having a domain.

  FIG. 3 is a schematic view showing a cross section of one particle of piezoelectric ceramic powder A3 having a coating layer formed by covalent bonding of a titanium coupling agent. In FIG. 3, the piezoelectric ceramic powder A3 has a coating layer 6 formed on the surface of the piezoelectric ceramic powder B5. Although not shown in the exposure, as in FIG. 2, the piezoelectric ceramic powder B5 has a micro domain of about 50 nm or less. In addition, the average particle size is 2 μm or less.

The sheet-like piezoelectric element in the first embodiment is manufactured as follows. First, the piezoelectric ceramic powder B5 is dipped in a solution containing a titanium coupling agent diluted to a predetermined concentration by dilution with a suitable solvent and dried, or the piezoelectric ceramic powder B5 is subjected to a titanium coupling of a predetermined amount of liquid. The coating layer 6 is formed by mixing the agent with a high-speed mixer, and a covalent bond is formed between the titanium coupling agent of the coating layer 6 and the piezoelectric ceramic by further processing at a high temperature. General titanium coupling agents, including the titanium coupling agent used here, have a form in which an alkoxy group is bonded to titanium. When forming a covalent bond, the alkoxy group and the hydroxyl group on the piezoelectric ceramic powder Accordingly, the corresponding alcohol is eliminated to form a metal-oxygen-titanium covalent bond. In addition, when forming a covalent bond, a catalyst such as an acid or a base can be used. In addition, the formed covalent bond is stable up to about 200 ° C., and the deterioration in a high temperature environment is small.

  Next, the piezoelectric ceramic powder A3 on which the coating layer is formed, the organic polymer 4 having flexibility, and a processing machine such as a kneader or a roll, and the piezoelectric ceramic powder A3 on which the coating layer is formed have flexibility. After kneading so that the organic polymer 4 is uniformly mixed and dispersed, it is processed using a processing machine such as a roll or a hot press to produce a sheet-shaped piezoelectric composition pressure-sensitive body 1. The In this kneading step, a titanium coupling agent may be further mixed.

  Application of conductive paste or conductive paint in which conductive powder and organic polymer are mixed on both surfaces of the sheet-like piezoelectric composition pressure-sensitive body 1, and the conductive powder is made of flexible organic material such as rubber or thermoplastic elastomer. The electrode 2 is formed by either a fusion method of a conductive sheet mixed and dispersed in a polymer or a deposition method of a conductive material and a forming method.

  Thereafter, a poling process is performed by applying a DC high voltage between the electrodes 2 in air or in a silicon oil bath in order to develop piezoelectricity, and a sheet-like piezoelectric element is manufactured.

  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 piezoelectric element are manifested by applying a high DC voltage between the electrodes 2 and poling the piezoelectric composition pressure-sensitive body 1. When a time-varying pressure is applied to a part or the entire surface of a sheet-like piezoelectric element that exhibits piezoelectricity, an oscillating charge corresponding to the acceleration generated in that part is induced between the electrodes 2. The pressure can be detected using this induced charge. Therefore, the piezoelectric element of the present invention can be used as a pressure-sensitive sensor such as a sensor for detecting body movement by installing it on an automobile door and installing it on a sensor for detecting pinching or a nursing bed.

  Since the piezoelectric ceramic powder B5 forms minute domains of about 50 nm or less, the piezoelectric constant d33 increases, and the vibration charge increases. As a result, the sensitivity is increased and the noise is relatively reduced, so that an effect that a special circuit for noise reduction is unnecessary is obtained.

  Further, by forming the coating layer 6 on the piezoelectric ceramic powder B5, the surface of the piezoelectric ceramic powder B5 can be made hydrophobic. For this reason, the compatibility with the organic polymer having hydrophobicity originally becomes good, the kneading property of both improves, and the productivity such as shortening of the kneading process time can be improved. In addition, when the particles have a very small particle size like the piezoelectric ceramic particles of the present invention, the state tends to become unstable even when kneading is possible. However, as in the present embodiment, by covalently bonding the titanium coupling agent to the piezoelectric ceramic, the kneading state is remarkably improved, and the characteristics of the obtained piezoelectric element are remarkably stabilized. At this time, if the coupling agent is also contained in the organic polymer, the compatibility between the polymer and the piezoelectric ceramic is further increased, and the above effect is further increased.

