JP2019106395A - Piezoelectric element sheet and method of manufacturing the same - Google Patents

Abstract

To make it possible to provide a piezoelectric element that exhibits a high piezoelectric constant, holds a charged charge for a long time, and holds a high piezoelectricity.SOLUTION: The piezoelectric element sheet includes: a fiber layered structure composed of a woven or non-woven fabric of glass fibers and/or ceramic fibers; and a sandwich structure in which a surface and a back surface of the fiber layered structure are coated with a coating layer composed of at least one coating resin selected from an imide resin and a fluorine resin.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a piezoelectric element sheet retaining high charge and a method of manufacturing the same.

  A piezoelectric element is an element that exhibits a piezoelectric effect that converts a force applied to a piezoelectric body into a voltage or converts a voltage into a force, and is used not only as an actuator and a sensor but also in an oscillation circuit and a filter circuit. It is used.

  Conventionally, piezoelectric ceramics such as perovskite compounds have been used as piezoelectric materials constituting such piezoelectric bodies, but in recent years, porous organic piezoelectric materials using porous organic materials having excellent formability are examined It is done. For example, EMFIT (Finland) provides a piezoelectric element sheet using a porous polypropylene material. This sheet has a structure in which independent pores are uniformly distributed throughout the sheet.

  Further, as such an organic piezoelectric material, development of a piezoelectric element which is excellent in moldability and excellent in heat resistance is promoted by making various heat resistant materials as a base material and making the material porous.

  The porous electret type element is proposed by patent documents 1-7. Patent Document 1 (Japanese Unexamined Patent Publication No. 2010-267906) discloses a porous electret in which a charge is injected into an organic polymer porous body obtained by stretching an organic polymer foam. Further, Patent Document 2 (Japanese Patent Laid-Open No. 2010-089494) discloses an electretized film subjected to high-voltage discharge treatment on a laminated film composed of a core layer composed of a biaxially stretched resin film and a surface stretched film at least on one side. There is. Patent Document 3 (Japanese Patent Laid-Open No. 2011-018897) discloses a porous resin sheet for a piezoelectric element in which a porous resin sheet prepared by phase separation agent extraction is charged using a microlayer separation structure. There is. The piezoelectric element which carried out the piezoelectric process of the laminated body of the porous fluororesin film and the non-porous fluororesin thin film is indicated by patent document 4 (Unexamined-Japanese-Patent No. 2012-164735). Patent Document 5 (Japanese Patent Laid-Open No. 2014-0931313) discloses an electret sheet in which a charge is injected into a laminated sheet consisting of a foamed olefin resin and a surface layer. Furthermore, Patent Document 6 (Japanese Patent Application Laid-Open No. 2016-072355) discloses a piezoelectric element comprising a porous base material (non-woven fabric or stretched film) and a surface layer (film-like) and having internally charged pores. There is. Patent Document 7 (WO2014 / 069477) discloses a piezoelectric laminate including a non-woven glass layer and a surface PFA layer.

Patent Documents 8 to 13 propose composite material piezoelectric elements of an inorganic material and a resin component.
For example, Patent Document 8 (JP-A-61-295678) discloses a piezoelectric film in which a rolled film of polytetrafluoroethylene (PTFE and dielectric powder) is charged. 2004-339008) discloses a self-supporting porous sheet for forming a piezoelectric element comprising an inorganic substance and a thermoplastic resin Patent Document 10 (Japanese Patent Application Laid-Open No. 2011-084735) discloses a thermoplastic resin Patent Document 11 (Japanese Unexamined Patent Publication No. 2011-216661) discloses a film having a layer separation structure from ceramic particles, a resin, and a phase separation agent. After preparing a resin sheet, a phase separation agent is extracted, and a porous sheet for a piezoelectric element is prepared by charging the internal bubbles. Patent Document 12 (Japanese Patent Application Laid-Open No. 2013-075945) discloses an electret sheet in which charges are injected and charged in a synthetic resin sheet composed of a synthetic resin and hollow silica particles. Patent Document 13 (WO 2015/005420) discloses a piezoelectric sheet containing an organic non-woven fabric and an inorganic filler.