On the other hand, pressure sensors such as those described above may be used in outdoor environments such as vibration or pressure sensors, or in high-temperature steam environments due to rain in summer, nursing beds, etc. For example, it is highly likely to be used in a humid environment such as incontinence or sweat, or in a high-temperature and high-humidity environment such as washing for keeping hygiene as bedding. 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 inside the piezoelectric element. When the temperature of the piezoelectric composition pressure-sensitive body is lower than the outside or when the water vapor is supersaturated on the surface of the piezoelectric composition pressure-sensitive body, the diffused water vapor is condensed and water is generated. A phenomenon occurs in which components and impurities of the piezoelectric ceramic powder constituting the pressure body are eluted. As a result, there is a problem that the electrical characteristics such as an increase in the capacitance of the piezoelectric element and a decrease in the electrical resistance occur, resulting in poor durability and, when used as a sensor, for detection and control. It is necessary to make the circuit adaptable to the initial change in electrical characteristics, and the circuit has a complicated configuration. In particular, when the particle diameter of the piezoelectric ceramic is small, the above-mentioned influence of humidity becomes significant. For example, when the average particle diameter is 2 μm or less, the surface area becomes large, so that moisture absorption easily proceeds.

  However, in the piezoelectric element of the present invention, the piezoelectric composition pressure-sensitive body is formed by forming the coating layer 6 formed by covalently bonding the titanium coupling agent to the piezoelectric ceramic powder B5 constituting the piezoelectric composition pressure-sensitive body 1. 1, even if water vapor is condensed to generate water, the penetration of water into the piezoelectric composition pressure-sensitive body 1 and the elution of components and impurities of the piezoelectric ceramic powder B5 are suppressed, and the capacitance as a piezoelectric element is increased. A decrease in electrical resistance can be prevented, and it is also thermally stable. As a result, the initial electrical characteristics of the 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 addition, when a conventional piezoelectric element absorbs water, the piezoelectric composition pressure-sensitive body softens, and the relationship between the pressure and the distortion of the piezoelectric element changes. Therefore, signal processing according to the change in the softness of the piezoelectric element is necessary. Although there is a possibility of erroneous detection, when the piezoelectric element of the present invention is used as a pressure-sensitive sensor, water is absorbed into the piezoelectric composition pressure-sensitive body 1 by the coating layer 6 covering the piezoelectric ceramic powder B5. Therefore, softening of the piezoelectric composition pressure-sensitive body 1 can be suppressed, and the initial piezoelectric characteristics can always be maintained. As a result, high reliability can be realized because signal processing according to changes in piezoelectric characteristics is not required.

  Moreover, since the softening of the piezoelectric composition pressure-sensitive body 1 constituting the piezoelectric element can be suppressed, a decrease in the tensile strength of the piezoelectric composition pressure-sensitive body 1 itself can be prevented, and the initial strength can be maintained. Excellent durability can be achieved.

  Further, the coating layer 6 having a contact angle with distilled water of 130 ° or more can remarkably reduce changes in electrical characteristics, piezoelectric characteristics, and mechanical strength of the piezoelectric element in a high temperature and high humidity environment. If this is a titanium coupling agent whose contact angle with respect to distilled water is 130 degrees or more, it is thought that high water resistance can be obtained with respect to the condensed water even in a high temperature environment. Desirably, the contact angle with distilled water, which is super water repellent, is 150 ° or more.

  By covalently bonding a titanium coupling agent to the piezoelectric ceramic B5, the contact angle of the coating layer 6 with respect to distilled water can be 130 ° or more.

  Moreover, the coating layer 6 of a titanium coupling agent can be formed of 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 coating layer 6 is a monomolecular layer, the amount of the coupling agent used can be remarkably reduced, so that the cost of the piezoelectric element can be reduced.

The coating layer 6 to which the titanium coupling agent is covalently bonded is first dried by immersing the piezoelectric ceramic powder B5 in a solution containing a titanium coupling agent diluted to a predetermined concentration by dilution with an appropriate solvent. Alternatively, the coating layer 6 is formed by mixing the piezoelectric ceramic powder B5 with a predetermined amount of a liquid titanium coupling agent with a high-speed mixer, and further processed at a high temperature, whereby the titanium coupling agent and the piezoelectric layer of the coating layer 6 are piezoelectric. It is obtained by forming a covalent bond between the ceramics B5.

  Moreover, as a titanium coupling agent, 1 type may be used independently and 2 or more types may be used in combination.

  As the piezoelectric ceramic powder B5 having a domain of approximately 50 nm or less used in the present invention, a powder obtained by microwave firing of a powder of about 100 nm produced by hydrothermal synthesis can be suitably used. The particle size of the ceramic powder obtained at this time is fine, and the average particle size is 2 μm or less.

  Further, the compound of the piezoelectric ceramic powder B5 used in the present invention is a compound having a perovskite structure such as lead titanate, lead zircon, lead zirconate titanate, bismuth / 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 B5 come into contact with an electrolyte such as water, the components of the piezoelectric ceramic powder B5 and impurities contained in the piezoelectric ceramic powder B5 are eluted. In particular, a compound having a perovskite structure including at least one element of Group I of the periodic table and Group II of the periodic table, particularly compounds of bismuth / sodium titanate, barium titanate, sodium niobate, and potassium niobate are water. In the environment under high temperature and high humidity, the elution of the alkaline component is large and the change in electrical characteristics is large. In addition, piezoelectric ceramics containing alkali components have a lower specific resistance than, for example, lead zirconate titanate. Therefore, when the alkali components are eluted, the absolute value of the electrical resistance is lower, and a constant voltage is always applied to the piezoelectric element. Therefore, there is a possibility that the circuit configuration for detecting pressure cannot be used as a pressure-sensitive sensor.

  In the present invention, a compound having a perovskite structure including at least one element of Group I of the Periodic Table and elements of Group II of the Periodic Table including alkali and alkaline earth components, and the main component is bismuth sodium titanate, barium titanate Since the coating layer 6 is formed on the piezoelectric ceramic powder B5 made of a compound containing at least one of sodium niobate and potassium niobate, the elution of alkali and alkaline earth components can be suppressed, and the electrical resistance is greatly increased. Can be used as a pressure-sensitive sensor even in a circuit configuration in which a constant voltage is constantly applied to a piezoelectric element to detect pressure, and has high practicality.

  In addition, the piezoelectric ceramic powder B5 compound is composed of barium titanate as a main component of a compound having a perovskite structure including at least one element of Group I of the periodic table and Group II of the periodic table. In addition, a high-sensitivity piezoelectric element with high sensitivity can be obtained, and even if the piezoelectric element is disposed of and exposed to an environment such as acid rain, lead is not eluted and the environment is not contaminated. In addition, since the coating layer 6 is provided on the piezoelectric ceramic powder B5 and the elution of the components of the piezoelectric ceramic powder B5 is prevented, the elution of metals other than lead is also suppressed, and the safety can be further improved.

The electrode 2 of the present invention is obtained by kneading at least one conductive powder of C, Pt, Au, Pd, Ag, Cu, Al, and Ni with a flexible organic polymer such as rubber or thermoplastic elastomer. A conductive layer formed by extrusion molding of the flexible conductive composition produced in the above, a conductive film coated with a conductive paint (paste) in which the above-described conductive powder is dispersed in an organic polymer, C, Pt, Au, Pd , Ag, Cu, Al, Ni A thin film deposited film formed by vacuum deposition, sputtering, CVD or the like on the piezoelectric composition pressure sensitive body 1 can be used.