JP, 2010-267906, A Unexamined-Japanese-Patent No. 2010-089494 JP, 2011-018897, A JP 2012-164735 A JP, 2014-093313, A JP, 2016-072355, A WO 2014/069477 Japanese Patent Application Laid-Open No. 61-295678 JP 2004-339008 A JP, 2011-084735, A JP, 2011-216661, A JP, 2013-075945, A WO 2015/005420

  These piezoelectric materials have room for improvement in terms of charge retention over a long time and high piezoelectricity retention.

An object of the present invention is to provide a piezoelectric element sheet which has a high piezoelectric constant, holds a charged charge for a long time, and holds a high piezoelectricity, and a method of manufacturing the same.
The present invention relates to, for example, the following [1] to [6].
[1] A fiber layered structure composed of a woven or non-woven fabric made of glass fibers and / or ceramic fibers,
A piezoelectric element sheet having a cover layer made of at least one resin selected from imide resin and fluorine resin, and having a sandwich structure of a fiber layer structure and a cover layer on the front and back of the fiber layer structure.
[2] The piezoelectric element sheet according to [1], wherein the fiber layer structure is a woven fabric.
[3] The weight ratio of the fiber layer structure to the coating layer in the piezoelectric element sheet is in the ratio of 95: 5 to 5 to 95 in the structure: coating layer [1] or [2] Piezoelectric element sheet described in.
[4] The piezoelectric element sheet according to any one of [1] to [3], wherein the porosity of the piezoelectric element sheet is 0.1 to 70% by volume.
[5] A fiber layered structure composed of woven fabric or non-woven fabric composed of glass fiber and / or ceramic fiber is immersed in a solution in which at least one resin selected from imide resin and fluorocarbon resin is dissolved or dispersed. Alternatively, after applying the solution to the front and back surfaces to form a covering layer to produce a sheet,
A method of manufacturing a piezoelectric element sheet, comprising charging the sheet.
[6] The method of manufacturing a piezoelectric element sheet according to [5], wherein the charging process is a corona discharge process.

  According to the present invention, it is possible to provide a piezoelectric element sheet which has a high piezoelectric constant, holds a charged charge for a long time, and holds a high piezoelectricity. Specifically, in the present invention, since the fiber layer structure made of insulating woven fabric or non-woven fabric is covered with a fluorocarbon resin or an imide resin so as to form a sandwich structure, the covering layer closes the fiber layer structure. By holding the charge in a state where the charge is disconnected from the external environment, the attenuation of the charge is suppressed, and the charge functions effectively to hold a high piezoelectric constant and a high piezoelectric coefficient.

The cross-sectional SEM photograph of the piezoelectric element sheet | seat concerning this invention is shown.

Hereinafter, the piezoelectric element sheet of the present invention will be described in more detail.
The piezoelectric element sheet of the present invention includes in the structure an insulating woven or non-woven fiber layered structure.
[Insulating woven or non-woven fabric]
The fibers constituting the insulating woven or non-woven fabric are composed of glass fibers or ceramic fibers such as rock wool, carbon fibers, alumina fibers, wollastonite and potassium titanate fibers. In addition, the carbon fiber uses an insulating thing.
The yarn constituting the woven fabric may be any of monofilament yarn, multifilament yarn and staple yarn. The weave is not particularly limited, and examples thereof include plain weave, twill weave, satin weave, twenty weave, and tubular weave. The woven structure is not particularly specified for the woven structure, yarn count, and yarn density.

  Non-woven fabrics can be used in various manufacturing methods such as wet papermaking, water punching, chemical bonding, thermal bonding, spun bonding, needle punching and stitch bonding, but their heat resistance, mechanical properties, From the viewpoint of solvent resistance, a thermal bonding method or a spun bonding method using a self-melting fiber is preferable. In the present invention, a woven fabric is preferred.

The basis weight of the insulating woven or non-woven fabric is preferably ²⁰ to 400 g / m ² , and the thickness is preferably 0.01 to 0.5 mm. If the weight per unit area and the thickness are less than the above lower limits, mechanical strength may be poor. If the above upper limits are exceeded, the flexibility of the piezoelectric element sheet may be insufficient.