  Examples of the flexible organic polymer 4 used in the present invention include a material containing at least one of a thermoplastic elastomer and rubber. Since these organic polymers 4 having flexibility can impart excellent elasticity and flexibility to the piezoelectric element, the piezoelectric element can obtain a large repulsive force and displacement with respect to the applied pressure. The piezoelectric characteristics can be improved.

  In particular, as the above-mentioned thermoplastic elastomer, chlorinated polyethylene and chlorosulfonated polyethylene increase the content of the piezoelectric ceramic powder A3 on which the coating layer in the piezoelectric composition pressure-sensitive body 1 is formed. Since the B5 content can be increased, the piezoelectric characteristics of the piezoelectric element can be improved.

  In addition to isopropoxy triisostearoyl titanate, isopropoxy tris (dioctyl pyrophosphate) titanate, diisopropoxy diisostearoyl titanate, isopropoxy tris (dioctyl pyrophosphate) titanate as the titanium coupling agent of the present invention, high-speed mixer It is preferable to use a liquid titanium coupling agent that does not require a solvent for solution from the viewpoint of easy uniform coating with piezoelectric ceramics.

  When chlorinated polyethylene or chlorosulfonated polyethylene is used as the organic polymer 4 having flexibility, the compatibility with the piezoelectric ceramic powder A3 on which the coating layer is formed is further improved, so that the kneading time is shortened. In addition, the piezoelectric characteristics can be improved, the piezoelectric characteristics can be stabilized, and the flexibility can be improved, and it can be easily molded into an arbitrary shape such as a sheet shape or a cable shape.

  The reason why the compatibility is good is that the SP value (solubility parameter) of isopropoxytriisostearoyl titanate and 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.

(Embodiment 2)
FIG. 4 is a cross-sectional view of the sheet-like piezoelectric element according to the second embodiment of the present invention. 4 differs from the first embodiment in that a protective layer 7 for protecting the piezoelectric composition pressure-sensitive body 1 and the electrode 2 is provided. In addition, the same code | symbol is attached | subjected to the same member as 1st Embodiment. As shown in FIG. 4, after the electrodes 2 are formed on both surfaces of the piezoelectric composition pressure-sensitive body 1, a protective layer 7 that covers the piezoelectric composition pressure-sensitive body 1 and the electrodes 2 is provided. The protective layer 7 is made of an organic polymer having elasticity so that the flexibility of the piezoelectric composition pressure-sensitive body 1 and the electrode 2 is not impaired, and a thermoplastic elastomer and a rubber material are particularly suitable. Although the thickness of the protective layer 7 is not limited, in order not to impair the piezoelectric characteristics of the piezoelectric composition pressure-sensitive body 1, it is preferable that the thickness is 0.2 to 2 mm. The protective layer 7 covers the piezoelectric composition pressure-sensitive body 1 and the electrode 2 by processing the organic polymer described above into a sheet shape using a processing machine such as a roll or a hot press, and folding or sandwiching the sheet. .

  Also in this embodiment, since the piezoelectric ceramic powder B5 forms a minute domain of about 50 nm or less as in the first embodiment, the piezoelectric constant d33 is increased, the sensitivity is increased, and the noise is relatively increased. As a result, a special circuit for reducing noise is not required.

  Similarly to the first embodiment, by forming the coating layer 6 on the piezoelectric ceramic powder B5, the kneading state is improved despite the fact that the piezoelectric ceramic particles have a very small particle size. The characteristics of the piezoelectric element obtained are also significantly stabilized.

  When the piezoelectric element having the above configuration is used in a high-temperature and high-humidity environment as in the first embodiment, since the protective layer 7 is present, the diffusion amount of water vapor into the piezoelectric composition pressure-sensitive body 1 is reduced. However, since the gap of the three-dimensional network molecular structure of the protective layer 7 is larger than the size of one molecule of water vapor, the diffusion of water vapor can be completely prevented when the thickness of the protective layer 7 is 2 mm or less. As in the first embodiment, water vapor is condensed and water is generated on the surface of the piezoelectric composition pressure-sensitive body 1. However, since the coating layer 6 is formed on the piezoelectric ceramic powder B5 constituting the piezoelectric composition pressure-sensitive body 1, the penetration of water into the piezoelectric composition pressure-sensitive body 1 is suppressed, and the components of the piezoelectric ceramic powder B5 are eluted. Can be reduced, and the same effect as in the first embodiment can be obtained.

(Embodiment 3)
FIG. 5 is a partial cross-sectional view of a cable-like piezoelectric element according to the third embodiment of the present invention. In FIG. 5, the cable-shaped piezoelectric element has a flexible piezoelectric composition pressure-sensitive body 9 formed on the outer surface of the core electrode 8, and the flexible outer electrode 10 is formed on the outer surface of the piezoelectric composition pressure-sensitive body 9. In addition, a protective layer 11 made of an electrically insulating elastic body is formed.

  The core electrode 8 has a configuration in which a metal such as copper is wound around a single or a plurality of metal wires, or converging wires of a large number of polyester fibers, and the piezoelectric composition pressure-sensitive body 9 is the first composition described above. The materials described in the embodiment are used.

  The flexible outer electrode 10 is composed 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. A conductive layer formed by winding the piezoelectric composition pressure-sensitive body 9 and at least one conductive powder of C, Pt, Au, Pd, Ag, Cu, Al, and Ni, or a rubber or thermoplastic elastomer. Apply a conductive layer formed by extruding a flexible conductive composition prepared by kneading a flexible organic polymer, and a conductive paint (paste) in which the above-mentioned conductive powder is dispersed in an organic polymer. A thin film formed of a conductive film, at least one conductive material of C, Pt, Au, Pd, Ag, Cu, Al, and Ni on the piezoelectric composition pressure sensitive body 9 by a method such as vacuum deposition, sputtering, or CVD. Uses vapor-deposited film It is.

  The protective layer 11 is made of the same material as the protective layer 7 described in the second embodiment, and is formed by extrusion molding of this material.

The cable-like piezoelectric element according to the third embodiment is manufactured as follows. First, the piezoelectric ceramic powder B5 and the titanium coupling agent are mixed with a high-speed mixer and further processed at a high temperature to form the coating layer 6 on the piezoelectric ceramic powder B5, and the piezoelectric ceramic powder A3 on which the coating layer is formed. Is made. The piezoelectric ceramic powder A3 having a coating layer and the flexible organic polymer 4 are processed using a processing machine such as a kneader or a roll, and the piezoelectric ceramic powder A3 having a coating layer is flexible. 4 is kneaded so as to be uniformly mixed and dispersed in 4, and then a sheet-shaped piezoelectric composition pressure-sensitive body is produced by a roll processing machine. Processing into pellets using a processing machine such as a pelletizer. Next, using the core electrode 8 as a core material, the pellet-shaped piezoelectric composition pressure-sensitive body is extruded using an extrusion molding machine, and the piezoelectric composition pressure-sensitive body 9 is formed around the core electrode 8. Next, at least one type of foil of C, Pt, Au, Pd, Ag, Cu, Al, and Ni is formed on both sides of a polymer film such as polyethylene terephthalate on the cable-shaped piezoelectric composition pressure-sensitive body 9. Flexible conductive composition prepared by winding an adhesive conductive film or kneading at least one conductive powder of C, Pt, Au, Pd, Ag, Cu, Al, Ni and an organic polymer Or by applying a conductive paint (paste) in which the above conductive powder is dispersed in an organic polymer, or at least of C, Pt, Au, Pd, Ag, Cu, Al, Ni The flexible outer electrode 10 is formed by either forming a thin film formed of one kind of conductive material by a method such as vacuum deposition, sputtering, or CVD. Further, the protective layer 11 is formed by using an electrical insulating elastic body using an extrusion molding machine. Thereafter, a poling process is performed by applying a DC high voltage between the core electrode 8 and the flexible outer electrode 10 in air or in a silicone oil bath in order to develop piezoelectricity. In addition, you may provide the protective layer 11 after performing the above-mentioned polling process.