  The porosity of the woven or non-woven fabric is preferably 1 to 90% by volume. If the porosity is less than the above lower limit, the piezoelectric properties may be insufficient when the piezoelectric element sheet is subjected to charging treatment, and if it exceeds the above upper limit, the mechanical strength may be inferior.

The void ratio of the woven fabric / non-woven fabric is a numerical value determined by the following equation based on the thickness, the fabric weight and the raw material density.
Void percentage (%) = [1- (Areal weight / (thickness / density))] × 100

From the viewpoint of charging characteristics, the insulating woven or non-woven fabric may be either positively charged or easily negatively charged. In addition, in combination with a covering layer constituting a sandwich structure described later, the charging tendency may be the same or different. In the present invention, using a glass woven fabric (woven fabric made of glass fibers) as the insulating woven fabric or nonwoven fabric exhibits a high piezoelectric constant and can maintain a high piezoelectric coefficient when combined with a sandwich structure described later. So preferred.
The layered structure formed of the woven fabric or the non-woven fabric may be referred to as a fiber layered structure in the present specification, and the fiber layered structure may be a single layer or two or more layered structures.
It is preferable that the fiber layered structure is a woven fabric because it is easy to form a sandwich structure described later.

[Sandwich structure]
The front surface and the back surface of the fiber layered structure are coated with a coating layer made of at least one coating resin selected from fluorocarbon resin and imide resin. As a result, the fiber layered structure constitutes a sandwich structure sandwiched by two covering layers.
In addition, it is covered with the surface and the back of the above-mentioned fiber layered structure (still, neither the surface nor the back distinguishes substantially). In addition, it is desirable that the side surfaces of the structure (end surfaces of the front and back surfaces) are also coated with a resin.

As a fluorine resin, a polytetrafluoroethylene polymer [PTFE], a copolymer of tetrafluoroethylene and perfluoroalkyl vinyl ether [PFA], a copolymer of tetrafluoroethylene and hexafluoropropylene [FEP], polychlorotrifluoro Ethylene [PCTFE], copolymer of tetrafluoroethylene and ethylene [ETFE], polyvinylidene fluoride [PVDF], polyvinyl fluoride [PVF], copolymer of tetrafluoroethylene and hexafluoropropylene and vinylidene fluoride [ THV] and the like. Examples of the imide resin include imide resins such as polyimide, polyamide imide, polyether imide, and bismaleimide.
From the viewpoint of charging characteristics, the coating resin may be one that tends to be negatively charged or one that is likely to be positively charged, but when combined with a glass woven fabric or non-woven fabric, the charge train is more negative than glass fibers. Materials such as fluorocarbon resin located on the side are preferably used.

  The coating resin is preferably a resin having a high melting temperature and a high thermal decomposition initiation temperature from the viewpoint of heat resistance properties, for example, a fluorine resin or an imide resin, and is preferably combined with the glass woven fabric described above Are preferably fluorocarbon resins, particularly PTFE. Use of such a fluorine resin or imide resin is more preferable because the obtained piezoelectric element sheet is excellent in heat resistance and weather resistance, and particularly excellent in temporal stability of piezoelectric characteristics at high temperatures of 70 ° C. or higher.

Piezoelectric element sheet
The piezoelectric element sheet of the present invention has a coating layer made of a coating resin on the front and back surfaces of a fiber layered structure made of an insulating woven or non-woven fabric. For this reason, in the fiber layered structure, woven fabric and non-woven fabric exist in the closed space in the coating layer made of the coating resin. Thus, high piezoelectric performance can be maintained. In addition, it is desirable that the side surfaces (end surfaces) of the front and back surfaces are also covered with a covering layer.
The coating resin constituting the coating layer is present only on the surface of the woven fabric and the non-woven fabric, and the coating resin does not extend to the inside. Therefore, it is not present inside the fiber layered structure substantially.