  The piezoelectric cable sensor thus manufactured is connected to the control circuit by removing the protective layer 11 and the piezoelectric composition pressure-sensitive body 9 at one end and exposing the core electrode 8 and the flexible outer electrode 10. Used as a pressure sensitive sensor.

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

  The piezoelectricity of the piezoelectric element is manifested by applying a DC voltage between the core electrode 8 and the flexible outer electrode 10 and poling the piezoelectric composition pressure sensitive body 9. By expressing the piezoelectricity in the piezoelectric composition pressure-sensitive body 9, when a time-varying pressure is applied to a part or the entire surface of the cable-shaped piezoelectric element, the core electrode 8 and the flexible outer electrode 10 are applied. In the meantime, an oscillating charge is induced according to the acceleration generated in the cable-shaped piezoelectric element of that portion. The pressure can be detected using this induced charge.

  Also in this embodiment, since the piezoelectric ceramic powder B5 forms a minute domain of about 50 nm or less as in the first embodiment, the piezoelectric constant d33 is increased, the sensitivity is increased, and the noise is relatively increased. As a result, a special circuit for reducing noise is not required.

  Similarly to the first embodiment, by forming the coating layer 6 on the piezoelectric ceramic powder B5, the kneading state is improved despite the fact that the piezoelectric ceramic particles have a very small particle size. The characteristics of the piezoelectric element obtained are also significantly stabilized.

  When the cable-shaped piezoelectric element having the above-described configuration is used as a pressure-sensitive sensor in a high-temperature and high-humidity environment as in the first embodiment, the protective layer 11 is present. However, since the gap of the three-dimensional network molecular structure of the protective layer 11 is larger than the size of one molecule of water vapor, the protective layer 11 can completely prevent the diffusion of water vapor. In the same manner as in the first embodiment, water passes through the flexible outer electrode 10, and water vapor is condensed on the surface of the piezoelectric composition pressure-sensitive body 9 to generate water. However, since the piezoelectric ceramic powder B5 constituting the piezoelectric composition pressure sensitive body 9 has the coating layer 6 that forms a covalent bond with the titanium coupling agent, the penetration of water is suppressed, and the component of the piezoelectric ceramic powder B5 is reduced. Elution can be reduced, and the same operation and effect as in the first embodiment can be obtained.

  The cable-shaped piezoelectric element is flexible and has a cable shape, so that it can be used for arrangements including bent portions and space-saving arrangements with limited mounting widths, and high temperature and high Even when used in a humid environment, it has excellent characteristics capable of maintaining the initial electrical characteristics, piezoelectric characteristics, and mechanical strength. Therefore, it is most suitable as an outdoor sensor that requires such arrangement conditions and characteristics, or a sensor for detecting pinching incorporated in an automobile door or the like.

The body motion sensor used for a nursing bed or the like needs to ensure detection of a large area, but the cable-like piezoelectric element of the present invention is arranged to meander on the bed, so In addition, it is possible to detect the body movement for a nursing bed in consideration of the usage environment peculiar to bedding such as a bed, for example, incontinence during use, sweat, and laundry for washing hygiene. It is an optimal configuration as a sensor.

(Example 1)
Piezoelectric ceramic powder using barium titanate with an average particle diameter of about 1.5 μm as the piezoelectric ceramic powder, and having the following coating layer formed on the surface of the piezoelectric ceramic powder with the titanium coupling agent described below, and being water-repellent. Was made. Further, it was confirmed by SEM observation that a domain of about 50 nm was formed in the piezoelectric ceramic.

  Specifically, isopropoxy triisostearoyl titanate was used as a titanium coupling agent, 1.5 wt% of this titanium coupling agent was mixed with a piezoelectric ceramic powder with a high-speed mixer, and further treated at 180 ° C. for 1 hour. .

  Next, the piezoelectric ceramic powder in which the coating layer is formed so that the piezoelectric ceramic powder is about 60% by volume and the chlorinated polyethylene is about 35% by volume, and chlorinated polyethylene as a flexible organic polymer and a roll machine. Were kneaded to prepare a piezoelectric composition pressure-sensitive body, and a piezoelectric composition pressure-sensitive sheet having a thickness of about 0.5 mm was prepared 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. A poling process was performed by applying a DC high voltage between the electrodes in air at 100 ° C. to produce 10 sheet-like piezoelectric elements having a width of 20 mm and a length of 120 mm.

  The sheet-like piezoelectric element produced as described above was subjected to a high-temperature and high-humidity test for 20 hours using a high-temperature and high-humidity tank at 85 ° C. and a relative humidity of 85%. Evaluation was carried out using a d33 meter (piezometer system PM300 / Piezo Test).

(Comparative Example 1)
For comparison, a coating layer of a titanium coupling agent was formed on the piezoelectric ceramic powder by the above-described high-speed mixer, but since no high-temperature treatment was performed, no covalent bond was formed, and the coating was held by van der Waals force. Using a piezoelectric ceramic powder, a similar sheet-like piezoelectric element was also produced and tested in the same manner.

(Comparative Example 2)
For comparison, a sheet-like material was used in the same manner as in Comparative Example 1 except that barium titanate powder having an average particle size of 3.5 μm and not having a fine domain of 100 nm or less was used as a piezoelectric powder. A piezoelectric element was fabricated and tested.

  It was found that about 30% of the titanium coupling agent remained in the piezoelectric ceramic after the solvent extraction with hexane, and these were covalently bonded to the surface of the piezoelectric ceramic. On the other hand, in the case of the comparative example, it was found that all the titanium coupling agents were extracted by the same extraction operation and were held by the piezoelectric ceramics by van der Waals force, not by covalent bonds.

The piezoelectric constant d33 before the high-temperature and high-humidity test (represented as a relative value with the average value of Example 1 being 100), d33 of each of the 10 produced piezoelectric elements, and their Cv values were compared with Example 1 in order. In order of Example 1 and Comparative Example 2, (piezoelectric constant d33 (relative value), Cv value of d33) = (100, 3%), (
41, 20%), (48%, 7%).

  The Cv value of the piezoelectric constant d33 of the example is small because the titanium coupling agent is firmly and stably covalently bonded to the surface of the piezoelectric ceramic to form a coating layer, so that the kneading and dispersion state becomes stable, and the kneading and mixing are stable. However, it is thought that the variation was reduced by proceeding easily. Also, the piezoelectric constant d33 of Comparative Example 1 is lower than that of the example because the kneading and dispersion state varies, so that fine bubbles are formed at the time of kneading. This is probably because no voltage was applied and the remanent polarization was reduced.

  Also, the piezoelectric constant d33 of Example 1 is larger than that of Comparative Example 2 because the piezoelectric ceramic powder used in Example 1 has a fine domain of 50 nm or less, so that the piezoelectric constant d33 of the piezoelectric ceramic itself is large. This is thought to be due to the rise.

  In Example 1, the piezoelectric constant d33 after the high-temperature and high-humidity test increased by 9%, whereas in Comparative Example 1 and Comparative Example 2, they increased by 26% and 38%, respectively.

  In Comparative Examples 1 and 2, since the titanium coupling agent was held in the piezoelectric ceramic powder only by van der Waals force, it was diffused from the surface of the piezoelectric body into the chlorinated polyethylene during the kneading. This is considered to be because the effect of preventing the invasion of water vapor is reduced because the binding force of the van der Waals force is weak. The increase in the piezoelectric constant is considered to be due to the pressure from the outside being relatively easily transmitted to the piezoelectric ceramic due to the softening of the chlorinated polyethylene due to the penetration of water vapor.