  A cross-sectional SEM photograph of one example of the piezoelectric sheet according to the present invention is shown in FIG. A woven fabric is used in FIG. The cross section is composed of a bundle of fibers constituting the fiber layered structure, and a coating layer on the front and back of the structure. In addition, the thread-like thing seen in a cross section originates in the coating resin in the extended coating layer for cross-sectional preparation. It is shown in FIG. 1 that the coating resin constituting the coating layer does not substantially infiltrate into the fiber layered structure.

  On the woven fabric surface, since the yarn consisting of fiber bundles is woven in a predetermined weave, it has a peak and a valley, but the cover layer is thick in the valley, for example, thin in the peak, and has a fiber layer structure It is formed to cover the entire body. In addition, the covering layer covers the entire surface or the back of the fiber layered structure so as to follow the unevenness of the peaks and valleys derived from the fiber bundle in a sheet shape, the peak of the fiber bundle The coating layer may be formed so as to cover only the upper side. Furthermore, the covering layer may be formed only on the ridges. The voids of the fiber layered structure are held as voids also as a piezoelectric sheet.

  Thus, by forming a sandwich structure in which the fiber layered structure and its surface and back surface are covered with the covering layer, the introduced charge is caused by the voids of the fiber layered structure and the material interface between the woven fabric / nonwoven fabric and the covering layer, etc. And function as a piezoelectric element sheet. In particular, by combining a glass woven fabric and a coating layer of a fluorine resin, excellent piezoelectric properties are exhibited, and by combining PTFE as a fluorine resin, a piezoelectric element sheet having a high piezoelectric constant and high piezoelectricity retention is obtained. be able to.

  The weight ratio of the fiber layer structure to the covering layer in the piezoelectric element sheet is preferably in a ratio of 95: 5 to 5:95 in weight ratio of fiber layer structure to covering layer, and further 80:20 to 30. The ratio of 70:70 is more preferable, and the ratio of 70:30 to 40:60 is particularly preferable. Within this range, the piezoelectric constant can be increased by increasing the number of voids and material interfaces in the piezoelectric element sheet capable of retaining electric charges, and the attenuation of the charges charged in the piezoelectric element sheet is suppressed, and piezoelectric The rate of retention can be increased.

The thickness of the piezoelectric element sheet is not particularly limited, and is, for example, 5 μm to 0.5 mm, and preferably 10 μm to 200 μm.
The piezoelectric constant | d33 | of the piezoelectric element sheet of the present invention is usually in the range of 10 to 2000 pC / N, preferably 100 to 2000 pC / N. When the piezoelectric constant | d33 | is small, the industrial value is low because the performance is low. On the other hand, it is difficult to reach when | d33 | exceeds the above range.

The piezoelectric constant | d33 | applies a stress (unit: N) so that expansion and contraction in the thickness direction occur in the sample, measures the charge (unit: pC) of the sample generated at that time, and gives the generated charge It can be determined from the stress ratio.
As a more specific measurement method of the piezoelectric constant | d33 |, a measurement method described in JP-A-2011-84735 can be exemplified.

  First, a sample in which conductive layers are provided as electrodes on both sides of a piezoelectric element sheet is prepared, the electrode on one side is used as a ground electrode, and the electrode on the other side is connected to a charge amplifier. Next, the sample is placed on the vibrator of the piezoelectric constant measurement device, and a weight attached with an acceleration sensor is placed on the sample. Subsequently, the sample is vibrated by the weight and the dynamic stress is applied in the thickness direction. The dynamic stress at this time can be obtained from the product of the acceleration of the vibrator measured from the acceleration sensor and the weight of the weight. The charge generated by the stress is output through the charge amplifier and can be obtained by observation using an oscilloscope.

  The piezoelectric element sheet of the present invention has fine voids inside the sheet, and the porosity is preferably 0.1 to 70% by volume, more preferably 1 to 60% by volume, 2 It is particularly preferable that it is 50% by volume. When the porosity of the piezoelectric element sheet is small, the charge storage capacity may be low, and the performance upon charge injection may be inferior. On the other hand, even if there are too many voids, the voids tend to be in communication with each other, the charge is likely to flow out through the communicated voids, and even if the charge is injected, the performance is likely to deteriorate with time. In addition, the elastic modulus of the piezoelectric element sheet may be extremely poor, the restorability in the thickness direction may be reduced, and the durability may be poor.

The porosity of the piezoelectric element sheet is calculated by measuring the volume and dimension calculated from the weight ratio of the coating resin and the glass fiber and / or ceramic fiber constituting the woven fabric / nonwoven fabric and the weight measurement value of the test piece as void free. It is measured by the difference between the volume and the volume.
Void ratio (%) = (1− (theoretical volume / measured volume)) × 100

(Method of manufacturing piezoelectric element sheet)
In the production method of the present invention, a solution in which at least one resin selected from imide resin and fluorine resin is dissolved or dispersed is a fiber layered structure made of woven fabric or non-woven fabric composed of glass fiber and / or ceramic fiber. Or after applying the solution to the front and back surfaces to form a covering layer to produce a sheet,
The sheet is charged.

  First, a fiber layer structure composed of an insulating woven fabric or non-woven fabric is dipped in a solution in which a coating resin is dissolved or dispersed, or the solution is applied to the front and back surfaces to form a coating layer. Thereafter, the obtained sheet is subjected to a charging process to inject charges.

Step of Forming a Coating Layer In the method of manufacturing a piezoelectric element sheet according to the present invention, a coating layer is formed on the surface and the back surface of a fiber-layered structure composed of an insulating woven or non-woven fabric.
In forming the covering layer, a coating solution in which the above-described resin is dissolved in a solvent or in which a particulate resin is dispersed in a dispersion medium is used. The solvent or dispersion medium is not particularly limited, and water, alcohols, ketones and the like can be used, but in the present invention, the use of water and alcohols is preferable in terms of handling and the like.

  As a method for forming a coating layer, a method of dropping a coating solution on a fiber layer structure composed of an insulating woven fabric or non-woven fabric, a method of applying a coating solution on a fiber layer structure composed of an insulating woven fabric or non-woven fabric And the method of making the solution immerse a fiber layer structure comprised from an insulating woven fabric or a nonwoven fabric in a solution etc. is mentioned. The coating method may, for example, be a spray spraying method, a flow coating method, a roll coating method, a brush coating method, a dip coating method, a spin coating method, a screen printing method, a casting method, a gravure printing method or a flexographic printing method.

  After the formation of the covering layer, the solvent (including the dispersion medium) may be removed by drying or the like, and then baking or heat treatment may be performed. The covering layer forming step may be performed a plurality of times, and although baking and heat treatment may be performed successively, forming and drying of the covering layer is repeated and baking and heat treatment are performed when the desired film thickness is obtained. May be From the viewpoint of breaking the electrical connection between the electric charge held inside the piezoelectric element sheet and the external environment, at least the surface of the sheet may be treated until the covering layer is formed without a gap.

The calcination and heat treatment are appropriately selected according to the type of the coating resin, and are performed, for example, at a temperature above the boiling point of the solvent or dispersion medium and / or at a temperature above the melting point (softening point) to the glass transition temperature.
In addition, a coating film made of the above-described resin separately prepared may be attached to a woven or non-woven fabric.

Charging Processing The sheet (hereinafter simply referred to as a sheet) in which the covering layer is formed on the fiber layer structure obtained by the charging processing is subjected to the charging processing according to the charging series of the material. As a result, charge is injected into the piezoelectric element sheet. The charge treatment method is not particularly limited.
(1) The sheet is held between a pair of flat plate electrodes, one flat plate electrode is grounded, and the other flat plate electrode is connected to a high voltage DC power supply to apply direct current or pulse high voltage to the sheet. Method of injecting a charge and charging the sheet,
(2) Method of charging the sheet by irradiating the sheet with ionizing radiation such as electron beam, X-ray or ultraviolet rays to ionize air molecules in the space surrounded by the insulating woven fabric or nonwoven fabric and the covering layer ,
(3) The flat plate electrode grounded on one side of the sheet is stacked in close contact, and a needle electrode or a wire electrode electrically connected to a DC high voltage power supply at a predetermined interval on the other side of the sheet The corona discharge is generated by concentration of the electric field near the tip of the needle electrode or the surface of the wire electrode to ionize the air molecules surrounded by the insulating woven fabric or the non-woven fabric and the covering layer to form the needle electrode or wire. There is a method of repelling air ions generated due to the polarity of the electrode to charge the piezoelectric element sheet.