  On the other hand, in Example 1, since the titanium coupling agent is covalently bonded to the piezoelectric ceramic powder, it does not diffuse during kneading, and the bond with the piezoelectric ceramic powder is strong. This is thought to be due to the fact that it was possible to suppress the intrusion. The increase in the piezoelectric constant was suppressed because the degree of softening of the chlorinated polyethylene due to the invasion of water vapor was small, and the ease with which the external pressure was transmitted to the piezoelectric ceramic did not change much.

  As described above, there is a difference in characteristics, but the titanium coupling agent is covalently bonded to the piezoelectric ceramic powder to form a coating layer, thereby suppressing changes in the electrical characteristics (piezoelectric performance) of the piezoelectric element due to humidity, A highly sensitive piezoelectric element having excellent durability and high piezoelectric constant can be obtained.

  As described above, since the piezoelectric element according to the present invention is highly sensitive, noise is relatively reduced, and an effect that a circuit for reducing noise is unnecessary is obtained. Moreover, since the kneading state of the piezoelectric ceramic and the organic polymer becomes stable, an effect of obtaining stable piezoelectric characteristics can be obtained. Furthermore, even when used in a high-temperature and high-humidity environment, water absorption of the piezoelectric composition pressure-sensitive body can be suppressed, so that changes in initial electrical characteristics, piezoelectric characteristics, and mechanical tensile strength can be prevented. . As described above, excellent durability and reliability can be realized. Therefore, it can be applied to a wide range of applications such as pressure-sensitive sensors that prevent car doors and windows from being caught in high-temperature, high-humidity environments, and pressure detection devices that detect the presence of a person by detecting the movement of a person with a nursing bed. is there.

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 a piezoelectric ceramic powder having a coating layer in the first embodiment of the present invention Sectional drawing of the sheet-like piezoelectric element in Embodiment 2 of this invention Embodiment 3 of the present invention Partial sectional view of a cable-like piezoelectric element

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Piezoelectric composition Pressure sensitive body 2 Electrode 3 Piezoelectric ceramic powder A
4 Flexible organic polymer 5 Piezoelectric ceramic powder B
6 Coating Layer 7 Protective Layer 8 Core Electrode 9 Piezoelectric Composition Pressure Sensitive Body 10 Flexible External Electrode 11 Protective Layer

Claims (8)

A piezoelectric ceramic powder in which a coating layer is formed by covalently bonding a titanium coupling agent to the surface of the particles and a flexible organic polymer are mixed, and the piezoelectric ceramic powder has a domain of approximately 50 nm or less. A piezoelectric element using a piezoelectric composition pressure sensitive body comprising the piezoelectric ceramic powder having an average particle size of 2 μm or less. The piezoelectric element using the piezoelectric composition pressure sensitive body according to claim 1, wherein the coating layer is made of a material having a contact angle with distilled water of 130 ° or more. The piezoelectric element using the piezoelectric composition pressure-sensitive body according to claim 1, wherein the coating layer is composed of a monomolecular layer. Piezoelectric ceramic powder is a compound having a perovskite structure including at least one element of Group I of the periodic table and Group II of the periodic table. Pressure-sensitive piezoelectric composition according to any one of claims 1 to 3 Piezoelectric element using the body. The piezoelectric element using the piezoelectric composition pressure-sensitive body according to any one of claims 1 to 4, wherein the piezoelectric ceramic powder is a compound containing barium titanate. The piezoelectric element using the piezoelectric composition pressure sensitive body according to claim 1, wherein the organic polymer having flexibility includes at least one of a thermoplastic elastomer and rubber. The piezoelectric element using the piezoelectric composition pressure sensitive body according to claim 6, wherein the thermoplastic elastomer contains at least one of chlorinated polyethylene and chlorosulfonated polyethylene. The titanium coupling agent includes at least one of isopropoxytriisostearoyl titanate and isopropoxytris (dioctylpyrophosphate) titanate. The piezoelectric composition pressure sensitive body according to any one of claims 1 to 7 is used. Piezoelectric element.

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