Among the above methods, the methods (2) and (3) are preferable, and the method (3) of corona discharge is more preferable, in that the processing to the piezoelectric element sheet is easily performed efficiently.
In the methods (1) and (3), when the absolute value of the voltage applied to the sheet is small, electric charges can not be sufficiently injected into the sheet, and a piezoelectric element sheet having high piezoelectric characteristics can be obtained. If it is too large, arc discharge occurs, and on the contrary, the sheet can not sufficiently inject charges into the sheet, and a piezoelectric element sheet having high piezoelectric characteristics may not be obtained. Is preferred, and more preferably 5 to 50 kV.

  In the method (2), when the absolute value of the accelerating voltage of the ionizing radiation to be applied to the sheet is small, the molecules in the air can not be sufficiently ionized, and a sufficient charge is injected to the piezoelectric element sheet In some cases, it is impossible to obtain a piezoelectric element sheet with high piezoelectric characteristics, and if it is large, ionizing radiation transmits air, so that it may not be possible to ionize molecules in the air. -15 kV is preferred.

  In the charging process, excessive charge may be injected into the sheet, and in this case, a discharge phenomenon may occur from the piezoelectric element sheet after the process, which may cause inconvenience in the later process. Therefore, the piezoelectric element sheet can also be subjected to charge removal processing of excess charge after charge processing. By performing the charge removal process, it is possible to remove the charge excessively given by the charge process and to prevent the discharge phenomenon. As the static elimination treatment, a known method such as a voltage application type static elimination (ionizer) or a self-discharge type static elimination, or a method using heat treatment (annealing) can be used. Although these general static eliminators can remove the charge on the surface, it is considered that they do not remove the charge accumulated inside the piezoelectric element sheet, particularly in the air gap. Therefore, it is considered that there is no influence that the performance of the piezoelectric element sheet is greatly reduced by the static elimination treatment.

  The charging treatment is preferably performed at a temperature not lower than the glass transition temperature of the coating resin and not higher than the melting point of the crystal part. If the temperature is higher than the glass transition point, the molecular motion of the amorphous part of the coating resin is active, and molecular arrangement suitable for the given charge is made, so that efficient charge processing is possible. On the other hand, if the melting point is exceeded, the coating resin can not maintain its structure, so the desired performance of the present invention may not be obtained.

  The injected charge is considered to be held in the void surrounded by the glass fiber or ceramic fiber and the coating resin, or at the interface between the fiber and the coating resin. By applying a compressive load in the sheet thickness direction, the obtained piezoelectric element sheet can extract electric charge through the front and back surfaces of the sheet. That is, charge transfer occurs to an external load (electric circuit) to obtain an electromotive force.

  The piezoelectric element sheet of the present invention exhibits a high piezoelectric constant, is excellent in charge retention property, and has a high charge retention amount, and thus can be used in various applications as a piezoelectric (electret) element. In particular, it can be used as an actuator, a sensing material, and a power generation material because it can respond to mechanical energy due to vibration or micro stress and can convert it to electrical energy.

  Since the piezoelectric element sheet of the present invention generates a charge response even under a micro stress, the surface charge for the stress is further controlled by controlling the structure of the insulating woven or non-woven fabric constituting the fiber layer structure and the piezoelectric element sheet. Since responsiveness can be adjusted, sensing materials such as actuators, vibrators, pressure sensors, vibration force sensors, pressure sensors, etc. that can be used in automobiles, outdoors, and in factories, and electromotive force generated by pressure or vibration are supplied as power. It can be used as a power generation material to be used as There is also a method in which the electromotive force is stored in a storage mechanism and used.

  In addition, since the piezoelectric element sheet of the present invention has heat resistance, moisture resistance, and weather resistance, it can be used in high temperature and high humidity environments which can not be used with conventional piezoelectric materials made of PVDF or the like, outdoors, etc. It is possible.

  EXAMPLES The present invention will next be described in more detail by way of examples, which should not be construed as limiting the invention thereto.

[Production example]
A fiber bundle was formed by bundling glass fibers having a single fiber diameter of 5 to 8 μm, and the obtained fiber bundle was plain-woven to prepare a glass woven fabric.
This glass woven fabric was immersed in a dispersion in which fine particles of PTFE were dispersed in water, and the front and back surfaces were immersed to produce a sheet in which a coating layer made of PTFE resin was formed on the front and back surfaces of the glass woven fabric (Example 1).

  A 25 μm thick PFA film is thermocompression bonded to the front and back of the same woven glass fabric, and the PFA film is thermocompression bonded to the front and back of the woven glass to form a sheet having a covering layer of PFA resin. Example 3).

On the other hand, only one side of the same glass woven fabric was dipped to form a coating layer made of PTFE resin (Comparative Examples 1 to 4). In addition, the frequency | count of immersion was 0 to 3 times.
At this time, the PTFE content ratio was determined by calculating the glass weight and the PTFE weight from weight changes before and after the test piece was cut out of each sheet and heated at 400 ° C. for 30 minutes in a nitrogen atmosphere. In addition, the void ratio is the theoretical volume of the test specimen calculated as void-free from the weight ratio of PTFE and glass calculated above and the actual weight value of the test specimen, and the volume calculated by the dimension measurement of the same test specimen It calculated from following equation the difference of
Porosity (volume%) = (1− (theoretical volume / measured volume)) × 100
Moreover, the PFA film was thermocompression-bonded only to the single side | surface of the same glass woven fabric, and the sheet | seat which formed the coating layer which consists of PFA resin was produced (comparative example 5).

[Example]
The sheet was charged by corona discharge for 90 seconds at an electrode distance of -15 kV, an inter-electrode voltage of -15 kV, and a current of 5 mA using a corona discharge device manufactured by Kasuga Electric Co., Ltd., and annealed at 100 ° C for 24 hours. A rectangular electrode ("FOIL" manufactured by Mitsubishi Aluminum Co., Ltd., 11 μm) made of aluminum foil was provided on both sides of the sheet to prepare a sample for evaluation. In Example 2, the same sheet as in Example 1 was used, and a sample for evaluation was prepared according to the same procedure except that charging was performed even at +15 kV.

<Measurement of piezoelectric constant>
A constant AC acceleration α (frequency: 90 to 300 Hz, size: 2 to 10 m / s ² ) is given in the thickness direction of the sample for evaluation, the response charge at that time is measured, and the piezoelectric constant | d33 | Was measured.
The results are shown in Tables 1 to 4. In addition, all the obtained data are average values of n = 8.

Claims (6)

A fiber layered structure composed of a woven or non-woven fabric of glass fibers and / or ceramic fibers;
A piezoelectric element sheet having a sandwich structure in which the surface and the back surface of the fiber layered structure are coated with a coating layer composed of at least one coating resin selected from imide resin and fluorine resin.   The piezoelectric element sheet according to claim 1, wherein the fiber layer structure is a woven fabric.   The weight ratio of the fiber layer structure to the covering layer in the piezoelectric element sheet is in the ratio of 95: 5 to 5 to 95 in the structure: covering layer weight ratio. Piezoelectric element sheet.   The porosity of a piezoelectric element sheet | seat is 0.1-70 volume%, The piezoelectric element sheet in any one of the Claims 1-3 characterized by the above-mentioned. Immersing in a solution in which at least one resin selected from imide resin and fluorine resin is dissolved or dispersed, or a fiber layered structure composed of a woven or non-woven fabric made of glass fiber and / or ceramic fiber, or After the solution is applied to the front and back to form a coating layer,
A method of manufacturing a piezoelectric element sheet, comprising: charging the obtained sheet.   The method of manufacturing a piezoelectric element sheet according to claim 5, wherein the charging process is a corona discharge process.